Showing papers by "University of Warwick published in 1983"

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. We show 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.

Critical Heuristics of Social Planning: A New Approach to Practical Philosophy

Abstract: CONTEMPORARY MODELS OF RATIONAL DISCOURSE. Karl R. Popper's Critical Rationalism: Blind Criticism? Jurgen Habermas' Critical Theory: Toward a Transformed Transcendental Approach. FROM KANTIAN A PRIORI SCIENCE TO CRITICAL HEURISTICS. Introduction to Kantian A Priori Science. Kantian A Priori Science and the Systems Idea: The Critically-Heuristic Turn. Kantian A Priori Science and the Process of Unfolding: The Dialectical Turn. APPLICATION. Toward a "Purposeful Systems" Paradigm of Planning. Project Cybersyn: The Chilean Experience with Cybernetics, 1971-73. Health Systems Planning: The Case of the 1976 Areawide Health Systems Plan for Central Puget Sound. Epilogue. Bibliography. Indexes.

One-Dimensional Schrödinger Equation with an Almost Periodic Potential

Abstract: Recent theories of scaling in quasiperiodic dynamical systems are applied to the behavior of a particle in an almost periodic potential. A special tight-binding model is solved exactly by a renormalization group whose fixed points determine the scaling properties of both the energy spectrum and certain features of the eigenstates. Similar results are found empirically for Harper's equation. In addition to ordinary extended and localized states, "critical" states are found which are neither extended nor localized according to conventional criteria.

On Least Squares Estimation when the Dependent Variable is Grouped

Abstract: This paper examines the problem of estimating the parameters of an underlying linear model using data in which the dependent variable is only observed to fall in a certain interval on a continuous scale, its actual value remaining unobserved. A Least Squares algorithm for attaining the Maximum Likelihood estimator is described, the asymptotic bias of the OLS estimator derived for the normal regressors case and a "moment" estimator presented. A "two-step estimator" based on combining the two approaches is proposed and found to perform well in both an economic illustration and simulation experiments.

Copper stress underlies the fundamental change in intracellular location of methane mono-oxygenase in methane-oxidizing organisms: Studies in batch and continuous cultures

Abstract: The intracellular location of methane mono-oxygenase (MMO) activity in the methanotroph Methylococcus capsulatus (Bath) has been shown to depend primarily on the availability of copper. MMO activity was observed in the particulate fraction of cell extracts under conditions of copper excess but switched to a soluble location in response to copper stress. The two activities could be differentiated by sensitivity to a range of inhibitors and by major changes in the polypeptide banding patterns on denaturing polyacrylamide gels. MMO activity concomitant with the oxidation of ethanol was only observed in cells with particulate MMO activity but could be lost independently in response to copper stress. Examination of other methanotrophs indicated that the copper effect could explain a similar switch in intracellular location observed in Methylosinus trichosporium OB3b but that some methanotrophs do not have the capacity to overcome copper stress in this way.

The Effect of Shareholding Dispersion on the Degree of Control in British Companies: Theory and Measurement

