Demographic processes of urbanisation in Delhi     

Diwakar A  Qureshi MH 《Population geography : a journal of the Association of Population Geographers of India》1992,14(1-2):27-36

"Metropolitanisation has been observed by experts as one of the main characteristics of Indian urbanisation. Rural to urban migration has been a major player in urban growth of metropolitan cities, particularly Delhi. Not only Delhi but its hinterland [are] urbanising fast as compared to the hinterlands of other major cities of India. There are several processes of urbanization viz. historical, physical, demographic and economic. In this paper the role of demographic processes in urban expansion of Delhi [is examined]."  相似文献   

Study of Cosmic-Ray Intensity Variations Associated with Anomalous,Long-Duration High-Speed Solar Wind Streams in 2003     

Laxmi Tripathi  Anil Kumar Tiwari  S. P. Agrawal 《Solar physics》2007,241(1):171-184

High-speed solar wind streams (HSWS) were identified for solar cycles 22 and 23 (up to 2004). Preliminarily, HSWS were classified in three groups according to their continuous period of occurrence. In the declining phase of solar cycle 23, 2003 is found to be anomalous, showing a very large number of HSWS events of long duration (> ten days). We have studied the effect of HSWS on the cosmic-ray intensity as well as their relationship with geomagnetic disturbance index Ap on yearly, daily, and hourly bases. The yearly average of solar-wind speed was also found to be maximum in 2003. Being within the declining phase of solar activity, the occurrence of solar flares in 2003 is quite low. In particular during HSWS, no solar flares have been observed. Associations with cosmic-ray changes do not support the notion that the HSWS are usually effective in producing significant cosmic-ray decreases. Out of 12 HSWS events observed during the period 2002 (December) to 2003, four events of significant cosmic-ray decreases at all the stations have been selected for further analysis. The cosmic-ray intensity has been found to decrease during the first phase of the event (first five days of HSWS) at all three neutron-monitor stations situated at different latitudes with different cutoff rigidities. The rigidity spectra of observed decreases in cosmic-ray intensity for these four cases have been found to be significantly different than that of Fds (Forbush decrease). In two cases the spectra are softer, whereas in the other two they are harder than that of Fds. However, if the average of all four events is considered together then the spectra of the decrease in cosmic rays during HSWS exactly match that of Fds. Such a result implies that initially individual events should be considered, instead of combining them together, as was done earlier. The Ap index is also found to generally increase in the first phase of the event. However, the four events selected on the basis of cosmic-ray decrease are not always associated with enhanced values of the Ap index. As such, the significance of our study is that further detailed investigations for much longer periods and on an event-by-event basis is required to understand the effect of coronal-hole-associated HSWS.  相似文献   

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

  相似文献   

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