• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.1
• /
• pp.28-35
• /
• 2016

The in-situ thermal response test for the design of a ground heat exchanger of geothermal heat pumps have difficulty in predicting the outlet temperature according to the variation of conditions due to the expense and time. This paper suggests a 3-D CFD analysis method to predict the heat transfer performance of vertical type ground heat exchanger, which is mostly used in national, and the outlet temperature and the slope of two in-situ thermal response tests were compared to test the proposed CFD reliability. The results of CFD analysis showed that the outlet temperature was predicted to within $0.5^{\circ}C$ of the actual value and the slope was predicted to within 1.6%. The reliability of the CFD analysis method was confirmed using this process, and the outlet temperature prediction of the two in-situ thermal response tests was obtained by changing ${\pm}20%$ of the flow rate and the effective thermal conductivity conditions, respectively. The results of CFD analysis showed that the outlet temperature of Case 1 was 28.0 (-20%) and $29.6^{\circ}C$ (+20%) for the flow rate variation and $29.6^{\circ}C$ (-20%) and $28.0^{\circ}C$ (+20%) for the effective thermal conductivity variation, and the outlet temperature of Case 2 was 28.4 (-20%) and $29.8^{\circ}C$ (+20%) for the flow rate variation and $29.7^{\circ}C$(-20%) and $28.4^{\circ}C$(+20%) for the effective thermal conductivity variation.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.12 no.3
• /
• pp.517-526
• /
• 2008

A one-chip DC-DC converter circuit for OLED(Organic Light-Emitting Diode) display module of automotive clusters is newly proposed. OLED panel driving voltage circuit, which is a charge-pump type, has improved characteristics in miniaturization, low cost and EMI(Electro-Magnetic Interference) compared with DC-DC converter of PWM(Pulse Width Modulator) type. By using bulk-potential biasing circuit, charge loss due to parasitic PNP BJT formed in charge pumping, is prevented. In addition, the current dissipation in start-up circuit of band-gap reference voltage generator is reduced by 42% and the layout area of ring oscillator is reduced by using a logic voltage VLP in ring oscillator circuit using VDD supply voltage. The driving current of VDD, OLED driving voltage, is over 40mA, which is required in OLED panels. The test chip is being manufactured using $0.25{\mu}m$ high-voltage process and the layout area is $477{\mu}m{\times}653{\mu}m$.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2014.10a
• /
• pp.581-584
• /
• 2014

In this paper, a micro-scale photovoltaic(PV) energy harvesting system is proposed where an MPPT(Maximum Power Point Tracking) control is implemented using an energy distribution technique. Miniature PV cells output very low energy and low voltages, and thus, they cannot be used to directly power the MPPT controller. In the proposed system, a start-up circuit boosts an internal Vcp, and the boosted Vcp is used to operate the internal MPPT control block. When the Vcp reaches a predefined value, a detector circuit makes the start-up block turn off and provide a power converter with the energy from the PV cell. When the Vcp decreases such that the MPPT controller can not be operated, the energy transferred to the power converter is blocked and the start-up circuit is reactivated. In this way, the MPPT function is achieved by alternately operating the start-up circuit and the power converter using the energy distribution technique, and the harvested energy is transferred to a load through a PMU(Power Management Unit). The proposed circuit is designed in a 0.35um CMOS process and its functionality has been verified through extensive simulations. The designed chip area including pads is $1430um{\times}1110um$.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.23 no.4
• /
• pp.104-111
• /
• 2019

Staged combustion cycle engines exhibit higher combustion performance compared with open cycle engines with a gas generator. An advanced research of the staged combustion cycle engine is going on for the next program following the KSLV-II program. Various experiments have been carried out for the technology demonstration model, TDM0A and TDM0B. The experiments on the combustion performance are aimed to understand the engine start condition and combustion characteristics. They also aim to develop the oxidizer-rich pre-burner and the combustor of the staged combustion cycle engine. The engine-shaped model, TDM1A is fabricated based on the experimental data. The combustion experiment of the TDM1A shows that the combustion pressure of the combustor is approximately 91 bar and the turbine rotation is approximately 28,00 rpm. The result is stable and satisfies the development requirements. The present paper reports on the development process and characteristics of engine models from TDM0A to TDM1A.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.14 no.2
• /
• pp.309-316
• /
• 2019

In this paper, a low-jitter delay-locked loop that compensates for local clock skew is presented. The proposed DLL consists of a phase splitter, a phase detector(PD), a charge pump, a bias generator, a voltage-controlled delay line(VCDL), and a level converter. The VCDL uses self-biased delay cells using current mode logic(CML) to have insensitive characteristics to temperature and supply noises. The phase splitter generates two reference clocks which are used as the differential inputs of the VCDL. The PD uses the only single clock from the phase splitter because the PD in the proposed circuit uses CMOS logic that consumes less power compared to CML. Therefore, the output of the VCDL is also converted to the rail-to-rail signal by the level converter for the PD as well as the local clock distribution circuit. The proposed circuit has been designed with a $0.13-{\mu}m$ CMOS process. A global CLK with a frequency of 1-GHz is externally applied to the circuit. As a result, after about 19 cycles, the proposed DLL is locked at a point that the control voltage is 597.83mV with the jitter of 1.05ps.

