Hybrid RES-HEP Systems Development

An inherent characteristic of renewable energy sources (RES)-based electricity generation systems is intermittency and non-controllability. Therefore, the prerequisite for a more significant use of RES within the energy system is the corresponding capacity of Electric Energy Storage (EES). The existing storage of Hydro Electric Power (HEP) is suggested as a possible solution to this issue. The paper contains a detailed analysis of the possible joint operation of Photovoltaic (PV) generator and HEP. The key element of this scenario is the HEP storage that would serve as EES. The analysis of the possible joint operation of the PV generator and HEP shows it as a natural, feasible and very acceptable solution that would enhance the features of both energy sources. Joint operation would increase the energy production sustainability, cut volatility and increase reliability, and therefore the value of the RES energy, as well as the efficiency of the HEP. The application of the hybrid system will significantly contribute to the share of RES in the energy system and thus to achieving the climate protection objectives.     

Low Psychological Resilience in Older Individuals: An Association with Increased Inflammation,Oxidative Stress and the Presence of Chronic Medical Conditions

The term resilience, which has been present in science for almost half a century, stands for the capacity of some system needed to overcome an amount of disturbance from the environment in order to avoid a change to another stable state. In medicine, the concept of resilience means the ability to deal with daily stress and disturbance to our homeostasis with the intention of protecting it from disturbance. With aging, the organism becomes more sensitive to environmental impacts and more susceptible to changes. Mental disturbances and a decline in psychological resilience in older people are potentiated with many social and environmental factors along with a subjective perception of decreasing health. Distinct from findings in younger age groups, mental and physical medical conditions in older people are closely associated with each other, sharing common mechanisms and potentiating each other’s development. Increased inflammation and oxidative stress have been recognized as the main driving mechanisms in the development of aging diseases. This paper aims to reveal, through a translational approach, physiological and molecular mechanisms of emotional distress and low psychological resilience in older individuals as driving mechanisms for the accelerated development of chronic aging diseases, and to systematize the available information sources on strategies for mitigation of low resilience in order to prevent chronic diseases.     

3D finite-element determination of stray losses in power transformer

This paper presents a three-dimensional (3D) finite-element (FE) analysis of eddy current losses generated in the tank walls and yoke clamps of a three-phase 40 MV A power transformer. The time harmonic FE model is used to compute the magnetic leakage field in the case of a short circuit condition of the power transformer. Three cases are analyzed to study the impact of modeling tank walls and yoke clamp plates in FE context in estimation of their losses. The load loss test was carried out on an experimental transformer to validate the simulation.     

War Damages and Reconstruction of Peru?a Dam

The paper describes the heavy damages caused by blasting in the Peru?a rockfill dam in Croatia in January 1993. Complete collapse of the dam by overtopping was prevented through quick action of the dam owner by dumping clayey gravel on the lowest sections of the dam crest and opening the bottom outlet of the reservoir, thus efficiently lowering the water level. After the damages were sufficiently established and alternatives for restoration of the dam were evaluated, it was decided to construct a diaphragm wall through the damaged core in the central dam part as the impermeable dam element and to rebuild the central clay core at the dam abutments. Reconstruction works are described.     

The integral capacitance,kinetics and mechanisms of the Cu/Cu(II) system in sulphuric acid media

Galvanostatic investigation has been carried out on the Cu/Cu(II) system 2 M H₂SO₄ + 0.7 M CuSO₄, at 298 K. The pseudo-capacitance (integral capacitance) has been extracted as a function of overvoltage from the portion of the charging curve prior to plateaux. It has been found that the pseudo-capacitance, for both anodic and cathodic processes depended upon the current density and time. On the basis of the above findings the reaction mechanism has been suggested to be Cu?Cu(I)_ad^v + ve^?, Cu(I)_ad^v?Cu(I) + (1 ? v)e^?, Cu(I)?Cu(II)e^?.     

