• Design & Manufacturing
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• v.16 no.4
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• pp.67-74
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• 2022

Injection molding is a cyclic process comprising of cooling phase as the largest part of this cycle. Providing efficient cooling in lesser cycle times is of significant importance in the molding industry. Recently, lots of researches have been done for rapid cooling of a hot-spot area using CO2 in injection molding. The CO2 flows under high pressure through small, flexible capillary tubes to the point of use, where it expands to create a snow and gas mixture at a temperature of -79℃. The gaseous CO2 removes heat from the mold and releases it into the atmosphere. In this paper, a CO2 cooling module was applied to an injection mold in order to cool a large area cavity uniformly and quickly, and the cooling performance of the injection mold was investigated. The product was a high-curvature molded part with a molding area of 300x100mm. Heat cartridges were installed in a stationary mold, and CO2 cooling module was inserted inside a movable mold. Through structural analysis, it was confirmed that the maximum deformation of mold with CO2 cooling module was 0.09mm. A CO2 feed system with a heat exchanger was used for cooling experiments. The CO2 was injected into the holes on both sides of the supply pipe of the cooling module and discharged through hexagon blocks to cool the mold. It took 5.8 seconds to cool the mold from an average temperature of 140℃ to 70℃. Through the experiment using CO2 cooling module, it was found that a cooling rate of up to 12.98℃/s and an average of 10.18℃/s could be achieved.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.8
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• pp.1503-1517
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• 1994

Intelligent Motion Planning System(IMPS) is presented for a robot to achieve an efficient path toward the given target point in two dimensional unknown environment is constructed with unrestricted obstacle shapes. IMPS consists of three components for making intelligent motion. These components are real-time motion planning algorithm based on a discontinous boundary method, fuzzy neural network decision system for heuristic knowledge representation, and world modeling with forgetting and reinforcing memory cells. First of all, in real-time motion planning algorithm, the behavior-based architectural method is used to generate subgoal. A behavior generates a subgoal independently by using the method of discontinuous boundary in sensed area. The discontinuous boundary method is a new proposed fast obstacle avoidance algorithm. The second component is fuzzy neural network decision system for accomplishing the subgoal. The heuristic rules are imbedded on the fuzzy neural network to make an intelligent decision. The last one is a forgetting, reinforcing memory technique for the construction of external world map. The activation values of all activated memory cells in grid space are decreased monotonically and after all they are burned out. Therefore, after sufficient journey, robot can have a stationary world map even if the dynaic obstacles exist. Using the IMPS, several simulations show the efficient achievement of target point in unknown enviroment with obstcles of various shapes.

• Korea journal of population studies
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• v.32 no.1
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• pp.139-164
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• 2009

The first demographic transition refers to the historical decline in mortality and fertility, as shown from the 18th Century in several European populations, and continuing present in most developing countries. The end point of the first demographic transition(FDT) was supposed to be a stationary and stable population corresponding with replacement fertility and zero population growth. In addition, households in all parts of the world would converge toward the nuclear and conjugal types, composed of married couples and their offspring. The second demographic transition(SDT), on the other hand, sees no such equilibrium as the end-point. Rather, new developments bring sub-replacement fertility, a multitude of living arrangements other than marriage, and the disconnection between marriage and procreation. Populations would face declining sizes if not complemented by new migrants. Over the last decades birth rates have been on the decline in all countries of the world, and it is estimated that already more than half of he world's population has below replacement level fertility. Measured in terms of the Total Fertility Rate (TFR), currently 34 countries have fertility levels of 1.5 or less. Similarly, Korea has been below lowest-low fertility for eight consecutive years since 2001 and below the replacement level for more than twenty years. In explaining the low fertility in Korea, some researchers explain the low fertility as revenge against a male-dominated society and institution, while others focus the impact of the employment instability. These studies share the basic ideas (spread of individualism, delayed marriage and childbearing, high divorce rate etc.) of a second demographic transition in order to explain the low fertility in Korea.

• Journal of the Korean earth science society
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• v.45 no.3
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• pp.203-213
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• 2024

