Application of a stochastic model to the frequency and duration of monsoon rainfall     

P. P. Kamte  K. D. Prasad  S. D. Dahale  V. V. Khade 《Pure and Applied Geophysics》1982,120(1):79-94

The paper deals with an application of a stochastic model to the frequency and duration of precipitation events. With the aid of the model, the magnitudes ofmth highest rainfall amount in 24 hours' duration with 97.5% probability are obtained for various climatic regimes over a tropical monsoon region. There is good agreement between them-day minimum rainfall estimated through the model and the observed value. The model satisfactorily explains the frequency of the extreme rainfall event.  相似文献   

Role of the Deccan volcanics in the reversal of short-period geomagnetic Z-variations at Alibag     

B.J. Srivastava  S.N. Prasad 《Physics of the Earth and Planetary Interiors》1974,9(2):157-160

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Dispersion-flocculation studies on hematite-clay systems     

B. Gururaj  J.P. Sharma  A. Baldawa  S.C.D. Arora  N. Prasad  A.K. Biswas 《International Journal of Mineral Processing》1983,11(4):285-302

Studies have been made on the separability of clay minerals such as kaolinite, illite and montmorillonite from hematite in dispersant-starch flocculant systems. The grossly different dispersibility of hematite from that of clay minerals aided separation by selective dispersion and flocculation. Moderate success has been achieved with a selectivity index nearing 4.0 (average recovery values around 80%).The studies have been extended to hematite recovery and clay rejection from the slimes of the Barsua iron ore washing plant owned by Rourkela Steel Plant, India. Limited success achieved in the starch selective flocculation method has been attributed to the difficulties associated with fine grain size, clay mineraloty and liberation.The ore exhibits the phenomenon of differential grinding. Hematite-rich coarser particles in the slime can be separated by differential settling in dispersant systems followed by selective flocculation in low-starch systems.  相似文献   

A study of the empirical functions of the height fields over India and their relation with the rainfall     

K. D. Prasad  D. R. Sikka 《Journal of Earth System Science》1982,91(3):167-187

The empirical orthogonal functions have been obtained for the individual summer monsoon (June through September) months using the grid point values of monthly 700 mb geopotential heights over Indian region. The data for 21 summer monsoon months for the years 1958 to 1978 have been used in the present computation. The major variance reduction is due to the first three dominant functions accounting over 80% of the total variance in each month. The variance reduction only due to the first function ranges from 45 to 65%. The first function has in-pbase oscillation throughout the area indicating that the area under study is homogeneous and the centre of the oscillation lies over northwest India. The amplitudes of the first function also show generally quasipers stence in their sign within a season. The second function has two centres of action over the region of monsoon trough which are in phase. The third function has also two centres oriented in the east-west direction but they are in the opposite phase. Fairly large values of correlation coefficients between the patterns of the different monsoon months suggest that the patterns for these months corresponding to the first and the second functions respectively are quite similar. The patterns for these months also evolve with time in a related way. The spectrum analysis to the time series of amplitudes indicates the presence of the quasi-periodicity of 3 years during these monsoon months. The amplitudes corresponding to the dominant functions are found to be significantly related with the rainfall of central and western parts of India  相似文献   

Noise-Storm Continua: Power Estimates for Electron Acceleration     

Prasad?SubramanianEmail author  Peter?A.?Becker 《Solar physics》2004,225(1):91-103

We use a generic stochastic acceleration formalism to examine the power L_in (erg s^-1) input to non-thermal electrons that cause noise-storm continuum emission. The analytical approach includes the derivation of the Greens function for a general second-order Fermi process, and its application to obtain the particular solution for the non-thermal electron distribution resulting from the acceleration of a Maxwellian source in the corona. We compare L_in with the power L_out observed in noise-storm radiation. Using typical values for the various parameters, we find that L_in 10²³–10²⁶ erg s^-1, yielding an efficiency estimate L_out/L_in in the range 10^-10 10^-6 for this non-thermal acceleration/radiation process. These results reflect the efficiency of the overall process, starting from electron acceleration and culminating in the observed noise-storm emission.  相似文献   

Reduced order observer based identification of base isolated buildings     

Satish?NagarajaiahEmail author  Prasad?Dharap 《地震工程与工程振动(英文版)》2003,2(2):237-244

The objective of this study is to identify system parameters from the recorded response of base isolated buildings, such as USC hospital building, during the 1994 Northridge earthquake. Full state measurements are not available for identification. Additionally, the response is nonlinear due to the yielding of the lead-rubber bearings. Two new approaches are presented in this paper to solve the aforementioned problems. First, a reduced order observer is used to estimate the unmeasured states. Second, a least squares technique with time segments is developed to identify the piece-wise linear system properties. The observer is used to estimate the initial conditions needed for the time segmented identification. A series of equivalent linear system parameters are identified in different time segments. It is shown that the change in system parameters, such as frequencies and damping ratios, due to nonlinear behavior of the lead-rubber bearings, are reliably estimated using the presented technique. It is shown that the response was reduced due to yielding of the lead-rubber bearings and period lengthening.  相似文献   

