Showing papers by "Centre national de la recherche scientifique published in 1993"
TL;DR: In this article, the main formulas governing the analysis of the Bragg magnetic scattering are summarized and shortly discussed and the method of profile fitting without a structural model to get precise integrated intensities and refine the propagation vector(s) of the magnetic structure is discussed.
Abstract: In spite of intrinsic limitations, neutron powder diffraction is, and will still be in the future, the primary and most straightforward technique for magnetic structure determination. In this paper some recent improvements in the analysis of magnetic neutron powder diffraction data are discussed. After an introduction to the subject, the main formulas governing the analysis of the Bragg magnetic scattering are summarized and shortly discussed. Next, we discuss the method of profile fitting without a structural model to get precise integrated intensities and refine the propagation vector(s) of the magnetic structure. The simulated annealing approach for magnetic structure determination is briefly discussed and, finally, some features of the program FullProf concerning the magnetic structure refinement are presented and discussed. The different themes are illustrated with simple examples.
11,923 citations
TL;DR: A unified framework for the design and the performance analysis of the algorithms for solving change detection problems and links with the analytical redundancy approach to fault detection in linear systems are established.
Abstract: This book is downloadable from http://www.irisa.fr/sisthem/kniga/. Many monitoring problems can be stated as the problem of detecting a change in the parameters of a static or dynamic stochastic system. The main goal of this book is to describe a unified framework for the design and the performance analysis of the algorithms for solving these change detection problems. Also the book contains the key mathematical background necessary for this purpose. Finally links with the analytical redundancy approach to fault detection in linear systems are established. We call abrupt change any change in the parameters of the system that occurs either instantaneously or at least very fast with respect to the sampling period of the measurements. Abrupt changes by no means refer to changes with large magnitude; on the contrary, in most applications the main problem is to detect small changes. Moreover, in some applications, the early warning of small - and not necessarily fast - changes is of crucial interest in order to avoid the economic or even catastrophic consequences that can result from an accumulation of such small changes. For example, small faults arising in the sensors of a navigation system can result, through the underlying integration, in serious errors in the estimated position of the plane. Another example is the early warning of small deviations from the normal operating conditions of an industrial process. The early detection of slight changes in the state of the process allows to plan in a more adequate manner the periods during which the process should be inspected and possibly repaired, and thus to reduce the exploitation costs.
3,830 citations
TL;DR: In this article, it was shown that the magnetization of the Mn12 cluster is highly anisotropic and the magnetisation relaxation time becomes very long below a temperature of 4 K, giving rise to pronounced hysteresis.
Abstract: MAGNETIC materials of mesoscopic dimensions (a few to many thousands of atoms) may exhibit novel and useful properties such as giant magnetostriction, magnetoresistivity and magnetocaloric effects1–4. Such materials also allow one to study the transition from molecular to bulk-like magnetic behaviour. One approach for preparing mesoscopic magnetic materials is to fragment bulk ferromagnets; a more controllable method is to take a 'bottom-up' approach, using chemistry to grow well defined clusters of metal ions5,6. Lis7 has described a twelve-ion manganese cluster in which eight of the Mn ions are in the +3 oxidation state (spin S=2) and four are in the +4 state (S=3/2). These ions are magnetically coupled to give an S=10 ground state8, giving rise to unusual magnetic relaxation properties8,9. Here we report that the magnetization of the Mn12 cluster is highly anisotropic and that the magnetization relaxation time becomes very long below a temperature of 4 K, giving rise to pronounced hysteresis. This behaviour is not, however, strictly analogous to that of a bulk ferromagnet, in which magnetization hysteresis results from the motion of domain walls. In principle, a bistable magnetic unit of this sort could act as a data storage device.
3,327 citations
TL;DR: Northern hybridization revealed that Fas ligand is expressed in activated splenocytes and thymocytes, consistent with its involvement in T cell-mediated cytotoxicity and in several nonlymphoid tissues, such as testis.
2,600 citations
TL;DR: This work presents the first cull band-structure calculations for periodic, elastic composites and obtains a «phononic» band gap which extends throughout the Brillouin zone.
