Showing papers by "Australian National University published in 1989"

Alternative Models for Conditional Stock Volatility

Abstract: This paper compares several statistical models for monthly stock return volatility. The focus is on U.S. data from 1834-19:5 because the post-1926 data have been analyzed in more detail by others. Also, the Great Depression had levels of stock volatility that are inconsistent with stationary models for conditional heteroskedasticity, We show the importance of nonlinearities in stock return behavior that are not captured by conventional ARCH or GARCH models. We also show the nonstationariry of stock volatility, even over the 1834-1925 period.

The informant questionnaire on cognitive decline in the elderly (IQCODE): socio-demographic correlates, reliability, validity and some norms

Abstract: The IQCODE is a questionnaire which asks an informant about changes in an elderly person's everyday cognitive function. The questionnaire aims to assess cognitive decline independent of pre-morbid ability. In the present study, the IQCODE was administered to a sample of 613 informants from the general population. In addition, the questionnaire was administered to informants of 309 dementing subjects who had filled it out one year previously. A principal components analysis, using the general population sample, confirmed that the IQCODE measures a general factor of cognitive decline. The questionnaire was found to have high internal reliability in the general population sample (alpha = 0.95) and reasonably high test-retest reliability over one year in the dementing sample (r = 0.75). The total IQCODE score, as well as each of the 26-items, was found to discriminate well between the general population and dementing samples. The correlation with education was quite small (r = -0.13), indicating that contamination by premorbid ability is not a problem.

Extension during continental convergence, with application to the Tibetan Plateau

Abstract: An explanation in terms of the thermal evolution of thickened continental lithosphere is offered to explain the transition, in the late Tertiary to Quaternary, from north-south compression to east-west extension in the strain rate field of the Tibetan Plateau. The lower part of the lithosphere consists of a thermal boundary layer which, when thickened by horizontal shortening, is colder and denser than its surroundings. Convective instability of the thickened thermal boundary layer and its replacement by hot asthenosphere would rapidly raise the surface elevation and gravitational potential energy of the overlying part of the lithosphere. The convective instability would happen in a time brief compared with the collision time scale but would only occur after there had already been substantial thickening of the lithosphere. The increase in surface height and of potential energy are sufficient for east-west extension to replace north-south compression as the dominant feature of the stress field.

A stochastic estimator of the trace of the influence matrix for laplacian smoothing splines

Abstract: An unbiased stochastic estimator of tr(I-A), where A is the influence matrix associated with the calculation of Laplacian smoothing splines, is described. The estimator is similar to one recently developed by Girard but satisfies a minimum variance criterion and does not require the simulation of a standard normal variable. It uses instead simulations of the discrete random variable which takes the values 1, -1 each with probability 1/2. Bounds on the variance of the estimator, similar to those established by Girard, are obtained using elementary methods. The estimator can be used to approximately minimize generalised cross validation (GCV) when using discretized iterative methods for fitting Laplacian smoothing splines to very large data sets. Simulated examples show that the estimated trace values, using either the estimator presented here or the estimator of Girard, perform almost as well as the exact values when applied to the minimization of GCV for n as small as a few hundred, where n is the number ...

A theory of the spatial and temporal dynamics of plant communities

Abstract: An individual-based model of plant competition for light that uses a definition of plant functional types based on adaptations for the simultaneous use of water and light can reproduce the fundamental spatial and temporal patterns of plant communities. This model shows that succession and zonation result from the same basic processes. Succession is interpreted as a temporal shift in species dominance, primarily in response to autogenic changes in light availability. Zonation is interpreted as a spatial shift in species dominance, primarily in response to the effect of allogenic changes in water availability on the dynamics of competition for light. Patterns of succession at different points along a moisture gradient can be used to examine changes in the ecological roles of various functional types, as well as to address questions of shifts in patterns of resource use through time.

A new model for the continuum concept

Abstract: A reformulation of the continuum concept is presented after considering the implications of the community/continuum controversy and current niche theory. Community is a spatial concept dependent on landscape pattern while the continuum is an environmental concept referring to an abstract space. When applying niche theory to plants, the mechanisms of competition are ill-defined and the assumption of bell-shaped response curves for species unrealistic.

