• Korean Journal of Materials Research
• /
• v.14 no.11
• /
• pp.780-785
• /
• 2004

The degradation mechanism of soft magnetic properties of $Fe-Hf-N/Cr/SiO_2$ thin films reacted with a bonding glass was investigated. When $Fe-Hf-N/Cr/SiO_2$ films were annealed under $600^{\circ}C$ without the bonding glass, the compositions and the soft magnetic properties of Fe-Hf-N layers were not changed. However, after reaction with the bonding glass at $550^{\circ}C$, the soft magnetic properties of the film were degraded. At $600^{\circ}C$, the saturation magnetization of the reacted film decreased to 13.5 kG, and its coercivity increased to 4 Oe, and its effective permeability decreased to 700. It was founded that O diffused from the glass into the Fe-Hf-N layers during the reaction and generated $HfO_2$ phases. It was considered that the soft magnetic properties of the $Fe-Hf-N/Cr/SiO_2$ films reacted with the bonding glass were primarily degraded by the formation of the Fe-Hf-O-N layer of which the Fe content was below 60 $at\%$, and secondarily degraded by the Fe-Hf-O-N layer above 70 $at\%$.

• Electronics and Telecommunications Trends
• /
• v.34 no.5
• /
• pp.71-80
• /
• 2019

Gallium nitride (GaN) can be used in high-voltage, high-power-density/-power, and high-speed devices owing to its characteristics of wide bandgap, high carrier concentration, and high electron mobility/saturation velocity. In this study, we investigate the technology trends for X-/Ku-band GaN RF power devices and MMIC power amplifiers, focusing on gate-length scaling, channel structure, and power density for GaN RF power devices and output power level and output power density for GaN MMIC power amplifiers. Additionally, we review the technology trends in gallium arsenide (GaAs) RF power devices and MMIC power amplifiers and analyze the technology trends in RF power devices and MMIC power amplifiers based on both GaAs and GaN. Furthermore, we discuss the current direction of national research by examining the national and international technology trends with respect to X-/Ku-band power devices and MMIC power amplifiers.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.19 no.1
• /
• pp.231-238
• /
• 2019

In this paper, we have studied how to improve the amplifiers efficiency by minimizing the combining loss when several unit power amplifiers are combined to obtain high output power. Specifically, we have developed Ka-band Spatial Combining Amplifier. The fabricated Spatial Combining Amplifier is a Ka-band 20W class SSPA, which uses a 5W class unit amplifier module 8EA designed using a GaN bare die. We also combined The unit amplifier module using 8-way spatial divider and combiner with a hybrid radial structure. The output combining loss of the fabricated spatial coupler is about 0.334dB, which is about 92.6% efficiency. In this paper, we developed a Spatial Combining Amplifier with a maximum saturation output of 10W and a power addition efficiency of over 15%. As a result, we achieved the maximum saturation output of 30W and the power addition efficiency of 19%.

• Journal of Oral Medicine and Pain
• /
• v.47 no.3
• /
• pp.135-143
• /
• 2022

Purpose: This study aimed to evaluate polysomnographic and cephalometric characteristics of patients with OSA according to obesity level based on the World Health Organization (WHO) Asian-Pacific BMI criteria. Methods: One hundred and thirty-one consecutive patients with obstructive sleep apnea (OSA) were evaluated using standard level 1 polysomnography and cephalometric analyses. The subjects were categorized into normal, overweight and obese groups according to the WHO Asian-Pacific BMI criteria. Respiratory indices and cephalometric parameters were compared among groups. Results: The 131 patients consisted of 111 males and 20 females, with a mean age of 44.1±12.4 years. The mean value of BMI was 25.3±3.4 kg/m² for all subjects, 20.6±2.2 kg/m² for normal (n=27), 24.0±0.5 kg/m² for overweight (n=33) and 27.6±2.2 kg/m² for obese (n=71). The obese group had a significantly higher apnea-hypopnea index (AHI) and respiratory arousal index and lower oxygen saturation level than the normal group (p<0.05). Total AHI, mean oxygen saturation level and respiratory arousal index were significantly correlated with BMI (p<0.001). A longer soft palate and anterior position of the hyoid bone were significantly correlated with BMI level (p ≤0.05). Conclusions: Obese patients have a higher risk of compromised craniofacial skeletal features and soft tissue structures, and severe OSA than non-obese patients.

