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A Comparison of Microcompositional Imaging Methods

Microscopy and Microanalysis 2002年第S2期8卷 462-463页

作者： Michael S. Isaacson Cornell University College of Engineering School of Applied and Engineering Physics W.M. Keck Foundation Program in Nanobiotechnology 241 Carpenter Hall Ithaca New York 14853

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Periodic Chirality Transformations Propagating On Bacterial Flagella

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Physical Review Letters 2002年第11期89卷 118102-118102页

作者： Daniel Coombs Greg Huber John O. Kessler Raymond E. Goldstein Theoretical Biology and Biophysics Los Alamos National Laboratory Los Alamos New Mexico 87545 Department of Physics University of Massachusetts Boston Massachusetts 02125 Department of Physics University of Arizona Tucson Arizona 85721 Program in Applied Mathematics University of Arizona Tucson Arizona 85721

When a helical bacterial flagellum, clamped at one end, is placed in an external flow, it has been observed that regions of the flagellum transform to the opposite chirality, and travel as pulses down the length of the filament, the process repeating periodically [H. Hotani, J. Mol. Biol. 156, 791 (1982)]. We propose a theory for this phenomenon based on a treatment of the flagellum as an elastic object with multiple stable configurations. The simplest possible implementation of the model accurately reproduces key features seen in experiment.

关键词： .Elastic helical reversal pitch chirality agella rotational Volume Number agellum

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Philosophical Magazine B 2002年第8期82卷

作者： A. Ṡlebarski M. B. Maple E. J. Freeman C. Sirvent M. Radlowska A. Jezierski E. Granado Q. Huang J. W. Lynn Department of Physics and Institute for Pure and Applied Physical Sciences University of California San DiegoLa Jolla California 92093-0360 USA Institute of Physics University of Silesia 40-007 Katowice Poland Department of Physics and Institute for Pure and Applied Physical Sciences University of California San DiegoLa Jolla California 92093-0360 USA Institute of Physics University of Silesia 40-007 Katowice Poland Institute of Molecular Physics Polish Academy of Sciences 60-179 Poznań Poland NIST Center for Neutron Research National Institute of Standards and Technology Gaithersburg Maryland 20899 USA Center for Superconductivity Research University of Maryland College Park Maryland 20742 USA NIST Center for Neutron Research National Institute of Standards and Technology Gaithersburg Maryland 20899 USA Materials Research Program University of Maryland College Park Maryland 20742 USA

Electrical resistivity ρ, magnetic susceptibility χ, specific heatC, X-ray photoelectron spectroscopy (XPS) and X-ray and neutron diffraction measurements were made on the compound CeRhSn. The measurements reveal an enhancement of the electronic specific heat coefficient γ =C(T)/T≈ 160 mJ mol−1K−2at about 1 K and non-Fermi-liquid-like temperature dependences ρ(T)αT0.75and χ(T)αT−0.5at low temperatures. At high temperatures, the physical properties indicate Kondo-intermediate-valence behaviour. The XPS measurements are consistent with a Ce valence of 3.07. The neutron diffraction measurements reveal anomalies in the planar Ce-Rh and Ce-Ce bond distances in the vicinity of 100 K which are apparently associated with the Ce valence instability in CeRhSn.

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A high frequency ultrasound array element using thermoelastic expansion in PDMS

A high frequency ultrasound array element using thermoelasti...

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IEEE Symposium (IUS) Ultrasonics

作者： T. Buma M. Spisar M. O'Donnell Applied Physics Program and Department of Biomedical Engineering University of Michigan Ann Arbor MI USA

ISBN: (纸本)0780371771

The thermoelastic effect was used to produce high frequency, broadband ultrasound in water. A pulsed diode laser, followed by an erbium doped fiber amplifier, was focused onto a light absorbing film deposited on a glass substrate. Conversion efficiency was improved by 18 dB using a polydimethylsiloxane (PDMS) film instead of a more commonly used metallic one. Radiation pattern measurements show that considerable energy is radiated at +/-45 degrees for frequencies beyond 75 MHz. These results show that the thermoelastic effect can be used to produce phased arrays for high frequency ultrasound imaging.