Controller reduction: concepts and approaches

Abstract: The problem of passing from a linear time-invariant high-order controller designed for a linear time-invariant plant (of presumably high order) to a low-order approximation of the controller is discussed. The approximation problem is often best posed as a frequency-weighted L/sub infinity / approximation problem. Many different controller representations are possible, giving different performances of the various reduction algorithms. >

Late Pleistocene and Holocene sea‐level change in the Australian region and mantle rheology

Abstract: SUMMARY Spatial and temporal variations in sea-level are produced by the melting of the Late Pleistocene ice and by the Earth's response to the redistribution in surface loads. By examining different parts of the sea-level curves of the past 20 000 yr from geographically widely distributed regions it becomes possible to constrain models of the melting history of the ice sheets and of the Earth's rheology. Observations from sites away from the former Arctic ice sheets, such as the Australian and South Pacific region, are particularly important for constraining the total meltwater volumes added into the oceans in the past 20 000 yr and the rates at which this occurred. These observations indicate that the Antarctic ice sheets provided a significant contribution to the sea-level rise at a rate that was approximately synchronous with the melting of the Laurentide ice sheet, except for the interval 9000–6000 yr ago when it may have lagged behind. Minor melting of the Antarctic ice sheet appears to have continued throughout the Late Holocene. Differential observations of the Late Holocene sea-level change recorded at sites in the same region are particularly useful for estimating parameters describing the Earth's non-elastic response to surface loading. The effective parameters used here are a lithospheric thickness, an upper mantle viscosity, and a lower mantle viscosity describing the response below 670 km depth. With the observations used here, it is not possible to separate the lithospheric thickness H from the upper mantle viscosity and the viscosity results are based on the assumption that 50 ≤H≤ 100 km. Neither do these observations provide a resolution of the depth dependence of viscosity in the upper mantle and the resulting estimates are effective parameters only. Differential sea-levels along continental margins and along the shores of large gulfs and bays constrain the effective upper mantle viscosity to be about (1–2) × 1020 Pa s−1 while differential values from islands of different sizes are suggestive of a somewhat lower value. The lower mantle (taken to be below 670 km depth) viscosity is about two orders of magnitude greater than this. The estimated ice and rheological models explain many of the Holocene sea-level observations throughout the Australian and southern Pacific region. The tilting of continental margins, as exemplified by observations of variable amplitudes of the Holocene high-stands and the variable times at which sea-levels first reached their present level along the north Queensland coast and Great Barrier Reef, is well represented by these models. Differential Holocene sea-levels observed along the narrow Spencers Gulf of South Australia are also well explained by the models and in neither case is it necessary to invoke tectonic motions. Predicted Late Holocene sea-levels at small-to medium-sized islands are characterized by small amplitude high-stands that reached their maximum values about 4000–2000 yr ago, consistent with observations from the Society, Cook and Tuamotu Islands.

Melting in an Archaean mantle plume: heads it's basalts, tails it's komatiites

Abstract: THE lower part of most Archaean greenstone sequences is dominated by interlayered basaltic and komatiitic (ultrabasic) flows. These two magma types are petrologically and geochemically distinct, yet they display a close spatial and temporal association. The origin of the anomalously high-temperature komatiitic liquids has been much debated because of the implications for the thermal structure and composition of the Archaean mantle. Here we argue that both the basalts and komatiites are produced by a starting thermal plume rising in a warmer Archaean mantle. Fluid-dynamics studies show that a starting plume consists of a hot axial jet, capped by a large head into which cooler surrounding mantle is entrained. Our calculations for such a flow indicate that komatiites could form by melting in the high-temperature axis of the plume and basalts by melting in the cooler head. The sudden onset and limited duration of the basalt/komatiite sequences, seen in the greenstone belts of Western Australia and elsewhere, are explained by this model.

The main bank system and corporate monitoring and control in Japan

Abstract: Analysis of the main bank system provides insights into the intermediate nature of economic organization in Japan. Close bank-firm ties are interpreted as evidence of a quasi-internal capital market in which the main bank internalizes the monitoring and control functions of the external capital market. A key insight is that the main bank system substitutes for the ‘missing’ takeover market in Japan. This interpretation is helpful in explaining some seemingly paradoxical aspects of bank behavior.

