• 한국산학기술학회논문지
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• 제20권2호
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• pp.644-648
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• 2019

본 연구에서는 구획 공간에서 가솔린 화재 시 내벽의 열전도 계수 변화에 따른 열유동 현상에 관한 기초 연구를 수행하였다. 이를 위해서 내벽의 열전도 계수가 $0.18W/m{\cdot}K$인 내화보드의 재질로 구성된 가로 0.4 m, 세로 0.6 m, 높이 0.6m인 축소된 구획공간을 제작하였으며, 개구부 면적이 $0.12m^2$이고 연료 팬의 크기가 $0.01m^2$인 조건에서 가솔린 화재실험을 수행하여 높이 0.37 m 국부지점의 온도와 총괄 발열량을 산출하였다. 벽면 열전도 계수 변화가 구획 공간 내부의 온도 분포에 미치는 영향을 분석하기 위해서 화재해석 프로그램인 FDS(Fire Dynamic Simulator)를 사용하여 동일한 발열량 조건에서 온도분포 측정값과 해석결과를 비교하였다. 그 결과 최대 발열량이 4.8 kW인 정상상태 구간에서 온도분포 예측 값이 10 % 이내로 일치하는 것을 확인하였으며, 벽면 열전도 계수가 $0.1W/m{\cdot}K$에서부터 $100W/m{\cdot}K$까지 증가한 결과 벽면의 평균 온도는 약 71% 정도 감소되는 것으로 예측되었다.

• 한국정보전자통신기술학회논문지
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• 제10권5호
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• pp.469-475
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• 2017

소프트웨어 개발시행 과정에서 소프트웨어 신뢰성은 매우 기본적이고 필수적인 문제 중에 하나이다. 소프트웨어 고장현상을 파악하기 위하여 비동질적인 포아송 과정에서 순간 고장률인 강도함수가 고장시간에 독립적으로 일정하거나, 증가형 혹은, 감소형 추세를 가질 수 있다. 본 논문에서는 소프트웨어 설계 과정에서 강도형태가 감소패턴을 따르는 랜들리 수명분포와 증가하다가 감소하는 어랑수명 분포를 활용한 소프트웨어 신뢰속성 모형에 대하여 신뢰도 장단점에 관한 연구를 하였다. 소프트웨어 고장현상을 파악하기 위하여 모수추정은 최우추정법을 적용하였다. 따라서, 본 논문에서는 소프트웨어 고장시간 자료를 적용하여 소프트웨어 신뢰도를 비교하고, 평가하였다. 그 결과, 랜들리 모형이 어랑분포 모형보다 신뢰도가 상승하는 것으로 나타났으나, 어랑분포 모형에서는 형상모수가 높을수록 높은 신뢰도를 나타내는 추세를 보였다. 본 논문를 통하여 소프트웨어 기획 부서에서는 특정한 수명분포와 형상모수를 활용함으로서 소프트웨어 고장분석을 활용한 소프트웨어 신뢰성 모형에 대한 신뢰성 속성을 적용한 데이터 및 기본 지식을 제공함으로서 소프트웨어 설계에 실질적인 도움을 줄 수 있다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.252.1-252.1
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• 2010

These studies convert to useful electricity from swine wastewater and to treat this wastewater. In order to operate the microbial fuel cell(MFC) for the swine wastewater, the anode volume of MFCs was scaled up with 5L in the vacant condition. Graphite felts and low-priced mesh stainless-less as electrode had mixed up and packed into the anode compartment. The meshed stainless-less electrode could also be acted the collector of electron produced by microorganisms in anode. For a cathode compartment, graphite felt loaded Pt/C catalyst was used. Graphite felt electrode embedded in the anode compartment was punched holds at regular intervals to prevent occurred the channeling phenomenon. The sources of seeding on microbial fuel cell was used a mixture of swine wastewater and anaerobic digestion sludge(1:1). It was enriched within 6 days. Swine wastewater was fed with 53.26 ml/min flow rate. The MFCs produced a current of about 17 mA stably used swine wastewater with $3,167{\pm}80mg/L$. The maximum power density and current density was 680 $mW/m^3$ and 3,770 $mA/m^3$, respectively. From these results it is showed that treatment of swine wastewater synchronizes with electricity generation using modified low priced microbial fuel cell.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.96-96
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• 2016

