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排序方式: 共有282条查询结果,搜索用时 15 毫秒
41.
Namrata Das Saroj Sundar Baral Parth Sarathi Mahapatra Trupti Das Gautam Roy Chaudhury Surendra Nath Das 《Theoretical and Applied Climatology》2012,110(1-2):55-63
Precipitation samples collected during 2005–2009 from a rural forest station of Bhubaneswar were analyzed for their chemical composition. The samples were collected through a wet-only (WO) collector and two bulk (B1 and B2) collectors. The ions were evenly balanced indicating good data quality. The overall pH of rainwater was slightly acidic and ~47% of all rain events during the period were acidic (pH?<?5.6). Multilinear regression analysis showed relation between the free acidity (H+) and other components in rainwater. Enrichment factors (EF) of the major components with respect to their sources such as marine and crustal were calculated. Maximum EF was observed for NO 3 ? for both marine and crustal sources for all the three collectors. Source apportionments were also carried for the ions. Trend analysis showed continuous increase in most of the ions over years during the study period driven by anthropogenic emissions. Statistical/factorial analysis established correlation among different ions. 相似文献
42.
T. Ch. Malleswara Rao G. Jai Sankar T. Roopesh Kumar 《Journal of the Indian Society of Remote Sensing》2012,40(2):191-200
The focus of this work is on developing a new hierarchical hybrid Support Vector Machine (SVM) method to address the problems
of classification of multi or hyper spectral remotely sensed images and provide a working technique that increases the classification
accuracy while lowering the computational cost and complexity of the process. The paper presents issues in analyzing large
multi/hyper spectral image data sets for dimensionality reduction, coping with intra pixel spectral variations, and selection
of a flexible classifier with robust learning process. Experiments conducted revealed that a computationally cheap algorithm
that uses Hamming distance between the pixel vectors of different bands to eliminate redundant bands was quite effective in
helping reduce the dimensionality. The paper also presents the concept of extended mathematical morphological profiles for
segregating the input pixel vectors into pure or mixed categories which will enable further computational cost reductions.
The proposed method’s overall classification accuracy is tested with IRS data sets and the Airborne Visible Infrared Imaging
Spectroradiometer Indian Pines hyperspectral benchmark data set and presented. 相似文献
43.
Heavy mineral analysis has been carried out in the Barakar Formation of the Talchir Gondwana Bbasin, Orissa. The characteristic
heavy minerals are garnet, zircon, tourmaline, rutile, biotite, chlorite, pyroxenes, hornblende, staurolite, sillimanite,
apatite, epidote, sphene, spinel and siderite including opaques and leucoxene. These heavy minerals are divisible into four
groups on the basis of principal component analysis and suggest derivation of Barakar sediments from pegmatite, acid and basic
igneous as well as low- and high-rank metamorphic rocks lying to the south of the Talchir Gondwana Basin. Though the heavy
mineral suites of all the sandstone samples are by and large similar, differences have been noticed in the frequencies of
many heavy minerals in vertical succession. Cyclic nature and vertical fluctuation of heavy mineral frequencies can be ascribed
to variation of the relief of the source area, sudden release of some of the minerals in the source region and/or existence
of favourable geochemical condition to escape partial dissolution. 相似文献
44.
Asha Nath G. K. Manohar K. K. Dani P. C. S. Devara 《Journal of Earth System Science》2009,118(5):467-481
Monthly variations of lightning activity over typical land and oceanic regions of India were examined using satellite data
(OTD) for a 5-year period (1995–1999). It is noted that the nature of variation between surface air maximum temperature (T
max), thunderstorm days (Thn), and lightning flash count over ER and WR showed remarkable correspondence and sensitivity with each other on monthly time
scale. As we move out of winter season and enter the monsoon season, via pre-monsoon season, the WR undergoes cooling relative
to the ER in the range 0.1–1.2°C. As a result, WR experiences reduction of thunder days and lowering in flash count. This
decrease in T
max, Thn, and flash count over WR may also be associated with relatively small values of T
θw
and CAPE in comparison with similar values over ER during the monsoon season. Our observation of associated reduction in
Thn and lightning count per 1°C cooling in surface air maximum temperature suggests reduction of ∼3.5 thunderstorms per station
and 73 flashes. Comparison of lightning flashes between pairs of coastal, oceanic, arid-zone, hilly, and island stations reveals
distinct relationship between climate regime and intensity of lightning activity. We may conclude the results of this study
by saying that the overhead lightning activity is a clear reflection of the status of the underlying ground-earth properties.
