Coercivity Enhancement in Nd<SUB>2</SUB>Fe<SUB>14</SUB>B Permanent Magnetic Powders through Rotating Diffusion Process with DyHx Powders

Moonhee Choi,Jihun Yu,Donghwan Kim,Inbae Kim,Yangdo Kim 한국자기학회 2011 Journal of Magnetics Vol.16 No.4

Nd2Fe14B permanent magnetic powders (iHc = 9.2 kOe, Br = 12.2 kG) were produced by HDDR process. Their coercivity was enhanced to 12.6 kOe through the grain boundary diffusion process with dysprosium hydride (DyHX). DyHX diffusion process was optimized through rotating diffusion process, resulting in distinct phases rich in Nd and Dy observable by field emission scanning microscopy and transmission electron microscopy. The mechanism of coercivity enhancement that resulted in restrain the coupling effect between Nd2Fe14B grains is also discussed.

Simultaneous enhancement in coercivity and remanence of Nd₂Fe₁₄B permanent magnet by grain boundary diffusion process using NdH_x

Choi, Moonhee,Cho, Seungchan,Song, Yeonghwan,Park, Sungkyun,Kim, Yangdo Elsevier 2015 CURRENT APPLIED PHYSICS Vol.15 No.4

<P><B>Abstract</B></P> <P>We have successfully developed a Dy-free grain boundary diffusion process with neodymium hydride (NdH<SUB>x</SUB>) alloy to the permanent magnet Nd<SUB>2</SUB>Fe<SUB>14</SUB>B powders using hydrogenation – disproportionation – desorption – recombination (HDDR) method. All the diffusion treatments were performed at 700–800 °C for various annealing time under the high vacuum with rotating diffusion method that effectively control the abnormal grain growth. The coercivities of Dy-treated Nd<SUB>2</SUB>Fe<SUB>14</SUB>B powders were varied from 9.5 kOe to 13.2 kOe but the remanence was decreased to 8.1 kG (10% reduction) depending on dysprosium hydride (DyH<SUB>x</SUB>) content and diffusion treated time. However, the coercivity and remanence of Dy-free diffusion treated powder have been increased to 12.2 kOe (28.5% enhancement) and 11.1 kG (22% enhancement) at the optimal diffusion treatment (800 °C for 3 h), respectively. This unique simultaneous enhancement is to isolate the magnetic coupling between Nd<SUB>2</SUB>Fe<SUB>14</SUB>B grains by creating non-magnetic Nd grain boundaries and enhance the alignment of the Nd<SUB>2</SUB>Fe<SUB>1</SUB>4B hard magnetic phase, fabricated by optimal diffusion conditions.</P>

Emergency Environmental Monitoring for the Decision-Aiding on Public Protective Actions during a Nuclear Accident

Yongho Choi,Geunsik Choi,Moonhee Han,Hansoo Lee,Changwoo Lee 대한방사선방어학회 2005 방사선방어학회지 Vol.30 No.2

주식회사의 법인격의 별개성 再論-"에버랜드 판결"에 대한 비판적 고찰을 통하여

崔文僖(Choi, MoonHee) 한양법학회 2009 漢陽法學 Vol.28 No.-

This paper deals with the distinct legal personality of the corporation through reviewing several Korean corporate law cases. Among them, I focus on the recent “Everland Convertible Bond Case”, in which the managers issued new convertible bonds(hereinafter “CBs”)to the controlling shareholder for less than fair market value. The Korean Supreme Court(hereinafter “KSC”) held that the defendant-corporate directors had not breached their fiduciary duties in issuing new CBs for less than fair market value. The core question is whether corporation or its shareholders suffer damages by issuing CBs to the non-shareholders at a discount. The KSC concluded that both corporation and its shareholders received the damages. This paper argues that the KSC’s conclusion should be subject to the close theoretical examination. Moreover, this paper deals with what the KSC’s decision means. One of the basic legal characteristics of the corporation is legal personality. The corporation as a distinct legal person serves as a single contracting party that is distinct from its owners, shareholders. This paper argues that the KSC overemphasizes on the distinct legal personality of corporation, and ignores that the profit and loss of corporation ultimately belong to its shareholders. The corporation has assets that are distinct from other assets owned by its shareholders. It does not mean shareholders are not the ultimate owners of the corporation.

