2,387 research outputs found
The density, construction and drag coefficient of electrostatic volcanic ash aggregates.
No full textRecent laboratory experiments have demonstrated that electrostatic charges generated during the fragmentation of volcanic pumice cause rapid aggregation of the silicate particles produced. Here, we present measurements of the mass and component particle size distribution of individual, electrostatically bound aggregates produced during these experiments. Particles produced by fracturing pumice aggregated as they fell ∼1.5 m within an enclosed fall chamber. Aggregate mass measurements indicate aggregate densities of ∼200 kg m−3 or less. The component particle size analysis demonstrates exponential-type cumulative distributions which are dominated (on a volume basis) by particles ∼10–40 μm in diameter and contain few particles >70 μm. By representing these particles as disks of 5 μm thickness the calculated aggregate densities are in agreement with those derived from the aggregate mass measurements and indicate a relatively constant aggregate density with size (in contrast with previous results from fall velocities). Combining the density measurements with fall velocity data allows the drag coefficient of aggregates to be determined. Empirical equations developed to describe the particle size distribution within aggregates are used to derive relative aggregation coefficients for the electrostatic aggregation process. Our results can be used within numerical models of volcanic plumes in order to improve their representation of electrostatic aggregation processes
Gulypyrones A and B and Phomentrioloxins B and C Produced byDiaporthe gulyae, a Potential Mycoherbicide for Saffron Thistle (Carthamus lanatus)
No full textA virulent strain of Diaporthe gulyae, isolated from stem cankers of sunflower and known to be pathogenic to saffron thistle, has been shown to produce both known and previously undescribed metabolites when grown in either static liquid culture or a bioreactor. Together with phomentrioloxin, a phytotoxic geranylcyclohexenetriol recently isolated from a strain of Phomopsis sp., two new phytotoxic trisubstituted α-pyrones, named gulypyrones A and B (1 and 2), and two new 1,O- and 2,O-dehydro derivatives of phomentrioloxin, named phomentrioloxins B and C (3 and 4), were isolated from the liquid culture filtrates of D. gulyae. These four metabolites were characterized as 6-[(2S)2-hydroxy-1-methylpropyl]-4-methoxy-5-methylpyran-2-one (1), 6-[(1E)-3-hydroxy-1-methylpropenyl]-4-methoxy-3-methylpyran-2-one (2), 4,6-dihydroxy-5-methoxy-2-(7-methyl-3-methyleneoct-6-en-1-ynyl)cyclohex-2-enone (3), and 2,5-dihydroxy-6-methoxy-3-(7-methyl-3-methyleneoct-6-en-1-ynyl)cyclohex-3-enone (4) using spectroscopic and chemical methods. The absolute configuration of the hydroxylated secondary carbon of the 2-hydroxy-1-methylpropyl side chain at C-6 of gulypyrone A was determined as S by applying a modified Mosher's method. Other well-known metabolites were also isolated including 3-nitropropionic, succinic, and p-hydroxy- and p-methylbenzoic acids, p-hydroxybenzaldehyde, and nectriapyrone. When assayed using a 5 mM concentration on punctured leaf disks of weedy and crop plants, apart from 3-nitropropionic acid (the main metabolite responsible for the strong phytotoxicity of the culture filtrate), phomentrioloxin B caused small, but clear, necrotic spots on a number of plant species, whereas gulypyrone A caused leaf necrosis on Helianthus annuus plantlets. All other compounds were weakly active or inactive
Use of a genetic algorithm to perform reliability analysis of unsaturated soil slopes
No full textRainfall induced landslides are a major cause of disturbance to transport networks in many parts of the world. In slopes where the water table is some depth below the ground surface, negative pore water pressure (suctions) develop in the near surface soils which contribute significantly to their overall stability. However, these suctions are transient and reduce as water percolates into the slope (and a wetting front develops) during periods of heavy or prolonged rainfall.
In this paper the development of a model for determining the reliability of a slope in which the soil properties are considered as random variables is presented. By transforming the variables into polar coordinates the complexities associated with defining the limit state function, which have affected many previous attempts at probabilistic analysis of slopes, can be overcome. The minimisation problem is solved in a powerful and efficient Genetic Algorithm environment.Other funderIarnród Éirean
From Dome to Disease: The Respiratory Toxicity of Volcanic Cristobalite
No full textExposure to fine-grained volcanic ash can potentially cause acute and chronic respiratory disease. The toxicity of ash is likely to vary depending on the type and style of eruption; eruptions at dome-forming volcanoes, in particular, can produce ash containing substantial quantities of respirable crystalline silica, a recognised human carcinogen and causative agent of silicosis. Volcanic domes crystallise crystalline silica as cristobalite, which is metastable at dome-forming temperatures (ca. 850 °C), through deposition from silica-saturated vapours and through devitrification of volcanic glass.
Five dome-forming volcanoes are studied to constrain the hazard posed by volcanic cristobalite, including: Colima, Mexico; Merapi, Indonesia; Mount St. Helens, USA; Santiaguito, Guatemala; and Unzen, Japan. The evolution of the cristobalite hazard is investigated from crystallisation in volcanic settings to its potential effect on biological systems, through a series of petrological, physicochemical and toxicological studies.
