162 research outputs found
Energy radiated from a fluctuating selfdual string
We compute the energy that is radiated from a fluctuating selfdual string in
the large limit of theory using the AdS-CFT correspondence. We
find that the radiated energy is given by a non-local expression integrated
over the string world-sheet. We also make the corresponding computation for a
charged string in six-dimensional classical electrodynamics, thereby
generalizing the Larmor formula for the radiated energy from an accelerated
point particle.Comment: 12 page
Computing topological invariants with one and two-matrix models
A generalization of the Kontsevich Airy-model allows one to compute the
intersection numbers of the moduli space of p-spin curves. These models are
deduced from averages of characteristic polynomials over Gaussian ensembles of
random matrices in an external matrix source. After use of a duality, and of an
appropriate tuning of the source, we obtain in a double scaling limit these
intersection numbers as polynomials in p. One can then take the limit p to -1
which yields a matrix model for orbifold Euler characteristics. The
generalization to a time-dependent matrix model, which is equivalent to a
two-matrix model, may be treated along the same lines ; it also yields a
logarithmic potential with additional vertices for general p.Comment: 30 pages, added references, changed conten
Kinetic Limit for Wave Propagation in a Random Medium
We study crystal dynamics in the harmonic approximation. The atomic masses
are weakly disordered, in the sense that their deviation from uniformity is of
order epsilon^(1/2). The dispersion relation is assumed to be a Morse function
and to suppress crossed recollisions. We then prove that in the limit epsilon
to 0 the disorder averaged Wigner function on the kinetic scale, time and space
of order epsilon^(-1), is governed by a linear Boltzmann equation.Comment: 71 pages, 3 figure
Development and validation of an algorithm to accurately identify atopic eczema patients in primary care electronic health records from the UK
Electronic health records hold great promise for clinical and epidemiologic research. Undertaking atopic eczema (AE) research using such data is challenging due to its episodic and heterogeneous nature. We sought to develop and validate a diagnostic algorithm that identifies AE cases based on codes used for electronic records used in the UK Health Improvement Network (THIN). We found that at least one of 5 diagnosis codes plus two treatment codes for any skin-directed therapy were likely to accurately identify patients with AE. To validate this algorithm, a questionnaire was sent to the physicians of 200 randomly selected children and adults. The primary outcome, the positive predictive value (PPV) for a physician-confirmed diagnosis of AE, was 86% (95%CI 80-91%). Additional criteria increased the PPV up to 95% but would miss up to 89% of individuals with physician-confirmed AE. The first and last entered diagnosis codes for individuals showed good agreement with the physician-confirmed age at onset and last disease activity; the mean difference was 0.8 years (95% CI -0.3,1.9) and -1.3 years respectively (95%CI -2.5, -0.1). A combination of diagnostic and prescription codes can be used to reliably estimate the diagnosis and duration of AE from the THIN primary care electronic health records in the UK
Multifractal characterisation of length sequences of coding and noncoding segments in a complete genome
The coding and noncoding length sequences constructed from a complete genome
are characterised by multifractal analysis. The dimension spectrum and
its derivative, the 'analogous' specific heat , are calculated for the
coding and noncoding length sequences of bacteria, where is the moment
order of the partition sum of the sequences. From the shape of the
and curves, it is seen that there exists a clear difference between the
coding/noncoding length sequences of all organisms considered and a completely
random sequence. The complexity of noncoding length sequences is higher than
that of coding length sequences for bacteria. Almost all curves for
coding length sequences are flat, so their multifractality is small whereas
almost all curves for noncoding length sequences are multifractal-like.
