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Results of 2D numerical simulations of thermonuclear burning propagation in a helium layer on a neutron star surface using the Euler-Lagrange TIGR-3T code are presented. This process is crucial for the development of type I X-ray bursts. Ignition and thermonuclear burning propagation are fairly easy to obtain when simulating a layer with a density at the bottom of 1.75 × 108 g cm−3. Such a simulation allows it to be compared with previous simulations based on other codes, including the simulation based on the MPM code described previously. However, this density is two orders of magnitude higher than can be obtained in observed bursters. The implementation of efficient numerical methods for the description of heat conduction and turbulence in the TIGR-3T code has allowed simulations to be performed for a layer with a density at the bottom of 1.8 × 107 g cm−3. The fulfilment of certain conditions on the size and shape of the initial temperature perturbation is required for the propagation of thermonuclear burning. Simulations reveal a peculiar burning propagation mechanism through compression of the layer ahead of the burning front by the matter transferred above the free surface.

Some thermonuclear X-ray bursters exhibit a high-frequency (about 300 Hz or more) brightness modulation at the rising phase of some bursts. These oscillations are explained by inhomogeneous heating of the surface layer on a rapidly rotating neutron star due to the finite propagation speed of thermonuclear burning. We suggest and substantiate a mechanism of this propagation that is consistent with experimental data. Initially, thermonuclear ignition occurs in a small region of the neutron star surface layer. The burning products rapidly rise and spread in the upper atmospheric layers due to turbulent convection. The accumulation of additional matter leads to matter compression and ignition at the bottom of the layer. This determines the propagation of the burning front. To substantiate this mechanism, we use the simplifying assumptions about a helium composition of the neutron star atmosphere and its initial adiabatic structure with a density of 1.75 × 108 g cm−3 at the bottom. 2D numerical simulations have been performed using a modified particle method in the adiabatic approximation.

We study the influence of turbulent mixing on the development of thermonuclear flashes in the surface layers of neutron stars. A simple K e model that includes various physical processes is used to describe the turbulent processes. In contrast to the widespread mixing-length theory, the K e model does not require using additional dimensional parameters, traces the development of turbulence in dynamics, describes the various turbulence development scenarios (gravitational and shear instabilities, convection, semiconvection, etc.) in a unified way, and can be used in multidimensional numerical simulations. Empirical constants of the model are chosen on the basis of experimental data and direct numerical simulations of typical processes. We have used the Era and Tigr-3T software packages to numerically simulate thermonuclear flashes in the accretion-renewable atmospheres of neutron stars. Turbulence is shown to accelerate significantly the transport of released energy to the stellar surface. Mixing equalizes the concentrations of matter components throughout the burning layer and increases the amount of matter involved in the thermonuclear burning during a flash.

This paper presents the results of temporal measurements of the soft X-ray radiation intensity in the spectral range of 10-40 eV emitted from the capillary plasma under discharge with a current pulse of 26 kA amplitude and rising rate of about 1012 A/s. The experiments were carried out on a pulsed-power facility SIGNAL with ceramic capillaries of 0.3 cm inner diameter and 15.7 cm length, which are filled with argon up to pressures in the range of 0.25-0.5 torr. To interpret the experimental results, a sequence of numerical calculations simulating gas dynamics and level-by-level ionic kinetics of argon plasma was used. The effect of X-ray lasing in the Ne-like line was found to be generated with a quanta energy of 26.4 eV, which lasted for approximately 1-2 ns, at a moment of about 33 ns after the current pulse start

Results are presented from time-resolved measurements of the soft X-ray emission in the 10-to 40-eV spectral range from the plasma of a pulsed capillary discharge in argon at current pulse amplitudes of up to 26 kA and a current rise time of ∼1012 A/s. The experiments were carried out with 0.3-cm-diameter 15.7-cm-long ceramic capillaries filled with argon at a pressure of 0.25–0.5 Torr in the SIGNAL electrophysical facility. The experimental data are interpreted via computer simulations of the magnetohydrodynamics and level-by-level ion kinetics of an argon plasma. The results obtained indicate that soft X-ray laser pulses with a photon energy of 26.4 eV and duration of 1–2 ns are generated ≈33 ns after the beginning of the discharge current pulse.

Results are presented from experiments on the laser generation of X-ray radiation at the wavelength λ=469 A (e=26.4 eV) on the 3p(J=0)−3s(J=1) transition of Ne-like Ar ions. Experiments were carried out on the SIGNAL electrophysical facility with a 3.1-mm-diameter 157-mm-long Al2O3 ceramic capillary filled with argon at a pressure of 0.2–1.0 Torr. The discharge current amplitude was I ∼ 25–40 kA, the current rise rate being dI/dt ∼ 1012 A/s. By a vacuum X-ray diode tuned to detect X-ray photons with energies in the range 10–40 eV, laser pulses with a duration of t 1 ∼ 1 ns and maximum energy of E 1,max ∼ 1 µJ were recorded. The pulses were generated 35 ns after the discharge current was switched on. The line spectra in the wavelength range of 150–500 A showed the bright λ=469 A line. The angular divergence of the generated X-ray laser beam was estimated to be Δϑ ∼ 2 mrad.

Results of computational and theoretical studies are presented. A formulation of the problem is given and approaches to its solution are described. Brief information is given on the models, difference methods, and software designed or adapted to perform direct numerical modeling of mass‐spectrometric measurements of cometary dust on PUMA instruments. The results of a number of computational experiments are presented.

