• Korean Journal of Veterinary Research
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• v.35 no.2
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• pp.245-254
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• 1995

The density of ATP-sensitive potassium($K_{APT}$) channels, that open as intracellular ATP concentration falls below a critical level, is very high in skeletal muscle surface membrane and those high density may imply that $K_{ATP}$ channels have very important physiological roles. To elucidate a role of $K_{ATP}$ in relation to fatigue, the modulating effects of potassium channel openers and blockers on the fatigue velocity(FV) of mouse extensor hallucis longus muscle(EHL) were investigated in vitro. Twitch contraction was induced by an electrical field stimulation (EFS: 24-48V, 20ms, 0.2-4Hz) and resulting contraction force was isometrically recorded. The twitch forces were gradually decreased to 25% of initial contraction force(ICF) in $37.52{\pm}1.55sec$($mean{\pm}s.e.m.$, n=135), indicating the fatigue phenomena. The mean velocity for development of the fatigue was measured during the period that twitch force decreased to half($FV_{0/0.5}$) and during the period from half to 25%($FV_{0.5/0.25}$) of ICF. The fatigue was induced once every one hour and the tissue response was stable for up to 4 hours. In control condition, ICF was $5.8{\pm}0.12g$ (n=144) and decreased to 50% of ICF with the mean fatigue velocity of $0.182{\pm}0.006g/sec$($FV_{0/0.5}$, n=135) and from 50% to 25% of ICF with $0.084{\pm}0.004g/sec$($FV_{0.5/0.25}$, n=135). Cromakalim($50{\mu}M$) significantly increased $FV_{0.5/0.25}$(n=4). Glibenclamide($IC_{50}>50{\mu}M$), $Ba^{2+}$($IC_{50}=10{\mu}M$), 4-aminopyridine($FV_{0/0.5}$, $IC_{50}=0.5mM$; $FV_{0.5/0.25}$, $IC_{50}=2mM$) decreased both $FV_{0/0.5}$ and $FV_{0.5/0.25}$ concentration-dependently up to 75%. $TEA^+$(30mM), E-4031($10{\mu}M$), tolbutamide(1mM) decreased $FV_{0.5/0.25}$, but apamin(300nM) and $TEA^+$(10mM) showed no significant effects. Our results suggest that activation of the $K_{ATP}$ channels may be major cause of $K^+$ outflux during development of the fatigue and the isolated EHL muscle could be an useful experimental preparation in studying the fatigue phenomena in skeletal muscle. In addition, the possibility of activation of delayed rectifier during the fatigue development remains to be studied further.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1367-1373
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• 2011

This research concerns the development of a compression/absorption high-temperature hybrid heat pump that uses a natural refrigerant mixture. Heat pumps based on the compression/absorption cycle offer various advantages over conventional heat pumps based on the vapor compression cycle, such as large temperature glide, temperature lift, flexible operating range, and capacity control. In this study, a lab-scale prototype hybrid heat pump was constructed with a two-stage compressor, absorber, desorber, desuperheater, solution heat exchanger, solution pump, liquid/vapor separator, and rectifier as the main components. The hybrid heat pump system operated at 10-kW-class heating capacity producing hot water whose temperature was more than $90^{\circ}C$ when the heat source and sink temperatures were $50^{\circ}C$. Experiments with various $NH_3/H_2O$ mass fractions and compressor/pump circulation ratios were performed on the system. From the study, the system performance was optimized at a specific $NH_3$ concentration.

