Destabilization of a Solar Prominence/Filament Field System by a Series of Eight Homologous Eruptive Flares

Homologous flares are flares that occur repetitively in the same active region, with similar structure and morphology. A series of at least eight homologous flares occurred in active region NOAA 11237 over 16 - 17 June 2011. A nearby prominence/filament was rooted in the active region, and situated near the bottom of a coronal cavity. The active region was on the southeast solar limb as seen from SDO/AIA, and on the disk as viewed from STEREO/EUVI-B. The dual perspective allows us to study in detail behavior of the prominence/filament material entrained in the magnetic field of the repeatedly-erupting system. Each of the eruptions was mainly confined, but expelled hot material into the prominence/filament cavity system (PFCS). The field carrying and containing the ejected hot material interacted with the PFCS and caused it to inflate, resulting in a step-wise rise of the PFCS approximately in step with the homologous eruptions. The eighth eruption triggered the PFCS to move outward slowly, accompanied by a weak coronal dimming. As this slow PFCS eruption was underway, a final ejective flare occurred in the core of the active region, resulting in strong dimming in the EUVI-B images and expulsion of a coronal mass ejection (CME). A plausible scenario is that the repeated homologous flares could have gradually destabilized the PFCS, and its subsequent eruption removed field above the acitive region and in turn led to the ejective flare, strong dimming, and CME.Comment: 11 pages, 12 figures, Accepted for publication in Ap

Impact of graphene oxide and highly reduced graphene oxide on cement based composites

This study examines and compares the performance of two specific forms of graphene nanomaterials in the cement based composite, namely graphene oxide (GO) and reduced graphene oxide (rGO). A typical forms of GO with the average C:O ratio of 54:46 and a rGO with the average C:O ratio of 82:18 were used in the cement based paste composites. rGO was treated with superplasticizer to improve its dispersibility in water. Both GO and rGO were used as 0.02, 0.04, 0.06 wt% of cement. The effect of GO and rGO on workability, early age hydration, microstructure, mechanical and transport properties was determined. Different characteristics of GO and rGO such as molecular structure, functional groups, d spacing, size and physical strength influenced the properties of the cement based composites. The workability and final setting time of composite gradually decreased compared to 100% PC (control) with higher dosages of GO up to 0.06 wt% (of cement), which is due to the dominant oxygen functional groups and the hydrophilic nature of GO. To the contrary, the workability and final setting time increased in the rGO composites compared to the control mix due to the almost hydrophobic nature of rGO and the presence of superplasticiser. The XRD and TGA quantification of the hydration products shows that GO composites have a greater content of Ca(OH)2 and C-S-H compared to rGO composites measured at 1, 7 and 28 days. Micropores (smaller than ∼10 µm) in GO composites were observed to be filled with calcium silicate hydrate (C-S-H) gel and crystalline compounds. Random pore filling nature was observed in rGO composites and ettringite was more common element in those pores. Meso and gel pores