23,723 research outputs found
Resummation for Nonequilibrium Perturbation Theory and Application to Open Quantum Lattices
Lattice models of fermions, bosons, and spins have long served to elucidate
the essential physics of quantum phase transitions in a variety of systems.
Generalizing such models to incorporate driving and dissipation has opened new
vistas to investigate nonequilibrium phenomena and dissipative phase
transitions in interacting many-body systems. We present a framework for the
treatment of such open quantum lattices based on a resummation scheme for the
Lindblad perturbation series. Employing a convenient diagrammatic
representation, we utilize this method to obtain relevant observables for the
open Jaynes-Cummings lattice, a model of special interest for open-system
quantum simulation. We demonstrate that the resummation framework allows us to
reliably predict observables for both finite and infinite Jaynes-Cummings
lattices with different lattice geometries. The resummation of the Lindblad
perturbation series can thus serve as a valuable tool in validating open
quantum simulators, such as circuit-QED lattices, currently being investigated
experimentally.Comment: 15 pages, 9 figure
Away-side azimuthal distribution in a Markovian parton scattering model
An event generator is constructed on the basis of a model of multiple
scattering of partons so that the trajectory of a parton traversing a dense and
expanding medium can be tracked. The parameters in the code are adjusted to fit
the \Delta\phi azimuthal distribution on the far side when the trigger momentum
is in the non-perturbative region, p_T(trigger)<4 GeV/c. The dip-bump structure
for 1<p_T(assoc)<2.5 GeV/c is reproduced by averaging over the exit tracks of
deflected jets. An essential characteristic of the model, called Markovian
Parton Scattering (MPS) model, is that the scattering angle is randomly
selected in the forward cone at every step of a trajectory that is divided into
many discrete steps in a semi-classical approximation of the non-perturbative
scattering process. Energy loss to the medium is converted to thermal partons
which hadronize by recombination to give rise to the pedestal under the bumps.
When extended to high trigger momentum with \pt(trigger) >8 GeV/c, the model
reproduces the single-peak structure observed by STAR without invoking any new
dynamical mechanism.Comment: 20 pages + 3 figure
Baryon number and strangeness: signals of a deconfined antecedent
The correlation between baryon number and strangeness is used to discern the
nature of the deconfined matter produced at vanishing chemical potential in
high-energy nuclear collisions at the BNL RHIC. Comparisons of results of
various phenomenological models with correlations extracted from lattice QCD
calculations suggest that a quasi-particle picture applies. At finite baryon
densities, such as those encountered at the CERN SPS, it is demonstrated that
the presence of a first-order phase transition and the accompanying development
of spinodal decomposition would significantly enhance the number of strangeness
carriers and the associated fluctuations.Comment: 10 pages, 4 figures, latex, to appear in the proceedings of the
Workshop on Correlations and Fluctuations in Relativistic Nuclear collisions,
(MIT, April 21-23,2005
Modeling 3-D objects with planar surfaces for prediction of electromagnetic scattering
Electromagnetic scattering analysis of objects at resonance is difficult because low frequency techniques are slow and computer intensive, and high frequency techniques may not be reliable. A new technique for predicting the electromagnetic backscatter from electrically conducting objects at resonance is studied. This technique is based on modeling three dimensional objects as a combination of flat plates where some of the plates are blocking the scattering from others. A cube is analyzed as a simple example. The preliminary results compare well with the Geometrical Theory of Diffraction and with measured data
Proteomics reveals that a high-fat diet induces rapid changes in hypothalamic proteins related to neuronal damage and inflammation
Peer reviewedPublisher PD
The chemical equilibration volume: measuring the degree of thermalization
We address the issue of the degree of equilibrium achieved in a high energy
heavy-ion collision. Specifically, we explore the consequences of incomplete
strangeness chemical equilibrium. This is achieved over a volume V of the order
of the strangeness correlation length and is assumed to be smaller than the
freeze-out volume. Probability distributions of strange hadrons emanating from
the system are computed for varying sizes of V and simple experimental
observables based on these are proposed. Measurements of such observables may
be used to estimate V and as a result the degree of strangeness chemical
equilibration achieved. This sets a lower bound on the degree of kinetic
equilibrium. We also point out that a determination of two-body correlations or
second moments of the distributions are not sufficient for this estimation.Comment: 16 pages, 15 figures, revtex
On piezophase effects in mechanically loaded atomic scale Josephson junctions
The response of an intrinsic Josephson contact to externally applied stress
is considered within the framework of the dislocation-induced atomic scale
Josephson effect. The predicted quasi-periodic (Fraunhofer-like)stress-strain
and stress-current patterns should manifest themselves for experimentally
accessible values of applied stresses in intrinsically defected (e.g.,twinned)
crystals.Comment: REVTEX (epsf style), 2 EPS figure
Sequential Desynchronization in Networks of Spiking Neurons with Partial Reset
The response of a neuron to synaptic input strongly depends on whether or not
it has just emitted a spike. We propose a neuron model that after spike
emission exhibits a partial response to residual input charges and study its
collective network dynamics analytically. We uncover a novel desynchronization
mechanism that causes a sequential desynchronization transition: In globally
coupled neurons an increase in the strength of the partial response induces a
sequence of bifurcations from states with large clusters of synchronously
firing neurons, through states with smaller clusters to completely asynchronous
spiking. We briefly discuss key consequences of this mechanism for more general
networks of biophysical neurons
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