Rolling and roll-drawing of ultrahigh molecular weight polyethylene reactor powders

Ultrahigh molecular weight polyethylene (UHMWPE) reactor powders have been found to be processable in the solid state by the techniques of rolling and roll-drawing. Plates of compacted UHMWPE reactor powder were prepared below their melting points. These plates were then rolled at 124°C. The maximum uniaxial draw ratio (DR) obtained by multiple rolling was about 10. In additional experiments, rolled plates of a DR of 6 were further drawn by tensile stretching at a temperature of 135°C. The specimens prepared by rolling and by the two-stage draw were characterized by tensile measurements, differential scanning calorimetry (DSC), and X-ray diffraction. Results show that, on rolling alone, the tensile modulus and tensile strength achieved were 3 GPa and 42 MPa, respectively, at a DR of 9.6. The rolled plates were effectively drawn further to a total DR of 86. Such highly drawn films exhibited tensile moduli and tensile strength up to 81 and 1.3 GPa, respectively. A high crystallinity and high crystal orientation were also obtained by the two-stage draw.     

Interaction of discoidal complexes of dimyristoyl phosphatidylcholine-cholesterol-apolipoprotein A-I with human plasma high density lipoprotein HDL3

The interaction of human plasma high density lipoproteins (HDL₃) with discoidal complexes of apolipoprotein A-I (apoA-I) and dimyristoyl phosphatidylcholine (DMPC) containing 0, 10, 20 or 30 mol % cholesterol was investigated. Discoidal complexes containing various amounts of cholesterol were prepared by incubating apoA-I and DMPC-cholesterol liposomes for 12 hr at 25 C; the protein-lipid complexes were isolated by gel filtration chromatography on Bio-Gel A15m. Increasing the cholesterol content from 0 to 30 mol % caused a decrease in the fluidity of the discoidal complexes as determined by fluorescence polarization with 1,6-diphenyl-1,3,5-hexatriene; a reduced phase-transition amplitude; a decrease in the ratio of apoA-I to DMPC; and an increase in the width of the discoidal complexes as determined by electron microscopy after negative staining. Incubation of the apoA-I-lipid complexes with HDL₃ resulted in a complete breakdown of the discoidal structures and a transfer of DMPC and cholesterol to HDL₃. As a result of lipid transfer, there was an increase in the size of HDL₃. These in vitro results may be of significance as they relate to the interconversion of HDL subfractions during lipoprotein-lipase-induced lipolysis of triglyceride-rich lipoproteins.     

THE INFLUENCE OF PROCESS PARAMETERS ON THE INTERFACIAL CHEMISTRY OF γ-GPS ON ALUMINIUM: A REVIEW

Within the “International Collaborative Programme on Organosilane Adhesion Promoters” (ICOSAP), scientists from the U.S. and Europe contributed to the understanding of an organosilane primer process, based on an aqueous solution of γ-glycidoxypropyl trimethoxysilane (γ-GPS), used currently for aerospace repair purposes. Parameters such as temperature of cure, ageing time, and concentration of the aqueous solution have been investigated, and this work reviews the effect that each variable has on the process, and the resulting integrity of the GPS/aluminium interface. The aim of the work was to provide a more environmentally friendly replacement for pretreatments containing Cr(VI) that are currently used, such as chromic acid anodising and acid etching employed for the structural adhesive bonding of aluminium.

The formation of covalent interfacial bonding is shown to be a function of the hydrolysis and condensation of the silane molecules in solution as well as the type of solvent used. The curing temperature of the aqueous film on the aluminium is also shown to have an effect on the chemistry of the resulting primer film and its efficacy as an adhesion promoter. All these parameters must be optimised to obtain durability that matches that obtained by a phosphoric acid anodising pretreatment. This work reports on the various studies performed towards this aim carried out within the remit of the ICOSAP initiative, with a particular emphasis on the interfacial chemistry between γ-GPS and the aluminium substrate, and indicates the manner in which the results point the way towards a viable, environmentally friendly pretreatment for the adhesive bonding of aluminium for aerospaceapplications.     

Interdiffusion Between Ti3SiC2–Ti3GeC2 and Ti2AlC–Nb2AlC Diffusion Couples

In this work, we report on the interdiffusion of Ge and Si in Ti₃SiC₂ and Ti₃GeC₂, as well as that of Nb and Ti in Ti₂AlC and Nb₂AlC. The interdiffusion coefficient, D _int, measured by analyzing the diffusion profiles of Si and Ge obtained when Ti₃SiC₂–Ti₃GeC₂ diffusion couples are annealed in the 1473–1773 K temperature range at the Matano interface composition (≈Ti₃Ge_0.5Si_0.5C₂), was found to be given by
D _int increased with increasing Ge composition. At the highest temperatures, diffusion was halted after a short time, apparently by the formation of a diffusion barrier of TiC. Similarly, the interdiffusion of Ti and Nb in Ti₂AlC–Nb₂AlC couples was measured in the 1723–1873 K temperature range. The D _int for the Matano interface composition, viz. ≈(Ti_0.5,Nb_0.5)₂AlC, was found to be given by
At 1773 K, the diffusivity of the transition metal atoms was ≈7 times smaller than those of the Si and Ge atoms, suggesting that the former are better bound in the structure than the latter.     

