11,314 research outputs found
Silicon-germanium spherical quantum dot infrared photodetectors prepared by the combination of bottom-up and top-down technologies
No full textMechanisms for accumulation and migration of technetium-99 in saltmarsh sediments
No full textThis thesis describes the development of analytical methods for both the bulk determination of 99Tc, and determination of 99Tc in sequential extracts from sediments. These methods have been used to collect data, which, along with trace and major element data have been used to interpret the mechanisms for 99Tc input, migration and accumulation in saltmarshes. The inventory of 99Tc stored in the Thornflatt Saltmarsh, Esk Estuary has also been determined. The routine determination of 99Tc in bulk samples uses 99mTc as a yield monitor. Samples are ignited stepwise to 550°C and the 99Tc is extracted using 8M nitric acid. Many contaminants are precipitated with Fe(OH)3 and the Tc in the supernant is pre-concentrated and further purified using anion-exchange chromatography. Final separation of Tc from Ru is achieved by extraction of Tc into 5% TnOA in xylene from 2M sulphuric acid. The yield is determined by γ-spectrometric analysis of 99mTc. Determination of 99Tc is made by liquid scintillation counting. Typical recoveries are in the order of 70-95% and the method has a detection limit of 1.7 Bq/kg for a sample size of 10g. Determination of Tc in sequential extracts uses operationally defined procedures to extract: exchangeable Tc, reducible Tc and oxidisable Tc. An initial water wash is used to extract any occluded Tc and a final leach in 8 M nitric acid is used to dissolve any residual Tc. The isolation of 99Tc uses TEVA resin for Extracts 1-4 and the decontamination procedure developed for bulk analysis for Extract 5. 99mTc was used as a yield monitor, and determination of 99Tc is by liquid scintillation counting. Limits of detection were dependent on the amount of 99mTc tracer used but were found to be as low as 2.4 Bq/kg for a sample size of 2g. A study was made of the mechanisms responsible for the accumulation and migration of Tc in estuarine sediments using sediments collected from saltmarshes at Thornflatt, Carlaverock and the Ribble Estuary. 99Tc was present at determinable activities in all the sediment cores taken from these sites. Good correlations between Tc and CaO as well as CO3 concentrations and poor correlation between Tc and radionuclides adsorbed to inorganic detritus infer a direct input of 99Tc to marsh sediments. Determination of 99Tc in biota living on the marsh also showed that this was not a significant pathway for input of Tc to the sediments. Sequential extraction data imply sorption to an organic fraction of the sediment. Stable element and sequential extraction data indicates that Tc is readily oxidised and remobilised before reprecipitation where redox conditions are favourable. Data indicate a reduction potential between those of the MnIV to MnII reaction and the FeIII to FeII reaction is necessary for re-accumulation to occur, as suggested by published thermodynamic data. Data collected from reducing sediments imply that similar mechanisms are responsible for the accumulation of Mn (e.g. reduction by sulphate reducing bacteria) and the accumulation of Tc. The inventory of 99Tc held within the Thornflatt saltmarsh is proportionally less than that of 137Cs or 241Am when compared to discharges from Sellafield. However a higher proportion of 99Tc is transferred from Seliafield and incorporated into saltmarsh sediments than is suggested by previously published standard distribution coefficient data. Saltmarsh sediments are therefore a more important sink of 99Tc than extrapolations made from inventories of other radionuclides would suggest
On the Role of Technical Cooperation in International Technology Transfers
Full text linkWe investigate whether and how technical cooperation aid (TC) facilitates technological diffusion from developed to developing countries, comparing it with foreign direct investment (FDI) and external openness. Extending the model of Benhabib and Spiegel (2005), we estimate the degree to which these three channels contribute to countries total factor productivity (TFP) growth rates. Our econometric model also allows us to identify whether a country will catch up to or diverge from the technological leader nation over time. Two sets of robust findings emerge. First, TC, FDI and openness all contribute to facilitate international technology transfers. Yet, among these three channels, openness seems to contribute the most, followed by TC. Also, TC seems to compensate for the lack of sufficient human capital in developing countries. Second, around 6 to 17 countries out of 85 in our sample fail to catch up to the technological leader over the 36 years. These results suggest that TC can play an important role in facilitating the technological catch up of developing countries.
