Showing papers on "Surface-area-to-volume ratio published in 1979"

The important of surface area/volume ratio to the rate of oxygen uptake by red cells.

Abstract: Dear Sir: Holland and Forster (1966) demonstrated experimentally that velocity constants for initial rates of oxygen uptake by fully reduced erythrocytes (k~) are inversely related to mean corpuscular volume (MCV) (Table I). They based k\" upon measurements of the rate of hemoglobin saturation with oxygen, so that the entire process included oxygen diffusion through the cell membrane, diffusion through the cell interior, and the chemical reaction of oxygen with hemoglobin. Cell thickness was considered the most obvious factor to account for decrease in k~ as cell volume increases. However, when they used an infinite sheet as a cell model, they did not establish a clear relationship between k~ and thickness. An inverse relationship was demonstrated between k~ and the radius (r) of a hypothetical sphere used as a cell model. Related material has been reviewed by Forster (1964). The present analysis is based upon the data in Table I. Average diameters (d) of sheep, rabbit, and human cells in plasma were taken from Ponder (1948); the other diameters are of dried cells (Altman and Ditmer, 1971) multiplied by 1.08 to correct for cell shrinkage. Red cell shape is considered to be that of a cylindrical disc, which differs little from a prolate spheroid and is easier to work with mathematically; thickness is taken as mean corpuscular thickness (MCT) as calculated by Wintrobe (1967). Surface area (S) and surface to volume ratio (S/V) are calculated as for a disc. All pairings between variables in Table I yield highly significant (P < 0.001) correlation coefficients, indicating that all of these characteristics are closely interrelated. If the calculations of M C T in Table I are accepted, then the increase of ~50% in cell thickness appears inadequate to account for a major portion of the 34-fold increase in cell volume, or the decrease in k~ to one-eighth of the maximal value. From Table I, we can see that increase in cell diameter is primarily responsible for the increase in MCV. The correlation coefficients which involve k\" show that its best correlation is with S /V (r ~ 0.92), followed by d (r --0.83), M C T (r --0 .76) , S (r --0.76) , and M C V (r --0.73). For these experiments, we believe that decreasing S / V has the critical role in limiting rate of oxygen uptake as cell size increases. Apparently the rate of hemoglobin saturation is limited primarily by the surface area through which oxygen can diffuse in relation to the cell volume (and hemoglobin content), which must become saturated, rather

Sintered ceramic body for cutting tools

Abstract: A sintered ceramic body for use in cutting tools which has an average crystal grain size of not more than about 2μ and comprises about 60 to 95% by volume of (a) Al2 O3 and the remainder being composed of (b) WC, provided that it may contain W2 C in which case the intensity ratio IW.sbsb.2C (101)/IWC (111) in X-ray diffraction using CuKα rays is not more than about 0.5, and (c) TiN, the volume ratio of components (b) to (c) being about 5:95 to 95:5.

Optimum design for solids circulation system with shrinking core kinetics in both reactor and regenerator

Abstract: The optimum volume ratio of reactor and regenerator which minimizes the total volume of the two is obtained for solids circulation systems where shrinking core kinetics hold for both gas-solid reaction and regeneration. For the general case the optimum volume ratio for a fixed flow rate of solids is represented graphically in terms of reaction and regeneration conditions. For a special case an approximate analytical solution for the minimization is obtained. The procedure to determine the optimum required volume for the reactor and that for the regenerator is also dealt with. The effect of reaction and regeneration conditions and of solids flow rate on the optimum volumes is discussed.