1,720,954 research outputs found
Implementation of Monte Carlo-Metropolis with simulated annealing for the design of aperiodically poled crystals that allow the generation of supercontinuum
No full textLos medios ferroeléctricos no lineales como el niobato de litio (LiNbO3) y el tantalato de litio (LiTaO3) permiten la conversión de luz de manera sintonizable a través de la técnica de cuasi-empatamiento de fases, la cual consiste en alternar el signo del coeficiente no lineal a lo largo del medio (modulación de la no linealidad) ya sea de manera periódica, con chirp o aperiódica. Uno de los procesos de conversión, conocido como conversión paramétrica descendente (PDC, por sus siglas en inglés), conlleva a la generación de espectros de emisión con ancho espectral amplio y continuo (mayores a 10 nm), llamados súpercontinuos. En este trabajo de tesis se estudió teóricamente el proceso de PDC, considerando las tres modulaciones antes mencionadas. Con modulaciones periódicas, la implementación de PDC con un bombeo sintonizado en la longitud de onda de cero dispersión de segundo orden del cristal, es posible la generación de señales con espectros cuyo ancho de banda puede llegar a ser superior a los 600 nm. Sin embargo, esta técnica no ofrece flexibilidad de sintonización porque está limitada a las propiedades lineales del medio, razón por la cual la mayoría de estas fuentes se encuentran sintonizadas en el infrarrojo. Por otro lado, las modulaciones con chirp permiten de manera sencilla la generación de anchos espectrales sintonizables, y que pueden ser llevados a un régimen experimental bajo un sistema de compensación, pero tienen el inconveniente de que los espectros resultantes presentan oscilaciones que no son fáciles de suprimir. En este proyecto de investigación, se propuso una metodología de optimización basada en Monte Carlo-Metropolis con recocido simulado que permite definir diseños de cristales con modulación aperiódica que conlleven a la generación de paquetes de onda en estado de fotón individual que exhiban espectros de banda ancha y características temporales deseables. Para el estudio se consideró como material LiNbO3 y se estudiaron diferentes configuraciones que involucran características espectrales particulares de la fuente de bombeo y las señales de generación. Adicionalmente en el modelo se incluyeron los efectos de la temperatura y defectos derivados del proceso de fabricación, sobre los espectros de generación y la tasa de generación. Particularmente, se presenta un diseño de cristal aleatorio que permite la generación de estados de fotón individual con ancho de banda amplio y limitados en transformada de Fourier. La caracterización...Non-linear ferroelectric mediums like lithium niobate (LiNbO3) and lithum tantalate (LiTaO3) allow tunable light conversion by using the quasi-phase matching technique, which consist on alternating the sign of the nonlinear coefficient through-out the medium (modulation of the non-linearity), which can be periodic, with chirp or aperiodic. One of the conversion processes, which is known as parametric down conversion (PDC), leads to the generation of emission spectra with wide and continuous bandwidth (greater than 10 nm), called supercontinuum. In this thesis the PDC process was theoretically studied considering the three modulations formerly mentioned. With periodic modulations, the PDC implementation with a pump wavelength tuned to the second order zero-dispersion condition, it is possible the generation of signals with spectral bandwidths above 600 nm. However, this technique doesn’t offer tunable flexibility because it is limited to the medium linear properties, and because of it most of these sources emit in the infrared. On the other hand, chirp modulation allows in a simple way the generation of broadband tunable spectra, that could be implemented on an experimental regime under a compensation system, but have the inconvenient that the resulting spectra presents oscillations which cannot be easily suppressed. In these research project, an optimization methodology was proposed based on Monte Carlo-Metropolis with simulated annealing that allows to define crystal designs with aperiodic modulations that could generate wave-packets in one photon states that exhibit broad spectral bandwidth and temporal desirable properties. For the study was considered the material congruent LiNbO3 and were studied different configurations that involve particular pump sources and generation signals. Additionally, on the model there were included the effects of temperature and fabrication defects and the impact on the spectra and the generation rate. Particularly, a crystal with a random design is presented that allows the generation of one photon state with broad bandwidth that is Fourier transformed limited. The design characterization was made by using the Wigner function on the heralded one photon state
Injection-seeded pulsed laser
No full textEste proyecto de tesis se basa en el diseño y elaboración de un láser pulsado semillado. Los láseres pulsados usando la técnica de Q-switch presentan efectos indeseados al momento de generar el pulso, entre ellos fluctuaciones de intensidad y energía de pulso a pulso, fluctuaciones en el tiempo de formación del pulso y ancho de banda grande. Esto se debe a que los pulsos se generan a partir de emisión espontánea, la cual es ruidosa. Para corregir estos efectos indeseados, se implementó la técnica de semillado, la cual consiste en inyectar una señal semilla en la cavidad que genera los pulsos, con el fin de que el pulso se genere a partir de ésta y no de la emisión espontánea ruidosa. En esta tesis se hizo un análisis teórico y experimental de un láser semillado. Se dedujeron las ecuaciones que describen el acoplamiento de los campos eléctricos de los modos de la cavidad con la inversión de población del medio y la influencia de la inyección de un haz en la formación del pulso; con estas ecuaciones se hicieron simulaciones de la formación de pulsos para compararlas con el experimento. Se diseñó y construyó un sistema láser de Nd:YAG que se compone de un láser semilla de Nd:YAG de onda continua, un láser pulsado en forma de cavidad de anillo bombeado longitudinalmente que usa un modulador electroóptico como Q-switch y un sistema de control de la longitud de la cavidad de anillo para hacer coincidir la frecuencia de oscilación del láser semilla con uno de los modos de la cavidad del láser pulsado. Se probó que es posible implementar la técnica de semillado en un láser pulsado al disminuir el tiempo de formación del pulso un 23 % y aumentando su potencia pico por pulso un 237 %. This thesis project is about the design and fabrication of an injection seeded pulsed laser. Pulsed Q-switched lasers present unwanted effects at pulse formation, among them intensity variations of their temporal profile and increased uncertainty in the pulse time formation. In order to correct these unwanted effects we implemented the injection seeding technique, which consists in injecting a seed signal into the laser cavity, with the purpose that the pulse doesn’t start from the noise in the gain medium, but rather from the seed, reducing the intensity variations in the temporal profile and decreasing the pulse formation uncertainty. The equations that describe the coupling of the electric field amplitudes of the cavity modes with the population inversion of the gain medium are deduced. By solving these equations numerically, we simulate the formation of pulses and analyze the influence of a seed beam on the properties of the pulses. A seeded Nd: YAG laser system was designed and built, which consists of a continuous wave Nd:YAG laser as a seed laser, a Q-switched pulsed ring cavity laser that uses an electrooptic modulator as a Q-switch and a length control of the ring cavity in order to match the oscillation frequency between the seed and the pulsed laser. It was proven that it is possible to use the injection seeding technique in a ring cavity pulsed laser, decreasing the pulse formation in a 23% and increasing the peak power to 237%.
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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