Radio observations of a few giant sources     

C. Konar  D. J. Saikia  C. H. Ishwara-Chandra  V. K. Kulkarni 《Monthly notices of the Royal Astronomical Society》2004,355(3):845-854

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Radio bubbles in the composite AGN-starburst galaxy NGC 6764     

Ananda Hota  D. J. Saikia 《Monthly notices of the Royal Astronomical Society》2006,371(2):945-956

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Field evidence,mineral chemical and geochemical constraints on mafic-felsic magma interactions in a vertically zoned magma chamber from the Chotanagpur Granite Gneiss Complex of Eastern India     

Bibhuti Gogoi  Ashima Saikia  Mansoor Ahmad 《Chemie der Erde / Geochemistry》2018,78(1):78-102

The Nimchak granite pluton (NGP) of Chotanagpur Granite Gneiss Complex (CGGC), Eastern India, provides ample evidence of magma interaction in a plutonic regime for the first time in this part of the Indian shield. A number of outcrop level magmatic structures reported from many mafic-felsic mixing and mingling zones worldwide, such as synplutonic dykes, mafic magmatic enclaves and hybrid rocks extensively occur in our study domain. From field observations it appears that the Nimchak pluton was a vertically zoned magma chamber that was intruded by a number of mafic dykes during the whole crystallization history of the magma chamber leading to magma mixing and mingling scenario. The lower part of the pluton is occupied by coarse-grained granodiorite (64.84–66.61?wt.% SiO₂), while the upper part is occupied by fine-grained granite (69.80–70.57?wt.% SiO₂). Field relationships along with textural and geochemical signatures of the pluton suggest that it is a well-exposed felsic magma chamber that was zoned due to fractional crystallization. The intruding mafic magma interacted differently with the upper and lower granitoids. The lower granodiorite is characterized by mafic feeder dykes and larger mafic magmatic enclaves, whereas the enclaves occurring in the upper granite are comparatively smaller and the feeder dykes could not be traced here, except two late-stage mafic dykes. The mafic enclaves occurring in the upper granite show higher degrees of hybridization with respect to those occurring in the lower granite. Furthermore, enclaves are widely distributed in the upper granite, whereas enclaves in the lower granite occur adjacent to the main feeder dykes.Geochemical signatures confirm that the intermediate rocks occurring in the Nimchak pluton are mixing products formed due to the mixing of mafic and felsic magmas. A number of important physical properties of magmas like temperature, viscosity, glass transition temperature and fragility have been used in magma mixing models to evaluate the process of magma mixing. A geodynamic model of pluton construction and evolution is presented that shows episodic replenishments of mafic magma into the crystallizing felsic magma chamber from below. Data are consistent with a model whereby mafic magma ponded at the crust-mantle boundary and melted the overlying crust to form felsic (granitic) magma. The mafic magma episodically rose, injected and interacted with an overlying felsic magma chamber that was undergoing fractional crystallization forming hybrid intermediate rocks. The intrusion of mafic magma continued after complete solidification of the magma chamber as indicated by the presence of two late-stage mafic dykes.  相似文献   

Petro-chemical investigation of some perhydrous Indian coals     

Bimala P. Baruah  Arpita Sharma  Binoy K. Saikia 《Journal of the Geological Society of India》2013,81(5):713-718

An attempt has been made to study the petro-chemical characteristics of some high sulphur sub-bituminous coal samples from Makum coalfield, Assam, India. The proximate and ultimate analyes were carried out and forms of sulphur were determined and their relationships with the Maceral constituents (vitrinite, liptinite, and inertinite) were investigated. The macerals (vitrinite+liptinite+inertinite) have significant relationships (R²>0.500) with volatile matter and carbon, whereas weak correlations were seen with rest of the physico-chemical characteristics of the coals. The study reveals that these coals are rich in vitrinites and sulphur and are aromatic in nature. These coals have good hydrocarbon potential.  相似文献   

Interaction of the WAT Source in A3395 with the Intracluster Medium     

Kiran Lakhchaura  K. P. Singh  D. J. Saikia  R. W. Hunstead 《Journal of Astrophysics and Astronomy》2011,32(4):493-494

Using X-ray observations from Chandra and XMM-Newton and radio observations from the Australia Telescope Compact Array (ATCA), we have examined the merging environment of the bimodal cluster Abell 3395. From X-ray data we have produced thermodynamic maps of the cluster. The Wide Angle Tail (WAT) galaxy seen in the radio is slightly offset from the X-ray emission peak of the southern part of the cluster. The unsharp masked Chandra image of the cluster does not show any deficit in the X-ray flux near the location of the source possibly because the thermal plasma has leaked into the cavities.  相似文献   

A multifrequency study of giant radio sources – II. Spectral ageing analysis of the lobes of selected sources     

M. Jamrozy  C. Konar  J. Machalski  D. J. Saikia 《Monthly notices of the Royal Astronomical Society》2008,385(3):1286-1296

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Prioritization of Sub-watersheds in Khanapara–Bornihat Area of Assam–Meghalaya (India) Based on Land Use and Slope Analysis Using Remote Sensing and GIS     

Santanu Sarma  Trivani Saikia 《Journal of the Indian Society of Remote Sensing》2012,40(3):435-446

