• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.2
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• pp.1-11
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• 2021

The cavity inside the combustor increases the mixing efficiency of fuel and air by inducing a oscillation of the flow and the recirculation area with a low speed, and enables continuous combustion by maintaining the flame. In this study, the characteristics of the internal flow by change in the shape parameters of the cavity were analyzed through experiments and two-dimensional computational analysis. It was observed that the flow in the supersonic combustor was greatly influenced by various shape parameters of cavity besides L/D. Even with the same L/D, it was confirmed that the flow type varies depending on the depth of the cavity, either open or closed type, and the aft ramp angle of the cavity and the height of the combustor also affect the flow characteristics. As a result, the change in the shape parameters of the cavity had a great influence on the total pressure loss.

• Journal of the Korea Society of Computer and Information
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• v.28 no.2
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• pp.131-142
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• 2023

In this paper, we propose a new station selection algorithm to solve the illegal parking problem of shared electric scooters and improve the service quality. Recently, as a solution to the urban transportation problem, shared electric scooters are attracting attention as the first and last mile means between public transportation and final destinations. As a result, the shared electric scooter market grew rapidly, problems caused by electric scooters are becoming serious. Therefore, in this study, text data are collected to understand the nature of the problem, and the problems related to shared scooters are viewed from the perspective of pedestrians and users in 'LDA Topic Modeling', and a station extension algorithm is based on this. Some parking lots have already been installed, but the existing parking lot location is different from the actual area of tow. Therefore, in this study, we propose an algorithm that can install stations at high actual tow density using mixed clustering technology using K-means after primary clustering by DBSCAN, reflecting the 'current state of electric scooter tow in Seoul'.

• Journal of the Korea Society of Computer and Information
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• v.28 no.1
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• pp.87-92
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• 2023

With the continuous development of the speech recognition system, the recognition rate for speech has developed rapidly, but it has a disadvantage in that it cannot accurately recognize the voice due to the noise generated by mixing various voices with the noise in the use environment. In order to increase the vocabulary recognition rate when processing speech with environmental noise, noise must be removed. Even in the existing HMM, CHMM, GMM, and DNN applied with AI models, unexpected noise occurs or quantization noise is basically added to the digital signal. When this happens, the source signal is altered or corrupted, which lowers the recognition rate. To solve this problem, each voice In order to efficiently extract the features of the speech signal for the frame, the MFCC was improved and processed. To remove the noise from the speech signal, the noise removal method using the Gaussian model applied noise deviation estimation was improved and applied. The performance evaluation of the proposed model was processed using a cross-correlation coefficient to evaluate the accuracy of speech. As a result of evaluating the recognition rate of the proposed method, it was confirmed that the difference in the average value of the correlation coefficient was improved by 0.53 dB.

• Land and Housing Review
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• v.14 no.2
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• pp.137-145
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• 2023

In this study, the characteristics such as flowability, bleeding rate, and strength of the CLSM (Controlled Low Strength Material) according to physical properties such as particle size distribution and particulate content of the pond ash were investigated as part of the practical development of technology for CLSM using pond ash. As a result of analyzing the properties of the collected pond ash, it was found that the density and particle size distribution characteristics were different. And 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 four 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 was determined 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.

• Korean Journal of Plant Resources
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• v.30 no.2
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• pp.152-159
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• 2017

The purpose of this study was to obtain basic data for using Aronia as a functional food material. The composition of anthocyanin was characterized and quantitated by LC-MS/MS, HPLC, and UV-VIS spectrophotometer techniques, respectively. The anthocyanin content was analyzed by temperature, time, pH, and the addition of citric acid. The UV-VIS spectrophotometer used for analysis of anthocyanin is less accurate than the LC-MS/MS method used in recent years. In the past, cyanidin-3-Glucoside was reported to be a major anthocyanin that contains Aronia. However, LC-MS/MS analysis in this study confirmed cyanidin-3-galactoside to be the major compound. The anthocyanin content of the Aronia powder began to decrease sharply at a temperature of $65^{\circ}C$ or higher when heated for 24 hours. In an aqueous solution of Aronia, the anthocyanin content was reduced by 50% at $65^{\circ}C$ for 10 hours and decreased by 85% at $85^{\circ}C$ within 10 hours. Above pH 8, the anthocyanin content was reduced by more than 50%. The results of this study will provide useful information to maintain anthocyanin content in the manufacturing process of Aronia. It could also be used to ensure the stability of anthocyanins in similar species of berries.

