Showing papers by "University of Western Australia published in 1988"

Feature Detection in Human Vision: A Phase-Dependent Energy Model

Abstract: This paper presents a simple and biologically plausible model of how mammalian visual systems could detect and identify features in an image. We suggest that the points in a waveform that have unique perceptual significance as 'lines' and 'edges' are the points where the Fourier components of the waveform come into phase with each other. At these points 'local energy' is maximal. Local energy is defined as the square root of the sum of the squared response of sets of matched filters, of identical amplitude spectrum but differing in phase spectrum by 90 degrees: one filter type has an even-symmetric line-spread function, the other an odd-symmetric line-spread function. For a line the main contribution to the local energy peak is in the output of the even-symmetric filters, whereas for edges it is in the output of the odd-symmetric filters. If both filter types respond at the peak of local energy, both edges and lines are seen, either simultaneously or alternating in time. The model was tested with a series of images, and shown to predict well the position of perceived features and the organization of the images.

Singular-Value Decomposition and the Grassberger-Procaccia Algorithm

Abstract: A singular-value decomposition leads to a set of statistically independent variables which are used in the Grassberger-Procaccia algorithm to calculate the correlation dimension of an attractor from a scalar time series. This combination alleviates some of the difficulties associated with each technique when used alone, and can significantly reduce the computational cost of estimating correlation dimensions from a time series.

A4 amyloid protein deposition and the diagnosis of Alzheimer's disease Prevalence in aged brains determined by immunocytochemistry compared with conventional neuropathologic techniques

Abstract: The histologic diagnosis of Alzheimer9s disease (AD) might be aided if a more sensitive marker of aberrant A4 amyloid protein deposition were available. We screened a sample of aged brains, using immunocytochemical methods to detect the A4 protein deposition, and found that, in comparison with conventional histologic techniques (silver impregnation and Congo red), immunocytochemistry is more sensitive and allows an easier demarcation between “normal” and “abnormal.” If A4 protein deposition is accepted as a definitive marker for AD, then the age-related prevalence of AD increases dramatically. To what degree these prevalence rates are reflected in clinically detectable impairment of higher cortical function remains to be determined.

On the O'Nan-Scott theorem for finite primitive permutation groups

Abstract: We give a self-contained proof of the O'Nan-Scott Theorem for finite primitive permutation groups.

Exercise and the Immune Response

Abstract: A growing number of reports have become available which implicate infectious disease with reduced performance in athletes. The immune system consists of both nonspecific and specific components geared to control infections. Adaptive immunity functions through both antibody-mediated and cell-mediated compartments to establish and maintain long term immunity to infectious agents. Evidence is accumulating to support the view that physical exercise can lead to modification of the cells of the immune system. However, studies have often not been well designed to control exercise protocols when examining the effects of exercise on the immune system. Large numbers of peripheral blood lymphocytes are mobilised with exercise and in vitro tests indicate that temporarily these cells may not be capable of responding normally to mitogens. These reactions appear to be influenced by hormones to some degree and there are reports that the cells of the immune system are extremely active biochemically and may depend on products from muscles to maintain their activity. Specific populations within the circulating leucocyte pool vary significantly with exercise and there is some evidence that the T4/T8 lymphocyte ratio may become significantly reduced. This reduction in ratio may be related to the variable responses to T and B cell mitogens recorded in vitro which overall suggests that a temporary immune suppression may exist following certain training or performance schedules. It is argued that this may lead to a temporary susceptibility to infection and could result from overtraining.

Epidemiology of malignant melanoma: intermittent or total accumulated exposure to the sun?

