Circulating Current Analysis for High-Speed Motors with Stranded Windings by Considering End and Temperature Effect

Yapeng Jiang,Junquan Chen,Xuan Teng,Dong Wang Korean Magnetics Society 2018 Journal of Magnetics Vol.23 No.4

This paper presents an improved circuit model for predicting additional copper loss caused by circulating current effect. Based on basic circuit equations and winding topology, this model takes account of both slot and end leakage inductance which are separately extracted by 2-D and 3-D finite element method. Several simplified windings are wounded in a stator to validate the accuracy of the proposed model. The results shows that this model has high accuracy and the maximum error of loss factor is about 1.5 %. In addition, it is found that the circulating current loss factor will decrease as the end winding length grows up or winding temperature increases.

Improving Dielectric Properties in Novel P(VDF‑HFP)/V2AlC MAX/Montmorillonite Composite Films via Interfacial Electric‑Leakage Depressing Strategy

Xiaofeng Xia,Junquan Zhou,Huimin Ding,Qin Li,Maolin Bo,Qihuang Deng,Yefeng Feng 대한금속·재료학회 2021 ELECTRONIC MATERIALS LETTERS Vol.17 No.1

Dielectric constants of polymer/conductor composites are often high, owing to strong interface interaction in those composites. They can be used for dielectric energy storage, but they usually have high dielectric loss and conductivity. In order toreduce the dielectric loss and conductivity in poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP))/V2AlC MAXcomposites, in this study, we explored the novel P(VDF-HFP)/V2AlC MAX/montmorillonite (MMT) ternary composites. Compared with binary composites, the ternary composites showed the mildly reduced dielectric constant, significantlydecreased dielectric loss and conductivity. Using highly-conductive V2AlCMAX filler aimed at taking advantage of thepolymer/MAX interface polarization to increase the dielectric response of composites. Employing well-insulating MMTfiller aimed at reducing the interface electric leakage conduction. At 1 kHz, the outstanding ternary composite with 2 wt%MMT and 20 wt% MAX could exhibit a high dielectric constant of ca. 27 and low dielectric loss of ca. 0.21. This workmight offer a new research idea for the construction of high-performance composite dielectric films containing modernMAX ceramic fillers.

Realizing Rationally-Balanced Dielectric Properties in Fluoropolymer/Cr2AlC MAX Composites Modified by 2D-BN

Qin Li,Junquan Zhou,Yanhui Chen,Xiaofeng Xia,Maolin Bo,Qihuang Deng,Yefeng Feng 한국고분자학회 2020 Macromolecular Research Vol.28 No.13

Polymer/conductor composite dielectric materials have a high dielectric constant. In recent years, composite dielectrics have become a study hotspot in highdensity energy storage capacitors. However, high dielectric loss and high electrical conductivity make the application of the composite materials very limited. In order to obtain composite materials with high dielectric constant, low dielectric loss and low conductivity, we added the insulating boron nitride (BN) filler into polymer/Cr2AlC composites. As a conductive filler, Cr2AlC ternary-layered-compound (MAX) ceramic has an interface polarization with the polymer matrix, thereby increasing the dielectric constant of the composites. The insulating BN has a very low electrical conductivity, which can effectively reduce the electrical conductivity and dielectric loss of the composites. Compared with the binary polymer/Cr2AlC composite materials, the ternary polymer/Cr2AlC/BN composite materials can achieve the low dielectric loss and low conductivity as well as properly-lowered dielectric constant. The ternary composite material filled with 10 wt% Cr2AlC and 2 wt% BN has a dielectric constant of about 30, a dielectric loss of about 0.7 and a conductivity of about 4.6×10- 7 S m-1 at 100 Hz. In this work, high-performance composite dielectrics were prepared through good cooperation between conductive and insulating ceramic fillers, which might provide an idea for design of promising energy storage capacitors.

Ultrastructural observations on spermiogenesis in the peanut worm, Phascolosoma esculenta (Sipuncula: Phascolosomatidea)

Lingli Long,Zhang Sheng,Junquan Zhu 한국통합생물학회 2015 Animal cells and systems Vol.19 No.3

Ultrastructural characteristics of spermiogenesis in the peanut worm, Phascolosoma esculenta (Phascolosomatidea), were observed by transmission electron microscopy (TEM). The spermiogenesis principally occurs in the coelom and can be divided into three stages (the early, middle and late stages) based on the chromatin morphology, acrosome development, spermatozoon midpiece and flagellum formation. Spermatids within a given spermatid mass develop synchronously. With the spermiogenesis proceeding, the spermatid masses become loosely structured, and later, adjacent spermatids are interconnected at one extremity of the cells. Gradually, condensation of the chromatin accelerates and is almost completed in late spermiogenesis, leaving the late spermatids with highly condensed homogeneous chromatin. In the spermatid head, the conical acrosome is generally composed of an acrosomal vesicle which is formed by the coalescence of small proacrosomal vesicles within the cytoplasm, a subacrosomal space that situates between the acrosomal vesicle and nucleus, and an acrosomal rod which develops from a bunch of filamentous material within the subacrosomal space. Certain mitochondria move posteriorly towards the nucleus, thus constituting the spermatozoon midpiece. The flagellum, originated from the distal centriole, appears in the early spermiogenesis. Ultimately, mature spermatidium dissociates into numerous spermatozoa, which are subsequently released as a single cell from the coelom into the nephridia. The spermatozoon has a prominent head, containing an acrosome and nucleus, a short midpiece and a slender tail. When compared with other sipunculans or invertebrates with external fertilization, the spermiogenesis of P. esculenta, presumably, is closely associated with its biological adaptations for the reproductive strategy.

