Showing papers by "University of Rennes published in 1999"
TL;DR: A set of general guidelines for structure refinement using the Rietveld (whole profile) method has been formulated by the International Union of Crystallography Commission on Powder Diffraction.
Abstract: A set of general guidelines for structure refinement using the Rietveld (whole-profile) method has been formulated by the International Union of Crystallography Commission on Powder Diffraction. The practical rather than the theoretical aspects of each step in a typical Rietveld refinement are discussed with a view to guiding newcomers in the field. The focus is on X-ray powder diffraction data collected on a laboratory instrument, but features specific to data from neutron (both constant-wavelength and time-of-flight) and synchrotron radiation sources are also addressed. The topics covered include (i) data collection, (ii) background contribution, (iii) peak-shape function, (iv) refinement of profile parameters, (v) Fourier analysis with powder diffraction data, (vi) refinement of structural parameters, (vii) use of geometric restraints, (viii) calculation of e.s.d.'s, (ix) interpretation of R values and (x) some common problems and possible solutions.
1,808 citations
TL;DR: All the data support the view that putrescine and derived polyamines (spermidine, spermine, long-chained polyamides) may have several functions during environmental challenges.
1,185 citations
TL;DR: In this article, geochemical and isotope tracer analyses of postcollisional mafic-ultramafic rocks from the Dabie terrane in central China show that they could have been generated by melting of such metasomatized mantle as a result of crust-mantle interaction.
842 citations
TL;DR: It is argued that fluctuations in the spider community structure allows the bioevaluation of human disturbances because of the close correspondence between the vegetation architecture and the composition of the associated spider community.
505 citations
440 citations
TL;DR: A growing number of serine-threonine kinases highly homologous to the Saccharomyces cerevisiae Ipl1p kinase have been isolated in various organisms.
Abstract: During the past five years, a growing number of serine-threonine kinases highly homologous to the Saccharomyces cerevisiae Ipl1p kinase have been isolated in various organisms. A Drosophila melanogaster homologue, aurora, was the first to be isolated from a multicellular organism. Since then, several related kinases have been found in mammalian cells. They localise to the mitotic apparatus: in the centrosome, at the poles of the bipolar spindle or in the midbody. The kinases are necessary for completion of mitotic events such as centrosome separation, bipolar spindle assembly and chromosome segregation. Extensive research is now focusing on these proteins because the three human homologues are overexpressed in various primary cancers. Furthermore, overexpression of one of these kinases transforms cells. Because of the myriad of kinases identified, we suggest a generic name: Aurora/Ipl1p-related kinase (AIRK). We denote AIRKs with a species prefix and a number, e.g. HsAIRK1.
323 citations
TL;DR: It is shown here that mutations in the nebulin gene located within this region are associated with the disease, and immunofluorescence studies with antibodies specific to the C-terminal region of nebulin indicate that the mutations may cause protein truncation possibly associated with loss of fiber-type diversity, which may be relevant to disease pathogenesis.
Abstract: The congenital nemaline myopathies are rare hereditary muscle disorders characterized by the presence in the muscle fibers of nemaline bodies consisting of proteins derived from the Z disc and thin filament. In a single large Australian family with an autosomal dominant form of nemaline myopathy, the disease is caused by a mutation in the α-tropomyosin gene TPM3. The typical form of nemaline myopathy is inherited as an autosomal recessive trait, the locus of which we previously assigned to chromosome 2q21.2-q22. We show here that mutations in the nebulin gene located within this region are associated with the disease. The nebulin protein is a giant protein found in the thin filaments of striated muscle. A variety of nebulin isoforms are thought to contribute to the molecular diversity of Z discs. We have studied the 3′ end of the 20.8-kb cDNA encoding the Z disc part of the 800-kDa protein and describe six disease-associated mutations in patients from five families of different ethnic origins. In two families with consanguineous parents, the patients were homozygous for point mutations. In one family with nonconsanguineous parents, the affected siblings were compound heterozygotes for two different mutations, and in two further families with one detected mutation each, haplotypes are compatible with compound heterozygosity. Immunofluorescence studies with antibodies specific to the C-terminal region of nebulin indicate that the mutations may cause protein truncation possibly associated with loss of fiber-type diversity, which may be relevant to disease pathogenesis.
