Showing papers by "University of Warwick published in 1985"

Impossibility of distributed consensus with one faulty process

Abstract: The consensus problem involves an asynchronous system of processes, some of which may be unreliable The problem is for the reliable processes to agree on a binary value In this paper, it is shown that every protocol for this problem has the possibility of nontermination, even with only one faulty process By way of contrast, solutions are known for the synchronous case, the “Byzantine Generals” problem

Dynamic Generalized Linear Models and Bayesian Forecasting

Abstract: Dynamic Bayesian models are developed for application in nonlinear, non-normal time series and regression problems, providing dynamic extensions of standard generalized linear models. A key feature of the analysis is the use of conjugate prior and posterior distributions for the exponential family parameters. This leads to the calculation of closed, standard-form predictive distributions for forecasting and model criticism. The structure of the models depends on the time evolution of underlying state variables, and the feedback of observational information to these variables is achieved using linear Bayesian prediction methods. Data analytic aspects of the models concerning scale parameters and outliers are discussed, and some applications are provided. Dynamic Bayesian models are developed for application in nonlinear, non-normal time series and regression problems, providing dynamic extensions of standard generalized linear models. A key feature of the analysis is the use of conjugate prior and...

Compton scattering and electron momentum determination

Abstract: When radiation is Compton-scattered the emerging beam is Doppler broadened because of the motion of the target electrons. An analysis of this broadened lineshape the Crompton profile, provides detailed information about the electron momentum distribution in the scatter. The technique is particularly sensitive to the behaviour of the slower moving outer electrons involved in bonding in condensed matter and can be used to test their quantum-mechanical description. The review begins with a brief survey of the historical development of the subject to within a decade of the present. The behaviour of quantum systems from a momentum viewpoint, is explained and the conditions under which the scattering experiment can be interpreted directly in terms of electron momentum density are discussed. The experimental techniques with gamma -rays, X-rays and electron beams are compared. Finally, recent results on insulators and conductors are surveyed and the extent to which they challenge conventional assumptions of band theory is critically reviewed.

Capital market information and industrial performance: the role of west german banks*

Abstract: In orthodox theory external capital markets play a dual role, supplying various forms of investment finance and disciplining firms which are inefficient, or fail to pursue profit goals. An extensive literature speaks of the efficiency of external capital markets, meaning that 'firms can make production-investment decisions, and investors can choose among the securities that represent ownership of firms' activities under the assumption that security prices at any time fully reflect all available information' (Fama, I970.)1 However, this concept of 'efficiency' is purely technical; it depends critically on what information is available, and we know there are problems of appropriability and failure in information markets, deriving ultimately from certain peculiarities of information as a commodity (Arrow, I962). Thus another, growing literature focusses on problems of achieving equilibrium in markets where agents are imperfectly or asymmetrically informed. Amongst other things, this literature shows that informational failures of the kind in question can lead to capital-rationing in loan and credit markets, and the use of strict collateral requirements as screening devices (Jaffee and Russell, I976; Stiglitz and Weiss, I98I; Cable and Turner, I983). These may then be expected to affect the efficiency of individual firms and the system as a whole. Capital shortage implies that some profitable investment opportunities are foregone, and production choices may also be distorted by the need to satisfy additional financial constraints, contrived to elicit signals of creditworthiness of the firms undertaking them. Similarly, the disciplining role of external capital markets can be impaired by information 'impactedness' (Williamson, I975) and the costs of mobilising and giving effect to shareholders' preferences. Thus in the principal-agent framework developed by Jensen and Meckling (I976) and Fama (I980), the degree of constraint on managerial pursuit of non-profit goals, as posited by managerial theorists, depends on the transactions costs of stock-owner intervention. The result is an optimal degree of departure from cost-minimising, profit-maximising behaviour, determined by the level of transactions costs. Institutional factors which affect the way information is distributed amongst agents can therefore have an important bearing on allocative and technical efficiency, and the West German system of industrial finance provides an in-

Nucleotide sequence of cloned cDNA coding for preproricin.

