Do SiC grains in Orgueil differ from those in Murchison?

Studies of individual presolar SiC grains have shown that most are enriched in Si-29, Si-30, and C-13, and depleted in N-15, compared to solar-system abundances and that many have large excesses of Mg-26, most plausibly from in situ decay of Al-26. Stone et al., observed that Si from a family of platy SiC grains define a linear array on a 3-isotope plot that does not pass through normal solar-system Si. In contrast, Si-isotope data from over 100 3-4 micron SiC grains from Murchison from an elongate ellipse enclosing the Stone et al. linear array but also including 'normal' solar-system Si. To investigate whether this difference in Si isotopes indicates different populations of SiC in the two meteorites and to improve the characterization of Orgueil SiC, we used the PANURGE ion microprobe to measure Si, C, N, and Mg isotopes and Al and Na concentrations in a suite of 2-5 micron SiC grains from a new sample of Orgueil

Carbon and nitrogen fixation and metabolite exchange in and between individual cells of Anabaena oscillarioides

Filamentous nitrogen fixing cyanobacteria are key players in global nutrient cycling, but the relationship between CO"2- and N"2-fixation and intercellular exchange of these elements remains poorly understood in many genera. Using high-resolution nanometer-scale secondary ion mass spectrometry (NanoSIMS) in conjunction with enriched H13CO"3- and 15N"2 incubations of Anabaena oscillarioides, we imaged the cellular distributions of C, N and P and 13C and 15N enrichments at multiple time points during a diurnal cycle as proxies for C and N assimilation. The temporal and spatial distributions of the newly fixed C and N were highly heterogeneous at both the intra- and inter-cellular scale, and indicative of regions performing active assimilation and biosynthesis. Subcellular components such as the neck region of heterocycts, cell division septae and putative cyanophycin granules were clearly identifiable by their elemental composition. Newly fixed nitrogen was rapidly exported from heterocysts and was evenly allocated among vegetative cells, with the exception of the most remote vegetative cells between heterocysts, which were N limited based on lower 15N enrichment. Preexisting functional heterocysts had the lowest levels of 13C and 15N enrichment, while heterocysts that were inferred to have differentiated during the experiment had higher levels of enrichment. This innovative approach, combining stable isotope labeling and NanoSIMS elemental and isotopic imaging, allows characterization of cellular development (division, heterocyst differentiation), changes in individual cell composition and cellular roles in metabolite exchange

Association between mitochondrial function measured by 31P Magnetic Resonance Spectroscopy and physical performance in older people with functional impairment

Abstract Background Mitochondrial dysfunction is a potential therapeutic target to improve skeletal muscle function, but the contribution of mitochondrial dysfunction to impaired skeletal muscle performance in older people remains unclear. The aim of this analysis was to test the association between measures of skeletal muscle mitochondrial function and physical performance in older people. Methods We analysed data from the Allopurinol in Functional Impairment trial. Participants aged 65 and over, who were unable to walk 400 m in 6 min, underwent 31P magnetic resonance spectroscopy of the calf after exercise at baseline and at 20 weeks follow up. The phosphocreatine recovery half‐life time (t1/2) was derived as a measure of mitochondrial function. Participants undertook the 6‐min walk test and the Short Physical Performance Battery. Muscle mass measured using the Akern 101 bio‐impedance analysis system. Bivariate correlations and multivariable regression analyses were conducted to determine associations between t1/2 and baseline factors. Results One hundred and seventeen participants underwent baseline 31P magnetic resonance spectroscopy, mean age 80.4 years (SD 6.0); 56 (48%) were female. Mean 6‐min walk was 291 m (SD 80), mean SPPB score was 8.4 (SD 1.9); t1/2 correlated significantly with Short Physical Performance Battery score (r = 0.22, P = 0.02) but not with 6‐min walk distance (r = 0.10, P = 0.29). In multivariable linear regression, muscle mass and total body weight, but not t1/2, were independently associated with Short Physical Performance Battery score and with 6‐min walk distance. Change in t1/2 was not significantly associated with change in Short Physical Performance Battery score (r = 0.03, P = 0.79) or with change in 6‐min walk distance (r = −0.11, P = 0.28). Conclusions Muscle mass, but not phosphocreatine recovery time, was consistently associated with Short Physical Performance Battery score and 6‐min walk distance in older people with functional impairment

Subsurface structure in polished fused silica and diamond turned single crystal silicon

The surface and near surface structure of glass and other optical materials is greatly influenced by the nature of the processes used to generate that surface. In high quality optics, the effects of process changes are often subtle and cannot be seen with conventional metrology. The presence of process induced damage in the near surface region is felt in a number of ways. Damage thresholds for optics subjected to high fluences are a particular problem in UV or high-powered laser systems. In high quality glass, the chemical and material composition of the outermost layer is influenced principally by the grinding, lapping and polishing processes used in fabrication. Performance in high fluence applications is often dominated by these process-induced inhomogeneities in the first few hundred nanometers of material. Each succeeding step in a process is designed to remove the damage from the previous operation. However, any force against the surface, no matter how slight will leave evidence of damage. Fabrication processes invariably create dislocations, cracks and plastic deformation between 100 nm and 500 nm below the surface. In glass polishing, the first 100 nm is comprised of material redeposited from the polishing solution. This redeposition layer is responsible for the extremely smooth surfaces that can be generated on glass. Unfortunately, this layer also conceals many flaws present in the deeper surface regions

