Showing papers by "University of Bath published in 1992"

A first course in order statistics

Abstract: Basic Distribution Theory Discrete Order Statistics Order Statistics from Some Specific Distributions Moment Relations, Bounds, and Approximations Characterizations Using Order Statistics Order Statistics in Statistical Inference Asymptotic Theory Record Values Bibliography Indexes.

Fracture mechanics for piezoelectric ceramics

Abstract: We Study cracks either in piezoelectrics, or on interfaces between piezoelectrics and other materials such as metal electrodes or polymer matrices. The projected applications include ferroelectric actuators operating statically or cyclically, over the major portion of the samples, in the linear regime of the constitutive curve, but the elevated field around defects causes the materials to undergo hysteresis locally. The fracture mechanics viewpoint is adopted—that is, except for a region localized at the crack tip, the materials are taken to be linearly piezoelectric. The problem thus breaks into two subproblems: (i) determining the macroscopic field regarding the crack tip as a physically structureless point, and (ii) considering the hysteresis and other irreversible processes near the crack tip at a relevant microscopic level. The first Subproblem, which prompts a phenomenological fracture theory, receives a thorough investigation in this paper. Griffith's energy accounting is extended to include energy change due to both deformation and polarization. Four modes of square root singularities are identified at the tip of a crack in a homogeneous piezoelectric. A new type of singularity is discovered around interface crack tips. Specifically, the singularities in general form two pairs: r1/2±ieand r1/2±ie, where e. and k are real numbers depending on the constitutive constants. Also solved is a class of boundary value problems involving many cracks on the interface between half-spaces. Fracture mechanics are established for ferroelectric ceramics under smallscale hysteresis conditions, which facilitates the experimental study of fracture resistance and fatigue crack growth under combined mechanical and electrical loading. Both poled and unpoled fcrroelectrie ceramics are discussed.

Magnetoferritin: in vitro synthesis of a novel magnetic protein

Abstract: The iron storage protein ferritin consists of a spherical polypeptide shell (apoferritin) surrounding a 6-nanometer inorganic core of the hydrated iron oxide ferrihydrite (5Fe2O3.9H2O). Previous studies have shown that the in vitro reconstitution of apoferritin yields mineral cores essentially identical to those of the native proteins. A magnetic mineral was synthesized within the nanodimensional cavity of horse spleen ferritin by the use of controlled reconstitution conditions. Transmission electron microscopy and electron diffraction analysis indicate that the entrapped mineral particles are discrete 6-nanometer spherical single crystals of the ferrimagnetic iron oxide magnetite (Fe3O4). The resulting magnetic protein, "magnetoferritin," could have uses in biomedical imaging, cell labeling, and separation procedures.

Equivalence scale relativities and the extent of inequality and poverty

Abstract: Most inequality and poverty theory analyzes "equivalent income" distributions for homogeneous populations: incomes are assumed to be deflated by an equivalence scale that accounts for differences in needs between households. Yet in practice there is no consensus about what the appropriate equivalence scale is. The authors analyze how the choice of equivalence scale affects inequality and poverty measures, and show that there is a systematic relationship between equivalence scale generosity and the extent of inequality and poverty. They consider most of the measures in common use and provide some empirical illustrations. Copyright 1992 by Royal Economic Society.

Self-emulsifying drug delivery systems: formulation and biopharmaceutic evaluation of an investigational lipophilic compound.

Abstract: Self-emulsifying drug delivery systems (SEDDSs) represent a possible alternative to traditional oral formulations of lipophilic compounds. In the present study, a lipophilic compound, WIN 54954, was formulated in a medium chain triglyceride oil/nonionic surfactant mixture which exhibited self-emulsification under conditions of gentle agitation in an aqueous medium. The efficiency of emulsification was studied using a laser diffraction sizer to determine particle size distributions of the resultant emulsions. An optimized formulation which consisted of 25% (w/w) surfactant, 40% (w/w) oil, and 35% (w/w) WIN 54954 emulsified rapidly with gentle agitation in 0.1 N HCl (37 degrees C), producing dispersions with mean droplet diameters of less than 3 microns. The self-emulsifying preparation was compared to a polyethylene glycol 600 (PEG 600) solution formulation by administering each as prefilled soft gelatin capsules to fasted beagle dogs in a parallel crossover study. Pharmacokinetic parameters were determined and the absolute bioavailability of the drug was calculated by comparison to an i.v. injection. The SEDDS improved the reproducibility of the plasma profile in terms of the maximum plasma concentration (Cmax) and the time to reach the maximum concentration (tmax). There was no significant difference in the absolute bioavailability of WIN 54954 from either the SEDDS or the PEG formulations.

