Structure and stability of rotating fluid disks around massive objects. I. Newtonian formulation     

D. K. Chakraborty  A. R. Prasanna 《Journal of Astrophysics and Astronomy》1981,2(4):421-437

In this paper we have presented a very general class of solutions for rotating fluid disks around massive objects (neglecting the self gravitation of the disk) with density as a function of the radial coordinate only and pressure being nonzero. Having considered a number of cases with different density and velocity distributions, we have analysed the stability of such disks under both radial and axisymmetric perturbations. For a perfect gas disk with γ= 5/3 the disk is stable with frequency (MG/r³)^1/2 for purely radial pulsation with expanding and contracting boundary. In the case of axisymmetric perturbation the critical γ_c for neutral stability is found to be much less than 4/3 indicating that such disks are mostly stable under such perturbations. On leave of absence from Government College, Jagdalpur 494005.  相似文献   

General relativistic analysis of structure and stability of charged fluid disks around compact objects     

A. R. Prasanna  D. K. Chakraborty 《Journal of Astrophysics and Astronomy》1981,2(1):1-27

In this paper we give a detailed general relativistic formulation of the study of structure and stability of charged fluid disks around compact objects like black holes neglecting the self-gravitation of the disk itself. Having presented the general equations for equilibrium as well as for perturbations we solve explicitly the cases of rigidly and differentially rotating thin disks, with constant charge density and zero pressure, confined to the equatorial plane of the black hole. By using normal mode analysis we have analysed the stability of such disks under purely radial perturbations and find that the disks are generally stable. On leave of absence from Government College, Jagadalpur 494005  相似文献   

Analysis of temporal sar and optical data for rice mapping     

Indrani?ChoudhuryEmail author  M.?Chakraborty 《Journal of the Indian Society of Remote Sensing》2004,32(4):373-385

This study investigates the potential of multi-temporal signature analysis of satellite imagery to map rice area in South 24 Paraganas district of West Bengal. Two optical data (IRS ID LISS III) and three RADARSAT SAR data of different dates were acquired during 2001. Multi-temporal SAR backscatter signatures of different landcovers were incorporated into knowledge based decision rules and kharif landcover map was generated. Based on the spectral variation in signature, the optical data acquired during rabi (January) and summer (March) season were classified using supervised maximum likelihood classifier. A co-incidence matrix was generated using logical approach for a combined “rabi-summer” and “kharif-rabi-summer” landcover mapping. The major landcovers obtained in South 24 Paraganas using remote sensing data are rice, water, aquaculture ponds, homestead, mangrove, and urban area. The classification accuracy of rice area was 98.2% using SAR data. However, while generating combined “kharif-rabi-summer” landcovers, the classification accuracy of rice area was improved from 81.6% (optical data) to 96.6% (combined SAR-Optical). The primary aim of the study is to achieve better accuracy in classifying rice area using the synergy between the two kinds of remotely sensed data.  相似文献   

Tropical systematic and random error energetics based on NCEP (MRF) analysis-forecast system — A barotropic approach     

S. De  D. R. Chakraborty 《Journal of Earth System Science》2004,113(2):151-166

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Mann–Kendall trend analysis of tropospheric ozone and its modeling using ARIMA     

Goutami Chattopadhyay  Parthasarathi Chakraborthy  Surajit Chattopadhyay 《Theoretical and Applied Climatology》2012,110(3):321-328

The present work reports studies on the spatial distribution of tropospheric ozone extending over both southern and northern hemispheres. This study is based on a univariate approach to the spatial data series obtained at regular spatial intervals. Mann?CKendall's (MK) trend analysis has been carried out to discern the trend within the spatial distribution of the tropospheric ozone, and it has been observed that in all seasons, except monsoon (JJAS), there is a linear trend within the spatial distribution. Studying both monthly and seasonal behavior through autoregressive integrated moving average (ARIMA), it has been revealed that ARIMA (0,2,2) can be used as a representative of the spatially distributed tropospheric ozone over southern and northern hemispheres. The representative model has been confirmed through the study of Willmott's index and prediction yield.  相似文献   

