Fazio B.,CNR Institute for Chemical and Physical Processes
Nature Photonics | Year: 2017
Coherent backscattering of light is observed when electromagnetic waves undergo multiple scattering within a disordered optical medium. So far, coherent backscattering of light has been studied extensively for elastic (or Rayleigh) light scattering. The occurrence of inelastic scattering affects the visibility of the backscattering effect by reducing the degree of optical coherence in the diffusion process. Here, we discuss the first experimental observation of a constructive interference effect in the inelastically backscattered Raman radiation from strongly diffusing silicon nanowire random media. The observed phenomenon originates from the coherent nature of the Raman scattering process, which typically occurs on a scale given by the phonon coherence length. We interpret our results in the context of a theoretical model of mixed Rayleigh–Raman random walks to shed light on the role of phase coherence in multiple scattering phenomena. © 2017 Nature Publishing Group
Surnev S.,University of Graz |
Fortunelli A.,CNR Institute for Chemical and Physical Processes |
Netzer F.P.,University of Graz
Chemical Reviews | Year: 2013
Hetero-oxide systems on metal single crystal supports, studied by the surface science approach is reviewed. The surface science approach involves in situ ultra-high vacuum studies, with atomic scale preparation control and atomic resolution in the characterization. The fabrication of metal-supported oxide nanostructures via UHV (ultrahigh vacuum) physical vapor deposition or related methods is a relatively simple procedure. However, the dependence of nanostructure growth on subtle details of kinetics and the existence of a number of energetically closely spaced metastable states in many oxide-metal systems make the preparation of oxide-metal hybrid structures a skillful experimental art. Interface geometry, interface chemistry, external growth variables, low dimensionality, and atomic scale defects have been singled out as important elements in determining structure and to facilitate a systematic presentation.
Sterpone F.,University of Paris Pantheon Sorbonne |
Melchionna S.,CNR Institute for Chemical and Physical Processes
Chemical Society Reviews | Year: 2012
Proteins from thermophilic and hyperthermophilic organisms are stable and function at high temperatures (50-100 °C). The importance of understanding the microscopic mechanisms underlying this thermal resistance is twofold: it is key for acquiring general clues on how proteins maintain their fold stable and for targeting those medical and industrial applications that aim at designing enzymes that can work under harsh conditions. In this tutorial review we first provide the general background of protein thermostability by specifically focusing on the structural and thermodynamic peculiarities; next, we discuss how computational studies based on Molecular Dynamics simulations can broaden and refine our knowledge on such special class of proteins. © 2012 The Royal Society of Chemistry.
Villani G.,CNR Institute for Chemical and Physical Processes
Physical Chemistry Chemical Physics | Year: 2010
Two different mechanisms to obtain the imino-enol tautomer of the adenine-thymine base pair, a concerted hydrogen atom transfer and a stepwise process, have been studied and compared. The first mechanism includes both the concerted movement of two hydrogen atoms, in the bridges that bond the two bases, and an electronic reorganisation of the bonds. The stepwise mechanism is the simplest one where there is a correlation between the movement of the hydrogen atoms, but two or more steps can be identified. In this study, a different behaviour has been found when the first atom to move is the hydrogen in the N-N bridge or that in the N-O one. © the Owner Societies.
Lombardo D.,CNR Institute for Chemical and Physical Processes
Biochemistry Research International | Year: 2014
Dendrimers are highly branched macromolecules obtained by stepwise controlled, reaction sequences. The ability to be designed for specific applications makes dendrimers unprecedented components to control the structural organization of matter during the bottom-up synthesis of functional nanostructures. For their applications in the field of biotechnology the determination of dendrimer structural properties as well as the investigation of the specific interaction with guest components are needed. We show how the analysis of the scattering structure factor S(q), in the framework of current models for charged systems in solution, allows for obtaining important information of the interdendrimers electrostatic interaction potential. The finding of the presented results outlines the important role of the dendrimer charge and the solvent conditions in regulating, through the modulation of the electrostatic interaction potential, great part of the main structural properties. This charge interaction has been indicated by many studies as a crucial factor for a wide range of structural processes involving their biomedical application. Due to their easily controllable properties dendrimers can be considered at the crossroad between traditional colloids, associating polymers, and biological systems and represent then an interesting new technological approach and a suitable model system of molecular organization in biochemistry and related fields. © 2014 Domenico Lombardo.