Abstract: We present the first full band-structure calculations for periodic, elastic composites. For transverse polarization of the vibrations we obtain a ``phononic'' band gap which extends throughout the Brillouin zone. A complete acoustic gap or a low density of states should have important consequences for the suppression of zero-point motion and for the localization of phonons, and may lead to improvements in transducers and in the creation of a vibrationless environment.
2,299 citations
Johns Hopkins University1, University of Helsinki2, National Institutes of Health3, University of Denver4, Los Alamos National Laboratory5, Fred Hutchinson Cancer Research Center6, University of Texas Health Science Center at San Antonio7, Centre national de la recherche scientifique8, Memorial University of Newfoundland9, University of Auckland10, Creighton University11
TL;DR: Somatic as well as germline mutations of the gene were identified in RER+ tumor cells, and this mutS homolog is likely to be responsible for HNPCC.
2,297 citations
TL;DR: In this article, the authors present records of sea surface temperature from North Atlantic sediments spanning the past 90 kyr which contain a series of rapid temperature oscillations closely matching those in the ice-core record, confirming predictions that the ocean must bear the imprint of the Dansgaard-Oeschger events.
Abstract: OXYGEN isotope measurements in Greenland ice demonstrate that a series of rapid warm-cold oscillations—called Dansgaard–Oeschger events—punctuated the last glaciation1. Here we present records of sea surface temperature from North Atlantic sediments spanning the past 90 kyr which contain a series of rapid temperature oscillations closely matching those in the ice-core record, confirming predictions that the ocean must bear the imprint of the Dansgaard–Oeschger events2,3. Moreover, we show that between 20 and 80 kyr ago, the shifts in ocean-atmosphere temperature are bundled into cooling cycles, lasting on average 10 to 15 kyr, with asymmetrical saw-tooth shapes. Each cycle culminated in an enormous discharge of icebergs into the North Atlantic (a 'Hein-rich event'4,5), followed by an abrupt shift to a warmer climate. These cycles document a previously unrecognized link between ice sheet behaviour and ocean–atmosphere temperature changes. An important question that remains to be resolved is whether the cycles are driven by external factors, such as orbital forcing, or by inter-nal ice-sheet dynamics.
2,179 citations
TL;DR: It is proposed that CBP may participate in cAMP-regulated gene expression by interacting with the activated phosphorylated form of CREB, which is activated as a result of phosphorylation by protein kinase A7.
Abstract: Cyclic AMP-regulated gene expression frequently involves a DNA element known as the cAMP-regulated enhancer (CRE). Many transcription factors bind to this element, including the protein CREB, which is activated as a result of phosphorylation by protein kinase A. This modification stimulates interaction with one or more of the general transcription factors or, alternatively, allows recruitment of a co-activator. Here we report that CREB phosphorylated by protein kinase A binds specifically to a nuclear protein of M(r) 265K which we term CBP (for CREB-binding protein). Fusion of a heterologous DNA-binding domain to the amino terminus of CBP enables the chimaeric protein to function as a protein kinase A-regulated transcriptional activator. We propose that CBP may participate in cAMP-regulated gene expression by interacting with the activated phosphorylated form of CREB.
2,041 citations
TL;DR: A new approach for generating null alleles of a gene by one step PCR amplification of the wild-type HIS3 gene at its own locus is described.
