Showing papers by "University of Rennes published in 1986"

Effect of steeper Archean geothermal gradient on geochemistry of subduction-zone magmas

Abstract: The comparative study of Archean and post-Archean granitic rocks shows significant changes with time. The high rare-earth element fractionation and the low Yb content of the Archean granitoids indicate the major role of garnet and hornblende, whereas these two minerals do not play a prominent part in the genesis of modern granitic rocks. This difference is a direct consequence of the cooling of Earth. In Archean time the subducted oceanic crust was young and warm, so it reached the conditions of melting before dehydration had occurred, leaving a garnet- and hornblende-bearing residue. In contrast, the modern subducted oceanic slab is generally old and cold, so it is dehydrated before it reaches the melting conditions of hydrous tholeiite; therefore, in the absence of a hydrous phase, it cannot melt at shallow depth. The fluids produced by dehydration reactions of modern crust rehydrate the overlying mantle wedge, which, in consequence, can undergo partial melting and give rise to calc-alkaline magmas; in this case, olivine and pyroxene are the most important residual phases. The location of calc-alkaline magma genesis in subduction-zone environments has migrated over time from the subducted Archean oceanic crust to the mantle wedge, a migration attributed to the progressive cooling of Earth.

Variations in the response of salt-stressed Rhizobium strains to betaines

Abstract: A total of 15 rhizobial strains representing Rhizobium meliloti, Rhizobium japonicum, Rhizobium trifolii, Rhizobium leguminosarum, Rhizobium sp. (Sesbania rostrata) and Rhizobium sp. (Hedysarum coronarium), were studied with regard to growth rate under salt stress in defined liquid media. In the presence of inhibitory concentrations of NaCl, enhancement of growth resulting from added glycine betaine was observed for R. meliloti strains and Rhizobium sp. (Hedysarum coronarium) but not for other Rhizobium species. The concentration of glycine betaine required for maximal growth stimulation was very low (1 mM) in comparison with the osmolarity of the medium. The stimulation was shown to be independent of any specific solutes. Other related compounds like proline betaine, carnitine, choline, γ-butyrobetaine and pipecolate betaine were also effective compounds in restoring the growth rate of cells grown in medium of elevated osmolarity. High rate of glycine betaine uptake was demonstrated in R. meliloti cells grown in media of increased osmotic strength. The intracellular concentration of this solute was found to be 308 mM in 0.3 M NaCl-grown cells and 17 times lower in minimal medium-grown cells. Glycine betaine was used for growth under conditions of low osmolarity but could not serve as sole carbon or nitrogen source in medium of increased osmotic strength. Experiments with [14C]glycine betaine showed that this molecule was not metabolized by cells subjected to osmotic stress, whereas it was rapidly converted to dimethylglycine, sarcosine and glycine in minimal medium-grown cells.

Applications of Total Pattern Fitting to a Study of Crystallite Size and Strain in Zinc Oxide Powder

Abstract: A novel approach to the determination of crystallite size and lattice strain by means of Total Pattern Analysis is described. Parameters to define the position, magnitude, breadth and shape of individual peaks are obtained by an adaptation of the pattern fitting program of Sonneveld and Visser (J. Appl. Cryst. 8, 1–7, 1975). A rapid assessment of the nature of the specimen broadening is given by a Williamson-Hall Plot. This leads to a more detailed study of line breadths by, for example, Voigt analysis applied to several orders of reflections or to single lines. Preliminary results are given for the application of this procedure to ‘size only’ and ‘size-strain’ samples of ZnO.

Mid-ocean ridge or marginal basin origin of the East Taiwan Ophiolite: chemical and isotopic evidence

Abstract: The East Taiwan Ophiolite (ETO) occurs as allochthonous fragments embedded in the Plio-Pleistocene Lichi Melange in the Coastal Range of eastern Taiwan. It is probably the youngest among the known ophiolitic complexes of the world. The overall geochemical and isotopic characteristics of the representative rock types are very “oceanic” and strongly argue for a mid-ocean or marginal basin origin of the ETO. The best criteria include: (1) major element compositions; (2) REE distribution patterns; (3) Nd isotopic ratios (some have ɛNd≧+12); (4) Pb isotopic ratios; and (5) the presence and nature of the red shale. This conclusion is supported by previous studies of metamorphic evolution of the ETO. The occurrence of both N- and P-type basalts in the ETO is firmly recognized for the first time by their REE distribution patterns. Neither type of basalt could be derived by fractional crystallisation from the other, nor by various degrees of partial melting from a common mantle source. Consequently, the genesis of basaltic magmas of the ETO has probably involved melting and mixing of a highly depleted asthenosphere and an enriched plume-type or hot-spot source. Because of the young age of formation (about 15 Ma) and the very recent tectonosedimentary emplacement (olistostromal origin) through arc-continent collision (about 4–5 Ma), the ETO was most likely generated in the spreading center of a small ocean or marginal basin (the South China Sea).

