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排序方式: 共有117条查询结果,搜索用时 15 毫秒
51.
Megha Maheshwari C. Mahesh Kamaljit Singh Rajkumar J. Pallipad Sandip R. Oza 《Marine Geodesy》2015,38(3):487-496
An attempt has been made to derive sea ice freeboard from Ka-band Altimeter (SARAL/AltiKa) over Arctic region for 15 March–15 April 2013 (spring) and 15 September–15 October 2013 (autumn). A waveform template matching technique is employed for classification of leads and floe pixels. The estimated sea ice freeboards were found in close agreement with “Operation IceBridge quick look” freeboards (RMSD = 0.30 m). The differences between the two freeboards were largely due to snow layer over sea ice (R = 0.8). The estimated freeboards were of the order of 0.08–0.15 m during the two seasons. 相似文献
52.
Detection of ionospheric perturbation due to a soft gamma ray repeater SGR J1550-5418 by very low frequency radio waves 总被引:1,自引:0,他引:1
Sushanta K. Mondal Sandip K. Chakrabarti Sudipta Sasmal 《Astrophysics and Space Science》2012,338(2):259-264
The properties of cylindrical and spherical dust acoustic (DA) solitary and shock waves in an unmagnetized electron depleted
dusty plasma consisting of inertial dust fluid and ions featuring Tsallis statistics are investigated by employing the reductive
perturbation technique. A Korteweg-de Vries Burgers (KdVB) equation is derived and its numerical solution is obtained. The
effects of ion nonextensivity and dust kinematic viscosity on the basic features of DA solitary and shock waves are discussed
in nonplanar geometry. It is found that nonextensive nonplanar DA waves behave quite differently from their one-dimensional
planar counterpart. 相似文献
53.
The environment prevalent in ocean necessitates the piles supporting offshore structures to be designed against lateral cyclic loading initiated by wave action, which induces deterioration in the strength and stiffness of the pile-soil system introducing progressive reduction in the bearing capacity associated with increased settlement of the pile foundation. A thorough and detailed review of literature indicates that significant works have already been carried out in the relevant field of investigation. It is a well established phenomenon that the variation of relative pile-soil stiffness (K rs ) and load eccentricity (e/D) significantly affect the response of piles subjected to lateral static load. However, the influence of lateral cyclic load on axial response of single pile in sand, more specifically the effect of K rs and e/D on the cyclic behavior, is yet to be investigated. The present work has aimed to bridge up this gap. To carry out numerical analysis (boundary element method), the conventional elastic approach has been used as a guideline with relevant modifications. The model developed has been validated by comparing with available experimental (laboratory model and field tests) results, which indicate the accuracy of the solutions formulated. Thereafter, the methodology is applied successfully to selected parametric studies for understanding the magnitude and pattern of degradation of axial pile capacity induced due to lateral cyclic loading, as well as the influence of K rs and e/D on such degradation. 相似文献
54.
S. S. Sreekumar P. Vinod Essy Samuel J. P. Malkar A. R. Rao M. K. Hingar V. P. Madhav D. Debnath T. B. Kotoch Anuj Nandi S. Shaheda Begum Sandip Kumar Chakrabarti 《Experimental Astronomy》2011,29(1-2):109-133
The onboard software and data communication in the RT-2 Experiment onboard the Coronas?CPhoton satellite is organized in a hierarchical way to effectively handle and communicate asynchronous data generated by the X-ray detectors. A flexible data handling system is organized in the X-ray detector packages themselves and the processing electronic device, namely RT-2/E, has the necessary intelligence to communicate with the three scientific payloads by issuing commands and receiving data. It has direct interfacing with the Satellite systems and issues commands to the detectors and processes the detector data before sending to the satellite systems. The onboard software is configured with several novel features like (a) device independent communication scheme, (b) loss-less data compression and (c) Digital Signal Processor. Functionality of the onboard software along with the data structure, command structure, complex processing scheme etc. are discussed in this paper. 相似文献
55.
