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81.
Abstract Some approaches of one-dimensional time-dependent magneto-hydrodynamic modeling of the structure of the inner coma of comet Halley are considered. The influence of the magnetic field diffusion on this structure is studied. The solution of Cravens (1989) approach containing classic magnetic diffusion is compared with an approach containing a specific diffusion, caused by non-instantaneous mass-loading of new ions. A case with no magnetic field is also considered. Common features of all the solutions are obtained. Special attention is paid to the sharp velocity jump, synchronized with a local density pick. Some differences between two types of magnetic field diffusion are discussed. A possible connection is supposed between this consideration and the large-scale shock fitting modeling of the solar plasma-comet interaction. 相似文献
82.
鄂东北大别杂岩中混合岩形成的动力学机制 总被引:3,自引:1,他引:3
本文针对中小位移量伸缩缝构造进行设计研究,提出了一种常温固化型桥梁伸缩缝。经过对伸缩量Δ20cm,Δ=40cm的多座桥梁的实验应用表明,这是一种适用于中小位移量桥梁中性能良好的伸缩缝,施工简便。其桥缝具体结构为,在两侧拍击区采用钢纤维混凝土增,缝内用高分子聚合物与一定比例的水泥及掺合物拌和均匀,经一段时间与桥面和加固铺装层固化成具有较高弹性和一定强度的整体式桥梁伸缩缝。其效果良好,供应用参考。 相似文献
83.
84.
在区域酸沉积模式(RADM)基础上,设计了一个高分辨对流层(TL)物质交换模式(EM3)。EM3在以下五个方面明显不同于RADM:第一,增加行星边界层(PBL)的垂直网格层次;第二、TL内考虑分层的垂直涡旋扩散系数型;第三,使用TL内分层的水平涡旋扩散系数型;第四,采用包含有植物冠层垂直结构影响的新干沉积速度型;第五,使用数值扩散小的二阶矩守恒平流格式.用EM3和RADM对OSCAR Ⅳ实例作对比模拟,结果表明EM3能更好地预测出TL内的三维物质分布规律,在同样条件下,两模式预测的PBL低层中心浓度比值均大于1.8,最大值可大于3。 相似文献
85.
在寻求层状云中催化剂扩散议程的解时,一般都假定风速为常值,但实际上风速是随高度变化的。该文在云中催化剂的数值模式中考虑了风速随高度的变化,用差分格式求其解,并进行了个例计算和比较分析。 相似文献
86.
87.
On the interpretation of peak metamorphic temperatures in light of garnet diffusion during cooling 总被引:13,自引:0,他引:13
F. S. SPEAR 《Journal of Metamorphic Geology》1991,9(4):379-388
Abstract Finite difference models of Fe-Mg diffusion in garnet undergoing cooling from metamorphic peak conditions are used to infer the significance of temperatures calculated using garnet-biotite Fe-Mg exchange thermometry. For rocks cooled from high grades where the garnet was initially homogeneous, the calculated temperature (Tcalc) using garnet core and matrix biotite depends on the size of the garnet, the ratio of garnet to biotite in the rock (Vgarnet/Vbiotite) and the cooling rate. For garnets with radii of 1 mm and Vgarnet/Vbiotite<1, Tcalc is 633, 700 and 777°C for cooling rates of 1, 10 and 100°C/Ma. For Vgarnet/Vbiotite= 1 and 4 and a cooling rate of 10° C/Ma, Tcalc is approximately 660 and 610° C, respectively. Smaller and larger garnets have lower and higher Tcalc, respectively. These results suggest that peak metamorphic temperatures may be reliably attained from rocks crystallized at conditions below Tcalc of the garnet core, provided that Vgarnet/Vbiotite is sufficiently small (<0.1) and that the composition of the biotite at the metamorphic peak has not been altered during cooling. Numerical experiments on amphibolite facies garnets with nominal peak temperatures of 550–600° C generate a ‘well’in Fe/(Fe + Mg) near the rim during cooling. Maximum calculated temperatures for the assemblage garnet + chlorite + biotite + muscovite + plagioclase + quartz using the Fe/(Fe + Mg) at the bottom of the ‘well’with matrix biotite range from 23–43° C to 5–12° C below the peak metamorphic temperature for cooling rates of 1 and 100° C/Ma, respectively. Maximum calculated temperatures for the assemblage garnet + staurolite + biotite + muscovite + plagioclase + quartz are approximately 70° C below the peak metamorphic temperature and are not strongly dependent on cooling rate. The results of this study indicate that it may be very difficult to calculate peak metamorphic temperatures using garnet-biotite Fe-Mg exchange thermometry on amphibolite facies rocks (Tmax > 550° C) because the rim composition of the garnet, which is required to calculate the peak temperature, is that most easily destroyed by diffusion. 相似文献
88.
The steepest descent(or ascent)search is employed for finding optimum diffusion coefficients in T42L9Gmodel,with a view to improving the model's computational stability or prediction accuracy.The method of thesteepest descent search is first described,in which the golden section search is chosen as the fundamental one-dimensional search used in the multi-dimentional steepest descent search,and then the optimization of the dif-fusion coefficients is described. 相似文献
89.
Evaluation and application of dialysis porewater samplers for microbiological studies at sediment-water interfaces 总被引:1,自引:1,他引:1
The equilibrium diffusion technique has become a valuable tool for ecological and biogeochemical studies in aquatic environments. In sediment ecosystems, changes in concentration of microbial metabolites with increasing depth can be determined dependably and reproducibly with this technique. Since the permeation characteristics of the membranes employed are crucial, selecting the proper membrane requires knowledge about its behavior under conditions which prevail in the natural environment. Thirteen polymer sheets were evaluated comparing permeation terms for biogeochemically relevant solutes, biodegradability, and mechanical strength. Cellulose-based dialysis membranes are most satisfactory when employed in low temperature anoxic environments. For this membrane, correction terms were calculated to account for diffusion losses during retrieval and sampling. Optimal incubation times can now be predicted from experimentally determined permeation coefficients for several porewater solutes. Dialysis porewater samplers (DPS) have been successfully applied during more than 100 independent experiments for the collection of interstitial water from surface sediments. DPS were used for water depths as deep as 290 meters. 相似文献
90.
We have theoretically considered the problem of interpretation of nutrient profiles in the upper ocean (100–2000m). We compare
the experimental depth profiles of nonconservative tracers, both stable and radioactive, with solutions of one-dimensional
steady state transport equations of increasing complexity including situations not encountered in the real oceans. Apart from
gaining insight into the nutrient transport processes, this analysis is useful in offering a way to obtain operational estimates
of depth dependent/independent eddy diffusivity and dissolution fluxes in the ocean. These parameters are essential for estimating
new production, total production and burial of carbon in the sediments. 相似文献