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81.
The finest open fractures (ultramicrofractures) were found from the study of surface density of open fractures in the rocks
from the super-deep Uralian borehole SG-4. The high-resolution method of the registration of open fractures in the rocks is
described. The typical structures of systems formed by open fractures are shown and their genesis is proposed. 相似文献
82.
Edward Olsen Andrew Davis Roy S. Clarke Ludolf Schultz Hartwig W. Weber Robert Clayton Toshiko Mayeda Eugene Jarosewich Paul Sylvester Lawrence Grossman Ming-Sheng Wang Michael E. Lipschutz Ian M. Steele James Schwade 《Meteoritics & planetary science》1994,29(2):200-213
Abstract— Watson, which was found in 1972 in South Australia, contains the largest single silicate rock mass seen in any known iron meteorite. A comprehensive study has been completed on this unusual meteorite: petrography, metallography, analyses of the silicate inclusion (whole rock chemical analysis, INAA, RNAA, noble gases, and oxygen isotope analysis) and mineral compositions (by electron microprobe and ion microprobe). The whole rock has a composition of an H-chondrite minus the normal H-group metal and troilite content. The oxygen isotope composition is that of the silicates in the HE iron meteorites and lies along an oxygen isotope fractionation line with the H-group chondrites. Trace elements in the metal confirm Watson is a new HE iron. Whole rock Watson silicate shows an enrichment in K and P (each ~2X H-chondrites). The silicate inclusion has a highly equilibrated igneous (peridotite-like) texture with olivine largely poikilitic within low-Ca pyroxene: olivine (Fa20), opx (Fs17Wo3), capx (Fs9Wo41) (with very fine exsolution lamellae), antiperthite feldspar (An1–Or5) with <1 μm exsolution lamellae (An1–3Or>40), shocked feldspar with altered stoichiometry, minor whitlockite (also a poorly characterized interstitial phosphate-rich phase) and chromite, and only traces of metal and troilite. The individual silicate minerals have normal chondritic REE patterns, but whitlockite has a remarkable REE pattern. It is very enriched in light REE (La is 720X C1, and Lu is 90X C1, as opposed to usual chonditic values of ~300X and 100–150X, respectively) with a negative Eu anomaly. The enrichment of whole rock K is expressed both in an unusually high mean modal Or content of the feldspar, Or13, and in the presence of antiperthite. Whole rock trace element data for the silicate mass support the petrography. Watson silicate was an H-chondrite engulfed by metal and melted at > 1550 °C. A flat refractory lithophile and flat REE pattern (at ~1x average H-chondrites) indicate that melting took place in a relatively closed system. Immiscible metal and sulfide were occluded into the surrounding metal host. Below 1100 °C, the average cooling rate is estimated to have been ~1000 °C/Ma; Widmanstätten structure formed, any igneous zoning in the silicates was equilibrated, and feldspar and pyroxene exsolution took place. Cooling to below 300 °C was completed by 3.5 Ga B. P. At 8 Ma, a shock event took place causing some severe metal deformation and forming local melt pockets of schreibersite/metal. This event likely caused the release of Watson into interplanetary space. The time of this event, 8Ma, corresponds to the peak frequency of exposure ages of the H-chondrites. This further confirms the link between HE irons and the H-chondrites, a relationship already indicated by their common oxygen isotope source. Watson metal structures are very similar to those in Kodaikanal. Watson, Kodaikanal and Netschaëvo form the young group of HE meteorites (ages 3.7 ± 0.2 Ga). They appear to represent steps in a chain of events that must have taken place repeatedly on the HE parent body or bodies from which they came: chondrite engulfed in metal (Netschaëvo); chondrite melted within metal (Watson); and finally melted silicate undergoing strong fractionation with the fractionated material emplaced as globules within metal (Kodaikanal). Watson fills an important gap in understanding the sequence of events that took place in the evolution of the IIE-H parent body(ies). This association of H-chondrite with HE metal suggests a surface, or near surface process-a suggestion made by several other researchers. 相似文献
83.
Glenn J. MacPherson Eugene Jarosewich Peter Lowenstein 《Meteoritics & planetary science》1993,28(1):138-142
Abstract— Magombedze is a light-dark structured H-chondrite breccia that fell in Zimbabwe on 1990 July 2 at 15:30 GMT. White clasts are moderately shocked and have equilibrated mafic silicates (pyroxene Fs16–18, olivine Fa18–19) together with clear optically-recognizable plagioclase of variable composition (An9–13 found); chondrules are distinct but contain no trace of preserved glass. The darker surrounding material contains a higher proportion of fine-grained metal and sulfide than the white clasts, and many of its constituent grains show little evidence of shock. Mafic silicates in the dark lithology are distinctly less-equilibrated (pyroxene Fs5–21, olivine Fa11–20) than those in the white clasts, and many chondrules preserve brown devitrified glass; some metamorphic plagioclase of variable composition (An11–22, found) is present. Some monoclinic pyroxene occurs in both fractions, but it is relatively common in the dark fraction. The white clasts are classified as H5, and the enclosing dark material is H3–5. 相似文献
84.
