Calcite crystals were grown in a closed system by recrystallization of synthetic and natural aragonite crystals, in the presence of various CaCl2-MgCl2 solutions with and without NaCl.The distribution of Mg2+ between calcite and solution at the entire temperature range is heterogeneous, closely following the Doerner-Hoskins (Doerner and Hoskins, 1925) distribution law. λMg2+C is strongly dependent on temperature, being: 0·0573 ± 0·0017 at 25°C, 0·0681 ± 0·0019 at 35°C, 0·0778 ± 0.0022 at 50°C, 0·0973 ± 0·0021 at 70°C, and 0·1163 ±0 ·0034 at 90°C. λMg2+C is independent of the absolute concentration of Ca2+ in solution as well as of the presence of NaCl.Relatively high λMg2+C values are obtained during the initial reaction stages when too-highly reactive synthetic aragonites are recrystallized. SEM micrographs show that calcite crystals grown from such aragonites are imperfect and that their earlier formed Mg-rich cores redissolve later, resulting in apparently inconsistent λMg2+C values.Calculations applying the new λMg2+C value for 25°C and the solubility data for magnesian calcites (Chaveet al., 1962) demonstrate that although no calcite should be expected to precipate directly from open sea water, its direct precipitation (or recrystallization from aragonite) is possible in closed diagenetic systems which still contain marine solutions, provided a temporary increase in the dissolved calcium concentration takes place.The λMg2+C values obtained allow for a new insight into processes of calcite cementation of reefs and a variety of other carbonate sediments, and for a more precise definition of dedolomitization chemistry. 相似文献
Data obtained by the near-infrared spectrometer carried by the NEAR-Shoemaker spacecraft show that the spectral properties of the asteroid Eros vary with temperature. The manner in which they vary demonstrates that the mineral olivine is a major constituent of the surface. The near-IR temperature-dependent spectral properties of Eros in the northern hemisphere, and for two individual regions on the surface, show clear evidence of the presence of the mineral olivine and are a close match to the temperature-spectral behavior of LL-type ordinary chondrite meteorites. While the presence of other olivine-rich meteorites cannot be excluded, H-type ordinary chondrites are clearly too pyroxene-rich to be permitted as a major surface component of Eros. The results of the thermal-spectral analysis are consistent with results from analysis of conventional reflectance spectra of the asteroid and contribute unambiguous detection of olivine to the understanding of the surface composition of Eros. 相似文献
This work studies the effects of long human habitation on site geotechnical conditions. It is focused on the city of Zefat that is located on the borders of the Dead Sea Transform in northern Israel. The city of Zefat, suffered severe damage and loss of life in historical earthquakes, as a consequence of earthquake induced landslides (EILS). In this work we evaluate the current EILS hazard for the city of Zefat using a GIS-based regional Newmark analysis, with calibration of the calculated Newmark displacement (representing EILS hazard) using maps of field evidence and historical documents testifying to slope instability that occurred in historical earthquakes.
We found that the core city of Zefat is built on a layered anthropogenic material, few meters deep which, was deposited as a result of more than 2000 years of human habitation. The anthropogenic material is mechanically weak, susceptible to slope failure and to amplification of seismic-shaking. It is responsible for the city's devastation in historical earthquakes and it is the source for the current high seismic hazard as well.
Our model shows that earthquakes of magnitudes (Mw) 5, 6 and 7 at distances of up to 10 km, 50 km and more than 100 km, respectively, are likely to induce landslides in the core city of Zefat. The current engineering status of the city is poor, and as a consequence severe damage and loss of life are expected in future earthquakes due to EILS, unless major engineering efforts are made. Cities in the Eastern Mediterranean with comparable long habitation histories (e.g., Jerusalem, Tiberias, Nablus, Amman) are expected to have similar geotechnical problems in their old sections and are advised to take appropriate engineering steps to reduce damage and loss of life in future earthquakes.
