1,720,958 research outputs found
Pauli paramagnetism of an ideal Fermi gas
No full textWe show how to use trapped ultracold atoms to measure the magnetic susceptibility of a two-component Fermi gas. The method is illustrated for a noninteracting gas of [superscript 6]Li, using the tunability of interactions around a wide Feshbach resonance. The susceptibility versus effective magnetic field is directly obtained from the inhomogeneous density profile of the trapped atomic cloud. The wings of the cloud realize the high-field limit where the polarization approaches 100%, which is not accessible for an electron gas.National Science Foundation (U.S.)United States. Office of Naval ResearchUnited States. Air Force Office of Scientific Research. Multidisciplinary University Research Initiative (Ultracold Molecules)United States. Army Research Office (Grant W911NF-07-1-0493)United States. Defense Advanced Research Projects Agency. Optical Lattice Emulator Progra
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
Ultracold Fermi gas with repulsive interactions
Full text linkThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 95-100).This thesis presents results from experiments of ultracold atomic Fermi gases with repulsive interaction. Itinerant ferromagnetism was studied by simulating the Stoner model with a strongly interacting Fermi gas of ultracold atoms. We observed nonmonotonic behavior of lifetime, kinetic energy, and size for increasing repulsive interactions, which is in good agreement with a mean-field model for the ferromagnetic phase transition. However, later research showed the absence of enhanced spin fluctuation, which is definitive evidence against the ferromagnetic phase transition. Still, our work triggered a lot of research on repulsive interactions in ultracold Fermi gases. A quantitative approach is taken to study ultracold Fermi gases with repulsive interaction. This is done by careful measurements of density profiles in equilibrium. First, Pauli paramagnetism is observed in trapped atomic samples which have an inhomogeneous density due to the harmonic confinement potential. We experimentally measure the susceptibility of ideal Fermi gas. This research shows that ultracold atoms can serve as model systems to demonstrate well-known textbook physics in a more ideal way than other systems. Then, Fermi gases with repulsive interactions are characterized by measuring their compressibility as a function of interaction strength. The compressibility is obtained from in-trap density distributions monitored by phase contrast imaging. For interaction parameters kFa > 0.25 fast decay of the gas prevents the observation of equilibrium profiles. For smaller interaction parameters, the results are adequately described by first-order perturbation theory. A novel phase contrast imaging method compensates for dispersive distortions of the images.by Ye-Ryoung Lee.Ph.D
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
Itinerant Ferromagnetism in a Fermi Gas of Ultracold Atoms
Full text linkCan a gas of spin-up and spin-down fermions become ferromagnetic because of repulsive interactions? We addressed this question, for which there is not yet a definitive theoretical answer, in an experiment with an ultracold two-component Fermi gas. The observation of nonmonotonic behavior of lifetime, kinetic energy, and size for increasing repulsive interactions provides strong evidence for a phase transition to a ferromagnetic state. Our observations imply that itinerant ferromagnetism of delocalized fermions is possible without lattice and band structure, and our data validate the most basic model for ferromagnetism introduced by Stoner.National Science Foundation (U.S.)United States. Office of Naval Research. Multidisciplinary University Research Initiative.United States. Army Research Office (Contract W911NF-07-1-0493)United States. Defense Advanced Research Projects Agency. Optical Lattice Emulator Progra
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