10,371 research outputs found

    The Core, Periphery, and Beyond: Stock Market Comovements among EU and Non-EU Countries

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    We thank conference participants at the 2016 Financial Management Association and our discussant Fernando Moreira, and two anonymous referees for immensely helpful comments. We also thank Andrew Patton and James P. LeSage for sharing their MATLAB codes for computing quantile dependence. The authors of this paper are responsible for any errors or omissions. The Securities and Exchange Commission, as a matter of policy, disclaims responsibility for any private publication or statement by any of its employees. The views expressed herein are those of the authors and do not necessarily reflect the views of the Commission or the authors\u27 colleagues on the staff of the Commission

    The analysis of very small samples of repeated measurements II: a modified box correction

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    There is a need for appropriate methods for the analysis of very small samples of continuous repeated measurements. A key feature of such analyses is the role played by the covariance matrix of the repeated observations. When subjects are few it can be difficult to assess the fit of parsimonious structures for this matrix, while the use of an unstructured form may lead to a serious lack of power. The Kenward-Roger adjustment is now widely adopted as a means of providing an appropriate inferences in small samples, but does not perform adequately in very small samples. Adjusted tests based on the empirical sandwich estimator can be constructed that have good nominal properties, but are seriously underpowered. Further, when such data are incomplete, or unbalanced, or non-saturated mean models are used, exact distributional results do not exist that justify analyses with any sample size. In this paper, a modification of Box's correction applied to a linear model based FF-statistic is developed for such small sample settings and is shown to have both the required nominal properties and acceptable power across a range of settings for repeated measurements

    Head and pelvic movement asymmetry during lungeing in horses with symmetrical movement on the straight

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    REASONS FOR PERFORMING STUDY: Lungeing is commonly used as part of standard lameness examinations in horses. Knowledge of how lungeing influences motion symmetry in sound horses is needed. OBJECTIVES: The aim of this study was to objectively evaluate the symmetry of vertical head and pelvic motion during lungeing in a large number of horses with symmetric motion during straight line evaluation. STUDY DESIGN: Cross‐sectional prospective study. METHODS: A pool of 201 riding horses, all functioning well and considered sound by their owners, were evaluated in trot on a straight line and during lungeing to the left and right. From this pool, horses with symmetric vertical head and pelvic movement during the straight line trot (n = 94) were retained for analysis. Vertical head and pelvic movements were measured with body mounted uniaxial accelerometers. Differences between vertical maximum and minimum head (HDmax, HDmin) and pelvic (PDmax, PDmin) heights between left and right forelimb and hindlimb stances were compared between straight line trot and lungeing in either direction. RESULTS: Vertical head and pelvic movements during lungeing were more asymmetric than during trot on a straight line. Common asymmetric patterns seen in the head were more upward movement during push‐off of the outside forelimb and less downward movement during impact of the inside limb. Common asymmetric patterns seen in the pelvis were less upward movement during push‐off of the outside hindlimb and less downward movement of the pelvis during impact of the inside hindlimb. Asymmetric patterns in one lunge direction were frequently not the same as in the opposite direction. CONCLUSIONS: Lungeing induces systematic asymmetries in vertical head and pelvic motion patterns in horses that may not be the same in both directions. These asymmetries may mask or mimic fore‐ or hindlimb lameness

    Movements of feral camels in central Australia determined by satellite telemetry

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    Movements of two female one-humped camels in central Australia were tracked using satellite telemetry between March 1986 and July 1987. During that time both animals travelled a minimum distance of over 1000 km within a radius of 125 km for one animal, and 200 km for the other. However, their movements were uite punctuated and both animals spent periods of up to several months in rleatively small areas before moving over longer distances to new areas. Both camels moved at greater rates overnight. An activity index, probably measuring feeding rate, declined during the study period for both animals. Patchy and sporadic rainfall may explain some of these results

    Length of Stay after Vaginal Birth: Sociodemographic and Readiness-for-Discharge Factors

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    Background: The impact of reductions in postpartum length of stay have been widely reported, but factors influencing length of hospital stay after vaginal birth have received less attention. The study purpose was to compare the sociodemographic characteristics and readiness for discharge of new mothers and their newborns at 3 discharge time intervals, and to determine which variables were associated with postpartum length of stay. Methods: The study sample comprised 1,192 mothers who were discharged within 2 postpartum days after uncomplicated vaginal birth at a tertiary perinatal center in the midwestern United States. The sample was divided into 3 postpartum length-of-stay groups: group 1 (18–30 hr), group 2 (31–42 hr), and group 3 (43–54 hr). Sociodemographic and readiness-for-discharge data were collected by self-report and from a computerized hospital information system. Measures of readiness for discharge included perceived readiness (single item and Readiness for Discharge After Birth Scale), documented maternal and neonatal clinical problems, and feeding method. Results: Compared with other groups, the longest length-of-stay group was older; of higher socioeconomic status and education; and with more primiparous, breastfeeding, white, married mothers who were living with the baby’s father, had adequate home help, and had a private payor source. This group also reported greater readiness for discharge, but their newborns had more documented clinical problems during the postbirth hospitalization. In logistic regression modeling, earlier discharge was associated with young age, multiparity, public payor source, low socioeconomic status, lack of readiness for discharge, bottle-feeding, and absence of a neonatal clinical problem. Conclusions: Sociodemographic chracteristics and readiness for discharge (clinical and perceived) were associated with length of postpartum hospital stay. Length of stay is an outcome of a complex interface between patient, provider, and payor influences on discharge timing that requires additional study. Including perceived readiness for discharge in clinical discharge criteria will add an important dimension to assessment of readiness for discharge after birth

