电能计量自动抄表技术的现状与展望

电能计量自动抄表技术是现代电力营销的重要技术手段,对通信方式的研究是其发展的重点。本文简要叙述了电能计量自动抄表技术产生的背景和电能计量自动抄表系统的组成,在分析自动抄表系统的通信方式及其选择的基础上阐述了电能计量自动抄表技术的现状和未来的研究热点与发展方向。     

基于PSO-SVM模型的液压系统故障诊断

针对液压系统在使用中故障频率较高、诊断方法受各种因素影响以及诊断准确率较低等问题,提出一种新的基于PSO-SVM模型的液压系统故障诊断方法.该方法首先对采集的故障信号数据进行预处理,使用自适应噪声完备集合经验模态分解(Complete EEMD with Adaptive Noise,CEEMDAN)结合模糊熵的方法进...     

SMDP-based sleep policy for base stations in heterogeneous cellular networks

A dense heterogeneous cellular network can effectively increase the system capacity and enhance the network coverage. It is a key technology for the new generation of the mobile communication system. The dense deployment of small base stations not only improves the quality of network service, but also brings about a significant increase in network energy consumption. This paper mainly studies the energy efficiency optimization of the Macro-Femto heterogeneous cellular network. Considering the dynamic random changes of the access users in the network, the sleep process of the Femto Base Stations (FBSs) is modeled as a Semi-Markov Decision Process (SMDP) model in order to save the network energy consumption. And further, this paper gives the dynamic sleep algorithm of the FBS based on the value iteration. The simulation results show that the proposed SMDP-based adaptive sleep strategy of the FBS can effectively reduce the network energy consumption.     

Highly Branched VS4 Nanodendrites with 1D Atomic‐Chain Structure as a Promising Cathode Material for Long‐Cycling Magnesium Batteries

Rechargeable magnesium batteries have attracted increasing attention due to the high theoretical volumetric capacities, dendrite formation‐free characteristic and low cost of Mg metal anodes. However, the development of magnesium batteries is seriously hindered by the lack of capable cathode materials with long cycling life and fast solid‐state diffusion kinetics for highly‐polarized divalent Mg²⁺ ions. Herein, vanadium tetrasulfide (VS₄) with special one‐dimensional atomic‐chain structure is reported to be able to serve as a favorable cathode material for high‐performance magnesium batteries. Through a surfactant‐assisted solution‐phase process, sea‐urchin‐like VS₄ nanodendrites are controllably prepared. Benefiting from the chain‐like crystalline structure of VS₄, the S₂^2‐ dimers in the VS₄ nanodendrites provide abundant sites for Mg²⁺ insertion. Moreover, the VS₄ atomic‐chains bonded by weak van der Waals forces are beneficial to the diffusion kinetics of Mg²⁺ ions inside the open channels of VS₄. Through a series of systematic ex situ characterizations and density functional theory calculations, the magnesiation/demagnesiation mechanism of VS₄ are elucidated. The VS₄ nanodendrites present remarkable performance for Mg²⁺ storage among existing cathode materials, exhibiting a remarkable initial discharge capacity of 251 mAh g^‐1 at 100 mA g^‐1 and an impressive long‐term cyclability at large current density of 500 mA g^‐1 (74 mAh g^‐1 after 800 cycles).     

A Review on Structure–Activity Relationship of Dietary Polyphenols Inhibiting α-Amylase

The inhibitory effects of dietary polyphenols against α-amylase have attracted great interest among researchers. The aim of this review is to give an overview of the research reports on the structure–activity relationship of polyphenols inhibiting α-amylase. The molecular structures that influence the inhibition are the following: (1) The hydroxylation of flavonoids improved the inhibitory effect on α-amylase; (2) Presence of an unsaturated 2,3-bond in conjugation with a 4-carbonyl group has been associated with stronger inhibition; (3) The glycosylation of flavonoids decreased the inhibitory effect on α-amylase depending on the conjugation site and the class of sugar moiety; (4) The methylation and methoxylation of flavonoids obviously weakened the inhibitory effect; (5) The galloylated catechins have higher inhibition than nongalloylated catechins; the catechol-type catechins were stronger than the pyrogallol-type catechins; the inhibition activities of the catechins with 2,3-trans structure were higher than those of the catechins with 2,3-cis structure; (6) Cyanidin-3-glucoside showed higher inhibition against than cyanidin and cyanidin-3-galactoside and cyanidin-3,5-diglucoside had no inhibitory activity; (7) Ellagitannins with β-galloyl groups at glucose C-1 positions have higher inhibitory effect than the α-galloyl and nongalloyl compounds and the molecular weight of ellagitannins is not an important element.     

抗冲ACR树脂的合成及其性能评价

采用种子乳液聚合法,以丙烯酸丁酯为核层单体、甲基丙烯酸甲酯为壳层单体、甲基丙烯酸烯丙酯为交联剂制备了抗冲ACR树脂。考察了不同加料方式对ACR乳液粒径及对PVC冲击性能的影响,结果表明:连续滴加方式可实现乳液粒径的稳定控制,并能得到性能优异的抗冲ACR树脂。     

钛/钢爆炸复合板界面连接机理与力学行为

本文表征了钛/钢爆炸焊接复合板的界面组织和剪切性能,研究爆炸复合过程的界面结合机理。结果表明,在金属板之间形成了波状界面组织,剧烈塑性变形造成钢基体发生明显的塑性流动,并在界面形成连续的漩涡形貌。TEM和XRD检测证实界面存在纳米尺度的过渡层,并包含有固溶体组织和少量金属间化合物。波状界面组织改善了复合板沿爆炸方向的界面剪切强度,剪切断口显示漩涡组织发生韧性断裂形貌。     

泡沫铝夹芯板粉末冶金发泡机理的SR-CT研究

利用同步辐射装置的SR-CT,通过图像的断层扫描及3D重建,对轧制复合-粉末冶金发泡工艺制备的泡沫铝夹芯板(AFS)进行了泡孔结构演化的研究,分析了发泡过程中孔隙率的变化及大尺寸连通孔的形成原因。研究结果表明:具有微米级空间分辨率的SR-CT可清晰地观测到泡孔萌生及生长各阶段的泡沫结构。泡孔在发泡15~30 s阶段生成,形状为垂直于轧制方向的类裂纹孔。发泡45 s时,泡孔开始发生明显合并,继续延长发泡时间易导致形成大尺寸连通孔。芯层泡沫铝的孔隙率在泡孔的萌生阶段及合并阶段增长幅度较大,减少混料时发泡剂的"团聚"及提高芯层粉末致密度可获得良好的芯层泡沫结构。     

Compressive and energy absorption properties of closed-cell magnesium foams

The quasi-static compressive mechanical behavior and deformation mechanism of closed-cell magnesium foams were studied, and the effects of the density of magnesium foams on the compressive and energy absorption properties were also discussed. The results show that the compressive process of closed-cell magnesium foams is characterized by three deformation stages: linear elastic stage, collapsing stage and densification stage. At the linear elastic stage, the peak compressive strength (σ ₀) and Young’s modulus (E ₀) increase as the density increases. Magnesium foams can absorb energy at the collapsing stage. In a certain strain range, the energy absorption capacity also increases as the density of magnesium foams increases.