The structure and energetics of several simple point defects in A15 Nb(3)Sn were investigated by means of computer simulations based on a pair-potential model of cohesion. The properties of vacancies ...on both the Nb and Sn sublattices, as well as those of simple antisite defects, were examined, and estimates were made of the energetics of several types of atom-vacancy exchange ("jump") processes. The results show an unusual structure for the vacancy on the Nb sublattice: the vacancy is "split" between two adjacent sites along the Nb chain with an atom midway between them. We find the Sn vacancy (on the Sn sublattice) to be metastable; this vacancy will "decompose" by an activated process into a more stable configuration consisting of a Nb atom on a Sn site adjacent to a split Nb-sublattice vacancy. We find that the lowest energy grouping of defects compatible with maintaining sublattice sites in the proper three-to-one ratio is the antisite defect pair; the lowest energy grouping which contains vacancies is found to consist of Nb-sublattice vacancies and Nb-on-Sn-sublattice antisite defects in the ratio of four of the former to one of the latter (quintuple defects). Our results also suggest that bulk Sn diffusion is slower than Nb diffusion; this is consistent with the belief that rapid Sn diffusion during Nb(3)Sn layer growth does not occur by bulk but by grain-boundary diffusion.
An optically fed phased array must be provided with a means of collimation as well as with a beam steering function. The same phase shifters which are used to steer the beam can be used to collimate ...the beam. The use of row-and-column phase commands, while greatly simplifying the beam steering function over that required for commanding individual elements, precludes the attainment of exact collimation. A consequent phase error across the aperture results in a loss of antenna gain. For a given order of approximation to the collimation function, the minimization of the gain loss is a valid criterion for completely specifying all the parameters of the approximate collimation function. The gain loss incurred can then be determined. This paper develops the equations necessary to specify any order of approximation to the collimation function and the expression for the gain loss. Examples illustrate the differences between first- and second-order approximations and the effect of another parameter (f/D) on the gain loss of a typical antenna system.
GENIE is a new neutrino event generator for the experimental neutrino physics community. The goal of the project is to develop a `canonical' neutrino interaction physics Monte Carlo whose validity ...extends to all nuclear targets and neutrino flavors from MeV to PeV energy scales. Currently, emphasis is on the few-GeV energy range, the challenging boundary between the non-perturbative and perturbative regimes, which is relevant for the current and near future long-baseline precision neutrino experiments using accelerator-made beams. The design of the package addresses many challenges unique to neutrino simulations and supports the full life-cycle of simulation and generator-related analysis tasks. GENIE is a large-scale software system, consisting of 120,000 lines of C++ code, featuring a modern object-oriented design and extensively validated physics content. The first official physics release of GENIE was made available in August 2007, and at the time of the writing of this article, the latest available version was v2.4.4.
Atraumatic so-called “spontaneous” rupture of the esophagus Abbott, Osier A.; Mansour, Kamal A.; Logan, William D. ...
The Journal of thoracic and cardiovascular surgery,
January 1970, 1970-01-00, Letnik:
59, Številka:
1
Journal Article
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