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Notes: A novel fibre optic sensor system has been developed for detection of acoustic emission.The sensor design was based on a 2×2 fused tapered optical fibre coupler configuration. Given theintended use of this sensor for the detection of acoustic emission in smart materials and structures,its lightweight, compatibility with composite material and immunity from electromagneticinterference are great advantages. Apart from the performance specification and reliability, theoverall cost of the sensor system is a major factor in their adoption by end-users. The manufacturingof this sensor is low-cost and the signal output from the sensor system developed can be directly fedto the commercial AE acquisition system. The demonstration of acoustic emission detection wasconducted using fibre coupler-based AE sensors in different materials and structures. The AEsources are various and depend on the different applications. In the current paper, we report on theuse of the fibre optic AE sensor system for concrete damage monitoring. An experiment on damagedetection on a composite plate with this fibre optical AE sensor is also reported in the paper

Notes: Summary Large mammals that formerly occupied the Kariba basin of the Middle Zambezi Valley have, since it was flooded, been forced to live in a restricted range of deciduous woodland habitats. Feeding records in a study area on the shore of Lake Kariba showed that most herbivore species were browsers, and that only the tree components of their diets varied significantly between vegetation types. The common species varied a proportion of their diet seasonally. However, each depended upon a small range of food staples which differed from those of other species and acted as food refuges for part of the year. Diets overlapped during the wet season because of diversification, and in the late dry season because of common use of a restricted range of plants remaining green. There was a good correlation between the ability of a species to avoid dietary overlap and its biomass in the study area. The chance of interspecific competition occurring increased in the late dry season when most of the species would formerly have migrated from the study area to the flood plain. Despite the enforced occupation of only part of their former annual range the more common herbivores maintained a considerable degree of ecological separation through utilisation of different foods.

Notes: Summary The export of 14C from leaves of Lycopersion esculentum (Mill.), Capsicum frutescens (L.) and Amaranthus caudatus (L.) was followed by in vivo counting after exposure of the leaf to a 5 min pulse of 14CO2. In all instances the time course of export showed two or more exponential phases. There was an initial rapid period of export which was followed by a slower phase after about 2 h. About 12–14 h after exposure to 14CO2 this second phase was superseded by an even slower phase of export which continued for more than 24 h. In tomatoes the initial phase was most rapid in plants bearing fruit which had been heated to 30°C instead of the standard 15–20°C; it was slowest when the fruit were removed. In Amaranthus the rate of the initial phase was shown to be positively correlated with photosynthesis and when the latter was prevented by either darkness or the absence of CO2 the rate of loss of 14C was reduced. The data were used to test a model of carbon movement from a leaf which postulated the presence of two carbon pools which turned-over at different rates. The photosynthetic carbon entered the pool with the faster rate of turn-over—the ‘labile’ pool—and exchanged with the other, ‘storage’, pool. Export from the leaf was from the ‘labile’ pool. The results suggested that a third, longer term, storage pool should be included in the model and that the exchange between the pools should be non-linear.

Notes: Abstract The onset of sonically induced cavitation in liquid helium at frequencies between 30 and 40 kHz has been studied. In helium II, two types of cavitation activity were identified: acoustic cavitation whose characteristic noise can be detected, and visible cavitation in which vaporous cavities grow to visible size. The onset of acoustic cavitation is statistical in nature with increasing event rates as the sound pressure amplitude is increased and whose threshold depends on the waiting time at that particular amplitude. The acoustic threshold sound pressure amplitude in helium II between 1.8° K andT λ was found to lie within 0.15 mb of 0.3 mb, the variation of ±0.15 mb occurring from one determination to another, whereas the sound pressure amplitude corresponding to the visible threshold was about a hundred times larger. These two distinct types of sonically induced cavitation appear to be unique to liquid helium. However, aboveT λ the two thresholds were found to coincide at a sound pressure amplitude within 0.4 mb of 0.8 mb. The characteristics of the onset of acoustic cavitation were found to be independent of applied static pressure of up to 1.5 atm above and belowT λ and in helium II they were unaffected by filtering, heat flushing, or rotating the liquid. The results suggest that liquid helium is nucleated by random events initiated by the ambient cosmic radiation or by vortices generated in the liquid, and they imply that at ultrasonic frequencies this liquid cannot withstand a tensile stress and behaves in this respect like water saturated with gas and containing dust motes. Attempts to determine the onset of acoustic cavitation by scattering light off the bubbles or by detecting sonoluminescence were not successful: The upper limit to the size of these bubbles was shown to be about 30 µm and the intensity of any sonoluminescence must have been less than 10−4 of that from cavitating water. The possibilities of exploiting the two types of cavitation activity in liquid helium in the construction of a posttriggerable ultrasonic bubble chamber for visualizing the tracks of ionizing particles are discussed, as are the theoretical background and future development of the work presented in this paper.