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191.
V. P. Solntsev R. I. Mashkovtsev A. V. Davydov E. G. Tsvetkov 《Physics and Chemistry of Minerals》2008,35(6):311-320
It is shown the possibility to determine the coordination of paramagnetic ions in disordered solid structures, e.g., in barium
borate glasses. For this purpose the electron paramagnetic resonance (EPR) method was used to study α-and β-BaB2O4 crystals and glasses of 45·BaO × 55·B2O3 and 40·BaO × 60·B2O3 (mol%) composition activated by Ag+ and Pb2+ ions. After the samples were exposed to X-rays at 77 K, different EPR centers were observed in them. In α-and β-BaB2O4 crystals and glasses the EPR centers Ag2+, Ag0, Pb+, Pb3+, and hole centers of O− type were studied. The EPR parameters of these centers and their arrangement in crystal structure were determined. It is
shown that Pb3+ ions in β-BaB2O4 crystals occupy Ba2+ position in an irregular polyhedron from the eight oxygen, whereas in α-BaB2O4 crystals they occupy Bа2 position in a sixfold coordination. Pb+ ions in α-BaB2O4 crystals occupy Bа1 position in a ninefold coordination from oxygen. In barium borate glasses, Pb3+ ions were studied in coordination polyhedron from six oxygen atoms and in a polyhedron from nine to ten oxygen atoms. It
is assumed that the established difference in the structural position of Pb3+ ions in glasses is due to their previous incorporation in associative cation–anion complexes (AC) and “free” structure-forming
cations (FC). Computer simulations have been performed to analyze the stability of specific associative complexes and to compare
their bond lengths with experimental data. 相似文献
192.
Nutrient ecology and trace gas processing are intimately coupled in the surface ocean and participate in key linkages through the Earth biogeochemical system. We have added water column photochemistry for volatile sulfur and organic compounds to large scale nutrient cycle modules, in order to create a one dimensional, open ocean ecochemistry simulator. Phyto- and zooplankton, recyclers and biological waste products are represented through N and Fe densities. Dimethyl sulfide, carbonyl sulfide and the methyl halides are tracked individually along with certain precursors and nonmethane hydrocarbons. The model is applied along the 180 degree meridian in the Northern Hemisphere. Ecodynamics are validated against satellite ocean color maps. Biological/photochemical production terms are then iterated upon to match measured distributions for the trace gases. Data are most complete for dimethyl sulfide. Major patterns in its climatology are captured within individual ecological provinces. However, at the basin scale reduced sulfur release must be varied over almost an order of magnitude because the mechanism developed contains only one plant taxon. Based on sparser data, first order rate constants are estimated for phytoplanktonic exudation of the methyl halides. Parameters are also established for photolytic injection of carbonyl sulfide and propylene from the dissolved organics. Ocean general circulation models and interactive ocean-atmosphere transport simulations are discussed as frameworks for future application. 相似文献
193.
Wang Mingyu The University of Arizona Tucson Arizona USA Department of Water Resources Environmental Engineering China University of Geosciences Beijing Chen Jinsong Wan Li Department of Water Resources Environmental Engineering 《中国地质大学学报(英文版)》2001,12(3)
INTRODUCTIONGroundwaterorfluidflowmodelinginfracturedrocksisacomplicatedtheoreticalandappliedtopic.Boththeoreticallyandoperationally ,itisimportantinmanyfieldssuchasgeologicalandhydrogeologicalengineering ,environmentalengineeringandpetroleumengineerin… 相似文献
194.
G. Bourgault 《Mathematical Geology》1997,29(3):315-334
Parametric geostatistical simulations such as LU decomposition and sequential algorithms do not need Gaussian distributions.
It is shown that variogram model reproduction is obtained when Uniform or Dipole distributions are used instead of Gaussian
distributions for drawing i. i.d. random values in LU simulation, or for modeling the local conditional probability distributions
in sequential simulation. Both algorithms yield simulated values with a marginal normal distribution no matter if Gaussian,
Uniform, or Dipole distributions are used. The range of simulated values decreases as the entropy of the probability distribution
decreases. Using Gaussian distributions provides a larger range of simulated normal score values than using Uniform or Dipole
distributions. This feature has a negligible effect for reproduction of the normal scores variogram model but have a larger
impact on the reproduction of the original values variogram. The Uniform or Dipole distributions also produce lesser fluctuations
among the variograms of the simulated realizations. 相似文献
195.
Effects of eruption history and cooling rate on lava dome growth 总被引:1,自引:1,他引:0
To better understand the factors controlling the shapes of lava domes, laboratory simulations, measurements from active and prehistoric flows and dimensional analysis were used to explore how effusion history and cooling rate affect the final geometry of a dome. Fifty experiments were conducted in which a fixed volume of polyethylene glycol wax was injected into a tank of cold sucrose solution, either as one continuous event or as a series of shorter pulses separated by repose periods. When the wax cooling rates exceeded a critical minimum value, the dome aspect ratios (height/diameter) increased steadily with erupted volume over the course of a single experiment and the rate at which height increased with volume depended linearly on the time-averaged effusion rate. Thus the average effusion rate could be estimated from observations of how the dome shape changed with time. Our experimental results and dimensional analyses were compared with several groups of natural lava flows: the recently emplaced Mount St Helens and Soufrière domes, which had been carefully monitored while active; three sets of prehistoric rhyolite domes that varied in eruptive style and shape; and two sets of Holocene domes with similar shapes, but different compositions. Geometric measurements suggest that dome morphology can be directly correlated with effusion rate for domes of similar composition from the same locality, and that shape alone can be related to a dimensionless number comparing effusion rate and cooling rate. Extrapolation to the venusian pancake domes suggests that they formed from relatively viscous lavas extruded either episodically or at average effusion rates low enough to allow solidified surface crust to exert a dominating influence on the final morphology. 相似文献
196.
