Comptonization of an isotropic distribution in moving media: higher-order effects

We consider the Comptonization of an isotropic radiation field by a thermal distribution of electrons with non-vanishing bulk velocity. We include all relativistic effects, including induced scattering and electron recoil, in the derivation of a kinetic equation which is correct to O(theta^2, beta theta^2, beta^2 theta), where beta is the bulk velocity (in units of c) and theta is the ratio of the electron temperature to mass. The result given here manifestly conserves photon number, and easily yields the energy transfer rate between the radiation and electrons. We also confirm recent calculations of the relativistic corrections to the thermal and kinematic Sunyaev-Zel'dovich effect.Comment: Minor revisions. To appear in the Astrophysical Journa

Phylogenetic and phenotypic divergence of an insular radiation of birds

Evolutionary divergence of lineages is one of the key mechanisms underpinning large scale patterns in biogeography and biodiversity. Island systems have been highly influential in shaping theories of evolutionary diversification and here I use the insular Zosteropidae of the south west Pacific to investigate the roles of ecology and biogeography in promoting evolutionary divergence. Initially I build a phylogenetic tree of the study group and use it to reveal the pattern of colonisation and diversification. My results suggest a complex history of dispersal with the observed pattern most likely a result of repeated bouts of colonisation and extinction. I then use the new phylogeny to quantify the diversification rates of the Zosteropidae. I find a very high rate of lineage divergence and suggest the most likely explanation relates to extensive niche availability in the south west Pacific. I also find evidence for an overall slowdown in diversification combined with repeated bursts of accelerated speciation, consistent with a model of taxon cycles. I do not find evidence for sympatric speciation, however. Finally I combine morphological and phylogenetic data to investigate the mode of evolution, evidence for character displacement and influence of biogeography on trait evolution. I find little support for the traditional theory of character displacement in sympatric species. I do, however, find some support for biogeographic theories. Taken together my results do not support traditional theories on the ecological and biogeographical basis of divergence, even in those cases where Zosterops have been used as exemplars. This appears to be because those theories assume rather simple patterns of colonisation and a static ecological system. Instead, my results suggest that evolutionary diversification is dominated by recurrent waves of colonisation and extinction, which, viewed at any particular moment, tend to obscure any underlying ecological rules

Carotid artery disease screening : assessment of criteria

The Department of Radiology at St. Luke’s Hospital has provided a screening service for stroke related disease since April 1991. This consisted of Duplex Ultrasound screening (DUS) for Extracranial Carotid Artery Disease (ECAD) followed by angiography or intra-arterial digital subtraction angiography (lADSA) or digital intravenous angiography (DIVA) if ultrasound screening was positive for significant disease. The aim of this study was to evaluate in the local context, the various criteria for assessment already established overseas and to devise the best combination of these criteria to improve the detection of disease, thus improving the quality of the•local screening service. 504 patients have been screened for stroke related disease. Twelve patients (6M : 6F) with significant disease, who were considered for surgery, were referred for angiography, IADSA or DIVA. Comparison of these two modalities, DUS and vascular study, were made on 22 sides for the Multicentre Criteria (MCC), the Modified Seattle Criteria (MSC) and the Modified Washington Criteria (MWC). The accuracy, sensitivity, specificity, positive predictive value and negative predictive value were calculated for the MCC, the MSC and the MWC for peak systolic velocity. For the MCC the end diastolic velocity, the systolic velocity ratio and the diastolic velocity ratio were also compiled. The highest precision for extra cranial carotid artery disease screening can be achieved by a combination of the MCC or MSC for peak systolic velocity and with the systolic velocity ratio for the MCC.peer-reviewe

Strong field QED in lepton colliders and electron/laser interactions

Studies of strong field particle physics processes in electron/laser interactions and lepton collider interaction points are reviewed. These processes are defined by the high intensity of the electromagnetic fields involved and the need to take them into account as fully as possible. The main theoretical framework considered is the Furry picture. In this framework, the influence of a background electromagnetic field in the Lagrangian is calculated non perturbatively, involving exact solutions for quantised charged particles in the background field. These "dressed" particles go on to interact perturbatively with other particles. The background field starts to polarise the vacuum, in effect rendering it a dispersive medium. Particles encountering this dispersive vacuum obtain a lifetime, either radiating or decaying into pair particles at a rate dependent on the intensity of the background field. In fact, the intensity of the background field enters into the coupling constant of the strong field QED Lagrangian, influencing all particle processes. A number of new phenomena occur. Particles gain an intensity dependent rest mass shift that accounts for their presence in the dispersive vacuum. Multi photon events involving more than one external field photon occur at each vertex. Higher order processes which exchange a virtual strong field particle, resonate via the lifetimes of the unstable strong field states. Two main arenas of strong field physics are reviewed; those occurring in relativistic electron interactions with intense laser beams, and those occurring in the beam beam physics at the interaction point of colliders. This review outlines the theory, describes its significant novel phenomenology and details the experimental schema required to detect strong field effects and the simulation programs required to model them.Comment: Review article, 56 pages, 29 figures. Version 2 has corrected errata, 1 new reference, 5 updated figure