Showing papers by "Royal Holloway, University of London published in 1999"

Large Margin DAGs for Multiclass Classification

Abstract: We present a new learning architecture: the Decision Directed Acyclic Graph (DDAG), which is used to combine many two-class classifiers into a multiclass classifier. For an N-class problem, the DDAG contains N(N - 1)/2 classifiers, one for each pair of classes. We present a VC analysis of the case when the node classifiers are hyperplanes; the resulting bound on the test error depends on N and on the margin achieved at the nodes, but not on the dimension of the space. This motivates an algorithm, DAGSVM, which operates in a kernel-induced feature space and uses two-class maximal margin hyperplanes at each decision-node of the DDAG. The DAGSVM is substantially faster to train and evaluate than either the standard algorithm or Max Wins, while maintaining comparable accuracy to both of these algorithms.

Support Vector Method for Novelty Detection

Abstract: Suppose you are given some dataset 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 ν between 0 and 1. We propose a method to approach this problem by trying to estimate a function f which 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. We 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 unlabelled data.

Computer Security

Abstract: A completely up-to-date resource on computer securityAssuming no previous experience in the field of computer security, this must-have book walks you through the many essential aspects of this vast topic, from the newest advances in software and technology to the most recent information on Web applications security. This new edition includes sections on Windows NT, CORBA, and Java and discusses cross-site scripting and JavaScript hacking as well as SQL injection. Serving as a helpful introduction, this self-study guide is a wonderful starting point for examining the variety of competing security systems and what makes them different from one another.Unravels the complex topic of computer security and breaks it down in such a way as to serve as an ideal introduction for beginners in the field of computer securityExamines the foundations of computer security and its basic principlesAddresses username and password, password protection, single sign-on, and moreDiscusses operating system integrity, hardware security features, and memoryCovers Unix security, Windows security, database security, network security, web security, and software securityPacked with in-depth coverage, this resource spares no details when it comes to the critical topic of computer security.

A model of saccade generation based on parallel processing and competitive inhibition.

Abstract: During active vision, the eyes continually scan the visual environment using saccadic scanning movements. This target article presents an information processing model for the control of these movements, with some close parallels to established physiological pro- cesses in the oculomotor system. Two separate pathways are concerned with the spatial and the temporal programming of the move- ment. In the temporal pathway there is spatially distributed coding and the saccade target is selected from a "salience map." Both path- ways descend through a hierarchy of levels, the lower ones operating automatically. Visual onsets have automatic access to the eye control system via the lower levels. Various centres in each pathway are interconnected via reciprocal inhibition. The model accounts for a num- ber of well-established phenomena in target-elicited saccades: the gap effect, express saccades, the remote distractor effect, and the global effect. High-level control of the pathways in tasks such as visual search and reading is discussed; it operates through spatial se- lection and search selection, which generally combine in an automated way. The model is examined in relation to data from patients with unilateral neglect.

The development of an individualized questionnaire measure of perceived impact of diabetes on quality of life: the ADDQoL

Abstract: The objectives of the study were to design and develop a questionnaire to measure individuals' perceptions of the impact of diabetes on their quality of life (QoL). The design of the ADDQoL (Audit of Diabetes Dependent QoL) was influenced by patient-centred principles underlying the SEIQoL interview method. Respondents rate only personally-applicable life domains, indicating importance and impact of diabetes. Fifty-two out-patients with diabetes and 102 attending diabetes education open days provided data for psychometric analyses. Each of the 13 domain-specific ADDQoL items was relevant and important for substantial numbers of respondents. Factor analysis and Cronbach's alpha coefficient of internal consistency (0.85) supported combination of items into a scale. Insulin-treated patients reported greater impact of diabetes on QoL than table/diet-treated patients. People with microvascular complications showed, as expected, greater diabetes-related impairment of QoL than people without complications. Unlike other QoL measures, the ADDQoL is an individualized questionnaire measure of the impact of diabetes and its treatment on QoL. Preliminary evidence of reliability and validity is established for adults with diabetes. Findings suggest that the ADDQoL will be more sensitive to change and responsive to differences than generic QoL measures.

