Showing papers by "University of Bordeaux published in 2000"

Macroscopic Fibers and Ribbons of Oriented Carbon Nanotubes

Abstract: A simple method was used to assemble single-walled carbon nanotubes into indefinitely long ribbons and fibers. The processing consists of dispersing the nanotubes in surfactant solutions, recondensing the nanotubes in the flow of a polymer solution to form a nanotube mesh, and then collating this mesh to a nanotube fiber. Flow-induced alignment may lead to a preferential orientation of the nanotubes in the mesh that has the form of a ribbon. Unlike classical carbon fibers, the nanotube fibers can be strongly bent without breaking. Their obtained elastic modulus is 10 times higher than the modulus of high-quality bucky paper.

Frequency-band complex noninteger differentiator: characterization and synthesis

Abstract: The state-of-the-art on generalized (or any order) derivatives in physics and engineering sciences, is outlined for justifying the interest of the noninteger differentiation. The problems subsequent to its use in real-time operations are then set out so as to motivate the idea of synthesizing it by a recursive distribution of zeros and poles. An analysis of the existing work is also proposed to support this idea. A comprehensive study is given of the synthesis of differentiators with integer, noninteger, real or complex orders, and whose action is limited to any given frequency bandwidth. First, a definition, in the operational and frequency domains, of a frequency-band complex noninteger order differentiator, is given in a mathematical space with four dimensions which is a Banach algebra. Then, the determination of its synthesized form, by a recursive distribution of complex zeros and poles characterized by complex recursive factors, is presented. The complex noninteger differentiation order is expressed as a function of these recursive factors. The number of zeros and poles is calculated to be as low as possible while still ensuring the stability of the synthesized differentiator to be synthesized. A time validation is presented. Finally, guidelines are proposed for the conception of the synthesized differentiator.

Linear Time Solvable Optimization Problems on Graphs of Bounded Clique-Width

Abstract: Hierarchical decompositions of graphs are interesting for algorithmic purposes There are several types of hierarchical decompositions Tree decompositions are the best known ones On graphs of tree-width at most k , ie, that have tree decompositions of width at most k , where k is fixed, every decision or optimization problem expressible in monadic second-order logic has a linear algorithm We prove that this is also the case for graphs of clique-width at most k , where this complexity measure is associated with hierarchical decompositions of another type, and where logical formulas are no longer allowed to use edge set quantifications We develop applications to several classes of graphs that include cographs and are, like cographs, defined by forbidding subgraphs with ``too many'' induced paths with four vertices

Hydrological impact of heinrich events in the subtropical northeast atlantic

Abstract: Reconstructing the impact of Heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events. A high-resolution study of a marine sediment core from the Iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low-salinity arctic water masses during the last three Heinrich events. These paleoclimatic time series reveal the internal complexity of each of the last three Heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments.

Long-lasting Hyperalgesia Induced by Fentanyl in Rats: Preventive Effect of Ketamine

Abstract: BackgroundIt has been reported that μ-opioid receptor activation leads to a sustained increase in glutamate synaptic effectiveness at the N-methyl-D-aspartate (NMDA) receptor level, a system associated with central hypersensitivity to pain. One hypothesis is that postoperative pain may result partly

Multicenter Double-Blind, Randomized, Placebo-Controlled Trial of Levetiracetam as Add-On Therapy in Patients with Refractory Partial Seizures

Abstract: Summary: Purpose: To evaluate the efficacy and tolerability of levetiracetam (LEV, Keppra) as add-on therapy in patients with refractory partial seizures. Methods: In this European multicenter, double-blind, randomized, placebo-controlled trial, LEV (500 or 1,000 mg twice daily) was compared with placebo as add-on therapy in 324 patients with uncontrolled simple or complex partial seizures, or both, with or without secondary generalization. After enrollment, three parallel groups were assessed during a baseline period of 8 or 12 weeks, followed by a 4-week titration interval and a 12-week evaluation period. Results: LEV significantly decreased partial seizure frequency compared with placebo. A reduction in seizure frequency of 50% occurred in 22.8% of patients in the 1,000-mg group and 31.6% of patients in the 2,000-mg group, compared with 10.4% of patients in the placebo group. Administration of LEV did not affect plasma concentrations of concomitant an-tiepileptic drugs or alter vital signs or laboratory parameters. No significant difference in the incidence of adverse events was observed between treatment groups (70.8% for the 1,000-mg group and 75.5% for the 2,000-mg group), or between the LEV and placebo groups (73.2% for placebo group). The most commonly reported adverse effects in the LEV group were asthenia, headache, and somnolence. Conclusions: The antiepileptic efficacy and tolerability of LEV (1,000 mg/d and 2,000 mg/d, administered in two divided doses) as add-on therapy was established in patients with refractory partial seizures in this clinical study.

