Showing papers by "University of Newcastle published in 1988"

Lower bound limit analysis using finite elements and linear programming

Abstract: This paper describes a technique for computing lower bound limit loads in soil mechanics under conditions of plane strain. In order to invoke the lower bound theorem of classical plasticity theory, a perfectly plastic soil model is assumed, which may be either purely cohesive or cohesive-frictional, together with an associated flow rule. Using a suitable linear approximation of the yield surface, the procedure computes a statically admissible stress field via finite elements and linear programming. The stress field is modelled using linear 3-noded traingles and statically admissible stress discontinuities may occur at the edges of each triangle. Imposition of the stress-boundary, equilibrium and yield conditions leads to an expression for the collapse load which is maximized subject to a set of linear constraints on the nodal stresses. Since all of the requirements for a statically admissible solution are satisfied exactly (except for small round-off errors in the optimization computations), the solution obtained is a strict lower bound on the true collapse load and is therefore ‘safe’. A major drawback of the technique, as first described by Lysmer,1 is the large amount of computer time required to solve the linear programming problem. This paper shows that this limitation may be avoided by using an active set algorithm, rather than the traditional simplex or revised simplex strategies, to solve the resulting optimization problem. This is due to the nature of the constraint matrix, which is always very sparse and typically has many more rows that columns. It also proved that the procedure can, without modification, be used to derive strict lower bounds for a purely cohesive soil which has increasing strength with depth. This important class of problem is difficult to tackle using conventional methods. A number of examples are given to illustrate the effectiveness of the procedure.

The cervical zygapophysial joints as a source of neck pain.

Abstract: Diagnostic cervical medial branch blocks and zygapophysial joint blocks were used to test the hypothesis that the cervical zygapophyseal joints can be the source of pain in patients with idiopathic neck pain. Complete temporary relief of all symptoms was obtained in 17 out of 24 consecutive patients. Two major groups of patients were those with neck pain and headache stemming from the C2-3 joints, and those with neck pain and shoulder pain stemming from the C5-6 joints. Internal-control observations in nine of the 17 patients established the diagnostic validity of the blocks used. The high yield of positive responders in this study probably reflects the propensity of patients with zygapophysial joint syndromes to gravitate to a pain clinic when this condition is not recognised in conventional clinical practice.

Modified least squares algorithm incorporating exponential resetting and forgetting

Abstract: In this paper we present the general analysis of a class of least squares algorithms with emphasis on their dynamic performance particularly in the presence of poor excitation. The analysis is carried out in a deterministic framework and stresses geometrical interpretations. The core of this paper is the proposal and analysis of a new algorithm which incorporates exponential forgetting and resetting to an unprejudiced treatment of data when excitation is poor. The algorithm is particularly suitable for tracking time-varying parameters and is similar in computational complexity to the standard recursive least squares algorithm. The superior performance of the algorithm is verified via simulation studies.

Three-dimensional radiation in absorbing-emitting-scattering media using the discrete-ordinates approximation

Abstract: The discrete-ordinates S 4 approximation is used to study radiative transfer in three-dimensional rectangular enclosures containing an absorbing-emitting-scattering medium. The S 4 approximation is evaluated by comparison with the zone method and the spherical-harmonics P 3 approximation.

Calibration of X-probes for turbulent flow measurements

Abstract: We compare two methods of calibrating the yaw response of hot-wire probes: (i) the assumption that an effective angle, independent of the flow speed, can be deduced; (ii) the more general approach of determining the yaw response at a number of different speeds. The first, simpler, approach is shown to give surprisingly reasonable results for the usual turbulence statistics, even in high turbulence intensity flows. Some differences in the distribution of the inclination of the instantaneous velocity vector are observed. There is no advantage in using thek 2 factor to allow for longitudinal cooling.

