Showing papers by "University of Sydney published in 1993"
TL;DR: In this paper, a simple evolutionary procedure is proposed for shape and layout optimization of structures, where low stressed material is progressively eliminated from the structure during the evolution process, and various examples are presented to illustrate the optimum structural shapes and layouts achieved by this procedure.
1,975 citations
TL;DR: Data are found to support deposition models in which the highly tetrahedrally bonded form on nonhydrogenated amorphous carbon arises from the subplantation of incident ions, giving rise to a quenched increase in density and strain.
Abstract: A highly tetrahedrally bonded form on nonhydrogenated amorphous carbon (a-C) is produced by deposition from filtered medium-energy ion beams. A range of such films was grown and the ${\mathit{sp}}^{3}$-bonded fractions, plasmon energies, compressive stresses, and resistivities were measured as a function of ion energy. These properties are found to be strongly correlated and each to pass through a maximum at an ion energy of about 140 eV. The optimum ion energy is observed to depend on the type of carbon ions deposited and, possibly, on the deposition flux rate. The data are found to support deposition models in which the ${\mathit{sp}}^{3}$ bonding arises from the subplantation of incident ions, giving rise to a quenched increase in density and strain.
793 citations
TL;DR: In this paper, a simple model was proposed to explain the formation of compressive stress in thin films deposited with simultaneous bombardment by energetic ions or atoms, and it was shown that the stress σ is proportional to [ Y (1-v) ]E 1 2 (R j+kE 5 3 ), where E is the ion energy, R the net depositing flux, j the bombarding flux, k a material dependent parameter, Y the film material Young's modulus and v the Poisson ratio.
728 citations
27 Jun 1993
TL;DR: A general method is presented that allows predictions to use both instance-based and model-based learning, and improves with three approaches to constructing models and with eight datasets demonstrate improvements due to the composite method.
Abstract: This paper concerns learning tasks that require the prediction of a continuous value rather than a discrete class. A general method is presented that allows predictions to use both instance-based and model-based learning. Results with three approaches to constructing models and with eight datasets demonstrate improvements due to the composite method.
Keywords: learning with continuous classes, instance-based learning, model-based learning, empirical evaluation.
705 citations
TL;DR: In this paper, a simple model is described with which the entire force versus penetration behavior of indentation with a sphere, during loading and unloading, may be simulated from knowledge of the four test material parameters, Young's modulus, Poisson's ratio, flow stress at the onset of full plastic flow and strain hardening index, and the elastic properties of the indenter.
Abstract: A simple model is described with which the entire force versus penetration behavior of indentation with a sphere, during loading and unloading, may be simulated from knowledge of the four test material parameters, Young's modulus, Poisson's ratio, flow stress at the onset of full plastic flow and strain hardening index, and the elastic properties of the indenter. The underlying mechanisms are discussed and the predictions of the model are compared with data produced by an ultra low load, penetration measuring instrument.
641 citations
05 Apr 1993
TL;DR: This paper summarises the development of FOIL from 1989 up to early 1993 and evaluates its effectiveness on a non-trivial sequence of learning tasks taken from a Prolog programming text.
Abstract: FOIL is a learning system that constructs Horn clause programs from examples. This paper summarises the development of FOIL from 1989 up to early 1993 and evaluates its effectiveness on a non-trivial sequence of learning tasks taken from a Prolog programming text. Although many of these tasks are handled reasonably well, the experiment highlights some weaknesses of the current implementation. Areas for further research are identified.
607 citations
TL;DR: Sodium butyrate, a naturally occurring fatty acid, is present in the human large bowel in millimolar amounts as a result of bacterial fermentation of dietary fibre and the observation that this fatty acid can induce apoptosis could, in part, explain why a high‐fibre diet appears to be protective against colon cancer.