Abstract: Since A. A. Berle and G. C. Means published The Modern Corporation and Private Property in I932 their thesis of the separation of corporate ownership from control has given rise to a large literature devoted to elaborating, refuting or testing it. Much theoretical and empirical work has been done on the effects of variation in the location or type of control on company behaviour and performance. Two features which emerge very strongly from this literature are, first, that theoretical categories of 'control type' used are frequently based on a simple dichotomy into 'owner-controlled' versus ' management-controlled' firms rather than a continuum and, second, the corresponding measure of 'control type' is usually a zero-one dummy variable defined on the basis of some arbitrary statistical criterion in terms of the size of a controlling shareholding. Such criteria are usually applied rigidly to all firms with no allowance for differences in shareholding dispersion. This is illustrated by Table i which lists the result of a survey (meant to be representative rather than exhaustive) of methods of classification used in twenty empirical studies. In all these studies the location of control is either the main focus of the analysis or else an explanatory variable in multiple regression analyses (typically with company growth and/or profitability as the dependent variable). Eighteen of them use shareholdings as the main criterion, of which seventeen use the size of the largest bloc (including family holdings) as the relevant variable. This bloc ranges in size from 25 % down to 4 % with io o% and 5 % respectively as the most popular criteria. Berle and Means (I 932), Kamerschen (I968) and Larner (I970) take some account of dispersion in a subjective way; by using their own judgements. Kania and McKean's (I976) variation of their criterion according to the size ranking of the corporation may be interpreted as a rough-and-ready method of allowing for dispersion, making use of the fact that it tends to increase with firm size. The majority of the studies in Table i take no account of the dispersion of the remaining shareholdings, even though some of them go to some lengths to consider other criteria besides shareholding size. Whilst it has always been recognised that the dispersion of the smaller shareholdings has been relevant to control, a major obstacle has been the lack of a suitable way of summarising it. In general there are two approaches to summarising shareholder-size dis-

Influence of Substratum Wettability on Attachment of Freshwater Bacteria to Solid Surfaces

Abstract: We studied the attachment of a number of freshwater bacteria from River Sowe, Coventry, England, to test substrata. The attachment of each organism to hydrophobic and hydrophilic surfaces was evaluated, and further studies evaluated the attachment of selected isolates to a number of substrata with a range of water wettabilities. The wettability of each substratum was determined by contact angle measurements and was expressed as the work of adhesion (W(A)). No generic pattern of attachment to the test surfaces was found, although the majority of the organisms isolated showed a preference for the hydrophobic surface. A more detailed study of selected isolates showed a relationship between W(A) and number of attached cells. Each bacterium attached in maximum numbers to a surface that was characteristic of that organism and that had a W(A) between 75 and 105 mJ m.

Decomposition of Toric Morphisms

Abstract: (0.1) This paper applies the ideas of Mori theory [4] to toric varieties. Let X be a projective tonic variety (over any field) constructed from a simplicial fan F. The cone of effective 1-cycles NE(X) is polyhedral (1.7), spanned by the 1-strata l w ⊂ X; the condition that a 1-stratum l w gives an extremal ray R = Q + l w of NE(X) has a nice interpretation (2.10) in terms of the geometry of F around the wall w.

Hausdorff dimension for horseshoes

Abstract: We shall measure how thick a basic set of a C1 axiom A diffeomorphism of a surface is by the Hausdorff dimension of its intersection with an unstable manifold. This depends continuously on the diffeomorphism. Generically a C2 diffeomorphism has attractors whose Hausdorff dimension is not approximated by the dimension of its ergodic measures.

A proof of the impossibility of inductive probability

Abstract: Proofs of the impossibility of induction have been falling ‘dead-born from the Press’ ever since the first of them (in David Hume's Treatise of Human Nature) appeared in 1739. One of us (K.P.) has been producing them for more than 50 years. The present proof strikes us both as pretty.

Nonsurvey Techniques: A Critical Review of the Theory and the Evidence

Abstract: Nonsurvey methods, including methods of constructing regional input-output tables, reconciling estimates, and deriving sectoral multipliers where no input-output table exists, are critically evaluated from a theoretical point of view as well as in the light of available evidence. There are a number of weaknesses in the way many techniques are utilized, and there are decided advantages in pursuing an interregional or multiregional approach. The continuing claims about the accuracy of existing methods are also examined in the context of the efficacy of various test procedures.

Mangrove distribution in northwestern Australia in relationship to regional and local freshwater seepage

Abstract: The regional distribution of mangrove species along the tropical NW coast of Australia is closely related to climate. In subhumid regions with rainfall >1000 mm/yr mangals have 12 species which are recurring and common. The climate becomes more arid southwards and species richness decreases: 8 species are common in mangals in semiarid regions and 5 species are common in arid regions. Rainfall influences the distribution of species across tidal flats because of direct recharge to groundwater systems and also because of subsurface seepage along the hinterland edge. Much of the increase in species diversity is located along high parts of tidal flats and along the edge of the hinterland. At the local level stratigraphy forms an important part of the hydrology by determining the distribution of aquifers and aquacludes. Fresh water seeps into the tidal lands via buried, discrete aquifers and dilutes the highly hypersaline groundwater. Mangroves inhabit these local areas above the less saline groundwater. The influence of rainfall and freshwater seepage on mangals is presented as a unifying theme which helps to explain distribution and diversity of mangroves at both a regional and local level.

