Showing papers by "University of Sydney published in 1989"

Ecological Causes for the Evolution of Sexual Dimorphism: A Review of the Evidence

Abstract: Can sexual dimorphism evolve because of ecological differences between the sexes? Although several examples of this phenomenon are well known from studies on birds, the idea has often been dismissed as lacking general applicability. This dismissal does not stem from contradictory data so much as from the difficulties inherent in testing the hypothesis, and its apparent lack of parsimony, in comparison to the alternative explanation of sexual selection. The only unequivocal evidence for the evolution of sexual dimorphism through intersexual niche partitioning would be disproportionate dimorphism in trophic structures (e.g., mouthparts). This criterion offers a minimum estimate of the importance of ecological causes for dimorphism, because it may fail to identify most cases. A review of published literature reveals examples of sexually dimorphic trophic structures in most animal phyla. Many of these examples seem to be attributable to sexual selection, but others reflect adaptations for niche divergence between the sexes. For example, dwarf non-feeding males without functional mouthparts have evolved independently in many taxa. In other cases, males and females differ in trophic structures apparently because of differences in diets. Such divergence may often reflect specific nutritional requirements for reproduction in females, or extreme (sexually selected?) differences between males and females in habitats or body sizes. Ecological competition between the sexes may be responsible for intersexual niche divergence in some cases, but the independent evolution of foraging specializations by each sex may be of more general importance. If ecological causation for dimorphism can be demonstrated in so many cases, despite the inadequacies of the available criteria, the degree of sexual size dimorphism in many other animal species may well also have been influenced by ecological factors. Hence, it may be premature to dismiss this hypothesis, despite the difficulty of testing it.

Supply-side ecology and benthic marine assemblages

Abstract: Many marine invertebrates have a planktonic stage of their life history during which widespread dispersal and much mortality occur. The numbers surviving to recruit into habitats occupied by adults are therefore very variable in time and space. Models for the structure and dynamics of benthic assemblages tend to focus on processes causing death - often assuming consistent arrivals of recruits. Supply-side ecology is a newly fashionable term to describe recent interest in the long-realized consequences of variations in recruitment. Such variations have important influences on theory and empirical research in these assemblages.

Is Language Teachable? Psycholinguistic Experiments and Hypotheses

Abstract: In this article I demonstrate that the teachability of language is constrained by what the learner is ready to acquire. I set out a series of psychological constraints on teachability and relate these to the 'multidimensional model of SLA', taking a speech processing approach towards the explanation of language acquisition. This article supplies the empirical evidence for these constraints—namely experiments and longitudinal studies—which were available at the time of submission (1985). I take the position that while this research has important implications for formal interventions' in the acquisition process, the nature of such interventions do by no means follow from the research on teachability reported on in this article.

The structure of turbulent nonpremixed flames

Abstract: Flamelet theories are examined in the context of turbulent nonpremixed combustion. The criterion requiring that the reaction zone be thinner than the Kolmogoroff length scale is converted to one in which the range of mixture fraction over which reaction occurs is compared with the scalar scale for the small scale fluctuations. It is found that the criterion is violated in many of the flames of interest, particularly away from the nozzle in jet flames and in recirculating flows. Laser imaging data for scalar mixing is used to illustrate the structure of quasi-equilibrium distributed reaction (QEDR) flames at high Damkohler number. The structure is found to tend toward that of the scalar dissipation. The apparent success of flamelet theories in predicting mean concentrations of CO in hydrocarbon flames is ascribed to the metastable equilibrium of rich mixtures arising from chain terminating reactions of radicals with the fuel. Differences in flame structure for piloted jet diffusion flames near extinction of methane and CO/H 2 /N 2 fuels are discussed in terms of these fluid dynamic and kinetic insights.

Unknown attribute values in induction

Abstract: Simple techniques for the development and use of decision tree classifiers assume that all attribute values of all cases are available. Numerous approaches have been proposed with the aim of extending these techniques to cover real-world situations in which unknown attribute values are not uncommon. This paper compares the effectiveness of several approaches as measured by their performance on a collection of datasets.

Fibroblast growth factor (FGF) induces different responses in lens epithelial cells depending on its concentration.

