• 한국지하수토양환경학회:학술대회논문집
• /
• 한국지하수토양환경학회 2005년도 총회 및 춘계학술발표회
• /
• pp.114-116
• /
• 2005

Natural attenuation has been actively studied and often selected as final clean-up process in remediation of contaminated ground-water and soil for the last decade. Accordingly, understanding of natural processes affecting the fate and transport of contaminants in the subsurface becomes important for a success of implementation of the natural remediation strategy, Contaminant advection and diffusion processes in the unsaturated zone are naturally related to environmental changes in the atmosphere. The atmospheric pressure changes affecting the transport of contaminants in the subsurface are investigated in this study. Moisture content, trichloroethylene (TCE) concentration, temperature, and pressure variations in the subsurface were measured for the July, August, November, and December 2001 at Picatinny Arsenal, New Jersey. These data were used for a one-phase flow and one-component transport model in simulating the soil-gas flow and accordingly the TCE transport in the subsurface in accordance with the atmosphere pressure variations at the surface. The soil-gas velocities during the sampling periods varied with a magnitude of $10^{-6}\;to\;10^{-7}\;m\;s^{-1}$ at land surface. The TCE advection fluxes at land surface were several orders of magnitude smaller than the TCE diffusion fluxes. A sensitivy analysis indicated that advection fluxes were more sensitive to changes in geo-environmental conditions compared to diffusion fluxes. Of all the parameters investigated in this study, moisture content has the most significant effect on TCE advection and diffusion fluxes.

• 자원환경지질
• /
• 제32권1호
• /
• pp.101-111
• /
• 1999

Sedimentary organic matter, exposed to continental surficial environment, reacts with oxygen supplied from the atmosphee and forms carbon-containing oxidation products. Knowledge of the rate and mechanisms of sedimentary organic matter weathering is important because it is one of the major controls on atmospheric oxygen level through geologic time. Under the abiological conditions, the oxidation rate of coal organic matter by molecular oxygen is enhanced by the increase of oxygen concentration and temperature. At ambient temperature and pressure, aqueous coal oxidation results in the formation of dissolved $CO_2$ dissolved organic carbon and solid oxidation products which are all quantitatively significant reaction products. The effects of pH, ultraviolet light, and microbial activity on the weathering of sedimentary organic matter are poorly contrained. Based on the results of geochmical and environmental studies, it is believed that the photochemical reaction should play an important role in the decomposition and oxidation of sedimentary organic matter removed from the weathering profile. At higher pH conditions, the production rate of DOC can be accelerated due to base catalysis. These high molecular weight oranic matter can react with man-made pollutants such as heavy metal ions via adsorption/desorption or ion exchange reactions. The effect of microbial activity on the oxidative weathering of sedimentary organic matter is poorly understood and remains to be studied.

• 한국자동차공학회논문집
• /
• 제2권5호
• /
• pp.11-22
• /
• 1994

The pupose of this study is to measure droplet size and velocity simultaneously for a transient diesel fuel spray in a quiescent chamber at atmospheric temperature and pressure. Generally, diesel combustion phenomena is mainly governed by characteristics of injection system and fuel spray. Therefore we need to clarify these characteristics for developing more economical diesel systems. In this study, correlation between droplet size and velocity was measured at downstream distance from nozzle. Governing parameters are pump speed and fuel quantity for the detailed nature in this transient diesel fuel spray. It is observed effect to the droplet size and velocity distribution. Velocity(peak, mean, rms), number density and droplet size were investigated simulaneously using PDA in the spray. Various results are presented to illustrate the effects of operation factors and correlation between the droplet diameter and velocity.

• 한국항공우주학회지
• /
• 제39권4호
• /
• pp.348-353
• /
• 2011

액체 질소를 이용하여 극저온 단일 제트 유동의 특성을 관찰하였다. 고압 챔버 내부에 액체 질소를 분사하여 단일 제트를 생성, 주위기체압력을 변화시킴으로써 아임계 조건부터 초임계 조건의 주위 환경에 따른 제트의 특성 변화를 확인하였다. 또한 분사기의 길이 대 직경비 및 분사기 내부 형상의 변화에 따른 제트의 특성 변화를 파악하였다. 유동 가시화를 통하여 극저온 제트의 형상 및 액주의 지름을 측정하였으며, 이로부터 액주의 확산각을 계산하여 이전 연구 결과와 비교하였다. 아임계 조건 및 초임계 조건에서의 제트의 형상 변화를 관찰하였으며, 주위기체압력이 대기압과 동일할 경우 제트 유동에서 불안정이 발생함을 확인하였다. 또한 주위기체압력이 증가함에 따라 액주의 확산각이 점차 증가하다가 일정 압력 이상에서 거의 일정하게 유지됨을 확인하였다.

• 한국수소및신에너지학회논문집
• /
• 제13권3호
• /
• pp.214-223
• /
• 2002

Kinetic and effectiveness factors for methanol steam reforming using commercial copper-containing catalysts in a plug flow reactor were investigated over the temperature ranges of $180-250^{\circ}C$ at atmospheric pressure. The selectivity of $CO_2$/$H_2$ was almost 100%, and CO products were not observed under reaction conditions employed in this work. It was indicated that $CO_2$ was directly produced and CO was formed via the reverse water gas shift reaction after methanol steam reforming. The intrinsic kinetics for such reactions were well described by the Langmuir-Hinshelwood model based on the dual-site mechanism. The six parameters in this model, including the activation energy of 103kJ/mol, were estimated from diffusion-free data. The significant effect of internal diffusion was observed for temperature higher than $230^{\circ}C$ or particle sizes larger than 0.36mm. In the diflusion-limited case, this model combined with internal effectiveness factors was also found to be good agreement with experimental data.

