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The Origin of Coercivity Enhancement of Sintered NdFeB Magnets Prepared by Dy Addition
N. J. Yu,M. X. Pan,P. Y. Zhang,H. L. Ge 한국자기학회 2013 Journal of Magnetics Vol.18 No.3
The effect of Dy addition on the microstructure and magnetic properties of the sintered NdFeB magnets was investigated. The results of the microstructure analysis showed that Dy-free and Dy-doped samples are composed of Nd₂Fe ₁₄B (P42/mnm) and a trace of Nd-rich phase. Dy addition reduces significantly the pole density factor of (004), (006) and (008) crystal faces as estimated by the Horta formula. Accordingly, the coercivity of the Dy-doped sample increases from 2038 kA·m?1 up to 2288 kA·m?1. The Hcj(T)/Ms(T) versus /Ms(T) (Kronmuller-plot) behavior shows that the nucleation is the dominating mechanism for the magnetization reversal in these two kinds of magnets, and two microstructural parameters of αk and Neff are obtained. The Kronmuller-Plot gives evidence for an increase of the αk responsible for an increase of the coercivity as the result of the increase of the magnetic field as the magnetic domain reversed.
Pan C.B.,Zhao G.C.,Li S.M.,Shu M.F.,Wu J.,Wang J.M.Z.,Yin L.H.,Song W.H.,Zhu X.B,Yang J.,Sun Y.P. 한국물리학회 2022 Current Applied Physics Vol.34 No.-
Among Aurivillius layer-structured materials, CaBi2Nb2O9 is a best potential candidate for ultrahigh-temperature applications because of its highest Curie temperature of about 940 ◦C. In this paper, (1-x)CaBi2Nb2O9- xBaZr0.2Ti0.8O3 composite ceramics were prepared by conventional solid-state sintering method. The dielectric results show that the introduction of BaZr0.2Ti0.8O3 not only increases the permittivity of the material, but also reduces its dielectric loss. The optimum electrical properties were obtained in the x = 0.01 sample with piezoelectric coefficient (d33) of 15.1 pC/N and high ferroelectric remnant polarization (Pr) of 9.9 μC/cm2. Furthermore, the composite samples show good thermal depoling performance, the d33 of the x = 0.01 sample is 13.8 pC/N, which is about 91% of the initial value after depoling at 800 ◦C. Therefore, (1-x)CaBi2Nb2O9- xBaZr0.2Ti0.8O3 is one of the candidates for high temperature piezoelectric materials.
100KW DC Arc Plasma of CVD System for Low Cost Large Area Diamond Film Deposition
Lu, F.X.,Zhong, G.F.,Fu, Y.L.,Wang, J.J.,Tang, W.Z.,Li, G.H.,Lo, T.L.,Zhang, Y.G.,Zang, J.M.,Pan, C.H.,Tang, C.X.,Lu, Y.P. The Korean Ceramic Society 1996 The Korean journal of ceramics Vol.2 No.4
In the present paper, a new type of DC arc plasma torch is disclosed. The principles of the new magnetic and fluid dynamic controlled large orifice long discharge tunnel plasma torch is discussed. Two series of DC Plasma Jet diamond film deposition equipment have been developed. The 20kW Jet equipped with a $\Phi$70 mm orifice torch is capable of deposition diamond films at a growth rate as high as 40$\mu\textrm{m}$/h over a substrate area of $\Phi$65 mm. The 100kW high power Jet which is newly developed based on the experience of the low power model is equipped with a $\Phi$120 mm orifice torch, and is capable of depositing diamond films over a substrate area of $\Phi$110 mm at growth rate as high as 40 $\mu\textrm{m}$/h, and can be operated at gas recycling mode, which allows 95% of the gases be recycled. It is demonstrated that the new type DC plasma torch can be easily scaled up to even higher power Jet. It is estimated that even by the 100kW Jet, the cost for tool grade diamond films can be as low as less than $4/carat.
Tokamak plasma disruption precursor onset time study based on semi-supervised anomaly detection
X.K. Ai,W. Zheng,M. Zhang,D.L. Chen,C.S. Shen,B.H. Guo,B.J. Xiao,Y. Zhong,N.C. Wang,Z.J. Yang,Z.P. Chen,Z.Y. Chen,Y.H. Ding,Y. Pan Korean Nuclear Society 2024 Nuclear Engineering and Technology Vol.56 No.4
Plasma disruption in tokamak experiments is a challenging issue that causes damage to the device. Reliable prediction methods are needed, but the lack of full understanding of plasma disruption limits the effectiveness of physics-driven methods. Data-driven methods based on supervised learning are commonly used, and they rely on labelled training data. However, manual labelling of disruption precursors is a time-consuming and challenging task, as some precursors are difficult to accurately identify. The mainstream labelling methods assume that the precursor onset occurs at a fixed time before disruption, which leads to mislabeled samples and suboptimal prediction performance. In this paper, we present disruption prediction methods based on anomaly detection to address these issues, demonstrating good prediction performance on J-TEXT and EAST. By evaluating precursor onset times using different anomaly detection algorithms, it is found that labelling methods can be improved since the onset times of different shots are not necessarily the same. The study optimizes precursor labelling using the onset times inferred by the anomaly detection predictor and test the optimized labels on supervised learning disruption predictors. The results on J-TEXT and EAST show that the models trained on the optimized labels outperform those trained on fixed onset time labels.
