Showing papers by "Aix-Marseille University published in 1996"

The Role of Working Memory Resources in Simple Cognitive Arithmetic

Abstract: Two experiments tested the hypothesis that simple arithmetic requires working memory resources. Subjects were presented with a simple verification task (e.g. 8 + 4 = 12. True? False?) with (or without) secondary tasks. We varied the difficulty of the problems (i.e. easy vs hard problems) and the potential for inducing associative confusion (e.g. 8 4 = 12). Secondary tasks were chosen so as to overload the phonological loop and the central executive of the working memory system. We found greater disruption of performance on true problems when both the phonological loop and the central executive were overloaded, and greater disruption of performance on false problems when the central executive system was overloaded. This pattern of results is consistent with the working memory resource hypothesis and suggests that the central executive is a critical system involved in simple arithmetic. Finally, the results of the present study on both true and false problems and their implications for cognitive arithmetic ...

The animal lectin galectin-3 interacts with bacterial lipopolysaccharides via two independent sites.

Abstract: Galectin-3 is a beta-galactoside binding protein expressed by activated macrophages, epithelial cells, and certain other cell types. Galectin-3 has a C-terminal carbohydrate binding domain, an N-terminal part consisting of a proline- and glycine-rich repetitive domain, and a small N-terminal domain. Two independent LPS binding sites on galectin-3 were demonstrated by binding of biotinylated LPS to immobilized recombinant galectin-3. One appears to be the carbohydrate binding site in the C-terminal domain that confers binding of LPS from Klebsiella pneumoniae that has a beta-galactoside-containing polysaccharide chain. This binding is best demonstrated using galectin-3 immunocaptured by a mAb to the N-terminal part (M3/38) and is inhibited by lactose. In contrast, Salmonella minnesota R7 LPS (Rd mutant), which is devoid of beta-galactosides, appears to bind to a site within the N-terminal part of galectin-3. This interaction is best demonstrated using galectin-3 directly immobilized in wells, and it is inhibited by the Ab M3/38, but not by lactose. Binding inhibition by polymyxin B and the profile of inhibition by a panel of LPSs with different amounts of the inner and outer cores present indicate that this second binding site recognizes the lipid A/inner core region of LPSs.

Nucleation and Growth Mechanisms of Fe Oxyhydroxide in the Presence of PO4 Ions. 2. P K-Edge EXAFS Study

Abstract: P K-edge EXAFS spectroscopy has been used to determine the local environment of phosphorus during the hydrolysis of FeCl3 in the presence of phosphate. Measurements were performed on liquid samples and in the fluorescence mode. With the detection geometry adopted during experiments, the self absorption of fluorescence has been quantified and does not appear to be an important phenomenon. Thus no correction was made. In order to clearly identify the neighboring atoms around P, a multiple scattering approach has been used. Multiple scattering seems to be an important phenomenon in PO4/FeCl3 clusters. P K-edge EXAFS data show that even for very acidic solutions, pH < 1, all the phosphate ions are complexed to Fe. For a P/Fe molar ratio of 0.2 one phosphate progressively bonds one, two, and three irons when n (=[OH]/[Fe]) increases from 0 to 2.0. At n = 2, one phosphate bridges three iron dimers and two kinds of PO4−Fe linkages are detected. For P/Fe = 0.5, the number of irons linked to PO4 increases when n i...

Symbiosis between methane-oxidizing bacteria and a deep-sea carnivorous cladorhizid sponge