Abstract: In accordance with the sunlight hypothesis for its etiology, the incidence of malignant melanoma generally increases with increasing proximity to the equator. There are exceptions to this pattern, prominent among which is the tendency for incidence to increase with increasing distance from the equator beyond latitude 50 degrees north in Europe. This anomaly is probably explicable in terms of climatic factors, geographic variation in skin pigmentation, and the sun-seeking behavior of those in the north. The incidence of malignant melanoma is increasing at about 5% a year in most white populations, while there is no consistent tendency for it to increase in black populations. This difference suggests that the increase is due to increasing sun exposure. Evidence from recent case-control studies is consistent with both intermittent intense exposure and total accumulated exposure to the sun causing an increase in risk of malignant melanoma. Reconciliation of these two different patterns of effect of sun exposure may lie in more careful measurement of sun exposure and analysis of exposure specific to the site at which each melanoma is observed to occur.

Coral reef primary productivity: A beggar's banquet.

Abstract: Flashy venue, high attendance and much activity: but the food is plain and hard to find, and at the end of the day nobody leaves with much. Primary production in coral reef ecosystems proceeds rapidly through small packages. Maximum areal rates rival the best agricultures, but most of the organic production is conserved and recycled within component organisms and communities. Interactions with animals serve to maximize the productivity of both individual plants and extensive plant assemblages. The diverse aspects of the topic have attracted research for over 40 years. In this, the first of a two-part review, I describe the components of coral reef primary productivity at several levels of organization, and discuss recent approaches to their studs

Implementing packaged software

Abstract: This article presents a model of the implementation process for dedicated packages and describes a research project to test the model undertaken with the cooperation of a major computer vendor. Data were collected from y8 individuals in 18 firms using the package and from the package vendor. The results of the study offer some support for the model, along with suggestions for package implementation for both the customer and package vendor.

The nature, extent and significance of variation within the genus Echinococcus.

Abstract: Publisher Summary This chapter discusses the nature, extent, and significance of variation particularly, below the species level, in the causative agent of hydatid disease, Echinococcus. An application of current taxonomic procedures to the classification of a group of organisms in Echinococcus ensures an important role for the explanatory and predictive value of taxonomic determinations in studies on the epidemiology and control of hydatid disease. Despite increasing access to highly discriminatory differential criteria and a more flexible taxonomic approach, problems of nomenclature are likely to remain. Many genetically distinct populations within the recognized species of Echinococcus cannot be adequately allocated to a formal taxonomic category. However, in parasitic organisms the recognition of variation may be of great medical and agricultural significance and it is for this reason that the term “strain” has been widely used to describe intraspecific variants in Echinococcus and other parasites. It is essential that strains are indentified and characterized in each endemic area if effective control programs are to be instituted. Future research should aim to develop even more reliable and practically applicable differential criteria for this purpose. Biochemical and molecular dissection of the parasite in a quest toward this end may also unravel the functional nature of strain variation and provide direction for the development of chemotherapeutic agents.

A review of the histologic changes in vein-to-artery grafts, with particular reference to intimal hyperplasia

Abstract: • This article reviews the success of vein-to-artery grafts and the published data on patency rates and the major causes for graft failure, ie, intimal hyperplasia and atherosclerosis. It concentrates on the histogenesis of intimal hyperplasia and describes the histologic changes that occur in a vein graft after its insertion. The origin and behavior of intimal smooth-muscle cells are discussed in detail, with particular reference to their role in intimal hyperplasia. A brief experimental section Is included to show the specific identification of vein-graft intimal smooth-muscle cells using light-microscopic histochemistry and electron microscopy. ( Arch Surg 1988;123:691-696)

Courtship feeding and the fitness of female katydids (orthoptera: tettigoniidae).

