Average anisotropy characteristics of high energy cosmic ray particles and geomagnetic disturbance index Ap     

C. M. Tiwari  D. P. Tiwari  Ajay K. Pandey  Pankaj K. Shrivastava 《Journal of Astrophysics and Astronomy》2005,26(4):429-434

The average characteristics of the diurnal and semi-diurnal anisotropy of cosmic ray intensity at relativistic energies have been obtained by using data from the worldwide grid of neutron monitor for the period 1989 to 1996. The complex behaviour of the diurnal amplitudes and time of maxima (phase) and its association with the Ap index on a long-term and day-to-day basis have been studied. Even though the general characteristics, on a yearly average basis, have not changed significantly during this period, both the diurnal and semi-diurnal amplitudes and phases vary significantly, besides significant changes being observed for different interplanetary conditions on a short-term basis. It is found that the relationship between the Ap index and the diurnal vector is out of phase during the period 1991 to 1995. On a long-term basis, the correlation of diurnal variation with Ap index has been found to vary during the solar cycle. On a short-term basis, it has been observed that the high Ap days are usually associated with higher amplitudes with phase shifted to earlier hours.  相似文献   

High-Speed Solar wind Streams and Cosmic-Ray Intensity Variations During 1991–1996     

Shrivastava  Pankaj K.  Jaiswal  K.L. 《Solar physics》2003,214(1):195-200

High-speed plasma streams identified in the solar wind measurements can be separated into two categories: coronal-hole-associated streams and flare-generated streams. Effects of these plasma streams on cosmic-ray intensity are studied for the period of 1991–1996. It is investigated that both of these high-speed solar wind plasma streams (CS and FGS) are found equally effective in producing the cosmic-ray intensity decrease on short-term basis.  相似文献   

Isolating type-specific phenologies through spectral unmixing of satellite time series     

Jyoteshwar R. Nagol  Joseph O. Sexton  Anupam Anand  Ritvik Sahajpal  Thomas C. Edwards 《International Journal of Digital Earth》2018,11(3):233-245

Vegetation phenology is commonly studied using time series of multi-spectral vegetation indices derived from satellite imagery. Differences in reflectance among land-cover and/or plant functional types are obscured by sub-pixel mixing, and so phenological analyses have typically sought to maximize the compositional purity of input satellite data by increasing spatial resolution. We present an alternative method to mitigate this ‘mixed-pixel problem’ and extract the phenological behavior of individual land-cover types inferentially, by inverting the linear mixture model traditionally used for sub-pixel land-cover mapping. Parameterized using genetic algorithms, the method takes advantage of the discriminating capacity of calibrated surface reflectance measurements in red, near infrared, and short-wave infrared wavelengths, as well as the Normalized Difference Vegetation Index (NDVI) and the Normalized Difference Water Index. In simulation, the unmixing procedure reproduced the reflectances and phenological signals of grass, crop, and deciduous forests with high fidelity (RMSE?相似文献   

An Experimental Study of Compaction Grouting on Its Densification and Confining Effects     

Neha Shrivastava  Kouki Zen 《Geotechnical and Geological Engineering》2018,36(2):983-993

Compaction grouting (CPG) involves the injection of high viscosity mortar-type grout under relatively high pressure that displaces and compacts the soil in-place. Many case studies around the world prove the effectiveness of CPG to treat liquefiable soils. In these studies, mostly CPG has been developed and used on the basis of practical experiences, its densification and confining effects are not well understood until now. The objective of the present study is to bring out densification and confining effects of CPG. This paper presents a laboratory experimental study carried out to model a CPG treated ground. The study includes the experiments performed to decide appropriate consistency of grout material and appropriate relative contribution of factors such as overburden pressure, grout volume, injection speed and injection pressure that ensures efficient grouting. The effects of CPG are quantified in terms of lateral earth pressures and lateral displacements that are further defined in terms of coefficient of lateral earth pressure, K, and densification factor in the soil around grout column. This leads to a better understanding of its densification and confining effects. Although in practice, majority of the works with CPG have been related to its densification effect and lesser attention has been given to its confinement effect, in present experimental study, its confinement effect were prominent. Also at the farthest locations usually where field tests are carried out, its densification effect could not be found experimentally but its confinement effect was clear.  相似文献   

Natural glass from Deccan volcanic province: an analogue for radioactive waste form     

Nishi Rani  J. P. Shrivastava  R. K. Bajpai 《International Journal of Earth Sciences》2015,104(8):2163-2177

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Mineral chemistry of clays associated with the Late Cretaceous-early Palaeogene succession of the Um-Sohryngkew river section of Meghalaya,India: Palaeoenvironmental inferences and K/Pg transition     

Sucharita Pal  J. P. Shrivastava  Sanjay K. Mukhopadhyay 《Journal of the Geological Society of India》2015,86(6):631-647

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An estimate of the energy spectrum of gamma rays from the central region of the Galaxy and some implications     