Abstract: Dense bush-l~ke clumps of several hundred ~ n d ~ v l d u a l s of a new specles of Cladorhiza (Demosponglae, Poeciloscler~da) were observed near methane sources in mud volcanoes 4718 to 4943 m dcep In the Barbddos Trench The sponge tissue contalns 2 maln mo~pho log~ca l types of extracellular symbiotic bacteria small rod-shaped cells and larger cocco~d cells with stacked membranes Stdble carbon ~so tope values, the presence of methanol dehydrogenase and ultrastructural observatlons all lndlcate that at least some of the syrnblonts are methdnotrophic Ultrastructural e v ~ d e n c e of ~n l r ace l l~~ la r d ~ g e s t ~ o n of thp s y n ~ b ~ o n t s and the stable C and X values suggest that thc sponge obtalns a slgnlflcdnt portion of its nutr~tlon from the symbionts Ultrdstructure of the sponqe embryo suggests d ~ r e c t ransmission throuqh qc.neratlons In brooded embryos The sponge also ma~ntrilns a carnivorous feed~ng hdblt on tin\ swlmmlng prey, as do other cladorhlzlds K E Y L\/ORDS. Methanotrophy POI-~fera . Deep-sea . Symbiosis . Cold-seep communities

Greenberg's theorem for quasiconvex subgroups of word hyperbolic groups

Abstract: Analogues of a theorem of Greenberg about finitely generated subgroups of free groups are proved for quasiconvex subgroups of word hyperbolic groups. It is shown that a quasiconvex subgroup of a word hyperbolic group is a finite index subgroup of only finitely many other subgroups.

Pancreatic carboxyl ester lipase: a circulating enzyme that modifies normal and oxidized lipoproteins in vitro.

Abstract: Pancreatic carboxyl ester lipase (CEL) hydrolyzes cholesteryl esters (CE), triglycerides (TG), and lysophospholipids, with CE and TG hydrolysis stimulated by cholate. Originally thought to be confined to the gastrointestinal system, CEL has been reported in the plasma of humans and other mammals, implying its potential in vivo to modify lipids associated with LDL, HDL (CE, TG), and oxidized LDL (lysophosphatidylcholine, lysoPC). We measured the concentration of CEL in human plasma as 1.2+/-0.5 ng/ml (in the range reported for lipoprotein lipase). Human LDL and HDL3 reconstituted with radiolabeled lipids were incubated with purified porcine CEL without or with cholate (10 or 100 microM, concentrations achievable in systemic or portal plasma, respectively). Using a saturating concentration of lipoprotein-associated CE (4 microM), with increasing cholate concentration there was an increase in the hydrolysis of LDL- and HDL3-CE; at 100 microM cholate, the present hydrolysis per hour was 32+/-2 and 1.6+/-0.1, respectively, indicating that CEL interaction varied with lipoprotein class. HDL3-TG hydrolysis was also observed, but was only approximately 5-10% of that for HDL3-CE at either 10 or 100 microM cholate. Oxidized LDL (OxLDL) is enriched with lysoPC, a proatherogenic compound. After a 4-h incubation with CEL, the lysoPC content of OxLDL was depleted 57%. Colocalization of CEL in the vicinity of OxLDL formation was supported by demonstrating in human aortic homogenate a cholate-stimulated cholesteryl ester hydrolytic activity inhibited by anti-human CEL IgG. We conclude that CEL has the capability to modify normal human LDL and HDL composition and structure and to reduce the atherogenicity of OxLDL by decreasing its lysoPC content.

Energy dependence of the differences between the quark and gluon jet fragmentation

Abstract: Three jet events arising from decays of the Z boson, collected by the DELPHI detector, were used to measure differences in quark and gluon fragmentation. Gluon jets were anti-tagged by identifying b quark jets. Unbiased quark jets came from events with two jets plus one photon. Quark and gluon jet properties in different energy ranges were compared for the first time within the same detector. Quark and gluon jets of nearly the same energy in symmetric three jet event topologies were also compared. Using three independent methods, the average value of the ratio of the mean charged multiplicities of gluon and quark jets is = 1.241 ± 0.015 (stat.) ± 0.025 (syst.). Gluon jets are broader and produce fragments with a softer energy spectrum than quark jets of equivalent energy. The string effect has been observed in fully symmetric three jet events. The measured ratio R_{gamma} of the charged particle flow in the qoverline{q} inter-jet region of the qar{q}g and qar{q}gamma samples agrees with the perturbative QCD expectation. The dependence of the mean charged multiplicity on the hadronic center-of-mass energy was analysed in photon plus n-jet events. The value for alpha_s(M_Z) determined from these data using a QCD prediction with corrections at leading and next-to-leading order is αs(MZ)= 0.116 ± 0.003 (stat.) ± 0.009 (syst.).