Abstract: The systematic sequencing of the yeast S.cerevisiae genome has revealed a profusion of Open Reading Frames (ORFs). Although some of them have been previously studied, a large majority represents new genes (1, 2). Deletion of these ORFs is a convenient tool for their functional analysis, Here we describe a new approach for generating null alleles of a gene. Usually, a gene inactivation requires the in vitro creation of a construction in which a selectable marker is sandwiched by the 5' and the 3' flanking sequences of the target ORF. Classically, this strategy requires several cloning steps. In contrast, our approach generates such a construction by one step PCR amplification. Each oligodeoxynucleotide used contains two distinct regions, one which allows homologous recombination at the target locus and will be named the deleting sequence, the second part which permits the PCR amplification of a selectable marker. The deleting sequences, which are respectively the 5' (oligopro) and 3' (oligoterm) flanking sequences of the ORF, range from 35 to 51 nucleotides in length and are followed by a short stretch of 17 nucleotides homologous to the HI S3 selectable marker. Table 1 shows the composition of the deleting sequences, the sequence used for HIS3 amplification always being the same (5'-TCGTTCAGAATGACACG-3' for oligoterm and 5'-CTCTTGGCCTCCTCTAG-3' for oligopro. Following the PCR amplification, the crude mix was directly used to transform yeast by standard procedures (3). In a first set of experiments, we used W3O3-1B (MATa, ura3-l, trpl-1, ade2-l, leu2-3, 112, his3-ll, 15) as recipient strain. All the His transformants tested (a total of 30) presented the same pattern when analysed by Southern blot, corresponding to the insertion of the wild-type HIS3 gene at its own locus (data not shown). We thus used a recipient strain carrying a complete deletion of the HIS3 gene. With the diploid strain BMA 1 (a diploid from cross FY 1679-18B and FY 1679-28C, kindly provided by B.Dujon) containing the His3A200 allele (4), we routinely obtained more than 10 His transformants per plate. As the procedure appeared to be efficient enough, we tested by
1,357 citations
TL;DR: A new expression cloning strategy, based on the induction of a reporter gene by cyclic AMP, is used to isolate a complementary DNA encoding the type-I PACAP receptor, suggesting a novel mechanism for fine tuning of signal transduction.
Abstract: The two forms of pituitary adenylyl cyclase-activating polypeptide (PACAP-27 and -38) are neuropeptides of the secretin/glucagon/vasoactive intestinal polypeptide/growth-hormone-releasing hormone family and regulate hormone release from the pituitary and adrenal gland. They may also be involved in spermatogenesis, and PACAP-38 potently stimulates neuritogenesis and survival of cultured rat sympathetic neuroblast and promotes neurite outgrowth of PC-12 cells. The PACAP type-I receptor (found in hypothalamus, brain stem, pituitary, adrenal gland and testes), specific for PACAP, is positively coupled to adenylyl cyclase and phospholipase C. The recently cloned type II receptor does not discriminate between PACAP and vasoactive intestinal polypeptide and is coupled to only adenylyl cyclase. Here we have used a new expression cloning strategy, based on the induction of a reporter gene by cyclic AMP, to isolate a complementary DNA encoding the type-I PACAP receptor. On transfection of this cDNA, both PACAP-27 and -38 stimulate adenylyl cyclase with similar EC50 values (50% effective concentration, 0.1-0.4 nM), whereas only PACAP-38 stimulates phospholipase C with high potency (EC50 = 15 nM). Four other splice variants were isolated with insertions at the C-terminal end of the third intracellular loop. Expression of these cDNAs revealed altered patterns of adenylyl cyclase and phospholipase C stimulation, suggesting a novel mechanism for fine tuning of signal transduction.
1,183 citations
TL;DR: It is demonstrated that activation of these ubiquitously expressed MAP kinases is essential for growth, and growth factor activation of p42mapk and p44mapk is an absolute requirement for triggering the proliferative response.
Abstract: The mitogen-activated protein kinases (MAP kinases) p42mapk and p44mapk are serine/threonine kinases rapidly activated in cells stimulated with various extracellular signals by dual phosphorylation of tyrosine and threonine residues. They are thought to play a pivotal role in integrating and transmitting transmembrane signals required for growth and differentiation. Here we demonstrate that activation of these ubiquitously expressed MAP kinases is essential for growth. To specifically suppress MAP kinase activation in fibroblasts, we transiently expressed either the entire p44mapk antisense RNA or p44mapk kinase-deficient mutants (T192A or Y194F). As expected, and through independent mechanisms, both approaches strongly inhibited MAP kinase activation. The antisense reduced the expression of endogenous p42mapk and p44mapk by 90%, whereas overexpression of the T192A mutant inhibited growth factor activation of both endogenous MAP kinases by up to 70%. As a consequence, we found that the antisense as well as the T192A mutant of p44mapk inhibited growth factor-stimulated gene transcription (collagenase promoter assay with chloramphenicol acetyltransferase reporter) and cell growth. These effects were proportional to the extent of MAP kinase inhibition and reversed by coexpression of the wild-type p44mapk. Therefore we conclude that growth factor activation of p42mapk and p44mapk is an absolute requirement for triggering the proliferative response.
