1,720,963 research outputs found
Shape Instability and Topology in Ferroelectric Nematic Fluids - Study and Optical Control
No full textL'innovativa scoperta dei cristalli liquidi ferroelettrici nematici, identificati come tali nel 2020, introduce un nuovo stato della materia, sia ferroelettrico che completamente liquido, che porta a un'ampia gamma di effetti fisici inediti. In questo lavoro di tesi, abbiamo utilizzato un cristallo ferroelettrico, il Niobato di Litio, come piattaforma per manipolare e studiare la risposta del fluido ferroelettrico, sfruttando gli effetti piroelettrici e fotovoltaici del solido che convertono gli stimoli termici e luminosi in campi elettrici. Si studiano fenomeni elettrodinamici come l'instabilità di forma e il movimento dielettroforetico e si studiano la topologia dei domini polari in celle sottili. Dimostriamo anche il controllo ottico di tutti questi fenomeni, utilizzando substrati di Niobato di Litio irradiati da un laser focalizzato. In particolare, è possibile indurre e manipolare l'emissione di getti di fluido e il movimento delle gocce; d'altra parte, lo spot laser può generare un allineamento radiale dei domini polari, domini twistati o linee di difetto, a seconda della configurazione del setup. I risultati qui riportati contribuiscono alla comprensione del comportamento fisico di questa nuova classe di fluidi complessi e costituiscono un punto di partenza per progettare nuove applicazioni tecnologiche nel campo dell'opto-microfluidica, della robotica fluida e del poling ottico in sistemi liquidi.The groundbreaking discovery of Ferroelectric Nematic Liquid Crystals, identified as such in 2020, introduces a new state of the matter, both ferroelectric and fully liquid, leading to a broad range of novel physical effects. In this thesis work, we used a ferroelectric crystal, the Lithium Niobate, as a platform to manipulate and study the ferroelectric fluid response, exploiting the pyroelectric and photovoltaic effects of the solid that convert thermal and light stimuli in electric fields. The investigation of electro-dynamical phenomena such as shape instability and dielectrophoretic motion is reported, together with the study of polar domain patterns in thin cells. We also demonstrate the optical control of all these phenomena, using Lithium Niobate substrates irradiated by a focused laser. In particular, it is possible to induce and manipulate the emission of fluid jets and the droplet motion; on the other hand, the laser spot can generate radial alignment of the polar domains, π-twisted domains or line defects, depending on the setup configuration. The results reported here contribute to the understanding of the physical behavior of this new class of complex fluids and constitute a starting point to design new technological applications in the field of opto-microfluidic, soft robotics and optical poling in liquid systems
Optical Poling of Ferroelectric Liquids
Full text linkFerroelectric nematic liquid crystals combine fluidity, spontaneous polarity, optical birefringence, and strong nonlinear response, unlocking a rich landscape of phenomena and control strategies yet to be fully explored. Here, all-optical manipulation of polar domains and topological textures in ferroelectric nematic cells assembled from lithium niobate plates is demonstrated. In these devices, the photovoltaic response of the solid substrate couples to the fluid's polar director, enabling light-driven reorganization of the ferroelectric alignment. Under focused illumination in parallel-rubbed cells, the emergence of submillimeter-scale spiral-shaped radial domains is observed, in excellent agreement with the underlying material properties. Furthermore, it is shown that both domain structures and wall configurations can be reversibly reconfigured by varying light exposure, thereby tuning the degree of domain fragmentation and wall unpinning. These results establish light-induced polarization patterning as a versatile tool for dynamic control of nematic ferroelectric order, with promising applications in the design of reconfigurable linear and nonlinear photonic devices
Optical control of mass ejection from ferroelectric liquid droplets: A possible tool for the actuation of complex fluids
Full text linkWe report on the optical control of the recently observed electromechanical instability of ferroelectric liquid droplets exposed to the photovoltaic field of a lithium niobate ferroelectric crystal substrate. The ferroelectric liquid is a nematic liquid crystal in which almost complete polar ordering of the molecular dipoles generates an internal macroscopic polarization locally collinear to the mean molecular long axis. Upon entering the ferroelectric phase, droplets irradiated by unfocused beam undergo an electromechanical instability and disintegrate by the explosive emission of fluid jets. We show here that the regions of jets emission can be controlled by focusing the light beam in areas close to the droplet's edge. Once emitted, the fluid jets can be walked by moving the beam up to millimeter distance from the mother droplet. Reverting the lithium niobate substrate, jets become thinner and show the tendency of being repelled by the beam instead of being attracted, thus offering an additional tool for their optical manipulation. These observations may pave the way to intriguing applications of ferroelectric nematic fluids related to manipulation, actuation, and control of soft, flexible materials
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
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