Characterization of nicotinic receptor-mediated [3H]dopamine release from synaptosomes prepared from mouse striatum.

Abstract: This study establishes that presynaptic nicotinic receptors modulate dopamine release in the mouse striatum. Nicotinic agonists elicit a dose-dependent increase in the release of [3H]dopamine from synaptosomes prepared from mouse striatum. At low concentrations, this release is Ca2+ dependent, whereas at higher concentrations Ca(2+)-independent, mecamylamine-insensitive release was also observed. The Ca(2+)-dependent nicotine-evoked release was not blocked by alpha-bungarotoxin but was effectively blocked by neuronal bungarotoxin as well as several other nicotinic receptor antagonists. The relationship between potency for stimulation of release for agonists and potency for inhibition of release for antagonists was compared to the affinity of these compounds for the [3H]nicotine binding site. The overall correlation between release and binding potency was not high, but the drugs may be classified into separate groups, each of which has a high correlation with binding. This finding suggests either that more than one nicotinic receptor regulates dopamine release or that not all agonists interact with the same receptor in an identical fashion.

Evaluating investments in IT

Abstract: Evaluating the costs and benefits of IT projects is currently a major issue for senior general managers. This paper focuses on a particular aspect of the problem: how organizations appraise IT investments in taking the decision whether to go ahead with them or not. The paper looks first at the different roles of evaluation; second at what is done in practice and third at what might be done given the wide range of techniques that are available and the widely different circumstances in which appraisal is undertaken. A speculative heuristic is proposed for matching an evaluation method with a particular situation. The method is presented in the hope of stimulating further research into the matching problem.

Crystal assembly and phylogenetic evolution in heterococcoliths

Abstract: COCCOLITHS, the calcite plates formed by unicellular phyto-planktonic algae (coccolithophores, phylum Prymnesiophyta)1, are produced in enormous quantities and probably constitute the largest single carbonate sink in oceanic biogeochemical cycles. They are major sediment formers, are of great value to geologists as biostratigraphic indicators and have been extensively studied as models for biomineralization2,3. We have applied the understanding of coccolith biomineralization to the fossil record4 and present evidence from electron and optical microscopy that there has been a conserved mechanism of crystal nucleation throughout the 230 million year history of coccolithophores. This fundamental feature of coccolith growth, which we term the V/R model, involves the assembly of a ring of single crystals with alternating orientations, radial (R) and vertical (V), and provides a powerful tool for tracing phylogenies, identifying homologous structures and rationalizing the higher taxonomy of the group. The living cocco-lithophorid, Emiliania huxleyi, seemed anomalous because only R crystals had been observed; transmission electron microscopy of proto-coccolith rings, however, revealed relict V crystals which are overgrown by preferential development of R units in complete coccoliths. A speculative model based on a plicated macromolecular template is presented as a possible explanation for the conserved nucleation process.

Evaluation of a commercial microbial identification system based on fatty acid profiles for rapid, accurate identification of plant pathogenic bacteria

Abstract: D.E. STEAD, J.E. SELLWOOD, J. WILSON AND I. VINEY, 1992. Fatty acid profiles of 773 strains representing 25 taxa of plant pathogenic and related saprophytic bacteria were compared with two commercially available broad-spectrum libraries and one self-generated library based primarily on cultures from the National Collection of Plant Pathogenic Bacteria. The accuracy of identification at specific level was often 100%, although for some closely related species and infraspecific taxa accuracy was sometimes significantly less than this. The accuracy of identification of Xanthomonas campestris pathovars was much better than for Pseudomonas syringae pathovars. Almost all identifications were made within24–48 h. Standardization of cultural conditions was essential. Hydroxy fatty acids were of great taxonomic value in classification of Gram-negative bacteria. Improved library development and standardization of cultural and analytical techniques will further increase the accuracy of identification. Fatty acid profiling offers a valuable rapid, accurate method for identification of many bacteria.

