• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1A
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• pp.75-84
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• 2009

The present study assesses the chloride threshold level for corrosion of steel in concrete by examining the properties of four different binders used for blended concrete in terms of chloride binding, buffering of cement matrix to a pH fall and the corrosion behaviour. As binders, ordinary Portland cement (OPC), 30% pulverised fuel ash (PFA), 60% ground granulated blast furnace slag (GGBS) and 10% silica fume (SF) were used in a concrete mix. Testing for chloride binding was carried out using the water extraction method, the buffering of cement matrix was assessed by measuring the resistance to an artificial acidification of nitric acid, and the corrosion rate of steel in mortar with chlorides in cast was measured at 28 days using an anodic polarisation technique. Results show that the chloride binding capacity was much affected by $C_{3}A$ content and physical adsorption, and its order was 60% GGBS>30% PFA>OPC>10% SF. The buffering of cement matrix to a pH fall was varied with binder type and given values of the pH. From the result of corrosion test, it was found that the chloride threshold ranged 1.03, 0.65, 0.45 and 0.98% by weight of cement for OPC, 30% PFA, 60% GGBS and 10% SF respectively, assuming that corrosion starts at the corrosion rate of $0.1-0.2{\mu}A/cm^{2}$. The mole ratio of [$Cl^{-}$]:[$H^{+}$], as a new presentation of the chloride threshold, indicated the value of 0.008-0.009, irrespective of binder, which would be indicative of the inhibitive characteristic of binder.

• Tuberculosis and Respiratory Diseases
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• v.40 no.2
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• pp.135-146
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• 1993

Background: In acute pulmonary embolism it has been postulated that the constriction of bronchi and pulmonary artery secondary to neurohumoral response plays an important role in cardiopulmonary dysfunction in addition to the mechanical obstruction of pulmonary artery. Serotonin is considered as the most important mediator. Positive end expiratory pressure (PEEP) stimulates $PGI_2$ secretion from the vascular endothelium, but its role in acute pulmonary embolism is still in controversy. Methods: To study the cardiopulmonary effect and therapeutic role of Ketanserin, selective antagonist of 5-HT2 receptor, and PEEP in acute pulmonary embolism experimental acute pulmonary embolism was induced in dogs with autologous blood clot. The experimental animals were divided into 3 groups, that is control group, Ketanserin injection group and PEEP application group. Results: Thirty minutes after embolization, mean pulmonary arterial pressure and pulmonary vascular resistance increased and cardiac output decreased. $PaO_2,\;P\bar{v}O_2$ and oxygen transport decreased and physiological shunt and $PaCO_2$ increased. After injection of Ketanserin, comparing with control group, mean pulmonary arterial pressure, pulmonary vascular resistance and physiological shunt decreased, while cardiac output, $PaO_2$ and oxygen transport increased. All these changes sustained till 4 hours after embolization. After PEEP application pulmonary vascular resistance, $PaO_2$ and $PaCO_2$ increased, while physiological shunt, cardiac output and oxygen transport decreased. After discontinuation of PEEP, mean pulmonary arterial pressure and pulmonary vascular resistance decreased and were lower than control group, while $PaO_2$ and cardiac output increased and higher than control group. $PaCO_2$ decreased but showed no significant difference comparing with control group. Conclusion: It can be concluded that Ketanserin is effective for the treatment of acute pulmonary embolism. With PEEP hemodynamic status deteriorated, but improved better than control group after discontinuation of PEEP. Thus PEEP may be applied carefully for short period in acute pulmonary embolism if the hemodynamic status is tolerable.

• Journal of IKEEE
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• v.13 no.4
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• pp.23-27
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• 2009

Ohmic contact formation and etching processes for the fabrication of MBE (molecular beam epitaxy) grown GaSb-based p-channel HEMT devices on Si substrate have been studied. Firstly, mesa etching process was established for device isolation, based on both HF-based wet etching and ICP-based dry etching. Ohmic contact process for the source and drain formation was also studied based on Ge/Au/Ni/Au metal stack, which resulted in a contact resistance as low as $0.683\;{\Omega}mm$ with RTA at $320^{\circ}C$ for 60s. Finally, for gate formation of HEMT device, gate recess process was studied based on AZ300 developer and citric acid-based wet etching, in which the latter turned out to have high etching selectivity between GaSb and AlGaSb layers that were used as the cap and the barrier of the device, respectively.

