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111.
S. Seetha D. P. Sharma V. N. Padmini T. M. K. Marar K. Kasturirangan U. R. Rao J. C. Bhattacharyya 《Astrophysics and Space Science》1987,130(1-2):193-196
We present here new results on the periodic modulations in the optical light curves of EX Hydrae observed during 1982–84. The period analysis has been done using synchronous summation and discrete Fourier transform methods. We report new periodicities at 34.7 min and 26.7 min apart from confirming the detection of 46.3 min modulation recently reported. We also include our data to derive the rate of decrease of the 67 min period.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986. 相似文献
112.
Abhijit Bhattacharyya Sukumar Biswas Barun K. Chatterjee Mala Das Pradipta K. Das Tapan K. Das Tarun K. De M.H. Engineer Rabi N. Mukherjee Sibaji Raha S.C. Roy Swapan K. Saha A.K. Sen Bikash Sinha Debapriyo Syam 《Astrophysics and Space Science》1997,250(2):313-326
A Total Solar Eclipse (TSE) was observed from Diamond Harbour (lat. 22.2°N, long 88.2°E) on 24 October 1995. The variation of -ray intensity was measured in the energy range of 0.3–3.0 MeV for different time spans throughout the period of the eclipse. A CR-39 detector was used to look at the change in the fluxes of neutral and charged particles. The maximum drop ( 25%) in the intensity of -ray was observed in the range 2.5–3 MeV during TSE. The CR-39 results showed the appearance of a good number of tracks and a small variation of proton and neutron flux of 10% which was not significant statistically. Low energy -ray fluxes at sea level originate from the secondary electron-photon components of cosmic rays in the atmosphere; its modulation by TSE is interpreted as follows. The cooling of the atmosphere in the path of the umbra induces a reduction of the height of the main production layer of the nuclear component, as a result of which, fewer µ± mesons (from the decay of the± mesons) decay to e±. This leads to a small reduction in the flux of electron-photon component at sea level which originates from this branch; the main branch of e - component from 0 decay remains nearly unaffected. As the total mass of air remains the same, little or no change in the slow proton or the neutron flux at sea level is expected. These are consistent with the present observations. For a better understanding, further studies of this new phenomenon during future TSE are suggested. 相似文献
113.
Deeper groundwater chemistry and geochemical modeling of the arsenic affected western Bengal basin,West Bengal,India 总被引:1,自引:0,他引:1
A regional scale hydrogeochemical study of a ∼21,000-km2 area in the western Bengal basin shows the presence of hydrochemically distinct water bodies in the main semiconfined aquifer and deeper isolated aquifers. Spatial trends of solutes and geochemical modeling indicate that carbonate dissolution, silicate weathering, and cation exchange control the major-ion chemistry of groundwater and river water. The main aquifer water has also evolved by mixing with seawater from the Bay of Bengal and connate water. The isolated aquifers contain diagenetically altered water of probable marine origin. The postoxic main aquifer water exhibits overlapping redox zones (metal-reducing, sulfidic and methanogenic), indicative of partial redox equilibrium, with the possibility of oxidation in micro-scale environments. The redox processes are depth-dependent and hydrostratigraphically variable. Elevated dissolved As in the groundwater is possibly related to Fe(III) reduction, but is strongly influenced by coupled Fe–S–C redox cycles. Arsenic does not show good correlations with most solutes, suggesting involvement of multiple processes in As mobilization. The main river in the area, the Bhagirathi–Hoogly, is chemically distinctive from other streams in the vicinity and probably has little or no influence on deep groundwater chemistry. Arsenic in water of smaller streams (Jalangi and Ichamati) is probably introduced by groundwater discharge during the dry season. 相似文献
114.
115.
Parminder Singh Ranhotra Amalava Bhattacharyya 《Journal of the Geological Society of India》2010,75(3):527-532
Present study is an attempt to understand the tree line shift in relation to glacier fluctuations during Holocene based on
the exploratory palynological studies from a 1.3 m deep sediment profile located at 3,100 meters above mean sea level (mamsl),
Rukti valley, Kinnaur, Himachal Pradesh. The study reveals that during the early to middle Holocene, tree line taxa viz. Betula and Juniperus were well characterized in the site of investigation evident by higher percentage of their pollen grains in subsurface sediments
than those recorded during the late Holocene. This variation in distribution of these taxa suggests that till middle Holocene
tree line was close to the study site (3,100 mamsl) i.e. at lower altitude than its present day distribution between 3,800
to 3,900 mamsl. Accordingly, the glacier snout might also be at lower elevations (∼3,500 mamsl) than its present day location
at altitude (∼4,300 mamsl). 相似文献
116.
