31,017 research outputs found
Charmonium Spectral Functions and Transport Properties of Quark-Gluon Plasma
We study vacuum masses of charmonia and the charm-quark diffusion coefficient
in the quark-gluon plasma based on the spectral representation for meson
correlators. To calculate the correlators, we solve the quark gap equation and
the inhomogeneous Bethe-Salpeter equation in the rainbow-ladder approximation.
It is found that the ground-state masses of charmonia in the pseudoscalar,
scalar, and vector channels can be well described. For ,
the value of the diffusion coefficient is comparable with that obtained by
lattice QCD and experiments: . Relating the diffusion
coefficient with the ratio of shear viscosity to entropy density of
the quark-gluon plasma, we obtain values in the range .Comment: 5 pages, 4 figure
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Learning distance to subspace for the nearest subspace methods in high-dimensional data classification
The nearest subspace methods (NSM) are a category of classification methods widely applied to classify high-dimensional data. In this paper, we propose to improve the classification performance of NSM through learning tailored distance metrics from samples to class subspaces. The learned distance metric is termed as ‘learned distance to subspace’ (LD2S). Using LD2S in the classification rule of NSM can make the samples closer to their correct class subspaces while farther away from their wrong class subspaces. In this way, the classification task becomes easier and the classification performance of NSM can be improved. The superior classification performance of using LD2S for NSM is demonstrated on three real-world high-dimensional spectral datasets
From Individual to Collective Behavior of Unicellular Organisms: Recent Results and Open Problems
The collective movements of unicellular organisms such as bacteria or amoeboid (crawling) cells are often modeled by partial differential equations (PDEs) that describe the time evolution of cell density. In particular, chemotaxis equations have been used to model the movement towards various kinds of extracellular cues. Well-developed analytical and numerical methods for analyzing the time-dependent and time-independent properties of solutions make this approach attractive. However, these models are often based on phenomenological descriptions of cell fluxes with no direct correspondence to individual cell processes such signal transduction and cell movement. This leads to the question of how to justify these macroscopic PDEs from microscopic descriptions of cells, and how to relate the macroscopic quantities in these PDEs to individual-level parameters. Here we summarize recent progress on this question in the context of bacterial and amoeboid chemotaxis, and formulate several open problems
Mechanical modulation of single-electron tunneling through molecular-assembled metallic nanoparticles
We present a microscopic study of single-electron tunneling in nanomechanical
double-barrier tunneling junctions formed using a vibrating scanning nanoprobe
and a metallic nanoparticle connected to a metallic substrate through a
molecular bridge. We analyze the motion of single electrons on and off the
nanoparticle through the tunneling current, the displacement current and the
charging-induced electrostatic force on the vibrating nanoprobe. We demonstrate
the mechanical single-electron turnstile effect by applying the theory to a
gold nanoparticle connected to the gold substrate through alkane dithiol
molecular bridge and probed by a vibrating platinum tip.Comment: Accepted by Phys. Rev.
Nucleus Driven Electronic Pulsation
We derive and solve by the spectral method the equations for a neutral system
of ultra-relativistic electrons that are compressed to the radius of the
nucleus and subject to a driving force. This driving force can be thought of as
originating from a nuclear breathing mode, a possibility we discuss in detail
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