ALBERT

Description: summaryMesomorphic, stress-sensitive Pietrain pigs were found to have a lower insulin secretory response to intravenous tolbutamide, glucose and arginine, when compared with ectomorphic, stress-resistant Large White pigs. Pietrain pigs have also been observed to be insulin-insensitive in comparison with Large White pigs. The combination of a low production of and low sensitivity to insulin in the Pietrain breed could account for their enhanced sensitivity to lipolytic agents and for their reduced ability to deposit body fat.

Description: SUMMARYCalves were reared on milk replacer up to 5 weeks of age and given ad libitum access to pellets and chopped straw from 1 to 10 weeks of age. Major ingredients of the pellets were ground barley (B) or ground barley and grass meal in a 6:4 ratio (G). Included in these two basal diets were NaCl or NaHCO3, each at 2, 11, 20 or 29 g Na/kg D.M.Calves on G diets ate more than those on B diets but grew at a similar rate. The replacement value of grass meal for ground barley was 1·36:1. Most responses to Na inclusions were unaffected by the basal diets.Before weaning there were linear increases in food intake and growth rate related to Na level in the diet. At 29 g Na/kg D.M., total D.M. intake/kg0.75 and growth rate were respectively 31 and 23% greater than at 2 g Na/kg D.M. After weaning there were differential responses to the two salts. With NaHC03 there were linear increases in food intake and growth rate up to 20 g Na/kg D.M., at which level total D.M. intake/kg0.75 and growth rate were respectively 36 and 44% greater than at 2 g Na/kg D.M. With NaCl the only significant response was that total D.M. intake at 11 g Na/kg D.M. was 16% higher than at 2 g Na/kg D.M.Observations on acid-base balance and water intake indicated that inclusions of NaCl or NaHCO3 up to 20 g Na/kg D.M. were well tolerated by calves. Above this level there was a sharp increase in water intake, and with NaHCO3 there was a large base excess and high pH in the blood.

Description: SUMMARYS.24 perennial ryegrass was conserved by ensiling directly (control) and after treatment with a solution of formaldehyde at the rate of 6 g HCHO/100 g crude protein. After storage for 90 days, part of the formaldehyde-treated silage was dried in a high-temperature drier.The quantitative digestion of the energy, carbohydrate and nitrogen moieties of the three diets and the production of volatile fatty acids and microbial protein within the rumen were measured using five sheep fitted with re-entrant cannulae at the proximal duodenum and terminal ileum.Treatment with formaldehyde depressed organic matter and energy digestion within the rumen compared with untreated silage (P 〈 0·001) and a further depression was observed on the dehydrated material. Both formaldehyde-treated silages showed enhanced flows of total amino acids into the small intestine compared with the control silage and net absorption from the small intestine was elevated by 13 and 21% respectively on these two diets. On the untreated silage over 71% of the protein entering the small intestine was microbial in origin whereas, due to depressed microbial growth and increased protection of feed protein from rumen fermentation, microbial protein comprised only 17% of duodenal protein on the two formaldehyde-treated silage diets. Fifteen and 81 % of the dietary protein passed undegraded through the stomachs to the duodenum on the control and the two formaldehyde-treated silage diets respectively.Total VFA production within the rumen was not significantly influenced by the treatments imposed, but on the untreated silage only 56% of the energy apparently digested in the rumen was converted to VTA energy whilst a mean value of 74% was recorded on the other two diets.Estimates of the total energy absorbed gave values of 10·6, 11·9 and 10·7 MJ/kg D.M. for the control, formaldehyde and dried, formaldehyde silage diets with absorbed protein energy representing 21, 22 and 26% of the total absorbed energy respectively.

Description: We have observed two novel manifestations of the Weissenberg effect in viscoelastic liquids which are set into motion by the rotation of a circular rod. In the first experiment we floated a layer of STP on water. The STP climbs up the rod into the air and down the rod into the water. The ‘down-climb’ is much larger than the ‘up-climb’, their ratio being roughly the square root of the density difference (STP-air)/ (water–STP). The magnification of the down-climb may be regarded as normal-stress amplification. † The magnitudes of the up- and down-climbs are simultaneously in good agreement with the predictions of a theory of rod climbing when the angular frequency of the rod is small. In the second experiment, we set the rod into torsional oscillations. When the amplitude of the oscillation is small, the fluid climbs the rod; the climb is divided into an axisymmetric steady mean part and an oscillating part (Joseph 1976b; Beavers 1976). The mean axisymmetric climb dominates the total climb at low frequencies. At a higher critical speed the axisymmetric climbing bubble loses its stability to another time-periodic motion with the same period but with a ‘flower’ pattern displaying a certain integral number of petals. © 1977, Cambridge University Press. All rights reserved.

