Periodic control of continuous stirred tank reactors—III: Case of multistage reactors

The optimal periodic control of a multistage CSTR in which a nonisothermal parallel reaction is taking place is investigated. By applying the infinite-frequency pi criterion it is examined in what condition the optimal periodic control is proper. Then, the optimal steady control and the suboptimal periodic control are determined by numerical calculation. The results indicate that the improvement in the reactor performance for the periodic control relative to that for the steady control is very much increased with increase in the number of stages.     

Human placenta gangliosides

Gangliosides extracted from human placenta were composed of four major components (G1–G4), which were purified by silica beads column chromatography. The structures of these gangliosides were analyzed by exoglycosidase treatments, 400 MHz proton magnetic resonance spectroscopy and gas chromatography-mass spectrometry and were concluded to be as follows: Gangliosides containing more than 10 sugar residues were observed in addition to the above four major components. But ganglio-series gngliosides were undetectable in the placenta.     

Amino acid sequence of a four-iron-four-sulphur ferredoxin isolated from Bacillus stearothermophilus

A novel method of RNA fractionation based on a gradual release of the RNA molecules from ribonucleoprotein complexes has been used for the analysis of ribosomal and non-ribosomal complexes of rat liver cytoplasm. Adsorption of native ribonucleoproteins on a Celite column (occuring through only the protein moiety) followed by a consequent dissociation of RNP complexes brought about by various agents results in RNA fractionation in accordance with the tightness of the RNA-protein bonds. The cytoplasmic ribosomal and rapidly labelled non-ribosomal RNA species are separated into several fractions identified as 18S and 28S rRNA's, mRNA and messenger-like RNA. A relatively small fraction (about 10% of the total) of rRNA tenaciously bound to protein has been also revealed.     

Two-dimensional thickness measurements based on internal reflection ellipsometry

An imaging ellipsometer technique on internal reflection geometry that can measure the thickness distribution of a thin film possessing an assumed refractive index is described. Because a prism is used for the internal reflection geometry, it was theoretically predicted that angular derivation from the normal incidence on the prism surface affects only the psi value by a factor of 0.97 at maximum. Measurements were carried out for an optical system of silica substrate-TiO2 layer-silica layer-protein film-air, with a thin-film array of dried protein as the sample film. Thickness of the protein films was two-dimensionally estimated only from the measured map of the delta value by use of the simulated relationship between the thickness and the delta value. The thickness map obtained was coincident on the whole with the results according to a mechanical scanning. The detection limit was approximately +/- 0.2 nm. These findings validate the optical effect of a high-index additional layer to improve the sensitivity and precision of thickness measurements of the sample film on transparent substrates.     

Dibenzothiophene desulfurizing enzymes from moderately thermophilic bacterium Bacillus subtilis WU-S2B: purification, characterization and overexpression

The moderately thermophilic bacterium Bacillus subtilis WU-S2B desulfurized dibenzothiophene (DBT) at 50 degrees C through the selective cleavage of carbon-sulfur bonds. In this study, three enzymes involved in the microbial DBT desulfurization were purified and characterized. The first two enzymes, DBT monooxygenase (BdsC) and DBT sulfone monooxygenase (BdsA), were purified from the wild-type strain, and the last one, 2'-hydroxybiphenyl 2-sulfinic acid desulfinase (BdsB), was purified from the recombinant Escherichia coli overexpressing the gene, bdsB, with chaperonin genes, groEL/ES. The genes of BdsC and BdsA were also overexpressed. The molecular weights of BdsC and BdsA were determined to be 200 and 174 kDa, respectively, by gel filtration chromatography, suggesting that both enzymes had four identical subunits. BdsB had a monomeric structure of 40 kDa. The three enzymes were characterized and compared with the corresponding enzymes (DszC, DszA, and DszB) of mesophilic desulfurization bacteria. The specific activities of BdsC, BdsA, and BdsB were 84.2, 855, and 280 units/mg, respectively, and the latter two activities were higher than those of DszA and DszB. The heat stability and optimum temperature of BdsC, BdsA, and BdsB were higher than those of DszC, DszA, and DszB. Other enzymatic properties were investigated in detail.     

Residence time distribution of polymer melt in the T-die

Theoretical or rheological calculations for crosshead die geometry were thought not worthwhile until recently, and restrictor, or choker, bars were often excessively relied upon for film uniformity. Thus, the residence time distribution of a polymer melt was infrequently calculated especially in the T-die, because it was assumed to be very wide in T-dies. This report provides a general equation expressing the residence time distribution of polymer melts in T-dies, and indicates how to take an optimum combination of the flow-path dimensions in order to obtain both a high flow uniformity and a comparatively narrow residence time distribution across the die width. Such a T-die designed by the above considerations will produce a shorter heat history and improved physical properties of the sheet or film produced.     

Geometry design of a coat-hanger die with uniform flow rate and residence time across the die width

This article provides an approximate but sufficiently practical method of geometry design of a coat-hanger die having both uniform flow rate and residence time across the full width of the die. Such a die is often needed when a heat-sensitive resin such as poly(vinyl chloride) is sheeted, because different residence times across the die width are apt to cause a sheet defect in the transverse direction of the sheet. Although some assumptions were made facilitating mathematical analysis, an application of this method to a sheeting die 1 m wide gave good uniformity of flow rate and residence time.     

Dynamic characteristics and dual control of a ball screw drive with integrated piezoelectric actuator

This paper describes the precision continuous path tracking control by using a dual-actuated single stage. First, fine-drive mechanism and the dynamic model of the entire drive system are described. In the simulation model, the dynamic characteristic of the dual-actuated stage is investigated to see whether it can provide precise motion by using dual control. Second, the fine motion controller is designed. Adjusting the control parameters, a positioning resolution of 20 nm and a bandwidth of 260 Hz were obtained. Third, the frequency responses of coarse and fine drives are experimentally investigated. After that, the dual controller is designed based on the investigated dynamics. Finally, whether coarse motion and fine motion could work complimentarily by the dual servo is examined in the experiments. By using the simultaneous dual controller, tracking errors were reduced sufficiently compared to the single coarse control.