TL;DR: The results indicate that the Grbl/hSos1 complex couples activated EGF receptor to Ras signalling, and a synthetic 10-amino-acid peptide containing the sequence PPVPPR specifically blocks the interaction.
Abstract: Many of the actions of receptor tyrosine kinases are mediated by the protein Ras, including the activation of various downstream serine/threonine kinases and the stimulation of growth and differentiation. The human protein Grb2 binds to ligand-activated growth factor receptors and downstream effector proteins through its Src-homology (SH) domains SH2 and SH3, respectively, and like its homologue from Caenorhabditis elegans, Sem-5, apparently forms part of a highly conserved pathway by which these receptors can control Ras activity. Here we show that the SH3 domains of Grb2 bind to the carboxy-terminal part of hSos1, the human homologue of the Drosophila guanine-nucleotide-releasing factor for Ras, which is essential for control of Ras activity by epidermal growth factor receptor and sevenless. Moreover, a synthetic 10-amino-acid peptide containing the sequence PPVPPR specifically blocks the interaction. These results indicate that the Grb2/hSos1 complex couples activated EGF receptor to Ras signalling.
TL;DR: In this article, the same authors reported the synthesis of the related compound HgBa2CuO4+δ (Hg-1201), with only one CuO2 layer per unit cell, and showed that it is superconducting below 94 K.
Abstract: FOLLOWING the discovery1 of high-transition-temperature (high-Tc) superconductivity in doped La2CuO4, several families of related compounds have been discovered which have layers of CuO2 as the essential requirement for superconductivity: the highest transition temperatures so far have been found for thallium-bearing compounds2. Recently the mercury-bearing compound HgBa2Rcu2O6+δ (Hg-1212) was synthesized3 (where R is a rare-earth element), with a structure similar to the thallium-bearing superconductor TlBa2CaCu2O7 (Tl-1212), which has one T1O layer and two CuO2 layers per unit cell, and a Tc of 85 K (ref. 2). But in spite of its resemblance to Tl-1212, Hg-1212 was found not to be superconducting. Here we report the synthesis of the related compound HgBa2CuO4+δ (Hg-1201), with only one CuO2 layer per unit cell, and show that it is superconducting below 94 K. Its structure is similar to that of Tl-1201 (which has a Tc of < 10 K)4, but its transition temperature is considerably higher. The availability of a material with high Tc but only a single metal oxide (HgO) layer may be important for technological applications, as it seems that a smaller spacing between CuO2 planes leads to better superconducting properties in a magnetic field5.
TL;DR: A replication-deficient adenoviral vector that contained a reporter gene encoding beta-galactosidase infected rat nerve cells in vitro and in vivo and expressed beta-GalactosIDase in almost all sympathetic neurons and astrocytes in culture.
Abstract: The efficient introduction of genetic material into quiescent nerve cells is important in the study of brain function and for gene therapy of neurological disorders. A replication-deficient adenoviral vector that contained a reporter gene encoding beta-galactosidase infected rat nerve cells in vitro and in vivo. beta-Galactosidase was expressed in almost all sympathetic neurons and astrocytes in culture. After stereotactic inoculations into the rat hippocampus and the substantia nigra, beta-galactosidase activity was detected for 2 months. Infected cells were identified as microglial cells, astrocytes, or neurons with anatomical, morphological, and immunohistochemical criteria. No obvious cytopathic effect was observed.
TL;DR: The results suggest that the coupling of receptor tyrosine kinases to Ras signaling is mediated by a molecular complex consisting of GRB2 and hSos1, a guanine nucleotide exchange factor for Ras.
Abstract: A human complementary DNA was isolated that encodes a widely expressed protein, hSos1, that is closely related to Sos, the product of the Drosophila son of sevenless gene. The hSos1 protein contains a region of significant sequence similarity to CDC25, a guanine nucleotide exchange factor for Ras from yeast. A fragment of hSos1 encoding the CDC25-related domain complemented loss of CDC25 function in yeast. This hSos1 domain specifically stimulated guanine nucleotide exchange on mammalian Ras proteins in vitro. Mammalian cells overexpressing full-length hSos1 had increased guanine nucleotide exchange activity. Thus hSos1 is a guanine nucleotide exchange factor for Ras. The hSos1 interacted with growth factor receptor-bound protein 2 (GRB2) in vivo and in vitro. This interaction was mediated by the carboxyl-terminal domain of hSos1 and the Src homology 3 (SH3) domains of GRB2. These results suggest that the coupling of receptor tyrosine kinases to Ras signaling is mediated by a molecular complex consisting of GRB2 and hSos1.
