The CO-catalyzed conversion of H2S to H2 + sulfur part 2. The thermal decomposition of COS

The pyrolysis of COS has been studied over the temperature range 300 to 750°C using a variety of catalysts. The observed product distribution confirmed that two parallel reaction paths: 2 COS → 2 CO S₂ (2) and 2 COS → CO₂ + CS₂ (4) are involved in the decomposition. The decomposition yield increased with rising temperature, accompanied with a shift in selectivity. At temperatures lower than ～700°C the disproportionation reaction 4 was predominant, whereas at temperatures higher than 700°C, reaction 2 was favoured. In the high-temperature region (700 to 750°C) it was possible to achieve full suppression of reaction 4 with added CS₂. The pyrolysis of COS was also studied in a reactor packed with quartz chips without catalysts at high temperatures. Between 800 and 900°C, up to 99% conversion (with respect to the thermodynamic limit) could be achieved, with the almost complete absence of the disproportionation reaction 4. The results point to the commercial potential in the two-step reaction sequence: for the economic conversion of hydrogen sulfide to hydrogen and sulfur.     

Quantum computing and communications – Introduction and challenges

Computer engineers are continuously seeking new solutions to increase available processing speed, achievable transmission rates, and efficiency in order to satisfy users’ expectations. While multi-core systems, computing clouds, and other parallel processing techniques dominate current technology trends, elementary particles governed by quantum mechanics have been borrowed from the physicists’ laboratory and applied to computer engineering in the efforts to solve sophisticated computing and communications problems. In this paper, we review the quantum mechanical background of quantum computing from an engineering point of view and describe the possibilities offered by quantum-assisted and quantum-based computing and communications. In addition to the currently available solutions, the corresponding challenges will also be surveyed.     

Effect of the solid precursors on the formation of nanosized TiBx powders in RF thermal plasma

Continuous synthesis of TiB_x (x≈0.5–2) nanoparticles from various low cost solid precursors such as titanium and titanium dioxide admixed with boron and/or carbon in radiofrequency thermal plasma was studied. Feasibility of TiB₂ formation was predicted by thermodynamic equilibrium calculations in the 500–5000 K temperature range. In all the investigated system high temperature reactions resulted in nanometer-sized TiB_x powders with a mean size varying between 13 and 83 nm. The yield of particular runs ranged from 38% to 97%. Among the synthesized products in addition to TiB_x, oxidized precursor residues were also found in smaller quantities. Although addition of carbon to the precursors could not completely prevent surface oxidation of boride particles, it contributed to the reduction of the mean particle size of the formed TiB₂.     

Energy alternatives: the Indian perspective

India's immense geography provides her with a variety of ambient energy resources. This paper examines the non-conventional energy sources and their possible future in India. While the non-conventional energy sources include geothermal energy, waves, tides and ocean thermal energy in addition to direct solar radiation, the emphasis in the paper is on solar, biomass and wind energy applications. Conventional energy sources including coal, oil, gas and nuclear energy are not going to be adequate and the alternative sources discussed are not going to be capable of fully replacing the above sources in any foreseeable future. While these alternative sources are likely to be only a partial substitute and not a total replacement, their contribution can usually be well above 50 per cent of the total energy needs. The energy profile of the country has also been discussed.     

Fractal properties of AlGeNi layers on GaAs surfaces

The thermal interactions of thin AlGe and AlNiGe layers with a bulk GaAs monocrystal were investigated. The heat treatment of these systems was carried out in the working chamber of a scanning electron microscope. The SEM pictures were analysed using a fractal mathematical technique. It was found that the surface of the samples has fractal character. No temperature dependence of the fractal dimension was observed. The samples were also studied using the structural entropy versus filling factor maps of the samples in order to find their localization properties. The SEM pictures of AlGe perform mostly as a Gaussian functions, whereas the AlNiGe samples show usually a behaviour with exponential decay.     

Microstructural characterisation of syntactic foams

Three types of hollow microspheres with different average diameters (100–150 μm) and two aluminium alloys as matrix material were used to produce metal matrix syntactic foams (MMSFs) by pressure infiltration. The phases, which formed at matrix-filler interface, were investigated by X-ray diffraction (XRD) and energy dispersive spectrometry (EDS). The investigation showed that in syntactic foams, with the Al99.5 matrix, an exchange reaction took place between the matrix and the amorphous components of ceramic hollow microspheres. The reaction resulted in significant formation of alumina and Si precipitates. Because of this diffusion reaction, the hollow microspheres’ walls were degraded. In the case of the AlSi12 matrix the reaction was suppressed by the considerable Si content of the matrix. Therefore, the wall of the hollow microspheres remained unharmed and no real interface layer was found.     

Model-based angiogenic inhibition of tumor growth using modern robust control method

Cancer is one of the most destructive and lethal illnesses of the modern civilization. In the last decades, clinical cancer research shifted toward molecular targeted therapies which have limited side effects in comparison to conventional chemotherapy and radiation therapy. Antiangiogenic therapy is one of the most promising cancer treatment methods. The dynamical model for tumor growth under angiogenic stimulator/inhibitor control was posed by Hahnfeldt et al. in 1999; it was investigated and partly modified many times. In this paper, a modified version of the originally published model is used to describe a continuous infusion therapy. In order to generalize individualized therapies a robust control method is proposed using H_∞ methodology. Uncertainty weighting functions are determined based on the real pathophysiological case and simulations are performed on different tumor volumes to demonstrate the robustness of the proposed method.     

Alkylation of aromatics with diols in superacidic media

Friedel–Crafts alkylation of simple aromatics (benzene, toluene, o-, m- and p-xylene) with various types of diols in the presence of superacidic trifluoromethanesulfonic acid was studied. 1,2- and 1,3-diols were found to bring about only monoalkylation yielding unusual monoalkylated products: bis(1-methyl-2-phenylpropyl) ether was formed in the reaction of 2,3-butanediol, and 2,4-dimethyl-2,4-pentanediol produced mono- and di-tert-butyl-substituted benzenes. Higher diol homologues, in turn, undergo electrophilic cyclialkylative ring closure (cyclialkylation) to form tetralin derivatives with high selectivities and in good yields. Additional primary alkylation processes are monoalkylation to yield alkylbenzenes and the formation of diphenylalkanes. The products thus formed may participate in secondary transformations, which are a second cyclialkylation (formation of octahydroanthracene and -phenanthrene derivatives), isomerization and dehydrogenation. Mechanistic studies with stereoisomeric 2,5-hexanediols point to the involvement of open dicationic intermediates in the alkylation process. This revised version was published online in June 2006 with corrections to the Cover Date.     

Application of Comparative Method for Estimating Microporosity of Porous Solids in Adsorption from Solutions

The concept of a comparative method in terms of the liquid adsorption on solids is presented. This method is based on comparison of the excess adsorption isotherm on a porous solid with that measured on a reference nonporous adsorbent. It is proved that proposed approach gives the possibility for separating a total excess adsorption isotherm into partial isotherms, proper for micro- and mesopores. Several experimental systems are analyzed to illustrate the usefulness of the comparative method for evaluating the surface phase capacity, which presents an important quantity in the study of adsorption from solution in the whole concentration region. The comparative method examined for adsorption systems of microporous active carbons seems to be useful for investigating other porous materials as silica gels, zeolites or metal oxides.