A Statistical Study on Photospheric Magnetic Nonpotentiality of Active Regions and Its Relationship with Flares during Solar Cycles 22-23

A statistical study is carried out on the photospheric magnetic nonpotentiality in solar active regions and its relationship with associated flares. We select 2173 photospheric vector magnetograms from 1106 active regions observed by the Solar Magnetic Field Telescope at Huairou Solar Observing Station, National Astronomical Observatories of China, in the period of 1988-2008, which covers most of the 22nd and 23rd solar cycles. We have computed the mean planar magnetic shear angle (\bar{\Delta\phi}), mean shear angle of the vector magnetic field (\bar{\Delta\psi}), mean absolute vertical current density (\bar{|J_{z}|}), mean absolute current helicity density (\bar{|h_{c}|}), absolute twist parameter (|\alpha_{av}|), mean free magnetic energy density (\bar{\rho_{free}}), effective distance of the longitudinal magnetic field (d_{E}), and modified effective distance (d_{Em}) of each photospheric vector magnetogram. Parameters \bar{|h_{c}|}, \bar{\rho_{free}}, and d_{Em} show higher correlation with the evolution of the solar cycle. The Pearson linear correlation coefficients between these three parameters and the yearly mean sunspot number are all larger than 0.59. Parameters \bar{\Delta\phi}, \bar{\Delta\psi}, \bar{|J_{z}|}, |\alpha_{av}|, and d_{E} show only weak correlations with the solar cycle, though the nonpotentiality and the complexity of active regions are greater in the activity maximum periods than in the minimum periods. All of the eight parameters show positive correlations with the flare productivity of active regions, and the combination of different nonpotentiality parameters may be effective in predicting the flaring probability of active regions.Comment: 20 pages, 5 figures, 4 tables, accepted for publication in Solar Physic

Quasifission at extreme sub-barrier energies

With the quantum diffusion approach the behavior of the capture cross-section is investigated in the reactions $^{92,94}$Mo + $^{92,94}$Mo, $^{100}$Ru + $^{100}$Ru, $^{104}$Pd + $^{104}$Pd, and $^{78}$Kr + $^{112}$Sn at deep sub-barrier energies which are lower than the ground state energies of the compound nuclei. Because the capture cross section is the sum of the complete fusion and quasifission cross sections, and the complete fusion cross section is zero at these sub-barrier energies, one can study experimentally the unique quasifission process in these reactions after the capture.Comment: 3 pages, 3 figure

Enhanced electron-phonon coupling in NbB2 by nanoscaling the grain size

Nanocrystalline NbB2 powder has been synthesized via a single step solid-state reaction of precursor materials Nb2 O5 and NaBH4 . Phase composition, grain morphology, microstructure, phonon vibrations and superconducting properties were investigated by XRD, FESEM, HRTEM, Raman spectroscopy and PPMS. The results show that the grain size of nanocrystalline NbB2 is very sensitive to the reaction temperature and easy to aggregate to form micron scale of non-morphology powders. A systematic increase of the electron-phonon coupling constant with the nanoscaling grain size is observed, which we explain in terms of crystal defects and phonon vibrations. The zero-temperature critical fields, Hc1 (0) and Hc2 (0), have been estimated at 85 Oe and 7200 Oe, respectively, and the Ginzburg–Landau parameter κ is 5.1, confirming that NbB2 is a type-II superconductor

Soft rot disease caused by Dickeya fangzhongdai in epiphytic orchids in Vietnam

Soft rot diseases are becoming problematic in the cultivation of epiphytic orchids in Vietnam, but the causal agents are unknown. We investigated soft rot in Dendrobium anosmum, Phalaenopsis amabilis and Paphiopedilum concolor. Leaves of diseased plants with soft rot symptoms were sampled and cultures of Dickeya were obtained. The pathogen was identified as Dickeya fangzhongdai based on a phylogenetic analysis of 16s rRNA, dnaX, gapA and rplB. The pathogenicity of nine D. fangzhongdai isolates was confirmed in D. anosmum, Ph. amabilis and Pa. concolor in a nursery trial. The efficacy of a range of chemical agents was evaluated on the growth of D. fangzhongdai in vitro, and on D. fangzhongdai soft rot disease management in 1-year-old D. anosmum, Ph. amabilis and Pa. concolor plants. Cuprous oxide and Cu-bismerthiazol strongly inhibited the in vitro growth of D. fangzhongdai, and they reduced the soft rot lesion area of infected plants in vivo. These findings provide an interim option for producers to improve management of D. fangzhongdai soft rot disease in production nurseries in Vietnam

Observation of β-delayed 2He emission from the proton-rich nucleus 22Al

The β-delayed two-proton emission from 22Al was investigated experimentally through the implantation-decay method. A β-delayed two-proton decay branch from 22Al were identified based on the coincidence of the charged particles and γ-ray signals. The relative momentum (qpp) and the opening angle (θpp) distributions of the two β-delayed protons are measured and a strong peak at qpp∼20MeV/c, as well as a peak at θpp∼30∘ are observed clearly. The β-delayed 2He emission from 22Al with a probability of 29 (13)% by fitting the experimental data with the results of Monte Carlo simulations