Separability of very noisy mixed states and implications for nmr quantum computing

Abstract: We give a constructive proof that all mixed states of N qubits in a sufficiently small neighborhood of the maximally mixed state are separable (unentangled). The construction provides an explicit representation of any such state as a mixture of product states. We give upper and lower bounds on the size of the neighborhood, which show that its extent decreases exponentially with the number of qubits. The bounds show that no entanglement appears in the physical states at any stage of present NMR experiments. Though this result raises questions about NMR quantum computation, further analysis would be necessary to assess the power of the general unitary transformations, which are indeed implemented in these experiments, in their action on separable states.

The diagnosis of autism and Asperger syndrome: findings from a survey of 770 families

Abstract: As part of a wider survey of parents of children with autistic spectrum disorders in the UK, the diagnostic experiences of 614 parents of children with autism and 156 with Asperger syndrome were compared. Although the ages of the children in the two groups were very similar at the time of the survey, parents of children given a diagnosis of Asperger syndrome had experienced significantly longer delays and greater frustration in obtaining a diagnosis than those with a child with autism. In the 'autism group' the average age when diagnosis was confirmed was around 5.5 years; in the 'Asperger group' it was 11 years. Parents of children with a diagnosis of autism were generally aware of problems in their child's development by 18 months of age; in the Asperger group concerns emerged later, at around 30 months of age. Initial worries in both groups centred around abnormal social development but parents of children with Asperger syndrome were less likely to have noted communication problems. Stereotyped or repetitive behaviours were not prominent in the early years in either group. Despite the problems inherent in data collected by postal survey, many of the findings of this study are supported by other research. The practical implications of delayed diagnosis, especially in the case of more able children with Asperger syndrome are discussed.

Acute Stress Disorder and Posttraumatic Stress Disorder in Victims of Violent Crime

Abstract: OBJECTIVE: In a group of crime victims recruited from the community, the authors investigated the ability of both a diagnosis of acute stress disorder and its component symptoms to predict posttraumatic stress disorder (PTSD) at 6 months. METHOD: A mixed-sex group of 157 victims of violent assaults were interviewed within 1 month of the crime. At 6-month follow-up 88% were reinterviewed by telephone and completed further assessments generating estimates of the prevalence of PTSD. RESULTS: The rate of acute stress disorder was 19%, and the rate of subsequent PTSD was 20%. Symptom clusters based on the DSM-IV criteria for acute stress disorder were moderately strongly interrelated. All symptom clusters predicted subsequent PTSD, but not as well as an overall diagnosis of acute stress disorder, which correctly classified 83% of the group. Similar predictive power could be achieved by classifying the group according to the presence or absence of at least three reexperiencing or arousal symptoms. Logistic regr...

Meditation and attention: A comparison of the effects of concentrative and mindfulness meditation on sustained attention

Abstract: The performance of concentrative and mindfulness meditators on a test of sustained attention (Wilkins' counting test) was compared with controls. Both groups of meditators demonstrated superior performance on the test of sustained attention in comparison with controls, and long-term meditators were superior to short-term meditators. Mindfulness meditators showed superior performance in comparison with concentrative meditators when the stimulus was unexpected but there was no difference between the two types of meditators when the stimulus was expected. The results are discussed in relation to the attentional mechanisms involved in the two types of meditation and implications drawn for mental health.

Plastid division and development

Abstract: Plastids are an important group of plant cellular organelles and comprise one of the primary features that distinguish plant cells from those of other eukaryotes. Plastids are thought to have arisen as a result of an endosymbiotic event in which an early photosynthetic prokaryote invaded a primitive

Deconvolution gas chromatography/mass spectrometry of urinary organic acids--potential for pattern recognition and automated identification of metabolic disorders.

Abstract: The National Institute of Standards and Technology (NIST) Automated Mass Spectral Deconvolution and Identification System (AMDIS) is applied to a selection of data files obtained from the gas chromatography/mass spectrometry (GC/MS) analysis of urinary organic acids. Mass spectra obtained after deconvolution are compared with a special user library containing both the mass spectra and retention indices of ethoxime-trimethylsilyl (EO-TMS) derivatives of a set of organic acids. Efficient identification of components is achieved and the potential of the procedure for automated diagnosis of inborn errors of metabolism and for related research is demonstrated.