Evaluation of historical earthquake magnitudes based on reported local-damage may, however, lead to overestimated magnitudes where the damaged sites are built on anthropogenic talus (a common setting in the vicinity of the Dead Sea Transform). 相似文献
In this paper, we formulate a finite element procedure for approximating the coupled fluid and mechanics in Biot’s consolidation
model of poroelasticity. Here, we approximate the pressure by a mixed finite element method and the displacements by a Galerkin
method. Theoretical convergence error estimates are derived in a discrete-in-time setting. Of particular interest is the case
when the lowest-order Raviart–Thomas approximating space or cell-centered finite differences are used in the mixed formulation
and continuous piecewise linear approximations are used for displacements. This approach appears to be the one most frequently
applied to existing reservoir engineering simulators. 相似文献
In this paper, we formulate a finite element procedure for approximating the coupled fluid and mechanics in Biot’s consolidation
model of poroelasticity. Here, we approximate the pressure by a mixed finite element method and the displacements by a Galerkin
method. Theoretical convergence error estimates are derived in a continuous in-time setting for a strictly positive constrained
specific storage coefficient. Of particular interest is the case when the lowest-order Raviart–Thomas approximating space
or cell-centered finite differences are used in the mixed formulation, and continuous piecewise linear approximations are
used for displacements. This approach appears to be the one most frequently applied to existing reservoir engineering simulators. 相似文献
Turbulent flow in a corn canopy is simulated using large-eddy simulation (LES) with a Lagrangian dynamic Smagorinsky model.
A new numerical representation of plant canopies is presented that resolves approximately the local structure of plants and
takes into account their spatial arrangement. As a validation, computational results are compared with experimental data from
recent field particle image velocimetry (PIV) measurements and two previous experimental campaigns. Numerical simulation using
the traditional modelling method to represent the canopy (field-scale approach) is also conducted as a comparison to the plant-scale
approach. The combination of temporal PIV data, LES and spatial PIV data allows us to couple a wide range of relevant turbulence
scales. There is good agreement between experimental data and numerical predictions using the plant-scale approach in terms
of various turbulence statistics. Within the canopy, the plant-scale approach also allows the capture of more details than
the field-scale approach, including instantaneous gusts that penetrate deep inside the canopy. 相似文献
Particle image velocimetry (PIV) data obtained in a wind-tunnel model of a canopy boundary layer is used to examine the characteristics
of mean flow and turbulence. The vector spacing varies between 1.7 and 2.5 times the Kolmogorov scales. Conditional sampling
based on quadrants, i.e. based on the signs of velocity fluctuations, reveals fundamental differences in flow structure, especially
between sweep and ejection events, which dominate the flow. During sweeps, the downward flow generates a narrow, highly turbulent,
shear layer containing multiple small-scale vortices just below canopy height. During ejections, the upward flow expands this
shear layer and the associated small-scale flow structures to a broad region located above the canopy. Consequently, during
sweeps the turbulent kinetic energy (TKE), Reynolds stresses, as well as production and dissipation rates, have distinct narrow
peaks just below canopy height, whereas during ejections these variables have broad maxima well above the canopy. Three methods
to estimate the dissipation rate are compared, including spectral fits, measured subgrid-scale (SGS) energy fluxes at different
scales, and direct measurements of slightly underresolved instantaneous velocity gradients. The SGS energy flux is 40–60%
of the gradient-based (direct) estimates for filter sizes inside the inertial range, while decreasing with scale, as expected,
within the dissipation range. The spectral fits are within 5–30% of the direct estimates. The spectral fits exceed the direct
estimates near canopy height, but are lower well above and below canopy height. The dissipation rate below canopy height increases
with velocity magnitude, i.e. it has the highest values during sweep and quadrant 1 events, and is significantly lower during
ejection and quadrant 3 events. Well above the canopy, ejections are the most dissipative. Turbulent transport during sweep
events acts as a source below the narrow shear layer within the canopy and as a sink above it. Transport during ejection events
is a source only well above the canopy. The residual term in the TKE transport equation, representing mostly the effect of
pressure–velocity correlations, is substantial only within the canopy, and is dominated by sweeps. 相似文献