115,717 research outputs found

    The non-perturbative O(a)-improved action for dynamical Wilson fermions

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    We compute the improvement coefficient cswc_{sw} 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

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    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

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    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

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    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

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    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

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    We present a lattice gauge-fixing action SgfS_{gf} with the following properties: (a) SgfS_{gf} is proportional to the trace of (∑Ό∂ΌAÎŒ)2(\sum_\mu \partial_\mu A_\mu)^2, plus irrelevant terms of dimension six and higher; (b) SgfS_{gf} has a unique absolute minimum at Ux,ÎŒ=IU_{x,\mu}=I. 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

    Non-equispaced B-spline wavelets

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    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

    Microbial demethylation of dimethylsulfoniopropionate and methylthiopropionate

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    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.