타액 중 Δ9-Tetrahydrocannabinol 및 11-Nor-9-carboxy-Δ9-Tetrahydrocannabinol의 분석법 확립 및 안정성 검토

최혜영(Hyeyoung Choi),백승경(Seungkyung Baeck),장문희(Moonhee Jang),최화경(Hwakyung Choi),정희선(Heesun Chung) 대한약학회 2010 약학회지 Vol.54 No.4

Oral fluid has become increasingly popular as an alternative specimen in the field of driving under the influence of drugs (DUID) and work place drug testing. In this study, an analytical method for the detection and quantification of Δ9-tetrahydrocannabinol (THC) and its metabolite, 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THC-COOH) in oral fluid by SPE and GC-MS was established and fully validated. The stability of THC and THC-COOH in oral fluid during storage was also determined by examining the THC and THC-COOH concentration changes depending on time and container materials. Oral fluid samples were kept over 21 days at room temperature, -4oC and -20oC in two different specimen collection tubes; glass and polypropylene tubes. Three replicates for each condition with different temperature and types of a container were analyzed at five different time points over 21 days. When oral fluid samples were stored in glass tubes, the loss of both THC and THC-COOH was less than 10% at all room temperature, -4oC and -20oC. However, in polypropylene tubes, the loss of both THC and THC-COOH increased significantly over the study period. In particular, the concentration of THC decreased more rapidly than that of THC-COOH at room temperature and the maximal percentage of THC lost was 90.3% after 21 days. The result indicates that it would be necessary to collect oral fluid samples in glass containers and cool the samples until analysis in order to prevent the degradation of analytes.

Effects of mirror polishing brick surface on process yield of multi-wire slicing for thin single-crystalline silicon solar cells

Choi, Sunho,Jang, Boyun,Kim, Joonsoo,Song, Heeun,Baek, Taehyeon,Han, Moonhee Elsevier 2015 SOLAR ENERGY -PHOENIX ARIZONA THEN NEW YORK- Vol.122 No.-

<P><B>Abstract</B></P> <P>Thin silicon (Si) wafers with thickness of 100–140μm were obtained by using a multi-wire slicing process with a SiC slurry. We investigated the process yields of wafer slicing as well as physical/electrical properties of the sliced wafers with various thicknesses. As the wafer thickness decreases, the process yield abruptly decreased due to wafer breakage during the slicing process, and conventional polishing the brick surface was not enough to gain a considerable process yield. However, elimination of defects on the brick surface by mirror polishing resulted in an 83.1% enhancement of yield even for wafers with a thickness of 100μm. The number of wafers obtained was even higher than that of conventional 180μm-thick wafers (479 vs. 415 wafers in this research). Investigation of the microstructure of brick surfaces revealed that surface defects on bricks were main parameter to determine the yield of slicing process. Surface defects containing the micro-cracks introduced residual stress, which decreased the slicing process yield especially for thinner wafers. From measurements of physical and electrical properties, it was revealed that the relative total thickness variations (TTVs) and bowings increased and the characteristic fracture strength of sliced wafer and conversion efficiencies decreased as the wafer thickness decreased. For the wafer with thickness of 100μm, the relative TTV and bowing were 14.1% and 22.5mm, respectively. The conversion efficiency of a solar cell using this wafer was 17.6%, while that of a conventional Si solar cell using a 180μm-thick wafer was 18.4%.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Thin silicon wafers with thickness of 100–140μm were sliced by multi-wire slicing. </LI> <LI> Physical and electrical properties of thin Si wafers were investigated. </LI> <LI> Subsurface defects of the brick surface critically determined process yield in slicing Si wafers. </LI> </UL> </P>

Determination of AM-2201 metabolites in urine and comparison with JWH-018 abuse

Jang, Moonhee,Yang, Wonkyung,Shin, Ilchung,Choi, Hyeyoung,Chang, Hyejin,Kim, Eunmi Springer-Verlag 2014 International journal of legal medicine Vol.128 No.2

