Although a number of studies have been performed to assure that residual stress caused by a mismatch of alloy porcelain thermal expansion can contribute to clinical failure of a ceramometal restoratoin, the interactive influence of cooling rate on the magnitude of thermal expansion difference and on bond strength between them have not been extensively analyzed. The objective of this study was to determine the influence of cooling rate and the number of firing cycles on the expansion mismatch and the flexural failure resistance of metal porcelain strip. Tested alloys included one Pd-Ag alloy, one Ni-Cr-Be alloy with two kinds of porcelain, Vita and Ceramco. Metal specimens were cast into rods with a height of 13mm and a diameter of 5mm. Subsequently, the castings were subjected to scheduled firing cycles without porcelain. And the porcelain specimens after being fired were trimmed into a bar with a final dimension of 5 x 5 x 25mm. Thermal expansions of the alloys and porcelains were measured by using a push rod or a differential dialometer respectively. Porcelain glass transition temperatures and expansion values were derived alloy- porcelain pairs were assessed by comparing expansion values of the components at a porcelain glass transition temperature. Calculations were made using combinations of a Ni-Cr alloy or Pd-Ag alloy with each of two porcelain products. Metal- porcelain strip specimens were subjected to four point loading in an Instron testing machine until crack occured at the metal-cramic interface at the time of sharp decrease of load on recorder. On the basis of this study, the following conclusions may be stated : 1. Regardless of the kinds of ceramometal combinations, both of calculated and experimental data revealed that the double fired specimens exhibited a significantly lower flexural strength. 2. By the rise of the amount of mismatch, bond strength were decreased. 3. Thermal expansion value of Pd-Ag alloys were higher than of Ni-Cr alloys. 4. Expansion curves of metal were proportional to the increase of temperature and were not affected by the experimental conditions, however porcelains did not show the same magnitude of metal, and a shift of the glass transition temperature to higher temperatures was observed when cooled rapidly. 5. Alloy- porcelain thermal compatibility appeared more dependent on the porcelain than the alloy.
This study aims to analyze the changes of goals and contents of middle school geography education following up the changes in the Korean social studies curriculum over time. The main findings are as follows. First, From the Syllabus period to the Third Curriculum, geography education, history education, general social studies education in the middle school social studies were directed and managed independently. However from the 4th to the 7th Curriculum, the demand for the virtual integration in middle school social studies increased sharply. Since 2009 revision, social studies suffered an identity crisis as integrated subject matter because history education was separated from the social studies and interdisciplinary units were abolished. In spite of much criticism, however, an odd form of social studies integrating geography and general social studies still remains. Second, the stronger the demand for the social studies integration in middle school, students' social studies learning load had become heavier due to severe competition with other areas to ensure more portion in the integrated structure of social studies. Since geography education did not reflect the new tendency of the geography in the integrated structure of middle school social studies, the gap between the geography and geography education has increased and knowledges of geography growing became separated from students' experience. In conclusion, the integrated structure of social studies in the middle school hindered the geography education development as it limited the autonomy of geography education in terms of curriculum development.
Proceedings of the Korean Institute of Navigation and Port Research Conference
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2018.11a
/
pp.162-163
/
2018
This study introduces the R&D project of development of the 1st LNG bunkering barge in Korea. The Design and pilot test of Barge-To-Ship 500cbm LNG bunkering barge system for coastal trading LNG-fueled ship is proposed. The following technologies will be developed from the project ; Basic/Detail design and pilot test of LNG Bunkering barge system, Basic/Detail design and pilot test of LNG bunkering process system considering LNG loading/unloading, Basic/Detail design and pilot test of 500cbm LNG tank in type-C, Evaluation of bunkering performance according to conditions (environment, SIMOPs) by numerical simulation, Performance evaluation of bunkering barge, towed barge and Barge-To-Ship motion considering ocean environment load, and scenario in Barge-To-Ship LNG bunkering. This project will contribute expansion to LNG-fueled ship industry and pave the way to establish LNG bunkering hub port.
