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141.
The Thar Desert dune system in north-west India and eastern Pakistan provides a rich archive of past environmental, geomorphological and climatic change. Much of the knowledge about the timing of dune accumulation in the Thar stems from scattered and sporadic records, based on older luminescence dating protocols. If the Thar dune record is to be incorporated within a growing multiproxy framework of past climate and environmental dynamics, it is necessary to generate a systematic record of the timing of dunefield accumulation. From this, relationships to climate and other drivers of dune activity may then be better established. To this end, an intensive programme of field sampling and optically stimulated luminescence (OSL) dating was carried out from a dunefield in the east-central Thar Desert. This study presents the first detailed Holocene dune accumulation history from the region, and sheds light on the development of the multi-generational parabolic dune systems. In contrast to previously published work, we identify the importance of the Holocene and the last millennium as periods with a number of preserved accumulation phases. OSL ages suggest that accumulation was persistent during the early and mid-Holocene (within 11.7-5.5 ka), late Holocene (2-1 ka), as well as two major phases in the last millennium (600 – 200 a and within the last 70 a). Potential drivers of dune mobility in the last century include a strong anthropogenic dimension. Rapid net accumulation is recorded in the last 70 years, with rates varying between 2 and 5 m/year, in an environment where agricultural pressures have increased dramatically with the advent of irrigation schemes expanding into dunefield areas. © 2019 John Wiley & Sons, Ltd. 相似文献
142.
Lal C. Ram Nishant K. Srivastava Ramesh C. Tripathi Sanjay K. Thakur Awadhesh K. Sinha Sangeet K. Jha Reginald E. Masto Swapan Mitra 《Environmental Geology》2007,51(7):1119-1132
The maximum concentration of the majority of the trace metals in the leachates from shake and column test of lignite fly ash
(LFA) was within the prescribed limits; however, total dissolved solids, total hardness, cations and anions (except K+), being above the prescribed limits, may lead to the increase in the hardness and salinity in the soil on the disposal of
LFA. Present generation of huge amount of fly ash from thermal power plants (TPPs) is a big challenge concerning contamination
of soil, crop produce and surface and ground water bodies due to the presence of some of the toxic trace metals in it. The
leaching behavior of alkaline LFA (pH, 10.94), from TPP of Neyveli Lignite Corporation (NLC), India, was investigated by shake
and column tests using water and sodium acetate buffer. The leaching of trace metals from LFA was governed by their concentrations,
association with the ash particles, leaching duration and pH of the leachate (most influencing parameter). The leaching of
metals followed the order: buffer column > aqueous column > aqueous shake > buffer shake test. 相似文献
143.
In this note extending the technique developed for static fields by De (1964) to the static plane-symmetric solution of Taub (1951) and the conformastat gravitational universe of Das (1971) solutions for coupled gravitational and zero-rest-mass scalar fields have been obtained. Furthermore, it is found that the singularities of these empty spaces cannot be removed by the introduction of zero-rest-mass scalar fields. 相似文献
144.
R. K. Srivastava 《Astrophysics and Space Science》1989,154(2):333-336
FirstU, B, andV observations of UMa are presented. Light curves show light variations of varying amplitude. Colour indices also show small colour variations. 相似文献
145.
R. K. Srivastava 《Astrophysics and Space Science》1990,166(2):205-210
A slightly improved period (P=0
.
d
7408401) of the eclipsing binary system TX Ceti has been given, which is based on all available times of minima. The O-C diagrams based on the period given in PPEN (1980) and based on the new period, have been given. The period of TX Ceti shows fair constancy between the time interval 1928 to 1988. The present O-C diagrams do not confirm, either the presence of a third body or the presence of mass transfer as suggested earlier. 相似文献
146.
Summary The object of the present paper is to investigate the propagation of surface waves on a non-homogeneous aeolotropic cylindrical shell surrounded by vacuum. The elastic constantsc
ij
(i, j=1,2...) and density of the material of the shell are assumed to be of the form
and
respectively, where ij, 0 are constants andk
1,k
2 are any integers. 相似文献
147.
For the first time a rich assemblage of legume fruits is described from the Late Oligocene sediments of the Makum as well
as Dilli-Jeypore coalfields of Assam. A new genus Buteocarpon has been instituted for the fossil fruits resembling Butea Roxb. of the family Fabaceae. In addition, six new species of the genus Leguminocarpon Goeppert are also described. Their presence indicates a warm and humid climate in the region during the deposition of the
sediments. 相似文献
148.
This paper reports Rb-Sr isotope ages of the Neoproterozoic volcanics, and associated granitoids of the trans-Aravalli belt of northwestern India. All these rocks along with the earlier reported 779±10 Ma old felsic volcanics from Diri, and Gurapratap Singh of Pali district, Rajasthan, constitute the Malani Group. The study indicates that different rock suites belonging to the Malani Group represent a polyphase igneous activity which spanned for about 100 Ma ranging from 780 to 680 Ma. The granitoids of the Malani Group, i.e. peraluminous Jalore type, and peralkaline Siwana type, were emplaced around 730, and 700 Ma ago, respectively. These plutonic suites represent two different magmatic episodes within a short time interval. The initial Sr ratios of these granitoids suggest lower crustal derivation of the magma. The peralkaline granitoids, and the associated peralkaline rhyolites (pantellerites) are coeval, and cogenetic. The ultrapotassic rhyolite exposed at Manihari of Pali district represents the youngest magmatic activity at 681±20 Ma, having a very high initial Sr ratio of 0.7135±0.0033. The high initial Sr ratio of these rocks may be due to incorporation of radiogenic 87Sr from the country rock, by assimilation or fusion, into the residual fraction of the magma in the crust which gave rise to other differentiated rocks of the Group.40Ar39Ar studies of two Jalore granite samples indicate presence of post crystallisation thermal disturbance between 500550 Ma ago. The timing of this thermal overprinting on the Malani rocks is related to the widespread Pan-African thermo-tectonic event which is witnessed, and magmatically manifested in different part of the Indian shield. 相似文献
149.
We underline the importance of Alfvén wave dissipation in the magnetic funnels through the viscous and resistive plasma. Our
results show that Alfvén waves are one of the primary energy sources in the innermost part of coronal holes where the solar
wind outflow starts. 相似文献
150.
Vineet K. Srivastava Jai Kumar Padmdeo Mishra Badam Singh Kushvah 《Journal of Astrophysics and Astronomy》2018,39(5):63
In this paper, computation of the halo orbit for the KS-regularized photogravitational circular restricted three-body problem is carried out. This work extends the idea of Srivastava et al. (Astrophys. Space Sci. 362: 49, 2017) which only concentrated on the (i) regularization of the 3D-governing equations of motion, and (ii) validation of the modeling for small out-of-plane amplitude (\(A_z =110000\) km) assuming the third-order analytical approximation as an initial guess with and without differential correction. This motivated us to compute the halo orbits for the large out-of-plane amplitudes and to study their stability analysis for the regularized motion. The stability indices are described as a function of out-of-plane amplitude, mass reduction factor and oblateness coefficient. Three different Sun–planet systems: the Sun–Earth, Sun–Mars and the Sun–Jupiter are chosen in this study. Stable halo orbits do not exist around the \(L_{1}\) point, however, around the \(L_{2}\) point stable halo orbits are found for the considered systems. 相似文献