Description: Equations governing the current system in the upper layers of oceans and lakes were derived by Craik & Leibovich (1976). These incorporate the dominant effects of both wind and waves. Solutions comprising the mean wind-driven current and a system of ‘Langmuir’ cells aligned parallel to the wind were found for cases in which the wave field consisted of just a pair of plane waves. However, it was not clear that such cellular motions would persist for the more realistic case of a continuous wave spectrum. The present paper shows that, in the latter case, infinitesimal spanwise periodic perturbations will grow on account of an instability mechanism. Mathematically, the instability is closely similar to the onset of thermal convection in horizontal fluid layers. Physically, the mechanism is governed by kinematical processes involving the mean (Eulerian) wind-driven current and the (Lagrangian) Stokes drift associated with the waves. The relationship of this mechanism to instability models of Garrett and Gammelsrød is clarified. © 1977, Cambridge University Press. All rights reserved.

Description: 1. For experimental purposes the treatment of cotton seed with sulphuric acid, prior to planting, has always been the custom at Barberton. In view of the doubts about the benefits of this treatment which were expressed by Christidis (1936), experiments were carried out at Barberton in the 1938–9 and 1939–40 seasons, to provide concrete proof, if possible, of the advantages which it was believed resulted from it.2. A series of stand counts made soon after germination revealed definite benefits with acid treatment, in all experiments in both seasons. The seedlings emerged considerably earlier than those from untreated seeds, and the stands recorded at the final counts revealed a significant advantage for acid-treated seed, throughout the experiments. The second season's experiments gave a greater advantage for acid treating when meteorological conditions were bad than when they were good, but the advantage even with ideal weather was still significant. The benefit of acid treatment was shown to be greater, too, with poor samples of seed than with good, and with the smaller seed rate than with the greater.

Description: 1. Experience raised doubts as to the usefulness of filling gaps in bad stands of cotton at Barberton and experiments were conducted in two seasons to measure its effectiveness. The experiments gave clear-cut results.2. Randomized gaps ranging from 20 to 40% of the stand were filled and left open for comparison, the filling being done 13 and 19 days after planting.3. Any reduction in stand, though reducing yield per acre, led to large and significant increases in yield per plant, even when the spacing was 3 by 3 ft., wider than that normally used on the Station.4. Replanting the gaps in a bad stand did not lead to any increase in yield per acre; there were, in fact, indications that this practice actually reduced yield per acre, the refills preventing plants of the original sowing from benefiting fully from the extra space available to them in a bad stand.5. The general conclusion is that no useful purpose is served by refilling the gaps in poor stands of cotton with up to 40% of gaps.

Description: The oscillation of the wall shear stress caused by imposing sound on a turbulent boundary-layer flow constitutes a boundary condition for the solution of the acoustic wave equation. The no-slip condition at the wall requires the excitation of a shear wave which is superimposed on the sound wave. The shear wave propagates into the turbulent medium. The wall impedance (shear stress/velocity) of streamwise polarized shear waves has been measured in two different ways, namely (a) by evaluating the phase velocity and the attenuation of a plane sound, wave which propagates in turbulent pipe flow, and (b) by evaluating the resonance frequency and the quality factor of a longitudinally vibrating glass pipe which carries turbulent flow. The results, which were obtained over a wide range of Strouhal numbers, exhibit very good agreement between the two measuring methods. The wall shear stress impedance is strongly affected by the turbulence. This indicates that the turbulent shear stress is modulated by the shear wave. At all measuring conditions, the propagation of the shear wave was confined essentially to the inner portion of the turbulent boundary layer. In principle, two different Strouhal numbers, based on inner and outer variables respectively, describe the dynamics of the Reynolds stress, even in the inner layer (Laufer & Badri Narayanan 1971). However, it turns out that the outer Strouhal number (based on the diameter and the centre-line velocity) has no noticeable effect on the wall shear stress impedance. The dependence of the impedance on the inner Strouhal number (based on the friction velocity and the viscosity) reveals that the shear wave is strongly reflected at the edge of the viscous sublayer. It is concluded that the stress-to-strain ratio at the edge of the viscous sublayer corresponds either to a viscoelastic medium or even to a medium with negative viscosity. © 1977, Cambridge University Press. All rights reserved.

Description: A photogrammetrical technique has been used to study the interaction of two identical explosively produced spherical shock waves and to compare this interaction with the reflexion of one of the spherical shocks from the ground. It is postulated that there was no energy loss in the interaction of the two shock waves and that the interaction therefore simulated the reflexion of a spherical shock from an ideal non-energyabsorbing surface. The ‘ideal’ reflexions were compared with real reflexions from two types of ground surface: One smooth and the other rough. Experiments were carried out with the centres of the spherical shocks at two separations so that observations could be made of the interaction of shocks of different strength. Significant differences were shown to exist in both the strengths of the Mach shocks and in the triple-point trajectories over the different surfaces. The results are intended to aid in the evaluation of computer codes being developed to simulate spherical-shock reflexions from real surfaces. © 1977, Cambridge University Press. All rights reserved.

Description: This is a review of an IUTAM symposium held in Canberra on 20–23 July 1976. The subject matter ranged widely: From surf on beaches to waves of oceanic scale, and from elegant analysis to observations from tide gauges. © 1977, Cambridge University Press. All rights reserved.