Showing papers by "Brunel University London published in 1992"

Stress reduces the quality of gametes produced by rainbow trout.

Abstract: In this study we have used the rainbow trout as a model animal to study the biological consequences of stress in terms of gamete quality and quantity. Groups of 30 mature male and female rainbow trout were subjected to repeated acute stress during the 9 mo prior to spawning. Time of ovulation, fecundity, and egg size were recorded in mature females, and sperm counts were carried out on the milt from the male fish, from both the stressed and control groups. Eggs from ovulated females were fertilized with milt from males subjected to the same treatment regime. Approximately 300 eggs from each female were fertilized with a sperm dilution of 10-3 in diluent. Subsequent development of the fertilized eggs was then monitored. There were no differences in somatic weight or length between the two groups at the end of the experiment, but exposure of rainbow trout to repeated acute stress during reproductive development resulted in a significant delay in ovulation and reduced egg size in females, significantly lower sperm counts in males, and, perhaps most importantly, significantly lower survival rates for progeny from stressed fish compared to progeny from unstressed control fish. Hence, stress reduces the quality of gametes produced by rainbow trout.

The detector simulation program for the OPAL experiment at LEP

Abstract: The Monte Carlo program for the OPAL experiment at the LEP ee collider is described. This program is based on the GEANT simulation package. The general organization of the program is outlined, and a description is given of the techniques used for simulating the various subdetectors of OPAL. The performance of the program is illustrated by comparisons with recent data recorded by OPAL at LEP. (Submitted to Nucl. Instr. and Meth.) School of Physics and Space Research, University of Birmingham, Birmingham, B15 2TT, UK Dipartimento di Fisica dell' Universit a di Bologna and INFN, Bologna, 40126, Italy CNAF-INFN, Bologna, Italy Physikalisches Institut, Universitat Bonn, D-5300 Bonn 1, FRG Department of Physics, University of California, Riverside, CA 92521 USA Cavendish Laboratory, Cambridge, CB3 0HE, UK Carleton University, Dept of Physics, Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada Centre for Research in Particle Physics, Carleton University, Ottawa, Ontario K1S 5B6, Canada CERN, European Organisation for Particle Physics, 1211 Geneva 23, Switzerland Enrico Fermi Institute and Department of Physics, University of Chicago, Chicago Illinois 60637, USA Fakult at f ur Physik, Albert Ludwigs Universitat, D-7800 Freiburg, FRG Universitat Hamburg/DESY, II Inst. f ur Experimental Physik, 2000 Hamburg 52, FRG Physikalisches Institut, Universitat Heidelberg, Heidelberg, FRG Queen Mary and West eld College, University of London, London, E1 4NS, UK University College London, London, WC1E 6BT, UK Department of Physics, Schuster Laboratory, The University, Manchester, M13 9PL, UK Department of Physics and Astronomy, University of Maryland, College Park, Maryland 20742, USA Laboratoire de Physique Nucl eaire, Universit e de Montr eal, Montr eal, Quebec, H3C 3J7, Canada Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK DPhPE, CEN Saclay, F-91191 Gif-sur-Yvette, France International Centre for Elementary Particle Physics, University of Tokyo, Tokyo 113, Japan Brunel University, Uxbridge, Middlesex, UB8 3PH UK Nuclear Physics Department, Weizmann Institute of Science, Rehovot, 76100, Israel Present address: EPFL, Lausanne, Switzerland Present address: Applied Silicon Inc, Ottawa, Canada Present address: Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK On leave from Birmingham University, Birmingham B15 2TT, UK Present address: Culham Laboratory, Culham, Oxfordshire, UK Present address: Meiji Gakuin University, Yokohama 244, Japan

Voltage collapse proximity indicator: behaviour and implications

Abstract: With the increased loading and exploitation of the power transmission system, the problem of voltage stability and voltage collapse attracts more and more attention. A voltage collapse can take place in systems or subsystems, and can appear quite abruptly. Continuous monitoring of the system state is therefore required. This paper is concerned with the problem of voltage stability, and investigates a proposed voltage collapse proximity indicator applicable to the load points of a power system, based on the optimal impedance solution of a two-bus system. This indicator is generalised and applied to an actual system. The performance of this new indicator is investigated over both the stable and the unstable regions, as the load at a particular node or the system load increases. Tests show that the indicator can provide useful information at any operating point.

