Effects of the Substitution of Mischmetal for PrNd on the Microstructures and Magnetic Properties of Rapidly Quenched (MM)PrNd-Fe-B Nanocrystalline Magnets

Zeng-ru Zhao,Xin Wang,Xue-feng Zhang,Qiang Ma,Yan-li Liu,Yong-feng Li,Fei Liu,Gao-feng Wang 한국자기학회 2017 Journal of Magnetics Vol.22 No.1

Mischmetal of Bayan Obo ore was utilized to prepare the high performance (Pr7.34Nd21.86)1-xMMxFe68.7Al0.1-Cu0.12Co0.88B ribbons using melt-spinning method. Phase composition and magnetic properties were investigated at room temperature. The ribbons mainly consist of R2Fe14B phase in isotropic nanostructure. Both coercivity and maximum energy product decrease with the increase of MM content. The magnetic parameters of the ribbons with MM = 20 % in mass are Br = 7.38 kGs, Hcj = 13.66 kOe, (BH)max = 11.81 MGOe. Henkel plots were applied to demonstrate the exchange coupling interaction between grains.

A Comparison Study of the Catalytic Properties of Au-Based Nanocages, Nanoboxes, and Nanoparticles

Zeng, Jie,Zhang, Qiang,Chen, Jingyi,Xia, Younan American Chemical Society 2010 NANO LETTERS Vol.10 No.1

<P>We have evaluated the catalytic properties of Au-based nanostructures (including nanocages, nanoboxes, and solid nanoparticles) using a model reaction based on the reduction of <I>p</I>-nitrophenol by NaBH<SUB>4</SUB>. From the average reaction rate constants at three different temperatures, we determined the activation energy, the entropy of activation, and the pre-exponential factor for each type of Au nanostructure. The kinetic data indicate that the Au-based nanocages are catalytically more active than both the nanoboxes and nanoparticles probably due to their extremely thin but electrically continuous walls, the high content of Au, and the accessibility of both inner and outer surfaces through the pores in the walls. In addition, a compensation effect was observed in this Au-based catalytic system, which can be primarily interpreted by a model based on kinetic regime switching.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2010/nalefd.2010.10.issue-1/nl903062e/production/images/medium/nl-2009-03062e_0001.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl903062e'>ACS Electronic Supporting Info</A></P>

Fast-Transient Repetitive Control Strategy for a Three-phase LCL Filter-based Shunt Active Power Filter

Zeng, Zheng,Yang, Jia-Qiang,Chen, Shi-Lan,Huang, Jin The Korean Institute of Power Electronics 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.2

A fast-transient repetitive control strategy for a three-phase shunt active power filter is presented in this study to improve dynamic performance without sacrificing steady-state accuracy. The proposed approach requires one-sixth of the fundamental period required by conventional repetitive control methods as the repetitive control time delay in the synchronous reference frames. Therefore, the proposed method allows the system to achieve a fast dynamic response, and the program occupies minimal storage space. A proportional-integral regulator is also added to the current control loop to eliminate arbitrary-order harmonics and ensure system stability under severe harmonic distortion conditions. The design process of the corrector in the fast-transient repetitive controller is also presented in detail. The LCL filter resonance problem is avoided by the appropriately designed corrector, which increases the margin of system stability and maintains the original compensation current tracking accuracy. Finally, experimental results are presented to verify the feasibility of the proposed strategy.

Engineering Iron-Based Nanoparticles Spatially Dispersed on Mesoporous Carbon and Its Catalytic Activity for the Direct Oxidization of Benzene to Phenol

Qiang Sun,Long Liu,Yi-Ding Li,Zeng-Rong Wang,Xue Zhang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2018 NANO Vol.13 No.08

We report engineered iron-based nanoparticles supported on cagelike mesoporous carbon that leaves its most mesopores empty to retain an open pore network and are expected to be efficient catalyst with fast molecular diffusion/transportation. The nano-scale iron-based particle inlayed in mesoporous carbon catalyst was obtained via the introduction of N atoms as an anchor. Results of X-ray diffraction, N2 sorption and transmission electron microscopy showed that the cagelike mesoporous structure of the carbon matrix was retained during catalyst preparation and iron-based nanoparticles were spatially dispersed on the mesoporous carbon. Importantly, it was found that the obtained iron-based nanoparticles inlayed into mesoporous carbon with a low Fe loading of 1.26 wt.% was an appropriate catalyst for the benzene hydroxylation to phenol using H2O2 as the oxidant. At a low temperature of 30 ℃, 19.4% conversion to benzene and 14.6% phenol yield were obtained; in addition, the catalyst could be recycled at least four times.

Low Temperature Synthesis of Mesoporous SiC in Dual-Confined Spaces via Magnesiothermic Reduction

Zeng-Rong Wang,Long Liu,Xue Zhang,Jia-Lin Xu,Qiang Sun 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2019 NANO Vol.14 No.9

Silicon carbide (SiC), especially mesoporous SiC has been in immense vogue for more than a decade because of its intriguing properties and wide applications. However, it is still challenging to synthesize mesoporous SiC with good structural integrality, large specific surface area and desirable porosity at a low temperature. In this study, we reported a "dual-confined spaces"-assisted synthesis of mesoporous SiC using well-assembled SiO2/carbon composite as precursor via a magnesiothermic reduction process. The well-crystallinity mesoporous SiC presented a mesopore structure with high specific surface area of 267.3 m2 g -1 and large mesopore size of ca. 10 nm can be directly fabricated at a temperature of at least 550 ℃ and the optimum synthesis temperature is 650 ℃. During the synthesis, mesoporous carbon matrix and a pressure-tight stainless steel reactor were served as "dual-confined spaces" to avoid the aggregation of silica and the silicon residue left in the final SiC sample. Furthermore, the as-prepared mesoporous SiC showed prominent performance as catalyst support for the reduction of 4-nitrophenol to 4-aminophenol.

