A far-near field transformation using the fast multipole techniques

We are interested in deducing the coupling between an antenna and some surrounding structures via the only knowledge of the antenna far-field measured in an anechoic room. A new approach based on a multipole expansion of the Green's kernel is considered to evaluate the field in the vicinity of the antenna. Some numerical experiments illustrate the efficiency of the multipole techniques compared to the physical optic approach.     

Cross-shaped dielectric resonator antenna analysis using conformalfinite difference time domain method

A cross-shaped dielectric resonator antenna, designed for circular polarisation, is analysed via the conformal finite difference time domain technique. The conformal technique, which can handle canted surfaces that do not conform to the Cartesian system of co-ordinates, is used to generate accurate results with a relatively coarse mesh, e.g. it is shown that the conformal FDTD offers a 2:1 advantage over staircasing, without compromising accuracy     

Year round experimental study on a constant temperature and humidity air-conditioning system driven by ground source heat pump

Numerous studies about the ground source heat pump building heating and cooling systems have been constructed in office building, hotel, residential building and school et al. However, few researches about the constant temperature and humidity air-conditioning system driven by ground-coupled heat pumps were carried out. In this paper, a constant temperature and humidity air-conditioning system driven by ground source heat pump was designed and constructed in an archives building in Shanghai, China. During the operation in the cooling mode, the heat extraction from the condenser of the heat pump was divided: part was rejected to the soil while another was used to reheat the air in AHUs. According to the experimental results, the indoor temperature and relative humidity fulfilled the “Archives Design Code”. In summer, the heat rejected to the soil was reduced by 32%, which was helpful for the earth energy conservation. The soil temperature increased only 0.5 °C after the GSHP system operating for a year. The energy cost of the air-conditioning system was 56.1 kWh/m². Compared with air source heat pump system and water cooled unit with boiler system, the operating cost of ground source heat pump was reduced by 55.8% and 48.4%, respectively.     

Mechanisms, thermodynamics and kinetics of composite fouling of calcium oxalate and amorphous silica in sugar mill evaporators—A preliminary study

Deposition of amorphous silica (SiO₂) and calcium oxalate monohydrate (COM) on the calandria tubes of evaporators cause serious processing problems in many cane sugar mills. Previous studies on scale formation have concentrated on fouling of individual compounds and the development of inhibiting methods for each component. Since SiO₂ and COM co-exist in sugar mill evaporators, this paper investigates the mechanisms and behavior of composite fouling of COM and SiO₂ in binary systems. Batch tests conducted at different pH (6-8) and temperatures (60-80°C) show that the presence of SiO₂ in the supersaturated solutions of COM decreased the precipitation rate of COM and as such increased COM solubility. However, the presence of COM in the supersaturated solutions of SiO₂ accelerated SiO₂ polymerization and lowered the level of initial silica supersaturation required for polymerization. The formation of COM-SiO₂ complexes is used to propose the mechanism for the co-precipitation of SiO₂ and COM.     

On the photoluminescence of multilayer arrays of silicon rich oxide with high silicon content prepared by low pressure chemical vapor deposition

The photoluminescence emission of multilayer structures composed of layers of silicon rich oxide with high silicon content and layers of silicon rich oxide with low silicon content obtained by low pressure chemical vapor deposition is here presented. Different parameters for the preparation of the multilayers have been varied such as the Si concentration and the thicknesses of the layers. Additionally, the samples were oxidized at different temperatures. For all samples the photoluminescence seems to have the same origin: defects in the oxide matrix and defects at the interfaces between the Si nanocrystals. The structural and compositional properties of the multilayer structures are discussed.     

Critical current enhancement in Bi-2223/Ag superconducting tapes by controlling its first sintering process

Microstructural evolution of the Bi-2223 phase, liquid phase and secondary phase in the first sintering process has been studied by means of XRD and SEM/EDS. Experiments show that the first sintering temperature and time have a great influence on the Bi-2223 phase formation. The cooling rate after the first sintering process determines the type and grain size of the secondary phases, which in turn decides the critical current of the fully reacted tapes. The fast cooled sample contains a few secondary phase particles with very small size, whereas the slow cooled sample produces large CuO particles. The (Ca,Sr)₂CuO₃ and (Ca,Sr)₁₄Cu₂₄O₄₁ phases are easy to deform, while CuO phase particle has a high hardness and is difficult to deform during uniaxial press. The critical current is largely improved by controlling the cooling rate of the first sintering process.