• The Transactions of the Korean Institute of Power Electronics
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• v.5 no.4
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• pp.358-369
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• 2000

Shielded metal arc welding machines with AC transformer have been widely used for thin-plate welding applications. Because of being bulky, heavy and of tap-changing property, so the SMAW's are changing to new power electronic circuits such as inverter circuit in order to reduce the system size and also to improve the welding performances at input output sides. The PWM inverter arc welding machine with diode rectifier has better output welding performances but it is has the plentiful harmonics and the lower input power factor. To solve these problems, input current-controlled scheme is considered for PWM inverter arc welding system, and then total input power factor is maintained to be more than 99%. Also a new combined control is proposed which can control both instantaeous welding output voltage and current under constant power condition, and as a result the variations of instantaneous current and voltage can be reduced to very narrow range in the V-I curve relationship, and hence the variance of welding current and voltage become so reduced. In addition the spatter generated during welding process is greatly reduced up to 70%. And the overall effiency can be improved up to 10%, which becomes higher when the load is lower.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.116-116
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• 2018

부식은 재료와 사용 환경과의 상호작용에 의한 결과로서 일반적으로 두께의 감소와 균열의 발생 및 파손 등의 문제로 나타난다. 특히 사용환경 중에서 해수 분위기는 금속의 부식에 가장 유리한 조건이다. 따라서 해양환경 중 항만이나 조선 및 해양 산업 등에 많이 이용되는 강 구조물은 이에 대응하기 위하여 도장방식이나 음극방식을 사용하고 있다. 여기서 음극방식은 피방식체를 일정전위로 음극 분극하는 원리로써 외부전원을 인가하거나 비전위의 금속을 전기적으로 연결하여 방식하는 방법이다[1]. 한편, 해수 중에서 이와 같은 원리로 음극방식 할 경우에는 피방식체인 강재표면에 부분적으로 칼슘 또는 마그네슘 화합물 등의 생성물이 부착하는 현상을 볼 수 있게 된다. 이와 같이 수산화마그네슘($Mg(OH)_2$)및 탄산칼슘($CaCO_3$)을 주성분으로 하여 석출되는 석회질 피막(calcareous deposits)은 피방식체에 유입되는 음극방식 전류밀도를 감소시켜 주거나 물리적 장벽의 역할을 함으로써 외부의 산소와 물 등 부식환경으로부터 소지금속을 보호한다[2]. 그러나 석회질 피막은 소지금속과의 결합력, 막의 균일한 분포, 내식성 및 제작시간의 단축 등 해결해야 할 과제가 있다. 또한 여러 가지 환경 조건 등의 영향을 받아 그 피막의 형성 정도도 가늠하기 어렵기 때문에 음극방식 설계 시 그 정도에 따른 영향을 고려-반영하기가 곤란하다. 따라서 본 연구에서는 석출속도, 밀착성 및 내식특성을 향상시키기 위해 전착프로세스를 통해 해수 중 기체를 용해시켜 석회질 피막을 제작하고 막의 결정구조 제어 및 특성을 분석-평가하였다. 본 연구에 사용된 강 기판(Steel Substrate)은 일반구조용강(KS D 3503, SS400)을 사용하였으며, 외부전원은 정류기(Rectifier, xantrex, XDL 35-5T)를 사용하여 3 및 $5A/m^2$의 조건으로 인가하였다. 양극의 경우에는 해수에 녹아있는 이온 이외에 다른 성분들이 환원되는 것을 방지하기 위해 불용성 양극인 탄소봉(Carbon Rod)을 사용하였다. 이때 석출속도, 밀착성 및 내식특성 향상을 위해 해수에 주입한 기체의 양은 0.5 NL/min였으며, 기판 근처에 고정하여 음극 부근에서의 반응을 유도하였다. 각 조건별로 제작된 막의 표면 모폴로지, 조성원소 및 결정구조 분석을 실시하였으며, 석회질 피막의 밀착성과 내식특성을 평가하기 위해 규격에 따른 테이핑 테스트(Taping Test, ISO 2409)와 3 % NaCl 용액에서 전기화학적 양극 분극 시험을 진행하여 제작된 막의 내구성과 내식성을 분석-평가하였다. 시간에 따른 전착막의 외관관찰 결과 전류밀도의 증가와 함께 상대적으로 많은 피막이 형성되었고, 용해시킨 기체에 의해 더 치밀하고 두터운 피막이 형성됨을 확인할 수 있었다. 성분 및 결정구조 분석 결과 $Mg(OH)_2$ 성분의 Brucite 및 $CaCO_3$ 성분의 Calcite 및 Aragonite 구조를 확인하였으며, 용해시킨 기체의 영향으로 $CaCO_3$ 성분의 Aragonite 구조가 상대적으로 많이 검출되었다. 밀착성 및 내식성 평가를 실시한 결과 해수 중 용해시킨 기체에 의해 제작한 시편의 경우 견고하고 화학적 친화력이 높은 Aragonite 결정이 표면을 치밀하게 덮어 전해질로부터 산소와 물의 침입을 차단하는 역할을 하여 기체를 용해시키지 않은 3 및 $5A/m^2$ 보다 비교적 우수한 밀착성 및 내식 특성을 보이는 것으로 사료된다.

