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Publications dans les journaux scientifiques dans le domaine de l'ingénierie : 06-2010 trié par par titre, page: 23
» Simulating the aerodynamic performance and wake dynamics of a vertical-axis wind turbine
Résumé:
The accurate prediction of the aerodynamics and performance of vertical-axis wind turbines is essential if their design is to be improved but poses a significant challenge to numerical simulation tools. The cyclic motion of the blades induces large variations in the angle of attack of the blades that can manifest as dynamic stall. In addition, predicting the interaction between the blades and the wake developed by the rotor requires a high-fidelity representation of the vortical structures within the flow field in which the turbine operates. The aerodynamic performance and wake dynamics of a Darrieus-type vertical-axis wind turbine consisting of two straight blades is simulated using Brown's Vorticity Transport Model. The predicted variation with azimuth of the normal and tangential force on the turbine blades compares well with experimental measurements. The interaction between the blades and the vortices that are shed and trailed in previous revolutions of the turbine is shown to have a significant effect on the distribution of aerodynamic loading on the blades. Furthermore, it is suggested that the disagreement between experimental and numerical data that has been presented in previous studies arises because the blade-vortex interactions on the rotor were not modelled with sufficient fidelity. Copyright © 2010 John Wiley & Sons, Ltd.
Auteurs: Frank Scheurich, Timothy M. Fletcher, Richard E. Brown
Apparue dans: Wind Energy
Date publication: 06.-2010
Editeur: Wiley InterScience
Document complet vers site de l'éditeur
 
» Simulation of Flying Height and Response Time of Thermal Flying Height Control Sliders With Thermal Insulators
Résumé:
Thermal flying height control (TFC) has recently been implemented in magnetic recording disk drives to reduce the flying height at the read/write element of magnetic recording sliders. This paper investigates the flying height and response time of TFC sliders with single and dual TFC heaters and thermal insulators. Simulation results show that the presence of a thermal insulator has little effect on the response time of thermal protrusions. In addition, the effect of the dimensions of a TFC heater on the flying height and thermal response time is important. For a given heater power, the dual TFC heater design with thermal insulators can provide a very flexible control over flying height and response time of TFC sliders.
Auteurs: Li, H.;Zheng, H.;Fritzsche, J.;Amemiya, K.;Talke, F. E.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 1292 - 1294
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Simulation of Inhomogeneous Superconducting Properties of YBCO HTS Tapes
Résumé:
The critical performance of YBCO tape with inhomogeneous superconducting properties was simulated by use of a bad point distribution model and the Gaussian distribution model. The critical current and n value of the whole HTS tape was analysed. The reliability of the simulation was verified with the experimental data. The results of the two simulation models were compared each other. The influence of inhomogeneous properties on the critical performance of YBCO HTS tape was proved by simulation results which are helpful for the simulation of superconducting devices based on YBCO HTS tapes.
Auteurs: Zhou, Y. G.;Xiao, L. Y.;Zhang, G. M.;Zhang, Z. C.;Li, X. H.;Lin, L. Z.;Zhang, Z. F.;Dai, S. T.;
Apparue dans: IEEE Transactions on Applied Superconductivity
Date publication: 06.-2010, volume: 20, issue:3, pages: 1250 - 1253
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Simulation Study of Bit Patterned Media With Weakly Inclined Anisotropy
Résumé:
Recording properties of bit patterned media with weakly inclined anisotropy were studied by simulation. When a shielded planar head was used, a recording system with an areal density of 2.6 was expected for 30-degree inclined anisotropy media. Relatively large tolerance of around 4% in the anisotropy field and 7 degrees in orientation dispersion as well as write margins in down- and cross-track directions would be expected. Recording densities would be extended to 4 with additional exchange coupling between the dots. It is expected that bit patterned media with weakly inclined anisotropy is one of promising media for ultra high density recording.
Auteurs: Honda, N.;Yamakawa, K.;Ouchi, K.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 1806 - 1808
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Simulation-based optimization of Markov decision processes: An empirical process theory approach?
Résumé:
We generalize and build on the PAC Learning framework for Markov Decision Processes developed in Jain and Varaiya (2006). We consider the reward function to depend on both the state and the action. Both the state and action spaces can potentially be countably infinite. We obtain an estimate for the value function of a Markov decision process, which assigns to each policy its expected discounted reward. This expected reward can be estimated as the empirical average of the reward over many independent simulation runs. We derive bounds on the number of runs needed for the convergence of the empirical average...
Auteurs: Rahul, Jain , Pravin, Varaiya
Apparue dans: Automatica
Date publication: 06.-2010
Editeur: Elsevier B.V.
Document complet vers site de l'éditeur
 
» Simulations of Field Driven Domain Wall Interactions in Ferromagnetic Nanowires
Résumé:
The interaction of domain walls in a single ferromagnetic nanowire has been observed with micromagnetic simulation. Domain walls separating domains of opposite magnetization move towards each other when an external field is applied along the long axis of the wire resulting in a collision. The final magnetic state of the wire after the collision will contain either zero (domain wall annihilation) or two (domain wall conservation) domain walls. Here we explore the behavior that determines the final state, showing that it depends on the initial domain wall configuration, the speed the domain walls are moving with before the collision, and the dimensions of the nanowire. A model is also presented which helps to determine the repulsive force the conserved domain walls exert on each other.
Auteurs: Kunz, A.;Rentsch, E. W.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 1556 - 1558
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Simultaneous plasma and electric field diagnostics of microdischarge from hydrogen Balmer line shape
Résumé:
Hydrogen Balmer beta line shape from a microhollow gas discharge in argon with traces of hydrogen is used for simultaneous diagnostics of plasma and cathode sheath parameters. Simple model of relevant processes responsible for line broadening is developed and results favorably compared with experiment at 500 mbar with the electron density 3.8×1020 m-3 and electric field strength of 127 kV/cm in the cathode sheath region.
Auteurs: Spasojevic, Dj.;Cvejic, M.;Sisovic, N. M.;Konjevic, N.;
Apparue dans: Applied Physics Letters
Date publication: 06.-2010, volume: 96, issue:24, pages: 241501 - 241501-3
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Simultaneous Quadratic Stabilization for Discrete-Time Nonlinear Systems
Résumé:
A constructive method is developed for designing simultaneously quadratically stabilizing state feedback controllers for a collection of single-input discrete-time nonlinear systems. In the context of quadratic control Lyapunov functions a necessary and sufficient condition for the existence of simultaneously quadratically stabilizing state feedback laws is derived. An explicit formula for constructing continuous simultaneously stabilizing controllers is presented. The obtained results are verified by a numerical example.
Auteurs: Wu, J.-L.;
Apparue dans: IEEE Transactions on Automatic Control
Date publication: 06.-2010, volume: 55, issue:6, pages: 1443 - 1448
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Simultaneous velocity and pressure measurements using luminescent microspheres
Résumé:
Using the technique of modified rapid lifetime determination, pressure-sensitive microspheres, known as PrSBeads, were used to make quantitative oxygen measurements over two-dimensional areas within gaseous flows. Aerosolized PrSBeads in carrier gases of varying oxygen concentrations demonstrated point measurement precisions on the order of 0.1%–1%. A charge-coupled device featuring a double image frame (DIF) feature was used to make spatially resolved pressure measurements within gas phase flows. Errors on the order of 0.5 atm for one standard deviation were demonstrated when 2×2 pixel binning (162×128 pixel overall resolution) was used, but improved to 0.003–0.005 atm with the use of 32×32 pixel binning (10×8 pixel overall resolution). Experiments demonstrate the ability to resolve the oxygen concentration differences between a N2 jet and the surrounding ambient air environment and the ability to measure instantaneous air pressure changes within a square syringe as the plunger is moved in and out. In addition, instantaneous velocity measurements of the airborne PrSBeads in a square syringe were achieved using digital particle image velocimetry at frame rates of 6.4 Hz, thus validating PrSBeads as a tool to simultaneously measure the velocity and pressure within an aerodynamic flow.
Auteurs: Kimura, Fletcher;McCann, Jesse;Khalil, Gamal E.;Dabiri, Dana;Xia, Younan;Callis, James B.;
Apparue dans: Review of Scientific Instruments
Date publication: 06.-2010, volume: 81, issue:6, pages: 064101 - 064101-9
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Single Frequency Network System Coverage and Trial Testing of High Speed Railway Television System
Résumé:
The design of High Speed Railway Television (HSRT) system is presented in this paper. The system mainly includes two aspects, the coverage network and the modulation/demodulation technique. We suggest the deployment of HSRT single frequency network (SFN) taking GSM-R as reference and Advanced Digital Television Broadcasting—Terrestrial (ADTB-T) as demodulation technique (it is why HSRT is also called ADTB-R). Moreover, to ensure the reliable work of ADTB-T under the special environment of HSRT-SFN, directional coverage diversity receiving technique are proposed to simplify the equivalent channel model. The validity of this scheme is verified by theoretical analysis and also laboratory tests. The experimental network including the trial testing environment and equipment which constitute the network infrastructure of HSRT-SFN are described. The trial test results are presented to verify the validity of the network design which based on the directional coverage and diversity receiver. The test results accord with the theoretical analysis and prove that the HSRT-SFN is well suited for the special application of high speed railway television.
Auteurs: Gui, L.;Ma, W.;Liu, B.;Lu, J.;Shen, P.;
Apparue dans: IEEE Transactions on Broadcasting
Date publication: 06.-2010, volume: 56, issue:2, pages: 160 - 170
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Single-Crystal GaAs and GaSb on Insulator on Bulk Si Substrates Based on Rapid Melt Growth
Résumé:
A high-quality III–V material on Si substrates has been a primary goal for ultimate device integration. By using the rapid melt growth (RMG) method, we have demonstrated the transformation of amorphous to single crystal for both GaAs and GaSb on bulk Si substrates. High-resolution pictures and selective area diffraction patterns show single-crystal films directly seeded from the Si substrate and propagated along the patterned stripes on top of the insulating layer. Energy-dispersive X-ray spectroscopy was applied to investigate the stoichiometry of the compound material after resolidification. The results show a direct relationship between crystal quality and atomic composition, which suggests a congruent growth for the III–V material during the solidification process despite the possibility of out gassing during the RMG process. This provides a simple path for monolithic optical-electrical integration.
Auteurs: Chen, S-L.;Griffin, P. B.;Plummer, J. D.;
Apparue dans: IEEE Electron Device Letters
Date publication: 06.-2010, volume: 31, issue:6, pages: 597 - 599
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Single-Ended and Differential Radial Power Combiners Implemented With a Compact Broadband Probe
Résumé:
A radial power-combiner design is presented using broadband probes and a radial cavity configuration. The 8:1 combiner (which can also be used as a power divider) is demonstrated experimentally in both single-ended and differential configurations. The broadband probe is composed of cylindrical conductors and dielectric spacers, arranged on a rod for mechanical stability. The proposed radial power combiner provides low loss, broad bandwidth (800–1800 MHz), and high power capability.
Auteurs: Hong, Y.-P.;Kimball, D. F.;Asbeck, P. M.;Yook, J.-G.;Larson, L. E.;
Apparue dans: IEEE Transactions on Microwave Theory and Techniques
Date publication: 06.-2010, volume: 58, issue:6, pages: 1565 - 1572
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Single-Layer InAs Quantum Dots for High-Performance Planar Photodetectors Near 1.3
Résumé:
The potential of InAs quantum-dot (QD) photodetectors for room-temperature high-speed operation at wavelengths near 1.3 is evaluated. Specifically, planar metal–semiconductor–metal structures on GaAs substrates containing one absorption layer of self-assembled InAs QDs embedded in Ga(In)As matrices are fabricated, characterized, and analyzed. Light absorption, optically generated carrier transport, and collection mechanisms are studied. The role of the QD embedding matrix in the lateral transport of the photogenerated carriers is also studied by comparing structures with QDs in GaAs and matrices. Devices show low dark currents in tens of nanoamperes and high light sensitivity when adjusted to QD volumes, whereas external quantum efficiency remains in the range for all fabricated samples. The time response of the fabricated devices is obtained using an excitation wavelength resonant with QD interband transitions, thus allowing the photogeneration of electron–hole pairs inside the dots. Results prove detection capability of a single layer of QDs in a common photodetector structure with a full-width half-maximum time response on the order of 10 ps. A long tail, about 100 ps, but at a small fraction of the peak response amplitude, is also observed, suggesting mechanisms for charge transport and collection.
Auteurs: Persano, A.;Nabet, B.;Currie, M.;Convertino, A.;Leo, G.;Cola, A.;
Apparue dans: IEEE Transactions on Electron Devices
Date publication: 06.-2010, volume: 57, issue:6, pages: 1237 - 1242
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Single-Layer InAs Quantum Dots for High-Performance Planar Photodetectors Near 1.3
Résumé:
The potential of InAs quantum-dot (QD) photodetectors for room-temperature high-speed operation at wavelengths near 1.3 is evaluated. Specifically, planar metal–semiconductor–metal structures on GaAs substrates containing one absorption layer of self-assembled InAs QDs embedded in Ga(In)As matrices are fabricated, characterized, and analyzed. Light absorption, optically generated carrier transport, and collection mechanisms are studied. The role of the QD embedding matrix in the lateral transport of the photogenerated carriers is also studied by comparing structures with QDs in GaAs and matrices. Devices show low dark currents in tens of nanoamperes and high light sensitivity when adjusted to QD volumes, whereas external quantum efficiency remains in the range for all fabricated samples. The time response of the fabricated devices is obtained using an excitation wavelength resonant with QD interband transitions, thus allowing the photogeneration of electron–hole pairs inside the dots. Results prove detection capability of a single layer of QDs in a common photodetector structure with a full-width half-maximum time response on the order of 10 ps. A long tail, about 100 ps, but at a small fraction of the peak response amplitude, is also observed, suggesting mechanisms for charge transport and collection.
Auteurs: Persano, A.;Nabet, B.;Currie, M.;Convertino, A.;Leo, G.;Cola, A.;
Apparue dans: IEEE Transactions on Electron Devices
Date publication: 06.-2010, volume: 57, issue:6, pages: 1237 - 1242
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Single-Layer InAs Quantum Dots for High-Performance Planar Photodetectors Near 1.3
Résumé:
The potential of InAs quantum-dot (QD) photodetectors for room-temperature high-speed operation at wavelengths near 1.3 is evaluated. Specifically, planar metal–semiconductor–metal structures on GaAs substrates containing one absorption layer of self-assembled InAs QDs embedded in Ga(In)As matrices are fabricated, characterized, and analyzed. Light absorption, optically generated carrier transport, and collection mechanisms are studied. The role of the QD embedding matrix in the lateral transport of the photogenerated carriers is also studied by comparing structures with QDs in GaAs and matrices. Devices show low dark currents in tens of nanoamperes and high light sensitivity when adjusted to QD volumes, whereas external quantum efficiency remains in the range for all fabricated samples. The time response of the fabricated devices is obtained using an excitation wavelength resonant with QD interband transitions, thus allowing the photogeneration of electron–hole pairs inside the dots. Results prove detection capability of a single layer of QDs in a common photodetector structure with a full-width half-maximum time response on the order of 10 ps. A long tail, about 100 ps, but at a small fraction of the peak response amplitude, is also observed, suggesting mechanisms for charge transport and collection.
Auteurs: Persano, A.;Nabet, B.;Currie, M.;Convertino, A.;Leo, G.;Cola, A.;
Apparue dans: IEEE Transactions on Electron Devices
Date publication: 06.-2010, volume: 57, issue:6, pages: 1237 - 1242
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Single-Layer InAs Quantum Dots for High-Performance Planar Photodetectors Near 1.3
Résumé:
The potential of InAs quantum-dot (QD) photodetectors for room-temperature high-speed operation at wavelengths near 1.3 is evaluated. Specifically, planar metal–semiconductor–metal structures on GaAs substrates containing one absorption layer of self-assembled InAs QDs embedded in Ga(In)As matrices are fabricated, characterized, and analyzed. Light absorption, optically generated carrier transport, and collection mechanisms are studied. The role of the QD embedding matrix in the lateral transport of the photogenerated carriers is also studied by comparing structures with QDs in GaAs and matrices. Devices show low dark currents in tens of nanoamperes and high light sensitivity when adjusted to QD volumes, whereas external quantum efficiency remains in the range for all fabricated samples. The time response of the fabricated devices is obtained using an excitation wavelength resonant with QD interband transitions, thus allowing the photogeneration of electron–hole pairs inside the dots. Results prove detection capability of a single layer of QDs in a common photodetector structure with a full-width half-maximum time response on the order of 10 ps. A long tail, about 100 ps, but at a small fraction of the peak response amplitude, is also observed, suggesting mechanisms for charge transport and collection.
Auteurs: Persano, A.;Nabet, B.;Currie, M.;Convertino, A.;Leo, G.;Cola, A.;
Apparue dans: IEEE Transactions on Electron Devices
Date publication: 06.-2010, volume: 57, issue:6, pages: 1237 - 1242
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Single-Layer InAs Quantum Dots for High-Performance Planar Photodetectors Near 1.3
Résumé:
The potential of InAs quantum-dot (QD) photodetectors for room-temperature high-speed operation at wavelengths near 1.3 is evaluated. Specifically, planar metal–semiconductor–metal structures on GaAs substrates containing one absorption layer of self-assembled InAs QDs embedded in Ga(In)As matrices are fabricated, characterized, and analyzed. Light absorption, optically generated carrier transport, and collection mechanisms are studied. The role of the QD embedding matrix in the lateral transport of the photogenerated carriers is also studied by comparing structures with QDs in GaAs and matrices. Devices show low dark currents in tens of nanoamperes and high light sensitivity when adjusted to QD volumes, whereas external quantum efficiency remains in the range for all fabricated samples. The time response of the fabricated devices is obtained using an excitation wavelength resonant with QD interband transitions, thus allowing the photogeneration of electron–hole pairs inside the dots. Results prove detection capability of a single layer of QDs in a common photodetector structure with a full-width half-maximum time response on the order of 10 ps. A long tail, about 100 ps, but at a small fraction of the peak response amplitude, is also observed, suggesting mechanisms for charge transport and collection.
Auteurs: Persano, A.;Nabet, B.;Currie, M.;Convertino, A.;Leo, G.;Cola, A.;
Apparue dans: IEEE Transactions on Electron Devices
Date publication: 06.-2010, volume: 57, issue:6, pages: 1237 - 1242
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Single-Mode Excitation in High-Power Gyrotrons by Controlling Gun Perveance
Résumé:
Present-day gyrotrons intended for plasma heating and current-drive experiments operate in high-order modes. Therefore, in such gyrotrons, in the process of voltage rise, as a rule, higher frequency parasitic modes are excited prior to the desired mode. This excitation can be avoided when electron beams with lower current density at intermediate voltages are used. Then, when the voltage passes through the region of excitation of high-frequency parasitic modes, the beam current can be made lower than the start current of those modes. At the same time, when the voltage reaches the excitation zone of the desired mode, the current can be high enough for exciting the desired mode. Such lowering of the beam current at intermediate voltages can be realized by reducing the ratio of the space-charge-limited to the temperature-limited emission. The method is illustrated by an example showing how the excitation of a -mode can be avoided in a gyrotron designed for operation at the -mode. Applicability of this method to millimeter-wave megawatt-class gyrotrons is discussed. The method proposed has additional advantages for gyrotrons operating in power-modulated regimes which are used for suppression of neoclassical tearing modes in large-scale tokamaks and stellarators.
