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Hyein Ha,Jinhwi Cho,Ja Yeon Lee,Buyong Yun,Jihoon Lee,Min Chul Suh 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.87 No.-
A series of new asymmetric anthracene derivatives have been successfully synthesized for use in the lightemitting layer of solution processed bluefluorescent organic light emitting diodes (OLEDs), which couldbe used both as host and dopant. Especially, new synthetic bluefluorescent materials with anthracenemoieties without any alkyl chains showed high solubility in common organic solvents probably due totheir severely twisted internal structures. They also show moderately high thermal stability due to theirrigid internal core units. With those novel soluble bluefluorescent materials, we created moderatelyefficient solution-processedfluorescent OLEDs. And a new anthracene derivative [9-(9,10-di(naphthalen-2-yl)anthracen-2-yl)-9H-carbazole (DN-2-CzA)] as a host material exhibited moderately high efficiencyand external quantum efficiency of up to 3.2 cd/A and 1.6%, respectively, when we utilized 4,40-bis[4-(diphenylamino)styryl]biphenyl as a dopant. Meanwhile, the [N-(naphthalen-1-yl)-9,10-di(naphthalen-2-yl)-N-phenylanthra-cen-2-amine (DN-2-NPAA)] as a dopant material showed pretty good deviceperformance, up to 5.2 cd/A and 2.2% (EQE), when we utilized 2-tert-butyl-9,10-di(naphth-2-yl)anthracene as a host.
Electron transport mechanism of bathocuproine exciton blocking layer in organic photovoltaics
Lee, Jeihyun,Park, Soohyung,Lee, Younjoo,Kim, Hyein,Shin, Dongguen,Jeong, Junkyeong,Jeong, Kwangho,Cho, Sang Wan,Lee, Hyunbok,Yi, Yeonjin The Royal Society of Chemistry 2016 Physical chemistry chemical physics Vol.18 No.7
<P>Efficient exciton management is a key issue to improve the power conversion efficiency of organic photovoltaics (OPVs). It is well known that the insertion of an exciton blocking layer (ExBL) having a large band gap promotes the efficient dissociation of photogenerated excitons at the donor-acceptor interface. However, the large band gap induces an energy barrier which disrupts the charge transport. Therefore, building an adequate strategy based on the knowledge of the true charge transport mechanism is necessary. In this study, the true electron transport mechanism of a bathocuproine (BCP) ExBL in OPVs is comprehensively investigated by in situ ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy, density functional theory calculation, and impedance spectroscopy. The chemical interaction between deposited Al and BCP induces new states within the band gap of BCP, so that electrons can transport through these new energy levels. Localized trap states are also formed upon the Al-BCP interaction. The activation energy of these traps is estimated with temperature-dependent conductance measurements to be 0.20 eV. The Al-BCP interaction induces both transport and trap levels in the energy gap of BCP and their interplay results in the electron transport observed.</P>
Optimization of the Pot Volume and Substrate for Strawberry Cultivation in a Hydroponic System
Hyein Lee,Meiyan Cui,Byungkwan Lee,Hyunseung Hwang,Changhoo Chun 한국원예학회 2023 원예과학기술지 Vol.41 No.6
This study aimed to optimize the pot volume and substrate for strawberry pot cultivation through an analysis of strawberry growth and the composition of the drainage solution in a hydroponic cultivation system. Strawberry plants were cultivated for six months with various combinations of pot volumes (830 ㎤ and 1,140 ㎤) and substrates (commercial substrate, coir, and granular rockwool). On day 63 after transplantation, the growth of the strawberry plants was greatest when the plants were grown in pots with a volume of 830 ㎤ and with a commercial substrate. On day 182 after transplantation, growth was greatest when the plants were grown in pots with a volume of 830 ㎤ using a commercial substrate or coir, as well as in pots with a volume of 1,140 ㎤ using a commercial substrate. The drainage solution from the coir substrate exhibited a pH and electrical conductivity (EC) similar to those of the nutrient solution. The ion concentrations in the coir drainage solution were similar to those in the nutrient solution throughout the cultivation period. These results indicate that a pot volume of 830 cm3 and coir are most suitable for approximately six months of strawberry pot cultivation. In pot cultivation, the establishment of an appropriate range of substrate volumes considering the cultivation period is crucial. An analysis of changes in the drainage solution influenced by the substrate composition and cultivation duration can enhance nutrient management, optimize resource utilization, and promote the reuse of nutrient solutions in hydroponic systems. These findings contribute to the development of sustainable and efficient approaches to strawberry pot cultivation, emphasizing the maximization of resource utilization while ensuring the attainment of high-quality yields.
