Scallop Theorem and Swimming at the Mesoscale.

By comparing theoretical modeling, simulations, and experiments, we show that there exists a swimming regime at low Reynolds numbers solely driven by the inertia of the swimmer itself. This is demonstrated by considering a dumbbell with an asymmetry in coasting time in its two spheres. Despite deforming in a reciprocal fashion, the dumbbell swims by generating a nonreciprocal Stokesian flow, which arises from the asymmetry in coasting times. This asymmetry acts as a second degree of freedom, which allows the scallop theorem to be fulfilled at the mesoscopic scale.

Surface swimmers, harnessing the interface to self-propel.

In the study of microscopic flows, self-propulsion has been particularly topical in recent years, with the rise of miniature artificial swimmers as a new tool for flow control, low Reynolds number mixing, micromanipulation or even drug delivery. It is possible to take advantage of interfacial physics to propel these microrobots, as demonstrated by recent experiments using the proximity of an interface, or the interface itself, to generate propulsion at low Reynolds number. This paper discusses how a nearby interface can provide the symmetry breaking necessary for propulsion. An overview of recent experiments illustrates how forces at the interface can be used to generate locomotion. Surface swimmers ranging from the microscopic scale to typically the capillary length are covered. Two systems are then discussed in greater detail. The first is composed of floating ferromagnetic spheres that assemble through capillarity into swimming structures. Two previously studied configurations, triangular and collinear, are discussed and contrasted. A new interpretation for the triangular swimmer is presented. Then, the non-monotonic influence of surface tension and viscosity is evidenced in the collinear case. Finally, a new system is introduced. It is a magnetically powered, centimeter-sized piece that swims similarly to water striders.

Hepatitis B in a Belgian institution for mentally retarded patients: an epidemiological study.

This study describes the epidemiology of hepatitis B in a Belgian institution for mentally retarded patients. 8% of the 163 patients studied were HBs Ag carriers and 28.8% had anti-HBs. Among the HBs Ag carriers, 76.9% were HBe Ag positive. The HBs Ag carrier rate was higher in males, in patients with Down's syndrome or newcomers, and was slightly higher in patients living at parental home vs those living in the institution. A fall in the HBs Ag carrier rate was observed between the 5-14 and 15-24 age groups. A longitudinal study performed on 41 adult female patients, in the absence of any intercurrent vaccination, allowed us to determine a yearly seroconversion rate of 1.5% in this population. Data presented here confirm the risk of the institutionalized mentally retarded patients of contracting hepatitis B and becoming highly infectious HBs Ag carriers. They cast light on the various factors which have to be taken into account in this peculiar epidemiologic study and on the importance of early vaccination.

[Extensive resection of the small intestine in children]. / Résection étendue du grêle chez l'enfant.

Thirteen children aged 2 to 16 years have had a subtotal resection of small bowel, following a mid-gut volvulus in 10 cases. All children are still alive, and their growth was normal; 36 cumulative patient-years of parenteral nutrition and 11 years of constant rate enteral nutrition were performed. In 7 cases, where residual small bowel varied between 30 to 120 cm, termination of all artificial nutritional support was possible at a mean of 30 months after intestinal resection. On the other hand if resection was near total with less than 20 cm remaining, life long dependence on parenteral nutrition is unavoidable unless intestinal transplantation becomes feasible; with cyclic parental nutrition at home, their quality of life is near normal.