Polarity control of GaN epilayers grown on ZnO templates

We report the successful growth of Ga-polar GaN epilayers on O-polar ZnO templates pre-deposited on c-sapphire. Prior to GaN growth, NH₃ is exposed onto the ZnO template. The polarity of the GaN layers is confirmed by etching of the surface and by conversion beam electron diffraction (CBED), while the O-polar ZnO is confirmed by CBED. It is suggested that the NH₃ pre-exposure helps form a Zn₃N₂ layer, which possesses inversion symmetry and inverts the crystal from anion polar to cation polar.     

Parameter identification and design of a robust attitude controller using <Emphasis Type="Italic">H</Emphasis><Subscript>∞</Subscript> methodology for the raptor E620 small-scale helicopter

Rigorous control synthesis for an unmanned aerial vehicle necessitates the availability of a good, reasonable model for such a vehicle. The work reported in this paper focuses on the modeling of a rotary unmanned aerial vehicle (RUAV) and the development of a robust controller that can handle parameter uncertainties and disturbances. The parameters of the plant model are obtained through the use of the prediction error method with real flight data. The response of the identified linear model shows a good match with the measured flight data. The H _∞ control scheme is applied to obtain a robustly stable controller using the identified model. The proposed controller is analyzed using frequency-domain analysis and time-domain simulations. The performance of the proposed H _∞ controller is better than that of the conventional proportional derivative controller in that the proposed controller has a shorter settling time and less overshoot. Furthermore, the degradation of the proposed controller performance is negligible and stability is maintained when the input gains to the plant are doubled, which demonstrates the good performance and robustness of the controller.     

An optimal usage of NO x in a combined Pt/ceramic foam and a wall-flow monolith filter for an effective NO x -assisted soot oxidation

Topics in Catalysis - An NO2-assisted soot oxidation based filter candidate consists of Pt-coated ceramic foam in combination with a wall-flow monolith is proposed to acquire for an optimal usage...     

Ultrahigh temperature water gas shift catalysts to increase hydrogen yield from biomass gasification

Noble metal (Rh, Pt, Pd, Ir, Ru, and Ag) and Ni catalysts supported on CeO₂–Al₂O₃ were investigated for water gas shift reaction at ultrahigh temperatures. Pt/CeO₂–Al₂O₃ and Ru/CeO₂–Al₂O₃ demonstrated as the best catalysts in terms of activity, hydrogen yield and hydrogen selectivity. At 700 °C and steam to CO ratio of 5.2:1, Pt/CeO₂–Al₂O₃ converted 76.3% of CO with 94.7% of hydrogen selectivity. At the same conditions, the activity and hydrogen selectivity for Ru/CeO₂–Al₂O₃ were 63.9% and 85.6%, respectively. Both catalysts showed a good stability over 9 h of continuous operation. However, both catalysts showed slight deactivation during the test period. The study revealed that Pt/CeO₂–Al₂O₃ and Ru/CeO₂–Al₂O₃ were excellent ultrahigh temperature water gas shift catalysts, which can be coupled with biomass gasification in a downstream reactor.     

SERVICE IDEALISM: THE SENSE PERCEPTION OF PERSONALITY

The importance of service has been a central topic of study regarding marketing research. Good services influence customer perception toward services. This study aims to discover the components of services idealism and how to optimize the service toward services idealism. This research uses Genetic Algorithm to analyze optimal result of service idealism based on personality psychology. The data was obtained from customers who ever dined in Wang Steak (290) and Tasty (112) restaurants in Taiwan. The result confirms service idealism is influenced by service quality and brand knowledge significantly. Customers who have extraversion personality are more influenced by reliability and awareness of restaurant. Neuroticism personality is more influenced by empathy and brand image. Agreeableness personality is more influenced by responsive. Conscientiousness and openness personality are more influenced by brand awareness and service tangibility. In summary, service idealism is influenced by brand awareness and tangible of services for both restaurants.     

