Proton Threshold States in the 22Na(p,gamma)23Mg Reaction and Astrophysical Implications

Proton threshold states in 23Mg are important for the astrophysically relevant proton capture reaction 22Na(p,gamma)23Mg. In the indirect determination of the resonance strength of the lowest states, which were not accessible by direct methods, some of the spin-parity assignments remained experimentally uncertain. We have investigated these states with Shell Model, Coulomb displacement, and Thomas-Ehrman shift calculations. From the comparison of calculated and observed properties we relate the lowest relevant resonance state at E=7643 keV to an excited 3/2+ state in accordance with a recent experimental determination by Jenkins et al.. From this we deduce significantly improved values for the 22Na(p,gamma)23Mg reaction rate at stellar temperatures below T_9=0.1K.Comment: 8 pages, 4 figures, 6 table

Threshold Effects in Multi-channel Coupling and Spectroscopic Factors in Exotic Nuclei

In the threshold region, the cross section and the associated overlap integral obey the Wigner threshold law that results in the Wigner-cusp phenomenon. Due to flux conservation, a cusp anomaly in one channel manifests itself in other open channels, even if their respective thresholds appear at a different energy. The shape of a threshold cusp depends on the orbital angular momentum of a scattered particle; hence, studies of Wigner anomalies in weakly bound nuclei with several low-lying thresholds can provide valuable spectroscopic information. In this work, we investigate the threshold behavior of spectroscopic factors in neutron-rich drip-line nuclei using the Gamow Shell Model, which takes into account many-body correlations and the continuum effects. The presence of threshold anomalies is demonstrated and the implications for spectroscopic factors are discussed.Comment: Accepted in Physical Review C Figure correcte

Differential expression of the brassinosteroid receptor-encoding BRI1 gene in Arabidopsis

Abstract Brassinosteroid (BR)-regulated growth and development in Arabidopsis depends on BRASSINOSTEROID INSENSITIVE 1 (BRI1), the BR receptor that is responsible for initiating the events of BR signalling. We analysed the temporal and spatial regulation of BRI1 expression using stable transgenic lines that carried BRI1 promoter:reporter fusions. In both seedlings and mature plants the tissues undergoing elongation or differentiation showed elevated BRI1 gene activity, and it could be demonstrated that in the hypocotyl this was accompanied by accumulation of the BRI1 transcript and its receptor protein product. In seedlings the BRI1 promoter was also found to be under diurnal regulation, determined primarily by light repression and a superimposed circadian control. To determine the functional importance of transcriptional regulation we complemented the severely BR insensitive bri1-101 mutant with a BRI1-luciferase fusion construct that was driven by promoters with contrasting specificities. Whereas the BRI1 promoter-driven transgene fully restored the wild phenotype, expression from the photosynthesisassociated CAB3 and the vasculature-specific SUC2 and ATHB8 promoters resulted in plants with varying morphogenic defects. Our results reveal complex differential regulation of BRI1 expression, and suggest that by influencing the distribution and abundance of the receptor this regulation can enhance or attenuate BR signalling

R-matrix description of threshold phenomena

A R-Matrix description of threshold phenomena is presented. It includes, in addition to the Wigner cusp, anomalies caused by a resonance at the threshold. Threshold phenomena in s- and p-waves are discussed.On présente une description des phénomènes de seuil à l'aide de la matrice R, en considérant, à part le cusp de Wigner, les anomalies produites par une résonance dont l'énergie correspond au seuil. On discute aussi les phénomènes de seuil concernant les ondes s et p

EMPIRICAL EVIDENCE FOR RELATION BETWEEN THRESHOLD EFFECTS AND NEUTRON STRENGTH FUNCTION

In the present letter one proves, by analyzing experimental data, that the mass-dependent magnitude of threshold effects observed in deuteron stripping reactions on A ≈ 90 mass target nuclei is proportional to the 3p-wave neutron strength function. ‚ ¤ ´´µ°· ¡µÉ¥´ µ¸´µ¢¥ ´ ²¨ § Ô±¸ ¶¥·¨³¥´É ²Ó´ÒÌ ¤ ´´ÒÌ ¶·¨¢µ¤¨É¸Ö ¤µ± § É¥²Ó¸É¢µ ɵ£µ, Îɵ § ¢¨¸¨³ Ö µÉ ³ ¸¸Ò ¢¥²¨Î¨´ ¶µ·µ£µ¢ÒÌ ÔËË¥±Éµ¢,´ ¡²Õ¤ ¥³ÒÌ ¢ ·¥ ±Í¨ÖÌ ¤¥°É·µ´-µ£µ¸É·¨ ¶ ¶¨´£ ´ Ö¤· ̸³ ¸¸µ°A ≈ 90, ¶·µ ¶µ·Í¨o´ ²Ó´ 3p-¢µ²´µ¢µ°´¥°É·µ´´µ°¸¨²µ¢µ°Ë Ê´±Í¨¨

The role of virtual states in the appearance of two-neutron halo

The existence of loosely bound, spatially extended states in a two-particle plus core system is studied. The description is given in the Schrödinger picture by treating the interactions in the scattering length approximation. The treatment supports the statement that the most favourable case for the appearance of the two-neutron halo is the existence of large negative neutron-core scattering length (a virtual state) besides the n-n virtual state

OCT evaluation of single ceramic crowns: comparison between conventional and chair-side CAD/CAM technologies

Digital impressions were introduced to overcome some of the obstacles due to traditional impression materials and techniques. The aim of this in vitro study is to compare the accuracy of all ceramic crowns obtained with digital impression and CAD-CAM technology with the accuracy of those obtained with conventional impression techniques. Two groups of 10 crowns each have been considered. The digital data obtained from Group 1 have been processed and the all-ceramic crowns were milled with a CAD/CAM technology (CEREC MCX, Sirona). The all ceramic crowns in Group 2 were obtained with the classical technique of pressing (emax, Ivoclar, Vivadent). The evaluation of the marginal adaptation was performed with Time Domain Optical Coherence Tomography (TD OCT), working at a wavelength of 1300 nm. Tri-dimensional (3D) reconstructions of the selected areas were obtained. Based on the findings in this study, one may conclude that the marginal accuracy of all ceramic crowns fabricated with digital impression and the CAD/CAM technique is superior to the conventional impression technique. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only