6,332 publications from this institution
Abstract This chapter begins by discussing conceptual definitions and the multidimensional aspects of physical activity and exercise. It then describes self-reported methods and monitoring devices for measuring physical activity commonly used in epidemiologic studies. It discusses validation studies of physical activity questionnaires and methods used to correct for measurement errors in the analyses of physical activity and obesity and weight change.
difficult criticality design problems have been solved with the new geometry package in KENO-IV/CG, thus illustrating the power of the code to model difficult geometries with a minimum of effort.
The reliable fabrication of nanostructures is polymer materials , i.e. structures with feature sizes below 100 nm, is an important goal if progress in the application of such materials in electronic, magnetic, and optical devices is to be maintained. Replica molding has been used extensively to produce micrometer sized features. Here, the technique is extended to the nanometer regime such as that shown in the figure. fig. magnified image
Self‐assembled monolayers (SAMs) of hexadecanethiolate were patterned onto gold films supported on titanium‐primed silicon wafers using microcontact printing (μCP). Wet etching of the gold, and subsequently of the silicon, using three systems of resists based on these patterned SAMs, denoted by the shorthand labels Au/SAM, Ni/Au/SAM, and Au/SAM/polymer, produced features in silicon having dimensions in the 1 to 10 μm scale. In the Au/SAM system, the SAM acted as a resist to protect gold from etching by , and the resulting, patterned gold protected silicon from etching by (25% by volume) at 60°C. In the Ni/Au/SAM system, the pattern in the gold layer was transferred to an underlying nickel layer by etching in a bath consisting of conc , 30% , conc , and 30% aqueous solution of (5:5:1:4 by volume) at 35–40°C; in turn, the nickel acted as a resist to protect the silicon from etching. In the Au/SAM/polymer, a prepolymer of epoxy resin or polyurethane was self‐assembled onto hydrophilic SAMs on the surface that was patterned into regions of different interfacial free‐energy and wettability; after curing, the polymer served as the resist during etching gold by aqua regia, and etching silicon by . All three resists were compatible with etchants for silicon, and they masked the underlying silicon effectively.
Self-assembly is the autonomous organization of components into patterns or structures without human intervention. Self-assembling processes are common throughout nature and technology. They involve components from the molecular (crystals) to the planetary (weather systems) scale and many different kinds of interactions. The concept of self-assembly is used increasingly in many disciplines, with a different flavor and emphasis in each.
Dimensional reduction is applied to derive a one-dimensional energy functional governing tensile necking localization in a family of initially uniform prismatic solids, including as particular cases rectilinear blocks in plane strain and cylindrical bars undergoing axisymmetric deformations. The energy functional depends on both the axial stretch and its gradient. The coefficient of the gradient term is derived in an exact and general form. The one-dimensional model is used to analyze necking localization for nonlinear elastic materials that experience a maximum load under tensile loading, and for a class of nonlinear materials that mimic elastic-plastic materials by displaying a linear incremental response when stretch switches from increasing to decreasing. Bifurcation predictions for the onset of necking from the simplified theory compared with exact results suggest the approach is highly accurate at least when the departures from uniformity are not too large. Post-bifurcation behavior is analyzed to the point where the neck is fully developed and localized to a region on the order of the thickness of the block or bar. Applications to the nonlinear elastic and elastic-plastic materials reveal the highly unstable nature of necking for the former and the stable behavior for the latter, except for geometries where the length of the block or bar is very large compared to its thickness. A formula for the effective stress reduction at the center of a neck is established based on the one-dimensional model, which is similar to that suggested by Bridgman (1952).
This paper is dedicated to Charles and Marie-Louise
A crack in a brittle substrate parallel to the film/substrate interface is considered. Stress intensity factors are obtained as a function of fiim, substrate thickness, elastic properties and edge loads at arbitrary crack depth. These results, combined with the criterion K 11 = 0. are used to predict the steady-state cracking depth. The critical combination of residual stress and film thickness below which steady-state substrate cracking is avoided can be inferred provided the substrate toughness is known.