Showing papers by "University of Sydney published in 1991"

Compressive-stress-induced formation of thin-film tetrahedral amorphous carbon

Abstract: Thin tetrahedrally coordinated amorphous carbon (ta-C) films have been grown using a filtered vacuum arc. ta-C is a new allotrope of carbon whose existence was previously thought to be unlikely. A model is proposed which accounts for the formation and structure of these films on the basis of the compressive stress generated by the shallow implantation of carbon ions. An optimal range of beam energies between 15 and 70 eV, a high film stress, and a graphitic surface are predicted and confirmed by experimental evidence. Computer simulation of the growth confirms that high compressive stress is generated by impact energies in this range.

Improving the quality of student learning: the influence of learning context and student approaches to learning on learning outcomes

Abstract: Previous studies of the relationship between perceptions and/or evaluations of the learning environment and approaches to study have either not included measures of students' learning outcomes, or have included quantitative differences and not qualitative differences in learning outcomes. The studies reported in this paper focus on the relationship between qualitative differences in learning outcomes, perceptions/evaluations of the learning environment and approaches to study. The results support previous research in identifying relationships between perceptions/evaluations of the learning environment and approach to study and between approach to study and the quality of the learning outcomes. The second of the two studies reported also identifies a relationship between perceptions, approaches and the quality of the outcomes. The results suggest that perceived environments which encourage deep approaches are more likely to facilitate higher quality learning than environments designed to discourage surface approaches.

Second Language Instruction Does Make a Difference

Abstract: A number of studies on second language (SL) instruction point to the hypothesis that instruction is effective, but determining the effect experimentally has been problematic. Overall, three difficulties with previous attempts to demonstrate a causal relationship between SL instruction and second language acquisition can be identified: (a) inappropriate or inadequate research design, (b) failure to operationalize or even to describe the instructional treatment, and (c) choice of SL assessment measures. This article presents the findings of a recent empirical study which (a) show that SL instruction is effective; (b) show that attention to form, either via detailed analysis of structure or highlighting of target language (TL) structures in context, promotes acquisition of interlanguage (IL) grammar, but that only the latter comes hand-in-hand with comprehension of input; and (c) replicate earlier findings suggesting an important role for markedness theory in instructed IL development.

On changing continuous attributes into ordered discrete attributes

Abstract: The large real-world datasets now commonly tackled by machine learning algorithms are often described in terms of attributes whose values are real numbers on some continuous interval, rather than being taken from a small number of discrete values. Many algorithms are able to handle continuous attributes, but learning requires far more CPU time than for a corresponding task with discrete attributes. This paper describes how continuous attributes can be converted economically into ordered discrete attributes before being given to the learning system. Experimental results from a wide variety of domains suggest this change of representation does not often result in a significant loss of accuracy (in fact it sometimes significantly improves accuracy), but offers large reductions in learning time, typically more than a factor of 10 in domains with a large number of continuous attributes.

Cellular mechanisms of fatigue in skeletal muscle.

Abstract: Prolonged activation of skeletal muscle leads to a decline of force production known as fatigue. In this review we outline the ionic and metabolic changes that occur in muscle during prolonged activity and focus on how these changes might lead to reduced force. We discuss two distinct types of fatigue: fatigue due to continuous high-frequency stimulation and fatigue due to repeated tetanic stimulation. The causes of force decline are considered under three categories: 1) reduced Ca2+ release from the sarcoplasmic reticulum, 2) reduced myofibrillar Ca2+ sensitivity, and 3) reduced maximum Ca(2+)-activated tension. Reduced Ca2+ release can be due to impaired action potential propagation in the T tubules, and this is a principal cause of the tension decline with continuous tetanic stimulation. Another type of failing Ca2+ release, which is homogeneous across the fibers, is prominent with repeated tetanic stimulation; the underlying mechanisms of this reduction are not fully understood, although several possibilities emerge. Changes in intracellular metabolites, particularly increased concentration of Pi and reduced pH, lead to reduced Ca2+ sensitivity and reduced maximum tension, which make an important contribution to the force decline, especially with repeated tetanic stimulation.