• The Korean Journal of Physiology and Pharmacology
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• v.11 no.5
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• pp.207-213
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• 2007

This study was designed to characterize ureteral smooth muscle motility and also to study the effect of forskolin(FSK) and isoproterenol(ISO) on smooth muscle contractility in murine ureter. High $K^+$(50 mM) produced tonic contraction by $0.17{\pm}0.06mN$(n=19). Neuropeptide and neurotransmitters such as serotonin($5{\mu}M$), histamine($20{\mu}M$), and carbarchol(CCh, $10{\sim}50{\mu}M$) did not produce significant contraction. However, CCh($50{\mu}M$) produced slow phasic contraction in the presence of 25 mM $K^+$. Cyclopiazonic acid(CPA, $10{\mu}M$), SR $Ca^{2+}$-ATPase blocker, produced tonic contraction(0.07 mN). Meanwhile, inhibition of mitochondria by protonophore carbnylcyanide m-chlorophenylhydrazone(CCCP) also produced weak tonic contraction(0.01 mN). The possible involvement of $K^+$ channels was also pursued. Tetraethyl ammonium chloride(TEA, 10 mM), glibenclamide($10{\mu}M$) and quinidine($20{\mu}M$) which are known to block $Ca^{2+}$-activated $K^+$ channels($K_{Ca}$ channel), ATP-sensitive $K^+$ channels($K_{ATP}$) and nonselective $K^+$ channel, respectively, did not elicit any significant effect. However, $Ba^{2+}$($1{\sim}2mM$), blocker of inward rectifier $K^+$ channels($K_{IR}$ channel), produced phasic contraction in a reversible manner, which was blocked by $1{\mu}M$ nicardipine, a blocker of dehydropyridine-sensitive voltage-dependent L-type $Ca^{2+}$ channels($VDCC_L$) in smooth muscle membrane. This $Ba^{2+}$-induced phasic contraction was significantly enhanced by $10{\mu}M$ cyclopiazonic acid(CPA) in the frequency and amplitude. Finally, regulation of $Ba^{2+}$-induced contraction was studied by FSK and ISO which are known as adenylyl cyclase activator and $\beta$-adrenergic receptor agonist, respectively. These drugs significantly suppressed the frequency and amplitude of $Ba^{2+}$-induced contraction(p<0.05). These results suggest that $Ba^{2+}$ produces phasic contraction in murine ureteral smooth muscle which can be regulated by FSK and $\beta$-adrenergic stimulation.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.164-164
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• 2016

