Showing papers by "University of Warwick published in 1989"

An Empirical Comparison of Pruning Methods for Decision Tree Induction

Abstract: This paper compares five methods for pruning decision trees, developed from sets of examples. When used with uncertain rather than deterministic data, decision-tree induction involves three main stages—creating a complete tree able to classify all the training examples, pruning this tree to give statistical reliability, and processing the pruned tree to improve understandability. This paper concerns the second stage—pruning. It presents empirical comparisons of the five methods across several domains. The results show that three methods—critical value, error complexity and reduced error—perform well, while the other two may cause problems. They also show that there is no significant interaction between the creation and pruning methods.

An Empirical Comparison of Selection Measures for Decision-Tree Induction

Abstract: One approach to induction is to develop a decision tree from a set of examples. When used with noisy rather than deterministic data, the method involves three main stages – creating a complete tree able to classify all the examples, pruning this tree to give statistical reliability, and processing the pruned tree to improve understandability. This paper is concerned with the first stage – tree creation – which relies on a measure for “goodness of split,” that is, how well the attributes discriminate between classes. Some problems encountered at this stage are missing data and multi-valued attributes. The paper considers a number of different measures and experimentally examines their behavior in four domains. The results show that the choice of measure affects the size of a tree but not its accuracy, which remains the same even when attributes are selected randomly.

A Concept of Egalitarianism Under Participation Constraints

Abstract: We define a new solution concept for transferable utility cooperative games in characteristic function form, in a framework where individuals believe in equality as a desirable social goal, although private preferences dictate selfish behavior. This latter aspect implies that the solution outcome(s) must satisfy core-like participation constraints while the concern for equality entails choice of Lorenz maximal elements from within the set of payoffs satisfying the participation constraints

The molecular chaperone concept.

Abstract: Molecular chaperones are a ubiquitous family of proteins whose proposed role is to mediate the folding and assembly of other proteins into oligomeric structures. The essential function of molecular chaperones is to prevent the formation of incorrect structures which may result from the transient exposure of charged or hydrophobic surfaces normally involved in interactions between or within polypeptide chains. Such transient exposure may occur during the synthesis of polypeptides, the unfolding and refolding that occurs during their transport across membranes, the association of polypeptides made in one subcellular compartment with those made in another, changes in protein-protein interactions during the normal functioning of a complex, and recovery from stresses such as heat shock. Three classes of molecular chaperone are discussed: the nucleoplasmins, the BiP group, and the chaperonins.

Is there directional smelling

Abstract: The aim of the present study was to establish the crucial precondition for directional smelling, i.e. the ability of humans to discriminate between odorous stimuli perceived either from the right or from the left side. When the ‘pure’ odorants hydrogen sulphide or vanillin were used as stimulants localization was random. On the other hand stimulation with carbon dioxide or menthol yielded identification rates of more than 96%. These results established the fact that directional orientation, considering single momentary odorous sensations, can only be assumed, when the olfactory stimulants simultaneously excite the trigeminal somatosensory system.

Similarity transformation approach to identifiability analysis of nonlinear compartmental models.

Abstract: Through use of the local state isomorphism theorem instead of the algebraic equivalence theorem of linear systems theory, the similarity transformation approach is extended to nonlinear models, resulting in finitely verifiable sufficient and necessary conditions for global and local identifiability. The approach requires testing of certain controllability and observability conditions, but in many practical examples these conditions prove very easy to verify. In principle the method also involves nonlinear state variable transformations, but in all of the examples presented in the paper the transformations turn out to be linear. The method is applied to an unidentifiable nonlinear model and a locally identifiable nonlinear model, and these are the first nonlinear models other than bilinear models where the reason for lack of global identifiability is nontrivial. The method is also applied to two models with Michaelis-Menten elimination kinetics, both of considerable importance in pharmacokinetics, and for both of which the complicated nature of the algebraic equations arising from the Taylor series approach has hitherto defeated attempts to establish identifiability results for specific input functions.

