Centrifuge model studies on the stability of fibre-reinforced cemented paste backfill stopes

Cemented paste backfill (CPB) is used extensively in Australia for providing ground support during underground mining operations. This paper considered the use of polypropylene fibres to reinforce the partial or whole body of CPB models in laboratory centrifuge tests. Specimens were cast as non-reinforced (tailings, cement and water), quarter-height, half-height and full height fibre-reinforced CPB model stopes. The stability of CPB models with vertically exposed faces was investigated by a series of centrifuge tests. The modelling data showed that the prototype height of fibre reinforced CPB stopes could be much higher than that of unreinforced stopes depending on the extent of reinforcing. The vertical displacement and failure mass ratio of CPB models were also compared and discussed. The distinct failure modes showed that fibre reinforcement was effective in preventing the CPB failing into the strong box. Furthermore, virtually no fragments were spalled from the exposed faces of reinforced sections of the stopes. It indicated that the application of fibre reinforcement would potentially reduce ore dilution and recovery costs, because the risks of failure would be lowered and prototype stope sizes be enlarged.     

Analytic High‐Pressure Phase Equilibria. Part II: Gas Chromatography and Sampling Method Development

The phase equilibria of supercritical CO₂‐alkane‐alcohol mixtures were studied using online gas chromatography. Gas chromatograph design criteria and quantitative detector calibration methods are presented. An adapted manual calibration injection technique eliminated liner overload and pressure wave effects. Observation of the cell contents has proven essential for accurate vapor phase sampling. Visuals, often not visible to the naked eye, show that sampling can disrupt an equilibrated high‐pressure system even though pressure and temperature remain constant within 0.1 bar and 0.01 °C. Such disruptions may manifest in one of three phenomena: global mist formation, localized mist formation, or no‐warning droplet formation.     

Trains of thought on the tabletop: visualizing association of ideas improves creativity

According to the Search for Ideas in Associative Memory theory, ideas in a brainstorming session do not come one by one but rather in “trains of thought,” which are rapid accumulations of semantically related ideas. In order to visualize these trains of thought, we developed a brainwriting tabletop interface enabling users to link successive ideas together by means of graphical ropes. To test the effectiveness of this device, 48 participants (in groups of four) brainstormed for 20 min on the tabletop in one of two conditions: either with the train-of-thought interface (with graphical ropes), or without the ropes (control condition). The results show that visualizing the associations between ideas enabled the participants to produce longer trains of thought. We also assessed originality by collecting the unique ideas in the whole corpus of ideas produced by the different groups and observed that the train-of-thought condition produced more original ideas than the control one. One interpretation of this finding is that visualizing trains of thought increases cognitive stimulation, i.e., improves creativity by making others’ ideas more intelligible to the brainstorming partners, in comparison with the classical visualization of ideas as independent items.     

Peptide-dependent stimulation of the ATPase activity of the molecular chaperone BiP is the result of conversion of oligomers to active monomers

The molecular chaperone BiP purified from bovine liver (bBiP) exhibits a low basal level of ATPase activity that can be stimulated 3-6-fold by synthetic peptides (Flynn, G. C., Chappell, T. G., and Rothman, J. E. (1989) Science 245, 385-390). By contrast, recombinant murine BiP (rBiP) purified to homogeneity following expression in Escherichia coli exhibits a higher basal level of ATPase activity and is much less stimulated by synthetic peptides. Nondenaturing gel electrophoresis showed that rBiP is predominantly monomeric, while bBiP exists in multiple forms probably corresponding to differentially modified monomeric, dimeric, and higher oligomeric species. Some, but not all, synthetic peptides cause conversion of the oligomeric and modified species of bBiP to a monomeric form. We propose that the peptide-dependent ATPase stimulation observed for BiP reflects the conversion of inactive oligomeric and/or modified species into active monomers.     

Pressure drop modelling in cellular metallic foams

A theoretical model is presented for the prediction of pressure drop in a Newtonian fluid flowing through highly porous, isotropic metallic foams. The model is based on a rigorous assumption of piece-wise plane Poiseuille flow and a simplistic geometrical model, and shows promise to accurately predict the hydrodynamic conditions in both the Darcy and Forchheimer regimes, without a priori knowledge of the flow behaviour of the particular metallic foam.     

