Correlation coefficient patterns and their interpretation in three basaltic suites

Single stage magmatic fractionation processes result in igneous rock suites in which correlation coefficients between pairs of elements are generally high. The Tertiary lavas of E. Iceland are used as an illustration of this type of behaviour. When a second process such as fractionation at a different pressure, wall-rock assimilation, or mixing with a different magma, occurs, correlation coefficients are altered in a predictable way if the process and the chemical characteristics of the participating rocks, minerals and liquids are known. A computer program has been devised to simulate complete correlation coefficient matrices for any desired two- or multi-stage process e.g. fractional crystallisation coupled with contamination. Basaltic suites from Mahabaleshwar, India and the Rooi Rand, southern Africa show correlation coefficient patterns characteristic of multi-stage evolution, and these are interpreted with the aid of computer simulation. The Mahabaleshwar suite shows clear evidence of contamination by a granitic component. The Rooi Rand rocks however remain problematic.     

A Gill twin propeller-vane anemometer for flux measurements during moderate and strong winds

A wind velocity measuring system based on the Gill propeller anemometer is described. A method of calculating the vertical component, which allows for the non-cosine response and avoids the region of stall and nonlinear operation, is presented. A summary of the possible errors in Reynolds stress and drag coefficient estimates is given. A method of establishing the distance constant using field observations is presented. Finally, some preliminary results and some intercomparisons with other anemometers are described briefly.Now at the Institute of Ocean Sciences, Patricia Bay, B.C., Canada.     

A crystal fractionation model for the basaltic rocks of the New Georgia Group,British Solomon Islands

Study of the data provided by Stanton and Bell (1969) for certain basaltic rocks from the New Georgia Group reveals an apparent discrepancy between compositional variation and the sequence of phenocryst phases available for fractionation. The discrepancy none-the-less appears explicable in terms of two low-pressure crystal fractionation mechanisms. The first of these we term compensated crystal settling, a process which, it is postulated, allows a substantial amount of magma undergoing crystal settling to maintain its overall composition since crystals settling from it are continually replaced by compositionally similar crystals which settle into it from higher levels. The second process involves selective fractionation of phases sinking at different rates. Slow sinking of plagioclase relative to ferromagnesian minerals is believed to produce cumulus enrichment in plagioclase in the upper part of the chamber, the resultant magmas being erupted as highly porphyritic, high-alumina, basaltic andesites.     

Experimental and theoretical bond critical point properties for model electron density distributions for earth materials

Generalized X-ray scattering factor model experimental electron density distributions and bond critical point, bcp, properties generated in recent studies for the earth materials stishovite, forsterite, fayalite and cuprite with high energy single crystal synchrotron X-ray diffraction data and those generated with high resolution diffraction data for coesite and senarmonite were found to be adequate and in relatively good agreement, ~5% on average, with those calculated with quantum chemical methods with relatively robust basis sets. High resolution low energy single crystal diffraction data, recorded for the molecular sieve AlPO₄-15, were also found to yield model electron density distribution values at the bcp points for the AlO and PO bonded interactions that are in relatively good to moderately good agreement with the theoretical values, but the Laplacian values of the distribution at the points for the two bonded interactions were found to be in relatively poor agreement. In several cases, experimental bcp properties, generated with conventional low energy X-ray diffraction data for several rock forming minerals, were found overall to be in poorer agreement with the theoretical properties. The overall agreement between theoretical bcp properties generated with computational quantum methods and experimental properties generated with synchrotron high energy radiation not only provides a basis for using computational strategies for studying and modeling structures and their electron density distributions, but it also provides a basis for improving our understanding of the crystal chemistry and bonded interactions for earth materials. Theoretical bond critical point properties generated with computational quantum methods are believed to rival the accuracy of those determined experimentally. As such the calculations provide a powerful and efficient method for evaluating electron density distributions and the bonded interactions for a wide range of earth materials.Dedicated to Professor Robert F. Stewart of Carnegie Mellon University on his retirement for his brilliant and original work modeling electron density distributions.     

An overview of numerical modelling of the Sydney deepwater outfall plumes

In order to predict the behaviour of plumes from three deep ocean outfalls for sewage off Sydney, three-dimensional numerical modelling was used. The modelling suite was driven by data generated by an oceanographic monitoring station measuring wind, ocean currents, temperature and wave characteristics. Three different modelling phases are implemented daily, a nearfield model, a hydrodynamic model and a water quality model. Model output can be used by the New South Wales Environment Protection Authority to predict water quality at ocean beaches and inform the community.     

