1,720,997 research outputs found
Giovanni Di Napoli, Giovanni Pico della Mirandola e la problematica dottrinale del suo tempo
No full textSemeese Gustave. Giovanni Di Napoli, Giovanni Pico della Mirandola e la problematica dottrinale del suo tempo . In: Revue Philosophique de Louvain. Troisième série, tome 67, n°95, 1969. p. 493
Studio sperimentale e modellistico di innovazioni tecnologiche a livello componentistico e di sistema nel campo della refrigerazione: ottimizzazione e valutazione delle prestazioni termo-economiche-ambientali
No full textLa quasi totalità delle macchine per la climatizzazione e la refrigerazione impiegano cicli a compressione di vapore, caratterizzati da un’elevata efficienza nella conversione energetica. Attualmente, questi settori contribuiscono al 17% dei consumi totali di elettricità, quota destinata ad aumentare notevolmente, in quanto che le attuali unità installate (circa 4 miliardi) triplicheranno entro il 2050. Le tecnologie adoperanti cicli a compressione di vapore sono anche responsabili di un notevole impatto ambientale, sia indiretto che diretto. Riguardo il primo, esso è dovuto alle emissioni inquinanti causate dalla produzione di energia elettrica, prodotta in larga parte (80%) da fonti non rinnovabili. Ciò determina emissioni di sostanze climalteranti, responsabili dell’incremento della temperatura superficiale media della Terra, che nel 2100 potrebbe diventare di 3.6°C superiore rispetto ai livelli preindustriali. L’impatto ambientale diretto è invece connesso all’impiego di fluidi refrigeranti ad alto GWP. Tale scenario può essere parzialmente mitigato tramite l’adozione delle seguenti politiche: da un lato, la riduzione dei consumi energetici e del conseguente impatto ambientale indiretto, che passa attraverso l’implementazione di soluzioni che permettano di aumentare sia l’efficienza dei singoli componenti che dell’intero sistema. In secondo luogo, la riduzione dell’impatto diretto tramite sostituzione dei refrigeranti ad alto effetto serra con fluidi ecocompatibili. Di conseguenza, l’obiettivo del presente lavoro di tesi è quello di affrontare tali problematiche, con un approccio sia modellistico che sperimentale, al fine di investigare le prestazioni di refrigeranti a basso impatto ambientale e studiare le innovazioni sia a livello componentistico che di configurazione impiantistica, caratterizzandone l’efficienza, la fattibilità economica e la competitività sul mercato. In relazione alle innovazioni sui componenti di impianto, sia i compressori che scambiatori di calore sono oggetto di questo studio. In particolare, viene proposto uno studio numerico di un compressore lineare, con l’obiettivo di effettuarne un’analisi termo-economica ed individuare su quali parametri costruttivi risulta più conveniente agire per avere dei benefici sia in termini prestazionali che economici. Per gli scambiatori di calore, invece, è stato condotto uno studio sperimentale per la misura del coefficiente di scambio termico e delle perdite di carico durante l’evaporazione in tubi di refrigeranti a basso impatto ambientale (miscele R454C e R455A). La raccolta di dati sperimentali consente di effettuare una valutazione critica dei metodi predittivi presenti in letteratura, per fornire informazioni utili ai progettisti di scambiatori di calore circa le migliori correlazioni da impiegare per la valutazione del coefficiente di scambio termico di questi nuovi refrigeranti. In relazione alle innovazioni sui sistemi di produzione del freddo, è stato sviluppato un modello termodinamico di un ciclo ibrido ad eiettore, composto dall’unione di un ciclo diretto ed un ciclo inverso. L’eiettore permette la compressione del refrigerante senza l’impiego del compressore azionato elettricamente. Questo nuovo ciclo termodinamico, consentendo la produzione dell’effetto frigorifero tramite energia solare o calore di scarto da processi industriali, comporta una notevole riduzione dei consumi del sistema. Il sistema in esame è stato ottimizzato con riferimento a particolari applicazioni, riguardanti la climatizzazione residenziale o di navi da crociera, sfruttando, rispettivamente, energia solare o l'energia residua contenuta nei gas di scarto dei motori propulsivi. Il confronto termo-economico con la tecnologia di riferimento ha evidenziato la particolare convenienza di questi sistemi, ulteriormente incrementata con scenari di aumento del costo specifico dell'energia elettrica e dei combustibili fossili.Most of the cooling and heating appliances, both for refrigeration and air conditioning purposes, employ vapor compression cycles, due to their efficiency in energy conversion. Currently, refrigeration and air condition account for the 17% (almost 4000 TWh/year) of the total electricity consumption worldwide, and this share is likely to rise remarkably, due to the enormous increase of the installed units expected by 2050.