Abstract: We reported previously that epithelial cells in explants from neonatal rat lenses, when cultured in the presence of fibroblast growth factor (FGF), showed increased proliferation, cell migration and fibre differentiation; moreover, fibre differentiation in response to the basic form of FGF (bFGF) was virtually completely blocked by an anti-bFGF antibody. In the present study, we report a detailed analysis of the effects of bFGF on cells in the central region of lens epithelial explants. Proliferation in explants was assessed by measuring [3H]thymidine incorporation. Cell migration was measured by labelling cells in explants with fluorescein isothiocyanate (FITC)-dextran and monitoring them by UV fluorescence microscopy. Fibre differentiation in explants was assessed on the basis of beta-crystallin accumulation. This study showed that half maximal activities for the three responses, proliferation, migration and fibre differentiation, were achieved at different concentrations of bFGF, namely, 0.15, 3 and 40 ng ml-1, respectively. Thus, the response of lens epithelial cells to bFGF varied qualitatively, as well as quantitatively, as the concentration increased. Monitoring FITC-dextran injection cells for up to 5 days after exposure to bFGF allowed analysis of the interrelation between various responses to bFGF in individual cells. As expected some cells divided in response to FGF, mainly within the first three days. However, whether or not they divided, all labelled cells responded to FGF by migrating and elongating. Maximal migration occurred during the first day of culture and maximal elongation was achieved by day 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Minor Congenital Laryngeal Clefts: Diagnosis and Classification

Abstract: Cleft larynx is a rare congenital anomaly. Detection of an unsuspected minor cleft may be difficult, but the pediatric laryngologist should suspect the possibility of cleft larynx from the clinical features. Four minor clefts are reported, three cases of supraglottic interarytenoid cleft and one of partial cricoid cleft. The technique for endoscopic diagnosis and the distinctive features are described and a classification into four types is proposed.

Time-dependent kinematic dynamos with stationary flows

Abstract: Numerical solutions to the magnetic induction equation in a sphere have been obtained for a number of stationary velocity models. By searching for non-steady magnetic fields and in some circumstances showing that all magnetic field modes decay, the inability of several earlier researchers to find convergent steady solutions is explained. Results of previous authors are generally confirmed, but also extended to cover non-steady fields, different values of magnetic Reynolds number and other parameters, and higher truncation limits. Some non-decaying fields are found where only decaying or non-convergent results have previously been reported. Two flows $\epsilon s^0\_2 + t^0\_2$ and $\epsilon s^0\_2 + t^0\_1$, each consisting of two very simple axisymmetric rolls are seen to sustain growing fields provided that (i) the magnetic Reynolds number R and the poloidal to toroidal flow ratio $\epsilon$ are of appropriate magnitudes, and (ii) the meridional s$^0\_2$ flow is directed inwards along the equatorial plane and out towards the poles. An even simpler axisymmetric single roll flow $\epsilon s^0\_1 + t^0_1$ is also seen to support growing fields for appropriate $\epsilon$ and R. These simple flows dispel the somewhat prevalent belief that dynamo maintenance relies on the supporting flow being complex, and having length scale significantly less than that of the conducting fluid volume.

Bioavailability of hydroxychloroquine tablets in healthy volunteers

Abstract: 1. Five healthy volunteers received, in a randomised crossover design study, a 155 mg oral tablet and an intravenous infusion of 155 mg racemic hydroxychloroquine (200 mg hydroxychloroquine sulphate) to assess the bioavailability of the commercially available tablet (Plaquenil, Winthrop Laboratories, Australia). 2. The terminal elimination half-life of hydroxychloroquine is more than 40 days, thus blood and urine samples were collected for 5 months following each dose to characterise adequately the terminal elimination phase and obtain accurate estimates of the areas under the concentration-time curves. 3. The mean (+/- s.d.) fraction of the oral dose absorbed, estimated from the blood and urine data, was 0.74 (+/- 0.13). A wide range of estimates of the fraction of the oral dose absorbed was calculated from the plasma data (0.41 - 1.53), reflecting the difficulties of accurate measurement of hydroxychloroquine in plasma. 4. A period of 6 months is required to achieve 96% of steady-state levels of hydroxychloroquine with the usual once daily, oral dosage regimen. Pharmacokinetic factors may thus be partly responsible for the delayed action of the drug in rheumatic conditions. 5. Haemodialysis will not aid in the case of oral overdose with hydroxychloroquine. Although the proportionate increase in clearance may be large, the increase in the fraction of the dose excreted will be negligible. The extensive sequestration of the drug by tissues limits effectiveness of haemodialysis.

