设计和仿真无线局域网设备天线

对带有开关电路的2.4 GHz极化分集印刷天线进行电磁场及电磁场与电路协同仿真 通过采用极化分集技术,可以用低成本PCB基片制造具有良好接收机性能的无线局域网设备(WLAN)天线.本文将描述如何使用最新的三维电磁场(EM)仿真工具来设计和仿真一对2.4GHz正交极化的印刷偶极子天线,同时预测表面电流和相关的远场辐射图.     

Affixing poly(methyl methacrylate-co-acrylic acid) nanospheres with trimethoxyvinylsilane on silicon solar module to enhance its power conversion efficiency

Poly(methyl methacrylate-co-acrylic acid) [P(MMA-co-AA)] incorporated with 0–9 wt% of trimethoxyvinylsilane (TMVS) has been studied to investigate the effect of TMVS on the adhesion properties of P(MMA-co-AA) nanospheres coated on silicon substrate as well as on the power conversion efficiency (PCE) of silicon solar module coated with the polymer nanospheres. The incorporation of 7 and 9 wt% of TMVS into the copolymer has been found to render the copolymer stronger adhesion to glass substrate than the samples with lower amount of TMVS in them. The coating of the P(MMA-co-AA) nanospheres on the glass surface of solar module increases the light harvesting efficiency by serving as an anti-reflective layer. Solar module coated with an array of P(MMA-co-AA) nanospheres with 7 wt% of TMVS yielded the highest PCE enhancement of 98% under the illumination of an AM1.5 solar simulator. The natural weathering results indicate that the copolymer with 7% of TMVS was able to withstand prolonged natural weathering exposure and remained reasonably effective in PCE enhancement up to 130 days of outdoor exposure. This study demonstrates a cost-effective technique to bind [P(MMA-co-AA)] nanospheres onto the silicon surface of solar module via siloxane linkages and thus increases the PCE of the solar module effectively. The T_g of the copolymer increased linearly from 110.31 to 118.42 °C when 0–9 wt% of TMVS was added into it. Thermogravimetry results indicate that the incorporation of TMVS does not give any significant effect on the T_d of the copolymer, which occurs at about 390 °C.

     

Thermal Conductivity and Viscosity of Nanofluids Having Nanoencapsulated Phase Change Material

In this study, the thermal conductivity and viscosity of nanofluids, composed of a base fluid and nanoencapsulated phase change material (NEPCM), were investigated experimentally. The NEPCM was prepared by the encapsulation of n-nonadecane as phase change material with diethylenetriamine and toluene-2,4-diisocyanate using interfacial polymerization method. The NEPCM was characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC) analyses. In the preparation of the nanofluids containing NEPCM, two different base fluids, water and ethylene glycol (EG), were used. The concentration of NEPCM and the working temperature were selected as the main parameters. It was found that the viscosity of the nanofluids decreases with increasing temperature and increases with increasing solid concentration. The viscosity was also expressed as a function of the solid concentration and temperature. The thermal conductivity of the nanofluids was found to increase with increasing temperature. Thermal conductivity exhibited an increasing tendency with increasing solid concentration, but the changes in thermal conductivity according to base fluid are in the range of uncertainty of the measurement for both nanofluids with a solid volumetric fraction lower than 1.68%.     

Isolation and characterisation of collagen from the ribbon jellyfish (Chrysaora sp.)

Pepsin‐solubilised collagen from the ribbon jellyfish (Chrysaora sp., morphotype 1) umbrella (JPSC) was isolated and characterised. The yield of collagen varied (9–19%, based on ash‐free dry weight) depending on the amount of pepsin used. Type II collagen was the major component of extracted collagen. The peptide map of JPSC differed from that of standard collagen type II, which indicates their different primary structures. FTIR spectra of JPSC, however, did not differ significantly from those of type II collagen. The T_max of JPSC was 37.38 °C, which is higher than that of other marine collagens. Glycine was the main amino acid in JPSC (320 residues per 1000 residues), followed by glutamic acid, alanine, proline, aspartic acid and hydroxyproline. The isoelectric point of JPSC was 6.64. These results indicate that this jellyfish species has the potential to be a marine source of type II collagen that can be used in place of land‐based sources.     

Phase Transformations of α-Alumina Made from Waste Aluminum via a Precipitation Technique

We report on a recycling project in which α-Al₂O₃ was produced from aluminum cans because no such work has been reported in literature. Heated aluminum cans were mixed with 8.0 M of H₂SO₄ solution to form an Al₂(SO₄)₃ solution. The Al₂(SO₄)₃ salt was contained in a white semi-liquid solution with excess H₂SO₄; some unreacted aluminum pieces were also present. The solution was filtered and mixed with ethanol in a ratio of 2:3, to form a white solid of Al₂(SO₄)₃·18H₂O. The Al₂(SO₄)₃·18H₂O was calcined in an electrical furnace for 3 h at temperatures of 400–1400 °C. The heating and cooling rates were 10 °C/min. XRD was used to investigate the phase changes at different temperatures and XRF was used to determine the elemental composition in the alumina produced. A series of different alumina compositions, made by repeated dehydration and desulfonation of the Al₂(SO₄)₃·18H₂O, is reported. All transitional alumina phases produced at low temperatures were converted to α-Al₂O₃ at high temperatures. The X-ray diffraction results indicated that the α-Al₂O₃ phase was realized when the calcination temperature was at 1200 °C or higher.     

State‐space characterization of all solutions to a positive real control problem

Abstract

The purpose of this paper is to give a state‐space characterization of all internally stabilizing finite‐dimensional linear time‐invariant output feedback controllers for a given finite‐dimensional linear time‐invariant plant which ensure that the resulting closed‐loop transfer function is extended strictly positive real(ESPR). All such controllers are parameterized by a fixed linear fractional transformation with an ESPR, stable free parameter. The parameterized controllers have a state dimension not less than that of the open‐loop plant. The development uses only elementarily algebraic ideas beginning with a change of variables, an extended version of Kalman‐Yacubovich‐Popov positive real lemma, and Youla parameterization, thus the proofs given are simple and clear.