A Study of charged particle multiplicities in hadronic decays of the Z0

Abstract: We present an analysis of multiplicity distributions of charged particles produced inZ 0 hadronic decays. The results are based on the analysis of 82941 events collected within 100 MeV of theZ 0 peak energy with the OPAL detector at LEP. The charged particle multiplicity distribution, corrected for initial-state radiation and for detector acceptance and resolution, was found to have a mean 〈n ch〉=21.40±0.02(stat.)±0.43(syst.) and a dispersionD=6.49±0.02(stat.)±0.20(syst.). The shape is well described by the Lognormal and Gamma distributions. A negative binomial parameterisation was found to describe the shape of the multiplicity distribution less well. A comparison with results obtained at lower energies confirms the validity of KNO(-G) scaling up to LEP energies. A separate analysis of events with low sphericity, typically associated with two-jet final states, shows the presence of features expected for models based on a stochastic production mechanism for particles. In all cases, the features observed in the data are well described by the Lund parton shower model JETSET.

Theory and application of microindentation in studies of glide and cracking in single crystals of elemental and compound semiconductors

Abstract: The microhardness of Si (MP 1688 K), GaP (1623 K), GaAs (1510 K) and InP (1327 K) single crystals was determined by indentation (Vicker's hardness, VHN) of low-index facets at loads of 5–100g at 296–673 K, complementing earlier work on Ge and InSb. In the brittle range, extending up to about 0.35 T melt (K), cracking occurred preferentially along the diagonals of the indentations, and was observed at all loads, with the possible exception of the lowest (5 g) in the case of InP at 289 K. At higher temperatures the relative orientations of crack and slip traces on the crystal surface, as observed by SEM, suggested that cracks nucleated preferentially at the slip-band intersection, as was also noted by Hirsch et al. (Phil. Mag.3 (1985) 759) in GaAs above 600 K. As earlier in Ge, the VHN was found to depend on the load, L, as L p, and on the indentation diameter, d, as dn, with p = 1/2 and n = 2, as required by the model of indentation plasticity of Banerjee and Feltham [4, 5], but higher p and n values were found if chipping at the indentation edges was evident. The effect was related to the resulting decrease in indentation diameter due to the work lost, through chipping, by the indenter. Above about 0.35 T melt (K), relaxation of the dislocation structures entails a decrease of p and n; both parameters tend to zero as T → T melt. Shear and tensile stresses seem to co-operate in the process of plastic deformation, the role of normal stresses, acting across slip planes, predominating in the ‘brittle’ range.

Reactive power dispatch incorporating voltage stability

Abstract: The cause of the 1977 New York blackout has been proved to be the reactive-power problem. The 1987 Tokyo blackout was believed to be due to a reactive-power shortage and a voltage collapse at the summer peak load. These events have confirmed the importance of reactive-power planning and dispatching in maintaining the security of modern power systems. Appropriate control of system voltage profiles can enhance system security and may also reduce system losses. Previous investigations by the same authors have shown that a voltage collapse proximity indicator based on the optimal impedance solution of a two-bus system can be extended to an actual network. The authors describe a linear reactive power dispatch algorithm which incorporates this indicator to minimise the possibility of voltage collapse in the system.

Screening for diabetic retinopathy: a relative cost-effectiveness analysis of alternative modalities and strategies.

Abstract: Diabetic retinopathy is the most common cause of blindness among adults of working age in the UK. If the disease is detected early effective treatment can be provided and this has resulted in calls for a systematic national screening programme. Using data on the screening of 3423 diabetics collected as part of an experimental programme in three UK centres, the relative cost-effectiveness of various screening options is assessed. The paper utilises direct evidence on a number of single modality screening options, including ophthalmoscopy undertaken by general practitioners or ophthalmic opticians, and non-mydriatic photography. With the objective of increasing the sensitivity of screening and using data collected in the study, options based on two further potential screening strategies are modelled and evaluated: combined screening using both ophthalmoscopy and non-mydriatic photography; and selective screening where high-risk diabetics are directly referred to an ophthalmologist and low-risk cases are either left unscreened or are screened by one of the single or combined modality screening options. Given the objective of early detection, effectiveness is assessed in terms of the sensitivity and specificity of the referral decisions of screening options. Both health service and private resource costs of the various screening options are estimated, the latter in terms of travel and the opportunity cost of time. Cost effectiveness is evaluated in terms of the expected cost per true positive case of diabetic retinopathy referred by the screening options. To narrow the choice between the options, those subject to three-way domination with respect to the three choice variables of sensitivity, specificity and expected cost per true positive are excluded. Amongst the remaining options, the choice is dependent on the trade-off between the higher specifics of unselective single modality screening options and the higher sensitivities and lower expected costs per true positive case detected of combined modality and selective screening options.