Igneous microstructures in migmatites

Abstract: Clear differences between the microstructures of leucosomes and mesosomes occur in some nebulitic migmatites in the Proterozoic Arunta block, central Australia. The leucosomes show crystal faces of K-feldspar (microcline-microperthite), cordierite, andalusite, and plagio clase against quartz, indicating crystallization of a melt. In contrast, the mesosomes show predominantly polygonal grain shapes, modified by (001) crystal faces of biotite and rare crystal faces in some porphyroblasts of garnet, cordierite, and orthopyroxene, indicating re-crystallization in the solid state. The occurrence of abundant crystal faces in minerals such as feldspar, cordierite, and andalusite (which typically grow crystal faces in magmas, but generally not in metamorphic rocks) is evidence of former melt. Therefore, igneous microstructures can be preserved in leucosomes that have not undergone penetrative subsolidus deformation and recrystallization. The cores of many of the crystals of cordierite and K-feldspar have small, locally oriented inclusions similar to those in the same minerals in the mesosomes. These indicate that the cores remained solid during crystallization of the leucosome, which produced inclusion-free, euhedral rims. These crystals provide criteria for recognizing possible restite in granitoid magmas.

The objective structured interview for medical student selection

Abstract: An objective structured interview is an integral part of the process of selecting and admitting applicants to study medicine at this university. During the nine years (to the end of 1986) that the interview has been used 1600 candidates were interviewed out of roughly 13,000 applicants, and from these, 584 students were admitted to the course. Analysis of the interview data was carried out based on two aspects of student progress: graduation with honours and failure to complete the course of study. The interview as a whole, and especially some of the subscales, appears to identify students who may fail to complete the course: it may also help to predict which students are likely to graduate with honours.

A comparison of measurements of cerebral blood flow in the rabbit using laser Doppler spectroscopy and radionuclide labelled microspheres

Abstract: Laser Doppler spectroscopy has been evaluated for the measurement of cerebral blood flow (CBF) by correlation with simultaneous measurements by radionuclide labelled microspheres. The experimental procedures were carried out on five anaesthetised rabbits. The cortical tissue was exposed by means of a small burr hole and illuminated by a helium neon laser (632.8 nm). Reflected light was detected using a silicon photodiode, and CBF was calculated continuously from the power of the frequency weighted Doppler spectrum in the reflected light. Three successive measurements of CBF were made using the microsphere technique. Following an initial baseline measurement, CBF was increased by an infusion of metaraminol and then reduced by controlled haemorrhage. Laser Doppler spectroscopy provided continuous monitoring of blood flow fluctuations and during the haemorrhage it was possible to demonstrate CBF autoregulation until the mean blood pressure fell below 6.7 kPa (50 mmHg). A regression analysis was performed between the simultaneous CBF measurements from the two techniques using a least squares best fit straight line analysis (r = 0.92, P less than 0.001). It was concluded that the flow computed from laser Doppler spectroscopy varied linearly with CBF and offers the unique advantage of continuous and instantaneous measurements even during nonsteady state flow.

Influence of wall suction on the organized motion in a turbulent boundary layer

Abstract: The effect of wall suction on the organized motion of a tubulent boundary layer is examined experimentally both in a wind tunnel and in a water tunnel. In the windtunnel boundary layer, which developed over a slighly heated surface, temperature fluctuations were simultaneously obtained at several points, aligned in either the x (streamwise) or y (normal to the wall) direction. The temperature traces reveal the existence of two spatially coherent events, characterized either by a sudden decrease (cooling) or by a sudden increase (heating) of temperature. Estimates are presented for the average convection velocity, and average frequency of these events. The average convection velocity of ‘coolings’ is about 15% larger than that of ‘heatings’, the velocity of both events exhibiting an important local maximum in the buffer region. Near the wall, the convection velocity of both events is increased slightly by suction while their average frequency is reduced by suction. Away from the wall, the average inclination of ‘coolings’ and ‘heatings’ is about 40° without suction; suction does not alter the inclination of ‘coolings’ but increases that of ‘heatings’ to about 50°. Visualizations in the water tunnel indicate that suction increases the stability and the longitudinal coherence of low-speed streaks. They also show that suction reduces the average frequency of dye ejections into the outer layer.

The development of Akabane virus-induced congenital abnormalities in cattle.

