16,932 research outputs found
Thermocapillary effects in driven dewetting and self-assembly of pulsed laser-irradiated metallic films
In this paper the lubrication-type dynamical model is developed of a molten,
pulsed laser-irradiated metallic film. The heat transfer problem that
incorporates the absorbed heat from a single beam or interfering beams is
solved analytically. Using this temperature field, we derive the 3D long-wave
evolution PDE for the film height. To get insights into dynamics of dewetting,
we study the 2D version of the evolution equation by means of a linear
stability analysis and by numerical simulations. The stabilizing and
destabilizing effects of various system parameters, such as the peak laser beam
intensity, the film optical thickness, the Biot and Marangoni numbers, etc. are
elucidated. It is observed that the film stability is promoted for such
parameters variations that increase the heat production in the film. In the
numerical simulations the impacts of different irradiation modes are
investigated. In particular, we obtain that in the interference heating mode
the spatially periodic irradiation results in a spatially periodic film rupture
with the same, or nearly equal period. The 2D model qualitatively reproduces
the results of the experimental observations of a film stability and spatial
ordering of a re-solidified nanostructures
QCD Thermodynamics with Improved Actions
The thermodynamics of the SU(3) gauge theory has been analyzed with tree
level and tadpole improved Symanzik actions. A comparison with the continuum
extrapolated results for the standard Wilson action shows that improved actions
lead to a drastic reduction of finite cut-off effects already on lattices with
temporal extent . Results for the pressure, the critical temperature,
surface tension and latent heat are presented. First results for the
thermodynamics of four-flavour QCD with an improved staggered action are also
presented. They indicate similarly large improvement factors for bulk
thermodynamics.Comment: Talk presented at LATTICE96(finite temperature) 4 pages, LaTeX2e
file, 6 eps-file
String Tension and Thermodynamics with Tree Level and Tadpole Improved Actions
We calculate the string tension, deconfinement transition temperature and
bulk thermodynamic quantities of the SU(3) gauge theory using tree level and
tadpole improved actions. Finite temperature calculations have been performed
on lattices with temporal extent N_tau = 3 and 4. Compared to calculations with
the standard Wilson action on this size lattices we observe a drastic reduction
of the cut-off dependence of bulk thermodynamic observables at high
temperatures. In order to test the influence of improvement on long-distance
observables at T_c we determine the ratio T_c/sqrt(sigma). For all actions,
including the standard Wilson action, we find results which differ only little
from each other. We do, however, observe an improved asymptotic scaling
behaviour for the tadpole improved action compared to the Wilson and tree level
improved actions.Comment: 20 pages, LaTeX2e File, 8 coloured Postscript figures, new analysis
added, recent Wilson action string tension results included, figures replace
Data Mining and Quantitative Structure-Activity Relationships of Inhibitors for Treating Alzheimer's Disease
poster abstractAmyloid cleaving enzyme-1 (BACE1) is a target of interest for treating patients with Alzheimer’s disease (AD). As of 2007, more than 37 million people worldwide are afflicted with the disease. Incidence of the disease keeps increasing as the population ages and fewer people die of other diseases. ß-Amyloid precursor protein (APP) is a natural protein associated with neurons of the brain. In Alzheimer's disease, APP is cleaved by BACE1 at the beta-site, resulting in short 42 amino acid segments called amyloid-ß (Aß). Aggregation of Aß into plaques results in the death of neurons and is associated with AD. Inhibition of the BACE1 enzyme may prevent Aß formation and prevent the development or progression of AD. Known BACE1 inhibitors are analyzed using computational chemistry techniques, and quantitative structure-activity relationships (QSAR) are developed
Model-Independent Semileptonic Form Factors Using Dispersion Relations
We present a method for parametrizing heavy meson semileptonic form factors
using dispersion relations, and from it produce a two-parameter description of
the B -> B elastic form factor. We use heavy quark symmetry to relate this
function to B -> D* l nu form factors, and extract
|V_cb|=0.0355^{+0.0029}_{-0.0025} from experimental data with a least squares
fit. Our method eliminates model-dependent uncertainties inherent in choosing a
parametrization for the extrapolation of the differential decay rate to
threshold.Comment: uses lanlmac(harvmac) and epsf, 12 pages, 1 eps figure included (Talk
by BG at the 6-th International Symposium on Heavy Flavour Physics, Pisa,
Italy, 6--10 June, 1995
Resolving velocity space dynamics in continuum gyrokinetics
Many plasmas of interest to the astrophysical and fusion communities are
weakly collisional. In such plasmas, small scales can develop in the
distribution of particle velocities, potentially affecting observable
quantities such as turbulent fluxes. Consequently, it is necessary to monitor
velocity space resolution in gyrokinetic simulations. In this paper, we present
