• 한국전기전자재료학회논문지
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• 제25권5호
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• pp.345-348
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• 2012

The optical losses associated with the reflectance of incident radiation are among the most important factors limiting the efficiency of a solar cell. Therefore, photovoltaic cells normally require special surface structures or materials, which can reduce reflectance. In this study, nano-scale textured structures with anti-reflection properties were successfully formed on silicon. The surface of sicon wafer was etched by the inductively coupled plasma process using the gaseous mixture of $SF_6+O_2$. We demonstrate that the reflection characteristic has significantly reduced by ~0% compared with the flat surface. As a result, the power efficiency $P_{max}$ of the nano-scale textured silicon solar cell were enhanced up to 20%, which can be ascribed primarily to the improved light trapping in the proposed nano-scale texturing.

• Journal of Electrical Engineering and Technology
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• 제10권2호
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• pp.647-652
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• 2015

A fully coupled finite element analysis (FEA) technique was developed for analyzing the discharge phenomena and dielectric liquid flow while considering surface charge density effects in dielectric flow guidance. In addition, the simulated speed of surface charge propagation was compared and verified with the experimental results shown in the literature. Recently, electrohydrodynamics (EHD) techniques have been widely applied to enhance the cooling performance of electromagnetic systems by utilizing gaseous or liquid media. The main advantage of EHD techniques is the non-contact and low-noise nature of smart control using an electric field. In some cases, flow can be achieved using only a main electric field source. The driving sources in EHD flow are ionization in the breakdown region and ionic dissociation in the sub-breakdown region. Dielectric guidance can be used to enhance the speed of discharge propagation and fluidic flow along the direction of the electric field. To analyze this EHD phenomenon, in this study, the fully coupled FEA was composed of Poisson's equation for an electric field, charge continuity equations in the form of the Nernst-Planck equation for ions, and the Navier-Stokes equation for an incompressible fluidic flow. To develop a generalized numerical technique for various EHD phenomena that considers fluidic flow effects including dielectric flow guidance, we examined the surface charge accumulation on a dielectric surface and ionization, dissociation, and recombination effects.

• 대한기계학회논문집B
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• 제24권10호
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• pp.1368-1379
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• 2000

A numerical study on swirling pulverized coal combustion in an axisymmetric enclosure is carried out by applying the 2-phase weighted sum of gray gases model (WSGGM) approach with the discrete ordinate method (DOM) to model the radiative heat transfer equation. In the radiative transfer equation, the same polynomial equation and coefficients for weighting factors as those for gas are adopted for the coal/char particles as a function of partial pressure and particle temperature. The Eulerian balance equations for mass, momentum, energy, and species mass fractions are adopted with the standard and RNG k-${\varepsilon}$ turbulence model, whereas the Lagrangian approach is used for the particulate phase. The eddy-dissipation model is employed for the reaction rate for gaseous mixture, and the single-step and two-step first-order reaction model for the devolatilization process for coal. Special attention is given to establish the thermal boundary conditions on radiative transfer equation By comparing the numerical results with experimental ones, the radiation model used here is confirmed and found to provide an alternative for simulating the radiative transfer.

• Journal of Advanced Marine Engineering and Technology
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• 제34권3호
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• pp.351-359
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• 2010

Bi-fuel system in a spark ignition engine (SIE) is a rising phenomena in today's automobile technology. In a gasoline driven vehicle, alternatively adoption of compressed natural gas (CNG) could be used as a potential substitute to meet the energy requirement and this is possible by some minor changes in the hardware of the existing engine. Gasoline engine is widely used in the passenger cars, light, medium and heavy duty vehicles but the consumption status of the petroleum is decreasing worldwide and at the same time environmental pollution from automobiles is seriously establishes as a threat for every nation in respect to global warming and climate changes. Now-a-days most vehicles operate using CNG for its popularity stems, clean burning properties and cost effective solution compared to other alternative fuels. It refers as a good gaseous fuel because of its high octane number and self ignition temperature. Though the power output is slightly lesser than the gasoline fuel; its thermal efficiency is better than the gasoline for the same SIE. The research paper highlights the reduction of CO, reasonable outcomes of HC emissions with minor increase in $NO_x$ emissions compared with the gasoline fuel to bi-fuel mode in the SIE that meets the emission challenges.

• Plant Biotechnology Reports
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• 제4권3호
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• pp.179-183
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• 2010

Ethylene is a key gaseous hormone that controls various physiological processes in plants including growth, senescence, fruit ripening, and responses to abiotic and biotic stresses. In spite of some of these positive effects, the gas usually inhibits plant growth. While chemical fertilizers help plants grow better by providing soil-limited nutrients such as nitrogen and phosphate, overusage often results in growth inhibition by soil contamination and subsequent stress responses in plants. Therefore, controlling ethylene production in plants becomes one of the attractive challenges to increase crop yields. Some soil bacteria among plant growth-promoting rhizobacteria (PGPRs) can stimulate plant growth even under stressful conditions by reducing ethylene levels in plants, hence the term "stress controllers" for these bacteria. Thus, manipulation of relevant genes or gene products might not only help clear polluted soil of contaminants but contribute to elevating the crop productivity. In this article, the beneficial soil bacteria and the mechanisms of reduced ethylene production in plants by stress controllers are discussed.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.158.2-158.2
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• 2011