Building successful brands: The strategic options

Abstract: The debate on whether to include brands on the balance sheet has created a new interest in branding strategies. Successful brands clearly generate higher returns on sales and on investment. But quality and service, rather than advertising, is the best way of creating such brands. Acquisition strategies frequently produce inconsistent portfolios of brands. The policy towards brand extension is shown to depend upon the similarity of positioning strategies between current and new brands.

The singularity spectrum f (α) for cookie-cutters

Abstract: I use a thermodynamic formalism to study the spectrum f(α) which characterises the large fluctuations of pointwise dimension in a Gibbs state supported on a hyperbolic cookie-cutter. Amongst other things, it is proved thatf(α) is the Hausdorff dimension of the set of points with pointwise dimension α, that f(α) is real-analytic and that its Legendre transform τ(q) is related to the Renyi dimension Dq of the Gibbs state by the formula (1 − q)Dq = τ(q).

Insider Power in Wage Determination

Abstract: The paper argues that wage determination is best seen as a kind of rent sharing in which workers' bargaining power is influenced by conditions in the external labour market. It uses British establishment data from 1984 to show that pay depends upon a blend of insider pressure (including the employer's financial performance and oligopolistic position) and outsider pressure (including external wages and unemployment). Lester's feasible 'range' of wages appears typically to be between 8% and 22% of pay. Estimates of the unemployment elasticity of the wage lie in a narrow band around -0.1.

Modelling topological and metrical properties in physical processes

Abstract: Developing suitable representations for formalisingnon-trivial domain knowledge has always been cen-tral to AI. Within Naive Physics ie. the task ofencoding experiential knowledge of the world, fewformal theories have appeared that exhibit formalelegance, conciseness and generality to cover a widevariety of modelling problems. We outline a firstorder formalism being developed that meets thesecriteria. The formalism is particularly attractive inthat it provides the user with the means to modeleither spatial and/or temporal information asrequired. The power of the formalism is illustratedby modelling the process of phagocytosis of theamoeba, together with an outline of how many pro-perties of physical entities and relations betweenthem can be modelled within a unitary framework.1.0 IntroductionThe importance of representation within a formal frame-work has always been a central topic for discussionwithin AI. This has been particularly noticeable sinceHayes’ [1979, 1985a] call for the development of formal-isms supporting a clean semantics which can be used forthe representation of and reasoning about entities in non-trivial domains. In the spirit of Hayes’ Naive Physicsprogramme, we outline a concise rigorous formalismcurrently being developed. This exploits both topologicaland metrical information inherent in descriptions andexplanations encountered in everyday discourse about theworld. The formalism covers the representation of spatialand temporal topological information, and metrical infor-mation. Noting the controversy Hayes’ programmeseems to have engendered [Levesque, 1987] we areencouraged that this approach actually bodes well for atleast some of the central ideas Hayes advocated.The main structure of the paper is as follows. Section2 discusses the need to capture topological and metricalinformation, and relates this to assumptions underlyingthis and comparable work. Section 3 is a brief overviewof related work. Section 4 covers the formalism itself.

Automorphisms of compact groups

Abstract: We study finitely generated, abelian groups Γ of continuous automorphisms of a compact, metrizable group X and introduce the descending chain condition for such pairs (X, Γ). If Γ acts expansively on X then (X, Γ) satisfies the descending chain condition, and (X, Γ) satisfies the descending chain condition if and only if it is algebraically and topologically isomorphic to a closed, shift-invariant subgroup of GΓ, where G is a compact Lie group. Furthermore every such subgroup of GΓ is a (higher dimensional) Markov shift whose alphabet is a compact Lie group. By using the descending chain condition we prove, for example, that the set of Γ-periodic points is dense in X whenever Γ acts expansively on X. Furthermore, if X is a compact group and (X, Γ) satisfies the descending chain condition, then every ergodic element of Γ has a dense set of periodic points. Finally we give an algebraic description of pairs (X, Γ) satisfying the descending chain condition under the assumption that X is abelian.

