1,722,191 research outputs found
Theoretical and experimental study on a mechatronic speed variator device for HD Fuel-Injection-Common Rail Pump
Full text linkDa un punto di vista storico, la diffusione e il grande successo dei motori diesel sono dovuti all'introduzione del Common Rail System (CRS). Questo sistema di iniezione ha consentito un preciso dosaggio del carburante attraverso gli niettori agendo sui tempi di iniezione e regolando la pressione common rail. Inoltre, la capacità di controllare la pressione di iniezione ha permesso di eseguire più iniezioni, che è il punto cruciale per il moderno motore diesel per ridurre le emissioni inquinanti.
L'evoluzione del CRS nel tempo è principalmente legata al metodo utilizzato per controllare la pressione del common rail. Inizialmente, la regolazione della pressione common rail veniva eseguita dalla cosiddetta Pressure Control Valve (PCV). Questa valvola veniva montata direttamente sul common rail o, equivalentemente, in uscita alla pompa di alta pressione. Questa topologia garantisce una regolazione rapida e precisa della pressione, scaricando il carburante in eccesso nel serbatoio. L'inconveniente principale di questo approccio è rappresentato dalle fluttuazioni di pressione dovute al funzionamento della valvola, che agiscono da disturbo sul funzionamento degli iniettori. Inoltre, il ricircolo del flusso compresso al serbatoio provoca dissipazione di energia e riscaldamento indesiderato nel serbatoio del carburante.
Per ovviare agli svantaggi della PCV, nel moderno CRS è stata introdotta una Fuel Metering Unit (FMU), che consiste in una valvola montata sulla pompa ad alta pressione per regolarne il flusso in ingresso e quindi controllare la pressione common rail. Questo tipo di regolazione riduce la dissipazione di energia perché la quantità di carburante compresso dalla pompa è esattamente la quantità impostata dalla Engine Control Unit (ECU) per ottenere il corretto rapporto aria / carburante.
La nuova topologia di CRS proposta in questo lavoro, che è ancora in fase di sviluppo, introduce una trasmissione a variazione continua (CVT) tra il motore e la pompa ad alta pressione al posto del tradizionale giunto a ingranaggi. Consente la regolazione della velocità della pompa in base alla pressione common rail richiesta e al flusso di iniezione richiesto, riducendo così le perdite meccaniche nella pompa ad alta pressione.
In questo lavoro, riassumiamo i principali risultati ottenuti studiando l'efficacia di questo nuovo approccio. In particolare, presentiamo la strategia di controllo per un CRS completo dotato di una trasmissione a variazione continua, che è stata validata in simulazione, e un proof of concept sviluppato su una versione semplificata del sistema.From a historical point of view, the diffusion and the great success of diesel engines were induced by the introduction of the Common-Rail System (CRS). This injection system enabled precise metering of the fuel through the injector nozzles by acting on injection timings and by regulating the common-rail pressure. Moreover, the ability to control the injection pressure made it possible to perform multiple injections, which is the crucial point for the modern diesel engine to reduce pollutant emissions.
The evolution of the CRS over time is mostly related to the method used to control the rail pressure. Initially, the common-rail pressure regulation was performed by the so-called Pressure control valve (PCV). This valve was mounted directly on the common-rail or, equivalently, on the outlet port of the pump. This topology ensures a fast and precise regulation of the pressure by discharging the fuel in excess to the tank. The main drawback of this approach is represented by the pressure fluctuations due to the valve functioning, which acts as disturbances on the operation of the injectors. Furthermore, the recirculation of the compressed flow to the tank causes energy dissipation and undesired heating in the fuel tank.
To overcome the disadvantages of the PCV, in the modern CRS was introduced a Fuel Metering Unit (FMU), which consists of a valve mounted on the high-pressure pump to adjusts its inlet flow and thus control the common-rail pressure. This kind of regulation reduces energy dissipation because the quantity of fuel compressed by the pump and delivered to the rail is exactly the quantity set by the ECU to obtain the proper air/fuel ratio.
The new topology of CRS proposed in this work, which is still under development, introduces a Continuously Variable Transmission (CVT) between the engine and the high-pressure pump in place of a conventional gear coupling. It enables the adjustment of the pump speed according to the required common-rail pressure and demanded injection flow, thus reducing mechanical losses in the high-pressure pump.
In this work, we summarize the main results obtained investigating the effectiveness of this novel approach. In particular, we present the control strategy for a complete CRS equipped with a continuously variable transmission, which has been validated in simulation, and a preliminary experimental proof of concept performed on a simplified prototype version of the system
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
Advanced embedded systems for autonomous robots control
Full text linkIn recent years, Autonomous Underwater Vehicles (AUVs) and Remotely Operated Underwater Vehicles (ROUVs) have become essential for various underwater missions, including environmental monitoring, offshore resource exploration, structural inspection, and rescue operations. A primary challenge in these missions is precise underwater navigation, particularly during structure inspections, where acoustic and optical systems offer complementary benefits. These tasks require building a local 3D map of the object using inertial systems, a process complicated by the fact that global navigation methods like LBL (Long Base Line) or USBL (Ultra-Short Base Line) are often impractical due to acoustic signal transmission limitations from surface beacons. While optical systems deliver detailed object information, they are hindered by issues like stereo vision distortions, lighting variability, and noise from suspended particles. Conversely, Forward Looking Sonar (FLS) provides robustness against environmental noise but operates at lower resolution and in polar coordinates, complicating data alignment with optical data devices like stereo camera.
