Vittorio Rosato

Modelling interdependent infrastructures using interacting dynamical models

We investigate the consequence of failures, occurring on the electrical grid, on a telecommunication network. We have focused on the Italian electrical transmission network and the backbone of the internet network for research (GARR). Electrical network has been simulated using the DC power flow method; data traffic on GARR by a model of the TCP/IP basic features. The status of GARR nodes has been related to the power level of the (geographically) neighbouring electrical nodes (if the power level of a node is lower than a threshold, all communication nodes depending on it are switched off). The electrical network has been perturbed by lines removal: the consequent re-dispatching reduces the power level in all nodes. This reduces the number of active GARR nodes and, thus, its Quality of Service (QoS). Averaging over many configurations of perturbed electrical network, we have correlated the degradation of the electrical network with that of the communication network. Results point to a sizeable amplification of the effects of faults on the electrical network on the communication network, also in the case of a moderate coupling between the two networks.

Atomic hydrogen adsorption on a Stone–Wales defect in graphite

Abstract Ab initio electronic structure calculations have been used to evaluate the binding energy of atomic hydrogen to graphite lattice defects. Results show that carbon sites belonging to a Stone–Wales defect are preferred binding sites with respect to undefected sites. Upon hydrogen adsorption, carbon sites undergo a sizeable tetragonalization effect which is more pronounced on the defected sizes.

Experimental and theoretical investigation of the order-disorder transformation in Ni3Al

The crystalline disordered phase obtained by mechanical alloying of elemental 75 at. % Ni and 25 at. % Al powders has been investigated. The stability of this phase with respect to the thermal reordering process leading to the L1 2 structure has been analyzed by means of x-ray diffractometry, scanning electron microscopy, and differential scanning calorimetry. Atomistic simulations on an Ni 3 Al model, reproduced via molecular dynamics using a many-body potential, have been used to interpret experimental data. The ordering transformation takes place in an extended range of temperature (from 320 to 600 °C) and occurs simultaneously with the release of internal strain. Numerical simulations performed under different conditions show that the activation energy of the Ni-vacancy migration mechanism responsible for the ordering process depends on the local state of strain, thus suggesting an explanation for the considerable lowering of this energy in samples obtained by ball milling.

Atomic-Scale Modeling of the Interaction between Short Polypeptides and Carbon Surfaces

We performed a comparative study of the adsorption of an in vitro selected peptide on two different carbon surfaces: a flat graphene and a curved (0,15) nanotube. The sequence was selected from recent experiments, as the one giving the highest carbon affinity for carbon nanotubes. Rigid docking of the molecule on the two surfaces by a genetic algorithm was followed by molecular dynamics simulations with empirical force fields (OPLS-AA) in water at finite temperature. The total free energies of folding and adhesion and the quality of surface binding were determined, based on a combination of solvation energy, formation of hydrogen bonds, and amount of the apolar (hydrophobic) contact surface between peptide and carbon surface. For both cases, we find a strong adhesion energy and large nonpolar contact surface. Isoleucines and tryptophans are the most strongly bound residues to the two carbon surfaces, the latter one largely dominating. In the case of the carbon nanotube, the peptide shows several competing stable structures, corresponding to different possible molecular foldings, and a propensity to enhance the intramolecular stability by forming new hydrogen bonds. In both systems, different arrangements of the histidine and tryptophan residues enable a better adaptation to the carbon surfaces. These findings suggest that the experimentally observed surface specificity of the peptide on nanotubes may depend on its capability to support multiple strongly bound configurations.

Solid–liquid interface velocity and diffusivity in laser-melt amorphous silicon

We studied the microscopic kinetics of the amorphous-liquid interface in supercooled laser-melt silicon by means of molecular dynamics computer simulations. The interface velocity was obtained as a function of temperature by direct simulation of the interface motion in an amorphous-liquid model system. The temperature dependence of the kinetic prefactor was extracted from the interface velocity function and compared to the values of self-diffusivity obtained from independent molecular dynamics simulations of bulk amorphous Si. The kinetic prefactor for interfacial diffusion shows a distinctly non-Arrhenius behavior which is attributed to Fulcher–Vogel kinetics in the supercooled liquid.

Structure and dynamics of the anti-AMCV scFv(F8): effects of selected mutations on the antigen combining site.

The recombinant antibody fragment scFv(F8), which recognizes the coat protein of the plant virus AMCV, is characterized by peculiar high in vitro stability and functional folding even in reducing environments, making it fit for designing stable antibodies with desired properties. Mutagenesis and functional analysis evidenced two residues, at positions 47 and 58 of the V(H) chain, playing a crucial role in the antigen binding recognition. Here, we used a computational procedure to assess the effects of these mutations on the stability, structure and dynamics of the antigen-binding site. Structural models of the wild type scFv(F8) and of its H47 and H58 mutants were built by homology modelling and assessed by multiple 15.5ns of molecular dynamics simulations. Computational results indicate that the 47H substitution strongly affects the CDR-H(2) conformation, destabilizes the V(H)/V(L) interface and confers high conformational flexibility to the antigen-binding site, leading the mutant to functional loss. The mutation at position H58 strenghtens the binding site, bestowing a high antigen specificity on the mutant. The essential dynamics and the analysis of the protein-solvent interface further corroborate the correspondence between the extent of the structurally-determined flexibility of the binding site with the different functional behaviours proved by the wild-type and its mutants. These results may have useful implications for structure-based design of antibody combining site.

Stability of a Distributed Generation Network Using the Kuramoto Models

We derive a Kuramoto-like equation from the Cardell-Ilic distributed electrical generation network and use the resulting model to simulate the phase stability and the synchronization of a small electrical grid. It is well-known that a major problem for distributed generation is the frequency stability. This is a non linear problem and proper models for analysis are sorely lacking. In our model nodes are arranged in a regular lattice; the strength of their couplings are randomly chosen and allowed to vary as square waves. Although the system undergoes several synchronization losses, nevertheless it is able to quickly resynchronize. Moreover, we show that the synchronization rising-time follows a power-law.

Lattice dynamics of ordered and disordered Cu3Au with a tight-binding potential model

Abstract The phonon dispersion curves for both ordered and configurationally disordered cubic phases of Cu3Au are calculated using force constants derived from a many-body tight-binding potential. The derived phonon frequency spectra are used to estimate the vibrational contribution to the entropy difference between the two phases. A brief discussion concerning the relative values of interatomic force constants is included.

Atomistic simulation of liquid lead and lead–bismuth eutectic

Abstract Lead and the Pb–Bi eutectic (Pb 55.9 at.%) have been modeled by a n -body potential derived from a second moment approximation of a tight binding Hamiltonian. The thermal behavior of the two systems in the liquid phase has been reproduced and relevant structural parameters have been evaluated and compared with experimental data. The diffusion coefficients and the activation energy for diffusion have been also evaluated.

Advanced services for critical infrastructures protection

In this paper an overview of the first results of FP7 CIPRNet project is presented. Particularly, we demonstrate CIPRNet services for critical infrastructure protection (CIP) stakeholders. The role of the proposed services is to support decisions in the CIP domain. Moreover, those services are expected to serve as the underpinnings for the European Infrastructures Simulation and Analysis Centre (EISAC) which, similarly to the US NISAC, should provide operational services on CIP, for the benefits of CI operators, stakeholders and the Public Authorities committed to CIP.