• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.1
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• pp.103-110
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• 2011

This study is to comparatively analyze the characteristics of pH decrease in recycled fine aggregates for embankment and landfill produced from waste concrete by using natural process and artificial process. The result was as follows In case of recycled fine aggregates left outdoor, it was found that pH level was decreased if the thickness of embankment becomes thinner, or the materials left outdoors owing to high concentration of $CO_2$ in atmosphere caused by respirations of people. When the air was permeated, pH level was decreased more effectively. It was analyzed that this phenomenon was caused by efficient supply of $CO_2$ in the recycled fine aggregates owing to high-pressure ventilators. In case of water spraying treatment, sprayed water facilitated hydration of unhydrated cement to dissolve calcium hydroxides which neutralized $CO_2$ in the atmosphere during desiccation process and decrease pH level by a considerable margin. In case of Immersed treatment, decrease of pH was not sufficient. When facilitating the supply of $CO_2$, pH level of the recycled fine aggregates was decreased by the largest margin. It was analyzed that this phenomenon was caused by efficient supply of $CO_2$. From the above results, it was analyzed that the most effective method of reducing pH level of the recycled fine aggregates from the aspects of pH reduction performance, economic efficiency and workability was repeated wet-dry cycles of spraying water to the aggregates in the proportion of 1:0.5 by weight and then treating by forcefully blowing $CO_2$ gas into the aggregates.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.18 no.5
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• pp.1-18
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• 2019

A short-turn bus is a bus that is operated within a subsection of an existing bus line. Previous studies regarding short-turn buses decided optimal turn-back points for a single bus line rather than a bus network. Also, in-vehicle crowding which has a significant impact on transit convenience was rarely considered. Therefore, this study aimed to develop a methodology to set priorities for the introduction of short-turn buses of bus lines and sections, considering crowding. To achieve this objective, we calculated occupancies and crowding alleviation benefits of existing bus lines overlapping a new short-turn route based on transit card data, before and after the introduction of short-turn strategy. Also, operator and social costs caused by the introduction of short-turn buses were calculated. Those procedures were iterated over bus lines and sections to operate a short-turn service, and a section whose benefit-to-cost ratio (B/C) is the largest in a line was selected to operate a short-turn service in the line. After, priorities of bus lines to introduce short-turn services could be determined based on B/C values, and the optimum total fleet size could be determined when a short-turn strategy is applied in multiple lines.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.4
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• pp.84-90
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• 2013

In this study we propose an effective method, Coating processing methods, which can improve the quality of recycled aggregate relatively easily without new equipment investment and complex treatment process and verify the improved effect using the devised method, Coating processing methods. To attain the research aim we used adequately diluted silicate solution for coating and carried out several property valuation for twelve types of material with different coating method. Also we formed concrete with coated aggregates which showed the best property. In conclusion the aggregates with the method of repeated impregnation in the silicate and drying showed the most excellent quality while other coating methods also resulted in an improvement of aggregate quality but failed to meet the KS Standard. Lastly with the optimal material we could obtain the approved compressive strength from the concrete allowing it to be utilized for road facility of which standard compressive strength of design is under 24MPa.

• Horticultural Science & Technology
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• v.32 no.1
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• pp.46-52
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• 2014

This study was conducted to compare colony forming unit (CFU) of microorganisms in closed and open soilless culture systems for estimating the possibility for potential disease occurrence. Samples were collected at four different positions in four commercial greenhouses with closed or open soilless culture system using rock wool or coir as substrate, respectively. The distance between sampling positions was 3 cm starting from the substrate and the surface area of each position was $25cm^2$. The CFU of fungi was significantly higher in the open system, while that of bacteria was not significantly different but showed relatively lower in the closed system. Samples collected at the plastic surface of the substrates where little environmental effects occurred from drainage showed lower CFU than any other positions. The principal component analysis showed that samples collected on the drainage pathway highly affected the changes in microbial population in the greenhouse. These results indicated that greenhouses with closed soilless culture are expected to have more advantageous conditions for restraining the microbial growth, resulting in the lower potential of disease occurence in greenhouse ecosystem.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.141.1-141.1
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• 2015

