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Abstract The skin has multiple functions, and capillaries can penetrate the epidermis to shorten the diffusion path while allowing maintenance of overall epidermal thickness for nonrespiratory roles. However, a method for quantifying the capillary penetration extent is lacking. Such a method may facilitate making comparisons and detecting associations, potentially making the extent a useful variable in biological studies. We quantified the extent as the ratio of the average minimum thickness of epidermis overlying each capillary to the average epidermal thickness along a skin section and then explored its performance in the Emei mustache toad, Leptobrachium boringii, a species in which breeding males with loose skin call and fight each other with maxillary spines underwater. The ratio showed informative associations with other variables, such as perfused capillary density. It displayed small intragroup variation and could be more sensitive than other variables in revealing structural differences in the skin. The ratio estimates were lowest and were correlated with epidermal and stratum compactum thicknesses in breeding males, i.e., a covariation but not reinforcement against stabbing, constituting early evidence consistent with the increased extensibility of loose skin conferring a defensive advantage during combat in amphibians. In addition, our results lead to the hypothesis that high hemoglobin density along subepidermal capillaries favors the maintenance of low blood partial oxygen pressure and hence increases cutaneous oxygen uptake. We also provide evidence supporting the new idea that the cooccurrence of loose skin and underwater calling found in some frogs can be explained by the latter benefiting from a large functional respiratory surface area. Awareness of the usefulness of the ratio may promote its application and the quantification of the penetration. Regarding exchange surface design, these findings for L. boringii imply a case in which looseness increases surface area as well as prevents damage.

The skin has multiple functions, and capillaries can penetrate the epidermis to shorten the diffusion path while allowing maintenance of overall epidermal thickness for nonrespiratory roles. However, a method for quantifying the capillary penetration extent is lacking. Such a method may facilitate making comparisons and detecting associations, potentially making the extent a useful variable in biological studies. We quantified the extent as the ratio of the average minimum thickness of epidermis overlying each capillary to the average epidermal thickness along a skin section and then explored its performance in the Emei mustache toad, Leptobrachium boringii, a species in which breeding males with loose skin call and fight each other with maxillary spines underwater. The ratio showed informative associations with other variables, such as perfused capillary density. It displayed small intragroup variation and could be more sensitive than other variables in revealing structural differences in the skin. The ratio estimates were lowest and were correlated with epidermal and stratum compactum thicknesses in breeding males, i.e., a covariation but not reinforcement against stabbing, constituting early evidence consistent with the increased extensibility of loose skin conferring a defensive advantage during combat in amphibians. In addition, our results lead to the hypothesis that high hemoglobin density along subepidermal capillaries favors the maintenance of low blood partial oxygen pressure and hence increases cutaneous oxygen uptake. We also provide evidence supporting the new idea that the cooccurrence of loose skin and underwater calling found in some frogs can be explained by the latter benefiting from a large functional respiratory surface area. Awareness of the usefulness of the ratio may promote its application and the quantification of the penetration. Regarding exchange surface design, these findings for L. boringii imply a case in which looseness increases surface area as well as prevents damage. [ABSTRACT FROM AUTHOR]

This study analyzes and compares convective mass transfer coefficients: obtained directly from the drying kinetics and considering the theoretical diffusion model, taking into account shrinkage effect. Theoretical analysis allowed obtaining a modified Biot number. The reduction of the wet exchange surface is identified, from measurements of the drying kinetics, shrinkage phenomenon, surface temperature and parameters of dying air. This is the external surface, concerned with the exchanges with drying air. A significant decrease occurs at the beginning of the drying process and tends to a value close to zero when the product is dry. The evolution of convective mass transfer coefficient, during the drying process, can be evaluated. An important drop is observed. The decreasing of the convective mass transfer coefficient, during the drying process of shrinking products, is evaluated. [ABSTRACT FROM AUTHOR]

This work investigates the drying of yacón (Smallanthus sonchifolius), a source of fructooligosaccharides and inulin, two prebiotic compounds. Experiments were performed using an in-house device consisting of a magnetic suspension balance coupled to a drying chamber and an in-situ shadowgraphy system. This allowed the continuous acquisition of mass, sample volume and exchange surface area to be register versus time at different temperatures (50–70 °C) and relative humidities (10%–30%), which was never done with yacón. Once corrected by the actual area of the exchange surface, the drying kinetics (kg. s − 1 . m − 2 ) depicts two phases, a very long constant drying rate flux and a falling drying rate flux. Even though yacón samples lost up to 91% of their initial volume, an iso-volume deformation was observed: the reduction of sample volume equals the volume of removed water. Thanks to these two experimental facts, an extended, original, van Meel model is proposed to account for this huge change of sample shape in a predictive way. • Convective drying of yacón performed with an original device at controlled conditions. • The actual shape of the sample monitored continuously by digital image correlation. • Iso-volume deformation is evidenced: volume change equals volume of removed water. • The anisotropy ratio is explained by the anatomical structure, as observed by ESEM. • An extended van Meel model is proposed to account for large iso-volume deformation. [ABSTRACT FROM AUTHOR]