Showing papers by "University of Sydney published in 1979"

Transport properties of regular arrays of cylinders

Abstract: We extend a method devised by Lord Rayleigh to enable the calculation of the transport properties of circular cylinders in square and hexagonal arrays. The theory is confirmed by measurements on arrays of perfectly conducting cylinders, and also is compared with asymptotic formulae due to Keller (1963) and O’Brien (1977). It is used to furnish plots of equipotential lines within the array. It is also applied to the calculation of the optical properties of films with columnar structure. Detailed studies for copper films show both the good solar selectivity possible with voided structures and the transition from a good reflector to a metal black consequent upon structural changes.

The Ecology of Intertidal Gastropods

Abstract: Publisher Summary The structure and dynamics of biological communities cannot be understood without considerable background information about the ecology of the component species. Experimental manipulations of natural populations in field situations are often the most profitable method of determining the factors that affect the distribution and abundance of species. Intertidal organisms have proved to be suitable for such direct experimentation because of the ease of access to intertidal areas, the relatively sessile nature, and due to the great abundance of many of the organisms. The chapter elaborates the key observations made on the ecology of intertidal gastropods such as the factors affecting their establishment of distributional patterns and the maintenance of distributional patterns caused through their behavioral adaptations and physiological stress. It dwells on the competition and predation due to the distribution and abundance of population of intertidal gastropods, its reproductive biology, and the geographical distribution and influences of gastropods on the structure of intertidal communities. The chapter also lists the observations based on general hypotheses and highlights the gap in the knowledge on ecology and behavior of intertidal gastropods, thus, paving a foundation for future research and investigations.

Low natural killer-cell activity and immunoglobulin levels associated with smoking in human subjects

Abstract: Previous studies have shown that smoking is associated with a high incidence of certain malignancies and a high incidence of metastatic spread of melanoma. The purpose of the present study was to examine whether this high incidence of malignancy could be associated with certain aspects of immune function believed to be important in restricting tumour growth. Age-and sex-matched smoking and non-smoking normal subjects and male, smoking and non-smoking melanoma patients, were studied for the natural killing (NK) activity of their blood leukocytes against cultured melanoma and Chang cells. The levels of the various immunoglobulin classes in their sera and the E rosette levels of the normal subjects were also assessed. The results indicate that the NK activity of blood leukocytes from both normal subjects and melanoma patients who smoked was significantly lower against cultured melanoma cells than that of non-smokers. Smokers were also shown to have lower IgG and IgA Immunoglobulin levels in their sera compared to non-smokers but no differences in the percentage of E-rosetting (T) cells was detected. Recent studies provide some basis for the belief that the low NK activity and immunoglobulin levels in smokers may be related. These results further suggest that a closer examination of the effects of this environmental hazard on the immune system and its relation to malignancy is needed.

A rapid sensitive method for determining phospholipid phosphorus involving digestion with magnesium nitrate

Abstract: A method is described for the rapid determination of phospholipid phosphorus in samples containing less than 0.5 μg phosphorus. Phospholipid phosphorus is first converted to inorganic phosphate by heating a dried lipid extract briefly over a Bunsen flame in the presence of magnesium nitrate, then dissolving the resulting residue in dilute hydrochloric acid at 95 C. The determination of the inorganic phosphate content of the sample then requires only the addition of Triton X-100 and an acidic ammonium molybdate-malachite green reagent. Absorbance is measured at 650 nm after 5 min at room temperature.

Rabbit skeletal myosin isoenzymes from fetal, fast-twitch and slow-twitch muscles

Abstract: IT is generally accepted that myosin in vertebrate fast-twitch and slow-twitch muscles is structurally1–4 and immunochemically5–8 distinct and exists in several isoenzymatic forms9–14. The nature of myosin in developing mammalian skeletal muscles is controversial. Some authors15,16 consider it to be identical to adult fast-twitch myosin on the basis of light-chain composition and histochemistry. Others8 suggest that it may be a mixture of fast-twitch and slow-twitch myosins. Still others4,17 maintain it is a distinct fetal form of myosin differing in primary structure from adult myosins. In this report we show that (1) myosin in both neonatal and adult fast-twitch muscles of the rabbit exists in three electrophoretically distinct isoenzymatic forms which differ in light-chain composition, and (2) the two-dimensional peptide map of the heavy chains of neonatal muscle myosin is distinct from maps of both fast-twitch and slow-twitch myosins. These results clearly establish the existence of fetal myosin isoenzymes in developing mammalian muscles and resolve apparent contradictions in the literature.

