15,255 research outputs found
Tho2 dispersion-strengthened ni and ni-mo alloys produced by selective reduction
Preparation of nickel-thorium-molybdenum alloys by selective hydrogen reduction metho
Note on SLE and logarithmic CFT
It is discussed how stochastic evolutions may be linked to logarithmic
conformal field theory. This introduces an extension of the stochastic Loewner
evolutions. Based on the existence of a logarithmic null vector in an
indecomposable highest-weight module of the Virasoro algebra, the
representation theory of the logarithmic conformal field theory is related to
entities conserved in mean under the stochastic process.Comment: 10 pages, LaTeX, v2: version to be publishe
Stochastic evolutions in superspace and superconformal field theory
Some stochastic evolutions of conformal maps can be described by SLE and may
be linked to conformal field theory via stochastic differential equations and
singular vectors in highest-weight modules of the Virasoro algebra. Here we
discuss how this may be extended to superconformal maps of N=1 superspace with
links to superconformal field theory and singular vectors of the N=1
superconformal algebra in the Neveu-Schwarz sector.Comment: 13 pages, LaTe
Absence of Wavepacket Diffusion in Disordered Nonlinear Systems
We study the spreading of an initially localized wavepacket in two nonlinear
chains (discrete nonlinear Schroedinger and quartic Klein-Gordon) with
disorder. Previous studies suggest that there are many initial conditions such
that the second moment of the norm and energy density distributions diverge as
a function of time. We find that the participation number of a wavepacket does
not diverge simultaneously. We prove this result analytically for
norm-conserving models and strong enough nonlinearity. After long times the
dynamical state consists of a distribution of nondecaying yet interacting
normal modes. The Fourier spectrum shows quasiperiodic dynamics. Assuming this
result holds for any initially localized wavepacket, a limit profile for the
norm/energy distribution with infinite second moment should exist in all cases
which rules out the possibility of slow energy diffusion (subdiffusion). This
limit profile could be a quasiperiodic solution (KAM torus)
Minor parties and independents in times of change: Scottish local elections 1974 to 2007
This article explores the electoral performance of minor party and Independent candidates in Scottish local elections from 1974 to 2007. This is a period which began with a major restructuring of local government and ended with a change in the electoral system from first-past-the-post to the single transferable vote. It encompasses a second restructuring in the 1990s, the consolidation of the Scottish National Party as an electoral force, and the creation of the Scottish Parliament. Throughout the period, while there have been ebbs and flows, Independents and minor parties have remained significant players in local electoral politics in Scotland
Simulation of transition dynamics to high confinement in fusion plasmas
The transition dynamics from the low (L) to the high (H) confinement mode in
magnetically confined plasmas is investigated using a first-principles
four-field fluid model. Numerical results are in close agreement with
measurements from the Experimental Advanced Superconducting Tokamak - EAST.
Particularly, the slow transition with an intermediate dithering phase is well
reproduced by the numerical solutions. Additionally, the model reproduces the
experimentally determined L-H transition power threshold scaling that the ion
power threshold increases with increasing particle density. The results hold
promise for developing predictive models of the transition, essential for
understanding and optimizing future fusion power reactors
Discovery of a very extended X-ray halo around a quiescent spiral galaxy - the "missing link" of galaxy formation
Hot gaseous haloes surrounding galaxies and extending well beyond the
distribution of stars are a ubiquitous prediction of galaxy formation
scenarios. The haloes are believed to consist of gravitationally trapped gas
with a temperature of millions of Kelvin. The existence of such hot haloes
around massive elliptical galaxies has been established through their X-ray
emission. While gas out-flowing from starburst spiral galaxies has been
detected, searches for hot haloes around normal, quiescent spiral galaxies have
so far failed, casting doubts on the fundamental physics in galaxy formation
models. Here we present the first detection of a hot, large-scale gaseous halo
surrounding a normal, quiescent spiral galaxy, NGC 5746, alleviating a
long-standing problem for galaxy formation models. In contrast to starburst
galaxies, where the X-ray halo can be powered by the supernova energy, there is
no such power source in NGC 5746. The only compelling explanation is that we
are here witnessing a galaxy forming from gradually in-flowing hot and dilute
halo gas.Comment: New Astronomy, in pres
Nonparametric Bayesian Mixed-effect Model: a Sparse Gaussian Process Approach
Multi-task learning models using Gaussian processes (GP) have been developed
and successfully applied in various applications. The main difficulty with this
approach is the computational cost of inference using the union of examples
from all tasks. Therefore sparse solutions, that avoid using the entire data
directly and instead use a set of informative "representatives" are desirable.
The paper investigates this problem for the grouped mixed-effect GP model where
each individual response is given by a fixed-effect, taken from one of a set of
unknown groups, plus a random individual effect function that captures
variations among individuals. Such models have been widely used in previous
work but no sparse solutions have been developed. The paper presents the first
sparse solution for such problems, showing how the sparse approximation can be
obtained by maximizing a variational lower bound on the marginal likelihood,
generalizing ideas from single-task Gaussian processes to handle the
mixed-effect model as well as grouping. Experiments using artificial and real
data validate the approach showing that it can recover the performance of
inference with the full sample, that it outperforms baseline methods, and that
it outperforms state of the art sparse solutions for other multi-task GP
formulations.Comment: Preliminary version appeared in ECML201
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