Neurological Complications Resulting from Non-Oral Occupational Methanol Poisoning

Choi, Ji-Hyun,Lee, Seung Keun,Gil, Young-Eun,Ryu, Jia,Jung-Choi, Kyunghee,Kim, Hyunjoo,Choi, Jun Young,Park, Sun Ah,Lee, Hyang Woon,Yun, Ji Young The Korean Academy of Medical Sciences 2017 JOURNAL OF KOREAN MEDICAL SCIENCE Vol.32 No.2

<P>Methanol poisoning results in neurological complications including visual disturbances, bilateral putaminal hemorrhagic necrosis, parkinsonism, cerebral edema, coma, or seizures. Almost all reported cases of methanol poisoning are caused by oral ingestion of methanol. However, recently there was an outbreak of methanol poisoning via non-oral exposure that resulted in severe neurological complications to a few workers at industrial sites in Korea. We present 3 patients who had severe neurological complications resulting from non-oral occupational methanol poisoning. Even though initial metabolic acidosis and mental changes were improved with hemodialysis, all of the 3 patients presented optic atrophy and ataxia or parkinsonism as neurological complications resulting from methanol poisoning. In order to manage it adequately, as well as to prevent it, physicians should recognize that methanol poisoning by non-oral exposure can cause neurologic complications.</P>

Assessment of radiofrequency electromagnetic field exposure from personal measurements considering the body shadowing effect in Korean children and parents

Choi, Jonghyuk,Hwang, Jung-Hwan,Lim, Hyungrul,Joo, Hyunjoo,Yang, Hee-Sun,Lee, Yong-Han,Eeftens, Marloes,Struchen, Benjamin,Rö,ö,sli, Martin,Lee, Ae-Kyoung,Choi, Hyung-Do,Kwon, Jong Hwa,Ha, Min Elsevier 2018 The Science of the total environment Vol.627 No.-

<P><B>Abstract</B></P> <P>We aimed to assess the personal radiofrequency electromagnetic field (RF-EMF) exposure levels of children and adults through their activities, with consideration to the body shadowing effect. We recruited 50 child-adult pairs, living in Seoul, Cheonan, and Ulsan, South Korea. RF-EMF measurements were performed between September and December 2016, using a portable exposure meter tailored to capture 14 Korean radiofrequency (RF) bands ranging from 87.5 to 5875MHz. The participants carried the device for 48h and kept a time-activity diary using a smartphone application in flight mode. To enhance accuracy of the exposure assessment, the body shadowing effect was compensated during the statistical analysis with the measured RF-EMF exposure. The compensation was conducted using the hybrid model that represents the decrease of the exposure level due to the body shadowing effect. A generalized linear mixed model was used to compare the RF-EMF exposure levels by subjects and activities. The arithmetic (geometric) means of the total power density were 174.9 (36.6) μW/m<SUP>2</SUP> for all participants, 226.9 (44.6) for fathers, 245.4 (44.8) for mothers, and 116.2 (30.1) for children. By compensating for the body shadowing effect, the total RF-EMF exposure increased marginally, approximately 1.4 times. Each frequency band contribution to total RF-EMF exposure consisted of 76.7%, 2.4%, 9.9%, 5.0%, 3.3%, and 2.6% for downlink, uplink, WiFi, FM Radio, TV, and WiBro bands, respectively. Among the three regions, total RF-EMF exposure was highest in Seoul, and among the activities, it was highest in the metro, followed by foot/bicycle, bus/car, and outside. The contribution of base-station exposure to total RF-EMF exposure was the highest both in parents and children. Total and base-station RF-EMF exposure levels in Korea were higher than those reported in European countries.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Base-station RF exposure is major contribution in Korea. </LI> <LI> Total and base-station RF exposure levels in Korea were higher than those reported in European countries and Australia. </LI> <LI> Personal RF-EMF exposure depends on environments and behavioral pattern. </LI> <LI> Reading values at the personal exposure meter are affected by a human body. </LI> <LI> Body shadowing compensated the total RF-EMF by 1.4 times. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Performance of HFC32/HFC152a Mixture for Water-source Heat pumps

