1,720,967 research outputs found
Enforcing temporal consistency in physically constrained flow field reconstruction with FlowFit by use of virtual tracer particles
No full textAbstract Processing techniques for particle-based optical flow measurement data such as 3D particle tracking velocimetry (PTV) or the novel dense Lagrangian particle tracking method ‘Shake-the-Box’ (STB) can provide time-series of velocity and acceleration information scattered in space. The following post-processing is key to the quality of space-filling velocity and pressure field reconstruction from the scattered particle data. In this work we describe a straight-forward extension of the recently developed data assimilation scheme FlowFit, which applies physical constraints from the Navier–Stokes equations in order to simultaneously determine velocity and pressure fields as solutions to an inverse problem. We propose the use of additional artificial Lagrangian tracers (virtual particles), which are advected between the flow fields at single time instants to achieve meaningful temporal coupling. This is the most natural way of a temporal constraint in the Lagrangian data framework. FlowFit’s core method is not altered in the current work, but rather its input in the form of Lagrangian tracks. This work shows that the introduction of such particle memory to the reconstruction process significantly improves the resulting flow fields. The method is validated in virtual experiments with two independent DNS test cases. Several contributions are revised to explain the improvements, including correlations of velocity and acceleration errors in the reconstructions and the flow field regularization within the inverse problem
Extremes of fractional noises: A model for the timings of arrhythmic heart beats in post-infarction patients
No full textWe have analyzed symbol sequences of heart beat annotations obtained from 24-h electrocardiogram recordings of 184 post-infarction patients (from the Cardiac Arrhythmia Suppression Trial database, CAST). In the symbol sequences, each heart beat was coded as an arrhythmic or as a normal beat. The symbol sequences were analyzed with a model-based approach which relies on two-parametric peaks over the threshold (POT) model, interpreting each premature ventricular contraction (PVC) as an extreme event. For the POT model, we explored (i) the Shannon entropy which was estimated in terms of the Lempel–Ziv complexity, (ii) the shape parameter of the Weibull distribution that best fits the PVC return times, and (iii) the strength of long-range correlations quantified by detrended fluctuation analysis (DFA) for the two-dimensional parameter space. We have found that in the frame of our model the Lempel–Ziv complexity is functionally related to the shape parameter of the Weibull distribution. Thus, two complementary measures (entropy and strength of long-range correlations) are sufficient to characterize realizations of the two-parametric model. For the CAST data, we have found evidence for an intermediate strength of long-range correlations in the PVC timings, which are correlated to the age of the patient: younger post-infarction patients have higher strength of long-range correlations than older patients. The normalized Shannon entropy has values in the range 0.5<hLZ<1.0 which indicates a high degree of randomness in the PVC timings. For the CAST and the model data, the ranges of both measures were found to be in good accordance. The correlation between the age and the persistence strength found for the CAST data could be explained as a change of model parameters
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Über das Potential von lagrangem Transport in der Strömungsfeldrekonstruktion unter physikalischen Nebenbedingungen (On the Potential of Lagrangian Transport in Physically Constrained Flow Field Reconstructions)
No full textModerne Strömungsmessverfahren basieren auf Hochgeschwindigkeitskameraaufnahmen von in der Strömung mitbewegten Tracer Partikeln in ausgeleuchteten Ebenen oder Volumina. Die Bildverarbeitung sowie die zum Tracking eingesetzten Algorithmen spielen dabei eine Schlüsselrolle was die Qualität und Genauigkeit der erzeugten Daten betrifft. Die robuste Shake-The-Box Methode [Schanz et al., 2013] ermöglicht akkurates Partikeltracking auch bei hohen Partikeldichten, liefert jedoch räumlich versprenkelte Informationen. Aufwendige Interpolationsalgorithmen wurden entwickelt um unter Zuhilfenahme weiterer physikalischer Nebenbedingungen aus den Navier-Stokes Gleichungen zugleich Geschwindigkeits- und Beschleunigungsfelder als Lösung eines inversen Problems zu rekonstruieren. Damit ist es praktisch möglich, das klassische Nyquistlimit zu unterschreiten. Die volle zeitliche Entwicklung der Felder wurde bisher jedoch entweder nicht berücksichtigt [Gesemann et al., 2016] oder die zeitliche Kopplung durch aufwendige Zeitintegrationsverfahren resultierte in hohem Rechenaufwand [Schneiders and Scarano, 2018]. Diese Arbeit zeigt auf, dass die zeitliche Kopplung einzelner Zeitschritte durch virtuelle Lagrange Tracerpartikel die Rekonstruktionsfehler senken kann. Hierzu wurden künstliche Experimente auf Basis von DNS Rechnungen verwendet. Der Einfluss zusätzlicherFaktoren wie den Fehlerkorrelationen oder der Regularisierung des inversen Problems wird diskutiert.
Flow field measurements are nowadays performed with high-speed camera recordings of tracer particles in an illuminated fluid layer or volume. The following postprocessing is key to the quality of the resulting velocity and/or acceleration fields. Dense 3D particle tracking following the Shake-The-Box method [Schanz et al., 2013] yields accurate but scattered data. Sophisticated interpolation schemes were proposed that can make use of further physical constraints from the Navier-Stokesequations in order to simultaneously determine velocity and acceleration fields as solutions to an inverse problem. This allows to resolve structures beyond the classical Nyquist limit for each single field variable. So far, the full temporal domain has either not been considered yet [Gesemann et al., 2016] or the temporal coupling of several time instants via simulation methods resulted in high computational costs [Schneiders and Scarano, 2018]. This work shows that the introduction of memory to the reconstruction process (by temporal coupling) results in improved flow field reconstructions of artificial DNS experiments. For this purpose, additional artificial Lagrangian tracers (virtual particles) were advected between the fields, which is the most natural way to achieve temporal coupling in the framework of such algorithms. Several contributions like reconstruction error correlations and the flow field regularization within the inverse problem were revised to explain the improvements
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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