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Han‑Wool Jang,Seon Yeong Lee,Jong Yoon Lee,Han‑Ik Joh 한국탄소학회 2023 Carbon Letters Vol.33 No.1
Ammonia is considered a promising hydrogen carrier due to its high hydrogen density and liquefaction temperature. Considering that the energy efficiency generally decreases as chemical conversion is repeated, it is more efficient to directly use ammonia as a fuel for fuel cells. However, catalysts in direct ammonia fuel cells have the critical issues of sluggish ammonia oxidation reaction (AOR) rate and poisoning of reaction intermediates. In particular, the use of precious metal as cathodic catalysts has been limited due to ammonia crossover and poisoning. In this study, we introduce Fe-based single-atom catalysts with selective activity for the oxygen reduction reaction (ORR) even in the presence of ammonia. As the Fe content increased, the single-atom structure of the catalysts changed into Fe nanoparticles or carbides. Among our Fe–N–C catalysts, FeNC-50 with a Fe loading amount of 0.34 wt% showed the highest ORR performance regardless of the ammonia concentration. In particular, the difference in activity between the catalysts increased as the concentration increased. The FeNC-50 catalyst showed remarkable stability after 1000 cycles. Therefore, we believe that single-atom dispersion is an important factor in the development of stable non-precious catalysts with high activity and inactivity for the ORR and AOR, respectively.
Hyperarousal-state of Insomnia Disorder in Wake-resting State Quantitative Electroencephalography
Gyutae Jang,Han Wool Jung,Jiheon Kim,Hansol Kim,Ji‑Hyeon Shin,Chan-Hyung Kim,Do-Hoon Kim,Sang-Kyu Lee,Daeyoung Roh 대한정신약물학회 2024 CLINICAL PSYCHOPHARMACOLOGY AND NEUROSCIENCE Vol.22 No.1
Objective: Insomnia is associated with elevated high-frequency electroencephalogram power in the waking state. Although affective symptoms (e.g., depression and anxiety) are commonly comorbid with insomnia, few reports distinguished objective sleep disturbance from affective symptoms. In this study, we investigated whether daytime electroencephalographic activity explains insomnia, even after controlling for the effects of affective symptoms. Methods: A total of 107 participants were divided into the insomnia disorder (n = 58) and healthy control (n = 49) groups using the Mini-International Neuropsychiatric Interview and diagnostic criteria for insomnia disorder. The participants underwent daytime resting-state electroencephalography sessions (64 channels, eye-closed). Results: The insomnia group showed higher levels of anxiety, depression, and insomnia than the healthy group, as well as increased beta [t (105) = −2.56, p = 0.012] and gamma [t (105) = −2.44, p = 0.016] spectra. Among all participants, insomnia symptoms positively correlated with the intensity of beta (r = 0.28, p < 0.01) and gamma (r = 0.25, p < 0.05) spectra. Through hierarchical multiple regression, the beta power showed the additional ability to predict insomnia symptoms beyond the effect of anxiety (ΔR2 = 0.041, p = 0.018). Conclusion: Our results showed a significant relationship between beta electroencephalographic activity and insomnia symptoms, after adjusting for other clinical correlates, and serve as further evidence for the hyperarousal theory of insomnia. Moreover, resting-state quantitative electroencephalography may be a supplementary tool to assess insomnia.
이선영,이종윤,Han-Wool Jang,U Hyeok Son,Sungho Lee,조한익 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.117 No.-
FeANAC catalysts have attracted attention because of their superior oxygen reduction reaction (ORR)performance in alkaline media. However, there is a conflict between the active sites of FeANAC catalysts,namely single-atomic Fe–Nx sites and dual active sites consisting of atomic sites/iron carbide nanoparticles. Herein, we synthesized catalysts with different types of active sites by controlling the facile agingprocess. The main active sites varied from single active sites to dual active sites when the aging timeand Fe content was decreased and increased. A catalyst with 0.6 wt% Fe that is aged for 24 h(FeNC-24–0.6) has dual active sites, whereas a catalyst with 0.9 wt% Fe that is aged for 48 h(FeNC-48–0.9) consists mainly of single active sites. The catalysts showed outstanding ORR activity,exceeding the half-wave potential of the commercial 20 wt% Pt/C catalysts by 11 mV. Interestingly,the FeNC-48–0.9 catalyst exhibited a rare negative shift compared to the FeNC-24–0.6 catalyst in thedurability tests. Therefore, it is believed that increasing the number of single-atomic Fe–Nx sites is aneffective approach to enhance the ORR performance of FeANAC catalyst in alkaline media.
Lee Seon Yeong,Jang Han Wool,Lee Hae Ri,Joh Han-Ik 한국탄소학회 2021 Carbon Letters Vol.31 No.6
Metal–organic frameworks (MOFs) are widely used as supports for single-atom catalysts (SACs) owing to their high specifc surface area, porosity, and ordered metal–ligand structure. Their activity can be increased by increasing the number of electrochemically accessible active sites via the formation of atomically dispersed metal catalysts (M–Nx) that coordinate with nitrogen atoms on the MOF. Herein, we introduce the relationship between the size of the MOF as a starting material and the catalytic activity for the oxygen reduction reaction in alkaline media. The morphology and features of the MOFs are critically dependent on their size. Remarkably, cage-like MOFs below 33 nm are converted into collapsed structures and are connected between each MOF, even carbon fber- or tube-like features, after carbonization. SACs derived from medium-sized MOFs exhibit excellent activity and are comparable to commercial Pt/C catalysts owing to their porous structure. Therefore, we believed that controlling the size of MOFs containing active atoms is an efective method of modulating the morphological properties of the support and even the number of active sites that are closely related to the activity.
