Mud peeling and horizontal crack formation in drying clays

Mud peeling is a common phenomenon whereby horizontal cracks propagate parallel to the surface of a drying clay. Differential stresses then cause the layer of clay above the crack to curl up to form a mud peel. By treating the clay as a poroelastic solid, we analyse the peeling phenomenon and show that it is caused by the gradient in tensile stress at the surface of the clay, analogously to the spalling of thermoelastic materials. For a constant water evaporation rate at the clay surface we derive equations for the depth of peeling and the time of peeling as functions of the evaporation rate. Our model predicts a simple relationship between the radius of curvature of a mud peel and the depth of peeling. The model predictions are in agreement with the available experimental data available

Thick film silicon growth techniques

Thick film silicon ribbons were produced by means of the edge-defined, film-fed growth (EFG) technique. EFG is a process by which single crystals may be grown having a shape controlled by the outside dimensions of a die, the growth taking place from an extremely thin film of liquid fed by capillary action from a crucible below. The principal problem to be overcome in the application of this process to the growth of thick film silicon ribbon relates to the material, such as the shaping die. For the method to operate, this die material must be wet by the liquid silicon. To preserve semiconductor quality, the liquid silicon must not react significantly with the die material. The most promising die material for this application appears to be SiC and SiC-SiO2 admixture. In this case good wetting occurs between the molten silicon and the SiC. C is a relatively unharmful contaminant of Si and additions of quartz to SiC are found to decrease the extent of reaction

The role of 'African Chemists' in the health care system of the Eastern Cape province of South Africa

Self-medication is documented as an integral part of health care therapy in developing countries such as Ethiopia, Cameroon, Uganda and Mexico. In South Africa the types of illnesses and health problems that are referred to both traditional healers and biomedical practices have been well documented. However, very little literature exists on self-diagnosis, self-medication or sources of the medicines used for self-medication. This bias in the literature has come about largely because anthropological studies have focused on the later stages of the illness referral system when treatment is sought from a specialist for symptoms which have not responded to forms of self-medication. As a result of this, health care studies have documented the more exceptional exotic healing rituals and culturally bound syndromes of a particular society or community, and not discussed the more ordinary practices of self-medication of everyday illness. Self-medication is however an important initial response to illness and many illnesses are successfully managed at this stage. Amayeza stores (singular-iyeza store) — or ‘African chemists’ — are an important source of medicines for self-diagnosed illnesses. The current discussion focuses on the types of medicines and treatments that are obtained from amayeza stores without professional consultation in the Eastern Cape province of South Africa

The trade in medicinal plants in the Eastern Cape Province, South Africa

A study of the trade in medicinal plants in the Eastern Cape Province of South Africa undertook to document the species traded, to determine the quantities harvested annually, and to assess the economic value of the trade. All the participants involved at the different levels of the trade were included in the survey, that is, informal street hawkers, owners of amayeza esiXhosa stores, traditional healers, and consumers of traditional medicines. In total, 282 questionnaires were administered in six urban centres. It was found that poorly educated black middle-aged women of low economic standing dominate the trade. A minimum of 166 medicinal plant species were traded at the study sites alone, providing 525 tonnes of plant material valued at approximately R27 million annually. Plants were harvested from a diverse range of vegetation types including Valley Thicket, Afromontane Forest, Coastal Forest and Moist Upland Grassland, the most frequently sold species differing significantly from those documented in similar studies in other regions. The Forest Biome was the vegetation type found to be most threatened by over-harvesting. Of the species documented, 93% were being harvested unsustainably and 34 species have been prioritised for conservation management

Traditional veterinary medicine in the Alice district of the Eastern Cape Province, South Africa

