C-13-carbohydrate breath tests: Impact of physical activity on the rate-limiting step in lactose utilization

Background: (CO2)-C-13 breath tests can be used to monitor carbohydrate digestion in the small intestine. However, after ingestion of C-13-substrates, (CO2)-C-13 excretion in breath originates from two sources: a digestive/oxidative fraction, derived from the small intestine, and a fermentation fraction, derived from undigested substrate spill-over in the colon. In this study, the determinants of the digestive/oxidative fraction were analysed in order to improve the sensitivity/specificity of the C-13-carbohydrate breath tests. Methods: C-13-carbohydrate breath tests were performed in healthy adults using C-13-lactose, pre-digested C-13-lactose, C-13-glucose, and C-13-galactose as substrates. The effect of exercise (bicycling, 50 W), increasing the metabolism of digested/absorbed substrate, on the outcome of the test was analysed. Results: In rest, no difference was observed in the 4-h cumulative percentage dose recovered in breath (4-h cPDR) after administration of glucose, pre-digested lactose, and lactose, which were 20.3 +/- 4.5%, 19.2 +/- 5.5%, and 19.9 +/- 4.9%, respectively. The (CO2)-C-13 excretion rate after C-13-galactose consumption was significantly slower than after C-13-glucose consumption. Exercise increased 4-h cPDR of C-13-glucose significantly: 76.0 +/- 1.0% vs. 22.7 +/- 2.3%. This effect was also observed using C-13-lactose as substrate: 66.1 +/- 6.2% vs. 19.6 +/- 3.9%. One Subject had non-symptomatic lactose maldigestion indicated by a positive H-2 breath test. The (CO2)-C-13 breath test of this subject in rest was indistinguishable from that of the others (4-h cPDR 16.6 vs. 19.6 +/- 3.9%), whereas the test was clearly indicative during exercise (4-h cPDR 20.5 vs. 66.1 +/- 6.2%). Conclusion: In healthy volunteers in rest, glucose oxidation is the rate limiting step in lactose conversion into (CO2)-C-13. Increase of metabolism (for instance, by exercise) can shift this step to intestinal hydrolysis of lactose, making the C-13-lactose breath test more sensitive

Simulation of stretch forming with intermediate heat treatments of aircraft skins - a physically based modeling approach

In the aerospace industry stretch forming is often used to produce skin parts. During stretch forming a sheet is clamped at two sides and stretched over a die, such that the sheet gets the shape of the die. However for complex shapes it is necessary to use expensive intermediate heat-treatments in between, in order to avoid Lüders lines and still achieve large deformations. To optimize this process FEM simulations are performed. The accuracy of finite element analysis depends largely on the material models that describe the work hardening during stretching and residual stresses and work hardening reduction during heat treatments due to recovery and particle coarsening. In this paper, a physically based material modeling approach used to simulate the stretch forming with intermediate heat treatments and its predictive capabilities is verified. The work hardening effect during stretching is calculated using the dislocation density based Nes model and the particle coarsening and static recovery effects are modeled with simple expressions based on physical observations. For comparison the simulations are also performed with a phenomenological approach of work hardening using a power law. The Vegter yield function is used to account for the anisotropic and biaxial behavior of the aluminum sheet. A leading edge skin part, made of AA 2024 has been chosen for the study. The strains in the part have been measured and are used for validation of the simulations. From the used FEM model and the experimental results, satisfactory results are obtained for the simulation of stretching of aircraft skins with intermediate heat treatments and it is concluded that the physics based material modeling gives better results

Historical Pollution: In Search of a Legal Definition

The chapter introduces and investigates the concept of \u201chistorical pollution\u201d in the context of environmental law. The subject is complex, as the principal consideration in our analysis concerns the role of time in the causation of harmful consequences (both for the environment and human health), notably in view of the prolonged timeframe that separates the conduct (pollution) and the effect (contamination). The phenomenon under scrutiny has significant implications for both the legal and the social fields. Indeed, legal enforcement of putative crimes against the environment is generally ineffective precisely because of this temporal factor, and this also has consequences for social perceptions and the dynamics of victimization. Yet these considerations could also contribute to a definition of historical pollution, as\u2014 given the complexity and uncertainties that surround the phenomenon\u2014they suggest ways in which material cases could be used to frame a general understanding of the concept. Attention here is focused on pollution related to industrial activities since such cases are prominent in the field. The proposed definition strives to establish a general framework within which domestic analyses can be located, consistent with the particularities of each legal system. It represents one of the first steps into the unexplored terrain of historical pollution