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 Tc_c'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$_c$ 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$_c$ is found to increase with pressure. Even more drastic is the difference between the measured T$_c$, 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$_c$ nearing 100 K. We discuss possible causes as to why the experiment might have revealed T$_c$'s much lower than what is suggested by the present study. The main assertion of this paper is that the possibility of high T$_c$, 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 La2−x_{2-x}Srx_xCuO4_4: angular resolved photoemission and optical absorption

Due to the orthorhombic distortion of the lattice, the electronic hopping integrals along the $a$ and $b$ diagonals, the orthorhombic directions, are slightly different. We calculate their difference in the LDA and find $t_{a}^{\prime}-t_{b}^{\prime}\approx 8$meV. We argue that electron correlations in the insulating phase of La$_{2-x}$Sr$_{x}$CuO$_{4}$, i. e. at doping $x\leq 0.055,$ dramatically enhance the $(t_{a}^{\prime}-t_{b}^{\prime})$-splitting between the $a$- and $b$-hole valleys. In particular, we predict that the intensity of both angle-resolved photoemission and of optical absorption is very different for the $a$ and $b$ 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 $pd\sigma$ bands leads to a d-wave transition, the N=0 set which merely reproduces the LDA Fermi surface and velocities does not