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 $G_2$ 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

Evaluation of indexes for the quantitative and objective estimation of grapevine bunch compactness

Bunch compactness is a key factor on the determination of grape quality. The use of qualitative visual systems for its determination is quite controversial, hindering some studies that require objective and quantitative measures of the trait. Here, eleven indexes published in literature and eight designed in this survey were tested with three different criteria to determine their usefulness for the estimation of bunch compactness. A sample of 110 grape bunches of different morphology, from 11 different varieties, were classified by a panel of 14 judges according to the visual OIV descriptor Nº 204. Besides, a number of measures were taken from the same bunches, which were used for the indexes’ calculations. Several indexes designed here proved to be more suitable to obtain quantitative estimations for this trait in a genetically diverse set of varieties than the indexes previously published. Two of the selected indexes, CI-18 and CI-19, are based on the combination of six metrics from bunches (bunch weight, number of berries per bunch, number of seeds per berry, bunch length, first ramification length and either pedicel length or number of ramifications per bunch, respectively). These two indexes are more suitable for intervarietal studies where obtaining quantitative data is critical. Other selected index (CI-12) is based on two easy-to-measure characteristics of the bunch (weight and length), and it is proposed as a fast estimator of bunch compactness for the viticulture sector