Do-Hwan Kim

Transparent Flexible Graphene Triboelectric Nanogenerators

S. Kim, Dr. M. K. Gupta, K. Y. Lee, K.-S. Shin, S. K. Kim, K. H. Lee, Prof. S.-W. Kim School of Advanced Materials Science and Engineering Sungkyunkwan University (SKKU) Suwon 440–746 , Republic of Korea E-mail: kimsw1@skku.edu A. Sohn, Prof. D.-W. Kim School of Department of Physics Ewha Womens University Seoul 120–750 , Republic of Korea T. Y. Kim, D. Kim, Prof. S.-W. Kim SKKU Advanced Institute of Nanotechnology (SAINT) Center for Human Interface Nanotechnology (HINT) SKKU-Samsung Graphene Center Sungkyunkwan University (SKKU) Suwon 440–746 , Republic of Korea Dr. H.-J. Shin Samsung Advanced Institute of Technology Yongin 446–712 , Republic of Korea

Characteristic Analysis and Effect of Particulate Material in Drinking Water Distribution Networks

Particulates in drinking water distribution system (DWDS) are mostly influenced by internal corrosion of metal pipes and sediment in pipelines due to the solution of this effect is limited. The particle size, component and properties of compounds for particulates in distributed water are different and the difference of these characteristics will be occurred by the kind of facilities, pipe condition, external factors and supply system etc. In this study, conducting the investigation of water quality in DWDS researches with particulates in the water. Monitoring sites were each water supply reservoir and the end of water supply area in DWDS. To collect particulate material at each sampling site, glass microfiber filter type GF/C was performed using a filtration. Substances that the effect of the turbidity in the water according to particulate suspended solids and inorganic materials is due to the increasing particulates in the end of DWDS were increased. The result of compounds analysis by using X-ray diffraction (XRD) were Goethite (-FeOOH), Magnetite () in the end of DWDS and Quartz (), Yeelimite () at the effluent of waterworks and reservoirs. There were differences the compounds and sediments in the releasing or remaining water distribution facilities.

Atomic Observation of Filling Vacancies in Monolayer Transition Metal Sulfides by Chemically Sourced Sulfur Atoms

Chemical treatment using bis(trifluoromethane) sulfonimide (TFSI) was shown to be particularly effective for increasing the photoluminescence (PL) of monolayer (1L) MoS2, suggesting a convenient method for overcoming the intrinsically low quantum yield of this material. However, the underlying atomic mechanism of the PL enhancement has remained elusive. Here, we report the microscopic origin of the defect healing observed in TFSI-treated 1L-MoS2 through a correlative combination of optical characterization and atomic-scale scanning transmission electron microscopy, which showed that most of the sulfur vacancies were directly repaired by the extrinsic sulfur atoms produced from the dissociation of TFSI, concurrently resulting in a significant PL enhancement. Density functional theory calculations confirmed that the reactive sulfur dioxide molecules that dissociated from TFSI can be reduced to sulfur and oxygen gas at the vacancy site to form strongly bound S-Mo. Our results reveal how defect-mediated nonradiative recombination can be effectively eliminated by a simple chemical treatment method, thereby advancing the practical applications of monolayer semiconductors.

In-Depth Investigation of Statistical and Physicochemical Properties on the Field Study of the Intermittent Filling of Large Water Tanks

Large-demand customers, generally high-density dwellings and buildings, have dedicated ground or elevated water tanks to consistently supply drinking water to residents. Online field measurement for Nonsan-2 district meter area demonstrated that intermittent replenishment from large-demand customers could disrupt the normal operation of a water distribution system by taking large quantities of water in short times when filling the tanks from distribution mains. Based on the previous results of field measurement for hydraulic and water quality parameters, statistical analysis is performed for measured data in terms of autocorrelation, power spectral density, and cross-correlation. The statistical results show that the intermittent filling interval of 6.7 h and diurnal demand pattern of 23.3 h are detected through autocorrelation analyses, the similarities of the flow-pressure and the turbidity-particle count data are confirmed as a function of frequency through power spectral density analyses, and a strong cross-correlation is observed in the flow-pressure and turbidity-particle count analyses. In addition, physicochemical results show that the intermittent refill of storage tank from large-demand customers induces abnormal flow and pressure fluctuations and results in transient-induced turbid flow mainly composed of fine particles ranging within 2–4 μm and constituting Fe, Si, and Al.

The Component Analysis of Foreign Substance Occurred in Water Distribution Networks

Abstract : Customers water quality complaints by foreign substance in local water service can be able to call the main cause bring the distrust for tap water and inhibiting the rate of drinking water. In this study, foreign substances were collected in the target region. Foreign objects were subjected to qualitative and quantitative analysis of compounds and elements components to reveal the cause of detection. Also, resolve the complaints by foreign substance and improve the reliability for tap water providing high quality water supply scheme. Collected substances at the water quality complaint area were included in inorganic compounds due to internal corrosion and aging pipeline, as well as organic compounds containing a large amount of carbon (C) and oxygen (O) component. To decide and reduce for foreign substance, objective assessment of pipe condition in target area was required. Key Words : Foreign Substance, Water Quality Complaints, Tap Water, Inorganic Compounds, Organic Compounds

Efficiency improvement of buried contact solar cells using MgF/sub 2//CeO/sub 2/ double layer antireflection coatings

This paper describes an efficiency improvement of buried contact solar cell (BCSC) with a structure of MgF/sub 2//CeO/sub 2//Ag/Cu/Ni grid/n/sup +/ emitter/p-type Si base/P/sup +//Al. Theoretical and experimental investigations were performed on a double layer antireflection (DLAR) coating of MgF/sub 2//CeO/sub 2/. The authors investigated CeO/sub 2/ films as an AR layer because they have a proper refractive index of 2.46 and demonstrate the same lattice constant as Si substrate. An optimized DLAR coating showed a reflectance as low as 2.04% in the wavelengths ranged from 0.4 /spl mu/m to 1.1 /spl mu/m. BCSC cell efficiency was improved from 16.2% without any AR coating to 19.9% by employing DLAR coatings. Further details on MgF/sub 2//CeO/sub 2/ DLAR coatings on the BCSC cells are presented in this paper.