Showing papers by "University of Rennes published in 2000"

Granitoids of the Central Asian Orogenic Belt and Continental Growth in the Phanerozoic

Abstract: The Central Asian Orogenic Belt (CAOB), also known as the Altaid Tectonic Collage, is characterised by a vast distribution of Paleozoic and Mesozoic granitic intrusions. The granitoids have a wide range of compositions and roughly show a temporal evolution from calcalkaline to alkaline to peralkaline series. The emplacement times for most granitic plutons fall between 500 Ma and 100 Ma, but only a small proportion of plutons have been precisely dated. The Nd-Sr isotopic compositions of these granitoids suggest their juvenile characteristics, hence implying a massive addition of new continental crust in the Phanerozoic. In this paper we document the available isotopic data to support this conclusion. Most Phanerozoic granitoids of Central Asia are characterised by low initial Sr isotopic ratios, positive eNd(T) values and young Sm—Nd model ages (TDM) of 300-1200 Ma. This is in strong contrast with the coeval granitoids emplaced in the European Caledonides and Hercynides. The isotope data indicate their ‘juvenile’ character and suggest their derivation from source rocks or magmas separated shortly before from the upper mantle. Granitoids with negative eNd(T) values also exist, but they occur in the environs of Precambrian microcontinental blocks and their isotope compositions may reflect contamination by the older crust in the magma generation processes. The evolution of the CAOB is probably related to accretion of young arc complexes and old terranes (microcontinents). However, the emplacement of large volumes of post-tectonic granites requires another mechanism, probably through a series of processes including underplating of massive basaltic magma, intercalation of basaltic magma with lower crustal granulites, partial melting of the mixed lithologic assemblages leading to generation of granitic liquids, followed by extensive fractional crystallisation. The proportions of the juvenile or mantle component for most granitoids of Central Asia are estimated to vary from 70% to 100%.

Relevance of nonlinear lumped-parameter models in the analysis of depth-EEG epileptic signals.

Abstract: In the field of epilepsy, the analysis of stereoelectroencephalographic (SEEG, intra-cerebral recording) signals with signal processing methods can help to better identify the epileptogenic zone, the area of the brain responsible for triggering seizures, and to better understand its organization. In order to evaluate these methods and to physiologically interpret the results they provide, we developed a model able to produce EEG signals from “organized” networks of neural populations. Starting from a neurophysiologically relevant model initially proposed by Lopes Da Silva et al. [Lopes da Silva FH, Hoek A, Smith H, Zetterberg LH (1974) Kybernetic 15: 27–37] and recently re-designed by Jansen et al. [Jansen BH, Zouridakis G, Brandt ME (1993) Biol Cybern 68: 275–283] the present study demonstrates that this model can be extended to generate spontaneous EEG signals from multiple coupled neural populations. Model parameters related to excitation, inhibition and coupling are then altered to produce epileptiform EEG signals. Results show that the qualitative behavior of the model is realistic; simulated signals resemble those recorded from different brain structures for both interictal and ictal activities. Possible exploitation of simulations in signal processing is illustrated through one example; statistical couplings between both simulated signals and real SEEG signals are estimated using nonlinear regression. Results are compared and show that, through the model, real SEEG signals can be interpreted with the aid of signal processing methods.

Systematic Investigation of the Nature of The Coupling between a Ln(III) Ion (Ln = Ce(III) to Dy(III)) and Its Aminoxyl Radical Ligands. Structural and Magnetic Characteristics of a Series of {Ln(organic radical)2} Compounds and the Related {Ln(Nitrone)2} Derivatives

Abstract: Numerous molecular compounds in which a paramagnetic Ln(III) ion is in interaction with a second spin carrier such as a transition metal ion or an organic radical have been described. However, except for the isotropic Gd(III) ion, very little is known concerning the nature (ferro- or antiferromagnetic) and mechanism of the interaction involving a Ln(III) ion. This study addresses the problem of the interaction between the Ln(III) ions displaying spin−orbit coupling and an organic radical. The magnetic properties of a series of isostructural compounds, {Ln(organic radical)2(NO3)3}, comprising a Ln(III) ion (Ln = Ce to Dy) surrounded by two N,O-chelating aminoxyl radicals (3-nitronyl nitroxide-4,5-dimethyltriazole) have been investigated. The experimental approach used to get insight into the {Ln-Radical} coupling occurring within these compounds is based on the knowledge of the intrinsic paramagnetic contribution of the metal ion. This contribution has been deduced from the corresponding {Ln(Nitrone)2(NO3)...

