Safety assessment of genetically engineered yeast: elimination of mutagenicity of the yeast Saccharomyces cerevisiae by decreasing the activity of methylglyoxal synthase

Summary  Methylglyoxal synthase catalyses the transformation of dihydroxyacetonephosphate to methylglyoxal, a toxic 2-oxoaldehyde which is found to be present in the yeast Saccharomyces cerevisiae DKD-5D-H. Yeast cells in which genes for phosphoglucose isomerase, phosphofructokinase and triosephosphate isomerase had been extrachromosomally amplified by using a multi-copy plasmid showed an increased ability to induce mutagenesis in standard tests when compared to wild type yeast. This response is mainly due to the increased amount of methylglyoxal in the engineered cells. To decrease the mutagenic activity and make it possible to use genetically engineered yeasts for practical fermentation processes, a mutant having a decreased level of methylglyoxal synthase activity was isolated. When transformed with genes for the glycolytic enzymes, the mutant cells showed extremely low levels of methylglyoxal content and mutagenic activity, both levels being comparable with those of non-transformed DKD-5D-H cells.     

Structure analysis of Ni (1 1 0) surface using computer simulation of NICISS

The relaxation at a Ni (1 1 0) surface has been estimated using the computer simulation of the 180 neutral impact-collision ion scattering spectroscopy (NICISS). The computer simulations employing ACOCT program code based on the binary collision approximation (BCA) are performed for the case of 1.5 keV He⁺ ions incident along the direction of the Ni (1 1 0) surface. It is found that the experimental results are well reproduced by the ACOCT simulations including the inward relaxation of 7% of the first interlayer spacing and the outward relaxation of 5% of the second interlayer spacing at the Ni (1 1 0) surface.     

A piezoelectric-drive table and its application to micro-grinding of ceramic materials

A micro-positioning table with a 0.005 μm resolution has been developed to enhance the performance of a conventional grinding machine in the fine grinding of ceramics. A piezoelectric actuator with high stiffness and resolution has been applied to drive the table and to provide small depths of cut for the workpiece. The performance of the table is investigated with both open and closed-loop operation to drive the actuator. The accuracy and stiffness of the positioning are improved by means of the closed-loop control. Grinding experiments with ceramics, such as partially stabilized zirconia (PSZ) and hot-pressed silicon nitride (Si₃N₄), were carried out to demonstrate the performance of the table. The actual resolution of depth-of-cut control was determined by measuring ground groove depths on the ceramic surface. A mirror-like surface on the ceramic was easily obtained by grinding at the small depth of cut of 0.1 μm with the aid of the table.     

Effect of mechanical alloying beyond the completion of glass formation for Ni-Zr alloy powders

Elemental powders of nickel and zirconium were mechanically alloyed over a wide concentration range 10 to 90 at % Zr. The amorphous single phase was formed over the range 20 to 80 at % Zr. The effect of the excessive mechanical alloying on the glass formation was studied by continuing ball-milling beyond the completion of the glass formation for the powders with the average compositions Ni₃₀Zr₇₀, Ni₅₀Zr₅₀ and Ni₇₀Zr₃₀. A partial crystallization took place in all three cases and its initiation was the fastest in Ni₃₀Zr₇₀ and was delayed with decreasing zirconium content. The critical factor for triggering the crystallization was attributed to the oxygen contamination for the zirconium-rich Ni₃₀Zr₇₀ powders and to the reduction in glass-forming ability for the nickel-rich Ni₇₀Zr₃₀ powders. The latter conclusion is drawn from the facts that the impurity concentrations arising from the debris of the stainless steel balls and the vial are gradually accumulated with increasing milling time and that the effective zirconium concentration is reduced below the critical concentration of approximately 20 at % as a result of alloying with the elements iron, chromium and nickel in the stainless steel.     

Annealing of commercial block polypropylene. I. Thermal and physical properties

Investigations were carried out regarding the effect of annealing of ethylene–propylene block copolymer (block PP) moldings on their tensile impact strength (TIS), brittle temperature (Tb), and other mechanical properties. Annealing near the melting point improves TIS and Tb as the result of recrystallization. With a system in which a minute amount of talc is added as a nucleating agent, the degree of improving TIS through annealing is considerably less than that with a nonnucleated system. The effect of annealing on the impact strength is due to changes of fine texture and morphology of crystallites and is explicable by recrystallization and polymer diffusion. © 1992 John Wiley & Sons, Inc.     

Optical current transformer for gas insulated switchgear usingsilica optical fiber

The high accuracy optical current transformer (optical CT) for gas insulated switchgear (GIS) using a silica optical fiber has been developed. The linear birefringence was reduced by twisting the newly developed double coated optical fiber. The current of up to 8000 A was measured within electric noise error of 3.8 Arms and a sensitivity change of ±0.4% was observed over the temperature range from -20 to 90°C. This change corresponds to the temperature dependence of the Verdet constant of silica. When the vibrating acceleration of 8G was applied by the gas circuit breaker motion, no signals were distinguished from the background noise level of 3.8 Arms. The long term test was carried out and the accuracy of the measurements was kept to within ±0.15% during 8 hours. This is the first practical optical CT to satisfy all requirements for GIS     

Performance of a 3000/6000 V, 1000 kVA class superconducting transformer developed for a prospective power transmission model system integrated under superconducting environment (PROMISE)

A 3000/6000V, 1000 kVA class superconducting transformer (SC-Tr) was developed for a Prospective Power Transmission Model System Integrated under Superconducting Environment (PROMISE). In this transformer, the core and superconducting windings are immersed in liquid helium and the major insulation is provided by the liquid helium. This paper describes both the design features and measured characteristics of the SC-Tr. Fundamental characteristics of the SC-Tr are obtained through no-load, short-circuit tests and quench experiments. The results of the no-load test have verified that the SC-Tr has the capability to withstand ac voltage of 3000/6000 V of 60 Hz without any partial discharge. The short-circuit tests have proved that the SC-Tr is capable of carrying ac current of 170 Arms without quench in the superconducting windings. Furthermore, in a real-load experiment with the PROMISE, electric power of 3800 V-460 kVA of 50 Hz in high-voltage side is transmitted through this SC-Tr.