This study aimed to investigate the seasonal patterns of multiple bar formation in summer and flattening in winter on the macrotidal Sinduri beach in Taean, and to understand the processes their formation and subsequent flattening. Beach profiling has been conducted regularly over the last four years using a VRS-GPS system. Surface sediment samples were collected seasonally along the transectline, and grain size analyses were performed. Tidal current data were acquired using a TIDOS current observation system during both winter and summer. The Sinduri macrotidal beach consists of two geomorphic units: an upper high-gradient beach face and a lower gentler sloped intertidal zone. High berms and beach cusps did not develop on this beach face. The approximately 400-m-wide intertidal zone comprises distinct 2-5 lines of multiple bars. Mean grain sizes of sand bars range from 2.0 to 2.75 phi, corresponding to fine sands. Mean sizes show shoreward coarsening trend. Regular beach-profiling survey revealed that the summer profile has a multi-barred morphology with a maximum of five bar lines, whereas, the winter profile has a non-barred, flat morphology. The non-barred winter profiles likely result from flattening by scour-and-fill processes during winter. The growth of multiple bars in summer is interpreted to be formed by a break-point mechanism associated with moderate waves and the translation of tide levels, rather than the standing wave hypothesis, which is stationary at high tide. The break-point hypothesis for multi-bars is supported by the presence of the largest bar at mean sea-level, shorter bar spacing toward the shore, irregular bar spacing, strong asymmetry of bars, and the 10-30 m shoreward migration of multi-bars.

• Korean Journal of Food Science and Technology
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• v.28 no.3
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• pp.411-416
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• 1996

Supercritical fluid extraction of ${\beta}$-carotene from carrot was optimized to maximize ${\beta}$-carotene (Y) extraction yield. A central composite design involving extraction pressure ($X_1$ 200-,100 bar), temperature ($X_2,\;35-51^{\circ}C$) and time ($X_1$$ 60-200min) was used. Three independent factors ($X_1,\;X_2,\;X_3$) were chosen to determine their effects on the various responses and the function was expressed in terms of a quadratic polynomial equation,$Y={\beta}_0+{\beta}_1X_1+{\beta}_2X_2+{\beta}_3X_3+{\beta}_11X_12+{\beta}_22X_3^2+{\beta}_-12X_1X_2+{\beta}_12X_1X_2+{\beta}_13X_1X_3+{\beta}_23X_2X_3,$ which measures the linear, quadratic and interaction effects. Extraction yields of ${\beta}$-carotene were affected by pressure, time and temperature in the decreasing order, and linear effect of tenter point (${\beta}_11$) and pressure (${\beta}_1$) were significant at a level of 0.001(${\alpha}$). Based on the analysis of variance, the model fitted for ${\beta}_11$-carotene (Y) was significant at 5% confidence level and the coefficient of determination was 0.938. According to the response surface of ${\beta}$-carotene by cannoical analysis, the stationary point for quantitatively dependent variable (Y) was found to be the maximum point for extraction yield. Response area for ${\beta}$-carotene (Y) in terms of interesting region was estimated over $10,611{\mu}g$ Per 100 g raw carrot under extraction.

• Strategy21
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• s.31
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• pp.57-84
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• 2013

North Korea's continuous threats and provocative behaviors have aggravated tension on the Korean peninsula particularly with the recent nuclear weapons test. South Korea's best way to cope with this situation is to maintain the balance among three policy directions: dialogue, sanctions, and deterrence. Among the three, I argue that deterrence should be prioritized. There are different sources of deterrence such as military power, economic power, and diplomatic clouts. States can build deterrence capability independently. Alternatively, they may do so through relations with other states including alliances, bilateral relations, or multilateral relations in the international community. What South Korea needs most urgently is to maintain deterrence against North Korea's local provocations through the enhancement of independent military capability particularly by addressing the asymmetric vulnerability between militaries of the South and the North. Most of all, the South Korean government should recognize the seriousness of the negative consequences that North Korea's 'Nuclear shadow strategy' would bring about for the inter-Korea relations and security situations in Northeast Asia. Based on this understanding, it should develop an 'assertive deterrence strategy' that emphasizes 'multi-purpose, multi-stage, and tailored deterrence whose main idea lies in punitive retaliation.' This deterrence strategy requires a flexible targeting policy and a variety of retaliatory measures capable of taking out all targets in North Korea. At the same time, the force structures of the army, the air force, and the navy should be improved in a way that maximizes their deterrence capability. For example, the army should work on expanding the guided missile command and the special forces command and reforming the reserve forces. The navy and the air force should increase striking capabilities including air-to-ground, ship-to-ground, and submarine-to-ground strikes to a great extent. The marine corps can enhance its deterrence capability by changing the force structure from the stationary defense-oriented one that would have to suffer some degree of troop attrition at the early stage of hostilities to the one that focuses on 'counteroffensive landing operations.' The government should continue efforts for defense reform in order to obtain these capabilities while building the 'Korean-style triad system' that consists of advanced air, ground, and surface/ subsurface weapon systems. Besides these measures, South Korea should start to acquire a minimum level of nuclear potential within the legal boundary that the international law defines. For this, South Korea should withdraw from the Nuclear Non-proliferation Treaty. Moreover, it should obtain the right to process and enrich uranium through changing the U.S.-South Korea nuclear cooperation treaty. Whether or not we should be armed with nuclear weapons should not be understood in terms of "all or nothing." We should consider an 'in-between' option as the Japanese case proves. With regard to the wartime OPCON transition, we need to re-consider the timing of the transition as an effort to demonstrate the costliness of North Korea's provocative behaviors. If impossible, South Korea should take measures to make the Strategic Alliance 2015 serve as a persisting deterrence system against North Korea. As the last point, all the following governments of South Korea should keep in mind that continuing reconciliatory efforts should always be pursued along with other security policies toward North Korea.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.3
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• pp.104-111
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• 2018