Hyunjoo Choi,Donggyu Kang,Yohan Lee,Dongsoo Jung 한국해양환경·에너지학회 2012 한국해양환경공학회 학술대회논문집 Vol.2012 No.11

Mechanical properties of aluminum-based nanocomposite reinforced with fullerenes

CHOI, Kwangmin,SEO, Jiyeon,BAE, Donghyun,CHOI, Hyunjoo Elsevier 2014 Transactions of Nonferrous Metals Society of China Vol.24 No.suppl1

Relationships among the Performances of Naming, Discourse Production and IADL in Amnestic MCI

Hyunjoo Choi(최현주) 한국언어청각임상학회 2019 Communication Sciences and Disorders Vol.24 No.3

배경 및 목적: 도구적 일상생활 능력(instrumental ability of daily living, IADL)의 제한은 치매 발병 이전 단계인 경도인지장애(mild cognitive impairment, MCI) 환자에게도 나타나는 것으로 알려져 있다. 본 연구에서는 알츠하이머형 치매로 발전할 가능성이 높은 기억상실형 MCI (amnestic MCI, aMCI) 환자의 이름대기 및 담화산출 능력과 IADL 사이의 관련성을 살펴보았다. 방법: 본 연구는 aMCI 환자 50명을 대상으로 하였다. 이름대기 능력은 대면이름대기(Korean-Boston Naming Test, K-BNT)와 구어유창성 검사(의미, 음운)를 사용하였으며, 담화산출 능력은 그림설명을 통한 CIU (correct information unit) 비율로 측정하였다. IADL은 한국판 Lawton IADL검사를 사용하여 평가하였다. 결과: 첫째, aMCI 환자의 IADL은 연령 및 교육년수와는 유의한 상관이 나타나지 않았으며, 한국판 간이정신상태검사(Korean version of Mini-Mental Examination) 점수와 IADL 사이에는 유의한 상관이 있었다. 둘째, aMCI 환자의 IADL은 K-BNT 및 음운적 구어유창성 과제의 수행과는 유의한 상관이 나타나지 않았으나, 의미적 구어유창성 과제의 수행과 CIU 비율과는 유의한 상관을 보였다. 셋째, 회귀분석 결과 의미적 구어유창성 과제의 수행과 CIU 비율은 aMCI 환자의 IALD에 영향을 미치는 것으로 나타났다. 논의 및 결론: 이러한 결과는 aMCI 환자의 의미적 구어유창성 및 담화산출 능력과 IADL 사이에 관련성이 있음을 시사한다. Objectives: The limitations of the Instrumental Ability of Daily Living (IADL) are known to appear not only in patients with dementia of Alzheimer’s type, but also in patients with amnestic mild cognitive impairment (aMCI). The purpose of this study was to investigate the relationship between IADL and the ability of naming and discourse production in patients with aMCI. Methods: Fifty patients with aMCI participated in this study. The naming tests included confrontational naming (Korean version of Boston Naming Test [K-BNT]) and verbal fluency (semantics & phonemics). Discourse samples were collected from picture description tasks. IADL was assessed using the Korean version Lawton IADL test. Results: First, performances of IADL in patients with aMCI were not significantly correlated with age and education level. However, there was a significant correlation between the Korean version of the Mini-Mental Examination (K-MMSE) score and IADL. Second, performances of IADL in patients with aMCI were not significantly correlated with the performances of the K-BNT and phonemic fluency task. However, the performance of the semantic fluency task and correct information unit (CIU) ratio showed a significant correlation with IADL in patients with aMCI. Third, regression analysis revealed that the performance of the semantic fluency task and the CIU ratio affected the IALD of patients with aMCI. Conclusion: These results suggest that there is a relationship between performances of semantic fluency, discourse production and IADL in patients with aMCI.

