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41.
K. Ramesh Kumar Dheeraj Pande Arpan Misra L. K. Nanda 《Journal of the Geological Society of India》2011,77(1):89-94
The Didwana playa, the second largest playa in the eastern part of the Thar desert, is 5.6 km long and 2.4 km wide and supports
commercial salt production. The thickness of lake sediment package is reported to be 20 m and comprises fine grained clays
and silts, with abundant calcite, gypsum, and halite, associated with hypersaline water. Isolated hills of graphitic phyllite
and quartzite are seen on the western side of the lake. During the course of investigations for uranium in surficial environment
of semi-arid terrain of Rajasthan, ground water sampling defined a NE-SW trending uranium halo encompassing the Didwana playa.
Subsequent sampling of unlined dug wells, up to water table in central part of the playa, indicated uranium values up to 190
ppm and 2072 ppb in lake sediments and brine respectively. These values are of the order of 21 ppm and 192 ppb towards the
southwestern periphery of the lake. The average uranium content, as inferred from 12 samples in the central part of the lake,
is around 60 ppm over a thickness of 5 m. It appears that the uranium is loosely bonded to the sediments in amorphous form
and is, hence, easily leachable. Samples of brine (n=10), from both the central and southwestern portions of the lake, analysed
high (1,67,500–3,00,000 mg/l) TDS, HCO3− (1128–8395 mg/l), and SO4 (30,536–88,000 mg/l). These are of alkaline (pH: 7.2–9.3) and reducing (Eh: −200 to −340 mV) nature. Under these Eh-pH conditions
below the groundwater table, and for such uranium bearing groundwater, precipitation of primary uranium is expected. It is,
therefore, modelled that uranium in lake sediment package above water table is concentrated by evaporation process and by
chemical reduction below the water table. 相似文献
42.
R. S. Negi P. F. Augustine J. K. Nanda 《Journal of the Indian Society of Remote Sensing》1988,16(3):7-12
An area of 2500 sq. Km. has been covered by photogeological mapping with selected field checks which forms a part of Cuddapah basin in the Kumool and Prakasam Districts of A.P. The rocks exposed in the area belong to the Cumbum and Bairankonda Formations of Cuddapah Super Group. They occur more or less as an alternating sequence. These formations are bound on the east by Dharawar gneisses and on the west by Nandyal Shales. The Bairankonda Formation is predominantly arenaceous with quartzite as the main member, being easily identifiable in the aerial photographs by its characteristic topography, coarse drainage, light grey tone etc. The Cumbum Formation is mainly argillaceous with slate/phyllite as the main member, intercalated with minor quartzite band and is expressed on the photographs in dark tone with dendritic to sub-parellel drainage and occurs relatively at lower elevations, mostly in plains. The Dharwar (Archaean) gneisses underlying the vast plains in the east are recognised by the sandy nature of soil and by the thrusted contact of this unit with the Bairankondas. The Nandyal Shales occupying the large cultivated area in west have a darker tone and a dendritic drainage pattern. They are Upper Kurnool in age. All the litho-units have undergone pre-Kurnool deformation resulting into plunging/doubly plunging antiforms and synforms trending NNE-SSW and a few shear zones and faults. Due to severe deformation a very prominant foliation has developed in the Cumbum unit. Groove lineation has also been developed in the hinge portions of major folds. The magmatic activity in these formations has been witnessed with the emplacement of reibeckite syenite and Kimberlite plugs and veins. Geomorphologically the area may be divided into two prominant units namely (i) Denudational landforms comprising (a) hills, ridges, inselbergs, bornhardts and hogbacks on Bairankonda quartzites and phyllites (b) pediment and dissected pediment on Cumbum Shales and Dharwar gneisses and (ii) Depositional landforms such as (a) alluvial fans and colluvial fans (b) alluvial valley fills along river courses and (c) sand dunes in Dharwar gneisses. 相似文献
43.
M.S. Nanda Kumar Christopher J. Davis Rafael Bachiller 《Astrophysics and Space Science》2003,287(1-4):191-194
We present new near-IR and mid-IR images of relatively isolated massive star forming regions with a special emphasis on the candidate precursors to ultra-compact HII regions. These images reveal compact, almost circularly symmetric young stellar clusters, dominated by a single luminous massive member. The clusters indicate flattened structures and dynamically unrelaxed states. In 4 of these young clusters we have discovered a nearly centrally located, prominent dark region visible at 2μm. 10μm images show examples where the dark region is associated with embedded luminous members of the cluster, as well as cases with no central 10μm source. The dark patches without embedded sources could be dense cores surviving inside the (proto?)clusters or left over wreckage from cluster formation. These images support current theoritical simulations of cluster formation. 相似文献
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45.
A collocation method is used to obtain numerical values for the radiative transfer in absorbing, emitting, linearly anisotropically-scattering-inhomogeneous finite slab media. The results for the isotropic scattering are compared with those obtained by Thynell and Özisik (1986) for the homogeneous slab and with those obtained by Garcia and Siewert (1981) for the inhomogeneous slab. 相似文献
46.
This paper presents a case study of the analysis and design of slopes for the portal of an underground crude oil storage cavern site. The site selected for the slope study is characterized by residual soils and granitic rock formations, located in the southwestern part of India. It is observed that in tropical residual soils, most hillslope failures are caused by rainfall and thus it is important to consider hydrological conditions when attempting to analyze the stability of slopes in such material. Combinations of shallow slopes with lower overburden and high steep hillslope with large overburden were considered in the present study along with varying combinations of lateritic soils and weathered rock formations. The paper discusses the various investigations carried out to define the geotechnical properties of lateritic soil and weathered rock, followed by numerical modelling and remedial measures adopted to ensure the stability of slopes during design and construction phase. Since analysis and design procedures for such residual soils are not well established, comprehensive geological and geotechnical investigations were carried out prior to numerical model development for carrying out finite element studies in order to ascertain long term stability of slopes under differing ground conditions. The results of the stability analysis indicated that slope under existing condition were potentially unstable under rainy conditions and specific supporting measures were planned to ensure stability. Several alternatives were examined for improving the stability of slope taking into consideration existing facilities, space available for mobilization of equipments and environmental conditions in reference to specific project requirements. The convergence pattern obtained from geotechnical monitoring using optical targets along the slopes did not showed any alarming movement for over a year. 相似文献