Auteurs: Kashyn, D. G.;Nusinovich, G. S.;Sinitsyn, O. V.;Antonsen, T. M.;
Apparue dans: IEEE Transactions on Plasma Science
Date publication: 06.-2010, volume: 38, issue:6, pages: 1160 - 1167
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Single-Pass Bistatic SAR Interferometry Using Fixed-Receiver Configurations: Theory and Experimental Validation
Résumé:
In this paper, bistatic interferometry using fixed-receiver configurations is addressed both theoretically and experimentally. The analytical expressions for interferometric phase and height sensitivity are derived, and a full interferometric processing chain for digital elevation model (DEM) generation is presented. The derived expressions are general, and they can be applied to two possible acquisition geometries: backscattering and forward scattering. The theoretical developments are complemented with experimental results done with the bistatic receiver Synthetic Aperture radar Bistatic Receiver for INterferometric Applications. The obtained DEMs are compared with a DEM from the Shuttle Radar Topography Mission and a digital terrain model from the Institut Cartografic de Catalunya. The comparison allows one to validate the results and demonstrate to which particular features of the scene that the bistatic radar is sensitive.
Auteurs: Duque, S.;Lopez-Dekker, P.;Mallorqui, J. J.;
Apparue dans: IEEE Transactions on Geoscience and Remote Sensing
Date publication: 06.-2010, volume: 48, issue:6, pages: 2740 - 2749
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Sinking or Swimming in the Sea of Data
Résumé:
Editor in Chief Fred Douglis briefly discusses two presentations given at IC's recent editorial board meeting. He then describes situations in which too much data is a good thing, and when it's a bad thing.
Auteurs: Douglis, Fred;
Apparue dans: IEEE Internet Computing
Date publication: 06.-2010, volume: 14, issue:3, pages: 3 - 5
Editeur: IEEE
Document complet vers site de l'éditeur
 
» SIS 300 Dipole Model
Résumé:
FAIR (Facility for Antiproton and Ion Research), planned to be built at the site of GSI will include the 300 Tm fast-ramping heavy ion synchrotron SIS 300. In the frame of a collaboration between IHEP (Protvino, Russia) and GSI (Darmstadt, Germany) IHEP developed, produced and tested a superconducting model dipole. The main parameters of the dipole are a two-layer coil, 100 mm inner coil diameter and 1 m length. The magnet is designed for 6 T central magnetic field with a 1 T/s operating field ramp rate. The nominal operating current of 6720 A (6 T central magnetic field) was reached after the third quench and critical current of 7738 A (6.8 T central magnetic field) was reached after the eighteenth quench. The critical current of the dipole did not reduce up to ramp rate of 1300 A/s (1.15 T/s). AC losses for different magnetic field cycles were measured too.
Auteurs: Kozub, S.;Bogdanov, I.;Pokrovsky, V.;Seletsky, A.;Shcherbakov, P.;Shirshov, L.;Smirnov, V.;Sytnik, V.;Tkachenko, L.;Zubko, V.;Floch, E.;Moritz, G.;Mueller, H.;
Apparue dans: IEEE Transactions on Applied Superconductivity
Date publication: 06.-2010, volume: 20, issue:3, pages: 200 - 203
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Site-specific management units in a commercial maize plot delineated using very high resolution remote sensing and soil properties mapping
Résumé:
The joint use of satellite imagery and digital soil maps derived from soil sampling is investigated in the present paper with the goal of proposing site-specific management units (SSMU) within a commercial field plot. Very high resolution Quickbird imagery has been used to derive leaf area index (LAI) maps in maize canopies in two different years. Soil properties maps were obtained from the interpolation of ion concentrations (Na, Mg, Ca, K and P) and texture determined in soil samples and also from automatic readings of electromagnetic induction (EMI) readings taken with a mobile sensor.Links between the image-derived LAI and soil...
Auteurs: R., López-Lozano , M.A., Casterad , J., Herrero
Apparue dans: Computers and Electronics in Agriculture
Date publication: 06.-2010
Editeur: Elsevier B.V.
Document complet vers site de l'éditeur
 
» Size-dependent properties of ballistic silicon nanowire field effect transistors
Résumé:
A study on size-dependent subband structures of silicon nanowires (SiNWs) aligned along [100] direction, ranging from 0.77 to 2.69 nm in width, is performed by the first-principles calculation. Combined with a compact model adopting Landauer’s formula, on-currents of ballistic SiNW field effect transistors (FETs) are estimated and assessment of size-dependent performance is conducted. Size-dependent injection velocity strongly depends on Fermi level measured from the conduction band edge when carriers are degenerate. It is also supposed that the Fermi level has a peak value at a certain wire width. Despite variation in the size-dependent Fermi level and injection velocity, large SiNW FETs show large on-currents owing to their larger gate capacitances resulting from longer periphery. The on-current in the case of a multichannel SiNW FET reveals that size-dependent subband structures of nanowires have a serious effect on performance. As the results, although the normalized on-current decreases with decrease in wire width in the assessed multichannel FETs because both the saturation velocities and the normalized capacitances decrease, there can be a maximum in the normalized on-current in a larger wire owing to the maximized Fermi level and injection velocity.
Auteurs: Lee, Yeonghun;Kakushima, Kuniyuki;Shiraishi, Kenji;Natori, Kenji;Iwai, Hiroshi;
Apparue dans: Journal of Applied Physics
Date publication: 06.-2010, volume: 107, issue:11, pages: 113705 - 113705-7
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Slanted and Conical Electroplated Structures Created Using Photoresist Deformation
Résumé:
Electroplating structures with a reproducible slanted angle is difficult at the sub-micron scale. One application for this shape is in magnetic write heads, where a tapered magnetic pole near the surface of a magnetic head is desirable for writing magnetic media at higher areal densities. We will discuss a deep UV sensitive photoresist coupled with a shrink process which yields a convex shaped resist structure. Although the process is similar to a SAFIER process used in via hole applications, an altered thickness of the resist produced unexpected results. Furthermore, a metrology process will be presented to correlate resist deformation of a test structure with the reentrant angle at the base of the resist wall.
Auteurs: Lille, J.;Bonhote, C.;MacDonald, S. A.;Ver, A.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 1902 - 1905
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Slice loss concealment using bridge pictures in scalable video coding
Résumé:
The scalable extension of H.264/AVC (scalable video coding, SVC) provides spatial, temporal and/ or quality scalability with a coding performance that is comparable to that of H.264/AVC. As in the transmission of all types of compressed video, packet losses or errors may result in the degradation of SVC reconstructed video quality. A concealment method for SVC is proposed that uses the motion vectors (MVs) of higher temporal level pictures (bridge pictures) to estimate the MVs of a lost slice. The proposed scheme is tested on a spatial base layer and experimental results show that up to 2.2 dB performance improvement is obtained compared to the temporal direct method, which is a non-normative error concealment method of SVC.
Auteurs: Dereboylu, Z.;Worrall, S.;Cellatoglu, A.;Kondoz, A.;
Apparue dans: Electronics Letters
Date publication: 06.-2010, volume: 46, issue:12, pages: 842 - 843
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Slider Design Optimization for Lube-Surfing Head-Disk Interface Scheme
Résumé:
The stringent magnetic spacing requirement of future high-density magnetic disk drives requires new head disk interface scheme. One possible approach is the lube-surfing scheme—where majority of the slider body is flying while the reader/writer (R/W) element is thermally protruded to contact and penetrate the disk lubricant. This scheme, however, has many challenges to overcome to be feasible. One of these challenges is a slider with improved disk waviness-following capability especially for waviness with wavelength less than half the slider length. This paper explores air bearing design strategies to improve the waviness-following performance of a Femto slider. We propose a “W-shaped” trailing pad slider and investigated the impact of pad layout, etching depth and trailing pad size to the disk waviness-following performance. We have also incorporated a trenched trailing pad structure to reduce air bearing pressure over the R/W element so as to minimize the loss in air bearing pressure during lube contact and to improve the actuation efficiency.
Auteurs: Gonzaga, L. V.;Liu, B.;Yu, S.;Hua, W.;Zhou, W.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 1922 - 1924
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Sliding mode control for time-varying delayed systems based on a reduced-order observer?
Résumé:
In this paper, a stabilisation problem for a class of nonlinear systems is considered, where both the nonlinear term and the nonlinear uncertainty are mismatched and subject to time-varying delay. Under the assumption that the delay is known, a reduced-order observer is designed using an appropriate transformation. A sliding surface is proposed in an augmented space formed by the system outputs and the estimated states. The sliding mode dynamics are derived using an equivalent control approach, and the Lyapunov-Razumikhin approach is exploited to analyse the stability of the sliding motion. Then, a sliding mode control law is developed such that...
Auteurs: Xing-Gang, Yan , Sarah K., Spurgeon , Christopher, Edwards
Apparue dans: Automatica
Date publication: 06.-2010
Editeur: Elsevier B.V.
Document complet vers site de l'éditeur
 
» Sliding-Window Raptor Codes for Efficient Scalable Wireless Video Broadcasting With Unequal Loss Protection
Résumé:
Digital fountain codes have emerged as a low-complexity alternative to Reed–Solomon codes for erasure correction. The applications of these codes are relevant especially in the field of wireless video, where low encoding and decoding complexity is crucial. In this paper, we introduce a new class of digital fountain codes based on a sliding-window approach applied to Raptor codes. These codes have several properties useful for video applications, and provide better performance than classical digital fountains. Then, we propose an application of sliding-window Raptor codes to wireless video broadcasting using scalable video coding. The rates of the base and enhancement layers, as well as the number of coded packets generated for each layer, are optimized so as to yield the best possible expected quality at the receiver side, and providing unequal loss protection to the different layers according to their importance. The proposed system has been validated in a UMTS broadcast scenario, showing that it improves the end-to-end quality, and is robust towards fluctuations in the packet loss rate.
Auteurs: Cataldi, P.;Grangetto, M.;Tillo, T.;Magli, E.;Olmo, G.;
Apparue dans: IEEE Transactions on Image Processing
Date publication: 06.-2010, volume: 19, issue:6, pages: 1491 - 1503
Editeur: IEEE
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» Small gain problem in coupled differential-difference equations, time-varying delays, and direct Lyapunov method
Résumé:
This article presents a Lyapunov-Krasovskii formulation of scaled small gain problem for systems described by coupled differential-difference equations. This problem includes H[infin] problem with block-diagonal uncertainty as a special case. A discretization may be applied to reduce the conditions into linear matrix inequalities. As an application, the stability problem of systems with time-varying delays is transformed into the scaled small gain problem through a process of either one-term approximation or two-term approximation. The cases of time-varying delays with and without derivative upper-bound are compared. Finally, it is shown that similar conditions can also be obtained by a direct Lyapunov-Krasovskii functional method for coupled differential-functional equations. Numerical examples are presented to illustrate the effectiveness of the method in tackling systems with time-varying delays. Copyright © 2010 John Wiley & Sons, Ltd.
Auteurs: Keqin Gu, Yashun Zhang, Shengyuan Xu
Apparue dans: International Journal of Robust and Nonlinear Control
Date publication: 06.-2010
Editeur: Wiley InterScience
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» Small gap semiconducting organic charge-transfer interfaces
Résumé:
We investigated transport properties of organic heterointerfaces formed by single-crystals of two organic donor-acceptor molecules, tetramethyltetraselenafulvalene and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Whereas the individual crystals have unmeasurably high resistance, the interface exhibits a resistivity of few tens of megohm with a temperature dependence characteristic of a small gap semiconductor. We analyze the transport properties based on a simple band diagram that naturally accounts for our observations in terms of charge transfer between two crystals. Together with the recently discovered tetrathiafulvalene–TCNQ interfaces, these results indicate that single-crystal organic heterostructures create functional electronic systems with properties relevant to both fundamental and applied fields.
Auteurs: Nakano, M.;Alves, H.;Molinari, A. S.;Ono, S.;Minder, N.;Morpurgo, A. F.;
Apparue dans: Applied Physics Letters
Date publication: 06.-2010, volume: 96, issue:23, pages: 232102 - 232102-3
Editeur: IEEE
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» Small target detection using cross product based on temporal profile in infrared image sequences?
Résumé:
This paper presents a new small target detection method using cross product of temporal pixels based on temporal profiles in infrared (IR) image sequences. Temporal characteristics of small targets and various backgrounds are different. A new algorithm classifies target pixels and background pixels through hypothesis testing using the cross product of pixels on temporal profile and predicts the temporal backgrounds based on the results. Small target pixels are detected by subtracting the predicted temporal background profile from the original temporal profile. For performance comparison between the proposed method and the conventional methods, the receiver operating characteristics (ROC) curves were computed...
Auteurs: Tae-Wuk, Bae , Byoung-Ik, Kim , Young-Choon, Kim , Kyu-Ik, Sohng
Apparue dans: Computers & Electrical Engineering
Date publication: 06.-2010
Editeur: Elsevier B.V.
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» Small-signal analysis of high-performance p- and n-type SOI SB-MOSFETs with dopant segregation
Résumé:
In this paper, we present fully-depleted Schottky barrier MOSFETs with dopant-segregated NiSi source and drain junctions. Schottky barrier MOSFETs with a channel length of 80nm show high on-currents of 900?A/?m for n-type devices with As segregation at Vgs-Vt=3V and Vds=1.2V and 427?A/?m for p-type devices with B segregation at Vgs-Vt=-2.8V and Vds=-1.2V. A detailed high-frequency characterization proves the high-performance of the devices with cut-off frequencies fT of 117GHz for n-type and 63GHz for p-type Schottky barrier MOSFETs and clearly elucidates the effects of extrinsic and intrinsic device parameters as a function of the gate length.
Auteurs: C., Urban , M., Emam , C., Sandow , Q.T., Zhao , A., Fox , ...
Apparue dans: Solid-State Electronics
Date publication: 06.-2010
Editeur: Elsevier B.V.
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» Small-Signal Modeling of Mutual Saturation in Induction Machines
Résumé:
A small-signal model is derived for saturated induction machines. Inductances are allowed to saturate as a function of their own current (or flux), and the mutual saturation effect originating mainly from skewed or closed rotor slots is also included in the model. The model fulfills the reciprocity conditions, and it can be applied to parameter identification and to the analysis and development of flux-angle estimation methods. As application examples, the parameters of a 2.2-kW induction machine were identified using the data obtained from time-stepping finite-element analysis and locked-rotor measurements. The proposed model fits well to the data, and the fitted parameters are physically reasonable.
Auteurs: Hinkkanen, M.;Repo, A.-K.;Ranta, M.;Luomi, J.;
Apparue dans: IEEE Transactions on Industry Applications
Date publication: 06.-2010, volume: 46, issue:3, pages: 965 - 973
Editeur: IEEE
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» Smart Card Alliance reports on immigration reform
Résumé:
The Smart Card Alliance - the multi-industry group that promotes smartcard technology - has released a report, 'Securing Identity and Enabling Employment Verification: How Do Immigration Reform and Citizen Identification Align?' which, predictably, concludes that secure ID is fundamental to successful immigration reform.
Auteurs: [No author name available]
Apparue dans: Biometric Technology Today
Date publication: 06.-2010
Editeur: Elsevier B.V.
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» Smartphone-Based Vehicle-to-Driver/Environment Interaction System for Motorcycles
Résumé:
This letter concerns the definition and the implementation of an add-on interaction system for motorcycles. The system consists of a vehicle-to-driver and a vehicle-to-environment communication mechanism, which is based on a smartphone core and on a wireless Bluetooth medium. The system is focused to increase the safety level of a motorcycle and it is constituted by a vehicle with a CAN bus, a compact embedded electronic unit implementing a CAN-to-Bluetooth gateway, a smartphone and a Bluetooth helmet. The driver-to-vehicle interaction is based on an audio interaction located at helmet level. The driver-to-environment is represented by communication via the HTTP protocol. The vocal synthesis, the speech recognition, and the gateway to the web server are implemented on the smartphone. This letter presents the hardware architecture, the software architecture and some case-study implementation issues. An evaluation of the critical aspects of the system is also provided.
Auteurs: Spelta, C.;Manzoni, V.;Corti, A.;Goggi, A.;Savaresi, S. M.;
Apparue dans: IEEE Embedded Systems Letters
Date publication: 06.-2010, volume: 2, issue:2, pages: 39 - 42
Editeur: IEEE
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» SmCo With Perpendicular Anisotropy Induced by a (211) Textured Ni W Underlayer
Résumé:
In this work, we have successfully induced SmCo -(0001) texture using the Ni W-(211) underlayer. A tungsten (W) seed layer of 4 nm resulted in a nanocrystalline (211)-textured Ni W underlayer deposited at room temperature. Highly (0001)-textured SmCo was achieved after the sputtering deposition in the temperature range of 500–540 C. The crystallinity of the SmCo layer was reduced at higher deposition temperature ( C), probably due to W diffusion. The nano-grained SmCo thin film deposited at 500 C shows an out-of-plane coercivty of 12.7 kOe with a large perpendicular magnetic anisotropy. The thickness of Ni W underlayer can be reduced to 13 nm without a significant change in the large perpendicular magnetic coercivity of the SmCo thin film.
Auteurs: Zhang, L. N.;Hu, J. F.;Chen, J. S.;Ding, J.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 2082 - 2085
Editeur: IEEE
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» SmCo With Perpendicular Anisotropy Induced by a (211) Textured Ni W Underlayer
Résumé:
In this work, we have successfully induced SmCo5-(0001) texture using the Ni4W-(211) underlayer. A tungsten (W) seed layer of 4 nm resulted in a nanocrystalline (211)-textured Ni4W underlayer deposited at room temperature. Highly (0001)-textured SmCo5 was achieved after the sputtering deposition in the temperature range of 500-540°C. The crystallinity of the SmCo5 layer was reduced at higher deposition temperature (¿ 550°C), probably due to W diffusion. The nano-grained SmCo5 thin film deposited at 500°C shows an out-of-plane coercivty of 12.7 kOe with a large perpendicular magnetic anisotropy. The thickness of Ni4 W underlayer can be reduced to 13 nm without a significant change in the large perpendicular magnetic coercivity of the SmCo5 thin film.
Auteurs: Zhang, L.N.;Hu, J.F.;Chen, J.S.;Ding, J.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 2082 - 2085
Editeur: IEEE
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» SMES Based Dynamic Voltage Restorer for Voltage Fluctuations Compensation
Résumé:
This paper presents a superconducting magnetic energy storage (SMES) based dynamic voltage restorer (DVR) to protect consumers from the grid voltage fluctuations. Due to the characteristic of high energy density and quick response, a superconducting magnet is selected as the energy storage unit to improve the compensation capability of DVR. This paper analyses the operation principle of the SMES based DVR, and designs the DVR output voltage control method. The control system mainly consists of two parts, the PWM converter controller and the DC/DC chopper controller. The PWM converter controller adopts double-loop control strategy, with an inner current regulator and an outer voltage controller. Combining the coordinated control of DC/DC chopper, the DVR can regulate output voltage accurately and quickly to compensate the system voltage fluctuations. Using MATLAB SIMULINK, the models of the SMES based DVR is established, and the simulation tests are performed to evaluate the system performance.
