Mechanistic Insight in the Ethane Dehydrogenation Reaction over Cr/Al2O3 Catalysts

A Cr/Al₂O₃ alkane dehydrogenation catalyst exhibits a maximum in ethylene yield during an ethane dehydrogenation cycle. Isotopic labelling experiments with monolabelled ¹³C-ethane and deuterium were used to elucidate whether the initial activity increase could be due to formation of an active, larger hydrocarbon intermediate on the surface. The results strongly indicate that this is not the case, and instead point to a traditional reaction cycle involving adsorption of ethane to form an ethyl species, followed by desorption of ethene and hydrogen. Transient kinetic data suggest that ethane adsorption is the rate-determining step of reaction.     

Common failures of demand response

Demand response (DR) programs have recently become popular means of mitigating excessive claims on regional electricity networks and providing more reliable access to electric power. Many countries have experimented with DR pilot programs and some are beginning to incorporate similar schemes as permanent elements of the electricity sector. However, DR remains an experimental technique in much of the world as programs frequently fail to meet their goals and reach their potential. This paper examines the central structural and behavioral obstacles to success of DR programs and outlines some potential solutions which could greatly improve the functionality and success of such programs in the future.     

Differentiation of Greek Thyme Honeys According to Geographical Origin Based on the Combination of Phenolic Compounds and Conventional Quality Parameters Using Chemometrics

The aim of the present study was to differentiate Greek thyme honeys according to geographical origin, based on phenolic compound content and conventional physicochemical parameters using MANOVA and Linear Discriminant Analysis. Thirty-five thyme honey samples were collected during the harvesting period 2011 from four different regions in Greece (Irakleio, Hania, Kefalonia and Lakonia) known to produce thyme honey of good quality. The analysis of phenolic compounds (quercetin, myricetin, kaempferol, chrysin, and syringic acid) was performed by high pressure liquid chromatography. Conventional quality parameter analysis included the determination of the following: pH, free, lactonic and total acidity, electrical conductivity, moisture, ash, as well as lactonic/free acidity ratio and colour parameters L*, a*, b*. Using five phenolic compounds and 11 conventional quality parameters, thyme honey samples were satisfactorily classified (91.2 % correct prediction) according to geographical origin.     

Laser-engineered topography: correlation between structure dimensions and cell control

Topographical cues have a significant impact on cell responses and by this means, on the fabrication of innovative implant materials. However, analysis of cell-topography interactions in dependence of the surface feature dimensions is still challenging due to limitations in the fabrication technology. Here, we introduce surface structuring via picosecond laser systems, which enable a fast production of micro-sized topologies. Changes in the processing parameters further control the feature sizes of so-called spikes. Using surfaces with big and small spike-to-spike-distances for comparisons, we focussed on cell adhesion via extracellular matrix adsorption and focal adhesion complexes, morphology, localisation and proliferation of fibroblasts. The observed cell control was dependent on a turnover point related to the structure dimensions: only big spike-to-spike-distances reduced cell behaviour. Therefore, this technology offers a platform to study cell and tissue interactions with a defined microenvironment.     

Serum and urine metal levels in patients with metal-on-metal surface arthroplasty

The resurgence of metal-on-metal articulating surfaces for hip arthroplasty has also heightened concerns about the degree and magnitude of metal particle generation and the accompanying increase in circulating metal ion concentrations. In this study, we measured the concentration of chromium in serum and urine and the concentration of cobalt in serum in twenty-five patients with modern metal-on-metal surface arthroplasty of the hip in a prospective manner. The results showed that the mean post-operative chromium in serum levels were 22-fold, 23-fold and 21-fold higher at 3, 6 and 12 months post-operative, respectively, than pre-operative levels. The mean post-operative cobalt in serum levels were 8-fold, 7-fold and 6-fold higher at 3, 6 and 12 months post-operative, respectively, than pre-operative levels. The mean post-operative chromium in urine levels were 9-fold, 10-fold and 14-fold higher at 3, 6 and 12 months post-operative, respectively, than pre-operative levels. The values seen in this study with the current generation of surface arthroplasties are: (a) lower than those seen in an earlier generation of surface arthroplasties; (b) in the same range as those observed in association with metal-on-metal conventional total hip replacements, which typically have smaller head sizes; (c) higher than values observed in patients with conventional metal-on-polyethylene articulating couples.     

Viscosity of Conventional Cryolite-Alumina Melts

Russian Journal of Non-Ferrous Metals - Viscosity of conventional cryolite-alumina melts NaF–AlF3–CaF2–Al2O3 with a cryolite ratio (xNaF/xAlF3, mol/mol) 2.3 was studied in...     

Minimum Moment Method for Resource Leveling Using Entropy Maximization

The minimum moment method for resource leveling is revisited and restated as an entropy-maximization problem. The minimum moment method assumes that the moment of the daily resource demands about the horizontal axis of a project’s resource histogram is a good measure of the resource utilization and that the optimal resource allocation exists when the total moment is at a minimum, thus when the resource histogram is of rectangular shape. The entropy-maximization method proposed in this paper makes use of the general theory of entropy and two of its principal properties (subadditivity and maximality) to revisit the minimum moment method for resource leveling. The entropy-maximization method presented allows for activity stretching and provides resource allocation solutions that show improvement over previous approaches. A case study is also presented that validates the results.