Metamorphic zonal sequences of pelitic schists and gneisses from the area around Kandra (Jharkhand): Constraints from field and textural relationship     

Divya Prakash  Dhananjay Kumar Patel  Suparna Tewari  Manoj Kumar Yadav  Roopali Yadav 《Journal of the Geological Society of India》2017,89(2):139-144

The pelitic schists of the area around Kandra, Singhbhum district, Jharkhand belong to the Chaibasa Formation of the Singhbhum Group, which constitute a part of the youngest Precambrian orogenic cycle of the Singhbhum region. Structurally, the area represents the Singhbhum anticlinorium and is overlain by Dalma traps which form the synclinorium towards the north of the area around Kandra. This area mainly consists of medium to high grade rocks belonging to greenschist and amphibolite facies. These rocks are folded in the E-W trending doubly plunging folds (F₁) overturned towards the south with low plunges and superposed by cross-folds (F₂). The spatial distribution of the index minerals in the pelitic schists of the area shows Barrovian type of metamorphism. Four isograds, viz. biotite, garnet, staurolite and sillimanite have been delineated by the first appearance of the index minerals and also by isograd reactions. The textural relation suggests that sillimanite is formed from staurolite consumption reaction instead of kyanite consumption.  相似文献   

Dynamic stress concentration in pre-stressed poroelastic media due to moving punch influenced by shear wave     

Abhishek Kumar Singh  Anil Negi  Ram Prasad Yadav  Amit Kumar Verma 《Journal of Seismology》2018,22(5):1263-1274

During the occurrence of earthquake, the shear wave propagates in the rocks present inside/at the Earth’s crust. The propagation of shear wave may lead to the progression of punch present inside the rock medium. As a result of this, substantial stress accumulated at the vicinity of propagating punch inside rock medium which significantly affects the stability of various geological and human-made structure and, hence, may cause failure of structure. Therefore, the analysis of stress concentration at the vicinity of punch moving due to shear wave propagation has become prominent in the area of seismology. In the present paper, an analytical perspective has been employed to discuss the influence of velocity of moving punch associated with the propagation of shear wave on developed dynamic stress concentration (DSC) in three types of pre-stressed vertical transversely isotropic (VTI) poroelastic media viz. granite (an igneous rock); sandstone (a sedimentary rock); and marble (a metamorphic rock). The closed form expression of DSC for the force of constant intensity has been derived with the aid of Weiner-Hopf technique along with Galilean and two-sided Fourier integral transformations. The noticeable influence of different affecting parameters (viz. velocity of moving punch associated with the shear wave propagation, horizontal compressive/tensile initial stresses, vertical compressive/tensile initial stress, porosity, and anisotropy parameter) on dynamic stress concentration has also been reported. Numerical computation and graphical illustrations have been carried out for the aforementioned three different types of porous rocks to investigate the profound impact of affecting parameters on DSC. Moreover, some noteworthy peculiarities have also been derived from the obtained expression of dynamic stress concentration.  相似文献   

Large Area X-Ray Proportional Counter (LAXPC) Instrument on AstroSat and Some Preliminary Results from its Performance in the Orbit     

P. C. Agrawal  J. S. Yadav  H. M. Antia  Dhiraj Dedhia  P. Shah  Jai Verdhan Chauhan  R. K. Manchanda  V. R. Chitnis  V. M. Gujar  Tilak Katoch  V. N. Kurhade  P. Madhwani  T. K. Manojkumar  V. A. Nikam  A. S. Pandya  J. V. Parmar  D. M. Pawar  Jayashree Roy  B. Paul  Mayukh Pahari  Ranjeev Misra  M. H. Ravichandran  K. Anilkumar  C. C. Joseph  K. H. Navalgund  R. Pandiyan  K. S. Sarma  K. Subbarao 《Journal of Astrophysics and Astronomy》2017,38(2):30

