Investigation of moisture ingress into adhesive bonded structures using high frequency dielectric analysis

The effects on the dielectric characteristics of aluminium-adhesive bonded joint structures with different surface treatments on exposure to moisture at elevated temperatures are reported. Analysis of the frequency domain data as a function of the exposure time allows three major ageing processes to be identified; plasticization of the adhesive, changes in the state of interfacial oxide and generation of disbonded areas. Time domain data allows identification of regions where changes in the characteristics of the bond have occurred and complements the data obtained from frequency domain data. Mechanical tests on joints aged for 733 days indicate a large decrease in the shear strength has occurred consistent with the detection of marked changes in the dielectric traces. Anodization of the substrate increases the durability of joints in comparison with etched samples. This study illustrates the potential of this method for in-situ characterization of changes occurring both within the adhesive and the adhesive substrate interface. This revised version was published online in November 2006 with corrections to the Cover Date.     

Quantitative mechanical assessment of the extraocular muscles.

The active and passive behaviour of the extraocular muscles can be investigated by measuring the force that must be applied to rotate the eyeball when the muscles are relaxed (the forced duction test) or the force required to maintain the eyeball stationary while the contralateral eye follows a moving target (the force generation test). Apparatus and test procedures for carrying out both tests are described. Normal values and confidence intervals for the tests have been obtained and the results of muscle entrapment and palsy illustrated.     

A filarial nematode secreted product differentially modulates expression and activation of protein kinase C isoforms in B lymphocytes

Filarial nematodes, parasitic worms that cause elephantiasis, chronic skin lesions, and blindness in the tropics, release a number of molecules, some of which appear to be immunomodulatory/suppressive, into the host environment. Here we demonstrate that ES-62, a phosphorylcholine-containing glycoprotein released by the rodent filarial parasite Acanthocheilonema viteae, interferes with activation of B lymphocytes by differential modulation of protein kinase C isoform expression. Indeed, while ES-62 selectively down-regulates expression of the alpha, beta, iota/lambda, delta, and zeta isoforms of PKC, it up-regulates expression of PKC-gamma and -epsilon in B cells. Inhibitor studies suggest that ES-62 appears to promote down-regulation of PKC isoforms mainly by stimulating proteolytic degradation. ES-62 also disrupts the normal activation and nuclear translocation patterns of the alpha and iota/lambda isoforms of PKC following ligation of the Ag receptor. The effects of ES-62 on certain PKC isoforms were found to be modified by coculture with IL-4. Of particular interest was the observation that IL-4 prevented down-regulation of PKC alpha and iota/lambda, isotypes considered to be active in transducing mitogenic signals. Phosphorylcholine-containing secreted products (phosphorylcholine-ES) are also released by human filarial parasites; hence we discuss how these findings may relate to the nature of the human B cell response during filarial infections.     

Shutdown process simulation of a refrigeration plant having a twin screw compressor

Non-return valves in refrigeration systems are sources of inefficiency due to flow pressure drop, and of unreliability due to the accumulation of flow debris. Hence the attractiveness of schemes to remove them. In twin screw compressor plants of a certain configuration the suction non-return valve was removed and a reverse rotation brake was fitted to the free end of the motor shaft to prevent backflow of the (oil-laden) refrigerant and reverse rotation of the compressor rotors immediately following plant shutdown. Brake failures occurred on site. This paper describes one part of the subsequent investigation, namely the adaptation of a program created to calculate normal running torque to the process calculating the maximum static torque to occur following shutdown. Shutdown torques up to 60% greater than the running torque are predicted but are thought to be underestimates due to the distribution of oil following shutdown being different from that during normal operation. The authors believe that, following shutdown, the oil seals the exit leakage path across the contact line but clears away from the inlet path through the blow hole allowing unexpectedly high cavity pressures and torques to develop. In existing plants fitted with brakes chosen on the assumption that the shutdown torque will be no greater than the running torque, a safe shutdown may be obtained by opening the slide valve prior to shutdown.     

Fluorescence quenching by metal ions in lipid bilayers

Fluorescence quenching of perylene by Co2+ and Ni2+ ions has been investigated both below and above the phase transition temperature in small unilamellar DPPC vesicles. Classic F?rster type energy transfer was observed for perylene quenched by Co2+ ions below the phase transition when the effects of donor-donor energy transfer are taken into account. In the liquid crystalline phase a simple diffusion theory incorporating energy transfer was found to model the system well. For quenching by Ni2+ ions both above and below the phase transition temperature in lipid bilayers and in glycerol the data did not follow classic F?rster type energy transfer but indicated that an additional quenching mechanism was present. A mechanism other than F?rster behaviour was also observed for the quenching by Cr3+ ions in glycerol.     

Studies of MOCVD for high Tc thin films

In this article we report on results obtained from studies of the effect of total pressure and carrier gas flow rate on the rate of precursor evaporation for typical precursors used in the MOCVD of high temperature superconductors (HTS). We find that this process is under significant mass transfer control and we consider the implications of this for growth of HTS. In particular, we discuss the problems associated with the use of solid precursors and possible strategies for solving the difficulties.     

XPS Analysis of Submicrometer Barium Titanate Powder

A commercial submicrometer BaTiO₃ powder was analyzed using X-ray photoelectron spectroscopy. The analysis revealed the powder surfaces to be covered with a layer of physisorbed H₂O and chemisorbed –OH ions. A BaCO₃ residual not detected with XPS was shown to be present in the powder using X-ray diffraction, suggesting that the carbonate takes the form of discrete particles rather than of a continuous surface layer. A relaxed surface phase detected in previous XPS analyses of bulk BaTiO₃ was also shown to be present. Depth profiling revealed the powder surfaces to be Ti-rich, confirming the presence of a phase, or phases, to stoichiometrically balance the barium carbonate.     

Small-angle neutron scattering from polymer solutions: 2. The semi-concentrated region near the upper critical solution temperature

Small-angle neutron scattering experiments have been made on solutions of polystyrene in cyclohexane. From these experiments the radius of gyration has been determined as a function of polymer concentration at a fixed temperature (60°C). Additionally, the screening length has been determined as a function of temperature for a fixed polymer concentration of 36% (w/v). The results support the notion of an additional region of solution behaviour, the semi-concentrated region, predicted by mean field-type theory.