Impact of an urban effluent on antibiotic resistance of riverine Enterobacteriaceae and Aeromonas spp.

Abstract: In order to evaluate the impact of an urban effluent on antibiotic resistance of freshwater bacterial populations, water samples were collected from the Arga river (Spain), upstream and downstream from the wastewater discharge of the city of Pamplona. Strains of Enterobacteriaceae (representative of the human and animal commensal flora) (110 isolates) and Aeromonas (typically waterborne bacteria) (118 isolates) were selected for antibiotic susceptibility testing. Most of the Aeromonas strains (72%) and many of the Enterobacteriaceae (20%) were resistant to nalidixic acid. Singly nalidixic acid-resistant strains were frequent regardless of the sampling site for Aeromonas, whereas they were more common upstream from the discharge for enterobacteria. The most common resistances to antibiotics other than quinolones were to tetracycline (24.3%) and beta-lactams (20.5%) for Enterobacteriaceae and to tetracycline (27.5%) and co-trimoxazole (26.6%) for Aeromonas. The rates of these antibiotic resistances increased downstream from the discharge at similar degrees for the two bacterial groups; it remained at high levels for enterobacteria but decreased along the 30-km study zone for Aeromonas. Genetic analysis of representative strains demonstrated that these resistances were mostly (enterobacteria) or exclusively (Aeromonas) chromosomally mediated. Moreover, a reference strain of Aeromonas caviae (CIP 7616) could not be transformed with conjugative R plasmids of enterobacteria. Thus, the urban effluent resulted in an increase of the rates of resistance to antibiotics other than quinolones in the riverine bacterial populations, despite limited genetic exchanges between enterobacteria and Aeromonas. Quinolone resistance probably was selected by heavy antibiotic discharges of unknown origin upstream from the urban effluent.

Photodimerization of anthracenes in fluid solution:structural aspects

Abstract: Owing to their versatile photophysical and photochemical properties, anthracene and its derivatives are being employed in many systems, for instance as energy migration probes in polymers, triplet sensitizers, molecular fluorosensors, electron acceptor or donor chromophores in artificial photosynthesis, photochromic substrates in 3D memory materials, etc. One remarkable feature is their ability to photodimerize under UV irradiation which induces considerable changes in their physical properties. This account reports the preparative and structural aspects of this very useful and protean photocycloaddition.

Ten Years of Single-Molecule Spectroscopy

Abstract: Single-molecule spectroscopy (SMS) combines some of the advantages of local probe microscopies with those of optics. Since this field came into being 10 years ago, it has expanded at a breathtaking pace. From the first cryogenic experiments up to the recent studies of basic processes in molecular biology, single-molecule methods have found their way into an ever broadening range of applications. Their common feature is the complete elimination of ensemble averaging. By exposing individual variations as well as dynamical fluctuations, SMS provides new insights into any system with spatial or temporal inhomogeneity. The present article illustrates single molecule spectroscopic experiments at cryogenic temperatures, mainly from the authors' group. The results reviewed here range from molecular photophysics, to the dynamics of the solid matrix around the molecule, and to the interactions between a single molecule and electromagnetic fields, i.e., quantum optics. SMS is now ripe for a variety of applications i...

Fictitious domain approach for numerical modelling of Navier–Stokes equations

Abstract: This study investigates a fictitious domain model for the numerical solution of various incompressible viscous flows. It is based on the so-called Navier–Stokes/Brinkman and energy equations with discontinuous coefficients all over an auxiliary embedding domain. The solid obstacles or walls are taken into account by a penalty technique. Some volumic control terms are directly introduced in the governing equations in order to prescribe immersed boundary conditions. The implicit numerical scheme, which uses an upwind finite volume method on staggered Cartesian grids, is of second-order accuracy in time and space. A multigrid local mesh refinement is also implemented, using the multi-level Zoom Flux Interface Correction (FIC) method, in order to increase the precision where it is needed in the domain. At each time step, some iterations of the augmented Lagrangian method combined with a preconditioned Krylov algorithm allow the divergence-free velocity and pressure fields be solved for. The tested cases concern external steady or unsteady flows around a circular cylinder, heated or not, and the channel flow behind a backward-facing step. The numerical results are shown in good agreement with other published numerical or experimental data. Copyright © 2000 John Wiley & Sons, Ltd.

Mono- and dibasic proteolytic cleavage sites in insect neuroendocrine peptide precursors.

