Showing papers by "University of Queensland published in 1991"
2,699Â citations
TL;DR: In this paper, the authors used the pulsed gradient spin-echo (PGSE) NMR technique to characterize diffusion and flow in polystyrene spheres and found that the gradient pulse area plays the role of a wavevector, q, which can probe the structure in which the fluid diffuses.
Abstract: THE transport of fluids in porous media is of importance in a wide range of areas, such as oil recovery, heterogeneous catalysis and biological perfusion. The pulsed gradient spin-echo (PGSE) NMR technique has been used for many years to characterize diffusion and flow in such systems1–3. The analogy between NMR measurements in a field gradient and diffraction has been pointed out in the context of NMR imaging4 and, more recently, diffraction-like effects in the PGSE experiment have been discussed for diffusion in both impermeable5 and connected6 structures. The gradient pulse area plays the role of a wavevector, q, which can probe the structure in which the fluid diffuses. Here we report experimental confirmation of these predicted effects from proton NMR studies of a water-saturated, orientationally disordered, loosely packed array of monodisperse polystyrene spheres. The PGSE-NMR experiments may thus be used to provide an indirect, averaged image of the internal structure of porous solids at a resolution higher than that achievable with conventional NMR imaging. This is particularly advantageous for measurements on large samples, as the resolution available with the PGSE method depends only on the available range of gradient pulse amplitude and duration and is unconstrained by the factors determining resolution in conventional NMR imaging.
606Â citations
TL;DR: The partial ordering of events as defined by their causal relationships, that is, the ability of one event to directly, or transitively, affect another, is defined and its generalized and practical implementations in terms of partially ordered logical clocks are described.
Abstract: The partial ordering of events as defined by their causal relationships, that is, the ability of one event to directly, or transitively, affect another is defined. Its generalized and practical implementations in terms of partially ordered logical clocks are described. Such clocks can provide a decentralized definition of time for distributed computing systems, which lack a common time base. In their full generality, partially ordered logical clocks may be impractically expensive for long-lived computations. Several possible optimizations, depending on the application environment in which the clocks will be used, are described. Some applications are summarized. >
506Â citations
TL;DR: It is concluded that obese men harbor a double defect in GH dynamics involving both GH secretion and clearance, and that the severity of the GH secretory deficiency is proportionate to the degree of obesity.
Abstract: We have examined the mechanisms underlying reduced circulating GH concentrations in the obese human. Computer-assisted (deconvolution) analysis was used to determine endogenous GH secretory and clearance rates quantitatively from entire 24-h plasma GH concentration profiles. These analyses revealed that the half-life (t 1/2) of endogenous GH was significantly shorter in obese (11.7 +/- 1.6 min) than in normal weight subjects (15.5 +/- 0.81 min; P less than 0.01). The accelerated blood disposal rate of GH was not due to decreased circulating concentrations of GH-binding protein, since the latter were similar in obese (25 +/- 1.0%) and normal weight (24 +/- 2.3%) men. However, obese men had significantly fewer GH secretory bursts (3.2 +/- 0.53 vs. 9.7 +/- 0.67/day; P less than 0.01). Among the rare GH secretory bursts that occurred in obese subjects, there were significantly prolonged mean intersecretory burst intervals (282 +/- 65 vs. 131 +/- 11 min; P less than 0.05). The resultant daily GH production rate in obese men was reduced to one fourth that in normal weight individuals. Both GH secretion rate and burst frequency were negatively correlated with the degree of obesity (ponderal index). The decreases in GH burst frequency and half-life were specific, since GH secretory pulse amplitude (maximal rate of GH release), the mass of GH released per burst, and the duration of computer-resolved GH secretory bursts were not different in obese and normal weight men. We conclude that obese men harbor a double defect in GH dynamics involving both GH secretion and clearance, and that the severity of the GH secretory deficiency is proportionate to the degree of obesity.
486Â citations
TL;DR: The ability to use heterologous PCR primers, coupled with comparative mapping information will facilitate the use of DNA microsatellites in gene mapping studies in closely related species such as cattle and sheep, rat and mouse, or primates.
