• 한국정책학회보
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• v.21 no.1
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• pp.337-361
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• 2012

This study is conducted to provide empirical evidences which support that the problems of social isolation and loneliness of elderly can be alleviated by intervening the inter-generational relationship of the elderly by means of active ageing policy. The major empirical challenge to address this question is the possibility of selection bias caused by reversed causal relationship. To address this challenge, I constructed comparison group with 'Eligible Non-Participants' (ENP), and used instrumental variable method to estimate the empirical model. My findings indicate that inter-generational relationship, both in the aspects of economical solidarity and associational solidarity, is significantly improved as time use pattern of the elderly becomes more active. The improvement effect is intensively observed for the group of elderly who do not live with their adult children. The important policy implication of these findings is that the improvement of inter-generational relationship can be added as a new benefit of active ageing policy.

• Journal of Korean Ophthalmic Optics Society
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• v.16 no.1
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• pp.75-81
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• 2011

Purpose: The daily changes of accommodation at period 1 (08:00~10:00), period 2 (13:00~15:00) and period 3 (18:00~20:00) were surveyed with fifty two incipient presbyopia of from 38 to 49 years old. Methods: 52 incipient presbyopia subjects (30 men, 22 women) were classified into 4 groups (groupI: ${\geq}$ 7 hrs~group IV: < 3 hrs) according to near working amount. Their amplitude of accommodation, accommodative facility and relative amplitude of accommodation were inspected, respectively. Results: The amplitude of accommodation was measured to be the lowest for the groupI that near working time was the most during daily work, and the amplitude of accommodation of oculus dexter, oculus sinister and oculus uterque were the highest at period 2 in case of all the group I~IV. In the accommodative facility, it appeared that the oculus dexter, oculus sinister and oculus uterque of group I, oculus dexter and oculus sinister of group II, and oculus dexter, oculus sinister and oculus uterque of group III were the highest at period 2. The oculus uterque of group II and oculus dexter, oculus sinister and oculus uterque of group IV were the highest accommodative facility at period 3. It appeared that the negative relative accommodation was the highest at period 1 in case of all the group I~IV, and the positive relative accommodation was the highest at period 2 in case of the group I~III and was the highest at period 3 in case of the group IV. Conclusions: Because the difference of near working time affects the accommodation, it would become a help in solving the asthenopia symptom of the incipient presbyopia that opticians consider their near working time during daily work and take a checkup on their accommodation.

• Korean Journal of Agricultural and Forest Meteorology
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• v.26 no.3
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• pp.191-198
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• 2024

Puddling before rice transplanting, which has been practiced traditionally, is no longer considered an essential process due to the overall development of agriculture. Non-puddling, a technique that omits rotary plow in a flooded condition after leveling and transplants immediately. In this study, we conducted the first case study in South Korea on the differences between puddling and non-puddling, and uploaded some of the data to Github. The effects of shortening and dispersing practices during the busy farming season, suppressing soil plow pan formation, and preventing non-point pollution emissions were confirmed in the early stages before and after transplanting. However, some limitations such as weed occurrence when lots of rain or water management practices fail, so it is recommended to implement non-puddling in irrigated paddy fields.

• Journal of Korean Society of Transportation
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• v.33 no.2
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• pp.214-222
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• 2015

Jeju International Airport has become the most delayed airport in Korea, due to increased demand in air passengers and unexpected local weather condition. Observing the demands continuously grow for a decade, the airport is expected to be saturated in the near future. As a part of effort to prepare effective and timely measure for this expected situation, airport planners seeks the annual runway capacity, i.e., the appropriate number of flight operations in a given year with tolerable delay. In practice, the FAA formula is frequently adopted for the capacity estimation. The method, however, has intrinsic issues: 1) the hourly capacity imbedded in the formula is not clearly defined and thus the estimated value is vulnerable to be subjective judgement, and 2) the formula doesn't consider aircraft delay resulted from runway congestion. In this paper, we explain a novel method for estimating the daily runway capacity and then converting to the annual capacity taking into account the aircraft delay. In this paper, average delay of aircraft was measured using microscopic air traffic simulation model. Daily capacity of the runways were analyzed based on the simulation outputs and the method to assess the yearly capacity is introduced. Using a microscopic simulation model named TAAM, we measure the average aircraft delay at various levels of flight demand, and then estimate the practical daily runway capacity. The estimated daily and annual runway capacities of Jeju airport are about 460 operations a day which is equal to 169,000 operations year. The paper discusses how to verify the simulation model, and also suggests potential enhancement of the method.