Singularities of Electromagnetic Fields¶in Polyhedral Domains

Abstract: In this paper, we investigate the singular solutions of time-harmonic Maxwell equations in a domain which has edges and polyhedral corners. It is now well known that in the presence of non-convex edges, the solution fields have no square integrable gradients in general and that the main singularities are the gradients of singular functions of the Laplace operator [4,–5]. We show how this type of result can be derived from the classical Mellin analysis, and how this analysis leads to sharper results concerning the singular parts which belong to H 1. For the singular functions, we exhibit simple and explicit formulas based on (generalized) Dirichlet and Neumann singularities for the Laplace operator. These formulas are more explicit than the results announced in our note [10].

Effect of a crystallite size distribution on X‐ray diffraction line profiles and whole‐powder‐pattern fitting

Abstract: A distribution of crystallite size reduces the width of a powder diffraction line profile, relative to that for a single crystallite, and lengthens its tails. It is shown that estimates of size from the integral breadth or Fourier methods differ from the arithmetic mean of the distribution by an amount which depends on its dispersion. It is also shown that the form of `size' line profiles for a unimodal distribution is generally not Lorentzian. A powder pattern can be simulated for a given distribution of sizes, if it is assumed that on average the crystallites have a regular shape, and this can then be compared with experimental data to give refined parameters defining the distribution. Unlike `traditional' methods of line-profile analysis, this entirely physical approach can be applied to powder patterns with severe overlap of reflections, as is demonstrated by using data for nanocrystalline ceria. The procedure is compared with alternative powder-pattern fitting methods, by using pseudo-Voigt and Pearson VII functions to model individual line profiles, and with transmission electron microscopy (TEM) data.

Cationic Ruthenium Allenylidene Complexes as Catalysts for Ring Closing Olefin Metathesis

Abstract: A series of well accessible cationic ruthenium allenylidene complexes of the general type [(eta6-arene)(R3P)RuCl(=C=CR'2)]+ X- is described which constitute a new class of pre-catalysts for ring closing olefin metathesis reactions (RCM) and provide an unprecedented example for the involvement of metal allenylidenes in catalysis. They effect the cyclization of various functionalized dienes and enynes with good to excellent yields and show a great tolerance towards an array of functional groups. Systematic variations of their basic structural motif have provided insights into the essential parameters responsible for catalytic activity which can be enhanced further by addition of Lewis or Bronsted acids, by irradiation with UV light, or by the adequate choice of the "non-coordinating" counterion X-. The latter turned out to play a particularly important role in determining the rate and selectivity of the reaction. A similarly pronounced influence is exerted by remote substituents on the allenylidene residue which indicates that this ligand (or a ligand derived thereof) may remain attached to the metal throughout the catalytic process. X-ray crystal structures of the catalytically active allenylidene complexes 3b.PF6 and 15.OTf as well as of the chelate complex 10 required for the preparation of the latter catalyst are reported.

Er3+-doped phosphate glasses for fiber amplifiers with high gain per unit length

Abstract: The effect of the types of alkaline earth metal ions (Mg2+, Ca2+ and Ba2+) and concentration of Al2O3 and BaO on the refractive index and the effective emission linewidths of the 4I13/2−4I15/2 transition of Er3+ ions in phosphate glasses, 64P2O5 · 12Al2O3 · 3.5( Er 2 O 3 + La 2 O 3 )·20.5 MO ( M = Mg , Ca , Ba ) and 64P2O5 · 3.5(Er2O3+La2O3) · (21.5 − x)Al2O3 · (11+x) BaO (x=0,3.5,6.5 and 9.5) , were investigated. A single mode Er3+ doped phosphate glass fiber with a core diameter of 4 μm was fabricated by the rod-in-tube technique. A new Er3+ doped fiber amplifier is demonstrated pumping with a 980 nm fiber pigtailed-laser diode. A gain per unit length greater than 2 dB/cm is demonstrated, which is the largest gain per unit length for fiber amplifiers to our knowledge.