At the first part of our research we developed a nonlinear model of the ROUV in Computer-Aided Design (CAD) application and identified essential parameters, such as hydrostatic and hydrodynamic coefficients, through Computational Fluid Dynamics (CFD) simulations. These findings enabled accurate modeling of dynamic behaviors, including Coriolis effects and damping forces, forming the basis of the vehicle’s control equations. Additionally, a fractional-order PI controller was designed for yaw control, derived from a 6 DoF nonlinear model of the ROUV. The integration of Robot Operating System (ROS) and the Gazebo simulator allowed testing of control algorithms and sensor interactions within a digital twin environment, which included an Inertial Measurement Unit (IMU), FLS, Doppler Velocity Log (DVL) and stereo camera. This setup facilitated a smooth transition of navigation, computer vision, and path-planning functionalities from simulation to real-world deployment.
Based on the designed nonlinear model of the ROUV and the developed control algorithm, we integrated a multimodal inertial-visual mapping and navigation system. This system enabled us to analyze the impact of the vehicle’s movement on the accuracy and stability of the visual-inertial system in a dynamically changing environment. Mapping, navigation, and control of the underwater vehicle equipped with a visual-inertial system that merges multimodal data from FLS, DVL, IMU, and a stereo camera devices through unsupervised deep-learning detector and descriptor algorithm is a core study of this research.
Our research focuses on the geometric and computational integration of optical and sonar images. Given that a classical computer vision and supervised deep-learning feature matching algorithms is inadequate for opti-acoustic data fusion, we introduce an unsupervised feature matching approach tailored to sonar and optical datasets. This novel method enhances motion estimation by utilizing a hybrid direct and indirect matching strategy together with opti-acoustic epipolar constrains, where sonar data refines the depth of optical visual features. Both Sonar-to-Optical and Optical-to-Sonar mappings are employed to improve feature matching reliability under varying lighting and turbidity conditions.
In our research, we introduced opti-acoustic image processing, including a calibration approach for each device and both devices the sonar and stereo camera, along with imaging enhancements to improve data fusion quality. To further enhance degraded optical images, we implemented a method combining stereo calibration in air and further data improving via physically guided underwater image enhancement framework based on synthetic and real images integration. By integrating unsupervised deep learning algorithm we was able to map sonar features onto optical images, enhancing image depth estimation while preserving key details. Testing across various scene geometries showed substantial improvements in visual odometry accuracy, which is crucial for effective navigation and inspection in challenging underwater conditions.
Lastly, this research presents a robust framework for simulating underwater missions by combining CFD-based dynamics modeling, control algorithms, and sensor fusion techniques with optical and acoustic data. This comprehensive platform addresses underwater navigation and 3D mapping complexities, providing a unified system for testing and optimizing ROUV operations in diverse environments
Synthesis and characterization of novel hybrid perovskites featuring quaternary organoammonium cations with extended conjugation
Full text linkThe last decade has seen an unprecedented interest in hybrid metal halide perovskites semiconductors, as active layers in photovoltaic cells, with extraordinarily high efficiency values achieved, and for various different optoelectronic applications, especially light emission and radiation detection.
In fact, these materials have the advantage of being synthesized from affordable precursors by solution techniques, and of allowing a fine tuning of their photophysical properties through the modification of their composition. Regretfully, their utilization on a large scale is still hindered by their poor environmental stability, owed to the ammonium cations contained in them, which undergo hydrolysis reactions in the presence of water; for this reason, the main goal of the current research in the field of hybrid perovskites is represented by the improvement of their tolerance to moisture and other environmental agents (such as high temperature and O2).
The aim of this work was therefore the study of the possibility to enhance perovskite stability and performances, through the introduction of novel organic cations featuring the following characteristics: an extendedly conjugated structure, in order to modulate the optoelectronic properties of the materials, and the absence of hydrolysable protons, to avoid decomposition in the presence of moisture.
In particular, the synthesis and characterization of two novel water-insensitive and thermally stable hybrid metal halide perovskites, containing 4,4′-(anthracene-9,10-diylbis(ethyne-2,1-diyl))bis(1-methyl-1-pyridinium), (C30H22N2)2+ cation, is described in Chapters 3 and 4. The two materials, both of which showed intense photoluminescence, were prepared using different metals, lead in the first case and bismuth in the second, with the aim of exploring the possibility of replacing a toxic element such as lead (which is however the most frequently used metal in hybrid perovskites) with a safer alternative.
Moreover, the synthesis of a series of additional environmentally stable lead-based and bismuth-based hybrid materials, sharing the presence of quaternary conjugated bipyridinium cations is described in Chapter 5, together with a preliminary evaluation of their potentialities for applications
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
Authorial (audio) description: Creativity in the transfer of CSRs in Squid Game
No full textThe unprecedented growth of translation practices in the media sector has favoured the emergence of the creative industries, where creativity has taken centre stage and become the emblem of global cultural policies. The study addresses the role of creativity in the digital space of Netflix as a means of cross-cultural mediation and communication, and as a multidimensional tool in audio description (AD) to provide the end-users (the blind and visually impaired audiences) of digital audiovisual products with participatory and engaging forms of access to the audiovisual ‘planet’. The aim is to investigate whether and how creativity is used to transmit culture-specific references (CSRs) from a translation perspective within a highly discussed TV series streamed on Netflix. To do so, the rendering of the most significant CSRs in the Korean Netflix series Squid Game (SG) as transferred into the English and Italian ADs will be examined
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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