Showing papers by "University of Rennes published in 1984"

Molecular Biology of Osmoregulation

Abstract: The drought of 1983 resulted in some 10 billion dollars in agricultural losses and has focused attention on the vulnerability of our major crops to this devastating form of environmental stress. This article is concerned with the molecular biology of a new class of genes, called osm (osmotic tolerance) genes, that protect bacteria like Escherichia coli against osmotic stress and may work in a similar manner in plants and animals. Osm genes govern the production of a class of molecules, such as betaine and proline, that protect the cell and its constituents against dehydration. These osmoprotectant molecules have been known for many years to accumulate in plants but have only recently been shown to have potent antistress activity for bacteria.

Archean granulite gneisses from eastern Hebei Province, China: rare earth geochemistry and tectonic implications

Abstract: The granulite gneisses and their retrograded products of the Qianxi Group from eastern Hebei Province, China, have been investigated for their isotope and trace element geochemistry. A consistent age of about 2.5 AE has been obtained by the Rb-Sr and Sm-Nd whole-rock isochron methods, in agreement with the zircon U-Pb data (Pidgeon 1980; D.Y. Liu, unpubl.). Geochemical arguments from initial isotopic ratios (ISr and INd) and elemental distribution patterns have led us to conclude that this age of about 2.5 AE represents the time of granulite facies metamorphism, which must have followed closely the primary emplacement of their protoliths. Previous claims for early Archean ages (>3.5 AE) of these granulites are not substantiated. The mineral isotope systematics register an important thermal event at about 1.7 AE, roughly corresponding to the time of the widespread Luliang Orogeny (Ma and Wu 1981) or Chungtiao Movement (Huang 1978). The granulites of the Qianxi Group have diverse compositions ranging from ultrabasic through basic-intermediate to acid. Discriminant function calculations suggest that most analyzed samples have igneous parentage. Only a few show characteristics of metasedimentary rocks. The igneous protoliths apparently belong to two series — tholeiitic and calc-alkaline, with the latter dominating in abundance. The majority of the acid granulites have compositions corresponding to tonalite-granodiorite. Except for ultrabasic and metasedimentary rocks, all REE patterns are significantly fractionated with LREE enrichment. The degree of fractionation, as measured by the (La/Yb)N ratios, is most important in the acid granulites. These rocks often show positive Eu anomalies and HREE depletions that are typical of Archean TTG rocks (tonalitetrondhjemite-granodiorite). The existence of komatiites has been previously reported in this region. Although a few rocks have a major element chemistry similar to that for peridotitic komatiites, the lack of associated members in a komatiitic series and the scarcity of REE data have not confirmed the true komatiite occurrence in this region. Many Qianxi granulites are highly depleted in Rb relative to K and Sr. This preferential Rb depletion during granulite facies metamorphism has led to very high K/Rb and very low Rb/Sr ratios. The most comparable case is found in Lewisian granulites. Although the fractionated REE patterns of the basic granulites somewhat resemble those of continental flood basalts, the highly different abundances in other incompatible elements (Ti, Zr, and Ba) readily distinguish them from each other. Nevertheless, the LREE enriched patterns of the basic granulites may suggest an origin of their protoliths by partial melting of LREE-enriched mantle sources. On the other hand, the REE patterns of acid granulites suggest that their protoliths could be derived by partial melting of quartz eclogite, amphibolite or basic granulite. The close time relationship for a series of geologic events, namely, from initial melting of mantle peridotites, through fractional crystallisation of basaltic magmas, to granulite facies metamorphism, seems to occur in many granulite terrains. This relationship, together with the juxtaposition of lithologies of different origins and the exceptionally high pressure conditions (>10 Kb) can be best explained by crustal underplating combined with intracrustal thin-skinned thrusting and stacking of crustal slices. The “andesitic or island arc” model for the formation of the lower continental crust is not in good agreement with the present geochemical data.

Behavioural ecology of cockroaches

Abstract: Summary 1. Cockroaches are ubiquitous in most habitats where insects occur. Although most reports on cockroaches are physiological in nature, sufficient information is available to indicate that forest, desert, and cave-dwelling cockroaches select microhabitats on the basis of finely resolved environmental preferences. This is particularly true for oviparous females which select specific substrates for oviposition and embryogenesis. Selection and diel movements between microhabitats are related to diel changes in micrometeorological profiles and predation, feeding, and enhancement of sexual communication. 2. With some exceptions oviparous species live in wooded habitats; ovoviviparous species tend to occur in protected environments such as caves and logs. Oviparous species are exposed to greater predation, parasitism, and environmental pressures during embryogenesis than are ovoviviparous species, where internal incubation and some parental care reduce these risks. Most ovoviviparous species produce larger clutches, but the interval between broods is significantly longer than in oviparous species. Long gestation, clumping of food resources, and relatively little movement probably selected for male control of resources as a mate-attraction tactic in ovoviviparous species; agonistic interactions, and in some cases morphological specializations for fighting, and highly ritualized behaviours are common. In most oviparous species, volatile pheromone communication and resource-based aggregations are common. Rapid ovarian cycles and patchily distributed nutritional resources result in the need for greater mobility, and hence adults encounter greater risks.

