Analysis of brushless three-phase synchronous generator without exciter

Recently, a demand for small-capacity generators has been increasing as electric sources in small ships and automobiles or as portable electric sources driven by engines. It is desired that the structure of small-capacity generators be simple and robust, and that the generators be highly reliable, easily maintained and controlled. This paper describes an analysis of the original brushless synchronous generator without exciter. The output voltage can be adjusted in the wide range by controlling the stator dc current. To analyze the characteristics of this generator, the finite element method is applied. It is found that the results of theoretical analysis agree well with the experimental results.     

Effect of Forming Pressure on the Internal Structure of Alumina Green Bodies Examined with Immersion Liquid Technique

Green bodies prepared by compaction of alumina granules were made transparent by an immersion liquid technique, and the internal structure was characterized with an optical microscope to study the effect of forming pressure on the internal structure. Clear images obtained by the technique provide more detailed information than other existing methods for structures ranging from one to tens of micrometers. Intergranular pores were present between unfractured granules. Their sizes and concentration tended to decrease with increasing forming pressure. However, pores were clearly present even in the green body prepared at 600 MPa. A rod- and needlelike feature was also found and was concluded to correspond to a high-density region. The significance of large pores and high-density regions on processing as well as the details of the technique is discussed.     

Veno-right ventricular extracorporeal membrane oxygenation for thoracic surgery: an experimental study in dogs

Different photoactivatable derivatives of toxin 3 (CTX) Naja naja siamensis were obtained after CTX reaction with N-hydroxysuccinimide esters of p-azidobenzoic, p-azidotetraflourobenzoic, p-benzoylbenzoic and p-[3-(trifluoromethyl)-3H-diazirin-3-yl]benzoic acids. The ion-exchange HPLC profiles for the reaction products were very similar in four cases, with one predominant peak corresponding to the derivative containing the label at Lys23. After [125I]iodination, CTX photoactivatable derivatives were cross-linked to the nicotinic acetylcholine receptor from Torpedo californica under optimized conditions. The highest cross-linking yield (up to 16% of the bound toxin) was observed for azidobenzoyl-Lys23-CTX. Different receptor subunits were found to be labelled depending on the nature of the photoactivatable group: the azido derivatives labelled the gamma and delta subunits, benzoylbenzoyl derivative labelled the alpha and delta subunits, while p-[3-(trifluoromethyl)-3H-diazirin-3-yl]benzoyl derivative reacted with alpha, gamma and delta subunits. The cross-linking experiments in the presence of varying concentrations of (+)-tubocurarine demonstrated that the Lys23-attached diazirinyl group contacts the delta and alpha subunits in one ligand-binding site, whereas at the other site, for another CTX molecule, the contacts of the Lys23-diazirinyl are with gamma and alpha subunits. This means that the central loop in the two CTX molecules binds at the alpha/gamma and alpha/delta interfaces. Calculation of the sterically possible displacement of diazirinyl nitrogen, basing on the known X-ray structure of CTX, showed that this value does not exceed 13 A. The results obtained favor the disposition of the ligand-binding sites at the subunit interfaces, with the distance between alpha and delta, or alpha and gamma subunits at these sites being not more than 13 A.     

Microhardness measurements and the Hall-Petch relationship in an AlMg alloy with submicrometer grain size

An Al-3% Mg solid solution alloy was subjected to intense plastic deformation, using either equal-channel angular (ECA) pressing or torsion straining, to produce grain sizes in the submicrometer range. Static annealing at elevated temperatures led to grain growth and average grain sizes of up to > 100 μm. As-fabricated and statically annealed specimens were used to determine the variation in microhardness with grain size, and results confirm that the Hall-Petch relationship persists down to at least the finest grain size examined experimentally (∼90 nm). The results provide no evidence to support the claims of a negative Hall-Petch slope when the average grain size is very small, but there is evidence of a decrease in the slope of the Hall-Petch plot at the very finest grain sizes (< 150 nm); this is attributed to the increased participation of mobile extrinsic dislocations in the boundary regions when taking the hardness measurements.     