Tinnitus reaction questionnaire: psychometric properties of a measure of distress associated with tinnitus.

Abstract: The development of the Tinnitus Reaction Questionnaire (TRQ), a scale designed to assess the psychological distress associated with tinnitus, is described. Psychometric analyses of the TRQ are exam...

Changes of myoplasmic calcium concentration during fatigue in single mouse muscle fibers.

Abstract: Measurements of the intracellular free concentration of Ca2+ ([Ca2+]i) were performed during fatiguing stimulation of intact, single muscle fibers, which were dissected from a mouse foot muscle and loaded with fura-2. Fatigue, which was produced by repeated 100-Hz tetani, generally occurred in three phases. Initially, tension declined rapidly to approximately 90% of the original tension (0.9 Po) and during this period the tetanic [Ca2+]i increased significantly (phase 1). Then followed a lengthy period of almost stable tension production and tetanic [Ca2+]i (phase 2). Finally, both the tetanic [Ca2+]i and tension fell relatively fast (phase 3). The resting [Ca2+]i rose continuously throughout the stimulation period. A 10-s rest period during phase 3 resulted in a significant increase of both tetanic [Ca2+]i and tension, whereas a 10-s pause during phase 2 did not have any marked effect. Application of caffeine under control conditions and early during phase 2 resulted in a substantial increase of the tetanic [Ca2+]i but no marked tension increase, whereas caffeine applied at the end of fatiguing stimulation (tension depressed to approximately 0.3 Po) gave a marked increase of both tetanic [Ca2+]i and tension. The tetanic [Ca2+]i for a given tension was generally higher during fatiguing stimulation than under control conditions. Fatigue developed more rapidly in fibers exposed to cyanide. In these fibers there was no increase of tetanic [Ca2+]i during phase 1 and the increase of the resting [Ca2+]i during fatiguing stimulation was markedly larger. The present results indicate that fatigue produced by repeated tetani is caused by a combination of reduced maximum tension-generating capacity, reduced myofibrillar Ca2+ sensitivity, and reduced Ca2+ release from the sarcoplasmic reticulum. The depression of maximum tension-generating capacity develops early during fatiguing stimulation and it is of greatest importance for the force decline at early stages of fatigue. As fatigue gets more severe, reduced Ca2+ sensitivity and reduced Ca2+ release become quantitatively more important for the tension decline.

Structure and sequence of the rfb (O antigen) gene cluster of Salmonella serovar typhimurium (strain LT2).

Abstract: The rfb gene cluster of Salmonella LT2 has been cloned and sequenced. The genes rfbA, rfbB, rfbD, rfbF, rfbG, rfbK, rfbM and rfbP were located individually and the gene rfbL was located outside the cluster. Approximately 16 open reading frames were found in the region which is essential for the expression of O antigen. The gene products of rfbB and rfbG were found to have homology with the group of dehydrogenase and related enzymes described previously. Analysis of the G + C ratio of the rfb cluster extended the area of low-G + C composition previously found in the sequence of rfbJ to the whole rfb gene cluster. Three to five segments with discrete G + C contents and codon adaptation indices are present in the rfb region, indicating a heterogeneous origin of these segments. Potential promoters were found near the start of the rfb region, supporting the possibility that the rfb gene cluster is an operon.

Personality as a Vulnerability Factor to Depression

Abstract: One hundred and forty non-depressed primiparous women in a stable relationship completed two personality measures (the EPI and the IPSM) antenatally, and were then assessed for depression at several times post-natally. The risk of depression at six months was increased up to tenfold by high interpersonal sensitivity and threefold by high neuroticism. When previously depressed women were excluded from analyses, high interpersonal sensitivity and, to a lesser extent, high neuroticism were still associated with an increased risk of being depressed. Interpersonal sensitivity, as measured, is suggested as a refined personality risk factor to both the onset and recurrence of depression.

