• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.37 no.11
• /
• pp.1096-1103
• /
• 2009

The predictions of the material behavior for the structural stability of thrust chamber mixing head at very-low temperatures are very important since the head is highly pressurized by the liquid oxygen with very-low temperatures and experiences impact load by the thrust of combustion chamber. The constitutive equation to express tensile deformation behavior of the material at very-low temperature to predict deformation behavior of the mixing head is formulated by composition of thermal component and athermal component based on dislocation energy barrier model suggested by Kocks. Also, increase of thermal stress components by the increase of obstacles at low temperatures is formulated to the equation similar with Ramberg-Osgood equation. The suggested model predicted well the material's behavior at the wide temperature ranges from very-low temperature to ambient temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2007.06a
• /
• pp.296-296
• /
• 2007

Ferroelectric neodymium-substituted $Bi_4Ti_3O_{12}$(BTO) thin films have been successfully deposited on Pt/Ti/$SiO_2$/Si substrate by a sol-gel spin-coating process and the effect of crystallization temperature on their microstructure and ferroelectric properties were studied systematically. $Bi(TMHD)_3$, $Nd(TMHD)_3$, $Ti(O^iPr)_4$ were used as the precursors, which were dissolved in 2-methoxyethanol. The thin films were annealed at various temperatures from 600 to $720^{\circ}C$ in oxygen ambient for 1 hr, which was followed by post-annealed for 1 hr after depositing a Pt electrode to enhance the electrical properties. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the crystallinity and surface morphology of layered perovskite phase, respectively. The crystallinity of the BNT films was improved and the average grain size increased as the crystallization temperature increased from 600 to $720^{\circ}C$ at an interval of $40^{\circ}C$. The polarization values of the films were a monotonous function of the crystallization temperature. The remanent polarization value of the BNT thin films annealed at $720^{\circ}C$ was $24.82\;{\mu}C/cm^2$ at an applied voltage of 5 V.

• Fire Science and Engineering
• /
• v.19 no.4 s.60
• /
• pp.32-36
• /
• 2005

A water mist system was considered as a possible alternative to a gaseous suppression system that can not prevent re-ignition after fire extinguishment for a power transformer room. This study deals with the fire suppression capability of the water mist systems. High-and low-pressure water mist systems were examined to compare efficiency of both systems. The power transformer examined in this study occupied about $7\%$ of a $10m\times10m\times$ transformer room. Full-scale suppression tests were performed for six different fire scenarios: two spray fires, three pool fires and one cascade fire. The fire suppression test results demonstrated that the high-pressure system was superior to the low-pressure system, especially considering oxygen depletion and the ambient temperature distribution.

• Journal of the Korean institute of surface engineering
• /
• v.47 no.5
• /
• pp.239-243
• /
• 2014

The electrical and optical properties of amorphous In-Tin-Zinc-Oxide(ITZO) deposited at room temperature using rf-magnetron sputtering were investigated. The amorphous ITZO thin films were obtained at the composition of In:Sn:Zn = 6:2:2, 4:3:3, and 2:4:4, but the ITZO (8:1:1) showed a crystalline phase of bixbyite structure of In2O3. The resistivity of ITZO could be controlled by oxygen pressure in the sputtering ambient. The resistivity of post-annealed ITZO thin films exhibited the dependence on the amount of Indium. Optical energy band gap and transmittance increased as the amount of indium in ITZO increased. For the device application with ITZO, the bottom-gated thin-film transistor using ITZO as a active channel layer was fabricated. It showed a threshold voltage of 1.42V and an on/off ratio of $5.63{\times}10^7$ operated with saturation field-effect mobility of $14.2cm^2/V{\cdot}s$.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.166-166
• /
• 2010

