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91.
利用2006年南极威德尔海冬季科学考察期间由机载激光高度计测得的海冰上表面形态数据,以拖曳分割理论为基础研究了冰脊形拖曳力及其对冰-气总拖曳力的贡献以及中性条件下对应10 m高度处风速的冰-气拖曳系数Cdn(10)。结果显示,在密集冰区,冰脊形拖曳力及其对总拖曳力的贡献随冰脊强度(脊高/脊距)的增大呈递增趋势,而随粗糙长度的增大而减小,对应于威德尔海冬季典型冰脊强度和粗糙长度,占总拖曳力的35%,说明了冰脊形拖曳力在冰-气界面动量交换中的重要作用。Cdn(10)随冰脊强度的增大而增大,但冰脊强度较小时,Cdn(10)随粗糙长度增大而增大;而对较大的冰脊强度,Cdn(10)则随粗糙长度增大而减小。 相似文献
92.
The effect of iron on montmorillonite stability. (I) Background and thermodynamic considerations 总被引:1,自引:0,他引:1
It is envisaged that high-level nuclear waste (HLW) will be disposed of in underground repositories. Many proposed repository designs include steel waste canisters and bentonite backfill. Natural analogues and experimental data indicate that the montmorillonite component of the backfill could react with steel corrosion products to produce non-swelling Fe-rich phyllosilicates such as chamosite, berthierine, or Fe-rich smectite. In K-bearing systems, the alteration of montmorillonite to illite/glauconite could also be envisaged. If montmorillonite were altered to non-swelling minerals, the swelling capacity and self-healing properties of the bentonite backfill could be reduced, thereby diminishing backfill performance. The main aim of this paper was to investigate Fe-rich phyllosilicate mineral stability at the canister-backfill interface using thermodynamic modelling. Estimates of thermodynamic properties were made for Fe-rich clay minerals in order to construct approximate phase-relations for end-member/simplified mineral compositions in logarithmic activity space. Logarithmic activity diagrams (for the system Al2O3-FeO-Fe2O3-MgO-Na2O-SiO2-H2O) suggest that if pore waters are supersaturated with respect to magnetite in HLW repositories, Fe(II)-rich saponite is the most likely montmorillonite alteration product (if fO2(g) values are significantly lower than magnetite-hematite equilibrium). Therefore, the alteration of montmorillonite may not be detrimental to nuclear waste repositories that include Fe, as long as the swelling behaviour of the Fe-rich smectite produced is maintained. If fO2(g) exceeds magnetite-hematite equilibrium, and solutions are saturated with respect to magnetite in HLW repositories, berthierine is likely to be more stable than smectite minerals. The alteration of montmorillonite to berthierine could be detrimental to the performance of HLW repositories. 相似文献
93.
Dauphiné twinning and texture memory in polycrystalline quartz. Part 3: texture memory during phase transformation 总被引:1,自引:0,他引:1
Hans-Rudolf?WenkEmail author N.?Barton M.?Bortolotti S.?C.?Vogel M.?Voltolini G.?E.?Lloyd G.?B.?Gonzalez 《Physics and Chemistry of Minerals》2009,36(10):567-583
Samples of quartz-bearing rocks were heated above the α (trigonal)–β (hexagonal) phase transformation of quartz (625–950°C)
to explore changes in preferred orientation patterns. Textures were measured both in situ and ex situ with neutron, synchrotron
X-ray and electron backscatter diffraction. The trigonal–hexagonal phase transformation does not change the orientation of
c- and a-axes, but positive and negative rhombs become equal in the hexagonal β-phase. In naturally deformed quartzites measured by
neutron diffraction a perfect texture memory was observed, i.e. crystals returned to the same trigonal orientation they started
from, with no evidence of twin boundaries. Samples measured by electron back-scattered diffraction on surfaces show considerable
twinning and memory loss after the phase transformation. In experimentally deformed quartz rocks, where twinning was induced
mechanically before heating, the orientation memory is lost. A mechanical model can explain the memory loss but so far it
does not account for the persistence of the memory in quartzites. Stresses imposed by neighboring grains remain a likely cause
of texture memory in this mineral with a very high elastic anisotropy. If stresses are imposed experimentally the internal
stresses are released during the phase transformation and the material returns to its original state prior to deformation.
Similarly, on surfaces there are no tractions and thus texture memory is partially lost. 相似文献
94.