According to the network condition, the communication network overload could be occurred when media transmitting. Many researches are being carried out to lessen the network overload, such as the filtering, load distributing, frame dropping and many other methods. Among these methods, one of effective method is frame dropping that reduces specified video frames for bandwidth diminution. B frames are dropped and then I, P frames are dropped according to dependency among the frames in frame dropping. This paper proposes a scheme for protecting copyrights by encryption, when we apply frame dropping to reduce bandwidth of media following MPEG-4 file format. We designed two kinds of frame dropping: first one stores and then sends the dropped files and the other drops frames in real-time when transmitting. We designed three kinds of encryption methods in which DES algorithm is used to encrypt MPEG-4 data: macro block encryption in I-VOP, macro block and motion vector encryption in P-VOP, and macro block and motion vector encryption in I, P-VOP. Based on these three methods, we implemented a digital right management solution for MPEG-4 data streaming. We compared the results of dropping, encryption, decryption and quality of video sequences to select an optimal method, and there is no noticeable difference between the video sequences recovered after frame dropping and the ones recovered without frame dropping. The best performance in encryption and decryption of frames was obtained when we apply the macro block and motion vector encryption in I, P-VOP.
KIEE International Transaction on Systems and Control
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v.2D
no.2
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pp.78-91
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2002
In the thermal power plant, there are six manipulated variables: main steam flow, feedwater flow, fuel flow, air flow, spray flow, and gas recirculation flow. There are five controlled variables: generator output, main steam pressure, main steam temperature, exhaust gas density, and reheater steam temperature. Therefore, the thermal power plant control system is a multinput and output system. In the control system, the main steam temperature is typically regulated by the fuel flow rate and the spray flow rate, and the reheater steam temperature is regulated by the gas recirculation flow rate. However, strict control of the steam temperature must be maintained to avoid thermal stress. Maintaining the steam temperature can be difficult due to heating value variation to the fuel source, time delay changes in the main steam temperature versus changes in fuel flow rate, difficulty of control of the main steam temperature control and the reheater steam temperature control system owing to the dynamic response characteristics of changes in steam temperature and the reheater steam temperature, and the fluctuation of inner fluid water and steam flow rates during the load-following operation. Up to the present time, the Proportional-Integral-Derivative Controller has been used to operate this system. However, it is very difficult to achieve an optimal PID gain with no experience, since the gain of the PID controller has to be manually tuned by trial and error. This paper focuses on the characteristic comparison of the PID controller and the modified 2-DOF PID Controller (Two-Degrees-Freedom Proportional-Integral-Derivative) on the DCS (Distributed Control System). The method is to design an optimal controller that can be operated on the thermal generating plant in Seoul, Korea. The modified 2-DOF PID controller is designed to enable parameters to fit into the thermal plant during disturbances. To attain an optimal control method, transfer function and operating data from start-up, running, and stop procedures of the thermal plant have been acquired. Through this research, the stable range of a 2-DOF parameter for only this system could be found for the start-up procedure and this parameter could be used for the tuning problem. Also, this paper addressed whether an intelligent tuning method based on immune network algorithms can be used effectively in tuning these controllers.
Journal of the Korea Society of Computer and Information
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v.18
no.2
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pp.117-126
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2013
Path planning is an essential problem to make virtual characters navigate in many applications including computer games. In many cases, multiple characters move in a group and qualitative aspects of planned paths are emphasized rather than optimality unlike Robotics. In this paper, we propose a two-level path planning algorithm in which the global path is planned for a single character specified as a leader and then the local path is planned to avoid dynamic obstacles while the group following this path. The space for group movement is achieved in the form of square grid array called a grid window. Member characters are located relatively to the leader within a space and moved. The static environment is reduced to the configuration space of this grid window to generate a roadmap on which a grid window can move. In local path planning, only the leader avoids dynamic obstacles by using an artificial potential field and the rest of members are located relatively to the leader in the grid window, which reduces computational load. Efficient algorithms to implement the proposed planning methods are introduced. The simulation results show that a group can handle with dynamic obstacles effectively while moving along the planned path for a static environment.
