21,712 research outputs found

    Poissonian bursts in e-mail correspondence

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    Recent work has shown that the distribution of inter-event times for e-mail communication exhibits a heavy tail which is statistically consistent with a cascading Poisson process. In this work we extend the analysis to higher-order statistics, using the Fano and Allan factors to quantify the extent to which the empirical data depart from the known correlations of Poissonian statistics. The analysis shows that the higher-order statistics from the empirical data is indistinguishable from that of randomly reordered time series, thus demonstrating that e-mail correspondence is no more bursty or correlated than a Poisson process. Furthermore synthetic data sets generated by a cascading Poisson process replicate the burstiness and correlations observed in the empirical data. Finally, a simple rescaling analysis using the best-estimate rate of activity, confirms that the empirically observed correlations arise from a non-homogeneus Poisson process

    Development of GaAs and GaAs/1-x/P/x/ thin-film bipolar transistors Final report

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    Development of GaAs and GaAs/1-xPx thin film bipolar transistor

    Job Mobility and Wage Dynamics

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    Matched employer-employee data research has found that workersf wages are affected by the characteristics of the firms they work in, and that higher skilled workers tend to be employed by higher paying firms. This paper examines the contribution of workersf job mobility to their wage dynamics. We focus on the possible trade-off between moving to a better paying firm and losing a firm-tenure specific component of earnings, and examine what types of workers benefit from changing firms, rather than staying with their existing employer. Our analysis provides four main findings. First, although the raw earnings gains to jobmovers and stayers are about the same, we find that, after controlling for observable differences, job-movers have about 1.3 percent lower annual earnings growth than nonmovers. Second, we estimate that job-movers gain 0.3 percent per year on average from moving to higher paying firms, but lose 1.6 percent in transitory earnings associated with changing jobs. The gains from moving to better firms are larger for both younger and new entrant workers, while the transitory earnings losses are smaller. We interpret these findings as being due to an earnings growth trade-off for workers between moving to a higher paying firm and losing their tenure-related earnings at their existing firm. Third, we estimate that, on average, workers gain (almost) all of the change in firm earnings premiums when they change jobs. However, such gains are not equally shared by all workers. In particular, our estimates suggest that it is the higher ability workers (as measured by the estimated worker earnings premiums) whose earnings gain (or lose) the most from moving to a firm with higher (or lower) earnings premiums. Finally, we find that workersf earnings also benefit on average from a change in the average earnings of their co-workers. Controlling for other factors, we estimate that a 1 standard deviation change in the estimated average peer earnings is associated with about 0.25 percent change in a workerfs earnings on average.Earnings, Linked Employer-Employee Data, worker mobility, job turnover

    Understanding New Zealand s Changing Income Distribution 1983 98:A Semiparametric Analysis

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    This paper analyses changes in the distribution of equivalised gross household income and income inequality in New Zealand between 1983 and 1998. We analyse the distributional effects of changes in household structure, National Superannuation (old age pension), household socio- demographic attributes and employment outcomes, and in the economic returns to such attributes and employment outcomes, using a semiparametric kernel density approach, and assess the impact of these factors on alternative summary measures of inequality over the period. We find that changes in household structure and in the socio-demographic characteristics of households are the main factors contributing to the rise in inequality, while the large changes in the employment outcomes had a more modest impact, and there is little evidence of systematic effects of changes in the economic returns. The results are qualitatively robust to a variety of equivalisation, income, and weighting measures.Household income distribution; Inequality; Kernel density estimation

    Understanding New Zealand's Changing Income Distribution 1983-98: A Semiparametric Analysis

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    This paper analyses changes in the distribution of equivalised gross household income and income inequality in New Zealand between 1983 and 1998. We analyse the distributional effects of changes in household structure, National Superannuation (old age pension), household socio-demographic attributes and employment outcomes, and in the "economic returns" to such attributes and employment outcomes, using a semiparametric kernel density approach, and assess the impact of these factors on alternative summary measures of inequality over the period. We find that changes in household structure and in the socio-demographic characteristics of households are the main factors contributing to the rise in inequality, while the large changes in the employment outcomes had a more modest impact, and there is little evidence of systematic effects of changes in the economic returns. The results are qualitatively robust to a variety of equivalisation, income, and weighting measures.Household income distribution; Inequality; Kernel density estimation

    Perturbation theory for the effective diffusion constant in a medium of random scatterer

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    We develop perturbation theory and physically motivated resummations of the perturbation theory for the problem of a tracer particle diffusing in a random media. The random media contains point scatterers of density ρ\rho uniformly distributed through out the material. The tracer is a Langevin particle subjected to the quenched random force generated by the scatterers. Via our perturbative analysis we determine when the random potential can be approximated by a Gaussian random potential. We also develop a self-similar renormalisation group approach based on thinning out the scatterers, this scheme is similar to that used with success for diffusion in Gaussian random potentials and agrees with known exact results. To assess the accuracy of this approximation scheme its predictions are confronted with results obtained by numerical simulation.Comment: 22 pages, 6 figures, IOP (J. Phys. A. style

    The Polarized Spectrum of Apm 08279+5255

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    We report the discovery of significant linear polarization (p > 1%) in the hyperluminous z=3.87 BALQSO APM~08279+5255. The polarization spectrum is complex, with properties similar to those of other, lower redshift but more highly polarized BALQSOs. The resonance emission lines are unpolarized while the absorption troughs show polarization similar to or higher than the continuum. In particular, an apparent increase of polarization in the trough covering 1000-1030 angstroms (rest) supports the interpretation of this feature as a broad absorption component associated with OVI/Ly_beta local to the QSO, as opposed to an intervening damped Ly_alpha absorption system. The elevated polarization in some of the absorption features implies that we view the scattered (polarized) spectrum through a sightline with less absorbing material than the direct spectrum. Therefore, the complex structure of the polarization spectrum in this brilliant lensed BALQSO suggests that it will be an important laboratory for studying the structure of QSOs at high redshift.Comment: 8 pages, 1 figure. Accepted for publication in The Astrophysical Journal Letter
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