Showing papers by "University of Bath published in 1978"

Computing Dirichlet Tessellations in the Plane

Abstract: A finite set of distinct points divides the plane into polygonal regions, each region containing one of the points and comprising that part of the plane nearer to its defining point than to any other. The resultant planar subdivision is called the Dirichlet tessellation; it is one of the most useful constructs associated with such a point configuration. The regions, which we call tiles, are also known as Voronoi or Thiessen polygons. We describe a recursive algorithm for computing the tessellation in a highly efficient way, and discuss the problems which arise in its implementation. Samples of graphical output demonstrate the application of the program on a modest scale; its efficiency allows its application to large sets of data, and detailed discussion of space and time considerations is given, based in part on theoretical predictions and in part on test runs on up to 10,000 points.

The Holt-Winters Forecasting Procedure

Abstract: SUMMARY The Holt-Winters forecasting procedure is a simple widely used projection method which can cope with trend and seasonal variation. However, empirical studies have tended to show that the method is not as accurate on average as the more complicated Box-Jenkins procedure. This paper points out that these empirical studies have used the automatic version of the method, whereas a non-automatic version is also possible in which subjective judgement is employed, for example, to choose the correct model for seasonality. The paper re-analyses seven series from the Newbold-Granger study for which Box-Jenkins forecasts were reported to be much superior to the (automatic) Holt-Winters forecasts. The series do not appear to have any common properties, but it is shown that the automatic Holt-Winters forecasts can often be improved by subjective modifications. It is argued that a fairer comparison would be that between Box-Jenkins and a non-automatic version of Holt-Winters. Some general recommendations are made concerning the choice of a univariate forecasting procedure. The paper also makes suggestions regarding the implementation of the Holt-Winters procedure, including a choice of starting values.

Plasma-membrane lipid composition and ethanol tolerance in Saccharomyces cerevisiae.

Abstract: Populations of cells suspended anaerobically in buffered (pH 4.5) M ethanol remained viable to a greater extent when their plasma membranes were enriched in linoleyl rather than oleyl residues irrespective of the nature of the sterol enrichment. However, populations with membranes enriched in ergosterol or stigmasterol and linoleyl residues were more resistant to ethanol than populations enriched in campesterol or cholesterol and linoleyl residues. Populations enriched in ergosterol and cetoleic acid lost viability at about the same rate as those enriched in oleyl residues, while populations grown in the presence of this sterol and palmitoleic acid were more resistant to ethanol. Suspending cells in buffered ethanol for up to 24 h did not lower the ethanol concentration.

Nearly isochoric elastic deformations: Application to rubberlike solids

Abstract: An the assumption that volume changes taking place during the deformation of an elastic solid are of a small order of magnitude, an expression is obtained for the local volume change at arbitrary deformation and independently of any elastic symmetry (such as isotropy). It is given in terms of the deformation appropriate to the associated incompressible material under the same boundary conditions. The results are specialized to isotropic elastic solids and, more particularly, to a class of strain-energy functions which are appropriate to rubberlike solids. An analysis of simple tension on these lines has been given previously (o gden , 1976), but from a more specialized starting-point. The present work clarifies some features of the problem. Here, results are given for a non-homogeneous deformation, namely, torsion of a solid circular cylinder superposed on uniaxial tension. Calculations are made of the local and overall volume changes due to this combined deformation, and the predictions of the theory are assessed in the light of the limited experimental data which are available. The need for further experimental work is emphasized.

On the incremental equations in non-linear elasticity — II. Bifurcation of pressurized spherical shells

Abstract: Bifurcations of spherical elastic shells subsequent to a finite radially-symmetric inflation are analysed. In the case of a membrane, necessary and sufficient conditions for the initiation of asymmetric deformation modes are obtained in respect of an arbitrary (incompressible, isotropic) form of elastic strain-energy function. The method used differs from that used anywhere before, and the results obtained generalize, extend and elucidate those given previously for this problem. In particular, we find that aspherical bifurcations first become possible when the surface tension reaches a maximum. The corresponding analysis is given for thick shells, also for an arbitrary form of the strain-energy function. Despite the inhomogeneity of the deformation in this case, some analytical results are derived which have certain features in common with the membrane results. However, the bifurcation criteria for thick shells are not equivalent to those for the membrane. This is illustrated for particular forms of the strain-energy function. The results depend very much on the shell thickness. In particular, aspherical bifurcations are not possible for shells whose thickness is beyond some critical value. Nevertheless, membrane theory provides a good prediction of the behaviour of shells of moderate finite thickness.

