Fenomeni di diffusione delle notizie in siti di microblogging: modelli di analisi e studio di caso.

L'informazione è alla base della conoscenza umana. Senza, non si potrebbe sapere nulla di ciò che esiste, di ciò che è stato o di quello che potrebbe accadere. Ogni giorno si assimilano moltissime informazioni, che vengono registrate nella propria memoria per essere riutilizzate all'occorrenza. Ne esistono di vari generi, ma il loro insieme va a formare quella che è la cultura, educazione, tradizione e storia dell'individuo. Per questo motivo è importante la loro diffusione e salvaguardia, impedendone la perdita che costerebbe la dipartita di una parte di sé, del proprio passato o del proprio futuro. Al giorno d'oggi le informazioni possono essere acquisite tramite persone, libri, riviste, giornali, la televisione, il Web. I canali di trasmissione sono molti, alcuni più efficaci di altri. Tra questi, internet è diventato un potente strumento di comunicazione, il quale consente l'interazione tra chi naviga nel Web (ossia gli utenti) e una partecipazione attiva alla diffusione di informazioni. Nello specifico, esistono siti (chiamati di microblogging) in cui sono gli stessi utenti a decidere se un'informazione possa essere o meno inserita nella propria pagina personale. In questo caso, si è di fronte a una nuova "gestione dell'informazione", che può variare da utente a utente e può defluire in catene di propagazione (percorsi che compiono i dati e le notizie tra i navigatori del Web) dai risvolti spesso incerti. Ma esiste un modello che possa spiegare l'avanzata delle informazioni tra gli utenti? Se fosse possibile capirne la dinamica, si potrebbe venire a conoscenza di quali sono le informazioni più soggette a propagazione, gli utenti che più ne influenzano i percorsi, quante persone ne vengono a conoscenza o il tempo per cui resta attiva un'informazione, descrivendone una sorta di ciclo di vita. E' possibile nel mondo reale trovare delle caratteristiche ricorrenti in queste propagazioni, in modo da poter sviluppare un metodo universale per acquisirne e analizzarne le dinamiche? I siti di microblogging non seguono regole precise, perciò si va incontro a un insieme apparentemente casuale di informazioni che necessitano una chiave di lettura. Quest'ultima è proprio quella che si è cercata, con la speranza di poter sfruttare i risultati ottenuti nell'ipotesi di una futura gestione dell'informazione più consapevole. L'obiettivo della tesi è quello di identificare un modello che mostri con chiarezza quali sono i passaggi da affrontare nella ricerca di una logica di fondo nella gestione delle informazioni in rete.

Analisi biomeccanica del MAWASHI GERI JODAN in cinture nere di Karate: modelli tecnici a confronto

In martial arts there are several ways to perform the turning kick . Following the martial arts or different learning models many types of kicks take shape. Mawashi geri is the karate turning kick. At the moment there are two models of mawashi geri, one comes from the traditional karate (OLD), and the other newer (NEW), who agrees to the change of the rules of W.K.F. (World Karate Federation) happened in 2000 (Macan J. et all 2006) . In this study we are focus on the differences about two models the mawashi geri jodan of karate. The purpose of this study is to analyse cinematic and kinetic parameters of mawashi geri jodan. Timing of the striking and supporting leg actions were also evaluated A Vicon system 460 IR with 6 cameras at sample frequency of 200 Hz was used. 37 reflective markers have been set on the skin of the subjects following the “PlugInGait-total body model”. The participants performed five repetitions of mawashi geri jodan at maximum rapidity with their dominant leg against a ball suspended in front of them placed at ear height. Fourteen skilled subjects (mean level black belt 1,7 dan; age 20,9±4,8 yrs; height 171,4±7,3 cm; weight 60,9±10,2 Kg) practicing karate have been split in two group through the hierarchical cluster analysis following their technical characteristics. By means of the Mann Whitney-U test (Spss-package) the differences between the two groups were verified in preparatory and execution phase. Kicking knee at start, kicking hip and knee at take-off were different between the two groups (p < 0,05). Striking hip flexion during the spin of the supporting foot was different between the two groups (p < 0,05). Peak angular velocity of hip flexion were different between the two groups (p < 0,05). Groups showed differences also in timing of the supporting spin movement. While Old group spin the supporting foot at 30% of the trial, instead New start spinning at 44% of the trial. Old group showed a greater supporting foot spin than New (Old 110° Vs New 82°). Abduction values didn’t show any differences between the two groups. At the hit has been evaluated a 120° of double hips abduction, for the entire sample. Striking knee extension happened for everybody after the kicking hip flexion and confirm the proximal-distal action of the striking leg (Sorensen H. 1996). In contrast with Pearson J.N. 1997 and Landeo R 2007, peak velocity of the striking foot is not useful to describe kick performance because affected by the stature. Two groups are different either in preparatory phase or in execution phase. The body is set in difference manner already before the take-off of the kicking foot. The groups differ for the timing of the supporting foot action Trainer should pay attention to starting posture and on abduction capacities of the athletes.

