Showing papers by "Brunel University London published in 1990"

A butterfly subdivision scheme for surface interpolation with tension control

Abstract: A new interpolatory subdivision scheme for surface design is presented. The new scheme is designed for a general triangulation of control points and has a tension parameter that provides design flexibility. The resulting limit surface is C1 for a specified range of the tension parameter, with a few exceptions. Application of the butterfly scheme and the role of the tension parameter are demonstrated by several examples.

α-tocopherol consumption during low-density-lipoprotein oxidation

Abstract: 1. The kinetics of the depletion of alpha-tocopherol in human low-density lipoprotein (LDL) were measured during macrophage-mediated and cell-free oxidation. The formation of oxidatively modified, high-uptake species of LDL in these systems was not detectable until all of the endogenous alpha-tocopherol had been consumed. 2. Supplementation of the alpha-tocopherol content of LDL by loading in vivo extended the duration of the lag period during which no detectable oxidative modification occurred. 3. The addition of a flavonoid (morin) prevented both alpha-tocopherol consumption and oxidative modification of LDL. 4. The alpha-tocopherol contents of LDLs from a range of individual donors could not be used to predict their relative resistance to oxidation, indicating that other endogenous antioxidants may also be present, and quantitatively significant, in human LDL.

Reliability and replicability of the Approaches to Studying Questionnaire

Abstract: The Approaches to Studying Questionnaire (ASQ) was devised to measure individual differences in terms of four major study orientations. It achieves satisfactory levels of reliability and the distinction between a meaning orientation and a reproducing orientation has been consistently demonstrated across a variety of student groups. However, the validity of the remaining study orientations and of the constituent subscales is open to question. A shorm form of the ASQ is described, based upon the eight subscales that have been consistently identified with meaning orientation and reproducing orientation. The reliability and replicability of this new questionnaire are considered in the light of a critical evaluation of the analytic methods employed in previous research. Satisfactory levels of internal consistency and test-retest reliability are demonstrated, and factor analysis successfully retrieves the two primary study orientations. While the validity of its constituent subscales is still rather un...

A measurement of global event shape distributions in the hadronic decays of the Z 0

Abstract: We present measurements of global event shape distributions in the hadronic decays of theZ0. The data sample, corresponding to an integrated luminosity of about 1.3 pb−1, was collected with the OPAL detector at LEP. Most of the experimental distributions we present are unfolded for the finite acceptance and resolution of the OPAL detector. Through comparison with our unfolded data, we tune the parameter values of several Monte Carlo computer programs which simulate perturbative QCD and the hadronization of partons. Jetset version 7.2, Herwig version 3.4 and Ariadne version 3.1 all provide good descriptions of the experimental distributions. They in addition describe lower energy data with the parameter values adjusted at theZ0 energy. A complete second order matrix element Monte Carlo program with a modified perturbation scale is also compared to our 91 GeV data and its parameter values are adjusted. We obtained an unfolded value for the mean charged multiplicity of 21.28±0.04±0.84, where the first error is statistical and the second is systematic.

The dynamics of oocyte growth during vitellogenesis in the rainbow trout (Oncorhynchus mykiss).

Abstract: This report describes the dynamics of oocyte growth during vitellogenesis in a population of virgin female rainbow trout. Indices of ovarian development increased dramatically during the period of study: the gonadosomatic index (GSI) increased over 50-fold, reaching a peak of 20 just before ovulation; the mean oocyte diameter increased from less than 1 mm to 5.4 mm; and plasma levels of vitellogenin increased from less than 1.5 mg/ml to 25 mg/ml. There were no changes in the numbers of developing oocytes (measuring 0.5 mm or greater in diameter) from the time when the majority of oocytes undergoing secondary development had entered vitellogenesis in August to ovulation in February (averaging 4000 oocytes per fish). The increase in ovary weight during vitellogenesis was, therefore, due to an increase in the size of oocytes rather than to recruitment of more maturing oocytes. The numbers of vitellogenic oocytes in the ovary during the entire study also suggested that atresia of vitellogenic oocytes does not play a prominent role in determining fecundity. During early vitellogenesis, the volume of maturing oocytes within an ovary varied by as much as 250-fold. From September onwards, when all oocytes to be ovulated that season had entered vitellogenesis, a gradual uniformity in size began to develop, such that at ovulation, in February, all the eggs were very similar in size (there was less than a 2-fold variation in volume). The pattern of growth of oocytes in an ovary during vitellogenesis suggests that growth between oocytes is closely coordinated.

