An Efficient Implementation of Flux Formulae in Multidimensional Relativistic Hydrodynamical Codes

We derive and analyze a simplified formulation of the numerical viscosity terms appearing in the expression of the numerical fluxes associated to several High-Resolution Shock-Capturing schemes. After some algebraic pre-processing, we give explicit expressions for the numerical viscosity terms of two of the most widely used flux formulae, which implementation saves computational time in multidimensional simulations of relativistic flows. Additionally, such treatment explicitely cancells and factorizes a number of terms helping to amortiguate the growing of round-off errors. We have checked the performance of our formulation running a 3D relativistic hydrodynamical code to solve a standard test-bed problem and found that the improvement in efficiency is of high practical interest in numerical simulations of relativistic flows in Astrophysics.Comment: 10 pages, accepted for publication in Computer Physics Communication

Axisymmetric core collapse simulations using characteristic numerical relativity

We present results from axisymmetric stellar core collapse simulations in general relativity. Our hydrodynamics code has proved robust and accurate enough to allow for a detailed analysis of the global dynamics of the collapse. Contrary to traditional approaches based on the 3+1 formulation of the gravitational field equations, our framework uses a foliation based on a family of outgoing light cones, emanating from a regular center, and terminating at future null infinity. Such a coordinate system is well adapted to the study of interesting dynamical spacetimes in relativistic astrophysics such as stellar core collapse and neutron star formation. Perhaps most importantly this procedure allows for the unambiguous extraction of gravitational waves at future null infinity without any approximation, along with the commonly used quadrupole formalism for the gravitational wave extraction. Our results concerning the gravitational wave signals show noticeable disagreement when those are extracted by computing the Bondi news at future null infinity on the one hand and by using the quadrupole formula on the other hand. We have strong indication that for our setup the quadrupole formula on the null cone does not lead to physical gravitational wave signals. The Bondi gravitational wave signals extracted at infinity show typical oscillation frequencies of about 0.5 kHz.Comment: 17 pages, 18 figures, submitted to Phys. Rev.

Three-dimensional general relativistic hydrodynamics II: long-term dynamics of single relativistic stars

This is the second in a series of papers on the construction and validation of a three-dimensional code for the solution of the coupled system of the Einstein equations and of the general relativistic hydrodynamic equations, and on the application of this code to problems in general relativistic astrophysics. In particular, we report on the accuracy of our code in the long-term dynamical evolution of relativistic stars and on some new physics results obtained in the process of code testing. The tests involve single non-rotating stars in stable equilibrium, non-rotating stars undergoing radial and quadrupolar oscillations, non-rotating stars on the unstable branch of the equilibrium configurations migrating to the stable branch, non-rotating stars undergoing gravitational collapse to a black hole, and rapidly rotating stars in stable equilibrium and undergoing quasi-radial oscillations. The numerical evolutions have been carried out in full general relativity using different types of polytropic equations of state using either the rest-mass density only, or the rest-mass density and the internal energy as independent variables. New variants of the spacetime evolution and new high resolution shock capturing (HRSC) treatments based on Riemann solvers and slope limiters have been implemented and the results compared with those obtained from previous methods. Finally, we have obtained the first eigenfrequencies of rotating stars in full general relativity and rapid rotation. A long standing problem, such frequencies have not been obtained by other methods. Overall, and to the best of our knowledge, the results presented in this paper represent the most accurate long-term three-dimensional evolutions of relativistic stars available to date.Comment: 19 pages, 17 figure

Origins of the Ambient Solar Wind: Implications for Space Weather

The Sun's outer atmosphere is heated to temperatures of millions of degrees, and solar plasma flows out into interplanetary space at supersonic speeds. This paper reviews our current understanding of these interrelated problems: coronal heating and the acceleration of the ambient solar wind. We also discuss where the community stands in its ability to forecast how variations in the solar wind (i.e., fast and slow wind streams) impact the Earth. Although the last few decades have seen significant progress in observations and modeling, we still do not have a complete understanding of the relevant physical processes, nor do we have a quantitatively precise census of which coronal structures contribute to specific types of solar wind. Fast streams are known to be connected to the central regions of large coronal holes. Slow streams, however, appear to come from a wide range of sources, including streamers, pseudostreamers, coronal loops, active regions, and coronal hole boundaries. Complicating our understanding even more is the fact that processes such as turbulence, stream-stream interactions, and Coulomb collisions can make it difficult to unambiguously map a parcel measured at 1 AU back down to its coronal source. We also review recent progress -- in theoretical modeling, observational data analysis, and forecasting techniques that sit at the interface between data and theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue connected with a 2016 ISSI workshop on "The Scientific Foundations of Space Weather." 44 pages, 9 figure

