Local structure of directed networks

Previous work on undirected small-world networks established the paradigm that locally structured networks tend to have high density of short loops. On the other hand, many realistic networks are directed. Here we investigate the local organization of directed networks and find, surprisingly, that real networks often have very few short loops as compared to random models. We develop a theory and derive conditions for determining if a given network has more or less loops than its randomized counterpart. These findings carry broad implications for structural and dynamical processes sustained by directed networks

Damage Spreading and Criticality in Finite Random Dynamical Networks

We systematically study and compare damage spreading at the sparse percolation (SP) limit for random boolean and threshold networks with perturbations that are independent of the network size $N$. This limit is relevant to information and damage propagation in many technological and natural networks. Using finite size scaling, we identify a new characteristic connectivity $K_s$, at which the average number of damaged nodes $\bar d$, after a large number of dynamical updates, is independent of $N$. Based on marginal damage spreading, we determine the critical connectivity $K_c^{sparse}(N)$ for finite $N$ at the SP limit and show that it systematically deviates from $K_c$, established by the annealed approximation, even for large system sizes. Our findings can potentially explain the results recently obtained for gene regulatory networks and have important implications for the evolution of dynamical networks that solve specific computational or functional tasks.Comment: 4 pages, 4 eps figure

Molecular dynamics simulations of reflection and adhesion behavior in Lennard-Jones cluster deposition

We conduct molecular dynamics simulations of the collision of atomic clusters with a weakly-attractive surface. We focus on an intermediate regime, between soft-landing and fragmentation, where the cluster undergoes deformation on impact but remains largely intact, and will either adhere to the surface (and possibly slide), or be reflected. We find that the outcome of the collision is determined by the Weber number, We i.e. the ratio of the kinetic energy to the adhesion energy, with a transition between adhesion and reflection occurring as We passes through unity. We also identify two distinct collision regimes: in one regime the collision is largely elastic and deformation of the cluster is relatively small but in the second regime the deformation is large and the adhesion energy starts to depend on the kinetic energy. If the transition between these two regimes occurs at a similar kinetic energy to that of the transition between reflection and adhesion, then we find that the probability of adhesion for a cluster can be bimodal. In addition we investigate the effects of the angle of incidence on adhesion and reflection. Finally we compare our findings both with recent experimental results and with macroscopic theories of particle collisions.Comment: 18 pages, 13 figure

Structural transitions in a NiTi alloy: a multistage loading-unload cycle

NiTi shape memory alloys (SMAs) are increasingly used in many engineering and medical applications, because they combine special functional properties, such as shape memory effect and pseudoelasticity, with good mechanical strength and biocompatibility. However, the microstructural changes associated with these functional properties are not yet completely known. In this work a NiTi pseudo-elastic alloy was investigated by means of X-ray diffraction in order to assess micro-structural transformations under mechanical uniaxial deformation. The structure after complete shape recovery have been compared with initial state

Novel fiber-reinforced composite materials based on sustainable geopolymer matrix

Geopolymers are representing the most promising green and eco-friendly alternative to ordinary Portland cement and cementitious materials, thanks to their proven durability, mechanical and thermal properties. However, despite these features, the poor tensile and bending strengths usually exhibited by geopolymers due to their brittle and ceramic-like nature, can easily lead to catastrophic failure and represent the main drawback limiting the use of those materials in several applications. Fiber reinforced geopolymer composites may be considered a solution to improve flexural strength and fracture toughness. Different types of dispersed short fibers are here investigated as a reinforcing fraction for a geopolymer matrix based on an alkali-activated ladle-slag. It has been demonstrated that both organic and inorganic fibers can lead to a significant flexural strength enhancement. Moreover, the investigated geopolymers exhibit an increase in toughness, thus determining a switch from a brittle failure mode to a more ductile one

Ergodicity breaking in strong and network-forming glassy system

The temperature dependence of the non-ergodicity factor of vitreous GeO$_2$, $f_{q}(T)$, as deduced from elastic and quasi-elastic neutron scattering experiments, is analyzed. The data are collected in a wide range of temperatures from the glassy phase, up to the glass transition temperature, and well above into the undercooled liquid state. Notwithstanding the investigated system is classified as prototype of strong glass, it is found that the temperature- and the $q$-behavior of $f_{q}(T)$ follow some of the predictions of Mode Coupling Theory. The experimental data support the hypothesis of the existence of an ergodic to non-ergodic transition occurring also in network forming glassy systems

LA GESTIONE DEL RISCHIO NEL SETTORE DEI BENI CULTURALI: MUSEI, BIBLIOTECHE, ARCHIVI

contenuti del volume “La gestione del rischio nel settore dei beni culturali: musei, biblioteche, archivi”, secondo della Collana “La Formazione e la Ricerca nel settore dei Beni Culturali e Ambientali”, sono riconducibili preliminarmente ad un excursus storico sulla situazione normativa in materia di sicurezza dei beni culturali in Italia e a livello internazionale con la conseguente trattazione di procedure di valutazione e prevenzione, linee guida e sistemi di sicurezza, in particolare, negli ambienti confinati. Si rivolge, quindi, l’attenzione alle varie tipologie di rischio e alle corrispondenti metodologie scientifiche in un confronto di percorsi metodologici e monitoraggi stabiliti anche da Organizzazioni Internazionali, affrontando alcuni casi di studio che, nell’ambito del Laboratorio Diagnostico per i Beni Culturali del Dipartimento di Beni Culturali dell’Alma Mater Studiorum Università di Bologna, sono stati oggetto di studio e applicazione

Green synthesis of gold nanoparticles using Kiwifruit juice

The use of kiwifruit juice as a source of metal-reducing and stabilizing agents for the production of gold nanoparticles (AuNPs) was investigated. The reaction was carried out in batch by mixing appropriate amounts of kiwifruit juice and gold(III) chloride solution. The formation of AuNPs was monitored by measuring the intensity of the surface plasmon resonance (SPR) band of gold. The effects of temperature (20-60 °C), pH (8-12) and gold-to-polyphenol ratio (GPR) were investigated. Characterisation of AuNPs by XRD, DLS and zeta-potential measurements showed that they were highly crystalline, with an average hydrodynamic diameter of about 50 nm and a zeta-potential ranging between -29.2 and -21.7 mV. Under the best reaction conditions (60 °C, pH 9, GPR = 5 mol Au3+/mol GAE), AuNPs with an average size of about 30 nm were produced. The results obtained suggest that kiwifruit juice is a suitable medium for the production of small-sized and stable AuNPs