Numerical modelling of viscoelastic liquids using a finite-volume method

Abstract: A new staggered-grid, finite-volume method for the numerical simulation of isothermal viscoelastic liquids is presented. The main features of this method are the use of a primitive variable formulation, the location of the velocities, pressures and stresses on different staggered grids and the use of a third-order difference scheme for the discretization of the constitutive equations. The method is applied to a sudden-expansion, viscoelastic-flow problem for a range of Weissenberg numbers. For one case the mesh has been refined to demonstrate that the method is robust and viscoelastic effects are not filtered out as the mesh size decreases. All the computations have been performed on a PC equipped with a floating-point coprocessor. Although the method has been defined for, and applied to, two-dimensional problems, the technique is readily extendable to three dimensions without excessive cost.

A global determination of {Mathematical expression} at LEP

Abstract: The value of the strong coupling constant, $$\alpha _s (M_{Z^0 } )$$ , is determined from a study of 15 different observables in hadronicZ 0 and τ decays. The study includes global event shape variables, jet production rates, energy correlations, theZ 0 line shape and decay asymmetries and the hadronic branching fraction of τ-leptons. Differences between the αs values from the different observables can be consistently attributed to unknown higher order contributions to the calculations. These uncertaities may be parametrized by variations of the renormalization scale and of the parton virtuality to which the data are corrected, separately for each observable, resulting in a consistent description of the event shapes, jet rates and energy correlations with the value $$\alpha _s (M_{Z^0 } ) = 0.122_{ - 0.005}^{ + 0.006} $$ in . The error is dominated by the theoretical uncertainties. Application of recent calculations which include the resummation of leading and next-to-leading logarithms to all orders for some observables confirm this result with a reduced sensitivity to renormalization scale variations. TheZ 0 line shapes and τ-lepton branching ratios yield $$\alpha _s (M_{Z^0 } ) = 0.148 \pm 0.021$$ and $$\alpha _s (M_{Z^0 } ) = 0.123_{ - 0.007}^{ + 0.006} $$ , respectively, in . These measurements and their uncertainties are entirely independent of each other and from event shape and jet observables; the good agreement of the resulting αs values thus constitutes an important consistency check of the reliability of perturbative QCD.

Novel decade electronically tunable microwave oscillator based on the distrubuted amplifier

Abstract: The Letter suggests that a microwave distributed amplifier can be used as a decade-wide electronically tunable oscillator by using the output from the idle drain load as the feedback output and differentially varying the bias of the amplifier MESFETs, taken in pairs. CAD techniques predict that this approach should produce a decade tuning range with seven MESFETs in a nine stage configuration.

The Measurement and Analysis of Swirl in Steady Flow

Abstract: The influence of swirl on combustion in diesel and spark ignition engines is reviewed briefly, and this leads to a resume of the swirl measuring techniques. The numerous ways of analysing swirl data are summarised and the relations between the different swirl parameters are presented. Experimental results are presented from a diesel engine in which the flow has been measured by a hot wire anemometer, a paddle wheel and a swirl torquemeter. The performance of the different measurement techniques is compared. Further results are presented (from a spark ignition engine) which illustrate the influence of the inlet port, manifold and entry conditions on the swirl measurements. Integration techniques are reviewed for producing a single swirl parameter to characterise the combined performance of the inlet port, valve and camshaft. Finally, the difficulty in standardising measurements of barrel swirl are discussed. © Copyright 1992 Society of Automotive Engineers, Inc.

Increased activity of 6-phosphogluconate dehydrogenase and glucose-6-phosphate dehydrogenase in purified cell suspensions and single cells from the uterine cervix in cervical intraepithelial neoplasia.

Abstract: The activities of 6-phosphogluconate dehydrogenase and glucose-6-phosphate dehydrogenase have been measured in squamous epithelial cells of the uterine cervix from normal patients and cases of cervical intraepithelial neoplasia (CIN). A biochemical cycling method, which uses only simple equipment and is suited to routine use and to automation, was applied to cells separated by gradient centrifugation. In addition, cells were examined cytochemically, and the intensity of staining in the cytoplasm of single whole cells was measured using computerised microcytospectrophotometry. Twenty per cent of cells in samples from normal patients (n=61) showed staining intensities above an extinction of 0.15 at 540 nm, compared to 71% of cases of CIN 1 (n=14), 91% of cases of CIN 2 (n=11) and 67% of cases of CIN 3 (n=15). The cytochemical data do not allow definitive distinctions to be made between different grades of CIN whereas the biochemical assay applied to cell lysates shows convincing differences between normal samples and cases of CIN. There are no false negatives for CIN 3 (n=14) and CIN 2 (n=10) and 11% false negatives for CIN 1 (n=9) and 14% of false positives for normal cases (n=21). The results of this preliminary study with reference to automation are discussed [corrected].

