Bulk Comptonization spectra in blazars

We study the time dependent spectra produced via the bulk Compton process by a cold, relativistic shell of plasma moving (and accelerating) along the jet of a blazar, scattering on external photons emitted by the accretion disc and reprocessed in the broad line region. Bulk Comptonization of disc photons is shown to yield a spectral component contributing in the far UV band, and would then be currently unobservable. On the contrary, the bulk Comptonization of broad line photons may yield a significant feature in the soft X-ray band. Such a feature is time-dependent and transient, and dominates over the non thermal continuum only when: a) the dissipation occurs close to, but within, the broad line region; b) other competing processes, like the synchrotron self-Compton emission, yield a negligible flux in the X-ray band. The presence of a bulk Compton component may account for the X-ray properties of high redshift blazars that show a flattening (and possibly a hump) in the soft X-rays, previously interpreted as due to intrinsic absorption. We discuss why the conditions leading to a detectable bulk Compton feature might be met only occasionally in high redshift blazars, concluding that the absence of such a feature in the spectra of most blazars should not be taken as evidence against matter--dominated relativistic jets. The detection of such a component carries key information on the bulk Lorentz factor and kinetic energy associated to (cold) leptons.Comment: 8 pages; 4 figures; MNRAS, accepte

The behavior of laser modes in a medium with time varying dielectric constant

Time-varying modulation of dielectric constant effects on semiconductor laser mode

Radio Astronomical Polarimetry and the Lorentz Group

In radio astronomy the polarimetric properties of radiation are often modified during propagation and reception. Effects such as Faraday rotation, receiver cross-talk, and differential amplification act to change the state of polarized radiation. A general description of such transformations is useful for the investigation of these effects and for the interpretation and calibration of polarimetric observations. Such a description is provided by the Lorentz group, which is intimately related to the transformation properties of polarized radiation. In this paper the transformations that commonly arise in radio astronomy are analyzed in the context of this group. This analysis is then used to construct a model for the propagation and reception of radio waves. The implications of this model for radio astronomical polarimetry are discussed.Comment: 10 pages, accepted for publication in Astrophysical Journa

Employable knowledge: benchmarking education about standardization in the UK

For academics and students in the United Kingdom the main source of standards is via British Standards Institution (BSI). The research demonstrates that British, European and International Standards play a key role in many areas of education. In some disciplines their inclusion in the course is mandatory, e.g. in building construction and performing risk assessments of equipment. Where not a requirement, other courses successfully encourage students to understand and apply specific standards and principles from them, to their design and project work, in topic areas such as quality management and user-computer interface design. Assessment practice is a key part of learning and academics have indicated how this fitted into the learning activity, e.g. by expecting students to develop an understanding of standards and reference them in all assessed work. Likewise, students taking part in the survey also suggest that they were actively engaged with one or more standards and that their understanding was measured through an assessed activity. However, students also emphasised the importance of additional support, e.g. introduction to standards in the workplace or as part of work placements, by library staff as an information resource, and by presentations from BSI experts. Employers have also indicated the importance of students’ knowledge, understanding and appreciation of relevant standards in the right context, emphasising their desire for standards to be included more widely in the curriculum. The draft recommendations from this study were subject to International review and comment, the results from this review served to strengthen the recommendations of this work. This research was commissioned by British Standards Institution (BSI). This research was produced in association with the Department for Business, Innovation and Skills as part of its ongoing programme of support for standardization. Grateful thanks are due to all those who filled in the questionnaire or who attended the workshops

Families of Graphs With Chromatic Zeros Lying on Circles

We define an infinite set of families of graphs, which we call $p$-wheels and denote $(Wh)^{(p)}_n$, that generalize the wheel ($p=1$) and biwheel ($p=2$) graphs. The chromatic polynomial for $(Wh)^{(p)}_n$ is calculated, and remarkably simple properties of the chromatic zeros are found: (i) the real zeros occur at $q=0,1,...p+1$ for $n-p$ even and $q=0,1,...p+2$ for $n-p$ odd; and (ii) the complex zeros all lie, equally spaced, on the unit circle $|q-(p+1)|=1$ in the complex $q$ plane. In the $n \to \infty$ limit, the zeros on this circle merge to form a boundary curve separating two regions where the limiting function $W(\{(Wh)^{(p)}\},q)$ is analytic, viz., the exterior and interior of the above circle. Connections with statistical mechanics are noted.Comment: 8 pages, Late

Solid State Physics

Contains research objectives and reports on one research project

Solid State Physics

Contains research objectives

Psychometric Properties of the Abbreviated Perceived Motivational Climate in Exercise Questionnaire

The purpose of this study was to develop an abbreviated version of the Perceived Motivational Climate in Exercise Questionnaire (PMCEQ-A) to provide a more practical instrument for use in applied exercise settings. In the calibration step, 2 shortened versions’ measurement and latent model values were compared to each other and the original PMCEQ using a 3-group CFA invariance testing approach with previously collected exercise setting data (N = 5,427). Based on the model fit and reliability values, the 12-item version performed better than the 17-item version. The resultant 12-item PMCEQ-A’s CFA model estimates were then compared to the PMCEQ’s model values for 2 different, previously conducted studies of exercise settings (N = 414 and 770). The more parsimonious 12-item PMCEQ-A can be used by exercise psychology researchers to gain insight into members’ perspectives on the motivational climate and may lead to developing effective strategies to enhance members’ experiences and commitment

Scientific investigations in the Gulf of Mexico and Caribbean Sea during the 1974-1975 Calypso cruise, parts 1 and 2

The distribution and concentrations of the standing crop of phytoplankton and nutrient salts in the Gulf of Mexico and the Caribbean Sea were investigated to provide ground truth for correlating temperature and chlorophyll-a measurements with observations from NASA U-2 aircraft equipped with specially designed sensors for measuring ocean color phenomena. The physical, chemical, and biological data obtained is summarized. Sampling procedures and methods used for determining plant pigments, species composition of phytoplankton, nutrient salt analysis, and the euphotic zones are described