Evaluation of a pyramid die extrusion for a hollow aluminum profile using FE simulation

Liang Chen,Guoqun Zhao,Junquan Yu,Wendong Zhang 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.5

The pyramid die extrusion for a hollow aluminum profile was analyzed to investigate the potential of such innovative dies. For thispurpose, the pyramid and conventional porthole dies were respectively designed for a given hollow aluminum profile. And the extrusionprocess was comprehensively studied by performing different types of finite element simulation, such as the analysis of steady state,transient state and billet skin tracking. The effects of pyramid angle on the evaluation parameters of extrusion, such as extrusion load,material flow, exit temperature, length of transverse weld, quality of longitudinal weld, back end defect and die stress were overall analyzedand compared with the conventional porthole die. Through this study, the advantages and shortcomings of pyramid die were wellconcluded, which should be important information for die designers and makers.

Finely-reconciled high dielectric constant and low dielectric loss in ternary polymer/Cr2C3/montmorillonite composite films by filler-synergy strategy

Deng Qihuang,Zhou Junquan,Li Xianping,Feng Yefeng,Liang Yurun,Liu Qihang 한국물리학회 2021 Current Applied Physics Vol.22 No.-

Polymer/conductive ceramic composites with high dielectric constant have become research hotspot of dielectric capacitor materials. However, the conductivity and dielectric loss increase when high dielectric constant is achieved. In order to reconcile high dielectric constant and low dielectric loss, in this study, poly (vinylidene fluoride) (PVDF)/chromium carbide (Cr2C3)/montmorillonite (MMT) ternary composite films were prepared by solution cast. Dielectric response based on interfacial polarization was improved and dielectric constant of composites was increased. MMT ceramic was used to suppress interface leakage current. Compared with PVDF/ Cr2C3 composites, the conductivity and dielectric loss of ternary composites were reduced.

Epsilon-Fe₂O₃ is a novel intermediate for magnetite biosynthesis in magnetotactic bacteria

Tong Wen,Yunpeng Zhang,Yuanyuan Geng,Junquan Liu,Abdul Basit,Jiesheng Tian,Ying Li,Ji-Lun Li,Jing Ju,Wei Jiang 한국생체재료학회 2019 생체재료학회지 Vol.23 No.3

Background: Natural biological magnetite nanoparticles are widely distributed from microorganisms to humans. It is found to be very important in organisms, especially in navigation. Moreover, purified magnetite nanoparticles also have potential applications in bioengineering and biomedicine. Magnetotactic bacteria (MTB) is considered one of the most abundant species around the world which can form intracellular membrane enveloped magnetic nanoparticles, referred to as magnetosomes. To our knowledge, the biomineralization of magnetosome in MTB involves a serious of genes located on a large unstable genomic region named magnetosome island, which specially exists in MTB. The magnetite core of magnetosome formed via a Fe (III) ion intermediates, for instance, α-Fe2O3 and ferrihydrite. Though the biosynthesis of magnetosome represents a general biomineralization mechanism of biogenic magnetite, knowledge of magnetosome biosynthesis and biomineralization remains very limited. Method: Cells used in this study were cultured in a 7.5-L bioreactor, samples for intermediate capture were taken each certain time interval after the generation of magnetosome biosynthesis condition. High-resolution transmission electron microscopy were used to analyze the detailed structure of magnetosomes. The parameters of the crystal structures were obtained by Fast Fourier Transform analyses. Results: In this study, we identified a novel intermediate phase, ε-Fe2O3, during the magnetite maturation process in MTB via kinetic analysis. Unlike α-Fe2O3, which has been reported as a precursor during magnetosome biosynthesis in MTB before, ε-Fe2O3, due to its thermal instability, is a rare phase with scarce natural abundance. This finding confirmed that ε-Fe2O3 is an important novel intermediate during the biomineralization of magnetosome in MTB, and shed new light on the magnetosome biosynthesis pathway.

Increasing Secrecy Capacity via Joint Design of Cooperative Beamforming and Jamming

( Xinrong Guan ),( Yueming Cai ),( Weiwei Yang ),( Yunpeng Cheng ),( Junquan Hu ) 한국인터넷정보학회 2012 KSII Transactions on Internet and Information Syst Vol.6 No.4

In this paper, we propose a hybrid cooperative scheme to improve the secrecy rate for a cooperative network in presence of multiple relays. Each relay node transmits the mixed signal consisting of weighted source signal and intentional noise. The problem of power allocation, the joint design of beamforming and jamming weights are investigated, and an iterative scheme is proposed. It is demonstrated by the numerical results that the proposed hybrid scheme further improves secrecy rate, as compared to traditional cooperative schemes.