• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.50 no.4
• /
• pp.179-187
• /
• 2001

In recent years, the switching source devices have the advantage of small, light and high reliability with the high-frequency. But, high-frequency switching has disclosed disadvantage of result from stress and turn-on and turn-off peak losses at the switching instant. Accordingly, in this paper propose ZVS-HB type high-frequency resonant DC/DC converter using soft switching technique (Zero-Voltage-Switching, Zero-Current-Switching) with safety operating of circuit at diving on inductive zone, through the circuit design example using the capacitor $C_3,\;C_4$ with soft switching function and division characteristic of resonant Capacitor C, $C_1,\;C_2$, and, the characteristic analysis of circuit is generally described using normalized parameters. Also, this paper certified a rightfulness of characteristic analysis in comparison with a theoretical values and a experimental values obtain from experiment using MOSFET.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.27 no.1A
• /
• pp.51-57
• /
• 2002

In this paper, a simple interpolation technique in a frequency domain is proposed for the discrete Fourier transform(DFT) algorithm. Frequency and phase resolution capabilities of the DFT algorithm can be significantly improved by the proposed interpolation technique without increase of a DFT size(the number of points for the DFT). The new technique uses a diving point in amplitude and phase spectrums. As an application, the technique can be used for joint estimation of fine frequency and phase offsets in burst mode digital transmission. Simulation results show that the joint estimator using the technique is robust to estimation errors.

• Ocean and Polar Research
• /
• v.28 no.3
• /
• pp.225-236
• /
• 2006

Seagrass meadows are considered as critical habitats for a wide variety of marine organisms in coastal and estuarine ecosystems. In many cases, studies on the spatial/temporal distribution of seagrass have depended on direct observations using SCUBA diving. As an alternative method fur studying seagrass distribution, an application of hydroacoustic technique has been assessed for mapping seagrass distribution in Dongdae Bay, on the south coast of Korea, in September 2005. Data were collected using high frequency transducer (420 kHz split-beam), which was installed with towed body system. The system was linked to DGPS to make goo-referenced data. Additionally, in situ seagrass distribution has been observed using underwater cameras and SCUBA diving at four stations in order to compare with acoustic data. Acoustic survey was conducted along 23 transects with 3-4 blot ship speed. Seagrass beds were vertically limited to depths less than 3.5m and seagrass height ranged between 55 and 90cm at the study sites. Dense seagmss beds were mainly found at the entrance of the bay and at a flat area around the center of the bay. Although the study area was a relatively small, the vertical and spatial distributions of the seagrass were highly variable with bathymetry and region. Considering dominant species, Zostera marina L., preliminary estimation of seagrass biomass with acoustic and direct sampling data was approximately $56.55g/m^2$, and total biomass of 104 tones (coefficient variation: 25.77%) was estimated at the study area. Hydroacoustic method provided valuable information to understand distribution pattern and to estimate seagrass biomass.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.37 no.4
• /
• pp.302-307
• /
• 2001

The underwater background noise measured in Geoje and Tongyoung diving fishing ground from May to December, 2000 and analyzed to get optimum carrier frequency and transmitter power level for underwater wireless telephone design. The results obtained are summarized as follows: 1. At the Geoje and Tongyoung diving fishing ground, the lowest ambient noise band was 25~30kHz with 57dB and 52dB re 1$\mu$Pa, respectively. 2. At the Geoje and Tongyoung diving fishing ground, the lowest noise band during fishing activity was 67dB and 62dB re 1$\mu$Pa, respectively. 3. At the Geoje diving fishing ground, the noise of water jetter which is a digging machine for subbottom shells was 102dB re 1$\mu$Pa. 4. Considering the design parameters of underwater wireless telephone, it is found that the optimum carrier frequency band is around 30kHz and the transmitter source level should be at least 131dB re 1$\mu$Pa for 500m range telephone.

