Showing papers by "University of New South Wales published in 1972"

Instants and intervals.

Abstract: Many writers, in both philosophy and science, have been concerned at the remoteness of our time-language from the facts of actual observation. This was, in one way, Einstein’s starting-point in developing relativity theory: he said he was inspired by reading Berkeley. In Philosophy there is a strong strain of interest in supposedly primitive observational or phenomenal languages, languages whose features can be related directly to features of our experience of the world around us. Logical positivists, owing something to Mach and to Carnap’s early Logische Aufbau, have often assumed that the atoms of our experience have a form like “Red — here — now” or perhaps “Red (x, y, z, t)”, and that the whole of what we meaningfully say can be represented as a logical function, albeit very complicated, of statements of this form. ([1], [2], [6]: the formulations given seem to be first found explicitly in [2].) But, whatever we think about the ultimate thesis, there is one incongruity at its very base, namely, the presence in the atoms of coordinates of position and time of an apparently purely Newtonian or Kantian nature, unsupported by any attempt to give a phenomenal account of them.

The Bauschinger effect and discontinuous yielding

Abstract: Although the most popular definition of the Bauschinger effect refers to the lowering of the yield stress for reversed loading, the effect is more complex than was previously thought and it involves not only the initial yield strength, but the entire stress—strain curve after prestraining. The principal causes are believed to be associated with elastic stress and/or anisotropy in the resistance to dislocation motion. An experiment designed to test the Bauschinger effect, under the special ocnditions of discontinuous yielding in mild steel, is described. Three parameters are introduced for the evaluation and interpretation of the results. The density of mobile dislocations created by prestrain seems to be the most important factor affecting the magnitude of the Bauschinger effect. Using a new interpretation it is shown that the Bauschinger effect is greater the smaller the prestrain.

Changes in the Mouse Intestinal Microflora During Weaning: Role of Volatile Fatty Acids

Abstract: The influence of volatile fatty acids on the ecology of the bacterial flora of the mouse intestinal tract has been studied in three situations where large fluctuations in the composition of the microflora have been observed. Young mice were shown to ingest solid food particles when 11 days old; this correlated with the appearance of strictly anaerobic fusiform bacilli in the intestinal lumen and a 10,000-fold decrease in numbers of coliform bacilli. Over the same period, volatile fatty acids were shown by gas-liquid chromatography to appear in the intestinal content. It is suggested that the fusiform bacilli are responsible for the presence of the volatile acids (especially butyric acid) which exert an inhibitory effect on the coliform bacteria, resulting in the decline in numbers. When germ-free mice are placed in a specific pathogen-free mouse colony, changes in the intestinal flora occurred which were similar to those observed in the young mice approaching weaning. Once again, the decline in the coliform population correlated with the appearance of significant levels of butyric acid in the large intestine. In a further series of experiments, mice were fed penicillin and levels of the intestinal fatty acids were measured. The antibiotic eliminated the anaerobic fusiforms from the intestine, resulting in the disappearance of significant levels of butyric acid and a million-fold increase in the numbers of coliform bacilli.

Slip-Line Field Analysis for Orthogonal Machining Based upon Experimental Flow Fields:

Abstract: An experimental flow field for slow speed (0·5 in/min) orthogonal (plane strain) machining was analysed using slip-line field techniques. Although the experimental streamlines were not sufficiently...

The energy distribution of sputtered atoms from gold

Abstract: The energy spectra of atoms sputtered from a gold target have been measured as a function of ion energy and species for target temperatures in the range 100 to 1200°K. Both single crystal and polycrystal targets have been used, with surface topography monitored by a scanning electron microscope. The effect of raising the target temperature towards 1200°K is always to produce a low energy peak in the energy spectrum near 0.1 eV. This is found to have behaviour consistent with a thermal spike model, and at high temperature accounts for a large fraction of the total sputtering yield. The time-of-flight spectra show two peaks, one at about 10 eV the other at about 500 eV. The former was always present and when a crystal target was used with ejection along a axis it took on a kinked shape consistent with a contribution from focused collisions. The effect of increasing the temperature was to reduce this effect, presumably by thermal scattering of focused collisions. The 500 eV peak was also affec...

