Effect of general loss-cone distribution function on electrostatic ion-cyclotron instability in an inhomogeneous plasma: particle aspect analysis     

Ruchi Mishra  M. S. Tiwari 《Earth, Moon, and Planets》2007,100(3-4):195-214

The electrostatic ion-cyclotron instability (EICI) in low β (ratio of plasma to magnetic pressure), anisotropic, inhomogeneous plasma is studied by investigating the trajectories of the particles using the general loss-cone distribution function (Dory-Guest-Harris type) for the plasma ions. In particular, the role of the loss-cone feature as determined by the loss-cone indices, in driving the drift-cyclotron loss-cone (DCLC) instability is analysed. It is found that for both long and short wavelength DCLC mode the loss-cone indices and the perpendicular thermal velocity affect the dispersion equation and the growth rate of the wave by virtue of their occurrence in the temperature anisotropy. The dispersion relation for the DCLC mode derived here using the particle aspect analysis approach and the general loss-cone distribution function considers the ion diamagnetic drift and also includes the effects of the parallel propagation and the ion temperature anisotropy. It is also found that the diamagnetic drift velocity due to the density gradient of the plasma ions in the presence of the general loss-cone distribution acts as a source of free energy for the wave and leads to the generation of the DCLC instability with enhanced growth rate. The particle aspect analysis approach used to study the EICI in inhomogeneous plasma gives a fairly good explanation for the particle energisation, wave emission by the wave–particle interaction and the results obtained using this particle aspect analysis approach are in agreement with the previous theoretical findings using the kinetic approach.  相似文献   

Simultaneous measurements of black carbon and PM2.5, CO,and NO x variability at a locally polluted urban location in India     

S. Tiwari  D. S. Bisht  A. K. Srivastava  Örjan Gustafsson 《Natural Hazards》2015,75(1):813-829

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Sectoral zoning in natural fluorites from carbonatite rocks of Ambadongar,Gujarat     

R. K. Singh  R. N. Tiwari 《Journal of the Geological Society of India》2010,76(3):244-246

In this article, we want to examine the presence of various types of zoning and spatial distribution of luminescence activating trace elements including REEs in natural fluorites from carbonatite rocks of Ambadongar, Gujarat. At Ambadongar, fluorite occurs as veins and vugs in different colours e.g. blue, yellow, green and purple associated with carbonatite and alkaline rocks. Cathodoluminescence microscopy was used to study the internal morphology including growth sectors, growth bands and concentric zoning patterns in fluorite crystals.  相似文献   

Did the Indo‐Asian summer monsoon decrease during the Holocene following insolation?     

Manish Tiwari  Rengaswamy Ramesh  Ravi Bhushan  Madavalm S. Sheshshayee  Bammidipati L. K. Somayajulu  A. J. Timothy Jull  George S. Burr 《第四纪科学杂志》2010,25(7):1179-1188

A few studies from the western Arabian Sea indicate that the Indian summer (or southwest) monsoon (ISM), after attaining its maximum intensity at ca. 9 ka, declined during the Holocene, as did insolation. In contrast, earlier and later observations from both the eastern and the western Arabian Sea do not support this inference. Analysis of multiple proxies of productivity in a new sediment core from the western Arabian Sea fails to confirm the earlier, single‐proxy (e.g. abundance of Globigerina bulloides) based, inference of the Holocene weakening of ISM, following insolation. The reason for the observed decreasing trend in foraminiferal abundance – the basis for the earlier inference – could be the favouring of silicate rather than carbonate productivity by the increased ISM wind strength. Although ISM exhibits several multi‐millennial scale fluctuations, there is no evidence from several multi‐proxy data to conclude that it declined during the Holocene; this is consistent with the phase lag analysis of longer time series of monsoon proxies. Thus, on sub‐Milankovitch timescales, ISM did not follow insolation, highlighting the importance of internal feedbacks. A comparison with East Asian summer monsoon (EASM) records suggests that both ISM and EASM varied in unison, implying common forcing factors on such longer timescales. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Ozone distribution over India     

Tiwari  V. S. 《Pure and Applied Geophysics》1973,106(1):1010-1017

The spatial and temporal distribution of total ozone over India and its vertical distribution in theatmosphere during 1964–1969 was studied using Dobson spectrophotometer data at a network of six stations in India, Srinagar (34°N), New Delhi (28°N), Varanasi (24°N), Ahmedabad (23°N), Dum Dum (22°N), and Kodaikanal (10°N). The annual and seasonal variations show a clear phase-shift in the occurrence of the ozone maxima and minima as one proceeds from higher to lower latitudes in the tropics. In the northern stations (north of 25°N) the increase in total ozone during the course of the annual variation is caused by the fractional increase in all layers from the ground to 28 km, the main contribution coming from 10–24 km. Above 28 km the concentration changes roughly in accordance with photochemical production.In lower latitudes (south of 25°N) an increase in total ozone amount during the annual cycle is caused by a gradual increase in all the layers from the ground to 36 km above which the variation is negligible.  相似文献   

