800 V 4H-SiC RESURF-type lateral JFETs

This letter proposes to show that a lateral switching device has some unique advantages, including little dependence on substrate defects, low on-resistance, and a simple design of heat radiation. A reduced surface field (RESURF) type SiC-JFET is one of candidate devices for an electric or hybrid automobile application. Small RESURF-type SiC-JFETs with gate width of 200 /spl mu/m and a blocking voltage of 800 V were fabricated. The fabrication and characteristics of the devices are described and discussed.     

Realization of instantaneous torque control of an induction motor considering secondary flux as a parameter

Recently, many researches aiming at the realization of high‐performance and high‐precision control of induction motors have been reported, and instantaneous torque control of an induction motor can be regarded as one of the most important topics in this field. In previous works, the authors developed a new method to realize instantaneous torque control of an induction motor with a voltage‐source inverter, and demonstrated both its numerical simulations and experimental results. Unfortunately, the mathematically complicated derivation of the control method made it difficult to understand intuitively, and hindered us from analyzing the detailed characteristics of motor speed changes. In this paper, the authors propose a new method to realize instantaneous torque control of an induction motor, which differs from the concept of vector control. The proposed method is a two‐degree‐of‐freedom control which considers the instantaneous torque command and secondary flux command as parameters. The analytical solution reported here is a particular solution of the differential state equation of an induction motor, and can be expressed as a simple explicit function of the instantaneous torque command, secondary flux command, and motor speed. The authors show the validity of the proposed method through numerical simulations and experimental results. This paper aims the realization of high‐performance control of an induction motor. The authors propose a new method to realize instantaneous torque control without transient torque with a voltage‐source inverter. © 2001 Scripta Technica, Electr Eng Jpn, 137(1): 48–56, 2001     

Brushless self-excited three-phase synchronous generator without exciter

This paper describes principles together with analytic and experimental studies of an exciterless, brushless, and self-excited three-phase synchronous generator which was devised by authors. Since traditional brushless and dc self-excited three-phase synchronous generators without exciter did not have the self-exciting function by series characteristic component proportional to the load current inside the generator, they need auto-voltage regulating equipment or a transformer with three windings and condensers to obtain constant voltage characteristics. It also has the following problem in the case of two-pole traditional generator: oscillatory tension is generated at the shaft of the rotor caused by the magnetic force between magnetic poles of stator and rotor windings, and it causes mechanical vibration and noise. This paper proposes a new brushless and self-excited three-phase generator solving the aforementioned problems: the ratio of poles of the windings for providing power to load (armature and field windings) to the windings for supplying exciting power (stator and rotor exciting windings) is 1 to 5. Then oscillatory tension does not generate theoretically. Furthermore, a self-exciting three-phase generator using the 5th-harmonic component of armature reaction which makes series characteristic component proportional to the load current, currently is available. In this paper, the winding construction, the electric circuit, and the principle of the aforementioned generator are described, and the experimental results of the trial-produced generator show that the three-phase terminal voltage waveforms are almost sinusoidal and also balanced, and the voltage can be kept almost constant for the change of load. This generator has high reliability because of its simple construction.     

Diagnostic expert systems for defects in forged parts

This paper describes the development of a diagnostic expert system that identifies the cause of various manufacturing defects in hot forging and suggests remedies. The patterns of defect generation are various and due to many possible causes. They depend on part designs, tool designs and process conditions. Pertinent factors include part shape, the state of lubrication, location of the performed workpiece on the die and formability of the materials. This paper utilizs the theory of conditional probability to construct a diagnostic expert system that can adapt and learn its diagnostic mechanism through field data. A demonstration program, FORDIA, runs in HyperCard. FORDIA takes the part defect symptoms, uses conditional probability theory to identify possible causes and suggests remedies.     

Enzymatic enrichment of arachidonic acid from Mortierella single-cell oil

An attempt was made to enrich arachidonic acid (AA) from Mortierella single-cell oil, which had an AA content of 25%. The first step involved the hydrolysis of the oil with Pseudomonas sp. lipase. A mixture of 2.5 g oil, 2.5 g water, and 4000 units (U) Pseudomonas lipase was incubated at 40°C for 40 h with stirring at 500 rpm. The hydrolysis was 90% complete after 40 h, and the resulting free fatty acids (FFA) were extracted with n-hexane (AA content, 25%; recovery of AA, 91%). The second step involved the selective esterification of the fatty acids with lauryl alcohol and Candida rugosa lipase. A mixture of 3.5 g fatty acids/lauryl alcohol (1:1, mol/mol), 1.5 g water, and 1000 U Candida lipase was incubated at 30°C for 16 h with stirring at 500 rpm. Under these conditions, 55% of the fatty acids were esterified, and the AA content in the FFA fraction was raised to 51% with a 92% yield. The long-chain saturated fatty acids in the FFA fraction were eliminated as urea adducts. This procedure raised the AA content to 63%. To further elevate the AA content, the fatty acids were esterified again in the same manner with Candida lipase. The repeated esterification raised the AA content to 75% with a recovery of 71% of its initial content.     