Chapter 13 Integration of somatic and autonomic reactions within the midbrain periaqueductal grey: Viscerotopic, somatotopic and functional organization

Abstract: Publisher Summary Considerable evidence suggests that the cell dense region surrounding the midbrain aqueduct, the midbrain periaqueductal gray region (PAG), is a crucial neural substrate for the integration of an animal's reactions to threatening or stressful stimuli. This chapter describes the great diversity of PAG output functions that make an understanding of its functional organization prerequisite to the study of its neural organization. It considers the results of studies from laboratory that have employed the technique of intracerebral stimulation with excitatory amino acids (EAA) to map the diverse functional output zones that exist within the PAG. Results of anatomical studies of the PAG efferents, which may mediate certain outputs, have been considered in the chapter. Data pertaining to the afferent regulation of the functionally diverse PAG regions have also been discussed.

Intersexual Dietary Divergence and the Evolution of Sexual Dimorphism in Snakes

Abstract: Ecological causes for the evolution of sexual dimorphism can be confidently inferred only when the sexes differ in morphology or relative size of the feeding apparatus, in a direction inconsistent with that expected from sexual selection. Snakes are well suited for such an analysis because head sizes in this group are important for feeding but not for reproductive behavior. My data reveal significant sexual dimorphism in head size (relative to snout-vent length) in 47% of 114 species examined from seven families. Head size relative to body size is strongly correlated between males and females in comparisons among populations within species, among species within genera, and among genera within families. Hence, correlation between the sexes may powerfully constrain evolutionary shifts in dimorphism. Nonetheless, phylogenetic analysis identifies many independent origins and losses of the dimorphism. Geographic variation in relative head size and sexual dimorphism in head size are evident within wide-ranging ...

Low-Glycemic Index Foods Improve Long-Term Glycemic Control in NIDDM

Abstract: Objective To compare high- and low-glycemic index (GI) diets in the treatment of non-insulin-dependent diabetes mellitus (NIDDM). Research Design and Methods Sixteen subjects with well-controlled NIDDM and normal lipid profile, 10 of whom continued oral hypoglycemic medication, participated in the study. A diet that emphasized low-GI foods (e.g., porridge, pasta) was compared with a high-GI diet (e.g., processed cereals, potatoes). The GI of the low-GI diet was 15% lower than the high-GI diet (77 ± 3 vs. 91 ± 1) but otherwise similar in macronutrient composition and fiber, as determined by a 4-day weighed record. The diets were instituted under instruction from a dietitian who visited subjects at home on a weekly basis. Body weight was maintained within 1–2 kg. Results Glycemic control was improved on the low-GI diet compared with the high-GI diet (statistically significant findings, P < 0.05). Mean glycosylated hemoglobin at the end of the low-GI diet was 11% lower (7.0 ± 0.3%) than at the end of the high-GI diet (7.9 ± 0.5%), and the 8-h plasma glucose profile was lower (area under the curve above fasting 128 ± 23 vs. 148 ± 22 mmol.h-1.L-1, respectively). Mean fasting plasma glucose, total cholesterol triglycerides, and lipoproteins did not show important differences. Conclusions A low-GI diet gives a modest improvement in long-term glycemic control but not plasma lipids in normolipidemic well-controlled subjects with NIDDM.

Confirmatory Factor Analyses of Multitrait-Multimethod Data: A Comparison of Alternative Models:

Abstract: Alternative models for confirmatory factor analysis of multitrait-multimethod (MTMM) data were evaluated by varying the number of traits and methods and sample size for 255 MTMM matrices constructed from real data (Study 1), and for 180 MTMM matrices constructed from simulated data (Study 2). The correlated uniqueness model converged to proper solutions for 99% (Study 1) and 96% (Study 2) of the MTMM matrices, whereas the general model typically used converged to proper solutions for only 24% (Study 1) and 22% (Study 2) of the MTMM matrices. The general model was usually ill-defined (100% in Study 1, 90% in Study 2) for small MTMM matrices with small Ns, but performed better when the size of the MTMM matrix and N were larger. Even when both models converged to proper solutions, however, parameter estimates for the correlated uniqueness model were more accurate and precise in relation to known population parameters in Study 2.

