Industrial screening

Wills' Mineral Processing Technology provides practising engineers and students of mineral processing, metallurgy and mining with a review of all of the common ore-processing techniques utilized in modern processing installations. Now in its Seventh Edition, this renowned book is a standard reference for the mineral processing industry. Chapters deal with each of the major processing techniques, and coverage includes the latest technical developments in the processing of increasingly complex refractory ores, new equipment and process routes. This new edition has been prepared by the prestigious J K Minerals Research Centre of Australia, which contributes its world-class expertise and ensures that this will continue to be the book of choice for professionals and students in this field. This latest edition highlights the developments and the challenges facing the mineral processor, particularly with regard to the environmental problems posed in improving the efficiency of the existing processes and also in dealing with the waste created. The work is fully indexed and referenced.

Ecology of Rickettsia in South America

Until the year 2000, only three Rickettsia species were known in South America: (i) Rickettsia rickettsii, transmitted by the ticks Amblyomma cajennense, and Amblyomma aureolatum, reported in Colombia, Argentina, and Brazil, where it is the etiological agent of Rocky Mountain spotted fever; (ii) Rickettsia prowazekii, transmitted by body lice and causing epidemic typhus in highland areas, mainly in Peru; (iii) Rickettsia typhi, transmitted by fleas and causing endemic typhus in many countries. During this new century, at least seven other rickettsiae were reported in South America: Rickettsia felis infecting fleas and the tick-associated agents Rickettsia parkeri, Rickettsia massiliae, Candidatus ""Rickettsia amblyommii,"" Rickettsia bellii, Rickettsia rhipicephali, and Candidatus ""Rickettsia andeanae. "" Among these other rickettsiae, only R. felis, R. parkeri and R. massiliae are currently recognized as human pathogens. R. rickettsii is a rare agent in nature, infecting : <= 1% individuals in a few tick populations. Contrastingly, R. parkeri, Candidatus ""R. amblyommii, "" R. rhipicephali, and R. bellii are usually found infecting 10 to 100% individuals in different tick populations. Despite rickettsiae being transmitted transovarially through tick generations, low infection rates for R. rickettsii are possibly related to pathogenic effect of R. rickettsii for ticks, as shown for A. aureolatum under laboratory conditions. This scenario implies that R. rickettsii needs amplifier vertebrate hosts for its perpetuation in nature, in order to create new lines of infected ticks (horizontal transmission). In Brazil, capybaras and opossums are the most probable amplifier hosts for R. rickettsii, among A. cajennense ticks, and small rodents for A. aureolatum.

Coupling of composite resin cements to quartz fiber posts: A comparison of industrial and ""chairside"" treatments of the post surface

Purpose: To evaluate the influence of surface treatments on microtensile bond strength of luting resin cements to fiber posts. Materials and Methods: Forty-two quartz fiber posts (Light Post, RTD) were divided into 7 groups (n = 6) according to the surface treatment. I and 11: experimental patented industrial treatment consisting of zirconium oxide coating and silanization (RTD); III: industrial treatment followed by adhesive application (XPBond, Dentsply Caulk); IV: adhesive (XPBond); V: adhesive (Prime&Bond NT, Dentsply Caulk); VI: silane (Calibra Silane, Dentsply Caulk); VII: no treatment. Adhesives were used in the self-curing mode. Two cements (Sealbond, RTD - group 1, and Calibra, Dentsply Caulk - groups 11 to VII) were applied on the posts to produce cylindrical specimens. Post/cement interfaces were evaluated under SEM. The surface of the industrially coated posts was examined using energy dispersive analysis by x-ray. Cylinders were cut to obtain microtensile sticks that were loaded in tension at a crosshead speed of 0.5 mm/min until failure. Statistical analysis was performed using Kruskal-Wallis analysis of variance followed by Dunn`s multiple range test for post-hoc comparisons (p < 0.05). Weibull analysis was also performed. Results: The post/cement bond strength was significantly higher on fiber posts treated industrially (I: 23.14 +/- 8.05 MPa; II: 21.56 +/- 7.07 MPa; III: 22.37 +/- 7.00 MPa) or treated with XPBond adhesive (IV: 21.03 +/- 5.34 MPa) when compared to Prime&Bond NT application (V: 14.05 +/- 5.06 MPa), silanization (VI: 6.31 +/- 4.60 MPa) or no treatment (VII: 4.62 +/- 4.31) of conventional fiber posts (p < 0.001). Conclusion: The experimental industrial surface treatment and the adhesive application enhanced fiber post to resin cement interfacial strength. Industrial pretreatment may simplify the clinical luting procedure.