Line coupling in the temperature and frequency dependences of absorption in the microwindows of the 4.3 μm CO2 band

Abstract: The shapes of the self- and N2-broadened ν3CO2 fundamental vibration-rotation band in the microwindows (troughs between the lines) have been measured at various temperatures. Important deviations with respect to the superposition of Lorentzian profiles are observed. These deviations are interpreted in terms of line coupling, which redistributes the intensity in the whole band. In order to take into account this line coupling, two models are considered within the frame of the impact theory. The first model uses the strong-collision approximation to describe the rotational energy transferred by collisions. It leads to a simple analytical expression for the band profile. The second model is based on the exponential-gap law. These two models account well for the frequency dependence of the measured absorption in the microwindows and for the temperature dependence in the case of the N2-broadened CO2 band but not in the self-broadened case. The influence of the line-coupling rotational distribution, which differs significantly in the two models, is discussed. The possible role of the finite duration of collision in rotational energy transfer is examined.

Salt tolerance in Rhizobium: A possible role for betaines

Abstract: Rhizobium cells have evolved a variety of adaptative mechanisms to salt stress, such as accumulation of inorganic and organic solutes. A better understanding of the biochemical basis of osmoregulation in Rhizobium is of cardinal importance since the deleterious effect of salt stress on the survival and multiplication of these bacteria is well established. Current knowledge is briefly reviewed and experimental evidence on the beneficial effect of betaines on several Rhizobium strains is summarized. This information may help to shed light on similar adaptations in legumes of agricultural and economic importance.

Ionic conductvity and NMR investigation of quaternary glasses in the ZrF4BaF2ThF4LiF system

Abstract: The existence of glasses involving large amounts of LiF (up to 60%) within the ZrF4BaF2ThF4LiF quaternary systems has allowed the authors to study the evolution of transport properties with varying LiF content. A minimum of ionic conductivity bound to a maximum of activation energy has been detected when the atomic Li/F ratio is equal to ≅ 0.07. In the Li-low concentration domain, σ increases regularly and ΔE decreases simultaneously when the BaF2 concentration increases; on the contrary in the Li-high concentration region log σ and ΔE are quasi-linear functions, increasing and decreasing respectively, of the LiF rate. A 7Li and 19F NMR investigation has shown that Li+ and F− ions are simultaneously mobile and the temperature dependence of the number of mobile F− ions has been determined. In the Li-low concentration domain transport properties result from mixed contributions of mobile Li+ and F− ions, for high Li concentrations they depends only on the Li+ rate. Glasses with high Li-content have good electrical performnces (e.g. σ175°C ≅ 2.10−4ω−1 cm−1 for Zr0.20Ba0.10Li0.60Th0.10F2).

Air broadened linewidths, intensities, and spectral line shapes for CO(2) at 4.3 microm in the region of the AMTS instrument.

Abstract: The absolute intensities and air-broadening coefficients, together with their temperature dependence have been determined for a series of very high-J R lines in the ν3 band of CO2 located in the spectral region of some Advanced Moisture and Temperature Sounder (AMTS) channels. These channels are located in the transmission microwindows limited by these lines. The temperature dependence of the absorption coefficient in these microwindows has been measured for N2 and O2 broadening. It has been clearly demonstrated that a correcting shape factor χ(σ) independent of T cannot provide a good agreement between observed and calculated absorption in the range 193 K ⩽ T ⩽ 300 K for the spectral region of the AMTS channels.

Différences antigéniques entre des souches de Borrelia burgdorferi isolées d'Ixodes ricinus en Bretagne

Abstract: Resume Depuis ces derniers mois, les publications concernant les diverses formes cliniques chez l'homme des spirochetoses transmises par piqure de tiques Ixodinees se multiplient en France. Toutefois, ce n'est que tout recemment que des borrelies y ont ete observees chez Ixodes ricinus par nous dans plusieurs forets de Bretagne, et par d'autres dans une foret en Alsace. En ce qui concerne nos observations, le pourcentage de tiques infectees est parfois tres eleve : par exemple, 7 sur 27 nymphes et adultes femelles capturees dans 3 forets pres de Rennes – 29 sur 68 larves trouvees fixees sur des mulots dans une foret de la Sarthe. Nous rapportons ici les premiers isolements en France de Borrelia burgdorferi en culture, a partir de cette tique dans l'Ouest, soit recoltee a jeun par la technique du drapeau, soit gorgee et fixee sur petits mammiferes sauvages. 5 souches ont pu ainsi etre isolees : 4 de 2 points de la foret de Paimpont et 1 de la foret de Rennes. Ces souches ont ete caracterisees serologiquement vis-a-vis de 7 anticorps monoclonaux et comparees a la souche americaine de reference de B. burgdorferi, en mettant en jeu une reaction d'immuno-fluorescence indirecte. Cette etude permet les conclusions suivantes : les 4 souches isolees en foret de Paimpont presentent des reactions positives vis-a-vis de 6 des 7 antigenes monoclonaux testes. Elles semblent donc similaires aux borrelies isolees en Amerique du Nord, en Suisse et en Allemagne. Par contre, celle isolee en foret de Rennes, tres particuliere, ne reagit qu'avec 2 seulement des 7 anticorps monoclonaux testes. Cette reactivite de la souche de la foret de Rennes suggere que cet isolat est peutetre similaire aux souches suedoises isolees soit de patients atteints d'acrodermatite chronique atrophiante, soit d'I. ricinus. Il est ainsi evident qu'il n'existe pas qu'un seul type de souches en France, telles qu'elles se definissent par leurs proteines de surface. Ceci pose le probleme d'un role pathogene peut-etre different exerce par divers phenotypes. Le caractere particulier des proprietes antigeniques de la souche de la foret de Rennes souleve la question de son appartenance a l'espece B. burgdorferi. Elle peut toutefois etre consideree comme appartenant a cette espece, puisque le pourcentage d'homologie en A D N avec une souche type de B. burgdorferi atteint 61 %. Dans ce travail, nous confirmons l'observation, deja faite recemment par d'autres, de spirochetes chez des I. ricinus dans l'est de la France, chez des tiques recoltees, en ce qui nous concerne, en foret pres de Mutzig (Bas Rhin). Nos observations revelent par ailleurs le role epidemiologique sans doute important joue par les mulots (Apodemus sylvaticus et Apodemus flavicollis) comme hotes pour les stades jeunes d'I. ricinus. Ainsi, par exemple, un nombre moyen de larves d'I. ricinus de 26,7 par Apodemus a pu etre observe en foret pres de Sille-le-Guillaume dans la Sarthe.

