Quasi One-Dimensional Metal-Semiconductor Heterostructures.

The band offsets occurring at the abrupt heterointerfaces of suitable material combinations offer a powerful design tool for high performance or even new kinds of devices. Because of a large variety of applications for metal-semiconductor heterostructures and the promise of low-dimensional systems to present exceptional device characteristics, nanowire heterostructures gained particular interest over the past decade. However, compared to those achieved by mature two-dimensional processing techniques, quasi one-dimensional (1D) heterostructures often suffer from low interface and crystalline quality. For the GaAs-Au system, we demonstrate exemplarily a new approach to generate epitaxial and single crystalline metal-semiconductor nanowire heterostructures with atomically sharp interfaces using standard semiconductor processing techniques. Spatially resolved Raman measurements exclude any significant strain at the lattice mismatched metal-semiconductor heterojunction. On the basis of experimental results and simulation work, a novel self-assembled mechanism is demonstrated which yields one-step reconfiguration of a semiconductor-metal core-shell nanowire to a quasi 1D axially stacked heterostructure via flash lamp annealing. Transmission electron microscopy imaging and electrical characterization confirm the high interface quality resulting in the lowest Schottky barrier for the GaAs-Au system reported to date. Without limiting the generality, this novel approach will open up new opportunities in the syntheses of other metal-semiconductor nanowire heterostructures and thus facilitate the research of high-quality interfaces in metal-semiconductor nanocontacts.

Paracrine cell to cell interactions determine the effects of pituitary adenylate cyclase activating polypeptide (PACAP) on in vitro prolactin release from rat pituitary cells.

In static cultures of dispersed rat pituitary cells and in the reverse hemolytic plaque assay PACAP inhibits prolactin (Prl) secretion, while in vivo application of PACAP stimulates Prl release in rats. To elucidate the mechanism of this contradictory action, we compared the in vitro effects of PACAP on Prl secretion in cultures of dispersed or reaggregated cells and in pituitary fragments. While in monolayer cultures Prl release was inhibited by PACAP, in cultures of aggregated cells and in pituitary fragments Prl release was stimulated. Dopamine (DA) inhibited Prl release in either type of culture. PACAP also stimulated interleukin 6 (IL6) release under each of the experimental conditions. We conclude that PACAP has a direct inhibitory action on lactotropes. In addition, PACAP may induce the release of a paracrine acting factor within the pituitary which stimulates Prl release and which may be IL6. In the intact pituitary tissue and in reaggregated cells this paracrine factor stimulates Prl release more potently than PACAP directly inhibits Prl secretion resulting in a net effect of enhanced hormone release. In monolayer cultures, however, the direct inhibition is dominant, because the stimulatory paracrine factor is diluted in the culture medium. Therefore we suggest that paracrine cell to cell communication is crucial for the action of PACAP on Prl release.

Perceived seriousness of children's surgery and family adaptability and cohesion.

This study investigates the relationship between the family's perception of the seriousness of a child's surgery and the level of family adaptability and cohesion before and after the surgical event. Research hypotheses are based on the Family Crisis and Circumplex models of marital and family systems. Forty-one families were included in the pretest/posttest single group design in which a child underwent a tonsillectomy. Study findings do not consistently support the conceptual models, and implications for the testing of middle range family theories are described.