Free radical copolymerization of N,N‐dimethylaminoethyl methacrylate with styrene and methyl methacrylate: monomer reactivity ratios and glass transition temperatures

BACKGROUND: The properties of copolymers depend strongly on their composition; therefore in order to tailor some for specific applications, it is necessary to control their synthesis, and, in particular, to know the reactivity ratios of their constituent monomers. Free radical copolymerizations of N,N‐dimethylaminoethyl methacrylate (DMAEM) with styrene (ST) and methyl methacrylate (MMA) in toluene solution using 1‐di(tert‐butylperoxy)‐3,3,5‐trimethylcyclohexane as initiator at 70 °C were investigated. Monomer reactivity ratios were determined for low conversions using both linear and nonlinear methods. RESULTS: For the DMAEM/ST system the average values are r₁ = 0.43 and r₂ = 1.74; for the DMAEM/MMA system the average values are r₁ = 0.85 and r₂ = 0.86. The initial copolymerization rate, R_p, for DMAEM/ST sharply decreases as the content of ST in the monomer mixture increases up to 30 mol% and then attains a steady value. For the DMAEM/MMA copolymerization system the composition of the feed does not have a significant influence on R_p. The glass transition temperatures (T_g) of the copolymers were determined calorimetrically and calculated using Johnston's sequence length method. A linear dependence of T_g on copolymer composition for both systems is observed: T_g increases with increasing ST or MMA content. CONCLUSION: Copolymerization reactivity ratios enable the design of high‐conversion processes for the production of copolymers of well‐defined properties for particular applications, such as the improvement of rheological properties of lubricating mineral oils. Copyright © 2009 Society of Chemical Industry     

Electrochemical synthesis and corrosion behavior of polyaniline-benzoate coating on copper

Electrochemical polymerization of polyaniline (PANI) coating on copper electrode was performed galvanostatically in the current density range between 0.50 and 1.25 mA cm^?2, from aqueous solution of 0.3 mol dm^?3 sodium benzoate and 0.2 mol dm^?3 aniline. The corrosion behavior of PANI coated copper and copper electrode exposed to 0.5 mol dm^?3 sodium chloride solution was investigated by potentiodynamic and electrochemical impedance spectroscopy techniques. It was observed that thin PANI (5 μm) coating had provided efficient protection (～96%) to copper in 0.5 mol dm^?3 sodium chloride solution. Unusual initial impedance behavior to that normally observed with conventional organic coatings was attributed to dedoping of benzoate anions from the polymer coating.     

Helical winding’s magnetic field in power transformers

Helical winding is typically used for low voltage and high current winding of large generator transformers. Due to its distinct design (spiral form, small number of turns and high current), some additional eddy-current losses may be expected. Differences in magnetic field produced by helical and cylinder windings are presented in this paper. A simple closed-form expression for estimating the loss, which is based on numerical modeling, is proposed.     

Terpolymerization kinetics of N,N‐dimethylaminoethyl methacrylate/alkyl methacrylate/styrene systems

Low conversion kinetics of terpolymerization of N,N‐dimethylaminoethyl methacrylate (DMAEM) and dodecyl methacrylate (DDMA) with methyl methacrylate (MMA) or styrene (ST) was investigated. Reactions were performed at 70°C, in toluene solutions, using peroxide initiator. The interdependence between terpolymer and monomer feed composition was successfully described by Alfrey‐Goldfinger equation and the unitary, binary, and ternary azeotropes were calculated. In MMA‐containing system, the wide pseudoazeotropic region with existence of true azeotropic point was observed and experimentally confirmed at the DMAEM:MMA:DDMA molar ratio of 56:41:3. In the ST‐containing system compositional heterogeneity was significant, more than 10 mol%. Required copolymerization reactivity ratios were determined by linear and nonlinear methods. The glass transition temperatures of synthesized terpolymers are found to be between those of the corresponding homopolymers and relative to their content. Increase in the MMA or ST contents and decrease in the DDMA content in terpolymers results in an increase in their glass transition temperatures. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Optimization of Irrigation with Photovoltaic Pumping System

The usual methods for optimal sizing of photovoltaic (PV) irrigation water pumping systems, which separately considered the demand for hydraulic energy and possibilities of its production from available solar energy with the PV pumping system, are not optimal. However, by systematic approach to the problem, taking into account all relevant elements, from the PV water pumping system, water intake, local climate, soil, crops to method of irrigation, it is possible to optimize the determination of nominal power of the PV generator and obtain quality solutions. This paper presents one such method for optimal sizing. For the purpose of testing the proposed model for optimal sizing, in order to show to what extent it describes the system and to obtain corresponding research results, two areas were selected, in typical climate regions of Osijek and Split, as patterns of continental and coastal Croatia. By variation of certain values in the system, their effects on calculation of the optimal electric power of PV generator were observed.