1,720,966 research outputs found
CFD Analysis of Different Cooling Options for a Gyrotron Cavity
No full textThree different pressurized subcooled water cooling options [hypervapotron, mini-channels (MCs), and meander flow drivers] for a full-size gyrotron cavity are developed and analyzed using the commercial computational fluid dynamics code STAR-CCM+, to guarantee a pressure drop below the maximum acceptable, and the compliance with manufacturing constraints. The full-size designs are then transposed to corresponding mock-ups to identify the most suitable candidate for an experimental test. The conjugate multiphase heat transfer problem is solved in the three mock-up geometries, aimed at comparatively assessing their thermal performance at increasing heat load on the target up to 24 MW/m2. The most promising option for an effective cooling of the cavity results to be the mini-channels
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
Towards the optimization of the thermal-hydraulic performance of gyrotron collectors
No full textDifferent configurations of water-cooled Cu collector for gyrotrons are investigated using the StarCCM+CFD code, aimed at optimizing its thermal-hydraulic (TH) performance. Although the current collectors show a good performance, the collector can be subjected to transient heat loads, due to the spent electron beam, of up to several tens of MW/m2, and there is an interest to increase the gyrotron output power in the future. Furthermore, an optimized cooling will lead to improved reliability and lifetime of the collector. Starting from a hypervapotron (HV)-like collector, characterized by 100+ deep rectangular cavities with aspect ratio (AR)=3, we present in the first part of the paper a single-cavity steady-state parametric analysis of the effect of AR on the heat exhaust capabilities. The investigation is then extended to other collector designs, including circumferential ribs and dimples, in order to assess the options for further improvements of the TH performance. The peak Cu temperature is computed by the code and its minimization is the target of the present optimization exercise. A self-consistent estimate of the heat transfer coefficient between collector and coolant is also obtained, which could be useful for fatigue and lifetime assessments. In the second part of the paper the most promising collector geometries identified in the first part are analyzed in the case of a transient heat load (vertical sweeping), first at the level of a single spatial period of the collector structure, then at the full-collector level. The results of the TH transient analysis are compared with both the results of the first part and with the transient purely thermal analysis of the full collector, showing for all geometries considered in this study a room for cooling efficiency improvement with respect to the HV-like design with AR=3, at least in the operating conditions considered for this study (V ~4m/s, almost 100°C sub-cooling
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
CFD Analysis of Mini-Channel Cooling for a Gyrotron Cavity
No full textA pressurized sub-cooled water cooling option for a full-size gyrotron cavity, based on mini-channels, is developed and analyzed using the commercial computational fluid dynamics (CFD) tool STAR-CCM+. On the basis of this design, which guarantees a pressure drop below the maximum acceptable and the compliance with manufacturing constraints, we study the cooling of a representative mock-up to be experimentally tested in the near future. The solution of the conjugate heat transfer problem in the mock-up geometry is presented, aimed at assessing its thermal performance under increasing target heat load up to 24 MW/m2
Caractérisation d\u27oxydes cristallins à haute permittivité (LaAlO3, SrTiO3) en vue d\u27une intégration en microélectronique
No full textLa miniaturisation continue des composants microélectroniques nécessitera de disposer, à court terme, d\u27isolants alternatifs au SiO2. Le remplacement de la silice par un matériau high-K disposant d\u27une constante diélectrique plus élevée permet de repousser les limites fondamentales de l\u27intégration et en particulier de limiter les courants de fuite traversant les dispositifs. Les solutions industrielles à court terme sont basées sur la mise en uvre d\u27oxydes amorphes comme les oxynitrures de silicium ou les silicates d\u27hafnium. Ce choix impose quelques limitations du point de vue de la stabilité thermodynamique, des propriétés électriques finales En particulier, la recherche d\u27épaisseurs équivalentes électriques ultimes est considérée comme un des verrous technologiques les plus importants. A plus long terme, l\u27intégration d\u27oxydes high-K ternaires, éventuellement sous forme épitaxiée, devrait constituer une réponse à cette problématique. Devant ce constat, nous avons orienté notre travail autour du développement des propriétés électriques et physicochimiques de deux isolants amonts en film mince (5 80 nm) associés à deux méthodes d\u27élaboration : LaAlO3 (eLaAlO3=25) élaboré par épitaxie par jets moléculaires (MBE) et SrTiO3 (eSrTiO3=340) déposé par voie chimique depuis lutilisation de précurseurs organométalliques en phase vapeur (MOCVD) à injection. Dans le cas du LaAlO3, les caractéristiques électriques les plus favorables ont été obtenues dans le cas dun dépôt amorphe. Dans ces conditions, le film interfacial est évalué à 0,5 nm et la permittivité du volume à eLaAlO3=12,5, résultats comparables à létat de lart. Différentes stratégies de dépôts et de traitements ex-situ ont été envisagées afin de minimiser limpact des charges présentes dans les premiers nanomètres du film. Nous montrons que les propriétés électriques des couches polycristallines de SrTiO3 dépendent fortement de lépaisseur, de la cristallinité et de la composition. La présence dun bicouche de SiO2 (2-2,5 nm) et de silicate de strontium (2,5-4,0 nm) à l\u27interface pénalise la permittivité de lensemble (efilm=45-50 pour 80~nm), Enfin, nous avons mis en évidence par microscopie à force atomique (AFM) une conduction hétérogène sur la surface des couches polycristallines. Dans le cas du SrTiO3, la conduction est dominée par le grain. Un traitement ex-situ oxydant permet de minimiser le courant de fuite dans la partie cristalline
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
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