Late Pleistocene-Holocene morphosedimentary architecture, Spiti River, arid higher Himalaya     

Pradeep Srivastava  Yogesh Ray  Binita Phartiyal  Anupam Sharma 《International Journal of Earth Sciences》2013,102(7):1967-1984

The Spiti River drains the rain shadow zone of western Himalaya. In the present study, the fluvial sedimentary record of Spiti valley was studied to understand its responses to tectonics and climate. Geomorphic changes along the river enable to divide the river into two segments: (i) upper valley with a broad, braided channel where relict sedimentary sequences rise 15–50 m high from the riverbed and (ii) lower valley with a narrow, meandering channel that incises into bedrock, and here, the fluvio-lacustrine sediments reside on a bedrock bench located above the riverbed. The transition between these geomorphic segments lies along the river between Seko-Nasung and Lingti villages (within Tethyan Himalaya). Lithofacies analyses of the sedimentary sequences show six different lithofacies. These can be grouped into three facies associations, viz. (A) a glacial outwash; (B) sedimentation in a channel and in an accreting bar under braided conditions; and (C) formation of lake due to channel blockage by landslide activities. Seventeen optically stimulated luminescence ages derived from ten sections bracketed the phases of river valley aggradation between 14–8 and 50–30 ka. These aggradation phases witnessed mass wasting, channel damming and lake formation events. Our record, when compared with SW monsoon archives, suggests that the aggradation occurred during intensified monsoon phase of MIS 3/4 and that proceeded the Last Glacial Maxima. Thus, the study reports monsoon modulated valley aggradation in the NW arid Himalaya.  相似文献   

Precision pulsar timing with the ORT and the GMRT and its applications in pulsar astrophysics     

Bhal Chandra Joshi  Prakash Arumugasamy  Manjari Bagchi  Debades Bandyopadhyay  Avishek Basu  Neelam Dhanda Batra  Suryarao Bethapudi  Arpita Choudhary  Kishalay De  L. Dey  A. Gopakumar  Y. Gupta  M. A. Krishnakumar  Yogesh Maan  P. K. Manoharan  Arun Naidu  Rana Nandi  Dhruv Pathak  Mayuresh Surnis  Abhimanyu Susobhanan 《Journal of Astrophysics and Astronomy》2018,39(4):51

Radio pulsars show remarkable clock-like stability, which make them useful astronomy tools in experiments to test equation of state of neutron stars and detecting gravitational waves using pulsar timing techniques. A brief review of relevant astrophysical experiments is provided in this paper highlighting the current state-of-the-art of these experiments. A program to monitor frequently glitching pulsars with Indian radio telescopes using high cadence observations is presented, with illustrations of glitches detected in this program, including the largest ever glitch in PSR B0531+21. An Indian initiative to discover sub-\(\mu \)Hz gravitational waves, called Indian Pulsar Timing Array (InPTA), is also described briefly, where time-of-arrival uncertainties and post-fit residuals of the order of \(\mu \)s are already achievable, comparable to other international pulsar timing array experiments. While timing the glitches and their recoveries are likely to provide constraints on the structure of neutron stars, InPTA will provide upper limits on sub-\(\mu \)Hz gravitational waves apart from auxiliary pulsar science. Future directions for these experiments are outlined.  相似文献   

Ecological variables influencing the diversity and distribution of macrolichens colonizing <Emphasis Type="Italic">Quercus leucotrichophora</Emphasis> in Uttarakhand forest     

Shashi Upadhyay  Arun K. Jugran  Yogesh Joshi  Renu Suyal  Ranbeer S. Rawal 《山地科学学报》2018,15(2):307-318

Ecological variables play a significant role in determining the diversity and distribution of any living organism on earth. Lichens are not exceptional and are quite sensitive in comparison to other organisms; hence the present study focuses on the impact of ecological variables on the diversity and distribution of epiphytic macrolichens colonizing Quercus leucotrichophora across eight different sites (50 m × 50 m) in Thal Ke Dhar forest, Kumaun Himalaya, Uttarakhand, India. For sampling of macrolichens, 200 trees (25 trees from each site) of Q. leucotrichophora were selected from each site and five quadrats of 5 cm × 10 cm (1000 quadrats in totality) were drawn at the tree trunk. From all the sampled trees, a total of 54 species of epiphytic macrolichens belonging to 18 genera and five families were recorded. Various ecological variables, namely altitude, aspect, slope, diameter at breast height (DBH), and lopping percent (partial cutting of the twigs as disturbance), were also analyzed to investigate their influence on macrolichen species composition and distribution pattern in the study area. For the determination of relationships between these variables, statistical analysis, namely Pearson’s Correlation Coefficient, Polynomial regression analysis and Principal Component Analysis (PCA) were performed. Out of all variables, lopping was significantly correlated to species richness of epiphytic macrolichens (0.712*, p<0.05) and it was confirmed by Pearson’s Correlation Coefficient. Despite of having high anthropogenic pressure or impact through lopping, the maximum number of macrolichen species was recorded at elevation 2267 meter above sea level (m asl). The present study revealed that besides other ecological variables, lopping practices can act as a key parameter in controlling the diversity and distribution not only of epiphytic macrolichens but also of other life forms such as bryophytes, pteridophytes, insects, birds etc. and can be either negatively or positively correlated.  相似文献   