Auteurs: Shi, J.;Tang, Y.;Yang, K.;Chen, L.;Ren, L.;Li, J.;Cheng, S.;
Apparue dans: IEEE Transactions on Applied Superconductivity
Date publication: 06.-2010, volume: 20, issue:3, pages: 1360 - 1364
Editeur: IEEE
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» So, you are going to be an engineer!
Résumé:
Over many years, we have known people who had enrolled in an engineering curriculum and then decided that was not what they really wanted to do. There were also those who switched their engineering major when they decided there were conditions they preferred to work with that may not be available in their current planned field. For instance, one decided he would like to work outside, not in a laboratory or office, so he switched from a chemical to petroleum engineering curriculum, with the expectation that the new choice would have greater opportunity for outside work. Such changes are not uncommon, but the student must realize that the change may be costly, both in time and money. Depending on when the change is made, the degree completion may be pushed beyond the expected four years by two or more years—and suffer considerable additional costs.
Auteurs: Floyd, R.E.;Spencer, R.H.;
Apparue dans: IEEE Potentials
Date publication: 06.-2010, volume: 29, issue:3, pages: 9 - 21
Editeur: IEEE
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» Social Surroundings: Bridging the Virtual and Physical Divide
Résumé:
Social Surroundings is an application that uses smartphones and online social networks to help eliminate social barriers and encourage natural communication in public places.
Auteurs: Hosio, Simo;Kukka, Hannu;Riekki, Jukka;
Apparue dans: IEEE Multimedia
Date publication: 06.-2010, volume: 17, issue:2, pages: 26 - 33
Editeur: IEEE
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» Society News
Résumé:
Auteurs: Rodriguez-Andina, J.J.;
Apparue dans: IEEE Industrial Electronics Magazine
Date publication: 06.-2010, volume: 4, issue:2, pages: 45 - 47
Editeur: IEEE
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» Soft and Hard Failures of InGaN-Based LEDs Submitted to Electrostatic Discharge Testing
Résumé:
This letter reports an extensive analysis of the degradation mechanisms of InGaN-based light-emitting diodes (LEDs) submitted to reverse-bias electrostatic discharge (ESD). The results of this analysis indicate that two different failure modes, namely, “soft” and “hard” degradations, can be induced by ESD pulses. The “soft” failure mode takes place as a consequence of ESD events with moderate voltage/current levels and consists in a decrease in the reverse-bias leakage current of LEDs. This effect is due to the annihilation of some of the defective paths responsible for leakage-current conduction, possibly triggered by the injection of relatively high reverse-bias current densities. “Hard” failure takes place when high-voltage/current ESD pulses are applied to an LED. After hard failure, LEDs behave as short circuits. This process is due to the high voltage levels reached by the junction during an ESD event (with subsequent dielectric rupture) or to the injection of extremely high current densities through one of the localized paths responsible for reverse-current conduction.
Auteurs: Meneghini, M.;Tazzoli, A.;Butendeich, R.;Hahn, B.;Meneghesso, G.;Zanoni, E.;
Apparue dans: IEEE Electron Device Letters
Date publication: 06.-2010, volume: 31, issue:6, pages: 579 - 581
Editeur: IEEE
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» Soft Starting of Induction Motor With Torque Control
Résumé:
This paper presents a simple technique based on stator-flux estimation to control the electromagnetic torque of induction motors (IMs) during soft starting. The inherent problems related to pure integration of the back electromagnetic force to estimate the stator flux are minimized using the low-pass-filter approach. The experimental results are dealt with and compared with the usual current-control technique. The results obtained validate the proposed technique, showing its viability in applications where the objective is to fit the IM torque profile during starting or stopping according to the load torque.
Auteurs: Nied, N.;de Oliveira, J.;de Farias Campos, R.;Dias, R. P.;de Souza Marques, L. C.;
Apparue dans: IEEE Transactions on Industry Applications
Date publication: 06.-2010, volume: 46, issue:3, pages: 1002 - 1010
Editeur: IEEE
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» Software Reliability and Testing Time Allocation: An Architecture-Based Approach
Résumé:
With software systems increasingly being employed in critical contexts, assuring high reliability levels for large, complex systems can incur huge verification costs. Existing standards usually assign predefined risk levels to components in the design phase, to provide some guidelines for the verification. It is a rough-grained assignment that does not consider the costs and does not provide sufficient modeling basis to let engineers quantitatively optimize resources usage. Software reliability allocation models partially address such issues, but they usually make so many assumptions on the input parameters that their application is difficult in practice. In this paper, we try to reduce this gap, proposing a reliability and testing resources allocation model that is able to provide solutions at various levels of detail, depending upon the information the engineer has about the system. The model aims to quantitatively identify the most critical components of software architecture in order to best assign the testing resources to them. A tool for the solution of the model is also developed. The model is applied to an empirical case study, a program developed for the European Space Agency, to verify model's prediction abilities and evaluate the impact of the parameter estimation errors on the prediction accuracy.
Auteurs: Pietrantuono, Roberto;Russo, Stefano;Trivedi, Kishor S.;
Apparue dans: IEEE Transactions on Software Engineering
Date publication: 06.-2010, volume: 36, issue:3, pages: 323 - 337
Editeur: IEEE
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» Solar Biases in Microwave Imager Observations Assimilated at ECMWF
Résumé:
The European Centre for Medium-Range Weather Forecasts (ECMWF) assimilates microwave imager observations for their information on humidity, cloud, and precipitation. However, Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) first-guess (FG) departure biases exhibit a 46-day oscillation with a peak-to-peak amplitude of up to 3 K in brightness temperature, which is linked to the precession of the equator crossing time of the TRMM orbit. The TMI bias has a diurnal cycle, but neither the Special Sensor Microwave Imager nor the Advanced Microwave Scanning Radiometer for the Earth Observing System shows a similar variation, so the bias must be in the TMI instrument itself. Its cause is probably solar heating of the main reflector, which is not perfectly reflective. This means that the instrument measures a combination of Earth emission and the physical temperature of the reflector. This effect has been partly corrected by the data providers, but their correction assumes a constant reflector temperature. In contrast, the ECMWF FG departures suggest that the reflector temperature varies by up to 70 K through the orbit. A method is presented for correcting the bias in the ECMWF assimilation system. It is also noted that when building future conical-scanning microwave imagers, it is important to provide reflectors that are as nonemissive as possible and to also carefully record the reflector's actual (possibly frequency-dependent) emissivity. The in-space temperature of the reflector surface should also be recorded so that it can be used in bias correction.
Auteurs: Geer, A. J.;Bauer, P.;Bormann, N.;
Apparue dans: IEEE Transactions on Geoscience and Remote Sensing
Date publication: 06.-2010, volume: 48, issue:6, pages: 2660 - 2669
Editeur: IEEE
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» Solar cell efficiency tables (version 36)
Résumé:
Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined and new entries since January 2010 are reviewed. Copyright © 2010 John Wiley & Sons, Ltd.
Auteurs: Martin A. Green, Keith Emery, Yoshihiro Hishikawa, Wilhelm Warta
Apparue dans: Progress in Photovoltaics: Research and Applications
Date publication: 06.-2010
Editeur: Wiley InterScience
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» Solar-Assisted Electric Auto Rickshaw Three-Wheeler
Résumé:
Auto rickshaws are three-wheeled vehicles that are extensively used in many Asian countries as taxis of people and goods. Although the vehicle design is well suited to the environment in which it operates, it is a crude and inefficient design. Due to poor vehicle maintenance and the use of inefficient two- or four-stroke engines with very little pollution control, auto rickshaws present a grave pollution problem in major Indian cities. This paper details the overall development of an advanced solar-assisted electric auto rickshaw. Research on the conventional auto rickshaw is presented, as well as future conceptual infrastructure designs for electric rickshaws and the recent design research, simulations, and experimental validation of the next auto rickshaw. The proposed solar/battery electric three-wheeler is meant to match and exceed the conventional vehicle's performance but with a more intelligent and efficient design. We introduce the next overall design of the rickshaw in this paper as Auto Rickshaw 2.0, where the conventional vehicle is version 1.0. The technical development aim for Auto Rickshaw 2.0 is to decrease the total electric power needed for propulsion with an optimized battery system and a more efficient motor and inverter. Four system drive-train options are covered, a rickshaw prototype is built, and several configurations are simulated and analyzed in the Advanced Vehicle Simulator (ADVISOR) software. Additionally, conceptual infrastructure designs are modeled and optimized in the Hybrid Optimization Model for Electric Renewables (HOMER) software.
Auteurs: Mulhall, P.;Lukic, S. M.;Wirasingha, S. G.;Lee, Y.-J.;Emadi, A.;
Apparue dans: IEEE Transactions on Vehicular Technology
Date publication: 06.-2010, volume: 59, issue:5, pages: 2298 - 2307
Editeur: IEEE
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» Solid-Gas Surface Effect on the Performance of a MEMS-Class Nozzle for Micropropulsion
Résumé:
Steady-state performance of a three-dimensional flat-shaped micronozzle in underexpanded cold- and hot-gas operation has been analysed with numerical simulation. The flow regime is supersonic and characterized by a Knudsen number varying from slightly slip-flow by the nozzle throat, to moderate transitional regime near the nozzle lip. A second-order in Knudsen model has been implemented to incorporate the effects of the slip in velocity and temperature jump into a Navier-Stokes finite-volume commercial code, so fully thermal coupling between the gas and solid portions of the computational domain is imposed and the heat balance at the solid-surface is enforced from the temperature...
Auteurs: José Antonio, Moríñigo , José, Hermida-Quesada
Apparue dans: Sensors and Actuators A: Physical
Date publication: 06.-2010
Editeur: Elsevier B.V.
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» Solidly mounted BAW resonators with layer-transferred AlN using sacrificial Si surfaces
Résumé:
We present a new method to manufacture solidly mounted bulk acoustic wave resonators. This new process introduces the use of wafer bonding techniques and sacrificial surface removal to manufacture solidly mounted resonators having special properties. With the proposed process, Aluminum Nitride (AlN) thin films are obtained having exceptional c-axis crystal orientation with XRD rocking curve FWHM of 1.36° and material electromechanical coupling constant of 6.8% exceeding that of the epitaxial AlN electromechanical coupling constant. Fully functional single-mask resonators were successfully fabricated with this process working around 2.35GHz and enjoying Q-values as high as 1300.
Auteurs: Mohamed, Abd Allah , Robert, Thalhammer , Jyrki, Kaitila , Thomas, Herzog , Werner, Weber , ...
Apparue dans: Solid-State Electronics
Date publication: 06.-2010
Editeur: Elsevier B.V.
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» Solution Deposited NiO Thin-Films as Hole Transport Layers in Organic Photovoltaics
Résumé:
Organic solar cells require suitable anode surface modifiers in order to selectively collect positive charge carriers and improve device performance. We employ a nickel metal organic ink precursor to fabricate NiO hole transport layers on indium tin oxide anodes. This solution deposited NiO annealed at 250°C and plasma treated, achieves similar OPV device results reported with NiO films from PLD as well as PEDOT:PSS. We demonstrate a tunable work-functionby post-processing the NiO with an O2-plasma surface treatment of varied power and time. We find that plasma treatment is necessary for optimal device performance. Optimal devices utilizing a solution deposited NiO...
Auteurs: K. Xerxes, Steirer , Jordan P., Chesin , N. Edwin, Widjonarko , Joseph J., Berry , Alex, Miedaner , ...
Apparue dans: Organic Electronics
Date publication: 06.-2010
Editeur: Elsevier B.V.
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» Solution processed tetrasubstituted zinc phthalocyanine as an active layer in organic field effect transistors
Résumé:
Spun films of liquid crystalline peripheral-tetrasubstituted zinc (II) phthalocyanine (Pc) derivatives have been employed as active organic semiconducting layers in the fabrication of organic field effect transistors. The Pc molecules in the thin film formulation are stacked perpendicular to the substrate. Values of 1.8×10-4 cm2V-1s-1 and 103 were estimated for the field-effect mobility and on/off ratio, respectively, from the hysteresis-free transistor characteristics. The transistor can be switched on and off at a relatively low value of 3.7 V for threshold voltage. The carrier transport is believed to be largely determined by the multidomain Pc film structure.
Auteurs: Chaure, Nandu B.;Basova, Tamara;Zahedi, Marjan;Ray, Asim K.;Sharma, Ashwani K.;Durmus, Mahmut;Ahsen, Vefa;
Apparue dans: Journal of Applied Physics
Date publication: 06.-2010, volume: 107, issue:11, pages: 114503 - 114503-5
Editeur: IEEE
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» Solution-processed zinc–tin oxide thin-film transistors with low interfacial trap density and improved performance
Résumé:
Solution-processed amorphous oxide semiconductors are attractive channel materials in thin-film transistors (TFTs) for low-cost electronics. We demonstrate improved performance and uniformity of solution-processed zinc–tin oxide (ZTO) TFTs by optimizing the prebake process for the ZTO precursor film. ZTO prebake process prearranges the dielectric/semiconductor interface and minimizes the performance variation caused by the uneven thermal distribution during annealing process. Prearranging the interface also reduces interfacial trap density and results in improved performance. A mobility of 27.3 cm2/Vs, an on/off ratio of ∼107, and a subthreshold swing of 122 mV/decade have been obtained. Significant improvement in operational stability has also been observed.
Auteurs: Lee, Chen-Guan;Dodabalapur, Ananth;
Apparue dans: Applied Physics Letters
Date publication: 06.-2010, volume: 96, issue:24, pages: 243501 - 243501-3
Editeur: IEEE
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» Solving optimal power flow problems using a probabilistic α-constrained evolutionary approach
Résumé:
One of the most difficult tasks in any population-based approach is to deal with large-scale constrained systems without losing computational efficiency. To achieve such goal, a methodology based on two different techniques is presented. First, an evolutionary algorithm based on a cluster-and-gradient-based artificial immune system (CGbAIS) is used to improve computational time. For that, the CGbAIS uses the numerical information provided by the electrical power system and a clustering strategy that eliminates redundant individuals to speed up the convergence process. Second, to increase the capacity of dealing with constraints, a probabilistic a-level of relaxation is used. This approach treats separately the constraints and objective functions. It generates a lexicographic comparison process meaning that, if two individuals have their constraints below the current a-level, the one with the better objective function has a probability of winning the comparison. Otherwise, the individual with the lower penalty is selected regardless the value of the objective function. Combining these concepts together generates a computational framework capable of finding optimal solutions within a very interesting computational time. Applications using a mixed integer and continuous variables will illustrate the performance of the proposed method.
Auteurs: Honorio, L.M.;Leite da Silva, A.M.;Barbosa, D.A.;Delboni, L.F.N.;
Apparue dans: IET Generation, Transmission & Distribution
Date publication: 06.-2010, volume: 4, issue:6, pages: 674 - 682
Editeur: IEEE
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» Some extremal properties of daubechies filters and other orthonormal filters
Résumé:
New extremal properties of Daubechies 4-tap orthonormal filters are given: They maximize a certain functional, have the largest gain in (0, ?/2), and allow maximum energy compaction in [0, ?/2]. These properties do not carry over to Daubechies filters of arbitrary length. They complement what is known about Daubechies filters and highlight the specific role of the 4-tap filter. Moreover, we demonstrate that these properties cannot be fulfilled by any other orthonormal lowpass filter, regardless of its length.
Auteurs: María Elena, Domínguez-Jiménez , Paulo J.S.G., Ferreira
Apparue dans: Signal Processing
Date publication: 06.-2010
Editeur: Elsevier B.V.
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» Some New Developments on the Al-Alaoui and the Pei and Hsu s-to-z Transforms
Résumé:
This brief refocuses on three classes of s-to-z transforms. For each class, a closed-form expression is proposed, and a particular element, having an imaginary part of its frequency response very close to the ideal value, is presented. These s-to-z transforms are then related to all-pass infinite-impulse-response fractional delay filters, allowing another way to choose their degree of freedom.
Auteurs: Auger, F.;
Apparue dans: IEEE Transactions on Circuits and Systems II: Express Briefs
Date publication: 06.-2010, volume: 57, issue:6, pages: 471 - 475
Editeur: IEEE
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» Some Superconducting Magnets at IMP
Résumé:
Some superconducting magnets research at IMP (Institute of Modern Physics, CAS, Lanzhou) will be described in this paper. Firstly, a superconducting electron cyclotron resonance ion source (SECRAL) was successfully built to produce intense beams of highly charged heavy ions for Heavy Ion Research Facility in Lanzhou (HIRFL). An innovation design of SECRAL is that the three axial solenoid coils are located inside of a sextupole bore in order to reduce the interaction forces between the sextupole coils and the solenoid coils. For 28 GHz operation, the magnet assembly can produce peak mirror fields on axis of 3.6 T at injection, 2.2 T at extraction, and a radial sextupole field of 2.0 T at plasma chamber wall. Some excellent results of ion beam intensity have been produced and SECRAL has been put into operation to provide highly charged ion beams for HIRFL since May 2007. Secondly, a super-ferric dipole prototype of FAIR Super-FRS is being built by FCG (FAIR China Group) in cooperation with GSI. Its superconducting coils and cryostat is made and tested in the Institute of Plasma Physics (IPP, Hefei), and it more 50 tons laminated yoke was made in IMP. This super-ferric dipole static magnetic field was measured in IMP, it reach to the design requirement, ramping field and other tests will be done in the future. Thirdly, a 3 T superconducting homogenous magnetic field solenoid with a 70 mm warm bore has been developed to calibrate Hall sensor, some testing results is reported. And a penning trap system called LPT (Lanzhou Penning Trap) is now being developed for precise mass measurements.
Auteurs: Yuan, P.;Zhao, H. W.;Leibrock, H.;Ma, L. Z.;Sun, L. T.;Zhang, X. Q.;Zhang, B.;Guo, B. L.;Wu, W.;Yao, Q. G.;Wu, W. Y.;Wang, Q. L.;Wu, X.;Han, S. F.;He, Y.;Zhang, S. L.;
Apparue dans: IEEE Transactions on Applied Superconductivity
Date publication: 06.-2010, volume: 20, issue:3, pages: 214 - 217
Editeur: IEEE
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» Son of Carterfone: Network Neutrality or Regulation?
Résumé:
Ending network neutrality would benefit ISPs at the expense of Internet vendors, but would probably disadvantage users in general and could pose risks for privacy and innovation.