항만 및 해양 구조물은 육상과는 비교할 수 없을 정도로 가혹한 해수 환경에서 사용되며 계속적으로 부식 손상을 받는다. 따라서 강구조물이 장기적으로 안전하게 사용되기 위해서는 적절한 방식은 물론 철저한 유지관리가 필수적이다. 한편, 현재 해양환경 중 항만, 조선, 해양산업 등에 많이 이용되는 강구조물은 이에 대응하기 위하여 일반적으로 도장방식이나 음극방식이 사용되고 있다. 음극방식은 피방식체를 일정전위로 음극 분극하는 원리로써 외부전원을 인가하거나 비전위의 금속을 희생양극으로 연결하여 방식하는 방법이다. 이와같이 해수 중 음극방식을 실시할 경우 해수 중 용존하는 많은 이온들 중에서 특히 $Ca^{2+}$ 이나 $Mg^{2+}$ 이온이 탄산칼슘, 수산화마그네슘을 주성분으로하는 화합물로 형성된다. 이렇게 생성된 전착막은 산소 확산을 방지하는 물리적 장벽을 형성하고 부식율을 감소시키는 것으로 보고되고 있다. 그러나 전착막은 소지 금속과의 결합력이 불균일 함은 물론 막을 형성하는데 있어서 장시간이 소요된다는 단점이 있다. 따라서 본 연구에서는 해수 중 음극방식 응용 원리에 의해 전착막을 형성하고, 석출속도, 밀착성 및 내식특성을 향상시키기 위해 해수 중 기체를 용해시켜 제작한 막의 특성을 분석-평가하였다. 본 연구에 사용된 기판(substrate)은 일반구조용 강(SS400)을 사용하였으며, 면적은 $70mm{\times}30mm$, 두께는 1 mm로 제작하여 실험을 진행하였다. 외부전원은 정류기(Rectifier, xantrex, XDL 35-5T)를 사용하여 3 및 $5A/m^2$ 의 조건으로 인가하였고, 양극은 Carbon Rod를 사용하였다. 이때 해수에 주입한 이산화탄소의 양은 0.5 NL/min 였다. 각 조건별로 제작된 전착막에 대해 외관관찰, 석출량, 모폴로지, 조성원소 및 결정구조 분석을 실시하였고, 밀착성 및 내식특성을 평가하기 위해 테이핑 테스트(Taping Test, JIS K 5600-5-6)와 3.5 % NaCl 용액에서 전기화학적 양극 분극 시험을 진행하였다. 시간에 따른 전착막의 외관관찰 결과 전류밀도의 증가와 함께 상대적으로 많은 피막이 형성되었고, 용해시킨 기체에 의해 더 치밀하고 두터운 피막이 형성됨을 확인할 수 있었다. 성분 및 결정구조 분석 결과 $Mg(OH)_2$ 성분의 Brucite 및 $CaCO_3$ 성분의 Calcite 구조 및 Aragonite 구조를 확인하였으며, 용해시킨 기체의 영향으로 $CaCO_3$ 성분의 Aragonite 구조가 상대적으로 많이 검출되었다. 이는 해수 중 용해된 이산화탄소의 영향으로 인해 풍부한 ${CO_3}^{2-}$ 이온이 형성되고 용액 pH를 낮게 유지시켜 Ca 화합물 형성이 용이한 환경이 조성되는 것으로 판단된다. 밀착성 및 내식성 평가를 실시한 결과 해수중 용해시킨 기체에 의해 제작한 시편의 경우 견고하고 화학적 친화력이 높은 Aragonite 결정이 표면을 치밀하게 덮어 전해질로부터 산소와 물의 침입을 차단하는 역할을 하여 기체를 용해시키지 않은 $3A/m^2$ 및 $5A/m^2$ 보다 비교적 우수한 밀착성 및 내식 특성을 보이는 것으로 사료된다.