296 citations
TL;DR: In this paper, the concentrations of the platinum-group elements (PGE) Ir, Ru, Pt, and Pd were determined in 18 mantle-derived basalts from a variety of tectonic settings and six komatiites from three locations.
293 citations
TL;DR: In this paper, the authors investigated time harmonic Maxwell equations in heterogeneous media, where the permeability μ and the permittivity e are piecewise constant and the associated boundary value problem can be interpreted as a transmission problem.
Abstract: We investigate time harmonic Maxwell equations in heterogeneous media, where the permeability μ and the permittivity e are piecewise constant. The associated boundary value problem can be interpreted as a transmission problem. In a very natural way the interfaces can have edges and corners. We give a detailed description of the edge and corner singularities of the electromagnetic fields.
293 citations
TL;DR: In this paper, a review of the data that reliably constrain the minimum age for the initiation of extension in these metamorphic complexes is presented, and a preliminary scenario is proposed for the Neogene evolution of the Eastern Mediterranean, in which lateral extrusion of Anatolia occurred lately during southward spreading of the Aegean lithosphere.
285 citations
TL;DR: In this paper, the Hardy-Rellich inequalities containing derivatives of arbitrary (not necessarily integer) order l were obtained, and some new inequalities of this type were also obtained.
TL;DR: In this article, an analysis of existing theories of polarization of heterogeneous media shows that electrical spectroscopy can be useful for the interpretation of frequency spectra of complex dielectric permittivity or conductivity of waterbearing rocks and porous materials in general, and for the determination of water content, its thermodynamic state, the connectivity of water-bearing channels and their correlation lengths and the surface to volume ratio and surface charge in particular, in addition to the traditional formation factor.
Abstract: The complex dielectric permittivity e* of porous water-bearing rocks in the frequency range from a few to hundreds of megahertz reveals several intensive relaxation effects and a non-trivial dependence on the water content. At high frequencies, f > 10 MHz, both the real part of the complex dielectric permittivity e′ and the conductivity σ of water-bearing rocks are correctly predicted by the Maxwell–Wagner–Bruggeman–Hanai (MWBH) theory of composite dielectrics. This theory takes into account only the bulk properties of components, their partial volumes and the configuration of particles. The theory ignores two important factors: the surface contribution to polarization and the effect of clustering of components. At frequencies f < 10 MHz there are certain frequency domains which exhibit relaxation processes not predicted by MWBH theory. The characteristic times of these processes range from 10−6 to 10 s. These relaxation effects are related to different surface polarization processes which are, in order of increasing water content, (i) orientational polarization of bound water, (ii) polarization of liquid films or pockets, producing a polarization catastrophe effect, (iii) polarization of rough fractal surfaces, (iv) polarization of the ‘closed’ electrical double layer (EDL), when the displacement of the excess surface charges is limited by the external boundary of the EDL, and (v) polarization of the ‘open’ double layer, implying free exchange of excess ions with the bulk electrolyte and generation of transient diffusional potentials, which lag behind the applied field. Some theoretical models predict large effective values of relative dielectric constants in the range 105–106 at low frequencies. Knowledge of the characteristic signatures of these physical mechanisms is important for the correct interpretation of experimental data.
Analysis of existing theories of polarization of heterogeneous media shows that electrical spectroscopy can be useful for the interpretation of frequency spectra of complex dielectric permittivity or conductivity of water-bearing rocks and porous materials in general, and for the determination of water content, its thermodynamic state, the connectivity of water-bearing channels and their correlation lengths and the surface to volume ratio and surface charge in particular, in addition to the traditional formation factor, which is obtained from ohmic conductivity measurements.
TL;DR: Mycoplasmas typically have a number of distinct lipoproteins anchored on the outer face of the plasma membrane that have a potent modulin activity and are preferential targets of the host immune response.
TL;DR: Sulcal extraction and assisted labeling (SEAL) is implemented to automatically extract the two-dimensional surface ribbons that represent the median axis of cerebral sulci and to neuroanatomically label these entities to extract statistical information about both the spatial and the structural composition of the cerebral cortical topography.
