41,829 research outputs found
Pinning of stripes by local structural distortions in cuprate high-Tc superconductors
We study the spin-density wave (stripe) instability in lattices with mixed
low-temperature orthorhombic (LTO) and low-temperature tetragonal (LTT) crystal
symmetry. Within an explicit mean-field model it is shown how local LTT regions
act as pinning centers for static stripe formation. We calculate the
modulations in the local density of states near these local stripe regions and
find that mainly the coherence peaks and the van Hove singularity (VHS) are
spatially modulated. Lastly, we use the real-space approach to simulate recent
tunneling data in the overdoped regime where the VHS has been detected by
utilizing local normal state regions.Comment: Conference proceedings for Stripes1
Uni-directional polymerization leading to homochirality in the RNA world
The differences between uni-directional and bi-directional polymerization are
considered. The uni-directional case is discussed in the framework of the RNA
world. Similar to earlier models of this type, where polymerization was assumed
to proceed in a bi-directional fashion (presumed to be relevant to peptide
nucleic acids), left-handed and right-handed monomers are produced via an
autocatalysis from an achiral substrate. The details of the bifurcation from a
racemic solution to a homochiral state of either handedness is shown to be
remarkably independent of whether the polymerization in uni-directional or
bi-directional. Slightly larger differences are seen when dissociation is
allowed and the dissociation fragments are being recycled into the achiral
substrate.Comment: 9 pages, 4 figures, submitted to Astrobiolog
Is the Redshift Clustering of Long-Duration Gamma-Ray Bursts Significant?
The 26 long-duration gamma-ray bursts (GRBs) with known redshifts form a
distinct cosmological set, selected differently than other cosmological probes
such as quasars and galaxies. Since the progenitors are now believed to be
connected with active star-formation and since burst emission penetrates dust,
one hope is that with a uniformly-selected sample, the large-scale redshift
distribution of GRBs can help constrain the star-formation history of the
Universe. However, we show that strong observational biases in ground-based
redshift discovery hamper a clean determination of the large-scale GRB rate and
hence the connection of GRBs to the star formation history. We then focus on
the properties of the small-scale (clustering) distribution of GRB redshifts.
When corrected for heliocentric motion relative to the local Hubble flow, the
observed redshifts appear to show a propensity for clustering: 8 of 26 GRBs
occurred within a recession velocity difference of 1000 km/s of another GRB.
That is, 4 pairs of GRBs occurred within 30 h_65^-1 Myr in cosmic time, despite
being causally separated on the sky. We investigate the significance of this
clustering. Comparison of the numbers of close redshift pairs expected from the
simulation with that observed shows no significant small-scale clustering
excess in the present sample; however, the four close pairs occur only in about
twenty percent of the simulated datasets (the precise significance of the
clustering is dependent upon the modeled biases). We conclude with some
impetuses and suggestions for future precise GRB redshift measurements.Comment: Published in the Astronomical Journal, June 2003: see
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003AJ....125.2865
Free vibrations of laminated composite elliptic plates
The free vibrations are studied of laminated anisotropic elliptic plates with clamped edges. The analytical formulation is based on a Mindlin-Reissner type plate theory with the effects of transverse shear deformation, rotary inertia, and bending-extensional coupling included. The frequencies and mode shapes are obtained by using the Rayleigh-Ritz technique in conjunction with Hamilton's principle. A computerized symbolic integration approach is used to develop analytic expressions for the stiffness and mass coefficients and is shown to be particularly useful in evaluating the derivatives of the eigenvalues with respect to certain geometric and material parameters. Numerical results are presented for the case of angle-ply composite plates with skew-symmetric lamination
Finite element modeling and analysis of tires
Predicting the response of tires under various loading conditions using finite element technology is addressed. Some of the recent advances in finite element technology which have high potential for application to tire modeling problems are reviewed. The analysis and modeling needs for tires are identified. Reduction methods for large-scale nonlinear analysis, with particular emphasis on treatment of combined loads, displacement-dependent and nonconservative loadings; development of simple and efficient mixed finite element models for shell analysis, identification of equivalent mixed and purely displacement models, and determination of the advantages of using mixed models; and effective computational models for large-rotation nonlinear problems, based on a total Lagrangian description of the deformation are included
