The cool-flame oxidation ofn-heptane. Part I. The kinetic features of the reaction

The oxidation ofn-heptane has been investigated at subatmospheric pressures and temperatures from 220° to 360°C, and detailed kinetic data have been collected in the cool-flame region in an attempt to understand the phenomenon of cool-flame formation. A detailed ignition diagram has been constructed for a 1:1 fuel-oxygen mixture. At high pressures at temperatures above 355°C, ignition is a single stage process while at lower temperatures it is always initiated by a cool-flame, and appears in a two-stage phenomenon. Although there is a large temperature rise during this first stage it is insufficient to cause thermal ignition of the fuel, suggesting that initiation of the second stage is both chemical and thermal. During a cool-flame the temperature rise is sufficient to take the reaction mixture into the high temperature slow combustion region, when, presumably, the intermediate responsible for cool-flame formation is no longer formed. The flame is quenched, the temperature falls, and if sufficient intermediate is formed again, another flame propagates. Most of the work reported in this paper supports the “thermokinetic” theory of cool-flame formation involving one chain-branching intermediate. It is shown that in the cool-flame region there are complex relationships between cool-flame parameters (induction periods, pressure rise and maximum rate of pressure rise) and initial temperatures and pressures. These give rise to the observed complex shapes of the cool-flame and ignition limits. In turn all these phenomena reflect the complex temperature dependence of the propagation and branching reactions involved in the oxidation.     

THE IMPORTANCE OF PYROLYSIS IN DIESEL IGNITION OF RESIDUAL FUEL OILS

Recent attempts to increase yields of distillate fuels from crude oil have resulted in a decline in the ignition quality of residual fuel oils and claims of ignition problems in large marine Diesel engines. This has revived an interest in fundamental studies of the ignition of liquid fuels and in new ways of defining and measuring ignition quality.

As part of an extensive study of the ignition of a range of residual fuels oils and during the development of novel teats of ignition quality it became obvious that thermal cracking of the fuel could play an important part in the pre-ignition chemistry. This paper reports kinetic data from simple experiments performed on the pyrolyses of residual fuel oils. Small samples and high heating rates were used to try to match the conditions inside a Blow-speed Diesel engine. This data has been used to assess the contribution that thermal cracking makes to ignition processes.

Pyrolyses were carried out on a small silica-coated platinum coil in the inlet of a gas chromatograph. Light hydrocarbon pyrolysis products were formed, and the extent and rate of cracking determined at four temperatures.

Assuming that reaction took place on a surface surrounding the oil and that a constant supply of reactants were available, pseudo zero order rate constants for the initial part of the reaction were evaluated. They showed an Arrhenius relationship with temperature giving an overall apparent activation energy of 110 kJ mol^-1. Extrapolating rate constants to temperatures expected in Diesel engines, and assuming typical droplet sizes end ignition delays, it was shown that thermal cracking of fuels was possible before ignition and that it is likely that these reactions will have a strong influence on the processes leading to ignition. It was also shown that the presence of oxygen greatly increases the rate of thermal cracking.     

Seafood Phospholipids: Extraction Efficiency and Phosphorous Nuclear Magnetic Resonance Spectroscopy (31P NMR) Profiles

The absolute concentration of phospholipids (PL) (μmol g^?1, wet tissue) in five marine tissues was determined using quantitative phosphorous nuclear magnetic resonance spectroscopy (³¹P NMR). Hoki (Macruronus novaezelandiae) roe was identified as a “high‐PL” seafood, containing 15.97 ± 4.72 μmol g^?1 (wet tissue) of these compounds. This was 2–4× higher than the concentration of PL in monkfish (Lophius spp.) fillets (4.26 ± 1.52), arrow squid (Nototodarus sloanii) mantle (8.95 ± 0.89), Greenshell? mussel (Perna canaliculus) (7.04 ± 0.87), or hoki liver (6.03 ± 0.76). The amount of PL extracted from these tissues was dependent on the extraction method used, with the Folch (1957) method consistently extracting more oil (and more PL) from all five tissues than the Bligh and Dyer (1959) and Jensen (2003) methods. The individual PL profiles of each tissue are also reported.     

Oxygen sorption and transport in amorphous poly(ethylene furanoate)

Oxygen transport in amorphous poly(ethylene furanoate) (PEF) was studied at various temperatures using complementary permeation and pressure-decay sorption techniques. A significant reduction in oxygen permeability of ∼11× was observed at 35 °C for PEF compared to poly(ethylene terephthalate) (PET), and is attributed primarily to reduction in chain segment mobility for PEF resulting from a hindrance of furan ring flipping. A custom-built high accuracy sorption system allowed determination of temperature-dependent so-called dual-mode parameters that have not been reported for oxygen in any polyester. Energetic parameters, i.e. the enthalpy of sorption and activation energies of diffusion and permeation, were measured for oxygen in PEF and discussed in the context of PET and related polyesters. The current work presents the first detailed study of penetrant transport in PEF, which demonstrates the impressive performance enhancements of PEF compared to PET.     

