Relativistic jets are major sources of radio-frequency radiation in the Universe. Their study is complicated by the fact that the relativistic gas flows interact with interstellar space, with the ...formation of complex flows that are smaller than the jets but can affect the evolution of the entire jets. Adaptive grids have traditionally been used to simulate such multi-scale phenomena with high spatial resolution in the zone of complex jets and low resolution to reproduce the unperturbed gas flows. In this paper, a Patch-Block-Structured Adaptive-Mesh-Refinement technique is proposed for modeling multi-scale relativistic jets. To use this technique, mathematical tools for numerically solving the equations of special relativistic hydrodynamics are updated in a particular manner. The approach is applied to the evolution of a jet in interstellar space.
The Rusanov solver for solving hydrodynamic equations is one of the most robust schemes in the class of Riemann solvers. For special relativistic hydrodynamics, the robustness condition of the scheme ...is the most important property, especially for sufficiently high values of the Lorentz factor. At the same time, the Rusanov solver is known to be very dissipative. It is proposed to use a piecewise parabolic representation of physical variables to reduce the dissipation of the Rusanov scheme. Using this approach has made it possible to obtain a scheme with the same dissipative properties as Roe-type schemes and the family of Harten–Lax–van Leer schemes. Using the problem of the decay of a relativistic hydrodynamic discontinuity, it is shown that the present author’s version of the Rusanov scheme is advantageous in terms of reproducing a contact discontinuity. The scheme is verified on classical problems of discontinuity decay and on the problem of the interaction of two relativistic jets in the three-dimensional formulation.
A low-dissipation modification of Godunov’s method based on a multidimensional piecewise-parabolic representation of numerical solutions on a local stencil is proposed. The modification is based on ...operator splitting approach for force term and for an advective term. To resolve the force term the linearized Riemann problem was used. The Rusanov scheme to solve the advective transport term was used. The method is verified by some classical hydrodynamic tests. Its order of accuracy is studied on discontinuous and differentiable solutions. The efficiency of a parallel implementation of the numerical method is investigated as well. The performance of the method is demonstrated with a model problem of multiignition explosion of a thermonuclear supernova.
In this paper, the construction of the original “Harten–Lax–van Leer” method using a piecewise-linear reconstruction of physical variables is described. The thus obtained numerical method makes it ...possible to reproduce the pressure, density, and velocity profiles with low dissipation at the discontinuities. To verify the method, classical problems of discontinuity breakdown are used with analytical solutions based on various configurations of shock waves, contact discontinuities, and rarefaction waves. The order of accuracy of the numerical method is studied using a Sod-type problem. It is shown that the greatest decrease in the order of accuracy is when a rarefaction wave is reproduced. The numerical method is verified by means of a three-dimensional Sedov test of a point explosion and a problem of a supernova Ia type explosion with two symmetric ignition points leading to the formation of a G1.9+0.3-type remnant.
Type Ia supernovae play a key role in astrophysics, but the study of the mechanisms of their explosion is still incomplete. The mathematical simulation is the main apparatus for studying known and ...all potentially new scenarios of explosion of the type Ia supernovae. All scenarios are based on the nuclear combustion of the white dwarf matter, first of all, the nuclear combustion of carbon and the subsequent detonation with the supernova explosion. For simulation of the explosion of type Ia supernovae, a subgrid model of carbon static combustion is used. This model does not take into account the previous evolution and dynamics of white dwarfs, which leads to lower values of the combustion energy and, consequently, the supernova explosion energy. We propose a mathematical model of the turbulent combustion of carbon which more adequately describes the matter combustion taking into account the white dwarfs dynamics. Computational experiments show that the supersonic turbulent combustion allows increasing the explosion energy by several times. This is achieved by “pumping” the kinetic energy obtained due to the nonzero velocity dispersion into internal energy and by more active course of the nuclear reactions of the alpha-chain from carbon to iron and nickel. In the future, the above model will be used as a subgrid model of the combustion of the white dwarf matter.
We propose some new computational model of gravitational hydrodynamics with consideration of radiation transfer in diffusion approximation on tetrahedral meshes. This model is a qualitative extension ...of the classical gravitational hydrodynamics model adapted to simulation of star formation and evolution of protoplanetary disks. We describe computational methods of solving this problem and provide the results of numerical simulation of the solar mass cloud collapse.
New methane degradation nickel catalysts based on original and modified layered double hydroxides and multilayer carbon nanotubes have been synthesized. The synthesized systems have been ...characterized by a set of physicochemical methods, namely, X-ray diffraction (XRD) analysis, scanning electron microscopy, Raman spectroscopy, and the thermal method. The catalytic activity of the synthesized catalysts in the temperature range of 550–850°С has been studied. It has been shown that in the methane decomposition reaction, the sample with a modified Ni-containing layer exhibits two regions of catalytic activity (550–650 and 700–850°С), whereas the sample based on carbon nanotubes is characterized by a single region (700–850°С) and the system based on a layered double hydroxide does not show activity in the entire temperature range.
