Optimal planned maintenance with salvage cost for a two-unit standby redundant system

This paper considers the optimal spare ordering policies for a cold standby redundant system with two dissimilar units. Especially, the planned maintenance schedule with salvage cost is discussed. The failure time distributions for respective units are assumed to be arbitrary. By applying the expected cost per unit time in the steady-state and the stationary availability as criteria of optimality, the optimal ordering policy minimizing or maximizing each criterion is obtained under some economical and/or physical assumptions. Finally, numerical examples are presented, and the effect of the failure time distributions for the optimal ordering policy is examined in detail.     

Thermal performance of a packed bed reactor for a high‐temperature chemical heat pump

The thermal performance of a chemical heat pump that uses the reaction system of calcium oxide/lead oxide/carbon dioxide, which is developed for utilization of high‐temperature heat above 800°C, is studied experimentally. The thermal performance of a packed‐bed reactor of a calcium oxide/carbon dioxide reaction system, which stores and transforms a high‐temperature heat source in the heat pump operation, is examined under various heat pump operation conditions. The energy analysis based on the experiment shows that it is possible to utilize high‐temperature heat with this heat pump. This heat pump can store heat above 850°C and then transform it into a heat above 900°C under an approximate atmospheric pressure. An applied system that combines the heat pump and a high‐temperature process is proposed for high‐efficiency heat utilization. The scale of the heat pump in the combined system is estimated from the experimental results. Copyright © 2001 John Wiley & Sons, Ltd.     

Explanation of impact load curve in ball impact test in relation to thermal aging

Solder joints are required to have high impact strength for use in portable electronic products. To make solder joints with high impact strength, qualitative evaluation methods of impact strength are required. Ball impact tests have been widely adopted in evaluating the impact strength of solder joints because of their easy implementation. Impact load curves obtained from ball impact tests are used as an evaluation indicator of impact strength of solder joint. However, a relation between fracture behavior and impact load curve has not yet been clarified, and an explanation of the impact load curve has not yet been provided in detail. In addition to this, detailed study about the relation between IMC layer thickness and impact strength has not been performed, although the IMC layer thickness formed at the interface would significantly affect the impact strength of the solder joint. This study aimed to explain the impact load curve in the ball impact test and to reveal the effect of the IMC layer thickness on the impact strength of the solder joint. Sn–3.0Ag–0.5Cu solder was reflowed on an electroless Ni–P plated Cu substrate (Ni–P), and a ball impact test was then carried out to evaluate the impact strength. This study found that the ball impact test is effective to evaluate the interfacial strength of solder joints. In the impact load curve, it is estimated that the solder bump keeps deforming until the interfacial crack initiates (maximum load), and the interfacial crack initiates after the maximum load and propagates along the interface between the solder and Ni–P. The suitable evaluation of impact strength became possible by measuring the correspondence relation between the deformation distance of the solder bump after fracture and the energy until maximum load and the relation between the area fraction of the residual solder on the fractured pad and the energy after maximum load. And, it is proved that the impact strength decreased with increasing aging time because the growth of the IMC layer remarkably degraded the interfacial strength of the solder joint.     

Contrasting effects of water-soluble and water-insoluble dietary fibers on bile acid conjugation and taurine metabolism in the rat

The effect of the type of dietary fiber on the bile acid and taurine metabolism was examined in rats. Diets containing 10% of various water-soluble fibers (citrus pectin, konjak mannan, guar gum) as compared to a fiber-free diet increased biliary excretion of total bile acids. In contrast, water-insoluble dietary fibers (cellulose, corn bran, chitin; 10% in the diets) as well as cholestyramine (5% in the diet) considerably, decreased bile acid excretion. Water-soluble dietary fibermediated increases in bile acid excretion were totally attributable to increases in glycine-conjugates. Thus, these fibers greatly increased by the bile acid glycine-to-taurine ratio (G/T). Excretio of glycine conjugates decreased more than that of taurine conjugates in rats fed various water-insoluble dietary fibers. As a results, G/T in rats fed water-insoluble fibers was significantly lowered as compared to G/T in animals fed a fiber-free diet. Cholestyramine did not affect the G/T ratio of bile acids. Fecal bile acid excretion and the activities of hepatic cholesterol 7α-hydroxylase (EC 1.14.13.17) in rats fed various water-soluble dietary fibers approximately doubled as compared to the respective values for rats fed a fiber-free diet. Whereas cholestyramine greatly increased these parameters, water-insoluble fibers did not significantly affect them. Various water-soluble fibers decreased hepatic concentration and urinary excretion of taurine as well as the activity of hepatic cysteine dioxygenase (EC 1.13.11.20). In contrast, water-insoluble fibers considerably increased hepatic taurine concentrations and enzyme activities. The parameters for taurine metabolism were unaffected by cholestyramine. It was suggested that the types of dietary fiber affected hepatic taurine synthesis and thus modified bile acid glycine/taurine ratios.     

Attentional modulation of the mere exposure effect.

