Showing papers by "University of Montpellier published in 1999"
TL;DR: In this paper, the authors used extensive classical molecular-dynamics simulations to calculate the thermal conductivity of a model silica glass, with no other adjustable quantity and the standard equations of heat transport are used directly in the simulation box.
Abstract: We use extensive classical molecular-dynamics simulations to calculate the thermal conductivity of a model silica glass. Apart from the potential parameters, this is done with no other adjustable quantity and the standard equations of heat transport are used directly in the simulation box. The calculations have been done between 10 and 1000 K and the results are in good agreement with the experimental data at temperatures above 20 K. The plateau observed around 10 K can be accounted for by correcting our results taking into account finite-size effects in a phenomenological way.
418 citations
TL;DR: In this paper, the authors investigated the influence of the Carnegie Ridge collision on the North Andean convergent margin and found that the collision has been occurring for at least 2 Ma based on the basement uplift signal along trench-parallel transects.
397 citations
TL;DR: This work focuses attention on peroxynitrite, the product of the reaction between nitric oxide (NO) and superoxide, a strong oxidizing and nitrating agent which can react with all classes of biomolecules.
389 citations
TL;DR: Current understanding of the structure and function of members of the ERM family of proteins is discussed.
370 citations
TL;DR: Results from these studies indicate that Wolbachia are much more widely distributed in host tissues than previously appreciated and the relevance of these infection patterns to the evolution of WolbachIA/host symbioses and to potential applied uses of Wolachia is discussed.
364 citations
TL;DR: In this article, proximity-induced superconductivity in single-walled carbon nanotubes below 1 kelvin was observed, both in a single tube 1 nanometer in diameter and in crystalline ropes containing about 100 nano-tubes.
Abstract: Proximity-induced superconductivity in single-walled carbon nanotubes below 1 kelvin, both in a single tube 1 nanometer in diameter and in crystalline ropes containing about 100 nanotubes, was observed. The samples were suspended between two superconducting electrodes, permitting structural study in a transmission electron microscope. When the resistance of the nanotube junction is sufficiently low, it becomes superconducting and can carry high supercurrents. The temperature and magnetic field dependence of the critical current of such junctions exhibits unusual features related to their strong one-dimensional character.
338 citations
TL;DR: It is found that LY382884 is a selective antagonist at neuronal kainate receptors containing the GluR5 subunit, which has no effect on long-term potentiation (LTP) that is dependent onNMDA receptors but prevents the induction of mossy fibre LTP, which is independent of NMDA receptors.
Abstract: The ability of synapses to modify their synaptic strength in response to activity is a fundamental property of the nervous system and may be an essential component of learning and memory. There are three classes of ionotropic glutamate receptor, namely NMDA (N-methyl-D-aspartate), AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionic acid) and kainate receptors; critical roles in synaptic plasticity have been identified for two of these. Thus, at many synapses in the brain, transient activation of NMDA receptors leads to a persistent modification in the strength of synaptic transmission mediated by AMPA receptors. Here, to determine whether kainate receptors are involved in synaptic plasticity, we have used a new antagonist, LY382884 ((3S, 4aR, 6S, 8aR)-6-((4-carboxyphenyl)methyl-1,2,3,4,4a,5,6,7,8,8a-decahydro isoquinoline-3-carboxylic acid), which antagonizes kainate receptors at concentrations that do not affect AMPA or NMDA receptors. We find that LY382884 is a selective antagonist at neuronal kainate receptors containing the GluR5 subunit. It has no effect on long-term potentiation (LTP) that is dependent on NMDA receptors but prevents the induction of mossy fibre LTP, which is independent of NMDA receptors. Thus, kainate receptors can act as the induction trigger for long-term changes in synaptic transmission.
333 citations
TL;DR: In this paper, the electrochemical synthesis of nanoparticles of γ-Fe2O3 was performed in an organic medium, and the size distributions of the particles were narrow, with the average sizes varying from 3 to 8 nm.
