A5038078688- Solar and Space Plasma Dynamics
- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Surfactants and Colloidal Systems
- Solar Radiation and Photovoltaics
- Spectroscopy and Quantum Chemical Studies
- Ionosphere and magnetosphere dynamics
- Electrostatics and Colloid Interactions
- Polymer crystallization and properties
- Thermodynamic properties of mixtures
- Advanced Polymer Synthesis and Characterization
- Polymer Nanocomposites and Properties
- Natural Fiber Reinforced Composites
- Photochemistry and Electron Transfer Studies
- Analytical Chemistry and Chromatography
- Geomagnetism and Paleomagnetism Studies
- Characterization and Applications of Magnetic Nanoparticles
- Intermetallics and Advanced Alloy Properties
- Nuclear Physics and Applications
- Aluminum Alloys Composites Properties
- Advanced Welding Techniques Analysis
- Magnetic and Electromagnetic Effects
- Chemical and Physical Properties in Aqueous Solutions
- Astrophysics and Star Formation Studies
- Geology and Paleoclimatology Research
Indian Institute of Astrophysics
2022-2024
University of Oslo
2018-2022
Galgotias University
2022
UGC DAE Consortium for Scientific Research
2004-2019
Stockholm University
2016-2018
AlbaNova
2016-2018
Max Planck Institute for Solar System Research
2011-2017
Indian Institute of Technology Delhi
2017
Technische Universität Braunschweig
2011
Bhabha Atomic Research Centre
2000-2010
Context. Active regions are the most prominent manifestations of solar magnetic fields; their generation and dissipation fundamental problems in physics. Light bridges commonly present during sunspot decay, but a comprehensive picture role removal photospheric field is still lacking.
Abstract Spicules have often been proposed as substantial contributors toward the mass and energy balance of solar corona. While their transition region (TR) counterpart has unequivocally established over past decade, observations concerning coronal contribution spicules contested. This is mainly attributed to lack adequate coordinated observations, small spatial scales, highly dynamic nature, complex multithermal evolution, which are observed at limit our current observational facilities....
Spicules are elongated, jet-like structures that populate the solar chromosphere and rooted in lower atmosphere. In recent years, high-resolution observations advanced numerical simulations have provided insights into their properties, structures, dynamics. However, formation mechanism of spicules, particularly more dynamic type II which primarily found quiet Sun coronal holes, remains elusive. This study explores whether Ellerman bombs (QSEBs), ubiquitous small-scale magnetic reconnection...
Abstract Recent high-resolution solar observations have unveiled the presence of small-scale loop-like structures in lower atmosphere, often referred to as unresolved fine structures, low-lying loops, and miniature hot loops. These undergo rapid changes within minutes, their formation mechanism has remained elusive. In this study, we conducted a comprehensive analysis two small loops utilizing data from Interface Region Imaging Spectrograph (IRIS), Goode Solar Telescope (GST) at Big Bear...
We characterize, for the first time, type-II spicules in Ca II K 3934 Å using CHROMIS instrument at Swedish 1 m Solar Telescope. find that their line formation is dominated by opacity shifts with 3 minimum best representing velocity of spicules. The 2 features are either suppressed Doppler-shifted or enhanced via increased contribution from lower layers, leading to strongly but unshifted peaks, widening towards core as consistent upper-layer removal Doppler-shift. identify spicule spectra...
Context. Magnetic reconnection in the deep solar atmosphere can give rise to enhanced emission Balmer hydrogen lines, a phenomenon known as Ellerman bombs (EBs). It is most common observe EBs H α and β spectral lines. High-quality shorter-wavelength line observations of are rare, but have potential provide highly resolved view on magnetic reconnection. Aims. We aim evaluate ε 3970 Å an EB diagnostic by analyzing high-quality different Methods. Observations targets viewing angles were...
Quiet-Sun Ellerman bombs (QSEBs) are small-scale magnetic reconnection events in the lower solar atmosphere. Sometimes, they exhibit transition region counterparts, known as ultraviolet (UV) brightenings. Magnetic field extrapolations suggest that QSEBs can occur at various locations of a fan-spine topology, with UV brightening occurring null point through common process. We aim to understand how more complex configurations such interacting topologies cause dynamic phenomena were detected...
We study the velocity structure of penumbral filaments in deep photosphere to obtain direct evidence for convective nature sunspot penumbrae. A was observed at high spatial resolution with 1 m Swedish Solar Telescope photospheric C i 5380 Å absorption line. The Multi-Object Multi-Frame Blind Deconvolution method is used image restoration and straylight filtered out. report here discovery clear redshifts line multiple locations filaments. For example, bright head show larger concentrated...
Context. Ellerman bombs (EBs) are short-lived emission features, characterised by extended wing in hydrogen Balmer lines. Until now, no distinct signature of EBs has been found the He i 10 830 Å line, and conclusive observations D3 have never reported.
Aims. The fine-structure of the magnetic field in a sunspot penumbra upper chromosphere is to be explored and compared that photosphere.