Variations in cone photoreceptor abundance and the visual ecology of birds

The relative abundance and topographical distribution of retinal cone photoreceptors was measured in 19 bird species to identify possible correlations between photoreceptor complement and visual ecology. In contrast to previous studies, all five types of cone photoreceptor were distinguished, using bright field and epifluorescent light microscopy, in four retinal quadrants. Land birds tended to show either posterior dorsal to anterior ventral or anterior dorsal to posterior ventral gradients in cone photoreceptor distribution, fundus coloration and oil droplet pigmentation across the retina. Marine birds tended to show dorsal to ventral gradients instead. Statistical analyses showed that the proportions of the different cone types varied significantly across the retinae of all species investigated. Cluster analysis was performed on the data to identify groups or clusters of species on the basis of their oil droplet complement. Using the absolute percentages of each oil droplet type in each quadrant for the analysis produced clusters that tended to reflect phylogenetic relatedness between species rather than similarities in their visual ecology. Repeating the analysis after subtracting the mean percentage of a given oil droplet type across the whole retina (the 'eye mean') from the percentage of that oil droplet type in each quadrant, i.e. to give a measure of the variation about the mean, resulted in clusters that reflected diet, feeding behaviour and habitat to a greater extent than phylogeny.

Natural selection and quantitative genetics of life-history traits in Western women: A twin study

Whether contemporary human populations are still evolving as a result of natural selection has been hotly debated. For natural selection to cause evolutionary change in a trait, variation in the trait must be correlated with fitness and be genetically heritable and there must be no genetic constraints to evolution. These conditions have rarely been tested in human populations. In this study, data from a large twin cohort were used to assess whether selection Will cause a change among women in contemporary Western population for three life-history traits: age at menarche, age at first reproduction, and age at menopause. We control for temporal variation in fecundity (the baby boom phenomenon) and differences between women in educational background and religious affiliation. University-educated women have 35% lower fitness than those with less than seven years education, and Roman Catholic women have about 20% higher fitness than those of other religions. Although these differences were significant, education and religion only accounted for 2% and 1% of variance in fitness, respectively. Using structural equation modeling, we reveal significant genetic influences for all three life-history traits, with heritability estimates of 0.50, 0.23, and 0.45, respectively. However, strong genetic covariation with reproductive fitness could only be demonstrated for age at first reproduction, with much weaker covariation for age at menopause and no significant covariation for age at menarche. Selection may, therefore, lead to the evolution of earlier age at first reproduction in this population. We also estimate substantial heritable variation in fitness itself, with approximately 39% of the variance attributable to additive genetic effects, the remainder consisting of unique environmental effects and small effects from education and religion. We discuss mechanisms that could be maintaining such a high heritability for fitness. Most likely is that selection is now acting on different traits from which it did in pre-industrial human populations.

Industrial relations decentralisation and the growth of 12-hour shifts in Australia

In the last two decades, increasing numbers of workplaces in Australia have introduced 12-hour shifts. This increase is due, in part, to government policies aimed at promoting labour flexibility. The purpose of this paper is to examine the cover afforded by the Workplace Relations Act 1996 and other industrial relations legislation in terms of shift-workers’ health and safety. Particular reference is made to the broader social, economic and political context surrounding the introduction and use of 12-hour shifts, as it is this context that shapes the constraints and opportunities facing employers and employees in the work arrangements they choose and how they are negotiated. We conclude that the current system of regulating industrial relations in Australia is largely outcome-focused and inadequate. The bargaining process receives little regulation in terms of considering how changes could affect health and safety in the workplace or how changes might affect individual workers. As a result, the increased introduction of unsafe shiftworking arrangements is a worrying, and likely, prospect.

The visual ecology of avian photoreceptors

The spectral sensitivities of avian retinal photoreceptors are examined with respect to microspectrophotometric measurements of single cells, spectrophotometric measurements of extracted or in vitro regenerated visual pigments, and molecular genetic analyses of visual pigment opsin protein sequences. Bird species from diverse orders are compared in relation to their evolution, their habitats and the multiplicity of visual tasks they must perform. Birds have five different types of visual pigment and seven different types of photo receptor-rods, double (uneven twin) cones and four types of single cone. The spectral locations of the wavelengths of maximum absorbance (lambda (max)) of the different visual pigments, and the spectral transmittance characteristics of the intraocular spectral filters (cone oil droplets) that also determine photoreceptor spectral sensitivity, vary according to both habitat and phylogenetic relatedness. The primary influence on avian retinal design appears to be the range of wavelengths available for vision, regardless of whether that range is determined by the spectral distribution of the natural illumination or the spectral transmittance of the ocular media (cornea, aqueous humour, lens, vitreous humour). Nevertheless, other variations in spectral sensitivity exist that reflect the variability and complexity of avian visual ecology. (C) 2001 Elsevier Science Ltd. All rights reserved.