Estimating the Decant Rate from a Rehabilitated Opencast Colliery Using a Water Balance Approach

The long-term average decant rates from rehabilitated opencast collieries in South Africa are often estimated by assuming effective recharge rates through the spoils. However, large uncertainties are associated with these assumed recharge rates. Furthermore, this approach assumes that groundwater inflows and pit water outflows are negligible compared to the volumes of water recharged through the spoils. To obtain an estimate of the decant rate at a particular colliery, I used rainfall figures, pumping rates, and water elevations measured over a period of 6 months as well as estimated evaporation rates to construct a water balance. I then calculated a decant rate, independent of assumed recharge rates, that was significantly higher than a previous long-term estimate, despite the lower than average rainfall experienced during these 6 months. This discrepancy suggested that groundwater inflow was indeed contributing to the decant volumes. The decant rate during years of average rainfall was subsequently calculated by adding the estimated groundwater inflow to the recharge volumes found with the method based on assumed recharge. This decant rate was approximately 49 % greater than a previous estimate obtained by assuming negligible groundwater inflow. This study shows that the decant rates at rehabilitated opencast collieries could be significantly underestimated if the decants are assumed to be recharge-driven without considering the possibility of groundwater inflow. Underestimation of the decant rates will lead to flawed water management strategies, which could result in adverse environmental impacts.     

A Database Approach to Distributed State Space Generation

We study distributed state space generation on a cluster of workstations. It is explained why state space partitioning by a global hash function is problematic when states contain variables from unbounded domains, such as lists or other recursive datatypes. Our solution is to introduce a database which maintains a global numbering of state values. We also describe tree-compression, a technique of recursive state folding, and show that it is superior to manipulating plain state vectors.This solution is implemented and linked to the μCRL toolset, where state values are implemented as maximally shared terms (ATerms). However, it is applicable to other models as well, e.g., PROMELA models via the NIPS virtual machine. Our experiments show the trade-offs between keeping the database global, replicated, or local, depending on the available network bandwidth and latency.     

The effect of pretreatment on the fermentation of honeybush tea (Cyclopia maculata)

Different pretreatments (bruising, hot and cold water) were used to study their effect on fermentation as measured by the quality parameters of honeybush tea (Cyclopia maculata). Bruising and pretreatment with water (hot and cold) were investigated as means to increase the fermentation rate and to improve product quality. The development of the desired dark-brown colour and honey-like flavour during fermentation was faster in hot and cold water treated material and gave a more uniform coloured product than with the bruising pretreatment. Liquor characteristics also improved with water pretreatment. A red–brown extract, compared with the light yellow–brown of untreated samples, was obtained with the water pretreatment. Hot water pretreatment inactivated the enzymes polyphenol oxidase (PPO) and peroxidase (POD), but did not terminate or impair fermentation. The inactivation of the enzymes, together with high temperature (>60°C) fermentation, indicated a chemical oxidation process rather than an enzymatic reaction in honeybush tea fermentation. © 1998 SCI.     

Heat Removal from Power Electronics in Two Direction Sets Using Embedded Solid State Cooling Layers a Proposed Non-Numerical Calculation Method

The use of embedded cooling layers consisting of materials with high thermal conductivities can significantly reduce peak temperatures within solid-state heat-generating media. Inversely, such layers can also allow for increases in heat-generating densities for a given maximum peak temperature. This is applicable in, for instance, integrated passive power electronics, where power densities are limited by the low thermal conductivities of materials being used. In this paper, the thermal performance of embedded cooling layers in three-dimensional rectangular heat-generating components is investigated numerically for a boundary condition where heat escapes to the ambient in two orthogonal direction sets (sets of orthogonal positive and/or negative directions). The allowable increase in heat generation density for fixed maximum peak temperatures is described for a wide range of geometric shape conditions and thermal conductivities of materials present in such composite structures. Correlations were developed for conditions with and without significant thermal resistance at the internal interfaces of the material layers and externally between the composite component structure and the environment. Conventional one-dimensional and first-order approximations traditionally used in composite solid conduction problems can accurately account for neither the relative thickness of material layers, nor the impact that internal interfacial resistance has. This paper presents a method with which the peak temperature within a stacked sandwich structure containing embedded cooling layered and where heat is removed in two orthogonal direction sets can be determined without the use of a numerical package. The method was developed for a wide range of material properties, geometric sizes and interfacial resistance values.