Abstract: The electrochemical synthesis of nanoparticles of γ-Fe2O3 was performed in an organic medium. The size was directly controlled by the imposed current density, and the resulting particles were stabilized as a colloidal suspension by the use of cationic surfactants. The size distributions of the particles were narrow, with the average sizes varying from 3 to 8 nm. The amorphous character of the nanoparticles was clearly established by X-ray powder diffraction and TEM analysis. The microstructure of this phase could nevertheless be spectroscopically related to maghemite, γ-Fe2O3. 57Fe Mossbauer spectroscopy and magnetization measurements indicated that the dry powders exhibit superparamagnetic behavior at room temperature.
317 citations
TL;DR: Four crystal structures were determined of the catalytic domains of AC in complex with two different ATP analogs and various divalent metal ions, providing a model for the enzyme-substrate complex and demonstrating that two metal ions bind in the active site.
Abstract: Adenylyl cyclase (AC) converts adenosine triphosphate (ATP) to cyclic adenosine monophosphate, a ubiquitous second messenger that regulates many cellular functions. Recent structural studies have revealed much about the structure and function of mammalian AC but have not fully defined its active site or catalytic mechanism. Four crystal structures were determined of the catalytic domains of AC in complex with two different ATP analogs and various divalent metal ions. These structures provide a model for the enzyme-substrate complex and conclusively demonstrate that two metal ions bind in the active site. The similarity of the active site of AC to those of DNA polymerases suggests that the enzymes catalyze phosphoryl transfer by the same two-metal-ion mechanism and likely have evolved from a common ancestor.
305 citations
TL;DR: In this article, a closed formula for the structure constants in the SL(2, C )/SU(2)-WZNW model is derived by a method previously used in Liouville theory.
286 citations
TL;DR: This report presents the first evidence for the regulation of root genes involved in nutrient acquisition and assimilation by a signal that is translocated from shoot to root.
Abstract: Sulfate uptake and ATP sulfurylase activity in the roots of Arabidopsis thaliana and Brassica napus were enhanced by S deprivation and reduced following resupply of SO4(2-). Similar responses occurred in split-root experiments where only a portion of the root system was S-deprived, suggesting that the regulation involves inter-organ signaling. Phloem-translocated glutathione (GSH) was identified as the likely transducing molecule responsible for regulating SO4(2-) uptake rate and ATP sulfurylase activity in roots. The regulatory role of GSH was confirmed by the finding that ATP sulfurylase activity was inhibited by supplying Cys except in the presence of buthionine sulfoximine, an inhibitor of GSH synthesis. In direct and remote (split-root) exposures, levels of protein detected by antibodies against the Arabidopsis APS3 ATP sulfurylase increased in the roots of A. thaliana and B. napus during S starvation, decreased after SO4(2-) restoration, and declined after feeding GSH. RNA blot analysis revealed that the transcript level of APS1, which codes for ATP sulfurylase, was reduced by direct and remote GSH treatments. The abundance of AST68 (a gene encoding an SO4(2-) transporter) was similarly affected by altered sulfur status. This report presents the first evidence for the regulation of root genes involved in nutrient acquisition and assimilation by a signal that is translocated from shoot to root.
TL;DR: The top left corner of Fig. 1b on page 505 was cropped so that you could not view the calpain 3-stained nuclei in endomysia space, and the corrected figure is shown below.
Abstract: Nature Med. 5, 503– 511 (1999). The top left corner of Fig. 1b on page 505 was cropped so that you could not view the calpain 3-stained nuclei in endomysia space. The corrected figure is shown below. We regret this error.
TL;DR: The Northeast African-Arabian plate formed a segment of the passive margins of the Neotethys and Neothesys during the Permian to the Jurassic period as mentioned in this paper.
TL;DR: The first phytomining experiments were carried out in California using the Ni-hyperaccumulator Streptanthus polygaloides and it was found that a yield of 100 kg=ha of sulphur-free Ni could be produced as mentioned in this paper.
TL;DR: In this paper, the authors considered the contact dynamics as the prototype of an evolution conditioned by inequality constraints and provided a simplified setting for analysing some numerical and theoretical features also present in unilateral dynamics.
TL;DR: This algorithm can be used to compute the Galois (concept) lattice, the maximal antichains lattice or the Dedekind‐MacNeille completion of a partial order, without increasing time complexity.
