• Resources Recycling
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• v.30 no.6
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• pp.3-11
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• 2021

In this study, the effect of the solubility of ammonium metavanadate and the decomposition ratio of ammonium ions on a precipitation reaction-the precipitation of ammonium metavanadate by adding ammonium chloride to a sodium vanadate solution-was investigated. As the precipitation temperature and pH increased, the decomposition ratio of ammonium ions increased, and the decomposition ratio was greater than 81% at 45 ℃ and pH 9.3. This was approximately four times higher than that at pH 8. The result of the precipitation reaction, in view of these two factors that significantly influence the precipitation reaction, was that the precipitation yield increased as the temperature increased. However, the effect of temperature was not significant above 35 ℃. A kinetic study of the precipitation reaction revealed that the activation energy of the reaction was 42.3 kJ/mol. Therefore, considering the solubility of ammonium metavanadate, the lower the temperature, the better the vanadium recovery yield. Additionally, considering the decomposition of ammonium ions, the lower the pH of the aqueous solution, the more advantageous. However, at pH 8 or less, sodium polyvanadate is precipitated and the purity of vanadium oxide may reduce.

• Korean Journal of Ecology and Environment
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• v.54 no.3
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• pp.156-169
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• 2021

Traditional morphological identification difficulties, such as phenotypic plasticity, misidentification of cryptic species, and larval stage species, can be compensated for by using DNA analysis techniques, such as DNA barcoding, in surveying zooplankton populations, including species identification. Recently, the rapid development of DNA sequencing techniques has allowed DNA-based community analysis not only for zooplankton assemblages in various aquatic ecosystems but also for the gut contents of zooplankton that are limited by conventional methods such as visual and microscopic identification. Therefore, the application of DNA sequencing can help understand biological interactions through the analysis of zooplankton food sources. The present paper introduces the major DNA-based approaches in zooplankton research topics, including taxonomic approaches by DNA barcoding, community-level approaches by metabarcoding, and gut content analyses, summarizes the analysis methods, and finally suggests the methodological topics that need to be considered for future applications.

• Journal of Korea Water Resources Association
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• v.54 no.12
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• pp.1255-1263
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• 2021

While it could become an alternative water resource, fog could undermine traffic safety and operational performance of infrastructures. To reduce such adverse impacts, it is necessary to have spatially continuous fog risk information. In this work, tree-based machine-learning models were developed in order to quantify fog risks with routine meteorological observations alone. The Extreme Gradient Boosting (XGB), Light Gradient Boosting (LGB), and Random Forests (RF) were chosen for the regional fog models using operational weather and visibility observations within the Jeollabuk-do province. Results showed that RF seemed to show the most robust performance to categorize between fog and non-fog situations during the training and evaluation period of 2017-2019. While the LGB performed better than in predicting fog occurrences than the others, its false alarm ratio was the highest (0.695) among the three models. The predictability of the three models considerably declined when applying them for an independent period of 2020, potentially due to the distinctively enhanced air quality in the year under the global lockdown. Nonetheless, even in 2020, the three models were all able to produce fog risk information consistent with the spatial variation of observed fog occurrences. This work suggests that the tree-based machine learning models could be used as tools to find locations with relatively high fog risks.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.209-217
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• 2021

This paper investigates the effect of high strength hooked-end steel fiber content and aspect ratio on the compressive and flexural performance of concrete. A total of ten mixtures were prepared and tested. Concretes with specific compressive strength of 30 MPa were reinforced with three different aspect ratios (l/d) of steel fibers 64, 67, and 80 and three different percentages of steel fibers 0.25, 0.50, and 0.75% by volume of concrete. Tensile strengths of steel fibers with l/d of 64, 67, and 80 are 2,000, 2,400, and 2,100 MPa, respectively. The compressive and flexural properties of plain and steel fiber-reinforced concrete (SFRC) mixtures were evaluated and compared. The experimental results indicated that the incorporation of high-strength hooked-end steel fibers had significant effects on the compressive and flexural performance of concrete. With the increase of steel fiber content, compressive performances, such as Poisson's ratio and toughness, of concrete were improved. The steel fibers with the least l/d of 67 resulted in a larger enhancement of compressive performances. The residual flexural strength, that is, post-cracking flexural resistance and toughness, of concrete is mainly depended on the dosage and aspect ratio of steel fibers. The residual flexural strength at serviceability (SLS) and ultimate limit state (ULS) defined in fib Model Code 2010 (MC2010) is increased as the fiber content and aspect ratio increase.

