Showing papers by "Paul Sabatier University published in 1993"

Structure detection and statistical adaptive speckle filtering in SAR images

Abstract: Current speckle filters attempt to restore the radar reflectivity using only the multiplicative speckle noise assumption. The best known filters, namely the Frost, Lee or Kuan niters are adaptive filters based on the local statistics, computed in a fixed square window. In this way, the speckle is reduced as a function of the heterogeneity measured by the local coefficient of variation. When the radar reflectivity undergoes significant variations due to the presence of strong scatterers or structural features (edges or lines) in the processing window, such speckle filtering is less effective. In this paper it is shown that the filtering process can be controlled both by the coefficient of variation and by various geometrical ratio detectors. Through shape adaptive windowing, these detectors allow the use of large window sizes for better speckle reduction while preserving spatial resolution and structural features. The backscattered intensity is modelled as K-distributed within speckled targets and...

On Possibility/Probability Transformations

Abstract: The problem of converting possibility measures into probability measures has received attention in the past, but not by so many scholars. This question is philosophically interesting as part of the debate between probability and fuzzy sets. The imbedding of fuzzy sets into random set theory as done by Goodman and Nguyen (1985), Wang Peizhuang (1983), among others, has solved this question in principle. However the conversion problem has roots at least as much in the possibility/probability consistency principle of Zadeh (1978), that he proposed in the paper founding possibility theory.

Specific CI calculation of energy differences: Transition energies and bond energies

Abstract: A general strategy for the calculation of energy differences is proposed. It proceeds through the definition of a minimal model space and the low-order perturbative development of the corresponding Hamiltonian is used to establish a set of determinants contributing to the searched energy difference. The so-selected CI is treated variationally. This general strategy is applied here to the calculation of observables basically involving two electrons in two orbitals. The first one concerns the transition energies from the ground state to the lowest singlet and triplet states of atoms (Ar 1 S → 3,1 P, Ca 1 S → 3,1 P) or molecules (CH 2 1 A 1 → 3 B 1 , 2 1 A 1 ). The second problem concerns the CH bond energy in ethylene. In all cases the agreement of the results of that simple procedure with either experiment or full-CI is quite satisfactory.

Antioxidant activity of flavonoids: Efficiency of singlet oxygen (1Δg) quenching

Abstract: Flavonoids, polyphenolic pigments widely present in plants, have been reported to act as scavengers of various oxidizing species. However, most often an overall antioxidant effect was measured. In this paper we report the results of a systematic study of the reactivity of 13 selected flavonoids (from the flavonol, flavone, flavanone and flavane families) with singlet oxygen (1O2(1 delta g)) in order to establish a structure-activity relationship. The rate constants of the chemical reaction of these flavonoids with 1O2(k r) and their rate constants of 1O2 physical quenching (kq) have been determined by kinetic measurements and near-IR singlet oxygen luminescence. The efficiency of the physical quenching is mainly controlled by the presence of a catechol moiety on ring B, whereas the structure of ring C (particularly the presence of a hydroxyl group activating the double bond) is the main factor determining the efficiency of the chemical reactivity of these compounds with 1O2. The total reactivity factor determining the efficiency of the chemical reactivity of these compounds with 1O2. The total reactivity scale is dominated by kq, which is in general higher than kr. (+)-Catechin is the most efficient quencher of the series.

Drastic changes in the fluorescence properties of NBD probes with the polarity of the medium: involvement of a TICT state?

Abstract: The spectroscopic and photophysical properties of two 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) derivatives with different substituents on the nitrogen group are reported in 18 solvents. The solvatochromic shifts were analysed by correlating with polarity scales. The results, together with the help of modified neglect of diatomic overlap (MNDO) calculations, enable the polarity of the ground and first singlet excited states to be determined. Experiments based on variations in temperature and viscosity establish that the two probes undergo different de-excitation pathways. The possibilities of internal rotation leading to a twisted intramolecular charge transfer (TICT) state in the case of diethylamino-NBD are discussed. A study in binary solvent mixtures outlines specific solvent—solute interactions. Appropriate restrictions are emphasized on the utilization of NBD probes in biological fields.

