579 research outputs found
Nonuniversal and anomalous critical behavior of the contact process near an extended defect
We consider the contact process near an extended surface defect, where the
local control parameter deviates from the bulk one by an amount of
, being the distance from the
surface. We concentrate on the marginal situation, , where
is the critical exponent of the spatial correlation length, and
study the local critical properties of the one-dimensional model by Monte Carlo
simulations. The system exhibits a rich surface critical behavior. For weaker
local activation rates, , the phase transition is continuous, having an
order-parameter critical exponent, which varies continuously with . For
stronger local activation rates, , the phase transition is of mixed
order: the surface order parameter is discontinuous, at the same time the
temporal correlation length diverges algebraically as the critical point is
approached, but with different exponents on the two sides of the transition.
The mixed-order transition regime is analogous to that observed recently at a
multiple junction and can be explained by the same type of scaling theory.Comment: 8 pages, 8 figure
Nonequilibrium dynamics of the Ising chain in a fluctuating transverse field
We study nonequilibrium dynamics of the quantum Ising chain at zero
temperature when the transverse field is varied stochastically. In the
equivalent fermion representation, the equation of motion of Majorana operators
is derived in the form of a one-dimensional, continuous-time quantum random
walk with stochastic, time-dependent transition amplitudes. This type of
external noise gives rise to decoherence in the associated quantum walk and the
semiclassical wave-packet generally has a diffusive behavior. As a consequence,
in the quantum Ising chain, the average entanglement entropy grows in time as
and the logarithmic average magnetization decays in the same form. In
the case of a dichotomous noise, when the transverse-field is changed in
discrete time-steps, , there can be excitation modes, for which coherence
is maintained, provided their energy satisfies
with a positive integer . If the dispersion of is quadratic,
the long-time behavior of the entanglement entropy and the logarithmic
magnetization is dominated by these ballistically traveling coherent modes and
both will have a time-dependence.Comment: 12 pages, 10 figure
Long-range epidemic spreading in a random environment
Modeling long-range epidemic spreading in a random environment, we consider a
quenched disordered, -dimensional contact process with infection rates
decaying with the distance as . We study the dynamical behavior
of the model at and below the epidemic threshold by a variant of the
strong-disorder renormalization group method and by Monte Carlo simulations in
one and two spatial dimensions. Starting from a single infected site, the
average survival probability is found to decay as up to
multiplicative logarithmic corrections. Below the epidemic threshold, a
Griffiths phase emerges, where the dynamical exponent varies continuously
with the control parameter and tends to as the threshold is
approached. At the threshold, the spatial extension of the infected cluster (in
surviving trials) is found to grow as with a
multiplicative logarithmic correction, and the average number of infected sites
in surviving trials is found to increase as with
in one dimension.Comment: 12 pages, 6 figure
CPT and Lorentz violation as signatures for Planck-scale physics
In recent years, the breakdown of spacetime symmetries has been identified as
a promising research field in the context of Planck-scale phenomenology. For
example, various theoretical approaches to the quantum-gravity problem are
known to accommodate minute violations of CPT invariance. This talk covers
various topics within this research area. In particular, some mechanisms for
spacetime-symmetry breaking as well as the Standard-Model Extension (SME) test
framework will be reviewed; the connection between CPT and Lorentz invariance
in quantum field theory will be exposed; and various experimental CPT tests
with emphasis on matter--antimatter comparisons will be discussed.Comment: 6 page
Exact relationship between the entanglement entropies of XY and quantum Ising chains
We consider two prototypical quantum models, the spin-1/2 XY chain and the
quantum Ising chain and study their entanglement entropy, S(l,L), of blocks of
l spins in homogeneous or inhomogeneous systems of length L. By using two
different approaches, free-fermion techniques and perturbational expansion, an
exact relationship between the entropies is revealed. Using this relation we
translate known results between the two models and obtain, among others, the
additive constant of the entropy of the critical homogeneous quantum Ising
chain and the effective central charge of the random XY chain.Comment: 6 page
