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1.
The stability of a plane-stratified slab of perfectly conducting, rotating, compressible, inviscid plasma accelerated by a magnetic field is considered. Exact solutions for the growth rates of the unstable modes are determined for a -law gas when the undisturbed equilibrium is an isothermal atmosphere of semi-infinite extent with no frozen-in field. It is shown that the rotation has no effect on the region of unstable modes which has wavelengths long compared with the atmospheric scale height. On the other side, the growth rates in the presence of rotation are less than those in the absence of rotation for unstable modes. 相似文献
2.
The mafic dykes in Wadi Mandar-Wadi Um Adawi area are as follows: (1) calc-alkaline lamprophyre (i.e., kersantite and spessartite), (2) diabase, and (3) alkaline lamprophyre (i.e., camptonite). The field relations reveal that the emplacement of calc-alkaline lamprophyres preceded the diabase dykes, while alkaline lamprophyres emplaced later than the diabase dykes. Calc-alkaline are basaltic andesite, basaltic trachyandesite to basalt, while the diabase dykes and alkaline lamprophyres are basaltic in composition. These dykes are characterized by metaluminous character. Calc-alkaline lamprophyres and diabase dykes show transitional affinity from calc-alkaline to alkaline, while the alkaline lamprophyres exhibit more strong alkaline character. The mafic dykes were crystallized under temperature 1100–1150 °C and pressure 3–5 kbars in a high oxygen fugacity conditions. Fe-Ti oxides in the dykes are represented by ilmenite and Ti-magnetite. The chemistry of the sulfides hosted in those mafic dykes suggests a magmatic-hydrothermal origin for these minerals. The geochemical behavior of high field strength elements and large ion lithophile elements in these dykes excludes the derivation of diabase or alkaline lamprophyre either by partial melting or fractional crystallization from calc-alkaline lamprophyre. The parental magmatic sources of the studied dykes were generated from crustal material with addition of mantle-derived melt during the post-collisional stage. The mafic dykes in Wadi Mandar-Wadi Um Adawi area were generated from different magmatic sources by partial melting and subsequent fractional crystallization. In addition, the crustal contamination/assimilation process has a prominent role in the magmatic evolution of diabase and alkaline lamprophyre dykes. 相似文献
3.
The nonlinear Rayleigh-Taylor instability in the presence of magnetic field and mass and heat transfer is studied using a simplified formulation. The method of multiple scale expansion is employed for the investigation. It is found that the nonlinear effects of magnetic field and mass and heat transfer stabilize the classically unstable system. A simple non-dimensional parameter is also found to characterize the stability of the system. 相似文献
4.
Modeling of SMF tsunami hazard along the upper US East Coast: detailed impact around Ocean City,MD 总被引：1，自引：0，他引：1
5.
In this paper, we investigate spherically symmetric perfect fluid gravitational collapse in metric f(R) gravity. We take non-static spherically symmetric metric in the interior region and static spherically symmetric metric
in the exterior region of a star. The junction conditions between interior and exterior spacetimes are derived. The field
equations in f(R) theory are solved using the assumption of constant Ricci scalar. Inserting their solution into junction conditions, the
gravitational mass is found. Further, the apparent horizons and their time of formation is discussed. We conclude that the
constant scalar curvature term f(R
0) acts as a source of repulsive force and thus slows down the collapse of matter. The comparison with the corresponding results
available in general relativity indicates that f(R
0) plays the role of the cosmological constant. 相似文献
6.
7.
Groundwater vulnerability modeling is an alternative approach to evaluate groundwater contamination especially in areas affected by intensive anthropogenic activities. However, the DRASTIC model as a well-known method to assess groundwater vulnerability suffers from the inherent uncertainty associated with its seven essential parameters. In this study, three different fuzzy logic (FL) models (Sugeno fuzzy logic, Mamdani fuzzy logic, and Larsen fuzzy logic) are adopted to improve the DRASTIC system to be more realistic. The vulnerability map of groundwater from multiple aquifer systems (i.e., karstic, alluvium, and complex) in Basara basin, Iraq, was created using the FL models. Validation of the FL models results using NO3-N concentration obtained from wells and springs of the study area indicating that all of the three FL models are applicable for improving the DRASTIC model. However, each of the FL models has its own advantages for groundwater vulnerability estimation in different types of aquifer systems in the Basara basin. Therefore, this study proposes the supervised committee fuzzy logic (SCFL) as a multimodel method to combine the advantages of individual FL models. The SCFL method confirms that no water well with high NO3-N levels would be classified as low risk and vice versa. The study suggests that this approach has provided a convenient estimation of pollution risk in the study area and therefore, a more accurate prediction of the intrinsic vulnerability to pollution in the multiple aquifer system can be achieved through SCFL method. 相似文献
8.
