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Browsing by Author "Venkatakrishnan, P"

Browsing by Author "Venkatakrishnan, P"

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  • A New Technique for Solar Imaging Spectro-polarimetry using Shack-Hartmann and Fabry-Perot 
    Gosain, S; Sankarasubramanian, K; Venkatakrishnan, P; Bayanna, A. R (Astronomical Society of the Pacific, 2012-12)
    A new technique for solar imaging spectro-polarimetry is presented. Using the combination of a Shack-Hartmann (SH) and a Fabry-Pérot (FP) interferometer, high-cadence spectroscopic observations can be obtained at discrete ...
  • Nonlinear development of convective instability within slender flux tubes. I - Adiabatic flow 
    Venkatakrishnan, P (Indian Academy of Sciences, 1983-06)
    The nonlinear development of convective instability within slender flux tubes is studied using the method of characteristics. It is seen that the initial magnetic field influences the development of the instability. The ...
  • Nonlinear development of convective instability within slender flux tubes. II - The effect of radiative heat transport 
    Venkatakrishnan, P (Indian Academy of Sciences, 1985-03)
    Inclusion of radiative heat transport in the energy equation for a slender flux tube leads to oscillations of the tube. The amplitude of the oscillations depends on the radius of the tube when lateral heat exchange alone ...
  • Nonlinear response of slender magnetic flux tubes to external pressure fluctuations 
    Venkatakrishnan, P (Springer, 1986-04)
    The effect of applying external pressure fluctuations on slender flux tubes is studied as a nonlinear initial value problem. It is shown that persistent nonlinear resonant response to pressure fluctuations is possible for ...
  • Nonpotential magnetic fields at sites of gamma-ray flares 
    Hagyard, M. J; Venkatakrishnan, P; Smith, J. B. Jr (American Astronomical Society, 1990-06)
    The relation between the degree of nonpotentiality of photospheric magnetic fields and the occurrence of gama-ray flares is examined to determine whether there are special signatures of the stressed fields for this type ...
  • Observability of Coronal Heating Processes 
    Venkatakrishnan, P (Kluwer Academic Publishers, 1996)
    The mechanisms that could possibly heat the corona are briefly reviewed with emphasis on their observability. Observing enhanced wave flux at footpoints of active regions would confirm wave heating. Observation of nonthermal ...
  • On the absorption of He I 10830 Å line by spicules 
    Venkatakrishnan, P; Jain, S. K (Astronomical Society of India, 1983)
    The possible applications of the time-dependent measurements of the equivalent width of the He I 10830 A line for a better understanding of the growth of spicules and the evolution of coronal holes and x-ray bright points ...
  • On the correlation between line width and line depth of the solar HeI 1083 NM line 
    Venkatakrishnan, P; Sakurai, T; Suematsu, Y; Ichimoto, K (Astronomical Society of India, 1997)
    Seven sets of spectra in the region of the HeI 1083 nm absorption line of the active region NOAA 7558 + 7562 near the west limb, obtained at Norikura Solar Observatory, National Astronomical Observatory, Japan have been ...
  • On the evaluation of magnetic shear from H-alpha pictures 
    Venkatakrishnan, P (Kluwer Academic Publishers, 1993-01-10)
    It is shown that pre-flare activity in H-alpha filaments is unrelated to changes in magnetic shear. Changes in the shear angle are found to be related to either redeployment of the sources of magnetic flux relative to the ...
  • On the flare induced high-frequency global waves in the sun 
    Kumar, B; Mathur, S; García, R. A; Venkatakrishnan, P (Institute of Physics, 2010-03-01)
    Recently, Karoff & Kjeldsen presented evidence of strong correlation between the energy in the high-frequency part (5.3 < ν < 8.3 mHz) of the acoustic spectrum of the Sun and the solar X-ray flux. They have used disk-integrated ...
  • On the line profile changes observed during the X2.2 class flare in the active region NOAA 11158 
