• Structural Engineering and Mechanics
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• 제85권1호
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• pp.29-53
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• 2023

High-strength shielding concrete against gamma radiation is a priority for many medical and industrial facilities. This paper aimed to investigate the gamma-ray shielding properties of high-strength hematite concrete mixed with silica fume (SF) with nanoparticles of lead dioxide (PbO₂), tungsten oxide (WO₃), and bismuth oxide (Bi₂O₃). The effect of mixing steel fibres with the aforementioned binders was also investigated. The reference mixture was prepared for high-strength concrete (HSCC) containing 100% hematite coarse and fine aggregate. Thirteen mixtures containing 5% SF and nanoparticles of PbO₂, WO₃, and Bi₂O₃ (2%, 5%, and 7% of the cement mass, respectively) were prepared. Steel fibres were added at a volume ratio of 0.28% of the volume of concrete with 5% of nanoparticles. The slump test was conducted to workability of fresh concrete Unit weight water permeability, compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity tests were conducted to assess concrete's engineering properties at 28 days. Gamma-ray radiation of 137Cs emits photons with an energy of 662 keV, and that of 60Co emits two photons with energies of 1173 and 1332 keV were applied on concrete specimens to assess radiation shielding properties. Nanoparticles partially replacing cement reduced slump in workability of fresh concrete. The compressive strength of mixtures, including nanoparticles was shown to be greater, achieving 94.5 MPa for the mixture consisting of 7.5 PbO2. In contrast, the mixture (5PbO₂-F) containing steel fibres achieved the highest values for splitting tensile, flexural strength, and modulus of elasticity (11.71, 15.97, and 42,840 MPa, respectively). High-strength shielded concrete (7.5PbO2) showed the best radiation protection. It also showed the minimum concrete thickness required to prevent the transmission of radiation.

• 한국시뮬레이션학회논문지
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• 제19권1호
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• pp.161-171
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• 2010

많은 센서 네트워크 응용분야에서 센서 노드는 개방된 환경에 놓이게 된다. 공격자는 개방된 환경에 놓인 센서 노드를 물리적으로 획득할 수 있으며, 포획한 노드를 이용하여 허위보고서를 센서네트워크에 삽입 시킬 수 있다. 삽입된 허위보고서는 제한된 센서노드 에너지를 고갈 시키며, 허위 경보를 일으켜 심각한 문제를 야기 시킬 수도 있다. 이러한 공격을 막기 위해 Ye 등은 통계적 여과 기법(Statistical En-route Filtering) 방법을 제안하였다. 통계적 여과기법은 CoS(Center of Stimulus)로부터 생성된 이벤트 보고서가 베이스 스테이션으로 전송되는 동안 중간의 모든 노드들이 검증을 하게 된다. 본 논문은 통계적 여과 기법에 확률 검증 기법을 적용하여 에너지 효율적인 정적 확률 통계적 여과 기법을 제안하고자 한다. 베이스 스테이션과 이벤트 발생 지역까지의 거리가 멀어질수록 에너지 절약 효과가 극대화 될 것으로 기대된다.

• 청정기술
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• 제15권2호
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• pp.130-136
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• 2009

상용촉매인 Johnson Matthey사 KATALCO 83-3 촉매를 이용하여 마이크로 채널 반응기 (micro-channel reactor: MCR) 형태에 따른 메탄올 수증기 개질반응을 통한 수소제조반응 특성 연구를 수행하였다. 반응온도 200${\sim}$300$^{\circ}C$, 공간속도 3,000${\sim}$10,000 $hr^{-1}$, 촉매 크기 0.05${\sim}$2.2 mm 조건을 갖는 고정층 반응기에서 반응활성 실험을 수행한 결과, 촉매 크기 0.35 mm에서 최적의 반응활성을 나타났다. 이 결과를 토대로 stacked bed, boat bed 등 마이크로 채널 반응기 형태에 따른 반응활성을 연구한 결과, stacked bed type 마이크로 채널 반응기가 더 좋은 반응활성을 가짐을 알 수 있었다.