关键词： Frequency Ultrasonic imaging Thermoelasticity Phased arrays Pulsed laser deposition Optical pulses Pulse amplifiers Diode lasers Erbium Doped fiber amplifiers

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Resetting Wave Forms in Dictyostelium Territories

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Physical Review Letters 2001年第6期87卷 068101-068101页

作者： Kyoung J. Lee Raymond E. Goldstein Edward C. Cox National Creative Research Initiative Center for Neurodynamics and Department of Physics Korea University Seoul 136-701 Korea Department of Physics and Program in Applied Mathematics University of Arizona Tucson Arizona 85721 Department of Molecular Biology Princeton University Princeton New Jersey 08544

The mechanism by which spiral wave patterns appear in populations of Dictyostelium was probed experimentally by external chemical perturbation. Spiral waves, which often arise from the breakup of circular waves driven by pacemakers, typically entrain those pacemakers. We studied these processes by resetting the waves with a spatially uniform pulse of extrinsic cyclic AMP. A pattern of spirals reappeared if resetting was early in the signaling stage, but only targets emerged following late resetting, in a manner analogous to cardiac defibrillation. This supports recent hypotheses that wave pattern selection naturally occurs by slow temporal variation of the excitability of the cells.

关键词： Image analysis

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Transverse magnetic defect modes in two-dimensional triangular lattice photonic crystals

Transverse magnetic defect modes in two-dimensional triangul...

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Quantum Electronics and Laser Science Conference, QELS 2001

作者： Stojić, N. Glimm, J. Deng, Y. Haus, J.W. Department of Physics and Astronomy University at Stony Brook Stony BrookNY11794-3381 United States Department of Applied Mathematics and Statistics University at Stony Brook Stony BrookNY11794-3600 United States Electro-Optics Program University of Dayton DaytonOH45469-0254 United States

ISBN: (纸本)155752663X

关键词： Maxwell equations

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Three-dimensional theory of emittance in Compton scattering and x-ray protein crystallography

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Physical Review E 2001年第1期64卷 016501-016501页

作者： F. V. Hartemann H. A. Baldis A. K. Kerman A. Le Foll N. C. Luhmann, Jr. B. Rupp Institute for Laser Science and Applications Lawrence Livermore National Laboratory Livermore California 94550 Department of Applied Science University of California Davis California 95616 Center for Theoretical Physics and Physics Department Massachusetts Institute of Technology Cambridge Massachusetts 02139 Biology and Biotechnology Research Program Lawrence Livermore National Laboratory Livermore California 94550

A complete, three-dimensional theory of Compton scattering is described, which fully takes into account the effects of the electron beam emittance and energy spread upon the scattered x-ray spectral brightness. The radiation scattered by an electron subjected to an arbitrary electromagnetic field distribution in vacuum is first derived in the linear regime, and in the absence of radiative corrections; it is found that each vacuum eigenmode gives rise to a single Doppler-shifted classical dipole excitation. This formalism is then applied to Compton scattering in a three-dimensional laser focus, and yields a complete description of the influence of the electron beam phase-space topology on the x-ray spectral brightness; analytical expressions including the effects of emittance and energy spread are also obtained in the one-dimensional limit. Within this framework, the x-ray brightness generated by a 25 MeV electron beam is modeled, fully taking into account the beam emittance and energy spread, as well as the three-dimensional nature of the laser focus; its application to x-ray protein crystallography is outlined. Finally, coherence, harmonics, and radiative corrections are also briefly discussed.

关键词： X ray crystallography

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Transverse magnetic defect modes in two-dimensional triangular lattice photonic crystals

Transverse magnetic defect modes in two-dimensional triangul...

