• Journal of Pharmaceutical Investigation
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• 제25권4호
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• pp.353-363
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• 1995

The purpose of this study was to investigate the intestinal and nasal absorption enhancement of cefotaxime (CTX) by ion-pairing with counterions and to design an effective oral and intranasal drug delivery system for antibiotics. Counterions for absorption promotion were cationic surfactants [cetylpyridinium chloride (CP), cetrimide (CT) and benzalkonium chloride (BA)]. In the presence of counterions, the apparent partition coefficient of cefotaxime was increased depending on the molar concentration of the counterions. Anion interference was observed for ion-pairing of cefotaxime with counterions because of the counterbalance between an anion and counterions. The present study employed the in situ simultaneous nasal and intestinal perfusion technique in rats. The apparent permeabilities $(P_{app})$ of cefotaxime were $1.43{\pm}0.04{\times}10^{-5}\;cm/sec(mean{\pm}S.E)$ in the nasal cavity and 0 in the jejunum, respectively, which indicated that the intrinsic absorptivity of cefotaxime was greater in the nasal cavity than in the jejunum. When ionupairing formers were used, the decreasing order of apparent cefotaxime permeability $(P_{app},\;10^{-5}\;cm/sec)$, corrected for surface area of absorption, was as followings: $BA\;(7.50{\pm}0.36)\;>\;CT\;(4.92{\pm}0.24)\;>\;CP\;(3.01{\pm}0.17)$ in the jejunum and $BA\;(22.31{\pm}1.36)\;>\;CP\;(18.24{\pm}0.81)\;>\;CT \;(16.22{\pm}1.87)$ in the nasal cavity. The increase in permeability of cefotaxime was about 13-fold in the rat nasal cavity and was marked in the rat jejunum for ion-pairing with counterions as compared to those without ion-pairing. The damages of jejunal and nasal mucosal membrane by counterions were observed within approximately 2hrs after removal of ion-pair of cefotaxime with counterions from the nasal cavity and jejunum. These results suggest that CP can be used as an ion-pairing former in the jejunum and CP and CT can be used as ion-pairing formers in the nasal cavity for cefotaxime, as well as for poorly absorbed drugs with a negative charge due to ionization.

• 한국식품영양과학회지
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• 제28권2호
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• pp.429-437
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• 1999

A mathematical model was established for estimating changes in pressure and volume of permeable kimchi packages. The model comprises the CO2 gas production from kimchi and permeation of O2, CO2 and N2 through the permeable film or sheet. Using the developed model, the effects of various packaging variables on the pressure and volume changes were analyzed for rigid and flexible packag es of kimchi(3% salt content) at 15oC, and then effect of storage temperature was also looked into. In case of rigid pack of 400g, using the plastic sheet of high CO2 permeability and initial vacuumizing can help to relieve the problem of pressure build up. The lower fill weight can further reduce the pressure, but will result in higher packaging cost. For the flexible package of 3 kg, highly permeable films such as low density polyethylene(LDPE) and polypropylene can reduce the volume expansion. Higher ratio of CO2 permeability to O2 and N2 permeabilities are effective in reducing the volume expansion. Increased surface area cannot contribute to reduction of volume expansion for highly permeable flexible packages of kimchi. For the impermeable packages, pressure and volume at over ripening stage (acidity 1.0%) increase with decreased temperature, while those at optimum ripening stage(acidity 0.6%) change little with temperature. Pressure of permeable rigid LDPE package increases with tem perature at any ripening stage, and temperature affects the volume of flexible LDPE package very slightly. Experimental verification of the present results and package design with economical consid eration are needed as a next step for practical application.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.625-628
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• 2008

본 연구에서는 국내의 대표적인 보수재료인 폴리머시멘트계열의 단면복구재 3종 및 표면보호재 2종에 대해 촉진중성화 시험을 실시하여 국내 보수재료의 중성화 저항성능을 평가하였다. 기존의 KS 시험규격인 침투깊이 측정법과 함께 유럽시험규격인 BS EN 1062-6에서 규정한 등가공기층 확산두께산정을 적용하였다. 등가공기층 확산두께($S_D$)란 코팅재와 동일한 이산화탄소투과성과 동일한 조건을 가지고 있는 부동 공기층의 두께로서, 시편을 할렬 파괴하지 않으므로 동일한 시편으로 연속적인 시험을 진행할 수 있다는 장점이 있다. 시험결과 단면복구재의 경우 중성화깊이 측정법을 통해 이산화탄소 투과저항성을 평가할 수 있는 반면 표면보호재의 경우에는 이산화탄소 투과량 측정을 통한 등가공기층 두께 산정법이 효과적인 이산화탄소 투과저항성능 평가방법임을 밝혔다.

