Employer Demand for Welfare Recipients by Race

This paper uses new survey data on employers in four large metropolitan areas to examine the determinants of employer demand for welfare recipients. The results suggest a high level of demand for welfare recipients, though such demand appears fairly sensitive to business cycle conditions. A broad range of factors, including skill needs and industry, affect the prospective demand for welfare recipients among employers, while other characteristics that affect the relative supply of welfare recipients to these employers (such as location and employer use of local agencies or welfare-to-work programs) influence the extent to which such demand is realized in actual hiring. Moreover, the conditional demand for black (and to a lesser extent Hispanic) welfare recipients lags behind their representation in the welfare population and seems to be more heavily affected by employers’ location and indicators of preferences than by their skill needs or overall hiring activity. Thus, a variety of factors on the demand side of the labor market continue to limit the employment options of welfare recipients, especially those who are minorities.

Approximation of the scattering amplitude

The simultaneous solution of Ax=b and ATy=g is required in a number of situations. Darmofal and Lu have proposed a method based on the Quasi-Minimal residual algorithm (QMR). We will introduce a technique for the same purpose based on the LSQR method and show how its performance can be improved when using the Generalized LSQR method. We further show how preconditioners can be introduced to enhance the speed of convergence and discuss different preconditioners that can be used. The scattering amplitude gTx, a widely used quantity in signal processing for example, has a close connection to the above problem since x represents the solution of the forward problem and g is the right hand side of the adjoint system. We show how this quantity can be efficiently approximated using Gauss quadrature and introduce a Block-Lanczos process that approximates the scattering amplitude and which can also be used with preconditioners

Correlation-induced corrections to the band structure of boron nitride: a wave-function-based approach

We present a systematic study of the correlation-induced corrections to the electronic band structure of zinc-blende BN. Our investigation employs an ab initio wave-function-based local Hamiltonian formalism which offers a rigorous approach to the calculation of the polarization and local charge redistribution effects around an extra electron or hole placed into the conduction or valence bands of semiconducting and insulating materials. Moreover, electron correlations beyond relaxation and polarization can be readily incorporated. The electron correlation treatment is performed on finite clusters. In conducting our study, we make use of localized Wannier functions and embedding potentials derived explicitly from prior periodic Hartree-Fock calculations. The on-site and nearest-neighbor charge relaxation bring corrections of several eV to the Hartree-Fock band gap. Additional corrections are caused by long-range polarization effects. In contrast, the dispersion of the Hartree-Fock bands is marginally affected by electron correlations. Our final result for the fundamental gap of zinc-blende BN compares well with that derived from soft x-ray experiments at the B and N K-edges.Comment: 18 pages, 8 figures; the following article has been submitted to J. Chem. Phy

Optical waveguiding in proton-implanted GaAs

We have produced optical waveguides in n-type GaAs by implantation with 300-keV protons. The guiding is shown to be due to the elimination of charge carriers from the implanted region. Annealing of the waveguide leads to very large reductions in the 1.15-µ guided-wave absorption

Are Suburban Firms More Likely to Discriminate Against African Americans?

This paper presents a test of the hypothesis that employers in suburban locations are more likely to discriminate against African Americans than are employers located in central cities. Using a difference-in-difference framework, we compare central-city/suburban differences in racial hiring outcomes for firms where a white person is in charge of hiring (white employers, for short) to similar geographic differences in outcomes for firms where a black person is in charge of hiring (black employers). We find that both suburban black and white employers hire fewer blacks than their central-city counterparts. Moreover, the central-city/suburban hiring gap among black employers is as large as, or larger than, that of white employers. Suburban black employers, however, receive many more applications from blacks and hire more blacks than do white firms in either location.

Within Cities and Suburbs: Racial Residential Concentration and the Spatial Distribution of Employment Opportunities across Submetropolitan Areas

In this paper, we examine and compare the spatial distributions of jobs and people across submetropolitan areas using data on firms from the Multi-City Study of Urban Inequality and data on people from the U.S. Bureau of the Census. The results indicate that less-educated people and those on public assistance mostly reside in areas with high minority populations. Low-skill jobs are quite scarce in these areas, while the availability of such jobs relative to less-educated people in heavily white suburban areas is high. Large fractions of the low-skill jobs in these metropolitan areas are not accessible by public transit. Furthermore, there is significant variation within both central cities and suburbs in the ethnic composition of residents and in the availability of low-skill jobs. The ability of various minority groups to gain employment in each area depends heavily on the ethnic composition of the particular area.

Ion beam micromachining of integrated optics components

Thin film integrated optics components such as light guides, modulators, directional couplers, and polarizers demand high quality edge smoothness and high resolution pattern formation in dimensions down to submicrometer size. Fabrication techniques combining holographic and scanning electron beam lithography with ion beam micromachining have produced planar phase gratings with intervals as small as 2800 Å, guiding channel couplers in GaAs, and also wire- grid polarizers for 10.6-µm radiation

A Bramble-Pasciak-like method with applications in optimization

Saddle-point systems arise in many applications areas, in fact in any situation where an extremum principle arises with constraints. The Stokes problem describing slow viscous flow of an incompressible fluid is a classic example coming from partial differential equations and in the area of Optimization such problems are ubiquitous.\ud In this manuscript we show how new approaches for the solution of saddle-point systems arising in Optimization can be derived from the Bramble-Pasciak Conjugate Gradient approach widely used in PDEs and more recent generalizations thereof. In particular we derive a class of new solution methods based on the use of Preconditioned Conjugate Gradients in non-standard inner products and demonstrate how these can be understood through more standard machinery. We show connections to Constraint Preconditioning and give the results of numerical computations on a number of standard Optimization test examples

Properties of short-range and long-range correlation energy density functionals from electron-electron coalescence

The combination of density functional theory with other approaches to the many-electron problem through the separation of the electron-electron interaction into a short-range and a long-range contribution is a promising method, which is raising more and more interest in recent years. In this work some properties of the corresponding correlation energy functionals are derived by studying the electron-electron coalescence condition for a modified (long-range-only) interaction. A general relation for the on-top (zero electron-electron distance) pair density is derived, and its usefulness is discussed with some examples. For the special case of the uniform electron gas, a simple parameterization of the on-top pair density for a long-range only interaction is presented and supported by calculations within the ``extended Overhauser model''. The results of this work can be used to build self-interaction corrected short-range correlation energy functionals.Comment: revised version, to appear in Phys. Rev.

Ground state properties of heavy alkali halides

We extend previous work on alkali halides by calculations for the heavy-atom species RbF, RbCl, LiBr, NaBr, KBr, RbBr, LiI, NaI, KI, and RbI. Relativistic effects are included by means of energy-consistent pseudopotentials, correlations are treated at the coupled-cluster level. A striking deficiency of the Hartree-Fock approach are lattice constants deviating by up to 7.5 % from experimental values which is reduced to a maximum error of 2.4 % by taking into account electron correlation. Besides, we provide ab-initio data for in-crystal polarizabilities and van der Waals coefficients.Comment: accepted by Phys. Rev.