Argumentative inference in uncertain and inconsistent knowledge bases

Abstract: This paper presents and discusses several methods for reasoning from inconsistent knowledge bases. A so-called argumentative-consequence relation taking into account the existence of consistent arguments in favor of a conclusion and the absence of consistent arguments in favor of its contrary, is particularly investigated. Flat knowledge bases, i.e. without any priority between their elements, as well as prioritized ones where some elements are considered as more strongly entrenched than others are studied under different consequence relations. Lastly a paraconsistent-like treatment of prioritized knowledge bases is proposed, where both the level of entrenchment and the level of paraconsistency attached to a formula are propagated. The priority levels are handled in the framework of possibility theory.

Uncertainty in Constraint Satisfaction Problems: a Probalistic Approach

Abstract: We propose a framework for dealing with probabilistic uncertainty in constraint satisfaction problems, associating with each constraint the probability that it is a part of the real problem (the latter being only partially known). The probability degrees on the relevance of the constraints enable us to define, for each instanciation, the probability that it is a solution of the real problem. We briefly give a methodology for the search of the best solution (maximizing this probability).

Delocalization of quantum chaos by weak nonlinearity.

Abstract: The destruction of quantum localization of chaos by weak nonlinearity is analyzed on the basis of the Chirikov criterion of overlapping resonances. It is shown that for the nonlinear coupling constant there is a delocalization border above which localization is destroyed. In this delocalized phase, excitation is described by a universal anomalous subdiffusion law. Applications of this phenomenon to nonlinear wave propagation in disordered media and Anderson localization are discussed.

Multiple-order Raman scattering in crystalline and amorphous silicon.

Abstract: Raman-scattering measurements have been performed on c-Si and a-Si over a wide range of frequencies, including Stokes and anti-Stokes sides, and up to fourth order. All the features are accounted for by using the same physical parameters in both phases. In particular, it is shown that multiple-order scattering processes are not negligible, but rather of the same order of magnitude as first-order processes. In amorphous materials, light-scattering excess, spurious background, Boson-peak or hot-luminescence processes, which have been recently put forward, turn out to be mainly caused by high-order Raman-scattering processes.

Poisson vs. GOE Statistics in Integrable and Non-Integrable Quantum Hamiltonians

Abstract: We calculate the level statistics by finding the eigenvalue spectrum for a variety of one-dimensional many-body models, namely the Heisenberg chain, the t-J model and the Hubbard model. In each case the generic behaviour is GOE, however at points corresponding to models known to be exactly integrable Poisson statistics are found, in agreement with an argument we outline.

Quantum chaos in spin-fermion models.

Abstract: The full spectrum of a single hole in a quantum antiferromagnetic background (t-${\mathit{J}}_{\mathit{z}}$-${\mathit{J}}_{\mathrm{\ensuremath{\perp}}}$ model) is obtained by complete exact diagonalization of small two-dimensional clusters. Various statistical properties of the spectrum are investigated. On a very wide range of the parameters the level-spacing distribution follows Gaussian-orthogonal-ensemble Wigner law characteristic of chaotic spectra. At small separation, the spectral rigidity follows the universal behavior described by random-matrix theory and presents deviations at higher energies. We argue that quantum chaos is a generic feature of complex (i.e., nonintegrable) strongly correlated fermion systems. Our results suggest that random-matrix theory might be useful to investigate the incoherent part of dynamical correlation functions (such as the hole spectral density or the spin structure factor).

Incest avoidance, fluctuating asymmetry, and the consequences of inbreeding in Iridomyrmex humilis, an ant with multiple queen colonies

Abstract: Inbreeding may have important consequences for the genetic structure of social insects and thus for sex ratios and the evolution of sociality and multiple queen (polygynous) colonies. The influence of kinship on mating preferences was investigated in a polygynous ant species, Iridomyrmex humilis, which has within-nest mating. When females were presented simultaneously with a brother that had been reared in the same colony until the pupal stage and an unrelated male produced in another colony, females mated preferentially with the unrelated male. The role of environmental colony-derived cues was tested in a second experiment where females were presented with two unrelated males, one of which had been reared in the same colony until the pupal stage (i.e., as in the previous experiment), while the other had been produced in another colony. In this experiment there was no preferential mating with familiar or unfamiliar males, suggesting that colony-derived cues might not be important in mating preferences. Inbreeding was shown to have no strong effect on the reproductive output of queens as measured by the number of worker and sexual pupae produced. The level of fluctuating asymmetry of workers produced by inbreeding queens was not significantly higher than that of non-inbreeding queens. Finally, colonies headed by inbreeding queens did not produce adult diploid males. Based on the current hypotheses of sex-determination the most plausible explanations for the absence of diploid-male-producing colonies are that (i) workers recognized and eliminated these males early in their development, and/or (ii) there are multiple sex-determining loci in this species. It is suggested that even if inbreeding effects on colony productivity are absent or low, incest avoidance mechanisms may have evolved and been maintained if inbreeding queens produce a higher proportion of unviable offspring.