• Microbiology and Biotechnology Letters
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• v.17 no.1
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• pp.74-80
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• 1989

For improvement of photobiological hydrogen production, Rhodopseudomonas El5-1, a photo-synthetic becterium capable of producing n high yield of hydrogen, was immobilized and conditions for hydrogen production by immobilized cells were examined. The optimum concentration for the combined matrix was obtained when sodium alginate was used at final concentration of 4%. The immobilized cells may reduce the inhibitory effects of nitrogen or oxygen. To minimize the diffusion resistance of the nutrients in alginate gel, the bend size less than 2 mm in diameter was desirable. The immobilized cells were also able to utilize n wide range of organic substrates for the production of hydrogen. The hydrogen producing activity of the immobilized cells was maintained for 20 days without loss of activity during semi-continuous operation of the reactor by feeding of new medium periodically and continuous production of hydrogen could be successfully performed for 30 days.

• Food Science and Preservation
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• v.5 no.3
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• pp.275-280
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• 1998

The effects of Poria cores powder addition on bread making were investigated by evaluation of dough rasing power, rheological properties of dough by farinograph and extensograph color and sensory quality. As increment of Poria cocos powder, dough rasing power and extensibility were decreased but water absorption rate and resistance were increased. Time for dough formation, stability and v/v point of dough were increased when 5 and 10 percent of Poria cocos powder were added. Color of bread wasn't significantly different when Poria cocos powder was added up to 10 percent. Overall acceptance by sensory evaluation was the best when 5 percent of Poria cocos powder was added, tut there are no significant difference among breads which were made with various mixing rates of Poria cocos powder.

• Membrane Journal
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• v.25 no.4
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• pp.358-366
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• 2015

Flat membrane with $0.4{\mu}m$ pore size was prepared with PVdF (polyvinylidene fluoride) nanofiber, which has the advantages such as excellent strength, chemical resistance, nontoxic, non-combustibility. After that, spiral wound module was manufactured with it including a woven paper. Effect of pH was studied by comparing permeate fluxes and rejection rates of the spiral wound module using simulation solution including kaolin and humic acid. The recovery rate and filtration resistance were calculated after water back-washing at the end of filtration experiment. In addition, after the water filtrated by the spiral wound module was passed through a column filled with GAC (granular activated carbon), adsorption effect of GAC was investigated by measuring the turbidity and $UV_{254}$ absorbance.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.2
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• pp.115-124
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• 2001

In this paper, authors propose a new nonlinear rotor flux observer for rotor field oriented control of an induction motor which is designed based on the extended Luenberger Observer theory. Extended Luenberger Observer requires minimal solution of nonlinear partial differential equation on its coordinate transformation and linearization needed on a nonlinear observer design in general. The proposed rotor flux observer is derived from the 2 phase model of induction motor on the orthogonal coordination and it has the reduce gain matrix. Simulation and experimentation were performed under the conventional indirect vector control and direct vector control with the proposed observer at different rotor resistance. Simulation results show that the convergence of the proposed observer is influenced by the chosen eigenvalues. Experimentation results on load operation show the direct vector control with the proposed observer is better than the indirect vector control to maintain the characteristics of the vector control.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.140-140
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• 2017

