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Massani M.B.,INTI Plasticos | Vignolo G.M.,CONICET | Eisenberg P.,INTI Plasticos | Morando P.J.,CONICET | And 2 more authors.
LWT - Food Science and Technology | Year: 2013

Adsorption of bacteriocins produced by Lactobacillus curvatus CRL705, lactocin 705 (whose activity depends upon complementation of two peptides, lac705α and lac705β) and bacteriocin/s with strong anti-Listeria activity, on a multilayer film was investigated. Lactocin 705 adsorption equilibrium at 30 °C was reached from 1 h of film contact. This bacteriocin exhibited a Langmuir-type adsorption, showing a mass adsorption maximum of 0.72 ± 0.05 μg cm-2 and a minimum inhibition concentration of 1 μg ml-1. The influence of impurities, generated from bacteriocinogenic strains growth, on bacteriocins adsorption to the film was investigated by inhibition area evaluation in semisolid agar. Impurities from LAB growth strongly influenced adsorption and lactocin 705 antimicrobial activity on the film, while antilisterial bacteriocin/s adsorption remained unaffected. To explain these results, a lack of lac705β and lac705α peptides complementation necessary for antimicrobial activity, while no interactions among impurities and antilisterial bacteriocin/s during adsorption was suggested. Antilisterial bacteriocin/s activity on the film was not influenced by lactocin 705 adsorption; conformational reorganization of adsorbed antilisterial bacteriocin/s in the presence of lactocin 705 could allow the adsorption of both bacteriocins while maintaining antilisterial antimicrobial activity. This study highlights the technological importance of adsorption optimization to obtain effective antimicrobial food packaging systems. © 2013 Elsevier Ltd.


Perez R.A.,Comision Nacional de la Energia Atomica | Perez R.A.,CONICET | Perez R.A.,Instituto Sabato | Gordillo J.,Comision Nacional de la Energia Atomica | And 2 more authors.
Measurement: Journal of the International Measurement Confederation | Year: 2012

An experimental method used to study U diffusion at infinite dilution in materials is presented in this work. The spectra of α particles emitted by U at different depth in the material, after the diffusion annealing, is converted into diffusion profiles combining the knowledge on the stopping power of α-particles coming from particles accelerators into an algorithm developed here. Details of sample preparation and experimental set-up is given, as much as depth resolution and limits for the diffusion coefficients attainable with this technique. Diffusion of U in Mo and α-Ti are measured at several temperatures in order to check the technique. © 2012 Published by Elsevier Ltd. All rights reserved.


Crespo E.A.,National University of Comahue | Claramonte S.,Instituto Sabato | Ruda M.,Bariloche Atomic Center | Ruda M.,National University of Comahue | De Debiaggi S.R.,CONICET
International Journal of Hydrogen Energy | Year: 2010

From the atomistic simulation of pressure-composition isotherms of hydrogen absorption of Pd nanoparticles we calculated thermodynamic properties and evaluated them as a function of particle size. In the particle range studied both ΔH and ΔS decreased with particle size towards the corresponding bulk values. H atoms were segregated to the subsurface of the particles forming a shell structure that may explain an initial plateau shown in the particles isotherms that is not present in bulk simulations. We used potentials of the embedded-atom type (EAM) to describe the interaction between atoms and we performed Monte Carlo simulations to calculate the isotherms. © 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.


Bonny G.,Belgian Institute for Nuclear Sciences | Pasianot R.C.,CAC CNEA | Pasianot R.C.,CONICET | Pasianot R.C.,Instituto Sabato
Philosophical Magazine Letters | Year: 2010

Many-body interatomic potentials play an important role in atomistic modelling of materials. For pure elements it is known that there exist gauge transformations that can change the form of the potential functions without modifying its properties. These same transformations, however, fail when applied to alloys. Even though different research groups may use the same potentials to describe pure elements, the gauges employed for fitting alloys will generally be different. In this scenario, it is a priori impossible to merge them into one potential describing the combined system, and thus no advantage is taken from state-of-the-art developments in the literature. Here, we generalise the gauge transformations applied to pure species in order to leave the properties of alloys invariant. Based on these transformations, a strategy to merge potentials developed within different gauges is presented, aiming at the description of the combined system. Advantage of existing state-of-the-art potentials is so taken, thus focusing the efforts on fitting only the missing interactions. Such a procedure constitutes a helpful tool for the development of potentials targeted to alloys of increased complexity, while maintaining the description quality of their constituents. © 2010 Taylor and Francis.


Fernandez J.R.,Dep. Materiales | Fernandez J.R.,Instituto Sabato | Fernandez J.R.,CONICET | Pascuet M.I.,CONICET
Modelling and Simulation in Materials Science and Engineering | Year: 2014

A new interatomic potential in the framework of the modified embedded atom method (MEAM) to model U metal is presented. The potential acceptably reproduces the lattice parameters and cohesive energy of the orthorhombic αU. The relative stability of the experimentally observed phase at low temperatures with respect to several other structures (bct, bcc, simple cubic, tetragonal β Np, fcc and hcp) is also taken into account. Intrinsic point defect properties compare reasonably well with data from the literature. To determine the quality of the interaction, the potential is used to study a number of properties for the pure metal at finite temperatures and the results are compared with the available data. The obtained allotropic αU↔γU transformation and melting temperatures are in good agreement with experimental values. Based on the simulations, a new αU↔γU transformation mechanism is proposed. © 2014 IOP Publishing Ltd.