• Journal of Aquaculture
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• v.18 no.3
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• pp.154-159
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• 2005

This study was conducted to evaluate the effects of size grading on growth, feed efficiency and survival of juvenile olive flounder. Juvenile flounder were divided into four groups by initial average size; Small group $(1.3{\pm}0.23g)$, medium group $(3.1{\pm}0.45g)$, large group $(4.9{\pm}0.57g)$ and ungraded group $(3.3{\pm}1.66g)$. Triplicate groups of 100 fish were reared over 8 weeks. In final body weight distribution, frequency of the small size flounder (10 g) was markedly higher in the ungraded group than in the small group. Specific growth rate, feed efficiency and survival in the ungraded group were significantly lower (P<0.05) than those in the pooled data of the othor three graded groups, although feed intake in the ungraded group was significantly higher (P<0.05) than that of the pooled data of the other three graded groups. These results show that the small flounder gained significantly faster growth and higher survival in the absence of the large flounder. Therefore, size grading seems to be an important and necessary operation to improve the growth and survival of juvenile olive flounder (1-5 g).

• Journal of Preventive Medicine and Public Health
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• v.25 no.3 s.39
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• pp.247-268
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• 1992

This study was conducted to evaluate the effect of VDT work on eyes and vision among workers in a TV manufacturing plant. The study subjects consisted of 264 screen workers and 74 non-screen workers who were less than 40 years old male and had no history of opthalmic diseases such as corneal opacities, trauma, keratitis, etc and whose visual acuity on pre-employment health examination by Han's test chart was 1.0 or above. The screen workers were divided into two groups by actual time for screen work in a day : Group I, 60 workers, lesser than 4 hours a day and group II, 204 workers, more than 4 hours a day. From July to October 1992 a questionnaire was administered to all the study subjects for the general charateristics and subjective eye symptoms after which the opthalmologic tests such as visual acuity, spherical equivalent, lacrimal function, ocular pressure, slit lamp test, fundoscopy were conducted by one opthalmologist. The proportion of workers whose present visual acuity was decreased more than 0.15 in comparison with that on the pre-employment health examination by Han's test chart was 20.6% in Group II. 15.0% in Group I and 14.9% in non-screen workers. However, the differences in proportion were not statistically significant. The proportion of workers with decreased visual acuity was not associated with the age, working duration, use of magnifying glass and type of shift work (independent variables) in all of the three groups. However, screen workers working under poor illumination had a higher proportion of persons with decreased visual acuity than those working under adequate illumination (P<0.05) . The proportion of workers whose near vision was decreased was 27.5% in Group II, 18.3% in Group I, and 28.4% in non-screen workers and these differences in proportion were not statistically significant. Changes of near vision were not associated with 4 independent variables in all of the three groups. Six out of seven subjective eye symptoms except tearing were more common in Group I than in non-screen workers and more common in Group II than in Group I (P<0.01). Mean of the total scores for seven subjective symptoms of each worker(2 points for always, 1 point for sometimes, 0 point for never) was not significantly different between workers with decreased visual acuity and workers with no vision change. However, mean of the total scores for Group II was higher than those for the Group I and non-screen workers (P<0.01). Total eye symptom scores were significantly correlated with the grade of screen work, use of magnifying glass, and type of shift work. There was no independent variable which was correlated with the difference in visual acuity between the pre-employment health examination and the present state, the difference between far and near visions, lacrimal function, ocular pressure, and spherical equivalent. Multiple linear regression analysis for the subjective eye symptom scores revealed a positive linear relationship with actual time for screen work and shift work(P<0.01). In this study it was not observed that the VDT work decreased visual acuity but it induces subjective eye symptoms such as eye fatigue, blurred vision, ocular discomfort, etc. Maintenance of adequate illumination in the work place and control of excessive VDT work are recommended to prevent such eye symptoms.

• Journal of Environmental Impact Assessment
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• v.32 no.6
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• pp.419-430
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• 2023

In response to the periodic occurrence of cyanobacterial blooms in Korean freshwaters, various types of cyanobacteria removal technologies are being developed and implemented. Due to the differing principles behind these technologies, it is difficult to compare and evaluate their removal efficiencies. In this study, a standardized method for evaluating cyanobacteria removal efficiency was proposed by utilizing the results of removal operations using a mobile cyanobacteria removal device in the Seohwacheon area of Daechung Reservoir. During removal operations, the decrease in chlorophyll-a (chl-a) concentration (ΔChl-a) in the working area was calculated based on the amount of collected sludge, the efficiency rate, and the concentration of chl-a. Additionally, the required working days (WD) to reduce the chl-a concentration to 1 mg/m³ in the target area was calculated based on the area of the target zone, the maximum daily working area, and the efficiency rate. A method for calculating the cyanobacteria removal capacity was proposed based on the reduction rate of chl-a concentration in the water before and after the operation, the treatment capacity of the removal technology, and the water volume of the target area. The cyanobacteria removal capacity of the mobile cyanobacteria removal device used in this study was 6.64%/day (targeting the Seohwacheon area of Daechung Reservoir, approximately 500,000 m²), which was higher compared to other physical or physicochemical cyanobacteria removal technologies (0.02~4.72%/day). Utilizing the evaluation method of cyanobacteria removal efficiency presented in this study, it will be possible to compare and evaluate the cyanobacteria removal technologies currently being applied in Korea. This method could also be used to assess the performance and efficiency of physical or physicochemical combined cyanobacteria removal techniques in the "Guidelines for the Installation and Operation of Algae Removal Facilities and the Use of Algae Removal Agents" operated by the National Institute of Environmental Research.

