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31.
N. V. Chalapathi Rao Bernd Lehmann B. K. Panwar Alok Kumar Datta Mainkar 《Journal of the Geological Society of India》2013,82(6):595-600
We report the occurrence of garnierite (a general term referring to Ni-Mg bearing hydrous silicates in laterites) from the crater-facies Tokapal kimberlite of the Bastar craton, Central India. Garnierite occurs as discrete ovoid or amoeboid segregations (up to 200 mm) or as veinlets with up to 18.1 wt% NiO and high iron contents (up to 36.2 wt% FeOT). Chemical composition of the garnierite implies its derivation from a magnesium-rich protolith. Extensive lateritisation of the large crater-facies (~2.5 km diameter) saucer-shaped kimberlite under tropical weathering conditions, aided by suitable topography, drainage and favourable structural set-up, are the factors inferred to be responsible for the formation of garnierite in the Tokapal system. As lateritic nickel ores constitute significant resources for nickel exploration, the perspective of the Tokapal kimberlite as a nickel prospect needs to be investigated. 相似文献
32.
Assessment of heavy metals in sediments near Hazira industrial zone at Tapti River estuary, Surat, India 总被引:3,自引:1,他引:2
Bhavna A. Shah Ajay V. Shah Chirag B. Mistry Alok J. Navik 《Environmental Earth Sciences》2013,69(7):2365-2376
Heavy metal accumulation due to industrial activities has become a very sensitive issue for the survival of the aquatic life. Therefore, distributions of several heavy metals have been studied in the surface sediments of Tapti–Hazira estuary, Surat, to assess the impact of anthropogenic and industrial activities near estuary. Totally 60 sediment samples were collected from four different sites at Tapti–Hazira estuary, Surat from January 2011 to May 2011 and examined for metal contents. The average heavy metal load in the study area are found to be 43.28–77.74 mg/kg for Pb, 48.26–72.40 mg/kg for Cr, 117.47–178.80 mg/kg for Zn, 71.13–107.82 mg/kg for Ni, 123.17–170.52 mg/kg for Cu, 0.74–1.25 mg/kg for Cd, 14.73–21.69 mg/kg for Co. Calculated enrichment factors (EF) reveal that enrichment of Pb and Cd is moderate at all sites, whereas other metals Cr, Ni, Zn, Co, and Cu show significant to very high enrichment. Geo-accumulation index (I geo) results revealed that the study area is nil to moderately contaminated with respect to Cd, moderately to highly polluted with respect to Pb, Zn, and Cu and high to very highly polluted with respect to Co and Cr. 相似文献
33.
Neeraj Awasthi Jyotiranjan S. Ray Amzad H. Laskar Alok Kumar M. Sudhakar Rajneesh Bhutani Hetu C. Sheth Madhusudan G. Yadava 《Bulletin of Volcanology》2010,72(9):1131-1136
Barren Island (Andaman Sea) is the northernmost active volcano of the Indonesian Arc. To construct the eruptive history of
this little studied volcano, we measured 14C dates of inorganic carbon in sediment beds, and Sr and Nd isotopic ratios of seven discrete ash layers, in a marine sediment
core collected from 32 km southeast of the volcano. The study reveals that the volcano had seven major ash eruptions at ~70,
69, 61, 24, 19, 15, and 10 ka. The ash layers erupted from 70 ka through 19 ka have highly uniform Nd isotopic composition,
and since the ~15 ka eruption to the present the isotopic composition has been highly variable. Between ~24 ka and ~10 ka,
the volcano had large ash eruptions spaced at 4,500 year intervals. Isotopically correlating the precaldera lavas and ash
exposed on the volcano to the uppermost ash layer in the core, we infer that the caldera of Barren Island volcano is younger
than 10 ka. 相似文献
34.
A fuzzy‐logic control algorithm, based on the fuzzification of the MR damper characteristics, is presented for the semiactive control of building frames under seismic excitation. The MR damper characteristics are represented by force–velocity and force–displacement curves obtained from the sinusoidal actuation test. The method does not require any analytical model of MR damper characteristics, such as the Bouc‐Wen model, to be incorporated into the control algorithm. The control algorithm has a feedback structure and is implemented by using the fuzzy‐logic and Simulink toolboxes of MATLAB. The performance of the algorithm is studied by using it to control the responses of two example buildings taken from the literature—a three‐storey building frame, in which controlled responses are obtained by clipped‐optimal control and a ten‐storey building frame. The results indicate that the proposed scheme provides nearly the same percentage reduction of responses as that obtained by the clipped‐optimal control with much less control force and much less command voltage. Position of the damper is found to significantly affect the controlled responses of the structure. It is observed that any increase in the damper capacity beyond a saturation level does not improve the performance of the controller. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
35.
We report the result of simultaneous multi-wavelength observations of the TeV blazar Mrk 421 during February - March 2003. We observed Mrk 421 using the Pachmarhi Array of Cerenkov Telescopes (PACT) of Tata Institute of Fundamental Research at Pachmarhi, India. Other simultaneous data were taken from the literature and public data archives. We have analyzed the high quality X-ray (2-20keV) observations from the NASA Rossi X-Ray Timing Explorer (RXTE). We obtained a possible correlated variability between X-ray and J band (1.25 μ) near infrared (NIR) wavelength. This is the first case of X-ray and NIR correlated variability in Mrk 421 or any high energy peaked (HBL) blazar. The correlated variability reported here indicates a similar origin for the NIR and X-ray emissions. The emission is not affected much by the environment of the surrounding medium of the central engine of Mrk 421. The observations are consistent with the shock-in-jet model for the emissions. 相似文献
36.
