Traditional methods of monitoring health changes in animals are based entirely on the human senses. However, in modern dairy production systems humans are rarely present, this is particularly the case with the introduction of robotic milking. In these systems all the functions of milking are automated and cows visit at times of their own choosing. Systems of automatic health monitoring are therefore a priority for research to ensure that the health and reproductive status of the animals can be assessed for management purposes. These systems must be automatic, work in ¢eld conditions without technical support and cost a few pence per analysis. The ¢rst task is to obtain representative biological samples automatically and non-invasively. As milk is £owing into the milking machine from the cow this can be achieved with ease, except that milk is non-homogeneous with a changing lipid fraction during milking. Lipid soluble components such as progesterone and vitamin A are a¡ected by this change and a model has to be established to determine thresholds at di¡erent times during milking. Our main interests in dairy cows are in predicting ovulation, detecting metabolic imbalance and detecting preclinical mastitis in£am-matory response. Our team is developing a fully automated ovulation prediction system based on the screen-printed carbon electrode biosensor for progesterone demonstrated by Pemberton et al. (1998). In recent experiments the automated system was able to detect concentrations of progesterone between 2 and 30 ng/ml in stored milk samples (r 2 = 0.96). The results of ¢eld tests are presented showing a good correlation between ELISA and the biosensor (r 2 = 0.91) on samples of fresh milk. The results of the recent ¢eld tests show the ability of the biosensor to characterise ovulation cycles of cows and to detect pregnancy. We have identi¢ed a major lack of other biological models to detect disease with on-line sensors. Our next objective is to create an integrated system for biological research with sensor systems for urea, ketones, lipids and enzymes in milk. This will allow the development of diagnostic models based on analysing numerical sensor-derived data rather than human visual observations for signs of ill health in dairy cows.

Theories explaining the dependence of characteristic X-ray intensity on particle size in heterogeneous materials are reviewed. Several discrepancies between the theories and between theory and experiment have been discovered. A new theory is proposed based on a more rigorous physical model. It is shown to explain well-established phenomena at least as precisely as do previous formulae. Excellent agreement is also obtained with new observations of the variation of characteristic X-ray intensity with packing degree and, in samples consisting of only one type of particle, with both packing degree and particle size. The same basic theory also predicts the observed variation of X-ray Intensity backscattered from or transmitted through a sample. It is also shown that similar results are obtained with particles suspended In a homogeneous matrix, such as an aqueous slurry.

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VISTA is a 4-metre survey telescope currently being constructed on the NTT peak of ESO's Cerro Paranal Observatory. The telescope will be equipped with a dedicated infrared camera providing images of a 1.65 degree field of view. The telescope and camera are of an innovative f/3.26 design with no intermediate focus and no cold stop. The mosaic of 16 IR detectors is located directly at Cassegrain focus and a novel baffle arrangement is used to suppress stray light within the cryostat. The pointing and alignment of the telescope and camera is monitored by wavefront sensing elements within the camera cryostat itself. This paper describes the optical, mechanical, electronic and thermal design of the combined curvature sensor and auto-guider units positioned at the periphery of the camera field of view. Centroid and image aberration data is provided to the telescope control system allowing real time correction of pointing and alignment of the actively positioned M2 unit. Also described are the custom optics, mounted in the camera filter wheel, which are used to perform near on-axis high order curvature sensing. Analysis of the corresponding defocused images allows calibration tables of M1 actuator positions to be constructed for varying telescope declination and temperature.