A design for wideband planar arrays with broad beamwidth and low cross polarization is described. The single element of the array is composed of a coaxial-cable-fed slot antenna, a shorting pin, and a planar reflector. For the single antenna, the effects of the key parameters on H-plane beamwidth and cross polarization are respectively studied. An optimum design is given, and both of its measured and simulated results prove that the single antenna has the characteristics of wide beamwidth and low cross polarization within an operating bandwidth of about 50 %. Based on the optimum design, a 1× 4 linear array is developed and constructed. Experimental results demonstrate that the array operating in the range from 1.7 to 2.7 GHz has a return loss of less than 13dB, a cross polarization level of smaller than -20 dB, and a half-power beamwidth of 100°±10° in the H-plane.
Poly(lactic acid) (PLA)/graphene nanocomposites were prepared by solution blending using chloroform as a mutual solvent. Transmission electron microscopy (TEM) was used to examine the quality of the dispersion of graphene in the PLA matrix. The isothermal crystallization behaviors of PLA and PLA/graphene nanocomposites were investigated by differential scanning calorimetry (DSC). The isothermal crystallization kinetics were analyzed by Avrami model based on the DSC data. The results showed that the well dispersed graphene nanosheets could act as a heterogeneous nucleating agent and lead to an acceleration of crystallization during the PLA isothermal crystallization process. According to the Arrhenius equation, the activation energies were found to be -106.9 and -46.6 kJ/mol for pure PLA and PLA/0.1 wt % graphene nanocomposite, respectively. The crystal morphology were characterized with polarizing optical microscope (POM).
Because the temperature of heat medium in thermal recovery wells is very high, and casing is heated during steam injection process, which has become the main reason of casing failure. Therefore, it is very important to analyze crack propagation and casing failure under thermal mechanical coupling. Three-dimensional finite element model is investigated; geometry model is constructed with native and parasolid method in ADINA. The casing is modeled by native method and strata are modeled by parasolid method, casing are subtracted and merged with strata by Boolean Operation. Gravity and displacement loads are defined in structure model, and temperature load in thermal model. In structural model, casing is treated as thermoplastic material, and strata are treated as hot isotropic material. In thermal model, all materials are treated as heat conduction material. Thermal-mechanical coupling is calculated with the thermo-mechanical coupled analysis solver in ADINA, and casing damage process is calculated. According to the calculating results, the mechanism of casing damage is analyzed.
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