2,847 research outputs found
FFT for the APE Parallel Computer
We present a parallel FFT algorithm for SIMD systems following the `Transpose
Algorithm' approach. The method is based on the assignment of the data field
onto a 1-dimensional ring of systolic cells. The systolic array can be
universally mapped onto any parallel system. In particular for systems with
next-neighbour connectivity our method has the potential to improve the
efficiency of matrix transposition by use of hyper-systolic communication. We
have realized a scalable parallel FFT on the APE100/Quadrics massively parallel
computer, where our implementation is part of a 2-dimensional hydrodynamics
code for turbulence studies. A possible generalization to 4-dimensional FFT is
presented, having in mind QCD applications.Comment: 17 pages, 13 figures, figures include
QCD on \alpha-Clusters
It is shown that the 21264 Alpha processor can reach about 20% sustained
efficiency for the inversion of the Wilson-Dirac operator. Since fast ethernet
is not sufficient to get balancing between computation and communication on
reasonable lattice- and system-sizes, an interconnection using Myrinet is
discussed. We find a price/performance ratio comparable with state-of-the-art
SIMD-systems for lattice QCD.Comment: LATTICE99(machines), 3 page
Direct Graphene Growth on Insulator
Fabrication of graphene devices is often hindered by incompatibility between
the silicon technology and the methods of graphene growth. Exfoliation from
graphite yields excellent films but is good mainly for research. Graphene grown
on metal has a technological potential but requires mechanical transfer. Growth
by SiC decomposition requires a temperature budget exceeding the technological
limits. These issues could be circumvented by growing graphene directly on
insulator, implying Van der Waals growth. During growth, the insulator acts as
a support defining the growth plane. In the device, it insulates graphene from
the Si substrate. We demonstrate planar growth of graphene on mica surface.
This was achieved by molecular beam deposition above 600{\deg}C. High
resolution Raman scans illustrate the effect of growth parameters and substrate
topography on the film perfection. Ab initio calculations suggest a growth
model. Data analysis highlights the competition between nucleation at surface
steps and flat surface. As a proof of concept, we show the evidence of electric
field effect in a transistor with a directly grown channel.Comment: 13 pages, 6 figure
Quantifying the uncertainty in heritability
The use of mixed models to determine narrow-sense heritability and related quantities such as SNP heritability has received much recent attention. Less attention has been paid to the inherent variability in these estimates. One approach for quantifying variability in estimates of heritability is a frequentist approach, in which heritability is estimated using maximum likelihood and its variance is quantified through an asymptotic normal approximation. An alternative approach is to quantify the uncertainty in heritability through its Bayesian posterior distribution. In this paper, we develop the latter approach, make it computationally efficient and compare it to the frequentist approach. We show theoretically that, for a sufficiently large sample size and intermediate values of heritability, the two approaches provide similar results. Using the Atherosclerosis Risk in Communities cohort, we show empirically that the two approaches can give different results and that the variance/uncertainty can remain large
Die Bestimmungsgründe der räumlichen Verteilung des ökologischen Landbaus in Deutschland
Die Bestimmungsgründe der räumlichen Verteilung des ökologischen Landbaus sind nicht eindeutig geklärt. Daher werden verschiedene Faktoren hinsichtlich ihres Einflusses auf den Flächenanteil und die regionale Verteilung des ökologischen Landbaus in Deutschland untersucht.
In diesem Beitrag werden erste und in einigen Punkten noch vorläufige Ergebnisse eines laufenden Forschungsprojektes dargestellt
Calculation of the N to Delta electromagnetic transition matrix element
We present results on the ratio of electric quadrupole to magnetic dipole
amplitudes, , for the transition from lattice QCD. We consider both the quenched and the 2-flavor
theory.Comment: 3 pages, 4 figures, talk presented at Lattice2002(matrixel); Layout
of figures adjuste
transition form factors in Quenched and QCD
Calculations of the magnetic dipole, electric quadrupole and Coulomb
quadrupole amplitudes for the transition are presented
both in quenched QCD and with two flavours of degenerate dynamical quarks.Comment: Lattice2003(Matrix), 3 page
The Quest for Light Sea Quarks: Algorithms for the Future
As part of a systematic algorithm study, we present first results on a
performance comparison between a multibosonic algorithm and the hybrid Monte
Carlo algorithm as employed by the SESAM collaboration. The standard Wilson
fermion action is used on 32*16^3 lattices at beta=5.5.Comment: LaTeX, 3 pages, Lattice2001(algorithms
Observation of String Breaking in QCD
We numerically investigate the transition of the static quark-antiquark
string into a static-light meson-antimeson system. Improving noise reduction
techniques, we are able to resolve the signature of string breaking dynamics
for n_f=2 lattice QCD at zero temperature. This result can be related to
properties of quarkonium systems. We also study short-distance interactions
between two static-light mesons.Comment: 27 pages, 22 figures, changed decimal place of errors in 3 entries of
Table, corrected reference
Precision computation of the kaon bag parameter
Indirect CP violation in K \rightarrow {\pi}{\pi} decays plays a central role
in constraining the flavor structure of the Standard Model (SM) and in the
search for new physics. For many years the leading uncertainty in the SM
prediction of this phenomenon was the one associated with the nonperturbative
strong interaction dynamics in this process. Here we present a fully controlled
lattice QCD calculation of these effects, which are described by the neutral
kaon mixing parameter B_K . We use a two step HEX smeared clover-improved
Wilson action, with four lattice spacings from a\approx0.054 fm to
a\approx0.093 fm and pion masses at and even below the physical value.
Nonperturbative renormalization is performed in the RI-MOM scheme, where we
find that operator mixing induced by chiral symmetry breaking is very small.
Using fully nonperturbative continuum running, we obtain our main result
B_K^{RI}(3.5GeV)=0.531(6)_{stat}(2)_{sys}. A perturbative 2-loop conversion
yields B_K^{MSbar-NDR}(2GeV)=0.564(6)_{stat}(3)_{sys}(6)_{PT}, which is in good
agreement with current results from fits to experimental data.Comment: 10 pages, 7 figures. v2: Added one reference and one figure, replaced
2 figures for better readability and updated ensembles, conclusions
unchanged. Final, published versio
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