Adsorption and degradation of chlorsulfuron and metsulfuron-methyl in soils from different depths

Abstract: Summary Adsorption and degradation rates of chlorsulfuron and metsulfuron-methyl were measured in soil taken from depths of 0–20, 20–40 and 40–60 cm at eight sites. Adsorption of both herbicides was negatively correlated with soil pH, and positively correlated with soil organic matter content. When two soils with very high organic matter were excluded from the calculations, the correlations with organic matter content were no longer statistically significant but those with soil pH were affected only slightly. Degradation rates of both herbicides generally decreased with increasing depth in the soil and were positively correlated with microbial biomass and negatively correlated with soil pH. The possible significance of the results to persistence of the herbicides in the field is discussed. Resume Adsorption et degradation du chlorsulfuron methyl dans des sols issus de profondeurs differentes Les niveaux d'adsorption et de degradation du chlorsulfuron et du metsulfuron-methyl ont ete mesures dans des sols preleves a des profondeurs de 0–20; 20–40 et 40–60 cm dans huit sites. L'adsorption des deux herbicides exprimait une correlation negative avec le pH du sol, et positive avec la teneur en matieres organiques. Quand les deux sols a haute teneur en matieres organiques etaient exclus des calculs, la correlation avec la teneur en matiere organique n'etait plus statisti-quement significative, tandis que celle avec le pH etait seulement peu affectee. Les taux de degradation des deux herbicides baissent en general avec l'augmentation de la profondeur du sol, et exprimaient une correlation positive avec la biomasse microbienne et negative avec le pH du sol. La transposition possible de ces resultats a la persistance des herbicides au champ est discutee. Zusammenfassung Adsoption und Abbau von Chlorsulfuron und Metsulfuron in verschiedenen Bodentiefen Die Adsorptions- und Abbauraten von Chlorsulfuron und Metsulfuron in Bodenproben von 8 verschiedenen Orten aus 0–20, 20–40 und 40–60 cm Tiefe wurden gemessen. Die Adsorption der beiden Herbizide war mit dem pH-Wert negativ und mit der organischen Substanz positiv korreliert. Bei Herausnahme der Werte von 2 Boden mit besonders hohem Gehalt an organischer Substanz lies sich die Korrelation zur organi-schen Substanz nicht mehr statistisch sichern, wahrend die Berechnung fur den pH-Wert nur wenig beeinflust wurde. Die Abbaurate der beiden Herbizide nahm allgemein mit zunehmender Bodentiefe ab; sie war mit der mikrobiellen Biomasse positiv und mit dem pH-Wert negativ korreliert. Die Bedeutung der Ergebnisse fur die Persistenz der Herbizide im Freiland wird diskutiert.

Back to Woodworth: role of interlopers in the tip-of-the-tongue phenomenon.

Abstract: When a person reports that a word is on the tip of his or her tongue, that person often recalls instead another word that is similar in sound to the target word. Two opposite roles have been suggested for these interlopers. An older view (Woodworth, 1929) holds that they are instrumental in the development of tip-of-the-tongue (TOT) states because they obstruct successful retrieval of intended targets. A more recent view (R. Brown & McNeill, 1966) holds, on the other hand, that interlopers tend to nullify TOT states by facilitating complete retrieval of the intended targets. A study is reported in which participants were explicitly presented with interloper words. The results provide two planks of support for Woodworth's hypothesis. First, more TOT states occurred when the interloper was similar in sound to the target than when it was not. Second, more TOT states occurred when the interloper was presented at the actual time of retrieval than when it was presented earlier. It appears that interlopers tend to induce TOT states by obstructing retrieval, rather than to nullify them by facilitating retrieval.

