115,893 research outputs found
Phase Field Crystals as a Coarse-Graining in Time of Molecular Dynamics
Phase field crystals (PFC) are a tool for simulating materials at the atomic
level. They combine the small length-scale resolution of molecular dynamics
(MD) with the ability to simulate dynamics on mesoscopic time scales. We show
how PFC can be interpreted as the result of applying coarse-graining in time to
the microscopic density field of molecular dynamics simulations. We take the
form of the free energy for the phase field from the classical density
functional theory of inhomogeneous liquids and then choose coefficients to
match the structure factor of the time coarse-grained microscopic density
field. As an example, we show how to construct a PFC free energy for Weber and
Stillinger's two-dimensional square crystal potential which models a system of
proteins suspended in a membrane.Comment: 5 pages, 4 figures, typos corrected, more explanation in parts,
equilib vs non-equilib clarifie
Measuring the Higgs to Photon-Photon Branching Ratio at the Next Linear Collider
We examine the prospects for measuring the photon-photon branching ratio of a
Standard-Model-like Higgs boson () at the Next Linear Collider when
the Higgs boson is produced via --fusion: .
In particular, we study the accuracy of such a measurement and the statistical
significance of the associated signal as a function of the electromagnetic
calorimeter resolution and the Higgs boson mass. We compare results for the
--fusion production/measurement mode with the results obtained for the
production/measurement mode in a
parallel earlier study.Comment: 5 pages, full postscript file also available via anonymous ftp at
ftp://ucdhep.ucdavis.edu/gunion/htogamgam_sm96.ps To appear in ``Proceedings
of the 1996 DPF/DPB Summer Study on New Directions for High Energy Physics'
Higher covariant derivative regulators and non-multiplicative renormalization
The renormalization algorithm based on regularization methods with two
regulators is analyzed by means of explicit computations. We show in particular
that regularization by higher covariant derivative terms can be complemented
with dimensional regularization to obtain a consistent renormalized
4-dimensional Yang-Mills theory at the one-loop level. This shows that hybrid
regularization methods can be applied not only to finite theories, like \eg\
Chern-Simons, but also to divergent theories.Comment: 12 pages, phyzzx, no figure
Higher covariant derivative Pauli-Villars regularization does not lead to a consistent QCD
We compute the beta function at one loop for Yang-Mills theory using as
regulator the combination of higher covariant derivatives and Pauli-Villars
determinants proposed by Faddeev and Slavnov. This regularization prescription
has the appealing feature that it is manifestly gauge invariant and essentially
four-dimensional. It happens however that the one-loop coefficient in the beta
function that it yields is not as it should be, but The
difference is due to unphysical logarithmic radiative corrections generated by
the Pauli-Villars determinants on which the regularization method is based.
This no-go result discards the prescription as a viable gauge invariant
regularization, thus solving a long-standing open question in the literature.
We also observe that the prescription can be modified so as to not generate
unphysical logarithmic corrections, but at the expense of losing manifest gauge
invariance.Comment: 43 pages, Latex file (uses the macro axodraw.sty, instructions of how
to get it and use it included), FTUAM 94/9, NIKHEF-H 94/2
SEAHT: A computer program for the use of intersecting arcs of altimeter data for sea surface height refinement
The SEAHT program is designed to process multiple passes of altimeter data with intersecting ground tracks, with the estimation of corrections for orbital errors to each pass such that the data has the best overall agreement at the crossover points. Orbit error for each pass is modeled as a polynomial in time, with optional orders of 0, 1, or 2. One or more passes may be constrained in the adjustment process, thus allowing passes with the best orbits to provide the overall level and orientation of the estimated sea surface heights. Intersections which disagree by more than an input edit level are not used in the error parameter estimation. In the program implementation, passes are grouped into South-North passes and North-South passes, with the North-South passes partitioned out for the estimation of orbit error parameters. Computer core utilization is thus dependent on the number of parameters estimated for the set of South-North arcs, but is independent on the number of North-South passes. Estimated corrections for each pass are applied to the data at its input data rate and an output tape is written which contains the corrected data
Energy exponents and corrections to scaling in Ising spin glasses
We study the probability distribution P(E) of the ground state energy E in
various Ising spin glasses. In most models, P(E) seems to become Gaussian with
a variance growing as the system's volume V. Exceptions include the
Sherrington-Kirkpatrick model (where the variance grows more slowly, perhaps as
the square root of the volume), and mean field diluted spin glasses having +/-J
couplings. We also find that the corrections to the extensive part of the
disorder averaged energy grow as a power of the system size; for finite
dimensional lattices, this exponent is equal, within numerical precision, to
the domain-wall exponent theta_DW. We also show how a systematic expansion of
theta_DW in powers of exp(-d) can be obtained for Migdal-Kadanoff lattices.
Some physical arguments are given to rationalize our findings.Comment: 12 pages, RevTex, 9 figure
The influence of a local wall deformation on the development of natural instabilities in a laminar boundary layer
The natural instabilities which propagate in the laminar boundary layer of a flat plate composed of intermittent wave trains are described. A spectral analysis determines the frequency range and gives a frequency and the harmonic 2 only if there is a wall deformation. This analysis provides the amplitude modulation spectrum of the instabilities. Plots of the evolution of power spectral density are compared with the numerical results obtained from the resolve of the Orr-Sommerfeld equation, while the harmonic is related to a micro-recirculating flow near the wall deformation
Targeted deep surveys of high Galactic latitude HI with the GBT
Over 800 sq. deg. of high Galactic latitude sky have been mapped at 21 cm
with the Robert C. Byrd Green Bank Telescope (GBT). An improved knowledge of
the telescope's beam characteristics has allowed us to reliably map not only
regions of high column density, but also such regions as ELAIS N1, a targeted
Spitzer field, which have very low HI column density. The additional fields we
have observed cover a cross-section of dynamically and chemically interesting
regions as indicated by the presence of intermediate/high velocity gas and/or
anomalous far-IR (dust) colour.Comment: 7 pages, 5 figures. To appear in "The Dynamic ISM: A celebration of
the Canadian Galactic Plane Survey" ASP Conference Serie
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