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981.
G. Diego Gatta Nicola Rotiroti Martin Fisch Milen Kadiyski Thomas Armbruster 《Physics and Chemistry of Minerals》2008,35(9):521-533
The elastic and structural behaviour of the synthetic zeolite CsAlSi5O12 (a = 16.753(4), b = 13.797(3) and c = 5.0235(17) Å, space group Ama2, Z = 2) were investigated up to 8.5 GPa by in situ single-crystal X-ray diffraction with a diamond anvil cell under hydrostatic conditions. No phase-transition occurs within the P-range investigated. Fitting the volume data with a third-order Birch–Murnaghan equation-of-state gives: V 0 = 1,155(4) Å3, K T0 = 20(1) GPa and K′ = 6.5(7). The “axial moduli” were calculated with a third-order “linearized” BM-EoS, substituting the cube of the individual lattice parameter (a 3, b 3, c 3) for the volume. The refined axial-EoS parameters are: a 0 = 16.701(44) Å, K T0a = 14(2) GPa (βa = 0.024(3) GPa?1), K′ a = 6.2(8) for the a-axis; b 0 = 13.778(20) Å, K T0b = 21(3) GPa (βb = 0.016(2) GPa?1), K′ b = 10(2) for the b-axis; c 0 = 5.018(7) Å, K T0c = 33(3) GPa (βc = 0.010(1) GPa?1), K′ c = 3.2(8) for the c-axis (K T0a:K T0b:K T0c = 1:1.50:2.36). The HP-crystal structure evolution was studied on the basis of several structural refinements at different pressures: 0.0001 GPa (with crystal in DAC without any pressure medium), 1.58(3), 1.75(4), 1.94(6), 3.25(4), 4.69(5), 7.36(6), 8.45(5) and 0.0001 GPa (after decompression). The main deformation mechanisms at high-pressure are basically driven by tetrahedral tilting, the tetrahedra behaving as rigid-units. A change in the compressional mechanisms was observed at P ≤ 2 GPa. The P-induced structural rearrangement up to 8.5 GPa is completely reversible. The high thermo-elastic stability of CsAlSi5O12, the immobility of Cs at HT/HP-conditions, the preservation of crystallinity at least up to 8.5 GPa and 1,000°C in elastic regime and the extremely low leaching rate of Cs from CsAlSi5O12 allow to consider this open-framework silicate as functional material potentially usable for fixation and deposition of Cs radioisotopes. 相似文献
982.
Philippe E. Raison Regis Jardin Daniel Bouëxière Rudy J. M. Konings Thorsten Geisler Claudiu C. Pavel Jean Rebizant Karin Popa 《Physics and Chemistry of Minerals》2008,35(10):603-609
The crystallographic structures of the synthetic cheralite, CaTh(PO4)2, and its homolog CaNp(PO4)2 have been investigated by X-ray diffraction at room temperature. Rietveld analyses showed that both compounds crystallize in the monoclinic system and are isostructural to monazite LnPO4 (Ln = La to Gd). The space group is P21/n (I.T. = 14) with Z = 2. The refined lattice parameters of CaTh(PO4)2 are a = 6.7085(8) Å, b = 6.9160(6) Å, c = 6.4152(6) Å, and β = 103.71(1)° with best fit parameters R wp = 4.87%, R p = 3.69% and R B = 3.99%. For CaNp(PO4)2, we obtained a = 6.6509(5) Å, b = 6.8390(3) Å, c = 6.3537(8) Å, and β = 104.12(6)° and R wp = 6.74%, R p = 5.23%, and R B = 6.05%. The results indicate significant distortions of bond length and angles of the PO4 tetrahedra in CaTh(PO4)2 and to a lesser extent in CaNp(PO4)2. The structural distortions were confirmed by Raman spectroscopy of CaTh(PO4)2. A comparison with the isostructural compounds LnPO4 (Ln = Ce and Sm) confirmed that the substitution of the large rare earth trivalent cations with Ca2+ and Th4+ introduces a distortion of the PO4 tetrahedra. 相似文献
983.
