The identification of radiolytic decomposition products from tributyrin

In order to facilitate the detection of radiolytic products of triglycerides which may be of higher molecular weight than their precursor, a low molecular weight triglyceride, tributyrin, was selected as a model system, and gel permeation chromatography was used to effect their separation. The irradiation treatment was conducted under vacuum at 50 Mrad. Radiolytic products were collected by a precolumn technique for the highly volatile compounds; a combination of cold finger distillation and gel permeation for the less volatile fractions and finally gel permeation chromatography of the residue after distillation for the higher molecular weight compounds. A large number of compounds expected on the basis of previous work were identified in the present work from irradiated tributyrin. In addition, the techniques employed permitted the identification of several new compounds. These include butanetriol triesters, erythritol tetraesters, and other polyglycol polyesters.     

The Royal College examinations: preparation and practice

Membership examinations are complex and difficult. Important practical issues must be considered at an early stage, and you can improve upon your chance of success by addressing your learning style, revision strategy and examination technique.     

Flexural mechanical properties of thermally treated unidirectional and cross-ply Nicalon-reinforced calcium aluminosilicate composites

Long, square cross-section samples of a unidirectional and a cross-ply [0/90]3s silicon carbide (Nicalon) fibre calcium aluminosilicate glass-ceramic matrix composite have been subjected to a range of thermal treatments. They were held at temperatures up to 800 °C above room temperature for 1, 6 or 24 h then slowly cooled or quenched into water. The thermal cycle was repeated up to six times for a small number of samples. The effects of these thermal regimes on Young's modulus, onset of matrix cracking (as assessed by onset of non-linearity in the load–displacement curve) and flexure strength have been monitored using three-point flexure testing. In very broad terms, where clear trends emerged, the intermediate temperature differentials, i.e. 400–650 °C, have been found to have the most detrimental effects on properties, and this has been linked to expected changes in the carboneous interphase and its subsequent replacement by silica. © 1998 Kluwer Academic Publishers     

Activity pulses induce spontaneous flow reversals in viscoelastic environments

Complex interactions between cellular systems and their surrounding extracellular matrices are emerging as important mechanical regulators of cell functions, such as proliferation, motility and cell death, and such cellular systems are often characterized by pulsating actomyosin activities. Here, using an active gel model, we numerically explore spontaneous flow generation by activity pulses in the presence of a viscoelastic medium. The results show that cross-talk between the activity-induced deformations of the viscoelastic surroundings and the time-dependent response of the active medium to these deformations can lead to the reversal of spontaneously generated active flows. We explain the mechanism behind this phenomenon based on the interaction between the active flow and the viscoelastic medium. We show the importance of relaxation time scales of both the polymers and the active particles and provide a phase space over which such spontaneous flow reversals can be observed. Our results suggest new experiments investigating the role of controlled pulses of activity in living systems ensnared in complex mircoenvironments.     

Modification of maillard browning in a microwaved glucose/glycine model system by water-soluble natural antioxidants and foods containing them

Inhibition of pyrazine formation by natural antioxidants and the foods containing them was measured in a microwaved glucose/glycine model system. Inhibition of lipid oxidation by the same materials was assayed in both bulk and emulsion systems. Pyrazines were determined by solid-phase micro extraction followed by GC. Lipid oxidation volatiles were assayed by polyamide fluorescence produced by either a bulk oil display or a hematin- or 2,2′-azobis-(2-amidino=propane) dihydrochloride-accelerated lecithin or fish oil emulsion. It was shown that (i) the inhibition of pyrazine formation depends on high concentrations of water-soluble antioxidants; (ii) such antioxidants occur naturally in some foods and are usually polyphenols; (iii) during pyrazine inhibition, oxidized polyphenols show enhanced nonfluorescing browning similar to enzymic browning products; (iv) monophenols, which structurally cannot form quinone polymers on oxidation, inhibit pyrazines with less browning; (v) during the final pyrazine-forming phase of the Maillard reaction, polyphenolics and reducing agents such as glutathione and ascorbic acid are partially consumed with some nutritional loss; (vi) fruit powders of grape seed, grape skin, and red wine are highly pyrazine-inhibitory, steeped blueberry strongly so, but plum purees are moderately pro-pyrazine, and freeze-dried vegetables strongly pro-pyrazine; and (vii) black and green tea infusions are highly inhibitory, whereas spices have mixed effects.     

Bond of ribbed galvanized reinforcing steel in concrete

The ASTM beam end test (ASTM A944) has been used to compare the bond and slip behaviour of deformed (i.e. ribbed) galvanized, epoxy-coated and black steel bars in concrete. The objective was to determine whether galvanizing adversely affects bond strength. From a series of thirty specimens, the average bond strength of black steel and galvanized steel reinforcement used in these tests has been determined and bond stress has been shown to act uniformly over the embedded bar area. A slip value of approximately 0.4 mm has been confirmed to be associated with bond failure by concrete splitting. The results indicated that while epoxy coating resulted in a significant loss in bond strength of the order of 20% compared to black steel, there is no adverse effect on bond with the use of galvanized steel. Chromate treatment of galvanized bars is deemed unnecessary since there was no evidence of long term reduction in bond due to the possible effects of hydrogen gas evolution resulting from the reaction between zinc and wet concrete.     

Characterization of the foot withdrawal response to noxious radiant heat in the rat

The rat foot withdrawal response to noxious radiant heat has been used as a model of nociception that is particularly useful for measurements of unilateral changes in nociceptive responses. The purpose of these studies was to characterize the foot withdrawal response to graded rates of noxious skin heating. Response latencies and both surface and subsurface temperatures produced by 6 different intensities of radiant heat were measured to determine whether response latency is an appropriate measure of nociceptive threshold. With constant intensity heating, the temperature of the skin surface increased as logarithmic function of time, while subsurface temperature increased linearly with time. In contrast, a heating function that linearly increased the temperature at the skin surface increased the subsurface temperature as an exponential function of time. These results and published reports of nociceptive afferent recordings which used similar skin heating parameters, indicate that nociceptive foot withdrawal responses occur at about the same skin temperature as the activation of nociceptors. These results also indicate that since constant intensity heating produces linear increases in the subsurface temperature, then response latency can be used as an accurate measure of changes in nociceptive threshold produced by drug treatments. These observations lead to the conclusion that the foot withdrawal response latency is a valid and useful measure of nociceptive threshold in rodents.