Geometrical properties of disordered packings of hard disks

Abstract: We present experimental and theoretical results for geometrical properties of 2D packings of disks. We were mainly interested in the study of mixtures with disk size distribution which are of more practical interest than equal disks. Average geometrical properties, such as packing fraction of coordination number do not depend on the composition of the mixture, contrary to what would be expected from 3D experiments. We show the existence of a local order in the relative positions of grains with different sizes; this local order may modify the physical properties of the packing. An approximate theoretical expression for the packing fraction c of 2D close packings is given. It implies the knowledge of the average area of quadrilaterals of the network drawn from the real contacts only. For equal disk disordered packings, it yields the limit c=π 2 /12∼0.822 Presentation de resultats experimentaux et theoriques concernant les proprietes d'empilement bidimensionnels de disques, en particulier dans le cas de melanges avec distribution de taille des disques. Les proprietes moyennes, telles que compacite et coordinence, ne dependent pas de la composition du melange, contrairement a ce que l'on pourrait attendre au vu des experiences a 3-D. Mise en evidence de l'existence d'un ordre local dans la position relative de grains de tailles differentes, ordre pouvant modifier les proprietes physiques de l'empilement. Une expression theorique approchee pour la compacite d'empilements 2-D compacts est donnee

Experimental study on stacked triangular microstrip antennas

Abstract: The broadband behaviour of a pair of stacked triangular microstrip antennas is investigated experimentally. Recent experiments have shown that the bandwidth of a triangular microstrip antenna (TMA) can be broadened to as high as 17.5%.

Palaeomagnetism of the Ordovician Moulin de Chateaupanne formation, Vendee, western France

Abstract: Summary. A palaeomagnetic study of the Moulin de Chateaupanne formation reveals two characteristic components of magnetization. The first one, isolated by thermal treatment at intermediate temperatures, is strongly resistant to chemical leaching. Its direction (D= 217", I= +25", ag5 = 5.5) and the corresponding pole position (Lat = 21"S, Long = 320"E) are typical of the Hercynian overprints in the Armorican Massif. The second component, carried by fine-grained haematite, presents a steep downward direction (D = 228", I = + 81", ag5 = 6" ; pole position Lat = 34"N, Long = 343"E) already recognized in other Ordovician rock units from the same area. It is resistant to high-temperature demagnetization treatment and is believed to be of chemical origin, as assessed by a conglomerate test. A mutual consistency test with the nearby Thouars Massif suggests that the tilt of the formation has a sedimentary origin, and that the Thouars Massif has not suffered significant tilt during the Hercynian orogenic events.

Estimation of phase angles from the cross-spectral matrix

Abstract: The so-called signal subspace methods in spatial signal processing have been used up to now in the case of steering vectors depending upon very few parameters. For instance, they are used currently for steering vectors of the form (1, eiθ, e2iθ, ... , ei(N-1)θ)Twhich occur in the case of plane waves and a linear array of N equispaced sensors. We show, by providing a suitable algorithm, that these methods can be extended to the general case of steering vectors of the form (1, eiθ2, eiθ3, ... , eiθN)Twhere the phase angles θ 2 ,..., θ N are treated as free parameters. This kind of situation occurs, for instance, in the case of randomly distorted wavefronts, and/or flexible antennas of unknown geometry, when the fluctuations of the wavefronts and of the antenna are very slow with respect to the time constants used for the estimation of the cross-spectral matrices. As usual in signal subspace methods, the proposed algorithm works very well when the problem presents a strong degree of overdetermination (many more sensors than sources), and the cross-spectral matrix is estimated with good precision.