Reinforcing effects of carbon nanotubes in structural aluminum matrix nanocomposites

Choi, Hyunjoo,Shin, Jaehyuck,Min, Byungho,Park, Junsik,Bae, Donghyun Cambridge University Press (Materials Research Soc 2009 Journal of materials research Vol.24 No.8

<P>The reinforcing effects of carbon nanotubes (CNTs) are investigated for aluminum matrix composites. The composites present a strong bonding between CNTs and the aluminum matrix using a controlled mechanical milling process, producing a network structure of aluminum atoms around CNTs. At the same time, CNTs that are dispersed during the milling process can be located inside aluminum powders, thereby providing an easy consolidation route via thermomechanical processes. A composite containing 4.5 vol% multiwalled CNTs exhibits a yield strength of 620 MPa and fracture toughness of 61 MPa·mm<SUP>1/2</SUP>, the values of which are nearly 15 and seven times higher than those of the corresponding starting aluminum, respectively.</P>

Au-doped PtCo/C catalyst preventing Co leaching for proton exchange membrane fuel cells

Choi, Juhyuk,Cho, Jinwon,Roh, Chi-Woo,Kim, Beom-Sik,Choi, Min Suk,Jeong, Hojin,Ham, Hyung Chul,Lee, Hyunjoo Elsevier 2019 Applied catalysis. B, Environmental Vol.247 No.-

<P><B>Abstract</B></P> <P>Proton exchange membrane fuel cells (PEMFCs) are promising mobile power supply systems, and operate without noise or polluting emissions. Because the oxygen reduction reaction (ORR) at the cathode suffers from high overpotential and sluggish kinetics, many catalysts have been developed in efforts to enhance activity and durability for the ORR. However, most of them have complicated synthetic procedures which cannot be scaled-up easily, and have only been tested in a half-cell. High activity in a half-cell does not necessarily guarantee better performance in a single-cell. In this work, we synthesized an Au-doped PtCo/C catalyst using a simple method of gas-phase reduction and subsequent galvanic replacement, and its activity and durability were tested in a single-cell. When current densities were compared at 0.6 V after a durability test of 30,000 cycles in 0.6–1.0 V, the values were 1.40, 0.81, and 0.63 A cm<SUP>−2</SUP> for the Au-doped PtCo/C, acid-treated PtCo/C, and commercial Pt/C catalysts, respectively. Co leaching was much less in the Au-doped PtCo/C. Density functional theory (DFT) calculations confirmed that surface oxygen species bound more weakly at the catalyst surface and migration of a Co atom (Co segregation) to the surface was suppressed in the presence of Au. This facile method can provide a more realistic strategy to design better ORR catalysts for PEMFC application.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Au-doped PtCo/C catalyst was prepared by gas-phase reduction and subsequent galvanic replacement in a gram-scale. </LI> <LI> The Au-doped catalyst showed enhanced activity and durability for ORR in half-cell and single-cell tests. </LI> <LI> The maximum power density after durability tests was 1.12 W cm<SUP>−2</SUP> for Au-doped catalyst and 0.69 W cm<SUP>−2</SUP> for commercial Pt/C. </LI> <LI> DFT calculations confirmed that Co leaching could be suppressed by Au doping at Pt shell. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Ability of Sentence Comprehension according to Syntactic Complexity and Speech Rate in Patients with Dementia of Alzheimer’s Type

