1,720,980 research outputs found
Numerical methodology for design and evaluation of natural circulation systems for MSR applications
Full text linkThis work focuses on the development of a comprehensive numerical methodology for the study of natural circulation systems using molten salts as working fluid, in particular for its application in the design of passive safety systems for Molten Salt Reactors (MSRs). The goal of the methodology is to evaluate the performance of possible 3D natural circulation configurations through the description of their dynamic behavior, with a focus in the identification of bifurcation phenomena and performing a stability analysis. The numerical tool implementing this methodology is based on a CFD-based MATLAB-OpenFOAM coupling and has been evaluated against a numerical benchmark of a differentially heated cavity, showing good agreement with literature results. For a first assessment of the performance of the tool a simple 2D case of a simple natural circulation configuration known as Rayleigh-Bénard convection has been used. This configuration results from a 2D enclosure heated and cooled from the bottom and top surfaces respectively. The dynamic states of this system have been studied for a large range of both geometric and physical parameters, showing both steady state and oscillating solutions. A bifurcation diagram is produced, showing the transition between the different solutions. In the vicinity of certain bifurcation points hysteresis phenomenon has been observed. The numerical tool developed for the evaluation of natural circulation systems has shown a good performance both for the description of the thermal-hydraulic system as well as for the stability analysis. The complexity and variety of the possible solutions for this first assessment illustrates the need of a robust and systematic methodology for the considered applications which in practice will involve more complex geometries and additional underlying phenomena
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
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
Optimization and design procedure of a potassium Rankine cycle for Nuclear Electric Propulsion
Full text linkLAUREA MAGISTRALEL'esplorazione dello spazio profondo è stata protagonista negli ultimi anni di un rinnovato interesse che ha portato alla ricerca di tecnologie innovative in grado di rendere possibile questo genere di missioni così complesse. Nell'ambito della propulsione spaziale, quella nucleare di tipo elettrico è vista come un possibile punto di svolta: grazie alle alte potenze e al considerevole impulso specifico che è in grado di generare, i tempi di viaggio e i rischi associati a missioni di lunga durata possono essere apprezzabilmente ridotti. Attraverso una collaborazione con LPSC di Grenoble, questa tesi fa parte di un progetto per lo sviluppo di un codice di ottimizzazione capace di confrontare diversi modelli di reattore e di sistema di conversione dell'energia con l'obiettivo di definire, a seconda del carattere della missione, la configurazione propulsiva migliore. Nello specifico lo studio è dedicato all'individuazione di una procedura per determinare le condizioni ottimali di un ciclo Rankine dal punto di vista della massa specifica (kg/kWe) del sistema. Per cominciare vengono presentate le potenzialità di tale ciclo termodinamico combinato all'impiego di metalli liquidi come il potassio, ripercorrendo i risultati delle principali attività di ricerca svolte nei primi anni del programma spaziale statunitense. L'analisi prosegue mettendo in evidenza i benefici addizionali che l'adozione di un micro reattore a sali fusi da 1 MWth può garantire in quanto sorgente termica di lunga durata e praticamente auto-sufficiente. Per quel che riguarda la fisica del sistema, ogni calcolo è svolto grazie al linguaggio Modelica che è stato arricchito di un modello appositamente implementato per lo scambio termico del potassio. In seguito, i dati numerici così ottenuti vengono sfruttati in ambiente di programmazione Python per la creazione di un meta-modello, il quale viene a sua volta impiegato per finalizzare l'ottimizzazione. In conclusione i risultati mostrano che la massa specifica tende a diminuire fino a valori intorno a 4 kg/kWe all'aumentare della temperatura del condensatore che difatti stabilisce sia l'efficienza radiativa che quella dell'intero ciclo. Inoltre il sistema di raffreddamento costituisce il componente più pesante per tutte le configurazioni con potenza superiore a 100 kWe, per l'ottimizzazione delle quali l'efficienza totale resta un parametro essenziale.A renewed interest in deep space exploration has grown over the last few years, and groundbreaking technologies are being investigated worldwide to get these challenging missions closer to feasibility. In the field of spacecraft propulsion, the Nuclear Electric technology (NEP) is seen as a future game changer. Thanks to the high power and specific impulse achievable, travel time and safety hazards associated with long-duration flights might be reduced. In a collaboration with the LPSC of Grenoble, this thesis work is part of the endeavor of implementing an optimization code capable of comparing different nuclear reactor concepts as well as power conversion systems (PCS) in order to provide the best engine configuration for any mission requirement. The focus is especially dedicated to the definition of a procedure aimed at determining the best Rankine cycle design from a system-specific mass (kg/kWe) point of view. By retrieving research activities from the early days of the U.S. space power program, the potentialities of such a thermodynamic cycle when combined with liquid metals such as potassium are presented. Moreover, the analysis points out the additional benefits of adopting a 1 MWth molten salt micro-reactor as a long-lasting and virtually maintenance-free power source. All thermal-physical calculations related to the cycle are performed using the Modelica language, which has been extended by including a specifically developed heat transfer model for potassium flow. The numerical results thus obtained are employed within a Python environment to create a metamodel version of the system, which is then processed to finalize the optimization. Outcomes show the PCS specific mass significantly decreasing down to 4 kg/Kwe with the increase of condenser temperature, which drives both the cycle and radiator efficiency. The latter confirms to be the most massive component for power outputs above 100 kWe, with cycle efficiency remaining a key parameter for trade-off analysis
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