Stratigraphic context of fossil hominids from the Omo group deposits: northern Turkana Basin, Kenya and Ethiopia.

Abstract: The chronometric framework developed for Plio-Pleistocene deposits of the northern Turkana Basin is reviewed in light of recent advances in lithostratigraphy, geochemical correlation, paleomagnetic stratigraphy, and isotopic dating. The sequence is tightly controlled by 20 precise ages on volcanic materials. These ages are internally consistent but are at variance with estimates for the boundaries of the magnetic polarity time scale by about 0.07 my. This discrepancy can be only partially resolved at present. Based on the established chronometric framework and stratigraphic sequences, depositional ages can be estimated for significant marker beds. These ages can in turn be used to constrain the 449 hominid specimens thus far reported from the basin. Ages for most hominid specimens can be estimated with a precision of +/- 0.05 my. In addition, the chronometric framework will be applicable to other paleontological collections, archeological excavations, and future discoveries in the basin.

Direct entropy calculation from computer simulation of liquids

Abstract: We develop and test a direct method for computing two-particle excess entropies in the canonical ensemble. The method is based on a systematic expansion of the entropy into one-body, two-body, three-body, etc., contributions. Unlike earlier canonical ensemble methods the resulting expressions for the entropy are local. It is shown that, at liquid densities, the three-body (and higher) terms are small but not negligible. The largest discrepancies are found at intermediate densities.

Singular perturbation approximation of balanced systems

Abstract: The singular perturbation approximation technique for model reduction is related to the direct truncation technique if the system model to be reduced is stable, minimal, and internally balanced. It is shown that these two methods constitute two fully compatible model reduction techniques for a continuous-time system, and both methods yield a stable, minimal, and internally balanced reduced-order system with the same L/sub infinity /-norm error bound on the reduction. Although the upper bound for both reductions is the same, the direct truncation method tends to have smaller errors at high frequencies and larger errors at low frequencies, whereas the singular perturbation approximation method will display the opposite character. It is also shown that a certain bilinear mapping not only preserves the balanced structure between a continuous-time system and an associated discrete-time system, but also preserves the slow singular perturbation approximation structure. Hence, the continuous-time results on the singular perturbation approximation of balanced systems are easily extended to the discrete-time case. Examples are used to show the compatibility of and the differences in the two reduction techniques for a balanced system. >

The neuraminidase of influenza virus.

Abstract: It is the enzyme neuraminidase, projecting from the surface of influenza virus particles, which allows the virus to leave infected cells and spread in the body. Antibodies which inhibit the enzyme limit the infection, but antigenic variation of the neuraminidase renders it ineffective in a vaccine. This article describes the crystal structure of influenza virus neuraminidase, information about the active site which may lead to development of specific and effective inhibitors of the enzyme, and the structure of epitopes (antigenic determinants) on the neuraminidase. The 3-dimensional structure of the epitopes was obtained by X-ray diffraction methods using crystals of neuraminidase complexed with monoclonal antibody Fab fragments. Escape mutants, selected by growing virus in the presence of monoclonal antibodies to the neuraminidase, possess single amino acid sequence changes. The crystal structure of two mutants showed that the change in structure was restricted to that particular sidechain, but the change in the epitope was sufficient to abolish antibody binding even though it is known in one case that 21 other amino acids on the neuraminidase are in contact with the antibody.

3.96 Ga gneisses from the Slave province, Northwest Territories, Canada

Abstract: Ion microprobe U-Pb analyses of zircons have identified the Acasta gneisses, from the westernmost Slave province, Canada, as the oldest known intact terrestrial rocks. Zircons from two samples indicate that the tonalitic to granitic protoliths of the gneisses crystallized at 3962 ±3 Ma, confirming earlier indications, from conventional zircon and Nd analyses, of the rock9s antiquity. The U-Pb analyses indicate that in addition to recent Pb loss, the zircons underwent an early episode of Pb loss and that new zircons crystallized ca. 3.6 Ga. The gneisses were derived from a source that had a long-lived enrichment in light REE, possibly from even older rocks that may be present in the Slave province.