Abstract: Systematic mapping of the variability in cortical sulcal anatomy is an area of increasing interest which presents numerous methodological challenges. To address these issues, the authors have implemented sulcal extraction and assisted labeling (SEAL) to automatically extract the two-dimensional (2-D) surface ribbons that represent the median axis of cerebral sulci and to neuroanatomically label these entities. To encode the extracted three-dimensional (3-D) cortical sulcal schematic topography (CSST) the authors define a relational graph structure composed of two main features: vertices (representing sulci) and arcs (representing the relationships between sulci). Vertices contain a parametric representation of the surface ribbon buried within the sulcus. Points on this surface are expressed in stereotaxic coordinates (i.e., with respect to a standardized brain coordinate system). For each of these vertices, the authors store length, depth, and orientation as well as anatomical attributes (e.g., hemisphere, lobe, sulcus type, etc.). Each are stores the 3-D location of the junction between sulci as well as a list of its connecting sulci. Sulcal labeling is performed semiautomatically by selecting a sulcal entity in the CSST and selecting from a menu of candidate sulcus names. In order to help the user in the labeling task, the menu is restricted to the most likely candidates by using priors for the expected sulcal spatial distribution. These priors, i.e., sulcal probabilistic maps, were created from the spatial distribution of 34 sulci traced manually on 36 different subjects. Given these spatial probability maps, the user is provided with the likelihood that the selected entity belongs to a particular sulcus. The cortical structure representation obtained by SEAL is suitable to extract statistical information about both the spatial and the structural composition of the cerebral cortical topography. This methodology allows for the iterative construction of a successively more complete statistical models of the cerebral topography containing spatial distributions of the most important structures, their morphometrics, and their structural components.
TL;DR: In this article, experimental data on saturated mineral powders and rocks with various surface areas and surface chemistries confirm the existence of significant surface contributions to the electrical spectra of conductivity and polarization of water-bearing porous systems and the dominance of this contribution over MWBH values at low frequencies.
Abstract: SUMMARY In the frequency range from millihertz to hundreds of megahertz, many diVerent physical and physico-chemical processes contribute to the electrical polarization of porous water-bearing rocks. This makes the interpretation of their electrical spectra a complicated problem and requires both elaborate theories and model experiments. At high frequencies, the Maxwell‐Wagner‐Bruggeman‐Hanai (MWBH) theory of eVective media, which takes into account only bulk properties, shape and partial volume of components, is very appropriate. At low frequencies, surface films, polarization of the electrical double layer (EDL) and clustering of conductive components can produce very strong polarization; corresponding theoretical models are considered in a companion paper (Chelidze & Gueguen 1999, hereafter referred to as Paper I). This paper is devoted to the review of experimental data and their comparison with theoretical models. Experiments on saturated mineral powders and rocks with various surface areas and surface chemistries confirm the existence of significant surface contributions to the electrical spectra of conductivity and polarization of water-bearing rocks and the dominance of this contribution over MWBH values at low frequencies. The eVective dielectric constant of porous saturated rocks increases with the surface-to-volume ratio of the system and strongly depends on the surface charge (f potential). At f potential, equal to zero, the low-frequency dielectric permittivity (DP) is minimal. The experimental data on relaxation times and the magnitude of the surface polarization of water-bearing porous systems can be satisfactorily explained by theories of film polarization, diVusional polarization generated by deformation of an ‘open’ electrical double layer (EDL) and percolation.
TL;DR: The high temperature behavior of a sol-gel derived silicon oxycarbide glass containing 12 at.% carbon has been characterized by means of creep and in-situ ultrasonic echography measurements as discussed by the authors.
Abstract: The high temperature behavior of a sol-gel derived silicon oxycarbide glass containing 12 at.% carbon has been characterized by means of creep and in-situ ultrasonic echography measurements. Temperature induced changes include structural relaxation and densification from 1000 to 1200°C, and crystallization to form a fine and homogeneous β-SiC/glass-matrix nanocomposite with 2.5 nm large crystals above 1200°C. Young's modulus measurements clearly reveal a consolidation of the material upon annealing below 1200°C. Crystallization is almost complete after few hours at 1300°C and results in a significant increase in Young's modulus. The viscosity of the oxycarbide glass is much higher than that of fused silica, with two orders of magnitude difference at 1200°C, and the glass transition temperature ranges from 1320 to 1370°C.