The use of computational fluid dynamics in the optimisation of marine current turbines
No full textThe use of Computational Fluid Dynamics (CFD) in research and development in industry has become much more commonplace. Technological advances have improved the accuracy of codes although this is at the expense of computational power. CFD is a powerful tool if implemented correctly, and in order to do this it is important to understand when to use the different levels of code. This paper illustrates the relative merits of codes ranging from simple three dimensional panel codes to Reynolds Averaged Navier Stokes equations with regards to the optimisation of marine current turbines. It goes on to discuss turbulence models, fluid structure interactions and ultimately design, search and optimisation
Service-oriented models for audiovisual content storage
No full textWhat are the important topics to understand if involved with storage services to hold digital audiovisual content? This report takes a look at how content is created and moves into and out of storage; the storage service value networks and architectures found now and expected in the future; what sort of data transfer is expected to and from an audiovisual archive; what transfer protocols to use; and a summary of security and interface issues
A triazole derivative elicits autophagic clearance of polyglutamine aggregation in neuronal cells [Corrigendum]
No full textHsieh CH, Lee LC, Leong WY, Yang TC, Yao CF, Fang K. Drug Des Devel Ther. 2016;10:2947–2957.On page 2950, Figure 1, part B has been updated.Read the original article 
T0-Berekening: Status Quo van UNIBEST-TC
No full textDit rapport gaat in op de ontwikkelingen bij het UNIBETS-TC model. Met dit model wordt het cross-shore en longshore sediment transport berekend. Om inzicht te krijgen in de verbeteringen in het model wordt er in dit rapport een T0-berekening (een berekening op tijdstip T=0) gemaakt. Dit maakt het mogelijk de ontwikkelingen te evalueren door het te vergelijken met een dergelijke exercitie op het moment T1. Met de berekening wordt er antwoord gegeven op de vragen of het UNIBEST-TC model één heel jaar de ontwikkeling van het kustprofiel kan doorrekenen en in hoeverre het model de werkelijkheid beschrijft. Geconcludeerd wordt dat het (nieuwe) UNIBEST-TC model het dwarstransport in de goede orde van grootte bepaald, maar dat het model geen rekening houdt met het ontstaan van banken. Verder onderzoek is nodig. Het model houdt verder goed rekening met de interactie tussen langs- en dwarstransport en biedt daarnaast een goede mogelijkheid om het lot van een zandsuppletie te bestuderen
Performance prediction of a free stream tidal turbine with composite bend-twist coupled blades
No full textFree stream tidal turbines are a source of growing interest in the marine renewable energy field. Some designs use variable pitch blade control devices in order to maximize the efficiency of the turbines; however these are complex to design, construct and maintain under the severe load conditions sub sea devices experience.
There is an interest in the use of composite materials for potential improvements in hydrodynamic and structural performance of Horizontal Axis Tidal Turbines (HATT). In addition to the advantages of high strength-to-mass and high strength to stiffness ratios, anisotropy of the laminated fibre composites can be designed to allow 3D tailoring of the blade deformation. Anisotropic structures show different levels of elastic coupling, depending on the ply angle in the layers that comprise such a material. Passive control of a turbine blade can be achieved by taking advantage of the directionality of the anisotropic composite material.
A structure that undergoes both bending and twisting due to a pure bending load is said to exhibit bend-twist coupling. This type of behaviour has been identified as a potential method for load reduction - particularly fatigue loads, and an increase in both efficiency and annual energy capture in wind turbines [1]. Preliminary studies have since shown that this may also be the case for HATTs [2].
A computationally efficient, yet realistic, model has been developed in order to estimate the amount of induced twist present on a bend-twist coupled blade in a tidal stream. This model takes into account the effect on the induced twist of fibre orientation, blade loading and cross section, material mechanical properties, and shell thickness. The method has been incorporated into a Blade Element Momentum code, modified to predict the performance of free stream tidal devices; such that the performance of a HATT with composite bend-twist coupled blades could be estimated.
It has been shown that, when compared to a free stream tidal turbine with fixed blades of a similar configuration, a HATT that utilises composite bend-twist couple blades can reduced fatigue loading, bring the turbine efficiency closer to the Betz limit and increase the annual energy capture
Bond parameters affecting to failure of co-cured single and double lap joints subjected to static and dynamic tensile loads
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