Progetto di un Flussimetro Integrato in Microsistemi Fluidici per Analisi Genetiche

Negli ultimi anni si e' avuto un impulso sempre maggiore allo sviluppo e alla realizzazione di microsistemi in grado di misurare e controllare il flusso di gas e liquidi; infatti e' stato valutato che nel 2000 i sensori microfluidici coprivano il 19% del mercato dei MEMS (sistemi micro-elettro-meccanici). Grazie alle dimensioni estremamente ridotte questi sensori hanno il grosso vantaggio di poter avere un’ottima risoluzione spaziale e temporale, permettendo misure di flussi esigui, caratterizzati da velocita' dell’ordine dei millimetri al secondo. Per questa ragione si prestano ad essere integrati in microsistemi per analisi genetiche, in cui e' di fondamentale importanza indirizzare e controllare i movimenti di fluidi organici e soluzioni. Un microsistema in grado di effettuare in maniera quasi autonoma analisi genetiche potrebbe sostituire la strumentazione tradizionale, in quanto unirebbe alle dimensioni ridotte e alla trasportabilita' un’elevata velocità di analisi e bassi costi, sia per la minima richiesta di reagenti e campioni , sia per la possibilità di essere prodotto su larga scala sfruttando le tecnologie microelettroniche esistenti. Questo lavoro di tesi si pone in questo ambito e descrive il progetto di un Flussimetro da usare in Microsistemi per Analisi Genetiche. In particolare il dispositivo e' un sensore per la misura del flusso elettroosmotico in un microcapillare di vetro per analisi elettroforetiche. Con piccole modifiche la struttura puo', tuttavia, essere utilizzata in altre applicazioni per la misura di flussi di gas o liquidi. La tesi è articolata in cinque capitoli. Nel primo e' riportata un’introduzione generale ai MEMS, e una descrizione più dettagliata dei sensori di flusso integrati. Nel secondo capitolo si descrivono i microsistemi per analisi genetiche e l’importanza del controllo dei fenomeni elettrocinetici nei microcanali. Inoltre si da' una breve descrizione delle tecnologie realizzative usate. Il terzo capitolo e' incentrato su un’analisi teorica dei fenomeni elettrocinetici in microfluidica, a partire dalla formazione del doppio strato elettrico sulle pareti interne dei microcanali, fino allo studio dello streaming potential, dell’elettroforesi e dell’elettroosmosi. L’acquisizione di tali conoscenze e' fondamentale per poter simulare i diversi fenomeni elettrocinetici e per studiarne l’effetto in concomitanza con fenomeni di convezione e conduzione del calore nei microcanali. Negli ultimi due capitoli viene, infine, descritta la progettazione del sensore mediante un simulatore ad elementi finiti commerciale, Femlab®3.1. In particolare nel capitolo quarto sono riportate le simulazioni relative a diverse configurazioni del sensore e la dipendenza della sensibilita' dai parametri geometrici della struttura e dai materiali usati. Nel quinto capitolo viene illustrata la configurazione finale adottata per il flussimetro, le sue dimensioni e i materiali utilizzati. In base a questi dati vengono presentate delle nuove simulazioni volte a prevedere il comportamento del dispositivo reale e ad ottimizzarlo, ottenendo le ultime informazioni per il disegno del layout. In conclusione viene mostrato il layout finale con le relative maschere per litografia ottica e viene descritto il processo di fabbricazione del dispositivo

Application of a failure assessment diagram under rolling contact to components with hardness variable along the depth

Abstract A development of a failure assessment diagram for the evaluation of the safe working area of components subjected to rolling contact loading is here presented regarding the application to components whose hardness varies along the depth. The approach takes into account the influence of inherent defects in determining subsurface rolling contact fatigue, depending on working conditions, material properties and hardness profile along the depth. For this aim, crack propagation from inherent defects is assessed in terms of applied stress intensity factor range normalized with respect to short crack growth threshold, defect – free fatigue is assessed in terms of Dang Van stress normalized with respect to shear fatigue limit, where the material quantities depend on hardness variable with depth. These two normalized quantities are the coordinates of the points of a "reference curve" in the failure assessment diagram, which location indicates whether and where failure is expected to occur. By analysing different combinations of loading condition, inclusion dimension and hardness profile, it was possible obtaining a design diagram of general validity, which allows a fast prediction of safety against subsurface rolling contact fatigue

