排序方式： 共有36条查询结果，搜索用时 15 毫秒
11.
We investigated spherically symmetric solution for nonrelativistic cosmological fluid equations and thermodynamic equation of state for Newtonian stars. It was shown that the assumption of a polytropic equation, , at the center of the star only suffices to integrate the equations explicitly. Our exact solution yields many fruitful results such as stellar stability, spherical oscillation and collapses of stars. Pressure, temperature, and density profiles inside stars were obtained. Central densities, pressures and temperatures of the Newtonian stars such as Sun, Jupiter and Saturn were also calculated. Collapse and expansion mechanism was explained by the heat transfer mechanism inside star. The upper bound value of white dwarf mass obtained by the Newtonian cosmological fluid equations turns out to be comparable to the static limit of Chandrasekhar one. Motion of the Universe was also discussed within the framework of Newtonian mechanics. Our calculation results without considering nuclear reactions inside stars may be applicable to the formation of protostars. 相似文献
12.
The nomenclature of replacement deposits is reviewed in terms of two processes, namely those involving the reaction between: (a) carbonate and siliceous rocks and (b) carbonate and unusual solutions, commonly, but not always, related to granitoids. ‘Wrigglite’ skarn is an example of a replacement deposit produced by process (b). It is highly characteristic rock consisting of alternating light layers of fluorite ± other F‐rich minerals and dark layers composed usually of Fe‐rich minerals or, rarely, Be‐rich minerals. The layers formed parallel or sub‐parallel to fractures, which are now veins, by a Leisegang‐type diffusion process. Repeated periods of fracturing, with growth away from sequentially produced fractures, produced an apparently chaotic ‘wrigglite’ skarn. The skarn is invariably enriched in Fe, F, Sn, Be, W, Bi and Zn. For ‘wrigglite’ to form, fluorine must be greater than 9 weight percent in the rock, and the intrusion of a Sn‐leucogranite ('A‐type') high into the crust is needed. Recognition of ‘wrigglite’ is important because (1) in some areas it is an ore of Sn (Mt Bischoff, Tas.), rare earth metals (Bayan Obo, China) or Be (Lost River, Alaska); (2) it indicates a high‐level environment of emplacement of a Sn‐granitoid; and (3) it indicates clearly that intricate layering can be produced by a diffusional process and not only by primary sedimentation. 相似文献
13.
The purpose of this study was to evaluate the effects of climate change on the drought and flood risks of a multipurpose dam. To achieve this, A2 climate change scenarios of RegCM3 were collected about Chungju Dam in Korea. To analyze drought risks, weather data obtained by the statistical downscaling method were entered to produce runoff series by runoff modeling and water balance was analyzed based on water use scenarios to review changes in the storage volume under climate change. To analyze flood risks, changes in water levels of the dam in future flood seasons were reviewed based on the current dam operation method. The results of the review indicated that both the drought and the flood risks of the dam would increase in the future. The reason was considered to be the movement of the flood season’s runoff characteristics from July and August to August and September because of climate change. Therefore, for climate change adaptation planning, not only quantitative changes in hydrologic values but also changes in temporal characteristics should be considered and given importance. 相似文献
14.
Hanbin Kwak Joachim Saborowski Si-Young Lee Myoung-Soo Won Kyo-Sang Koo 《International journal of geographical information science》2013,27(9):1589-1602
Most forest fires in Korea are spatially concentrated in certain areas and are highly related to human activities. These site-specific characteristics of forest fires are analyzed by spatial regression analysis using the R-module generalized linear mixed model (GLMM), which can consider spatial autocorrelation. We examined the quantitative effect of topology, human accessibility, and forest cover without and with spatial autocorrelation. Under the assumption that slope, elevation, aspect, population density, distance from road, and forest cover are related to forest fire occurrence, the explanatory variables of each of these factors were prepared using a Geographic Information System-based process. First, we tried to test the influence of fixed effects on the occurrence of forest fires using a generalized linear model (GLM) with Poisson distribution. In addition, the overdispersion of the response data was also detected, and variogram analysis was performed using the standardized residuals of GLM. Second, GLMM was applied to consider the obvious residual autocorrelation structure. The fitted models were validated and compared using the multiple correlation and root mean square error (RMSE). Results showed that slope, elevation, aspect index, population density, and distance from road were significant factors capable of explaining the forest fire occurrence. Positive spatial autocorrelation was estimated up to a distance of 32 km. The kriging predictions based on GLMM were smoother than those of the GLM. Finally, a forest fire occurrence map was prepared using the results from both models. The fire risk decreases with increasing distance to areas with high population densities, and increasing elevation showed a suppressing effect on fire occurrence. Both variables are in accordance with the significance tests. 相似文献
15.
16.
