1,721,124 research outputs found
A modified Bowen ratio method to determine sensible and latent heat fluxes
No full textThe sensible heat flux (H) and the latent heat flux (λE) were measured above a grassland during June, 1997 (LINEX-97/1 Experiment), using the eddy covariance method (EC) and the Bowen ratio/Energy balance method (BREB). The results indicate that HBREB is about (30 ± 20) Wm-2 higher than HEC, and λEBREB is about (180 ± 40) Wm-2 higher than λEEC during the daytime, and this is mainly caused by an imbalance in the closure of the surface energy balance in the BREB. In order to avoid the inaccuracies associated with the surface energy balance method, we propose a modified Bowen ratio method (MBR) to determine sensible and latent heat fluxes without using the surface energy balance equation. The results and error analysis show that MBR can give more accurate results than BREB. For the MBR, a measurement system using a sonic anemometer together with temperature and humidity measurements at two levels is being recommended to obtain sensible and latent heat fluxes
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
Measuring and understanding site-specific wind and turbulence characteristics for wind energy applications
No full textOnshore wind energy has become the most important source of renewable energy in Germany. This success also lead to rapid developments in turbine technology. The strongly increased turbine size creates a need for the application of new measurement technologies to replace tall, expensive and inflexible measurement masts. For this reason, Doppler-lidar measurements have become increasingly popular in the wind energy community. Yet, for measurements in complex terrain and for turbulence measurements, conically scanning lidars still suffer from systematic errors. However, especially in complex terrain accurate measurements of the mean wind speed and turbulence intensity are key for resource and site suitability assessment, as modelling is often associated with high uncertainties. Also, the relation of observed turbulence quantities to surface characteristics and the atmospheric stability regime is often difficult for the experimentalist. This dissertation focuses on the aforementioned problems and presents different approaches to resolve them. The complex terrain error of conically scanning lidars is analysed experimentally and using flow modelling. The simulations revealed a high sensitivity to land cover, especially forest generally reduces the error. Among the investigated models, the linear flow model showed the worst performance in predicting the observed error. The RANS-models could reproduce the right pattern and magnitude of the lidar error. As an alternative the multi-lidar (ML) approach is investigated. The value of the ML-approach, when compared to a single conically scanning lidar, is demonstrated experimentally in complex terrain for the first time. Given an appropriate setup, measuring with two or three lidars in the same point significantly improved the agreement with a high quality reference measurement. This can greatly reduce the uncertainties of lidar measurements in complex flow regimes. The multi-lidar approach was also experimentally demonstrated to be a promising approach to measure turbulence statistics in complex terrain. In contrast, the conically scanning lidar showed a strong overestimation, when compared to the reference measurements. One of the problems which remains unsolved in the ML-approach is the attenuation of small scale turbulence by the spatial averaging of the lidar. This was also clearly visible in the spectral analysis of the ML-experiment. This dissertation approaches the problem by investigating the capability of a pulsed lidar to measure the dissipation rate of turbulent kinetic energy (TKE) using three different methods: A previously described method based on short term variances is corrected to remove significant systematic errors which were present. Moreover, a theoretically suggested method based on the structure function of the radial velocity fluctuations is experimentally evaluated for the first time. The third approach uses the power-spectral density in the inertial sub-range. It is shown that, given the knowledge about the spatial averaging function of the lidar and a careful removal of the noise, the dissipation rate of TKE can be estimated with a reasonable accuracy. However, the experimentally determined form of the spatial averaging function and the one derived from theoretical considerations showed significant differences. The differences between the investigated methods to derive the dissipation rate of TKE are mainly found in their applicability to different experimental setups with the structure-function approach providing the most flexible option. Finally, the dissertation investigates observed turbulence quantities and their relation to surface characteristics and stability at a 200-m-mast at a forested hilltop site. A simple approach based on footprint modelling is developed to characterise the surface ruggedness and roughness in the area of effect of the measurement. It is shown that especially the normalised standard deviation of the wind along the stream lines exhibits a high correlation to the surface characteristics within the footprint. Atmospheric stability also had a strong influence on the representative turbulence intensity at the