Anti-nutritive activities of cereal non-starch polysaccharides in broiler diets and strategies minimizing their effects

Abstract: The non-starch polysaccharides (NSPs) of cereals exhibit anti-nutritive activity when present in broiler diets. The high levels of arabinoxylans (pentosans) in rye and β-glucans in barley are respo...

Relating approaches to study and quality of learning outcomes at the course level

Abstract: Summary. Research into qualitative differences in students' approaches to study, the quality of learning outcomes, and the relations between them has, in the main, been conducted on learning resulting from involvement in small academic tasks such as reading an academic article. This study, based on a sample of 122 first year university nursing students, focused on student learning on the whole course. The results of the study confirmed the hypothesised relationship between approach and outcome at the course level. In the process, an indicator of qualitative differences in learning outcomes at the course level was developed. The results also provided further support for the validity of three subscales of the Approaches to Study Inventory, and cast further doubt on the use of assessment results as measures of learning outcomes.

Cytogenesis in the monkey retina

Abstract: Time of cell origin in the retina of the rhesus monkey (Macaca mulatta) was studied by plotting the number of heavily radiolabeled nuclei in autoradiograms prepared from 2- to 6-month-old animals, each of which was exposed to a pulse of 3H-thymidine (3H-TdR) on a single embryonic (E) or postnatal (P) day. Cell birth in the monkey retina begins just after E27, and approximately 96% of cells are generated by E120. The remaining cells are produced during the last (approximately 45) prenatal days and into the first several weeks after birth. Cell genesis begins near the fovea, and proceeds towards the periphery. Cell division largely ceases in the foveal and perifoveal regions by E56. Despite extensive overlap, a class-specific sequence of cell birth was observed. Ganglion and horizontal cells, which are born first, have largely congruent periods of cell genesis with the peak between E38 and E43, and termination around E70. The first labeled cones were apparent by E33, and their highest density was achieved between E43 and E56, tapering to low values at E70, although some cones are generated in the far periphery as late as E110. Amacrine cells are next in the cell birth sequence and begin genesis at E43, reach a peak production between E56 and E85, and cease by E110. Bipolar cell birth begins at the same time as amacrines, but appears to be separate from them temporally since their production reaches a peak between E56 and E102, and persists beyond the day of birth. Muller cells and rod photoreceptors, which begin to be generated at E45, achieve a peak, and decrease in density at the same time as bipolar cells, but continue genesis at low density on the day of birth. Thus, bipolar, Muller, and rod cells have a similar time of origin. The maximal temporal separation of cell birth is between cones and amacrine cells so that cell generation exhibits two relatively distinct phases: the first phase gives rise to ganglion, horizontal, and cone cells, and the second phase to amacrine, bipolar, rod, and Muller cells. In addition, cells of the first phase are generated faster than the second phase cells, and there are differences in the topography of spread of labeled cells between the two phases. Each cell class displays a central-to-peripheral gradient in genesis, although the spatiotemporal characteristics of the gradients differ between the classes.(ABSTRACT TRUNCATED AT 400 WORDS)

The Influence of Human Immunodeficiency Virus Type 1 Infection on the Development of the Hepatitis B Virus Carrier State

Abstract: To assess the influence of human immunodeficiency virus type 1 (HIV-1) infection on the natural history of acute hepatitis B virus (HBV) infection, a study was undertaken of the clinical records of all 77 homosexual men with documented seroconversion to anti-hepatitis B core antibody (anti-HBc) between visits to either of two Sydney clinics between 1985 and 1989. HIV-1-seropositive subjects developed chronic HBV infection (positive for hepatitis B surface antigen [HBsAg] greater than 6 months) more frequently (7/31, 23%) than HIV-1-seronegative ones (2/46, 4%; P = .026). HIV-positive subjects who cleared HBsAg had significantly more circulating CD4+ lymphocytes (mean, 547 x 10(6)/l) than those who did not (352 x 10(6)/l, P less than .005). A subset of subjects who acquired both viruses between visits had an even higher rate of chronic infection (4/10, 40%). Icteric illnesses were reported more frequently by HIV-1-seronegative (11/46, 24%) than -seropositive subjects (3/31, 10%; P = .20). These findings indicate a potential for an increased reservoir of HBV infection in the community as a consequence of the HIV-1 epidemic.