Resource-poor farmers in rural and peri-urban areas have limited access to veterinary care in terms of support services (from state and private veterinarian and animal health technicians), information about the prevention and treatment of livestock diseases, and preventative and therapeutic veterinary medicines. This results in reduced productivity and in livestock disease and deaths, which is a great burden on these farmers, who can least afford the loss of their animals. There is a need to encourage disadvantaged farmers to use available resources and methods, at minimal cost, and to improve their productivity. One of these resources is ethnoveterinary medicine. A list of 53 plants used as veterinary medicines by stock farmers in the Alice district in the Eastern Cape is presented together with their preparation and methods of administration

Thick film silicon growth techniques

Silicon ribbon growth experiments were conducted using orifices (dies) fabricated from SiC-SiO2 mixtures, fused quartz, SiC, and fine-grained, high density graphite. The best results were obtained from graphite dies. A number of different approaches was tried in modifying the thermal gradient in the dies and in holding the dies. The best results here were obtained from a 0.25-in. thick Mo disc holding a graphite die directly and fitting the die quite closely. Ribbon growths as wide as 9 mm were obtained, while the longest ribbon was 450 x 3.5 x 0.5 mm. Resistivities of ribbons grown from graphite dies have been measured over the range of 0.03 to 1.6 ohm-cm. Some thoughts and literature findings are presented regarding refractory oxide materials as potential orifices

Study of the general mechanism of stress corrosion of aluminum alloys and development of techniques for its detection Quarterly report, 1 May - 31 Aug. 1968

Mechanism of stress corrosion cracking in aluminum alloys and techniques for detection of surface defect

Accessibility of 3D Game Environments for People with Aphasia: An Exploratory Study

People with aphasia experience difficulties with all aspects of language and this can mean that their access to technology is substantially reduced. We report a study undertaken to investigate the issues that confront people with aphasia when interacting with technology, specifically 3D game environments. Five people with aphasia were observed and interviewed in twelve workshop sessions. We report the key themes that emerged from the study, such as the importance of direct mappings between users’ interactions and actions in a virtual environment. The results of the study provide some insight into the challenges, but also the opportunities, these mainstream technologies offer to people with aphasia. We discuss how these technologies could be more supportive and inclusive for people with language and communication difficulties

Sintering Kinetics of Plasma-Sprayed Zirconia TBCs

A model of the sintering exhibited by EB-PVD TBCs, based on principles of free energy minimization, was recently published by Hutchinson et al. In the current paper, this approach is applied to sintering of plasma-sprayed TBCs and comparisons are made with experimental results. Predictions of through-thickness shrinkage and changing pore surface area are compared with experimental data obtained by dilatometry and BET analysis respectively. The sensitivity of the predictions to initial pore architecture and material properties are assessed. The model can be used to predict the evolution of contact area between overlying splats. This is in turn related to the through-thickness thermal conductivity, using a previously-developed analytical model

Ice-lens formation and connement-induced supercooling in soils and other colloidal materials

We present a new, physically-intuitive model of ice-lens formation and growth during the freezing of soils and other dense, particulate suspensions. Motivated by experimental evidence, we consider the growth of an ice-filled crack in a freezing soil. At low temperatures, ice in the crack exerts large pressures on the crack walls that will eventually cause the crack to split open. We show that the crack will then propagate across the soil to form a new lens. The process is controlled by two factors: the cohesion of the soil, and the confinement-induced supercooling of the water in the soil; a new concept introduced to measure the energy available to form a new ice lens. When the supercooling exceeds a critical amount (proportional to the cohesive strength of the soil) a new ice lens forms. This condition for ice-lens formation and growth does not appeal to any ad hoc, empirical assumptions, and explains how periodic ice lenses can form with or without the presence of a frozen fringe. The proposed mechanism is in good agreement with experiments, in particular explaining ice-lens pattern formation, and surges in heave rate associated with the growth of new lenses. Importantly for systems with no frozen fringe, ice-lens formation and frost heave can be predicted given only the unfrozen properties of the soil. We use our theory to estimate ice-lens growth temperatures obtaining quantitative agreement with experiments. The theory is generalizable to complex natural-soil scenarios, and should therefore be useful in the prediction of macroscopic frost heave rates