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921.
In order to study the structure of a chemically homogeneous star in equilibrium, a density profile of the form T N exp(–µm(–)/kT) is suggested. As for polytropes, qualitative aspects of the resulting stellar model can be discussed analytically. In particular it is shown that one reobtains forN=3 Eddington's standard model, whereas forN<3 nearly polytropic models result. WhenN>3, the effective polytropic index does vary appreciably over the star. Numerical results indicate that the proposed density profile is quite reasonable in view of the simplicity of the model. From a comparison of the degree of precision of a polytropic approximation with that of the newly proposed model it follows that the new approximation is definitely better than the polytropic one. It is suggested that the model may be useful to study the structure of stellar clouds, clusters and (spherical) galaxies.Now at Department of Applied Mathematics, Queen Mary College, University of London, England.  相似文献   
922.
First systematic data on the variations of εNd(T) in the Neoproterozoic sedimentary sequence of the Baikal–Patom fold belt (Northern Transbaikalia) are reported. The range of obtained εNd(T) is–19.4…–2.0. It was established that the rocks of the Ballaganach and most part of the Dal’nyaya Taiga groups are characterized by εNd(T) from–19.4 to–16.3. Upsection, beginning from the Khomolkha Formation, the rocks show a sharp change in the initial Nd isotope composition (εNd(T)–8.3…–2.0). The results of Sm-Nd study of metasedimentary rocks of the BPB, as well as the comparison of their Sm-Nd characteristics with those of the inferred source areas suggest that the input of terrigenous material at the early stage of sedimentation in the Baikal–Patom belt was mainly related to the destruction of the Early Proterozoic crust of the Siberian craton. Owing to a change of sedimentation setting from passive continental margin to the “foreland” basin at the late stage, the terrigenous material of the Siberian craton was diluted by clastics from juvenile Neoproterozoic crust of the Baikal–Muya belt.  相似文献   
923.
Summary The author gives more general relations derived for characteristic frequencies of a more complex plasma model. One may assume that expressions derived herein, represent a more appropriate approximation of reality, especially in regions of ionospheric and magnetospheric plasma with a higher concentration of heavy ions.  相似文献   
924.
Zusammenfassung Das Gebiet um die Ostsee ist als erdmagnetisch stark gestört bekannt. Die Karte zeigt die Verteilung der intensiven Anomalien, wo Z 2000 and 5000 überschreitet. Der Gruppierung dieser Anomalien kann man eine ung.N Richtung zuschreiben.
Summary The area around the Baltic Sea is known as magnetically intensely disturbed. The map shows the distribution of most intensive anomalies, where Z is more than 2000 and 5000 . The direction of the group of these intensive anomalies can be as appr.N supposed.
  相似文献   
925.
926.
A technique for determining the height of the convective atmospheric boundary layer (CBL) with a 915 MHz boundary-layer profiler is discussed. The results are compared with CBL heights determined from radiosonde measurements. The profiler provides continuous CBL height measurements with very good time resolution (30 minutes or less), allowing for detailed understanding of the growth and fluctuations of the CBL. In addition, the profiler provides information about the degree of definition of the CBL top and the thickness of the entrainment zone. The measurements discussed were taken during the Rural Oxidants in the Southern Environment II (ROSE II) experiment.  相似文献   
927.
Lithology and Mineral Resources - Upper Paleozoic sections in Taimyr comprise genetic rock complexes of different zones: deep-water shelf; offshore transition zone; shoals, deltas, and beaches of...  相似文献   
928.
Climate change signals in Saudi Arabia are investigated using the surface air temperature (SAT) data of 19 meteorological stations, well distributed across the country. Analyses are performed using cumulative sum, cumulative annual mean, and the Mann–Kendall rank statistical test for the period of 1978–2010. A notable change in SAT for the majority of stations is found around 1997. The results show a negative temperature trend (cooling) for all stations during the first period (1978–1997), followed by a positive trend (warming) in the second period (1998–2010) with reference to the entire period of analysis. The Mann–Kendall test confirms that there is no abrupt cooling at any station during the analysis period, reflecting the warming trend across the country. The warming trend is found to be 0.06 °C/year, while the cooling trend is 0.03 °C/year, which are statistically significant.  相似文献   
929.
Non‐associated flow rule is essential when the popular Mohr–Coulomb model is used to model nonlinear behavior of soil. The global tangent stiffness matrix in nonlinear finite element analysis becomes non‐symmetric when this non‐associated flow rule is applied. Efficient solution of this large‐scale non‐symmetric linear system is of practical importance. The standard Krylov solver for a non‐symmetric solver is Bi‐CGSTAB. The Induced Dimension Reduction [IDR(s)] solver was proposed in the scientific computing literature relatively recently. Numerical studies of a drained strip footing problem on homogenous soil layer show that IDR(s = 6) is more efficient than Bi‐CGSTAB when the preconditioner is the incomplete factorization with zero fill‐in of global stiffness matrix Kep (ILU(0)‐Kep). Iteration time is reduced by 40% by using IDR(s = 6) with ILU(0)‐Kep. To further reduce computational cost, the global stiffness matrix Kep is divided into two parts. The first part is the linear elastic stiffness matrix Ke, which is formed only once at the beginning of solution step. The second part is a low‐rank matrix Δ, which is re‐formed at each Newton–Raphson iteration. Numerical studies show that IDR(s = 6) with this ILU(0)‐Ke preconditioner is more time effective than IDR(s = 6) with ILU(0)‐Kep when the percentage of yielded Gauss points in the mesh is less than 15%. The total computation time is reduced by 60% when all the recommended optimizing methods are used. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
930.
<正>The presence of rich natural resources and their rational use is the basis of dynamic and sustainable development of the state and society in general.The most effective integrated use of natural resources,which include mineral resources,predetermines the development of productive forces,the development of new areas,and the deployment of new industries,solves the problems of employment and contributes to economic growth of the  相似文献   
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