1,720,995 research outputs found
Problemi di controllo ottimo per sistemi non lineari con struttura State-Dependent Coefficient, implicazioni ed aspetti computazionali
No full textLa categoria di sistemi dinamici più assodata e studiata da maggior tempo è quella dei sistemi lineari; tuttavia, la maggior parte dei sistemi reali è non lineare, l’approccio State Dependent Coefficient (SDC) propone un metodo per
rappresentarli con strutture simili a quelle del mondo lineare ma conservando la loro natura non lineare. I sistemi lineari tempo invarianti sono stati ampiamente studiati, è possibile identificare chiaramente le caratteristiche come aggiungibilità, osservabilità e stabilità. Le tecniche di controllo possono raggiungere l’ottimo globale in modo matematicamente certo se il sistema soddisfa i requisiti richiesti. La strategia più frequente è quella di linearizzare il sistema attorno al punto di lavoro, ottenendo delle prestazioni soddisfacenti valide nell’intorno locale, questo approccio in molti casi è troppo restrittivo. Ad esempio, nel campo aerospaziale, dove i dispositivi lavorano in ogni parte dell’atmosfera in condizioni significativamente diverse, oppure più semplicemente in applicazioni dove il punto di lavoro si allontana da quello di linearizzazione. A differenza di tecniche di controllo non lineari, come sliding mode o feedback linearization, il controllo State Dependent Riccati Equation (SDRE) propone un’alternativa ibrida. Utilizzando la teoria del controllo ottimo lineare, è possibile estendere
l’efficacia del controllo Linear Quadratic Regulator (LQR) a sistemi non lineari passando attraverso l’uso di matrici SDC ed il controllo SDRE. Questo permette di controllare il sistema in un’area dello spazio di stato più estesa dell’intorno del punto di lavoro dove si sarebbe linearizzato il sistema. La tecnica di controllo SDRE è stata applicata su diversi dispositivi, come missili, aereomobili, UAV, sistemi autonomi, sistemi biomedicali e robot. La robustezza, flessibilità di questa tecnica e la possibilità odierna di implementare il controllo in tempo reale hanno attirato l’attenzione della comunità. Nonostante la crescente documentazione sulla tecnica SDRE è presente tutt’oggi una significativa mancanza di giustificazioni teoriche sulla scelta delle matrici SDC e la loro efficacia nel rappresentare il sistema. In questa tesi viene illustrato come rappresentare un sistema in spazio di stato con termini dipendenti dallo stato stesso. Sono stati raccolti i metodi più comuni per costruire le matrici SDC migliorandone alcuni aspetti e proponendoalternative. Il controllo SDRE con struttura SDC viene utilizzato e studiato in efficienza, efficacia e duttilità con metodi noti in letteratura e nuove modalità. Viene proposta una soluzione alternativa per tale controllo nella scelta della funzione di costo, estendibile anche al noto LQR. In conclusione, sono illustrate tutte le tecniche su diversi casi di studio utilizzati comunemente in letteratura ed alcuni casi di applicazione reale.The category of dynamical systems most established and studied for the longest time is that of linear systems; however, most of the real systems are non-linear, the State Dependent Coefficient (SDC) approach proposes a method to represent them with structures similar to those of the linear world retaining their non-linear nature. Linear time invariant systems have been extensively studied, it is possible to clearly identify characteristics such as reachability, observability and stability. The control techniques can achieve the overall optimum in a mathematically certain way if the system meets the requirements. The most frequent strategy is to linearize the system around the working point, obtaining satisfactory performances valid in the local neighborhood, this approach in many cases is too restrictive. For example, in the aerospace field, where the devices work in every part of the atmosphere under significantly different conditions, or more simply in applications where the working point moves away from that of linearization. Unlike non-linear control techniques, such as sliding mode or feedback linearization, the State Dependent Riccati Equation (SDRE) control offers a hybrid alternative. Using the theory of linear optimal control, it is possible to extend the effectiveness of the Linear Quadratic Regulator (LQR) control to non-linear systems through the use of SDC matrices and SDRE control. This allows to control the system in an area of the state space that is larger than the neighborhood working point where the system has been linearized. The SDRE control technique has been applied to various devices, such as missiles, aircraft, UAVs, autonomous systems, biomedical systems and robots. The robustness, flexibility of this technique and today's ability to implement control in real time have attracted the attention of the community. Despite the growing documentation on the SDRE technique, there is still a significant lack of theoretical justifications on the choice of SDC matrices and their effectiveness in representing the system.
This thesis illustrates how to represent a system in state space with terms dependent on the state itself. The most common methods for constructing SDC matrices have been collected, improving some aspects and proposing alternatives. The SDRE control with SDC structure is used and studied in efficiency, efficacy and ductility with methods known in the literature and new modalities. An innovative solution is proposed for this control in the choice of the Q matrix, which can also be extended to the well-known LQR. In conclusion, all the techniques on different case studies commonly used in literature and some real application cases are illustrated
On the falls of two wheeled vehicles
No full textThe study and analysis of two-wheeled vehicle’s falls and critical situations are difficult tasks to perform due to the rather elaborate dynamics that come into play. However, to prevent such events, it is necessary a good understanding of the conditions that trigger them. To this purpose, suitable tools able to show how the vehicle's parameters may influence its dynamic behavior are required. In the present paper the analysis of the major falls relative to a two-wheeled vehicle is performed by means of dynamics simulations based on the motorcycle model presented by the authors in prior works. The simulations are also discussed in relation to alternative descriptions provided by theoretical instruments reported in the literature and the substantial consistency of the results is shown
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
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
Embedded low level control of DC motors for actuating robotic legs
No full textIn this paper an embedded system for accurate control of torque, speed and position of DC motors which actuate the joints of a robotic leg is presented. The proposed embedded system is not based on dedicated and expensive motor controllers but on a general pourpose embedded board equipped with a 32bit microcontroller. For each motor the embedded system can selectively operate in three different control modes: torque, speed and position, to control concurrently at least three DC motors
with different control tasks. Each motor is simply equipped with a rotatory encoder and a low-cost current sensor which provides measures of velocity and current as feedback signals. The experimental results show that the embedded controller
is able to regulate the motor variables with interesting timeresponses. Although the embedded controller was designed for
the proposed robotic application, it is applicable to other systems where the concurrent control of several DC-motors is required
- …