Interactions between seed priming treatments and nine seed lots of carrot, celery and onion. I. Laboratory germination

Abstract: SUMMARY Samples of three seed lots of each of three cultivars of carrot, celery and onion were primed in polyethylene glycol solution for 2 weeks at 15 °C. Priming reduced the mean germination times (recorded at 15 °C) of all seed lots (compared to the untreated control) by 3–4 days in carrot, 6–10 days in celery and 3–5 days in onion. The largest reductions in mean germination time occurred in the slowest-germinating seed lots. There were highly significant interactions between priming and cultivars, and between priming and seed lots within cultivars for each species. Drying back the primed seeds at 15 °C increased the mean germination times (compared to primed seed which had not been dried) by 0·6 day in carrot and 1·4 days in celery, and there was no interaction with cultivars or seed lots. The corresponding increase for onion was either 1·0 or 1·8 days, according to the cultivar, but this variation was largely attributable to differences in time taken for the dried seeds to re-imbibe. Seeds dried back at 30 °C germinated 0·2·0·7 day (depending on the species) later than those dried at 15 °C. Percentage germination was not affected by either priming or drying back. Priming reduced the spread of germination times in all cultivars. For primed and dried-back seed, the spread of germination times was larger than that of primed seed in certain cultivars, but was always smaller than that of untreated seeds.

Visual detection of host plants by cabbage root flies

Abstract: Using mimics of real plants, we found that female cabbage root flies, Delia radicum (L.), detected plants within host patches at least partly on the basis of leaf colour and area, with leaf pattern playing an insignificant role in the case of multi-leaved plants. Composition of the background, whether bare soil or green grass, did not affect female ability to distinguish between leaf mimics of different colour. The contribution of visual stimuli in eliciting female landings on individual plants within a patch decreased as distance between the plants was increased. RESUME Reperage visuel des plantes-hotes par Delia radicum En utilisant les leurres de veritables plantes, nous nous sommes apercus que les femelles de Delia radicum L. detectaient des plantes dans un lot tout au moins en partie d'apres la couleur et la taille des feuilles, tandis que la forme des feuilles ne jouait qu'un role insignifiant chez les plantes a nombreuses feuilles. La composition du fond, du sol nu ou de l'herbe verte, ne modifiait pas l'aptitude des femelles a distinguer entre les couleurs des leurres des feuilles. La contribution des stimuli visuels dans l'induction de l'atterrissage des femelles sur des plantes determinees dans un lot diminuait en fonction de la distance entre les plantes.

Amino Acid assimilation and electron transport system activity in attached and free-living marine bacteria.

Abstract: Amino acid assimilation and electron transport system activity of a marine Pseudomonas sp. was evaluated to determine whether the activity of bacteria attached to solid surfaces differed from that of free-living bacteria or bacteria which had been attached but subsequently desorbed from the substratum (detached bacteria). Bacteria were allowed to attach to glass and to a range of plastic surfaces (Thermanox, polyvinylidene fluoride, polyethylene, polytetrafluoroethylene). Microautoradiography and staining with a tetrazolium salt to demonstrate electron transport system activity were used to compare the activity of these organisms with that of free-living or detached cells. The water-wettability of the surfaces was evaluated by measuring the advancing contact angle (θA) of water on each surface, to determine whether there was a relationship between activity and substratum hydrophilicity. There was an increase in the proportion of leucine-assimilating attached bacteria and in the proportion of attached cells demonstrating electron transport system activity with an increase in substratum θA, but the relationship between activity of attached and free-living cells depended on the substratum. Activity appeared to promote firm attachment, and detached bacteria assimilated fewer amino acids than did attached cells. There was no general effect of surfaces on attached bacterial activity, and attached cells may be more, or less, active than free-living cells, depending on the amino acid, its concentration, and substratum properties.