Auteurs: Lesk, Michael;
Apparue dans: IEEE Security & Privacy
Date publication: 06.-2010, volume: 8, issue:3, pages: 77 - 82
Editeur: IEEE
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» Sorting Genomes by Reciprocal Translocations, Insertions, and Deletions
Résumé:
The problem of sorting by reciprocal translocations (abbreviated as SBT) arises from the field of comparative genomics, which is to find a shortest sequence of reciprocal translocations that transforms one genome Pi into another genome Gamma, with the restriction that Pi and Gamma contain the same genes. SBT has been proved to be polynomial-time solvable, and several polynomial algorithms have been developed. In this paper, we show how to extend Bergeron's SBT algorithm to include insertions and deletions, allowing to compare genomes containing different genes. In particular, if the gene set of Pi is a subset (or superset, respectively) of the gene set of Gamma, we present an approximation algorithm for transforming Pi into Gamma by reciprocal translocations and deletions (insertions, respectively), providing a sorting sequence with length at most OPT + 2, where OPT is the minimum number of translocations and deletions (insertions, respectively) needed to transform Pi into Gamma; if Pi and Gamma have different genes but not containing each other, we give a heuristic to transform Pi into Gamma by a shortest sequence of reciprocal translocations, insertions, and deletions, with bounds for the length of the sorting sequence it outputs. At a conceptual level, there is some similarity between our algorithm and the algorithm developed by El Mabrouk which is used to sort two chromosomes with different gene contents by reversals, insertions, and deletions.
Auteurs: Qi, Xingqin;Li, Guojun;Li, Shuguang;Xu, Ying;
Apparue dans: IEEE/ACM Transactions on Computational Biology and Bioinformatics
Date publication: 06.-2010, volume: 7, issue:2, pages: 365 - 374
Editeur: IEEE
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» Source and Boundary Implementation in Vector and Scalar DGTD
Résumé:
We summarize the boundary and source implementation for the several formulations of the discontinuous Galerkin time domain method (DGTD). Since DGTD with zeroth-order scalar basis functions using the upwind flux, coincides with the finite volume time domain (FVTD), many of the concepts developed for FVTD can be ported to DGTD in any of its different formulations (scalar/vector basis, upwind/centered flux). Numerical examples illustrate the different alternatives.
Auteurs: Alvarez, J.;Angulo, L. D.;Pantoja, M. F.;Bretones, A. R.;Garcia, S. G.;
Apparue dans: IEEE Transactions on Antennas and Propagation
Date publication: 06.-2010, volume: 58, issue:6, pages: 1997 - 2003
Editeur: IEEE
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» Source Camera Identification Using Enhanced Sensor Pattern Noise
Résumé:
Sensor pattern noises (SPNs), extracted from digital images to serve as the fingerprints of imaging devices, have been proved as an effective way for digital device identification. However, as we demonstrate in this work, the limitation of the current method of extracting SPNs is that the SPNs extracted from images can be severely contaminated by details from scenes, and as a result, the identification rate is unsatisfactory unless images of a large size are used. In this work, we propose a novel approach for attenuating the influence of details from scenes on SPNs so as to improve the device identification rate of the identifier. The hypothesis underlying our SPN enhancement method is that the stronger a signal component in an SPN is, the less trustworthy the component should be, and thus should be attenuated. This hypothesis suggests that an enhanced SPN can be obtained by assigning weighting factors inversely proportional to the magnitude of the SPN components.
Auteurs: Li, C.-T.;
Apparue dans: IEEE Transactions on Information Forensics and Security
Date publication: 06.-2010, volume: 5, issue:2, pages: 280 - 287
Editeur: IEEE
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» Source-channel rate optimization for progressive image transmission over block fading relay channels [Transactions Papers]
Résumé:
In this paper, we are concerned with the design and analysis of joint source-channel coding schemes for block fading channels with relay-assisted distributed spatial diversity. Assuming a progressive image coder with a constraint on the transmission bandwidth, we formulate a joint source-channel rate allocation scheme that maximizes the expected source throughput. Specifically, using Gaussian as well as BPSK inputs on flat Rayleigh fading channels, we lower bound the average packet error rate by the corresponding mutual information outage probability, and derive the average throughput expression as a function of channel code rates as well as channel SNR for both a frequency-division multiplexing-based baseline system without relaying, and a half-duplex relay system with a decodeand- forward protocol. At high signal-to-noise ratio (SNR), for the systems considered in this paper, we show that our rate optimization problem is a convex function of the channel code rates, and we show that a known recursive algorithm can be used to predict the performance of both systems.
Auteurs: Kim, H.;Annavajjala, R.;Cosman, P.C.;Milstein, L.B.;
Apparue dans: IEEE Transactions on Communications
Date publication: 06.-2010, volume: 58, issue:6, pages: 1631 - 1642
Editeur: IEEE
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» Sovietization of Czechoslovakian Computing: The Rise and Fall of the SAPO Project
Résumé:
After World War II, Antonín Svoboda returned to Czechoslovakia with experience in building analog computers, a keen interest in digital computing technology, and aspirations to establish a computer industry in his homeland. Svoboda's original ideas were further developed by his students and colleagues and reflected in the design of SAPO, the first Czechoslovakian computer, in the 1950s.
Auteurs: Durnova, Helena;
Apparue dans: IEEE Annals of the History of Computing
Date publication: 06.-2010, volume: 32, issue:2, pages: 21 - 31
Editeur: IEEE
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» Space Charge Distribution Measurement in Complex Insulating Structures
Résumé:
Electrical insulation involves more and more complex structures in which the electric field or the material can be heterogeneous. For testing space charge buildup in such structures, one-dimensional measurements are still often used owing to their simplicity. The sample complexity may, however, induce spurious effects that can be confused with space charge. In this paper, from the underlying physics of the pressure-wave propagation (PWP) and the electro-acoustic (PEA) methods, limitations of the one-dimensional model are shown and an analysis procedure is given. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.
Auteurs: Stéphane Holé
Apparue dans: IEEJ Transactions on Electrical and Electronic Engineering
Date publication: 06.-2010
Editeur: Wiley InterScience
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» Space Charge Measurement in MgO/LDPE Nanocomposite up to Breakdown under DC Ramp Voltage
Résumé:
To understand the basic electric properties of nanosized magnesium oxide (MgO)/low-density polyethylene (LDPE) nanocomposites under an applied DC voltage, the DC breakdown strength and space charge up to the breakdown under a DC ramp voltage were investigated. Compared to that of the LDPE sample, the sample containing a MgO nanofiller (hereafter, called a nanocomposite) had a higher DC breakdown strength. In the case of the LDPE sample, the homo charges, which contained a large negative charge and a small positive charge, were only observed near the electrodes just prior to breakdown. However, in the case of the nanocomposite sample, the positive charge increased as the average field increased until the average field reached a certain value. After that, the positive charge decreased as the average field increased until breakdown occurred. The field enhancement rate (=maximum field/average field) of the nanocomposite sample increased with the average field, until it became saturated. After peaking, the field enhancement rate of the nanocomposite sample decreased as the average field increased. These observations suggest that, instead of the MgO nanofiller suppressing the electronic avalanche, it suppresses the conduction current, which was determined by the space charge, leading to the higher DC breakdown strength. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.
Auteurs: Yoshinobu Murakami, Shunsuke Okuzumi, Masayuki Nagao, Masumi Fukuma, Yoitsu Sekiguchi, Manabu Goshowaki, Yoshinao Murata
Apparue dans: IEEJ Transactions on Electrical and Electronic Engineering
Date publication: 06.-2010
Editeur: Wiley InterScience
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» Space Vectors Modulation for Nine-Switch Converters
Résumé:
Recently, nine-switch inverter and nine-switch-z-source inverter have been proposed as dual output inverters. In this paper, the space vector modulation (SVM) of nine-switch inverter and nine-switch-z-source inverter is proposed. The proposed method increases the sum of modulation indices up to 15% in contrast with the conventional, scheme in which the sum of modulation indices is equal or less than one. The extra voltage available for a given input dc-voltage, translates to a higher torque–-a critical factor for defining the capacity of products in marketplace. Also, in order to further reduce the cost of power devices and also thermal heat effect, and to reduce the number of semiconductor switching, specific SVM switching pattern is presented. This feature will be advantageous for high-power inverter applications where cost and efficiency are key decision factors. Furthermore, a novel SVM is proposed for minimizing total harmonic distortion. The performance of the proposed SVM for both nine-switch inverter and nine-switch-z-source inverter is verified by simulation. Experimental results validate the simulation results as well as the superiority of the proposed SVM.
Auteurs: Dehghan Dehnavi , S. M.;Mohamadian, M.;Yazdian, A.;Ashrafzadeh, F.;
Apparue dans: IEEE Transactions on Power Electronics
Date publication: 06.-2010, volume: 25, issue:6, pages: 1488 - 1496
Editeur: IEEE
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» Space-time clutter rejection and target passive detection using the APES method
Résumé:
A new method to reject ground clutter using the Amplitude and Phase EStimation (APES) method is proposed. The theoretical approach is followed by the application of this method to the rejection of such an interference in the frameof a bistatic passive radar using digital video broadcasting - terrestrial (DVB-T) transmitters.
Auteurs: Raout, J.;Santori, A.;Moreau, E.;
Apparue dans: IET Signal Processing
Date publication: 06.-2010, volume: 4, issue:3, pages: 298 - 304
Editeur: IEEE
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» SPARE—A Scalable Algorithm for Passive, Structure Preserving, Parameter-Aware Model Order Reduction
Résumé:
This paper describes a flexible and efficient new algorithm for model order reduction of parameterized systems. The method is based on the reformulation of the parameterized system as a perturbation-like parallel interconnection of the nominal transfer function and the nonparameterized transfer function sensitivities with respect to the parameter variations. Such a formulation reveals an explicit dependence on each parameter which is exploited by reducing each component system independently via a standard nonparameterized structure preserving algorithm. Therefore, the resulting smaller size interconnected system retains the structure of the original system with respect to parameter dependence. This allows for better accuracy control, enabling independent adaptive order determination with respect to each parameter and adding flexibility in simulation environments. It is shown that the method is efficiently scalable and preserves relevant system properties such as passivity. The new technique can handle fairly large parameter variations on systems whose outputs exhibit smooth dependence on the parameters, also allowing design space exploration to some degree. Several examples show that besides the added flexibility and control, when compared with competing algorithms, the proposed technique can, in some cases, produce smaller reduced models with potential accuracy gains.
Auteurs: Villena, J. F.;Silveira, L. M.;
Apparue dans: IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems
Date publication: 06.-2010, volume: 29, issue:6, pages: 925 - 938
Editeur: IEEE
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» Sparse Approximation Through Boosting for Learning Large Scale Kernel Machines
Résumé:
Recently, sparse approximation has become a preferred method for learning large scale kernel machines. This technique attempts to represent the solution with only a subset of original data points also known as basis vectors, which are usually chosen one by one with a forward selection procedure based on some selection criteria. The computational complexity of several resultant algorithms scales as in time and in memory, where is the number of training points and is the number of basis vectors as well as the steps of forward selection. For some large scale data sets, to obtain a better solution, we are sometimes required to include more basis vectors, which means that is not trivial in this situation. However, the limited computational resource (e.g., memory) prevents us from including too many vectors. To handle this dilemma, we propose to add an ensemble of basis vectors instead of only one at each forward step. The proposed method, closely related to gradient boosting, could decrease the required number of forward steps significantly and thus a large fraction of computational cost is saved. Numerical experiments on three large scale regression tasks and a classification problem demonstrate the effectiveness of the proposed approach.
Auteurs: Sun, P.;Yao, X.;
Apparue dans: IEEE Transactions on Neural Networks
Date publication: 06.-2010, volume: 21, issue:6, pages: 883 - 894
Editeur: IEEE
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» Sparse Bayesian Learning of Filters for Efficient Image Expansion
Résumé:
We propose a framework for expanding a given image using an interpolator that is trained in advance with training data, based on sparse Bayesian estimation for determining the optimal and compact support for efficient image expansion. Experiments on test data show that learned interpolators are compact yet superior to classical ones.
Auteurs: Kanemura, A.;Maeda, S.-I.;Ishii, S.;
Apparue dans: IEEE Transactions on Image Processing
Date publication: 06.-2010, volume: 19, issue:6, pages: 1480 - 1490
Editeur: IEEE
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» Sparse Non-Gaussian Component Analysis
Résumé:
Non-Gaussian component analysis (NGCA) introduced in offered a method for high-dimensional data analysis allowing for identifying a low-dimensional non-Gaussian component of the whole distribution in an iterative and structure adaptive way. An important step of the NGCA procedure is identification of the non-Gaussian subspace using principle component analysis (PCA) method. This article proposes a new approach to NGCA called sparse NGCA which replaces the PCA-based procedure with a new the algorithm we refer to as convex projection.
Auteurs: Diederichs, E.;Juditsky, A.;Spokoiny, V.;Schutte, C.;
Apparue dans: IEEE Transactions on Information Theory
Date publication: 06.-2010, volume: 56, issue:6, pages: 3033 - 3047
Editeur: IEEE
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» Sparse Recovery Using Sparse Matrices
Résumé:
In this paper, we survey algorithms for sparse recovery problems that are based on sparse random matrices. Such matrices has several attractive properties: they support algorithms with low computational complexity, and make it easy to perform incremental updates to signals. We discuss applications to several areas, including compressive sensing, data stream computing, and group testing.
Auteurs: Gilbert, A.;Indyk, P.;
Apparue dans: Proceedings of the IEEE
Date publication: 06.-2010, volume: 98, issue:6, pages: 937 - 947
Editeur: IEEE
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» Sparse Representation for Computer Vision and Pattern Recognition
Résumé:
Techniques from sparse signal representation are beginning to see significant impact in computer vision, often on nontraditional applications where the goal is not just to obtain a compact high-fidelity representation of the observed signal, but also to extract semantic information. The choice of dictionary plays a key role in bridging this gap: unconventional dictionaries consisting of, or learned from, the training samples themselves provide the key to obtaining state-of-the-art results and to attaching semantic meaning to sparse signal representations. Understanding the good performance of such unconventional dictionaries in turn demands new algorithmic and analytical techniques. This review paper highlights a few representative examples of how the interaction between sparse signal representation and computer vision can enrich both fields, and raises a number of open questions for further study.
Auteurs: Wright, J.;Ma, Y.;Mairal, J.;Sapiro, G.;Huang, T. S.;Yan, S.;
Apparue dans: Proceedings of the IEEE
Date publication: 06.-2010, volume: 98, issue:6, pages: 1031 - 1044
Editeur: IEEE
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» Sparse Representations in Audio and Music: From Coding to Source Separation
Résumé:
Sparse representations have proved a powerful tool in the analysis and processing of audio signals and already lie at the heart of popular coding standards such as MP3 and Dolby AAC. In this paper we give an overview of a number of current and emerging applications of sparse representations in areas from audio coding, audio enhancement and music transcription to blind source separation solutions that can solve the “cocktail party problem.” In each case we will show how the prior assumption that the audio signals are approximately sparse in some time-frequency representation allows us to address the associated signal processing task.
Auteurs: Plumbley, M. D.;Blumensath, T.;Daudet, L.;Gribonval, R.;Davies, M. E.;
Apparue dans: Proceedings of the IEEE
Date publication: 06.-2010, volume: 98, issue:6, pages: 995 - 1005
Editeur: IEEE
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» Sparsity and Compressed Sensing in Radar Imaging
Résumé:
Remote sensing with radar is typically an ill-posed linear inverse problem: a scene is to be inferred from limited measurements of scattered electric fields. Parsimonious models provide a compressed representation of the unknown scene and offer a means for regularizing the inversion task. The emerging field of compressed sensing combines nonlinear reconstruction algorithms and pseudorandom linear measurements to provide reconstruction guarantees for sparse solutions to linear inverse problems. This paper surveys the use of sparse reconstruction algorithms and randomized measurement strategies in radar processing. Although the two themes have a long history in radar literature, the accessible framework provided by compressed sensing illuminates the impact of joining these themes. Potential future directions are conjectured both for extension of theory motivated by practice and for modification of practice based on theoretical insights.
Auteurs: Potter, L. C.;Ertin, E.;Parker, J. T.;Cetin, M.;
Apparue dans: Proceedings of the IEEE
Date publication: 06.-2010, volume: 98, issue:6, pages: 1006 - 1020
Editeur: IEEE
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» Spatial Harmonics and Homogenization of Negative-Refractive-Index Transmission-Line Structures
Résumé:
In this paper, we discuss negative-refractive-index transmission-line (NRI-TL) metamaterial structures with respect to spatial harmonics. The power in the fundamental spatial harmonic is shown to yield a measure that relates to the homogeneity of the metamaterial. It is shown that NRI-TL metamaterials yield highly homogeneous field distributions if both the unit cell is short compared to the guided wavelength, and if the unloaded unit cell is short compared to the “free space” wavelength. Based on the homogeneity, we provide practical design choices for NRI-TL metamaterial unit cells. Under the restriction of a high homogeneity we derive expressions for extracting an effective permittivity and permeability. Circuit theory results and full-wave eigenmode simulations of two NRI-TL structures are presented.
Auteurs: Zedler, M.;Eleftheriades, G. V.;
Apparue dans: IEEE Transactions on Microwave Theory and Techniques
Date publication: 06.-2010, volume: 58, issue:6, pages: 1521 - 1531
Editeur: IEEE
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» Spatial stability of non-steady Stokes flow along a pipe
Résumé:
Estimates for the growth and decay of the cross-section total energy flux in the form of exponential lower and upper bounds are obtained for non-steady Stokes flow in a semi-infinite three-dimensional pipe of uniform star-shaped cross-section. The method depends upon the derivation and integration of a first-order differential inequality.
Auteurs: R.J., Knops , C., Lupoli
Apparue dans: International Journal of Engineering Science
Date publication: 06.-2010
Editeur: Elsevier B.V.
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» Spatial-Temporal Color Video Reconstruction From Noisy CFA Sequence
Résumé:
Single-sensor digital video cameras use a color filter array (CFA) to capture video and a color demosaicking (CDM) procedure to reproduce the full color sequence. The reproduced video frames suffer from the inevitable sensor noise introduced in the video acquisition process. This paper presents a spatial-temporal denoising and demosaicking scheme that works without explicit motion estimation. We first perform patch based denoising on the mosaic CFA video. For each CFA patch to be denoised, similar patches are selected within a local spatial-temporal neighborhood. The principal component analysis is performed on the selected patches to remove noise. We then apply an initial single-frame CDM to the denoised CFA data, and subsequently post-process the demosaicked frames by exploiting the spatial-temporal redundancy to reduce the color artifacts. The experimental results on simulated and real noisy CFA sequences demonstrate that the proposed spatial-temporal CFA video denoising and demosaicking scheme can significantly reduce the noise-caused color artifacts and effectively preserve the image edge structures.
