Statistical mechanics of strong and weak point vortices in a cylinder

The motion of one-hundred point vortices in a circular cylinder is simulated numerically and compared with theoretical predictions based on statistical mechanics. The novel aspect considered here is that the vortices have greatly different circulation strengths. As envisaged by Onsager, such an arrangement leads to a substantial amplification of statistical trends such as the preferred clustering of the strong vortices in either same-signed or oppositely-signed pairs, depending on the overall energy level. A microcanonical ensemble based on the conserved total energy E and angular momentum M for the whole vortex system is then used, in which the few strong vortices are treated as a subsystem in contact with a reservoir composed of the many weak vortices. It is shown that allowing for the finite size of this reservoir is essential in order to predict the statistics of the strong vortices accurately. Notably, this goes beyond the standard canonical ensemble with positive or negative temperature. A certain approximation is then shown to allow a single random sample of uniformly distributed vortex configurations to be used to predict the strong vortex statistics for all possible values of E and M. Detailed predictions for distribution functions are then made for comparison with three simulated cases of near-zero M and low, neutral, or high E. It is found that the statistical mechanics predictions compare remarkably well with the numerical results, including a prediction of vortex accumulation at the cylinder wall for low values of E.Comment: In press, Physics of Fluid

Differential mortality and wealth accumulation

An issue central to the life-cycle theory of consumer behavior, and to many policy questions, is asset accumulation and decumulation. One of the main implications of the life-cycle model is that assets are decumulated in the last part of life. Most empirical studies of asset accumulation use cross-sectional data to estimate mean or median wealth-age profiles, but the use of cross sections to estimate the age profile of assets is full of pitfalls. If, for example, wealth and mortality are related, in that poorer individuals die at a younger age, one overestimates the last part of the wealth-age profile when using cross-sectional data because means (or other measures of location) are taken over a population which becomes "richer" as it ages. In our examination of the effect of differential mortality on cross-sectional estimates of wealth-age profiles, we quantify the dependence of mortality rates on wealth and then use these estimates to "correct" wealth-age profiles for sample selection due to differential mortality. We estimate mortality rates as a function of wealth and age for a sample of married couples drawn from the Survey of Income and Program Participation (SIPP). Our results show that accounting for differential mortality produces wealth profiles with significantly more dissaving among the elderly.

Human factors aspects of control room design: Guidelines and annotated bibliography

A human factors analysis of the workstation design for the Earth Radiation Budget Satellite mission operation room is discussed. The relevance of anthropometry, design rules, environmental design goals, and the social-psychological environment are discussed

Workshop on Fuzzy Control Systems and Space Station Applications

The Workshop on Fuzzy Control Systems and Space Station Applications was held on 14-15 Nov. 1990. The workshop was co-sponsored by McDonnell Douglas Space Systems Company and NASA Ames Research Center. Proceedings of the workshop are presented

An Assessment of Integrated Flywheel System Technology

The current state of the technology in flywheel storage systems and ancillary components, the technology in light of future requirements, and technology development needs to rectify these shortfalls were identified. Technology efforts conducted in Europe and in the United States were reviewed. Results of developments in composite material rotors, magnetic suspension systems, motor/generators and electronics, and system dynamics and control were presented. The technology issues for the various disciplines and technology enhancement scenarios are discussed. A summary of the workshop, and conclusions and recommendations are presented

Parametric and Semi-parametric Estimations of the Return to Schooling in South Africa

This paper estimates return to schooling for african and coloured women in South Africa. It compares parametric and semiparametric estimates of the sample selection model for the case of return to schooling. The parametric estimator is the one proposed by Heckman (1979) and the semiparametric estimator proposed by Newey (1991) and Klein and Spady (1993). It also attempts to correct endogeneity and mesurement error by using instruments of schooling. Following recent literature, the paper uses community variables primary and secondary school proximity and availability as instruments. Using instrumental variables increases the return to schooling substantially. Parametric corrections does not change the results but semiparametric corrections increases the return even morereturn to schooling, sample selection bias, semiparametric regression, instrumental variables, south africa

Welfare Polls: A Synthesis

Welfare polls are survey instruments that seek to quantify the determinants of human well-being. Currently, three welfare polling formats are dominant: contingent valuation (CV) surveys, quality-adjusted life year (QALY) surveys, and happiness surveys. Each format has generated a large, specialized, scholarly literature, but no comprehensive discussion of welfare polling as a general enterprise exists.This Article seeks to fill that gap. Part I describes the trio of existing formats. Part II discusses the current and potential uses of welfare polls in governmental decisionmaking. Part III analyzes in detail the obstacles that welfare polls must overcome to provide useful well-being information, and concludes that they can be genuinely informative. Part IV synthesizes the case for welfare polls, arguing against two types of challenges: the revealed-preference tradition in economics, which insists on using behavior rather than surveys to learn about well-being; and the civic republican tradition in political theory, which accepts surveys but insists that respondents should be asked to take a citizen rather than consumer perspective. Part V suggests new directions for welfare polls