Highly elongated,low‐aspect‐ratio tokamak produced by negative‐biased theta pinch

Ultra Low Aspect Ratio Tokamaks (ULART) are produced by using a negative‐biased theta‐pinch device. A slender conducting rod which serves as a toroidal field coil is newly installed along a geometrical center axis of the theta‐pinch coil. The ULART is quickly formed for about 10 μs by applying programmed current flows from three sets of fast banks and a slow bank to these coils and is sustained for about 100 μs. The plasma diagnosed from a magnetic probe array has a low aspect ratio A = 1.1 and a poloidal surface with a high elongation ratio κ = 10. The safety factor reaches about 30 near the separatrix edge when I_p = 280 kA flows in the plasma and I_tfc = 30 kA in the conducting rod. A preliminary result on global MHD characteristics of the ULART is also given. The plasma is unstable with respect to a vertical displacement and a toroidal n = 1 mode. The amplitudes of these modes depend on the values of I_tfc and κ. © 2001 Scripta Technica, Electr Eng Jpn, 134(4): 19–27, 2001     

Construction of an inverse model with cutoff filter and its application to a model feedback control system

An inverse system for a given time‐invariant system has been used as a compensator. However, in control systems which include traditional inverse systems, the adverse effects of sensor noise may seriously influence the systems, because the inverse system generally has high gain in the high‐frequency area. Therefore, in these control systems other compensators than the inverse system must be constructed with complex properties. In this paper, a method of design of a new inverse model with cutoff filter for the Model Feedback Control System (MFCS) is proposed. The inverse model designed by the proposed method is an approximate inverse model for a given model. The approximation can be evaluated by the norm criterion for the difference between the model and the biproper transfer function used for construction of the inverse model. In order to demonstrate the usefulness of the proposed inverse model, this inverse model is applied to the MFCS. By theoretical and numerical analysis it can be shown that the proposed inverse model can reduce sufficiently the effects of sensor noise in the MFCS. © 2000 Scripta Technica, Electr Eng Jpn, 133(4): 79–90, 2000     

Measurement of the damping coefficient of an electric power system by use of a superconducting magnet energy storage system

In this paper, a new application of superconducting magnetic energy storage (SMES) for diagnosis of power systems is proposed. Basic experiments for measurement of damping coefficient of power systems by use of SMES are carried out in an experimental system with a small generator, artificial transmission lines, and a small SMES. The SMES produces small power disturbances in the power system without affecting its operating conditions. The small power oscillations in the power system due to continuous power disturbances generated by SMES are observed. The relations among the damping coefficient, the power disturbances, and the power change of SMES are discussed for a one-machine infinite-bus system. The damping coefficients of the power system are obtained by investigating the oscillations due to the sinusoidal power changes of the SMES. The possibility of estimation of the steady-state power system stability by monitoring the damping coefficients of an operating power system by the use of SMES can be shown experimentally. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 119(3): 40–48, 1997     

Identification of enzyme responsible for erythritol utilization and reaction product in yeast Lipomyces starkeyi

We have identified the enzyme responsible for erythritol utilization and its reaction product in the yeast Lipomyces starkeyi CBS 1807. The enzyme, a polyol dehydrogenase requiring NAD+ as a coenzyme, was induced by erythritol in this yeast. We confirmed that the enzyme product was L-erythrulose by MS, NMR, and polarimeter analyses, meaning that we clarified the first step of erythritol utilization in yeasts for the first time. In the case of the oxidative reaction, D-threitol, (2R,3R)-2,3-butanediol, and erythritol were much better substrates than 21 other polyols tested. These three substrates are tetroses and have an R configuration at C-3, and whose third carbon results in easiest oxidation in this enzyme. The research of the substrate specificity in the reductive reaction demonstrated that L-erythrulose and dihydroxyacetone were better substrates, that D-acetoin was inactive and L-erythrose (aldose) was slightly active.     

A new multi-scale simulation model of the circulation: from cells to system

We developed a comprehensive cell model that simulates the sequential cellular events from membrane excitation to contraction in the human ventricle. By combining this ventricular cell model with a lumped circulation model, we examined how blood pressure dynamics in the ventricle and aorta are related to the cellular processes. To convert cell contraction into ventricular pressure using Laplace's law, we introduced a simple geometric model of a ventricle: one shaped like a thin-walled hemisphere. The force of contraction of a single cell induces tension in the hemispheric ventricular wall, which generates the ventricular and aortic pressures in the lumped circulation model. The time courses of the hemodynamic properties, as well as the volume-pressure trajectory of the left ventricle, were well reproduced. Our multi-scale cardiovascular model, which covers from cardiac cells to the circulatory system, simulates the typical characteristics of heart mechanics, such as the pressure-volume relationship, stroke volume and the effect of the increased maximum free calcium concentration on cardiovascular hemodynamics. To test the cell-circulation coupling characteristics of the model, we simulated the effects of a decrease in L-type calcium channel conductance (cell level) on left ventricular pressure (system level). The variation due to different pacing frequencies for myocyte excitation was also investigated to assess the effects of heart rate on cardiac cells and the circulatory system.     