Recently, TFTs based on amorphous oxide semiconductors (AOSs) such as ZnO, InZnO, ZnSnO, GaZnO, TiOx, InGaZnO(IGZO), SnGaZnO, etc. have been attracting a grate deal of attention as potential alternatives to existing TFT technology to meet emerging technological demands where Si-based or organic electronics cannot provide a solution. Since, in 2003, Masuda et al. and Nomura et al. have reported on transparent TFTs using ZnO and IGZO as active layers, respectively, much efforts have been devoted to develop oxide TFTs using aforementioned amorphous oxide semiconductors as their active layers. In this thesis, I report on the performance of thin-film transistors using amorphous indium gallium zinc oxides for an active channel layer at room temperature. $SiO_2$ was employed as the gate dielectric oxide. The amorphous indium gallium zinc oxides were deposited by RF magnetron sputtering. The carrier concentration of amorphous indium gallium zinc oxide was controlled by oxygen pressure in the sputtering ambient. Devices are realized that display a threshold voltage of 1.5V and an on/off ration of > $10^9$ operated as an n-type enhancement mode with saturation mobility with $9.06\;cm^2/V{\cdot}s$. The devices show optical transmittance above 80% in the visible range. In conclusion, the fabrication and characterization of thin-film transistors using amorphous indium gallium zinc oxides for an active channel layer were reported. The operation of the devices was an n-type enhancement mode with good saturation characteristics.

• Journal of Korean Society on Water Environment
• /
• v.36 no.6
• /
• pp.581-591
• /
• 2020

In this study, two types of reactors were operated to examine the properties of methanol uptake under the high-rate denitrification process. In a sequencing batch reactor, the denitrifying activity was enriched up to 0.80 g-N/g-VSS-day for 72 days. Then, the enriched denitrifying sludge was transferred to a completely stirred tank reactor (CSTR). At the final phase on Day 46-50, the nitrogen removal efficiency was around 100% and the total nitrogen removal rate reached 0.097±0.003 kg-N/㎥-day. During the continuous process, the sludge settling index (SVI30) was stabilized as 118.3 mL/g with the biomass concentration of 1,607 mg/L. The continuous denitrifying process was accelerated by using a sequencing batch reactor (SBR) with a total nitrogen removal rate of 0.403±0.029 kg-N/㎥-day with a high biomass concentration of 8,433 mg-VSS/L. Because the reactor was open to ambient air with the dissolved oxygen range of 0.2-0.5 mg-O2/L, an increased organic carbon requirement of 5.58±0.70 COD/NO3--N was shown for the SBR in comparison to the value of 4.13±0.94 for the test of the same biomass in a completely anaerobic batch reactor. The molecular analysis based on the 16S rRNA gene showed that Methyloversatilis discipulorum and Hyphomicrobium zavarzinii were the responsible denitrifiers with the sole organic carbon source of methanol.

• Korean Journal of Metals and Materials
• /
• v.47 no.9
• /
• pp.591-596
• /
• 2009

$TiN_xO_y/TiN_x$ multi-layer thin films with a high resistance(${\sim}k{\Omega}$) were deposited on $SiO_2/Si$ substrates at room temperature by sputtering. The $TiN_x$ thin films show island and smooth surface morphology in samples prepared by ${\alpha}$ and RF magnetron sputtering, respectively. $TiN_xO_y/TiN_x$ multi-layer in has been developed to control temperature coefficient of resistance(TCR) by the incorporation of $TiN_x$ layer(positive TCR) inserted into $TiN_xO_y$ layers(negative TCR). Electrical and structural properties of sputtered $TiN_xO_y/TiN_x$ multi-layer films were investigated as a function of annealing temperature. In order to achieve a stable high resistivity, multi-layer films were annealed at various temperatures in oxygen ambient. Samples annealed at $700^{\circ}C$ for 1 min exhibited good TCR value of approximately $-54 ppm/^{\circ}C$ and a stable high resistivity around $20k{\Omega}/sq$. with good reversibility.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.26 no.5
• /
• pp.743-754
• /
• 2022