An XPS study of amorphous MoO3/SiO films deposited by co-evaporation

Abstract: X-ray photoelectron spectroscopic (XPS) core-level spectra of MoO3/SiO thin films are presented The effects of changes in composition, substrate temperature during deposition and annealing on the binding energy of Mo(3d) and Si(2p) core lines in mixed films are compared with those of MoO3 and SiO Appreciable changes in Mo(3d) peak positions and slight changes in Si(2p) peak positions are observed The change in binding energy of the Mo(3d) doublet may be attributed to the effective incorporation of silicon ions in an MoO3 lattice which may cause the molybdenum orbital to be a little less tightly bound This helps in the internal electron transfer from the oxygen (2p) to the molybdenum (4d) level as a result of which the molybdenum is readily changed to lower oxidation states during heat treatment XPS spectra show that the position of the Si(2p) core state shifts monotonically with increasing oxygen concentration from the value of 1018 to 1026 eV

Pluralism, Reformed Pluralism and Neopluralism: the Role of Pressure Groups in Policy‐Making

Abstract: The critics of pluralism have often been rejected by pluralists who argue that their criticism has either attacked a caricature or they have defined pluralism so vaguely as to make it difficult to criticize with certainty.’ It is certainly true that a crude stereotype of pluralism has frequently been the subject of debate rather than the true arguments of pluralists. Therefore, the aim of this article is to present the ‘best-case’ definition of pluralism and to demonstrate that problems remain with even the most sophisticated models of pluralism. The article will also examine pluralists’ attempts to overcome their critics and evaluate how successful they have been in this task. It will demonstrate that the recent adaptations of pluralism have made many useful advances but that there is still room for further improvement.

Numerical Methods for the Solution of Special and General Sixth-Order Boundary-Value Problems, with Applications to Benard Layer Eigenvalue Problems

Abstract: A family of numerical methods is developed for the solution of special nonlinear sixth-order boundary-value problems. Methods with second-, fourth-, sixth- and eighth-order convergence are contained in the family. The problem is also solved by writing the sixth-order differential equation as a system of three second-order differential equations. A family of second- and fourth- order convergent methods is then used to obtain the solution. A second-order convergent method is discussed for the numerical solution of general nonlinear sixth-order boundary-value problems. This method, with modifications where necessary, is applied to the sixth-order eigenvalue problems associated with the onset of instability in a Benard layer. Numerical results are compared with asymptotic estimates appearing in the literature.

Doing business in the temple? managers and quality assurance in the public services

Abstract: Quality’ is now high on the policy agenda for many of our major public services. This article raises the question of what are the respective roles in securing quality of, on the one hand, professional service deliverers and, on the other, managers. It reviews a range of possible roles for managers and concludes that some of these are likely to be illegitimate and ineffective. Even the more appropriate roles will, however, often prove difficult to establish in practice. The article concludes with an examination of some possible key design features for successful relationships between managers and professional service deliverers. These are examined against the background of specific changes currently underway in the health care and education sectors.

The development of a radioimmunoassay for carp, Cyprinus carpio, vitellogenin.

Abstract: The development of an easily — performed and robust radioimmunoassay (RIA) to carp, Cyprinus carpio, vitellogenin (c-VTG) is described. Purified c-VTG was iodinated using Iodogen. The resulting c-VTG label was useful for up to 60 days. High titre antibodies were raised in rabbits to the purified c-VTG. The practical operating range of the c-VTG RIA was between 2 and 200 ng. ml-1. VTG was detected in plasma from all female mirror carp investigated, and all plasmas diluted parallel to the standard. The plasma VTG level in female carp increased concomitantly with the GSI; levels increasing from the ng. ml-1 level in juveniles to a maximum of 1 mg. ml-1 in fully mature females. VTG level was a far more sensitive index of the degree of sexual development than was GSI. In males, blood levels of VTG were always undetectable. Vitellogenic plasma from all subspecies of C. carpio (e.g. mirror, common, Koi) diluted parallel to the standard, as did blood from most other female cyprinids, such as the roach (Rutilis rutilis), bream (Abramis brama), and dace (Leuciscus leuciscus), but not all. These results suggest that the structure of VTG is highly conserved within this family. However, plasma from vitellogenic salmonids did not cross-react in the RIA. The relationship between plasma VTG and calcium levels was studied in both carp and rainbow trout. In rainbow trout it was found that plasma calcium levels do not rise above basal levels until the VTG level exceeds about 1 mg. ml-1, and therefore in this species it is only useful as an indicator of the degree of ovarian development in the later stages of the reproductive cycle. In the carp, however, and probably other cyprinids, blood VTG levels do not appear to naturally exceed about 1 mg.ml-1, and plasma calcium levels are not suitable as an indirect measure of the VTG level.

