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Aging effects in microcrystalline silicon films studied by transient photoconductivity
No full textMeasurements of dark conductivity, steady-state and transient photoconductivity in undoped and boron-doped microcrystalline silicon films exposed to room air are reported. Two aging processes are identified: (i) an increase in dark conductivity and mobility-lifetime product occurring over several days, that may be reversed by heating to 160 °C under vacuum, and subsequently re-cycled, (ii) an irreversible change in the density of states occurring over a period of several months. It is proposed that the reversible effect is associated with charge transport in a region of electron accumulation induced by weakly-adsorbed water, whereas the irreversible effect, identified from its transient photocurrent signature, is associated with a true change in the density of states within the transport path, possibly as a result of slow chemical reactions at silicon grain boundaries
How do carers of people with long term neurological conditions experience the provision of replacement care:Final report to the Department of Health R&D grant 053/0012
No full textFree Trade and Empire in the Anglo-Irish Commercial Propositions of 1785
No full textWilliam Pitt's 1785 proposal for a free trade area between Britain and Ireland attempted to use free trade as a mechanism of imperial integration. It was a response to the agitation for political reform in Ireland and followed the attainment of legislative independence in 1782. The proposal aimed at coordinating economic and fiscal policy between the kingdoms without imposing explicit political controls. This article establishes that the measure failed because of the lack of consensus around the idea of free trade. Three contrasting ideas of free trade became apparent in the debates around the propositions of 1785: imperial or neomercantilist free trade, Smithean free trade, and national or neo-Machiavellian free trade. Imperial free trade was critical of monopolies but sought to organize trade to the benefit of the imperial metropole; Smithean free trade saw open markets as a discipline that assured efficiency but required imperial institutional frameworks, legally secured, to function. Neo-Machiavellian free trade asserted the right of every political community to organize its trade according to its interests. The article establishes the genealogy of these three positions in pamphlet debates and political correspondence in Britain and Ireland from 1689 to 1785. It argues that majority political opinion in Ireland, with exceptions, understood free trade in a neo-Machiavellian sense, while Pitt was committed to a Smithean ideal. The propositions collapsed because these internal tensions became more evident under the pressure of criticism. Liberal political economy did not of itself offer a route to a British exceptionality that finessed the tensions inherent in empire.</p
LEGO storytelling:an initial observational study to enable children to become partners in their own assessment
No full textThis paper will explore the validity of an approach to assessment by reporting initial findings from pre study work with young children who have been observed playing with LEGO in a nursery setting. It will demonstrate how these interactions have informed our views on children as potential participants in their own assessment using traditional construction toys and the ways new technology could be used to truly listen and assess knowledge through the valuable medium of storytelling. Initial observations highlighted the following interesting aspects: (i) In the classroom, many of the “live” conversations that took place between the practitioner and the child were relatively shallow, rushed and interrupted. (ii) Video recordings of children enacting stories do not serve as the basis of a learning conversation as the children don't remember the story and are distracted by their own presence in the video. (iii) The children built stories with ready made objects and elemental objects rather than the more abstract bricks.Keywords: Innovation, technology, research projects, assessment, storytelling LEGO, young children, Scottish Curriculum. <br/
Properties of thin-film silicon solar cells at very high irradiance
No full textThe focussed beam of a low-power helium–neon laser is used to study accelerated light-induced degradation (Staebler–Wronski effect) and high steady-state photocarrier generation rates in amorphous and microcrystalline silicon thin-film solar cells, at up to 13 MW m- 2 irradiance. Even at these high power densities, COMSOL® simulations indicate that heat diffusion into the substrate, aided by spreading conduction via the Ag back-contact, restricts the temperature rise to less than 14 °C. Short-circuit current may be measured directly, and the I–V characteristic estimated by taking into account shunting by the inactive part of the cell. The improved resistance to degradation of microcrystalline silicon cells is shown to persist to high irradiance. Computer simulations of an amorphous silicon solar cell are presented that are consistent with measured un-degraded and degraded properties, and offer insight into prevailing defect creation processes and carrier recombination mechanisms
Oscillatory pipe flows of a yield-stress fluid
No full textOscillatory pipe flows of aqueous Carbopol solutions are investigated both experimentally and analytically. Using the PIV technique, the velocity profiles are measured and compared with the numerical solutions based on an elasto-viscoplastic rheological model, in which an elastic spring is serially connected to a regularized Bingham viscoplastic model. The rheological parameters, such as shear modulus of elasticity, yield stress and viscosity, are estimated from steady-shear measurements. Good agreement between the experiments and the model results is observed. It is apparent that the elasticity plays an important role in the unsteady flows of the soft yield-stress fluid studied herein
In vitro study of a multi-layer piezoelectric crystal attic hearing implant
No full textWe have developed a prototype middle-ear hearing implant which uses a multilayer piezoelectric actuator. Tn this series of experiments the actuator was attached to the medial wall of the attic so that it makes contact with the body of the incus. Initial in vitro evaluation has been carried out using a laser vibrometer (Polytec CLV) to measure stapes velocity. Stapes displacement is calculated by mathematical integration. The device used in this way is particularly effective at transmitting high frequency sound to the stapes. When switched off the actuator impairs the transmission of sound to the ossicular chain at low frequencies, but this effect is only 7 dB at most. The stapes displacements resulting from the action of the implant have a linear relationship with the voltages used to drive the system. The high capacitance of the present actuator means that its power requirements are higher than that of other comparable devices. An optimal method of coupling the device to the incus has yet to be identified.</p
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