Dispersion of particles in an infinite-horizon Lorentz gas

We consider a two-dimensional Lorentz gas with infinite horizon. This paradigmatic model consists of pointlike particles undergoing elastic collisions with fixed scatterers arranged on a periodic lattice. It was rigorously shown that when $t\to\infty$, the distribution of particles is Gaussian. However, the convergence to this limit is ultraslow, hence it is practically unattainable. Here we obtain an analytical solution for the Lorentz gas' kinetics on physically relevant timescales, and find that the density in its far tails decays as a universal power law of exponent $-3$. We also show that the arrangement of scatterers is imprinted in the shape of the distribution.Comment: Article with supplemental material: 10 pages, 4 figure

A walnut-containing meal had similar effects on early satiety, CCK, and PYY, but attenuated the postprandial GLP-1 and insulin response compared to a nut-free control meal.

Regular nut consumption is associated with lower adiposity and reduced weight gain in adulthood. Walnut feeding studies have observed minimal effect on body weight despite potential additional energy intake. Several mechanisms may explain why consuming nuts promotes weight control, including increased early phase satiety, possibly reflected in postprandial response of gastrointestinal and pancreatic peptides hypothesized to affect appetite. The purpose of this study was to compare postprandial insulin, glucagon and gastrointestinal peptide response and satiety following a meal with ∼54% of energy from walnuts or cream cheese, using a within-subject crossover study design in overweight/obese adults (N = 28). Sixty minutes after the walnut-containing meal, glucagon-like peptide-1 was lower than after the reference meal (p=0.0433), and peptide YY, cholecystokinin and ghrelin did not differ after the two meals. Sixty and 120 min after the walnut-containing meal, pancreatic polypeptide (p = 0.0014 and p = 0.0002) and glucose-dependent insulinotropic peptide (p < 0.0001 and p = 0.0079) were lower than after the reference meal, and 120 min after the walnut-containing meal, glucagon was higher (p=0.0069). Insulin and C-peptide increased at 60 min in response to both meals but were lower at 120 min after the walnut-containing meal (p=0.0349 and 0.0237, respectively). Satiety measures were similar after both meals. These findings fail to support the hypothesis that acute postprandial gastrointestinal peptide response to a walnut-containing meal contributes to increased satiety. However, inclusion of walnuts attenuated the postprandial insulin response, which may contribute to the more favorable lipid profile observed in association with regular walnut consumption

Excretal Near Infrared Reflectance Spectrometry to monitor the nutrient content of diets of grazing young ostriches (Struthio camelus)

Feeding systems in which young ostriches feed on pasture but have access to concentrates provide better welfare than confined systems but are sustainable only if nutrition is carefully controlled. This study was conducted to evaluate the potential of "excretal NIRS", a methodology that associates excretal spectral information in the near infrared (NIR) region with dietary attributes, in predicting dietary quality and nutrient intake in grazing ostrich chicks. Sixty sets of excretal and dietary information from chicks fed only concentrate or also grazing lucerne, barley, sulla or natural pastures, were used. The coefficient of determination (R2) and the standard error of cross validation (SECV) served to evaluate calibration quality. The prediction of dietary concentrate content ranging 420 to 1000 g/kg of DMI, was highly linear (R2 = 0.96), with SECV of 63 g/kg. Similar R2 values were noted for the dietary contents of crude protein (CP), acid detergent fibre (ADF) and ash; that for the prediction of neutral detergent fibre (NDF) was lower (0.87). Ash, CP, NDF and ADF were predicted with SECV values of 14.8, 5.0, 8.9 and 10.7 g/kg DM diet, respectively. The calibration for apparent total organic matter digestibility was of poor quality. Good (R2 = 0.95) and acceptable (R2 = 0.86) calibrations were obtained for the daily intakes of pasture and concentrate, respectively, with SECVs of 75 and 131 g/d. Predictions of ash (R2 = 0.85, SECV = 11 g/d) and ADF (R2 = 0.80, SECV = 19 g/d) intakes had mediocre accuracy, and calibrations for CP and NDF intakes were even poorer. These results suggest that excretal NIRS may be useful to predict dietary intake and composition for grazing ostriches when applied to a known nutritional environment attended with calibration standards. Keywords: Ratites, faecal NIRS, nutrition; pasture, herbivorySouth African Journal of Animal Science Vol. 36 (4) 2006: pp. 248-25