105 research outputs found

    The Structure of Polyfulvenes

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    Cationic polymerisation of 6,6-disubstituted pentafulvenes yields highly unsaturated, reactive macromolecules of high mo- . lecular weight. The mechanistic pathways leading to the polymers are discussed, and the structure XIV of the polymers has been elucidated by a combination of spectroscopic methods as well as by comparison with model compounds. In contrast to reports in the literature, the main process in thermal oligomerisation of simple pentafulvenes at 20 °c is a Diels-Alder reaction giving products of type XXI. Anionic polymerisation of pentafulvenes is initiated by traces of sodium cyclopentadienide or phenylsodium respectively. The reaction products consist of a mixture of oligomers of the series (fulvene)n. This surprising result can be explained by structure elucidation of the fulvene dimers, which gives formula XX. The mechanistic aspects of the reaction are discussed

    The Structure of Polyfulvenes

    Get PDF
    Cationic polymerisation of 6,6-disubstituted pentafulvenes yields highly unsaturated, reactive macromolecules of high mo- . lecular weight. The mechanistic pathways leading to the polymers are discussed, and the structure XIV of the polymers has been elucidated by a combination of spectroscopic methods as well as by comparison with model compounds. In contrast to reports in the literature, the main process in thermal oligomerisation of simple pentafulvenes at 20 °c is a Diels-Alder reaction giving products of type XXI. Anionic polymerisation of pentafulvenes is initiated by traces of sodium cyclopentadienide or phenylsodium respectively. The reaction products consist of a mixture of oligomers of the series (fulvene)n. This surprising result can be explained by structure elucidation of the fulvene dimers, which gives formula XX. The mechanistic aspects of the reaction are discussed

    Repeatability and Reproducibility of Decisions by Latent Fingerprint Examiners

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    The interpretation of forensic fingerprint evidence relies on the expertise of latent print examiners. We tested latent print examiners on the extent to which they reached consistent decisions. This study assessed intra-examiner repeatability by retesting 72 examiners on comparisons of latent and exemplar fingerprints, after an interval of approximately seven months; each examiner was reassigned 25 image pairs for comparison, out of total pool of 744 image pairs. We compare these repeatability results with reproducibility (inter-examiner) results derived from our previous study. Examiners repeated 89.1% of their individualization decisions, and 90.1% of their exclusion decisions; most of the changed decisions resulted in inconclusive decisions. Repeatability of comparison decisions (individualization, exclusion, inconclusive) was 90.0% for mated pairs, and 85.9% for nonmated pairs. Repeatability and reproducibility were notably lower for comparisons assessed by the examiners as “difficult” than for “easy” or “moderate” comparisons, indicating that examiners' assessments of difficulty may be useful for quality assurance. No false positive errors were repeated (n = 4); 30% of false negative errors were repeated. One percent of latent value decisions were completely reversed (no value even for exclusion vs. of value for individualization). Most of the inter- and intra-examiner variability concerned whether the examiners considered the information available to be sufficient to reach a conclusion; this variability was concentrated on specific image pairs such that repeatability and reproducibility were very high on some comparisons and very low on others. Much of the variability appears to be due to making categorical decisions in borderline cases

    The effectiveness of surgical correction of uterine prolapse: cervical amputation with uterosacral ligament plication (modified Manchester) versus vaginal hysterectomy with high uterosacral ligament plication

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    Item does not contain fulltextINTRODUCTION AND HYPOTHESIS: The objective of this study is to evaluate cervical amputation with uterosacral ligament plication (modified Manchester) and compare it to vaginal hysterectomy with high uterosacral ligament plication procedure with special regard to the middle compartment. METHODS: Consecutive women with pelvic organ prolapse who underwent either vaginal hysterectomy or a modified Manchester procedure were included. Assessments were made preoperatively and at 1-year follow-up, including physical examination with pelvic organ prolapse quantification standardised questionnaires (incontinence impact questionnaire, urogenital distress inventory, and defaecatory distress inventory). RESULTS: Between 2002 and 2007, 156 patients were included. Ninety-eight patients returned for a 1-year follow-up. In the modified Manchester group, we found no middle compartment recurrence versus two (4%) in the vaginal hysterectomy group. Anterior and posterior compartment prolapse recurrences (stage >or=2) were similar (approximately 50%). Considering operating time and blood loss, modified Manchester was more favourable. There was no difference in the pre- and postoperative subjective scores. The overall functional outcome was acceptable. CONCLUSIONS: We found an excellent performance of both procedures regarding middle compartment recurrences

