34,868 research outputs found
Non-perturbative Renormalization of Improved Staggered Bilinears
We compute Z-factors for general staggered bilinears on fine (a \approx 0.09
fm) MILC ensembles using both asqtad and HYP-smeared valence actions, comparing
the results to the predictions of one-loop perturbation theory. This is an
extension of previous work on the coarse (a \approx 0.12 fm) MILC ensembles. It
provides a laboratory for studying NPR methodology in the staggered context,
and is an important stepping stone for fully non-perturbative matching factors
in ongoing computations of B_K and other weak matrix elements. We also
implement non-exceptional RI/SMOM renormalization conditions using the asqtad
action and present first results.Comment: 7 pages, 4 figures. Contribution to the 30th International Symposium
on Lattice Field Theory, June 24-29, 2012, Cairns, Australi
The Cluster Abundance in Flat and Open Cosmologies
We use the galaxy cluster X-ray temperature distribution function to
constrain the amplitude of the power spectrum of density inhomogeneities on the
scale corresponding to clusters. We carry out the analysis for critical density
universes, for low density universes with a cosmological constant included to
restore spatial flatness and for genuinely open universes. That clusters with
the same present temperature but different formation times have different
virial masses is included. We model cluster mergers using two completely
different approaches, and show that the final results from each are extremely
similar. We give careful consideration to the uncertainties involved, carrying
out a Monte Carlo analysis to determine the cumulative errors. For critical
density our result agrees with previous papers, but we believe the result
carries a larger uncertainty. For low density universes, either flat or open,
the required amplitude of the power spectrum increases as the density is
decreased. If all the dark matter is taken to be cold, then the cluster
abundance constraint remains compatible with both galaxy correlation data and
the {\it COBE} measurement of microwave background anisotropies for any
reasonable density.Comment: Uuencoded package containing LaTeX file (uses mn.sty) plus 7
postscript figures incorporated using epsf. Total length 10 pages. Final
version, to appear MNRAS. COBE comparison changed to 4yr data. No change to
results or conclusion
Comment on ``Method to analyze electromechanical stability of dielectric elastomers" [Appl. Phys. Lett. 91, 061921 (2007)]
The model of Zhao and Suo can be readily generalized to predict the critical
breakdown electric field value of elastomers with arbitrary elastic
strain energy function. An explicit expression for is presented for
elastomeric thin films under biaxial strain and comparisons are made with
experimental data using a two term Ogden rubber elasticity model. Simplified
results for uniaxial and for equi-biaxial stress provide further insight into
the findings of Zhao and Suo.Comment: 2 page
Comprehensive analysis of the simplest curvaton model
We carry out a comprehensive analysis of the simplest curvaton model, which is based on two non-interacting massive fields. Our analysis encompasses cases where the inflaton and curvaton both contribute to observable perturbations, and where the curvaton itself drives a second period of in inflation. We consider both power spectrum and non-Gaussianity observables, and focus on presenting constraints in model parameter space. The fully curvaton-dominated regime is in some tension with observational data, while an admixture of inflaton-generated perturbations improves the fit. The inflating curvaton regime mimics the predictions of Nflation. Some parts of parameter space permitted by power spectrum data are excluded by non-Gaussianity constraints. The recent
BICEP2 results [1] require that the in inflaton perturbations provide a significant fraction of the total perturbation, ruling out the usual curvaton scenario in which the inflaton perturbations are negligible, though not the admixture regime where both inflaton and curvaton contribute to the spectrum
Imaging with two-axis micromirrors
We demonstrate a means of creating a digital image by using a two axis tilt
micromirror to scan a scene. For each different orientation we extract a single
grayscale value from the mirror and combine them to form a single composite
image. This allows one to choose the distribution of the samples, and so in
principle a variable resolution image could be created. We demonstrate this
ability to control resolution by constructing a voltage table that compensates
for the non-linear response of the mirrors to the applied voltage.Comment: 8 pages, 5 figures, preprin
Theory of Mott insulator/band insulator heterostructure
A theory of heterostructures comprised of LaTiO (a Mott insulator) and
SrTiO (a band insulator) is presented. The band structure of the Ti %
-electrons is treated with a nearest neighbor tight-binding approximation; the
electric fields arising from the La/Sr charge difference and the
carriers are treated within a Hartree approximation; and the on-site
interactions are treated by unrestricted Hartree-Fock. The phase diagram as a
function of interaction strength and layer number is determined and predictions
are made for optical conductivity experiments. A note worthy finding is that
the edges of the heterostructure are generally metallic.Comment: 11 pages, 9 figure
Microstructure versus Size: Mechanical Properties of Electroplated Single Crystalline Cu Nanopillars
We report results of uniaxial compression experiments on single-crystalline Cu nanopillars with nonzero initial dislocation densities produced without focused ion beam (FIB). Remarkably, we find the same power-law size-driven strengthening as FIB-fabricated face-centered cubic micropillars. TEM analysis reveals that initial dislocation density in our FIB-less pillars and those produced by FIB are on the order of 10^(14)  m^(-2) suggesting that mechanical response of nanoscale crystals is a stronger function of initial microstructure than of size regardless of fabrication method
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