Spectral formation in a radiative shock: application to anomalous X-ray pulsars and soft gamma-ray repeaters

In the fallback disk model for the persistent emission of Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs), the hard X-ray emission arises from bulk- and thermal Comptonization of bremsstrahlung photons, which are generated in the accretion column. The relatively low X-ray luminosity of these sources implies a moderate transverse optical depth to electron scattering, with photons executing a small number of shock crossings before escaping sideways. We explore the range of spectral shapes that can be obtained with this model and characterize the most important parameter dependencies. We use a Monte Carlo code to study the crisscrossing of photons in a radiative shock in an accretion column and compute the resulting spectrum. As expected, high-energy power-law X-ray spectra are produced in radiative shocks with photon-number spectral index larger than or about 0.5. We find that the required transverse optical depth is between 1 and 7. Such spectra are observed in low-luminosity X-ray pulsars. We demonstrate here with a simple model that Compton upscattering in the radiative shock in the accretion column can produce hard X-ray spectra similar to those seen in the persistent and transient emission of AXPs and SGRs. In particular, one can obtain a high-energy power-law spectrum, with photon-number spectral index ~ 1 and a cutoff at 100 - 200 keV, with a transverse Thomson optical depth of ~ 5, which is shown to be typical in AXPs/SGRs.Comment: Accepted for publication in A&

Solution of Massless Spin One Wave Equation in Robertson-Walker Space-time

We generalize the quantum spinor wave equation for photon into the curved space-time and discuss the solutions of this equation in Robertson-Walker space-time and compare them with the solution of the Maxwell equations in the same space-time.Comment: 16 Pages, Latex, no figures, An expanded version of paper published in International Journal of Modern Physics A, 17 (2002) 113

First quantized electron and photon model of QED and radiative processes

In this study we combine the classical models of the massive and massless spinning particles, derive the current-current interaction Lagrangian of the particles from the gauge transformations of the classical spinors, and discuss radiative processes in electrodynamics by using the solutions of the Dirac equation and the quantum wave equations of the photon. The longitudinal polarized photon states give a new idea about the vacuum concept in electrodynamics.Comment: LaTeX file, 20 pages, 7 figures. to appear in Canadian Journal of Physic

Metamaterial based telemetric strain sensing in different materials

Cataloged from PDF version of article.We present telemetric sensing of surface strains on different industrial materials using split-ring-resonator based metamaterials. For wireless strain sensing, we utilize metamaterial array architectures for high sensitivity and low nonlinearity-errors in strain sensing. In this work, telemetric strain measurements in three test materials of cast polyamide, derlin and polyamide are performed by observing operating frequency shift under mechanical deformation and these data are compared with commercially-available wired strain gauges. We demonstrate that hard material (cast polyamide) showed low slope in frequency shift vs. applied load (corresponding to high Young's modulus), while soft material (polyamide) exhibited high slope (low Young's modulus). (C) 2010 Optical Society of America

Use of evidence to support healthy public policy: a policy effectiveness-feasibility loop

Public policy plays a key role in improving population health and in the control of diseases, including non-communicable diseases. However, an evidence-based approach to formulating healthy public policy has been difficult to implement, partly on account of barriers that hinder integrated work between researchers and policy-makers. This paper describes a “policy effectiveness–feasibility loop” (PEFL) that brings together epidemiological modelling, local situation analysis and option appraisal to foster collaboration between researchers and policy-makers. Epidemiological modelling explores the determinants of trends in disease and the potential health benefits of modifying them. Situation analysis investigates the current conceptualization of policy, the level of policy awareness and commitment among key stakeholders, and what actually happens in practice, thereby helping to identify policy gaps. Option appraisal integrates epidemiological modelling and situation analysis to investigate the feasibility, costs and likely health benefits of various policy options. The authors illustrate how PEFL was used in a project to inform public policy for the prevention of cardiovascular diseases and diabetes in four parts of the eastern Mediterranean. They conclude that PEFL may offer a useful framework for researchers and policy-makers to successfully work together to generate evidence-based policy, and they encourage further evaluation of this approach

Pearling: stroke segmentation with crusted pearl strings

We introduce a novel segmentation technique, called Pearling, for the semi-automatic extraction of idealized models of networks of strokes (variable width curves) in images. These networks may for example represent roads in an aerial photograph, vessels in a medical scan, or strokes in a drawing. The operator seeds the process by selecting representative areas of good (stroke interior) and bad colors. Then, the operator may either provide a rough trace through a particular path in the stroke graph or simply pick a starting point (seed) on a stroke and a direction of growth. Pearling computes in realtime the centerlines of the strokes, the bifurcations, and the thickness function along each stroke, hence producing a purified medial axis transform of a desired portion of the stroke graph. No prior segmentation or thresholding is required. Simple gestures may be used to trim or extend the selection or to add branches. The realtime performance and reliability of Pearling results from a novel disk-sampling approach, which traces the strokes by optimizing the positions and radii of a discrete series of disks (pearls) along the stroke. A continuous model is defined through subdivision. By design, the idealized pearl string model is slightly wider than necessary to ensure that it contains the stroke boundary. A narrower core model that fits inside the stroke is computed simultaneously. The difference between the pearl string and its core contains the boundary of the stroke and may be used to capture, compress, visualize, or analyze the raw image data along the stroke boundary