Pellet—clad bonding during PCMI

Pellet—clad mechanical interaction adjacent to the mouths of radial cracks in the pellet can lead to local clad strain intensification. in particular, if during operation bonding has occurred between the pellet and the clad, preventing relative azimuthal motion, very high strains would result and many clad failures would be expected. These are however not observed. We present here the results of a detailed analysis of the stress field in the region of the mouth of the pellet crack. These show there to be very high radial tensile stresses, not previously predicted, acting on the bond. Such stresses provide a highly plausible mechanism for the failure of the bond. These will permit the strain associated with the opening of pellet cracks during power ramps to be distributed over a relatively large arc of the cladding, and thus explain the low failure rate observed.     

Shifts of soil enzyme activities in wetlands exposed to elevated CO(2)

Wetlands play a key role in global biogeochemical cycles, and as such, the effects of global climatic changes on these systems are of great importance. In this study, we assessed impacts of elevated CO(2) on soil enzyme activities in different types of wetlands. We hypothesised that elevated CO(2), by increasing DOC supply into the soil, would modify enzyme activities. Intact soil cores collected from four wetlands (a bog, a fen, a gully mire, and a marsh) in north Wales and Korea were incubated either under ambient conditions (370 ppm) or elevated CO(2) conditions (double ambient) for 4-2 months. Elevated CO(2) increased DOC concentrations in the pore-water, by which soil microbes appeared to be affected. Enzyme activities exhibited various responses. For example, elevated CO(2) had no effect on beta-glucosidase activity in any soil, suggesting little direct impact on carbon mineralisation. However, N-acetylglucosaminidase activity increased significantly (P<0.05, n=5) in the cores from the bog, whilst a similar response was found in the gully mire for phosphatase activity. Such changes were absent from the fen and marsh where inorganic nutrients were abundant, suggesting that enzyme activities involved in N or P mineralisation only increase under elevated CO(2) when nutrient limitation is strongly exerted.     

Record 12.34% stabilized conversion efficiency in a large area thin‐film silicon tandem (MICROMORPH™) module

Mass‐adoption of thin‐film silicon (TF‐Si) photovoltaic modules as a renewable energy source can be viable if the cost of electricity production from the module is competitive with conventional energy solutions. Increased module performance (electrical power generated) is an approach to reduce this cost. Progress towards higher conversion efficiencies for ‘champion’ large area modules paves the way for mass‐production module performance to follow. At TEL Solar AG, Trübbach, Switzerland, significant progress in the absolute stabilized module conversion efficiency has been achieved through optimized solar cell design that integrates high‐quality amorphous and microcrystalline TF‐Si‐deposited materials with efficient light management and transparent conductive oxide layers in a tandem MICROMORPH™ module. This letter reports a world record large area (1.43 m²) stabilized module conversion efficiency of 12.34% certified by the European Solar Test Installation; an increase of more than 1.4% absolute compared with the previous record for a TF‐Si triple junction large area module. This breakthrough result generates more than 13.2% stabilized efficiency from each equivalent 1 cm² of the active area of the full module. Copyright © 2015 John Wiley & Sons, Ltd.     

Air-plasma treated polyethylene fibres: effect of time and temperature ageing on fibre surface properties and on fibre-matrix adhesion

The effect of a low energy air-plasma treatment of extended chain polyethylene (ECPE) fibres (Spectra®900) on the adhesion with a matrix of epoxy resin has been studied. Surface energies of fibre and matrix were calculated by contact angles, measured with a Wilhelmy microbalance in different liquids, and the adhesion between fibres and the matrix was evaluated through a pull-out test. The results showed an increase in fibre-matrix adhesion by a factor of ca. 1.5 calculated by surface energy measurements, and by a factor of ca. 4 measured by the pull-out tests. Time (up to six months) and temperature (in the range 20–120 °C for 2 h) ageing caused some decrease in adhesion with respect to the values evaluated just after the fibre plasma treatment. The plasma treatment did not affect the fibre's mechanical properties.On leave from Dept. of Chemistry, University of Naples Federico II, Italy.     

Buffer layers for high-quality epitaxial YBCO films on Si

Efforts aimed at producing device-quality YBa₂Cu₃ O_7-δ (YBCO) films on Si, which have resulted in films with properties comparable to what can be achieved with conventional oxide substrates such as SrTiO₃, are described. It is reported how epitaxial YBCO films were grown on Si(100) using an intermediate buffer layer of yttria-stabilized zirconia (YSZ). Both layers are grown with an entirely in situ process by pulsed laser deposition (PLD). Ion channeling revealed a high degree of crystalline perfection with a channeling minimum yield for Ba as low as 12%. The normal state resistivity was 250-300 μΩ-cm at 300 K; the critical temperature, Tc (R=0), was 86-88 K, with a transition width of 1 K. Critical current densities of 2×10⁷ at 4.2 K and 2.2×10⁶ at 77 K have been achieved. Noise measurements indicate that these films are suitable for use in highly sensitive far-infrared bolometers. Applications of this technology to produce in situ reaction patterned microstrip lines are discussed     

Hermitian cubic boundary elements for two-dimensional potential problems

A hermite interpolation based formulation is presented for the boundary element analysis of two-dimensional potential problems. Two three-noded Hermitian Cubic Elements (HCE) are introduced for the modelling of corners or points with non-unique tangents on the boundary. These elements, along with the usual two-noded HCE, are used in numerical examples. The results obtained show that faster convergence can be achieved using HCE compared with using Lagrange interpolation type Quadratic Elements (QE), for about the same amount of computing resources.     

The decontamination of a disused gas works site

This paper describes work carried out at a site which was to be cleared prior to its use for erection of a large retail superstore together with its adjacent car park. A preliminary site investigation indicated that contamination, especially by tar, was widespread and that numerous underground pipes and tanks were also present. During site clearance approximately 10,000 m³ of contaminated solid material was removed and deposited in two licensed landfill sites 25 km and 40 km from the gas works. Liquid tar was adsorbed onto contaminated solids prior to disposal. A below-ground gas holder was used as a holding tank for contaminated aqueous liquids to enable suspended solids and immiscible organics to separate. After removal of contaminated material the site was covered with clean, crushed and compacted stone having known geotechnical characteristics.     

Melting performance in the single screw extrusion of thermoplastics

Melting performance experiments involving three different thermoplastics and three different screw designs have been carried out on a well-instrumented single screw extruder equipped for cold screw extractions. In the case of the particular polystyrene used it was possible to deduce, from measurements made on the extracted screw, the velocity, and hence acceleration, of the solid bed of compacted polymer at points along the screw channel. The experimental results are successfully compared with the performance predicted by a previously established model, the most important feature of which is the ability to allow the solid bed to deform freely and hence to accelerate. The results show that the bed does indeed suffer significant and non-uniform acceleration and that the model can predict both this acceleration and the resulting bed break-up which leads to surging.