Metabolic and Hormonal Responses to Exercise in Children and Adolescents

Abstract: Ethical and methodological factors limit the availability of data on metabolic and hormonal responses to exercise in children and adolescents. Despite this, it has been reported that young individuals show age-dependent responses to short and long term exercise when compared with adults. Adenosine triphosphate (ATP) and phosphocreatine stores are not age-dependent in children and adolescents. However, phosphorus-31 nuclear magnetic resonance spectroscopy (31PNMR) studies showed smaller reductions in intramuscular pH in children and adolescents during high intensity exercise than adults. Muscle glycogen levels at rest are less important in children, but during adolescence these reach levels observed in adults. Immaturity of anaerobic metabolism in children is a major consideration, and there are several possible reasons for this reduced glycolytic activity. There appear to be higher proportions of slow twitch (type I) fibres in the vastus lateralis part of the quadriceps in children than in untrained adults, and anaerobic glycolytic ATP rephosphorylation may be reduced in young individuals during high intensity exercise. Reduced activity of phosphofructokinase-1 and lactate dehydrogenase enzymes in prepubertal children could also explain the lower glycolytic capacity and the limited production of muscle lactate relative to adults. These observations may be related to reduced sympathetic responses to exhaustive resistance exercise in young people. In contrast, children and adolescents are well adapted to prolonged exercise of moderate intensity. Growth and maturation induce increases in muscle mass, with proliferation of mitochondria and contractile proteins. However, substrate utilisation during exercise differs between children and adults, with metabolic and hormonal adaptations being suggested. Lower respiratory exchange ratio values are often observed in young individuals during prolonged moderate exercise. Data indicate that children rely more on fat oxidation than do adults, and increased free fatty acid mobilisation, glycerol release and growth hormone increases in preadolescent children support this hypothesis. Plasma glucose responses during prolonged exercise are generally comparable in children and adults. When glucose is ingested at the beginning of moderate exercise, plasma glucose levels are higher in children than in adults, but this may be caused by decreased insulin sensitivity during the peripubertal period (as shown by glucose: insulin ratios). Conclusions: Children are better adapted to aerobic exercise because their energy expenditure appears to rely more on oxidative metabolism than is the case in adults. Glycolytic activity is age-dependent, and the relative proportion of fat utilisation during prolonged exercise appears higher in children than in adults.

Non-linear optical properties of chalcogenide glasses measured by Z-scan

Abstract: To explore the potentialities of chalcogenide glasses for ultrafast optical switching, the non-linear refractive indices of different compositions are measured. Several binary glasses in the [Ge–Se] system, As2S3 and As2Se3 glasses, as well as ternary glasses in the [Ge–Se–As] system have been characterized. Non-linear measurements have been performed by the Z-scan technique, at different intensities, with the picosecond pulses emitted by a 10 Hz Q-switched mode-locked Nd-YAG laser at 1064 nm, in adequate conditions to characterize ultrafast non-linearities. Non-linear refractive indices as high as 22×10 −18 m 2 / W have been obtained in the ternary system. In the case of As2S3 and As2Se3 glasses, a significant variation of the value of the non-linear index of refraction with the laser intensity has been observed which is attributed to a fifth order non-linearity.

Free radical scavenging and antioxidant effects of lactate ion: an in vitro study.

Abstract: Divergent literature data are found concerning the effect of lactate on free radical production during exercise. To clarify this point, we tested the pro- or antioxidant effect of lactate ion in vi...