Expression of Human Carbonic Anhydrase in the Cyanobacterium Synechococcus PCC7942 Creates a High CO2-Requiring Phenotype Evidence for a Central Role for Carboxysomes in the CO2 Concentrating Mechanism

Abstract: Active human carbonic anhydrase II (HCAII) protein was expressed in the cyanobacterium Synechococcus PCC7942 by means of transformation with the bidirectional expression vector, pCA. This expression was driven by the bacterial Tac promoter and was regulated by the IacIQ repressor protein, which was expressed from the same plasmid. Expression levels reached values of around 0.3% of total cell protein and this protein appeared to be entirely soluble in nature and located within the cytosol of the cell. The expression of this protein has dramatic effects on the photosynthetic physiology of the cell. Induction of expression of carbonic anhydrase (CA) activity in both high dissolved inorganic carbon (C(i)) and low C(i) grown cells leads the creation of a high C(i) requiring phenotype causing: (a) a dramatic increase in the K(0.5) (C(i)) for photosynthesis, (b) a loss of the ability to accumulate internal C(i), and (c) a decrease in the lag between the initial C(i) accumulation following illumination and the efflux of CO(2) from the cells. In addition, the effects of the expressed CA can largely be reversed by the carbonic anhydrase inhibitor ethoxyzolamide. As a result of the above findings, it is concluded that the CO(2) concentrating mechanism in Synechococcus PCC7942 is largely dependent on (a) the absence of CA activity from the cytosol, and (b) the specific localization of CA activity in the carboxysome. A theoretical model of photosynthesis and C(i) accumulation is developed in which the carboxysome plays a central role as both the site of CO(2) generation from HCO(3(-) ) and a resistance barrier to CO(2) efflux from the cell. There is good qualitative agreement between this model and the measured physiological effects of expressed cytosolic CA in Synechococcus cells.

Models of Integrated Photosynthesis of Cells and Leaves

Abstract: The kinetics of ribulose bisphosphate carboxylase-oxygenase (Rubisco) are integrated with the stoichiometry of NADPH consumption and production in a simplified model of C $\_3$ chloroplast photosynthesis. The extension to a leaf is discussed with reference to the gradient of irradiance that is always present within the leaf. The optimal arrangement of photosyntheic capacity is discussed in this context. Attention is then given to the effects of gradients of CO $\_2$ concentration that sometimes occur when stomata close in a heterogeneous fashion.

Apatite replacement and rare earth mobilization, fractionation, and fixation during weathering

Abstract: During an electron microscope study of the weathering of granite from southern New South Wales, Australia, an assemblage of minerals including florencite and rhabdophane was discovered replacing apatite. Light rare earth elements released from allanite early in weathering apparently combined with P released by leaching of primary apatite to form secondary phases exhibiting a range of morphologies and compositions. Chondrite normalized fractionation patterns La > Nd > Sm > Ce; La > Ce > Nd ≥ Sm and La = Sm = Nd > Ce were identified. The rare earth elements were present in very small crystals and aggregates of secondary minerals (< 10 μm) and coexisted with clays and secondary Fe-Ti oxides. The weathered granite was enriched about 6 to 10 times in all rare earth elements except Ce relative to fresh granite if the abundances were corrected for apparent enrichment due to reduction in density. The rare earth elements were probably derived from higher in the weathering profile, possibly by destruction of florencite and rhabdophane in very intensively weathered rock. Ce remained relatively immobile during weathering, probably due to its oxidation to Ce4+.

Union-Oligopoly Bargaining

Abstract: A model is developed highlighting interactions between firm-level union-employer bargaining and industry-level oligopolistic price-setting, combining models of parametric conjectural variation oligopoly and asymmetric Nash-bargaining. Wages can only be bargained up if product market behavior is noncompetitive or if unions act on an industry-wide basis. If bargaining is efficient, wages are monotonically increasing in product market collusion, but the relationship may be reversed if bargaining covers only the wage. The relationship between profit markets and wages and some macroeconomic implications are explored. Copyright 1989 by Royal Economic Society.

