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   

Planktonic algae and epiphyton of the littoral in lake Peipsi, Estonia   总被引：3，自引：0，他引：3  

Reet Laugaste  Külli Lessok 《Limnologica》2004,34(1-2):90

The littoral plankton of Lake Peipsi (3555 km², mean depth 7.1 m) was studied in summer 1980 and 2000–2002, and the epiphyton was studied on two dominating macrophytes, Phragmites australis (Cav.) Trin. ex Steud. and Potamogeton perfoliatus L., in 2000. The purpose of the study was to estimate to what extent the littoral phytoplankton and epiphytic algae (their biomass, chlorophyll a content and dominant species) can be used as a criterion for the trophic state of the lake. In wind-open areas, phytoplankton biomass in the littoral is commonly more than ten times higher than in open water due to the presence of the macroscopic cyanobacterium Gloeotrichia echinulata (J.S. Smith) P. Richter. This alga is abundant in the moderately eutrophic northern lake's part and rare in the strongly eutrophic southern part; hence also biomass in the southern part is considerably lower. In open water, phytoplankton biomass increases southward with increasing trophy. Algal biomass in the littoral depends on wind direction and can change completely in a few days. Epiphyton biomass and Chla content increased southward with increasing trophic state. They both revealed significant Spearman correlations (P < 0.05) with wind index and transparency (negative), and with abundance of the host plant, both reed and pondweed (positive). The phytoplankton biomass of the littoral of the large and shallow Lake Peipsi can not be used as a criterion of trophic state, however, the species composition of the dominants, particularly cyanobacteria, is well applicable for this purpose. The biomass and Chla content of the epiphyton can be used as a criterion for trophic state.  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   

Stochastic modeling of length of day and universal time     

Kamal Hamdan  Li-Yu Sung 《Journal of Geodesy》1996,70(6):307-320

We propose a general stochastic model for the UT1/LOD system and derive the corresponding Kalman filter model. This stochastic model consists of an arbitrary sum of continous time autoregressive moving average (ARMA) processes, each chosen to characterize a different frequency band. The transition matrix which corresponds to the overall system and the time-dependent process noise covariance matrix are derived.Based on the general formulation, several models for UT1 were derived from spectral analysis of the Space 92 UT1 series (Gross,1993). Using Space 92 as the reference series, the candidate models were compared based on their ability to predict UT1 and LOD up to 30 days in the absence of data. These candidate models were compared with the JPL operational Kalman Earth Orientation Filter (KEOF) which assumes a random walk model for LOD (Morabito et al.,1987). The results of the comparison revealed that autoregressive modeling the 40–50 day oscillation in the LOD reduces the LOD prediction error by 10prediction.  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   

Bentonite as a Natural Adsorbent for the Sorption of Iron from the Ground Water Exploited from Aswan Area, Egypt     

Gharib M. Taha  Kamal Abou Elmagd 《Ground Water Monitoring & Remediation》2004,24(1):47-52

Sorption of dissolved Fe²⁺ on bentonite was studied using a batch technique. The distribution coefficient, K_d , was evaluated for a bentonite-iron system as a function of contact time, pH, sorbent and sorbate concentrations, and temperature. Sorption results were interpreted in terms of Freundlich's and Langmuir's equations. Thermodynamic parameters for the sorption system were determined at three temperatures: 298°, 308°, and 318°K. The values of ΔH°(-4.0 kjmol⁻¹) and ΔG°(-2.46 Kjmol⁻¹) at 298°K (25°C) suggest that sorption of iron on bentonite is an exothermic and a spontaneous process. The ΔG° value became less negative at higher temperatures and, therefore, less iron was sorbed at higher temperatures. The desorption studies with 0.01 M CaCl₂ and deionized water at iron loading on bentonite showed that more than 90 wt% of the iron is irreversibly sorbed, probably due to the fixation of the iron by isomorphous replacement in the crystal lattice of the sorbent.  相似文献   

Principal Component Analysis for Water Quality Assessment of the Ganga River in Uttar Pradesh,India     

Kamal Jyoti Maji  Ramjee Chaudhary 《Water Resources》2019,46(5):789-806

Water Resources - The present study is an attempt to apply principal component analysis (PCA) for spatial assessment of water quality parameters that are responsible for water quality deterioration...  相似文献   

Simple Methodology for Estimating the Groundwater Recharge Potential of Rural Ponds and Lakes Using Remote Sensing and GIS Techniques: a Spatiotemporal Case Study of Roorkee Tehsil,India     

Ishita Bhatnagar  Kamal Jain 《Water Resources》2020,47(2):200-210

Water Resources - Groundwater resources are depleting at an alarming rate all over the world. Therefore, ensuring water security is the foremost priority of every nation. This paper presents a...  相似文献   

Assessment of glacier stored water in Karakoram Himalaya using satellite remote sensing and field investigation     

Kamal Kant SINGH  Harendra Singh NEGI  Dhiraj Kumar SINGH 《山地科学学报》2019,(4)

Karakoram Himalaya(KH) has continental climatic conditions and possesses largest concentration of glaciers outside the polar regions. The melt water from these glaciers is a major contributor to the Indus river. In this study, various methods have been used to estimate the ice volume in the Karakoram Range of glaciers such as Coregistration of Optically Sensed Images and Correlation(COSI-Corr) method and Area-Volume relations. Landsat 8 satellite data has been used to generate the ice displacement, velocity and thickness map. Our study for 558 Karakoram glaciers revealed that the average ice thickness in Karakoram is 90 m. Ground Penetrating Radar(GPR) survey has been conducted in one of the KH glacier i.e. Saser La glacier and the collected GPR data is used for the validation of satellite derived thickness map. GPR measured glacier thickness values are found comparable with satellite estimated values with RMSE of 4.3 m. The total ice volume of the Karakoram glaciers is estimated to be 1607±19 km3(1473±17 Gt), which is equivalent to 1473±17 km3 of water equivalent. Present study also covers the analysis of glacier surface displacement, velocity and ice thickness values with reference to glacier mean slope.  相似文献   

Seismic identification of geothermal prospecting in Harrat Rahat,Northern Arabian Shield     

Al-Amri  Abdullah M.  Abdelrahman  Kamal  Mellors  Robert  Harris  David 《Arabian Journal of Geosciences》2020,13(8):1-11

Influenced by mining activities in adjacent coal seams, stresses on rocks surrounding roadway were redistributed, and the roadways in lower coal seam were subjected to the asymmetrical roof falling and roof sagging. Considering stresses effect on the plastic zone around the roadway, numerical models were carried out by FLAC to investigate plastic zone with respect to stress ratio and direction of stresses. The relationship between the properties of surrounding rock and plastic zone boundary was also investigated by another numerical model and analytical study, whereby the tailgate stability of panel 30,501 in Tashan coal mine was implemented. It is shown that the rocks surrounding a roadway in the lower coal seam were subjected to unequal stresses, and the principal stress direction was deflected from the original direction. High stresses and big stress ratio can produce butterfly-shaped or X-shaped plastic zone. The direction of stresses was deflected, causing the plastic zone around the roadway to be transferred from the shoulder to the roof of the roadway. Consequently, asymmetrical stresses produce asymmetrical plastic zone. On this basis, the tailgate should be assigned conditions of the stresses and stress ratio at a low level. In this way, the tailgate was arranged at the position where the horizontal distance from the roadway in the lower seam to the centre line of the coal pillar in the upper seam (x) is 52.5 m, and was stable relatively.  相似文献