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Ramadevi N.,Praveena R.,Venkatramu V.,Basavapoornima Ch.,Lavín V.,Joshi B.D. 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.10
Lu3Sc2Ga3O12 garnet nanorods co-doped with Tm3+ and Yb3+ optically active ions have been synthesized by Pechini sol– gel method, and their structural, morphological and luminescence properties have been explored. X-ray difraction pattern confrmed that the synthesized Lu3Sc2Ga3O12 nanomaterials were crystallized in cubic garnet structure with an average crystallite size of 30 nm. Morphology of these powders confrmed the formation of rods with an average length of 8 μm and diameter of 90 nm. The difuse refectance spectra were used to obtain partial energy-level structure of Tm3+ and Yb3+ ions in Lu3Sc2Ga3O12 nanorods. Intense blue Stokes luminescence of Tm3+ ions at around 454 nm, under 360 nm ultraviolet excitation, as well as anti-Stokes luminescence at around 483 nm and co-operative luminescence at 490 nm, under near-infrared 980 nm excitation, have been measured. The intensity of these peaks increased with increasing of Yb3+ concentration up to 5 mol% and then decreased due to energy transfer between optically active ions. In addition, luminescence at ~ 545 and 565 nm has been observed in the anti-Stokes spectra which is due to the energy transfer from Ln3+ ions to the impurities such as Er3+ and Ho3+ ions. Laser pump power-dependent luminescence spectra confrmed that three photons were involved to populate the 1 G4 level in the upconversion mechanism. Luminescence decay curves have been measured for 1 D2 level and have been found to be non-exponential with an average lifetime of 20 μs. The non-exponential nature of decay curves is ascribed to energy transfer among Tm3+ ions through cross-relaxation processes. Colour co-ordinates of the samples excited at 980 nm lie in the blue–green region and also near to the white light region in the CIE diagram. All these results indicate that the present garnet nanorods could be a promising optically active material for the solid-state display devices.
A TRIO OF CONFINED FLARES IN AR 11087
Joshi, Anand D.,Forbes, Terry G.,Park, Sung-Hong,Cho, Kyung-Suk IOP Publishing 2015 The Astrophysical journal Vol.798 No.2
<P>We investigate three flares that occurred in active region, AR 11087, observed by the Dutch Open Telescope (DOT) on 2010 July 13, in a span of three hours. The first two flares have soft X-ray class B3, whereas the third flare has class C3. The third flare not only was the largest in terms of area and brightness but also showed a very faint coronal mass ejection (CME) associated with it, while the earlier two flares had no associated CME. The active region, located at 27 degrees N, 26 degrees E, has a small U-shaped active region filament to the south of the sunspot, and a quiescent filament is located to its west. H alpha observations from DOT, as well as extreme-ultraviolet images and magnetograms from the STEREO spacecraft and Solar Dynamics Observatory, are used to study the dynamics of the active region during the three flares. Our observations imply that the first two flares are confined and that some filament material drains to the surface during these flares. At the onset of the third flare downflows are again observed within the active region, but a strong upflow is also observed at the northern end of the adjacent quiescent filament to the west. It is at the latter location that the CME originates. The temporal evolution of the flare ribbons and the dynamics of the filaments are both consistent with the idea that reconnection in a pre-existing current sheet leads to a loss of equilibrium.</P>
PRE-ERUPTION OSCILLATIONS IN THIN AND LONG FEATURES IN A QUIESCENT FILAMENT
Joshi, Anand D.,Hanaoka, Yoichiro,Suematsu, Yoshinori,Morita, Satoshi,Yurchyshyn, Vasyl,Cho, Kyung-Suk American Astronomical Society 2016 The Astrophysical journal Vol.833 No.2
<P>We investigate the eruption of a quiescent filament located close to an active region. Large-scale activation was observed in only half of the filament in the form of pre-eruption oscillations. Consequently only this half erupted nearly 30 hr after the oscillations commenced. Time-slice diagrams of 171 angstrom images from the Atmospheric Imaging Assembly were used to study the oscillations. These were observed in several thin and long features connecting the filament spine to the chromosphere below. This study traces the origin of such features and proposes their possible interpretation. Small-scale magnetic flux cancellation accompanied by a brightening was observed at the footpoint of the features shortly before their appearance, in images recorded by the Helioseismic and Magnetic Imager. A slow rise of the filament was detected in addition to the oscillations, indicating a gradual loss of equilibrium. Our analysis indicates that a change in magnetic field connectivity between two neighbouring active regions and the quiescent filament resulted in a weakening of the overlying arcade of the filament, leading to its eruption. It is also suggested that the oscillating features are filament barbs, and the oscillations are a manifestation during the pre-eruption phase of the filaments.</P>
