Observational signatures of electron-driven chromospheric evaporation in a white-light flare

We investigate observational signatures of explosive chromospheric evaporation during a white-light flare (WLF) that occurred on 2022 August 27. Using the moment analysis, bisector techniques, and the Gaussian fitting method, red-shifted velocities of less than 20 km/s are detected in low-temperature spectral lines of Ha, C I and Si IV at the conjugated flare kernels, which could be regarded as downflows caused by chromospheric condensation. Blue-shifted velocities of about 30-40 km/s are found in the high-temperature line of Fe XXI, which can be interpreted as upflows driven by chromospheric evaporation. A nonthermal hard X-ray (HXR) source is co-spatial with one of the flare kernels, and the Doppler velocities are temporally correlated with the HXR fluxes. The nonthermal energy flux is estimated to be at least (1.3+-0.2)*10^10 erg/s/cm^2. The radiation enhancement at Fe I 6569.2 A and 6173 A suggests that the flare is a WLF. Moreover, the while-light emission at Fe I 6569.2 A is temporally and spatially correlated with the blue shift of Fe XXI line, suggesting that both the white-light enhancement and the chromospheric evaporation are triggered and driven by nonthermal electrons. All our observations support the scenario of an electron-driven explosive chromospheric evaporation in the WLF.Comment: The manuscript was accepted for publication in ApJ, and it was a part of the ApJ Focus Issue "Early results from the Chinese Ha Solar Explorer (CHASE)

Observational signature of continuously operating drivers of decayless kink oscillation

Decayless kink oscillations, which are nearly omnipresent in the solar corona, are believed to be driven by continuously operating energy supply. In this letter, we investigate an external continuous excitation of an apparent decayless oscillation during an X1.1 flare on June 20, 2023 (SOL2023-06-20T16:42).The decayless kink oscillation was identified in the coronal loop at extreme ultraviolet (EUV) wavelengths and the associated flare quasi-periodic pulsations (QPPs) were simultaneously observed in passbands of hard X-ray (HXR), microwave, and ultraviolet (UV) emissions. The kink oscillation is detected as a transverse oscillation of the coronal loop, which reveals five apparent cycles with an average period of about 130-10 s. The oscillation amplitude does not show any significantly decay, suggesting a decayless oscillation. At the same time, the solar flare occurs in the vicinity of the oscillating loop and exhibits five main pulses in HXR, microwave, and UV emissions, which could be regarded as flare QPPs. They have similar periods of about 100-130 s, which may indicate successive and repetitive energy releases during the flare impulsive phase. The peak of each loop oscillation cycle appears to follow the pulse of the QPPs, suggesting that the transverse oscillation is closely associated with flare QPPs. Our observations support the scenario where the repetitive energy released following flare QPPs could be invoked as external, continuously operating drivers of the apparent decayless kink oscillation.Comment: accepted by A&

One-Minute Quasi-Periodic Pulsations during an M-Class Solar Flare

We study the Quasi-Periodic Pulsations (QPPs) of an M4.4 class solar flare, which occurred in active region NOAA 11165 on 8 March 2011. With the Fast Fourier Transform (FFT) method, we decompose the flare light curve into fast- and slowly-varying components. The 100 s (0.01 Hz) is selected as the cutoff threshold between the fast- and slowly-varying components. One-minute QPPs are found around flare peak at soft X-ray (SXR) and Extreme Ultraviolet (EUV). Using the data from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), the intermittent jets are detected and the interesting fact is that the jets also display one-minute period. The correlationship between the fast-varying components of SXR or EUV emissions and the jets suggests that the QPPs on light curves and periodic jets could come from the same origination, e.g., the periodic magnetic reconnection in this event

Hydrothermal Synthesis g‑C₃N₄/Nano-InVO₄ Nanocomposites and Enhanced Photocatalytic Activity for Hydrogen Production under Visible Light Irradiation

