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European Conference on Antennas and Propagation, EuCAP

作者： Georgios K. Avdikos Theodore Zervos Hristos T. Anastassiu Nikolaos K. Uzunoglu School of Applied Mathematics and Physics National and Technical University of Athens Zografou Greece National Centre for Scientific Research Demokritos Institute of Informatics and Telecommunications Athens Greece Communications and Networks Design & Development Department Hellenic AeroSpace Industry SA Viotia Greece School of Electrical and Computer Engineering National and Technical University of Athens Zografou Greece

Ferroelectric materials have been gaining much interest over the last decades due to the unique operational characteristics they demonstrate, when a dc electric field is applied. This paper investigates the scattering analysis of electromagnetic waves from materials with high permittivity that follows a linear spatial variation along one axis. The surface integral equation (SIE) and volume integral equation (VIE) methods are invoked to compute the currents and the radar cross section (RCS). The number of unknowns for the VIE is, as expected, larger than for the SIE method. The RCS and the induced current are associated in such a way that one can approximate the linear variation with relatively few elements (unknowns).

关键词： Ferroelectric materials Permittivity Electromagnetic scattering Radar scattering Integral equations Electromagnetic analysis Radar cross section Linear approximation Dielectric materials Microwave antenna arrays

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Optical properties of AIN film

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Guangzi Xuebao/Acta Photonica Sinica 2006年第2期35卷 221-223页

作者： Yan, Guojun Chen, Guangde Qiu, Fusheng Fan, Zhaoyan Applied Physic Department Xi'an Jiaotong University Xi'an 710049 China Department of Electrical Computer Engineering Northwestern University Evanston IL 60208 United States Department of Physics Kansas State University Manhattan KS 66506 United States

An X-diffraction, a transmittance spectrum and absorption spectrums at different temperatures of an AIN film deposited on a (001) SiC substrate by MBE were measured on a X-diffractometer and an UV spectrophotometer (190 nm-800 nm) respectively. The X-diffraction spectrum shows that there are strains in the c-axial orientation of the AIN, these strains are caused by the dismatching of crystal lattice constant of the AIN and the SiC substrate, and these strains will cause the stresses in the AIN film;the transmittance spectrum of the AIN shows that the direct-band-gap of the AIN is about 6.2 eV;and obvious knees or a shoulders structure around 6.2 eV existing in the absorption spectrums are considered to be caused by the free exciton absorptions in the AIN film, if not considered the formation energy of the free exciton, 6.2 e is the value of the direct-band-gap of the AIN film;the knees or the shoulder structure and position don't change with the temperature in the absorption spectrums of the AIN, which shows that the temperature doesn't influence the value of the direct-band-gap of the AIN obviously, this is probable, which is caused by the stresses existing in the AIN film.

关键词： Absorption spectrum AIN film Free exciton The direct-band-gap energy Transmittance spectrum

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Real-time depth-mapping three-dimension TV camera (Axi-Vision Camera)

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Systems and computers in Japan 2006年第8期37卷 77-89页

作者： Kawakita, Masahiro Iizuka, Keigo Iino, Yoshiki Kikuchi, Hiroshi Fujikake, Hideo Aida, Tahito Science and Technical Research Laboratories Japan Broadcasting Corporation Tokyo 157-8510 Japan Department of Electrical and Computer Engineering University of Toronto Ont. M5S 1A4 Canada Hiroshima Broadcasting Station Japan Broadcasting Corporation Hiroshima 730-8672 Japan NHK Science and Technical Research Laboratories Optical Society of America Japan Society of Applied Physics Institute of Image Information and Television Engineers of Japan University of Toronto Canada Japanese Liquid Crystal Society IEICE Illuminating Engineer Institute of Japan Department of Electronic Circuits Osaka City University

A three-dimension camera (Axi-Vision camera) has been developed that is capable of producing a color image of an object and performing high-speed mapping of depth information from the camera to the object. With this camera, intensity-modulated near-infrared light is irradiated onto the object, and distances to points on the object are computed from the image captured by a camera that has a high-speed shutter. Since a two-dimensional scanning mechanism for a laser beam or complex computational processing is unnecessary in this depth mapping system, the distance to the object can be detected at high speed for each pixel of a TV image. For the present paper, a three-dimension camera adapted to a standard television signal was constructed by development of a high-output light-emitting-diode (LED) array light source capable of high-speed intensity modulation, an image intensifier capable of high-speed shutter operation on the nanosecond order, and an optical system. The prototype camera can output a depth image with a resolution of 768 × 493 pixels at a frame rate of 15 Hz, the characteristic depth mapping resolution of the camera is 1.8 cm (when the distance from the camera to the object is 2 m), and the camera can capture an image of a person-sized object. It was also shown that the depth information thus obtained could be applied to live-action filming and to CG and other new types of image synthesis. © 2006 Wiley Periodicals, Inc.

