1,720,959 research outputs found
Manipulation of droplets and cells in microfluidic platforms
No full textManipulation of liquid droplets and cells is crucial for several key processes such as heat transfer,
energy generation, and clinical diagnostics. In particular, encapsulation of single cells in droplets
is becoming a powerful tool to map cellular heterogeneity in diseased and healthy tissues, even
at the single-cell level.
This PhD thesis is focused on the development of engineered smart surfaces and microfluidic
Platforms for the manipulation of droplets and cells. The work has two main goals: on the one
hand, manipulation of water droplets by light patterns projected on engineered surfaces, and
on the other hand, encapsulation of cells within droplets in microfluidic devices designed for a
large variety of essays, primarily single-cell sequencing.
Manipulation of droplets on engineered surfaces. Lithium Niobate (LN) is a functional
Material characterized by photoactivated properties such as the photovoltaic effect: when
illuminated (typically by a laser) ,charge accumulation occurs at the two faces of the material. This
leads to the formation of virtual reconfigurable electrodes, which can be exploited to manipulate
neutral and charged fluids through dielectrophoretic and electrophoretic effects. As happens for
any solid surface, the motion of droplets on LN is hard to control over large distances because of
droplet pinning on surface defects. Taking inspiration from the natural world, a special coating,
called liquid-infused surface (LIS), is realized on the surface of the material. A liquid surface is
smooth down to the molecular scale and is a defect-free surface; therefore, it enables low-friction
droplet motion, avoiding uncontrolled pinning on surface defects. An optofluidic platform based
on the photovoltaic effect of Lithium Niobate is realized: droplets are actuated, merged, and
even split on illuminated LN, tuning a few experimental parameters such as droplet volume, the
illumination pattern, and light intensity. Remarkably, controlled merging and splitting, typically
performed in closed devices, is achieved by optowetting on an engineered surface.
Encapsulation of cells in microfluidic droplets. The second focus is on the manipulation
of cells within microfluidic channels. The main limitations of the use of cells in microfluidics
are their sedimentation inside the storage container and, for some applications, the necessity
to work in a highly diluted regime. Consequently, a cell mixing device (CMD) is developed
to limit cell sedimentation. It is characterized from a biological point of view, monitoring
cell viability under different experimental conditions, and studying the injection of cells into a
microfluidic device. It is discovered to play an important role in limiting cell sedimentation,
and cell viability is not affected. To increase the number of droplets with one cell encapsulated,
inertial microfluidic and Dean flows are exploited: it is possible to create stable trains, where
cells are aligned and separated one from each other. Then, the encapsulation of single cells
aligned via inertial microfluidics in droplets is investigated. This last step becomes crucial to
understand whether it is possible to increase the concentration of cells with respect to the case
of single-cell experiments, obtaining a larger number of droplets with one single cell inside. As a
consequence, the integration of the inertial microfluidics part with the single-cell encapsulation
part on the same microfluidic platform is finally discussed
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
Drop motion optically induced on photorefractive surfaces
Full text linkLa microfluidica di gocce è quella branca della fisica, cui uno degli obiettivi
fondamentali è produrre e manipolare gocce su substrati in modo attivo,
modificandone la bagnabilità . La tecnica comunemente sfruttata è
l’elettrowetting, che consiste nell’applicare una differenza di potenziale tra
l’elettrodo e la goccia in modo da polarizzarla e controllarne il movimento. Ma
l’eletrowetting presenta delle limitazioni: in primis non è caratterizzato da
riconfigurabilità in quanto sono necessari elettrodi fissi di metallo per applicare la
differenza di potenziale voluta ed inoltre costose strumentazioni sono necessarie
per costruire il device. Per risolvere le precedenti problematiche, negli ultimi anni
una nuova tecnica è stata sviluppata e chiamata optowetting: consiste nel creare
elettrodi virtuali riconfigurabili, illuminando in generale con luce visibile e
coerente dei materiali specifici. Una materiale adatto per l’optowetting è il
Niobato di Litio (LiNbO 3 ), il quale è caratterizzato da una proprietà chiamata
effetto fotovoltaico. In lavori svolti in precedenza, si è notato che le condizioni
ambientali (in particolare l’umidità), in cui le misure sono eseguite, possono