Reviews

RATIONAL LANDSCAPES AND HUMANISTIC GEOGRAPHY by E. Reiph, Croom Helm, 1981. £14.95 (hardback).

COUNTRYSIDE CONSERVATION by Bryn Green. Resource Management Series No. 3, Editors Richard Munton and Judith Rees, George Allen and Unwin, London, 1981. £6.95 (paperback), £13.00 (hardback).

HISTORY OF THE FARMSTEAD: THE DEVELOPMENT OF ENERGY SOURCES by John Weller. 248 pages. Faber & Faber, London, 1982. £5.95 (paperback).

JOURNAL OF ENVIRONMENTAL PSYCHOLOGY edited by David V. Canter. Vol. 1 (4 numbers) Academic Press.     

Microfluidic based platform for characterization of protein interactions in hydrogel nanoenvironments

Hydrogel posts in microfluidic devices were investigated as reaction environments for characterizing protein interactions with the goal of mimicking the complexity of a biological environment. The hydrogel environment can be easily tuned to study specific properties of the biological environment. In this study, the hydrogel pore size was tuned to mimic the effect of confinement/crowding on protein interactions. Arrays of polyacrylamide posts of different cross-link ratios (4 and 10%) were fabricated inside microfluidic channels via photopolymerization. Fluorescence-labeled proteins (protein A (PA) and immunoglobulins (IgG)) were transported into the posts via diffusion, and their interaction was studied using FRET. As the pore size of the hydrogel decreased, the binding between the proteins was enhanced. The degree to which crowding enhances a binding interaction depends on the intrinsic properties of the proteins; we observed that, inside the hydrogel post, the PA-goat IgG affinity was increased more than PA-rabbit IgG affinity. The integration of controlled nanoenvironments (hydrogels) with controlled microenvironments (microchannels) provides enhanced parametric control for studying protein interactions, which would be beneficial in developing sensors, in diagnostics, and for mimicking the biological environment at both the cell and the tissue level.     

Microcantilever-based sensors: effect of morphology, adhesion, and cleanliness of the sensing surface on surface stress

The surface stress response of micromechanical cantilever-based sensors was studied as a function of the morphology, adhesion, and cleanliness of the gold sensing surface. Two model systems were investigated: the adsorption of alkanethiol self-assembled monolayers at the gas-solid interface and the potential-controlled adsorption of anions at the liquid-solid interface. The potential-induced surface stress, on a smooth and continuous polycrystalline Au(111)-textured microcantilever in 0.1 M HClO4, is in excellent agreement with macroscopic Au(111) single-crystal electrode results. It is shown that ambient contaminants on the sensing surface dramatically alter the surface stress-potential response. This observation can be misinterpreted as evidence that for polycrystalline Au(111) microcantilever electrodes, surface stress is dominated by surface energy change. Results for anions adsorption on gold are in contrast to the gas-phase model system. We demonstrate that the average grain size of the gold sensing surface strongly influences the magnitude of the surface stress change induced by the adsorption of octanethiol. A 25-fold amplification of the change in surface stress is observed on increasing the average gold grain size of the sensing surface from 90 to 500 nm.     

Omega-3 Fatty Acids and Total Polychlorinated Biphenyls in 26 Dietary Supplements

ABSTRACT: A limited sampling and analysis of commercial supplements found 51% to 124% eicosapentaenoic acid (EPA) and 61% to 153% docosahexaenoic acid (DHA) as provided on product labels. Daily intakes of EPA plus DHA from label recommendations would provide 123% to 1087% of the adequate intake (AI) for pregnant and lactating women (that is, 0.13 to 0.14 g/day) and up to 43% of the daily reference dose (RfD) for polychlorinated biphenyls (PCB) for a 60-kg person. However, if a smaller dose of the supplements were taken to meet the AI, only 0.9% to 11.5% of the RfD for PCB would be obtained. Algal oil supplements did not have detectable PCB residues, but those products only provided DHA and not EPA.     

Testing, Regulation and Control: shifting education narratives

This paper explores the impact of the 1988 Education Reform Act in England Wales on education ideologies. In particular it considers the changing narratives of the pupil being brought about through profiling, testing and streaming. Using Foucault's notion of 'moral technologies', the paper examines the regulation of pupil behaviour and the construction of pupil identity through systems of classification and grading. This argument is supported by school-based research into the use of testing and profiling by teachers. The paper concludes that the pedagogic aspirations of child centredness and the National Curriculum converge in the everyday practices of primary school teachers.