• The korean journal of orthodontics
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• v.27 no.1
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• pp.129-140
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• 1997

Conventional cephalometrics have inherent errors because their evaluation is performed in two-dimension for threedimensional object. To compensate these errors, three-dimensional cephalograms - derivation of three-dimensional data from conventional lateral and postero-anterior cephalograms - were developed. In this study, the accuracy and precision of three dimensional cephalograms were determined by means of 10 linear and 12 angular measurements on 36 acrylic skull models and by the comparison of conventional lateral cephalograms. The results were as follows 1. Mean difference between three-dimensional cephalograms and actual models in linear measurements was $0.94{\pm}0.62mm$ and mean rate of magnification of three-dimensional cephalograms was $100.31{\pm}0.91%$. There were no statistically significant differences between three-dimensional cephalograms and actual models in linear measurements(${\alpha}=0.1$). 2. Mean difference between conventional lateral cephalograms and actual models in linear measurements was $6.44{\pm}1.48mm$ and mean rate of magnification of lateral cephalograms was $106.99{\pm}1.45%$. There were statistically significant differences between lateral cephalograms and actual models in linear measurements(P<0.005). 3. Mean difference between three-dimensional cephalograms and actual models in angular measurements was $1.22{\pm}0.82^{\circ}$ and mean rate of magnification of three-dimensional cephalograms was $105.71{\pm}12.07%$. There were no statistically significant differences between three-dimensional cephalograms and actual models in angular measurements(${\alpha}=0.1$). 4. Mean difference between conventional lateral cephalograms and actual models in angular measurements was $1.70{\pm}0.94^{\circ}$ and mean rate of magnification of lateral cephalograms was $106.35{\pm}15.70%$. There were no statistically significant differences between lateral cephalograms and actual models in angular measurements(${\alpha}=0.1$). There were similarity between three-dimensional and lateral cephalograms in angular measurements.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.31 no.3
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• pp.228-239
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• 1995

A model experiment on the pair midwater trawl net which is prevailing in Denmark is carried out to get the basic data available for Korean pair bottom trawlers. The model net was made in 1/30 scale considering the Tauti's Similarity law of fishing gear and the dimension of experimental tank. The vertical opening, horizontal opening, towing tension and net working depth of the model net were determined in the tank within the towing velocity 0.46~1.15m/sec, front weight 15.5~62.0g and distance between paired boats 5~8m(which correpond to 2~5k't in towing velocity, 70~280kg in weight and 150~240m in distance respectively in the prototype net). The results got from the model experiment can be converted into the full scale net as follows; 1. Vertical opening showed the largest value of 32m at the condition of 2k't in towing velocity, 280kg in front weight and 150m in the distance between paired boats, and the smallest value of 6m at the condition of 5k't in towing velocity, 70kg in front weight and 240m in the distance between paired boats. 2. Horizontal opening showed the largest value of 45m at the condition of 5k't in towing velocity, 70kg in front weight and 240m in the distance between paired boats, and the smallest value of 33m at the condition of 2k't in towing velocity, 280kg in front weight and 150m in the distance between paired boats. 3. Towing tension showed the largest value of 10, 000kg at the condition of 5k't in towing velocity, 280kg in front weight and 240m in the distance between paired boats, and the smallest value of 1, 600kg at the condition of 2k't in towing velocity, 70kg in front weight and 150m in the distance between paired boats. 4. Net working depth showed the largest value of 38m at the condition of 2k't in towing velocity, 280kg in front weight and 150m in the distance between paired boats, and the smallest value of 6m at the condition of 5k't in towing velocity, 70kg in front weight and 240m in the distance between paired boats. 5. Net opening area showed the largest value of 1, 100m super(2) at the condition of 2k't in towing velocity, 280kg in front weight and 180m in the distance between paired boats, and the smallest value of 250m super(2) at the condition of 5k't in towing velocity, 70kg in front weight and 240m in the distance between paired boats.