Showing papers by "University of Melbourne published in 1994"

Assembly of porphyrin building blocks into network structures with large channels

Abstract: CRYSTAL engineering—the deliberate design and construction of crystal structures from molecular components—promises to provide solid-state materials with specific and useful chemical, mechanical, electronic or optical properties1. In most of the molecular crystals considered so far, van der Waals forces and hydrogen bonding govern the crystal packing2–7. Zeolites, pillared clays and related microporous materials, which have been studied extensively because their porous structures convey useful catalytic activity8,9, can now also be 'engineered' to some extent10,11. We are exploring ways12–14 to construct channelled solids with very different chemical architectures and potentially different catalytic activity from those of zeolites. Here we show that porphyrin building blocks can be used to construct three-dimensional networks with the topology of the PtS structure, containing large channels. In our materials the channels are filled with solvent molecules, and crystalline order is lost on solvent removal. Nevertheless, the results show that it is possible to use simple molecular building blocks to engineer specific frameworks which, if they can be made robust, may offer new catalytic potential.

Integrated probabilistic data association

Abstract: This paper presents an integrated probabilistic data association algorithm which provides recursive formulas for both data association and track quality (probability of track existence), allowing track initiation and track termination to be fully integrated into the association and smoothing algorithm. Integrated probabilistic data association is of similar computational complexity to probabilistic data association and as demonstrated by simulation, achieves comparable performance to the more computationally expensive interactive multiple model probabilistic data association algorithm which also integrates initiation and tracking. >

A Heparin-binding Domain in the Amyloid Protein Precursor of Alzheimer's Disease Is Involved in the Regulation of Neurite Outgrowth

Abstract: The amyloid protein precursor (APP) of Alzheimer9s disease is synthesized as an integral transmembrane protein that is released from cells in culture following proteolytic cleavage. The function of released APP is not known, although there is evidence that the protein may bind to components of the extracellular matrix (ECM). In the present study, substratum-bound APP stimulated neurite outgrowth in cultures of chick sympathetic and mouse hippocampal neurons. This effect was dependent upon the presence of substratum-bound heparan sulfate proteoglycans (HSPG). The effect of APP on neurite outgrowth was comparable to that of laminin. A 14 K N-terminal fragment of APP was found to bind heparin and a region close to the N-terminus of APP (residues 96–110) identified as a potential heparin-binding domain based on secondary structure predictions and molecular modeling. Mutagenesis of three basic residues (lysine-99, arginine-100, and arginine-102) resulted in a recombinant protein (APPhep) with decreased heparin-binding capacity. A peptide homologous to the heparin-binding domain was synthesized and found to bind strongly to heparin and to inhibit binding of 125I-labeled APP to heparin (IC50 approximately 10(- 7) M). The peptide blocked the effect of APP on neurite outgrowth (IC50 approximately 10(-7) M), whereas two other peptides homologous to other domains in APP had no effect. The results indicate that the binding of APP to HSPG in the ECM may stimulate the effects of APP on neurite outgrowth.

The Bone Density of Female Twins Discordant for Tobacco Use

Abstract: Background Smoking is recognized as a risk factor for vertebral, forearm, and hip fractures. Since bone density is an important determinant of bone strength, we conducted a study to ascertain whether a deficit in bone density is associated with tobacco use and, if so, to identify the responsible mechanisms. Methods We conducted a cross-sectional study of bone density at the lumbar spine and the femoral neck and shaft in 41 pairs of female twins (21 monozygotic pairs), 27 to 73 years of age (mean, 49), who were discordant for at least 5 pack-years of smoking (mean, 23; maximum, 64). Bone density was measured by dual-photon absorptiometry. The difference in bone density between the members of a pair was expressed as a percentage of the mean value for the pair. Results For every 10 pack-years of smoking, the bone density of the twin who smoked more heavily was 2.0 percent lower at the lumbar spine (P = 0.01), 0.9 percent lower at the femoral neck (P = 0.25), and 1.4 percent lower at the femoral shaft (P = 0....

