26 research outputs found
The Dynamics of Brane-World Cosmological Models
Brane-world cosmology is motivated by recent developments in string/M-theory
and offers a new perspective on the hierarchy problem. In the brane-world
scenario, our Universe is a four-dimensional subspace or {\em brane} embedded
in a higher-dimensional {\em bulk} spacetime. Ordinary matter fields are
confined to the brane while the gravitational field can also propagate in the
bulk, leading to modifications of Einstein's theory of general relativity at
high energies. In particular, the Randall-Sundrum-type models are
self-consistent and simple and allow for an investigation of the essential
non-linear gravitational dynamics. The governing field equations induced on the
brane differ from the general relativistic equations in that there are nonlocal
effects from the free gravitational field in the bulk, transmitted via the
projection of the bulk Weyl tensor, and the local quadratic energy-momentum
corrections, which are significant in the high-energy regime close to the
initial singularity. In this review we discuss the asymptotic dynamical
evolution of spatially homogeneous brane-world cosmological models containing
both a perfect fluid and a scalar field close to the initial singularity. Using
dynamical systems techniques it is found that, for models with a physically
relevant equation of state, an isotropic singularity is a past-attractor in all
orthogonal spatially homogeneous models (including Bianchi type IX models). In
addition, we describe the dynamics in a class of inhomogeneous brane-world
models, and show that these models also have an isotropic initial singularity.
These results provide support for the conjecture that typically the initial
cosmological singularity is isotropic in brane-world cosmology.Comment: Einstein Centennial Review Article: to appear in CJ
Reduction of doxorubicin-induced genotoxicity by Handroanthus impetiginosus in mouse bone marrow revealed by micronucleus assay
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Full-scale demonstration of Low-NO{sub x} Cell{trademark} Burner retrofit: Long-term testing
The Low-NO{sub x} Cell{trademark} Burner (LNCB) concept was developed by Babcock & Wilcox (B&W) to effectively reduce the NO{sub x} emissions from pulverized-coal-fired boilers equipped with cell burners. These boilers were built mostly in the mid to late 1960s. Small (6-million Btu/hr) and intermediate (100-million Btu/hr) prototype versions of the concept were developed jointly by B&W and the Electric Power Research Institute (EPRI) during the mid-to-late 1980s. The design of B&W LNCBs allows direct replacements of the originally installed cell burners without pressure-part modifications. During this US Department of Energy (DOE) Clean Coal III program, Dayton Power and Light Company (DP&L) served as the host utility using its J.M. Stuart Station Unit {number_sign}4 (JMSS 4) for the first full-scale LNCB demonstration. This unit has a rated output capacity of 605 MW{sub e}. After the LNCB retrofit and burner optimization contract phases in late 1991, JMSS 4 underwent a long- term (nine months) test period from July 1992 to March 1993. The objective of this test was to determine the overall performance of this boiler after the LNCB retrofit. The long-term test involved determinations of the boiler emission performance and evaluations of waterwall corrosion potential, as well as a study of the overall operability of the LNCB system. Specific tasks performed during this long-term test include: (1) laboratory corrosion study; (2) field corrosion panel study; (3) in-furnace gas species probing; and (4) boiler emissions performance study. This report summarizes the long- term test results