The sensorless control of high efficiency air compressors using a permanent magnet type synchronous motor as an oil-free air compressor is quite common. However, due to the nature of the air compressor, it is difficult to install a position sensor. In order to control the permanent magnet type synchronous motor at variable speed, the inclusion of a position sensor to grasp the position of the rotor is essential. Therefore, in order to achieve sensorless control, it is essential to use a permanent magnet type synchronous motor in the compressor. The position estimation method based on the back electromotive force, which is widely used as the sensorless control method, has a limitation in that position errors occur due either to the phase delay caused by the use of a stationary coordinate system or to the estimated back electromotive force in the transient state caused by the use of a synchronous coordinate system. Therefore, in this paper, we propose a method of estimating the position and velocity using a rotation angle tracking observer and reducing the speed ripple through a disturbance observer. An experimental apparatus was constructed using Freescale's MPU and the feasibility of the proposed algorithm was examined. It was confirmed that even if a position error occurs at a certain point in time, the position correction value converges to the actual vector position when the position error value is found.

• The Journal of the Korea Contents Association
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• v.17 no.7
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• pp.67-78
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• 2017

This study aims to analyze the status for the improvement of rehabilitation facilities of the products manufactured by severely disabled. So, This study analyze rehabilitation facilities of 289. The results of this study were as follows. First, sheltered workshop rate is 57.1%, Welfare group of disabled is 29.8%, Work program is 13.1%. And Total worker is 8,358 people(average 28.92 people), worker with disabled is 6,119 people(average 21.17 people). Second, Most of the certificated item is printing/advertising(18.6%) and food(14.3%), office/stationary(12.8%) and so on. Third, Total sales is 17.8 million won and sale cost is 15.7 million won and net income is 2.1 million won. Also, The longer the certificated period, the higher the sales. Forth, It is supported to purchasing improve sales, improve employment of the disabled, improve wage of the disabled, improve working condition. Fifth, it is necessary to successful of extension of priority purchasing ratio, additional purchasing point, support system of market. Base on this results, the implications for improvement on rehabilitation facilities wer discussed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.2
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• pp.597-603
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• 2010

The amount of pollutants from stationary sources of businesses classified into 1-3 type in Gyeongju was found to be 0.70 ton/yr for PM-10, 13.95 ton/yr for $SO_2$, and 37.12 ton/yr for NOx ; with respect to area sources, 1.02 ton/yr for PM-10, 13.44 ton/yr for $SO_2$, and 21.10 ton/yr for NOx ; and with respect to mobile sources 963.91 ton/yr for PM-10, 1415.02 ton/yr for $SO_2$, and 5612.70 ton/yr for NOx. This study surveyed the concentration distribution of PM-10, $SO_2$, and NO2 in the air in around Gyeongju and Pohang, and found that high concentration was mainly distributed around Pohang Steel Industrial Complex and the around of mobile sources. In Gyeongju area, $SO_2$ was predicted to increase from 0.002 ppm in 2006 to 0.005 ppm in 2015, and that of $NO_2$ was predicted to increase from 0.004 ppm to 0.010 ppm during the same period. At this point, practicing guidelines to reduce air pollutants and management plan for environmental pollutants should be devised, and also practicing and management programs to protect the stone cultural properties from environmental pollutants and other chemical, physical, and biological factors should be actively introduced.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.12
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• pp.679-684
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• 2017

Friction Stir Welding is a metal welding technique, in which friction heat between a welding tool and a welding material is used to weld parts at temperatures below the melting point of a material. In this study, the temperature and velocity changes in a magnesium alloy (AZ31) during the welding process were analyzed by computational flow dynamics technique while welding the material using a friction stir welding technique. For the analysis, the modeling and analysis were carried out using Fluent as a fluid analysis tool. First, the welding material was assumed to be a temperature-dependent Newtonian fluid with high viscosity, and the rotation region and the stationary region were simulated separately to consider the rotational flow generated by the rotation of the welding tool having a helical groove. The interface between the welding tool and welding material was given the friction and slip boundary conditions and the heat transfer effect to the welding tool was considered. Overall, the velocity and temperature characteristics of the welded material according to time can be understood from the results of transient analysis through the above flow analysis modeling.