1,721,153 research outputs found
Advanced Optical Techniques for micro-Fluid Dynamics
No full textThe impact of microfluidic technologies in the field of life sciences has dramatically increased during the last years, due to the need to develop new products for real applications. The work reported in the present dissertation is focused on the development of optical systems for the study of fluid dynamic phenomena at the micro and nano-scale. The research activities were carried out in the frame of two main topics and, consequently, the dissertation is divided into two main parts.
The first part of the dissertation is focused on the experimental study of cavitation in liquids, in which a bubble is generated by focusing a laser beam under extremely controlled conditions. The aim is addressing all different phases of the process. Cavitation is studied using a combined system of a fast camera, for the complete reconstruction of the plasma shape and bubbles dynamics, and a fiber optical hydrophone (FOHP), for the detection of the pressure shock waves in proximity of the bubble. The breakdown phenomenon and the bubble dynamics have been characterized when the optical arrangement of the focusing system is modified, e.g. using different expansion factors of the beam expander to change the focusing angle of the laser beam, or when the laser pulse energy is tuned. Data analysis shows a strong correlation between the number of plasma sites and the number of shock waves detected by the fiber hydrophone.
The second part of the dissertation is focused on the study of a particular class of surface electromagnetic waves and on their use for sensing applications. Such waves are sustained at the surface of finite one-dimensional photonic crystals (1DPC) and are generally named Bloch surface waves (BSW). The robustness of optical sensors based on BSW has been investigated experimentally and numerically. The distributions of sensor characteristics caused by the fabrication uncertainties in dielectric layer thicknesses have been analysed. It is demonstrated that the performance of the surface wave sensors is sufficiently robust with respect to the changes of the photonic crystal layer thicknesses. Layer thickness optimization of the photonic crystal, carried out to achieve low limit of detection, leads to an improvement of the robustness of the surface wave sensors that is attributed to Bloch states lying deeper in the photonic band gap.
The work reported in the dissertation demonstrates the use of an optical sensing platform based on BSW as a novel optical tool to probe in real time the fluid flow at a boundary wall of a microfluidic channel under dynamic conditions. Exploiting the properties of the BSW, we can put into evidence the temporal evolution of the interface during the injection of liquids with different refractive index (RI). We introduce ξ defined as the distance between the interface of the liquids of different RI and the 1DPC surface. Reconstructed experimental maps of ξ(z,t), as a function of time and of the position across the μ-fluidic channel, allow us to recovery the temporal evolution of the fluids interface in proximity of the wall. From the data analysis, the diffusion coefficient of a solute in water is measured and found in good agreement with the literature value.
Moreover, biosensors based on BSWs have been studied and their practical application was demonstrated by detecting a specific glycoprotein, Angiopoietin 2, that is involved in angiogenesis and inflammation processes, and to detect clinically relevant concentrations of the breast cancer biomarker ERBB2 in cell lysates. The protocol used for the label-free detection of Angiopoietin 2 is described and the results of an exemplary assay are given, confirming that an efficient detection can be achieved. The limit of detection of the biochips for Angiopoietin 2, based on the protocol used, is 1.5 pg/mm^2 in buffer solution. To detect soluble ERBB2, we develoed an optical set-up which operates in both label-free and fluorescence modes. The resolution obtained in both modes meet international guidelines and recommendations (15 ng/mL ) for ERBB2 quantification assays, providing an alternative tool to phenotype and diagnose molecular cancer subtypes.
During the last part of the doctorate period, the two research directions pursued during the first and the second part, devoted to bubble cavitation and to BSW based sensors, merged in a new innovative setup. Starting from the BSW concept, a new type of optical hydrophone based on BSW for the detection of pressure shock waves with a larger sensitivity than FOHP has been proposed and setup. Some preliminary and encouraging results are presented and discussed
Vacuum Instability and Pair Production in an Optical Setting
No full textIn the Dirac-sea picture, the physics of pair production and instability of the quantum electrodynamics
vacuum in presence of an oscillating electric field resembles the phenomenon of interband transition of
light waves in photonic superlattices induced by a geometric curvature. We realize a binary wave guide
superlattice with a curved optical axis mimicking dynamical pair production induced by two counterpropagating
ultrastrong laser pulses. Our optical analogue enables visualization of formation of electronpositron
pair in physical space as splitting of a wave packet, originally representing an electron in the
Dirac sea
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
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