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101.
TEM and XRD determination of crystallite size and lattice strain as a function of illite crystallinity in pelitic rocks 总被引:2,自引:0,他引:2
W.-T. JIANG D. R. PEACOR P. ÁRKAI M. TÓTH & J. W. KIM 《Journal of Metamorphic Geology》1997,15(2):267-281
Average crystallite size and mean-square strain of illite in rock specimens and clay separates were measured independently in TEM images and by single-line Fourier (Voigt method) profile analysis of the c. 1 nm peak of XRD patterns for a prograde sequence of pelitic rocks (illite crystallinity indices=0.17–0.58°Δ2θ) from the Gaspé Peninsula, Quebec. The TEM-determined crystallite sizes in clay separates approximate those determined by Fourier profile analyses and those calculated from illite crystallinity indices by the Scherrer equation, with the exception of the diagenetic sample. The crystallite sizes and mean-square strains of illite in rock samples exhibit a trend similar to that determined by profile analyses, but the average crystallite sizes are up to five times larger than those measured for clay separates. TEM images show that all rock samples have a wide range of crystallite sizes, and the proportions of larger crystallites increase with metamorphic grade. The diagenetic illite is defect-rich, fine-grained (mean thickness by volume=c. 70 nm), 1Md material. Anchizonal illite tends to occur as separate aggregates of small 1Md and larger 2M1 crystals (c. 200 nm), comprising arrays of subparallel coalescing packets. The epizone sample has thick (c. 400 nm), defect-free crystals of muscovite occurring in stacks of parallel layers, or subhedral crystals intergrown with large-angle boundaries. Cleaved crystals that are free of intracrystalline layer terminations are dominant in clay separates of all samples, having ranges of smaller sizes with volume-average thicknesses of c. 43, 43, and 81 nm (c. 14, 28, 67 nm by the Voigt method), respectively, for the three zones. The results suggest that illite crystallinity indices do not provide a direct measure of a single microstructural state of illite in rocks, although they yield consistent limits for average crystallite sizes for the anchizone (23 & 48 nm here). Therefore, they serve as a general parameter of the degree of recrystallization on a relative basis, in part because the contributions of all peak-broadening variables (mixed layering, size and strain) decrease regularly with prograde regional metamorphism of pelites. The microstructural changes caused by rock disaggregation are probably a function of those variables as well. The data collectively demonstrate a trend from metastable, defect-rich, small crystals towards a stable assemblage of larger, defect-free crystals, through dissolution of strained crystals and neocrystallization, consistent with the Ostwald step rule. 相似文献
102.
Shu-Qing YANG Sung-Cheol KOH In-Soo KIM Young-Chae SONG 《国际泥沙研究》2007,22(1):27-38
This paper re-examines Bagnold’s theorem of sediment transport. Different from the stream power defined by Bagnold, i.e., τoV, this study shows that the total load of sediment-laden flow, gt, is related to near bed energy dissipation rate, i.e., τou*’. An attempt is made to explain the empirical relation. The ratio (=k) of measured total load, gt, to the product of near bed velocity, u*’, and energy dissipation rate, τou*’, is analyzed. It is found that k is independent of the Rouse number, Z, if Z is greater than 2.6, but the coefficient k decreases with the increase of Z when Z < 2.6. An empirical relation between k and Z is developed. A systematic and thorough analysis of 1,458 sets of data collected from 16 rivers and canals confirms that the proposed formula can be used to compute the total load with accuracy. 相似文献
103.
104.
Based on the maximum-entropy(ME)principle,a new power spectral estimator for random waves is derived in the form of S~(ω)=a/8H~2(2π)~(d 1)ω~-~((d 2))exp[-b(2π/ω)~n],by solving a variational problem subject to some quite general constraints.This robust method is comprehensive enough to describe the wave spectra even in extreme wave conditions and is superior to periodogram method that is not suitable to process comparatively short or intensively unsteady signals for its tremendous boundary effect and some inherent defects of FFT.Fortunately,the newly derived method for spectral estimation works fairly well,even though the sample data sets are very short and unsteady,and the reliability and efficiency of this spectral estimator have been preliminarily proved. 相似文献
105.
Shu-Qing YANG In-Soo KIM Daniel S. KOH Young-Chae SONG 《中国海洋工程》2005,19(4):557-570
The aim of this paper is to present an analytical expression for the streamwise velocity distribution in a non-uniform flow in the presence of waves; the correlation between the horizontal and vertical velocity components has been compreheusively examined. Different from previous researches which attributed the deviation of velocity from the classical log-law to the wave Reynolds stress, i.e. - ρ uv^- only, this study demonstrates that the momentum flux caused by mean velocities, i.e., u^- and v^-, is also responsible for the velocity deviation, and it is found that the streamwise velocity for a flow in the presence of non-zero wall-normal velocity does not follow the classical log-law, but the modified log-law proposed in this study based on simplified mixing-length theorem. The validity of the modified log-law has been verified by use of available experimental data from published sources for combined wave-current flows, and good agreement between the predicted and observed velocity profiles has been achieved. 相似文献
106.