A new code for the Hall-driven magnetic evolution of neutron stars

Over the past decade, the numerical modeling of the magnetic field evolution in astrophysical scenarios has become an increasingly important field. In the crystallized crust of neutron stars the evolution of the magnetic field is governed by the Hall induction equation. In this equation the relative contribution of the two terms (Hall term and Ohmic dissipation) varies depending on the local conditions of temperature and magnetic field strength. This results in the transition from the purely parabolic character of the equations to the hyperbolic regime as the magnetic Reynolds number increases, which presents severe numerical problems. Up to now, most attempts to study this problem were based on spectral methods, but they failed in representing the transition to large magnetic Reynolds numbers. We present a new code based on upwind finite differences techniques that can handle situations with arbitrary low magnetic diffusivity and it is suitable for studying the formation of sharp current sheets during the evolution. The code is thoroughly tested in different limits and used to illustrate the evolution of the crustal magnetic field in a neutron star in some representative cases. Our code, coupled to cooling codes, can be used to perform long-term simulations of the magneto-thermal evolution of neutron stars.This work was partly supported by the Spanish grant AYA 2010-21097-C03-02 and CompStar, a Research Networking Program of the European Science Foundation. D. Viganò is supported by a fellowship from the Prometeo program for research groups of excellence of the Generalitat Valenciana (Prometeo/2009/103)

Natural production of chloroform by fungi

Chloroform production was detected in the headspace of pure cultures of the basidiomycetes Mycena metata and Peniophora pseudopini and the deuteromycete Caldariomyces fumago. The average production rates were in the range of 0.07-70 μg/l culture fluid/day for Caldariomyces fumago and 0.7-40 ng/1 culture fluid/day for the basidiomycetes; they depended on the composition of the medium, pH and the initial concentration of oxygen. In incidental cases, chloroform was identified in the headspace of pure cultures of the basidiomycetes Agaricus arvensis, Bjerkandera sp. BOS55, and Phellinus pini. It is suggested that fungi are important sources of elevated concentrations of chloroform in soil air

The effect of an endorectal balloon and off-line correction on the interfraction systematic and random prostate position variations: a comparative study.

Contains fulltext : 48173.pdf (publisher's version ) (Closed access)PURPOSE: To investigate the effect of an endorectal balloon (ERB) and an off-line correction protocol on the day-to-day, interfraction prostate gland motion, in patients receiving external beam radiotherapy for prostate cancer. METHODS AND MATERIALS: In 22 patients, irradiated with an ERB in situ (ERB group) and in 30 patients without an ERB (No-ERB group), prostate displacements were measured daily in three orthogonal directions with portal images. Implanted gold markers and an off-line electronic portal imaging correction protocol were used for prostate position verification and correction. Movie loops were analyzed to evaluate prostate motion and rectal filling variations. RESULTS: The off-line correction protocol reduced the systematic prostate displacements, equally for the ERB and No-ERB group, to 1.3-1.8 mm (1 SD). The mean 3D displacement was reduced to 2.8 mm and 2.4 mm for the ERB and No-ERB group, respectively. The random interfraction displacements, relative to the treatment isocenter, were not reduced by the ERB and remained nearly unchanged in all three directions: 3.1 mm (1 SD) left-right, 2.6 mm (1 SD) superior-inferior, and 4.7 mm (1 SD) for the anterior-posterior direction. These day-to-day prostate position variations can be explained by the presence of gas and stool beside the ERB. CONCLUSIONS: The off-line corrections on the fiducial markers are effective in reducing the systematic prostate displacements. The investigated ERB does not reduce the interfraction prostate motion. Although the overall mean displacement is low, the day-to-day interfraction motion, especially in anterior-posterior direction, remains high compared with the systematic displacements

Choice between prostatectomy and radiotherapy when men are eligible for both: a randomized controlled trial of usual care vs decision aid

Item does not contain fulltextWHAT'S KNOWN ON THE SUBJECT? AND WHAT DOES THE STUDY ADD?: Many patients are eligible for more than one treatment option for prostate cancer. In usual care, urologists have a large influence on the treatment choice. Decision aids, providing balanced information on the pros and cons of different treatment options, improve the match between patient preferences and treatment received. In men eligible for both surgery and external beam radiotherapy, treatment choice differed by hospital. Across the participating hospitals, the decision aid consistently led to fewer patients remaining undecided on their treatment preference and more patients choosing brachytherapy. OBJECTIVES: To examine the treatment choice for localized prostate cancer in selected men who were eligible for both prostatectomy and radiotherapy. To examine whether increased patient participation, using a decision aid, affected the treatment choice. PATIENTS AND METHODS: From 2008 to 2011, 240 patients with localized prostate cancer were enrolled from three separate hospitals. They were selected to be eligible for both prostatectomy and external beam radiotherapy. Brachytherapy was a third option for about half of the patients. In this randomized controlled trial, patients were randomized to a group which only discussed their treatment with their specialist (usual care group) and a group which received additional information from a decision aid presented by a researcher (decision aid group). The decision aid was based on a literature review. Predictors of treatment choice were examined. RESULTS: Treatment choice was affected by the decision aid (P = 0.03) and by the hospital of intake (P < 0.001). The decision aid led to more patients choosing brachytherapy (P = 0.02) and fewer patients remaining undecided (P < 0.05). Prostatectomy remained the most frequently preferred treatment. Age, tumour characteristics or pretreatment urinary, bowel or erectile functioning did not affect the choice in this selected group. Patients choosing brachytherapy assigned more weight to convenience of the procedure and to maintaining erectile function. CONCLUSIONS: Traditionally, patient characteristics differ between surgery and radiotherapy groups, but not in this selected group of patients. Men eligible for both prostatectomy and radiotherapy mostly preferred prostatectomy, and the treatment choice was influenced by the hospital they visited. Giving patients evidence-based information, by means of a decision aid, led to an increase in brachytherapy