331 research outputs found
Density of quasiparticle states for a two-dimensional disordered system: Metallic, insulating, and critical behavior in the class D thermal quantum Hall effect
We investigate numerically the quasiparticle density of states
for a two-dimensional, disordered superconductor in which both time-reversal
and spin-rotation symmetry are broken. As a generic single-particle description
of this class of systems (symmetry class D), we use the Cho-Fisher version of
the network model. This has three phases: a thermal insulator, a thermal metal,
and a quantized thermal Hall conductor. In the thermal metal we find a
logarithmic divergence in as , as predicted from sigma
model calculations. Finite size effects lead to superimposed oscillations, as
expected from random matrix theory. In the thermal insulator and quantized
thermal Hall conductor, we find that is finite at E=0. At the
plateau transition between these phases, decreases towards zero as
is reduced, in line with the result
derived from calculations for Dirac fermions with random mass.Comment: 8 pages, 8 figures, published versio
Residual-based localization and quantification of peaks in x-ray diffractograms
We consider data consisting of photon counts of diffracted x-ray radiation as
a function of the angle of diffraction. The problem is to determine the
positions, powers and shapes of the relevant peaks. An additional difficulty is
that the power of the peaks is to be measured from a baseline which itself must
be identified. Most methods of de-noising data of this kind do not explicitly
take into account the modality of the final estimate. The residual-based
procedure we propose uses the so-called taut string method, which minimizes the
number of peaks subject to a tube constraint on the integrated data. The
baseline is identified by combining the result of the taut string with an
estimate of the first derivative of the baseline obtained using a weighted
smoothing spline. Finally, each individual peak is expressed as the finite sum
of kernels chosen from a parametric family.Comment: Published in at http://dx.doi.org/10.1214/08-AOAS181 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Multifractality at the spin quantum Hall transition
Statistical properties of critical wave functions at the spin quantum Hall
transition are studied both numerically and analytically (via mapping onto the
classical percolation). It is shown that the index characterizing the
decay of wave function correlations is equal to 1/4, at variance with the
decay of the diffusion propagator. The multifractality spectra of
eigenfunctions and of two-point conductances are found to be
close-to-parabolic, and .Comment: 4 pages, 3 figure
On the length of chains of proper subgroups covering a topological group
We prove that if an ultrafilter L is not coherent to a Q-point, then each
analytic non-sigma-bounded topological group G admits an increasing chain <G_a
: a of its proper subgroups such that: (i) U_{a in b(L)} G_a=G; and
For every sigma-bounded subgroup H of G there exists a such that H is a
subset of G_a. In case of the group Sym(w) of all permutations of w with the
topology inherited from w^w this improves upon earlier results of S. Thomas
Exploratory assessment of anchovy 27.9a-west using a surplus production model.
The aim of this WD was to explore surplus production models to assess the western component of the anchovy 27.9a stock. Models were fitted to catch per quarter or semester (1991 – 2021) and to one biomass index, the spring acoustic survey (1999 – 2021), or two biomass indices, the acoustic survey and the autumn groundfish survey (1991 – 2018) using SPiCT. Various assumptions regarding the shape of the production curve, the initial biomass depletion and the intrinsic growth rate of the population were combined such that models varied from nearly unconstrained (more complex) to increasingly constrained (less complex). Bi-annual catch data and two survey indices lead to a higher number of convergent models. Several models passed all ICES criteria to accept a SPiCT assessment, except for a higher level of uncertainty in F/FMSY than the agreed one for long-lived stocks. A model assuming a Schaefer production curve, a prior on r from a meta-analysis and, an initial depletion rate of 80%, showed better retrospective analysis, survey hindcast cross-validation and convergence performance than other candidate models. The results indicated that F/FMSY was below 1 across most of the period, B/BMSY fluctuated well below 1 until 2010 and above 1 since 2016. The present results may be considered for further work in a benchmark workshop
Dimensionality dependence of the wave function statistics at the Anderson transition
The statistics of critical wave functions at the Anderson transition in three
and four dimensions are studied numerically. The distribution of the inverse
participation ratios (IPR) is shown to acquire a scale-invariant form in
the limit of large system size. Multifractality spectra governing the scaling
of the ensemble-averaged IPRs are determined. Conjectures concerning the IPR
statistics and the multifractality at the Anderson transition in a high spatial
dimensionality are formulated.Comment: 4 pages, 4 figure
Improved measurement of the K+->pi+nu(nu)over-bar branching ratio
An additional event near the upper kinematic limit for K+-->pi(+)nu(nu) over bar has been observed by experiment E949 at Brookhaven National Laboratory. Combining previously reported and new data, the branching ratio is B(K+-->pi(+)nu(nu) over bar)=(1.47(-0.89)(+1.30))x10(-10) based on three events observed in the pion momentum region 211<P<229 MeV/c. At the measured central value of the branching ratio, the additional event had a signal-to-background ratio of 0.9
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