Showing papers by "Royal Holloway, University of London published in 2001"

Estimating the Support of a High-Dimensional Distribution

Abstract: Suppose you are given some data set drawn from an underlying probability distribution P and you want to estimate a "simple" subset S of input space such that the probability that a test point drawn from P lies outside of S equals some a priori specified value between 0 and 1. We propose a method to approach this problem by trying to estimate a function f that is positive on S and negative on the complement. The functional form of f is given by a kernel expansion in terms of a potentially small subset of the training data; it is regularized by controlling the length of the weight vector in an associated feature space. The expansion coefficients are found by solving a quadratic programming problem, which we do by carrying out sequential optimization over pairs of input patterns. We also provide a theoretical analysis of the statistical performance of our algorithm. The algorithm is a natural extension of the support vector algorithm to the case of unlabeled data.

GRADISTAT: a grain size distribution and statistics package for the analysis of unconsolidated sediments

Abstract: Grain size analysis is an essential tool for classifying sedimentary environments. The calculation of statistics for many samples can, however, be a laborious process. A computer program called GRADISTAT has been written for the rapid analysis of grain size statistics from any of the standard measuring techniques, such as sieving and laser granulometry. Mean, mode, sorting, skewness and other statistics are calculated arithmetically and geometrically (in metric units) and logarithmically (in phi units) using moment and Folk and Ward graphical methods. Method comparison has allowed Folk and Ward descriptive terms to be assigned to moments statistics. Results indicate that Folk and Ward measures, expressed in metric units, appear to provide the most robust basis for routine comparisons of compositionally variable sediments. The program runs within the Microsoft Excel spreadsheet package and is extremely versatile, accepting standard and non-standard size data, and producing a range of graphical outputs including frequency and ternary plots. Copyright © 2001 John Wiley & Sons, Ltd.

On Kernel-Target Alignment

Abstract: We introduce the notion of kernel-alignment, a measure of similarity between two kernel functions or between a kernel and a target function. This quantity captures the degree of agreement between a kernel and a given learning task, and has very natural interpretations in machine learning, leading also to simple algorithms for model selection and learning. We analyse its theoretical properties, proving that it is sharply concentrated around its expected value, and we discuss its relation with other standard measures of performance. Finally we describe some of the algorithms that can be obtained within this framework, giving experimental results showing that adapting the kernel to improve alignment on the labelled data significantly increases the alignment on the test set, giving improved classification accuracy. Hence, the approach provides a principled method of performing transduction.

Illness narratives: fact or fiction?

Abstract: There is currently considerable renewed interest in narrative analysis in the humanities, social sciences and medicine. Illness narratives, particularly those of patients or lay people, are a particular focus in health related settings. This paper discusses the background to this interest, especially its roots in critiques of medical dominance and distinctions between disease and illness, drawn by sociologists and anthropologists in the 1970s. The current emphasis on patient or personal narratives can also be seen to stem from changes in morbidity patterns, the expansion of information about disease and illness, and in public debates about the effectiveness of medicine. The paper then goes on to outline a framework for analysing illness narratives. This involves exploring three types of narrative form: ‘contingent narratives’ which address beliefs about the origins of disease, the proximate causes of an illness episode, and the immediate effects of illness on everyday life; ‘moral narratives’ that provide accounts of (and help to constitute) changes between the person, the illness and social identity, and which help to (re) establish the moral status of the individual or help maintain social distance; and ‘core narratives’ that reveal connections between the lay person’s experiences and deeper cultural levels of meaning attached to suffering and illness. Here, distinctions are drawn between such sub forms as heroic, tragic, ironic and comic, and regressive/progressive narratives. Finally, the paper discusses some of the methodological issues raised by narrative analysis. Given the complex character of illness narratives, their social and psychological functions, together with the motivational issues to which they relate, it is suggested that they constitute a major challenge for sociological analysis. From this viewpoint current claims about narrative analysis in medicine need to be treated with caution.

The Difference Between Consecutive Primes, II

Abstract: The authors sharpen a result of Baker and Harman (1995), showing that [x, x + x0.525] contains prime numbers for large x. An important step in the proof is the application of a theorem of Watt (1995) on a mean value containing the fourth power of the zeta function. 2000 Mathematical Subject Classification: 11N05.

