Showing papers by "University of Warwick published in 1975"

Estimation Methods for Models of Spatial Interaction

Abstract: Autoregressive models for spatial interaction have been proposed by several authors (Whittle [15] and Mead [11], for example). In the past, computational difficulties with the ML approach have led to the use of alternative estimators. In this article, a simplified computational scheme is given and extended to mixed regressive-autoregressive models. The ML estimator is compared with several alternatives.

Study of physiologic specialization in Plasmodiophora brassicae: Proposals for attempted rationalization through an international approach

Abstract: A new set of differential hosts is described and proposed for research into physiologic specialization in Plasmodiophora brassicae , and methods are suggested for the performing of differentiation tests The differential set comprises five hosts each of Brassica campestris, B napus and B oleracea Thirty-four European P brassicae collections were differentiated A modification of the binary notation system of nomenclature is adopted for coding P brassicae populations, the latter term being preferred to physiologic race The coding system described is amenable to considerable expansion

Analysis of mathematical programming problems prior to applying the simplex algorithm

Abstract: Large practical linear and integer programming problems are not always presented in a form which is the most compact representation of the problem. Such problems are likely to posses generalized upper bound(GUB) and related structures which may be exploited by algorithms designed to solve them efficiently. The steps of an algorithm which by repeated application reduces the rows, columns, and bounds in a problem matrix and leads to the freeing of some variables are first presented. The ‘unbounded solution’ and ‘no feasible solution’ conditions may also be detected by this. Computational results of applying this algorithm are presented and discussed. An algorithm to detect structure is then described. This algorithm identifies sets of variables and the corresponding constraint relationships so that the total number of GUB-type constraints is maximized. Comparisons of computational results of applying different heuristics in this algorithm are presented and discussed.

The possibility of predicting solute uptake and plant growth response from independently measured soil and plant characteristics

Abstract: A model of the way the rate of growth of a plant may be affected by the level of supply of a nutrient is presented. Growth rate is linked to the nutrient level of the photosynthetic tissues, which is assumed to control changes in the net assimilation rate, the leaf area per unit shoot weight, the shoot: root ratio, the root surface area, and the distribution of nutrient between root and shoot. The uptake of nutrient depends on the concentration of nutrient at the root surface, the root surface area and its absorbing power. All these relationships may be determined in stirred solution culture. A method of applying this information to soil grown plants is suggested.

A survey of volatile components of some allium species in terms of s-alk(en)yl-l-cysteine sulphoxides present as flavour precursors

Abstract: The volatile flavour components of 27 Allium species and cultivars, mostly edible but including some decorative species for comparison, have been investigated by a series of gas and thin-layer chromatographic and u.v. spectrophotometric methods. By means of simulation experiments with synthetic precursors and intermediates, the data have been interpreted in terms of the amino acid precursors present in the intact tissues and the species classified as containing (a) S-1-propenyl-, (b) S-2-propenyl- and (c) S-methyl-L-cysteine sulphoxides as their principal flavour precursors. Characteristic examples of the three types are A. cepa L. (onion), A. sativum L. (garlic) and A. aflatunense B. Fedtschenko, respectively. An object of the work has been to demonstrate broad chemical similarities between species as well as their differences, which are emphasised in keys for classification on the basis of morphological characters. In addition to onion, leek, shallot, garlic and chives, species such as A. chinense, A. fistulosum and A. tuberosum have widespread use as food, particularly in the Far East. The literature on this aspect has been briefly summarised.

Chayanov and the economics of the Russian Peasantry

Abstract: The years after 1900 saw the emergence of the “neo‐populist” tradition as a leading tendency of economic thought in the study of the Russian peasantry. By the 1920s Aleksandr Vasil'evich Chayanov had become one of the most influential spokesmen of this tradition. His school was dispersed in 1930. But in the Western study of modern peasantries, his work is once more increasingly influential. The article considers Chayanov's place in the development of economic thought and of political controversy, and tries to locate this in the context of the history of the Russian peasantry itself. Problems and theories in the allocation of labour supplies are particularly examined. Finally, we raise the question of ideology in economic thought.

An equation to predict the leaching of surface-applied nitrate

Abstract: The fraction (f) of surface-applied nitrate leached below any depth h cm in a uniform soil profile may be calculated from the equationwhere P is the quantity of water draining through the soil (in cm) and Vm is the percentage volumetric field capacity. The fraction of nitrate retained is then (1—f).This equation has been tested using published data. Values of h corresponding to the mean displacement (f = 0·5) were calculated for a wide range of soil and weather conditions and the results compared with mean displacements measured in the field. Similar comparisons were made with the leaching equation of Rousselle (1913) and Levin (1964). The new equation gives good agreement with the observed data, whereas the Rousselle-Levin equation generally overestimates the mean displacement of nitrate. Methods of applying the equations to field situations are discussed.

