4,934 research outputs found
Asymptotic behaviour of a class of inhomogeneous scalar field cosmologies
The asymptotic behaviour of a class of inhomogeneous scalar field cosmologies
with a Liouville type of potential is studied. We define a set of new variables
for which the phase space of the system of Einstein equations is bounded. This
allows us to perform a complete analysis of the evolution of these cosmologies.
We also discuss the extension of the cosmic no-hair theorem.Comment: 23 pages, latex, 3 figures, to appear in J. Math. Phys., figures also
available tarred and gzip'ed at http://tp.lc.ehu.es/figures.g
Scalar Field Inhomogeneous Cosmologies
Some exact solutions for the Einstein field equations corresponding to
inhomogeneous cosmologies with an exponential-potential scalar field
which generalize solutions obtained previously are considered. Several
particular cases are studied and the properties related to generalized
inflation and asymptotic behaviour of the models are discussed.Comment: 21 pages LaTeX, 3 figures appended as a uuencoded compressed tar fil
Cell type-specific regulation of choline acetyltransferase gene expression - Role of the neuron-restrictive silencer element and cholinergic-specific enhancer
This study demonstrates the presence of positive and negative regulatory elements within a 2336-base pair-long region of the rat choline acetyltransferase (ChAT) gene promoter that cooperate to direct cell type-specific expression in cholinergic cells. A 21-base pair-long neuron-restrictive silencer element (NRSE) was identified in the proximal part of this region. This element was recognized by the neuron-restrictive silencer factor (NRSF), previously shown to regulate expression of other neuron-specific genes. The ChAT NRSE was inactive in both cholinergic and non-cholinergic neuronal cells, but repressed expression from a heterologous promoter in non-neuronal cells. Specific deletion of this element allowed ChAT gene promoter activity in non-neuronal cells, and overexpression of NRSF repressed ChAT gene promoter activity in cholinergic cells. The distal part of the ChAT gene promoter showed cholinergic-specific enhancing activity, which stimulated promoter activity in cholinergic cells, but was inactive in non-cholinergic neuronal and non-neuronal cells. This enhancer region suppressed the activity of the ChAT NRSE in cholinergic cells, even after NRSF overexpression. Thus, at least two kinds of regulatory elements cooperate to direct ChAT gene expression to cholinergic neurons, namely a neuron-restrictive silencer element and a cholinergic-specific enhancer
On the evolution of a large class of inhomogeneous scalar field cosmologies
The asymptotic behaviour of a family of inhomogeneous scalar field
cosmologies with exponential potential is studied. By introducing new variables
we can perform an almost complete analysis of the evolution of these
cosmologies. Unlike the homogeneous case (Bianchi type solutions), when k^2<2
the models do not isotropize due to the presence of the inhomogeneitiesComment: 23 pages, 1 figure. Submitted to Classical and Quantum Gravit
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