A COMPARISON OF CAPITAL MEASURES IN U.S. AGRICULTURE
This study compares two panel data sets that measure capital input at the state-level in U.S. agriculture. Despite a number of similarities between the data sets, such as the composition of assets, aggregation procedures, and time frame, an examination of the final estimates of capital service flows reveals that they are drastically different for all 48 contiguous states. We examine the methods used to construct the capital series for each data set, consider some important differences in data sources and the types of data used to construct the capital measures, and outline the main assumptions concerning depreciation, service lives, interest rates, aggregation, and the scope of goods included in each of the data sets. The analysis indicates that an important statistic in the index of capital services in U.S. agriculture is the stock of buildings on farms. We conclude that the primary difference between the measures of capital input in the data sets relates to differences in estimates of the stock of buildings on farms. Given the apparent importance of the measure of the stock of buildings in the aggregate index of capital services in U.S. agriculture, more research is needed to ensure that the measure of the stock of buildings is accurate and meaningful. Once this has been accomplished there should be more agreement on an accurate measure of capital services in U.S. agriculture.Agricultural and Food Policy,
Three-loop HTLpt thermodynamics at finite temperature and chemical potential
In this proceedings we present a state-of-the-art method of calculating
thermodynamic potential at finite temperature and finite chemical potential,
using Hard Thermal Loop perturbation theory (HTLpt) up to
next-to-next-leading-order (NNLO). The resulting thermodynamic potential
enables us to evaluate different thermodynamic quantities including pressure
and various quark number susceptibilities (QNS). Comparison between our
analytic results for those thermodynamic quantities with the available lattice
data shows a good agreement.Comment: 5 pages, 6 figures, conference proceedings of XXI DAE-BRNS HEP
Symposium, IIT Guwahati, December 2014; to appear in 'Springer Proceedings in
Physics Series
Global Facilitation of Attended Features Is Obligatory and Restricts Divided Attention
Peer reviewedPublisher PD
Coreshine in L1506C - Evidence for a primitive big-grain component or indication for a turbulent core history?
The recently discovered coreshine effect can aid in exploring the core
properties and in probing the large grain population of the ISM. We discuss the
implications of the coreshine detected from the molecular cloud core L1506C in
the Taurus filament for the history of the core and the existence of a
primitive ISM component of large grains becoming visible in cores. The
coreshine surface brightness of L1506C is determined from IRAC Spitzer images
at 3.6 micron. We perform grain growth calculations to estimate the grain size
distribution in model cores similar in gas density, radius, and turbulent
velocity to L1506C. Scattered light intensities at 3.6 micron are calculated
for a variety of MRN and grain growth distributions to compare with the
observed coreshine. For a core with the overall physical properties of L1506C,
no detectable coreshine is predicted for an MRN size distribution. Extending
the distribution to grain radii of about 0.65 m allows to reproduce the
observed surface brightness level in scattered light. Assuming the properties
of L1506C to be preserved, models for the growth of grains in cores do not
yield sufficient scattered light to account for the coreshine within the
lifetime of the Taurus complex. Only increasing the core density and the
turbulence amplifies the scattered light intensity to a level consistent with
the observed coreshine brightness. The grains could be part of primitive
omni-present large grain population becoming visible in the densest part of the
ISM, could grow under the turbulent dense conditions of former cores, or in
L1506C itself. In the later case, L1506C must have passed through a period of
larger density and stronger turbulence. This would be consistent with the
surprisingly strong depletion usually attributed to high column densities, and
with the large-scale outward motion of the core envelope observed today.Comment: 6 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
- …