Cognitive-processing bias in chronic pain: a review and integration.

Abstract: Do patients with chronic pain selectively process pain- and illness-related stimuli? The evidence with regard to attention, interpretation, and recall biases is critically reviewed, A model is proposed to account for the findings in which it is suggested that biases in information processing in chronic pain are the result of overlap between 3 schemas: pain, illness, and self. With frequent repeated or continued experience of pain, the pain schema becomes enmeshed with illness and self-schemas. The extent of the enmeshment and the salient content of the schema determine the bias. A fundamental assumption is that all patients with pain selectively process sensory-intensity information. A clinical implication of the results is that processing biases that extend beyond this healthy and adaptive process to enmesh the self-schema with pain and illness schemas could maintain and exacerbate distress and illness behavior in patients with chronic pain.

Continental breakup in magmatic provinces: An Ethiopian example

Abstract: Mechanical processes largely control the along-axis segmentation of continental rifts; however, asthenospheric processes strongly influence the along-axis segmentation of mid- ocean ridges. We examine the distribution of strain and magmatism in the transitional active Main Ethiopian rift. Magmatic construction, diking, and faulting during the past 1.6 m.y. have created ∼20-km-wide, ∼60-km-long magmatic segments with or without axial valleys. Magmatic segments are arranged en echelon within the ∼100-km-wide rift valley bounded by mid-Miocene border faults. Geodetic data show that magmatic segments accommodate >80% of the strain across the rift, indicating that border faults are no longer the locus of extension. Comparison with mid-ocean ridges suggests that magmatic segments, rather than detachment faults, mark the ocean-continent boundary in rifts with a ready magma supply. Magmatic margins, therefore, may contain detachments abandoned during continental breakup. The processes of localized dike intrusion with underplating would produce strips of mafic crust transitional to oceanic crust, but without coherent seafloor-spreading magnetic anomalies.

Centennial-Scale Holocene Climate Variability Revealed by a High-Resolution Speleothem δ18O Record from SW Ireland

Abstract: Evaluating the significance of Holocene submillennial δ 18 O variability in the Greenland ice cores is crucial for understanding how natural climate oscillations may modulate future anthropogenic warming. A high-resolution oxygen isotope record from a speleothem in southwestern Ireland provides evidence for centennial-scale δ 18 O variations that correlate with subtle δ 18 O changes in the Greenland ice cores, indicating regionally coherent variability in the early Holocene. Evidence for previously undetected early Holocene cooling events is presented, but mid- to late-Holocene ice rafting in the North Atlantic appears to have had little impact on δ 18 O at this ocean margin site.

Estimating Receptive Field Size from fMRI Data in Human Striate and Extrastriate Visual Cortex

Abstract: Functional magnetic resonance imaging (fMRI) was used to estimate the average receptive field sizes of neurons in each of several striate and extrastriate visual areas of the human cerebral cortex. The boundaries of the visual areas were determined by retinotopic mapping procedures and were visualized on flattened representations of the occipital cortex. Estimates of receptive field size were derived from the temporal duration of the functional activation at each cortical location as a visual stimulus passed through the receptive fields represented at that location. Receptive fields are smallest in the primary visual cortex (V1). They are larger in V2, larger again in V3/VP and largest of all in areas V3A and V4. In all these areas, receptive fields increase in size with increasing stimulus eccentricity. The results are qualitatively in line with those obtained by others in macaque monkeys using neurophysiological methods.

