1,951 research outputs found
Educational Progress Across Immigrant Generations in California
Explores the disparities in levels of educational progress among different immigrant population groups in California. Examines factors that influence educational attainment among youth by race, ethnicity, and generation. Includes policy considerations
Superconductivity in Boron under pressure - why are the measured T's so low?
Using the full potential linear muffin-tin orbitals (FP-LMTO) method we
examine the pressure-dependence of superconductivity in the two metallic phases
of Boron: bct and fcc. Linear response calculations are carried out to examine
the phonon frequencies and electron-phonon coupling for various lattice
parameters, and superconducting transition temperatures are obtained from the
Eliashberg equation. In both bct and fcc phases the superconducting transition
temperature T is found to decrease with increasing pressure, due to
stiffening of phonons with an accompanying decrease in electron-phonon
coupling. This is in contrast to a recent report, where T is found to
increase with pressure. Even more drastic is the difference between the
measured T, in the range 4-11 K, and the calculated values for both bct and
fcc phases, in the range 60-100 K. The calculation reveals that the transition
from the fcc to bct phase, as a result of increasing volume or decreasing
pressure, is caused by the softening of the X-point transverse phonons. This
phonon softening also causes large electron-phonon coupling for high volumes in
the fcc phase, resulting in coupling constants in excess of 2.5 and T
nearing 100 K. We discuss possible causes as to why the experiment might have
revealed T's much lower than what is suggested by the present study. The
main assertion of this paper is that the possibility of high T, in excess
of 50 K, in high pressure pure metallic phases of boron cannot be ruled out,
thus substantiating the need for further experimental investigations of the
superconducting properties of high pressure pure phases of boron.Comment: 16 pages, 8 figures, 1 Tabl
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
An Exploratory Analysis of the Relationship between Student Earnings and Postsecondary Retention
Policy makers are becoming increasingly concerned about the high percentage of students who attend postsecondary education without completing a degree. Researchers have studied numerous potential determinants of retention behavior for postsecondary students, such as financial aid, socioeconomic status, academic preparedness, academic and social integration, and expected future wages. However, none of these studies considers students’ earnings while in school as a potential determinant of retention. Using an administrative data from postsecondary institutions matched with administrative earnings data from the state’s unemployment insurance department, our results indicate that student earnings are negatively correlated to student retention in Kentucky postsecondary institutions. Our preferred model, hazard, indicates that a percentage increase in earnings reduces time to stopout with a probability of 1.767%. Even after controlling for student intentions, students are more likely to stopout at the rate of 1.050%. Ability as measured by first-term GPA in KCTCS and credits earned in the first semester positively affects retention
A simple one-dimensional model of heat conduction which obeys Fourier's law
We present the computer simulation results of a chain of hard point particles
with alternating masses interacting on its extremes with two thermal baths at
different temperatures. We found that the system obeys Fourier's law at the
thermodynamic limit. This result is against the actual belief that one
dimensional systems with momentum conservative dynamics and nonzero pressure
have infinite thermal conductivity. It seems that thermal resistivity occurs in
our system due to a cooperative behavior in which light particles tend to
absorb much more energy than the heavier ones.Comment: 5 pages, 4 figures, to be published in PR
MELD remains the best predictor of mortality in outpatients with cirrhosis and severe ascites
BACKGROUND: The Model for Endstage Liver Disease (MELD) score may put patients with severe ascites at a disadvantage because they often have a poor quality of life and high mortality despite a favourable MELD score. AIM: To develop a model that is better than the MELD score at predicting 1-year mortality among patients with cirrhosis, severe ascites and MELD ≤18. METHODS: We used data from a randomised trial (SPARe-1) of patients with cirrhosis and severe ascites to develop a model to predict 1-year mortality. We used stepwise backward elimination and Cox regression to identify the strongest predictors. Performance was assessed with the C index and the Brier score. We examined performance in an external cohort of trial participants with cirrhosis and severe ascites (SPARe-2 participants). RESULTS: We included 308 patients with a 1-year mortality of 20.4%. The final prediction model (Severe Ascites Mortality score, "SAM score") included four variables: serum bilirubin, serum sodium, history of SBP (yes or no) and diabetes (yes or no). No indicators of quality of life were included. After correction for optimism bias, the SAM and MELD scores had nearly identical predictive ability. The external validation cohort included 149 patients whose 1-year mortality was 22.4%. The MELD score performed marginally better in this cohort, partly because the effects of SBP and diabetes on mortality were much smaller in this cohort. CONCLUSION: We did not succeed in developing a prediction model that was superior to the MELD score among patients with cirrhosis and severe ascites
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
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