Gheo-shih: an ancient pre-Columbian plaza

This paper describes the configuration and cultural context of the oldest known designed space in central America, Gheo-Shih, dating from 5,000 - 4,000 BC. This site may have been a ceremonial space, being employed in a similar fashion to ceremonial spaces of Native American cultures from the North American Great Basin. It contains physical features that set precedents and are similar to the geomantic features of later nearby Mesoamerican cultures.     

Phenomenological aspects of a modified fragmentation test using small quantities of explosive

This paper describes the phenomenological aspects of a modified fragmentation test which utilizes an annulus of high explosive in contact with the inner wall of a cylinder of material under test. The shock interactions within the cylinder wall on detonation of the explosive are modelled using a one-dimensional Lagrangian computer code. Predictions of fragment velocities are made in this work. The velocities are found to be influenced by the spallation of the cylinder and this effect can be accounted for in the model by using the position of the spall surfaces which have been obtained from experimental firings of cylinders.

The fragment velocities are found to be much lower than those predicted for a conventional fragmentation test which utilizes a cylinder completely filled with high explosive and this suggests that the post-fragmentation damage of the fragments on recovery from the modified fragmentation test will be small. Experimental evidence from the steel cylinders tested in this work shows that the fragmentation mechanisms operating at the initiation of the test are similar to those reported for a conventional fragmentation test.     

A simple SCC specimen incorporating heat transfer with a crevice or deposits

A simple stress-corrosion cracking (SCC) specimen, suitable for slow strain rate testing and incorporating heat transfer, with an artificial crevice or deposits has been designed and tested. It appears that when the solute level is above a certain value it can concentrate. The kinetics of solute accumulation and the concentration that can be induced in the specimen have been determined. Build up of solute from the ppm level in the bulk environment to the level required to cause cracking can take hours, not days or years. The limiting concentration reached is controlled by thermodynamics, specifically the available superheat. A brief review of relevant literature suggests that this experimental approach to predicting SCC has significant advantages over a modelling or measurement approach. The specimen also lends itself to a monitoring role--a modern version of the Schroeder embrittlement detector.     

Mathematical analysis of viscometric (polymer) flow fields in capillaries: Taylor dispersion revisited

A general formulation for capillary flow of two miscible fluids – one a dilute plug of polymer fluid inserted into a fully developed Poiseuille flow of the other, a Newtonian stream – is examined for its long time behavior. Phenomenologically, the system evolves from an initial state, that of a plug within the boundaries of sharp, well defined fronts inside a Newtonian stream, to a more homogenized state in the very long time scale. This problem was addressed by G.I. Taylor but with regard to a system of two Newtonian fluids, leading to the well-known results commonly described as `Taylor axial dispersion'. In this paper, a general and systematic perturbation analysis is presented from which Taylor's result is recovered as a special case of a more general solution which applies to fluids incorporating elastic properties. In particular, the influence of viscoelasticity and (polymer) diffusivity on the observed pressure profile in the capillary conduit is examined. This effect is clearly separated out for small Peclet number flows using asymptotic and numerical analysis. The results identify the influence of fluid viscosity, elasticity, and diffusivity on the observed pressure profile and form the basis for the improved characterization of polymeric elasticity using capillaries – a finding that is of significant scientific and commercial interest. These results were obtained by the authors as a class of observations resulting from the perturbation analysis of forced-flow capillary devices in viscoelastic fluid property investigation.     

Phase diagram modeling for titanium alloys with light element impurities

It is well known that low levels of light element impurities, such as oxygen and nitrogen, can significantly modify phase equilibria in conventional titanium alloys. However, although the role of nitrogen and oxygen as alpha stabilizers is well established, little quantitative work exists in ternary and higher order systems. Moreover the effect of such elements on equilibria with phases other than cx-and P-Ti is often unknown. The problems in measuring light elements at the microscopic level adds to the difficulty of establishing partitioning, and old axioms are often transferred to new alloys with little evidence that they are applicable. As part of a current program on titanium alloys, phase diagram modeling has been performed for a variety of titanium alloys with additions of oxygen and nitrogen. This paper presents results for the system Ti-Al-V-O-(N,C) with particular reference to the O additions to the commercially important alloy Ti-6A1-4V. This paper was presented at the International Phase Diagram Prediction Symposium sponsored by the ASM/MSD Thermodynamics and Phase Equilibria Committee at Materials Week, October 21–23,1991, in Cincinnati, OH. The symposium was organized by John Morral, University of Connecticut, and Philip Nash, Illinois Institute of Technology.     

Bioprocess applications of model-based estimation techniques

The last decade has seen the development of a number of approaches for estimating those variables which are difficult to measure on-line in industrial process situations. Whilst a range of techniques is available, a common element is the use of process knowledge in the form of a system model. In the case of bioprocess systems, although a large range of models has been presented in the literature, their use in estimation schemes on an industrial scale has been limited. A number of reasons can be identified for their low level of utilisation. Of particular significance is the uncertainty which exists in quantifying system performance and the process-model mismatch which inevitably results. The level of ‘pre-defined model’ uncertainty, together with the knowledge gained during the course of the fermentation, serves to dictate estimator structure. The paper considers a range of estimation strategies and contrasts, through industrial applications, their performance characteristics and utility.