Numerical simulation of small perturbation on an accretion disk due to the collision of a star with the disk near the black hole

In this paper, perturbations of an accretion disk by a star orbiting around a black hole are studied. We report on a numerical experiment, which has been carried out by using a parallel-machine code originally developed by D\"{o}nmez (2004). An initially steady state accretion disk near a non-rotating (Schwarzschild) black hole interacts with a "star", modeled as an initially circular region of increased density. Part of the disk is affected by the interaction. In some cases, a gap develops and shock wave propagates through the disk. We follow the evolution for order of one dynamical period and we show how the non-axisymetric density perturbation further evolves and moves downwards where the material of the disk and the star become eventually accreted onto the central body. When the star perturbs the steady state accretion disk, the disk around the black hole is destroyed by the effect of perturbation. The perturbed accretion disk creates a shock wave during the evolution and it loses angular momentum when the gas hits on the shock waves. Colliding gas with the shock wave is the one of the basic mechanism of emitting the $X-$rays in the accretion disk. The series of supernovae occurring in the inner disk could entirely destroy the disk in that region which leaves a more massive black hole behind, at the center of galaxies.Comment: 20pages, 8 figures, accepted for publication in Astrophysics and Space Scienc

Newtonian Cosmology in Lagrangian Formulation: Foundations and Perturbation Theory

The ``Newtonian'' theory of spatially unbounded, self--gravitating, pressureless continua in Lagrangian form is reconsidered. Following a review of the pertinent kinematics, we present alternative formulations of the Lagrangian evolution equations and establish conditions for the equivalence of the Lagrangian and Eulerian representations. We then distinguish open models based on Euclidean space $\R^3$ from closed models based (without loss of generality) on a flat torus \T^3. Using a simple averaging method we show that the spatially averaged variables of an inhomogeneous toroidal model form a spatially homogeneous ``background'' model and that the averages of open models, if they exist at all, in general do not obey the dynamical laws of homogeneous models. We then specialize to those inhomogeneous toroidal models whose (unique) backgrounds have a Hubble flow, and derive Lagrangian evolution equations which govern the (conformally rescaled) displacement of the inhomogeneous flow with respect to its homogeneous background. Finally, we set up an iteration scheme and prove that the resulting equations have unique solutions at any order for given initial data, while for open models there exist infinitely many different solutions for given data.Comment: submitted to G.R.G., TeX 30 pages; AEI preprint 01

Oscillating structure of \gamma-bursts and their possible origin

As it is well-known that the hydrodinamic collapse of the massive star iron core should lead to the production of a hot neutron star. The assumption is made that the thermonuclear burning of the envelope matter, accreting onto the hot neutron star, can proceed in the oscillatoric regime (analogously to that happens during heat explosion of the carbon-oxigene cores of stars with smaller masses). Local density oscillations in the vicinity of the neutron star surface can generate shock waves, in which the stratification of the electron-positron plasma from the rest of the matter can happen due to the light preasure. In the case of the spherically symmetric collapse of the compact star it can lead to the production of the expanding relativistic fireball shells with characteristic oscillation time of ~ 10^{-2} s, observed in the cosmological \gamma-bursts (GRB), can occur. It is pointed out that nonrotating massive Wolf-Rayet's (WR) stars could be the source for the GRB, whose collapses, according to a number of observations, can happen without any noticeable ejection of the envelope.Comment: 11 pages, latex-file, 2 eps figure

A prospective study in children with a severe form of atopic dermatitis: clinical outcome in relation to cytokine gene polymorphisms

Background and Objective: <br/> <br/> The course of atopic dermatitis (AD) in childhood is characterized by typical changes in phenotype, including a shift from skin involvement to respiratory allergy usually around the third year of age. We thus designed a prospective study to monitor the outcome of severe AD and to investigate the association between cytokine gene polymorphisms and clinical manifestations. Methods: <br/> <br/> Clinical and laboratory follow-up of 94 patients with severe AD and 103 healthy controls was performed using routine methodology. Allele, genotype, and haplotype frequencies of single nucleotide polymorphisms of 13 selected cytokine/receptor genes were analyzed using PCR with sequence-specifi c primers. Results: <br/> <br/> In our study, genotypes of 7 polymorphisms—IL-4 -1098G/T and -590C/T, IL-6 -174C/G and nt565A/G, and IL-10 -1082A/G, -819C/T, and -592A/C were signifi cantly associated with atopic AD (P<.05). A signifi cant association was also found for TNF-α AA and IL-4 GC haplotypes and AD. We confirm the progressive clinical improvement of AD together with a decrease in the severity index SCORAD (SCORing atopic dermatitis) during childhood (P<.05). We found signifi cant differences between IL-4Rα +1902 A/G and positivity of tree pollen–specifi c IgE (P<.05) in the AD group. Moreover, a weak association was also found between IL-10 -819C/T and IL-10 -590A/C and the appearance of allergic rhinitis (P<0.1). Conclusions: <br/> <br/> We confirmed a clinical shift in allergic phenotype in the fi rst 3 years of life, and showed an association between IL-4, IL-6, and IL-10 polymorphisms and AD. Our data indicate that IL-4α and IL-10 polymorphisms may be considered predictive factors of respiratory allergy in children with AD