183,946 research outputs found
Gluon Bremsstrahlung in Weakly-Coupled Plasmas
I report on some theoretical progress concerning the calculation of gluon
bremsstrahlung for very high energy particles crossing a weakly-coupled
quark-gluon plasma. (i) I advertise that two of the several formalisms used to
study this problem, the BDMPS-Zakharov formalism and the AMY formalism (the
latter used only for infinite, uniform media), can be made equivalent when
appropriately formulated. (ii) A standard technique to simplify calculations is
to expand in inverse powers of logarithms . I give an example where
such expansions are found to work well for where
is the bremsstrahlung gluon energy. (iii) Finally, I report on perturbative
calculations of .Comment: 4 pages, 2 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee [change from v2:
minor changes for publication
Cumulative Step-size Adaptation on Linear Functions
The CSA-ES is an Evolution Strategy with Cumulative Step size Adaptation,
where the step size is adapted measuring the length of a so-called cumulative
path. The cumulative path is a combination of the previous steps realized by
the algorithm, where the importance of each step decreases with time. This
article studies the CSA-ES on composites of strictly increasing functions with
affine linear functions through the investigation of its underlying Markov
chains. Rigorous results on the change and the variation of the step size are
derived with and without cumulation. The step-size diverges geometrically fast
in most cases. Furthermore, the influence of the cumulation parameter is
studied.Comment: arXiv admin note: substantial text overlap with arXiv:1206.120
Cumulative Step-size Adaptation on Linear Functions: Technical Report
The CSA-ES is an Evolution Strategy with Cumulative Step size Adaptation,
where the step size is adapted measuring the length of a so-called cumulative
path. The cumulative path is a combination of the previous steps realized by
the algorithm, where the importance of each step decreases with time. This
article studies the CSA-ES on composites of strictly increasing with affine
linear functions through the investigation of its underlying Markov chains.
Rigorous results on the change and the variation of the step size are derived
with and without cumulation. The step-size diverges geometrically fast in most
cases. Furthermore, the influence of the cumulation parameter is studied.Comment: Parallel Problem Solving From Nature (2012
A Proof of the Isoenergetic KAM-Theorem from the “Ordinary” One
A proof is given of the isoenergetic KAM-theorem for Hamiltonian systems, using the “ordinary” KAM-theorem and a transversality argument.
Results from the NEMO 3 experiment
The aim of the NEMO 3 experiment is the search for neutrinoless double beta
decay and precise measurement of two-neutrino double beta decay of several
isotopes. The experiment has been taking data since 2003. Since no evidence for
neutrinoless double beta decay of Mo100 and Se82 has been found, a 90% C.L.
lower limit on the half-life of this process and corresponding upper limit on
the effective Majorana neutrino mass are derived. The data are also interpreted
in terms of alternative models, such as weak right-handed currents or Majoron
emission. In addition, NEMO 3 has performed precision measurements of the
two-neutrino double beta decay for seven different isotopes. The most recent
experimental results of NEMO 3 are presented in this paper.Comment: 5 pages, 2 tables, talk at the 10th ICATPP Conference (Como, Italy, 8
- 12 October 2007
Visualizing Color Plasma Instabilities
I discuss recent advances in the understanding of non-equilibrium gauge field
dynamics in plasmas which have particle distributions which are locally
anisotropic in momentum space. In contrast to locally isotropic plasmas such
anisotropic plasmas have a spectrum of soft unstable modes which are
characterized by exponential growth of transverse (chromo)-magnetic fields at
short times. The long-time behavior of such instabilities depends on whether or
not the gauge group is abelian or non-abelian. I will report on recent
numerical simulations which attempt to determine the long-time behavior of an
anisotropic non-abelian plasma within hard-loop effective theory. For novelty I
will present an interesting method for visualizing the time-dependence of SU(2)
gauge field configurations produced during our numerical simulations.Comment: 10 pages, 5 figures. Contribution to Proceedings of Workshop on
Quark-Gluon-Plasma Thermalization, Vienna, Austria, Aug 10-12. For full
resolution images see
http://www.fias.uni-frankfurt.de/home/strickland/instability
Bose-Einstein condensates in `giant' toroidal magnetic traps
The experimental realisation of gaseous Bose-Einstein condensation (BEC) in
1995 sparked considerable interest in this intriguing quantum fluid. Here we
report on progress towards the development of an 87Rb BEC experiment in a large
(~10cm diameter) toroidal storage ring. A BEC will be formed at a localised
region within the toroidal magnetic trap, from whence it can be launched around
the torus. The benefits of the system are many-fold, as it should readily
enable detailed investigations of persistent currents, Josephson effects, phase
fluctuations and high-precision Sagnac or gravitational interferometry.Comment: 5 pages, 3 figures (Figs. 1 and 2 now work
Autodocumentation
Automated documentation systems with expanded capabilities for reusing existing programs are considered by allowing a relatively inexpensive determination of program capabilities. A theoretical approach to such a system is proposed. Tree structure variations are examined, along with assignment statements, conditional branches, loops, and an automated analyzer
A new Truncated Fourier Transform algorithm
Truncated Fourier Transforms (TFTs), first introduced by Van der Hoeven,
refer to a family of algorithms that attempt to smooth "jumps" in complexity
exhibited by FFT algorithms. We present an in-place TFT whose time complexity,
measured in terms of ring operations, is comparable to existing not-in-place
TFT methods. We also describe a transformation that maps between two families
of TFT algorithms that use different sets of evaluation points.Comment: 8 pages, submitted to the 38th International Symposium on Symbolic
and Algebraic Computation (ISSAC 2013
On examples of difference operators for -valued functions over finite sets
Recently V.I.Arnold have formulated a geometrical concept of monads and apply
it to the study of difference operators on the sets of -valued
sequences of length . In the present note we show particular examples of
these monads and indicate one question arising here
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