The Phosphoenolpyruvate/Phosphate Translocator Is Required for Phenolic Metabolism, Palisade Cell Development, and Plastid-Dependent Nuclear Gene Expression

Abstract: The Arabidopsis chlorophyll a/b binding protein (CAB) gene underexpressed 1 (cue1) mutant underexpresses light-regulated nuclear genes encoding chloroplast-localized proteins. cue1 also exhibits mesophyll-specific chloroplast and cellular defects, resulting in reticulate leaves. Both the gene underexpression and the leaf cell morphology phenotypes are dependent on light intensity. In this study, we determine that CUE1 encodes the plastid inner envelope phosphoenolpyruvate/phosphate translocator (PPT) and define amino acid residues that are critical for translocator function. The biosynthesis of aromatics is compromised in cue1, and the reticulate phenotype can be rescued by feeding aromatic amino acids. Determining that CUE1 encodes PPT indicates the in vivo role of the translocator in metabolic partitioning and reveals a mesophyll cell-specific requirement for the translocator in Arabidopsis leaves. The nuclear gene expression defects in cue1 suggest that a light intensity-dependent interorganellar signal is modulated through metabolites dependent on a plastid supply of phosphoenolpyruvate.

Religious and ethnic group influences on beliefs about mental illness: a qualitative interview study.

Abstract: An in-depth qualitative interview study is reported, with respondents ( N=52; all female) from the following urban-dwelling religious groups: White Christian, Pakistani Muslim, Indian Hindu, Orthodox Jewish and Afro-Caribbean Christian. Qualitative thematic analysis of open-ended interview responses revealed that the degree to which religious coping strategies were perceived to be effective in the face of depressive and schizophrenic symptoms, varied across the groups, with prayer being perceived as particularly effective among Afro-Caribbean Christian and Pakistani Muslim groups. Across all non-white groups, and also for the Jewish group, there was fear of being misunderstood by outgroup health professionals, and among Afro-Caribbean Christian and Pakistani Muslim participants, evidence of a community stigma associated with mental illness, leading to a preference for private coping strategies. The results lend further support to recent calls for ethnic-specie c mental health service provision and highlight the utility of qualitative methodology for exploring the link between religion and lay beliefs about mental illness.

Autobiographical memory processes and the course of depression.

Abstract: The authors report a 6-month follow-up study of clinically depressed patients. At baseline, 2 indexes of autobiographical memory functioning were assessed: the presence of spontaneous intrusive memories of stressful life events and performance on the Autobiographical Memory Test (J. M. G. Williams & K. Broadbent, 1986), which measures overgeneral memory. The index of overgeneral memory was associated with greater levels of spontaneous intrusion of stressful memories. Overgeneral memory did not predict outcome, but depression at follow-up was predicted by the amount of intrusion and avoidance of stressful memories, even after controlling for initial severity of psychiatric symptoms.

Process algebra and non-interference

Abstract: The information security community has long debated the exact definition of the term "security". Even if we focus on the more modest notion of confidentiality the precise definition remains controversial. In their seminal paper, Goguen and Meseguer (1982) took an important step towards a formalisation of the notion of absence of information flow with the concept of non-interference. This too was found to have problems and limitations, particularly when applied to systems displaying non-determinism which led to a proliferation of refinements of this notion and there is still no consensus as to which of these is "correct". We show that this central concept in information security is closely related to a central concept of computer science: that of the equivalence of systems. The notion of non-interference depends ultimately on our notion of process equivalence. However what constitutes the equivalence of two processes is itself a deep and controversial question in computer science with a number of distinct definitions proposed in the literature. We illustrate how several of the leading candidates for a definition of non-interference mirror notions of system equivalence. Casting these security concepts in a process algebraic framework clarifies the relationship between them and allows many results to be carried over regarding, for example, composition and unwinding. We also outline some generalisations of non-interference to handle partial and conditional information flows.