• Journal of Ginseng Research
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• v.23 no.4
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• pp.230-234
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• 1999

Potassium channels play an important role in regulating vascular smooth muscle tone. Four types of $K^+$ channels areknown to be expressed in vascular smooth muscle cells, and maxi $Ca^{2+}-activated\;K^+$ channel $(BK_{Ca})$ is a dominant type of $K^+$ channels in these cells. Because total ginseng saponins and ginsenoside $Rg_3$ cause vasodilation with unclear mechanisms, we hypothesized that total ginseng saponins and ginsenoside $Rg_3$ induce vasodilation via activation of maxi $Ca^{2+}-activated\;K+$ channels. Whole-cell BKe. currents were voltage-dependent with half maximum activation at -14 mV, and the currents were sensitive to nanomolar ChTX and millimolar TEA. External application of total ginseng saponins increased the anlplitude of the whole-cell BKe. current in a concentration-dependent manner. Single-channel analysis indicates that total ginseng saponins caused the channel opening for a longer period of time. Ginsenoside $Rg_3$ increased the amplitude of whole-cell $K_{Ca}$ currents without affecting voltage dependence of the currents and increased single-channel open time. Hence, the results suggest that ginseng saponin-induced vasodilation may be due to activation of $K_{Ca}$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.9
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• pp.883-891
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• 2013

In wireless smart phone charging scenario, the transmitter pad is larger than the size of the receiver pad. Thus, it is important to supply a constant power to the receiver regardless of its location. In this paper, we propose a new method to regulate the receiver's power by adjusting a drain bias of class E power amplifier. The proposed LF-band wireless power transfer system is as follows: a buck converter power supply which is controlled by a pulse width modulation(PWM) IC TL494, a class E amplifier using a low cost IRF510 power MOSFET, a transmitter coil whose dimension is $16cm{\times}18cm$, a receiver coil whose dimension is $6cm{\times}8cm$, and a full bridge rectifier using Schottky diodes. A measured performance show a maximum output power of 4 W and system efficiency of 67 % if we fix the bias voltage. If we adjust the bias voltage, the received power can be maintained at a constant power of 2 W regardless of receiver pad location.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.12 no.2
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• pp.99-107
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• 1998

This dissertationhas confirmed the non-flam mability of cast mold transformer that is increasingly used lately. As a research progress, the investigation has been performed on the installation status and each line of the subway system which have the most mold transformer accidents, and the impediment status of the transformer for rectifier and the high-voltage distribution transformer per each manufacturer. Then, a high voltage mold of the actual mold transformer has been installed in the horiwntal heating furnace and the heat has been applied by the standard heating temperature curve of KSF 2257(Fireproof testing meth od of the construction structures: 1993). Accordingly, the combustibility of the mold transformer based on the test results has been found that 78 minutes has been required for the complete burning per the KSF 2257 combustion test curve and that, after stopping the heat application of the horizontal furnace after ignition, the flame progress has not been made but shown as the self-extinguishing characteristics when the flame progress has been checked. Thus, the non-flammability and self-extinguishability of the mold transformer have been confirmed. The result of this dissertation has indicated that the accident involving mold transformer has been progressed and expanded by the dielectric breakdown or void due to the crack in the mold rather than a fire accident caused by a short-circuit or an overload.r an overload.

• Journal of IKEEE
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• v.20 no.1
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• pp.45-53
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• 2016

This paper presents a CMOS interface circuit for vibration energy harvesting with MPPT (Maximum Power Point Tracking). In the proposed system a PMU (Power Management Unit) is employed at the output of a DC-DC boost converter to provide a regulated output with low-cost and simple architecture. In addition an MPPT controller using FOC (Fractional Open Circuit) technique is designed to harvest maximum power from vibration devices and increase efficiency of overall system. The AC signal from vibration devices is converted into a DC signal by an AC-DC converter, and then boosted through the DC-DC boost converter. The boosted signal is converted into a duty-cycled and regulated signal and delivered to loads by the PMU. A full-wave rectifier using active diodes is used as the AC-DC converter for high efficiency, and a DC-DC boost converter architecture using a schottky diode is employed for a simple control circuitry. The proposed circuit has been designed in a 0.35um CMOS process, and the designed chip occupies $915{\mu}m{\times}895{\mu}m$. Simulation results shows that the maximum power efficiency of the entire system is 83.4%.