Showing papers by "University of Western Australia published in 1986"

Convergence of an annealing algorithm

Abstract: The annealing algorithm is a stochastic optimization method which has attracted attention because of its success with certain difficult problems, including NP-hard combinatorial problems such as the travelling salesman, Steiner trees and others. There is an appealing physical analogy for its operation, but a more formal model seems desirable. In this paper we present such a model and prove that the algorithm converges with probability arbitrarily close to 1. We also show that there are cases where convergence takes exponentially long—that is, it is no better than a deterministic method. We study how the convergence rate is affected by the form of the problem. Finally we describe a version of the algorithm that terminates in polynomial time and allows a good deal of ‘practical’ confidence in the solution.

Mach bands are phase dependent

Abstract: The prevailing explanation of Mach bands, the paradoxical bands of light and dark seen where luminance gradients meet plateaux, is that they are due to lateral inhibition in the visual system1–4. This explanation equates Mach bands with distortions in a processed luminance distribution due to selective attenuation of low frequency components. But square waveforms exhibit no Mach bands2,5,6, although they should also be distorted after processing. Measurements of the contrast required to see Mach bands in trapezoidal waveforms and manipulations of their spectra lead us to conclude that phase relationships between Fourier components are important to the structure we perceive. A model based on the odd and even symmetry of visual receptive fields explains our results.

Increased Cerebral Glucose‐6‐Phosphate Dehydrogenase Activity in Alzheimer's Disease May Reflect Oxidative Stress

Abstract: The activities of the hexose monophosphate pathway enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were measured at autopsy in control and Alzheimer's disease brains. Enzyme activities did not vary between different areas of brain and were unaltered by age. In Alzheimer's disease, the activities of both enzymes were increased, the glucose-6-phosphate dehydrogenase activity being almost double the activity of normal controls. We propose that this increased enzyme activity is a response to elevated brain peroxide metabolism.

Seeing objects in motion

Abstract: This paper reports estimates of the conjoint spatiotemporal tuning functions of the neural mechanisms of the human vision system which detect image motion. The functions were derived from measurements of the minimum contrast necessary to detect the direction of drift of a sinusoidal grating, in the presence of phase-reversed masking gratings of various spatial and temporal frequencies. A mask of similar spatial and temporal frequencies to the test grating reduces sensitivity considerably, whereas one differing greatly in spatial or temporal frequency has little or no effect. The results show that for test gratings drifting at 8 Hz, the tuning function is bandpass in both space and time, peaked at the temporal and spatial frequency (SF) of the test (SFs were 0.1, 1 or 5 c deg –1 ; c represents cycles throughout). For a grating of 5 c deg –1 drifting at 0.3 Hz, the function is bandpass in space but lowpass in time. Fourier transform of the frequency results yields a function in space-time which we term the ‘spatiotemporal receptive field’. For movement detectors (bandpass in space and time) the fields comprise alternating ridges of opposing polarity, elongated in space-time along the preferred velocity axis of the detector. We suggest that this organization explains how detectors analyse form and motion concurrently and accounts, at least in part, for a variety of perceptual phenomena, including summation, reduction of motion smear, metacontrast, stroboscopic motion and spatiotemporal interpolation.

Effects of phosphorus on the formation of mycorrhizas by gigaspora calospora and glomus fasciculatum in relation to root carbohydrates

Abstract: Summary We compared the effects of phosphorus (P) supply on the formation of vesicular-arbuscular (VA) mycorrhizas in Trifolium subterraneum L. by Gigaspora calospora (Nicol. & Gerd.) Gerd. and Glomus fasciculatum (Thaxter sensu Gerd.) Gerd & Trappe. For both fungi, increasing the supply of P decreased the percentage of root length infected. At low P, this decrease was associated with a reduction in the growth of the fungi inside the root. At higher P, the growth of the fungi outside the root was also reduced. These detrimental effects of P on the growth of both mycorrhizal fungi were correlated with reductions in the concentrations of soluble carbohydrates in root extracts and root exudates but were not correlated with the concentrations of free amino-nitrogen in extracts or exudates. The percentage of root length infected by G. calospora was decreased to a greater extent than that of G. fasciculatum with increasing P supply. This could partially be explained by the lower concentrations of soluble carbohydrates in the roots of plants inoculated with G. calospora. Additionally, the percentage of root length infected by G. calospora appeared to be more sensitive to reductions in the supply of soluble carbohydrates than that of G. fasciculatum. Growth responses to inoculation were dependent on the species of mycorrhizal fungus and the P level. Enhancements and depressions in the growth of tops could be explained in terms of increased and decreased P uptake.

Influence of the epithelium on responsiveness of guinea-pig isolated trachea to contractile and relaxant agonists.

