31,614 research outputs found
Universal zero-bias conductance through a quantum wire side-coupled to a quantum dot
A numerical renormalization-group study of the conductance through a quantum
wire side-coupled to a quantum dot is reported. The temperature and the
dot-energy dependence of the conductance are examined in the light of a
recently derived linear mapping between the Kondo-regime temperature-dependent
conductance and the universal function describing the conductance for the
symmetric Anderson model of a quantum wire with an embedded quantum dot. Two
conduction paths, one traversing the wire, the other a bypass through the
quantum dot, are identified. A gate potential applied to the quantum wire is
shown to control the flow through the bypass. When the potential favors
transport through the wire, the conductance in the Kondo regime rises from
nearly zero at low temperatures to nearly ballistic at high temperatures. When
it favors the dot, the pattern is reversed: the conductance decays from nearly
ballistic to nearly zero. When the fluxes through the two paths are comparable,
the conductance is nearly temperature-independent in the Kondo regime, and a
Fano antiresonance in the fixed-temperature plot of the conductance as a
function of the dot energy signals interference. Throughout the Kondo regime
and, at low temperatures, even in the mixed-valence regime, the numerical data
are in excellent agreement with the universal mapping.Comment: 12 pages, with 9 figures. Submitted to PR
Exact renormalization group equation in presence of rescaling anomaly
Wilson's approach to renormalization group is reanalyzed for supersymmetric
Yang-Mills theory. Usual demonstration of exact renormalization group equation
must be modified due to the presence of the so called Konishi anomaly under the
rescaling of superfields. We carry out the explicit computation for N=1 SUSY
Yang-Mills theory with the simpler, gauge invariant regularization method,
recently proposed by Arkani-Hamed and Murayama. The result is that the
Wilsonian action S_M consists of two terms, i.e. the non anomalous term, which
obeys Polchinski's flow equation and Fujikawa-Konishi determinant contribution.
This latter is responsible for Shifman-Vainshtein relation of exact
beta-function.Comment: 19 pages, no figures; an appendix and reference added; typos
correcte
Heterogeneous spin state in the field-induced phase of volborthite as seen via 51V nuclear magnetic resonance
We report results of 51V NMR in the field-induced phase of volborthite
Cu3V2O7(OH)dot2H2O, a spin-1/2 antiferromagnet on a distorted kagome lattice.
In magnetic fields above 4.5 T, two types of V sites with different spin-echo
decay rates are observed. The hyperfine field at the fast decaying sites has a
distribution, while it is more homogeneous at the slowly decaying sites. Our
results indicate a heterogeneous state consisting of two spatially alternating
Cu spin systems, one of which exhibits anomalous spin fluctuations contrasting
with the other showing a conventional static order.Comment: 5 pages, 4 figure
Summary of Working Group I: Hadron Structure
A summary is given on the main aspects which were discussed by the working
group. They include new results on the deep inelastic scattering structure
functions and and their parametrizations, the
measurement of the gluon density, recent theoretical work on the small
behavior of structure functions, theoretical and experimental results on
, the direct photon cross section, and a discussion of the event
rates in the high range at Tevatron and the high range at HERA, as
well as possible interpretations.Comment: 22 pages latex, including 8 figures (ps,eps), to appear in the
Proceedings of the International Conference on Deep Inelastic Scattering,
Chicago, April 1997, AI
On the preciseness of subtyping in session types
Subtyping in concurrency has been extensively studied since early 1990s as one of the most interesting issues in type theory. The correctness of subtyping relations has been usually provided as the soundness for type safety. The converse direction, the completeness, has been largely ignored in spite of its usefulness to define the greatest subtyping relation ensuring type safety. This paper formalises preciseness (i.e. both soundness and completeness) of subtyping for mobile processes and studies it for the synchronous and the asynchronous session calculi. We first prove that the well-known session subtyping, the branching-selection subtyping, is sound and complete for the synchronous calculus. Next we show that in the asynchronous calculus, this subtyping is incomplete for type-safety: that is, there exist session types T and S such that T can safely be considered as a subtype of S, but T ≤ S is not derivable by the subtyping. We then propose an asynchronous sub-typing system which is sound and complete for the asynchronous calculus. The method gives a general guidance to design rigorous channel-based subtypings respecting desired safety properties
Thermal dependence of the zero-bias conductance through a nanostructure
We show that the conductance of a quantum wire side-coupled to a quantum dot,
with a gate potential favoring the formation of a dot magnetic moment, is a
universal function of the temperature. Universality prevails even if the
currents through the dot and the wire interfere. We apply this result to the
experimental data of Sato et al.[Phys. Rev. Lett. 95, 066801 (2005)].Comment: 6 pages, 3 figures. More detailed presentation, and updated
references. Final version
Statistical Analysis of Spectral Line Candidates in Gamma-Ray Burst GRB870303
The Ginga data for the gamma-ray burst GRB870303 exhibit low-energy dips in
two temporally distinct spectra, denoted S1 and S2. S1, spanning 4 s, exhibits
a single line candidate at ~ 20 keV, while S2, spanning 9 s, exhibits
apparently harmonically spaced line candidates at ~ 20 and 40 keV. We evaluate
the statistical evidence for these lines, using phenomenological continuum and
line models which in their details are independent of the distance scale to
gamma-ray bursts. We employ the methodologies based on both frequentist and
Bayesian statistical inference that we develop in Freeman et al. (1999b). These
methodologies utilize the information present in the data to select the
simplest model that adequately describes the data from among a wide range of
continuum and continuum-plus-line(s) models. This ensures that the chosen model
does not include free parameters that the data deem unnecessary and that would
act to reduce the frequentist significance and Bayesian odds of the
continuum-plus-line(s) model. We calculate the significance of the
continuum-plus-line(s) models using the Chi-Square Maximum Likelihood Ratio
test. We describe a parametrization of the exponentiated Gaussian absorption
line shape that makes the probability surface in parameter space
better-behaved, allowing us to estimate analytically the Bayesian odds. The
significance of the continuum-plus-line models requested by the S1 and S2 data
are 3.6 x 10^-5 and 1.7 x 10^-4 respectively, with the odds favoring them being
114:1 and 7:1. We also apply our methodology to the combined (S1+S2) data. The
significance of the continuum-plus-lines model requested by the combined data
is 4.2 x 10^-8, with the odds favoring it being 40,300:1.Comment: LaTeX2e (aastex.cls included); 41 pages text, 10 figures (on 11
pages); accepted by ApJ (to be published 1 Nov 1999, v. 525
On de-Sitter Geometry in Cosmic Void Statistics
Starting from the geometrical concept of a 4-dimensional de-Sitter
configuration of spheres in Euclidean 3-space and modelling voids in the
Universe as spheres, we show that a uniform distribution over this
configuration space implies a power-law for the void number density which is
consistent with results from the excursion set formalism and with data, for an
intermediate range of void volumes. The scaling dimension of the large scale
structure can be estimated as well. We also discuss the effect of restricting
the survey geometry on the void statistics. This work is a new application of
de-Sitter geometry to cosmology and also provides a new geometrical perspective
on self-similarity in cosmology.Comment: 8 pages, 4 figures, accepted by MNRAS. Minor changes, appendix adde
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