• Journal of Fisheries and Marine Sciences Education
• /
• v.29 no.2
• /
• pp.593-606
• /
• 2017

This study aims to provide preliminary data capable of suggesting directivity of an initiating start by understanding consumer awareness through analysis of SNS social big data on marine sports. This study selected windsurfing, yacht, jet ski, scuba diving and sea fishing as research subjects, and produced following results by setting period of total 1 month from January 22 through February 22, 2017 on the SNS (twitter, blog) through the Social MatrixTM service of Daumsoft Co., Ltd., and analyzing frequency of mention, associated words etc. First, sports that was mentioned the most out of marine sports was yacht, which was 3,273 cases on twitter and 2,199 on blog respectively. Second, the word which was shown the most associated with marine sports was the attribute showing unique characteristic of marine sports, which was 6,261 cases in total.

• The Korean Journal of Emergency Medical Services
• /
• v.18 no.2
• /
• pp.45-58
• /
• 2014

Purpose: This study aimed to investigate the level of knowledge and education regarding basic life support (BLS) among scuba divers. Methods: Data collected from 125 scuba divers in Jeju-do were subjected to frequency, t-test, ANOVA, and Chi-square analyses using the SPSS 18.0 program. Results: 42.1% of the subjects was trained BLS for more than an hour less than 4 hours, and 52.6% of the subjects was trained BLS for less than 3 months in scuba diving institutions. Statistically significant difference was observed in the competence for performing cardiopulmonary resuscitation during BLS education according to gender and age further regarding the necessity of BLS education, significant difference was observed with respect to age, job, academic background, monthly income, and participation period of scuba divers. The divers wished to learn cardiopulmonary resuscitation (72.8%), medical first aid (8.0%), and measures to be taken in cases of trauma (8.0%). The knowledge score for BLS among scuba divers was significantly different depending on the gender, age, marital status and frequency of participation. Conclusion: It is necessary to develop and implement a safety education program for scuba divers.

• Fashion & Textile Research Journal
• /
• v.21 no.1
• /
• pp.46-58
• /
• 2019

This study analyzes the effects of lifestyle on wetsuits purchasing behavior and identifies various characteristics among lifestyle groups. A questionnaire survey of 213 domestic consumers with water sport activity and wetsuits experience indicated the following results: 1) Lifestyle factors were analyzed as 6 factors: social relation ships, development orientation, trend & appearance, domestic, positive acknowledgement of hobbies, pursuit of practicality. And the wetsuits selection criteria was 4 factors: wearing fitness, product information, design, reputation. 2) Social relationships, development orientation, positive acknowledgement of hobbies and pursuit of practicality factors had a positive effect fitness. Trend & appearance, development orientation, and pursuit of practicality factors had a positive effect on product information factors ; in addition, development orientation, and trend & appearance, a positive acknowledgement of hobbies factors had a positive effect design factors. Social relationships, trend & appearance, and pursuit of practicality factors had a positive effect on reputation factors. However, trend & appearance factors negatively affected the wearing fitness factors and the positive acknowledgement of hobbies factors had negative effect on product information, reputation factors. 3) The three groups of lifestyle factors showed differences in monthly average purchasing of clothes, average annual purchasing expenditures for water sports related products, number of water sport activity days and frequency, product selection criteria.

• Journal of Ecology and Environment
• /
• v.41 no.3
• /
• pp.45-53
• /
• 2017

Background: There have been many studies on the growth conditions of Zostera marina and Zostera japonica, but few studies have examined how spatial and temporal factors affect growth in established seagrass beds or the distribution range and shoot density. This study aims to clarify the factors that determine the temporal and spatial distribution of Zostera marina and Zostera japonica in the Seto Inland Sea east of Yamaguchi Prefecture. Methods: The study site is in Hiroshima Bay of the Seto Inland Sea, along the east coast of Yamaguchi Prefecture, Japan. We monitored by diving observation to confirm shoot density, presence or absence of both species and observed water temperature, salinity by sensor in study sites. Results: The frequency of occurrence of Zostera marina was high in all seasons, even in water depths of D.L. + 1 to -5 m ($80{\pm}34%$ to $89{\pm}19%$; mean ${\pm}$ standard deviation), but lower (as low as $43{\pm}34%$) near the breakwall, where datum level was 1 to 2 m, and it was further reduced in datum level -5 m and deeper. The frequency of occurrence of Zostera japonica was highest in water with a datum level of +1 to 0 m. However, in datum level of 0 m or deeper, it became lower as the water depth became deeper. Datum level +1 m to 0 m was an optimal water depth for both species. The frequency of occurrence and the shoot density of both species showed no negative correlation. In 2011, the daily mean water temperature was $10^{\circ}C$ or less on more days than in other years and the feeding damage by S. fuscescens in the study sites caused damage at the tips. Conclusions: We considered that the relationship between these species at the optimal water depth was not competitive, but due to differences in spatial distribution, Zostera marina and Zostera japonica do not influence each other due to temperature conditions and feeding damage and other environmental conditions. Zostera japonica required light intensity than Zostera marina, and the water depth played an important role in the distribution of both species.

