• 한국환경과학회지
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• 제30권6호
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• pp.429-439
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• 2021

Food waste is both an industrial and residential source of pollution, and there has been a great need for food waste reduction. As a preliminary step in this study, waste reduction is quantitatively modeled. This study presents two models based on kinetics: a simple kinetic model and a mass transport-shrinking model. In the simple kinetic model, the smaller is the reaction rate constant ratio k₁, the lower the rate of conversion from the raw material to intermediate products. Accordingly, the total elapsed reaction time becomes shorter. In the mass transport-shrinking model, the smaller is the microbial decomposition resistance versus the liquid mass transfer resistance, the greater is the reduction rate of the radius of spherical waste particles. Results showed that the computed reduction of waste mass in the second model agreed reasonably with that obtained from a few experimantal trials of biodegradation, in which the microbial effect appeared to dominate. All calculations were performed using MATLAB 2020 on PC.

• 한국재료학회지
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• 제32권12호
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• pp.528-532
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• 2022

Recently, the necessity of designing and applying tool materials that perform machining of difficult-to-cut materials in a cryogenic treatment where demand is increasing. The objective of this study is to evaluate the performance of cryogenically treated WC-5 wt% NbC hard materials fabricated by a pulsed current activated sintering process. The densely consolidated specimens are cryogenically exposed to liquid nitrogen for 6, 12, and 24 h. All cryogenically treated samples exhibit compressive stress in the sintered body compared with the untreated sample. Furthermore, a change in the lattice constant leads to compressive stress in the specimens, which improves their mechanical performance. The cryogenically treated samples exhibit significant improvement in mechanical properties, with a 10.5 % increase in Vickers hardness and a 60 % decrease in the rupture strength compared with the untreated samples. However, deep cryogenic treatment of over 24 h deteriorates the mechanical properties indicating that excessive treatment causes tensile stress in the specimens. Therefore, the cryogenic treatment time should be controlled precisely to obtain mechanically enhanced hard materials.

• 콘크리트학회논문집
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• 제23권1호
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• pp.121-127
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• 2011

이 연구는 친환경적인 콘크리트 결합재로서 천연황토의 적용 가능성을 알아보기 위해 지오폴리머 반응법(geopolymerization)으로 얻어진 천연황토 경화체의 특성을 분석하였다. 이를 위해 천연황토와 알칼리 용액을 1 : 0.55 비율로 혼합하여 천연황토 페이스트를 제조하고 $60^{\circ}C$와 $20^{\circ}C$에서 양생시켜 재령에 따른 압축강도와 중량변화를 측정하였다. 또한, X-ray 회절분석(XRD)을 통해 반응 생성물을 확인하고 그 형상을 주사전자현미경(SEM)으로 촬영하였으며 수은압입법으로 경화체의 공극률을 분석하였다. 그 결과, 지오폴리머 반응법으로 얻어진 천연황토 경화체는 액상 규산나트륨($Na_2SiO_3$)와 8 M 수산화나트륨(NaOH) 수용액을 1:4.5비율로 제조한 알칼리 용액을 사용하고 $60^{\circ}C$에서 7일간 양생하였을 때 압축강도 29.1 MPa을 발현하는 천연황토 페이스트의 제조가 가능하였다. 또한, 개별 양생온도($20^{\circ}C$, $60^{\circ}C$)에서 압축강도 발현은 수분증발 비율에 따라 유사한 경향을 나타내므로 수분증발에 유리한 높은 양생 온도에서 반응을 유도하는 것이 조기 강도 발현에 유리한 것으로 사료된다.

• 전기학회논문지
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• 제57권3호
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• pp.398-402
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• 2008

Recently, the development of superconducting fault current limiters (SFCLs) has been required as power demands increase in the power system. A distribution-level prototype resistive SFCL using coated conductor (CC) has been developed by Hyundai Heavy Industries Co., Ltd. and Yonsei University for the first time in the world. The ratings of the SFCL are 13.2kV/630A at normal operating condition. A novel non-inductive winding method is used in fabricating coils so there is almost zero impedance during normal operation. The distribution SFCL is cooled by sub-cooled liquid nitrogen $(LN_2)$ of 65K and 3 bar to enhance cryo-dielectric performance, critical current density, and thermal conductivity. In order to make reliable operation of an SFCL in real power systems, we monitored and controled its operation conditions by using supervisory control and data acquisition (SCADA) method. Thus, a monitoring system for the SFCL employing information technology (IT) is proposed and developed to be on the lookout for the operation conditions such as inside temperature, inside pressure, $LN_2$ level, voltage and current. Since operation temperature should be kept constant, bang-bang control for temperature feedback with a heater attached to the cold head of cryo-cooler is applied to the system. Short-circuit tests with prospective fault current of 10kA and AC dielectric withstand voltage tests up to 143kV for 1 minute were successfully performed at Korea Electrotechnology Research Institute. This paper deals with the development of a distribution level SFCL and its monitoring system for reliable operation.