Effect of modified Chaplygin gas in anisotropic universe     

Shuvendu Chakraborty  Ujjal Debnath 《Astrophysics and Space Science》2009,321(1):53-56

In this work, we have studied the model of modified Chaplygin gas and its role in accelerating phase of the universe for anisotropic model. We have assumed that the equation of state of this modified model is valid from the radiation era to ΛCDM model. We have obtained the possible relation between the hessence and the modified Chaplygin gas. We have also use the statefinder parameters for characterize different phase of the universe diagrammatically.  相似文献   

High-resolution satellite image segmentation using Hölder exponents     

Debasish Chakraborty  Gautam Kumar Sen  Sugata Hazra 《Journal of Earth System Science》2009,118(5):609-617

Texture in high-resolution satellite images requires substantial amendment in the conventional segmentation algorithms. A measure is proposed to compute the Hölder exponent (HE) to assess the roughness or smoothness around each pixel of the image. The localized singularity information is incorporated in computing the HE. An optimum window size is evaluated so that HE reacts to localized singularity. A two-step iterative procedure for clustering the transformed HE image is adapted to identify the range of HE, densely occupied in the kernel and to partition Hölder exponents into a cluster that matches with the range. Hölder exponent values (noise or not associated with the other cluster) are clubbed to a nearest possible cluster using the local maximum likelihood analysis.  相似文献   

A numerical study on the role of atmospheric forcing on mixed layer depth variability in the Bay of Bengal using a regional ocean model     

Dandapat  Sumit  Chakraborty  Arun  Kuttippurath  Jayanarayanan  Bhagawati  Chirantan  Sen  Radharani 《Ocean Dynamics》2021,71(10):963-979

Ocean Dynamics - This study investigates the role of driving atmospheric forces [winds, net heat flux, and evaporation–precipitation (E–P)] and the possible mechanisms on the mixed...  相似文献   

Anisotropic cosmological models with bulk viscosity for variable <Emphasis Type="Italic">G</Emphasis> and Λ     

Subenoy Chakraborty  Anusua Roy 《Astrophysics and Space Science》2008,313(4):389-392

In this paper we have considered axially symmetric Bianchi-I, Kantowski Sachs and Bianchi-III space-time models with bulk viscosity, where the gravitational constant G and the cosmological term Λ vary with time. In Einstein equations this variation in G and Λ are taken in such a way as to preserve the energy momentum tensor. Solutions are obtained with the cosmological term varying inversely with square of time.  相似文献   

Cancer risks from exposure to vehicular air pollution: a household level analysis of intra-ethnic heterogeneity in Miami,Florida     

Jayajit Chakraborty  Timothy W. Collins  Sara E. Grineski 《Urban geography》2017,38(1):112-136

Quantitative environmental justice (EJ) research has relied on aggregated data from census units to determine disproportionate hazard exposure. Additionally, variables typically used to analyze ethnic inequities in exposure (e.g., percent Hispanic) are too broad and assume a degree of homogeneity that may not exist, given the diversity of ethnic minority populations. We address these limitations through a study that utilizes primary household level survey data and cancer risk estimates from the National-Scale Air Toxics Assessment (NATA) to analyze intra-ethnic inequities in exposure to vehicular air pollutants in the Miami metropolitan area, Florida. Our analysis disaggregates the Hispanic category based on five characteristics (language proficiency, U.S. citizenship, nativity, unemployment status, and national origin) and finds that risk burdens are significantly higher for Hispanic respondents who are foreign-born, unemployed, and of Cuban origin. Findings highlight the advantages of downscaling EJ analyses to the household level and considering intra-ethnic heterogeneity in EJ research and policy.  相似文献