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2003 MRS Fall Meeting

作者： McDonald, Joel P. Picard, Yoosuf N. Yalisove, Steven M. Liu, Hsiao-Hua Blaszczak, Joseph Guo, Lingji J. Dept. of Materials Science and Engineering University of Michigan Ann Arbor MI 48109-2176 United States Center for Ultrafast Optical Science University of Michigan Ann Arbor MI 48109-2099 United States Applied Physics Program University of Michigan Ann Arbor MI 48109-1120 United States Dept. of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI 48109-2122

Nanomorphing with ultrafast lasers may have a significant role in direct write stamp production. Surface conditions play a critical role in the ablative properties of materials. We have conducted femtosecond laser (pulse duration;120 fs, wavelength;780 nm) threshold studies of silicon with the native oxide and silicon with atomically clean surfaces in an ultra-high vacuum environment. We have discovered that a -1.5 nm thick oxide layer can alter the ablation threshold of Si (100) by 25 ± 5%. Additionally, our work has shown that collateral damage can be controlled on the nanoscale. Transmission electron microscopy (TEM) images of femtosecond laser machined holes in Si (100) show that collateral damage extends only 10 nm from the edge. © 2004 Materials Research Society.

关键词： Ultrafast phenomena

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Segregation in a monolayer of magnetic spheres

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Physical Review E 2004年第3期70卷 031304-031304页

作者： Justin Stambaugh Zachary Smith Edward Ott Wolfgang Losert Institute for Research in Electronics and Applied Physics and Department of Physics University of Maryland College Park Maryland 20742 USA Department of Physics Colorado School of Mines Golden Colorado 80401 USA 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

Segregation and pattern formation is investigated for binary mixtures of granular magnetic spheres in a vertically vibrated monolayer. The spheres, all of equal mass and size, have a maximum surface magnetic field B induced by encased cylindrical magnetic cores of length l. For binary mixtures of particles with equal l but different B, we find that the particles spontaneously segregate when driven. For fixed vibration frequency, the segregation rate increases roughly linearly with driving acceleration over the amplitudes investigated. For systems of fixed particle number density, the rate of segregation also decreases as the volume fraction of “strong” (high B) particles increases. We find that segregation also occurs in binary mixtures of particles with equal B, but different l. Finally, using a simple model of spheres with dipolar and higher magnetic moments, we show that the observed segregation phenomena occur in conjunction with a decrease in magnetic energy.

关键词： Binary mixtures

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Omnidirectional reflector using a low refractive index material

Omnidirectional reflector using a low refractive index mater...

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IEEE Conference on High Performance Devices

作者： J.Q. Xi M. Ojha Woojin Cho T. Gessmann E.F. Schubert J.L. Plawsky W.N. Gill Future Chip Constellation Rensselaer Polytech. Inst. Troy NY USA Department of Electrical Computer and Systems Engineering Rensselaer Polytechnic Institute Troy NY USA Department of Physics Applied Physics & Astronomy

Triple-layer omni-directional reflectors (ODRs) consisting of a semiconductor, a transparent quarter-wavelength dielectric layer and metal layer have high reflectivities at all angles of incidence. In this paper, triple-layer ODRs are demonstrated that incorporate nanoporous SiO/sub 2/, a novel low-refractive-index (low-n) material with refractive indices n /spl Lt/ 1.46 as well as dense SiO/sub 2/ (n = 1.46). GaP and Ag serve as the semiconductor and metal layer materials, respectively. An angle-integrated transverse electric (TE) mode reflectivity of R/sub avg/|/sub TE/ = 99.9 % and transverse magnetic (TM) mode reflectivity R/sub avg/|/sub TM/ = 98.9 % are calculated for the triple-layer ODRs employing nanoporous SiO/sub 2/. Reflectivity measurements, including the angular dependence of R, are presented. Novel hybrid ODRs consisting of semiconductor, a several micron thick low-n dielectric material layer, a distributed Bragg reflector (DBR) and metal layer have outstanding reflectivities for all incident angles. GaP and Ag serve as the semiconductor and metal layer, respectively. Nanoporous SiO/sub 2/ is used as the low-n material. TiO/sub 2/ and dense SiO/sub 2/ serve as the DBR materials. The angle-intergrated reflectivities of the TE and TM modes are calculated to be larger than 99.9% for the hybrid ODRs. The results indicate the great potential of the ODRs for light-emitting diodes with high light extraction efficiency.

