Rarita-Schwinger Potentials in Quantum Cosmology

This paper studies the two-spinor form of the Rarita-Schwinger potentials subject to local boundary conditions compatible with local supersymmetry. The massless Rarita-Schwinger field equations are studied in four-real-dimensional Riemannian backgrounds with boundary. Gauge transformations on the potentials are shown to be compatible with the field equations providing the background is Ricci-flat, in agreement with previous results in the literature. However, the preservation of boundary conditions under such gauge transformations leads to a restriction of the gauge freedom. The recent construction by Penrose of secondary potentials which supplement the Rarita-Schwinger potentials is then applied. The equations for the secondary potentials, jointly with the boundary conditions, imply that the background four-geometry is further restricted to be totally flat.Comment: 23 pages, plain TeX, no figures. The paper has been completely revise

Spin-3/2 potentials in backgrounds with boundary

This paper studies the two-spinor form of the Rarita-Schwinger potentials subject to local boundary conditions compatible with local supersymmetry. The massless Rarita-Schwinger field equations are studied in four-real-dimensional Riemannian backgrounds with boundary. Gauge transformations on the potentials are shown to be compatible with the field equations providing the background is Ricci-flat, in agreement with previous results in the literature. However, the preservation of boundary conditions under such gauge transformations leads to a restriction of the gauge freedom. The recent construction by Penrose of secondary potentials which supplement the Rarita-Schwinger potentials is then applied. The equations for the secondary potentials, jointly with the boundary conditions, imply that the background four-geometry is further restricted to be totally flat. The analysis of other gauge transformations confirms that, in the massless case, the only admissible class of Riemannian backgrounds with boundary is totally flat

Experimental and Simulation Study on Coproduction of Hydrogen and Carbon Nanomaterials by Catalytic Decomposition of Methane-Hydrogen Mixtures

Among all hydrocarbons, the methane molecule contains the highest amount of hydrogen with respect to carbon. Therefore, the catalytic decomposition of methane is considered as an efficient approach to produce hydrogen along with nanostructured carbon product. On the other hand, the presence of hydrogen in the composition of the initial gas mixture is required for the stable operation of the catalyst. In present work, the experiments on the catalytic decomposition of methane–hydrogen mixture were performed in a flow-through quartz reactor equipped with McBain balances under atmospheric pressure. The catalyst NiO-CuO/Al2O3 was prepared by the mechanochemical activation technique. The maximum carbon yield of 34.9 g/gcat was obtained after 2 h of experiment at 610 °C. An excess of hydrogen in the reaction mixture provided the long-term activity of the nickel–copper catalyst. The durability tests ongoing for 6 h within a temperature range of 525–600 °C showed no noticeable deactivation of the catalyst. Two kinetic models, D1a and M1a, were proposed for the studied decomposition of the methane–hydrogen mixture over the nickel–copper catalyst. The kinetic constants for these models were determined by means of mathematical modelling

Study of MgO transformation into MgF2 in the presence of CF2Cl2•

Alkaline-earth metal oxide aerogels prepared by sol–gel method followed by autoclave drying are nanocrystalline mesoporous materials with high reactivity. Bulk solid-state reaction of MgO aerogels with CF2Cl2 takes place after a long induction period, during which the active sites are accumulated on the surface of the nanoparticles. It was found that vanadium addition has a promoting effect on this reaction accelerating the process of the active sites formation. A method for characterization of electron-acceptor sites by electron spin resonance spectroscopy using perylene as the spin probe was developed. A good correlation was observed between the rate of the CF2Cl2 destructive sorption and the concentration of weak electron-acceptor sites. Simplified models of such sites were suggested. The acid sites on the modified MgO surface were supposed to be originated from separation of the charged fragments resulting in the surface polarization. Uncompensated oxygen substitution for chlorine and/or fluorine ions leads to appearance of Lewis acid sites while HCl/HF chemisorption results in Bronsted acid sites formation

Experimental and Simulation Study on Coproduction of Hydrogen and Carbon Nanomaterials by Catalytic Decomposition of Methane-Hydrogen Mixtures

Among all hydrocarbons, the methane molecule contains the highest amount of hydrogen with respect to carbon. Therefore, the catalytic decomposition of methane is considered as an efficient approach to produce hydrogen along with nanostructured carbon product. On the other hand, the presence of hydrogen in the composition of the initial gas mixture is required for the stable operation of the catalyst. In present work, the experiments on the catalytic decomposition of methane–hydrogen mixture were performed in a flow-through quartz reactor equipped with McBain balances under atmospheric pressure. The catalyst NiO-CuO/Al2O3 was prepared by the mechanochemical activation technique. The maximum carbon yield of 34.9 g/gcat was obtained after 2 h of experiment at 610 °C. An excess of hydrogen in the reaction mixture provided the long-term activity of the nickel–copper catalyst. The durability tests ongoing for 6 h within a temperature range of 525–600 °C showed no noticeable deactivation of the catalyst. Two kinetic models, D1a and M1a, were proposed for the studied decomposition of the methane–hydrogen mixture over the nickel–copper catalyst. The kinetic constants for these models were determined by means of mathematical modelling

Selected Aspects of Hydrogen Production via Catalytic Decomposition of Hydrocarbons

Owing to the high hydrogen content, hydrocarbons are considered as an alternative source for hydrogen energy purposes. Complete decomposition of hydrocarbons results in the formation of gaseous hydrogen and solid carbonaceous by-product. The process is complicated by the methane formation reaction when the released hydrogen interacts with the formed carbon deposits. The present study is focused on the effects of the reaction mixture composition. Variations in the inlet hydrogen and methane concentrations were found to influence the carbon product’s morphology and the hydrogen production efficiency. The catalyst containing NiO (82 wt%), CuO (13 wt%), and Al2O3 (5 wt%) was prepared via a mechanochemical activating procedure. Kinetics of the catalytic process of hydrocarbons decomposition was studied using a reactor equipped with McBain balances. The effects of the process parameters were explored in a tubular quartz reactor with chromatographic analysis of the outlet gaseous products. In the latter case, the catalyst was loaded piecemeal. The texture and morphology of the produced carbon deposits were investigated by nitrogen adsorption and electron microscopy techniques