Showing papers by "University of Bath published in 1976"

Volume changes associated with the deformation of rubber-like solids

Abstract: V olume changes accompanying the deformation of rubber-like solids are analysed on the basis of isotropic elasticity theory. In particular, a simple, but general, result relating the volume and the stretch in simple tension is obtained. This is achieved by the introduction of certain modified principal stretches which allow the dependence of the strain energy on the isochoric and the dilatational parts of the deformation to be considered separately. The fact that volume changes in rubber-like solids are typically of order 0.01 % is used to linearize the stress-deformation relations in the dilatation. This enables the dilatation to be given explicitly as a function of the stretch in simple tension. Specific results are obtained for certain classes of constitutive law and good agreement with the experimental data for simple tension is demonstrated. Results for equi-biaxial tension and pure shear are also given in anticipation of further experimental data becoming available. The need for volume-change data for a wide variety of types of strains is emphasized.

The basis of food selection in flounders, Platichthys flesus (L.), in the Severn Estuary

Abstract: The factors influencing the selection of food by flounders, Platichthys flesus (L.), have been investigated by analysing collections made in the Severn Estuary for 1 year and the results of experiments. Flounders measuring between 6–0 and 35 cm fed heavily on the polychaete Nereis diversicolor in February and on the amphipod Gammarus salinus between February and April. Thereafter these species were replaced by the mysid Neomysis integer with the decapod Crangon vulgaris. Flounders shorter than 6.0 cm, fed mainly on Neomysis integer regardless of month. Numerous factors were involved in the choice of the food including (1) the maximum and minimum length of prey, (2) its spatial distribution in the water column, (3) its degree of concealment, (4) its motility and ability to escape predation, (5) conditioning of the flounders for certain foods, (6) the fish's swimming speed and (7) the turbidity and temperature of the water. Although the average length of ingested prey remained unchanged as the fish grew in size, an increase in the maximum and minimum lengths was observed. The percentage of stomachs that contained no identifiable remains in flounders greater than 6–0 cm averaged 80–95 % during part of the winter and 60% in the summer and between January and March. These changes partly reflected the influence of low water temperature on the metabolic rate and availability of prey. The dry weight of the stomach contents in flounders longer than 6–0 cm was lowest in winter but high values were recorded in the spring. This latter feature was probably because the rate of feeding was greater than that of digestion. During the summer, under more normal feeding conditions, the weight of the stomach contents remained relatively low compared to other fish populations. Flounders shorter than 6–0 cm always contained more food in their stomachs on a unit weight basis than larger individuals, reflecting metabolic rate and hunting efficiency.

The self-force on a planar dislocation loop in an anisotropic linear-elastic medium

Abstract: A proper prescription for the in-plane self-force on each element of a plane dislocation loop is developed by computing the first variation of the loop self-energy during an arbitrary virtual planar change in the loop configuration. The appropriate self-energy is defined to be the strain energy exterior to a tube of radius e surrounding the loop. The expression derived for the self-force on a loop element ds depends on the local curvature at ds , on certain elastic data for an infinite straight dislocation tangent to the loop at ds , and only weakly on the ‘cut-off’ radius e. The theory of stress fields of dislocations in anisotropic media is sufficiently advanced to permit easy numerical evaluation of the self-force expression. The analysis further reveals that the singular behavior of the self-stresses in the plane of the loop near an element ds is that of an infinite straight dislocation tangent to ds plus a curvature-dependent logarithmic singularity which is proportional to the line-tension of this tangent dislocation.

Crystal structure of green rust formed by corrosion of cast iron

Abstract: THE principal solid corrosion products of iron in water are magnetite and hydrated forms of ferric oxide, depending on the degree of oxidation. The occurrence of intermediate products, termed green rusts, was reported by Keller1 in 1948, since when the formation and decomposition of these compounds, precipitated from aqueous solution by controlled oxidation of ferrous hydroxide, have been extensively studied2–5. It has been proposed2,3 that specific anions are incorporated in the crystal structure of some green rusts, although no substantial evidence has been found to confirm this. A number of green rusts have been classified crystallographically3 as follows: first, rhombohedral green rusts I (GRI) formed in Cl−, SO42− and Br− solutions and (second), hexagonal green rust II (GRII) formed only in SO42− solutions by decomposition of GRI. The interrelationships between the various products involved in the oxidation of ferrous hydroxide have been summarised by Misawa et al.5 In this paper a preliminary account is given of the crystal structure of a rhombohedral green rust formed by corrosion of iron which, although of similar unit cell dimensions to GRI, differs structurally from those previously reported.

