Showing papers by "University of Melbourne published in 1975"

Phase relationships in the zirconia-yttria system

Abstract: Metastable and equilibrium phase relationships in the system ZrO2:YO1.5 have been studied by X-ray diffraction. The conditions for the retention of a zirconia-rich tetragonal phase at ambient temperature are established. The existence of a miscibility gap, closed below the solidus temperature, in the yttria-rich solid solution region is proposed. Some evidence for partially ordered phases is presented.

Role of stem cell migration in initiation of mouse foetal liver haemopoiesis

Abstract: THEORIES of the development of mammalian hepatic haemopoiesis have polarised around two viewpoints. One hypothesis suggests that multipotential haemopoietic stem cells (HSC) migrate from the yolk sac and colonise the developing hepatic primordia1. According to the other view, hepatic haemopoietic tissue arises from the transformation of liver mesenchyme cells and thus has no direct relationship with vitelline haemopoiesis2. To solve this developmental problem, it is necessary to establish techniques, either in vivo or in vitro, to maintain hepatic tissue in a foetal state. In vitro studies have demonstrated that hepatic haemopoietic tissue can develop if tissues are explanted after the 28-somite stage3. Thus, these experiments did not verify the inductive model2 of hepatic haemopoiesis, although the in vitro conditions may have curtailed haemopoietic induction without altering hepatic differentiation. With an exogenous source of yolk-sac-derived HSC attempts have been made to colonise pre-28-somite hepatic explants in vitro, using the appearance of granulopoiesis as an indication of successful recombination. These experiments were not conclusive since granulopoiesis was observed with yolk sac cells in vitro in the absence of hepatic tissue (G.R.J., unpublished).

The use of glycoxylic acid for the fluorescence histochemical demonstration of peripheral stores of noradrenaline and 5-hydroxytryptamine in whole mounts

Abstract: The reactions of glyoxylic acid with peripheral stores of noradrenaline and 5-hydroxytryptamine to provide a fluorescence histochemical method for their localization have been investigated. Incubation in glyoxylic acid, followed by drying and heating of whole mount preparations gives an intense and well localized reaction. For incubation, a concentration of 2% glyoxylic acid, buffered to pH 7 at room temperature for 30 minutes gives ideal results. The method is equally good if the pH is varied in the range 6 to 9 or if the tissue is stored in the incubation mixture for up to 6 hours. Ideal development of the fluorophore requires an initial excess of moisture in the tissue, that this moisture is driven off during development, and that the tissue is protected from further moistening. A suitable method of achieving these ends is to heat partially dried tissue at 100°C for 4 minutes and then cover it with paraffin oil. 5-hydroxytryptamine can be readily distinguished from noradrenaline because it forms a fluorophore after reaction at pH 3.5, whereas noradrenaline does not. Both amines can be visualized after incubation at neutral pH. Comparison with the formaldehyde vapour technique reveals three main advantages (and no disadvantages) of the glyoxylic acid method: (1) it gives a finer localization with higher fluorescence yield, (2) the glyoxylic acid method is less susceptible to variations in procedure and, (3) it is both simpler and quicker to apply.

Scaling laws for pipe-flow turbulence

Abstract: Using hot-wire-anemometer dynamic-calibration methods, fully developed pipe-flow turbulence measurements have been taken in the Reynolds-number range 80 × 103 to 260 × 103. Comparisons are made with the results of previous workers, obtained using static-calibration methods. From the dynamic-calibration results, a consistent and systematic correlation for the distribution of turbulence quantities becomes evident, the resulting correlation scheme being similar to that which has previously been established for the mean flow. The correlations reported have been partly conjectured in the past by many workers but convincing experimental evidence has always been masked by the scatter in the results, no doubt caused by the difficulties associated with static-calibration methods, particularly the earlier ones. As for the mean flow, the turbulence intensity measurements appear to collapse to an inner and outer law with a region of overlap, from which deductions can be made using dimensional arguments. The long-suspected similarity of the turbulence structure and its consistency with the established mean-flow similarity appears to be confirmed by the measurements reported here.

Critical Points in Flow Patterns

Abstract: Publisher Summary This chapter analyzes the critical points in the framework of phase-space trajectory analysis that enables a wealth of topological language to be utilized in fluid mechanics, such as separation points, separation lines, and regions of reversed flow. This technique is applied to the problem of viscous flow, and then the approach is extended to inviscid rotational flow, with slip at the boundary. This appears to be the appropriate model for turbulent boundary layers approaching obstacles. There are certain topological restraints that greatly restrict the range of possible flow patterns for a given geometry. The classification of critical points in phase planes may be extended to cases where a three- or higher dimensional phase space is required, but this involves considerable complexity.