An atomistic study of cracks in diamond-structure crystals

Abstract: The structuxe of atomically sharp equilibrium cracks in diamond, silicon and germanium is calculated. The treatment considers a long plane crack formed by bond rupture across the (111) cleavage plane, critically loaded in tension. Within a small 'core' region immediately surrounding the crack tip the interatomic interactions are represented by a potential function specially constructed to match macroscopic fracture parameters. Anisotropic linear elastic theory is invoked to provide boundary conditions for the core region, and a first approximation for lattice-point displacements within. The core atoms are then relaxed to a configuration of minimum potential energy by computer. The results indicate that continuum theory is capable of giving remarkably accurate predictions of the crack-tip displacement field, except within about three atom spacings from the tip, despite marked nonlinearity in the interatomic force function. These results are discussed in terms of existing continuum models of crack-tip structure: in particular, Barenblatt's model of a cusp-shaped tip region is found to be inapplicable to diamond-structure crystals. The crack-tip geometry is better pictured as a narrow slit terminated by a single line of bonds close to the rupture point. Brief reference is made to the possible extension of the treatment to other classes of highly brittle solid, especially glassy materials, and to the relevance of the results to some fracture problems of practical importance. The fracture of an ideally brittle solid is essentially an atomic process, in which cohesive bonds are ruptured at the tip of the growing crack. Yet traditionally the rnathematical treatment of the mechanics of fracture propagation has been developed almost exclusively from continuum concepts. The chief reason for this lies in the interest of simplicity, a proper description of the atomic configuration at a crack tip requiring seemingly formidable analysis in terms of a suitable structural model for the given solid. The continuum approach, based on linear elasticity theory, has in fact proved adequate in many fracture-mechanics problems: in particular, the growth of a semi-brittle crack in most 'engineering materials' can be described in terms of a macroscopic 'plastic zone' encasing the tip. Many mechanical properties, on the other hand, are highly sensitive to events occurring over distances no greater than a few interatomic spacings. For instance, the energetics of dislocations in plastic crystals, particularly covalently-bonded crystals, may depend largely on the atomic structure of the dislocation core. The ideally brittle crack provides a similar case, the crack front advancing one atomic

The morphogenesis and possible evolutionary origins of fungal sclerotia

Abstract: Summary 1. Fungal sclerotia are able to survive adverse conditions for long periods and they are formed by many important plant pathogens. An understanding of the factors involved in their initiation and development may lead to a method of repressing their formation in nature, thereby reducing the chances of survival of fungi that depend on them as persistent resting stages in their life-cycles. Also, data on sclerotial morphogenesis may be applicable to other multihyphal fungal structures. 2. There are three types of sclerotial development. The most primitive and least common is the loose type, which is illustrated by Rhizoctonia solani. The sclerotium forms by irregular branching of the mycelium followed by intercalary septation and hyphal swelling. When mature, it consists of loosely interwoven hyphae that are rich in food reserves and darkly pigmented. The main types of development are terminal and lateral. The former develops from the coalescence of initials that are produced by a well-defined pattern of branching at the tip of a hypha or tips of closely associated hyphae, e.g. Botrytis cinerea. Lateral sclerotia are formed by the interweaving of side branches of one or several main hyphae. When only one main hypha is involved the sclerotium is of the lateral, simple type, e.g. Sclerotinia gladioli. If several main hyphae give rise to a sclerotium, the term strand type has been used. Sclerotium rolfsii is the classical example. 3. There is a considerable literature on the effects of environmental conditions on the initiation, development and maturation of sclerotia but few attempts have been made to interpret the data. Phenolics and/or polyphenol oxidases have been found to be connected with morphogenesis of the protoperithecium of Neurospora crassa, the perithecium of Podospora anserina and of Hypomyces sp. and the basidiocarp of Schixophyllum commune. A close correlation has been shown between melanin synthesis and microsclerotial development by Verticillium but there appears to be no literature on the role of phenolics and polyphenol oxidases in the morphogenesis of sclerotia. Possibly these substances may inhibit growth of the apices of main hyphae by changing the permeability of the membrane, by inducing a thickening of the cell wall at the tip or by reducing the plasticity of the wall. Such a check in growth could trigger-off the formation of initials close to the margin of the colony or elsewhere in the culture. Sulphydryl groups and disulphide bonds are of great significance in morphogenesis of organisms and are probably involved in sclerotial initiation. The formation of a large number of hyphal branches is a prerequisite for sclerotial initiation and mycelial branching is possible only if there is plasticity of hyphal walls. The ability of the wall to be moulded is possibly related to changes in the sulphur linkages of the protein of the protein-carbohydrate complexes of the cell wall and could be influenced by sulphur availability or the activity of specific enzymes. 4. After a sclerotial primordium has been initiated, further increase in size will depend on the continued, active translocation of nutrients to the site of development. Movement of nutrients to sclerotia is through a few translocatory hyphae. Presumably, nutrients will continue to move into the young sclerotium as long as a concentration or pressure gradient is maintained. Energy and substances for the formation of new branches are supplied in this way and as the requirements for hyphal branches are reduced, excess nutrients become available for conversion to inactive or insoluble reserves and for exudation. The exudates are often complex, consisting of proteins, including enzymes, lipids and carbohydrates. Many sclerotia have a mucilaginous matrix in which the medullary hyphae are embedded. Sclerotium-forming, fungal species that are not regarded as having such a matrix appear to secrete a layer of mucilage over the surface of sclerotial hyphae. This mucilage could have a morphogenetic function and serve as an adhesive which loosely binds hyphae together. More permanent unions are by hyphal fusions or anastomoses. 5. The sclerotium matures within a few days of attaining its maximum size. The rind effectively seals off the medullary hyphae from the surroundings and the translocatory hyphae cease to function. Thus the sclerotium is isolated both physiologically and nutritionally. The endogenous reserves enable the structure to exist in the absence of exogenous nutrients and then, when conditions become suitable, to germinate. 6. The sclerotium appears to provide an example of convergent evolution whereby analogous structures, which have become adapted to resist adverse conditions, have evolved. Data are available mainly for Typhula spp. and ScZerotinia spp. Sclerotia may be degenerate sexual reproductive structures, hyphal aggregates that have developed from closely interwoven conidiophores and undifferentiated conidia or they may be modified vegetative structures.