Grain refinement and superplasticity in a magnesium alloy processed by equal-channel angular pressing

The extrusion/equal channel angular pressing (EX-ECAP) processing procedure, in which magnesium-based alloys are subjected to extrusion followed by ECAP, was applied to a Mg-7.5 pct Al-0.2 pct Zr alloy prepared by casting. Microstructural inspection showed the EX-ECAP process was effective in reducing the grain size from ∼21 μm after extrusion to an as-pressed grain size of ∼0.8 μm. It is shown through static annealing that these ultrafine grains are reasonably stable up to 473 K, but grain growth occurs at higher temperatures. Tensile specimens were cut from the billets prepared by EX-ECAP and testing showed these specimens exhibited superplasticity at relatively low temperatures with maximum elongations up to >700 pct. By processing through EX-ECAP to a higher imposed strain and thereby increasing the area fraction of high-angle boundaries, it is demonstrated that there is a potential for achieving high-strain-rate superplasticity. This article is based on a presentation made at the Symposium entitled “Phase Transformations and Deformation in Magnesium Alloys,” which occurred during the Spring TMS meeting, March 14–18, 2004, in Charlotte, NC, under the auspices of the ASM-MSCTS Phase Transformations Committee.     

Achieving enhanced ductility in a dilute magnesium alloy through severe plastic deformation

Experiments were conducted to evaluate the utility of a new processing procedure developed for Mg-based alloys in which samples are subjected to a two-step processing route of extrusion followed by equal-channel angular pressing (designated as EX-ECAP). The experiments were conducted using a Mg-0.6 wt pct Zr alloy and, for comparison purposes, samples of pure Mg. It is shown that the potential for successfully using ECAP increases in both materials when adopting the EX-ECAP procedure. For the Mg-Zr alloy, the use of EX-ECAP produces a grain size of ∼1.4 μm when the pressing is undertaken at 573 K. By contrast, using EX-ECAP with pure Mg at 573 K produces a grain size of ∼26 μm. Tensile testing of the Mg-Zr alloy at 523 and 573 K after processing by EX-ECAP revealed the occurrence of significantly enhanced ductilities with maximum elongations of ∼300 to 400 pct.     

Processing and characterization of nanostructured Cu-carbon nanotube composites

Carbon nanotube (CNT) reinforced nanostructured Cu matrix composite with a grain size less than 25 nm has been successfully fabricated via a combination of ball milling and high-pressure torsion. CNTs were found to be homogeneously dispersed into the metal matrix, leading to grain refinement with a narrow grain size distribution and significant increase in hardness.     

Effect of Hydrogen on Tensile Properties of Ultrafine-Grained Type 310S Austenitic Stainless Steel Processed by High-Pressure Torsion

This study addresses a hydrogen effect on the tensile properties of a type 310S austenitic stainless steel with ultrafine-grained structures produced by high-pressure torsion (HPT) and subsequent annealing. The mean grain size was reduced to ~85 nm by the HPT processing. The grain size was increased by the post-HPT annealing, but the grain size of ~265 nm was retained after annealing at 1023 K (750 °C). The tensile strength of ~1.2 GPa, which is approximately twice as much as that of the solution-treated specimen, was attained in the 1023 K (750 °C) post-HPT-annealed specimen. The elongation to failure was restored up to ~15 pct by the post-HPT annealing, although it was still insufficient in comparison with the ~55 pct elongation of the solution-treated specimen. There was no change in the tensile strength of the HPT-processed specimens and the post-HPT-annealed specimens by hydrogen charging with the hydrogen content in the range of ~20 to 40 mass ppm. The HPT-processed and the 773 K (500 °C) post-HPT-annealed specimens exhibited a ductility loss through the fully shear type fracture. The hydrogen charge into higher temperature post-HPT-annealed specimens with σ-FeCr precipitates led to a mild hydrogen embrittlement.     

Homogeneous Strain Introduction Using Reciprocation Technique in High-Pressure Sliding

Metallurgical and Materials Transactions A - This study examines strain distribution occurring in the high-pressure sliding (HPS) processing for rods of pure Al and an AZ61 alloy. The strain...     

c-axis oriented ZnO formed in a rotating magnetic field with various rotation speeds

A rotating magnetic field was used to fabricate c-axis oriented zinc oxide. The influence of rotating speed on orientation structure was also examined. The aligned axes had the largest diamagnetic susceptibility, which axis was difficult to align with a static magnetic field. In c-axis oriented ZnO, the degree of orientation (Lotgering factor) in the green compact ranged from 0.2 to 0.5 along c-axis. The Lotgering factor increased with rotating speed. For all samples with the rotating magnetic field, the degrees of orientation increased up to above 0.9 after sintering at 1573 K.