2-Amino-4-phosphonobutyric acid as a glutamate antagonist on locust muscle

Abstract: THE characterisation of glutamate receptors in nerve and muscle membranes requires compounds which interact specifically with these receptors. In the vertebrate central nervous system various substances are reported to act as agonists or antagonists of glutamate (reviewed in refs 1 and 2). At the locust and crustacean nerve-muscle junctions, where the receptors are readily accessible for biochemical and pharmacological characterisation, comparatively few compounds activate the glutamate-sensitive receptors or antagonise the excitatory action of glutamate3–9 and so such substances are needed. We report here that the glutamate analogue, DL-2-ammo-4-phosphonobuytyric acid (DL-APB) (Fig. 1), inhibits the binding of glutamate to ‘receptor-like’ hydrophobic proteolipids isolated from locust muscle10,11 and antagonises the excitatory action of glutamate applied iontophoretically to receptors present in the locust muscle membrane. The shape and charge distribution of DL-APB are appropriate for interaction with glutamate receptors2,7,12.

Digital simulation of faulted e.h.v. transmission lines with particular reference to very-high-speed protection

Abstract: Increasing demands for ultralow fault clearance times in electrical power systems require that measurements be made from information derived from power lines during a very short interval after fault inception. For research and development purposes, the precise nature of this information is required, and in this paper modern transmission-line theory is used to predict the fault-transient behaviour of multiconductor overhead lines to a greater degree of accuracy than has hitherto been possible. The nonlinear nature of simulating fault-transient phenomena has been overcome, and it is shown that even on lines which have traditionally been regarded as electrically short, very severe transient conditions can exist. The necessity for an accurate representation of the frequency variance of line parameters is established, and the various factors which influence fault transient phenomena are considered. The paper concludes with a presentation of the results of studies relating to a very long transmission line.

Methods for Determination of Composition and Thermodynamic Properties of Combustion Products for Internal Combustion Engine Calculations

Abstract: SYNOPSISTwo alternative methods are described for the calculation of gas composition. These are:- 1. Complete chemical equilibrium; 2. A combination of chemical rate equations for some slower reactions with partial equilibrium for faster reactions. Some calculated results are given in the form of comparisons between the two methods, showing the changes in gas composition caused by a temperature rise and fall with a constant rate of change of temperature. Equations are also given for the thermodynamic properties of individual species which may be used together with the appropriate gas composition to obtain properties of the gas mixture.

Oxygen flux across the integument of the avian egg during incubation

Abstract: 1. The oxygen flux across the integument of eggs of domestic fowl, domestic duck, mallard, moorhen, pheasant and turkey shows a ten‐fold increase during the first week of incubation. 2. Suggestions are made as to how this is brought about. An assessment is also made of the contribution of the various components to the overall “resistance“ of the integument.

The basis of food selection in some estuarine fishes. Eels, Anguilla anguilla (L.), whiting, Merlangius merlangus (L.), sprat, Sprattus sprattus (L.) and stickleback, Gasterosteus aculeatus L.

Abstract: The factors influencing the selection of food by eels, Anguilla anguilla, whiting, Merlanglus merlangius, sprat, Sprattus sprattus, and stickleback, Gasterosteus aculeatus have been investigated by analysing collections made in the Severn Estuary for 1 year. Non–migratory (yellow) eels measuring from 19–5–56–5 cm in length fed mainly on either the decapod Crangon vulgaris or on the mysid Neomysis integer during the warmer months but ceased to feed in the winter. Whiting measuring between 2–5 and 15 cm fed almost exclusively on C. vulgaris, N. integer and the sand goby, Pomatoschistus minutus. Sprats fed chiefly on either the arnphipod Gammarus salinus or N. integer. Sticklebacks seldom contained any food in their stomachs despite the presence of large quantities of suitable prey and the high level of hunting efficiency. Gammarus salinus, although normally abundant in the environment, was usually ingested in disproportionately small quantities by all fishes except sprats reflecting its concealment among floating weeds and a selection against small (less than 1 cm) organisms. Because of the limitations of size and the unusually efficient escape reaction of larger animals, only young representatives of Crangon vulgaris were captured. The isopod Eurydice pulchra was rarely eaten by any of the fishes even though it was common in the environment. Burrowing polychaetes, mainly Nereis diversicolor, were never utilized possibly due to the difficulty involved in removing these organisms from the substrate. Neomysis integer was the most frequently consumed organism. Although the average length of prey ingested by the whitings increased with the size of fish, this was not the case for the other species. The proportion of non–feeding eels and the dry weight of stomach contents of this species depended on the temperature of the water but were not related to the availability of prey and tidal conditions whereas the feeding of whiting could not be related to any environmental parameter.

