37,622 research outputs found
Comment on "Generalized exclusion processes: Transport coefficients"
In a recent paper Arita et al. [Phys. Rev. E 90, 052108 (2014)] consider the
transport properties of a class of generalized exclusion processes. Analytical
expressions for the transport-diffusion coefficient are derived by ignoring
correlations. It is claimed that these expressions become exact in the
hydrodynamic limit. In this Comment, we point out that (i) the influence of
correlations upon the diffusion does not vanish in the hydrodynamic limit, and
(ii) the expressions for the self- and transport diffusion derived by Arita et
al. are special cases of results derived in [Phys. Rev. Lett. 111, 110601
(2013)].Comment: (citation added, published version
Diffusion of interacting particles in discrete geometries
We evaluate the self-diffusion and transport diffusion of interacting
particles in a discrete geometry consisting of a linear chain of cavities, with
interactions within a cavity described by a free-energy function. Exact
analytical expressions are obtained in the absence of correlations, showing
that the self-diffusion can exceed the transport diffusion if the free-energy
function is concave. The effect of correlations is elucidated by comparison
with numerical results. Quantitative agreement is obtained with recent
experimental data for diffusion in a nanoporous zeolitic imidazolate framework
material, ZIF-8.Comment: 5 pages main text (3 figures); 9 pages supplemental material (2
figures). (minor changes, published version
Adsorption and desorption in confined geometries: a discrete hopping model
We study the adsorption and desorption kinetics of interacting particles
moving on a one-dimensional lattice. Confinement is introduced by limiting the
number of particles on a lattice site. Adsorption and desorption are found to
proceed at different rates, and are strongly influenced by the
concentration-dependent transport diffusion. Analytical solutions for the
transport and self-diffusion are given for systems of length 1 and 2 and for a
zero-range process. In the last situation the self- and transport diffusion can
be calculated analytically for any length.Comment: Published in EPJ ST volume "Brownian Motion in Confined Geometries
A Note on Flux Induced Superpotentials in String Theory
Non-vanishing fluxes in M-theory and string theory compactifications induce a
superpotential in the lower dimensional theory. Gukov has conjectured the
explicit form of this superpotential. We check this conjecture for the
heterotic string compactified on a Calabi-Yau three-fold as well as for warped
M-theory compactifications on Spin(7) holonomy manifolds, by performing a
Kaluza-Klein reduction.Comment: 19 pages, no figure
Quantum Gravity Corrections for Schwarzschild Black Holes
We consider the Matrix theory proposal describing eleven-dimensional
Schwarzschild black holes. We argue that the Newtonian potential between two
black holes receives a genuine long range quantum gravity correction, which is
finite and can be computed from the supergravity point of view. The result
agrees with Matrix theory up to a numerical factor which we have not computed.Comment: 14 pages, Tex, no figure
Smectic Phases with Cubic Symmetry: The Splay Analog of the Blue Phase
We report on a construction for smectic blue phases, which have quasi-long
range smectic translational order as well as long range cubic or hexagonal
order. Our proposed structures fill space with a combination of minimal surface
patches and cylindrical tubes. We find that for the right range of material
parameters, the favorable saddle-splay energy of these structures can stabilize
them against uniform layered structures.Comment: 4 pages, 4 eps figures, RevTe
ROSAT HRI Observations of the Crab Pulsar: An Improved Temperature upper limit for PSR 0531+21
ROSAT HRI observations have been used to determine an upper limit of the Crab
pulsar surface temperature from the off-pulse count rate. For a neutron star
mass of 1.4 \Mo and a radius of 10 km as well as the standard distance and
interstellar column density, the redshifted temperature upper limit is\/
K . This is the lowest temperature
upper limit obtained for the Crab pulsar so far. Slightly different values for
are computed for the various neutron star models available in the
literature, reflecting the difference in the equation of state.Comment: 5 pages, uuencoded postscript, to be published in the Proceedings of
the NATO Advanced Study Insitute on "Lives of the Neutron Stars", ed. A.
Alpar, U. Kiziloglu and J. van Paradijs ( Kluwer, Dordrecht, 1995 )
Non-sequential triple ionization in strong fields
We consider the final stage of triple ionization of atoms in a strong
linearly polarized laser field. We propose that for intensities below the
saturation value for triple ionization the process is dominated by the
simultaneous escape of three electrons from a highly excited intermediate
complex. We identify within a classical model two pathways to triple
ionization, one with a triangular configuration of electrons and one with a
more linear one. Both are saddles in phase space. A stability analysis
indicates that the triangular configuration has the larger cross sections and
should be the dominant one. Trajectory simulations within the dominant symmetry
subspace reproduce the experimentally observed distribution of ion momenta
parallel to the polarization axis.Comment: 9 pages, 8 figures, accepted for publication in Phys. Rev.
Compactifications of Heterotic Theory on Non-Kahler Complex Manifolds: I
We study new compactifications of the SO(32) heterotic string theory on
compact complex non-Kahler manifolds. These manifolds have many interesting
features like fewer moduli, torsional constraints, vanishing Euler character
and vanishing first Chern class, which make the four-dimensional theory
phenomenologically attractive. We take a particular compact example studied
earlier and determine various geometrical properties of it. In particular we
calculate the warp factor and study the sigma model description of strings
propagating on these backgrounds. The anomaly cancellation condition and
enhanced gauge symmetry are shown to arise naturally in this framework, if one
considers the effect of singularities carefully.
We then give a detailed mathematical analysis of these manifolds and
construct a large class of them. The existence of a holomorphic (3,0) form is
important for the construction. We clarify some of the topological properties
of these manifolds and evaluate the Betti numbers. We also determine the
superpotential and argue that the radial modulus of these manifolds can
actually be stabilized.Comment: 75 pages, Harvmac, no figures; v2: Some new results added, typos
corrected and references updated. Final version to appear in JHE
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