No abstract

Permeabilities of the luminal and basolateral membranes of pancreatic duct cells to CO2 and HCO3− were examined in interlobular duct segments isolated from guinea‐pig pancreas. Intracellular pH (pHi) was measured by microfluorometry in unstimulated, microperfused ducts loaded with the pH‐sensitive fluoroprobe 2′7′‐bis(2‐carboxyethyl)‐5(6)‐carboxyfluorescein (BCECF). When HCO3−/CO2 was admitted to the bath, pHi decreased transiently as a result of CO2 diffusion and then increased to a higher value as a result of HCO3− uptake across the basolateral membrane by Na+‐HCO3− cotransport. When HCO3−/CO2 was admitted to the lumen, pHi again decreased but no subsequent increase was observed, indicating that the luminal membrane was permeable to CO2 but did not allow HCO3− entry to the cells from the lumen. Only when the luminal HCO3− concentration was raised above 125 mm was HCO3− entry detected. The same was true of duct cells stimulated with forskolin. Recovery of pHi from an acid load, induced by exposure to an NH4+ pulse, was dependent on basolateral but not luminal Na+ and could be blocked by basolateral application of methylisobutylamiloride and H2DIDS. This indicates that the Na+‐H+ exchangers and Na+‐HCO3− cotransporters are located exclusively at the basolateral membrane. In the presence of HCO3−/CO2, substitution of basolateral Cl− with glucuronate caused larger increases in pHi than substitution of luminal Cl−. This suggests that the anion exchanger activity in the basolateral membrane is greater than that in the luminal membrane. We conclude that the luminal and basolateral membranes are both freely permeable to CO2, but while the basolateral membrane has both uptake and efflux pathways for HCO3−, the luminal membrane presents a significant barrier to the re‐entry of secreted HCO3−, largely through the inhibition of the luminal anion exchanger by high luminal HCO3− concentrations.

This study characterizes the microstructure and its associated crystallographic features of bulk maraging steels fabricated by selective laser melting (SLM) combined with a powder bed technique. The fabricated sample exhibited characteristic melt pools in which the regions had locally melted and rapidly solidified. A major part of these melt pools corresponded with the ferrite (α) matrix, which exhibited a lath martensite structure with a high density of dislocations. A number of fine retained austenite (γ) with a <001> orientation along the build direction was often localized around the melt pool boundaries. The orientation relationship of these fine γ grains with respect to the adjacent α grains in the martensite structure was (111) γ //(011) α and [-101] γ //[-1-11] α (Kurdjumov-Sachs orientation relationship). Using the obtained results, we inferred the microstructure development of maraging steels during the SLM process. The results depict that new and diverse high-strength materials can be used to develop industrial molds and dies.

The hydrogen permeability of Pd-Ag alloy membranes has been investigated over a wide temperature range between 100 C and 500 C. The hydrogen permeation coef cient, Φ, for Pd-23mol%Ag decreases with decreasing temperature above 300 C, in good agreement with the previous literature. However, Φ starts to increases below 250 C, and a peak is observed at around 180 C. Considering the silver concentration and operating temperature, the α-α phase transition never occurs in this condition. In other words, the α-α phase transition is not the reason for the anomalous peak behavior of Pd-23mol%Ag alloy at low temperature. In addition, it is con rmed that the diffusion-limiting hydrogen permeation reaction takes place from room temperature up to 500 C. To understand the reason for the peak appearance, the hydrogen permeability has been analyzed in view of the new description of hydrogen permeation based on hydrogen chemical potential. As a result, it is found that the temperature dependence of the PCT factor, f PCT , is dominant for the peak appearance, meaning that the corresponding pressure-composition-isotherms (PCT curves) are essential for the understanding of hydrogen permeability of the alloy. Dependences of the pressure condition and silver concentration on the peak behavior have also been investigated. The peak temperature increases with increasing the hydrogen pressure at feed side. In addition, the peak appears at lower temperature and becomes remarkable with decreasing silver concentration of Pd-Ag alloy membrane. In other words, the composition of Pd-Ag alloy membranes must be designed based on the operating temperature or pressure condition. Thus, this study suggests new possibilities of alloy design for Pd-Ag alloy membranes.