Melting kinetics of granitic powder aggregates at 1175°C, 1 atm.

Melting experiments of pressed granitic powders (10% < 3.23 m, 50% < 31.63 m, 90% < 169.85 m) have been performed at 1175°C, 1 atm for different run durations (5, 10, 40 mn and 3, 24, 68 h). During partial melting, quartz and feldspars progressively decrease in abundance, the amount of melt produced increases sharply after 40 mn and leads to a strong decrease of the porosity of the powder (from 42% before heat-treatment to 10% after 68 h). In the 5 mn charge, thin glass films (1-2 m) appear cementing small particles grains and narrow glass channels are formed and trapped within both albite and K-feldspar. Newly-formed K-feldspars appear in the 10 and 40 mn charges. They are both texturally and compositionally distinctive from the original feldspars. All feldspars have totally disappeared after 3 h and quartz (up to 330 m) persists in the longest experiment (68 h). For durations longer than 40 mn, glass compositions are chemically zoned. They vary mainly between two end-members, one rich in normative feldspar components and poor in normative quartz and the other rich in normative quartz corresponding to areas close to the quartz interface. The melting reaction is governed by disequilibrium melting. Two melting regimes were identified: (1) a low melt fraction regime corresponding to heterogeneous nucleation of melt at the surface and within interiors of both albite and K-feldspar and (2) a high melt fraction regime kinetically controlled by diffusive mass transport within the melt layer. The lack of leucite implies that the melting relations of K-feldspar observed in this study are congruent. About 50 days are needed for the melting reaction to approach chemical equilibrium at 1175°C

Dynamic Crystallization of a Haplogranitic Melt - Application to Pegmatites

International audienceBoth equilibrium and dynamic crystallization experiments have been performed on a hydrous haplogranitic melt at 200 MPa to model nucleation and growth mechanisms and simulate pegmatite textures. The equilibrium results provide a reference frame (phase assemblages and compositions, liquidus and solidus temperatures and dependence with the melt H2O concentration) to parametrize the kinetic experiments. The seven H2O-saturated dynamic crystallization experiments followed a specific time-temperature path. After a pre-conditioning step at 800 °C, charges were cooled between 3.5 and 7 °C/min to 700, 660 and 600 °C corresponding to ΔT of 20, 60 and 120 °C. Dwell times ranged from 42 up to 1440h. Variable mineral assemblages and textures, and two types of polymineralic assemblages were obtained depending on ΔT and t. For ΔT = 120 °C, crystallization is sequential and includes graphic quartz-alkali feldspar intergrowths characteristic of pegmatite textures. The crystallization sequence reflects nucleation and growth of kinetically-favored metastable phases and solid solution compositions from the supercooled melt. Early alkali feldspars are more K-rich than expected at equilibrium and late albites more Na-rich. The K-rich graphic texture progressively evolves to a Na-rich intergrowth texture. Melts also follow a progressive though limited sodic evolution with time. At the interface of growing alkali feldspars, melts are enriched in SiO2 and depleted in Al2O3, Na2O and, to a lesser extent, K2O. H2O accumulates at the interface reaching concentration levels higher (by 1-2 wt%) than the saturation. Rejection of SiO2 and H2O at the interface controls the effective undercooling in the local melt and promotes rapid textural changes toward larger grain sizes at the front of graphic zones. Textural ripening takes place contemporaneously to sequential crystallization. Growth rates for quartz and alkali feldspar are tightly grouped, between 7.3 x 10-11 and 1.6 x 10-12 m s-1. Textures from the dynamic crystallization experiments closely resemble natural pegmatites but layered aplite units have not been reproduced. Our results confirm and strengthen the importance of liquidus undercooling to generate pegmatite textures

Effects of hypoxia on respiratory physiology of turbot, Scophthalmus maximus.

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Effect of Induced Mild Hypothermia on Acid-Base Balance During Experimental Acute Sepsis in Rats

International audienceThe aim of this study was to determine the effect of induced mild hypothermia (34°C) on acid-base balance in septic rats. Twenty-eight male Sprague-Dawley rats median weight 306 g, range 251–333 g were used. After anesthesia and when the target temperature was reached (normothermia: 38°C or induced mild hypothermia: 34°C), sepsis was induced by cecal ligation and perforation. Measurements of cardiopulmonary parameters and blood samples were performed at T0h (occurring immediately after chirurgical procedures), T2h, T4h (at each temperature), and T6h (at 34°C only). Blood oxygen saturation, heart and respiratory rates, arterial blood pH, carbon dioxide partial pressure, sodium, potassium, chloride and calcium concentrations, hematocrit, blood lactate, tumor necrosis factor-α and interleukin-6 concentrations were measured on anesthetized rats. Other parameters such as bicarbonate concentration, hemoglobin concentration, base excess, and anion gap were estimated from measured parameters. Main results showed that an increase in both cytokines concentrations was observed in septic rats compared with sham rats. This increase was less marked at 34°C compared with 38°C. Moreover, sepsis induction led to a marked metabolic acidosis and hypothermia delayed this acidosis. Induced mild hypothermia delays the evolution of cytokines and metabolic acidosis during experimental sepsis

Effect of Induced Mild Hypothermia on Acid-Base Balance During Experimental Acute Sepsis in Rats

International audienceThe aim of this study was to determine the effect of induced mild hypothermia (34°C) on acid-base balance in septic rats. Twenty-eight male Sprague-Dawley rats median weight 306 g, range 251–333 g were used. After anesthesia and when the target temperature was reached (normothermia: 38°C or induced mild hypothermia: 34°C), sepsis was induced by cecal ligation and perforation. Measurements of cardiopulmonary parameters and blood samples were performed at T0h (occurring immediately after chirurgical procedures), T2h, T4h (at each temperature), and T6h (at 34°C only). Blood oxygen saturation, heart and respiratory rates, arterial blood pH, carbon dioxide partial pressure, sodium, potassium, chloride and calcium concentrations, hematocrit, blood lactate, tumor necrosis factor-α and interleukin-6 concentrations were measured on anesthetized rats. Other parameters such as bicarbonate concentration, hemoglobin concentration, base excess, and anion gap were estimated from measured parameters. Main results showed that an increase in both cytokines concentrations was observed in septic rats compared with sham rats. This increase was less marked at 34°C compared with 38°C. Moreover, sepsis induction led to a marked metabolic acidosis and hypothermia delayed this acidosis. Induced mild hypothermia delays the evolution of cytokines and metabolic acidosis during experimental sepsis

Some Basic Methods in Respiratory Physiology Studies Applied in the Siberian Sturgeon

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Does Induction Time of Mild Hypothermia Influence the Survival Duration of Septic Rats?

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Acid-Base Balance and Ammonia Loading in the Siberian Sturgeon Acipenser baerii, Exposed to High Concentrations of Ammonia

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Consequences of High Levels of Ammonia Exposure on the Gills Epithelium and on the Haematological Characteristics of the Blood of the Siberian Sturgeon, Acipenser baerii

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