a set of computationally efficient diagnostics for measuring velocity space
resolution in gyrokinetic simulations and apply them to a range of plasma
physics phenomena using the continuum gyrokinetic code GS2. For the cases
considered here, it is found that the use of a collisionality at or below
experimental values allows for the resolution of plasma dynamics with
relatively few velocity space grid points. Additionally, we describe
implementation of an adaptive collision frequency which can be used to improve
velocity space resolution in the collisionless regime, where results are
expected to be independent of collision frequency.Comment: 20 pages, 11 figures, submitted to Phys. Plasma
Simple Structure-Based Approach for Predicting the Activity of Inhibitors of Beta-Secretase (BACE1) Associated with Alzheimer's Disease
poster abstractBeta-site amyloid precursor protein cleaving enzyme-1 (BACE1) is a target of interest for treating patients with Alzheimer’s disease (AD). Inhibition of BACE1 may prevent amyloid-ß (Aß) plaque formation and the development or progression of Alzheimer’s disease. Known BACE1 inhibitors were analyzed using computational chemistry and cheminformatics techniques to search for quantitative structure− activity relationships (QSAR). A remarkable relationship was found with only two simple descriptors with a square of the linear correlation coefficient r2 of 0.75. The main descriptor is the number of hydrophobic contacts in the range 4−5 Å between the atoms of the ligand and active site. The other descriptor is the number of short (<2.8 Å) hydrogen bonds. Our approach uses readily available structural data on protein- inhibitor complexes in the Protein Data Bank (PDB) but would be equally applicable to proprietary structural biology data. The findings can aid structure-based design of improved BACE-1 inhibitors. If an inhibitor has less observed activity than predicted by our correlation, the compound should be retested because the first assay may have underestimated the compound’s true activity
New Constraints on Dispersive Form Factor Parameterizations from the Timelike Region
We generalize a recent model-independent form factor parameterization derived
from rigorous dispersion relations to include constraints from data in the
timelike region. These constraints dictate the convergence properties of the
parameterization and appear as sum rules on the parameters. We further develop
a new parameterization that takes into account finiteness and asymptotic
conditions on the form factor, and use it to fit to the elastic \pi
electromagnetic form factor. We find that the existing world sample of timelike
data gives only loose bounds on the form factor in the spacelike region, but
explain how the acquisition of additional timelike data or fits to other form
factors are expected to give much better results. The same parameterization is
seen to fit spacelike data extremely well.Comment: 24 pages, latex (revtex), 3 eps figure
SU(3) Latent Heat and Surface Tension from Tree Level and Tadpole Improved Actions
We analyze the latent heat and surface tension at the SU(3) deconfinement
phase transition with tree level and tadpole improved Symanzik actions on
lattices with temporal extent and 4 and spatial extent , 6 and 8. In comparison to the standard Wilson action we do find a
drastic reduction of cut-off effects already with tree level improved actions.
On lattices with temporal extent results for the surface tension and
latent heat obtained with a tree level improved action agree well with those
obtained with a tadpole improved action. A comparison with
calculations, however, shows that results obtained with tadpole action remain
unaffected by cut-off effects even on this coarse lattice, while the tree level
action becomes sensitive to the cut-off. For the surface tension and latent
heat we find and , respectively.Comment: 11 pages, LaTeX2e File, 3 Postscript figure
The Kepler Light Curves of AGN: A Detailed Analysis
We present a comprehensive analysis of 21 light curves of Type 1 AGN from the
Kepler spacecraft. First, we describe the necessity and development of a
customized pipeline for treating Kepler data of stochastically variable sources
like AGN. We then present the light curves, power spectral density functions
(PSDs), and flux histograms. The light curves display an astonishing variety of
behaviors, many of which would not be detected in ground-based studies,
including switching between distinct flux levels. Six objects exhibit PSD
flattening at characteristic timescales which roughly correlate with black hole
mass. These timescales are consistent with orbital timescales or freefall
accretion timescales. We check for correlations of variability and
high-frequency PSD slope with accretion rate, black hole mass, redshift and
luminosity. We find that bolometric luminosity is anticorrelated with both
variability and steepness of the PSD slope. We do not find evidence of the
linear rms-flux relationships or lognormal flux distributions found in X-ray
AGN light curves, indicating that reprocessing is not a significant contributor
to optical variability at the 0.1-10% level.Comment: 39 pages including 2 appendices. Accepted for Publication in the
Astrophysical Journal, with higher resolution figure
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