Large area X-ray propositional counter (LAXPC) instrument on AstroSat is aimed at providing high time resolution X-ray observations in 3–80 keV energy band with moderate energy resolution. To achieve large collecting area, a cluster of three co-aligned identical LAXPC detectors, is used to realize an effective area in access of \({\sim }6000\,\hbox {cm}^{2}\) at 15 keV. The large detection volume of the LAXPC detectors, filled with xenon gas at \({\sim }\)2 atmosphere pressure, results in detection efficiency greater than 50%, above 30 keV. In this article, we present salient features of the LAXPC detectors, their testing and characterization in the laboratory prior to launch and calibration in the orbit. Some preliminary results on timing and spectral characteristics of a few X-ray binaries and other type of sources, are briefly discussed to demonstrate that the LAXPC instrument is performing as planned in the orbit.  相似文献   

SPIN: An Inversion Code for the Photospheric Spectral Line     

Rahul Yadav  Shibu K. Mathew  Alok Ranjan Tiwary 《Solar physics》2017,292(8):105

Inversion codes are the most useful tools to infer the physical properties of the solar atmosphere from the interpretation of Stokes profiles. In this paper, we present the details of a new Stokes Profile INversion code (SPIN) developed specifically to invert the spectro-polarimetric data of the Multi-Application Solar Telescope (MAST) at Udaipur Solar Observatory. The SPIN code has adopted Milne–Eddington approximations to solve the polarized radiative transfer equation (RTE) and for the purpose of fitting a modified Levenberg–Marquardt algorithm has been employed. We describe the details and utilization of the SPIN code to invert the spectro-polarimetric data. We also present the details of tests performed to validate the inversion code by comparing the results from the other widely used inversion codes (VFISV and SIR). The inverted results of the SPIN code after its application to Hinode/SP data have been compared with the inverted results from other inversion codes.  相似文献   

Probabilistic assessment of tropical cyclones’ extreme wind speed in the Bay of Bengal: implications for future cyclonic hazard     

Bhardwaj  Pankaj  Singh  Omvir  Yadav  R. B. S. 《Natural Hazards》2020,101(1):275-295

Natural Hazards - Tropical cyclones (TCs) of the Bay of Bengal (BoB) cause catastrophic loss over the coasts at the time of landfall in India, Bangladesh, Myanmar and Sri Lanka. To strengthen...  相似文献   

Low energy secondary cosmic ray flux (gamma rays) monitoring and its constrains     

Anil Raghav  Ankush Bhaskar  Virendra Yadav  Nitinkumar Bijewar 《Astrophysics and Space Science》2015,355(2):347-352

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The Pleiades apex and its kinematical structure     

W. H. Elsanhoury  E. S. Postnikova  N. V. Chupina  S. V. Vereshchagin  Devesh P. Sariya  R. K. S. Yadav  Ing-Guey Jiang 《Astrophysics and Space Science》2018,363(3):58

A study of cluster characteristics and internal kinematical structure of the middle-aged Pleiades open star cluster is presented. The individual star apexes and various cluster kinematical parameters including the velocity ellipsoid parameters are determined using both Hipparcos and Gaia data. Modern astrometric parameters were taken from the Gaia Data Release 1 (DR1) in combination with the Radial Velocity Experiment Fifth Data Release (DR5). The necessary set of parameters including parallaxes, proper motions and radial velocities are used for \(n=17\) stars from Gaia DR1+RAVE DR5 and for \(n=19\) stars from the Hipparcos catalog using SIMBAD data base. Single stars are used to improve accuracy by eliminating orbital movements. RAVE DR5 measurements were taken only for the stars with the radial velocity errors not exceeding \(2~\mbox{km}/\mbox{s}\). For the Pleiades stars taken from Gaia, we found mean heliocentric distance as \(136.8 \pm 6.4\) pc, and the apex position is calculated as: \(A_{CP}=92^{\circ }.52\pm 1^{\circ }.72\), \(D_{CP}=-42^{\circ }.28\pm 2^{\circ }.56\) by the convergent point method and \(A_{0}=95^{\circ }.59\pm 2^{\circ }.30\) and \(D_{0}=-50^{\circ }.90\pm 2^{\circ }.04\) using AD-diagram method (\(n=17\) in both cases). The results are compared with those obtained historically before the Gaia mission era.  相似文献   