The analysis of stress in natural populations

Abstract: Populations usually persist despite environmental variations. Experimental analysis of responses to stress must include distinction between potential stresses (environmental perturbations that might not cause stress) and actual stress (phenomena that cause a response by the population). This is made difficult by large temporal fluctuations in abundances of many organisms. Monitoring can measure this variability but is insufficient to predict the potential impact of most stresses. Experimental analyses of stresses are also made difficult by differences among populations in their inertia (lack of response to perturbation), resilience (magnitude of stresses from which a population can recover) and stability (rate of recovery following a stress). These attributes of populations cause a range of responses to intermittent, temporary and acute (or ‘pulse’) stresses and to long-term, chronic (‘press’) disturbances. The timing, magnitude and order of stresses can cause different responses by populations. Synergisms between simultaneous or successive stresses can also have unpredictable effects on populations and cause complexity in interpretations of patterns of competition and predation. Experimental manipulations are needed to understand the likely effect of environmental disturbances on populations. The appropriate experiments are those designed to measure the effects of different types, magnitudes and frequencies of simulated stresses. These will be more revealing than the more common experimental analyses used to determine why and how observed changes in abundances of populations are caused by existing stresses.

Absence of immunoreactive vasoactive intestinal polypeptide in tissue from the lungs of patients with asthma.

Abstract: Vasoactive intestinal polypeptide (VIP) is a neuropeptide present in the nerve fibers of normal lungs, where it acts to relax bronchial smooth muscle. To determine its presence or absence in the lungs of patients with asthma, we examined lung tissue obtained at autopsy or lobectomy from five patients with asthma and nine without asthma. The avidin–biotin–peroxidase complex technique was used to stain tissue for immunoreactivity to VIP. At least 80 tissue sections from each patient were examined microscopically; the airway diameter ranged from 100 μm to 1.2 cm. Immunoreactive VIP was seen within nerves in more than 92 percent of the sections from the lungs of patients without asthma. No VIP was seen in any of 468 sections we could evaluate that were obtained from the lungs of patients with asthma. As a control for the nonspecific destruction of neuropeptides, immunostaining for substance P was also carried out. Abundant amounts of this neuropeptide were seen within nerves in tissue from the lungs ...

Depositional model of a macrotidal estuary and floodplain, South Alligator River, Northern Australia

Abstract: The South Alligator River, Northern Territory of Australia, has a macrotidal estuary. Tidal influence (spring tidal range 5–6 m at the mouth) extends 105 km up the channel. It is dominated by freshwater in the wet season (December-April) with a salt wedge near the mouth, but is well mixed and becomes saline throughout the dry season. The tidal channel can be divided into four different channel types: an estuarine funnel, a sinuous meandering segment, a cuspate meandering segment (in which the inside of bends are pointed) and an upstream tidal channel. The distribution of morphologically defined land classes and morphological units within each land class on the floodplain flanking the estuary differs from one channel type to another. Several stratigraphic and morphostratigraphic units have been recognized from drill holes on the coastal and deltaic-estuarine plains, and a model of development is proposed on the basis of extensive radiocarbon chronology and palynology. The coastal plain has prograded with most rapid sedimentation between 5000 and 3000 yr BP. A similar pattern of progradation is identified in the estuarine funnel. In the sinuous segment of the estuary the channel has migrated laterally across the floodplain. Previous channel positions are indicated by palaeochannels and the meander tract is occupied by laminated channel sediments. Within the cuspate segment there are numerous sinuous palaeochannels on the plains. In the upstream segment, the channel and palaeochannels have long straight reaches with irregular bends and discontinuous levees, and channel avulsion is indicated. Mangrove mud is a widespread stratigraphic unit throughout the plains. The initial phase of development is a transgressive phase. 8000–6800 yr BP, when mangrove forests extended landwards into a pre-existing valley as sea-level rose. As sea-level stabilized, the transgressive phase was followed by a widespread mangrove phase, termed the ‘big swamp’ 6800–5300 yr BP. The mangrove forests disappeared from most of the plains as vertical accretion continued, and were replaced by grass and sedge-covered floodplains. During the sinuous phase, about 5300–2500 yr BP, the channel migrated laterally and eroded the deltaicestuarine plain and deposited lateral accretion deposits (laminated channel sediments). Part of the channel of the South Alligator River has then progressed from sinuous to cuspate in form, and erosion of river banks has occurred. Transgressive and big swamp phases occurred under rising and stabilizing sea-level, respectively. Later morphodynamic channel adjustments occurred under conditions of stable sea-level. The depositional model has direct application to other estuaries in northern Australia, and may be applied to other areas where sea-level change has been similar.

