• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.26 no.1
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• pp.14-19
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• 1990

This paper describes on the characteristics of the acoustic echoes from the scattering layers by the aggregation of marine organisms which was measured by using a 50kHz echo sounder on board of the training ship SAEBADA belong to National Fisheries University of Pusan during the summer, 1989 in the East China Sea. A data acquisition system was used to record digitally the envelope of the echoes and the frequency distribution of echo amplitudes on the whole water column was examined as a function of time during the sunrise and sunset periods. Acoustic data showed that the abundance distribution of marine organisms according to depth in the servery area changed with time and that the organisms were most active during the twilight of morning, and the echo strength on the water column or scattering layer was also strongest during this time. Additional results of this survey suggest that other interest, such as the relationship between environmental conditions and biomass depth distribution, could be also investigated in hydroacoustic method.

• Journal of Astronomy and Space Sciences
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• v.21 no.4
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• pp.505-528
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• 2004

We have reproduced the records of lunar occultation recorded in the History of Three Kingdoms(삼국사기), the History of the Koryo Dynasty (고려사), the Annals of the Choson Dynasty (朝鮮王朝實錄), the Daily Records of Royal Secretariat of the Choson Dynasty (승정원일기), and obtained the epochs of their realizations. We analysed these results to understand how the system of hours had been kept and when a day began. During most of the periods encompassed by these annals, the 12 double hours(12진각법) and the system of 100 divisions of the day (백각법) had been used when the lunar and the solar eclipses were calculated by royal astronomers. In these systems, the starting point of a day is midnight. On the other hand, the five watch system of hours (경점법), in which a night is divided into five watches, was also used. In this system, a day begins at the sunrise. We found that the traditional twilight, called dusk and dawn (혼명) and used in the east Asian countries, largely corresponds to the nautical twilight in modern concepts. This fact means that the Korean expressions and words for time system in every day life had originated form the five watch system of hours. We pointed out that the sunrise and sunset were convenient boundary lines to ancient astronomers, as well as to farmers in the agricultural society. Our results can be used to determine the exact epoch of each astronomical record in chronicles.

• Journal of the Korean Solar Energy Society
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• v.32 no.5
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• pp.41-51
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• 2012

Heliostat field is the most important subsystem in the tower type solar thermal power plant since its optical performance affects the total system efficiency most significantly while the construction cost of it is the major part of total construction cost in such a power plant. Thus a well designed heliostat field to maximize the optical efficiency as well as to minimize the land usage is very important. This work presents methodology, procedures and result of heliostat filed design for 200kW solar thermal power plant built recently in Daegu, Korea. A $2{\times}2(m)$ rectangular shaped receiver located at 43(m) high and tilted $28^{\circ}$ toward heliostat field, 450 of heliostats of which the reflective surface is formed by 4 of $1{\times}1(m)$ flat plate mirror facet, and the land area having about $140{\times}120(m)$ size are used to form the heliostat field. A procedure to deploy 450 heliostats in radial staggered nonblocking formation is developed. Also the procedures to compute the cosine effect, intercept ratio, blocking and shading ratio in the field are developed. Finally the heliostat filed is designed by finding the optimal radial distance and azimuthal spacing in radial staggered nonblocking formation such that the designed heliostat field optical efficiency could be maximized. The designed heliostat field has 77% of annual average optical efficiency, which is obtained by annually averaging the optical efficiencies computed between the time of where sun elevation angle becomes $10^{\circ}$ after sunrise and the time of where sun elevation angle becomes $10^{\circ}$ before sunset in each day.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.7
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• pp.2334-2340
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• 2010

Sun position computed by Michalsky shows maximum $1.5^{\circ}$, $0.88^{\circ}$ and 2 minutes differences in azimuth, altitude, and sunrise and sunset times respectively compared with Korean Almanac. The 2-axis solar tracking system, which consist control panel with ATmega128 CPU, BLDC motor-cylinder actuator and 2-axis link mechanism, was developed. Computed azimuth and altitude of sun for a current time, and latitude and longitude of tracker position built are controlled in real time by BLDC motor-cylinder actuators comparing with the position feed-backed by Hall sensor. The use of BLDC motor is free in maintenance. Implementation of a home-return function by Hall sensor is to minimize the cumulative error.