Partially asymmetric exclusion models with quenched disorder
We consider the one-dimensional partially asymmetric exclusion process with
random hopping rates, in which a fraction of particles (or sites) have a
preferential jumping direction against the global drift. In this case the
accumulated distance traveled by the particles, x, scales with the time, t, as
x ~ t^{1/z}, with a dynamical exponent z > 0. Using extreme value statistics
and an asymptotically exact strong disorder renormalization group method we
analytically calculate, z_{pt}, for particlewise (pt) disorder, which is argued
to be related to the dynamical exponent for sitewise (st) disorder as
z_{st}=z_{pt}/2. In the symmetric situation with zero mean drift the particle
diffusion is ultra-slow, logarithmic in time.Comment: 4 pages, 3 figure
Entanglement entropy of aperiodic quantum spin chains
We study the entanglement entropy of blocks of contiguous spins in
non-periodic (quasi-periodic or more generally aperiodic) critical Heisenberg,
XX and quantum Ising spin chains, e.g. in Fibonacci chains. For marginal and
relevant aperiodic modulations, the entanglement entropy is found to be a
logarithmic function of the block size with log-periodic oscillations. The
effective central charge, c_eff, defined through the constant in front of the
logarithm may depend on the ratio of couplings and can even exceed the
corresponding value in the homogeneous system. In the strong modulation limit,
the ground state is constructed by a renormalization group method and the
limiting value of c_eff is exactly calculated. Keeping the ratio of the block
size and the system size constant, the entanglement entropy exhibits a scaling
property, however, the corresponding scaling function may be nonanalytic.Comment: 6 pages, 2 figure
Promising Bioactivity of Vitamin B1-Au Nanocluster: Structure, Enhanced Antioxidant Behavior, and Serum Protein Interaction
In the current work, we first present a simple synthesis method for the preparation of novel Vitamin-B1-stabilized few-atomic gold nanoclusters with few atomic layers. The formed nanostructure contains ca. eight Au atoms and shows intensive blue emissions at 450 nm. The absolute quantum yield is 3%. The average lifetime is in the nanosecond range and three main components are separated and assigned to the metalâmetal and ligandâmetal charge transfers. Based on the structural characterization, the formed clusters contain Au in zero oxidation state, and Vitamin B1 stabilizes the metal cores via the coordination of pyrimidine-N. The antioxidant property of the Au nanoclusters is more prominent than that of the pure Vitamin B1, which is confirmed by two different colorimetric assays. For the investigation into their potential bioactivity, interactions with bovine serum albumin were carried out and quantified. The determined stoichiometry indicates a self-catalyzed binding, which is almost the same value based on the fluorometric and calorimetric measurements. The calculated thermodynamic parameters verify the spontaneous bond of the clusters along the protein chain by hydrogen bonds and electrostatic interactions
Recent colonization and nest site selection of the Hooded Crow (Corvus corone cornix L.) in an urban environment.
On the Origin of the Spiral Morphology in the Elias 2-27 Circumstellar Disk
The young star Elias 2-27 has recently been observed to posses a massive circumstellar disk with two prominent large-scale spiral arms. In this Letter, we perform three-dimensional Smoothed Particle Hydrodynamics simulations, radiative transfer modeling, synthetic ALMA imaging, and an unsharped masking technique to explore three possibilities for the origin of the observed structures - an undetected companion either internal or external to the spirals, and a self-gravitating disk. We find that a gravitationally unstable disk and a disk with an external companion can produce morphology that is consistent with the observations. In addition, for the latter, we find that the companion could be a relatively massive planetary-mass companion (âČ10-13 M Jup ) and located at large radial distances (between â300-700 au). We therefore suggest that Elias 2-27 may be one of the first detections of a disk undergoing gravitational instabilities, or a disk that has recently undergone fragmentation to produce a massive companion.We acknowledge support from the DISCSIM project, grant agreement 341137 under ERC-2013-ADG. F.M. acknowledges support from The Leverhulme Trust. This Letter uses the following ALMA data: ADS/JAO.ALMA# 2013.1.00498.S. This work used the Darwin DiRAC HPC cluster at the University of Cambridge and was undertaken on the Cambridge COSMOS SMP system, part of the STFC DiRAC HPC Facility supported by BIS NeI capital grant ST/J005673/1 and STFC grants ST/H008586/1, ST/K00333X/1
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