Pasianot R.C.,Gerencia Materiales | Perez R.A.,CONICET | Perez R.A.,Instituto Sabato
Journal of Nuclear Materials | Year: 2013

We revisit the ultra-fast diffusion characteristics of Fe, Co, Ni, and Cu solutes, in the hcp hosts Ti and Zr, by using Density Functional Theory. The energetics of several point defect configurations, deemed relevant for solute diffusion, is evaluated. The results support the long standing beliefs that the diffusing species is interstitial in nature, and that some kind of complexing is involved at low temperatures. Though quantitative agreement with experiment is difficult to assess, we show that a rather simple dissociative model is able to rationalize the observed trends, in particular, why the Arrhenius graphs are straight for Ti whereas, generally, they are curved downwards for Zr. © 2012 Elsevier B.V. All rights reserved.


Maristany G.H.,Instituto Sabato | Rodriguez M.A.,CONICET | Carranza R.M.,General Electric | Rebak R.B.,General Electric
NACE - International Corrosion Conference Series | Year: 2016

Ni-Fe-Cr alloys, such as alloys N06600, N06690 and N08800, are used in steam generator tubing of nuclear power reactors due to their high mechanical strength and corrosion resistance at high temperature. Failure of those alloys is associated with crevices formed between tubing and tube sheet or tube support plates, or fouling formed during operation. In this work, the crevice corrosion susceptibility of these alloys was analyzed. Crevice corrosion was studied at atmospheric pressure in 5 M, 1 M, 0.1 M and 0.01 M NaCI solutions at 30 °C, 60 °C and 90 °C using artificially creviced specimens. Alloy specimens were polarized potentiodynamically up to 300 pA (~25 |jA/cm2) and held at that current for 2 hours; then the potential scan was reversed until reaching alloy repassivation. All the alloys suffered from crevice corrosion. Test reproducibility was higher under more aggressive conditions (i.e., higher temperature and chloride concentration). The repassivation potential decreased with increasing temperature and chloride concentration indicating higher crevice corrosion susceptibility. Crevice corrosion resistance increased in the order alloy N06690 < alloy N06600 < alloy N08800. Corrosion potential measurements and potentiodynamic polarization experiments were performed in simulated crevice-like solutions to understand these results. © 2016 by NACE International.


Mieza J.I.,Centro Atomico Constituyentes | Mieza J.I.,Instituto Sabato | Vigna G.L.,Centro Atomico Constituyentes | Domizzi G.,Centro Atomico Constituyentes
Journal of Nuclear Materials | Year: 2011

Delayed Hydride Cracking (DHC) is a failure mechanism that may occur in zirconium alloys used in nuclear reactor core components. The knowledge of the direct effects of the variables affecting the cracking velocity could be used to minimize the risk of crack propagation. In practice, most of these variables - as for example the alloy yield stress and hydrogen diffusion coefficient - are coupled and vary during reactor operation, leading to a complex variable dependence of the cracking mechanism. In order to get an insight into the relative effect of these variables, experimental data and a theoretical approach using a generally accepted DHC model were used in this work. A series of DHC velocity measurements were made in Zr-2.5Nb tube with different heat treatments. The yield stress, the Nb concentration in β phase, and hydrogen solvus of the alloy were measured for different heat treatments. Niobium concentration in β phase gave an indirect indication of β-phase continuity and, with a proper correlation, of the hydrogen diffusion coefficient. The obtained values were used as inputs in a theoretical calculation of cracking velocity. Good agreement between experimental data and predicted values was obtained, showing that hydrogen diffusion coefficient was the most relevant variable affecting DHC velocity cracking. Furthermore, this approach has been demonstrated to be useful in estimating DHC velocity in irradiated materials. © 2011 Elsevier B.V. All rights reserved.


Pasianot R.C.,Gerencia Materiales | Pasianot R.C.,CONICET | Pasianot R.C.,Instituto Sabato
Journal of Nuclear Materials | Year: 2016

We study the structure of several standard and non-standard self-interstitial configurations in a series of hcp metals, by using Density Functional Theory as embodied in the computer codes SIESTA and WIEN2k. The considered metals include Be, Mg, Ti, Zr, Co, Zn, and Cd, thus spanning the whole range of experimental c/a ratios, different kinds of bonding, and even magnetism (Co). The results show the importance of low symmetry configurations, closely related to the non-basal crowdion, in order to rationalize the experimental data on self-interstitial structure and migration. © 2016 Elsevier B.V.


Pasianot R.C.,CNEA CAC | Pasianot R.C.,CONICET | Pasianot R.C.,Instituto Sabato | Perez R.A.,CNEA CAC | And 2 more authors.
Physica B: Condensed Matter | Year: 2012

Electronic structure techniques, as embodied in the SIESTA code, are presently used for assessing self-diffusion in the hcp transition metals Zr and Ti. Several issues pertaining to this apparently hard case and not routinely found in the literature, are touched upon, a partial list including: (i) the suitability of available pseudopotentials, (ii) the need to employ fine space grids for the numerical integrations, (iii) the need of a rather large basis set, (iv) the reliability of the simulation cell size and boundary conditions, etc. All of which affect the precision of the magnitudes to be evaluated, namely, in the framework of transition state theory and assuming a standard vacancy mechanism, formation energy and entropy, migration energies, and attempt frequencies. © 2011 Elsevier B.V. All rights reserved.

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