Amphiphilic components of the Murchison carbonaceous chondrite: surface properties and membrane formation.

Abstract: We have investigated physicochemical properties of amphiphilic compounds in carbonaceous meteorites. The primary aim was to determine whether such materials represent plausible sources of lipid-like compounds that could have been involved as membrane components in primitive cells. Samples of the Murchison CM2 chondrite were extracted with chloroform-methanol, and the chloroform-soluble material was separated by two-dimensional thin layer chromatography. Fluorescnece, iodine stains and charring were used to identify major components on the plates. These were than scraped and eluted as specific fractions which were investigated by fluorescence and absorption spectra, surface chemical methods, gas chromatography-mass spectrometry, and electron microscopy. Fraction 5 was strongly fluorescent, and contained pyrene and fluoranthene, the major polycyclic aromatic hydrocarbons of the Murchison chondrite. This fraction was also present in extracts from the Murray and Mighei CM2 chondrites. Fraction 3 was surface active, forming apparent monomolecular films at air-water interfaces. Surface force measurements suggested that fraction 3 contained acidic groups. Fraction 1 was also surface active, and certain components could self-assemble into membranous vesicles which encapsulated polar solutes. The observations reported here demonstrate that organic compounds plausibly available on the primitive Earth through meteoritic infall are surface active, and have the ability to self-assemble into membranes.

Vertical mixing due to the breaking of critical internal waves on sloping boundaries

Abstract: A laboratory experiment is used to examine the vertical mixing resulting from the breaking of internal waves on a sloping boundary in a continuously stratified fluid. Attention is confined to the case of critical waves when the slope of the group velocity vector of the incident waves is equal to the bottom slope. Along the sloping boundary a turbulent bottom boundary layer forms with a thickness dependent on the incident wave amplitude. The mixing efficiency, defined as the ratio of the increase in potential energy due to mixing to the loss of kinetic energy by the incident waves, is dependent upon the stability of the flow and has an upper bound of approximately 0.20.By examining the increase in potential energy of the fluid as a result of sustained mixing, we are able to compute the transition value of the dissipation etr below which no mixing occures. For mixing due to the breaking of critical internal waves on sloping boundaries we find that etr = (8±2)νN2. From comparisons with experiments with grid-generated turbulence, this suggests that while etr/νN2 = 0(10) in the available data sets, the specific value of etr may be mechanism dependent.

Carbon isotope discrimination and the ratio of carbon gained to water lost in barley cultivars

Abstract: A negative correlation between water-use efficiency (W), defined as the ratio of moles of carbon in the plant to moles of water transpired, and carbon isotope discrimination (Δ) was established for barley in pot experiments using 12 cultivars. The correlation was strong in two independent experiments in four different controlled environment where ambient temperature and vapour pressure deficit were varied and plants were either well-watered or given limited amounts of water. Variation among cultivars was found in both Δ and W and rankings of both parameters, according to cultivar, were similar in different environments. Limiting water usually increased water-use efficiency of plants. Total dry matter can be substituted for moles of carbon when calculating water-use efficiency but the correlation between W and Δ were calculated using the carbon content of dry matter. There were differences varied significantly among cultivars. Despite these differences, correlations were also large between whole plant W and Δ of any of the plant parts. The amount of dry matter partitioned into reproductive growth varied genetically, as did the effect of stress on the partitioning. Growth, W and Δ of barley were compared with theory derived from gas exchange properties and with other literature. The effect on W of variation in vapour pressure deficit in these experiments was removed by multiplying W by vapour pressure deficit to derive the parameter, k(Pa mol C/mol H2O). This allowed comparisons among experiments with different vapour pressure deficits. The mean k for these barley cultivars was similar to that calculated by others for grasses. However, variation was found, and, in contrast with previous work which treats k as a species constant, we conclude that there is promise in selecting for increased k.

