• Current Optics and Photonics
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• 제7권3호
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• pp.297-303
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• 2023

In this paper, we demonstrated a high-energy (285 mJ) mid-infrared flashlamp-pumped electro-optically 𝚀-switched Er:YAG master oscillator power amplifier (MOPA) system and comprehensively investigated its temporal, spectral, and spatial characteristics. To increase the output energy, we optimized the delay between the timings at which the flashlamps of the master oscillator and power amplifier were triggered. In addition, the output energy was improved while minimizing thermal effects by cooling the MOPA system to a temperature slightly above the dew point. Consequently, the MOPA structure boosted the output energy without damaging the lithium niobate Pockels cell, which is a crucial element in 𝚀-switching. This design realized pulses with energies up to 0.285 J and pulse durations of approximately 140 ns at a wavelength of 2,936.7 nm. This high-energy mid-IR Er:YAG MOPA system can be used for various scientific, engineering, and military underwater applications.

• 한국초전도ㆍ저온공학회논문지
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• 제11권3호
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• pp.20-25
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• 2009

The quench detection system of the KSTAR (Korea Superconducting Tokamak Advanced Research) primarily uses the resistive voltage measurement due to a quench. This method is to detect the resistive voltage generated by a quench, which is continuously maintained above the preset voltage threshold for a given holding time. As the KSTAR PF (Poloidal Field) coils are operated in the pulse current mode, the large inductive voltages are generated. Therefore the voltage threshold and the quench holding time should be determined by considering both the inductive voltages measured during the operation, and the maximum conductor temperature rise through the quench analysis. In this paper, the compensation methods for minimizing the inductive voltages are presented for the KSTAR PF coils. The quench hot spot analysis of the PF coils was carried out by the analytical and numerical methods for determining the proper values of the quench voltage threshold and the allowable quench protection delay time.

• 한국초전도ㆍ저온공학회논문지
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• 제11권3호
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• pp.1-5
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• 2009

It is important to predict AC loss in $Nb_3Sn$ and NbTi cable-in-conduit-conductor (CICC) reliably for the design and operation of large superconducting coils. The hysteresis loss in the superconducting filaments and coupling loss within strands and among strands in a cable or composite are dominant ac losses in superconducting magnets. The coupling loss in a superconductor can be characterized by identifying the coupling constant time $n{\tau}$. To reduce the coupling loss, all the strands (superconductor and Cu) in KSTAR (Korea Superconducting Tokamak Advance Research) are chromium plated with thickness of $l{\pm}0.5{\mu}m$. The ac losses of PF1, PF5 and PF6 coils has been measured by calorimetric method while applying trapezoidal current pulses with various ramp rate from 0.5 kA/s to 2 kA/s. The coupling time constants for $Nb_3Sn$ coils are $25{\sim}55$ ms and the values are not co-related with the coil size, the time constants for NbTi coil is 30 ms.

• The Korean Journal of Physiology
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• 제27권2호
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• pp.175-183
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• 1993

There are many report suggesting that influx and intracellular calcium concentration $([Ca^{2+}]_i)$ are related to cell signalling in various cells. However, it has not been reported that calcium channel activation is affected by the substances involved in signal transduction pathways in the mouse eggs. In this study, the effects of isoprenaline (ISP) and cyclic AMP on calcium influx through calcium channels were investigated to show their relationship with the signal transduction process in unfertilized mouse eggs. Using whole cell voltage clamp techniques, calcium currents, elicited by the depolarizing pulses of 300 ms duration (from -50 mV to 50 mV in 10 mV increments) from a holding potential of -80 mV, were recorded. The current-voltage (I-V) relation of calcium currents was shown to be bell-shaped; the current began to activate at -50 mV and reached its maximum $(-1.33{\pm}0.16\;nA:\;mean{\pm}S.E.,\;n=7)$ at -10 mV, then decayed at around 50 mV. Calcium currents were fully activated within $7\;ms{\sim}20\;ms$ and completely inactivated 200 ms after onset of the step pulse. ISP within the concentration ranges of $10^{-8}\;M{\sim}10^{-4}\;M$ dose-dependently increased the amplitude calcium current. The permeable cyclic AMP analogue,8-bromocyclic AMP, also increased its maximal amplitude by 46ft at $10^{-5}\;M$, while protein kinase inhibitor (PKI), which is known to inhibit 0.02 phosphorylating units of cyclic AMP-dependent protein kinase (PKA) per microgram decreased calcium currents. Currents recorded in the presence of PKI were resistant to increase by the application of $10^{-5}\;M$. Also, PKI inhibited the calcium current increase elicited by ISP treatment. These results suggest that $\beta-adrenergic$ regulation of the calcium channel is mediated by the cAMP-dependent protein kinase. This signal transduction pathway might play a role in regulating $[Ca^{2+}]_i$, level due to the increase of calcium influx in mouse eggs.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.172-173
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• 2012