关键词： Refractive index Nanoporous materials Reflectivity Semiconductor materials Dielectric materials Tellurium Distributed Bragg reflectors Inorganic materials Magnetic materials Magnetic semiconductors

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Formation mechanisms of statistically degenerate quasi-2D confined exciton systems

Formation mechanisms of statistically degenerate quasi-2D co...

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International Quantum Electronics Conference, IQEC

作者： Lai, C.W. Chemla, D.S. Gossard, A.C. Applied Science and Technology University of California at Berkeley Berkeley CA 94720 United States Physics Department University of California at Berkeley Berkeley CA 94720 United States Materials Sciences Division Lawrence Berkeley National Laboratory CA 94720 United States Department of Electrical and Computer Engineering University of California at Santa Barbara Santa Barbara CA 93106 United States

Photoluminescence of exciton systems confined in small areas evolves into extensive ordered ring structures. These systems exhibit oscillatory long (μs) photoluminescence decays, suggesting continuous exciton formati... 详细信息

关键词： Excitons

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Toward building a robust and intelligent video surveillance system: a case study

Toward building a robust and intelligent video surveillance ...

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IEEE International Conference on Multimedia and Expo (ICME)

作者： E.Y. Chang Yuan-Fang Wang I-Jeng Wang Department of Electrical and Computer Engineering University of California Santa Barbara CA USA Department of Computer Science University of California Santa Barbara CA USA Applied Physics Laboratory Johns Hopkins University Laurel MD USA

With the proliferation of inexpensive cameras, availability of large-capacity disk storage, and the ubiquitous presence of high-speed, broad-band communication networks, it is now economically and technically feasible to construct and deploy multi-camera video surveillance systems. In line with this is the need of intelligent, robust, (semi-)automated video analysis paradigms to assist the operators in scene analysis and event classification. In this paper, we summarize our current research work toward realizing such a multi-camera video surveillance system. Interested readers can visit our web sites http://***/ ~ echang and http://***/ ~ yfwang for more information

关键词： Robustness Intelligent systems Intelligent structures Video surveillance computer aided software engineering Cameras Streaming media Pervasive computing Training data Hardware

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Desynchronization Waves and Localized Instabilities in Oscillator Arrays

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Physical Review Letters 2004年第11期93卷 114101-114101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 consider a ring of identical or near-identical coupled periodic oscillators in which the connections have randomly heterogeneous strength. We use the master stability function method to determine the possible patterns at the desynchronization transition that occurs as the coupling strengths are increased. We demonstrate Anderson localization of the modes of instability and show that such localized instability generates waves of desynchronization that spread to the whole array. Similar results should apply to other networks with regular topology and heterogeneous connection strengths.

关键词： Oscillistors

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Omni-directional reflector using a low refractive index material

Omni-directional reflector using a low refractive index mate...

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作者： Xi, J.-Q. Ojha, Manas Cho, Woojin Gessmann, Th. Schubert, E.F. Plawsky, J.L. Gill, W.N. Future Chip 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 Chemical and Biological Engineering 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

Triple-layer omni-directional reflectors (ODRs) consisting of a semiconductor, a transparent quarter-wavelength dielectric layer and metal layer have high reflectivities at all angles of incidence. In this paper, triple-layer ODRs are demonstrated that incorporate nanoporous SiO2, a novel low-refractive-index (low-n) material with refractive indices n « 1.46 as well as dense SiO2 (n = 1.46). GaP and Ag serve as the semiconductor and metal layer materials, respectively. An angle-integrated transverse electric (TE) mode reflectivity of RaVg|TE = 99.9 % and transverse magnetic (TM) mode reflectivity Ravg| TM = 98.9 % are calculated for the triple-layer ODRs employing nanoporous SiO2. Reflectivity measurements, including the angular dependence of R, are presented. Novel hybrid ODRs consisting of semiconductor, a several micron thick low-n dielectric material layer, a distributed Bragg reflector (DBR) and metal layer have outstanding reflectivities for all incident angles. GaP and Ag serve as the semiconductor and metal layer, respectively. Nanoporous SiO2 is used as the low-n material. TiO2 and dense SiO2 serve as the DBR materials. The angle-intergrated reflectivities of the TE and TM modes are calculated to be larger than 99.9 % for the hybrid ODRs. The results indicate the great potential of the ODRs for light-emitting diodes with high light extraction efficiency. © World Scientific Publishing Company.

