Drawbacks of impedance networks

This paper presents the influence of voltage‐fed impedance networks, known as Z‐source and quasi–Z‐source, as well as some more sophisticated networks on the static and dynamic properties of voltage source inverters. The impedance networks increase output voltage distortions with the second harmonic of the fundamental harmonic and decrease the power efficiency. The distortions of the output voltage increase for the discontinuous current mode of the impedance network. The DC voltage boost factor depends on the impedance network power losses. The impedance networks add 2 resonant frequencies that are very close each other to the control transfer function of the inverter in the frequency range that is close to the fundamental frequency. The influence of the impedance network on the control transfer function depends on the effective damping resistance in the impedance network. The impedance network operation during the “shoot‐through” time increases the damping of the inverter output filter. The effective damping resistances and the inductance of the coils depend on the power losses in the magnetic materials. Theoretical models along with experimental verification can help to estimate the real influence of impedance networks on the inverter properties.     

Determination of Pyrrolizidine Alkaloids in Honey with Sensitive Gas Chromatography-Mass Spectrometry Method

Pyrrolizidine alkaloids (PAs) are secondary metabolites produced by plants as a chemical defense against herbivores. Plants containing PAs are widely distributed in almost all geographical regions posing a risk of honey contamination. To provide safety of honey and decrease the potential risk for the consumers, a sensitive method based on gas chromatography-mass spectrometry enabling determination of a content of 1,2-unsaturated PAs in honey was developed. Honey samples were purified on MCX cartridges, and PAs were eluted with a solvent mixture consisting of ethyl acetate, methanol, ammonia, and triethylamine. Subsequently, 1,2-unsaturated alkaloids were reduced to their common backbone structures and derivatized with heptafluorobutyric anhydride. The method was validated according to SANTE 2015. All received parameters are in consistence with the document requirements as recovery ranged from 73.1 to 93.6%. The repeatability and reproducibility were calculated as relative standard deviation and ranged from 3.9 to 8.6% and from 10.6 to 17.8%, respectively. The limit of quantification was determined as 1 μg kg^?1. Good linearity of the method was obtained with the coefficient of determination R ²?>?0.99. The method was applied to 40 Polish and 14 Asian honey sample analyses.     

The accuracy of oxygen flux measurements using microelectrodes

An electrochemical analog of a biofilm was constructed to test the accuracy of oxygen flux measurements using microelectrodes. We used a cathodically polarized graphite felt attached to the bottom of a flat plate open channel reactor as the reactive surface consuming oxygen. The oxygen flux to the felt was calculated from the polarization current. Microelectrodes were used to measure the oxygen profiles above and within the graphite felt. From the shape of the oxygen profile we evaluated the oxygen flux to the graphite felt. This provided us with two sets of data, the true oxygen flux, calculated from polarization current, and the oxygen flux estimated from microelectrode measurements. Comparing these two fluxes, for different flow velocities, showed that the fluxes evaluated from the polarization current were different from those evaluated from the oxygen profiles. The differences were likely caused by the presence of the microelectrode in the mass boundary layer and/or by the simplifying assumptions accepted in computational procedures employed to calculate oxygen fluxes. For low flow velocities, between zero and 1.0 cm s⁻¹, the differences were velocity sensitive; the higher the flow velocity, the bigger the difference. For higher flow velocities, between 1 cm s⁻¹ and 3 cm s⁻¹, the flux of oxygen estimated from the microelectrode measurements was consistently approximately 80% higher than the true oxygen flux estimated from the polarization current.     

Nitrification process in activated sludge with suspended marble particles

The process of nitrification in activated sludge was investigated. As the solid support for nitrifiers' growth a suspension of marble particles has been used. The results proved the possibility of successful nitrification of 100 mg l^?1 NH₄-N simultaneously with the removal of 600 mg l^?1 COD.     

Role of vanadium sites in NO and O2 adsorption processes over VOx/CeO2-ZrO2 catalysts – EPR and IR studies

The interaction of NO and O₂ with 5 mol.% of vanadia deposited on Ce_0.10Zr_0.90O₂ and Ce_0.69Zr_0.31O₂ supports by wet impregnation was studied by means of EPR and IR. The supports were structurally characterized by XRD and Raman spectroscopy. Influence of the phase composition of the support on vanadium speciation as well as on surface architecture of the oxovanadium entities was discussed. The NO forms adsorbed on vanadium-containing systems were compared to those observed on bare CeO₂-ZrO₂ supports. The main products appearing on the catalysts surface during the consecutive reaction with NO and O₂ were identified and their thermal evolution was observed. Changes in vanadium speciation accompanying redox processes related to NO and O₂ activation were also observed and discussed.     

Hydrogen South Africa (HySA) Systems Competence Centre: Mission,objectives, technological achievements and breakthroughs

A long-term (15-year) Hydrogen and Fuel Cell Technologies (HFCT) Research, Development, and Innovation (RDI) strategy was officially launched in September 2008 by the Department of Science and Technology (DST) in South Africa. The Hydrogen South Africa (HySA) programme is based upon the beneficiation of the country's large Platinum Group Metal (PGM) resources. HySA comprises of three Centres of Competence: HySA Catalysis, HySA Infrastructure and HySA Systems. HySA Systems, a Systems Integration and Technology Validation Competence Centre on HFCT was established in 2007 at the South African Institute for Advanced Materials Chemistry (SAIAMC) at the University of the Western Cape (UWC). The main objective with HySA Systems is to (i) develop Hydrogen and Fuel Cell systems, demonstrators, prototypes and products, (ii) perform technology validation and system integration and (iii) focus on system oriented material R&D in two key HySA-programmes: (1) Combined Heat and Power (CHP) and (2) Hydrogen Fuelled Vehicles (HFV). HySA Systems is also responsible for the development, prototyping, testing and commissioning of the following key technologies: High Temperature (HT) Membrane Electrode Assemblies (MEAs), HT-Proton Exchange Membrane (PEM) fuel cells, metal hydrides for hydrogen storage and compression systems, hydrogen fuel cell/battery power modules, palladium membranes, and lithium-ion batteries. HySA Systems has successfully: a) implemented some pilot plant manufacturing facilities/capabilities for HFC components and systems in South Africa, b) been partnering with key international HFC and local industries, c) established a local Supply Chain of SMMEs, d) set up industrial/commercial agreements with national/international HFC players, e) been disseminating their findings/work in High Impact Factor Journals and National/International Conferences, and f) innovated and thus generated Intellectual Property in key HFC technologies.     