Sequential translation of capsid and membrane protein genes of alphaviruses

Abstract: INVESTIGATIONS of the multiplication of alphaviruses such as Semliki Forest virus (SPY) or Sindbis virus have suggested that the three glycoproteins1 (E1, E2 and E3) located in the viral envelope are initially synthesised as a large precursor poly-peptide which contains the amino acid sequences of them all2–7. This protein, NVP97 (ref. 5), is cleaved to give E1 and another precursor polypeptide, NVP63, which is in turn cleaved to give E2 and E3 (refs 6 and 7). By analogy with the picorna-virus system, it has been widely suggested that all the viral structural proteins are derived by cleavage of a common precursor and, indeed, proteins of a size sufficient to encompass the viral capsid protein, as well as the envelope proteins, have been found in infected cells treated with amino acid analogues and inhibitors of proteolytic enzymes10,11, and in cells infected with certain classes of temperature-sensitive mutant2,3,12,13. Doubts have been cast on the validity of the analogy, however, by reports8,9,16–19 that cell-free translation of SFV or Sindbis virus mRNA in several systems resulted in the production of discrete viral proteins. This situation is in marked contrast to that of translation of picornavirus RNA, in which a spectrum of polypeptides of various lengths is formed by premature termination at many points along the messenger; since no post-translational cleavage seems to take place, no polypeptides found in the mature virus or in infected cells are formed20,21. The possibility arose, therefore, that the alphavirus capsid protein and envelope proteins are synthesised independently.

Industrial Revolution in England and France: Some Thoughts on the Question, 'Why was England First?'

Abstract: A MAJOR concern of economic historians since World War II has been to interpret the process of industrialization in now developed countries. One prominent line of approach has been to compare the experience of the European economies in the eighteenth century, and much of the inquiry has been conceptualized along the following lines. "The Industrial Revolution poses two problems: (i) Why did this first breakthrough to a modern industrial system take place in Western Europe? and (2) Why, within this European experience, did change occur when and where it did ?" 2 This comparative approach has been seen as a particularly valuable way of yielding insights into the process of economic growth in general and the causes of the English Industrial Revolution in particular. Thus Crouzet argues that "The economic historian interested in the key problem of growth is bound to find the comparative approach particularly fruitful. A systematic comparison of the eighteenth-century English economy with that of another country-and France as the leading continental power at that time seems the obvious choice-should bring out more clearly what factors were peculiar to England and might have determined what is a unique phenomenon, the English Industrial Revolution of the eighteenth century."3 Since Crouzet wrote, much of the literature has accepted the usefulness of the question, "Why was England first ?" and the specific question, "Why did England experience the onset of the Industrial Revolution before France ?" has been promoted to a position of great prominence.4 There is by now an extensive literature offering a wide variety of responses to these questions. The answers seem to fall into three types. First, there are studies which single out a single crucial reason. To cite just a couple of examples we find views as diverse as those of Kemp ("if one overriding reason can be given for the slower transformation of the continent ... it must be the continued prevalence of the traditional agrarian structures")5 and Hagen ("the differences in personality rather than differential circumstances are the central explanation of Britain's

The accuracy of predictions

Abstract: This paper, I am sorry to say, is deeply sceptical. It is also rather technical. And the scepticalities, I fear, are no easier to renounce than are the techni calities. The paper presents an elementary mathematical result that appears to impinge negatively on any reasonable theory of knowledge with empiricist pretensions. Moreover, it offers nothing positive as a sweetener. This is not because I would not like to endorse something constructive. It is because there is nothing constructive that I would like to endorse. The central problem is this: in what ways and by what standards can we compare two false scientific theories! An eminently plausible sugges tion for quantitative (or numerical) theories will be shown to be useless. This is the suggestion that a quantitative theory B is a better theory than is A at least if it is uniformly more accurate; that is, if the predictions that B makes, given some shared initial conditions, are never farther from the true values (or the observed values) than the predictions that A makes, and sometimes are closer. It will be shown that if an interesting theory B stands in this relation to a theory A then the theory B is true. No false quantitative theory is uniformly more accurate than is any other. I have expressed this crudely, and I have oversimplified enormously. I shall to some extent refine the expression and in some degree under simplify the discussion in the ensuing sections, whose content is here briefly summarized. In Section I, I sketch Popper's theory of verisimilitude, together with recent criticisms of it that are independently due to Pavel Tichy and myself. In Section II, I ask whether Tarski's idea of content can be widened in any useful way, especially in the context of quantitative theories. And in Section III, I wonder whether the accuracy of quantitative theories can be used as an indication of their verisimilitude. Section IV is a short section on terminology and notation. In Section V my main result is proved; Section VI examines essentialism, and the relativization of theories to problems. In Section VII, I look at some of the methodological ramifi

Protein synthesis in chloroplasts. Characteristics and products of protein synthesis in vitro in etioplasts and developing chloroplasts from pea leaves.

