A QM/MM equation-of-motion coupled-cluster approach for predicting semiconductor color-center structure and emission frequencies

Valence excitation spectra are computed for all deep-center silicon-vacancy defect types in 3C, 4H, and 6H silicon carbide (SiC) and comparisons are made with literature photoluminescence measurements. Nuclear geometries surrounding the defect centers are optimized within a Gaussian basis-set framework using many-body perturbation theory or density functional theory (DFT) methods, with computational expenses minimized by a QM/MM technique called SIMOMM. Vertical excitation energies are subsequently obtained by applying excitation-energy, electron-attached, and ionized equation-of-motion coupled-cluster (EOMCC) methods, where appropriate, as well as time-dependent (TD) DFT, to small models including only a few atoms adjacent to the defect center. We consider the relative quality of various EOMCC and TD-DFT methods for (i) energy-ordering potential ground states differing incrementally in charge and multiplicity, (ii) accurately reproducing experimentally measured photoluminescence peaks, and (iii) energy-ordering defects of different types occurring within a given polytype. The extensibility of this approach to transition-metal defects is also tested by applying it to silicon-substitutional chromium defects in SiC and comparing with measurements. It is demonstrated that, when used in conjunction with SIMOMM-optimized geometries, EOMCC-based methods can provide a reliable prediction of the ground-state charge and multiplicity, while also giving a quantitative description of the photoluminescence spectra, accurate to within 0.1 eV of measurement in all cases considered.Comment: 13 pages, 4 figures, 6 tables, 5 equations, 100 reference

Integrating Research of Three Pillar Institutions 2008-2012

The Wittgenstein Centre is a collaboration among the World Population Program of the International Institute for Applied Systems Analysis (IIASA), the Vienna Institute of Demography of the Austrian Academy of Sciences (VID/OeAW), the Demography Group and the Research Institute on Human Capital and Development of the Vienna University of Economics and Business (WU). The Centre combines the partners' strengths in the fields of demography, human capital formation, and analysis of the returns to education. It builds on a highly successful collaboration that has already generated significant scientific advances. "Human capital" refers to the human resource base in terms of the number of people and their changing structure by age, gender, location, education, health status, cognitive skills and other relevant characteristics. Our intent is to provide a sound scientific foundation for decision-making at various levels. This 5-year report introduces these efforts by presenting achievements and results as well as core scientists and their focus

On the Concentration of Childbearing in China, 1955-1981

Based on period parity progression ratios derived from the one-per-thousand fertility survey by Feeney and Yu (1987) completed parity distributions implied by period fertility are calculated for the years 1959-1981. Concentration analysis of these distributions using Lorenz curves and the proportion of women that had half the children was almost invariant over time (around 33%-35%) despite the dramatic fertility decline since the mid 1960s. This is in sharp contrast to a great number of other countries where the fertility transition has been accompanied by sharply increasing concentration. The very egalitarian way in which fertility declined in the Chinese population seems to be a unique case in world history

Dynamics of strong and radiative decays of Ds-mesons in the hadrogenesis conjecture

The positive parity scalar D$_{s0}^*$(2317) and axial-vector D$_{s1}^*$(2460) charmed strange mesons are generated by coupled-channel dynamics through the s-wave scattering of Goldstone bosons off the pseudoscalar and vector D(D$_s$)-meson ground states. The specific masses of these states are obtained as a consequence of the attraction arising from the Weinberg-Tomozawa interaction in the chiral Lagrangian. Chiral corrections to order Q$_\chi^2$ are calculated and found to be small. The D$_{s0}^*$(2317) and D$_{s1}^*$(2460) mesons decay either strongly into the isospin-violating $\pi^0$D$_s$ and $\pi^0$D$_s^*$ channels or electromagnetically. We show that the $\pi^0$-$\eta$ and (K$^0$D$^+$-K$^+$D$^0$) mixings act constructively to generate strong widths of the order of 140 keV and emphasize the sensitivity of this value to the $KD$ component of the states. The one-loop contribution to the radiative decay amplitudes of scalar and axial-vector states is calculated using the electromagnetic Lagrangian to chiral order Q$_\chi^2$. We show the importance of taking into account processes involving light vector mesons explicitly in the dynamics of electromagnetic decays. The radiative width are sensitive to both $\eta D_s$ and $KD$ components, hence providing information complementary to the strong widths on the positive parity $D_s$-meson structure.Comment: 4 pages, Invited Contribution to QNP09, Beijing, September 21-26, 200

Scenario Analysis in Population Projection

This paper focuses on the approach to population projections that has been labeled scenario analysis. It looks at the original meaning of "scenario" and then discusses its appropriate usage in population projections with respect to several criteria, especially that of consistency of assumptions. Next, the paper describes the practical considerations and actual experiences in an IIASA effort to define alternative scenarios for 12 world regions to the year 2030 through discussions of a group of experts. Because of differential expertise and an uneasiness of experts to numerically define alternative scenarios, an interactive group process was chosen rather than a larger Delphi. On practical and theoretical grounds it became apparent that individual responsibility and judgement of the authors cannot be replaced by an anonymous "objective" entity making the assumptions. Finally, the paper discusses what kind of alternative variants (or scenarios) the users can handle and do expect. It is exemplified through the specific question whether the UN should change its current practice of making population projections. Pro and contra arguments are listed concerning the proposal to include alternative mortality assumptions into the three main variants that are widely publicized