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J. M. Léger J. Haines C. Chateau G. Bocquillon M. W. Schmidt S. Hull F. Gorelli A. Lesauze R. Marchand 《Physics and Chemistry of Minerals》2001,28(6):388-398
The structure of the cristobalite-like polymorph of phosphorus oxynitride PON has been refined using neutron powder diffraction
data. It is tetragonal, space group I&4macr;2d, Z=4. The four P–(O,N) distances are equal but the tetrahedron is compressed along c. In AX2 or ABX4 compounds, the tetragonal I&4macr;2d or I&4macr; structure is obtained when the average ratio of the cation to anion radius is below 1.186, whereas the tetragonal P41212 or orthorhombic C2221 structure is obtained at low temperatures for larger ratios. The cell parameters of this PON polymorph have been determined
as a function of hydrostatic pressure by in situ angle dispersive X-ray powder diffraction in a diamond-anvil cell. Under
truly hydrostatic pressure, a strong anisotropic behavior is observed with the c parameter being nearly incompressible. Very slight anisotropic stress strongly modifies the high-pressure behavior. According
to the pressure-temperature conditions of treatment, three phases, cristobalite-, moganite-, and quartz-like, have been obtained
by quenching experiments, and the P–T phase diagram of PON was derived. The high-pressure behavior of the α-quartz, moganite, and cristobalite-like polymorphs
of PON and SiO2 is discussed.
Received: 7 August 2000 / Accepted: 21 January 2001 相似文献
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J. Haines J. M. Léger C. Chateau A. S. Pereira 《Physics and Chemistry of Minerals》2000,27(8):575-582
Germanium dioxide was found to undergo a transition from the tetragonal rutile-type to the orthorhombic CaCl2-type phase above 25 GPa. The detailed structural evolution of both phases at high pressure in a diamond anvil cell has been investigated by Rietveld refinement using angle-dispersive, X-ray powder-diffraction data. The square of the spontaneous strain (a−b)/(a+b) in the orthorhombic phase was found to be a linear function of pressure and no discontinuities in the cell constants and volume were observed, indicating that the transition is second-order and proper ferroelastic. Compression of the GeO6 octahedra was found to be anisotropic, with the apical Ge-O distances decreasing to a greater extent than the equatorial distances and becoming shorter than the latter above 7 GPa. Above this pressure, the GeO6 octahedron exhibits the common type of tetragonal distortion predicted by a simple ionic model and observed for most rutile-type structures such as those of the heavier group-14 dioxides and the metal difluorides. Above the phase transition, the columns of edge-sharing octahedra tilt about their two fold axes parallel to c and the rotation angle reaches 10.2(5)° by 36(1) GPa so as to yield a hexagonal close-packed oxygen sublattice. The compressibility increases at the phase change as is expected for a second-order transition at which an additional compression mechanism becomes available. 相似文献
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This paper uses the OECD’s global recursive-dynamic general equilibrium model ENVLinkages to examine the mid-term economic consequences and the optimal energy supply mix adjustments of a simultaneous implementation of i) a progressive fossil fuel subsidy reform in emerging and developing economies and ii) a progressive phase out of nuclear energy, mostly affecting OECD countries, China and Russia. The analysis is then transposed in the context of climate change mitigation to depict the corresponding implications for CO2 emissions, to assess the interactions between the two energy policies, and to derive how the associated costs are affected by the different policies. The phase-out scenario projects a nuclear capacity halved by 2035 as compared to the Baseline, corresponding to $120 billion losses in value-added of the nuclear industry for that year. The nuclear phase-out leaves GDP and real household consumption marginally affected in energy importing countries. A multilateral subsidy reform is more likely to affect international fossil fuel prices and alter patterns of global energy use. The fossil fuel subsidy reform, when implemented together with nuclear phase-out, more than offsets negative consequences on household consumption but still leads to a decrease in global CO2 emissions. The combined policies help save the equivalent of current energy consumption in the Middle East. Combining a climate policy, an effective fossil fuel subsidy reform, even with a lower nuclear share in the power mix, brings about multiple benefits to OECD countries which reduce their energy bill and achieve large climate change mitigation at lower cost. 相似文献
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The homogenization method is used to determine the formulation of the behaviour of both saturated and unsaturated porous media. This approach makes it possible to assess the validity of the effective stress concept as a function of the properties of the porous media at the microscopic scale. Furthermore, the influence of the morphologies of the solid and fluid phases on the macroscopic behaviour is studied. The strain induced by drying is examined as a function of the morphological properties. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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Susan Hanson Robert Nicholls N. Ranger S. Hallegatte J. Corfee-Morlot C. Herweijer J. Chateau 《Climatic change》2011,104(1):89-111