• 한국지반신소재학회논문집
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• 제6권1호
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• pp.33-38
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• 2007

연직배수재는 필터와 코어로 형성되며, 필터의 주요기능으로 첫째, 흙 입자의 유실을 방지할 수 있는 흙 보유성과 둘째, Clogging 또는 Blinding현상 발생 없이 간극수를 원활히 배출시키는 투수성을 갖추어야 한다. 상대적으로 투수성이 낮은 지반에서 미세입자로 인하여 필터의 투수성을 저하시키는 필터폐색(Clogging) 현상이 발생하는데 필터의 폐색현상(Clogging)이 점진적으로 증가하면, 간극수의 흐름을 저하시켜 결국 압밀지연을 초래한다. 지반-필터의 거동에 따른 설계(시방)기준은 토목섬유 필터의 간극크기와 흙의 입도의 상관관계에 의해 결정되어야 하나, 국내에서는 필터폐색(Clogging)현상과 지반-필터의 거동 분석 없이 필터재의 유효입경(AOS, Apparent Opening Size)만을 고려하여 필터의 설계(시방)기준을 일률적으로 적용하고 있다. 따라서, 본 연구에서는 3가지 종류의 연직배수재 필터를 대상으로 필터의 거동 및 필터폐색(Clogging)현상을 평가하고자 실내시험을 수행하였고, 이를 토대로 ${\bigcirc}{\bigcirc}$지역에서 연직배수재 필터의 설계(시방)기준을 선정하여 적용하였다.

• Geomechanics and Engineering
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• 제21권2호
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• pp.207-213
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• 2020

Umbrella Arch Method (UAM) often employed in the tunnel construction under poor rock mass conditions in Korea. Insertion of steel pipes at the periphery of the tunnel and infiltration of grouts along the pipes into the rock masses increases tunnel stability. There are two major effects of grouts expected at the tunnel face: 1) increase of face stability by enhancing the frictional resistance of discontinuities and 2) decrease of permeability along the rock masses. Increase of resistance and decrease of permeability requires a certain curing time for the grout. In Korea, we require 24 hours for curing of grout, which means no progress of excavation for 24 hours after infiltration of grouts. This step delays the tunnel construction sequences. To eliminate such inefficiency, we propose MTG (Method for Tunnel construction using Grouting technology), which uses extended length of steel pipes (14 m) compared to conventional pipe roof method (12 m). The merit of MTG is the reduction of curing time. Because of the approximately 2 m extension of the length of steel pipe, blasting can be done after infiltration of grouting. For this paper, we conducted experiments on the shear strength behaviors of grout infilled rock joint with elapsing of curing time and blasting induced vibration. The results show that blasting induced vibration under MTG does not influence the mechanical features of grout material, which indicates no influence on the mechanical behaviors of grout, contributing to the stability of tunnels during excavation. This result indicates that MTG is a cost effective and fast construction method for tunneling in Korea.

• 한국추진공학회지
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• 제8권4호
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• pp.16-25
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• 2004

구리분말 소결윅 히트파이프의 열수송 한계를 예측하는 이론적 해석을 수행하였다. 히트파이프의 직경은 8 mm이고 물을 작동유체로 사용하였다. 입자의 직경을 대표적인 5 가지로 분류하여 각각의 유효 모세관 반경($r_c$) 기공률($\varepsilon$), 투파율(K)을 토대로 작동온도와 윅 두에 그리고 경사각에 따른 모세관압력과 열수송 한계, 열저항을 분석하였다. 소결윅의 모세관한계는 입자 직경이 크고 윅 두께가 증가하며 작동온도가 높을수록 증가했다 기공률과 모세관 반경이 증가할수록 열수송 한계가 높아졌으며, 윅 두께가 증가함에 따라 열저항이 크게 상승하였다.