The “How” and “What” of learning physics

Abstract: Recent research on student learning in higher education has increasingly focussed on experiential aspects of how students approach their studies and what they learn from their studies. In this paper we describe the results of a study using phenomenographic research techniques, which focusses on student learning in a first year university physics course. The study, using interviews with sixteen volunteer students from the course, shows that only those students who actively sought to change their conceptions of the subject matter did so, while those who sought only to reproduce that subject matter did not.

Elementary observations on 2-categorical limits

Abstract: With a view to further applications, we give a self-contained account of indexed limits for 2-categories, including necessary and sufficient conditions for 2-categorical completeness. Many important 2-categories fail to be complete but do admit a wide class of limits. Accordingly, we introduce a variety of particular 2-categorical limits of practical importance, and show that certain of these suffice for the existence of indexed lax- and pseudo-limits. Other important 2-categories fail to admit even pseudo-limits, but do admit the weaker bilimits; we end by discussing these.

Elastic Stability of Cylindrical Shells with Weld Depressions

Abstract: Metal silos and tanks are subject to axial compressive stresses in their cylindrical shell walls. The buckling strength is very sensitive to geometric imperfections in the wall. The most regular and well‐defined imperfection is the local depression adjacent to a circumferential weld, caused by the plate rolling process and shrinkage of the weld.This paper examines the elastic buckling strengths of thin cylindrical shells under axial compression, with imperfections arising at circumferential welded joints. The effects of the welded joint depression amplitude, the shell radius‐to‐thickness ratio, a change of shell plate thickness at the weld, and internal pressurization are all examined. The study is confined to cylinders with a radius‐to‐thickness ratio in excess of 100, as thicker shells are rare for these structures. It is shown that a welded joint depression is one of the most deleterious practical imperfection forms currently known.

An Asian-specific 9-bp deletion of mitochondrial DNA is frequently found in Polynesians.

Abstract: One hundred fifty Polynesians from five different island groups (Samoans, Maoris, Niueans, Cook Islanders, and Tongans) were surveyed for the presence of an Asian-specific length mutation of mitochondrial (mt) DNA by using enzymatic amplification with thermostable Taq DNA polymerase. Ninety-three percent of Polynesians exhibited this 9-bp deletion, including 100% of Samoans, Maoris, and Niueans. The same deletion was also found in 8% of Tolais from New Britain and in 14% of coastal New Guineans. A deletion frequency of 82% in Fijians confirmed their ethnic affinity to Polynesians. In contrast, the deletion was absent in 30 New Guinea highlanders and 31 Australian aborigines, the only exception being an aborigine who also had the Southeast Asian triplicated zeta-globin gene rearrangement in his nuclear DNA. These data support the theories claiming that an independent group of pre-Polynesian ancestors who colonized into the Pacific were ultimately derived from east Asia.

Purification of botrocetin from Bothrops jararaca venom. Analysis of the botrocetin-mediated interaction between von Willebrand factor and the human platelet membrane glycoprotein Ib-IX complex.