Abstract: A prospective study of the incidence and severity of congenital deformities of calves, attributable to maternal infection by Akabane virus, was carried out on a population of 174 susceptible animals that were between one and nine months pregnant at the time of infection. The study was carried out in the Hunter Valley of New South Wales during 1983, after an epidemic of Akabane virus infection in late February to early March 1983. The incidence of virus-induced abnormalities in calves and fetuses was 17.8 per cent (31/174). The highest incidence of abnormalities occurred during the third and sixth months of gestation (27 to 29 per cent). The earliest abnormality was observed after infection at 76 days of gestation, and the last after infection at 249 days. The development of the pathological entities of hydranencephaly/porencephaly and arthrogryposis were found to be quite distinct. Cases of hydranencephaly and porencephaly developed after infection between 76 and 104 days of gestation whereas arthrogryposis developed after infection between 103 and 174 days of infection. It was concluded that the type of congenital deformity produced by maternal infection with Akabane virus was dependent on the stage of fetal development at the time of infection. The data suggest that the infection was transplacental and that fetuses of less than two months of age were protected from infection.

Connection between continuous and discrete Riccati equations with applications to kalman filtering

Abstract: The aim of the paper is to explore the relationship between the continuous-time Riccati equation and the corresponding discrete-time equation with fast sampling. The interconnection is established by formulating the discrete case using delta operators. The application of these results to the Kalman filtering problem highlights the importance of analogue prefiltering in the sampling process. A secondary benefit arising from the use of the delta operator is that improved numerical behaviour is obtained for solution algorithms, compared with that obtainable with the usual shift operator.

A steepest edge active set algorithm for solving sparse linear programming problems

Abstract: A steepest edge active set algorithm is described which is suitable for solving linear programming problems where the constraint matrix is sparse and has more rows than columns. The algorithm uses a steepest edge criterion for selecting the search direction at each iteration and recurrence relations are derived which enable it to execute efficiently. The canonical form for the active set method is convenient for many applications and may be exploited to devise a simple crash procedure which is employed prior to phase one. A complete two-phase algorithm which incorporates the crash procedure is outlined. Only one artificial variable is needed to determine if the linear programming problem has a feasible solution in phase one. Some computational results are given to illustrate the effectiveness of the algorithm for a range of sparse linear programming problems. Comparisons between the steepest edge criterion and the traditional Dantzig criterion suggest that the former usually requires fewer iterations and often leads to substantial savings for large problems.

Lifestyle factors in monozygotic and dizygotic twins.

Abstract: In examining genetic influences on biological variables using twins, it may be important to examine the distribution between and within twin pairs of demographic and lifestyle factors that may themselves affect the biological variable being studied. We explored the distribution of demographic and lifestyle factors that may affect blood lipid levels or ischaemic heart disease (IHD) risk among a sample of 106 monozygotic (MZ) and 94 like-sex dizygotic (DZ) twin pairs. In our sample, MZ twins were statistically significantly different from DZ twins only in marital status, cigarette smoking habits, and the ratio of polyunsaturated to saturated fat (P:S ratio) in their dietary intake. The latter variable was among many dietary variables examined (using 4-day weighed food diaries), and the size of the difference in intake was small. When comparisons were made of the similarities within twin pairs, we found members of MZ twin pairs to be statistically significantly closer than DZ twins in educational achievement, occupation, cigarette smoking, and exercise habits, and the number of days a week on which alcohol was consumed. These last three variables were consistently closer among twins with closer contact than among those with a smaller degree of current shared environment. For 12 of the 13 nutrients examined, the within-pair correlations were higher for MZ than for DZ twins, although our test for significant genetic variance showed statistical significance only for intake of complex carbohydrates. We conclude that MZ twins share demographic and lifestyle factors that might influence the risk of IHD and blood lipid levels to a greater degree than do DZ twins, although it is difficult to say if these similarities in lifestyle result from genetic influences or not. Nevertheless, ascribing differences between correlations in MZ and DZ twin pairs for lipid levels as being purely "genetic"--as implicit in conventional measures of heritability--is likely to overestimate the influence of genetic factors.

Patients as a direct source of information on adverse drug reactions.

