Influence of magnetic fabric anisotropy on seismic wave velocity in paramagnetic granites from NW Himalaya: Results from preliminary investigations     

Koushik Sen  Ruchika Sharma  B. R. Arora  Vikram Gupta 《Journal of the Geological Society of India》2010,76(5):322-330

Anisotropy of Magnetic Susceptibility (AMS) and seismic wave velocity studies of some paramagnetic Himalayan granitoids show good correlation between magnetic fabric anisotropy and P wave velocity (Vp). Vp shows strong positive correlation with magnetic lineation (L) and degree of magnetic anisotropy (P′) having correlation coefficient (r) values of 0.93 and 0.89 respectively. Both Vp and Vs show positive correlation with the SiO₂ content of Proterozoic and Paleozoic granitoids. Velocity of S wave (Vs) shows negative correlation with mean magnetic susceptibility (K_m) having ‘r’ value of 0.86. The correlation between Vs-K_m, V_p-P′, V_p-L also shows >95% probability in Spearman’s rank correlation. Based on the results from the present sample size it is suggested that, in paramagnetic granites, V_p is proportional to intensity of deformation and preferred orientation of minerals as well as the mineralogy. On the other hand, Vs is more dependent on the mineralogy alone.  相似文献   

Evaluation of seismic events detection algorithms     

B. K. Sharma  Amod Kumar  V. M. Murthy 《Journal of the Geological Society of India》2010,75(3):533-538

Identification of seismic events from continuously recorded seismic data in real-time through a Digital Seismic Data Recording system is a difficult task. Despite the vast amount of research in this field, the signal processing and event parameters discrimination algorithms have not yet fully come of age. Presently, we have a wide spectrum of trigger algorithms, ranging from a very simple amplitude threshold type to the sophisticated ones based on pattern recognition approaches. Some of the other approaches use adaptive technique and neural network methods. Researchers are continuously making efforts for the development of algorithms using various techniques, which produce minimum false trigger. Some approaches have been reported which are accurate for detecting first phase of events and take minimum possible computational time. In this paper several approaches for detecting event signals in background noise are presented and their precision evaluation is discussed.  相似文献   

Influence of magnetic fabric anisotropy on seismic wave velocity in paramagnetic granites from NW Himalaya: Results from preliminary investigations     

Koushik Sen  Ruchika Sharma  B. R. Arora  Vikram Gupta 《Journal of the Geological Society of India》2010,76(4):322-330

Anisotropy of Magnetic Susceptibility (AMS) and seismic wave velocity studies of some paramagnetic Himalayan granitoids show good correlation between magnetic fabric anisotropy and P wave velocity (Vp). Vp shows strong positive correlation with magnetic lineation (L) and degree of magnetic anisotropy (P′) having correlation coefficient (r) values of 0.93 and 0.89 respectively. Both Vp and Vs show positive correlation with the SiO₂ content of Proterozoic and Paleozoic granitoids. Velocity of S wave (Vs) shows negative correlation with mean magnetic susceptibility (K_m) having ‘r’ value of 0.86. The correlation between Vs-K_m, V_p-P′, V_p-L also shows >95% probability in Spearman’s rank correlation. Based on the results from the present sample size it is suggested that, in paramagnetic granites, V_p is proportional to intensity of deformation and preferred orientation of minerals as well as the mineralogy. On the other hand, Vs is more dependent on the mineralogy alone.  相似文献   

Comparative study of MLT mean winds using MF radars located at 16.8°N and 8.7°N     

A. K. Sharma  M. V. Rokade  R. Kondala Rao  S. Gurubaran  P. T. Patil 《Journal of Earth System Science》2010,119(4):461-470

The main aim of the paper is to describe mesosphere and lower thermosphere (MLT) wind field observed between June 2000 and May 2002 by medium frequency (MF) radars at two locations near the equatorial region and at tropical latitude. We have presented and compared observations of mean horizontal winds in the mesosphere and lower thermosphere (MLT) region over Kolhapur (16.8°N, 74.2°E) and Tirunelveli (8.7°N, 77.8°E). Our analysis reveals annual oscillation in the zonal wind and semi-annual oscillation in the meridional wind over Kolhapur. On the other hand, results over Tirunelveli reveal semi-annual oscillation (SAO) in the zonal wind and annual oscillation in the meridional wind. Also we have observed enhanced magnitude of wind speed in spring equinox period of 2002 exhibiting the signatures of the quasi-biennial oscillation (QBO) over Tirunelveli.  相似文献   

Elevation,slope aspect and integrated nutrient management effects on crop productivity and soil quality in North-west Himalayas,India     

Birendra Nath Ghosh  Narinder Kumar Sharma  Nurnabi Meherul Alam  Raman Jeet Singh  Gopal Prasad Juyal 《山地科学学报》2014,11(5):1208-1217

