Robust stability of linear systems: Some computational considerations

The cases of both additive and multiplicative perturbations were discussed and a number of relationships between the two cases were given. A number of computational aspects of the theory were also discussed, including a proposed new method for evaluating general transfer or frequency response matrices. The new method is numerically stable and efficient, requiring only operations to update for new values of the frequency parameter

Elastic orifice automatically regulates gas bearings

Elastic, pressure-sensitive orifice is used to automatically regulate the rate of gas flow into bearings under varying loads. Formed of a molded elastomer, theses orifices increase the stability of gas bearings

Slit regulated gas journal bearing Patent

Slit regulated gas journal bearin

Recirculation of a Two-phase Fluid by Thermal and Capillary Pumping

Closed-cycle gas supply system for gas bearings using thermal and capillary pumpin

After the Epidemic: Recent Trends in Youth Violence in the United States

The epidemic of youth violence in the United States peaked in 1993 and has been followed by a rapid, sustained drop. In parallel with our earlier treatment (Cook and Laub 1998), we assess two types of explanation for this drop -- those that focus on 'cohort' effects (including the effects of abortion legalization) and those that focus on 'period' effects (including the effects of the changing crack-cocaine trade). Once again we are able to reject the cohort-type explanations, yet also find contradictions with an account based on the dynamics of crack markets. The 'way out' of this epidemic has not been the same as the 'way in.' The relative importance in homicide of youths, racial minorities, and guns, all of which increased greatly during the epidemic, has remained high during the drop. Arrest patterns tell a somewhat different story, in part because of changing police practice with respect to aggravated assault. Finally, we demonstrate that the rise and fall of youth violence has been narrowly confined with respect to race, sex, and age, but not geography. Given the volatility in the rates of juvenile violence, forecasting rates is a risky business indeed. Effectively narrowing the range of plausible explanations for the recent ups and downs may require a long time horizon, consideration of a broader array of problem behaviors, and comparisons with trends in other countries.

Monte Carlo Estimation of the Density of the Sum of Dependent Random Variables

We study an unbiased estimator for the density of a sum of random variables that are simulated from a computer model. A numerical study on examples with copula dependence is conducted where the proposed estimator performs favourably in terms of variance compared to other unbiased estimators. We provide applications and extensions to the estimation of marginal densities in Bayesian statistics and to the estimation of the density of sums of random variables under Gaussian copula dependence

Aerodynamic characteristics of two-dimensional wing configurations at angles of attack near -90 deg

Wind tunnel tests were conducted to determine the drag of two-dimensional wing sections operating in a near-vertical flow condition. Various leading- and trialing-edge configurations, including plain flaps of 25, 30, and 35% chord were tested at angles of attack from -75 to -105 deg. Reynolds numbers examined ranged from approximately 0.6 x 10 to the 6th power to 1.4 x 10 to the 6th power. The data were obtained using a wind tunnel force and moment balance system and arrays of chordwise pressure orifices. The results showed that significant reductions in drag, beyond what would be expected by virtue of the decreased frontal area, were obtainable with geometries that delayed flow separation. Rapid changes in drag with angle of attack were noted for many configurations. The results, however, were fairly insensitive to Reynolds number variations. Drag values computed from the pressure data generally agreed with the force data within 2%

Attitude control for spacecraft Patent

Attitude control device for space vehicle