The Distribution of Transition Metals in Basic Rocks As Determined by Activation Analysis

The research carried out may conveniently be summarised in two sections. In the first section, accurate analyses have been obtained for the scandium, titanium, chromium, manganese, iron, cobalt and nickel content of basic volcanic rocks from a wide variety of geographical locations. (Reunion Island, British Solomon Islands, Juan Fernandez Islands, Hawaii, Red Sea Islands, Iceland and Greenland). Neutron activation analysis has been shown to be an excellent method for the determination of scandium, chromium, manganese, iron, cobalt and nickel in small samples of rock material. The results obtained for a number of international standard rocks are in very good agreement with reported analyses and indicate that activation analysis should be considered one of the most accurate and sensitive techniques available for the analyses of geological samples. The second section has dealt with the transition metal concentrations in the minerals of basic volcanic rocks. Results were obtained for systems which have hitherto not been investigated. It has been shown that the non-spherical distribution of the d-electrons surrounding the transition metal ion exerts a major influence on the partitioning of the ion between olivine and clinopyroxene phenocrysts and the groundmass of basic volcanic rocks. It has been demonstrated, for the first time, that a linear relationship exists between Ink, where k, the partition coefficient, is defined as: [M] crystal [M] groundmass, M being a transition metal ion, and the octahedral site preference energy (O.S.P.E.) of the ion, defined as the tetrahedral crystal field stabilisation energy minus the octahedral crystal field stabilisation energy for the partitioning of the divalent transition metal ions, Mn2+, Fe2+, Co2+ and Ni2+ between olivine and groundmass and clinopyroxene and groundmass of a range of basic volcanic rocks. Zoning of the phenocrysts does not seem to effect the linearity of the plot of Ink Vs O.S.P.E. No systematic variation of the slope of the line Ink Vs O.S.P.E. with either alkalic or tholeiitic basalt type is evident. However, these rock samples containing only olivine phenocrysts tend to have lower values for the partition coefficients. Crystal field effects have also been shown to be significant in the partitioning of the trivalent transition metal ions, Sc3+ and Cr3+, between clinopyroxene phenocrysts and the groundmass of a range of basic volcanic rocks. These results are consistent with and can be explained by the assumption that these transition metal ions occupy tetrahedral and octahedral sites in the magma while only octahedral or near octahedral sites are available in the olivine and pyroxene structures

Wakefulness affects synaptic and network activity by increasing extracellular astrocyte-derived adenosine

Loss of sleep causes an increase in sleep drive and deficits in hippocampal-dependent memory. Both of these responses are thought to require activation of adenosine A1 receptors (adorA1Rs) and release of transmitter molecules including ATP, which is rapidly converted to adenosine in the extracellular space, from astrocytes in a process termed gliotransmission. Although it is increasingly clear that astrocyte-derived adenosine plays an important role in driving the homeostatic sleep response and the effects of sleep loss on memory (Halassa et al., 2009; Florian et al., 2011), previous studies have not determined whether the concentration of this signaling molecule increases in response to wakefulness. Here, we show that the level of adorA1R activation increases in response to wakefulness in mice (Mus musculus). We found that this increase affected synaptic transmission in the hippocampus and modulated network activity in the cortex. Direct biosensor-based measurement of adenosine showed that the net extracellular concentration of this transmitter increased in response to normal wakefulness and sleep deprivation. Genetic inhibition of gliotransmission prevented this increase and attenuated the wakefulness-dependent changes in synaptic and network regulation by adorA1R. Consequently, we conclude that wakefulness increases the level of extracellular adenosine in the hippocampus and that this increase requires the release of transmitters from astroctyes

Quaternary Cu2ZnSnSe4 thin films for solar cells applications

Polycrystalline thin films of Cu2ZnSnSe4 (CZTSe) were produced by selenisation of Cu(Zn,Sn) magnetron sputtered metallic precursors for solar cell applications. The p-type CZTSe absorber films were found to crystallize in the stannite structure (a = 5.684 Ã… and c = 11.353 Ã…) with an electronic bandgap of 0.9 eV. Solar cells with the structure were fabricated with device efficiencies up to 3.2%

Deposition and characterization of copper chalcopyrite based solar cells using electrochemical techniques

Cu(In,Ga)Se2 films were electrodeposited on molybdenum substrates from a single pH buffered bath and annealed in a reducing selenium atmosphere. The opto-electronic properties of the films were characterized using a potentiostatically- controlled three electrode setup and an electrolyte contact. Pulsed illumination was used to determine the carrier type and the speed of photoresponse. Chopped monochromatic illumination was used to measure photocurrent spectra. The electrodeposited copper chalcopyrite films were compared with films prepared by sputtering and spraying techniques

New students, new learning, new environments in higher education : literacies in the digital age

Information literacy is developing new meanings and importance in the online age of teaching and learning in higher education. Information literacy, as a highly prized graduate attribute, is related to the development of lifelong learning capacities. Its strong re-emergence in the form of digital literacy in the context of major online developments at Deakin University is considered through four cases. In each case the reader is asked to consider how the teaching staff members have conceived critical discipline-based information and digital literacies, how these conceptions are related to desired learning outcomes, the types of digital and online environments designed to support the development of these literacies, and how each one contributes to the development of lifelong learning capacities. Information and digital literacy is enlivened through being situated in broader understandings of new generations of learners, new forms of learning and new e-supported learning environments. Educational design, evaluation, research and technology implications of these new types of digital and online-based teaching and learning environments are finally examined.<br /

