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Onset of synchronization in large networks of coupled oscillators

Physical Review E 2005年第3期71卷 036151-036151页

作者： Juan G. Restrepo Edward Ott Brian R. Hunt Institute for Research in Electronics and Applied Physics University of Maryland College Park Maryland 20742 USA Department of Mathematics University of Maryland College Park Maryland 20742 USA Department of Physics and Department of Electrical and Computer Engineering University of Maryland College Park Maryland 20742 USA Institute for Physical Science and Technology University of Maryland College Park Maryland 20742 USA

We study the transition from incoherence to coherence in large networks of coupled phase oscillators. We present various approximations that describe the behavior of an appropriately defined order parameter past the transition and generalize recent results for the critical coupling strength. We find that, under appropriate conditions, the coupling strength at which the transition occurs is determined by the largest eigenvalue of the adjacency matrix. We show how, with an additional assumption, a mean-field approximation recently proposed is recovered from our results. We test our theory with numerical simulations and find that it describes the transition when our assumptions are satisfied. We find that our theory describes the transition well in situations in which the mean-field approximation fails. We study the finite-size effects caused by nodes with small degree and find that they cause the critical coupling strength to increase.

关键词： Oscillators (electronic)

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Limits on the time delay induced by slow-light propagation

Limits on the time delay induced by slow-light propagation

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Quantum Electronics and Laser Science Conference (QELS)

作者： R.W. Boyd D.L. Gauthier A.L. Gaeta A.E. Willner Institute of Optics University of Rochester Rochester NY USA Department of Physics Duke University Durham NC USA School of Applied and Engineering Physics Cornell University Ithaca NY USA Department of Electrical and Computer Engineering University of Southern California Los Angeles CA USA

We show that there are no fundamental limits to the maximum time delay that can be achieved for pulses propagating through slow-light media, thus suggesting the importance of slow-light methods for practical applicati... 详细信息

关键词： Delay effects Optical pulses Optical propagation Optical buffering Optical signal processing Optical materials High speed optical techniques Optical solitons Optical control Space vector pulse width modulation

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Enhanced terahertz emission from impurity compensated GaSb

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Physical Review B 2005年第4期72卷 045328-045328页

作者： Ricardo Ascázubi Carl Shneider Ingrid Wilke Robinson Pino Partha S. Dutta Department of Physics Applied Physics and Astronomy Rensselaer Polytechnic Institute 110 8th Street Troy New York 12180 USA Department of Electrical Computer and Systems Engineering Rensselaer Polytechnic Institute 110 8th Street Troy New York 12180 USA

We report femtosecond optically excited terahertz (THz) emission from tellurium doped GaSb at room temperature. The influence of the majority and minority carrier type and concentrations on the strength of the THz emission is investigated. Strong enhancement of THz emission in GaSb is observed as a result of compensation of native acceptors by tellurium donors. Surface field acceleration and the photo-Dember effect are identified as THz emission mechanisms in GaSb and modeled in dependence of the majority and minority carrier type and concentrations in our GaSb samples. THz emission from p-type GaSb is dominated by the photo-Dember effect whereas THz emission from n-type GaSb is dominated by surface field acceleration. The doping conditions under which THz emission is maximized are identified.

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Optical thin films with very low refractive index and their application in photonics devices

Optical thin films with very low refractive index and their ...

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2005 MRS Fall Meeting

作者： Xi, J.-Q. Kim, Jong Kyu Ye, Dexian Juneja, Jasbir S. Lu, T.-M. Lin, Shawn-Yu Schubert, E.F. Future Chips Constellation Rensselaer Polytechnic Institute 110 8th Street Troy NY 12180 United States Department of Physics Applied Physics and Astronomy Rensselaer Polytechnic Institute 110 8th Street Troy NY 12180 United States Department of Electrical Computer and Systems Engineering Rensselaer Polytechnic Institute 110 8th Street Troy NY 12180 United States Department of Chemical and Biological Engineering Rensselaer Polytechnic Institute 110 8th Street Troy NY 12180 United States