Lack of integrin alpha-chain endoproteolytic cleavage in furin-deficient human colon adenocarcinoma cells LoVo.

Abstract: In the present report the biosynthesis of the integrin alpha-chains endowed with constitutive endoproteolytic cleavage was evaluated in LoVo cells where furin, a subtilisin-like convertase involved in post-translational endoproteolytic processing, is not functional. It was found that cell-surface alpha 3, alpha 6 and alpha v subunits were not processed endoproteolytically into heavy and light chains as they were in HT29-D4 cells, a furin-competent cell line. Complete removal of N-linked oligosaccharides and pulse-chase experiments confirmed that the cleavage of the alpha 6 integrin subunit occurring 45 min after translation in HT29 cells did not take place in LoVo cells. Apart from cleavage deficiency, alpha 6 subunit glycosylation, association with beta 4 subunits and targeting to the plasma membrane seemed comparable in LoVo and HT29 cells. The pro-alpha 6 and the pro-alpha 3 subunits immunopurified from LoVo cells were highly sensitive to endoproteolysis by recombinant furin. Furin cleavage was calcium dependent and resulted in the conversion of the 140 kDa pro-alpha 6 into a 120 kDa heavy chain. These results suggest strongly that furin is involved in the endoproteolytic processing of cleavable integrin alpha subunits.

Pancreatic Regenerating Gene Overexpression in the Nonobese Diabetic Mouse During Active Diabetogenesis

Abstract: The reg gene has previously been shown to be associated with regeneration of pancreatic islets. Strategies for influencing the replication and the growth of the β-cell mass may be important for prevention and/or treatment of type I diabetes. In this study, we have examined the level of reg gene expression at various degrees of diabetogenesis in the pancreas of the NOD mouse (male, female, and cyclophosphamide-treated male) using both human reg cDNA as the probe and dot blot analysis. The expression of the reg gene was found to be significantly increased in female mice compared with male mice, and in both cases, the expression level was not influenced by age. Nondiabetic female mice have a significantly higher expression of the gene than diabetic female mice, and there was a positive correlation between the age of diabetes onset and the reg mRNA level. In addition, overexpression of the reg gene was found in male mice treated by cyclophosphamide, an agent known to be a potent inducer of diabetes in male NOD mice. None of these results were found in the diabetes-resistant control OF1 mice, in which pancreatic reg gene expression did not differ between female and male mice treated or untreated with cyclophosphamide. All of these data suggest that there is a strong correlation between reg gene expression in the pancreas of the NOD mouse and the likelihood of developing diabetes.

Alteration of G alpha subunits mRNA levels in bromocriptine resistant prolactinomas.

Abstract: Patients with prolactinoma are commonly treated with the D2 dopamine agonist bromocriptine, which in most cases, normalizes prolactin (PRL) levels. However, resistance to bromocriptine has been observed in 5 to 18% of tested prolactinomas and is associated to a decrease in both D2 receptor density and mRNA levels. In this study, we used quantitative RT-PCR to investigate whether expression of G alpha proteins could be also modified in bromocriptine resistant prolactinomas. No difference in G alpha o mRNA levels or in the relative expression of G alpha s between bromocriptine sensitive and bromocriptine resistant prolactinomas was observed. In contrast, the relative expression of G alpha i2 was found to be decreased in bromocriptine resistant prolactinomas when compared to that of bromocriptine sensitive prolactinomas. Interestingly, the relative G alpha i2 expression was correlated to both bromocriptine inhibition of in vitro PRL secretion and D2 receptor mRNA levels. Bromocriptine resistance could thus result from a decrease in D2 dopamine receptors associated with a decrease in G alpha i2 expression.

