Microscopic Growth Mechanisms for Carbon Nanotubes

The uncatalyzed edge growth of carbon nanotubes was investigated by first-principles molecular dynamics simulations. At experimental temperatures the open end of single-walled nanotubes closed spontaneously into a graphitic dome, which may explain why these nanotubes do not grow in the absence of transition metal catalysts. On the other hand, chemical bonding between the edges of adjacent coaxial tubes ("lip-lip" interactions) trapped the end of a double-walled nanotube in a metastable energy minimum, thus preventing dome closure. These calculations show that this end geometry exhibits a high degree of chemical activity and easily accommodates incoming carbon fragments, supporting a model of growth by chemisorption from the vapor phase.     

Associations between anti-Fasciola hepatica antibody levels in bulk-tank milk samples and production parameters in dairy herds

Our primary objective was to determine the relationships between Fasciola-specific antibody levels in bulk-tank milk and measures of productivity to estimate economic losses that are associated with Fasciola infections. A bulk-tank milk sample was collected in March 2004 from 1105 dairy herds in Flanders and the antibody levels against Fasciola hepatica (ODRf) and Ostertagia ostertagi (ODRo) were determined. The association of ODRf with four production parameters (milk yield, milk-protein %, milk-fat % and inter-calving interval) was assessed by multivariable linear-regression models. Production data were available for 463 out of the 1105 herds sampled. An increase in ODRf from the 25% quantile (0.428) to the 75% quantile (1.064) was associated with a decrease in the annual average milk yield of 0.7kg/(cowday) (P=0.002), with a decrease in the average milk-fat % of 0.06% (P<0.001) and with an increase of the mean inter-calving interval of 4.7 days (P=0.03). No significant relationship was found with the average milk-protein %. When the relationships of ODRf and ODRo with milk yield were tested simultaneously, we saw an additive rather than synergistic effect of concurrent infections.     

Predicting milk-production responses after an autumn treatment of pastured dairy herds with eprinomectin

The objectives of this study were (1) to determine the effect of a treatment with eprinomectin in autumn of pastured dairy herds on the anti-Ostertagia ostertagi bulk-tank milk antibody level, (2) to determine the overall effect of this treatment on three milk-production parameters (milk yield, protein % and fat %) and (3) to investigate the value of the pre-treatment Ostertagia-specific bulk-tank milk antibody level to predict the production response after anthelmintic treatment. One hundred and nineteen herds in Flanders (Belgium) were randomly assigned to a treatment with eprinomectin or a placebo in October 2004. Bulk-tank milk samples were collected monthly from August 2004 until April 2005, and the antibody levels against O. ostertagi were determined as optical density ratios (ODRs) with an ELISA. The treatment effect over the 4 months following treatment on three production parameters (milk yield, milk-protein %, milk-fat %) was estimated by mixed models with herd as a random effect. The treatment effect on milk yield was also investigated within six categories of the pre-treatment ODR. The ODR values were lower in the eprinomectin group than in the control group at each time point after treatment. The overall effect on milk yield was estimated at 1.2 kg/cow/day, whereas no effect on the milk-protein % and milk-fat % was observed. Herds in the highest pre-treatment ODR category (>0.84) had a positive milk-yield response of 4.0 kg/cow/day (95%-confidence interval: 1.0; 7.0), while the 95%-confidence intervals of the milk-yield responses in the other categories all included zero. This study demonstrates that treatment with eprinomectin of pastured dairy cows in autumn will lower the Ostertagia-specific bulk-tank milk antibody level during the stabling period and can result in a consistent increase in milk yield. The results indicate that an O. ostertagi bulk-tank milk ELISA can be used to identify the herds where the greatest milk-yield response after an anthelmintic treatment is expected.