453Â citations
TL;DR: The term "internal consistency" has been used extensively in classical psychometrics to refer to the reliability of a scale based on the degree of within-scale item intercorrelation, as measured by say the split-half method or more adequately by Cronbach's (1951) (Psychometrika, 16, 297-334) alpha, as well as the KR20 and KR21 coefficients as discussed by the authors.
432Â citations
TL;DR: In this investigation, even 3-year-olds often responded correctly when asked to predict the initial behavior of a story character with a false belief, and this results are discussed in terms of the conversational worlds of children and adults.
427Â citations
TL;DR: It is demonstrated that the junctional connections between rod-signal interneurons in mammalian retina can be visualized by tracer coupling, following intracellular injection of the biotinylated compounds, biocytin and Neurobiotin.
403Â citations
TL;DR: A model for intrinsic decoherence in quantum mechanics is proposed, based on a simple modification of unitary Schrodinger evolution, with testable consequences including anomalous dispersion of a free particle, decay of oscillatory systems, destruction of interference-fringe visibility, and a phase shift of interference fringes.
Abstract: A model for intrinsic decoherence in quantum mechanics is proposed, based on a simple modification of unitary Schrodinger evolution. On sufficiently small time scales the system evolves by a random sequence of unitary phase changes generated by the Hamiltonian. The Schrodinger equation is obtained to zeroth order in the expansion parameter. Higher-order corrections lead to a loss of coherence in the energy basis. The rate of coherence loss becomes very large as the energy scale of the system is increased. The expansion parameter determines an uncertainty in the time step on very short times scales. A number of testable consequences are derived including anomalous dispersion of a free particle, decay of oscillatory systems, destruction of interference-fringe visibility, and a phase shift of interference fringes.
402Â citations
TL;DR: Concerted evolution of rDNA in parthenogenetic lizards of hybrid origin is strongly biased toward one of two parental sequences, which is consistent with biased gene conversion as the operative mechanism.
Abstract: Concerted evolution is the production and maintenance of homogeneity within repeated families of DNA. Two mechanisms--unequal crossing over and biased gene conversion--have been the principal explanations of concerted evolution. Concerted evolution of ribosomal DNA (rDNA) arrays is thought to be largely the result of unequal crossing over. However, concerted evolution of rDNA in parthenogenetic lizards of hybrid origin is strongly biased toward one of two parental sequences, which is consistent with biased gene conversion as the operative mechanism. The apparent gene conversions are independent of initial genome dosage and result in homogenization of rDNA arrays across all nucleolar organizer regions.
371Â citations
TL;DR: The 16S rDNA genes of an apparently pure culture of a psychrophilic and strict barophilic bacterium (WHB 46) were studied by PCR-mediated amplification and cloning into phage M13 mp18 and it was found that culture WHB 46 is actually composed of two closely related species.
Abstract: The 16S rDNA genes of an apparently pure culture of a psychrophilic and strict barophilic bacterium (WHB 46) were studied by PCR-mediated amplification and cloning into phage M13 mp18. Sequence analysis of five individual clones revealed the presence of two different 16S rDNA types. The homology value of 90% indicates that culture WHB 46 is actually composed of two closely related species (WHB 46-1 and 46-2). Both strains are members of the γ-subdivision of proteobacteria. Analysis of a sixth clone (WHB 46-1/2) leads to the conclusion that it represents a 16S rDNA hybrid molecule assembled during the PCR reaction. This hypothesis was confirmed by secondary structure analysis of the chimeric rDNA. The appearance of such hybrid molecules point to a potential risk in studies on the diversity of bacterial populations by analysis of rDNA pattern via PCR-mediated amplification because they suggest the existence of organisms that do not actually exist in the sample investigated.
TL;DR: The concept of resource partitioning, as originally developed, relates to evolutionary change in species in response to selection pressures generated by interspecific competition but has taken on another meaning, one that is not defined in terms of evolutionary function, and which refers simply to differences in resource use between species regardless of the origins of the differences.
TL;DR: A gene, pilT, within the twitching motility region is predicted to encode a 344-amino acid protein which has strong homology to a variety of other bacterial proteins, which suggest that these are all related members of a specialised protein export pathway which is widespread in the eubacteria.
