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21.
The flow of laser radiation in a plane-parallel cylindrical slab of active amplifying medium with axial symmetry is treated as a problem in radiative transfer. The appropriate one-dimensional transfer equation describing the transfer of laser radiation has been derived by an appeal to Einstein'sA, B coefficients (describing the processes of stimulated line absorption, spontaneous line emission, and stimulated line emission sustained by population inversion in the medium) and considering the rate equations to completely establish the rational of the transfer equation obtained. The equation is then exactly solved and the angular distribution of the emergent laser beam intensity is obtained; its numerically computed values are given in tables and plotted in graphs showing the nature of peaks of the emerging laser beam intensity about the axis of the laser cylinder. 相似文献
22.
Pranab Ghosh 《Monthly notices of the Royal Astronomical Society》2000,315(1):89-97
We introduce a multipolar scheme for describing the structure of stationary, axisymmetric, force-free black hole magnetospheres in the '3+1' formalism. We focus here on Schwarzschild spacetime, giving a complete classification of the separable solutions of the stream equation. We show a transparent term-by-term analogy of our solutions with the familiar multipoles of flat-space electrodynamics. We discuss electrodynamic processes around disc-fed black holes in which our solutions find natural applications: (i) 'interior' solutions in studies of the BlandfordZnajek process of extracting the rotational energy of holes, and of the formation of relativistic jets in active galactic nuclei and 'microquasars'; (ii) 'exterior' solutions in studies of accretion disc dynamos, disc-driven winds and jets. On the strength of existing numerical studies, we argue that the poloidal field structures found here are also expected to hold with good accuracy for rotating black holes, except for the cases of the maximum possible rotation rates. We show that the closed-loop exterior solutions found here are not in contradiction with the MacdonaldThorne theorem, as these solutions, which diverge logarithmically on the horizon of the hole , only apply to those regions that exclude . 相似文献
23.
In this paper, we have considered a model of our universe containing five components as its constituents. Then, we have done
here the statefinder diagnostics for this model. This model can successfully explain the accelerated expansion of the universe
given that it satisfies a certain condition. Here we have considered the modified Chaplygin gas as the dynamically changing
part of the dark energy component of our universe. Chaplygin gas provides early deceleration and late time acceleration of
the universe. The graphical representation of statefinder parameters shows that the total evolution of the universe starts
from radiation era to phantom model. 相似文献
24.
M. K. Das Pankaj Narang S. Mahajan M. Yuasa 《Journal of Astrophysics and Astronomy》2009,30(3-4):177-185
We have investigated the out of plane equilibrium points of a passive micron size particle and their stability in the field of radiating binary stellar systems Krüger-60, RW-Monocerotis within the framework of photo-gravitational circular restricted three-body problem. We find that the out of plane equilibrium points (L i , i = 6, 7, 8, 9) may exist for range of β 1 (ratio of radiation to gravitational force of the massive component) values for these binary systems in the presence of Poynting-Robertson drag (hereafter PR-drag). In the absence of PR-drag, we find that the motion of a particle near the equilibrium points L 6,7 is stable in both the binary systems for a specific range of β 1 values. The PR-drag is shown to cause instability of the various out of plane equilibrium points in these binary systems. 相似文献
25.
P. Kharb D. V. Lal V. Singh J. Bagchi C. H. Ishwara Chandra A. Hota C. Konar Y. Wadadekar P. Shastri M. Das K. Baliyan B. B. Nath M. Pandey-Pommier 《Journal of Astrophysics and Astronomy》2016,37(4):34
We present detailed science cases that a large fraction of the Indian AGN community is interested in pursuing with the upcoming Square Kilometre Array (SKA). These interests range from understanding low luminosity active galactic nuclei in the nearby Universe to powerful radio galaxies at high redshifts. Important unresolved science questions in AGN physics are discussed. Ongoing low-frequency surveys with the SKA pathfinder telescope GMRT, are highlighted. 相似文献
26.
The results of a number of laboratory model tests for the short‐term ultimate uplift capacity of a circular plate anchor embedded in saturated soft kaolinite and montmorillonite are presented. The tests were conducted with and without venting the bottom of the plate anchor in order to determine the variation of the suction force with embedment ratio. The variation of the suction force is presented in terms of the undrained shear strength of the clay and also the net ultimate uplift capacity. 相似文献
27.
