The Influence of Adherend Topography on the Fracture Toughness of Aluminium-Epoxy Adhesive Joints in Humid Environments

The adherend surface topography has a dramatic effect on the durability of structural bonds formed between aluminium and an epoxy adhesive. Systematic changes in the micro-roughness of an aluminium adherend were achieved using an ultra-milling technique to prepare surfaces with topographies ranging from ultra-flat to a sawtooth profile with a base angle of approximately 60° and a peak-to-valley depth of 10 μm. The fracture toughness of double-cantilever beam specimens, stressed in the Mode 1 direction and exposed to a humid environment was found to change by a factor of approximately one hundred as the sawtooth profile angle was increased. These changes in fracture toughness may be accounted for through complex interrelationships between moisture diffusion and interphase mechanical properties, each with a strong dependence on the surface micro-topography.     

Ultrasonic measurements of the elastic stiffness constants of oriented polyethylene

High density polyethylene (Rigidex 9), a high density copolymer of polyethylene and poly(butene-1) (Rigidex 2000), and low density polyethylene (Alkathene WJG 11) were oriented by hot drawing. The crystalline texture, as determined by wide- and low-angle X-ray diffraction, was a highly oriented chain axis in the draw direction with random orientation transversely and with lamellae surfaces perpendicular to the draw direction. Elastic stiffness constants were measured by a contact-probe ultrasonic pulse technique at 2.5 MHz both before and after annealing in a temperature range which did not significantly alter the crystalline texture. Assuming orthorhombic symmetry the nine stiffness constants of Rigidex 2000 and the three longitudinal and three shear stiffness constants of Rigidex 9 were measured after drawing and after subsequent annealing. Only the longitudinal constants of Alkathene were measured, as shear waves could not be transmitted. The longitudinal stiffness in the draw direction was markedly affected by drawing and by annealing, while the crystalline texture remained substantially unchanged; by comparison the other stiffness constants showed little change. Drawn Rigidex 9 reached a tensile modulus in the draw direction of 69 GPa. The results are compared with ‘static’ and low frequency measurements reported in the literature.     

A study on the orientation effects in polyethylene in the light of crystalline texture

Special sample types established and characterised in Parts 1 and 2 [1,2] were examined systematically under different modes of external deformation at constant temperatures. The structural changes recorded by means of wide- and low-angle X-ray patterns fully substantiated the bodily rotation of the otherwise unaltered crystallites in accordance with the interlamellar slip mechanism postulated in Parts 1 and 2, both in tension and under two modes of compression. Dimensional changes, however, were significantly in excess of those expected from the rotation of crystallites, but were uniquely correlated with this relation in the different samples under different conditions of deformation. This points to a unique structural and mechanistic interrelation between the crystallites and more compliant amorphous regions. As the X-ray long periods were unaffected by the deformation, the more extensible material cannot be identical to that associated with the lamellar periodicity, a fact which points to a previously unsuspected superlamellar regularity in the texture. A simple structural suggestion is made.     

Power system transmission network expansion planning using AC model

An optimisation technique to solve transmission network expansion planning problem, using the AC model, is presented. This is a very complex mixed integer nonlinear programming problem. A constructive heuristic algorithm aimed at obtaining an excellent quality solution for this problem is presented. An interior point method is employed to solve nonlinear programming problems during the solution steps of the algorithm. Results of the tests, carried out with three electrical energy systems, show the capabilities of the method and also the viability of using the AC model to solve the problem.     

Factors affecting in vitro formation of tannin-protein complexes

In interaction of condensed tannins from Desmodium intortum and Lotus pedunculatus and tannic acid (hydrolysable tannin) with salivary mucoproteins (from sheep and goats), plant leaf proteins and bovine serum albumin were evaluated. These studies were carried out over a pH range of 2-0-9-0 and different inorganic ion conditions to simulate conditions in which dietary proteins would interact with tannins in a ruminant digestive tract. Insoluble tannin-protein interactions were found at pH 4–5–5–5 for bovine serum albumin and 3–5–5–5 for plant leaf protein. The present study showed that pH alone was not the sole determinant for tannin-protein complex formation, since tannin-protein complexation was found in the pH range 6-0–6-5 when different inorganic ions were added to the solutions. Insoluble complexes were not formed with salivary proteins, although precipitation by tannic acid was achieved at 5°C. This suggests that tannins may form soluble rather than insoluble complexes with salivary proteins. It was concluded that purified F1 leaf protein (the major protei occurring in leaf tissue) ought to be used as the test protein for evaluating tannin-protein interactions for in vitro assay procedures. Using this method it was calculated that 27–43% and 19–40% of available plant protein may interact with condensed tannins from Desmodium intortum and Lotus pedunculatus, respectively.     