We report the first results of quasi-simultaneous two passband optical monitoring of six quasi-stellar objects to search for micro-variability. We carried out photometric monitoring of these sources in an alternating sequence of R and V passbands, for five radio-quiet quasi-stellar objects (RQQSOs), 0748 + 291, 0824 + 098, 0832 + 251, 1101 + 319, 1225 + 317 and one radio-loud quasi-stellar object (RLQSO), 1410 + 429. No micro-variability was detected in any of the RQQSOs, but convincing micro-variability was detected in the RLQSO on two successive nights it was observed. Using the compiled data of optical micro-variability of RQQSOs till date, we got the duty cycle for micro-variability in RQQSOs is ~10%. The present investigation indicates that micro-variability is not a persistent property of RQQSOs but an occasional incident. 相似文献
37.
Hetu C. Sheth Jyotiranjan S. Ray Ranjini Ray Loÿc Vanderkluysen John J. Mahoney Alok Kumar Anil D. Shukla Partha Das Subhrashis Adhikari Bikashkali Jana 《Contributions to Mineralogy and Petrology》2009,158(3):357-380
Many tholeiitic dyke-sill intrusions of the Late Cretaceous Deccan Traps continental flood basalt province are exposed in
the Satpura Gondwana Basin around Pachmarhi, central India. We present field, petrographic, major and trace element, and Sr–Nd–Pb
isotope data on these intrusions and identify individual dykes and sills that chemically closely match several stratigraphically
defined formations in the southwestern Deccan (Western Ghats). Some of these formations have also been identified more recently
in the northern and northeastern Deccan. However, the Pachmarhi intrusions are significantly more evolved (lower Mg numbers
and higher TiO2 contents) than many Deccan basalts, with isotopic signatures generally different from those of the chemically similar lava
formations, indicating that most are not feeders to previously characterized flows. They appear to be products of mixing between
Deccan basalt magmas and partial melts of Precambrian Indian amphibolites, as proposed previously for several Deccan basalt
lavas of the lower Western Ghats stratigraphy. Broad chemical and isotopic similarities of several Pachmarhi intrusions to
the northern and northeastern Deccan lavas indicate petrogenetic relationships. Distances these lava flows would have had
to cover, if they originated in the Pachmarhi area, range from 150 to 350 km. The Pachmarhi data enlarge the hitherto known
chemical and isotopic range of the Deccan flood basalt magmas. This study highlights the problems and ambiguities in dyke-sill-flow
correlations even with extensive geochemical fingerprinting. 相似文献
38.
Jessica P Karia M C Porwal P S Roy G Sandhya 《Journal of the Indian Society of Remote Sensing》2001,29(3):129-135
Studies on spatial distribution of the different forests during 1970 to 1999 using integrated remote sensing and GIS techniques reveals that area under forests in the Kalarani Round, is progressively reducing with the time. In 1970 forest area was found to be 22.75 sq km. in 1989 it was 15.34 sq km and in 1999 it was only 12.93 sq km. Thus. there is considerable loss in the tree cover from 1989 to 1999. Jhanpa and Kalarani R.F. are the example of this. Ground surveys indicate that the majority of the loss is caused by heavy grazing pressure there by decreasing regeneration of vegetation. If suitable measures are not taken. whole area may be converted into wasteland in due course of time. Another reason for the forest loss, could be land encroachments by villagers for their overwhelming needs. Karali R.F. is not much disturbed apart from the plantation raised in the foothills. Outside the reserve forest boundary, the change was observed due to construction of Narmada Sagar canal. 相似文献
39.
In the present study, forest type classification using Landsat TM False Colour Composite (FCC) bands 2, 3, 4 has been evaluated for mapping highly heterogeneous forest environment of Western Ghats (Kerala). Visual interpretation of Landsat TM FCC has been carried out to identify bioclimatic vegetation types. For accuracy estimation maps prepared from 1∶15,000 scale black-and-white aerial photographs have been used as ground check data. For comparison aerial photomap classes have been aggregated to match with Landsat-TM-derived map. The classification accuracy of ten major bioclimatic and landcover types was estimated using systematic sampling procedure. The overall classification accuracy of the forest types for the study area was 88.33%. 相似文献
40.
This paper describes a hybrid fuzzy weights-of-evidence (WofE) model for mineral potential mapping that generates fuzzy predictor
patterns based on (a) knowledge-based fuzzy membership values and (b) data-based conditional probabilities. The fuzzy membership
values are calculated using a knowledge-driven logistic membership function, which provides a framework for treating systemic
uncertainty and also facilitates the use of multiclass predictor maps in the modeling procedure. The fuzzy predictor patterns
are combined using Bayes’ rule in a log-linear form (under an assumption of conditional independence) to update the prior
probability of target deposit-type occurrence in every unique combination of predictor patterns. The hybrid fuzzy WofE model
is applied to a regional-scale mapping of base-metal deposit potential in the south-central part of the Aravalli metallogenic
province (western India). The output map of fuzzy posterior probabilities of base-metal deposit occurrence is classified subsequently
to delineate zones with high-favorability, moderate favorability, and low-favorability for occurrence of base-metal deposits.
An analysis of the favorability map indicates (a) significant improvement of probability of base-metal deposit occurrence
in the high-favorability and moderate-favorability zones and (b) significant deterioration of probability of base-metal deposit
occurrence in the low-favorability zones. The results demonstrate usefulness of the hybrid fuzzy WofE model in representation
and in integration of evidential features to map relative potential for mineral deposit occurrence. 相似文献