Sines, steps and droplets: Semiparametric Bayesian modeling of arrival time series

I describe ongoing work developing Bayesian methods for flexible modeling of arrival time series data without binning, aiming to improve detection and measurement of X-ray and gamma-ray pulsars, and of pulses in gamma-ray bursts. The methods use parametric and semiparametric Poisson point process models for the event rate, and by design have close connections to conventional frequentist methods currently used in time-domain astronomy.Comment: 4 pages, 1 figure; to appear in the proceedings of IAU Symposium 285, "New Horizons in Time Domain Astronomy" (proceedings eds. Elizabeth Griffin, Bob Hanisch, and Rob Seaman), Cambridge University Press; see http://www.physics.ox.ac.uk/IAUS285

Absolute Timing of the Crab Pulsar with RXTE

We have monitored the phase of the main X-ray pulse of the Crab pulsar with the Rossi X-ray Timing Explorer (RXTE) for almost eight years, since the start of the mission in January 1996. The absolute time of RXTE's clock is sufficiently accurate to allow this phase to be compared directly with the radio profile. Our monitoring observations of the pulsar took place bi-weekly (during the periods when it was at least 30 degrees from the Sun) and we correlated the data with radio timing ephemerides derived from observations made at Jodrell Bank. We have determined the phase of the X-ray main pulse for each observation with a typical error in the individual data points of 50 us. The total ensemble is consistent with a phase that is constant over the monitoring period, with the X-ray pulse leading the radio pulse by 0.0102+/-0.0012 period in phase, or 344+/-40 us in time. The error estimate is dominated by a systematic error of 40 us in the radio data, arising from uncertainties in the variable amount of pulse delay due to interstellar scattering and instrumental calibration. The statistical error is 0.00015 period, or 5 us. The separation of the main pulse and interpulse appears to be unchanging at time scales of a year or less, with an average value of 0.4001+/-0.0002 period. There is no apparent variation in these values with energy over the 2-30 keV range. The lag between the radio and X-ray pulses may be constant in phase (rotational) or constant in time (linear pathlength). We are not (yet) able to distinguish between these two interpretations.Comment: 11 pages, 2 figure

C1− Continuous crack propagation for mixed-mode fracture problems

In this work a C1− continuous crack propagation algorithm is proposed to improve the numerical simulation of localized deformation patterns, using higher order elements. The algorithm is applied for a standard smeared crack model and is validated by a mixed-mode fracture problem. From the results a reduction of mesh-induced directional bias is observed

Addressing Youth Perceptions of Harm in Marijuana Prevention Programming

The inverse relationship between perception of harm and substance use is clearly supported by decades of research – youth are less likely to engage in substance use when it is seen as harmful. However, despite strong theoretical and practical reasons to focus on perception of harm as a change-producer in prevention programming, little is known about what is effective in impacting perception of harm for youth marijuana use. To investigate the impact of existing prevention efforts designed to influence youth perception of harm and, consequently, youth marijuana use, we reviewed seven privately- or federally-funded online registries (e.g., Blueprints for Healthy Youth Development, Substance Abuse and Mental Health Administration’s National Registry of Evidence Based Programs and Practices) to identify evidence-based programs with marijuana-related outcomes for youth. We found 36 registry-identified programs with demonstrated impact on youth marijuana use. Although many of these programs may have actively or passively sought to alter perception of harm, only ten measured marijuana- or drug-related perception of harm as an intermediate outcome. Drawing on the commonalities of evidence-based programs with significant impacts on youth marijuana perception of harm, as well as lessons learned from other health behavior change efforts, we recommend best practices to provide state and local decision-makers with information on altering youth perception of harm for marijuana and on evaluating the impact of these efforts

X-ray Phase-Resolved Spectroscopy of PSRs B0531+21, B1509-58, and B0540-69 with RXTE

The Rossi X-ray Timing Explorer ({\sl RXTE}) has made hundreds of observations on three famous young pulsars (PSRs) B0531+21 (Crab), B1509-58, and B0540-69. Using the archive {\sl RXTE} data, we have studied the phase-resolved spectral properties of these pulsars in details. The variation of the X-ray spectrum with phase of PSR B0531+21 is confirmed here much more precisely and more details are revealed than the previous studies: the spectrum softens from the beginning of the first pulse, turns to harden right at the pulse peak and becomes the hardest at the bottom of the bridge, softens gradually until the second peak, and then softens rapidly. Different from the previous studies, we found that the spectrum of PSR B1509-58 is significantly harder in the center of the pulse, which is also in contrast to that of PSR B0531+21. The variation of the X-ray spectrum of PSR B0540-69 seems similar to that of PSR B1509-58, but with a lower significance. Using the about 10 years of data span, we also studied the real time evolution of the spectra of these pulsars, and no significant evolution has been detected. We have discussed about the constraints of these results on theoretical models of pulsar X-ray emission.Comment: 42 pages, 24 figure

Modeling the Structural Response of Reinforced Glass Beams using an SLA Scheme

This paper investigates whether a novel computational sequentially linear analysis(SLA) technique, which is especially developed for modeling brittle materialresponse, is applicable for modeling the structural response of metal reinforcedglass beams. To do so, computational SLA results are compared with experimentalresults of four-point bending tests. The results show similarities in loaddisplacementcurves and to some extent also in cracking behaviour. Overall, it isconcluded that the SLA scheme is a very promising technique to model thestructural response of reinforced glass beams, which will be even further improvedin future research

NGC 3627: a galaxy-dwarf collision?

