Integrated Optimal Management of Ground-Water Pollution and Withdrawal     

Ashok K. Keshari  Bithin Datta 《Ground water》1996,34(1):104-113

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Radial vibration of a composite spherical shell     

Jayasri Datta 《Pure and Applied Geophysics》1973,104(1):530-538

Summary This paper deals with radial vibration of a composite spherical shell made up of orthotropic materials by the application of a periodic shearing stress on the outer surface. Two cases have been discussed. In the first the elastic constants of the material of the composite body are assumed to remain constant while in the second they are proportional to the distance from the centre of the composite body. Results were obtained in terms of Bessel functions.  相似文献   

Lepton loss and entropy generation in stellar collapse     

B. Datta  P. P. Deo 《Astrophysics and Space Science》1983,90(1):109-115

The effects of uncertainties in determining the loss of neutrinos and the generation of entropy during the collapse of a stellar core are studied using a simple spherically-symmetric homologous collapse model with an improved treatment for the excited nuclei. It is found that the neutrino loss and entropy generation are not altogether insensitive to most variations of the assumptions regarding the input physics, collapse rate and initial conditions and in particular the need to determine accurately beta capture rates in stellar collapse is pointed out.  相似文献   

Response of a circular cylindrical shell to disturbances in a half-space—numerical results     

Nabil El-Akily  S. K. Datta 《地震工程与结构动力学》1981,9(5):477-487

In this paper we present numerical results representing the response of an elastic cylindrical shell to disturbances in an elastic half-space. These numerical results show the radial displacement at the middle surface of the shell and the hoop stress in the shell. The incident disturbance is in the form of a plane dilatational wave or a Rayleigh wave.  相似文献   

Bondi flow revisited     

Satadal Datta 《Astrophysics and Space Science》2016,361(8):260

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Line-of-Sight Anisotropies in the Cosmic Dawn and Epoch of Reionization 21-cm Power Spectrum     

Suman?MajumdarEmail authorView author&#;s OrcID profile  Kanan?K.?Datta  Raghunath?Ghara  Rajesh?Mondal  T.?Roy?Choudhury  Somnath?Bharadwaj  Sk.?Saiyad?Ali  Abhirup?Datta 《Journal of Astrophysics and Astronomy》2016,37(4):32

The line-of-sight direction in the redshifted 21-cm signal coming from the cosmic dawn and the epoch of reionization is quite unique in many ways compared to any other cosmological signal. Different unique effects, such as the evolution history of the signal, non-linear peculiar velocities of the matter etc. will imprint their signature along the line-of-sight axis of the observed signal. One of the major goals of the future SKA-LOW radio interferometer is to observe the cosmic dawn and the epoch of reionization through this 21-cm signal. It is thus important to understand how these various effects affect the signal for its actual detection and proper interpretation. For more than one and half decades, various groups in India have been actively trying to understand and quantify the different line-of-sight effects that are present in this signal through analytical models and simulations. In many ways the importance of this sub-field under 21-cm cosmology have been identified, highlighted and pushed forward by the Indian community. In this article, we briefly describe their contribution and implication of these effects in the context of the future surveys of the cosmic dawn and the epoch of reionization that will be conducted by the SKA-LOW.  相似文献   

Modelling the 21-cm Signal from the Epoch of Reionization and Cosmic Dawn     

T. Roy Choudhury  Kanan Datta  Suman Majumdar  Raghunath Ghara  Aseem Paranjape  Rajesh Mondal  Somnath Bharadwaj  Saumyadip Samui 《Journal of Astrophysics and Astronomy》2016,37(4):29

Studying the cosmic dawn and the epoch of reionization through the redshifted 21-cm line are among the major science goals of the SKA1. Their significance lies in the fact that they are closely related to the very first stars in the Universe. Interpreting the upcoming data would require detailed modelling of the relevant physical processes. In this article, we focus on the theoretical models of reionization that have been worked out by various groups working in India with the upcoming SKA in mind. These models include purely analytical and semi-numerical calculations as well as fully numerical radiative transfer simulations. The predictions of the 21-cm signal from these models would be useful in constraining the properties of the early galaxies using the SKA data.  相似文献   

Probing Individual Sources during Reionization and Cosmic Dawn using Square Kilometre Array HI 21-cm Observations     

Kanan K. Datta  Raghunath Ghara  Suman Majumdar  T. Roy Choudhury  Somnath Bharadwaj  Himadri Roy  Abhirup Datta 《Journal of Astrophysics and Astronomy》2016,37(4):27

Detection of individual luminous sources during the reionization epoch and cosmic dawn through their signatures in the HI 21-cm signal is one of the direct approaches to probe the epoch. Here, we summarize our previous works on this and present preliminary results on the prospects of detecting such sources using the SKA1-low experiment. We first discuss the expected HI 21-cm signal around luminous sources at different stages of reionization and cosmic dawn. We then introduce two visibility based estimators for detecting such signals: one based on the matched filtering technique and the other relies on simply combing the visibility signal from different baselines and frequency channels. We find that the SKA1-low should be able to detect ionized bubbles of radius \(R_{\mathrm {b}} \gtrsim 10\) Mpc with ～100 h of observations at redshift z～8 provided that the mean outside neutral hydrogen fraction \(\mathrm {x}_{\text {HI}} \gtrsim 0.5\). We also investigate the possibility of detecting HII regions around known bright QSOs such as around ULASJ1120+0641 discovered by Mortlock et al. (Nature 474, 7353 (2011)). We find that a 5σ detection is possible with 600 h of SKA1-low observations if the QSO age and the outside x_HI are at least ～2×10⁷ Myr and ～0.2 respectively. Finally, we investigate the possibility of detecting the very first X-ray and Ly- α sources during the cosmic dawn. We consider mini-QSOs like sources which emits in X-ray frequency band. We find that with a total ～ 1000 h of observations, SKA1-low should be able to detect those sources individually with a ～ 9σ significance at redshift z=15. We summarize how the SNR changes with various parameters related to the source properties.  相似文献   

Diffraction of SH-Waves in a Spherically Isotropic Medium by a Rigid or Fluid Spherical Core     

Subhendu K. Datta  Arvind H. Shah 《Geophysical Journal International》1970,21(1):33-46

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A new semiconductor thermometer for geothermal measurements     

Satyabrata Datta 《Pure and Applied Geophysics》1965,61(1):123-126

Summary A portable solid state device designed and constructed for the measurement of temperature variation with depth inside a borehole is described. Saturation current (which is highly dependent on ambient temperature) in a reverse biased PN junction has been utilised for the purpose of measurement. The equipment is inexpensive and possesses several advantages over other types of instruments for geothermal measurement regarding simplicity in construction and operation.The paper is published by the kind permission of the Director General, Geological Survey of India.  相似文献