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Cooperative recombination of electron-hole pairs in semiconductor quantum wells under quantizing magnetic fields

Physical Review B 2010年第15期81卷 155314-155314页

作者： Y. D. Jho X. Wang D. H. Reitze J. Kono A. A. Belyanin V. V. Kocharovsky Vl. V. Kocharovsky G. S. Solomon Department of Information and Communications Gwangju Institute of Science and Technology Gwangju 500-712 Republic of Korea Department of Physics University of Florida Gainesville Florida 32611 USA National High Magnetic Field Laboratory Florida State University Tallahassee Florida 32310 USA Department of Electrical and Computer Engineering Rice University Houston Texas 77005 USA Department of Physics Texas A&M University College Station Texas 77843 USA Institute of Applied Physics Russian Academy of Sciences 603950 Nizhny Novgorod Russia Joint Quantum Institute NIST & University of Maryland Gaithersburg Maryland 20899 USA

We present results of detailed investigations of light emission from semiconductor multiple quantum wells at low temperatures and high magnetic fields excited by intense femtosecond laser pulses. The intensity and linewidth as well as the directional and statistical properties of photoemission strongly depended on the magnetic field strength and pump laser fluence. We also investigated the effects of spot size, temperature, excitation geometry, and excitation pulse width on the emission properties. The results suggest that the initially incoherent photoexcited electron-hole pairs spontaneously form a macroscopic coherent state upon relaxation into the low-lying magnetoexcitonic states, followed by the emission of a superfluorescent burst of radiation. We have developed a theoretical model for superfluorescent emission from semiconductor quantum wells, which successfully explained the observed characteristics.

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Passive decoy-state quantum key distribution with practical light sources

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Physical Review A 2010年第2期81卷 022310-022310页

作者： Marcos Curty Xiongfeng Ma Bing Qi Tobias Moroder ETSI Telecomunicación Department of Signal Theory and Communications University of Vigo Campus Universitario E-36310 Vigo (Pontevedra) Spain Institute for Quantum Computing & Department of Physics and Astronomy University of Waterloo N2L 3G1 Waterloo Ontario Canada Center for Quantum Information and Quantum Control Department of Physics and Department of Electrical & Computer Engineering University of Toronto M5S 3G4 Toronto Ontario Canada Quantum Information Theory Group Institute of Theoretical Physics I University of Erlangen-Nürnberg D-91058 Erlangen Germany Max Planck Institute for the Science of Light D-91058 Erlangen Germany

Decoy states have been proven to be a very useful method for significantly enhancing the performance of quantum key distribution systems with practical light sources. Although active modulation of the intensity of the laser pulses is an effective way of preparing decoy states in principle, in practice passive preparation might be desirable in some scenarios. Typical passive schemes involve parametric down-conversion. More recently, it has been shown that phase-randomized weak coherent pulses (WCP) can also be used for the same purpose [M. Curty et al., Opt. Lett. 34, 3238 (2009).] This proposal requires only linear optics together with a simple threshold photon detector, which shows the practical feasibility of the method. Most importantly, the resulting secret key rate is comparable to the one delivered by an active decoy-state setup with an infinite number of decoy settings. In this article we extend these results, now showing specifically the analysis for other practical scenarios with different light sources and photodetectors. In particular, we consider sources emitting thermal states, phase-randomized WCP, and strong coherent light in combination with several types of photodetectors, like, for instance, threshold photon detectors, photon number resolving detectors, and classical photodetectors. Our analysis includes as well the effect that detection inefficiencies and noise in the form of dark counts shown by current threshold detectors might have on the final secret key rate. Moreover, we provide estimations on the effects that statistical fluctuations due to a finite data size can have in practical implementations.

关键词： Photodetectors

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Advances in Moving Horizon Estimation for Nonlinear Systems

Advances in Moving Horizon Estimation for Nonlinear Systems

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2010 49th IEEE Conference on Decision and Control

作者： Angelo Alessandri Marco Baglietto Giorgio Battistelli Victor Zavala Department of Production Engineering Thermoenergetics and Mathematical Models DIPTEM-University of Genoa P.le Kennedy Pad. D 16129 Genova Italy Department of Communications Computer and System Sciences DIST-University of Genoa Via Opera Pia 13 16145 Genova Italy Dipartimento di Sistemi e Informatica Universita degli Studi di Firenze Via di S. Marta 3 50139 Firenze Italy Mathematics and Computer Science Division Argonne National Laboratory 9700 South Cass Ave Bldg. 221 Argonne IL 60439 USA

