Stability of an MHD shear flow with a piecewise linear velocity profile

In this paper we present the results of the stability analysis of a simple shear flow of an incompressible fluid with a piecewise linear velocity profile in the presence of a magnetic field. In the flow, a finite transitional magnetic-free layer with a linear velocity profile is sandwiched by two semi-infinite regions. One of these regions is magnetic-free and the flow velocity in the region is constant. The other region is magnetic and the fluid in it is quiescent. The magnetic field is constant and parallel to the flow in the transitional layer. The fluid density is constant both in the magnetic as well as the magnetic-free regions, while it has a jump-type discontinuity at the boundary between the transitional layer and the magnetic region. The effect of gravity is included in the model, and it is assumed that the lighter fluid is overlaying the heavier one, thus no Rayleigh-Taylor instability is present. The dispersion equation governing the normal-mode stability of the flow is derived and its properties are analysed. We study stability of two cases: (i) magnetic-free flow in the presence of gravity, and (ii) magnetic flow without gravity. In the first case, the flow stability is controlled by the Rayleigh number, R. In the second case, the control parameter is the inverse squared Alfvénic Mach number, H . Stability of a particular monochromatic perturbation also depends on its dimensionless wavenumber α. We combine the analytical and numerical approaches to obtain the neutral stability curves in the (α,R)-plane in the case of the magnetic-free flow, and in the (α,H)-plane in the case of the magnetic flow. The dependence of the instability increment on R in the first case, and on H in the second case is treated. We apply the results of the analysis to the stability of a strongly subsonic portion of the heliopause. Our main conclusion is as follows: The inclusion of a transitional layer near the heliopause into the model increases by an order of magnitude the strength of the interstellar magnetic field required to stabilize this portion of the heliopause in comparison with the corresponding stabilizing strength of the magnetic field required when modelling the heliopause as a tangential discontinuity

Study of nerve fibers nature reinforcing duodenal contractions by electrical stimulation of sympathetic nerve

The subject of the article is to investigate the mechanism of increased reactions by electrical stimulation of the sympathetic nerve. Materials and methods: Experiments on dogs have shown that stimulant reactions during blockade of a-adrenergic by phentolamine and (3-adrenergic receptors with propranolol were completely eliminated by lizer-gol —the blocker of 5-HT12-receptors. Results: Infusion of lizergol did not influence on duodenal motor activity and the function of the vagus nerve. Conclusion: Effector neuron is found out to be serotonergic and its action is provided by 5-HT1 2 receptor

Algebraic Geometry over Free Metabelian Lie Algebra I: U-Algebras and Universal Classes

This paper is the first in a series of three, the aim of which is to lay the foundations of algebraic geometry over the free metabelian Lie algebra $F$. In the current paper we introduce the notion of a metabelian Lie $U$-algebra and establish connections between metabelian Lie $U$-algebras and special matrix Lie algebras. We define the $\Delta$-localisation of a metabelian Lie $U$-algebra $A$ and the direct module extension of the Fitting's radical of $A$ and show that these algebras lie in the universal closure of $A$.Comment: 34 page

Mass Loss Evolution and the Formation of Detached Shells around TP-AGB Stars

The origin of the so called 'detached shells' around AGB stars is not fully understood, but two common hypotheses state that these shells form either through the interaction of distinct wind phases or an eruptive mass loss associated with a He-shell flash. We present a model of the formation of detached shells around thermal pulse asymptotic giant branch (TP-AGB) stars, based on detailed modelling of mass loss and stellar evolution, leading to a combination of eruptive mass loss and wind interaction. The purpose of this paper is first of all to connect stellar evolution with wind and mass loss evolution and demonstrate its consistency with observations, but also to show how thin detached shells around TP-AGB stars can be formed. Previous attempts to link mass loss evolution with the formation of detached shells were based on approximate prescriptions for the mass loss and have not included detailed modelling of the wind formation as we do here. (abridged)Comment: 16 pages, 15 figures. Accepted for publication in Astronomy & Astrophysic

XMM-Newton X-ray Observations of the Wolf-Rayet Binary System WR 147

We present results of a 20 ksec X-ray observation of the Wolf-Rayet (WR) binary system WR 147 obtained with XMM-Newton. Previous studies have shown that this system consists of a nitrogen-type WN8 star plus an OB companion whose winds are interacting to produce a colliding wind shock. X-ray spectra from the pn and MOS detectors confirm the high extinction reported from IR studies and reveal hot plasma including the first detection of the Fe K-alpha line complex at 6.67 keV. Spectral fits with a constant-temperature plane-parallel shock model give a shock temperature kT(shock) = 2.7 keV [T(shock) ~ 31 MK], close to but slightly hotter than the maximum temperature predicted for a colliding wind shock. Optically thin plasma models suggest even higher temperatures, which are not yet ruled out. The X-ray spectra are harder than can be accounted for using 2D numerical colliding wind shock models based on nominal mass-loss parameters. Possible explanations include: (i) underestimates of the terminal wind speeds or wind abundances, (ii) overly simplistic colliding wind models, or (iii) the presence of other X-ray emission mechanisms besides colliding wind shocks. Further improvement of the numerical models to include potentially important physics such as non-equilibrium ionization will be needed to rigorously test the colliding wind interpretation.Comment: 8 pages, 7 figure

