29 research outputs found

    AMRA: An Adaptive Mesh Refinement Hydrodynamic Code for Astrophysics

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    Implementation details and test cases of a newly developed hydrodynamic code, AMRA, are presented. The numerical scheme exploits the adaptive mesh refinement technique coupled to modern high-resolution schemes which are suitable for relativistic and non-relativistic flows. Various physical processes are incorporated using the operator splitting approach, and include self-gravity, nuclear burning, physical viscosity, implicit and explicit schemes for conductive transport, simplified photoionization, and radiative losses from an optically thin plasma. Several aspects related to the accuracy and stability of the scheme are discussed in the context of hydrodynamic and astrophysical flows.Comment: 41 pages, 21 figures (9 low-resolution), LaTeX, requires elsart.cls, submitted to Comp. Phys. Comm.; additional documentation and high-resolution figures available from http://www.camk.edu.pl/~tomek/AMRA/index.htm

    Algorithmic comparisons of decaying, isothermal, supersonic turbulence

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    Contradicting results have been reported in the literature with respect to the performance of the numerical techniques employed for the study of supersonic turbulence. We aim at characterising the performance of different particle-based and grid-based techniques on the modelling of decaying supersonic turbulence. Four different grid codes (ENZO, FLASH, TVD, ZEUS) and three different SPH codes (GADGET, PHANTOM, VINE) are compared. We additionally analysed two calculations denoted as PHANTOM A and PHANTOM B using two different implementations of artificial viscosity. Our analysis indicates that grid codes tend to be less dissipative than SPH codes, though details of the techniques used can make large differences in both cases. For example, the Morris & Monaghan viscosity implementation for SPH results in less dissipation (PHANTOM B and VINE versus GADGET and PHANTOM A). For grid codes, using a smaller diffusion parameter leads to less dissipation, but results in a larger bottleneck effect (our ENZO versus FLASH runs). As a general result, we find that by using a similar number of resolution elements N for each spatial direction means that all codes (both grid-based and particle-based) show encouraging similarity of all statistical quantities for isotropic supersonic turbulence on spatial scales k<N/32 (all scales resolved by more than 32 grid cells), while scales smaller than that are significantly affected by the specific implementation of the algorithm for solving the equations of hydrodynamics. At comparable numerical resolution, the SPH runs were on average about ten times more computationally intensive than the grid runs, although with variations of up to a factor of ten between the different SPH runs and between the different grid runs. (abridged)Comment: accepted by A&A, 22 pages, 14 figure

    Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

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    Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M&gt;70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0&lt;e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

    Ultralight vector dark matter search using data from the KAGRA O3GK run

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    Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

    Considering heroin-assisted treatment and supervised drug consumption sites in the United States.

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    Current levels of opioid-related morbidity and mortality in the United States are staggering. Data for 2017 indicate that there were more than 47,000 opioid-involved overdose deaths, and one in eight adults now reports having had a family member or close friend die from opioids. Increasing the availability and reducing the costs of approved medications for those with an opioid use disorder (OUD) is imperative; however, jurisdictions addressing OUDs and overdose may wish to consider additional interventions. Two interventions that are implemented in some other countries but not in the United States are heroin-assisted treatment (HAT; sometimes referred to as supervised injectable heroin treatment) and supervised consumption sites (SCSs; sometimes referred to as overdose prevention sites). Given the severity of the opioid crisis, there is urgency to evaluate tools that might reduce its impact and save lives. In this mixed-methods report, the authors assess evidence on and arguments made about HAT and SCSs and examine some of the issues associated with implementing them in the United States

    Validating continuous gravitational-wave candidates from a semicoherent search using Doppler modulation and an effective point spread function

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    Following up large numbers of candidates in continuous gravitational wave searches presents a challenge, particularly in regard to computational power and the time required to manually scrutinize each of the candidates. It is important to design and test good follow-up procedures that are safe (i.e., minimize false dismissals) and computationally efficient across many search configurations. We investigate two follow-up procedures, or "vetoes," both of which exploit the Doppler modulation predicted in astrophysical signals. In particular, we introduce the concept of using an effective point spread function as part of our veto criteria. We take advantage of a well-established semicoherent search algorithm based on a hidden Markov model to study various search configurations and to generalize the veto criteria by considering the overall veto performance in terms of efficiency and safety. The results can serve as a guideline for follow-up studies in future continuous gravitational wave searches using a hidden Markov model algorithm. The results also apply qualitatively to other semicoherent search algorithms.Comment: 24 pages, 15 figure
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