Paramagnetic impurity effects in NMR determinations of hydrogen diffusion and electronic structure in metal hydrides. Gd 3 + in Y H 2 and La H 2.25

Abstract: Measurements are reported of the temperature dependence of the proton spin-lattice and spin-spin relaxation times ${T}_{1}$ and ${T}_{2}$ in yttrium and lanthanum dihydrides containing controlled levels of gadolinium as low as 50 ppm. The results demonstrate unambiguously that paramagnetic ions in concentrations so low as to have heretofore been regarded as insignificant have marked effects on the magnitude, frequency dependence, and temperature dependence of ${T}_{1}$ and to a lesser extent on ${T}_{2}$, and on the electronic structure and hydrogen diffusion parameters derived therefrom. The ${\mathrm{Gd}}^{3+}$ ion contributes an additional spin-lattice relaxation rate ${T}_{1p}$, which in these hydrides arises entirely from the dipolar coupling between impurity and proton moments. Proton magnetization is transported to the relaxation centers by spin diffusion at low temperatures and by hydrogen-atom diffusion at intermediate and high temperatures. The rate ${R}_{1p}$ is directly proportional to Gd-ion concentration at both low and high temperatures, but in the atom diffusion regime ${R}_{1p}$ is 20-25 times greater than for spin diffusion. The impurity-induced relaxation is shown to have profound effects on the apparent nuclear-nuclear dipolar relaxation rate ${R}_{1d}$ associated with hydrogen diffusion. At impurity levels as low as 10 ppm Gd, a secondary minimum appears in the temperature dependence of ${T}_{1}$ which may be readily misinterpreted in terms of a second motional process with lower activation energy. Even lower impurity levels yield a characteristic "slope-change" effect, which may be construed as indicating a change in the activation energy for hydrogen diffusion. At low temperatures ${R}_{1p}$ interferes with the determination of the conduction-electron contribution ${R}_{1e}$ and the Korringa product ${T}_{1e}T$. Separation of ${R}_{1e}$ and ${R}_{1p}$ is complicated by the fact the ${R}_{1p}$ is not temperature independent as has typically been assumed. Methods of achieving this separation are discussed, and it is shown experimentally that this difficulty can be circumvented by replacing the major part of the hydrogen with deuterium, thereby inhibiting spin diffusion. Measurement of ${T}_{1}$ as a function of resonance frequency and of ${T}_{2}$ can also be of value in separating the various sources of relaxation.

Ricin and Ricinus communis agglutinin subunits are all derived from a single-size polypeptide precursor.

Abstract: Antibodies have been raised in rabbits against the individually purified A and B subunits of the toxic castor bean lectin, ricin, and against the A′ and B′ subunits of Ricinus communis agglutinin type I. Each of the antisera recognised a single polypeptide species of Mr 60 500 when maturing castor bean endosperm mRNA was translated in vitro in a rabbit-reticulocyte-derived system. When dog pancreatic microsomal vesicles were included in the translational system, each subunit antiserum precipitated a group of 66 000–68 000-Mr core-glycosylated polypeptides which had been translocated into the lumen of the vesicles. The 60 500-Mr polypeptide appeared to be a common precursor to all four individual lectin subunits since (a) its glycosylated (66 000 – 68 000-Mr) forms were readily detected in the endoplasmic reticulum fraction isolated from maturing castor bean endosperm and (b) pulse-chase studies showed that the glycosylated precursors disappeared from the endoplasmic reticulum fraction with the concomittant appearance of authentic lectin subunits in a soluble protein fraction which included protein body matrix components. Antiserum prepared against whole R. communis agglutinin, type I, also precipitated the 65 000-Mr precursor in vitro and in vivo, but in addition precipitated a non-glycosylated 34 000-Mr polypeptide. This smaller protein is not a lectin subunit precursor, contradicting an earlier suggestion. It is most probably a precursor to the 2-S albumin storage proteins found in castor bean endosperm protein bodies

