1,595 research outputs found
Self-Gravitating Strings In 2+1 Dimensions
We present a family of classical spacetimes in 2+1 dimensions. Such a
spacetime is produced by a Nambu-Goto self-gravitating string. Due to the
special properties of three-dimensional gravity, the metric is completely
described as a Minkowski space with two identified worldsheets. In the flat
limit, the standard string is recovered. The formalism is developed for an open
string with massive endpoints, but applies to other boundary conditions as
well. We consider another limit, where the string tension vanishes in
geometrical units but the end-masses produce finite deficit angles. In this
limit, our open string reduces to the free-masses solution of Gott, which
possesses closed timelike curves when the relative motion of the two masses is
sufficiently rapid. We discuss the possible causal structures of our spacetimes
in other regimes. It is shown that the induced worldsheet Liouville mode obeys
({\it classically}) a differential equation, similar to the Liouville equation
and reducing to it in the flat limit. A quadratic action formulation of this
system is presented. The possibility and significance of quantizing the
self-gravitating string, is discussed.Comment: 55 page
Galaxy Clustering Topology in the Sloan Digital Sky Survey Main Galaxy Sample: a Test for Galaxy Formation Models
We measure the topology of the main galaxy distribution using the Seventh
Data Release of the Sloan Digital Sky Survey, examining the dependence of
galaxy clustering topology on galaxy properties. The observational results are
used to test galaxy formation models. A volume-limited sample defined by
enables us to measure the genus curve with amplitude of at
Mpc smoothing scale, with 4.8\% uncertainty including all systematics
and cosmic variance. The clustering topology over the smoothing length interval
from 6 to Mpc reveals a mild scale-dependence for the shift
() and void abundance () parameters of the genus curve. We find
substantial bias in the topology of galaxy clustering with respect to the
predicted topology of the matter distribution, which varies with luminosity,
morphology, color, and the smoothing scale of the density field. The
distribution of relatively brighter galaxies shows a greater prevalence of
isolated clusters and more percolated voids. Even though early (late)-type
galaxies show topology similar to that of red (blue) galaxies, the morphology
dependence of topology is not identical to the color dependence. In particular,
the void abundance parameter depends on morphology more strongly than on
color. We test five galaxy assignment schemes applied to cosmological N-body
simulations of a CDM universe to generate mock galaxies: the
Halo-Galaxy one-to-one Correspondence model, the Halo Occupation Distribution
model, and three implementations of Semi-Analytic Models (SAMs). None of the
models reproduces all aspects of the observed clustering topology; the
deviations vary from one model to another but include statistically significant
discrepancies in the abundance of isolated voids or isolated clusters and the
amplitude and overall shift of the genus curve. (Abridged)Comment: 24 pages, 19 figures, 10 tables, submitted to ApJS. Version with full
resolution images is available at
http://astro.kias.re.kr/~cbp/doc/dr7Topo.pd
Static Einstein-Maxwell Solutions in 2+1 dimensions
We obtain the Einstein-Maxwell equations for (2+1)-dimensional static
space-time, which are invariant under the transformation
. It is shown that the
magnetic solution obtained with the help of the procedure used in
Ref.~\cite{Cataldo}, can be obtained from the static BTZ solution using an
appropriate transformation. Superpositions of a perfect fluid and an electric
or a magnetic field are separately studied and their corresponding solutions
found.Comment: 8 pages, LaTeX, no figures, to appear in Physical Review
Cosmological constant influence on cosmic string spacetime
We investigate the line element of spacetime around a linear cosmic string in
the presence of a cosmological constant. We obtain the metric and argue that it
should be discarded because of asymptotic considerations. Then a time dependent
and consistent form of the metric is obtained and its properties are discussed.Comment: 3 page
Transformation of Morphology and Luminosity Classes of the SDSS Galaxies
We present a unified picture on the evolution of galaxy luminosity and
morphology. Galaxy morphology is found to depend critically on the local
environment set up by the nearest neighbor galaxy in addition to luminosity and
the large scale density. When a galaxy is located farther than the virial
radius from its closest neighbor, the probability for the galaxy to have an
early morphological type is an increasing function only of luminosity and the
local density due to the nearest neighbor (). The tide produced by the
nearest neighbor is thought to be responsible for the morphology transformation
toward the early type at these separations. When the separation is less than
the virial radius, i.e. when , its morphology
depends also on the neighbor's morphology and the large-scale background
density over a few Mpc scales () in addition to luminosity and
. The early type probability keeps increasing as increases if
its neighbor is an early type. But the probability decreases as
increases when the neighbor is a late type. The cold gas streaming from the
late type neighbor can be the reason for the morphology transformation toward
late type. The overall early-type fraction increases as increases
when . This can be attributed to the hot halo gas
of the neighbor which is confined by the pressure of the ambient medium held by
the background mass. We have also found that galaxy luminosity depends on
, and that the isolated bright galaxies are more likely to be recent
merger products. We propose a scenario that a series of morphology and
luminosity transformation occur through distant interactions and mergers, which
results in the morphology--luminosity--local density relation.Comment: 14 pages, 7 figures, for higher resolution figures download PDF file
at http://astro.kias.re.kr/docs/trans.pdf ; references added and typos in
section 3.2 corrected; Final version accepted for publication in Ap
Self-Dual Chern-Simons Solitons in (2+1)-Dimensional Einstein Gravity
We consider here a generalization of the Abelian Higgs model in curved space,
by adding a Chern--Simons term. The static equations are self-dual provided we
choose a suitable potential. The solutions give a self-dual
Maxwell--Chern--Simons soliton that possesses a mass and a spin
Gott Time Machines, BTZ Black Hole Formation, and Choptuik Scaling
We study the formation of BTZ black holes by the collision of point
particles. It is shown that the Gott time machine, originally constructed for
the case of vanishing cosmological constant, provides a precise mechanism for
black hole formation. As a result, one obtains an exact analytic understanding
of the Choptuik scaling.Comment: 6 pages, Late
Experiment K-6-03. Gravity and skeletal growth, part 1. Part 2: Morphology and histochemistry of bone cells and vasculature of the tibia; Part 3: Nuclear volume analysis of osteoblast histogenesis in periodontal ligament cells; Part 4: Intervertebral disc swelling pressure associated with microgravity
Bone area, bone electrophysiology, bone vascularity, osteoblast morphology, and osteoblast histogenesis were studied in rats associated with Cosmos 1887. The results suggest that the synchronous animals were the only group with a significantly larger bone area than the basal group, that the bone electrical potential was more negative in flight than in the synchronous rats, that the endosteal osteoblasts from flight rats had greater numbers of transitional Golgi vesicles but no difference in the large Golgi saccules or the alkaline phosphatase activity, that the perioteal vasculature in the shaft of flight rats often showed very dense intraluminal deposits with adjacent degenerating osteocytes as well as lipid accumulations within the lumen of the vessels and sometimes degeneration of the vascular wall (this change was not present in the metaphyseal region of flight animals), and that the progenitor cells decreased in flight rats while the preosteoblasts increased compared to controls. Many of the results suggest that the animals were beginning to recover from the effects of spaceflight during the two day interval between landing and euthanasia; flight effects, such as the vascular changes, did not appear to recover
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