Group galaxies very often show distinct signs of interaction with both companion galaxies and the intragroup medium. X-ray observations are particularly helpful because they provide information on the temperatures and the densities of the hot gas in galaxies and intergalactic space. This can put important constraints on the nature and timescales of these interactions. We use the XMM-Newton X-ray observations of NGC 3627 in the Leo Triplet galaxy group to explain peculiar features visible in the polarized radio maps. We analyzed soft X-ray (0.2-1 keV) emission from NGC 3627 to study the distribution of the hot gas and its temperature in different areas of the galaxy. Any change throughout the disk can reflect distortions visible in the radio polarized emission. We also studied two bright point sources that are probably tightly linked to the evolution of the galaxy. We find an increase in the temperature of the hot gas in the area of the polarized radio ridge in the western arm of the galaxy. In the eastern part of the disk we find two ultra-luminous X-ray sources. We note a large hot gas temperature difference (by a factor of 2) between the two bar ends. The polarized radio ridge in the western arm of NGC 3627 is most likely formed by ram-pressure effects caused by the movement of the galaxy through the intragroup medium. To explain the distortions visible in the eastern part of the disk in polarized radio maps, the asymmetry of the bar, and the distortion of the eastern arm, we propose a recent collision of NGC 3627 with a dwarf companion galaxy.Comment: 8 pages, 6 figures, 5 tables. Accepted for publication in Astronomy and Astrophysic

Critical analysis on the use of the shove test for investigating the shear-sliding behavior of brick masonry

The shove test (ASTM Standard C1531) is an experimental technique aimed at studying the shear-sliding behavior of brick masonry. It can be executed according to various testing methods that differ in the way the vertical compression load is applied and in the way bricks and/or joints are locally removed for inserting jacks. One of the most critical aspects is the correct evaluation of the compressive stress state on the sliding brick. The objective of the present paper is to investigate the capability of the shove test in determining the shear strength parameters of brick masonries and to highlight the main advantages and disadvantages of the various testing methods. To this aim, nonlinear numerical simulations of the shove test were performed by adopting a brick-to-brick modeling strategy. The 2D numerical model was calibrated and validated through comparisons with experimental results of triplet tests and shove tests. The numerical analyses allowed to understand the influence the different testing methods and the masonry mechanical properties, such as dilatancy, may have on the test results. Based on the numerical outcomes, correction factors were calibrated for the proper evaluation of the compressive stress state on the sliding brick. Improvements with regards to the experimental procedures, i.e. additional test phases and measurements, were also proposed to enhance the results interpretation

SN1993J VLBI (I): The Center of the Explosion and a Limit on Anisotropic Expansion

Phase-referenced VLBI observations of supernova 1993J at 24 epochs, from 50 days after shock breakout to the present, allowed us to determine the coordinates of the explosion center relative to the quasi-stationary core of the host galaxy M81 with an accuracy of 45 micro-arcsec, and to determine the nominal proper motion of the geometric center of the radio shell with an accuracy of 9micro-arcsec/yr. The uncertainties correspond to 160 AU for the position and 160 km/s for the proper motion at the distance of the source of 3.63 Mpc. After correcting for the expected galactic proper motion of the supernova around the core of M81 using HI rotation curves, we obtain a peculiar proper motion of the radio shell center of only 320 +/- 160 km/s to the south, which limits any possible one-sided expansion of the shell. We also find that the shell is highly circular, the outer contours in fact being circular to within 3%. Combining our proper motion values with the degree of circular symmetry, we find that the expansion of the shockfront from the explosion center is isotropic to within 5.5% in the plane of the sky. This is a more fundamental result on isotropic expansion than can be derived from the circularity of the images alone. The brightness of the radio shell, however, varies along the ridge and systematically changes with time. The degree of isotropy in the expansion of the shockfront contrasts with the asymmetries and polarization found in optical spectral lines. Asymmetric density distributions in the ejecta or more likely in the circumstellar medium, are favored to reconcile the radio and optical results. We see no sign of any disk-like density distribution of the circumstellar material, with the average axis ratio of the radio shell of SN1993J being less than 1.04.Comment: 21 pages, LaTex + 5 Figures (encapulsated PostScript), Accepted for Publication in the Astrophysical Journa

Regulatory Impact Assessment: A survey of selected developing and emerging economies

Regulatory impact assessment (RIA) involves a systematic appraisal of the social, economic and environmental impacts of proposed regulations and other kinds of policy instruments before they are adopted. A vast amount of academic literature in the last decade has charted the diffusion of RIA in OECD countries and EU member states. However, relatively little is known about the extent to which RIA has been adopted and implemented in developing countries. The last research attempting to shed light on this issue over a decade ago found that a number of were beginning to apply some form of regulatory assessment but that its development was at an early stage. Since then RIA has become almost universally adopted in OECD and EU member states as well as promoted as a tool for good (regulatory) governance in developing countries by international donors and organizations such as OECD, the International Finance Corporation of the World Bank Group (IFC). What, then, is the extent of RIA adoption and implementation in these countries today? This working paper addresses this question through a survey of RIA in 14 developing and emerging economies based on documentary analysis as well as semi-structured interviews with key stakeholders. The survey explores topics such as the legal and institutional framework of RIA, organizational capacity, and use of tools and methods (e.g. Cost Benefit Analysis). The results suggest that while an increasing number of developing countries have made efforts to introduce RIA in their decision making processes, these efforts have not yet led to a sustainable RIA system which significantly contributes to the good regulatory governance of these countries