Coagulation and electrokinetic behavior of TiO2 and Al2O3 colloidal dispersions

Abstract: The detailed electrokinetic and coagulation behavior of TiO 2 and Al 2 0 3 hydrous oxide colloids, is reported as a function of pH and indifferent electrolyte concentration. The isoelectric point values for Ti0 2 (pH 5.9) and Al 2 0 3 (pH 8.9) were obtained by both techniques. Comparison of the observed coagulation rates with those calculated on the basis of observed ζ-potentials using the Derjaguin—Landau—Verwey—Overbeek theory supports the general validity of the theory for oxide colloids. Specifically rapid coagulation, whether induced by pH or KNO 3 concentration changes, occurs at |ζ| ⩽ 14 ± 4 mV in all systems.

Long-chain polyunsaturated fatty acids in the mammalian brain.

Abstract: Introduction The lipid-rich nature of the brain has been recognized for a long time and it is thought that the presence of myelin in the brain accounts for most of the lipid. However, brain grey matter is also rich in lipid (mostly glycerophospholipids) by comparison with other tissues (Svennerholm, 1968). The polyunsaturated fatty acids (PUFA) associated with tissue glycerophospholipids are derived from both the linoleic and linolenic acid series. There is a tissue and species variation in the types of PUFA and in the ratio of total 06:total 0 3 fatty acids (FA) in glycerophospholipids. This generalization appears to be valid for all tissues except the grey matter of the brain where, in a wide variety of different mammals, only three major PUFA occur: these are 20:406, 22:406 and 22:603 (Table I). Even in marine mammals, where the ratio, dietary 06:03 FA may be as low as 0.1, there is a similar profile in the brain PUFA (Bernhard, Lesch & Neuhaus-Meier, 1969; Leech, 1969). Another feature of the brain lipids is the low level of linoleic acid compared with the levels in tissues such as liver and muscle.

Some aspects of tissue water relations in three populations of Eucalyptus viminalis Labill

Abstract: SUMMARY Using the pressure bomb technique, measurements have been made of the tissue water relations of seedlings of three populations of Eucalyptus viminalis, and of adult shoots of trees from two contrasting sites, to facilitate an understanding of the physiological basis of intra-specific variation in drought resistance. For both juvenile and adult material, the shoot water potential of the most drought resistant population declined most rapidly with decreasing water content. Estimates of the fraction of water in the cell walls at full turgor were also greatest for this population, averaging 0.36 for juvenile and 0.40 for adult material. Calculated values for the bulk modulus of elasticity of the walls were very variable, but tended to be higher, in adult than juvenile tissues. The results suggest that in dry habitats there has been selection for plants which, during temporary periods of drying, can maintain a water content above the critical level for cell damage. Differences between two very closely situated field populations emphasize the need to consider the role of edaphic as well as climatic factors in selection for drought resistance.

Dopaminergic mediation of the interoceptive cue produced by d-amphetamine in rats.

Abstract: After rats were trained to differentiate between the effects of d-amphetamine and saline in a state-dependent task, pretreatment with the tyrosine hydroxylase inhibitor, α-methyl-p-tyrosine, significantly decreased amphetamine discrimination. Pretreatment with the dopamine-Β-hydroxylase inhibitor, disulfiram, or with the tryptophan hydroxylase inhibitor, p-chloro-phenylalanine, was observed to have no effect on the rats' ability to discriminate d-amphetamine. Administration of haloperidol, a selective dopamine receptor blocker, completely abolished the amphetamine discrimination, whereas α- and Β-adrenergic receptor blockade had no effect. Apomorphine, a dopamine receptor stimulant, produced amphetamine-like responses and this was, likewise, abolished by pretreatment with haloperidol. These data suggest that dopaminergic systems mediate the interoceptive cue produced by d-amphetamine in rats, and these results are discussed in relation to possible dopamine mediation of amphetamine psychosis and paranoid schizophrenia.

