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Magnetic-field dependence of low-lying spectra in magnetic quantum rings and dots

Physical Review B 2005年第19期71卷 195305-195305页

作者： C. M. Lee W. Y. Ruan J. Q. Li Richard C. H. Lee Department of Materials Science and Engineering Shenzhen University Shenzhen 518060 China Department of Electrical and Computer Engineering University of Illinois at Urbana—Champaign Urbana Illinois 61801 USA and Department of Applied Physics South China University of Technology Guangzhou 510641 China

In this paper, the magnetic-field dependence of low-lying spectra of a single-electron magnetic quantum ring and dot, formed by inhomogeneous magnetic fields, are calculated using the numerical diagonalization scheme. The effects of on-center acceptor and donor impurities are also considered. In the presence of an acceptor impurity, transitions in the orbital angular momentum, L, are found for both the magnetic quantum ring and the magnetic quantum dot when the magnetic field is varied.

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Femtosecond laser ablation of silicon (100) with thermal oxide thin films of varying thickness

Femtosecond laser ablation of silicon (100) with thermal oxi...

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Conference on Lasers and Electro-Optics, CLEO 2005

作者： McDonald, Joel P. Ray, Katherine E. Mistry, Vanita R. Mourou, Gérard Yalisove, Steven M. Center for Ultrafast Optical Science Department of Electrical Engineering University of Michigan Ann Arbor MI 48109-2099 United States Applied Physics Program 2477 Randall Laboratory University of Michigan Ann Arbor MI 48109-1120 United States College of Engineering University of Michigan Ann Arbor MI 48109 United States Department of Materials Science and Engineering 2200 Hayward Street Ann Arbor MI 48109-2136 United States

Femtosecond laser ablation of Silicon (100) with thermal oxide thin films was studied in order to further understand the ablative properties of thin films and to evaluate their influence on the ablation of the substra... 详细信息

ISBN: (纸本)1557527709

关键词： Laser ablation

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Feature tracking in VR for cumulus cloud life-cycle studies 05

Feature tracking in VR for cumulus cloud life-cycle studies

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Proceedings of the 11th Eurographics conference on Virtual Environments

作者： E. J. Griffith F. H. Post M. Koutek T. Heus H. J. J. Jonker Faculty of Electrical Engineering Mathematics and Computer Science Delft University of Technology The Netherlands Department of Multi-Scale Physics Faculty of Applied Sciences Delft University of Technology Netherlands

ISBN: (纸本)9783905673210

Feature tracking in large data sets is traditionally an off-line, batch processing operation while virtual reality typically focuses on highly interactive tasks and applications. This paper presents an approach that uses a combination of off-line preprocessing and interactive visualization in VR to simplify and speed up the identification of interesting features for further study. We couch the discussion in terms of our collaborative research on using virtual reality for cumulus cloud life-cycle studies, where selecting suitable clouds for study is simple for the skilled observer but difficult to formalize. The preprocessing involves identifying individual clouds within the data set through a 4D connected components algorithm, and then saving isosurface, bounding box, and volume information. This information is then interactively visualized in our VR Cloud Explorer with various tools and information displays to identify the most interesting clouds. In a small pilot study, reasonable performance, both in the preprocessing phase and the visualization phase, has been measured.

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Efficient message authentication for spread spectrum wireless communications

Efficient message authentication for spread spectrum wireles...

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MILCOM, Military Communications Conference

作者： Shengkuan Xiao D. Carman C. Boncelet Department of Electrical & Computer Engineering University of Delaware Newark DE USA Information Operations Group Johns Hopkins University-Applied Physics Laboratory Laurel MD USA

In this paper, we present a new scheme to reduce the communications requirements to send message authentication tags (MAC's), by sending the MAC's over direct sequence spread spectrum wireless channels. We greatly reduce the number of chips required by considering the chip sequence as a whole. In one example, based on the IS-95 CDMA digital cellular standard, we reduce the chips needed from 3072 to 1142 by a hard decision decoding scheme, and to 728 by a soft decision decoding scheme, achieving savings of factors about three and four, respectively.