Properties of Sisal-CNSL Composites

Abstract: Cashew nut shell liquid (CNSL) is a natural monomer blend that has been condensation poylmerized with formaldehyde in the presence of an alkaline catalyst to produce a thermosetting resin. Plain woven mats of mercerized sisal fibre have been impregnated with CNSL-formaldehyde resin to produce plain and corrugated laminated composites that have a mean tensile strength of 24.5 MPa and Young's modulus of 8.8 GPa. Bending tests have demonstrated that the corrugated composites have adequate strength for roofing applications. Dynamic mechanical thermal analysis has been used to assess the effect of simulated sunlight on composites as a function of time. After long irradiation times it has been deduced that the resin component of the composite undergoes further cross-linking whilst the reinforcing cellulosic sisal fibres suffer some degradation.

Brood sorting by ants: distributing the workload over the work-surface

Abstract: Leptothorax unifasciatus ant colonies occupy flat crevices in rocks in which their brood is kept in a single cluster. In artificial nests made from two glass plates sandwiched together, designed to mimic the general proportions of their nest sites in the field, such colonies arrange their brood in a distinct pattern. These patterns may influence the priority with which different brood are tended, and may therefore influence both the division of labour and colony demography. Different brood stages are arranged in concentric rings in a single cluster centred around the eggs and micro-larvae. Successively larger larvae are arranged in progressive bands away from the centre of the brood cluster. However, the largest and oldest brood items, the prepupae and pupae, are placed in an intermediate position between the largest and most peripheral larvae and the larvae of medium size. Dirichlet tessellations are used to analyze these patterns and show that the tile areas, the area closer to each item than its neighbours, allocated to each type of item increase with distance from the centre of the brood cluster. There is a significant positive correlation between such tile areas and the estimated metabolic rates of each type of brood item. The ants may be creating a “domain of care” around each brood item proportional to that item's needs. If nurse workers tend to move to the brood item whose tile they happen to be within when they have care to donate, they may apportion such care according to the needs of each type of brood. When colonies emigrate to new nests they rapidly recreate these characteristic brood patterns.

Doing the right thing: Ants, honeybees and naked mole-rats

Abstract: Traditionally the division of labour in social insects has been divided into two types: physical and temporal polyethism. New theoretical models indicate that temporal polyethism may be an emergent property rather than an organizational principle. Current research is revealing the relationship between temporal polyethism and the role of nonspecialized individuals within species of physically polymorphic social insects.

Polymerization of methyl methacrylate initiated by ultrasound

Abstract: Irradiation of methyl methacrylate with high-intensity ultrasound produces radicals which can initiate polymerization, although a concurrent degradation reaction occurs. The effect of a number of parameters on the process has been studied and a quantitative model proposed which allows their correlation. Suitable manipulation of the experimental conditions, mainly the temperature and ultrasonic intensity, allows the preparation of polymers with controlled molecular weight, polydispersity, and tacticity

Cell surface accessibility of GLUT4 glucose transporters in insulin-stimulated rat adipose cells. Modulation by isoprenaline and adenosine.