We synthesized g-C₃N₄/nano-InVO₄ heterojunction-type photocatalyts by in situ growth of InVO₄ nanoparticles onto the surface of g-C₃N₄ sheets via a hydrothermal process. The results of SEM and TEM showed that the obtained InVO₄ nanoparticles 20 nm in size dispersed uniformly on the surface of g-C₃N₄ sheets, which revealed that g-C₃N₄ sheets was probably a promising support for in situ growth of nanosize materials. The achieved intimate interface promoted the charge transfer and inhibited the recombination rate of photogenerated electron–hole pairs, which significantly improved the photocatalytic activity. A possible growth process of g-C₃N₄/nano-InVO₄ nanocomposites was proposed based on different mass fraction of g-C₃N₄ content. The obtained g-C₃N₄/nano-InVO₄ nanocomposites could achieve effective separation of charge-hole pairs and stronger reducing power, which caused enhanced H₂ evolution from water-splitting compared with bare g-C₃N₄ sheets and g-C₃N₄/micro-InVO₄ composites, respectively. As a result, the g-C₃N₄/nano-InVO₄ nanocomposite with a mass ratio of 80:20 possessed the maximum photocatalytic activity for hydrogen production under visible-light irradiation

The Bi-Functional Paxilline Enriched in Skin Secretion of Tree Frogs (<i>Hyla japonica</i>) Targets the KCNK18 and BK_Ca Channels

The skin secretion of tree frogs contains a vast array of bioactive chemicals for repelling predators, but their structural and functional diversity is not fully understood. Paxilline (PAX), a compound synthesized by Penicillium paxilli, has been known as a specific antagonist of large conductance Ca2+-activated K+ Channels (BKCa). Here, we report the presence of PAX in the secretions of tree frogs (Hyla japonica) and that this compound has a novel function of inhibiting the potassium channel subfamily K member 18 (KCNK18) channels of their predators. The PAX-induced KCNK18 inhibition is sufficient to evoke Ca2+ influx in charybdotoxin-insensitive DRG neurons of rats. By forming π-π stacking interactions, four phenylalanines located in the central pore of KCNK18 stabilize PAX to block the ion permeation. For PAX-mediated toxicity, our results from animal assays suggest that the inhibition of KCNK18 likely acts synergistically with that of BKCa to elicit tingling and buzzing sensations in predators or competitors. These results not only show the molecular mechanism of PAX-KCNK18 interaction, but also provide insights into the defensive effects of the enriched PAX

Video1_Flare quasi-periodic pulsation associated with recurrent jets.MP4

Quasi-periodic pulsations (QPPs), which carry time features and plasma characteristics of flare emissions, are frequently observed in light curves of solar/stellar flares. In this study, we investigated non-stationary QPPs associated with recurrent jets during an M1.2 flare on 2022 July 14. A quasi-period of ∼45±10 s, determined by the wavelet transform technique, is simultaneously identified at wavelengths of soft/hard X-ray and microwave emissions, which are recorded by the Gravitational Wave High-Energy Electromagnetic Counterpart All-sky Monitor, Fermi and the Nobeyama Radio Polarimeters, respectively. A group of recurrent jets with an intermittent cadence of about 45 ± 10 s are found in the Atmospheric Imaging Assembly (AIA) image series at 304 Å, but they are 180 s earlier than the flare QPP. All observational facts suggest that the flare QPPs could be excited by recurrent jets, and they should be associated with non-thermal electrons that are periodically accelerated by a repeated energy release process, such as repetitive magnetic reconnection. Moreover, the same quasi-period is discovered at double footpoints connected by a hot flare loop in AIA 94 Å, and the phase speed is measured to be ∼1,420 km s−1. Based on the differential emission measure, the average temperatures, number densities, and magnetic field strengths at the loop top and footpoint are estimated to be ∼7.7/6.7 MK, ∼7.5/3.6 × 1010 cm−3, and ∼143/99 G, respectively. Our measurements indicate that the 45-s QPP is probably modulated by the kink-mode wave of the flare loop.</p