A framework to analyze noise factors of automotive perception sensors

Automated vehicles (AVs) are one of the breakthroughs of this century. The main argument to support their development is increased safety and reduction of human and economic losses; however, to demonstrate that AVs are safer than human drivers billions of miles of testing are required. Thus, realistic simulation and virtual testing of AV systems and sensors are crucial to accelerate the technological readiness. In particular, perception sensor measurements are affected by uncertainties due to noise factors; these uncertainties need to be included in simulations. This letter presents a framework to exhaustively analyze and simulate the effect of the combination of noise factors on sensor data. We applied the framework to analyze one sensor, the light detection and ranging (LiDAR), but it can be easily adapted to study other sensors. Results demonstrate that single noise factor analysis gives an incomplete knowledge of measurement degradation and perception is dramatically hindered when more noises are combined. The proposed framework is a powerful tool to predict the degradation of AV sensor performance

Modified pseudo-elastic approach for modelling cyclic response of biological heart valves

A modified pseudo-elastic approach is proposed to model cyclic response on biological heart valves. The model takes into account hysteretic effects, in combination with hyperelastic anisotropic behaviour of valve leaflets, allowing reproduction of different loading and unloading paths. FEM implementation considered a biological heart valve during the closure phase

Influence of micro-notches on the fatigue strength and crack propagation of unfilled and short carbon fiber reinforced PEEK

Short carbon fiber reinforced (SCFR) PEEK is a highly attractive material for lightweight structures; improving knowledge about the influence of local imperfections on its fatigue behavior is essential for the design of real components. To this aim, fatigue strength and crack propagation of two grades of SCFR PEEK and neat matrix were investigated by testing at different stress levels specimens with a micro-notch consisting of a small blind hole (range diameter 0.1–1 mm). Overall, the presence of a micro-notch resulted in a decrease of fatigue strength compared to un-notched condition, but with different sensitivity and crack propagation patterns; while a higher fiber volume fraction enhanced fatigue strength and resistance to crack propagation, the combination of a lower fiber content and inclusion of additive particles had a negative effect. Crack propagation in the notched region was also evaluated. The average values of Paris' law exponential coefficients were similar and within the range of literature values, without apparent correlation with reinforcement type. Preliminary investigations in the presence of the smallest micro-notches seem to indicate the presence of a threshold size below which the influence of a small notch is comparable with that of material inherent defects, but further testing is necessary

Fatigue behavior and cyclic damage of peek short fiber reinforced composites

Fatigue strength and failure mechanisms of short fiber reinforced (SFR) PEEK have been investigated in the past by several research groups. However some relevant aspects of the fatigue behavior of these materials, like cyclic creep and fatigue damage accumulation and modeling, have not been studied yet, in particular in presence of both fillers and short fibers as reinforcement. In the present research these aspects were considered by carrying out uni-axial fatigue tests in load control (cycle ratio R = 0) on neat PEEK and PEEK based composites reinforced either with short carbon fibers only or with addition of fillers (graphite and PTFE). For each material stress-life curves were obtained and compared. Fatigue fracture surfaces were analyzed to identify failure mechanisms in presence of different reinforcement types. The evolution of cyclic creep strain was also monitored as a function of the number of cycles, thus allowing investigation on the correlation between cyclic creep parameters and fatigue life. The evolution of cyclic damage with loading cycles was then compared by defining a damage parameter related to the specimen stiffness reduction observed during the tests. Progressive cyclic damage evolution of short fiber reinforced PEEK composites presented significantly different patterns depending on applied stress level and on the presence of different reinforcement typologies. In order to reproduce the different fatigue damage kinetics and stages of progressive damage accumulation observed experimentally, a cyclic damage model was finally developed and implemented into a finite element code by which a satisfactory agreement between numerical prediction and experimental data at different stress levels for each examined material