D'Ulivo A.,CNR Institute for Chemical and Physical Processes
Spectrochimica Acta - Part B Atomic Spectroscopy | Year: 2010
The state of knowledge of the mechanisms involved in the chemical generation of volatile species (CHG) arising from aqueous phase reaction of classical hydride forming elements, transition and noble metals with borane complexes (mainly NaBH4), has been critically reviewed in the light of evidences and literature data published in the last fifty years. The mechanisms, which are necessary to describe the reactivity of CHG system, are essentially: (i) the mechanism of hydrolysis of borane complexes, (ii) the mechanism of formation of volatile species, (iii) the mechanism of liquid phase interference and (iv) the mechanism of action of additives. Only the mechanisms (i) and (ii) have reached a good degree of rationalization, whereas more experimental evidences are necessary for the mechanisms (iii) and (iv). A more general reaction model for analytical CHG can be drawn according to the present state of knowledge, which is valid for both classical hydride forming elements and transition and noble metals. It is based on the formation of analyte-borane complex (ABC) intermediates through which takes place the direct, stepwise transfer of hydrogen atoms from boron to analyte substrate MLn, (M is a metal or semi-metal, L is a ligand). By this way the original analyte substrate is stepwise converted to hydrido metal complexes MHxL y, then to the final products (hydride, metal atoms, etc). The clarification of several controversial aspects and the ruling out of wrong concepts, among them the "nascent" hydrogen theory, can been achieved in the light of the present state of knowledge. © 2010 Elsevier B.V. All rights reserved.
Angelani L.,CNR Institute for Chemical and Physical Processes
Physical Review Letters | Year: 2012
The phenomenon of collective predation is analyzed by using a simple individual-based model reproducing spatial animal movements. Two groups of self-propelled organisms are simulated by using Vicseklike models including steric intragroup repulsion. Chase and escape are described by intergroups interactions, attraction (for predators) or repulsion (for preys) from nearest particles of the opposite group. The quantitative analysis of some relevant quantities (total catch time, lifetime distribution, predation rate) allows us to characterize many aspects of the predation phenomenon and gives insights into the study of efficient escape strategies. The reported findings could be of relevance for many basic and applied disciplines, from statistical physics, to ecology, and robotics. © 2012 American Physical Society.
Rizzo T.,CNR Institute for Chemical and Physical Processes
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2013
I consider branches of replica-symmetry-breaking (RSB) solutions in glassy systems that display a dynamical transition at a temperature Td characterized by a mode-coupling-theory dynamical behavior. Below Td these branches of solutions are considered to be relevant to the system complexity and to off-equilibrium dynamics. Under general assumptions I argue that near Td it is not possible to stabilize the one-step (1RSB) solution beyond the marginal point by making a full RSB (FRSB) ansatz. However, depending on the model, there may exist a temperature T* strictly lower than Td below which the 1RSB branch can be continued to a FRSB branch. Such a temperature certainly exists for models that display the so-called Gardner transition and in this case TG
Saitta A.M.,CNRS Institute of Mineralogy, Materials Physics and Cosmochemistry |
Saija F.,CNR Institute for Chemical and Physical Processes
Proceedings of the National Academy of Sciences of the United States of America | Year: 2014
The celebrated Miller experiments reported on the spontaneous formation of amino acids from a mixture of simple molecules reacting under an electric discharge, giving birth to the research field of prebiotic chemistry. However, the chemical reactions involved in those experiments have never been studied at the atomic level. Here we report on, to our knowledge, the first ab initio computer simulations of Miller-like experiments in the condensed phase. Our study, based on the recent method of treatment of aqueous systems under electric fields and on metadynamics analysis of chemical reactions, shows that glycine spontaneously forms from mixtures of simple molecules once an electric field is switched on and identifies formic acid and formamide as key intermediate products of the early steps of the Miller reactions, and the crucible of formation of complex biological molecules. © 2014 PNAS.
Melchionna S.,CNR Institute for Chemical and Physical Processes
Journal of Computational Physics | Year: 2011
A method to simulate bodies suspended in a Lattice Boltzmann solvent is proposed. It is based on a generalized reaction force that enforces no-slip boundary conditions at the fluid-body interface as the limiting case of an iterative procedure. A smooth version of the Heaviside function allows to treat spherical particles of arbitrary size and produces smooth hydrodynamic forces as particles move in the continuum. Numerical tests demonstrate the accuracy of the method in reproducing the hydrodynamic field around a single particle and the fluid-mediated forces between pairs of particles. The drag force experienced by a particle moving in a straight channel and at various Reynolds numbers is studied as a non-trivial testcase. © 2011 Elsevier Inc.