Nanotechnology mostly employs nano-materials and nano-structures with distinctive properties based on their size, structure, and composition. It is quite difficult to produce nano-materials and nano-structures with identical sizes, structures, and compositions in large quantities, because of spatiotemporal fluctuation of production processes. In other words, fluctuation is the bottleneck in nanotechnology. We propose three strategies to suppress such fluctuations: employing 1) difference between linear and nonlinear phenomena, 2) difference in time constants, and 3) nucleation as a bottleneck phenomenon. We are also developing nano- and micro-scale guided assembly using plasmas as a plasma nanofabrication.1-5) We manipulate nano- and micro-objects using electrostatic, electromagnetic, ion drag, neutral drag, and optical forces. The accuracy of positioning the objects depends on fluctuation of position and energy of an object in plasmas. Here we evaluate such fluctuations and discuss the mechanism behind them. We conducted in-situ evaluation of local plasma potential fluctuation using tracking analysis of fine particles (=objects) in plasmas. Experiments were carried out with a radio frequency low-pressure plasma reactor, where we set two quartz windows at the top and bottom of the reactor. Ar plasmas were generated at 200 Pa by applying 13.56MHz, 450V peak-to-peak voltage. The injected fine particles were monodisperse methyl methacrylate-polymer spheres of $10{\mu}m$ in diameter. Fine particles were injected into the reactor and were suspended around the plasma/sheath boundary near the powered electrode. We observed binary collision of fine particles with a high-speed camera. The frame rate was 1000-10000 fps. Time evolution of their distance from the center of mass was measured by tracking analysis of the two particles. Kinetic energy during the collision was obtained from the result. Potential energy formed between the two particles was deduced by assuming the potential energy plus the kinetic energy is constant. The interaction potential is fluctuated during the collision. Maximum amplitude of the fluctuation is 25eV, and the average is 8eV. The fluctuation can be caused by neutral molecule collisions, ion collisions, and fluctuation of electrostatic force. Among theses possible causes, fluctuation of electrostatic force may be main one, because the fine particle has a large negative charge of -17000e and the corresponding electrostatic force is large compared to other forces.

• 한국안전학회지
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• 제31권4호
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• pp.55-63
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• 2016

A dust explosion is a phenomenon of strong blast wave propagation involving destruction which results from dust pyrolysis and rapid oxidation in a confined space. There has been some research done to find individual explosion characteristics and common physical laws for various dust types. However, there has been insufficient number of studies related to the heat of combustion of materials and the oxygen consumption energy about materials in respect of dust explosion characteristics. The present study focuses on the relationship between dust explosion characteristics of wood dust samples and oxygen consumption energy. Since it is difficult to estimate the weight of suspended dust participating in explosions in dust explosion and mixtures are in fuel-rich conditions concentrations with equivalent ratios exceeding 1, methods for estimating explosion overpressure by applying oxygen consumption energy based on unit volume air at standard atmospheric pressure and temperature are proposed. In this study an oxygen consumption energy model for dust explosion is developed, and by applying this model to TNT equivalent model, initial explosion efficiency was calculated by comparing the results of standardized dust explosion experiments.

