117,347 research outputs found
The non-perturbative O(a)-improved action for dynamical Wilson fermions
We compute the improvement coefficient that multiplies the
Sheikholeslami-Wohlert term as a function of the bare gauge coupling for two
flavour QCD. We discuss several aspects concerning simulations with improved
dynamical Wilson fermions.Comment: Latex file, 2 figures, 6 pages, talk given by K.J. at the
International Symposium on Lattice Field Theory, 21-27 July 1997, Edinburgh,
Scotlan
A Polynomial Hybrid Monte Carlo Algorithm
We present a simulation algorithm for dynamical fermions that combines the
multiboson technique with the Hybrid Monte Carlo algorithm. We find that the
algorithm gives a substantial gain over the standard methods in practical
simulations. We point out the ability of the algorithm to treat fermion
zeromodes in a clean and controllable manner.Comment: Latex, 1 figure, 12 page
Study of Liapunov Exponents and the Reversibility of Molecular Dynamics Algorithms
We study the question of lack of reversibility and the chaotic nature of the
equations of motion in numerical simulations of lattice QCD.Comment: latex file with 3 pages, 1 figure. Talk presented at Lattice'96 by C.
Li
Speeding up the HMC: QCD with Clover-Improved Wilson Fermions
We apply a recent proposal to speed up the Hybrid-Monte-Carlo simulation of
systems with dynamical fermions to two flavor QCD with clover-improvement. For
our smallest quark masses we see a speed-up of more than a factor of two
compared with the standard algorithm.Comment: 3 pages, lattice2002, algorithms, DESY Report-no correcte
Liapunov Exponents and the Reversibility of Molecular Dynamics Algorithms
We study the phenomenon of lack of reversibility in molecular dynamics
algorithms for the case of Wilson's lattice QCD. We demonstrate that the
classical equations of motion that are employed in these algorithms are chaotic
in nature. The leading Liapunov exponent is determined in a range of coupling
parameters. We give a quantitative estimate of the consequences of the
breakdown of reversibility due to round-off errors.Comment: Latex2e file, 4 figures, 19 page
A Gauge-Fixing Action for Lattice Gauge Theories
We present a lattice gauge-fixing action with the following
properties: (a) is proportional to the trace of , plus irrelevant terms of dimension six and higher; (b)
has a unique absolute minimum at . Noting that the
gauge-fixed action is not BRST invariant on the lattice, we discuss some
important aspects of the phase diagram.Comment: 13 pages, Latex, improved presentation, no change in result
Microbial demethylation of dimethylsulfoniopropionate and methylthiopropionate
As discussed in chapter 1 , there is an increased interest in the production of certain natural sulfur-containing flavor compounds or flavor precursors. Production of natural flavors is becoming increasingly important, because consumerts end to prefer natural compounds for health reasons. With the aid of extraction techniques it is possible to obtain flavors directly from plant material, but these methods are time consuming and expensive, because the most interesting flavors are present in only very low concentrations. A more recent method to produce flavors is based on a biotechnological approach where natural precursors, isolated mainly from plant material, can be convertedt o the desired flavor in a bioreactor with the aid of enzymes and/or microorganisms.
Non-equispaced B-spline wavelets
This paper has three main contributions. The first is the construction of
wavelet transforms from B-spline scaling functions defined on a grid of
non-equispaced knots. The new construction extends the equispaced,
biorthogonal, compactly supported Cohen-Daubechies-Feauveau wavelets. The new
construction is based on the factorisation of wavelet transforms into lifting
steps. The second and third contributions are new insights on how to use these
and other wavelets in statistical applications. The second contribution is
related to the bias of a wavelet representation. It is investigated how the
fine scaling coefficients should be derived from the observations. In the
context of equispaced data, it is common practice to simply take the
observations as fine scale coefficients. It is argued in this paper that this
is not acceptable for non-interpolating wavelets on non-equidistant data.
Finally, the third contribution is the study of the variance in a
non-orthogonal wavelet transform in a new framework, replacing the numerical
condition as a measure for non-orthogonality. By controlling the variances of
the reconstruction from the wavelet coefficients, the new framework allows us
to design wavelet transforms on irregular point sets with a focus on their use
for smoothing or other applications in statistics.Comment: 42 pages, 2 figure
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