Melorheostosis and the sclerotomes: a radiological correlation.

Abstract: Melorheostosis is characterised radiologically by hyperostotic linear densities in bone. These densities have a peculiarly segmental distribution which does not correspond with the anatomical course of blood vessels or mixed nerve roots of the limbs. So far this distribution has lacked any valid explanation, although it has been suggested to be a developmental error as a result of an embryonic metameric disturbance. Inman and Saunders in 1944 described a sensory nerve supply to skeletal structures with ‘sclerotomes’ representing the zones of the skeleton supplied by individual spinal sensory nerves. Radiographs of 30 cases from the Radiological Museum of the Institute of Orthopaedics, London, have been reviewed and an attempt has been made to correlate the sclerosing lesions with the sclerotomes. The investigation was handicapped by paucity of films and clinical information, but in 19 cases the skeletal abnormalities were considered to correspond with a single sclerotome or part thereof. These studies were convincing when films of an affected hand or foot were available. In the remaining 11 cases multiple sclerotomes appeared to be involved and the clinical manifestations were correspondingly more severe. It is proposed that melorheostosis may be the late result of a segmental sensory nerve lesion, to account for its sclerodermal distribution. The association with linear scleroderma is discussed, since it has been suggested that these cutaneous lesions are related to the same nerve segment. Eight cases showed para-articular ossification of soft tissues which may be related to involvement of a corresponding myotome.

The analysis of finite elasto-plastic consolidation

Abstract: SUMMARY A theoretical formulation and a numerical solution method are proposed for the problem of the time dependent consolidation of an elasto-plastic soil subject to finite deformations. The soil is assumed to be a two-phase material with a skeleton which may yield according to a general yield criterion with plastic flow governed by a general flow law, and whose pore fluid flows according to Darcy’s Law. Governing equations are cast in a rate form and constitutive laws are expressed in a frame indifferent manner. The method of analysis is illustrated by several examples of practical interest for both a soil with an elastic skeleton and a soil with an elasto-plastic skeleton which obeys a Mohr-Coulomb yield criterion and a non-associated flow law.

A correlation of receptive field properties with conduction velocity of cells in the rat's retino-geniculo-cortical pathway.

Abstract: 1. The receptive field properties and responses to electrical stimulation of 126 P-cells recorded from the dorsal lateral geniculate nucleus (LGNd) were studied in the hooded rat. 2. Eighty-five cells had a concentric (Kuffler, 1953) receptive field organisation (46 off-centre on-surround; 39 on-centre off-surround). Of the remaining cells 29 had co-extensive on/off excitatory discharge regions, nine had on-centres with suppressive surrounds and two cells gave on-responses but had no suppressive surround. One cell was identified as suppressed-by-contrast. 3. On the basis of the battery of tests developed for the identification of cell types in the cat's retina and LGNd, 35 of the cells with a Kuffler-type receptive field organisation were identified as Y-like. The majority of the remaining cells, both concentric and others, reminded us of the different subclasses of W-cells of the cat. Nine concentric cells in most of the tests exhibited X-like properties. 4. All of the Y-like cells were driven by relatively fast conducting retinal ganglion cell axons, comprising the t1 conduction velocity group. The majority of the remaining cells were driven by slower axons comprising t2 or t3 conduction velocity groups. 5. Thus, in the rat, as in other mammalian species studied so far, there is a correlation between the conduction velocity groups in the retino-geniculo-cortical pathway and the functional groups based on the cells’ receptive field properties. There seem to be functional equivalents of the cat's Y- and W-cell classes but evidence for a distinct X-like class of cells is lacking.

‘Mere Auxiliaries to the Commonwealth’: Women and the Origins of Liberalism

Abstract: Married women pose an acute, but now unacknowledged, problem for liberal theory. The character and magnitude of the problem can only be fully understood if the development of liberal theory is exam...

Disposition of synethetic glucocorticoids. I. Pharmacokinetics of dexamethasone in healthy adults.