Novel Composite Scaffolds for Tooth Regeneration using Human Dental Pulp Stem Cells
( Ki Taek Lim ),( Han Wool Choung ),( Ae Lee Im ),( Jang Ho Kim ),( Chong Su Cho ),( Yun Hoon Choung ),( Soung Hoo Jeon ),( Pill Hoon Choung ),( Jong Hoon Chung ) 한국조직공학과 재생의학회 2010 조직공학과 재생의학 Vol.7 No.5
In this study, the properties and biocompatibilities of composite scaffolds were investigated to develop an appropriate scaffold for dental tissue regeneration using human dental pulp stem cells. Composite scaffolds consisted of poly-D,L-lactic acid (P(D,L)LA) and bioceramic materials of tooth powders fabricated using sintered teeth. Highly porous composite bioceramic scaffolds promoted biocompatibility and had the interconnected pores that could adequately support cell adhesion and proliferation. Also, we investigated the properties and biocompatibilities of composite scaffolds prepared by a solvent casting/particulate leaching method and a gas forming method. We prepared the composite ceramic scaffold using toothapatites obtained from extracted teeth, and assessed the biocompatibility of the composite scaffolds by the two methods in order to find out the most appropriate scaffolds for tooth regeneration. The human dental pulp stem cells seeded on the composite scaffolds were easily attached and well proliferated as confirmed by a cytotoxicity test, cell adhesion assessment and histological study. Through experimental results, composite bone scaffolds were able to be proven as appropriate scaffolds for dental tissue regeneration using human dental pulp stem cells.
( Hong Sik Choi ),( Ki Taek Lim ),( Jang Ho Kim ),( Joo Young Park ),( Soung Hoo Jeon ),( Han Wool Choung ),( Chong Su Cho ),( Yun Hoon Choung ),( Pill Hoon Choung ),( Jong Hoon Chung ) 한국조직공학·재생의학회 2010 조직공학과 재생의학 Vol.7 No.5
In this study two types of scaffolds which have taken the merits of polymer and bioceramics were prepared, and in vitro and in vivo effects of the novel degradable polymer-bioceramic scaffolds seeded with human dental pulp stem cells (hDPSCs) were investigated. Three elements were considered for the scaffolds; poly-DL-lactide (PDLLA), as degradable polymer, and tooth apatite (TA) and β-tricalciumphosphate (TCP) as degradable bioceramics. The first scaffold consists of PDLLA exclusively, the second of PDLLA and TA (1:1) and the third of PDLLA, TA and TCP (1:1:1). The scaffolds were compared with each other in vitro and in vivo using hDPSCs as their cell source. hDPSCs were isolated from extracted third molars, cultured, attached, proliferated and differentiated prior to the in vitro and in vivo experiments. Scanning electron microscope observation was carried out to reveal the attachment and growth of hDPSCs on the surfaces of three scaffolds, and the quantitative assay of cell proliferation was also detected. It was shown that hDPSCs attached and spread further in the polymer-bioceramic groups (PDLLA/TA/TCP and PDLLA/TA) compared to the polymer group (PDLLA), and there was also less inflammatory reaction in the polymer-bioceramic scaffolds, transplanted subcutaneously in the dorsal area of immunocompromised mice. In addition, the polymer-bioceramic groups (PDLLA/TA/TCP, PDLLA/TA) showed intensive cementum- like mineralization in vivo. Thus, it could be concluded that the polymer-bioceramic groups might serve as novel potential scaffolds for tooth bioengineering.
동적인 전기장이 다마신 구리 배선에서의 절연파괴에 미치는 영향
연한울,송준영,임승민,배장용,황유철,주영창,Yeon, Han-Wool,Song, Jun-Young,Lim, Seung-Min,Bae, Jang-Yong,Hwang, Yuchul,Joo, Young-Chang 한국마이크로전자및패키징학회 2014 마이크로전자 및 패키징학회지 Vol.21 No.4
다마신 구리 배선에서의 동적인 전기장에 따른 절연체 파괴거동을 연구하였다. DC, 단극성, 및 이극성 펄스 조건 중에서 절연체의 수명은 이극성 펄스 조건에서 가장 길었다. DC 및 단극성 펄스 조건에서는 절연체에 가해지는 전기장의 방향이 바뀌지 않지만 이극성 펄스 조건에서는 전기장의 방향이 반복적으로 180도 바뀌기 때문에, 이극성 펄스 조건에서는 절연체의 구리오염이 억제되고, 이로 인해서 절연체 수명이 이극성 펄스 조건에서 가장 긴 것으로 판단된다. 단극성 펄스 조건에서 펄스 주파수가 커질수록 DC 조건보다 절연체의 수명이 증가하였다. 이는 절연체 수명에 구리오염 뿐만 아니라 내재적인 절연파괴현상이 상당한 영향을 미치며, 절연체 분자결합파괴가 일어날 확률은 펄스 폭이 좁아질수록 감소한다고 판단된다. Effect of dynamic electric fields on dielectric breakdown behavior in Cu damascene interconnects was investigated. Among the DC, unipolar, and bipolar pulse conditions, the longest dielectric lifetime is observed under the bipolar condition because backward Cu ion drift occurs when the direction of electric field is changed by 180 degrees and Cu contamination is prohibited as a results. Under the unipolar pulse condition, the dielectric lifetime increases as pulse frequency increases and it exceed the lifetime under DC condition. It suggests that the intrinsic breakdown of dielectrics significantly affect the dielectric breakdown in addition to Cu contamination. As the unipolar pulse width decreases, dielectric bond breakdown is more difficult to occur.