• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.9
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• pp.1087-1093
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• 2012

In this paper, we implemented a HF-band magnetic-field communication system consisting of an amplitude shift keying(ASK) transmitter, a pair of loop antennas, and an ASK receiver. Especially, we suggested a new ASK transmitter architecture, where a drain bias of class E amplifier is switched alternatively between two voltage levels with respect to input data. A maximum 5 W class E amplifier was designed using a low cost IRF510 power MOSFET at the frequency of 6.78 MHz. A measured sensitivity of the designed ASK receiver is -78 dBm, which consists of a log amplifier, a filter, and a comparator. Maximum communication range of magnetic-wave communication system with loop antennas was calculated using magnetic field equations in both near-field and far-field ranges. Also, in order to verify the calculated values, an indoor propagation loss was measured using a pair of loop antennas whose dimensions are $30{\times}30cm$. Maximum operating range is estimated about 35 m in case of transmitter's output power of 1 W and receiver sensitivity of -70 dBm, respectively. Finally, the communication field test using the designed ASK transmitter and receiver was successfully done at the distance of 5 m.

• Journal of Environmental Health Sciences
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• v.41 no.4
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• pp.249-258
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• 2015

Objectives: This study aims to investigate the correlations between the prevalence of allergic rhinitis (AR) and cytokines among elementary school children in an industrial city, Ulsan, South Korea, and to identify major environmental risk factors associated with AR prevalence. Methods: We conducted a case-control study in June 2009 and February 2010 in order to evaluate the relationship between AR and related cytokines. Data on physician-treated prevalence over the past 12 months and potential risk factors for AR were compiled through a questionnaire from a survey of 339 schoolchildren living in different urban environments. Logistic regression analysis was carried out with propensity score matched data (n=180) to assess the influences of cytokines (IL-13, IL-33, IL-4 and IL-5) on AR prevalence and to determine which environmental factors affected AR. Results: In univariate analysis, the AR prevalence was influenced by family history of AR (mother and siblings), environmental factors (odor condition and irritated symptoms of air pollution), and indoor allergens (D. farinae and D. pteronyssinus). The t-test demonstrated that eosinophils, Immunoglobulin E (IgE), and interleukins (IL-13 and IL-5) were statistically significantly different according to treatment of allergic rhinitis over the preceeding 12 months. The results of the multiple logistic regression analysis showed that a statistically significant association between several factors (such as irritated symptoms of air pollution (OR 4.075, CI 1.735-9.568), IL-13 (OR 0.825, CI 0.734-0.928), odor condition (OR 2.409, CI 0.908-6.389), and AR history of siblings (OR 2.217, CI 0.999-4.921)) and the prevalence of AR was found after adjusting for confounders. Conclusion: These results suggest that AR prevalence is significantly associated with cytokine level, genetic background, and outdoor environmental factors. Although living in a polluted area and genetic background can contribute to an increased risk of childhood AR, cytokine level should be considered as an important factor in the treatment of AR in the last 12 months.

• Journal of Bio-Environment Control
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• v.29 no.2
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• pp.105-109
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• 2020

This study was conducted to the improvement of solar light-based artificial light supply system and effect of lettuce cultivation. The artificial light supply system was consisted of units such as light source, power, system measurement and controller. The light source supply was composed of a solar transmitter and an LED lamp. The power supply consisted of an leakage breaker, SMPS, LED controller and relay. The solar transmitter was made of a quartz optical fiber with optimal light transmission. Artificial light used white lamp among LEDs. System measurement and control consisted of touch screen, Zigbee communication module and light quantity sensor. The results of test confirmed that the LED light is automatically activated when the intensity measured by the light intensity sensor is 200 μmolm^-2s^-1 or less. Moreover, the leaf length, root length, chlorophyll content and root fresh weight of optical fiber treatment was hight than LED lamp treatment. Therefore, it can be inferred that the energy-saving solar light collector device can be effective in the indoor lettuce production. However, the use of LED lamp is also recommended to assure the availability of sufficient sunlight in cloudy and rainy days.