4륜 장착 자동차의 토크 전달은 2륜 구동, 4륜 구동 모드를 간단히 전환하는 방식(part time 4WD)과 항시 사륜 구동 모드에서 전후륜의 토크 전달비를 제어하는 방식(AWD, all wheel drive)이 있다. 경제의 발달에 따라서 취미 인구의 확대로 국내에만 180만 명의 R/C car 사용자가 있다. 이 중 2WD-4WD의 전환을 differential lock mechanism으로 구현한 수입산 모델의 가격이 1,000,000원을 호가하지만 가변 제어 방식이 아닌, 정차 후 2-4륜 구동 전환 방식을 적용하고 있으며 상대적으로 내구성이 떨어진다. DC motor의 출력이 늘어나고 배터리의 성능이 좋아진 현재 소형 RC car의 최고 속도는 80 km/h 정도로 빨라졌다. 그러나 마찰 계수가 낮은 노면(실내의 대부분 평활 처리된 복도)에서는 2륜 구동 모드의 활용도가 매우 낮다. 미끄러운 노면에서 후륜 구동 모드로는 oversteer가 발생하여 차량이 스핀하기 쉽고 전륜 구동 모드로는 understeer가 발생하여 제대로 된 코너링이 어렵다. 상시 4륜 구동 모드는 에너지 소모가 크고 전후륜이 tight coupling되어 있는 문제 때문에 일반적인 노면에서 부드러운 코너링이 잘 이루어지지 않는 문제가 있다. 본 연구에서 제안하는 방식은 그림 1와 같이 center shaft의 중간에 영구 자석으로 만들어진 토크 전달용 판이 있고 그 사이에 자계를 차폐할 수 있는 강자성체 셔터를 서보 기구에 연결하여 서보 회전각에 따라서 구동 쪽의 토크가 피구동축으로 전달되는 양을 연속 가변제어할 수 있다. 토크 전달용 판의 차폐 면적에 따른 토크 전달양을 전/후륜 바퀴의 Static torque를 통해 측정하였으며(그림 2), 공중 상태에서 즉 공기저항만을 고려한 상태에서의 RPM 회전수 차이 측정(그림3)을 통해 구동 쪽의 회전수가 피구동축으로 전달되는 양을 측정하여 연속가변 토크 제어 전달 기구의 성능을 확인하였다. 이 기구는 현재 1차적으로는 remote controller의 ch 3(ON/OFF제어 방식)에 연결하여 특정한 양의 토크를 전륜 쪽으로 보낼 수 있도록 구현이 가능하며, ch 2(PID제어 방식)에 연결하여 연속 가변 조절이 가능하도록 구현이 가능하다. 부가적으로 Arduino board를 내장하여 전후륜의 휠센서에서 입력되는 신호를 감지하여 자동적으로 전후륜에 배분되는 토크를 제어할 수 있도록 설계 중에 있다.

• Korean Journal of Food Science and Technology
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• v.45 no.3
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• pp.370-375
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• 2013

Propolis is a resinous mixture found in the tree buds, sap flows, and other botanical sources, which is used by honey bees in the construction of their hives. Antimicrobial effects of propolis were evaluated against Streptococcus mutans KCTC 3065, S. sobrinus KCTC 3308, S. sobrinus KCTC 5134, and Porphyromonas gingivalis KCTC 5352 by an agar diffusion assay. Sensitivity of these microorganisms to propolis was evaluated in broth containing different concentrations of propolis at $37^{\circ}C$, followed by observation using transmission electron microscopy (TEM). Propolis inhibited all oral microorganisms tested at the minimum inhibitory concentration (MIC) of $0.14mg/{\mu}L$ in the agar diffusion assay. Treatment with 0.06 and $0.22mg/{\mu}L$ of propolis had a bactericidal effect in a concentration- and treatment time-dependent manner against the tested microorganisms. TEM of propolis-treated S. mutans KCTC 3065 and P. gingivalis KCTC 5352 revealed structural damage of the cell membrane. The activity of propolis was affected by heat and pH treatment. The results indicate that propolis shows antibacterial activity against oral microorganisms and that it has potential for future applications in the food industry.

• Korean Journal of Food Science and Technology
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• v.30 no.5
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• pp.1064-1069
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• 1998

Tetrasodium polyphosphate peroxidate (TPP) increased the farinograph stability, maximum resistance by extensigraph and amylograph peak viscosity of a noodle flour produced from Australian Standard White wheat (protein 8.76%, ash 0.380%) at concentration of $0.2{\sim}0.4%$ based on flour weight. The addition of 0.3% TPP increased the moisture content of Kalguksoo, handmade fresh noodle, by 1.5%. No significant differences however were observed in cooking properties. Sensory evaluation revealed that the color, texture and preference of cooked noodle were significantly better in the presence of TPP. The fresh noodle with 0.3%, TPP delayed the development off-flavor by 7 hr during storage at $20^{\circ}C$ and $25^{\circ}C$.