The purpose of this study is to find out the effect of aerobic exercise through convergence on exhaled carbon monoxide and cardiorespiratory function of female college students who participated in nonsmoking. The subjects were female college students from University D in Metropolitan City D, and those who started smoking 2 years ago and who do not engage in regular physical activities were first selected, and a total of 18 people who indicated their intention to participate in the experiment were selected to receive a pledge of nonsmoking and consent to the experiment. The selected subjects were classified into 9 people in the exercise group and 9 in the control group by wireless assignment, and individual exercise intensity was set through the maximum exercise load test to establish an accurate exercise program. Individual exercise intensity is set to 50%HRmax for 1-3 weeks, 60%HRmax for 4-6 weeks, 70%HRmax for 7-9 weeks. In order to apply the correct exercise intensity during exercise, a Polar heart rate monitor was used for control and the following results were obtained. First, the change in carbon monoxide decreased by three levels from 21.17±3.67ppm (Red 2 16-25ppm, habitual smokers) before participation in the exercise group that participated in aerobic exercise for 9 weeks to 1.36±0.76ppm (Green, 0-6ppm, non-smokers) after participation, and the control group also showed the same effect from 22.35±2.08ppm (Red 2 16-25ppm, habitual smokers) to 2.81±0.51ppm (Green, 0-6ppm, non-smokers). Second, the change in cardiorespiratory function showed a significant increase in all of the maximum oxygen intake, maximum heart rate, and maximum ventilation in the exercise group who participated in aerobic exercise for 9 weeks, but there was no significant change in the control group. Therefore, aerobic exercise showed the effect of improving the cardiorespiratory function by releasing carbon monoxide and supplying sufficient oxygen to various organs.
The significant reason for studying computer science lies in the efficient resolution of various problems which can arise in actual life. Consequently, algorithm education is very important in the computer science and plays a great part in helping to enhance the creative ability to solve problems and to improve the programming ability. However, the current algorithm education at an computer science educational institute for the gifted has inadequate systematic quality and is only treated as a part of programming education. From this perspective, this paper carried out following studies in order to design the algorithm education for elementary computer science prodigies. First, the core educational contents was selected by extracting the common elements from existing books related to algorithm education, common study contents on algorithm lesson websites and the study area of ACM's computer algorithm. Second, using the development criteria and selected educational contents, the educational theme for the If weeks load was set. Additionally, the algorithm educational contents were designed for the elementary computer science prodigy based on such theme. Third, the activity site for the use of prodigy educational institute was developed with the background in the educational contents for the elementary computer science prodigy. Fourth, the Delphi analysis technique was used to verify the appropriateness of contents and activity site developed in this paper. It was carried out in 2 separate processes where the first process verified the design of educational contents, and the second process verified the appropriateness of developed activity site.
Many transmission towers, high-rise buildings and bridges are constructed near steep slopes and are supported by large-diameter piles. These structures may be subjected to large lateral loads, such as violent winds and earthquakes. Widely used types of foundations for these structures are pier foundations, which have large-diameters with high stiffness. The behavior of a pier foundation subjected to lateral loads is similar to that of a short rigid pile because both elements seem to fail by rotation developing passive resistance on opposite faces above and below the rotation point, unlike the behavior of a long flexible pile. This paper describes the results of several numerical studies performed with a three-dimensional finite element method (FEM) of model tests of a laterally loaded short pile located near slopes, respectively. In this paper, the results of model tests of single piles and pile groups subjected to lateral loading, in homogeneous sand with 30$^{\circ}$ slopes and horizontal ground were analyzed by the 3-D FE analyses. The pile was assumed to be linearly elastic. The sand was assumed to have non-associative characteristics, following the MC-DP model. The failure criterion is governed by the Mohr-Coulomb equation and the plastic potential is given by the Drucker-Prager equation. The main purpose of this paper is the validation of the 3-D elasto-plastic FEM by comparisons with the experimental data.
Journal of the Korean Institute of Intelligent Systems
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v.22
no.3
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pp.361-366
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2012
This paper presents speed control of an electric motorcycle using a fuzzy controller. The electric motorcycle required to meet not only fast throttle response but also stability, when it is on a cruise. However, a 1.5KW (50cc) electric motorcycles selling in the current market are difficult to cruise under the following conditions which are occupant's weight, load weight, wind resistance and road conditions (dirt roads, asphalt road). Because of these reasons, the rapid speed changing occurs in uphill and downhill road. To solve these problems, The input value for Improved fuzzy controller use the speed error and error variance. The output value for improved fuzzy controller uses Q-axis of the motor controlled variable. The D-axis of the motor output for improved fuzzy control uses D-axis controlled variable in proportional to Q-axis controlled variable. Improved fuzzy controller drives the electric motorcycle equipped with IPMSM. The control subject used in this paper is a 1.5KW electric motorcycle equipped with improved fuzzy controller that was used to control the motor speed. To control IPMSM Type of motor torque, D, Q-axis current controller was used. The Fuzzy controller using the proposed algorithm is demonstrated by experimental hardware simulator.
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