Ellerman Bomb-like brightenings of the hydrogen Balmer line wings in quiet Sun (QSEBs) are a signature fundamental process magnetic reconnection at smallest observable scale solar lower atmosphere. We analyze high spatial resolution observations (0.1 arcsec) obtained with Swedish 1-m Solar Telescope to explore signatures QSEBs H$\beta$ line. find that ubiquitous and uniformly distributed throughout Sun, predominantly occurring intergranular lanes. up 120 FOV for single moment time; this is...
The force-free parameter α, also known as helicity or twist parameter, bears the same sign magnetic under some restrictive conditions. single global value of α for a whole active region gives degree per unit axial length. We investigate effect polarimetric noise on calculation and energy an analytical bipole. bipole has been generated using field approximation with constant energy. parameters obtained from are used to generate Stokes profiles Unno–Rachkovsky solutions polarized radiative...
Context. Magnetic reconnection in the deep solar atmosphere can give rise to enhanced emission Balmer hydrogen lines, a phenomenon referred as Ellerman bombs. Recent high-quality H β observations indicate that bombs are more common than previously thought, and it was estimated at any time, about half million present quiet Sun. Aims. We performed an extensive statistical characterization of quiet-Sun (QSEBs) these new observations. Methods. analyzed 1 h dataset Sun observed with Swedish 1-m...
Abstract Mixtures of polystyrene and high density polyethylene were injection molded from recycled virgin polymers to generate cocontinuous structures. The mechanical properties these blends evaluated assess their conformance rule mixtures behavior in general identify areas synergy or incompatibility specific. Flexural tensile data for showed that generally the are not additive, except a region composition near 35/65 PS/HDPE has been identified previously materials. Analysis crystallinity...
Combined small-angle neutron scattering (SANS) and x-ray (SAXS) studies have been performed on charged micelles of anionic surfactants alkali metal dodecyl sulphate (MDS, M = Li, Na, Rb Cs) in aqueous solution. The dimensions the obtained using SANS as neutrons are mostly scattered by hydrogenous core micelles. contrast for head groups counterions is very small, so they not seen with neutrons. On other hand, x-rays electron density fluctuation, which proportional to atomic number, thus used...
Context. The He i 1083 nm is a powerful diagnostic for inferring properties of the upper solar chromosphere, in particular magnetic field. basic formation line one-dimensional models well understood, but influence complex three-dimensional structure chromosphere and corona has however never been investigated. This must play an essential role because images taken show structures with widths down to 100 km.
Spectroscopic observations of the emission lines formed in solar transition region (TR) commonly show persistent downflows order 10--15 km/s. The cause such downflows, however, is still not fully clear and has remained a matter debate. We aim to understand by studying coronal TR responses recently reported chromospheric downflowing rapid red shifted excursions (RREs), their impact on heating atmosphere. have used two sets coordinated data from SST, IRIS, SDO for analyzing response RREs...
The effect of hydrotropes, sodium salts butyl benzene sulfonate (Na-BBS), viz., n-butyl (Na-nBBS), iso-butyl (Na-iBBS), and tert-butyl (Na-tBBS), on microstructures cetyl trimethylammonium bromide (CTAB) in aqueous solutions has been studied using small-angle neutron scattering (SANS) viscosity changes. CTAB increased with the addition but differently different isomers. This behavior is attributed to structural differences hydrotropes. SANS studies indicated growth micelles hydrotropes while...
The effect of head group polarity and spacer chain length bis-cationic surfactants on shape, size rheology surfactant aggregates in aqueous solution has been investigated through small angle neutron scattering (SANS) viscosity measurements. A series C12H25N+(CH3)(C2H4OH)–(CH2)s–N+(CH3)(C2H4OH)C12H25 2Br−, referred to as 12-s-12 MEA, where two highly polar quaternary amine centers are covalently connected polymethylene spacers at level, synthesized characterized. Critical micellar...
Umbral flashes (UF) and running penumbral waves (RPWs) in sunspot chromospheres leave a dramatic imprint the intensity profile of Ca II 854.2 nm line. Recent studies have focussed on also explaining observed polarization profiles, that show even more variations during passage these shock fronts. While most can be explained with an almost constant magnetic field as function time, several reported changes inferred strength UF phases. In this study we investigate origin periodic by analyzing...
Aims. We investigate the vertical gradient of magnetic field sunspots in photospheric layer.
The surface active and association properties of diblock triblock type, E18B9 E13B10E13, copolymers in aqueous solutions have been studied by tension, small angle neutron scattering, viscosity methods. Various fundamental parameters such as critical micelle concentration, area per molecule at water/air interface, the excess concentrations estimated. thermodynamics micellization has monitored. Both micellize through close processes is found to be entropy driven. SANS analysis showed that...
Association properties of two silicone surfactants based on poly(dimethylsiloxane)-graft-polyethers in aqueous solutions 2-butoxyethanol, poly(ethylene glycol), and glucose were determined using various techniques such as surface tension, small-angle neutron scattering, viscosity. Dilute solution phase diagrams also constructed, cloud points measured for different concentrations both the additive solutions. The thermodynamic parameters micellization obtained from temperature-dependent data...