• Resources Recycling
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• v.29 no.1
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• pp.25-34
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• 2020

Electrochemical Quartz Crystal microbalance is a tool that is capable of measuring nanogram-scale mass change on electrode surface. When applying alternating voltage to the quartz crystal with metal electrode formed on both sides, a resonant frequency by inverse piezoelectric effect depends on its thickness. The resonant frequency changes sensitively by mass change on its electrode surface; frequency increase with metal dissolution and decrease with metal deposition on the electrode surface. The relationship between resonant frequency and mass change is shown by Sauerbrey equation so that the mass change during metal dissolution can be measured in real time. Especially, it is effective in the case of reaction mechanism and rate studies accompanied by precipitation, volatilization, compound formation, etc. resulting in difficulties on ex-situ AA or ICP analysis. However, it should be carefully considered during EQCM experiments that temperature, viscosity, and hydraulic pressure of solution, and stress and surface roughness can affect on the resonant frequency. Application of EQCM was shown as a case study on leaching of platinum using aqueous chlorine for obtaining activation energy. A platinum electrode of quartz crystal oscillator with 1000 Å thickness exposed to solution was used as leaching sample. Electrogenerated chlorine as oxidant was purged and its concentration was controlled in hydrochloric acid solution. From the experimental results, platinum dissolution by chlorine is chemical reaction control with activation energy of 83.5 kJ/mol.

• The Journal of the Korea institute of electronic communication sciences
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• v.19 no.1
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• pp.31-38
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• 2024

The digital phase-locked loop(DPLL) is one of the circuits composed of a digital detector, digital loop filter, voltage-controlled oscillator, and divider as a fundamental circuit, widely used in many fields such as electrical and circuit fields. A state estimator using various mathematical algorithms is used to improve the performance of a digital phase-locked loop. Traditional state estimators have utilized Kalman filters of infinite impulse response state estimators, and digital phase-locked loops based on infinite impulse response state estimators can cause rapid performance degradation in unexpected situations such as inaccuracies in initial values, model errors, and various disturbances. In this paper, we propose a two-layer Frobenius norm-based finite impulse state estimator to design a new digital phase-locked loop. The proposed state estimator uses the estimated state of the first layer to estimate the state of the first layer with the accumulated measurement value. To verify the robust performance of the new finite impulse response state estimator-based digital phase locked-loop, simulations were performed by comparing it with the infinite impulse response state estimator in situations where noise covariance information was inaccurate.

• Clinical and Experimental Pediatrics
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• v.48 no.6
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• pp.599-605
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• 2005

Purpose : The purpose of this study was to examine the causes, clinical courses and outcomes in children with acute respiratory distress syndrome(ARDS), and evaluate the physiologic variables as prognostic factors in the patients. Methods : Retrograde medical chart review was carried out in 24 patients who were diagnosed with ARDS at the pediatric intensive care unit(PICU) during 20-month period. Results : The incidence of ARDS among all PICU admission was 3.7 percent and the mortality rate was 37.5 percent, which was 14.8 percent of overall deaths in PICU. The most common causes of ARDS were pneumonia and sepsis. We found significant differences between survivors and nonsurvivors in $PaO_2/FiO_2$ ratio(P/F ratio), alveolar arterial oxygen gradient and oxygenation index(OI) on the second day from the onset of ARDS. Therapies for ARDS such as high frequency oscillator ventilation(HFOV), recruitment maneuver and low dose corticosteroid improved the P/F ratio and OI, especially in survivors. Conclusion : The mortality rate of children with ARDS was 37.5 percent; an important cause of death in PICU. HFOV, recruitment maneuver and low dose corticosteroid seemed to be effective in pediatric ARDS. The P/F ratio, alveolar arterial oxygen gradient and OI on the second day from the onset of ARDS may be useful as prognostic factors.