Multi-chronometric ages and origin of Archaean tonalitic gneisses in Finnish Lapland: A case for long crustal residence time

Abstract: The Tojottamanselka gneisses of the Koitelainen region, northern Finland, have been dated by the Sm-Nd and the common Pb methods. The Sm-Nd data of seven samples from a small area (100 m × 100 m) define an isochron ofT=3.06±0.12 (2σ) Ga, with correspondingINd=0.50848±9 (2σ), oreNd(T)=−3.7±1.8. This age is in good agreement with the zircon U-Pb discordia age (3.1 Ga) reported by Kroner et al. (1981) and is interpreted as the time of magmatic emplacement. The distinctly negativeeNd(T) value is found for the first time for Archean tonalitic gneisses and implies derivation of these magmas by remelting of continental material with a long (200–500 Ma) crustal residence time. A few samples, on the other hand, possesseNd(T) values close to zero, hence they are thought to be derived by partial melting of basaltic sources with nearchondritic REE distribution patterns.

Paleozoic evolution of the Armorica plate on the basis of paleomagnetic data

Abstract: New paleomagnetic data support the contention that Armorica and Gondwana formed a coherent block until Ordovician time. However, by Early Devonian time, Armorica collided with the North American–northern European assembly to form the Old Red Continent, and the collision itself was responsible for the Acadian orogeny, not for the earlier Taconic orogeny as postulated previously. The Carboniferous collision of Gondwana with the Old Red Continent subsequently formed Pangaea and produced the Appalachian-Hercynian orogeny.

Crystallization in fluoride glasses: I. Devitrification on reheating

Abstract: The devitrification of glass from the BaF 2 LaF 3 ZrF 3 AlF 3 quaternary system is studied as a function of sample size and heating rate by differential scanning calorimetry. Results are analyzed in terms of a theory of non-isothermal crystallization kinetics similar to that of Matusita and Sakka but modified to allow for diffusion controlled growth of the crystallites.

Simplified models for the temperature dependence of linewidths at elevated temperatures and applications to CO broadened by Ar and N2

Abstract: The broadening coefficients for i.r. lines of CO perturbed by Ar are calculated in the temperature range 300–3500 K using the formalism previously developed by two of us (D.R. and J.B.). The results are compared with high-resolution spectroscopic measurements of shock-heated CO-Ar gas mixtures. A simplified model is proposed to describe the temperature dependence of the linewidths. The resulting model is applied to CO broadened by N 2 and the results are critically discussed.

Dynamics of laser eigenstates

Abstract: The spatial representation of the generalized potentials associated with the two eigenstates of a quasi-isotropic laser, in the frame of the Landau theory, predicts two different types of first-order phase transitions. The different dynamics of the corresponding vectorial bistabilities are confirmed by an experiment with a laser with two oscillating nondegenerate eigenstates. Polarization instabilities predicted in the first type of transition are experimentally shown.

Radiometric Ages (Rb-Sr, Sm-Nd, U-Pb) and REE Geochemistry of Archaean Granulite Gneisses from Eastern Hebei Province, China

Abstract: The granulite gneisses and their retrograded products of the Qianxi Group from eastern Hebei Province, China, have been investigated for their isotope and trace element geochemistry. A consistent age of about 2.5 Ga has been obtained by the Rb-Sr and Sm-Nd whole-rock isochron methods, in agreement with the zircon U-Pb data (Pidgeon 1980; Liu et al. 1984). Geochemical arguments from initial isotopic ratios (ISr and INd) and elemental distribution patterns have led us to conclude that this age of about 2.5 Ga represents the time of granulite facies metamorphism, which must have followed closely the primary emplacement of the gneiss protoliths. Previous claims for early Archaean ages (⩾3.5 Ga) of these granulites are not substantiated. The mineral isotope systematics register an important thermal event at about 1.7 Ga, roughly corresponding to the time of the widespread Luliang Orogeny (Ma and Wu 1981) or Chungtiao Movement (Huang 1978).

Nouveaux chalcogénures et chalcohalogénures à clusters tétraédriques Nb4 ou Ta4

Abstract: The new chalcogenides GaNb4X8 (X  S, Se), GaTa4Se8 and the selenoiodide NbSeI were obtained by high temperature synthesis from the elements. They crystallize with cubic symmetry (space group, F43m). The structure can be described as being made of [Me4X4] units (Me  Nb, Ta), with Me-Me bonds in tetrahedral Me4 clusters. The compounds are isostructural with the molybdenum chalcogenides MMo4S8 (M  Al, Ga), GaMo4Se8 and the thiohalides Mo4S4Y4 (Y  Cl, Br, I). Their magnetic properties seem to agree well with those of intermetallic compounds with very high densities of states.

