626 research outputs found
Stationary states of a spherical Minority Game with ergodicity breaking
Using generating functional and replica techniques, respectively, we study
the dynamics and statics of a spherical Minority Game (MG), which in contrast
with a spherical MG previously presented in J.Phys A: Math. Gen. 36 11159
(2003) displays a phase with broken ergodicity and dependence of the
macroscopic stationary state on initial conditions. The model thus bears more
similarity with the original MG. Still, all order parameters including the
volatility can computed in the ergodic phases without making any
approximations. We also study the effects of market impact correction on the
phase diagram. Finally we discuss a continuous-time version of the model as
well as the differences between on-line and batch update rules. Our analytical
results are confirmed convincingly by comparison with numerical simulations. In
an appendix we extend the analysis of the earlier spherical MG to a model with
general time-step, and compare the dynamics and statics of the two spherical
models.Comment: 26 pages, 8 figures; typo correcte
Image restoration using the Q-Ising spin glass
We investigate static and dynamic properties of gray-scale image restoration
(GSIR) by making use of the Q-Ising spin glass model, whose ladder symmetry
allows to take in account the distance between two spins. We thus give an
explicit expression of the Hamming distance between the original and restored
images as a function of the hyper-parameters in the mean field limit. Finally,
numerical simulations for real-world pictures are carried out to prove the
efficiency of our model.Comment: 27pages, 13figures, revte
Brucellosis in wildlife in Africa:a systematic review and meta-analysis
This study aimed to consolidate current knowledge of wildlife brucellosis in Africa and to analyse available predictors of infection. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. Information on species, test used, test results, area, rainfall, livestock and wildlife contact and year of study were extracted. This systematic review revealed 42 prevalence studies, nine disease control articles and six articles on epidemiology. Brucella abortus, Brucella melitensis, Brucella inopinata and Brucella suis were reported in wildlife. The prevalence studies revealed serological evidence of brucellosis in buffalo, antelope (positive in 14/28 species), carnivores (4/12) and other species (7/20) over the last five decades. Buffalo populations were more likely to be infected and had a higher seroprevalence than other species; the pooled seroprevalence was 13.7% (95% CI 10.3–17.3%) in buffalo, 7.1% (95% CI 1.1–15.5%) in carnivores and 2.1% (95% CI 0.1–4.9%) in antelope. Wildlife in high rainfall areas (≥ 800 mm) were more likely to be infected, and infected populations showed higher seroprevalence in high rainfall areas and in studies published after 2000. Domestic animal contact was associated with increased seroprevalence in antelope and carnivore species, but not in buffalo, supporting the hypothesis that buffalo may be a reservoir species
LAF1, a MYB transcription activator for phytochrome A signaling
The photoreceptor phytochrome (phy) A has a well-defined role in regulating gene expression in response to specific light signals. Here, we describe a new Arabidopsis mutant, laf1 (long after far-red light 1) that has an elongated hypocotyl specifically under far-red light. Gene expression studies showed that laf1 has reduced responsiveness to continuous far-red light but retains wild-type responses to other light wavelengths. As far-red light is only perceived by phyA, our results suggest that LAF1 is specifically involved in phyA signal transduction. Further analyses revealed that laf1 is affected in a subset of phyA-dependent responses and the phenotype is more severe at low far-red fluence rates. LAF1 encodes a nuclear protein with strong homology with the R2R3-MYB family of DNA-binding proteins. Experiments using yeast cells identified a transactivation domain in the C-terminal portion of the protein. LAF1 is constitutively targeted to the nucleus by signals in its N-terminal portion, and the full-length protein accumulates in distinct nuclear speckles. This accumulation in speckles is abolished by a point mutation in a lysine residue (K258R), which might serve as a modification site by a small ubiquitin-like protein (SUMO)
Tilted and crossing vortex chains in layered superconductors
In the presence of the Josephson vortex lattice in layered superconductors, a
small c-axis magnetic field penetrates in the form of vortex chains. In
general, the structure of a single chain is determined by the ratio of the
London [] and Josephson [] lengths, . The chain is composed of tilted vortices at large
's (tilted chain) and at small 's it consists of a crossing
array of Josephson vortices and pancake-vortex stacks (crossing chain). We
study chain structures at intermediate 's and found two types of phase
transitions. For the ground state is given by the crossing
chain in a wide range of pancake separations .
