Showing papers by "Paul Sabatier University published in 1997"

Self-organization in social insects.

Abstract: Self-organization was introduced originally in the context of physics and chemistry to describe how microscopic processes give rise to macroscopic stuctures in out-of-equilibrium systems, Recent research that extends this concept to ethology suggests that it provides a concise description of a wide range of collective phenomena in animals, especially in social insects. This description does not rely on individual complexity to account for complex spatiotemporal features that emerge at the colony level, but rather assumes that intractions among simple individuals can produce highly structured collective behaviours.

Granite is Never Isotropic: An Introduction to AMS Studies of Granitic Rocks

Abstract: This paper develops the author’s and co-workers’ findings that well-organized crystalline fabrics are ubiquitous in granitic rocks. Traditional structural and microstructural measurements of foliation and lineation in granites, performed directly in the field, in the laboratory from macroscopic oriented samples, and applied to entire plutons, reveal that magmatic structures may be homogeneous over huge areas. Hence structural mapping of granitoid massifs is of great interest in the understanding of magma emplacement and deformation in the crust. The low-field magnetic fabric measurement (AMS), a low cost, quick and easy technique, gives a quantitative description of the crystalline fabric and is now used systematically for structural mapping of granites. The present state of the « art » on the magnetic fabrics in granites is reviewed, based on the distinction between the paramagnetic, or magnetite-free, and the ferromagnetic, or magnetite-bearing granites. Magnetic fabrics in granitic rocks are discussed in relation to their variability at various scales and their kinematic and rheological significance. Finally, the relationship between fabrics and modes of emplacement is discussed.

Remarks on the Proper Use of the Broken Symmetry Approach to Magnetic Coupling

Abstract: The effect of nonorthogonality in the broken symmetry approach to magnetic coupling has been explicitly considered for the first time in Hartree−Fock and a variety of DFT methods. On the basis of the results for three different systems, representative of a variety of physical situations it is shown that the most often quoted trend concerning the much larger degree of delocalization of magnetic orbitals obtained from DFT, as opposed to Hartree−Fock, is not fully justified. A new and simple way to relate the overlap integral entering into the calculation and the spin density is proposed and tested in a variety of model systems.

Competence and virulence of Streptococcus pneumoniae: Adc and PsaA mutants exhibit a requirement for Zn and Mn resulting from inactivation of putative ABC metal permeases

Abstract: The adcCBA putative operon of Streptococcus pneumoniae, an important human pathogen, was identified in a search for transformation-deficient mutants. It was found to exhibit homology to ATP-binding cassette (ABC) transport operons encoding streptococcal adhesins such as FimA of Streptococcus parasanguis and PsaA of S. pneumoniae. The latter was recently shown to be essential for virulence as judged by intranasal or intraperitoneal challenge of mice. We suggested previously that AdcA, together with a set of 14 proteins, including PsaA and homologous adhesins, defines a new family of external solute-binding proteins specific for metals. In this work, Northern analysis revealed the existence of two adcB-adcA specific transcripts originating within adcC or further upstream, consistent with the hypothesis that adc is an operon. Investigation of growth of adc and psaA mutants in synthetic medium revealed that the addition of Zn improved the growth rate of the former, whereas the latter exhibited an absolute requirement for added Mn. A psaA-adc double mutant turned out to be essentially non-viable unless both metals were added in the appropriate ratio. Taken together, these results suggest a previously undocumented requirement of S. pneumoniae for Zn and Mn. The addition of Zn also restored near-normal spontaneous transformation of adc mutant cells in standard transformation medium. Zn was found to be specifically required soon after contact of cells with the competence-stimulating peptide, revealing an unsuspected need for Zn in transformation of S. pneumoniae. The removal of Mn from standard transformation medium also resulted in transformation deficiency of psaA mutant cells. Taken together, these results lead us to propose that Adc is an ABC-type Zn permease, the first such protein complex identified in any organism, and that Psa is an ABC-type Mn permease complex.

The family of box ACA small nucleolar RNAs is defined by an evolutionarily conserved secondary structure and ubiquitous sequence elements essential for RNA accumulation.