A multicenter proton magnetic resonance spectroscopy study of neurological complications of AIDS.

Abstract: Human immunodeficiency virus (HIV) infection as seen in Europe and the United States has predominantly been contracted through male homosexual sex or intravenous drug abuse. In infected subjects, the brain is frequently affected both clinically and neuropathologically. The aim of this multicenter study has been to evaluate the value of single-voxel proton magnetic resonance spectroscopy (MRS) in the assessment of the neurological complications of acquired immunodeficiency syndrome (AIDS). MRS (voxel size = 8 ml, TR/TE = 1600/135 msec) was performed in 137 HIV-1-seropositive patients and 64 healthy controls without risk factors at three clinical MR sites operating at 1.5 T. The first result of this multicenter trial is that good reproducibility of results among participating sites was found. This demonstrates the reliability and robustness of MRS in the study of in vivo brain metabolism. In HIV patients, there was no significant correlation between metabolite ratios of brain detected by MRS and CD...

Selective adaptation of the cuticular hydrocarbon profiles of the slave-making ants Polyergus rufescens Latr. and their Formica rufibarbis Fab. and F. Cunicularia Latr. slaves

Abstract: The results of comparisons between the cuticular hydrocarbon mixtures of the slave-making ants Polyergus rufescens, their Formica rufibarbis and F. cunicularia slaves and between slave and free-living workers (which were probably related to one another) from each Formica species showed the following. (1) Several products were common to all three species. (2) Each of the two Formica species had its own particular products. (3) The Polyergus cuticular mixture did not contain any species-specific hydrocarbons but had some components in common with either rufibarbis or cunicularia. Because these products were present in Polyergus, whichever Formica species they enslaved, Polyergus must be able to synthesize their own cuticular hydrocarbons. (4) Cohabitation with another species as the result of slave making had no qualitative effects on the individual cuticular hydrocarbon mixtures: their composition was the same in the Polyergus whether living with F. rufibarbis or F. cunicularia and in the Formica of each species whether free living or enslaved. (5) The Polyergus resembled their Formica slaves, however, due to a tendency to adjust the proportions of some of the common hydrocarbons to those of their slaves; this tendency seems to have been reciprocal, although it was less marked in the case of the Formica. (6) The chemical signatures of mixed colonies inhabited by the same slave species depended mainly on the cuticular characteristics of the Formica slaves but also on those of the Polyergus, which differed from one colony to another. The finding that cuticular hydrocarbon mixtures of individuals of both species (slaves and slave makers) interacting within a mixed colony kept their species-specific hydrocarbons while the proportions of the common products showed a tendency to adapt to those of the other species suggests that there exists a selective mechanism probably involving the regulation of the synthesis of these products.

Acute fracture of the distal tibial physis: role of gradient-echo MR imaging versus plain film examination.

Abstract: Recent reports indicate that, compared with MR imaging, plain film radiography often underestimates the extent of injury in children with physeal fracture-separation. Such underestimation may have significant therapeutic and prognostic outcomes. We performed this study to assess the benefit of MR imaging compared with plain film radiography in the diagnosis and immediate treatment of acute fractures of the distal tibial physis.Twenty-nine patients with acute fractures, including 15 Salter-Harris II, four Salter-Harris III, four Salter-Harris IV, and six triplane fractures, were prospectively examined by MR imaging with gradient-echo sequences. The MR images were compared with plain film radiographs. All cases were reviewed in a blind fashion by two experienced radiologists to determine the Salter-Harris classification on the basis of first plain film radiographs and then MR images. Two experienced pediatric surgeons were asked to propose treatment on the basis of first plain film radiographs and then MR i...

