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111.
M. TRIBAUDINO A. M. FIORETTI F. MARTIGNAGO G. MOLIN 《Meteoritics & planetary science》1997,32(5):671-678
Abstract— Frontier Mountain (FRO) 90054, from Antarctica, is a rare clino- and orthopyroxene-bearing ureilite with a coarse equigranular oriented texture (grains up to 3 mm); it is classified as a low-shock Ca-rich type. The crystal chemistry of its clinopyroxene (Wo39.3En54.6Fs6.1), orthopyroxene (En84 2Fs11Wo4.8) and olivine (Fa12.6Fo86.9) was investigated by single-crystal x-ray structural refinements and transmission electron microscope (TEM) observations to obtain data on the evolutionary history of the parent body. The M1 octahedron and unit cell volumes of the orthopyroxene and clinopyroxene are consistent with low-pressure crystallization. The closure temperatures for intracrystalline Mg-Fe2+ ordering yielded values of 674 °C and 804 °C for opx and 596 °C for cpx, which indicate high-temperature equilibration and fast cooling. Trasmission electron microscope investigations were performed on clinopyroxene, orthopyroxene and pigeonite. The (100) twin lamellae in the clinopyroxene and intergrowth of clino- and orthoenstatite lamellae in orthopyroxene most probably originated by deformation. Exsolution was not observed in any of the phases, which suggests rapid cooling. Analysis by TEM also revealed interstitial Na-rich glass and pigeonite with sharp h + k odd reflections and rare stacking faults parallel to (100). Textural and crystal chemical data, obtained by TEM, indicated rapid cooling that was probably due to fast radiative heat loss as a result of the disintegration of the parent body into small fragments, which subsequently reassembled into a larger body. One or more collisional events caused fine-scale stacking faults and partial melting. 相似文献
112.
The Ratcliff Site in southwestern Virginia lies in a small second-order stream valley filled with approximately 3.5 m of organic-rich deposits that contain bones of mammoth, mastodon, deer (or antelope), logs, and plant macrofossils. Radiocarbon analyses indicate the age of the organic-rich sediment ranges from > 44,000 to 29,100 14C yr BP, a time period with no fossil remains reported in this region of the Appalachians. Analyses of field observations, textural data, organic carbon content, and plant macrofossils indicate that the organic-rich sediments contain interbedded standing-water and debris-flow deposits. Up to 6 m of oxidized debris-flow sediments bury the organic-rich sediments. The presence of Rubus parviflorus (Thimble Berry) throughout the deposit indicates the site had a boreal environment from > 44,000 to 29,100 14C yr BP. Plant macrofossil evidence indicates the uplands had stands of spruce/jack-pine forests while the valley contained ponds and associated wetlands. Three debris flows occurred at the site between approximately 38,000 and 29,000 14C yr BP, suggesting a recurrence interval for major storms of approximately 3000 yr, even though the apparent stability of the boreal environment implies a climate not conducive to catastrophic rainstorms. This conflicting combination of features suggests that during the middle Wisconsinan this area experienced generally cool climates, dominated by polar air masses, but was punctuated by relatively brief warm periods marked by incursions of tropical air masses. 相似文献
113.
S. Nazzareni P. Comodi L. Bindi G. Garbarino A. Bobrov 《Physics and Chemistry of Minerals》2012,39(7):553-559
We investigated the high-pressure behaviour of Fe3+-bearing hydrous phase-X, (K1.307Na0.015)(Mg1.504Fe 0.373 3+ Al0.053Ti 0.004 4+ )Si2O7H0.36, up to 34?GPa at room temperature by synchrotron X-ray powder diffraction. The lattice parameters behave anisotropically, with the [001] direction stiffer than [100]. In the 10?4 to 22?GPa pressure range, the axial bulk moduli are K 0a ?=?112(3) GPa and K′?=?4, and K 0c ?=?158(2) GPa and K′?=?4, and the anisotropy of the lattice parameters is β0c :β0a ?=?0.71:1. The cell volumes are fitted by a second-order Birch–Murnaghan equation of state giving a bulk modulus of K 0?=?127(1) GPa and K′?=?4 in the same pressure range. After 22?GPa, a discontinuity in volume and lattice parameters can be recognized. Sample did not become amorphous up to 34?GPa. The coupled substitution K?+?Mg?=?[]?+?Fe3+ has only a limited influence on the bulk modulus and structural stability of phase-X. 相似文献
114.
The results of field studies are used to establish the factors that control the interaction between surface water and unconfined groundwater in the region, to study the process of their interaction, and to propose empirical relationships for transient flow. Combined model calculations were also made, and their results and other formulas were compared with the results of field studies conducted by other researchers in large river valleys under dry and moderate climate conditions. 相似文献
115.
A statistically relevant correlation between the reaction rate coefficient, k
OH, for the OH radical reaction with 161 organic compounds in the gas phase at 300 K, and the corresponding vertical ionisation energies E
i,v, reveals two classes of compounds: aromatics where –log(k
OH/cm3s-1)3/2E
i,v(eV)–2 and aliphatics where –log(k
OH/cm3s-1)4/5E
i,v(eV)+3. The prediction of the rate coefficient, k
OH, for the reaction of OH with organic molecules from the above equations has a probability of about 90%. Assuming a global diurnal mean of the OH radical concentration of 5×105 cm3, the upper limit of the tropospheric half-life of organic compounds and their persistence can be estimated. 相似文献
116.
As the population of California grows, the discharge of domestic and industrial waste water and power-plant cooling water
into coastal waters continuously increases. About 0.75 × 106 m3 of industrial waste water, 3.75 × 106 m3 of domestic waste water, and 26.5 × 106 m3 of thermal effluent are discharged daily into California's nearshore waters. These waters do not have an infinite capacity
to break down and disperse the pollutants. Waste water discharged near shore may remain there for considerable time and have
a significant effect on water quality and marine life.
The low population and wet climate of the northern coastal region have led to small discharges of waste water but very large
inputs of fresh water to the ocean. Southward along the Pacific Coast the climate becomes more arid, and population increases.
This combination leads to a large excess of waste-water over fresh-water discharge. Many individual waste-water discharges
exceed the average daily discharge of most of the rivers which enter the coastal waters. 相似文献
117.
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119.
120.
I. S. Veselovsky K. Mursula N. G. Ptitsyna M. I. Tyasto O. S. Yakovchouk 《Geomagnetism and Aeronomy》2009,49(2):163-168
Based on an analysis of the available archived data from the Russian network of geomagnetic stations, it has been indicated that the known event of August–September 1859 was the first and the greatest event in the series of the recurrent geomagnetic storms. Similar series were repeatedly observed in the next years. These series are caused by the processes on the Sun and in the heliosphere related to the superposition of the solar wind flows. The sporadic and regular components in joint activity of the complex, including active regions and coronal holes on the rotating Sun, play the role of the Bartels M regions responsible for initiation and development of geomagnetic storms. Neither coronal holes nor active regions can separately explain observations. During interpretation, active regions and coronal holes should be considered as a unified complex. 相似文献