Modelling time series of groundwater levels is investigated by three fuzzy logic (FL) models, Sugeno (SFL), Mamdani (MFL) and Larsen (LFL), using data from observation wells. One novelty in the study is the re-use of these three models as multiple models through the following strategies: (a) simple averaging, (b) weighted averaging and (c) committee machine techniques; these are implemented using artificial neural networks (ANN). These strategies provide some evidence that (i) multiple models improve on the performance of individual models and those using committee machines perform better than the other two options; and (ii) committee machine models produce defensible modelling results to develop management scenarios. The study investigates water table declines through management scenarios and shows that in this aquifer water use has higher impacts on water table variations than climatic variations. This provides evidence of the need for planned management in the study area. 相似文献
9.
Ahmed G. Abd Allah 《Arabian Journal of Geosciences》2012,5(2):217-231
Volcanic-hosted (Cu–Zn–Pb) massive sulfide mineralizations are described from four prospects in the Eastern Desert: Helgate,
Maaqal, Derhib, and Abu Gurdi. Helgate and Maaqal prospects are hosted in island arc volcanics in a well-defined stratigraphic
level. Massive sulfides form veins and lenses. Although these veins and lenses are locally deformed, sulfides from Helgate
and Maaqal prospects show primary depositional features. They form layers and colloidal textures. Sphalerite, pyrite, chalcopyrite,
and galena are the major sulfides. Gangue minerals are represented by chlorite, quartz, and calcite. The sulfide mineralizations
at Helgate and Maaqal are Zn-dominated. Derhib and Abu Gurdi prospects occur as disseminations, small massive lenses, and
veins along shear zones in talc tremolite rocks at the contact between metavolcanics and metasedimentary rocks. The host rocks
at Derhib and Abu Gurdi are metamorphosed to lower amphibolite facies as revealed by silicate mineral assemblage and chemistry.
Chalcopyrite, pyrite, sphalerite, and galena are the major sulfide minerals while pyrrhotite is less common. Recrystallization,
retexturing and remobilization of sulfide minerals are reflecting postdepositional metamorphic and structural modifications.
Electrum and Ag–Pb–Bi tellurides are common accessories. Gangue minerals comprise amphiboles of actinolite and actinolitic
hornblende composition, talc, and chlorite. The ores at Derhib and Abu Gurdi are Cu–Zn and Zn-dominated, respectively. The
distinct geological, petrographical, and geochemical differences between sulfide mineralizations at Helgate–Maaqal on one
hand and Derhib and Abu Gurdi on the other hand suggest two genetic types of sulfide mineralizations; Helgate–Maaqal prospects
(type 1) are similar to the Archean analogs from Canada (Noranda type), while Derhib and Abu Gurdi (type 2) show similarity
to ophiolite-associated deposits similar to those described from Cyprus, Oman, and Finland. In genetic type 1, ore minerals
were deposited on the seafloor; the role of postdepositional hydrothermal activity is limited. In genetic type 2, base metals
were part of the ultramafic rocks and were later redistributed and mobilized during deformation to be deposited along shear
zones. The dominance and diversity of tellurides in genetic type 2 highlight the role of metamorphic–hydrothermal fluids. 相似文献
10.
In this paper, we solve the field equations in metric f(R) gravity for Bianchi type VI
0 spacetime and discuss evolution of the expanding universe. We find two types of non-vacuum solutions by taking isotropic
and anisotropic fluids as the source of matter and dark energy. The physical behavior of these solutions is analyzed and compared
in the future evolution with the help of some physical and geometrical parameters. It is concluded that in the presence of
isotropic fluid, the model has singularity at [(t)\tilde]=0\tilde{t}=0 and represents continuously expanding shearing universe currently entering into phantom phase. In anisotropic fluid, the
model has no initial singularity and exhibits the uniform accelerating expansion. However, the spacetime does not achieve
isotropy as t→∞ in both of these solutions. 相似文献