• 대한기계학회논문집B
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• 제35권8호
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• pp.825-829
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• 2011

본 연구에서는, 미소유체시스템 상에서 정밀한 유체 제어를 위해 입력압력이 변하여도 일정한 유량을 유지할 수 있는 수동형 유량제어기를 개발함에 있어, 주기적으로 변화하는 압력에 대한 유량제어기의 동적특성을 평가하였다. 압력 변화의 주기보다 짧은 시간 내에 유량을 측정하기 위하여 입자영상속도계(Particle Image Velocimetry, PIV) 방법을 이용하였다. 지름이 $0.7{\mu}m$ 인 형광입자가 담긴 탈이온수를 유량제어기에 공급하고, 펄스레이저와 형광현미경을 이용하여 $10{\mu}s$ 간격의 연속된 사진을 얻고 이를 분석하여 유량제어기를 통과한 후의 유체의 속도를 측정하였다. 개발된 유량제어기는 20kPa 과 50kPa 사이를 주기적으로 변화하는 60Hz 의 압력 하에서 0.194${\pm}$0.014m/s의 일정한 유속을 유지함을 실험적으로 확인하였다. 압력의 주파수를 1~60Hz 까지 변화시켜가며 수행한 실험에서도 유량제어기는 압력의 주파수에 상관없이 $5.82{\pm}0.29\;{\mu}l/s$ 의 일정한 유량 공급이 가능함을 확인하였다.

• 한국산업보건학회지
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• 제6권1호
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• pp.28-37
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• 1996

Benzidine, an aromatic amine used primarily in the manufacture of azo dyes, is recognized as a urinary bladder carcinogen in humans. In rats, mice, and hamsters, chronic exposure to benzidine resulted in tumors of the liver. The present study was undertaken to suggest analyzing the metabolites of benzidine with the optimal condition, identify the metabolites of benzidine, and observe time variance of the metabolites in the isolated perfusated rat liver. N-acetylbenzidine was synthesized by acetylation of benzidine with acetic anhydride and separated by thin layer chromatography(TLC) and high performance liquid chromatography(HPLC). To analysis benzidine and the metabolites of benzidine, HPLC operating condition has been optimized by means of preliminary experiment. The mobile phase consisted of acetonitrile(37%) in phosphate buffer, flow rate maintained at 1.0 ml/min. Optimal detective conditions were electrochemicaldetector(ECD) at 0.75 V for benzidine and N-acetylbenzidine and ultravioletdetector(UVD) at 287 nm for N,N'-diacetylbenzidine. The separation system was composed of a guard column and a separation column(Polymer C18, $4.6{\times}250cm$) at a temparature of $40^{\circ}C$. The perfusion system was equilibrated for 30 minutes before addition of benzidine to the perfusate. Samples of the perfusate were collected at time intervals(0, 10, 20, 30, 60, 90, 120 min) during the 2 hour perfusion. Before analyzing samples by HPLC/ECD/UVD, samples had been treated with sep-pak. Samples of perfusate analyzed by HPLC/ECD/UVD and the metabolites of benzidine in the isolated perfused rat liver were N-acetylbenzidine and N,N'-diacetylbenzidine. Benzidine metabolized over 60% during the initial 30 minutes of perfusion, extensively by 1 hour, and was undetectable in the perfusate. N-acetylbenzidine increased by 30 minutes of perfusion, declined. N,N'-diacetylbenzidine increased the 0-90 minutes period, remained constant during the 90-120 minutes period.

• 대한수의학회지
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• 제35권4호
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• pp.815-822
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• 1995

The toxicokinetics of rifapentine was studied after an oral administration to beagle dogs. High-performance liquid chromatography(HPLC) using column-switching technique was performed to determine the serum concentrations of rifapentine. The pharmacokinetic profiles of rifapentine were analysed using one-compartment open model. Following a single oral administration of 10mg/kg, pharmacokinetic parameters were determined as follows: maximum serum concentration($C_{max}$), $28.90{\mu}g/ml$; maximum concentration time($T_{max}$), 3.7hr; elimination half-life($t_{1/2}$, 4.7hr; area under the curve(AUC), $339.0{\mu}g{\cdot}hr/ml$; volume of disiribution/bioavailability (Vd/F), 0.21 l/kg; lag time, 24min; absorption rate constant($k_a$), $0.445hr^{-1}$; elimination rate constant($k_{el}$), $0.148hr^{-1}$. After 6 month multiple oral doses of 10mg/kg/day, parameters were as follows: $C_{max}$, $34.40{\mu}g/ml$; $T_{max}$, 2.6hr; $t_{1/2}$, 6.7hr; AUC, $391.3{\mu}g{\cdot}hr/ml$; Vd/F, 0.291/kg; $k_a$, $0.976hr^{-1}$; $k_{el}$, $0.104hr^{-1}$. The consistant kinetic parameters after a single and multiple oral administration show that there was no accumulation of rifapentine after 6 month oral administration. We also simulated the concentration of rifapentine after oral multiple administration of 10 and 50mg/kg/ day, based on the parameters obtained form the single administration. The measured serum concentrations of rifapentine were well fitted to the simulated results. The simulated results show that rifapentine readily reaches to steady-state after about 3 doses and the steady-state serum concentrations($C_{ss}$) are fluctuated in between $2.2{\sim}25.2{\mu}g/ml$, and $10.6{\sim}125.2{\mu}g/ml$ at the doses of 10 and 50mg/kg/day, respectively.