TL;DR: The relationships among mothers' ratings of marital adjustment, parenting disagreements, and three child problem factors (aggression, anxiety, and immaturity) after the child's age and family socioeconomic status were controlled revealed that parenting disagreement predicted aggression in all groups and that both marital adjustment and parenting disagreements predicted anxiety in boys.
Abstract: Although there is agreement that marital problems are associated either directly or indirectly with particular child behavior problems, there is disagreement about the types of marital conflict associated with these problems and the differential effects on boys and girls in clinic and nonclinic samples. We examined the relationships among mothers' ratings of marital adjustment, parenting disagreements, and three child problem factors (aggression, anxiety, and immaturity) after the child's age and family socioeconomic status were controlled. These relationships were compared with samples of boys and girls (3 to 8 years of age) from clinic and nonclinic populations, revealing that parenting disagreement predicted aggression in all groups and that both marital adjustment and parenting disagreement predicted anxiety in boys. Neither marital variable predicted immaturity. Possible reasons for the results (including methodological limitations of the present data) are discussed.
TL;DR: The interaction and the competition of a set of transverse cavity modes, which belong to a frequency-degenerate family, are analyzed and the predicted phase singularities in each pattern agree in detail with those found by theory.
Abstract: We analyze the interaction and the competition of a set of transverse cavity modes, which belong to a frequency-degenerate family. The laser turns out to be able to realize several different stationary spatial patterns, which differ in the transverse configuration of the intensity or of the field and are met by varying the values of the control parameters. A striking feature that emerges in almost all steady-state patterns is the presence of dark points, in which both the real and the imaginary part of the electric field vanish and such that, if one covers a closed loop around one of these points, the field phase changes by a multiple of 2\ensuremath{\pi}, which corresponds to the topological charge of the point. We show in detail the analogy of these phase singularities to the vortex structures well known in such fields as, for example, hydrodynamics, superconductivity, and superfluidity. In our case, at steady state, these singularities are arranged in the form of regular crystals, nd the equiphase lines of the field exhibit a notable similarity to the field lines of the electrostatic field generated by a corresponding set of point charges. We analyze in detail the patterns that emerge in the cases 2p+l=2 and 2p+l=3, where p and l are the radial and angular modal indices, respectively, and we compare the results with the experimental observations obtained from a ${\mathrm{Na}}_{2}$ laser. The observed patterns agree in detail with those found by theory; in particular, they exhibit the predicted phase singularities in each pattern. The transitions from one pattern to another, that one observes under variation of the control parameters, basically agree with those predicted by theory.
TL;DR: A family of attraction/repulsion--distance functions is described, and it is shown that cohesion was best served by an upwardly convex behaviour--distance function in which maximum attraction equaled maximum repulsion.
TL;DR: Apoptosis has been shown to be involved in deleting autoreactive T-cells during the normal development of tolerance, so apoptotic deletion of myelin/oligodendrocyte-specific lymphocytes in the central nervous system in EAE might explain both the subsidence of inflammation and the acquisition of tolerance in this autoimmune disease.
TL;DR: It is shown that the local-recurrent global-feedforward model performs better than the local/local recurrent global feedforward model and the learning rule minimizing a mean square error criterion is derived.
Abstract: A new neural network architecture involving either local feedforward global feedforward, and/or local recurrent global feedforward structure is proposed. A learning rule minimizing a mean square error criterion is derived. The performance of this algorithm (local recurrent global feedforward architecture) is compared with a local-feedforward global-feedforward architecture. It is shown that the local-recurrent global-feedforward model performs better than the local-feedforward global-feedforward model.
TL;DR: The results demonstrate that the fatty acid composition and lipid content of heterotrophically-grown microalgae can be favourably manipulated by varying culture conditions.