DME is acronym of dimethyl ether, which is spotlighted as an ideal fuel to produce hydrogen due to its high hydrogen/carbon ratio, high energy density and easiness to carry. In this research, we calculated thermodynamic hydrogen (or syngas) yield from DME autothermal reforming and compared to other fuels. The reforming efficiency was about 80% above $700^{\circ}C$. Lower OCR has higher reforming efficiency but, it requires additional heat supply since the reactions are endothermic. SCR has no significant effect on the reforming efficiency. The optimized condition is $700^{\circ}C$, SCR 1.5, OCR 0.45 without additional heat supply. Comparing to other commercial gaseous fuels (methane and propane), DME has higher selectivity of $H_2O$ and $CO_2$ than the others due to the oxygen atom in the molecule. To apply DME autothermal reforming to real system, a proper catalyst is required. Therefore, it is performed the experiment comparing various novel metal catalysts based on CGO. Experiments were performed at calculated condition. The composition of product was measured and reforming efficiency was calculated. The catalysts have similar efficiency at high temperature(${\sim}800^{\circ}C$) but, CGO-Ru has the highest efficiency at low temperature ($600^{\circ}C$).

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.237-240
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• 2004

Sulfur Hexafluoride, SF6 is widely used for leak detection and as a gaseous dielectric in transformers, condensers and circuit breakers. SF6 gas is also effective as a cleanser in the semiconductor industry. This paper presents a numerical study of the sealing force of disk type seal in SF6 gas safety valve. The sealing force on the disk seal is analyzed by the FEM method based on the Taguch's experimental design technique. Disk seals in SF6 gas safety valve are designed with 9 design models based on 3 different contact length, compressive ratio and gas pressure. The calculated results of Cauchy stress and strain showed that the sealing characteristics of Teflon PTFE is more effective compared to that of FKM(Viton), which is related to the stiffness of the materials. And also, the contact length of the disk seal is important design parameter for sealing the SF6 gas leakage in the safety valve.

• 한국가시화정보학회지
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• 제3권2호
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• pp.51-56
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• 2005

Acoustic excitations were imposed to coaxial air jet of non-premixed jet flame with hydrogen gaseous injected axially in the center of the flow. The frequencies of excitation were three dominant resonant frequencies at 1L, 2L, 3L. modes including specially 514 Hz (2L-mode) which was estimated theoretically as longitudinal mode of combustor characteristics. The mixing enhancement by acoustic forcing has been investigated quantitatively using PLIF and PIV. The effect of acoustic excitation on combustion process was significant to enhance mixing rate that coincides with specific resonant frequencies. And the behavior of vortex-interaction on flame structure was a good evidence to investigate the phenomenon of shear/mixing layer of fuel-air jet structure. The results obtained in this study concludes that generated streamwise vortex by acoustic excitation has a potential to enhance the mixing rate and abating NOx emissions.

• 한국대기환경학회지
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• 제24권6호
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• pp.693-703
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• 2008

The important source of the mercury in water-column is the influx of atmosphere mercury, via dry and wet deposition. In this study, wet deposition of mercury was estimated to be $14.56{\mu}g/m^2$ during 15 months at the Lake Soyang, which is a little higher than those observed in the several rural US Mercury Deposition Network (MDN) sites with similar precipitation depth. The mercury concentration in precipitation did not show a positive correlation with atmospheric RGM (reactive gaseous mercury) concentration, while maintaining good correlation with atmospheric $PM_{2.5}$ at Soyang Dam. This result suggests that the contribution of particulate Hg to the total Hg wet deposition should be more significant than that of RGM. In this study, both precipitation depth and precipitation type affected the amount of wet deposition and the concurrent mercury levels in precipitation. There was generally an inverse relationship between precipitation depth and Hg concentration in precipitation. Precipitation type was another factor that exerted controls on the Hg concentration in precipitation. As a result, the highest concentration of Hg was observed in snow, followed by in mixture (snow+rain) and in rain.

• Asian Journal of Atmospheric Environment
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• 제11권2호
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• pp.61-70
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• 2017

This study evaluated the human health risk in terms of the excess number of mortality and morbidity in the megacity Mumbai, India due to air pollution. AirQ software was used to enumerate the various health impacts of critical pollutants in Mumbai in past 22 years during 1992-2013. A relationship concept based on concentration-response relative risk and population attributable-risk proportion was employed by adopting World Health Organization (WHO) guideline for concentrations of air pollutants like $PM_{10}$, $SO_2$ and $NO_2$. For the year 1992 in Mumbai, it was observed that excess number of cases of total mortality, cardiovascular mortality, respiratory mortality, hospital admission due to COPD, respiratory disease and cardiovascular disease were 8420, 4914, 889, 149, 10568 and 4081 respectively. However, after 22 years these figures increased to 15872, 9962, 1628, 580, 20527 and 7905 respectively, but all of these reached maximum in the year 2006. From the result, it is also noted that except COPD morbidity the excess number of cases from 1992-2002 to 2003-2013 increased almost by 30%; and the excess number of mortality and morbidity is basically due to particulate matter ($PM_{10}$) than due to gaseous pollutants.