• The Journal of Korean Society for Radiation Therapy
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• v.16 no.2
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• pp.69-79
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• 2004

In the process of photon treatments, linear accelerators with energies higher than 10 MV produce neutrons through the (${\gamma}$, n) interactions with the composite materials of the linac head md these materials further produce the induced radiations. We investigate the possible risks from these induced radiations especially in the wedge filters to the radiation workers. Wedge filters are used to modify the isodose profiles in the radiation treatment using the linear accelerator and always be handled by the radiation workers. For the background radiation, we measured the radiation in both the waiting room and the outside of the building for two hospitals, S and H. The results of S hospital were $0.11\;{\mu}Sv/hr$ and $0.10\;{\mu}Sv/hr$ for waiting room and outside respectively, and in the case of H hospital, they were $0.12\;{\mu}Sv/hr$ and $0.11\;{\mu}Sv/hr$. Using a survey meter, we measured the radiation from wedge filters inserted in 10 MV and 15 MV Siemens linear accelerators. The time series measurements were done in ${\sim}1$ minutes after exposure of 5 Gy of monitor units for the field size of $25{\times}25cm^2$. The starting value of 10 MV machine was about $3.26\;{\mu}Sv/hr$, which was three times higher than that of 10 MV. The measured radiation was from $^{28}Al$ and $^{53}Fe$ with a half life of 3.5 min. If the treatment patients are $20{\sim}50$ per day and the number of process of wedge filter change per patient is one or two, the annual dose equivalent is $0.08{\sim}0.4\;mSv$ for 10 MV, and $0.27{\sim}1.36\;mSv$ for 15 MV, which are in the range of dose equivalent limits of radiation workers.

• Journal of radiological science and technology
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• v.35 no.2
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• pp.141-149
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• 2012

The aims of this study are to assess external radiation exposed doses of body and hands of nuclear medicine workers who handle radiation sources, and to measure radiation exposed doses of the hands induced by a whole body bone scan with high frequency and handling a radioactive sources like $^{99m}Tc$-HDP and $^{18}F$-FDG in the PET/CT examination. Skillful workers, who directly dispense and inject from radiation sources, were asked to wear a TLD on the chest and ring finger. Then, radiation exposed dose and duration exposed from daily radiation sources for each section were measured by using a pocket dosimeter for the accumulated external doses and the absorbed dose to the hands. In the survey of four medical institutions in Incheon Metropolitan City, only one of four institutions has a radiation dosimeter for local area like hands. Most of institutions uses radiation shielding devices for the purpose of protecting the body trunk, not local area. Even some institutions were revealed not to use such a shielding device. The exposed doses on the hands of nuclear medicine workers who directly handles radioactive sources were approximately twice as much as those on the body. The radiation exposure level for each section of the whole body bone scan with high frequency and that of the PET/CT examination showed that radiation doses were revealed in decreasing order of synthesis of radioactive medicine and installation to a dispensing container, dispensing, administering and transferring. Furthermore, there were statistically significant differences of radiation exposure doses of the hands before and after wearing a syringe shielder in administration of a radioactive sources. In this study, although it did not reach the permissible effective dose for nuclear medicine, the occupational workers were exposed by relatively higher dose level than the non-occupational workers. Therefore, the workers, who closely exposed to radioactive sources should be in compliance with safety management regulations, and take actions to maximally reduce locally exposed dose to hands monitoring with ring TLD.

• Journal of the Korean Society for Marine Environment & Energy
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• v.5 no.2
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• pp.50-61
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• 2002

This paper - following 'Functional requirement of marine waste cleaning ships and organization of the fleets'[1] - describes on the preliminary conceptual design procedure for the multi-purpose marine waste cleaning system for shallow waters. The working area of this system is Yellow Sea and part of South Sea of South Korea. As the first step, we determined the functional requirements including the daily target of waste collecting. Then, the preliminary conceptual design and general arrangements were carried out. In order to evaluate the safety and efficiency of this designed system, the stability check and the computer graphic simulation were carried out. Finally, the sea trial performance test of integrated systems in Yeosoo ports was performed and the designed system was shown its validity and effectiveness.