1,721,036 research outputs found
See one. Do one. Teach one. A perfect paradigm for education and training in neuroendoscopy.
No full textThe redox boundaries of earth's interior
No full textThe interior of the Earth is an important reservoir for elements that are chemically bound in minerals, melts, and gases. Analyses of the proportions of redox-sensitive elements in ancient and contemporary natural rocks provide information on the temporal redox evolution of our planet. Natural inclusions trapped in diamonds, xenoliths, and erupted magmas provide unique windows into the redox conditions of the deep Earth, and reveal evidence for heterogeneities in the mantle's oxidation state. By examining the natural rock record, we assess how redox boundaries in the deep Earth have controlled elemental cycling and what effects these boundaries have had on the temporal and chemical evolution of oxygen fugacity in the Earth's interior and atmosphere
Partition coefficient of phosphorus between liquid metal and silicate melt with implications for the Martian magma ocean
No full textPhosphorus in Martian mantle is believed to be five to ten times more abundant than in Earth's mantle, and the distribution of this essential ingredient for life between different deep reservoirs is critical for understanding the habitability of the red planet. In this study, we investigated the behavior of phosphorus in a Martian magma ocean scenario, and measured the partition coefficient of phosphorus (DP) between liquid metal and silicate melt within the pressure range of 3–8 GPa, temperatures between 1973 and 2173 K and oxygen fugacity ranging from −1.5 to ~ −2.5 as normalized to the iron-wüstite oxygen buffer. Our results show DP increasing with pressure but decreasing with temperature. A decrease of oxygen fugacity has a negative effect on DP. The moderately siderophile character of phosphorus indicates that the Martian core might be an important reservoir of phosphorous. Based on our experimental results and phosphorus abundance in Martian mantle and bulk Mars, a minimum pressure of 5.8–10.4 GPa is estimated at the base of Martian magma ocean or during the impact melting if a contribution from the late accretion scenario is taken into account. The shallow Martian magma ocean would avail the preservation of volatiles after the rapid solidification of the planet
Effect of age on Pine wood microstructure studied by micro-MRI and diffusion-NMR
No full textWood is a natural complex material widely used from men in the past to create artworks. One of its main anatomical elements is the annual ring that varies according to the species, the weather conditions under which the tree has grown and to possible adversities. To observe the anatomy of waterlogged archaeological wood could be complicated because of its degradation. However, knowing the state of conservation is very important for the future restoration. In this work a non-destructive approach based on the combined use of MRI and diffusion on the modern and ancient pine wood is presented. Micro-MR images allow to observe the diagnostic features. The molecular NMR diffusion analysis, with the estimation of the pores diameter and the tortuosity, provide important information about the effect of age on the wood microstructure. At the end of the analysis the unaltered sample can be repositioned in its original location on the artwork
The oxidation state of spinel-peridotites from the Hyblean plateau and the modeled composition of coexisting C-O-H fluids
No full textCan quasicrystals survive in planetary collisions?
Full text linkWe investigated the compressional behavior of i-AlCuFe quasicrystal using diamond anvil cell under quasi-hydrostatic conditions by in situ angle-dispersive X-ray powder diffraction measurements (in both compression and decompression) up to 76 GPa at ambient temperature using neon as pressure medium. These data were compared with those collected up to 104 GPa using KCl as pressure medium available in literature. In general, both sets of data indicate that individual d-spacing shows a continuous decrease with pressure with no drastic changes associated to structural phase transformations or amorphization. The d/d0, where d0 is the d-spacing at ambient pressure, showed a general isotropic compression behavior. The zero-pressure bulk modulus and its pressure derivative were calculated fitting the volume data to both the Murnaghan- and Birch-Murnaghan equation of state models. Results from this study extend our knowledge on the stability of icosahedrite at very high pressure and reinforce the evidence that natural quasicrystals formed during a shock event in asteroidal collisions and survived for eons in the history of the Solar System. [Figure not available: see fulltext.
Magnification of growth hormone-secreting tumor cells: could electron microscopy be a new paradigm for outcome in acromegaly?
No full textCarbon concentration increases with depth of melting in Earth’s upper mantle
No full textCarbon in the upper mantle controls incipient melting of carbonated peridotite and so acts as a critical driver of plate tectonics. The carbon-rich melts that form control the rate of volatile outflux from the Earth’s interior, contributing to climate evolution over geological times. However, attempts to constrain the carbon concentrations of the mantle source beneath oceanic islands and continental rifts is complicated by pre-eruptive volatile loss from magmas. Here, we compile literature data on magmatic gases, as a surface expression of the pre-eruptive volatile loss, from 12 oceanic island and continental rift volcanoes. We find that the levels of carbon enrichment in magmatic gases correlate with the trace element signatures of the corresponding volcanic rocks, implying a mantle source control. We use this global association to estimate that the mean carbon concentration in the upper mantle, down to 200 km depth, is approximately 350 ppm (range 117–669 ppm). We interpret carbon mantle heterogeneities to reflect variable extents of mantle metasomatism from carbonated silicate melts. Finally, we find that the extent of carbon enrichment in the upper mantle positively correlates with the depth at which melting starts. Our results imply a major role of carbon in driving melt formation in the upper mantle
A SYSTEM TO STUDY THE STABILITY OF THE WIRES OF MULTIWIRE PROPORTIONAL CHAMBERS EXPOSED TO A 10-G TIME VARIABLE FORCE-FIELD
No full textWe report the results of a system to test the behavior of the wires of multiwire proportional chambers (MWPC) exposed for 10 min to a uniform force field of about 10 G strength and variable in time in the frequency range 0-2000 Hz. This acceleration will be present when the chambers, mounted inside a cosmic ray spectrometer, are launched by the Space Shuttle towards the NASA Space Station "FREEDOM." We have reproduced these conditions in the laboratory by an electronic device and we have found that, after repeated cycles of this treatment, the wire performance remained unchanged. This system can also be used to control the tension of the wires of a MWPC during its normal testing procedure
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