Jang-Woon WANG Jae-Jin KIM Wonsik CHOI Da-Som MUN Jung-Eun KANG Hataek KWON Jin-Soo KIM Kyung-Soo HAN 《大气科学进展》2017,34(12):1404-1414
This study investigated the flow characteristics altered by Jang Bogo Antarctic Research Station using computational fluid dynamics(CFD) modeling. The topography and buildings around Jang Bogo Station were constructed with computeraided-design data in the CFD model domain. We simulated 16 cases with different inflow directions, and compared the flow characteristics with and without Jang Bogo Station for each inflow direction. The wind data recorded by the site's automatic weather station(AWS) were used for comparison. Wind rose analysis showed that the wind speed and direction after the construction of Jang Bogo Station were quite different from those before construction. We also investigated how virtual wind fences would modify the flow patterns, changing the distance of the fence from the station as well as the porosity of the fence. For westerly inflows, when the AWS was downwind of Jang Bogo Station, the decrease in wind speed was maximized(-81% for west-northwesterly). The wind speed reduction was also greater as the distance of the fence was closer to Jang Bogo Station. With the same distance, the fence with medium porosity(25%–33%) maximized the wind speed reduction.These results suggest that the location and material of the wind fence should be selected carefully, or AWS data should be interpreted cautiously, for particular prevailing wind directions. 相似文献
107.
In this study, the correlation between simulated and measured radar velocity spectrum width(σv) is investigated. The results show that the dendrites growth zones(DGZs) and needles growth zones(NGZs) mostly contain dendrites(DN) and needles(NE), respectively.Clear σv zones(1.1 < σv(m s–1) < 1.3 and 0.3 < σv(m s–1) < 0.7 for the DGZ and NGZ, respectively) could be identified in the case studies(27 and 28 February 2016) n... 相似文献
108.
LEE Jeong-Hyun KIM Byeong-Jun LIANG Kun PARK Tae-Yoon S. CHOH Suk-Joo LEE Dong-Jin WOO Jusun 《《地质学报》英文版》2016,90(6):1946-1954
Mid to late Cambrian thrombolites and maze-like maceriate reefs from the western North China Platform, Wuhai, Inner Mongolia, northwestern China, occur in the middle of a succession dominated by thin-bedded lime mudstone-shale/marlstone alternations, and are laterally surrounded by limestone conglomerate and/or grainstone. Thrombolite, characterized by meter-scale lenticular mounds composed of millimeter- to centimeter-scale mesoclots and wackestone matrix, occurs in the lower middle part of the sequence. Thrombolite mesoclots are composed of microstromatolites with alternating dark gray and light gray micritic laminae. The maze-like maceriate reefs occur in the middle to the upper part of the sequence, commonly forming lenticular mounds up to 1 m thick. They are characterized by centimeter- to decimeter-scale branched maze-like structures, whose biogenic portions (maceria) are selectively dolomitized. The maceriae are composed of poorly preserved microstromatolites and siliceous sponges. Inter-macerial sediments consist of lime mud and scattered bioclasts. These Wuhai reefs are generally similar to but older than various other Cambrian reefs previously reported from the Shandong region, northeastern China. 相似文献
109.
An experimental study of a seismically isolated and a comparable non-isolated bridge is presented. The bridge model featured flexible piers, weighed 158kN and was tested on a shake table with an array of real and simulated seismic motions with peak acceleration in the range 0⋅1–1⋅1g. When isolated, the bridge deck was supported by four spherically shaped sliding bearings (known as Friction Pendulum System or FPS bearings) with friction coefficient under dynamic conditions in the range 0⋅07–0⋅12. The experimental results demonstrated a substantial improvement in the ability of the isolated bridge to sustain all levels of seismic excitation under elastic conditions. 相似文献
110.
Ages determined with the 40Ar/39Ar isotopic system affirms the Early Cretaceous volcanic activity in the Barton Peninsula, King George Island, Antarctica. Two specimens of basaltic andesite collected from the lowermost volcanic sequence of the peninsula were irradiated and analyzed in different experiments, yielding an identical age spectrum, and two magmatic thermal events of the Early Cretaceous (120.4± 1.6 Ma, 119± 1 Ma) and Early Tertiary (53.1± 1.5 Ma, 52± 1 Ma) are distinguished. The former is interpreted to represent the primary cooling age of basaltic andesite, whereas the latter is the thermal reset age caused by the intrusion of granitic pluton. These new ages clearly indicate that volcanism was active during the Early Cretaceous on the Barton Peninsula and that intensive hydrothermal alteration and mineralization of Mesozoic volcanic rocks resulted from Tertiary magmatism. 相似文献