ISBN: (纸本)9781424477456

In the last decade, moving horizon estimation (MHE) has emerged as a powerful technique for tackling the problem of estimating the state of a dynamic system in the presence of nonlinearities and disturbances. MHE is based on the idea of minimizing an estimation cost function defined on a sliding window composed of a finite number of time stages. The cost function is usually made up of two contributions: a prediction error computed on a recent batch of inputs and outputs;an arrival cost that serves the purpose of summarizing the past data. However, the diffusion of such techniques has been hampered by: i) the difficulty in choosing the arrival cost so as to ensure stability of the overall estimation scheme;ii) the request of an adequate computational effort on line. In this paper, both problems are addressed and possible solutions are proposed. First, by means of a novel stability analysis, it is constructively shown that under very general observability conditions a quadratic arrival cost is sufficient to ensure the stability of the estimation error provided that the weight matrix is adequately chosen. Second, a novel approximate MHE algorithm is proposed that is based on nonlinear programming sensitivity calculations. The approximate MHE algorithm has the same stability properties of the optimal one which make the overall approach suitable to be applied in real settings. Preliminary simulation results confirm the effectiveness of proposed method.

关键词： Cost functions Horizon sliding windows Moving Dynamic systems Error of prediction

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Active learning through problem based learning methodology in engineering education

Active learning through problem based learning methodology i...

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39th Annual Frontiers in Education Conference: Imagining and engineering Future CSET Education, FIE 2009

作者： Lacuesta, Raquel Palacios, Guillermo Fernández, Luis Department of Computer Science and Systems Engineering University of Zaragoza Spain Department of Electronic Engineering and Communications University of Zaragoza Spain Department of Computing University of Alcalá Spain

ISBN: (纸本)9781424447152

The main objective of this experience lies on the development of positive learning aptitudes on engineering students. The experience presented in this paper has been carried out with the help of the problembased learning (PBL) methodology. Solutions of mediumhigh complexity problems by students make them work on the development of different skills. The teaching model turns into a significant and autonomous learning model where students are conscious of their compromise with this process (learning). The obtained results are a starting point to other authors willing to use active learning methodologies within the framework of engineering degrees. Both lecturers and students involved in the experience have done a positive assessment of the methodology. © 2009 IEEE.

关键词： Students

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Work in progress - Hypermedia tool for the development of specific and generic competences in the framework of engineering education

Work in progress - Hypermedia tool for the development of sp...

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39th Annual Frontiers in Education Conference: Imagining and engineering Future CSET Education, FIE 2009

作者： Palacios, Guillermo Lacuesta, Raquel Fernández, Luis Department of Electronic Engineering and Communications University of Zaragoza Spain Department of Computer Science and Systems Engineering University of Zaragoza Spain Department of Computing University of Alcalá Spain

ISBN: (纸本)9781424447152

This work introduces a didactic framework for electronic teaching and learning based on a hypermedia tool which integrates the principles of the learning theories from a cognitive point of view. It exhibits a great deal of flexibility and easiness of adaptation for other subjects belonging to technological areas in engineering education. The proposed open learning environment has a modular design which allows a lecturer to organize subjects by grouping the different and specific resources in a simple and structured way. The main goal pursued is to improve the teaching and learning process by providing the collaborative work among lectures, joining efforts in the teaching process. It also establishes a didactic methodology based on the conceptual relations to be acquired by students, encouraging both personal work and learning self-regulation, so student acquisition of competences and skills is reinforced. ©2009 IEEE.

关键词： engineering education

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Joint application of STBC and RAKE receivers in multipath Rayleigh fading channels

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IEEE communications Letters 2009年第9期13卷 646-648页

作者： Wang, Szu-Chi Lin, Wei-Sen Chen, Hsiao-Hwa Institute of Computer Science and Information Engineering National Ilan University Yilan Taiwan Institute of Communications Engineering National Sun Yat-Sen University Kaohsiung city Taiwan Department of Engineering Science National Cheng Kung University Tainan City 70101 Taiwan

This letter investigates the issues on joint application of STBC systems and RAKE receivers in a CDMA system. We show the advantages of using STBC-RAKE receivers in multipath Rayleigh fading channels via error probability analysis and extensive computer simulations. Specifically, this study leads to a better understanding of the interplay between spatial diversity by STBC and multipath diversity via RAKE receivers. © 2009 IEEE.

关键词： Rayleigh fading

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Application of neural network analysis to automatic detection of road surface conditions utilizing tire noise from vehicles

Application of neural network analysis to automatic detectio...

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ICCAS-SICE 2009 - ICROS-SICE International Joint Conference 2009

作者： Kongrattanaprasert, Wuttiwat Nomura, Hideyuki Kamakura, Tomoo Ueda, Koji Department of Electronic Engineering University of Electro-Communications Tokyo Japan School of Computer Science Daido University Nagoya Japan

ISBN: (纸本)9784907764296

This paper proposes a new method for automatically detecting the states of the road surface from tire noises of vehicles. The methods are based on a Fast Fourier Transform analysis, an artificial neural network, and the mathematical theory of evidence. The proposed classification is carried out in sets of multiple neural networks using the learning vector quantization networks. The outcomes of the networks are then integrated using the voting decision making scheme. It seems then feasible to detect passively and readily the states of the surface: i.e., as a rule of thumb, dry, wet, snowy and slushy state, automatically. The classification results in the validation set were greater than 80% in accuracy. © 2009 SICE.