Abstract: The potency (pD2) and maximal contractile effect (Emax) of histamine, acetylcholine, carbachol and K+ were assessed from cumulative concentration-effect curves in guinea-pig isolated tracheal ring preparations with and without an intact epithelium. Estimates of Emax were not significantly different in epithelium-denuded preparations compared with those measured in intact preparations; pD2 values for acetylcholine, carbachol and K+ were not significantly altered. In contrast, the potency of histamine was significantly increased by about 4 fold in preparations devoid of epithelial cells. Estimates of potency and Emax were also determined for the smooth muscle relaxants isoprenaline, forskolin and theophylline (which increase intracellular cyclic AMP) and for nitroglycerin (which increases cyclic GMP) in both intact and epithelium-stripped tracheal rings. The pD2 values for these relaxants were not significantly altered by the removal of the epithelium. However, with the exception of nitroglycerin, Emax values for these relaxants were significantly lower in stripped than in intact tracheal rings that had been maximally precontracted with carbachol. The autoradiographic localisation of binding sites for the non-selective beta-adrenoceptor ligand [125I]-iodocyanopindolol (I-CYP) showed that the epithelium of the guinea-pig trachea had a 75 +/- 16% greater density of beta-adrenoceptors than the smooth muscle. Removing the epithelium did not significantly alter either the density of smooth muscle binding sites or the affinity of I-CYP binding. It was concluded that the reduced functional response of guinea-pig trachea to isoprenaline was probably not due to smooth muscle beta-adrenoceptor dysfunction. Results indicate that the epithelium plays an important role in the modulation of responsiveness of guinea-pig trachea to histamine and relaxants that mediate their effects by selectively increasing intracellular cyclic AMP levels.

Recognition of Positive and Negative Bandpass-Filtered Images

Abstract: A study is reported in which the significance for vision of low- and high-spatial-frequency components of photographic positive and negative images was investigated by measuring recognition of bandpass-filtered photographs of faces. The results show that a 1.5 octave bandpass-filtered image contains sufficient visual information for good recognition performance, provided the filter is centred close to 20 cycles facewidth−1. At low spatial frequencies negatives are more difficult to recognize than positives, but at high spatial frequencies there is no difference in recognition, implying that it is the low-frequency components of negatives which present difficulties for the visual system.

Modeling the diurnal mixed layer

Abstract: The numerical model presented here is based on the one-dimensional equations for momentum, heat, salt, and turbulent kinetic energy integrated over the diurnal mixed layer. Two noteworthy features are the inclusion of the energetics of billowing due to Kelvin-Helmholtz instability at the base of the mixed layer, and a closure hypothesis which retains average mixed-layer turbulent kinetic energy as an explicit variable, rather than assuming it to be a fixed proportion of external energy input. The importance of both these features is illustrated in the application of the model to the data for 1 day which included several mixing processes: a fairly calm morning with uninterrupted solar heating, followed by rapid mixed-layer deepening during a strong afternoon sea breeze, and finally a relatively cool night with little wind. The data contain rapidly changing meteorological inputs as well as evidence of strong billow formation and collapse and thus provide an ideal test of the importance of both billow energetics and the temporal effects in the turbulent kinetic energy budget. The model does not account for processes occurring below the mixed layer nor for the effects of horizontal advection. Within these constraints, model results agree well with measured temperatures and represent an improvement over the results of a slab model without billow energetics.

Bilingual lexical representation: The status of spanish-english cognates

Abstract: Two experiments were conducted to determine the functional status of cognates. Two hypotheses were considered. According to the first hypothesis, language is a critical feature governing lexical or...

Spatial and temporal variation in the macroinvertebrate fauna of streams of the northern jarrah forest, Western Australia: community structure

Abstract: Highest stream discharge occurs during winter (June-November) reducing to negligible flow over late summer and autumn (January-May). Low flows in summer were associated with warm water, lower dissolved oxygen, increased concentrations of cations and, in many cases, lower pH. Temporal changes in abundance, diversity and evenness indicated that the invertebrate fauna became dominated by a few taxa during the summer months. Summer and winter faunas were distinguished at most sites and were associated with seasonal changes in the physical and chemical environment. This seasonality is not typical of stream systems previously studied in Australia. Large spatial differences also occurred over small distances among sites in 2 similar-sized forested catchments. Velocity and depth were highly associated with the observed temporal changes in the fauna, though other variables, including concentrations of cations and water temperature, were also important. Spatial differences were correlated with concentrations of cations which may simply reflect differences in the geologies of the catchments.

Pectic zymograms and taxonomy and pathogenicity of the Ceratobasidiaceae

Abstract: The pectic enzymes of 140 isolates of Rhizoctonia-1ike fungi from the Western Australian grainbelt were examined by electrophoresis and found to fall into 11 distinct zymogram groups (ZG). Isolates within a ZG had a similar cultural and morphological appearance and were either all multinucleate or all binucleate. Some isolates from most ZGs sporulated when transferred from potato-dextrose-marmite agar to water agar. Isolates from within a ZG had the same teleomorph. Pathogenicity of the isolates was tested against wheat and lupins. All isolates from within a ZG were consistent in the type of lesions they produced and in their virulence towards these hosts. Rhizoctonia patch disease of cereals and lupins appears to be caused by isolates from ZG 1 and ZG 2. Severe reddish-brown and brown hypocotyl rots of lupins were caused by ZG 3 and ZG 4 isolates respectively. Five Ceratobasidium groups (CZG), one Waitea group (WZG) and ZG 5 had weak to nil pathogenicity towards wheat and lupins.