Abstract: The primary structure of a precursor protein that contains the toxic (A) and galactose-binding (B) chains of the castor bean lectin, ricin, has been deduced from the nucleotide sequence of cloned DNA complementary to preproricin mRNA. A cDNA library was constructed using maturing castor bean endosperm poly(A)-rich RNA enriched for lectin precursor mRNA by size fractionation. Clones containing lectin mRNA sequences were isolated by hybridization using as a probe a mixture of synthetic oligonucleotides representing all possible sequences for a peptide of the ricin B chain. The entire coding sequence of preproricin was deduced from two overlapping cDNA clones having inserts of 1614 and 1049 base pairs. The coding region (1695 base pairs) consists of a 24-amino-acid N-terminal signal sequence (molecular mass 2836 Da) preceding the A chain (267 amino acids, molecular mass 29 399 Da), which is joined to the B chain (262 amino acids, molecular mass 28 517) by a 12-amino-acid linking region (molecular mass 1385 Da).

To win friends and influence people

Abstract: The Elements of Graphing Data. By William S. Cleveland. Wadsworth:1985. Pp.323. Hbk 27.95, 37.80; pbk 18.95, 25.60.

Novel Role for Phycoerythrin in a Marine Cyanobacterium, Synechococcus Strain DC2.

Abstract: Cyanobacterial picoplankton contribute substantially to oceanic primary productivity. The colored protein phycoerythrin is the major component of their light-harvesting apparatus. It was found that in Synechococcus strain DC2 a variable proportion of the light energy absorbed by phycoerythrin is lost as autofluorescence and therefore is not passed to a photoreaction center. Phycoerythrin may serve two functionally distinct roles in this organism: as a nitrogen reserve and as a collector of quanta for photosynthesis.

Acetylene as a suicide substrate and active site probe for methane monooxygenase from Methylococcus capsulatus (Bath)

Abstract: Acetylene was shown to be an inhibitor of cell-free methane monooxygenase (MMO) activity in Methylococcus capsulatus (Bath). Inhibition was demonstrated for both the soluble and particulate forms of the enzyme and was dependent on the presence of both NADH and oxygen. Inactivation of the enzyme complex was irreversible and was due to binding of the acetylene to specific proteins of the enzyme complex. The use of radiolabelled [14C]acetylene provided a method for visualisation of the bound inhibitor: protein complex on sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE). Acetylene was shown to bind to proteins which are associated with methane-oxidising activity and it is proposed that acetylene acts as a suicide substrate.

Universal low-frequency behaviour in the a.c. hopping conductivity of disordered systems

Abstract: The empirical scaling law σ(ω, T)/σ(0, T)=f[Aω/σ(0, T)] is implied for a.c. conductivities calculated in the extended pair approximation (EPA) for a variety of models in parameter ranges that are typical experimentally. The number A depends upon the model considered; ω and σ represent frequency and conductivity, respectively, in reduced units. It is shown that, for energy-independent hopping in the EPA, the law becomes more accurate when ω→0 and σ(0)→0. Numerical results for an energy-dependent model imply similar behaviour. The same law gives a good account of experimental data on conduction in amorphous germanium, impurity bands, and polyacetylene. A quasi-universal behaviour of the frequency-dependent conductivity is suggested, in which the specific nature of a given material is manifest only in its d.c. conductivity and in the value of A for a given f(x). In consequence the ωs law is reinterpreted; s depends upon σ(ω)/σ(0) and is not related to the distribution of hopping rates via the pair a...

Degradation of the herbicide mecoprop [2-(2-methyl-4-chlorophenoxy)propionic Acid] by a synergistic microbial community.