Abstract: The purpose of this study was to determine whether cultured colonic adenoma and carcinoma cells undergo apoptosis (programmed cell death) in vitro and whether specific growth and dietary factors, thought to be involved in the control of growth and differentiation of human colonic cells, could induce cell death through apoptosis. In cell lines originating from 6 colorectal adenomas and 7 carcinomas, spontaneous apoptosis was observed. Sodium butyrate, a naturally occurring fatty acid, is present in the human large bowel in millimolar amounts as a result of bacterial fermentation of dietary fibre. Sodium butyrate, at physiological concentrations, induced apoptosis in 2 adenoma cell lines, RG/C2 and AA/Cl, and in the carcinoma cell line PC/JW/FI. In contrast, transforming growth factor beta 1, which is thought to have an important role in the control of growth in colonic epithelium, did not induce apoptosis. Neither RG/C2 nor PC/JW/FI contain wild-type p53, therefore this tumour-suppressor gene is not required to mediate signals for the induction of apoptosis in colonic tumour cells. Our studies report the induction of apoptosis in colonic tumour cells by the naturally occurring fatty acid sodium butyrate. Since sodium butyrate is produced by bacterial fermentation of dietary fibre, the observation that this fatty acid can induce apoptosis could, in part, explain why a high-fibre diet appears to be protective against colon cancer. Escape from the induction of programmed cell death may be an important event in colorectal carcinogenesis.
534 citations
TL;DR: It is shown that two separate and sequential events, arrested development and cell death, bring about B cell elimination, defining a novel pathway for B cell Elimination, involving an initial stage vulnerable to breakdown in autoimmune disease.
526 citations
TL;DR: Asymmetrical analyses of variance derived from repeated measures models can be used to detect many types of impact that are not identifiable using widely recommended BACI (Before/After, Control/Impact) sampling.
Abstract: Procedures used to detect environmental impacts that occur as a result of planned disturbances are often inadequate. Widely used designs for univariate measures, such as the abundance of a population, lack proper spatial replication and have unjustified patterns of temporal sampling. Asymmetrical analyses of variance derived from repeated measures models can be used to detect many types of impact that are not identifiable using widely recommended BACI (Before/After, Control/Impact) sampling. These asymmetrical, beyond BACI designs are also more logical because of spatial replication. The mechanics of these procedures are discussed, including worked examples of calculations, considerations of their power to detect impacts of a specified magnitude and the integration of various temporal and spatial scales into the design. Related issues are briefly discussed concerning optimization of sampling and how to proceed when no data are available before a disturbance.
445 citations
TL;DR: Suggestions are made for increasing the life span of sperm during preservation and microencapsulation by adding agents that may stabilize membranes, counter peroxidation and decrease calcium uptake.
Abstract: When sperm of the ram, bull, boar and stallion are cold-shocked by rapid cooling to near freezing point, motility and metabolic activity are irreversibly depressed and the acrosome and plasma membrane disrupted. Ram sperm become susceptible to cold shock in the proximal corpus region of the epididymis when the cytoplasmic droplet has moved backwards to the distal portion of the sperm midpiece. The membrane constituents phospholipids and cholesterol are important in cold shock which causes loss of lipid from sperm. The susceptibility of sperm to cold shock is linked with a high ratio of unsaturated:saturated fatty acids in the phospholipids and a low cholesterol content. The high unsaturated fatty acid content of sperm also makes them susceptible to damage from peroxidation which adversely affects motility, metabolism, ultrastructure and fertility. Hydroxynonenal, a product of fatty acid peroxidation, depresses the motility and oxygen uptake of ram sperm in vitro and may react with the -SH groups of the axonemal microtubules. High calcium concentrations in the external medium may decrease the motility and metabolism of sperm and 'calcium intoxication' may be a factor in cold shock. Lowering the environmental temperature increases calcium uptake by sperm and the effect is aggravated if the rate of cooling is rapid. Phospholipids, particularly those in egg yolk, protect sperm to some extent from cold shock and also prevent increased calcium flux into the sperm. Suggestions are made for increasing the life span of sperm during preservation and microencapsulation by adding agents that may stabilize membranes, counter peroxidation and decrease calcium uptake.
394 citations
TL;DR: Although this study supported the validity of the EPDS, a replication of this study on a larger sample of post-partum women is suggested.
Abstract: One hundred and three post-partum women completed the Edinburgh Postnatal Depression Scale (EPDS) and were interviewed using the Diagnostic Interview Schedule. A cut-off score of 12.5 on the Edinbu...
TL;DR: Urinary excretion rates of the three isoflavones (daidzein, genistein, glycitein) over a 3-day period following soya challenge showed moderate variation, suggesting some individual variabilities in ability to deconjugate and to absorb dietary is oflavones, while some of this variability may reflect varying individual ability to ferment dietary isOflavones per se.
TL;DR: F Fluorimetric experiments indicated that the mechanism of resistance mediated by QacE, the protein specified by qACE, is active export energized by proton motive force.