Highly Hindered Amido-Lithium and Amido-Magnesium Complexes. Crystal-Structures of [Li(Mu-N(SiMe3)2)(Tetrahydrofuran)]2 and [MgBus(Mu-N(SiMe3)2)]2

Abstract: Treatment of hexamethyldisilazane in thf (tetrahydrofuran) with LiBu in hexane yields [Li{μ-N(SiMe3)2}(thf)]2, (1). MgBu8Bu in heptane with hexamethyldisilazane results in initially formation of [MgBus(μ- N(SiMe3)2}]2, (2), then ?Mg{N(SiMe3)2}2,(3). The structures of (1) and (2) have been determined by X-ray diffraction. Remarkably, they are isomorphous: crystals are tetragonal, space group P4n2 with a 9.970(7), c 16.753(9) Ǻ for (1), and a 9.524(6), c 17.385(9) Ǻ for (2), with Z = 2. The lattices are comprised of discrete molecules with symmetry 222, and thus Bus disorder in (2), yith the amido ligands bridging three- coordinate metal centres [Li-N 2.025(9), Li-O 1.882(14) Ǻ, Li-N-Li 73.7(5)°, N-Li-N 106.3(6)°, O-Li-N 126.8(3)° (1); Mg-N 2.118(4), Mg-C 2.08(1) Ǻ, Mg-N-Mg 87.1(2)°, N-Mg-N 92.9(2)°; C-Mg-N 133.6(1)°(2)].

Application of the Wigner–Ville Distribution to Temperature Gradient Microstructure: A New Technique to Study Small-Scale Variations

Abstract: The Wigner–Ville distribution, a new tool in the time–frequency analysis of signals, is applied to temperature gradient microstructure records. In particular, the Wigner–Ville distribution is used to compute the local instantaneous and maximum frequencies of the signal as a function of depth, and these frequencies are then related to the dissipation of turbulent kinetic energy. The method is applied to two temperature gradient microstructure records from the Wellington Reservoir. It is shown that a high resolution estimate of the dissipation is obtained that provides insight into the patchiness, the wavenumber content, and the Reynolds–Froude number variability of the integral scales of motion in a strongly stratified water column.

Effects of external NaCl on the growth of Atriplex amnicola and the ion relations and carbohydrate status of the leaves

Abstract: Atriplex amnicola, was grown in nutrient solution cultures with concentrations of NaCl up to 750 mol m−3. The growth optimum was at 25–50 mol m−3 NaCl and growth was 10–15% of that value at 750 mol m−3 NaCl. Sodium chloride at 200 mol m−3 and higher reduced the rate of leaf extension and increased the time taken for a leaf to reach its maximal length. Concentrations of Na+, K+ and Mg2+ in leaves of different ages were investigated for plants grown at 25, 200 and 400 mol m−3 NaCl. Although leaves of plants grown at 200 and 400 mol m−3 NaCl had high Na+ concentrations at young developmental stages, much of this Na+ was located in the salt bladders. Leaves excluding bladders had low Na+ concentrations when young, but very high in Na+ when old. In contrast to Na+, K+ concentrations were similar in bladders and leaves excluding bladders. Concentrations of K+ were higher in the rapidly expanding than in the old leaves. At 400 mol m−3 NaCl, the K+:Na+ ratios of the leaves excluding bladders were 0.4–0.6 and 0.1 for rapidly expanding and oldest leaves, respectively. The Na+ content in moles per leaf, excluding bladders, increased linearly with the age of the leaves; concurrent increases in succulence were closely correlated with the Na + concentration in the leaves excluding the bladders. Soluble sugars and starch in leaves, stems and buds were determined at dusk and dawn. There was a pronounced diurnal fluctation in concentrations of carbohydrates. During the night, most plant parts showed large decreases in starch and sugar. Concentrations of carbohydrates in most plant organs were similar for plants grown at 25 and 400 mol m−3 NaCl. One notable exception was buds at dusk, where sugar and starch concentrations were 30–35% less in plants grown at 400 mol m−3 NaCl than in plants grown at 25 mol m−3 NaCl. The data indicate that the growth of A. amnicola at 400 mol m−3 NaCl is not limited by the availability of photosynthate in the plant as a whole. However, there could have been a growth limitation due to inadequate organic solutes for osmotic regulation.

Controls on the Formation of Komatiite-Associated Nickel-Copper Sulfide Deposits

Abstract: Nickel-copper sulfide deposits associated with rocks of komatiitic affinity may be divided into two associations on the basis of host rock composition and ore distribution: (1) stratiform, massive-matrix-disseminated sulfides hosted by cumulate komatiite lava flows (lava conduits), or strata-bound, coarse disseminated sulfides hosted by cumulate komatiite bodies near volcanic vents, and (2) strata-bound, finely disseminated sulfides and more restricted massive sulfides hosted by subvolcanic komatiitic dunites (high-level magma chambers). These deposits represent a continuum in environments of emplacement from distal volcanic through proximal and central volcanic to subvolcanic.