1,721,446 research outputs found
Sviluppo di metodi di progettazione per lo studio del danneggiamento a fatica di componenti meccanici
Full text linkA multidisciplinary approach to mechanical design, able to focus not only on the specific component but on the whole technical system surrounding it, is necessary to successfully deal with the actual complexity of technical innovation and industrial progress.
For this purpose, the aim of this work is to deepen some problems of fatigue damage of mechanical components by means of different design methods in order to show the advantages and the inventive step coming from their synergic employ.
At first, theoretical methods for fatigue design of mechanical components and welded structures are analysed and compared to the recommendations given by design standards as regards some specific structural problems of welded details. In this way, the advantages of joining different theoretical methods is pointed out by the comparison with some experimental data. Then, the complex problems of fatigue damage of a more complicated mechanical component as a church bell are analysed. A dedicated software for the simulation of the dynamic behaviour of bells is developed in the context of a European research project. In order to deepen the reasons and the influencing parameters in the damage phenomena and to allow a future application of simulations’ results for fatigue life predictions, the experimental fatigue behaviour of bell bronze is analysed. In this context, theoretical models are employed to summarise fatigue test results on both plain and notched specimens. Finally, different theoretical, numerical and experimental approaches to mechanical design are employed for the development of a electromechanical test bench for torsion fatigue tests that has to be seen as a first step forward future implementations of flexible test systems for both material analysis and components testing. Starting from a fatigue damage problem, this activity requires to collect different skills in both mechanical design and electric and control applications. The result of a synergic employ of these skills is the possibility to get both effective scientific improvements through the validation of theoretical models by means of dedicated fatigue test campaigns and a solid cooperation with business companies by providing reliable data on components resistance and useful suggestions to improve design against fatigue.L’attuale complessità dell’innovazione tecnica e dello sviluppo industriale richiedono sempre più l’adozione di un approccio alla progettazione meccanica di tipo multidisciplinare che consideri non solo il singolo componente ma l’intero sistema tecnico nel quale è inserito.
Il presente lavoro di tesi si propone di approfondire ed integrare, applicandoli a varie problematiche, diversi metodi per lo studio del danneggiamento a fatica di componenti meccanici soggetti a carichi di esercizio, illustrando i vantaggi e il potenziale innovativo che deriva dalla sinergia di questi approcci.
Il lavoro si sviluppa a partire dall’approfondimento di modelli teorici per la progettazione a fatica di componenti e strutture saldate proposti in letteratura che vengono applicati allo studio di particolari problematiche strutturali e confrontati con i metodi proposti dalle normative di progettazione. In questo modo viene messa in rilievo, sulla base di evidenze sperimentali, la necessità di integrazione di diversi approcci teorici. Lo studio si allarga quindi a considerare le problematiche di danneggiamento a fatica di un componente meccanico complesso quale le campane da chiesa. Questo argomento, nato dalla partecipazione ad un progetto di ricerca europeo, viene affrontato sia dal punto di vista dello sviluppo di un programma per la simulazione del comportamento dinamico delle campane, sia dal punto di vista della caratterizzazione sperimentale del comportamento a fatica del materiale. Questo secondo approccio, che prevede anche l’applicazione di modelli teorici per la sintesi dei risultati, oltre ad approfondire cause e parametri di influenza nei fenomeni di danneggiamento, ha l’obbiettivo di rendere possibile, in futuro, l’applicazione dei risultati delle simulazioni per previsioni di resistenza a fatica delle campane. Infine, l’integrazione e l’effetto sinergico di diversi approcci allo studio di problematiche di danneggiamento a fatica trovano completa concretizzazione nello sviluppo di un banco elettromeccanico per prove a fatica in torsione. Quest’attività, punto di partenza per lo sviluppo di sistemi di prova flessibili per la caratterizzazione di materiali e la prova di componenti, permette di far convergere metodi specifici con competenze trasversali che ampliano i confini della progettazione meccanica in senso stretto, dimostrando di avere grandi potenzialità dal punto di vista dei risvolti applicativi sia per la ricerca che per le collaborazioni con realtà industriali