Computation of genetic contributions from pedigrees.

Abstract: A simple procedure is outlined by which genetic contributions of individuals to later generations can be estimated. The method, which involves simple matrix operations, is well suited to automatic computation.

Speed of response or bandwidth of voluntary system controlling elbow position in intact man.

Abstract: Power-spectral analysis was used to measure the bandwidth of the frequency of movement at the human elbow joint. The maximum frequency of voluntary movement was found to be limited by muscle damping and limb inertia rather than by central processes and, for oscillation of the arm about the elbow, was 4–6 Hz. The maximum frequency at which a subject could move his elbow coherently with a kinaesthetic stimulus was found to be 2 Hz, so that movements with a frequency between 2–6 Hz must be open-loop in nature and there-fore must be learned or preprogrammed.

The bain strain, lattice correspondences, and deformations related to martensitic transformations

Abstract: The contribution of E. C. Bain in identifying the correspondence and pure strain involved in ferrous martensitic transformations is reviewed, together with later work which has confirmed Bain’s hypothesis. Modern crystallographic theories of martensitic transformations have their origin in Bain’s recognition that a pure strain by itself would produce a major accommodation problem between the parent and product phases; thus, additional lattice invariant processes have been introduced. Some aspects of the crystallographic theories are considered and attention is drawn to the increased number of factorizations of a total strain that become possible when sequences of three (or more) strains are considered instead of the usual two. Some implications of the recent double shear theory (and double interface mechanism) and plastic accommodation model are examined. The nucleation of martensitic transformations with respect to the Bain strain is considered briefly.

Immunological response of mice to members of the autochthonous intestinal microflora

Abstract: Based on agglutination, complement fixation, bactericidal, and opsonization tests, it is evident that suspensions of a Bacteroides sp. isolated from the mouse intestine and given by parenteral routes do not initiate antibody formation in mice. Rats also respond poorly to the antigenic stimulus. In contrast, suspensions of other bacterial species isolated from the rodent intestine are highly immunogenic. Furthermore, high titers of antibody are produced in rabbits, guinea pigs, and sheep after parenteral injection of the Bacteroides suspensions. Marked differences in the absolute and relative numbers of Bacteroides in the intestinal contents of rodents and the latter three animal species have been demonstrated. It is proposed that the immunological unresponsiveness of rodents to this organism is related to its existence as a member of the autochthonous microflora in these animals.

Glucagon in heart failure and in cardiogenic shock. Experience in 50 patients.

Abstract: Intravenous glucagon, in doses of 2.5-15 mg/hour, was administered to 50 patients for periods of 1-7 days. Forty patients had either intractable heart failure or cardiogenic shock or both; the remaining 10 had less severe heart disease. In all patients glucagon was added to conventional therapy. Twenty-two of the 40 with very severe heart failure showed a clinical improvement, and 18 were discharged from the hospital; 16 of the 18 patients who did not respond died in the hospital. Only two of the 10 with less severe heart disease improved with glucagon but all could be discharged from the hospital. Glucagon did not initiate or aggravate a tendency to arrhythmias in any of the 17 patients with acute myocardial infarction. In two patients with bradycardia and cardiac failure due to beta-adrenergic blocking drugs, glucagon increased heart rate and there was clinical improvement in heart failure. However, there was no effect in two patients with digitalis-induced nodal bradycardia and heart failure. Nausea wa...