A note on the stability of helical velocity and magnetic fields     

Rama Kant  S. K. Trehan 《Astrophysics and Space Science》1985,110(2):297-300

The stability of nonparallel helical velocity and magnetic fields in a plasma cylinder with free boundaries is examined. It is shown that, in case of weak helicity, the stability of the system remains unaffected.  相似文献   

Nonlinear waves in superposed fluids     

R. Kant  S. K. Malik 《Astrophysics and Space Science》1982,86(2):345-360

A weakly nonlinear theory of wave propagation in superposed fluids in the presence of magnetic fields is presented in this paper. We derive the equations governing the evolution of the amplitude of the progressive as well as the standing waves. It is demonstrated that the waves can be unstable against modulation in the presence of the magnetic fields. We also obtain the nonlinear cut off wave number which separates the region of stability from instability.  相似文献   

Chhotanagpur granite gneiss in relation to the schistose rocks around Murhu,Ranchi district,Bihar: a structural approach     

D. S. Bhattacharyya  Anjan Ghosal  V. Ravi Kant 《Journal of Earth System Science》1990,99(2):269-277

Structural analysis of the Chhotanagpur gneiss and the adjoining schistose rocks of the Singhbhum Group indicates perfect conformity in their structures on macroscopic, mesoscopic and microscopic scales. This precludes the possibility of the gneissic rocks having intruded into the deformed and metamorphozed schistose rocks. The observed features can be best explained by considering the gneissic rocks as the basement and the schistose rocks as the cover, both deformed and metamorphozed together. However, this does not exclude the possibility of the gneissic rocks being reactivated and intruding elsewhere.  相似文献   

Sensitivity analysis of electromagnetic measurements over exponentially varying conductivity earth models     

R. P. Singh  Yash Kant 《Geophysical Journal International》1995,121(1):111-116

Sensitivity analysis of electromagnetic (EM) measurements is important to quantify the effect of the subsurface conductivity on the measured response. Knowledge of the sensitivity functions helps in solving inverse problems related to field data. In the present paper, we have derived the sensitivity functions for exponentially varying conductivity earth models. The effect of the exponential variation of conductivity has been illustrated graphically on the sensitivity functions. The effect of varying the periods of the electromagnetic waves on the sensitivity functions has also been studied, which gives the characteristic behaviour of the sensitivity functions. This characteristic behaviour provides information about the exponentially decreasing or increasing conductivity earth models.  相似文献   

Experimental Investigations on Laminated Rubber Bearings   总被引：1，自引：0，他引：1  

Sarvesh?Kumar?JainEmail author  Shashi?Kant?Thakkar 《Bulletin of Earthquake Engineering》2005,3(1):129-136

Increasing application of base isolation as a seismic protection method has subsequently increased its analytical and experimental studies. Being the most critical part of the base isolated buildings, accurate evaluation of structural properties and precise modeling of isolation devices is of utmost importance in predicting the response of the buildings during the earthquakes. This technical note is concerned with experimental study on laminated rubber bearings. Free vibration and harmonic base excitation tests are performed on a three-storey building model to evaluate the properties of the structure, efficiency of the system, and effect of base excitations. It is found that these experimental methods can effectively be used for this purpose.  相似文献   

Unplanned urban growth: land use/land cover change in the Guwahati Metropolitan Area,India     

Chandra Kant Pawe 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2018,118(1):88-100

Unplanned urban growth, particularly in developing countries has led to changes in land use/land cover (LULC). Numerous Indian cities face problems of unplanned LULC change due to nominal or non-existent planning efforts compounded by rapid urban population growth. The Guwahati Metropolitan Area (GMA) is one such urban centre. The present study assesses the trajectories of LULC change using Landsat imageries acquired in 1976, 1989, 2002 and 2015. Natural and semi natural vegetated area and artificial and natural water bodies decreased while built-up areas, cultivated and managed areas, and natural and semi natural non-vegetated areas increased. The built-up area increased from 23.9 in 1976 to 115.1 km² in 2015 becoming the dominant land cover class accounting for 41.8% of the total geographical area. During this period, natural and semi natural vegetated land were reduced by 88.9 km² at an annual rate of 2.2 km². Over the years there was an increasing trend of built-up land and cultivated and managed areas in the peripheral areas of the city while natural and semi natural vegetated land diminished. Consequently, as in many other developing countries, there is an urgent need for the governmental authorities and other stakeholders to implement effective urban planning policies.  相似文献   

Time-averaged near-bed suspended sediment concentrations under waves and currents: Comparison of measured and model estimates     

David A. Cacchione  Peter D. Thorne  Yogesh Agrawal  Nicholas J. Nidzieko 《Continental Shelf Research》2008

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