The biology and ecology of lotic microcrustaceans

Abstract: SUMMARY 1. Copepoda, Ostracoda and ‘Cladocera‘ are important meiobenthic Crustacea which can be both numerically abundant and species rich in running waters. Harpacticoids and ostracods are well adapted to benthic life because they are typical crawlers, walkers, and burrowers. Many cladocerans are substratum dwellers, but most benthic species among these can also swim. Cyclopoids which are generally good swimmers are nevertheless often bottom frequenters and actively colonise sediment interstices (the hyporheic zone). 2. The subclass Copepoda includes 10 orders. With 53 families, the order Harpacticoida dominates the benthos. Only five of these families are represented in fresh waters (ca. 1 000 species and subspecies). The order Cyclopoida includes 12 families of which the Cyclopidae is well represented in freshwater habitats with 900 species and subspecies. Freshwater Ostracods belong to the order Podocopida (5 000 species) with three superfamilies occurring in running fresh waters. The group ‘Cladocera‘ contains four orders, 12 families, more than 80 genera, and 450‐600 freshwater species. Most of the benthic species are found in the families Chydoridae (39 genera), Macrothricidae, Ilyocryptidae and Sididae. 3. For each of the three major taxa, morphological characteristics are presented, specimen collection and preparation are described and references to available taxonomical keys are provided. 4. Biological characteristics are extremely diverse among and within the three taxa, resulting in a great variety of strategies in meiobenthic crustaceans. Characteristics of reproduction, sexual dimorphism, cyclomorphosis and population parameters (i.e. clutch size, lifespan, growth, moulting) are provided for some of the most common species. 5. Important differences between the three main taxa were found at the species level. Ecological requirements such as hydraulic microhabitats and geomorphologic features of the streambed are the major determinants of species diversity and abundance for benthic microcrustacea of lotic habitats. Many studies on the ecology of these communities are limited by a lack of knowledge of the life history characterisitics of lotic (especially interstitial) crustacean populations.

Responses of an avian predator to variations in prey density at a temperate latitude

Abstract: Fluctuating prey populations and their effects on avian predator population dynamics have been studied particularly at high latitudes, where prey populations, especially microtines, are known to be cyclic; raptors show both numerical and functional responses to variations in their prey. In this paper, we investigate the response of a migratory raptor (Montagu's Harrier, Circus pygargus) to variations in abundance of its main prey (common vole, Microtus arvalis) in France. We document multiannual fluctuation in the abundance of common voles. The numerical response of Montagu's Harrier to this variable food supply was studied using breeding parameters (breeding density, breeding phenology, and various measures of breeding success). Breeding density and mean clutch size were strongly correlated with spring vole abundance, whereas mean brood size at fledging was correlated positively with summer vole abundance. The mechanism involved in the numerical response of Montagu's Harrier indicates that dispersal and ...

Post-collisional Neogene magmatism of the Mediterranean Maghreb margin: a consequence of slab breakoff

Abstract: A 1 200 km-long linear magmatic belt extends along the Mediterranean coast of the Maghreb from Eastern Tunisia to Morocco. This belt is mainly composed of Langhian calc-alkaline metaluminous to peraluminous granitoids and associated andesites/dacites in Central and Eastern Algeria. In Tunisia and Oranie/Western Morocco, calc-alkaline activity started later (during the Serravallian) and was followed by the emplacement of alkali basalts and basanites since the Tortonian to the Pliocene and, in some places, the Pleistocene. Available data on the tectonic setting, petrology, age and geochemistry of this belt show that most of its striking features, e.g. (1) very low magma production rate, subduction-related geochemical imprint, extensive crustal contamination for the calc-alkaline magmatism and (2) progressive magmatic change from calc-alkaline to alkaline, are consistent with magma generation during a slab breakoff process as proposed by Carminati et al. in 1998. The magmatism associated with this breakoff started in Central Eastern Algeria at 16 Ma, then propagated eastwards and westwards. The upward flow of asthenospheric enriched plume-type mantle through the tear in the downgoing slab first triggered melting of the overlying lithospheric mantle which had been metasomatised during a previous subduction period. Heat supply from this uprising asthenosphere may have warmed up the continental crust and made its involvement in assimilation processes easier. As the asthenosphere ascended through the ‘window’ in the slab, partial melting occurred at the uprising boundary between asthenosphere and lithosphere, generating basalts with transitional characteristics between those of calc-alkaline and alkaline basalts. As the asthenospheric upwelling proceeded, partial melting then occurred in the sole asthenospheric mantle, producing alkali basalts.

