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This paper analyzes the difference between zero-sequence magnetizing impedances (Z(0M)) of a 3-phase core-type transformer. Z(0M) in per-unit is smaller for an external winding than foran internal winding. The difference between both Z(0M) values is similar to the positive-sequence short-circuit impedance between both windings for units without magnetic shunts on the tank wall as well as for units without tank. This fact can be observed in measured values, and in the results of 3D models. However, the results of simple 2D models do not show this behavior; therefore, this paper demonstrates that this fact only can be explained from 3D models. The results are shown for different cases: transformers with and without magnetic shunts on the tank wall, and transformers without tank. In transformers with magnetic shunts on the tank wall, or in magnetostatic simulations of transformers with tank, the difference between both Z(0M) values is not very similar to the positive-sequence short-circuit impedance between both windings.

This paper evaluates the evolution of environmental performance in the context of the European Union (EU), over the period 1993-2010. The context is particularly relevant, due to the traditionally high concerns of the EU about these issues, which has triggered off several initiatives and regulations on environmental protection. In this setting, we conduct a two-stage analysis which develops environmental performance indicators in the first stage for each pair country-year, and evaluates its evolution in the second. More specifically, in the first stage we estimate specific efficiencies for three air-pollutants (CO2e, SO2, NOx), along with an eco-efficiency indicator, for which we use the slack-free directional distance functions in the Data Envelopment Analysis framework (as opposed to the more extended intensity ratios), whereas in the second stage we propose to using a model of explicit distribution dynamics which takes into account how the entire distributions of these indicators evolve. Our results indicate that the dynamics underlying the evolution of the indicators analyzed are indeed remarkable. Although the eco-efficiency indicator has improved over the last two decades, it has been during the last decade when performance has shown a more convergent path. However, in the case of the more traditional indicators (CO2e, SO2, NOx) the abatement opportunities are still remarkable, especially in the case of SO2. HighlightsWe evaluate the evolution of environmental performance in the context of the EU.We estimate specific efficiencies for CO2e, SO2, NOx and an eco-efficiency indicator.We propose using a model of explicit distribution dynamics.Results indicate that the dynamics of the indicators are complex.Despite the recent progresses, the abatement opportunities are still remarkable.

Ammonia increases buffer capacity of methanogenic medium in mesophilic anaerobic reactor thus increasing the stability of anaerobic digestion process. Optimal ammonia concentration ensures sufficient buffer capacity while not inhibiting the process. It was found out in this paper that this optimum depends on the quality of anaerobic sludge under investigation. The optimal concentrations for methanogens were 2.1, 2.6 and 3.1 g/L of ammonia nitrogen in dependence on inoculum origin. High ammonia nitrogen concentration (4.0 g/L) inhibited methane production, while low ammonia nitrogen concentration (0.5 g/L) caused low methane yield, loss of biomass (as VSS) and loss of the aceticlastic methanogenic activity. It was found out that negative effect of low ammonia nitrogen concentration on biomass is caused not only by low buffer capacity but also by insufficiency of nitrogen as nutrient. It was also found out that anaerobic sludge with higher ammonia nitrogen concentration (4.2 g/L) tolerates even concentration of volatile fatty acids (160 mmol/L) which causes inhibition of the process with low ammonia nitrogen concentration (0.2 g/L).

Most of the Catalonian population and urban areas are located along the Mediterranean coastal zone and for this analysis three largest Catalonia’s cities are chosen: Barcelona, Terrassa and Tarragona. Each city is a geographical representative of a different climate type according to the re-analysed Köppen-Geiger climate classification. The objective of this research is to demonstrate the effects of regional climate variations on the potential of natural ventilation (NV) application in building design. The first part of the article presents the availability of NV corresponding to yearly climate conditions applying the methodology “Climate Potential for Natural Ventilation” (CPNV). In continuation, the second analysis is calculated with building energy simulation software and displays possible refrigeration energy savings in three geographical locations. Mixed-mode (or hybrid-mode) and night-ventilation techniques are applied for the cooling process of a hypothetical low-rise office building model. Peer Reviewed

We present the summary of several years of research about the inhibitor effect of NO2- on the corrosion of reinforcements. We have studied their inhibitor effect using galvanostatic and potentiodynamic polarization curves and we have measured the corrosion rates using the Polarization Resistance method (linear polarization). We have verified by this last technique, Rp, that the NO2- in concrete, if they are used in sufficient proportion, are a complete inhibitor when the Cl are added during the mixing (e.g. mixing whith sea water, CaCl2 as an accelerator in inbitor). Inssufficient amounts of NO2- have never provoked more corrosion in our experiments in concrete. The presence of NO2- always have produced a beneficial effect. The NO2- are also beneficial in carbonated concrete, suppressing or, at least, reducing the attacked area and the corrosion rate of the reinforcements.

This paper presents the design of an extended Kalman filter (EKF) as a state-of-charge (SoC) estimator for a lithium–titanate (LTO) battery cell. The design is based on a Thevenin model of the equivalent battery electrical circuit with two parallel resistive-capacitive (RC) elements for the emulation of electrolyte polarization effects. The effectiveness of the proposed SoC estimator is verified through computer simulations on the comprehensive nonlinear battery simulation model featuring battery parameter vs. SoC variations, which is subject to highly dynamic loading regimes.

We have a system that is unable to keep students excited about their own learning and educational performance. In light of this situation it is the responsibility of educators to make a broad and global reflection on what must be changed and how this change may be managed. We believe that change is possible and there is no objective more necessary for society than investing in its future project. This paper proposes an exhaustive analysis of the current situation of the secondary school teachers and from there on justifies the change through the teaching practice based on innovation and with a better training in pedagogical and didactical issues.