Structural investigation of xenon-ion-beam-irradiated glassy carbon

Abstract: Raman spectroscopy, cross-sectional transmission electron microscopy, and electron-energy-loss spectroscopy have been used to monitor the ion-beam-induced transformation in glassy carbon irradiated with 320-keV Xe ions to doses between 5\ifmmode\times\else\texttimes\fi{}${10}^{12}$ and 6\ifmmode\times\else\texttimes\fi{}${10}^{16}$ ions/${\mathrm{cm}}^{2}$. It was found that (i) the ion beam amorphizes the glassy carbon structure; (ii) the amorphization is accompanied by a compaction of the glassy carbon from an initial density of 1.55 to 2.2\ifmmode\pm\else\textpm\fi{}0.2 g/${\mathrm{cm}}^{3}$; and (iii) approximately 15% of the graphitelike bonds in glassy carbon are converted to diamondlike bonds in the amorphization process. The transformation of glassy carbon to an amorphous state occurs in two distinct stages as a function of ion dose. For damage levels up to 0.2 displacements per atom (dpa) the effect of the ion beam is to decrease the average graphitic crystallite size. Above 0.2 dpa, disorder in bond length and bond angle away from ideal graphitic threefold coordination occurs leading to complete amorphization at high doses. The amorphization, compaction, and presence of \ensuremath{\approxeq}15% ${\mathit{sp}}^{3}$ bonds in the implanted layer of glassy carbon results in a surface layer which is significantly more resistant to abrasion than as-grown glassy carbon.

Edge crossings in drawings of bipartite graphs

Abstract: Systems engineers have recently shown interest in algorithms for drawing directed graphs so that they are easy to understand and remember. Each of the commonly used methods has a step which aims to adjust the drawing to decrease the number of arc crossings. We show that the most popular strategy involves an NP-complete problem regarding the minimization of the number of arcs in crossings in a bipartite graph. The performance of the commonly employed “barycenter” heuristic for this problem is analyzed. An alternative method, the “median” heuristic, is proposed and analyzed. The new method is shown to compare favorably with the old in terms of performance guarantees. As a bonus, we show that the median heuristic performs well with regard to the total length of the arcs in the drawing.

Multiple Corticospinal Neuron Populations in the Macaque Monkey Are Specified by Their Unique Cortical Origins, Spinal Terminations, and Connections

Abstract: In primates, multiple corticospinal projections from the sensorimotor cortex operate in concert to regulate voluntary action. We examined the soma distributions of all those corticospinal neuron populations projecting to different zones in the cervical and more caudal spinal segments in the macaque that are labeled with retrogradely transported fluorescent tracers; 2-4 differentiable dyes were injected into different sites in the cervical spinal cord of each of 11 monkeys. Lamina V of the cerebral cortex, in which all corticospinal neuron somas were located, was unfolded with computer assistance to form a flat surface, and local soma densities were displayed on this plane as contour and 3-D maps. At least nine discrete, somatotopically organized corticospinal projections were identified. Three separate corticospinal projections originated in frontal cortex. The first projected mostly from area 4 (approximately 35% of the total contralateral neuron population), but also from the adjacent dorsolateral area 6a alpha (approximately 6% of total). The second large corticospinal projection (approximately 15% of total) originated in the supplementary motor area and a third small projection (approximately 2.6% of total) projected from the "postarcuate" cortex. Two separate corticospinal neuron populations were identified in areas 24 (approximately 6% of total) and 23 (approximately 4% of total) of the cingulate cortex. Thus, nearly 70% of the contralateral corticospinal projection originated in frontal and cingulate cortex. At the boundary between the primary motor and somatosensory cortex there was a sharp change in the pattern of projections. Only approximately 2.2% of the contralateral corticospinal projection originated in area 3a, rising to approximately 9% in areas 3b/1, and approximately 13% in areas 2/5. The projections from SII and insula totaled 3.4%. Ipsilateral and contralateral corticospinal projection patterns were similar, but the ipsilateral projection was only approximately 8.1% of that from the contralateral cortex. Each corticospinal neuron population had terminals in the intermediate zone of all spinal segments; additionally, there were ventral horn projections from the primary motor and cingulate cortex, and dorsal horn projections from the somatosensory cortex. Recognizing a number of separate populations of corticospinal neurons in the frontal, parietal, and insular cortex, each with unique thalamic and cortical inputs, and each of which has continuous access to all spinal motoneuron populations, underlines the importance of cortical and spinal connections linking them and coordinating their action. No coherent model of the cortical control of limb movements that incorporates this functional anatomy yet exists.

