Spherical Domain Walls in Higher Dimension     

Farook Rahaman  Subenoy Chakraborty 《Astrophysics and Space Science》2000,274(4):701-709

We have presented a spherically symmetric domain wall in five dimensionalspace-time with non-vanishing stress component in the directionperpendicular to the plane of the wall. The general solution to Einstein'sequations for such domain wall is obtained using functional separabilityof metric coefficients.  相似文献   

Estimation of mean grain size of seafloor sediments using neural network   总被引：2，自引：0，他引：2  

Chanchal De  Bishwajit Chakraborty 《Marine Geophysical Researches》2012,33(1):45-53

The feasibility of an artificial neural network based approach is investigated to estimate the values of mean grain size of seafloor sediments using four dominant echo features, extracted from acoustic backscatter data. The acoustic backscatter data were collected using a dual-frequency (33 and 210 kHz) single-beam, normal-incidence echo sounder at twenty locations in the central part of the western continental shelf of India. Statistically significant correlations are observed between the estimated average values of mean grain size of sediments and the ground-truth data at both the frequencies. The results indicate that once a multi-layer perceptron model is trained with back-propagation algorithm, the values of mean grain size can reasonably be estimated in an experimental area. The study also revealed that the consistency among the estimated values of mean grain size at different acoustic frequencies is considerably improved with the neural network based method as compared to that with a model-based approach.  相似文献   

Junction conditions and consequences of quasi-spherical space-time with electro-magnetic field and Vaidya metric     

Soma Nath  Ujjal Debnath  Subenoy Chakraborty 《Astrophysics and Space Science》2008,313(4):431-436

In this work the junction conditions between the exterior Reissner-Nordstrom-Vaidya space-time with the interior quasi-spherical Szekeres space-time have been studied for analyzing gravitational collapse in the presence of a magneto-hydrodynamic fluid undergoing dissipation in the form of heat flow. We have discussed about the apparent horizon and have evaluated the time difference between the formation of apparent horizon and central singularity.   相似文献   

Modeling Dust Jets And Shells From Comet Hale-Bopp     

Vasundhara  R.  Chakraborty  Pavan  Hänel  Andreas  Heiser  Erwin 《Earth, Moon, and Planets》1997,78(1-3):321-328

Persistent jet and shell structures from comet Hale-Bopp showing gradual changes in the shapes and orientations with aspect angle and solar illumination geometry indicate long lived active sources. A model to simulate the dust features has been applied to the series of observations from September 1996 to May 1997. Most of the structures can be explained as arising due to ejections from persistent active regions at comet-o-centric latitudes near +65°, +55°, −5° to −15°, −35° and −65°. The best fitting pole positions vary between 255° ±10° and 275° ± 10° in right ascension and −45° ± 10° to −75° ± 10° in declination. Lower limits on the dust and gas production rates at various epochs are presented. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

String membranes in higher dimensions     

Subenoy Chakraborty  Nivedita Pramanik 《Astrophysics and Space Science》1996,235(2):263-267

We shall study homogeneous and isotropic clouds formed of String membranes. These membranes are considered in extra dimensions of a higher dimensional Bianchi-I space-time. Some solutions are found for the field equations of the system.  相似文献   

Propagation of plane relativistic shock waves in the presence of a magnetic field     

G. Deb Ray  T. K. Chakraborty 《Astrophysics and Space Science》1978,56(1):119-128

In this paper we obtain similarity solutions for the propagation of plane relativistic shock waves in the presence of a transverse magnetic field for the medium, where the nucleon number density obeys a power law of distance from the plane of explosion. The shock surface moves with constant velocity and the total energy of the disturbance is dependent on time. The solutions are applicable only to an isothermal medium or a cold gas.  相似文献   

Is the outcrop topology of dolerite dikes of the Precambrian Singhbhum Craton fractal?     

Nibir Mandal  Atin Kumar Mitra  Santanu Misra  Chandan Chakraborty 《Journal of Earth System Science》2006,115(6):643-660

In the Precambrian Singhbhum Craton of eastern India, newer dolerite dikes occur profusely with varying outcrop lengths. We have analysed the nature of their length-size and orientation distributions in relation to the theory of fractals. Two orientational sets of dikes (NW-SE and NE-SW) are present. Both the sets show strongly non-power-law size distributions, as reflected in non-linear variations in logarithmic space. We analyzed thousands of data, revealing that polynomial functions with a degree of 3 to 4 are the best representatives of the non-linear variations. Orientation analysis shows that the degree of dispersions from the mean trend tends to decrease with increasing dike length. The length-size distributions were studied by simulating fractures in physical models. Experimental fractures also show a non-power-law distribution, which grossly conforms to those of the dolerite dikes. This type of complex size distributions results from the combined effects of nucleation, propagation and coalescence of fractures.  相似文献   

On disturbances produced by a time-periodic twist on the surface of a spheroidal cavity     

Mr. S. K. Chakraborty M. Sc. 《Pure and Applied Geophysics》1958,40(1):15-18

Summary The problem of disturbances in an elastic medium produced by a twist on the surface of a spheroidal cavity has been solved using spheroidal functions.  相似文献   

Dynamic response of pipelines to moving loads     

S. K. Datta  T. Chakraborty  A. H. Shah 《地震工程与结构动力学》1984,12(1):59-72

Vibration of buried pipelines induced by moving axial and radial loads has been studied in this paper. A thin shell model has been used for the pipeline, which is assumed to be lying in an infinite isotropic homogeneous elastic medium. In order to allow for the possible motion of the pipe out of phase with the surrounding ground a very thin layer of viscoelastic material is assumed to separate the pipe from the ground. Calculations indicate the presence of the interfacial viscoelastic layer does not influence the pipe response in a significant manner. So all the numerical results presented here are for the case when the pipe is assumed to be perfectly bonded. These show that the maximum pipewall displacements and stresses occur in a soft soil at long wavelengths.  相似文献   

Improving Ocean State by Assimilating SARAL/AltiKa Derived Sea Level and Other Satellite-Derived Data in MITGCM     

Abhisek Chakraborty  Raj Kumar  Sujit Basu  Rashmi Sharma 《Marine Geodesy》2015,38(3):328-338

Assimilation of satellite-derived surface datasets has been explored in the study. Three types of surface data, namely sea level anomaly, sea surface temperature and sea surface salinity, have been used in various data assimilation experiments. The emphasis has been on the extra benefit arising out of the additional sea level assimilation and hence there are two parallel runs, in one of which sea level assimilation has been withheld. The model used is a state-of-the art ocean general circulation model (OGCM) and the assimilation method is the widely used singular evolutive extended Kalman filter (SEEK). Evaluation of the assimilation skill has been carried out by comparing the simulated depth of the 20°C isotherm with the same quantity measured by buoys and Argo floats. Simulated subsurface temperature and salinity profiles have also been compared with the same profiles measured by Argo floats. Finally, surface currents in the assimilation runs have been compared with currents measured by several off-equatorial buoys. Addition of sea level has been found to substantially improve the quality of simulation. An important feature that has been effectively simulated by the addition of sea level in the assimilation scheme is the near-surface temperature inversion (2-3°C) in the northern Bay of Bengal.  相似文献