Showing papers by "University of Bath published in 1979"

Diffusions, Markov processes, and martingales

Abstract: This celebrated book has been prepared with readers' needs in mind, remaining a systematic treatment of the subject whilst retaining its vitality. The second volume follows on from the first, concentrating on stochastic integrals, stochastic differential equations, excursion theory and the general theory of processes. Much effort has gone into making these subjects as accessible as possible by providing many concrete examples that illustrate techniques of calculation, and by treating all topics from the ground up, starting from simple cases. Many of the examples and proofs are new; some important calculational techniques appeared for the first time in this book. Together with its companion volume, this book helps equip graduate students for research into a subject of great intrinsic interest and wide application in physics, biology, engineering, finance and computer science.

Bifurcation of inflated circular cylinders of elastic material under axial loading—II. Exact theory for thick-walled tubes

Abstract: B ifurcations of circular cylindrical elastic tubes subjected to inflation combined with axial loading are analysed. Membrane tubes are considered in detail as a background to the more difficult analysis of thickwalled tubes described in the companion paper (Part II). Our results for membranes reinforce and extend those given by R.T. Shield and his co-workers. Two modes of bifurcation are investigated: firstly, a bulging (axisyrmmetric) mode; secondly, a prismatic mode in which the cross-section of the tube becomes non-circular. Necessary and sufficient conditions for the existence of modes of either type are given in respect of an arbitrary (incompressible isotropic) form of elastic strain-energy function. For a closed tube with a fixed axial loading many features of the results have close parallels with recent findings by D.M. Haughton and R.W. Ogden for spherical membranes. On the other hand, some results for tubes with fixed ends have no such parallel. In particular, bifurcation may, under certain conditions, occur before the inflating pressure reaches a maximum. A combination of the two modes is interpreted in terms of bending for a tube under axial compression, and the relative importance of the bending and bulging modes is discussed in relation to the length to radius ratio of the tube. The analytical results are illustrated for specific forms of strain-energy function. Corresponding analysis is given for thick-walled tubes in Part II.

Inhibitory effect of ethanol on growth and solute accumulation by Saccharomyces cerevisiae as affected by plasma-membrane lipid composition.

Abstract: Incorporation of ethanol (1.0 or 1.25 M) into exponential-phase cultures of Saccharomyces cerevisiae NCYC 366 growing anaerobically in a medium supplemented with ergosterol and an unsaturated fatty acid caused a retardation in growth rate, which was greater when the medium contained oleic rather than linoleic acid. Ethanol incorporation led to an immediate drop in growth rate, and ethanol-containing cultures grew at the slower rate for at least 10 h. Incorporation of ethanol (0.5 M) into buffered (pH 4.5) cell suspensions containing d-[6-3H] glucose, d-[1-14C] glucosamine, l-[U-14C] lysine or arginine, or KH232PO4 lowered the rate of solute accumulation by cells. Rates of accumulation of glucose, lysine and arginine were retarded to a greater extent when cells had been grown in the presence of oleic rather than linoleic acid. This difference was not observed with accumulation of phosphate. Ethanol was extracted from exponential-phase cells by four different methods. Cells grown in the presence of linoleic acid contained a slightly, but consistently, lower concentration of ethanol than cells grown in oleic acid-containing medium. The ethanol concentration in cells was 5–7 times greater than that in the cell-free medium.

The construction of the paranormal: nothing unscientific is happening*

Abstract: RECENT studies have exposed the social components involved in the assessment of the validity of scientific findings, a process normally thought of as being in some way immune to social forces. This programme has developed from the work of Wittgenstein I through the 'Copernican Revolution' in the history and philosophy of science, associated with the writing of Kuhn, Lakatos, Feyerabend, and Lakatos and Musgrave,\" to an explicitly relativistic sociologyof science, as argued, for instance, by Barnes, and Collins and Cox.\" Detailed case-studies of the social processes involved in knowledge production have been carried out by the present authors. Collins' has attempted to show the social component involved in the process of 'testing' findings by the replication of experiments in the case of the physical phenomena of gravity waves, and extended this analysis to the case of replication in parapsychology.5 Pinch,\" by considering the part played by a particular proof, has attempted to show the social components associated with the rejection of the work of the physicist, David Bohm, on the foundations of quantum theory. In this paper we will be concerned with examining the processes involved in the attempt to establish the existence of a certain class of phenomena referred to as paranormal phenomena. In particular we intend to analyse the tactics used by parapsychologists in their efforts to gain scientific recognition for their discipline and its findings, and the tactics used by orthodox scientists to deny them this stamp of legitimacy. In analysing these tactics it is hoped that something will

