Nearly simultaneous optical, ultraviolet, and x ray observations of three PG quasars

Nearly simultaneous optical, ultraviolet, and x ray observations of three low redshift quasars are presented. The EXOSAT x ray spectra span the range of observed spectral indices for quasars from the canonical 0.7 energy index typical of Seyfert galaxies for PG0923+129 (Mrk 705) to the steep spectral indices frequently seen in higher luminosity quasars with an index of 1.58 for PG0844+349 (Ton 951). None of the quasars exhibits any evidence for a soft x ray excess. This is consistent with accretion disk spectra fit to the IR through UV continua of the quasars -- the best fitting disk spectra peak at approximately 6 eV with black hole masses in the range 5 x 10(exp 7) to 1 x 10(exp 9) solar mass and mass accretion rates of approximately 0.1 times the Eddington-limited rate. These rather soft disk spectra are also compatible with the observed optical and ultraviolet line ratios

Nonsingular stress and strain fields of dislocations and disclinations in first strain gradient elasticity

The aim of this paper is to study the elastic stress and strain fields of dislocations and disclinations in the framework of Mindlin's gradient elasticity. We consider simple but rigorous versions of Mindlin's first gradient elasticity with one material length (gradient coefficient). Using the stress function method, we find modified stress functions for all six types of Volterra defects (dislocations and disclinations) situated in an isotropic and infinitely extended medium. By means of these stress functions, we obtain exact analytical solutions for the stress and strain fields of dislocations and disclinations. An advantage of these solutions for the elastic strain and stress is that they have no singularities at the defect line. They are finite and have maxima or minima in the defect core region. The stresses and strains are either zero or have a finite maximum value at the defect line. The maximum value of stresses may serve as a measure of the critical stress level when fracture and failure may occur. Thus, both the stress and elastic strain singularities are removed in such a simple gradient theory. In addition, we give the relation to the nonlocal stresses in Eringen's nonlocal elasticity for the nonsingular stresses.Comment: 24 pages, 6 figures, to appear in: International Journal of Engineering Scienc

Measuring the U.S. Health Care System: A Cross-National Comparison

Compares U.S. healthcare data including hospital beds and physicians, hospital and physician visits, healthcare spending, and high-tech procedures per capita, as well as life expectancy with those of twenty-nine other industrialized countries

Workforce Reorganization and the Worker

In this paper we study the joint decision process of changing the structure of jobs and laying off individual workers in a firm that downsizes its workforce. A hierarchical decision model is proposed and estimated using personnel data from a firm in demise comparing the characteristics of the individual workers and the structure of the firm's labour force before and after its reorganization. Our results show that workers in jobs in the top levels of each skill group's hierarchy are better protected against downsizing due to larger productivity shocks and larger firing costs.hierarchies, restructuring, control span, job displacement