Antioxidant activity,color characteristics,total phenol content and general HPLC fingerprints of six Polish unifloral honey types

Total phenolic content, antioxidant activity (two assays: 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) and ferric reducing antioxidant power (FRAP)), and color coordinates (CIE (Commission Internationale de l'Eclairage) L*a*b*) for six Polish unifloral honeys (black locust, rapeseed, lime, goldenrod, heather and buckwheat) were assessed for several batches of the same honey type and statistically evaluated. Total phenolic content (121.6–1173.8 mg GAE/kg) was similar to the values previously reported for other European honeys and it was also correlated with the color parameters as well as antioxidant activity. The honeys' color ranged from pale yellow to dark amber. Dark buckwheat honey with much higher phenolic content (1113.0 mg GAE/kg) exhibited higher antioxidant activity (5.7 mmol Fe²⁺/kg and 1.2 mmol TEAC/kg). CIE L*a*b* color coordinates can be helpful for identifying and distinguishing between several honey types, such as heather and buckwheat, but almost no differences were found among very light honeys (rapeseed, goldenrod, black locust and lime). High-performance liquid chromatographic (HPLC) analysis revealed general characteristic fingerprints of Polish unifloral honeys with significant differences among the samples of other honey types.     

Kapazit?t der verschiedenen Teile des Verdauungsapparates des Rothirsches (Cervus elaphus L.)

Zusammenfassung An drei Hirschen wurden die Gewichte und Volumina des Verdauungstraktes festgestellt. Die absolute und relative Kaparität, das Verhältnis der Kapazität zum Körpergewicht sowie die Länge und Gewichte der einzelnen Verdauungsabschnitte und deren Inhalt sind in Tabellen angegeben.

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Summary In case of three red deer weights and volumes of the digestive tract were stated. Absolute and relative capacity, the relation of capacity to body weights as well as length and weights of different digestive sections and their contents have been stated in tables.

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Résumé Sur trios cerfs on déterminait les poids et les volumes de l'appareil de la digestion. La capacité absolue et relative, la rélation de la capacité au poids du corps, ainsi que la longueur et les poids des diffrentes sections digestives et leur contenu sont présentés en tableaux.

     

Influence of flexible segment length on the phase structure and properties of poly(hexamethylene 2,5-furandicarboxylate)-block-biopolytetrahydrofuran copolymers

Two series of biobased poly(ether-ester)s comprised of poly(hexamethylene 2,5-furandicarboxylate) (PHF) as the rigid segments and biopolytetrahydrofuran (pTHF) with different molecular masses (1000 and 2000 g/mol) as the flexible segments were synthesized employing polycondensation in the molten state. The study mainly focuses on comparing these two series in terms of the length of the flexible segment. The content of pTHF segments in the copolymer chains varied from 25 to 75 wt.%. The molecular structure and composition, phase structure, and thermal and mechanical properties were characterized by nuclear magnetic resonance (¹H NMR) and Fourier-transformed infrared (FTIR) spectroscopies, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and positron annihilation lifetime spectroscopy (PALS). In addition, mechanical performance and thermo-oxidative and thermal stability have been investigated. Moreover, cyclic tensile properties were studied to evaluate the elastic properties. ¹H NMR and FTIR spectroscopies demonstrate that the syntheses were correctly carried out, which made it possible to obtain the desired compositions of the block copolymers with high molecular masses. The decrease in T_m1, T_c1, and X_cPHF values was visible, along with the increase in the flexible segment content. Moreover, the characteristic properties measured by PALS and the values of temperatures designated from TGA (inert and oxidizing atmosphere) did not vary between copolymer series PHF-b-F-pTHF1000 and PHF-b-F-pTHF2000. In turn, along with an increase in flexible segment content and the length of the pTHF, the values of tensile modulus, stress at break, and hardness decrease, while the value of elongation at break increases.     

River Floods in the Changing Climate—Observations and Projections

River flood damages, worldwide, have increased dynamically in the last few decades, so that it is necessary to interpret this change. River flooding is a complex phenomenon which can be affected by changes coupled to terrestrial, socio-economic and climate systems. The climate track in the observed changes is likely, even if human encroaching into the harm’s way and increase in the damage potential in floodplains can be the dominating factors in many river basins. Increase in intense precipitation has already been observed, with consequences to increasing risk of rain-induced flooding. Projections for the future, based on climate model simulations, indicate increase of flood risks in many areas, globally. Over large areas, a 100-year flood in the control period is projected to become much more frequent in the future time horizon. Despite the fact that the degree of uncertainty in model-based projections is considerable and difficult to quantify, the change in design flood frequency has obvious relevance to flood risk management practice. The number of flood-affected people is projected to increase with the amount of warming. For a 4°C warming the number of flood-affected people is over 2.5 times higher than for a 2°C warming. The present contribution addresses the climate track in an integrated way, tackling issues related to multiple factors, change detection, projections, and adaptation to floods.