Firm Valuation Over Lifecycle: A Perspective on Growth Option

Qiang Li,Hao Liu,Yong Zeng 韓國證券學會 2018 한국증권학회지 Vol.47 No.6

This paper investigates the roles of the dynamic of growth options in determining possible change trends of firm valuation over a firm’s lifecycle. The theoretical results show that the gradual exercising of endowed growth options will cause a downward trend of firm valuation over lifecycle, while the creating of new growth options can mitigate the downward trend. In particular, there may be an upward trend of firm valuation for firms able to continually create growth options over time. The evidence on 2354 Chinese listed firms during the period of 1998–2015 supports theoretical predictions well.

Influence Regularity of Aluminum, Copper and Stainless-steel on SF₆ PD Decomposition Characteristics Components

Zeng, Fuping,Luo, Jing,Tang, Ju,Zhou, Qian,Yao, Qiang The Korean Institute of Electrical Engineers 2017 Journal of Electrical Engineering & Technology Vol.12 No.1

$SF_6$ decomposition products can be used to detect partial discharge (PD), but the metal materials in a PD area can significantly affect $SF_6$ decomposition characteristics. Disregarding the effect of metal materials on such characteristics inevitably result in certain errors when using them to diagnose the internal insulation faults of gas-insulated switchgears. This paper investigates the influence regularity on the main stable decomposition components of $SF_6$ (namely $SO_2F_2$ and $SOF_2$) of the commonly metal materials uesd in GIS, such as aluminum (Al), copper (Cu) and stainless steel (SS). Firstly, an experimental platform is constructed to simulate $SF_6$ decomposition under a PD area, and the influence regularities of Al, Cu and SS on the concentration, formation rate and saturation time of $SO_2F_2$ and $SOF_2$ are obtained. Secondly, the influence mechanism of Al, Cu and SS are preliminary explored combined with the chemical activity of the metal materials.

Modulation signal analysis and parameter selection for modular multi-level converters with harmonic injection method

Zeng, Qifan,Xiao, Fei,Ren, Qiang,Ai, Sheng The Korean Institute of Power Electronics 2020 JOURNAL OF POWER ELECTRONICS Vol.20 No.2

The harmonic injection method is widely used in modular multilevel converters (MMCs) to suppress the significant amplitude of the submodule (SM) capacitor voltage fluctuation under low-frequency operation. A method is required to inject high-frequency common-mode voltages and circulating currents, which both occupy modulation space and are prone to over-modulation. This paper focuses on the modulation signal required for circulating current injection, which has been neglected in previous studies. In addition, this paper redefines the amplitude references of the injected harmonics to reserve modulation space for the injected circulating current. By analyzing the characteristics of an MMC system with the harmonic injection method, the relationship between the modulation signal for the circulating current and other variables (such as the output modulation index, output frequency and injection frequency) is obtained. Using the obtained relationship, a strategy for selecting the amplitude and frequency of the injected harmonics is presented to avoid over-modulation under variable conditions while suppress the SM capacitor voltage fluctuation. The theoretical analysis, the proposed injection method and its parameter selection strategy are verified by experimental results.

Fast-Transient Repetitive Control Strategy for a Three-phase LCL Filter-based Shunt Active Power Filter

Zheng Zeng,Jia-Qiang Yang,Shi-Lan Chen,Jin Huang 전력전자학회 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.2

A fast-transient repetitive control strategy for a three-phase shunt active power filter is presented in this study to improve dynamic performance without sacrificing steady-state accuracy. The proposed approach requires one-sixth of the fundamental period required by conventional repetitive control methods as the repetitive control time delay in the synchronous reference frames. Therefore, the proposed method allows the system to achieve a fast dynamic response, and the program occupies minimal storage space. A proportional-integral regulator is also added to the current control loop to eliminate arbitrary-order harmonics and ensure system stability under severe harmonic distortion conditions. The design process of the corrector in the fast-transient repetitive controller is also presented in detail. The LCL filter resonance problem is avoided by the appropriately designed corrector, which increases the margin of system stability and maintains the original compensation current tracking accuracy. Finally, experimental results are presented to verify the feasibility of the proposed strategy.

Seed-Mediated Synthesis of Ag Nanocubes with Controllable Edge Lengths in the Range of 30−200 nm and Comparison of Their Optical Properties

Zhang, Qiang,Li, Weiyang,Moran, Christine,Zeng, Jie,Chen, Jingyi,Wen, Long-Ping,Xia, Younan American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.32

<P>Silver nanocubes with edge lengths controllable in the range of 30−200 nm were synthesized using an approach based on seeded growth. The keys to the success of this synthesis are the use of single-crystal Ag seeds to direct the growth and the use of AgNO<SUB>3</SUB> as a precursor to elemental Ag, where the byproduct HNO<SUB>3</SUB> can block both the homogeneous nucleation and evolution of single-crystal seeds into twinned nanoparticles. Either spherical (in the shape of a cuboctahedron) or cubic seeds could be employed for this growth process. The edge length of the resultant Ag nanocubes can be readily controlled by varying the amount of Ag seeds used, the amount of AgNO<SUB>3</SUB> added, or both. For the first time, we could obtain Ag nanocubes with uniform edge lengths controllable in the range of 30−200 nm and then compare their localized surface plasmon resonance and surface-enhanced Raman scattering properties.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-32/ja104931h/production/images/medium/ja-2010-04931h_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja104931h'>ACS Electronic Supporting Info</A></P>