TL;DR: While analyzing the changes in the internal ionic status of the leaf explants in response to the salt treatment, it became clear that the internal Na + and Ca 2+ levels exert a positive effect on Pro, tyramine, Agm and Dap levels and a negative one on the levels of Put and Spd.
TL;DR: The results suggest that the accumulation of collagen I may specifically contribute to the remodeling of extracellular matrix in fibrotic livers by inducing MMP2 activation.
TL;DR: In this paper, the Gibbs free energies of formation of hydroxy-Green Rusts obtained are: ΔfG° (Fe3(OH)7, cr, 282.15 K) = −1799.7 ± 6 kJ mol−1, ΔfMg°(Fe2(H2O)5 + 2e− + 7 H+ = 3 Fe2++ + 8 H2O at an average temperature of 9 ± 1°C, and 1 atm. pressure.
TL;DR: The 143 genera, or subgenera, described so far in the literature are reviewed in order to exclude invalid taxa and obvious junior synonyms, and a suprageneric classification of the whole Chitinozoa group based on diagnostic features and stratigraphic range is given.
Abstract: The successful definition of chitinozoan genera depends primarily on the precision of the criteria used. A standardized morphological terminology based upon details from scanning electron microscope observations of the most representative taxa bearing these characters is therefore proposed. The 143 genera, or subgenera, described so far in the literature are reviewed in order to exclude invalid taxa and obvious junior synonyms. Particular attention is paid to preventing the overlap of generic definitions of the 56 genera ultimately retained. A brief account of the diagnostic features and stratigraphic range of selected genera is given, and basic information concerning the type material of these genera is listed. Finally, a suprageneric classification of the whole Chitinozoa group based on diagnostic features whose hierarchy is established on statistical and evolutionary grounds, is given. One new subfamily, Pogonochitininae, three new genera, Baltochitina, Hyalochitina, and Saharochitina, and a new species Baltochitina nolvaki, are defined. The sub-species Fungochitina fungiformis spinifera is elevated to a specific rank.
TL;DR: Many Archean and Proterozoic greenstone belts contain volcanic rocks that erupted subaqueously but interacted with continental crust on their way to the surface as discussed by the authors, pointing to emplacement in a tectonic setting that was rare to absent throughout the Phanerozoic.
TL;DR: The existence of numerous interactions between medial limbic structures and the neocortex during TLE seizures is demonstrated, which could have implications for surgical strategies and the prognosis of epilepsy surgery, particularly when limited resection is indicated.
TL;DR: Long-range ferromagnetic ordering at 3 K is observed for the title compound, which may be considered as a fully localized mixed-valence species as well as a mixed-spin species (low-spin and high-spin Mn(2+) ions).
Abstract: Long-range ferromagnetic ordering at 3 K is observed for the title compound, which may be considered as a fully localized mixed-valence species (Mo(3+) and Mo(4+)) as well as a mixed-spin species (low-spin and high-spin Mn(2+) ions). Its two-dimensional structure consists of heart-shaped 48-membered rings, and each ring contains 16 metal centers (see picture).
TL;DR: In a non-convex polyhedron, such a splitting of the spectrum disappears partly or completely, in relation with the non-H2 singularities of the Laplace-Dirichlet eigenfunctions as mentioned in this paper.
Abstract: In a convex polyhedron, a part of the Lame eigenvalues with hard simple support boundary conditions does not depend on the Lame coefficients and coincides with the Maxwell eigenvalues. The other eigenvalues depend linearly on a parameter s linked to the Lame coefficients and the associated eigenmodes are the gradients of the Laplace–Dirichlet eigenfunctions. In a non-convex polyhedron, such a splitting of the spectrum disappears partly or completely, in relation with the non-H2 singularities of the Laplace–Dirichlet eigenfunctions. From the Maxwell equations point of view, this means that in a non-convex polyhedron, the spectrum cannot be approximated by finite element methods using H1 elements. Similar properties hold in polygons. We give numerical results for two L-shaped domains. Copyright © 1999 John Wiley & Sons, Ltd.