    Bayanna, A. R; Kumar, B; Venkatakrishnan, P; Mathew, S. K; Ravindra, B; Mathur, S; Garcia, R. A (IOP Publishing, 2014-02)
    The solar active region NOAA 11158 produced a series of flares during its passage through the solar disk. The first major flare (of class X2.2) of the current solar cycle occurred in this active region on 2011 February 15 ...
  • On the Rapid Variations of Solar Magnetic Fields 
    Venkatakrishnan, P; Kumar, B; Ravindra, B (Astronomical Society of India, 2003)
    We report on the rapid variations of solar magnetic fields that appear to be enhanced significantly above the background variability, at a few locations within the solar active regions, as observed with the Michelson Doppler ...
  • On the saturation of the refractive index structure function. I - Enhanced hopes for long baseline optical interferometry 
    Venkatakrishnan, P; Chatterjee, S (Royal Astronomical Society, 1987-01)
    The Kolomogorov- Obukhov law for the refractive index structure function is shown to be only an approximation valid in the inertial sub range of turbulence. The inclusion of saturation effects for larger separations leads ...
  • On the saturation of the refractive index structure function. II - Influence of the correlation length on astronomical 'seeing' 
    Venkatakrishnan, P (Royal Astronomical Society, 1987-12)
    A physical length scale in the wavefront corresponding to the parameter (r/sub0/) characterizing the loss in detail in a long exposure image is identified, and the influence of the correlation scale of turbulence as r/sub ...
  • Onset of Hydrodynamic Non-Equilibrium in Helmet Streamers 
    Venkatakrishnan, P (Kluwer Academic Publishers, 1996-06)
    The steady-state solar wind solution is examined for different geometries of the flow tube that mimics a helmet streamer. Onset of non-equilibrium is seen whenever the spatial variation of the flow geometry crosses critical ...
  • Optical astronomyusing radio techniques:Imaging capella with unprecedented resolution 
    Venkatakrishnan, P (Indian Academy of Sciences, 1996-08)
  • Performance Evaluation of Adaptive Optics Systems 
    Sridharan, R; Raja Bayanna, A; Srivastava, N; Kumar, B; Ravindra, B; Gupta, S. K; Jain, N; Ambastha, A; Venkatakrishnan, P (Astronomical Society of India, 2003)
    Adaptive Optics (AO) systems improve the resolution of ground based telescopes and allow for long exposure images. Their performance depends on the seeing conditions at the time of observations. In this paper, we evaluate ...
  • A personal-computer-based imaging Stokes polarimeter for solar observations 
    Ananth, A. V; Venkatakrishnan, P; Narayanan, R. S; Bhattacharyya, J. C (Springer, 1994-05)
    For measurements of vector magnetic field over solar active regions, a Stokes polarimeter for studying the polarization profiles on selected spectral lines is described. This paper gives details of the relevant charged ...
  • A phenomenological, kinematical model of the coronal magnetic fields in terms of thin flux tubes rising from the photosphere 
    Gokhale, M. H; Venkatakrishnan, P (Indian Academy of Sciences, 1978-11)
    A kinematical model is necessary for understanding the gross structure of the coronal magnetic field and its slow evolution in consistency with the small scale structure of the photospheric fields. Here we have developed ...
  • Proposed visible emission line space solar coronagraph 
    Singh, J; Prasad, B. R; Venkatakrishnan, P; Sankarasubramanian, K; Banerjee, D; Bayanna, R; Mathew, S; Murthy, J; Subramaniam, P; Ramesh, R; Kathiravan, S; Nagabhushana, S; Mahesh, P. K; Manoharan, P. K; Uddin, W; Sriram, S; Amit Kumar; Srivastava, N; Koteswara Rao; Nagendra, C. L; Chakraborty, P; Sriram, K. V; Venkateswaran, R; Krishnamurthy, T; Sreekumar, P; Sarma, K. S; Murthy, R; Navalgund, K. H; Samudraiah, D. R. M; Narayan Babu, P; Patra, A (Indian Academy of Sciences, 2011-01-25)
    The outer atmosphere of the sun – called the corona – has been observed during total solar eclipse for short periods (typically < 6 min), from as early as the eighteenth century. In the recent past, space-based instruments ...

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