• Journal of Radiation Protection and Research
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• 제17권2호
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• pp.49-59
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• 1992

이온 또는 착화된 상태의 방사성핵종의 이동에 대한 착화제의 영향을 조사하기 위하여 새로운 모델이 제시되었다. 착화된 방사성핵종의 이동거동은 착화제와 착화된 방사성핵종의 열화를 포함하는 대류-확산 이동방정식에 의해 해석되었다. 이 수학적 모델은 해석적인 방법 에 의해 구해졌으며 지연요소를 조사함으로써 분석되었다. 계산결과들은 감소된 지연요소에 의해 착화된 방사성핵종의 이동속도가 이온형태의 방사성핵종보다 매우 빠름을 보여주었다. 따라서 원자력발전소로부터의 착화제의 발생과 환경으로의 유출을 감소시킬 수 있는 새로운 구제책이 필요하다고 하겠다.

• Journal of Pharmaceutical Investigation
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• 제15권2호
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• pp.53-62
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• 1985

Pivampicillin hydrochloride is a kind of broad spectrum antibiotics with bactericidal action, and is used in many countries, although it has bitter taste, unpleasant odour and side effects of irritating gastric mucosa, nausea, penicillin allergy, etc. For the improvement of such side effects of pivampicillin hydrochloride, microcapsules, with wall of ethylcellulose, have been prepared by coacervation method. The shape was observed through the scanning electron microscope, the release of the drug into an aqueous medium was studied and the effects of core: ethylcellulose ratio were interpreted as well as making sensory evaluation of taste and odour. There was decreasing trend in dissolution rate of the drug with the increase of core: ethylcellulose ratios, and the smaller microcapsules released their contents more rapidly. A linear relationship was established between the amount of ethylcellulose and the time for 60% release of the drug, and the release pattern was found to have similar characteristics to the release of the drug from an insoluble porous matrix. The release of the drug in the artificial intestinal fluids (pH 6.8) was found to be similar to that in water, while the release in the artificial gastric juice (pH 1.2) was slightly slower. Bioavailability of microcapsule was compared with that of pivampicillin hydrochloride in rabbits using serum concentration and urinary excretion measurements. Microcapsule gave showed slightly higher serum level than pivampicillin hydrochloride from 2 hours after administration, while no significant difference was observed in the accumulated urinary excretion rate between pivampicillin hydrochloride and microcapsule. The ulcer index of pivampicillin hydrochloride administered group was 2.6, and microcapsule administered group was 1.5, while control group was 0.8. Therefore it may be concluded that microencapsulation of pivampicillin hydrochloride is a useful pharmaceutical approach to protect the gastrointestinal tract from being injured by direct contact of pivampicillin hydrochloride without any significant difference of bioavailability.

• Journal of Electrochemical Science and Technology
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• 제11권3호
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• pp.273-281
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• 2020

Constructing and making highly active and stable nanostructured Pt-based catalysts with ultralow Pt loading are still electrifying for electrochemical applications such as water electrolysis and fuel cells. In this study, MoO₃ ribbons (RBs) of few micrometer in length is successfully synthesized via hydrothermal synthesis. Subsequently, 3-dimentional (3D)-silicate layer for about 10 to 15 nm is introduced via chemical deposition onto the pre-formed MoO₃ RBs; to setup the platform for Pt metaldots (MDs) deposition. In comparison with the bare MoO₃ RBs, the MoO₃-Si has served as a efficient solid-support for stabilizing and accommodating the uniform deposition of sub-2 nm Pt MDs. Such a structural design would effectively assist in improving the electronic conductivity of a fabricated MoO₃-Si-Pt catalyst towards MOR; the interfaced, porous and 3D silicate layer has assisted in an efficient mass transport and quenching the poisonous CO_ads species leading to a significant electrocatalytic performance for MOR in alkaline medium. Uniformly decorated, sub-2 nm sized Pt MDs has synergistically oxidized the MeOH in association with the MoO₃-Si solid-support hence, synergistic catalytic activity has been achieved. Present facile approach can be extended for fabricating variety of highly efficient Metal Oxide-Metal Nanocomposite for energy harvesting applications.

• 한국자동차공학회논문집
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• 제14권1호
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• pp.68-78
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• 2006

In the past few years, considerable efforts have been directed towards the further development of Urea-SCR(selective catalytic reduction) technique for diesel-driven vehicle. Although urea possesses considerable advantages over Ammonia$(NH_3)$ in terms of toxicity and handling, its necessary decomposition into Ammonia and carbon dioxide complicates the DeNOx process. Moreover, a mobile SCR system has only a short distance between engine exhaust and the catalyst entrance. Hence, this leads to not enough residence times of urea, and therefore evaporation and thermolysis cannot be completed at the catalyst entrance. This may cause high secondary emissions of Ammonia and isocyanic acid from the reducing agent and also leads to the fact that a considerable section of the catalyst may be misused for the purely thermal steps of water evaporation and thermolysis of urea. Hence the key factor to implementation of SCR technology on automobile is fast thermolysis, good mixing of Ammonia and gas, and reducing Ammonia slip. In this context, this study performs three-dimensional numerical simulation of urea injection of heavy-duty diesel engine under various injection pressure, injector locations and number of injector hole. This study employs Eulerian-Lagrangian approach to consider break-up, evaporation and heat and mass-transfer between droplet and exhaust gas with considering thermolysis and the turbulence dispersion effect of droplet. The SCR-monolith brick has been treated as porous medium. The effect of location and number of hole of urea injector on the uniformity of Ammonia concentration distribution and the amount of water at the entrance of SCR-monolith has been examined in detail under various injection pressures. The present results show useful guidelines for the optimum design of urea injector for reducing Ammonia slip and improving DeNOx performance.

• 한국지반공학회논문집
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• 제29권1호
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• pp.93-107
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• 2013

입상체의 열전도도 산정에 관한 연구는 다공질 매질이나 지반공학에서 다양하게 사용될 수 있다. 입상체의 열전도도 산정은 입자들 사이의 에너지 관계에 대한 모사를 통해 "유효 열전도도"를 획득하는 것으로 발전하였다. 본 연구는 불포화토의 유효 열전도도를 산정하기 위해 3차원 개별 요소법을 이용하여 입자를 생성하고 기존 네트워크 모델을 수정하여 적용하였다. 수정된 네트워크 모델을 검증하기 위해 3가지 다른 크기의 글라스 비즈와 주문진사를 이용하여 실내시험을 통해 흙-수분 특성 곡선과 포화도에 따른 시료의 열전도도를 산정하였다. 수정된 네트워크 모델에서는 흙-수분 특성 곡선을 사용하여 입자 사이의 평균 유효 열전달 실린더 반경을 조정하고 모델에 적용하였다. 일련의 실내시험과 수정된 네트워크 모델을 사용하여 결과를 비교한 결과, 흙-수분 특성 곡선을 적용한 네트워크 모델은 주어진 불포화 조건에서 입상체 시료의 유효 열전도도를 합리적으로 모사할 수 있는 것으로 나타났다. 또한, 포화상태의 유효 열전달 실린더 반경 계수로 정규화한 예측식을 제안하였다. 제안한 예측식을 통해 기존 네트워크 모델을 사용하여 불포화 상태에서 입상체의 유효 열전도도를 산정할 수 있다.