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

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

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.

Fertility Timing, Wages, and Human Capital

Women who have first births relatively late in life earn higher wages. This paper offers an explanation of this fact based on a staple life-cycle model of human capital investment and timing of first birth. The model yields conditions (that are plausibly satisfied) under which late childbearers will tend to invest more heavily in human capital than early childbearers. The empirical analysis finds results consistent with the higher wages of late childbearers arising primarily through greater measurable human capital investment.

Minimum Wages and Poverty

The principal justification for minimum wage legislation resides in improving the economic condition of low-wage workers. Most previous analyses of the distributional effects of minimum wages have been confined to simulation exercises employing rather restrictive assumptions that guarantee the conclusion that an increase in the minimum wage reduces poverty. In contrast, we adopt a more flexible "reduced-form" approach that links increases in both federal and state minima to contemporaneous changes in poverty rates. For the period 1983-96, we find indication of a poverty-reducing effect of minimum wages among older junior-high dropouts and among teenagers. --

Evaluation of a hybrid, anisotropic, multilayered, quadrilateral finite element

A multilayered finite element with bending-extensional coupling is evaluated for: (1) buckling of general laminated plates; (2) thermal stresses of laminated plates cured at elevated temperatures; (3) displacements of a bimetallic beam; and (4) displacement and stresses of a single-cell box beam with warped cover panels. Also, displacements and stresses for flat and spherical orthotropic and anisotropic segments are compared with results from higher order plate and shell finite-element analyses

Intermittent Synchronization in a Pair of Coupled Chaotic Pendula

Numerical simulations have been carried out for a pair of unidirectionally coupled identical pendula under the action of a common external ac torque. Both the master pendulum and the slave pendulum were in chaotic states. The only form of persistent locking appeared to be a computational artifact; otherwise the synchronization of slave to master was found to be intermittent

The Effects of Technological Change on Earnings and Income Inequality inthe United States

This paper explores the relationship between technological change and inequality in the U.S. since the late 1960's. The analysis focuses primarily on studying patterns and trends in the dispersion of various distributions of earnings and income during this recent period of rapid technological progress. We review relevant literature and perform several empirical analyses using microdata from the March Current Population Surveys from 1968 to 1986. Our main findings are that there is little empirical evidence that earnings inequality, measured across individual workers, has increased since the late 1960's, and even less evidence to support the hypothesis that any changes that have occurred have resulted from the effect of technological change on the demand for labor. However, we do find evidence of an increase since the late 1960's in the inequality of total family income, measured across families. Moreover, much of the increase appears to be due to changes in family composition and labor supply behavior, suggesting that the main effects of recent technological change on inequality have been supply-side in nature.

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.