We propose to characterise the bacteria according to the types of the
curves of their noncoding length sequences.Comment: 15 pages with 5 figures, Latex, Accepted for publication in Physica
The partition function of interfaces from the Nambu-Goto effective string theory
We consider the Nambu-Goto bosonic string model as a description of the
physics of interfaces. By using the standard covariant quantization of the
bosonic string, we derive an exact expression for the partition function in
dependence of the geometry of the interface. Our expression, obtained by
operatorial methods, resums the loop expansion of the NG model in the "physical
gauge" computed perturbatively by functional integral methods in the
literature. Recently, very accurate Monte Carlo data for the interface free
energy in the 3d Ising model became avaliable. Our proposed expression compares
very well to the data for values of the area sufficiently large in terms of the
inverse string tension. This pattern is expected on theoretical grounds and
agrees with previous analyses of other observables in the Ising model.Comment: 28 pages, 4 figure
Electron correlation effects in a wide channel from the quantum Hall edge states
The spatial behavior of Landau levels (LLs) for the quantum Hall
regime at the edge of a wide channel is studied in a self-consistent way by
using a generalized local density approximation proposed here. Both exchange
interaction and strong electron correlations, due to edge states, are taken
into account. They essentially modify the spatial behavior of the occupied
lowest spin-up LL in comparison with that of the lowest spin-down LL, which is
totally empty. The contrast in the spatial behavior can be attributed to a
different effective one-electron lateral confining potentials for the
spin-split LLs. Many-body effects on the spatially inhomogeneous spin-splitting
are calculated within the screened Hartree-Fock approximation. It is shown
that, far from the edges, the maximum activation energy is dominated by the gap
between the Fermi level and the bottom of the spin-down LL, because the gap
between the Fermi level and the spin-up LL is much larger. In other words, the
maximum activation energy in the bulk of the channel corresponds to a highly
asymmetric position of the Fermi level within the gap between spin-down and
spin-up LLs in the bulk. We have also studied the renormalization of the
edge-state group velocity due to electron correlations. The results of the
present theory are in line with those suggested and reported by experiments on
high quality samples.Comment: 9 pages, 4 figure
Algebraic analysis of a model of two-dimensional gravity
An algebraic analysis of the Hamiltonian formulation of the model
two-dimensional gravity is performed. The crucial fact is an exact coincidence
of the Poisson brackets algebra of the secondary constraints of this
Hamiltonian formulation with the SO(2,1)-algebra. The eigenvectors of the
canonical Hamiltonian are obtained and explicitly written in closed
form.Comment: 21 pages, to appear in General Relativity and Gravitatio
Coupled-mode equations and gap solitons in a two-dimensional nonlinear elliptic problem with a separable periodic potential
We address a two-dimensional nonlinear elliptic problem with a
finite-amplitude periodic potential. For a class of separable symmetric
potentials, we study the bifurcation of the first band gap in the spectrum of
the linear Schr\"{o}dinger operator and the relevant coupled-mode equations to
describe this bifurcation. The coupled-mode equations are derived by the
rigorous analysis based on the Fourier--Bloch decomposition and the Implicit
Function Theorem in the space of bounded continuous functions vanishing at
infinity. Persistence of reversible localized solutions, called gap solitons,
beyond the coupled-mode equations is proved under a non-degeneracy assumption
on the kernel of the linearization operator. Various branches of reversible
localized solutions are classified numerically in the framework of the
coupled-mode equations and convergence of the approximation error is verified.
Error estimates on the time-dependent solutions of the Gross--Pitaevskii
equation and the coupled-mode equations are obtained for a finite-time
interval.Comment: 32 pages, 16 figure
High precision Monte Carlo simulations of interfaces in the three-dimensional Ising model: a comparison with the Nambu-Goto effective string model
Motivated by the recent progress in the effective string description of the
interquark potential in lattice gauge theory, we study interfaces with periodic
boundary conditions in the three-dimensional Ising model. Our Monte Carlo
results for the associated free energy are compared with the next-to-leading
order (NLO) approximation of the Nambu-Goto string model. We find clear
evidence for the validity of the effective string model at the level of the NLO
truncation.Comment: 20 pages, 1 figur
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