• Journal of the Korean earth science society
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• v.22 no.5
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• pp.350-359
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• 2001

The purpose of this study is to develop theme-based integrated science unit by the interdisciplinary approach and to analyze it's effects on the science achievement and the attitude towards science learning. 'Interaction' and 'Stability' were selected as the integrated themes, and the main concept and subconcept in relation to the themes were extracted from the four areas of science, and the learning contents were constructed in the integrated ways. While the main concept have relevance to subconcept in the interaction, the main concept have little relevance to subconcept in the stability. Therefore, the stability was to fit with middle school integrated science theme, but the interaction was not. The theme-based integrated science units developed was implemented in middle school, and the results are follows. First, the science achievement of group of theme-based integrated science teaching is significantly higher than those of group of traditional teaching. Second, the scores of the test of attitude toward science learning of the group of theme-based integrated science teaching is significantly higher than those of group of traditional teaching. Third, the students' perception of theme-based integrated science teaching was positive. The students have participation, interest, motivation in theme-based integrated science teaching, and students have difficulty in learning theme-based integrated science teaching.

• Korean Journal of Soil Science and Fertilizer
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• v.26 no.3
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• pp.197-203
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• 1993

Greenhouse experiments were conducted to avaluate strain competition, nodulation, patterns of nodule occupancy and population changes of Bradyrhizobium sp. strain HCR-46 $str^{r}cep^{r}$ and CB756 $str^{r}rif^{r}$ in the rhizosphere of peanut(Arachis hypogaea L.) under different root temperatures. Inoculated with two strains using seed coating with peat slurry under different root temperatures, population of each strain in the rhizosphere increased with plant growth and multiplication rate of inoculum in the unit weight of root were showed the highest from 10 to 15days after sowing. The multiplication rate of inoculum in the rhizosphere was $28^{\circ}C$>$34^{\circ}C$>$22^{\circ}C$. The density of HCR-46 $str^{r}cep^{r}$ was more increased than that of CB756 $str^{r}rif^{r}$ under $22^{\circ}C$ and $28^{\circ}C$. While the density of two strains showed no difference under $34^{\circ}C$. Inoculated with HCR-46 $str^{r}cep^{r}$ and CB756 $str^{r}rif^{r}$, respectively at 22, 28 and $34^{\circ}C$, nodulation of each strain was dominated in its inoculation portion. Inoculated with the mixture of HCR-46 $str^{r}cep^{r}$ and CB756 $str^{r}rif^{r}$, occupancy rate of HCR-46 $str^{r}cep^{r}$ was dominated over that of CB756 $str^{r}rif^{r}$ at $22^{\circ}C$ and $28^{\circ}C$, but that was similar between them at $34^{\circ}C$. Dry mass, nodulation, nitrogen content per plant and nitrogenase activity showed higher at $28^{\circ}C$ than at $32^{\circ}C$ and $22^{\circ}C$, while those were higher in HCR-46 $str^{r}cep^{r}$ and mixing HCR-46 $str^{r}cep^{r}$ with CB756 $str^{r}rif^{r}$ than in CB756 $str^{r}rif^{r}$.

• Journal of the Korea Organic Resources Recycling Association
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• v.11 no.3
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• pp.75-86
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• 2003

In the near future, the capacity of conventional anaerobic digester is thought to be insufficient because of the increase of the total solids from expansion of intercepting sewer, sewage quantity and direct input of night soil from near apartment districts. The objectives of this study was to investigate the improvement of digestion efficiency using microbial agent(Bio-dh). The system was a pilot-scale, two-staged, anaerobic sludge digestion system. The first-stage digester was heated and mixed. The agitation velocity of the first-stage digester was 120rpm. The second-stage digester was neither heated nor mixed. The Digestion temperature was kept at $35{\pm}1^{\circ}C$ The detention time of digester was 19 days. The dosage of sewage sludge and microbial agent were $0.65m^3/day$ and $0.5{\ell}/day$, respectively. The experiments was run for 25days. Three times a week, $COD_{Mn}$ and SS of effluent, TS, VS, and biogas production rate were measured. Temperature, pH, and alkalinity were measured daily. The results were as follows ; Without microbial agent, digestion efficiencies ranged 46.0%~50.9%(mean=48.6%), with microbial agent(Bio-dh), digestion efficiencies ranged 52.8%~57.3%(mean=54.2%). Consequently, microbial agent(Bio-dh) increased the sludge digestion efficiency about 12%. Also, Without microbial agent, the mean concentration of $COD_{Mn}$ and SS of second-stage digester effluent were 1,639mg/L, 4,888mg/L respectively. With microbial agent, the mean concentration of $COD_{Mn}$ and SS of second-stage digester effluent were 859mg/L, 2,405mg/L respectively. Consequently, microbial agent(Bio-dh) increased the removal efficiency of $COD_{Mn}$ and SS about 47.6% and 50.8%, respectively.

