Sequence comparison of the ARG4 chromosomal regions from the two related yeasts,Saccharomyces cerevisiae and Saccharomyces douglasii

A 3·6 kb DNA fragment from Saccharomyces douglasii, containing the ARG4 gene, has been cloned, sequenced and compared to the corresponding region from Saccharomyces cerevisiae. The organization of this region is identical in both yeasts. It contains besides the ARG4 gene, another complete open reading frame (ORF) (YSD83) and a third incomplete one (DED81). The ARG4 and the YSD83 coding regions differ from their S. cerevisiae homologs by 8.1% and 12·5%, respectively, of base substitutions. The encoded proteins have evolved differently: amino acid replacements are significantly less frequent in Arg4 (2·8%) than in Ysc83 (12·4%) and most of the changes in Arg4 are conservative, which is not the case for Ysc83. The non-coding regions are less conserved, with small AT-rich insertions/deletions and 20% base substitutions. However, the level of divergence is smaller in the aligned sequences of these regions than in silent sites of the ORFs, probably revealing a higher degree of constraints. The Gcn4 binding site and the region where meiotic double-strand breaks occur, are fully conserved. The data confirm that these two yeasts are evolutionarily closely related and that comparisons of their sequences might reveal conserved protein and DNA domains not expected to be found in sequence comparisons between more diverged organisms.     

SIMULTANEOUS WATER AND SOLUTE TRANSPORT IN SHRINKING MEDIA - PART 2

A simple compartmental model of simultaneous water and solute transport was developed on agar gel cubes, for particular situations in which high water loss is accompanied by shrinkage and flux interaction. The model provided a good fit for the different situations tested, and proved to behave adequately in a wider application field. Furthermore, it made it possible to obtain a simulation of the evolution of the solute contents in both compartments which was consistent with the previous studies.     

Extinguishing class B fires with dry chemicals: Scaling studies

In a continuing study of flame extinguishment,^1,2,3,4 we report on scaling studies for dry chemicals on larger heptane diffusion flames (0.29 m² and 2.32 m² pans). We demonstrate again that small particle sizes extinguish most effectively. Extinguishment is related to heat absorption by decomposing or vaporizing particles. We show that the limiting particle size for each dry chemical—that is, the maximum size which completely decomposes or vaporizes in the flame—is independent of flame size for the systems studied. We broaden and apply the concept of latent or maximum effectiveness^2,3 to pan fires of all sizes. Finally, we describe and characterize an aerodynamic effect in the transport of powders, where large particles with their higher momentum entrain and drag smaller, more effective particles into the flame.We also show that extinction curves, involving the ratio of real-to-latent extinction weight and the proportion of small to large particles, have predictable shapes and predictable quantitative levels for most dry chemicals. We have developed the real-to-latent concept along with scaling equations for agent mixtures and for a wide spectrum of agents and particle sizes.     

Characteristics of glaucoma drainage implants during dynamic and steady-state flow conditions

OBJECTIVE: This study aimed to ascertain whether the Optimed, Krupin, and Ahmed drainage devices function as valves that vary resistance depending on flow conditions to maintain pressure within a desired range. STUDY DESIGN: Experimental study. INTERVENTION: The three devices and a control cannula were submerged in fluid and perfused with balanced salt solution using a computer-driven apparatus that continuously monitors flow (Q) and pressure (P). In one set of experiments, the flow rates were maintained at 2, 5, 10, 25, or 50 microliters/min until steady-state pressures were achieved. In another set of experiments, the flow rate was increased linearly from 0 to 100 microliters/min over 15 to 20 minutes. MAIN OUTCOME MEASURES: The resistance of each implant was calculated from the first set of experiments by dividing the change in pressure (P) by the change in flow (Q) between successive perfusion rates. Flow-pressure curves were plotted from the experiments in which perfusion rate was increased linearly. RESULTS: Resistance remained relatively constant for the cannula (0.18-0.24 mmHg/microliter/min), the Krupin (0.09-0.25 mmHg/microliter/min), and the Optimed implants (0.04-0.08) throughout the tested flow rates. For the Ahmed device, conversely, resistance decreased proportionally (2.86-0.05 mmHg/microliter/min) to the increase in flow. When flow rate was increased linearly from 0 to 100 microliters/min, the Optimed and Krupin devices as well as the cannula generated a linear pressure response with a constant slope. The pressure in the two devices increased at a rate of 0.11 mmHg/microliter compared to 0.23 mmHg/microliter/min for the cannula. The flow-pressure curve for the Ahmed implant was distinct with a steep initial pressure rise and an essentially constant pressure of 12 mmHg thereafter. CONCLUSION: The Optimed and Krupin devices displayed resistance and pressure responses to various flow conditions that were similar to those of a cannula or flow resistor. In these devices, resistance remained relatively stable and pressure increased linearly with flow. The Ahmed device, conversely, functioned as a valve that closely regulated pressure within a desired range by decreasing or increasing resistance as a function of flow.     

Reactive blending via coordination chemistry—extraordinary mechanical response for atactic 1,2-polybutadiene complexed with palladium chloride

Experimental evidence in solution and in the solid state suggests that atactic 1,2-polybutadiene and palladium chloride form coordination complexes with unusual mechanical properties. Ternary phase diagrams with tetrahydrofuran as the solvent highlight regions where gelation is favored relative to precipitation. The strongest evidence for a network structure is based on the facts that (i) solid films swell in heptane, and (ii) infrared spectroscopy identifies a new absorption characteristics of three-membered rings and dihapto coordination of the olefinic sidegroup in 1,2-polybutadiene to the metal center in palladium chloride-bis(acetonitrile). Carbon-13 solid state NMR spectroscopy suggests that the polymeric palladium complex is a glass when the salt concentration is 4 mol%. NMR linewidth data together with the pulse sequence parameters suggest that the chain backbone of the polymeric palladium complex experiences a significant reduction in molecular mobility which is consistent with diamagnetic glassy materials. Most importantly, the elastic modulus of polybutadiene increases by three orders of magnitude during the transition from rubbery to glassy behavior. This type of mechanical response cannot be explained by a filler effect, crystallite reinforcement, or antiplasticization. Transition-metal coordination concepts applied to polymeric materials suggest that the enhancement in mechanical properties is a direct consequence of ‘coordination crosslinks’ where the palladium salt bridges different polymer chains. However, palladium-catalyzed rections of the olefinic sidegroup, generating a chemically crosslinked network, represent a second explanation of the significantly enhanced macroscopic physical properties of 1,2-polybutadiene in the presence of the transition-metal salt. Reactive blending via metal-ligand coordination represents a new mechanism to compatibilize polymeric mixtures that would otherwise exhibit phase separation.     

Caracterisation physico-chimique du ferrite de calcium et de lanthane Ca2LaFe3O8

In the Ca₂Fe₂O₅LaFeO₃ system a new ferrite of formula Ca₂LaFe₃O₈ has been isolated. As its precise cristallographic structure is not known, the structural model previously proposed has been tested by Mössbauer spectroscopy and magnetic measurements. The Fe³⁺ ions occupy one tetrahedral and two octahedral sites. The magnetic behaviour of Ca₂LaFe₃O₈ is close to those of Ca₂Fe₂O₅ and LaFeO₃. The Néel temperature is 735 K. The various exchange integrals have been calculated using a method previously applied to Ca₂Fe₂O₅.