A close and continuous monitoring of lightning activity may be considered as a need of present day scientific studies. 相似文献
45.
Marthinus Cloete Rodger J. Hart Herbert K. Schmid Martyn Drury Chris M. Demanet K. Vijaya Sankar 《Contributions to Mineralogy and Petrology》1999,137(3):232-245
Submicroscopic opaque particles from highly shocked granite-gneisses close to the core of the Vredefort impact structure
have been investigated by means of micro-analytical techniques with high spatial resolution such as electron diffraction,
orientation contrast imagery and magnetic force microscopy. The opaque particles have been identified as nano- to micro-sized
magnetite that occur in several distinct modes. In one sample magnetite occurs along relict planar deformation features (PDFs)
in quartz, generally accepted as typical shock lamellae. The magnetite particles along shock lamellae in quartz grains virtually
all show uniform crystallographic orientations. In most instances, the groups of magnetite within different quartz grains
are systematically misorientated such that they share a subparallel <101> direction. The magnetite groups of all measured
quartz grains thus appear to have a crystallographic preferred orientation in space. In a second sample, orientations of magnetite
particles have been measured in microfractures (non-diagnostic of shock) of quartz, albite and in the alteration halos, (e.g.
biotite grains breaking down to chlorite). The crystallographic orientations of magnetite particles are diverse, with only
a minor portion having a preferred orientation. Scanning electron microscopy shows that magnetite along the relict PDFs is
invariably associated with other microcrystalline phases such as quartz, K-feldspar and biotite. Petrographic observations
suggest that these microcrystalline phases crystallized from locally formed micro-melts that intruded zones of weakness such
as microfractures and PDFs shortly after the shock event. The extremely narrow widths of the PDFs suggest that heat may have
dissipated rapidly resulting in melts crystallizing relatively close to where they were generated. Magnetic force microscopy
confirms the presence of magnetic particles along PDFs. The smallest particles, <5 μm with high aspect ratios 15:1 usually
exhibit intense, uniform magnetic signals characteristic of single-domain magnetite. Consistent offsets between attractive
and repulsive magnetic signals of individual single-domain particles suggest consistent directions of magnetization for a
large proportion of particles.
Received: 16 November 1998 / Accepted: 17 May 1999 相似文献
46.
47.
Abstract As the quest for deep-sea mineral resources is gaining momentum, environment and ocean mining have become important aspects of study. Because many of these deposits occur in international waters, the concern for environmental conservation in view of the effects of deep-sea mining is resulting in these effects being studied in different oceans, and efforts to develop regulations governing this exploitation are also underway at national and international levels. The impact assessment of deep-sea mining needs to encompass a variety of subjects, including environmental, socioeconomic, technological, and legal aspects. At the same time, effects of in situ environmental conditions on mining activities also need to be considered for effecient performance by the mining system. Differences in the degree of impact have been noticed during the mining simulation experiments by different investigating agencies. Therefore, interparameter comparisons, standardization of methods, and improvement in mining design are important considerations for proper utilization of resources, conservation of environment, and cost efficiency of the mining operations. 相似文献
48.
Sangeeta Sharma Jogendra Nath Sarma 《Journal of the Indian Society of Remote Sensing》2013,41(4):895-904
An analysis of the drainage network of a part of Sivasagar district, Assam, India, is undertaken to reveal the role of neotectonic activity of the area. A number of fluvial geomorphic anomalies have been identified in the area. A prominent annular drainage anomaly is displayed by the major rivers—the Dikhu, Jhanzi, Namdang, Dorika and Disang, whose courses are carved in response to the ongoing tectonic deformation in the area. This study reveals that the development of topography and drainage system of the study area have been influenced by active subsurface geological structures. Formation of paleochannels, compressed meanders, reticulate streams, swamps, sagging of grounds, stream alignments, lineaments, knick points and abandonment of rivers as well as development of smaller drainage anomalies also substantiate the active nature of the subsurface structures. 相似文献
49.
