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21.
The structure of coesite has been determined at ten pressures up to a maximum of 8.68 GPa by single-crystal X-ray diffraction.
The dominant mechanism of compression is the reduction of four of the five independent Si–O–Si angles within the structure.
There is no evidence of the fifth linkage, Si1–O1–Si1, deviating from 180°. Some Si–O bond distances also decrease by up to
1.6% over the pressure range studied. The pattern of Si–O–Si angle reduction amounts to a rotation of the Si2 tetrahedron
around the [001] direction. This rotation induces significant internal deformation of the Si1 tetrahedron. Comparison of the
experimental data with rigid-unit distance least-squares simulations of coesite suggests that this pattern of compression,
the anomalous positive values of both s23 and K′′ in the equation of state of coesite, its high elastic anisotropy and the unusual straight Si1–O1–Si1 linkage within
the structure are all consequences of the connectivity of the tetrahedral framework.
Received: 11 July 2002 / Accepted: 14 January 2003
Acknowledgements The help of Christian Baerlocher of ETH Zurich in providing both the DLS-76 software and advice in its use is gratefully
acknowledged, as are discussions with Paul Ribbe of Virginia Tech and the comments of two anonymous reviewers. The data analysis
was supported by the National Science Foundation under grant EAR-0105864 to N.L. Ross and R.J. Angel. 相似文献
22.
Interatomic potential parameters have been derived at simulated temperatures of 0 K and 300 K to model pyrite FeS2. The predicted pyrite structures are within 1% of those determined experimentally, while the calculated bulk modulus is within 7%. The model is also able to simulate the properties of marcasite, even though no data for this phase were included in the fitting procedure. There is almost no difference in results obtained for pyrite using the two potential sets; however, when used to model FeS2 marcasite, the potential fitted at 0 K performs better. The potentials have also been used to study the high-pressure behaviour of pyrite up to 44 GPa. The calculated equation of state gives good agreement with experiment and shows that the Fe–S bonds shorten more rapidly that the S–S dimer bonds. The behaviour of marcasite at high pressure is found to be similar to that of pyrite. 相似文献
23.
止水帷幕在高层建筑深基坑中的应用 总被引:2,自引:0,他引:2
某高层建筑基坑西侧紧邻一道河沟,水量较大,采取三重管高压摆喷帷幕止水[1~4],施工完成后通过监测,未发现渗漏、地下水位明显下降和周围建筑物沉降现象。 相似文献
24.
25.
26.
Sarbari Ghosh Utpal Kumar De Atmospheric Science Research Department of Physics Jadavpur University Calcutta India Received April revised July 《大气科学进展》1997,(1)
AComparativeStudyoftheAtmosphericLayersbelowFirstLiftingCondensationLevelforInstantaneousPre-MonsoonThunderstormOcurenceatAga... 相似文献
27.
XU Guobin Senior Research Engineer Tianjin Institute of Hydroelectric Investigation Design Research Ministry of Water Resources. Dongting Road Hexi District Tianjin P R. China. BAI Shilu Senior Research Engineer Tianjin Institute o 《国际泥沙研究》1997,(3)
I.INTRODUCTIONReseri,oirsonoverloadedriverswillreachthestateofrelativeequilibriumwithcontinuousdevelopmentofsedimentation.Insuchcase,thereisdePOsitinfrontofthedam.Thereforethesiltpressureonthedambodyisconsiderablylarge.Sedimentationelevationinfrontofthedamisoneofthefactorsofcalculatingthesiltpressure.Inaddition,tokeeplong-termworkingstorageinreservoif,itisnecessarytoinstallbottomoutlets.Asthereisapressureconduitinfrontoftheoperatinggateofthebottomoutlet,thesedimelltenteredtheconduitwill… 相似文献
28.
通过1982年梅雨期的个例分析,研究和比较了中国和日本梅雨我的结构。分析表明:1.梅雨锋区系统对流层上部宽广的斜压区和对流层低层较狭窄的弱斜压区共同组成;2.在两个个例中,中国剖面上锋区均呈“椅”型结构。日本剖面上,6月呈均匀倾斜结构,7月略呈“椅型”,涡度场上中国剖面为相当正压结构,日本剖面为斜压结构;3.梅雨锋区系统可民是均匀斜压区在不均匀和加热情况下结构改变结果;4.中国大陆雨区高层大量潜热 相似文献
29.
In this paper we study the infiltration of DNAPL in a porous medium containing a single low-permeable lens. Our aim is to
determine whether or not DNAPL infiltrates into the lens. A key role is played by the capillary pressure: DNAPL cannot infiltrate
into the lens unless the capillary pressure exceeds the entry pressure of the lens. In the model this is reflected by an interface
condition, the extended capillary pressure condition. To derive analytical approximations we first consider a steady-state
DNAPL plume in a homogeneous medium. This results in an estimate of the DNAPL plume width as a function of depth, and an asymptotic
solution for small saturations. Assuming that the extent of the lens is much larger than the width of the unperturbed DNAPL
plume in the homogeneous medium, we derive an explicit criterion for DNAPL infiltration into the lens in terms of a critical
inflow rate. A numerical algorithm is presented in which the extended capillary pressure condition is incorporated. The numerical
and analytical results show good qualitative agreement.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
30.
同心环状空间是工程上较常见到的流体流动空间,在此空间中流体流动情况的分析较复杂。工程上对其流动情况的分析常常是引用流体力学中的分析结果,但往往由于对环状空间结构的条件重视不够,引用时很容易出毛病。经过仔细推导分析,指出其应用条件,并有助于对同心环状空间中流体流动时压力损失的分析与计算 相似文献