On Charged Analogues of Buchdahl’S Type Fluid Spheres     

Y.?K.?Gupta  Mukesh?KumarEmail author 《Astrophysics and Space Science》2005,299(1):43-59

In this article the charged analogues of recently derived Buchdahl’s type fluid spheres have been obtained by considering a particular form of electric field intensity. In this process, Einstein–Maxwell field equations yield eight different classes of solutions, joining smoothly with the exterior Reissner–Nordstrom metric at the pressure free intersurface. Out of the eight solutions only seven could be utilized to represent superdense star models with ultrahigh surface density of the order 2×10¹⁴ gm cm⁻³. The maximum masses of the star models were found to be 8.223931M_Θ and 8.460857M_Θ subject to strong and weak energy conditions, respectively, which are much higher than the maximum masses 3.82M_Θ and 4.57M_Θ allowed in the neutral cases. The velocity of sound seen to be less than that of light throughout the star models.  相似文献   

Some studies on solar microwave bursts in relation to the phases of the associated Hα-flares and their spectral nature     

S. K. Sarkar  T. Chattopadhyay  M. K. Das Gupta 《Solar physics》1975,40(2):411-415

Occurrences of the flare-associated microwave bursts as well as their peak flux and energy excess spectra have been examined in relation to the pre- and post-maximum phases of the respective flares during the period 1969–72. Results obtained are: (i) about 76% of the flare-associated bursts occur in the pre-maximum phase and the remaining 24% occurs in the post-maximum phase irrespective of the flare classification, intensity-wise or area-wise; (ii) ‘impulsive’ and ‘gradual rise and fall’ bursts are relatively more important in the pre-maximum phase while ‘post burst increase’ bursts show comparatively higher occurrences in the post-maximum phase; (iii) peak flux and energy excess spectra of the concurrent microwave bursts in the pre-maximum phase of the flare are mostly of ‘inverted U’ and ‘increasing with frequency’ spectral types. Of these, ‘impulsive’ bursts are predominantly of the ‘inverted U’ and the ‘grf’ bursts are of the ‘increasing with frequency’ spectral type.  相似文献   

Errata     

B.V. Krishna MurthyK. Sen Gupta 《Planetary and Space Science》1972

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South Equatorial Current (SEC) driven changes at DSDP Site 237, Central Indian Ocean, during the Plio-Pleistocene: Evidence from Benthic Foraminifera and Stable Isotopes   总被引：1，自引：0，他引：1  

Anil K. Gupta  Moumita Das  K. Bhaskar 《Journal of Asian Earth Sciences》2006,28(4-6):276-290

This study attempts to analyse paleoceanographic changes in the Central Indian Ocean (Deep Sea Drilling Project Site 237), linked to monsoon variability as well as deep-sea circulation during the Plio-Pleistocene. We used factor and cluster analyses of census data of the 34 most dominant species of benthic foraminifera that enabled us to identify five biofacies: Astrononion umbilicatulum–Uvigerina proboscidea (Au–Up), Pullenia bulloides–Bulimina striata (Pb–Bs), Globocassidulina tumida–Nuttallides umbonifera (Gt–Nu), Gyroidinoides nitidula–Cibicides wuellerstorfi (Gn–Cw) and Cassidulina carinata–Cassidulina laevigata (Cc–Cl) biofacies. Knowledge of the environmental preferences of modern deep-sea benthic foraminifera helped to interpret the results of factor and cluster analyses in combination with oxygen and carbon isotope values. The biofacies indicative of high surface productivity, resulting from a stronger South Equatorial Current (Au–Up and Pb–Bs biofacies), dominate the early Pliocene interval (5.6–4.5 Ma) of global warmth. An intense Indo-Pacific ‘biogenic bloom’ and strong Oxygen Minimum Zone extended to intermediate depths (1000–2000 m) over large parts of the Indian Ocean in the early Pliocene. Since 4.5 Ma, the food supply in the Central Indian Ocean dropped and fluctuated while deep waters were corrosive (biofacies Gt–Nu, Gn–Cw). The Pleistocene interval is characterized by an intermediate flux of organic matter (Cc–Cl biofacies).  相似文献   

Aerosol characteristics during winter fog at Agra,North India     

P. D. Safai  S. Kewat  G. Pandithurai  P. S. Praveen  K. Ali  S. Tiwari  P. S. P. Rao  K. B. Budhawant  S. K. Saha  P. C. S. Devara 《Journal of Atmospheric Chemistry》2008,61(2):101-118

Simultaneous measurements on physical, chemical and optical properties of aerosols over a tropical semi-arid location, Agra in north India, were undertaken during December 2004. The average concentration of total suspended particulates (TSP) increased by about 1.4 times during intense foggy/hazy days. Concentrations of SO₄ ²⁻, NO₃ ⁻, NH₄ ⁺ and Black Carbon (BC) aerosols increased by 4, 2, 3.5 and 1.7 times, respectively during that period. Aerosols were acidic during intense foggy/hazy days but the fog water showed alkaline nature, mainly due to the neutralizing capacity of NH₄ aerosols. Trajectory analyses showed that air masses were predominantly from NW direction, which might be responsible for transport of BC from distant and surrounding local sources. Diurnal variation of BC on all days showed a morning and an evening peak that were related to domestic cooking and vehicular emissions, apart from boundary layer changes. OPAC (Optical properties of aerosols and clouds) model was used to compute the optical properties of aerosols. Both OPAC-derived and observed aerosol optical depth (AOD) values showed spectral variation with high loadings in the short wavelengths (<1 μm). AOD value at 0.5 μm wavelength was significantly high during intense foggy/hazy days (1.22) than during clear sky or less foggy/hazy days (0.63). OPAC-derived Single scattering albedo (SSA) was 0.84 during the observational period, indicating significant contribution of absorbing aerosols. However, the BC mass fraction to TSP increased by only 1% during intense foggy/hazy days and thereby did not show any impact on SSA during that period. A large increase was observed in the shortwave (SW) atmospheric (ATM) forcing during intense foggy/hazy days (+75.8 W/m²) than that during clear sky or less foggy/hazy days (+38 W/m²), mainly due to increase in absorbing aerosols. Whereas SW forcing at surface (SUF) increased from −40 W/m² during clear sky or less foggy/hazy days to −76 W/m² during intense foggy/hazy days, mainly due to the scattering aerosols like SO₄ ^2-.  相似文献   