Water Self-Softening Processes at Waterfall Sites 总被引:1,自引:0,他引:1
David Dian ZHANG 《《地质学报》英文版》2004,78(5):1154-1161
Many rivers in tropical and subtropical karst regions are supersaturated with respect to CaCO3 and have high water hardness. After flowing through waterfall sites, river water is usually softened, accompanied by tufa formation, which is simply described as a result of water turbulence in fast-flowing water. In this paper, a series of laboratory experiments are designed to simulate the hydrological conditions at waterfall sites. The influences of air-water interface, water flow velocity, aeration and solid-water interface on water softening are compared and evaluated on a quantitative basis. The results show that the enhanced inorganic CO2 outgassing due to sudden hydrological changes occurring at waterfall sites is the principal cause of water softening at waterfall sites. Both air-water interface area and water flow velocity increase as a result of the "aeration effect", "low pressure effect" and "jet-flow effect" at waterfall sites, which greatly accelerates CO2 outgassing and therefore makes natural w 相似文献
95.
In Europe, the Wide Wheel abrasion (WWA) test and the B?hme abrasion (BA) test are among the most widely used standard test
methods for determining abrasion resistance of natural stones, the former being the reference test method in EN 14157 Standard.
However, it is stated in the Annex-A (Informative) of EN 14157 Standard that very limited data are available to provide correlations
between these two test methods. To be able to fill this gap, in this study, 25 different natural stones belonging to sedimentary,
metamorphic and igneous groups were tested for their abrasion resistance as well as physico-mechanical properties. Also, for
a better interpretation of abrasion resistance characteristics of the tested stone materials, relationships between abrasion
resistance and physico-mechanical properties were statistically examined. A statistically significant linear correlation (R
2 = 0.85; P value = 0.000) was established between the WWA test and the BA test, which could be used in practice for converting the measured
abrasion resistance values from one testing method to another. It was also found that the correlation between these two test
methods improved significantly (R
2 = 0.93; P value = 0.001) when relatively high-porosity stone materials (porosity ≥1%) were separately evaluated. Both methods of abrasion
resistance employed in the present study showed statistically significant linear correlations with uniaxial compressive strength
and Brazilian tensile strength, the former proving to be a more influencing parameter on resistance to abrasion. Also, from
the point view of representing actual abrasion mechanism of stone materials in practice, the necessity of simulating multi-directional
foot traffic in abrasion testing methods was discussed. In this respect, the reference test method in the EN 14157 Standard
was criticized for not fully meeting this requirement. It was also pointed out that the reference method could have some drawbacks
when applied to coarse-grained granitic rocks having cleavable minerals such as plagioclase and orthoclase feldspars. 相似文献
96.
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99.
The climate–population relationship has long been conceived. Although the topic has been repeatedly investigated, most of
the related works are Eurocentric or qualitative. Consequently, the relationship between climate and population remains ambiguous.
In this study, fine-grained temperature reconstructions and historical population data sets have been employed to statistically
test a hypothesized relationship between temperature change and population growth (i.e., cooling associated with below average
population growth) in China over the past millennium. The important results were: (1) Long-term temperature change significantly
determined the population growth dynamics of China. However, spatial variation existed, whilst population growth in Central
China was shown to be responsive to both long- and short-term temperature changes; in marginal areas, population growth was
only sensitive to short-term temperature fluctuations. (2) Temporally, the temperature–population relationship was obscured
in some periods, which was attributable to the factors of drought and social buffers. In summary, a temperature–population
relationship was mediated by geographic factors, the aridity threshold, and social factors. Given the upcoming threat posed
by climate change to human societies, this study seeks to improve our knowledge and understanding of the climate–society relationship. 相似文献
100.
Kristie?L.?EbiEmail author Jessica?Hartman Nathan?Chan John?Mcconnell Michael?Schlesinger John?Weyant 《Climatic change》2005,73(3):375-393
Climate is one factor that determines the potential range of malaria. As such, climate change may work with or against efforts
to bring malaria under control. We developed a model of future climate suitability for stable Plasmodium falciparum malaria transmission in Zimbabwe. Current climate suitability for stable malaria transmission was based on the MARA/ARMA
model of climatic constraints on the survival and development of the Anopheles vector and the Plasmodium falciparum malaria parasite. We explored potential future geographic distributions of malaria using 16 projections of climate in 2100.
The results suggest that, assuming no future human-imposed constraints on malaria transmission, changes in temperature and
precipitation could alter the geographic distribution of malaria in Zimbabwe, with previously unsuitable areas of dense human
population becoming suitable for transmission. Among all scenarios, the highlands become more suitable for transmission, while
the lowveld and areas with low precipitation show varying degrees of change, depending on climate sensitivity and greenhouse
gas emission stabilization scenarios, and depending on the general circulation model used. The methods employed can be used
within or across other African countries. 相似文献