Carbohydrate feeding before exercise: effect of glycemic index.

Abstract: Low glycemic index (GI) foods may confer an advantage when eaten before prolonged strenuous exercise by providing a slow-release source of glucose to the blood without an accompanying insulin surge. To test this hypothesis, eight trained cyclists pedalled to exhaustion one hour after ingestion of equal carbohydrate portions of four test meals: lentils, a low GI food (LGI); potato, a high GI food (HGI), and glucose and water. Plasma glucose and insulin levels were lower after LGI than after HGI from 30 to 60 min after ingestion (p less than 0.05). Plasma free fatty acid (FFA) levels were highest after water (p less than 0.05) followed by LGI and then glucose and HGI. From 45 to 60 min after ingestion, plasma lactate was higher in the HGI trial than in the LGI trial (p less than 0.05) and remained higher throughout the period of exercise. The rank order from lowest to highest for total carbohydrate oxidation during exercise was water, lentils, glucose and potato. Endurance time was 20 min longer after LGI than after HGI (p less than 0.05). These findings suggest that a low GI pre-game meal may prolong endurance during strenuous exercise by inducing less post-prandial hyperglycemia and hyperinsulinemia, lower levels of plasma lactate before and during exercise, and by maintaining plasma glucose and FFA at higher levels during critical periods of exercise.

Breakdown of self-tolerance in anergic B lymphocytes.

Abstract: PRODUCTION of autoantibodies, which characterizes most autoimmune diseases, is normally avoided by active elimination1–7 or functional inactivation (anergy) 8–15 of B and T lymphocytes bearing receptors for self antigens. The mechanisms leading to the escape of self-reactive clones from these normal tolerance mechanisms in autoimmune diseases nevertheless remain obscure. Here, we demonstrate that clonal anergy in B lymphocytes is a reversible process, and that silenced self-reactive B cells can be reactivated under particular conditions to give rise to vigorous antibody responses. Reactivation of anergic lymphocytes may explain many examples of transient autoimmune reactions in normal individuals, and may under pathological conditions be important in the development of chronic autoimmune disease.

Substance P immunoreactive nerves in airways from asthmatics and nonasthmatics

Abstract: Substance P has been localized to nerves supplying smooth muscle, blood vessels and glands in the human lung and may play a major role in the pathophysiology of asthma. We performed a morphological study, using the avidin biotin peroxidase immunostaining technique, to examine sections of airway wall from subjects with and without asthma for the presence of substance P immunoreactive nerve fibres. Airways of 200 microns-12 mm were obtained from autopsy, lobectomy and bronchoscopy. Quantitative morphological analysis was performed on 3 mm diameter airways from three asthmatic and three nonasthmatic subjects collected at autopsy, and on biopsies of 10 mm diameter airways from eight asthmatic and thirteen nonasthematic subjects. There was an increase in both the number and the length of substance P immunoreactive nerve fibres, in airways from subjects with asthma when compared with airways from subjects without asthma. Fibres were found in the lamina propria and surrounding vessels and glands. The fibres were commonly seen as bundles rather than as single fibres. There was no difference in the number of substance P nerves between normal subjects and subjects with chronic airflow limitation (CAL). The difference in the number, length and morphological characteristics of the substance P immunoreactive nerves between asthmatic and nonasthmatic subjects were striking.

