7,372 research outputs found
Structural and dynamical heterogeneities in two-dimensional melting
Using molecular dynamics simulation, we study structural and dynamical
heterogeneities at melting in two-dimensional one-component systems with 36000
particles. Between crystal and liquid we find intermediate hexatic states,
where the density fluctuations are enhanced at small wave number k as well as
those of the six-fold orientational order parameter. Their structure factors
both grow up to the smallest wave number equal to the inverse system length.
The intermediate scattering function of the density S(k,t) is found to relax
exponentially with decay rate Gamma_k ~ k^z with z~2.6 at small k in the
hexatic phase.Comment: 6 pages, 8 figure
Non-singlet Q-deformed N=(1,0) and N=(1,1/2) U(1) actions
In this paper we construct N=(1,0) and N=(1,1/2) non-singlet Q-deformed
supersymmetric U(1) actions in components. We obtain an exact expression for
the enhanced supersymmetry action by turning off particular degrees of freedom
of the deformation tensor. We analyze the behavior of the action upon restoring
weekly some of the deformation parameters, obtaining a non trivial interaction
term between a scalar and the gauge field, breaking the supersymmetry down to
N=(1,0). Additionally, we present the corresponding set of unbroken
supersymmetry transformations. We work in harmonic superspace in four Euclidean
dimensions.Comment: 14 pages, typos corrected, equation (2.8) replaced by a more
illustrative one, version to appear in PL
Out of equilibrium correlations in the XY chain
We study the transversal XY spin-spin correlations in the non-equilibrium
steady state constructed in \cite{AP03} and prove their spatial exponential
decay close to equilibrium
The - divergence and Mixing times of quantum Markov processes
We introduce quantum versions of the -divergence, provide a detailed
analysis of their properties, and apply them in the investigation of mixing
times of quantum Markov processes. An approach similar to the one presented in
[1-3] for classical Markov chains is taken to bound the trace-distance from the
steady state of a quantum processes. A strict spectral bound to the convergence
rate can be given for time-discrete as well as for time-continuous quantum
Markov processes. Furthermore the contractive behavior of the
-divergence under the action of a completely positive map is
investigated and contrasted to the contraction of the trace norm. In this
context we analyse different versions of quantum detailed balance and, finally,
give a geometric conductance bound to the convergence rate for unital quantum
Markov processes
Instantons in N=1/2 Super Yang-Mills Theory via Deformed Super ADHM Construction
We study an extension of the ADHM construction to give deformed
anti-self-dual (ASD) instantons in N=1/2 super Yang-Mills theory with U(n)
gauge group. First we extend the exterior algebra on superspace to
non(anti)commutative superspace and show that the N=1/2 super Yang-Mills theory
can be reformulated in a geometrical way. By using this exterior algebra, we
formulate a non(anti)commutative version of the super ADHM construction and
show that the curvature two-form superfields obtained by our construction do
satisfy the deformed ASD equations and thus we establish the deformed super
ADHM construction. We also show that the known deformed U(2) one instanton
solution is obtained by this construction.Comment: 32 pages, LaTeX, v2: typos corrected, references adde
Monotonicity of quantum relative entropy revisited
Monotonicity under coarse-graining is a crucial property of the quantum
relative entropy. The aim of this paper is to investigate the condition of
equality in the monotonicity theorem and in its consequences such as the strong
sub-additivity of the von Neumann entropy, the Golden-Thompson trace inequality
and the monotonicity of the Holevo quantity.The relation to quantum Markovian
states is briefly indicated.Comment: 13 pages, LATEX fil
Measurement of neutrino oscillation with KamLAND: Evidence of spectral distortion
We present results of a study of neutrino oscillation based on a 766 ton/year exposure of KamLAND to reactor antineutrinos. We observe 258 v_e candidate events with energies above 3.4 MeV compared to 365.2±23.7 events expected in the absence of neutrino oscillation. Accounting for 17.8±7.3 expected background events, the statistical significance for reactor v_e over bar (e) disappearance is 99.998%. The observed energy spectrum disagrees with the expected spectral shape in the absence of neutrino oscillation at 99.6% significance and prefers the distortion expected from v_e oscillation effects. A two-neutrino oscillation analysis of the KamLAND data gives Δm^2=7.9_(-0.5)^(+0.6)x10^(-5) eV^2. A global analysis of data from KamLAND and solar-neutrino experiments yields
Δm^2=7.9_(-0.5)^(+0.6)x10^(-5) eV^2 and tan^2θ=0.40_(-0.07)^(+0.10), the most precise determination to date
On homogeneous CR manifolds and their CR algebras
In this paper we show some results on homogeneous CR manifolds, proved by
introducing their associated CR algebras. In particular, we give different
notions of nondegeneracy (generalizing the usual notion for the Levi form)
which correspond to geometrical properties for the corresponding manifolds. We
also give distinguished equivariant CR fibrations for homogeneous CR manifolds.
In the second part of the paper we apply these results to minimal orbits for
the action of a real form of a semisimple Lie group \^G on a flag manifold
\^G/Q.Comment: 14 pages. AMS-LaTeX v2: minor revisio
Entanglement and nonextensive statistics
It is presented a generalization of the von Neumann mutual information in the
context of Tsallis' nonextensive statistics. As an example, entanglement
between two (two-level) quantum subsystems is discussed. Important changes
occur in the generalized mutual information, which measures the degree of
entanglement, depending on the entropic index q.Comment: 8 pages, LaTex, 4 figure
Identification of the protein kinases Pyk3 and Phg2 as regulators of the STATc-mediated response to hyperosmolarity
Cellular adaptation to changes in environmental osmolarity is crucial for cell survival. In Dictyostelium, STATc is a key regulator of the transcriptional response to hyperosmotic stress. Its phosphorylation and consequent activation is controlled by two signaling branches, one cGMP- and the other Ca(2+)-dependent, of which many signaling components have yet to be identified. The STATc stress signalling pathway feeds back on itself by upregulating the expression of STATc and STATc-regulated genes. Based on microarray studies we chose two tyrosine-kinase like proteins, Pyk3 and Phg2, as possible modulators of STATc phosphorylation and generated single and double knock-out mutants to them. Transcriptional regulation of STATc and STATc dependent genes was disturbed in pyk3(-), phg2(-), and pyk3(-)/phg2(-) cells. The absence of Pyk3 and/or Phg2 resulted in diminished or completely abolished increased transcription of STATc dependent genes in response to sorbitol, 8-Br-cGMP and the Ca(2+) liberator BHQ. Also, phospho-STATc levels were significantly reduced in pyk3(-) and phg2(-) cells and even further decreased in pyk3(-)/phg2(-) cells. The reduced phosphorylation was mirrored by a significant delay in nuclear translocation of GFP-STATc. The protein tyrosine phosphatase 3 (PTP3), which dephosphorylates and inhibits STATc, is inhibited by stress-induced phosphorylation on S448 and S747. Use of phosphoserine specific antibodies showed that Phg2 but not Pyk3 is involved in the phosphorylation of PTP3 on S747. In pull-down assays Phg2 and PTP3 interact directly, suggesting that Phg2 phosphorylates PTP3 on S747 in vivo. Phosphorylation of S448 was unchanged in phg2(-) cells. We show that Phg2 and an, as yet unknown, S448 protein kinase are responsible for PTP3 phosphorylation and hence its inhibition, and that Pyk3 is involved in the regulation of STATc by either directly or indirectly activating it. Our results add further complexities to the regulation of STATc, which presumably ensure its optimal activation in response to different environmental cues
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