Macroscopic Surface Area Research Articles

Gestational changes in pig placental weight, area and DNA content in the second half of pregnancy

Weight and macroscopic surface area of the pig placenta reached a maximum at day 101 and decreased thereafter. However, between day 101 and day 111 (full term 113/115) the epitheliochorial tissue layer increased in area due to the continuing formation of folds. Although lightweight placentae had small macroscopic surface areas, they possessed larger areas per unit weight throughout the second half of gestation. From day 70 to day 92 the lightest placentae, when compared with their heaviest litter mates, had from 15 to 150 per cent more macroscopic surface area per unit weight. In the middle third of gestation there was a phase of rapid cell division, in consequence of which mean cell size was reduced. By the beginning of the last third of gestation mean cell size had reached a steady value, with no demonstrable change thereafter. Cell multiplication continued until day 101 when growth in weight had ceased.

Relationship of fetal to placental size: the pig model

Placental weight and macroscopic surface area are closely correlated with fetal weight throughout the second half of gestation in the pig. The limiting effect of placental size on fetal weight becomes more obvious as gestation advances. Fetal weight/placental weight ratio increases as placental weight decreases. Within individual litters, lightweight placentas have up to 150% more macroscopic surface area per unit placental weight.

Electrophysiological analysis of rat renal sugar and amino acid transport. I. Basic phenomena.

The electrical events associated with the absorption of D-glucose or L-amino acids in renal proximal tubules were studied in microperfusion experiments on rat kidneys in vivo. Intratubular application of these substrates led concomitantly to: 1) a shift of the transepithelial potential into lumen negative direction, 2) a partial depolarization of the tubular cell membranes and 3) a reduction of the electrical resistance of the brushborder membrane. By means of rapid perfusion experiments it was possible to discern two phases in the potential response to substrate perfusion, a fast initial response which reflects a substrate-induced Na+ ion current from lumen to cell, and a slower secondary response which reflects the relaxation of the intracellular ion and substrate concentrations towards new steady states. A quantitative analysis of the data yielded estimates of 1) the apical (Ra) and basal (Rb) cell membrane resistances and of the shunt resistance, Rs, of rat proximal tubule of approximately Ra = 255 omega cm2, Rb = 92 omega cm2 and Rs = 5 omega cm2 (all referred to the quasi macroscopic surface area of the tubular lumen), 2) the conductance of the Na+ and glucose cotransport pathway and 3) the driving forces acting on the cotransport mechanism in the brushborder membrane. The latter were found to be a) the electrical cell membrane potential of -74 mV, b) the Na+ ion concentration gradient between the tubular lumen (clumNa = 145 mmol/l) and the cytoplasm (ccellNa approximately 33 mmol/l) which corresponds to an additional equivalent potential of 51 mV and c) the substrate concentration gradient, which varies according to the experimental conditions. Moreover the analysis provided a quantitative estimate of the relationship between the substrate-induced changes in transepithelial potential or short circuit current and the actual cotransport current in the brushborder membrane. Based on this analysis it is concluded that the stoichiometry of Na+ and glucose flux coupling in the brushborder membrane of rat proximal tubule is close to 1.0.

Bis(2,2'-biquinoline)copper(I) nitrate as an in situ spectrophotometric probe of cadmium sulfide/cuprous sulfide heterojunction formation

Amyl alcohol solutions of the bis(2,2'-biquinoline)copper(I) cation, I, react with single-crystal, n-type CdS to yield n-CdS/p-Cu/sub 2/S heterojunctions. The intense visible absorption band of I (lambda/sub max/ 545 nm; epsilon approx. 6300 M/sup -1/ cm/sup -1/ at 25/sup 0/C) provides an in situ spectrophotometric probe of heterojunction formation: spectral changes can be correlated with the extent of reaction. Kinetic studies using the nitrate salt of I reveal that initial reaction rates are directly proportional to CdS macroscopic surface area, first order in the concentration of I, and temperature dependent with an apparent activation energy of 13 +- 2 kcal/mol between 60 and 90/sup 0/C. Mechanistic aspects of the reaction are discussed.

Low-temperature oxidation of a bituminous coal. Infrared spectroscopic study of samples from a coal pile

A Fourier-Transform i.r. spectroscopic study has been made of coal samples from a test pile of a bituminous coal which was subject to spontaneous heating. Samples taken from the pile at various depths (various temperatures) and at intervals of 3 months were fractionated into four fractions with different particle sizes so as to distinguish ‘macropore’ oxidation effects from ‘micropore’ oxidation effects. The spectra show that initially a carboxylic acid-type compound is formed. This compound seems to decompose in a later stage of the oxidation. Analysis of the results suggests that macropore oxidation (a diffusion-limited process across the macroscopic interface of the particle) predominates. If so, removal of a small proportion of fines with a relatively large, specific macroscopic surface area would result in a reduction of the spontaneous heating of the pile.

The liquid repellency of a number of fluorochemical finished cotton fabrics

The liquid repellency to liquids of varying surface tensions was examined for a number of differently woven cotton fabrics that were treated with a fluorochemical textile finish. Expressions for the liquid-solid and liquid-air interfaces per unit of macroscopic surface area have been derived and used to calculate the apparent surface contact angles. Comparison with experimental data has shown that these expressions are correct. Liquid-yarn advancing contact angles have been obtained from measurements of the pressure required to force the liquid through the pores in the fabrics. The abrupt drop of repelling performance for liquids of surface tension under 25 dynes/cm. is discussed in terms of textile structure and fiber surface.