Hyunjoo Choi 한국언어청각임상학회 2019 Communication Sciences and Disorders Vol.24 No.3

배경 및 목적: 알츠하이머형 치매 환자의 문장이해 능력은 구문 복잡성에 영향을 받는 것으로 알려져 있으나, 느린 말속도에 의한 영향은 논쟁적이다. 본 연구는 알츠하이머형 치매 환자와 일반노인을 대상으로 구문 복잡성과 말속도에 따른 문장이해 수행 차이를 동시에 알아보는 것을 목적으로 하였다. 방법: 알츠하이머형 치매 환자 30명과 일반노인 30명이 본 연구에 참여하였다. 구문 복잡성에 따른 문장이해 능력은 토큰테스트를 사용하여 평가하였으며, 말속도는 Praat 프로그램을 이용하여 보통 말속도와 느린 말속도로 조정하였다. 결과: 첫째, 말속도와 관계없이 알츠하이머형 치매 환자 집단은 일반노인 집단에 비해 문장이해 능력이 저하되어 있었다. 둘째, 일반노인, 알츠하이머형 치매 환자 집단 모두 구문 복잡성이 증가할수록 문장이해 능력이 저하되었으며, 이러한 효과는 알츠하이머형 치매 환자에게서 더 두드러지게 나타났다. 셋째, 느린 말속도는 일반노인, 알츠하이머형 치매 환자 모두 문장이해 능력을 향상시키지 못했으며, 구문적으로 복잡한 문장에서의 느린 말속도는 문장이해 수행을 오히려 저하시켰다. 논의 및 결론: 이러한 연구결과를 통하여 알츠하이머형 치매 환자의 구문 복잡성에 따른 문장이해 능력의 저하 특성을 확인하였으며, 느린 말속도에 따른 문장이해 능력의 변화는 구문 복잡성에 따라 달라짐을 알 수 있다. Objectives: The ability of sentence comprehension in patients with dementia of Alzheimer’s type (DAT) is known to be influenced by syntactic complexity, but the effects of slow speech rate are controversial. The purpose of this study was to investigate the difference of sentence comprehension ability according to the syntactic complexity and slow speech rate in healthy elderly adults and patients with DAT. Methods: Thirty elderly adults and 30 patients with DAT participated in this study. Sentence comprehension ability according to syntactic complexity was evaluated by using a token test, and the speech rate was adjusted to normal speech rate and slow speech rate using the Praat program. Results: First, DAT patients had lower sentence comprehension than elderly adults in both speech rates. Second, as the syntactic complexity increased, the ability to comprehend sentences decreased in both elderly adults and patients with DAT, and this effect was more prominent in patients with DAT. Third, slow speech rate did not improve sentence comprehension ability in both elderly adults and patients with DAT, and slow speech rate in syntactically complex sentences decreased sentence comprehension ability. Conclusion: The results of this study confirmed the characteristics of the deficit the according to the syntactic complexity in patients with DAT, and the effect of sentence comprehension ability due to slow speech rate was different according to syntactic complexity.

Relationships among the Word-Finding Behaviors Ratio, Subjective Memory, and Objective Memory in Healthy Elderly Adults

Hyunjoo Choi 한국청각언어재활학회 2022 Audiology and Speech Research Vol.18 No.1

Purpose: The purpose of this study is to identify relationships among the word-finding behaviors ratio using discourse production task, subjective memory, and objective memory in healthy elderly adults. Methods: Ninety-five healthy elderly adults participated in this study. Participants were used to picture description tasks. To evaluate the subjective memory deficit of the elderly, Subjective Memory Complaints Questionnaire (SMCQ) was used, and to evaluate the objective memory deficit, the Seoul Verbal Learning Test (SVLT) was used. Results: First, the ratio of word-finding behaviors in the elderly appeared in the order of empty words, repetitions, insertions, time fillers, delays, word reformulations, and substitutions. Second, the SMCQ score, which evaluates subjective memory, showed a significant positive correlation with the ratio of global index, repetitions, and insertions. Third, the ratio of global index, repetitions, insertions, delays, and substitutions of word-finding behaviors were significantly correlated with the objective memory of the elderly. Finally, the most significant predictor variable in the global index ratio of word-finding behaviors of the elderly was the delayed recall score of SVLT. Conclusion: The results of this study suggested that the ratio of wordfinding behaviors by the spontaneous speech-based naming test is closely related to the subjective and objective memory in healthy elderly adults.

Word-Finding Behaviors of Discourse Production Task in Healthy Elderly Adults

Hyunjoo Choi 한국청각언어재활학회 2020 Audiology and Speech Research Vol.16 No.4

Purpose: The purpose of this study is to investigate whether there is a difference in word-finding behaviors in the discourse production task according to the age group of the elderly, from the young-old to the old-old. Methods: A total of 103 healthy elderly adults (55 to 85 years old) participated in this study. To exanimation of word-finding behaviors in the discourse, a picture description task was used. And, as the word naming task, the confrontational naming and the verbal fluency tasks were used. Results: First, according to the age group, the difference in the ratio of wordfinding behaviors were statistically significant. Especially, there were significant differences according to the age group of the elderly in word-finding behaviors of repetitions, empty words, insertions, and delays. Second, the difference in performances of word naming task (Korean version-Boston Naming Test and semantic verbal fluency) according to the age group of the elderly was found to be significant. Finally, the performance of the word naming task showed a significant correlation with the ratio of word-finding behaviors in the discourse production task. Conclusion: This study has clinical significance in that it analyzed various word-finding behaviors in a natural environment where the problem of naming appears in elderly adults.