Showing papers by "University of Manchester published in 1983"

Tentative steps toward a development method for interfering programs

Abstract: Development methods for (sequential) programs that run in isolation have been studied elsewhere. Programs that run in parallel can interfere with each other, either via shared storage or by sending messages. Extensions to earlier development methods are proposed for the rigorous development of interfering programs. In particular, extensions to the specification method based on postconditions that are predicates of two states and the development methods of operation decomposition and data refinement are proposed. 41 references.

Laboratory studies of the charging of soft hail during ice crystal interactions

Abstract: A laboratory investigation of electric charge transfer during the impact of vapour-grown ice crystals and supercooled water droplets upon a simulated soft-hailstone target has shown that the magnitude of the charge transferred to the riming surface when crystals separate from it is a function of temperature, crystal dimension, relative velocity, liquid water content, and impurity content of the water droplets and hence the impurity content of the riming target. The sign of the charge transfer depends on temperature, liquid water content and droplet and rime impurity content. In the absence of crystals, no charge transfer was detected during riming. In the absence of supercooled water droplets, crystals impacting at 10ms1 on an evaporating rime target produced a small negative charge on the rime of less than − 0.25fC per separating crystal. When the target surface grew by vapour diffusion it gained a small positive charge during such interactions. Much larger charges and completely different charge transfer behaviour was noted during riming. The target became positively charged at high liquid water contents and temperatures above a critical value, but negatively charged at lower temperatures or with lower liquid water contents. The critical sign reversal temperature at a liquid water content of 1 gm−3 was about − 20°C. At − 10°C with a liquid water content of 2gm−3, a 125 μm crystal impacting at 3ms−1 charged the target by +101C upon separation. The charge transfer increased sharply with impact speed and crystal size. Warming the positively charging rime to cause it to evaporate failed to reverse the sign of the charge transfer. Experiments with impurities showed that the sign reversal temperature increased if the droplets contained contaminants at concentrations found in cloud water. It is suggested that there are two distinct charge transfer processes during crystal interactions with an ice target, the dominant one requiring the presence of supercooled water droplets. Careful control and knowledge of the microphysical properties of the clouds used in these experimental simulations has permitted an examination of charge transfer under many of the conditions used in previous studies. The results provide an understanding of the differences and a reconciliation between some of the previously disparate findings in terms of the two distinct charge transfer regimes.

Nonlinear Schrödinger equations and simple Lie algebras

Abstract: We associate a system of integrable, generalised nonlinear Schrodinger (NLS) equations with each Hermitian symmetric space. These NLS equations are considered as reductions of more general systems, this time associated with a reductive homogeneous space. The nonlinear terms are related to the curvature and torsion tensors of the appropriate geometrical space. The Hamiltonian structure is investigated using “r-matrix” techniques and shown to be “canonical” for all these equations. Throughout the reduction procedure this Hamiltonian structure does not degenerate. Each of the above systems of equations is gauge equivalent to a generalised ferromagnet. Reductions of the latter are discussed in terms of the corresponding NLS type equations.

Diffusion in oscillatory pipe flow

Abstract: The rate of mass transfer of a diffusing substance along a pipe is augmented by an oscillatory motion of the ambient fluid in the pipe. The increase of the flux is evaluated for the cases of a circular pipe and of a two-dimensional channel. Results are given for a general cross-section in the limiting cases of slow and fast oscillations of the flow.

Testing Restrictions in a Flexible Dynamic Demand System: An Application to Consumers' Expenditure in Canada

Abstract: Traditionally, restrictions on systems of demand equations have been tested using static models, whilst being estimated with time series data. This paper develops a vector time series model of expenditure shares in the context of a singular dynamic demand system. The model allows for non-symmetric and non-homogeneous short run behaviour. The homogeneity and symmetry restrictions are only examined in the long run structure. Results based on Canadian time series data are presented and reject the current practise of static modelling while restrictions suggested by economic theory are not rejected when imposed on the long run structure.

