21,623 research outputs found
Persistence of black holes through a cosmological bounce
We discuss whether black holes could persist in a universe which recollapses
and then bounces into a new expansion phase. Whether the bounce is of classical
or quantum gravitational origin, such cosmological models are of great current
interest. In particular, we investigate the mass range in which black holes
might survive a bounce and ways of differentiating observationally between
black holes formed just after and just before the last bounce. We also discuss
the consequences of the universe going through a sequence of dimensional
changes as it passes through a bounce.Comment: 8 pages, 1 figur
Intermediate inflation in light of the three-year WMAP observations
The three-year observations from the Wilkinson Microwave Anisotropy Probe
have been hailed as giving the first clear indication of a spectral index
n_s<1. We point out that the data are equally well explained by retaining the
assumption n_s=1 and allowing the tensor-to-scalar ratio r to be non-zero. The
combination n_s=1 and r>0 is given (within the slow-roll approximation) by a
version of the intermediate inflation model with expansion rate H(t) \propto
t^{-1/3}. We assess the status of this model in light of the WMAP3 data.Comment: 4 pages RevTeX4 with one figure. Minor changes to match PRD accepted
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Stability criterion for self-similar solutions with a scalar field and those with a stiff fluid in general relativity
A stability criterion is derived in general relativity for self-similar
solutions with a scalar field and those with a stiff fluid, which is a perfect
fluid with the equation of state . A wide class of self-similar
solutions turn out to be unstable against kink mode perturbation. According to
the criterion, the Evans-Coleman stiff-fluid solution is unstable and cannot be
a critical solution for the spherical collapse of a stiff fluid if we allow
sufficiently small discontinuity in the density gradient field in the initial
data sets. The self-similar scalar-field solution, which was recently found
numerically by Brady {\it et al.} (2002 {\it Class. Quantum. Grav.} {\bf 19}
6359), is also unstable. Both the flat Friedmann universe with a scalar field
and that with a stiff fluid suffer from kink instability at the particle
horizon scale.Comment: 15 pages, accepted for publication in Classical and Quantum Gravity,
typos correcte
Study of growth parameters for refractory carbide single crystals quarterly status report no. v, mar. 1 - jun. 1, 1965
Growth parameters for refractory carbide single crystal
Bistability in a simple fluid network due to viscosity contrast
We study the existence of multiple equilibrium states in a simple fluid
network using Newtonian fluids and laminar flow. We demonstrate theoretically
the presence of hysteresis and bistability, and we confirm these predictions in
an experiment using two miscible fluids of different viscosity--sucrose
solution and water. Possible applications include bloodflow, microfluidics, and
other network flows governed by similar principles
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An atlas of CO2 storage potential in the nearshore waters of the Texas coast – American Recovery and Reinvestment Act – “Gulf of Mexico Miocene CO2 site characterization mega-transect”
Bureau of Economic Geolog
Structural and functional conservation of the human homolog of the Schizosaccharomyces pombe rad2 gene, which is required for chromosome segregation and recovery from DNA damage
The rad2 mutant of Schizosaccharomyces pombe is sensitive to UV irradiation and deficient in the repair of UV damage. In addition, it has a very high degree of chromosome loss and/or nondisjunction. We have cloned the rad2 gene and have shown it to be a member of the Saccharomyces cerevisiae RAD2/S. pombe rad13/human XPG family. Using degenerate PCR, we have cloned the human homolog of the rad2 gene. Human cDNA has 55% amino acid sequence identity to the rad2 gene and is able to complement the UV sensitivity of the rad2 null mutant. We have thus isolated a novel human gene which is likely to be involved both in controlling the fidelity of chromosome segregation and in the repair of UV-induced DNA damage. Its involvement in two fundamental processes for maintaining chromosomal integrity suggests that it is likely to be an important component of cancer avoidance mechanisms
The Influence of Thin Clay Layers on the Design and Performance of a Flexible Cantilever Retaining Wall
This case study presents the methods that were used successfully to redesign and monitor the performance of a flexible cantilever retaining wall, incorporating an in situ support berm, at a site where thin, weak clay layers were detected in the foundation during construction. A potential mode of failure termed berm-block sliding , where the retaining wall pushes out the entire support berm as a block along the clay layers, governed the design analysis. Evidence of presheared planes within the clay layers required that the design shear strength parameters be based on residual values. The clay had a significant cohesion component which was utilized in the design along with an observational method towards construction and post-construction behavior. The observational approach included a comprehensive instrumentation and monitoring program and the development of a remedial stabilization contingency plan to be implemented if necessary. This design methodology resulted in significant cost savings
A complete classification of spherically symmetric perfect fluid similarity solutions
We classify all spherically symmetric perfect fluid solutions of Einstein's
equations with equation of state p/mu=a which are self-similar in the sense
that all dimensionless variables depend only upon z=r/t. For a given value of
a, such solutions are described by two parameters and they can be classified in
terms of their behaviour at large and small distances from the origin; this
usually corresponds to large and small values of z but (due to a coordinate
anomaly) it may also correspond to finite z. We base our analysis on the
demonstration that all similarity solutions must be asymptotic to solutions
which depend on either powers of z or powers of lnz. We show that there are
only three similarity solutions which have an exact power-law dependence on z:
the flat Friedmann solution, a static solution and a Kantowski-Sachs solution
(although the latter is probably only physical for a1/5, there are
also two families of solutions which are asymptotically (but not exactly)
Minkowski: the first is asymptotically Minkowski as z tends to infinity and is
described by one parameter; the second is asymptotically Minkowski at a finite
value of z and is described by two parameters. A complete analysis of the dust
solutions is given, since these can be written down explicitly and elucidate
the link between the z>0 and z<0 solutions. Solutions with pressure are then
discussed in detail; these share many of the characteristics of the dust
solutions but they also exhibit new features.Comment: 63 pages. To appear in Physical Review
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