Time Offsets for Non-orthogonal CDMA Signals

A simple interference reduction method for non-orthogonal downlink CDMA channels is presented in which non-orthogonal CDMA signals are transmitted with different time offsets. An expression of multiple access interference (MAI) is developed and a reduction of MAI power is evaluated by using a numerical method and a computer simulation. The value of the time offset is determined in order to minimize the MAI and the implementation complexity. The performance of the proposed method is evaluated for various channel models.     

Pre-Activation of CO2 at Cobalt Phthalocyanine-Mg(OH)2 Interface for Enhanced Turnover Rate

Cobalt phthalocyanine (CoPc) anchored on heterogeneous scaffold has drawn great attention as promising electrocatalyst for carbon dioxide reduction reaction (CO₂RR), but the molecule/substrate interaction is still pending for clarification and optimization to maximize the reaction kinetics. Herein, a CO₂RR catalyst is fabricated by affixing CoPc onto the Mg(OH)₂ substrate primed with conductive carbon, demonstrating an ultra-low overpotential of 0.31 ± 0.03 V at 100 mA cm⁻² and high faradaic efficiency of >95% at a wide current density range for CO production, as well as a heavy-duty operation at 100 mA cm⁻² for more than 50 h in a membrane electrode assembly. Mechanistic investigations employing in situ Raman and attenuated total reflection surface-enhanced infrared absorption spectroscopy unravel that Mg(OH)₂ plays a pivotal role to enhance the CO₂RR kinetics by facilitating the first-step electron transfer to form anionic *CO₂⁻ intermediates. DFT calculations further elucidate that introducing Lewis acid sites help to polarize CO₂ molecules absorbed at the metal centers of CoPc and consequently lower the activation barrier. This work signifies the tailoring of catalyst-support interface at molecular level for enhancing the turnover rate of CO₂RR.     

Highly Utilized Active Sites on Pt@Cu/C for Ethanol Electrocatalytic Oxidation in Alkali Metal Hydroxide Solutions

Using ethanol electrocatalytic oxidation reaction (EOR) with a lower reaction potential to replace oxygen evolution reaction (OER) and integrating hydrogen evolution reaction (HER) have a promising development prospect for more energy-saving electrolytic hydrogen production. However, the main challenges of EOR are insufficient catalytic activity, high overpotential, and slow kinetics. Active sites on the electrocatalysts surface are occupied by alkali metal ion hydrate clusters by noncovalent interactions, which is considered to be one of the major causes of these challenges. To reduce the effect of the noncovalent interactions on the catalytic activity of the electrocatalyst, copper is chosen and doped in the form of a single atom in the electrocatalyst (Pt@Cu/C) to increase the electrocatalyst conductivity and make the anode contain more positive charge in this study. Then, alkali metal ion hydrate clusters are difficult to adsorb at the active site of Pt@Cu/C. The EOR electrocatalytic activity of Pt@Cu/C is up to 8184 mA mg_Pt⁻¹, which is ≈4.8 times as high as that of Pt/C. The two-electrode hydrogen production device using Pt@Cu/C as anode for coupled EOR&HER requires a smaller voltage of 0.60 V to reach 10 mA cm⁻² compared with that of Pt/C (0.76 V).     

基于子空间的三阶多项式相位信号快速稀疏分解算法

针对稀疏分解冗余字典中原子数量庞大的缺点,该文提出一种三阶多项式相位信号的快速稀疏分解算法。该算法根据三阶多项式相位信号的特点,把原有信号变换成两个子空间信号,并根据这两个子空间信号构建相应的冗余字典,然后采用正交匹配追踪法来完成其稀疏分解,最后利用稀疏分解原理完成原有信号的稀疏分解。该算法把原有信号变换成两个不同子空间信号,构建了两个不同的冗余字典,对比采用一个冗余字典库,这种采用两个冗余字典的算法大大减少了原子数量,并且通过快速傅里叶变换,在一个冗余字典进行稀疏分解时,同时找到另一个冗余字典中的最匹配的原子。因此该算法通过减少原子数量和采用快速傅里叶变换大大加快了稀疏分解速度。实验结果表明,相比于采用Gabor原子构建的冗余字典,采用匹配追踪算法与遗传算法及最近提出的基于调制相关划分的快速稀疏分解,它的稀疏分解速度更快,并且具有更好的收敛性。     

