Mass loss from Wolf-Rayet stars     

Mahendra Singh  U. S. Chaubey 《Astrophysics and Space Science》1986,124(2):389-396

The observed times of minimum light derived from the photometry of the Wolf-Rayet eclipsing binary stars CQ Cep and V444 Cyg are used to estimate the mass-loss rate of the Wolf-Rayet components in several modes of mass-loss and mass-exchange.  相似文献   

Spectrophotometric observations and evolutionary status of ten Be stars     

Mahendra Singh  U. S. Chaubey 《Astrophysics and Space Science》1987,129(2):251-260

The continuum energy distribution data of ten Be stars — namely, HR 1761, HR 1786, HR 1820, Ori, Ori, OT Gem, Lyr, HR 7983, Cyg, and 59 Cyg — have been presented in the wavelength range 3200–8000 Å. The observed energy distribution curve shows near infrared excess for majority of Be stars and a double Balmer jump for HR 8047 and HR 8146. Empirical effective temperatures of these stars have been estimated by comparing the observed continuum energy distributions with that of computed theoretical models given by Kurucz (1979).On the basis of an HR diagram with evolutionary tracks for different solar masses the masses of these Be stars have been estimated. Position of these studied stars on the HR diagram suggests that these Be stars may be in the stage of core contraction after exhausting hydrogen at the centre and have undergone hydrogen exhaustion in the thick shell.  相似文献   

Spectrophotometry of some Be stars     

Mahendra Singh 《Astrophysics and Space Science》1986,120(1):133-138

The continuum energy distribution of six Be stars, namely 25 Cyg, 31 Peg, HR 8758, 14 Lac, 12 Vul, and Psc, in the wavelength region 3200–7800 Å, are presented. Comparing the observed energy distributions with those of theoretical models given by Kurucz (1979), their effective temperatures are determined.A near-infrared excess emission at wavelengths above 6000 Å is seen in most of the stars.  相似文献   

Initial mass functions of Wolf-Rayet stars     

Mahendra Singh 《Astrophysics and Space Science》1986,124(1):101-104

On the basis of evolutionary tracks on the HR diagram the lower limit of initial mass functions for Wolf-Rayet stars are estimated. The lower limit to the initial masses of the Wolf-Rayet stars seems to be 20M and in this respect there is no significant difference between the WN and WC stars.  相似文献   

Applicability of Critical State Concept in Determination of Triaxial Strength of Non-Persistent Jointed Rock     

Shaunik  Divya  Singh  Mahendra 《Geotechnical and Geological Engineering》2021,39(6):4615-4638

Geotechnical and Geological Engineering - Rocks encountered in civil and mining engineering structures are generally intersected by discontinuities. The triaxial strength behaviour of a jointed...  相似文献   

Seismic analysis of multiply supported secondary systems with dynamic interaction effects     

Ricardo A. Burdisso  Mahendra P. Singh 《地震工程与结构动力学》1987,15(8):1005-1022

For a proper response spectrum analysis of a secondary system with multiple supports, the seismic inputs are required to be defined in terms of the auto and cross floor response spectra. If no feed-back or interaction effect from the secondary system to its supporting primary structure is suspected, these inputs can be developed by a direct analysis of the supporting structure alone. However, sometimes the effect of the interaction on the secondary system response can be quite significant. Herein, a method is developed to incorporate the feed-back effect, through proper modification of the interaction-free floor spectrum inputs. The interaction coefficients are used to effect such modifications in different floor spectral quantities. A procedure for the calculation of the interaction coefficients is proposed. The modified floor spectra when used as inputs to the secondary system do introduce the interaction effect in the secondary system response. A successful application of this method is demonstrated by numerical examples of secondary systems with three different secondary-to-primary system mass ratios.  相似文献   

Land Cover Mapping for Namdapha National Park (Arunachal Pradesh), India Using Harmonized Land Cover Legends     

Mahendra S. Lodhi  Prasanna K. Samal  Shivaji Chaudhry  L. M. S. Palni  P. P. Dhyani 《Journal of the Indian Society of Remote Sensing》2014,42(2):461-467