Oxidation of monohydric phenol substrates by tyrosinase. An oximetric study

Abstract: The purity of commercially available mushroom tyrosinase was investigated by non-denaturing PAGE. Most of the protein in the preparation migrated as a single band under these conditions. This band contained both tyrosinase and dopa oxidase activity. No other activity of either classification was found in the preparation. Oxygen consumption by tyrosinase during oxidation of the monohydric phenol substrates tyrosine and 4-hydroxyanisole (4HA) was monitored by oximetry in order to determine the stoichiometry of the reactions. For complete oxidation, the molar ratio of oxygen: 4HA was 1:1. Under identical conditions, oxidation of tyrosine required 1.5 mol of oxygen/mol of tyrosine. The additional oxygen uptake during tyrosine oxidation is due to the internal cyclization of dopaquinone to form cyclodopa, which undergoes a redox reaction with dopaquinone to form dopachrome and dopa, which is then oxidized by the enzyme, leading to an additional 0.5 mol of oxygen/mol of original substrate. Oxygen consumption for complete oxidation of 200 nmol of 4HA was constant over a range of concentrations of tyrosinase of 33-330 units/ml of substrate. The maximum rate of reaction was directly proportional to the concentration of tyrosinase, whereas the length of the lag phase decreased non-linearly with increasing tyrosinase concentration. Activation of the enzyme by exposure to citrate was not seen, nor was the lag phase abolished by exposure of the enzyme to low pH. Michaelis-Menten analysis of tyrosinase in which the lag phase is abolished by pre-exposure of the enzyme to a low concentration of dithiothreitol gave Km values for tyrosine and 4HA of 153 and 20 microM respectively.

Recently published work on EUROPT-1, a 6% Pt/SiO2 reference catalyst

Abstract: EUROPT-1 is a 6% Pt/SiO 2 catalyst which has been thoroughly characterised with respect to its composition, structure, chemisorption behaviour and catalytic properties Extensive further work on this catalyst has been published and this is now reviewed Debye function analysis of X-ray diffraction spectra suggest platinum particles to be cubooctahedral, although preliminary extended X-ray absorption fine structure results do not accord with this model Further isotherms for carbon monoxide, hydrogen and oxygen chemisorption have been reported and enthalpies of adsorption for the last two gases measured Limited results on structure-insensitive reactions such as exchange of methane with deuterium and alkene hydrogenation are available Methane homologation as well as skeletal reactions of alkanes in the presence of hydrogen represent structure-sensitive reactions Some further work on ethane, propane and n-butane is reported; detailed results on n-hexane and methylcyclopentane include changes in rates and selectivities as a function of hydrogen and hydrocarbon pressure They are interpreted in terms of availability of surface hydrogen and hydrogen effects on the formation of carbonaceous deposits of various degree of dehydrogenation Effects of sintering have also been studied, and active centres for various reactions have been tentatively suggested On the whole, EUROPT-1 shows behaviour which is characteristic of platinum catalysts containing small platinum particles but in some limited respects it shows unusual and unexpected properties Reactions of some oxygenated compounds are described briefly Catalytic properties of EUROPT-1 can be modified by metals, oxides, sulphur and nitrogen; treatment with cinchonidine converts it into an enantioselective catalyst for the hydrogenation of methyl pyruvate Finally the importance of selecting appropriate reference supported metal catalyst (s) is stressed and the future role for EUROPT-1 as a possible candidate is pointed out; results must however be compared under carefully defined conditions if they are to have real value

Mechanism of sintering between polypropylene beads

Abstract: Using experimental results obtained by hot-stage light microscopy, the sintering behaviour of off-reactor spherical grades of polypropylene and poly(methyl methacrylate) were considered. Sintering rates were found to be strongly influenced by initial particle size, melt temperature and viscosity and could be modelled using the Frenkel equation. Examination of the microstructure between sintered polypropylene particles revealed a distinct transcrystalline zone, which was relatively insensitive to sintering temperature and cooling rate.