• 대한한방내과학회지
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• 제1권1호
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• pp.25-34
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• 1976

The extract of commercial mistletoe caused transient contraction of mouse ileum in vitro at the level of $7{\times}10^{-4}g/ml$ and augmented significantly its peristalsis. When the ileum was pre-treated With $10^{-6}g/ml$ of adrenaline the administration of the extract at a level of $10^{-4}g/ml$ blocked the contraction. The increase inperistalsis and intention was also observed in rabbit ileum in vitro with the administration of the extract at a level of $10^{-1}g/ml$ but these phenomenon were inhibited by the adrenaline treatment at a level of $10^{-6}g/ml.$ When the extract was applied to spirally cut strips of thoracic aorta at the level of $10^{-3}g/ml$ the contractile action of adrenaline was significantly inhibited. When the extract was infused to auricular blood vessel of rabbit at the rate of $10^{-4}g/ml,\;10^{-3}g/ml,\;10^{-2}g/ml$ and $10^{-1}g/ml$ increases in number of drops by 70%, 77%, 93% and 100% were observed if the maximum number of drops caused by $10^{-1}g/ml$ is considered to be 100%. The duration of prolongation was proportionate to the increase in concentration of the extract. Hypotensive action of the extract and its duration were proportionately increased as the quantity of the extract increased. The increase in number and depth of respiration observed during the hypotensive status was brought to the normal when the tension became normal. In view of these observations it is concluded that the extract of commercial mistletoe has a contractile action of acetylcholine effect in the ileum of mouse and rabbit, loosens both aorta and smooth muscle and promotes peripheral circulation. As for the hypotensive action it is concluded that the action is brought about by the decrease in peripheral circulatory resistance due to the antagonism between acetylcholine and adrenaline.

• Journal of Communications and Networks
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• 제11권5호
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• pp.518-528
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• 2009

IEEE 802.11 wireless local area network (WLAN) has become the prevailing solution for wireless Internet access while transport control protocol (TCP) is the dominant transport-layer protocol in the Internet. It is known that, in an infrastructure-based WLAN with multiple stations carrying long-lived TCP flows, the number of TCP stations that are actively contending to access the wireless channel remains very small. Hence, the aggregate TCP throughput is basically independent of the total number of TCP stations. This phenomenon is due to the closed-loop nature of TCP flow control and the bottleneck downlink (i.e., access point-to-station) transmissions in infrastructure-based WLANs. In this paper, we develop a comprehensive analytical model to study TCP dynamics in infrastructure-based 802.11 WLANs. We calculate the average number of active TCP stations and the aggregate TCP throughput using our model for given total number of TCP stations and the maximum TCP receive window size. We find out that the default minimum contention window sizes specified in the standards (i.e., 31 and 15 for 802.11b and 802.11a, respectively) are not optimal in terms of TCP throughput maximization. Via ns-2 simulation, we verify the correctness of our analytical model and study the effects of some of the simplifying assumptions employed in the model. Simulation results show that our model is reasonably accurate, particularly when the wireline delay is small and/or the packet loss rate is low.

• Journal of Korean Society for Atmospheric Environment
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• 제17권E3호
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• pp.91-99
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• 2001

Plasma reactor was used to generate a high potential difference between two surfaces of concentric pyrex tubes by electrical current. The annular gap of the reactor was calculated by trial and error from the breakdown voltage equation and set at 0.45 cm. The overall objective of this research was to know the effects of the frequency, humidity, and residence time on the formation of nitrogen oxides in a plasma reactor. The primary voltage varied from 50 to 90 volts and the frequency was varied in increments of 10 Hz from 60 to 650 Hz at the primary voltage of 90. The increase in the secondary voltage was not linear but exponential at high frequencies. At a maximum concentration of about 745 ppm, the frequency and secondary voltage was 600 Hz and 4,200 volts, respectively. All tests for the effects of humidity on NO$_{x}$ production were performed at the optimal setting of 90 colts and 600 Hz frequency. Since the NO$_{x}$ production was not an one dimensional phenomenon, competing reactions were assumed to occur in the discharge chamber. The sharp peak concentration of 1,810 ppm was observed at 38% of relative humidity, The enhanced production was choked off, and the production rate rapidly dropped to 3 ppm at above 40% of relative humidity. It is assumed that the corona attacks the most vulnerable molecules in the reaction chamber before attacking other more lightly bonded molecules, possibly at humidities above 38% and the optimized 90 volt setting. Thus, there was not enough energy left after attacking all water molecules to decompose an appreciable amount of $N_2$. If nitrogen breakdown does not occur, then oxides of nitrogen are not likely to be produced.ced.

