PVP-assisted synthesis of hollow Ni0.75Zn0.25Fe2O4 nanospheres for lithium-ion batteries

Hollow Ni_0.75Zn_0.25Fe₂O₄ nanospheres with a diameter of about 250–300 nm and thickness of 30–40 nm have been successfully fabricated through a PVP (polyvinylpyrrolidone)-assisted hydrothermal strategy. PVP plays an important role in the formation of hollow structure and a plausible formation mechanism of hollow Ni_0.75Zn_0.25Fe₂O₄ nanospheres is also proposed in this paper. The as-fabricated hollow Ni_0.75Zn_0.25Fe₂O₄ nanospheres display a good dispersibility and high specific surface area of 34.7 m² g⁻¹. Hollow Ni_0.75Zn_0.25Fe₂O₄ nanospheres also demonstrate satisfactory cycle life and rate performance when evaluated as a lithium ion battery negative electrode. Namely, after 120 cycles, the discharge specific capacity is 1321.3 mAh g⁻¹ at 200 mA g⁻¹, and the capacity retention rate is as high as 99.2%. Furthermore, the average discharge capacities are 1482.5, 1451.5, 1330.9, 1232.3, 1031.2 and 944.8 mAh g⁻¹ under the current densities of 100, 200, 500, 1000, 2000 and 4000 mA g⁻¹, respectively. The promising electrochemical performance of the hollow Ni_0.75Zn_0.25Fe₂O₄ nanosphere could be attributed to the unique hollow structure of nanospheres, which offers a higher specific surface area and shorten transmission pathways of electrons and ions, buffering the volume expansion during the Li⁺ insertion/desorption process.     

无线电能传输中电谐振耦合机理分析

针对在无线电能传输分析中多以磁耦合谐振技术为主,缺少对电谐振耦合机理的分析这一问题,文中根据对称性原理,提出无线电能传输机理中应该包含磁谐振耦合和电谐振耦合两种谐振耦合机理,并从电路的对偶性角度出发,给出了电谐振耦合电路模型并推导出传输功率增益的理论公式。通过对电路参数的分析得出了传输功率增益的变化规律,为无线电能传输系统的设计提供了参考。     

频变耦合双通带滤波器的综合方法

为了解决频变耦合双通带滤波器缺少有效综合方法的问题,文中提出一种优化综合方法.该方法首先通过频率变换技术得到滤波器在归一化双通带域内的特征多项式,然后应用经典的耦合矩阵综合方法得到双通带滤波器的全规范耦合矩阵,进而以矩阵的特征值为趋近目标构造目标函数,最后应用梯度优化算法进行优化获得了双通带滤波器的频变耦合矩阵.文中对...     

Substrate-independent and large-area synthesis of carbon nanotube thin films using ZnO nanorods as template and dopamine as carbon precursor

In this study, we introduce a method for large-area and substrate-independent synthesis of the big-inner-diameter carbon nanotube (BIDI-CNT) thin films by utilizing polydopamine (PDA) as carbon source and ZnO nanorods (NRs) as sacrificing template for the first time. ZnO NRs with hexagonal morphology were coated with PDA films via the ammonium persulfate-induced polymerization of dopamine at neutral pH for avoiding the degradation of amphoteric ZnO at alkaline pH needed by the conventional oxygen-induced polymerization of dopamine. After carbonization in N₂ atmosphere at 500 °C followed by ZnO removal, the hollow BIDI-CNTs with tuned wall thickness and hexagonal morphology were obtained. In addition, the obtained BIDI-CNTs were found to be N-doped. Furthermore, on the base of the outstanding substrate-independent growth properties of both ZnO NRs and PDA, the large area thin films of the N-doped BIDI-CNTs could be synthesized on various solid substrates, for instance, Al₂O₃, gold, fluorine-doped tin oxide-coated glass, platinum, silicon, mica, and quartz.     

低温烧结中介电常数微波介质陶瓷材料的研究进展

中介电常数微波介质陶瓷是现代通讯技术中4GHz～8GHz频率范围内的关键基础材料,综述了低温烧结中介电常数微波陶瓷的研究现状,介绍了几种重要的低温烧结中介电常数微波陶瓷体系,指出了几种体系材料存在的问题以及努力的方向和预期进展.     

分布式发电系统中四桥臂逆变器控制策略

由分布式电源构成的电网是弱电网,并且给各类负载供电,针对这类电网的特点和电网中负载的状况,本文提出采用四桥臂逆变器作为分布式发电系统的并网接口,提出基于带通滤波器的分序方法和分序控制策略,解决了四桥臂逆变器基于单同步旋转坐标的双环控制系统稳态性能差的问题,在此基础上搭建了实验平台,实验结果表明,本文提出的方案彻底改善了逆变器控制系统的稳态特性,极大地提高了分布式发电系统在不对称负载下的运行能力。     

Energy management of a hybrid energy system (PV / PEMFC and lithium-ion battery) based on hydrogen minimization modeled by macroscopic energy representation

This research work is designed for the management of the electric power of an autonomous hybrid system which generally integrates several subsystems, whose main source of production is solar energy (photovoltaic panels) coupled with a hydrogen fuel cell using a storage device (lithium battery).This energy coupling behavior is used in a wide range of operating conditions ensuring the originality of the exploitation of the energy produced to supply electricity to remote regions and isolated urban regions of southern Algeria, which will be modeled by a recent graphic formalism methodology macroscopic energy representation and controlled by a simple method the maximum control structure that takes into account all the inputs and outputs of the system. This hybrid system is controlled by an energy management strategy by acting on a common continuous bus with variable residential load via a DC/DC converter, allowing control of the amount of energy between the different energy resources to minimize the use of the fuel cell from which to minimize hydrogen consumption. Another is used to maintain the voltage of this bus at its reference via the battery by regulating the bidirectional DC/DC converter.     

悬置微带线滤波器的尺寸综合设计方法

针对基于经验公式设计的悬置微带线滤波器精度不高的问题,文中提出了悬置微带线滤波器的尺寸综合设计方法。建立悬置微带线滤波器的传输线谐振腔和耦合结构的等效电路模型并详细分析了耦合结构电抗斜率对传输线谐振腔的影响。通过全波仿真软件准确提取耦合结构的电抗斜率参数,逐级修正传输线谐振腔的物理长度,避免了耗时的全波仿真优化。最后,设计了一款5阶切比雪夫响应的悬置微带线滤波器,仿真结果与理论结果吻合良好,验证了设计方法的正确性和有效性。     

基于自适应滤波器分序算法的锁相方法

针对常规锁相方法在电网异常时不能有效地检测出电网相位和幅值的问题,采用自适应滤波器提取电网电压的正序基波分量,根据正序基波分量检测电网的相位和幅值.针对电网相位突变的情况,在分析锁相环数学模型的基础上,提出了电网正序电压的q轴分量的直接前馈方法,有效地提高了系统的动态特性和相位检测精度,并从理论上分析了电网幅值变化对锁相环的稳定性和稳定裕度的影响.仿真结果证明了所提锁相方法的可行性.