Vaterite Deposition During Eggshell Formation in the Cormorant, Gannet and Shag, and in ‘Shell-less’ Eggs of the Domestic Fowl.

Abstract: The eggshells of the cormorant (Phalacrocorax carbo), domestic fowl (Gallus domesticus), gannet (Sula bassana), guinea fowl (Numida meleagris), greater flamingo (Phoenicopterus ruber), and shag (Phalacrocorax aristotelis) have been separated into two groups on the basis of the composition of their outer stratum. In the domestic fowl, guinea fowl and greater flamingo the outer stratum is an organic cuticle while in the sea-birds it is an inorganic cover rich in vaterite. The calcareous deposits on the membranes of eggs of the domestic fowl which are shell-less at oviposition have been shown to consist essentially of the vaterite form of calcium carbonate. Reasons for the occurrence of this polymorph of calcium carbonate are discussed with relation to the physiology of the birds.

Blood cell formation in the River lamprey, Lampetra fluviatilis

Abstract: Haemopoiesis has been studied throughout the life cycle of the parasitic lamprey, Lumpetra fluviatilis, with supplementary data being provided by its nonparasitic derivative, Lampetra planeri. Attention was paid to the location of the principal haemopoietic sites in both the larval and post-larval stages and to the mode of differentiation of the blood cells. In the prolarva, the formation of blood cells takes place initially in the blood islands but, at the time when the gut starts to rotate, this role is taken over by the typhlosole. After the ammocoete has reached about 20 mm in length, division and maturation of blood cells were also clearly detected in the intertubular and fat cell region of the nephric fold. Both the typhlosole and nephric fold discharge blood cells into the circulation and throughout the rest of larval life constitute the main sites of lymphopoiesis, erythropoiesis and granulopoiesis. At the beginning of transformation, however, both these structures undergo involution and by the end of metamorphosis the haemopoietic function has been assumed by the fat column. This latter organ remains active throughout the adult phase until near the end of the spawning run at which time it undergoes massive degenerative changes. Differentiation of blood cells from the fixed cells of haemopoietic tissues occurs only in the blood islands of the prolarva and in the typhlosole during the very earliest stages of its development. Throughout the rest of the life cycle, the mode of formation of blood cells was the same in haemopoietic tissues containing a reticular network (typhlosole, fat cell region of the nephric fold and fat column) as in haemopoietic tissue where there was no such fibrous arrangement (the intertubular tissue of the more ventral regions of the opisthonephric kidney). Haemopoietic tissues could be seen to be formed in all the above structures by the accumulation of immature cells in tissue spaces which form a suitable environment for cell division and maturation. Descriptions are given of lineages leading from small lymphocyte-like stem cells to erythrocytes and to eosinophilic and neutrophilic granulocytes, and from large lymphocytes to macrophages.

Concomitants and correlation estimates

Abstract: SUMMARY We investigate the estimation of the correlation coefficient in a bivariate normal distribution using only the information contained in the concomitants of the ordered observations of one of the variables. Univariate order statistics can provide a fruitful basis for the estimation of location and scale parameters, and a natural representation of extremal characteristics of samples. Attempts to extend the concepts and procedures to the bivariate situation have met with little success since there is no direct extension of the order concept to more than one dimension. Conditional, marginal or partial ordering principles are more readily defined and have been briefly considered. We shall apply a method of conditional ordering, based on concomitants (David, 1973; David & Galambos, 1974), to the estimation of the correlation coefficient, p, in a bivariate normal distribution, N(,a1,jt2, o2, o2, p), where 2t2 and oJ are known. The results provide a useful practical method of estimating p in cases of limited sample information, i.e. where our only knowledge of the first marginal sample is the ranks of the observations.