A Nonuniform Influence Innovation Diffusion Model of New Product Acceptance

Abstract: A nonuniform influence NUI innovation diffusion model for forecasting first adoptions of a new product is proposed. An extension of the Bass model, the proposed model overcomes three limitations of the existing single-adoption diffusion models. First, the current models generally assume that the word-of-mouth effect remains constant over the entire diffusion span. However, for most innovations, the word-of-mouth effect is likely to increase, decrease or remain constant over time. Second, the existing models assume that an innovation must attain its maximum penetration rate before capturing a prespecified level of potential market, for example, 50%. That is, they restrict the location of the inflection point for the diffusion curves. Third, the current models assume that the adoption patterns after and before the location of maximum penetration rate are mirror images of each other. That is, the diffusion curve is symmetric. By allowing the word-of-mouth effect to systematically vary over time, the proposed model allows the diffusion curve to be symmetrical as well as nonsymmetrical, with the point of inflection responding to the diffusion process. Data from five consumer durables are analyzed to illustrate the generality of the model.

Working memory in children

Abstract: It is frequently assumed that the development of children’s abilities in short-term memory reflects changes in a unitary short-term store. This approach makes only poor contact with recent research on adults, which suggests the idea of a more complex ‘ working memory ’ system consisting of a limited-capacity central processor controlling a number of special-purpose stores. Two such stores are (i) the articulatory loop, a subsystem involved in subvocal rehearsal and associated with memory span, and (ii) the visuo-spatial scratch-pad, involved in imagery. This paper considers the applicability of the working memory framework to the study of children’s memory. In adults, memory span for words is affected by their length, varying linearly with the rate at which they can be articulated, and thus presumably rehearsed. Studies of the developmental growth of memory span in children show that the same linear relation describes performance, with older children’s better memory associated with faster rates of articulation. It appears from this that developmental change corresponds to an increase in the efficiency of subvocal rehearsal, with the decay characteristic of the articulatory loop remaining constant. However, although this simple developmental pattern is observed in memory for sequences of spoken words it is not present when the items are nameable pictures. Further investigation shows that older children use the articulatory loop to remember picture names: their performance is sensitive to phonemic similarity of the names and articulatory interference. However, younger children’s performance is not affected by either of these factors but is sensitive to visual similarity. It is suggested that such children may be storing material in the visuo-spatial scratch-pad. An additional aspect of working memory is that separate mechanisms are thought to be involved in memory span and the ‘recency effect’, the tendency for recent items in a list to be remembered well in unordered recall. A review of evidence obtained with children suggests that age differences in these two phenomena are independent. In general, therefore, it seems difficult to interpret the developmental changes reported here in terms of a unitary short-term store, and it is concluded that working memory provides a more promising approach.

Heat and power networks in process design. Part I: Criteria for placement of heat engines and heat pumps in process networks

Abstract: The general problem of heat and power integration in process networks is complex and to date not fully understood. The subject covers site combined heat and power, on-plant power generation, heat pumps, and refrigeration systems. This paper is the first of a two-part series and explains the concept of ''appropriate'' heat engine and heat pump placement in process networks based on a fundamental new insight. ''Appropriate'' placement takes advantage of integration opportunities with the remainder of the process and yields marginal efficiencies far greater than could be achieved through stand-alone heat engines. Conversely, ''inappropriate'' placement can never offer an advantage over stand-alone systems. Part II describes procedures for preliminary design, involving heat engine, and heat pump equipment selection and performance assessment.

Customer analysis for strategy development in industrial markets

Abstract: This paper reports on concepts and techniques which have been developed for analysing customers and used as an aid to assessing the strategic position of companies in industrial markets. The emphasis on supplier/customer relationships presented here derives from the interaction approach to marketing and purchasing strategy. Many industrial markets are highly concentrated, and many companies develop in conjunction with key customers in a symbiotic relationship, where strategy evolves as proposals made by either side are either accepted or rejected. To take account of this we propose a 3-stage framework for analysing customers which builds on and transforms techniques traditionally used for an analysis of products. The purpose of the analysis is to improve the allocation of scarce marketing and technical resources, to reappraise the company's competitive position with different customer groups and to ensure that key relationships are managed effectively.

Patterns of urine flow and electrolyte excretion in healthy elderly people.

Abstract: Twenty four young (mean age 29.2 years, range 25-35) and 21 elderly (mean age 66.5, range 60-80) healthy subjects collected their urine in timed aliquots over 24 hours. The elderly subjects had been selected for their fitness by clinical and laboratory examinations and all lived independently at home. Sodium and potassium excretions were reduced in the elderly subjects compared with the young subjects, potassium excretion considerably so. This was despite similar 24 hour urine volumes and total solute excretion by both groups. The ratios of rates of excretion of water, electrolytes, and solutes during the night to the rates of excretion during the day were found to be higher in the elderly than the young subjects. Reduced day to night ratios of urinary excretion may be partly responsible for complaints of nocturia and sleep disturbance in elderly people.