Isolation of a cDNA clone and localization of the human glutathione S-transferase 3 genes to chromosome bands 11q13 and 12q13-14

Abstract: A partial cDNA clone of the glutathione S-transferase 3 gene (GST3) was obtained by screening a lambda gt11 human lung cDNA library with antiserum to human lung GST3. The sequence of this cDNA showed two base differences from the coding sequence of a GST3 cDNA isolated from a human placental cDNA library. Hybridization of the cloned GST3 cDNA to human chromosomes resulted in a primary peak of grains over band 11q13, a localization predicted by prior experiments. An unexpected strong secondary peak of grains was obtained over bands 12q13 and 12q14, indicating that there is a GST3-like gene on the long arm of chromosome 12 in man.

Depositional model of a macrotidal estuary and floodplain, South Alligator River, Northern Australia

Abstract: The South Alligator River, Northern Territory of Australia, has a macrotidal estuary. Tidal influence (spring tidal range 5–6 m at the mouth) extends 105 km up the channel. It is dominated by freshwater in the wet season (December-April) with a salt wedge near the mouth, but is well mixed and becomes saline throughout the dry season. The tidal channel can be divided into four different channel types: an estuarine funnel, a sinuous meandering segment, a cuspate meandering segment (in which the inside of bends are pointed) and an upstream tidal channel. The distribution of morphologically defined land classes and morphological units within each land class on the floodplain flanking the estuary differs from one channel type to another. Several stratigraphic and morphostratigraphic units have been recognized from drill holes on the coastal and deltaic-estuarine plains, and a model of development is proposed on the basis of extensive radiocarbon chronology and palynology. The coastal plain has prograded with most rapid sedimentation between 5000 and 3000 yr BP. A similar pattern of progradation is identified in the estuarine funnel. In the sinuous segment of the estuary the channel has migrated laterally across the floodplain. Previous channel positions are indicated by palaeochannels and the meander tract is occupied by laminated channel sediments. Within the cuspate segment there are numerous sinuous palaeochannels on the plains. In the upstream segment, the channel and palaeochannels have long straight reaches with irregular bends and discontinuous levees, and channel avulsion is indicated. Mangrove mud is a widespread stratigraphic unit throughout the plains. The initial phase of development is a transgressive phase. 8000–6800 yr BP, when mangrove forests extended landwards into a pre-existing valley as sea-level rose. As sea-level stabilized, the transgressive phase was followed by a widespread mangrove phase, termed the ‘big swamp’ 6800–5300 yr BP. The mangrove forests disappeared from most of the plains as vertical accretion continued, and were replaced by grass and sedge-covered floodplains. During the sinuous phase, about 5300–2500 yr BP, the channel migrated laterally and eroded the deltaicestuarine plain and deposited lateral accretion deposits (laminated channel sediments). Part of the channel of the South Alligator River has then progressed from sinuous to cuspate in form, and erosion of river banks has occurred. Transgressive and big swamp phases occurred under rising and stabilizing sea-level, respectively. Later morphodynamic channel adjustments occurred under conditions of stable sea-level. The depositional model has direct application to other estuaries in northern Australia, and may be applied to other areas where sea-level change has been similar.

Geochemical and Isotopic Constraints on the Origin of the Jurassic Dolerites of Tasmania

Abstract: The Jurassic dolerites of Tasmania represent a small part of the widespread Mesozoic magmatism of Gondwana, and possess some of the most extreme isotopic and elemental signatures observed in tholeiitic rocks. This study documents the remarkable uniformity of the magma in major, trace element and isotopic composition at the time of emplacement. Many of the trace element and isotopic characteristics compare more closely with those of continental crustal rocks than with typical mantle-derived materials, indicating the dominance of a crustal component in the petrogenesis of these tholeiites. Difficulties in reproducing the trace element signatures of the dolerites using calculations involving crustal assimilation, and the unreasonable isotopic compositions required of the contaminant, make such models unlikely.We argue that a more likely explanation involves the introduction of a small quantity of sediment (≤3 wt.%) into a depleted mantle source by the process of subduction. It is envisaged that the trace element and isotopic compositions of the mantle source were overprinted by the crustal signatures owing to the low abundance of incompatible trace elements originally present. These crustal signatures were subsequently inherited by magmas produced during partial melting. © 1989 Oxford University Press.