1,720,965 research outputs found
Injection rate measurement of a scr injector operating in flash-boiling conditions
No full textIn the present paper an experimental campaign aimed at analyzing the hydraulic behavior of a SCR injector operated with high temperature Urea-Water Solution (UWS) is presented. In previous analyses, the effects exerted by UWS high temperature on the spray evolution were investigated in terms of spray shape and sizing. It was observed that increasing the injected liquid temperature so to approach flash-boiling conditions results in an increase of the spray cone angle and in reduced penetration. Moreover, the spray sizing is significantly reduced improving the UWS to ammonia conversion rate. The main objective of the present research is the investigation of the effects exerted by flash-boiling on the injector hydraulics in terms of mean and shot-to-shot injected mass and injection rate. In order to investigate the injector actual hydraulic behavior when injecting high temperature fluid, an innovative instrument named dINJ Injection Analyzer was developed at the University of Perugia. This instrument detects the shot-to-shot injection rate profile and injected volume while preserving the normal operation conditions for the injector, i.e. with the injected spray developing in a gaseous environment. The proposed instrument is based on the detection of the pressure time-history in a closed vessel acting as isolated fuel rail during the injection process. According to this approach the typical constraints of conventional Injection Analyzers requiring a pressurized volume (a closed vessel or a pipe) are overcome. A low pressure injector, as long as a GDI injector, can be operated with the prescribed pressure differential, maintained throughout the injection process. Moreover, the injection in a gaseous environment allows both the onset of peculiar flow conditions (flash-boiling) and the application of additional diagnostics as imaging. In the paper, after a preliminary validation of the proposed instrument with a Port-Fuel-Injection (PFI) injector, the hydraulic analysis of a SCR doser supplied with UWS at temperature ranging from ambient to 130 °C is presented and discussed, analysing the mean injected mass trend with temperature, the shot-to-shot dispersion and the injection rate profile demonstrating the effect of the flash-boiling phenomenon on the discharge process. A partial limitation of the current analysis is given by the ambient pressure and temperature conditions maintained in the vessel downstream the injector nozzle. The investigation will be completed in the future by an upgrade of the experimental setup in order to control not only the pressure and temperature of the UWS in the nozzle but also the pressure and temperature level of the gaseous environment in which the spray evolves
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
Analisi sperimentale e numerica di un sistema di iniezione ad attuazione diretta per motori Diesel
No full textNel presente lavoro si riportano i risultati di un’analisi sperimentale e numerica del comportamento idraulico e dell’evoluzione degli spray di un innovativo sistema di iniezione ad attuazione diretta per motori Diesel light duty. Il sistema d’iniezione analizzato - Magneti Marelli Diesel Direct Injection, DDI - è basato sull’attuazione diretta dello spillo iniettore mediante solenoide. Il sistema DDI opera con pressioni di iniezione fino a 600 bar, con un polverizzatore multi-foro che consente di ottenere una distribuzione di getti di combustibile in camera di combustione adatta per applicazioni Diesel industriali ed automotive di piccola cilindrata. Nella fase attuale della ricerca, i cui risultati sono riportati nel presente lavoro, il comportamento idraulico del sistema DDI in termini di volume iniettato e di portata istantanea è stato analizzato in diverse condizioni di funzionamento. L’evoluzione degli spray risultante in queste condizioni è stata inoltre analizzata in condizioni di camera quiescente mediante tecniche di visualizzazione per determinare le principali caratteristiche geometriche del getto. Il successivo confronto con le simulazioni computazionali è il punto di partenza per lo sviluppo di una metodologia che, mediante l'integrazione di codici di calcolo 1D e 3D, sia in grado di descrivere l'evoluzione dello spray e la sua interazione con la carica presente all’interno della camera di combustione. In questa fase del lavoro si è valutato il comportamento dei principali modelli CFD utilizzati per la simulazione dello spray di combustibile con approccio lagrangiano, in condizioni di pressione di iniezione non convenzionali per applicazioni Diesel. Si riportano quindi i confronti sperimentali-numerici con i principali risultati conseguiti nel corso di un campagna di validazione dei modelli di atomizzazione, valutando anche gli effetti di alcuni parametri, quali la dimensione media della cella computazionale, sull'evoluzione dello spray
Blood pressure continuous measurement through a wearable device: development and validation of a cuffless method
Full text linkThe present study aims to develop and validate a cuffless method for blood pressure continuous measurement through a wearable device. The goal is achieved according to the time-delay method, with the guiding principle of the time relation it takes for a blood volume to travel from the heart to a peripheral site. Inversely proportional to the blood pressure, this time relation is obtained as the time occurring between the R peak of the electrocardiographic signal and a marker point on the photoplethysmographic wave. Such physiological signals are recorded by using L.I.F.E. Italia’s wearable device, made of a sensorized shirt and wristband. A linear regression model is implemented to estimate the corresponding blood pressure variations from the obtained time-delay and other features of the photoplethysmographic wave. Then, according to the international standards, the model performance is assessed, comparing the estimates with the measurements provided by a certified digital sphygmomanometer. According to the standards, the results obtained during this study are notable, with 85% of the errors lower than 10 mmHg and a mean absolute error lower than 7 mmHg. In conclusion, this study suggests a time-delay method for continuous blood pressure estimates with good performance, compared with a reference device based on the oscillometric technique
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
Experimental Investigation on the Effects on Performance and Emissions of an Automotive Euro 5 Diesel Engine Fuelled with B30 from RME and HVO
No full textThe effects of using blended renewable diesel fuel (30% vol.), obtained from Rapeseed Methyl Ester (RME) and Hydrotreated Vegetable Oil (HVO), in a Euro 5 small displacement passenger car diesel engine have been evaluated in this paper. The hydraulic behaviour of the common rail injection system was verified in terms of injected volume and injection rate with both RME and HVO blends fuelling in comparison with commercial Diesel. Further, the spray obtained with RME B30 was analysed and compared with Diesel in terms of global shape and penetration, to investigate the potential differences in the air-fuel mixing process. Then, the impact of a biofuel blend usage on engine performance at full load was first analysed, adopting the same reference calibration for all the tested fuels. Afterwards, the effects of a biofuel blend usage on brake specific fuel consumption and on exhaust emissions were also evaluated at 7 different part load operating conditions, representative of the New European Driving Cycle. Finally, soot-NOx trade-off obtained by means of EGR sweeps were performed in the same operating points, in order to gather detailed information about further possible emissions benefits that could be achieved through a more extensive ECU recalibration
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
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