• Journal of the Korean Institute of Gas
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• v.25 no.3
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• pp.27-38
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• 2021

We devised the system to automatically shutdown the boiler and to fundamentally block the harmful gases, including carbon monoxide, into the indoor when the exhaust system swerves: (1) The discharge pressure of the exhaust gas decreases when the exhaust pipe is disconnected. The monitoring system of the exhaust pipe is implemented by measuring the output voltage of APS(Air Pressure Sensor) installed to control the amount of combustion air. (2) The operating software was modified so that when the system recognizes the fault condition of a flue pipe, the boiler control unit displays the fault status on the indoor regulator while shutting down the boiler. In accordance with the ventilation facility standards in the "Rules for Building Equipment Standards" by the Ministry of Land, Infrastructure and Transport, experiments were conducted to ventilate indoor air. When carbon monoxide leaked in worst-case scenario, it was possible to prevent poisoning accidents. However, since 2013, the number of indoor air exchange times has been mitigated from 0.7 to 0.5 times per hour. We observed the concentration exceeding TWA 30 ppm occasionally and thus recommend to reinforce this criterion. In conclusion, if the flue pipe fault detection and the indoor air ventilation system are introduced, carbon monoxide poisoning accidents are expected to decrease significantly. Also when the manufacturing and inspection steps, the correct installation and repair are supplemented with the user's attention in missing flue, it will be served to prevent human casualties from carbon monoxide poisoning.

• Journal of Climate Change Research
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• v.4 no.4
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• pp.371-384
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• 2013

The appearance of abnormal weather caused by climate change have both direct and indirect impact on the society. Especially, agriculture is brought up as a socially important interest having direct impact of climate change in growth and harvest of crops. This study aims to perform vulnerability assessment for the South Korea's two main imported grains, maize and wheat. The production vulnerability assessment of maize and wheat in USA and China to temperature variability, which has a great impact in production, is performed. First, grain cultivation period which affects productivity of main grain production country was selected based on the main cultivation period from several references and previous studies. Then, Intergovernmental Panel on Climate Change AR5 greenhouse gas scenario RCP(representative concentration pathways)8.5 scenarios was used to select the future climate that correspond to the cultivation period of maize and wheat for each producing country. According to the result of production vulnerability analysis using adaptation (temperature changing trend) and sensitivity(temperature variability), the productivity of wheat was higher in USA, while productivity of maize was higher in China. In the future, the result showed that productivity of all two grains will be favorable in USA. The result of production vulnerability assessment through this study can later be used as a preparation data for the coming fluctuation in grain price due to climate change.

• Korean Journal of Remote Sensing
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• v.34 no.6_1
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• pp.1025-1032
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• 2018

Snow Cover is a form of precipitation that is defined by snow on the surface and is the single largest component of the cryosphere that plays an important role in maintaining the energy balance between the earth's surface and the atmosphere. It affects the regulation of the Earth's surface temperature. However, since snow cover is mainly distributed in area where human access is difficult, snow cover detection using satellites is actively performed, and snow cover detection in forest area is an important process as well as distinguishing between cloud and snow. In this study, we applied the Normalized Difference Snow Index (NDSI) and the Normalized Difference Vegetation Index (NDVI) to the geostationary satellites for the snow detection of forest area in existing polar orbit satellites. On the rest of the forest area, the snow cover detection using $R_{1.61{\mu}m}$ anomaly technique and NDSI was performed. As a result of the indirect validation using the snow cover data and the Visible Infrared Imaging Radiometer (VIIRS) snow cover data, the probability of detection (POD) was 99.95 % and the False Alarm Ratio (FAR) was 16.63 %. We also performed qualitative validation using the Himawari-8 Advanced Himawari Imager (AHI) RGB image. The result showed that the areas detected by the VIIRS Snow Cover miss pixel are mixed with the area detected by the research false pixel.