Currently GaN based LED is known to show high internal or external efficiency at low current range. However, this LED operation occurs at high current range and in this range, a significant performance degradation known as 'efficiency droop' occurs. Auger process, carrier leakage process, field effect due to lattice mismatch and thermal effects have been discussed as the causes of loss of efficiency, and these phenomena are major hindrance in LED performance. In order to investigate the main effects of efficiency loss and overcome such effects, it is essential to obtain relative proportion of measurements of internal quantum efficiency (IQE) and various radiative and nonradiative recombination processes. Also, it is very important to obtain radiative and non-radiative recombination times in LEDs. In this research, we measured the IQE of InGaN/GaN multiple quantum wells (MQWs) LEDs with PSS and Planar substrate using modified ABC equation, and investigated the physical mechanism behind by analyzing the emission energy, full-width half maximum (FWHM) of the emission spectra, and carrier recombination dynamic by time-resolved electroluminescence (TREL) measurement using pulse current generator. The LED layer structures were grown on a c-plane sapphire substrate and the active region consists of five 30 ${\AA}$ thick In0.15Ga0.85N QWs. The dimension of the fabricated LED chip was $800um{\times}300um$. Fig. 1. is shown external quantum efficiency (EQE) of both samples. Peak efficiency of LED with PSS is 92% and peak efficiency of LED with planar substrate is 82%. We also confirm that droop of PSS sample is slightly larger than planar substrate sample. Fig. 2 is shown that analysis of relation between IQE and decay time with increasing current using TREL method.

• 전자공학회논문지
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• 제50권12호
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• pp.40-48
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• 2013

본 논문에서는 0.18um CMOS(1P6M) 공정을 이용하여 무인차량용 단거리 라이다 시스템을 위한 멀티채널 트랜스임피던스 증폭기(TIA) 어레이 회로를 구현하였다. 트랜스임피던스 증폭기 어레이 구조는 전압모드 $4{\times}4$ 채널 Inverter TIA 어레이와 전류모드 $4{\times}4$ 채널 Common-Gate(CG) TIA 어레이 두 가지를 설계했으며, 전체적으로 $4{\times}8$의 32-채널을 갖도록 설계하였다. 먼저, Inverter TIA는 피드백 저항을 가진 Inverter 입력구조와 CML 출력버퍼단으로 구성되어 있으며, 저잡음 및 저전력 특성뿐 아니라, virtual ground를 갖도록 설계함으로써 DC 전류조절이 가능하여 이득과 출력 임피던스 컨트롤이 가능하도록 하였다. 또한, CG-TIA는 on-chip bandgap reference로부터 bias 전압을 이용하고, 소스팔로워 출력버퍼를 사용하여 고주파수 이득을 높였으며, 기본적인 구조 상 CG-TIA는 채널당 칩 면적이 Inverter TIA에 비해 1.26배 작게 설계되었다. 포스트 레이아웃 시뮬레이션 결과, 제안한 Inverter TIA 어레이는 각 채널당 57.5-dB${\Omega}$ 트랜스임피던스 이득, 340-MHz 대역폭, 3.7-pA/sqrt(Hz) 평균 잡음전류 스펙트럼 밀도, 및 2.84-mW (16채널 45.4-mW) 전력소모를 가졌다. CG-TIA 어레이는 채널당 54.5-dB${\Omega}$ 트랜스임피던스 이득, 360-MHz 대역폭, 9.17-pA/sqrt(Hz) 평균 잡음전류 스펙트럼 밀도, 4.24-mW (16채널 67.8-mW) 전력소모를 가졌다. 단, 펄스 시뮬레이션 결과, CG-TIA 어레이가 200-500-Mb/s 동작속도에서 훨씬 깨끗하게 구분 가능한 출력펄스를 보였다.

