The NASA high temperature superconductivity program

It has been recognized from the onset that high temperature superconductivity held great promise for major advances across a broad range of NASA interests. The current effort is organized around four key areas: communications and data, sensors and cryogenics, propulsion and power, and space materials technology. Recently, laser ablated YBa2Cu3O(7-x) films on LaAIO produced far superior RF characteristics when compared to metallic films on the same substrate. This achievement has enabled a number of unique microwave device applications, such as low insertion loss phase shifters and high Q filters. Melt texturing and melt quenched techniques are being used to produce bulk materials with optimized magnetic properties. These yttrium enriched materials possess enhanced flux pinning characteristics and will lead to prototype cryocooler bearings. Significant progress has also occurred in bolometer and current lead technology. Studies are being conducted to evaluate the effect of high temperature superconducting materials on the performance and life of high power magneto-plasma-dynamic thrusters. Extended studies were also performed to evaluate the benefit of superconducting magnetic energy storage for LEO space station, lunar and Mars mission applications. The project direction and level of effort of the program are also described

Trace formula for a dielectric microdisk with a point scatterer

Two-dimensional dielectric microcavities are of widespread use in microoptics applications. Recently, a trace formula has been established for dielectric cavities which relates their resonance spectrum to the periodic rays inside the cavity. In the present paper we extend this trace formula to a dielectric disk with a small scatterer. This system has been introduced for microlaser applications, because it has long-lived resonances with strongly directional far field. We show that its resonance spectrum contains signatures not only of periodic rays, but also of diffractive rays that occur in Keller's geometrical theory of diffraction. We compare our results with those for a closed cavity with Dirichlet boundary conditions.Comment: 39 pages, 18 figures, pdflate

Do CEOs Exercise Their Stock Options Earlier than Other Executives?

This paper looks at the timing chosen by CEOs to exercise their stock options and to sell their shares of stock compared to the timing chosen by other top executives in the firm. We first present a model that predicts when CEOs should exercise their options and/or sell their shares, and when other top managers should. Using a tournament approach we find that other top executives should exercise their stock options later than the CEO. We test this model using an unique data set of Canadian companies from 1993 onward. Our results seem to support the theoretical model as non-CEO executives seem to exercise their stock options about a calendar year later than the CEO. Moreover, non-CEO executive a more likely to exercise when a new CEO has been appointed, confirming our tournament model results. Nous étudions dans cet article le moment choisi par le PDG d'une compagnie pour lever ses options ou vendre ses actions dans la compagnie comparativement au moment choisi par les autres hauts dirigeants de la compagnie. Nous présentons premièrement un modèle théorique de tournoi qui fait des prédictions quant au moment opportun pour le PDG et les autres dirigeants de lever leurs options et/ou de vendre leurs actions dans la compagnie. Nous montrons théoriquement dans un tel modèle de tournoi que les hauts dirigeants devraient lever leurs options après le PDG. Nous testons ce modèle en utilisant une base de données unique de compagnies canadiennes de 1993 à 1999. Nos résultats empiriques semblent supporter notre modèle théorique puisque les hauts dirigeants semblent lever leurs options un an plus tard que le PDG. De plus, les hauts dirigeants semblent plus enclins à lever leurs options lorsqu'un nouveau PDG vient d'être nommé, confirmant ainsi notre modèle de tournoi.CEO and Executive Compensation, Options, Timing of Exercised Options., Contributions volontaires, pertes publiques, risque, ambiguïté, données expérimentales

The Effect of Rewards and Sanctions in Provision of Public Goods

A growing number of field and experimental studies focus on the institutional arrangements by which individuals are able to solve collective action problems. Important in this research is the role of reciprocity and institutions that facilitate cooperation via opportunities for monitoring, sanctioning, and rewarding others. Sanctions represent a cost to both the participant imposing the sanction and the individual receiving the sanction. Rewards represent a zero sum transfer from participants giving to those receiving rewards. We contrast reward and sanction institutions in regard to their impact on cooperation and efficiency in the context of a public goods experiment.

Approximate Bayesian Computation in State Space Models

A new approach to inference in state space models is proposed, based on approximate Bayesian computation (ABC). ABC avoids evaluation of the likelihood function by matching observed summary statistics with statistics computed from data simulated from the true process; exact inference being feasible only if the statistics are sufficient. With finite sample sufficiency unattainable in the state space setting, we seek asymptotic sufficiency via the maximum likelihood estimator (MLE) of the parameters of an auxiliary model. We prove that this auxiliary model-based approach achieves Bayesian consistency, and that - in a precise limiting sense - the proximity to (asymptotic) sufficiency yielded by the MLE is replicated by the score. In multiple parameter settings a separate treatment of scalar parameters, based on integrated likelihood techniques, is advocated as a way of avoiding the curse of dimensionality. Some attention is given to a structure in which the state variable is driven by a continuous time process, with exact inference typically infeasible in this case as a result of intractable transitions. The ABC method is demonstrated using the unscented Kalman filter as a fast and simple way of producing an approximation in this setting, with a stochastic volatility model for financial returns used for illustration