Seasonal, succession of algae in rivers. i. examples from the avon, a large slow‐flowing river1

Abstract: SUMMARY The epipelic, epilithic and epiphytic algae in a large slow-flowing river (the Avon) situated in southern England usually exhibited a pronounced bloom during early spring probably in response, to increasing daylength. Although floods caused a reduction in the standing crop of most communities both through scouring action and possibly long-term alteration of microhabitat, they also seemed essential for the renovation of sediment and, rock substrates after periods of rapid algal growth. Because of the attachment characteristics of the predominant epiphytic species, the community attached to Cladophora remained relatively unaffected by flooding. Water velocity may have been important in determining the species composition of some communities, particularly the epiphytic associations. Nutrients probably seldom limited development, but during part of the summer competition with planktonic diatoms for silicon appeared to limit attached algae. During the summer, large scale detachment (which greatly reduced algal density) apparently correlates with a high photosynthetic rate. Algal, numbers in the plankton occasionally decreased in response to a loss of buoyancy of the predominant species.

Effect of I% cyproterone acetate in Cetomacrogol Cream BPC (Formula A) on sebum excretion rate in patients with acne

Abstract: Acne vulgaris has been shown to be associated with seborrhoea, and seborrhoea is androgen dependent. Cyproterone acetate is an anti-androgen which, when given orally, reduces sebum excretion (Burton, Laschet & Shuster, 1973) ̂ ^d improves acne (Winkler, 1968; Leo-Rossberg et al., 1971; Hammerstein et al., 1975). It has not yet been widely used in acne, as it has unacceptable side-effects such as loss of secondary sexual characteristics and libido in men and animal experiments suggest it may produce feminization of the male fetus in pregnant women. Topical application has been investigated in patients with acne by Cunliffe, Shuster & Cassels-Smith (1969), but there was no significant decrease in sebum excretion or improvement in the patients' acne. Dimethylsulphoxide (DMSO) 50% was used to improve penetration ofthe anti-androgen, however, and doubt has since been raised about the suitability of DMSO as the vehicle (Cunliffe & Cotterill, 1975). We here report the effect of topical 1% cyproterone acetate in suspension in Cetomacrogol cream BPC (Formula A). Fourteen patients, nine female aged 15-27 years and five male aged 18-24 years, with moderate to severe acne were studied. The sebum excretion rate (SER) was measured by the gravimetric method of Strauss & Pochi (1961) as modified by Cunliffe & Shuster (1969). SER was measured in all patients before treatment. The cream was applied twice a day to both sides ofthe forehead. Measurements were repeated in all patients after 4 weeks, and in eight patients after 8-12 weeks' treatment. As can be seen from Table i, there was no significant difference in the SER before and after treatment. None of the patients showed any marked improvement in their acne, and no side-effects were reported.

Polyphase induction motors

Abstract: It has been shown in chapter 1 that the polyphase induction motor can be considered as a polyphase transformer with variable frequency in the short-circuited secondary winding and an equivalent circuit can be derived per phase of the motor in the same general way as that of a transformer. It is apparent that each winding will have resistance and leakage inductance. The leakage reactance of the rotor will, however, be dependent on the frequency of the rotor current and, since the rotor frequency is Sf, the slip frequency, where S=(N S −N)/N S is the slip and f is the supply frequency, the rotor leakage reactance is given by SX2 where X2 is the standstill value of the rotor leakage reactance. Thus an equivalent circuit for the rotor can be drawn as shown in Fig. 5.1.

Gill Morphometrics of the Lampreys Lampetra fluviatilis (L.) and Lampetra planeri (Bloch)

Abstract: Morphometric measurements have been made on various gill components of different stages in the life cycle of the anadromous parasitic lamprey, Lampetra fluviatilis, and its nonparasitic derivative Lampetra planeri. The total gill area, expressed in terms of body weight, of both larval (1462–2717 mm2 g–1) and adult (1402–2337 mm2 g–1) L. fluviatilis are greater than those previously recorded in the rather meagre literature on lamprey gill measurements and are comparable with those found in the most active teleosts. The gills of the two Lampetra species are apparently identical in the larval stages and those of metamorphosing and adult L. planeri are similar to those of metamorphosing L. fluviatilis. Although the pharyngeal arrangement of lampreys differs greatly from that of teleosts, there are many features of the gills indicative of convergence between the two groups. Thus, in a given stage in the life cycle of lampreys, the secondary lamellae on either side of the filaments also alternate, become more widely spaced as the filament length increases and increase in area as the body weight becomes greater. Furthermore, the fractional cumulative increase in secondary lamellae area along a line following the presumed direction of water flow is also represented by a sigmoid curve. While at metamorphosis the pharynx becomes considerably modified to accommodate the change from a unidirectional to a tidal respiratory water flow, the total gill areas of the ammocoete are similar to those of metamorphosing stages which have attained adult characteristics. However, there are clearly differences in some of the components that influence and contribute towards the total gill area. Thus, in terms of body weight, the number and total length of the filaments and the total number of secondary lamellae, together with the number of secondary lamellae found on a given distance of filament, are greater in late metamorphosing stages, while the reverse is true for the average bilateral area of the secondary lamellae which is considerably greater in ammocoetes.

