Revisiting Field Burial by Accretion onto Neutron Stars     

Dipanjan Mukherjee 《Journal of Astrophysics and Astronomy》2017,38(3):48

The surface magnetic field strength of millisecond pulsars (MSPs) is found to be about 4 orders of magnitude lower than that of garden variety radio pulsars (with a spin of \({\sim }\)0.5–5 s and \(B{\sim }10^{12}\hbox { G}\)). The exact mechanism of the apparent reduction of field strength in MSPs is still a subject of debate. One of the proposed mechanisms is burial of the surface magnetic field under matter accreted from a companion. In this article we review the recent work on magnetic confinement of accreted matter on neutron stars poles. We present the solutions of the magneto-static equations with a more accurate equation of state of the magnetically confined plasma and discuss its implications for the field burial mechanism.  相似文献   

Fluoride enrichment in aquifers of the Thar Desert: controlling factors and its geochemical modelling     

Chander Kumar Singh  Rina Kumari  Neha Singh  Javed Mallick  Saumitra Mukherjee 《水文研究》2013,27(17):2462-2474

The groundwater is the only source of drinking water in the Jaisalmer district of Rajasthan, India. The study area is a part of the Thar Desert. It has low and scattered population and no industries; hence, the possibility of anthropogenic input of fluoride is almost negligible. Thus, the enrichment of fluoride is only possible due to geochemical processes taking place in the groundwater of the region. A total of 100 groundwater samples, 34 samples from Jaisalmer and 66 samples from the Pokharan administrative blocks, were collected. It was observed that the concentration of fluoride ranged from 0.08 mg/l to 4.56 mg/l in the groundwater of Jaisalmer and from 0.56 mg/l to 6.60 mg/l in the samples of the Pokharan block. The alkaline condition (average pH, 7.7 ± 0.22 and 8.01 ± 0.25 in Jaisalmer and the Pokharan administrative block, respectively) in the region favours fluorite dissolution. Ion exchange, dissolution of calcite, semi‐arid climate, alkaline conditions and weathering are responsible for fluoride enrichment in the groundwater of the study area. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Microcomputer aided lineament analysis of Son-Mahanadi Valley coal basins,Central India from Landsat data     

T K Mukherjee  R V Savanur 《Journal of the Indian Society of Remote Sensing》1988,16(1):47-54

In the overall tectonic set up of various coal basins of the Peninsular India, the Son-Mahanadi Valley coal basins of Central India have a unique disposition. The coal measures sediments of Peninsular India are developed along well defined E-W and NW-SE trending linear narrow belts. The Son-Mahanadi Valley basins represent the tract where NW-SE trending Mahanadi Valley basins seemingly merge with the major east-west trending Damodar-Koel-Son-Satpura alignment. Landsat data of Son-Mahanadi Valley basins in the four spectral bands (0.5 to 1.1 Micrometers) were used to pick up the lineaments which are possibly of geologic origin. Detailed analysis of lineaments were carried out with the help of three softwares. Diglin (to produce rose diagram) and PLLIN (to plot digitized lineaments to produce a map on any scale) by a Hewlett Packard 45 series microcomputer equipped with graphics screen, plotter, digitiser and floppy disc unit. Detailed analysis revealed a pronounced direction roughly, N 70°E which is present in the northern half of the area while N 40°W direction is present alongwith N 70°E in the southern half. These trends correspond to the NW-SE trending Mahanadi Valley and to the E-W trending Damodar-Son Satpura belt. The above clearly brings out the striking parallelism between the lineament trends in the basement and the overlying coal bearing Gondwana Sediments. This parallelism is suggestive of a genetic relationship between the two.  相似文献   

Perturbations in tropical middle atmosphere during winter, 1984–1985     

B. K. Mukherjee  K. Indira  K. K. Dani 《Meteorology and Atmospheric Physics》1987,37(1):17-26

Summary Using high altitude rocketsonde data for Thumba (8.5 N, 76.9E) and Balasore (21.5 N, 86.9E) and the stratalert messages for high latitudes for the winter (December–March) 1984–1985, an examination has been made to study the perturbations in the temperature and winds in the tropical middle atmosphere and their linkage with the dynamical events occurring over the high-latitude middle atmosphere during that winter.The results of analysis indicated occurrence of strong cooling in the mesosphere over a period of seven days (5–12 December 1984) and the depth of the cooling layer was 15 km. This incident was followed by a strong warming over a period of seven days (12–19 December 1984) and the depth of the warming layer was 13 km. The major warming event, which occurred over high latitudes during the later part of December and the first week of January, was followed by the cooling in the mesosphere and warming in the stratosphere at Thumba. Also the zonal winds were strong easterly and the meridional winds were northerly in the upper stratosphere and the lower mesosphere over tropics during the same period. Weaker zonal winds/stronger easterly winds were generally noticed to be associated with coolings/warmings over tropics.With 7 Figures  相似文献   