Improper utilization of natural resources without any conservation work is the prime cause of the watershed deterioration. Fast developmental activities and population pressure in the hills of Khanapara?CBornihat area near Guwahati city (about 10?km east of Guwahati) results rapid alteration of the land use/land cover in the recent times. This also causes the growth of land use over the unsuitable topography. As a result, there is a general degradation of the natural resources within the area. So, urgent measures have to be adopted to take up the conservation measure for the management of natural resources. Watershed wise conservation is considered to be the most acceptable and convenient approach. In the context of watershed management, watershed prioritization gained importance in natural resource management. The present study makes an attempt to prioritize the sub-watersheds for adopting the conservation measure. The prioritization is based on land use and slope analysis using Remote Sensing and GIS techniques in Khanapara?CBornihat area of Assam and Meghalaya state (India). The study area of 323.17?sq. km is divided into three 5th order, four 4th order and two 3rd order sub-watersheds. Land use/Land cover change analysis of the sub-watersheds has been carried out using multi temporal data of SOI toposheets of 1972 and IRS LISS III imagery of 2006. The study shows the significance changes in land use pattern especially in settlement and forest lands from 1972 to 2006. Slope map of the sub-watersheds prepared from the contour values in the toposheets show the wide variation of slope in the area ranging from 0° to 87°. Based on the extent/nature of land use/land cover changes over time and land use/land cover??slope relationship analysis, the sub-watersheds are classified into three categories as high, medium and low in terms of priority for conservation and management of natural resources.  相似文献   

Environmental assessment and nano-mineralogical characterization of coal,overburden and sediment from Indian coal mining acid drainage     

Madhulika Dutta  Jyotilima Saikia  Silvio R. Taffarel  Frans B. Waanders  Diego de Medeiros  Cesar M.N.L. Cutruneo  Luis F.O. Silva  Binoy K. Saikia 《地学前缘(英文版)》2017,8(6):1285-1297

The deterioration of environmental conditions is the major contributory factor to poor health and quality of life that hinders sustainable development in any region.Coal mining is one of the major industries that contribute to the economy of a country but it also impacts the environment.The chemical parameters of the coal,overburden,soil and sediments along with the coal mine drainage(CMD)were investigated in order to understand the overall environmental impact from high sulphur coal mining at northeastern coalfield(India).It was found that the total sulphur content of the coal is noticeably high compared to the overburden(OB)and soil.The volatile matter of the coal is sufficiently high against the high ash content of the soil and overburden.The water samples have a High Electrical Conductivity(EC)and high Total Dissolve Solid(TDS).Lower values of pH,indicate the dissolution of minerals present in the coal as well as other minerals in the mine rejects/overburden.The chemical and nano-mineralogical composition of coal,soil and overburden samples was studied using a High Resolution-Transmission Electron Microscopy(HR-TEM),Energy Dispersive Spectroscopy(EDS),Selected-Area Diffraction(SAED),Field Emission-Scanning Electron Microscopy(FE-SEM)/EDS,X-ray diffraction(XRD),Fourier Transform Infrared Spectroscopy(FTIR),Raman and Ion-Chromatographic analysis,and Mossbauer spectroscopy.From different geochemical analysis it has been found that the mine water sample from Ledo colliery has the lowest pH value of 3.30,Tirap colliery samples have the highest electrical conductivity value of5.40 ms cm~(-1)Both Ledo and Tirap coals have total sulphur contents within the range 3-3.50%.The coal mine water from Tirap colliery(TW-15 B)has high values of Mg~(2+)(450 ppm),and Br~-(227.17 ppm).XRD analysis revealed the presence of minerals including quartz and hematite in the coals.Mineral analysis of coal mine overburden(OB)indicates the presence both of pyrite and marcasite which was also confirmed in XRD and Mossbauer spectral analysis.The presented data of the minerals and ultra/nano-particles present shows their ability to control the mobility of hazardous elements,suggesting possible use in environmental management technology,including restoration of the delicate Indian coal mine areas.  相似文献   

Phase-reference mapping of a weak-cored double-lobed source in the 1636+473 system using MERLIN and Global VLBI     

M. J. Rioja  R. W. Porcas  S. Garrington  A. Alberdi  D. J. Saikia 《New Astronomy Reviews》1999,43(8-10)

We present maps and astrometric results from first epoch, simultaneous MERLIN and Global VLBI observations of the very weak core of a double-lobed radio source, using as reference the bright, compact, flat-spectrum quasar 1636+473 A, 20 arcsec away. The observations were made in May 1995 at 5 GHz. The phase-referenced VLBI map of the weak core, of resolution 1.5 mas, contains a high percentage of the core flux density seen in the MERLIN map. Further hybrid mapping iterations reveal a faint, one-sided core extension on the same side as the MERLIN jet. We explore the effect of both temporal and other coherence losses on the phase-reference map. We relate our results to the structural asymmetry in weak AGN cores within the context of unification models.  相似文献   

H i in NGC 5433 and its environment: high-latitude emission in a small galaxy group     

Kristine Spekkens  Judith A. Irwin  D. J. Saikia 《Monthly notices of the Royal Astronomical Society》2004,352(4):1145-1160

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