Non-thermal transient sources from rotating black holes     

Maurice H. P. M. van Putten  Alok C. Gupta 《Monthly notices of the Royal Astronomical Society》2009,394(4):2238-2246

Rotating black holes can power the most extreme non-thermal transient sources. They have a long-duration viscous time-scale of spin-down, and produce non-thermal emissions along their spin-axis, powered by a relativistic capillary effect. We report on the discovery of exponential decay in Burst and Triensient Source Experiment (BATSE) light curves of long gamma-ray bursts (GRBs) by matched filtering, consistent with a viscous time-scale, and identify ultra-high energy cosmic rays (UHECRs) about the Greisen–Zatsepin–Kuzmin (GZK) threshold with linear acceleration of ion contaminants along the black hole spin-axis, consistent with black hole masses and lifetimes of Fanaroff–Riley type II (FR II) active galactic nuclei (AGN). We explain the absence of UHECRs from BL Lac objects due to UHECR emissions preferably at appreciable angles away from the black hole spin-axis. Black hole spin may be the key to unification of GRBs and their host environments, and to AGN and their host galaxies. Our model points to long-duration bursts in radio from long GRBs without supernovae and gravitational waves from all long GRBs.  相似文献   

Time relationship between regional deformation and fabric development in the Peralimala pluton,South India — Inferences from magnetic fabric     

K. R. Praveen  V. Prasannakumar  Manish A. Mamtani 《Journal of the Geological Society of India》2009,73(6):803-812

Anisotropy of magnetic susceptibility (AMS) is investigated in samples of Peralimala (PM) pluton (ca. 550 Ma) and adjacent gneiss, gabbro, mylonite and amphibolite from the Moyar Shear Zone (MSZ), Southern Granulite Terrane (SGT) with an aim to decipher the time-relationship between fabric development in the pluton and regional tectonics. Magnetic foliation recorded in the PM pluton is sub-parallel to the WNW-ESE striking MSZ. Magnetic foliation and lineation trajectories are sigmoidal and curve into the shear zone. A dextral sense of shear is deciphered from the trajectories, which is similar to that reported within the MSZ in some earlier studies. It is inferred that the PM pluton has developed post-emplacement deformation-fabric related to reactivation of the MSZ during Pan-African age. Based on the data and existing information about regional tectonics of the area, the possibility of the (a) PM pluton being a Deformed Alkali Rock and Carbonatite (DARC) and (b) MSZ marking an ancient suture zone, is discussed.  相似文献   

Saraswati Nadi in Haryana and its linkage with the Vedic Saraswati River — Integrated study based on satellite images and ground based information     

B. K. Bhadra  A. K. Gupta  J. R. Sharma 《Journal of the Geological Society of India》2009,73(2):273-288

Detailed studies on the status of Saraswati Nadi of northern Haryana have been carried out using multi date and multi resolution satellite images, GIS techniques and ground data. Palaeochannels have been delineated using remote sensing techniques and validated using discovered archaeological sites, sedimentological data from drilled wells and water quality data. Detailed analysis of hydrological data (rainfall and stream discharge), catchment area and petrographic analysis of rock samples have been done to decipher the dwindling state of Saraswati Nadi. Likelihood of Adi Badri as the place of origin of Saraswati Nadi and its possible linkage with the Vedic Saraswati River is discussed. Suggestions have been given for safeguarding and revival of Saraswati Nadi as a national heritage.  相似文献   

Pronab Kumar Banerjee (1933–2008)     

Arindam Gupta 《Journal of the Geological Society of India》2009,73(3):438-438

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Rapid incorporation of lipids into macromolecules during experimental decay of invertebrates: Initiation of geopolymer formation     

Neal S. Gupta  George D. Cody  O. Erik Tetlie  Derek E.G. Briggs  Roger E. Summons 《Organic Geochemistry》2009,40(5):589-594

Diagenetic alteration is critical for the preservation of fossil cuticles of plant and animal origin and to the formation of kerogen. The process takes place over millions of years, but the stage at which it is initiated is not known. Laboratory decay experiments were carried out on shrimps, scorpions and cockroaches to monitor changes in the chitin–protein of the arthropod cuticle and associated lipids. The cockroach and scorpion exoskeleton remained largely unaltered morphologically, but the shrimp experienced rapid decomposition within a month, which progressed through the 44 week duration of the experiment as revealed using electron microscopy. Mass spectrometry and ¹³C NMR (nuclear magnetic resonance) spectroscopy revealed the association of an n-alkyl component with labile lipids, such as fatty acids with up to 24 carbon atoms, which were incorporated into the decaying macromolecule. The scorpion and cockroach cuticle did not reveal the incorporation of additional lipids, indicating that decay is important in initiating in situ lipid association. This experiment provides evidence that lipids can become associated with carbohydrate and proteinaceous macromolecules during the very early stages of decay, representing the first stage in the transformation process that contributes to the aliphatic rich composition ubiquitous in organic fossils and kerogen.  相似文献