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Lee, Seungchul,Song, Jaesun,Jo, Yong-Ryun,Choi, Kyoung Soon,Lee, Jongmin,Seo, Sehun,Kim, Taemin Ludvic,Jang, Ho Won,Jeon, Cheolho,Kim, Bong-Joong,Kim, Bongjae,Lee, Sanghan American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.47
<P>Nonequilibrium deposition is a remarkable method for the in situ growth of unique nanostructures and phases for the functionalization of thin films. We introduce a distinctive structure of a mixed-phase, composed of BiVO<SUB>4</SUB> and β-Bi<SUB>2</SUB>O<SUB>3</SUB>, for photoelectrochemical water splitting. The mixed-phase is fabricated via nonequilibrium deposition by adjusted oxygen partial pressure. According to density functional theory calculations, we find that vanadium exsolution can be facilitated by introducing oxygen vacancies, enabling the fabrication of a nanostructured mixed-phase. These unique structures enhance charge migration by increasing the interfacial area and properly aligning the band offset between two crystalline phases. Consequently, the photocurrent density of the nanostructured mixed-phase thin films is about twice that of pristine BiVO<SUB>4</SUB> thin films at 1.23 V<SUB>RHE</SUB>. Our work suggests that nonequilibrium deposition provides an innovative route for the structural engineering of photoelectrodes for the understanding of fundamental properties and improving the photocatalytic performance for solar water splitting.</P> [FIG OMISSION]</BR>
Changes in prevalence of Helicobacter pylori infection after subtotal gastrectomy.
Suh, Seungchul,Nah, Jong Chun,Uhm, Min Sik,Jung, Youn Mu,Kim, Nayoung,Lee, Dong Ho,Jung, Hyun Chae,Song, In Sung G. Thieme 2012 Hepato-gastroenterology Vol.59 No.114
<P>There have been few reports comparing pre and postoperative prevalence of Helicobacter pylori infection and gastritis in patients with gastric cancer surgery.</P>
Choi, Heechae,Song, Jin Dong,Lee, Kwang-Ryeol,Kim, Seungchul American Chemical Society 2015 Inorganic Chemistry Vol.54 No.8
<P>The visible-light absorption and luminescence of wide band gap (3.25 eV) strontium titanate (SrTiO3) are well-known, in many cases, to originate from the existence of natural oxygen deficiency in the material. In this study based on density functional theory (DFT) calculations, we provide, to the best of our knowledge, the first report indicating that oxygen vacancies in the bulk and on the surfaces of SrTiO3 (STO) play different roles in the optical and magnetic properties. We found that the doubly charged state of oxygen vacancy (V-O(2+)) is dominant in bulk SrTiO3 and does not contribute to the sub-band gap photoexcitation or intrinsic magnetism of STO. Neutral oxygen vacancies (V-O(0)) on (001) surfaces terminated with both TiO2 and SrO layers induce magnetic moments, which are dependent on the charged state of VO. The calculated absorption spectra for the (001) surfaces exhibit mid-infrared absorption (<0.5 eV) and sub-band gap absorption (2.5-3.1 eV) due to oxygen vacancies. In particular, V-O(0) on the TiO2-terminated surface has a relatively low formation energy and magnetic moments, which can explain the recently observed spin-dependent photon absorptions of STO in a magnetic circular dichroism measurement [Rice, W. D.; et al. Nat. Mater.13, 481, 2014].</P>
김태완(Taewan Kim),이승철(Seungchul Lee) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4
데이터 기반 예후의 성능은 측정치로부터 뽑아낸 특징 인자(feature)의 성능에 의존한다. 높은 수준의 예후 성능을 달성하기 위해서는, 기계의 건강 상태를 잘 나타내도록 특징 인자들이 잘 디자인하여야 하며, 특징 인자들은 일반적으로 원 신호에서 계산되거나 통계적 신호처리 기법들을 통해 얻어진다. 이렇게 만들어진 특징 인자들은 그 자체로 건강 지표로 사용되거나, 또는 다른 특징 인자들과 함께 새로운 건강 지표를 구성한다. 그러나 기존의 많은 건강 지표들은 기계의 종류마다 만들어지는 방식이 다르며, 높은 수준의 도메인 지식이 요구된다. 이러한 단점을 해결하기위해, 우리는 데이터 기반 방법인 적대적 오토 인코더 [1] 기반 건강 지표 (AAE-HI)를 추출할 수 있는 일반적인 방법론을 제안한다. PRONOSTIA [2]에서 수집된 된 구름 베어링의 가속 열화 실험의 데이터셋을 사용하여 AAE-HI를 검증하였다. AAE-HI는 원 신호에서 높은 수준의 단조성 (monotonicity)과 시간에 대한 상관성 (trendability)을 가진 건강 지표를 뽑아낼 수 있었으며, 이를 구름 베어링의 잔존 수명과 비교하여 열화 과정에 대한 정보를 충분히 담고 있다는 것을 보였다. The performance of data-driven prognostics heavily depends on the features extracted from measured raw signals. Therefore, in order to enhance the prognostic performance, features must be carefully designed to represent the machine’s health condition. Conventional key features are often obtained by statistical signal processing techniques. Then, these features themselves are used as health indicators (HI) or fed to construct HIs. However, many conventional HIs are heavily relying on the type of machine components and expert domain knowledge. To solve these drawbacks, we propose a fully data-driven method, that is, the adversarial autoencoder-based health indicator (AAE-HI) [1]. Accelerated tests of bearing degradation collected from PRONOSTIA [2](open dataset) were used to justify the proposed AAE-HI method. It is shown that our proposed AAE-HI can autonomously learn and find features which well represent monotonicity and trendability of bearing degradation process. Finally, the performance of AAE-HI in RUL prediction is compared with other traditional HIs.
Hydrogen-free defects in hydrogenated black TiO<sub>2</sub>
Choi, Heechae,Moon, Seong-I,Song, Teaseup,Kim, Seungchul The Royal Society of Chemistry 2018 Physical chemistry chemical physics Vol.20 No.30
<P>Black anatase TiO2 has surprisingly enhanced solar energy harvesting efficiency and electrical conductivity, which makes it a promising material in a wide range of energy and environmental applications. Several experimental and theoretical studies have successfully revealed the mechanisms of band gap reduction by surface hydrogenation of anatase TiO2. However, recent experimental evidence suggests the existence of bulk point defects that yield infrared (∼1.0 eV) photoabsorption and high conductivity of black anatase TiO2. In the current study, using a combination of <I>ab initio</I> molecular dynamics simulations and electronic structure calculations, we successfully explain the physical properties, metallicity, and infrared/microwave absorption (<I>i.e.</I>, black color) of highly reduced anatase TiO2 crystal in a hydrogenated state with a newly found pair defect (Tii-VO)<SUP>4+</SUP>. Hydrogen atoms in the bulk are unnecessary to understand the observed properties.</P>