1,597 research outputs found
Summary of the Superconducting RF Linac for Muon Collider and Neutrino Factory
Project-X is a proposed project to be built at Fermi National Accelerator
Laboratory with several potential missions. A primary part of the Project-X
accelerator chain is a Superconducting linac, and In October 2009 a workshop
was held to concentrate on the linac parameters. The charge of the workshop was
to "..focus only on the SRF linac approaches and how it can be used...". The
focus of Working Group 2 of this workshop was to evaluate how the different
linac options being considered impact the potential realization of Muon
Collider (MC) and Neutrino Factory (NF) applications. In particular the working
group charge was, "to investigate the use of a multi-megawatt proton linac to
target, phase rotate and collect muons to support a muon collider and neutrino
factory". To focus the working group discussion, three primary questions were
identified early on, to serve as a reference: 1) What are the proton source
requirements for muon colliders and neutrino factories? 2) What are the issues
with respect to realizing the required muon collider and neutrino factory
proton sources? a. General considerations b. Considerations specific to the two
linac configurations identified by Project-X. 3) What things need to be done
before we can be reasonably confident that ICD1/ICD2 can be upgraded to provide
the neutrino factory / muon collider needs? A number of presentations were
given, and are available at the workshop web-site. This paper does not
summarize the individual presentations, but rather addresses overall findings
as related to the three guiding questions listed above.Comment: 6 pp. Workshop on Applications of High Intensity Proton Accelerators
19-21 Oct 2009: Batavia, Illinoi
Universal Statistics of the Critical Depinning Force of Elastic Systems in Random Media
We study the rescaled probability distribution of the critical depinning
force of an elastic system in a random medium. We put in evidence the
underlying connection between the critical properties of the depinning
transition and the extreme value statistics of correlated variables. The
distribution is Gaussian for all periodic systems, while in the case of random
manifolds there exists a family of universal functions ranging from the
Gaussian to the Gumbel distribution. Both of these scenarios are a priori
experimentally accessible in finite, macroscopic, disordered elastic systems.Comment: 4 pages, 4 figure
Probabilistic analysis of algorithms for dual bin packing problems
In the dual bin packing problem, the objective is to assign items of given size to the largest possible number of bins, subject to the constraint that the total size of the items assigned to any bin is at least equal to 1. We carry out a probabilistic analysis of this problem under the assumption that the items are drawn independently from the uniform distribution on [0, 1] and reveal the connection between this problem and the classical bin packing problem as well as to renewal theory.
Progressive Probabilistic Hough Transform for line detection
We present a novel Hough Transform algorithm referred to as Progressive Probabilistic Hough Transform (PPHT). Unlike the Probabilistic HT where Standard HT is performed on a pre-selected fraction of input points, PPHT minimises the amount of computation needed to detect lines by exploiting the difference an the fraction of votes needed to detect reliably lines with different numbers of supporting points. The fraction of points used for voting need not be specified ad hoc or using a priori knowledge, as in the probabilistic HT; it is a function of the inherent complexity of the input data. The algorithm is ideally suited for real-time applications with a fixed amount of available processing time, since voting and line detection is interleaved. The most salient features are likely to be detected first. Experiments show that in many circumstances PPHT has advantages over the Standard HT
Probing the tails of the ground state energy distribution for the directed polymer in a random medium of dimension via a Monte-Carlo procedure in the disorder
In order to probe with high precision the tails of the ground-state energy
distribution of disordered spin systems, K\"orner, Katzgraber and Hartmann
\cite{Ko_Ka_Ha} have recently proposed an importance-sampling Monte-Carlo
Markov chain in the disorder. In this paper, we combine their Monte-Carlo
procedure in the disorder with exact transfer matrix calculations in each
sample to measure the negative tail of ground state energy distribution
for the directed polymer in a random medium of dimension .
In , we check the validity of the algorithm by a direct comparison with
the exact result, namely the Tracy-Widom distribution. In dimensions and
, we measure the negative tail up to ten standard deviations, which
correspond to probabilities of order . Our results are
in agreement with Zhang's argument, stating that the negative tail exponent
of the asymptotic behavior
as is directly related to the fluctuation exponent
(which governs the fluctuations
of the ground state energy for polymers of length ) via the simple
formula . Along the paper, we comment on the
similarities and differences with spin-glasses.Comment: 13 pages, 16 figure
Fluctuating Fronts as Correlated Extreme Value Problems: An Example of Gaussian Statistics
In this paper, we view fluctuating fronts made of particles on a
one-dimensional lattice as an extreme value problem. The idea is to denote the
configuration for a single front realization at time by the set of
co-ordinates of the
constituent particles, where is the total number of particles in that
realization at time . When are arranged in the ascending order
of magnitudes, the instantaneous front position can be denoted by the location
of the rightmost particle, i.e., by the extremal value
. Due to interparticle
interactions, at two different times for a single front
realization are naturally not independent of each other, and thus the
probability distribution [based on an ensemble of such front
realizations] describes extreme value statistics for a set of correlated random
variables. In view of the fact that exact results for correlated extreme value
statistics are rather rare, here we show that for a fermionic front model in a
reaction-diffusion system, is Gaussian. In a bosonic front model
however, we observe small deviations from the Gaussian.Comment: 6 pages, 3 figures, miniscule changes on the previous version, to
appear in Phys. Rev.
Contest based on a directed polymer in a random medium
We introduce a simple one-parameter game derived from a model describing the
properties of a directed polymer in a random medium. At his turn, each of the
two players picks a move among two alternatives in order to maximize his final
score, and minimize opponent's return. For a game of length , we find that
the probability distribution of the final score develops a traveling wave
form, , with the wave profile unusually
decaying as a double exponential for large positive and negative . In
addition, as the only parameter in the game is varied, we find a transition
where one player is able to get his maximum theoretical score. By extending
this model, we suggest that the front velocity is selected by the nonlinear
marginal stability mechanism arising in some traveling wave problems for which
the profile decays exponentially, and for which standard traveling wave theory
applies
Universal distribution of threshold forces at the depinning transition
We study the distribution of threshold forces at the depinning transition for
an elastic system of finite size, driven by an external force in a disordered
medium at zero temperature. Using the functional renormalization group (FRG)
technique, we compute the distribution of pinning forces in the quasi-static
limit. This distribution is universal up to two parameters, the average
critical force, and its width. We discuss possible definitions for threshold
forces in finite-size samples. We show how our results compare to the
distribution of the latter computed recently within a numerical simulation of
the so-called critical configuration.Comment: 12 pages, 7 figures, revtex
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