Competitive On-line Statistics

Abstract: Summary A radically new approach to statistical modelling, which combines mathematical techniques of Bayesian statistics with the philosophy of the theory of competitive on-line algorithms, has arisen over the last decade in computer science (to a large degree, under the influence of Dawid's prequential statistics). In this approach, which we call “competitive on-line statistics”, it is not assumed that data are generated by some stochastic mechanism; the bounds derived for the performance of competitive on-line statistical procedures are guaranteed to hold (and not just hold with high probability or on the average). This paper reviews some results in this area; the new material in it includes the proofs for the performance of the Aggregating Algorithm in the problem of linear regression with square loss. Resume Cet article decrit une approch nouvelle a modelage statistique combinant les techniques mathematiques de statistique Bayesienne avec la philosophie de la theorie de algorithmes competitives en ligne. Dans cette approche, qui emergeait durant le decennie derniere dans I'informatique, on ne suppose pas que les donnees sont produites par une mecanaisme stochastique; au lieu de cela, il est prouve que les procedures statistiques competitives en ligne atteignent toujours (et non, par exemple, avechaute probabilite) quelque but desirable (explicitant la bonne performance sur les donnees reeles). Cet article pass en revue des plusieurs resultats dans cette domaine; son materiel neuf comprend les preuves pour la performance de le algorithme agregent dans le probleme de la regression linegression lineaire avec la perte carree.

Analog models of restraining stepovers in strike-slip fault systems

Abstract: Scaled sandbox models have successfully simulated the geometries and progressive evolution of antiformal pop-up structures developed in a weak sedimentary cover above restraining stepovers in offset sinistral strike-slip fault systems in rigid basement. Models were run both with and without synkinematic sedimentation, which was added incrementally to cover the growing antiformal structures. Vertical and horizontal sections of the completed models permit the full three-dimensional (3-D) structure of the pop-ups to be analyzed in detail. Three representative end-member experiments are described: 30° underlapping restraining stepovers; 90° neutral restraining stepovers; and 150° overlapping restraining stepovers. The experimental pop-ups are typically sigmoidal to lozenge-shaped, antiformal structures having geometries that are dependent on both the stepover angle and stepover width in the underlying basement faults. Underlapping restraining stepovers typically form elongate lozenge-shaped pop-ups; 90° neutral restraining stepovers produce shorter, squat rhomboidal pop-ups; and overlapping restraining stepovers produce sigmoidal antiformal pop-ups. Trans pop-up cross fault systems are characteristic at large displacements on the basement fault system. Above the offset principal displacement zones, the pop-ups are commonly small, narrow, positive flower structures, whereas in the stepover region, they widen out and become markedly asymmetric. This pop-up asymmetry switches across the center of the stepover, where the pop-ups are largely symmetical. Maximum rotations measured within the central highly uplifted region of the pop-ups increase from 7° counterclockwise for the underlapping (30°) stepovers, to 14° counterclockwise for the neutral (90°) stepovers, to 16° counterclockwise for the overlapping (150°) stepovers. In models where no synkinematic sediments were added during deformation, the pop-up structures are bound by convex, flattening-upward, oblique-slip reverse fault systems that link downward to the offsets in the basement fault system. In contrast, in the (Begin page 234) experiments where synkinematic sediments were added incrementally during deformation, the pop-ups are formed by oblique-slip reverse faults that steepen upward into the synkinematic strata with the formation of fault-propagation growth folds. The analog models are compared with natural examples of pop-up structures and show strong similarities in structural geometries and stratal architectures. These models may provide structural templates for seismic interpretation of complex contractional structures in offset strike-slip fault systems.

Latent Semantic Kernels

Abstract: Kernel methods like support vector machines have successfully been used for text categorization. A standard choice of kernel function has been the inner product between the vector-space representation of two documents, in analogy with classical information retrieval (IR) approaches. Latent semantic indexing (LSI) has been successfully used for IR purposes as a technique for capturing semantic relations between terms and inserting them into the similarity measure between two documents. One of its main drawbacks, in IR, is its computational cost. In this paper we describe how the LSI approach can be implemented in a kernel-defined feature space. We provide experimental results demonstrating that the approach can significantly improve performance, and that it does not impair it.

`You're only as Good as Your Last Job': The Labour Process and Labour Market in the British Film Industry

Abstract: Recent debates surrounding the future of work and non-standard forms of employment have, especially in the United States, used the film industry as an exemplar and signifier of future industrial change. Much research conducted in the film industry implicitly or explicitly draws on the flexible specialisation framework to understand industrial organisation and labour market operation. It is the contention of this paper, however, that the dual labour market analysis associated with flexible specialisation explanations is too simplistic, failing to reflect the range of factors affecting labour market organisation and operation. The resulting static and atomised analysis is, as such, ill-equipped to conceptualise the complex patterns of organisation and movement evident in the highly uncertain context of film making. Furthermore, the operation and organisation of the labour market cannot be understood independently of the management of labour within the labour process. Production company management set the context and targets of work (in terms of work scheduling, pay, and conditions) and departmental heads retain method autonomy and control the recruitment and performance of ‘their’ group members. However, this is the case within a context in which people need to continually re-secure work and maintain positions within groups and contacts. Therefore, a seeming lack of control over tasks at the point of production is reinforced by the use of labour market mechanisms and influences their form.