Abstract: Nucleotide sequence analysis of ORF1 from the integron on the broad-host-range plasmid R751 revealed that the first 94 of 110 codons of ORF1 from R751 are identical to ORF4, an open reading frame from the 3' conserved segment of other integrons found in gram-negative bacteria, after which point they diverged completely. The predicted products of both ORF1 and ORF4 share homology with the multidrug exporter QacC. Phenotypic analysis revealed that ORF1 specifies a resistance profile to antiseptics and disinfectants almost identical to that of qacC, whereas ORF4 specifies much lower levels of resistance to these compounds. ORF4, whose product lacks the C-terminal 16 amino acids of the ORF1 protein, may have evolved by the interruption of ORF1 from the insertion of a DNA segment carrying a sulI sulfonamide resistance determinant. Hence, ORF1 was designated qacE, and its partially functional deletion derivative, ORF4, was designated qacE delta 1. Fluorimetric experiments indicated that the mechanism of resistance mediated by QacE, the protein specified by qacE, is active export energized by proton motive force. Amino acid sequence comparisons revealed that QacE is related to a family of small multidrug export proteins with four transmembrane segments.
TL;DR: The notion of extensivity was introduced in this article, which is a generalization of the notion of extensive and distributive categories (see Section 2.2.1). But it is not the natural notion to consider the existence of pullbacks.
TL;DR: In this article, the authors used a full information maximum likelihood estimation procedure of the hierarchical logit form to obtain suitable scaling parameters to make one or more data sets comparable and illustrate the advantages of the dual data strategy by comparing the results with those obtained from models estimated independently with revealed preference and stated preference data.
Abstract: There is growing interest in exploring the view that both revealed preference (RP) and stated preference (SP) data have useful information and that their integration will enrich the overall explanatory power of RP choice models. These two types of data have been independently used in the estimation of a wide variety of discrete choice applications in marketing. In order to combine the two data sources, each with independent choice outcomes, allowance must be made for their different scaling properties. The approach uses a full information maximum likelihood estimation procedure of the hierarchical logit form to obtain suitable scaling parameters to make one or more data sets comparable. We illustrate the advantages of the dual data strategy by comparing the results with those obtained from models estimated independently with RP and SP data. Data collected as part of a study of high speed rail is used to estimate a set of illustrative mode choice models.
TL;DR: The immediate cause of low-frequency fatigue appears to be a reduced tetanic [Ca2+]i, which is probably a consequence of a reduced Ca2+ release from the sarcoplasmic reticulum.
Abstract: Low-frequency fatigue is a form of muscle fatigue that follows intense muscle activity and is characterized by reduced tetanic tension at low frequencies of stimulation while tetanic tension at high stimulus frequencies is close to normal. The present experiments were performed on isolated single fibers of mouse in which tension and intracellular calcium concentration ([Ca2+]i) were measured. Fatigue was produced by intermittent short tetani continued until tension had declined to 30% of control. Comparison of low- (30- and 50-Hz) and high- (100-Hz) frequency tetani under control conditions and after 30 min of recovery from fatigue showed that low-frequency fatigue was present. During low-frequency fatigue, tetanic [Ca2+]i was substantially reduced at all stimulus frequencies but there was no change in Ca2+ sensitivity or maximum Ca(2+)-activated tension. One possible cause of the reduced tetanic [Ca2+]i is failure of conduction of the action potential in the T tubule, leading to reduced [Ca2+]i in the center of the fiber. However, imaging of [Ca2+]i across the fiber during low-frequency fatigue did not show any such gradient, suggesting that Ca2+ release is uniform across the fiber. Another possible mechanism is that changes in the Ca2+ pumping ability of the sarcoplasmic reticulum might affect tetanic [Ca2+]i. Measurements of the sarcoplasmic reticulum pump function showed a small slowing of Ca2+ uptake rate during low-frequency fatigue, which is unlikely to cause the reduced tetanic [Ca2+]i. In conclusion, the immediate cause of low-frequency fatigue appears to be a reduced tetanic [Ca2+]i, which is probably a consequence of a reduced Ca2+ release from the sarcoplasmic reticulum.
TL;DR: In this article, it is suggested that the direct effect of high temperatures on milk yield may result from a redirection of blood flow to the skin and away from other tissues, including the mammary gland.