关键词： Mirrors

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Magnitude of the intrinsic optical brain imaging signal reflects neural function

Magnitude of the intrinsic optical brain imaging signal refl...

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Biomedical Topical Meeting, BIOMED 2004

作者： Jones, David G. Murphy, Kathryn M. McMaster Optical Brain Imaging Laboratory Canada Department of Electrical& Computer Engineering McMaster University HamiltonONL8S 4K1 Canada Department of Psychology McMaster University HamiltonONL8S 4K1 Canada Applied Radiation & Medical Physics McMaster University HamiltonONL8S 4K1 Canada

We sought to assess whether the magnitude of the intrinsic optical imaging signal in rat visual cortex is related to the underlying response properties of visual cortical receptive fields and to perceptual function. &... 详细信息

ISBN: (纸本)1557527695

关键词： Brain mapping

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Determining carrier densities in InMnAs by cyclotron resonance

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Physica E: Low-dimensional Systems and Nanostructures 2004年第3-4期20卷 378-381页

作者： G.D. Sanders Y. Sun C.J. Stanton G.A. Khodaparast J. Kono D.S. King Y.H. Matsuda S. Ikeda N. Miura A. Oiwa H. Munekata Department of Physics University of Florida Gainesville FL 32611 USA Department of Electrical and Computer Engineering Rice University Houston TX 77003 USA Department of Applied Physics Stanford University Stanford CA 94305 USA Department of Physics Okayama University Okayama Japan Institute of Solid State Physics University of Tokyo Kashiba Chiba 277-8581 Japan Imaging Science and Engineering Lab Tokyo Institute of Technology Yokohama Kanagawa 226-8503 Japan

Accurate determination of carrier densities in ferromagnetic semiconductors by Hall measurements is hindered by the anomalous Hall effect , and thus alternative methods are being sought. Here, we propose that cyclotron resonance (CR) is an excellent method for carrier density determination for InMnAs-based magnetic structures. We develop a theory for electronic and magneto-optical properties in narrow gap InMnAs films and superlattices in ultrahigh magnetic fields oriented along [001]. In n-type InMnAs films and superlattices, we find that the e-active CR peak field is pinned at low electron densities and then begins to shift rapidly to higher fields above a critical electron concentration allowing the electron density to be accurately calibrated. In p-type InMnAs, we observe two h-active CR peaks due to heavy and light holes. The line shapes depend on temperature and line broadening. The light hole CR requires higher hole densities and fields. Analyzing CR line shapes in p-films and superlattices can help determine hole densities.

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Finite element modeling of ultrasonic separation at the microscale

Finite element modeling of ultrasonic separation at the micr...

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IEEE Symposium (IUS) Ultrasonics

作者： M.K. Araz Chung-Hoon Lee A. Lal Applied and Engineering Physics Cornell University Ithaca NY USA Veeco Process Equipment Inc. Santa Barbara CA USA Electrical and Computer Engineering Department Sonic MEMS Laboratory Cornell University Ithaca NY USA

In this paper, the working principle of an acoustic chromatography device is investigated by the analytical and finite element modeling (FEM) approach. Analytical and simulation results, compared to the inteferometric scan and the experimental results, confirm that the inertial field due to the flexural waves on the capillary has the major role for manipulation of particles. Disagreement between phase velocity from the simple beam bending solution and experiments at high frequencies are also discussed.

关键词： Finite element methods Microfluidics Silicon compounds Polyimides Acoustical engineering Acoustic devices Analytical models Frequency Acoustic waves Bonding

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