• Applied Chemistry for Engineering
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• v.33 no.2
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• pp.126-132
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• 2022

Alkaline fuel cells using liquid fuels such as hydrazine and ammonia are gaining great attention as a clean and renewable energy solution possibly owing to advantages such as excellent energy density, simple structure, compact size in fuel container, and ease of storage and transportation. However, common shortcomings including cathode flooding, fuel crossover, side yield reactions, and fuel security and toxicity are still challenging issues. Real time monitoring of fuel concentrations integrated into a fuel cell device can help improving fuel cell performance via predicting any loss of fuels used at a cathode for efficient energy production. There have been extensive research efforts made on developing real-time sensing platforms for hydrazine and ammonia. Among these, recent advancements in electrochemical sensors offering high sensitivity and selectivity, easy fabrication, and fast monitoring capability for analysis of hydrazine and ammonia concentrations will be introduced. In particular, research trend on the integration of metallic and metal oxide nanoparticles and also their hybrids with carbon-based nanomaterials into electrochemical sensing platforms for improvement in sensitivity and selectivity will be highlighted.

• Journal of Space Technology and Applications
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• v.2 no.2
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• pp.104-120
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• 2022

The Small Scale magNetospheric and Ionospheric Plasma Experiment (SNIPE)'s scientific goal is to observe spatial and temporal variations of the micro-scale plasma structures on the topside ionosphere. The four 6U CubeSats (~10 kg) will be launched into a polar orbit at ~500 km. The distances of each satellite will be controlled from 10 km to more than ~1,000 km by the formation flying algorithm. The SNIPE mission is equipped with identical scientific instruments, Solid-State Telescopes(SST), Magnetometers(Mag), and Langmuir Probes(LP). All the payloads have a high temporal resolution (sampling rates of about 10 Hz). Iridium communication modules provide an opportunity to upload emergency commands to change operational modes when geomagnetic storms occur. SNIPE's observations of the dimensions, occurrence rates, amplitudes, and spatiotemporal evolution of polar cap patches, field-aligned currents (FAC), radiation belt microbursts, and equatorial and mid-latitude plasma blobs and bubbles will determine their significance to the solar wind-magnetosphere-ionosphere interaction and quantify their impact on space weather. The formation flying CubeSat constellation, the SNIPE mission, will be launched by Soyuz-2 at Baikonur Cosmodrome in 2023.

• Journal of the Korean Electrochemical Society
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• v.25 no.3
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• pp.95-104
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• 2022

The development of non-flammable all-solid-state batteries (ASSLBs) has become a hot topic due to the known drawbacks of commercial lithium-ion batteries. As the possibility of applying sulfide solid electrolytes (SSEs) for electric vehicle batteries increases, efforts for the low-cost mass-production are actively underway. Until now, most studies have used high-energy mechanical milling, which is easy to control composition and impurities and can reduce the process time. Through this, various SSEs that exceed the Li⁺ conductivity of liquid electrolytes have been reported, and expectations for the realization of ASSLBs are growing. However, the high-energy mechanical milling method has disadvantages in obtaining the same physical properties when mass-produced, and in controlling the particle size or shape, so that physical properties deteriorate during the full process. On the other hand, wet chemical synthesis technology, which has advantages in mass production and low price, is still in the initial exploration stage. In this technology, SSEs are mainly manufactured through producing a particle-type, solution-type, or mixed-type precursor, but a clear understanding of the reaction mechanism hasn't been made yet. In this review, wet chemical synthesis technologies for SSEs are summarized regarding the reaction mechanism between the raw materials in the solvent.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.1
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• pp.55-61
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• 2023

This study aims to develop CLSM fill material for emergency restoration using landfill coal ash. As a result of examining physical properties such as particle size distribution and fines content of landfill coal ash, bottom ash, fly ash, and general soil were mixed, and SP was found to have a density of 2.03 and a residual particle pass rate of 7.8 %. CLSM materials that secure fluidity in unit quantities without using chemical admixtures such as glidants and water reducing agents have a high risk of material separation due to bleeding. As a result of this experiment, it was found that the bleeding ratio did not satisfy the standard in the case of the specimen with a large amount of fly ash and a lot of addition of mixing water. As a result of the compressive strength test, the strength development of 0.5 MPa or more for 4 hours was found to be satisfactory for the specimens using hemihydrate gypsum with a unit binder amount of 200 or more, and the remaining gypsum showed poor strength development. Although it is judged that landfill coal ash can be used as a CLSM material, it is necessary to identify and apply the physical and chemical characteristics of coal ash buried in the ash treatment plant of each power generation company.

