• Korean Journal of Materials Research
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• v.23 no.11
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• pp.643-648
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• 2013

Activated carbon (AC) was synthesized from rice husks using the chemical activation method with KOH, NaOH, a combination of (NaOH + $Na_2CO_3$), and a combination of (KOH + $K_2CO_3$) as the chemical activating reagents. The activated carbon with the highest surface area (around $2000m^2/g$) and high porosity, which allows the absorption of a large number of ions, was applied as electrode material in electric double layer capacitors (EDLCs). The AC for EDLC electrodes is required to have a high surface area and an optimal pore size distribution; these are important to attain high specific capacitance of the EDLC electrodes. The electrodes were fabricated by compounding the rice husk activated carbons with super-P and mixed with polyvinylidene difluoride (PVDF) at a weight ratio of 83:10:7. AC electrodes and nickel foams were assembled with potassium hydroxide (KOH) solution as the electrolyte. Electrochemical measurements were carried out with a three electrode cell using 6 M KOH as electrolyte and Hg/HgO as the reference electrode. The specific capacitance strongly depends on the pore structure; the highest specific capacitance was 179 F/g, obtained for the AC with the highest specific surface area. Additionally, different activation times, levels of heating, and chemical reagents were used to compare and determine the optimal parameters for obtaining high surface area of the activated carbon.

• Journal of Aerospace System Engineering
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• v.15 no.3
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• pp.71-78
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• 2021

Since most functions of modern aircraft are controlled by software, software errors are directly related to aircraft safety. The criterion in Chapter 15 of the MIL-HDBK-516C addresses safe development and verification of military aircraft software. As the U.S. Air Force repeatedly experienced non-compliance with Chapter 15 criterion of the MIL-HDBK-516C, it published an Airworthiness Circular (AC-17-01) as a guide to meeting the criterion. In this paper, Chapter 15 of MIL-HDBK-516C, AC-17-01 and the SW Qualification Guideline (DO-178C) as applied by the Federal Aviation Administration are compared and analyzed. For the analysis, a matching ratio formula between the MIL-HDBK-516C criteria specified in AC-17-01 and the DO-178C specified in MIL-HDBK-516C criteria is defined. The sections that satisfy MIL-HDBK-516C criterion are derived when AC-17-01 or DO-178C matches. Based on the analysis results, the aircraft software development process is established and examples of application of Chapter 15 of MIL-HDBK-516C are addressed.

• The Korean journal of internal medicine
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• v.39 no.3
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• pp.458-468
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• 2024

Background/Aims: The SAMe-TT₂R₂ score is used for assessing anticoagulation control (AC) quality with warfarin. However, it is hard to apply SAMe-TT₂R₂ score in Asian patients with atrial fibrillation (AF), because it has not been proven in those populations. This study aimed to validate the SAMe-TT₂R₂ score in Asian patients with AF and suggest a modified SAMe-TT₂R₂ score for this population. Methods: We analyzed 710 Korean patients with AF who were using warfarin. The AC quality was assessed as the mean time in therapeutic range (TTR). Each component of SAMe-TT₂R₂ score was evaluated for the relationship with AC. Further clinical factors that predict AC were analyzed. Identified factors were re-assorted and constructed as SA₂Me-TTR scoring system. Results: Of the components of the SAMe-TT₂R₂ score, female, age, and rhythm control were associated with AC. Heart failure and renal insufficiency were newly identified factors associated with AC. The modified SA₂Me-TTR score was reconstructed with the relevant risk factors (S, female gender, 1 point; A, age < 60 yr, 2 points; Me, medical history of heart failure, 1 point; T, treatment for rhythm control, 1 point; T, history of stroke or transient ischemic attack, 1 point; R, renal insufficiency, 1 point). The modified SA₂Me-TTR score demonstrated an excellent relationship with the grading of AC. The modified SA₂Me-TTR score ≤ 1 identified patients with good AC (hazard ratio 2.46, 95% CI 1.75-3.47). Conclusions: The modified SA₂Me-TTR score was useful for guiding oral anticoagulants selection in Asian patients with AF.