Machine-Learning Applications of Algorithmic Randomness

Abstract: Machine-LearningApplicationsofAlgorithmicRandomnessVolodyaovk,AlexGammerman,CraigSaundersComputerLearningResearchCentreandDepartmentofScienceRoyalHollowa,UniversitofLondon,Egham,SurreyTW200EX,Englandfvovk,alex,craigg@dcs.rhbnc.ac.ukMostmachinelearningalgorithmssharethefollowingdrawback:theyonlyoutputbarepredictionsbutnotthecon denceinthosepredictions.Inthe1960salgorithmicinfor-mationtheorysupplieduniversalmeasuresofcon dencebuttheseare,unfortunately,non-computable.Inthispap erwecombinetheideasofalgorithmicinformationtheorywiththetheoryofSupp ortVectormachinestoobtainpracticableapproximationsuni-versalmeasuresofcon dence.Weshowthatinsomestandardproblemsofpatternrecog-nitionourapproximationsworkell.1INTRODUCTIONTwoimp ortantdi erencesofmostmo dernmetho dsmachinelearning(suchasstatisticaltheory,seeVapnik[21],1998,orPACtheory)fromclassicalstatisticalmetho dsarethat:machinelearningmetho dspro ducebarepredic-tions,withoutestimatingcon denceinthosepre-dictions(unlike,eg,predictionoffutureobser-vationsintraditionalstatistics(Guttman[5],1970));manymachinelearningmetho dsaredesignedtowork(andtheirp erformanceisanalysed)un-derthegeneraliidassumption(unlikeclas-sicalparametricstatistics)andtheyareabletodealwithextremelyhigh-dimensionalhyp othesisspaces;cfVapnik[21](1998).Inthispap erwewillfurtherdeveloptheapproachofGammermanetal[4](1998)andSaunders[17Figure1:Ifthetrainingsetonlycontainsclear2sand7s,weouldliktoattachmucloercon dencethemiddleimagethantorightandleftones(1999),wherethegoalistoobtaincon dencesforpredictionsunderthegeneraliidassumptioninhigh-dimensionalsituations.Figure1demonstratesthede-sirabilityofcon dences.Themaincontributionthispap erisemb eddingtheapproachesofGammermanetal[4](1998)andSaunderset[17(1999)intoagen-eralschemebasedonthenotionofalgorithmicran-domness.Aswillb ecomeclearlater,theproblemofassigningcon dencestopredictionsiscloselyconnectedtheproblemofde ningrandomsequences.ThelatterproblemwassolvedbyKolmogorov[8](1965),whobasedhisde nitionontheexistenceUniver-salTuringMachine(thoughitb ecameclearthatKol-mogorov'sde nitiondo essolvetheproblemofde ningrandomsequencesonlyafterMartin-Lof 'spap er[15],1966);Kolmogorov'sde nitionmovedthenotionofrandomnessfromthegreyareasurroundingprobabil-itytheoryandstatisticstomathematicalcomputersci-ence.Kolmogorovb elievedhisnotionofrandomnesstob easuitablebasisforapplicationsofprobability.Unfor-tunately,fateideaasdi erentfromKol-mogorov's1933axioms(Kolmogorov[7],1933),which

Transduction with Confidence and Credibility

Abstract: In this paper we follow the same general ideology as in [Gammerman et al., 1998], and describe a new transductive learning algorithm using Support Vector Machines. The algorithm presented provides confidence values for its predicted classifications of new examples. We also obtain a measure of "credibility" which serves as an indicator of the reliability of the data upon which we make our prediction. Experiments compare the new algorithm to a standard Support Vector Machine and other transductive methods which use Support Vector Machines, such as Vapnik's margin transduction. Empirical results show that the new algorithm not only produces confidence and credibility measures, but is comparable to, and sometimes exceeds the performance of the other algorithms.

A randomized controlled trial of individual psychological debriefing for victims of violent crime.