关键词： Real time systems

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YBa₂Cu₃O_7-δ thick films on Ag prepared by the Electrophoretic Deposition technique

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Journal of physics: Conference Series 2006年第1期43卷 134-137页

作者： Dusoulier, L. Denis, S. Fagnard, J.-F. Henrist, C. Vanderheyden, B. Vanderbemden, Ph. Rulmont, A. Dirickx, M. Ausloos, M. Cloots, R. Vertruyen, B. SUPRATECS Chemistry Institute B6 University of Liège B-4000 Liège Belgium SUPRATECS Communication Information Systems and Sensors Department Royal Military Academy B-1000 Brussels Belgium SUPRATECS Department of Electrical Engineering and Computer Science B28 University of Liège B-4000 Liège Belgium Center for Applied Technology in Microscopy (CAT) University of Liège Belgium SUPRATECS Physics Institute B5 University of Liège B-4000 Liège Belgium

YBa2Cu3O7-δ thick films have been deposited onto Ag substrates by the Electrophoretic Deposition (EPD) technique. Different microstructures and electrical behaviours were observed depending on the starting powder. Co...

YBa₂Cu₃O_7-δ thick films have been deposited onto Ag substrates by the Electrophoretic Deposition (EPD) technique. Different microstructures and electrical behaviours were observed depending on the starting powder. Coatings prepared from commercial powder displayed significant porosity and the superconducting transition width was found to be magnetic-field dependent. Films produced from home-made coprecipitated powder are denser but contain some secondary phases. No dependence of the resistive transition as a function of magnetic field (H 20 Oe) was observed in that case. © 2006 IOP Publishing Ltd.

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Computational and experimental analysis of THz double negative metamaterials

Computational and experimental analysis of THz double negati...

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2005 IEEE Antennas and Propagation Society International Symposium and USNC/URSI Meeting

作者： Wongkasem, N. Akyurtlu, A. Li, J. Tibolt, A. Kang, Z. Goodhue, W.D. Department of Electrical and Computer Engineering University of Massachusetts Lowell MA 01854 Department of Physics and Applied Physics University of Massachusetts Lowell MA 01854

ISBN: (纸本)0780388836

Several double negative (DNG) metamaterial (MTM) designs in the terahertz (THz) frequency regime are developed using the Finite-Difference Time-Domain (FDTD) method. Materials fabricated using one of the models exhibit a DNG pass band at THz frequencies and the observed pass band characteristics are in good agreement with the model results. © 2005 IEEE.

关键词： Materials science

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Elastic and Magnetic Dynamics of Nanomagnet-Ordered Arrays Impulsively Excited by Subpicosecond Laser Pulses

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Physical Review Letters 2006年第21期97卷 217201-217201页

作者： A. Comin C. Giannetti G. Samoggia P. Vavassori D. Grando P. Colombi E. Bontempi L. E. Depero V. Metlushko B. Ilic F. Parmigiani Sincrotrone Trieste I-34012 Basovizza Trieste Italy and Dipartimento di Matematica e Fisica Università Cattolica del Sacro Cuore I-25121 Brescia Italy Dipartimento di Fisica “A. Volta ” Università degli Studi di Pavia I-27100 Pavia Italy CNR-INFM CRS S3 and Dipartimento di Fisica Università di Ferrara I-44100 Ferrara Italy Dipartimento di Elettronica Università degli Studi di Pavia I-27100 Pavia Italy Laboratorio di Chimica per le Tecnologie Università degli Studi di Brescia I-25123 Brescia Italy Department of Electrical and Computer Engineering University of Illinois at Chicago Chicago Illinois 60607 USA Cornell Nanofabrication Facility School of Applied and Engineering Physics Cornell University Ithaca New York 14853 USA Dipartimento di Fisica Università degli Studi di Trieste I-34127 Trieste Italy and Sincrotrone Trieste I-34012 Basovizza Trieste Italy

This Letter reports on the first observation of elastic and magnetic dynamics of ordered arrays of permalloy nanodots excited by low-intensity 120 fs light pulses. The first order of the diffraction pattern, generated by the probe beam in a pump-probe configuration, is used for time-resolved reflectivity and time-resolved magneto-optical Kerr effect measurements. The nonadiabatical absorption of the pump triggers an acoustic standing wave, detected by the reflected probe signal, with a frequency related to the array wave vector. Instead, the magneto-optical signal exhibits, on the nanosecond time scale, the signature of the heat-exchange diffusion processes. In addition, a clear oscillation of the magnetic signal, at a frequency close to the frequency of the acoustic wave, is unambiguously detected. Finally, the interplay between the elastic and magnetic dynamics is analyzed and interpreted.