Abstract: Regulatory peptides are synthesized as part of larger precursors that are subsequently processed into the active substances. After cleavage of the signal peptide, further proteolytic processing occurs predominantly at basic amino acid residues. Rules have been proposed in order to predict which putative proteolytic processing sites are actually used, but these rules have been established for vertebrate peptide precursors and it is unclear whether they are also valid for insects. The aim of this paper is to establish the validity of these rules to predict proteolytic cleavage sites at basic amino acids in insect neuropeptide precursors. Rules describing the cleavage of mono- and dibasic potential processing sites in insect neuropeptide precursors are summarized below. Lys-Arg pairs not followed by an aliphatic or basic amino acid residue are virtually always cleaved in insect regulatory peptide precursors, but cleavages of Lys-Arg pairs followed by either an aliphatic or a basic amino acid residue are ambiguous, as is processing at Arg-Arg pairs. Processing at Arg-Lys pairs has so far not been demonstrated in insects and processing at Lys-Lys pairs appears very rare. Processing at single Arg residues occurs only when there is a basic amino acid residue in position -4, -6, or -8, usually an Arg, but Lys or His residues work also. Although the current number of such sites is too limited to draw definitive conclusions, it seems plausible that cleavage at these sites is inhibited by the presence of aliphatic residues in the +1 position. However, cleavage at single Arg residues is ambiguous. When several potential cleavage sites overlap the one most easily cleaved appears to be processed. It cannot be excluded that some of the rules formulated here will prove less than universal, as only a limited number of cleavage sites have so far been identified. It is likely that, as in vertebrates, ambiguous processing sites exist to allow differential cleavage of the same precursor by different convertases and it seems possible that the precursors of allatostatins and PBAN are differentially cleaved in different cell types. Arch. Insect Biochem. Physiol. 43:49-63, 2000.

Daidzein is more efficient than genistein in preventing ovariectomy-induced bone loss in rats.

Abstract: We investigated the ability of genistein and daidzein, two soybean isoflavones, compared with that of 17 alpha-ethinylestradiol, to prevent bone loss in ovariectomized rats, a model for postmenopausal osteoporosis. Female Wistar rats (n = 65; 12 mo old) were either sham-operated (SH; n = 13) or ovariectomized (OVX; n = 52). On d 0, OVX rats were randomly assigned to groups as follows: 13 received genistein [G; 10 mcg/(g body weight. d)], 13 were treated with daidzein [D; 10 mcg/(g body weight. d)], 13 received 17 alpha-ethinylestradiol [E(2); 30 mcg/kg body weight. d)] and 13 were untreated (OVX). Compounds were mixed with a soy protein-free powdered semipurified diet and given orally for 3 mo. On d 90, the bone mineral density (BMD) in lumbar vertebrae, femur and its metaphyseal and diaphyseal zones (rich in cancellous and cortical bone, respectively) was lower in OVX than in SH (P < 0.01). In D or E(2), the four BMD were not different from SH, whereas in G, only the diaphyseal BMD was not different from SH. Image analysis performed in the distal femur metaphysis revealed that the cancellous bone area was lower in OVX than in SH (P < 0.01). Only the area in D was not different from that in SH. Finally, the bone turnover, which was higher in OVX than in SH (P < 0.005 and P < 0.05 for plasma osteocalcin concentration and urinary deoxypyridinoline excretion, respectively), was not different in G, D or E(2) compared with SH. Therefore, consumption of 17 alpha-ethinylestradiol or daidzein was more efficient than genistein in preventing ovariectomy-induced bone loss in rats.

The viable but non-culturable state of wine micro-organisms during storage.

Abstract: V. MILLET and A. LONVAUD-FUNEL.2000.Colony counting and DEFT did not give the same results when wine micro-organisms were enumerated. Both methods were used to monitor the population of acetic acid bacteria (AAB) and lactic acid bacteria (LAB) during wine storage. Results suggest that part of the populations had reached a viable but non-culturable (VBNC) state. These cells were unable to produce colonies but could hydrolyse fluorescent esters and could be counted by DEFT. For AAB, O2 deprivation quickly induced this state. Recovery from this state was very rapid as soon as O2 was available. The response was not so clear for LAB during wine storage. However, a similar state was induced by sulfiting. Moreover, filtration of wine stored in barrels and contaminated by Brettanomyces, AAB and LAB demonstrated that cell size was not homogeneous. Cells which remained in wine after several weeks could pass through a 0·45-μm membrane. However, when they re-entered a growing phase, they were again retained by membrane filtration. During and after the decline phase, wine micro-organisms might survive as smaller cells in a VBNC state.

