Preparation and characterization of nanostructured ZnO thin films for photoelectrochemical splitting of water

Nanostructured zinc oxide thin films (ZnO) were prepared on conducting glass support (SnO₂: F overlayer) via sol-gel starting from colloidal solution of zinc acetate 2-hydrate in ethanol and 2-methoxy ethanol. Films were obtained by spin coating at 1500 rpm under room conditions (temperature, 28–35°C) and were subsequently sintered in air at three different temperatures (400, 500 and 600°C). The evolution of oxide coatings under thermal treatment was studied by glancing incidence X-ray diffraction and scanning electron microscopy. Average particle size, resistivity and bandgap energy were also determined. Photoelectrochemical properties of thin films and their suitability for splitting of water were investigated. Study suggests that thin films of ZnO, sintered at 600°C are better for photoconversion than the films sintered at 400 or 500°C. Plausible explanations have been provided.     

Isentropic compressibility of aqueous and methanolic electrolytic solution

We studied the effect of ion-solvent and ion-ion interactions on the isentropic compressibility of aqueous and methanolic electrolytic solutions. In aqueous electrolytic solutions a critical concentration is attained and correlated with the completion of the primary hydration shell. Such a situation is lacking in methanolic solutions. An expression has been derived for estimating the hydration numbers of the electrolyte in its solutions by using the isentropic compressibility data. This paper is dedicated to Professor Wha Young Lee on the occasion of his retirement from Seoul National University.     

The effect of enhanced milk yield of dairy cows by frequent milking or suckling on intake and digestibility of the diet

The prevalence of osteoporosis and the incidence of fractures are substantially lower in black than in white subjects, a finding generally attributed to racial differences in adult bone mass. Whether these racial differences are present in childhood is the subject of considerable interest, as the amount of bone gained during growth is a major determinant of future susceptibility to fractures. We measured the density and size of the vertebrae and femurs of 80 black and 80 white healthy children, 8-18 yr of age, matched for age, gender, height, weight, and stage of sexual development, using computed tomography. Race had a significant and differential effect on the bones in the axial and appendicular skeletons. In the axial skeleton, black children had greater cancellous bone density, but similar cross-sectional area of the vertebral bodies. In contrast, in the appendicular skeleton, black children had greater femoral cross-sectional area, but similar cortical bone area and cortical bone density. Compared to white children, vertebral bone density and femoral cross-sectional area at sexual maturity were, on the average, 10.75% and 5.7% higher, respectively, in black children. Such significant variations may contribute to the racial differences in the prevalence of osteoporosis between black and white adults.     

Simulation of electric resistance furnace operation by means of numerical modelling

Contents A method of analysing thermal processes in electric resistance furnace, using the numerical technique and the one-dimensional, multidirectional, nonlinear model is presented. The way of calculation is shown on examples of real industrial furnaces. The analysis of heating-up with constant power and with constant temperatur speed are shown. The examination of model imperfection is carried out, including one-dimension representation, time and space discretization, non-constancy of thermophysical parameters and the effect of ambience. Practical aspects of method application are metioned.

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Simulation der Wärmeprozesse in Widerstandsöfen mittels eines numerischen Modells-Möglichkeiten und Grenzen

Übersicht Die dargestellte Methode zur Analyse der Wärmeprozesse in Widerstandsöfen umfaßt die numerische Behandlung und das eindimensionale nichtlineare Mehrwegmodell. Die Berechnung wird am Beispiel realer Industrieöfen erklärt. Eine Analyse der Anheizung mit konstanter Leistung und mit konstanter Temperaturgeschwindigkeit wird durchgeführt. Die Fehlerquellen des Modells werden quantitativ untersucht, und zwar die eindimensionale Darstellung, Zeit- und Raumdiskretisation, nichtkonstante Wärmeparameter und der Einfluß der Umgebung. Praktische Ausblicke der Methodenanwendung werden erwähnt.