Modelli Matematici per Transizioni di Fase in Materiali Speciali

In questa Tesi vengono trattati alcuni temi relativi alla modellizzazione matematica delle Transizioni di Fase, il cui filo conduttore è la descrizione basata su un parametro d'ordine, originato dalla Teoria di Landau. Dopo aver presentato in maniera generale un modo di approccio alla dinamica delle transizioni mediante campo di fase, con particolare attenzione al problema della consistenza termodinamica nelle situazioni non isoterme, si considerano tre applicazioni di tale metodo a transizioni di fase specifiche: la transizione ferromagnetica, la transizione superconduttrice e la transizione martensitica nelle leghe a memoria di forma (SMA). Il contributo maggiore viene fornito nello studio di quest'ultima transizione di fase per la quale si è elaborato un modello a campo di fase termodinamicamente consistente, atto a descriverne le proprietà termomeccaniche essenziali.

Modellazione multibody di veicoli ferroviari: sviluppo ed implementazione di modelli innovativi per l'analisi del contatto ruota - rotaia

The wheel - rail contact analysis plays a fundamental role in the multibody modeling of railway vehicles. A good contact model must provide an accurate description of the global contact phenomena (contact forces and torques, number and position of the contact points) and of the local contact phenomena (position and shape of the contact patch, stresses and displacements). The model has also to assure high numerical efficiency (in order to be implemented directly online within multibody models) and a good compatibility with commercial multibody software (Simpack Rail, Adams Rail). The wheel - rail contact problem has been discussed by several authors and many models can be found in the literature. The contact models can be subdivided into two different categories: the global models and the local (or differential) models. Currently, as regards the global models, the main approaches to the problem are the so - called rigid contact formulation and the semi – elastic contact description. The rigid approach considers the wheel and the rail as rigid bodies. The contact is imposed by means of constraint equations and the contact points are detected during the dynamic simulation by solving the nonlinear algebraic differential equations associated to the constrained multibody system. Indentation between the bodies is not permitted and the normal contact forces are calculated through the Lagrange multipliers. Finally the Hertz’s and the Kalker’s theories allow to evaluate the shape of the contact patch and the tangential forces respectively. Also the semi - elastic approach considers the wheel and the rail as rigid bodies. However in this case no kinematic constraints are imposed and the indentation between the bodies is permitted. The contact points are detected by means of approximated procedures (based on look - up tables and simplifying hypotheses on the problem geometry). The normal contact forces are calculated as a function of the indentation while, as in the rigid approach, the Hertz’s and the Kalker’s theories allow to evaluate the shape of the contact patch and the tangential forces. Both the described multibody approaches are computationally very efficient but their generality and accuracy turn out to be often insufficient because the physical hypotheses behind these theories are too restrictive and, in many circumstances, unverified. In order to obtain a complete description of the contact phenomena, local (or differential) contact models are needed. In other words wheel and rail have to be considered elastic bodies governed by the Navier’s equations and the contact has to be described by suitable analytical contact conditions. The contact between elastic bodies has been widely studied in literature both in the general case and in the rolling case. Many procedures based on variational inequalities, FEM techniques and convex optimization have been developed. This kind of approach assures high generality and accuracy but still needs very large computational costs and memory consumption. Due to the high computational load and memory consumption, referring to the current state of the art, the integration between multibody and differential modeling is almost absent in literature especially in the railway field. However this integration is very important because only the differential modeling allows an accurate analysis of the contact problem (in terms of contact forces and torques, position and shape of the contact patch, stresses and displacements) while the multibody modeling is the standard in the study of the railway dynamics. In this thesis some innovative wheel – rail contact models developed during the Ph. D. activity will be described. Concerning the global models, two new models belonging