Propagation of shear waves in viscoelastic medium at irregular boundaries   总被引：2，自引：1，他引：1  

Amares Chattopadhyay  Shishir Gupta  Vikash K. Sharma  Pato Kumari 《Acta Geophysica》2010,58(2):195-214

The aim of the paper is to study the shear wave propagation in a viscoelastic layer over a semi-infinite viscoelastic half space due to irregularity in the viscoelastic layer. It is of great interest to study the propaga-tion of shear waves in the assumed medium having a non planar boundary due to its similarity to most of the real situations. The perturbation method is applied to find the displacement field. The effect of complex wave number on dissipation factor is analysed. Finally, as an application, the result obtained has been used to get the reflected field in viscoelastic layer when the shear wave is incident on an irregular boundary in the shape of parabolic irregularity as well as triangular notch. It is observed that the amplitude of this reflected wave decreases with increasing length of the notch, and increases with increasing depth of the irregularity.  相似文献   

Application of a conceptual method for separating runoff components in daily hydrographs in Kimakia forest catchments,Kenya     

J. M. Mugo  T. C. Sharma 《水文研究》1999,13(17):2931-2939

This paper highlights the use of a conceptual method for separating runoff components in daily hydrographs, contrary to the traditionally used graphical method of separation. In the conceptual method, the components, viz. surface flow, interflow and baseflow, are regarded as high, medium and low frequency signals and their separation is done using the principle of a recursive digital filter commonly used in signal analysis and processing. It requires estimates of the direct runoff (β_d) and surface runoff (β_s) filter parameters which are obtained by a least‐squares procedure involving baseflow and interflow indices based on graphical and recursive digital filter estimation techniques. The method thus circumvents the subjective element associated with the graphical procedure of hydrograph separation, in which case the eye approximation and/or one's skill at plotting is the prime basis for the whole analysis. The analysis based on three forest catchments in Kimakia, Kenya, East Africa, revealed that β_d=K_b and β_s=K_i , where K_b and K_i are the baseflow and interflow recession constants. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Assessing the carbon sequestration potential of subtropical pine forest in north-western Himalayas — A GIS approach   总被引：1，自引：0，他引：1  

D. P. Sharma  M. Singh 《Journal of the Indian Society of Remote Sensing》2010,38(2):247-253

The present investigation was carried out to determine carbon sequestration potential of Solan Forest Division of Himachal Pradesh during 2006–2007. There are six land uses viz., Chir pine, Ban oak, Deodar, Other broadleaves, Culturable and Un-culturable, which are distributed in 538 compartments along altitudinal gradient from 900 to 2,100m. The study reveals that among various land uses, the Other broadleaved species will result in maximum expected carbon (19.88 Mt) which will be 28.81, 23.95, and 3.07 times higher than standing carbon in Ban oak, Deodar and Chir pine, respectively. The Solan Forest Division on the whole, has potential to sequester 17 times more carbon over standing carbon of 1.67 Mt, if forest species are extended to their corresponding altitudinal limits in the “land area available for planting” i.e., Uncultrable land area in the forest division however, to have an accurate estimate of the carbon sequestration potential of the area, other attributes that decides the establishment of plantation of different species such as slope, aspect, soil, climate, etc. need to be taken into consideration beside altitude.  相似文献   

Geospatial modeling of Brown oak (<Emphasis Type="Italic">Quercus semecarpifolia</Emphasis>) habitats in the Kumaun Himalaya under climate change scenario     

S. Saran  R. Joshi  S. Sharma  H. Padalia  V. K. Dadhwal 《Journal of the Indian Society of Remote Sensing》2010,38(3):535-547

The study explores the use of multiple criteria decision techniques in predicting spatial niche of Brown oak (also known as Kharsu oak, Quercus semecarpifolia Sm.) formation in midaltitude (2,400–3,500 meter amsl) Kumaun Himalaya. Predictive models using various climatic and topographical factors influencing Brown oak’s growth and survival were developed to define its current ecological niche. Analytical Hierarchical Process (AHP) method involving Saaty’s pair-wise comparison was performed to rank the explanatory powers of each compared variable. Variables were suitably weighted using fuzzy factor standardization scheme to reflect their relative importance in defining species niche. An optimum indicator was then chosen for deriving a site suitability map of brown oak. This study establishes the role of aspect in the current distribution of the species along with known influence of altitude. Future niches of oak has been tracked in the projected climate change scenario of +1°C and +2°C rise in temperature and 20 mm in precipitation. The results show that on predicted +1°C and +2°C increase in temperature, present habitat of brown oak distribution may be reduced by 40 per cent and 76 per cent respectively.  相似文献   

Geospatial multiple logistic regression approach for habitat characterization of scarce plant population: A case study of <Emphasis Type="Italic">Pittosporum eriocarpum</Emphasis> Royle (an endemic species of Uttarakhand,India)     

H. Padalia  R. R. Bharti  Y. P. S. Pundir  K. P. Sharma 《Journal of the Indian Society of Remote Sensing》2010,38(3):513-521