85.
Coupled hydrological and atmospheric modeling is an efficient method for snowmelt runoff forecast in large basins. We use short-range precipitation forecasts of mesoscale atmospheric Weather Research and Forecasting(WRF) model combining them with ground-based and satellite observations for modeling snow accumulation and snowmelt processes in the Votkinsk reservoir basin(184,319 km2). The method is tested during three winter seasons(2012–2015). The MODIS-based vegetation map and leaf area index data are used to calculate the snowmelt intensity and snow evaporation in the studied basin. The GIS-based snow accumulation and snowmelt modeling provides a reliable and highly detailed spatial distribution for snow water equivalent(SWE) and snow-covered areas(SCA). The modelling results are validated by comparing actual and estimated SWE and SCA data. The actual SCA results are derived from MODIS satellite data. The algorithm for assessing the SCA by MODIS data(ATBD-MOD 10) has been adapted to a forest zone. In general, the proposed method provides satisfactory results for maximum SWE calculations. The calculation accuracy is slightly degraded during snowmelt periods. The SCA data is simulated with a higher reliability than the SWE data. The differences between the simulated and actual SWE may be explained by the overestimation of the WRF-simulated total precipitation and the unrepresentativeness of the SWE measurements(snow survey). 相似文献
86.
Force-directed layout of origin-destination flow maps 总被引:1,自引:0,他引:1
Bernhard Jenny Daniel M. Stephen Ian Muehlenhaus Brooke E. Marston Ritesh Sharma Eugene Zhang 《International journal of geographical information science》2017,31(8):1521-1540
This paper introduces a force-directed layout method for creating origin-destination flow maps. Design principles derived from manual cartography and automated graph drawing to increase readability of flow maps and graph layouts are taken into account. The origin-destination flow maps produced with our algorithm show flows with quadratic Bézier curves that reduce flow-on-flow and flow-on-node overlaps, and avoid sharp or irregular bends in flow lines. A survey of expert cartographers found that flow maps created with our automated method are similar in quality to manually produced flow maps. 相似文献
87.
88.
Patterns in coastal wetland loss in the northern Gulf of Mexico were examined using aerial imagery from 1955–56 and 1978. Five qualitative types of wetland changes are evident: (1) spoil bank-parallel pond formation, (2) pond formation with apparent random distribution for the smallest ponds, but very clumped distribution for larger ponds, (3) semi- or complete impoundment resulting in open water formation, (4) cutting off of stream channels upstream of where a spoil bank crosses a natural channel, and (5) erosion at the land-water interface. Only ponds <20 ha formed and disappeared in the interval, and it is clear that wetland breakup, not erosion at the pond-lake edge, is the dominant form of wetland-to-open water conversion. Canals and their spoil banks are spatially related to wetland-to-water conversion which is evident up to 2 km away from those man-made features. The indirect impacts of canals and spoil banks vary regionally, for example, with sediment compaction rates that increase with increasing sediment deposition. These results are consistent with the hypothesis that canals and spoil banks are a major factor driving wetland loss rates because they change wetland hydrology. 相似文献
89.
Eugene J. Palka 《GeoJournal》1995,37(2):201-208
This paper revisits and interrelates the scope of military geography and the changing role of the military, two themes previously addressed in the 1993 and 1994 special editions ofGeoJournal. I begin by tracing the evolution of military geography in the US from World War I through the end of the Gulf War to reveal the demise of the subfield within American academic geography. Within the context of the post-Cold War era, I describe the military's reorientation and emphasize the need and opportunity to broaden the scope of military geography accordingly. The military's current operating environment is best characterized by operations other than war, undertaken on an unprecedented scale. Military geographers and regional, systematic, and technical experts throughout the discipline now have an unparalleled opportunity to contribute to the success of peacekeeping, humanitarian, and disaster assistance missions with which the military is currently preoccupied. Initiatives by academic geographers would not only enhance mission accomplishment from the military and federal government's perspective, but might also help to revive military geography as a legitimate subfield by demonstrating that military geographic endeavors can be both socially responsible and politically correct, particularly within operations other than war. 相似文献
90.
Joanne H. Shorter J. Barry Mcmanus Charles E. Kolb Eugene J. Allwine Brian K. Lamb Byard W. Mosher Robert C. Harriss Uwe Partchatka Horst Fischer Geoffrey W. Harris Paul J. Crutzen Hans-Josef Karbach 《Journal of Atmospheric Chemistry》1996,24(2):121-140
We have investigated methane emissions from urban sources in the former East Germany using innovative measurement techniques including a mobile real-time methane instrument and tracer release experiments. Anthropogenic and biogenic sources were studied with the emphasis on methane emissions from gas system sources, including urban distribution facilities and a production plant. Methane fluxes from pressure regulating stations ranged from 0.006 to 24. l/min. Emissions from diffuse sources in urban areas were also measured with concentration maps and whole city flux experiments. The area fluxes of the two towns studied were 0.37 and 1.9 g/m2/s. The emissions from individual gas system stations and total town emissions of this study are comparable to results of similar sites examined in the United States. 相似文献