Abstract: Eukaryotic cells contain a large number of small nucleolar RNAs (snoRNAs) A major family of snoRNAs features a consensus ACA motif positioned 3 nucleotides from the 3' end of the RNA In this study we have characterized nine novel human ACA snoRNAs (U64-U72) Structural probing of U64 RNA followed by systematic computer modeling of all known box ACA snoRNAs revealed that this class of snoRNAs is defined by a phylogenetically conserved secondary structure The ACA snoRNAs fold into two hairpin structures connected by a single-stranded hinge region and followed by a short 3' tail The hinge region carries an evolutionarily conserved sequence motif, called box H (consensus, AnAnnA) The H box, probably in concert with the flanking helix structures and the ACA box characterized previously, plays an essential role in the accumulation of human U64 intronic snoRNA The correct processing of a yeast ACA snoRNA, snR36, in mammalian cells demonstrated that the cis- and trans-acting elements required for processing and accumulation of ACA snoRNAs are evolutionarily conserved The notion that ACA snoRNAs share a common secondary structure and conserved box elements that likely function as binding sites for common proteins (eg, GAR1) suggests that these RNAs possess closely related nucleolar functions

On Talagrand's deviation inequalities for product measures

Abstract: We present a new and simple approach to some of the deviation inequalities for product measures deeply investigated by M. Talagrand in the recent years. Our method is based on functional inequalities of Poincare and logarithmic Sobolev type and iteration of these inequalities. In particular, we establish with theses tools sharp deviation inequalities from the mean on norms of sums of independent random vectors and empirical processes. Concentration for the Hamming distance may also be deduced from this approach.

Cinnamoyl CoA reductase, the first committed enzyme of the lignin branch biosynthetic pathway: cloning, expression and phylogenetic relationships.

Abstract: Summary Cinnamoyl CoA:NADP oxidoreductase (CCR, EC 1.2.1.44) catalyzes the conversion of cinnamoyl CoA esters to their corresponding cinnamaldehydes, i.e. the first specific step in the synthesis of the lignin monomers. The cloning of a cDNA encoding CCR in Eucalyptus gunnii (EUCCR) is reported here. The identity of the EUCCR cDNA was demonstrated by comparison with peptide sequence data from purified CCR and functional expression of the recombinant enzyme in Escherichia coli. Sequence analysis revealed remarkable homologies with dihydroflavonol-4-reductase (DFR), the first enzyme of the anthocyanin biosynthetic pathway. Moreover, significant similarities were found with mammalian 3β-hydroxysteroid dehydrogenase and bacterial UDP-galactose-4-epimerase, suggesting that CCR shared a common ancestor with these enzymes and can therefore be considered as a new member of the mammalian 3β-hydroxysteroid dehydrogenase/ plant dihydroflavonol reductase superfamily. In Eucalyptus gunnii, CCR is encoded by one gene containing four introns whose positions are similar to those of introns I, II, III and V in DFR genes from dicots. In agreement with the involvement of CCR in lignification, the CCR transcript was shown to be expressed in lignified organs, i.e. root and stem tissues, and was localized mainly in young differentiating xylem. On the other hand, its abundance in Eucalyptus leaves suggests that monolignols may be precursors of end products other than lignins. This first characterization of a gene corresponding to CCR opens new possibilities to genetically engineer plants with lower lignin content. This is particularly important for woody plants such as Eucalyptus which are used for pulp making.

Nonlinear filtering : Interacting particle resolution

Abstract: In this Note, we study interacting particle approximations of discrete time and measure valued dynamical systems. Such systems have arisen in such diverse scientific disciplines as in Propagation of Chaos Theory (see [12] and [19]), and in Nonlinear Filtering Theory. The main contribution of this Note is to prove the convergences to the optimal filter of such approximations, yielding what seemed to be the first mathematically well-founded convergence results for such approximations of the nonlinear filtering equations. This new treatment was influenced primarily by the development of genetic algorithms (see [16] and [3]), and secondarily by the papers of H. Kunita and L. Stettner, [17] and [18] respectively.