The mechanism of operation of WO3-based H2S sensors

Abstract: WO3-based sensors are selective and sensitive to H2S. Their mode of operation has been investigated and the materials characterized using scanning electron microscopy, Hg-porosimetry, X-ray fluorescence and X-ray diffraction. Thermal analyses have also been carried out. The reaction mechanism is facilitated via an anion-exchange process. The results of the characterization processes are described and the kinetics of reaction are also analysed, which will allow for the optimization of these devices.

Particle Packing in Ceramic Injection Molding

Abstract: The shrinkage of ceramic injection molding suspensions caused by pyrolytic removal of the organic vehicle was measured for initial ceramic volume fractions from 0.48 to 0.64. Shrinkage was inversely related to initial ceramic volume fraction V, and maximum volume fraction after pyrolysis V*,max was 0.65. The factors which restrict shrinkage are discussed. The maximum volume fraction, obtained from semiempirical equations relating the viscosity of suspensions to volume fraction of powder (Vmax) was 0.73 to 0.76. Both the viscosity of the suspensions and the shrinkage on removal of the organic vehicle can be interpreted in terms of a free volume of fluid over and above that needed to fill interstices between contacting particles. Thermomechanical measurements also show that the free-volume concept helps to interpret the transition from fluid to quasi-solid properties as the organic vehicle is removed by pyrolysis from a molded body.

The effect of aluminium inclusions on the dielectric breakdown of polyethylene

Abstract: A narrow size distribution of irregular aluminium particles was blended into power cable insulation grade polyethylene. Some batches of the resulting material were then melt-filtered to reduce the size of particles present and narrow the distributions further. The failure statistics of the loaded polymers were then determined under AC ramped stress. The data have been fitted to extreme value statistics, and trends with size and density of defect can clearly be identified. In addition, for the filtered material, a minimum breakdown field can be associated with a given filter size: a result of commercial importance. Some indications exist to suggest that different modes of failure operate at high and low fields. Candidates for these modes are analysed and discussed in terms of the distributions of defects present. Local field enhancement due to the included flaws were calculated using finite-element techniques. The results are compared with a percolation model of breakdown. Predictions are found to quantify accurately the reduction in the characteristic strength of the material over the narrow range of defect concentrations examined.

An in vitro culture system for studying vitellogenin uptake into ovarian follicles of the rainbow trout, Salmo gairdneri

Abstract: The development of a short-term culture system to study vitellogenin (VTG) sequestration in vitro into vitellogenic follicles of the rainbow trout, Salmo gairdneri, is described. The outer epithelial cell layer of the trout follicle restricted VTG uptake considerably and its removal was a prerequisite to study VTG uptake in vitro. Vitellogenic follicles divested of the surface epithelium sequestered VTG at rates of up to 170 ng·mm2 follicle surface−1·h−1 (ng·mm−2·h−1). Uptake of VTG over an 8 h period of incubation was linear. Increasing the titre of VTG in the culture medium induced greater rates of sequestration in a dose-dependent manner; follicles cultured in medium containing 45 mg VTG·ml−1 sequestered 170 ± 9ng·mm−2·h−1 whereas those follicles cultured in medium containing 2 mg·ml−1 only incorporated 6 ± 0.5 ng·mm−2·h−1. Uptake of VTG was temperature dependent with higher temperatures inducing higher levels of incorporation. Sequestration of VTG persisted at temperatures below 5°C, showing that the uptake mechanisms are adapted to low temperatures in this species. Size of follicles also had a considerable bearing on the rate of VTG sequestration; follicles of less than 1 mm diameter (pre-vitellogenic follicles) did not sequester VTG in amounts that were detectable. All follicles measuring 1 mm or greater in diameter sequestered VTG. As the follicles increased in size between approximately 1 and 3 mm in diameter there was an increase in both the total amount of VTG sequestered and the rate of uptake of VTG relative to surface area. Limited data suggested that in follicles closely approaching ovulation the rate of VTG sequestration was considerably reduced.

