Robust decentralized control of parallel dc/dc converters

Robust decentralized linear feedback controllers for parallel operating dc/dc converters, using the structured singular value approach, are investigated. Different structures of decentralized controllers were applied and tested. The controllers were designed for structured and unstructured modeluncertainty. The gain directionality compensation, due to a high condition number was considered.Eine robuste und dezentralisierte Regelung für parallele Gleichstromwandler wurde untersucht. Verschiedene Strukturen des Regelungsverfahren wurden angewandt und getestet. Die Regelung wurde für den Fall der strukturierten und unstrukturierten Perturbation entworfen.     

Multilayer multimode optical fibre

Multilayer multimode fibres are considered by means of the ray theory, and the optimal distribution of refractive index with respect to pulse broadening is found. It is concluded that even with a low number of layers we can reduce pulse broadening significantly. Low sensitivity to the variations of refractive index distribution is predicted.     

Messung und Berechnung des Wärmeübergangs von einem Heizrohr an eine Kohlewirbelschicht in Wasserdampf und Inertgas

Zusammenfassung Zur Durchführung endothermer Reaktionen zwischen Gas und Feststoff in einer Wirbelschicht werden h?ufig Rohrbündel zur W?rmeübertragung eingebaut. Es wird eine wirtschaftliche Bewertung von Bündeln aus runden Rohren nach w?rmetechnischen Gesichtspunkten vorgenommen. Innerhalb des Projektes “Prototypanlage Nukleare Proze?w?rme—PNP” arbeitet die Bergbau-Forschung gemeinsam mit anderen Firmen an einem Kohlevergasungsverfahren, in dem die W?rme aus Hochtemperaturkernreaktore (HTR) genutzt wird. In der vorliegenden Arbeit wird die W?rmeübertragung von einem Heizrohr an, eine gasdurchtr?mte Wirbelschicht untersucht, deren Kenntnis für die Verwirklichung der allothermen Wasserdampfvergasung wichtig ist. Im einzelnen werden theoretische und experimentelle Untersuchungen zur Aufkl?rung des Mechanismus des W?rmeübergangs vom Heizrohr an, die Wirbelschicht beim Vergasungsproze? durchgeführt. Auszug aus der Dissertation vonV. Petrovic, Aachen 1978.     

Comparison of tillage systems according to fuel consumption

Nowadays, tractor is still the basic power unit in almost all production processes in agriculture, including tillage. The structure of tractor–machinery systems depends on many parameters: seeding system, soil conditions, farm area etc. These relevant parameters are defined in this paper, as well as the energy inputs introduced in the tillage through the consumed fuel. Altogether, they simultaneously represent the input variables in the selection criteria of tractor–machinery systems. A method of selecting the optimal tractor for different tillage technologies is presented in this paper. The results obtained show that fuel energy consumption for all tractors in the conditions of conventional tillage is in range from 412 to 740 MJ/ha. In the case of mulch technology the energy consumption varied from 183 to 266 MJ/ha and in the case of zero tillage the energy consumption varied from 80 to 284 MJ/ha. These results show obvious differences in energy inputs regarding the applied production technology.     

Uncertainty of Trypsin Inhibitor Activity Measurement of Legume Crops Using Microtiter Plate Method

Trypsin inhibitors could limit utilization of legumes in human nutrition, but they could also have beneficial health effects. The objective of this study was to measure trypsin inhibitor activity (TIA) of different legumes using microtiter plate method and to identify factors that contribute to uncertainty of TIA measurement. TIA measurements were performed on seeds of faba bean, pea, common vetch, soybean, and common bean cultivars. The significant effect of legume crop on TIA measurement uncertainty was confirmed with P = 0.045. Certain sources of measurement uncertainty were related with the content of trypsin inhibitors (Tis) in legume seeds. In respect to that, significant effect of level of sample dilution (P ? 0.001) was confirmed. Significant influence of the repeated absorbance measurement of sample reaction mixture on uncertainty of TIA measurement was identified (P ? 0.001), and it took 60% of overall TIA measurement uncertainty for soybean cultivars. TIA of soybean cultivars exceeded 90 TUI/mg. Repeated absorbance measurement of positive control reaction mixture took 70% of TIA measurement uncertainty of cultivars with TIA lesser than 4.5 TUI/mg. Graduated cylinder used for preparation of the final sample solutions took the range from 45 to 90% of overall TIA measurement uncertainty of the cultivars whose TIA were in the middle of previously mentioned. The uncertainty of TIA measurement of legume crops was not studied before; thus, this study pointed out that acquiring insight into factors contributing to uncertainty of TIA measurement could give directions for improvement of TIA testing if microtiter plate method is used.     

The dependence of the photocatalytic activity of TiO2/carbon nanotubes nanocomposites on the modification of the carbon nanotubes

Nanostructural TiO₂/modified multi-wall carbon nanotubes photocatalysts were prepared by hydrolysis of Ti(iso-OC₃H₇)₄ providing chemical bonding of anatase TiO₂ nanoparticles onto oxidized- or amino-functionalized multi-wall carbon nanotubes (MWCNT). The processes of functionalization of the MWCNT and the deposition of TiO₂ influence the photocatalytic activity of the synthesized nanocomposites. The phase composition, crystallite size, and the structural and surface properties of the obtained TiO₂/modified-MWCNT nanocomposite were analyzed from XRD, FEG-SEM, TEM/HRTEM and FTIR data, as well low temperature N₂ adsorption. In the photocatalytic study, the TiO₂/oxidized-MWCNT catalyst showed the highest and the TiO₂/amino functionalized-MWCNT catalysts somewhat lower degradation rates, indicating that the enhancement of photocatalysis was supported by the more effective electron transfer properties of the oxygen- than amino-containing functional groups, which support the efficient charge transportation and separation of the photogenerated electron-hole pairs.     

Electrical properties of niobium doped barium bismuth-titanate ceramics

BaBi₄Ti_4–5/4xNb_xO₁₅ (BBNTx, x = 0, 0.05, 0.15, 0.30) ceramics have been prepared by solid state method. XRD data indicate the formation of single-phase-layered perovskites for all compositions. SEM micrographs suggest that the grain size decreases with Nb doping. The effect of niobium doping on the dielectric and relaxor behavior of BaBi₄Ti₄O₁₅ ceramics was investigated in a wide range of temperatures (20–777 °C) and frequencies (1.21 kHz to 1 MHz). Nb doping influences T_c decrease as well as the decrease of dielectric permittivity at Curie temperature. At room temperature, undoped BaBi₄Ti₄O₁₅ exhibits dielectric constant of ～204 at 100 kHz, that slightly increases with Nb doping. The conductivity of BBNT5 ceramics is found to be lower than that of other investigated compositions. The value of activation energy of σ_DC was found to be 0.89 eV, 1.01 eV, 0.93 eV and 0.71 eV for BBT, BBNT5, BBNT15 and BBNT30, respectively.