We propose a new code named AstroPhi for simulation of the dynamics of astrophysical objects on hybrid supercomputers equipped with Intel Xenon Phi computation accelerators. The details of parallel ...implementation are described, as well as changes to the computational algorithm that facilitate efficient parallel implementation. A single Xeon Phi accelerator yielded 27-fold acceleration. The use of 32 Xeon Phi accelerators resulted in 94% parallel efficiency. Several collapse problems are simulated using the AstroPhi code.
Program title: AstroPhi
Catalogue identifier: AEUM_v1_0
Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEUM_v1_0.html
Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland
Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html
No. of lines in distributed program, including test data, etc.: 99604
No. of bytes in distributed program, including test data, etc.: 305433
Distribution format: tar.gz
Programming language: C++.
Computer: MVS-10P - RSC Tornado, Xeon E5-2690 8C 2.900 GHz, Infiniband FDR, Intel Xeon Phi SE10X.
Operating system: Linux.
Has the code been vectorized or parallelized?: Parallelized on MPI + OpenMP for Intel MIC architecture, 32 Intel Xeon Phi (60 cores per 1 Intel Xeon Phi = 1920 cores of Intel Xeon Phi).
RAM: 137438953472 bytes (128 GB) bytes
Classification: 1.9.
External routines: MPI, OpenMP for Intel Xeon Phi, FFTW 2.1.5
Nature of problem:
Complex numerical simulation of dynamics of astrophysical objects plays an important role due to significant growth of observational astronomic data. The new astrophysical models and codes need to be developed for detailed simulation of different physical effects in astrophysics with the use of modern supercomputers with hybrid architecture.
Solution method:
AstroPhi code consisting of particle-in-cell and Godunov methods combination adapted for hybrid supercomputer architecture.
Restrictions:
For this version maximum grid size is restricted to 10243.
Running time:
Typical running on MVS-10P is 24 h. The test provided only takes a few minutes.
The aim of the present study was to evaluate the cytotoxicity against MCF-7 cells and acute intraperitoneal toxicity of amphiphilic poly-N-vinylpyrrolidone nanoparticles to confirm possibility of ...their application for creation of novel drug delivery systems. The effect of cellular uptake of polymeric nanoparticles on human cancer cell line MCF-7 cells was investigated by MTT assay. MTT analysis showed that tested amphiphilic polymers were essentially non-toxic. In acute toxicity studies, LD50 and other toxicity indexes were evaluated, under which no deaths or treatment related complications were observed even in high concentration treatment for 14 days of experiment. For histological analysis, organs of the animals were weighed and examined. No animal died during the study and no significant changes have been observed regarding body weight, feed consumption, organ weight or histological data. Obtained results show that amphiphilic poly-N-vinylpyrrolidone nanoparticles possessed no toxicity against cells and in animals after intraperitoneal administration. Thus, amphiphilic PVP nanoparticles demonstrate high potential as carriers for novel high-effective drug delivery systems.
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•Amphiphilic poly-N-vinylpyrrolidone nanoparticles were prepared and characterized.•No cytotoxicity was shown for the NVP-based polymeric nanoparticles against MCF-7 cells in MTT assay.•No acute toxicity was demonstrated for the NVP-based polymeric nanoparticles after single intraperitoneal administration in mice and rats.
Aims. We study the possible atmospheric mass loss from 57 known transiting exoplanets around F, G, K, and M-type stars over evolutionary timescales. For stellar wind induced mass loss studies, we ...estimate the position of the pressure balance boundary between Coronal Mass Ejection (CME) and stellar wind ram pressures and the planetary ionosphere pressure for non- or weakly magnetized gas giants at close orbits. Methods. The thermal mass loss of atomic hydrogen is calculated by a mass loss equation where we consider a realistic heating efficiency, a radius-scaling law and a mass loss enhancement factor due to stellar tidal forces. The model takes into account the temporal evolution of the stellar EUV flux by applying power laws for F, G, K, and M-type stars. The planetary ionopause obstacle, which is an important factor for ion pick-up escape from non- or weakly magnetized gas giants is estimated by applying empirical power-laws. Results. By assuming a realistic heating efficiency of about 10–25% we found that WASP-12b may have lost about 6–12% of its mass during its lifetime. A few transiting low density gas giants at similar orbital location, like WASP-13b, WASP-15b, CoRoT-1b or CoRoT-5b may have lost up to 1–4% of their initial mass. All other transiting exoplanets in our sample experience negligible thermal loss (≤1%) during their lifetime. We found that the ionospheric pressure can balance the impinging dense stellar wind and average CME plasma flows at distances which are above the visual radius of “Hot Jupiters”, resulting in mass losses <2% over evolutionary timescales. The ram pressure of fast CMEs cannot be balanced by the ionospheric plasma pressure for orbital distances between 0.02–0.1 AU. Therefore, collisions of fast CMEs with hot gas giants should result in large atmospheric losses which may influence the mass evolution of gas giants with masses <MJup. Depending on the stellar luminosity spectral type, planetary density, heating efficiency, orbital distance, and the related Roche lobe effect, we expect that at distances between 0.015–0.02 AU, Jupiter-class and sub-Jupiter-class exoplanets can lose several percent of their initial mass. At orbital distances ≤0.015 AU, low density hot gas giants in orbits around solar type stars may even evaporate down to their coresize, while low density Neptune-class objects can lose their hydrogen envelopes at orbital distances ≤0.02 AU.