关键词： Nanostructured materials

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Selection rules for one- and two-photon absorption by excitons in carbon nanotubes

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Physical Review B 2006年第24期73卷 241406(R)-241406(R)页

作者： Eduardo B. Barros Rodrigo B. Capaz Ado Jorio Georgii G. Samsonidze Antonio G. Souza Filho Sohrab Ismail-Beigi Catalin D. Spataru Steven G. Louie Gene Dresselhaus Mildred S. Dresselhaus Departamento de Física Universidade Federal do Ceará Fortaleza Ceará CEP 60455-760 Brazil Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge Massachusetts 02139-4307 USA Instituto de Física Universidade Federal do Rio de Janeiro Caixa Postal 68528 Rio de Janeiro Rio de Janeiro 21941-972 Brazil Divisão de Metrologia de Materiais Instituto Nacional de Metrologia Normalização e Qualidade Industrial—Inmetro R. Nossa Senhora das Graças 50 Xerém Duque de Caxias Rio de Janeiro 25245-020 Brazil Departamento de Física Universidade Federal de Minas Gerais Belo Horizonte Minas Gerais 30123-970 Brazil Department of Applied Physics Yale University New Haven Connecticut 06520 USA Department of Physics University of California at Berkeley Berkeley California 94720 USA Materials Science Division Lawrence Berkeley National Laboratory Berkeley California 94720 USA Francis Bitter Magnet Laboratory Massachusetts Institute of Technology Cambridge Massachusetts 02139-4307 USA

Recent optical absorption and emission experiments showed that the lower energy optical transitions in carbon nanotubes are excitonic in nature, as predicted by theory. These experiments were based on the symmetry aspects of free electron-hole states and bound excitonic states. The present work shows, however, that group theory does not predict the selection rules needed to explain the two photon experiments. We obtain the symmetries and selection rules for the optical transitions of excitons in single-wall carbon nanotubes within the approach of the group of the wave vector, thus providing important information for the interpretation of theoretical and experimental optical spectra of these materials.

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Resource allocation for periodic applications in a shipboard environment

Resource allocation for periodic applications in a shipboard...

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19th IEEE International Parallel and Distributed Processing Symposium, IPDPS 2005

作者： Shestak, Vladimir Chong, Edwin K. P. Maciejewski, Anthony A. Siegel, H.J. Benmohamed, Lotfi Wang, I.-Jeng Daley, Rose Colorado State University Department of Electrical and Computer Engineering Fort Collins CO 80523-1373 Colorado State University Department of Computer Science Fort Collins CO 80523-1373 Johns Hopkins University Applied Physics Laboratory 11100 Johns Hopkins Road Laurel MD 20723-6099 Department of Electrical and Computer Engineering Colorado State University Department of Electrical and Computer Engineering Department of Mathematics Colorado State University IEEE Colorado State University Department of Computer Science ACM Eta Kappa Nu Electrical Engineering Honor Society Sigma Xi Science Honor Society Upsilon Pi Epsilon Computing Sciences Honor Society Johns Hopkins University Applied Physics Laboratory JHU/APL Applied Physics Lab. IR and D

ISBN: (纸本)0769523129

Providing efficient workload management is an important issue for a large-scale heterogeneous distributed computing environment where a set of periodic applications is executed. The considered distributed system is expected to operate in an environment where the input workload is likely to change unpredictably, possibly invalidating a resource allocation that was based on the initial workload estimate. The tasks consist of multiple application strings, each made up of an ordered sequence of applications. There are quality of service (QoS) constraints that must be satisfied for each string. This work addresses the problem of finding a robust initial allocation of resources to application strings that is able to absorb some level of unknown input workload increase without rescheduling. An allocation feasibility analysis is presented followed by four heuristics for finding a near-optimal allocation of resources. The performance of the proposed heuristics is evaluated and compared using simulation. The proposed heuristics also are compared to a mathematically derived upper bound. © 2005 IEEE.

关键词： Resource allocation

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Real-time software receiver tracking of GPS L2 civilian signals using a hardware simulator

Real-time software receiver tracking of GPS L2 civilian sign...

