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
Atmospheric concentrations of polycyclic aromatic hydrocarbons (PAHs) in Santiago de Chile city were evaluated to study particulate PAHs profiles during cold and spring weather periods. Urban atmospheric particulate matter PM10 was collected using High Volume PM10 samplers. Fifteen samples of 24 h during austral winter and 20 samples of 24 h during spring, 2000 were collected at two sampling sites (North–East and Central areas of the city) whose characteristics were representative of the prevailing conditions. Seventeen PAHs were quantified and total PAHs concentration ranged from 1.39 to 59.98 ng m−3, with a seasonal variation (winter vs. spring ratio) from 0.5 to 12.6 ng m−3. Molecular diagnostic ratios were used to characterize and identify PAHs emission sources such as combustion and biogenic emissions. Results showed that the major sources of respirable organic aerosol PM10 in Santiago are mobile and stationary ones. 相似文献
Grain‐size distribution is a fundamental tool for interpreting sedimentary units within depositional systems. The techniques assessed in this study are commonly used to determine grain‐size distributions for sand‐dominated sediments. However, the degree of consistency and differences in interpretation when using a combination of grain‐size methods have not yet been assessed systematically for sand‐dominated fluvial sediments. Results obtained from laser diffraction, X‐ray attenuation and scanning electron microscopy grain‐size analysis techniques were compared with those obtained from the traditional sieve/hydrometer method. Scanning electron microscopy was shown to provide an inaccurate quantitative analysis of grain‐size distributions because of difficulties in obtaining representative samples for examination. The X‐ray attenuation method is unsuitable for sand‐dominated sediments because of its upper size range of only 300 μm. The consistently strong correlation between the laser diffraction results and the sieve/hydrometer results shows that these methods are comparable for sand‐dominated fluvial sediments. Provided that sample preparation is consistent, the latter two methods can be used together within a study of such sediments while maintaining a high degree of accuracy. These results indicate that data for sand‐dominated fluvial sediments gained from the long‐established sieve/hydrometer method can be compared with confidence to those obtained by modern studies using laser diffraction techniques. 相似文献
The order-disorder phase transitions in NaNO3 and CaCO3 are simulated by molecular dynamics. The simulations are based on the potentials calculated from the Gordon–Kim modified
electron gas formalism extended to molecular ions. We successfully reproduced the transition temperature Tc and the abnormally large c axis thermal expansion observed in experiment. The phase transitions in NaNO3 and CaCO3 were found to be initiated by ±60 and ±180° reorientation of the NO3 and CO3 ions about the c axis. The orientations of NO3 and CO3 ions are continuous with six preferred calcite-type orientations above the phase-transition temperature.
Received: 30 January 2001 / Accepted: 11 May 2001 相似文献
We report on a comparative study of nearby shocked clouds with and without star formation, based on IRAS, HI(21cm), CO(1-0) NH3 (and other molecular line) observations. The dark clouds L1780 (no star formation) and L1251 (high SFE) are discussed here. Their density and velocity structure are compared with the predictions of the HD model of Horváth & Tóth (1995), Paper I. 相似文献
We have observed C2H2 and HCN rovibrational transitions near 13µm in absorption against GL2591. We also have observed rotational transitions at 0.6-3 mm of CS, HCN, H2CO, and HCO+. Analysis of the rotational lines, which arise in the extended cloud around the source, shows that no single density model can explain all the data. Models with density and temperature gradients do much better; in particular models withn(r) r–1.5 can reproduce the observed pattern of emission line strengths. The abundances show significant depletion compared to models of gas-phase chemistry. The rovibrational data were analyzed in comparison to the absorption line analysis of CO by Mitchellet al. (1989). Our data are consistent with the C2H2 and HCN absorption arising in the same warm (200 K) and hot (1010 K) components seen in CO, but we see little evidence for the cold (38 K) component seen in CO. The rovibrational lines from higher states (J 21) indicate that the hot HCN deviates from LTE, leading to a density of about 3 × 107 cm–3. Comparison of the two data sets shows that the rovibrational absorption of HCN, rather than arising in the extended envelope, must come from a region with a small angular extent. A model in which early-time gas phase abundances are preserved on grain mantles and released at high temperature can explain the data. 相似文献