However, due to attractive coupling between deformed pancake stacks, the
equilibrium separation can not exceed some maximum value depending on the
in-plane field and . The first phase transition takes place with
decreasing pancake-stack separation at , and rather
wide range of the ratio , . With
decreasing , the crossing chain goes through intermediate strongly-deformed
configurations and smoothly transforms into a tilted chain via a second-order
phase transition. Another phase transition occurs at very small densities of
pancake vortices, , and only when exceeds a
certain critical value . In this case a small c-axis field penetrates
in the form of kinks. However, at very small concentration of kinks, the kinked
chains are replaced with strongly deformed crossing chains via a first-order
phase transition. This transition is accompanied by a very large jump in the
pancake density.Comment: Proceeding of the NATO ARW "Vortex dynamics in superconductors and
other complex systems", Yalta, Crimea, Ukraine, 13-17 September 2004, To be
published in the Journ. of Low Temp. Phys., 16 pages, 6 figure
A Formal Study of the Privacy Concerns in Biometric-Based Remote Authentication Schemes
With their increasing popularity in cryptosystems, biometrics have attracted more and more attention from the information security community. However, how to handle the relevant privacy concerns remains to be troublesome. In this paper, we propose a novel security model to formalize the privacy concerns in biometric-based remote authentication schemes. Our security model covers a number of practical privacy concerns such as identity privacy and transaction anonymity, which have not been formally considered in the literature. In addition, we propose a general biometric-based remote authentication scheme and prove its security in our security model
Thermodynamics of Mesoscopic Vortex Systems in 1+1 Dimensions
The thermodynamics of a disordered planar vortex array is studied numerically
using a new polynomial algorithm which circumvents slow glassy dynamics. Close
to the glass transition, the anomalous vortex displacement is found to agree
well with the prediction of the renormalization-group theory. Interesting
behaviors such as the universal statistics of magnetic susceptibility
variations are observed in both the dense and dilute regimes of this mesoscopic
vortex system.Comment: 4 pages, REVTEX, 6 figures included. Comments and suggestions can be
sent to [email protected]
Incommensuration Effects and Dynamics in Vortex Chains
We examine the motion of one-dimensional (1D) vortex matter embedded in a 2D
vortex system with weak pinning using numerical simulations. We confirm the
conjecture of Matsuda et al. [Science 294, 2136 (2001)] that the onset of the
temperature induced motion of the chain is due to an incommensuration effect of
the chain with the periodic potential created by the bulk vortices. In
addition, under an applied driving force we find a two stage depinning
transition, where the initial depinning of the vortex chain occurs through
soliton like pulses. When an ac drive is added to the dc drive, we observe
phase locking of the moving vortex chain.Comment: 4 pages, 4 postscript figure
Parallel dynamics of continuous Hopfield model revisited
We have applied the generating functional analysis (GFA) to the continuous
Hopfield model. We have also confirmed that the GFA predictions in some typical
cases exhibit good consistency with computer simulation results. When a
retarded self-interaction term is omitted, the GFA result becomes identical to
that obtained using the statistical neurodynamics as well as the case of the
sequential binary Hopfield model.Comment: 4 pages, 2 figure
Test of Replica Theory: Thermodynamics of 2D Model Systems with Quenched Disorder
We study the statistics of thermodynamic quantities in two related systems
with quenched disorder: A (1+1)-dimensional planar lattice of elastic lines in
a random potential and the 2-dimensional random bond dimer model. The first
system is examined by a replica-symmetric Bethe ansatz (RBA) while the latter
is studied numerically by a polynomial algorithm which circumvents slow glassy
dynamics. We establish a mapping of the two models which allows for a detailed
comparison of RBA predictions and simulations. Over a wide range of disorder
strength, the effective lattice stiffness and cumulants of various
thermodynamic quantities in both approaches are found to agree excellently. Our
comparison provides, for the first time, a detailed quantitative confirmation
of the replica approach and renders the planar line lattice a unique testing
ground for concepts in random systems.Comment: 16 pages, 14 figure
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