Inductive electric fields in the magnetosphere     

M. Roy  Ramaswamy Rajaram 《Planetary and Space Science》1979,27(6):817-819

A quantitative estimate of the electric fields induced by the time dependent ring current is made incorporating the drifts and induced electric fields in a self-consistent manner. It has been shown that in the ring current region, the results of the self-consistent calculations deviate substantially from the first order estimates hitherto obtained. Since for a rapidly varying ring current, the induced electric field can be of the same order as the convection electric field in the magnetosphere, these deviations have to be taken into account in substorm studies.  相似文献   

Study of Aeromagnetic Data Over Part of Eastern Ghat Mobile Belt and Bastar Craton     

S.P. Anand  Mita Rajaram   《Gondwana Research》2003,6(4):859-865

A portion of the aeromagnetic anomaly map of India, from 17⁰ to 20⁰ N and 78^o to 84^o E has been analysed to understand the tectonics of the region. The distribution of magnetic sources in the study region are clearly brought out in the analytic signal map and found to be associated with charnockitic rocks, iron formation and trap flows. The Godavari Graben is devoid of any magnetic sources. High-grade charnockitic rocks on surface and sub-surface, flank the shoulders of the Godavari Graben on either side. From the analysis of magnetic data, Sileru Shear Zone (SSZ) is identified as the contact of the Bastar craton and the Eastern Ghat Mobile Belt (EGMB). The Eastern Ghat is divided into two blocks: Block-N north of Srikakulam is devoid of magnetic sources while the charnockitic rocks are the main magnetic carriers in Block-S. The difference in magnetic characteristics of the two blocks has been attributed to the difference in metamorphic history. Block-N has an over print of amphibolite facies metamorphism while Block-S to the south depicts granulite facies metamorphism. The Euler solutions within the EGMB shows that the magnetic sources along SSZ is shallower than the south east implying that the exhumation process in the EGMB has a differential rate.  相似文献   

Obituary     

Mita Rajaram 《Journal of the Geological Society of India》2018,92(6):770-770

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SporadicE ionization associated with meteor events     

Girija Rajaram  H Chandra 《Journal of Earth System Science》1991,100(3):255-265

Two meteor events which were sighted in the Gujarat skies of India, were accompained by the visibility of sporadicE ionization on the ionograms recorded at Ahmedabad (Geog. Lat. 23·2°N, long. 72·30°E). The first event was the Dhajala fireball which flashed into the geoatmosphere along an E-N to W-S trail at about 20·40 h IST on 28 January 1976; the closest distance of the ground projection of meteor trail from Ahmedabad was 50km. The other event was a possible meteor group sighted over Ahmedabad on 28 May 1978, at about 21·10 h IST. This work describes the nature of the sporadicE ionization observed on Ahmedabad ionograms during the two events. Features of theEs echo during the Dhajala event which indicate that it could be of meteoric origin are discussed. Meteor theory is used to relate the observed ionization with the physical dimensions of the Dhajala meteorite as obtained by other workers.  相似文献   

Soil-structure interaction experiment using impulse response     

A. Mita  K. Yoshida  S. Kumagai  K. Shioya 《地震工程与结构动力学》1989,18(5):727-744

A new experimental method using a finite soil model with no special treatement on its boundaries is employed for soil-structure intration problems to simulate the semi-infinitenesss of the actual soil medium. The present method utlizies the characteristics of transient response to an impluse load to obtain the impedance functions and effective input motions for surface and embedded foundations. This technique is applicable to a linear elastic system whose impulse response decreases to a small enough value before observing the reflected waves. The experimentally obtained impedance functions and effective input motions are compared with those obtained by the direct boundary integral equation method and the hybrid approach. Good agreement between the xperimental and analytical results validates the present method as well as the accuracy of the numerical tools.  相似文献   