Auteurs: Zhang, L.;Dong, W.;Wu, X.;Shi, G.;
Apparue dans: IEEE Transactions on Circuits and Systems for Video Technology
Date publication: 06.-2010, volume: 20, issue:6, pages: 838 - 847
Editeur: IEEE
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» Spatio-Temporal Data Fusion for 3D+T Image Reconstruction in Cerebral Angiography
Résumé:
This paper provides a framework for generating high resolution time sequences of 3D images that show the dynamics of cerebral blood flow. These sequences have the potential to allow image feedback during medical procedures that facilitate the detection and observation of pathological abnormalities such as stenoses, aneurysms, and blood clots. The 3D time series is constructed by fusing a single static 3D model with two time sequences of 2D projections of the same imaged region. The fusion process utilizes a variational approach that constrains the volumes to have both smoothly varying regions separated by edges and sparse regions of nonzero support. The variational problem is solved using a modified version of the Gauss–Seidel algorithm that exploits the spatio-temporal structure of the angiography problem. The 3D time series results are visualized using time series of isosurfaces, synthetic X-rays from arbitrary perspectives or poses, and 3D surfaces that show arrival times of the contrasted blood front using color coding. The derived visualizations provide physicians with a previously unavailable wealth of information that can lead to safer procedures, including quicker localization of flow altering abnormalities such as blood clots, and lower procedural X-ray exposure. Quantitative SNR and other performance analysis of the algorithm on computational phantom data are also presented.
Auteurs: Copeland, A. D.;Mangoubi, R. S.;Desai, M. N.;Mitter, S. K.;Malek, A. M.;
Apparue dans: IEEE Transactions on Medical Imaging
Date publication: 06.-2010, volume: 29, issue:6, pages: 1238 - 1251
Editeur: IEEE
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» Speak to Win (Tracy, B.; 2008) [Book Review]
Résumé:
In 12 chapters, the author moves through topics such as the art of speaking, preparation and planning, the strong opening, platform mastery, vocal mastery, the strong conclusion, and a few other tips on negotiation thrown in along the way. While the book could provide ideas for an accomplished or experienced speaker, it could also serve as a quick reference for someone embarking on a new career or career enhancement.
Auteurs: Floyd, R.E.;
Apparue dans: IEEE Transactions on Professional Communication
Date publication: 06.-2010, volume: 53, issue:2, pages: 183 - 184
Editeur: IEEE
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» Speak to Win Book Review
Résumé:
Auteurs: Tracy, B.;
Apparue dans: IEEE Transactions on Professional Communication
Date publication: 06.-2010, volume: 53, issue:2, pages: 183 - 184
Editeur: IEEE
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» Special Section on Relay Communications
Résumé:
Auteurs: Yuen, C.;
Apparue dans: IEEE Transactions on Vehicular Technology
Date publication: 06.-2010, volume: 59, issue:5, pages: 2118 - 2119
Editeur: IEEE
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» Spectral dependency of superconducting single photon detectors
Résumé:
We investigate the effect of varying both incoming optical wavelength and width of NbN nanowires on the superconducting single photon detectors (SSPD) detection efficiency. The SSPD are current biased close to critical value and temperature fixed at 4.2 K, far from transition. The experimental results are found to verify with a good accuracy predictions based on the “hot spot model,” whose size scales with the absorbed photon energy. With larger optical power inducing multiphoton detection regime, the same scaling law remains valid, up to the three-photon regime. We demonstrate the validity of applying a limited number of measurements and using such a simple model to reasonably predict any SSPD behavior among a collection of nanowire device widths at different photon wavelengths. These results set the basis for designing efficient single photon detectors operating in the infrared (2–5 μm range).
Auteurs: Maingault, L.;Tarkhov, M.;Florya, I.;Semenov, A.;Espiau de Lamaestre, R.;Cavalier, P.;Goltsman, G.;Poizat, J.-P.;Villegier, J.-C.;
Apparue dans: Journal of Applied Physics
Date publication: 06.-2010, volume: 107, issue:11, pages: 116103 - 116103-3
Editeur: IEEE
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» Spectral Reflectance Imaging for a Multiplexed, High-Throughput, Label-Free, and Dynamic Biosensing Platform
Résumé:
There are a number of emerging optical biosensing techniques utilizing interferometric and resonant characteristics of light. We have recently demonstrated an interferometric technique, the spectral reflectance imaging biosensor (SRIB) that uses optical wave interference to detect changes in the optical path length as a result of capture of biological material on the microarray surface without the need for labels and secondary reagents. In this paper, we review the principles and performance of the SRIB technique in the context of label-free biosensors and demonstrate its high-throughput, quantitative and calibrated, versatile, and dynamic (kinetic) capabilities. A unique aspect of the SRIB system is that the measurement technique is independent of surface conformation and allows for utilization of novel polymeric coatings for surface binding, thus providing a versatile and high-density platform. We present experimental results on multiplexed antibody/antigen arrays and DNA hybridization in real time, as well as specific binding of whole virus particles. The simplicity of the overall system, its high sensitivity and compatibility with glass surface chemistries, and a linear dynamic range of nearly four orders of magnitude makes SRIB a promising platform for multiplexed detection of different biological analytes in a complex sample, with potential impact in research and clinical applications.
Auteurs: Ozkumur, E.;Lopez, C. A.;Yalcin, A.;Connor, J. H.;Chiari, M.;Unlu, M. S.;
Apparue dans: IEEE Journal of Selected Topics in Quantum Electronics
Date publication: 06.-2010, volume: 16, issue:3, pages: 635 - 646
Editeur: IEEE
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» Spectrum sensing with active cognitive systems
Résumé:
Spectrum sensing is critical for cognitive systems to locate spectrum holes. In the IEEE 802.22 proposal, short quiet periods are arranged inside frames to perform a coarse intra-frame sensing as a pre-alarm for fine inter-frame sensing. However, the limited sample size of the quiet periods may not guarantee a satisfying performance and an additional burden of quiet-period synchronization is required. To improve the sensing performance, we first propose a quiet-active sensing scheme in which inactive customer-provided equipments (CPEs) will sense the channels in both the quiet and active periods. To avoid quiet-period synchronization, we further propose to utilize (optimized) active sensing, in which the quiet periods are replaced by `quiet samples¿ in other domains, such as quiet sub-carriers in OFDMA systems. By doing so, we not only save the need for synchronization, but also achieve selection diversity by choosing quiet sub-carriers based on channel conditions. The proposed active sensing scheme is also promising for spectrum sharing applications where both the cognitive and primary systems can be active simultaneously.
Auteurs: Song, S.H.;Hamdi, K.;Letaief, K.B.;
Apparue dans: IEEE Transactions on Wireless Communications
Date publication: 06.-2010, volume: 9, issue:6, pages: 1849 - 1854
Editeur: IEEE
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» Spectrum Shaping for Heterodyne Detection of Wavelength-Swept WDM Signal: Feasibility Study of Mach–Zehnder Interferometer-Type Periodic Filter
Résumé:
In this paper, we investigate the performance of a spectrum shaping technique for the suppression of image-induced crosstalk during the heterodyne detection of wavelength-swept wavelength-division-multiplexed (WDM) signals. In particular, we focus on a Mach–Zehnder interferometer (MZI) filter as a promising candidate for a spectrum shaping filter. We calculate the relationship between the power penalty, signal-to-crosstalk ratio (SCR) and free spectral range (FSR) of the MZI filter, the bandwidth of an IF filter, and the bit rate per channel, taking into consideration three tandem configurations of plural MZIs with different FSRs. And, to clarify the tolerance to the wavelength drift that occurs in actual systems, we investigate the impact of the wavelength mismatch between a WDM signal and a local light. The calculated results provide the criteria for suppressing the image-induced penalty quantitatively, and the SCR improvements that are realized when the tandem configurations are used. The results also indicate that each type of MZI tandem configuration has merits and demerits, depending on the ratio of the bit rate per channel to the channel spacing and the reception quality requirements. Furthermore, we also describe experiments that we performed with respect to the generation, spectrum shaping, and selective heterodyne detection of a three-channel super-dense WDM signal with a channel spacing of 25 GHz transmitted at 1.0 Gb/s per channel, by using tandem configurations of three MZI filters ( , 12.5, and 6.25 GHz). The experimental results agreed well with the calculated results, which are based on the consideration discussed in Sections III and IV , and the results confirmed that the image rejection was well performed. Moreover, we confirmed that we can suppress the SCR degradation b- - y using the tandem configurations for a spectrum shaper. The allowable normalized wavelength mismatch for a degradation of 1.0 dB can be enhanced from 0.012 for 1-MZI to 0.016 and 0.04 for 2-MZI and 3-MZI configurations, respectively.
Auteurs: Taniguchi, T.;Sakurai, N.;Kimura, H.;Hadama, H.;
Apparue dans: Journal of Lightwave Technology
Date publication: 06.-2010, volume: 28, issue:11, pages: 1693 - 1702
Editeur: IEEE
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» Spectrum shaping: a new perspective on cognitive radio¿part I: coexistence with coded legacy transmission
Résumé:
A new approach to cognitive radio based on the premise that the legacy link is not fully loaded by the legacy service is presented. The assumption implies that there is a non-negligible margin to accommodate a cognitive transmission; this accommodation is achieved by spectrum shaping of the cognitive user. Much prior work on cognitive systems captures the effect of interference by the interference power level. In contrast, the current work characterizes interference by its induced degradation on the legacy user. Despite ignorance of the legacy user¿s message, the spectrum shaped cognitive user can always operate at its full available power. As a result, logarithmic growth of the cognitive transmission rate is achievable. In Part I of this two-part paper, analysis is provided for both scalar and vector system models where the legacy system employs coded transmission (Part II examines analog legacy users). The logarithmic growth rates, i.e., the prelog coefficients, of cognitive transmission rates in the high-power regime, are established for both the scalar and vector system models considered.
Auteurs: Zhang, W.;Mitra, U.;
Apparue dans: IEEE Transactions on Communications
Date publication: 06.-2010, volume: 58, issue:6, pages: 1857 - 1867
Editeur: IEEE
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» Speedup of FEM Micromagnetic Simulations With Graphical Processing Units
Résumé:
We have adapted our finite element micromagnetic simulation software to the massively parallel architecture of graphical processing units (GPUs) with double-precision floating point accuracy. Using the example of Standard Problem #4 with different numbers of discretization points, we demonstrate the high speed performance of a single GPU compared with an OpenMP-parallelized version of the code using eight CPUs. The adaption of both the magnetostatic field calculation and the time integration of the Landau-Lifshitz-Gilbert equation routines can lead to a speedup factor of up to four. The gain in computation performance of the GPU code increases with increasing number of discretization nodes. The computation time required for high-resolution micromagnetic simulations of the magnetization dynamics in large magnetic samples can thus be reduced effectively by employing GPUs.
Auteurs: Kakay, A.;Westphal, E.;Hertel, R.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 2303 - 2306
Editeur: IEEE
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» SPICE Macromodel of Spin-Torque-Transfer-Operated Magnetic Tunnel Junctions
Résumé:
The electrical behavior of a magnetic tunnel junction (MTJ) using spin-torque-transfer (STT) switching was modeled using a SPICE subcircuit. The subcircuit is a two-terminal device that exhibits the electrical characteristics of an STT-MTJ. These characteristics include all the major transient characteristics of an MTJ, including the hysteresis, bias voltage dependence of the resistance, and the critical switching current versus the critical switching time. The model was designed to work over a wide range of operating conditions. Simulation and analysis of an MTJ-based D flip-flop are presented to demonstrate possible applications of the model.
Auteurs: Harms, J. D.;Ebrahimi, F.;Yao, X.;Wang, J.-P.;
Apparue dans: IEEE Transactions on Electron Devices
Date publication: 06.-2010, volume: 57, issue:6, pages: 1425 - 1430
Editeur: IEEE
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» Spin Accumulation in Cr Nanoparticles in Single Electron Tunneling Regime
Résumé:
We have studied spin-dependent single electron tunneling in Cr nanoparticles with a diameter of 4 nm using Fe/MgO/Cr-nanoparticles/MgO/Fe double tunnel junctions. The transport properties are governed by the Coulomb blockade, showing suppression of current at low bias voltages. Magnetoresistance is clearly observed at a bias voltage over 0.25 V, and the magnetoresistance ratio increases with increasing bias voltage. These results suggest that the magnetoresistance is due to the spin accumulation in Cr nanoparticles. With some assumption, the minimum value of spin relaxation time in Cr nanoparticles is roughly estimated to be on the order of tens of nanoseconds .
Auteurs: Koda, T.;Mitani, S.;Mizuguchi, M.;Takanashi, K.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 2060 - 2062
Editeur: IEEE
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» Spin Coulomb Drag in a One-Dimensional Spin-Polarized Conductor
Résumé:
The spin Coulomb drag is a distinctive feature of spin-polarized transport. The current of majority spins can induce a current of minority spin carriers via the transconductivity. The friction is caused by the Coulomb interaction between up- and down-spin. This interaction reduces the current but does not change the spin-polarization. We calculate the conductivities and the transconductivity for a spin-polarized interacting 1-D electron gas for a lattice without inversion symmetry in the presence of nonmagnetic impurities. Due to the Luttinger liquid properties, the temperature dependence of the transport correlation functions follows power laws of with nonuniversal exponents.
Auteurs: Schlottmann, P.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 1346 - 1349
Editeur: IEEE
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» Spin injection and circular polarized electroluminescence from InAs-based spin-light emitting diode structures
Résumé:
We have investigated circularly polarized electroluminescence (EL) from hybrid II-Mn-VI/III–V light emitting diodes (LED’s) at low temperatures in magnetic fields upto 10 T. Both magnetic (the Brillouin paramagnet Cd1-xMnxSe) and nonmagnetic (CdSe) injectors were studied. Electrons, spin unpolarized (n-CdSe) or spin-polarized (n-CdMnSe), were injected into wide InAs quantum wells, where they recombined with unpolarized holes injected from p-type InAs/AlAsSb layers. Detailed measurements and modeling of the circular polarization of the resulting midinfrared EL were carried out to explore and quantify the additional complexities of this materials system compared with the extensively studied GaAs-based spin-LED structures. We show that optical and spin polarization in narrow gap semiconductors such as InAs are not simply related to each other. To analyze the complex relationship, we have developed and used a detailed rate equation model, which incorporates the band-structure of electrons and holes in a magnetic field, a finite ratio of recombination and spin-flip times, and the spin polarization of the CdMnSe spin-aligner as a function of injection current. The latter was determined in situ by circular polarized photoluminescence measurements on the injector material. Experimentally, the circular polarization degrees of magnetic and nonmagnetic structures are observed to be very similar, when the magnetic samples have low effective Mn incorporation. This results from a combination of the consequently low spin polarization of the aligner and comparable spin and recombination life times in InAs.
Auteurs: Meining, C. J.;Stier, A. V.;McCombe, B. D.;Chado, I.;Grabs, P.;Schmidt, G.;Molenkamp, L. W.;
Apparue dans: Journal of Applied Physics
Date publication: 06.-2010, volume: 107, issue:11, pages: 114510 - 114510-10
Editeur: IEEE
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» Spin Torque Oscillator With Negative Magnetic Anisotropy Materials for MAMR
Résumé:
Microwave assisted magnetic recording (MAMR) has recently emerged as a candidate to solve the trilemma in magnetic recording. In MAMR the magnetizations of recording medium can be switched with much lower magnetic field by magnetic resonance, which however requires a higher frequency oscillator than 20 GHz. In this paper, it is described that spin torque oscillator (STO) using a magnetic material with a large negative uniaxial anisotropy has a possibility to generate higher frequency and stable magnetic field and it might be preferable to a conventional oscillator with soft magnetic materials.
Auteurs: Yoshida, K.;Yokoe, M.;Ishikawa, Y.;Kanai, Y.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 2466 - 2469
Editeur: IEEE
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» Spin Torques in Point Contacts to Exchange-Biased Ferromagnetic Films
Résumé:
Hysteretic magneto-resistance of point contacts formed between non-magnetic tips and single ferromagnetic films exchange-pinned by antiferromagnetic films is investigated. The analysis of the measured current driven and field driven hysteresis agrees with the recently proposed model of the surface spin-valve, where the spin orientation at the interface can be different from that in the bulk of the film. The switching in magneto-resistance at low fields is observed to depend significantly on the direction of the exchange pinning, which allows identifying this transition as a reversal of interior spins of the pinned ferromagnetic films. The switching at higher fields is thus due to a spin reversal in the point contact core, at the top surface of the ferromagnet, and does not exhibit any clear field offset when the exchange-pinning direction or the magnetic field direction is varied. This magnitude of the switching field of the surface spins varies substantially from contact to contact and sometimes from sweep to sweep, which suggests that the surface coercivity can change under very high current densities and/or due to the particular microstructure of the point contact. In contrast, no changes in the effect of the exchange biasing on the interior spins are observed at high currents, possibly due to the rapid drop in the current density away from nanometer sized point contact cores.
Auteurs: Yanson, I. K.;Naidyuk, Y. G.;Balkashin, O. P.;Fisun, V. V.;Triputen, L. Y.;Andersson, S.;Korenivski, V.;Yanson, Y. I.;Zabel, H.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 2094 - 2096
Editeur: IEEE
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» Spin Transfer on Low Resistance-Area MgO-Based Magnetic Tunnel Junctions Prepared by Ion Beam Deposition
Résumé:
This work reports spin transfer switching results on nano-sized MgO-based magnetic tunnel junctions (MTJs) prepared by Ion Beam deposition (IBD). Nano-devices with areas down to 60 nm 180 nm have been successfully nanofabricated. The MgO deposition conditions were optimized aiming at reducing the resistance-area (RA) product, and RA value as low as 0.8 could be successfully obtained for 0.75 nm thick MgO barriers. The average switching current density of 5.45 can be obtained for a MTJ nanopillar with the dimension of 225 nm 730.3 nm with low RA of 1.47 .
Auteurs: Yang, J.;Macedo, R.;Debs, M. G.;Ferreira, R.;Cardoso, S.;Freitas, P. J. P.;Teixeira, J. M.;Ventura, J. O.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 2002 - 2004
Editeur: IEEE
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» Spin Transfer Switching and MR Properties of Co/Pt Multilayered Free Layers for Submicron Sized Magneto-Optical Light Modulation Device
Résumé:
Co/Pt multilayered films show strong perpendicular magnetic anisotropy and have a large magneto-optical Kerr effect in the short wavelength side. To use these films with submicron spatial light modulators driven by spin transfer switching (STS), we fabricated current perpendicular to plane giant magnetoresistance (CPP-GMR) and tunnel magnetoresistance (TMR) devices with Co/Pt multilayers for free layers and investigated the MR properties, the STS characteristics, and the Kerr effects. A Kerr hysteresis loop was clearly observed in the CPP-GMR device, which was 125 180 nm . Full magnetization reversal of the Co/Pt multilayered film by spin transfer torque was demonstrated for a CPP-GMR device with a Cu-based top electrode. On the other hand, there was hardly any resistance change in a CPP-GMR with a transparent top electrode due to the low MR ratio of the device. A TMR stack with a Ag buffer layer showed a strong perpendicular magnetic anisotropy. An MR curve was detected for a TMR device with a transparent top electrode.