Dhruba Mukhopadhyay Nandini Chattopadhyay Tapas Bhattacharyya 《Journal of the Geological Society of India》2010,75(1):18-31
The structural geometry of the Anasagar gneiss dome in the axial zone of the South Delhi Fold Belt is controlled by polyphase
folding. It is classified as a thrust-related gneiss dome and not as a metamorphic core complex. Four phases of deformation
have affected both the gneiss and the enveloping supracrustal rocks. D2 and D3 deformations probably represent early and late stages of a progressive deformation episode in a simple shear regime combined
with compression. The contact between the gneiss and the supracrustal rocks is a dislocation plane (thrust) with top-to-east
sense of movement which is consistent with the vergence of the D2 folds. The thrust had a ramp-and-flat geometry at depth. At the present level of exposure it is a footwall flat (that is,
parallel to the gneissosity in the footwall), but it truncates the bedding of the hanging wall at some places and is parallel
at others. The thrusting was probably broadly coeval with the D2 folds and the thrust plane is locally folded by D2. D2 and D3 folds have similar style and orientation as the first and second phases respectively of major folds in the Delhi Supergroup
of the South Delhi Fold Belt and these are mutually correlatable. It is suggested that D1 may be Pre-Delhi in age. Available
geochronological data indicate that the emplacement of the Anasagar gneiss predated the formation of volcanic rocks in the
Delhi Supergroup and also predated the main crust forming event in the fold belt. The Anasagar gneiss and its enveloping supracrustal
rocks are probably older than the Delhi Supergroup. 相似文献
117.
118.
To date, most studies of the effectiveness of geotextiles on soil erosion rates and processes have been conducted in laboratory experiments for less than 1 h. Hence, at Hilton (52°33′ N, 2°19′ W), UK, the effectiveness of employing palm‐mat geotextiles for soil erosion control under field conditions on arable loamy sands was investigated. Geotextile‐mats constructed from Borassus aethiopum (Borassus palm of West Africa) and Mauritia flexuosa (Buriti palm of South America) leaves are termed Borassus mats and Buriti mats, respectively. Duplicate runoff plots (10 m × 1 m on a 15° slope) had five treatments (bare, permanent grass, Borassus total plot cover, Borassus buffer strip and Buriti buffer strip). Borassus covered plots had about 72% ground cover and to differentiate between this treatment and Borassus buffer strips, the former treatment is termed Borassus completely‐covered. Runoff and eroded soil were collected from each bounded plot in a concrete gutter, leading to a receptacle. Results from 08/01/2007–23/01/2009 (total precipitation = 1776·5 mm; n = 53 time intervals) show that using Borassus buffer strips (area coverage ~10%) on bare soil decreased runoff volume by about 71% (P > 0·05) and soil erosion by 92% (P < 0·001). Bare plots had nearly 29·1 L m?2 runoff and 2·36 kg m?2 soil erosion during that period. Borassus buffer strip, Buriti buffer strip and Borassus completely‐covered plots had similar effects in decreasing runoff volume and soil erosion. Runoff volumes largely explain the variability in soil erosion rates. Although buffer strips of Borassus mats were as effective as whole plot cover of the same mats, the longevity of Borassus mats was nearly twice that of Buriti mats. Thus, use of Borassus mats as buffer strips on bare plots is highly effective for soil erosion control. The mechanisms explaining the effectiveness of buffer strips require further studies under varied pedo‐climatic conditions. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
119.
The efficiency of low cost citrus peels as biosorbents for removal of cadmium ions from aqueous solution was investigated in a fixed bed column, a process that could be applied to treat industrial wastewaters similar to commonly used ion exchange columns. Effluent concentration versus time profiles (i.e., breakthrough curves) were experimentally determined in a laboratory‐scale packed bed column for varying operational parameters such as flow rate (2, 9, and 15.5 mL/min), influent cadmium concentration (5, 10, and 15 mg/L), and bed height (24, 48, and 72 cm) at pH 5.5. Column operation was most efficient for empty bed contact times of at least 10 min, which were apparently necessary for mass transfer. While the sorption capacity was largely unaffected by operational variables, the Thomas (Th) rate constant increased with the flow rate, and slightly decreased with increasing column length. Three widely used semi‐mechanistic models (Th, Bohart–Adams, and Yoon–Nelson) were shown to be equivalent and the generalized model was compared with a two‐parameter empirical model (dose‐response). The latter was found to be able to better simulate the breakthrough curve in the region of breakthrough and saturation. 相似文献
120.
Amalava Bhattacharyya Nivedita Mehrotra Santosh K. Shah 《Journal of the Geological Society of India》2011,77(6):521-526
Palynological analysis of sub surface samples at 1.20 m deep sediment profile from Srinagar, southwest Tripura, provides information
on vegetation and climate during 7000–3000 years B.P. During this time span, the area is occupied by moist deciduous forest
under warm humid climate with intermittent changes in precipitation regime i.e., comparatively less humid around 6.8 Kyr B.P.
and 3.7–3.8 Kyr B.P. 相似文献