Comparison of methods for modelling the behaviour of bubbles produced by marine seismic airguns

Three models for the dynamics of seismic airgun‐generated bubbles and their associated far‐field signals are developed and compared with geophysical data. The first model of an airgun‐generated bubble uses a spherical approximation, the second is an approximate Lagrangian model which allows for small deformations from a spherical shape, whilst the final model is an axisymmetric boundary‐integral method which permits the bubble to evolve into highly non‐spherical geometries. The boundary‐integral method also allows both geometric interference and strong dynamic interactions in multi‐bubble studies. When comparing the spherical model to experimental data there are three apparent, significant differences: the magnitude of the primary pressure peak, which is greater in the model; the subsequent decay of the pressure peaks and motion – the experimental data demonstrating greater decay and a slower rise rate; and the frequency of oscillation, which is slower in the experimental data. It is believed that the first discrepancy is due to the initial stages of expansion where the compressed air is forced to sparge through the airgun ports. The other differences indicate that there is some other energy‐loss mechanism which is not accounted for in the spherical bubble model. Non‐spherical bubble behaviour is investigated through the use of two different deformable many‐bubble codes and their predictions are compared with the spherical model and experimental data. The Lagrangian model predicts the formation of a buoyancy‐driven liquid jet on the first collapse of a typical airgun bubble; however, the model breaks down when the bubble becomes significantly deformed, due to a low‐order spherical‐harmonic approximation for the potential. The axisymmetric boundary‐integral code models the jet shape accurately and it is found that these bubbles evolve to toroidal geometries when the jet impacts on the opposite surface of the bubble. This highly non‐spherical behaviour is readily observed on high‐speed films of airgun bubbles, and is one key source of energy loss; it damps the pulsations of the bubble and slows its rise speed. Inter‐bubble interactions are investigated using the two deformable bubble models, and the predictions are compared to field data. It was found that as the bubbles approach each other, their periods of oscillation increase in accordance with observations, and jets are formed in the direction of motion upon collapse.     

Regional Sources of Methyl Chloride, Chloroform and Dichloromethane Identified from AGAGE Observations at Cape Grim, Tasmania, 1998–2000

There are large uncertainties in identifying and quantifying the natural and anthropogenic sources of chloromethanes – methyl chloride (CH₃Cl), chloroform (CHCl₃) and dichloromethane (CH₂Cl₂), which are responsible for about 15% of the total chlorine in the stratosphere. We report two years of in situ observations of these species from the AGAGE (Advanced Global Atmospheric Gas Experiment) program at Cape Grim, Tasmania (41° S, 145° E). The average background levels of CH₃Cl, CHCl₃ and CH₂Cl₂ during 1998–2000 were 551± 8, 6.3± 0.2 and 8.9± 0.2 ppt (dry air mole fractions expressed in parts per 10¹²) respectively, with a two-year average amplitude of the seasonal cycles in background air of 25, 1.1 and 1.5 ppt respectively. The CH₃Cl and CHCl₃ records at Cape Grim show clear episodes of elevated mixing ratios up to 1300 ppt and 55 ppt respectively, which are highly correlated, suggesting common source(s). Trajectory analyses show that the sources of CH₃Cl and CHCl₃ that are responsible for these elevated observations are located in coastal-terrestrial and/or coastal-seawater regions in Tasmania and the south-eastern Australian mainland. Elevated levels of CH₂Cl₂ (up to 70 ppt above background) are associated mainly with emissions from the Melbourne/Port Phillip region, a large urban/industrial complex (population 3.5 million) 300 km north of Cape Grim.Now at the Centre for Atmospheric ChemistryNow at School of Environmental Sciences     

Performance analysis of a stand-alone high-sensitivity receiver

The use of GPS for personal location using wireless devices requires satellite signal measurements both outdoors and indoors. In the outdoor environment propagation paths may range from line-of-sight to shaded or blocked. The indoor environment may range from single-floor wooden constructions to high-rise buildings and underground facilities. In this paper, a high-sensitivity receiver which operates in unaided stand-alone mode is tested under a range of shaded and blocked signal environments, ranging from residential outdoor areas to urban canyons and residential houses. The measurement analysis is performed in both the observation and position domains. The results show that the receiver tested is able to yield measurements with C/N₀ degradations in excess of 20 dB-Hz, as compared to line-of-sight measurements. Position results are a function of the geometry of the remaining satellites, which in turn is a function of the environment. Electronic Publication