Interactions between seed priming treatments and nine seed lots of carrot, celery and onion. II. Seedling emergence and plant growth

Abstract: SUMMARY Samples of three seed lots of each of three cultivars of carrot, celery and onion were primed in polyethylene glycol solution for two weeks at 15 °C. Seedling emergence was recorded in the field for carrot and onion and in the glasshouse for celery. Compared to the untreated control, priming increased the percentage seedling emergence in certain poorly-emerging seed lots of carrot and celery, but had no effect on onion. Mean emergence times were reduced by priming in all seed lots, by 3–5, 5–8 and 3–9 days in carrot, celery and onion respectively. The largest effects occurred in the slowest-emerging seed lots. There were significant interactions between priming and seed lots within cultivars in carrot and celery and between priming and cultivars in celery and onion. Priming generally reduced the spread of emergence times, but the effects were not statistically significant in carrot. Drying back the primed seeds had no effect on percentage emergence in onion, but reduced it (compared to primed seed which had not been dried-back) in certain carrot and celery seed lots. Primed and dried-back seeds emerged later than primed seeds, by up to 1·5, 2·6 and 2·6 days in carrot, celery and onion respectively. The spread of emergence times was generally larger for primed and dried-back seeds than for primed seeds, but the differences were not always statistically significant. Plant fresh weights were recorded 9, 7 and 12 wk after sowing for carrot, celery and onion, respectively. In each species, mean plant weight was inversely related to seedling emergence time; thus plants grown from primed seed were always heavier than the controls, by up to 33%, 182% and 47% in carrot, celery and onion respectively.

Costs and Benefits of an Anti-Inflationary Policy: Questions and Issues

Abstract: This paper analyses how the output or unemployment cost of achieving a sustainable reduction in the rate of inflation depends on the structure of the wage-price process and how the "sacrifice ratio" can be minimized. In models where the natural rate is invariant under the anti-inflationary policies, price level inertia is not sufficient for a positive sacrifice ratio. Without sluggishness in the core inflation rate, a zero sacrifice ratio can be achieved simply through intelligent demand management. With sluggish core inflation, the sacrifice ratio is positive unless intelligent demand management is complemented by cost-reducing fiscal measures o reffective incomes policy. Letting the exchange rate float does not reduce the sacrifice ratio. If core inflation is partly backward-looking and partly forward-looking, current core inflation may be a function of current and past expectations of future recessions. Conventional sacrifice ratio calculations ignore forward-looking aspects of behaviour and may therefore underestimate the true cost of disinflation. If there is hysteresis in the natural rate (e.g. through a gradual adjustment of the natural rate towards the actual rate) and if there is sluggish core inflation, the sacrifice ratio will become infinite.Whenever sluggish core inflation is present, credibility of the anti-inflationary (monetary) policy alone cannot obviate a positive sacrifice ratio.

Monitoring sap nitrate in vegetable crops: Comparison of test strips with electrode methods, and effects of time of day and leaf position

Abstract: A field crop of 3‐month old cabbages was sampled every 2 h from 0600 h until 2000 h. At each sampling, an upper, middle and lower leaf were taken from four plants, and their petiole nitrate status measured by three methods (a) “Merckoquant”; test strips (b) specific ion electrode on a fresh macerated extract and (c) the same electrode on an extract of oven dry tissue. All three methods led to similar conclusions: there were very big differences in concentration with leaf position, the middle leaf having the highest; there were large concentration differences between plants, especially for the lower leaves; the effect of time of day was not significant. The test strips are capable of giving satisfactory results provided that sufficient plants are sampled, but values thus obtained for sap may be lower than for macerated fresh tissue, especially at the low end of the concentration range.