Neutron Star Kicks from Asymmetric Collapse

Many neutron stars are observed to be moving with spatial velocities, in excess of 500km/s. A number of mechanisms have been proposed to give neutron stars these high velocities. One of the leading classes of models proposed invokes asymmetries in the core of a massive star just prior to collapse. These asymmetries grow during the collapse, causing the resultant supernova to also be asymmetric. As the ejecta is launched, it pushes off (or ``kicks'') the newly formed neutron star. This paper presents the first 3-dimensional supernova simulations of this process. The ejecta is not the only matter that kicks the newly-formed neutron star. Neutrinos also carry away momentum and the asymmetric collapse leads also to asymmetries in the neutrinos. However, the neutrino asymmetries tend to damp out the neutron star motions and even the most extreme asymmetric collapses presented here do not produce final neutron star velocities above 200km/s.Comment: 7 pages, 4 figures, see http://qso.lanl.gov/~clf/papers/kick.ps.gz for full figure

Gravitational Waves from Axisymmetric, Rotational Stellar Core Collapse

We have carried out an extensive set of two-dimensional, axisymmetric, purely-hydrodynamic calculations of rotational stellar core collapse with a realistic, finite-temperature nuclear equation of state and realistic massive star progenitor models. For each of the total number of 72 different simulations we performed, the gravitational wave signature was extracted via the quadrupole formula in the slow-motion, weak-field approximation. We investigate the consequences of variation in the initial ratio of rotational kinetic energy to gravitational potential energy and in the initial degree of differential rotation. Furthermore, we include in our model suite progenitors from recent evolutionary calculations that take into account the effects of rotation and magnetic torques. For each model, we calculate gravitational radiation wave forms, characteristic wave strain spectra, energy spectra, final rotational profiles, and total radiated energy. In addition, we compare our model signals with the anticipated sensitivities of the 1st- and 2nd-generation LIGO detectors coming on line. We find that most of our models are detectable by LIGO from anywhere in the Milky Way.Comment: 13 pages, 22 figures, accepted for publication in ApJ (v600, Jan. 2004). Revised version: Corrected typos and minor mistakes in text and references. Minor additions to the text according to the referee's suggestions, conclusions unchange

The effect of precipitation and application rate on dicyandiamide persistence and efficiency in two Irish grassland soils

peer-reviewedThe nitrification inhibitor dicyandiamide (DCD) has had variable success in reducing nitrate (NO3-) leaching and nitrous oxide (N2O) emissions from soils receiving nitrogen (N) fertilisers. Factors such as soil type, temperature and moisture have been linked to the variable efficacy of DCD. Since DCD is water soluble it can be leached from the rooting zone where it is intended to inhibit nitrification. Intact soil columns (15 cm diameter by 35 cm long) were taken from luvic gleysol and haplic cambisol grassland sites and placed in growth chambers. DCD was applied at 15 or 30 kg DCD ha-1, with high or low precipitation. Leaching of DCD, mineral N and the residual soil DCD concentrations were determined over eight weeks High precipitation increased DCD in leachate and decreased recovery in soil. A soil x DCD rate interaction was detected for the DCD unaccounted (proxy for degraded DCD). In the cambisol degradation of DCD was high (circa 81%) and unaffected by DCD rate. In contrast DCD degradation in the gleysol was lower and differentially affected by rate, 67 and 46% for the 15 and 30 kg ha-1 treatments, respectively. Differences DCD degradation rates between soils may be related to differences in organic matter content and associated microbiological activity. Variable degradation rates of DCD in soil, unrelated to temperature or moisture, may contribute to varying DCD efficacy. Soil properties should be considered when tailoring DCD strategies for improving nitrogen use efficiency and crop yields, through the reduction of reactive nitrogen loss.This research was financially supported under the National Development Plan, through the Research Stimulus Fund, administered by the Department of Agriculture, Food and the Marine under grants 07519 and 07545

Two-Dimensional Hydrodynamics of Pre-Core Collapse: Oxygen Shell Burning

By direct hydrodynamic simulation, using the Piecewise Parabolic Method (PPM) code PROMETHEUS, we study the properties of a convective oxygen burning shell in a SN 1987A progenitor star prior to collapse. The convection is too heterogeneous and dynamic to be well approximated by one-dimensional diffusion-like algorithms which have previously been used for this epoch. Qualitatively new phenomena are seen. The simulations are two-dimensional, with good resolution in radius and angle, and use a large (90-degree) slice centered at the equator. The microphysics and the initial model were carefully treated. Many of the qualitative features of previous multi-dimensional simulations of convection are seen, including large kinetic and acoustic energy fluxes, which are not accounted for by mixing length theory. Small but significant amounts of carbon-12 are mixed non-uniformly into the oxygen burning convection zone, resulting in hot spots of nuclear energy production which are more than an order of magnitude more energetic than the oxygen flame itself. Density perturbations (up to 8%) occur at the `edges' of the convective zone and are the result of gravity waves generated by interaction of penetrating flows into the stable region. Perturbations of temperature and electron fraction at the base of the convective zone are of sufficient magnitude to create angular inhomogeneities in explosive nucleosynthesis products, and need to be included in quantitative estimates of yields. Combined with the plume-like velocity structure arising from convection, the perturbations will contribute to the mixing of nickel-56 throughout supernovae envelopes. Runs of different resolution, and angular extent, were performed to test the robustness of theseComment: For mpeg movies of these simulations, see http://www.astrophysics.arizona.edu/movies.html Submitted to the Astrophysical Journa

