A study of possible temporal and latitudinal variations in the properties of the solar tachocline     

Sarbani Basu  H. M. Antia 《Monthly notices of the Royal Astronomical Society》2001,324(2):498-508

Temporal variations of the structure and the rotation rate of the solar tachocline region are studied using helioseismic data from the Global Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI) obtained during the period 1995–2000. We do not find any significant temporal variation in the depth of the convection zone, the position of the tachocline or the extent of overshoot below the convection zone. No systematic variation in any other properties of the tachocline, like width, etc., is found either. The possibility of periodic variations in these properties is also investigated. Time-averaged results show that the tachocline is prolate with a variation of about 0.02 R_⊙ in its position. Neither the depth of the convection zone nor the extent of overshoot shows any significant variation with latitude.  相似文献   

A multivariate statistical study of copper mineralization in the central section of Mosaboni Mine, Eastern Singhbhum, India     

A. K. Saha  S. N. Sarkar  Swapna Basu  Dhruba Ganguly 《Mathematical Geology》1986,18(2):215-235

A multivariate statistical analysis was carried out with log-transformed values of Cu, Ni, Co, Pb, Zn, Ag, Cr, Mn, Ca, and Sr in several sets of samples collected across the mineralized base metal zone in sheared soda granite, feldspathic schist, and chlorite schist from the central section of Mosaboni Mine of the famous Singhbhum Copper Belt of eastern India. Linear correlation coefficient matrices of two sets of ore samples (>0.5% Cu)—one from levels 18 and 21 and the other from levels 25 and 28—indicate two well-defined and distinct clusters comprising Cu, Ni, Co, Pb, and Zn on one hand and Ca, Sr, and Mn on the other. Varimax-rotatedR-mode factor analysis of two above-noted sample sets, taken along with available geologic information, indicates that over 80% of the variability in data matrices for 9–10 elements can be accounted for by four distinct processes: (a) an early phase of copper mineralization which apparently replaced Mn, Ca, and Sr in the host rock; (b) a silicate-cum-oxide phase of crystallization/recrystallization of host rock; (c) remobilization of sulfide-forming ore elements (Cu, Ni, Co, Pb, and Zn); and (d) a phase of mineralization of Ag which appears to have replaced Cr, Ca and Cu. Process (c) was quantitatively most important. Factor score studies are suggestive of preferred introduction of Ni, Co, Pb, and Zn along central parts of preexisting copper-mineralized zones.  相似文献   

Estimation of Raft Settlement Based on Linear Elastic Finite Element Analysis     

Bhartiya  Priyanka  Chakraborty  Tanusree  Basu  Dipanjan 《Geotechnical and Geological Engineering》2022,40(6):2907-2919

Geotechnical and Geological Engineering - A detailed parametric study based on linear-elastic three-dimensional finite element (FE) analysis with proper raft–soil interaction is performed for...  相似文献   

Precambrian crustal growth and tectonics: introduction     

Vinod K. Singh  Ram Chandra  Asish R. Basu  Surendra P. Verma  Tapas K. Biswal 《International Geology Review》2015,57(11-12):v-viii

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Reply to: Comments on “Trace element and isotopic evidence for Archean basement in the Lonar crater impact breccia, Deccan volcanic province” by Ramananda Chakrabarti and Asish R. Basu     

Ramananda Chakrabarti  Asish R. Basu  Arundhuti Ghatak 《Earth and Planetary Science Letters》2006,250(3-4):669-670

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The effect of a finite mass reservoir on the collapse of spherical isothermal clouds and the evolution of protostellar accretion     

E. I. Vorobyov  Shantanu Basu 《Monthly notices of the Royal Astronomical Society》2005,360(2):675-684

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Asteroseismic determination of helium abundance in stellar envelopes     

Sarbani Basu  Anwesh Mazumdar  H. M. Antia  Pierre Demarque 《Monthly notices of the Royal Astronomical Society》2004,350(1):277-286

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Effect of soil interaction on the performance of liquid column dampers for seismic applications     

Aparna Ghosh  Biswajit Basu 《地震工程与结构动力学》2005,34(11):1375-1389

The effects of soil–structure interaction (SSI) while designing the liquid column damper (LCD) for seismic vibration control of structures have been presented in this study. The formulation for the input–output relation of a flexible‐base structure with attached LCD has been presented. The superstructure has been modelled by a single‐degree‐of‐freedom (SDOF) system. The non‐linearity in the orifice damping of the LCD has been replaced by equivalent linear viscous damping by using equivalent linearization technique. The force–deformation relationships and damping characteristics of the foundation have been described by complex valued impedance functions. Through a numerical stochastic study in the frequency domain, the various aspects of SSI on the functioning of the LCD have been illustrated. A simpler approach for studying the LCD performance considering SSI, using an equivalent SDOF model for the soil–structure system available in literature by Wolf (Dynamic Soil–Structure Interaction. International Series in Civil Engineering and Engineering Mechanics. Prentice‐Hall: Englewood Cliffs, NJ, 1985) has also been presented. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Self-regulated gravitational accretion in protostellar discs     

E. I. Vorobyov  Shantanu Basu 《Monthly notices of the Royal Astronomical Society》2007,381(3):1009-1017

We present a numerical model for the evolution of a protostellar disc that has formed self-consistently from the collapse of a molecular cloud core. The global evolution of the disc is followed for several million years after its formation. The capture of a wide range of spatial and temporal scales is made possible by use of the thin-disc approximation. We focus on the role of gravitational torques in transporting mass inward and angular momentum outward during different evolutionary phases of a protostellar disc with disc-to-star mass ratio of order 0.1. In the early phase, when the infall of matter from the surrounding envelope is substantial, mass is transported inward by the gravitational torques from spiral arms that are a manifestation of the envelope-induced gravitational instability in the disc. In the late phase, when the gas reservoir of the envelope is depleted, the distinct spiral structure is replaced by ongoing irregular non-axisymmetric density perturbations. The amplitude of these density perturbations decreases with time, though this process is moderated by swing amplification aided by the existence of the disc's sharp outer edge. Our global modelling of the protostellar disc reveals that there is typically a residual non-zero gravitational torque from these density perturbations, i.e. their effects do not exactly cancel out in each region. In particular, the net gravitational torque in the inner disc tends to be negative during first several million years of the evolution, while the outer disc has a net positive gravitational torque. Our global model of a self-consistently formed disc shows that it is also self-regulated in the late phase, so that it is near the Toomre stability limit, with a near-uniform Toomre parameter Q ≈ 1.5–2.0. Since the disc also has near-Keplerian rotation, and comparatively weak temperature variation, it maintains a near-power-law surface density profile proportional to r ^−3/2.  相似文献   

Magnitude and redshift distributions of QSOs     

D. Basu 《Astrophysics and Space Science》1983,94(2):463-468

The peak in the distribution of apparent magnitude (V) of QSOs at 18.0 can be explained by loss of QSOs forV<-18.0 arising out of selection effects due to the availability of search lines necessary for the determination of redshifts and due to the misidentification of QSOs as Main-Sequence stars. ForV>18.0, the number of objects seem to fall off as they become progressively fainter and detection efficiency goes down. The present analysis also shows that a strong correlation exists between apparent magnitude and redshift of QSOs indicating redshifts are of cosmological origin.  相似文献