Smooth Parametric Surfaces and n-Sided Patches

Abstract: The theory of ‘geometric continuity’ within the subject of CAGD is reviewed. In particular, we are concerned with how parametric surface patches for CAGD can be pieced together to form a smooth Ck surface. The theory is applied to the problem of filling an n-sided hole occurring within a smooth rectangular patch complex. A number of solutions to this problem are surveyed.

The purification and partial characterization of carp, Cyprinus carpio, vitellogenin.

Abstract: A procedure is described for the isolation of intact vitellogenin (c-VTG) from the carp, Cyprinus carpio. VTG was induced in juvenile females using oestradiol-17β and purified from the plasma using a combination of gel-filtration chromatography on Sepharose 6B and ion exchange chromatography on DEAE-cellulose. Purification procedures were conducted at low temperatures (below 9°C) in the presence of the proteolytic enzyme inhibitor aprotinin to prevent degradation. Intact c-VTG had an apparent molecular mass of 390,000 Daltons, but when extracted from plasma in the absence of aprotinin it underwent proteolysis into at least 2 protein fragments (apparent molecular masses of 230,000 and 96,000 Daltons), showing an instability of the native dimer. An amino acid analysis of c-VTG showed that its composition was almost identical to goldfish VTG, a species closely allied to the true carps and also similar to other oviparous vertebrate VTGs. Collectively, these data indicate that using these purification procedures VTG from carp, and probably other teleost species, can be isolated in an intact, highly purified form.

Studies on the hyperplasia (‘regeneration’) of the rat liver following partial hepatectomy. Changes in lipid peroxidation and general biochemical aspects

Abstract: Using the experimental model of partial hepatectomy in the rat, we have examined the relationship between cell division and lipid peroxidation activity. In rats entrained to a regime of 12 h light/12 h dark and with a fixed 8 h feeding period in the dark phase, partial hepatectomy is followed by a rapid regeneration of liver mass with cycles of synchronized cell division at 24 h intervals. The latter phenomenon is indicated in this study by pulses of thymidine kinase activity having maxima at 24 h, 48 h and 72 h after partial hepatectomy. Microsomes prepared from regenerating livers show changes in lipid peroxidation activity (induced by NADPH/ADP/iron or by ascorbate/iron), which is significantly decreased relative to that in microsomes from sham-operated controls, again at 24 h, 48 h and 72 h after the operation. This phenomenon has been investigated with regard to possible underlying changes in the content of microsomal fatty acids, the microsomal enzymes NADPH:cytochrome c reductase and cytochrome P-450, and the physiological microsomal antioxidant alpha-tocopherol. The cycles of decreased lipid peroxidation activity are apparently due, at least in part, to changes in microsomal alpha-tocopherol content that are closely associated in time with thymidine kinase activity.

Willingness to accept risk in the treatment of rheumatic disease.

Abstract: STUDY OBJECTIVE--The aim was to assess patients willingness to accept mortal risk in the drug treatment of chronic rheumatic disease. DESIGN--A non-random sample of consecutive patients were interviewed with a standardised survey instrument. SETTING--The study took place in the Royal National Hospital for Rheumatic Diseases, Bath, UK. PATIENTS--100 consecutive in- and out-patients aged 65 or less were interviewed, 50 with rheumatoid arthritis and 50 with ankylosing spondylitis. Mean age was 48 years with mean disease duration of 14 years. The rheumatoid arthritis group was mainly female (84%), v 26% in the ankylosing spondylitis group. MEASUREMENTS AND MAIN RESULTS--Risk preferences were elicited using the method of standard gamble in the context of a hypothetical new drug. Patients indicated the maximum percentage probability of mortality they regarded as acceptable to achieve four different levels of benefit: total cure (20.7%), relief of pain (16.9%), relief of stiffness (13.1%), return to normal functioning (14.5%). Rheumatoid arthritis patients displayed a higher (p less than 0.05) willingness to accept risk than ankylosing spondylitis patients for all gambles except relief of stiffness. Analysis of variance indicated that willingness to accept risk decreases with the duration of disease and increases with reductions in self assessed health status. CONCLUSIONS--Evaluative methods such as standard gamble can elicit useful risk-benefit preference data from patients to assist those who manage clinical risks.

Rewriting the museums' fictions: Taxonomies, stories and readers

Abstract: The set of objects the Museum displays is sustained only by the fiction that they somehow constitute a coherent representational universe…. Should the fiction disappear, there is nothing left of the Museum but (‘bric-a-brac’), a heap of meaningless and valueless fragments of objects which are incapable of substituting themselves either metonymically for the original objects or metaphorically for their representations. (Donato 1979: 223)