Radiographic changes in the patella after total knee arthroplasty without resurfacing the patella. Comparison of osteoarthrosis and rheumatoid arthritis

Two groups of patients were studied, both in accordance with ACR criteria. First group (41 cases) suffering R.A. Second group (36 cases) suffering O.A. In both pathologies MMPs, ICAM and VCAM from synovial fluid and plasma were studied. Measurements were made with ELISA-sandwich in a Metrolab spectrophotometer at 410 nm for MMPs, and 491 nm for ICAM and VCAM. As control, samples of patients with noninflammatory muscle skeletal disorders or traumatic arthritis and healthy witness were used. Synovial concentration of MMPs in R.A. was 1402 +/- 76 ng/ml, a higher significant value (p < 0.0001) compared with osteoarthritis: 353 +/- 23 ng/ml. In the witness plasma, MMPs were not detected. Plasmatic and synovial levels of the adhesion molecules present different values in both pathologies and between them. Synovial ICAM level in R.A. (280 +/- 9.8 ng/ml) is significantly higher than in O.A. (163 +/- 10 ng/ml) (p < 0.001), but lower than the plasmatic ones (370 +/- 35 ng/ml) (p < 0.001). All these values are significantly higher than the normal plasma (121 +/- 6.5 ng/ml) (p < 0.01, p < 0.005, and p < 0.0001, respectively) VCAM increase regarding basal values (140 +/- 5.6 ng/ml) (p < 0.001) and in a similar proportion for both pathologies (R.A.: 186 +/- 9.3 ng/ml and O.A.: 207 +/- 14.3 ng/ml). Their plasmatic levels were higher (270 +/- 45 and 320 +/- 38 ng/ml) (p < 0.001) but without significative difference between them. There is correlation among MMPs, ICAM and VCAM variations. The variability can be explained by concomitance several evolutive steps. Each pathology shows a different grade of cellularity, inverted predominance in the relation TIMPs/ collagenase and different generator mechanisms of MMPs. Our findings reinforce the importance as diagnostic guide of adhesion molecules dosage, and possible therapeutic use of MMPs inhibitors and ICAM or VCAM antagonists en R.A. and related pathologies.     

Material performance in a solvent extraction Liquefaction plant in Japan

Corrosion behaviour of various steels and alloys in the solvent extraction coal liquefaction process in Japan has been studied by the inplant testing in a 1 ton/ day plant and by the laboratory tests related to it. The severest corrosion was observed in the high pressure separator, corrosion thickness loss and pitting depth being the greatest and stress corrosion cracking being observed for 18–8 series austenitic stainless steels. The cause may be the occurrence of water condensate containing high Cl^? and H₂S. Otherwise corrosion was relatively mild. No obvious symptom of notorious organic-chloride corrosion reported in the U.S. has been observed.     

Surface Diffusivity under High-Pressure Gas

The sintering behavior of TiO₂ under high-pressure gas (100 MPa) was studied with respect to densification rate, decreasing rate of specific surface area, and narrowing rate of pore size distribution. At the low sintering temperature (800°C) used in this study, the densification rate under high- pressure gas was similar to that under low (i.e., 1 atm) pressure. The specific surface area decreased and the pore size distribution narrowed at a faster rate under high- pressure gas than under low-pressure gas. These results imply that high-pressure gas enhances surface diffusion.     

Size-controlled simple fabrication of free-standing, ultralong metal nanobelt array

Free-standing, ultralong (up to several millimeters) nanobelts of gold, silver, and copper were fabricated by a template approach. Firstly, a metal nanofin array was prepared on a substrate via metal nanocoating of the template surface and selective removal of the metal top layer and template. Electroless plating and sputtering were employed for the metal nanocoating. In this approach, the minimum width and thickness of the Au nanobelt were 95 and 30 nm, respectively. Systematic control of the nanobelt width (from 95 to 350 nm) was successfully achieved by adjusting the template height. Free-standing nanobelts of several millimeters in length were fabricated and maintained their unique structure and alignment, even on a mesh grid.