ALBERT

Description: In this paper the pressure field during the early development of turbulent vortex rings at two Reynolds numbers is determined using temporally resolved two-dimensional and stereoscopic particle image velocimetry (PIV). The pressure gradient terms are obtained by solving the incompressible Euler equation so that the drag coefficients of the vortex rings can be evaluated. Maxworthy (J. Fluid Mech., vol. 64, 1974, pp. 227-239) and Glezer & Coles (J. Fluid Mech., vol. 211, 1990, pp. 243-283) each developed models to describe the long-term physics of turbulent vortex rings: the former developed a semi-empirical model which permits loss of impulse via the shedding of vorticity into the wake whereas the latter developed a similarity model based on invariance of the hydrodynamic impulse. Maxworthy's model implies that a significant correction to the similarity solution is required to account for the drag on the vortex ring bubble. We show that during the early development of the turbulent vortex rings the drag is very small and the similarity scaling can basically be retained. © 2012 Cambridge University Press.

Description: In this paper we examine the invariants p and q of the reduced 2 × 2 velocity gradient tensor (VGT) formed from a two-dimensional (2D) slice of an incompressible three-dimensional (3D) flow. Using data from both 2D particle image velocimetry (PIV) measurements and 3D direct numerical simulations of various turbulent flows, we show that the joint probability density functions (p.d.f.s) of p and q exhibit a common characteristic asymmetric shape consistent with 〈 0. An explanation for this inequality is proposed. Assuming local homogeneity we derive = 0 and q = 0. With the addition of local isotropy the sign of is proved to be the same as that of the skewness of u1/x 1, hence negative. This suggests that the observed asymmetry in the joint p.d.f.s of p-q stems from the universal predominance of vortex stretching at the smallest scales. Some advantages of this joint p.d.f. compared with that of Q-R obtained from the full 3 × 3 VGT are discussed. Analysing the eigenvalues of the reduced strain-rate matrix associated with the reduced VGT, we prove that in some cases the 2D data can unambiguously discriminate between the bi-axial (sheet-forming) and axial (tube-forming) strain-rate configurations of the full 3 × 3 strain-rate tensor. © 2013 Cambridge University Press.

Description: The statistics of the velocity gradient tensor A = ∇u, which embody the fine scales of turbulence, are influenced by turbulent 'structure'. Whilst velocity gradient statistics and dynamics have been well characterised, the connection between structure and dynamics has largely focused on rotation-dominated flow and relied upon data from numerical simulation alone. Using numerical and spatially resolved experimental datasets of homogeneous turbulence, the role of structure is examined for all local (incompressible) flow topologies characterisable by A. Structures are studied through the footprints they leave in conditional averages of the Q = -Tr(A2)/2 field, pertinent to non-local strain production, obtained using two complementary conditional averaging techniques. The first, stochastic estimation, approximates the Q field conditioned upon A and educes quantitatively similar structure in both datasets, dissimilar to that of random Gaussian velocity fields. Moreover, it strongly resembles a promising model for velocity gradient dynamics recently proposed by Wilczek & Meneveau (J. Fluid Mech., vol. 756, 2014, pp. 191-225), but is derived under a less restrictive premise, with explicitly determined closure coefficients. The second technique examines true conditional averages of the Q field, which is used to validate the stochastic estimation and provide insights towards the model's refinement. Jointly, these approaches confirm that vortex tubes are the predominant feature of rotation-dominated regions and additionally show that shear layer structures are active in strain-dominated regions. In both cases, kinematic features of these structures explain alignment statistics of the pressure Hessian eigenvectors and why local and non-local strain production act in opposition to each other. © 2015 Cambridge University Press.

Description: Three animal experiments were carried out to investigate the effect of condensed tannins (CT) on parasitic gastrointestinal (GI) nematode infections of sheep. Experiment 1 investigated the long-term effect of varying dietary levels (0–80 g/kg diet) of quebracho tannin (QT) on faecal egg counts (FEC) and feed consumption of lambs with experimental Haemonchus contortus infection. Dietary QT did not cause significant reductions in FEC although at high inclusions of QT there was an indication of a reduction in FEC. Some undesirable effects of tannins were also observed; feed consumption was significantly reduced (P