• Journal of the Korean Geosynthetics Society
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• v.16 no.2
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• pp.139-148
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• 2017

Ground subsidence caused by damaged water pipe and sewer is recently increasing due to the aging of city and pipeline in many city. Although many recent studies have verified characteristics of ground subsidence due to wastewater pipe breakdown, research about characteristics of ground subsidence due to water pipe is insignificant. subsidence due to water pipe is insignificant. This study aims to identify the ground failure mechanism caused by water and sewer pipe breakdown. Accordingly, we conducted an indoor model experiment to verify characteristics of ground subsidence considering characteristics of ground and ground failure. The water pipe pressure and velocity head was considered to find out ground subsidence mechanism. Also comparative analysis is conducted by analyzing relative density and fine-grain content considering embedded condition of water pipe. When the relative density and seepage pressure is low, small scale ground subsidence can occur, but when the conditions are opposite, ground subsidence occur in large scale and expands to ground level over time. Furthermore, it is acknowledgeable that ground cavity that is formed after soil run off due to seepage in deep earth, maintains steady strength and stays on the ground level for long period.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.9
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• pp.712-722
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• 2018

This paper conducts parametric studies on flapping wing design, one of the most important design parameters of insect-mimicking aerial vehicles. Experimental study on wing shape was done through comparison and analysis of thrust, pitching moment, power consumption, and thrust-to-power ratio. A two-axis balance and hall sensor measure force and moment, and flapping frequency, respectively. Wing configuration is biplane configuration which can develop clap and fling effect. A reference wing shape is a simplified dragonfly's wing and studies on aspect ratio and wing area were implemented. As a result, thrust, pitching moment, and power consumption tend to increase as aspect ratio and area increase. Also, it is found that the flapping mechanism was not normally operated when the main wing has an aspect ratio or area more than each certain value. Finally, the wing shape is determined by comparing thrust-to-power ratio of all wings satisfying the required minimum thrust. However, the stability is not secured due to moment generated by disaccord between thrust line and center of gravity. To cope with this, aerodynamic dampers are used at the top and bottom of the fuselage; then, indoor flight test was attempted for indirect performance verification of the parametric study of the main wing.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.10
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• pp.2523-2529
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• 2014

Location estimation service can be provided outdoors using various location estimation system based on GPS. However, location estimation system is based on existing indoor resources as GPS cannot be used because of insufficient visible satellites and weak signals. The fingerprinting technique that uses WLAN signal, in particular, is good to use indoors because it uses RSSI provided by AP to estimate location. However, its accuracy may vary depending on how accurate data the offline stage used where the fingerprinting map is built. The study sampled various data at the stage that builds the fingerprinting map and suggested a location estimation system that enhances its precision by saving the data of high frequency among them to improve this problem. The suggested location estimation system based on majority sampling data estimates location by filtering RSSI data of the highest frequency at the client and server to be saved at a map, building the map and measuring a similar distance. As a result of the test, the location estimation precision stood at minimum 87.5 % and maximum 90.4% with the margin of error at minimum 0.25 to 2.72m.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.27 no.1
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• pp.38-45
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• 2017

Objectives: Radon may be second only to smoking as a cause of lung cancer. Radon is a colorless, tasteless radioactive gas that is formed via the radioactive decay of radium. Therefore, radon levels can build up based on the amount of radium contained in construction materials such as phospho-gypsum board or when ventilation rates are low. This study provides our findings from evaluation of radon gas at facilities and offices in an industrial complex. Methods: We evaluated the office rooms and processes of 12 manufacturing factories from May 14, 2014 to September 23, 2014. Short-term data were measured by using real-time monitoring detectors(Model 1030, Sun Nuclear Co., USA) indoors in the office buildings. The radon measurements were recorded at 30-minute intervals over approximately 48 hours. The limit of detection of this instrument is $3.7Bq/m^3$. Also, long-term data were measured by using ${\alpha}-track$ radon detectors(${\alpha}-track$, Rn-tech Co., Korea) in the office and factory buildings. Our detectors were exposed for over 90 days, resulting in a minimum detectable concentration of $7.4Bq/m^3$. Detectors were placed 150-220 cm above the floor. Results: Radon concentrations averaged $20.6{\pm}17.0Bq/m^3$($3.7-115.8Bq/m^3$) in the overall area. The monthly mean concentration of radon by building materials were in the order of gypsum>concrete>cement. Radon concentrations were measured using ${\alpha}-track$ in parallel with direct-reading radon detectors and the two metric methods for radon monitoring were compared. A t-test for the two sampling methods showed that there is no difference between the average radon concentrations(p<0.05). Most of the office buildings did not have central air-conditioning, but several rooms had window- or ceiling-mounted units. Employees could also open windows. The first, second and third floors were used mainly for office work. Conclusions: Radon levels measured during this assessment in the office rooms of buildings and processes in factories were well below the ICRP reference level of $1,000Bq/m^3$ for workplaces and also below the lower USEPA residential guideline of $148Bq/m^3$. The range of indoor annual effective dose due to radon exposure for workers working in the office and factory buildings was 0.01 to 1.45 mSv/yr. Construction materials such as phospho-gypsum board, concrete and cement were the main emission sources for workers' exposure.