Strikes, Free Riders, and Social Customs

Abstract: In recent years there has been a growing literature on the role of social customs in the labour market. Marsden (1986), for example, has emphasised the importance of group norms and social custom in various labour market contexts. Jones (1984) develops an economic model of conformist behaviour in which an individual's work effort is determined partly by tradition and by the behaviour of other workers. A central theme of the literature is that a rational economic agent does not inhabit a social vacuum and hence that individual behaviour is influenced, to some extent, by the actions of others. The approach promises the possibility of an escape from the free-riders problem, which, as we shall investigate, might have a number of labour market applications. Such a potential has been suggested by a number of writers in different fields. Eiser (1978), writing from a socio-psychological perspective, has stressed the role of social norms in producing cooperative outcomes in the theoretical context of the prisoner’s dilemma. Such an emphasis is consistent with Sen's (1977) argument that the concept of commitment might offer a solution to the free rider problems.

Multiple access communication system

Abstract: The multiple access communication system according to the invention comprises at least one primary station (2) and a plurality of secondary stations (32, 34, 36). The primary station (2) and the secondary stations (32, 34, 36) are interconnected via a network, e.g. a coaxial cable network or a hybrid fiber/coax network. The secondary stations (32, 34, 36) can transmit return signals in a return signal frequency band to the primary station (2). However, the secondary stations (32, 34, 36) are arranged for transmitting the return signals in only a part of the return signal frequency band containing relatively little noise, e.g. the upper part of the return signal frequency band. The network comprises means (40) for mapping the return signals of the secondary stations (32, 34, 36) onto the full return signal frequency band, e.g. by means of a frequency converter (48, 50). In this way, the communication system is much less sensitive to noise, while still the same number of secondary stations (32, 34, 36) can be handled by the communication system.

Memory impairments and communication in relatively able autistic children.

Abstract: Autistic people have specific memory difficulties. The effects of these difficulties on communication in relatively able autistic children and learning impaired controls were assessed in three experiments. The experiments tested the ability to: (1) carry out instructions; (2) ask questions without repetition; and (3) answer questions about past activities. When specific memory skills were required autistic children's communication was impaired relative to controls. When the need to use these skills was eliminated from the tasks the autistic children performed as well as controls. Some practical and theoretical implications of the findings are discussed.

Isolation and nucleotide sequences of cDNA clones encoding ADP-glucose pyrophosphorylase polypeptides from wheat leaf and endosperm.

Abstract: A cDNA clone (WL : AGA.1) encoding wheat leaf ADP-glucose pyrophosphorylase has been isolated from a λgt11 expression library, by immunological screening with anti-spinach leaf ADP-glucose pyrophosphorylase serum. The WL : AGA.1 cDNA is 948 bp long and contains approximately 55% of the complete wheat leaf ADP-glucose pyrophosphorylase mRNA sequence, estimated from Northern blot experiments. A wheat endosperm cDNA library was subsequently constructed in λgt11 and six clones hybridising to the cDNA insert of clone WL : AGA.1 were isolated. The longest of these wheat endosperm ADP-glucose pyrophosphorylase cDNAs, clone WE : AGA.7, is nearly full-length (1798 bp), indicated by Northern blot analysis of wheat endosperm mRNA and nucleotide sequence analysis.Southern hybridisation analysis and restriction enzyme mapping indicated that the wheat leaf and wheat endosperm ADP-glucose pyrophosphorylase cDNAs and genes are members of two distinct gene families. In addition, restriction enzyme mapping revealed polymorphism in the wheat endosperm ADP-glucose pyrophosphorylase cDNAs, indicating the existence of at least two wheat endosperm ADP-glucose pyrophosphorylase gene sub-families.Subsequent nucleotide sequence analysis indicates that there is approximately 55% identity between wheat leaf and wheat endosperm ADP-glucose pyrophosphorylase cDNAs. In contrast, members of each sub-family of endosperm cDNA, represented by clones WE : AGA.3 and WE : AGA.7, are 96% identical.

KAM theory in configuration space.

Abstract: A new approach to the Kolmogorov-Arnold-Moser theory concerning the existence of invariant tori having prescribed frequencies is presented. It is based on the Lagrangian formalism in configuration space instead of the Hamiltonian formalism in phase space used in earlier approaches. In particular, the construction of the invariant tori avoids the composition of infinitely many coordinate transformations. The regularity results obtained are applied to invariant curves of monotone twist maps. The Lagrangian approach has been prompted by a recent study of minimal foliations for variational problems on a torus by J. Moser.

