• Journal of the Korean Society for Precision Engineering
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• v.23 no.9 s.186
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• pp.102-110
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• 2006

We discuss two possibilities of using femtosecond pulse lasers as a new interferometric light source for enhanced precision surface-profile metrology. First, a train of ultra-fast laser pulses yields repeated low temporal coherence, which allows unequal-path scanning interferometry, which is not feasible with white light. Second, the high spatial coherence of femtosecond pulse lasers enables large-sized optics to be tested in nonsymmetric configurations with relatively small-sized reference surfaces. These two advantages are verified experimentally using Fizeau and Twyman-Green type scanning interferometers.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.20 no.4
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• pp.328-340
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• 1987

In order to clarify major reasons of a poor harvest, the Porphyra-cultivation ground was investigated in Kwangyang Bay in terms of the laver production per unit area, diseases, and fouling organisms from January to April in 1986. The laver production per unit area of the control station was more than that of the study area at 'Soppal' cultivation ground, while the difference at the cultivation groud using 'nets' seemed to be insignificant. The vertical attachment range of laver was directly associated with the production per unit area at 'Soppal' cultivation ground. The number of young thalli of 1-3 mm length was almost similar between control and study sites at 'nets' cultivation ground. Two kinds of diseases in cultured laver, the crape and shot hole, were prevalent during the study period. However, the affected thalli were gradually decreased at the end of the study period. Major fouling organisms attached to 'Soppal' were Balanus albicostatus, Enteromorpha prolifera, Capsosiphon fulvescens, and Scytosiphon lomentaria. In conclusion, the poor harvest of laver in 1986 may result from such following problems as the decrease in vertical attachment range of laver and fouling problems as the decrease in vertical attachment range of laver and fouling organisms at 'Soppal' cultivation ground, prevalence of certain diseases, changes in environmental conditions, arrangement and maintenance of facilities for laver cultivation.

• Korean Journal of Optics and Photonics
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• v.20 no.5
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• pp.272-275
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• 2009

In order to enhance the background noise filtering performance of the white light interferometry(WLI), we demonstrate the noise filtering performance of preprocessing of the measured fringe signals. The WLI was realized through a mirau interferometer which was equipped with a green LED. When measuring large-height and rough surface objects, the illumination optics are considered the numerical aperture(NA) and the depth of focus(DOF). In this case, the limited NA of the illumination optics has a considerable impact on the interference fringe. Therefore, we propose a preprocessing method that uses the intensity difference between the measured intensity and the moving average intensity. The performance is demonstrated by measuring an array of metal solder balls fabricated on printed circuit board(PCB). The proposed method reduces the noise pixels by 15 percent.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.98-98
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• 2013

태양의 활동영역에서 관측할 수 있는 흑점은 주로 흑점군으로 관측되며, 태양폭발현상의 발생을 예보하기 위한 중요한 관측 대상 중 하나이다. 현재 태양 폭발을 예보하는 모델들은 McIntosh 흑점군 분류법을 사용하며 통계적 모델과 기계학습 모델로 나누어진다. 컴퓨터는 흑점군의 형태학적 특성을 연속적인 값으로 계산하지만 흑점군의 형태적 다양성으로 인해 McIntosh 분류법과 일치하지 않는 경우가 있다. 이러한 이유로 컴퓨터가 계산한 흑점군의 형태학적인 특성을 예보에 직접 적용하는 것이 필요하다. 우리는 흑점군을 검출하기 위해 최소신장트리(Minimum spanning tree : MST)를 이용한 계층적 군집화 기법을 수행하였다. 그래프(Graph)이론에서 최소신장트리는 정점(Vertex)과 간선(Edge)으로 구성된 간선의 가중치의 합이 최소인 트리이다. 우리는 모든 흑점을 정점, 그들의 연결을 간선으로 적용하여 최소신장트리를 작성하였다. 또한 최소신장트리를 활용한 계층적 군집화기법은 초기값에 따른 군집화 결과의 차이가 없기 때문에 흑점군 검출에 있어서 가장 적합한 알고리즘이다. 이를 통해 흑점군의 기본적인 형태학적인 특성(개수, 면적, 면적비 등)을 계산하고 최소신장트리를 통해 가장 면적이 큰 흑점을 중심으로 트리의 깊이(Depth)와 차수(Degree)를 계산하였다. 이 방법을 2003년 SOHO/MDI의 태양 가시광 영상에 적용하여 구한 흑점군의 내부 흑점수와 면적은 NOAA에서 산출한 값들과 각각 90%, 99%의 좋은 상관관계를 가졌다. 우리는 이 연구를 통해 흑점군의 형태학적인 특성과 더불어 예보에 직접적으로 활용할 수 있는 방법을 논의하고자 한다.

