Nonlinear, relativistic Langmuir waves in astrophysical magnetospheres

Large amplitude, electrostatic plasma waves are relevant to physical processes occurring in the astrophysical magnetospheres wherein charged particles are accelerated to relativistic energies by strong waves emitted by pulsars, quasars, or radio galaxies. The nonlinear, relativistic theory of traveling Langmuir waves in a cold plasma is reviewed. The cases of streaming electron plasma, electronic plasma, and two-streams are discussed

On-off intermittency and amplitude-phase synchronization in Keplerian shear flows

We study the development of coherent structures in local simulations of the magnetorotational instability in accretion discs in regimes of on-off intermittency. In a previous paper [Chian et al., Phys. Rev. Lett. 104, 254102 (2010)], we have shown that the laminar and bursty states due to the on-off spatiotemporal intermittency in a one-dimensional model of nonlinear waves correspond, respectively, to nonattracting coherent structures with higher and lower degrees of amplitude-phase synchronization. In this paper we extend these results to a three-dimensional model of magnetized Keplerian shear flows. Keeping the kinetic Reynolds number and the magnetic Prandtl number fixed, we investigate two different intermittent regimes by varying the plasma beta parameter. The first regime is characterized by turbulent patterns interrupted by the recurrent emergence of a large-scale coherent structure known as two-channel flow, where the state of the system can be described by a single Fourier mode. The second regime is dominated by the turbulence with sporadic emergence of coherent structures with shapes that are reminiscent of a perturbed channel flow. By computing the Fourier power and phase spectral entropies in three-dimensions, we show that the large-scale coherent structures are characterized by a high degree of amplitude-phase synchronization.Comment: 17 pages, 10 figure

Searching for an anomalous tˉqγ\bar t q \gamma coupling via single top quark production at a γγ\gamma\gamma collider

We investigate the potential of a high-energy $\gamma\gamma$ collider to detect an anomalous $\bar t q \gamma$ coupling from observation of the reaction $\gamma \gamma \to t\bar q$, $\bar t q$, where $q=c$ or $u$. We find that with $b$-tagging and suitable kinematic cuts this process should be observable if the anomalous coupling $\kappa/\Lambda$ is no less than about 0.05/TeV, where $\Lambda$ is the scale of new physics associated with the anomalous interaction. This improves upon the bound possible from observation of top decays at the Tevatron.Comment: 13 pages, RevTeX, 1 PS figur

Years of Service and Probability of Promotion

This study provides evidence which we believe challenges some conventional assumptions about the promotion process. Based on survey information collected from a large random sample of U.S. private sector firms, we reach two main conclusions. First,seniority independent of productivity appears to play a significant role even in nonunion promotion decisions. Second, the differences between union and nonunion promotion processes, at least with regard to the weight assigned to seniority per se, appear to be important but less dramatic than is popularly supposed.

Unemployment, Unsatisfied Demand for Labor, and Compensation Growth in the United States, 1956-1980

This paper presents two key facts which call into question the value of unemployment rates as barometers of labor market tightness. First, while both unemployment rates and unsatisfied labor demand proxies perform reasonably well on their own in compensation growth equations, in models which include both, only the unsatisfied demand variable appears to matter. Second, the past decade's outward shifts in Phillips plots can to a substantial degree be tied to outward shifts in plots pairing the relevant unemployment rate and unsatisfied demand proxies. The paper also provides results which indicate that Phillips relationships which are defined in terms of unsatisfied demand variables appear to be somewhat more stable than those using unemployment rates. Taken together, our findings have a clear message for those concerned with macroeconomic theory and policy: labor market pressure on wages can be more reliably assessed by looking at measures of unsatisfied labor demand than by looking at the unemployment rates on which most earlier analyses have focused.

Can Productive Capacity Differentials Really Explain Earnings Differentials Associated with Demographic Characteristics? Case of Experience

This study uses computerized personnel microdata on the white male managerial and professional employees at a major U.S. corporation to address the following question: Can the additional earnings which are associated with more labor market experience at a point in time really be explained by higher productivity at the same point in time? Our answer to this question, based on both cross-sectional and longitudinal information, is that performance plays a substantially smaller role in explaining cross-sectional experience-earnings differentials and earnings growth than is claimed by those who have adopted the human capital explanation of the experience-earnings profile. This response depends critically on our assumption that the performance ratings which supervisors give to their white male managerial and professional subordinates adequately reflect the subordinates' relative productivity in the year of assessment; we present a great deal of evidence which strongly supports this assumption.

The non-linearity between <ln A> and <Xmax> induced by the acceptance of fluorescence telescopes

The measurement of the average depth of the shower maximum is the most commonly used observable for the possible inference of the primary cosmic-ray mass composition. Currently, different experimental Collaborations process and present their data not in the same way, leading to problems in the comparability and interpretation of the results. Whereas is expected to be proportional to in ideal conditions, we demonstrate that the finite field-of-view of fluorescence telescopes plus the attenuation in the atmosphere can introduce a non-linearity into this relation, which is specific for each particular detector setup

Improved real-space genetic algorithm for crystal structure and polymorph prediction

Existing genetic algorithms for crystal structure and polymorph prediction can suffer from stagnation during evolution, with a consequent loss of efficiency and accuracy. An improved genetic algorithm is introduced herein which penalizes similar structures and so enhances structural diversity in the population at each generation. This is shown to improve the quality of results found for the theoretical prediction of simple model crystal structures. In particular, this method is demonstrated to find three new zero-temperature phases of the Dzugutov potential that have not been previously reported