Catastrophic eruption of magnetic flux rope in the corona and solar wind with and without magnetic reconnection

It is generally believed that the magnetic free energy accumulated in the corona serves as a main energy source for solar explosions such as coronal mass ejections (CMEs). In the framework of the flux rope catastrophe model for CMEs, the energy may be abruptly released either by an ideal magnetohydrodynamic (MHD) catastrophe, which belongs to a global magnetic topological instability of the system, or by a fast magnetic reconnection across preexisting or rapidly-developing electric current sheets. Both ways of magnetic energy release are thought to be important to CME dynamics. To disentangle their contributions, we construct a flux rope catastrophe model in the corona and solar wind and compare different cases in which we either prohibit or allow magnetic reconnection to take place across rapidly-growing current sheets during the eruption. It is demonstrated that CMEs, even fast ones, can be produced taking the ideal MHD catastrophe as the only process of magnetic energy release. Nevertheless, the eruptive speed can be significantly enhanced after magnetic reconnection sets in. In addition, a smooth transition from slow to fast eruptions is observed when increasing the strength of the background magnetic field, simply because in a stronger field there is more free magnetic energy at the catastrophic point available to be released during an eruption. This suggests that fast and slow CMEs may have an identical driving mechanism.Comment: 7 pages, 4 figures, ApJ, in press (vol. 666, Sept. 2007

Response of Oncomelania snail distribution on land use in Sichuan, China

Schistosomiasis is one of the four major infectious diseases that require prevention and control in China. It is mainly distributed along the middle and downstream areas of the Yangtze River and some hilly areas in Sichuan, Yunnan, and so on. Oncomelania snail is the only intermediate parasite in the schistosome life cycle; thus, reducing the number of snails can decrease the incidence of schistosomiasis by limiting its transmission. The number and distribution of snails is closely related to the environment, which is largely influenced by different habitats. To determine the relationship of snail number and spatial distribution with typical habitats, we selected different land use/plant cover types, investigated the snail distribution and analyzed the physical and chemical properties of the soil. The results show that among the different land use types, higher rates of live snail and live snail frame occurred along the riverbanks, wild land and ditches, followed by dry land, paddies, and forest lands. No live snail was found in bamboo stands of Sinocalmus affinis. An analysis of the physical and chemical properties of different land use types revealed higher soil pH value (8.41) in bamboo stands, which is beyond the suitable range for snails and possibly the key to inhibiting snails’ survival. These results imply that in the land growing bamboo (Neosinocalmus affinis) the snail could not propagate owing to soil pH rising. Therefore, the research would provide to some extent, the guidance for snail control through optimizing land use systems.Key words: Bamboo stand, habitat, Oncomelania snail, Neosinocalmus affinis

Etching suspended superconducting hybrid junctions from a multilayer

A novel method to fabricate large-area superconducting hybrid tunnel junctions with a suspended central normal metal part is presented. The samples are fabricated by combining photo-lithography and chemical etch of a superconductor - insulator - normal metal multilayer. The process involves few fabrication steps, is reliable and produces extremely high-quality tunnel junctions. Under an appropriate voltage bias, a significant electronic cooling is demonstrated