• 대한치과교정학회지
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• 제47권4호
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• pp.238-247
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• 2017

Objective: The aim of this study was to compare recycled and unused orthodontic miniscrews to determine the feasibility of reuse. The comparisons included both miniscrews with machined surfaces (MS), and those with etched surfaces (ES). Methods: Retrieved MS and ES were further divided into three subgroups according to the assigned recycling procedure: group A, air-water spray; group B, mechanical cleaning; and group C, mechanical and chemical cleaning. Unused screws were used as controls. Scanning electron microscopy, energy-dispersive X-ray spectrometry, insertion time and maximum insertion torque measurements in artificial bone, and biological responses in the form of periotest values (PTV), bone-implant contact ratio (BIC), and bone volume ratio (BV) were assessed. Results: Morphological changes after recycling mainly occurred at the screw tip, and the cortical bone penetration success rate of recycled screws was lower than that of unused screws. Retrieved ES needed more thorough cleaning than retrieved MS to produce a surface composition similar to that of unused screws. There were no significant differences in PTV or BIC between recycled and unused screws, while the BV of the former was significantly lower than that of the latter (p < 0.05). Conclusions: These results indicate that reuse of recycled orthodontic miniscrews may not be feasible from the biomechanical aspect.

• 한국지하수토양환경학회지:지하수토양환경
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• 제29권1호
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• pp.39-50
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• 2024

Slags from steel-making industry have been recycled at a target rate of 95% and most of them are recycled as media-contact type such as fill and cover materials in Korea. However, as they contain free phase CaO during their generation, they may not only expand and collapse upon contact with water, but high pH leachate and heavy metals leaching may occur. In this study, the Korean leaching procedure (KLP) and up-flow percolation test were performed for the samples collected from 17 steel-making production plants in Korea. The waste quality criteria were met in all tests, but pH of the samples was above 10. There are no regulations on the pH of leachate in most of the countries, however, Germany, Italy, and Australia have set a pH range of 10 to 13 for the leachates. Although slag leachate cannot be considered hazardous based only on its high pH, it is necessary to reduce the pH of leachate to minimize the impact on the surrounding environment. Furthermore, conflicting regulations on wastes handling and management in Korea created confusion on the types of wastes subject to recycling. Therefore, an appropriate management plan for steel-making slags needs to be established. To this end, this study attempted to provide a guideline for managing steel-making slag waste by considering international guidelines and current management practices in Korea.

• Communications for Statistical Applications and Methods
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• 제15권1호
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• pp.105-115
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• 2008

환경부가 2003년 이후 생산자 책임 재활용 제도를 시행함에 있어 각 기업의 처리 대상 재활용 실적(양)을 측정하는 것이 중요한 문제가 되었다. 이때 각 기업의 처리 적의 중요한 변수가 비 대상품목의 혼입비율이고 이를 매년 기업 단위로 12회 이상 조사해 오고 있다. 하지만 혼입 비율을 조사함에 있어 조사자의 안전성, 악취, 정확한 비대상품 식별의 어려움 등등 여러 가지문제가 발생함에 따라 적은 조사 회수로도 정확한 혼입비율을 측정할 수 있는 방법에 대한 현장 조사자들의 요구가 있어 왔다. 이에 본 논문은 최근 통계학 분야에서 활발하게 연구되어 지고 있는 Judgement Post-stratification(이후 JPS)라는 특별한 표본조사 방법을 적용해 볼 것을 제안한다. 본 논문에서는 JPS 방법의 효율성을 모의실험을 통하여 현재 사용되고 있는 Simple Random Sampling (이후 SRS)방법과 비교, 표본수가 같은 경우 그 우수성을 이야기하였고, 이를 실제 2004년 환경자원공사에서 수행한 실제 조사 자료에 적용하여 JPS를 이용한 방법이 기존의 방법을 적은 조사회수로도 충분히 대체 할 수 있음을 보였다.

• 대한산업공학회지
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• 제34권1호
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• pp.32-41
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• 2008

This paper studies a joint EOQ and EPQ model in which a stationary demand can be satisfied by recycled products as well as newly purchased products. The model assumes that a fixed quantity of the used products are collected from customers and later recovered for reuse. The recovered products are regarded as perfectly new ones. We also assume that the number of orders for newly purchasing items and the number of recovery setups in a cycle can be mutually independent integers. Under these assumptions, we develop an optimization model obtaining the economic order quantity for newly procured products, the optimal lot size for the recovery process, and the sequence of the orders and the setups, simultaneously. And then a simple solution procedure to find a local optimal control parameter set is proposed. To validate the model and the solution procedure, finally, some computational experiments are presented.

• Nuclear Engineering and Technology
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• 제52권12호
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• pp.2867-2873
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• 2020

In reprocessed uranium, derived from an impoverished fuel of light-water moderated reactors, there are isotopes of ^{232, 234, 236}U, which make its recycling remarkably difficult. A method of concentration of ²³⁵U target isotope in cascade's additional product was proposed to recover the isotopic composition of reprocessed uranium. A general calculation procedure is presented and a parameters' optimization of multi-flow cascades with additional products. For the first time a numeric model of a cascade that uses the cuts of partial flows of stages with relatively high separation factors was applied in this procedure. A novel computing experiment is carried out on separation of reprocessed uranium hexafluoride with providing a high concentration of ²³⁵U in cascade's additional product with subsequent dilution. The parameters of cascades' stages are determined so as to allow reducing the ^{232, 234, 236}U isotope content up to the acceptable. It was demonstrated that the dilution of selected products by the natural waste makes it possible to receive a low enriched uranium hexafluoride that meets the ASTM C996-15 specification for commercial grade.