Extreme rainfall event of July 25–27, 2005 over Mumbai, West Coast, India     

Anup K. Prasad  Ramesh P. Singh 《Journal of the Indian Society of Remote Sensing》2005,33(3):365-370

Extreme localised rainfall events are part of monsoon system occurring every year. Satellite data (TRMM and other geostationary satellites) together with ground observations will be useful in providing spatial and temporal variability of atmospheric changes. The short and long term variability is required for better understanding of the local and regional climatic conditions through detailed modelling. Such information will play a key role in real time data analysis and dissemination system to the disaster management groups in the country to minimize losses due to these extreme rainfall events.  相似文献   

Tectonic and climatic control of the changes in the sedimentary record of the Karnali River section (Siwaliks of western Nepal)   总被引：1，自引：0，他引：1  

Pascale  Huyghe  Jean-Louis  Mugnier  Ananta Prasad  Gajurel  Bernard  Delcaillau 《Island Arc》2005,14(4):311-327

Abstract A multidisciplinary study was conducted on the section of the Siwalik Group sediments, approximately 5000 m thick, exposed along the Karnali River. Analysis of facies, clay mineralogy and neodymium isotope compositions revealed significant changes in the sedimentary record, allowing discussion of their tectonic or climatic origin. Two major changes within the sedimentary fill were detected: the change from a meandering to a braided river system at ca 9.5 Ma and the change from a deep sandy braided to a shallow sandy braided river system at ca 6.5 Ma. The 9.5‐Ma change in fluvial style is contemporaneous with an abrupt increase of ?_Nd(0) values following a ?_Nd(0) minimum. This evolution indicates a change in source material and erosion of Lesser Himalayan rocks within the Karnali catchment basin between 13 and 10 Ma. The tectonic activity along the Ramgarh thrust caused this local exhumation. By changing the proximity and morphology of relief, the forward propagation of the basal detachment to the main boundary thrust was responsible for the high gradient and sediment load required for the development of the braided river system. The change from a deep sandy braided to a shallow sandy braided river system at approximately 6.5 Ma was contemporaneous with a change in clay mineralogy towards smectite‐/kaolinite‐dominant assemblages. As no source rock change and no burial effect are detected at that time, the change in clay mineralogy is interpreted as resulting from differences in environmental conditions. The facies analysis shows abruptly and frequently increasing discharges by 6.5 Ma, and could be linked to an increase in seasonality, induced by intensification of the monsoon climate. The major fluvial changes deciphered along the Karnali section have been recognized from central to western Nepal, although they are diachronous. The change in clay mineralogy towards smectite‐/kaolinite‐rich assemblages and the slight decrease of ?_Nd(0) have also been detected in the Bengal Fan sedimentary record, showing the extent and importance of the two major events recorded along the Karnali section.  相似文献   

Study of Structural Disorder in Natural Tourmalines by Infrared Spectroscopy   总被引：1，自引：0，他引：1  

P.S.R. Prasad   《Gondwana Research》2005,8(2):265-270

Fourier Transformation Infrared (FTIR) spectroscopy in the range 2000-10000 cm^-1 was used to examine tourmalines from metarhyolites near Majjur within the Gadag Schist Belt and are compared with those from known compositions from quartz vein from gold mineralised area. FTIR spectra in this region are comprised of fundamental and combinational vibrational modes of hydroxyl ions delineating their structural environment. In these samples three fundamental vibrations observed at 3730-3720, 3637-3627 and 3550-3500 cm^-1 and combination modes at 4529, 4454, 4356 and 4238 cm^-1, and the Electron Probe analysis indicate that the tourmalines could be classified in to dravite-schrol series. However, additional shoulder mode observed around 3490 cm^-1 in tourmaline from Gadag Schist Belt, indicates structural disorder.  相似文献   

Lunar ranging instrument for Chandrayaan-1     

J. A. Kamalakar  K. V. S. Bhaskar  A. S. Laxmi Prasad  R. Ranjith  K. A. Lohar  R Venketeswaran  T. K. Alex 《Journal of Earth System Science》2005,114(6):725-731

Lunar Laser Ranging Instrument (LLRI) proposed for the first Indian lunar mission Chandrayaan-1 is aimed to study the topography of the Moon’s surface and its gravitational field by precisely measuring the altitude from a polar orbit around the Moon. Altimetry data close to the poles of the Moon would also be available from the instrument, which was not covered by earlier missions. This instrument supplements the terrain mapping camera and hyperspectral imager payloads on Chandrayaan-1. The instrument consists of a diode pumped Nd:YAG pulsed laser transmitter having 10 nsec pulse width and a receiver system. The receiver system features 17 cm diameter Ritchey—Chrétien collecting optics, Si Avalanche Photo Detector (APD), preamplifiers, constant fraction discriminators, time-of-flight measurement unit and spacecraft interface. Altimeter resolution of better than 5 m is targeted. The received signal strength of LLRI depends on laser pulse backscatter from the Moon’s surface. Moon’s surface being a poor reflector, the choice of receiver size and its type and the selection of detector play an important role in getting a good signal-to-noise ratio and in turn achieving the target resolution. At the same time, the spacecraft puts a limitation on payload size and weight. This paper discusses the proposed LLRI system for Chandrayaan-1 and signal-to-noise ratio estimation.  相似文献