• Journal of IKEEE
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• v.23 no.2
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• pp.727-734
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• 2019

This paper confirms whether the movement or specific operation of the muscles in the process of transferring a person from the brain can find a signal showing an essential feature of a certain part of the brain. As a rule, the occurrence of EEG(Electroencephalogram) changes when a signal is received from a specific action or from an induced action. These signals are very vague and difficult to distinguish from the naked eye. Therefore, it is necessary to define a signal for analysis before classification. The EEG form can be divided into the alpha, beta, delta, theta and gamma regions in the frequency ranges. The specific size of these signals does not reflect the exact behavior or intention, since the band or energy difference of the activated frequencies varies depending on the EEG measurement domain. However, if different actions are performed in a specific method, it is possible to classify the movement based on EEG activity and to determine the EEG tendency affecting the movement. Therefore, in this article, we first study the EEG expression pattern based on the activation of the left and right biceps EMG, and then we determine whether there is a significant difference between the EEG due to the activation of the left and right muscles through EEG. If we can find the EEG classification criteria in accordance with the EMG activation, it can help to understand the form of the transmitted signal in the process of transmitting signals from the brain to each muscle. In addition, we can use a lot of unknown EEG information through more complex types of brain signal generation in the future.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.5
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• pp.657-673
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• 2019

A monitoring method based on acoustic emission (AE) sensor has been widely used to evaluate the damage of structures in underground rock. The acoustic emission signal generated from cracking in material is analyzed as various acoustic emission parameters in time and frequency domain. To investigate from initial crack generation to final failure of rock material, it is important to understand the characteristics of acoustic emission parameters according to the stress ratio and rock strength. In this study, uniaxial compression tests were performed using very strong and weak rock specimen in order to investigate the acoustic emission parameters when the failure of specimen occurred. In the results of experimental tests, the event, root-mean-square (RMS) voltage, amplitude, and absolute energy of very strong rock specimen were larger than those of the weak rock specimen with an increase of stress ratio. In addition, the acoustic emission parameters related in frequency were more affected by specification (e.g., operation and resonant frequency) of sensors than the stress ratio or rock strength. It is expected that this study may be meaningful for evaluating the damage of underground rock when the health monitoring based on the acoustic emission technique will be performed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.590-596
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• 2019

Uses of fossil fuels like coal and oil increases with industrial development, and problems like abnormal climate come up as greenhouse gas increases. Accordingly, studies are actively conducted on eco-friendly renewable energy as a replacement for the main resources, and especially, wood pellets with high thermal efficiency are in the limelight as an alternative fuel in thermal power stations and gas boilers. However, despite a constant increase in their usage, few studies are conducted on their risks like fire and spontaneous combustion. Thus, this study found the auto-ignition temperature and critical ignition temperature of wood pellets with a change in flow rate in a thermostatic bath, using a sample vessel with 20 cm in length, 20 cm in height and 14 cm in thickness to predict their ignition characteristics. Consequently, at the flow rate of 0 NL/min, as the core temperature of the sample increased to higher than the ambient temperature, they ignited at $153^{\circ}C$, when the critical ignition temperature was $152.5^{\circ}C$. At the flow rates of 0.5 NL/min and 1.0 NL/min, it was $149.5^{\circ}C$, and at the flow rate of 1.5 NL/min, it was $147.5^{\circ}C$. Consequently, at the same storage, the more the flow rate, the lower the critical ignition temperature became.