Technologies employing vapor compression cycles are responsible for a huge environmental impact, both indirect and direct. The indirect environmental impact is related to the pollutant emissions due to the electricity generation, that is currently produced mainly (80%) by means of non-renewables sources. This aspect causes the emission of substances, such as CO2 and other greenhouse gases, that lead to an increase of the Earth average temperature, expected by 2100 to be 3.6°C higher compared to the preindustrial levels. The direct environmental impact, instead, is connected to the release in atmosphere of hydrofluorocarbons (HFC) refrigerants with high global warming potential (GWP).
This scenario can be partially mitigated by implementing the following policies: from one side, higher efficiency both at component and at system level, that lead to a reduction of the energetic consumption and the related indirect environmental impact. From the other side, the reduction of the direct environmental impact can be achieved with the ban of high GWP refrigerants and the use of alternative eco-friendly substances.
For these reasons, the aim of the present thesis is to deepen the mentioned issues with a double approach, both modelling and experimental, to analyse the performance of low-GWP refrigerants and to investigate the innovations both at component and at system levels, to define the efficiency, the economic feasibility and the competitiveness on the market.
As regards the innovation at components level, both compressors and heat exchangers are addressed. Particularly, a numerical thermo-economic analysis of a linear compressor is firstly proposed, with the purpose to highlight the main design parameters having the higher influence on the compressor performance and costs in order to optimize its design. Concerning the heat exchangers, an experimental investigation on the flow boiling heat transfer coefficient and pressure drop measurement of low-GWP refrigerants (mixtures R454C and R455A) is performed. The experimental data collected allow to carry out a critical assessment of several predictive methods available in scientific literature, in order to provide useful information to engineers involved in the heat exchangers design process.
As regards the innovation in cold production systems, a thermodynamic model of a ejector hybrid cycle is developed. The novel cycle is made up by a direct/indirect system, with the presence of an ejector that allows to compress the refrigerant without using a compressor. The proposed thermodynamic cycle provides the cool production by means of solar energy or waste heat from industrial processes, allowing a reduction of the electricity consumption. The system under investigation has been optimized for different applications, that are residential air conditioning by using the solar energy and the air conditioning system of a cruise ship, exploiting the residual heat of the exhaust gas released from the propulsion diesel engines. The thermo-economic comparison highlighted the convenience of these systems with respect to traditional electric chillers, especially in scenarios with high specific cost of the electric energy and of the fossil fuels
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
Laser ablation for prostate tumors: analysis of different bioheat transfer models
No full textThermal therapies, such as laser ablation, are garnering interest for treating several diseases, in a non-invasive way, preventing surgical treatments and, for example, allowing the preservation of prostate functions in the case of prostate cancer. Nevertheless, approved therapies for cancer treatments are still missing, limiting the reliability of such methodologies, since an insufficient exposure time and thermal power settings could lead to incomplete tumor ablation, its redevelopment and metastasis occurrence. Consequently, it is fundamental to develop accurate bioheat transfer models providing guidelines to surgeons, helping to improve treatment effectiveness. However, as several models have been developed, the study aims to compare four bioheat transfer models, namely the simplified Pennes' approach, two porous media-based methods, i.e. the Local Thermal Equilibrium and the Local Thermal Non-Equilibrium equations, and the non-Fourier approach, namely Dual Phase Lag equation. The effects of laser power, tissue porosity and blood vessels diameter are investigated. The finite elements (FEM) commercial software Comsol Multiphysics is employed to investigate a 2D axisymmetric domain, consisting of two concentric spheres (the tumor and the healthy tissue). The laser source is modeled with the Beer-Lambert's law, assuming a laser source with a gaussian distribution. Results in terms of temperature field and necrotic region are presented, developing linear correlations by fitting FEM results. Finally, the difference among the necrotic areas predicted with the different approaches is reported, providing high discrepancies especially for highly vascularized tissue, with a lower damaged surface predicted in case of porous media approaches
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
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
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