High-pressure Raman studies of methane hydrate were performed using a diamond anvil cell in the pressure range of 0.1–86 GPa
at room temperature. Raman spectra of the methane molecules revealed that new softened intramolecular vibration mode of ν1 appeared at 17 GPa and that the splitting of vibration mode of ν3 occurred at 15 GPa. The appearance of these two modes indicates that an intermolecular attractive interaction increases between
the methane molecules and the host water molecules and between the neighboring methane molecules. These interactions might
result in the exceptional stability of a high-pressure structure, a filled ice Ih structure (FIIhS) for methane hydrate, up
to 40 GPa. At 40 GPa, a clear change in the slope of the Raman shift versus pressure occurred, and above 40 GPa the Raman
shift of the vibration modes increased monotonously up to 86 GPa. A previous XRD study showed that the FIIhS transformed into
another new high-pressure structure at 40 GPa. The change in the Raman spectra at 40 GPa may be induced by the transition
of the structure. 相似文献
Bentonite clay is a micro-inhomogeneous material, which consists of clay minerals (mainly montmorillonite), macro-grains (mainly quartz), water, air and others. Properties of the saturated bentonite clay are essentially characterized by the montmorillonite and water (i.e. montmorillonite hydrate). We analyze the molecular behavior of sodium montmorillonite hydrate Na1/3Al2[Si11/3Al1/3]O10(OH)2·nH2O by applying a molecular dynamics (MD) simulation method. And by using the MD results we calculate the swelling property of the montmorillonite hydrate, and compare with an experimental result. Next, by using the same MD procedure we treat a montmorillonite mineral with a large number of external water molecules to check the properties of the water. Here we treat pure- and salt-water. Then we calculate the diffusivity and viscosity of water molecules and Na+ and Cl− ions.
For extending the microscopic characteristics of constituent materials to a macroscopic seepage behavior of the micro-inhomogeneous material we apply a homogenization analysis (HA). That is, starting with the Navier–Stokes equation with distributed viscosity that is calculated by the former MD procedure we determine macroscopic permeability characteristics of bentonite for both cases of pure- and salt-water. Then, by using the permeability property we calculate long-term consolidation behavior of buffering clay, which is planed to be used for high-level radioactive waste (HLRW) management. Here the deformation is treated under the well-defined Cam clay model. 相似文献
The Banda Sea earthquake of November 4, 1963 (h = 100 km, mB = 7.8) is probably one of the largest intermediate-depth shocks to have occurred worldwide this century. The mechanism of this earthquake is studied in detail on the basis of P-wave first motion, surface wave and aftershock data. From the analysis of long-period multiple surface waves, a seismic moment of 3.1 × 1028 dyn-cm is obtained, which is the largest reported so far for any intermediate or deep focus shock. This value, together with the estimated fault area of 90 × 70 km2, gives an average dislocation of 7.0 m and a stress drop of 120 bar. This event represents an oblique thrust movement on a plane with dip direction N170°E, dip 48° and rake 52°. A geometrical consideration for the fault plane and the configuration of the inclined seismic zone beneath the Banda arc suggests, almost definitely, that the large-scale faulting took place within the subducted plate and offset it. Further repetition of such large-scale faulting might eventually break the subducted plate. The 1963 Banda Sea earthquake thus represents a seismological manifestation of the large-scale deformation of the subducted plate in the mantle. 相似文献
The Resonance Capacity Method is proposed for the earthquake response analysis of hysteretic structures. Resonance Capacity is a physical quantity of structures which is related to the hysteretic energy absorbed by structures in one cycle and is equated to the acceleration, velocity and displacement amplitudes α0, d0 and d0 of earthquake ground motions at resonance.1 According to the idealized trapezoidal approximation of earthquake ground motions in the logarithmic period–velocity plane as proposed by Veletsos and Newmark,8 the Resonance Capacity property applies in each period range, short, medium and long, where α0, v0 and d0 respectively are approximately constant. In the medium range of periods, the energy dissipated in hysteretic loops and the deformation amplitudes of a single-degree system with elasto–plastic force–deformation relationships are calculated for the case of El Centro 1940, 18 May earthquake, by this Resonance Capacity Method. The result is compared with results from conventional numerical response analyses obtained by Berg and Thomaides,14 Kato and Akiyama12 and Veletsos and Newmark,8 and the general agreement is seen to be good. Therefore, it may be possible to apply this Resonance Capacity Method over the entire range of periods. By means of this method the earthquake response analysis of hysteretic systems can be performed easily, and the hysteretic energy and fatigue characteristics of structures may be taken into account directly, up to the point of fracture. 相似文献