Abstract: The effect of the carbon to nitrogen (C/N) ratio of the medium and the aeration rate on the lipid content and fatty acid composition ofChlorella sorokiniana was investigated using heterotrophic, batch culture. Both parameters had a significant effect. A C/N ratio of approximately 20, was found to indicate a change from carbon to nitrogen limitation forC. sorokiniana. Cell lipid content was at a minimum at this value and increased at both higher and lower C/N values. Low C/N ratios favoured a high proportion of trienoic fatty acids at the expense of monoenoic acids. Aeration enhanced cell growth, fatty acid yield and the synthesis of unsaturated dienoic and trienoic fatty acids, but reduced cell lipid content. The results demonstrate that the fatty acid composition and lipid content of heterotrophically-grown microalgae can be favourably manipulated by varying culture conditions.
TL;DR: Recent studies have shown that in elite atheletes, physical stress during training and competition leads to a suppression of mucosal immunity as evidenced by a reduction in salivary IgA.
Abstract: Immunological mechanisms have been implicated in the pathogenesis of periodontal disease for over 25 years. Studies throughout the 1970s established that advanced forms of the disease were dominated by B-cells/plasma cells while early and putative stable forms of the disease were dominated by T-cells/lymphocytes. Based on these observations, a model of disease was put forward which highlighted a possible T-cell/macrophage immunoregulatory imbalance being involved in disease pathogenesis. Studies throughout the 1980s have supported such a concept although the precise nature of this imbalance remains elusive. At the same time, clinical studies have established that patient susceptibility may be of overriding importance in determining disease outcome. In this context therefore, factors which influence this susceptibility should be fundamental in determining periodontal disease activity. These factors may include genetic variation between individuals in the way in which they respond to periodontopathic bacteria upon which environmental factors would be superimposed. These environmental factors would include anything that altered the balance between the host and the parasite and may be as diverse as recent viral infections resulting in T-cell anergy or physical and mental stress. Recent studies have shown that in elite atheletes, physical stress during training and competition leads to a suppression of mucosal immunity as evidenced by a reduction in salivary IgA. The subsequent effect of these environmental factors at the level of the periodontium, however, remains to be determined.
TL;DR: This paper investigated attachment style differences in subjects' reports of their romantic partners and found that the content of subjects' references to attachment-related issues was strongly related to their self-reported attachment style and was consistent with the essential characteristics of the three styles.
Abstract: The present study investigated attachment style differences in subjects' reports of their romantic partners. The sample consisted of seventy-four undergraduates (thirty-seven males and thirty-seven females) who had been in a dating relationship for at least 1 month. Subjects supplied a verbal description of their current dating partner and later completed the single-item measure of attachment style developed by Hazan & Shaver (1987). The verbal reports were tape-recorded and transcribed. The transcripts were coded for spontaneous references to attachment related issues, and content scales were also developed to tap idealization, a number of aspects of relationship quality and attitudes towards the partner's social network (family and friends). The content of subjects' references to attachment-related issues was strongly related to their self-reported attachment style and was consistent with the essential characteristics of the three styles. The content scales revealed attachment style effects for scales m...
TL;DR: Self-management has been inadequately assessed and attempts to improve self-management have relied excessively on providing information, so more research is needed to clarify determinants of self- management, and interventions to improve Self-management will need to change these determinants.
Abstract: Diabetes has no known cure and is a leading source of morbidity and mortality. Clinical management involves patients managing a complex and variable regimen. This article reviews the determinants of effective self-management and the methods of promoting better self-management. Trait variables (e.g., personality and demographics) have been presumed to affect self-management, but evidence suggests they have little impact. The important determinants of self-management are transient situational factors such as psychological stress and social pressure to eat. Interventions to promote better self-management have reported initial improvements in blood glucose control, but the long-term effects are unclear. We conclude that self-management has been inadequately assessed and that attempts to improve self-management have relied excessively on providing information. More research is needed to clarify determinants of self-management, and interventions to improve self-management will need to change these determinants.
TL;DR: Of 1102 consecutive patients treated with beta irradiation after pterygium removal at the Queensland Radium Institute from 1973 through 1978, 503 had a follow- up ophthalmologic examination in 1989, while a further 82 had at least a 10-year follow-up from ophthalMologic records.
TL;DR: Generalized anxiety disorder (GAD) is one of the least studied and least clearly conceptualized of the anxiety disorders as discussed by the authors, however, there is a strong correlation between GAD and high trait anxiety.
