Direct simultaneous measurement of rotational and translational accomodation coefficients

When molecules of a low density diatomic gas strike a solid surface both translational energy and the internal energy modes of rotation and vibration will contribute the energy exchange that occurs. Theoretical studies indicate that accomodation coefficient for rotational energy should be less than that for translational energy, and this is confirmed by experimental results. The experimental apparatus described in this paper uses the electron bream fluorescence detector to measure simultaneously both rotational and translational energy accommodation coefficients of room temperature nitrogen reflecting from a solid surface. A bakeable ultra high vacuum system was built to provide a clean vacuum environment for control of the solid surface properties. In addition to being the only known direct measurement of rotational accomodation coefficient the system offers an advantage over some previous methods of translational accommodation measurement in that there are few restrictions on solid surface temperature or composition.     

Graphite thermal expansion relationship for different temperature ranges

For practical reasons, the coefficient of thermal expansion (CTE) has to be measured over a particular temperature range, for example 20-120 °C, 20-400 °C or 500-700 °C. However, in many cases, engineers or scientists involved in the assessment of graphite components such as nuclear reactor moderator bricks, electrodes or moulds require CTE over temperature ranges other than that of the original measurement. This paper compares three different techniques used to convert CTE from one temperature range to another. The method used by the UK nuclear industry is compared with techniques proposed by two international companies. There was close agreement between two of the methods. However there was some divergence in the case of the third method. This may be related to the type of graphite (fine-grain) for which the third method was developed.     

A standard Pascal event simulation package

A package implemented using standard Pascal is described. It provides the user with basic tools for discrete event-orientated simulation, and includes facilities for scheduling and causing pending events, handling of LIFO and FIFO queues, control of periodical dumping of statistics and comprehensive initialization and error routines. Two versions of the package have been implemented, using tree and linked list structures for scheduled events. Their relative performances are compared. The tree structure proves to be more efficient except in the minority of cases where the set of scheduled events has to be searched frequently; it also provides a much more efficient scheduling algorithm than does a linked list structure. This package is primarily intended as a communication network design tool, and a simple example of this type of usage is included. It could also be used in undergraduate teaching. Coding examples are given for the main procedures, in the two implementations.     

Use of organic acids for the control of Clostridium perfringens in cooked vacuum-packaged restructured roast beef during an alternative cooling procedure

This study was conducted to determine how well Clostridium perfringens spores germinate and grow in restructured roast beef treated with different commercial organic salts during an alternative chilling procedure. The meat was prepared according to an industrial recipe (10% water, 1.5% sodium chloride, and 0.5% sodium triphosphate). The base meat was treated with sodium citrate at 2 or 4.8% (wt/wt), buffered to a pH of 5.6, 5.0, or 4.4 (six treatments); a 60% (wt/wt) solution of sodium lactate at 2 or 4.8% (wt/wt); sodium acetate at 0.25% (wt/wt); or sodium diacetate at 0.25% (wt/wt). Untreated meat was used as a control. Meat samples were inoculated with a three-strain cocktail of C. perfringens spores (strains ATCC 10388, NCTC 8238, and NCTC 8239). Meat was vacuum packaged in bags and cooked in a stirred water bath to an internal temperature of 75 degrees C for 20 min, and then the bags were cooled from 54.4 to 4.4 degrees C within 18 h. Samples were taken after inoculation, after cooking, and after chilling. Spore and vegetative cell counts were obtained after incubation at 37 degrees C for 8 to 10 h in Fung's Double Tubes containing tryptose sulfite agar without egg yolk enrichment. Cooking was not sufficient to eliminate C. perfringens spores. Over the 18-h cooling period, sodium citrate, sodium lactate, and sodium diacetate reduced the growth of C. perfringens to < 1 log unit, a growth level that meets U.S. Department of Agriculture performance standards. The use of sodium citrate or sodium lactate at a concentration of > or = 2% (wt/wt) inhibited C. perfringens growth over the 18-h cooling period.     