• Journal of the Korean Geotechnical Society
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• v.24 no.1
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• pp.51-59
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• 2008

In this study, cyclic shear characterics of sand-clay mixtures were analyzed. In order to perform cyclic triaxial tests on sand clay mixtures, natural clays with activity and silica sand were mixed variously to reproduce soils with wide range of grain size compositions. Test specimens with various fines contents were prepared by the moisture compaction and pre-consolidation methods, while paying attention to the void ratio expressed in terms of the sand structure and clay structures, and undrained cyclic shear tests were performed. In the test results, cyclic shear strength decreased with increasing of sand granular void ratio below 20% of fine contents. When the granular void ratio of the test specimen exceeded the maximum void ratio of the silica sand, the clay matrix dominated the soil structure, and soil structures were not influenced by compaction energy. It was observed that, the matrix structure of the coarse particles has great effect on the undrained cyclic shear strength characteristics for sand-clay mixtures, and therefore, it is more appropriate to pay more attention to the density of the sand structure, rather than to the fines content.

• Journal of the Korean Geotechnical Society
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• v.23 no.5
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• pp.143-151
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• 2007

The factors affecting the geotechnical properties of cemented sands are known to be relative density, cementation level, stress level, and particle characteristics such as particle size, shape and surface conditions. It has been widely accepted that the friction angle of cemented sands is not affected by cementation while the cohesion of cemented sands was significantly influenced by cementation. The cementation that is a critical component of the strength of cemented sands will be broken with increasing confining pressure and great caution is required in evaluating the cohesion of cemented specimens due to their fragilities. In this study, a series of drained shear tests were performed with specimens at various cementation levels and confining stresses to evaluate the strength parameters of cemented sands. From the experiments, it was concluded that the cohesion intercept of cemented sand experiences three distinctive zone(cementation control zone, transition zone, and stress control zone), as the cementation level and the confining stress varies. In addition, for accurate evaluation of the strength parameters, the level of confining stress triggering the breakage of cementation bond should be determined. In this study, the relationship between the maximum confining stresses capable of maintaining the cementation bond intact and unconfined compression strength of the cemented sand was established.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3C
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• pp.201-207
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• 2006

Soil tests are generally conducted using a membrane to measure a pore water pressure. However, it has also been recognized that the membrane penetrates into the specimen by the change of the confining pressure, and it results in the erroneous measurement in the pore water pressure and the volumetric strain. This study examined the effectiveness of the correction equation of the membrane penetration on the basis of the experimental data acquired during the isotropic unloading and the cyclic shear process using the hollow cylindrical shear test equipment. The results showed that the membrane penetration by the correction equation could be overestimated when the mean effective stress was lower than 20kPa in this study. The limitations originated from the sudden increase near the zero effective stress, and in order to prevent the overestimation in low effective stress condition, the use of the constant a was proposed in this study. Furthermore, the correction equation for the membrane penetration had to be applied carefully when the initial relative density was high and the density changes were occurred by the relocation of the soil particle by the liquefaction.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.687-693
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• 2006

