Alleviation Technique for Thermal Concentration on Specific Switching Devices in Zero‐Speed Driving of PMSM

In this paper, a technique is proposed for alleviating the thermal concentration on specific switching devices by using a zero‐sequence voltage in a three‐level inverter that drives a permanent magnet synchronous motor (PMSM) in a zero‐speed and high‐torque condition. The use of the PMSM in home electronics and industrial products has become widespread, since it can realize miniaturization and a high efficiency drive. However, a large DC current flows when the PMSM is used in a zero‐speed and high‐torque condition, for example, in the hill‐start of electric vehicles, start or stop of elevators, or servo lock of servo pressing machines, and so on. In these cases, the current flows in the specific switching devices and heat generation is locally concentrated. This problem is unavoidable in a conventional two‐level inverter. A technique that can change the current path in a three‐level inverter and control the losses generated in the switching devices is proposed. We evaluated the effects of the proposed technique through a circuit simulation in which the electrical characteristics of a commercially available power device were applied. The proposed technique can reduce the highest loss of the switching devices in the three‐level inverter by about 40% as compared to that in a conventional inverter. Moreover, a method is proposed that suppresses the neutral point potential variation between the power supplies. This method can also reduce the maximum loss of the specific switching devices by about 30%.     

Heat-Induced Tendering of Turban Shell (Batillus cornutus) Muscle

The foot, opercular and visceral muscles were excised from the turban shell Batillus cornutus, and their heat-induced changes in toughness and ultrastructure were compared. When heated up to 30°C, the toughness of foot muscle decreased in the upper and middle regions, but increased in the lower region. The toughness of these three regions decreased at temperatures between 50-70°C, where collagen might be denatured. Some changes in toughness were also observed in the opercular muscle by heating up to 30°C, whereas the toughness of visceral muscle remained unchanged over a wide range of temperature. Transmission electron microscopy showed that the intrinsic structure of collagen fibrils in each muscle was lost at 60°C, with partial swelling.     

Renaturation of α1 Chains from Shark Skin Collagen Type 1

Renaturation of α1 chains from shark skin collagen (1) was measured by the increase in optical rotation and viscosity. The rotation change of the α1(1) chains became constant after 18 hr, while the viscosity increased further with time. Size exclusion chromatographic patterns of renaturation products of α1 (I) chain gave similar results to that of native collagen. The renaturation products remelted with rising temperature in a similar way to the melting of native collagen as judged from the rotation-temperature curve.     

Autoxidation of Bluefin Tuna Myoglobin Associated with Freezing and Thawing

Bluefin tuna oxymyoglobin (oxyMb) solutions were frozen either quickly at ?80°C or slowly at ?2O°C, thawed, and the metmyoglobin (metMb) to total myoglobin (Mb) ratio (metMb%) determined. When quick freezing was applied, autoxidation was clearly pH-dependent, with a minimum (metMb%, 15–40) at around pH 5.9–6.3. When slowly frozen and thawed, on the other hand, tuna Mb generally showed an extremely high metMb%. Freezing and thawing partially insolubilized tuna Mb, depending upon pH. The Mb showed the minimum ratio of insolubilization at pH 6–6.3 again. Insolubilization of tuna Mb was markedly accelerated by NaCl.     

Implementable L ∞ penalty-function method for semi-infinite optimization

This paper considers general non-linear semi-infinite programming problems and presents an implementable method which employs an exact L _∞ penalty function. Since the L _∞ penalty function is continuous even if the number of representative constraints changes, trust-region techniques may effectively be adopted to obtain global convergence. Numerical results are given to show the efficiency of the proposed algorithm.     

Preparation and characterization of ZrF4-BaF2-EuF3 planar glass films by electron cyclotron resonance plasma-enhanced chemical vapor deposition

An electron cyclotron resonance plasma-enhanced chemical vapor deposition apparatus, which is suitable for producing planar fluoride glass films, was developed. A ZrF4-BaF2-EuF3 planar glass film was synthesized by using -diketonates of Zr, Ba and Eu as starting materials and NF3 as a fluorinating gas. A CaF2 single crystal plate and a fused quartz glass plate were employed as substrates. The planar glass film obtained was colorless and transparent. As an attempt a planar waveguide which has a ZrF4-BaF2/ZrF4-BaF2-EuF3/ZrF4-BaF2 sandwich structure was also formed on a CaF2 substrate. The planar glass film and the planar waveguide were characterized by using techniques such as XPS, X-ray diffraction, DTA, ellipsometry, IR absorption, Mössbauer spectroscopy and SEM.     

Electrical Conductivity of Polycrystalline Li2SiO3 and γ-LiAlO2

Conductivities of polycrystalline Li₂SiO₃ and γ-LiAlO₂ were measured by the two-terminal ac method at T =450° to 1000°C. Intrinsic and extrinsic regions were observed. The activation energies of conductivities in the extrinsic region for both samples agreed well with those of lithium diffusion obtained by T ₁ analysis of nuclear magnetic relaxation.     

Preparation of High-Strength Calcium Phosphate Glass-Ceramics by Unidirectional Crystallization

Unidirectionally crystallized CaO-P₂O₅ glass-ceramics were produced by reheating glass rods between 450° and 580°C (glass transition temperature ∼500°C) under a temperature gradient of 30°C/cm. These glass-ceramics exhibit high bending strength (∼650MN/m²) and toughness. Sample preparation is described and compared with conventional unidirectional solidification of melts. The characteristic mechanical properties are discussed in terms of the texture of the glass-ceramics.     

Surface modification of calcium metaphosphate fibers

-calcium metaphosphate fibers having high aspect ratios of 10–120 with diameters of 2–10 m show high strength and good biocompatibility. When the fibers are soaked in simulated body fluid at 37 °C, however, no calcium phosphate phase is newly formed on the fibers. In the present work, by treating the fibers at 70 °C with dilute NaOH aqueous solution, the surface phase was converted successfully into the orthophosphate phase that was in fine sizes and was adhered. After soaking the treated fibers in simulated body fluid at 37 °C for 30 days, a new calcium phosphate phase was precipitated. This was attributed to the surface phase modified using dilute NaOH. The treated fibers are expected to show bone-bonding ability, i.e. bioactivity. ©2000 Kluwer Academic Publishers