4,332 research outputs found
Significance of the late Archaean granulite facies terrain boundaries, Southern West Greenland
Three distinct episodes and occurrences of granulite metamorphism in West Greenland are described: (1) the oldest fragmentary granulites occur within the 3.6-Ga Amitsoq gneisses and appear to have formed 200 Ma after the continental crust in which they lie (Spatially associated rapakivi granites have zircon cores as old as 3.8 Ga, but Rb-Sr, whole-rock Pb-Pb, and all other systems give 3.6 Ga, so these granulites apparently represent a later metamorphic event); (2) 3.0-Ga granulites of the Nordlandet Peninsula NW of Godthaab, developed immediately after crustal formation in hot, dry conditions, are carbonate-free, associated with voluminous tonalite, and formed at peak metamorphic conditions of 800 C and 7 to 8 kbar (Synmetamorphic trondhjemite abounds and the activity of H2O has been indicated by Pilar to have varied greatly); and (3) 2.8-Ga granulites south of Godthaab, lie to the south of retrogressed amphibolite terranes. Prograde amphibolite-granulite transitions are clearly preserved only locally at the southern end of this block, near Bjornesund, south of Fiskenaesset. Progressively deeper parts of the crust are exposed from south to north as a major thrust fault is approached. Characteristic big hornblende pegmatites, which outcrop close to the thrust in the east, have been formed by replacement of orthopyroxene. Comparable features were not seen in South Indian granulites. It was concluded that no one mechanism accounts for the origin of all granulites in West Greenland. Various processes have interacted in different ways, and what happened in individual areas must be worked out by considering all possible processes
Five patients with oedema: written for the Wightman Prize in Clinical Medicine, 1962
This is an account of five patients seen in
:. iards 21, 23 and 24 of the Royal Infirmary,
Edinburgh; all the patients suffered from some
form of oedema. The severity of the oedema
varied greatly in the different patients, as did
the factors responsible for its appearance. This
account aims merely to recount the clinical
histories, with special emphasis on the oedema,
and to discuss the causes as revealed in each
patient.In the interests of brevity and clarity, it
has been necessary to omit some of the details of
the history and clinical findings in each patient
where they were not strictly relevant to the
problem of oedema, but any details of special
interest have also been included. Although this
is intended primarily as a clinical account, the
discussion of the pathogenesis of oedema in each
patient must, as so often in medicine today,
delve into mechanisms at a microscopic and even at
a molecular level. At this level, the discussion
runs the risk of either being too brief and
dogmatic, or else too detailed and inconclusive;
and at any level the discussion must inevitably be
incomplete. Many of the theories of the
pathogenesis of oedema are speculative and
controversial, and the more complete the reading
of the literature, the more confusing the
picture becomes. The author has attempted, in
this account, to discuss some of the more
important factors in the production of oedema,
but has tried to avoid confusing himself and the
reader with too much detail.Oedema, which may be defined as a localised or
generalised increase in the volume of the interstitial fluid, can arise in many diseases, and
be the result of the interplay of a number of
factors. These factors are not well understood - but the first patient suffered from oedema of a type where the simpler explanations would seem to
suffice
The geology and petrogenesis of the southern closepet granite
The Archaean Closepet Granite is a polyphase body intruding the Peninsular Gneiss Complex and the associated supracrustal rocks. The granite out-crop runs for nearly 500 km with an approximate width of 20 to 25 km and cut across the regional metamorphic structure passing from granulite facies in the South and green schist facies in the north. In the amphibolite-granulite facies transition zone the granite is intimately mixed with migmatites and charnockite. Field observations suggests that anatexis of Peninsular gneisses led to the formation of granite melt, and there is a space relationship between migmatite formation, charnockite development and production and emplacement of granite magma. Based on texture and cross cutting relationships four major granite phases are recognized: (1) Pyroxene bearing dark grey granite; (2) Porphyritec granite; (3) Equigranular grey granite; and (4) Equigranular pink granite. The granite is medium to coarse grained and exhibit hypidiomorphic granular to porphyritic texture. The modal composition varies from granite granodiorite to quartz monzonite. Geochemical variation of the granite suite is consistent with either fractional crystallization or partial melting, but in both the cases biotite plus feldspar must be involved as fractionating or residual phases during melting to account trace element chemistry. The trace element data has been plotted on discriminant diagrams, where majority of samples plot in volcanic arc and within plate, tectonic environments. The granite show distinct REE patterns with variable total REE content. The REE patterns and overall abundances suggests that the granite suite represents a product of partial melting of crustal source in which fractional crystallization operated in a limited number of cases
