1,720,977 research outputs found
Selbstgetriebene Teilchen durch Licht
No full textIn this thesis I review the main features of active systems, both biological and artificial, and I propose a novel technique to obtain self-propelling microscopic colloids. To achieve the propulsion we exploit the phoretic forces that come into play when a Janus particle modifies asymmetrically its surrounding. A lot of experimental effort is dedicated to design active colloids that approximately behave as self-propelled hard spheres. This allows us to investigate the role of the active motion to induce more complex phenomena when bulk conditions are lost. To support our experimental findings we actively compare our results with numerical simulation of interacting hard colloids. We indeed find that the off-equilibrium physics that describes these active objects is rich of novel surprising features.In dieser Arbeit untersuche ich die wesentlichen Eigenschaften biologischer und künstlicher aktiver Systeme und stelle eine neue Technik zur Herstellung von selbstgetriebenen mikroskopischen Kolloiden vor. Um den Antrieb zu erhalten nutzen wir phoretische Kräfte, welche ins Spiel kommen, wenn ein Janus-Teilchen seine Umgebung asymmetrisch verändert. Erheblicher experimenteller Aufwand wird der Entwicklung aktiver Kolloide gewidmet, welche sich näherungsweise als selbstgetriebene harte Kugeln verhalten. Dies ermöglicht es uns, die Rolle der aktiven Bewegung hinsichtlich ihrer Phänomene unter komplexeren Bedingungen zu untersuchen. Zur Unterstützung unserer experimentellen Erkenntnisse vergleichen wir diese mit numerischen Simulationen von miteinander wechselwirkenden harten Kugeln. Tatsächlich beobachten wir, dass die Nichtgleichgewichtsphysik, welche diese aktiven Objekte beschreibt, voller neuer und überraschender Besonderheiten steckt
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
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
Sedimentation and Levitation of Catalytic Active Colloids
Full text linkGravitational effects in colloidal suspensions can be easily turned off by
matching the density of the solid microparticles with the one of the
surrounding fluid. By studying the motion of catalytic microswimmers with
tunable buoyant weight, we show that this strategy cannot be adopted for active
colloidal suspensions. If the average buoyant weight decreases, pronounced
accumulation at the top wall of a sample cell is observed due to a
counter-alignment of the swimming velocity with the gravitational field. Even
when the particles reach a flat wall, gravitational torques still determine the
properties of the quasi two-dimensional active motion. Our results highlight
the subtle role of gravity in active systems.Comment: 4 pages, 4 figure
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