S. Abhilash Someshwar Das S. R. Kalsi M. Das Gupta K. Mohankumar John P. George S. K. Banerjee S. B. Thampi D. Pradhan 《Pure and Applied Geophysics》2007,164(8-9):1491-1509
Pre-monsoon rainfall around Kolkata (northeastern part of India) is mostly of convective origin as 80% of the seasonal rainfall
is produced by Mesoscale Convective Systems (MCS). Accurate prediction of the intensity and structure of these convective
cloud clusters becomes challenging, mostly because the convective clouds within these clusters are short lived and the inaccuracy
in the models initial state to represent the mesoscale details of the true atmospheric state. Besides the role in observing
the internal structure of the precipitating systems, Doppler Weather Radar (DWR) provides an important data source for mesoscale
and microscale weather analysis and forecasting. An attempt has been made to initialize the storm-scale numerical model using
retrieved wind fields from single Doppler radar. In the present study, Doppler wind velocities from the Kolkata Doppler weather
radar are assimilated into a mesoscale model, MM5 model using the three-dimensional variational data assimilation (3DVAR)
system for the prediction of intense convective events that occurred during 0600 UTC on 5 May and 0000 UTC on 7 May, 2005.
In order to evaluate the impact of the DWR wind data in simulating these severe storms, three experiments were carried out.
The results show that assimilation of Doppler radar wind data has a positive impact on the prediction of intensity, organization
and propagation of rain bands associated with these mesoscale convective systems. The assimilation system has to be modified
further to incorporate the radar reflectivity data so that simulation of the microphysical and thermodynamic structure of
these convective storms can be improved. 相似文献
28.
Supriyo Kumar Das Joyanto Routh Alakendra N. Roychoudhury J. Val Klump 《Journal of Paleolimnology》2008,39(3):349-360
We used elemental carbon, nitrogen, phosphorus and hydrogen ratios (C/N, N/P and H/C) with total organic carbon (TOC) and
total phosphorus (TP) as well as stable carbon and nitrogen isotopes (δ13C and δ15N) to investigate the source and depositional conditions of organic matter in sediments from Zeekoevlei, the largest freshwater
lake in South Africa. Typical C/N (10–12), H/C ratios (≥1.7) and δ13Corganic values (−22 to −19‰) together with the increase in TOC concentration indicate elevated primary productivity in lower middle
(18–22 cm) and top (0–8 cm) sections of the sediment cores. Seepage of nutrients from a nearby waste water treatment plant,
rapid urbanization and heavily fertilized farming in the catchments are responsible for the increased productivity. Consistent
with this, measured δ15Norganic values (∼11‰) indicate increased raw sewage input towards the top-section of the core. Although cyanobacterial blooms are
evident from the low δ15N values (∼3‰) in mid-section of the core, they did not outnumber the phytoplankton population. Low N/P ratio (∼0) and high
TP (100–2,200 mg l−1) support cyanobacterial growth under N limited condition, and insignificant input of macrophytes towards the organic matter
pool. Dredging in 1983, caused sub-aerial exposure of the suspended and surface sediments, and affected organic matter preservation
in the upper mid-section (12–14 cm) of the core. 相似文献
29.
30.
Brijraj K. Das 《Environmental Geology》2005,49(2):230-239
A study of the water and sediment chemistry of the Nainital, Bhimtal, Naukuchiyatal and Sattal Lakes of Kumaun, has shown that the water of these lakes are alkaline and that electrical conductivity, total dissolved solid and bicarbonate HCO
3
−
are much higher in Nainital than in the other three lakes. The weathering of limestone lithology and anthropogenic pollution, the latter due to the very high density of population in the Nainital valley, are the primary sources of enhanced parameters. The low pH of Nainital Lake water is due to low photosynthesis and enhanced respiration, increasing CO2 in the water and the consequent enhancement of Ca2+ and HCO
3
−
. The dissolved oxygen in Nainital Lake is less compared to other lakes, indicating anoxic conditions developing at the mud–water interface at depth. The PO
4
3−
content in Nainital is higher (124 μg/l), showing an increasing trend over time leading to eutrophic conditions. The trace metals (Cu, Co, Zn, Ni, Mn, and Sr) are present in greater amounts in the water of Nainital Lake than in the other three lakes, though Fe and Cr are high in Bhimtal and Fe in Naukuchiyatal. The higher abundance is derived from the leaching of Fe–Mg from metavolcanic and metabasic rocks. Most of the heavy metals (Cr, Ni, Cu, Mn, Fe, Sr, and Zn) significantly enrich the suspended sediments of the lakes compared to the bed sediments which due to their adsorption on finer particles and owing to multiple hydroxide coating and organic content, except for Fe, which is enriched in the bed sediments. The high rate of sedimentation, 11.5 mm/year in Nainital, compared to Bhimtal with 4.70 mm/year, Naukuchiyatal with 3.72 mm/year, and Sattal with 2.99 mm/year, has resulted in shorter residence time, poor sorting of grains, and lesser adsorption of heavy metals, leading consequently, their depletion in the bed sediments of Nainital Lake. 相似文献