41,281 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
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
Non-perturbative gadget for topological quantum codes
Many-body entangled systems, in particular topologically ordered spin systems
proposed as resources for quantum information processing tasks, often involve
highly non-local interaction terms. While one may approximate such systems
through two-body interactions perturbatively, these approaches have a number of
drawbacks in practice. Here, we propose a scheme to simulate many-body spin
Hamiltonians with two-body Hamiltonians non-perturbatively. Unlike previous
approaches, our Hamiltonians are not only exactly solvable with exact ground
state degeneracy, but also support completely localized quasi-particle
excitations, which are ideal for quantum information processing tasks. Our
construction is limited to simulating the toric code and quantum double models,
but generalizations to other non-local spin Hamiltonians may be possible.Comment: 13 pages, 8 figures, PRL Accepte
Beltrami-like fields created by baroclinic effect in two-fluid plasmas
A theory of two-dimensional plasma evolution with Beltrami-like flow and
field due to baroclinic effect has been presented. Particular solution of the
nonlinear two-fluid equations is obtained. This simple model can explain the
generation of magnetic field without assuming the presence of a seed in the
system. Coupled field and flow naturally grow together. The theory has been
applied to estimate B-field in laser-induced plasmas and the result is in good
agreement with experimental values.Comment: 3 page
Characteristic Bisimulation for Higher-Order Session Processes
Characterising contextual equivalence is a long-standing issue for higher-order (process) languages. In the setting of a higher-order pi-calculus with sessions, we develop characteristic bisimilarity, a typed bisimilarity which fully characterises contextual equivalence. To our knowledge, ours is the first characterisation of its kind. Using simple values inhabiting (session) types, our approach distinguishes from untyped methods for characterising contextual equivalence in higher-order processes: we show that observing as inputs only a precise finite set of higher-order values suffices to reason about higher-order session processes. We demonstrate how characteristic bisimilarity can be used to justify optimisations in session protocols with mobile code communication
Probing the three-gluon correlation functions by the single spin asymmetry in p^\uparrow p\to DX
We study the single transverse-spin asymmetry for the inclusive open-charm
production in the pp-collision, p^\uparrow p\to DX, induced by the three-gluon
correlation functions in the polarized nucleon. We derive the corresponding
twist-3 cross section formula in the leading order with respect to the QCD
coupling constant. As in the case of the semi-inclusive deep inelastic
scattering, ep^\uparrow\to eDX, our result differs from the previous result in
the literature. We also derive a "master formula" which expresses the twist-3
cross section in terms of the gg\to c\bar{c} hard scattering cross section. We
present a model calculation of the asymmetry at the RHIC energy, demonstrating
the sensitivity of the asymmetry on the form of the three-gluon correlation
functions.Comment: 25 pages, 7 figures. Final version to appear in PRD. Some changes in
the section of numerical calculation include
A model study of cooperative binding of ionic surfactants to oppositely charged flexible polyions
A novel statistical model for the cooperative binding of monomeric ligands to
a linear lattice is developed to study the interaction of ionic surfactant
molecules with flexible polyion chain in dilute solution. Electrostatic binding
of a ligand to a site on the polyion and hydrophobic associations between the
neighboring bound ligands are assumed to be stochastic processes. Ligand
association separated by several lattice points within defined width is
introduced for the flexible polyion. Model calculations by the Monte Carlo
method are carried out to investigate the binding behavior. The hypothesis on
the ligand association and its width on the chain are of importance in
determining critical aggregation concentration and binding isotherm. The
results are reasonable for the interpretations of several surfactant-flexible
polyion binding experiments. The implications of the approach are presented and
discussed.Comment: 11 pages, 9 figure
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