5,222 research outputs found
Critical behavior and entanglement of the random transverse-field Ising model between one and two dimensions
We consider disordered ladders of the transverse-field Ising model and study
their critical properties and entanglement entropy for varying width, , by numerical application of the strong disorder renormalization group
method. We demonstrate that the critical properties of the ladders for any
finite are controlled by the infinite disorder fixed point of the random
chain and the correction to scaling exponents contain information about the
two-dimensional model. We calculate sample dependent pseudo-critical points and
study the shift of the mean values as well as scaling of the width of the
distributions and show that both are characterized by the same exponent,
. We also study scaling of the critical magnetization, investigate
critical dynamical scaling as well as the behavior of the critical entanglement
entropy. Analyzing the -dependence of the results we have obtained accurate
estimates for the critical exponents of the two-dimensional model:
, and .Comment: 10 pages, 9 figure
Corner contribution to percolation cluster numbers in three dimensions
In three-dimensional critical percolation we study numerically the number of
clusters, , which intersect a given subset of bonds, . If
represents the interface between a subsystem and the environment, then
is related to the entanglement entropy of the critical diluted
quantum Ising model. Due to corners in there are singular corrections
to , which scale as , being
the linear size of and the prefactor, , is found to be
universal. This result indicates that logarithmic finite-size corrections exist
in the free-energy of three-dimensional critical systems.Comment: 6 pages, 7 figures. arXiv admin note: text overlap with
arXiv:1210.467
Boundary critical phenomena of the random transverse Ising model in D>=2 dimensions
Using the strong disorder renormalization group method we study numerically
the critical behavior of the random transverse Ising model at a free surface,
at a corner and at an edge in D=2, 3 and 4-dimensional lattices. The surface
magnetization exponents are found to be: x_s=1.60(2), 2.65(15) and 3.7(1) in
D=2, 3 and 4, respectively, which do not depend on the form of disorder. We
have also studied critical magnetization profiles in slab, pyramid and wedge
geometries with fixed-free boundary conditions and analyzed their scaling
behavior.Comment: 7 pages, 11 figure
Random transverse-field Ising chain with long-range interactions
We study the low-energy properties of the long-range random transverse-field
Ising chain with ferromagnetic interactions decaying as a power alpha of the
distance. Using variants of the strong-disorder renormalization group method,
the critical behavior is found to be controlled by a strong-disorder fixed
point with a finite dynamical exponent z_c=alpha. Approaching the critical
point, the correlation length diverges exponentially. In the critical point,
the magnetization shows an alpha-independent logarithmic finite-size scaling
and the entanglement entropy satisfies the area law. These observations are
argued to hold for other systems with long-range interactions, even in higher
dimensions.Comment: 6 pages, 4 figure
Corner contribution to percolation cluster numbers
We study the number of clusters in two-dimensional (2d) critical percolation,
N_Gamma, which intersect a given subset of bonds, Gamma. In the simplest case,
when Gamma is a simple closed curve, N_Gamma is related to the entanglement
entropy of the critical diluted quantum Ising model, in which Gamma represents
the boundary between the subsystem and the environment. Due to corners in Gamma
there are universal logarithmic corrections to N_Gamma, which are calculated in
the continuum limit through conformal invariance, making use of the
Cardy-Peschel formula. The exact formulas are confirmed by large scale Monte
Carlo simulations. These results are extended to anisotropic percolation where
they confirm a result of discrete holomorphicity.Comment: 7 pages, 9 figure
From fracture to fragmentation: discrete element modeling -- Complexity of crackling noise and fragmentation phenomena revealed by discrete element simulations
Discrete element modelling (DEM) is one of the most efficient computational
approaches to the fracture processes of heterogeneous materials on mesoscopic
scales. From the dynamics of single crack propagation through the statistics of
crack ensembles to the rapid fragmentation of materials DEM had a substantial
contribution to our understanding over the past decades. Recently, the
combination of DEM with other simulation techniques like Finite Element