Supersingular Curves in Cryptography

Abstract: Frey and Ruck gave a method to transform the discrete logarithm problem in the divisor class group of a curve over Fq into a discrete logarithm problem in some finite field extension Fqk. The discrete logarithm problem can therefore be solved using index calculus algorithms as long as k is small. In the elliptic curve case it was shown by Menezes, Okamoto and Vanstone that for supersingular curves one has k ≤ 6. In this paper curves of higher genus are studied. Bounds on the possible values for k in the case of supersingular curves are given which imply that supersingular curves are weaker than the general case for cryptography. Ways to ensure that a curve is not supersingular are also discussed. A constructive application of supersingular curves to cryptography is given, by generalising an identity-based cryptosystem due to Boneh and Franklin. The generalised scheme provides a significant reduction in bandwidth compared with the original scheme.

Evolution of leaf-form in land plants linked to atmospheric CO2 decline in the Late Palaeozoic era

Abstract: The widespread appearance of megaphyll leaves, with their branched veins and planate form, did not occur until the close of the Devonian period at about 360 Myr ago. This happened about 40 Myr after simple leafless vascular plants first colonized the land in the Late Silurian/Early Devonian, but the reason for the slow emergence of this common feature of present-day plants is presently unresolved. Here we show, in a series of quantitative analyses using fossil leaf characters and biophysical principles, that the delay was causally linked with a 90% drop in atmospheric pCO2 during the Late Palaeozoic era. In contrast to simulations for a typical Early Devonian land plant, possessing few stomata on leafless stems, those for a planate leaf with the same stomatal characteristics indicate that it would have suffered lethal overheating, because of greater interception of solar energy and low transpiration. When planate leaves first appeared in the Late Devonian and subsequently diversified in the Carboniferous period, they possessed substantially higher stomatal densities. This observation is consistent with the effects of the pCO2 on stomatal development and suggests that the evolution of planate leaves could only have occurred after an increase in stomatal density, allowing higher transpiration rates that were sufficient to maintain cool and viable leaf temperatures.

Movements and activity of male and female dogfish in a tidal sea lough: alternative behavioural strategies and apparent sexual segregation

Abstract: Movements and habitat selection of male and female dogfish, Scyliorhinus canicula, in a tidal sea lough in south-west Ireland were determined over two temporal scales. Continuous acoustic tracking of four individuals (two males, two females) for 6 days was used to monitor fine-scale changes in behaviour patterns and extent of home ranges. Mark-recapture by number-tagging dogfish captured at sampling stations during August-September in consecutive years was used to reveal long-term philopatric behaviour. Transmitter-tagged male dogfish showed very similar behavioural patterns of low activity during the day in deep water (12–24 m depth) followed by more rapid movements into shallow areas (<4 m) at dusk to feed, before returning to the core space in deep water at dawn. Home ranges occupied by males overlapped almost entirely and were centred in an area where tidal currents form gyres and large crab prey are found. Female S. canicula exhibited a different behavioural strategy. They refuged in caves in shallow water (0.5–1.5 m) during the day and during the 6-day tracking period were nocturnally active two or three times, primarily in deep water. Activity areas of females did not overlap with those of males. Acoustic telemetry, netting, underwater surveys and tag returns revealed males and females were apparently segregated by sex in the lough. Mark-recapture data showed males and females were recaptured from the locations where they were originally caught between 359 and 371 days earlier suggesting at least seasonal segregation in consecutive years. Because female dogfish store sperm enabling temporal separation of the energetically demanding act of copulation with the process of egg-laying, we suggest that this apparent spatial segregation by sex could be driven by the need for females to conserve energy by limiting multiple matings during a time when mating coincides with a peak in egg production and laying.