ISBN: (纸本)1558998551

The refractive index contrast in dielectric multilayer structures, optical resonators and photonic crystals is an important figure of merit, which creates a strong demand for high quality thin films with a very low refractive index. SiO2 nano-rod layers with low refractive indices n = 1.08, the lowest ever reported in thin-film materials, is grown by oblique-angle e-beam deposition of SiO2 with vapor incident angle θ - 85°, Scanning electron micrographs reveal a highly porous columnar structure of the low-refractive-index (low-n) film. The gap between the SiO2 nano-rods is ≤ 50 nm, i.e. much smaller than the wavelength of visible light, and thus sufficiently small to make scattering very small, Optical micrographs of the low-n film deposited on a Si substrate reveal a uniform specular film with no apparent scattering. The unprecedented low index of the SiO2 nano-rod layer is confirmed by both ellipsometry measurements and thin film interference measurements. A single-pair distributed Bragg reflector (DBR) employing the SiO2 nano-rod layer is demonstrated to have enhanced reflectivity, showing the great potential of low-n films for applications in photonic structures and devices. © 2006 Materials Research Society.

关键词： Thin films

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A method of simulating intensity modulation-direct detection WDM systems

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Optoelectronics Letters 2005年第1期1卷 57-60页

作者： HUANG Jing YAO Jian-quan LI En-bang School of Precision Instruments and Optoelectronics Engineering Tianjin University TianJin 300072 China Applied Physics Department South China University of Technology Guangzhou 510640 China School of Electrical Computer and Telecommunications Engineering Faculty of Infonnatics University of Wollongong NSW 2522 Australia

In the simulation of Intensity Modulation-Direct Detection WDM Systems,when the dispersion and nonlinear effects play equally important roles,the intensity fluctuation caused by cross-phase modulation may be overestimated as a result of the improper step ***,the step size in numerical simulation should be selected to suppress false XPM intensity modulation (keep it much less than signal power).According to this criterion,the step size is variable along the *** a WDM system,the step size depends on the channel *** type of transmission fiber has different step *** the split-step Fourier method,this criterion can reduce simulation time,and when the step size is bigger than 100 meters,the simulation accuracy can also be improved.

关键词：光纤通信 WDW 光突法交换信号传输强度模拟

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ONLINE TRAFFIC LIGHT CONTROL THROUGH GRADIENT ESTIMATION USING STOCHASTIC FLUID MODELS

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IFAC Proceedings Volumes 2005年第1期38卷 90-95页

作者： Christos G. Panayiotou William C. Howell Michael Fu Department of Electrical and Computer Engineering University of Cyprus Nicosia Cyprus Department of Mathematics Applied Mathematics Scientific Computation Program University of Maryland College Park MD 20742 USA Smith School of Business and Institute for Systems Research University of Maryland College Park MD 20742 USA

In this paper, we consider the problem of dynamically regulating the timing of traffic light controllers in busy cities. We use a Stochastic Fluid Model (SFM) to model the dynamics of the queues formed at an intersection. Based on this model, we derive gradients of the queue lengths with respect to the green/red light lengths within a signal cycle. We report preliminary numerical results comparing the performance of the estimates with finite-difference and smoothed perturbation analysis estimates. Then all estimators are used to optimize the traffic system via Stochastic Approximation.

关键词： Traffic control perturbation analysis stochastic approximation

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Low-noise, high-energy, single-mode, femtosecond fiber laser system

Low-noise, high-energy, single-mode, femtosecond fiber laser...

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Conference on Lasers and Electro-Optics (CLEO)

作者： F.O. Ilday J. Chen A. Winter F.X. Kartner F.W. Wise O. Shkurikhin D. Gapontsev Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics Massachusetts Institute of Technology Cambridge MA USA Department of Applied Physics Cornell University Ithaca NY USA IPG-Photonics Oxford MA USA

Truly single-mode amplification of femtosecond pulses from a fiber oscillator to /spl sim/100 nJ is demonstrated. Amplitude and phase noise characterization of the source and its robustness demonstrates its potential ... 详细信息

关键词： Fiber lasers Pulse amplifiers Optical fibers Optical fiber polarization Optical fiber amplifiers Ultrafast optics Optical pulses Oscillators Laser noise Optical fiber couplers

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Solid-state lighting: Toward superior illumination

