6,332 publications from this institution
Carbon nanotubes represent ideal probes for high-resolution structural and chemical imaging of biomolecules with atomic force microscopy. Recent advances in fabrication of carbon nanotube probes with sub-nanometer radii promise to yield unique insights into the structure, dynamics and function of biological macromolecules and complexes.
A dual-phase composite comprised of an isotropic distribution of two elastic—perfectly plastic phases is considered. Each phase is characterized by a Mises yield surface and its associated tensile flow stress. The limiting tensile flow stress of the composite is computed in terms of the flow stresses of the phases and their respective volume fractions using a fully non-linear self-consistent model which identifies one phase as particulate and the other as matrix. It is found that the uniform strain-rate upper bound, which is just the rule of mixtures in terms of the phase flow stresses, provides an excellent approximation to the composite flow stress as long as the flow stresses of the phases do not differ by more than a factor of two. The results are applied to obtain some insight into the effect of a non-uniform isotropic distribution of rigid particles in reinforcing an elastic-perfectly plastic matrix. By identifying the tensile flow stresses of the two phases with flow stresses of particle-rich and particle-poor regions, one can predict the dependence of the limit flow stress of the composite on certain types of non-uniform distributions of the rigid particle reinforcements.
No abstract is provided for this article.
The ductile vs brittle behaviour of metal-ceramic interfaces is discussed within an atomistic framework, in which the mechanical response of an interfacial crack is assumed to be ultimately controlled by the competition between atomic decohesion and dislocation nucleation ahead of the crack tip. As in later versions of the Rice-Thomson model, this competition may be evaluated in terms of the parameters G cleave, the energy release rate for cleavage of the metal-ceramic interface, and G disl, the energy release rate associated with the emission of a single dislocation within the metal. The various models of dislocation nucleation are discussed, with emphasis on an approach which makes use of Peierls-like stress vs displacement relations on a slip plane ahead of a crack tip. A recent analytical result by Rice shows that for a mode II or III shear crack, with a slip plane parallel to the ack plane, a dislocation is emitted when G = γus (G is the energy release rate corresponding to the “screened” crack tip stress field and γus is the “unstable stacking” energy associated with the sliding of atomic planes past one another). This treatment permits the existence of an extended dislocation core, which eliminates the need for the core cutoff radii required by the Rice-Thomson model of emission. Results are presented here for the nucleation of dislocations under more realistic assumptions for metal-ceramic cracks, namely, the emission on inclined slip planes within a mixed-mode crack-tip field. The specific case of a copper crystal bonded on a {221} face to sapphire is analyzed, and the results are used to interpret the recent experimental observations of Beltz and Wang [Acta metall. mater. 40, 1675 (1992)] on directional toughness along this type of interface.
Addition of 2,4-dimethylbenzenesulfenyl chloride to sialic acid glycal gives crystalline 2-chloro-3-thiosialic acid 3 in 85% yield. Reaction of 3 with sodium thiomethoxide in acetonitrile at 0 °C affords the sialic acid donor α-2-(methylthio)-3-thiosialic acid 4 in quantitative yield. Sialylation of glycosyl acceptors 9 and 10 with 4 in the presence of phenylsulfenyl triflate (PST) as promotor in CH3CN at −40 °C gives α-sialosides in good yield and excellent stereoselectivity. No β-sialosides are formed in either case. Removal of the auxiliary 3-(2,4-dimethylphenyl)thio group is achieved in high yield using Ph3SnH and AIBN in refluxing toluene. Protected GM3 trisaccharide and 6-sial-2-yllactose were obtained on a gram scale.
No abstract is provided for this article.
Abstract Objectives: Our aim in this cross‐sectional study was to investigate whether self‐reported gingivitis and tooth loss were associated with elevated levels of C‐reactive protein (CRP) using the same study population where these dental conditions have earlier been associated with prevalent angina pectoris. Material and Methods: The study population consisted of those Northern Finland birth cohort 1966 members who lived in Northern Finland or in the Helsinki region ( n =8463) at the time of the survey (1996–1997). The participation rate in a health examination was 71% ( n =6033). Gingivitis and tooth loss were determined on the basis of self‐reported questions. Prevalence proportion ratios (PPR) and 95% confidence intervals (CI) were estimated using multivariate regression models. Results: The results showed that self‐reported gingivitis and tooth loss were weakly associated with elevated levels of CRP (>3 mg/l): adjusted PPR 1.1, CI 1.0–1.3 and PPR 1.1, CI 0.7–1.7, respectively. The proportion of variation in CRP explained by self‐reported gingivitis and tooth loss was small, being <1%. Conclusion: The results suggest that self‐reported gingivitis and tooth loss have a miniscule effect on CRP levels among a general population of young adults.
The mechanics of the formation and propagation of ridges on compressed stiff film/compliant substrate systems is studied theoretically and experimentally. Ridges form on bilayer systems where the elastomeric substrate is subject to a significant pre-stretch prior to attachment of the film. When the bilayer is then subject to increasing overall compressive strain, sinusoidal wrinkles first form and subsequently become unstable giving way to localized ridges with relatively large amplitudes. Two-dimensional plane strain simulations for neo-Hookean film/substrate systems reveal the transition from wrinkles to ridges under increasing compression and the reverse transition from ridges to wrinkles when the overall compression is subsequently reduced. For a significant range of pre-stretch, the two transition strains differ, and a significant hysteresis response is observed in a complete cycle of loading and unloading. The Maxwell equal-energy condition has been identified associated with co-existence of wrinkles and ridges and with the three-dimensional steady-state propagation condition for the ridges. Experiments conducted with a specially designed film/substrate loading system have been performed that confirm the essential features of ridge formation and the hysteretic behavior in loading/unloading cycles that span the two transitions.