微波真空电子器件用无氧铜材料的蒸发特性

作为微波真空电子器件的常用材料之一,无氧铜材料的蒸发特性会对微波真空电子器件的电性能产生影响.该文利用超高真空测试设备,研究了处理工艺对无氧铜材料的蒸发性能的影响,采用X射线测厚仪测试了蒸发的铜膜厚度,用扫描电镜(SEM)观测了无氧铜材料的表面形貌.结果表明表面宏观形貌粗糙度对无氧铜材料的蒸发性能影响不大,但处理工艺对蒸发性能影响很大;无氧铜材料经过酸洗后,会大大增加蒸发量;无氧铜材料经过烧氢处理,可降低蒸发量,而经过去油清洗并烧氢处理的无氧铜的蒸发量极低.对无氧铜材料进行了表面分析,发现无氧铜材料的真空蒸发性能与材料的表面形貌状态有关,当表面微观形貌比较光滑、无孔洞等缺陷时,无氧铜材料的真空蒸发量就少.     

天然气净化厂硫磺回收及尾气处理过程有机硫的产生与控制措施

天然气净化厂硫磺回收及尾气处理装置尾气中有机硫含量对SO_2减排有重要影响。研究表明,硫磺回收装置的燃烧炉、催化反应器及尾气处理装置的加氢水解反应器中均会生成有机硫。对此,可通过减少酸气中烃类含量、提高燃烧炉温度、选择合适催化剂类型以及保持较高的加氢水解反应温度等措施,有效降低有机硫的生成量。同时,对于过程中生成的有机硫,应优化催化剂组合方式,在各级反应器中叠加水解,并保持加氢水解单元的高效转化,将进入灼烧炉的有机硫含量降至最低,从而实现生产装置尾气排放达标。     

正交试验优化转杯纺织物浆纱工艺的实践

为解决高紧度转杯纺织物织造断经多、打纬阻力大、易出波纹疵点等问题,分析了该类品种的生产难点,并以十万纬断经数和波纹疵点为指标通过正交试验对浆液黏度、压浆力、浆纱车速、浆纱回潮率、浆纱伸长和卷曲张力进行了优化,最终织机效率达87％以上,波纹疵点得到明显减少.认为:优选浆纱工艺是解决该类产品生产质量问题的关键.     

Lignin-based Hydrogels for Biological Application

Lignin is the most abundant aromatic compound found in nature.The rich functional groups of lignin are responsible for its antibacterial,antioxidant, anti-ultraviolet, and biocompatible properties. As modified lignin has a higher molecular weight, water solubility, and better surface activity, it is a good candidate for the construction of new biological materials. Ligninbased hydrogels are a type of functional materials with broad application prospects in the biomedical field. This review aimed...     

液相色谱-串联质谱法测定腐乳中的生物胺

建立了一种使用液相色谱-串联质谱（LC-MS/MS）技术检测腐乳中9种生物胺的方法。样品经5%三氯乙酸水溶液提取后,进行液相色谱-串联质谱法测定,采用外标法定量。对检测方法进行方法学验证,9种生物胺在质量浓度为10～200 ng/mL范围内线性相关系数R2＞0.999,方法检出限为0.03 mg/kg,定量限为0.1 mg/kg,回收率在85%～101%之间,相对标准偏差（RSD）在0.9%～4.8%之间。该方法结果精密、准确、重复性好、操作简单,适用于腐乳中9种生物胺的测定。