Flux Jumps and H-T Diagram of Instability for MgB2

We present a study of magneto-thermal instabilities in polycrystalline MgB₂ superconductor, by magnetic hysteresis loop measurements and by investigations of magnetic flux dynamics with a miniature Hall probe. Temperature and magnetic field ranges where the flux jumps may be observed have been determined. On the basis of measurements of the magnetic flux dynamics, an average magnetic diffusivity describing the process of the flux jump is estimated. This parameter is compared with the thermal and magnetic diffusivities calculated on the basis of available data for thermal conductivity, heat capacity and resistivity. It is shown that the estimated value of the field of the first flux jump is influenced significantly by the field dependence of specific heat. In order to explain the observed phenomenon, the temperature reached by the sample during the flux jump at different magnetic fields is calculated.     

Hydrodechlorination of CCl<Subscript>4</Subscript> on Pt–Au/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts

A series of Pt/Al₂O₃ catalysts were prepared by the impregnation method and were characterized by TEM, XRD, H₂ and CO chemisorptions, and investigated in the hydrodechlorination of tetrachloromethane. Three Pt-rich, Pt–Au/Al₂O₃ catalysts (Pt₁₀₀, Pt₉₅Au₅ and Pt₉₀Au₁₀) showed a similar metal particle size (~2.5–2.7 nm), so observed changes in the catalytic behavior are ascribed to alloying effect, especially because a considerable degree of Pt–Au mixing was achieved in the bimetallic samples. It appeared that by introducing very small amount of gold (10 at.%) to platinum, the catalytic activity is increased. It is argued that the occurrence of this moderate synergistic effect is associated with a decreased tendency of surface chloriding when platinum is alloyed with gold. Zbigniew Kowalczyk—deceased.     

Development of volatile profile of Kumpiak podlaski dry-cured ham during traditional ripening

Main aim of this research was to trace the development of volatile profile of Kumpiak podlaski dry-cured ham during traditional curing and ripening for 30 weeks. Volatiles were extracted from each 6-week period of ripening, and overall fifty-three aroma compounds were identified. Changes in chemical groups share between cured and fully ripened ham were observed: aldehydes (35.49 → 31.37%), ketones (25.18 → 14.62%), alcohols (17.97 → 15.74%), esters (3.37 → 12.04%), hydrocarbons (7.69 → 6.81%), fatty acids (0.02 → 0.53%), terpenes (2.26 → 9.70%) and heterocyclic aromatic compounds (0.99 → 0.78%). The 18th week of ripening is crucial for the aroma of Kumpiak podlaski ham due to start of continuous decrease in ketones and increase in esters’ and terpenes’ share. Formation of esters and terpenes originated from the presence of local herbs and the development of microflora. Principal component analysis (PCA) showed clear separation of samples from each 6-week period of ripening. Obtained results relying on thirty-seven compounds enabled to make a preliminary determination of ripening markers.     

Probing palladium-cobalt/NaY catalysts by neopentane conversion

Neopentane conversion in hydrogen was used as a catalytic probe for zeolite encaged PdCo particles. Activity and selectivity strongly depend on the pretreatment conditions. PdCo/NaY catalysts exhibit higher isomerization selectivity than Pd/NaY in conformity with previous results on SiO₂ supported Pd and PdCo. This is remarkable, because reduced Co/SiO₂ displays 100% selectivity for hydrogenolysis. The isomerization selectivity thus appears to be a useful measure for the extent of alloying between Pd and Co.On leave from Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland.     

Selection of material for X-ray tomography analysis and DEM simulations: comparison between granular materials of biological and non-biological origins

Granular Matter - Field observations were carried out in Qingtu Lake observation array on the vertical electric field $$(E_{z})$$ , where the average spatial resolution can reach 1&nbsp;m. Our...     

