Agents, nodes & resources: Universal naming system for a coordination middleware

La tesi si propone di sviluppare un modello, l'architettura e la tecnologia per il sistema di denominazione del Middleware Coordinato TuCSoN, compresi gli agenti, i nodi e le risorse. Identità universali che rappresentano queste entità, sia per la mobilità fisica sia per quella virtuale, per un Management System (AMS, NMS, RMS) distribuito; tale modulo si occupa anche di ACC e trasduttori, prevedendo questioni come la tolleranza ai guasti, la persistenza, la coerenza, insieme con il coordinamento disincarnata in rete, come accade con le tecnologie Cloud. All’interno dell’elaborato, per prima cosa si è fatta una introduzione andando a descrivere tutto ciò che è contenuto nell’elaborato in modo da dare una visione iniziale globale del lavoro eseguito. Di seguito (1° capitolo) si è descritta tutta la parte relativa alle conoscenze di base che bisogna avere per la comprensione dell’elaborato; tali conoscenze sono relative a TuCSoN (il middleware coordinato con cui il modulo progettato dovrà interfacciarsi) e Cassandra (sistema server distribuito su cui si appoggia la parte di mantenimento e salvataggio dati del modulo). In seguito (2° capitolo) si è descritto JADE, un middleware da cui si è partiti con lo studio per la progettazione del modello e dell’architettura del modulo. Successivamente (3° capitolo) si è andati a spiegare la struttura e il modello del modulo considerato andando ad esaminare tutti i dettagli relativi alle entità interne e di tutti i legami fra esse. In questa parte si è anche dettagliata tutta la parte relativa alla distribuzione sulla rete del modulo e dei suoi componenti. In seguito (4° capitolo) è stata dettagliata e spiegata tutta la parte relativa al sistema di denominazione del modulo, quindi la sintassi e l’insieme di procedure che l’entità consumatrice esterna deve effettuare per ottenere un “nome universale” e quindi anche tutti i passaggi interni del modulo per fornire l’identificatore all’entità consumatrice. Nel capitolo successivo (5° capitolo) si sono descritti tutti i casi di studio relativi alle interazioni con le entità esterne, alle entità interne in caso in cui il modulo sia o meno distribuito sulla rete, e i casi di studio relativi alle politiche, paradigmi e procedure per la tolleranza ai guasti ed agli errori in modo da dettagliare i metodi di riparazione ad essi. Successivamente (6° capitolo) sono stati descritti i possibili sviluppi futuri relativi a nuove forme di interazione fra le entità che utilizzano questo modulo ed alle possibili migliorie e sviluppi tecnologici di questo modulo. Infine sono state descritte le conclusioni relative al modulo progettato con tutti i dettagli in modo da fornire una visione globale di quanto inserito e descritto nell’elaborato.

The behaviour of osteocyte dendritic processes in bone under cyclic load (il comportamento dei processi dendritici degli osteociti nel tessuto osseo sottoposti a carico ciclico)

Bone is continually being removed and replaced through the actions of basic multicellular units (BMU). This constant upkeep is necessary to remove microdamage formed naturally due to fatigue and thus maintain the integrity of the bone. The repair process in bone is targeted, meaning that a BMU travels directly to the site of damage and repairs it. It is still unclear how targeted remodelling is stimulated and directed but it is highly likely that osteocytes play a role. A number of theories have been advanced to explain the microcrack osteocyte interaction but no complete mechanism has been demonstrated. Osteocytes are connected to each other by dendritic processes. The “scissors model" proposed that the rupture of these processes where they cross microcracks signals the degree of damage and the urgency of the necessary repair. In its original form it was proposed that under applied compressive loading, microcrack faces will be pressed together and undergo relative shear movement. If this movement is greater than the width of an osteocyte process, then the process will be cut in a “scissors like" motion, releasing RANKL, a cytokine known to be essential in the formation of osteoclasts from pre-osteoclasts. The main aim of this thesis was to investigate this theoretical model with a specific focus on microscopy and finite element modelling. Previous studies had proved that cyclic stress was necessary for osteocyte process rupture to occur. This was a divergence from the original “scissors model" which had proposed that the cutting of cell material occurred in one single action. The present thesis is the first study to show fatigue failure in cellular processes spanning naturally occurring cracks and it's the first study to estimate the cyclic strain range and relate it to the number of cycles to failure, for any type of cell. Rupture due to shear movement was ruled out as microcrack closing never occurred, as a result of plastic deformation of the bone. Fatigue failure was found to occur due to cyclic tensile stress in the locality of the damage. The strain range necessary for osteocyte process rupture was quantified. It was found that the lower the process strain range the greater the number of cycles to cell process failure. FEM modelling allowed to predict stress in the vicinity of an osteocyte process and to analyse its interaction with the bone surrounding it: simulations revealed evident creep effects in bone during cyclic loading. This thesis confirms and dismisses aspects of the “scissors model". The observations support the model as a viable mechanism of microcrack detection by the osteocyte network, albeit in a slightly modified form where cyclic loading is necessary and the method of rupture is fatigue failure due to cyclic tensile motion. An in depth study was performed focusing on microscopy analysis of naturally occurring cracks in bone and FEM simulation analysis of an osteocyte process spanning a microcrack in bone under cyclic load.

Numerical and experimental investigation of structural stiffness influence on ratcheting convection cell in granular soils under cyclic loading

Lateral cyclic loaded structures in granular soils can lead to an accumulation of irreversible strains by changing their mechanical response (densification) and forming a closed convective cell in the upper layer of the bedding. In the present thesis the convective cell dimension, formation and grain migration inside this closed volume have been studied and presented in relation to structural stiffness and different loads. This relation was experimentally investigated by applying a cyclic lateral force to a scaled flexible vertical element embedded in dry granular soil. The model was monitored with a camera in order to derive the displacement field by means of the PIV technique. Modelling large soil deformation turns out to be difficult, using mesh-based methods. Consequently, a mesh-free approach (DEM) was chosen in order to investigate the granular flow with the aim of extracting interesting micromechanical information. In both the numerical and experimental analyses the effect of different loading magnitudes and different dimensions of the vertical element were considered. The main results regarded the different development, shape and dimensions of the convection cell and the surface settlements. Moreover, the Discrete Element Method has proven to give satisfactory results in the modelling of large deformation phenomena such as the ratcheting convective cell.