2,469 research outputs found
Design rules for dislocation filters
The efficacy of strained layer threading dislocation filter structures in
single crystal epitaxial layers is evaluated using numerical modeling for (001)
face-centred cubic materials, such as GaAs or Si(1-x)Ge(x), and (0001)
hexagonal materials such as GaN. We find that threading dislocation densities
decay exponentially as a function of the strain relieved, irrespective of the
fraction of threading dislocations that are mobile. Reactions between threading
dislocations tend to produce a population that is a balanced mixture of mobile
and sessile in (001) cubic materials. In contrast, mobile threading
dislocations tend to be lost very rapidly in (0001) GaN, often with little or
no reduction in the immobile dislocation density. The capture radius for
threading dislocation interactions is estimated to be approx. 40nm using cross
section transmission electron microscopy of dislocation filtering structures in
GaAs monolithically grown on Si. We find that the minimum threading dislocation
density that can be obtained in any given structure is likely to be limited by
kinetic effects to approx. 1.0e+04 to 1.0e+05 per square cm.Comment: 18 pages, 9 figure
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Development and performance of iron based oxygen carriers containing calcium ferrites for chemical looping combustion and production of hydrogen
Chemical looping combustion (CLC) is a cyclic process in which an oxygen carrier (OC), is firstly reduced by a fuel, e.g. syngas, and then oxidised in air to produce heat. If the OC is Fe2O3, the oxidation can take place in steam to produce hydrogen, i.e. chemical looping hydrogen production (CLH). This paper presents an investigation of CaO modified Fe2O3 OCs for CLC and CLH. The performance of the mechanically mixed OCs were examined in a thermogravimetric analyser and a fluidised bed. It was found that the addition of CaO gives cyclic stability and additional capacity to produce hydrogen via CLH, at the expense of reduced oxygen carrying capacity for CLC, owing to the formation of calcium ferrites, such as Ca2Fe2O5.The authors would like to thank Prof. Clare Grey for her invaluable help in the XRD analysis and Z. Saracevic for support in operating the gas adsorption analyser. This work was supported by the Engineering and Physical Sciences Research Council (EPSRC grant EP/I070912/1). The first author is grateful to IDB (Islamic Development Bank) - Cambridge International Scholarship body for financial support for PhD study. W. L acknowledges funding from the National Research Foundation (NRF), Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme.This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.ijhydene.2015.11.06
Raman excitation spectroscopy of carbon nanotubes: effects of pressure medium and pressure
Raman excitation and emission spectra for the radial breathing mode (RBM) are
reported, together with a preliminary analysis. From the position of the peaks
on the two-dimensional plot of excitation resonance energy against Raman shift,
the chiral indices (m, n) for each peak are identified. Peaks shift from their
positions in air when different pressure media are added - water, hexane,
sulphuric acid - and when the nanotubes are unbundled in water with surfactant
and sonication. The shift is about 2 - 3 cm-1 in RBM frequency, but
unexpectedly large in resonance energy, being spread over up to 100meV for a
given peak. This contrasts with the effect of pressure. The shift of the peaks
of semiconducting nanotubes in water under pressure is orthogonal to the shift
from air to water. This permits the separation of the effects of the pressure
medium and the pressure, and will enable the true pressure coefficients of the
RBM and the other Raman peaks for each (m, n) to be established unambiguously.Comment: 6 pages, 3 Figures, Proceedings of EHPRG 2011 (Paris
The Chemical and Biological Effect of a Gulf Stream Intrusion Off St. Augustine, Florida
During a 3-day anchor station in shelf waters off St. Augustine, Florida we observed the effect of an intruding mass of deeper Gulf Stream water. The shelf waters were relatively low in nutrients and salinity while the Gulf Stream waters were high in salinity and nutrients. Onshore currents correlated with increases in nitrate and chlorophyll concentrations.
The advection of higher nutrient Gulf Stream water coincided with high chlorophyll (∼ mg chl a m−3) concentrations and dense populations of Phaeocystis pouchetii (up to 3.12 × 10°1−1). Zooplankton sampling was impossible in the bottom layer because of the dense Phaeocystis bloom. The dominant zooplankton in the upper layer was the doliolid Dolioletta gegenbauri f. tritonis. Concentrations reached 1561 m−3
77-4 Hydrographic and Biological Observations at an Anchor Station Off St. Augustine, Florida (Eastward Cruise E-1G-75)
The intrusion of deep, nutrient-rich Gulf Stream water into the shelf waters off the southeastern United States is probably the major source of nutrients in the shelf waters and consequently intrusions have a major impact on the biota. This particular cruise was one of the first to be designed to find the front that represents the interface between intruding Gulf Stream waters and normal shelf water. Once the front was delineated an anchor station was occupied to observe the time change at a particular location as the front moved back and forth past the station.
The methods used and resultant data from that cruise are presented to aid others in the analyses of intrusions and related phenomena
Demand Management Incentives Review: Creating a level playing field for network DM in the National Electricity Market
This review assesses and quantifies the financial barriers to DM created by existing economic regulatory incentives for distribution network businesses. the Australian Renewable Energy Agency (ARENA) commissioned ISF to conduct the review to support the Australian Energy Regulator (AER) in developing the new DM Incentive Scheme required by a change to the National Electricity Rules in 2015
The Halo Model of Large Scale Structure for Warm Dark Matter
We present a comprehensive analysis of the halo model of cosmological large
to small-scale structure statistics in the case of warm dark matter (WDM)
structure formation scenarios. We include the effects of WDM on the linear
matter power spectrum, halo density profile, halo concentration relation, halo
mass function, subhalo density profile, subhalo mass function and biasing of
the smooth dark matter component. As expected, we find large differences at the
smallest physical scales in the nonlinear matter power spectrum predicted in
the halo model between WDM and cold dark matter even for reasonably high-scale
WDM particle masses. We find that significant effects are contributed from the
alteration of the halo density profile and concentration, as well as the halo
mass function. We further find that the effects of WDM on the subhalo
population are important but sub-dominant. Clustering effects of the biasing of
the smooth component in WDM is not largely significant.Comment: 15 pages, 21 figures; submitted to Phys. Rev.
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