104 research outputs found
On the accretion disc properties in eclipsing dwarf nova EM Cyg
In this paper we analyzed the behavior of the unusual dwarf nova EM Cyg using
the data obtained in April-October, 2007 in Vyhorlat observatory (Slovak
Republic) and in September, 2006 in Crimean Astrophysical Observatory
(Ukraine). During our observations EM Cyg has shown outbursts in every 15-40
days. Because on the light curves of EM Cyg the partial eclipse of an accretion
disc is observed we applied the eclipse mapping technique to reconstruct the
temperature distribution in eclipsed parts of the disc. Calculations of the
accretion rate in the system were made for the quiescent and the outburst
states of activity for different distances.Comment: 6 pages, 3 figures, accepted in Astrophysics and Space Scienc
Spectral Difference Method for Unstructured Grids II: Extension to the Euler Equations
Entropy Stable Finite Volume Approximations for Ideal Magnetohydrodynamics
This article serves as a summary outlining the mathematical entropy analysis of the ideal magnetohydrodynamic (MHD) equations. We select the ideal MHD equations as they are particularly useful for mathematically modeling a wide variety of magnetized fluids. In order to be self-contained we first motivate the physical properties of a magnetic fluid and how it should behave under the laws of thermodynamics. Next, we introduce a mathematical model built from hyperbolic partial differential equations (PDEs) that translate physical laws into mathematical equations. After an overview of the continuous analysis, we thoroughly describe the derivation of a numerical approximation of the ideal MHD system that remains consistent to the continuous thermodynamic principles. The derivation of the method and the theorems contained within serve as the bulk of the review article. We demonstrate that the derived numerical approximation retains the correct entropic properties of the continuous model and show its applicability to a variety of standard numerical test cases for MHD schemes. We close with our conclusions and a brief discussion on future work in the area of entropy consistent numerical methods and the modeling of plasmas
Causal Relationship between Obesity and Vitamin D Status: Bi-Directional Mendelian Randomization Analysis of Multiple Cohorts
M.-L. Lokki työryhmän Genetic Invest Anthropometric Trai jäsen.Peer reviewe
Dust-obscured star formation and AGN fuelling in hierarchical models of galaxy evolution
A large fraction of the luminous distant submm-wave galaxies recently
detected using SCUBA on the JCMT appear to be associated with interacting
optical counterparts. We investigate these systems using a simple hierarchical
clustering model of galaxy evolution, in which the large luminosity of the
SCUBA galaxies is assumed to be generated at the epoch of galaxy mergers in a
burst of either star formation activity or the fuelling of an active galactic
nucleus (AGN). The models are well constrained by the observed spectrum of the
FIR/submm background radiation and the 60-micron counts of low-z IRAS galaxies.
The ratio between the total amount of energy released during mergers and the
mass of dark matter involved must increase sharply with z at z<1, and then
decrease at higher z, independent of the fraction of the luminosity of mergers
that is produced by starbursts and AGN. One additional parameter - the
reciprocal of the product of the duration of the enhanced luminosity produced
by the merger and the fraction of mergers that induce an enhanced luminosity,
which we call the activity parameter - is introduced, to allow the relationship
between merging dark matter haloes and the observed counts of distant dusty
galaxies to be investigated. The observed counts can only be reproduced if the
activity parameter is greater by a factor of about 5 and 100 at redshifts of 1
and 3 respectively, compared with the present epoch. Hence, if mergers account
for the SCUBA galaxies, then the merger process must have been much more
violent at high redshifts. We discuss the counts of galaxies and the intensity
of background radiation in the optical/near-IR wavebands in the context of
these hierarchical models, and thus investigate the relationship between the
populations of SCUBA and Lyman-break galaxies.Comment: 18 pages, 12 figures, in press at MNRAS. Final proof versio
Eight new T4.5-T7.5 dwarfs discovered in the UKIDSS large area survey data release 1
The definitive version is available at www.blackwell-synergy.com Copyright Blackwell Publishing DOI : 10.1111/j.1365-2966.2007.12023.xPeer reviewe
The development of an unstructured grid solver for reactive compressible flow applications
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