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Exchange bias and magnetotransport properties in IrMn/NiFe/FeMn structures

Physical Review B 2008年第18期78卷 184413-184413页

作者： Z. B. Guo Y. H. Wu J. J. Qiu B. Y. Zong G. C. Han Data Storage Institute Agency for Science Technology and Research (A*STAR) DSI Building 5 Engineering Drive 1 Singapore 117608 Department of Electrical and Computer Engineering National University of Singapore Singapore 119260

For the double exchange-biased IrMn/NiFe/FeMn structures, the pinning directions at IrMn/NiFe and NiFe/FeMn interfaces were set either parallel or antiparallel to each other by field annealing. Exchange bias and magnetotransport properties in IrMn/NiFe/FeMn trilayers were studied and compared with those of IrMn/NiFe and NiFe/FeMn bilayers. The dependence of exchange bias on the thickness of NiFe layer was different for parallel and antiparallel pinnings. A remarkable increase in resistance was observed which should be attributed to domain-wall resistance induced by the twisted spin structure. The spin configuration of twisted spin structure was simulated by one-dimensional atomic model.

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Distributed precoder optimization for interfering MISO channels

Distributed precoder optimization for interfering MISO chann...

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ITG Workshop on Smart Antennas

作者： David A. Schmidt Andreas Grundinger Wolfgang Utschick Michael L. Honig Institute for Signal Processing Technische Universität München Munich Germany Department of Electrical Engineering and Computer Science Northwestern University Evanston IL USA

In this paper, we examine the problem of two multiple-input-single-output (MISO) links that interfere with each other. We discuss some straightforward strategies for the users to optimize their rates and show how a certain degree of cooperation between the users can lead to an improvement of both individual links. We propose an algorithm that is based on the users exchanging 'interference prices' and is realizable in a distributed manner. The algorithm converges towards a locally sum-rate optimal solution and exhibits nearly identical performance as a non-distributed gradient ascent algorithm, outperforming the straightforward strategies over the complete range of noise powers.

关键词： Interference Transmitters Receiving antennas Transmitting antennas Time sharing computer systems Additive noise Array signal processing Signal processing computer science Throughput

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Multiple Heterogeneous Ant Colonies with Information Exchange

Multiple Heterogeneous Ant Colonies with Information Exchang...

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Congress on Evolutionary Computation

作者： Arash Arami Bijan Rahmizadeh Rofoee Caro Lucas Control and Intelligent Processing Center of Excellence (CIPCE) school of Electrical and Computer Engineering University of Tehran Tehran Iran Electrical and Computer Engineering Department Tabriz University Tabriz Iran School of Cognitive Science Institute of Studies in Theoretical Physics and Mathematics Tehran Iran CIPCE school of Electrical and Computer Engineering University of Tehran Tehran Iran

The method of multiple heterogeneous ant colonies with information exchange (MHACIE) is presented in this paper with emphasis on the speed of finding the optimal solution and the corresponding computational complexity. The proposed method which is inspired by biology and psychology has a structure composed of several ant colonies. These colonies participate in solving problems in a concurrently manner and also exchange information with each other in communicational steps. Each ant colony is considered as an intelligent agent with behavioral traits. These behavioral traits play a key role in the solving procedure, in interrelation circumstances and in installation of relations. Faster solutions have been achieved using different employments of agents in the algorithm structure. Experimental results show the superiority of Multiple heterogeneous ant colonies algorithm in comparison to the standard ant colony system (ACS) and particle swarm optimization (PSO) algorithms on different benchmarks. A dynamic, control engineering benchmark is also provided in order to gain a more complete evaluation of the proposed algorithm.

关键词： Benchmark testing Evolution (biology) Optimization Heuristic algorithms Evolutionary computation Electronic mail Educational institutions

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Crystalline Amorphous Semiconductor Superlattice

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Physical Review Letters 2008年第13期100卷 136101-136101页

作者： T. C. Chong L. P. Shi X. Q. Wei R. Zhao H. K. Lee P. Yang A. Y. Du Data Storage Institute A⋆STAR (Agency for Science Technology and Research) Singapore 117608 Electrical Computer Engineering Department National University of Singapore Singapore 117576 Singapore Synchrotron Light Source (SSLS) National University of Singapore Singapore 117603 Institute of Microelectronics A⋆STAR (Agency for Science Technology and Research) Singapore 117685

A new class of superlattice, crystalline amorphous superlattice (CASL), by alternatively depositing two semiconductor materials, is proposed. CASL displays three states depending on the component materials’ phase: both polycrystalline phases, both amorphous phases, and one polycrystalline phase while another amorphous phase. Using materials capable of reversible phase transition, CASL can demonstrate reversibility among three states. GeTe/Sb2Te3 CASL has been synthesized and proved by x-ray reflectometry and TEM results. The reversible transition among three states induced by electrical and laser pulse was observed. The changes in the optical absorption edge, electrical resistivity, thermal conductivity, and crystallization temperature as a function of layer thickness are interpreted as quantum or nanoeffects. The unique properties of CASL enable the design of materials with specific properties.