TL;DR: This study was able to show that the production and consumption of lactic acid, and the moderate hydrogen inhibition and regulation of the acidic products of the acidogenic bacteria, can be successfully modelled.
TL;DR: In neurons of the dorsal motor nucleus of the vagus, the current underlying the AHP had two components: a rapidly decaying component that was maximal following the action potential and a slower component that had a distinct rising phase that required influx of extracellular Ca2+ for their activation.
TL;DR: In this paper, a prospective study of 138 students facing a mid-year psychology exam was undertaken to examine the proposed effects of coping resources, including (internal) control beliefs, self-esteem, (low) neuroticism, low) denial, and social support, and variables that reflect the person's appraisal of the specific situation.
TL;DR: The rapidity with which new or expanded fields are seen following denervation indicates that the normally unexpressed inputs around a receptive field are not only potential inputs but are inherently viable.
Abstract: 1. Acute effects of permanent and temporary denervation of the flying fox thumb were examined to test the hypothesis that a large area of skin around the cutaneous receptive field of multiunits (MRF) at a locus in primary somatosensory cortex (SI) supplies viable inputs which can be rapidly unmasked by interruption of the dominant input from the area of the MRF. 2. The immediate effect of amputation of the thumb at loci where the original receptive field was entirely removed was to produce large MRFs on adjacent body areas (wrist, forearm, prowing, and finger membranes). Greatly expanded MRFs were also produced when amputation removed only part of the original MRF at a cortical locus. 3. The probable source of input to account for the new receptive fields is the extensive arborization of ascending projections within the somatosensory pathway, which supply a cortical locus with a potential input from a far larger area than is represented in its normal receptive field. The rapidity with which new or expanded fields are seen following denervation indicates that the normally unexpressed inputs around a receptive field are not only potential inputs but are inherently viable. Hence the most likely explanation for the results of this study is that the effect of the denervation is to disrupt an inhibitory influence that normally has the role of shaping the receptive field. 4. Temporary anesthesia of all or part of a MRF produced similar initial effects to amputation. When responsiveness returned to the locally anesthetized area (after 10-30 min), an expanded MRF persisted for a short time after which the boundaries of the MRF shrank. This rapid reversal suggests that a mechanistic rather than a plastic change is the basis for the acute effect of a small denervation on SI.
TL;DR: Apoptosis was found to play a variable role in the response of tumours to heating, with the lowest levels produced in human melanoma lines and the highest levels in some Burkitt's lymphoma lines.
Abstract: There is now abundant evidence that apoptosis, the cell death mechanism responsible for physiological deletion of cells, can be triggered by mild hyperthermia. However, the overall importance of this mode of death in heated tumours has not yet been established. In this light and electron microscopic study, apoptosis induced by 43 degrees C or 44 degrees C water bath heating for 30 min in a range of murine and human tumours growing in vitro and in four murine tumours growing as solid nodules in vivo, was identified on the basis of its characteristic morphology, and the amount present quantified. Apoptosis was found to play a variable role in the response of tumours to heating, with the lowest levels produced in human melanoma lines (less than 1%) and the highest levels in some Burkitt's lymphoma lines (up to 97%). In these latter tumours the induction of apoptosis is clearly a major component of the hyperthermic response.
Journal Article•
TL;DR: Clinical significance of enamel hypoplasia includes poor esthetics, tooth sensitivity, malocclusion and predisposition to dental caries, which may provide diagnostic clues as to genetic influences and systemic diseases, as well as to any trauma during the span of dental development.
Abstract: Clinical significance of enamel hypoplasia includes poor esthetics, tooth sensitivity, malocclusion and predisposition to dental caries. It may provide diagnostic clues as to genetic influences and systemic diseases, as well as to any trauma during the span of dental development. These systemic factors include birth trauma, infections, nutritional disorders, metabolic diseases, and exposures to chemicals such as tetracycline, lead, and fluoride. Inherited types form a relatively small component overall, including genetic abnormalities of enamel formation, or dental features of many inherited diseases or dysmorphic syndromes. Developmental enamel defects range in prevalence from 4 percent to 60 percent, depending on the criteria and the population studied. It is likely that many of these individual factors may in fact act through a central mechanism: mineral deficiency.