In situ strength measurements on natural upper-mantle minerals 总被引:1,自引:0,他引:1
Junji Yamamoto Jun-ichi Ando Hiroyuki Kagi Toru Inoue Akihiro Yamada Daisuke Yamazaki Tetsuo Irifune 《Physics and Chemistry of Minerals》2008,35(5):249-257
Using in situ strength measurements at pressures up to 10 GPa and at room temperature, 400, 600, and 700°C, we examined rheological
properties of olivine, orthopyroxene, and chromian-spinel contained in a mantle-derived xenolith. Mineral strengths were estimated
using widths of X-ray diffraction peaks as a function of pressure, temperature, and time. Differential stresses of all minerals
increase with increasing pressure, but they decrease with increasing temperature because of elastic strain on compression
and stress relaxation during heating. During compression at room temperature, all minerals deform plastically at differential
stress of 4–6 GPa. During subsequent heating, thermally induced yielding is observed in olivine at 600°C. Neither orthopyroxene
nor spinel shows complete stress relaxation, but both retain some stress even at 700°C. The strength of the minerals decreases
in the order of chromian-spinel ≈ orthopyroxene > olivine for these conditions. This order of strength is consistent with
the residual pressure of fluid inclusions in mantle xenoliths. 相似文献
984.
D. Gournis A. Lappas M. A. Karakassides D. Többens A. Moukarika 《Physics and Chemistry of Minerals》2008,35(1):49-58
Neutron powder diffraction measurements on lithium and cesium saturated montmorillonite samples before and after heat treatment
at 300°C are studied, in order to undertake a complete refinement of crystal structure and unravel the migration mechanism
for the interlayer cations of Li or Cs. Rietveld analysis of the corresponding diffraction patterns finds that montmorillonite
crystallizes in the C2/m space group with unit cell dimensions consistent with the size of the specific interlayer cation. We show that thermal treatment
affects the two types of samples in a different way. This is with respect to their unit cell dimensions and the migration
of Li from the 2b to the 2c clay lattice site, in constrast to the Cs positioning which remains effectively unchanged. 相似文献
985.
Emilia Palonen 《GeoJournal》2008,73(3):219-230
As in most parts of Central and Eastern Europe, there is a tradition in Hungary of changing street names and memorials in
the wake of major political transitions. This article focuses on the change of street names and memorials, i.e. the city-text,
in Hungary’s political capital, Budapest, between 1985 and 2001. The city-text in Budapest became a locus of dispute between
different political authorities, including the nation state, the metropolitan municipality, and the district, each bearing
different political ideals during and after the fall of communism. Discursive changes in the post-communist city-text emerged
expressing specific conceptions of national sovereignty, but the direction of the changes were debated. Different levels of
administration in Budapest and Hungary had divergent visions of what the new discourse on national sovereignty should be.
The changes, therefore, did not express a simple transition to an agreed-upon post-communist value system, but were the result
of a symbolic struggle between different levels of administration over what should be commemorated in the city-text. 相似文献
986.
Lars Olov Andersson 《Physics and Chemistry of Minerals》2008,35(9):505-520
The EPR spectra of Maxixe-type beryl contain a large number of overlapping signals. The angular dependence of the 1:3:3:1
signal typical for the CH3 radical shows that this radical is located at the center of the channel cavity with its symmetry axis parallel to the crystal
c-axis and is rotating around this axis. Its EPR spectrum is axially symmetric with g
// = 2.00263, g
⊥ = 2.00249 and A// = 2.288 mT, A⊥ = 2.256 mT. These anisotropies have the opposite signs of those found for surface-adsorbed methyl radicals. Hydrogen atoms
are located at position 2a at the center of the beryl cavity and the EPR parameters of the narrow doublet signal are A
0 = 1,407 MHz and g = 2.00230. Another doublet signal, which is broader and has axial symmetry with g
// = 2.00265, g
⊥ = 2.00625 and A// = 0.895 mT, A⊥ = 0.885 mT, could come from a HCO3 radical. One narrow and easily saturated signal with g
// = 2.00227 and g
⊥ = 2.00386 is interpreted to arise from a carbon monoxide radical in the beryl channel, oriented with its axis parallel to
the crystal c-axis. Additional weak doublet lines, which have similar g values as the carbon monoxide radical, are created by nearby hydrogens. A powder spectrum with g
// = 2.0017 and g
⊥ = 2.0004 appears upon UV irradiation of the single crystal and is easily saturated. This spectrum is interpreted to arise
from a carbon dioxide radical, which rotates around its symmetry axis. 相似文献
987.
