Radial tidal current field in a semi-enclosed rectangular basin: formation and evolution     

钱学生  陈永平  张长宽  潘毅 《中国海洋湖沼学报》2015,33(4):1085-1099

The radial tidal current field accounts for the formation of the radial sand ridges in the South Yellow Sea. Understanding the formation and evolution of this radial tidal current field is vital to assessing the morphodynamic features in the area. A semi-enclosed rectangular basin with and without a coastal barrier was schematized from the topography of the Bohai Sea and Yellow Sea. The 2D tidal current field in this basin was simulated using the DELFT3D-FLOW model. The concept of tidal wave refraction, which highlights the effect of the sloped or stepped submarine topography on the propagation of the tidal waves, was introduced to explain the formation of the radial tidal current field. Under the effect of tidal wave refraction, co-phase lines of the counterclockwise rotating tidal wave and incident tidal wave are transformed into clockwise and counterclockwise deflections, respectively, leading to the convergence and divergence of the flow field. Regardless of whether a coastal barrier exists or not, the outer radial tidal current field might emerge over certain topography. The responses of the radial tidal current field in this basin to the environmental variations such as coastline changes and bottom erosions were discussed. Results show that local protrusion near the focal point of the radial tidal current field will have limited effects on the location of the tidal system. However, a remarkable shift of the amphidromic point toward the entrance and central axis of this basin and a movement of the focal point of the radial tidal current field toward the entrance could be caused by the significant seaward coastline advance and submarine slope erosion.  相似文献   

Study of magnetic field geometry and extinction in Bok globule CB130     

A. Chakraborty  H. S. Das 《Astrophysics and Space Science》2016,361(9):321

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From Nearby Low Luminosity AGN to High Redshift Radio Galaxies: Science Interests with Square Kilometre Array     

P. Kharb  D. V. Lal  V. Singh  J. Bagchi  C. H. Ishwara Chandra  A. Hota  C. Konar  Y. Wadadekar  P. Shastri  M. Das  K. Baliyan  B. B. Nath  M. Pandey-Pommier 《Journal of Astrophysics and Astronomy》2016,37(4):34

We present detailed science cases that a large fraction of the Indian AGN community is interested in pursuing with the upcoming Square Kilometre Array (SKA). These interests range from understanding low luminosity active galactic nuclei in the nearby Universe to powerful radio galaxies at high redshifts. Important unresolved science questions in AGN physics are discussed. Ongoing low-frequency surveys with the SKA pathfinder telescope GMRT, are highlighted.  相似文献   

Dynamical behavior of size-graded dust grains levitated in rotating magnetized astroplasmas     

G. C. Das  Rupa Chakraborty 《Astrophysics and Space Science》2011,335(2):415-423

Our purpose is to examine the formation of different sheaths in rotating astroplasmas embedded in an ambient magnetic field. Sequel to our recent work (Das and Chakraborty in Astrophys. Space Sci., 2011) we remodeled our present study with the view to finding of robust sheath over the Earth’s Moon along with the formation of dust clouds therein. Based on using the pseudopotential analysis, a modified Sagdeev potential equation has been derived, which, in turns, quantifies the interaction of Coriolis force and magnetic field and to derive the different natures of sheath and dust atmosphere. The application of this result to the input numeric data of the lunar environment and dynamical behaviors of dust levitation has been studied. Our study finds that the dust particles having a spatial segregation within the sheath region form dust clouds in spaces.  相似文献   

Variations in the X-ray eclipse transitions of Cen X-3     

Jincy Devasia  Biswajit Paul  Marykutty James  Kavila Indulekha 《中国天文和天体物理学报》2010,10(11)

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Energy dissipation in wave propagation in general-relativistic plasma     

Ajanta Das  S. Chatterjee 《Astrophysics and Space Science》2010,330(2):329-336

Based on a recent communication by the present authors the question of energy dissipation in magnetohydrodynamical waves in an inflating background in general relativity is examined. It is found that the expanding background introduces a sort of dragging force on the propagating wave such that, unlike the Newtonian case, energy gets dissipated as it progresses. This loss in energy having no special-relativistic analogue is, however, not mechanical in nature as in case of an elastic wave. It is also found that the energy loss is model dependent and also depends on the number of dimensions.  相似文献   

Evidence for structural discordance in the inverted metamorphic sequence of Sikkim Himalaya: Towards resolving the Main Central Thrust controversy     

Saibal Gupta  Aditi Das  Sudipta Goswami  Ananda Modak  Suman Mondal 《Journal of the Geological Society of India》2010,75(1):313-322

