408,804 research outputs found
Dimensional Reduction via Noncommutative Spacetime: Bootstrap and Holography
Unlike noncommutative space, when space and time are noncommutative, it seems
necessary to modify the usual scheme of quantum mechanics. We propose in this
paper a simple generalization of the time evolution equation in quantum
mechanics to incorporate the feature of a noncommutative spacetime. This
equation is much more constraining than the usual Schr\"odinger equation in
that the spatial dimension noncommuting with time is effectively reduced to a
point in low energy. We thus call the new evolution equation the spacetime
bootstrap equation, the dimensional reduction called for by this evolution
seems close to what is required by the holographic principle. We will discuss
several examples to demonstrate this point.Comment: 15 pages, harvmac. v2: typos corrected and some changes mad
Study of Apollo water impact. Volume 1 - Hydrodynamic analysis of Apollo water impact Final report
Mathematical model for Apollo command module impact analysis on wate
Measuring CP Violating Phases at a Future Linear Collider
At a future Linear Collider one will be able to determine the masses of
charginos and neutralinos and their pair production cross sections to high
accuracies. We show how systematically including the cross sections into the
analysis improves the measurement of the underlying mass parameters, including
potential CP violating phases. In addition, we investigate how experimental
errors will affect the determination of these parameters. We present a first
estimate on the lower limit of observable small phases and on the accuracy in
determining large phases.Comment: 10 pages, 6 figures, RevTeX3.1, Version to be published in Physics
Letters B, physics setup improved, figures added, conclusions unchange
A self-learning particle swarm optimizer for global optimization problems
Copyright @ 2011 IEEE. All Rights Reserved. This article was made available through the Brunel Open Access Publishing Fund.Particle swarm optimization (PSO) has been shown as an effective tool for solving global optimization problems. So far, most PSO algorithms use a single learning pattern for all particles, which means that all particles in a swarm use the same strategy. This monotonic learning pattern may cause the lack of intelligence for a particular particle, which makes it unable to deal with different complex situations. This paper presents a novel algorithm, called self-learning particle swarm optimizer (SLPSO), for global optimization problems. In SLPSO, each particle has a set of four strategies to cope with different situations in the search space. The cooperation of the four strategies is implemented by an adaptive learning framework at the individual level, which can enable a particle to choose the optimal strategy according to its own local fitness landscape. The experimental study on a set of 45 test functions and two real-world problems show that SLPSO has a superior performance in comparison with several other peer algorithms.This work was supported by the Engineering and Physical Sciences Research Council of U.K. under Grants EP/E060722/1 and EP/E060722/2
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Performance analysis of the IEEE 802.11e block ACK scheme in a noisy channel
A block ACK (BTA) scheme has been proposed in IEEE 802.11e to improve medium access control (MAC) layer performance. It is also a promising technique for next-generation high-speed wireless LANs (WLANs) such as IEEE 802.11n. We present a theoretical model to evaluate MAC saturation throughput of this scheme. This model takes into account the effects of both collisions and transmission errors in a noisy channel. The accuracy of this model is validated by NS-2 simulations
Fluctuation limits of strongly degenerate branching systems
Functional limit theorems for scaled fluctuations of occupation time
processes of a sequence of critical branching particle systems in with
anisotropic space motions and strongly degenerated splitting abilities are
proved in the cases of critical and intermediate dimensions. The results show
that the limit processes are constant measure-valued Wienner processes with
degenerated temporal and simple spatial structures.Comment: 15 page
Least-Squares Approximation by Elements from Matrix Orbits Achieved by Gradient Flows on Compact Lie Groups
Let denote the orbit of a complex or real matrix under a certain
equivalence relation such as unitary similarity, unitary equivalence, unitary
congruences etc. Efficient gradient-flow algorithms are constructed to
determine the best approximation of a given matrix by the sum of matrices
in in the sense of finding the Euclidean least-squares
distance
Connections of the results to different pure and applied areas are discussed
Associated Charmonium Production in Low Energy p-pbar Annihilation
The QCD mechanisms underlying the exclusive strong decays and hadronic
production amplitudes of charmonium remain poorly understood, despite decades
of study and an increasingly detaled body of experimental information. One set
of hadronic channels of special interest are those that include
baryon-antibaryon states. These are being investigated experimentally at BES
and CLEO-c in terms of their baryon resonance content, and are also of interest
for the future PANDA experiment, in which charmonium and charmonium hybrids
will be produced in p-pbar annihilation in association with light mesons. In
this paper we develop a simple initial-state light meson emission model of the
near-threshold associated charmonium production processes p pbar -> pi0 ccbar,
and evaluate the differential and total cross sections for these reactions in
this model. (Here we consider the ccbar states eta_c, J/psi, psi', chi_0 and
chi_1.) The predicted near-threshold cross section for p pbar -> pi0 J/psi is
found to be numerically similar to two previous theoretical estimates, and is
roughly comparable to the (sparse) existing data for this process. The
theoretical charmonium angular distributions predicted by this model are far
from isotropic, which may be of interest for PANDA detector design studies.Comment: 6 pages, 4 figures, uses graphicx and feynm
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