Long term oxidation resistance and thermal stability of Ni-aluminide/Fe-aluminide duplex diffusion coatings formed on ferritic steels at low temperatures

A coating with a duplex structure consisting of an outer Ni₂Al₃ layer and an inner Fe₂Al₅ layer was formed on a commercial type of ferritic steel P92 using a two step process of electroless Ni/B plating followed by pack aluminising at 650 °C. Nearly 11,000 h oxidation test in air and more than 13,000 h isothermal annealing test in argon atmosphere were carried out to assess the long term oxidation resistance and thermal stability at 650 °C. The amount of oxidation was only about 0.66 mg/cm² for the coating as compared to 10.3 mg/cm² for the uncoated steel after nearly 11,000 h oxidation test. Inward Al diffusion took place during oxidation test, which led to the transformation of the outer Ni₂Al₃ layer to NiAl and increase in the Al diffusion depth. However, once the outer Ni₂Al₃ layer was completely transformed to NiAl, it stayed stable during the remaining period of oxidation test, providing long term oxidation resistance. Kirkendall voids formed and grew and then finally disappeared in the coating layers due to interdiffusion processes taking place at the oxidizing temperature at the interfaces between different layers of the duplex coating. No spallation was observed in the coating during the entire period of the oxidation or isothermal annealing tests.     

Ultrahigh molecular weight polyethylene as used in articular prostheses (a molecular weight distribution study)

Currently there is widespread use of ultrahigh molecular weight polyethylene (UHMWPE) acetabular components in total joint replacement prostheses. What has been most surprising about the wear of UHMWPE under such circumstances is the occurrence of brittle fracture. Such fracture had not been observed in the usual engineering tests done in the laboratory on UHMWPE. It was only when prosthese which had been removed from patients were examined or run in hip joint simulators with serum or synovial fluid as the lubricant, that brittle fracture was encountered. The problem of environment-enhanced brittle fracture in plastics dates back to 1946. Interestingly, the phenomenon was first described in polyethylene. The prime variables involved are polymer molecular weight, sensitizing environment, stress filed, and temperature. Other things being equal, brittle behavior in polyethylene is extremely sensitive to the amount of low molecular weight polymer present. In the light of the foregoing we have studied the molecular weight distribution in six commercially available UHMWPE components. These were obtained from six different manufacturers. The specimens were characterized both on their bearing (wear) surfaces and in their interior bulk. The results obtained indicate that:

• 1 The UHMWPE components contain substantial amounts of low molecular weight polymer.
• 2 The UHMWPE components differ significantly in molecular weight distribution.
• 3 The UHMWPE components contain substantial amounts of crosslinked polymer.

     

Temperature-sensitive mutants of influenza A virus. XIV. Production and evaluation of influenza A/Georgia/74-ts-1[E] recombinant viruses in human adults

The two temperature-sensitive (ts) lesions present in influenza A/Hong Kong/68-ts-1[E] (H3N2 68) virus were transferred via genetic reassortment to influenza A/Georgia/74 (H3N2 74) wild-type virus. A recombinant clone possessing both ts lesions and the shutoff temperature of 38 C of the Hong Kong/68 ts donor and the two surface antigens of the Georgia/74 wild-type virus was administered to 32 seronegative adult volunteers. Thirty-one volunteers were infected, of whom only five experienced mild afebrile upper respiratory tract illness. The wild-type recipient virus was a cloned population that induced illness in five of six infected volunteers. Therfore, the attenuation exhibited by the Georgia/74-ts-1[E] virus could reasonably be assumed to be due to the acquisition of the two ts-1[E] lesions by the Georgia/74 wild-type virus. The serum and nasal wash antibody responses of the ts-1[E] vaccinees were equivalent to those of the volunteers who received wild-type virus. The two ts lesions present in the Hong Kong/68-ts-1[E] virus have now been transferred three times to a wild-type virus bearing a new hemagglutinin, and in each instance the new ts recombination exhibited a similar, satisfactory level of attenuation and antigenicity for adults. It seems likely that the transfer of the ts-1[E] lesions to any new influenza virus will regularly result in attenuation of a recombinat virus possessing the new surface antigens.     

Spectrophotometric determination of diphenhydramine. HC1 in pharmaceutical preparations

A new spectrophotometric method has been developed for determining diphenhydramine. HC1, based on solvent extraction into chloroform of the complex formed with bromocresol green. The complex solution in chloroform showed maximum absorption at 415 nm and obeyed Beer's law over the concentration range of 3.0-12.0 microgram/ml. The molar absorptivity of the complex was 2.02 x 10(4). Complex formation and extraction was complete and quantitative over the pH range from 2 to 5. The ratio of diphenhydramine to bromocresol green was 1:1. Excipients, coloring matter, flavoring agents, and other substances likely to be present in diphenhydramine preparations do not interfere in the determination. Direct determinations in tablet, capsule, sirup, and lotion preparations were carried out satisfactorily, and the average recovery was 100 +/- 1.0%.     

产品设计对改进产品生命终期的影响

本研究的主要目标是在鼓励创造性思维的同时，建立一个结构化方法用于阐明产品生命周期策略。当前提倡采用适用于大多数产品的通用规则。联系“通用性”原则，与“放之四海皆准”的方法相比，本研究找出了影响产品生命终期的主要因素。研究结果可分为两个核心部分。第一，根据产品的技术特性，该方法论确定了合理的产品生命终期策略第二，为了评估和验证该方法，将产品生命终期策略的分类和当前工业实践进行了对比，开发的产品生命终期设计顾问(ELDA)软件，指导生产商确定适合的产品生命终期策略。对产品生命终期进行分类的能力使得设计者能够重新设计对环境负荷较小产品。这篇文章为设计者和生产管理者提供了合适的产品生命终期策略。通过更深入的理解相应产品的生命终期策略，本文的研究结果能够帮助设计者开发适合他们情况的、系统的产品生命终期策略。通过技术革新或者价值链的改进，将ELDA的结果运用于生命终期改善。