There is no highly conserved embryonic stage in the vertebrates : implications for current theories of evolution and development

Abstract: &p.1: Embryos of different species of vertebrate share a common organisation and often look similar. Adult differences among species become more apparent through divergence at later stages. Some authors have suggested that members of most or all vertebrate clades pass through a virtually identical, conserved stage. This idea was promoted by Haeckel, and has recently been revived in the context of claims regarding the universality of developmental mechanisms. Thus embryonic resemblance at the tailbud stage has been linked with a conserved pattern of developmental gene expression ‐ the zootype. Haeckel’s drawings of the external morphology of various vertebrates remain the most comprehensive comparative data purporting to show a conserved stage. However, their accuracy has been questioned and only a narrow range of species was illustrated. In view of the current widespread interest in evolutionary developmental biology, and especially in the conservation of developmental mechanisms, re-examination of the extent of variation in vertebrate embryos is long overdue. We present here the first review of the external morphology of tailbud embryos, illustrated with original specimens from a wide range of vertebrate groups. We find that embryos at the tailbud stage ‐ thought to correspond to a conserved stage ‐ show variations in form due to allometry, heterochrony, and differences in body plan and somite number. These variations foreshadow important differences in adult body form. Contrary to recent claims that all vertebrate embryos pass through a stage when they are the same size, we find a greater than 10-fold variation in greatest length at the tailbud stage. Our survey seriously undermines the credibility of Haeckel’s drawings, which depict not a conserved stage for vertebrates, but a stylised amniote embryo. In fact, the taxonomic level of greatest resemblance among vertebrate embryos is below the subphylum. The wide variation in morphology among vertebrate embryos is difficult to reconcile with the idea of a phyogenetically-conserved tailbud stage, and suggests that at least some developmental mechanisms are not highly constrained by the zootype. Our study also highlights the dangers of drawing general conclusions about vertebrate development from studies of gene expression in a small number of laboratory species. &kwd:words Morphogenesis · Developmental biology · Comparative anatomy · Comparative study · Embryology&bdy:

Tracing the topology of the October 18–20, 1995, magnetic cloud with ∼0.1–10² keV electrons

Abstract: Five solar impulsive ∼1–10² keV electron events were detected while the WIND spacecraft was inside the magnetic cloud observed upstream of the Earth on October 18–20, 1995. The solar type III radio bursts produced by these electrons can be directly traced from ∼1 AU back to X-ray flares in solar active region AR 7912, implying that at least one leg of the cloud was magnetically connected to that region. Analysis of the electron arrival times shows that the lengths of magnetic field lines in that leg vary from ∼3 AU near the cloud exterior to ∼1.2 AU near the cloud center, consistent with a model force-free helical flux rope. Although the cloud magnetic field exhibits the smooth, continuous rotation signature of a helical flux rope, the ∼0.1-1 keV heat flux electrons and ∼1–10² keV energetic electrons show numerous simultaneous abrupt changes from bidirectional streaming to unidirectional streaming to complete flux dropouts. We interpret these as evidence for patchy disconnection of one end or both ends of cloud magnetic field lines from the Sun.

Fuzzy information engineering: a guided tour of applications

Abstract: Partial table of contents: CLARIFYING INFORMATION: SENSING AND ENHANCING. Elicitation, Pooling, and Assessment of Expert Opinion in the Possibilistic Framework (S. Sandri). CLARIFYING INFORMATION: ABSTRACTING AND MODELING. Learning from Imperfect Data (B. Bouchon-Meunier, et al.). RETRIEVING INFORMATION: QUERYING. Extending SQL Retrieval Features for the Handling of Flexible Queries (P. Bosc & O. Pivert). A Fuzzy SQL Summary Language for Data Discovery (D. Rasmussen & R. Yager). RETRIEVING INFORMATION: REASONING. Fuzzy Set Methods in Inheritance Networks (R. Yager). EXPLOITING INFORMATION: DECISION-MAKING. Operators in Models of Decision Making (H. Zimmermann). Risk Management with Imprecise Information (K. Engermann, et al.). EXPLOITING INFORMATION: DESIGNING AND OPTIMIZING. Fuzzy Scheduling: Principles and Experiments (H. Fargier). Index.

Poincaré’s inequalities and Talagrand’s concentration phenomenon for the exponential distribution

Abstract: We present a simple proof, based on modified logarithmic Sobolev inequalities, of Talagrand’s concentration inequality for the exponential distribution. We actually observe that every measure satisfying a Poincare inequality shares the same concentration phenomenon. We also discuss exponential integrability under Poincare inequalities and its consequence to sharp diameter upper bounds on spectral gaps.

