Numerical analysis of distribution patterns in the British and European floras

Imperial Users onl

Spatio-temporal generalization of the Harris criterion and its application to diffusive disorder

We investigate how a clean continuous phase transition is affected by spatio-temporal disorder, i.e., by an external perturbation that fluctuates in both space and time. We derive a generalization of the Harris criterion for the stability of the clean critical behavior in terms of the space-time correlation function of the external perturbation. As an application, we consider diffusive disorder, i.e, an external perturbation governed by diffusive dynamics, and its effects on a variety of equilibrium and nonequilibrium critical points. We also discuss the relation between diffusive disorder and diffusive dynamical degrees of freedom on the example of model C of the Hohenberg-Halperin classification, and we comment on Griffiths singularities.Comment: 7 pages, 2 eps figures embedded, final version as publishe

The US space station and its electric power system

The United States has embarked on a major development program to have a space station operating in low earth orbit by the mid-1990s. This endeavor draws on the talents of NASA and most of the aerospace firms in the U.S. Plans are being pursued to include the participation of Canada, Japan, and the European Space Agency in the space station. From the start of the program these was a focus on the utilization of the space station for science, technology, and commercial endeavors. These requirements were utilized in the design of the station and manifest themselves in: pressurized volume; crew time; power availability and level of power; external payload accommodations; microgravity levels; servicing facilities; and the ability to grow and evolve the space station to meet future needs. President Reagan directed NASA to develop a permanently manned space station in his 1984 State of the Union message. Since then the definition phase was completed and the development phase initiated. A major subsystem of the space station is its 75 kW electric power system. The electric power system has characteristics similar to those of terrestrial power systems. Routine maintenance and replacement of failed equipment must be accomplished safely and easily and in a minimum time while providing reliable power to users. Because of the very high value placed on crew time it is essential that the power system operate in an autonomous mode to minimize crew time required. The power system design must also easily accommodate growth as the power demands by users are expected to grow. An overview of the U.S. space station is provided with special emphasis on its electrical power system

Bayesian Bootstrap Analysis of Systems of Equations

Research Methods/ Statistical Methods,

Neurochemical substrates and neuroanatomical generators of the event-related P300

The present review focuses on the current knowledge of the neurochemical processes and neuronal structures involved in the generation of P300. The increasing knowledge in this area facilitates the physiological interpretation of P300 findings as well as the link between P300 research and other research findings in biological psychiatry. Concerning the question of neurochemical substrates, the glutamatergic, GABAergic, cholinergic, noradrenergic, dopaminergic and serotonergic influences on P300 are reviewed. The knowledge of the generating structures of P300 is summarized from intracranial studies, magnetoencephalographic investigations, lesion and animal studies

Bayesian Analysis of a Japanese Meat Demand System: A Robust Likelihood Approach

This paper presents an application of Bayesian analysis to an AIDS model of Japanese meat demand extending previous approaches in three ways: (1) The methodology employed is robust with respect to the likelihood function but retains the generic, easily programmable character of algorithms offered by Monte Carlo Integration approaches based on the normal likelihood function. (2) In addition to inequality constraints, linear exact restrictions and stochastic prior information are subjected to a Bayesian posterior analysis of validity and incorporated into Bayesian point estimates of model parameters and elasticities. (3) In order to assess the influence of the prior density on posterior distributions of model parameters relative to the likelihood, a measure quantifying the "degree of prior influence" on the posterior is defined. Das Diskussionspapier stellt eine Bayes'sche Analyse eines AIDS Modells Japanischer Fleischnachfrage vor, die eine Erweiterung fruherer Ansatze in den folgenden drei Punkten darstellt:(1) Die verwendete Methode ist robust bezuglich der Likelihood Funktion, erhalt dabei aber die Flexibilitat und einfache Umsetzung von Algorithmen basierend auf Monte Carlo Integration und der Annahme der Normalverteilung. (2) Zusatzlich zu Ungleichheitsbedingungen werden exakte Restriktionen und stochastische a-priori Information einer Bayes'schen a-posteriori Analyse unterzogen und in die Bayes'sche Punktschatzung von Parametern und Elastizitaten einbezogen. (3) Ein Index zur Messung des Einflusses der a-priori Information auf die a-posteriori Verteilung der Modellparameter wird vorgestellt.Demand and Price Analysis,

SIMULTANEOUS EQUATIONS BAYESIAN BOOTSTRAP

This paper introduces a semi-parametric bootstrapping approach to Bayesian analysis of structural parameters in simultaneous equation systems that extends the single and multivariate regression approaches of Heckelei and Mittelhammer (1996, 2002) to models with endogenous regressors. Monte Carlo evidence demonstrated the considerable accuracy of the procedure in approximating posterior distributions, even for small sample sizes.Research Methods/ Statistical Methods,

A real-time audio spectral analyser using active filters with adjustable parameters

Imperial Users onl

Labor Market Entry Conditions, Wages and Job Mobility

Economic conditions at the time of labour market entry can induce wage differentials between workers entering the labour market at different points in time. While the existence and persistence of these entry wage differentials are well documented, little is known about their interaction with employees' mobility behaviour. This paper contributes to this research area by analyzing the interaction between job mobility and entry wage differentials using German administrative data. The results suggest that labour market entrants earning less than the average starting wage are more likely to change jobs, directly from employer to employer as well as indirectly via an unemployment spell. In addition they are more likely to change occupation. Moreover, job mobility tends to reduce the effects of labour market entry conditions, implying that job mobility operates as an adjustment mechanism that mitigates entry wage differentials. These results hold not only for high-skilled, but also for medium-skilled and unskilled workers.mobility, job-to-job, wages, labour market entry, initial conditions