Extracellular Proteins Limit the Dispersal of BiogenicNanoparticles

High spatial-resolution secondaryion microprobespectrometry, synchrotron radiation Fourier-transform infraredspectroscopy and polyacrylamide gel analysis demonstrate the intimateassociation of proteins with spheroidal aggregates of biogenic zincsulfide nanocrystals, an example of extracellular biomineralization.Experiments involving synthetic ZnS nanoparticles and representativeamino acids indicate a driving role for cysteine in rapid nanoparticleaggregation. These findings suggest that microbially-derivedextracellular proteins can limit dispersal of nanoparticulatemetal-bearing phases, such as the mineral products of bioremediation,that may otherwise be transported away from their source by subsurfacefluid flow

Evolution of oxygen isotopic composition in the inner solar nebula

Changes in the chemical and isotopic composition of the solar nebula with time are reflected in the properties of different constituents that are preserved in chondritic meteorites. CR carbonaceous chondrites are among the most primitive of all chondrite types and must have preserved solar nebula records largely unchanged. We have analyzed the oxygen and magnesium isotopes in a range of the CR constituents of different formation temperatures and ages, including refractory inclusions and chondrules of various types. The results provide new constraints on the time variation of the oxygen isotopic composition of the inner (<5 AU) solar nebula - the region where refractory inclusions and chondrules most likely formed. A chronology based on the decay of short-lived 26Al (t1/2 ~ 0.73 Ma) indicates that the inner solar nebula gas was 16O-rich when refractory inclusions formed, but less than 0.8 Ma later, gas in the inner solar nebula became 16O-poor and this state persisted at least until CR chondrules formed ~1-2 Myr later. We suggest that the inner solar nebula became 16O-poor because meter-size icy bodies, which were enriched in 17,18O due to isotopic self-shielding during the ultraviolet photo dissociation of CO in the protosolar molecular cloud or protoplanetary disk, agglomerated outside the snowline, drifted rapidly towards the Sun, and evaporated at the snowline. This led to significant enrichment in 16O-depleted water, which then spread through the inner solar system. Astronomical studies of the spatial and/or temporal variations of water abundance in protoplanetary disks may clarify these processes.Comment: 27 pages, 5 figure

Geochemistry, mineralogy and geology of the Jason Pb-Zn deposits

Three separate stratiform Pb-Zn deposits occur on the Jason property in the Macmillan Pass area of the Yukon, Canada. The deposits are contained within chert conglomerates and finer grained clastic rocks of Middle to Late Devonian age. The deposits are on the eastern margin of the Cambro-Ordovician Selwyn basin and are associated with a fault-bounded, second or third-order subbasin, referred to as the MacPass graben. Three different facies of mineralization and associated sedimentation have been defined on the basis of field relationships, drill core descriptions and correlations, and detailed petrography, Facies A comprises massive to thick-bedded galena and sphalerite with abundant pyrrhotite and pyrite. This facies is extensively crosscut by galena-bearing quartz siderite and quartz ankerite veins and has the highest combined Pb-Zn-Ag concentrations. Facies A is proximal to the hydrothermal source represented by the veins. Facies B has a mineralogic assemblage and textures common to facies A but is considerably thinner. Abundant soft sediment deformation features indicate facies B formed from slumping of unstable accumulations of material from facies A. Facies C contains well-bedded sphalerite

Isotopic studies of Mg, Fe, Mo, Ru and W in Fremdlinge from Allende refractory inclusions

The isotopic abundances of Mg, Fe, Mo, Ru and W in Fremdlinge and a refractory metal nugget in coarse-grained, Ca-Al-rich inclusions from the Allende meteorite have been determined using the PANURGE ion microprobe. These data represent the first measurement of the isotopic composition of Fremdlinge. No evidence for large, non-mass-dependent deviations (≳1%) from normal solar isotopic abundances was found for any of the elements measured. The only hint, of a nonlinear isotopic anomaly is for Mo in Fremdling 1 of Allende inclusion 5171; the measured ^(100)Mo/^(98)Mo ratio lies slightly more than two standard deviations above the value measured in standards. Isotopic variations due to mass-dependent fractionation are suggested for Mo in two Fremdlinge, Zelda of Egg 6 and Fremdling 1 of 5171, and for Ru in a refractory metal nugget in the FUN inclusion Cl. Mo is enriched in the lighter isotopes by ~ 4‰/amu and ~ 9‰/amu, respectively, while Ru is enriched in the heavier isotopes by ~ 4‰/amu. Despite their unusual mineralogy and extreme enrichment in refractory siderophile elements, Fremdlinge do not contain an enhanced component from a single nucleosynthetic source, but appear to contain the normal solar system mixture of є-, s-, and r-process material. While the possibility that some Fremdlinge may have formed under presolar conditions cannot be excluded, we believe that the chemical, petrologic and isotopic data are most plausibly interpreted in terms of the origin of Fremdlinge within the solar nebula