On genericity for holomorphic curves in four-dimensional almost-complex manifolds

Abstract: We consider spaces of immersed (pseudo-)holomorphic curves in an almost complex manifold of dimension four. We assume that they are either closed or compact with boundary in a fixed totally real surface, so that the equation for these curves is elliptic and has a Fredholm index. We prove that this equation is regular if the Chern class is ≥ 1 (in the case with boundary, if the ambient Maslov number is ≥ 1). Then the spaces of holomorphic curves considered will be manifolds of dimension equal to the index.

Temporal Coherent Control in Two-Photon Transitions: From Optical Interferences to Quantum Interferences

Abstract: Temporal coherent control of an excited state wave packet is produced by a sequence of two identical ultrashort laser pulses. We show theoretically and experimentally in the case of the (6s-7d) two-photon transition in Cs that optical and quantum interferences take place and are clearly distinguished. {copyright} {ital 1997} {ital The American Physical Society}

Global inventory of NO x sources

Abstract: Nitrogen oxides are key compounds for the oxidation capacity of the troposphere. NOx concentrations depend on the proximity of sources because of their short atmospheric lifetime. An accurate knowledge of the distribution of their sources and sinks is therefore crucial. At global scale, the dominant sources of nitrogen oxides - combustions of fossil fuel (∼50%) and biomass burning (∼20%) - are basically anthropogenic. Natural sources, including lightning and microbial activity in soils, represent therefore less than 30% of total emissions. Fertilizer use in agriculture constitutes an anthropogenic perturbation to the microbial source. The methods to estimate the magnitude and distribution of these dominant sources of nitrogen oxides are discussed. Some minor sources which may play a specific role in tropospheric chemistry such as NOx emission from aircraft in the upper troposphere or input from production in the stratosphere from N2O photodissociation are also considered.

Persistence exponents for fluctuating interfaces

Abstract: Numerical and analytic results for the exponent $\ensuremath{\theta}$ describing the decay of the first return probability of an interface to its initial height are obtained for a large class of linear Langevin equations. The models are parametrized by the dynamic roughness exponent $\ensuremath{\beta}$, with $0l\ensuremath{\beta}l1$; for $\ensuremath{\beta}=\frac{1}{2}$ the time evolution is Markovian. Using simulations of solid-on-solid models, of the discretized continuum equations as well as of the associated zero-dimensional stationary Gaussian process, we address two problems: The return of an initially flat interface, and the return to an initial state with fully developed steady-state roughness. The two problems are shown to be governed by different exponents. For the steady-state case we point out the equivalence to fractional Brownian motion, which has a return exponent ${\ensuremath{\theta}}_{S}=1\ensuremath{-}\ensuremath{\beta}$. The exponent ${\ensuremath{\theta}}_{0}$ for the flat initial condition appears to be nontrivial. We prove that ${\ensuremath{\theta}}_{0}\ensuremath{\rightarrow}\ensuremath{\infty}$ for $\ensuremath{\beta}\ensuremath{\rightarrow}0$, ${\ensuremath{\theta}}_{0}g~{\ensuremath{\theta}}_{S}$ for $\ensuremath{\beta}l$$\frac{1}{2}$ and ${\ensuremath{\theta}}_{0}l~{\ensuremath{\theta}}_{S}$ for $\ensuremath{\beta}g$$\frac{1}{2}$, and calculate ${\ensuremath{\theta}}_{0,S}$ perturbatively to first order in an expansion around the Markovian case $\ensuremath{\beta}=$$\frac{1}{2}$. Using the exact result ${\ensuremath{\theta}}_{S}=1\ensuremath{-}\ensuremath{\beta}$, accurate upper and lower bounds on ${\ensuremath{\theta}}_{0}$ can be derived which show, in particular, that ${\ensuremath{\theta}}_{0}g~(1\ensuremath{-}\ensuremath{\beta}{)}^{2}/\ensuremath{\beta}$ for small $\ensuremath{\beta}$.

