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Enhancing the conductance of a two-electron nanomechanical oscillator

Physical Review B 2008年第3期77卷 035428-035428页

作者： J. R. Johansson L. G. Mourokh A. Yu. Smirnov Franco Nori Frontier Research System The Institute of Physical and Chemical Research (RIKEN) Wako-shi Saitama 351-0198 Japan Department of Physics Queens College The City University of New York Flushing New York 11367 USA Department of Engineering Science and Physics College of Staten Island The City University of New York Staten Island New York 10314 USA CREST Japan Science and Technology Agency Kawaguchi Saitama 332-0012 Japan Center for Theoretical Physics Applied Physics Program Center for the Study of Complex Systems Physics Department The University of Michigan Ann Arbor Michigan 48109-1040 USA

We consider electron transport through a mobile island (i.e., a nanomechanical oscillator) which can accommodate one or two excess electrons and show that, in contrast to immobile islands, the Coulomb blockade peaks, associated with the first and second electrons entering the island, have different functional dependences on the nano-oscillator parameters when the island coupling to its leads is asymmetric. In particular, the conductance for the second electron (i.e., when the island is already charged) is greatly enhanced in comparison to the conductance of the first electron in the presence of an external electric field. We also analyze the temperature dependence of the two conduction peaks and show that these exhibit different functional behaviors.

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An efficient approximation for the real-time implementation of the Mixture of Trajectory Models decoder

An efficient approximation for the real-time implementation ...

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IEEE Biomedical Circuits and Systems (BIOCAS)

作者： William Bishop Byron M. Yuy Gopal Santhanam Afsheen Afshar Stephen I. Ryu Krishna V. Shenoy The Johns Hopkins University Applied Physics Laboratory Laurel Maryland USA Department of Electrical Engineering Standford University California USA Department of Electrical Engineering Stanford University Stanford California USA Medical Scientist Training Program Stanford University Stanford California Department of Neurosurgery Stanford University Stanford California Neurosciences Program Stanford University Stanford California

The mixture of trajectory models (MTM) decoder has been used to reconstruct arm trajectories from neural activity. While it produces reasonable results, the computational demands of previously published versions may be too high for many real-time systems. We have developed a novel method of approximating the MTM state posteriors that does not require the use of Newtonpsilas method. We show that this method results in only a small decrease in decoding performance yet reduces computational cost by 56.4%. Additionally, an MTM algorithm using this method of approximating the state posteriors produces more accurate decoded trajectories when using small bin sizes than an MTM algorithm using a Gaussian observation model. The more efficient formulation of the MTM algorithm presented here provides an alternative approximation of this algorithm for use on resource constrained embedded systems.

关键词： Decoding Newton method Iterative algorithms Laboratories physics computing Real time systems Approximation algorithms Biomedical engineering Neurosurgery Educational institutions

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Hysteretic jumps in the response of layered superconductors to electromagnetic fields

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Physical Review B 2008年第18期78卷 184504-184504页

作者： V. A. Yampol’skii T. M. Slipchenko Z. A. Mayzelis D. V. Kadygrob S. S. Apostolov S. E. Savel’ev Franco Nori Advanced Science Institute The Institute of Physical and Chemical Research (RIKEN) Wako-shi Saitama 351-0198 Japan A. Ya. Usikov Institute for Radiophysics and Electronics Ukrainian Academy of Sciences 61085 Kharkov Ukraine V. N. Karazin Kharkov National University 61077 Kharkov Ukraine Department of Physics Loughborough University Loughborough LE11 3TU United Kingdom Department of Physics Center for Theoretical Physics Applied Physics Program Center for the Study of Complex Systems University of Michigan Ann Arbor Michigan 48109-1040 USA

We consider here a layered superconductor subject to an externally applied moderately strong electromagnetic field. We predict hysteretic jumps in the dependence of the surface reactance of the superconductor on the amplitude H0 of the incident electromagnetic wave. This very unusual nonlinear phenomenon can be observed in thin superconducting slabs at not very strong ac amplitudes if the frequency of the irradiating field is close to the Josephson plasma frequency. Using the set of coupled sine-Gordon equations, we derive the expression for the phase shift χ of the reflected wave and obtain the conditions for the appearance of hysteresis in the χ(H0) dependence.

