3,248 research outputs found
The thermal conductivity reduction in HgTe/CdTe superlattices
The techniques used previously to calculate the three-fold thermal
conductivity reduction due to phonon dispersion in GaAs/AlAs superlattices
(SLs) are applied to HgTe/CdTe SLs. The reduction factor is approximately the
same, indicating that this SL may be applicable both as a photodetector and a
thermoelectric cooler.Comment: 5 pages, 2 figures; to be published in Journal of Applied Physic
Green Function Monte Carlo with Stochastic Reconfiguration
A new method for the stabilization of the sign problem in the Green Function
Monte Carlo technique is proposed. The method is devised for real lattice
Hamiltonians and is based on an iterative ''stochastic reconfiguration'' scheme
which introduces some bias but allows a stable simulation with constant sign.
The systematic reduction of this bias is in principle possible. The method is
applied to the frustrated J1-J2 Heisenberg model, and tested against exact
diagonalization data. Evidence of a finite spin gap for J2/J1 >~ 0.4 is found
in the thermodynamic limit.Comment: 13 pages, RevTeX + 3 encapsulated postscript figure
ADHD Differences on the Stanford Binet Intelligence Scale, Fifth Edition
Attention-deficit/hyperactivity disorder (ADHD) is a common psychiatric diagnosis in childhood that requires a level of attention or hyperactivity that falls short of the expected developmental level. Past research shows cognitive discrepancies in ADHD populations with verbal deficiencies observed primarily in tasks that require a combined auditory and verbal component. Working memory has been a long acknowledged deficit in persons with ADHD. This research examines cognitive differences among children with ADHD on working memory and other components of the Stanford Binet, 5th edition (SB5). Stanford Binet verbal and nonverbal working memory was hypothesized to be different for the ADHD sample compared to controls and between ADHD subtypes. Participants were gathered from the Stanford Binet standardization sample that were diagnosed with ADHD and matched with a group of normal controls. Data was analyzed using ANOVA followed by a cluster analysis of discrepancies found at subtest and testlet levels. Due to matching and statistical control, results showed no differences in FSIQ, VIQ, or PIQ between normals and those with ADHD, but those with ADHD took an average of 20 minutes longer to complete the SB5, consistently showed greater response variability, and exhibited significant differential item functioning for Vocabulary, Object Series/Matrices, and the routing scales. Deficits in working memory appear to account for these differences
Quantum simulations of the superfluid-insulator transition for two-dimensional, disordered, hard-core bosons
We introduce two novel quantum Monte Carlo methods and employ them to study
the superfluid-insulator transition in a two-dimensional system of hard-core
bosons. One of the methods is appropriate for zero temperature and is based
upon Green's function Monte Carlo; the other is a finite-temperature world-line
cluster algorithm. In each case we find that the dynamical exponent is
consistent with the theoretical prediction of by Fisher and co-workers.Comment: Revtex, 10 pages, 3 figures (postscript files attached at end,
separated by %%%%%% Fig # %%%%%, where # is 1-3). LA-UR-94-270
Center of mass and relative motion in time dependent density functional theory
It is shown that the exchange-correlation part of the action functional
in time-dependent density functional theory , where
is the time-dependent density, is invariant under the
transformation to an accelerated frame of reference , where is an arbitrary
function of time. This invariance implies that the exchange-correlation
potential in the Kohn-Sham equation transforms in the following manner:
. Some of the
approximate formulas that have been proposed for satisfy this exact
transformation property, others do not. Those which transform in the correct
manner automatically satisfy the ``harmonic potential theorem", i.e. the
separation of the center of mass motion for a system of interacting particles
in the presence of a harmonic external potential. A general method to generate
functionals which possess the correct symmetry is proposed
Density-functionals not based on the electron gas: Local-density approximation for a Luttinger liquid
By shifting the reference system for the local-density approximation (LDA)
from the electron gas to other model systems one obtains a new class of density
functionals, which by design account for the correlations present in the chosen
reference system. This strategy is illustrated by constructing an explicit LDA
for the one-dimensional Hubbard model. While the traditional {\it ab initio}
LDA is based on a Fermi liquid (the electron gas), this one is based on a
Luttinger liquid. First applications to inhomogeneous Hubbard models, including
one containing a localized impurity, are reported.Comment: 4 pages, 4 figures (final version, contains additional applications
and discussion; accepted by Phys. Rev. Lett.
Parent‐offspring inference in inbred populations
Genealogical relationships are fundamental components of genetic studies. However, it is often challenging to infer correct and complete pedigrees even when genome-wide information is available. For example, inbreeding can obscure genetic differences between individuals, making it difficult to even distinguish first-degree relatives such as parent-offspring from full siblings. Similarly, genotyping errors can interfere with the detection of genetic similarity between parents and their offspring. Inbreeding is common in natural, domesticated, and experimental populations and genotyping of these populations often has more errors than in human data sets, so efficient methods for building pedigrees under these conditions are necessary. Here, we present a new method for parent-offspring inference in inbred pedigrees called specific parent-offspring relationship estimation (spore). spore is vastly superior to existing pedigree-inference methods at detecting parent-offspring relationships, in particular when inbreeding is high or in the presence of genotyping errors, or both. spore therefore fills an important void in the arsenal of pedigree inference tools
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