Preface     

Sundaram S. Iyer  Asit Choudhuri  Johildo S.F. Barbosa 《Gondwana Research》1998,1(3-4):329-330

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Stable Isotope Investigations on the Granulite Facies Terrains of Brazil: A Review     

S.S. Iyer  A. Choudhuri  J.S.F. Barbosa 《Gondwana Research》1998,1(3-4):393-402

Stable isotope data from three areas in the granulite facies terrains of Brazil are assembled and discussed. All the three areas (Jequié, Guaxupé and São José do Rio Pardo) are from the São Francisco Craton. The carbon isotope composition of the fluid inclusion CO₂ in the Archean granulite terrain of Jequié indicate the participation of two distinct sources, an upper mantle source and an internal source of Archean organic matter. The isotope data may be interpreted in terms of the granulite genesis due to the intrusion of magma in the lower crust. The singularly uniform carbon isotope data for CO₂ fluid inclusion of plutonic granulites is a clear indication of the magmatic addition of CO₂-rich volatiles from deeper crustal sources. In the São José do Rio Pardo area sulfur and carbon isotope data of scapolites from the granulites imply the derivation of volatiles from internal sources. The whole rock oxygen isotope data of the amphibolite and granulite facies gneisses from Guaxupé indicate a small scale variation of d¹⁸O values, compatible with the chemical data, suggesting the preservation of pre-metamorphic oxygen isotope composition. The isotope data of the granulites from São Francisco Craton indicate non-pervasive fluid flow during metamorphism.  相似文献   

High velocity anomaly beneath the Deccan volcanic province: Evidence from seismic tomography     

H M Iyer  V K Gaur  S S Rai  D S Ramesh  CVR Rao  D Srinagesh  K Suryaprakasam 《Journal of Earth System Science》1989,98(1):31-60

Analysis of teleseismicP-wave residuals observed at 15 seismograph stations operated in the Deccan volcanic province (DVP) in west central India points to the existence of a large, deep anomalous region in the upper mantle where the velocity is a few per cent higher than in the surrounding region. The seismic stations were operated in three deployments together with a reference station on precambrian granite at Hyderabad and another common station at Poona. The first group of stations lay along a west-northwesterly profile from Hyderabad through Poona to Bhatsa. The second group roughly formed an L-shaped profile from Poona to Hyderabad through Dharwar and Hospet. The third group of stations lay along a northwesterly profile from Hyderabad to Dhule through Aurangabad and Latur. Relative residuals computed with respect to Hyderabad at all the stations showed two basic features: a large almost linear variation from approximately +1s for teleseisms from the north to—1s for those from the southeast at the western stations, and persistance of the pattern with diminishing magnitudes towards the east. Preliminary ray-plotting and three-dimensional inversion of theP-wave residual data delineate the presence of a 600 km long approximately N−S trending anomalous region of high velocity (1–4% contrast) from a depth of about 100 km in the upper mantle encompassing almost the whole width of the DVP. Inversion ofP-wave relative residuals reveal the existence of two prominent features beneath the DVP. The first is a thick high velocity zone (1–4% faster) extending from a depth of about 100 km directly beneath most of the DVP. The second feature is a prominent low velocity region which coincides with the westernmost part of the DVP. A possible explanation for the observed coherent high velocity anomaly is that it forms the root of the lithosphere which coherently translates with the continents during plate motions, an architecture characteristic of precambrian shields. The low velocity zone appears to be related to the rift systems (anomaly 28, 65 Ma) which provided the channel for the outpouring of Deccan basalts at the close of the Cretaceous period.  相似文献   

Soil and soil conservation survey for watershed management in parts of North cachar hills and karbi — Anglong districts of ASSAM     

M. L. Manchanda  Jitendra Prasad  H. S. Iyer  S. K. Deb  R. Pathak 《Journal of the Indian Society of Remote Sensing》1984,12(1):7-18

Soil and Soil Conservation surveys for watershed management were conducted using aerial photos of 1:60,000 scale in parts of North Cachar and Karbi-Anglong districts of Assam. The area was divided into different river catchments and sub-watersheds. The erosion, slope, landuse and soils in relation to physiogrphy were studied in each sub-watershed. The different physiographic units identified in the area were high, medium, low and very low hills; pediplains; alluvial plain and the valleys. These units were further subdivided based on slope, landuse and erosion etc. The soils were classified according to Soil Taxonomy. For priority determination, weightage was alloted to each of the sub-watersheds considering their physiography, slope, landuse, erosion,soil texture, depth and delivery ratio and sediment yield was calculated for each subwatershed. It has been found that out of 122875 ha, an area of 1745 ha had very high priority, 30590 ha high, 37290 ha medium, 51957 ha low and 1294 ha very low priority for soil conservation purposes.  相似文献   

Broad-band spectral evolution and temporal variability of IGR J17091-3624 during its 2016 outburst: <Emphasis Type="Italic">SWIFT</Emphasis> and <Emphasis Type="Italic">NuSTAR</Emphasis> results     

Radhika D.  Sreehari H.  A. Nandi  N. Iyer  S. Mandal 《Astrophysics and Space Science》2018,363(9):189