An adaptive coding scheme for time-varying channels

Abstract: An adaptive coding scheme for digital communication over time-varying channels is presented. The scheme is based on a finite-state Markov channel model. Emphasis is on the adaptation of the error protection to the actual channel state. The throughput gains that are achieved by the adaptive scheme relative to the conventional nonadaptive coding methods are demonstrated by several examples. Of special interest is the use of punctured convolutional codes with maximum-likelihood Viterbi algorithm to enable adaptive encoding and decoding without modifying the basic structure of the encoder and the decoder. >

Structure of the macroglia of the retina: sharing and division of labour between astrocytes and Müller cells.

Abstract: A detailed comparison is made between astrocytes and Muller cells of the cat's retina, with emphasis on their structural specialisations. Evidence is presented that astrocytes and Muller cells both contribute to the formation of the inner glia limitans of the retina, the glia limitans of vessels, and the glial sheaths of neurones. In particular, it was noted that both astrocytes and Muller cells wrap bundles of ganglion cells axons, that both contribute processes to the glial convergence on the initial segments and node-like structures of axons, and that both wrap the somas of neurones in the ganglion cell layer. Further, it was noted that adherent junctions form between astrocytes, between Muller cells, and between astrocytes and Muller cells, but not between these cells and neurones, or among neurones. These similarities suggest that astrocytes and Muller cells function interchangeably in many respects, and we suggest that they be regarded as variants of macroglia. Quantitative differences between astrocytes and Muller cells were noted in their ensheathment of neurones. In particular, the glial sheaths around the somas of ganglion cells are formed predominantly by Muller cells, and the glial processes attached to node-like specialisations of their axons are formed mainly by astrocytes. One qualitative difference was noted between the two cell classes. The gap junctions which form between astrocytes do not form between Muller cells or between cells of the two classes. From these differences, and previously established features of their shape, orientation, distribution and origin, a hypothesis is developed of the specialisation of macroglia represented by Muller cells.

Medications and Multiple Falls in Elderly People: The St Louis OASIS Study

Abstract: The purpose of this study was to identify associations between the use of commonly taken medications and groups of medications and the risk of falls in elderly people living in the community. A stratified random sample of 1358 persons aged 65 years and over was selected from the 15,000 members of an educational organization for functionally independent, community-dwelling elderly people in St Louis, Missouri. Twenty-seven per cent of subjects reported at least one fall in the past year and 8% reported two or more falls. After adjusting for potential confounders (including age, sex, relevant medical conditions, health status, cognitive impairment, use of alcohol, depression and use of other medications), the following medications were found to be important risk factors for multiple falls: diazepam [odds ratio (OR): 3.7, 95% confidence interval (CI): 1.5-9.3], diltiazem (OR: 1.8, 95% CI: 0.8-4.1), diuretics (OR: 1.8, 95% CI: 1.2-2.8) and laxatives (OR: 2.1, 95% CI: 1.0-4.5). We conclude that caution is needed before prescribing diuretics and psychotropics, especially diazepam, for elderly people. The safety of diltiazem in this age group should be assessed further.

Behaviour of beach profiles during accretion and erosion dominated periods

Abstract: Beach profiles have been surveyed at monthly intervals between 1972 and 1988 at Moruya on the South Coast of New South Wales, Australia. Four profile sites have been used as a data set to provide an understanding of changes to beach volume, width, and shape. Moruya beach represents a moderately high energy, microtidal environment, which responds in a dramatic way to major storm events such as those experienced in the mid-1970s. This study distinguishes between profile characteristics associated with such a period (erosion-dominated or EDP) compared with periods when accretion dominated (ADP) accompanied by foredune expansion in both height and width.

Dimuon production in proton-copper collisions at sqrt s =38.8 GeV.

Abstract: Experimental results on the production of dimuons by 800-GeV protons incident on a copper target are presented. The results include measurements of both the continuum of dimuons and the dimuon decays of the three lowest-mass $\ensuremath{\Upsilon}$ $S$ states. A description of the apparatus, data acquisition, and analysis techniques is included. A comparison of the results with data taken at lower incident energies indicates a scaling behavior of the continuum dimuon yields.