• Journal of the Korean Electrochemical Society
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• v.2 no.4
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• pp.232-236
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• 1999

A solar cell based on dye-sensitized photoelectric conversion was studied by electrochemical and spec-trofluorometric methods for the purposes of enhancing its efficiency and stability of $TiO_2$ solar cells. Nanocrystalline $TiO_2$ was used to prepare photoelectrodes, and photosensitizing dyes such as malachite green oxalate, basic blue3, rhodamine B, and bromocresol purple were chosen as sensitizers. Electrochemical oxidation potentials and absorption and emission wavelengths of dyes were used to determine energy levels of the dyes. By comparing excited energy levels of the dyes with the conduction band edge potential $(E_{c,s})\;of\;TiO_2$ calculated by using the flat-band potential $(E_{fb})\;of\;TiO_2$, properties of a dye required to fabricate a high efficient photosensitizing solar cell with high short-circuit current $(J_{sc})$ were suggested. Enhanced stability of photocurrent was obtained by coating a $TiO_2|ITO$ electrode with Polypyrrole that Possibly Prevented the recombination between the conduction band electrons and oxidized dyes and suppressed the direct electrode redox reactions of dyes on ITO.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.4
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• pp.665-670
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• 2020

Buffer layer in CIGS thin-film solar cells improves energy conversion efficiency through band alignment between the absorption layer and the window layer. ZnS is a non-toxic II-VI compound semiconductor with direct-transition band gaps and n-conductivity as well as with excellent lattice matching for CIGS absorbent layers. In this study, the structural and optical properties of ZnS thin films, deposited by RF magnetron sputtering method and subsequently performed by the rapid thermal annealing treatment, were investigated for the buffer layer. The zincblende cubic structures along (111), (220), and (311) were shown in all specimens. The rapid thermal annealed specimens at the relatively low temperatures were polycrystalline structure with the wurtzite hexagonal structures along (002). Rapid thermal annealing at high temperatures changed the polycrystalline structure to the single crystal of the zincblende cubic structures. Through the chemical analysis, the zincblende cubic structure was obtained in the specimen with the ratio of Zn/S near stoichiometry. ZnS thin film showed the shifted absorption edge towards the lower wavelength as annealing temperature increased, and the mean optical transmittance in the visible light range increased to 80.40% under 500℃ conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.5
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• pp.940-947
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• 2006

A variety of actuators fur an implantable artificial heart have been studied. They, all, however, share the disadvantages of a complicated energy conversion mechanism and of the need to use bearings. A ferrofluidic actuator directly drives magnetic fluids by applying a magnetic field to these fluids; it does not require bearings. In this study, the feasibility of a ferrofluidic actuator for an implantable artificial heart was studied. An way of two Poles of ring solenoids was mounted near the acrylic tube $({\phi}\;7.4mm)$. A rubber sack (volume : $2m{\ell}$ was connected to both ends of the acrylic tube. The sack were encased in a rigid chamber that had inlet and outlet ports. The acrylic tube and the rubber sack were filled with water encased in a rigid chamber magnetic fluid and the iron cylinder were immersed in the water. Two experiment method was conducted. 1) distance between stoppers were 72mm and 2) distance between stoppers were 104mm. A stroke volume was stability and $0.96m{\ell}$ was obtained in the experiment 1 and $1.92m{\ell}$ in the experiment 2. The energy efficiency of Experiment method 2 is about five times than Experiment method 2. A magnetic fluid-driven blood pump could be feasible if the magnetic fluid with high magnetization (3 times yester than the current value) is developed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.328-328
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• 2007