Solvable senescence model with positive mutations

We build upon our previous analytical results for the Penna model of senescence to include positive mutations. We investigate whether a small but non-zero positive mutation rate gives qualitatively different results to the traditional Penna model in which no positive mutations are considered. We find that the high-lifespan tail of the distribution is radically changed in structure, but that there is not much effect on the bulk of the population. Th e mortality plateau that we found previously for a stochastic generalization of the Penna model is stable to a small positive mutation rate.Comment: 3 figure

Phase conversion in a weakly first-order quark-hadron transition

We investigate the process of phase conversion in a thermally-driven {\it weakly} first-order quark-hadron transition. This scenario is physically appealing even if the nature of this transition in equilibrium proves to be a smooth crossover for vanishing baryonic chemical potential. We construct an effective potential by combining the equation of state obtained within Lattice QCD for the partonic sector with that of a gas of resonances in the hadronic phase, and present numerical results on bubble profiles, nucleation rates and time evolution, including the effects from reheating on the dynamics for different expansion scenarios. Our findings confirm the standard picture of a cosmological first-order transition, in which the process of phase conversion is entirely dominated by nucleation, also in the case of a weakly first-order transition. On the other hand, we show that, even for expansion rates much lower than those expected in high-energy heavy ion collisions, nucleation is very unlikely, indicating that the main mechanism of phase conversion is spinodal decomposition. Our results are compared to those obtained for a strongly first-order transition, as the one provided by the MIT bag model.Comment: 12 pages, 10 figures; v2: 1 reference added, minor modifications, matches published versio

A simple and quick sensitivity analysis method for methane isotopologues detection with GOSAT-TANSO-FTS

Measurements of methane isotopologues can differentiate between different source types, be they biogenic (e.g. marsh lands) or abiogenic (e.g. industry). Global measurements of these isotopologues would greatly benefit the current disconnect between ‘top-down’ (knowledge from chemistry transport models and satellite measurements) and ‘bottom-up’ (in situ measurement inventories) methane measurements. However, current measurements of these isotopologues are limited to a small number of in situ studies and airborne studies. In this paper we investigate the potential for detecting the second most common isotopologue of methane (13CH4) from space using the Japanese Greenhouse Gases Observing Satellite applying a quick and simple residual radiance analysis technique. The method allows for a rapid analysis of spectral regions, and can be used to teach university students or advanced school students about radiative transfer analysis. Using this method we find limited sensitivity to 13CH4, with detections limited to total column methane enhancements of >6%, assuming a desert surface albedo of >0.3

Vector meson spectral function and dilepton rate in an effective mean field model

We have studied the vector meson spectral function (VMSF) in a hot and dense medium within an effective QCD model namely the Nambu-Jona-Lasinio (NJL) and its Polyakov Loop extended version (PNJL) with and without the effect of isoscalar vector interaction (IVI). The effect of the IVI has been taken into account using the ring approximation. We obtained the dilepton production rate (DPR) using the VMSF and observed that at moderate temperature it is enhanced in the PNJL model as compared to the NJL and Born rate due to the suppression of color degrees of freedom.Comment: 5 pages, 7 figures, conference proceedings of the XXI DAE-BRNS HEP Symposium, IIT Guwahati, December 2014; to appear in 'Springer Proceedings in Physics Series

Is Entrepreneurial Success Predictable? An Ex-Ante Analysis of the Character-Based Approach

This paper empirically analyzes whether the character-based approach, which focuses on the personality structure and the human capital of business founders, allows prediction of entrepreneurial success. A unique data set is used consisting of 414 persons whose personal characteristics were analyzed by different methods, namely an one-day assessment center (AC) and a standardized questionnaire, before they launched their business. Results are partly unexpected and weaker than previous ex-post findings: first, we found correlations between the AC data and the questionnaire in one subgroup only. Second, the predictive power of the AC data is slightly better than that of the questionnaire, but lower than expected in theory. Interestingly, for those subgroups where the AC data have low predictive power, the questionnaire does better. Third, when success is measured in terms of employees hired, the character-based approach is a poor predictor. Copyright 2008 The Authors.

Phase holograms in PMMA with proximity effect correction

Complex computer generated phase holograms (CGPH's) have been fabricated in PMMA by partial e-beam exposure and subsequent partial development. The CGPH was encoded as a sequence of phase delay pixels and written by the JEOL JBX-5D2 E-beam lithography system, a different dose being assigned to each value of phase delay. Following carefully controlled partial development, the pattern appeared rendered in relief in the PMMA, which then acts as the phase-delay medium. The exposure dose was in the range 20-200 micro-C/sq cm, and very aggressive development in pure acetone led to low contrast. This enabled etch depth control to better than plus or minus lambda(sub vis)/60. That result was obtained by exposing isolated 50 micron square patches and measuring resist removal over the central area where the proximity effect dose was uniform and related only to the local exposure. For complex CGPH's with pixel size of the order of the e-beam proximity effect radius, the patterns must be corrected for the extra exposure caused by electrons scattered back up out of the substrate. This has been accomplished by deconvolving the two-dimensional dose deposition function with the desired dose pattern. The deposition function, which plays much the same role as an instrument response function, was carefully measured under the exact conditions used to expose the samples. The devices fabricated were designed with 16 equal phase steps per retardation cycle, were up to 1 cm square, and consisted of up to 100 million 0.3-2.0 micron square pixels. Data files were up to 500 MB long and exposure times ranged to tens of hours. A Fresnel phase lens was fabricated that had diffraction limited optical performance with better than 85 percent efficiency