K. C. Anand  S. A. Stephens 《Astrophysics and Space Science》1972,18(2):387-402

High resolution surveys of the galactic centre suggest the existence of an extended nonthermal source (Bulge) with an intensity much larger than the total background radiation in that direction. In this paper, we have first evaluated the physical conditions existing in this restricted region of space from an analysis of the radio spectrum and shown that if the distribution of matter, magnetic fieldB(r) and cosmic ray densityk(r) in the plane of the Galaxy is of gaussian type then at the centreB (0)=25–30 G andk(0)=25–35 times that in the near interstellar space. It is also found that most of the absorption in the Sagittarius A spectrum at low frequencies takes place in the Bulge and one requires a small additional absorption to take place in the line of sight corresponding to n _e ²10 cm^–6 pc at a temperature typically of clouds 100 K. The gamma ray spectra from the Bulge arising from interactions of cosmic rays with matter and radiation are then calculated in detail. A comparison made with the estimated background gamma ray spectra from the disk reveals that a detector with angular resolution 6° having a threshold of a few times 10^–6 photons cm^–2 s^–1 can detect this source; this bulge is not found to be a good X-ray source for detection. From a comparison of these calculations with the observed flux above 100 MeV, the following inferences have been deduced: (i) the lower limit to the magnetic field strength at the centre is 12 G, (ii) the observed gamma ray flux towards the Anti-centre can be well explained as due to interactions of cosmic rays with matter alone and a similar explanation towards the center reveals that cloud complexes could be more in the inner parts of the Galaxy than in the outer parts, and (iii) the observed flux values are found to be inconsistent with the existence of submillimeter radiation in the galactic scale.  相似文献   

Chromium isotopes identify the extraterrestrial component in impactites from Dhala impact structure,India     

Aryavart Anand  Anuj Kumar Singh  Klaus Mezger  Jayanta Kumar Pati 《Meteoritics & planetary science》2023,58(5):722-736

The Dhala structure in north-central India is a confirmed complex impact structure of Paleoproterozoic age. The presence of an extraterrestrial component in impactites from the Dhala structure was recognized by geochemical analyses of highly siderophile elements and Os isotopic compositions; however, the impactor type has remained unidentified. This study uses Cr isotope systematics to identify the type of projectile involved in the formation of the Dhala structure. Unlike the composition of siderophile elements (e.g., Ni, Cr, Co, and platinum group elements) and their inter-element ratios that may get compromised due to the extreme energy generated during an impact, Cr isotopes retain the distinct composition of the impactor. The distinct ε⁵⁴Cr value of −0.31 ± 0.09 for a Dhala impact melt breccia sample (D6-57) indicates inheritance from an impactor originating within the non-carbonaceous reservoir, that is, the inner Solar System. Based on the Ni/Cr ratio, Os abundance, and Cr isotopic composition of the samples, the impactor is constrained to be of ureilite type. Binary mixing calculations also indicate contamination of the target rock by 0.1–0.3 wt% of material from a ureilite-like impactor. Together with the previously identified impactors that formed El'gygytgyn, Zhamanshin, and Lonar impact structures, the Cr isotopic compositions of the Dhala impactites argue for a much more diverse source of the objects that collided with the Earth over its geological history than has been supposed previously.  相似文献   

Investigation on the Cyclonic Seastate along Southeast Coast of India     

K. V. Anand  V. Sundar 《Marine Geodesy》2013,36(1):58-78

The east coast of the Indian Peninsula experiences the effects of a devastating cyclone at least annually. The Thane cyclone of 29–30 December 2011 has been once such event that resulted in significant damages along the coastline of Tamil Nadu on the southeast coast of India (13° 9′ 10′ N and 80° 21′E). Waves as high as 8–12 m in a water depth of 20 m have been measured. Such huge waves, combined with a storm surge of 0.5 m, lead to severe damages to coastal structures during the passage of the cyclone. As a part of an exercise in assessing the sediment transport rates through measurements of the hydrodynamic driving parameters along the coast of major port of Chennai instruments were deployed for the measurement of waves and flow field. The measurement campaign was carried out at a location of about 120 km north of the cyclone made landfall. The ENCEP wind data formed the input for executing the WAM model for the simulation of wave characteristics, which are compared with the measured wave data. The agreement between them is found to be good. The details of the analysis of the results are presented and discussed in this paper.  相似文献   

Development of an artificial neural network based multi-model ensemble to estimate the northeast monsoon rainfall over south peninsular India: an application of extreme learning machine   总被引：2，自引：0，他引：2  

Nachiketa Acharya  Nitin Anand Shrivastava  B. K. Panigrahi  U. C. Mohanty 《Climate Dynamics》2014,43(5-6):1303-1310

The south peninsular part of India gets maximum amount of rainfall during the northeast monsoon (NEM) season [October to November (OND)] which is the primary source of water for the agricultural activities in this region. A nonlinear method viz., Extreme learning machine (ELM) has been employed on general circulation model (GCM) products to make the multi-model ensemble (MME) based estimation of NEM rainfall (NEMR). The ELM is basically is an improved learning algorithm for the single feed-forward neural network (SLFN) architecture. The 27 year (1982–2008) lead-1 (using initial conditions of September for forecasting the mean rainfall of OND) hindcast runs (1982–2008) from seven GCM has been used to make MME. The improvement of the proposed method with respect to other regular MME (simple arithmetic mean of GCMs (EM) and singular value decomposition based multiple linear regressions based MME) has been assessed through several skill metrics like Spread distribution, multiplicative bias, prediction errors, the yield of prediction, Pearson’s and Kendal’s correlation coefficient and Wilmort’s index of agreement. The efficiency of ELM estimated rainfall is established by all the stated skill scores. The performance of ELM in extreme NEMR years, out of which 4 years are characterized by deficit rainfall and 5 years are identified as excess, is also examined. It is found that the ELM could expeditiously capture these extremes reasonably well as compared to the other MME approaches.  相似文献