Response of a circular foundation on a uniform half-space to elastic waves     

J. E. Luco  A. Mita 《地震工程与结构动力学》1987,15(1):105-118

An alternative technique to obtain the dynamic response of a massless rigid circular foundation resting on a uniform elastic half-space when subjected to harmonic plane waves is presented. The technique relies on the use of an integral representation involving the free-field ground motion and the contact tractions obtained in the course of calculating the dynamic force–displacement relationship of the foundation for external forces. Tables listing the translational and rotational components of the response of the foundation for non-vertically incident SH, P, SV and Rayleigh waves are presented.  相似文献   

Active control of the seismic response of structures by combined use of base isolation and absorbing boundaries     

J. E. Luco  A. Mita  H. L. Wong 《地震工程与结构动力学》1992,21(6):525-541

The relative advantages of several control strategies to reduce the seismic response of multi-storey structures are studied. The strategies involve the separate or combined use of passive base isolation mechanisms and active control forces. The base isolation mechanism is modelled as an equivalent linear soft storey with high damping. The active control forces are selected so that an absorbing boundary is obtained at the top of the structure and non-reflecting or reflecting boundaries are obtained at the base of the building. It is found that the best results are obtained when a passive base isolation system is combined with an active absorbing boundary placed at the top of the building. However, the incremental gains resulting from adding a base isolation system to a structure already controlled by a roof-top active absorbing boundary are significant only for relatively soft base isolation systems. Also, the incremental gains appear to decrease as the number of storeys of the structure increases.  相似文献   

Motion of charged particles in the magnetosphere     

G. K. Mukherjee  R. Rajaram 《Astrophysics and Space Science》1981,74(2):287-301

The adiabatic motion of charged particles in the magnetosphere has been investigated using Mead-Fairfield magnetospheric field model (Mead and Fairfield, 1975). Since the motion of charged particles in a dipolar field geometry is well understood, we bring out in this paper some important features in characteristic motion due to non-dipolar distortions in the field geometry. We look at the tilt averaged picture of the field configuration and estimate theoretically the parameters like bounce period, longitudinal invariant and the bounce averaged drift velocities of the charged particle in the Mead-Fairfield field geometry. These parameters are evaluated as a function of pitch angle and azimuthal position in the region of ring current (5 to 7 Earth radii from the centre of the Earth) for four ranges of magnetic activity. At different longitudes the non-dipolar contribution as a percentage of dipole value in bounce period and longitudinal invariant show maximum variation for particles close to 90° pitch angles. For any low pitch angle, these effects maximize at the midnight meridian. The radial component of the bounce averaged drift velocity is found to be greatest at the dawn-dusk meridians and the contribution vanishes at the day and midnight meridians for all pitch angles. In the absence of tilt-dependent terms in the model, the latitudinal component of the drift velocity vanishes. On the other hand, the relative non-dipolar contribution to bounce averaged azimuthal drift velocity is very high as compared to similar contribution in other characteristic parameters of particle motion. It is also shown that non-dipolar contribution in bounce period, longitudinal invariant and bounce averaged drift velocities increases in magnitude with increase in distance and magnetic activity.  相似文献   

‘Sub-human’ beyond citizenship. A review of Nasir Uddin's The Rohingya.     

Prem Kumar Rajaram 《Singapore journal of tropical geography》2023,44(1):170-173

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Stability of a collisionless contact discontinuity     

R. Rajaram  G. L. Kalra  J. N. Tandon 《Astrophysics and Space Science》1980,67(1):137-145

The stability of a contact discontinuity in a collisionless plasma is examined. It is shown that the discontinuity can become unstable when the pressure component normal to the magnetic field is not continuous across the discontinuity. Even when the system is unstable, the growth rates are very small and unimportant in the context of wave propagation, except when the propagation is almost normal to the field. The instability could, however, lead to the slow dissipation of contact discontinuities in the solar wind and in the day side of the cusp region of the solar wind-magnetosphere boundary.  相似文献