Abstract: A microbial community isolated from wheat root systems was capable of growth on mecoprop as the sole carbon and energy source. When exposed to fresh herbicide additions, the community was able to shorten the lag phase from 30 days to less than 24 h. The community comprised two Pseudomonas species, an Alcaligenes species, a Flavobacterium species, and Acinetobacter calcoaceticus. None of the pure cultures was capable of growing on mecoprop. Certain combinations of two or more community constituents were required before growth commenced. The mecoprop-degrading community could also degrade 2,4-dichlorophenoxyacetic acid and 2-methyl-4-chlorophenoxyacetic acid but not 2,4,5-trichlorophenoxyacetic acid.

Decomposing multipliers for economic systems involving regional and world trade

Abstract: This paper is concerned with the analysis of linkages between economic systems and the spillover and possible feedback effects one system may have on another. It is not a new topic, the initial stimulus in the literature coming from Machlup (I943) and the seminal papers by Metzler (I950) and Chipman (I950). Almost precisely the same questions raised by these authors have been readdressed subsequently by many writers and in a variety of contexts. Most recently, Goodwin (I983) has developed a world matrix multiplier with much the same overall objectives as Machlup and Metzler in mind. Metzler's proposition was to understand 'the mechanism by which an expansion or contraction of income in one region or country is transmitted to other regions or countries '.' In addition, he assumed that 'the conclusions apply without modification to the regions within a single country, or, indeed to any regional classification of the world economy, such as the economies comprising Eastern Europe, Western Europe, Latin America, and similar regions'.2 In fact the question has also long occupied the attention of many regional economists working in the context of sub-national regions. The question of interdependence between sub-national regional economies generally assumes a special importance simply because such regions are relatively open economies and are subject to fewer natural and artificial barriers to commodity trade and factor movements than may exist between countries.3 Even so, interest has focused almost exclusively on regional interdependence through commodity trade and within the framework of multiregional input-output systems.4 However, there are some exceptions; Klein and Glickman (I 9 77) have developed a multiregional model of a fairly aggregative nature which incorporates other regional interdependencies. A review of this and similar models has been carried out by Glickman (I97 7). Paralleling this interest in inter-regional interdependence at the sub-national level, there has been a revived interest in questions of linkage at the international level, with the advent of the project LINK model (pioneered by Klein and Hickman),5 the United Nations model of the world economy (Leontief et al.

Diagnostic checks of non‐standard time series models

Abstract: Diagnostic checks have become a standard tool for helping to assess the adequacy of a forecasting system since Box and Jenkins' (1970) ARIMA modelling technique became popular. However, most of the research has developed checks for normal or second-order stationary models. This paper gives various diagnostic checks that can be performed simply on nonnormal, non-standard models such as the class of multiprocess models (Harrison and Stevens, 1976), where residuals are definitely not normal. The performance to date of these models can then be objectively scrutinized on-line. Examples, including a generalized cusum technique, are given to illustrate the effectiveness of the techniques on specific series.

Electron transfer reactions in the soluble methane monooxygenase of Methylococcus capsulatus (Bath).

Abstract: 1 Aerobic stopped-flow experiments have confirmed that component C is the methane monooxygenase component responsible for interaction with NADH. Reduction of component C by NADH is not the rate-limiting step for component C in the methane monooxygenase reaction. 2 Removal and reconstitution of the redox centres of component C suggests a correlation between the presence of the FAD and Fe2S2 redox centres and NADH: acceptor reductase activity and methane monooxygenase activity respectively, consistent with the order of electron flow: NADH FAD Fe2S2 component A. This order suggests that component C functions as a 2e−1/1e−1 transformase, splitting electron pairs from NADH for transfer to component A via the one-electron-carrying Fe2S2 centre. 3 Electron transfer has been demonstrated between the reductase component, component C and the oxygenase component, component A, of the methane monooxygenase complex from Methylococcus capsulatus (Bath) by three separate methods. This intermolecular electron transfer step is not rate-determining for the methane monooxygenase reaction. 4 Intermolecular electron transfer was independent of component B, the third component of the methane monooxygenase. Component B is required to switch the oxidase activity of component A to methane monooxygenase activity, suggesting that the role of component B is to couple substrate oxidation to electron transfer, via the methane monooxygenase components.

