Mixing and mass transfer in concentric-tube airlift fermenters: Newtonian and non-newtonian media

The mixing and mass transfer characteristics in concentric-tube airlift gas-liquid contactors intended for possible use as fermenters are discussed. Liquid velocities, circulation times, gas hold-ups, and volumetric mass transfer coefficients were measured in water and aqueous carboxy methyl cellulose solutions. Measurements were made in an inverted conical-bottom device with draft tubes of three different diameters. An increase of liquid velocities at the column axis and a corresponding decrease of volumetric mass transfer coefficients due to the introduction of draft tubes were found for water as the liquid medium. For the non-Newtonian fluids, a complicating influence of the draft tubes on liquid velocity and mass transfer, which is attributed to a combination of factors related to improvement of liquid circulation and reduction of apparent viscosity, was observed.     

Turbulent heat and mass transfer in dilute polymer solutions

A new model based on Levich's three-zone model is developed to discuss the turbulent heat and mass transfer in drag-reducing solutions. The proposed model, which has no adjustable parameters and is represented in an explicit form, provides satisfactory predictions of the maximum heat and mass transfer reduction in smooth and rough pipes. The mass transfer to a disk rotating in drag-reducing solutions is also discussed using the proposed model.     

Catalytic activity of alkaline-earth Y zeolites and concentration of bare metal ions located in the site II of faujasite structure

The concentration of the bare metal ions located in the Site II of the alkaline-earth Y zeolites was determined from the CO adsorption, and the concentration sequence was obtained as follows: SrY>CaY>MgY>BeY. This sequence corresponded well to the radius of exchanged cation. Catalytic activity of alkaline-earth Y zeolites for the disproportionation reaction of NO, further, was discussed, and activity order of per unit amount of bare Site II cation was determined as follows: BeY>MgY>CaY>SrY>BaY. This order corresponded well to the strength of the electrostatic field of alkaline-earth Y zeolites.     

Synthetic strategies of marine polycyclic ethers via intramolecular allylations: linear and convergent approaches

Strategies for the synthesis of polycyclic ethers based on intramolecular allylations are overviewed. The intramolecular condensation of allylic stannanes and aldehydes is a powerful tool for the synthesis of oxepane derivatives. The reaction is successfully applied to the iterative total synthesis of hemibrevetoxin B (2). Further, the intramolecular allylation of alpha-acetoxy ethers provides an efficient method for the convergent synthesis of polycyclic ethers. The usefulness of the latter strategy is demonstrated in the convergent total synthesis of gambierol (4).     

Effect of coal particle size on the coal hydrogenation reaction — In relation to the plasticity of coal

The effect of coal particle size on the catalytic hydrogenation of dry coal was investigated for three Hokkaido coals (Japan) of different ranks. It was found that the effect of coal particle size on conversion is dependent on coal rank. A greater difference in conversion with respect to coal particle size is noticed for coals of lower carbon content. The physical appearance of the products in the autoclave after the reaction suggests that the effect of particle size on conversion is dependent on the plastic properties of the heated coal sample. When the reaction proceeds with coal in the plastic state, the effect of particle size is small. As indicated by the product distribution, the plastic properties of a coal sample are related to the yield of asphaltene (hexane insoluble/benzene solubles) and/or the structural parts of original coal which yield asphaltene.     

Saccharomyces cerevisiae mata mutant cells defective in pointed projection formation in response to α-factor at high concentrations

We have isolated Saccharomyces cerevisiae MAT a mutant cells that do not form a pointed projection but elongate in response to α-factor at high concentrations. Complementation tests defined three genes, PPF1, PPF2, and PPF3 (for pointed projection formation), necessary for pointed projection formation. Allelism tests with genes known to be needed for projection formation revealed that PPF1 is identical to SPA2, while PPF2 and PPF3 are not allelic to SST2, STE2, SPA2, BEM1 or SLK1/SSP31/BCK1. The morphology of MAT a ppf mutants treated with high concentrations of α-factor is similar to that of MAT a PPF cells treated with α-factor at low concentrations. Quantitative mating tests showed that PPF2 and PPF3 are not essential for mating in either MAT a or MATα background. Monitoring of division arrest and expression of an α-factor-inducible gene revealed that mutations in the PPF genes do not affect the responses of MAT a cells to low concentrations of α-factor. Unlike wild-type cells, the ppf mutants exhibited early recovery from α-factor-induced division arrest. Furthermore, vegetatively growing ppf3-1 cells are slightly defective in cell separation of mother and daughter cells and in selection of the correct bud sites in all cell types. These results indicate that PPF2 and PPF3 are involved in the response to α-factor at high concentrations and that PPF3 is also required for proper establishment of polarity in vegetative growth.     

Schottky barrier height variation with metallurgical reactions in aluminum-titanium-gallium arsenide contacts

The behaviour of A1/Ti/n-GaAs Schottky contacts under heat treatment at around 400°C have been studied for their application to GaAs MESFETs. Barrier heights have been determined using both I-V and C-V measurements as a function of heat treatment time. Reaction products due to heat treatment have been studied by X-ray diffraction and Auger electron spectroscopy. The A1/Ti/n-GaAs Schottky contacts barrier height shows an $\text{“N”-}\text{shaped}$ variation in response to heat treatment time. A marked reduction in barrier height follows a slight increase at the initial annealing stage. The barrier height then takes a minimum value. The slight increase in barrier height at the initial stage in the heat treatment is brought about by a Ti and GaAs reaction. The marked barrier height reduction is closely correlated to formation of the compound Al₃Ti. The increase in barrier height observed after the reduction can be explained in terms of GaAlAs formation at the metal-semiconductor interface. This seems to indicate that heat treatment is essential for application of Al/Tin-GaAs Schottky contacts to practical devices.