5,127 research outputs found
Short time dynamics with initial correlations
The short-time dynamics of correlated systems is strongly influenced by
initial correlations giving rise to an additional collision integral in the
non-Markovian kinetic equation. Exact cancellation of the two integrals is
found if the initial state is thermal equilibrium which is an important
consistency criterion. Analytical results are given for the time evolution of
the correlation energy which are confirmed by comparisons with molecular
dynamics simulations (MD)
Bulk rheology and microrheology of active fluids
We simulate macroscopic shear experiments in active nematics and compare them
with microrheology simulations where a spherical probe particle is dragged
through an active fluid. In both cases we define an effective viscosity: in the
case of bulk shear simulations this is the ratio between shear stress and shear
rate, whereas in the microrheology case it involves the ratio between the
friction coefficient and the particle size. We show that this effective
viscosity, rather than being solely a property of the active fluid, is affected
by the way chosen to measure it, and strongly depends on details such as the
anchoring conditions at the probe surface and on both the system size and the
size of the probe particle.Comment: 12 pages, 10 figure
Some remarks on one-dimensional force-free Vlasov-Maxwell equilibria
The conditions for the existence of force-free non-relativistic
translationally invariant one-dimensional (1D) Vlasov-Maxwell (VM) equilibria
are investigated using general properties of the 1D VM equilibrium problem. As
has been shown before, the 1D VM equilibrium equations are equivalent to the
motion of a pseudo-particle in a conservative pseudo-potential, with the
pseudo-potential being proportional to one of the diagonal components of the
plasma pressure tensor. The basic equations are here derived in a different way
to previous work. Based on this theoretical framework, a necessary condition on
the pseudo-potential (plasma pressure) to allow for force-free 1D VM equilibria
is formulated. It is shown that linear force-free 1D VM solutions, which so far
are the only force-free 1D VM solutions known, correspond to the case where the
pseudo-potential is an attractive central potential. A general class of
distribution functions leading to central pseudo-potentials is discussed.Comment: Physics of Plasmas, accepte
Giant Intrinsic Carrier Mobilities in Graphene and Its Bilayer
We have studied temperature dependences of electron transport in graphene and
its bilayer and found extremely low electron-phonon scattering rates that set
the fundamental limit on possible charge carrier mobilities at room
temperature. Our measurements have shown that mobilities significantly higher
than 200,000 cm2/Vs are achievable, if extrinsic disorder is eliminated. A
sharp (threshold-like) increase in resistivity observed above approximately
200K is unexpected but can qualitatively be understood within a model of a
rippled graphene sheet in which scattering occurs on intra-ripple flexural
phonons
Replica field theories, Painleve transcendents, and exact correlation functions
Exact solvability is claimed for nonlinear replica sigma models derived in
the context of random matrix theories. Contrary to other approaches reported in
the literature, the framework outlined does not rely on traditional "replica
symmetry breaking" but rests on a previously unnoticed exact relation between
replica partition functions and Painleve transcendents. While expected to be
applicable to matrix models of arbitrary symmetries, the method is used to
treat fermionic replicas for the Gaussian unitary ensemble (GUE), chiral GUE
(symmetry classes A and AIII in Cartan classification) and Ginibre's ensemble
of complex non-Hermitean random matrices. Further applications are briefly
discussed.Comment: published version, 4 pages, revtex
On the heavy quark mass expansion for the operator Qbar gamma_5 Q and the charm content of eta, eta'
Recently in the context of studies of the intrinsic charm content of the
nucleon and of the eta' meson two groups have arrived at different results for
the 1/m^3 term of the heavy quark expansion for operator
differing by the factor of six. We show that the form of both results violates
certain general conditions. Using the expression for the axial anomaly with the
finite Pauli-Villars regularization we obtain a new expression for 1/m^3 term
of the heavy quark expansion for . With this new result we
obtain an estimate for the constant f_{\eta'}^{(c)}=-2 MeV.Comment: 4 page
Embedded monopoles in quark eigenmodes in SU(2) Yang-Mills Theory
We study the embedded QCD monopoles (``quark monopoles'') using low-lying
eigenmodes of the overlap Dirac operator in zero- and finite-temperature SU(2)
Yang-Mills theory on the lattice. These monopoles correspond to the
gauge-invariant hedgehogs in the quark-antiquark condensates. The monopoles
were suggested to be agents of the chiral symmetry restoration since their
cores should suppress the chiral condensate. We study numerically the scalar,
axial and chirally invariant definitions of the embedded monopoles and show
that the monopole densities are in fact globally anti-correlated with the
density of the Dirac eigenmodes. We observe, that the embedded monopoles
corresponding to low-lying Dirac eigenvalues are dense in the chirally
invariant (high temperature) phase and dilute in the chirally broken (low
temperature) phase. We find that the scaling of the scalar and axial monopole
densities towards the continuum limit is similar to the scaling of the
string-like objects while the chirally invariant monopoles scale as membranes.
The excess of gluon energy at monopole positions reveals that the embedded QCD
monopole possesses a gluonic core, which is, however, empty at the very center
of the monopole.Comment: 29 pages, 27 figures, RevTeX 4.0; revised to match the published
version (clarifying remarks, references and acknowledgments are added
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