On the nature of problems in consulting practice

Abstract: OR consultants who wish to help clients with complex policy issues need to find ways of taking account of personal and illegitimate features of a client's understanding of his situation, as well as the technical features which are usually considered. This paper is an attempt to discuss the practice of operational research in ways which reflect its political complexity, rather than the techniques, which are more commonly described in the published papers and texts. The discussion leads to the suggestion that practitioners could usefully devote some energy to reflecting upon the processes used in effective problem solving.

Ecology and behaviour

Abstract: Characteristically, hagfishes are adapted for life at considerable depths at high salinities and low light intensities, but within the group there are distinct species differences, particularly in the depths to which they penetrate. Myxine glutinosa normally occurs between 50–100 m, but has been recorded down to 1100 m off the Norwegian coast and in Japanese waters M. garmani is found between 400–800 m. In some inner fiords, M. glutinosa may occur in much shallower water at about 30 m, but in these areas there may be marked stratification with the freshwater overlying water of high salinity (Tambs-Lyche, 1969). Myxine is apparently less tolerant of reduced salinity than some species and this may explain its absence from the Baltic. From its distribution, it has been inferred that the upper temperature limit for this species is between 10–13°C. When hauled to the surface in a trap from deep water, the animals are stressed by the rapid change in salinity and exude large quantities of mucus.

Singular optimal controls for second-order saturating systems

Abstract: The synthesis of optimal controls for second-order linear systems with a saturable scalar input is considered. A non-quadratic cost functional is introduced which, as in the case of quadratic cost, can give rise to singular solutions ; the associated optimal controls are explicitly characterized and, in contrast to the case of quadratic cost, act over a finite time interval only. For a double integrator system it is shown that, under certain conditions, the optimal control is identical to the minimum-time solution.

The nervous system

Abstract: Although some progress has been made towards a functional analysis of the cyclostome spinal cord, this task has been made more difficult by virtue of its peculiar characteristics which have impeded direct comparisons with the distribution of the cells and fibres in the spinal cord of higher vertebrates. The unique ribbon-like shape of the cord (said to be shared only by Latimeria) is almost certainly a secondary acquisition, since a more usual cylindrical form is present in earlier ontogenetic stages. Whiting (1972) considers that this flattened shape may have been due to the downward expansion of the dorsal fat column; a structure that he believes may already have been developed by heterostracans (Section 4.4). In the absence of medullated nerve fibres there is no sharp division between white and grey matter, although the cells form a broad central mass surrounded by the fibres. Distinct dorsal and ventral horns are also missing and the dorsal and ventral spinal nerve roots of the lamprey are unique in failing to unite. In myxinoids, where the nerve roots do unite, these junctions lie far outside the spinal cord in the region of the parietal muscles.

Polar-loop transmitter

Abstract: A new approach to the design of s.s.b. transmitters, which overcomes the problems of the present-day transmitters, is proposed. This is based on the generation of r.f. energy at channel frequency and the use of a feedback control system to regulate the output spectrum of the transmitter so that it approximates arbitrarily closely to that of a low-level s.s.b. signal generated in a conventional way. The principles of design are applicable to all frequencies and power levels, and also readily adaptable to other modes of modulation.