Photoluminescence and resonant raman spectra of silicon films produced by size-selected cluster beam deposition

Abstract: Silicon clusters and nanocrystals have been generated by CO 2-laser-induced decomposition of SiH 4 in a flow reactor. By introducing a conical nozzle into the reaction zone, the clusters are extracted into a molecularbeam machine and analyzed with a time-of-flight mass spectrometer ~TOFMS!. Since the clusters have a size-dependent velocity, a mechanical velocity selector is used to further narrow their size distribution and to select a specific mean size. Employing this technique, silicon clusters with different preselected mean sizes have been deposited at low energy on various substrates. Photoluminescence ~PL! and resonant Raman spectra of the resulting films are presented. The crystallite sizes deduced from the Raman spectra confirm the TOFMS measurements. The PL spectra are shifted with decreasing cluster size to smaller wavelengths. Our results agree very well with theoretical predictions for silicon quantum dots. @S0163-1829~97!08035-1#

Adrenergic regulation of adipocyte metabolism

Abstract: Five adrenoceptor (AR) subtypes (beta 1, beta 2, beta 3, alpha 2 and alpha 1), are involved in the control of white and brown fat cell function. A number of metabolic events are controlled by the adrenergic system in fat cells. The stimulatory effect of catecholamines on lipolysis and metabolism is mainly connected to increments in cAMP levels, cAMP protein kinase activation and phosphorylation of various target proteins. Norepinephrine and epinephrine operate through differential recruitment of alpha 2- and beta-AR subtypes on the basis of their relative affinity for the different subtypes (the relative order of affinity is alpha 2 > beta 1 > or = beta 2 > beta 3 for norepinephrine). Antagonistic actions at the level of cAMP production exist between alpha 2- and beta 1-, beta 2- and beta 3-AR-mediated lipolytic effects in human white fat cells. The role of fat cell alpha 2-ARs, which largely outnumber beta-ARs in fat cells of certain fat deposits, in human and primate has never been clearly understood. The other AR type which is not linked to lipolysis regulation, the alpha 1-AR, is involved in the control of glycogenolysis and lactate production. Pharmacological approaches using in-situ microdialysis and selective alpha 2- and beta-AR agonists and antagonists have revealed sex- and tissue-specific differences in the adrenergic control of fat cell function and nutritive blood flow in the tissue surrounding the microdialysis probe.

Experimental Evidence of a Ferromagnetic Ground State (S = 9/2) for a Dinuclear Gd(III)−Ni(II) Complex

Abstract: The structural determination of a dinuclear Gd(III)−Ni(II) entity confirms the strict dinuclearity of the complex while the magnetic properties evidence the presence of a ferromagnetic interaction between the paramagnetic (S = 1) nickel ion and the gadolinium center (S = 7/2), with a J value of 3.6 cm-1.

Emergence of Quantum Chaos in Finite Interacting Fermi Systems

Abstract: We study the level spacing statistics $P(s)$ in many-body Fermi systems and determine a critical two-body interaction strength ${U}_{c}$ at which a crossover from Poisson to Wigner-Dyson statistics takes place. Near the Fermi level, the results allow one to find a critical temperature ${T}_{\mathrm{ch}}$ above which quantum chaos and thermalization set in.

Some Syntactic Approaches to the Handling of Inconsistent Knowledge Bases: A Comparative Study Part 1: The Flat Case

Abstract: This paper presents and discusses several methods for reasoning from inconsistent knowledge bases. A so-called argued consequence relation, taking into account the existence of consistent arguments in favour of a conclusion and the absence of consistent arguments in favour of its contrary, is particularly investigated. Flat knowledge bases, i.e., without any priority between their elements, are studied under different inconsistency-tolerant consequence relations, namely the so-called argumentative, free, universal, existential, cardinality-based, and paraconsistent consequence relations. The syntax-sensitivity of these consequence relations is studied. A companion paper is devoted to the case where priorities exist between the pieces of information in the knowledge base.

Carbon nanotubes grown in situ by a novel catalytic method

Abstract: Carbon nanotubes can be produced by the catalytic decomposition of hydrocarbons on small metal particles. However, nanotubes are generally produced together with non-tubular filaments and tubes coated by pyrolytic carbon. We propose a novel catalyst method for the in situ production, in a composite powder, of a huge amount of single- and multiwalled carbon nanotubes, having a diameter between 1.5 and 15 nm and arranged in bundles up to 100 μm long. We anticipate that dense materials prepared from such composite powders could have interesting mechanical and physical properties.