Effects of sintering atmosphere on the superconductivity of MgB<sub>2</sub>
Zhou, S,Zhang, Y,Pan, A V,Dou, S X,Chung, K C,Kim, Y K,Yoo, J M IOP Publishing Ltd 2009 Superconductor science & technology Vol.22 No.4
<P>Pure MgB<SUB>2</SUB> bulk samples were sintered in different atmospheres: high purity Ar, high purity Ar with 0.01<I>% </I>O<SUB>2</SUB>, high purity Ar with 0.03<I>% </I>O<SUB>2</SUB> and high purity Ar with 5<I>% </I>H<SUB>2</SUB>. The superconductivity and microstructure of these samples were studied. It was found that in the range of this study the impurity gas in Ar had strong effects on aspects of the superconductivity such as critical current density, <I>J</I><SUB>c</SUB>, the irreversibility field, <I>H</I><SUB>irr</SUB>, and the upper critical field <I>H</I><SUB>c2</SUB>. When the samples were sintered in Ar with O<SUB>2</SUB> impurity, their low field <I>J</I><SUB>c</SUB> decreased as the O<SUB>2</SUB> content increased. The high field <I>J</I><SUB>c</SUB>, in contrast, was improved as the concentration of the O<SUB>2</SUB> impurity increased. For the sample sintered in Ar with H<SUB>2</SUB> impurity, its <I>J</I><SUB>c</SUB> is significantly higher than that of the sample sintered in high purity Ar. The smaller grain size and crystallinity degradation caused by the impure atmosphere is proposed to be the reason for the <I>J</I><SUB>c</SUB> improvement in both the O<SUB>2</SUB> and the H<SUB>2</SUB> added to the Ar gas sintering cases. </P>
Zhang, Y.,Jia, R.X.,Pan, M.H.,Lu, Y.,Cui, X.S.,Kim, N.H.,Sun, S.C. Butterworths, etc 2017 Theriogenology Vol. No.
T-2 toxin is a type A mycotoxin produced by various Fusarium species, while HT-2 toxin is a major metabolite of T-2 toxin. Both T-2 toxin and HT-2 toxin are known to have deleterious effects on animals. Our previous work showed that HT-2 treatment caused the failure of porcine oocyte maturation. In this study, we reported that HT-2 also affected porcine embryo development. In HT-2 toxin treated group, all the percentages of embryos in 2-cell, 4-cell and blastocyst stage were significantly lower compared with those in control groups. We then explored the causes from the epigenetic modification aspect of the oocytes. The analysis of fluorescence intensity showed that 5-methyl cytosine (5 mC) level was increased after exposure to HT-2 toxin in porcine oocytes, indicating that the general DNA methylation level increased in the treated porcine oocytes. In addition, histone modifications were also affected, since our results showed that H3K4me2 and H3K9me2 levels were increased in the oocytes from HT-2-treated group. Therefore, our results indicated that HT-2 toxin decreased porcine embryo developmental competence through altering the epigenetic modifications of oocytes.
Passive Q-switching of microchip lasers based on Ho:YAG ceramics
Lan, R.,Loiko, P.,Mateos, X.,Wang, Y.,Li, J.,Pan, Y.,Choi, S. Y.,Kim, M. H.,Rotermund, F.,Yasukevich, A.,Yumashev, K.,Griebner, U.,Petrov, V. Optical Society of America 2016 Applied Optics Vol.55 No.18
<P>A Ho:YAG ceramic microchip laser pumped by a Tm fiber laser at 1910 nm is passively Q-switched by single-and multi-layer graphene, single-walled carbon nanotubes (SWCNTs), and Cr2+:ZnSe saturable absorbers (SAs). Employing SWCNTs, this laser generated an average power of 810 mW at 2090 nm with a slope efficiency of 68% and continuous wave to Q-switching conversion efficiency of 70%. The shortest pulse duration was 85 ns at a repetition rate of 165 kHz, and the pulse energy reached 4.9 mu J. The laser performance and pulse stability were superior compared to graphene SAs even for a different number of graphene layers (n = 1 to 4). A model for the description of the Ho:YAG laser Q-switched by carbon nanostructures is presented. This modeling allowed us to estimate the saturation intensity for multi-layered graphene and SWCNT SAs to be 1.2 +/- 0.2 and 7 +/- 1 MW/cm(2), respectively. When using Cr2+:ZnSe, the Ho:YAG microchip laser generated 11 ns/25 mu J pulses at a repetition rate of 14.8 kHz. (C) 2016 Optical Society of America</P>