• Journal of Korean Ophthalmic Optics Society
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• v.9 no.1
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• pp.53-68
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• 2004

Protein deposit buildup on soft contact lenses(SCLs) is responsible for discomfort, optical defects and is even damaging to the eye. To better understand protein deposit formation on SCL, we investigated the pattern of protein attachment on patient-worn SCLs and the effect of the protein on the contact angle of SCLs and the transmission of visible light. This study used data from a clinical trial where subjects wore either daily-wear SCL(etafilcon A, N=40) for various period up to 14 days, or extended-wear SCL(balafilcon A, N=40) for 8 h day or night. The adsorption of protein in daily-wear SCLs was significantly increased in patient-worn time-dependent manner although the lenses were cleaned everyday by using the multi-purpose SCL solution. After 2 weeks wearing, the protein on the SCL influenced the contact angle of the lenses. Furthermore, the transmission of visible light of the lenses decreased up to almost 7%. Extended-wear SCLs worn during the closed eye condition were found to deposit significantly more protein than SCLs worn during the open eye condition. The amounts of protein adsorbed both after daily SCL wear and after overnight SCL wear were not affected the contact angle and the transmission of visible light of the lenses. The protein deposit buildup on SCL related to the corneal temperature and pH of tear fluid.

• Journal of Korea Multimedia Society
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• v.9 no.11
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• pp.1483-1495
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• 2006

The navigation mesh represents a terrain as a set of triangles on which characters may move around. The navigation mesh cab be generated automatically, and it is more flexible in representing 3D surface. The number of triangles to represent a terrain may vary according to the structure of the terrain. As characters are moving around on a navigation mesh, the path planning can be performed more easily by projecting the 3D surfaces into 2D space. However, when the terrain is represented with an elaborated mesh of large number of triangles to achieve more realistic movements, the path finding can be very inefficient because there are too many states(triangles) to be searched. In this paper, we propose an efficient method of path finding in 3D games where the terrain is represented by navigation meshes. Our method uses the visibility tests. When the graph-based search is applied to elaborated polygonal meshes for detailed terrain representation, the path finding can be very inefficient because there are too many states(polygons) to be searched. In our method, we reduce the search space by using visibility tests so that the search can be fast even on the detailed terrain with large number of polygons. First we find the visible vertices of the obstacles, and define the heuristic function as the distance to the goal through those vertices. By doing that, the number of states that the graph-based search visits can be substantially reduced compared to the plane search with straight-line distance heuristic.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.32 no.1
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• pp.105-111
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• 1999

To investigate the relationships between ocean environmental characteristics and thechange of the catch, we analyzed various environmental factors such as mean temperature, salinity, current vectors, lunar day and wind vectors from 1995 to 1996 and the catch fluctuation of Hanlim set net from 1994 to 1996. The results are as follow ; 1) The proportion of fishes caught in Hanlim set net is highest for horse mackere1 ($69.2\%$) and is followed by common mackerel ($18.4\%$), hair tail ($5.6\%$), squid ($2.7\%$) and rabbit fish ($1.4\%$) in order. Two peaks in the monthly catch appeared in June and October in the operation period of May- December. 2) The flow direction was northward in flood time and southeastward in ebb time around the Hanlim set net. Thus, the vortical mixing of sea water was active and continued for more than 3 hours. In addition, mean daily temperature was low due to the presence of middle and bottom water in offshore. Increase in salinity or high salinity of sea water provides a favorable condition for catches of fishes. Catches in the first quarter and the last quarter of the moon were larger than that in full moon and the last of the month. In particular, when south or southeasterly wind velocity reaches about 3$\~$6.5 m/s, the possibility of catches increases.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.5
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• pp.553-568
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• 2018

