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.     

Vinyl acetate monomer—a pilot plant study

The kinetics of the reaction of acetic acid and acetylene over zinc acetate-activated carbon catalyst was investigated over a wide range of process variables in a pilot reactor. Although various catalytic reaction mechanisms were postulated, the rate of reaction was most satisfactorily correlated by a mechanism of surface reaction between charged adsorbed acetic acid and acetylene, which assumes that the rate controlling step was the irreversible charged adsorption of acetylene and acetic acid.     

Consistent structure determination of a noisy measurement system model

This paper describes a fast and accurate method for defining the structure of a noisy measurement system model without a previous parameters evaluation. The procedure is based on the following steps: (i) choosing a stable system structure; (ii) determing the real model order; (iii) estimating the model parameters. In (i) a value of the model order greater than the supposed one is assumed; in (ii), in order to determine the real structure, samples of the input/output signals of the actual model and the over-parametrised one are used; in (iii), by means of unbiased identification techniques, the model parameters are evaluated. The proposed method can be used both in batch and real-time processing. Experimental results concerning a single input-single output linear process with different model order and noise statistical properties are given.     

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.     

Hierarchical Evolution of High Definition Television

This paper presents an economically attractive system for the hierarchical evolution of High Definition Television (HDTV) compatible with the NTSC installed base. It describes the two main signals of this system: HDMAC-60 and HDNTSC. The first, HDMAC-60, is a feeder signal for use between the program origination and program redistribution points, and used also as a DBS emission format. The second, HDNTSC, is a delivery signal for high definition terrestrial broadcast, CATV distribution and VCR plus laser video disc applications. We propose this emission system as a means for transmitting HDTV pictures to consumers on the North American continent.     

VIAM and Materials Science

Metal Science and Heat Treatment -     

Epoxide polymerization

Summary Poly(propylene oxide), PPO, obtained using diphenylzinc, Ph₂Zn, and using the diphenylzinc-water system at various molar ratios H₂O/Ph₂Zn, were studied through ¹H NMR and IR spectroscopy establishing that the polymerization initiates by coordition of propylene oxide (PO) to a terminal zinc atom of the active species followed by consecutive insertions of PO units at this zinc atom. The PPO obtained showed Ph-and HO-, HO-and HO-end-groups depending on the molar ratio H₂O/Ph²Zn used, and also HO-and PhO-end-groups when oxygen was present in the polymerization system.