• Nuclear Engineering and Technology
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• 제53권6호
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• pp.2025-2037
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• 2021

The influence of lead cations on natural quartz (QZ) from Egypt as a glass shielding material for the composition with nominal formula (10Na₂O - (90 - x) QZ - xPbO (where x = 30, 35, 40, 45 and 50 mol %)) was examined. The studied samples are synthesized via the melt quenching method at 1050 ℃. The X-ray diffraction XRD patterns were confirmed the glass nature for studied samples. Moreover, the optical properties, and the transparency for all compositions were examined by UV-Vis spectroscopy. Also, the major elemental composition of the natural quartz were estimated via the X-ray fluorescence (XRF) technique. Further, the density and molar volume were determined. Furthermore, the nuclear shielding parameters such as, mass attenuation coefficient, effective atomic number, electronic density, the total atomic, and electronic cross sections as well as the mean free path, and the half value layer with different gamma ray energies (81 keV-1407 keV) were calculated. Besides, the results showed that the shielding behavior towards the gamma ray radiation for all glass samples was increased as the increment in PbO concentration in the glass system.

• 자원환경지질
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• 제38권5호
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• pp.513-523
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• 2005

울산 달천광산의 지하수 및 토양 중에 함유되어 있는 비소의 오염현황을 파악하고, pH와 산화-환원 전위 값의 변화에 따른 자연저감 능력을 평가하였다. 달천광산 지역 비소 오염의 주 근원광물인 유비철석의 광미 내 함량은 최대 $2\%$이며, 비독사석, 니콜라이트, 램멜스버가이트, 거스도르파이트, 코발트석과 황철석 등의 비소함유광물 역시 비소오염의 근원이 되고 있으며, 비소함량은 광물에 따라 다양한 차이를 보인다 광미장 내 유비철석과 황철석의 표면이 부분적으로 철산화물과 철비산염으로 산화된 것을 관찰할 수 있어, 풍화반응이 상당히 진행되었음을 알 수 있다. 지하수 내 비소의 함량과 pH는 뚜렷한 상관관계를 보이지 않지만, 포화대 및 비포화대의 지하수의 비소 농도는 Eh가 감소함에 따라 농도가 감소하는 정(+)의 상관관계를 보인다. RMB(Red Mud Bauxite)는 비소제거 효율이 우수하여 달천광산 지역의 비소로 오염된 지하수 및 토양을 복원 시 자연저감 촉진제로 이용될 수 있을 것이다.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2011년도 학술대회 및 정기총회
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• pp.33-36
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• 2011

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2005년도 INTERNATIONAL SYMPOSIUM ON SOIL & GROUNDWATER ENVIRONMENT
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• pp.245-246
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• 2005

• 한국지하수토양환경학회지:지하수토양환경
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• 제19권4호
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• pp.62-69
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• 2014

In the results of monitoring nitrate concentration in more than 8,000 groundwater wells around agro-livestock, the average and maximum nitrate concentration was 9.4 mg/L and 101.2 mg/L, respectively. Since about 31% of the monitoring wells was exceed the quality standard for drinking water, nitrate control such as remediation or source regulation is required to conserve safe-groundwater in South Korea. Typical nitrate-treatment technologies include ion exchange, reverse osmosis, and biological denitrification. Among the treatment methods, biological denitrification by indigenous microorganism has environmental and economic advantages for the complete elimination of nitrate because of lower operating costs compared to other methods. Major mechanism of the process is microbial reduction of nitrate to nitrite and nitrogen gas. Three functional genes (nosZ, nirK, nirS) that encode for the enzyme involved in the pathway. In this work, we tried to develop simple process to determine possibility of natural denitrification reaction by monitoring the functional gene. For the work, the functional genes in nitrate-contaminated groundwater were monitored by using PCR with specific target primers. In the result, functional genes (nosZ and nirK) encoding denitrification enzymes were detected in the groundwater samples. This method can help to determine the possibility of natural-nitrate degradation in target groundwater wells without multiplex experimental process. In addition, for field-remediation application we selected nitrate-contaminated site where 200~600 mg/L of nitrate is continuously detected. To determine the possibility of nitrate-degradation by stimulated-natural attenuation, groundwater was sampled in two different wells of the site and nitrate concentration of the samples was 300 mg/L and 616 mg/L, respectively. Fumarate for different C/N ratio was added into microcosm bottles containing the groundwater to examine denitrification rate depending on carbon concentration. In the result, once 1.5 times more than amount of fumarate stoichiometry required was added, the 616 mg/L of nitrate and 300 mg/L of nitrate were completely degraded in 8 days and 30 days. The nitrite, byproduct of denitrification process, was also completely degraded during the experimental period.