Prefabricated insulating panels

Abstract: A building panel is provided having a channel in its back surface which matingly receives a rigidifying element. A fastener plate secures the panel to a substrate by slidable engagement with the rigidifying element.

Structure determination of the formate intermediate on Cu(110) by use of x-ray-absorption fine-structure measurements.

Abstract: A unique assignment of both the orientation and the adsorption site of formate (HCOO) on Cu(110) has been made by analysis of near-edge and extended x-ray-absorption fine structure. The species lies with its molecular plane perpendicular to the surface, aligned along the [$1\overline{1}0$] directions, and on top of the copper atoms of the outermost layer; the oxygen atoms almost bridge two copper atoms with an average Cu-O bond length of 1.98\ifmmode\pm\else\textpm\fi{}0.07 \AA{}, essentially identical to that in bulk copper formate.

The Linear-Quadratic Control Problem for Retarded Systems with Delays in Control and Observation

Abstract: THE OBJECT of this paper is to solve the linear-quadratic control problem (LQCP) for retarded functional differential equations (RFDE) with delays in the input and output variables. This will be done within the general semigroup-theoretic framework which has been developed in [28]. For retarded systems with undelayed input and output variables the LQCP has been studied by various authors for about twenty years. We mention the work of Krasovskii [20], Kushner & Barnea [21], Alekal, Brunovskii, Chyung & Lee [1], Delfour & Mitter [14], Curtain [6], Manitius [25], Delfour, McCalla & Mitter [13], Delfour, Lee & Manitius [11], Delfour [8], Banks & Burns [2]. First results on systems with a single-point delay in the state and control variables can be found in Koivo & Lee [19] and Kwong [22]. Ichikawa [16] has developed a comprehensive evolution equation approach for the treatment of the LQCP for RFDEs with input delays. His idea was to include a past segment of the input function in the state of the system. A completely different approach to this problem has been developed by Vinter & Kwong [30] for RFDEs with distributed input delays. Their approach has been generalized to RFDEs with general delay, in the state and control variables by Delfour [9, 10] and to neutral systems by Karrakchu [18] in her recent thesis. The LQCP for neutral systems with output delays has been studied by Datko [7] and Ito & Tarn [17].

Further characterisation of the FAD and Fe2S2 redox centres of component C, the NADH:acceptor reductase of the soluble methane monooxygenase of Methylococcus capsulatus (Bath).

Abstract: The absorbance contributions of the FAD and Fe2S2 redox centres of component C of the soluble methane monooxygenase complex have been resolved, using mersalyl to destroy the Fe2S2 centre. The Fe2S2 seems to be very similar to that of spinach ferredoxin, by its absorbance and electron paramagnetic resonance (EPR) spectra, and the FAD semiquinone is a neutral semiquinone. Spectrophotometry near room temperature and EPR spectroscopy near liquid-helium temperature allow the three redox couples of component C to be ordered. Component C can exist in Oe-1 (oxidised), 1e-1 (semiquinone), 2e-1 (mostly semiquinone and reduced Fe2S2), and 3e-1 forms (dihydroquinone and reduced Fe2S2), under equilibrium conditions. The ability of component C to support odd-electron forms is consistent with its proposed role as a 2e-1/1e-1 transformase, splitting electron pairs from NADH for passage to component A in one-electron steps. (The FAD appears to interact with NADH, and transfers single electrons to the Fe2S2, for donation to component A at a constant redox potential.) The mid-point potentials of component C were found using redox dyes and EPR spectroscopy and were: FAD/FAD., Em = -150 mV; Fe2S2/Fe2.S2,Em = -220 mV; FAD./FAD..,Em = -260 mV. the presence of NADH did not alter these mid-point potentials. These mid-point potentials are consistent with the role of component C as the NADH:component A reductase, passing electrons from NADH (Em = -320 mV) onto component A (Em = +150 mV and Em = -150 mV). The reducing power from NADH appears to be required by component A to activate one atom of oxygen, to insert into methane, and the reducing equivalents derived from NADH end up with the other oxygen atom, as water.