• 한국컴퓨터산업학회논문지
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• 제8권2호
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• pp.107-112
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• 2007

피부과용 레이저 파장은 아주 얇은층의 조직두께에서 물의 흡수가 거의 90%이상 일어나는데 병소의 표피나 조직은 거의 물로 구성되어 흡수로 인해 증발효과를 가질 수가 있다. 표피를 절개, 층별로 증발 시킬 수 있으며 조직의 정확한 절개가 가능하다. 혈관이나 림프시스템에도 봉합수술이 가능하고 수술부위가 건조하고 눈으로 볼수 있고 무출혈 수술이 가능하다. 특히, 펄스에 대한 튜브양단 출력의 안정이 매우 중요함으로, 본 연구에서는 고주파 방식의 전력변환 장치를 사용하여 부피를 줄이고 의료용 레이저의 전류파형을 쉽게 제어할 수 있어 다양한 치료 효과를 낼 수 있다. ZVS(Zero Voltage Switching)나 ZVZCS(Zero Voltage and Zero Current Switching)를 도입하면 스위칭 손실을 줄일 수 있어 더욱 유리하다. 제안된 의료용 레이저의 전력부에는 1차측 도움에 의한 ZVZCS기법을 도입하여 넓은 부하 범위에서 안정된 soft-switching을 할 수가 있고 제어부는 microcontroller를 구성하여 출력전류 파형을 사용자가 임의의 형태를 갖도록 하였다. 설계 및 제작하여 실험한 결과, 기존장비에 비해 20%의 향상된 결과를 가져왔고, 추후 시스템적으로 보완을 하면 우수한 결과가 될 것으로 사려된다.

• 대한의용생체공학회:의공학회지
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• 제22권6호
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• pp.487-496
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• 2001

본 연구에서는 PIC(마이크로 컨트롤러)를 이용하여 전정계 기능 검사를 할 수 있도록 앙극 (bipolar) 자극이 가능한 정전류 자극기를 제작하였다. 정전류원이 구동할 수 있는 최대 부하와 최대 전류는 각각 3$k\Omega$. 5mA로 하였다. 그리고 자극 패턴은 직류. 정현파, 혹은 펄스파가 가능하도록 제작하였다. 정상인 20명을 대상으로 전기 자극 방법에 따른 안구 운동을 영상 안구운동 검사기(videooculograph; VOG)를 이용하여 분석하였다. 자극 패턴은 직류. 자극 시간은 30초로 하여. 전류의 세기에 대한 안진 반응을 살펴보기 위해 각 피검자마다 자극 전류가 0.75. 1, 2. 3mA인 경우에 대하여 실험하였다 자극 전류의 세기가 2mA 이상일 때는 검사 대상자 모두에게서 안진이 발생하였다 전류의 세기를 0.75에서 3mA로 증가시켰을 때. 느린 성분의 안구운동 속도의 평균은 1.1에서 4.8 deg/sec로 증가하였고. 안진의 평균 횟수 또한 17회에서 48회로 증가하였다. 전기 자극으로 인한 빠른 성분의 안구운동은 일관되게 음 자극을 가하는 전극이 있는 방향으로 나타났으며 좌우 반응의 타이를 나타내는 비대칭도는 전류가 증가할수록 감소하였다. 본 연구는 전기 자극을 이용한 전정 기능 평가와 전정 안반사의 생리기전 연구의 기초 자료로 활용할 수 있을 것으로 사료된다.

