Geometrical-based statistical macrocell channel model for mobileenvironments

We develop a statistical geometric propagation model for a macrocell mobile environment that provides the statistics of angle-of-arrival (AOA) of the multipath components, which are required to test adaptive array algorithms for cellular applications. This channel model assumes that each multipath component of the propagating signal undergoes only one bounce traveling from the transmitter to the receiver and that scattering objects are located uniformly within a circle around the mobile. This geometrically based single bounce macrocell (GBSBM) channel model provides three important parameters that characterize a channel: the power of the multipath components, the time-of-arrival (TOA) of the components, and the AOA of the components. Using the GBSBM model, we analyze the effect of directional antennas at the base station on the fading envelopes. The level crossing rate of the fading envelope is reduced and the envelope correlation increases significantly if a directional antenna is employed at the base station     

Early Gaseous Oxygen Enrichment to Enhance Magnetite Pellet Oxidation

It is suggested that oxygen enrichment in the gas atmosphere, during continuous heating of magnetite pellets, can cause pellets to be oxidized throughout their volumes, eliminating unoxidized cores. The peculiarities of the oxidation kinetics of magnetite concentrate imply that such oxygen enrichment might be particularly effective at lower temperatures. This suggestion was tested by developing and testing a mixed-control model for pellet oxidation (to allow the sizes of unreacted cores to be predicted), and by experimentally testing the effects of oxygen enrichment at relatively low temperatures (“early oxygen enrichment”). The results confirmed that the extents (depth) of oxidation and pellet strength were both improved significantly by applying oxygen enrichment up to 873 K (600 °C), as part of a heating cycle up to 1073 K (800 °C).     

Anisotropic Mechanical Behavior of AlSi10Mg Parts Produced by Selective Laser Melting

AlSi10Mg cylinders produced by laser powder-bed fusion have somewhat different yield behavior for cylinders with XY orientation and Z orientation. Earlier yielding for Z-oriented samples is likely related to micro-residual stress, resulting from the difference in thermal expansion of the aluminum matrix and cellular silicon. Smaller tensile reduction in area of Z-oriented samples is related to tearing along the softer region at the boundaries of melt pools, where the silicon cell spacing is larger. Indentation measurements confirmed the lower hardness at the edges of melt pools.     

Silicon carbide matrix composites reinforced with two-dimensional titanium carbide – Manufacturing and properties

Within this paper, it is explored how two-dimensional Ti₂C sheets addition affects silicon carbide matrix composites in terms of the microstructure and mechanical properties. In order to consolidate the powder mixtures, powder metallurgy processing followed by Spark Plasma Sintering was performed to prepare the sinters. According to our knowledge, this is the first attempt to apply delaminated MXene phases as a reinforcing phases of ceramic matrix composites. The delaminated MXene phases were characterized using a high-resolution transmission microscope (HRTEM) and X-ray photoelectron spectroscopy (XPS). Significant improvement of the fracture toughness and hardness for the composites reinforced with 1.5?wt% 2D Ti₂C compared to the reference sample were observed. It is expected that the applied reinforcing phase will have an influence on the fracture mechanism, and so this has also been investigated. Two of the main mechanisms of crack propagations (crack deflection and bridging) were observed.     

Impact of Organic Solvents on Physicochemical Properties of Nanofiltration and Reverse‐Osmosis Membranes

Polymeric membranes subjected to the permeation of n‐hexane were characterized and the influence of pretreatment with ethanol on the properties of the membranes was studied to assess membrane performance and stability. The results suggest that the selectivity of the membrane depends not only on the pore size, but also to a great extent on the interaction between solvent and polymer. An increase in membrane roughness and contact angle was observed for all membranes after pretreatment with ethanol and n‐hexane permeation. Moreover, the surface free energy decreased after solvents exposure, indicating an increase in membrane surface hydrophobicity and polymer swelling. The studied membranes show feasibility of use for the recovery of solvents, if suitable process parameters are selected.     

Three‐dimensional optimisation of a fuel gas channel of a proton exchange membrane fuel cell for maximum current density

Proton exchange membrane (PEM) fuel cells operated with hydrogen and air offer promising alternative to conventional fossil fuel sources for transport and stationary applications because of its high efficiency, low‐temperature operation, high power density, fast start‐up and potable power for mobile application. Power levels derivable from this class of fuel cell depend on the operating parameters. In this study, a three‐dimensional numerical optimisation of the effect of operating and design parameters of PEM fuel cell performance was developed. The model computational domain includes an anode flow channel, membrane electrode assembly and a cathode flow channel. The continuity, momentum, energy and species conservation equations describing the flow and species transport of the gas mixture in the coupled gas channels and the electrodes were numerically solved using a computational fluid dynamics code. The effects of several key parameters, including channel geometries (width and depth), flow orientation and gas diffusion layer (GDL) porosity on performance and species distribution in a typical fuel cell system have been studied. Numerical results of the effect of flow rate and GDL porosity on the flow channel optimal configurations for PEM fuel cell are reported. Simulations were carried out ranging from 0.6 to 1.6 mm for channel width, 0.5 to 3.0 mm for channel depth and 0.1 to 0.7 for the GDL porosity. Results were evaluated at 0.3 V operating cell voltage of the PEM fuel cell. The optimisation results show that the optimum dimension values for channel depth and channel width are 2.0 and 1.2 mm, respectively. In addition, the results indicate that effective design of fuel gas channel in combination with the reactant species flow rate and GDL porosity enhances the performance of the fuel cell. The numerical results computed agree well with experimental data in the literature. Consequently, the results obtained provide useful information for improving the design of fuel cells. Copyright © 2011 John Wiley & Sons, Ltd.     

Modeling and fabrication of three-dimensional silicon substrates with tailored shape and microtopography parameters for CdTe films

Seven models were constructed for the surface of three-dimensional silicon substrates. We proposed models of upright and inverted pyramids (and frusta) and models of substrates with triangular and prismatic cross sections. In modeling, we took into account the capabilities of photolithography and anisotropic etching of silicon wafers. We modeled the light ray trajectory in a thin-film three-dimensional CdS/CdTe solar cell with a large surface area. Three-dimensional microtextured substrates were fabricated using photomasks and modeling and calculation results. Their surface morphology was studied by scanning electron microscopy. The elemental composition of the microtextured silicon substrates was determined.     

Activity of immobilized lipoxygenase used for the formation of perhydroxyacids

Lipoxygenase-produced oxidized fatty acids may serve as intermediates in chemical and pharmaceutical syntheses. For practical applications the enzyme should be immobilized to prevent its loss at product retrieval and to enable a continuous process. In this study the immobilization of soybean lipoxygenase on various neutral and charged supports was investigated. The best results were obtained using cellulose-based anion exchangers. The activity of the immobilized lipoxygenase was lower than the activity of the free enzyme, which was possibly caused by diffusion limitation of the fatty acids to or from the support beads.