Current Phase Lead Compensation in Single-Phase PFC Boost Converters With a Reduced Switching Frequency to Line Frequency Ratio

Traditional design of the current loop controller in a single-phase power factor correction boost converter is not suitable for applications with higher line frequencies (up to 800 Hz) because of the zero-crossing distortion and high harmonic content due to the current phase lead effect. Increasing the control bandwidth and switching frequency in order to avoid this effect would reduce converter efficiency and is objectionable. The paper presents the leading-phase admittance cancellation (LPAC) technique, which improves the current-shaping control structure and eliminates the current phase lead without increasing the bandwidth requirement. The LPAC method extends the allowable line frequency range from 1/150 to 1/5 of the current loop bandwidth. The LPAC method is load-invariant and superior to other previously proposed methods. The LPAC network can be added to existing designs, which would require only two passive components in the simplest case     

Modulation of Electron Structure and Dehydrogenation Kinetics of Nickel Phosphide for Hydrazine-Assisted Self-Powered Hydrogen Production in Seawater

The electrocatalytic production of hydrogen from seawater provides a low-cost way to realize energy conversion, but is restricted by high potential for seawater electrolysis and the chlorine oxidation reaction (ClOR) at the anode. Here, the self-growth of Mo-doped Ni₂P nanosheet arrays with rich P vacancies on molybdenum-nickel foam (MNF) (Mo-Ni₂P_v@MNF) is reported as bifunctional catalyst for Cl-free hydrogen production by coupling hydrogen evolution reaction (HER) with hydrazine oxidation reaction (HzOR) in seawater. Impressively, the Mo-Ni₂P_v@MNF electrode as bifunctional catalyst has an excellent activity for overall hydrazine splitting (OHzS) with an ultralow voltage of only 571 mV at 1000 mA cm⁻² and can maintain stability for an ultra-long time of 1000 h at 100 mA cm⁻². Moreover, integration of OHzS into self-assembled hydrazine fuel cells (DHzFC) or solar cells can enable the self-powered H₂ production. The industrial hydrazine sewage as feed for the above eletrolysis system can be degraded to ≈5 ppb rapidly. Density functional thoery calculations demonstrate that the electronic structure modulation induced by P vacancies and Mo doping can not only achieve thermoneutral ΔG_H* for hydrogen evolution reaction but also enhance dehydrogenation kinetics from *N₂H₄ to *NHNH₂ for HzOR, achieving enhanced dehydrogenation kinetics.     

Electrothermal coupling analysis of current crowding and Joule heating in flip-chip packages

Solder bumps serve as electrical paths as well as structural support in a flip-chip package assembly. Owing to the differences of feature sizes and electric resistivities between a solder bump and its adjacent traces, current densities around the regions where traces connect the solder bump increase in a significant amount. This current crowding effect along with the induced Joule heating would accelerate fatigue failure due to electromigration. In this paper we apply the three-dimensional electrothermal coupling analysis to investigate current crowding and Joule heating in a flip-chip package assembly carrying different constant electric currents under different ambient temperatures. Experiments are conducted to calibrate temperature-dependent electric resistivities of solder alloy, Al trace, and Cu trace, and to verify the numerical model by comparing calculated and measured maximum temperatures on the die surface. Through the electrothermal coupling analysis, effects of current crowding and Joule heating induced by different solder bump structures are examined and compared.     

机械工程学科2012年度科学基金管理工作综述

综述了2012年度国家自然科学基金委员会机械工程学科科学基金项目的评审及资助情况;以机械摩擦学与表面技术和高能束制造两个典型领域申报项目为例,对申请热点进行了分析。回顾了国家自然科学基金委员会科学处在促进学术交流与合作、重大项目立项、重大研究计划项目中期评估和青年人才队伍培养等方面的管理举措;总结了科学基金项目研究进展与人才培养成果情况。     

南海海边整层大气相干长度的测量与分析

大气相干长度是描述光波大气传输中湍流效应的重要参量,具有区域变化特性。海边大气相干长度的测量结果很少有报道,利用差分像运动法大气相干长度仪观测了茂名博贺海边的整层大气相干长度,获得了海边大气相干长度的全天数据。数据分析表明,海边整层大气相干长度日变化明显,夜晚起伏无规则,上半夜平均天文视宁度好于下半夜,白天最差;与陆地数据比较得知,海边整层大气相干长度日变化不如陆地上的剧烈,海边日变化成近"V"型,陆地上的为近"U"型;通过分析比较,提出了一些启发性的见解。     

Optimization of polymer light emitting devices using TiOx electron transport layers and prism sheets

The internal and external efficiency of polymer light emitting devices were found can be simultaneously improved by insertion a high refractive index material, titanium oxide (TiO_x), to the emission layer and a prism sheet attached to the substrate. The TiO_x layer increased the internal efficiency due to a better electron injection and hole confinement. However, it led a wider angular emission profile with more photons trapped in the substrate. By using the prism sheet, those trapped light was efficiently coupled to the air. The extraction efficiency enhancement was increased from 33.1% to 54.4% and the overall current efficiency was improved up to 86%.     

非关联双模场对Kerr介质中电子绝热跃迁转移现象的影响

本文研究了充满Kerr介质的高Q腔中非关联双模相干态场与级联三能级原子非共振相互作用情况下,电子的绝热跃迁转移现象与非关联场之间的关系。数值计算显示:级联三能级原子在与非关联双模相干态的相互作用下,该现象依然存在,但呈现不同于原子与关联场相互作用的新特征。     

一种确定高窄带滤光片峰值波长的方法

本文介绍一种主动式高窄带滤光片峰值波长的测量方法。该方法可以有效的测量出窄带滤光片的敏感波长，而不需要太复杂的设备。通过染料激光谐振腔的模式竞争，可以测量出滤光片的透射或反射波的波长。     

SNCP环带链的组网与维护

在实际传输网络结构中,有些站点由于条件限制不能与其它站点连接成环.过去采用通道保护(PP)环带链组网,环链网元间业务在环上没有保护;随着技术的发展,提出了子网连接保护(SNCP)环带链组网方式,确保环链网元间业务在环上得到保护,使网络的稳定性和可靠性大大提高.     

Armoring LiNi1/3Co1/3Mn1/3O2 Cathode with Reliable Fluorinated Organic–Inorganic Hybrid Interphase Layer toward Durable High Rate Battery

Ternary layered oxide materials have attracted extensive attention as a promising cathode candidate for high‐energy‐density lithium‐ion batteries. However, the undesirable electrochemical degradation at the electrode–electrolyte interface definitively shortens the battery service life. An effective and viable approach is proposed for improving the cycling stability of the LiNi_1/3Co_1/3Mn_1/3O₂ cathode using lithium difluorophosphate (LiPO₂F₂) paired with fuoroethylene carbonate (FEC) as co‐additives into conventional electrolytes. It is found that the co‐additives can greatly reduce the interface charge transfer impedance and significantly extend the life span of LiNi_1/3Co_1/3Mn_1/3O₂//Li (NMC//Li) batteries. The developed cathode demonstrates exceptional capacity retention of 88.7% and remains structural integrity at a high current of 5C after 500 cycles. Fundamental mechanism study indicates a dense, stable fluorinated organic–inorganic hybrid cathode‐electrolyte interphase (CEI) film derived from LiPO₂F₂ in conjunction with FEC additives on the surface of NMC cathode material, which significantly suppresses the decomposition of electrolyte and mitigates the dissolution of transition metal ions. The interfacial engineering of the electrode materials stabilized by the additives manipulation provides valuable guidance for the development of advanced cathode materials.