Role of interleukin‐1β and tumour necrosis factor‐α in lipopolysaccharide‐induced sickness behaviour: a study with interleukin‐1 type I receptor‐deficient mice

Abstract: Interleukin-1 (IL-1) mediates symptoms of sickness during the host response to infection. IL-1 exerts its effects via several subtypes of receptors. To assess the role of IL-1 receptor type I (IL-1RI) in the sickness-inducing effects of IL-1, IL-1beta and the cytokine inducer lipopolysaccharide were administered to IL-1RI-deficient mice (IL-1RI-/-). Sickness was assessed by depression of social exploration, anorexia, immobility and body weight loss. IL-1RI-/- mice were resistant to the sickness-inducing effects of IL-1beta administered intraperitoneally (2 microg/mouse) and intracerebroventricularly (2 ng/mouse), but still fully responsive to lipopolysaccharide administered intraperitoneally (2.5 microg/mouse) and intracerebroventricularly (3 ng/mouse). The sensitivity of IL-1RI-/- mice to lipopolysaccharide was not due to a higher brain expression of proinflammatory cytokines other than IL-1, since lipopolysaccharide-induced expression of brain IL-1 beta, tumour necrosis factor-alpha (TNF-alpha) and IL-6 transcripts were identical in IL-1RI-/- and control mice when measured by semiquantitative reverse-transcriptase polymerase chain reaction 1 h after treatment. Blockade of TNF-alpha action in the brain by intracerebroventricular administration of a fragment of the soluble TNF receptor, TNF binding protein (3.6 microg/mouse), attenuated the depressive effects of intraperitoneal injection of lipopolysaccharide (1 microg/mouse) on behaviour in IL-1RI-/- but not in control mice. Since IL-1RI-/- mice were not more sensitive to intracerebroventricularly TNF-alpha (50 ng) than control mice, these results indicate that IL-1RI mediates the sickness effect of IL-1 and that TNF-alpha simply replaces IL-1 when this last cytokine is deficient.

Abolition and reversal of strain differences in behavioral responses to drugs of abuse after a brief experience.

Abstract: Inbred strains of mice are largely used to identify the genetic basis of normal and pathological behaviors. This report demonstrates that a moderate period of food shortage, an ecologically common experience, can reverse or abolish strain differences in behavioral responses to the abused psychostimulant amphetamine. The period of food shortage occurred when the animals were mature and was terminated before the administration of amphetamine. Strain differences in behavior appear highly dependent on environmental experiences. Consequently, to identify biological determinants of behavior, an integrated approach considering the interaction between environmental and genetic factors needs to be used.

Discrete velocity model and implicit scheme for the bgk equation of rarefied gas dynamics

Abstract: We present a numerical method for computing transitional flows as described by the BGK equation of gas kinetic theory. Using the minimum entropy principle to define a discrete equilibrium function, a discrete velocity model of this equation is proposed. This model, like the continuous one, ensures positivity of solutions, conservation of moments, and dissipation of entropy. The discrete velocity model is then discretized in space and time by an explicit finite volume scheme which is proved to satisfy the previous properties. A linearized implicit scheme is then derived to efficiently compute steady-states; this method is then verified with several test cases.

Amphiphilic Stars and Dendrimer-Like Architectures Based on Poly(Ethylene Oxide) and Polystyrene

Abstract: Newly designed star-shaped and dendrimer-like copolymers made of poly(ethylene oxide) (PEO) and polystyrene (PS) were synthesized by sequential anionic polymerization of ethylene oxide and atom transfer radical polymerization (ATRP) of styrene, the switch from the first to the second mechanism being obtained by selective transformation of “living” oxanionic sites. First, tri- and tetrafunctional initiators were used to anionically polymerize ethylene oxide and produce tri- and tetraarmed PEO stars. Next, the OH end groups of PEO star branches were derivatized into 2-bromopropionate groups giving rise to the corresponding tri- and tetrabromoester ended-PEO stars; the latter served as macroinitiators for the ATRP of styrene at 100 °C in the presence of CuBr/2,2‘-bipyridine catalyst system affording amphiphilic star block copolymers PEOn-b-PSn (n = 3 or 4). PEOn-b-PS2n (n = 3 or 4) dendrimer-like copolymers constituted of an inner PEO part and an outer PS layer were prepared by introducing a branching agent ...

Were the North Atlantic Heinrich events triggered by the behavior of the European ice sheets

Abstract: Theories explaining the origin and distribution of Heinrich layers—abrupt, massive discharges of ice-rafted detritus—generally attribute these layers to the Laurentide ice sheet. However, doubt has been cast by the discovery that sediments also originated from European ice sheets. Here we present isotopic (Sr-Nd) fingerprints of Heinrich layers obtained in cores from the European margin. They reveal that for most of the Heinrich layers, the icebergs were calved first from the European ice sheets, predating the Laurentide surges. Accelerator mass spectrometry 14C ages reveal that the oceanic Heinrich events were synchronous with their dust equivalents in the Greenland ice cores, implying a direct ocean-atmosphere link. The typical Laurentide surge seems to have occurred over a short time span, after about 1.5 k.y. of iceberg release from the European ice sheets. This suggests that the Laurentide ice sheet responded to a stimulus created by events in the European sector.