The Severn Barrage and other tidal energy options: Hydrodynamic and power output modeling

Details are given herein of the current main proposals for tidal energy provision from the Severn Estuary, in the UK, with particular emphasis being focused on the Severn Barrage project, as originally promoted by the Severn Tidal Power Group. In particular, emphasis has focused on assessing the potential hydro-environmental impacts and power outputs of a barrage across the estuary, with an unstructured grid, high resolution, model being developed and applied to the estuary to assess the implications of each of five shortlisted proposed schemes on the hydrodynamic, geomorphologic, flood risk and faecal indicator organism changes within the estuary. An outline is given of recent research on power refinements to the model to assess the options for power generation. The results show that the Severn Barrage has the potential to reduce the tidal currents in a highly dynamic estuary. This leads to the reduction of suspended sediment loads (particularly upstream of the barrage), an increase of light penetration within the water column and, potentially, an increase in the benthic bio-diversity and the level of aquatic life in the estuary. The results also show that the Severn Barrage will reduce markedly the risk of flooding upstream of the barrage and to a lesser extent downstream of the structure. In contrast the alternative options have far less impact on flood risk changes. In addition to the Severn Barrage some results are shown herein for a typical lagoon option, namely the Fleming Lagoon.     

The effect of various dietary factors on the size distribution of lymph fat particles in rat

By means of cellulose acetate electrophoresis and measurement of radioactivity, lipoproteins (d≤1,006) of lymph collected from rats fed a diet containing fats added to labeled fatty acids for 20–24 hr, have been separated into two kinds differing in their size. Fats with different saturated and unsaturated fatty acid content were tested: corn oil, lard, mutton tallow, tripalmitin, corn oil-lard mixture, and randomized palmitic-linoleic triglycerides. Factors studied were: (a) increased amounts of these fats given alone or included in a test meal; (b) added amounts of nutrients (other than fats) in the test meal; (c) adaptation to a diet containing 20% fat for 10 days. The major part of the labeled lymph lipid was always transported by the smaller particles. Size distribution of lymph fat particles was influenced by some of the factors studied. Generally, unsaturated fats produced higher amounts of larger particles.     

Controllability of Product Moisture Content When Nonscreened Sawdust Is Dried in a Spouted Bed

The control of the dried product's moisture content is of importance in the production of fuel pellets. Tests have been made in air and superheated steam in a spouted bed using the outlet temperature of the drying medium as a control parameter of the dried material's moisture content. For superheated steam different settings for the inlet medium temperature are also used. In the moisture content interval of 8-17% wet base there is a linear correlation between the dried material moisture content and the outlet temperature of the drying medium. When drying nonscreened sawdust in a spouted bed it is recommendable to use the outlet temperature of the drying medium as a control parameter of the dried material moisture content. This is independent of the size of the sawdust, whether superheated steam or air is used as a drying medium.     

High-aspect-ratio nanoporous membranes made by reactive ion etching and e-beam and interference lithography

Nanoporous membranes engineered to mimic natural filtration systems can be used in “smart” implantable drug delivery systems, hemodialysis membranes, bio-artificial organs, and other novel nano-enabled medical devices. Conventional membranes exhibit several limitations, including broad pore size distributions and low pore densities. To overcome these problems, lithographic approaches were used to develop porous silicon, silicon nitride, ultrananocrystalline diamond (UNCD), and polymer film membranes. Here we report processing of high porosity, high-aspect-ratio membranes by two techniques: UNCD fabricated by reactive ion etching after e-beam lithography and epoxy fabricated by interference lithography.     

Oral acetylsalicylic acid induces biliary cholesterol secretion in the rat

Several agents can alter biliary cholesterol secretion, critical for cholesterol excretion and gallstone formation. Although salicylate effects on bile formation and gallstones have been studied, biliary lipid secretion has not been measured during oral aspirin treatment. We examined whether oral acetylsalicylic acid affects bile lipid secretion. Three groups of young rats were fed chow for 3 wk. Two of the groups then received aspirin at either 1.67 or 3.33 g/kg diet for 4 d. Serum, hepatic, and bile lipids were measured, as were enzymes of cholesterol synthesis and esterification. With oral aspirin, bile cholesterol secretion increased by 42% and hepatic cholesteryl ester content decreased by 40%. Serum cholesterol and hepatic free cholesterol did not change. To evaluate mechanisms of the cholesterol hypersecretion, hypothyroid animals fed low-fat or fish oil diets and repleted with triiodothyronine were also studied. Aspirin stimulated cholesterol secretion to a degree similar to triiodothyronine. An additive response was seen in fish oilfed rats. Aspirin did not appear to have a primary action on 3-hydroxy-3-methylglutaryl-CoA reductase or acyl CoA:cholesterol acyltransferase activities, and had no direct effect on esterification of cholesterol by isolated hepatocytes. Aspirin may directly increase cholesterol transport into bile or have cell membrane effects which alter cholesterol transport. It remains to be determined whether the observed alterations in bile cholesterol secretion are specific to the rat or also apply to humans.     

Photooxidation of polystyrene: Irradiation at 254 and 365 nm

Studies have been made of the near surface photooxidation of atactic polystyrene films prepared in the absence of air. The samples were photooxidized on exposure to air at two frequencies, 254 and 365 nm, using a calibrated mercury irradiation source with filters. Most studies were made at 40°C and as a function of irradition time with the reactions characterized by changes in molecular weight and composition. The former was evaluated by gel permeation chromatography and the latter by transmission Fourier transform infrared spectroscopy and by multiple-internal-reflectance infrared spectra using different angles and different crystals to evaluate compositions as a function of film depth. Species identified in photooxidation include the generation of hydroperoxides and the appearance of carbonyl bands with the latter identified by the spectral shift asociated with the exposure of the photooxidized polystyrene surface to ammonia. These results suggest that principal products of near-surface oxidation of polystyrene are carboxylic acids.