The kinetic fragility of liquids as manifestation of the elastic softening

We show that the fragility $m$, the steepness of the viscosity and relaxation time close to the vitrification, increases with the degree of elastic softening, i.e. the decrease of the elastic modulus with increasing temperature, in universal way. This provides a novel connection between the thermodynamics, via the modulus, and the kinetics. The finding is evidenced by numerical simulations and comparison with the experimental data of glassformers with widely different fragilities ($33 \le m \le 115$), leading to a fragility-independent elastic master curve extending over eighteen decades in viscosity and relaxation time. The master curve is accounted for by a cavity model pointing out the roles of both the available free volume and the cage softness. A major implication of our findings is that ultraslow relaxations, hardly characterised experimentally, become predictable by linear elasticity. As an example, the viscosity of supercooled silica is derived over about fifteen decades with no adjustable parameters.Comment: 7 pages, 6 figures; Added new results, improved the theoretical sectio

Steering self-organisation through confinement

Self-organisation is the spontaneous emergence of spatio-temporal structures and patterns from the interaction of smaller individual units. Examples are found across many scales in very different systems and scientific disciplines, from physics, materials science and robotics to biology, geophysics and astronomy. Recent research has highlighted how self-organisation can be both mediated and controlled by confinement. Confinement is an action over a system that limits its units’ translational and rotational degrees of freedom, thus also influencing the system's phase space probability density; it can function as either a catalyst or inhibitor of self-organisation. Confinement can then become a means to actively steer the emergence or suppression of collective phenomena in space and time. Here, to provide a common framework and perspective for future research, we examine the role of confinement in the self-organisation of soft-matter systems and identify overarching scientific challenges that need to be addressed to harness its full scientific and technological potential in soft matter and related fields. By drawing analogies with other disciplines, this framework will accelerate a common deeper understanding of self-organisation and trigger the development of innovative strategies to steer it using confinement, with impact on, e.g., the design of smarter materials, tissue engineering for biomedicine and in guiding active matter

New insights into the genetic etiology of Alzheimer's disease and related dementias

Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele

Controlling competition between crystallization and glass formation in binary colloids with an external field

The mechanism by which a liquid may become arrested, forming a glass, is a long-standing problem. So far no clear structural mechanism has been found. One promising approach is to use real space analysis of colloidal dispersions at the single-particle level to reveal local structural details which are inaccessible to many experimental techniques. Here we report a simple method to control glass formation which enables us to tackle the competition between crystallization and vitrification. While monodisperse colloidal hard spheres may readily crystallize, polydisperse suspensions tend to form glassy structures. We exploit the difference in sedimentation velocities of colloidal particles of different sizes, leading to a sediment which changes continuously in composition as a function of height, revealing glassy and crystalline states

Pianificazione e progettazione elettrica di un sistema di vehicle-sharing per il centro storico della citta di Lucca.

Il presente lavoro di tesi nasce da una reale proposta avanzata dal Prof. Antonio Pratelli nel 2008 al Comune di Lucca, nell’ambito di uno studio per il potenziamento dell’accessibilità alla ZTL del centro cittadino. Lo studio, in realtà più ampio, prevedeva al suo interno la realizzazione del sistema di vehicle-sharing che, tramite questa tesi, si è cercato di concretizzare attraverso un’analisi ingegneristica dal punto di vista trasportistico e veicolistico. Inizialmente si è approfondita la conoscenza della realtà urbana in cui si è andati ad operare, per mezzo di uno studio antropologico e territoriale, che ha confermato la bontà della proposta iniziale, e dato il via alle considerazioni successive. Si sono presentati i sopralluoghi del parcheggio ‘Palatucci’, in cui realizzare la stazione di noleggio: del parcheggio si sono prodotti, per via analitica, tutti i parametri relativi ai flussi d’arrivo e partenza necessari a conoscerne la logistica durante il giorno feriale tipo. A questo punto, in base ad essi, si è cercato di prevedere matematicamente l’utilizzo potenziale futuro dei veicoli messi a disposizione degli automobilisti che si recano quotidianamente in centro. Ciò ha consentito di dimensionare numericamente la flotta in base all’utilizzo del parcheggio, tramite un modello matematico flessibile che potrà adattarsi, in futuro, anche ad un’eventuale variazione del traffico interno al parcheggio stesso. In base a considerazioni legate all’urbanistica cittadina ed all’esperienza dei tecnici comunali, si sono individuate destinazioni e percorsi tipici che successivamente si sono tradotti in profili di velocità. Gli stessi profili sono diventati profili di missione per i nostri studi. A questo punto si è sviluppato un modello semplificato, ma non semplicistico, di veicolo elettrico, per effettuare valutazioni preliminari riguardanti le potenze in gioco, le prestazioni, i consumi e l'autonomia in vista di una prossima realizzazione di tali veicoli. Successivamente sono stati inseriti inseriti i dati tecnici ipotizzati per i veicoli reali e quindi sono state svolte le simulazioni. Per la realizzazione di tale modello si è utilizzato un software diverso da quelli tradizionalmente usati per la modellazione dei sistemi dinamici, con lo scopo di testare la validità del programma sotto l'aspetto della semplicità di modellazione. In ultima analisi, si è stimato il costo complessivo del sistema, mettendo in risalto i notevoli vantaggi a livello di immagine di cui il Comune di Lucca beneficerebbe offrendo ai suoi cittadini un complemento ideale alla loro attività quotidiana. Ogni considerazione fatta all’interno di tale tesi, quindi, risulta essere propedeutica a quella successiva

Direct observation of hydrodynamic instabilities in a driven non-uniform colloidal dispersion

A Rayleigh–Taylor-like instability of a dense colloidal layer under gravity in a capillary of microfluidic dimensions is considered. We access all relevant lengthscales with particle-level microscopy and computer simulations which incorporate long-range hydrodynamic interactions between the particles. By tuning the gravitational driving force, we reveal a mechanism whose growth is connected to the fluctuations of specific wavelengths, non-linear pattern formation and subsequent diffusion-dominated relaxation. Our linear stability theory captures the initial regime and thus predicts mixing conditions, with important implications for fields ranging from biology to nanotechnology

Multi-particle collision dynamics simulations of sedimenting colloidal dispersions in confinement

The sedimentation of an initially inhomogeneous distribution of hard-sphere colloids confined in a slit is simulated using the multi-particle collision dynamics scheme which takes into account hydrodynamic interactions mediated by the solvent. This system is an example for soft matter driven out of equilibrium where various length and time scales are involved. The initial laterally homogeneous density profiles exhibit a hydrodynamic Rayleigh–Taylor-like instability. Solvent backflow effects lead to an intricate non-linear behaviour which is analyzed via the solvent flow field and the colloidal velocity correlation function. Our simulation data are in good agreement with real-space microscopy experiments