Stabilized Magnesium/Perfluoropolyether Nanocomposite Films by Helium Droplet Cluster Assembly

The production of stable, pre‐reactive, nanocomposite mixtures of magnesium and a perfluoropolyether (PFPE) has been achieved through the application of helium droplet cluster assembly. The nanocomposite films presented in this work demonstrated clear thermal desorption features that indicate the formation of an MgF₂ passivation layer between unreacted magnesium cores and PFPE shells upon heating. Additional heating resulted in the later rupture of the MgF₂ layer and release of trapped magnesium. The passivation behavior occurred only after deposition with the input of thermal energy, demonstrating the ability of helium droplets to assemble and deposit clusters in a pre‐reactive state.     

Queue Lengths and Waiting Times for Multiserver Queues with Abandonment and Retrials

We consider a Markovian multiserver queueing model with time dependent parameters where waiting customers may abandon and subsequently retry. We provide simple fluid and diffusion approximations to estimate the mean, variance, and density for both the queue length and virtual waiting time processes arising in this model. These approximations, which are generated by numerically integrating only 7 ordinary differential equations, are justified by limit theorems where the arrival rate and number of servers grow large. We compare our approximations to simulations, and they perform extremely well.     

Indium tin oxide nanopillar electrodes in polymer/fullerene solar cells

Using high surface area nanostructured electrodes in organic photovoltaic (OPV) devices is a route to enhanced power conversion efficiency. In this paper, indium tin oxide (ITO) and hybrid ITO/SiO(2) nanopillars are employed as three-dimensional high surface area transparent electrodes in OPVs. The nanopillar arrays are fabricated via glancing angle deposition (GLAD) and electrochemically modified with nanofibrous PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(p-styrenesulfonate)). The structures are found to have increased surface area as characterized by porosimetry. When applied as anodes in polymer/fullerene OPVs (architecture: commercial ITO/GLAD ITO/PEDOT:PSS/P3HT:PCBM/Al, where P3HT is 2,5-diyl-poly(3-hexylthiophene) and PCBM is [6,6]-phenyl-C(61)-butyric acid methyl ester), the air-processed solar cells incorporating high surface area, PEDOT:PSS-modified ITO nanoelectrode arrays operate with improved performance relative to devices processed identically on unstructured, commercial ITO substrates. The resulting power conversion efficiency is 2.2% which is a third greater than for devices prepared on commercial ITO. To further refine the structure, insulating SiO(2) caps are added above the GLAD ITO nanopillars to produce a hybrid ITO/SiO(2) nanoelectrode. OPV devices based on this system show reduced electrical shorting and series resistance, and as a consequence, a further improved power conversion efficiency of 2.5% is recorded.     

Iron repressible outer membrane proteins of Moraxella bovis and demonstration of siderophore-like activity

Moraxella bovis (strain Epp 63), grown in RPMI 1640 medium supplemented with desferrioxamine mesylate (0.05 mg/ml) resulted in cell free culture supernatants with an increased chromeazurol-S response indicating the presence of high affinity iron binding ligand(s). Supernatants of cultures where growth occurred in tryptic soy broth, RPMI 1640, or RPMI 1640-desferrioxamine supplemented with ferrous sulfate (10 micrograms/ml) were negative on the chromeazurol-S test. Growth of M. bovis in RPMI 1640 or RPMI 1640-desferrioxamine medium induced the expression of previously unrecognized outer membrane proteins whose expression was repressed when the medium was supplemented with iron and which were not produced when growth occurred in tryptic soy broth.