2,597 research outputs found
Electronic Structure of the Chevrel-Phase Compounds SnMoSe: Photoemission Spectroscopy and Band-structure Calculations
We have studied the electronic structure of two Chevrel-phase compounds,
MoSe and SnMoSe, by combining photoemission
spectroscopy and band-structure calculations. Core-level spectra taken with
x-ray photoemission spectroscopy show systematic core-level shifts, which do
not obey a simple rigid-band model. The inverse photoemission spectra imply the
existence of an energy gap located eV above the Fermi level, which is
a characteristic feature of the electronic structure of the Chevrel compounds.
Quantitative comparison between the photoemission spectra and the
band-structure calculations have been made. While good agreement between theory
and experiment in the wide energy range was obtained as already reported in
previous studies, we found that the high density of states near the Fermi level
predicted theoretically due to the Van Hove singularity is considerably reduced
in the experimental spectra taken with higher energy resolution than in the
previous reports. Possible origins are proposed to explain this observation.Comment: 8 pages, 5 figure
Estimating the Social Value of Higher Education: Willingness to Pay for Community and Technical Colleges
Much is known about private returns to education in the form of higher earnings. Less is known about social value, over and above the private, market value. Associations between education and socially-desirable outcomes are strong, but disentangling the effect of education from other causal factors is challenging. The purpose of this paper is to estimate the social value of one form of higher education. We elicit willingness to pay for the Kentucky Community and Technical College System directly through a stated-preferences survey and compare our estimate of total social value to our estimates of private value in the form of increased earnings. Our earnings estimates are based on two distinct data sets, one administrative and one from the U.S. Census. The difference between the total social value and the increase in earnings is our measure of the education externality. Our work differs from previous research by eliciting values directly in a way that yields a total value including any external benefits and by focusing on education at the community college level. Our preferred estimate indicates the social value of expanding the system substantially exceeds private value by approximately 50 percent.social returns, education externalities, contingent valuation, earnings
Genetic ancestry of participants in the National Children's Study.
BackgroundThe National Children's Study (NCS) is a prospective epidemiological study in the USA tasked with identifying a nationally representative sample of 100,000 children, and following them from their gestation until they are 21 years of age. The objective of the study is to measure environmental and genetic influences on growth, development, and health. Determination of the ancestry of these NCS participants is important for assessing the diversity of study participants and for examining the effect of ancestry on various health outcomes.ResultsWe estimated the genetic ancestry of a convenience sample of 641 parents enrolled at the 7 original NCS Vanguard sites, by analyzing 30,000 markers on exome arrays, using the 1000 Genomes Project superpopulations as reference populations, and compared this with the measures of self-reported ethnicity and race. For 99% of the individuals, self-reported ethnicity and race agreed with the predicted superpopulation. NCS individuals self-reporting as Asian had genetic ancestry of either South Asian or East Asian groups, while those reporting as either Hispanic White or Hispanic Other had similar genetic ancestry. Of the 33 individuals who self-reported as Multiracial or Non-Hispanic Other, 33% matched the South Asian or East Asian groups, while these groups represented only 4.4% of the other reported categories.ConclusionsOur data suggest that self-reported ethnicity and race have some limitations in accurately capturing Hispanic and South Asian populations. Overall, however, our data indicate that despite the complexity of the US population, individuals know their ancestral origins, and that self-reported ethnicity and race is a reliable indicator of genetic ancestry
Consanguinity and rare mutations outside of MCCC genes underlie nonspecific phenotypes of MCCD.
