The kilosecond variability of X-ray sources in nearby galaxies     

Soma Mandal  Ranjeev Misra  Gulab C. Dewangan 《天体物理学报》2013,(12):1445-1454

Chandra observations of 17 nearby galaxies were analyzed and 166 bright sources with X-ray counts 〉 100 were chosen for temporal analysis. Fractional root mean square （rms） variability amplitudes were estimated for light curves, binned at 4 kilosecond （ks）, with length 〈 40 ks. While there are nine ultra-luminous X- ray sources （ULXs） with unabsorbed luminosity （in the 0.3-8.0 keV band） L 〉 1039 erg s-1 in the sample for which the fractional rms variability is constrained to be 〈 10%, only two of them show variability. One of the variable ULXs exhibits a secular transition and has an ultra-soft spectrum with temperature - 0.3 keV while the other is a rapidly varying source in NGC 0628, which has previously been com- pared to the Galactic microquasar GRS 1915＋105. These results seem to indicate that ULXs are typically not highly variable on ks timescales, except for some ultra-soft ones. Among the relatively low luminosity sources （L - 10^38 erg s-1）, we find five of them to be variable. Apart from an earlier known source in NGC 1569, we identify a source in NGC 2403 that exhibits persistent high amplitude fluctuations. In general, the variability of the sources does not seem to be correlated with hardness, which indicates that they may not be due to variations in any absorbing material, but instead could reflect instabilities in the inner accretion disk.  相似文献   

Mechanical Aspects of Micropiles Made of Reinforced Polyurethane Resins     

R. Valentino  E. Romeo  A. Misra 《Geotechnical and Geological Engineering》2013,31(2):463-478

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A study-based ranking of LiDAR data visualization schemes aided by georectified aerial images     

Suddhasheel Ghosh  Bharat Lohani  Neeraj Misra 《制图学和地理信息科学》2013,40(2):138-150

Light Detection and Ranging (LiDAR) collects dense 3D topographic information in the form of points. LiDAR data can be displayed either through direct rendering of the point cloud or by generalizing features extracted through classification or segmentation. We are working in the domain of visualizing LiDAR data sets and have developed certain pipelines for visualization. These pipelines have been presented elsewhere. We present a technique for the evaluation of visualization schemes for LiDAR data, by conducting a visualization experience survey for 13 pre-processing and visualization schemes where 60 participants rated these schemes on a 10 point scale on a questionnaire. The paper establishes a ranking for the different visualization schemes described herein. Finally, this paper establishes that our heuristic-based algorithm (presented elsewhere) performs almost equal to a classification-based visualization pipeline made using professional software. We believe that the presented technique can be used to assess other geospatial visualization schemes.  相似文献   

Daily atmospheric variability in the South American monsoon system   总被引：1，自引：1，他引：0  

V. Krishnamurthy  Vasubandhu Misra 《Climate Dynamics》2011,37(3-4):803-819

The space–time structure of the daily atmospheric variability in the South American monsoon system has been studied using multichannel singular spectrum analysis of daily outgoing longwave radiation. The three leading eigenmodes are found to have low-frequency variability while four other modes form higher frequency oscillations. The first mode has the same time variability as that of El Nino-Southern Oscillation (ENSO) and exhibits strong correlation with the Pacific sea surface temperature (SST). The second mode varies on a decadal time scale with significant correlation with the Atlantic SST suggesting an association with the Atlantic multidecadal oscillation (AMO). The third mode also has decadal variability but shows an association with the SST of the Pacific decadal oscillation (PDO). The fourth and fifth modes describe an oscillation that has a period of about 165 days and is associated with the North Atlantic oscillation (NAO). The sixth and seventh modes describe an intraseasonal oscillation with a period of 52 days which shows strong relation with the Madden-Julian oscillation. There exists an important difference in the variability of convection between Amazon River Basin (ARB) and central-east South America (CESA). Both regions have similar variations due to ENSO though with higher magnitude in ARB. The AMO-related mode has almost identical variations in the two regions, whereas the PDO-related mode has opposite variations. The interseasonal NAO-related mode also has variations of opposite sign with comparable magnitudes in the two regions. The intraseasonal variability over the CESA is robust while it is very weak over the ARB region. The relative contributions from the low-frequency modes mainly determine the interannual variability of the seasonal mean monsoon although the interseasonal oscillation may contribute in a subtle way during certain years. The intraseasonal variability does not seem to influence the interannual variability in either region.  相似文献   

Nighttime E region plasma irregularities over an equatorial station Trivandrum     

H.S.S. Sinha  R. Pandey  Shweta Sharma  R.N. Misra 《Journal of Atmospheric and Solar》2011,73(17-18):2444-2452

