Power transistor switching characterization

The switching properties of power transistors are investigated. The devices studied were housed in IO-3 cases and were of an n(+)-p-n(-)-n(+) vertical dopant structure. The effects of the magnitude of the reverse-base current and temperature on the reverse-bias second breakdown characteristics are discussed. Brief discussions of device degradation due to second breakdown and of a constant voltage turn-off circuit are included. A description of a vacuum tube voltage clamp circuit which reduces clamped collector voltage overshoot is given

Omitted-Ability Bias and the Increase in the Return to Schooling

Over the 1980s there were sharp increases in the return to schooling estimated with conventional wage regressions. We use both a signaling model and a human capital model to explore how the relationship between ability and schooling could have changed over this period in ways Chat would have increased the schooling coefficient in these regressions. Our empirical results reject the hypothesis that an increase in the upward bias of the schooling coefficient, due to a change in the relationship between ability and schooling, underlies the observed increase in the return to education over the 1980s. We also find that the increase in the return to education has occurred largely for workers with relatively high levels of academic ability.

Inverting Chaos: Extracting System Parameters from Experimental Data

Given a set of experimental or numerical chaotic data and a set of model differential equations with several parameters, is it possible to determine the numerical values for these parameters using a least-squares approach, and thereby to test the model against the data? We explore this question (a) with simulated data from model equations for the Rossler, Lorenz, and pendulum attractors, and (b) with experimental data produced by a physical chaotic pendulum. For the systems considered in this paper, the least-squares approach provides values of model parameters that agree well with values obtained in other ways, even in the presence of modest amounts of added noise. For experimental data, the “fitted” and experimental attractors are found to have the same correlation dimension and the same positive Lyapunov exponent

Changes in the Structure of Family Income Inequality in the United States and Other Industrial Nationa During the 1980s

We examine the detailed structure of family income inequality in the United States, Canada, and Australia at various points during the 1980s. In each of these countries we find that income inequality increased among married couple families and that the increases are closely associated with increases in the inequality of husbands' earnings. However, only in the United States is the increased inequality of husbands' earnings also associated with an increase in education-earnings differentials. In addition, increased earnings inequality is associated with increases in both the variance of wages and the variance of labor supply in the United States and Canada, but only with an increase in the variance of labor supply in Australia. Evidence of an increase in married-couple income inequality is found for France and the United Kingdom, but not for Sweden or the Netherlands. For married couple families in Canada, Sweden, the United Kingdom, and the United States, we find that increased inequality of family income is closely associated with an increased correlation between husbands' and wives' earnings. A more detailed examination of this correlation in Canada and the United States suggests that the increase in this correlation cannot be explained by an increase in the similarity of husbands' and wives' observable labor market characteristics in either country. Rather, it is explained partly by changes in the way those characteristics translate into labor market outcomes and, more important, by changes in the interspousal correlation between unobservable factors that influence labor market outcomes.

Intermittent Synchronization of Resistively Coupled Chaotic Josephson Junctions

Numerical simulations have been used to investigate the dynamics of a pair of resistively linked Josephson junctions with ac bias. For suitable choices of parameters, the chaotic states of the two junctions become intermittently synchronized. Intervals of synchronization are interleaved between bursts of desynchronized activity. The distributions of these laminar times and their dependence on the coupling strength are determined. The role of phase winding in the definition of synchronization intervals is considered

Superconductivity near lattice instability: the case of NbC1−x_{1-x}Nx_x and NbN

Using density functional theory within the local density approximation we report a study of the electron-phonon coupling in NbC$_{1-x}$N$_x$ and NbN crystals in the rocksalt structure. The Fermi surface of these systems exhibits important nesting. The associated Kohn anomaly greatly increases the electron-phonon coupling and induces a structural instability when the electronic density of states reaches a critical value. Our results reproduce the observed rise in $T_{c}$ from 11.2 K to 17.3 K as the nitrogen doping is increased in NbC$_{1-x}$N$_x$. To further understand the contribution of the structural instability to the rise of the superconducting temperature, we develop a model for the Eliashberg spectral function in which the effect of the unstable phonons is set apart. We show that this model together with the McMillan formula can reproduce the increase of $T_{c}$ near the structural phase transition.Comment: 6 pages, 5 figures, submission PR

Tensile testing apparatus

An improved mechanical extensometer is described for use with a constant load creep test machine. The dead weight of the extensometer is counterbalanced by two pairs of weights connected through a pulley system and to rod extension and leading into the furnace where the test sample is undergoing elevated temperature (above 500 F.) tensile testing. Novel gripper surfaces, conical tip and flat surface are provided in each sampling engaging platens to reduce the grip pressure normally required for attachment of the extensometer to the specimen and reduce initial specimen bending normally associated with foil-gage metal testing

"Changes in Earnings Differentials in the 1980s: Concordance, Convergence, Causes, and Consequence"

This paper analyzes changes in U.S. earnings differentials in the 1980s between race, gender, age, and schooling groups. There are four main sets of results to report. First, the economic position of less-educated workers declined relative to the more-educated among almost all demographic groups. Education-earnings differentials clearly rose for whites, but less clearly for blacks, while employment rate differences associated with education increased more for blacks than for whites. Second, much of the change in education-earnings differentials for specific groups is attributable to measurable economic factors: to changes in the occupational or industrial structure of employment; to changes in average wages within industries; to the fall in the real value of the minimum wage and the fall in union density; and to changes in the relative growth rate of more educated workers. Third, the earnings and employment position of white females, and to a lesser extent of black females, converged to that of white males in the 1980s, across education groups. At the same time, the economic position of more-educated black males appears to have worsened relative to their white-male counterparts. Fourth, there has been a sizable college-enrollment response to the rising relative wages of college graduates. This response suggests that education-earnings differentials may stop increasing, or even start to decline, in the near future.

NASA EM Followup of LIGO-Virgo Candidate Events

We present a strategy for a follow-up of LIGO-Virgo candidate events using offline survey data from several NASA high-energy photon instruments aboard RXTE, Swift, and Fermi. Time and sky-location information provided by the GW trigger allows for a targeted search for prompt and afterglow EM signals. In doing so, we expect to be sensitive to signals which are too weak to be publicly reported as astrophysical EM events