40,828 research outputs found
Asymptotic Learning Curve and Renormalizable Condition in Statistical Learning Theory
Bayes statistics and statistical physics have the common mathematical
structure, where the log likelihood function corresponds to the random
Hamiltonian. Recently, it was discovered that the asymptotic learning curves in
Bayes estimation are subject to a universal law, even if the log likelihood
function can not be approximated by any quadratic form. However, it is left
unknown what mathematical property ensures such a universal law. In this paper,
we define a renormalizable condition of the statistical estimation problem, and
show that, under such a condition, the asymptotic learning curves are ensured
to be subject to the universal law, even if the true distribution is
unrealizable and singular for a statistical model. Also we study a
nonrenormalizable case, in which the learning curves have the different
asymptotic behaviors from the universal law
Electron screening in the liquid-gas mixed phases of nuclear matter
Screening effects of electrons on inhomogeneous nuclear matter, which
includes spherical, slablike, and rodlike nuclei as well as spherical and
rodlike nuclear bubbles, are investigated in view of possible application to
cold neutron star matter and supernova matter at subnuclear densities. Using a
compressible liquid-drop model incorporating uncertainties in the surface
tension, we find that the energy change due to the screening effects broadens
the density region in which bubbles and nonspherical nuclei appear in the phase
diagram delineating the energetically favorable shape of inhomogeneous nuclear
matter. This conclusion is considered to be general since it stems from a
model-independent feature that the electron screening acts to decrease the
density at which spherical nuclei become unstable against fission and to
increase the density at which uniform matter becomes unstable against proton
clustering.Comment: 12 pages, 8 figures, accepted for publication in Physical Review
Modulation of Superconducting Properties by Ferroelectric Polarization in Confined FE-S-FE Films
We show that the electric polarization at the interface with ultrathin
superconducting (S) films sandwiched between ferroelectric (FE) layers allows
achievement of substantially stronger modulation of inner carrier density and
superconducting transition temperature as compared to FE-S bilayers typically
used in superconducting FETs. We find that not only the larger penetration
depths but also the pairing symmetry should be responsible for the fact that
the electric field effect in high temperature superconductors is much stronger
than in conventional systems. Discussing the advantages of multilayers, we
propose a novel design concept for superconducting electric field-effect
transistors based on ferroelectric films.Comment: 5 pages RevTex4, 6 figure
Novel Charge Order and Superconductivity in Two-Dimensional Frustrated Lattice at Quarter Filling
Motivated by the various physical properties observed in
-(BEDT-TTF)X, we study the ground state of extended Hubbard model
on two-dimensional anisotropic triangular lattice at 1/4-filling with
variational Monte Carlo method. It is shown that the nearest-neighbor Coulomb
interaction enhances the charge fluctuation and it induces the anomalous state
such as charge-ordered metallic state and the triplet next-nearest-neighbor
-wave superconductivity. We discuss the relation to the real materials and
propose the unified view of the family of -(BEDT-TTF)X.Comment: 4 pages, 5 figure
Constraints on Association of Single-pulse Gamma-ray Bursts and Supernovae
We explore the hypothesis, similar to one recently suggested by Bloom and
colleagues, that some nearby supernovae are associated with smooth,
single-pulse gamma-ray bursts, possibly having no emission above ~ 300 keV. We
examine BATSE bursts with durations longer than 2 s, fitting those which can be
visually characterized as single-pulse events with a lognormal pulse model. The
fraction of events that can be reliably ascertained to be temporally and
spectrally similar to the exemplar, GRB 980425 - possibly associated with SN
1998bw - is 4/1573 or 0.25%. This fraction could be as high as 8/1573 (0.5%) if
the dimmest bursts are included. Approximately 2% of bursts are morphologically
similar to GRB 980425 but have emission above ~ 300 keV. A search of supernova
catalogs containing 630 detections during BATSE's lifetime reveals only one
burst (GRB 980425) within a 3-month time window and within the total 3-sigma
BATSE error radius that could be associated with a type Ib/c supernova. There
is no tendency for any subset of single-pulse GRBs to fall near the
Supergalactic Plane, whereas SNe of type Ib/c do show this tendency. Economy of
hypotheses leads us to conclude that nearby supernovae generally are not
related to smooth, single-pulse gamma-ray bursts.Comment: 25 pages, 5 figure
Phase Diagram of Spinless Fermions on an Anisotropic Triangular Lattice at Half-filling
The strong coupling phase diagram of the spinless fermions on the anisotropic
triangular lattice at half-filling is presented. The geometry of inter-site
Coulomb interactions rules the phase diagram. Unconventional charge ordered
phases are detected which are the recently reported pinball liquid and the
striped chains. Both are induced by the quantum dynamics out of classical
disordered states and afford extremely correlated metallic states and the
particular domain wall-type of excitations, respectively. The disorder once
killed by the quantum effect revives at the finite temperature, which is
discussed in the terms of the organic -ET.Comment: 4pages 6figure
Efficient method for simulating quantum electron dynamics under the time dependent Kohn-Sham equation
A numerical scheme for solving the time-evolution of wave functions under the
time dependent Kohn-Sham equation has been developed. Since the effective
Hamiltonian depends on the wave functions, the wave functions and the effective
Hamiltonian should evolve consistently with each other. For this purpose, a
self-consistent loop is required at every time-step for solving the
time-evolution numerically, which is computationally expensive. However, in
this paper, we develop a different approach expressing a formal solution of the
TD-KS equation, and prove that it is possible to solve the TD-KS equation
efficiently and accurately by means of a simple numerical scheme without the
use of any self-consistent loops.Comment: 5 pages, 3 figures. Physical Review E, 2002, in pres
Universal Features of Quantized Thermal Conductance of Carbon Nanotubes
The universal features of quantized thermal conductance of carbon nanotubes
(CNTs) are revealed through theoretical analysis based on the Landauer theory
of heat transport. The phonon-derived thermal conductance of semiconducting
CNTs exhibits a universal quantization in the low temperature limit,
independent of the radius or atomic geometry. The temperature dependence
follows a single curve given in terms of temperature scaled by the phonon
energy gap. The thermal conductance of metallic CNTs has an additional
contribution from electronic states, which also exhibits quantized behavior up
to room temperature.Comment: 4 pages, 5 figures. accepted for publication in Phys. Rev. Let
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