Abstract: Background. It has been suggested that giving people the opportunity talk about a traumatic experience may prevent the development of later disorder. We tested the efficacy of two brief interventions, education and psychological debriefing, designed to prevent adverse psychological reactions to criminal victimization.Methods. Individuals who had been the victims of a violent crime within the past month were written to and invited to take part in a study of their attitudes to crime and punishment: 2161 were contacted and 243 replied, of whom 157 were eligible and were randomly assigned either to an education condition, to a psychological debriefing plus education condition, or to an assessment only condition. Education involved providing information about normal post-traumatic reactions. Debriefing involved in-depth probing about events, thoughts and feelings experienced during the crime. Subjects were recruited from police and hospital sources and interviewed in their own homes: 138 were followed up at 6 months, and 92 at 11 months.Results. Outcome was assessed using a DSM-III-R diagnosis of PTSD, the Post-traumatic Symptom Scale, the Impact of Event Scale and the Beck Depression Inventory. All groups improved over time but there were no between-group differences.Conclusions. No evidence was found to support the efficacy of brief one-session interventions for preventing post-traumatic symptoms in individual victims of violent crime.

The Thought Control Questionnaire - Psychometric properties in a clinical sample, and relationships with PTSD and depression

Abstract: Background. Recent developments in research suggest that particular attempts to control thoughts may contribute to the problem of intrusion. An instrument capable of identifying strategies for dealing with unwanted intrusions in clinical populations may be used for differentiating between thought control strategies that may or may not be helpful.Methods. The Thought Control Questionnaire (TCQ) (Wells & Davies, 1994) developed and validated on a normal sample, was administered to a clinical sample in order to investigate the consistency of the original factor structure and its psychometric properties. The sensitivity of the scale to change associated with recovery was also examined. Relationships between individual differences in thought control strategies and psychiatric symptoms in patients with DSM-IV major depression, and PTSD with or without major depression were investigated.Results. The Scree Test suggested a six-factor solution which was rotated. This solution split the original distraction subscale into separate behavioural and cognitive distraction, otherwise the subscales were almost identical to those obtained in non-clinical subjects. As this split has been shown to be unreliable, further analyses in this study were based on the five-factor version of the TCQ obtained by Wells & Davies (1994). Predictors of recovery and of symptoms in PTSD and depression were explored.Conclusions. Correlations between the TCQ subscales and other measures suggest that particular thought control strategies may be associated with the symptoms of PTSD and depression. The TCQ scales appear to be sensitive to changes associated with recovery. Significant differences emerged in thought control strategies between depressed and PTSD patients. Hierarchical regression analysis showed distraction, punishment and reappraisal control strategies predicted depression scores in depressed patients while use of distraction predicted intrusions in PTSD.

Phytoene synthase-2 enzyme activity in tomato does not contribute to carotenoid synthesis in ripening fruit.

Abstract: The characteristic yellow fruit phenotype of the r,r mutant and Psy-1 (phytoene synthase-1) antisense tomatoes is due to a mutated or down-regulated phytoene synthase protein, respectively, resulting in the virtual absence of carotenoids. Based on detailed carotenoid determinations Psy-1 appeared to barely contribute to the formation of carotenoids in chloroplast-containing tissues. Despite the virtual absence of carotenoids in ripe fruit the formation of phytoene in vitro was detected in fruit of both mutants. When [14C]isopentenyl pyrophosphate (IPP) was used as the substrate for phytoene synthase a reduction (e.g. r,r mutant, 5-fold) in the formation of phytoene was observed with an accumulation (e.g. r,r mutant, 2-fold) of the immediate precursor geranylgeranyl pyrophosphate (GGPP). Contrastingly, reduced phytoene synthase activity was not detected when [3H]GGPP was used as the substrate. The profile of phytoene formation during ripening was also different in the down-regulated mutants compared to the wild-type. Using specific primers, RT-PCR analysis detected the presence of Psy-2 transcripts in the down-regulated mutants and wild-type throughout fruit development and ripening. These data were supported by the detection of phytoene synthase protein on western blots. Both GGPP formation and phytoene desaturation were elevated in these mutants. Therefore, it appears that despite the absence of carotenoids in ripe fruit, both the mutants have the enzymic capability to synthesize carotenoids in this tissue. Implications of the data with respect to the regulation of carotenoid formation and the channelling of prenyl lipid precursors in tomato (and its potential manipulation) are discussed.