Dynamic Games and the Time Inconsistency of Optimal Policy in Open Economies

Abstract: It has been argued that the Bretton Woods system (of pegged but adjustable exchange rates) set up after World War II was designed specifically to prevent the manipulation of exchange rates in pursuit of national macroeconomic objectives (see R. Cooper) ; so it is perhaps no coincidence that the ending of pegged rates has led to the re-emergence of theories and policies involving such "manipulation". Before the war, when inflation was low and unemployment high in the major industrialised nations, this involved "competitive depreciation" as countries tried to gain employment ; in the late 1970's and early 1980's, however, countries like the UK and the US have embarked on policies of competitive appreciation in order to cut inflation, regarded as the first priority. Sharp movements in exchange rates, however, constitute a threat to orderly trade and stimulate protectionism, as Bergsten (1981) argues.

Precursors of ricin and Ricinus communis agglutinin. Glycosylation and processing during synthesis and intracellular transport.

Abstract: During synthesis in vivo the castor bean lectin precursors initially appear in the endoplasmic reticulum as a group of core glycosylated polypeptides of relative molecular mass 64 000–68 000. Pretreatment of intact castor bean endosperm tissue with tunicamycin partially inhibits the cotranslational core glycosylation step and results in the accumulation of a single sized unglycosylated precursor polypeptide of relative molecular mass 59 000. The glycosylated precursors in the endoplasmic reticulum were enzymically converted to the 59 000-Mr from by incubation with endoglucosaminidase H. Intracellular transport of the glycosylated lectin precursors from the endoplasmic reticulum to a denser vesicle fraction was accompanied by modifications to the oligosaccharide moieties which conferred resistance to the action of endoglucosaminidase H. The post-translational addition of fucose to the carbohydrate chain was identified as one of the oligosaccharide modification steps. Fucose addition was catalysed by a glycosyltransferase associated with a smooth-surfaced membrane fraction which was distinct from the endoplasmic reticulum and which was tentatively identified as the Golgi apparatus. Glycosylation was not essential for intracellular transport of the lectin precursors: unglycosylated precursor synthesized in the presence of tunicamycin gave rise to unglycosylated lectin subunits in the protein bodies.

Response of potatoes to N fertilizer: dynamic model

Abstract: A simulation model is described to interpret N fertilizer experiments on potatoes. It calculates the total growth of dry matter, the N uptake, the partition of dry matter and of N between tuber and foliage and the distribution of inorganic N down the profile for each day during the growing season. The validity of the model was tested against measurements of these parameters made at approximately fortnightly intervals on plots that received N fertilizer and those that received none in 4 experiments on a sand, 4 on a sandy loam and 3 on a clay soil. Simulated values were in reasonably good agreement with the measured values in all experiments. Overall the sums of squares of the differences between the simulated and measured values of the %N in the total plant, and the total amount of inorganic N in the top metre of soil and the logarithms of the total weight of dry matter, tuber dry weight, N uptake in the entire plant and N uptake in the tubers were each less than 25% of the sum of squares of the measured values about the mean. Only 9 inputs were required for the model. It was found essential to take account of differences in spring and summer leaching but not of inter-site differences in mineralization rate.

Redefining institutional racism

Abstract: (1985). Redefining institutional racism. Ethnic and Racial Studies: Vol. 8, No. 3, pp. 323-348.

Method and apparatus for detecting a contraband substance

Abstract: A method of detecting contraband substances in freight cargo containers in which the container is agitated to disturb particulates therein, and air containing such particulates is then sampled and the particulates collected The collected particulates include naturally occurring particulates which have absorbed vapors of the contraband substance during the entire time that the container has been closed, and also include particulates of the contraband substance itself The collected particulates are then heated to a temperature above 160° C to drive off vapors indicative of the contraband substance and the vapors are analyzed in a mass analyzer