New antenna design approach – 3D polymer printing and metallization. experimental test at 14–18 GHz

This paper proves a new approach for rapid prototyping of radio antennas through 3D printing and chemical metallization. For this purpose, a standard metal pyramidal horn prototype is compared with its 3D printed replica. Three different 3D polymer printers are tested. The printed samples are assessed nondestructively by an X-ray Industrial Computed Tomography (CT) scanner, and then metalized via chemical deposition and chemical-electrochemical deposition. Copper with two different layer thicknesses and nickel materials are deployed and verified as a metallization opportunity. Again the CT scanner, X-ray fluorescent analysis and nanoindentation technique were used to perform the metallization quality estimation. As a result, a qualitative polymer prototype was produced having weight of 13 g – ten times lighter than the original. The prototype was successfully metalized and was able to be soldered. The radio-measurement comparison with the metal original for frequencies 14–18 GHz showed no significant differences. Finally, a simple dynamometric test confirmed the bonding between the metal and the polymer. To the best of our knowledge this is the first known comprehensive analysis of the possibility to print 3D lightweight wideband polymer antenna prototypes with a stable chemical metallization and radio properties very close to the original at 14–18 GHz.     

Monitoring Phenolic Composition of Maturing Maize Stover by High Performance Liquid Chromatography and Pyrolysis/Gas Chromatography/Mass Spectrometry*

Maize stovers collected every 14 days over an 84-day growth period were subjected to high-performance liquid chromatography with electrochemical detector (HPLC-ED) and pyrolysis/gas chromatography/mass spectrometry (PY/GC/MS) in order to monitor changes in the phenolic composition. Prior to HPLC-ED analyses, ground samples were sequentially extracted with (i) methanol, (ii) 0·1M sodium hydroxide and (iii) 2M sodium hydroxide in the presence of nitrobenzene to separate, respectively, free phenolic monomers, alkali-labile phenolic monomers and alkali-resistant lignin. In turn, solution (ii) was treated with alkaline nitrobenzene to obtain (iv) alkali-labile lignin. Pyrolysis was carried out on ground native samples by using a platinum heated filament pyrolyser. Increases in the absolute phenolic concentrations in the residues of 0·1M sodium hydroxide extraction and in the ratio of alkali-resistant lignin vs total lignin were observed by HPLC-ED during the first 28–42 days of maturation, reaching a steady level in the remaining maturation period. A linear increase of syringyl units vs guaiacyl units was for found the alkali-resistant lignin fraction over the entire period of maturation. Similar trends were showed by PY/GC/MS with regard to relative lignin content and syringyl/guaiacyl ratio. Both techniques showed their usefulness to gauge changes in the phenolic composition during the lignification process.     

Urease-induced metallization of gold nanorods for the sensitive detection of Salmonella enterica Choleraesuis through colorimetric ELISA

We applied urease-induced silver metallization on the surface of gold nanorods (AuNR) to improve colorimetric ELISA for the rapid and sensitive detection of Salmonella enterica Choleraesuis. To this end, we introduced a biotin-streptavidin system as a bridge to determine the correlation between urease and S. enterica Choleraesuis concentrations. The captured urease can catalyze the hydrolysis of urea into carbon dioxide and ammonia, and the generated ammonia can then induce the deposition of silver shell on the surface of AuNR in the presence of silver nitrate and glucose. With the decreased aspect ratio (length divided by width) of AuNR, a multicolor change of AuNR solution and a significant blue shift in the longitudinal localized surface plasmon resonance absorption peak (Δλ_max) of AuNR were obtained at the target concentrations of 1.21 × 10¹ to 1.21 × 10⁸ cfu/mL. Consequently, the detection limits of our proposed colorimetric ELISA were as low as 1.21 × 10² cfu/mL for qualitative detection with naked eyes, and 1.21 × 10¹ cfu/mL for quantitative detection, in which changes in Δλ_max of AuNR were recorded with a microplate reader. These values were at least 2 to 3 orders of magnitude lower than those obtained with conventional horseradish peroxidase-based ELISA. The analytical performance of our developed colorimetric ELISA in terms of selectivity, accuracy, reliability, and practicability were investigated by analyzing S. enterica Choleraesuis-spiked pasteurized whole milk samples.     

碳纳米管修饰电极差分脉冲伏安法测定微量Pb2+

以碳纳米管(CNT)修饰玻碳电极为工作电极,于-1.0V吸附富集后差分脉冲伏安法测定水中微量铅离子,实验优化了支持电解质、pH、CNT用量。从富集电位正向扫描至0V,在-0.58V处产生铅的阳极溶出峰,溶出峰电流值与Pb2+浓度在0.005～1μg/mL范围内呈良好的线性关系,线性方程为y=16.0911x-0.2284(r=0.9962),检测下限为0.005μg/mL,回收率为95.4%～105.5%,6次重复测定RSD为1.69%。碳纳米管显著改善了铅离子检测信号,所提出的检测方法简单、灵敏、快速、选择性好,能应用于实际样品测定。     

电化学氧化羊毛表面的物理性质

通过电解锰酸钾化合物的水溶液得到高锰酸钾饱和盐溶液并对羊毛表面进行氧化．将电化学氧化前后的羊毛进行表面结构、断裂强度、摩擦系数的测定，对电化学氧化与高锰酸钾饱和盐溶液直接氧化后的羊毛进行比较与研究．结果表明：羊毛表面结构的改变对羊毛物理性质有显著影响，电化学氧化较高锰酸钾直接氧化后的羊毛具有明显优势．     

食品机械的防腐蚀措施

介绍了食品机械的腐蚀机理及其防止措施。