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Conference on Lasers and Electro-Optics (CLEO)

作者： N. Stojic J. Glimm Y. Deng J.W. Haus Department of Physics and Astronomy University of Stony Brook Stony Brook NY USA Department of Applied Mathematics and Statistics University of Stony Brook Stony Brook NY USA Electro Optics Program University of Dayton Dayton OH USA

Summary form only given. We used the finite-difference time-domain method to solve Maxwell equations. More specifically, we applied the non-dissipative Yee's algorithm with a duality relation between the spatial representations of the electric and magnetic fields that represents both the differential and integral forms of Maxwell equations. The computational domain consists of 19 photonic lattice cells in the periodic structure for /spl epsi/ in the x and y direction and 8 mesh cells in the z direction. Each photonic lattice cell has been divided into 40/spl times/40 computational mesh cells, but due to duality of the discretization mesh, effectively we determined each field on only 20/spl times/20 points inside a photonic lattice cell. Periodic boundary conditions were used in all three directions. We observed the spatial distribution of the magnetic and electric fields and the movement of the mode resonance through the photonic band gap as the defect radius is changed. In addition, we determined the dependence of the localization (the field energy confined at the defect cell) on frequency (defect radius). We also found well localized defect modes.A defect in the form of an air hole with a modified radius was introduced in the center of a triangular lattice.

关键词： Lattices Maxwell equations Optical computing Magnetic confinement Magnetic resonance Finite difference methods Time domain analysis Magnetic fields Integral equations Periodic structures

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Transverse magnetic defect modes in two-dimensional triangular-lattice photonic crystals

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Physical Review E 2001年第5期64卷 056614-056614页

作者： N. Stojić J. Glimm Y. Deng J. W. Haus Department of Physics and Astronomy State University of New York at Stony Brook Stony Brook New York 11794-3381 Center for Data Intensive Computing Brookhaven National Laboratory Building 463B Upton New York 11973-5751 Department of Applied Mathematics and Statistics State University of New York at Stony Brook Stony Brook New York 11794-3600 Electro-Optics Program The University of Dayton Dayton Ohio 45469-0254

We present a numerical study of the localized transverse magnetic (TM) defect modes in a two-dimensional, triangular-lattice photonic crystal. The sample consists of an array of circular, air cylinders in a dielectric medium (GaAs). The defect modes were calculated by using a parallel version of the finite-difference time-domain method on the Yee mesh. To validate our computations the results for the transverse electric case were checked against experimental results and the numerical results using a different method. We study the spatial symmetry for TM modes, obtained by changing the dipole excitation frequency. Also, we vary the defect-cylinder radius to tune the resonant frequency across the band gap. The TM mode is found to be highly localized at the defect in the photonic lattice.

关键词： Electromagnetic wave propagation

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Reviews

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Metascience 2001年第1期10卷 50-149页

作者： Hugh Clapin Katherine Neal John Wennerbom Barbara Nunn Deborah Dysart Andy Pickering Lisa Featherstone Hiram Caton Dale Jacquette Laura Ruetsche William A. Turner Cornelia Lüdecke Birgit Lohmann James Ladyman Jonathan Coopersmith David Oldroyd Dennis Dean Michael Ruse Nicolas Rasmussen William N. Kaghan Martin Bridgstock Geoffrey Cocks Stephanie H. Kenen Ivan Crozier Sokhieng Au Desmond Barrett Mark Cortiula Ian D. Lawrie Department of Philosophy The University of Sydney Sydney Australia Unit for History and Philosophy of Science The University of Sydney Sydney Australia Philosophy Program Research School of Social Sciences Australian National University Canberra Australia Applied Linguistic Institute and Department of English University of Missouri Kansas City USA Department of Sociology University of Illinois Urbana USA Department of Modern History Macquarie University Sydney Australia Faculty of Arts Griffith University Nathan Australia Department of Philosophy Pennsylvania State University University Park USA Department of Philosophy University of Pittsburgh Pittsburgh USA LIMSI-CNRS Orsay Cedex France Institut für Geschichte der Naturwissenschaften Ludwig-Maximilians-Universität München Germany School of Science Griffith University Nathan Australia Department of Philosophy University of Bristol Bristol UK Department of History Texas A&M University College Station USA School of Science and Technology Studies The University of New South Wales Sydney Australia Evanston USA Philosophy Department Florida State University Tallahassee USA Technology Management and Technical Communications Sakson & Taylor Seattle USA Department of History Albion College Albion USA Department of History of Science Harvard University Cambridge USA History of Science and Technology University of California Berkeley USA Division of Science and Technology Museum of Applied Arts and Sciences Sydney Australia Department of Physics and Astronomy The University of Leeds Leeds UK

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