Abstract: Interaction of von Willebrand factor (vWF) with its platelet receptor only occurs in vitro in the presence of a modulator such as ristocetin. We have recently confirmed that the human platelet membrane glycoprotein (GP) Ib-IX complex is the receptor involved in the ristocetin-dependent binding of vWF by reconstitution with the purified components [Berndt, M.C., Du, X., & Booth, W.J. (1988) Biochemistry 27, 633-640]. We have now developed a similar solid-phase reconstitution assay using an alternate modulator, botrocetin, for the competitive analysis of functional domains in both vWF and the GP Ib-IX complex. Botrocetin was purified from Bothrops jararaca venom by ammonium sulfate fractionation and subsequent DEAE-cellulose and hydroxylapatite chromatography. The purified protein was a 25-kilodalton (kDa) disulfide-linked dimer with apparent subunit molecular weights of 14,000 and 14,500. Binding studies with immobilized botrocetin demonstrated that botrocetin bound to vWF and to a 52/48-kDa region of vWF that contains the GP Ib binding domain, but not to glycocalicin, a proteolytic fragment of GP Ib that contains the vWF binding site. Binding of 125I-labeled vWF to GP Ib-IX complex coated beads and to platelets was strictly botrocetin-dependent with half-maximal binding at a botrocetin concentration of congruent to 0.27 microM. Botrocetin-dependent binding of vWF was specific, saturable, and comparable to that observed with ristocetin. An anti-vWF monoclonal antibody, 3F8, inhibited ristocetin- but not botrocetin-dependent binding of vWF, suggesting the presence of distinct ristocetin and botrocetin modulator sites on vWF. The botrocetin reconstitution assay was at least an order of magnitude more sensitive than the corresponding ristocetin assay for the competitive analysis of functional domains on both vWF and the GP Ib-IX complex and has confirmed the localization of the vWF-binding domain to the 45-kDa N-terminal region of GP Ib.

The effect of concurrent human immunodeficiency virus infection on chronic hepatitis B: a study of 150 homosexual men.

Abstract: To determine the influence of concurrent human immunodeficiency virus (HIV) infection on chronic hepatitis B virus (HBV) infection, 150 male homosexual chronic hepatitis B surface antigen (HBsAg) carriers were studied. Of these, 82 subjects (55Vo) tested positive for antibodies to HIV. They were more likely to express hepatitis B "e" antigen (HBeAg) (i^ .001) and HBV-DNA (/^ .0005) in serum than were HIV-seronegative individuals. However, the degree of immune suppression did not influence HBeAg-HBV-DNA expression. In HBeAg-seropositive subjects, concurrent HIV infection was associated with lower serum alanine transferase levels (P < .001). This effect increased with the degree of immune suppression as determined by CD4* lymphocyte counts. Conversely, in patients negative for HBeAg, there was a weak trend towards higher alanine transferase levels with concurrent HIV. This study suggests that chronic hepatitis B may be less severe when accompaned by HIV infection; however, greater viral replication may make it more contagious and resistant to antiviral therapy. These data support an immune-mediated pathogenesis for hepatitis B and have implications for its control. In the USA, western Europe, and Australia, both human immunodeficiency virus (HIV) and hepatitis B virus (HBV) are transmitted mainly by sexual or parenteral routes. The epidemiologies of the two infections overlap such that <90% of persons with the acquired immunodeficiency syndrome (AIDS) have

Induction of lens fibre differentiation by acidic and basic fibroblast growth factor (FGF).

Abstract: Explants of epithelial cells from newborn rat lenses undergo changes characteristic of fibre differentiation when cultured with neural retina or retina-conditioned medium. Here we show that similar changes occur when acidic and basic fibroblast growth factor (FGF) are used instead of retina-conditioned medium. When cultured without FGF, epithelial explants contained negligible amounts of β-crystallin, a lens protein found only in fibre cells. However, at saturating concentrations of FGF, about 20 μg β-crystallin was produced per explant in 5 days. The response was dose-dependent, half maximal response requiring 55 and 290 ng/ml of basic and acidic FGF, respectively. FGF also stimulated cell proliferation and cell migration. All three responses to basic FGF were blocked by an antibody specific for basic FGF. The concentration of FGF required to produce a maximal response was lower for cell proliferation and migration than for β-crystallin accumulation. The results suggest a possible role for FGF in...