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.

     

A RANDOM PARAMETER PROCESS FOR MODELING AND FORECASTING TIME SERIES

Abstract. A generalized autoregressive (GAR) process {Z ( t ) ; t = 0 , ±1, …} is defined to satisfy the recurrence relation Z(t) = A_θ (t)Z (t -l)+ u( t ), where {A_θ(t); t = 0,±1, …} is itself a stochastic process depending on a vector parameter θ and where {u( t ); t = 0, ±1, …} is white noise with Eu ² ( t ) = a ². This paper develops theory and methodology and implementing the class of GAR processes for time series modeling and forecasting. Conditions on the 'parameter process' { A _θ ( t ); t = 0, ±1, …} are obtained for the existence of a GAR process; necessary and sufficient conditions on { A_θ ( t ) ; t = 0, ±1, …} for existence of a stationary GAR process are also obtained. Procedures are developed for computing maximum likelihood estimates of the parameters 0 and u² and for computing the minimum mean squared error forecasts for GAR processes.     

The analysis of phospholipids in soy lecithin by HPLC

A high performance liquid chromatography (HPLC) method is described for the HPLC analysis of major phospholipids in soy lecithin. The method entails dissolving soy lecithin in chloroform prior to analysis. The HPLC determination uses a normal phase column and a mobile phase of acetonitrilemethanol-H₃PO₄ with detection at 205 nm. The data presented illustrates that the method is rapid, accurate and precise for the determination of phospholipid in soy lecithin.     

Modification of alkenyl chain profile in plasmalogens of rat heart mitochondria by dietary trielaidin

Effects of dietary trielaidin upon the alkenyl chain profile of plasmalogens were studied using heart mitochondria of rats fed a semi-purified diet containing 10% of fat supplement in which elaidic acid accounted for 69% of total fatty acids. Alkyl substituted dioxane (ASD) derivatives of the alkenyl groups of plasmalogens were prepared and analyzed by silver nitrate TLC and by GLC on different phases (BDS and OV-275). After two months of feeding the experimental diet, 40% of the ASD contained atrans-octadecenyl chain, suggesting that dietary elaidic acid was reduced in vivo to the corresponding alcohol and incorporated into plasmalogens. There was a simultaneous decrease in the percentage of ASD containing saturated chains, but the percentage of ASD substituted withcis-octadecenyl chains was not significantly affected. These observations suggested that elaidic acid may compete with saturated fatty acids, but not withcis-octadecenoic acids during the plasmalogen biosynthesis. Feeding trielaidin did not seem to have any significant influence on the relative proportions of plasmalogens, which accounted for 11–12%, on a phosphorus basis, of total heart mitochondria phospholipids.     

Talk in virtual contexts: reflecting on participation and online learning models

Computer-mediated conferencing has been adopted, particularly for purposes of online course provision, as a method that can deliver community. Widespread interest in a communities-of-practice approach within both informal and formal learning has strengthened perceptions of the value of creating a community online. A case study of asynchronous computer conferencing for the purposes of leadership development in schools is the focus for a study of the features and the discursive quality of the online interaction that occurred. Two analytical approaches are used: discourse analysis and social network analysis. These highlighted different aspects of the case, in terms of the role of peers versus the expert moderator (or 'hotseat guest'), the extent of readership versus contribution and the tone and content of the discussion. Evidence that contributors were learning from the interaction was identified and strong links with place-based communities of practice were also evident. Nevertheless, the online interaction could not be said to constitute a community or to be evidently developing in that direction. Its features as a network, where weak links were key to a sharing and knowledge-construction process, were more salient. Networks offer the potential for weak connections that have a particular value for connecting across dispersed practitioners and potentially bridging between communities of practice and other forms of organisation and groupings.     

Consistent flavor naming predicts recognition memory in children and young adults

The relationship between flavor naming and recognition memory was evaluated in groups of children and young adults who either self-generated flavor names or chose flavor names from a list of four alternatives. The adults were more successful at naming and remembering the flavors, with the age differences in naming performance tending to be larger than differences in memory performance. Differences in recognition memory among the age groups were modest, ranging from 3% to 12%. Providing flavor labels improved naming accuracy, but not naming consistency or memory for younger children (4-7 years old). Labels improved naming accuracy and consistency for the older children (8-11 years old), and showed a trend toward improving memory. Labels improved naming accuracy, consistency and recognition memory in adults. Consistent naming was a powerful predictor of recognition memory for each age group and test condition. Consistently named flavors were remembered correctly on 88% of the trials while inconsistently named flavors showed no evidence of memory. It was concluded that flavor recognition memory and naming consistency were both rooted in successfully matching flavor percepts to a multi-dimensional flavor representation that includes semantic information.     

Oxidation of Starch by Thermochemical Processing

The oxidation of starches of different amylose content with several oxidants has been investigated to maximize carboxyl content, increase water solubility and give products with new and novel properties. Methods of preparation studied were ambient-batch, jet cooking, jet cooking-drum drying, and drum drying alone. Other variables evaluated were reaction pH, jet cooking temperature, and oxidant concentration. Hypochlorite was the most effective oxidant and gave the highest carboxyl content in all preparation methods. Oxidized starches prepared by jet cooking and/or drum drying were of low viscosity and water soluble. SEM's of commercial oxidized starch showed intact granular structure, whereas samples prepared by instantaneous high temperature procedures showed complete gelatinization. Gel permeation chromatography showed structural depolymerization of the starches when high temperature processing was used. Copper binding capacity was evaluated on selected samples.     

Floral Odor Bouquet Loses its Ant Repellent Properties After Inhibition of Terpene Biosynthesis

In their natural environment, plants are synchronously confronted with mutualists and antagonists, and thus benefit from signals that contain messages for both functional groups of interaction partners. Floral scents are complex blends of volatiles of different chemical classes, including benzenoids and terpenoids. It has been hypothesized that benzenoids have evolved as pollinator attracting signals, while monoterpenoids serve as defensive compounds against antagonists. In order to test this hypothesis, we reduced terpene emission in flowers of Phlox paniculata with specific biosynthetic inhibitors and compared the responses of Lasius niger ants to natural and inhibited floral scent bouquets. While the natural odors were strongly repellent to ants, the bouquets with a reduced emission rate of terpenoids were not. The loss of the flowers’ ability to repel ants could be attributed predominantly to reduced amounts of linalool, a monoterpene alcohol. Flying flower visitors, mainly hoverflies, did not discriminate between the two types of flowers in an outdoor experiment. Since individual compounds appear to be capable of either attracting pollinators or defending the flower from enemies, the complexity of floral scent bouquets may have evolved to allow flowers to respond to both mutualists and antagonists simultaneously.     

Using Electrical Capacitance Tomography to Investigate Gas Solid Contacting

An ECT system has been shown to be useful in observing differences in particle behaviour in a bubbling fluidised bed. An image analysis technique is further described that utilises the construction of solids concentration profiles at three key values, x = 0.2, x = 0.5 and x = 0.8, which have been identified as important solids concentrations in a new Bubble Structure Model. Significant differences in the bubble structure are shown to result when the concentration of fine particles is slightly increased in a bubbling fluidised bed. Changes of this type would seriously alter the gas solid contact efficiency in the fluidised bed, which would significantly influence selectivity of in‐bed catalytic reactions and gas residence time.