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Dubrovnik, Croatia

Toczydlowska D.,Polish Academy of Sciences | Kedra-Krolik K.,Polish Academy of Sciences | Nejbert K.,University of Warsaw | Preocanin T.,University of ZagrebZagreb | And 2 more authors.
Physical Chemistry Chemical Physics | Year: 2015

The electrochemical signatures of Fe(ii) interactions with iron(iii) oxides are poorly understood, despite their importance in controlling the amount of mobilized iron. Here, we report the potentiometric titration of α,γ-Fe2O3 oxides exposed to Fe(ii) ions. We monitored in situ surface and ζ potentials, the ratio of mobilized ferric to ferrous, and the periodically analyzed nanoparticle crystal structure using X-ray diffraction. Electrokinetic potential reveals weak but still noticeable specific sorption of Fe(ii) to the oxide surface under acidic conditions, and pronounced adsorption under alkaline conditions that results in a surface potential reversal. By monitoring the aqueous iron(ii/iii) fraction, we found that the addition of Fe(ii) ions produces platinum electrode response consistent with the iron solubility-activity curve. Although, XRD analysis showed no evidence of γ-Fe2O3 transformations along the titration pathway despite iron cycling between aqueous and solid reservoirs, the magnetite formation cannot be ruled out. This journal is © the Owner Societies.

Marusic K.,University of ZagrebZagreb | Curkovic H.O.,University of ZagrebZagreb | Takenouti H.,French National Center for Scientific Research
Journal of the Electrochemical Society | Year: 2013

The aim of this study was to investigate the efficiency of 1-H benzimidazole as a corrosion inhibitor in protection of cultural artifacts made of bronze. For that purpose1-H benzimidazole was studied on bare and patinated Cu-6Sn bronze, exposed to urban environments. Dissolution of bare and patinated bronze was investigated by potentiodynamic techniques and electrochemical impedance spectroscopy. The microstructure of the bronze surface exposed to the inhibitor was examined by SEM/EDS. 1-H benzimidazole showed a very good protective effect in sulfate/carbonate media which simulate urban acid rainfall. Benzimidazole protected the Cu-6Sn bronze covered by electrochemical patina by stabilizing the patina layer and by slowing down dissolution of bronze substrate. © 2013 The Electrochemical Society.

Tokic A.,University of Tuzla | Milardic V.,University of ZagrebZagreb | Uglesic I.,University of ZagrebZagreb | Jukan A.,University of Tuzla
Electric Power Systems Research | Year: 2015

Abstract This paper presents a simplified model of a three-phase transformer developed in the state-space form using the linear graph theory. The algorithm for generating the coefficient matrixes of the state-space equation is described. Stiff detection procedures of differential equation systems that describe the three-phase transformer inrush current transients are explained. It is shown that the time-domain transient response of three-phase transformers mathematically describes extremely stiff systems. The numerical integration methods based on strong stable (A and L) backward differentiation formulae are used to solve extremely stiff differential equation systems arising from the state-space formulation of the transformer inrush current transient equations. A comparison of the measured and simulated three-phase transformer inrush currents showed very good agreement. The proposed procedure of modeling and the simulation method are useful tools that can be applied to other electrical transients where extremely stiff systems appear. © 2015 Elsevier B.V.

Babic K.,University of ZagrebZagreb | Rotach M.W.,University of Innsbruck | Klaic Z.B.,University of ZagrebZagreb
Agricultural and Forest Meteorology | Year: 2016

The local scaling approach was examined based on the multi-level measurements of atmospheric turbulence in the wintertime (December 2008–February 2009) stable atmospheric boundary layer (SBL) established over a heterogeneous surface influenced by mixed agricultural, industrial and forest surfaces. The heterogeneity of the surface was characterized by spatial variability of both roughness and topography. Nieuwstadt's local scaling approach was found to be suitable for the representation of all three wind velocity components. For neutral conditions, values of all three non-dimensional velocity variances were found to be smaller at the lowest measurement level and larger at higher levels in comparison to classical values found over flat terrain. Influence of surface heterogeneity was reflected in the ratio of observed dimensionless standard deviation of the vertical wind component and corresponding values of commonly used similarity formulas for flat and homogeneous terrain showing considerable variation with wind direction. The roughness sublayer influenced wind variances, and consequently the turbulent kinetic energy and correlation coefficients at the lowest measurement level, but not the wind shear profile. The observations support the classical linear expressions for the dimensionless wind shear (ϕm) even over inhomogeneous terrain after removing data points associated with the flux Richardson number (Rf) greater than 0.25. Leveling-off of ϕm at higher stabilities was found to be a result of the large number of data characterized by small-scale turbulence (Rf > 0.25). Deviations from linear expressions were shown to be mainly due to this small-scale turbulence rather than due to the surface heterogeneities, supporting the universality of this relationship. Additionally, the flux-gradient dependence on stability did not show different behavior for different wind regimes, indicating that the stability parameter is sufficient predictor for flux-gradient relationship. Data followed local z-less scaling for ϕm when the prerequisite Rf  ≤ 0.25 was imposed. © 2016 Elsevier B.V.

Krivec S.,University of ZagrebZagreb | Poljak M.,University of ZagrebZagreb | Suligoj T.,University of ZagrebZagreb
Solid-State Electronics | Year: 2016

Electron mobility is investigated in sub-20 nm-thick InGaAs channels, sandwiched between different gate oxides (SiO2, Al2O3, HfO2) and InP as substrate, using physics-based numerical modeling. Effects of body thickness downscaling to 2 nm, different gate oxides, and surface orientation [(1 0 0) and (1 1 1)] are examined by including all electron valleys and all relevant scattering mechanisms. We report that ultra-thin (1 1 1) Al2O3-InGaAs-InP devices offer greater electron mobility than (1 0 0) devices even in the extremely-thin channels. Furthermore, ultra-thin (1 0 0) InGaAs devices outperform SOI in terms of electron mobility for body thicknesses above ∼4 nm, while (1 1 1) InGaAs channels are superior to SOI for all body thickness values above ∼3 nm. The study of different gate oxides indicates that HfO2 is the optimum gate dielectric regardless of device orientation, offering a mobility improvement of up to 124% for (1 1 1) and 149% for (1 0 0) surface orientation, when compared to the initial Al2O3-InGaAs-InP structure. The (1 1 1) orientation offers improvement over (1 0 0) device irrespective of the body thickness and gate oxide material, with the highest difference reported for SiO2, followed by Al2O3 and HfO2. © 2015 Elsevier Ltd.

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