The Stone Powder Sludge(below SPS) is the by-product from the process that translates stone power of 8mm under as crushed fine aggregate. It is the sludge as like cake that has average particle size of $7{\mu}m$, absorbing water content of 20 to 60%, and $SiO_2$ content of 60% over. Because of high water content of SPS, it is not only difficult to handle, transport, and recycle, but also makes worse the economical efficiency due to high energy consuming to drying. This study is aim to recycle SPS as it is without drying. Target product is the lightweight foamed concrete that is made from the slurry mixed with pulverized mineral compounds and foams through hydro-thermal reaction of CaO and $SiO_2$. Although in the commercial lightweight foamed concrete CaO source is the cement and $SiO_2$ source is high purity silica powder with $SiO_2$ of 90%, we tried to use the SPS as $SiO_2$ source. From the experiments with factors such as foam addition rate and replacement proportion of SPS, we find that the lightweight foamed concrete with SPS shows the same trends as the density and strength of lightweight foamed concrete increases according to decrease of foam addition rate. But in the same condition, the lightweight foamed concrete with SPS is superior strength and density to that with high purity silica. This trends is distinguished according to increase of replacement proportion of SPS, also the analysis of XRF shows that the hydro thermal reaction translates SPS to tobermorite. Although SPS has low $SiO_2$ contents, the lightweight foamed concrete with SPS has superior strength and density, because it reacts well with CaO due to extremely fine particles. We conclude that it is possible to replace the high purity silica as SPS in the lightweight foamed concrete experimentally.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.29 no.5
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• pp.586-594
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• 1996

This study was designed to determine the level of soybean meal (SM) that could be substituted for fish meal in the diet for Korean rockfish (Sebastes schlegeli). A control diet with white fish meal as only protein source was included, SM was substituted at levels of $5\%,\;10\%,\;15\%,\;and\;20\%$ for portions of the fish meal in the diet. Amino acids (met+lys) supplementation and two different SM particle sizes (0.5 mm and 0.25 mm) in the $20\%$ SM diet were compared. In addition, combination of $10\%$ SM, $10\%$ corn gluten meal (CGM) and $10\%$ meat and bone meal (MBM) was substituted for the fish meal in the diet. Duplicate groups of the 30 fish averaging 22.9 g were fed one of 8 isoproteic $(48\%)$and isolipidic $(7.5\%)$ experimental diets to satiation twice a day for 9 weeks. No significant differences were found among fish fed the control, substituting up to $20\%\;SM,\;20\%$ SM containing amino acids, and $10\%\;SM+10\%\;CGM+10\%$ MBM diets in weight gain, feed efficiency, daily feed intake, and protein retention (P>0.05). Feed efficiency, daily feed intake and protein retention in fish fed the diet containing $20\%$ SM with 0.5 mm particle size were not significantly different to those in fish fed the diets containing less than $20\%\;SM\;(P>0.05)$, however, weight gain was significantly lower than that of the control and $5\%\;SM\;diets\;(P<0.05)$. It is concluded that SM ran be used as a partial substitute for fish meal up to $20\%$ in the diet, and that the inclusion of SM with an adequate combination of several protein sources can replace larger amounts of fish meal in the diet.

• Journal of Korean Society of Forest Science
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• v.89 no.1
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• pp.24-32
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• 2000

We investigated the patterns of soil horizon evolution and its water distribution on three different forest stands covered with Larix leptolepis, Pinus koraiensis, and Qercus mongolica on the Experimental Forest of Kyunghee University, located in Kwangju, Kyunggi-Do. Compared to the properties of depths of O and A horizons evolved on the Pinus koraiensis stand, the depths of O and A horizons on the forest stands of Larix leptolepis and Qercus mongolica were shallower, indicating that the soil horizon were deeply influenced by geographical characteristics, its erosive and sedimentary distinction, vegetation cover and its population density. And the bulk densities of the sites selected were lower in the high slope gradient than that in the lower slope gradient at the same depth of soil profile. Therefore, the changes of the soil bulk densities were closely related to the soil organic matter and the vertical transport of soil particle throughout soil depths. On the other hand, the bulk density and organic matter content in soil can influence the water transport phenomena, resulting in decrease of the hydraulic conductivity as the increase in the bulk density, while the organic matter can not affect the hydraulic conductivity on the soil surface layer. For a rainfall infiltration characteristics from a lysimeter experiment established on the stand of Larix leptolepis, the bulk density and slope gradient strongly influenced the vertical transport of water, as well as the lateral movement of rainfall. Conclusively, the characteristics of water movement and distribution in the forest stand can be determined not by the geographical factor such as slope gradient but also by the bulk density and organic matter content remained in soils.