Fracture toughness and surface energies of minerals: theoretical estimates for oxides, sulphides, silicates and halides

Theoretical estimates of the ideal fracture toughness and surface energies of 48 minerals have been modelled by treating them as ionic solids, using the Born model of bonding. Development of the toughness model required calculation of the crystal binding enthalpy from thermodynamic data and the use of published elastic constants for single crystals. The principal minerals studied were oxides, sulphides and silicates, plus a few halides and sulphates. The study showed grain boundary fracture is most likely in single-phase polycrystalline minerals. However, the fracture toughness for grain boundary cracking in pure minerals is not significantly lower than that for intragranular cracking. The computed critical stress intensity values for intragranular cracking, K_IC, ranged from 0.131 to 2.774 MPa m^1/2. The critical energy release rates for intragranular cracking, , ranged from 0.676 to 20.75 J m⁻². The results are discussed with relevance to mineral comminution, including energy considerations, particle impact efficiency, and lower limiting particle size.     

Chickenpox immunisation in New Zealand

PREVENTION: The appropriate use of varicella vaccine, effective in the prevention of chickenpox, has been considered by a Ministry of Health Working Party in 1996 and 1997, including discussion at a workshop held in Wellington, 26-27 June 1996. The introduction of varicella vaccine into the routine childhood immunisation schedule was not supported at this stage. The use of the only varicella vaccine for which the Minister of Health has given consent for distribution in New Zealand, Varilrix (SmithKline Beecham Limited), in healthy children aged nine months to 13 years inclusive, was supported. Consent has not been given for the use of Varilrix in immunocompromised people or in adults. This report discusses other groups that could be candidates for vaccination, such as children with deteriorating renal function and susceptible health care workers who regularly come into contact with especially vulnerable patients. In these cases, the vaccine would need to be administered on a named patient basis. The use of Varilrix in immunocompromised people was not supported. SURVEILLANCE: Enhanced surveillance of chickenpox and zoster are required in New Zealand. Adverse reactions to Varilrix should be carefully monitored. OUTBREAK CONTROL: There are insufficient data at present to support the use of Varilrix in outbreak control. The frequency, cost and current management of nosocomial outbreaks should be ascertained. This information may also assist in the decision whether to incorporate a varicella vaccine into the routine childhood immunisation schedule in the future.     

Multimedia information using mobile computers: accessing the digital campus and the digital library

Abstract

It is clear that the role of the information resource is changing. Major publishers have been slow to adapt to the emergence of a global digital medium, but there are now signs that a great deal of information will be delivered on-line, (although at present only about 25 databases account for 80% of usage in UK and optical publishing is still in its early stages). However, digital publishing on the Internet — with services for libraries such as just-in-time purchasing and delivery, for example — will be a driving force in creating the ‘global digital medium’. One issue that will become increasingly relevant is how the individual user accesses rich multimedia data in the most appropriate way. The ‘digital university campus’ and the ‘digital library’ are coming to be important concepts, with the aim that users of information services will receive information on-line supported by a ‘ubiquistructure’ of information technology. For the ‘digital campus’ this means that not only scholarly but also teaching activities are based on interactive access to information, and where not only the digital library but also the digital bookshop and the digital classroom are becoming possible with the development of 140Mb/s SuperJANET links. However, it is recognised that libraries will not be truly digital for the foreseeable future, and that libraries will maintain traditional and digital media side by side. In this paper, reporting on work at the University of Bristol's Educational Technology Service multimedia resources unit MRU, and the University of the West of England's Centre for Personal Information Management (in collaboration with Hewlett-Packard Research Laboratories and the University of Bristol's Centre for Communications Research), we look the ‘digital library’ and ‘digital campus’ from the perspective of the individual user and her information needs. We are particularly interested in the use of small, mobile computers as access points to the global digital medium. We suggest that, in an environment of change — where the traditional campus and the traditional library exist alongside the digital campus and digital library — the most appropriate form of access technology is based on ‘personal technology’ which allows a linking between digital information and traditional paper-based information.     

APPLICATION OF FUZZY LOGIC IN ENVIRONMENTAL RISK ASSESSMENT: SOME THOUGHTS ON FUZZY SETS

The fuzzy set of a concept is defined by a distribution function of the degree of belief (DoB) in a qualitative parameter (the concept), over a range of variation in a quantitative or less-qualitative parameter (the scale). The concept may be determined by different scaling parameters and each parameter on its own is not necessarily unique. So the form of a fuzzy set depends almost entirely on the scale selected. In the environmental field, regulators, health authorities, epidemiologists, politicians, environmentalists, engineers, and the general public often define a concept, such as contamination, in different ways. The only term which is more or less unequivocally understood by all interested groups is the final "risk" often associated with dollar value. Proper definition and scaling of fuzzy sets can provide a common language through which experts from different disciplines can communicate through the entire process of risk assessment. Uncertainty in the input information propagates (but is neither magnified nor dampened) in a fuzzy way, so that the output remains fuzzy and can then be translated into either quantitative risk values or qualitative linguistic expressions. In this paper, we examine a real risk assessment case scenario using fuzzy arithmetic.     

Simulating the mine-mill interface

ABSTRACT

A dynamic simulation of a mille-mill complex has been conducted using networked microcomputers (IBM PC/AT and IBM PC/XT)). These models allow simultaneous operation of an open pit using shovels and trucks, a primary crusher, and a secondary crushing plant, Each process transmits information via the network, linking all operations together. The effects of blasting, ore quality, equipment utilization and configuration on productivity can be studied either interactively or from a report listing at the end of each shift. Programs are menu driven leading the user through the decisions required in day to day operations. The mine-mill simulator is currently being used as a teaching tool at Queen is University to provide senior mining and mineral processing engineering students with an experience and appreciation for the operating problems across the mine-mill interface. The need for coordination and close communication between the mine and mill can be aptly demonstrated using these models. The simulator could be used to contribute to the training of operating personnel in a real mining operation.