Cyclic variations in the permeability of the cell wall of Saccharomyces cerevisiae.

To study cell-cycle-related variations in wall permeability of Saccharomyces cerevisiae, two approaches were used. First, an asynchronous culture was fractionated by centrifugal elutriation into subpopulations containing cells of increasing size. The subpopulations represented different stages of the cell cycle as judged by light microscopy. Cell wall porosity increased when these subpopulations became enriched with budded cells. Secondly, synchronous cultures were obtained by releasing MATa cells from alpha-factor induced G1-arrest. These cultures grew synchronously for at least two generations. The cell wall porosity increased sharply in these cultures, shortly before buds became visible and was maximal during the initial stages of bud growth. It decreased in cells which had completed nuclear migration and before abscission of the bud had occurred. The porosity reached its lowest value during abscission and in unbudded cells. We examined the incorporation of mannoproteins into the wall during the cell cycle. SDS-extractable mannoproteins were incorporated continuously. However, the incorporation of glucanase-extractable mannoproteins, which are known to affect cell wall porosity, showed cyclic oscillations and reached its maximum after nuclear migration. This coincided with a rapid decrease in cell wall porosity, indicating that glucanase-extractable mannoproteins might contribute to this decrease.     

Longitudinal analysis of semiconductor lasers with low reflectivity facets

An analysis is made of longitudinal effects in semiconductor lasers with low facet reflectivities. For this purpose, a self-consistent model is used based on the beam propagation method, which takes into account both the lateral and longitudinal dimension. The calculations show that longitudinal effects have a significant influence on the output fields in the laser.     

THE ORIGIN AND MIGRATION PATHS OF HYDROCARBONS ACCUMULATED IN THE LOWER CRETACEOUS SANDSTONE "GIANT" TAR ACCUMULATIONS OF ALBERTA-II

The first part of this study was published in the last issue, 7 , (4) 381–402, October 1984. The conclusion on p. 103, and references which follow, apply to both papers.     

The effect of tension during drying on the structure and mechanics of poly(p-phenylene benzobisthiazole) fibers

The effect of tension during drying on the structure and mechanics of poly(p-phenylene benzobisthiazole) (PBT) fibers has been investigated. The application of tension during drying on PBT fibers spun from anisotropic solutions of PBT/Polyphosphoric acid (PPA) results in an enhancement of tensile modulus and yield strength with a reduction in strain to break. The alterations in the tensile properties can be attributed to the straightening of the wet fibrillar network and the reduction in the axial compressive stresses which develop during drying. Modifications in the mechanical behavior of PBT fibers through tension drying can be achieved regardless of the initial spin draw ratio of the fiber. Additionally, tension drying provides a means to maximize the potential stiffness of PBT fibers which have a low spin draw ratio. Lastly, these investigations show that in the processing of PBT fibers, preventing the onset of buckling and aligning the wet fibrillar network with tension during drying is more effective in enhancing the tensile properties than straightening the dried buckled fibers.     

Testing the Ortega hypothesis: Facts and artifacts

We examine the assumptions and data base used by researchers who have tested the Ortega hypothesis. We find that the assumptions are not supported by the data and that the data are faulty. We conclude that the results are artifactual. We recommend that any policy implemented on the basis of this research be suspended.     

Constriction resistance at high signal frequencies

This paper describes the dependence of constriction resistance on signal frequency. This dependence was calculated for circular constrictions ranging in diameter from 10 to 100 /spl mu/m, and for frequencies ranging from dc to 1 GHz. The results indicate that the magnitude of constriction resistance does not deviate appreciably from values predicted by Holm's classical analytical expression, as long as the skin depth is large compared with the constriction radius. For skin depths that are much smaller than the constriction radius, constriction resistance decreases with increasing frequency to an apparent limiting value independent of the constriction radius. At high frequencies, constriction resistance constitutes only one of two components of the total connection resistance measured in practice. The second component of connection resistance is determined by details of the geometry and dimensions of the contact interface, and increases with signal frequency.     

Nash equilibrium bidding strategies in a bilateral electricitymarket

This paper examines bidding strategies in a bilateral market in which generating companies submit bids to loads. A load accepts electricity delivery from the generator with the lowest bid at its bid price as long as this price is not higher than the load's willingness to pay. Necessary and sufficient conditions of Nash equilibrium (NE) bidding strategy are derived based on a generic generating cost matrix and the loads' willingness to pay vector. The study shows that in any NE, efficient allocation is achieved. Furthermore, all Nash equilibria are revenue equivalent for the generators. Based on the necessary and sufficient conditions, this problem is formulated as an optimal assignment problem. Network optimization techniques are applied to calculate NE bid prices for the generators