The reaction specificities of the thylakoidal processing peptidase and Escherichia coli leader peptidase are identical.

Abstract: Proteins which are transported across the bacterial plasma membrane, endoplasmic reticulum and thylakoid membrane are usually synthesized as larger precursors containing amino-terminal targeting signals. Removal of the signals is carried out by specific, membrane-bound processing peptidases. In this report we show that the reaction specificities of these three peptidases are essentially identical. Precursors of two higher plant thylakoid lumen proteins are efficiently processed by purified Escherichia coli leader peptidase. Processing of one precursor, that of the 23 kd photosystem II protein, by both the thylakoidal and E. coli enzymes generates the correct mature amino terminus. Similarly, leader (signal) peptides of both eukaryotic and prokaryotic origin are cleaved by partially purified thylakoidal processing peptidase. No evidence of incorrect processing was obtained. Both leader peptidase and thylakoidal peptidase are inhibited by a synthetic leader peptide.

Proton environments and hydrogen-bonding in hydrous silicate glasses from proton NMR

Abstract: The dissolution of water in magmas has profound effects on their physical and chemical properties, and an understanding of this process continues to be of major importance in igneous petrology and geochemistry. Systematic studies of the physical properties of hydrous melts, and infrared1,2, Raman2,3 and 29Si NMR4 spectro-scopic studies of glasses quenched from melts, have provided valuable information, but many questions remain unanswered. Previous proton NMR studies of glasses have generally concentrated on lineshape, to distinguish between the proton environments in Si–OH groups and in molecular H2O (refs 5, 6). Here we present proton NMR results in glasses quenched from hydrous melts, which allow us to resolve different proton sites on the basis of chemical-shift differences. Four separate proton resonances are resolved in a silica glass containing 8.7 wt% H2O, and a strongly hydrogen-bonded Si–OH group is identified in hydrous alkali and alkaline-earth disilicate glasses. Quantitative estimates of water speciation in the silica glasses agree with those from 29Si NMR4. Future proton NMR measurements which resolve different chemical environments will play an important role in elucidating the structures of hydrogen-bearing disordered solids.

The relative movement and persistence in soil of chlorsulfuron, metsulfuron‐methyl and triasulfuron