Abstract A study has been made of a basic state of axisymmetric flow, at large rotational Reynolds numbers, in a double-diffusive stratified fluid contained in a vertically-mounted, differentially-rotating cylindrical cavity. The aim is to describe the qualitative characteristics of the flow of a fluid, the density of which is stratified by two diffusive effects, i.e., temperature and salinity gradients. Attention is confined to situations in which the temperature and salinity gradients make opposing contributions to the overall density profile, the undisturbed stratification being gravitationally stable. Finite difference numerical solutions of the governing Navier-Stokes equations have been obtained using the Boussinesq approximation. The results are presented in a way that illustrates the explicit effects of double-diffusivity when the cavity aspect ratio, height/radius, is O(1). The principal non-dimensional parameters characterizing the flow field are identified. In the interior core, the primary dynamic balance is between the horizontal density gradient and the vertical shear of the prevailing azimuthal velocity. The effective stratification is seen to decrease as the double-diffusivity increases, even if the overall stratification parameter, St, is held constant. The solute field contains a very thin boundary layer structure at large Lewis numbers. The effective stratification increases with the Prandtl number. Results have been derived for extreme values of the cavity aspect ratio. For small cavity aspect ratios, the dominant dynamic ingredients are viscous diffusion and rotation. For large aspect ratios, the bulk of the flow field is determined by the rotating sidewall. In this case, the direct influence of the double-diffusivity is minor. 相似文献
17.
The objective of this study was conducted to identify the possibility of using Chironomus metallothionein (MT) and vitellogenin (VTG) as biomarkers of stress caused by endocrinedisrupting chemicals (EDCs), heavy metals, herbicides and veterinary antibiotics. We characterized the MT and VTG cDNA in Chironomus riparius and evaluated their mRNA expression profiles following exposure to different environmental pollutants. The gene expression analysis showed that the MT mRNA levels increased significantly after long-term exposure to cadmium (Cd), copper (Cu), Lead (Pb), di(2-ethylhexyl) phthalate (DEHP), and 2,4-dichlorophenoxyacetic acid (2,4-D). Moreover, the VTG mRNA expression increased significantly in C. riparius larvae exposed to BPA, NP, DEHP, Cd, 2,4-D and fenbendazole. Evaluation of the long-term effects of environmental pollutants revealed up regulation of Chironomus MT mRNA in response to DEHP exposure among EDCs, and the level of the VTG mRNA was increased significantly following treatment with Cd and herbicide 2,4-D at all concentrations in a dose-dependent manner. These results indicate that VTG could be used as a potential biomarker of herbicide and Cd as well as EDCs, while MT was a potential biomarker of heavy metals such as Cd, Cu, and Pb in aquatic environments. 相似文献
18.
D. V. Phani Kumar A. K. Patra Y.-S. Kwak K.-H. Kim G. Yellaiah 《Astrophysics and Space Science》2009,323(3):225-233
In this paper, we attempt to identify the driving forces responsible for the generation of low-latitude E-region field-aligned
irregularities (FAIs). It is evident that the low-latitude E-region FAIs occur both during the day and night with preferential
occurrence being most during local sunrise period. Simultaneous measurements are made with Gadanki radar and nearby located
Ionosonde for understanding the low-latitude Es–FAIs relationship. The observations suggest that the occurrence and SNR of
FAIs have a close relationship with f
t
E
s
−−f
b
E
s
. Finally, using the past electron density profiles and reasonable values of electric field, we have shown that it is generally
difficult with the gradient drift instability to explain low-latitude E-region FAIs when electric field alone is considered
as driving agency. We hypothesize that neutral winds play important role for the generation of irregularities at low latitudes
outside the electrojet belt either by forming sharp Es layers or by enhancing the differential drift of electrons and ions
or by both. 相似文献
19.
A series of experiments and simulations were performed to ascertain the rate at which phosphorus is released using a water quality model in Saemangeum Lake, an artificially constructed lake located in an estuary. The general inflow of seawater once a day contributed to the formation of a halocline in the lake water, which caused variation in the vertical concentration of dissolved oxygen. The halocline was mainly observed in the deep downstream regions of Saemangeum Lake that are close to the op... 相似文献
20.
Teunis A. P. Kwak 《Contributions to Mineralogy and Petrology》1974,44(1):57-80
Existing staurolite breakdown reactions are briefly discussed and examples of each of the main types suggested from textural evidence from different well studied areas are analyzed. From the staurolite textural data, it is shown that: the pseudomorphic replacement is generally equal area; the replacement is usually by a single mineral or, where a number occur, one volumetrically greatly predominates; and successive reaction coronas exist around a single reactant grain. The analogy between the textural coronas and “monomineralic zones” at the contact of dissimilar rock types is drawn with the subsequent inference that reaction coronas in some, if not most, cases are out of equilibrium with the rest of the assemblage as well as the reactant mineral. In staurolite reaction textures, different grains in a single thin section normally have: different amounts (ratios) of product minerals, different product minerals, some grains which have reacted while others have not and different grains which have reacted to different degrees. Traverses of essentially total chemical analyses across staurolite grains in two test sections showed that considerable intertextural chemical variation in single thin sections exist which is much greater than the chemical variations within textures. Variations of, from 0.59 to 1.86 weight percent ZnO in different homogeneous staurolite grains occur in a single thin section (Z-5670911) and measurable variations of Si, Al, Fe, Mg and Mn are recorded. In all the textures analyzed both Zn and Al was deficient on the product side of balanced reactions, and particularly Zn can be shown to have been lost from the area of the section. The chemical and textural conclusions show that the limits of equilibrium systems, from which metamorphic reactions can be inferred, must be confined to the boundaries of the pseudomorphic texture, which means that ionic (complex bearing ?) species are involved and these systems must be treated as being open. 相似文献