TL;DR: In this article, the effect of deformation regime on the development of olivine lattice-preferred orientations (LPO) and associated seismic anisotropy within continental deformation zones is investigated.
TL;DR: In this article, the authors examined different assumptions of budburst models and selected those which are best supported by the data, defining new models able to predict external data, and fitted and tested using external data.
Abstract: Classical budburst models (Spring Warming, Sequential, Parallel and Alternating) are unable to fully predict external data, partly because of the methods of optimization used to adjust them. The purpose of this study was to examine different assumptions of budburst models and select those which are best supported by the data, defining new models able to predict external data. Eight models, each differing in one assumption, were fitted and tested using external data. The dataset used to test the models was deduced from aeropalynological data at two stations in France. The results show that some of the models proposed are able to accurately predict external dates of flowering of most of the studied species. The assumptions of those models have been individually tested and shown to improve the models accuracy. Robust estimates of the best predictor models of 12 tree species are presented. The analysis of hypothetical provenance transfer of two species, Buxus sempervirens and Platanus acerifolia, between the two study sites, shows that P. acerifolia estimates are similar in both environments whereas B. sempervirens estimates are variable. This result, which agrees with the genetic characteristics of both species, shows that local adaptation of phenology can also be studied through modelling approaches.
TL;DR: In this article, a self-consistent numerical model for the extension of a brittle layer that can spontaneously produce normal-fault structures was proposed, and it was shown that structures very similar to those observed in both oceanic and continental core complexes are produced by rotation of the inactive part of the model fault after very large offset.
Abstract: The nature of the physical processes responsible for the formation of continental and oceanic metamorphic core complexes is widely debated. The controversy focuses primarily on whether the low-angle normal faults observed in these environments formed and slipped at low angles or were rotated from an original high-angle orientation after large offsets. We describe a self-consistent numerical model for the extension of a brittle layer that can spontaneously produce normal-fault structures. In our formulation, a fault or faults form because strength is locally reduced with increasing strain. If the reduction in fault strength is <∼10% of the total strength of the layer, then faults lock after an offset smaller than the layer thickness and new faults form. Larger strength reduction leads to single faults that continue to slip no matter how large the fault offset. If the strength reduction occurs by the loss of cohesion, then we see the unlimited offset faults for layers <11–22 km thick for reasonable values of cohesion. The key result of this study is that structures very similar to those observed in both oceanic and continental core complexes are produced by rotation of the inactive part of the model fault after very large offset.
TL;DR: In this article, a quasi-two-dimensional optical system consisting of a triangular array of air cylinders etched through a laser-like Ga(Al)As waveguiding heterostructure is described.
Abstract: We describe experiments on a quasi-two dimensional (2-D) optical system consisting of a triangular array of air cylinders etched through a laser-like Ga(Al)As waveguiding heterostructure. Such a configuration is shown to yield results very well approximated by the infinite 2-D photonic crystal (PC). We first present a set of measurements of the optical properties (transmission, reflection, and diffraction) of slabs of these photonic crystals, including the case of in-plane Fabry-Perot cavities formed between two such crystals. The measurement method makes use of the guided photoluminescence of embedded quantum wells or InAs quantum dots to generate an internal probe beam. Out-of-plant, scattering losses are evaluated by various means. In a second part, in-plane micrometer-sized photonic boxes bounded by circular trenches or by two-dimensional photonic crystal are probed by exciting spontaneous emission inside them. The high quality factors observed in such photon boxes demonstrate the excellent photon confinement attainable in these systems and allow to access the detail of the modal structure. Last, some perspectives for applications are offered.
TL;DR: In this paper, a method of nitrate determination by ultraviolet absorption spectrometry is proposed based on the measurement of sample absorbance at a single wavelength (220 nm), which was chosen on the basis of the absorption spectra of the main components of artificial seawater in the ultraviolet domain No reagents are used and no sophisticated instruments are necessary.
