Possibility of continuous monitoring of celestial X-ray sources through their ionization effects in the nocturnal D-region ionosphere     

D. P. sharma  A. K. Jain  S. C. Chakravarty  K. Kasturirangan  K. R. Ramanathan  U. R. Rao 《Astrophysics and Space Science》1972,17(2):409-425

The electron production rates in the night-time D-region arising from the transit of strong celestial X-ray sources Sco X-1, Tau X-1 and Galactic Center are estimated and compared with the ambient electron production rates resulting from other known stable agencies. Using the experimentally measured values of the night-time electron densities, the number of additional electrons/cc expected from the passage of these sources is computed. For the 164 kHz transmission from Tashkent, received at Ahmedabad, the associated enhancement in the attenuation is calculated using the full wave admittance technique of Barron and Budden. Reasonable agreement is shown to exist between the calculated values of the attenuation and those of direct observations.  相似文献   

Evidence for short term changes in the intensity and spectrum of hard X-rays from Cyg X-1     

A. K. Jain  U. B. Jayanthi  K. Kasturirangan  U. R. Rao 《Astrophysics and Space Science》1976,45(2):433-438

The paper presents experimental evidence for the existence of fast intensity fluctuations with time scales of the order of a minute in the X-ray emission from Cyg X-1 at energies greater than 29 keV. Spectral variations over time intervals of 20–25 min are also observed in the same energy range. Whereas, similar intensity and spectral fluctuations have been reported earlier at lower energies the observations presented here is the first evidence for the existence of similar fluctuations at high energies.  相似文献   

On dielectronic recombination coefficients of the H,He and Ne sequences     

N. K. Jain  Udit Narain 《Solar physics》1976,50(2):361-363

A modified expression for dielectronic recombination coefficients for the recombining ions pertaining to the H, He and Ne sequences is presented. The results are in nice agreement with the extensive computations of Ansari et al. (1970) for the cases considered.  相似文献   

The Non-Linear Stability of L4 in the Restricted Three-Body Problem when the Bigger Primary is a Triaxial Rigid Body     

P. P. Hallan  Sanjay Jain  K. B. Bhatnagar 《Celestial Mechanics and Dynamical Astronomy》2000,77(3):157-184

The non-linear stability of L ₄ in the restricted three-body problem has been studied when the bigger primary is a triaxial rigid body with its equatorial plane coincident with the plane of motion. It is found that L ₄ is stable in the range of linear stability except for three mass ratios:where A₁, A₂ depend upon the lengths of the semi axes of the triaxial rigid body. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

A spatially and temporally adaptive solution of Richards’ equation     

Cass T. Miller  Chandra Abhishek  Matthew W. Farthing 《Advances in water resources》2006

Efficient, robust simulation of groundwater flow in the unsaturated zone remains computationally expensive, especially for problems characterized by sharp fronts in both space and time. Standard approaches that employ uniform spatial and temporal discretizations for the numerical solution of these problems lead to inefficient and expensive simulations. In this work, we solve Richards’ equation using adaptive methods in both space and time. Spatial adaption is based upon a coarse grid solve and a gradient error indicator using a fixed-order approximation. Temporal adaption is accomplished using variable order, variable step size approximations based upon the backward difference formulas up to fifth order. Since the advantages of similar adaptive methods in time are now established, we evaluate our method by comparison with a uniform spatial discretization that is adaptive in time for four different one-dimensional test problems. The numerical results demonstrate that the proposed method provides a robust and efficient alternative to standard approaches for simulating variably saturated flow in one spatial dimension.  相似文献   

Plasma Heating by Forced Magnetic Reconnection     

Rekha Jain  Grigory E. Vekstein 《Astrophysics and Space Science》1998,264(1-4):113-128

A model of forced magnetic reconnection in a force-free magnetic field is considered, which allows calculation of the magnetic energy release during the current sheet reconnection. The dependence of this energy on characteristics of the magnetic configuration has been studied, and it was found that the released energy becomes very large when the field is near the marginal tearing stability. A persistent plasma heating provided by ongoing external driving and internal reconnection is also derived. It shows a typical relaxation-type dependence on the driving frequency, with dissipation becoming most efficient when the time-scales of the driving and reconnection are comparable. Possible implications of the obtained results for the problem of solar coronal heating are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

A new measure for cosmic shear     

Peter Schneider  Ludovic van Waerbeke  Bhuvnesh Jain  & Guido Kruse 《Monthly notices of the Royal Astronomical Society》1998,296(4):873-892

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Large-scale cenozoic tectonics of Central and South-central Asia: Products of continental collision     

Umesh Chandra 《Physics of the Earth and Planetary Interiors》1979,20(1):33-41

Three basic tectonic units, the Eurasian continent, the Rigid Boundary Zone and the Indian continent, are recognized. The Rigid Boundary Zone is identified with aseismic lineaments on an epicenter map of the Himalayas and their vicinity. The origin of the Himalayan syntaxes, their re-entrant character, and the observation that most of the Himalayas are made up of rocks belonging geologically to the Indian peninsular shield, are explained by deformation of the Indian continent within this Rigid Boundary Zone since the continental collision. The focal mechanism solutions of six earthquakes in the Indian Peninsula support the inference derived from the model that the high stresses generated by the continental collision may be very extensive spatially, and that the entire Indian Peninsula may be under a state of left lateral shear along NNE vertical planes.  相似文献   

Implications of pre-mesozoic orogeny in the geological evolution of the Himalaya and Indo-Gangetic Plains     

A.K. Jain  R.K. Goel  N.G.K. Nair 《Tectonophysics》1980,62(1-2)

