Physical and chemical properties of polypyrrole–carbon fiber interphases formed by aqueous electrosynthesis

The properties of carbon fibers modified by aqueous electrochemical synthesis of pyrrole has been determined by using the dynamic contact angle analyzer (DCA), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). Electrochemical process parameters such as the initial pyrrole concentration, electrolyte concentration, applied voltage, electrolyte type, and reaction time were systematically varied, and their impact on the polypyrrole–carbon fiber interphases surface free energy and morphology was ascertained. The surface free energies of the polypyrrole–carbon fiber interphases were obtained by using single fiber filaments. SEM analysis of the interphases revealed several distinct surface structures, including smooth, porous, granular, microspheroidal, and leafoidal morphologies. The noncoated but commercially surface oxidized carbon fibers have smooth surface morphology with occasional longitudinal striations. FTIR analysis of the polypyrrole interphases confirmed that the counterions derived from the electrolytes were incorporated into the film. The surface free energies of the electrochemically formed polypyrrole–carbon fiber interphases equivalent to 60–75 dynes/cm, was determined to be up to 40% higher than that for the surface oxidized but unsized carbon fibers equivalent to 50 dynes/cm. This improvement in the surface free energies of the polypyrrole–carbon fiber interphases suggests easy wettability by polymer matrices such as epoxy resin, γ ˜ 47 dynes/cm and, polyimide matrix, γ ˜ 45 dynes/cm. © 1996 John Wiley & Sons, Inc.     

The DMACA–HCl Protocol and the Threshold Proanthocyanidin Content for Bloat Safety in Forage Legumes

A protocol using HCl-acidified 4-dimethylaminocinnamaldehyde (DMACA) was developed for screening proanthocyanidins (PA) in plants. Individual PA-containing cells could be observed following staining of decolourised leaves with DMACA. The quantitative assay using DMACA-HCl to detect soluble PA and butanol–HCl to detect insoluble PA could detect PA content lower than 0·4 mg g⁻¹ dry matter (DM). The DMACA–HCl protocol is recommended for PA detection in low-PA plants because of its higher sensitivity than vanillin–acid protocols. Twenty-two forage legume species, most of which had been reported free of leaf PA but bloat-safe, were re-examined using the DMACA–HCl protocol. PA-positive cells were observed in leaves of 15 species. Measurable amounts of PA were detected in leaves of seven species, with the PA content ranging from 0·6 to 11 mg g⁻¹ DM. White clover ( Trifolium repens L), red clover ( T pratense L) and lucerne ( Medicago sativa L) were also found to have PA-positive leaf trichomes. By analysis of these data and the literature, the threshold PA content for bloat safety in forage legumes was estimated to be 1–5 mg PA g⁻¹ DM.     

Comparative performance analysis of PEM and solid oxide steam electrolysers

This paper presents a comprehensive overview of comparative performance characteristics of proton exchange membrane (PEM) and solid oxide steam (SOS) electrolysers based on a thermodynamic analysis. The main factors which influence electrolyser energy and exergy efficiencies were temperature, summation of overpotentials, applied voltage, and to a lesser extent pressure. It is found that anodic overpotentials make up a majority of the total overpotentials in both electrolyser types studied and therefore further development of catalysts to reduce the overpotentials was recommended.     

Exergy Efficiency of Two-Phase Flow in a Shell and Tube Condenser

This study deals with a comprehensive efficiency investigation of a TEMA “E” shell and tube condenser through exergy efficiency as a potential parameter for performance assessment. Exergy analysis of condensation of pure vapor in a mixture of non-condensing gas in a TEMA “E” shell and tube condenser is presented. This analysis is used to evaluate both local exergy efficiency of the system (along the condensation path) and for the entire condenser, i.e., overall exergy efficiency. The numerical results for an industrial condenser with a steam–air mixture and cooling water as working fluids indicate significant effects of temperature differences between the cooling water and the environment on exergy efficiency. Typical predicted cooling water and condensation temperature profiles are illustrated and compared with the corresponding local exergy efficiency profiles, which reveal a direct (inverse) influence of the coolant (condensation) temperature on the exergy efficiency. Further results provide verification of the newly developed exergy efficiency correlation with a set of experimental data.     

Analysis of Current–Voltage Measurements on Long-Wavelength HgCdTe Photodiodes Fabricated on Si Composite Substrates

We have performed a detailed study of dark current versus voltage to understand existing limitations in dark current and address the nonuniformity of dark current in devices fabricated on HgCdTe grown on silicon substrates. One interesting observation is that trap-assisted tunneling, g-r currents, are not found close to zero bias in certain devices. Devices from the low end of the R ₀ A distribution show heavy shunting paths close to zero bias. We believe that these shunting paths may be the limiting cause of tail distributions in fabricated focal plane array tail distributions. Possible causes for these shunting paths are surface charges associated with dislocation cores and impurity gettering at dislocation cores. The measured non-anti-reflection (AR)-coated quantum efficiency (QE) was 0.576 at 78 K and displays the classical response versus wavelength. The measured QE on isolated single devices is consistent with the 256 × 256 focal-plane array mean QE. Obtained average dark currents are on the order of mid 10⁻⁵ A cm^–2, which is one order of magnitude higher than dark currents obtained from arrays on lattice-matched substrates. On average, arrays on lattice-mismatched substrates show performance characteristics inferior to those of arrays fabricated on lattice-matched substrates. This inferior performance is due to array pixel operability, as can be seen from the tail of the distribution and the average dark currents, which are one order of magnitude higher than those obtained on lattice-matched substrates.     

Microbiological quality of retail cheeses made from raw, thermized or pasteurized milk in the UK

Two studies of retail fresh, ripened and semi-hard cheeses made from raw, thermized or pasteurized milk were undertaken in the UK during 2004 and 2005 to determine the microbiological quality of these products. Using microbiological criteria in European Commission Recommendations 2004/24/EC and 2005/175/EC, 2% of both raw, thermized (37/1819 samples) and pasteurized (51/2618 samples) milk cheeses were of unsatisfactory quality. Raw or thermized milk cheeses were of unsatisfactory quality due to levels of Staphylococcus aureus at 10(4)cfu g(-1), Escherichia coli at 10(5)cfu g(-1), and/or Listeria monocytogenes at 10(2)cfu g(-1), whereas pasteurized milk cheeses were of unsatisfactory quality due to S. aureus at 10(3)cfu g(-1) and/or E. coli at 10(3)cfu g(-1). Salmonella was not detected in any samples. Cheeses were of unsatisfactory quality more frequently when sampled from premises rated as having little or no confidence in management and control systems, and stored/displayed at above 8 degrees C. Raw or thermized milk cheeses were also more likely to be of unsatisfactory quality when they were unripened types, and pasteurized milk cheeses when they were: semi-hard types; from specialist cheese shops or delicatessens; cut to order. These results emphasize the need for applying and maintaining good hygiene practices throughout the food chain to prevent contamination and/or bacterial growth. Labelling of cheeses with clear information on whether the cheese was prepared from raw milk also requires improvement.