• Horticultural Science & Technology
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• v.28 no.3
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• pp.476-483
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• 2010

Total bacterial populations were cultured from the Hydroball cultivation media in the rhizospheres of 9 different plants including $Hedera$ $helix$ L. and $Dracaena$ $deremensis$ cv. Warneckii Compacta, etc. These cultured bacterial populations were studied to test if the bacterial populations in the plant growing pots may play a role on removal of volatile organic compounds (VOCs) such as benzene and toluene in the air. To meet this objective, first, we tested the possibility of removal of VOCs by the cultured total bacteria alone. The residual rates of benzene by the inoculation of total bacterial populations from the different plant growth media were significantly different, ranging from 0.741-1.000 of $Spathiphyllum$ $wallisii$ 'Regal', $Pachira$ $aquatica$, $Ficus$ $elastica$, $Dieffenbachia$ sp. 'Marrianne' Hort., $Chamaedorea$ $elegans$, compared to the control with residual rate of 0.596 (LSD, $P$=0.05). This trend was also similar with toluene, depending on different plants. Based on these results, we inoculated the bacterial population cultured from $P.$ $aquatica$ into the plant-growing pots of $P.$ $aquatica$, $F.$ $elastica$, and $S.$ $podophyllum$ inside the chamber followed by the VOCs injection. The inoculated bacteria had significant effect on the removal of benzene and toluene, compared to the removal efficacy by the plants without inoculation, indicating that microbes in the rhizosphere could play a significant role on the removal of VOCs along with plants.

• Korean Journal of Remote Sensing
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• v.35 no.5_2
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• pp.841-850
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• 2019

The purpose of this study is to strengthen the capability of rapid mapping for disaster through improving the positioning accuracy of mapping and fusion of multi-sensing point cloud data derived from Unmanned Aerial Vehicles (UAVs) and disaster investigation vehicle. The positioning accuracy was evaluated for two procedures of drone mapping with Agisoft PhotoScan: 1) general geo-referencing by self-calibration, 2) proposed geo-referencing with optimized camera model by using fixed accurate Interior Orientation Parameters (IOPs) derived from indoor camera calibration test and bundle adjustment. The analysis result of positioning accuracy showed that positioning RMS error was improved 2~3 m to 0.11~0.28 m in horizontal and 2.85 m to 0.45 m in vertical accuracy, respectively. In addition, proposed data fusion approach of multi-sensing point cloud with the constraints of the height showed that the point matching error was greatly reduced under about 0.07 m. Accordingly, our proposed data fusion approach will enable us to generate effectively and timelinessly ortho-imagery and high-resolution three dimensional geographic data for national disaster management in the future.

• The Journal of Engineering Geology
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• v.31 no.3
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• pp.333-342
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• 2021

In this study was conducted to measure the water content and dry unit weight of the ground using TDR (Time Domain Reflectometry) in order to supplement the problems of the conventional compaction management method. The Flat TDR system is a device that does not cause ground disturbance, and in order to verify the measured values, the dry density and water content were measured for samples of the ground subject at 7 sites other than Jumunjin Standard Temple. The water content section was divided into 6 sections of 3, 6, 9, 12, 15, and 18%, and the experimental results were confirmed according to the unified classification method. As a result of the indoor experiment, the water content showed an error of about 0.7% for the SP sample and about 1.3% for the SM sample. In addition, the dry unit weight confirmed an error of about 7% for the SP sample and about 5% for the SM sample. It was confirmed that stable values were derived in sandy or silty sandy ground except for clay or gravel. Through the experimental results, it was confirmed that the measured values of the flat TDR system derive similar values to the existing traditional compaction management method, and it was determined that the flat TDR equipment was suitable for construction sites that require quick constructability and economic feasibility.