University of ZagrebZagreb

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University of ZagrebZagreb

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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.

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.

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.

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.

Dzaja D.,University of ZagrebZagreb | Hladnik A.,University of ZagrebZagreb | Bicanic I.,University of ZagrebZagreb | Bakovic M.,University of ZagrebZagreb | Petanjek Z.,University of ZagrebZagreb
Frontiers in Neuroanatomy | Year: 2014

In this article we first point at the expansion of associative cortical areas in primates, as well as at the intrinsic changes in the structure of the cortical column. There is a huge increase in proportion of glutamatergic cortical projecting neurons located in the upper cortical layers (II/III). Inside this group, a novel class of associative neurons becomes recognized for its growing necessity in both inter-areal and intra-areal columnar integration. Equally important to the changes in glutamatergic population, we found that literature data suggest a 50% increase in the proportion of neocortical GABAergic neurons between primates and rodents. This seems to be a result of increase in proportion of calretinin interneurons in layers II/III, population which in associative areas represents 15% of all neurons forming those layers. Evaluating data about functional properties of their connectivity we hypothesize that such an increase in proportion of calretinin interneurons might lead to supra-linear growth in memory capacity of the associative neocortical network. An open question is whether there are some new calretinin interneuron subtypes, which might substantially change micro-circuitry structure of the primate cerebral cortex. © 2014 Džaja, Hladnik, Bičanić, Baković and Petanjek.

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.

Krbot Skoric M.,University of Zagreb | Adamec I.,University of Zagreb | Jerbic A.B.,University of ZagrebZagreb | Gabelic T.,University of Zagreb | And 4 more authors.
Clinical EEG and Neuroscience | Year: 2015

The aim of the present study was to examine human central nervous system response to three different odors. Electrophysiological activity was recorded in the baseline state and for 3 odors, lemon, peppermint, and vanilla, in 16 healthy participants. Electrodes were separated into groups according to the spatial position on the head. Fast Fourier transformation was performed on every set, and mean value of activity in theta was exported. As theta showed statistically significant results, further analysis was based only on the theta frequency band. On electrodes FP1, F3, Fz, F4, F8, T7, C3, Cz, C4, T8, TP9, CP5, CP1, CP2, CP6, P7, P3, Pz, P4, P8, PO9, and PO10 there was statistically significant difference in the electrical activity of the brain between four conditions. For peppermint and lemon, there was statistically significant difference in activity between different regions - F(1.576, 23.637) = 16.030, P =.000 and F(1.362, 20.425) = 4.54, P =.035, respectively - where the activity in the central area was significantly reduced compared with the activity in the other 4 areas and in the left and right anterior and left posterior area, respectively. There was no statistically significant difference for vanilla between specific areas, F(1.217, 18.257) = 1.155, P =.309. The results indicate that olfactory stimuli can affect the frequency characteristics of the electrical activity of the brain. © EEG and Clinical Neuroscience Society.

Bain A.R.,University of British Columbia | Ainslie P.N.,University of British Columbia | Hoiland R.L.,University of British Columbia | Barak O.F.,University of Split | And 8 more authors.
Journal of Physiology | Year: 2016

Key points: The present study describes the cerebral oxidative and non-oxidative metabolism in man during a prolonged apnoea (ranging from 3 min 36 s to 7 min 26 s) that generates extremely low levels of blood oxygen and high levels of carbon dioxide. The cerebral oxidative metabolism, measured from the product of cerebral blood flow and the radial artery-jugular venous oxygen content difference, was reduced by ∼29% at the termination of apnoea, although there was no change in the non-oxidative metabolism. A subset study with mild and severe hypercapnic breathing at the same level of hypoxia suggests that hypercapnia can partly explain the cerebral metabolic reduction near the apnoea breakpoint. A hypercapnia-induced oxygen-conserving response may protect the brain against severe oxygen deprivation associated with prolonged apnoea. Abstract: Prolonged apnoea in humans is reflected in progressive hypoxaemia and hypercapnia. In the present study, we explore the cerebral metabolic responses under extreme hypoxia and hypercapnia associated with prolonged apnoea. We hypothesized that the cerebral metabolic rate for oxygen (CMRO2) will be reduced near the termination of apnoea, attributed in part to the hypercapnia. Fourteen elite apnoea-divers performed a maximal apnoea (range 3 min 36 s to 7 min 26 s) under dry laboratory conditions. In a subset study with the same divers, the impact of hypercapnia on cerebral metabolism was determined using varying levels of hypercapnic breathing, against the background of similar hypoxia. In both studies, the CMRO2 was calculated from the product of cerebral blood flow (ultrasound) and the radial artery-internal jugular venous oxygen content difference. Non-oxidative cerebral metabolism was calculated from the ratio of oxygen and carbohydrate (lactate and glucose) metabolism. The CMRO2 was reduced by ∼29% (P < 0.01, Cohen's d = 1.18) near the termination of apnoea compared to baseline, although non-oxidative metabolism remained unaltered. In the subset study, in similar backgrounds of hypoxia (arterial O2 tension: ∼38.4 mmHg), severe hypercapnia (arterial CO2 tension: ∼58.7 mmHg), but not mild-hypercapnia (arterial CO2 tension: ∼46.3 mmHg), depressed the CMRO2 (∼17%, P = 0.04, Cohen's d = 0.87). Similarly to the apnoea, there was no change in the non-oxidative metabolism. These data indicate that hypercapnia can partly explain the reduction in CMRO2 near the apnoea breakpoint. This hypercapnic-induced oxygen conservation may protect the brain against severe hypoxaemia associated with prolonged apnoea. © 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society

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