Mineralogical and geochemical characteristics of two bauxitic profiles, Fria, Guinea Republic

Abstract: Bauxite deposits of the Fria district, Guinea, have been exploited since 1960. These lateritic bauxites, located on the upper parts of plateaus, result from weathering of paleozoic schists. The ores are composed of gibbsite associated with pyrophyllite, Al-substituted gœthite, and kaolinite. Pyrophyllite and Al-substituted gœthite may contain up to 9% of the total Al2O3 content of the bauxite; this cannot be recovered through the Bayer process because these phases are insoluble in the leaching solutions. Kaolinite is soluble under Bayer leaching but this dissolution induces precipitation of sodium aluminosilicates, which apart from loss of further alumina results in decreasing efficiency of the process through scale formation. Detailed knowledge of the distribution of the different ore types and their mineralogical composition is necessary for efficient processing.

First-order necessary conditions for infinite-horizon variational problems

Abstract: We establish rigorously several pointwise or asymptotic firstorder necessary conditions for infinite-horizon variational problems in general form, in the framework of continuous time. We obtain several new results, and we extend to general differentiable Lagrangians\(L(t,x,\dot x)\) some results known only in special cases. To realize this aim, we justify two different ways to associate a family of finite-horizon problems to an infinite-horizon problem.

Effect of segregation on the shape of grain boundary diffusion profiles : Experimental study of the Cu-Ag system

Abstract: Grain boundary diffusion of Ag in Cu and in a Cu-0.091 at.% Ag alloy has been investigated. An experimental method to separate the effect of different grain boundaries present in the samples and the effect of segregation on grain boundary diffusion profiles is described. It is shown that in the case of silver diffusion in pure copper the curved penetration plots are due to segregation effects. For pure Cu the obtained activation energy and pre-exponential factor of the triple product P are (90 ± 6.2)kJ mol−1 and (3.7+7.3 −2.5) × 10−14 m3s−1, respectively. For Cu(Ag) alloy these values are (119.4 ± 6.6)kJ mol−1 and (2.1+4.8 −1.5) × 10−12m3s−1, respectively. The activation energy of grain boundary segregation is estimated as 37± 13kJmol−1.

Clonal cell cultures from adult spinal cord of the amphibian urodele Pleurodeles waltl to study the identity and potentialities of cells during tail regeneration.

Abstract: The urodele amphibians are nearly the only adult vertebrates able to regener- ate their missing or amputated tail. The most strik- ing feature of this model lies in the ability of the spinal cord (SC) to differentiate, within the regen- erating tail, a new ependymal tube from which the SC and the peripheral nervous system originate. A fundamental question is whether, in response to tail excision, the ependymoglia of the old SC stump behaves as an embryonic neuroepithelium. To evaluate this possibility, cell lines from primary cell cultures of adult SC were established for the first time in newts, and two cell clones, immuno- chemically characterized as ependymoglial cell populations, could be obtained. To analyze the po- tentialities of these clonal cells, after transplanta- tion in tail regenerates, cell-marking experiments, using either in vitro transfection with lac2 gene or the lineage tracer lysinated rhodamine dextran (LRD), were performed. One to 2 weeks postim- plantation, most of labeled derivatives were iden- tified as melanocytes. Interestingly, labeled cells were also seen integrated in the ependymoglia of the regenerating SC. Two to 6 weeks after implan- tation in young regenerates, we also observed LRD-labeled elongated cells close to nerves or myofibers which were unambiguously identified as Schwann cells by galactocerebroside staining. Taken together, these findings showed that clonal cells derived from adult newt SC cultures could largely find, in regenerate mesenchyme, suitable environmental conditions to differentiate into mel- anocytes or Schwann cells. Because these two cell types arise from neural crest cells during embryo- genesis, this supports the interesting view that multipotent cells are still present in the SC of adult urodeles.