The mere exposure effect refers to the phenomenon where previous exposures to stimuli increase participants’ subsequent affective preference for those stimuli. This study explored the effect of selective attention on the mere exposure effect. The experiments manipulated the to-be-attended drawings in the exposure period (either red or green polygons in Experiments 1 and 2; both red and green polygons in Experiments 3 and 4) and black to-be-evaluated drawings in the affective judgment period (morphologically identical to the red or green polygons in Experiments 1 and 4; morphologically identical to the composite drawings in Experiments 2 and 3). The results showed a significant mere exposure effect only for the target shapes involved in attentional selection, even when the participants could recognize the nontarget shapes. This indicates that selective attention modulated the mere exposure effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

High-melt-strength polypropylene with electron beam irradiation in the presence of polyfunctional monomers

High-melt-strength polypropylene (PP) was achieved with irradiation by an electron beam generated from an accelerator in the presence of polyfunctional monomers (PFM). Among 16 PFMs, the relatively shorter molecular chain bifunctional monomers such as 1,4-butanediol diacrylate (BDDA) and 1,6-hexanediol diacrylate (HDDA) were the most effective for enhancing the melt strength of PP. The concentration and dose of the HDDA to obtain the high melt strength PP in irradiation under nitrogen gas atmosphere were 1.5 mmol/100 g PP and 1 kGy, respectively. DSC measurement and dynamic mechanical analysis showed that the thermal behavior of the high-melt-strength PP was different from that of the original PP. Crystallinity and crystallization temperature during cooling after heating were lower and higher in high melt strength PP than original PP, respectively. Elongational viscosity at 180°C of the high-melt-strength PP showed a remarkable increase at a certain elongational time with constant strain rate, demonstrating the typical property of high-melt-strength samples. This implies that a few higher molecular chains of PP, formed by intermolecular combination of its chain by HDDA in irradiation, give higher melt strength to induce entanglement of molecular chains. © 1996 John Wiley & Sons, Inc.     

Irradiation effects of boron carbide used as control rod elements in fast breeder reactors

The paper describes radiation effects on 8₄C pellets used as control rod elements in the Enrico Fermi Fast Breeder Reactor. Pellet swelling (Δ$\text{V/V}$) caused by irradiation was less than 1% in which crystal lattice swelling was less than 20%. Many microcracks, a main cause of pellet swelling, appeared in the irradiated pellets. The production of microcracks was related to graphite precipitation in the pellets before irradiation. Open pores which did not exist in the unirradiated pellets were formed in the irradiated ones. In a unit cell of B₄C, the α-axis elongated by 0.025 Å and the $\text{c-}\text{axis}$ shrank by 0.07 Å by irradiation. Moreover, we found three recovery stages which were from room temperature to 400°C, from 400 to 750°C and from 850 to 1100°C. The recovery mechanisms in the irradiated pellets are discussed in terms of the helium behavior.     

Relationship between local structure and stability in hen egg white lysozyme mutant with alanine substituted for glycine

We prepared five mutant lysozymes in which glycines whose dihedralangles are located in the region of the left-handed helix, Gly49,Gly67, Gly71, Gly102 and Gly117, were mutated to an alanineresidue. From analyses of their thermal stabilities using differentialscanning calorimetry, most of them were more destabilized thanthe native lysozyme, except for the G102A mutant, which hasa stability similar to that of the native lysozyme at pH 2.7.As for the destabilized mutant lysozymes, their X-ray crystallographicanalyses showed that their global structures did not changebut that the local structures changed slightly. By examiningthe dihedral angles at the mutation sites based on X-ray crystallographicresults, it was found that the dihedral angles at these mutationsites tended to adopt favorable values in a Ramachandran plotand that the extent and direction of their shifts from the originalvalue had similar tendencies. Therefore, the change in dihedralangles may be the cause of the slight local structural changesaround the mutation site. On the other hand, regarding the mutationof G102A, the global structure was almost identical with thatof the native structure but the local structure was drasticallychanged. Therefore, it was suggested that the drastic localconformational change might be effective in releasing the unfavorableinteraction of the native state at the mutation site.     

Concentration of docosahexaenoic acid in glyceride by hydrolysis of fish oil withcandida cylindracea lipase

In an attempt to concentrate the content of DHA (docosahexaenoic acid) in a glyceride mixture containing triglyceride, diglyceride and monoglyceride, fish oil was hydrolyzed with six kinds of microbial lipase. After the hydrolysis, free fatty acid was removed and fatty acid components of the glyceride mixtures were analyzed. When the hydrolysis withCandida cylindracea lipase was 70% complete, the DHA content in the glyceride mixture was three times more than that in the original fish oil. The EPA (eicosapentaenoic acid) content became almost 70% of the original fish oil. Hydrolysis with other lipases did not result in an increase in the DHA content in the glyceride mixtures. Hydrolysis of DHA-rich tuna oil (DHA content is about 25%) withCandida cylindracea lipase resulted in 53% DHA in the glyceride mixture. The EPA content, however, remained close to that of the original tuna oil. In this report, the acyl chain specificity of lipases is evaluated in terms of hydrolysis resistant value (HRV). HRV is the ratio between the DHA contents in the glyceride mixture of hydrolyzed oil and original oil. HRV clearly indicates differences in hydrolysis between DHA and other fatty acids (e.g., saturated and monoenoic acids).