• 한국자동차공학회논문집
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• 제18권2호
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• pp.114-121
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• 2010

As a vehicle speed increases, more vibration energy is transmitted from chassis to a driver. Current isolation system for the driver's seat by damping control can reduce the transmitted vibration energy near resonance area. But in higher frequency region than natural frequency multiplied by $\sqrt{2}$, the vibration energy transmitted to the driver has a tendency to be increased. Therefore, the method by natural frequency reduction of the system is preferred to increase the effectiveness of the anti-vibration. However, the natural frequency could not be freely reduced due to the nature of the isolation system structure. A new passive suspension system to reduce the natural frequency is proposed. The theoretical analysis and experimental results show better vibration attenuation compared with the current isolation system.

• 환경위생공학
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• 제19권4호
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• pp.19-24
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• 2004

The objective of this study was to develop a mechanistically based mathematical model that would consider the interdependence of VOCs transport, microbial activity, and sorptive interactions in a moist, unsaturated soil. Because the focus of the model was on description of natural attenuation, the advective VOCs transport that is induced in engineered remediation processes such as vapor extraction was not considered. The utility of the model was assessed through its ability to describe experimental observations from diffusion experiments using toluene as a representative VOCs in well-defined soil columns that contained a toluene degrading bacterium, Pseudomonas putida G7 md Fl, as the sole active microbial species. The gas-liquid mass-transfer was found to be a key parameter controlling the ability of bacteria to degrade VOCs. This finding indicates that soil size and geometry are likely to be important parameters in assessing the possible success of natural attenuation of VOCs in contaminated unsaturated soils. Therefore we found that Pseudomonas putida G7 and Fl were very effective to remove of refractory pollutants such as toluene in soil by Bio-filter

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2004년도 총회 및 춘계학술발표회
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• pp.255-259
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• 2004

본 연구에서는 유류오염 토양현장샘플을 이용한 실험실 규모의 회분식 실험을 통해 다양한 환원조건하에서 BTEX와 MTBE의 자연정화 평가 및 현장 생복원 기술 적용 타당성을 검토하는데 있다. 첫째, 오염토양과 비오염 토양에서 충분한 전자수용체의 존재는 유류오염물질의 생분해능을 증가시킬 수 있었음 알았다. 둘째, 같은 토양이라도 전자수용체의 종류와 유류오염물질의 특성에 따른 생분해능의 다양성을 확인할 수 있었다. 셋째, BTEX에 비해 MTBE의 분해가 매우 느림을 확인하였다. 본 실험은 아직 초기 단계의 실험으로 현장 조건을 충분히 만족 시키지는 못한다. 추가적인 pH 변화에 따른 전자수용체의 이용 특성 및 토양-지하수 microcosm test, 혐기성 생분해 부산물인 $CO_2$, $N_2$ 또는 $N_2$O, TBA의 연구가 실시되어야 하겠다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 I
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• pp.229-234
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• 2001

A practical and effective semi-active on-off control law is developed for vibration attenuation of a natural, multi-degree-of-freedom suspension system, when its operational response mode is available. It does not need the accurate system parameters and dynamics of semi-active actuator. It reduces the total vibratory energy of the system including the work done by external disturbances and the maximum energy dissipation direction of the semi-active control device is tuned to the operational response mode of the structure. The effectiveness of the control law is illustrated with a three degree-of-freedom excavator cabin model.

• 전자공학회논문지A
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• 제29A권4호
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• pp.7-13
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• 1992

Diffraction loss occurs when the propagation path is obstructed by mountains and hills between a base station antenna and a moving vehicle antenna in mobile-radio communication. In this paper an approximate mathematical model using Fresnel-Kirchhoff diffraction theory is considered to predict propogation attenuation by natural obstacles with lateral profiles having general shapes. Field tests are conducted using helical and crossed drooping dipole antenna at 820 MHz. The theoretical analysis used in estimating the effects of hills agrees reasonably with experimental data. The results seem to be useful for estimating the level of received power, the minimum allowable input power, the optimum site of base station and consequently, planning terrestrial microwave links.