The effect of the gradual thermal decomposition of surface oxygen species on the chemical and catalytic properties of oxidized activated carbon

The physicochemical properties, surface chemical structure and some catalytic properties of a series of carbons prepared by nitric acid oxidation of an activated carbon and subsequent heat treatment under vacuum and mild temperature conditions (423-573 K) were studied. The porous structure characteristics of the partially evacuated samples were estimated from low-temperature nitrogen adsorption data. The thermal analysis and the quantitative determination of surface functional groups by selective neutralization of bases and pH-metric titration were carried out. The dehydration of 2-methylpropan-2-ol was used as a test reaction. While gradual annealing in vacuum alters the surface only slightly, it does differentiate strongly the number and the acidic strength of the surface groups. Progressive heating under mild conditions removes mainly those surface groups that are located in macropores or on the outer surface of the carbon. According to TPD results, the decomposed surface groups are single carboxylic groups, as expected. The decomposition of single, strong carboxylic groups is accompanied by rearrangements of other carboxylic groups with the simultaneous formation of additional cyclic structures like anhydrides, lactones or lactols. Catalytic tests support our previous findings that oxidized carbons have a high dehydration activity. This activity is controlled not only by the number and the strength of acidic groups, but also by their accessibility. There exists an optimum concentration of surface acidic groups above which the activity decreases due to steric restrictions.     

Hydrodechlorination of Tetrachloromethane Over Supported Platinum Catalysts. Effects of Hydrogen Partial Pressure and Catalyst’s Screening Protocol on the Catalytic Performance

Two series of silica- and alumina-supported platinum catalysts were investigated in the hydrodechlorination (HdCl) of tetrachloromethane. During an initial period of reaction carried out at a lower H₂/CCl₄ ratio the catalysts, especially those characterized by high metal dispersion, deactivated with time-on-stream. Two catalyst screening protocols were used. The first one concerned a gradually increased hydrogen partial pressure, whereas during the second one the H₂ pressure was decreased. Although, in general, the hydrogen-rich reaction conditions resulted in improved catalyst performance (higher overall activity and selectivity to CHCl₃), the second protocol led to even better results. Reasons for such a behaviour are suggested. Because of very high activity of a few tested samples, changes in CCl₄ conversion with the hydrogen partial pressure do not reflect real reaction orders in hydrogen. The same reason may lead to falsification of apparent activation energies. In certain cases the relation between conversion and hydrogen pressure showed a maximum, suggesting that HdCl undergoes via a Langmuir?CHinshelwood mechanism, when hydrogen and CCl₄ compete for metal surface sites. Both carbon- and chlorine-containing deposits were found in the post-reaction catalyst samples.     

The Effects of Social Networking Sites on Consumer–Brand Relationships

In the era of a vastly changing marketing communications environment, social media and social networking sites (SNS) have become an attractive outlet for brand promotions and advertising. As traditional media such as television, radio, and newspapers prove ineffective in establishing a valuable rapport with consumers, it is social networks which are expected to build bonds and engage online users into an amusing dialog, play, and intercourse with brands. This study applies an experimental design to assess the effects of SNS on the relationship between brands and consumers. Customer-based brand equity is adopted in this study as a reflective measure of consumer–brand connection. In order to evaluate hypothesized interactions, the linear mixed effects models are used. The results show very little (if any) impact of SNS on brand equity. Relevant explanations are discussed and further research directions are indicated.     

Hydrodechlorination of 1,1-Dichlorotetrafluoroethane on Supported Palladium Catalysts. A Static-Circulation Reactor Study

Supported palladium catalysts were studied in CF₃CFCl₂ hydrodechlorination at 100°C using a static-circulation system. In order to minimize catalyst's deactivation a large excess of hydrogen was employed (H₂/CF₃CFCl₂ ratio 54/1). In spite of this precaution significant inhibition of the process occurred, associated with blocking palladium surface by hydrogen chloride species. Differences in the catalytic behavior of alumina-supported and unsupported palladium are discussed. A mild dependence between the catalytic activity and Pd dispersion was found. The Pd/Al₂O₃ catalyst characterized by low metal dispersion was more active than highly dispersed catalysts, showing the overall activity and selectivity to CF₃CFH₂ comparable with those observed by other authors for palladium single crystals. It is speculated that the most active sites for hydrodechlorination are plane atoms, whereas low coordination sites (on edges and corners of metal crystallites) are less suitable.