A Converse Comparison Theorem for BSDEs and Related Properties of g-Expectation

Abstract: In [1], Z. Chen proved that, if for each terminal condition $\xi$, the solution of the BSDE associated to the standard parameter $(\xi, g_1)$ is equal at time $t=0$ to the solution of the BSDE associated to $(\xi, g_2)$ then we must have $g_1\equiv g_2$. This result yields a natural question: what happens in the case of an inequality in place of an equality? In this paper, we try to investigate this question and we prove some properties of ``$g$-expectation'', notion introduced by S. Peng in [8].

Progressive crustal contamination of the Bushveld Complex: evidence from Nd isotopic analyses of the cumulate rocks

Abstract: We report the first Nd isotopic data on the cumulate rocks of the Bushveld Complex, South Africa. We analysed 17 whole-rock samples covering 4700 m of stratigraphy through the Lower, Critical and Main Zones of the intrusion at Union Section, north-western Bushveld Complex. The basal ultramafic portions of the complex have markedly higher ɛNd(T) (−5.3 to −6.0) than the gabbronoritic Main Zone (ɛNd(T) −6.4 to −7.9). The rocks of the Upper Critical Zone have intermediate values. These results are in agreement with new Nd isotope data on marginal rocks and sills in the floor of the complex that are generally interpreted as representing chilled parental magmas, and with published Sr isotopic data, all of which show a larger crustal component in the upper part of the intrusion. In contrast, the concentrations of many highly incompatible trace elements are decoupled from the isotopic signatures. The basal portions of the complex have higher ratios of incompatible to compatible trace elements than the upper portions. The variations of isotopic and trace-element compositions are interpreted in terms of a change in the nature of the crustal material that contaminated Bushveld magmas. Those magmas that fed into the lower part of the complex had assimilated a relatively small amount of incompatible trace-element-rich partial melt of upper crust, whereas magmas parental to the upper part of the complex had assimilated a higher proportion of the incompatible trace-element-poor residue of partial melting.

Modulation of HLA-G Antigens Expression by Human Cytomegalovirus: Specific Induction in Activated Macrophages Harboring Human Cytomegalovirus Infection

Abstract: After infection, human CMV (HCMV) establishes a latent and persistent infection in immature myeloid progenitors and peripheral blood monocytes. Completion of the HCMV life cycle is possible upon maturation of monocytes to tissue macrophages and under permissive circumstances, e.g., immunosuppression. We investigated the hypothesis that HLA-G molecules could be induced during HCMV reactivation in activated macrophages to favor virus dissemination. In this study, we provide evidence that HLA-G Ags are produced during viral reactivation in macrophages generated after allogeneic stimulation of HCMV latently infected monocytes. While HLA-G surface expression is up-regulated, classical MHC-I molecules are partially down-regulated by HCMV. In vivo, bronchoalveolar macrophages collected from patients suffering from acute HCMV pneumonitis also express HLA-G molecules. The direct correlation between HLA-G Ag induction and HCMV infection was confirmed in U-373 MG astrocytoma cells. Soluble HLA-G expression is stimulated upon HCMV infection, and this modulation depends on the cooperative action of the two immediate-early-1 pp72 and immediate-early-2 pp86 products. Because HLA-G transcription is active in macrophages and U-373 MG astrocytoma cells, it is likely that the modulation of HLA-G protein expression during HCMV replication occurs at a post-transcriptional level. Our data suggest that induction of HLA-G molecules could be an additional mechanism that helps HCMV to subvert host defenses.

Important crustal growth in the Phanerozoic: Isotopic evidence of granitoids from east-central Asia

Abstract: The growth of the continental crust is generally believed to have been essentially completed in the Precambrian, and the amount of juvenile crust produced in the Phanerozoic is considered insignificant. Such idea of negligible growth in the Phanerozoic is now challenged by the revelation of very large volume of juvenile crust produced in the period of 500 to 100 Ma in several orogenic belts. While appreciable volumes of juvenile terranes in North America (Canadian Cordillera, Sierra Nevada and Peninsular Range, Appalachians) have been documented based on Nd isotopic data, the mass of new crust formed in the East-Central Asian Orogenic Belt (ECAOB), eastern part of the Altaid Tectonic Collage, appears to be much greater than the above terranes combined. New and published Nd-Sr isotope data indicate that the Phanerozoic granitoids from the southern belt of the ECAOB (Xinjiang-West Mongolia-Inner Mongolia-NE China) as well as from Mongolia and Transbaikalia were generated from sources dominated by a depleted mantle component. These granitoids represent a significant growth of juvenile crust in the Phanerozoic.

