A Symplectic Integrator for Hill's Equations

Hill's equations are an approximation that is useful in a number of areas of astrophysics including planetary rings and planetesimal disks. We derive a symplectic method for integrating Hill's equations based on a generalized leapfrog. This method is implemented in the parallel N-body code, PKDGRAV and tested on some simple orbits. The method demonstrates a lack of secular changes in orbital elements, making it a very useful technique for integrating Hill's equations over many dynamical times. Furthermore, the method allows for efficient collision searching using linear extrapolation of particle positions.Comment: 15 pages, 2 figures; minor revisions; accepted for publication in the Astronomical Journa

Foundation degrees in biomedical science: the student experience

The first cohort of students on a University of Westminster foundation degree completed the course recently. Here, Chrystalla Ferrier, Kelly Brookwell and Paul Quinn employ some reflective practice

Pre-school experience and Key Stage 2 performance in English and Mathematics

This report considers children\u27s educational attainment in English and mathematics at the end of primary school (age 11). Children\u27s educational attainment in English and mathematics was derived from their national Key Stage 2 assessments. The analyses have considered the child\u27s level of Key Stage 2 attainment in terms of the effects of child, family, home environment and preschool experience variables as well as the child\u27s ability at the start of primary school

Financial Metrics In Wide-Moat Firms

According to Morningstar companies with certain structural characteristics enjoy economic moats. Compared to benchmark indices, Morningstar hypothesizes that over a ten-year time frame these firms will evidence superior price appreciation. Based on analysis of 1360 companies, this study supports the thesis of historical performance among wide-moat firms

Selective Bias: Asian Americans, Test Scores, and Holistic Admissions

Selective Bias: Asian Americans, Test Scores, and Holistic Admissions evaluates the common arguments made by affirmative action critics and Students for Fair Admissions, which is suing Harvard University and has lawsuits pending against the University of North Carolina and the University of Texas at Austin over their admissions practices. The report finds no strong evidence of discrimination against Asian American applicants in admissions to highly selective colleges

Blinded patient preference for morphine compared to placebo in the setting of chronic refractory breathlessness – an exploratory study

Context Patients’ preference for morphine therapy has received little attention in the setting of chronic refractory breathlessness. However, this is one important factor in considering longer term therapy. Objectives The aim of this secondary analysis is to explore blinded patient preference of morphine compared to placebo for this indication and to define any predictors of preference. Methods Data were pooled from three randomized, double-blind, crossover, placebo-controlled studies of morphine (four days each) in chronic refractory breathlessness. Blinded patient preferences were chosen at the end of each study. A multivariable regression model was used to establish patient predictors of preference. Results Sixty-five participants provided sufficient data (60 males; median age 74 years; heart failure 55%, chronic obstructive pulmonary disease 45%; median Eastern Cooperative Oncology Group performance status 2). Forty-three percent of participants preferred morphine (32% placebo and 25% no preference). Morphine preference and younger age were strongly associated: odds ratio = 0.85, 95% confidence interval 0.78, 0.93;

A spectropolarimetric view on the nature of the peculiar Type I SN 2005hk

We report two spectropolarimetric observations of SN 2005hk, which is a close copy of the "very peculiar" SN 2002cx, showing low peak luminosity, slow decline, high ionization near peak and an unusually low expansion velocity of only about 7,000 km s^-1. Further to the data presented by Chornock et al., (2006), at -4 days before maximum, we present data of this object taken on 9 November 2005 (near maximum) and 23 November (+ two weeks) that show the continuum and most of the spectral lines to be polarized at levels of about 0.2-0.3%. At both epochs the data corresponds to the Spectropolarimetric Type D1. The general low level of line polarization suggests that the line forming regions for most species observed in the spectrum have a similar shape to that of the photosphere, which deviates from a spherical symmetry by <10%. In comparison with spectropolarimetry of Type Ia and Core-collapse SNe at similar epochs, we find that the properties of SN 2005hk are most similar to those of Type Ia SNe. In particular, we find the low levels of continuum and line polarization to indicate that the explosion mechanism is approximately spherical, with homogeneous ejecta (unlike the chemically segregated ejecta of CCSNe). We discuss the possibility that SN 2005hk was the result of the pure deflagration of a white dwarf and note the issues concerning this interpretation.Comment: ApJ accepted, uses emulateapj, 16 pages, 10 figures, figures 3 and 4 update

Spectropolarimetry of the Type Ia SN 2007sr Two Months After Maximum Light

We present late time spectropolarimetric observations of SN 2007sr, obtained with the VLT telescope at ESO Paranal Observatory when the object was 63 days after maximum light. The late time spectrum displays strong line polarization in the CaII absorption features. SN 2007sr adds to the case of some normal Type Ia SNe that show high line polarization or repolarization at late times, a fact that might be connected with the presence of high velocity features at early times