Factors in childhood as predictors of asthma in adult life

Abstract: Objective: To determine which factors measured in childhood predict asthma in adult life. Design: Prospective study over 25 years of a birth cohort initially studied at the age of 7. Setting: Tasmania, Australia. Subjects—1494 men and women surveyed in 1991-3 when aged 29 to 32 (75% of a random stratified sample from the 1968 Tasmanian asthma survey of children born in 1961 and at school in Tasmania). Main outcome measures: Self reported asthma or wheezy breathing in the previous 12 months (current asthma). Results: Of the subjects with asthma or wheezy breathing by the age of 7, as reported by their parents 25.6% (190/741) reported current asthma as an adult compared with 10.8% (81/753) of subjects without parent reported childhood asthma (P

Employee Attachment and Noncoercive Conditions of Work The Case of Dental Hygienists

Abstract: Recent sociological arguments have claimed that employee attachment in corporatist organizations is produced, not with direct coercive measures, but indirectly by employers controlling various structural conditions of work. It is argued that this also occurs in smaller organizations that do not exhibit internal labor markets nor other corporatist organization characteristics. Specifically, in smaller organizations that are structured more traditionally with the employer deciding work schedules, pay, distribution of profits, and so on, the features of employee social integration, autonomy/participation, and legitimacy of the authority structure are just as important as they are in the larger corporatist firms. This claim is generally supported with data on the job satisfaction, the organizational commitment, the intent to stay, and the turnover of dental hygienists working in dental offices that are controlled by the employer, the dentist. Work group integration and legitimacy-producting features were foun...

Almost all regular graphs are hamiltonian

Abstract: In a previous article the authors showed that almost all labelled cubic graphs are hamiltonian In the present article, this result is used to show that almost all r‐regular graphs are hamiltonian for any fixed r ⩾ 3, by an analysis of the distribution of 1‐factors in random regular graphs Moreover, almost all such graphs are r‐edge‐colorable if they have an even number of vertices Similarly, almost all r‐regular bipartite graphs are hamiltonian and r‐edge‐colorable for fixed r ⩾ 3 © 1994 John Wiley & Sons, Incg1

Optimal waveform selection for tracking systems

Abstract: Investigates adaptive waveform selection schemes where selection is based on overall target tracking system performance. Optimal receiver assumptions allow the inclusion of transmitted waveform specification parameters in the tracking subsystem defining equations. The authors give explicit expressions for two one-step ahead optimization problems for a single target in white Gaussian noise when the tracker is a conventional Kalman filter. These problems may be solved to yield the most improvement possible in tracking performance for each new transmitted pulse. In cases where target motion is restricted to one dimension, closed-form solutions to the local (one step ahead) waveform optimization problem have been obtained. The optimal waveform selection algorithms in the paper may be included with conventional Kalman filtering equations to form an enhanced Kalman tracker. Simulation examples are presented to illustrate the potential of the waveform selection schemes for the optimal utilization of the capabilities of modern digital waveform generators, including multiple waveform classes. The extension of the basic waveform optimization scheme to more complex tracking scenarios is also discussed. >

Measurement of functional severity of asthma in children.

Abstract: The usefulness of surveys for measuring the severity of asthma in school-age children depends on the availability of reliable and valid questionnaires. The aim of this study was to develop a measure of functional severity of asthma over the previous 12 mo, for use in population studies and in investigating treatment regimens. Of 10,198 children surveyed, 9,192 (90%) in school Years 2, 7, and 10 (mean ages 8, 13, and 16 yr) in Melbourne were screened for wheeze. The parents of the 1,267 children with wheeze were interviewed. Symptoms and restriction of activity due to asthma were analyzed using factor analysis and the partial credit version of the item response theory measurement model. The result was a continuous severity scale that was highly consistent with the data, and with goodness of fit statistics indicating the severity of 97% of children was well described by the scale. The scale correlated significantly with school absence due to wheeze (r = 0.35), functional impairment during the 2 wk before interview (Functional Status II-R [FSII-R], r = 0.30), visits to medical care for wheeze (r = 0.22), and amount of medication (r = 0.36). For descriptive purposes, a simple index with four bands of severity was developed from the continuous severity scale: low severity (47% of children with wheeze), moderate (30%), mild (18%), and high (5%). The scale and index facilitate standardized description of the impact of asthma on daily life on the basis of responses to six survey questions.

An empirical assessment of the “fit”between strategy and management information system design

Abstract: This paper was motivated by the limited understanding of the role of accounting vis a vis other information in supporting the needs of management. The paper reports the findings of a study which examined differences in the design parameters of management information systems in firms adopting different strategic priorities. Based on a sample of 49 business unit general managers, the findings indicate that the effectiveness of business units is dependent on a match between the design of the information system and the firm's strategic posture. Information systems which have the characteristics of a broad scope system were found to be more effective in firms employing a strategy of continuous product/market development and innovation (Prospectors) than in firms which were protecting a comparatively narrow and stable product-market (Defenders). The results have important implications for management accountants involved in the design and implementation of management information systems, especially in firms adopting a more innovative strategic posture. In particular, the study sheds light on the role of accounting as part of the “mosaic” of information provided to managers for decision making.