Molecular cloning and expression of a Eucalyptus gunnii cDNA clone encoding cinnamyl alcohol dehydrogenase

Abstract: Cinnamyl alcohol dehydrogenase (CAD) catalyses the reduction of hydroxycinnamyl aldehydes (sinapyl, paracoumaryl, coniferyl aldehydes) to the corresponding alcohols which are the direct monomeric precursors of lignins Recently, we have purified from Eucalyptus gunnii two isoforms of CAD (CAD1 and CAD2), distinct in their biochemical and functional properties In this paper, we report the cloning of a CAD cDNA (pEuCAD2) isolated by screening a lambda gt11 library generated from cell suspension culture of Eucalyptus gunnii, using a tobacco CAD cDNA as a probe This full-length clone (1392 bp) encodes a protein of 356 amino acids which corresponds to the subunit molecular weight of the CAD2 isoform Sequence analysis revealed that CAD2 is very well conserved among species (78% homology with CAD from tobacco, a herbaceous angiosperm, and 81% with the partial sequence from a gymnosperm, loblolly pine) The identity of this clone was unambiguously demonstrated (1) by comparison with peptide sequence data from purified CAD2 and (2) by functional expression of the recombinant enzyme in Escherichia coli Recombinant CAD showed the same properties as the natural isoform CAD2, in terms of electrophoretic mobility, polypeptide structure, substrate specificity and antigenicity The CAD2 transcript is equally abundant in stems and leaves and at the limit of detection in roots At the tissue level the CAD2 gene is highly expressed in xylem and virtually undetectable in phloem

Multiple ion association in supercritical aqueous solutions of single electrolytes

Abstract: Solute speciation in supercritical aqueous alkali metal halide solutions plays an important role in various industrial and natural processes, for example, corrosion of metals, solvent extraction, crystal growth, metamorphism, and the formation of hydrothermal ore deposits. To better characterize such speciation, degrees of formation of polyatomic clusters of sodium and chlorine ions have been computed with the aid of dissociation constants generated from Monte Carlo calculations which are consistent with both supercritical conductance measurements and electrostatic theory. The calculations indicate that the solute in alkali-halide solutions is successively dominated by increasingly complex polyatomic clusters as the solute molality increases at pressures and temperatures where the dielectric constant of water is 15.

Catnip (Nepeta cataria L.) essential oil: analysis of chemical constituents, bacteriostatic and fungistatic properties

Abstract: The composition of the essential oil of flowering catnip (Nepeta cataria L., Lamiaceae) was analyzed by means of GC/MS. Besides the already known nepetalactones 4aα, 7α, 7aα-nepetalactone; 3,4β-dihydro-4aα, 7α, 7aα-nepetalactone; 4aα, 7α, 7aβ-nepetalactone and β-caryophyllene, five new constituents were identified: dimethyl-3,7 oxa-1 bicyclo [3,3,0] oct-2-ene, piperitone, thymol methyl ether, hexenyl benzoate and humulene oxide. The essential oil of two samples of the plant, collected at two different stages of development, was compared as to their nepetalactone content. The oil samples and a hexane extract were subjected to microbiological tests (five bacteria and seven fungi) and compared to natural compounds known for their antimicrobiological activities.

Control of the transition to chaos in neural networks with random connectivity

Abstract: The occurrence of chaos in recurrent neural networks is supposed to depend on the architecture and on the synaptic coupling strength. It is studied here for a randomly diluted architecture. We produce a bifurcation parameter independent of the connectivity that allows a sustained activity and the occurrence of chaos when reaching a critical value. Even for weak connectivity and small size, we find numerical results in accordance with the theoretical ones previously established for fully connected infinite sized networks. Moreover the route towards chaos is numerically checked to be a quasiperiodic one, whatever the type of the first bifurcation is. In the discussion, we connect these results to some recent theoretical results about highly diluted networks. Hints are provided for further investigations to elicit the role of chaotic dynamics in the cognitive processes of the brain.