This paper contains the results of the development and performance evaluation of the environmental data monitoring system for the fish farm. For the hardware development, the analogue sensor is used to collect dissolved oxygen, pH, salinity, and temperature of the fish farm water, and the digital sensor is used for collecting ambient temperature, humidity, and location information via a GPS module to be sent to cloud-based Firebase DB. A set of LoRa transmitters and receivers is used as a communication module to upload the collected data. The data stored in Firebase is retrieved as a graph on a web and mobile application to monitor the environmental data changes in real-time. A notification will be delivered if the collected data is outside the determined optimal value. To evaluate the performance of the developed system, a response time from hardware modules to web and mobile applications is ranging from 6.2 to 6.85 seconds, which indicates satisfactory results.

• Composites Research
• /
• v.36 no.5
• /
• pp.342-348
• /
• 2023

There has been increasing demand for real-time monitoring of body and ambient temperatures using wearable devices. Graphene-based thermistors have been developed for high-performance flexible temperature sensors. In this study, the temperature coefficient of resistance (TCR) of monolayer graphene was controlled by coating polyethylenimine (PEI) on graphene surfaces to enhance its temperature-sensing performances. Monolayer graphene grown by chemical vapor deposition (CVD) was wet-transferred onto a target substrate. To facilitate the interfacial doping by PEI, the hydrophobic graphene surface was altered to be hydrophilic by oxygen plasma treatments while minimizing defect generation. The effect of PEI doping on graphene was confirmed using a back-gated field-effect transistor (FET). The CVD-grown monolayer graphene coated with PEI exhibited an improved TCR of -0.49(±0.03) %/K in a temperature range of 30~50℃.

• Journal of Preventive Medicine and Public Health
• /
• v.15 no.1
• /
• pp.145-151
• /
• 1982

Breslau's report on the two stillbirths induced by illuminating gas poisoning made many investigators explore the hazards. of carbon monoxide(CO) poisoning to pregnancy. The pregnant woman, her fetus, and the newborn infant have been identified to be particularly vulnerable to CO even in low concentration. Several factors, such as placental barrier, membrane resistance of maternal and fetal red blood cells etc., were considered to be related to the delayed elimination of CO from fetus. Slower elimination of CO from fetus than from mother was confirmed in several in vivo studies. But there are few studies which have confirmed the difference of carboxyhemoglobin (HbCO) dissociation in adult and fetal bloods. Author investigated the effects of hemoglobin itself on the elimination of CO from mother and fetus. By observing the difference of CO dissociation from adult and fetal hemoglobin at the various partial pressures of oxygen, the author tries to suggest the base of the proper treatment measure for the CO poisoning of pregnant woman and newborn infant. The results were as follows: 1. The total hemoglobin amounts of adults and fetal bloods were $16.1{\pm}0.50gm%\;and\;15.7{\pm}0.32gm%$, respectively. The fetal hemoglobin proportions in adult and fetal bloods were $1.2{\pm}0.15%\;and\;72.7{\pm}3.01%$, respectively. 2. Adult and fetal bloods saturated by CO to 100% HbCO were exposed to ambient air$(21%\;O_2),\;100%\;O_2\;and\;3\;ATAO_2$. After 30 minutes exposure, the HbCO saturations of adult blood were 96.7%, 70.9%, and 52.8%, respectively, and those of fetal blood were 98.5%, 76.1%, and 62.2%, respectively. HbCO dissociation was proportional to the partial pressure of oxygen and the most marked dissociation was shown under 3 ATA $O_2$, HbCO dissociation of fetal blood was slower than that of adult blood in all conditions. According to the above results, it is possible that CO poisoning make more serious damage to the fetus and newborn infant than to the adult due to the delayed dissociation of HbCO. Thus in the treatment of CO poisoning of pregnant woman and newborn infant, hyperbaric oxygen therapy seems to be the most eflective treatment measure, but the duration of hyperbaric oxygenation should be lengthened accordingly.