Two-dimensional calculations by the TIGR code [Izv. Sib. Otd. Akad. Nauk SSSR 8, 74 (1967); Vop. Atom. Nauk Tekh. Met. Prog. Chisl. Resh. Zad. Mat Fiz. 3, 34, (1984)] have verified the main result of the theoretical research on the limitation of perturbation growth at the ablation front, which appeared in the planar foils irradiated by laser flow in the regime of accelerated motion of the ablation front. It is shown by calculations that the growth rate γ, characterizing the perturbation growth, achieves its maximal value γm at some wave number km, which is defined by initial parameters of the problem—acceleration at the ablation front g and velocity of ablation ua. It is in good agreement qualitatively and quantitatively, with theoretical results obtained earlier by some authors. It is shown by calculations that for k>km, as it proceeds from the theory, the growth rate decreases down to zero. Simulations of turbulent mixing on the basis of the Ke model is implemented. For the thin foil case considered, an analytic estimate of the effect of turbulent mix, which included Takabe’s formula, showed ablation reduced in the coefficient in the mixing equation by a factor of 25. Theoretical and numerical research on the influence of turbulent mixing on the performance of the compressed part of the plate has been conducted.

The Iskra-6 laser facility with energy up to 300 kJ is planned to be created in Russia. The results of 1D- and 2D-simulations of a single-shell cryogenic target and a double-shell non-cryogenic target to achieve thermonuclear ignition at the Iskra-6 laser facility are discussed.

The results of ID-ERA and 2D-TIGR, OMEGA codes calculations of compression and burn of indirect-driven targets for the thermonuclear ignition and Engineering Test Facility are presented. The possibility to obtain high-energy yield of G > 100 with driver energy of Ed = 5−10 MJ by using the heavy-ion one-beam accelerator as the main driver and powerful laser for fast ignition of thermonuclear detonation of cylindrical targets is pointed out.

Frequently during its lifetime a human organism is subjected to the acoustical and similar to them vibrating impacts. Under the certain conditions such influence may cause physiological changes in the organs functioning. Thus the study of the oscillatory mechanical impacts to the organism is very important task of the numerical physiology. It allows to investigate the endurance limits of the organism and to develop protective measures in order to extend them. The noise nuisances affects to the most parts of the organism disrupting their functions. The vibrating disturbances caused to the lung function as one of the most sensitive to the acoustical impacts is considered in this work. The model proposed to describe the air motion in trachea-bronchial tree is based on the one dimensional no-linear theory including mass and momentum conservation for the air flow in flexible tubes similar to the model of blood flow in large vessels [1]. It combined with the single-component model of alveole [1], [2]. Two types of vibrating impacts were simulated that affect the thorax and the nasopharynx. The conducted simulations allowed us to detect two resonance frequencies that lay in the ranges from 3 Hz to 8 Hz and from 40 to 70 Hz when the thorax was affected (fig.1). For the nasopharynx disturbances no resonance states were found. Open image in new window Fig. 1. Dependencies of the integral volume and pressure of the lungs from oscillatory impacts.

Blood system functions are very diverse and important for most processes in human organism. One of its primary functions is matter transport among different parts of the organism including tissue supplying with oxygen, carbon dioxide excretion, drug propagation etc. Forecasting of these processes under normal conditions and in the presence of different pathologies like atherosclerosis, loss of blood, anatomical abnormalities, pathological changing in chemical transformations and others is significant issue for many physiologists. In this connection should be pointed out that global processes are of special interest as they include feedbacks and interdependences among different regions of the organism. At the modern level of computer engineering the most adequate physical model for the dynamical description of cardiovascular system is the model of non-stationary flow of incompressible fluid through the system of elastic tubes. Mechanics of such flow is described by nonlinear set of hyperbolic equations including mass and momentum conservation joined with equation of state that determines elastic properties of the tube [1]. As we interested in global processes the models of the four vascular trees (arterial and venous parts of systemic and pulmonary circulation) must be closed with heart and peripheral circulation models. Heart operation is described by the model of fluid flow averaged by volume through the system of extensible chambers that results in the set of stiff ordinary differential equations [1]. When combined these models allow us to consider functional changes and responses as during one cardiac cycle and at a longer periods upon 10 minutes that Open image in new window Fig. 1. Pressure wave propagation through the large pulmonary arteries during one cardiac cycle. Grayscale designates divergence from the minimum pressure in each vessel.

The results are presented of numerical simulations of the self‐similar problem on shear turbulent mixing of plain layers. The simulations used 2D k‐e model. The dependence was obtained of mixing zone growth rate on the layers density ratio in the incompressible limit. Influence of compressibility is also discussed.

Summary form only given. 2D radiation MHD simulations show that mass flows from separate wires join at the half of radius. To understand this phenomenon a sequence of 2D simulation runs have been done: 1) pure hydrodynamics without magnetic field and radiation transport; 2) including magnetic field; 3) including radiation transport. It is obtained that two factors plays an important role: development of hydroinstabilities (Kelvin, RT and RM) and "frozen-in" magnetic field. The "cold start" of separate wire explosion in an array has been the subject of interest in order to understand the implosion dynamics. Mass inflow dependence on initial distance between wires is analyzed. The complicated dynamic structure of exploded wire determines the mechanism of plasma entrainment from single wire towards the axis. The dense core formed at the axis of single wire is surrounded by liquid-vapor mixture with strong perturbations. Wide range equation of state accounting metastable properties and elastic-plastic properties of matter has been used. Calculations show that the mixture is the result of overheating instability. The interaction of shock wave generated by neighboring wire and media with different densities leads to MHD instabilities. Results of numerical simulation have been compared with experimental data obtained on generator ANGARA (TRINITI, Russia) and with the data calculated by using the model of delaying of plasma formation. Dependence of processes on power input rate has been estimated.

The results of 1D-ERA and 2D-TICR, 2D-OMEGA codes calculations of compression and burn of indirect-driven targets for the thermonuclear ignition and Hybrid Nuclear-Fusion Reactor are presented.