Abstract: The pharmacokinetics of dexamethasone alcohol is described in six male and six female healthy adult volunteers who each received 8 mg of dexamethasone phosphate by bolus intravenous injection. Quantitation of the alcohol was done using a high-performance liquid Chromatographic method with improved specificity. Statistical evaluation of the results generated by nonlinear least-squares regression analysis of the plasma concentration-time data shows that the phosphate ester is very rapidly hydrolyzed to the alcohol and a biexponential equation is the simplest poly exponential equation that is consistent with the data. The terminal phase half-lifet1/2β was significantly greater (p<0.05) in males (mean 201.5 min) than in females (mean 142.3 min). The prolongedt1/2β in males did not appear to be caused by an impaired capacity to eliminate dexamethasone since the total plasma clearance did not differ between males (mean 247.5ml/min) and females (mean 242.9 ml/min). There was, however, a high positive correlation betweent1/2β and\(V_{d_{ss} } \) among the 12 adults (r=0.92, p<0.001). There were also significant correlations between\(V_{d_{ss} } \) and body weight (r=0.67, p<0.05) andt1/2β (r=0.80, p<0.01).The difference in body weight between the sexes seems to be the main factor contributing to the difference observed int1/2β. An average of only 2.6% of the dose was found unchanged in a 24-hr urine sample, and hence it appears that dexamethasone is primarily eliminated by extrarenal, probably hepatic, mechanisms.

Amine Uniport at the Plasmalemma of Charophyte Cells" I. Current-Voltage Curves, Saturation Kinetics, and Effects of Unstirred Layers

Abstract: In voltage-clamped cells of the algaeChara andNitella an inward current of positive charge occurs when NH 4 + or CH3NH 3 + is added to the external medium. There is a simultaneous increase in membrane conductance, agreeing with earlier evidence that the current represents the inward uniport of the amine ion.

Hyperexcitability of motor and sensory neurons in neuromyotonia.

Abstract: Two members of a family with a neuropathy resembling Charcot-Marie-Tooth disease were unable to relax their muscles after voluntary contraction. Muscle spasm often outlasted voluntary contraction by 30 seconds or more before subsiding into myokymia and fasciculations. The posture of the hand during muscle spasm resembled that of tetany, and Trousseau's and Chvostek's signs were present although no abnormality of calcium or magnesium metabolism could be demonstrated. Muscle spasms ceased during medication with carbamazepine, 600 mg daily. Nerve stimulation, electromyography, and regional neuromuscular blockade with curare indicated that the condition originated in peripheral nerve, while microneurographic recordings showed that sensory as well as motor fibers were hyperexcitable. Sural nerve biopsy revealed axonal degeneration involving myelinated and unmyelinated fibers. It was concluded that the neural hyperexcitability is caused by a membrane defect resulting in a low threshold for excitation throughout the length of the axon.

Distribution of potassium and chloride permeability over the surface and T-tubule membranes of mammalian skeletal muscle.

Abstract: The distribution of K and Cl permeability,PK andPCl, over the surface and T-tubule membranes of red rat sternomastoid fibers has been determined. Membrane potential,Vm, was recorded with 3-m KCl-filled glass microelectrodes. Changes inVm with changes in [K]o or [Cl]o were used to estimatePCl/PK in normal and detubulated preparations. The results show that the T-tubule membrane has a highPCl and is therefore different from the T-tubule membrane of amphibian fibers. Analysis of the time course of depolarization when [K]o was raised (in SO4 solutions) showed thatPK was distributed over the surface and T-tubule membranes. Two observations suggested that T-tubulePCl was higher than the surfacePCl. Firstly, in normal fibers, the depolarization caused by an increase in [K]o was 3.5 times greater in SO4 solutions than in Cl solutions. In marked contrast, the depolarization in glycerol-treated fibers was independent of [Cl]o. Secondly, the rapid change inVm when [Cl]o was changed was reduced by 80% after glycerol treatment. Both observations suggest thatPCl was low in glycerol-treated fibers.PCl/PK was calculated from theVm data using Goldman, Hodgkin and Katz equations for Na and K or for Na, K, and Cl. In normal fibersPCl/PK=4.5 and in glycerol-treated fibersPCl/PK=0.28. Since it is unlikely that glycerol treatment would increasePK, the reduction in the ratio must follow the loss of Cl permeability “channels” in the T-tubule membrane.

