1,720,958 research outputs found
High energy ultrafast tunable mid-IR sources for the application in strong field physics and spectroscopy
No full textLa spettroscopia ultraveloce nella regione spettrale del medio infrarosso (midIR) ha diverse applicazioni in fisica, chimica e nelle scienze biologiche. Infatti, le risonanze rotovibrazionali delle molecole risiedono in questa regione spettrale. Oltre a ciò, l’utilizzo di impulsi nel medio infrarosso permette diverse applicazioni nella fisica dell’interazione con campi ad alta intensità. Tuttavia, fino ad ora, le sorgenti di impulsi ultrabrevi nella regione del medio infrarosso sono state inferiori a quelle nel visibile e nel vicino infrarosso sia in termini di potenza, che di banda e durata dell’impulso. Questi fattori limitano enormemente le possibilità di utilizzo di tali sorgenti in esperimenti di questo tipo. Questo lavoro di tesi riporta lo sviluppo di un amplificatore ottico parametrico (OPA) volto alla generazione di
impulsi ultrabrevi a pochi cicli ottici e alta energia nella regione spettrale del medio infrarosso (tunabili da 2,8 μm a 4 μm). Le possibilità offerte dalla sorgente sono dimostrate in due esperimenti. Nel primo, è stata esplorata la generazione di armoniche di ordine elevato in gas atomici e molecolari utilizzando uno schema a due colori per aumentare l’energia di cutoff della radiazione XUV e la dipendenza delle traiettorie elettroniche dal campo nel
medio infrarosso è ampiamente discussa. Nel secondo esperimento tale tecnica è stata estesa alla generazione di armoniche di ordine elevato in solidi semiconduttori in funzione dalla polarizzazione degli impulsi, sfruttando una geometria in trasmissione. Entrambi questi
risultati sono riportati e discussi in questo lavoro di tesi.Ultrafast spectroscopy in the mid-IR wavelength region has several applications in the fundamental physics, chemistry and biological science. For a spectrum of molecules, it’s vibrational and rovibrational resonance lies in the mid-IR spectral region. Besides this, mid-
IR pulses have several applications in strong-field physics. However up-to-now, ultrafast light sources in the mid-IR region have been inferior to those in the visible or near-IR wavelength
region in terms of power, bandwidth and pulse duration. These factors severely limiting the ultrafast spectroscopy and strong-field physics in these spectral regions. This thesis reports
the development of an optical parametric amplifier for the generation of high energy, ultrafast few-cycle pulses in the mid-IR wavelength region (2.8 μm to 4 μm). The potential of the source is proved by conducting two experiments. In the first set of experiments, the study
of high harmonic generation in atomic and molecular gases (using two-colour scheme) to enhance the harmonic cut-off energy in the XUV region and the trajectory dependence of tunnel ionized electrons in the presence of mid-IR electric field are extensively studied. I also extended this technique to study the high harmonics generation from semiconductor
solid materials and studied the polarization dependence of the mid-IR pulses in the harmonic
generation in transmission geometry. These results are reported and discussed in this thesis.DIPARTIMENTO DI FISICA32STAGIRA, SALVATOREFINAZZI, MARC
High-order harmonic generation spectroscopy by recolliding electron caustics
Get PDFSpectral focusing of the recolliding electron in high-order harmonic generation driven by two-color fields is shown to be a powerful tool for isolating and enhancing hidden spectral features of the target under study. In previous works we used this technique for probing multi-electron effects in xenon and we compared our experimental results with time-dependent configuration-interaction singles calculations. We demonstrate here that this technique can be exploited for reconstructing the enhancement factor of the xenon giant dipole resonance and we discuss the sensitivity of this method to macroscopic effects. We then extend the technique to argon in order to test the applicability of this procedure to other targets
Molecular Orbital Tomography Based on High-Order Harmonic Generation: Principles and Perspectives
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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
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