关键词： Message authentication Spread spectrum communication Wireless communication Decoding Multiaccess communication Collaboration Government Security Digital signatures physics computing

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Improved modulation spectrum through multi-scale modulation frequency decomposition

Improved modulation spectrum through multi-scale modulation ...

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

作者： S. Sukittanon L.E. Atlas J.W. Pitton K. Filali Department of Electrical Engineering University of Washington Seattle WA USA Applied Physics Laboratory (APL) University of Washington Seattle WA USA Department of Computer Science & Engineering University of Washington Seattle WA USA

The modulation spectrum is a promising method to incorporate dynamic information in pattern classification. It contains important cues about the nonstationary content of a signal and yields complementary improvements when it is combined with conventional features derived from short-term analysis. Many prior modulation spectrum approaches are based on uniform modulation frequency decomposition. The drawbacks of these approaches are high dimensionality and a lack of a connection to human perception of modulation. The paper presents multi-scale modulation frequency decomposition and shows an improvement over the standard modulation spectrum in a digital communication signal classification task. Features derived from this representation provide lower classification error rates than those from a constant-bandwidth modulation spectrum, whether used alone or in combination with short-term features.

关键词： Frequency modulation Pattern classification Signal analysis Humans Fourier transforms Amplitude modulation Digital modulation Error analysis Pattern analysis Hidden Markov models

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Enhanced terahertz emission from porous InP

Enhanced terahertz emission from porous InP

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Optical Terahertz Science and Technology, OTST 2005

作者： Reid, M. Cravetchi, I.V. Fedosejevs, R. Tiginyanu, I.M. Sirbu, L. Boyd, Robert W. Department of Electrical and Computer Engineering University of Alberta Edmonton AB T6G 2V4 Canada Laboratory of Low Dimensional Semiconductor Structures Institute of Applied Physics Academy of Sciences and Technical University of Moldova 2004 Chisinau Moldova Institute of Optics University of Rochester Rochester NY 14627 United States

Terahertz and second-harmonic emission from bulk and porous InP samples is investigated under irradation with femtosecond Ti:Sapphire laser pulses. The emission from the porous samples is enhanced relative to the bulk... 详细信息

ISBN: (纸本)1557527865

关键词： III-V semiconductors

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

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

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2005 International Semiconductor Device Research Symposium

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 1108th Street Troy NY 12180 United States Department of Physics Applied Physics and Astronomy Rensselaer Polytechnic Institute 1108th Street Troy NY 12180 United States Department of Electrical Computer and Systems Engineering Rensselaer Polytechnic Institute 1108th Street Troy NY 12180 United States Department of Chemical and Biological Engineering Rensselaer Polytechnic Institute 1108th Street Troy NY 12180 United States

ISBN: (纸本)1424400848

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 &le 50 nm, i.e. much smaller than the wavelength of visible light, and thus sufficiently small to make scattering negligibly 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. © 2005 IEEE.

关键词： Thin films

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Monotonic Convergent Iterative Learning Controller Design Based on Interval Model Conversion

Monotonic Convergent Iterative Learning Controller Design Ba...

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IEEE International Symposium on Intelligent Control (ISIC)

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-Applied Physics Laboratory Laurel MD USA

This paper presents the design of a robust iterative learning controller for the case of a plant with interval model uncertainty in the "A-matrix" of its state space description. First order perturbation theory is utilized to find bounds on the eigenvalues and eigenvectors of the powers of A when A is an interval matrix. These bounds are then used for calculation of the interval uncertainty of the Markov matrix, which can then be used to design an iterative learning controller that ensures monotonic convergence for all systems in the interval plant

关键词： Uncertainty State-space methods Matrix converters Convergence Control systems Motion control Intelligent systems physics computing Design engineering USA Councils

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Onset of synchronization in large networks of coupled oscillators

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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： LIMIT-CYCLE OSCILLATORS LARGE POPULATIONS COMPLEX NETWORKS KURAMOTO

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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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