• Tuberculosis and Respiratory Diseases
• /
• 제83권2호
• /
• pp.116-121
• /
• 2020

Particulate matter (PM) is suspended dust that has a diameter of <10 ㎛ and can be inhaled by humans and deposited in the lungs, particularly the alveoli. Recent studies have shown that PM has an adverse effect on respiratory diseases. The aim of this article is to review respiratory diseases associated with PM. According to existing studies, PM is associated with chronic obstructive pulmonary disease, bronchial asthma, and several other respiratory diseases and increases the mortality rates of these diseases. Moreover, increased exposure in the high concentration of atmospheric PM is associated with the development of lung cancer. The most simple and common way to protect an individual from airborne PM is to wear a face mask that filters out PM. In areas of high concentration PM, it is recommended to wear a face mask to minimize the exposure to PM. However, the use of N95 or KF94 masks can interfere with respiration in patients with chronic respiratory diseases who exhibit low pulmonary function, leading to an increased risk of respiratory failure. Conclusionally, reduction of the total amount of PM is considered to be important factor and strengthening the national warning notification system to vulnerable patients and proper early management of exacerbated patients will be needed in the future.

• 한국전자파학회논문지
• /
• 제25권1호
• /
• pp.123-129
• /
• 2014

고도 탐지 정확도는 장거리 다기능 레이더 등에서 필수적으로 분석되어야 하는 성능이지만, 기상 등 대기 현상에 의한 영향이 크기 때문에 정확한 분석이 어렵다. 따라서 고도에 따른 굴절율을 사용하여 보상을 수행하는데, 본 논문에서는 고층 기상에 의한 대기 굴절율을 고려할 수 있는 광선 추적 모의환경을 구축하고, 실환경 굴절율과 모델링된 굴절율을 각각 고려하여, 모델링된 굴절율을 실환경에 적용시 발생할 수 있는 고도 오차를 분석하였다. 모델링된 굴절율을 이용하여 고도 오차 보상값을 산출하였으며, 보상에 의한 결과를 모델링하여 고도 보상시 발생할 수 있는 고도 정확도를 정규함수로 모델링하여 통계적으로 분석하였다.

• Nuclear Engineering and Technology
• /
• 제31권1호
• /
• pp.29-48
• /
• 1999

Local two-phase flow parameters of subcooled flow boiling in inclined annulus were measured to investigate the effect of inclination on the internal flow structure. Two-conductivity probe technique was applied to measure local gas phasic parameters, including void fraction, vapor bubble frequency, chord length, vapor bubble velocity and interfacial area concentration. Local liquid velocity was measured by Pilot tube. Experiments were conducted for three angles of inclination; 0$^{\circ}$(vertical), 30$^{\circ}$, 60$^{\circ}$. The system pressure was maintained at atmospheric pressure. The range of average void fraction was up to 10% and the average liquid superficial velocities were less than 1.3 m/sec. The results of experiments showed that the distributions of two-phase How parameters were influenced by the angle of channel inclination. Especially, the void fraction and chord length distributions were strongly affected by the increase of inclination angle, and flow pattern transition to slug flow was observed depending on the How conditions. The profiles of vapor velocity, liquid velocity and interfacial area concentration were found to be affected by the non-symmetric bubble size distribution in inclined channel. Using the measured distributions of local phasic parameters, an analysis for predicting average void fraction was performed based on the drift flux model and flowing volumetric concentration. And it was demonstrated that the average void fraction can be more appropriately presented in terms of flowing volumetric concentration.

• 반도체디스플레이기술학회지
• /
• 제10권4호
• /
• pp.101-106
• /
• 2011

There are various methods in the flat panel display manufacture. The cost reduction effect is very big in case of using the screen printing method. The screen printing method is much used in the process of forming PDP barrier and can apply to the process of arranging the pillars for maintaining the vacuum gap of the vacuum glazing panel. The pillar which is one of the core elements for comprising vacuum glazing maintains the vacuum gap overcoming the vacuum pressure difference with the atmospheric pressure generated in vacuum glazing. At the same time, the deformation phenomenon by vacuum pressure is relived. In this paper, by using FEM about three considered in the pillar design and arrangement kinds of limiting factors, the simulation was performed. The pillar optimum arrangement method at within the maximum allowable tensile stress and heat transfer coefficients according to the arrangement try to be presented based upon the analyzed result data review and this validity tries to be verified by FEM.

• Journal of the Optical Society of Korea
• /
• 제19권5호
• /
• pp.514-520
• /
• 2015

This paper presents a novel shore-to-sea maritime data transmission system based on time-code diversity, using visible light in maritime environments to overcome the limitations of conventional maritime wireless communications. The proposed system is primarily comprised of existing LED-based lighthouses and maritime transceivers (marine beacons, buoys, etc.), and thus is considered cost-effective in terms of implementation. We first analyze maritime visible-light communications on the basis of the unique properties of a maritime environment, i.e. sea states (wave height, wind speed, etc.), plus atmospheric turbulence, using the Pierson-Moskowitz (PM) and JONSWAP (JS) spectrum models. It is found that the JS model outperforms the PM model, and that the coverage distance depends on the LED power and sea states. To combat maritime fading conditions that significantly degrade performance and coverage distance, we propose a time-code diversity (TCD) scheme in which the delayed versions of the original data are retransmitted using orthogonal Walsh codes. This TCD scheme is found to be superior, in that it offers three orders of magnitude in terms of BER performance, compared to a conventional (non-TCD) transmission scheme. The proposed scheme is robust and efficient in overcoming the effect of impairments present in maritime environments with a BER of approximately $10^{-5}$and a data rate of 100 Kbps at a distance of 1 km.