Abstract: Katydid males (Requena verticalis) produce spermatophores with a large sperm-free spermatophylax, which is eaten by the female after mating. In this study, I asked 1) how do spermatophylax nutrients affect the fitness of the mated female and her progeny? 2) does this male-produced food substitute for other food in the diet of the female, or is it a source of specialized nutrients? and 3) does an increase in the size of the spermatophylax eaten influence female reproduction in the same way as the additional spermatophylaxes that would be obtained from multiple mating? An experimental increase either in dietary protein or the number of spermatophylaxes eaten increased the number of eggs produced. However, spermatophylax size had no effect on egg number. An increase in either the size or number of spermatophylaxes eaten resulted in an increase in egg size. There was no influence of protein in the general diet on egg size. This suggests that males provide nutrition not available from other sources. Although there were no direct effects of number of spermatophylaxes eaten by females on the overwintering survival of their progeny, offspring from females producing larger eggs had a relatively higher probability of surviving winter. The amount of spermatophylax eaten had no influence on the mean adult size of progeny but significantly increased the mean date at which sons matured to adulthood. There was no influence of dietary protein on these variables. Since maturation date is positively correlated with adult size in both sexes, it is suggested that the influence of courtship feeding on maturation date may result in an increase in adult size and thus the fitness of sons. A significant correlation between the size of the female and the mean size of her sons (but not daughters) suggests that there is also a heritable component to body size.

Mortality in miners and millers of crocidolite in Western Australia.

Abstract: It is known that 6505 men and 411 women were employed in the mining and milling of crocidolite at Wittenoom in the Pilbara region of Western Australia between 1943 and 1966. Employment was usually brief (median duration four months) and exposure intense (median estimated cumulative exposure 6 fibres/cc years). The vital status of 73% of the men and 58% of the women employed in the industry was known at 31 December 1980, providing 95 264 person-years of follow up with 820 deaths in men and 4914 person-years with 23 deaths in women. The standardised mortality ratio (SMR) for all causes in men was 1.53 (95% confidence interval 1.43 to 1.64). Statistically significant excess death rates were observed in men for neoplasms, particularly malignant mesothelioma (32 deaths), neoplasms of the trachea, bronchus, and lung (SMR 2.64), and neoplasms of the stomach (SMR 1.90); respiratory diseases, particularly pneumoconiosis (SMR 25.5); infections, particularly tuberculosis (SMR 4.09); mental disorders particularly alcoholism (SMR 4.87); digestive diseases, particularly peptic ulceration (SMR 2.46) and cirrhosis of the liver (SMR 3.94); and injuries and poisonings, particularly non-transport accidents (SMR 2.36). The excess mortality from pneumoconiosis, malignant mesothelioma, and respiratory cancers, but not stomach neoplasms, was dependent on time since first exposure and cumulative exposure. There was no increase in mortality from laryngeal cancer (SMR 1.09) or neoplasms other than those listed. The SMR for all causes in women was 1.47 (95% confidence interval 0.98-2.21) and for neoplasms 1.99; there was one death from malignant pleural mesothelioma.

Oestrogen therapy after the menopause--boon or bane?

Abstract: The results of this analysis are unequivocal: in the aggregate of all studies\"ever use\" of oestrogentherapydoes not alter the risk of breast cancer by any measurableamount.However, theP values suggest that the individual relative risks are not all consistent with the summary estimate of relative risk. Examinationof the contributions of the individual studies to the over-all value of chi-squared on which theP values were based showed that, in most cases, the studies with relative risks thatweresubstantiallydifferent from the summary estimate were distributedapproximatelyequally between those studies with relative risks that were greater than the summary estimate and those studies with relative risks that were less thanthe summary estimate. Thus, it seems unlikely that the summary estimates are biased appreciably by these studies. Analyses were alsoundertakenof studies in which relative risks were presented in categories of estimated dose of oestrogens (as measured by total cumulative dose, durationof use or dose per day), according to whether the women had had an artificial or natural menopause, and by a past history of benign breast diseaseor a family history of breast cancer. Only when the relative risk for the highest dose category in each study was used, or when women with a family history of breast cancer were studied, was there any suggestion that oestrogens might influence the incidence of breast cancer. In the former case, the summary relative risk was 1.04with a 95% 20 studies have been published from which quantitativemeasures of theassociationbetween oestrogen therapy and breast cancer can be derived. 2 7 The estimates of the effect of oestrogen therapy on breast cancer vary from a \"statisticallysignificant\"halvingeffect\" to a similarly\"significant\" doubling of therisk.\" So which results do we believe? The technique of \"meta-analysis\"provides one path to an answer to this question.Meta-analysis is: • the processof combiningstudyresults [ ... It] is a systematicreviewing strategyfor addressingresearchquestionsthat is especially useful when results from several studies disagree with regard to magnitudeor direction of effect,whensamplesizes areindividually too small to detect an effect and label itstatisticallysignificant,or when a large trial is too costly and time-consumingto perform. The Table summarizes the results of a meta-analysisthatis based on 23 studiesof oestrogens and breast cancer, including that of Rohan and McMichael, from which numerical estimates of relative risk could bederived,\"\"The summary estimates of relative risk were derived from the individual relative risks by computinga weighted mean of theirnaturallogarithms where the weight that was assigned to eachlogarithmof relative risk was inversely proportionalto its variance.\" Chi-squaredstatistics were calculated to permit the estimationof the probability (the P value for heterogeneity) that the individual relative risks were all consistent with the summary estimate of relative risk.

