66,442 research outputs found
Nonperturbative results for the mass dependence of the QED fermion determinant
The fermion determinant in four-dimensional quantum electrodynamics in the
presence of O(2)XO(3) symmetric background gauge fields with a nonvanishing
global chiral anomaly is considered. It is shown that the leading mass
singularity of the determinant's nonperturbative part is fixed by the anomaly.
It is also shown that for a large class of such fields there is at least one
value of the fermion mass at which the determinant's nonperturbative part
reduces to its noninteracting value.Comment: This is an extended version of the author's paper in
Phys.Rev.D81(2010)10770
Majoranas with and without a 'character': hybridization, braiding and Majorana number
In this paper we demonstrate under what conditions a pseudo-spin degree of
freedom or character can be ascribed to the Majorana bound states (MBS) which
can be created at the end of one dimensional non-interacting systems,
corresponding to D, DIII and BDI in the usual classification scheme. We have
found that such a character is directly related to the class of the topological
superconductor and its description by a , rather than a
, invariant which corresponds to the BDI class. We have also
found that the DIII case with mirror symmetry, which supports multiple MBS, is
in fact equivalent to the BDI class with an additional time-reversal symmetry.
In all cases where a character can be given to the Majorana states we show how
to construct the appropriate operator explicitly in various examples. We also
examine the consequences of the Majorana character by considering possible
hybridization of MBS brought into proximity and find that two MBS with the same
character do not hybridize. Finally, we show that having this character or not
has no consequence on the braiding properties of MBS.Comment: 10 pages, 1 figur
The construction of a reliable potential for GeO2 from first-principles
The construction of a reliable potential for GeO2, from first-principles, is
described. The obtained potential, which includes dipole polarization effects,
is able to reproduce all the studied properties (structural, dynamical and
vibrational) to a high degree of precision with a single set of parameters. In
particular, the infrared spectrum was obtained with the expression proposed for
the dielectric function of polarizable ionic solutions by Weis et al. [J.M.
Caillol, D. Levesque and J.J. Weis, J. Chem. Phys. 91, 5544 (1989)]. The
agreement with the experimental spectrum is very good, with three main bands
that are associated to tetrahedral modes of the GeO2 network. Finally, we give
a comparison with a simpler pair-additive potential.Comment: 9 pages, 8 figure
Distributed Reasoning in a Peer-to-Peer Setting: Application to the Semantic Web
In a peer-to-peer inference system, each peer can reason locally but can also
solicit some of its acquaintances, which are peers sharing part of its
vocabulary. In this paper, we consider peer-to-peer inference systems in which
the local theory of each peer is a set of propositional clauses defined upon a
local vocabulary. An important characteristic of peer-to-peer inference systems
is that the global theory (the union of all peer theories) is not known (as
opposed to partition-based reasoning systems). The main contribution of this
paper is to provide the first consequence finding algorithm in a peer-to-peer
setting: DeCA. It is anytime and computes consequences gradually from the
solicited peer to peers that are more and more distant. We exhibit a sufficient
condition on the acquaintance graph of the peer-to-peer inference system for
guaranteeing the completeness of this algorithm. Another important contribution
is to apply this general distributed reasoning setting to the setting of the
Semantic Web through the Somewhere semantic peer-to-peer data management
system. The last contribution of this paper is to provide an experimental
analysis of the scalability of the peer-to-peer infrastructure that we propose,
on large networks of 1000 peers
Magnetocapacitance effect in perovskite-superlattice based multiferroics
We report the structural and magnetoelectrical properties of
LaCaMnO/BaTiO perovskite superlattices grown on
(001)-oriented SrTiO by the pulsed laser deposition technique. Magnetic
hysteresis loops together with temperature dependent magnetic properties
exhibit well-defined coercivity and magnetic transition temperature (T)
\symbol{126}140 K. electrical studies of films show that the
magnetoresistance (MR) is dependent on the BaTiO thickness and negative
as high as 30% at 100K are observed. The electrical studies reveal
that the impedance and capacitance in these films vary with the applied
magnetic field due to the magnetoelectrical coupling in these structures - a
key feature of multiferroics. A negative magnetocapacitance value in the film
as high as 3% per tesla at 1kHz and 100K is demonstrated, opening the route for
designing novel functional materials.Comment: To be published in Applied Physics Letter
Cellular automata models of traffic flow along a highway containing a junction
We examine various realistic generalizations of the basic cellular automaton
model describing traffic flow along a highway. In particular, we introduce a
{\em slow-to-start} rule which simulates a possible delay before a car pulls
away from being stationary. Having discussed the case of a bare highway, we
then consider the presence of a junction. We study the effects of acceleration,
disorderness, and slow-to-start behavior on the queue length at the entrance to
the highway. Interestingly, the junction's efficiency is {\it improved} by
introducing disorderness along the highway, and by imposing a speed limit.Comment: to appear in J. Phys. A:Math.& General. 15 pages, RevTeX, 3
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