关键词： Neural networks

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Diversity analysis of bit-interleaved coded multiple beamforming

Diversity analysis of bit-interleaved coded multiple beamfor...

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2009 IEEE International Conference on communications, ICC 2009

作者： Hong, Ju Park Ayanoglu, Ender Center for Pervasive Communications and Computing Department of Electrical Engineering and Computer Science University of California Irvine CA United States

ISBN: (纸本)9781424434350

In this paper, diversity analysis of bit-interleaved coded multiple beamforming (BICMB) is extended to the case of general spatial interleavers, removing a condition on their previously known design criteria and quantifying the resulting diversity order. The diversity order is determined by a parameter Qmax which is inherited from the convolutional code and the spatial de-multiplexer used in BICMB. We introduce a method to find this parameter by employing a transfer function approach as in finding the weight spectrum of a convolutional code. By using this method, several Qmax values are shown and verified to be identical with the results from a computer search. The diversity analysis and the method to find the parameter are supported by simulation results. By using the Singleton bound, we also show that Q max is lower bounded by the product of the number of streams and the code rate of an encoder. The design rule of the spatial de-multiplexer for a given convolutional code is proposed to meet the condition on the maximum achievable diversity order. ©2009 IEEE.

关键词： Convolutional codes

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Fast Intra-Network and Cross-layer Handover (FINCH) for WiMAX and mobile internet

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IEEE Transactions on Mobile Computing 2009年第4期8卷 558-574页

作者： Yeh, Jui-Hung Chen, Jyh-Cheng Agrawal, Prathima Realtek-NCTU Joint Research Center National Chiao Tung University Hsinchu 30010 Taiwan Department of Computer Science Institute of Communications Engineering National Tsing Hua University Hsinchu 300 Taiwan Department of Electrical and Computer Engineering Wireless Engineering Research and Education Center Auburn University Auburn AL 36849 United States

To support fast and efficient handovers in mobile WiMAX, we propose Fast Intra-Network and Cross-layer Handover (FINCH) for intradomain (intra-CSN) mobility management. FINCH is a complementary protocol to Mobile IP (MIP), which deals with interdomain (inter-CSN) mobility management in mobile WiMAX. FINCH can reduce not only the handover latency but also the end-to-end latency for MIP. Paging extension for FINCH is also proposed to enhance the energy efficiency. The proposed FINCH is especially suitable for real-time services in frequent handover environment, which is important for future mobile WiMAX networks. In addition, FINCH is a generic protocol for other IEEE 802-series standards. This is especially beneficial for the integration of heterogeneous networks, for instance, the integration of WiMAX and WiFi networks. Both mathematical analysis and simulation are developed to analyze and compare the performance of FINCH with other protocols. The results show that FINCH can support fast and efficient link layer and intradomain handovers. The numerical results can also be used to select proper network configurations. © 2006 IEEE.

关键词： Energy efficiency

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Performance analyses of OFDMCDMA receivers in multipath fading channels

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IEEE Transactions on Vehicular Technology 2009年第9期58卷 4805-4818页

作者： Chen, Jun-Da Ueng, Fang-Biau Chang, Jui-Chi Su, Hsien Institute of Computer and Communication Engineering Jinwen University of Science and Technology Taipei 231-54 Taiwan Department of Electrical Engineering National Chung Hsing University Taichung 402 Taiwan ZyXEL Communications Corporation Hsinchu 300 Taiwan

Orthogonal frequency-division multiplexing (OFDM) is a promising scheme for multicarrier (MC) transmission. The combination of OFDM and code-division multiple access (CDMA) which is referred to as OFDM-CDMA, has recently attracted much research interest in wireless communications. In this paper, we evaluate the downlink performance for two forms of adaptive OFDM-CDMA receivers in multipath fading channels: 1) MC-CDMA and 2) MC-direct sequence (DS)-CDMA. We propose theoretical minimum mean square errors (MMSEs) for MC-CDMA and MC-DS-CDMA to compare the performances in different situations. Moreover, one drawback of OFDM schemes is the rate reduction due to the cyclic prefix (CP) overhead, which significantly affects the channel utilization in MCDS-CDMA systems. We propose adaptive receiver structures with both subcarrier-and code-interval equalizations to improve the performance of MC-DS-CDMA systems with shorter or no CP. Simulation results demonstrate the effectiveness of the proposed receivers and the correctness of the theoretical derivations. © 2009 IEEE.

关键词： Orthogonal frequency division multiplexing

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