TL;DR: It is suggested that high house dust mite allergen levels in a humid, subtropical region act to significantly increase bronchial responsiveness in sensitized children, and that Alternaria allergens have a similar but less potent action in a dry, rural region.
Abstract: The relation of house dust mite allergen levels to asthma and allergy was examined in two population samples of children aged 8-11 years in northern New South Wales. We studied 805 children in Lismore (a hot, humid, coastal region) and 770 in Moree/Narrabri (a hot, dry inland region). Respiratory symptoms were measured by questionnaire, bronchial hyperresponsiveness (BHR) by histamine inhalation test, and allergy by skin-prick tests. Current asthma was defined as the presence of both wheeze in last 12 months and BHR. Der p I levels were measured in dust from the bed and floors in the homes of 57 randomly selected children in the coastal region and of 74 inland children. Der p I levels were significantly higher by the coast (83.0 vs 11.2 microg/g, P < 0.001). House dust mite sensitivity was of similar prevalence in both regions (28.6 vs 26.4%, n.s.) but Alternaria sensitivity was higher inland (4.0 vs 15.2% P<0.001). Bronchial responsiveness was more severe in coastal children sensitized to house dust mites and in inland children who were sensitized to Alternaria. The adjusted odds ratios for current asthma in children sensitized to house dust mites were 21.3 (95% CI 10.5, 43.2) by the coast and 2.7 (95% CI 1.3, 5.4) inland, and in children sensitized to Alternaria were 3.4 (95% CI 1.3, 9.1) in the coastal region and 5.6 (95% CI 3.1, 10.1 inland. These studies suggest that high house dust mite allergen levels in a humid, subtropical region act to significantly increase bronchial responsiveness in sensitized children, and that Alternaria allergens have a similar but less potent action in a dry, rural region.
TL;DR: The Boundary Element Method is presented and benchmarked with existing Slender Body Theory results and reflection solutions for the motion of spheres and slender bodies near plane boundaries to model the swimming of a microorganism with a spherical cell body, propelled by a single rotating flagellum.
TL;DR: The results indicate that Müller cells share the ability of astrocytes to induce the formation of barrier properties by vascular endothelial cells, and suggest that Müllers cells play a major role in the formationof barrier properties in retinal vessels.
TL;DR: The O antigen is a bacterial surface polysaccharide made up of repeats of a short oligosaccharide and genetic analysis indicates that these were acquired by interspecific gene transfer in Salmonella.
TL;DR: In this article, the authors defend the view that the ordinary notions of cause and effect have a direct and essential connection with our ability to intervene in the world as agents, which is a well-known but rather unpopular philosophical approach to causation.
Abstract: In this paper we defend the view that the ordinary notions of cause and effect have a direct and essential connection with our ability to intervene in the world as agents.' This is a well-known but rather unpopular philosophical approach to causation, often called the manipulability theory. In the interests of brevity and accuracy, we prefer to call it the agency theory.2 Thus the central thesis of an agency account of causation is something like this: an event A is a cause of a distinct event B just in case bringing about the occurence of A would be an effective means by which a free agent could bring about the occurrence of B. In our view the unpopularity of the agency approach to causation may be traced to two factors. The first is a failure to appreciate certain distinctive advantages that this approach has over its various rivals. We have drawn attention to some of these advantages elsewhere, and we summarize below. However, the second and more important factor is the influence of a number of stock objections, objections that seem to have persuaded many philosophers that agency accounts face insuperable obstacles. In this paper we want to show that these objections have been vastly overrated.
TL;DR: In this article, compressive biaxial stress fields in thin film boron nitride are shown to provide a means of accessing the region of the phase diagram in which cubic BN (c-BN) is the stable phase.
TL;DR: The use of immunohistochemical detection of Fos has allowed visualization of several populations of neurons likely to be involved in the central neural processing of vascular headache syndromes, particularly migraine.
TL;DR: In all communities, people with asthma, diabetes, heart disease and arthritis were the most, and people with AIDS, mental retardation, psychiatric illness and cerebral palsy, the least accepted of the disability groups.
TL;DR: A PTAC model is proposed and compared with other four possible candidates and an application of the model to improve the estimation of local cerebral metabolic rate of glucose is presented, expected to be useful for generating realistic PTAC curves in computer simulation studies of other tracers and their kinetic modeling characteristics.