탄소나노튜브는 우수한 전기적 특성과 더불어 열전도도, 강도, 높은 화학적 안정성, 바이오 물질과의 친화성 때문에 많은 응용이 가능하며 최근까지도 활발히 연구되는 대표적인 탄소질의 물질이다. 이러한 다중 벽 탄소나노튜브를 제품화시키기 위해서는 특정 용매에서 용이한 분산성을 지닐 수 있도록 기능화 공정이 필수적이고 많은 양의 파우더를 기능화 시킬 수 있는 장비의 구조 및 공정개선이 요구된다. 플라즈마 기술을 이용한 건식의 순환형 나노분산 파우더 플라즈마 반복처리장치를 통하여 기능화 처리된 탄소나노튜브를 습식공정에 비해 간편한 공정으로 재현성 있고 균일한 결과로 많은 양의 확보가 가능하다. 이에 탄소나노튜브의 기능화 결과를 제시함으로써 본 장비를 소개하고자 한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.2C
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• pp.155-160
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• 2008

In this letter, we propose a new design of recursive systematic convolutional (RSC) codes based on the distance spectrum properties which can maximize the performance. Good constituent RSC codes of code rate 1/2 are searched by computer and presented in a table. Their performances are shown by computer simulation. New designed codes shows faster convergences according to iterative decoding and good performances.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.95-95
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• 2016

한반도 중부지방은 2014년과 2015년에 연이은 강수량 부족으로 많은 지역에서 가뭄 현상이 나타났다. 특히, 한반도는 여름철에 강수가 집중되는 몬순기후대에 속하기 때문에 여름철 강수량은 생활용수나 농업용수 확보 등 이수 측면에서 매우 중요하다 할 수 있다. 이러한, 한반도(남한)의 중부지역 가뭄을 유발하는 강수량의 부족 현상은 대략 5-10년(평균 7-8년) 주기로 반복된다. 그리고 이러한 10여년 주기 변동성과 더불어 예외적인 경우가 발생하고 매번 그 심도도 변화한다. 이러한 주기성을 우연이라 보기는 어려울 것이나 예외적인 경우나 심도를 가늠할 수 없다는 점(인과관계가 불분명하다는 점)에서 확정론적 현상이라 단정하기도 어려운 현실이다. 따라서 본 연구에서는 이러한 주기적 가뭄을 야기하는 강수량 변동의 원인을 지구물리학적 측면에서 추론해 보고자 한다. 가뭄은 인위적인 조건에 의해서도 발생하고 인과관계에 따른 정의도 다양하지만, 본 연구에서는 자연 상태에서 강수량의 부족에 의한 가뭄 조건만을 고려하였다. 강수과정은 지구의 물순환 운동에 의해 야기되고 지구의 물순환 운동은 지구의 역학적 운동 및 상호작용 관계에 의해 발생한다고 알려져 있다. 따라서 본 연구에서는, 지구물리 과정의 일부로 강수과정을 유발하는 지표인자로 SST와 같은 기후 인자에 대해 변동 주기의 상관성을 범지구적인 시공간 규모에서 검토하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.105-114
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• 1993

The ciculation due to bottom density current produced by a dense inflow into a small reservoir is analysed by numerical scheme. Before the front of the density current arrives at the downstream end, the mixing in the reservoir is mainly caused by the anticlockwise vortex formed at the downstream of plunging point along the movement of bottom density current. Upon the arrival of the front of the density current at the downstream end an internal surge is created through an internal hydraulic jump. With repeated propagation of the internal surge back and forth the mixing in the reservoir is progressed and the thickness of dense layer is increased upward. The dilution of the overflow at downstream end is found to depend on inflow densimetric Froude number, reservoir length and elapsed time. The time required for the overflow to attain a specified dilution increases as reservoir length increases and Fre decreases.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2005.05a
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• pp.768-772
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• 2005

TSP(Traveling Salesman Problem) has been a nagging NP-complete problem to test almost every algorithmic idea in combinatorial optimization in vain. The main bottleneck is how to get the integer results {0,1} and to avoid sub-tours. We suggest simple and practical method in two steps. Firstly for every node, an initial Hamiltonian cycle us produced on the nearest neighbour concept. The node with nearest distance is to be inserted to form a increased feasible cycle. Secondly we improve the initial solution by exchanging 2 cuts of the grand tours. We got practical results within 1 from the optimum in 30 minutes for up to 200 nodes problems. TSP of real world type might be tackled practically in our formulation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1265-1272
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• 2011

We performed numerical simulations of the recirculation flow of an electrolyte fluid in a circular container driven by an AC electromagnetic force for solving continuity and momentum equations. We also conducted an experiment to obtain flow data, which were in good agreement with the numerical simulation results. Furthermore, we performed a parametric study on both numerical and experimental aspects and found that the fluid velocity increases with an increase in the electrolyte concentration and magnetic intensity and with a decrease in the fluid depth and AC frequency.