Increasing concern for biodiversity conservation at species level resulted in the development of cost effective tools for getting information at larger scale. Modeling distribution of species using remote sensing and geographic information has already proved its potentials to get such information with less effort. Pittosporum eriocarpum Royle is an endemic and threatened tree species of Uttarakhand, yet till now its regional distribution is poorly known. This study using geospatial modelling tools indentified several localities of potential occurrence of this species in the Mussoorie hills and Doon valley, and also provides information on its habitat specificity. The main objective of the study is to predict the suitable habitats for endangered plant species in Himalayan region using logistic regression model where availability of sufficient data on species presenceabsence is a major limitation for larger areas.  相似文献   

Landslide Susceptibility Zonation through ratings derived from Artificial Neural Network     

Shivani Chauhan  Mukta Sharma  M.K. Arora  N.K. Gupta 《International Journal of Applied Earth Observation and Geoinformation》2010

In the present study, Artificial Neural Network (ANN) has been implemented to derive ratings of categories of causative factors, which are then integrated to produce a landslide susceptibility zonation map in an objective manner. The results have been evaluated with an ANN based black box approach for Landslide Susceptibility Zonation (LSZ) proposed earlier by the authors. Seven causative factors, namely, slope, slope aspect, relative relief, lithology, structural features (e.g., thrusts and faults), landuse landcover, and drainage density, were placed in 42 categories for which ratings were determined. The results indicate that LSZ map based on ratings derived from ANN performs exceedingly better than that produced from the earlier ANN based approach. The landslide density analysis clearly showed that susceptibility zones were in close agreement with actual landslide areas in the field.  相似文献   

The major lightning regions and associated casualties over India     

Yadava  Pramod Kumar  Soni  Manish  Verma  Sunita  Kumar  Harshbardhan  Sharma  Ajay  Payra  Swagata 《Natural Hazards》2020,101(1):217-229

Natural Hazards - Lightning, a climate-related highly localized natural phenomenon, claims lives and damage properties. These losses could only be reduced by the identification of active seasons...  相似文献   

Google Earth Engine for concurrent flood monitoring in the lower basin of Indo-Gangetic-Brahmaputra plains     

Lal  Preet  Prakash  Aniket  Kumar  Amit 《Natural Hazards》2020,104(2):1947-1952

Natural Hazards - The present study focused on the recent flood inundation (July 2020) that occurred in the lower Indo-Gangetic-Brahmaputra plains (IGBP) using concurrent C-band Sentinel-1A...  相似文献   

Crusting effects on erosion processes under simulated rainfall on a tropical Alfisol     

R. M. Bajracharya  R. Lal 《水文研究》1998,12(12):1927-1938

Sealing and crusting of soil surfaces have dramatic effects on water infiltration into and runoff from soils, thereby greatly influencing erosion processes. This study focused on the effect of the initial stage of crusting on inter-rill erosion processes for a crust-prone Alfisol sampled from south-central India. Soil aggregates ranging from 2·4 to 8 mm collected from ploughed (PL) and naturally vegetated (NV) treatments were subjected to rainfall simulation under laboratory conditions. Runoff from PL soil aggregates was 2–2·5 times higher, while percolation was 20–100% lower, than for NV aggregates. Soil wash and splash losses were 0·5–3 times greater for PL than for NV soil. Runoff and inter-rill erosion were significantly higher during the wet simulation run compared with the dry run. The results indicated that NV soil aggregates were more resistant to breakdown from raindrop impact and slaking, and subject to less rapid sealing, than PL soil. Total soil loss was influenced most by initial aggregate stability and the extent of seal development. Splash and wash losses of soil both increased as a result of surface sealing regardless of soil condition for short (30–60 min) rainfall durations. High drying rates resulted in the highest crust bulk densities. Increased crust strength for PL soil compared with NV soil reflected the greater susceptibility of cultivated soil to surface sealing and crusting. © 1998 John Wiley & Sons, Ltd.  相似文献   

An analysis of non-normal Markovian extremal droughts     

T. C. Sharma 《水文研究》1998,12(4):597-611

In many arid and semi-arid environments of the world, years of extended droughts are not uncommon. The occurrence of a drought can be reflected by the deficiency of the rainfall or stream flow sequences below the long-term mean value, which is generally taken as the truncation level for the identification of the droughts. The commonly available statistics for the above processes are mean, coefficient of variation and the lag-one serial correlation coefficient, and at times some indication of the probability distribution function (pdf) of the sequences. The important elements of a drought phenomenon are the longest duration and the largest severity for a desired return period, which form a basis for designing facilities to meet exigencies arising as a result of droughts. The sequences of drought variable, such as annual rainfall or stream flow, may follow normal, log-normal or gamma distributions, and may evolve in a Markovian fashion and are bound to influence extremal values of the duration and severity. The effect of the aforesaid statistical parameters on the extremal drought durations and severity have been analysed in the present paper. A formula in terms of the extremal severity and the return period ‘T’ in years has been suggested in parallel to the flood frequency formula, commonly cited in the hydrological texts. © 1998 John Wiley & Sons, Ltd.  相似文献