Effect of electrical stimulation of the crossed olivocochlear bundle on temporary threshold shifts in auditory sensitivity. I. Dependence on electrical stimulation parameters.

Abstract: 1. This study examines the effect on auditory desensitization of electrically stimulating the crossed olivocochlear bundle (COCB) at the floor of the fourth ventricle. Auditory desensitization was induced by a loud high-frequency pure tone exposure and measured as temporary threshold shifts (TTS) in the sensitivity of the compound action potential recorded from the cochlea. COCB stimulation simultaneous with the loud sound exposure reduced the TTS. This reduction was contingent on the COCB stimulus being presented as a continuous burst for the entire duration (1 min) of the exposure. 2. The reduction in TTS could be abolished by prior administration of strychnine. The action of strychnine on these TTS effects of continuous COCB stimulation paralleled its action on the classical COCB effects elicited by pulsed short COCB trains. If the action of strychnine on the classical COCB effects was allowed to reverse, then continuous COCB stimulation reduced TTS as effectively as before. 3. The most effective COCB stimulus was found to be one that was presented at a high rate of stimulation simultaneous with the exposure. The COCB effect on TTS was also found to be a tonic one; smaller but significant reductions in TTS could still be obtained with the exposure presented 5 min after COCB stimulation though not when the delay was 10 min. The tonic reductions in TTS appeared to occur without any persisting changes at the cochlea. Normal cochlear responses remeasured in the delay between the stimulus and exposure were not altered. 4. It was hypothesized that the persisting effect responsible for TTS reductions did not occur at the cochlea but at some central site facilitated by antidromic action potentials along the COCB fibers. Subsequent exposure to loud sounds would activate the central site primed by the prior COCB stimulus. This hypothesis was tested by stimulating the COCB alone as before, but then lesioning the fibers before presenting the exposure. Persistent cochlear effects of the COCB stimulus should have still resulted in a reduction in TTS. However, if the persistent effect was at a more central location, lesioning the fibers would allow afferent input to act at the facilitated central location but would not allow subsequent expression of COCB effects at the cochlea. In this case, no reductions in TTS could be expected--precisely the results that were obtained in these experiments. Thus the COCB system appeared to have a "memory" component facilitated by prior stimulation and activated by a subsequent exposure.

Thermal simulation of a lake with winter ice cover1

Abstract: A one-dimensional thermodynamic model of a two-component ice and snow cover is added to an existing one-dimensional lake mixing model. Emphasis is placed on the thermodynamic coupling between the ice and mixing models-absent in previous models. The two-dimensional effects of partial ice cover are incorporated into this one-dimensional framework by using a minimum ice thickness. The model is applied to Lake Laberge, Yukon Territory, and to Babine Lake, British Columbia, for periods covering the formation and demise of full ice cover. The results of the model are compared to snow and ice measurements in the first case and to water column data during the spring period in the second. The comparisons are good, implying that the ice and snow model is performing satisfactorily and emphasizing the importance of the coupling between the ice and the underlying water. The successful simulation of the observed mixed layer under the ice, driven by convective stirring caused by short-wave heating below the temperature of maximum density, is an example of the ability of the model to provide physical insight into processes occurring in lakes.