Studies on the mechanism of action of amantadine.

Abstract: 1 The effect of amantadine hydrochloride on various aspects of catecholamine metabolism in the rat brain has been investigated. 2 Amantadine failed to have any significant effect on brain concentrations of dopamine or noradrenaline even when administered daily for 9 days. 3 Amantadine had no effect on the rate of decline of noradrenaline and dopamine concentrations after alpha-methyl-p-tyrosine. 4 In vitro amantadine inhibited dopamine uptake into synaptosomes only at high concentrations, and caused little release of dopamine from synaptosomes. 5 There is no evidence from these results to suggest that the anti-Parkinsonian effect of amantadine is related to an action on dopaminergic mechanisms.

Environmentalism and Utopia

Abstract: Despite the increasing public concern with environmental issues, there has been surprisii^Iy little reaction by sociologists. Yet apart from the magnitude of the possible threats to human survival, even a cursory reading of the flood of books, articles, pamphlets, and conference reports opens up a rich store of challenging and stimulating analyses and prescriptions—including far-reaching blueprints for the future of human society. Indeed one of the most fascinating facets of this voluminous literature is the way in which environmental problems are so readily used as levers to promote particular redpes for soda] action.' Yet it is precisely at this point that the difficulties facing any attempt at generalisation emerge. If there is anything that can be described as an environmental^t movement, what unites it is an agreement that the environment is a problematic issue of major importance. Beyond this, consensus evaporates into a bewildering disagreement over what are the most pressing environmental dangers, what are their caus^ and how they can best be tackled. And of central interest for this paper is the wide diversity of ideologies and Utopias which can be detected just beneath the surface of arguments about pollution, limits to growth, or the population explosion, ranging from recipes for anarcho-sodalist communes, or for proto-feudal communities, to technocratic solutions for world government.

The Effect of Variable Geometry on the Operating Range and Surge Margin of a Centrifugal Compressor

Abstract: Two variable geometry techniques have been applied to a small turbocharger compressor, with the objective of trying to move the peak pressure ratio operating point to lower flow rates, thereby yielding a broad flow range map. Variable prewhirl guide vanes and variable vaneless diffuser passage height have been studied separately. The results obtained with both techniques are compared and the relative merits and demerits with respect to improved flow range and isentropic efficiency penalties are considered.Copyright © 1976 by ASME

Ultrastructural studies on prolactin and growth hormone cells in Anguilla pituitaries in vitro.

Abstract: Eel hemi-pituitaries were cultured in vitro on high or low sodium media which are known to affect differentially prolactin and growth hormone release. Ultrastructural examination of the prolactin cells after 24 h culture showed the Golgi bodies were markedly more abundant and widely distributed in hemi-pituitaries from the low sodium medium. Secretory granule release profiles and dense bodies were also more frequent, but the percentage of the cytoplasmic volume occupied by secretory granules was lower than on the high sodium medium. RER was only slightly modified. Significant differences were noted in the shape and processes of the non-granulated (stellate) cells of the RPD, but there were only slight differences in the ultrastructure of the somatotropes.

Matched asymptotic expansions in nonlinear fracture mechanics—I. longitudinal shear of an elastic perfectly-plastic specimen

Abstract: A method of analysis based upon matched asymptotic expansions is proposed for a cracked specimen which is subjected to longitudinal shear (mode III) loading. This gives the small-scale yielding estimate of linear fracture mechanics as a first approximation, and provides systematic refinements which take account of the nonlinear interaction between the elastic and the plastic regions. Explicit solutions can be generated for any specimen which is amenable to a linear elastic analysis. Fracture parameters, such as crack opening displacement and the J integral, are expressed as power series in the ratio of applied stress to yield stress, and three terms are given explicitly. These are defined from linear elastic solutions alone. The edge-cracked strip and cracking from a semi-circular notch are studied as examples. Comparison with an exact solution for the former geometry suggests that the three-term expansions give useful results up to 75 % of limit load. The latter example is new and shows the effect of a notch on a crack at loads beyond the normal range of validity of linear elastic fracture mechanics.