• Journal of Astronomy and Space Sciences
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• v.31 no.1
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• pp.15-23
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• 2014

We present preliminary observations of the field-aligned-irregularities (FAIs) in the E and F regions during the solar minimum (2009 - 2010) using the 40.8 MHz coherent backscatter radar at Daejeon ($36.18^{\circ}N$, $127.14^{\circ}E$, $26.7^{\circ}N$ dip latitude) in South Korea. The radar, which consists of 24 Yagi antennas, observes the FAIs using a single beam with a peak power of 24 kW. The radar has been continuously operated since December 2009. Depending on the manner of occurrence of the backscatter echoes, the E-region echoes are largely divided into two types: quasi-periodic (QP) and continuous echoes. Our observations show that the QP echoes occur frequently above an altitude of 105 km in the post-sunset period and continuous echoes occur preferentially around an altitude of 105 km in the post-sunrise period. QP echoes appear as striated discrete echoes for a period of about 10 - 20 min. The QP-type echoes occur more frequently than the continuous-type echoes do and the echo intensity of the QP type is stronger than that of the continuous type. In the F region, the FAIs occur at night at an altitude interval of 250 - 450 km. As time proceeds, the occurrence height of the FAIs gradually increases until early in the morning and then decreases. The duration of the F-region FAIs is typically a few hours at night, although, in rare cases, FAIs persist throughout the night or appear even after sunrise. We discuss the similarities and differences of the FAIs observed by the Daejeon radar in comparison with other radar observations.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.2
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• pp.137-142
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• 2021

A Photovoltaic power streetlight is a system that uses solar energy to charge a secondary battery and then uses it for night lighting through a lamp, and can be configured as a standalone or grid-connected type by installing an LED streetlight at the load end. The energy generated through the solar cell module can be charged to the secondary battery through the charge/discharge control device, and then the LED street light can be turned on and off by comparing the power generation voltage and the charging voltage according to the monitoring of solar radiation, or by setting a specific time after sunset or sunrise. Based on these contents, this paper designed and manufactured a simulated solar power streetlight for education using new and renewable energy utilization and storage functions. Using these educational equipment, students can 1) understand the flow of energy change using renewable energy including sunlight as electric energy, 2) understand new and renewable energy, and cultivate basic design and manufacturing application power of related products, 3) The use of new and renewable energy through power conversion and strengthening of practical training and analysis through hardware production can be instilled.

• Journal of Astronomy and Space Sciences
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• v.36 no.2
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• pp.87-96
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• 2019

We investigate solar and lunar motions in the Seonmyeong (SM) calendar that was compiled by Xu, Ang of the Tang dynasty (A.D. 618-907) in China and used for 71 years from 822 to 892. This calendar was also used in Korea during the Goryeo dynasty (A.D. 918-1392) and in Japan for 823 years from 862 to 1684, the longest time among the three countries. Referring to historical documents of China, Korea, and Japan, we analyze the calendrical methods of calculating the daily apparent movements of the Sun and Moon in the SM calendar, which were considered their unequal motions, and compare the movements with the results of modern calculations for three periods in the Goryeo dynasty: 919, 1155, and 1392 years (i.e., the beginning, middle, and ending of the dynasty, respectively). We find that a quadratic equation was employed to obtain the daily movement of the Sun using physical quantities on the instant of each solar term, which was tabulated in its calendar book such as the Goryeosa (History of the Goryeo Dynasty). For quantitative analysis, we compute the mean absolute difference (MAD) of the daily apparent movement between the SM calendar and modern calculations and obtain 0.33, 0.30, and 0.31 arcmin for the periods of 919, 1155, and 1392 years, respectively. Meanwhile, we find relatively large MAD values in the daily movement of the Moon: 0.217, 0.284, and 0.240 degrees for each corresponding year. An interesting point is that the MAD value in the lunar motion shows the maximum in 1155 years, and is the minimum in the solar motion. In conclusion, we believe that this study will facilitate in the understanding of the SM calendar further, particularly in the calendrical methods of calculating sunrise, sunset, and eclipse times.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.10 no.3
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• pp.16-24
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• 2011

