Autoionization rate coefficients for some ions of astrophysical interest     

H. P. Mital  U. Narain 《Solar physics》1978,57(2):341-343

Autoionization rate coefficients for some quadruply and quintuply ionized atoms have been computed in the temperature range 10⁵–10⁸ K. Typical temperature dependence has been found and simple expressions are given for their quick estimation.  相似文献   

Nanoflares and heating of the solar corona     

U. Narain  K. Pandey 《Journal of Astrophysics and Astronomy》2006,27(2-3):93-100

Coronal heating by nanoflares is presented by using observational, analytical, numerical simulation and statistical results. Numerical simulations show the formation of numerous current sheets if the magnetic field is sheared and bipoles have unequal pole strengths. This fact supports the generation of nanoflares and heating by them. The occurrence frequency of transients such as flares, nano/microflares, on the Sun exhibits a power-law distribution with exponent α varying between 1.4 and 3.3. For nanoflares heating α must be greater than 2. It is likely that the nanoflare heating can be reproduced by dissipating Alfven waves. Only observations from future space missions such as Solar-B, to be launched in 2006, can shed further light on whether Alfven waves or nanoflares, heat the solar corona.  相似文献   

Fluid Institutions: Commons in Transition in the Periurban Interface     

Aditya Kumar Singh  Vishal Narain 《社会与自然资源》2019,32(5):606-615

Amidst growing concern about the decline of the commons, this case underscores the importance of understanding how the commons are refashioned and remade to address emerging challenges in periurban spaces. This article describes how institutions surrounding the use of common property resources get transformed and evolve in periurban contexts. What were once johads – common property village ponds – undergo a change in their usage from storing rainwater to storing waste water of the city for irrigation. This emerges as a collective response to the uncertainty attached to the availability of waste water. New institutions evolve with regard to contributions to waste water infrastructure, as well as the appropriation of waste water. Further research should document the changing use of village commons and the emergence of new institutions governing them.  相似文献   

On Coronal Loop Heating by Torsional Alfvén Waves     

U. Narain  P. Agarwal  R.K. Sharma  L. Prasad  B.N. Dwivedi 《Solar physics》2001,199(2):307-315

Heating of coronal loops by linear resonant Alfvén waves, excited by the footpoints motions in the photosphere, has been studied. The analysis of single-layer heating is extended to multilayer heating, in semiempirical treatment. Heating and nonthermal velocities in different layers of loops in X-ray bright points, active regions, and large-scale structures are estimated. The average value of velocity is found to be in agreement with the observations.  相似文献   

Nonlinear Viscous Damping of Surface AlfvÉn Waves in Polar Coronal Holes     

Udit Narain  Rakesh Kumar Sharma 《Solar physics》1998,181(2):287-287

We quantitatively re-examine the nonlinear viscous damping of surface Alfvén waves in polar coronal holes, using recently reported observational data on electron density and temperature and the magnetic field spreading near the edges. It is found that in the nonlinear regime the viscous damping of surface Alfvén waves becomes a viable mechanism of solar coronal plasma heating when strong spreading of magnetic field is taken into account. Our estimations confirm that coronal heating is more pronounced in the nonlinear case than in the linear one in presence of magnetic field spreading.  相似文献   

Bianchi type-VI0 perfect fluid cosmological models with magnetic field     

S. R. Roy  J. P. Singh  S. Narain 《Astrophysics and Space Science》1985,111(2):389-397

In this paper we discuss Bianchi type-VI₀ cosmological models with perfect fluid distribution and magnetic field directed along the axial direction. Einstein's equations have been solved for the condition that the expansion scalar bears a constant ratio to the anisotropy in the direction of a space-like unit vector ⁱ.  相似文献   

On some properties of prominence eruptions and the associated CMEs in solar cycle 23     

Pooja Gupta  Mohit Gupta  Ruby Yadav  Udit Narain 《Astrophysics and Space Science》2014,352(2):395-402

This work includes a study of some properties such as speed, apparent width, acceleration and latitudes, etc. of all types of Prominence Eruptions (PEs) and the associated Coronal Mass Ejections (CMEs) observed during the period of 1997–2006 by Nobeyama Radioheliograph (NORH) and SOHO/LASCO covering the solar cycle 23. The average speed of prominences and associated CMEs are 51 km/sec and 559 km/sec, respectively. The average angular width is 32^° and 74^°, respectively. As expected the associated CMEs are relatively faster and wider than the prominences.  相似文献   

Large-scale alignment of optical polarizations from distant QSOs using coordinate-invariant statistics     

Pankaj Jain  Gaurav Narain  S. Sarala 《Monthly notices of the Royal Astronomical Society》2004,347(2):394-402

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Initiation of CMEs: A review     

Nishant Mittal  Udit Narain 《Journal of Atmospheric and Solar》2010,72(9-10):643-652

Solar coronal mass ejections (CMEs) are a striking manifestation of solar activity seen in the solar corona, which bring out coronal plasma as well as magnetic flux into the interplanetary space and may cause strong interplanetary disturbances and geomagnetic storms. Understanding the initiation of CMEs and forecasting them are an important topic in both solar physics and geophysics. In this paper, we review recent progresses in research on the initiation of CMEs. Several initiation mechanisms and models are discussed. No single model/simulation is able to explain all the observations available to date, even for a single event.  相似文献   

On properties of radio-rich coronal mass ejections     

Joginder Sharma  Nishant Mittal  Vivek Tomar  Udit Narain 《Astrophysics and Space Science》2008,317(3-4):261-265

We have studied properties of the radio-rich coronal mass ejections (CMEs) (observed during 1997–2006) which produce type II (1–14 MHz) i.e. decametric–hectometric or DH radio burst. These DH CMEs are relatively faster and wider than the normal CMEs. The average speed and apparent width of these CMEs is 1048 km/s and 98°, respectively. Majority (about 54%) of DH CMEs decelerate, but about 21% show positive acceleration. The remaining 25% move with little acceleration. These special characteristics of radio-rich CMEs could be used to identify the population of geoeffective CMEs, which are quite relevant to space weather.  相似文献