Reliability of Lead-Free Solder Joints Under Combined Shear and Compressive Loads

In electronic assemblies, solder joints are used to create electrical connections, remove heat, and mechanically support the components. When an electronic device is powered on, the solder joints and the board they are attached to heat up, expanding at different rates. Due to the difference in expansion, shear stress is imposed on the solder joints. As the device is powered on and off, this shear stress can eventually fracture the solder joint, causing the device to fail. Therefore, to increase the lifespan of electronics, it is important to investigate the mechanical properties of solder alloys. The present study investigates how the SAC 305 solder alloy (96.5% Tin, 3% Silver, 0.5% Copper) degrades under simultaneous compressive loading and shear cycling. The effect of compressive load on solder joint life has not been systematically studied in prior work but is critical to understand as large heat sinks are bolted onto increasingly large electronic assemblies, adding compressive stress on solder joints. To gather data, we constructed a custom shear tester. Shear loads were applied using a programmable motor. A pulley system applied compressive loads. Tests were conducted on a large number of samples under varying shear and compressive loads. The data showed that, for compressive loads below 30N, increasing the compressive load decreased the rate of damage to the sample. However, at the highest compressive load of 45N, the sample fractured immediately. This suggests that applying small compressive loads to critical components of electronic devices could improve their long-term reliability

Submerged Aquatic Bryophytes in Colour Lake, a Naturally Acidic Polar Lake with Occasional Year-round Ice-cover

Colour Lake is a small, naturally acidic (pH 3.7) lake on Axel Heiberg Island (Canadian High Arctic) that experiences occasional year-round ice cover. We investigated the benthic vegetation of this lake, with a specific aim of determining whether the annual growth of benthic bryophytes reflects the state of summer ice cover. We found the bed of the lake to be almost completely covered by mosses or liverworts to a depth of 22 m. The mosses showed annual growth bands 10-30 mm in length, visible as changes in leaf density and size. Four to five bands retained recognizable leaves and measurable amounts of chlorophyll-a (chla), and up to 12 bands were recognizable from leaf scars. We could not find a consistent relationship between band length and persistence of ice cover for a given year. We suggest that this lack is due to the complex effects of ice cover on moss growth conditions, specifically on the water temperature and irradiance at depth. Photosynthetic characteristics of Calliergon over a range of light and temperature conditions, determined using pulse amplitude-modulated fluorometry, are presented in support of this argument. We conclude that moss banding patterns are an unreliable method of hindcasting episodic failure of ice to melt in Arctic lakes.Le lac Colour est un petit lac de l'île Axel Heiberg, située dans l'Extrême-Arctique canadien, dont l'acidité (pH = 3,7) est naturelle et qui reste parfois englacé toute l'année. On a étudié la végétation benthique de ce lac, dans le but précis de déterminer si la croissance annuelle des bryophytes benthiques reflète l'état de la couverture de la glace en été. On a trouvé que le lit du lac est presque entièrement recouvert de mousses ou d'hépatiques jusqu'à une profondeur de 22 m. Les mousses affichaient des bandes de croissance annuelles de 10 à 30 mm de longueur, visibles sous la forme d'un changement dans la densité et la taille de la feuille. De 4 à 5 bandes conservaient des feuilles reconnaissables et des quantités mesurables de chlorophylle-a (chla), et jusqu'à 12 bandes étaient reconnaissables d'après les cicatrices foliaires. On n'a pu trouver de rapport constant entre la longueur de la bande et la persistance du manteau glaciel pour une année donnée. On suggère que ce manque est dû aux effets complexes du manteau glaciel sur les conditions de croissance de la mousse, en particulier sur la température de l'eau et l'irradiance en profondeur. Les attributs photosynthétiques de Calliergon pour une gamme de conditions d'éclairement et de température données, déterminés par fluorimétrie par impulsions à amplitude modulée, sont présentés à l'appui de cette thèse. On conclut que les schémas de rubanement de la mousse constituent une méthode peu fiable de prévision a posteriori des interruptions épisodiques de fonte de la glace dans les lacs arctiques

Supernova feedback and the energy deposition in molecular clouds

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Final published version available at: https://doi.org/10.1093/mnras/staa451.Feedback from supernovae is often invoked as an important process in limiting star formation, removing gas from galaxies and, hence, as a determining process in galaxy formation. Here, we report on numerical simulations, investigating the interaction between supernova explosions and the natal molecular cloud. We also consider the cases with and without previous feedback from the high-mass star in the form of ionizing radiation and stellar winds. The supernova is able to find weak points in the cloud and creates channels through which it can escape, leaving much of the well-shielded cloud largely unaffected. This effect is increased when the channels are preexisting due to the effects of previous stellar feedback. The expanding supernova deposits its energy in the gas that is in these exposed channels, and, hence, sweeps up less mass when feedback has already occurred, resulting in faster outflows with less radiative losses. The full impact of the supernova explosion is then able to impact the larger scale of the galaxy in which it abides. We conclude that supernova explosions have only moderate effects on their dense natal environments but that with preexisting feedback, the energetic effects of the supernova are able to escape and affect the wider scale medium of the galaxy.Peer reviewe