• Restorative Dentistry and Endodontics
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• 제18권2호
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• pp.261-276
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• 1993

The purpose of this study was to evaluate for the cytotoxicity of glass-ionomer cement liners(GC liningcement, Ketac-bond, Vitrebond and Fuji lining LC) on the fibroblasts cultured from human pulp. The fibroblasts were cultured in DMEM-10% FBS medium. The measurement of pH, succinate dehydrogenase (SDH) activity test and $^{51}Chromium$ release test were performed. Viable cell count and $^{14}C$-leucine incorporation rate were evaluated following culture time of 2, 4 and 6 days. The results of this study were as follows : 1. The pH in all cements was to be neutralized as time elapsed, and Fuji lining LC was the lowest pH value among them. 2. SDH activity was more inhibited in GC lining cement and Vitrebond than Ketac-bond and Fuji lining LC with the setting process, and GC lining cement and Ketac-bond were reduced after 5 minute's setting and then elevated as time elapsed. 3. In SDH activity test following exposure time, the activity in Vitrebond, GC lining cement and Fuji lining LC was inhibited with increased exposure time, but it was fairly constant in Ketac-bond. 4. Overall the liquid component was more inhibited than the powder component of glass-ionomer cement in SDH activity test. 5. In $^{51}Cr$-release test, Fuji lining LC was the most released of all the cements tested and followed by : Vitrebond, Ketac-bond, GC lining cement. 6. In viable cell count, the number of cells increased as the culture day proceeded in Ketac-bond, but they decreased in GC lining cement. Fuji lining LC was only observed after 2 days culture and there was not observed the whole culture days in Vitrebond. 7. In $^{14}C$-leucine incorporation rate test, protein synthesis was decreased with the number of culture days in GC lining cement, Vitrebond and Fuji lining LC, but it was followed that of control in Ketacbond.

• 한국분무공학회지
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• 제20권2호
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• pp.65-69
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• 2015

In this study, the thermal performance of vehicle's cooling system is experimentally investigated using the water/coolant-based $Al_2O_3$ nanofluids as working fluids. For the purpose, the water/coolant-based $Al_2O_3$ nanofluids are prepared by twostep method with gum arabic. In order to obtain the well-suspended nanofluids, the agglomerated $Al_2O_3$ nanoparticles are precipitated using centrifugal force and the experiments are performed with supernatant of them. The thermal conductivity is measured by transient hot wire method and the thermal conductivity of nanofluids is enhanced up to 4.8% as compared to that of base fluids. Moreover, the cooling performance of water/coolant-based $Al_2O_3$ nanofluids is evaluated using vehicle's engine simulator under the constant RPM condition. The results show that the cooling performance of automobile engine increases up to 5.9% using prepared nanofluids. To investigate the effect of nanofluids on exhaust gas, the $NO_x$ emission is measured during the operation with respect to time and 10.3% of $NO_x$ emission is decreased. The experimental results imply that the water/coolant-based $Al_2O_3$ nanofluids might be used as a next-generation vehicles' coolant

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.125-130
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• 2001

Experimental and analytical researches have been conducted on the twin-fluid atomizers for better droplet breakup during the past decades. But, the studies on the disintegration mechanism still present a great challenge to understand the drop behavior and breakup structure. In an effort to describe the aerodynamic behavior of the sprays issuing from the internal mixing counter-swirling nozzle, the spatial distribution of axial (U) radial (V) and tangential (W) components of droplet velocities are investigated across the radial distance at several axial locations of Z=30, 50, 80, 120 and 170mm, respectively. Experiments were conducted for the liquid flow rates which was kept constant at 7.95 g/s and the air injection pressures were varied from 20 kPa to 140 kPa. Counter-swirling internal mixing nozzles manufactured at angles of $15^{\circ},\;30^{\circ},\;45^{\circ}$ and $60^{\circ}$ the central axis with axi-symmetric tangential-drilled holes was considered. The distributions of velocities and turbulence intensities are comparatively analyzed. PDPA is installed to specify spray flows, which have been conducted along the axial downstream distance from the nozzle exit. Ten thousand of sampling data was collected at each point with time limits of 30 second. 3-D automatic traversing system is used to control the exact measurement. It is observed that the sprays with all swirl angle have the maximum SMD for on air injection pressure of 20 kPa and 140 kPa with centerline, respectively. The nozzle with swirl angle of $60^{\circ}$ has vest performance.