1,722,217 research outputs found
Coherence and contextuality in scattering experiments
No full textAt a first sight, the description of a scattering experiment seems to be easy and unambiguous. A projectile, as for instance an electron or an ion, flies out of an accelerator with a given momentum p toward an atom or molecule, assumed to be at rest in the collision chamber, and interacts with it. This interaction might lead to different outcomes. For instance, the target might reach an excited bound state, or even loss an electron. These are only two examples of a myriad of options, which are usually called "channels". Thus, we can talk about the elastic channel, the excitation channel, the ionization channel, etc. Finally, one or some of the products of the collision are collected in order to investigate one of these channels.A closer look reveals that the description of any of these experiments is not quite as straight forward. More specifically, one major complication is that the Schrodinger equation is not analytically solvable for more than two mutually interacting particles, even when the underlying forces are precisely known. This is known as the few-body problem (FBP), which is formulated in the introduction to this book and theoretically discussed in other chapters. The FBP, in turn, is afflicted with an additional major complication which is usually overlooked. Addressing this drawback of the standard descriptions of the FBP is the main objective of the present chapter. Both the initial preparation of the projectiles and the final detection of the outgoing particles occur at macroscopic distances, and therefore it is assumed that they cannot have any effect on the scattering event, which occurs in a region of atomic dimensions. In other words, we might say that a scattering experiment is independent of its context. Furthermore, since both the beam of projectiles and the target gas can be described by pure quantum states, we are dealing with a purely coherent process.Unfortunately (or fortunately, depending on how each of us cope with uncertainties and broken paradigms), when we look deeper into this kind of experiments, we find out that they are trickier than expected. As we will discuss in the present chapter, all and every statement in the previous paragraph is false or at least doubtful. In what follows, we will discuss these issues, paying special attention to the assumption of coherence and lack of contextuality. But first, we will explore some basic ideas in very simple terms, which will pave the way for the discussion ahead.Fil: Barrachina Tejada, Raul Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Navarrete, F.. Kansas State University; Estados UnidosFil: Ciappina, M.F.. Czech Academy of Sciences. Institute of Physics. ELI Beamlines; República ChecaFil: Schulz, Michael. Missouri University of Science and Technology. Department of Physics and LAMOR ; Estados Unido
Building peace from below: Exploring experiments in the Democratic Republic of Congo and Somalia
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
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