Chemical etching of optical fibre tips - experiment and model

The formation of chemically etched fibre tips for use in optical scanning probe microscopy is addressed. For tips formed at a cleaved fibre end in the bulk of a buffered HF acid solution the morphological features (tip height, cone angle) are found to depend strongly on the temperature and etchant composition. The tip formation process is analysed and explained in terms of a simple model in which the only pertinent physical parameters are the fibre core diameter and etch rates of the fibre core and cladding. The etch rates are determined in separate experiments as a function of temperature (in the range 24-50 degreesC) for etchant solutions of de ionised water: 50% HF acid: 40% NH4F in the volume ratio 1 : 1 : X for X=2, 4 and 6, and used in the model to yield a correct description of the experimental tip cone angles. The model is successfully extended to the intriguing case of negative tip formation which initiates in a normal, positive tip structure. By contrast, tip formation in the meniscus region of a bare fibre/etchant/organic solvent system is found to be independent of etchant composition and temperature. (C) 2000 Elsevier Science B.V. All rights reserved.

Thermoforming carbon fibre-reinforced thermoplastic composites

The use of carbon fibre composites is growing in many sectors but their use remains stronger in very high value industries such as aerospace where the demands of the application more easily justify the high energy input needed and the corresponding costs incurred. This energy and cost input is returned through gains over the whole life of the product, with for example, longer maintenance intervals for an aircraft and lower fuel burn. Thermoplastic composites however have a different energy and cost profile compared to traditional thermosets with notable differences in recyclability, but this profile is not well quantified or documented. This study considers the key process control parameters and identifies an optimal window for processing, along with the effect this has on the final characteristics of the manufactured parts. Interactions between parameters and corresponding sensitivities are extracted from the results.

The effect of increasing dietary fibre and the provision of straw racks on the welfare of sows housed in small static groups

This study assessed the effects of increasing dietary fibre levels in concentrate rations and providing access to straw in racks on the welfare of pregnant sows housed in small static groups. In a 2 x 2 factorial design experiment, 128 Large White x Landrace pregnant sows were offered one of two diets: (i) High fibre diet with 9% crude fibre, or (ii) Control diet with 4.5% CF, and one of two levels of access to a foraging substrate: (i) access to straw in racks or (ii) no straw. The study was replicated eight times using groups of four sows, and treatment periods lasted four weeks. Sows were housed in pens with voluntary cubicles and a slatted exercise area and were offered a wet diet twice a day. Back-fat levels were measured before sows were mixed into groups at 28 days post partum, and four weeks later. Aggressive interactions were recorded on the day of mixing, and injury scores were recorded one week post mixing. Scan sampling was used to collect data on general activity, posture and location of the sows, and on sham-chewing and bar-biting behaviours across the treatment period. In addition, detailed focal observations were carried out on all sows across the treatment period. Straw usage was also recorded. There were no treatment effects on changes in back-fat levels over the treatment period. Treatments had no effect on post-mixing aggression or on injury scores. However, focal observations showed that sows with access to straw were involved in fewer bouts of head-thrusting over the treatment period. Control diet sows spent more time inactive than sows on the high fibre diet, however high fibre diet sows spent more time lying with eyes closed than sows on the control diet. Sows on the high fibre diet with access to straw showed less sham-chewing and bar-biting behaviour than sows in other treatments. These results show that although a diet containing 9% crude fibre promoted resting behaviour, it was necessary to combine it with access to straw to reduce stereotypic behaviour of sows in small static groups.