Estimation of Fatigue Limit of a A356-T6 Automotive Wheel in Presence of Defects

The automotive wheel is a critical safety component in the vehicle and, for such a reason, it has also to meet strict requirements about technological properties. This component is produced by low pressure die casting technique and the casting defects related to the process have to be properly considered having a high effect in decreasing both static and dynamic resistance of the component. Effectively, casting defects like porosities influence the fatigue crack initiation and strongly affect the fatigue life too. One of the most common problem in the real component is the mismatch between the experimental data and literature. In fact, many scientific researches were carried out on small samples produced in a controlled condition and therefore it is difficult to direct transfer the laboratory results to a real cast component with a well-defined shape and different thicknesses. In the present study, an aluminum alloy A356-T6 wheel was analyzed in order to correlate the fatigue performance taking in to account the casting defects. The fatigue limit of the component was studied by rotating bending fatigue tests executed on the whole wheels. Microfractographic analyses on the broken wheels were carried out on the fracture surfaces using a Scanning Electron Microscope in order to identify the crack initiation zone: it was recognized that the crack always started from shrinkage porosities. The statistical population of these defects was therefore investigated on samples taken from the wheel in crack nucleation positions of the spoke and the maximum expected defect size on the component was estimated by the statistics of extreme values. The experimental fatigue limit was finally compared with the theoretical value predicted with the Murakami’s method

Benchmarking the Robustness of Panoptic Segmentation for Automated Driving

Precise situational awareness is required for the safe decision-making of assisted and automated driving (AAD) functions. Panoptic segmentation is a promising perception technique to identify and categorise objects, impending hazards, and driveable space at a pixel level. While segmentation quality is generally associated with the quality of the camera data, a comprehensive understanding and modelling of this relationship are paramount for AAD system designers. Motivated by such a need, this work proposes a unifying pipeline to assess the robustness of panoptic segmentation models for AAD, correlating it with traditional image quality. The first step of the proposed pipeline involves generating degraded camera data that reflects real-world noise factors. To this end, 19 noise factors have been identified and implemented with 3 severity levels. Of these factors, this work proposes novel models for unfavourable light and snow. After applying the degradation models, three state-of-the-art CNN- and vision transformers (ViT)-based panoptic segmentation networks are used to analyse their robustness. The variations of the segmentation performance are then correlated to 8 selected image quality metrics. This research reveals that: 1) certain specific noise factors produce the highest impact on panoptic segmentation, i.e. droplets on lens and Gaussian noise; 2) the ViT-based panoptic segmentation backbones show better robustness to the considered noise factors; 3) some image quality metrics (i.e. LPIPS and CW-SSIM) correlate strongly with panoptic segmentation performance and therefore they can be used as predictive metrics for network performance

A new Monte Carlo muon generator for cosmic-ray muon applications

Cosmic rays, thanks to their ubiquity and high penetration capability, have been successfully used in scientific research ever since their discovery. As soon as their knowledge improved, applications in the civil/environmental field were also developed: muon radiography (or muography, based on the flux attenuation) and muon tomography (based on the scattering angle) have been used to study the inner structure of volcanoes, to seek hidden rooms in Egyptian pyramids, to search for heavy metals in containers, and so on. And besides these imaging techniques, cosmic ray muons are also widely used for detector testing and alignment practically in every Nuclear Physics or Particle Physics experiment. Since most of these applications are sensitive to the angular and momentum distribution of cosmic muons, an accurate modelling of these distributions is a key feature for any generation tool conceived to simulate the cosmic muon flux. This can make the generator quite time-consuming, which is a strong limit when one needs to reach high statistics or to study large structures. A new Monte Carlo generator for cosmic-ray muons, named Efficient COsmic MUon Generator (EcoMug for short), especially designed to be fast (≳ 10^5 muons generated per second on a standard machine) without losing accuracy, is presented here. It is written as a header-only C++11 library, ready to be integrated into whatever C++ code, in particular C++ code based on Geant4 simulation tool. By default, EcoMug relies on a simple and effective parametrisation of the experimental data of cosmic ray differential flux at sea level, taken from the literature, but the library is written in such a way that every user can easily replace it with his own user-defined parametrisation. Unlike other tools, EcoMug is able to generate muons from different kind of surfaces (plane, cylinder and half-sphere), while keeping the correct angular and momentum distribution of generated tracks inside a fiducial volume. This allows to optimise the generation surface according to the system under study, and leads to a further improvement of the overall simulation efficiency. In this contribution we will present the main features of EcoMug, starting from its mathematical foundation, and eventually showing some interesting applications