Cell wall-degrading enzymes of vascular wilt fungi. II. Properties and modes of action of polysaccharidases of Verticillium albo-atrum and Fusarium oxysporum f. sp. lycopersici

Abstract: Single polysaccharidases of Verticillium albo-atrum degraded cell walls from vascular and other tissues of tomato stems without previous or simultaneous action of other enzymes. Endoxylanase, exo-galactanase and exo-arabinase of the pathogen had pH optima c . 5, 3 and 5 respectively. Cellulase degraded soluble and insoluble cellulose at optimum pH c . 7. Polygalacturonase (PG) and pectin lyase (PTE) behaved as typical endo-enzymes causing a rapid decrease in viscosity of solutions of substrates at rates proportional to the degree of substrate polymerisation. Although PTE degraded pectin at random, only unsaturated dimer was released from polypectate and cell walls. PG released galacturonic acid and oligogalacturonides which were rapidly degraded to the monomer but an exo-enzyme was not detected; this activity compares with the dual endo-exo action of homogeneous polygalacturonases from other pathogens and “multiple attack” of certain α-amylases. Wide and narrow range isoelectric focusing resolved PG into four endo-components of pI 5·0 5·9 6·2 and 6·7 and PTE into two fractions with activity profiles almost identical with the acidic PG components. PTE of V. albo-atrum and Fusarium oxysporum f. sp. lycopersici had a partial Ca 2+ requirement and pH optimum c . 9 which altered with substrate methylation. Activity of endo-PG of V. albo-atrum but not exo-PG of F. oxysporum was restricted by Ca 2+ ; calcium pectate gels were resistant to degradation. Pectic enzymes of V. albo-atrum macerated tomato stem tissue after long lag periods; other cell wall-degrading enzymes were ineffective. PTE of F. oxysporum macerated tissue more rapidly and was used alone or with other enzymes to compare degradation of tissue and cell walls isolated from susceptible or isogenically wilt-resistant tomato cultivars. There was no relation between varietal resistance and the susceptibilities of cell walls to enzymic degradation.

A Digital Synthesis Procedure Under Function Symmetries and Mapping Methods

Abstract: A new mathematically based method of synthesis for combinational digital networks is presented, based upon the recognition of symmetry patterns in the functions being synthesized. The design procedure is structured such that at each stage of the synthesis a relevant gate assembly is indicated, which leaves a simplified "remainder" function to be synthesized at the next stage of the realization. This decomposition procedure optimally uses gates with a fan in of two, but post-synthesis reconfiguration for amalgamation into larger fan-in gates is available.

The oblique compression of two elastic spheres

Abstract: A fundamental problem in the behaviour of the packing of spheres is that of the oblique compression of just two spheres. Here, the solution of this problem is obtained for the case of two identical homogeneous isotropic elastic spheres, since much use can then be made of the existing symmetry. In particular, the normal and shear components of traction on the contact area can be treated separately. Considerations of the normal force show that the contact area is circular and, furthermore, that this part of the solution is precisely that of normal Hertzian contact. To obtain that part of the solution corresponding to shear, two criteria are used. The first is that of no slip between the spheres, and the second is that the energy flux across the contact area must obey the appropriate symmetries of the problem. These symmetries are sufficient to make the solution unique. This solution differs greatly from that obtained when the spheres are first compressed normally and then sheared. In particular, it is shown that if slip does occur, then it will be in the form of sliding; whereas in the latter case, slip occurs only within a circular annulus.