Physical Properties of Umbral Dots Observed in Sunspots: A <Emphasis Type="Italic">Hinode</Emphasis> Observation     

Rahul Yadav  Shibu K. Mathew 《Solar physics》2018,293(4):54

Umbral dots (UDs) are small-scale bright features observed in the umbral part of sunspots and pores. It is well established that they are manifestations of magnetoconvection phenomena inside umbrae. We study the physical properties of UDs in different sunspots and their dependence on decay rate and filling factor. We have selected high-resolution, G-band continuum filtergrams of seven sunspots from Hinode to study their physical properties. We have also used Michelson Doppler Imager (MDI) continuum images to estimate the decay rate of selected sunspots. An identification and tracking algorithm was developed to identify the UDs in time sequences. The statistical analysis of UDs exhibits an averaged maximum intensity and effective diameter of 0.26 \(I_{\mathrm{QS}}\) and 270 km. Furthermore, the lifetime, horizontal speed, trajectory length, and displacement length (birth–death distance) of UDs are 8.19 minutes, 0.5 km?s^?1, 284 km, and 155 km, respectively. We also find a positive correlation between intensity–diameter, intensity–lifetime, and diameter–lifetime of UDs. However, UD properties do not show any significant relation with the decay rate or filling factor.  相似文献   

Study of simultaneous presence of DD and PP electric fields during the geomagnetic storm of November 7–8, 2004 and resultant TEC variation over the Indian Region     

P. Galav  Shweta Sharma  S. S. Rao  B. Veenadhari  T. Nagatsuma  R. Pandey 《Astrophysics and Space Science》2014,350(2):459-469

During very intense geomagnetic storm of November 7–8, 2004 simultaneous presence of storm time disturbance dynamo and eastward and westward directed prompt penetration electric fields inferred from the ground based magnetometer data in the 75^° E sector is presented. Magnetometer observations show that, on the whole, average ΔH variation on 8 November remains below the night time level compared to its quiet day variation. A number of upward and downward excursions have been observed between 0130 UT and 0800 UT in the ΔH variation on 8 November. These excursions in ΔH have been attributed to the episodes of eastward and westward prompt penetrating electric fields. Ionospheric response in the equatorial ionization anomaly region along 75^° E has also been studied using the total electron content data recorded at five GPS stations, namely Udaipur, Bengaluru (IISC), Hyderabad (HYDE), Maldives (MALD) and Diego Garcia (DGAR). Observation of markedly suppressed EIA, in conjunction with ΔH variation which was m negative during the daytime on 8 November, indicates the presence of an external field of opposite polarity (the disturbance dynamo electric field) that either undermined, or overshadowed the daytime ambient (eastward) electric field to the extent that the equatorial plasma fountain could not become effective.  相似文献   

On some properties of prominence eruptions and the associated CMEs in solar cycle 23     

Pooja Gupta  Mohit Gupta  Ruby Yadav  Udit Narain 《Astrophysics and Space Science》2014,352(2):395-402

This work includes a study of some properties such as speed, apparent width, acceleration and latitudes, etc. of all types of Prominence Eruptions (PEs) and the associated Coronal Mass Ejections (CMEs) observed during the period of 1997–2006 by Nobeyama Radioheliograph (NORH) and SOHO/LASCO covering the solar cycle 23. The average speed of prominences and associated CMEs are 51 km/sec and 559 km/sec, respectively. The average angular width is 32^° and 74^°, respectively. As expected the associated CMEs are relatively faster and wider than the prominences.  相似文献