Solar flares are the most powerful explosions occurring in the solar system, which may lead to disastrous space weather events and impact various aspects of our Earth. So far, it is still a big challenge in modern astrophysics to understand the origin of solar flares and predict their onset. Based on the analysis of soft X-ray emission observed by the Geostationary Operational Environmental Satellite (GOES), this work reported a new discovery of very long-periodic pulsations occurred in the preflare phase before the onset of solar flares (preflare-VLPs). These pulsations are typically with period of 8 -30 min and last for about 1 -2 hours. They are possibly generated from LRC oscillations of plasma loops where electric current dominates the physical process during magnetic energy accumulation in the source region. The preflare-VLP provides an essential information for understanding the triggering mechanism and origin of solar flares, and may help us to response to solar explosions and the corresponding disastrous space weather events as a convenient precursory indicator.

Herein, high quality ultralong tin selenide (SnSe) nanowires (NWs) have been synthesized via physical vapor deposition (PVD) without catalyst. The length of the synthesized SnSe NWs are hundreds of microns and even up to one millimeter, while the mean diameter is about 270 nm, and the aspect ratio of ultralong SnSe NWs can be over 3000. The microstructural characterizations indicate that the SnSe NWs are well-crystallized single crystals with growth direction along the normal {011} planes. The formation of the SnSe NWs is addressed by an oriented one-dimensional growth driven by the dynamic factors in the vapor–solid process. The near-infrared optical band gap of the SnSe NWs has been determined.

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