Asymptotic forms of a simplified version of the non-linear Reissner equations for clamped elastic spherical caps under outward pressure

A new, simplified version of Reissner's equations for the torsionless, axisymmetric deformation of elastically isotropic shells of revolution suffering small strains but large angles of rotation is specialized to clamped spherical caps under uniform outward pressure. The non-dimensional equations contain a thickness parameter, a shallowness parameter, and a load parameter. The latter two are written as powers of the former and the dependent variables scaled so that as the thickness parameter goes to zero, meaningful limit equations emerge. Seventeen distinct sets of simplified equations are found. In thirteen cases these are linear and the solutions are listed. These results should provide a useful set of benchmarks for testing the efficacy of numerical codes which often have difficulties with very thin shells.This research was supported by the National Science Foundation under grant MSM-8412334     

An investigation of the impacts of climate change on wave energy generation: The Wave Hub,Cornwall, UK

In this paper a generic methodology is presented that allows the impacts of climate change on wave energy generation from a wave energy converter (WEC) to be quantified. The methodology is illustrated by application to the Wave Hub site off the coast of Cornwall, UK. Control and future wave climates were derived using wind fields output from a set of climate change experiments. Control wave conditions were generated from wind data between 1961 and 2000. Future wave conditions were generated using two IPCC wind scenarios from 2061 to 2100, corresponding to intermediate and low greenhouse gas emissions (IPCC scenarios A1B and B1 respectively). The quantitative comparison between future scenarios and the control condition shows that the available wave power will increase by 2–3% in the A1B scenario. In contrast, the available wave power in the B1 scenario will decrease by 1–3%, suggesting, somewhat paradoxically, that efforts to reduce greenhouse gas emissions may reduce the wave energy resource. Meanwhile, the WEC energy will yield decrease by 2–3% in both A1B and B1 scenarios, which is mainly due to the relatively low efficiency of energy extraction from steeper waves by the specific WEC considered. Although those changes are relatively small compared to the natural variability, they may have significance when considered over the lifetime of a wave energy farm. Analysis of downtime under low and high thresholds suggests that the distribution of wave heights at the Wave Hub will have a wider spread due to the impacts of climate change, resulting in longer periods of generation loss. Conversely, the estimation of future changes in joint wave height-period distribution provides indications on how the response and power matrices of WECs could be modified in order to maintain or improve energy extraction in the future.     

Viral diffusion of technology products: a comprehensive stage framework

Information Systems and e-Business Management - The level of viral diffusion expected after a technology product or service is launched is important for determining the marketing budget,...     

Knowledge-based parametric tools for concrete masonry walls: Conceptual design and preliminary structural analysis

The paper explores the potential uses of parametric modeling to embed construction and structural design knowledge in the form of generative rules and feedback rule-checking functions. The goal of the research reported here is to relate knowledge regarding constructive and structural principles during conceptual design in order to improve early decision-making. For that purpose we have developed a series of functions to guide conceptual design exploration by providing timely evaluation of design alternatives. The research focuses on load-bearing concrete masonry walls, and on basic requirements for doubly curved walls as a design case study. The research extends the Building Object Behavior methodology developed by Lee and others to elucidate, translate and implement design expertise into parametric rules and behaviors. The paper introduces the methodology in the context of a prototype modeling tool for early-stage design of concrete masonry walls and discusses the implications of a parametric modeling approach for conceptual design and collaboration.     

Nanoconfinement of spider silk fibrils begets superior strength, extensibility, and toughness

Silk is an exceptionally strong, extensible, and tough material made from simple protein building blocks. The molecular structure of dragline spider silk repeat units consists of semiamorphous and nanocrystalline β-sheet protein domains. Here we show by a series of computational experiments how the nanoscale properties of silk repeat units are scaled up to create macroscopic silk fibers with outstanding mechanical properties despite the presence of cavities, tears, and cracks. We demonstrate that the geometric confinement of silk fibrils to diameters of 50 ± 30 nm is critical to facilitate a powerful mechanism by which hundreds of thousands of protein domains synergistically resist deformation and failure to provide enhanced strength, extensibility, and toughness at the macroscale, closely matching experimentally measured mechanical properties. Through this mechanism silk fibers exploit the full potential of the nanoscale building blocks, regardless of the details of microscopic loading conditions and despite the presence of large defects. Experimental results confirm that silk fibers are composed of silk fibril bundles with diameters in the range of 20-150 nm, in agreement with our predicted length scale. Our study reveals a general mechanism to map nanoscale properties to the macroscale and provides a potent design strategy toward novel fiber and bulk nanomaterials through hierarchical structures.     

Electrochemically Stimulated Release from Liposomes Embedded in a Polyelectrolyte Multilayer

Triggered release of an entrapped dye from vesicles embedded in a polyelectrolyte multilayer (PEM), as a consequence of the electrochemically induced local pH change in the vicinity of the electrode, is reported. The PEM was deposited on an indium tin oxide (ITO) electrode wherein lipid vesicles filled with a fluorescent dye were embedded. The use of vesicles with a strong negative charge and the polyelectrolyte species of the PEM matrix with a polycation as topmost layer enabled the generation of a stable layer of liposomes in the PEM.     

Microstructural Changes and Kinetics of Reduction of Hematite to Magnetite in CO/CO2 Gas Atmospheres

Metallurgical and Materials Transactions B - The microstructures of porous magnetite formed on gaseous reduction of dense hematite have been examined using high-resolution scanning electron...