Anti-selectin therapy for the treatment of inflammatory diseases
No full textLeukocyte migration into the tissues represents a key process in the pathogenesis of inflammatory diseases. Data obtained in clinical trials have convincingly shown that inhibition of leukocyte migration into the target organs represents an effective therapeutic approach for diseases in which inflammation has a noxious effect. Leukocyte tethering and rolling are the earliest steps of leukocyte adhesion cascade in inflamed vessels. Selectins are type I transmembrane glycoproteins that bind sialylated carbohydrate structures in a calcium-dependent manner and are involved in the tethering and rolling of leukocytes under physiological and pathological conditions. Three selectins have been identified: L-, P- and E-selectin. Current understanding of the glycosylation-dependent selectin function reveals a complex role for selectins and their ligands during inflammatory diseases. Among selectin ligands, mucin P-selectin glycoprotein ligand-1 (PSGL-1) binds all three selectins and has a well-documented role in organ targeting during inflammation in animal models. However, although inhibition of selectins and their ligands in animal models of inflammatory diseases has proven the validity of this approach in vivo, only a limited number of anti-selectin drugs have been tested in humans. Recent results obtained in clinical trials for asthma and psoriasis show that, although very challenging, the development of selectin antagonists holds concrete promise for the therapy of inflammatory diseases
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
The emerging role of neutrophils in neurodegeneration
Full text linkNeutrophils are the first line of defense in the innate immune system, helping to maintain tissue homeostasis as well as eliminating pathogens and self-components. The traditional view of neutrophils as simple phagocytes has been revised over the last decade as new research reveals their unappreciated complexity. Neutrophils are phenotypically and functionally heterogeneous, allowing them to act as modulators of both inflammation and immune responses. During acute inflammation, neutrophils perform a variety of beneficial effector functions, but when inflammation is induced by injury (sterile inflammation) the benefits of neutrophils in tissue repair are more controversial. In several pathological conditions, including cancer and autoimmune diseases, neutrophils can trigger harmful tissue damage. Interestingly, neutrophils are also key players in neuroinflammatory disorders, during which they transmigrate in the central nervous system, acquire a toxic phenotype, home in on neurons, and release harmful molecules that compromise neuronal functions. In this review, we discuss recent data that redefine the cell biology and phenotype of neutrophils, focusing on the role of these cells in multiple sclerosis and Alzheimer's disease, both of which feature strong neuroinflammatory components
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
Live Imaging of Immune Responses in Experimental Models of Multiple Sclerosis
Full text linkExperimental autoimmune encephalomyelitis (EAE) is the most common animal model of multiple sclerosis (MS), a chronic inflammatory autoimmune disease of the central nervous system (CNS) characterized by multifocal perivascular infiltrates that predominantly comprise lymphocytes and macrophages. During EAE, autoreactive T cells first become active in the secondary lymphoid organs upon contact with antigen presenting cells (APCs), and then gain access to CNS parenchyma, through a compromised blood–brain barrier, subsequently inducing inflammation and demyelination. Two-photon laser scanning microscopy (TPLSM) is an ideal tool for intravital imaging because of its low phototoxicity, deep tissue penetration and high resolution. In the last decade, TPLSM has been used to visualize the behavior of T cells and their contact with APCs in the lymph nodes and target tissues in several models of autoimmune diseases. The leptomeninges and cerebrospinal fluid represent particularly important points for T cell entry into the CNS and reactivation following contact with local APCs during the preclinical phase of EAE. In this review, we highlight recent findings concerning the pathogenesis of EAE and MS, emphasizing the use of TPLSM to characterize T cell activation in the lymph nodes and CNS, as well as the mechanisms of tolerance induction. Furthermore, we discuss how advanced imaging unveils disease mechanisms and helps to identify novel therapeutic strategies to treat CNS autoimmunity and inflammation
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
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