Coesite and stishovite in a shocked lunar meteorite, Asuka-881757, and impact events in lunar surface.

Microcrystals of coesite and stishovite were discovered as inclusions in amorphous silica grains in shocked melt pockets of a lunar meteorite Asuka-881757 by micro-Raman spectrometry, scanning electron microscopy, electron back-scatter diffraction, and transmission electron microscopy. These high-pressure polymorphs of SiO(2) in amorphous silica indicate that the meteorite experienced an equilibrium shock-pressure of at least 8-30 GPa. Secondary quartz grains are also observed in separate amorphous silica grains in the meteorite. The estimated age reported by the (39)Ar/(40)Ar chronology indicates that the source basalt of this meteorite was impacted at 3,800 Ma ago, time of lunar cataclysm; i.e., the heavy bombardment in the lunar surface. Observation of coesite and stishovite formed in the lunar breccias suggests that high-pressure impact metamorphism and formation of high-pressure minerals are common phenomena in brecciated lunar surface altered by the heavy meteoritic bombardment.

Effects of water on the alpha-beta transformation kinetics in san carlos olivine

In experiments at 13.5 gigapascals and 1030 degreesC, the growth rate of wadsleyite, which forms from transformation of olivine, was substantially enhanced by the presence of water. Wadsleyite had a low dislocation density and subgrain boundaries in wet runs. Water enhanced the dislocation recovery in wadsleyite and therefore caused inelastic relaxation of the localized pressure drop associated with the transformation, resulting in an increase of the growth rate in wet runs. These results imply that even a small amount of water of 0. 05 weight percent can weaken wadsleyite in the mantle.

Grain Growth Rates of MgSiO3 Perovskite and Periclase Under Lower Mantle Conditions

The grain growth rates of MgSiO3 perovskite and periclase in aggregates have been determined at 25 gigapascals and 1573 to 2173 kelvin. The average grain size (G) was fitted to the rate equation, and the grain growth rates of perovskite and periclase were G10.6 = 1 x 10(-57.4) t exp(-320.8/RT) and G10.8 = 1 x 10(-62.3) t exp(-247.0/RT), respectively, where t is the time, R is the gas constant, and T is the absolute temperature. These growth rates provide insight into the mechanism for grain growth in minerals relevant to the Earth's lower mantle that will ultimately help define the rheology of the lower mantle.

Flotation of diamond in mantle melt at high pressure.

Experiments show that diamond floats in a primitive mantle melt at around 20 gigapascals and 2360 degrees C and in a melt formed by partial melting of the transition zone at about 16 gigapascals and 2270 degrees C. These observations constrain magma densities at high pressure. Diamond precipitated or trapped in a silicate melt at the base of the transition zone or the lower mantle floats and has been accumulating in the transition zone since early in Earth's history. Thus, the transition zone could be a reservoir of diamond.

The Phase Boundary Between agr- and beta-Mg2SiO4 Determined by in Situ X-ray Observation.

The stability of Mg(2)SiO(4), a major constituent in the Earth's mantle, has been investigated experimentally by in situ observation with synchrotron radiation. A cubic-type high-pressure apparatus equipped with sintered diamond anvils has been used over pressures of 11 to 15 gigapascals and temperatures of 800 degrees to 1600 degrees C. The phase stability of alpha-Mg(2)SiO(4) and beta-Mg(2)SiO(4) was determined by taking account of the kinetic behavior of transition. The phase boundary between alpha-Mg(2)SiO(4) and beta-Mg(2)SiO(4) is approximated by the linear expression P = (9.3 +/- 0.1) + (0.0036 +/- 0.0002)T where P is pressure in gigapascals and T is temperature in degrees Celsius.

The process of calcification during development of the rat tracheal cartilage characterized by distribution of alkaline phosphatase activity and immunolocalization of types I and II collagens and glycosaminoglycans of proteoglycans.

The rat tracheal cartilage was shown to calcify during development. The process of calcification was characterized in terms of distribution of alkaline phosphatase (ALP) activity and alterations to immunolocalization of types I and II collagens and glycosaminoglycans of proteoglycans during the development of the tracheal cartilage, in comparison with calcification of the epiphyseal growth plate cartilage. ALP activity was not identified in the tracheal cartilage in the course of calcification, which therefore differed from that in the growth plate. The tracheal cartilage matrix was not resorbed or invaded by type I collagen during calcification. This suggests that no osteogenesis is involved in calcification of the cartilage. Immunoreactivity for type II collagen became weaker in the central region of the tracheal cartilage during development. No net loss of proteoglycans was identified with Alcian blue staining after calcification of the tracheal cartilage. Immunoreactivity for chondroitin 4-sulphate increased in the calcified tracheal cartilage, while reactivity for chondroitin 6-sulphate was weaker in the calcified area than in the surrounding uncalcified region of the tracheal cartilage. The alteration of the extracellular matrices during development may be involved in the calcification of the rat tracheal cartilage.

BMPs induce direct bone formation in ectopic sites independent of the endochondral ossification in vivo.

Bone formation in vivo occurs via two major processes, one of which depends on pre-existing cartilage, and the other does not. Bone morphogenetic proteins (BMPs) have been suggested to induce cartilage formation from non-skeletogenic mesenchymal cell population, which results in osteogenesis through the endochondral sequence. In the present study we examined if BMPs could cause direct bone formation independent of pre-existing cartilage using bovine fibrous collagen membrane (FCM) as a carrier for BMPs. Bovine metatarsal bone was extracted in 4 M guanidine HC1 and BMPs were partially purified through the hydroxyapatite chromatography and the Heparin-Sepharose CL6B chromatography. The carrier was loaded with BMPs and then implanted in Wistar rats subcutaneously. The implants were fixed together with surrounding tissue every week after implantation and processed for von Kossa stain, immunohistochemistry, and electron microscopy. The phenotypes of bone and cartilage were identified histologically and immunohistochemically using antibodies against type I and type II collagen. Cartilage and bone were independently induced by 2 weeks. The bone formed directly on the collagen substrate of FCM without pre-existing cartilage. Calcification occurred in the carrier as well as the cartilage and bone matrix. The present study suggests that the BMPs induce osteogenesis in vivo independent of the endochondral sequence.

Glucose-phosphorylating enzymes of Candida yeasts and their regulation in vivo.

Three glucose-phosphorylating enzymes having different specificities for glucose and fructose were separated from the cell-free extract of Candida tropicalis by means of ammonium sulfate fractionation and chromatography on DEAE-cellulose and Sephadex G-100. Two of them, which phosphorylated fructose 1.5 times faster than glucose, were designated as hexokinase I and II (ATP : D-hexose 6-phosphotransferase, EC 2.7.1.1.), and the other with very low or no fructose-phosphorylating activity, as glucokinase (ATP : D-glucose 6-phosphotransferase, EC 2.7.1.2). Km values for glucose with both hexokinase I and glucokinase were 0.3 mM, and that for fructose with hexokinase I was 2.2 mM. Time-course changes in the levels of these enzymes in C. tropicalis growing on glucose and on n-alkane revealed that hexokinase was induced specifically by the sugars, while glucokinase was a constitutive enzyme. Addition of cycloheximide to the culture medium prevented the increase in the hexose-phosphorylating activity and in the Fru/Glu ratio (the ratio of enzymatic phosphorylation of fructose to that of glucose) in the cells. Although Candida lipolytica also contained hexokinase and glucokinase, both enzymes seemed to be constitutive.