关键词： Crystalline materials

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An Energy Efficient, Low Cost, Hybrid Storage System Based on Utility

An Energy Efficient, Low Cost, Hybrid Storage System Based o...

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Japan-China Joint Workshop on Frontier of computer science and Technology (FCST)

作者： Lingfang Zeng Dan Feng Bharadwaj Veeravalli Qingsong Wei Key Laboratory of Information Storage Ministry of Education Huazhong University of Science and Technology China Department of Electrical and Computer Engineering National University of Singapore Singapore Data Storage Institute Singapore

To get large disk-like characteristics and offset the significant power demands of hard disk drives, we propose a fully functional hybrid archive system (called Pseudodisk) composed of an array of disks and a tape library. To get an energy conservation, low cost archive system, Pseudodisk uses data value model and utility function to guild data management. Two novel algorithms are proposed for data placement and data migration, which are referred to as utility-based data placement (UDP) and and system utility percentage (SUP) algorithms respectively. To validate the efficiency of the proposed archive system, we conduct the performance evaluation and the power-saving simulation.

关键词： Energy efficiency Energy storage Power demand Hard disks Libraries Energy conservation Cost function Power system modeling Energy management Power system management

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A shared-relay cooperative diversity scheme based on joint channel and network coding

A shared-relay cooperative diversity scheme based on joint c...

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International Symposium on Information Theory and Its Applications, ISITA

作者： Xiaoyan Xu Mark F. Flanagan Christian Koller Norbert Goertz Institute for Digital Communications Joint Research Institute for Signal & Image Processing University of Edinburgh UK Department of Electronics Computer Science and Systems (DEIS) University of Bologna Italy Department of Electrical Engineering University of Notre Dame Notre Dame IN USA

ISBN: (纸本)9781424420681

In cooperative communications, the technique of algebraic code superposition (or network coding) may efficiently utilize limited communications resources to produce spatial diversity. In this paper, we propose a simple cooperative diversity scheme for the scenario of two sources sharing a single relay. No cooperative coding is required at the sources, and only very simple interleave-and-superpose operations are performed at the relay. We propose a novel computationally efficient message passing algorithm at the destination's decoder which utilizes spatial diversity gathered over multiple transmission frames. We show that despite the simplicity of the proposed scheme, diversity gains are efficiently leveraged by the simple combination of channel coding at the sources and network coding at the relay.

关键词： Network coding Decoding Relays Parity check codes Electronic mail Fading Message passing Diversity methods Information theory Digital communication

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The extended invariance principle applied to joint time-delay, frequency, and DOA estimation

The extended invariance principle applied to joint time-dela...

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International Conference on Acoustics, Speech, and Signal processing (ICASSP)

作者： Felix Antreich Josef A. Nossek Gonzalo Seco A. Lee Swindlehurst Institute for Communications and Navigation German Aerospace Center Wessling Germany Institute for Circuit Theory & Signal Processing Munich University of Technology Germany Department of Telecommunications & Systems Engineering Universitat Autonoma de Barcelona Spain Department of Electrical Engineering & Computer Science University of California Irvine CA USA

This paper deals with the joint estimation of temporal (time- delay, Doppler frequency) and spatial (direction-of-arrival, DOA) parameters of several replicas of a known signal in an unknown spatially correlated field. Unstructured and structured models have been proposed in the literature. The former suffers from a severe performance degradation in some scenarios, whereas the latter involves huge complexity. It is shown how the extended invariance principle (EXIP) can be applied to obtain estimates with the quality of those of the structured model, but with the complexity of the unstructured one. We present a method to improve the quality of the time- delay and Doppler estimates obtained with an unstructured spatial model when an estimate of the DOAs is available. Exemplarily, simulation results for time-delay estimation for GPS (global positioning system) are included and confirm that our proposal approaches the Cramer-Rao lower bound (CRLB) of the structured model even when suboptimal DOA estimates obtained by ESPRIT are introduced.

关键词： Frequency estimation Direction of arrival estimation Global Positioning System Delay estimation data models Sensor arrays Signal processing Gaussian noise Aerospace engineering Navigation

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Robust H∞ compensation for external vibration on hard disk drives in mobile applications

Robust H∞ compensation for external vibration on hard disk ...