Description: It has been previously shown in this laboratory that feeding a model condensed tannin, quebracho tannin, reduces the small intestinal nematode burden in sheep and rats. The aim of the current programme was to determine whether this occurs through direct toxicity against the parasites. Both in vivo and in vitro studies were conducted. The first study compared the effect of dietary quebracho tannin (40 g/kg) on the establishment of the parasitic nematodes Nippostrongylus brasiliensis and Trichinella spiralis in the rat small intestine. The burden of N. brasiliensis, which, although closely associated with the mucosa, actually dwells within the small intestinal lumen, was significantly reduced (P0·05) by the dietary inclusion of quebracho tannin. The second study involved monitoring the survival of adult N. brasiliensis and T. spiralis when incubated in vitro in varying concentrations of quebracho tannin in Hanks’ balanced salt solution. The survival of N. brasiliensis was compromised at concentrations as low as 0·01% (w/v) quebracho tannin but improved with the addition of 0·1% (w/v) polyethylene glycol, which binds to, and inactivates, tannin. T. spiralis was similarly affected, but much more rapidly. These results suggest that dietary quebracho tannin may reduce nematode worm burdens through a toxic effect that requires direct contact between parasite and tannin. This raises the possibility that feeding locally available plant material containing condensed tannins may be an alternative method for controlling parasite infections, especially in areas such as the tropics and subtropics.

Description: The aim of this study was to determine whether the inclusion of a condensed tannin (quebracho tannin, QT) and/or the elevation of dietary protein could reduce Trichostrongylus colubriformis establishment and existence in the small intestine of lambs. Thirty-six lambs (mean liveweight 32·6±3·9 kg) were randomly allocated to one of six experimental groups, groups 1–5 were parasitized with a trickle infection of 3000 infective Trichostrongylus colubriformis larvae daily, whilst group 6 remained as uninfected controls. Experimental diets were formulated to contain 222 g CP/kg (high protein) or 97 g CP/kg (low protein) with or without the inclusion of 50 g QT/kg. All six animal groups were fed the low protein diet, group 2 fed low protein diet+QT, for one month prior to infection (groups 1–5). Once nematode eggs were observed in the faeces, diets were abruptly changed in three experimental groups. Group 1 remained on the low protein diet, group 2 remained on the low protein+QT diet, group 3 changed to the high protein diet, group 4 changed to the high protein+QT diet, group 5 changed to the low protein+QT diet and group 6 remained uninfected and fed the low protein diet. Production, haematological and parasitological parameters were monitored at regular intervals. Results show that parasitized animals fed the high protein diet achieved growth rates similar to those of uninfected low protein-fed lambs. Inclusion of dietary QT did not depress liveweight gain. Total daily faecal egg counts declined after feeding the high protein diet. Inclusion of QT into the low protein diet also reduced faecal egg counts to similar levels observed in the high protein-fed lambs. The inclusion of QT into the high protein diet did not further reduce faecal egg counts. No significant differences in the haematological parameters measured were observed between infected animals (groups 1–5), suggesting that the beneficial effect of dietary QT in the low protein diet is unlikely to be mediated through an immune response. These data suggest that the inclusion of QT in low protein diets may be an alternative to feeding high protein diets to reduce nematode burden in lambs.

Description: By a variety of exposure routes it is possible that the toxic heavy metals cadmium, arsenic and mercury could enter the diet of farm animals and hence contaminate food products derived from those animals. Therefore, there is a need to be able to assess the likely levels of contamination in animal tissues if exposed to contaminated feed and also to estimate how rapidly an animal will decontaminate once the source of contamination is removed from the feed. The development of dynamic models to predict changes in the degree of heavy metal contamination in tissues of ruminants have been hindered by the lack of data on the transfer and excretion rates of these metals from tissues. A study is described during which dairy cows were given a single intraruminal administration of 109Cd, 73As and 203Hg and measurements made of the subsequent concentrations of the radioisotopes in body tissues and milk. The resultant data were used to adapt previously developed compartment models describing the behaviour of the metals in sheep for use with dairy cows. Two changes were made to the sheep models: (i) a new excretion route was included to describe transfer to milk; (ii) the rate coefficients (with the exception of those involving gut absorption and transfer) were adjusted according to the ratio of the metabolic live-weights (live-weight (kg)0·75) of the sheep to that of the cattle. The models predicted levels of the metals in the cattle tissues and milk reasonably well.

Description: The carbonate matrix of several pyroclastic tuff rings and cones in the Monduli-Arusha area of northern Tanganyika, is believed to be of volcanic carbonatitic origin. One of the pyroclastic tuff rings contains ejected blocks of ultrabasic composition which are minera-logically similar to the cognate xenoliths found in kimberlite pipes.

Description: The writer had the opportunity last summer, with Dr. B. J. Harrington as assistant, to re-examine the rock formations of Prince Edward Island, of which a notice was given in the second edition of his “Acadian Geology.” The report of our reconnaissance, which has been published by the local government, with a map, sections, and figures of fossils, may be referred to for details; but I propose in this paper to notice a few points of general scientific interest not dwelt on in the report.