On farm bio-resource recycling has been given greater emphasis with the introduction of conservation agriculture specifically withclimate change scenarios in the mid-hills of the north-west Himalaya region（NWHR）. Under this changing scenario, elevation, slope aspect and integrated nutrient management（INM） may affect significantly soil quality and crop productivity. A study was conducted during 2009-2010 to 2010-2011 at the Ashti watershed of NWHR in a rainfed condition to examine the influence of elevation, slope aspect and integrated nutrient management（INM） on soil resource and crop productivity. Two years of farm demonstration trials indicated that crop productivity and soil quality is significantly affected by elevation, slope aspect and INM. Results showed that wheat equivalent yield（WEY） of improved technology increased crop productivity by -20%-37% compared to the conventional system. Intercropping of maize with cowpea and soybean enhanced yield by another 8%-17%. North aspect and higher elevation increased crop productivity by 15%-25% compared to south aspect and low elevation（except paddy）. Intercropping of maize with cowpea and soybean enhanced yield by another 8%-15%. Irrespective of slope, elevation and cropping system, the WEY increased by -30% in this region due to INMtechnology. The influence of elevation, slope aspect and INM significantly affected soil resources（SQI） and soil carbon change（SCC）. SCC is significantly correlated with SQI for conventional（R2 = 0.65＊）, INM technology（R2 = 0.81＊） and for both technologies（R2 = 0.73＊）. It is recommended that at higher elevation.（except for paddy soils） with a north facing slope, INM is recommended for higher crop productivity; conservation of soil resources is recommended for the mid hills of NWHR; and single values of SCC are appropriate as a SQI for this region.  相似文献   

Intercomparison of Oceansat-2 and ASCAT Winds with In Situ Buoy Observations and Short-Term Numerical Forecasts     

S. Indira Rani  M. Das Gupta  Priti Sharma  V. S. Prasad 《大气与海洋》2014,52(1):92-102

Sea surface winds from the Oceansat-2 scatterometer (OSCAT) are important inputs to Numerical Weather Prediction (NWP) models. The Indian Space Research Organization (ISRO) recently updated the OSCAT retrieval algorithm in order to generate better products. An attempt has been made in this study to evaluate the updated OSCAT winds using buoy observations and the 6-hour short-term forecasts from the T574L64 model from the National Centre for Medium Range Weather Forecasting (NCMRWF) during the 2011 monsoon. The results of the OSCAT evaluation are also compared with those from the Advanced Scatterometer (ASCAT) on-board the Meteorological Operational Satellite-A (MetOp-A) which were evaluated in the same way. The root mean square differences (RMSDs) for wind speed and direction, are within 2?m?s^?1 and 20° for both scatterometers. The RMSDs for OSCAT are slightly higher than those for ASCAT, and this difference may be attributed in part to the difference in frequency and resolution of the scatterometer payloads. The bias and standard deviation for ASCAT winds are also lower than those for OSCAT winds with respect to the model short-range forecast, and this can be attributed to the regular assimilation of ASCAT winds in the model.  相似文献   

Deposition and mobilization of functionalized multiwall carbon nanotubes in saturated porous media: effect of grain size,flow velocity and solution chemistry     

Prabhakar Sharma  Dixiao Bao  Fritjof Fagerlund 《Environmental Earth Sciences》2014,72(8):3025-3035

Carbon nanotubes (CNTs) are widely manufactured nanoparticles which are utilized in a number of consumer products, such as sporting goods, electronics and biomedical applications. Due to their accelerating production and use, CNTs constitute a potential environmental risk if they are released to soil and groundwater systems. It is, therefore, essential to improve the current understanding of environmental fate and transport of CNTs. The current study systematically investigated the effect of solution chemistry (pH and ionic strength) and physical conditions (collector grain size and flow rate) on the deposition and mobilization of functionalized multiwall carbon nanotubes (MWCNTs) using a series of column experiments under fully saturated conditions. A one-dimensional convection–dispersion model including collector efficiency for cylindrical nanoparticles was used to simulate the transport of MWCNTs in porous media. It was observed that an increase in pH resulted in increased mobility of MWCNTs. However, the transport of MWCNTs was strongly dependent on ionic strength of the background solution and a critical deposition concentration was observed between 3 and 4 mM NaCl concentration, with more than 99 % filtration of MWCNTs at 4 mM. The finer sand grains were able to filter a significant amount of MWCNTs (15 % more than coarse sand) from the inflow solution; this was likely caused by grain-to-grain straining mechanisms in the finer sand. A decrease in pore water velocity also led to more deposition of MWCNTs due to lowering of the kinetic energy of the particles. The results from this study indicated that a weak secondary minimum existed under unfavorable conditions for deposition, but the particles were trapped at both primary and secondary minimum.  相似文献   

