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Disc Embedded (disc + embedded)

Distribution by Scientific Domains
Physics and Astronomy75%

Selected Abstracts

Axisymmetric interaction of a rigid disc with a transversely isotropic half-space

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2010
Amir Aabbas Katebi
Abstract A theoretical formulation is presented for the determination of the interaction of a vertically loaded disc embedded in a transversely isotropic half-space. By means of a complete representation using a displacement potential, it is shown that the governing equations of motion for this class of problems can be uncoupled into a fourth-order partial differential equation. With the aid of Hankel transforms, a relaxed treatment of the mixed-boundary value problem is formulated as dual integral equations, which, in turn, are reduced to a Fredholm equation of the second kind. In addition to furnishing a unified view of existing solutions for zero and infinite embedments, the present treatment reveals a severe boundary-layer phenomenon, which is apt to be of interest to this class of problems in general. The present solutions are analytically in exact agreement with the existing solutions for a half-space with isotropic material properties. To confirm the accuracy of the numerical evaluation of the integrals involved, numerical results are included for cases of different degrees of the material anisotropy and compared with existing solutions. Further numerical examples are also presented to elucidate the influence of the degree of the material anisotropy on the response. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Testing modified Newtonian dynamic with Local Group spiral galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2007
Edvige Corbelli
ABSTRACT The rotation curves and the relative mass distributions of the two nearby Local Group spiral galaxies, M31 and M33, show discrepancies with modified Newtonian dynamic (MOND) predictions. In M33, the discrepancy lies in the kinematics of the outermost regions. It can be alleviated by adopting tilted ring models compatible with the 21-cm datacube but different from the one that best fits the data. In M31, MOND fails to fit the falling part of the rotation curve at intermediate radii, before the curve flattens out in the outermost regions. Newtonian dynamics in a framework of a stellar disc embedded in a dark halo can explain the complex rotation curve profiles of these two galaxies, while MOND has some difficulties. However, given the present uncertainties in the kinematics of these nearby galaxies, we cannot address the success or failure of MOND theory in a definite way. More sensitive and extended observations around the critical regions, suggested by MOND fits discussed in this paper, may lead to a definite conclusion. [source]

Numerical modelling of the vertical structure and dark halo parameters in disc galaxies

ASTRONOMISCHE NACHRICHTEN, Issue 7 2010
A. Khoperskov
Abstract The non-linear dynamics of bending instability and vertical structure of a galactic stellar disc embedded into a spherical halo are studied with N-body numerical modelling. Development of the bending instability in stellar galactic disc is considered as the main factor that increases the disc thickness. Correlation between the disc vertical scale height and the halo-to-disc mass ratio is predicted from the simulations. The method of assessment of the spherical-to-disc mass ratio for edge-on spiral galaxies with a small bulge is considered. Modelling of eight edge-on galaxies: NGC 891, NGC 4738, NGC 5170, UGC 6080, UGC 7321, UGC 8286, UGC 9422 and UGC 9556 is performed. Parameters of stellar discs, dark haloes and bulges are estimated. The lower limit of the dark-to-luminous mass ratio in our galaxies is of the order of one within the limits of their stellar discs. The dark haloes dominate by mass in the galaxies with very thin stellar discs (NGC 5170, UGC 7321 and UGC 8286) (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The constant-density region of the dark haloes of spiral galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2001
Paolo Salucci
We determine a crucial feature of the dark halo density distribution from the fact that the luminous matter dominates the gravitational potential at about one disc scalelength Rd, but at the optical edge the dark matter has already become the main component of the galaxy density. From the kinematics of 137 spirals we find that the dark matter halo density profiles are self-similar at least out to Ropt and show core radii much larger than the corresponding disc scalelengths. The luminous regions of spirals consist of stellar discs embedded in dark haloes with roughly constant density. This invariant dark matter profile is very difficult to reconcile with the fundamental properties of the density distribution of cold dark matter haloes. With respect to previous work, the present evidence is obtained by means of a robust method and for a large and complete sample of normal spirals. [source]