Large area matrix-addressed image detectors are a recent technology for x-ray imaging with medical diagnostic and other applications. The imaging properties of x-ray pixel detectors depend on the quantum efficiency of x-rays, the generated signal of each x-ray photon and the distribution of the generated signal between pixels. In a phosphor coated detector the light signal is generated by electrons captured in the phosphor screen. In our study we simulated the lateral spread distributions for phosphor coupled detector by Monte Carlo simulations. Most simulations of such detectors simplify the setup by only taking the conversion layer into account neglecting behind. The Monte Carlo code MCNPX has been used to simulate the complete interaction and subsequent charge transport of x-ray radiation. This has allowed the analysis of charge sharing between pixel elements as an important limited factor of digital x-ray imaging system. The parameters are determined by lateral distribution of x-ray photons and x-ray induced electrons. The primary purpose of this study was to develop a design tool for the evaluation of geometry factor in the phosphor coupled optical imaging detector. In order to evaluate the spatial resolution for different phosphor material, phosphor geometry we have developed a simulation code. The developed code calculates the energy absorption and spatial distribution based on both the signal from the scintillating layer and the signal from direct detection of x-ray in the detector. We show that internal scattering contributes to the so-called spatial resolution drop of the image detector. Results from the simulation of spatial distribution in a phosphor pixel detector are presented. The spatial resolution can be increased by optimizing pixel size and phosphor thickness.

• Journal of Soil and Groundwater Environment
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• v.11 no.3
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• pp.59-65
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• 2006

Reductive dechlorination of chlorophenols by nickel coated iron was investigated to understand the feasibility of using Ni/Fe for the in situ remediation of contaminated groundwater. Zero valent iron (ZVI) was amended with Ni(II) ions to form bimetal (Ni/Fe). Dechlorination of 4-chlorophenol and formation of intermediates was studied using Ni/Fe. Effects of initial contaminant concentration, bimetal loading, presence of humic acid, and solution chemistry were also evaluated. Experimental results showed that Ni/Fe bimetal was so effective that more than 95% of 4-CP degradation was achieved within 240 minutes. Pseudo first-order rate constant for the dechlorination reaction was well correlated with bimetal loading. Humic acid competed for the reactive sites on the nickel coated iron with chlorophenols, lowering the dechlorination efficiency. No significant changes in solution pH were observed in the dechlorination of chlorophenols with Ni/Fe in the absence of buffer, indicating that reactivity of bimetal (Ni/Fe) could be prolonged. Phenol was found as a dechlorination intermediate of the conversion of 4-chlorophenol compound by Ni/Fe.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.276-276
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• 2010

Localized surface plasmon resonance (LSPR) has been explored recently as a promising approach to increase energy conversion efficiency in photovoltaic devices, particularly for thin film hydrogenated amorphous silicon (a-Si:H) solar cells. The LSPR is frequently excited via an electromagnetic (EM) radiation in proximate metallic nanostructures and its primary con sequences are selective photon extinction and local EM enhancement which gives rise to improved photogeneration of electron-hole (e-h) pairs, and consequently increases photocurrent. In this work, high-dielectric-constant (k) $ZrO_2$ (refractive index n=2.22, dielectric constant $\varepsilon=4.93$ at the wavelength of 550 nm) is proposed as spacing layer to enhance the LSPR for application to the thin film silicon solar cells. Compared to excitation of the LSPR using $SiO_2$ (n=1.46, $\varepsilon=2.13$ at the wavelength of 546.1 nm) spacing layer with Au nanoparticles of the radius of 45nm, that using $ZrO_2$ dielectric shows the advantages of(i) ~2.5 times greater polarizability, (ii) ~3.5 times larger scattering cross-section and ~1.5 times larger absorption cross-section, (iii) 4.5% higher transmission coefficient of the same thickness and (iv) 7.8% greater transmitted electric filed intensity at the same depth. All those results are calculated by Mie theory and Fresnel equations, and simulated by finite-difference time-domain (FDTD) calculations with proper boundary conditions. Red-shifting of the LSPR wavelength using high-k $ZrO_2$ dielectric is also observed according to location of the peak and this is consistent with the other's report. Finally, our experimental results show that variation of short-circuit current density ($J_{sc}$) of the LSPR enhanced a-Si:H solar cell by using the $ZrO_2$ spacing layer is 45.4% higher than that using the $SiO_2$ spacing layer, supporting our calculation and theory.

