Imidazole catalysis in carbamate and polyurethane formation

Polyurethanes have been prepared from the reactions of the diimidazole and ditriazole adducts of 2,4-toluene diisocyanate and ethylene glycol or polyols. Suitable formulations have been developed from these components which are useful in preparing polyurethane coatings and foams. Imidazole was established as an effective catalyst for the reactions of the diphenol adduct of 2,4-toluene diisocyanate with polyols. Imidazolecatalyzed polyurethane formation from the phenol-blocked diisocyanate occurs readily between 100° and 140°C. A mechanism for the catalytic activity of imidazole in these reactions is proposed.     

Reversible bistable switching in nanoscale thiol-substituted oligoaniline molecular junctions

Single molecular monolayers of oligoaniline dimers were integrated into sub-40-nm-diameter metal nanowires to form in-wire molecular junctions. These junctions exhibited reproducible room temperature bistable switching with zero-bias high- to low-current state conductance ratios of up to 50, switching threshold voltages of approximately +/-1.5 V, and no measurable decay in the high-state current over 22 h. Such switching was not observed in similarly fabricated saturated dodecane (C12) or conjugated oligo(phenylene ethynylene) (OPE) molecular junctions. The low- and high-state current versus voltage was independent of temperature (10-300 K), suggesting that the dominant transport mechanism in these junctions is coherent tunneling. Inelastic electron tunneling spectra collected at 10 K show a change in the vibrational modes of the oligoaniline dimers when the junctions are switched from the low- to the high-current state. The results of these measurements suggest that the switching behavior is an inherent molecular feature that can be attributed to the oligoaniline dimer molecules that form the junction.     

Novel ultrananocrystalline diamond probes for high-resolution low-wear nanolithographic techniques

A hard, low-wear probe for contact-mode writing techniques, such as dip-pen nanolithography (DPN), was fabricated using ultrananocrystalline diamond (UNCD). Molding within anisotropically etched and oxidized pyramidal pits in silicon was used to obtain diamond tips with radii down to 30 nm through growth of UNCD films followed by selective etching of the silicon template substrate. The probes were monolithically integrated with diamond cantilevers and subsequently integrated into a chip body obtained by metal electroforming. The probes were characterized in terms of their mechanical properties, wear, and atomic force microscopy imaging capabilities. The developed probes performed exceptionally well in DPN molecular writing/imaging mode. Furthermore, the integration of UNCD films with appropriate substrates and the use of directed microfabrication techniques are particularly suitable for fabrication of one- and two-dimensional arrays of probes that can be used for massive parallel fabrication of nanostructures by the DPN method.     

Grapefruit Oil Enhances Attraction of Mexican Fruit Flies to a Synthetic Food-Odor Lure

We investigated the attractiveness of grapefruit oil to the Mexican fruit fly. Only high concentrations were attractive in laboratory wind-tunnel bioassays. Attraction of flies to grapefruit oil was not enhanced if they had previous experience with grapefruit. In citrus orchard experiments, undiluted grapefruit oil attracted Mexican fruit flies and enhanced attraction to traps baited with a synthetic food-odor lure emitting ammonia and other nitrogenous chemicals. This is the first demonstration of host fruit odor increasing attraction to another type of attractive blend in Mexican fruit fly. These results indicate differences in the way the flies respond to undiluted grapefruit oil compared with previously tested fruit odors.     

Results of an intervention for the improvement of operating room quality and safety. Note 1: anesthetic gases

The proliferation of human melanoma cell line A375-6 is inhibited by several cytokines, including interleukin-1 (IL-1) and interleukin-6 (IL-6). However, during a long period of culture, the cells progressively acquire resistance to IL-1 irrespective of functional IL-1 receptor expression. These cells constitutively produce IL-1alpha and IL-6, and also acquire resistance to IL-6. In order to investigate the mechanism of the acquired resistance to these cytokines, we performed somatic cell hybridization experiments. Parental cells for the construction of hybrid cells were rendered G418- or hygromycin B-resistant by transfection with expression vectors containing drug-resistant genes. Hybridization was conducted using IL-1-resistant subclones A375-R8 and R19 and an IL-1 highly sensitive clone C2-1, which was originally resistant but became sensitive to IL-1 upon transfection with a human type I IL-1 receptor (IL-1R) expression plasmid. Cells produced by hybridization of resistant cells and C2-1 cells appeared to be sensitive to IL-1 and IL-6. In contrast, production of IL-1 was augmented in the hybrid cells. These results suggest that resistance to IL-1 and IL-6 is a recessive phenotype, while production of IL-1 is dominant in melanoma cells.     

MODELLING THE CONDITIONS FOR FATIGUE FAILURE IN METAL MATRIX COMPOSITES

Abstract— An investigation on the fatigue crack growth (FCG) and fatigue failure in metal matrix composites (MMCs) has been conducted using a model based on micromechanical elasto-plastic fracture mechanics (EPFM) principles. To evaluate the model, comparisons between experimental and predicted fatigue life have been made for two silicon carbide strengthened (SCS)-6/Ti-based MMCs. Conditions for crack arrest and crack instability have also been considered in order to define the fatigue damage limits. Crack arrest occurs from the added effects of fibre bridging and the constraint provided by the fibre on matrix microplasticity, while crack instability is achieved when the fibre constraint effect is minimum and the fatigue resistance of the material is reduced due to the accumulation of fatigue damage. Comparisons of the predicted fatigue damage limits with experimental results show good agreement which underlines the usefulness of a microstructural fracture mechanics model.     

Mecanismes de colmatage et performances comparées de quatre membranes d'alumine: Cas de l'ultrafiltration de gelatine

This paper deals with gelatin ultrafiltration using alumina membranes of various pore sizes (0.2, 0.8, 1.4 et 2.0 μm). Pressure, tangential velocity and concentration effects are successively examined. From both a quantitative analysis of experimental data (pure solvent fluxes with clean or prefouled membranes, ultrafiltration fluxes, percent protein rejection) and the application of traditional model equations (filtration theory, film model), fundamental hypotheses are suggested concerning membrane functional characteristics. In particular, it is how fouling mechanisms and protein deposit structures are related to membrane characteristics. Finally, a comparison of membrane performances leads to the conclusion that the best fluxes and percent protein rejections are obtained using the 0.2 μm pore size membrane.