A new multidimensional, energy-dependent two-moment transport code for neutrino-hydrodynamics

We present the new code ALCAR developed to model multidimensional, multi energy-group neutrino transport in the context of supernovae and neutron-star mergers. The algorithm solves the evolution equations of the 0th- and 1st-order angular moments of the specific intensity, supplemented by an algebraic relation for the 2nd-moment tensor to close the system. The scheme takes into account frame-dependent effects of order O(v/c) as well as the most important types of neutrino interactions. The transport scheme is significantly more efficient than a multidimensional solver of the Boltzmann equation, while it is more accurate and consistent than the flux-limited diffusion method. The finite-volume discretization of the essentially hyperbolic system of moment equations employs methods well-known from hydrodynamics. For the time integration of the potentially stiff moment equations we employ a scheme in which only the local source terms are treated implicitly, while the advection terms are kept explicit, thereby allowing for an efficient computational parallelization of the algorithm. We investigate various problem setups in one and two dimensions to verify the implementation and to test the quality of the algebraic closure scheme. In our most detailed test, we compare a fully dynamic, one-dimensional core-collapse simulation with two published calculations performed with well-known Boltzmann-type neutrino-hydrodynamics codes and we find very satisfactory agreement.Comment: 30 pages, 12 figures. Revised version: several additional comments and explanations, results remain unchanged. Accepted for publication in MNRA

The Political and Economic Implications of the Asian Carp Invasion

“Asian carp will kill jobs and ruin our way of life.”1 Such is the sentiment expressed by Michigan Attorney General Mike Cox and many other politicians and interest groups in the Great Lakes Region. The invasion of non-native species into the Great Lakes is a public policy problem that has the ability to severely damage the region’s environment and economy. Alterations to the region’s waterways have led to the threat of invasive species overwhelming, and in fact, destroying the natural ecosystem of the world’s largest body of freshwater. The issue of invasive species has resulted in a clash between numerous industries crucial to the Great Lakes states’ economies. The argument over approaches to combating the problem of Asian carp displays how the use of a common resource can clash with high economic and political consequences

Contemporary State Policies Toward Anti-Semitism in Germany and Poland

Broadly speaking, this research is intended to shed light on how post-genocide societies attempt to address a traumatic history and reconcile the problems of ethnic and religious hatred. Germany and Poland are especially ripe cases for such research given their historical memories of the Holocaust and unique legal and diplomatic efforts to counter anti-Semitism. However, since many of the policies on this issue have only been implemented in the past ten to fifteen years, there has not yet been a comprehensive study that has evaluated their effectiveness. This dissertation will attempt to fill this gap in the literature and provide new insight as to how states can best grapple with this problem. The central question for this research is: Have state policies been effective in reducing levels of anti-Semitic attitudes and incidents in Germany and Poland since 1990? This question will be investigated by first examining the historical development of anti-Semitism in each country, then discussing the policies implemented to address the problem, and finally evaluating the results of such measures. From a public policy perspective, this research will contribute to our understanding of the approaches taken by these two countries and discover which measures have been most effective in reducing anti-Semitic behavior and ideology. The findings show that while the policies implemented have tended to be effective in reducing general anti-Semitic attitudes and helping revive domestic Jewish communities, they have been less successful in reducing levels of anti-Semitic crime. The policy analysis portions of the dissertation provide a number of explanations for these outcomes and acknowledge areas for potential policy improvement. This research has implications not only for the region of Central Europe, but also other societies that continue to grapple with problems of ethnic and religious hatred

Neutron-star radius constraints from GW170817 and future detections

We introduce a new, powerful method to constrain properties of neutron stars (NSs). We show that the total mass of GW170817 provides a reliable constraint on the stellar radius if the merger did not result in a prompt collapse as suggested by the interpretation of associated electromagnetic emission. The radius R_1.6 of nonrotating NSs with a mass of 1.6 M_sun can be constrained to be larger than 10.68_{-0.04}^{+0.15} km, and the radius R_max of the nonrotating maximum mass configuration must be larger than 9.60_{-0.03}^{+0.14} km. We point out that detections of future events will further improve these constraints. Moreover, we show that a future event with a signature of a prompt collapse of the merger remnant will establish even stronger constraints on the NS radius from above and the maximum mass M_max of NSs from above. These constraints are particularly robust because they only require a measurement of the chirp mass and a distinction between prompt and delayed collapse of the merger remnant, which may be inferred from the electromagnetic signal or even from the presence/absence of a ringdown gravitational-wave (GW) signal. This prospect strengthens the case of our novel method of constraining NS properties, which is directly applicable to future GW events with accompanying electromagnetic counterpart observations. We emphasize that this procedure is a new way of constraining NS radii from GW detections independent of existing efforts to infer radius information from the late inspiral phase or postmerger oscillations, and it does not require particularly loud GW events.Comment: 7 pages, 5 figures, accepted for publication in ApJ

Three-Dimensional Core-Collapse Supernova Simulations with Multi-Dimensional Neutrino Transport Compared to the Ray-by-Ray-plus Approximation

Self-consistent, time-dependent supernova (SN) simulations in three spatial dimensions (3D) are conducted with the Aenus-Alcar code, comparing, for the first time, calculations with fully multi-dimensional (FMD) neutrino transport and the ray-by-ray-plus (RbR+) approximation, both based on a two-moment solver with algebraic M1 closure. We find good agreement between 3D results with FMD and RbR+ transport for both tested grid resolutions in the cases of a 20 solar-mass progenitor, which does not explode with the employed simplified set of neutrino opacities, and of an exploding 9 solar-mass model. This is in stark contrast to corresponding axisymmetric (2D) simulations, which confirm previous claims that the RbR+ approximation can foster explosions in 2D in particular in models with powerful axial sloshing of the stalled shock due to the standing accretion shock instability (SASI). However, while local and instantaneous variations of neutrino fluxes and heating rates can still be considerably higher with RbR+ transport in 3D, the time-averaged quantities are very similar to FMD results because of the absence of a fixed, artificial symmetry axis that channels the flow. Therefore, except for stochastic fluctuations, the neutrino signals and the post-bounce evolution of 3D simulations with FMD and RbR+ transport are also very similar, in particular for our calculations with the better grid resolution. Higher spatial resolution has clearly a more important impact than the differences by the two transport treatments. Our results back up the use of the RbR+ approximation for neutrino transport in 3D SN modeling.Comment: 25 pages, 16 figures; referee comments included, new appendix added; accepted by Ap

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