Since last few decades RS-GIS is playing vital role in studying and mapping spatiotemporal responses of land cover, however, as a matter of fact, the mapping outputs largely depend on the expert's/user's preferences because location specific and people specific land cover classification systems are adopted autonomously for image classification in GIS. This may actually lead to an ambiguous definition of a particular land cover type when such different maps are compared at global level. In 1993, FAO and UNEP started efforts for development of a software tool know as LCCS which is a comprehensive standardized tool capable of providing land cover characterization to all possible land cover types in the world regardless of spatial relevance, mapping scale, data collection method etc. Adding to the global efforts of land cover legend harmonization and mapping, this study presents development of harmonized land cover legends for Namdapha National Park located in north-eastern Indian Himalayan region using LCCS and subsequent mapping. The potential of Remote Sensing (RS) and Geographical Information Systems (GIS) in forest/land cover mapping is very well recognized. Therefore, adopting the developed harmonized legends for the study area, land cover mapping was done using RS-GIS approach.  相似文献   

Spatially resolved methane band photometry of Saturn: I. Absolute reflectivity and center-to-limb variations in the 6190-, 7250-, and 8900-Å bands     

Robert A. West  Martin G. Tomasko  Bradford A. Smith  Mahendra P. Wijesinghe  Lyn R. Doose  Harold J. Reitsema  Stephen M. Larson 《Icarus》1982,51(1):51-64

We present spatially resolved measurements of Saturn's absolute reflectivity in methane bands at 6190, 7250, and 8900 Å and in nearby continuum regions. Images were obtained through narrow-band interference filters with a 500 × 500-pixel charge-coupled device. Band/continuum ratios were measured to high accuracy by referencing to the ring brightness in each image. Several data processing techniques enhanced the quality of the observations. These are the use of the ring symmetry to find center position and orientation, accurate subtraction of ring light, and constrained image deconvolution. Uncertainty in the continuum absolute reflectivity is ±10%. Uncertainties in band/continuum ratios are from one to several percent. The Equatorial Zone was much brighter than any other latitude in the strong 8900 band image. Northern mid-latitudes were brighter than southern mid-latitudes. The latter observation indicates fewer high-altitude aerosols in the south, a possible result of atmospheric dynamics or seasonal sublimation of NH₃ crystals. The data are tabulated and presented in a form suitable for quantitative scattering model analyses.  相似文献   

Characteristics of chaotic pulse trains generated by lightning flashes     

Chandima Gomes  Vernon Cooray  Mahendra Fernando  Raul Montano  Upul Sonnadara 《Journal of Atmospheric and Solar》2004,66(18):428

Pulse trains of irregular pulse characteristics and erratic amplitudes are observed in lightning flashes. These are termed “chaotic pulse trains” in this study. The average width of the individual pulses of these pulse trains is in the range of a few microseconds, with the lower limit of individual measurements extending into the sub-microsecond region. The typical pulse separation lies in the range of 2–. The pulse duration shows a consistent distribution with the most probable value at 400–. Chaotic pulse trains occur most often immediately prior to subsequent strokes. However, they occur also a few milliseconds to several tens of milliseconds prior to return strokes and sometimes do not precede return strokes at all. Twenty-six percent of the total subsequent strokes recorded in this study were preceded by chaotic pulse trains. A few of these pulse trains have occurred in a sequence of several tens of millisecond intervals in between return strokes. We have also found them to occur within very intense cloud flashes. These chaotic pulse trains have features that are different from those of other known pulse trains reported in the lightning literature. Hence, they may be caused by a physical process that has not yet been identified.  相似文献   

A response spectrum approach for seismic performance evaluation of actively controlled structures     

Mahendra P. Singh  Sarbjeet Singh  Enrique E. Matheu 《地震工程与结构动力学》2000,29(7):1029-1051

To evaluate and measure the effectiveness of active control schemes in reducing the response of structures subjected to earthquake excitations, it is common to use recorded or artificially generated earthquakes as input motions. This paper introduces the response spectrum analysis to evaluate linear control systems for seismic inputs defined by code‐prescribed or site‐specific ground response spectra. Using such a method one can evaluate a control system in a single analysis for the ensemble of time histories that are represented by the input response spectra. The response spectrum analysis can also facilitate the implementation of comprehensive parametric studies. A generalized response spectrum method is used to analyse systems with non‐symmetrical matrices that are caused by the general nature of the control actions imposed on the structure. The application of the method is demonstrated on several numerical examples of a building structure where the control force is applied through an active tuned‐mass damper. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献