Comparison of Transfer-to-Continuum and Eikonal Models of Projectile Fragmentation Reactions

Spectroscopic properties of nuclei are accessible with projectile fragmentation reactions, but approximations made in the reaction theory can limit the accuracy of the determinations. We examine here two models that have rather different approximations for the nucleon wave function, the target interaction, and the treatment of the finite duration of the reaction. The nucleon-target interaction is treated differently in the eikonal and the transfer-to-continuum model, but the differences are more significant for light targets. We propose a new parameterization with that in mind. We also propose a new formula to calculate the amplitude that combines the better treatment of the wave function in the eikonal model with the better treatment of the target interaction in the transfer-to-continuum model.Comment: 21 pages, latex file including 3 tables. 5 figures. Submitted to Phys. Rev.

Initial State Dependence of the Breakup of Weakly Bound Carbon Isotopes

The one-neutron nuclear breakup from the Carbon isotopes $^{19}$C and $^{17}$C, is calculated as an example of application of the theory of transfer to the continuum reactions in the formulation which includes spin coupling. The effect of the energy sharing between the parallel and transverse neutron momentum distributions is taken into account thus resulting in a theory which is more general than sudden eikonal approaches. Both effects are necessary to understand properly the breakup from not too weakly bound $l_i>1$ orbitals. Breakup which leaves the core into an excited state below particle threshold is also considered. The core-target interaction is treated in the smooth cut-off approximation. By comparing to presently available experimental data we show how to make some hypothesis on the quantum numbers and occupancy of the neutron initial state. Possible ambiguities in the interpretation of inclusive cross sections are discussed.Comment: 22 RevTeX pages,3 ps figures. Phys. Rev. C, accepte

Silk reinforced with graphene or carbon nanotubes spun by spiders

Here, we report the production of silk incorporating graphene and carbon nanotubes directly by spider spinning, after spraying spiders with the corresponding aqueous dispersions. We observe a significant increment of the mechanical properties with respect to the pristine silk, in terms of fracture strength, Young's and toughness moduli. We measure a fracture strength up to 5.4 GPa, a Young's modulus up to 47.8 GPa and a toughness modulus up to 2.1 GPa, or 1567 J/g, which, to the best of our knowledge, is the highest reported to date, even when compared to the current toughest knotted fibres. This approach could be extended to other animals and plants and could lead to a new class of bionic materials for ultimate applications

Molecular systematics and evolution of the Cyanocorax jays

Phylogenetic relationships were studied in the genus Cyanocorax (Aves: Corvidae) and related genera, Psilorhinus and Calocitta, a diverse group of New World jays distributed from the southern United States south to Argentina. Although the ecology and behavior of some species in the group have been studied extensively, lack of a molecular phylogeny has precluded rigorous interpretations in an evolutionary framework. Given the diverse combinations of plumage coloration, size, and morphology, the taxonomy of the group has been inconsistent and understanding of biogeographic patterns problematic. Moreover, plumage similarity between two geographically disjuct species, the Tufted Jay (Cyanocorax dickeyi) from western Mexico and the White-tailed Jay (C. mystacalis) from western Ecuador and Peru, has puzzled ornithologists for decades. Here, a phylogeny of all species in the three genera is presented, based on study of two mitochondrial and three nuclear genes. Phylogenetic trees revealed the non-monophyly of Cyanocorax, and the division of the whole assemblage in two groups: “Clade A” containing Psilorhinus morio, both species in Calocitta, Cyanocorax violaceus, C. caeruleus, C. cristatellus, and C. cyanomelas, and “Clade B” consisting of the remaining species in Cyanocorax. Relationships among species in Clade A were ambiguous and, in general, not well resolved. Within Clade B, analyses revealed the monophyly of the “Cissilopha” jays and showed no evidence for a sister relationship between C. mystacalis and C. dickeyi. The phylogenetic complexity of lineages in the group suggests several complications for the understanding biogeographic patterns, as well as for proposing a taxonomy that is consistent with morphological variation. Although multiple taxonomic arrangements are possible, recommendations are for recognizing only one genus, Cyanocorax, with Psilorhinus and Calocitta as synonyms. Se estudiaron las relaciones filogenéticas en los géneros Cyanocorax, Psilorhinus y Calocitta (Aves: Corvidae), un grupo diverso de urracas del Nuevo Mundo cuyas especies se distribuyen desde el sur de los Estados Unidos hasta Argentina. Aunque la ecología y el comportamiento de algunas especies en el grupo han sido estudiadas extensamente, la falta de una filogenia molecular ha impedido la interpretación rigurosa de estos estudios en un marco evolutivo. Dadas las diversas combinaciones de coloración de plumaje, tamaño y morfología presentes en las especies del grupo, su taxonomía ha sido inconsistente y la interpretación de sus patrones biogeográficos ha sido problemática. Mas aún, la similitud de plumaje en especies que están geográficamente distantes, como Cyanocorax dickeyi del oeste de Mexico y C. mystacalis del oeste de Ecuador y Perú, ha sido difícil de interpretar. Se presenta una filogenia para todas las especies en los tres géneros, basada en el estudio de dos genes nucleares y dos genes mitocondriales. Los árboles filogenéticos mostraron la parafilia de Cyanocorax y la división de todas las especies en dos grupos: “Clado A” en el cual se encuentran Psilorhinus morio, ambas especies Calocitta, Cyanocorax violaceus, C. caeruleus, C. cristatellus, y C. cyanomelas, y “Clado B” en el cual se encuentran el resto de las especies de Cyanocorax. Las relaciones entre especies del Clado A fueron ambiguas y, en general, poco resueltas. En el Clado B, los análisis mostraron la monofilia de las especies en “Cissilopha”, pero no indicaron la monofilia de C. mystacalis + C. dickeyi. La complejidad filogenética de los linajes en el grupo sugiere varias complicaciones en el entendimiento de su biogeografía y taxonomía. Con base en los resultados filogenéticos se reconoce un solo género, Cyanocorax, con Psilorhinus y Calocitta como sinónimos

Core excitation in Coulomb breakup reactions

Within the pure Coulomb breakup mechanism, we investigate the one-neutron removal reaction of the type A(a,b$\gamma$)X with $^{11}$Be and $^{19}$C projectiles on a heavy target nucleus $^{208}$Pb at the beam energy of 60 MeV/nucleon. Our intention is to examine the prospective of using these reactions to study the structure of neutron rich nuclei. Integrated partial cross sections and momentum distributions for the ground as well as excited bound states of core nuclei are calculated within the finite range distorted wave Born approximation as well as within the adiabatic model of the Coulomb breakup. Our results are compared with those obtained in the studies of the reactions on a light target where the breakup proceeds via the pure nuclear mechanism. We find that the transitions to excited states of the core are quite weak in the Coulomb dominated process as compared to the pure nuclear breakup.Comment: Revtex format, five postscript figures included, to appear in Phys. Rev.