    Multiple Deprivation, Severity and Latent Sub-Groups:Advantages of Factor Mixture Modelling for Analysing Material Deprivation

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    Material deprivation is represented in different forms and manifestations. Two individuals with the same deprivation score (i.e. number of deprivations), for instance, are likely to be unable to afford or access entirely or partially different sets of goods and services, while one individual may fail to purchase clothes and consumer durables and another one may lack access to healthcare and be deprived of adequate housing . As such, the number of possible patterns or combinations of multiple deprivation become increasingly complex for a higher number of indicators. Given this difficulty, there is interest in poverty research in understanding multiple deprivation, as this analysis might lead to the identification of meaningful population sub-groups that could be the subjects of specific policies. This article applies a factor mixture model (FMM) to a real dataset and discusses its conceptual and empirical advantages and disadvantages with respect to other methods that have been used in poverty research . The exercise suggests that FMM is based on more sensible assumptions (i.e. deprivation covary within each class), provides valuable information with which to understand multiple deprivation and is useful to understand severity of deprivation and the additive properties of deprivation indicators

    A comparative analysis of Patient-Reported Expanded Disability Status Scale tools.

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    BACKGROUND: Patient-Reported Expanded Disability Status Scale (PREDSS) tools are an attractive alternative to the Expanded Disability Status Scale (EDSS) during long term or geographically challenging studies, or in pressured clinical service environments. OBJECTIVES: Because the studies reporting these tools have used different metrics to compare the PREDSS and EDSS, we undertook an individual patient data level analysis of all available tools. METHODS: Spearman's rho and the Bland-Altman method were used to assess correlation and agreement respectively. RESULTS: A systematic search for validated PREDSS tools covering the full EDSS range identified eight such tools. Individual patient data were available for five PREDSS tools. Excellent correlation was observed between EDSS and PREDSS with all tools. A higher level of agreement was observed with increasing levels of disability. In all tools, the 95% limits of agreement were greater than the minimum EDSS difference considered to be clinically significant. However, the intra-class coefficient was greater than that reported for EDSS raters of mixed seniority. The visual functional system was identified as the most significant predictor of the PREDSS-EDSS difference. CONCLUSION: This analysis will (1) enable researchers and service providers to make an informed choice of PREDSS tool, depending on their individual requirements, and (2) facilitate improvement of current PREDSS tools.University of Southampton and National Institute of Health Research (NIHR)

    Mixture of latent trait analyzers for model-based clustering of categorical data

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    Model-based clustering methods for continuous data are well established and commonly used in a wide range of applications. However, model-based clustering methods for categorical data are less standard. Latent class analysis is a commonly used method for model-based clustering of binary data and/or categorical data, but due to an assumed local independence structure there may not be a correspondence between the estimated latent classes and groups in the population of interest. The mixture of latent trait analyzers model extends latent class analysis by assuming a model for the categorical response variables that depends on both a categorical latent class and a continuous latent trait variable; the discrete latent class accommodates group structure and the continuous latent trait accommodates dependence within these groups. Fitting the mixture of latent trait analyzers model is potentially difficult because the likelihood function involves an integral that cannot be evaluated analytically. We develop a variational approach for fitting the mixture of latent trait models and this provides an efficient model fitting strategy. The mixture of latent trait analyzers model is demonstrated on the analysis of data from the National Long Term Care Survey (NLTCS) and voting in the U.S. Congress. The model is shown to yield intuitive clustering results and it gives a much better fit than either latent class analysis or latent trait analysis alone

    Predictive factors for overactive bladder symptoms after pelvic organ prolapse surgery

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    Contains fulltext : 89696.pdf (publisher's version ) (Closed access)INTRODUCTION AND HYPOTHESIS: This study focussed on the factors which predict the presence of symptoms of overactive bladder (OAB) after surgery for pelvic organ prolapse (POP). METHODS: Consecutive women who underwent POP surgery with or without the use of vaginal mesh materials in the years 2004-2007 were included. Assessments were made preoperatively and at follow-up, including physical examination (POP-Q) and standardised questionnaires (IIQ, UDI and DDI). RESULTS: Five hundred and five patients were included with a median follow-up of 12.7 (6-35) months. Bothersome OAB symptoms decreased after POP surgery. De novo bothersome OAB symptoms appeared in 5-6% of the women. Frequency and urgency were more likely to improve as compared with urge incontinence and nocturia. The best predictor for the absence of postoperative symptoms was the absence of preoperative bothersome OAB symptoms. CONCLUSION: The absence of bothersome OAB symptoms preoperatively was the best predictor for the absence of postoperative symptoms.1 september 201
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