Auteurs: Machida, K.;Furukawa, K.;Funabashi, N.;Aoshima, K.-I.;Kuga, K.;Ishibashi, T.;Shimidzu, N.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 2171 - 2174
Editeur: IEEE
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» Spin wave assisted current induced magnetic domain wall motion
Résumé:
The interaction between the propagating spin waves and the current driven motion of a transverse domain wall in magnetic nanowires is studied by micromagnetic simulations. If the speed of domain walls due to current induced spin transfer torque is comparable to the velocity driven by spin waves, the speed of domain wall is improved by applying spin waves. The domain wall velocity can be manipulated by the frequency and amplitude of spin waves. The effect of spin waves is suppressed in the high current density regime in which the domain wall is mostly driven by current induced spin transfer torque.
Auteurs: Jamali, Mahdi;Yang, Hyunsoo;Lee, Kyung-Jin;
Apparue dans: Applied Physics Letters
Date publication: 06.-2010, volume: 96, issue:24, pages: 242501 - 242501-3
Editeur: IEEE
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» Spin- and Spray-Deposited Single-Walled Carbon-Nanotube Electrodes for Organic Solar Cells
Résumé:
Organic bulk-heterojunction solar cells using thin-film single-walled carbon-nanotube (SWCNT) anodes deposited on glass are reported. Two types of SWCNT films are investigated: spin-coated films from dichloroethane (DCE), and spray-coated films from deionized water using sodium dodecyl sulphate (SDS) or sodium dodecyl benzene sulphonate (SDBS) as the surfactant. All of the films are found to be mechanically robust, with no tendency to delaminate from the underlying substrate during handling. Acid treatment with HNO3 yields high conductivities >1000 S cm-1 for all of the films, with values of up to 7694 ± 800 S cm-1 being obtained when using SDS as the surfactant. Sheet resistances of around 100 [Omega] sq-1 are obtained at reasonable transmission, for example, 128 ± 2 [Omega] sq-1 at 90% for DCE, 57 ± 3 [Omega] sq-1 at 65% for H2O:SDS, and 68 ± 5 [Omega] sq-1 at 70% for H2O:SDBS. Solar cells are fabricated by successively coating the SWCNT films with poly(3,4-ethylenedioxythiophene):poly(styrene sulphonate) (PEDOT:PSS), a blend of regioregular poly(3-hexylthiophene) (P3HT) and 1-(3-methoxy-carbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM), and LiF/Al. The resultant devices have respective power conversions of 2.3, 2.2 and 1.2% for DCE, H2O:SDS and H2O:SDBS, with the first two being at a virtual parity with reference devices using ITO-coated glass as the anode (2.3%).
Auteurs: Sungsoo Kim, Jonghyuk Yim, Xuhua Wang, Donal D.C. Bradley, Soonil Lee, John C. deMello
Apparue dans: Advanced Functional Materials
Date publication: 06.-2010
Editeur: Wiley InterScience
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» Spin-Flipping Associated With the Antiferromagnet IrMn
Résumé:
We have used current-perpendicular-to-plane magnetoresistance measurements of Py-based exchange-biased spin-valves containing IrMn inserts of thickness to estimate the spin-flipping probability of the antiferromagnet IrMn. From to 1 nm, we find a rapid decrease in , by about a factor of 50—here is the area through which the CPP current flows, and and are the resistances with the moments of the two Py layers oriented anti-parallel (AP) or parallel (P) to each other. We attribute this decrease to very strong spin-flipping in the IrMn/Cu interfacial region, with effective spin diffusion length 0.24 nm, only about 1 monolayer (ML). But for from 2 to 5 nm, the decrease of with increasing IrMn thickness is much slower. The reason for this slowing is not yet clear.
Auteurs: Acharyya, R.;Nguyen, H. Y. T.;Pratt, W. P.;Bass, J.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 1454 - 1456
Editeur: IEEE
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» Spiral periodic structure inside chaotic region in parameter-space of a Chua circuit
Résumé:
In this letter we investigate, via numerical simulations, the parameter-space of the set of autonomous first-order differential equations of a Chua circuit. We show that this parameter-space presents self-organized periodic structures immersed in a chaotic region, forming a single spiral structure that coils up around a focal point. Additionally, bifurcation diagrams are used to show that those periodic structures also organize themselves in period-adding cascades, along specific directions that point towards this same focal point. Copyright © 2010 John Wiley & Sons, Ltd.
Auteurs: Holokx A. Albuquerque, Paulo C. Rech
Apparue dans: International Journal of Circuit Theory and Applications
Date publication: 06.-2010
Editeur: Wiley InterScience
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» Spontaneous long and short-range ferroelectric ordering in Pb0.55La0.30TiO3 ceramics
Résumé:
In this work, we investigated the temperature dependence of short and long-range ferroelectric ordering in Pb0.55La0.30TiO3 relaxor composition. High-resolution x-ray powder diffraction measurements revealed a clear spontaneous macroscopic cubic-to-tetragonal phase transition in the PLT relaxor sample at ∼60 K below the maximum of the dielectric constant peak (Tm). Indeed, the x-ray diffraction (XRD) data showed that at 300 K (above Tm but below the Burns temperature, TB) the long-range order structure corresponds to a macroscopic cubic symmetry, space group number 221 (Pm-3m), whereas the data collected at 20 K revealed a macroscopic tetragonal symmetry, space group number 99 (P4mm) with c/a=1.0078, that is comparable to that of a normal ferroelectric. These results show that for samples with tetragonal composition, the long-range ferroelectric order may be recovered spontaneously at cryogenics temperatures, in contrast to ferroelectric samples with rhombohedral symmetry. On the other hand, x-ray absorption spectroscopy investigations intriguingly revealed the existence of local tetragonal disorder around Ti atoms for temperatures far below Tm and above TB, for which the sample presents macroscopic tetragonal and cubic symmetries, respectively.
Auteurs: Mastelaro, V. R.;Mascarenhas, Y. P.;Neves, P. P.;Mir, M.;Doriguetto, A. C.;Michalowicz, A.;Moscovici, J.;Lente, M. H.;Eiras, J. A.;
Apparue dans: Journal of Applied Physics
Date publication: 06.-2010, volume: 107, issue:11, pages: 114103 - 114103-9
Editeur: IEEE
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» Sputtered Ru-Ti, Ru-N and Ru-Ti-N films as Cu diffusion barreier
Résumé:
Ultrathin Ru-Ti alloy, Ru-N and Ru-Ti-N films were fabricated as diffusion barriers to Cu metallization. The thermal stability, phase formation surface morphology and atomic depth profile of the Cu/Ru-Ti(10nm)/Si, Cu/Ru-N(10nm)/Si and Cu/Ru-Ti-N(10nm) /Si structures after annealing at different temperatures were investigated. Comparing to the single Ru layer, both N doping and Ti alloying improve the thermal stability and diffusion barrier properties to Cu. The Cu on the Ru-Ti layer has better morphology than Cu on the Ru-N layer, while the Ru-Ti-N layer has the best thermal stability and has great potential to be applied as a single layer diffusion barrier.
Auteurs: Ji, Li , Hai-Sheng, Lu , Yong-Wei, Wang , Xin-Ping, Qu
Apparue dans: Microelectronic Engineering
Date publication: 06.-2010
Editeur: Elsevier B.V.
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» Square-root second-order extended Kalman filter and its application in target motion analysis
Résumé:
In this study, a new non-linear filter based on second-order extended Kalman technology and squareroot Kalman algorithm is proposed and applied to the problem of target motion analysis (TMA). By orthogonalising the state vectors with the square root of covariance matrix, the authors reduce the computational complexity in the second-order extended Kalman algorithm, and then we deduce a secondorder extended Kalman algorithm based on square-root Kalman technology, which is more numerically stable and can guarantee positive and semi-definiteness of the state covariance. The authors apply the new algorithm to a TMA problem, and prove with both numerical simulation and actual experimentation that their algorithm performs well in the significant non-linear systems.
Auteurs: Daowang, F.;Teng, L.;Tao, H.Z.;
Apparue dans: IET Radar, Sonar & Navigation
Date publication: 06.-2010, volume: 4, issue:3, pages: 329 - 335
Editeur: IEEE
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» SRAM Read/Write Margin Enhancements Using FinFETs
Résumé:
Process-induced variations and sub-threshold leakage in bulk-Si technology limit the scaling of SRAM into sub-32 nm nodes. New device architectures are being considered to improve control and reduce short channel effects. Among the likely candidates, FinFETs are the most attractive option because of their good scalability and possibilities for further SRAM performance and yield enhancement through independent gating. The enhancements to read/write margins and yield are investigated in detail for two cell designs employing independently gated FinFETs. It is shown that FinFET-based 6-T SRAM cells designed with pass-gate feedback (PGFB) achieve significant improvements in the cell read stability without area penalty. The write-ability of the cell can be improved through the use of pull-up write gating (PUWG) with a separate write word line (WWL). The benefits of these two approaches are complementary and additive, allowing for simultaneous read and write yield enhancements when the PGFB and PUWG designs are used in combination.
Auteurs: Carlson, A.;Guo, Z.;Balasubramanian, S.;Zlatanovici, R.;King Liu, T.-J.;Nikolic, B.;
Apparue dans: IEEE Transactions on Very Large Scale Integration Systems
Date publication: 06.-2010, volume: 18, issue:6, pages: 887 - 900
Editeur: IEEE
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» Ssecrett and NeuroTrace: Interactive Visualization and Analysis Tools for Large-Scale Neuroscience Data Sets
Résumé:
Data sets imaged with modern electron microscopes can range from tens of terabytes to about one petabyte. Two new tools, Ssecrett and NeuroTrace, support interactive exploration and analysis of large-scale optical-and electron-microscopy images to help scientists reconstruct complex neural circuits of the mammalian nervous system.
Auteurs: Won-Ki Jeong;Beyer, J.;Hadwiger, M.;Blue, R.;Law, C.;Vazquez-Reina, A.;Reid, R.C.;Lichtman, J.;Pfister, H.;
Apparue dans: IEEE Computer Graphics and Applications
Date publication: 06.-2010, volume: 30, issue:3, pages: 58 - 70
Editeur: IEEE
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» SSRF Phase-I Insertion Devices
Résumé:
Shanghai Light Source (SSRF) is a third generation synchrotron radiation facility with the intermediate energy of 3.5 GeV. Two wigglers W80 and W140, one elliptically polarizing undulator EPU100 of the APPLE-II type with 4.3 meters long and two in-vacuum undulators IVU25-1,2 with 2 meters long have been built in the phase-I of SSRF project. This paper describes the design parameters, the magnet configurations and the magnetic field performances of these five IDs. The electron trajectories, the phase errors and the predicated on-axis spectral fluxes with the measured magnetic fields of two in-vacuum undulators are also presented. The R.M.S. phase errors of less than 4 are obtained for the EPU100 in the horizontal polarization mode as well as in the vertical polarization mode. The maximum R.M.S. phase errors for two in-vacuum undulators are 3.1 and 2.2 respectively and the ratio of the photon flux to the ideal case is larger than 80% on the 11th harmonic.
Auteurs: Zhou, Q.;Zhang, W.;Zhang, M.;Wang, H.;Lu, J.;
Apparue dans: IEEE Transactions on Applied Superconductivity
Date publication: 06.-2010, volume: 20, issue:3, pages: 254 - 257
Editeur: IEEE
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» Stability Analysis of a Wave-Energy Conversion System Containing a Grid-Connected Induction Generator Driven by a Wells Turbine
Résumé:
This paper presents the dynamic-stability analyzed results of both dynamic simulations and steady-state performance of a wave-energy power generation system containing a grid-connected induction generator (IG) driven by a Wells turbine. The stator windings of the IG are connected directly to a power grid through a step-up transformer and a transmission line. A dq axis equivalent-circuit model is employed to establish the IG, the transmission line, and the grid to derive the complete dynamic equations of the studied system under three-phase balanced loading conditions. A frequency-domain approach based on eigenvalue analysis and a time-domain scheme based on nonlinear-model simulations are both carried out to systematically determine the dynamic stability of the studied system under various operating conditions. It can be concluded from the simulation results that the studied wave-energy power generation system subject to different disturbance conditions can maintain stable operation.
Auteurs: Wang, L.;Chen, Z.-J.;
Apparue dans: IEEE Transactions on Energy Conversion
Date publication: 06.-2010, volume: 25, issue:2, pages: 555 - 563
Editeur: IEEE
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» Stability and Protection of Coils Wound With YBCO Bundle Conductor
Résumé:
The thermal behavior of a high-temperature superconducting (HTS) coil is significantly different from that of a low-temperature superconducting (LTS) coil. A HTS conductor has a greater volumetric heat capacity at the operating temperature envisaged for practical applications. Therefore, a HTS coil is much less likely to be quenched than a LTS coil by mechanical disturbances such as the heat generated by the cracking of the impregnation material or by the friction resulting from wire movements. However, the HTS conductor is cyclically subjected to tensile strain because electrical charging and discharging are repeated in real applications involving the Superconducting Magnetic Energy Storage (SMES) system. The superconducting characteristics may locally deteriorate due to this cyclic strain. Therefore, to enhance the reliability and safety of the HTS coil, a quench protection scheme is needed. Because the normal-zone propagation velocity is quite low, detecting a non-recovering normal zone is difficult in HTS coils, and quenching produces excessive overheating that may cause the conductor to melt. In this study, we focus on a coil wound with a YBCO bundle conductor used in SMES applications and investigate the redistribution characteristics of the transport current in and the thermal behavior of the coil during a quench; we use a newly developed computer code based on the finite element method (FEM) and an equivalent circuit. We also discuss a protection scheme to dump the magnetic energy stored in the coils on an external resistance connected in parallel.
Auteurs: Ueda, H.;Ishiyama, A.;Shikimachi, K.;Hirano, N.;Nagaya, S.;
Apparue dans: IEEE Transactions on Applied Superconductivity
Date publication: 06.-2010, volume: 20, issue:3, pages: 1320 - 1323
Editeur: IEEE
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» Stability and Quench Test for NbTi CIC Conductor of JT-60SA Equilibrium Field Coil
Résumé:
The EF coil conductors of JT-60SA are designed with the NbTi cable in conduit conductor because the maximum magnetic field goes up to 6.2 T. The prototype NbTi conductor was developed and tested to confirm the capability of the real conductor. The prototype conductor was proven to have enough Tcs margin under the operating conditions investigated in previous test. In this study, the quench test was operated to measure the stability margin and the normal state propagation. Firstly, the MQE under the Tcs margin of 0.2 K was found to be 80 mJ/cc-strand which is almost the same as that of the previous CIC conductor to result in enough stability margins on EF coil operation. Secondly, the propagation velocity to upstream direction and downstream direction were found to be about 0.47 m/s and 0.54 m/s, respectively. Finally, the quench analysis was conducted to calculate the maximum temperature during quench. The analysis results showed that the maximum temperature reached about 70 K, which is within the permissible value of 150 K for the EF coils.
Auteurs: Murakami, H.;Ichige, T.;Kizu, K.;Tsuchiya, K.;Yoshida, K.;Obana, T.;Hamaguchi, S.;Takahata, K.;Mito, T.;Imagawa, S.;
Apparue dans: IEEE Transactions on Applied Superconductivity
Date publication: 06.-2010, volume: 20, issue:3, pages: 512 - 516
Editeur: IEEE
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» Stability and stabilization of aperiodic sampled-data control systems using robust linear matrix inequalities?
Résumé:
Stability analysis of an aperiodic sampled-data control system is considered for application to networked and embedded control. The stability condition is described in a linear matrix inequality to be satisfied for all possible sampling intervals. Although this condition is numerically intractable, a tractable sufficient condition can be constructed with the mean value theorem. Special attention is paid to tightness of the sufficient condition for less conservative stability analysis. A region-dividing technique for the reduction of conservatism and generalization to stabilization are also discussed. An example demonstrates the efficacy of the approach.
Auteurs: Yasuaki, Oishi , Hisaya, Fujioka
Apparue dans: Automatica
Date publication: 06.-2010
Editeur: Elsevier B.V.
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» Stability and Stabilization of Two Time Scale Switched Systems in Discrete Time
Résumé:
In this technical note, stability and stabilization of two time scale switched linear systems in the singular perturbation form are addressed in discrete time. We show that, under an arbitrary switching rule, stability of the slow and fast switched subsystems is not sufficient to assess stability of the original two time scale switched system, even if the singular perturbation parameter tends to zero. Therefore, we propose LMI based conditions that guarantee the asymptotic stability of the two time scale switched system using switched quadratic Lyapunov functions. These conditions express the fact that the coupling between fast and slow subsystems has to be taken into account in addition to stability properties of the two subsystems, when the switching rule is arbitrary. The presented conditions are extended to state feedback control design. A numerical example illustrates the features of the proposed approach.
Auteurs: Malloci, I.;Daafouz, J.;Iung, C.;
Apparue dans: IEEE Transactions on Automatic Control
Date publication: 06.-2010, volume: 55, issue:6, pages: 1434 - 1438
Editeur: IEEE
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» Stability Investigation of a LTS/HTS Hybrid Conductor
Résumé:
A new concept of LTS/HTS hybrid conductor was recently proposed. However, little theoretical and experimental research has been done in aspects of its stability. Based on the electromagnetic model of the hybrid conductors, current redistribution between LTS and HTS is numerically investigated in transient process. Furthermore, temperature distribution, quench velocity and minimum quench energy are also simulated by solving thermal-magnetic coupling equivalent equations. Comparing with conventional superconducting conductor, the simulated results show that the stability of the hybrid conductor can be greatly improved and it has potential application in large scale and conduction cooled superconducting magnet.
Auteurs: Liu, H.;Wang, Y.;Zhang, H.;Qu, Y.;
Apparue dans: IEEE Transactions on Applied Superconductivity
Date publication: 06.-2010, volume: 20, issue:3, pages: 2176 - 2179
Editeur: IEEE
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» Stability of Domain Walls in Ferromagnetic Nanorings
Résumé:
The stability of domain walls in ferromagnetic nanorings is investigated via calculation of the minimum energy path that separates a domain wall from the vortex state of a ferromagnetic nanoring. Trapped domains are stable when they exist between certain types of transverse domain walls, i.e., walls in which the edge defects on the same side of the magnetic strip have equal sign and thus repel. Here the energy barriers between these configurations and vortex magnetization states are obtained using the string method. Due to the geometry of a ring, two types of walls must be distinguished that differ by their overall topological index and exchange energy. The minimum energy path corresponds to the expulsion of a vortex. The energy barrier for annihilation of a wall is compared to the activation energy for transitions between the two ring vortex states.
Auteurs: Chaves-O'Flynn, G. D.;Bedau, D.;Vanden-Eijnden, E.;Kent, A. D.;Stein, D. L.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 2272 - 2274
Editeur: IEEE
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» Stability of Domain Walls in Ferromagnetic Nanorings
Résumé:
The stability of domain walls in ferromagnetic nanorings is investigated via calculation of the minimum energy path that separates a domain wall from the vortex state of a ferromagnetic nanoring. Trapped domains are stable when they exist between certain types of transverse domain walls, i.e., walls in which the edge defects on the same side of the magnetic strip have equal sign and thus repel. Here the energy barriers between these configurations and vortex magnetization states are obtained using the string method. Due to the geometry of a ring, two types of walls must be distinguished that differ by their overall topological index and exchange energy. The minimum energy path corresponds to the expulsion of a vortex. The energy barrier for annihilation of a wall is compared to the activation energy for transitions between the two ring vortex states.
