This book, first published in 1998, treats turbulence from the point of view of dynamical systems. The exposition centres around a number of important simplified models for turbulent behaviour in systems ranging from fluid motion (classical turbulence) to chemical reactions and interfaces in disordered systems.The modern theory of fractals and multifractals now plays a major role in turbulence research, and turbulent states are being studied as important dynamical states of matter occurring also in systems outside the realm of hydrodynamics, i.e. chemical reactions or front propagation. The presentation relies heavily on simplified models of turbulent behaviour, notably shell models, coupled map lattices, amplitude equations and interface models, and the focus is primarily on fundamental concepts such as the differences between large and small systems, the nature of correlations and the origin of fractals and of scaling behaviour. This book will be of interest to graduate students and researchers interested in turbulence, from physics and applied mathematics backgrounds.
The intestinal production of skatole and its deposition in backfat was investigated in 35 uncastrated crossbred male pigs. The pigs were fed five purified non-commercial diets containing either casein or brewers yeast slurry as protein source. The yeast slurry diet was used alone or supplemented with either wheat bran (200 g/kg), sugar-beet pulp (200 g/kg), or soya oil (100 g/kg).Skatole concentrations in backfat, and in digesta in different sections of the gastro-intestinal tract were measured at slaughter (mean weight 112 kg). There were large variations in skatole concentrations in the hind gut of different animals given the same diet. Although there was some correlation between skatole in intestinal contents and deposition in adipose tissue, there were also large variations between individual animals in their response to intestinal skatole. Nevertheless, there was a clear effect of diet on both intestinal skatole production and skatole deposition in backfat. The use of casein as a protein source decreased microbial skatole production, the total amount in the gut, and the concentration in the backfat. Addition of sugar-beet pulp to the yeast slurry diet increased microbial activity in the intestine (measured as ATP content, concentration of short-chain fatty acids, and lowering of digesta pH). There was a decreased rate of skatole production during in vitro incubations of intestinal content, and less skatole in the hind gut and backfat.In vitro fermentations of freeze-dried Heal effluent inoculated with faecal bacteria, and addition of substrates to in vitro incubations of intestinal contents, demonstrated that tryptophan availability rather than microbial activity was the limiting factor for skatole production.The results show that skatole production depends on the amount of protein entering the hind gut and the proteolytic activity of the intestinal microbiota. Protein fermentation in the hind gut can be decreased either by using more readily digestible protein sources (for example casein rather than yeast slurry) which reduce the amount of protein passing through to the hind gut, or by adding an alternative energy source which is more readily metabolized by the hind gut microbiota (for example supplementation of the yeast slurry diet with sugar-beet pulp). This provides a basis for the rational design of diets which will decrease skatole concentrations in the carcass.
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