The estuarine phase in the spawning run of the River lamprey Lampetra fluviatilis

Abstract: The biology of the very early stages in the upstream migration of the River lamprey has been studied using samples taken from the cooling water intake screens of the Oldbury Power Station in the Severn Estuary Examination of the numbers of lampreys caught at different times indicate that an increase in freshwater discharge is the predominant environmental factor responsible for initiating the movement from the sea into the estuary, although temperature may also be a contributory factor The migrants could be separated on the basis of size into typical and praecox forms whose mean lengths during peak abundance were approximately 300 and 240 mm respectively, the corresponding weights being about 53 and 22 g respectively The typical forms were occasionally found in the estuary as early as July and as late as April, with peak abundance generally being reached in November, whereas the praecox forms were present mainly between January and March The ratio of typical to praecox forms over the four years of sampling was estimated as 33 : 1 In both size categories, the gonadosomic and hepatosomic ratio was greater in females than males Evidence was also found in the typical forms for a correlation between high numbers and an increased proportion of males Measurement of a number of different characters, including lengths, weights and condition factors, as well as gonadosomic, hepatosomic and gut ratios, suggest that, although the typical forms enter the estuary over a long period of time, the onset of the changes leading to sexual maturity are more synchronous A small number of the later typical migrants, however, exhibited different characteristics to those of the majority of the animals comprising this size category Measurements made on typical animals from Oldbury in November indicate that they can regulate their plasma ions in salinities as high as 70% of full strength sea water

A Psychosocial Model of Stress and Its Application to Managerial Unemployment

Abstract: This paper describes a model of psychosocial stress attempting to explain the psychological response state of stress and physical disease (strain) related to stress, from the consequences of an individual's failure to master self-threatening problems. The model is phenomenological, focusing on an individual's perceived organizational and nonorganizational demands, and how these are modified by personality factors. Behavioral approaches for dealing with threat, and the effectiveness of such approaches, are discussed. The model is used as a framework to analyze qualitative and quantitative data derived from a study of unemployed managers. The themes which characterize the highand the low-stress managers are delineated, and the overall implications of the findings are discussed, with particular focus on the management of stress in organizations.

Multicriteria Programming for Financial Planning

Abstract: Multiobjective programming methods would appear to offer a very attractive alternative to conventional single objective LP models for medium term financial planning. However, prior to implementation, many technical and procedural problems need to be solved. This paper presents in case study form some of these problems and discusses possible approaches to their solution.

A note on microbial growth on hen egg‐shells

Abstract: 1. Two strains of cuticle‐digesting pseudomonads were isolated from the surface of hens’ egg‐shells that had been stored in a humid atmosphere at 25 °C. Digestion was due to a protease, the demonstration of which was only achieved in media containing cuticle. 2. The egg‐shells were colonised by yeasts also, but the growth of these organisms appeared to be dependent upon the pseudomonads for the release of nutrients from the cuticle. 3. The pseudomonads would not grow on cuticle in situ unless the relative humidity was about 100%.

Machine Classification of Sedimentary Sea Bottoms

Abstract: The side-scan sonar method for study of the sea bottom enjoys widespread use at the present time The interpretation of the records is restricted to those observers having some experience, and is offered in terms of geological and man-made features, bottom topography, and sediment types The most subjective opinions are perhaps found in the latter category, and it is here that the attention of this paper is focused By drawing on ideas of texture quantification, this paper explores the potential of using a number of textural features to characterize small areas of side-scan sonar record with the view of producing, via a pattern-recognition procedure, classification decisions in the context of sedimentary sea-bottom identification In this initial investigation, high levels of correct classification probabilities were achieved using small numbers of textural features derived from relative signal level variations rather than absolute ones, together with an uncomplicated decision rule

Effect of partial suppression of heat loss to coolant on the high output diesel engine cycle

Abstract: The paper describes the results of a detailed cycle analysis applied to a high output 6 cylinder truck diesel engine: 1) conventional form; 2) with a uniformly distributed layer of silicon nitride giving approximately isothermal wall conditions; and 3) with adiabatic wall conditions. For case (1) the benefits are largely limited to increased exhaust enthalpy, suggesting the desirability of turbocompounding. Case (2) gives marked improvement in cycle efficiency as well as raised exhaust enthalpy. Paper number 790823.