An increasingly utilized strategy for expanding conservation in the developing world has been the promotion of protected areas
that supersede national borders. Alternatively known as transfrontier biosphere reserves, transfrontier or transboundary conservation
areas, or Peace Parks, these protected areas are aggressively advanced by conservation agencies for their purported ecological
and economic benefits. This article provides a comparative assessment of two case studies to understand the various impacts
of transboundary conservation. The Great Limpopo Transfrontier Park, which unites protected areas in South Africa, Mozambique
and Zimbabwe, is contrasted with efforts to protect jaguars along the United States–Mexico border. We argue that while these
cases are promising for the purposes of biodiversity protection, they demonstrate that transboundary conservation can minimize
political context, contributes to the hegemony of international conservation agendas, and remains closely linked to economic
neoliberalism and decentralization in the developing world.
相似文献
Brian KingEmail: |
988.
Until recently the traditional spatial configuration of the European geography was based upon the core-periphery model. The
‘pentagon’, broadly defined as lying between London, Paris, Milan, Munich and Hamburg, was seen as the core area characterised
by having the highest concentration of economic development in the European Union (EU), with the remainder of the European
territory viewed as peripheral, albeit to varying degrees. In a number of cases such peripheral areas equated with clear regional
disparities. The elaboration of the European Spatial Development Perspective (ESDP) (CEC, European spatial development perspective, towards balanced and sustainable development in the territory of the
European Union, 1999) challenged this core-periphery model. European spatial planning policies, aimed at encouraging social
and economic, and with ever increasing importance, territorial cohesion, seek amongst other aspects to encourage the development
of a balanced and polycentric urban system. This paper adopts a network analysis approach to the analysis of air passenger
flows between some 28 principal European metropolitan urban regions. The evaluation of these flows contributes to an enhanced
comprehension of the spatial dynamics of the European metropolitan territory which goes beyond that deriving from the more
standard analyses of the individual components of the urban system. Several indicators are used, deriving from gravitational
modelling techniques, to analyse the complexity of the air passenger flows. A multidimensional scaling (MDS) technique is
introduced in order to interpret and visualise the resulting spatial configuration and positioning of the different metropolitan
centres within the conceptual European ‘space of air passenger flows’, thereby contrasting with the more traditional map-based
geographical image of Europe, based upon Cartesian coordinates.
相似文献
Malcolm C. BurnsEmail: |
989.
This paper explores the links between a strategic policy, urban consolidation, and house prices by examining the changes in
the mix of housing and in house price for the period 1991–2004. We contend that urban consolidation could be seen as a source
of additional supply, (which might be expected to be felt in lower prices and so contribute to a local policy objective) but
also as a stimulus to demand (by developers who could bid up the price of lots where it was understood more housing could
be built). Analyses were carried out at the metropolitan and sub-regional scales using correlation tests. The research finds
very weak statistical connections, and concludes that this policy has not been associated with price changes. 相似文献
990.
Numerical estimation of REV and permeability tensor for fractured rock masses by composite element method 总被引:2,自引:0,他引:2
The Monte Carlo method is used to generate parent stochastic discrete fracture network, from which a series of fractured rock samples of different sizes and orientations are extracted. The fracture network combined with a regular grid forms composite element mesh of the fractured rock sample, in which each composite element is composed of sub‐elements incised by fracture segments. The composite element method (CEM) for the seepage is implemented to obtain the nodal hydraulic potential as well as the seepage flow rates through the fractured rock samples. The application of CEM enables a large quantity of stochastic tests for the fractured rock samples because the pre‐process is facilitated greatly. By changing the sizes and orientations of the samples, the analysis of the seepage characteristics is realized to evaluate the variation of the permeability components, the existence of the permeability tensor and the representative element volume. The feasibility and effectiveness are illustrated in a numerical example. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献