Curved saccade trajectories: voluntary and reflexive saccades curve away from irrelevant distractors.

Abstract: In this study we examined the impact of irrelevant distractors upon trajectories of reflexive and voluntary saccades. Observers made saccades to visual targets above and below fixation as directed by target appearance (reflexive) or by a central directional cue (voluntary) in the presence of an irrelevant distractor stimulus (a cross) whose appearance was simultaneous with target onset. We recorded saccade latency, amplitude and the magnitude of saccade curvature relative to the direct route from the start-to-end of the saccade. Previous studies of saccades curvature have used distractors to provide information about the saccade task and, as a result, have only examined trajectories of voluntary saccades. However, we have shown that both reflexive and voluntary saccades curved away from irrelevant distractors. The effect of irrelevant distractors indicates that observers do not need to attend to distractors in a voluntary fashion for distractors to modify saccade trajectories. Furthermore, it highlights an important parallel in curvature of saccades and reach trajectories, namely that both curve away from irrelevant distractors. The second important observation was that reflexive, as well as voluntary, saccades curved away from distractors. This suggests that curvature is not solely a consequence of voluntary control. These results have been considered within the context of inhibition-based theories of curvature derived from studies of saccade and manual reach trajectories.

Stackelberg Beats Cournot — On Collusion and Efficiency in Experimental Markets

Abstract: We report on an experiment designed to compare Stackelberg and Cournot duopoly markets with quantity competition. We implement both a random matching and a fixed-pairs version for each market. Stackelberg markets yield, regardless of the matching scheme, higher outputs than Cournot markets and, thus, higher efficiency. For Cournot markets, we replicate a pattern known from previous experiments. There is stable equilibrium play under random matching and partial collusion under fixed pairs. We also find, for Stackelberg markets, that competition becomes less intense when firms remain in pairs but we find considerable deviations from the subgame perfect equilibrium prediction which can be attributed to an aversion to disadvantageous inequality.

A blind, randomized, controlled trial of cognitive-behavioural intervention for patients with recent onset rheumatoid arthritis: preventing psychological and physical morbidity.

Abstract: This study examined the efficacy of a cognitive and behavioural intervention (CBT) for patients with recent onset, seropositive rheumatoid arthritis. Fifty-three participants with a diagnosis of classical or definite rheumatoid arthritis, who were seropositive and had less than 2 years of disease history were recruited into the trial. All participants received routine medical management during the study, although half were randomly allocated to receive an adjunctive psychological intervention. All pre- and post-treatment assessments were conducted blind to the allocation. Analyses were conducted of treatment completers and also by intention-to-treat. Significant differences were found between the groups at both post-treatment and 6-month follow-up in depressive symptoms. While the CBT group showed a reduction in depressive symptoms, the same symptoms increased in the Standard group. At outcome but not follow-up, the CBT group also showed reduction in C-reactive protein levels. However, the CBT group did show significant improvement in joint involvement at 6-month follow-up compared with the Standard group, indicating physical improvements above those achieved with standard care. These results indicate that cognitive-behavioural intervention offered as an adjunct to standard clinical management early in the course of RA is efficacious in producing reductions in both psychological and physical morbidity

From global knowledge management to internal electronic fences: contradictory outcomes of intranet development

Abstract: This paper considers the adoption of intranet technology as a vehicle for encouraging organization-wide knowledge sharing within a large, global bank. Ironically, the outcome of intranet adoption was that, rather than integrate individuals across this particular organization, the intranet actually helped to reinforce the existing functional and national boundaries with ‘electronic fences’. This could be partly explained by the historical emphasis on decentralization within the bank, which shaped and limited the use of the intranet as a centralizing, organization-wide tool. This is possible because the intranet can be described as an interactive and decentred technology, which therefore has the potential for multiple interpretations and effects. Thus, while the intranet is often promoted as a technology that enables processes of communication, collaboration and social coordination it also has the potential to disable such processes. Moreover, it is argued that to develop an intranet for knowledgesharing requires a focus on three distinctive facets of development. These different facets may require very different, sometimes contradictory, sets of strategies for blending the technology and the organization, thus making it extremely difficult for a project team to work effectively on all three facets simultaneously. This was evidenced by the fact that none of the independent intranet-implementation projects considered actually managed to encourage knowledge-sharing as intended, even within the relatively homogeneous group for which it was designed. Broader knowledge-sharing across the wider organizational context simply did not occur even among those who were working on what were defined as ‘knowledge management’ projects. A paradox is that knowledge-sharing via intranet technologies may be most difficult to achieve in contexts where knowledge management is the key objective.

