Kinetics and mechanism of oxidative coupling of methane over sodium-manganese oxide catalyst

The kinetics of methane oxidative coupling (OCM) was studied using 1 g of Na-Mn₂O₃ catalyst at 1073 to 1123 K, in an integral flow reactor (I.d. = 10 mm), at atmospheric pressure with methane and oxygen partial pressures of 0.27 and 0.13 bar, respectively, so that the ratio of CH₄ to O₂ was 2. The flow rate range was 50 to 200 ml/min. the kinetic data were analyzed by the Rideal-redox type of rate equation assuming the methyl radical and active surface oxygen to be the steady-state intermediates. Oxidation and reduction rate constants (K_ox, K_red) for methane consumption were calculated from experimental catalysis results by computer simulation using the multiple least squares method. The activation energies at rate constants K_ox and K_red for this type of catalyst were reported as 43.26 and 62.2 kcal/mol, respectively.     

The effect of propofol on the electroencephalogram of patients with epilepsy

The effect of propofol on the electroencephalogram (EEG) in patients with epilepsy is still unclear. Case reports with electroencephalographic documentation highlight pro- and anticonvulsant effects and beta activation of the EEG. This prospective study sought to determine the effect of propofol in 17 patients undergoing cortical resection for intractable epilepsy. Each patient received 2 mg/kg of propofol intravenously and the EEG was recorded from chronically implanted subdural electrodes placed during a previous craniotomy. Frequency of interictal spikes, time to burst suppression, and appearance of beta activation were recorded. The median frequency of interictal spikes decreased significantly from 2 spikes/min before to 0 spikes/min after propofol (P = 0.001). Seizure activity did not increase after propofol. Profound burst suppression and an increase in beta activity were noted consistently. The use of propofol in patients with epilepsy seems to be safe but may interfere with the recording of EEG spikes.     

The effects of molasses on the fermentation of chopped whole-plant leucaena

The incorporation of molasses (22.5 and 45.0 kg t^?1, fresh wt basis) with chopped whole-plant leucaena (Leucaena leucocephala) at the time of ensiling, increased the rate of fermentation as compared to the control (no molasses). The silage (leucaenalage) prepared with molasses had a lower pH, higher residual water-soluble carbohydrates, greater quantities of acetic and lactic acid and lower levels of volatile nitrogen, non-protein nitrogen and free amino acids than did the leucaenalage containing no molasses. The extent of these changes increased as the level of the molasses was increased.     

Coupling Bank Stability and Bed Deformation Models to Predict Equilibrium Bed Topography in River Bends

Attempts to include river bank erosion predictors within morphological models are becoming increasingly common, but uncertainty surrounds the procedures used to couple bed deformation and bank erosion submodels in a way that maintains the mass continuity of eroded bank sediment. Herein we present a coupling procedure that comprises two discrete elements. First, immediately following bank failure, the slumped debris comes to rest at the bank toe as a planar surface inclined at an “angle of repose.” Second, we use a fractional transport model to simulate the subsequent erosion and deposition of the failed bank material debris. The method is demonstrated with an example in which an equilibrium bed topography model is combined with a river bank erosion model to predict the morphological response of a river bend to a large flow event.     

Low-temperature Magnesiothermic Synthesis of Mesoporous Silicon Carbide from an MCM-48/Polyacrylamide Nanocomposite Precursor

Mesoporous silicon carbide with high specific surface area was successfully synthesized from an MCM-48/ polyacrylamide nanocomposite precursor in the temperature range of 550—600℃（below the melting point of Mg） by means of a magnesiothermic reduction process.The MCM-48/polyacrylamide precursor nanocomposite was prepared by in-situ polymerization of acrylamide monomer in the presence of mesoporous MCM-48 synthesized by sol-gel method.The physicochemical properties and microstructures of the nanocomposite precursor and the low-temperature SiC product were characterized by X-ray diffraction（XRD）, differential scanning calorimetry-thermo gravimetric analysis（DSC-TGA）,transmission electron microscopy （TEM） and N₂ adsorption—desorption.TEM micrographs and Brunauer—Emmett—Teller（BET） gas adsorption studies showed that the SiC powder was nanocrystalline and had a specific surface area of 330 m²/g and a mesoporosity in the range of 2—10 nm.The presence of an exothermic peak in the DSC trace corresponds to the self-combustion process of the SiC magnesiothermic synthesis.The results also show that the carbon in excess to that required to produce SiC plays a role in the reduction of the SiO₂.The mechanism of magnesiothermic synthesis of mesoporous SiC is discussed.     

Exploring the impact of chloride-induced corrosion on seismic damage limit states and residual capacity of reinforced concrete structures

A non-linear finite element (FE) framework for time-dependent capacity assessment of corroded rectangular reinforced concrete (RC) columns is developed. The proposed non-linear FE model includes the impact of corrosion on inelastic buckling and low-cycle fatigue degradation of longitudinal reinforcement. The proposed non-linear FE model is validated against a set of experimental data and then extended to evaluate the impact of corrosion on damage limit states to be used in seismic performance and evaluation of corroded structures. This is done through a parametric study on hypothetical RC columns, varied in axial force ratios, mass loss ratios, cover crack widths and confinement levels. Moreover, the application of the proposed model in seismic collapse capacity assessment of corroded structures is shown through non-linear dynamic analyses of prototype columns. Results show that, depending on the axial force ratio, corrosion changes the failure mechanism of the columns. The results of this study suggest that in seismic fragility analysis of corroded structures, the damage limit states should be considered as time-variant parameters.