Chromophoric Dissolved Organic Matter (CDOM) plays a dominant role in absorbing UV-VIS light and is also important in the biogeochemical carbon cycle due to the production of carbon dioxide from photo-oxidation at the sea surface in marine environments. Since absorption by CDOM was recently found to be responsible for increasing the energy absorbed in the mixed layer by 40 % over pure seawater, the importance of CDOM absorption in seawater for increasing sea surface temperature has come to be well recognized. We measured aCDOM and the absorption characteristics of CDOM during spring 2012 and 2014 in the southwestern East Sea. Distribution of CDOM in spring 2012 and 2014 was compared and S value was used to find the source of CDOM in the study area. As a result, the average $a_{CDOM}$ was $0.237m^{-1}$ ($0.009{\sim}0.988m^{-1}$) and the average S value was $16{\mu}m^{-1}$,which shows coastal properties. Also a positive correlation between Chl a and CDOM was observed ($r^2=0.34$), with an especially strong correlation near coastal stations. aCDOM in 2014 was about 40 % higher than aCDOM in 2012 during spring in the study area. This difference in aCDOM concentration resulted not only from annual variation but also from stratification and photobleaching in late spring 2012. This observation implies the possibility of flux of carbon dioxide into the atmosphere as a result of photo-oxidation in the East Sea.

• Korean Journal of Remote Sensing
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• v.23 no.4
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• pp.311-321
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• 2007

The diffuse attenuation coefficient for down-welling irradiance $K_d({\lambda})$, which is the propagation of down-welling irradiance at wavelength ${\lambda}$ from surface to a depth (z) in the ocean, and underwater visibility are important optical parameters for ocean studies. There have been several studies on $K_d({\lambda})$ and underwater visibility around the world, but only a few studies have focused on these properties in the Korean sea. Therefore, in the present study, we studied $K_d({\lambda})$ and underwater visibility around the coastal area of the Yellow Sea, and developed $K_d({\lambda})$ and underwater visibility algorithms for ocean color satellite sensor. For this research we conducted a field campaign around the Yellow Sea from $19{\sim}22$ September, 2006 and there we obtained a set of ocean optical and environmental data. From these datasets the $K_d({\lambda})$ and underwater visibility algorithms were empirically derived and compared with the existing NASA SeaWiFS $K_d({\lambda})$ algorithm and NRL (Naval Research Laboratory) underwater visibility algorithm. Such comparisons over a turbid area showed small difference in the $K_d({\lambda})$ algorithm and constants of our result for underwater visibility algorithm showed slightly higher values.

• Korean Journal of Ichthyology
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• v.34 no.1
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• pp.44-56
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• 2022

Fish fauna was observed off the coast of Busan (Cheongsapo) and Ulsan (Bangeojin) using underwater visual census from November 2016 to October 2017. A total of 1,486 individuals of 25 species in Cheongsapo and 3,859 individuals of 31 species were identified in Bangeojin. Dominant species in the number of individuals were Trachurus japonicus (20.9%), Halichoeres tenuispinis (12.6%), and Chromis notata (11.9%) in Cheongsapo, Siganus fuscescens (42.0%), Pempheris japonica (8.4%), and Chromis notata (8.0%) in Bangeojin. There was no significant difference in the species composition of Cheongsapo and Bangeojin but spring vs. summer, spring vs. autumn, summer vs. winter, autumn vs. winter showed a significant difference. Contribution species of seasonal differences were commonly high rates by Halichoeres tenuispinis and Parajulis poecilepterus. Of the total 38 species, 17 (44.7%) temperate, 6 (15.8%) tropical, and 15 (39.5%) subtropical species observed coastal waters off Cheongsapo and Bangeojin.