1,720,956 research outputs found
Thermal profiles and improved confinement accessibility in RFX-mod and TCV
Get PDFHumans do not live by bread alone. Physically we are puny creatures with limited prowess, but with unlimited dreams. In the last few decades humankind reached the Moon (1969) and
built airports over the sea (1994), but 925 million people are still under- or malnourished (2010). To follow his dream to ensure every human being the same adequate quality of life, humankind needs energy. The long-term world energy scenarios (50-80 years) foresee the need for reliable, sustainable and environmental friendly sources of energy. Thermonuclear fusion is one of the main actors in the energetic basket, it offers the possibility to produce large supplies of energy at relatively low costs reducing the impact on the environment. In fact, thermonuclear fusion represents a promising chance to generate energy without the emission of carbon dioxide and the production of long living radioactive wastes. Moreover, the raw materials used as fuel in the fusion reactions, deuterium and tritium, are easily available on Earth. This chance motivates the efforts on the controlled thermonuclear fusion research. Anyway, the development of nuclear fusion as an energy source is one of the most complex scientific and technical tasks ever undertaken for non-military purposes. The nuclear fusion obtained by magnetic confinement of plasma emerged in the latest years as the most promising concept to menage the power produced by fusion reactions. The studies developed in that direction, since the fifties, yielded more and more encouraging results and important breakthroughs both in physics and technology and inspired the ITER project. This experimental reactor could give, in the next few decades, the definitive answers to many questions on the scientific and technological feasibility of a fusion reactor. One of the major concerns in magnetic confinement fusion research is the quest for the best
plasma performance, which is intimately linked to two main issues: plasma confinement and boundary conditions. Both, incidentally, are connected to plasma stability. The link between confinement and boundary conditions is very strong and found many evidences. For example in the tokamak (the magnetic confinement configuration main line) the quest for a mild plasma-wall interaction a controlled recycling led to the discovery of an ameliorated operating mode with high performance. As a matter of fact, H-mode was discovered in
ASDEX the first diverted device. In RFPs (an alternative magnetic confinement configuration) a spontaneous transition to an ameliorated plasma state, the QSH state, is due to a reduced chaos obtained with an accurate control of the magnetic boundary conditions. In turn, the access to the QSH state led to a favorable edge topology characterized by better boundary conditions. The onset of the QSH state induces an edge helical ripple which reduce the plasma wall interaction. My research activity, reported in this thesis work, focused on the accessibility conditions and characterization of improved confinement regimes in TCV tokamak and RFX-mod RFP devices. In RFX-mod my research activity focused on the study and the characterization of electron temperature profiles. Temperature is one of the key parameters that qualifies fusion plasma performance and, in RFX-mod plasmas, it is mainly determined by three quantities: plasma current, electron density and plasma magnetic state. Through a large statistical analysis the temperature profile variations were investigated and related to the main macroscopic and operational plasma parameters. This analysis resulted in scaling laws for central temperature, external temperature and temperature gradient. Some further analysis was dedicated to a distinctive feature: the appearance of transport and thermal barriers which result in better plasma performance. The formation of an Internal Transport Barrier (eITB) is triggered by the growth of a dominant MHD tearing mode which, in turn, leads to a reduced magnetic chaos
in the plasma core. Starting from previous analysis, these eITBs were investigated and their influence of the whole temperature profile addressed. Besides the established phenomena related to eITBs, the occasional appearance of extremely high gradients in the external region of the plasma column was observed. Some general observations and a first speculation on the physical mechanism leading to their formation will be presented. The work ends up in a wide and general picture which tries to clear up the physics governing the temperature profile
modifications and proposes possible operations to trigger them. Present day tokamaks high performance scenarios rely on the possibility to access the high confinement mode (H-mode). Transition from the standard confinement mode (L-mode) to the H-mode is typically achieved when the external input power exceeds a threshold. This power threshold is found to strongly depend on plasma density, toroidal magnetic field and plasma size, but many experiments have shown this power threshold to also depend on plasma shape and configuration geometry. My activity at TCV aimed at the study of such dependence, in particular the influence of X-point location on H-mode power threshold was investigated. During a two months stay in 2011, a series of experiments was dedicated to such a study. Significant variations in the power threshold due to a reduction of the X-point height has been documented, in agreement with the scaling observed in other machines. Moreover, the well-established non-monotonic density dependence of the H-mode power threshold has
been measured and recorded. In this thesis work the analysis procedure followed to the TCV experimental campaign is reported
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
Knowledge-based models for SBRT prostate treatments
No full text<p><span>Two </span><span><span>knowledge-based models (KBP) for SBRT prostate treatments plans are made available. </span></span></p>
<p><span>A KBP-model (ST-model) was created from the 73 highest-quality historically available moderately hypo-fractionated (70Gy/28fx and 60Gy/20fx) prostate treatments. </span></p>
<p><span>A second KBP model (SBRT-model) was created, trained and validated using thirty-six clinical VMAT SBRT prostate plans based on the HYPO-RT-PC (42.7Gy/7fx) and PACE-B (36.25Gy/5fx) clinical trial protocols. </span></p>
<p><span>They are based on the commercial platform RapidPlan v15.6 (Varian Medical Systems, Palo Alto, CA).</span></p>
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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