Experimental and numerical studies of precast connection under progressive collapse scenario
Joshi, Digesh D.,Patel, Paresh V.,Rangwala, Husain M.,Patoliya, Bhautik G. Techno-Press 2020 Advances in concrete construction Vol.9 No.3
Progressive collapse in a structure occurs when load bearing members are failed and the adjoining structural elements cannot resist the redistributed forces and fails subsequently, that leads to complete collapse of structure. Recently, construction using precast concrete technology is adopted increasingly because it offers many advantages like faster construction, less requirement of skilled labours at site, reduced formwork and scaffolding, massive production with reduced amount of construction waste, better quality and better surface finishing as compared to conventional reinforced concrete construction. Connections are the critical elements for any precast structure, because in past, major collapse of precast structure took place because of connection failure. In this study, behavior of four different precast wet connections with U shaped reinforcement bars provided at different locations is evaluated. Reduced 1/3<sup>rd</sup> scale precast beam column assemblies having two span beam and three columns with removed middle column are constructed and examined by performing experiments. The response of precast connections is compared with monolithic connection, under column removal scenario. The connection region of test specimens are filled by cast-in-place micro concrete with and without polypropylene fibers. Performance of specimen is evaluated on the basis of ultimate load carrying capacity, maximum deflection at the location of removed middle column, crack formation and failure propagation. Further, Finite element (FE) analysis is carried out for validation of experimental studies and understanding the performance of structural components. Monolithic and precast beam column assemblies are modeled using non-linear Finite Element (FE) analysis based software ABAQUS. Actual experimental conditions are simulated using appropriate boundary and loading conditions. Finite Element simulation results in terms of load versus deflection are compared with that of experimental study. The nonlinear FE analysis results shows good agreement with experimental results.
Supersonically sprayed thermal barrier layers using clay micro-particles
Kim, D.Y.,Lee, J.G.,Joshi, B.,Lee, J.H.,Al-Deyab, S.S.,Yoon, H.G.,Yang, D.R.,Yarin, A.,Yoon, S.S. Elsevier 2016 Applied clay science Vol.120 No.-
<P>Several clay minerals were supersonically sprayed onto flexible substrates to form highly thermally and electrically insulating materials which could be wrapped onto protected surfaces. Among these clay minerals, montmorillonite (Mt) revealed the best thermal insulating properties. (C) 2015 Elsevier B.V. All rights reserved.</P>
Probing charge transport in manganite film through switching parameters
Rathod K.N.,Boricha Hetal,Sagapariya Khushal,Hirpara Bharavi,Dhruv Davit,Joshi A.D.,Pandya D.D.,Singh J.P.,Chae K. H.,Asokan K.,Solanki P.S.,Shah N.A. 한국물리학회 2021 Current Applied Physics Vol.28 No.-
We have investigated the bipolar resistive switching of Y0.95Ca0.05MnO3 (YCMO) thin film on Si substrate using pulsed laser deposition. Simulation of Mn L3,2 near-edge X-ray absorption fine structure has been executed by CTM4XAS to corroborate the presence of a mixed-valence state of Mn ions and oxygen vacancies. The charge transport in the film is described by the space charge limited mechanism. Murgatroyd and space charge limited mechanism relations are used to calculate the mobility and other switching parameters at high resistance state. With a decrease in the switching layer (near to positively biased electrode) thickness, better resistive switching was observed. This work indicates that the localized switching thickness and temperature strongly affect the resistive switching of the YCMO film.