Abstract: To determine whether patients should participate directly in detecting adverse reactions to drugs their ability to provide written reports of symptoms experienced during treatment with amoxycillin or trimethoprim-sulphamethoxazole was investigated. When compared with telephone interviews forms on which patients reported events were reliable (the observed agreement with the same statements posed during telephone calls was 85%, kappa = 0.56) and valid (sensitivity = 54%, specificity = 94%). Patients were also supplied with forms that invited them to report adverse reactions, and their perceptions were compared with those of a panel of experts, who were informed of all clinical events that had been reported during the detailed telephone interviews. Patients were more conservative than the experts in attributing clinical events to drug treatment. The extent of agreement varied and was notably poor for skin and bowel complaints (kappa = 0.13 in each case). The performance of event report forms and reaction report forms as instruments of detection was compared in a hypothetical situation in which the experts' views represented the "truth" about adverse reactions to a new drug. Event reporting had a higher sensitivity than reaction reporting (42% v 24%) but a lower specificity (58% v 98%). National centres monitoring adverse drug reactions should probably resist pressure to accept reports of reactions directly from the public, but a system based on large scale reporting of events might be valuable in aiding the early detection of symptomatic reactions to new drugs.

Effects of aluminium on fluoride uptake by plants

Abstract: SUMMARY The effect of aluminium on the uptake and transport of fluoride by bean (Phaseolus vulgaris L.) was examined by means of water culture. Tomato (Lycopersicon esculentum Mill.) was used in one experiment. Exposing bean roots to NaF led to fluoride concentrations in the roots and first leaves of 47 and 17 times respectively those of controls. In contrast, the same concentration of F given as AlF3 gave concentrations 83 and 68 times respectively those of controls. Both roots and leaves showed an increase in concentration of 0-42 mol of F for each mol of Al, in contrast to the 3 :1 molar ratio of F to Al in the AlF3 solution. Giving the Al (as AlC13) before NaF also led to significant increases in uptake and transport of F compared with controls. Fluoride was readily washed out of roots whether it was presented as NaF or AlF3. Analysis of xylem exudate of tomato given AlF3 showed that 44 % of the fluoride was associated with metals compared with 4-7 % in controls. It was concluded that when F is presented as F-, it remains largely in the apoplast and that it enters the xylem by leaking past the endodermal barrier at the root tip or where laterals emerge. In complexing with Al, the negative charge on the F- is neutralized, decreasing Donnan exclusion and therefore leading to a higher concentration of F in the apoplast. The formation of fluoride-aluminium complexes in plant tissues would be expected to decrease the toxicity of both elements.

Studies of fluid and spermatozoal transport in the extratesticular genital ducts of the Japanese quail.

Abstract: Stereological studies of the spermatic ducts of the quail were carried out for comparison between different parts of the system and those of other species, and to provide a basis for future physiological studies. Duct length, surface areas and volumes of various components of the ducts were determined. Values were subsequently used to calculate net fluxes of fluid across the duct epithelium, spermatozoal velocity and the distribution of spermatozoa throughout the system. It was concluded that the extratesticular spermatic ducts are divided into 2 main parts: (1) the ductuli efferentes where spermatozoa spend a brief period (8 minutes) and which are adapted for considerable net fluid reabsorption (100 microliters/cm2/h), and (2) the connecting ducts, ductus epididymidis and ductus deferens where spermatozoa spend a longer period (24 hours) and which are involved in little net fluid transport (0.14-2.1 microliter/cm2/h). Most spermatozoa (92.3%) are located in the ductus deferens. The velocity of spermatozoal transport is much the same through the quail spermatic ducts (0.37 mm/min) as through the mammalian epididymis, the difference between classes in the duration of spermatozoal transport being due to differences in the distance that they travel. In a comparison between estimates of spermatozoal concentration using stereological methods and direct counts of spermatozoa in samples collected using micropuncture procedures it was concluded that both methods gave similar results.

The demand for m 1: a forward looking buffer stock model

Abstract: A FORWARD looking model of the demand for Ml based on minimising multi-period quadratic costs is derived. The dynamic response of the demand for money differs depending on whether shocks are anticipated or unanticipated. The restrictions implicit in the forward model are tested and the model is compared with a conventional ADL backward looking model.

