• Transactions of the Korean hydrogen and new energy society
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• v.22 no.1
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• pp.92-99
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• 2011

Barium cerate ($BaCeO_3$) related perovskite ceramics currently dominate the high-temperature proton conductor field. Unfortunately, these materials have very stringent environmental limitations necessitating the costly and complex conditioning or cleaning of the application feed-gas. Commercial realization has been hampered, in part, because of the reactivity of $BaCeO_3$ with $CO_2$, and to some extent $H_2O$. And sintered $BaCeO_3$ decomposed at a rate comparable to the powder samples. In this article, the chemical stability and the structural changes of $BaCe_{0.9-X}Y0.1La_XO_{3-\delta}$ (X=0, 0.1, 0.2) have been systematically investigated in the atmosphere containing carbon dioxide ($CO_2$) and water vapor ($H_2O$). The sintering characteristics were studied in $1600^{\circ}C$, sintered pellets disintegrate and decompose upon contacting boiling water on the surface only.

• Ceramist
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• v.21 no.2
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• pp.4-18
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• 2018

Lastly, neuromorphic computing chip has been extensively studied as the technology that directly mimics efficient calculation algorithm of human brain, enabling a next-generation intelligent hardware system with high speed and low power consumption. Three-terminal based synaptic transistor has relatively low integration density compared to the two-terminal type memristor, while its power consumption can be realized as being so low and its spike plasticity from synapse can be reliably implemented. Also, the strong electrical interaction between two or more synaptic spikes offers the advantage of more precise control of synaptic weights. In this review paper, the results of synaptic transistor mimicking synaptic behavior of the brain are classified according to the channel material, in order of silicon, organic semiconductor, oxide semiconductor, 1D CNT(carbon nanotube) and 2D van der Waals atomic layer present. At the same time, key technologies related to dielectrics and electrolytes introduced to express hysteresis and plasticity are discussed. In addition, we compared the essential electrical characteristics (EPSC, IPSC, PPF, STM, LTM, and STDP) required to implement synaptic transistors in common and the power consumption required for unit synapse operation. Generally, synaptic devices should be integrated with other peripheral circuits such as neurons. Demonstration of this neuromorphic system level needs the linearity of synapse resistance change, the symmetry between potentiation and depression, and multi-level resistance states. Finally, in order to be used as a practical neuromorphic applications, the long-term stability and reliability of the synapse device have to be essentially secured through the retention and the endurance cycling test related to the long-term memory characteristics.

• Composites Research
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• v.33 no.3
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• pp.147-152
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• 2020

In this study, void behavior of composite laminate by local internal pressure gradient due to structural geometry and surface film application condition was experimentally evaluated through fabrication of spar/skin integrated structure specimens. Viscosity comparison and thermal analysis for both carbon fiber prepreg and surface film were conducted and cure characteristic and rate difference were analyzed. 2 types of spar/skin integrated structural specimens were prepared based on different application condition of surface film. Subsequently, those specimens were evaluated through visual surface inspection, non-destructive and destructive inspection. In a specimen #1 with full application of surface film, low pressurized area of composite laminate created by pressure gradient of structural geometry had voids. It exhibited that voids could not be evacuated and were locked in cured laminate by the influence of pre-cured surface film with relatively faster cure rate. In a specimen #2 without surface film, it revealed that all internal voids disappeared in the cured laminate. Therefore, it is verified that surface film acts as barrier film preventing void movement and evacuation during autoclave cure.

• Composites Research
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• v.33 no.2
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• pp.44-49
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• 2020

The cure kinetics of carbon fiber-reinforced prepreg for Vacuum Bag Only(VBO) process was studied by differential scanning calorimetry (DSC). The total heat of reaction (ΔH_total = 537.1 J/g) was defined by the dynamic scanning test using prepregs and isothermal scanning tests were performed at 130℃~180℃. The test results of isothermal scanning were observed that the heat of reaction was increased as the temperature elevated. The Kratz model was applied to analyze the cure kinetics of resin based on the test results. To verify the simulation model, the degree of cure from panels using different cure cycles were compared with the measurement. The simulation model showed that the error against the experimental value was less than 3.4%.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.4
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• pp.378-385
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• 2014