The nature of the stimulation of the growth of Streptococcus lactis by yeast extract

Abstract: Yeast extract was fractionated on Sephadex G-25 into 7 fractions. The fraction most stimulatory to the growth of Streptococcus lactis C10 contained over 70% of the amino N present in yeast extract and consisted of a wide variety of free amino acids and a small amount of peptide material. Examination of possible replacement factors for this fraction revealed that the amino -acid material present was largely responsible for the stimulation of Str. lactis C10. Purine and pyrimidine bases and inorganic constituents also contributed to the stimulation. In addition, yeast extract contained a component which decomposed H2O2, a metabolite which accumulates in the growth medium under aerobic conditions and inhibits growth. The nature of the stimulation was studied by isolating slow and fast acid-producing colonies of Str. lactis C10. It appeared that yeast extract and other amino-acid supplements prevented an observed inhibition of the growth of the slow variants below pH 6.0, apparently by satisfying a nutritional deficiency caused by a drop in pH.

Preferred Orientation in Quartz Ribbon Mylonites

Abstract: Quartz mylonites composed of elongate ribbon quartz without appreciable recrystallization at grain boundaries were examined and contrasted One was from a lower greenschist facies environment at Mount Isa, Australia, in which the c -axis preferred orientation of the ribbons is either a pronounced orthorhombic distribution or a small-circle distribution (with a small opening angle) about the normal to the foliation and lineation The other was an upper greenschist or lower amphibolite facies mylonite from Risfjallet in the Swedish Caledonides, in which the c -axis preferred orientation of the ribbon is a maximum lying close to the foliation and normal to the lineation Variation in preferred orientation can be accounted for by temperature and (or) strain-rate differences, with basal-slip mechanisms predominant at lower temperatures and prismatic slip (and possibly other slip systems), together with diffusion-controlled processes, predominant at higher temperatures

Steering reversals as a measure of driver performance and steering task difficulty

Abstract: A review is made of past work in which steering reversal rates were used as a measure of driver performance. The data from two previously reported experiments carried out in a controlled situation, are used to compare steering reversal rates with other performance measures. It is shown that, while steering reversal rates correlate with other measures of control frequency, they do not necessarily correlate with measures of absolute steering performance. This result is consistent with the view that frequency characteristics provide a measure of steering task difficulty rather than steering performance. It is shown that, when considering steering task difficulty, care must be taken to differentiate between the difficulty imposed by the task constraints and the factors which affect the driver's ability to maintain a level of performance commensurate with those constraints.

Synthetic substrate for cyclic AMP-dependent protein kinase.

Abstract: MOST hormones and neurotransmitters are thought to stimulate the synthesis of adenosine 3′,5′-cyclic monophosphate (cyclic AMP) which in turn activates protein kinases1. On activation, the protein kinases transfer the terminal phosphate group of ATP to serine or threonine residues in enzymic or membrane proteins involved in metabolic regulation, thereby either activating or inactivating them. Only a few key proteins are phosphorylated1,2 which raises the question of the molecular basis for the recognition of a particular serine by the cyclic AMP-dependent protein kinases. Cohen et al.2 considered this problem with respect to the phosphorylation of phosphorylase kinase and glycogen synthetase and concluded that the cyclic AMP-dependent protein kinase recognises some specific three-dimensional configuration formed by a particular amino acid sequence at the site of phosphorylation. The features of this structure, however, remain to be defined. It has been shown3 that small peptides from myelin basic protein could act as substrates, thus reducing the number of parameters for consideration.

Major Patterns of Gene Activity During Development in Holometabolous Insects

Abstract: Publisher Summary This chapter provides an overview of the broader features of the patterns of gene activity seen in insect development. The extreme metamorphoses of Calliphora and Lucilia, which are emphasized in the chapter, are built around single protein species, calliphorin and lucilin, respectively. Such proteins serve for the transfer of nitrogenous reserves, in the form of amino acids, from the feeding larva stage to the adult. At the commencement of metamorphosis in Calliphora, over 60 per cent of the total soluble protein of the insect is composed of calliphorin synthesized in the larval fat body and stored conjointly in hemolymph and in the fat body proteinaceous spheres. Proteins from histolysis of larval tissues play a subordinate but significant role in metamorphosis. The larval proteins are utilized during metamorphosis both metabolically and as the source of amino acids for the synthesis of adult proteins. The patterns of gene activity in the larval Holometabola reflect synthesis of storage proteins, synthesis of structural arid enzymic components of the larval cells, synthesis of specialized larval secretions, such as silks and puparial glues, and finally the synthesis of the enzymes of cell destruction.

