15,474 research outputs found
Even Orientations and Pfaffian graphs
We give a characterization of Pfaffian graphs in terms of even orientations,
extending the characterization of near bipartite non--pfaffian graphs by
Fischer and Little \cite{FL}. Our graph theoretical characterization is
equivalent to the one proved by Little in \cite{L73} (cf. \cite{LR}) using
linear algebra arguments
A note on 2--bisections of claw--free cubic graphs
A \emph{--bisection} of a bridgeless cubic graph is a --colouring
of its vertex set such that the colour classes have the same cardinality and
all connected components in the two subgraphs induced by the colour classes
have order at most . Ban and Linial conjectured that {\em every bridgeless
cubic graph admits a --bisection except for the Petersen graph}.
In this note, we prove Ban--Linial's conjecture for claw--free cubic graphs
The effect of different regulators in the non-local field-antifield quantization
Recently it was shown how to regularize the Batalin-Vilkovisky (BV)
field-antifield formalism of quantization of gauge theories with the non-local
regularization (NLR) method. The objective of this work is to make an analysis
of the behaviour of this NLR formalism, connected to the BV framework, using
two different regulators: a simple second order differential regulator and a
Fujikawa-like regulator. This analysis has been made in the light of the well
known fact that different regulators can generate different expressions for
anomalies that are related by a local couterterm, or that are equivalent after
a reparametrization. This has been done by computing precisely the anomaly of
the chiral Schwinger model.Comment: 9 pages, Revtex. To appear in Int. J. Mod. Phys.
Efficiency of a Brownian information machine
A Brownian information machine extracts work from a heat bath through a
feedback process that exploits the information acquired in a measurement. For
the paradigmatic case of a particle trapped in a harmonic potential, we
determine how power and efficiency for two variants of such a machine operating
cyclically depend on the cycle time and the precision of the positional
measurements. Controlling only the center of the trap leads to a machine that
has zero efficiency at maximum power whereas additional optimal control of the
stiffness of the trap leads to an efficiency bounded between 1/2, which holds
for maximum power, and 1 reached even for finite cycle time in the limit of
perfect measurements.Comment: 9 pages, 2 figure
J/Psi suppression in colliding nuclei: statistical model analysis
We consider the suppression at a high energy heavy ion collision. An
ideal gas of massive hadrons in thermal and chemical equilibrium is formed in
the central region. The finite-size gas expands longitudinally in accordance
with Bjorken law. The transverse expansion in a form of the rarefaction wave is
taken into account. We show that suppression in such an environment,
when combined with the disintegration in nuclear matter, gives correct
evaluation of NA38 and NA50 data in a broad range of initial energy densities.Comment: 14 pages, 13 figures. Accepted for publication in Phys. Rev.
Hamiltonian Derivations of the Generalized Jarzynski Equalities under Feedback Control
In the presence of feedback control by "Maxwell's demon," the second law of
thermodynamics and the nonequilibrium equalities such as the Jarzynski equality
need to be generalized. In this paper, we derive the generalized Jarzynski
equalities for classical Hamiltonian dynamics based on the Liouville's theorem,
which is the same approach as the original proof of the Jarzynski equality
[Phys. Rev. Lett. 78, 2690 (1997)]. The obtained equalities lead to the
generalizations of the second law of thermodynamics for the Hamiltonian systems
in the presence of feedback control.Comment: Proceedings of "STATPHYS - Kolkata VII", November 26-30, 2010,
Kolkata, Indi
Leakage Effect on J/psi Pt Distributions in Different Centrality Bins for Pb-Pb Collisions at E/A=160 GeV
A transport approach including a leakage effect for J/psi's in the transverse
phase space is used to calculate the ratios between the J/psi transverse
momentum distributions in several centrality bins for Pb-Pb collisions at E/A =
160 GeV. From the comparison with the CERN-SPS data, where the centrality is
characterized by the transverse energy Et, the leakage effect is extremely
important in the region of high transverse momentum and high transverse energy,
and both the threshold and the comover models can describe the ratio well for
all centrality bins except the most central one (Et < 100 GeV), for which the
comover model calculation is considerably better than the threshold one.Comment: 4 pages, 2 figures, REVTEX3.1, accepted for publication in Phys. Rev.
Weakly correlated electrons on a square lattice: a renormalization group theory
We study the weakly interacting Hubbard model on the square lattice using a
one-loop renormalization group approach. The transition temperature T_c between
the metallic and (nearly) ordered states is found. In the parquet regime, (T_c
>> |mu|), the dominant correlations at temperatures below T_c are
antiferromagnetic while in the BCS regime (T_c << |mu|) at T_c the d-wave
singlet pairing susceptibility is most divergent.Comment: 12 pages, REVTEX, 3 figures included, submitted to Phys. Rev. Let
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