Importance of Mevalonate-Derived Products in the Control of HMG-CoA Reductase Activity and Growth of Human Lung Adenocarcinoma Cell Line A549

Abstract: HMG-CoA reductase catalyzes the synthesis of mevalonate, a crucial intermediate in the biosynthesis of cholesterol and non-sterol isoprenoid compounds essential for cell growth. The HMG-CoA reductase activity of the A549 tumor cell line is higher than that of normal human fibroblasts. This deregulation in mevalonate needs was not due to an alteration in the activated state of the enzyme by short-term regulation. We show that the HMG-CoA reductase in A549 cell line was subject to a multivalent feedback control. A high fraction (40%) of the reductase activity was devoted to non-sterol products. In contrast, normal fibroblasts had only 15-20% of the reductase activity that generated non-sterol products. We also show that cholesterol and at least one of the non-sterol products are necessary for optimal cell growth of A549 cells. Our data strongly suggest that A549 cells produce more non-sterol substances which may be related to increased requirements of mevalonate for upregulated cell growth.

La dynamique des pseudogroupes de rotations

Abstract: We study dynamical systems on the circle generated by a finite number of partially defined rotations. We construct new examples with all orbits dense (this leads to non-simplicial free actions of free groups on ℝ-trees). We study the generic dynamics for these pseudogroups and their 1-parameter families. We show that, in suitable 2-parameter families, the set of pseudogroups having a dense orbit is a Sierpinski curve. We generalize results on interval exchange transformations obtained by Boshernitzan, Veech, Rips.

Purification and characterization of elicitor‐induced lipoxygenase in tobacco cells

Abstract: Summary Lipoxygenase activity was induced in a tobacco cell suspension culture by treatment with glycopeptide elicitors prepared from the cell walls of Phytophthora parasitica var, nicotianae, and in tobacco seedlings infected by this fungal pathogen. Upon purification and characterization, the enzyme appeared to have a molecular weight of 96000, a pl of 5.1 and a Km of 20.9 μM with linoleic acid as substrate. According to its acidic optimum pH, it belongs to type-2 lipoxygenases. Using linoleic, linolenic and arachidonic acids as substrates, the products formed in vitro by lipoxygenase were characterized. 9- and 5-hydroperoxides were the main products obtained from the C18 and C20 fatty acids, respectively, thereby indicating that a 5-lipoxygenase accounts for most of the elicitor-induced activity, since the main site of insertion of molecular oxygen is on C-5 of arachidonic acid. Small amounts of 13-hydroperoxides were also formed from the C18 fatty acids. In vitro, the strongest inhibitors of tobacco lipoxygenase were n-propylgallate and nordihydroguaiaretic acid. The possible involvement of this enzyme in signaling phenomena leading to defense induction in plants via jasmonic acid and other fatty acid-derived products is discussed.

Palaeomagnetic rotations and fault kinematics in the Rif Arc of Morocco

Abstract: Palaeomagnetic and structural investigations in the Rif arc of Morocco indicate that there have been large rotations associated with a pattern of outwardly directed thrusting. Rock magnetic experiments in conjunction with thermal and alternating field demagnetization demonstrate that eight sites in Jurassic and Cretaceous limestones along the Internal/External boundary have a stable remanent magnetization. This is, in most cases, rotated anticlockwise by as much as 100° from the expected Mesozoic declination but in the Tetuan area there are large clockwise rotations. Kinematic indicators from fault surfaces indicate the following. (1) In the eastern Rif there has been predominantly south-directed thrusting, partly overprinted by extensional and sinistral strike-slip faults. (2) At the eastern end of the N 70°E striking Jebha Fault zone there is a pattern of dominant sinistral NE-trending and subsidiary dextral SE-trending strike-slip faults, overprinted by normal faults while at the western end deformation consists largely of south directed thrusting. (3) In the northern section of the chain, where the structural trends are dominantly N-S, thrusting is directed W to NW. It is suggested that the data are best explained by differential motion and rotation of thrust sheets during outwardly directed thrusting around the arc.