Abstract: This method of nitrate determination by ultraviolet absorption spectrometry is based on the measurement of sample absorbance at a single wavelength (220 nm), which was chosen on the basis of the absorption spectra of the main components of artificial seawater in the ultraviolet domain No reagents are used and no sophisticated instruments are necessary For standards prepared in artificial seawater, the relationship between absorbance and nitrate concentration is linear up to 500 μmol N L−1 and the detection limit is 1 μmol N L−1 Precision is 15% Urea and amino acids did not interfere at concentrations typical of seawater The method also measures nitrite, but this interference only becomes important for species which excrete large amounts of nitrite The method is extremely rapid, simple to implement and does not require the use of toxic chemicals such as cadmium It should prove useful for monitoring quickly the nitrate concentrations in laboratory cultures of marine phytoplankton
TL;DR: In this paper, the authors used a total energy, non-orthogonal, tight-binding parametrisation which is shown to provide results in good agreement both with calculations using higher levels of theory and the available experimental data.
Abstract: , BC2N, and C3N4. These studies have been carried out using a total-energy, non-orthogonal, tight-binding parametrisation which is shown to provide results in good agreement both with calculations using higher levels of theory and the available experimental data. Our results predict that of all types of nanotubes considered, carbon nanotubes have the highest Young’s modulus. We have considered tubes of different diameters, ranging from 0.5 to 2 nm, and find that in the limit of large diameters the mechanical properties of nanotubes approach those of the corresponding flat graphene-like sheets.
TL;DR: Molecular and cellular knowledge of these processes will be necessary to improve plant metal resistance and occurrence of naturally tolerant plants which hyperaccumulate metals provides helpful tools for this research.
Abstract: Metal toxicity for living organisms involves oxidative and/or genotoxic mechanisms Plant protection against metal toxicity occurs, at least in part, through control of root metal uptake and of long distance metal transport Inside cells, proteins such as ferritins and metallothioneins, and glutathion-derived peptides named phytochelatins, participate in excess metal storage and detoxification Low molecular weight organic molecules, mainly organic acids and amino acids and their derivatives, also play an important role in plant metal homeostasis When these systems are overloaded, oxidative stress defense mechanisms are activated Molecular and cellular knowledge of these processes will be necessary to improve plant metal resistance Occurrence of naturally tolerant plants which hyperaccumulate metals provides helpful tools for this research
TL;DR: The first molecular phylogeny of tribe Diseae (Orchidoideae: Orchidaceae) is presented, with Morphological characters fully congruent with the well-supported groups identified in the ITS phylogeny.
Abstract: We present here the first molecular phylogeny of tribe Diseae (Orchidoideae: Orchidaceae). Nuclear ribosomal ITS1, 5.8S rDNA, and ITS2 sequences were compared for 30 Diseae, 20 Orchideae, and four Cranichideae and Diurideae outgroups. ITS - rDNA sequences exhibited a transition:transversion ratio of 1.3 and extensive ITS length polymorphism. Phylogenetic analyses using maximum parsimony identified seven major core orchidoid groups. The branching order of the five Diseae and two Orchideae clades was weakly supported but indicated paraphyly of Diseae, with Disperis sister to the rest, followed by successive divergence of Brownleea, Disinae, Coryciinae sensu stricto (s.s.), Satyriinae, and terminated by Orchidinae plus Habenariinae. Within the monophyletic Disinae, Herschelia and Monadenia were nested within a paraphyletic Disa and clustered with D. sect. Micranthae. Within monophyletic Satyriinae, Satyridium rostratum plus Satyrium bicallosum was sister to the rest of Satyrium, and then Satyrium nepalense plus S. odorum was distinct from a cluster of six species. Coryciinae are paraphyletic because Disperis is sister to all other core orchidoids. Coryciinae s.s. are sister to Satyriinae plus Orchideae, with Pterygodium nested within Corycium. Maximum likelihood analysis supported possible affinities among Disinae, Brownleeinae, and Coryciinae but did not support monophyly of Diseae or an affinity between Disinae and Satyriinae. Morphological characters are fully congruent with the well-supported groups identified in the ITS phylogeny.
TL;DR: In this paper, the authors present a systematic overview of the cross sections for the production of pairs of (light) neutral Higgs bosons at the LHC for the Standard Model and its minimal supersymmetric extension.