This paper presents a first estimate of the exposure of the world’s large port cities (population exceeding one million inhabitants
in 2005) to coastal flooding due to sea-level rise and storm surge now and in the 2070s, taking into account scenarios of
socio-economic and climate changes. The analysis suggests that about 40 million people (0.6% of the global population or roughly
1 in 10 of the total port city population in the cities considered) are currently exposed to a 1 in 100 year coastal flood
event. For assets, the total value exposed in 2005 across all cities considered is estimated to be US$3,000 billion; corresponding
to around 5% of global GDP in 2005 (both measured in international USD) with USA, Japan and the Netherlands being the countries
with the highest values. By the 2070s, total population exposed could grow more than threefold due to the combined effects
of sea-level rise, subsidence, population growth and urbanisation with asset exposure increasing to more than ten times current
levels or approximately 9% of projected global GDP in this period. On the global-scale, population growth, socio-economic
growth and urbanization are the most important drivers of the overall increase in exposure particularly in developing countries,
as low-lying areas are urbanized. Climate change and subsidence can significantly exacerbate this increase in exposure. Exposure
is concentrated in a few cities: collectively Asia dominates population exposure now and in the future and also dominates
asset exposure by the 2070s. Importantly, even if the environmental or socio-economic changes were smaller than assumed here
the underlying trends would remain. This research shows the high potential benefits from risk-reduction planning and policies
at the city scale to address the issues raised by the possible growth in exposure. 相似文献
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The volumes of the pure synthetic pyrope, spessartine and uvarovite garnets have been determined by powder x-ray diffraction as a function of pressure up to 25 GPa in a diamond anvil cell at room temperature. Experiments in different pressure transmitting media have been systematically carried out to determine the effects of anisotropic stress components, which were found to be substantial and have been taken into account. Assuming that the bulk moduli determined from ultrasonic experiments have the lowest uncertainties, the following values for the pressure derivatives of the bulk modulus of uvarovite, spessartine and pyrope were respectively obtained: 4.7±0.7, 7?7.3±1 and 3.4±1. The value for pyrope can be attributed to the small size of the Mg2+ cation in its dodecahedral site. 相似文献
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Jessica Saïag Pierre‐Yves Collin Jean‐Pierre Sizun Frdric Herbst Ophlie Faÿ‐Gomord Carmela Chateau Smith Bruno Caline ric Lasseur 《Sedimentology》2019,66(7):2976-3007
Microtexture describes the type of particles and their arrangement in matrix samples at scanning electron microscopy scale. Although a microtexture classification exists for micritic limestone, it cannot be directly applied to chalk. This study therefore proposes a classification of chalk microtextures and discusses the origin of microtexture variability. Chalk was sampled at thirteen spatio‐temporal locations along the coastline of northern France (Cenomanian–Santonian). Four criteria are defined to describe, characterize and determine chalk matrix microtexture: (i) mineralogical content; (ii) biogenic fraction; (iii) micritic fraction; and (iv) cement fraction. From these criteria, two major groups are defined: Pure Chalk Microtexture Group, with seven classes, and Impure Chalk Microtexture Group, divided into two subgroups: Argillaceous Microtexture with four classes and Siliceous Microtexture with two classes. Microtexture variability is related both to initial sedimentation and to diagenesis. Sedimentological conditions (for example, climate and distance from shore) affect chalk composition (carbonate content and type of insoluble particles), thus influencing microtexture. Changes in Pure Chalk Microtexture are the result of increasing diagenetic intensity. This classification can also be used to characterize the microtexture of subsurface chalk reservoirs. Reservoir quality depends on the petrophysical and mechanical properties of reservoir rocks, which can be better understood by exploring their sedimentary and diagenetic history, revealed by the study of chalk microtexture variability. 相似文献
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B. Forel F. Monna C. Petit O. Bruguier R. Losno P. Fluck C. Begeot H. Richard V. Bichet C. Chateau 《Journal of Geochemical Exploration》2010
Two peat sequences were sampled in the vicinity of the main mining districts of the Vosges Mountains: Sainte-Marie-aux-Mines and Plancher-les-Mines. Lead isotopic compositions and excess lead fluxes were calculated for each of these radiocarbon-dated sequences. Geochemical records are in very good agreement with the mining history of the area, well known over the last millennium. Except for an anomaly corresponding to the Middle Bronze Age which has not yet been resolved, there is no clear geochemical evidence of local metal production in the Vosges before the 10th century as excess lead deposition archived between 500 BC and 500 AD is attributed to long-range transport of polluted particulate matter. The approach described here can be applied to other mining districts where archaeological evidence is scarce or even lacking, but where past exploitation is suspected. 相似文献
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