Pyroxenite xenoliths from an alkali trachybasalt in the Glen Innes area,northeastern New South Wales

Pyroxenite xenoliths are relatively common in an alkali trachybasalt in the Glen Innes area in northeastern New South Wales where they coexist with peridotite xenoliths, probably lherzolitic. The pyroxenites vary widely in modal composition. Several pyroxenite xenoliths are characterised by megacrystals of subcalcic clinopyroxene and enstatite, the former comprising a unique group of high pressure pyroxenes in which exsolution of orthopyroxene has proceeded on a megascopic scale. Garnet is absent from all mineral assemblages. Mineralogical and experimental data suggest that the subcalcic clinopyroxene and orthopyroxene megacrystals equilibrated initially at temperatures and pressures of the order of 1350–1450° C and 10–23 kb respectively. The most common xenoliths, namely diopsideorthopyroxene assemblages in which there is evidence of subsolidus annealing, equilibrated at comparable pressures but a significantly lower temperatures (ca. 1000° C). It is suggested that the pyroxenites and associated peridotite xenoliths are samples of essentially unmodified layered upper mantle.     

The February 1986 solar activity: A comparison of GIOTTO,VEGA-1, and IMP-8 solar wind measurements with MHD simulations

Large disturbances in the interplanetary medium were observed by several spacecraft during a period of enhanced solar activity in early February 1986. The locations of six solar flares and the spacecraft considered here encompassed more than 100° of heliolongitude. These flares during the minimum of cycle 21 set the stage for an extensive multi-spacecraft comparison performed with a two-dimensional, magnetohydrodynamic (MHD) numerical experiment. The plasma instruments on the European Space Agency (ESA)'s GIOTTO spacecraft, on its way to encounter Comet Halley in March 1986, made measurements of the solar wind for up to 8 hours per day during February. We compare solar wind measurements from the Johnstone Plasma Analyzer (JPA) experiment on GIOTTO with the MHD simulation of the interplanetary medium throughout these events. Using plasma data obtained by the IMP-8 satellite in addition, it appears that an extended period of high solar wind speed is required as well as the simulated flares to represent the interplanetary medium in this case. We also compare the plasma and magnetometer data from VEGA-1 with the MHD simulation. This comparison tends to support an interpretation that the major solar wind changes at both GIOTTO and VEGA-1 on 8 February, 1986 were due to a shock from a W05° solar flare on 6 February, 1986 (06:25 UT). The numerical experiment is considered, qualitatively, to resemble the observations at the former spacecraft, but it has less success at the latter one.     

Libration dynamics and stability of electrodynamic tethers in satellite deorbit

This paper studies libration dynamics and stability of deorbiting nano-satellites by short and bare electrodynamic tethers. A critical aspect of satellite deorbit by an electrodynamic tether is to maintain the tether aligned with the local vertical and stable while subjected to external perturbations. The dynamics of electrodynamic tether system in deorbit application is divided into the orbital motion of the center of system’s mass and the tether libration motion relative to that center. Major space environmental perturbations including the current-induced electrodynamic force, atmospheric drag, oblateness effect of the Earth, irregularity of geomagnetic field, variable plasma density, solar radiation pressure, and lunisolar gravitational attractions are considered in the dynamic analysis. Quantitative analyses are provided in order to characterize the order of the perturbative torques during the deorbit process. A single index is derived from the libration energy to stabilize the libration motion by regulating the current in the tether through simple on-off switching. Numerical results show that the libration dynamics of an electrodynamic tether has significant impacts on the deorbit process and the electrodynamic tether cannot effectively deorbit satellites without libration stability control. The proposed current regulation strategy is simple and very effective in stabilizing libration motion of an electrodynamic tether.     

http://www.sciencedirect.com/science/article/pii/S1674987111001290

The Three Gorges Dam(TGD) of the Yangtze River.China,is one of the largest irrigation and hydroelectric engineering projects in the world.The effects of huge man-made projects like TGD on fauna and macrophyte are obvious,mainly through changes of water dynamics and flow pattern;however, it is less clear how microorganisms respond to such changes.This research was aimed to examine differences in microbial diversity at different seasons and locations(in front of and behind the TGD).In addition, differences between particle-attached and free-living communities were also examined.The community structures of total and potentially active microorganisms in the water columns behind and in front of the TGD were analyzed with the DNA- and RNA-based 16S rRNA gene phylogenetic approaches over three different seasons.Clone libraries of 16S rRNA genes were prepared after amplification from extracted DNA and.for some samples,after preparing cDNA from extracted rRNA.Differences were observed between sites at different seasons and between free-living and particle-attached communities.Both bacterial and archaeal communities were more diverse in summer than in winter, due to higher nutrient levels and warmer temperature in summer than in winter.Particle-attached microorganisms were more diverse than free-living communities,possibly because of higher nutrient levels and heterogeneous geochemical micro-environments in particles.Spatial variations in bacterial community structure were observed,i.e..the water reservoir behind the TGD(upstream) hosted more diverse bacterial populations than in front of the dam(downstream),because of diverse sources of sediments and waters from upstream to the reservoir.These results have important implications for our understanding of responses of microbial communities to environmental changes in river ecosystems affected by dam construction.     

Comparative analysis of marine paleogene sections and biota from West Siberia and the Arctic Region

The analysis of the main biospheric events that took place in West Siberia and the Arctic region during the Early Paleogene revealed the paleogeographic and paleobiogeographic unity of marine sedimentation basins and close biogeographic relations between their separate parts. Most biotic and abiotic events of the first half of the Paleogene in the Arctic region and West Siberia were synchronous, unidirectional, and interrelated. Shelf settings, sedimentation breaks, and microfaunal assemblages characteristic of these basins during the Paleogene are compared. The comparative analysis primarily concerned events of the Paleocene-Eocene thermal maximum (PETM) and beds with Azolla (aquatic fern). The formation of the Eocene Azolla Beds in the Arctic region and West Siberia was asynchronous, although it proceeded in line with a common scenario related to the development of a system of estuarine-type currents in a sea basin partly isolated from the World Ocean.     

3D Coronal Density Reconstruction and Retrieving the Magnetic Field Structure during Solar Minimum

Measurement of the coronal magnetic field is a crucial ingredient in understanding the nature of solar coronal phenomena at all scales. We employed STEREO/COR1 data obtained during a deep minimum of solar activity in February 2008 (Carrington Rotation CR 2066) to retrieve and analyze the three-dimensional (3D) coronal electron density in the range of heights from 1.5 to 4 R_⊙ using a tomography method. With this, we qualitatively deduced structures of the coronal magnetic field. The 3D electron-density analysis is complemented by the 3D STEREO/EUVI emissivity in the 195 Å band obtained by tomography for the same CR. A global 3D MHD model of the solar corona was used to relate the reconstructed 3D density and emissivity to open/closed magnetic-field structures. We show that the density-maximum locations can serve as an indicator of current-sheet position, while the locations of the density-gradient maximum can be a reliable indicator of coronal-hole boundaries. We find that the magnetic-field configuration during CR 2066 has a tendency to become radially open at heliocentric distances greater than 2.5 R_⊙. We also find that the potential-field model with a fixed source surface is inconsistent with the boundaries between the regions with open and closed magnetic-field structures. This indicates that the assumption of the potential nature of the coronal global magnetic field is not satisfied even during the deep solar minimum. Results of our 3D density reconstruction will help to constrain solar coronal-field models and test the accuracy of the magnetic-field approximations for coronal modeling.