The most common method of reducing roll motion of ship-shaped floating systems is the use of bilge keel which act as damping elements. The estimation of the damping introduced by bilge keel is still largely based on empirical methods. The present work adopts the CFD approach to the estimation of roll damping, both without and with bilge keel and validates the results with experiments conducted in a wave flume. Specifically, free oscillation tests are conducted at model scale to obtain roll damping, both by experiments and CFD simulation and reasonably good comparisons are obtained. The experiments also include PIV study of the flow field and attempt has been made to correlate the measured flow field with that obtained by CFD. The CFD methodology has the potential to determine rationally the size and orientation of bilge keels in design with reasonably accurate estimate of the additional roll damping that it provides to ship's roll motion. 相似文献
197.
198.
Presence of the outer perforated cylinder reduces the direct wave impact on the inner cylinder, which has been testified by many researchers. However, the force reduction mechanism, which is complicated due to the wave-porous structure interaction, needs to be addressed in detail. The present study explains the mechanism with the aid of the computational fluid dynamics (CFD) tool STAR CCM+. This package is chosen for its capabilities to simulate viscous and turbulence effects caused by passage of waves. For the present study, flow fields around the twin cylinders with different orientations are examined with and without the outer perforated cover. Mechanism contributing to the reduction of force on the existing structure is explained in physical terms, and force reduction is quantified. The present study has direct application in the retrofitting application of offshore members. 相似文献
199.
Different operating conditions (e.g. design and off-design) may lead to a significant difference in the hydrodynamics performance of a ship, especially in the total resistance and wake field of ships. This work investigated the hydrodynamic performance of the well-known KRISO 3600 TEU Container Ship (KCS) under three different operating conditions by means of Particle Image Velocimetry (PIV) and Computational Fluid Dynamics (CFD). The comparison results show that the use of PIV to measure a ship’s nominal wake field is an important method which has the advantages of being contactless and highly accurate. Acceptable agreements between the results obtained by the two different methods are achieved. Results indicate that the total resistances of the KCS model under two off-design conditions are 23.88% and 13.92% larger than that under the designed condition, respectively. 相似文献
200.
Olivier Maury Yunne-Jai Shin Blaise Faugeras Tamara Ben Ari Francis Marsac 《Progress in Oceanography》2007,74(4):500-514
Numerical simulations using a physiologically-based model of marine ecosystem size spectrum are conducted to study the influence of primary production and temperature on energy flux through marine ecosystems. In stable environmental conditions, the model converges toward a stationary linear log–log size-spectrum. In very productive ecosystems, the model predicts that small size classes are depleted by predation, leading to a curved size-spectrum.It is shown that the absolute level of primary production does not affect the slope of the stationary size-spectrum but has a nonlinear effect on its intercept and hence on the total biomass of consumer organisms (the carrying capacity). Three domains are distinguished: at low primary production, total biomass is independent from production changes because loss processes dominate dissipative processes (biological work); at high production, ecosystem biomass is proportional to primary production because dissipation dominates losses; an intermediate transition domain characterizes mid-production ecosystems. Our results enlighten the paradox of the very high ecosystem biomass/primary production ratios which are observed in poor oceanic regions. Thus, maximal dissipation (least action and low ecosystem biomass/primary production ratios) is reached at high primary production levels when the ecosystem is efficient in transferring energy from small sizes to large sizes. Conversely, least dissipation (most action and high ecosystem biomass/primary production ratios) characterizes the simulated ecosystem at low primary production levels when it is not efficient in dissipating energy.Increasing temperature causes enhanced predation mortality and decreases the intercept of the stationary size spectrum, i.e., the total ecosystem biomass. Total biomass varies as the inverse of the Arrhenius coefficient in the loss domain. This approximation is no longer true in the dissipation domain where nonlinear dissipation processes dominate over linear loss processes. Our results suggest that in a global warming context, at constant primary production, a 2–4 °C warming would lead to a 20–43% decrease of ecosystem biomass in oligotrophic regions and to a 15–32% decrease of biomass in eutrophic regions.Oscillations of primary production or temperature induce waves which propagate along the size-spectrum and which amplify until a “resonant range” which depends on the period of the environmental oscillations. Small organisms oscillate in phase with producers and are bottom-up controlled by primary production oscillations. In the “resonant range”, prey and predators oscillate out of phase with alternating periods of top-down and bottom-up controls. Large organisms are not influenced by bottom-up effects of high frequency phytoplankton variability or by oscillations of temperature. 相似文献