9,113 research outputs found
Gravitational radiations of generic isolated horizons and non-rotating dynamical horizons from asymptotic expansions
Instead of using a three dimensional analysis on quasi-local horizons, we
adopt a four dimensional asymptotic expansion analysis to study the next order
contributions from the nonlinearity of general relativity. From the similarity
between null infinity and horizons, the proper reference frames are chosen from
the compatible constant spinors for an observer to measure the energy-momentum
and flux near quasi-local horizons. In particular, we focus on the similarity
of Bondi-Sachs gravitational radiation for the quasi-local horizons and compare
our results to Ashtekar-Kirshnan flux formular. The quasi-local energy momentum
and flux of generic isolated horizons and non-rotating dynamical horizons are
discussed in this paper.Comment: PRD, 15 page
In situ lateral earth pressure and its effect on vertical hydraulic conductivity in a glacial till deposit
The problem of permeability and preferential direction of groundwater flow in fractured glacial till has increasingly attracted the attention of researchers, particularly with regard to the possible contribution of fractures to contamination of groundwater;This research consists of a field and a laboratory phase. In the field tests, stepped blade tests (SBT) were conducted at several depths and boring locations in a glacial till deposit containing vertical and sub-vertical fractures to determine if there was any directional anisotropic nature of lateral stresses attributable to glacial flow and the formation of the fractures;The laboratory tests included soil classification and triaxial confining permeability test. Soil classification was to verify the character of till deposit at the test site. The triaxial confining test, in which a modified triaxial cell was used, was to study the effect of lateral stresses on vertical permeability of the intact and split soil samples;Soil classification indicates that the soils at the test site through the boring depth can be classified as a basal till deposit which matches the properties of the Alden Member of the Dows Formation of Des Moines Lobe;The results of SBTs indicate that the lateral stress distribution at the test site is isotropic and independent of the direction of the glacial till flow or topographic location. The isotropic lateral stress distribution implies that the vertical and sub-vertical fractures are caused by desiccation and other weathering processes rather than shear stresses induced by glacial action;The permeability tests on intact samples show that the in-situ lateral stress has a significant influence on the measurement of hydraulic conductivity. The results of the test on split samples indicate that the artificial fractures may be closed under a certain confining stress. The results of the permeability tests suggest that controlling the confining stresses in the test is important
Domain wall space-times with a cosmological constant
We solve vacuum Einstein's field equations with the cosmological constant in
space-times admitting 3-parameter group of isometries with 2-dimensional
space-like orbits. The general exact solutions, which are represented in the
advanced and retarded null coordinates, have two arbitrary functions due to the
freedom of choosing null coordinates. In the thin-wall approximation, the
Israel's junction conditions yield one constraint equation on these two
functions in spherical, planar, and hyperbolic domain wall space-times with
reflection symmetry. The remain freedom of choosing coordinates are completely
fixed by requiring that when surface energy density of domain walls
vanishes, the metric solutions will return to some well-known solutions. It
leads us to find a planar domain wall solution, which is conformally flat, in
the de Sitter universe.Comment: 9 pages. no figur
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