Auteurs: Chaves-O'Flynn, G. D.;Bedau, D.;Vanden-Eijnden, E.;Kent, A. D.;Stein, D. L.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 2272 - 2274
Editeur: IEEE
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» Stability of Domain Walls in Ferromagnetic Nanorings
Résumé:
The stability of domain walls in ferromagnetic nanorings is investigated via calculation of the minimum energy path that separates a domain wall from the vortex state of a ferromagnetic nanoring. Trapped domains are stable when they exist between certain types of transverse domain walls, i.e., walls in which the edge defects on the same side of the magnetic strip have equal sign and thus repel. Here the energy barriers between these configurations and vortex magnetization states are obtained using the string method. Due to the geometry of a ring, two types of walls must be distinguished that differ by their overall topological index and exchange energy. The minimum energy path corresponds to the expulsion of a vortex. The energy barrier for annihilation of a wall is compared to the activation energy for transitions between the two ring vortex states.
Auteurs: Chaves-O'Flynn, G. D.;Bedau, D.;Vanden-Eijnden, E.;Kent, A. D.;Stein, D. L.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 2272 - 2274
Editeur: IEEE
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» Stability of Domain Walls in Ferromagnetic Nanorings
Résumé:
The stability of domain walls in ferromagnetic nanorings is investigated via calculation of the minimum energy path that separates a domain wall from the vortex state of a ferromagnetic nanoring. Trapped domains are stable when they exist between certain types of transverse domain walls, i.e., walls in which the edge defects on the same side of the magnetic strip have equal sign and thus repel. Here the energy barriers between these configurations and vortex magnetization states are obtained using the string method. Due to the geometry of a ring, two types of walls must be distinguished that differ by their overall topological index and exchange energy. The minimum energy path corresponds to the expulsion of a vortex. The energy barrier for annihilation of a wall is compared to the activation energy for transitions between the two ring vortex states.
Auteurs: Chaves-O'Flynn, G. D.;Bedau, D.;Vanden-Eijnden, E.;Kent, A. D.;Stein, D. L.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 2272 - 2274
Editeur: IEEE
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» Stability of Domain Walls in Ferromagnetic Nanorings
Résumé:
The stability of 2¿ domain walls in ferromagnetic nanorings is investigated via calculation of the minimum energy path that separates a 2¿ domain wall from the vortex state of a ferromagnetic nanoring. Trapped domains are stable when they exist between certain types of transverse domain walls, i.e., walls in which the edge defects on the same side of the magnetic strip have equal sign and thus repel. Here the energy barriers between these configurations and vortex magnetization states are obtained using the string method. Due to the geometry of a ring, two types of 2¿ walls must be distinguished that differ by their overall topological index and exchange energy. The minimum energy path corresponds to the expulsion of a vortex. The energy barrier for annihilation of a 2¿ wall is compared to the activation energy for transitions between the two ring vortex states.
Auteurs: Chaves-O'Flynn, G.D.;Bedau, D.;Vanden-Eijnden, E.;Kent, A.D.;Stein, D.L.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 2272 - 2274
Editeur: IEEE
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» Stability of a time-delayed aeroelastic system with a control surface
Résumé:
This paper investigates the effects of time delay on the flutter instability of an actively controlled airfoil in an incompressible flow field. Firstly, in view of the presence of time delays in the actual control system, multiple time delays in feedback loop are introduced to the present flutter suppression system. Next, the stability boundaries of the closed-loop system with multiple time delays are obtained by solving a polynomial eigenvalue problem, and are validated by numerical simulations. The results demonstrate that time delays in control loop have strong effects on the stability of controlled aeroelastic systems and should not be ignored...
Auteurs: Y.H., Zhao
Apparue dans: Aerospace Science and Technology
Date publication: 06.-2010
Editeur: Elsevier B.V.
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» Stability of General Coupled Inertial Agents
Résumé:
We investigate the stability of a system of multiple inertial agents, using the decomposition approach, in which the velocity/position coupling can be generally non-balanced. The stability of the system is determined by two sorts of factors: the velocity/position coupling and the damping/stiffness gains. We indicate all possibly invariant quantities of the system and give sufficient conditions for stability. Also, our result gives a less conservative estimate to design the damping/stiffness gains of the system for stability than some other recent results.
Auteurs: Li, W.;Spong, M. W.;
Apparue dans: IEEE Transactions on Automatic Control
Date publication: 06.-2010, volume: 55, issue:6, pages: 1411 - 1416
Editeur: IEEE
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» Stability preservation analysis in direct discretization of fractional order transfer functions
Résumé:
In this paper, a class of the direct methods for discretization of fractional order transfer functions is studied in the sense of stability preservation. The stability boundary curve is exactly determined for these discretization methods. Having this boundary helps us to recognize whether the original system and its discretized model are the same in the sense of stability. Finally, some illustrative examples are presented to evaluate achievements of the paper.
Auteurs: Milad, Siami , Mohammad, Saleh Tavazoei , Mohammad, Haeri
Apparue dans: Signal Processing
Date publication: 06.-2010
Editeur: Elsevier B.V.
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» Stability region bifurcations of nonlinear autonomous dynamical systems: Type-zero saddle-node bifurcations
Résumé:
The behavior of stability regions of nonlinear autonomous dynamical systems subjected to parameter variation is studied in this paper. In particular, the behavior of stability regions and stability boundaries when the system undergoes a type-zero sadle-node bifurcation on the stability boundary is investigated in this paper. It is shown that the stability regions suffer drastic changes with parameter variation if type-zero saddle-node bifurcations occur on the stability boundary. A complete characterization of these changes in the neighborhood of a type-zero saddle-node bifurcation value is presented in this paper. Copyright © 2010 John Wiley & Sons, Ltd.
Auteurs: F. M. Amaral, L. F. C. Alberto
Apparue dans: International Journal of Robust and Nonlinear Control
Date publication: 06.-2010
Editeur: Wiley InterScience
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» Stability Test of a Superconducting W7-X Coil With Respect to Mechanical Disturbances
Résumé:
The superconducting magnet system of the Wendelstein 7-X (W7-X) stellarator experiment consists of 50 non-planar and 20 planar coils which are supported by the central support structure and inter-coil structure elements. This highly loaded support system is prone to mechanical disturbances like stick-slip effects. On the other hand, the coils are built up from cable-in-conduit-conductors (CICC) whose strands are highly compressed by Lorentz forces during operation. Residual elastic energy release within a cable can be triggered by shock waves and corresponding frictional heat generation may occur. The released energy might come into the order of the conductor stability limit and possibly cause a quench. An experiment was performed to simulate the impact of such mechanical disturbances on W7-X coils with stability margins corresponding to different operation conditions. A non-planar coil installed within the magnet test facility was energized and then hit by a pendulum via a stainless steel transfer rod. The test has shown that mechanical disturbances expected in W7-X are not able to induce a quench in any of the foreseen W7-X operation scenarios.
Auteurs: Hathiramani, D.;Bergmann, T.;Bykov, V.;Chen, P.;Danner, W.;Dudek, A.;Fellinger, J.;Freundt, S.;Genini, L.;Hochel, K.;Kallmeyer, J. P.;Lingertat, J.;Viebke, H.;Weber, S.;Schauer, F.;
Apparue dans: IEEE Transactions on Applied Superconductivity
Date publication: 06.-2010, volume: 20, issue:3, pages: 543 - 546
Editeur: IEEE
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» Stabilization of controlled positive discrete-time T-S fuzzy systems by state feedback control
Résumé:
This paper deals with sufficient conditions of asymptotic stability and stabilization for nonlinear discrete-time systems represented by a Takagi-Sugeno-type fuzzy model whose state variables take only nonnegative values at all times t for any nonnegative initial state. This class of systems is called positive systems. The conditions of stabilizability are obtained with state feedback control. This work is based on multiple Lyapunov functions. The results are presented in linear matrix inequalities form. A real plant is studied to illustrate this technique. Copyright © 2010 John Wiley & Sons, Ltd.
Auteurs: Abdellah Benzaouia, Abdelaziz Hmamed, Ahmed EL Hajjaji
Apparue dans: International Journal of Adaptive Control and Signal Processing
Date publication: 06.-2010
Editeur: Wiley InterScience
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» Stabilization of networked control systems with nonuniform random sampling periods
Résumé:
In this paper, a new linear delayed delta operator switched system model is proposed to describe networked control systems with packets dropout and network-induced delays. The plant is a continuous-time system, which is sampled by time-varying random sampling periods. A general delta domain Lyapunov stability criterion is given for delta operator switched systems with time delays. Sufficient conditions for asymptotic stability of closed-loop networked control systems with both packets dropout and network-induced delays are presented in terms of linear matrix inequalities (LMIs). A verification theorem is given to show the solvability of the stabilization conditions by solving a class of finite LMIs. Both the case of data packets arrive instantly and the case of invariant sampling periods in delta operator systems are given, respectively. Three numerical examples are given to illustrate the effectiveness and potential of the developed techniques. Copyright © 2010 John Wiley & Sons, Ltd.
Auteurs: Hongjiu Yang, Yuanqing Xia, Peng Shi
Apparue dans: International Journal of Robust and Nonlinear Control
Date publication: 06.-2010
Editeur: Wiley InterScience
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» Stabilization of sets with application to multi-vehicle coordinated motion?
Résumé:
In this paper, we develop stability and control design framework for time-varying and time-invariant sets of nonlinear dynamical systems using vector Lyapunov functions. Several Lyapunov functions arise naturally in multi-agent systems, where each agent can be associated with a generalized energy function which further becomes a component of a vector Lyapunov function. We apply the developed control framework to the problem of multi-vehicle coordinated motion to design distributed controllers for individual vehicles moving in a specified formation. The main idea of our approach is that a moving formation of vehicles can be characterized by a time-varying set in the state...
Auteurs: Sergey G., Nersesov , Parham, Ghorbanian , Amir G., Aghdam
Apparue dans: Automatica
Date publication: 06.-2010
Editeur: Elsevier B.V.
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» Stabilizing Vehicle Lateral Dynamics With Considerations of Parameter Uncertainties and Control Saturation Through Robust Yaw Control
Résumé:
This paper presents a robust yaw-moment controller design for improving vehicle handling and stability with considerations of parameter uncertainties and control saturation. The parameter uncertainties dealt with are the changes of vehicle mass and moment of inertia about the yaw axis and the variations of cornering stiffnesses. The control saturation considered is due to the physical limitations of actuators and tires. Both polytopic and norm-bounded approaches are used to describe parameter uncertainties, and a norm-bounded approach is applied to handle the saturation nonlinearity. The conditions for designing such a controller are derived as linear matrix inequalities (LMIs). A nonlinear vehicle model is utilized to validate the effectiveness of the proposed approach. The simulation results show that the designed controller can improve vehicle handling and stability, regardless of the changes in vehicle mass and moment of inertia and the variations of road surfaces and saturation limitations.
Auteurs: Du, H.;Zhang, N.;Dong, G.;
Apparue dans: IEEE Transactions on Vehicular Technology
Date publication: 06.-2010, volume: 59, issue:5, pages: 2593 - 2597
Editeur: IEEE
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» Stable Inverted Polymer/Fullerene Solar Cells Using a Cationic Polythiophene Modified PEDOT:PSS Cathodic Interface
Résumé:
A cationic and water-soluble polythiophene [poly[3-(6-pyridiniumylhexyl)thiophene bromide] (P3PHT+Br-)] is synthesized and used in combination with anionic poly(3,4-ethylenedioxythiophene):poly(p-styrenesulfonate) (PEDOT:PSS)- to produce hybrid coatings on indium tin oxide (ITO). Two coating strategies are established: i) electrostatic layer-by-layer assembly with colloidal suspensions of (PEDOT:PSS)-, and ii) modification of an electrochemically prepared (PEDOT:PSS)- film on ITO. The coatings are found to modify the work function of ITO such that it could act as a cathode in inverted 2,5-diyl-poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) polymer photovoltaic cells. The interfacial modifier created from the layer-by-layer assembly route is used to produce efficient inverted organic photovoltaic devices (power conversion efficiency [sim]2%) with significant long-term stability in excess of 500 h.
Auteurs: David A. Rider, Brian J. Worfolk, Kenneth D. Harris, Abeed Lalany, Kevin Shahbazi, Michael D. Fleischauer, Michael J. Brett, Jillian M. Buriak
Apparue dans: Advanced Functional Materials
Date publication: 06.-2010
Editeur: Wiley InterScience
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» Stable, Glassy, and Versatile Binaphthalene Derivatives Capable of Efficient Hole Transport, Hosting, and Deep-Blue Light Emission
Résumé:
Organic light-emitting diodes (OLEDs) have great potential applications in display and solid-state lighting. Stability, cost, and blue emission are key issues governing the future of OLEDs. The synthesis and photoelectronics of a series of three kinds of binaphthyl (BN) derivatives are reported. BN1-3 are "melting-point-less" and highly stable materials, forming very good, amorphous, glass-like films. They decompose at temperatures as high as 485-545 °C. At a constant current density of 25 mA cm-2, an ITO/BN3/Al single-layer device has a much-longer lifetime (>80 h) than that of an ITO/NPB/Al single-layer device (8 h). Also, the lifetime of a multilayer device based on BN1 is longer than a similar device based on NPB. BNs are efficient and versatile OLED materials: they can be used as a hole-transport layer (HTL), a host, and a deep-blue-light-emitting material. This versatility may cut the cost of large-scale material manufacture. More importantly, the deep-blue electroluminescence (emission peak at 444 nm with CIE coordinates (0.16, 0.11), 3.23 cd A-1 at 0.21 mA cm-2, and 25200 cd m-2 at 9 V) remains very stable at very high current densities up to 1000 mA cm-2.
Auteurs: Bin Wei, Ji-Zhong Liu, Yong Zhang, Jian-Hua Zhang, Hua-Nan Peng, He-Liang Fan, Yan-Bo He, Xi-Cun Gao
Apparue dans: Advanced Functional Materials
Date publication: 06.-2010
Editeur: Wiley InterScience
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» Stacking fault formation in the long wavelength InGaN/GaN multiple quantum wells grown on m-plane GaN
Résumé:
Nonpolar GaN-based light emitting diodes (LEDs) and laser diodes (LDs) show great promise. However, long wavelength emitters (λ>500 nm) have reduced performance in comparison with violet and blue nonpolar emitters. We present results of transmission electron microscopy studies of long wavelength (1100) m-plane GaN LED series and m-plane GaN LDs grown on high quality bulk GaN substrates. I1 basal plane stacking faults form in the high In content InxGa1-xN quantum wells (x∼0.26) for thicker wells. The I1 faults are bounded by sessile Frank–Shockley partial dislocations that likely limit the radiative efficiency of long wavelength m-plane emitters.
Auteurs: Wu, Feng;Lin, You-Da;Chakraborty, Arpan;Ohta, Hiroaki;DenBaars, Steven P.;Nakamura, Shuji;Speck, James S.;
Apparue dans: Applied Physics Letters
Date publication: 06.-2010, volume: 96, issue:23, pages: 231912 - 231912-3
Editeur: IEEE
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» State estimation in Multi-Microgrids
Résumé:
In this paper, a Multi-Microgrid state estimator is proposed, following the concept of distribution state estimators, where a limited number of real-time measurements are available. Since state estimation (SE) solution is impossible with these limited measurements, forecasted values of load injections at buses remote from the substations are needed, for a given period that coincides with the real-time measurements. The proposed state estimator is based on the traditional WLS algorithm and uses few real-time measurements, mainly at the primary (MV) or secondary (LV) substations and DG locations, and pseudo-measurements for the load bus estimates. The impact of the accuracy of distributed generation (DG) voltage magnitude measurements and load pseudo measurements on the bus voltage estimates is also investigated. Grid-connected and islanded modes are simulated and monitored. Topology errors at the main substations and feeders, where there is sufficient measurement redundancy, are also examined. Test results are given for a 55-bus distribution network including DG. Copyright © 2010 John Wiley & Sons, Ltd.
Auteurs: George N. Korres, Nikos D. Hatziargyriou, Petros J. Katsikas
Apparue dans: European Transactions on Electrical Power
Date publication: 06.-2010
Editeur: Wiley InterScience
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» State-of-the-Art Intelligent Mechatronics in Human–Machine Interaction [Guest Introduction]
Résumé:
Intelligent mechatronics is a machine system that has its own entity and equips humanlike or creaturelike smart abilities. The concept of intelligence is, however, ambiguous; hence, there is no clear definition because the meanings and nuances are modified according to the individual intention of a designer who deals with the concept. In this column, the characteristics and system structure of intelligent mechatronics are briefly mentioned. Several types of state-of-the-art intelligent mechatronics, such as communicative, network, human-assistive, and cognitive types, are introduced.
Auteurs: Harashima, F.;Suzuki, S.;
Apparue dans: IEEE Industrial Electronics Magazine
Date publication: 06.-2010, volume: 4, issue:2, pages: 9 - 13
Editeur: IEEE
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» Statistical Evaluation of Process Damage Using an Arrayed Test Pattern in a Large Number of MOSFETs
Résumé:
Evaluating the statistical variations of MOSFETs is important for realizing accurate analog circuits and large-scale-integration devices. A new evaluation method for the statistical variation of the electrical characteristics of MOSFETs is presented. We have developed a test circuit for understanding the statistical and local variations of MOSFETs in a very short time. We demonstrate that the electrical characteristics in more than one million MOSFETs, such as the threshold voltage and the subthreshold swing (S-Factor), are measured in 30 min and that the measured results are very efficient in developing the fabrication process, the process equipment, and the device structure to reduce the statistical and local characteristic variation.
Auteurs: Watabe, S.;Teramoto, A.;Abe, K.;Fujisawa, T.;Miyamoto, N.;Sugawa, S.;Ohmi, T.;
Apparue dans: IEEE Transactions on Electron Devices
Date publication: 06.-2010, volume: 57, issue:6, pages: 1310 - 1318
Editeur: IEEE
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» Statistics of Optical Coherence Tomography Data From Human Retina
Résumé:
Optical coherence tomography (OCT) has recently become one of the primary methods for noninvasive probing of the human retina. The pseudoimage formed by OCT (the so-called B-scan) varies probabilistically across pixels due to complexities in the measurement technique. Hence, sensitive automatic procedures of diagnosis using OCT may exploit statistical analysis of the spatial distribution of reflectance. In this paper, we perform a statistical study of retinal OCT data. We find that the stretched exponential probability density function can model well the distribution of intensities in OCT pseudoimages. Moreover, we show a small, but significant correlation between neighbor pixels when measuring OCT intensities with pixels of about 5 . We then develop a simple joint probability model for the OCT data consistent with known retinal features. This model fits well the stretched exponential distribution of intensities and their spatial correlation. In normal retinas, fit parameters of this model are relatively constant along retinal layers, but varies across layers. However, in retinas with diabetic retinopathy, large spikes of parameter modulation interrupt the constancy within layers, exactly where pathologies are visible. We argue that these results give hope for improvement in statistical pathology-detection methods even when the disease is in its early stages.