Room temperature magneto-optic effect in silicon light-emitting diodes
In weakly spin-orbit coupled materials, the spin-selective nature of
recombination can give rise to large magnetic-field effects, for example on
electro-luminescence from molecular semiconductors. While silicon has weak
spin-orbit coupling, observing spin-dependent recombination through
magneto-electroluminescence is challenging due to the inefficiency of emission
due to silicon's indirect band-gap, and to the difficulty in separating
spin-dependent phenomena from classical magneto-resistance effects. Here we
overcome these challenges to measure magneto-electroluminescence in silicon
light-emitting diodes fabricated via gas immersion laser doping. These devices
allow us to achieve efficient emission while retaining a well-defined geometry
thus suppressing classical magnetoresistance effects to a few percent. We find
that electroluminescence can be enhanced by up to 300\% near room temperature
in a seven Tesla magnetic field showing that the control of the spin degree of
freedom can have a strong impact on the efficiency of silicon LEDs
The role of intermolecular coupling in the photophysics of disordered organic semiconductors: Aggregate emission in regioregular polythiophene
We address the role of excitonic coulping on the nature of photoexcitations
in the conjugated polymer regioregular poly(3-hexylthiophene). By means of
temperature-dependent absorption and photoluminescence spectroscopy, we show
that optical emission is overwhelmingly dominated by weakly coupled
H-aggregates. The relative absorbance of the 0-0 and 0-1 vibronic peaks
provides a powerfully simple means to extract the magnitude of the
intermolecular coupling energy, approximately 5 and 30 meV for films spun from
isodurene and chloroform solutions respectively.Comment: 10 pages, 4 figures, published in Phys. Rev. Let
Describing the Sward Structure of Wheat and Annual Ryegrass Swards Grazed by Lambs in Southern NSW
Dual-purpose wheats are now an established part of the feed base on many mixed-farms in southern NSW. However agronomic practices can vary and it is unknown whether row spacing will impact the availability of forage for grazing by sheep. Intake has been shown to be affected by a range of factors including tiller length, pasture height, sward density and pasture mass (Allden and Whittaker 1970; Black and Kenney 1984). This study sought to describe the differences in sward structure of grazed wheat swards at two different row spacings in terms of mean height, row height and bulk density and compare this to an annual ryegrass pasture presented as a continuous pasture
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Hydrogen migration at restructuring palladium-silver oxide boundaries dramatically enhances reduction rate of silver oxide.
Heterogeneous catalysts are complex materials with multiple interfaces. A critical proposition in exploiting bifunctionality in alloy catalysts is to achieve surface migration across interfaces separating functionally dissimilar regions. Herein, we demonstrate the enhancement of more than 104 in the rate of molecular hydrogen reduction of a silver surface oxide in the presence of palladium oxide compared to pure silver oxide resulting from the transfer of atomic hydrogen from palladium oxide islands onto the surrounding surface formed from oxidation of a palladium-silver alloy. The palladium-silver interface also dynamically restructures during reduction, resulting in silver-palladium intermixing. This study clearly demonstrates the migration of reaction intermediates and catalyst material across surface interfacial boundaries in alloys with a significant effect on surface reactivity, having broad implications for the catalytic function of bimetallic materials
Transport Properties of Highly Aligned Polymer Light-Emitting-Diodes
We investigate hole transport in polymer light-emitting-diodes in which the
emissive layer is made of liquid-crystalline polymer chains aligned
perpendicular to the direction of transport. Calculations of the current as a
function of time via a random-walk model show excellent qualitative agreement
with experiments conducted on electroluminescent polyfluorene demonstrating
non-dispersive hole transport. The current exhibits a constant plateau as the
charge carriers move with a time-independent drift velocity, followed by a long
tail when they reach the collecting electrode. Variation of the parameters
within the model allows the investigation of the transition from non-dispersive
to dispersive transport in highly aligned polymers. It turns out that large
inter-chain hopping is required for non-dispersive hole transport and that
structural disorder obstructs the propagation of holes through the polymer
film.Comment: 4 pages, 5 figure
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