• Journal of Soil and Groundwater Environment
• /
• v.14 no.6
• /
• pp.87-94
• /
• 2009

Surfactant-enhanced air sparging (SEAS) was developed to suppress the surface tension of groundwater prior to air sparging resulting in higher air saturation and larger contact area between NAPL and gas during air sparging. Larger contacting interface between NAPL and gas means faster mass transfer of contaminants from NAPL to gas phase. This new technique, however, is limited to relatively volatile contaminants because vaporization is its basic mechanism of mass transfer. In this study, SEAS was tested at an elevated temperature for a semi-volatile n-decane, which is expected not to be a good candidate of SEAS application due to its low vapor pressure at ambient temperature. Three sparging experiments were conducted using 1-dimensional column (5 cm id, 80 cm length) packed with sand; (1) ambient temperature ($23^{\circ}C$), column saturated with distilled water, (2) SEAS at ambient temperature ($23^{\circ}C$), for n-decane contaminated sand, (3) SEAS at elevated temperature ($73^{\circ}C$), for n-decane contaminated sand. Higher air saturation was achieved by SEAS compared to that by air sparging without surfactant application. The n-decane removal efficiency of SEAS at elevated temperature was significantly higher(> 10 times) than that of ambient SEAS. The n-decane concentrations in the gas effluent from column during SEAS at $73^{\circ}C$ are found to be 10 times of those measured at ambient temperature. Thus, SEAS technique can be applied for removal of semi-volatile contaminants provided that an appropriate technique for elevating aquifer temperature is available.

• Proceedings of the IEEK Conference
• /
• 2004.06b
• /
• pp.605-608
• /
• 2004

A $Pt/Al_xGa_{l-x}N$ Schottky type Ultra-violet photodetector was modeled and simulated using the commercial SILVACO software program. In the carrier transport, we applied field model and other analytic model to determine the electron saturation velocity and low field mobility for GaN and $Al_xGa_{l-x}N$. A C-Interpreter function was defined to described the mole-fraction for the ternary compound semiconductor such as $Al_xGa_{l-x}N$. As comparing the simulated and experimental results, we found that the simulated result for type-1 has $15.9 nA/cm^2$ of leakage current at 5V. We confirmed a good agreement of photo-current in the UV Photo-detector, while applying the absorption coefficient and reflective index of active $Al_xGa_{l-x}N$ and other layers. There had been an intensive search for the proper refractive indices of the layers.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.12 no.3
• /
• pp.155-160
• /
• 1979

Mechanical agitation in fermentation process enhances the fermentation activity of microbes by means of oxygen supply and frequent collision with substrate. However, the fermentation activity of microaerophilic bacteria is inhibited by the excess oxygen resulted from the mechanical agitation. On this account, a a strain of Lactobacillus bulgarius was cultured to know the inhibition effect of the mechanical agitation and determine the optimum conditions for tile process of lactic acid fermentation. The growth rate of L. bulgaricus and the consumption rate of tile substrate revealed an identical pattern in changes. The two rates were constant in the range of the modified Reynolds number of $1\times10^5\;to\;5\times10^5$ while they showed linear increase in the range of the modified Reynolds number of $1\times10^5\;to\;10\times10^5$. Under the conditions of the modified Reynolds number more than $10\times10^5$, the both rates decreased. At the modified Reynolds number of $10\times10^5$, the maximum specific growth rate and the saturation constant of L. bulgaricus were 0.58/hr and 6.74g/l, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.18 no.5
• /
• pp.423-430
• /
• 2005

In this paper, we have simulated a Symmetric Dual-gate Single-Si TFT which has three split floating $n^{+}$ zones. This structure reduces the kink-effect drastically and improves the on-current. Due to the separated floating $n^{+}$ zones, the transistor channel region is split into four zones with different lengths defined by a floating $n^{+}$ region. This structure allows an effective reduction of the kink-effect depending on the length of two sub-channels. The on-current of the proposed dual-gate structure is 0.9 mA while that of the conventional dual-gate structure is 0.5 mA at a 12 V drain voltage and a 7 V gate voltage. This results show a $80 {\%}$ enhancement in on-current by adding two floating $n^{+}$ zones. Moreover we observed the reduction of electric field In the channel region compared to conventional single-gate TFT and the reduction of the output conductance in the saturation region. In addition we also confirmed the reduction of hole concentration in the channel region so that the kink-effect reduces effectively.

