2,624 research outputs found
Sigma models with singularities in Euclidean spacetime of dimension 0<=D<4 and in the limit N->infinity
For the case of the single-O()-vector linear sigma models the critical
behaviour following from any singularity in the action is worked out in
the double scaling limit , , . After an exact elimination of Gaussian degrees of freedom, the
critical objects such as coupling constants, indices and susceptibility matrix
are derived for all and spacetime dimensions . There appear
exceptional spacetime dimensions where the degree of the singularity
is more strongly constrained than by the renormalizability requirement.Comment: LaTeX, 25 pages, no figure
Double Scaling Limits, Airy Functions and Multicritical Behaviour in O(N) Vektor Sigma Models
O(N) vector sigma models possessing catastrophes in their action are studied.
Coupling the limit N --> infinity with an appropriate scaling behaviour of the
coupling constants, the partition function develops a singular factor. This is
a generalized Airy function in the case of spacetime dimension zero and the
partition function of a scalar field theory for positive spacetime dimension.Comment: 14 pages, LaTe
On the critical behaviour of hermitean f-matrix models in the double scaling limit with f >= 3
An algorithm for the isolation of any singularity of f-matrix models in the
double scaling limit is presented. In particular it is proved by construction
that only those universality classes exist that are known from 2-matrix models.Comment: 24 pages, LaTex, correction of some notation errors and addition of
four reference
Physics of rotation in stellar models
In these lecture notes, we present the equations presently used in stellar
interior models in order to compute the effects of axial rotation. We discuss
the hypotheses made. We suggest that the effects of rotation might play a key
role at low metallicity.Comment: 32 pages, 7 figures, lectures, CNRS school, will be published by
Springe
DESIGN CONSIDERATIONS FOR DIGITAL IMAGE LIBRARIES
Design of digital image libraries requires choices for numerous configuration aspects, such as resolution and display settings. These aspects can be categorized into different types of design criteria based on whether they are a human viewing and usage factor, or a stage in the image library management process. The criteria can also be applied in a hierarchy of nested versions of access to the library to suit different usage circumstances. Here we present a framework for design criteria using this approach, and apply it to some example cases
Structure Formation Inside Triaxial Dark Matter Halos: Galactic Disks, Bulges and Bars
We investigate the formation and evolution of galactic disks immersed in
assembling live DM halos. Disk/halo components have been evolved from the
cosmological initial conditions and represent the collapse of an isolated
density perturbation. The baryons include gas (which participates in star
formation [SF]) and stars. The feedback from the stellar energy release onto
the ISM has been implemented. We find that (1) The growing triaxial halo figure
tumbling is insignificant and the angular momentum (J) is channeled into the
internal circulation; (2) Density response of the disk is out of phase with the
DM, thus diluting the inner halo flatness and washing out its prolateness; (3)
The total J is neathly conserved, even in models accounting for feedback; (4)
The specific J for the DM is nearly constant, while that for baryons is
decreasing; (5) Early stage of disk formation resembles the cat's cradle -- a
small amorphous disk fueled via radial string patterns; (6) The initially
puffed up gas component in the disk thins when the SF rate drops below ~5
Mo/yr; (7) About 40%-60% of the baryons remain outside the SF region; (8)
Rotation curves appear to be flat and account for the observed disk/halo
contributions; (9) A range of bulge-dominated to bulgeless disks was obtained;
Lower density threshold for SF leads to a smaller, thicker disk; Gravitational
softening in the gas has a substantial effect on various aspects of galaxy
evolution and mimics a number of intrinsic processes within the ISM; (10) The
models are characterized by an extensive bar-forming activity; (11) Nuclear
bars, dynamically coupled and decoupled form in response to the gas inflow
along the primary bars.Comment: 18 pages, 16 figures, accepted by the Astrophysical Journal. Minor
revisions. The high-resolution figures can be found at
http://www.pa.uky.edu/~shlosman/research/galdyn/figs07a
Diagnoses to unravel secular hydrodynamical processes in rotating main sequence stars
(Abridged) We present a detailed analysis of the main physical processes
responsible for the transport of angular momentum and chemical species in the
radiative regions of rotating stars. We focus on cases where meridional
circulation and shear-induced turbulence only are included in the simulations.
Our analysis is based on a 2-D representation of the secular hydrodynamics,
which is treated using expansions in spherical harmonics. We present a full
reconstruction of the meridional circulation and of the associated fluctuations
of temperature and mean molecular weight along with diagnosis for the transport
of angular momentum, heat and chemicals. In the present paper these tools are
used to validate the analysis of two main sequence stellar models of 1.5 and 20
Msun for which the hydrodynamics has been previously extensively studied in the
literature. We obtain a clear visualization and a precise estimation of the
different terms entering the angular momentum and heat transport equations in
radiative zones. This enables us to corroborate the main results obtained over
the past decade by Zahn, Maeder, and collaborators concerning the secular
hydrodynamics of such objects. We focus on the meridional circulation driven by
angular momentum losses and structural readjustements. We confirm
quantitatively for the first time through detailed computations and separation
of the various components that the advection of entropy by this circulation is
very well balanced by the barotropic effects and the thermal relaxation during
most of the main sequence evolution. This enables us to derive simplifications
for the thermal relaxation on this phase. The meridional currents in turn
advect heat and generate temperature fluctuations that induce differential
rotation through thermal wind thus closing the transport loop.Comment: 16 pages, 18 figures. Accepted for publication in A&
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