1,720,972 research outputs found
Delta kick cooling for cold atom interferometry and its application in space missions
Get PDFStudent will design, build and test experimental quantum optics systems to study the interaction of single atom-resonant photons and atom-resonant entangled photon pairs with atomic systems.Delta kick cooling (DKC) gives control over the free expansion of Bose-Einstein-Condensates for the purpose of atom interferometry. Recent projects and future proposals on how to apply DKC for cold atom interferometry in space missions are outlined. This thesis provides both a classical analytical as well as a numerical solution to the evolution of the atom cloud distribution in phase space of a thermal ensemble. It investigates how duration and strength of the kick will influence the same. Furthermore, a numerical solution to the Gross-Pitaevskii Equation for the DKC of a Bose-Einstein condensate is presented
Delta kick cooling for cold atom interferometry and its application in space missions
No full textStudent will design, build and test experimental quantum optics systems to study the interaction of single atom-resonant photons and atom-resonant entangled photon pairs with atomic systems.Delta kick cooling (DKC) gives control over the free expansion of Bose-Einstein-Condensates for the purpose of atom interferometry. Recent projects and future proposals on how to apply DKC for cold atom interferometry in space missions are outlined. This thesis provides both a classical analytical as well as a numerical solution to the evolution of the atom cloud distribution in phase space of a thermal ensemble. It investigates how duration and strength of the kick will influence the same. Furthermore, a numerical solution to the Gross-Pitaevskii Equation for the DKC of a Bose-Einstein condensate is presented
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
Wave-packet evolution during laser pulses driving an atomic clock transition
No full textSingle-photon optical transitions enable novel applications of atom interferometry to dark-matter and gravitational-wave detection. This work investigates the wave-packet evolution for an atom's center of mass during a laser pulse driving such a transition. Particular attention is paid to the effects of finite pulse duration on the central trajectory of the atomic wave packets and the phase that they acquire in the diffraction process. While the resulting deviations of the central trajectories are typically quite small, they can have a significant impact on the interferometric phase shift in high-precision measurements and a detailed analysis is therefore important. Our approach relies on a description of the matter-wave propagation in terms of central trajectories and centered wave packets
Wave-packet evolution during a laser pulse for single- and two-photon atomic diffraction
No full textHigh-precision atom interferometry allows application to dark-matter and gravitational-wave detection. This work investigates the wave-packet evolution for an atom's center of mass during a laser pulse driving a single photon or Raman transition of arbitrary duration as well as a Bragg transition in the deep Bragg regime. We consider the effects of finite pulse duration on the central trajectory of the atomic wave packets for beam splitter and mirror pulses, as well as pulses with arbitrary pulse areas, with square and gaussian pulse shapes. The investigation further includes the most general case involving non-vanishing detuning. While the resulting deviations of the central trajectories are typically quite small, they can have a significant impact on the interferometric phase shift in high-precision measurements and a detailed analysis is therefore important. Our approach relies on a description of the matter-wave propagation in terms of central trajectories and centered wave packets
Wave-packet evolution during laser pulses driving an atomic clock transition
No full textSingle-photon optical transitions enable novel applications of atom interferometry to dark-matter and gravitational-wave detection. This work investigates the wave-packet evolution for an atom's center of mass during a laser pulse driving such a transition. Particular attention is paid to the effects of finite pulse duration on the central trajectory of the atomic wave packets and the phase that they acquire in the diffraction process. While the resulting deviations of the central trajectories are typically quite small, they can have a significant im- pact on the interferometric phase shift in high-precision measurements and a detailed analysis is therefore important. Our approach relies on a description of the matter-wave propagation in terms of central trajectories and centered wave packets
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
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