On the incremental equations in non-linear elasticity — I. Membrane theory

Abstract: A new formulation of the equations of membrane theory in non-linear elasticity is described. It is based on the consistent use of certain conjugate variables averaged through the (undeformed) thickness of the thin shell which the membrane approximates. The deformation gradient is taken as the basic measure of deformation, and its average value as the membrane measure of deformation. It is shown that the average elastic strain energy can be regarded as a function of the average deformation gradient to within an error which is of the second order in a certain small parameter. Moreover, to the same order, the average strain energy is a potential function for the average nominal stress. This means that the averages of the conjugate variables (nominal stress and deformation gradient) are also conjugate. In terms of the average conjugate variables, the membrane equilibrium equations are obtained by averaging from the equilibrium equations of the full three-dimensional theory. Discussion of the order of magnitude of the errors involved in the membrane approximation is a feature of the analysis. The corresponding incremental equations are also derived as a prelude to their application in certain bifurcation problems. One such problem is examined in the companion paper (Part II) in which results for thick shells and membranes are compared.

Growth and movements of the twaite shad, Alosa fallax (Lacépède), in the Severn Estuary

Abstract: Between July 1974 and April 1977, appreciable numbers of 0 group twaite shad, Alosa fallax, have been collected from the cooling water intake screens of the Nuclear Power Stations at Oldbury-upon-Severn and Berkeley on the Severn Estuary and at Hinkley Point on the Bristol Channel, England. Young of the year first appeared at Oldbury in July at a size of approximately 32 mm standard length, and grew to approximately 61 mm by October. The downstream migration in the late summer and autumn appeared to be closely correlated with water temperature since movement reached a peak soon after the temperature in the Estuary had declined below 19° C, and ceased altogether below 9° C. Thereafter, there was virtually no movement of shad until temperatures rose sharply above 7° C in the spring. Maturing adult twaite shad were captured in late April and May as they moved into freshwater to spawn, probably in mid-June. Males were recorded slightly earlier during the migration and were generally younger than females. Furthermore, mean lengths and weights for individuals belonging to the different age classes indicated that males were also smaller. Logarithmic relationships between length and weight of young and adult A. fallax and for the variation with size in the number of rakers on the first gill arch are presented.

The Maceration of Vegetable Tissue by a Strain of Bacillus subtilis

Abstract: Pectate lyase (PAL EC 4.2.2.2), pectinesterase (PE EC 3.1.1.11), L-arabinanase, D-xylanase, D-galactanase and neutral protease activities were identified in culture filtrates prepared from a strain B3 of Bacillus subtilis isolated from carrot. The PAL was purified by ion-exchange chromatography and iso-electric focusing and its properties examined. PAL had a pI of 9·85 and a molecular weight of 33000. Optimum activity occurred at pH 8–9 and 60–65°C. Calcium and to a lesser extent strontium were stimulatory while ethylenediamine tetraacetic acid led to inactivation. Thin layer chromatography separations of the end products of reactions and viscosity measurements suggested that the enzyme acted in a random manner. When examined over a range of pH values both culture filtrate and the purified PAL produced two distinct peaks of maceration (pH 6–6·5 and 8–9) against carrot or potato tissues. Evidence was obtained that although the presence of lyase was the sole external factor responsible for the maceration of carrot at pH 6·0, it acted in conjunction with a heat-labile, high molecular weight factor extractable from carrot tissue. Carrot extracts were unable to macerate carrot but liberated reducing groups from polygalacturonic acid and it is suggested that the factor may be, in part at least, carrot polygalacturonase. Maceration at pH 8·5 was largely accounted for by PAL and PE activities.

Shrinkage stresses in glass/resin composites

Abstract: A simple model has been used to calculate the residual stresses in polyester-resin/glass fibre composites that arise when the material is cooled from the post-curing temperature. An elementary elasticity solution for shrink-fit stresses gives a value of the order of 24 MNm−2 for interfacial pressures in a single fibre model, and it appears that this stress is between 10 and 20% lower if the matrix is a hypothetical material having the properties of a composite. The pull-out stress for a glass fibre in polyester resin is estimated to be 7.6 MNm−2, in good agreement with earlier experimental results.