Plasticity and adaptive radiation of dermapteran parental behavior: results and perspectives

Abstract: Publisher Summary The chapter describes the relationships between phenotypic plasticity through the development and intra- and inter-specific radiation specifically in regard to dermapteran parental behavior. Mainly adults, and specifically, dynamics of their reproductive cycle are concerned. The great majority of studies on behavioral ontogeny concern “higher” animals mainly mammals, where mother-infant relationships imply a type of social bond (psychosocial level) that is not found in insects (biosocial level). This chapter is also guided by the question of behavioral transformations linked with speciation, in particular Darwinian behavioral adaptations arising from the conventional Darwinian mechanism of selection upon genetic variation. It also describes the development of dermapteran parental behavior, then examines this process within the context of intra- and inter-specific adaptive radiation, and lastly, it discusses the theoretical implications of this epigenetic approach.

Loi des grands nombres et perturbations pour des produits réductibles de matrices aléatoires indépendantes

Abstract: Soit X=(X n ) n=1 ∞ une suite de matrices aleatoires reelles d×d independantes de meme loi μ. On etudie le comportement asymptotique de la suite (1/n Log∥X n ...X 1 x∥) n

Electrical properties and optical absorption of SnSe evaporated thin films

Abstract: Resistivity, Hall effect, and optical absorption coefficient measurements are performed on SnSe evaporated thin films. The resistivity decreases with increasing temperature whereas the Hall mobility and carrier density increase with increasing temperature. An exponential 1/T law is observed for each of these variations. The results are explained in terms of a grain boundary potential barrier mechanism. The optical absorption coefficient is measured at 300 K over the photon energy range 0.8 to 1.3 eV. An analysis of absorption measurements indicates that the SnSe thin film absorption edge is due to allowed direct transitions across an energy gap of about 1.21 eV. Les proprietes de transport et les variations du coefficient d'absorption des couches minces de SnSe ont ete determinees. Quand la temperature croǐt, la resistivite diminue tandis que la mobilite et la concentration de porteurs augmentent. Les variations de ϱ, μ et p obeissent a une loi exponentielle en 1/T. Les resultats ont ete interpretes par le modele de barrieres de potentiel au niveau des joints de grains. Le coefficient d'absorption a ete determine a 300 K dans la region 0,8 a 1,3 eV. L'analyse des resultats obtenus indique que le SnSe en couche mince presente une transition directe avec une largeur de bande interdite de l'ordre de 1,21 eV.

Susceptance computation of a meander-line polarizer layer

Abstract: The solution to the problem of scattering of a plane wave by an infinite periodic array of meander-line thin conductors on a dielectric sheet is considered. Numerical results on perpendicular and parallel polarization susceptances are given as well as a comparison with experimental data over a large frequency range. Results showing variations of array's susceptances with respect to constitutive parameters are also presented.

A 2.5 G.a. reworked sialic crust: Rb-Sr ages and isotopic geochemistry of late archaean volcanic and plutonic rocks from E. Finland

Abstract: In east-central Finland, Archaean terrains present three main lithologic units: a) gneissic basement, emplaced from 2.86 G.a. to 2.62 G.a., b) greenstone belt (2.65 G.a.) and c) calc-alkaline magmatism (2.50 G.a. to 2.40 G.a). Twenty three rocks of the calc-alkaline suite have been chosen for geochronologic and Rb-Sr isotopic studies. These rocks are subdivided into three groups: 1) acid volcanics from Luoma, 2) augen gneiss from Arola, and 3) post kinematik pink leucogranite from Arola. The 2.50±0.10 G.a. age of the Luoma volcanics indicates that they represent the upper part of a greenstone belt composed of a single sequence of volcanic rocks. The ages, initial 87Sr/86Sr (ISr) and major element compositions of the augen gneisses of Arola and Suomussalmi indicate that these rocks are the plutonic equivalents of the Luoma acid volcanics. The Arola pink leucogranite marks the terminal phase of Archaean magmatic activity (from 2.86 G.a. to 2.41 G.a.). This was followed by at least 0.40 G.a. of quiescence. The ISr and major element compositions suggest that the genesis of the calc-alkaline magmatic rocks involved crustal materials, but all their geochemical features cannot be explained without the participation of mafic greenstone belt materials. The first crustal components had low I and low K2O/ Na2O ratios while the younger ones (calc-alkaline magmas) had medium to high ISr and high K2O/Na2O ratios. Thus the petrogenetic processes have changed with time from ensimatic to ensialic, implying major reworking of preexisting crustal materials. This evolution leads to the accretion of the continental crust from the mantle.

Morphological Analysis and Growth of Crystallites During Annealing of ZnO

Abstract: A detailed analysis of the crystallite shape of zinc oxide produced by thermal decomposition of zinc hydroxynitrate was performed as a function of temperature from 280° to 700°C. The shape and size were analyzed by X-ray line-broadening measurements. Evolution from cylinder to right hexagonal prism shapes is observed during annealing of the loose powder. A homothetic growth of crystallites is observed through the initial stage of annealing. Relations between surface area and X-ray crystallite size are presented and discussed in terms of the packing factor. Results suggest that two parallel growth processes take place during annealing.