Purpose3-Methylcrotonyl-CoA carboxylase deficiency (MCCD) is an autosomal recessive disorder of leucine catabolism that has a highly variable clinical phenotype, ranging from acute metabolic acidosis to nonspecific symptoms such as developmental delay, failure to thrive, hemiparesis, muscular hypotonia, and multiple sclerosis. Implementation of newborn screening for MCCD has resulted in broadening the range of phenotypic expression to include asymptomatic adults. The purpose of this study was to identify factors underlying the varying phenotypes of MCCD.MethodsWe performed exome sequencing on DNA from 33 cases and 108 healthy controls. We examined these data for associations between either MCC mutational status, genetic ancestry, or consanguinity and the absence or presence/specificity of clinical symptoms in MCCD cases.ResultsWe determined that individuals with nonspecific clinical phenotypes are highly inbred compared with cases that are asymptomatic and healthy controls. For 5 of these 10 individuals, we discovered a homozygous damaging mutation in a disease gene that is likely to underlie their nonspecific clinical phenotypes previously attributed to MCCD.ConclusionOur study shows that nonspecific phenotypes attributed to MCCD are associated with consanguinity and are likely not due to mutations in the MCC enzyme but result from rare homozygous mutations in other disease genes.Genet Med 17 8, 660-667
Reply to comment on "Simple one-dimensional model of heat conduction which obeys Fourier's law"
In this reply we answer the comment by A. Dhar (cond-mat/0203077) on our
Letter "Simple one dimensional model of heat conduction which obeys Fourier's
law" (Phys. Rev. Lett. 86, 5486 (2001), cond-mat/0104453)Comment: 1 pag., 1 fi
Anisotropies in insulating LaSrCuO: angular resolved photoemission and optical absorption
Due to the orthorhombic distortion of the lattice, the electronic hopping
integrals along the and diagonals, the orthorhombic directions, are
slightly different. We calculate their difference in the LDA and find
meV. We argue that electron
correlations in the insulating phase of LaSrCuO, i. e. at
doping dramatically enhance the -splitting between the - and -hole valleys. In particular, we predict
that the intensity of both angle-resolved photoemission and of optical
absorption is very different for the and nodal points
Combined density-functional and dynamical cluster quantum Monte Carlo calculations for three-band Hubbard models for hole-doped cuprate superconductors
Using a combined local density functional theory (LDA-DFT) and quantum Monte
Carlo (QMC) dynamic cluster approximation approach, the parameter dependence of
the superconducting transition temperature Tc of several single-layer
hole-doped cuprate superconductors with experimentally very different Tcmax is
investigated. The parameters of two different three-band Hubbard models are
obtained using the LDA and the downfolding Nth-order muffin-tin orbital
technique with N=0 and 1 respectively. QMC calculations on 4-site clusters show
that the d-wave transition temperature Tc depends sensitively on the
parameters. While the N=1 MTO basis set which reproduces all three
bands leads to a d-wave transition, the N=0 set which merely reproduces the LDA
Fermi surface and velocities does not
The challenges of diagnosing osteoporosis and the limitations of currently available tools
Abstract
Dual-energy X-ray absorptiometry (DXA) was the first imaging tool widely utilized by clinicians to assess fracture risk, especially in postmenopausal women. The development of DXA nearly coincided with the availability of effective osteoporosis medications. Although osteoporosis in adults is diagnosed based on a T-score equal to or below ââ2.5 SD, most individuals who sustain fragility fractures are above this arbitrary cutoff. This incongruity poses a challenge to clinicians to identify patients who may benefit from osteoporosis treatments. DXA scanners generate 2 dimensional images of complex 3 dimensional structures, and report bone density as the quotient of the bone mineral content divided by the bone area. An obvious pitfall of this method is that a larger bone will convey superior strength, but may in fact have the same bone density as a smaller bone. Other imaging modalities are available such as peripheral quantitative CT, but are largely research tools. Current osteoporosis medications increase bone density and reduce fracture risk but the mechanisms of these actions vary. Anti-resorptive medications (bisphosphonates and denosumab) primarily increase endocortical bone by bolstering mineralization of endosteal resorption pits and thereby increase cortical thickness and reduce cortical porosity. Anabolic medications (teriparatide and abaloparatide) increase the periosteal and endosteal perimeters without large changes in cortical thickness resulting in a larger more structurally sound bone. Because of the differences in the mechanisms of the various drugs, there are likely benefits of selecting a treatment based on a patientâs unique bone structure and pattern of bone loss. This review retreats to basic principles in order to advance clinical management of fragility fractures by examining how skeletal biomechanics, size, shape, and ultra-structural properties are the ultimate predictors of bone strength. Accurate measurement of these skeletal parameters through the development of better imaging scanners is critical to advancing fracture risk assessment and informing clinicians on the best treatment strategy. With this information, a âtreat to targetâ approach could be employed to tailor current and future therapies to each patientâs unique skeletal characteristics.https://deepblue.lib.umich.edu/bitstream/2027.42/143867/1/40842_2018_Article_62.pd
Heat Conduction and Entropy Production in a One-Dimensional Hard-Particle Gas
We present large scale simulations for a one-dimensional chain of hard-point
particles with alternating masses. We correct several claims in the recent
literature based on much smaller simulations. Both for boundary conditions with
two heat baths at different temperatures at both ends and from heat current
autocorrelations in equilibrium we find heat conductivities kappa to diverge
with the number N of particles. These depended very strongly on the mass
ratios, and extrapolation to N -> infty resp. t -> infty is difficult due to
very large finite-size and finite-time corrections. Nevertheless, our data seem
compatible with a universal power law kappa ~ N^alpha with alpha approx 0.33.
This suggests a relation to the Kardar-Parisi-Zhang model. We finally show that
the hard-point gas with periodic boundary conditions is not chaotic in the
usual sense and discuss why the system, when kept out of equilibrium, leads
nevertheless to energy dissipation and entropy production.Comment: 4 pages (incl. 5 figures), RevTe
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