• Journal of Soil and Groundwater Environment
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• v.7 no.4
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• pp.77-86
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• 2002

Surfactant enhanced in-situ soil flushing was performed to remediate the soil and groundwater at an oil contaminated site, where had been used as a military vehicle repair area for 40 years. A section from the contaminated site (4.5 m $\times$ 4.5 m $\times$ 6.0 m) was selected for the research, which was composed of heterogeneous sandy and silt-sandy soils with average $K_d$ of 2.0$\times$$10^{-4}$cm/sec. Two percent of sorbitan monooleate (POE 20) and 0.07% of iso-prophyl alcohol were mixed for the surfactant solution and 3 pore volumes of surfactant solution were injected to remove oil from the contaminated section. Four injection wells and two extraction wells were built in the section to flush surfactant solution. Water samples taken from extraction wells and the storage tank were analyzed on a gas-chromatography (GC) for TPH concentration in the effluent with different time. Five pore volumes of solution were extracted while TPH concentration in soil and groundwater at the section were below the Waste Water Discharge Limit (WWDL). The effluent TPH concentration from wells with only water flushing was below 10 ppm. However, the effluent concentration using surfactant solution flushing increased to 1751 ppm, which was more than 170 times compared with the concentration with only water flushing. Total 18.5 kg of oil (TPH) was removed from the soil and groundwater at the section. The concentration of heavy metals in the effluent solution also increased with the increase of TPH concentration, suggesting that the surfactant enhanced in-situ flushing be available to remove not only oil but heavy metals from contaminated sites. The removal efficiency of surfactant enhanced in-situ flushing was investigated at the real contaminated site in Korea. Results suggest that in-situ soil flushing could be a successful process to remediate contaminated sites distributed in Korea.

• Korean Journal of Food Science and Technology
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• v.26 no.4
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• pp.442-447
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• 1994

Effect of different mixing ratio of non-glutinous and glutinous rice on physical and rheological properties of extrudate prepared in a single screw extruder were examined. The extrusion conditions in term of screw speeds, moisture content and die temperature were 258 rpm, 18% and $120^{\circ}C$, respectively. The resisdence time distribution of the most of materials were within 30 second and small portion of them went up to 80 second. The expansion ratio was the highest value (2.93) for 70% of glutinous rice in the mixture, while the lowest value for 100% of non-glutinous rice. Breaking strength was in the range between 1,051g and 1,117g for $10{\sim}20%$ of glutinous rice in the mixture, while the lowest value (737g) for 80%r of glutinous rice. As the amount of glutinous rice increased, L and a values were increased and b value was decreased. The uncooked cold paste viscosity had 400 B.U. for 100% non-glutinous rice , while no peak for the 100% glutinous rice. As the amount of glutinous rice increased up to 100%, the water absorption index (WAI) was decreased, while water solubility index (WSI) was increased. The rheological properties of extrudate were accounted by the law of Oswald. The flow behavior index of extrudate was less than 1.0, which showed pseudoplastic behavior. Yield stress was the highest value for 20% of glutinous rice in the mixture and the lowest value for $80{\sim}100%$ of glutinous; rice. Number of air cell was between 128 and 159 for $80{\sim}100%$ of glutinous rice in the mixture, while $81{\sim}84%$ for $0{\sim}20%$ of glutinous rice. The degree of shapefact was increased more when the mixtures of glutinous and non-glutinous rice was used than when glutinous or non-glutinous rice was only used.