Abstract: Insulin-stimulated glucose transport activity in rat adipocytes is inhibited by isoprenaline and enhanced by adenosine. Both of these effects occur without corresponding changes in the subcellular distribution of the GLUT4 glucose transporter isoform. In this paper, we have utilized the impermeant, exofacial bis-mannose glucose transporter-specific photolabel, 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis-(D-mannos- 4-yloxy)-2-propylamine (ATB-BMPA) [Clark & Holman (1990) Biochem. J. 269, 615-622], to examine the cell surface accessibility of GLUT4 glucose transporters under these conditions. Compared with cells treated with insulin alone, adenosine in the presence of insulin increased the accessibility of GLUT4 to the extracellular photolabel by approximately 25%, consistent with its enhancement of insulin-stimulated glucose transport activity; the plasma membrane concentration of GLUT4 as assessed by Western blotting was unchanged. Conversely, isoprenaline, in the absence of adenosine, promoted a time-dependent (t1/2 approximately 2 min) decrease in the accessibility of insulin-stimulated cell surface GLUT4 of > 50%, which directly correlated with the observed inhibition of transport activity; the plasma membrane concentration of GLUT4 decreased by 0-15%. Photolabelling the corresponding plasma membranes revealed that these alterations in the ability of the photolabel to bind to GLUT4 are transient, as the levels of both photolabel incorporation and plasma membrane glucose transport activity were consistent with the observed GLUT4 concentration. These data suggest that insulin-stimulated GLUT4 glucose transporters can exist in two distinct states within the adipocyte plasma membrane, one which is functional and accessible to extracellular substrate, and one which is non-functional and unable to bind extracellular substrate. These effects are only observed in the intact adipocyte and are not retained in plasma membranes isolated from these cells when analysed for their ability to transport glucose or bind photolabel.

Fractal approximation of image blocks

Abstract: A method for block coding of images based on a least squares fractal approximation by a self-affine system (SAS) is presented. The computational cost of the approximation is linear in the number of pixels in the image. The approximation to a rectangularly tiled block involves evaluating various low-order moments over the block, and solving a system of four linear equations for each tile. The method is applied to a standard test image and the effects of various optimizations are shown. A quantitative comparison with the adaptive discrete cosine transform at 8:1 compression is made. The fidelity of the fractal method shows promise and its greater speed and simplicity compared to other fractal transforms suggest immediate applications such as interactive browsing of remote image archives or image representation in multimedia systems. >

An improved method for deriving optimal one-sided group sequential tests

Abstract: SUMMARY We derive one-sided group sequential tests for normal responses which minimize expected sample size; minimization is at a single value of the normal mean or integrated with respect to a normal density. The methods employed are much faster and also numerically more stable than those of Jennison (1987). They provide solutions for cases with as many as 200 groups and, for small numbers of groups, facilitate optimization over the choice of group sizes. We present a new method for constructing near-optimal tests when group sizes are unpredictable, based on interpolating the error spending function of an optimal test with a large number of groups.

Employment, technology and industrial relations in the UK clearing banks: is the honeymoon over?

Abstract: Employment in UK retail banking has begun to decline as all the major institutions shed workers. Technological, organizational and market-driven reasons for the job losses in the major clearing banks are discussed. Irrevocable long-term changes in employers' industrial relations and human resource strategies are identified as necessary accompaniments to pushing the current retrenchment through in the context of a developing general crisis in employment relations.

Fractal block coding of images

Abstract: An original method is presented for the efficient fractal approximation of rectangular grey-scale image blocks. Its application to the block coding of images is applied to standard test images, and compared to ADCT coding. Fractal coding by this method is relatively efficient and holds promise for applications in which low computational cost is a priority. >

Homoclinic orbits in the dynamic phase-space analogy of an elastic strut

Abstract: The equationis a possible dimensionless version of a model for the configuration of a very long strut resting on a nonlinear elastic foundation with axial loading P. By seeking to establish the existence of homoclinic orbits connecting the zero equilibrium of (*), now regarded as defining a four dimensional dynamical system, to itself one is pursuing the so-called ‘dynamical phase-space analogy’ for the spatial configuration suggested by the form of the equation. The existence of homoclinic solutions is then interpreted as indicating the presence of spatially localized buckling of the deformed strut.

Aid, the public sector and the market in less developed countries: A return to the scene of the crime

Abstract: The paper returns to the question of what is the correct structural form for the relationship between aid, other financial flows, and economic growth rates, using a crosssection approach and – for the first time – data for the entire 1980s as well as the 1960s and 1970s. For the 1980s the aggregate partial regression coefficient of aid on growth emerges, for the first time, as positive and (just) significant, although this result does not survive the partitioning of the sample into sub-groups. It remains obvious that the effect of aid on growth is country-specific, and in the later part of the paper we test a new approach under which aid effectiveness passes through a cycle, first increasing and then diminishing as a country's stage of economic development alters. If this approach is accepted (and the initial results, with an informal test, are promising) the overall crosssection relationship between aid and growth, abstracting from other influences, will be neutral in most periods.