• The Korean Journal of Physiology and Pharmacology
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• 제8권1호
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• pp.7-15
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• 2004

Nitric oxide (NO) system has been implicated in a wide range of physiological functions in the nervous system. However, the role of NO in regulating the neural activity in the gustatory zone of nucleus tractus solitarius (NTS) has not been established. The present study was aimed to investigate the role of NO in the gustatory NTS neurons. Sprague-Dawley rats, weighing about 50 g, were used. Whole cell patch recording and immunohistochemistry were done to determine the electrophysiological characteristics of the rostral gustatory nucleus of the tractus solitaries and distribution of NO synthases (NOS). Neuronal NOS (nNOS) immunoreactivity was strongly detected along the solitary tract extending from rostral to caudal medulla. Resting membrane potentials of NTS neurons were $-49.2{\pm}2\;mV$ and action potential amplitudes were $68.5{\pm}2\;mV$ with a mean duration measured at half amplitude of $1.7{\pm}0.3\;ms$. Input resistance, determined from the response to a 150 ms, -100 pA hyperpolarizing current pulse, was $385{\pm}15\;M{\Omega}$, Superfusion of SNAP or SNP, NO donors, produced either hyperpolarization (68%), depolarization (5%), or no effect (27%). The hyperpolarization was mostly accompanied by a decrease in input resistance. The hyperpolarization caused by SNAP or SNP increased the time to initiate the first action potential, and decreased the number of action potentials elicited by current injection. SNP or SNAP also markedly decreased the number of firing neural discharges of the spontaneous NTS neural activity under zero current. Superfusion of L-NAME, a NOS inhibitor, slightly depolarized the membrane potential and increased the firing rate of NTS neurons induced by current injection. ODQ, a soluble guanylate cyclase inhibitor, ameliorated the SNAP-induced changes in membrane potential, input resistance and firing rates. 8-Br-cGMP, a non-degradable cell-permeable cGMP, hyperpolarized the membrane potential and decreased the number of action potentials. It is suggested that NO in the gustatory NTS has an inhibitory role on the neural activity of NTS through activating soluble guanylate cyclase.

• 기본간호학회지
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• 제9권1호
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• pp.27-44
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• 2002

The main purpose of this study was to identify the effect of hand massage on pain and anxiety related to chest tube removal in patients with a lobectomy. The research design of this study was a nonequivalent control group non-synchronized design. Of the twenty nine adult subjects, fourteen were assigned to the experimental group and fifteen to the control group. The data were obtained over 3 months from a medical center in Seoul. The instruments used to assess trait state anxiety was the Spielberger Trait-State anxiety Inventory. For pain and psychological anxiety. The Visual Analogue Scale was used. Hiko analogue sphygmo-manometer(2001) was used to check blood pressure and pulse rate as indicators of physiological anxiety Subjects in the experimental group received hand massage for 5 minutes just before chest tube was removed, and subjects assigned to the control group did not receive hand massage. Data were analysed with $x^2$-test and Mann-Whitney U test using the SPSSWIN 10.0 program. The results of the study are as follows : 1. Hypothesis 1: 'there will be a significant difference between two groups in the level of pain after chest tube removal' was supported (u = 23.00, p < 0.001). 2. Hypothesis 2: 'there will be a significant difference between the two groups in the level of psychological anxiety after chest tube removal' was supported (u = 3.00, p < 0.001). 3. Hypothesis 3: 'there will be a significant difference between the two groups in physiological anxiety(systolic, diastolic blood pressure and pulse rate) after chest tube removal' was supported(u =55.50, p = 0.01 ; u = 41.50, p = 0.01 ; u = 20.50, p < 0.001, relatively). The findings of this study indicate that hand massage is effective for pain and anxiety related to chest tube removal in patients with lobectomy. Therefore, hand massage is recommended as an effective nursing intervention for relieving pain and anxiety in patients undergoing chest tube removal. Further research is needed to identify the proper duration and timing to achieve the optimal effect of hand massage. A larger subject population is required to apply the current findings to the general population. Further research is also needed to assess the effects of hand massage in other patient subsets. Finally, it would be interesting to see if the effects of hand massaging would be attenuated when performed by a non-medical specialist.