Showing papers by "Paul Sabatier University published in 1983"

Convergence of an improved CIPSI algorithm

Abstract: The configuration interaction CIPSI algorithm defines three classes of determinants of decreasing importance; the most important ones (∼ 100) are generators, the mean class (∼ 10 3 ) is treated variationally or to the fourth order, while the less important ones (∼ 10 5 ) are treated to the second order only. The accuracy of the result is studied as a function of the borders between the classes in the case of H 2 O (double-zeta basis set), where the exact solution is known, and for the nearly degenerate CN + problem.

Ab initio molecular calculations including spin-orbit coupling. I. Method and atomic tests

Abstract: Ab initio pseudopotentials accounting for monoelectronic spin-orbit effects are derived. The spin-orbit coupling is introduced through an effective hamiltonian in a basis of L - S states. Results are presented for some states of the argon and indium atoms.

On the different binding affinities of CRP at the lac, gal and malT promoter regions

Abstract: We have determined the stoichiometry of CRP binding to various DNA fragments carrying the lac, malT or gal promoters in the presence of cAMP, using a gel electrophoresis method. In each case, one dimer of CRP binds to the functional CRP site upstream of the transcription start. At the lac promoter, a second CRP dimer can bind to the operator region. Direct binding analysis and competition experiments performed at 200 microM cAMP allow us to measure the affinity of CRP for these different sites and to correlate them with variations in the consensus sequences, already proposed. The order is lac greater than malT greater than gal greater than lac operator greater than lac L8 much greater than non specific sites. No strong coupling exists between the two lac sites when on the same fragment. Conversely, we have studied, at constant CRP concentrations, the cAMP levels required to obtain half maximal binding to a particular DNA site : the required cAMP level increases inversely as the affinity for CRP. These variations may account for the differential activation of various cAMP sensitive operons in vivo. Anomalies in the migrations of the 1:1 complexes between CRP and DNA have been analysed and related to the size and to the position of the CRP site in the fragment. The electrophoretic mobility of the complexes depends not only on the size of the fragment but on the position of the CRP site : the mobility is lower when CRP binds near the center of the fragment. This effect is due to a clear change in the persistence length of the DNA induced by CRP binding. We suggest that, upon binding, the protein introduces a local bend (or a kink) in the DNA structure.

Isoenzymes of hydroxycinnamate: CoA ligase from poplar stems properties and tissue distribution

Abstract: Three different forms of hydroxycinnamate: CoA ligase (EC 6.2.1-) have been separated by chromatofocusing from poplar stems. These three forms exhibit different substrate specificities and tissue distribution. A correlation was established between the monomeric composition of lignins isolated from xylem and sclerenchyma and the pattern of hydroxycinnamate: CoA ligase isoforms in these tissues. The results obtained indicate that, in poplar, the hydroxycinnamate: CoA ligase isoenzymes could play an important role in the control of the monomeric composition of lignins.

Hydrodynamic instabilities and photochemical reactions

Abstract: Although many photochemical structures obtained in irradiated solutions have been investigated recently1–4, the origin of these patterns has remained unclear. Evidence has been presented which suggests that these structures are due to evaporative cooling. Using the Schlieren technique, photographs of prepatterns have been obtained before illumination and we show here that these prepatterns are associated with convective motions in the bulk. As a result, the hydrodynamic motions must be given proper consideration in the interpretation of spatio-temporal chemical patterns. The photochemical reaction also provides a useful way of visualizing slow convective motions.

Ab initio molecular calculations including spin-orbit coupling. II. Molecular test on the InH molecule and application to the g states of the Ar2* excimer

Abstract: Ab initio CI relativistic calculations with non-empirical core pseudopotentials are achieved for the valence states of InH and the gerade Rydberg states of the Ar2* excimer using the quasi-degenerate perturbation theory in the Λ · Σ coupling scheme.

A synthetic view of approximate reasoning techniques

Abstract: This paper presents a review of different approximate reasoning techniques which have been proposed for dealing with uncertain or imprecise knowledge, especially in expert systems based on production rule methodology. Theoretical approaches such as Bayesian inference, Shafer's belief theory or Zadeh's possibility theory as well as more empirical proposals such as the ones used in MYCIN or in PROSPECTOR, are considered. The presentation is focused on two basic inference schemes : the deductive inference and the combination of several uncertain or imprecise evidences relative to a same matter. Several kinds of uncertainty are taken into account in the models which are described in the paper : different degrees of certainty or of truth may be associated with the observed or produced facts or with the " if.., then..." rules; moreover the statements of facts or of rules may be imprecise or fuzzy and the values of the degrees of certainty which are used may be only approximately known. An extensive bibliography, to which it is referred in the text, is appended.

A genetic study of various enzyme polymorphisms in Pleurodeles waltlii (Urodele Amphibian). II. Peptidases: demonstration of sex linkage.

Abstract: The existence of four peptidases was demonstrated by starch gel electrophoresis in Pleurodeles waltlii: PEP-1, PEP-2, PEP-3, and PEP-4. Peptidases-3 and -4 are monomorphic, and peptidases-1 and -2 are polymorphic. The heredity of the polymorphisms was studied using individuals arising from crosses or of gynogenetic origin. Peptidase-1 is dimeric; its polymorphism depends on a pair of codominant alleles, Pep-1A and Pep-1B, which are situated on the Z and W sex chromosomes, respectively, in close proximity to, or even within, the sex differential segment. As the differential segment is very close to the centromere, the PEP-1 locus therefore also appears to be closely linked to it. Expression of the PEP-1 locus was shown to be independent of the sex hormone environment. This locus is the first case reported in amphibians of an enzyme marker linked to the genetic sex. It allows the sex of Pleurodeles to be determined before they reach sexual maturity. Peptidase-2 is monomeric. Its polymorphism depends on a pair of codominant alleles on an autosomal PEP-2 locus. The high proportion of heterozygous animals in the gynogenetic offspring of females heterozygous for the PEP-2 locus indicates segregation which is independent of the centromere. Analysis of the offspring of doubly heterozygous females (i.e., for two of the loci—LDH-B, G6PDH, PEP-1, and PEP-2) shows that the four loci are independent.