TL;DR: A simple orbital model was used to predict the electronic structure of the metal ions required to achieve a high ordering temperature, and the synthesis and magnetic properties of two compounds, [Cr5(CN)12].10H2O and Cs0.75 [Cr2.125( CN)6]�5H2 O, are reported, together with the strategy for further work.
Abstract: Molecular-based magnets with high magnetic-ordering temperatures, T(c), can be obtained by mild chemistry methods by focusing on the bimetallic and mixed-valence transition metal micro-cyanide of the Prussian blue family. A simple orbital model was used to predict the electronic structure of the metal ions required to achieve a high ordering temperature. The synthesis and magnetic properties of two compounds, [Cr(5)(CN)(12)].10H(2)O and Cs(0.75) [Cr(2.125)(CN)(6)].5H(2)O, which exhibited magnetic-ordering temperatures of 240 and 190 kelvin, respectively, are reported, together with the strategy for further work.
TL;DR: In this article, a 1.5 turbulence closure model in an ocean general circulation model of the equatorial Atlantic is presented, where the eddy viscosity and diffusivity involved in the vertical mixing are defined as the product of a characteristic turbulent velocity and a characteristic mixing length.
Abstract: The embedment of a 1.5 turbulence closure model in an ocean general circulation model of the equatorial Atlantic is presented. The eddy viscosity and diffusivity involved in the vertical mixing are defined as the product of a characteristic turbulent velocity—the root square of the turbulent kinetic energy—and a characteristic mixing length. The turbulent kinetic energy is defined through a prognostic equation while the turbulent length scales are defined by a diagnostic formulation. The results of an experiment that includes this closure scheme are compared to the results issued from another experiment that includes a Richardson number-dependent parameterization of the mixing coefficients. The two simulations were performed over the tropical Atlantic during the 1982–1984 period, which allows direct comparisons with data from the FOCAL and SEQUAL experiments. Obvious contrasts between the two experiments on the sea surface temperature and on the dynamics indicate that the turbulent vertical diffu...
TL;DR: It is shown that a wide class of tensor-scalar theories can pass the present weak-field gravitational tests and exhibit nonperturbative strong-field deviations away from general relativity in systems involving neutron stars.
Abstract: It is shown that a wide class of tensor-scalar theories can pass the present weak-field gravitational tests and exhibit nonperturbative strong-field deviations away from general relativity in systems involving neutron stars. This is achieved without requiring either large dimensionless parameters, fine tuning, or the presence of negative-energy modes. This gives greater significance to tests of the strong gravitational field regime, notably binary pulsar experiments.
TL;DR: A transgenic mouse strain carrying the rearranged T cell receptor genes from a diabetogenic T cell clone derived from a NOD mouse is generated, permitting us to exclude some possible mechanisms of protection.
TL;DR: In this article, the energy levels for the electron and the hole are calculated with the spherical confinement, the nonparabolicity of the conduction band, and the valence band degeneracy taken into account.
Abstract: CdSe is used as a prototype to show the implications of valence-band degeneracy for the optical properties of strongly quantum-confined nanocrystals. Absorption spectra and photoluminescence spectra obtained under intermediate and strong pulsed excitation show the presence of new structures. The energy levels for the electron and the hole are calculated with the spherical confinement, the nonparabolicity of the conduction band, and the valence band degeneracy taken into account. The oscillator strengths of the dipole-allowed transitions are also calculated. This model is found to be in good agreement with the experimental observations, which originate mainly from the quantization of the energy spectrum of holes with due account given to valence-band degeneracy.
TL;DR: Several members of the PR-5 group from tobacco and other plant species were shown to display significant in vitro activity of inhibiting hyphal growth or spore germination of various fungi probably by a membrane permeabilizing mechanism.