π-Complex Intermediates in Homogeneous and Heterogeneous Catalytic Exchange Reactions of Hydrocarbons and Derivatives with Metals

Abstract: The exchange of unsaturated and aromatic hydrocarbons and their derivatives with isotopic hydrogen on group VIII transition metals has been reviewed. Both classical and π-complex heterogeneous mechanisms proposed to account for the observed behavior have been compared. Evidence to distinguish between the application of the heterogeneous associative and dissociative π-complex exchange mechanisms is discussed. The recently discovered homogeneous equivalent of the above heterogeneous reactions is described in detail. Homogeneous associative and dissociative π-complex mechanisms are proposed to explain aromatic hydrogen exchange. Mechanisms are also proposed to explain the pattern of exchange observed homogeneously with platinum in the alkyl groups of alkyl aromatics. Possible mechanistic relationships between heterogeneous and homogeneous systems are considered using as representative unsaturated and aromatic series, the polycyclic hydrocarbons, the monohalogenated benzenes, the alkyl benzenes (and ...

The influence of progesterone and estradiol upon migraine.

Abstract: The effect of progesterone and estradiol withdrawl upon menstrual migraine was examined in 8 regularly menstruating women (aged 23-45) who regularly suffered from migraine. The influence of estradiol alone was examined in 2 nonmenstruating women whose headaches had ended with cessation of menstruation. In 6 of the 8 regularly menstruating women determinations of hormonal level and migraine occurrence were made in a pre-treatment control cycle. It was found that migraine occurrence generally took place during or at the end of the phase of hormone withdrawl in a normal cycle. Progesterone was then administered intramuscularly to each woman in 25-75 mg doses 3-6 days before the expected onset of menstruation and continued until Day 2 in order to maintain the levels of progesterone that would normally occur at the middle of the luteal phase. Estradiol was administered in another cycle in single 10-20 mg doses in slow-release form. Hormone levels were measured daily. The 2 nonmenstruating women received single doses of estradiol. Progesterone treatment did not prevent the onset of migraine in 5 of the 6 women treated (though 1 of the 5 suffered a much less severe and shorter attack) and caused postponement of menstruation in 4 of the 6. In the estradiol cycle all 8 women had migraines delayed for 3-9 days. In 5 of 6 women tested the migraine occurred when the level of estradiol in the plasma dropped below 20 ng/100 ml. In the sixth woman a second injection of estradiol was given in an attempt to maintain a high level. This attempt failed and the migraine occurred despite the fact that the estradiol level was rising. The nonmenstruating women both experienced migraine. It appears that once estradiol withdrawl occurs the mechanism for migraine cannot be stopped. This suggests migraine might be initiated by the withdrawl of a metabolite of estradiol rather than by estradiol itself. The withdrawl of progesterone plays little if any part in the etiology of menstrual migraine.

The high-temperature oxidation of iron-chromium-nickel alloys containing 0–30% chromium

Abstract: The oxidation behavior of iron-chromium-nickel alloys containing 0–30% chromium has been determined for oxidation at 1000°C in static pure oxygen atmospheres. Particular emphasis has been placed on the correlation between the kinetics of oxidation and the morphologies and compositions of the scales produced. Maximum oxidation resistance was associated with the formation of chromic oxide scales on alloys containing greater than 20% chromium. The loss of an oxide species from these scales by volatilization may limit the usefulness of alloys protected by chromic oxide scales to a temperature less than 1000°C.

Nucleolar behaviour in Triticum

Abstract: The maximum number of major nucleoli (macronucleoli) per nucleus of hexaploid, tetraploid and diploid wheat, Aegilops speltoides and Ae. squarrosa corresponded to the number of satellited chromosomes of each species. Smaller nucleoli (micronucleoli) were rare or absent in all of these species except the hexaploid, in which they were predominantly organized on chromosome arm 5Ds. — Fewer than the maximum number of macronucleoli in a mitotic interphase nucleus resulted from fusion of developing nucleoli. Enforced proximity of nucleolus-organizing regions resulted in more frequent fusion of nucleoli. — Analyses of related interphase nuclei showed that nucleoli, and hence probably chromosomes, undergo limited movement during mitotic interphase. These observations also indicate that specific chromosomes do not occupy specific sites in the interphase nucleus.