Abstract: In tracer kinetic modeling with Positron Emission Tomography (PET), the direct measurement (piecewise linear approximation) of plasma time-activity curve of tracer (PTAC) is often used as the input function to estimate regional physiological parameters. However, no explicit general model is available for PTAC itself, which limits the further study of the effects of PTAC, such as PTAC measurement noise or PTAC sampling schedules, on the physiological parameters estimation. A PTAC model is proposed in this paper and compared with other four possible candidates. Eight sets of [18F]-fluoro-2-deoxy-D-glucose (FDG) experimental data were used to test the models and several statistical criteria were used to validate their adequacy. An application of the model to improve the estimation of local cerebral metabolic rate of glucose (LCMRGlc) is presented. This model is also expected to be useful for generating realistic PTAC curves in computer simulation studies of other tracers and their kinetic modeling characteristics.
TL;DR: A heuristic model to account for the development and maintenance of problem gambling is provided with the aim of directing clinical management and future research.
Abstract: A heuristic model to account for the development and maintenance of problem gambling is provided with the aim of directing clinical management and future research. Previous explanations of problem gambling have been limited in two main ways. Firstly, the models have been primarily descriptive, and secondly they have generally lacked clinical value. Most explanations have ignored the mechanisms through which this behaviour becomes problematic, and have not identified the relationships between different variables.
TL;DR: Effective treatment of sleep apnea with nCPAP was associated with a significant fall in both systolic and diastolic BP independent of changes in body weight or alcohol consumption, suggesting thatSleep apnea was an independent factor contributing to elevated nighttime and daytime BP in these patients.
Abstract: Ambulatory blood pressure (BP) was measured noninvasively (Oxford Medilog ABP) at 15-minute intervals for 24 hours before and after 8 weeks of treatment with nasal continuous positive airway pressure (nCPAP) in 19 men with obstructive sleep apnea (OSA). We included both normotensive and hypertensive patients, but hypertensives were studied after withdrawal of antihypertensive drugs. Ambulatory BP before and after treatment was compared using patients as their own controls. Treatment with nCPAP was successfully established in 14 of the 19 patients (74%). Blood pressure fell significantly in patients who were successfully treated: 24-hour mean BP (systolic/diastolic) decreased from 141 +/- 18/89 +/- 11 mm Hg to 134 +/- 19/85 +/- 13 mm Hg (p < 0.05). The reduction in 24-hour mean systolic BP occurred during both day and night, but a significant fall in mean diastolic BP was only observed during the day. The mean blood pressure fell in both normotensive and hypertensive patients. Patients who were inadequately treated with nCPAP had no reduction in mean 24-hour BP. Effective treatment of sleep apnea with nCPAP was associated with a significant fall in both systolic and diastolic BP independent of changes in body weight or alcohol consumption, suggesting that sleep apnea was an independent factor contributing to elevated nighttime and daytime BP in these patients.
TL;DR: Endogenous amino acid flows to the ileum in fasted cockerels were significantly lower than those obtained both by feeding the nitrogen-free diet, and from regression analysis in either broilers or cockrels.
Abstract: 1. Ileal endogenous amino acid losses were determined in broiler chickens and in cannulated cross-bred layer strain cockerels using either a nitrogen-free diet, regression analysis or a 48 h fast. 2. Endogenous amino acid flows to the ileum in fasted cockerels were significantly lower than those obtained both by feeding the nitrogen-free diet, and from regression analysis in either broilers or cockerels. Regression analysis gave the highest flows. 3. The apparent digestibility coefficients of amino acids in a diet containing 200 g/kg crude protein were lower in broilers (0.84) than in cockerels (0.88). When corrected, by regression analysis, for the contribution of endogenous amino acids, the true digestibility coefficients became 0.90 and 0.92 respectively.
TL;DR: The results strongly suggest that a de novo dominant mutation of the Po gene is responsible for at least some sporadic cases of Dejerine–Sottas disease.
Abstract: We have investigated the myelin P0 gene on chromosome 1 as a candidate gene in two sporadic cases with Dejerine-Sottas disease or hereditary motor and sensory neuropathy (HMSN) type III. We found different mutations, a cysteine substitution for serine 63 in the extracellular domain and an arginine substitution for glycine 167 in the transmembrane domain. The patients were genetically heterozygous for the normal allele and the mutant allele, which was absent in their parents and in one hundred unrelated, healthy controls. The results strongly suggest that a de novo dominant mutation of the P0 gene is responsible for at least some sporadic cases of Dejerine-Sottas disease.