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International Workshop on Advanced Motion Control (AMC)

作者： Chunling Du Sam Shuzhi Ge Fan Hong Jingliang Zhang F. L. Lewis Agency for Science Technology and Research Singapore SG Department of Electrical and Computer Engineering National University of Singapore Singapore A*STAR Data Storage Institute(DSI) 5 Engineering Drive 1 117608 Singapore Automation and Robotics Research Institute University of Texas Arlington USA

Compensation for external vibration impact on the positioning accuracy of hard disk drives is considered with the presence of actuator uncertainty in this paper. The low-frequency mode change due to actuator pivot nonlinearity of the voice-coil- motor (VCM) actuator is described as frequency and damping uncertainty. A robust feedforward controller is then designed in continuous time domain by using H infin method to attenuate the impact with the aid of a sensor to detect external vibrations. The linear matrix inequality (LMI) approach is adopted to solve the robust H infin feedforward control design problem. The application results in a 1.8-inch disk drive with an accelerometer to measure acceleration signal show that 27% to 91% reduction of the position error signal is achieved with the robust feedforward controller when the frequency changes in 70 plusmn 50 Hz and damping in 0.4 plusmn 0.3. The effectiveness of the robust feedforward control is also demonstrated to be better than nominal feedforward control.

关键词： Robustness Hard disks Robust control Actuators Uncertainty Frequency Damping Accelerometers Vibration control Linear matrix inequalities

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Spin transverse separation in a two-dimensional electron-gas using an external magnetic field with a topological chirality

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Physical Review B 2008年第24期78卷 245321-245321页

作者： S. G. Tan M. B. A. Jalil Xiong-Jun Liu T. Fujita Data Storage Institute Agency for Science Technology and Research (A*STAR) DSI Building 5 Engineering Drive 1 Singapore 117608 Singapore Department of Electrical and Computer Engineering Information Storage Materials Laboratory National University of Singapore 4 Engineering Drive 3 Singapore 117576 Singapore Department of Physics National University of Singapore 2 Science Drive 3 Singapore 117542 Singapore

We propose a two-dimensional electron-gas (2DEG) system in which an external magnetic field with a small chirality is applied to provide a topological spin gauge field that separates conduction electrons of opposite spins in the transverse direction. Additionally, the vertical electric field in the 2DEG, together with spin-orbit coupling, produces a SU(2) gauge field which reinforces or opposes the effect of the spin gauge. The system thus provides a tunable spin separation effect, where an applied gate voltage on the 2DEG can be used to modulate the transverse spin current. As this method leads to the enhancement or cancellation of spin separation due to the intrinsic spin-orbit coupling effect only, it may naturally distinguish the extrinsic effect from the intrinsic one.

关键词： spin-orbit interactions two-dimensional electron gas

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What we expect from weakly dissipating materials at the range of plasmon resonance frequencies

What we expect from weakly dissipating materials at the rang...

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IEEE PhotonicsGlobal@Singapore, IPGC

作者： B. S. Luk'yanchuk T. C. Chong L. P. Shi M. I. Tribelsky Z. B. Wang L. Li C.-W. Qiu C. J. R. Sheppard J. H. Wu Agency for Science Data Storage Institute Singapore Electronics and Automation Moscow State Institute of Radioengineering Moscow Russia Aerospace and Civil Engineering University of Manchester UK Department of Electrical and Computer Engineering National University of Singapore Singapore Division of Bioengineering National University of Singapore Singapore School of Mechanical Engineering Xi'an Jiaotong University China

Development of modern materials, including nanoclusters, cluster assembled materials and metamaterials is among the actual challenges for the development of future nanotechnologies. Here we discuss the peculiarities of far-field and near-field light scattering by plasmonic nanoparticles, and possible applications of weakly dissipating materials. Over the last few years many peculiarities of light scattering have been found for nanoparticles in the regime of plasmon resonances. Optical excitation of localized plasmons is accompanied by inverse process - transformation of localized resonant plasmons into scattered light. When radiative damping prevails over the dissipative damping, the effects of anomalous light scattering result in sharp giant optical resonances and complicated near-field structure of the Poynting vector field, see e.g. [1-4]. Here we present peculiarities of far-field and near-field light scattering by plasmonic nanoparticles with weak dissipation and anisotropy.

关键词： Plasmons Resonant frequency Resonance light scattering Light scattering Nanoparticles Optical scattering Damping Nanostructured materials Assembly Metamaterials

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