2,509 research outputs found

    Damage Spreading and Criticality in Finite Random Dynamical Networks

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    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 NN. 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 KsK_s, at which the average number of damaged nodes dˉ\bar d, after a large number of dynamical updates, is independent of NN. Based on marginal damage spreading, we determine the critical connectivity Kcsparse(N)K_c^{sparse}(N) for finite NN at the SP limit and show that it systematically deviates from KcK_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

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    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

    Novel fiber-reinforced composite materials based on sustainable geopolymer matrix

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    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

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

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    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

    Ergodicity breaking in strong and network-forming glassy system

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    The temperature dependence of the non-ergodicity factor of vitreous GeO2_2, fq(T)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 qq-behavior of fq(T)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


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    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

    bending damages in galvanized ductile cast irons

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    Abstract Ductile cast irons (DCIs) are characterized by mechanical properties close to low and medium carbon steels. Carbon atoms are mainly localized in graphite nodules, which are dispersed in a metallic matrix. The microstructure of metallic matrix can be ferritic, austenitic, pearlitic, martensitic or their mix, depending on chemical composition and heat treatment. Thanks to the high castability and low production costs, DCIs are used in many fields (e.g., automotive and pipes). The wide utilization of DCIs in many fields and critical application leads to particular attention to the corrosion phenomenon. Hot dip galvanizing is one of most important protection process, used to protect metallic materials (mainly steels) against corrosion in many aggressive environments. In this work, a ferritic-pearlitic DCI (GS500) was galvanized by using a pure Zn bath at 440°C to generate a zinc coating. Bending tests on galvanized specimen were performed to generate crack damage in the coating phases. The bending cracks path propagation in zinc coatings were observed using both a light optical microscope and scanning electron microscope. A damage parameter, defined as a number of radial crack for a millimeter of the deformed arc, was evaluated for each zinc coating intermetallic phases
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