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A miniature sensor for electrical field measurements in dusty planetary atmospheres

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Journal of physics: Conference Series 2008年第1期142卷

作者： Renno, N.O. Kok, J.F. Kirkham, H. Rogacki, S. Atmospheric Oceanic and Space Sciences University of Michigan Ann Arbor United States Atmospheric Oceanic and Planetary Physics University of Oxford Oxford United Kingdom Applied Physics Program University of Michigan Ann Arbor MI United States Jet Propulsion Laboratory California Institute of Technology Pasadena CA United States

Dusty phenomena such as regular wind-blown dust, dust storms, and dust devils are the most important, currently active, geological processes on Mars. Electric fields larger than 100 kV/m have been measured in terrestrial dusty phenomena. Theoretical calculations predict that, close to the surface, the bulk electric fields in martian dusty phenomena reach the breakdown value of the isolating properties of thin martian air of about a few 10 kV/m. The fact that martian dusty phenomena are electrically active has important implications for dust lifting and atmospheric chemistry. Electric field sensors are usually grounded and distort the electric fields in their vicinity. Grounded sensors also produce large errors when subject to ion currents or impacts from clouds of charged particles. Moreover, they are incapable of providing information about the direction of the electric field, an important quantity. Finally, typical sensors with more than 10 cm of diameter are not capable of measuring electric fields at distances as small as a few cm from the surface. Measurements this close to the surface are necessary for studies of the effects of electric fields on dust lifting. To overcome these shortcomings, we developed the miniature electric-field sensor described in this article. © 2008 IOP Publishing Ltd.

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Paradigmatic flow for small-scale magnetohydrodynamics: Properties of the ideal case and the collision of current sheets

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Physical Review E 2008年第6期78卷 066401-066401页

作者： E. Lee M. E. Brachet A. Pouquet P. D. Mininni D. Rosenberg Geophysical Turbulence Program National Center for Atmospheric Research P.O. Box 3000 Boulder Colorado 80307-3000 USA Department of Applied Physics and Applied Mathematics Columbia University 500 W. 120th Street New York New York 10027 USA École Normale Supérieure 24 Rue Lhomond 75231 Paris France Departamento de Física Facultad de Ciencias Exactas y Naturales Universidad de Buenos Aires Ciudad Universitaria 1428 Buenos Aires Argentina

We propose two sets of initial conditions for magnetohydrodynamics (MHD) in which both the velocity and the magnetic fields have spatial symmetries that are preserved by the dynamical equations as the system evolves. When implemented numerically they allow for substantial savings in CPU time and memory storage requirements for a given resolved scale separation. Basic properties of these Taylor-Green flows generalized to MHD are given, and the ideal nondissipative case is studied up to the equivalent of 20483 grid points for one of these flows. The temporal evolution of the logarithmic decrements δ of the energy spectrum remains exponential at the highest spatial resolution considered, for which an acceleration is observed briefly before the grid resolution is reached. Up to the end of the exponential decay of δ, the behavior is consistent with a regular flow with no appearance of a singularity. The subsequent short acceleration in the formation of small magnetic scales can be associated with a near collision of two current sheets driven together by magnetic pressure. It leads to strong gradients with a fast rotation of the direction of the magnetic field, a feature also observed in the solar wind.

关键词： Paradigmatic small-scale magnetohydrodynamics Collisions model cars magnetic field Spatial resolution grid point Ideal magnetohydrodynamics direction of rotation Exponential Decay current sheet Magnetic pressure CPU time Flow acceleration energy spectra

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Erratum: Toward the jamming threshold of sphere packings: Tunneled crystals (Journal of applied physics (2007) 102 (093511))

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Journal of applied physics 2008年第12期103卷

作者： Torquato, S. Stillinger, F.H. Department of Chemistry Princeton University Princeton NJ 08544 United States Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 United States Princeton Institute for the Science and Technology of Materials Princeton University Princeton NJ 08544 United States Princeton Center for Theoretical Physics Princeton University Princeton NJ 08544 United States

No abstract available

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Negative Poisson’s Ratio Materials via Isotropic Interactions

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Physical Review Letters 2008年第8期101卷 085501-085501页

作者： Mikael C. Rechtsman Frank H. Stillinger Salvatore Torquato Department of Physics Princeton University Princeton New Jersey 08544 USA Department of Chemistry Princeton University Princeton New Jersey 08544 USA Program in Applied and Computational Mathematics and PRISM Princeton New Jersey 08544 USA Princeton Center for Theoretical Science Princeton New Jersey 08544 USA School of Natural Sciences Institute for Advanced Study Princeton New Jersey 08544 USA

We show that under tension a classical many-body system with only isotropic pair interactions in a crystalline state can, counterintuitively, have a negative Poisson’s ratio, or auxetic behavior. We derive the conditions under which the triangular lattice in two dimensions and lattices with cubic symmetry in three dimensions exhibit a negative Poisson’s ratio. In the former case, the simple Lennard-Jones potential can give rise to auxetic behavior. In the latter case, a negative Poisson’s ratio can be exhibited even when the material is constrained to be elastically isotropic.