• 한국자기학회지
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• 제15권6호
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• pp.320-324
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• 2005

[ $3\%$ ] 규소강판에 대한 코어손실 특성은 규소장판에 포함된 실리콘 함유량, 불순물의 농도, 투자율, 자구의 구조 등에 의존한다. 자구 미세화는 고 투자율을 갖는 규소강판의 코어손실을 감소시키는 좋은 방법이다. 본 연구에서는 펄스형 Nd : YAG 레이저를 규소강판에 조사함으로써 규소강판의 자구를 미세화 하여 코어손실을 최소화 할 수 있는 최적조건을 분석하였다. 조사된 레이저빔의 spot 크기는 $100{\mu}m$, 펄스 당 에너지는 10${\~}$35mJ, 스크라이빙 줄 간격은 5mm로 결정하였으며 펄스폭이 30ns인 Nd:YAG 레이저를 사용하여 규소강판의 코어손실을 최대 $17\%$까지 개선하였다.

• 농업과학연구
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• 제47권3호
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• pp.485-496
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• 2020

Recent changes in the disaster environment have greatly increased the possibility of internal erosion in deteriorated reservoirs; thus, countermeasure methods are required to enhance the drainage performance of embankments. Sand filters have been mainly used to prevent internal erosion; however, due to the sand depletion and environmental problems, new alternative materials are required to replace the sand in the filter zone. In this study, crushed stone was used instead of sand as a material that could satisfy permeability, material supply, demanding conditions, and economic efficiency. Although crushed stone has excellent drainage performance, it has a clogging phenomenon due to its high permeability. Accordingly, the materials need to be separated with a geotextile wrapping method. Additionally, the 3D numerical analysis and a large model experiment were conducted to evaluate the seepage characteristics and in-site application of the crushed stone filter. As a result, the crushed stone filter showed an excellent dispersion effect by reducing the pore water pressure by about 9.5 times that of the sand filter. In addition, it was shown that the safety factor for piping increased significantly by reducing internal erosion. When comparing the economics and supply and demand conditions of the material, crushed stone was evaluated as an effective method to reduce the internal erosion of embankments at deteriorated reservoirs.

• 한국철도학회논문집
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• 제14권2호
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• pp.151-159
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• 2011

본 논문에서는 시공이음 및 세그먼트 연결부 등 불연속 구간을 포함하고 있는 튜브 구조물에 대한 기밀성 평가를 위해 실험에 기초한 연구를 수행하였다. 실제 진공튜브 시스템을 위해 적용 가능한 콘크리트 라이닝을 최대한 모사할 수 있도록 콘크리트 관 1개로 구성된 일체형 튜브(N1) 1기, 동 콘크리트 관 두 개를 연결시킨 연결식 튜브 시험체(N2) 1기, 그리고 콘크리트 세그먼트형 튜브(S) 1기 등 총 3기의 시험체를 제작하여 각 시험체에 대해 내부 기압을 0.1atm로 낮춘 후 시간에 따른 내부 기압의 변화를 측정하였다. 기밀성 실험 결과 얻어진 흐름 곡선으로부터 시스템의 등가 투기계수를 산출하였는데 이음부가 많을수록 시스템의 등가투기계수는 높아지는 경향을 보였다. 또한 실험 결과를 바탕으로 가정된 튜브 단면 변화에 따른 기밀성의 민감도를 해석적으로 분석하였는데 튜브 구조물의 두께 및 직경이 커질수록 시스템 기밀성이 더 향상될 뿐 아니라 기밀성 보강의 효과가 더욱 커진다는 것을 알 수 있었다.

• 한국수소및신에너지학회논문집
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• 제27권3호
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• pp.276-282
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• 2016

The effects of conductive additives in a $La_{0.8}Sr_{0.2}MnO_3$ perovskite bifunctional electrode for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were investigated in an alkaline solution. Highly porous carbon black (CB) and Ni powder were added to the bifunctional electrodes as conductive additives. The surface morphologies of electrodes containing CB and Ni were observed by scanning electron microscopy (SEM). The current densities for both ORR and OER were changed by the addition of CB. The conductive additive changed physical properties of bifunctional electrodes such as the sheet conductance, gas permeability and contact angle. It was observed that the air permeability of electrode was most effective to enhance the currents for ORR and OER.