Cainozoic ferns and their distribution

Abstract: The phytogeographic distribution of Cainozoic ferns is reported based upon a critical re-appraisal of the macrofossil and mesofossil record also taking account of evidence from a few highly diagnostic spores. Well-documented circum-Arctic Cainozoic floras show ferns (Woodwardia, Onoclea, Osmunda, Coniopteris and to a lesser extentAzolla) distributed around the pole to very high paleolatitudes. Some ferns are shared between the mid-paleolatitudes of North America and Europe as would be predicted from the distributions of other biota. Evidence for the composition of Cainozoic fern floras is minimal in some regions (e.g., Antarctica, Central and South America, Africa, India, South East Asia), so the absence of fern fossils from these areas has no biogeographical significance. Matoniaceae were abundant in the preceding Mesozoic. However, the absence of Cainozoic macrofossils, and the fact that no CainozoicMatonisporites spores areMatonia-like, indicates that Matoniaceae had attained their modern relict distribution by, or very early in, the Cainozoic. The important Mesozoic families Marattiaceae and Dipteridaceae are also not represented by Cainozoic macrofossils. They probably also showed Cainozoic restriction but spores are not sufficiently diagnostic to enable testing of this hypothesis. Other ferns, which were also important in the Mesozoic (e.g., Dicksoniaceae, Gleicheniaceae), have patchy, equivocal, or inadequately published Cainozoic records. The dispersed spore record may provide an opportunity to track Cainozoic Gleicheniaceae but this approach is not without problems. Most well-represented Cainozoic fern families, genera and subgenera show widespread Cainozoic ranges, typically with considerable range extensions over their living relatives, both onto other continents and north and south to higher paleolatitudes. These include Schizaeaceae (Lygodium, Anemia, and the extinctRuffordia), Osmundaceae (Osmunda), Pteridaceae (Acrostichum), Thelypteridaceae (Cyclosorus), Lophosoriaceae (Lophosoria), Cyatheaceae (theCnemidaria/Cyathea decurrens clade) and the heterosporous water fernAzolla (Azollaceae). A few well-represented ferns show Cainozoic distributions similar to those of the present day (e.g.,Salvinia [Salviniaceae] andCeratopteris [Pteridaceae] (the latter by the Neogene and based only on spores]) but even these had slightly broader ranges in the Cainozoic. Some Cainozoic ferns have apparently local distributions, e.g.,Blechnum dentatum (Blechnaceae) in Europe; and others are so far represented at only one or few sites, e.g.,Dennstaedtiopsis (Dennstaedtiaceae),Botrychium (Ophioglossales),Grammitis (Grammitidaceae), andMakotopteris andRumohra (Dryopteridaceae). Cainozoic fossils assigned toDryopteris (and some other dryopteroids) require revision along with those of Thelypteridaceae, the latter having high potential to provide useful paleobiogeographic evidence, at least of theCyclosorus group. Cainozoic records of Hymenophyllaceae and Polypodiaceae are here considered unconfirmed.

Organisational resistance strategies to unwanted accounting and finance changes: the case of general medical practice in the UK

Abstract: This paper explores the resistance strategies of organisations to unwanted changes. It is concerned with the way satellite organisations are created to provide a counter force to environmental disturbances such as changes introduced in the context of what has come to be called New Public Management. Its particular focus is with the attempt to develop and institutionalize external, “public” forms of resistance rather than undertake more internal, “private” forms. The specific empirical focus is general medical practice in the UK, where commissioning groups were formed as an alternative to GP fundholding. To help analyse this empirical detail we draw insights from Habermas’s model of society, organisational change theory and institutional theory. In the process the paper not only amplifies the empirical reactions of GP practices in the UK but also uses this empirical detail to develop the nature of this theoretical base by adding new dimensions concerning organisational resistance.