Osteoblasts mediate thyroid hormone stimulation of osteoclastic bone resorption.

Abstract: Thyroid hormones increase bone turnover in vivo and stimulate bone resorption in vitro. Clinical states associated with excess circulating thyroid hormone levels are known to produce osteoporosis. To determine the effect of T3 on bone resorption, we used an isolated rat osteoclast bone resorption assay in the absence or presence of added osteoblasts. This makes it possible to distinguish between direct and indirect effects of thyroid hormones on osteoclasts. In short settlement osteoclast cultures, which contain relatively few osteoblasts, 24-h treatment with T3 (10(-10)-10(-8) M) produced no stimulation of bone resorption. However, after 48-h incubation in the presence of T3, an increase in resorption was observed (2.3-fold at 10(-9) M). In cocultures of osteoclasts and osteoblasts (UMR 106-01 osteoblast-like cells or long settlement cultures), T3 stimulated resorption at 24 h. Furthermore, stimulation of resorption occurred when osteoblasts (UMR 106-01 or rat calvarial cells) were pretreated with T3 and the subsequent osteoblast-osteoclast cocultures conducted for 24 h in the absence of T3. Thus, direct exposure of osteoclasts to T3 was not required for the stimulatory effect. Treatment for 48 h with T3 (10(-9) M) or PTH (10(-8) M) had no effect on bone resorption in osteoblast-free cultures derived from human osteoclastoma tumours. T4 was 100-fold less potent than T3 as a stimulator of osteoclast activity, and rT3 had no effect. T3-induced stimulation was inhibited by salmon calcitonin (10(-10) M). These findings indicate that thyroid hormone can act on osteoblasts to indirectly stimulate osteoclastic bone resorption.

Residential Water Use: Predicting and Reducing Consumption1

Abstract: This project had two goals: to explain variation in residential water consumption and to evaluate methods of encouraging residents to reduce their consumption. Survey data for both studies were collected by mail questionnaire in early 1991, and water consumption figures were recorded between June and August of that year. In Study 1 (n = 264) a three-variable regression model (number of residents, clothes washing machine loads, and property value) accounted for 60% of the variance. Attitudes, habits and values were very poor predictors of water consumption. In Study 2 (n =226) households were divided into three treatment groups: feedback only, feedback and dissonance, and a control group. Repeated-measures ANOVA revealed that high consumers receiving dissonance and feedback or feedback alone had significantly reduced their water consumption in the treatment period. The implications of these findings are discussed.

A study of the fine‐scale motions of incompressible time‐developing mixing layers

Abstract: The geometry of dissipating motions in direct numerical simulations (DNS) of the incompressible mixing layer is examined. All nine partial derivatives of the velocity field are determined at every grid point in the flow, and various invariants and related quantities are computed from the velocity gradient tensor. Motions characterized by high rates of kinetic energy dissipation and high enstrophy density are of particular interest. Scatter plots of the invariants are mapped out and interesting and unexpected patterns are seen. Depending on initial conditions, each type of shear layer produces its own characteristic scatter plot. In order to provide more detailed information on the distribution of invariants at intermediate and large scales, scatter plots are replaced with more useful number density contour plots. These essentially represent the unnormalized joint probability density function of the two invariants being cross‐plotted. Plane mixing layers at the same Reynolds number, but with laminar and turbulent initial conditions, are studied, and comparisons of the rate‐of‐strain topology of the dissipating motions are made. The results show conclusively that, regardless of initial conditions, the bulk of the total kinetic energy dissipation is contributed by intermediate scale motions, whose local rate‐of‐strain topology is characterized as unstable‐node‐saddle–saddle (two positive rate‐of‐strain eigenvalues, one negative). In addition, it is found that, for these motions, the rate‐of‐strain invariants tend to approximately follow a straight line relationship, characteristic of a two‐dimensional flow with out of plane straining. In contrast, fine‐scale motions, which have the highest dissipation, but which only contribute a small fraction of the total dissipation tend toward a fixed ratio of the principal rates of strain.

The genetic, molecular and phenotypic consequences of selection for insecticide resistance.

Abstract: Studies of insecticide resistance allow theories of the adaptive process to be tested where the selective agent, the insecticide, is unambiguously defined. Thus, the consequences of selection of phenotypic variation can be investigated in genetic, biochemical, molecular, population biological and, most recently, developmental contexts. Are the options limited biochemically and molecularly? Is the genetic mechanism monogenic or polygenic, general or population/species specific? Are fitness and developmental patterns associated? These questions of general evolutionary significance can be considered with experimental approaches to determine how insecticide resistance evolves.