36 research outputs found
Relativistic and Newtonian core-shell models: analytical and numerical results
We make a detailed analysis of Newtonian as well as relativistic core-shell
models recently proposed to describe a black hole or neutron star surrounded by
shells of matter, and in a seminal sense also galaxies, supernovae and star
remnants since there are massive shell-like structures surrounding many of them
and also evidences for many galactic nuclei hiding black holes. We discuss the
unicity of the models in relation to their analyticity at the black hole
horizon and also to the full elimination of conical singularities. Secondly, we
study the role played by the presence/lack of discrete reflection symmetries
about equatorial planes in the chaotic behavior of the orbits, which is to be
contrasted with the almost universal acceptance of reflection symmetries as
default assumptions in galactic modeling. We also compare the related effects
if we change a true central black hole by a Newtonian central mass. The
numerical findings are: 1- The breakdown of the reflection symmetry about the
equatorial plane in both Newtonian and relativistic core-shell models does i)
enhance in a significant way the chaoticity of orbits in reflection symmetric
oblate shell models and ii) inhibit significantly also the occurrence of chaos
in reflection symmetric prolate shell models. In particular, in the prolate
case the lack of the reflection symmetry provides the phase space with a robust
family of regular orbits that is otherwise not found at higher energies. 2- The
relative extents of the chaotic regions in the relativistic cases (i. e. with a
true central black hole) are significantly larger than in the corresponding
Newtonian ones (which have just a central potential).Comment: AASTEX, 22 pages plus 28 postscript figures, to appear in Ap.
The origin of the light distribution in spiral galaxies
We analyse a high-resolution, fully cosmological, hydrodynamical disc galaxy simulation, to study the source of the double-exponential light profiles seen in many stellar discs, and the effects of stellar radial migration upon the spatiotemporal evolution of both the disc age and metallicity distributions. We find a ‘break’ in the pure exponential stellar surface brightness profile, and trace its origin to a sharp decrease in the star formation per unit surface area, itself produced by a decrease in the gas volume density due to a warping of the gas disc. Star formation in the disc continues well beyond the break. We find that the break is more pronounced in bluer wavebands. By contrast, we find little or no break in the mass density profile. This is, in part, due to the net radial migration of stars towards the external parts of the disc. Beyond the break radius, we find that ∼60 per cent of the resident stars migrated from the inner disc, while ∼25 per cent formed in situ. Our simulated galaxy also has a minimum in the age profile at the break radius but, in disagreement with some previous studies, migration is not the main mechanism producing this shape. In our simulation, the disc metallicity gradient flattens with time, consistent with an ‘inside-out’ formation scenario. We do not find any difference in the intensity or the position of the break with inclination, suggesting that perhaps the differences found in empirical studies are driven by dust extinction
Upregulation of CENP-H in tongue cancer correlates with poor prognosis and progression
<p>Abstract</p> <p>Background</p> <p>Centromere protein H (CENP-H) is one of the fundamental components of the human active kinetochore. Recently, CENP-H was identified to be associated with tumorigenesis. This study was aimed to investigate the clinicopathologic significance of CENP-H in tongue cancer.</p> <p>Methods</p> <p>RT-PCR, real time RT-PCR and Western blot were used to examine the expression of CENP-H in tongue cancer cell lines and biopsies. CENP-H protein level in paraffin-embedded tongue cancer tissues were tested by immunohistochemical staining and undergone statistical analysis. CENP-H-knockdown stable cell line was established by infecting cells with a retroviral vector pSuper-retro-CENP-H-siRNA. The biological function of CENP-H was tested by MTT assay, colony formation assay, and Bromodeoxyuridine (BrdU) incorporation assay.</p> <p>Results</p> <p>CENP-H expression was higher in tongue cancer cell lines and cancer tissues (T) than that in normal cell and adjacent noncancerous tongue tissues (N), respectively. It was overexpressed in 55.95% (94/168) of the paraffin-embedded tongue cancer tissues, and there was a strong correlation between CENP-H expression and clinical stage, as well as T classification. CENP-H can predict the prognosis of tongue cancer patients especially those in early stage. Depletion of CENP-H can inhibit the proliferation of tongue cancer cells (Tca8113) and downregulate the expression of Survivin.</p> <p>Conclusion</p> <p>These findings suggested that CENP-H involves in the development and progression of tongue cancer. CENP-H might be a valuable prognostic indicator for tongue cancer patients within early stage.</p
Dynamics of Disks and Warps
This chapter reviews theoretical work on the stellar dynamics of galaxy
disks. All the known collective global instabilities are identified, and their
mechanisms described in terms of local wave mechanics. A detailed discussion of
warps and other bending waves is also given. The structure of bars in galaxies,
and their effect on galaxy evolution, is now reasonably well understood, but
there is still no convincing explanation for their origin and frequency. Spiral
patterns have long presented a special challenge, and ideas and recent
developments are reviewed. Other topics include scattering of disk stars and
the survival of thin disks.Comment: Chapter accepted to appear in Planets, Stars and Stellar Systems, vol
5, ed G. Gilmore. 32 pages, 17 figures. Includes minor corrections made in
proofs. Uses emulateapj.st
Periodic orbits and their bifurcations in a 3-D system
We study some simple periodic orbits and their bifurcations in the Hamiltonian Mathematical expression. We give the forms of the orbits, the characteristics of the main families, and some existence diagrams and stability diagrams. The existence diagram of the family 1a contains regions that are stable (S), simply unstable (U), doubly unstable (DU) and complex unstable (Δ). In the regions S and U there are lines of equal rotation number m/n. Along these lines we have bifurcations of families of periodic orbits of multiplicity n. When these lines reach the boundary of the complex unstable region, they are tangent to it. Inside the region Δ there are lines m/n, along which the orbits 1a, described n-times, are doubly unstable; however, along these lines there are no bifurcations of n-ple periodic orbits. The families bifurcating from 1a exist only in certain regions of the parameter space (ε, η). The limiting lines of these regions join at particular points representing collisions of bifurcations. These collisions of bifurcations produce a nonuniqueness of the various families of periodic orbits. The complicated structure of the various bifurcations can be understood by constructing appropriate stability diagrams. © 1994 Kluwer Academic Publishers