TL;DR: In this article, the authors introduce the notion of Leibniz algebras, which are modules over a commutative ring k, equipped with a bilinear map.
Abstract: The homology of Lie algebras is closely related to the cyclic homology of associative algebras [LQ]. In [L] the first author constructed a \"noncommutative\" analog of Lie algebra homology which is, similarly, related to Hochschild homology [C, L]. For a Lie algebra g this new theory is the homology of the complex C,(g) ... ~ ~| g|-+ ... ~1 ~ k, whose boundary map d is given by the formula d(gl|174 = ~ (-1)J(gl@'\"|174174174 \" l
TL;DR: In this paper, a table is given to replace the 1983 atomic mass table and the differences with the earlier table are briefly discussed and information is given of interest for the users of this table.
TL;DR: It is shown that picomolar concentrations of three neurotrophins, brain-derived neurotrophic factor, neurotroph in-3 and neurotrophin-5, can prevent the death of cultured embryonic rat spinal motor neurons and may be physiological motor neuron growth factors.
Abstract: Embryonic spinal motor neurons are thought to depend for survival on unidentified factors secreted both by their peripheral targets and by cells within the central nervous system1. The neurotrophins are a family of polypeptides required for survival of discrete central and peripheral neuronal populations in vivo and in vitro2,3. In spite of their ability to reduce motor neuron death in vivo4–6, the known neurotrophins have been thought to be without direct effect on motor neurons7–10. Here we show that picomolar concentrations of three of them, brain-derived neurotrophic factor, neurotrophin-3 and neurotrophin-5, can prevent the death of cultured embryonic rat spinal motor neurons. Furthermore, messenger RNA coding for neurotrophins is present at appropriate stages in spinal cord and limb bud, and mRNA for their receptors is found in motor neurons. These neurotrophins may therefore be physiological motor neuron growth factors.
TL;DR: The results reveal the existence of a skeletogenic ground pattern program common to at least the mesenchymal NCC that originated from rhombomeres 2 and 4 and the appearance of an atavistic reptilian pterygoquadrate element in Hoxa-2 mutants suggests that this ground pattern is intermediate between reptiles and mammals.
TL;DR: The three-dimensional structure of the lipase–-procolipase complex, co-crystallized with mixed micelles of phosphatidylcholine and bile salt, has been determined at 3 Å resolution by X-ray crystallography.
Abstract: The three-dimensional structure of the lipase-procolipase complex, co-crystallized with mixed micelles of phosphatidylcholine and bile salt, has been determined at 3 A resolution by X-ray crystallography. The lid, a surface helix covering the catalytic triad of lipase, adopts a totally different conformation which allows phospholipid to bind to the enzyme's active site. The open lid is an essential component of the active site and interacts with procolipase. Together they form the lipid-water interface binding site. This reorganization of the lid structure provokes a second drastic conformational change in an active site loop, which in its turn creates the oxyanion hole (induced fit).
TL;DR: A dedicated device with an integrated DC-SQUID has been developed to detect the presence of persistent currents of about 4 nA in a mesoscopic single loop etched in a GaAs-GaAlAs heterojunction.
Abstract: We have detected the presence of persistent currents of about 4 nA in a mesoscopic single loop etched in a GaAs-GaAlAs heterojunction For this purpose a dedicated device with an integrated DC-SQUID has been developed
TL;DR: The observed RARγ null phenotype suggests a high degree of functional redundancy among the RARs, and the variable penetrance of some of the observed defects is discussed in light of this redundancy and stochastic variation of gene activity.
TL;DR: The ice-core record of local temperature, dust accumulation and air composition at Vostok station, Antarctica, now extends back to the penultimate glacial period (∼140-200 kyr ago) and the end of the preceding interglacial as discussed by the authors.
Abstract: The ice-core record of local temperature, dust accumulation and air composition at Vostok station, Antarctica, now extends back to the penultimate glacial period (∼140–200 kyr ago) and the end of the preceding interglacial. This yields a new glaciological timescale for the whole record, which is consistent with ocean records. Temperatures at Vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one. Concentrations of CO2 and CH4 correlate well with temperature throughout the record.