Simultaneous determination of methylphenidate and ritalinic acid in hair using LC<b>–</b>MS<b>/</b>MS

Jang, Moonhee,Kim, Jihyun,Shin, Ilchung,Kang, Seojin,Choi, Hyeyoung,Yang, Wonkyung Elsevier 2019 Forensic Science International Vol.294 No.-

<P><B>Abstract</B></P> <P>Methylphenidate (MPH) is one of the most commonly prescribed stimulants for attention deficit hyperactivity disorder and its abuse is on the rise with its growing availability. Some analytical methods have been reported for the detection of MPH in hair. However, the concentration range of MPH as well as its metabolite, ritalinic acid (RA) in the hair of MPH abuse cases has not been reported. In this study, a sensitive and reliable liquid chromatography-tandem mass spectrometry method was developed and validated for the simultaneous determination of MPH and RA in hair. Sample preparation was carried out by a simple methanol extraction using 10mg of hair. Limits of detection for MPH and RA in hair were 0.5pg/mg and 1pg/mg, respectively, and the limits of quantification (LOQs) were 1pg/mg for both the analytes. Validation results showed good linearity in the range of 1–100pg/mg with acceptable precision and accuracy. The developed method was applied to real hair samples obtained from ten drug users who obtained MPH illegally without a prescription. MPH concentrations in the hair samples ranged from 1.0pg/mg to 265.0pg/mg, and RA was present at concentrations <LOQ–76.3pg/mg. In this study, hair analysis and background findings revealed that most subjects have abused illicit substances (methamphetamine, Δ<SUP>9</SUP>-tetrahydrocannabinol, zolpidem etc.) other than MPH. The low picogram range of LODs for MPH and RA in hair was achieved with the present method and the results from real sample analysis would provide useful information related to MPH abuse under forensic settings.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An LC–MS/MS method was developed to document methylphenidate use in hair specimens. </LI> <LI> Target analytes were methylphenidate and its metabolite, ritalinic acid. </LI> <LI> A simple sample preparation was carried out with a small amount of sample. </LI> <LI> The method was successfully applied to authentic hair samples from methylphenidate abuse cases. </LI> </UL> </P> <P><B>Graphical Abstract</B></P> <P>[DISPLAY OMISSION]</P>

Electric Field-Enhanced Fabrication of Densified Single-Walled Carbon Nanotube Films

Hee-Young Choi,이해원,주재범,Moonhee Lee,김성경 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.I

The fabrication of single-walled carbon nanotube (SWNT) films on a chemically modified substrate was investigated. Two techniques, chemical self-assembly and an electrodeposition, were used to develop SWNT films on templates. The number of SWNTs deposited on substrates by electrodeposition was higher than that observed using the chemical self-assembly method. The electrodeposited SWNT films demonstrated strong interfacial contact between SWNTs and substrates. The density of SWNTs attached to substrates was shown to be increased dramatically by the application of an external electric field.

0.6~6 GHz 초 광대역 쿼드릿지 혼 안테나 설계

최철진(Cheoljin Choi),이문희(Moonhee Lee),손태호(Taeho Son) 대한전기학회 2019 전기학회논문지 Vol.68 No.1

In this paper, a 0.6∼6GHz quad-ridge horn antenna which can be used for the antenna measurement of 5.8GHz WiFi system from lowest frequency band of mobile LTE (Long Term Evolution) is designed and implemented. The quad-ridge horn antenna has quadruple ridges of exponential function, a back-short and a cavity. Based on this structure, we design the cavity size, ridge gap and feed gap to have broadband characteristics. For implementation, the plates material of aluminum and copper are used for the horn and four ridges, respectively. And the insulator supports are used to maintain the gap between ridges. By measurement, antenna has the gain of 6.2~13.35dBi with the return loss of less than –6dB (under VSWR 3 : 1) in the entire design band. The results of this study can be widely used to the antenna studies on the mobile communication including low frequency band of LTE, the EMI measurement and the standard calibration measurement.