Explicit Formulation of the Shields Diagram for Incipient Motion of Sediment

The Shields diagram remains the most widely used criterion for incipient motion of sediment. However its implicit nature makes applications rather inconvenient. By deploying Guo’s logarithmic matching method twice, this technical note develops an explicit formulation of the Shields diagram, enabling the critical Shields parameter to be determined directly from fluid and sediment characteristics without resorting to any trial and error procedure or iteration. An extended application of the logarithmic matching method is demonstrated.     

Surface modification of calcium carbonates studied by inverse gas chromatography and the effect on mechanical properties of filled polypropylene

Inverse gas chromatography (IGC) has been used to characterize the surfaces of a pure calcitic calcium carbonate as well as samples that had been treated with sodium polyacrylate and/or stearic acid. The dispersive components of the surface free energy for the pure material agreed well with related literature data. Polar contributions to the surface interactions with a range of probes were determined. The results show that the surface treatments reduced the polarities of the surfaces and that modification with stearic acid produced a non-polar, low-energy surface. Some mechanical properties of the polypropylene composites containing the modified calcium carbonates were found to correlate well with the filler surface energies. Copyright © 2004 Society of Chemical Industry     

Retained austenite and tempered martensite embrittlement

The problems of detecting the distribution of small amounts (5 pct or less) of retained austenite films around the martensite in quenched and tempered experimental medium carbon Fe/c/x steels are discussed and electron optical methods of analysis are emphasized. These retained austenite films if stable seem to be beneficial to fracture toughness. It has been found that thermal instability of retained austenite on tempering produces an embrittlement due to its decomposition to interlath films of M₃C carbides. The fractures are thus intergranular with respect to martensite but transgranular with respect to the prior austenite. The temperature at which this occurs depends upon alloy content. The effect is not found in Fe/Mo/C for which no retained austenite is detected after quenching, but is present in all other alloys investigated.     

Porosity and texture of basic zirconium nitrate

Studies have been made of the development of texture and porosity in basic zirconium nitrate samples subjected to heat treatment at temperatures between 25 and 500°C. Scanning electron microscopy indicates that progressive disintegration of the amorphous material occurs over this temperature range, generating approximately spherical particles. Nitrogen gas adsorption studies, supplemented by mercury porosimetry measurements, show that these particles possess some microporosity (pore diameter < 2 nm), although the major factor controlling their adsorptive properties is an intrinsic mesoporosity related to a pore diameter within the range 2–50 nm and produced by the successive elimination of water and nitrato ligands with increasing temperature. Crystallisation occurs when the system is heated above 500°C, leading to the conversion of the amorphous material to the cubic variety of zirconia.     

A simulated annealing approach to integrated production scheduling

This paper describes an approach to manufacturing planning that seeks to integrate both process planning and scheduling. We show that separating these two related tasks, as is the common practice, can impose constraints that substantially reduce the quality of the final schedule. These constraints arise from premature decisions regarding operation sequence and allocation of manufacturing resources. Having formulated an integrated process planning and scheduling problem, we describe a solution technique based on simulated annealing. We compare this approach with others reported in the literature, considering both their generality and performance. In particular, we perform a detailed empirical comparison between simulated annealing and the popular technique of dispatching rules. Our results, achieved with two distinct sets of example problems, show that simulated annealing can produce solutions of significantly higher quality than those achieved through a published dispatching rule approach.     

A generalization of atom location by channelling enhanced microanalysis

The technique of atom location by channelling enhanced microanalysis (ALCHEMI), has limitations in practical application. A generalization of this technique, with the underlying idea that additional relationships can be generated by performing these experiments at an appropriate number of orientations depending upon the stoichiometry of the original compound has been developed. The precise number of orientations required to solve the distributions in a whole class of related compounds is expressed in terms of the stoichiometry of the original compound along with the alloying additions.     

Interactive visual modeling for performance

An overview is given of Q+, an interactive tool for performance modeling that uses graphical input and visual output. Two major enhancements are a subnetwork capability for structuring models hierarchically and an integrated expression capability. New capabilities are custom icons and temporal browsing. With a Q+ icon palette, users can draw their own icons and manipulate existing ones. The browser allows browsing, editing and updating Q+ information, which can be textual or graphical. Automatic model building, operations management, and experimental design with Q+ are discussed     

Climate sensitivity of marine energy

Marine energy has a significant role to play in lowering carbon emissions within the energy sector. Paradoxically, it may be susceptible to changes in climate that will result from rising carbon emissions. Wind patterns are expected to change and this will alter wave regimes. Despite a lack of definite proof of a link to global warming, wind and wave conditions have been changing over the past few decades. Changes in the wind and wave climate will affect offshore wind and wave energy conversion: where the resource is constrained, production and economic performance may suffer; alternatively, stormier climates may create survival issues. Here, a relatively simple sensitivity study is used to quantify how changes in mean wind speed—as a proxy for wider climate change—influence wind and wave energy production and economics.     

Hard missile impact on reinforced concrete

New penetration, scabbing and perforation formulae are derived for use in the design of reinforced concrete barriers to withstand impact by hard missiles. This is done by using dimensional analysis together with physical theories for the various impact processes. This leads to impact formulae with unknown coefficients which are then determined by an analysis of all available test data. The new formulae so derived are simple and, because of their parametric formulation, have a range of applicability easily definable in terms of impact parameters. The analysis indicates that some recently proposed impact formulae are not safe from the point of view of barrier design because the test data used for their derivation was affected by global movement of the barriers which reduced the measured local damage.