Modelling further extended the field of applicability. In this paper we briefly
review the motivations and basic idea behind the DEM approach to cohesive
particulate matter and then we give an overview of on-going developments and
applications of the method focusing on two fields where recent success has been
achieved. We discuss current challenges of this rapidly evolving field and
outline possible future perspectives and debates
Excess entropy and central charge of the two-dimensional random-bond Potts model in the large-Q limit
We consider the random-bond Potts model in the large- limit and calculate
the excess entropy, , of a contour, , which is given by the
mean number of Fortuin-Kasteleyn clusters which are crossed by . In two
dimensions is proportional to the length of , to which -
at the critical point - there are universal logarithmic corrections due to
corners. These are calculated by applying techniques of conformal field theory
and compared with the results of large scale numerical calculations. The
central charge of the model is obtained from the corner contributions to the
excess entropy and independently from the finite-size correction of the
free-energy as: , close to previous
estimates calculated at finite values of .Comment: 6 pages, 7 figure
Entanglement between random and clean quantum spin chains
The entanglement entropy in clean, as well as in random quantum spin chains
has a logarithmic size-dependence at the critical point. Here, we study the
entanglement of composite systems that consist of a clean and a random part,
both being critical. In the composite, antiferromagnetic XX-chain with a sharp
interface, the entropy is found to grow in a double-logarithmic fashion , where is the length of the chain. We have also
considered an extended defect at the interface, where the disorder penetrates
into the homogeneous region in such a way that the strength of disorder decays
with the distance from the contact point as . For
, the entropy scales as , while for , when the extended interface defect
is an irrelevant perturbation, we recover the double-logarithmic scaling. These
results are explained through strong-disorder RG arguments.Comment: 12 pages, 7 figures, Invited contribution to the Festschrift of John
Cardy's 70th birthda
Development of Myxobolus dispar (Myxosporea : Myxobolidae) in an oligochaete alternate host, Tubifex tubifex
The development of Myxobolus dispar Thelohan, 1895, a myxosporean parasite of the gills of common carp (Cyprinus carpio L.) was studied in experimentally infected oligochaetes Tubifex tubifex Muller. After infection of uninfected tubificids with mature spores of M. dispar development of actinosporean stages was first observed light microscopically 21 days after initial exposure. In histological sections, early pansporocysts were located in the gut epithelium of experimental oligochaetes, while advanced stages occupied mostly the outer layers of the gut and the coelozoic space. Mature pansporocysts, each containing 8 raabeia spores, appeared 199 days after initial exposure. Following damage of the intestinal wall and rupture of the pansporocysts, free actinosporean stages were found in the gut lumen of the oligochaetes. Actinospores of M. dispar emerged from the worms after 217 days of intra-oligochaete development. They were floating in the water and showed a unique raabeia form. Each raabeia sport had three pyriform polar capsules and a cylindrical-shaped sporoplasm with approximately 32 secondary cells. The spore body joined the three caudal projections without a style. Caudal projections were bifurcated at the end and the two main branches had further small bifurcations. The total length of the raabeia sport was approximately 158 mu m. The prevalence of infection in 240 experimentally infected Tubifex specimens was 99.2%. No infection was found in the control oligochaetes
Comment on ``Magnetoresistance Anomalies in Antiferromagnetic YBaCuO: Fingerprints of Charged Stripes''
In a recent Letter Ando et al (cond-mat/9905071) discovered an anomalous
magnetoresistance(MR) in hole doped antiferromagnetic YBaCuO,
which they attributed to charged stripes, i.e., to segregation of holes into
lines. In this Comment we show that the experiments, albeit being interesting,
do not prove the existence of stripes. In our view the anomalous behavior is
due to an (a,b) plane anisotropy of the resistivity in the bulk and to a
magnetic field dependent antiferromagnetic (AF) domain structure. It is
unlikely that domain walls are charged stripes.Comment: 1 page, Accepted to PRL, Reply exists by authors of original pape
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