Forest type mapping and volume stratification of man-made forests with aerial photographs     

KP. Tiwari 《Journal of the Indian Society of Remote Sensing》1974,2(2):65-73

The use of panchromatic (black & white) aerial photographs on 1:15,000 scale for forest type mapping and evolving a suitable basis of volume stratification for man-made forests of Haldwani Division of U.P. is discussed. Forest types by species, height and density were identified and ground survey data collected in 0.1 hectare circular plots were used to evolve the basis of volume stratification by statistical analysis. The methodology used for pilot studies before regional surveys are undertaken is presented.  相似文献   

Effect of couple-stresses in a semi-infinite elastic medium due to impulsive twist over the surface     

Giriraj Tiwari 《Pure and Applied Geophysics》1971,91(1):71-75

Summary Displacement due to impulsive twist in a semi-infinite elastic medium is calculated in the light of Cosserats theory of couple stresses [1, 2]. Numerical results are obtained for a particular  相似文献   

Identification of groundwater prospective zones by using remote sensing and geoelectrical methods in Jharia and Raniganj coalfields, Dhanbad district, Jharkhand state   总被引：3，自引：0，他引：3  

Basudeo Rai  A. Tiwari  V. S. Dubey 《Journal of Earth System Science》2005,114(5):515-522

The Dhanbad district in Jharkhand faces acute water scarcity and is chronically drought-prone. The groundwater resources in the area have not been fully exploited. The present study was undertaken to evaluate the groundwater prospective zones. Landsat-5 Multi Spectral Scanner (MSS) data of band 2 and band 4 and false colour composite (FCC) of band 2, 3, 4 were interpreted visually to differentiate different hydromorphogeological units and to delineate the major trends of lineaments. The different geomorphic features identified are linear ridges, residual hills, and pediplain, buried pediment and dissected pediplain, besides lineaments. The study shows that the pediplain and buried pediments are promising zones for groundwater prospecting. The occurrence and movement of groundwater is restricted to the unconsolidated material, weathered and fractured rocks. For the selection of tube well sites, geoelectrical resistivity investigations have been carried out at the sites, which were found suitable based on hydrogeomorphological and hydrogeological studies. Twenty-six Vertical Electrical Soundings (VES) have been carried out by using Schlumberger electrode configuration, which have brought out 3 to 7 layered sub-surface layers. The resistivity of water-bearing weathered/fractured rocks varies from 120–150 ohm m. The integrated studies have revealed that the blue colour zones are most promising for groundwater exploration and dug wells may be dug up to depths of 30±5m.  相似文献   

Periodicities of palaeomagnetic intensity and palaeoclimatic variations: a Walsh spectral approach     

J.G. Negi  R.K. Tiwari 《Earth and Planetary Science Letters》1984,70(1):139-147

The Walsh power spectral technique has been applied to the non-sinusoidal palaeoclimatic (theGloborotalia menardii climatic curve) and palaeomagnetic intensity variation records of the last 1.2 Myr. The analysis reveals, in the case of palaeomagnetic variations, statistically significant peaks (at 90% confidence level) centered around 150, 60 and 24 kyr. The palaeoclimatic spectrum, however, indicates only two significant peaks of 60 and 24 kyr. The identical periodicities in both the phenomena may suggest a causal link between the geomagnetic intensity variations and climatic changes.  相似文献   

Analyzing hyper-spectral and multi-spectral data fusion in spectral domain     

H. Pande  Poonam S. Tiwari  Shashi Dobhal 《Journal of the Indian Society of Remote Sensing》2009,37(3):395-408

Image fusion is the combination of two or more different images to form a new image by using a certain algorithm. Despite the fact that the number and kind of satellite imagery are daily increasing, using fusion techniques, in a proper way, to eliminate the redundancy in data and increase the quality of data is an important challenge in Remote Sensing Image Processing. Fusion of multispectral images with a hyperspectral image generates a composite image which preserves the spatial quality from the high resolution (MS) data and the spectral characteristics from the hyperspectral data. For the present study three fusion algorithms (Principal Component Transformation, Colour Normalized and Gram-Scmidt Transformation) were analysed for Hyperion and IKONOS MSS data. Their ability to preserve the spectral quality of fused data, in comparison with original hyper-spectral image, has been investigated.  相似文献