Distribution of silicic acid (Si(OH)4) in bottom water was investigated in the central Seto Inland Sea under stratified conditions in summer. Water samples were collected at 10 stations on April 24 and 25 and July 7 and 8, 2012. In July, stratification progressed, and a cold water mass (dome) of <20 °C appeared. In response to the cold dome, low oxygen content was observed in the bottom layer of the eastern part of Hiuchi-Nada. In this water mass site, apparent oxygen utilization values calculated from dissolved oxygen (DO) concentrations increased, coinciding with increase of Si(OH)4 concentrations from April to July. This suggests that increase of Si(OH)4 [dissolution of biogenic silica (diatom frustules)] was accompanied by DO consumption due to degradation of organic matter such as plankton soft tissue. These findings suggest that a bacterial degradation of the organic matrix that covers diatom frustules could accelerate the dissolution of biogenic silica in bottom water under stratified conditions. 相似文献
Abstract An ice core sampling program was conducted during the North Water (NOW) Polynya Project 1998 Experiment in northern Baffin Bay during April‐May 1998. The physical properties of snow and sea ice as well as the microstructure and stable isotopic composition of first‐year landfast sea ice near the polynya were investigated. The thickness of sea ice at the sampling sites ranged between 147 and 194 cm with thinner snow cover during the period between mid‐April and late May. The ice was characterized as typical first‐year landfast sea ice, being composed of a thin granular ice layer at the top and an underlying columnar ice layer towards the bottom of the ice. The samples obtained at a site closer to the ice edge of the polynya contained a thin granular ice layer originating from frazil ice near the ice bottom. Formation of frazil ice was considered to be caused by turbulent processes induced by winds, waves and currents forced from the polynya and also mixing with water masses produced at the polynya. 相似文献
Marble has a great potential to understand a history of various geological events occurring during tectonic processes. In order to decode metamorphic–metasomatic records on C–O isotope compositions of marble at mid-crustal conditions, we conducted a C–O–Sr isotope study on upper amphibolite-facies marbles and a carbonate–silicate rock from the Hida Belt, which was once a part of the crustal basement of the East Asian continental margin. Carbon and oxygen isotope analyses of calcite from marbles (Kamioka area) and a carbonate–silicate rock (Wadagawa area) show a large variation of δ13C [VPDB] and δ18O [VSMOW] values (from −4.4 to +4.2 ‰ and +1.6 to +20.8 ‰, respectively). The low δ13C values of calcites from the carbonate–silicate rock (from −4.4 to −2.9 ‰) can be explained by decarbonation (CO2 releasing) reactions; carbon–oxygen isotope modeling suggests that a decrease of δ13C strongly depends on the amount of silicate reacting with carbonates. The occurrence of metamorphic clinopyroxene in marbles indicates that all samples have been affected by decarbonation reactions. All δ18O values of calcites are remarkably lower than the marine-carbonate values. The large δ18O variation can be explained by the isotope exchange via interactions between marble, external fluids, and/or silicates. Remarkably low δ18O values of marbles that are lower than mantle value (~+5 ‰) suggest the interaction with meteoric water at a later stage. Sr isotope ratios (87Sr/86Sr = 0.707255–0.708220) might be close to their protolith values. One zircon associated with wollastonite in a marble thin-section yields a U–Pb age of 222 ± 3 Ma, which represents the timing of the recrystallization of marble, triggered by H2O-rich fluid infiltration at a relatively high-temperature condition. Our isotope study implies that the upper amphibolite-facies condition, like the Hida Belt, might be appropriate to cause decarbonation reactions which can modify original isotope compositions of marble if carbonates react with silicates. 相似文献
We present a fully sampled C18O (1–0) map towards the southern giant molecular cloud (GMC) associated with the H ii region RCW 106, and use it in combination with previous 13CO (1–0) mapping to estimate the gas column density as a function of position and velocity. We find localized regions of significant 13CO optical depth in the northern part of the cloud, with several of the high-opacity clouds in this region likely associated with a limb-brightened shell around the H ii region G333.6−0.2. Optical depth corrections broaden the distribution of column densities in the cloud, yielding a lognormal distribution as predicted by simulations of turbulence. Decomposing the 13CO and C18O data cubes into clumps, we find relatively weak correlations between size and linewidth, and a more sensitive dependence of luminosity on size than would be predicted by a constant average column density. The clump mass spectrum has a slope near −1.7, consistent with previous studies. The most massive clumps appear to have gravitational binding energies well in excess of virial equilibrium; we discuss possible explanations, which include magnetic support and neglect of time-varying surface terms in the virial theorem. Unlike molecular clouds as a whole, the clumps within the RCW 106 GMC, while elongated, appear to show random orientations with respect to the Galactic plane. 相似文献