TL;DR: In this paper, the influence of wood aggregates on the thermal and mechanical performance of a clay-cement-wood composite is analyzed. And the authors show that the addition of wood to clayey concrete improves its insulation characteristics, reduces its mechanical strength and increases its deformability.
Abstract: The introduction of wood aggregates to produce low density composites is an interesting technique allowing the reuse of wastes from both the aggregate-mining and wood processing industries. This paper describes the influence that the proportion of wood aggregates has on the thermal and mechanical performance of a clay-cement-wood composite. First, the composite material and its production technique are presented. Then, the thermal conductivity, mechanical strengths and the porosity of the matrix are experimentally evaluated. Finally, it is shown that the addition of wood to clayey concrete improves its insulation characteristics, reduces its mechanical strength and increases its deformability.
TL;DR: In a longitudinal study of 395 normal 10- to 24-year-old female volunteers, 105 of whom were initially premenarcheal, lumbar bone mineral density and content were measured by dual-energy X-ray absorptiometry (DXA) at inclusion and after a 2-year interval, the BMD and BMC relative gains were highly correlated with the height and weight relative gains and with the time since menarche.
Abstract: In a longitudinal study of 395 normal 10- to 24-year-old female volunteers, 105 of whom were initially premenarcheal, lumbar bone mineral density (BMD) and content (BMC) were measured by dual-energy X-ray absorptiometry (DXA) at inclusion and after a 2-year interval. The mean age of menarche was 13.1 þ 1.1 years (n = 395). In a multiple regression analysis the BMD and BMC relative gains were highly correlated with the height and weight relative gains and with the time since menarche (r= 0.91 and r= 0.93, respectively). The mean relative annual increments in body height, in L2–4 vertebral height, in BMD and in BMC peaked respectively at 1.5, 1.0, 0.6 and 0.7 years before menarche. The four perimenarcheal years, beginning with the first pubertal clinical signs, are essential for bone acquisition, since 46.7% of adult BMC is acquired during this period. Two years after menarche, BMC is 85% of the adult value. Seven years after menarche no further significant variation in BMC is observed. In 206 menstruating women 27–47 years old, a DXA lumbar measurement was also performed after a 4-year interval. There was a small but significant increase of 0.3 %/year in BMD and 0.7 %/year in BMC, contrasting with the results in the young population. This could be explained by a volumetric expansion with aging, which is supported by a small increase in L2–4 area (0.4 %/year). In conclusion, this longitudinal study on the lumbar site emphasizes the importance of the pre- and perimenarcheal period, when half of lumbar adult BMC is acquired. This suggests that greater attention must be paid to this period regarding nutrition and physical activity.
TL;DR: In this paper, the authors studied a western lowland gorilla population visiting the Maya salt clearing (north of the Parc national d'Odzala, P.N.O., Congo) over an 8 month period.
Abstract: Population studies are an essential part of conservation actions. Under exceptional observation conditions we studied a western lowland gorilla population visiting the Maya salt-clearing (north of the Parc national d'Odzala, P.N.O., Congo) over an 8 month period; 36 groups and 18 solitary individuals (a total of 420 individuals) have been identified visiting the clearing, which suggests a high gorilla density in the region. Ninety-six percent of the gorillas entered the clearing in groups. One-male groups had a mean size of 11.2. Ninety percent of solitary individuals were silver-back males. Compared with other populations of both lowland gorillas and mountain gorillas, the Maya population had the highest immature rate and the highest number of infants per female. Ecological correlates that could explain the attractiveness of the Maya clearing are discussed. The present status and the renewal rate of the Maya population indicate the need for further studies and confirm the importance of developing eco-tourism in this region as part of the sustainable park management activities developed by the ECOFAC programme (European Union). The results also provide arguments to support the proposal for extending the P.N.O. to include this region, which is rich in salt-clearings and attracts many other key-species of mammal such as forest elephants.
TL;DR: Blichert-Toft et al. as discussed by the authors measured the Hf isotope compositions of four Al-depleted komatiites from the 3.45 Ga Barberton Greenstone Belt in South Africa and six Al-undepleted KOMATIITs from 2.7 to 1.9 Ga belts in Canada and Zimbabwe.