关键词： Lennard-Jones potential

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The use of a virtual integration environment for the real-time implementation of neural decode algorithms

The use of a virtual integration environment for the real-ti...

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Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC)

作者： William Bishop Byron M. Yu Gopal Santhanam Afsheen Afshar Stephen I. Ryu Krishna V. Shenoy R. Jacob Vogelstein James Beaty Stuart Harshbarger Applied Physics Laboratory Johns Hopkins University Laurel MD USA Gatsby Computational Neuroscience Unit University College London London Canada Neurosciences Program University of Stanford Stanford CA USA Department of Electrical Engineering University of Stanford Stanford CA USA Department of Electrical Engineering Stanford University California USA

We have developed a virtual integration environment (VIE) for the development of neural prosthetic systems. This paper, the second of two companion articles, describes the use of the VIE as a common platform for the implementation of neural decode algorithms. In this paper, a linear filter decode and a recursive Bayesian algorithm are implemented as separate signal analysis modules of the VIE for the real-time decode of end effector trajectory. The process of implementing each algorithm is described and the real-time behavior as well as computational cost for each algorithm is examined. This is the first report of the real-time implementation of the Mixture of Trajectory Models decode [10]. These real-time algorithms can be easily interfaced with pre-existing modules of the VIE to control simulated and real devices.

关键词： Real-time systems Trajectory Signal analysis End effectors Synchronization Training Delays

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Modeling heterogeneous materials via two-point correlation functions. II. Algorithmic details and applications

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Physical Review E 2008年第3期77卷 031135-031135页

作者： Y. Jiao F. H. Stillinger S. Torquato Department of Chemistry Princeton University Princeton New Jersey 08544 USA Princeton Institute for the Science and Technology of Materials Princeton University Princeton New Jersey 08544 USA Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA Princeton Center for Theoretical Physics Princeton University Princeton New Jersey 08544 USA and School of Natural Sciences Institute for Advanced Study Princeton New Jersey 08540 USA

In the first part of this series of two papers, we proposed a theoretical formalism that enables one to model and categorize heterogeneous materials (media) via two-point correlation functions S2 and introduced an efficient heterogeneous-medium (re)construction algorithm called the “lattice-point” algorithm. Here we discuss the algorithmic details of the lattice-point procedure and an algorithm modification using surface optimization to further speed up the (re)construction process. The importance of the error tolerance, which indicates to what accuracy the media are (re)constructed, is also emphasized and discussed. We apply the algorithm to generate three-dimensional digitized realizations of a Fontainebleau sandstone and a boron-carbide/aluminum composite from the two-dimensional tomographic images of their slices through the materials. To ascertain whether the information contained in S2 is sufficient to capture the salient structural features, we compute the two-point cluster functions of the media, which are superior signatures of the microstructure because they incorporate topological connectedness information. We also study the reconstruction of a binary laser-speckle pattern in two dimensions, in which the algorithm fails to reproduce the pattern accurately. We conclude that in general reconstructions using S2 only work well for heterogeneous materials with single-scale structures. However, two-point information via S2 is not sufficient to accurately model multiscale random media. Moreover, we construct realizations of hypothetical materials with desired structural characteristics obtained by manipulating their two-point correlation functions.

关键词： RECONSTRUCTING RANDOM-MEDIA TOPOLOGY OPTIMIZATION MICROSTRUCTURES COMPOSITES DESIGN TRANSPORT

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Modeling reflectance and fluorescence spectra of human pancreatic tissues for cancer diagnostics

Modeling reflectance and fluorescence spectra of human pancr...

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Frontiers in Optics, FiO 2008

作者： Wilson, Robert H. Chandra, Malavika Scheiman, James Heidt, David Simeone, Diane McKennae, Barbara Myceka, Mary-Ann Applied Physics Program University of Michigan Ann Arbor MI 48109-2099 United States Dept. of Internal Medicine University of Michigan Ann Arbor MI 48109-2099 United States Comprehensive Cancer Center University of Michigan Ann Arbor MI 48109-2099 United States Dept. of Surgery University of Michigan Ann Arbor MI 48109-2099 United States Dept. of Pathology University of Michigan Ann Arbor MI 48109-2099 United States Dept. of Biomedical Engineering University of Michigan Ann Arbor MI 48109-2099 United States

Reflectance and fluorescence spectroscopy were used in a limited pilot study to probe freshly excised human pancreatic tissues;mathematical modeling of the data quantitatively showed biologically relevant physical dif... 详细信息

ISBN: (纸本)9781557528612

关键词： Fluorescence spectroscopy

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