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High-Speed Imaging and Electrochemical Studies during the Freezing of Supercooled Aqueous Droplets
Get PDFIn der vorliegenden Arbeit werden Wassertropfen mit einem Durchmesser von etwa 2-3 mm akustisch levitiert
oder zwischen sehr dünnen Drahtringen positioniert, um Randeffekte zu vermeiden,
und um bis zu 24 K unterkühlt. Weil die Schmelzenthalpie nicht schnell genug an die Umgebung abgegeben
werden kann und nur teilweise im Tropfen gespeichert werden kann, spaltet sich der Gefrierprozess
in zwei Phasen auf. Per Hochgeschwindigkeitskamera wird in einem für diese Arbeiten entwickelten Kühlsystem
in unterkühlten Wassertropfen ein Eiswachstum mit konstanter, schneller Geschwindigkeit
beobachtet. Sie liegt in der Größenordnung von 0,1 m/s und wächst mit steigender Unterkühlung zunächst
linear bis quadratisch an. Dagegen wird für stark unterkühlte Tropfen eine Tendenz zu einem
Geschwindigkeitsmaximum beobachtet. Es wird ein neues Modell zur Beschreibung der Gefriergeschwindigkeit
vorgestellt, welches in gutem Einklang mit den experimentellen Befunden steht.
Um die komplexen Wärmeproduktions- und -transportprozesse beim Gefrieren der Tropfen
zu erfassen, wurden zwei Modelle im Rahmen von FEM-Simulationen entwickelt und damit die
Evolution der Verteilungen von Wärme und dendritischem Eis für viele Kombinationen von Radius,
Unterkühlung, Gefriergeschwindigkeit und relativer Tropfengeschwindigkeit berechnet. Es
wird gezeigt, dass erst für sehr kleine Tropfen die Oberfläche groß genug ist,
um einen signifikanten Anteil der Schmelzwärme an die Umgebung abzugeben und der kritische Radius,
der ein einstufiges Gefrieren ermöglicht, zwischen 0,1 und 1 Mikrometern zu erwarten
und hauptsächlich von der Unterkühlung sowie der Gefriergeschwindigkeit abhängig ist.
Diese Grenze liegt innerhalb der Größenverteilung der unterkühlten Tropfen in der Atmosphäre.
Als ein wesentliches Ergebnis dieser Arbeit werden erstmalig jeweils ein elektrischer Effekt für
die erste und die zweite Gefrierstufe an unterkühlten Tropfen beobachtet und untersucht. Der
Effekt in der ersten Gefrierstufe zeigt einen charakteristischen Doppelpeak mit einer Amplitude
von bis zu 3 V, ist abhängig von der Art der Ionen und der Unterkühlung. Während der Effekt
für höhere Konzentrationen abrupt einbricht, verschwindet er nicht mit abnehmender Ionenkonzentration.
Der beobachtete Effekt der zweiten Gefrierstufe ähnelt in seiner Gestalt dem bekannten
Workman-Reynolds-Effekt und ist in seiner Stärke und Polarität von der vorausgehenden dendritischen Phase,
insbesondere von ihrer Gefrierrichtung, abhängig.In this work water droplets with a diameter of about 2-3 mm are levitated acoustically or
positioned between thin wire loops to minimize wall effects and cooled down up to 249 K.
Because the heat cannot be released to the environment quickly enough and can only be partially stored in the system,
the freezing process splits in two stages. In this work fast and constant freezing speeds of
supercooled water droplets are measured with a high-speed camera in a newly developed cooling chamber.
The ice grows roughly planar through the droplet. Furthermore, details of the dendritic structure are noted
in some cases. The freezing speed is in the order of 0.1 m/s and increases with supercooling linearly
to quadratically, but for the strongest supercoolings the freezing speed tends to reach a maximum.
Based on the theory of Wilson and Frenkel a new model is presented, which predicts the freezing speed
as a function of supercooling under consideration of the dendritic freezing stage and is in good agreement
with the experimental data. Two new finite element models are have been developed to unravel the complex
heat production and transfer processes during the whole freezing of the supercooled droplets.
So, the evolution of heat and ice portion are computed for many combinations of droplet radii, supercoolings,
freezing speeds and relative droplet speeds. It is shown, that only for very small droplets a significant
portion of the freezing enthalpy is released to the environment. As a further important result
the critical radius, which allows a one step freezing, is estimated to exist between 0.1 and 1 micrometers.
This critical radius depends mainly on the supercooling temperature and the freezing speed and
meets well the size distribution of droplets in the atmosphere.
Further results are the observation of two electric effects during both freezing steps. The
effect in the first step shows a characteristic double peak with an amplitude of 3 V and depends
on sort and concentration of the ions as well as on the supercooling. Whereas the effect vanishes
for high concentrations, it persist to exist even for very low concentrations in contrast to the
Workman-Reynolds-freezing-potential. The characteristics of this effect in the second freezing
step is similar to the WRFP and the polarity as well as the strength of the effect are depending on
the direction of proceeding dendritic freezing step.
The findings are relevant in particular for atmospheric physics and chemistry
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
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
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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