Altered aminoglycoside pharmacokinetics in the critically ill.

Abstract: We studied prospectively 49 patients being treated in an intensive care unit with aminoglycosides for gram-negative sepsis. Pharmacokinetic data were calculated from three post-dose serum levels using a one-compartment model. Doses required to achieve peak levels between 5 and 10 mg/l with trough levels approximately 1.0 mg/l ranged between 2 and 12 mg/kg per day (mean dose 7 mg/kg per day). During therapy 60% of the patients had a change in their apparent volume of distribution (Vd) of greater than 20%. These patients were likely to have confirmed infection and to be febrile at the start of treatment. Two to three weeks after discharge ten patients were restudied after a single dose of aminoglycoside. There was a reduction in mean Vd from 0.24 to 0.18 l/kg (P less than 0.02). Critically ill patients have significantly larger volumes of distribution and may require larger doses per kilogram of body weight of aminoglycoside to achieve therapeutic concentrations. Due to considerable variation in kinetic parameters, the use of standard doses or dosing nomograms is not recommended.

The perceived competence of intellectually talented students.

Abstract: Upper primary gifted boys and girls were compared with nongifted children on self-perceptions of competence in four areas: cognitive, physical, social, and general self-worth. Gifted students perce...

Substructures in a turbulent spot

Abstract: Substructures within a turbulent spot which develops in a slightly heated laminar boundary layer have been identified using arrays of cold wires aligned in either a streamwise direction or in a direction normal to the wall. At any given streamwise distance from the spot origin, histograms of the number of detected substructures exhibit a peak, defining the most probable spot or the spot with the most likely number of substructures. The number of substructures in the most probable spot increases with streamwise distance but all substructures are convected at approximately the same velocity for any given distance from the wall. This velocity is approximately equal to that of the leading edge of the spot and increases slightly with distance from the wall. The increase in the number of substructures accounts for the streamwise growth of the spot. A simple relation is derived for determining the number of substructures at a particular streamwise station and a geometrical construction is proposed for identifying the origin of a new substructure. There is sufficient evidence for suggesting that the new substructures are formed near the trailing edge of the spot. The convection velocity, inclination and lengthscales of the substructures compare favourably with the corresponding characteristics of hairpin vortices.

Expression of the gangliosides GM3, GD3 and GD2 in tissue sections of normal skin, naevi, primary and metastatic melanoma.

Abstract: Expression of the gangliosides GM3, GD3 and GD2 was studied in tissue sections from 19 naevi, 29 primary and 83 metastatic melanoma using the ABC immunoperoxidase technique. GM3 was not detected in normal skin whereas GD2 was detected on the basal and stratum spinosum of the epidermis and on peripheral nerves in the dermis. GD3 was expressed on melanocytes but not on most other components of normal skin. However, GD3 was strongly expressed on epidermis adjacent to naevi and primary melanoma whereas GD2, in contrast to that in normal skin, was not expressed on the epidermis adjacent to 26/29 primary melanoma. All naevi were positive for GM3 and GD3 except that GM3 was not detected on junctional components of naevi. GD2 was not expressed on naevi except in areas showing neuroid differentiation. Studies on melanoma revealed that approximately 60% of primary and 75% of metastatic melanoma expressed GM3 to a varying extent. With 2 exceptions, all primary and metastatic melanomas expressed GD3 although there was variable expression within most of the individual tumours. GD2 was detected in only approximately 25% of primary and 50% of metastatic melanomas. Both GD2 and GD3 were detected on lymphocytes surrounding melanoma. The higher expression of GD2 on metastases compared to primary melanomas was consistent with the view that GD2 expression was associated with increased metastatic potential. However, the low proportion of metastases expressing GD2 and the absence of any correlation with thickness of the primary tumour suggested that GD2 expression was not a reliable marker of metastatic potential. No differences could be detected in ganglioside expression on metastases in skin or lymph nodes. These results appear to have implications for the use of MAbs against gangliosides in therapy of melanoma and in the study of melanocytic differentiation.