1,720,968 research outputs found
Strategies for pushing nonlinear microscopy towards its performance limits
Get PDFThe requirement for imaging living structures with higher contrast and resolution has been covered by the inherent advantages offered by nonlinear microscopy (NLM). However, to achieve its full potential there are still several issues that must be addressed. To do so, it is very important to identify and adapt the key elements in a NLM for achieving an optimized interaction among them. These are 1) the laser source 2) the optics and 3) the sample properties for contrast generation. In this thesis, three strategies have been developed for pushing NLM towards its limits based on the light sample interaction optimization.
In the first strategy it is experimentally demonstrated how to take advantage of the sample optical properties to generate label-free contrast, eliminating the requirement of modifying the sample either chemically or genetically. This is carried out by implementing third harmonic generation (THG) microscopy. Here, it is shown how the selection of the ultra-short pulsed laser (USPL) operating wavelength (1550 nm) is crucial for generating a signal that matches the peak sensitivity of most commercial detectors. This enables reducing up to seven times the light dose applied to a sample while generating an efficient signal without the requirement of amplification schemes and specialized optics (such as the need of ultraviolet grade). To show the applicability of the technique, a full developmental study of in vivo Caenorhabditis elegans embryos is presented together with the observation of wavelength induced effects. The obtained results demonstrate the potential of the technique at the employed particular wavelength to be used to follow morphogenesis processes in vivo.
In the second strategy the limits of NLM are pushed by using a compact, affordable and maintenance free USPL sources. Such device was designed especially for two-photon excited fluorescence (TPEF) imaging of one the most widely used fluorescent markers in bio-imaging research: the green fluorescent protein. The system operating parameters and its emission wavelength enables to demonstrate how matching the employed fluorescent marker two-photon action cross-section is crucial for efficient TPEF signal production at very low powers. This enables relaxing the peak power conditions (40 W) to excite the sample. The enhanced versatility of this strategy is demonstrated by imaging both fixed and in vivo samples containing different dyes. More over the use of this laser is employed to produce second harmonic generation images of different samples. Several applications that can benefit by using such device are outlined. Then a comparison of the employed USPL source is performed versus the Titanium sapphire laser (the most used excitation source in research laboratories). The final goal of this strategy is to continue introducing novel laser devices for future portable NLM applications. In this case, the use of chip-sized semiconductor USPL sources for TPEF imaging is demonstrated. This will allow taking NLM technology towards the sample and make it available for any user.
In the last strategy, the light interaction with the optical elements of a NLM workstation and the sample were optimized. The first enhancement was carried out in the laser-microscope optical path using an adaptive element to spatially shape the properties of the incoming beam wavefront. For an efficient light-sample interaction, aberrations caused by the index mismatch between the objective, immersion fluid, cover-glass and the sample were measured. To do so the nonlinear guide-star concept, developed in this thesis, was employed for such task. The correction of optical aberrations in all the NLM workstation enable in some cases to have an improvement of more than one order of magnitude in the total collected signal intensity.
The obtained results demonstrate how adapting the interaction among the key elements of a NLM workstation enables pushing it towards its performance limits.La creciente necesidad de observar estructuras complicadas cada vez con mayor contraste y resolución han sido cubiertas por las ventajas inherentes que ofrece la microscopia nolineal. Sin embargo, aun hay ciertos aspectos que deben ser ajustados para obtener su máximo desempeño. Para ello es importante identificar y adaptar los elementos clave que forman un microscopio optimizar la interacción entre estos. Dichos elementos son: 1) el laser, 2) la
óptica y 3) las propiedades de la muestra. En esta tesis, se realizan tres estrategias para llevar la eficiencia de la microscopia nolineal hacia sus límites.
En la primera estrategia se demuestra de forma experimental como obtener ventaja de las propiedades ópticas de la muestra para generar contraste sin el uso de marcadores mediante la generación de tercer harmónico. Aquí se muestra como la selección de la longitud de onda del láser de pulsos ultracortos es crucial para que la señal obtenida concuerde con la máxima sensibilidad del detector utilizado. Esto permite una reducción de la dosis de luz con la que se expone la muestra, elimina intrínsecamente el requerimiento de esquemas de amplificación de señal y de óptica de tipo ultravioleta (generalmente empleada en este tipo de microscopios). Mediante un estudio comparativo con un sistema convencional se demuestra que los niveles de potencia óptica pueden ser reducidos hasta siete veces. Para demostrar las ventajas de dicha técnica se realiza un estudio completo sobre el desarrollo embrionario de Caenorhabditis elegans y los efectos causados por la exposición de la muestra a dicha longitud de onda. Los resultados demuestran el potencial de la técnica para dar seguimiento a procesos morfogénicos en muestras vivas a la longitud de onda utilizada.
En la segunda estrategia se diseñó una fuente de pulsos ultracortos que es compacta, de costo reducido y libre de mantenimiento para excitar mediante la absorción de dos fotones uno de los marcadores más utilizados en el entorno biológico, la proteína verde fluorescente. Los parámetros de operación en conjunto con la longitud de onda emitida por el sistema proporcionan la máxima eficiencia permitiendo el uso de potencias pico muy bajas (40 W),
ideales para relajar la exposición de la muestra. La versatilidad de esta estrategia se demuestra empleando muestras fijas y vivas con diferentes marcadores fluorescentes. Este láser también es empleado para la obtención de señal de segundo harmónico en diferentes muestras. Adicionalmente, se llevó a cabo un estudio comparativo entre la fuente desarrollada y un sistema Titanio zafiro (uno de los láseres más utilizados en laboratorios de
investigación). El objetivo final de esta estrategia es introducir fuentes novedosas para aplicaciones portátiles basadas en procesos nolineales. En base a esto se demuestra el uso de dispositivos construidos sobre un microchip para generar imágenes de fluorescencia de dos fotones. Esto permitirá llevar la tecnología hacia la muestra biológica y hacerla disponible para cualquier usuario.
En la última estrategia se optimiza de la interacción de la luz con los elementos ópticos del microscopio y la muestra. La primera optimización se lleva a cabo en la trayectoria óptica que lleva el láser hacia el microscopio empleando un elemento adaptable que modifica las propiedades espaciales de la luz. Para mejorar la interacción de la luz y la muestra se miden las aberraciones causadas por la diferencia de índices refractivos entre el objetivo, el medio
de inmersión y la muestra. Esto se realizo empleando el concepto de la “estrella guía nolineal” desarrollado en esta tesis. Mediante la corrección de las aberraciones en el sistema de microscopia nolineal se obtiene una mejora, en algunos casos de un orden de magnitud, en la intensidad total medida.
Los resultados obtenidos en esta tesis demuestran como el adaptar la interacción entre los elementos clave en un microscopio nolineal permiten llevar su desempeño hacia los límites.DOCTORAT EN FOTÒNICA (Pla 2007
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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