We study the relationship between full-disk solar radiative flux at different wavelengths and average solar photospheric magnetic-flux
density, using daily measurements from the Kitt Peak magnetograph and other instruments extending over one or more solar cycles.
We use two different statistical methods to determine the underlying nature of these flux – flux relationships. First, we
use statistical correlation and regression analysis and show that the relationships are not monotonic for total solar irradiance
and for continuum radiation from the photosphere, but are approximately linear for chromospheric and coronal radiation. Second,
we use signal theory to examine the flux – flux relationships for a temporal component. We find that a well-defined temporal
component exists and accounts for some of the variance in the data. This temporal component arises because active regions
with high magnetic-field strength evolve, breaking up into small-scale magnetic elements with low field strength, and radiative
and magnetic fluxes are sensitive to different active-region components. We generate empirical models that relate radiative
flux to magnetic flux, allowing us to predict spectral-irradiance variations from observations of disk-averaged magnetic-flux
density. In most cases, the model reconstructions can account for 85 – 90% of the variability of the radiative flux from the
chromosphere and corona. Our results are important for understanding the relationship between magnetic and radiative measures
of solar and stellar variability. 相似文献
56.
Sandip K. Chakrabarti 《Journal of Astrophysics and Astronomy》1989,10(3):261-277
We present the analytic theory of dissipative and non-dissi-pative shocks in the rotating outflows in both the pseudo-Newtonian
and the Schwarzschild geometry. We include the effects of the self gravity of the surrounding massive disc and show that the
flow may have as many as five critical points when the angular momentum and the disc mass are sufficiently high. This leads
to the possibility of the multipleannular shocks within the flow. We derive the expressions correlating the pre-shock and the post-shock quantities for all the three
principal types of discontinuities. From these relations it is shown that for given initial flow parameters such as the angular
momentum and the energy there could be as many as eighteen formal shock locations out of which at most two are chosen in reality.
Detailed classification of the parameter space in terms of the initial flow parameters will be discussed elsewhere 相似文献
57.
Giuseppe Lanzafame D. Molteni & Sandip K. Chakrabarti 《Monthly notices of the Royal Astronomical Society》1998,299(3):799-804
Viscous Keplerian discs become sub-Keplerian close to a black hole since they pass through sonic points before entering into it. We study the time evolution of polytropic viscous accretion discs (both in one- and two-dimensional flows) using smoothed particle hydrodynamics. We discover that for a large region of the parameter space spanned by energy, angular momentum and polytropic index, when the flow viscosity parameter is less than a critical value, standing shock waves are formed. If the viscosity is very high then the shock wave disappears. In the intermediate viscosity, the disc oscillates very significantly in the viscous time-scale. Our simulations indicate that these centrifugally supported high density regions close to a black hole play an active role in the flow dynamics, and consequently, the radiation dynamics. 相似文献
58.
59.
Dibyendu Nandy 《Astrophysics and Space Science》2002,282(1):209-219
We report here results from a dynamo model developed on the lines of the Babcock-Leighton idea that the poloidal field is
generated at the surface of the Sun from the decay of active regions. In this model magnetic buoyancy is handled with a realistic
recipe – wherein toroidal flux is made to erupt from the overshoot layer wherever it exceeds a specified critical field B
c (105 G). The erupted toroidal field is then acted upon by the α-effect near the surface to give rise to the poloidal field. In
this paper we study the effect of buoyancy on the dynamo generated magnetic fields. Specifically, we show that the mechanism
of buoyant eruption and the subsequent depletion of the toroidal field inside the overshoot layer, is capable of constraining
the magnitude and distribution of the magnetic field there. We also believe that a critical study of this mechanism may give
us new information regarding the solar interior and end with an example, where we propose a method for estimating an upper
limit of the difusivity within the overshoot layer.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
60.