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Background and objective: In developing countries low maternal vitamin A stores combined with increased demands of pregnancy and lactation may lead to its deficiency in breastfed infants. This study evaluates the effects of maternal supplementation with a high dose of vitamin A on the serum retinol levels of exclusively breastfed infants, and their morbidity in the first six months of life. Setting: Hospital based. Study design: Randomised controlled trial. Subjects and methods: Mothers of the test group (n=150) were orally supplemented with a single dose of retinol (209 µmol) soon after delivery and were advised exclusive breastfeeding for six months. Before supplementation retinol levels were estimated in the mothers' and newborns' blood, and in colostrum. On follow up, breastmilk and infants' serum retinol contents were assessed monthly for six months. Retinol level <0.7 µmol/l indicated vitamin A deficiency. Morbidity patterns like vitamin A deficiency, diarrhoea, febrile illnesses, acute respiratory infection, measles, and ear infection were also studied and compared between the two groups. Results: Presupplement mean maternal serum retinol levels were 0.98 and 0.92 µmol/l and mean breastmilk levels were 3.85 and 3.92 µmol/l in the test and control groups respectively (p>0.05). Mean cord blood retinol levels were also comparable (0.68 v 0.64 µmol/l). After supplementation, the test group showed a rise in mean breastmilk retinol content (12.08 v 2.96 µmol/l) which remained significantly higher for four months. The infants' mean serum retinol level, initially 322.06% of the baseline value, was significantly higher for five months. In the control group, significant numbers of mothers and infants showed deficient breastmilk and serum retinol throughout the follow up (p<0.01). Decreased incidence and duration of various diseases were also found in the test group suggesting lesser morbidity. Conclusion: Maternal supplementation with single megadose vitamin A is an effective strategy for vitamin A prophylaxis of exclusively breastfed infants of 0-6 months.

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Stable high performance in a polymer electrolyte fuel cell ͑PEFC͒ requires efficient removal of product water and heat from the reaction sites. The most important coupling between water and heat transport in PEFC, through the liquid-vapor phase change, remains unexplored. This paper sheds light on physical characteristics of liquid-vapor phase change and its role in PEFC operation. A two-phase, nonisothermal numerical model is used to elucidate the phase-change effects inside the cathode gas diffusion layer ͑GDL͒ of a PEFC. Locations of condensation and evaporation are quantified. Operating conditions such as the relative humidity ͑RH͒ of inlet gases and materials properties such as the thermal conductivity of GDL are found to have major influence on phase change. Condensation under the cooler land surface is substantially reduced by decreasing the inlet RH or increasing the GDL thermal conductivity. The RH effect is more pronounced near the cell inlet, whereas the GDL thermal conductivity affects the phase-change rate more uniformly throughout the flow length.Liquid-vapor phase change, or specifically evaporation/ condensation, plays a pivotal role in the coupled water and thermal management of polymer electrolyte fuel cells ͑PEFCs͒. Although a large body of literature exists to explore two-phase transport in PEFCs analytically, experimentally, and numerically, 1-14 direct examination of the phase change phenomena has been absent. This work sheds light on the physical characteristics of phase-change phenomena and their role in fuel cell operation. Another objective is to prompt the development of in situ and direct measurements of the phase-change rate as an important parameter to the fundamental understanding and design improvement of PEFCs.In two-phase modeling of PEFCs, local thermodynamic equilibrium is often assumed between the liquid and gas phases at the evaporation/condensation interface. This assumption implies that negligibly small supersaturation of water vapor exists in the gas phase when condensation or evaporation occurs. The chemical equilibrium occurs at the microscale and in the vicinity of an interface. The existence of interfacial equilibrium at a phase-change interface does not mean a zero phase-change rate. Indeed, a finite phasechange rate can coexist with the interfacial equilibrium condition. Analogously, an extremely facile electrochemical reaction yields negligibly small overpotential or an equilibrium condition, but there is still a reaction current occurring at the electrochemical interface.In general, the phase-change rate can be expressed as 15-18where H is directly proportional to the area of the interfacial surface where phase change occurs. In porous layers of fuel cells, the liquidvapor interfacial area is usually sufficiently large thatthus yielding equilibrium phase change. If H is not sufficiently large, there exists nonequilibrium phase change. Wang et al. 15 theoretically showed that the coefficient H is proportional to aD H 2 O /r p , where r p is the pore radius, a is th...