to the semi – elastic approach will be presented; the models satisfy the following specifics: 1) the models have to be 3D and to consider all the six relative degrees of freedom between wheel and rail 2) the models have to consider generic railway tracks and generic wheel and rail profiles 3) the models have to assure a general and accurate handling of the multiple contact without simplifying hypotheses on the problem geometry; in particular the models have to evaluate the number and the position of the contact points and, for each point, the contact forces and torques 4) the models have to be implementable directly online within the multibody models without look - up tables 5) the models have to assure computation times comparable with those of commercial multibody software (Simpack Rail, Adams Rail) and compatible with RT and HIL applications 6) the models have to be compatible with commercial multibody software (Simpack Rail, Adams Rail). The most innovative aspect of the new global contact models regards the detection of the contact points. In particular both the models aim to reduce the algebraic problem dimension by means of suitable analytical techniques. This kind of reduction allows to obtain an high numerical efficiency that makes possible the online implementation of the new procedure and the achievement of performance comparable with those of commercial multibody software. At the same time the analytical approach assures high accuracy and generality. Concerning the local (or differential) contact models, one new model satisfying the following specifics will be presented: 1) the model has to be 3D and to consider all the six relative degrees of freedom between wheel and rail 2) the model has to consider generic railway tracks and generic wheel and rail profiles 3) the model has to assure a general and accurate handling of the multiple contact without simplifying hypotheses on the problem geometry; in particular the model has to able to calculate both the global contact variables (contact forces and torques) and the local contact variables (position and shape of the contact patch, stresses and displacements) 4) the model has to be implementable directly online within the multibody models 5) the model has to assure high numerical efficiency and a reduced memory consumption in order to achieve a good integration between multibody and differential modeling (the base for the local contact models) 6) the model has to be compatible with commercial multibody software (Simpack Rail, Adams Rail). In this case the most innovative aspects of the new local contact model regard the contact modeling (by means of suitable analytical conditions) and the implementation of the numerical algorithms needed to solve the discrete problem arising from the discretization of the original continuum problem. Moreover, during the development of the local model, the achievement of a good compromise between accuracy and efficiency turned out to be very important to obtain a good integration between multibody and differential modeling. At this point the contact models has been inserted within a 3D multibody model of a railway vehicle to obtain a complete model of the wagon. The railway vehicle chosen as benchmark is the Manchester Wagon the physical and geometrical characteristics of which are easily available in the literature. The model of the whole railway vehicle (multibody model and contact model) has been implemented in the Matlab/Simulink environment. The multibody model has been implemented in SimMechanics, a Matlab toolbox specifically designed for multibody dynamics, while, as regards the contact models, the CS – functions have been used; this particular Matlab architecture allows to efficiently connect the Matlab/Simulink and the C/C++ environment. The 3D multibody model of the same vehicle (this time equipped with a standard contact model based on the semi - elastic approach) has been then implemented also in Simpack Rail, a commercial multibody software for railway vehicles widely tested and validated. Finally numerical simulations of the vehicle dynamics have been carried out on many different railway tracks with the aim of evaluating the performances of the whole model. The comparison between the results obtained by the Matlab/ Simulink model and those obtained by the Simpack Rail model has allowed an accurate and reliable validation of the new contact models. In conclusion to this brief introduction to my Ph. D. thesis, we would like to thank Trenitalia and the Regione Toscana for the support provided during all the Ph. D. activity. Moreover we would also like to thank the INTEC GmbH, the society the develops the software Simpack Rail, with which we are currently working together to develop innovative toolboxes specifically designed for the wheel rail contact analysis.