influenzare il processo di scarica del Niobato di Litio, quando il pattern di
illuminazione non risulta più esser presente. Questo progetto di tesi è
caratterizzato da 2 obiettivi principali: il primo consiste nel studiare il ruolo
dell’umidità sulla scarica del Niobato di Litio (bisogna aggiungere che in
letteratura non ci sono articoli che trattano di questo specifico tema). Per
raggiungere questo obiettivo una specifica camera per controllare l’umidità
attorno al campione in LiNbO 3 è creata ed il ruolo dell’umidità sulla scarica del
materiale è studiato tramite una misura indiretta, dato che non è possibile
misurare in modo diretto la densità di carica accumulata sulla superficie del
materiale al variare dell’umidità locale. Il secondo obiettivo della tesi consiste nel
manipolare in modo attivo gocce sulla superficie del materiale. Per ridurre
l’attrito tra la goccia in movimento e la superficie sottostante, sulla superficie di
LiNbO 3 è realizzato un coating in modo da ottenere una Liquid-Infused Surface
(LIS). Per illuminare il campione in LiNbO 3 uno Spatial-Light Modulator (SLM) è
utilizzato; questo dispositivo riceve la luce laser in input, la modula in fase e
permette di creare il pattern di illuminazione voluto sul campione. Per quanto
riguarda le misure relative alla mobilità di gocce, in primis l’attrazione di gocce
verso un pattern di illuminazione è studiato, monitorando come cambia il tempo
specifico di attrazione. Successivamente il moto di gocce lungo un pattern scelto
lineare o curvilineo è studiato; dopo di che il processo di merging tra 2 o più gocce
in movimento è ottenuto. Infine come misure preliminari vengono studiati il moto
di goccia lungo una striscia con un gradiente lineare di illuminazione e si è cercato
di ottenere lo splitting di una goccia in una o più parti
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
Fenomeni fotoindotti su cristalli liquidi in un dispositivo opto-microfluidico di LiNbO3
Full text linkIl seguente lavoro di tesi si occupa di studiare il processo di riorientazione dei cristalli liquidi sottoposti all'azione di un campo elettrico. Il set-up sperimentale si compone di una piattaforma opto-microfluidica integrata in niobato di litio, contenente un canale microfluidico in cui i cristalli liquidi possono esser inseriti e delle guide di luce, le quali opportunamente illuminate permettono di monitorare il fenomeno fisico cercato. Per produrre il campo elettrico vengono sfruttati gli effetti fotorifrattivo e fotovoltaico di volume, che caratterizzano il niobato di litio quando è soggetto ad illuminazione non omogenea. Sono state eseguite 5 run diverse di misure sperimentali in 5 giornate differenti per studiare la riproducibilità del fenomeno.
La tesi è strutturata in 3 parti fondamentali: nella prima parte viene presentato il niobato di litio, descrivendone la struttura cristallina e le principali proprietà fisiche. Nella seconda parte vengono descritti i cristalli liquidi, focalizzando l'attenzione sulle principali proprietà quali viscosità, ancoraggio ed interazioni con campi elettrici. Nella terza parte vengono presentate le misure sperimentali eseguite, descrivendo il set-up sperimentale, le misure di calibrazione ed i risultati ottenuti. Infine nella sezione conclusioni vengono proposti dei miglioramenti che si possono apportare al set-up sperimentale ed alla procedura di misura per studiare il fenomeno in modo più approfondito.
The following thesis deals with studying the reorientation process of liquid crystals subjected to the action of an electric field. The experimental set-up contains an opto-microfluidic platform made by lithium niobate, containing a microfluidic channel in which liquid crystals can be inserted inside and some waveguides, which allow to study the physical phenomenon, if they are under right illumination. The photorefractive effect and the bulk photovoltaic effect of lithium niobate, when it is under non homogeneous illumination
are used to produce the electric field. 5 different run of experimental measurements were done in 5 different days in order to study the physical phenomenon.
The thesis is divided into 3 fundamental parts: in the first part the lithium niobate is described, focusing the attention on the crystal structure and its physical properties. In the
second part liquid crystals are described, focusing the attention on some physical properties such as viscosity, anchoring and interactions with electric fields. In the third part the experimental set-up, the calibration measurements and the results obtained from the measurements are described. Finally in the section “Conclusions” some possible improvements of the experimental set-up and measurement procedure are described in order to study the physical phenomenon in a better way.ope
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