Imran A. Dar K. Sankar Tanzeem S. Shah Mithas A. Dar 《Arabian Journal of Geosciences》2012,5(2):233-243
Nitrate contamination in the groundwater from various sources is one of the major problems of water resources in Liddercatchment, Kashmir. Systematic sampling was carried out during summer 2007, with a view to understand the source of nitrate ions in the groundwater of the Lidder catchment. Twelve sample sites were selected and samples were taken for a baseline study to understand the geochemistry of the groundwater and to assess the overall physico-chemical characteristics. Results showed that NO 3 ? concentration in ranged from 18.72?mg/L to 75.93?mg/L with an average of 47.03?mg/L. More than 80% (83.33%) of the samples collected from various sampling stations had nitrate concentrations exceeding the threshold value of 20?mg/L, and 58.33% of the samples collected had nitrate concentrations higher than 50?mg/L, the maximum acceptable nitrate concentration for drinking water. There is a wide spatial variation in the nitrate concentration in the groundwater. Monitoring the water quality of various sampling stations showed that the lowest concentrations of nitrate were found in the wet season (January, February, and December), while the highest concentrations were found in the dry season (August, September). Numerous human perturbations have been detected affecting the water quality of Lidder catchment. Disposal of sewage and animal wastes was found to contribute about 85% of total nitrate pollution in the study area. Based on the trend analysis (using previous data), future scenario of nitrate pollution has been predicted in the study area. The results of this study are useful to highlight one of the most important environmental problems, namely the degradation of the water quality, and may serve to alert and encourage local and national authorities to take substantial steps and actions to protect and manage water quality. 相似文献
50.
The 1897 Great Shillong earthquake revealed considerable seismic susceptibility in Guwahati City, such as soil liquefaction,
landslides, and surface fissures. In an attempt to quantify the seismic vulnerability of the city based on geological, seismological,
and geotechnical aspects concerning seismic site characterization, in-depth analysis was performed using a microtremor survey
with recordings of five small to moderate magnitude (4.8 ≤ mb ≤ 5.4) earthquakes that occurred in 2006 and geotechnical investigations using the Standard Penetration Test (SPT). Additionally,
the basement topography was established using vertical electrical resistivity sounding and selected drill-hole information.
Region-specific relationships are derived by correlating the estimated values of predominant frequency, shear-wave velocity,
and basement depth indicating conformity with the predominant frequency distribution and the basin topography underlain by
a hard granitic basement. Most parts of the city adhere to the predominant frequency range of 0.5–3.5 Hz, setting aside areas
of deep sediment fills or hilly tracts, suggesting that the existing moderate-rise RC buildings in the territory are seismically
vulnerable. Furthermore, the geotechnical assessment of the soil liquefaction potential reveals widespread susceptibility
across the terrain. Eventually, a site classification map of the city is prepared following the National Earthquake Hazard
Program (NEHRP) provision. The average site amplification factor from geotechnical modeling for site class D is about 3 in
the frequency range of 2–4 Hz. In addition, earthquake data yield an average site amplification factor of 4–6 in the frequency
range of 1.2–5.0 Hz at the seismic stations located in site class E and F. High site amplifications of around 5.5 and 7.5
at 2 Hz, respectively, are observed at AMTRON and IRRIG seismic stations, which are located in the proximity of Precambrian
rocks, indicating probable basin edge effects—scattering and diffraction of incident energy. Interplay of dispersed valleys
surrounded by small hillocks in the study region is likely to induce micro-basin effects where the sediment thickness/depth
vis-à-vis predominant frequency and basin geometry in conjunction play pivotal roles in the augmentation of site response. 相似文献