16,339 research outputs found
Coulomb Glasses: A Comparison Between Mean Field and Monte Carlo Results
Recently a local mean field theory for both eqilibrium and transport
properties of the Coulomb glass was proposed [A. Amir et al., Phys. Rev. B 77,
165207 (2008); 80, 245214 (2009)]. We compare the predictions of this theory to
the results of dynamic Monte Carlo simulations. In a thermal equilibrium state
we compare the density of states and the occupation probabilities. We also
study the transition rates between different states and find that the mean
field rates underestimate a certain class of important transitions. We propose
modified rates to be used in the mean field approach which take into account
correlations at the minimal level in the sense that transitions are only to
take place from an occupied to an empty site. We show that this modification
accounts for most of the difference between the mean field and Monte Carlo
rates. The linear response conductance is shown to exhibit the Efros-Shklovskii
behaviour in both the mean field and Monte Carlo approaches, but the mean field
method strongly underestimates the current at low temperatures. When using the
modified rates better agreement is achieved
Coulomb gap in the one-particle density of states in three-dimensional systems with localized electrons
The one-particle density of states (1P-DOS) in a system with localized
electron states vanishes at the Fermi level due to the Coulomb interaction
between electrons. Derivation of the Coulomb gap uses stability criteria of the
ground state. The simplest criterion is based on the excitonic interaction of
an electron and a hole and leads to a quadratic 1P-DOS in the three-dimensional
(3D) case. In 3D, higher stability criteria, including two or more electrons,
were predicted to exponentially deplete the 1P-DOS at energies close enough to
the Fermi level. In this paper we show that there is a range of intermediate
energies where this depletion is strongly compensated by the excitonic
interaction between single-particle excitations, so that the crossover from
quadratic to exponential behavior of the 1P-DOS is retarded. This is one of the
reasons why such exponential depletion was never seen in computer simulations.Comment: 6 pages, 1 figur
Nucleation of Spontaneous Vortices in Trapped Fermi Gases Undergoing a BCS-BEC Crossover
We study the spontaneous formation of vortices during the superfluid
condensation in a trapped fermionic gas subjected to a rapid thermal quench via
evaporative cooling. Our work is based on the numerical solution of the time
dependent crossover Ginzburg-Landau equation coupled to the heat diffusion
equation. We quantify the evolution of condensate density and vortex length as
a function of a crossover phase parameter from BCS to BEC. The more interesting
phenomena occur somewhat nearer to the BEC regime and should be experimentally
observable; during the propagation of the cold front, the increase in
condensate density leads to the formation of supercurrents towards the center
of the condensate as well as possible condensate volume oscillations.Comment: 5 pages, 3 figure
Measuring the saturation scale in nuclei
The saturation momentum seeing in the nuclear infinite momentum frame is
directly related to transverse momentum broadening of partons propagating
through the medium in the nuclear rest frame. Calculation of broadening within
the color dipole approach including the effects of saturation in the nucleus,
gives rise to an equation which describes well data on broadening in Drell-Yan
reaction and heavy quarkonium production.Comment: 11 pages, 5 figures, based on the talk presented by B.K. at the INT
workshop "Physics at a High Energy Electron Ion Collider", Seattle, October
200
Theory of Diamagnetism in the Pseudogap Phase: Implications from the Self energy of Angle Resolved Photoemission
In this paper we apply the emerging- consensus understanding of the fermionic
self energy deduced from angle resolved photoemisssion spectroscopy (ARPES)
experiments to deduce the implications for orbital diamagnetism in the
underdoped cuprates. Many theories using many different starting points have
arrived at a broadened BCS-like form for the normal state self energy
associated with a d-wave excitation gap, as is compatible with ARPES data.
Establishing compatibility with the f-sum rules, we show how this self energy,
along with the constraint that there is no Meissner effect in the normal phase
are sufficient to deduce the orbital susceptibility. We conclude, moreover,
that diamagnetism is large for a d-wave pseudogap. Our results should apply
rather widely to many theories of the pseudogap, independent of the microscopic
details.Comment: 15 pages, 8 figure
Fluctuations effects in high-energy evolution of QCD
Recently, Iancu and Triantafyllopoulos have proposed a hierarchy of evolution
equations in QCD at high energy which generalises previous approaches by
including the effects of gluon number fluctuations and thus the pomeron loops.