• 한국기계가공학회지
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• 제20권9호
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• pp.1-10
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• 2021

Recently, the repair and recycling of damaged mechanical parts via metal additive manufacturing processes have been industrial points of interest. This is because the repair and recycling of damaged mechanical parts can reduce energy and resource consumption. The directed energy deposition(DED) process has various advantages such as the possibility of selective deposition, large building space, and a small heat-affected zone. Hence, it is a suitable process for repairing damaged mechanical parts. The shaft is a core component of various mechanical systems. Although there is a high demand for the repair of the shaft, it is difficult to repair with traditional welding processes because of the thermal deformation problem. The objective of this study is to propose a repair procedure for a damaged shaft using the DED process and discuss its applications. Three types of cases, including a small shaft with a damaged surface, a medium-size shaft with a worn bearing joint, and a large shaft with serious damage, were repaired using the proposed procedure. The microstructure and hardness were examined to discuss the characteristics of the repaired component. The efficiency of the repair of the damaged shaft is also discussed.

• 자원리싸이클링
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• 제22권1호
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• pp.3-10
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• 2013

본 발표는 국내 흑색 점판암으로부터 우라늄 및 바나듐 회수의 일반적인 현황 및 연구개발에 관한 내용이다. 우라늄 화합물(yellow cake)의 세계적인 수급 및 향후 전망뿐만 아니라, 국내 우라늄광의 매장량, 품위 및 특성에 대해 설명하였다. 그리고 국내 우라늄광의 기술개발에 관한 기 연구 실적 및 수행중인 연구과제의 개략적인 내용에 대해 기술하였다. 또한, 우라늄 및 바나듐 성분이 함유된 국내 흑색 점판암을 대상으로 하여 침출, 분리정제 및 회수에 관한 기술을 하였다.

• 경영과학
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• 제27권3호
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• pp.15-31
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• 2010

We consider a reverse logistics network design problem for recycling. The problem consists of three stages of transportation. In the first stage products are transported from retrieval centers to disassembly centers. In the second stage disassembled modules are transported from disassembly centers to processing centers. Finally, in the third stage modules are transported from either processing centers or a supplier to a manufacturer, a recycling site, or a disposal site. The objective is to design a network which minimizes the total transportation cost. We design a cooperative coevolutionary algorithm to solve the problem. First, the problem is decomposed into three subproblems each of which corresponds to a stage of transportation. For subproblems 1 and 2, a population of chromosomes is constructed. Each chromosome in the population is coded as a permutation of integers and an algorithm which decodes a chromosome is suggested. For subproblem 3, an heuristic algorithm is utilized. Then, a performance evaluation procedure is suggested which combines the chromosomes from each of two populations and the heuristic algorithm for subproblem 3. An experiment was carried out using test problems. The experiments showed that the cooperative coevolutionary algorithm generally tends to show better performances than the previous genetic algorithm as the problem size gets larger.

• 화약ㆍ발파
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• 제21권3호
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• pp.49-60
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• 2003

발파기술의 급속한 발전으로 재개발을 위한 노후 구조물에 대한 리모델링, 해체등이 다시 활성화될 조짐이 있다. 이에 1991. 8 이후 시작된 우리나라의 발파해체 공법을 재조명하고 그 개선방안을 정리하였다. 그 결과 최근의 발파해체공법은 기계식해체공법에 비해 약 60∼70%의 공기단축효과와 함께 5층이상 고층 구조물의 경우 경제성이 매우 높은 것으로 분석되었으며, 구조물 해체공법의 경제적 효과와 환경안전 및 재활용효과를 극대화하기 위하여 진동. 소음. 비석. 분진 예측프로그램의 활용 및 미비점 개선 등 각종 컴퓨터 예측시스템을 개발해야 할 것이다. 발파해체 시 발생된 건설폐기물의 재활용도를 높이기 위하여 도로 보조기충재 및 콘크리트용 골재활용에 대한 일정비율 사용 의무화 등 관련 법령개정이 필요하며 해체물의 분류, 처리 등에 폐기물 전문업체의 적극적 참여 및 추가적인 연구개발이 필요한 것으로 사료된다.

• Biotechnology and Bioprocess Engineering:BBE
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• 제5권5호
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• pp.355-361
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• 2000

A recycling reactor system operated under sequential anoxic and oxic conditions for the treatment of swine wastewater has been developed, in which piggery slurry is fermentatively and aerobically treated and then part of the effluent is recycled to the pigsty. This system significantly removes offensive smells (at both the pigsty and the treatment plant), BOD and others, and may be cost effective for small-scale farms. The most dominant heterotrophic were, in order, Alcaligenes faecalis, Brevundimonas diminuta and Streptococcus sp., while lactic acid bacteria were dominantly observed in the anoxic tank. We propose a novel monitoring system for a recycling piggery slurry treatment system through the use of neural networks. In this study, we tried to model the treatment process for each tank in the system (influent, fermentation, aeration, first sedimentation and fourth sedimentation tanks) based upon the population densities of the heterotrophic and lactic acid bacteria. Principal component analysis(PCA) was first applied to identify a relationship between input and output. The input would be microbial densities and the treatment parameters, such as population densities of heterotrophic and lactic acid bacteria, suspended solids(SS), COD, NH$_4$(sup)+-N, ortho-phosphorus (o-P), and total-phosphorus (T-P). then multi-layer neural networks were employed to model the treatment process for each tank. PCA filtration of the input data as microbial densities was found to facilitate the modeling procedure for the system monitoring even with a relatively lower number of imput. Neural network independently trained for each treatment tank and their subsequent combined data analysis allowed a successful prediction of the treatment system for at least two days.