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List of symbols B speed of temperature rising - c specific heat - C _c radiation constant of the black body - d thickness - E energy - G conductance - J node point - m mass - P power - S surface - T absolute temperature, temperature - TN new temperature - t time - x space coordinate - overall heat transfer coefficient - emissivity - thermal conductivity - mass density - temperature - aperature factor Indices ak accumulated - a outer, ambient - c convection - g loss - gr heater - i, j order numbers - n normal - otv opening - p floor, surface - r radiation - rad radiation through openings - s charge, overall - sp surface - sr average - st steady state - u inner - z wall - zad reference     

Expedient airfield runway repair using folded fibreglass mat

For expedient airfield runway repair, the US Air Force has developed a folded fibreglass mat to cover craters repaired with a well-compacted granular base material. The objective of this study was to evaluate the adequacy of using polymer plugs to anchor the mat to a repaired asphalt pavement for heavy aircraft operations. The effort consisted of materials testing, field experiments and analytical modelling. An 89,800-kg (198,000-pound) load cart having the footprint of a single C-5 main gear was pulled on a mat with wheels locked to simulate full braking forces. Anchor bushings were instrumented to measure anchor loads. A simplified numerical model was developed for anchor load analysis which has been validated against the load cart test data. The anchor system sustained the braking forces from all the load cart tests without failure. The polymer plug anchors have adequate vertical pull-out capacity to resist the uplifting force from the ‘bow wave’ formation of the mat. The polymer plug anchors also have adequate resistance to fatigue loads.     

Effect of standard phenolic compounds and olive oil phenolic extracts on acrylamide formation in an emulsion system

In this work the effect of standard phenolic compounds such as trolox, phenolic acids (ferulic, gallic, protocatechuic and caffeic acid) and secoiridoids, extracted from virgin olive oil (VOO), on acrylamide formation in an emulsion system was investigated. The emulsion system was heated in an oil bath at different temperatures and for different periods of time. At 105 and 115 °C the generated amounts of acrylamide were negligible during the monitoring time. At 125 °C addition of standard phenolic compounds reduced acrylamide formation which was more pronounced at initial time of heating (20 min) reaching up to 70%. Protocatechuic and gallic acid were more effective than trolox, caffeic and ferulic acid in acrylamide reduction at the final time intervals of heating (30–60 min). On the contrary, addition of VOO extract in the emulsion system resulted in a remarkable increase of acrylamide level, which was ascribed to secoiridoids’ structure containing aldehydic groups.     

Vertically aligned nanocrystalline Cu–ZnO thin films for photoelectrochemical splitting of water

Cu-incorporated nanocrystalline ZnO thin films were deposited on glass substrate by sol–gel. To a solution of zinc acetate 2-hydrate in dimethyl formamide, calculated quantities of copper acetate were added. The clear solution, obtained after 2 h of continuous stirring, was coated on ITO plates. Pre-annealing at 250 °C was followed by sintering at 400, 500, and 600 °C. XRD analysis revealed dominant evolution of hexagonal ZnO with a possible simultaneous growth of meta-stable cubic ZnO. AFM and SEM analysis indicated preferential growth of nanocrystallites along c-axis. Optical characterization led to two prominent absorption thresholds in the UV region; one matching with the band gap of bulk ZnO and the second at slightly higher energy, suggesting quantum confinement effect in nanocrystallites. Cu incorporation influenced the two band gap energies differently. Photoelectrochemical splitting of water using 1% at. Cu–ZnO film sintered at 600 °C resulted in 141% gain in photocurrent at zero bias.     

Results of a novel algorithm for the calculation of the characteristic temperatures in power oil transformers

Contents The application of the originally developed thermal model, intended to oil power transformers analyses, is presented in the paper. The model delivers the value of the insulation Hot-spot temperature, as the most critical quantity during transformer loading, and the value of the thermal ageing, both for variable load and variable ambient temperature. The results obtained using the original thermal model are compared with the experimental results and the results obtained by the model from the international standard IEC 354. A program is developed for this purpose, allowing some additional analysis in respect to the basic algorithm from IEC 354.Besides, using experimentally obtained results, some approximations of the thermal model from IEC 354 and some factors important for development of thermal models are also analyzed.

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Ergebnisse eines neuen Verfahrens zur Berechnung der charakteristischen Temperaturen in Leistungsöltransformatoren

Übersicht Das Thema dieses Beitrages ist die Anwendung eines von uns neuentwickelten thermischen Modells zur Analyse von Öltransformatoren. Das Modell liefert den Temperaturwert der Isolation an der heißesten Stelle, welches während der Belastung des Transformators der kritischste Wert ist, sowie die Werte der thermischen Alterung des Transformators, beides unter veränderlicher Belastung und Umgebungstemperatur. Die Ergebnisse unseres Modells werden mit Experimentaluntersuchungen und mit den Resultaten des Modells IEC Standard 354 verglichen. Dafür wurde ein Rechenprogramm ausgearbeitet, das größere Möglichkeiten zur Analyse als das Grundmodell Standard 354 hat.Schließlich werden einige Vereinfachungen für das IEC-Modell vorgeschlagen und wichtige Faktoren, die während der thermischen Modellentwicklungen auftreten analysiert.