investigated hilltop site. The prevalence of stable conditions for wind speeds between 6-12 m/s lead to a significantly reduced turbulence intensity in this wind speed range, which is in the order of the difference between standard turbulence classes for wind turbines.Die Windenergie an Land ist der wichtigste Energieträger unter den erneuerbaren Energien in Deutschland. Dieser Erfolg ging mit einer schnellen Entwicklung in der verwendeten Technologie einher. Mit den stark gewachsenen Anlagenhöhen werden klassische mastbasierte Messungen teuer und sind zudem unflexibel. Durch diesen Trend sind Lidar-Messungen in den vergangen Jahren im Bereich Windenergie immer populärer geworden. Allerdings sind diese im komplexen Gelände mit systematischen Fehlern behaftet und weisen bei der Messung von Turbulenz erhebliche Ungenauigkeiten auf. Demgegenüber sind besonders im komplexen Gelände Messungen der Windgeschwindigkeit und Turbulenzeigenschaften wichtig, da die Modellierung hier mit großen Unsicherheiten verbunden ist. Allgemein erweist sich auch die Interpretation experimentell bestimmter turbulenter Windbedingungen im komplexen und heterogenen Gelände als schwierig. Ebenso ist die Abschätzung des Einflusses der atmosphärischen Stabilität auf die repräsentative Turbulenzintensität, die zur Bestimmung der Eignung einer Windenergieanlage wichtig ist, oft schwierig. Die vorgelegte Dissertation befasst sich mit den beschriebenen Problemen und entwickelt dazu verschiedene Lösungsansätze. Zuerst wurde der Fehler eines konisch scannenden Lidars experimentell und mittels Strömungssimulation untersucht. In den Ergebnissen der Modellierung zeigte sich eine große Abhängigkeit des Lidar-Fehlers von der Oberflächenbedeckung. Bei einem bewaldeten Hügel war der Fehler gegenüber einer unbewaldeten Oberfläche deutlich reduziert. Auch zwischen den verwendeten Modellen zeigten sich große Unterschiede. So war die Übereinstimmung zwischen den RANS-Modellen und den experimentell bestimmten Fehlern deutlich besser als für das untersuchte lineare Model. Als Alternative zu konisch scannenden Lidars wurde die Multi-Lidar (ML) Methode für den Einsatz im komplexen Gelände untersucht. Dabei konnte erstmals experimentell gezeigt werden, dass die Messfehler in der mittleren Windgeschwindigkeit gegenüber konisch scannenden Lidars deutlich reduziert werden können, wenn zwei oder drei Lidars im gleichen Punkt messen. Dies bietet die Möglichkeit die Unsicherheiten in Lidar-Messungen im komplexen Gelände deutlich zu reduzieren. Auch bei den Turbulenzmessungen zeigte sich die ML-Methode als vielversprechend. Im Gegensatz dazu wurde bei der Messung des konisch scannenden Lidars eine deutliche Überschätzung der Referenzmessung beobachtet. Eines der ungelösten Probleme mit dem ML-Ansatz ist jedoch die Dämpfung kleiner Turbulenzskalen durch die räumliche Mittelung der Lidar-Messung. Dies konnte deutlich in der Analyse der Spektren aus dem ML-Experiment beobachtet werden. Die vorgelegte Dissertation untersucht in diesem Kontext die Möglichkeit aus Lidar-Messungen die Dissipationsrate turbulenter kinetischer Energie (TKE) abzuleiten. Dazu wurden drei Ansätze verglichen. Die erste Methode ist eine Weiterentwicklung und Korrektur eines zuvor veröffentlichten Ansatzes, der auf der Varianz der radialen Windgeschwindigkeit innerhalb kurzer Messperioden beruht. Gegenüber dem ursprünglichen Ansatz können durch die Weiterentwicklung erhebliche systematische Fehler vermieden werden. Der zweite Ansatz basiert auf der Strukturfunktion der radialen Windgeschwindigkeit und wurde bisher nur theoretisch beschrieben. In dieser Arbeit wird er zum ersten Mal experimentell überprüft. Der dritte Ansatz führt die Bestimmung der Dissipationsrate der TKE basierend auf einer Analyse der Powerspektren im Trägheitsbereich durch. Die Arbeit zeigt, dass es möglich ist die Dissipationsrate der TKE aus Lidar-Messungen mit zufriedenstellender Genauigkeit zu schätzen. Allerdings muss dazu die räumliche Mittelungsfunktion des Lidars bekannt sein. Bei der experimentellen Untersuchung der räumlichen Mittelungsfunktion zeigten sich jedoch signifikante Unterschiede zu den vorher durchgeführten theoretischen Überlegungen. Der Unterschied zwischen den Methoden zur Bestimmung der Dissipationsrate der TKE liegt vor allem in ihrer Anwendbarkeit auf verschiedene Messkonfigurationen. Hier zeigt die Methode basiernd auf der Strukturfunktion die größte Flexibilität. Neben der Entwicklung von Methoden im Bereich der Lidar-Messungen präsentiert die Arbeit auch Messungen verschiedener Turbulenzgrößen vom 200-m-Mast des Fraunhofer IWES am Rödeser Berg. Zur Interpretation des Zusammenhangs zwischen den Eigenschaften der Oberfläche im Einflussbereich der Messung und den Beobachtungen wurde ein einfaches Tool basierend auf dem Footprintansatz entwickelt. Besonders für die normalisierte Standardabweichung entlang der Strömungslinien zeigten sich hohe Korrelationen mit der Rauigkeit und dem Zerklüftungsgrad der Oberfläche im modellierten Footprint. Neben den Oberflächeneigenschaften hatte auch die atmosphärische Stabilität einen großen Einfluss auf die Turbulenzeigenschaften. Besonders im für die Ermüdungslasten wichtigen Bereich zwischen 6-12 m/s war die Turbulenzintensität aufgrund des häufigen Auftretens stabiler Schichtung signifikant reduziert
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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