Visual suppression from nondominant eye in the lateral geniculate nucleus: a comparison of cat and monkey.

Abstract: We have studied the suppression of firing in single LGN cells of cat and monkey in response to visual stimulation of the nondominant eye. In the cat LGN most of the cells of each of the main laminae show this nondominat suppression. X cells having their dominant input from the ipsilateral eye were suppressed to a significantly greater degree than any other cell type in the cat LGN. In the monkey LGN nondominant suppression was absent in all 19 X-like cells studied, whereas 6 of 21 Y-like cells showed nondominant suppression. Thus nondominant suppression is present in the magnocellular laminae of the monkey LGN, where the Y-like cells are found, but appears to be absent from the parvocellular laminae, where the X-like cells are found.

Development of the segmental innervation of the chick forelimb.

Abstract: A number of recent studies have shown that during embryonic development the initial innervation of a target structure may be made up, in part, by axons which do not form part of the mature innervation of that structure. In the present study we have examined the motor innervation of the major muscles of the chick forelimb at different stages of development using HRP-uptake-labelling of motoneurons, electrophysiological recording and measurement of muscle contraction. In the mature White Leghorn chick the major contribution to the motor innervation of the forelimb is from spinal segments 14, 15 and 16. Using the HRP-labelling technique we have shown that at stages 26-29 of development motoneurons in segments 12-17 have axon terminals in the presumptive biceps muscle. Between stages 30 and 35, however, the axon terminals arising from segments 12, 13, 16 and 17 are lost, leaving the mature innervation from segments 14 and 15. We have also observed the loss of innervation of the biceps muscle by segment 16 using electrophysiological recording of compound action potentials in the biceps nerve and by measurement of the local contraction of the biceps muscle in response to stimulation of the segmental nerves. Similar changes in the innervation of the triceps, extensor metacarpi radialis, flexor carpi ulnaris and flexor digitorum profundus muscles have also been observed. These results are discussed in relation to the hypothesis that (i) the motoneuron pools and muscles in the developing spinal cord and forelimb are matched, (ii) that some axons which arrive in a particular muscle during early development are unable to form a stable connexion and (iii) that the inability of an axon terminal to form a stable connexion in a muscle results in the death of the motoneuron. Intracellular recording from muscle cells at stage 35 shows that the synaptic site on each cell is innervated by about three separate axons. Over the next few stages, however, all but one of the innervating axons is lost. From our contraction studies it is clear that the removal of the excess axon terminals after stage 35 is not associated with the establishment of the mature segmental innervation pattern of the muscle.

Properties of neurons in cat's dorsal lateral geniculate nucleus: a comparison between medial interlaminar and laminated parts of the nucleus.

Abstract: We studied the receptive field properties of 460 cells in the cat's dorsal lateral geniculate nucleus (LGNd), 108 cells were located in the medial interlaminar nucleus (MIN) and 352 in the laminated part of the LGNd. In both the MIN and laminated parts of the LGNd, relay cells belonging to all three functional classes (W, X and Y) have been identified. Of cells in the laminated LGNd, about 32.5% were Y cells, about 54.5% were X cells and about 8.5% were W cells. By contrast, in the MIN, about 84% were Y cells, only about 4.5% being X cells and about 7.5%, W cells. In the laminated LGNd, Y cells represented 25% of cells with receptive fields near the area centralis (0–3° eccentricity group) and about 42% in the group of cells with the most peripherally located receptive fields (20–40° eccentricity group). A similar but much weaker trend was observed in the MIN. In the laminated LGNd but not in the MIN the receptive field center sizes increased with increasing eccentricity of receptive field position. At any eccentricity, receptive field centers of MIN Y cells tended to be larger than those of Y cells in the laminated LGNd. Response latency ranges to orthodromic and antidromic stimulation were the same for cells located in the laminated LGNd and those in the MIN. However, the mean response latency to stimulation of the optic chiasm was significantly shorter for Y cells in MIN than for Y cells in the laminated LGNd. Our results suggest that the most numerous cells observed histologically in the MIN, class 1 cells of Guillery ('66) are morphological equivalents of Y cells.