Effect of hydration on electrical conductivity of DNA duplex: Green’s function study combined with DFT

The electrical conductivity of DNA duplex is affected by many factors such as DNA base sequence, hydration of DNA duplex, connecting configuration between DNA duplex and electrodes, thermal fluctuation of DNA duplex structure. We here investigate the electrical conducting properties of DNA duplexes sandwiched between Au electrodes by molecular simulations using nonequilibrium Green’s function method coupled with density functional theory. The results reveal the dependence of electrical conductivity on DNA base sequence as well as hydration, which are in qualitative agreement with experiment. The present results indicate the important role played by hydrating water molecules in the electrical conductivity through DNA duplexes.     

Nickel-free stainless steel avoids neointima formation following coronary stent implantation

SUS316L stainless steel and cobalt–chromium and platinum–chromium alloys are widely used platforms for coronary stents. These alloys also contain nickel (Ni), which reportedly induces allergic reactions in some subjects and is known to have various cellular effects. The effects of Ni on neointima formation after stent implantation remain unknown, however. We developed coronary stents made of Ni-free high-nitrogen austenitic stainless steel prepared using a N₂-gas pressurized electroslag remelting (P-ESR) process. Neointima formation and inflammatory responses following stent implantation in porcine coronary arteries were then compared between the Ni-free and SUS316L stainless steel stents. We found significantly less neointima formation and inflammation in arteries implanted with Ni-free stents, as compared to SUS316L stents. Notably, Ni²⁺ was eluted into the medium from SUS316L but not from Ni-free stainless steel. Mechanistically, Ni²⁺ increased levels of hypoxia inducible factor protein-1α (HIF-1α) and its target genes in cultured smooth muscle cells. HIF-1α and their target gene levels were also increased in the vascular wall at SUS316L stent sites but not at Ni-free stent sites. The Ni-free stainless steel coronary stent reduces neointima formation, in part by avoiding activation of inflammatory processes via the Ni-HIF pathway. The Ni-free-stainless steel stent is a promising new coronary stent platform.     

Processing of Al/SiC composites in continuous solid–liquid co-existent state by SPS and their thermal properties

Silicon carbide (SiC)-particle-dispersed-aluminum (Al) matrix composites were fabricated in a unique fabrication method, where the powder mixture of SiC, pure Al and Al–5mass% Si alloy was uniquely designed to form continuous solid–liquid co-existent state during spark plasma sintering (SPS) process. Composites fabricated in such a way can be well consolidated by heating during SPS processing in a temperature range between 798 K and 876 K for a heating duration of 1.56 ks. Microstructures of the composites thus fabricated were examined by scanning electron microscopy and no reaction was detected at the interface between the SiC particle and the Al matrix. The relative packing density of the Al–matrix composite containing SiC was higher than 99% in a volume fraction range of SiC between 40% and 55%. Thermal conductivity of the composite increased with increasing the SiC content in the composite at a SiC fraction range between 40 vol.% and 50 vol.%. The highest thermal conductivity was obtained for Al–50 vol.% SiC composite and reached 252 W/mK. The coefficient of thermal expansion of the composites falls in the upper line of Kerner’s model, indicating strong bonding between the SiC particle and the Al matrix in the composite.     

Boiling heat transfer from a horizontal flat plate in a pool of liquid hydrogen

Heat transfer from a flat plate facing upward immersed in a liquid hydrogen pool was measured for the pressures from atmospheric to 1.1 MPa. The flat plate heater used was 10 mm in width, 100 mm in length and 0.1 mm in thickness. Critical heat fluxes (CHFs) in saturated boiling increased with the increase in pressure up to around 0.3 MPa and then decreased with further pressure increase. The CHFs under subcooled condition at each pressure increased with the increase in sub-cooling. Discussions were made on the experimental results by comparing with those of the other cryogenic liquids and also the Kutateladze’s equations under saturated and subcooled conditions. The experimental CHFs were much smaller than the Kutateladze’s equation for higher pressure up to critical. The heater surface temperature was found to reach the critical temperature before the occurrence of hydrodynamic instability and jump to the film boiling regime at the lower heat flux in the higher pressure range. It was suggested that the CHFs are determined not by the heat flux but by the temperature in the higher pressure range.     

High-cycle fatigue characteristics of quasi-isotropic CFRP laminates over 10 cycles (Initiation and propagation of delamination considering interaction with transverse cracks)

High-cycle fatigue features of over 10⁸ cycles, particularly the initiation and propagation of edge delamination considering the effects of transverse cracks, were investigated using quasi-isotropic carbon-fiber-reinforced plastic (CFRP) laminates with a stacking sequence of [45/0/−45/90]_s in this study. In the relationship between a transverse crack density and initiation and growth of edge delamination, it was found that fatigue damage growth behavior varied depending on applied stress. It was observed that edge delamination initiated and grew at parts where transverse cracks were dense at ordinary applied stress, whereas it was observed that edge delamination grew before or simultaneously with transverse crack propagation at a low applied stress and high-cycle loading. In addition, the critical transverse crack density where delamination begins growing was calculated to evaluate the interaction between transverse crack and edge delamination growth.