Is Production and Operations Management a Discipline?: A citation/co-citation Study

Abstract: For the past 20 years, the field of production and operations management (POM) has tried to establish itself as a discipline distinct from operations research (OR), management science (MS) and industrial engineering (IE). Sceptics argue that POM has failed to develop its own body of literature, lacks a distinct intellectual structure and that there is little appreciation of what it stands for. In this paper we use bibliometric techniques (a factor analysis of co‐citations) to investigate the intellectual pillars of the POM literature and explore whether these are distinct from those commonly associated with its rival fields. We also use simple non‐parametric techniques to show that the research agenda of European POM scholars differs substantially from that of their North American counterparts, and argue that such transatlantic differences may have exacerbated the difficulties POM has experienced in developing as a respected academic discipline.

How New is the New Local Governance? Lessons from the United Kingdom

Abstract: In recent times, a conventional wisdom concerning the governance of cities has emerged It revolves around the contention that policy and planning frameworks are increasingly closed off from public and democratic accountability, in order to facilitate the pursuit of efficiency over equity objectives The implication is that ‘old’ styles of governance were more open and accountable, while the ‘new’ seek to close off debate and streamline procedures Yet the evidence to sustain such claims seems limited; this paper situates the policies and practices of local government in the UK within a historical perspective, and develops the contention that the claimed differences between old and new styles of governance are overdrawn Using empirical material from two UK cities, we demonstrate that there are significant continuities in the procedures and practices of policy-makers, in terms of policy objectives, styles and modes of accountability In this sense, greater clarity is required in terms of what constitutes both the old and new modes of local governance in the British cities

On the relation between arbuscular mycorrhizal colonization and plant 'benefit'

Abstract: A simple model is proposed which describes the relation between the extent of mycorrhizal colonization of a plant and the 'benefit' (positive or negative) derived by that plant. 'Benefit' is defined as the percent change in a plant performance parameter of a mycorrhizal individual relative to the mean of a number of mycorrhizal plants, grown in identical conditions. The model predicts a general curvilinear relation between colonization density and benefit, where benefit is maximized at some value of colonization. It is based on the fact that the relation of plant P uptake to mycorrhizal colonization is often non-linear. Four examples of empirical data which provide a good fit to the model, with third-order polynomial regression are given. It is suggested that if the curvilinear relation is of general occurrence then it can provide an explanation for many of the apparently anomalous results seen in the mycorrhizal literature.

Prequential probability: principles and properties

Abstract: Forecaster has to predict, sequentially, a string of uncertain quantities ( X 1,X 2,...) , whose values are determined and revealed, one by one, by Nature. Various criteria may be proposed to assess Forecaster's empirical performance. The weak prequential principle requires that such a criterion should depend on Forecaster's behaviour or strategy only through the actual forecasts issued. A wide variety of appealing criteria are shown to respect this principle. We further show that many such criteria also obey the strong prequential principle, which requires that, when both Nature and Forecaster make their choices in accordance with a common joint distribution P for ( X 1,X 2,...) , certain stochastic properties, underlying and justifying the criterion and inferences based on it, hold regardless of the detailed specification of P . In order to understand further this compliant behaviour, we introduce the prequential framework, a game-theoretic basis for probability theory in which it is impossible to violate the prequential principles, and we describe its connections with classical probability theory. In this framework, in order to show that some criterion for assessing Forecaster's empirical performance is valid, we have to exhibit a winning strategy for a third player, Statistician, in a certain perfect-information game. We demonstrate that many performance criteria can be formulated and are valid in the framework and, therefore, satisfy both prequential principles.

The Private Finance Initiative: Clarification of a Future Research Agenda

Abstract: The Private Finance Initiative in the UK, whereby the public sector actively seeks private finance for developments in its services/buildings, can be traced to the Chancellor of the the Exchequer’s Autumn Statement of 1992. However, the seeking of private finance had been a Government concern for many years before this time even though it was only in 1992 that it gained a real impetus and direction. Since then it has developed and expanded into all areas of Government and into local authorities and has been carried forward, with equal, if not greater, enthusiasm, by the recently elected Labour Government. This paper provides an introduction to this new development in the public sector in the UK, tracing its historical development from its ‘macro’ emphasis, through to the ‘micro’ outworking of these policies across the entire public sector. This summary provides the base to draw up a future research agenda for PFI, which forms the major concern of the paper.