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18th International Technical Meeting of the Satellite Division of The Institute of Navigation, ION GNSS 2005

作者： Ledvina, B.M. Psiaki, M.L. Powell, S.P. Kintner, P.M. Applied Research Laboratories University of Texas Austin Sibley School of Mechanical and Aerospace Engineering Cornell University School of Electrical and Computer Engineering Cornell University Department of Mechanical and Aerospace Engineering Cornell University Space Plasma Physics Group School of Electrical and Computer Engineering Cornell University Department of Electrical and Computer Engineering Cornell University Department of Living With Star Geospace Mission Definition Team

A dual-frequency civilian L1/L2 GPS receiver has been tested that runs 12 tracking channels in real time using a software correlator. This work is part of an effort to develop flexible receivers that can use the new GPS L2 CM/CL signals as they become available on L2 without the need for new correlator hardware. The receiver consists of an RF front end, a system of shift registers, a digital data acquisition (DAQ) system, and software that runs on a 3.4 GHz PC. An analog mixing RF front end composed of separate L1 and L2 signal channels converts the L1 C/A code and L2 CM/CL code signals into two 2-bit digital data streams sampled at 5.714 MHz. The shift registers parallelize the two 2-bit data streams, which the DAQ reads into the PC's memory using direct memory access. The PC performs base-band mixing and PRN code correlations in a manner that directly simulates a hardware digital correlator. It also performs the usual signal tracking and navigation functions, under the control of a real-time Linux operating system. The main contributions of this work are a design for an inexpensive dual-frequency GPS civilian L1/L2 RF front end and demonstration of GPS civilian L1/L2 software receiver running on a GPS signal simulator. This RF front end uses two commercially-available GPS RF front ends designed for the LI C/A code signal. To accommodate the L2 CM/CL code signal, a synthesizer and mixer are located upstream of the RF front end and are used to up-convert the L2 signal to the LI frequency minus roughly 6 kHz. The successful operation of the receiver while connected to a hardware simulator indicates that the receiver should function when the first civilian L2 signals become available. The GPS civilian L1/L2 software receiver tracks 12 channels in real time and has a navigation accuracy of 1-3 meters. It requires 8f % of the processing capabilities of a 3.4 GHz Intel Pentium 4 PC.

关键词： Global positioning system

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High-power packages for phosphor-based white-light-emitting diode lamps

High-power packages for phosphor-based white-light-emitting ...

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2005 International Semiconductor Device Research Symposium

作者： Luo, Hong Kim, Jong Kyu Xi, Yangang Cho, Jaehee Sone, Cheolsoo Park, Yongjo Schubert, E. Fred Department of Physics Applied Physics and Astronomy Rensselaer Polytechnic Institute Troy NY 12180 Electrical Computer and Systems Engineering Department Rensselaer Polytechnic Institute Troy NY 12180 Photonics Program Team Samsung Advanced Institute of Technology Suwon 440-600 Korea Republic of

ISBN: (纸本)1424400848

With the rapid development of high-power white light-emitting diodes (LEDs), advances in packaging are required to further improve the device performance. In this work, an optimized packaging configuration for high power LED lamps with enhanced phosphorescence efficiency is presented based on ray-tracing simulations and experimental results. Figure 1 shows two phosphor arrangements, namely a "proximate phosphor" and a "remote phosphor" arrangement. The surface of the reflector cup is assumed to be either specular or diffuse. Three different encapsulant geometries, i.e., a "flat" (no cap), "convex" (spherical cap with height h = r/2), and "hemispherical" (h = r) top surface, are used in the simulations. Figure 2 shows phosphorescence efficiency with different packaging configurations obtained by ray-tracing simulation. The packaging configuration with remote phosphor, diffuse reflector cup and hemispherical encapsulation shows a 50% enhancement of phosphorescence efficiency compared to conventional packaging configuration. This improvement is attributed to reduced absorption of the phosphorescence by the LED chip and the reduction of deterministic optical modes trapped inside the encapsulant of remote-phosphor and diffuse reflector cup configuration. The angular dependence of the reflectivity for a diffuse Ag reflector and a specular Ag reflector is measured and shown in Figure 3. The roughened Ag reflector has a more than two orders of magnitude higher diffusely reflected power compared with the specular Ag reflector, which leads to the extraction of the trapped optical modes occurring in packaging structures with specular reflector cups. Dichromatic LED lamps comprising an ultraviolet GaN LED (λ = 400 nm) with a blue phosphor and a blue GaInN LED (λ = 470 nm) with a yellow phosphor are fabricated with different phosphor arrangements and reflector cups. The emission spectra of the reference primary LED emitters and of the dichromatic lamps operating at 20 mA are mea

关键词： Chip scale packages

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