12,684 research outputs found
Superconductivity-Related Insulating Behavior
We present the results of an experimental study of superconducting,
disordered, thin-films of amorphous Indium Oxide. These films can be driven
from the superconducting phase to a reentrant insulating state by the
application of a perpendicular magnetic field (). We find that the high-
insulator exhibits activated transport with a characteristic temperature,
. has a maximum value () that is close to the
superconducting transition temperature () at = 0, suggesting a
possible relation between the conduction mechanisms in the superconducting and
insulating phases. and display opposite dependences on the
disorder strength.Comment: Tex file and 5 figures; Revised version; To appear in Phys. Rev.
Lett. (2004
Intraflagellar transport particle size scales inversely with flagellar length: revisiting the balance-point length control model
Chlamydomonas reinhardtii IFT particle trains, important for flagella maintenance and assembly, are observed to decrease in size as a function of cilia length
Remnant Break-up and Muon Production in Cosmic Ray Air Showers
We discuss the relation between remnant fragmentation in inelastic
high-energy hadronic interactions and muon production in extensive cosmic ray
air showers. Using a newly developed tool, a simple and flexible hadronic event
generator, we analyze the forward region of hadronic interactions. We show that
measurements of the Feynman-x distribution in the beam fragmentation region at
LHCf will be key to understanding muon production in air showers
quantitatively.Comment: 6 pages, 6 figure
Small-angle impurity scattering and the spin Hall conductivity in 2D systems
An arbitrarily small concentration of impurities can affect the spin Hall
conductivity in a two-dimensional semiconductor system. We develop a
Boltzmann-like equation that can be used for impurity scattering with arbitrary
angular dependence, and for arbitrary angular dependence of the spin-orbit
field b(k) around the Fermi surface. For a model applicable to a 2D hole system
in GaAs, if the impurity scattering is not isotropic, we find that the spin
Hall conductivity depends on the derivative of b with respect to the energy and
on deviations from a parabolic band structure, as well as on the angular
dependence of the scattering. In principle, the resulting spin Hall
conductivity can be larger or smaller than the ``intrinsic value'', and can
have opposite sign. In the limit of small angle scattering, in a model
appropriate for small hole concentrations, where the band is parabolic and b ~
k^3, the spin Hall conductivity has opposite sign from the intrinsic value, and
has larger magnitude. Our analysis assumes that the spin-orbit splitting
and the transport scattering rate tau^{-1} are both small compared to the Fermi
energy, but the method is valid for for arbitrary value of b*tau.Comment: Errors corrected, references adde
Semiclassical theory of spin-polarized shot noise in mesoscopic diffusive conductors
We study fluctuations of spin-polarized currents in a three-terminal
spin-valve system consisting of a diffusive normal metal wire connected by
tunnel junctions to three ferromagnetic terminals. Based on a spin-dependent
Boltzmann-Langevin equation, we develop a semiclassical theory of charge and
spin currents and the correlations of the currents fluctuations. In the three
terminal system, we show that current fluctuations are strongly affected by the
spin-flip scattering in the normal metal and the spin polarizations of the
terminals, which may point in different directions. We analyze the dependence
of the shot noise and the cross-correlations on the spin-flip scattering rate
in the full range of the spin polarizations and for different magnetic
configurations. Our result demonstrate that noise measurements in
multi-terminal devices allow to determine the spin-flip scattering rate by
changing the polarizations of ferromagnetic terminals.Comment: 12 pages, 5 figure
Constraints on Parity-Even Time Reversal Violation in the Nucleon-Nucleon System and Its Connection to Charge Symmetry Breaking
Parity-even time reversal violation (TRV) in the nucleon-nucleon interaction
is reconsidered. The TRV -exchange interaction on which recent analyses
of measurements are based is necessarily also charge-symmetry breaking (CSB).
Limits on its strength relative to regular -exchange are
extracted from recent CSB experiments in neutron-proton scattering. The result
(95% CL) is considerably lower than limits
inferred from direct TRV tests in nuclear processes. Properties of
-exchange and limit imposed by the neutron EDM are briefly discussed.Comment: RevTex, 8 pages. Factor ten error in cited neutron EDM corrected,
discussion and two references adde
Dynamical scaling of the quantum Hall plateau transition
Using different experimental techniques we examine the dynamical scaling of
the quantum Hall plateau transition in a frequency range f = 0.1-55 GHz. We
present a scheme that allows for a simultaneous scaling analysis of these
experiments and all other data in literature. We observe a universal scaling
function with an exponent kappa = 0.5 +/- 0.1, yielding a dynamical exponent z
= 0.9 +/- 0.2.Comment: v2: Length shortened to fulfil Journal criteri
Avalanches in the lung: A statistical mechanical model
We study a statistical mechanical model for the dynamics of lung inflation
which incorporates recent experimental observations on the opening of
individual airways by a cascade or avalanche mechanism. Using an exact mapping
of the avalanche problem onto percolation on a Cayley tree, we analytically
derive the exponents describing the size distribution of the first avalanches
and test the analytical solution by numerical simulations. We find that the
tree-like structure of the airways together with the simplest assumptions
concerning opening threshold pressures of each airway, is sufficient to explain
the existence of power-law distributions observed experimentally.Comment: 4 pages, Figures avaliable by mail from [email protected], REVTE
Storage of correlated patterns in a perceptron
We calculate the storage capacity of a perceptron for correlated gaussian
patterns. We find that the storage capacity can be less than 2 if
similar patterns are mapped onto different outputs and vice versa. As long as
the patterns are in general position we obtain, in contrast to previous works,
that in agreement with Cover's theorem. Numerical simulations
confirm the results.Comment: 9 pages LaTeX ioplppt style, figures included using eps
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