Inverted metamorphism in the Himalayas is closely associated with the Main Central Thrust (MCT). In the western Himalayas, the Main Central Thrust conventionally separates high grade metamorphic rocks of the Higher Himalayan Crystalline Sequence (HHCS) from unmetamorphosed rocks of the Inner sedimentary Belt. In the eastern Himalayas, the Inner sedimentary Belt is absent, and the HHCS and meta-sedimentary Lesser Himalayan Sequence (LHS) apparently form a continuous Barrovian metamorphic sequence, leading to confusion about the precise location of the MCT. In this study, it is demonstrated that migmatitic gneisses of the sillimanite zone in the higher structural levels of the HHCS are multiply deformed, with two phases of penetrative fabric formation (S_1HHCS and S_2HHCS) followed by third folding event associated with a spaced, NW-SE trending, north-east dipping foliation (S_3HHCS). The underlying LHS schists (kyanite zone and lower) are also multiply deformed, with the bedding S₀ being isoclinally folded (F_1LHS), and subsequently refolded (F_2LHS and F_3LHS). The contact zone between the HHCS and LHS is characterized by ductile, top-to-the southwest shearing and stabilization of a pervasive foliation that is consistently oriented NW-SE and dips northeast. This foliation is parallel to the S_3HHCS foliation in the HHCS, and the S_2LHS in the LHS. Early lineations in the HHCS and LHS also show different dispersions across the contact shear zone, implying that pre-thrusting orientations of the two units were distinct. The contact shear zone is therefore interpreted to be a plane of structural discordance, shows a shear sense consistent with thrust movement and is associated with mineral growth during Barrovian metamorphism. It may well be considered to represent the MCT in this region.  相似文献   

Felsic tuff from Rutland Island — A pyroclastic flow deposit in Miocene-sediments of Andaman-Java subduction complex     

Tapan Pal  Biswajit Ghosh  Anindya Bhattacharya  S. K. Bhaduri 《Journal of Earth System Science》2010,119(1):19-25

The bedded felsic tuff exposed in Rutland Island, Andaman, consists of two facies:

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white massive tuff with ill-defined bedding contacts (facies-A) and  相似文献    69. Extended Finite Element Method for the Analysis of Discontinuities in Rock Masses   总被引：1，自引：0，他引：1   Debasis Deb  Kamal C. Das 《Geotechnical and Geological Engineering》2010,28(5):643-659 The strength and deformability of rock mass primarily depend on the condition of joints and their spacing and partially on the engineering properties of rock matrix. Till today, numerical analysis of discontinuities e.g. joint, fault, shear plane and others is conducted placing an interface element in between two adjacent rock matrix elements. However, the applicability of interface elements is limited in rock mechanics problems having multiple discontinuities due to its inherent numerical difficulties often leading to non-convergent solution. Recent developments in extended finite element method (XFEM) having strong discontinuity imbedded within a regular element provide an opportunity to analyze discrete discontinuities in rock masses without any numerical difficulties. This concept is based on partition of unity principle and can be used for cohesive rock joints. This paper summarizes the mathematical frameworks for the implementation of strong discontinuities in 3 and 6 nodded triangular elements and also provides numerical examples of the application of XFEM in one and two dimensional problems with single and multiple discontinuities.  相似文献    70. Support and Information Effect Modeling for Recoverable Reserve Estimation of a Beach Sand Deposit in India      Mainak Thakur  Biswajit Samanta  Debashish Chakravarty 《Natural Resources Research》2014,23(2):231-245 Application of geostatistics in estimating recoverable reserves of beach sand deposit is rare. This paper made an attempt to estimate local recoverable reserves using disjunctive kriging and discrete Gaussian model considering support and information effects for a beach sand deposit located in the eastern part of India. The dependence of different selective mining unit (SMU) sizes and different production sampling strategies on the estimated tonnage, metal quantity, and the ore tonnage versus metal quantity relationships has been examined. The results of the study show that nonlinear geostatistics should be used for more precise assessment of the grade, ore tonnage, and metal quantity and their relationships, which are necessary for recoverable reserve estimation. In selective mining operation, both support and information effects have significant influence on recoverable reserve. Recoverable reserve estimation based on SMU involves estimating grade distributions of mining unit with much bigger support than the available drill core sample data. Information effect comes into picture from the real scenario where the actual grades of the blocks remain unknown even during mining. At the mining stage, discrimination of ore and waste blocks is carried out based on estimated grades of the production samples and it is likely that the blocks might be misclassified as either ore or waste and thus sent to wrong destination. Information effect modeling makes the estimation more reliable by taking care of misclassification.  相似文献    [首页] « 上一页 [2] [3] [4] [5] [6] 7 [8] [9] [10] [11] [12] 下一页 » 末  页»