Abstract: The reconstruction of the Higgs potential in the Standard Model or supersymmetric theories demands the measurement of the trilinear Higgs couplings. These couplings affect the multiple production of Higgs bosons at high energy colliders. We present a systematic overview of the cross sections for the production of pairs of (light) neutral Higgs bosons at the LHC. The analysis is carried out for the Standard Model and its minimal supersymmetric extension.
TL;DR: The Mayari-Baracoa belt is a part of the east-west-trending Cuban ophiolitic belt as discussed by the authors, which is composed of two large, chromite-rich massifs, the Mayari Cristal and Moa Baracoa.
Abstract: The Mayari-Baracoa belt occupies the easternmost part of the east-west-trending Cuban ophiolitic belt. It comprises two large, chromite-rich massifs: Mayari-Cristal and Moa-Baracoa. Neither of these massifs show a complete ophiolite sequence, but they consist of a part of an ideal section made up of (1) harzburgites grading upward into interlayered harzburgites and dunites, (2) interlayered harzburgites (with minor dunites) and gabbros, (3) gabbros, microgabbros, dolerites, and diabase dikes, and (4) pillowed basalt, cherts, and radiolarites. Chromite deposits can be grouped into three mining districts according to the chemistry of chromite ore: the Mayari district and the Sagua de Tanamo district, both in the Mayari-Cristal massif, and the Moa-Baracoa district in the Moa-Baracoa massif. The latter is the most important as it contains more than 5.5 million tons of ore.
TL;DR: In this article, mafic melts in the Ronda peridotite are classified into four groups: tapped into cracks forming intrusive dykes, spinel tectonites, spinel websterites, and coarse-grained pyroxenites.
Abstract: melt fractions that percolated pervasively throughout the massif and On the basis of their structural and compositional characteristics, had a refractory, calc-alkaline character. Locally, these melts were mafic rocks in the Ronda peridotite are classified into four groups: tapped into cracks forming intrusive dykes. group A (garnet-bearing rocks) occurring in the spinel tectonite domain; group B (spinel websterites) along the recrystallization front; group C (Ti-rich spinel pyroxenites) in the granular tectonite and plagioclase tectonite domains; and group D (Cr-rich pyroxenites) as composite layers along the recrystallization front, dykes in the
TL;DR: It is shown that introgression might counteract the evolution of isolating mechanisms in diploid-polyploid contact zones, and tests of hypotheses relating to the dynamics and evolution of polyploid complexes are carried out.
Abstract: Hybrid zones between cytotypes with different ploidy levels are particularly interesting for studying the ecology and the evolution of reproductive interactions between closely related taxa. Diploid–polyploid hybrid zones differ fundamentally from those between diploids in that they reflect certain conditions that are characteristic of the early stage of polyploid establishment, and allow tests of hypotheses relating to the dynamics and evolution of polyploid complexes. Recent theoretical and empirical studies have provided important data on the evolution of isolating mechanisms in diploid–polyploid contact zones, but have also shown that introgression might counteract the evolution of isolating mechanisms.
TL;DR: In this paper, a review of possible explanations for these effects is presented and leads to the conclusion that a majority of abnormal magnetic fabrics, often encountered in magnetite-rich volcanic rocks, are due to abnormal preferred orientations or distributions of magnetite grains.
TL;DR: It is shown that resistance alleles can also be used as markers to dissect population processes at a microevolutionary scale and provide a firm basis on which to devise an insecticide treatment strategy that will better control the evolution of resistance genes and the growth of mosquito populations.
Abstract: The evolution of pesticide resistance provides some of the most striking examples of darwinian evolution occurring over a human life span. Identification of resistance alleles opens an outstanding framework in which to study the evolution of adaptive mutations from the beginning of pesticide application1,2,3, the evolution of interactions between alleles (dominance4) or between loci (epistasis5,6). Here we show that resistance alleles can also be used as markers to dissect population processes at a microevolutionary scale. We have focused on the antagonistic roles of selection and migration involved in the dynamics of local adaptation with reference to allelic frequencies at two resistance loci in the mosquito Culex pipiens. We find that their frequencies follow an annual cycle of large amplitude (25%), and we precisely unravel the seasonal variation of migration and selection underlying this cycle. Our results provide a firm basis on which to devise an insecticide treatment strategy that will better control the evolution of resistance genes and the growth of mosquito populations.