Stratospheric Aerosol Measurements II: The Worldwide Distribution

Abstract: Global surveys of stratospheric and upper tropospheric aerosols have been made using balloon-borne photoelectric particle counters. The natural variability observed at each flight station was small enough so that typical profiles could be identified. Data are presented in the form of latitude cross sections showing lines of constant aerosol mixing ratio. The stratospheric aerosol layer is clearly delineated as well as small transient layers in the troposphere and lower stratosphere. At high and low latitudes the aerosol mixing ratio profile apparently experiences a simple shift in altitude corresponding to the change in local tropopause height.

The relationship of plasma levels of pindolol in hypertensive patients to effects on blood pressure, plasma renin and plasma noradrenaline levels.

Abstract: SUMMARY 1 Fifteen, previously untreated, hypertensive patients were given 20 mg of pindolol, orally. The systolic and diastolic blood pressures fell significantly in 1 h; the effect was maximal 4 h after pindolol, and persisted for at least 8 h. 2 After oral administration of 20 mg of pindolol, its concentration in the plasma reached a peak in 2–3 h. At the end of 8 h, pindolol was not detectable in the plasma. 3 There was a significant relationship between the peak concentration of pindolol in plasma and the maximal change in blood pressure in fifteen previously untreated hypertensive patients. In a separate study of ninety-nine hypertensive outpatients taking 15–80 mg of pindolol daily, the blood pressure responses corresponded generally to the concentration of pindolol in plasma 2–3 h after the morning dose. 4 There were no significant changes in plasma renin activity, plasma renin concentration or plasma noradrenaline concentration in the previously untreated patients taking 20 mg of pindolol. There was no relationship between initial plasma renin or noradrenaline levels and blood pressure responses to pindolol. Nor was there any significant relationship between the changes in plasma renin or noradrenaline levels and the changes in blood pressure.

Changes in Myosin Distribution in Dedifferentiating and Redifferentiating Smooth-Muscle Cells in Tissue-Culture

Abstract: Isolated smooth muscle cells and fibroblasts from the newborn guinea-pig vas deferens were grown in culture In the first 2 days, all cells characterized as smooth muscle by phase-contrast microscopy reacted intensely with fluoresceinated antibodies against smooth muscle myosin The fluorescence was in the form of particles (termed here “myosin aggregates”), which were often aligned to give the cell a striated appearance After 3–5 days, coarse fluorescent fibrils were also visible These were termed “attachment fibrils” (“A-fibrils”) since they were thought to represent myosin in microfilament bundles Between 6 and 7 days in culture, the smooth muscle cells began to dedifferentiate morphologically At this time, the “myosin aggregates” became clumped and less intensely fluorescent “A-fibrils” also decreased in fluorescence intensity By 8 days in culture, the dedifferentiated cells had undergone intense proliferation and gave only a minimal reaction with myosin antibodies However, when a confluent monolayer of cells formed on day 9 or 10, they immediately began to redifferentiate ultrastructurally and to regain immunofluorescence in both “myosin aggregates” and “A-fibrils” Throughout the entire culture period, cells characterized as fibroblasts by phase contrast microscopy gave only a weak reaction with fluoresceinated antibodies to myosin showing “A-fibrils” but no “myosin aggregates”

Comparison of the reaction of cultured smooth and cardiac muscle cells and fibroblasts to specific antibodies to myosin.

Abstract: Immunofluorescent staining with anti-smooth or anti-striated muscle myosin was carried out for 30 minutes at room temperature (18–20° C) on cultures of smooth muscle cells and fibroblasts from guinea-pig vas deferens, taenia coli and ureter, rabbit aorta and chicken gizzard and of cardiac muscle cells and fibroblasts from rat ventricle With antismooth muscle myosin, smooth muscle cells showed an intense fluorescent staining in fine fibrils with an “interrupted” appearance running parallel to the longitudinal axis of the cell throughout the cytoplasm, and also in coarser, “non-interrupted” fibrils (termed here “attachment fibrils”) concentrated at the surface of the cell adjacent to the glass coverslip Fibroblasts in the same cultures showed similar, but much weaker, reactions When anti-striated myosin was added to the smooth muscle cultures, staining of neither cell type was observed In contrast, cardiac muscle cells in cultures of rat ventricle did not react with anti-smooth muscle myosin, but gave bright fluorescent A-band staining with anti-striated myosin Fibroblasts in the ventricle cultures were unreactive with anti-striated muscle myosin but gave the characteristic weak reaction with anti-smooth muscle myosin Thus immunofluorescent staining with anti-smooth muscle myosin is useful for distinguishing between isolated smooth muscle cells and fibroblasts in tissue culture