We report on the 2016 outburst of the transient Galactic Black Hole candidate IGR J17091-3624 based on the observation campaign carried out with SWIFT and NuSTAR. The outburst profile, as observed with SWIFT-XRT, shows a typical ‘q’-shape in the Hardness Intensity Diagram (HID). Based on the spectral and temporal evolution of the different parameters, we are able to identify all the spectral states in the q-profile of HID and the Hardness-RMS diagram (HRD). Both XRT and NuSTAR observations show an evolution of low frequency Quasi periodic oscillations (QPOs) during the low hard and hard intermediate states of the outburst rising phase. We also find mHz QPOs along-with distinct coherent class variabilities (heartbeat oscillations) with different timescales, similar to the \(\rho \)-class (observed in GRS 1915+105). Phenomenological modelling of the broad-band XRT and NuSTAR spectra also reveals the evolution of high energy cut-off and presence of reflection from ionized material during the rising phase of the outburst. Further, we conduct the modelling of X-ray spectra of SWIFT and NuSTAR in 0.5–79 keV to understand the accretion flow dynamics based on two component flow model. From this modelling, we constrain the mass of the source to be in the range of \(10.62\mbox{--}12.33~\mbox{M}_{\odot }\) with 90% confidence, which is consistent with earlier findings.  相似文献   

Observational aspects of outbursting black hole sources: Evolution of spectro-temporal features and X-ray variability     

H. Sreehari  Anuj Nandi  D. Radhika  Nirmal Iyer  Samir Mandal 《Journal of Astrophysics and Astronomy》2018,39(1):5

We report on our attempt to understand the outbursting profile of Galactic Black Hole sources, keeping in mind the evolution of temporal and spectral features during the outburst. We present results of evolution of quasi-periodic oscillations, spectral states and possible connection with jet ejections during the outburst phase. Further, we attempt to connect the observed X-ray variabilities (i.e., ‘class’/‘structured’ variabilities, similar to GRS 1915+105) with spectral states of black hole sources. Towards these studies, we consider three black hole sources that have undergone single (XTE J1859+226), a few (IGR J17091-3624) and many (GX 339-4) outbursts since the start of RXTE era. Finally, we model the broadband energy spectra (3–150 keV) of different spectral states using RXTE and NuSTAR observations. Results are discussed in the context of two-component advective flow model, while constraining the mass of the three black hole sources.  相似文献   

Scanning sky monitor (SSM) onboard AstroSat     

M. C. Ramadevi  S. Seetha  Dipankar Bhattacharya  B. T. Ravishankar  N. Sitaramamurthy  G. Meena  M. Ramakrishna Sharma  Ravi Kulkarni  V. Chandra Babu  Kumar  Brajpal Singh  Anand Jain  Reena Yadav  S. Vaishali  B. N. Ashoka  Anil Agarwal  K. Balaji  G. Nagesh  Manoj Kumar  Dhruti Ranjan Gaan  Prashanth Kulshresta  Pankaj Agarwal  Mathew Sebastian  A. Rajarajan  D. Radhika  Anuj Nandi  V. Girish  Vivek Kumar Agarwal  Ankur Kushwaha  Nirmal Kumar Iyer 《Experimental Astronomy》2017,44(1):11-23

Scanning Sky Monitor (SSM) onboard AstroSat is an Xray sky monitor in the soft X-ray band designed with a large field of view to detect and locate transient X-ray sources and alert the astronomical community about interesting phenomena in the X-ray sky. SSM comprises position sensitive proportional counters with 1D coded mask for imaging. There are three detector units mounted on a platform capable of rotation which helps covering about 50% of the sky in one full rotation. This paper discusses the elaborate details of the instrument and few immediate results from the instrument after launch.  相似文献   

On Darbyshire's Method of Analysing Microseims     

H. M. Iyer 《Geophysical Journal International》1969,17(4):443-444

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Influence of morphodynamic variability over seasonal beach sediments and its probable effect on coastal development     

A.R. Gujar  P. GanesanS.D. Iyer  S.S. GaonkarN.V. Ambre  V.J. LovesonP.G. Mislankar 《Ocean & Coastal Management》2011,54(7):514-523

Seasonal variations and effect of oceanographic processes such as erosion and/or accretion along beaches are important to understand their impact on coastal morphological variations. Detailed investigations were taken up to analyse the volumetric and morphologic variations of the beaches between Pirwadi (latitude 16° 12′ N, longitude 73° 26.55′ E) and Sarjekot (latitude 16° 05′ N, longitude 73° 27.80′ E) of South Maharashtra, Central West Coast of India. This stretch is known for its rich deposits of ilmenite, magnetite and chromite. This study is based on the results of seasonal topographic profiles carried out between October 2004 and December 2005. The volume variations of the sediments, i.e. an account of accretion and/or erosion, were estimated considering the October 2004 profile as the base reference, over which the values of other seasons are compared. The results of beach profiling from Pirwadi to Talashil indicate the seasonal variations in the beach configuration and the gradient.In the studied areas the vulnerable areas are Tondavali, Talashil and Pirwadi in a decreasing order of erosion while Bagwadi shows lesser erosion. Several reasons can be attributed for these erosional trends. Among which the prominent are rip currents, wave dynamics, variable coastal configuration, beach gradient and temporary monsoonal seaward flowing streams. In contrast, significant deposition occurs throughout the year at Hirlewadi due to sediment transported by due south by littoral currents. Therefore, considering the sensitivity of the fragile coastal system, future developmental activities (mining, tourism, etc.) need to be planned in tandem with the required protective measures such as construction of reinforced concrete curved wall and geotextiles.  相似文献   

Application of solid state nuclear track detectors in fission studies     

R H Iyer 《Journal of Earth System Science》1981,90(4):437-460

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