• Korean Journal of Materials Research
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• v.10 no.5
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• pp.350-353
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• 2000

Thermotropic liquid crystalline polymer(LCP) has been used for the alignment of ferroelectric liquid crystal (FLC) molecules and the surface morphology of the resulting polymeric thin film has been observed by atomic forced microscope. The uniform alignment of FLC molecules on the surface of thermotropic LCP thin film was obtained even though microgroove structures were not formed. The contrast ratio of sample cell was about 23:1 including two polarizers and a good memory capability due to the bistability of FLC was obtained. After AC field stabilization at 20V, the typical stripe-shaped patterns appeared.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.11
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• pp.942-948
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• 2007

Popular techniques for producing hydrogen by converting methane include steam reforming and catalyst reforming. However, these are high temperature and high pressure processes limited by equipment, cost and difficulty of operation. Low temperature plasma is projected to be a technique that can be used to produce high concentration hydrogen from methane. It is suitable for miniaturization and fur application in other technologies. In this research, the effect of changing each of the following variables was studied using an AC GlidArc system that was conceived by the research team: the gas components ratio, the gas flow rate, the catalyst reactor temperature and voltage. Results were obtained for methane and hydrogen yields and intermediate products. The system used in this research consisted of 3 electrodes and an AC power source. In this study, air was added fur the partial oxidation reaction of methane. The result showed that as the gas flow rate, the catalyst reactor temperature and the electric power increased, the methane conversion rate and the hydrogen concentration also increased. With $O_2/C$ ratio of 0.45, input flow rate of 4.9 l/min and power supply of 1 kW as the reference condition, the methane conversion rate, the high hydrogen selectivity and the reformer energy density were 69.2%, 32.6% and 35.2% respectively.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.11
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• pp.129-136
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• 2019

Non-structural elements are vulnerable to earthquake ground motion. In this study, an experimental study for the electrical non-structural element was performed using tri-axial shaking table tests. A 100kVA UPS(Uninterruptible Power Supply system) was used as the test specimen. The test specimen was anchored to the concrete slab using the conventional installation detail. The input acceleration were generated in accordance with ICC-ES AC156 code. Scale factors of the input acceleration with respect to the required response spectrum defined in ICC-ES AC156 were from 25% to 600%. Based on the test results, damage and dynamic characteristics of UPS were evaluated and analyzed including natural frequency, damping ratio, acceleration time history response, dynamic amplification factor and relative displacement.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.816-825
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• 1994

The purpose of this study is to develop the non-destructive material evaluation method of aluminum alloy base metal matrix composite(MMC) by ultrasonics. Five aluminum base MMC specimens were fabricated in which the fractional ratios of fiber were changed from 0% to 31%. Relations among acoustic properties, microstructural features and elastic constant were compared. The ultrasonic velocity method was useful for nondestructive elastic constant measurement of composite materials, since the method had as same accuracy as conventional strain measurement method. Furthermore, velocity, attenuation and backscattering behaviors for each specimen also related to fractional ratio of fiber and these relations could utilize ultrasonic non-destructive evaluation of fiber structure in MMC.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.1
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• pp.59-65
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• 2018

A new single-stage flyback power converter with PFC for electrolytic capacitor-less LED driver is proposed in this study. This method minimizes the peak-to-average ratio of the LED driving pulsating current by adding the LED driving current near the LED current valley area, as well as the third harmonic component injection into the input current. The reduced peak current value of the LED drive current minimizes the thermal stress of the LED itself, thereby increasing the reliability of the LED, as well as achieving a long lifetime. Simulation and experimental results show the usefulness of the proposed topology.

• ETRI Journal
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• v.28 no.5
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• pp.664-667
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• 2006

We propose an efficient audio transcoding algorithm that can convert audio streams from terrestrial digital television broadcasting service stations to those for terrestrial digital multimedia broadcasting hand-held receivers. The proposed algorithm avoids the complicated psychoacoustic analysis by calculating the scalefactors of the bit-sliced arithmetic coding encoder directly from the signal-to-noise ratio parameters of the AC-3 decoder. The bit-allocation process is also simplified by cascading the nested distortion control loop. Through subjective evaluation, it is shown that the proposed algorithm provides comparable audio quality to tandem coding but it requires much smaller complexity.

• Food Science and Preservation
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• v.8 no.3
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• pp.326-330
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• 2001

The characteristics of used wine yeast strains were as follows, S6U showed low fermentation speed than those of other yeast strains, but this strain fermented completely later. The wine fermented by W-3 was very low contents of total acid, 0.75% and the ones fermented by UCD530 and AC- contained much extract, 3.26 mg/L and 3.22 mg/L respectively. The wine fermented by CEG and CS2 were predominant in yellowness, and EC1118 produced large amount of acetaldehyde, 49.9 mg/L than those of other strains. EC1118 and CY3079 displayed low methylene blue dyeing ratio, below 15%, meaning high alcohol tolerance yeast. UCD530 produced extremely high contents of glycerol, succinate and lactate compared with other strains. These properties revealed that UCD530 was a typical Saccharomyces bayanus species. The main organic acids produced by wine yeasts were pyruvate, lactate, succinate and acetate. The concentration of acetate in experimental wine could be divided into two parts, one group had concentration below 170 mg/L (UCD530, EC1118, AC-, CY3079, W-3), and the other had concentration up to 350 mg/L (S6U, CEG, CS2).