• 한국신재생에너지학회:학술대회논문집
• /
• 2011.05a
• /
• pp.149-149
• /
• 2011

청정 에너지원으로 높은 잠재력을 가지고 있는 가스하이드레이트는 상업적 기술개발이 미확보된 상태임에도, 우리나라에서 부존이 직접적으로 확인되었기 때문에 에너지원으로서 그 중요성이 부각되고 있다. 현재 전세계적으로 가스하이드레이트 개발 및 생산에 관한 연구가 활발히 진행되고 있으며 이에 대한 기초자료로서 가스하이드레이트가 함유된 퇴적층의 물성자료가 필요하다. 이에 따라 본 연구에서는 입도 분포별 총 5가지의 미고결 시료를 대상으로 투과도, p파속도, 전기비저항 측정을 수행하였다. 연구에 사용된 미고결 시료는 Hama#5($774{\mu}m$), #6($485{\mu}m$), #7($258{\mu}m$), #8($106{\mu}m$) 4가지와 Hama#6과 Hama#7을 1:1($371{\mu}m$)로 혼합하여 사용하였다. 실험에 사용된 장비는 가스하이드레이트를 인공적으로 생성시키기 위해 퇴적층을 모사할 수 있는 고압셀과 자료획득장비, 유체 주입장비, 온도 유지장비이다. 또한 투과도 측정에는 차압계, 전기비저항 측정에 RLC meter, p파속도 측정에 음파 송수신장비를 사용하여 각각의 물성을 측정하였다. 실험과정을 단계별로 요약하면 먼저 시료를 고압셀에 충진한 뒤 주입된 물의 양으로부터 공극률을 측정하고, 절대 투수계수를 측정하였다. 그 후, 메탄가스를 주입하여 퇴적층 내 수포화도(water saturation)를 잔류상태(irreducible saturation)로 유지시키고 메탄가스를 추가적으로 주입하여 원하는 압력까지 가압한 뒤 온도를 $1^{\circ}C$로 낮추었다. 가스하이드레이트의 생성은 급격한 압력강하로부터 알 수 있다. 최종적으로 가스하이트레이트가 함유된 퇴적층의 상대 투수계수를 측정하기 위해 메탄가스를 주입하였고 각각의 측정장비를 통해 전기비저항 및 p파 속도를 측정하였다.$V_g$, $V_h$, $V_w$, $V_ss$는 각각 가스의 부피, 하이드레이트의 부피, 물의 부피, 모래의 부피이다. 또한 수포화도, $S_w=\frac{V_w}{V_v}$이며 하이드레이트 포화도, $S_h=\frac{V_w}{V_v}$, 가스 포화도, $S_g=\frac{V_g}{V_v}$로 정의된다. 본 실험의 결과 투과도는 가스의 부피비, $\frac{V_g}{V}=nS_g$에 민감한 반응을 보였으며, 비저항은 공극수의 부피비, $\frac{V_w}{V}=nS_w$에 민감한 반응을 보였다. 또한 p파 속도는 고체의 부피비, $\frac{V_s+V_h}{V}=n(1-S_h)$에 민감한 반응을 보였다. 이러한 실험의 결과는 가스하이드레이트 개발, 생산 연구에 있어 기초 물성자료로 활용되는데 도움을 줄 것이다.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.39 no.1
• /
• pp.11-16
• /
• 2012

Effect of supplementary intranasal midazolam on oral sedation of children The purpose of this study was to compare the cardiopulmonary parameters of two sedation regimens during dental treatment: (1) Oral chloral hydrate(CH) and hydroxyzine(HZ) with nitrous oxide-oxygen($N_2O/O_2$) inhalation(CH-HZ group); (2) Oral chloral hydrate(CH) and hydroxyzine(HZ) with nitrous oxide-oxygen($N_2O/O_2$) inhalation and supplementary intranasal(IN) midazolam administration(MIDA group). Among the patients of OO hospital who received dental treatment under sedation over the past 5 years, 44 patients were selected for each group of CH-HZ and MIDA according to their age, gender and weight. Following parameters that were recorded every 5 minutes were compared: 1) Heart rate(HR) 2) $O_2$ saturation 3) End tidal carbon dioxide concentration($EtCO_2$) 4) Respiratory rate(RR) 33 patients of Group MIDA who have complete data of 15 minutes before and after supplementary IN midazolam administration were selected. And measurements 15 minutes before and after midazolam administration in same patient were evaluated. The results were as follows: 1. Heart rate was significantly higher in MIDA group than in CH-HZ group, but it was within normal range. 2. Comparing HR, $O_2$ saturation, EtCO2, RR between before and after of supplementary IN midazolam administration in the same patient, the differences were not statistically significant.