• Analyses & Alternatives
• /
• v.7 no.2
• /
• pp.35-77
• /
• 2023

This study aims to solve the entangled loop between demographic transition (DT) and economic growth by analyzing cross-country data. We undertake a national-level group analysis to verify the compressed transition of demographic variables over time. Assuming that the LA (latecomer advantage) on DT over time exists, we verify that the DT of the latecomer is compressed by providing a formal proof of LA on DT over income. As a DT has the double-kinked functions of income, we check them in multiple aspects: early maturation, leftward threshold, and steeper descent under a contour map and econometric methods. We find that the developing countries (the latecomer) have speedy DT (CDT, compressed DT) as well as speedy income such that DT of the latecomers starts at lower levels of income, lasts for a shorter period, and finishes at the earlier stage of economic development compared to that of developed countries (the early mover). To check the balance of DT, we classify countries into four groups of DT---balanced, slow, unilateral, and rapid transition countries. We identify that the main causes of rapid transition are due to the strong family planning programs of the government. Finally, we check the effect of latecomer's CDT on economic growth inversely: we undertake the simulation of the CDT effect on economic growth and the aging process for the latecomer. A worrying result is that the CDT of the latecomer shows a sharp upturn of the working-age population, followed by a sharp downturn in a short period. Compared to early-mover countries, the latecomer countries cannot buy more time to accommodate the workable population for the period of demographic bonus and prepare their aging societies for demographic onus. Thus, we conclude that CDT is not necessarily advantageous to developing countries. These outcomes of the latecomer's CDT can be re-interpreted as follows. Developing countries need power sources to pump up economic development, such as the following production factors: labor, physical and financial capital, and economic systems. As for labor, the properties of early maturation and leftward thresholds on DTs of the latecomer mean that demographic movement occurs at an unusually early stage of economic development; this is similar to a plane that leaks fuel before or just before take-off, with the result that it no longer flies higher or farther. What is worse, the property of steeper descent represents the falling speed of a plane so that it cannot be sustained at higher levels, and then plummets to all-time lows.

• Economic and Environmental Geology
• /
• v.53 no.1
• /
• pp.1-9
• /
• 2020

Magnesium silicate minerals such as serpentine [Mg₃Si₂O₅(OH)₄] have a high potential for the sequestration of CO₂; thus, their reactivity toward dissolution under CO₂-free and CO₂-containing conditions in acidic solvents is a critical process with respect to their carbonation reactions. To examine the carbonation efficiency and dissolution mechanism of serpentine, hydrothermal treatment was performed to the starting material via a modified direct aqueous carbonation process at 100 and 150℃. The serpentine dissolution experiments were conducted in H₂SO₄ solution with concentration range of 0.3-1 M and at a CO₂ partial pressure of 3 MPa. The initial pH of the solution was adjusted to 13 for the carbonation process. Under CO₂-free and CO₂-containing conditions, the carbonation efficiency increased in proportion to the concentration of H₂SO₄ and the reaction temperature. The leaching rate under CO₂-containing conditions was higher than that under CO₂-free conditions. This suggests that shows the presence of CO₂ affects the carbonation reaction. The leaching and carbonation efficiencies at 150℃ in 1 M H₂SO₄ solution under CO₂-containing conditions were 85 and 84%, respectively. The dissolution rate of Mg was higher than that of Si, such that the Mg : Si ratio of the reacted serpentine decreased from the inner part (approximately 1.5) to the outer part (less than 0.1). The resultant silica-rich layer of the reaction product ultimately changed through the Mg-depleted skeletal phase and the pseudo-serpentine phase to the amorphous silica phase. A passivating silica layer was not observed on the outer surface of the reacted serpentine.

