1,720,979 research outputs found
Related Data for: Plasma focus neutron energy and anisotropy measurements using zirconium-beryllium pair activation detectors
No full textZirconium and beryllium fast-neutron activation detectors are used to investigate the fusion neutron emission from the NX3 Plasma Focus (PF) device operated in deuterium gas, with 7.2 kJ bank energy. Both Zr and Be activation cross-sections increase with energy, but with different trends, enabling an effective neutron
energy eff n to be inferred from the Zr/Be count ratio. The relationship between eff
n and Zr/Be count ratio is established by MCNP5 simulation. Compact Zr/Be detector pairs were positioned at 0◦ and 90◦ to the PF axis, permitting measurements of neutron yield, energy- and fluence-anisotropy to be made for each shot. Series of NX3 shots were performed for D2 gas pressures ranging from 1.5 to 10 mbar. Typical effective neutron energies eff n for the 0◦ and 90◦ directions are found to be ∼2.8 MeV and ∼2.5 MeV, respectively. The highest neutron yields of ∼109 neutron/shot were observed for 5 mbar D2 gas pressure. Neutron fluence-anisotropy nBe for individual shots ranged from ∼2.5 to ∼4.5. The mean value ⟨nBe⟩ exhibits a steady decline with increasing D2 gas pressure. By contrast, neutron energy-anisotropy n remains almost constant as the D2 gas pressure is varied. The effect of blocking the forward D+ ion beam with an obstacle plate positioned 6 cm in front of the anode tip is also studied. Marked reductions in both neutron yield and fluence-anisotropy are observed, whilst the effective neutron energy eff n increases slightly at both 0◦ and 90◦ directions. Fusion contributions from thermonuclear or gyrating-particle processes are found to be negligible. All results are completely consistent with a straightforward beam–target model of PF fusion
Meeting the challenge of problem based learning in physics
No full textA modified Problem Based Learning (PBL) approach has been implemented and evaluated for the laboratory sessions of the Thermal Physics first year undergraduate module in academic year 99/00. The principal objective of this PBL approach is to get away from the 'cookbook' approach to teaching laboratories, and instead transform them into micro-research projects which demand higher order cognitive involvement of the students. This modified PBL approach involved conducting two hour laboratory sessions for each experiment: one hour from each of two consecutive weekly classes. The first week's session was rounded off with a question and answer session aimed at promoting higher order cognitive involvement by the students in the experimental work. The students conducted and discussed the experiments in groups of 3 to 4, while I acted as facilitator. One observation is that the weaker students in the class are uncomfortable with the lack of a detailed experimental demonstration. Comparing the student reports for academic year 99/00 (PBL approach) with those from 97/98 (conventional approach), indicates that student's have higher cognitive understanding of the experiments enabling them to answer questions more competently, and their integration and retention of knowledge is enhanced. Moreover the students were more involved and devoted more energy and enthusiasm to the experimental work when the modified PBL approach was employed in comparison to the more conventional approach to laboratory work
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
First experimental results using singer product apertures
No full textWe present the first experimental results obtained using Singer product apertures. We image X-rays scattered from spherical aluminium targets, using a Crypix detector. Despite the relatively low resolution of the apertures, 13 × 13 and 21 × 21 pixels drilled into a tungsten sheet, much higher resolutions are achieved in practice using Fenimore and Cannon’s fine sampling and delta decoding techniques
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