Abstract: The function of plastid ribosomes in pea (Pisum sativum L.) was investigated by characterizing the products of protein synthesis in vitro in plastids isolated at different stages during the transition from etioplast to chloroplast. Etioplasts and plastids isolated after 24, 48 and 96h of greening in continuous white light, use added ATP to incorporate labelled amino acids into protein. Plastids isolated from greening leaves can also use light as the source of energy for protein synthesis. The labelled polypeptides synthesized in isolated plastids were analysed by electrophoresis in sodium dodecyl sulphate-ureapolyacrylamide gels. Six polypeptides are synthesized in etioplasts with ATP as energy source. Only one of these polypeptides is present in a 150 000g supernatant fraction. This polypeptide has been identified as the large subunit of Fraction I protein (3-phospho-D-glycerate carboxylyase EC 4.1.1.39) by comparing the tryptic 'map' of its L-(35S)methionine-labelled peptides with the tryptic 'map' of large subunit peptides from Fraction I labelled with L-(35S)methionine in vivo. The same gel pattern of six polypeptides is seen when plastids isolated from greening leaves are incubated with either added ATP or light as the energy source. However, the rates of synthesis of particular polypeptides are different in plastids isolated at different stages of the etioplast to chloroplast transition. The results support the idea that plastid ribosomes synthesize only a small number of proteins, and that the number and molecular weight of these proteins does not alter during the formation of chloroplasts from etioplasts.

Translation of Semliki‐Forest‐Virus Intracellular 26‐S RNA

Abstract: The addition of 26-S RNA isolated from baby hamster kidney cells infected with Semliki Forest virus to cell-free extracts of L-cells causes the synthesis of several specific polypeptides. These polypeptides have been characterised and compared with the structural proteins of Semliki Forest virus by (a) polyacrylamide gel electrophoresis, (b) affinity chromatography using immobilised immunoglobulin G specific for the viral envelope glycoproteins and (c) tryptic peptide maping. The results show that 26-S RNA codes for all three structural proteins of the virus but that in vitro little, if any, glycosylation of the envelope polypeptides occurs.

Growth Regulators and the Phytochrome-Mediated Dormancy of Celery Seeds

Abstract: Seeds of five celery (Apium graveolens L.) cultivars germinated at 15°C in the light or dark but at 22°C only in the light. This light requirement was overcome by treatment with a mixture of the gibberellins GA4 and GA7 (GA4/7) but interactions of cytokinins, daminozide, ethephon, EDTA and N-phenyl-N′-4-pyridylurea (NC5392) with GA4/7 were observed. Varietal differences in response to GA4/7 concentration and the requirement for cytokinins were related to the upper temperature limits for germination of the different cultivars. Seeds of cultivars responding to low concentrations of GA4/7 appeared to contain less natural inhibitor than those requiring either high concentrations of GA4/7 or cytokinin in addition to low GA4/7. The cytokinin requirement for germination was partially removed by leaching the seeds with water. Interaction studies with applied hormones indicated that in seeds incubated in the light inhibition by abscisic acid was partially alleviated by N6-benzyladenine but not by GA4/7 application. The implications of these results are discussed in relation to the involvement of natural plant hormones in the dormancy mechanism of celery seeds.

Distribution of flavour components in onion (Allium cepa L.), leek (Allium porrum) and garlic (Allium sativum)

Abstract: Dry bulb onions and leeks, at the marketable stage of development, were dissected into nine and ten fractions respectively, comprising the stem and leaves in succession from the oldest outer layers Each fraction was separately analysed for flavour components by determination of thiosulphinate and pyruvate Similarly, garlic cloves were divided into five fractions There was a consistent pattern of flavour distribution in the seven onion varieties studied The dried outer scales were virtually free from flavour components, the concentrations of which (on a fresh weight basis) increased progressively from a minimum value in the outer leaf to the innermost tissue and the stem The latter often contained more than twice the concentration present in the outer leaf The pattern in the roots and edible portions of leek differed in detail from that in onion Flavour intensity increased progressively from the outer leaf to the inner tissues and the concentrations in both the roots and the stem were approximately equivalent to that of the fourth leaf numbered from the outer leaf The pattern of flavour distribution in garlic cloves was simpler than that of onion and leek The storage leaf accounted for the bulk of the weight of the clove as well as its flavour content Some aspects of knowledge of the metabolism of inorganic nitrogen and sulphur compounds in roots and other tissues and transport of the corresponding metabolites have been briefly reviewed as the basis of a preliminary interpretation of the above observations Attention has been drawn to the bearing of the results on preparation of onion for cooking and processing and on sampling for analysis

Effects of Temperature on the Germination and Emergence of Lettuce (Lactuca Sativa, L.) Varieties

Abstract: SummaryThe response of seed germination to temperature, over the range 5-33°C, was studied for 22 varieties of the Crisp, Cos and Butterhead types of lettuce. The overall patterns of response were similar in all varieties, irrespective of the storage conditions or origin of the seed lot. The optimum temperature for germination in all varieties was between 15°C and 22°C, but there was a marked upper temperature limit for germination ranging from 25.7+0.9°C in cv Hilde to 32.8+0.9°C in cv Avoncrisp. In the main, the Crisp types germinated well at 30°C, which inhibited germination in the Butterhead types.In a field experiment where eighteen of these varieties were sown during a period of hot sunny weather, two distinct patterns of emergence were observed, apparently related to the prevailing soil temperatures and the upper temperature limits for germination of each variety. In varieties with a high upper temperature limit for germination, seedling emergence was rapid even during periods of high soil temperat...