Effect of the contraction of Zn-O bonds on X-ray emission spectra

Physics and Chemistry of Minerals - The X-ray emission spectra were measured for tetrahedrally coordinated Zn ion in several synthetic compounds. Intensity ratios of L β and L α spectral...     

Estimation of electron temperature by VLF waves propagating in directions near the resonance cone

A ray tracing computer program for non-ducted whistler mode waves in a warm plasma in the magnetosphere is developed, where electron temperature effects are taken into account. The refractive index is calculated from the warm-plasma approximation and is used in the ray tracing after its accuracy has been checked by comparison with the hot-plasma solution without approximation. The ray paths do not depend appreciably on electron temperature. However, there are regions where the waves are heavily damped by Landau damping. By paying attention to this damping region, the electron temperature can be estimated from a satellite observation of the Doppler shift and damping of a ground-based VLF signal.     

Nanophase magnetite in matrix of anomalous EL3 chondrite Northwest Africa (NWA) 8785

NWA 8785 is a remarkable EL3 chondrite with a high abundance (~34 vol%) of an Fe-rich matrix. This is the highest matrix abundance known among enstatite chondrites (ECs) and more similar to the matrix abundances in some carbonaceous and Rumuruti chondrites. X-ray diffraction and TEM data indicate that the fine-grained portion of the NWA 8785 matrix consists of nanoscale magnetite mixed with a noncrystalline silicate material and submicron-sized enstatite and plagioclase grains. This is the first report of magnetite nanoparticles in an EL3. The Si content of the metal (0.7 wt%), presence of ferroan alabandite, and its O isotopic composition indicate NWA 8785 is EL3-related. Having more abundant matrix than in other ECs, and that the matrix is rich in magnetite nanoparticles, which are not present in any other EC, suggest classification as an EL3 anomalous. Although we cannot completely exclude any of the mechanisms or environments for formation of the magnetite, we find a secondary origin to be the most compelling. We suggest that the magnetite formed due to hydrothermal activity in the meteorite parent body. Although ECs are relatively dry and likely formed within the nebular snow line, ices may have drifted inward from just beyond the snow line to the region where the EL chondrites were accreting, or more likely the snow line migrated inward during the early evolution of the solar system. This may have resulted in the condensation of ices and provided an ice-rich region for accretion of the EL3 parent body. Thus, the EL3 parent body may have had hydrothermal activity and if Earth formed near the EC accretion zone, similar bodies may have contributed to the Earth's water supply. NWA 8785 greatly extends the range of known characteristics of ECs and EC parent body processes.     

Agricultural risk management policies under climate uncertainty

Climate change is forecasted to increase the variability of weather conditions and the frequency of extreme events. Due to potential adverse impacts on crop yields it will have implications for demand of agricultural risk management instruments and farmers’ adaptation strategies. Evidence on climate change impacts on crop yield variability and estimates of production risk from farm surveys in Australia, Canada and Spain, are used to analyse the policy choice between three different types of insurance (individual, area-yield and weather index) and ex post payments. The results are found to be subject to strong uncertainties and depend on the risk profile of different farmers and locations; the paper provides several insights on how to analyse these complexities. In general, area yield performs best more often across our countries and scenarios, in particular for the baseline and marginal climate change (without increases in extreme events). However, area yield can be very expensive if farmers have limited information on how climate change affects yields (misalignment in expectations), and particularly so under extreme climate change scenarios. In these more challenging cases, ex post payments perform well to increase low incomes when the risk is systemic like in Australia; Weather index performs well to reduce the welfare costs of risks when the correlation between yields and index is increased by the extreme events. The paper also analyses the robustness of different instruments in the face of limited knowledge of the probabilities of different climate change scenarios; highlighting that this added layer of uncertainty could be overcome to provide sound policy advice under uncertainties introduced by climate change. The role of providing information to farmers on impacts of climate change emerges as a crucial result of this paper as indicated by the significantly higher budgetary expenditures occurring across all instruments when farmers’ expectations are misaligned relative to actual impacts of climate change.     

Demonstration of crystalline forsterite grain formation due to coalescence growth of Mg and SiO smoke particles

Abstract— Experimental studies of coalescence between Mg grains and SiO grains in smoke reveal the direct production of crystalline forsterite grains. The present results also show that different materials can be produced by grain‐grain collisions, which have been considered one of the models of grain formation in the interstellar medium. The fundamentals of coalescence growth in smoke, which have been developed in our series of experiments, are presented in this paper. Mg₂Si polyhedral grains were obtained in a Mg grain‐rich atmosphere. Mg₂SiO₄ polyhedral grains were obtained in a SiO grain‐rich atmosphere. The IR spectra of the resultant grains showed the characteristics of crystalline forsterite.     

A survey of emission-line stars in the perseus dark cloud

The results of an objective prism survey of H_α emission-line stars in a 5° × 5° region around NGC 1333 are presented. We have identified 25 stars as having H_α -line in emission, of which 11 have been discovered in the Lick H_α-survey. The limiting magnitude of the present survey is about 16.7 mag. in blue. These are suspected to be mainly T Tauri stars. Based on the UGR(Kiso) multiexposure plates, we have found that, on the [(G - U), (R - G)]-diagram, the domain of H_α emission line stars is fairly well delineated and separate from other stars. Some interesting features in their space distribution are also discussed briefly.