In this research, we investigate electrical performance and electrochemical properties of graphene supported Pt (Pt/G) and PtM (M = Ni and Y) alloy catalysts (PtM/Gs) that are synthesized by modified polyol method. With the PtM/Gs that are adopted for oxygen reduction reaction (ORR) as cathode of proton exchange membrane fuel cells (PEMFCs), their catalytic activity and ORR performance and electrical performance are estimated and compared with one another. Their particle size, particle distribution and electrochemically active surface (EAS) area are measured by TEM and cyclic voltammetry (CV), respectively. On the other hand, regarding ORR activity and electrical performance of the catalysts, (i) linear sweeping voltammetry by rotating disk electrode and rotating ring-disk electrode and (ii) PEMFC single cell tests are used. The TEM and CV measurements demonstrate particle size and EAS of PtM/Gs are compatible with those of Pt/G. In case of PtNi/G, its half-wave potential, kinetic current density, transferred electron number per oxygen molecule and $H_2O_2$ production % are excellent. Based on data obtained by half-cell test, when PEMFC singlecell tests are carried out, current density measured at 0.6V and maximum power density of the PEMFC single cell employing PtNi/G are better than those employing Pt/G. Conclusively, PtNi/Gs synthesized by modified polyol shows better ORR catalytic activity and PEMFC performance than other catalysts.

• Journal of Korean Society on Water Environment
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• v.23 no.4
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• pp.482-489
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• 2007

Fluorescence properties and carbohydrate content were investigated using ultrafiltrated size fractions of dissolved organic matters (DOM) originated from different sources. The materials included a treated sewage, an algal organic matter, and a soil leachate, all of which are major constituents of dissolved organic matter in a typical urban river. Four different size fractions were separated from the three sources of each DOM. The size distribution demonstrated that a higher molecular weight fraction was more present in soil leachate compared to two other source DOMs. A higher content of carbohydrates was observed in the following order - algal DOM > treated sewage > soil leachate. A wide range of specific UV absorbance was observed from size fractions of a single source DOM, indicating that aromatic carbon structures are heterogeneously distributed within one source of DOM. The structural heterogeneity was the most pronounced for the soil leachate. The fluorescence index ($F_{450}/F_{500}$) of the treated sewage was similar to that (2.0) typically obtained from autochthonous DOM, suggesting that the treated sewage exhibited autochthonous organic matter-like properties. No protein-like fluorescence intensities were observed for all of the soil leachate size fractions whereas they were observed with two other source DOMs. Based upon the fluorescence peak ratios from fluorescence excitation-emission matrix (EEM), two discrimination indices could be suggested to distinguish three different source DOMs. It is expected that the suggested discrimination indices will be useful to predict the sources of DOM in a typical urban river affected by treated sewage.

• Advances in materials Research
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• v.8 no.1
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• pp.37-46
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• 2019

Electrochemical double layer capacitors (EDLCs) which are fabricated using carbon based electrodes have been emerging at an alarming rate to fulfill the energy demand in the present day world. Activated charcoal has been accepted as a very suitable candidate for electrodes but its cost is higher than natural graphite. Present study is about fabrication of EDLCs using composite electrodes with activated charcoal and Sri Lankan natural graphite as well as a gel polymer electrolyte which is identified as a suitable substitute for liquid electrolytes. Electrochemical Impedance Spectroscopy, Cyclic Voltammetry and Galvanostatic Charge Discharge test were done to evaluate the performance of the fabricated EDLCs. Amount of activated charcoal and natural graphite plays a noticeable role on the capacity. 50 graphite : 40 AC : 10 PVdF showed the optimum single electrode specific capacity value of 15 F/g. Capacity is determined by the cycling rate as well as the potential window within which cycling is being done. Continuous cycling resulted an average single electrode specific capacity variation of 48 F/g - 16 F/g. Capacity fading was higher at the beginning. Later, it dropped noticeably. Initial discharge capacity drop under Galvanostatic Charge Discharge test was slightly fast but reached near stable upon continuous charge discharge process. It can be concluded that initially some agitation is required to reach the maturity. However, the results can be considered as encouraging to initiate studies on EDLCs using Sri Lankan natural graphite.