Adhesion of Polyethylene to Copper: Reactions between Copper Oxides and the Polymer

Abstract: In order to get good adhesion between polyethylene and copper previous workers have oxidised the metal in an alkaline solution to give a matt black oxide layer. It was thought that the good adhesion was a consequence of copper (II) oxide in this layer oxidising the polymer and being reduced to copper (I) oxide in the process. In this paper, changes in oxide composition during bonding by melt coating at 200° C were followed by coulometric reduction supported by x-ray and electron diffraction. It is shown that for coating times required to get good adhesion, the changes of composition of the oxide film are not the result of interaction with the polymer. The change from the higher to lower oxide is probably due to reaction with the base metal: CuO + Cu→ Cu2O

Biological activities of complement.

Abstract: Complement is a system of serum proteins whose main function is to defend the body against infection. Although it has a reputation as a dauntingly complex system, this results chiefly from confusion in the nomenclature, which has varied considerably with time as more components were discovered, for example as ‘component C3’ became subdivided into several components one of which is still called ‘C3’. Moreover, three different nomenclatures have been used concurrently for the proteins of part of the system. These discrepancies have been resolved and a standard nomenclature is now in

Time-encoded speech

Abstract: A new method of digitising speech waveforms is described, based on the comparison of successive segments of the waveform with a suitably stored catalogue of possible distinct shapes.

Genetic structure of a natural population of Coriolus versicolor (L. ex Fr.) Quél.

Abstract: Experiments were carried out to investigate genetic relationships within a population of Coriolus versicolor (a polyporaceous basidiomyceto causing white rot of wood) present in a birch stump. The population consisted of individual dikaryons occupying longitudinally continuous columns of decay separated from one another by narrow, dark, relatively undecayed interaction zones. These dikaryons were shown to be genetically homogeneous throughout their respective decay columns by dedikaryotization procedures. They were mutually antagonistic when paired in culture, but monokaryons derived from their fruit-bodies were interfertile. Experiments using synthesized dikaryons indicated that antagonism is inevitable between genetically distinct mycelia, but that the intensity of interaction diminishes with increased relatedness. Results of pairings between synthesized dikaryons and monokaryons varied according to the relatedness of the isolates. Antagonism invariably occurred when the monokaryon contained a nucleus differing from both nuclei in the dikaryon, but this did not necessarily prevent dikaryotization. Often in this situation dikaryotized sectors developed in the monokaryon visibly separated by zones of antagonism (‘tracks’). Where the monokaryon contained the same nucleus as one of the components of the dikaryon, antagonism usually occurred initially, but normally the colonies eventually fused.

Pore Size Versus Pore Number in Avian Eggshells

Abstract: The “porosity” of avian eggshells is analysed and discussed. Pore geometry has been shown to be related to egg weight yet experimental evidence shows that the “porosity” of eggshells can change independently of egg weight. Some ideas on the means by which such alterations occur are presented.

Aspects of the biology and heavy metal accumulation of ciliata mustela

Abstract: The feeding habits, rates of growth, fecundity and other aspects of the general biology of five-bearded rockling from the Severn Estuary and the Bristol Channel are reviewed for the period 1974/76. Additionally the changes in heavy metal accumulation during this time have been measured and an attempt has been made to relate them to the diet of the fish.

Images of the ‘floating voter’: or, the ‘political business cycle’ revisited*

Abstract: This paper interprets the British government's failure to achieve better control of the business cycle, not in terms of technical inefficiency, but as a politically rational pursuit of a class of ‘floating voters' perceived by it to change their economic priorities according to the variable which is currently ‘in crisis’. It then investigates whether this perception is accurate, and finds broadly in the affirmative in spite of a growing salience of inflation over time, on the strength of Gallup poll data from 1953–75. The finding of previous studies that government popularity declines cyclically between elections is interpreted in terms of its greater discretion in matters of economic (and other) policy variables in the mid-term, and the hypothesis is put forward that a more economically informed electorate might ipso facto have less unstable preferences.