Ultrasound is re®ected from a liquid layer between two solid bodies. This re®ection depends on the ultrasonic frequency, the acoustic properties of the liquid and solid, and the layer thickness. If the wavelength is much greater than the liquid-layer thickness, then the response is governed by the sti¬ness of the layer. If the wavelength and layer thickness are similar, then the interaction of ultrasound with the layer is controlled by its resonant behaviour. This sti¬ness governed response and resonant response can be used to determine the thickness of the liquid layer, if the other parameters are known.In this paper, ultrasound has been developed as a method to determine the thickness of lubricating lms in bearing systems. An ultrasonic transducer is positioned on the outside of a bearing shell such that the wave is focused on the lubricant-lm layer. The transducer is used to both emit and receive wide-band ultrasonic pulses. For a particular lubricant lm, the re®ected pulse is processed to give a re®ection-coe¯cient spectrum. The lubricant-lm thickness is then obtained from either the layer sti¬ness or the resonant frequency.The method has been validated using ®uid wedges at ambient pressure between ®at and curved surfaces. Experiments on the elastohydrodynamic lm formed between a sliding ball and a ®at surface were performed. Film-thickness values in the range 50{ 500 nm were recorded, which agreed well with theoretical lm-formation predictions. Similar measurements have been made on the oil lm between the balls and outer raceway of a deep-groove ball bearing.

Quantifying the contribution of wild (naturally spawned) and hatchery Chinook salmon (Oncorhynchus tshawytscha) to the mixed-stock ocean fishery is critical to understanding their relative importance to the persistence of salmon stocks. The inability to distinguish hatchery and wild salmon has inhibited the detection of declines or recoveries for many wild populations. By using Chinook salmon of known hatchery and wild origin, we established a baseline for separating these two sources using otolith microstructure. Otoliths of wild salmon contained a distinct exogenous feeding check likely reflecting an abrupt transition in food resources from maternal yolk not experienced by fish reared in hatcheries. Daily growth increments in otoliths from hatchery salmon immediately after the onset of exogenous feeding were wider and more uniform in width than those in wild fish. The discriminant function that we used to distinguish individuals reared in hatcheries or in the wild was robust between years (1999 and 2002), life history stages (juveniles and adults), and geographic regions (California, British Columbia, and Alaska) and classified fish with ~91% accuracy. Results from our mixed-stock model estimated that the contribution of wild fish was 10% ± 6%, indicating hatchery supplementation may be playing a larger role in supporting the central California coastal fishery than previously assumed.

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Otolith Sr:Ca ratios near primordia (Sr:CaCore) have been used to distinguish progeny of resident and anadromous Oncorhynchus mykiss and to estimate rates of exchange between the two forms; however, the influences of confounding variables on Sr:CaCore have not been quantified. We analyzed Sr:CaCore in juvenile O. mykiss produced at 13 California hatcheries that spawn primarily resident or anadromous broodstock. Mean Sr:CaCore of progeny of resident females increased with increasing Sr:Ca ratio of the stream (Sr:CaWater) in which the mother spawned (r 2 = 0.71). Mean Sr:CaCore of progeny of anadromous females averaged 1.0  10 -3 higher, also increased with Sr:CaWater, and decreased with increasing migratory difficulty (distance  elevation) of the mother (r 2 = 0.96). Model results predict that discrimination of sympatric progeny is equally good among streams where Sr:CaWater is less than 5 mmolÁmol -1 , but limited at higher Sr:CaWater or when anadromous females return to freshwater 6 months or more before spawning (e.g., summer steelhead). The models also provide an alternative method of interpreting Sr:CaCore data that can improve discrimination between sympatric progeny. Analysis of adults from one stream and eight hatchery sites suggested that resident females made little or no contribution to populations of anadromous adults, but anadromous females contributed to populations of resident adults.Résumé : Les rapports Sr:Ca des otolithes près du primordium (Sr:Ca noyau ) ont servi à distinguer la progéniture d'Oncorhynchus mykiss résidants et anadromes et à estimer les taux d'échange entre les deux formes; cependant, les influences des variables confondantes sur Sr:Ca noyau n'ont jamais été mesurées. Nous avons analysé les Sr:Ca noyau chez de jeunes O. mykiss produits dans 13 piscicultures de Californie qui font principalement de la reproduction de stocks reproducteurs résidants ou anadromes. Le rapport Sr:Ca noyau moyen des petits des femelles résidantes augmente avec l'accroissement du rapport Sr:Ca du cours d'eau (Sr:Ca eau ) dans lequel la mère fraye (r 2 = 0,71). Le rapport Sr:Ca noyau moyen des petits de femelles anadromes est en moyenne de 1,0  10 -3 plus élevé, il augmente aussi avec la valeur de Sr:Ca eau et il décroît en fonction de la difficulté de la migration (distance  altitude) de la mère (r 2 = 0,96). Les résultats de notre modélisation prédisent que la discrimination des petits vivant en sympatrie est également bonne dans les cours d'eau où Sr:Ca eau est moins de 5 mmolÁmol -1 , mais la discrimination est limitée aux valeurs plus élevées de Sr:Ca eau ou lorsque les femelles anadromes retournent en eau douce six mois ou plus avant la fraie (par ex., les truites arc-en-ciel anadromes d'été). Les modèles fournissent aussi une méthode de rechange pour l'interprétation des données de Sr:Ca noyau qui peut améliorer la discrimination entre les petits qui vivent en sympatrie. Une analyse d'adultes provenant d'un cours d'eau et de huit sites de pisciculture indique que les femelles résidantes fournis...