• Composites Research
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• v.31 no.6
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• pp.371-378
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• 2018

In this study, the thermoelastic properties of poly lactic acid (PLA) based nanocomposites are predicted by molecular dynamics (MD) simulation and a micromechanics model. The stereocomplex mixed with L-lactic acid (PLLA) and D-lactic acid (PDLA) is modeled as matrix phase and a single walled carbon nanotube is embedded as reinforcement. The glass transition temperature, elastic moduli and thermal expansion coefficients of pure matrix and nanocomposites unit cells are predicted though ensemble simulations according to the hydrolysis. In micromechanics model, the double inclusion (D-I) model with a perfect interface condition is adopted to predict the properties of nanocomposites at the same composition. It is found that the stereocomplex nanocomposites show prominent improvement in thermal stability and interfacial adsorption regardless of the hydrolysis. Moreover, it is confirmed from the comparison of MD simulation results with those from the D-I model that the interface between CNT and the stereocomplex matrix is slightly weak in nature.

• Nuclear Engineering and Technology
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• v.53 no.11
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• pp.3824-3836
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• 2021

Workers' safety from radiological exposure in a 1 ton/day capacity spent resin treatment facility was evaluated according to the operating times and outflow rate due to process related leakages. The conservative annual dose based on the operating times of the workers exceeded the dose limit by at least 7.38E+01 mSv for close work. The realistic dose range was derived as 1.62E+01 mSv-6.60E+01 mSv. The conservative and realistic annual doses for remote workers were 1.33E+01 mSv and 3.00E+00 mSv respectively, which were less than the dose limit. The MWR was identified as the major contributor to worker exposure within the 1 h period required for removal of radioactive materials. The dose considering both internal and external exposures without APF was derived to be 1.92E+01 mSv for conservative evaluation and 4.00E+00 mSv for realistic evaluation. Furthermore, the dose with APF was derived as 7.27E-01 mSv for conservative evaluation and 1.51E-01 mSv for realistic evaluation. Considering the APF for leakage from all parts, the dose range was derived as 1.25E+00 mSv-2.03E+00 mSv for conservative evaluation and 2.61E-01 mSv-4.23E-01 mSv for realistic evaluation. Hence, it was confirmed that radiological safety was secured in the event of a leakage accident.

• Safety and Health at Work
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• v.12 no.1
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• pp.114-118
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• 2021

Background: Exposure to particulate matter (PM) emitted from vehicle exhaust might disrupt systemic function and elevate the risk of cardiovascular disease. In this study, we examined the changes of cardiometabolic biomarkers among vehicle inspectors exposed daily to PM0.25 and components. Methods: This cross-sectional study was conducted at two vehicle inspection centers, Pulogadung and Ujung Menteng, located in East Jakarta, Indonesia. The exposed respondents were 43 workers from vehicle inspection centers, and the unexposed group consisted of 22 staff officers working in the same locations. Vehicle exhaust particulate matter was measured for eight hours using a Leland Legacy personal pump attached to a Sioutas Cascade Impactor. The used filters were 25 and 37-mm quartz filters. The particulate matter concentration was analyzed using a gravimetric method, whereas trace elements were analyzed using energy dispersive X-ray fluorescence. An EEL Smoke Stain Reflectometer analyzed black carbon. Results: The personal exposure concentrations of PM0.25 were 10.4-fold higher than those in unexposed groups. Calcium and sulfur were the major components in the obtained dust, and their levels were 3.3- and 7.2-fold higher, respectively, in the exposed group. Based on an independent-samples t-test, high-density lipoprotein, triglyceride, HbA1c, total immunoglobulin E, high-sensitivity C-reactive protein, tumor necrosis factor-alpha, and nitric oxide levels were significantly different between the groups. Conclusions: In summary, it was suggested that PM0.25 exposure from vehicle exhaust might affect cardiometabolic biomarkers change.