• Applied Chemistry for Engineering
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• v.25 no.1
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• pp.1-13
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• 2014

Lithium ion batteries (LIBs) are the state-of-the-art technology among electrochemical energy storage and conversion cells, and are still considered the most attractive class of battery in the future due to their high specific energy density, high efficiency, and long cycle life. Rapid development of power-hungry commercial electronics and large-scale energy storage applications (e.g. off-peak electrical energy storage), however, requires novel anode materials that have higher energy densities to replace conventional graphite electrodes. Germanium (Ge) and silicon (Si) are thought to be ideal prospect candidates for next generation LIB anodes due to their extremely high theoretical energy capacities. For instance, Ge offers relatively lower volume change during cycling, better Li insertion/extraction kinetics, and higher electronic conductivity than Si. In this focused review, we briefly describe the basic concepts of LIBs and then look at the characteristics of ideal anode materials that can provide greatly improved electrochemical performance, including high capacity, better cycling behavior, and rate capability. We then discuss how, in the future, Ge anode materials (Ge and Ge oxides, Ge-carbon composites, and other Ge-based composites) could increase the capacity of today's Li batteries. In recent years, considerable efforts have been made to fulfill the requirements of excellent anode materials, especially using these materials at the nanoscale. This article shall serve as a handy reference, as well as starting point, for future research related to high capacity LIB anodes, especially based on semiconductor Ge and Si.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.5
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• pp.647-655
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• 2021

The IMO (International Maritime Organization) is discussing the improvement of energy ef iciency of ships in order to reduce greenhouse gas emissions from ships. Currently, by applying an ORC power generation system using waste heat generated from ships, high energy conversion efficiency can be expected from ships. This technology uses an organic medium based on Freon or hydrocarbons as the working fluid, which evaporates at a lower temperature range than water. Through this, it is possible to generate steam (gas) and generate power at a low and low temperature relatively. In this study, the analysis of heat flow between the refrigerant and waste heat in the ORC power generation system, which is an organic Rankine cycle, is analyzed using 3D simulation techniques to determine the temperature change, velocity change, pressure change, and mass change of the fluid flowing of the WHRU (Waste Heat Recovery Unit) inside and the outside the structure. The purpose of this study is to analyze how the mass change affects the structure, and this study analyzed the heat transfer of the heat exchanger from the refrigerant and the exhaust gas of the ship's main engine in the ORC power generation system using this technique.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.29-34
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• 2019

Silicon carbide is considered to be a potentially useful material for high-temperature electronic devices, as its large energy band gap and the p-type and/or n-type conduction can be controlled by impurity doping. Particularly, electric conductivity of porous n-type SiC semiconductors fabricated from ${\beta}-SiC$ powder at $2000^{\circ}C$ in $N_2$ atmosphere was comparable to or even larger than the reported values of SiC single crystals in the temperature region of $800^{\circ}C$ to $1000^{\circ}C$, while thermal conductivity was kept as low as 1/10 to 1/30 of that for a dense SiC ceramics. In this work, for the purpose of decreasing sintering temperature, it was attempted to fabricate porous reaction-sintered bodies at low temperatures ($1400-1600^{\circ}C$) by thermal decomposition of polycarbosilane (PCS) impregnated in n-type ${\beta}-SiC$ powder. The repetition of the impregnation and sintering process ($N_2$ atmosphere, $1600^{\circ}C$, 3h) resulted in only a slight increase in the relative density but in a great improvement in the Seebeck coefficient and electrical conductivity. However the power factor which reflects the thermoelectric conversion efficiency of the present work is 1 to 2 orders of magnitude lower than that of the porous SiC semiconductors fabricated by conventional sintering at high temperature, it can be stated that thermoelectric properties of SiC semiconductors fabricated by the present reaction-sintering process could be further improved by precise control of microstructure and carrier density.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.488-496
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• 2018

This study examined the Gangwon Province's current implementation of its elimination of invasive plants and explored a plan to effectively manage invasive plants. The percentage of the distribution of the plants was 39.6% for riverside areas, 23.3% for roadside areas, 12.4% for roadside & riverside areas, and 4.6% for areas around farm land and river banks. To ensure the systematic management of invasive plants, the current study suggests a) developing an invasive plants monitoring and management system; b) reinvigorating the participation of residents, private organizations, and military posts; c) planting of native replacement plants and the conversion of the locations as attractions, and d) nurturing the project for using invasive plants. For policy directions to be pursued based on the results of the study, the following are suggested: a) improving laws and systems regarding invasive plants, b) developing a cooperative system for managing invasive plants, c) implementing the training of civilian professionals, d) implementing the elimination of invasive plants, e) developing replacement plants for cities and counties, f) fostering industries that tap into invasive plants, and g) using the Han River Water System Management Fund for funding and greater efficiency.