Effectiveness of platinum and iridium in improving the resistance of Ni‐Al to thermal cycling in air–steam mixtures

The aim of this work was to assess the value of platinum and iridium additions, with and without hafnium, to binary Ni‐Al alloys, intended to act as models for aluminide coatings. Attention was focused on a (γ + γ′) Ni‐22Al alloy, but comparisons were made with β‐Ni‐50Al. All compositions are given in at%. Alloys were exposed to flowing gases at a total pressure of 1 bar for one thousand 1 h cycles at 1200 °C. Compared to binary Ni‐Al alloys, the Pt‐modified alloys performed much better (with or without Hf) in dry air. Thermal cycling in air + 12% H₂O led to more rapid weight losses, due to enhanced spalling. Again, the addition of Pt was beneficial, but weight losses were still significant in the absence of Hf additions. A Ni‐22Al‐15Pt + Hf alloy slowly lost weight by scale spallation over 1000 cycles, but a Ni‐22Al‐30Pt + Hf alloy resisted weight loss. Partial substitution of Ir for Pt was beneficial in both wet and dry air. However, in the case of wet air, Hf additions were necessary to prevent slow spallation losses.     

Methanol synthesis from CO2 over Cu/ZnO catalysts prepared from various coprecipitated precursors

Various precursors of Cu/ZnO catalysts were prepared by coprecipitation methods. By varying the conditions of coprecipitation, precursors having different structures (aurichalcite, malachite, hydrozincite, or their mixture) were obtained at given Cu/Zn ratios, ranging from 30/70 to 70/30. In a wide range of the Cu/Zn ratios, the catalysts derived from the precursors containing aurichalcite exhibited high performance in the methanol synthesis from CO₂.     

Formation and fate of chlorination by-products in reverse osmosis desalination systems

Chlorination by-products may be formed during pretreatment or posttreatment disinfection in reverse osmosis (RO) desalination systems, potentially posing health, aesthetic and ecological risks. To assess the formation and fate of by-products under different conditions likely to be encountered in desalination systems, trihalomethanes, dihaloacetonitriles, haloacetic acids, and bromophenols were analyzed in water samples from a pilot-scale seawater desalination plant with a chlorine pretreatment system and in benchscale experiments designed to simulate other feed water conditions. In the pilot plant, RO rejection performance as low as 55% was observed for neutral, low-molecular-weight by-products such as chloroform or bromochloroacetonitrile. Benchscale chlorination experiments, conducted on seawater from various locations indicated significant temporal and spatial variability for all by-products, which could not be explained by measured concentrations of organic carbon or bulk parameters such as SUVA₂₅₄. When desalinated water was blended with freshwater, elevated concentrations of bromide in the blended water resulted in dihaloacetonitrile concentrations that were higher than those expected from dilution. In most situations, the concentration of chlorination by-products formed from continuous chlorination of seawater or blending of desalinated water and freshwater will not compromise water quality or pose significant risks to aquatic ecosystems.     

A Pulse Combustion-Spray Pyrolysis Process for the Preparation of Nano- and Submicrometer-Sized Oxide Particles

The preparation of nano- and submicrometer particles using an integrated pulse combustion–spray pyrolysis process was investigated for the first time. Zinc oxide nanoparticles with average sizes ranging from 20 to 40 nm were synthesized using a salt precursor with a lower decomposition temperature than the pulse combustion (PC) temperature. Particles of a doped-type oxide, gadolinium oxide-doped with europium, were also produced from a precursor, whose decomposition temperature was higher than the PC temperature, and were observed to be ellipsoidal–toroidal in shape and submicrometer in size. The high-intensity fluctuating pressures generated by PC and the precursor decomposition temperature are proposed as the reasons for the formation of either nanoparticles or aspherical particles. In addition, hot gas fluctuating flow in PC enhanced energy transfer, resulting in more crystalline particles, as compared with particles produced by conventional spray pyrolysis.