| 1. |
- Dhiman, Vinit, et al.
(författare)
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Multiband optical variability of the TeV blazar PG 1553+113 in 2019
- 2022
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 519:2, s. 2796-2811
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Tidskriftsartikel (refereegranskat)abstract
- We report the flux and spectral variability of PG 1553 + 113 on intra-night (IDV) to short-term time-scales using BVRI data collected over 91 nights from 28 February to 8 November 2019 employing 10 optical telescopes: three in Bulgaria, two each in India and Serbia, and one each in Greece, Georgia, and Latvia. We monitored the blazar quasi-simultaneously for 16 nights in the V and R bands and 8 nights in the V, R, I bands and examined the light curves (LCs) for intra-day flux and colour variations using two powerful tests: the power-enhanced F-test and the nested ANOVA test. The source was found to be significantly (>99 per cent) variable in 4 nights out of 27 in R-band, 1 out of 16 in V-band, and 1 out of 6 nights in I-band. No temporal variations in the colours were observed on IDV time-scale. During the course of these observations the total variation in R-band was 0.89 mag observed. We also investigated the spectral energy distribution (SED) using B-, V-, R-, and I-band data. We found optical spectral indices in the range of 0.878 +/- 0.029 to 1.106 +/- 0.065 by fitting a power law (F-nu proportional to nu(-alpha)) to these SEDs of PG 1553 + 113. We found that the source follows a bluer-when-brighter trend on IDV time-scales. We discuss possible physical causes of the observed spectral variability.
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| 2. |
- Gupta, Alok C., et al.
(författare)
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Long-term Multiband Near-infrared Variability of the Blazar OJ 287 during 2007-2021
- 2022
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Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 260:2, s. 39-
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Tidskriftsartikel (refereegranskat)abstract
- We present the most extensive and well-sampled long-term multiband near-infrared (NIR) temporal and spectral variability study of OJ 287, considered to be the best candidate binary supermassive black hole blazar. These observations were made between 2007 December and 2021 November. The source underwent similar to 2-2.5 mag variations in the J, H, and Ks NIR bands. Over these long-term timescales there were no systematic trends in either flux or spectral evolution with time or with the source's flux states. However, on shorter timescales, there are significant variations in flux and spectra indicative of strong changes during different activity states. The NIR spectral energy distributions show diverse facets at each flux state, from the lowest to the highest. The spectra are, in general, consistent with a power-law spectral profile (within 10%) and many of them indicate minor changes (observationally insignificant) in the shift of the peak. The NIR spectra generally steepen during bright phases. We briefly discuss these behaviors in the context of blazar emission scenarios/mechanisms, OJ 287's well-known traditional behavior, and implications for models of the source central engine invoked for its long-term optical semiperiodic variations.
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| 3. |
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| 4. |
- Zhang, Zhongli, et al.
(författare)
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Research on the heat resistance and electrical properties of fluorinated polyimide/nano-Al2O3/nano-Si3N4 composite materials
- 2024
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Ingår i: Polymer. - : Elsevier. - 0032-3861 .- 1873-2291. ; 294
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Tidskriftsartikel (refereegranskat)abstract
- Polyimide (PI) refers to a polymer containing an imide ring characteristic structure on the main chain. It has excellent thermal stability, insulation properties and other characteristics. The Tesla transformer is the core component of the primary pulse source of the high -current electron beam accelerator. It is also an essential component of the energy storage pulse power supply. Therefore, it has broad application prospects in the fields of national defense and civil industry. If the insulation performance of the turn -to -turn coils of the Tesla transformer does not meet the standards, it will break down during high -voltage corona discharge, causing transformer failure. Therefore, it is crucial to improve the insulation performance of Tesla transformer inter -turn wrapping materials. The incorporation of fluorinecontaining groups has proven to be a transformative strategy that significantly enhances the physical, chemical, optical, and electrical properties of PI films. In addition, numerous studies have demonstrated that introducing inorganic fillers into the polyimide matrix can substantially enhance the insulating properties of polyimide films. This paper specifically concentrates on elevating the insulating and thermal attributes of polyimide. Initially, a range of polyimide films was synthesized for performance assessment by employing various fluorinated dianhydride and diamine components, utilizing them as substrates. Then, we used nanosilicon nitride (nano-Si3N4) and nano -alumina (nano-Al2O3) as doping phases to prepare PI composite films, which reduced the dielectric constant and increased the breakdown strength.
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