ПИТАННЯ РОЗРОБКИ НОРМАТИВІВ ДИСТАНЦІЙНОГО НАВЧАННЯ В ПІСЛЯДИПЛОМНІЙ МЕДИЧНІЙ ОСВІТІ

Main principles of model building of the postgraduate medical education grounded on internally-correspondence principles with usage of distance technologies are considered and proved. Step-by-step transition to self-instruction which should be supported by the certificated educational and methodical materials for distance training is regulated.Рассматриваются и обосновываются основные принципы разработки модели последипломного медицинского образования, основанного на очно-заочных принципах с использованием дистанционных технологий. Регламентируется постепенный переход на самостоятельную работу, которая должна поддерживаться сертифицированными учебно-методическими материалами для дистанционного обучения.Розглядаються та обґрунтовуються основні принципи розробки моделі післядипломної медичної освіти, заснованої на очно-заочних принципах з використанням дистанційних технологій. Регламентується поступовий перехід на самостійну роботу, що повинна бути підтримана сертифікованими навчально-методичними матеріалами для дистанційного навчання

Quasi-simultaneous XMM-Newton and VLA observation of the non-thermal radio emitter HD\168112 (O5.5III(f^+))

We report the results of a multiwavelength study of the non-thermal radio emitter HD168112 (O5.5III(f^+)). The detailed analysis of two quasi-simultaneous XMM-Newton and VLA observations reveals strong variability of this star both in the X-ray and radio ranges. The X-ray observations separated by five months reveal a decrease of the X-ray flux of ~30%. The radio emission on the other hand increases by a factor 5-7 between the two observations obtained roughly simultaneously with the XMM-Newton pointings. The X-ray data reveal a hard emission that is most likely produced by a thermal plasma at kT ~2-3 keV while the VLA data confirm the non-thermal status of this star in the radio waveband. Comparison with archive X-ray and radio data confirms the variability of this source in both wavelength ranges over a yet ill defined time scale. The properties of HD168112 in the X-ray and radio domain point towards a binary system with a significant eccentricity and an orbital period of a few years. However, our optical spectra reveal no significant changes of the star's radial velocity suggesting that if HD168112 is indeed a binary, it must be seen under a fairly low inclination.Comment: 17 pages, 11 figures (10 postscript + 1 gif

Two-dimensional Anderson-Hubbard model in DMFT+Sigma approximation

Density of states, dynamic (optical) conductivity and phase diagram of paramagnetic two-dimensional Anderson-Hubbard model with strong correlations and disorder are analyzed within the generalized dynamical mean-field theory (DMFT+Sigma approximation). Strong correlations are accounted by DMFT, while disorder is taken into account via the appropriate generalization of the self-consistent theory of localization. We consider the two-dimensional system with the rectangular "bare" density of states (DOS). The DMFT effective single impurity problem is solved by numerical renormalization group (NRG). Phases of "correlated metal", Mott insulator and correlated Anderson insulator are identified from the evolution of density of states, optical conductivity and localization length, demonstrating both Mott-Hubbard and Anderson metal-insulator transitions in two-dimensional systems of the finite size, allowing us to construct the complete zero-temperature phase diagram of paramagnetic Anderson-Hubbard model. Localization length in our approximation is practically independent of the strength of Hubbard correlations. However, the divergence of localization length in finite size two-dimensional system at small disorder signifies the existence of an effective Anderson transition.Comment: 10 pages, 10 figures, improve phase diagra

РЕНТГЕНОЛОГИЧЕСКИЕ ПРОЯВЛЕНИЯ ТУБЕРКУЛЕЗА У ВИЧ-ИНФИЦИРОВАННЫХ ЛИЦ

The co-infection HIV-TB is a serious global problem of the last two decades. Radiological manifestations of tuberculosis have particular features depending on suppression of immune system. The purpose of this work was studying of radiological manifestations of tuberculosis in HIV-positive patients and detection of relationship between radiological manifestations and HIV infection stage. The basic methods to solve this problem were clinical and laboratory diagnostic minimum and digital radiography. Additional methods included CT, fiber-optic bronchoscopy and invasive interventions. The results of this research show that most often patients are being infected with tuberculosis at stages of HIV-infection 4Б-В (RF classification) with significant suppression of immune system. Spread of the radiological manifestations reflecting a tendency to generalization of a tubercular inflammation is directly proportional to the stage of HIV infection at which tuberculosis was identified. The dissemination of specific focuses can occur in the hematogenous, lymphogenous and mixed way. Today diagnostic radiology remains the primary method in identifying tuberculosis in HIV-positive patients.Сочетание ВИЧ-инфекции и туберкулеза - важная общемировая проблема последних двух десятилетий. Рентгенологические проявления специфического процесса могут иметь свои особенности в зависимости от степени угнетения иммунитета. Цель данной работы состояла в изучении рентгенологических проявлений туберкулеза, возникшего у ВИЧ-инфицированных лиц, выявление зависимости рентгенологической картины от стадии ВИЧ-инфекции. Основными методами при ее выполнении были клинико-лабораторный диагностический минимум, цифровое рентгенотомографическое обследование. Дополнительными методами служили компьютерная томография (КТ), фибробронхоскопия и инвазивные вмешательства. Результаты проведенного исследования показывают, что наиболее часто туберкулезом заболевают больные на стадиях ВИЧ-инфекции 4Б-4В при существенном подавлении функций иммунной системы. Распространенность лучевых синдромов, отражающих тенденцию к генерализации туберкулезного воспаления, прямо пропорциональна стадии ВИЧ-инфекции, на которой был выявлен туберкулез. Распространение специфических очагов в легких может происходить гематогенным, лимфогенным и смешанным путем. На сегодняшний день лучевая диагностика остается основным методом выявления туберкулеза у ВИЧ-инфицированных пациентов