Solid-state lighting: Toward superior illumination

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作者： Shur, Michael S. Žukauskas, Arturas IIEE Japan Department of Electrical Computer and Systems Engineering and Physics Rensselaer Polytechnic Institute Troy NY 12180 United States Institute of Materials Science and Applied Research Vilnius University Vilnius 10222 Lithuania Department of Solid State Electronics United States Department of Physics Applied Physics and Astronomy United States Center for Broadband Data Transport Science and Technology Rensselaer Polytechnic Institute Troy NY United States American Physical Society United States Electrochemical Society United States World Innovation Foundation United States Eta Kappa Nu Electromagnetic Academy Materials Research Society United States American Society for Engineering Education United States SPIE United States American Association for the Advancement of Science United States IEEE Sensor Council United States Institute of Materials Science and Applied Research Lithuania Department of Semiconductor Physics Lithuania Lithuanian Physical Society Lithuania Lithuanian Materials Research Society Lithuania Lithuanian Academy of Sciences Lithuania

Solid-state lighting technology is now emerging as a cost-competitive, energy-efficient alternative to conventional electrical lighting. We review the history of lighting, discuss the benefits and challenges of the solid-state lighting technologies, and compare two approaches for generating white light from solid-state sources based on phosphor LEDs (which could be considered as solid-state replacement of fluorescent tubes) and multichip LED lamps, which offer many advantages, such as chromaticity control, better light quality, and higher efficiency. © 2005 IEEE.

关键词： Solid state devices

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Picosecond 14.7 nm interferometry of high intensity laser-produced plasmas

Picosecond 14.7 nm interferometry of high intensity laser-pr...

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作者： Dunn, James Filevich, Jorge Smith, Raymond F. Moon, Stephen J. Rocca, Jorge J. Keenan, Roisin Nilsen, Joseph Shlyaptsev, Vyacheslav N. Hunter, James R. Andrew, N.G. Marcqni, Mario C. Lawrence Livermore National Laboratory Livermore Livermore CA NSF ERC for Extreme Ultraviolet Science and Technology Department of Electrical and Computer Engineering Colorado State University Fort Collins CO Department of Applied Science University of California Davis-Livermore Livermore CA University of British Columbia Vancouver Department of Physics University of Buenos Aires Argentina Lawrence Livermore National Laboratory L-251 P.O. Box 808 Livermore CA 94551

We have developed a compact, 14.7 nm, sub-5 ps X-ray laser source at Lawrence Livermore National Laboratory (LLNL) together with a Mach-Zehnder type diffraction grating interferometer built at Colorado State University for probing dense, high intensity laser-produced plasmas. The short wavelength and pulse length of the probe reduces refraction, absorption effects within the plasma and minimizes plasma motion blurring. This unique diagnostic capability gives precise two-dimensional (2D) density profile snapshots and is generating new data for rapidly evolving laser-heated plasmas. Areview of the results from dense, mm-scale line focus plasma experiments will be described with detailed comparisons to hydrodynamic simulations. Copyright © 2005 Cambridge University Press.

关键词： Laser produced plasmas

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Monotonic convergent iterative learning controller design with iteration varying model uncertainty

Monotonic convergent iterative learning controller design wi...

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IEEE International Conference on Mechatronics and Automation

作者： Hyo-Sung Ahn K.L. Moore YangQuan Chen Center for Self-Organizing and Intelligent Systems CSOIS Department of Electrical and Computer Engineering Utah State University Logan UT USA Research and Technology Development Center Applied Physics Laboratory Johns Hopkins University Laurel MD USA Center for Self-Organizing and Intelligent Systems CSOIS Department of Electrical and Computer Engineering Utah State University Laurel UT USA

In iterative learning control, model uncertainty issue has been studied in various ways. But, in existing works, the model uncertainty has been considered as iteration invariant, that is, it does not change on the iteration axis. Furthermore, in these works, monotone convergence problem has not been properly studied. In this paper, new monotonic convergence condition of iteration varying model uncertain iterative learning control system is derived. So, the main goal of this paper is to guarantee the monotone convergence of the iteration varying model uncertainty system until the tracking error is reduced below the previously calculated base-line error boundary. Through the numerical example, the validity of the suggested method is illustrated.

关键词： Uncertainty Convergence Intelligent systems physics computing Error correction Laboratories Control system synthesis History Testing Equations

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