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Laboratory simulation of thermal erosion: possible application to pollution problems
- N. Makhloufi, F. Costard, J. Aguirre Puente, J. Costard, R. Posado Cano, G. Guillemet
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- Journal:
- Polar Record / Volume 35 / Issue 192 / January 1999
- Published online by Cambridge University Press:
- 27 October 2009, pp. 67-72
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In the Arctic, thermal erosion results from ground thawing produced by heat transfer when water is flowing upon the frozen ground. A mathematical model has been proposed to determine the efficiency of the process and the rate of thermal erosion. Considering a constant heat-transfer coefficient, the resulting thermal flux at the groundsurface produces ground thaw, and the unfrozen sediments can be removed by the water flow. A particular case of an ablation model consists of an immediate removing of sediments by a strong flow and by the action of gravity. An experimental hydraulic device was built to test the authors' theoretical ablation model, describing a fluvial thermalerosionprocess. The effect of different parameters (Reynolds number, water temperature, ground-ice temperature) on the rate of thermal erosion for samples of frozen sand was investigated. Results from the experiments are in agreement with theoretical estimates using the mathematical model. Moreover, this study shows a hierarchy of parameters in terms of efficiency of the fluvial thermal-erosion process.
A discussion of the possible effects of the contaminants on the erosion rate leads the authors to propose two kinds of experiments: a contaminated frozen sample eroded by a water flow, varying in this case the thermophysical properties of the sample (density, specific heat capacity, a latent heat, and change of phase), and an experiment consisting of erosion of a frozen sample by contaminated flow. This second case is also complex due to many mechanical, hydrodynamic and thermal interactions at the ground surface. This paper reports results of thermal erosionfrom experiments with icesaturated sand. A pure ice sample is used to determine the heat-transfer coefficient.
Dietary fibre for gestating sows: effects on parturition progress, behaviour, litter and sow performance
- R. Guillemet, A. Hamard, H. Quesnel, M. C. Père, M. Etienne, J. Y. Dourmad, M. C. Meunier-Salaün
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In pig production, parturition progress is a key event for sow’s reproductive performance, evaluated by piglet survival and piglets’ performance. The aim of this study was to investigate the impact of feeding a high-fibre (HF) diet during gestation on parturition progress and reproductive performance of sows. Forty-two primiparous sows (Large-White × Landrace crossbred) were fed during gestation either a control diet (C diet; 2.40 kg/day, 3.2% crude fibre, in % of dry matter (DM)), or a HF diet (2.80 kg/day, 12.4% crude fibre, in % of DM). All sows received 33 MJ digestible energy per day. Continuous video recordings were done on the parturition day to determine postural changes (standing, sitting, lying) and behavioural activities (nesting behaviour, uterine contractions, restlessness, social behaviour towards piglets) during parturition. Duration of parturition and individual birth intervals were also measured. Piglets’ growth was evaluated by weekly weighing from birth until weaning, at 26.5 days of age. Sows were weighed and backfat thickness was measured at mating, on day 105 of gestation, on the 1st day post partum, and at weaning. Durations of parturition and of birth intervals were not affected by the gestation diet and averaged 211 ± 12 min and 16.5 ± 0.9 min (mean ± s.e.), respectively. During the parturition progress, the gestation diet did not affect the frequency and the time devoted to postural and behavioural activities. Dietary treatment during gestation did not influence duration of gestation and weaning-to-oestrus interval, as well as litter size, and number of stillborn and weaned piglets. Piglet weight at birth did not differ between gestation dietary treatments but piglets nursed by HF sows showed a 13.5% greater growth rate during the 1st week of life (P < 0.01) and tended to be heavier at weaning (P = 0.06) compared with C piglets. The HF sows were leaner at the end of gestation (P < 0.05), but variations of sows’ weight during gestation and lactation were not affected by the gestation diet. All sows lost the same amount of backfat thickness during lactation. During lactation, the average daily feed intake was not significantly affected by the gestation diet. This study shows that substituting a control diet for a HF diet during gestation has limited effects on farrowing progress and reproductive performance, but improved piglets’ growth rate during the 1st week of life and tended to increase their live weight at weaning.