Inventory replenishment policies for deteriorating items in a declining market

Abstract: In this paper two mathematical models are developed for an inventory system in which the units are deteriorating at a constant rate and the demand rate decreases negative exponentially. In the first model it is assumed that replenishment orders are placed at equal intervals while in the second model the replenishment times are also variables and hence there is no need for the replenishment orders to be placed at equal intervals. Optimal replenishment policies are determined for both cases. A numerical example is used to illustrate the theory. Computational results indicate that the constant replenishment period policy leads to a higher total cost.

A study of the antibacterial activity of some polyhexamethylene biguanides towards Escherichia coli ATCC 8739.

Abstract: The antibacterial action of some polyhexamethylene biguanides upon Escherichia coli has been investigated. An amine ended dimer (AED) (n= 2), a polydisperse mixture sold by I.C.I. Limited as the active ingredient of Vantocil IB (PHMB, n= 5.5) and a high molecular weight (HMW) fraction (n≤ 10) of PHMB were used. PHMB and the high molecular weight fraction totally inhibited growth and motility of Esch. coli in liquid culture, whilst amine ended dimer never totally inhibited either function, irrespective of concentration. Growth inhibition and bacteriocidal activity increased with increasing levels of biocide-polymerization. The three compounds, whilst being active over different concentration ranges, possessed similar concentration exponents and temperature coefficients. Cytoplasmic membrane damage and disruption of the cell envelope, indicated by loss from the cells of 260 nm absorbing materials, inorganic phosphate, and changes in permeability towards the dye 2-p-toluidinylnaphthylene-6-sulphonate, was observed at concentrations which were markedly bactericidal whilst bacteristatic concentrations caused only loss of potassium. Loss of cytoplasmic materials from treated cells in all instances followed first-order kinetics. This indicated that irreversible damage was initiated and completed within a short time of contact between cells and biocide. Alteration of cytoplasmic membrane permeability towards various cations was assessed by measuring rates of lysis of sphaeroplasts in isotonic solutions of Na, Li and Cs acetate. For a given biocide concentration, the rates of lysis were inversely proportional to the hydrated ionic radii of the cation. This indicated that the damage to the cytoplasmic membrane was non-specific and proportional to biocide concentration. Temperature coefficients (Q10) of approximately 2.0 for the loss of 260 nm absorbing material, inorganic phosphate and potassium from treated cell-suspensions and bacteriocidal activity suggested that death of cells and cytoplasmic membrane damage are directly associated and are a direct result of biocide action, rather than mediated through the induction of autolytic enzymes.

What is a conservative substitution

Abstract: It is commonly recognised that many evolutionary changes of amino acid sequence in proteins are conservative: a substitution of one amino acid residue for another has a far greater chance of being accepted if the two residues are similar in properties. Here we investigate what properties are most important in determining the similarity of two amino acids, from the evolutionary point of view. Our results confirm earlier observations that the hydrophobicity and the molecular bulk of the side chain tend to be conserved. More importantly they also show that evolutionary pressures favour the conservation of secondary structure, and that all these properties can be arranged in a two dimensional diagram in which distances well preserve the observed substitution frequencies between amino acids. These results were obtained by a multi-dimensional scaling technique; and are independent of any prior opinions about conserved properties. Thus, it is demonstrated that all relations of importance to single amino acid substitutions can be represented by a single figure, which is much more comprehensible and useful than the usual tabular representation of substitution frequencies. Such a figure conveniently portrays the “stereochemical code” for conservative substitution.

Heat and power networks in process design. Part II: Design procedure for equipment selection and process matching

Abstract: In Part I, criteria for heat engine and heat pump placement in chemical process networks were derived, based on the ''temperature interval'' (T.I) analysis of the heat exchanger network problem. Using these criteria, this paper gives a method for identifying the best outline design for any combined system of chemical process, heat engines, and heat pumps. The method eliminates inferior alternatives early, and positively leads on to the most appropriate solution. A graphical procedure based on the T.I. analysis forms the heart of the approach, and the calculations involved are simple enough to be carried out on, say, a programmable calculator. Application to a case study is demonstrated. Optimization methods based on this procedure are currently under research.