The vehicle electronic control system is being developed as the legal and social demand for ensuring driver's safety is rising. The various Driver Assistance Systems with various sensors such as radars, camera, and lasers are in practical use because of the falling price of hardware and the high performance of sensor and processer. In the preceding study of this research, the program was developed to recognize the experiment vehicle's driving lane and the cars nearby or approaching the experiment vehicle throughout the images taken by CCD camera. In addition, the 'dangerous driving analysis program' which is Vision System basis was developed to analyze the cause and consequence of dangerous driving. However, the Vision system developed in the previous studyhad poor recognition rate of lane and vehicles at the time of passing a tunnel, sunrise, or sunset. Therefore, through mounting the brightness response algorithm to the Vision System, the present study is aimed to analyze the causes of driver's dangerous driving clearly by improving the recognition rate of lane and vehicle, regardless of when and where it is.

• Journal of Science Education
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• v.34 no.2
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• pp.432-439
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• 2010

The purpose of this study is to investigate the characteristics of the ionosphere by monitoring VLF radio wave. For this purpose, we set up the SID(Sudden Ionospheric Disturbance) monitoring station in Pohang($36.03^{\circ}N$, $129.35^{\circ}E$), Korea receiving VLF radio wave(22.2kHz) transmitted from Ebino($32.04^{\circ}N$, $130.81^{\circ}E$), Japan. The observed data of radio wave intensities are analyzed to interpret the condition of the ionosphere. We can summarize the results as follows: Radio waves show regular daily variation. We can confirm the daily variation as a result of the formation of D layer. In relation to formation or extinction of D layer, intensity of radio wave gets weak right after sunrise and sunset. Southing altitude also affects the intensity of day time radio wave. At night when D layer disappears, the radio waves shows very irregular changes. The observed radio waves also shows the influence of the seasonal ionospheric variation. Long term observation could provide more detailed interpretation of daily as well as seasonal variation of ionosphere.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.24 no.5
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• pp.315-326
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• 1991

This study was tried for a mathematical approaches related to daily fluctuations in the stomach fullness of Agrammus agrammus. The specimen was collected by angling and gill net from September 1984 to August 1985 off Shinsudo, Samchonpo. Fullness of the stomachs was increased in the early morning and the late afternoon, decreased in the late morning, at noon, and during the night. That is, feeding activity of the fish was more intense at sunrise and sunset. Daily feeding activity of the fish in a day was divided into the time period of gastric evacuation and both feeding and gastric evacuation. Stomach fullness with the lapse of time in the time period of gastric evacuation was geometrically decreased. Stomach fullness in the time period of both feeding and gastric evacuation was affected by gastric evacuation rates, feeding rates, and maximum fullness of the stomach. These parameters were able to estimate from the method estimating the regression coefficient in the relationship between the time(t) and the stomach fullness$(F_t)$, or between stomach fullness at the time t and $t+\Deltat$. The rates of feeding and gastric evacuation were the highest in spring and the lowest in winter. The relationships between time(t) and stomach fullness$(F_t)$ in the time period of gastric evacuation and both feeding and gastric evacuation induced from hypotheses were respectively as follows. $$F_t=F_{to}e^{-r(t-to)}$$, $$F_t=F\infty-(F\infty-F_{to})e^{-(p+r)(t-{to})}$$