• 약학회지
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• 제26권4호
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• pp.239-251
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• 1982

The rate of deterioration of contractile force of isolated hearts from control and panax ginseng treated rats was determined and response of contractile force of the hearts from ginseng treated rats to several autonomic and other drugs was investigated. Rats weighing 150-250g were administrered orally with ginseng ethanol extract (100mg/kg) and total ginseng saponin (50mg/kg/day) for a week. Ginsenoside Rb$_{1}$ (5mg/kg/day) and ginsenoside Re (5mg/kg/day) were administered respectively for a week. The isolated hearts from rats were perfused with Krebs-Henseleit solution by using Langendorff perfusion apparatus. The control group was only able to maintain approximately 75.5% of their initial strength after 60 min of perfusion, whereas ginseng ethanol extract, total ginseng saponin treated hearts were able to sustain nearly their initial strength even after 60 min. Ginsenoside Rol treated hearts also sustained 93% of their initial strength, but there was no significant difference in the deterioration percentage of the contractile force of ginsenoside Re treated hearts. Experiments were conducted to study the response to perfusion of ginseng treated animal heart with epinephrine, isoproterenol, propranolol, and phenobarbital. The isolated hearts were perfused with Krebs-Henseleit solution containing epinephrine (10$^{-6}$ M), isoproterenol ($10^{-7}$M), propranolol ($10^{-6}$M) and phenobarbital (7{\times}10^{-3}M$) respectively. The maximum inotropic effect of epinephrine and isoproterenol was observed after 2~3 minutes of drug perfusion. Effect of epinephrine on ginseng ethanol extract and total ginseng saponin treated hearts was reduced compared with control. On the other hand, this phenomenon was not observed in ginsenoside Re treated rats but on ginsenoside $Rb_{1}$ treated rats. The positive inotropic effect of isoproterenol was reduced in the hearts from ginseng treated rats compared with control heart, Propranolol or phenobaribital decreased the contractile force in the control rats. The depressant effect of propranolol and phenobarbitat on ginseng treated rat hearts was less than those of control rat hearts. The result suggest that ginseng ethanol extract , ind total ginseng saponin and ginsenoside $Rb_{1}$ may protect the deterioration of contractile force of the heart and may attenuate the response to several drugs on hearts.

• 한국항만경제학회지
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• 제27권4호
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• pp.207-218
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• 2011

본고에서는 환율과 경기가 우리나라의 대 동남아시아 항만 수출입에 미치는 영향을 분석하였다. 분석을 시작하기 이전에 먼저 단위근 검정과 공적분 검정을 이용하여 변수와 모형이 안정적인가를 살펴보았다. 단위근 검정 결과 1차 차분한 시계열자료는 귀무가설의 기각에 성공함에 따라 Johansen 검정을 실시하여 적어도 하나의 공적분 벡터가 존재하는 것으로 나타났다. 이에 따라 공적분 벡터와 VECM을 추정하였다. 추정결과 대체적으로 가격변수와 소득변수의 부호는 이론과 일치하였다. 수출의 경우 수출의 환율탄력성의 경우 그 크기의 순서는 인도네시아가, 수출의 소득탄력성의 경우는 베트남이 가장 큰 것으로 나타났다. 그리고 오차수정항 크기의 순서는 베트남이 가장 큰 것으로 나타났다. 또한 수입의 경우 수입과 소득의 환율탄력성의 경우 그 크기의 순서는 베트남이 가장 큰 것으로 나타났다. 그리고 오차수정항 크기의 순서는 말레이시아가 가장 큰 것으로 나타났다. 결론적으로 대부분의 국가들에서 수출의 환율과 경기탄력성보다 수입의 환율과 경기탄력성이 크게 나타남으로써 수출시장 확대에는 큰 한계가 존재함을 보여주었다.