Abstract: Summary. Adsorption and degradation rates of triasulfuron in 8 different soils were negatively correlated with soil pH and were generally lower in subsoils than in soils from the plough layer. The half-life at 20°C varied from 33 days in a top soil at pH 5·8 to 120 days in a subsoil at pH 7·4. Adsorption distribution coefficients in these two soils were 0·55 and 0·19, respectively. Movement and persistence of residues of chlorsulfuron, triasulfuron and metsulfuron-methyl were compared in a field experiment prepared in spring 1987. Triasulfuron was less mobile in the soil than the other two compounds. Residues of all three herbicides were largely confined to the upper 40–50 cm soil 148 days after application. With an initial dose of 32 g ha−1, residues in the surface soil layers were sufficient to affect growth of lettuce and sugar-beet sown approximately one year after application. Laboratory adsorption and degradation data were used with appropriate weather data in a computer model of herbicide transport in soil. The model gave good predictions of total soil residues during the first five months following application, and also predicted successfully the maximum depth of penetration of the herbicides into the soil during this period. However, more herbicide was retained close to the soil surface than was predicted by the model. The model predicted extensive movement of the herbicides in the soil during winter but did not predict that residues sufficient to affect crop growth could be present in the upper 15–20 cm soil after one year. Resume. Le mouvement relatif et la persistance dans le sot du chlorsulfuron metsulfur on-methyl et triasulfuron L'absorption et les taux de degradation du triasulfuron dans huit sols differents etaient corrles negativement avec le pH du sol, et generalement plus bas dans le sous-sol, qu'a partir de la semelle de labour. La demi-vie a 20°C variant de 33 jours au pH de 5,8 par le sol de surface a 120 jours au pH de 7,4 par le sous sol. Les coefficients d'adsorption dans ces deux sols etaient de 0,55 et 0,19 respectivement. Le mouvement et la persistance des residus de chtorsulfuron, triasulfuron et metsulfuron-methyl ont ete compares dans un champ d'experimentation prepare au printemps 1987. Le triasulfuron est moins mobile dans le sol que les deux autres composes. Les residus de trios herbicides etaient en majorite confines dans tes 40 a 50 cm superieurs du sol 148 jours apres l'application. Avec une dose initiale de 32 g ha−1, les residus dans les couches superficielies du sol etaient suffisantes pour affecter la croissance de laitues ou betteraves sucrieres semees environ un an apres l'application. Les donnees de Laboratoire sur l'adsorption et la degradation ont ete utilisees avec des donnees climatiques appropriees dans un modele informatique du transport de l'herbicide dans le sol. Le modele donne de bonnes previsions du total de residus dans le sol pour les cinq mois apres l'application, et prevoit egalement avec succes la profondeur maximale de penetration dans le sol durant cette periode. Cependant, plus d'herbicide est retenu pres de la surface du sol que ce qui est prevu par le modele. Le modele prevoit des mouvements importants dans le sol durant l'hiver mais ne prevoit pas que les residus soient suffisants pour affecter la croissance des cultures dans les 15–20 cm superieurs du sol apres un an. Zusammenfassung. Beweglichkeit und Persistenz von Chlorsulforon, Metsulfuron-methyt und Triasulfuron im Boden Die Adsorptions- und Abbauraten von Triasulfuron in acht verschiedenen Boden waren mit dem pH-Wert des Bodens negative korreliert und waren im Unterboden generell niedriger als im Bearbeitungshorizont. Die Halbwertszeit bei 20°C lag zwischen 33 Tagen im Oberboden mit pH = 5,8 und 120 Tagen im Unterboden mit pH = 7,4. Die Adsorptions-Koeffizienten in den beiden Bodenschichten waren 0,55 bzw. 0,19. Die Ruckstandssituation von Chlorsulfuron, Triasulfuron und Metsulfuron-methyl wurde in einem im Fruhjahr 1987 begonnenen Feldversuch verglichen. Triasulfuron war im Boden weniger beweglich als die beiden anderen Wirkstoffe. Die Ruckstande der 3 Herbizide waren 148 Tage nach der Ausbringung besonders in den oberen 40–50 cm des Bodens zu finden. Bei einem Initialbelag von 32 g ha−1 waren die Ruckstande an der Bodenoberflache hoch genug, Salat und Zuckerruben ungefahr ein Jahr nach der Applikation zu schadigen. Adsorptions- und Abbaudaten aus Laboruntersuchungen wurden zusammen mit Witterungsdaten in einem Computer-Modell zur Beschreibung des Herbizidtransports im Boden simuliert. Das Modell ergab eine gute Prognose der Gesamtruckstande und der Einwaschungstiefe der Herbizide fur die ersten zwei Monate nach der Applikation, Nahe der Bodenoberflache wurden jedoch grosere Ruckstande gemessen, als mit dem Modell vorhergesagt. Im Gegensatz dazu sollte nach dem Modell wahrend des Winters eine starke Einwaschung eintreten, so das nach 1 Jahr in den oberen 15–20 cm des Bodens keine Ruckstande zu erwarten waren, die eine Folgekultur schadigen.

Magic angle spinning NMR of alkali phospho-alumino-silicate glasses

Abstract: MAS-NMR has been used to explore the structure of sodium phospho-alumino-silicate glasses. Adding P 2 O 5 to sodium silicates causes repolymerisation of the silicate network and formation of sodium ortho-, pyro- and eventually metaphosphate units. At high P 2 O 5 concentrations the structure is determined by the incorporation of silica into a sodium phosphate glass as either chain end species or as an “SiP 2 O 7 ” phase. Removal of sodium from these glasses or substitution of alumina for P 2 O 5 destroys the “SiP 2 O 7 ” phase.