2,899 research outputs found
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 . 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 , at which the average number of damaged nodes ,
after a large number of dynamical updates, is independent of . Based on
marginal damage spreading, we determine the critical connectivity
for finite at the SP limit and show that it
systematically deviates from , 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
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
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
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
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
Ergodicity breaking in strong and network-forming glassy system
The temperature dependence of the non-ergodicity factor of vitreous GeO,
, 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 -behavior of 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
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