In situ measurements of electron density were made over Trivandrum (8.5°N, 76.9°E) during nighttime to study E-region plasma density irregularities. Irregularities, with vertical scale sizes from a few km to 15 cm, were detected during rocket ascent and descent. Electron density profiles during ascent and descent of an earlier nighttime rocket flight from Trivandrum are also presented. Some of the important results are as follows: (i) horizontal gradients in electron density exist in 110–120 km region with horizontal scale size of at least 40 km, (ii) based on the presence/absence of electron density structures during ascent and descent of both flights, the horizontal distance over which the gradient drift instability operates is found to be at least 80 km and 90 km, for both the flights, (iii) observed irregularities in regions of negative density gradient are suggested to be produced through the gradient drift instability (GDI) driven by vertical polarization electric field as well as by electric field produced through wind shears and those in positive gradient regions by wind driven GDI, (iv) largest irregularity amplitude (≈30%) was associated with steepest gradients and so was the presence of smallest vertical scale sizes (12 m to 15 cm), which were absent at other altitudes, (v) the spectral index of irregularities was in the range of ?2.2±0.2 for large scales (few kilometers>λ>50 m), ?3.25±0.25 for medium scales (50 m>λ>10 m) and ?2.6±0.1 for smaller scales (10 m>λ>1 m) and (vi) irregularities in large and medium scales are expected to be produced directly through GDI and the small and sum-meter scales through non-linear GDI.  相似文献   

Modeling the effects of aerosols to increase rainfall in regions with shortage     

J. B. Shukla  Shyam Sundar  A. K. Misra  Ram Naresh 《Meteorology and Atmospheric Physics》2013,120(3-4):157-163

It is well known that the emissions of hot gases from various power stations and other industrial sources in the regional atmosphere cause decrease in rainfall around these complexes. To overcome this shortage, one method is to introduce artificially conducive aerosol particles in the atmosphere using aeroplane to increase rainfall. To prove the feasibility of this idea, in this paper, a nonlinear mathematical model is proposed involving five dependent variables, namely, the volume density of water vapour, number densities of cloud droplets and raindrops, and the concentrations of small and large size conducive aerosol particles. It is assumed that two types of aerosol particles are introduced in the regional atmosphere, one of them is of small size CCN type which is conducive to increase cloud droplets from vapour phase, while the other is of large size and is conducive to transform the cloud droplets to raindrops. The model is analyzed using stability theory of differential equations and computer simulation. The model analysis shows that due to the introduction of conducive aerosol particles in the regional atmosphere, the rainfall increases as compared to the case when no aerosols are introduced in the atmosphere of the region under consideration. The computer simulation confirms the analytical results.  相似文献   

The fidelity of a regional coupled model in capturing the relationship between intraseasonal variability and the onset/demise of the Indian summer monsoon     

Karmakar  Nirupam  Misra  Vasubandhu 《Climate Dynamics》2020,54(11):4693-4710

Climate Dynamics - Onset and demise of the Indian summer monsoon (ISM) and intraseasonal variability (ISV) embedded within the ISM are dominant climatological phenomena observed over the Indian...  相似文献   

Shock waves in a self-gravitating gas     

Santosh Kumar  N. K. Misra 《Astrophysics and Space Science》1990,168(1):39-57

The CCW method (see Chester, 1854; Chisnell, 1955; Whitham, 1958) has been used to investigate the propagation of diverging shock waves through an ideal gas under its own gravitation having an initial density distribution ₀ = exp(–r , where is the density at the plane/axis/origin, respectively, for plane, cylindrical, and spherical symmetry of the shock and, is non-dimensional constant, for the two situations: viz., (i) when the shock is weak and (ii) when it is strong, simultaneously. Analytical relations for shock velocity and shock strength have been obtained. Expressions for the pressure, the density and the particle velocity immediately behind the shock have been derived. Their numberical estimates for plane and cylindrical symmetry of the shock, have been computed.  相似文献   

Corrected Hawking temperature of (2+1) dimensional BTZ (Banados-Teitelboim-Zanelli) rotating Black Hole by using tunneling method     

C. R. Mahanta  Rajesh Misra 《Astrophysics and Space Science》2013,348(2):437-440

We study the (2+1) dimensional BTZ (Banados-Teitelboim-Zanelli) rotating Black Hole. Along with the scalar field it obeys the Klein-Gordon equation of motion. We use the dragging coordinate system to isolate the r–t sector from the metric. By considering the massless particle and scalar field, we calculate the corrected Hawking temperature with the help of tunneling method.  相似文献   

Effect of data gaps on correlation dimension computed from light curves of variable stars     

Sandip V. George  G. Ambika  R. Misra 《Astrophysics and Space Science》2015,357(1):1-11

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