1,720,954 research outputs found
Experimental Determination of the Performances during the Cold Start-Up of an Air Compressor Unit for Electric and Electrified Heavy-Duty Vehicles
Full text linkCompressed air is crucial on an electric or electrified heavy-duty vehicle. The objective of this work was to experimentally determine the performance parameters of the first prototype of an electric-driven sliding-vane air compressor, specifically designed for electric and electrified heavy-duty vehicles, during the transient conditions of cold start-ups. The transient was analyzed for different thermostatic temperatures: 0 °C, −10 °C, −20 °C, and −30 °C. The air compressor unit was placed in a climatic chamber and connected to the electric grid, the water-cooling loop, and the compressed air measuring and controlling rig. The required start-up time was greater the lower the thermostatic temperature, ranging from 30 min at 0 °C to 221 min at −30 °C and depending largely on the volume of the lubricant oil filled initially. The volume flow rate of the compressed air was lower than nominal at the beginning, but it showed a step increase well beyond nominal when the oil reached 50 °C and then decreased gently towards nominal, while the input power kept steady at nominal after a short initial peak. These facts must be considered when estimating the time and the energy required by the air compressor unit to fill up the compressed air tanks of the vehicles
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
Experimental determination of the performances during the extreme cold start-up of an air compressor for electric heavy vehicles
No full textLAUREA MAGISTRALEI compressori volumetrici sono utilizzati nel settore trasporti per l’alimentazione tramite aria compressa, degli ausiliari e del sistema frenante. Negli ultimi anni, l’elettrificazione del settore del trasporto su strada porta un incremento nell’utilizzo di veicoli elettrici pesanti quali bus e camion. Convenzionalmente nei veicoli a diesel il compressore viene trainato dal motore a combustione interna, mentre nei veicoli elettrici esso presenta un apposito motore elettrico alimentato dalle batterie. Nei veicoli a combustibile il compressore è riscaldato mediante il motore, pratica che non avviene nella configurazione elettrica. L’avviamento in condizioni estremante fredde può portare problemi relazionati a fenomeni di congelamento e al cambiamento delle proprietà fisico chimiche dell’olio, quindi problemi di lubrificazione. È rilevante indagare sui tempi di riempimento dei serbatoi del sistema frenante e sui consumi elettrici del compressore in questa fase. La tesi è svolta in collaborazione all’azienda Ing. Enea Mattei S.p.A., azienda leader nella produzione di compressori rotativi a palette, e si pone l’obiettivo di valutare le prestazioni del nuovo compressore XT65, in condizioni estremamente fredde. Il compressore XT65 presenta una serie di vantaggi che lo rende particolarmente adatto ai veicoli elettrici pesanti quali, bassa velocita di rotazione, un design compatto e modulare, minimo peso e vibrazioni, costi competitivi, alta affidabilità e rendimento. Presso il Laboratorio di Micro-Cogenerazione del Politecnico di Milano, le prove vengono svolte a varie temperature 0, -10, -20, e -30 °C, nelle condizioni di start-up. Il conseguimento dello stato stazionario viene inteso come il raggiungimento della temperatura di 80 °C nel separatore aria/olio del compressore. I risultati mostrano di essere ripetibili data la sovrapposizione delle curve a stessa temperatura; l’unica eccezione si presenta nelle prove a -30 °C, dove si nota un andamento differente delle curve dopo 70 min. La camera climatica infatti non è in grado di mantenere questa temperatura per tutta la durata della prova. La temperatura influisce nettamente sulle prestazioni del compressore, il tempo di start-up presenta un aumento considerevole passando da 28.8 min nei test a 0°C fino ad 221.2 min ad -30°C, con un incremento del 668%. La potenza risulta in prima analisi costante intorno a 2.7 kW, all’accensione presenta un picco di 3 kW a 0°C e di 3.5 kW a -30°C. La portata mostra un incremento alla diminuzione della temperatura con valori medi che vanno da 198 nl/min a 0°C a 210 nl/min a -30°C. Lo stesso andamento si nota nella portata specifica con misure in un range da 74 nl//kW/min a 79 nl//kW/min rispettivamente a 0°C e -30°C.Volumetric compressors are used in the transport sector for the supply of compressed air at the braking system and at the auxiliaries. In recent years, the electrification of road transport sector has led to an increase in the use of heavy electric vehicles such as buses and trucks. Conventionally in diesel vehicles the compressor is driven by the internal combustion engine, while in electric vehicles the compressor is coupled with an electric motor powered by the batteries. In the fuel-powered vehicles the compressor is heated by the engine, this does not occur in the electrical configuration. Star-up in extremely cold conditions can lead some problems related to freezing phenomena and to the change in the physical and chemical properties of the oil, that can lead improper lubrification. Is important to investigate the filling times of the brake system reservoirs and the electricity consumption of the compressor in the start-up. The thesis is carried out in collaboration with the company Ing. Enea Mattei, a leading company in the production of rotary vane compressors and has the aim of evaluating the performance of the new XT65 compressor in extremely cold condition. The XT65 compressor has a series of advantages which makes it particularly suitable for heavy electric vehicles such as, low rotation speed, a compact and modular design, minimum weight and vibrations, competitive costs, high reliability and efficiency. At the Micro-Cogeneration Laboratory of the Politecnico of Milan, the tests are carried out at various temperatures 0, -10, -20, and -30°C, in the transient-state. The reaching of the steady-state is intended as the achievement of the temperature of 80°C in the compressor air/oil separator. The results are repeatable thanks to the overlap of the curves at the same temperature. The only exception occurs in the tests at -30°C where is observed a different trend of the curves after 70 min, in fact, the climatic chamber is unable to maintain this temperature along the test. The temperature clearly affects the performance of the compressor, the start-up time shows a considerable increase from 28.8 min in the tests at 0 °C up to 221.2 min at-30°C, with an increase of 668%. The power is in the first analysis constant around 2.7 kW, at start it has a peak of 3 kW at 0 °C and 3.5 kW at -30 °C. The flow rate increases when temperature go down with average values ranging from 198 nl/min at 0°C to 210 nl/min at -30°C. The same trend can be seen in the specific flow rate with measurements in a range from 74 nl/kW/min to 79 nl/kW/min respectively at 0 °C and -30 °C
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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