In this paper, we present the first numerical simulations of the Langevin
equation which reproduces that hierarchy. This equation is formally the
Balitsky-Kovchegov equation supplemented with a noise term accounting for the
relevant fluctuations. In agreement with theoretical predictions, we find that
the effects of the fluctuations is to reduce the saturation exponent and to
induce geometric scaling violations at high energy.Comment: 12 pages, 7 figures, minor corrections, version appeared in Phys.
Rev.
Glauber - Gribov approach for DIS on nuclei in N=4 SYM
In this paper the Glauber-Gribov approach for deep-inelastic scattering (DIS)
with nuclei is developed in N=4 SYM. It is shown that the amplitude displays
the same general properties, such as geometrical scaling, as is the case in the
high density QCD approach. We found that the quantum effects leading to the
graviton reggeization, give rise to an imaginary part of the nucleon amplitude,
which makes the DIS in N=4 SYM almost identical to the one expected in high
density QCD. We concluded that the impact parameter dependence of the nucleon
amplitude is very essential for N=4 SYM, and the entire kinematic region can be
divided into three regions which are discussed in the paper. We revisited the
dipole description for DIS and proposed a new renormalized Lagrangian for the
shock wave formalism which reproduces the Glauber-Gribov approach in a certain
kinematic region. However the saturation momentum turns out to be independent
of energy, as it has been discussed by Albacete, Kovchegov and Taliotis. We
discuss the physical meaning of such a saturation momentum and argue
that one can consider only within the shock wave approximation.Comment: 40pp.,9 figures in eps file
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Use and cost of disease-modifying therapies by Sonya Slifka Study participants: has anything really changed since 2000 and 2009?
Background:Disease-modifying therapies benefit individuals with relapsing forms of multiple sclerosis, but their utility remains unclear for those without relapses. Objective:To determine disease-modifying therapy use and costs in 2009, compare use in 2009 and 2000, and examine compliance with evidence-based guidelines. Methods:We determined the extent and characteristics of disease-modifying therapy use by participants in the Sonya Slifka Longitudinal Multiple Sclerosis Study (Slifka) in 2000 (n=2156) and 2009 (n=2361) and estimated out-of-pocket and total (payer) costs for 2009. Two multivariable logistic regressions predicted disease-modifying therapy use. Results:Disease-modifying therapy use increased from 55.3% in 2000 to 61.5% in 2009. In 2009, disease-modifying therapy use was reported by 76.5% of participants with relapsing-remitting multiple sclerosis, 73.2% with progressive-relapsing multiple sclerosis, 62.5% with secondary progressive multiple sclerosis, and 41.8% with primary progressive multiple sclerosis. Use was significantly associated with relapsing-remitting multiple sclerosis, shorter duration of illness, one to two relapses per year, non-ambulatory symptoms, using a cane, younger age, higher family income, and having health insurance. Average annual costs in 2009 were US16,302-18,928 for payers. Conclusion:Use rates were highest for individuals with relapsing-remitting multiple sclerosis, but substantial for those with progressive courses although clinical trials have not demonstrated significant benefits for them
Elliptic Schlesinger system and Painlev{\'e} VI
We construct an elliptic generalization of the Schlesinger system (ESS) with
positions of marked points on an elliptic curve and its modular parameter as
independent variables (the parameters in the moduli space of the complex
structure). ESS is a non-autonomous Hamiltonian system with pair-wise commuting
Hamiltonians. The system is bihamiltonian with respect to the linear and the
quadratic Poisson brackets. The latter are the multi-color generalization of
the Sklyanin-Feigin-Odeskii classical algebras. We give the Lax form of the
ESS. The Lax matrix defines a connection of a flat bundle of degree one over
the elliptic curve with first order poles at the marked points.
The ESS is the monodromy independence condition on the complex structure for
the linear systems related to the flat bundle.
The case of four points for a special initial data is reduced to the
Painlev{\'e} VI equation in the form of the Zhukovsky-Volterra gyrostat,
proposed in our previous paper.Comment: 16 pages; Dedicated to the centenary of the publication of the
Painleve VI equation in the Comptes Rendus de l'Academie des Sciences de
Paris by Richard Fuchs in 190
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