Stochastic Modeling of Multiwavelength Variability of the Classical BL Lac Object OJ287 on Timescales Ranging from Decades to Hours

We present the results of our power spectral density analysis for the BL Lac object OJ 287, utilizing the Fermi-LAT survey at high-energy.-rays, Swift-XRT in X-rays, several ground-based telescopes and the Kepler satellite in the optical, and radio telescopes at GHz frequencies. The light curves are modeled in terms of continuous-time autoregressive moving average (CARMA) processes. Owing to the inclusion of the Kepler data, we were able to construct for the first time the optical variability power spectrum of a blazar without any gaps across similar to 6 dex in temporal frequencies. Our analysis reveals that the radio power spectra are of a colored-noise type on timescales ranging from tens of years down to months, with no evidence for breaks or other spectral features. The overall optical power spectrum is also consistent with a colored noise on the variability timescales ranging from 117 years down to hours, with no hints of any quasi-periodic oscillations. The X-ray power spectrum resembles the radio and optical power spectra on the analogous timescales ranging from tens of years down to months. Finally, the.-ray power spectrum is noticeably different from the radio, optical, and X-ray power spectra of the source: we have detected a characteristic relaxation timescale in the Fermi-LAT data, corresponding to similar to 150 days, such that on timescales longer than this, the power spectrum is consistent with uncorrelated (white) noise, while on shorter variability timescales there is correlated (colored) noise

Converging or Diverging? A comparative analysis of contingent employment practice in Europe over a 10-year period

Tregaskis lead author. This output was selected as one of the 12 ‘Papers of Excellence’ shortlisted for the Academy of Management’s inaugural 2007 IHRM Scholarly Research Award.The file attached to this record is a post-peer-review, pre-copyedit version of an article published in the Journal of International Business Studies. The definitive publisher-authenticated version Tregaskis, O. and Brewster, C. (2006) Converging or diverging? A comparative analysis of trends in contingent employment practice in Europe over a decade. Journal of International Business Studies, 37 (1), pp. 111-126. is available online at: http://dx.doi.org/10.1057/palgrave.jibs.8400174This paper makes a unique contribution to the HRM convergence-divergence debate by examining whether organizations operating in Europe, over the 10-year time period preceding 2000, are converging in their adoption of contingent employment practice. The susceptibility of contingent employment practice to both convergent and divergent pressures acts as a useful analytical lens. Data are drawn from organizations operating in Germany, Spain, Sweden, the Netherlands and the UK in 1991 (2918 organizations), 1995 (2048 organizations) and 2000 (1555 organizations).The results suggest that convergence is limited by the institutional embeddedness of organizations