Interannual variability of middle atmosphere and Indian summer monsoon     

B. K. Mukherjee  K. Indira  Bh. V. Ramana Murty 《Meteorology and Atmospheric Physics》1986,35(1-2):64-69

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Free vibrations of coupled shear walls     

P. R. Mukherjee  A. Coull 《地震工程与结构动力学》1972,1(4):377-386

The continuous connection method of analysis is extended to deal with the free vibrations of a coupled shear wall structure. The natural modes and frequencies are determined from the Galerkin technique, and the dynamic response following an imposed lateral displacement is evaluated. A comparison is made between theoretical predictions of natural frequencies and the results from tests on model structures.  相似文献   

Gas interaction effects on lunar bonded particles and their implications     

Nalin R. Mukherjee 《Earth, Moon, and Planets》1976,15(3-4):403-413

Some of the bonded particles of lunar soil samples separated upon exposure to reactive gases such as oxygen, water vapor, their mixtures, acids and bases. The bondings between particles susceptible to gas-disruption seemed to be generally weak and appeared to have taken place via highly radiation-damaged layers at the particle surfaces. These amorphous layers with an average thickness of about 0.05µm were produced by the solar wind exposure of about 2000 years. Therefore, the solar wind was responsible for the formation of these weak bondings and also probably responsible for disruption of these bondings. Apollo 11 and 12 landed in the equatorial region and about 1500 km apart. Thus, the solar wind effects on materials at these sites should have been about the same and the proportion of bonded particles separated by reactive gas exposure should also have been about the same; but the number of separations observed was about 2.7 (average) times greater in the Apollo 11 soil sample than in the Apollo 12 soil sample. This finding suggests that the number of weakly bonded particles and probably the solar-wind damaged amorphous layer particles at these sites was about in the same proportion. It is, therefore, considered that materials from certain depth (practically not exposed to the solar wind) of another site were transported and mixed during recent years (considerably less than 2000 years) with the original materials of the Apollo 12 site. This is consistent with the conclusions made by other investigators.  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   

Natural vibrations of shear wall buildings on flexible supports     

A. Coull  P. R. Mukherjee 《地震工程与结构动力学》1978,6(3):295-316

A shear wall building is considered as an assembly of plane and curvilinear shear walls tied together by floor slabs to act as a composite unit. Based on this conception and the continuous medium approach, the governing dynamic equations and boundary conditions are derived from energy principles, using Vlasov's theory of thin-walled beams. All primary and secondary inertia forces, as well as the influence of elastic foundation flexibility, have been taken into consideration. A numerical solution of the dynamic equations is achieved by employing the Ritz-Galerkin technique, yielding both natural frequencies and mode shapes. The technique is applicable to buildings containing coupled and non-coupled, open section shear walls oriented in plan in any arbitrary manner. The use of the method is illustrated by the example of a complex building with unsymmetric plan, and the analytical natural frequencies of two shear wall building models are compared with those obtained experimentally by other investigators.  相似文献   

Some thermodynamical and microphysical aspects of monsoon clouds     

A Mary Selvam  A S Ramachandra Murty  R Vijayakumar  S K Paul  G K Manohar  R S Reddy  B K Mukherjee  Bh. V. Ramana Murty 《Journal of Earth System Science》1980,89(2):215-230

The thermodynamical and microphysical characteristics of monsoon clouds in the Poona, Bombay and Rihand regions were investigated using extensive aircraft in-cloud observations. The number of clouds sampled at Poona, Bombay and Rihand is 2199, 169 and 104 respectively. The temperatures inside the cloud are colder than its environment at Poona and Rihand. The maximum difference is about 3°C at the cloud base level and the difference decreased with height. At Bombay the difference is less than 1°C and at some levels the temperatures inside the cloud are warmer than its environment. The lapse rates of temperatures inside the cloud are slightly less than those in the immediate environment of the cloud. The environmental lapse rates are nearly equal to the saturated adiabatic value. The positive increments in liquid water content (LWC) are associated with the increments in temperature inside the cloud. Similarly positive increments in temperatures inside the cloud are associated with the increments in temperature of its immediate environment at the same level or the layer immediately above. The maximum cloud lengths observed at Poona and Bombay respectively are 14 and 3 km. The horizontal cross-section of LWC showed a maximum number of 13 peaks in clouds at Poona while only 7 peaks were observed at Bombay. The location of maximum LWC in the horizontal cross-section is more or less at the centre of the cloud. The LWC profile showed an increase with height from the base of the cloud at Poona and Bombay. There is no marked variation of LWC with height at Rihand. The total droplet concentration at different altitudes at Poona and Bombay is in the range 28–82 cm^?3. The size distribution of cloud droplets experienced a broadening effect with increase in height from the cloud base at Poona. The broadening effect at Bombay is not as marked as that at Poona.  相似文献