Cyanophyte blooms: The role of cell buoyancy1

Abstract: A one-dimensional model of growth diffusion and scaling arguments show that bloom formation in epilimnctic cyanophytcs is attributable to the passive mechanism of positive buoyancy of the cells, which enhances the average exposure of the population to light. The effects of interacting turbulent diffusion, photic depth, mixed-layer depth, and diurnal mixed-layer excursions on population growth rate and biomass production differ radically for positively and negatively buoyant cells. Over the typical range of sinking and rising velocities for lake phytoplankton and the characteristic velocities of turbulent mixing, the proportion of the maximum achievable growth rate attained is always greater for a positively buoyant species until significant self-shading occurs. The magnitude of the difference is determined by the ratio of photic depth (z,) to mixed-layer depth (z,,); the advantages of positive buoyancy decrease as zp approaches z,,,. Results furthermore suggest that a positively buoyant population is able to track diurnal mixed-layer excursions and thus to experience a more favorable average daily z, : z, ratio than is possible for a negatively buoyant population.

Isoenzyme electrophoresis of 30 isolates of Giardia from humans and felines

Abstract: Thirty isolates of Giardia duodenalis from humans and felines were compared by isoenzyme electrophoresis. Using 10 enzyme systems, 13 different zymodemes were distinguished. The majority of zymodemes could be divided into two groups: one group comprising human and feline isolates with worldwide geographic distribution; the other group containing human isolates restricted to Western Australia. A number of isolates showed multiple-banded patterns and the genetic significance of these findings is discussed. The marked heterogeneity of G. duodenalis demonstrated in this study is considered in relation to the epidemiology of giardiasis. The findings are consistent with felines serving as a reservoir of infection to humans.

Courtship feeding in katydids benefits the mating male's offspring

Abstract: For species exhibiting courtship feeding it is typically argued that the food gift presented by males is a sexually-selected trait in serving to acquire fertilizations. An alternative hypothesis is that the trait is maintained by natural selection for parental investment in which the fitness of the mating male's offspring is increased. Here I argue that the spermatophylax, a nutritious part of the spermatophore provided to female katydids, Requena verticalis, functions mainly as parental investment. Previous research suggested that variation in the size of the male donation in this species (1) did not influence the ability of males to transfer ejaculates and (2) resulted in variation in offspring fitness. In the present paper genetic markers and radiolabels are used to show that the offspring are fathered by the males that donate the nutrients. Although these results indicate that the large spermatophylax is maintained by selection for increased parental investment, it is likely that this male offering originated in a sexual selection context whereby males fed females in order to obtain fertilizations.

The Reliability of Fecal Analysis as a Method for Determining the Diet of Insectivorous Mammals

Abstract: The reliability of fecal analysis for dietary assessment was evaluted in four species of insectivorous mammals. In separate experiments, invertebrates were fed to captive animals by one author, and feces were analyzed, without prior knowledge of diet composition, by the other author. There was overall agreement between ranked frequencies of different taxa of invertebrates consumed and recovered in feces. However, underestimation of numbers of invertebrates in feces was more evident (1) as increasing numbers of the same type of invertebrate were ingested, (2) for soft-bodied than for hard-bodied invertebrates, (3) for small than for large invertebrates, and (4) for well-fed than for hungry insectivores. We conclude that fecal analysis is a relatively reliable method for determining the diet of generalist insectivores that eat hard-bodied prey, especially if the results are expressed as the number of animals in which a prey item is found rather than as the minimum number of prey eaten per animal. However, we caution that there are more potential sources of bias in fecal analysis than realized previously.