Rural mobilization as rural development: exploring the impacts of new regionalism in Wales and Finland

In the current European context, ‘rural development’ is now a much over‐used and misunderstood term. Far from denoting a specific concern for the particular social and economic problems of ‘peripheral rural communities’, since the Cork Declaration of 1996, European policy making, both at central and regional levels, has more meaningfully adopted broader principles of ‘integrated rural development’. However, while many member states are beginning to move away from a sectoral ‘silo’ approach with regard to the management of their rural areas, in recent years the parallel arenas of environmental, cultural, regional and economic development agendas have all become much more vibrant. Looking at the rural regions of Wales in the UK and Ostrobothnia in western Finland, this paper examines some of these contemporary and parallel arenas with regard to their influence in shaping the nature of rural governance. While a rural development policy network is seen to be developing, major questions are raised about how this will position itself in the unfolding multi‐level governance structure.     

Compliant layer acetabular cups: friction testing of a range of materials and designs for a new generation of prosthesis that mimics the natural joint

Total joint replacements (TJRs) have a limited lifetime, but the introduction of components that exhibit good lubricating properties with low friction and low wear could extend the life of TJRs. A novel acetabular cup design using polyurethane (PU) as a compliant layer (to mimic the natural joint) has been developed. This study describes a series of friction tests that have been used to select the most appropriate material, optimize the design parameters, and fine-tune the manufacturing processes of these joints. To determine accurately the mode of lubrication under which these joints operate, a synthetic lubricant was used in all these tests. Friction tests were carried out to assess the lubrication of four PU bearing materials. Corethane 80A was the preferred material and was subjected to subsequent testing. Friction tests conducted on acetabular cups, manufactured using Corethane 80A articulating against standard, commercially available femoral heads, demonstrated friction factors approaching those for full-fluid-film lubrication with only approximately 1 per cent asperity contact. As the joint produces these low friction factors within less than half a walking cycle after prolonged periods of loading, start-up friction was not considered to be a critical factor. Cups performed well across the full range of femoral head sizes, but a number of samples manufactured with reduced radial clearances performed with higher than expected friction. This was caused by the femoral head being gripped around the equator by the low clearance cup. To avoid this, the cup design was modified by increasing the flare at the rim. In addition to this the radial clearance was increased. As the material is incompressible, a radial clearance of 0.08 mm was too small for a cup diameter of 32 mm. A clearance of between 0.10 and 0.25 mm produced a performance approaching full-fluid-film lubrication. This series of tests acted as a step towards the optimization of the design of these joints, which has now led to an in vivo ovine model.     

Dynamics and generation of stress waves in cracked graphite moderator bricks

In the present study, static and dynamic analyses have been performed for graphite moderator bricks with and without key grooves under the different initial loading conditions of pure bending and slot rotation by using the finite element method. The possibilities of the occurrence of multiple cracking due to internal stresses have been investigated in terms of the (1) initial loading condition; (2) vibration mode shapes; and (3) damping of the bricks. Firstly, modal dynamic analysis has been carried out, and the effect of the initial loading conditions, such as pure bending and slot rotation, on the dynamic stress responses was investigated. It was found that stress enhancement was more significant under the condition of pure bending than that of slot rotation. For pure bending, the key groove which was opposite to the primary cracking site had the maximum dynamic circumferential stress. This implied that secondary cracking might occur at this position under pure bending. Secondly, in order to investigate the dominant mode shape for the stress enhancement, natural frequency analysis has been conducted. Fast Fourier Transformation (FFT) has also been performed to convert time–domain stress responses into frequency–domain stress responses. The initial loading conditions determined which mode shape was dominant for the stress enhancement. It was also suggested that a fundamental mode shape principally contributed to the occurrence of the multiple cracking. Thirdly, modal damping analysis has been performed, and the effect of damping on the stress enhancement was studied. It was found that damping had little effect on the initial peak of the dynamic stress response. This suggested that secondary cracking might still occur at the key groove opposite the primary cracking site, even if damping was present. The results of the analysis give a fundamental insight into the mechanism that may lead to multiple cracking in graphite components subject to internal stresses. However, the effects of 3-D, crack propagation speed and external restraint have not been taken into consideration in the present study. These effects may mitigate the possibility of secondary cracking, and are parts of further investigation.