• Korean Journal of Applied Biomechanics
• /
• v.16 no.1
• /
• pp.139-149
• /
• 2006

This study is to analyze the kinematic variables of inward $1{\frac{1}{2}}$ somersault in platform diver. For the manner, 3 people form the national diving team in the year 2000were chosen as the subjects and two S-VHS video cameras set in 60frames/sec were used for recording their motions. Coordinated raw positions data through digitizing are smoothing by butter-worth's low-pass filterin method at a cut off frequency 6.0Hz. and the direct linear transformation(DLT) method was employed to obtain 3-D position coordinates. The conclusions were as follows. However, horizontal distance which is the change of the COG, form the point of the jump to the point of Event 3 where the player is out of the board range completely, Subject B showed 105.1cm and 71.1cm of the vertical distance which are shorter horizontal distance and higher vertical distance, thus, took a great advantage of the position to prepare for the entry. Therefore, if a player takes higher position by speeding up the vertical velocity at the moment of the jumping off the board, and stays in the air longer, the player can have more time to show his skill. Because of the use of the characteristics of the inward somersault, keeping the safe distance form the board is important but in order to higher the completeness, it is ideal to keep the horizontal distance little over 100cm. Also, the angles of shoulder and elbow from Event 1 to 4, depending on swing of the arms, motions in the air, getting ready for the entry, showed some difference individual by individual, according to the velocity of the thigh and shank showed much difference while getting ready and take-off, and it's because of the individual's different bending and straightening for horizontal and vertical distance.

• Korean Journal of Environmental Agriculture
• /
• v.20 no.2
• /
• pp.86-92
• /
• 2001

The current study was conducted to elucidate the optimum density of free-ranging ducks in a rice-duck farming system in terms of effects on duck behavior, and growth and yield of rice plants. Four paddy fields were used for this experiment, with 6, 9, 12 and 15 birds per plot, respectively. Ducklings at eight days of age were free ranged in experimental paddy plots (4.0 a each) on the 9th day after the transplantation of rice plants. Ducks were kept in the plot for seventy days, at which point rice plants reached the earing stage. Foraging, moving, working, resting, diving and pecking behaviors of the ducks were observed two times during the experimental period. Also, rice plant growth and yield according to the density of ducks per plot were examined. The foraging and moving behavior of free-ranging ducks in paddy fields for 12 hours during the daytime tended to be longer in the 12-bird plot, and working behavior was significantly (P<0.01) longer in the 12-bird plot than in the other three plots. The resting behavior was significantly (P<0.01) higher in the 9- and 15-bird plots than in the 12-bird plot. The frequency of moving behavior for 6 hours during the daytime in the 15-bird plot tended to be lower than that in the other three plots, but this difference was not significant. The amount of diving and pecking behavior in the 9-bird plot was significantly (P<0.05) higher than that in the other three plots, and the number of hills pecked tended to be higher with increasing of duck density. From thirty days after ducks were introduced to the paddy fields, the length of rice plants tended to be significantly (P<0.05) shorter in high free-ranging density plots as compared to low free-ranging density plots. The number of tillers per hill was not affected by the free-ranging density. The culm length of rice plants was significantly (P<0.05) shorter in the 12- and 15-bird plots than in the other two plots, however, the duck free-ranging density did not affect panicle length. The dry weight of the root of rice plants was increased with high free-ranging density, but there was no such increase in the top parts of the rice plants. The percent of rice plants badly damaged by free-ranging density tended to be lower in the order of 12-, 9-, 6- and 15-bird plots. The number of ears, ripening grains and crop yield per hill of rice plants in the 12-bird plot were significantly (P<0.05) higher than those of the other three plots. Therefore, the yield of each rice plant per 10 a was significantly increased in the 12-bird plot.