1,720,971 research outputs found
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
Intense Extreme Ultraviolet Pulses for Attosecond Pump-Probe Experiments
No full textAttosecond science enables the study of ultrafast dynamics on atomic scales, providing fundamental insights into light–matter interaction. This thesis work aims to advance the development and application of an attosecond light source capable of delivering extreme ultraviolet (XUV) pulses with exceptionally high intensity.High-order harmonic generation (HHG) is a nonlinear process where a strong laser—typically in the infrared (IR) spectral region—is focused into a gas target, producing attosecond pulses in the XUV spectral region. These pulses are commonly used in pump-probe experiments, where a pump pulse excites the system and a probe pulse interrogates the induced dynamics, allowing for time-resolved measurements of ultrafast processes.XUV–IR pump-probe schemes investigate electron dynamics via interactions that involve a single XUV and several infrared photons. However, infrared-driven processes can add complexity to the interpretation of the induced dynamics. In contrast, XUV–XUV pump-probe schemes provide a more direct approach, in which single-photon-induced dynamics are probed by a single second photon. Reaching the regime in which two XUV photons are absorbed requires high intensities, but the inherently low conversion efficiency of HHG poses a major challenge. To overcome this limitation, generation conditions, phase-matching conditions, and the wavefront characteristics of the driving field must be optimized.This thesis demonstrates advancements in generating intense attosecond XUV pulses by optimizing the HHG process. Additionally, it explores how generation conditions affect the harmonic focus position and waist, influencing the ability to refocus the XUV pulses to a high-intensity spot. Beyond source optimization, applications of intense attosecond pulses in XUV–XUV and XUV–IR pump-probe experiments are investigated, enabling studies of electron dynamics upon photoionization. These experiments provide new insights into photoionization and ultrafast charge migration, enhancing our understanding of attosecond dynamics.By refining attosecond pulse generation, this thesis contributes to the next generation of high-intensity ultrafast light sources, opening new possibilities for time-resolved studies in atomic and molecular physics
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
Generation and Characterization of Intense Attosecond Pulses
No full textResearch on ultrafast dynamics in atoms and molecules requires short pulses. In order to resolve processes taking place on a femtosecond timescale sufficiently, these pulses require a duration on the attosecond time scale. This thesis is about the generation of such attosecond pulses via high harmonic generation (HHG) in argon gas by a terawatt infrared (IR) laser source. The pulses are applied in a pump-probe principle on two different noble gases, helium and neon. Reconstruction of Attosecond Beating By Interference of Two-photon Transition (RABBIT) is performed to characterize the relative emission time delay between harmonics, and to reconstruct the temporal domain of the attosecond pulse. Methods used for analyzing and improving the data extraction are introduced. Particularly the angle-resolved analysis gives unique insights into the ionization dynamics.The shortest time frame one can imagine is perhaps the blink of an eye or a flick of a finger. These events are rarely faster than 100 milliseconds. The attosecond pulses which are produced at the Intense XUV Beamline in Lund are way shorter than that. If they were lined up one after the other, one could fit a quadrillion pulses within this time. Of course, nobody is sitting there counting these pulses, but even measurement instruments have a hard time with this task. There is no sensor or electronical device which is able to detect them directly. A tough method named after a cute animal, the so-called RABBIT technique is used to obtain the information. Hereby, the fact that light behaves like a wave and interferes is used. By a lucky coincidence of nature, two attosecond pulses of the same energy are always generated. Since they are created at the same time, they interfere with each other in such way that a special pattern is formed that can be reliably measured when scanning over a much larger time frame of femtoseconds (one trillion of a second). A picture is received which shows how many photons are measured depending on the time (in femtoseconds) and electron kinetic energy, which is proportional to the wavelength of the pulses we have generated. The part of most interest is how the line structures in this picture, referred to so-called harmonics or sidebands, oscillate over time. Advanced methods are applied for analysis and improvement of the phase extraction of this oscillation. That information allows us to reconstruct the real pulse structure over time. This explains why RABBIT stands for Reconstruction of attosecond laser beating by interference of two photon transitions. Two different noble gases, helium and neon are investigated in this thesis by applying this technique. So far, we have seen how to measure the pulses, but no explanation for the reason why there is a need for doing this has been stated. What’s special about the pulses is that they are amongst the shortest we are currently able to create and not many research facilities are doing this at the time. Whenever we venture into previously unexplored areas there are also great discoveries. The research on attosecond pulses brings us closer to the explanation on how ionization of atoms is happening since this process takes place on a very short time frame as well, the femtosecond range. Hence, the observation requires even shorter pulses than that in order to resolve what is happening. Finally, this is an approach to a better understanding of fundamental physics and the result will contribute to an improved basic theory about charge migration processes in atomic physics and chemistry
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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