    Avian malaria is absent in juvenile colonial herons (Ardeidae) but not Culex pipiens mosquitoes in the Camargue, Southern France

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    Apicomplexan blood parasites Plasmodium and Haemoproteus (together termed “Avian malaria”) and Leucocytozoon are widespread, diverse vector-transmitted blood parasites of birds, and conditions associated with colonial nesting in herons (Ardeidae) and other waterbirds appear perfect for their transmission. Despite studies in other locations reporting high prevalence of parasites in juvenile herons, juvenile Little Egrets (Egretta garzetta) previously tested in the Camargue, Southern France, had a total absence of malaria parasites. This study tested the hypotheses that this absence was due to insufficient sensitivity of the tests of infection; an absence of infective vectors; or testing birds too early in their lives. Blood was sampled from juveniles of four species shortly before fledging: Little Egret (n = 40), Cattle Egret (Bubulcus ibis; n = 40), Black-crowned Night-Heron (Nycticorax nycticorax, n = 40), and Squacco Heron (Ardeola ralloides; n = 40). Sensitive nested-Polymerase Chain Reaction was used to test for the presence of parasites in both birds and host-seeking female mosquitoes captured around the colonies. No malaria infection was found of in any of the heron species. Four different lineages of Plasmodium were detected in pooled samples of female Culex pipiens mosquitoes, including two in potentially infective mosquitoes. These results confirm that the absence of malaria parasites previously demonstrated in Little Egret is not due to methodological limitations. Although the prevalence of infection in mosquitoes was low, conditions within the colonies were suitable for transmission of Plasmodium. These colonial heron species may have evolved strategies for resisting malaria infection through physiological or behavioral mechanisms

    On the properties of GEE estimators in the presence of invariant covariates

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    In this paper it is shown that the use of non-singular block invariant matrices of covariates leads to `generalized estimating equations' estimators (GEE estimators; Liang, K.-Y.&Zeger, S. (1986). Biometrika, 73(1), 13-22) which are identical regardless of the `working' correlation matrix used. Moreover, they are efficient (McCullagh, P. (1983). The Annals of Statistics, 11(1), 59-67). If on the other hand only time invariant covariates are used the efficiency gain in choosing the `correct' vs. an `incorrect' correlation structure is shown to be negligible. The results of a simple simulation study suggest that although different GEE estimators are no more identical and are no more as efficient as an ML estimator, the differences are still negligible if both time and block invariant covariates are present

    Μελέτη επί της τρισδιάστατης απεικόνισης και αυτόματης ανακατασκευής τρισδιάστατων προϊστορικών αγγείων

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    88 σ.Στην παρούσα διπλωματική εργασία γίνεται, αρχικά, μία αναφορά σε αρχές της θεωρίας των καμπυλών και επιφανειών της διαφορικής γεωμετρίας οι οποίες αποτελούν ένα απαραίτητο μαθηματικό υπόβαθρό της σχετικής προσέγγισης. Δίνεται έμφαση σε βασικές έννοιες, όπως της καμπύλης, της επιφάνειας αλλά και άλλων μεγεθών-εργαλείων που τις συνοδεύουν, ούτως ώστε να γίνει εφικτή η προσέγγιση στο θέμα της αυτόματης ανασυγκρότησης θραυσμάτων. Στην συνέχεια, ακολουθεί περιγραφή της επεξεργασίας, την οποία υπέστησαν τρισδιάστατες απεικονίσεις θραυσμάτων αγγείων, οι οποίες προέρχονται από την τρισδιάστατη σάρωση των πραγματικών θραυσμάτων με τρισδιάστατο σαρωτή. Η παραπάνω επεξεργασία αποτελεί προκαταρκτικό στάδιο για την εφαρμογή μίας νέας μεθόδου η οποία προσφέρει αποτελεσματική λύση στο πρόβλημα της αυτόματης εικονικής ανασυγκρότησης των θραυσμένων αγγείων για την οποία γίνεται αναφορά στη συνέχεια.In this thesis, initially, a report on principles of the theory of curves and surfaces, in differential geometry, takes place. These principles are the mathematical background of this thesis. The understanding of basic concepts such as curve , surface and other sizes–tools which surround them, is emphasized thanks to which the approach to automatic reconstruction of fragments is feasible. Then, follows a description of the processing that was applied in three-dimensional representations of broken vessels. These represantations derived from the three-dimensional scan of the real fragments with three-dimensional scanner. The above process is a preliminary step for the implementation of a new method which is an effective solution to the problem of automatic virtual reconstruction of broken vessels to which reference is made below.Ιωάννης Γ. Κοτζά
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