Theoretical investigation of the hydrogenation induced atomic rearrangements in palladium rich intermetallic compounds MPd 3 (M=Mg, In, Tl)

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Soil carbon stock in the tropical rangelands of Australia: Effects of soil type and grazing pressure, and determination of sampling requirement

On-going, high-profile public debate about climate change has focussed attention on how to monitor the soil organic carbon stock (C) of rangelands (savannas). Unfortunately, optimal sampling of the rangelands for baseline C - the critical first step towards efficient monitoring - has received relatively little attention to date. Moreover, in the rangelands of tropical Australia relatively little is known about how C is influenced by the practice of cattle grazing. To address these issues we used linear mixed models to: (i) unravel how grazing pressure (over a 12-year period) and soil type have affected C and the stable carbon isotope ratio of soil organic carbon (δC) (a measure of the relative contributions of C and C vegetation to C); (ii) examine the spatial covariation of C and δC; and, (iii) explore the amount of soil sampling required to adequately determine baseline C. Modelling was done in the context of the material coordinate system for the soil profile, therefore the depths reported, while conventional, are only nominal.Linear mixed models revealed that soil type and grazing pressure interacted to influence C to a depth of 0.3m in the profile. At a depth of 0.5m there was no effect of grazing on C, but the soil type effect on C was significant. Soil type influenced δC to a soil depth of 0.5m but there was no effect of grazing at any depth examined. The linear mixed model also revealed the strong negative correlation of C with δC, particularly to a depth of 0.1m in the soil profile. This suggested that increased C at the study site was associated with increased input of C from C trees and shrubs relative to the C perennial grasses; as the latter form the bulk of the cattle diet, we contend that C sequestration may be negatively correlated with forage production. Our baseline C sampling recommendation for cattle-grazing properties of the tropical rangelands of Australia is to: (i) divide the property into units of apparently uniform soil type and grazing management; (ii) use stratified simple random sampling to spread at least 25 soil sampling locations about each unit, with at least two samples collected per stratum. This will be adequate to accurately estimate baseline mean C to within 20% of the true mean, to a nominal depth of 0.3m in the profile

Water Reservoirs in Small Planetary Bodies: Meteorites, Asteroids, and Comets

Asteroids and comets are the remnants of the swarm of planetesimals from which the planets ultimately formed, and they retain records of processes that operated prior to and during planet formation. They are also likely the sources of most of the water and other volatiles accreted by Earth. In this review, we discuss the nature and probable origins of asteroids and comets based on data from remote observations, in situ measurements by spacecraft, and laboratory analyses of meteorites derived from asteroids. The asteroidal parent bodies of meteorites formed ≤4 Ma after Solar System formation while there was still a gas disk present. It seems increasingly likely that the parent bodies of meteorites spectroscopically linked with the E-, S-, M- and V-type asteroids formed sunward of Jupiter's orbit, while those associated with C- and, possibly, D-type asteroids formed further out, beyond Jupiter but probably not beyond Saturn's orbit. Comets formed further from the Sun than any of the meteorite parent bodies, and retain much higher abundances of interstellar material. CI and CM group meteorites are probably related to the most common C-type asteroids, and based on isotopic evidence they, rather than comets, are the most likely sources of the H and N accreted by the terrestrial planets. However, comets may have been major sources of the noble gases accreted by Earth and Venus. Possible constraints that these observations can place on models of giant planet formation and migration are explored