Sedimentary variations of geomorphic subenvironments at Al-Lith area,central-west coast of Saudi Arabia,Red Sea     

A. S. Basaham  A. M. Gheith  A. A. A. Khawfany  R. Sharma  N. H. Hashimi 《Arabian Journal of Geosciences》2014,7(3):951-970

Sediment characteristics are the indicators of the intensity and geological history of the processes active in an area. Their association with different geomorphic features also signifies the present day conditions of deposition. In this study, variations in sediment characteristics associated with different geomorphic features, such as the coastal zone, two islands and a lagoon in the Al-Lith area of central-west coast of Saudi Arabia have been analysed. Whereas, the detrital sediments (sand?+?mud) are common (61–87 %) in most of the subunits of the coastal zone; the nondetrital (carbonate rich) sediments are more common (54–95 %) on the two islands as well as the lagoon; indicating distinct sources of sediments in these regions. The variation of sediment texture between sand and sandy silt in most geomorphic units, also shows that they are exposed to high-energy conditions, whereas occurrence of heavy minerals in small proportions (<7 %) indicates limited inputs from land-based igneous and metamorphic rocks. Sediment mean size vs. standard deviation shows that the sediment characteristics of a geomorphic unit (e.g. beach or sand bar) on the coast and on the island are different owing to different processes responsible for their formation.  相似文献   

Compositional variation in magma through early neogene in the Northeast Indian Ocean: A testimony from glass shards     

J. P. Shrivastava  V. Sharma 《Journal of the Geological Society of India》2014,84(2):181-186

We report unusual occurrence of glass shards with diverse morphologies and compositions in the volcanic ash associated with the early Neogene marine stratigraphic succession (early Miocene to early middle Miocene) of Andaman-Nicobar Islands, Northeast Indian Ocean. These small, ash-size (200 to 800 μm) broken pieces of glass shards when viewed under Scanning Electron Microscope (SEM), represent distinctive — platy, sickle, bicuspate, concentric, angular, horn shape and slivers with broken angular bubble wall — morphologies. Glass shards are colourless. But, a few are grey or reddish-brown, indicate high Fe content. Chilled, juvenile, angular and blocky shards show fragments of highly viscous, silicic magma. Spindle and ribbon-shape shards form from a low viscosity basalt and rhyolite. Electron Probe Micro Analyzer (EPMA) was used to measure low concentration variations of major oxides within individual amorphous silicate solid glass shards whose disordered atomic structure is that of a liquid derived from a silicate melt. Major elemental chemistry of early Miocene glass shards from Colebrook island show low silica, alkalis, high FeO_(T) MgO and CaO, whereas, early middle Miocene glass shards from Inglis island show high silica, alkalis, low FeO_(T), MgO and CaO contents. These data-sets when plotted on ternary TotalAlkali-Silica and Na₂O+K₂O-MgO-FeO_(T) diagrams show that their data plots lie within the basaltic-andesite, tephri-phonolite, rhyolite and trachyte fields. These glass shards which were present in the provenance, formed by explosive eruption of lavas, ranging in composition from basalt to rhyolite with andesite/ basalt-andesite being the most common magma types erupted sub-areally, implying island arc type of tectono-magmatic setting for the formation of these lavas. However, more evolutionary variant rhyolite was most likely formed by crystal fractionation.  相似文献   

The chemical composition of tertiary Indian coal ash and its combustion behaviour – a statistical approach: Part 2     

Arpita Sharma  Ananya Saikia  Puja Khare  D K Dutta  B P Baruah 《Journal of Earth System Science》2014,123(6):1439-1449

In Part 1 of the present investigation, 37 representative Eocene coal samples of Meghalaya, India were analyzed and their physico-chemical characteristics and the major oxides and minerals present in ash samples were studied for assessing the genesis of these coals. Various statistical tools were also applied to study their genesis. The datasets from Part 1 used in this investigation (Part 2) show the contribution of major oxides towards ash fusion temperatures (AFTs). The regression analysis of high temperature ash (HTA) composition and initial deformation temperature (IDT) show a definite increasing or decreasing trend, which has been used to determine the predictive indices for slagging, fouling, and abrasion propensities during combustion practices. The increase or decrease of IDT is influenced by the increase of Fe₂O₃, Al₂O₃, SiO₂, and CaO, respectively. Detrital-authigenic index (DAI) calculated from the ash composition and its relation with AFT indicates Sialoferric nature of these coals. The correlation analysis, Principal Component Analysis (PCA), and Hierarchical Cluster Analysis (HCA) were used to study the possible fouling, slagging, and abrasion potentials in boilers during the coal combustion processes. A positive relationship between slagging and heating values of the coal has been found in this study.  相似文献