We rationalise the presence of metastable cristobalite below its stability field in all domes studied by way of a textural investigation, and conclude that the incorporation of aluminium and sodium into the silica structure facilitates crystallisation. Since particle toxicology is dependent on composition and structure, the observation of cation substitutions is expanded in a geochemical and thermodynamic investigation of volcanic cristobalite to constrain its mineralogy. We find that incorporation of 1-4 wt. % aluminium leads to a poorly-ordered cristobalite structure. This investigation facilitates a mineralogical comparison of the cristobalite hazard among volcanic locations and provides the framework for assessing volcanic cristobalite toxicity. We investigate the ability of volcanic ash to elicit an in vitro pro-inflammatory response, focusing on silica-mediated experiments, and relate the influence of structure and composition to the potential physiological burden. We find that volcanic cristobalite can be mineralogically considered as a single entity among locations, and that cristobalite-bearing ash is less toxic than expected. Nonetheless, we recommend that eruptions be considered on a case-by-case basis to most effectively aid the risk mitigation work of disaster managers globally
Effect of rainfall intensity on infiltration into partly saturated slopes
No full textThis paper describes the development of a
model to analyse the rate of infiltration and run-off
experienced by a partly saturated soil slope during
rainfall. The paper first reviews some of the most
popular infiltration models used in geotechnical analysis,
and highlights some of the problems associated
with their application. One particular model, the
Horton Equation is extended to include rainfall
intensity directly in its formulation. The new model
is shown to predict infiltration responses, which agree
with field measurements. In the final section the
influence of the rainfall intensity and pattern of rainfall
(variation of rainfall intensity) on the infiltration
response of a soil is investigated using the new model.Other funderIarnród Éirean
An advanced adjustable switch hybrid (Ash) concept for high power automotive converters
No full textIn this paper, we introduce an Adjustable Switch Hybrid (ASH) converter concept. The ASH targets the optimization of the electrical performance of high-powered automotive drive-trains depending on the different load conditions during drive cycles. The new concept employs in principle the previously reported Cross Switch (XS) Hybrid having a parallel arrangement of bipolar Silicon IGBTs and unipolar SiC MOSFETs for benefiting from the different electrical characteristics of each paralleled device. However, the ASH relies on a computational approach for the continuous and dynamic adjustments of the Si-IGBT to the SiC MOSFET area ratio through the gate units depending on the load conditions. In practical terms, changes in the loading conditions can be sensed and data will then be sent back to the ASH gate drive unit for the optimum device ratio selection. In other words, the ASH provides the drivetrain with an Electronic Transmission System or Gear type functionality.Accepted Author ManuscriptDC systems, Energy conversion & Storag
Structure and Absolute Configuration of Kongiidiazadione, a New Phytotoxic 3-Substituted-5-Diazenylcyclopentendione Produced byDiaporthe Kongii
No full textA new 3-substituted-5-diazenylcyclopentendione named kongiidiazadione was isolated from culture filtrates of Diaporthe kongii, associated with stem cankers on sunflower in Australia. Kongiidiazadione was characterized by spectroscopic (essentially nuclear magnetic resonance [NMR] and high-resolution, electrospray ionization, mass spectrometry [HRESIMS]) methods as (-)-5-diazenyl-3-hydroxymethyl-cyclopent-3-en-1,2-dione. The stereochemistry of the diazenyl group was determined by IR spectroscopy, while the (R) absolute configuration at C(5) was assigned by computational analysis of its electronic circular dichroism (ECD) spectrum. When assayed on leaf disks of different plant species at 5 mM, the kongiidiazadione had a differential impact, causing clear necrosis, in particular to Helianthus annuus. Moreover, kongiidiazadione proved to have a weak antibacterial activity against gram-positive Bacillus amyloliquefaciens
Nathan Gray : What they brought back
No full textPublished to accompany the exhibition held at Gertrude Contemporary Project Room, Melbourne Art Fair, 4-8 August 2010.Catalogue essay by Ash Kilmartin
Pore solution composition of alkali-activated slag/fly ash pastes
No full textThe pore solutions of a series of hardened alkali-activated slag/fly ash pastes were extracted by the steel-die method, and analyzed using ICP-OES analysis technique. According to the saturation index from thermodynamic calculations, the pore solutions of alkali-activated slag pastes kept oversaturated with respect to solid reaction products with time. In the pore solutions of alkali-activated fly ash pastes, an increase of temperature (from 40 °C to 60 °C) led to decreases of the concentrations of Si, Al, Ca, Na, OH−, K, Fe and Mg, while the soluble silicate in the alkaline activator resulted in increases of the concentrations of these elements. Compared to the alkali-activated slag paste with the same alkaline activator, 50% replacement of slag by fly ash did not result in a substantial change of the pore solution composition. Based on the experimental results, conceptual models were proposed to describe the elemental concentrations in the pore solutions.Accepted Author ManuscriptMaterials and Environmen
Structure and Absolute Configuration of Kongiidiazadione, a New Phytotoxic 3-Substituted-5-Diazenylcyclopentendione Produced by Diaporthe Kongii
No full textA new 3-substituted-5-diazenylcyclopentendione named kongiidiazadione was isolated from culture filtrates of Diaporthe kongii, associated with stem cankers on sunflower in Australia. Kongiidiazadione was characterized by spectroscopic (essentially nuclear magnetic resonance [NMR] and high-resolution, electrospray ionization, mass spectrometry [HRESIMS]) methods as (-)-5-diazenyl-3-hydroxymethyl-cyclopent-3-en-1,2-dione. The stereochemistry of the diazenyl group was determined by IR spectroscopy, while the (R) absolute configuration at C(5) was assigned by computational analysis of its electronic circular dichroism (ECD) spectrum. When assayed on leaf disks of different plant species at 5 mM, the kongiidiazadione had a differential impact, causing clear necrosis, in particular to Helianthus annuus. Moreover, kongiidiazadione proved to have a weak antibacterial activity against gram-positive Bacillus amyloliquefaciens. Chirality 00:000-000, 2015. © 2015 Wiley Periodicals, Inc
- …