Auteurs: Grzywacz, N. M.;de Juan, J.;Ferrone, C.;Giannini, D.;Huang, D.;Koch, G.;Russo, V.;Tan, O.;Bruni, C.;
Apparue dans: IEEE Transactions on Medical Imaging
Date publication: 06.-2010, volume: 29, issue:6, pages: 1224 - 1237
Editeur: IEEE
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» Status of Resistive Magnets in the LHC Injectors Chain
Résumé:
About 4650 normal conducting magnets are presently installed in the CERN accelerators complex, more than 3000 of them belonging to the LHC injector chain and 163 installed in the LHC. The oldest magnets have been in operation for 50 years, and some of them are submitted to aggressive conditions, either in terms of radiation, extreme water cooling conditions or temperature. The smallest magnets in the linacs weigh a few kilograms, whilst each of the main magnets of the Proton Synchrotron weighs 33 tons. The paper reviews the status of these magnets and gives some examples of findings and relevant recent actions undertaken to ensure their reliable operation in the coming years.
Auteurs: Tommasini, D.;Bauche, J.;Bodart, D.;Lopez, R.;Newborough, A.;Sgobba, S.;Thonet, P.;Zickler, T.;
Apparue dans: IEEE Transactions on Applied Superconductivity
Date publication: 06.-2010, volume: 20, issue:3, pages: 348 - 351
Editeur: IEEE
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» Status of the EDIPO Project
Résumé:
The aim of this paper is to present an up to date review of the status of the European DIPOle (EDIPO) project whose objective is to build a new facility to perform both DC and AC tests of large superconductor samples in high magnetic background field (up to 12.5 T). EDIPO was designed by EFDA, is being built by BNG (Babcock-Noell) and, once completed, it shall be installed near the existing SULTAN facility at the Paul-Scherer-Institute, (CRPP, Villigen, Switzerland). The results presented focus on the manufacture of the dummy coil (which is a 1:1 model of one of the EDIPO poles) that was completed in spring 2009. Details are given about the dummy coil winding results, coil reaction heat treatment, impregnation and acceptance tests. Moreover, a progress status is provided about the manufacturing of the other parts of the EDIPO magnet assembly, in particular with respect to the manufacturing of the test-well, AC coils, yoke sheets cutting and assembly, the outer cylinder production and welding (316 LN steel, 35 mm thick) and the coils ends preparation. Some results regarding the R&D studies are also reported about the winding trials carried out to improve the winding accuracy and the numerical simulations made to support coil winding (e.g. conductor spring back).
Auteurs: Portone, A.;Baker, B.;Combescure, D.;Fernandez-Cano, E.;Salpietro, E.;Testoni, P.;Theisen, E.;
Apparue dans: IEEE Transactions on Applied Superconductivity
Date publication: 06.-2010, volume: 20, issue:3, pages: 600 - 603
Editeur: IEEE
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» Status Quo—The Silent Killer
Résumé:
In a slow economy, most firms find themselves in a "status quo" stance. After taking organization-wide cost-cutting measures, executives often look to IT to create value. This expectation during a down cycle isn't typically aligned with the retrenchment stance. Taking certain steps, including developing and discussing a series of diagrams, can improve IT management in the down market and position IT and the organization for the future uptick.
Auteurs: Costello, Tom;
Apparue dans: IT Professional
Date publication: 06.-2010, volume: 12, issue:3, pages: 61 - 64
Editeur: IEEE
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» Status Report of the SULTAN Test Facility
Résumé:
One year of operation and test activity of the SULTAN test facility at CRPP-Villigen, from October 2008 to October 2009 is reviewed. The main improvements of the facility include a new control system for the cryo-plant and a new electric motor for the helium compressor. The range of operation for the SULTAN samples has been improved in terms of cyclic loading rate. The test campaigns from October 2008 to October 2009 include eight ITER TF conductor samples, two JT60SA samples and a number of other developmental samples. The highlights of the test campaign and the statistical data about cool-downs, warm-ups and test duration are reported. For the eight ITER TF samples, more detail is given about the joint development, the standard test program and the data reduction for the assessment of the results. Eventually, an outlook in the next operation period is also discussed.
Auteurs: Bruzzone, P.;Stepanov, B.;Wesche, R.;Bagnasco, M.;Cau, F.;Herzog, R.;Calvi, M.;Vogel, M.;Jenni, M.;Holenstein, M.;Rajainmaki, H.;
Apparue dans: IEEE Transactions on Applied Superconductivity
Date publication: 06.-2010, volume: 20, issue:3, pages: 455 - 457
Editeur: IEEE
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» Status Report on the Toroidal Field Coils for the ITER Project
Résumé:
The magnet system for ITER comprises 18 Toroidal Field (TF) Coils using cable-in-conduit superconductor, which operate at 4.5 K in supercritical helium.
Auteurs: Savary, F.;Bonito-Oliva, A.;Gallix, R.;Knaster, J.;Koizumi, N.;Mitchell, N.;Nakajima, H.;Okuno, K.;Sborchia, C.;
Apparue dans: IEEE Transactions on Applied Superconductivity
Date publication: 06.-2010, volume: 20, issue:3, pages: 381 - 384
Editeur: IEEE
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» Steady-State Analysis of a Permanent-Magnet-Assisted Salient-Pole Synchronous Generator
Résumé:
This paper presents a simple mathematical model for the steady-state analysis of a permanent-magnet-assisted salient-pole synchronous generator (PMa-SG). The PMa-SG is a new type of salient-pole SG that has PMs between the adjacent pole shoes. The developed model takes into account the magnetic saturation and core loss, and enables quantitative predictions of load characteristics from the no-load test data. The validity of the developed model is confirmed experimentally. The effect of the PMs on the performance characteristics of the PMa-SG is also investigated.
Auteurs: Fukami, T.;Hayamizu, T.;Matsui, Y.;Shima, K.;Hanaoka, R.;Takata, S.;
Apparue dans: IEEE Transactions on Energy Conversion
Date publication: 06.-2010, volume: 25, issue:2, pages: 388 - 393
Editeur: IEEE
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» Steady-State Stability of Current Mode Active-Clamp ZVS DC–DC Converters
Résumé:
Active-clamp dc–dc converters are pulsewidth-modulated converters having two switches featuring zero-voltage switching at frequencies beyond 100 kHz. Generalized equivalent circuits valid for steady-state and dynamic performance have been proposed for the family of active-clamp converters. The active-clamp converter is analyzed for its dynamic behavior under current control in this paper. The steady-state stability analysis is presented. On account of the lossless damping inherent in the active-clamp converters, it appears that the stability region in the current-controlled active-clamp converters get extended for duty ratios, a little greater than 0.5, unlike in conventional hard-switched converters. The conventional graphical approach fails to assess the stability of current-controlled active-clamp converters due to the coupling between the filter inductor current and resonant inductor current. An analysis that takes into account the presence of the resonant elements is presented to establish the condition for stability. This method correctly predicts the stability of the current-controlled active-clamp converters. A simple expression for the maximum duty cycle for subharmonic free operation is obtained. The results are verified experimentally.
Auteurs: Masihuzzaman, M.;Lakshminarasamma, N.;Ramanarayanan, V.;
Apparue dans: IEEE Transactions on Power Electronics
Date publication: 06.-2010, volume: 25, issue:6, pages: 1546 - 1555
Editeur: IEEE
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» Steady-state transport characteristics of photoconductor based on dye-sensitized solar cell
Résumé:
In the present work, three photoconductors based on dye-sensitized nanocrystalline TiO2 are designed with two dye-sensitized solar cells (DSSCs) connected together using a common counter electrode but different connecting approaches for electrolytes and TiO2 film. DC steady-state transport measurements on source and drain corresponding to the photoanodes of two constituent DSSC units, respectively, show that the three photoconductive devices exhibit similar transistor characteristics, regardless of their different electronic connecting approaches. It is revealed that their transport characteristics are determined by the effective areas of the photoanode and the counter electrode, rather than the connection of electrolytes and TiO2 film. Furthermore, it is demonstrated that the dominant factor of transport behavior is the imbalanced energy band caused by the match of intrinsic potential within two constituent DSSC units. Due to unique mechanism and relatively simple fabrication process, the present phototransistors have potentials for an economical and efficient light-operated switch as well as an emerged optical communication device.
Auteurs: Xu, J.;Wang, X. Q.;Lu, Y. M.;Liu, Z. Y.;Cai, C. B.;
Apparue dans: Journal of Applied Physics
Date publication: 06.-2010, volume: 107, issue:11, pages: 114511 - 114511-5
Editeur: IEEE
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» Steganalysis by Subtractive Pixel Adjacency Matrix
Résumé:
This paper presents a method for detection of steganographic methods that embed in the spatial domain by adding a low-amplitude independent stego signal, an example of which is least significant bit (LSB) matching. First, arguments are provided for modeling the differences between adjacent pixels using first-order and second-order Markov chains. Subsets of sample transition probability matrices are then used as features for a steganalyzer implemented by support vector machines. The major part of experiments, performed on four diverse image databases, focuses on evaluation of detection of LSB matching. The comparison to prior art reveals that the presented feature set offers superior accuracy in detecting LSB matching. Even though the feature set was developed specifically for spatial domain steganalysis, by constructing steganalyzers for ten algorithms for JPEG images, it is demonstrated that the features detect steganography in the transform domain as well.
Auteurs: Pevny, T.;Bas, P.;Fridrich, J.;
Apparue dans: IEEE Transactions on Information Forensics and Security
Date publication: 06.-2010, volume: 5, issue:2, pages: 215 - 224
Editeur: IEEE
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» Steganography Development Offers Promise
Résumé:
Topics include a new Bluetooth version that uses less energy, an innovative steganography approach, a proposed specification that promises to enable rich typography on the Web, and a social network for scientists.
Auteurs: Paulson, Linda Dailey;
Apparue dans: Computer
Date publication: 06.-2010, volume: 43, issue:6, pages: 18 - 21
Editeur: IEEE
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» Stiffness and Damping in Fe, Co, and Ni Nanowire-Based Magnetorheological Elastomeric Composites
Résumé:
The stiffness and damping properties of the aligned magnetorheological (MR) elastomer composites filled with 10 wt% Fe, Co, and Ni nanowires were investigated under normalized strain amplitude of 1, 2, and 3%, cyclic deformation frequency of 1 Hz, and magnetic flux density of 0, 0.1, and 0.2 T. The highest values of the dynamic stiffness are observed for the Ni- and the lowest for the Fe-based composites within the whole range of strain amplitude and magnetic flux density. The MR effect on the dynamic stiffness is the most significant for 1% strain amplitude and it almost completely disappears for 3% amplitude for all composites. The equivalent damping coefficient values have maxima for 1% strain amplitude for all composites. These values abruptly drop with an increase of strain amplitude to 2% and only slightly change as strain amplitude is further increased to 3%. The MR effect on the equivalent damping coefficient is high for all composites and strain amplitudes.
Auteurs: Padalka, O.;Song, H. J.;Wereley, N. M.;Filer II, J. A.;Bell, R. C.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 2275 - 2277
Editeur: IEEE
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» Stochastic ellipsoid methods for robust control: Multiple updates and multiple cuts?
Résumé:
Efficient randomized algorithms are developed for solving robust feasibility problems with multiple parameter-dependent convex constraints. Two complementary strategies are presented, both of which exploit the multiplicity to achieve fast convergence. One is the stochastic ellipsoid method with multiple updates. In each iteration of this algorithm, an ellipsoid which describes a candidate of the solution set is updated many times via the multiple constraints with one random sample, while at most one update is allowed in the original method. The other is the stochastic ellipsoid method with multiple cuts. Here, a new update rule is presented to construct a smaller ellipsoid...
Auteurs: Takayuki, Wada , Yasumasa, Fujisaki
Apparue dans: Automatica
Date publication: 06.-2010
Editeur: Elsevier B.V.
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» Stochastic Modular Robotic Systems: A Study of Fluidic Assembly Strategies
Résumé:
Modular robotic systems typically assemble using deterministic processes where modules are directly placed into their target position. By contrast, stochastic modular robots take advantage of ambient environmental energy for the transportation and delivery of robot components to target locations, thus offering potential scalability. The inability to precisely predict component availability and assembly rates is a key challenge for planning in such environments. Here, we describe a computationally efficient simulator to model a modular robotic system that assembles in a stochastic fluid environment. This simulator allows us to address the challenge of planning for stochastic assembly by testing a series of potential strategies. We first calibrate the simulator using both high-fidelity computational fluid-dynamics simulations and physical experiments. We then use this simulator to study the effects of various system parameters and assembly strategies on the speed and accuracy of assembly of topologically different target structures.
Auteurs: Tolley, M. T.;Kalontarov, M.;Neubert, J.;Erickson, D.;Lipson, H.;
Apparue dans: IEEE Transactions on Robotics
Date publication: 06.-2010, volume: 26, issue:3, pages: 518 - 530
Editeur: IEEE
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» Stop-band and band-pass filters in coplanar waveguide technology implemented by means of electrically small metamaterial-inspired open resonators
Résumé:
In this study, coplanar waveguide (CPW) stop-band filters based on open split ring resonators (OSRRs) are presented for the first time. The filters consist on a cascade of transmission line sections, acting as impedance inverters, alternating with shunt connected OSRRs. An order-3 Butterworth stop-band filter is presented as an illustrative example. The second part of the study deals with the application of these stop-band filters to improve the out-of-band rejection (through spurious suppression) of wideband band-pass filters implemented by means of open complementary split ring resonators (OCSRRs). The combination of OCSRRs (the complementary counterparts of OSRRs) and OSRRs for the design of CPW band-pass filters is used for the first time in the proposed prototype device example. The achieved results are promising and are indicative of the possibilities of these electrically small open resonators (OSRRs and OCSRRs).
Auteurs: Velez, A.;Aznar, F.;Duran-Sindreu, M.;Bonache, J.;Martin, F.;
Apparue dans: IET Microwaves, Antennas & Propagation
Date publication: 06.-2010, volume: 4, issue:6, pages: 712 - 716
Editeur: IEEE
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» Strain and crystal defects in thin AlN/GaN structures on (0001) SiC
Résumé:
High-resolution x-ray diffraction was used to compare strain relaxation and defect populations in thin GaN/AlN heterostructures (total thickness ≈480 nm) grown on (0001) SiC using metalorganic chemical vapor deposition (MOCVD) and hydride vapor epitaxy (HVPE) techniques. The results of high-resolution x-ray diffraction measurements (rocking curves and reciprocal space mapping) were corroborated using transmission electron microscopy. Differently grown films exhibited dissimilar strain relaxation and defect populations that were related to specific growth conditions. In the MOCVD films, grown under lower deposition rates, the elastic strain in the AlN and GaN layers was fully relaxed at the initial stages of the epitaxial growth yielding nearly similar densities of threading dislocation segments (TDS) in layer volumes. Additional, “secondary” elastic stresses in these layers were attributed to the excess of point defects. In the HVPE films, grown under higher (five to ten times) deposition rates, these layers were over relaxed and the density of TDS in the GaN layer was an order of magnitude larger than that in AlN. The MOCVD-grown sample was devoid of planar defects whereas the HVPE film contains significant densities of stacking faults in both GaN and AlN layers. Formation of “secondary” extended defects was interpreted in terms of creation and structural transformation of point defects during epitaxial growth. Differences in strain levels, types, and defect populations/distributions for the two heterostructures were attributed to the different growth rates for MOCVD and HVPE.
Auteurs: Faleev, N.;Levin, I.;
Apparue dans: Journal of Applied Physics
Date publication: 06.-2010, volume: 107, issue:11, pages: 113529 - 113529-7
Editeur: IEEE
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» Strain Effects on the Electric and Magnetic Properties of the Magnetoresistive Films
Résumé:
We have synthesized (100) films on , , , and MgO substrates using pulsed laser deposition and investigated their electric and magnetic properties. The structural, electric and magnetic properties of the LBMO films seemed to be dependent on lattice mismatch between LBMO and the substrate. The characteristics of the LBMO film on STO with negligible lattice mismatch were close to those of the bulk LBMO. Interestingly, the uniaxial-type stress acting on the LBMO film by the NGO substrate induced a distinctive difference in the magnetic hysteresis and the magnetoresistance curves measured for two orthogonal in-plane directions. A sudden drop of 0.6% in the low field magnetoresistance curve of the LMBO on the NGO is probably related to spin dependent scattering of charge carriers going through magnetic domains or grains. On the other hand, the LAO and the MgO substrates with a large lattice mismatch of 5% did not effectively induced homogeneous lattice strain to the LBMO film.
Auteurs: Jeong, D.;Dho, J.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 1883 - 1885
Editeur: IEEE
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» Strain Effects on the Electric and Magnetic Properties of the Magnetoresistive Films
Résumé:
We have synthesized (100) films on , , , and MgO substrates using pulsed laser deposition and investigated their electric and magnetic properties. The structural, electric and magnetic properties of the LBMO films seemed to be dependent on lattice mismatch between LBMO and the substrate. The characteristics of the LBMO film on STO with negligible lattice mismatch were close to those of the bulk LBMO. Interestingly, the uniaxial-type stress acting on the LBMO film by the NGO substrate induced a distinctive difference in the magnetic hysteresis and the magnetoresistance curves measured for two orthogonal in-plane directions. A sudden drop of 0.6% in the low field magnetoresistance curve of the LMBO on the NGO is probably related to spin dependent scattering of charge carriers going through magnetic domains or grains. On the other hand, the LAO and the MgO substrates with a large lattice mismatch of 5% did not effectively induced homogeneous lattice strain to the LBMO film.
Auteurs: Jeong, D.;Dho, J.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 1883 - 1885
Editeur: IEEE
Document complet vers site de l'éditeur
 
» Strain Effects on the Electric and Magnetic Properties of the Magnetoresistive Films
Résumé:
We have synthesized (100) films on , , , and MgO substrates using pulsed laser deposition and investigated their electric and magnetic properties. The structural, electric and magnetic properties of the LBMO films seemed to be dependent on lattice mismatch between LBMO and the substrate. The characteristics of the LBMO film on STO with negligible lattice mismatch were close to those of the bulk LBMO. Interestingly, the uniaxial-type stress acting on the LBMO film by the NGO substrate induced a distinctive difference in the magnetic hysteresis and the magnetoresistance curves measured for two orthogonal in-plane directions. A sudden drop of 0.6% in the low field magnetoresistance curve of the LMBO on the NGO is probably related to spin dependent scattering of charge carriers going through magnetic domains or grains. On the other hand, the LAO and the MgO substrates with a large lattice mismatch of 5% did not effectively induced homogeneous lattice strain to the LBMO film.
Auteurs: Jeong, D.;Dho, J.;
Apparue dans: IEEE Transactions on Magnetics
Date publication: 06.-2010, volume: 46, issue:6, pages: 1883 - 1885
Editeur: IEEE
Document complet vers site de l'éditeur
 


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