Chemical and Structural Transformation of Aggregated Al13 Polycations, Promoted by Salicylate Ligand

Abstract: The chemical and structural consequences of the interaction between aggregates made of Al13 polycations and salicylate ligand were examined using adsorption isotherms, electrophoresis, infrared spectroscopy, Fraunhofer light diffraction, and static light scattering spectroscopy. Drastic changes were observed for a pseudo equilibrium ligand concentration equimolar to Al13. Below this concentration, salicylate forms monodentate complexes with the charged aluminum sites, decreasing the electrostatic repulsion between Al13 particles. A densification of the aggregates is evident by an increase of the apparent fractal dimension from 1.8 to 2.9. No dissolution was observed in this concentration range. Above this ligand concentration, excess adsorption of salicylate causes charge reversal, and dissolution of the aggregates, in the form of soluble complexes and small clusters was observed. The consequences were a size reduction and loosening of the aggregates. In aquatic media, such radical in situ changes are abl...

Study of rare $b$ decays with the DELPHI detector at LEP

Abstract: Rare decays of beauty particles were studied in several charmless modes using the data collected with the DELPHI detector at LEP from 1991 to 1994. These decays are mediated by both tree levelb→u and one-loop penguin b → s, d transitions. Evidence for charmlessB decays was obtained in two body hadronic modes. The branching ratios ofB d,s 0 toπ + π − orK + π − andB u − toρ 0 π − orK*0 π − were found to be (2.8 −1.0 +1.5 ±0.2)×10−5 and (1.7 −0.8 +1.2 ±0.2)×10−4 respectively. The fraction of these decays with a charged kaon in the final state that is not from the spectators quark, was measured to be 0.58±0.18. Upper limits were set at 90% confidence level on the branching ratios for three and four body charmless hadronic decays in the range of (1–3)×10−4, for inclusive radiativeb → sγ decays at 5.4×10−4, for the exclusive radiative decaysB d 0 → K*(892)0 γ andB s 0 → φ(1020)γ at 2.1×10−4 and 7.0×10−4 respectively, and for dineutrino decays b → sννˉ , in the exclusive channels B0d → K∗(892)0ννˉ and B0s → ϕ(1020)ννˉ at 1.0×10−3 and 5.4×10−3 respectively. The limits on dineutrino decays constrain theories with a newU(1) gauge boson coupling predominantly to the third family of fermions.

Method for characterizing masses in digital mammograms

Abstract: A method for characterizing tumoral masses in mammograms is described. It is based on two significant features of breast cancer, namely the degree of spiculation and the presence of fuzzy areas in the boundary of the tumor. The quantization of these features is performed by means of polar and pseudopolar representations of the neighborhood of the tumor to take advantage of its symmetry . The degree of spiculation is deduced from a shape parameter that characterizes the irregularity of the boundary after enhancing divergent structures. The radial component of the gradient on the boundary provides a measurement of fuzzy appearance. In the next step, the identification of malignant and benign tumors is achieved with a two-level hierarchical classification using a Bayesian classifier. A set of 19 masses are processed and results are presented and discussed.

Tau hadronic branching ratios

Abstract: From 64492 selected tau-pair events, produced at the Zeta(o) resonance, the measurement of the tau decays into hadrons from a global analysis using 1991, 1992 and 1993 ALEPH data is presented. Special emphasis is given to the reconstruction of photons and pi(o)'s, and the removal of fake photons. A detailed study of the systematics entering the pi(o) reconstruction is also given. A complete and consistent set of tau hadronic branching ratios is presented for 18 exclusive modes. Most measurements are more precise than the present world average. The new level of precision reached allows a stringent test of tau - mu universality in hadronic decays, g(tau)/g(mu) = 1.0013 +/- 0.0095, and the first measurement of the vector and axial-vector contributions to the non-strange hadronic tau decay width: R(tau,V) = 1.788 +/- 0.025 and R(tau,A) = 1.694 +/- 0.027. The ratio (R(tau,V) - R(tau,A))/(R(tau,V) + R(tau,A)), equal to (2.7 +/- 1.3) %, is a measure of the importance of QCD non-perturbative contributions to the hadronic tau decay width.