The Ways for Bi on Pt to Enhance Formic Acid Oxidation
Hyein Lee,Young Jun Kim,Youngku Sohn,Choong Kyun Rhee The Korean Electrochemical Society 2023 Journal of electrochemical science and technology Vol.14 No.1
This work presents a correlation between the behavior of formic acid oxidation (FAO) on various Bi-modified Pt(poly) disk electrodes and their morphologies observed on Bi-modified Pt(111) disk electrodes using electrochemical scanning tunneling microscopy (EC-STM) to understand the effects of Bi on Pt. To distinguish the FAO activities of Bi on Pt and plain Pt around Bi, additional Pt was intentionally deposited using two different routes: direct route and iodine route. In direct route, Pt was directly deposited on Bi islands and plain Pt sites around Bi islands, while in iodine route, Pt was exclusively deposited on Bi islands by protecting plain Pt sites with adsorbed iodine. Thus, a comparison of FAO performances on the two Bi-modified Pt electrodes with additional Pt (deposited in the different ways) disclosed a difference in FAO performances on plain Pt sites and Bi islands. When Bi coverage was ~0.04, the Bi deposits were scattered Bi islands enhancing FAO on Pt(poly). The additional Pt deposits using direct route increased FAO efficiency, while the ones using iodine route slightly decreased FAO current. The EC-STM observations indicated that Pt deposits around Bi islands, not on Bi islands, were responsible for the FAO current increase on Bi-modified Pt(poly). The FAO efficiency on Bi-modified Pt(poly) with a Bi coverage of ~0.25 increased by a factor of 2. However, the additional Pt deposits using the two Pt deposition routes notably decreased the FAO current. The dependency of FAO on Bi coverage was discussed in terms of electronic effect and ensemble effect.
Development of a compact optical torque sensor with decoupling axial-interference effects for pHRI
Lee, Hyein,Kim, Sangjoon J.,Chang, Handdeut,Kim, Jung Elsevier 2018 Mechatronics Vol.52 No.-
<P>This paper presents the design of an optical torque sensor that can structurally decouple the effect of axial-interference for use in various robotics applications. Torque sensors are widely used in the joints of intelligent service or wearable robots to realize safe human-robot interaction. Whole robot body sensing using torque sensors is essential for safe interaction. However, most torque sensors are bulky, heavy and expensive. Therefore, many optical-based torque sensors have been proposed to deal with such problems, but the issue of axial-interference still remains. We resolved the axial-interference problem via the geometrical structure of the sensor body and differential signaling using two reflective optical sensors. The moment interference error was successfully decreased from 4.49% (with one optical sensor) to 0.11% (with two optical sensors) using the proposed sensor structure while maintaining a compact size, lightweight, and low cost. Static tests and dynamic tests were carried out and analyzed for accuracy error, hysteresis, and repeatability. We then compared the performance of an impedance controller that is widely used in service and wearable robots using the proposed sensor and a commercial torque sensor with respect to various control loop rates. The control performance of the proposed sensor was comparable to that of commercial sensors.</P>
Lee, Sang Wook,Ryu, Chae-Min,Shin, Jung-Hyun,Choi, Daeheon,Kim, Aram,Yu, Hwan Yeul,Han, Ju-Young,Lee, Hye-Yeon,Lim, Jisun,Kim, Yong Hwan,Heo, Jinbeom,Lee, Seungun,Ju, Hyein,Kim, Sujin,Hong, Ki-Sung,Ha Korean Continence Society 2018 International Neurourology Journal Vol.22 No.S1
<P><B>Purpose</B></P><P>To evaluate the therapeutic effect of human embryonic stem cell (hESC)-derived multipotent mesenchymal stem cells (M-MSCs) on ketamine-induced cystitis (KC) in rats.</P><P><B>Methods</B></P><P>To induce KC, 10-week-old female rats were injected with 25-mg/kg ketamine hydrochloride twice weekly for 12 weeks. In the sham group, phosphate buffered saline (PBS) was injected instead of ketamine. One week after the final injection of ketamine, the indicated doses (0.25, 0.5, and 1×10<SUP>6</SUP> cells) of M-MSCs (KC+M-MSC group) or PBS vehicle (KC group) were directly injected into the bladder wall. One week after M-MSC injection, the therapeutic outcomes were evaluated via cystometry, histological analyses, and measurement of gene expression. Next, we compared the efficacy of M-MSCs at a low dose (1×10<SUP>5</SUP> cells) to that of an identical dose of adult bone marrow (BM)-derived MSCs.</P><P><B>Results</B></P><P>Rats in the KC group exhibited increased voiding frequency and reduced bladder capacity compared to rats of the sham group. However, these parameters recovered after transplantation of M-MSCs at all doses tested. KC bladders exhibited markedly increased mast cell infiltration, apoptosis, and tissue fibrosis. Administration of M-MSCs significantly reversed these characteristic histological alterations. Gene expression analyses indicated that several genes associated with tissue fibrosis were markedly upregulated in KC bladders. However the expression of these genes was significantly suppressed by the administration of M-MSCs. Importantly, M-MSCs ameliorated bladder deterioration in KC rats after injection of a low dose (1×10<SUP>5</SUP>) of cells, at which point BM-derived MSCs did not substantially improve bladder function.</P><P><B>Conclusions</B></P><P>This study demonstrates for the first time the therapeutic efficacy of hESC-derived M-MSCs on KC in rats. M-MSCs restored bladder function more effectively than did BM-derived MSCs, protecting against abnormal changes including mast cell infiltration, apoptosis and fibrotic damage.</P>