Dipolar and Non‐Dipolar Pyridine and Bipyridine Metal Complexes for Nonlinear Optics

Abstract: Metal complexes of pyridine and bipyridine-type ligands represent an important class of nonlinear optical (NLO) materials: (i) They can incorporate a variety of functionalised ligands with a wide range of metals which can give rise to tuneable NLO properties; (ii) they are generally associated with intense low-lying charge-transfer excitations such as metal to ligand charge-transfer (MLCT) or intraligand charge-transfer (ILCT); (iii) bipyridyl ligands are also good building blocks that allow the construction of octupolar complexes with a defined geometry and symmetry. This review describes the recent developments in the design of such dipolar and octupolar chromophores for second-order nonlinear optics.

Bcl-w Forms Complexes with Bax and Bak, and Elevated Ratios of Bax/Bcl-w and Bak/Bcl-w Correspond to Spermatogonial and Spermatocyte Apoptosis in the Testis

Abstract: Bcl-w, a prosurvival member of the Bcl-2 family, is essential for spermatogenesis. However, the mechanisms by which Bcl-w participates in the regulation of apoptosis in the testis are largely unknown. To explore the potential role of Bcl-w in the regulation of apoptosis in the testis, the expression of Bcl-w mRNA and protein during testicular development and spermatogenesis, the dimerization with the proapoptosis members of the Bcl-2 family, and the responses to hormonal stimulation in vitro and apoptosis-inducing signals in vivo were investigated. Both Bcl-w mRNA and protein were detected in Sertoli cells, spermatogonia, and spermatocytes, as well as in Leydig cells. The steady-state levels of Bcl-w mRNA and protein were much higher in Sertoli cells than in spermatogonia and spermatocytes. In the adult rat testis, both Bcl-w mRNA and protein in Sertoli cells displayed a stage-specific expression pattern. Bcl-w could form complexes with Bax and Bak but not with Bad. Bax and Bak were immunohistochemically localized to the same cell types as Bcl-w, but with higher expression levels in spermatocytes and spermatogonia than in Sertoli cells. FSH could up-regulate Bcl-w mRNA levels in the seminiferous tubules cultured in vitro, whereas no effect was observed when testosterone was applied. Three animal models that display spermatogonial apoptosis induced by blockade of stem cell factor/c-kit interaction by a function-blocking anti-c-kit antibody, spermatocyte apoptosis induced by methoxyacetic acid, and apoptosis of spermatogonia, spermatocytes, and spermatids induced by testosterone withdrawal after ethylene dimethane sulfonate treatment were employed to check the changes of Bcl-w, Bax, and Bak protein levels during apoptosis of specific germ cells. In all three models, the ratios of Bax/Bcl-w and Bak/Bcl-w were significantly elevated. The present study suggests that Bcl-w is an important prosurvival factor of Sertoli cells, spermatogonia, and spermatocytes and participates in the regulation of apoptosis by binding proapoptotic factors Bax and Bak. The ratios of Bax/Bcl-w and Bak/Bcl-w may be decisive for the survival of Sertoli cells, spermatogonia, and spermatocytes.

Role of gelatinases MMP-2 and MMP-9 in tissue remodeling following acute lung injury.

Abstract: Acute lung injury is characterized by a severe disruption of alveolo-capillary structures and includes a variety of changes in lung cell populations. Evidence suggests the occurrence of rupture of the basement membranes and interstitial matrix remodeling during acute lung injury. The dynamic equilibrium of the extracellular matrix (ECM) under physiological conditions is a consequence of the balance between the regulation of synthesis and degradation of ECM components. Matrix metalloproteinases (MMPs) represent a group of enzymes involved in the degradation of most of the components of the ECM and therefore participate in tissue remodeling associated with pathological situations such as acute lung injury. MMP activity is regulated by proteolytic activation of the latent secreted proenzyme and by interaction with specific tissue inhibitors of metalloproteinases. This review details our knowledge of the involvement of MMPs, namely MMP-2 and MMP-9, in acute lung injury and acute respiratory distress syndrome.