An integrated geological analysis of the Himalaya and Indo-Gangetic Plains demonstrates that the Great Vindhyan Basin incorporating large parts of these morphotectonic units were uplifted into an uneven landmass due to the Pre-Mesozoic orogenic cycle. This uneven landmass was eroded off largely during a considerable part of the Devonian and Carboniferous thereby causing partial absence of sedimentary sequences of these periods except in parts of the Tethys Himalaya. The Late Paleozoic epeirogenic movements brought about renewed sedimentation in the Lesser and Tethys Himalayas in the Krol and Tethys Basins, respectively, which was terminated by the Himalayan Orogeny during Late Cretaceous—Early Eocene.  相似文献   

Lower Miocene (Aquitanien-Burdigalian) palaeobiogeography of the Indian subcontinent     

Dr. Ashok Sahni  Mr. Harish Chandra Mitra 《International Journal of Earth Sciences》1980,69(3):824-848

The paper analytically discusses certain palaeoecological criteria in the reconstruction of Lower Miocene (Aquitanian-Burdigalian) palaeobiogeography of the Indian subcontinent. The period is characterised by major marine transgressions and a prolific marine invertebrate and terrestrial vertebrate faunas. Faunal affinities of molluscs from western (Sind-Baluchistan) and eastern (Garo Hills) sectors are distinct and different. Molluscs of Garo Hills show affinity to Burmese species, whereas Sind-Baluchistan species shows similarity to that of the Mediterranean region. Marine molluscs resemble with the present-day taxa of the Arabian Sea and Bay of Bengal, where more than 35% species are common. This similarity is also evidenced by marine elasmobranchs, where approximately 33% species and 86% genera are similar to that of the Recent taxa. Terrestrial mammals show an intermingling of southern U.S.S.R. and African forms along with the presence of probably some groups belonging to the Indian subcontinent.Angiosperms are the dominant group. The Lower Miocene floras of the eastern and the western sectors are entirely different. The palm,Sabal major andPinus are reported from various localities. The climate in the western sector and South India was tropical, whereas in the eastern sector, it was variable.The Lower Miocene period is also marked by the contraction of Sindhu Sea, Bangla Sea and the Burmese Gulf southwards resulting in the final disappearance of the sea by the Pliocene.

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Zusammenfassung Die Paläobiogeographie des unteren Miocän (Aquitan-Burdigal) läßt sich auf dem indischen Subkontinent aus den palökologischen Daten rekonstruieren. Zu dieser Zeit gab es viele marine Invertebraten und terrestrische Vertebraten-Faunen, die große marine Transgression anzeigen. Die Mollusken des Westens (Find-Baluchistan) und Ostens (Garo-Gebirge) sind unterschiedlich. Die Mollusken des Garo-Gebirges sind mit den Spezies von Burma verwandt. Dagegen sind die Faunen von Sind-Baluchistan für die mediterrane Faunenprovinz typisch. Die marinen Mollusken sind verwandt mit den Faunen des Arabischen Meeres und der Bucht von Bengalen; etwa 35% der Spezies sind gleich. Von den marinen Elasmobranchien sind ungefähr 33 % Spezies und 86% Genera gleich wie man sie in den rezenten Faunen findet. Terrestrische Sänger zeigen eine Mischung von südlicher U.S.S.R. und Afrika mit einigen Teilen des Indischen Subkontinentes.In den Pflanzen-Gruppen herrschen die Angiospermen vor. Die Untermiocän-Flora der östlichen und westlichen Gebiete ist ganz unterschiedlich. Der Palme, dieSabal Major undPinus sind aus verschiedenen Lokalitäten bekannt. Das Klima im Westen und im Süden Indiens war tropisch, im Osten dagegen war es wechselfeucht.Das Untermiocän-Meer im Gebiet Sind, Bangladesh und Burma verschwindet vor dem Pliozän.

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Résumé Cet article analyse certains critères paléoécologiques dans la reconstitution de la paléogéographie du Miocène inférieur (Aquitanien-Burdigalien) de l'Inde subcontinentale. La période est caractérisée par de grandes transgressions marines et par des faunes abondantes d'invertébrés marins et de vertébrés terrestres. Les affinités fauniques des mollusques sont différentes dans les secteurs occidentaux (Sind-Baluchistan) et orientaux (Garo Hills). Les mollusques des Garo Hills montrent des affinités avec les espèces de Burma, tandis que les espèces de Sind-Béloutchistan montrent des similitudes avec celles de la région méditerranéenne. Les mollusques marins ont des ressemblances avec les taxons actuels de la Mer d'Arabie et du Golfe du Bengal, où plus de 35% des espèces sont les mÊmes. Cette similarité vaut aussi pour les élasmobranches marin, dont 33% des espèces et 86% des genres ressemblent aux taxons récents. Les mammifères terrestres montrent un mélange de formes du sud de l'U.S.S.R. et de formes africaines, allant de pair avec la présence de certains groupes probables appartenant au sous-continent indien.Les angiospermes forment le groupe dominant. Les formes du Miocène inférieur des secteurs orientaux et occidentaux sont entièrement différentes. Le palmier, le grand Sabal et le pin, sont connus dans différentes localités. Le climat dans le secteur occidental et dans l'Inde méridionale était tropical, tandis que dans le secteur oriental, il était variable.La période du Miocène inférieur est également marquée par le rétrécissement de la Mer de Sindhu, de la Mer de Bangla et du Golfe de Burma vers le sud, avec comme résultat la disparition finale de la mer au Pliocène.

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(Aquitanian Nurdigalian) . . (Sind- Beluchistan) (Garo Hills) . , . : 35% . Elasmobranchs 33 % 86 % . , . . , Sabal major . , , , , , — . Sindhu, .

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