• Journal of The Korean Association For Science Education
• /
• v.32 no.5
• /
• pp.805-822
• /
• 2012

The purpose of this study was to explore the patterns of group model development about blood flow in the heart and reasoning process by small group interaction. The subjects were 14, 8th graders in a Science Gifted Center. The group discussion was made possible by using triggering questions that can be answered based on experiences of hands-on activities such as a siphon pump analogy model activity and a dissection of pigs' hearts. Despite participating in same activities, the groups showed different model development patterns: unchanged, persuasive, and elaborated. Due to the critical revising, the group's explanatory model was elaborated and developed in the added and elaborated pattern. As critical revising is a core element of the developing model, it is important to promote a group interaction so that students become critical and receptive. The pedagogical analogy model and conflict situation enabled students to present elaborated reasoning. The Inquiry activity with the pedagogical analogy model promote students' spontaneous reasoning in relation to direct experience. Therefore offering a pedagogical analogy model will help students evaluate, revise and develop their models of concerned phenomena in science classroom. Conflict situation by rebuttal enable students to justify more solid and elaborate a model close to the target model. Therefore, teachers need to facilitate a group atmosphere for spontaneous conflict situation.

• Journal of Gastric Cancer
• /
• v.1 no.1
• /
• pp.55-59
• /
• 2001

Purpose: Several studies of an endoscopic mucosal resection(EMR) have been reported, but reports about benign protruding lesions that arise at the scar of EMR for early gastric cancer (EGC) or a gastric adenoma are rare. The purpose of this study was to elucidate endoscopic and histological characteristics of benign protruding lesions which arise at the scar of an EMR for EGC and a gastric flat adenoma. Materials and Methods: In 101 lesions (73 gastric flat adenomas and 28 EGCs) from 96 patients, 16 lesions developed new protruding lesions that arose at the scar of the EMR. We retrospectively analyzed the endoscopic findings of initial and protruding lesions, and several other clinical factors (H. pylori infection, eradication therapy, and proton pump inhibitor (PPI) or H2-blocker use). Results: 1. The mean duration until detection of the protruding lesion was 8.9 months ($1.5\∼27$). Protruding lesions arose at the scar of the EMR in 1 of 28 EGCs ($3.6\%$) and from 15 of 73 gastric flat adenomas ($20.5\%$). All of the patients were men. 2. With respect to the endoscopic findings, the shapes of the protruding lesions were as follows: 10 Yamada (Y) I, 4 Y-II, 1 Y-III, and 1 flat lesion. Histological examination of the protruding lesions revealed regenerating hyperplasia in 5 lesions, intestinal metaplasia in 5, and both in 6. 3. The incidence of these lesions was higher in cases of tubular adenomas with focal high-grade dysplasia than in cases of tubular adenomas without dysplasia (p<0.05). 4. The incidence of H. pylori infection was higher in patients ($81.7\%$) who developed a protruding lesion than in those ($51.8\%$) who did not develop (p=0.029); also, the incidence of use of PPI was higher in those patients (p=0.045). However, eradication therapy for H. pylori and duration of use of PPI or H2-blocker showed no difference between groups. Conclusions: It may be possible that the potential hyperplasia that may reside in normal mucosa surrounding EGC or a gastric adenoma might awaken during the healing process of the EMR ulcer and develop to benign protruding lesions. And, H. pylori and PPI might also be related to the development of the protruding lesions.

• Journal of Korean Society of Environmental Engineers
• /
• v.28 no.5
• /
• pp.549-557
• /
• 2006

The characteristics of supercritical water oxidation have been studied to decompose the waste anionic exchange resins which were produced from a power plant. The waste resins from a power plant were mixture of anionic and cationic exchange resins. The waste anionic exchange resins had been separated from the waste resins using a solid-liquid fluidized bed. It was confirmed that the cationic exchange resins were not included in the separated anionic exchange resins by the elemental and thermogravimetric analysis. A slurry of anionic exchange resins which could be fed continuously to a supercritical water oxidation apparatus by a high pressure pump was prepared using a wet ball mill. Although the COD of liquid effluent had been reduced more than 99.9% at 25.0 MPa and $500^{\circ}C$ within 2 min, the total nitrogen content was reduced only 41%. The addition of nitric acid to the slurry could reduce the total nitrogen content in treated water. The central composite design as a statistical desist of experiments had been applied to optimize the conditions of decomposing anionic resin slurry by means of the COD and total nitrogen contents in treated waters as the key process output variables. The COD values of treated waters had been reduced sufficiently to $99.9{\sim}100%$ af the reaction conditions of $500{\sim}540^{\circ}C$, 25.0 MPa within 2 min. The effects of temperature and nitric acid concentration on COD were not significant. However, the effect of nitric acid concentration on the total nitrogen was found to be significant. The regression equation for the total nitrogen had been obtained with nitric acid concentration and the coefficient of determination($r^2$) was 95.8%.