• 한국지반공학회논문집
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• 제24권10호
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• pp.161-174
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• 2008

국내 점성토 지반 및 풍화토 지반의 전단파속도 특성을 파악하기 위하여 표준관입시험(SPT), 부유형 PS 속도검층(SPS) 및 다운홀 등의 시험을 수행하였으며, SPT와 SPS 속도검층 결과로부터 지층별 전단파 속도를 분석하였다. 본 연구대상 지역에서 측정된 전단파 속도를 점성토와 풍화토로 나누어 분석하여 지반강도와 전단파속도와의 상관관계로부터 경험식을 제안할 수 있었는데, 점성토에서는 여러 학자들에 의하여 기존에 제안된 경험식과 유사한 결과를 나타내었으나 풍화토에서는 기존 경험식에 의한 값과 연구대상 지역에서 측정한 실측값과는 다소 차이가 있음을 확인하였다. 아울러 연구 대상지역에 대한 전단파 속도의 깊이에 따른 영향을 제시하였고 이 결과를 Ohta 등(1978)의 경험식과 비교, 검토하였다.

• 한국지반공학회논문집
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• 제23권8호
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• pp.77-85
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• 2007

본 연구에서는 선정된 부산 신항만 공사 지역의 연약 점토층을 대상으로 비배수전단강도 값을 분석하고 CPT적용을 위한 콘계수의 변화특성 및 영향인자를 비교분석하고자 한다. 이를 위해 다양한 현장시험과 실내시험 결과를 분석하였으며, 현장시험에서 구해진 콘계수와 실내시험에서 얻어진 결과를 토대로 한 이론적인 콘계수와의 비교를 통해 해당 현장에 가장 적합한 이론식을 선정하고자 한다. 본 연구에서 사용된 이론식은 Baligh(1975)와 Yu(1993)의 공동 확장 이론과 Teh and Houlsby(1991)와 Yu 등(2000)의 정적 상태 해석법이 사용되었으며, 공동 확장 해석법이 현장 시험을 통해 측정된 콘계수와 부합하는 결과를 나타내었다.

• 한국물환경학회지
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• 제39권2호
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• pp.153-161
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• 2023

The reservoir tank in an apartment is crucial for maintaining the quality of drinking water after it has undergone treatment. Investigating the water quality and potential contaminants in the reservoir tank is essential to ensure the safety of the drinking water. This study examined the water quality and precipitated suspended solids that accumulate at the bottom of the reservoir tanks in four apartments located in Gyeonggi province. As a result of the water quality investigation, turbidity increased proportionally to the distance from the water treatment plant (WTP) to the household. Heavy metals were also detected in the reservoir tank inlet but not in the water supplied from the WTP. The precipitated suspended solids (SS) in the reservoir tank contain high levels of heavy metals and total organic carbon (TOC). The precipitated SS mainly consists of Al, Mn, and Fe, which are expected to be a combination with turbidity-inducing substances. The X-ray diffraction (XRD) analysis revealed the presence of γ-FeO(OH), MnO₂, and β-Fe₂O₃ in the SS. Additionally, F-EEM analysis indicates that the dissolved organic matter in the SS is mainly derived from a natural water source and microorganism activities, including metal-oxidizing bacteria and biofilms that can absorb metal ions. Based on these findings, several countermeasures can be taken to prevent the inflow of SS into the household, including regularly cleaning the reservoir tank, replacing or cleaning old pipes in the water supply system, and implementing monitoring and filtering systems to manage the SS.

• 한국음향학회지
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• 제42권3호
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• pp.227-232
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• 2023

수중 소음 공해는 해양 환경에 막대한 영향을 미친다. 본 연구에서는 기포층을 갖는 구조물의 음향 방사 효율을 추정하기 위한 간이 해석법을 제안하였다. 선행 연구 결과를 바탕으로 공기층에 의한 삽입 손실은 감쇠량과 동등하다고 가정하고, 기포층에 의한 삽입 손실은 수치해석 결과의 후처리 기법을 사용하여 계산되었다. 제안된 방법의 검증을 위해 판 구조물에 대한 음향-구조 완전 연성 해석을 수행하였다. 음향-구조 완전 연성 해석은 상용 유한 요소 프로그램 COMSOL Multiphysics를 사용하여 수행되었으며, 기포층의 음향 특성은 Commander 및 Prosperetti 이론을 사용하여 구현하였다. 음향 방사 효율 비교를 통해 간이 해석법과 완전 연성 해석 결과의 경향이 유사함을 확인하였다. 이러한 결과를 바탕으로 기포층을 갖는 쐐기 구조물의 방사 효율 메커니즘을 예측할 수 있음을 확인하였다.

• ALGAE
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• 제38권2호
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• pp.127-139
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• 2023

Cryptic stages of diverse macroalgae present in natural substrata, "the bank of microscopic forms", were isolated into clonal cultures and identified based on both morphological characteristics and DNA barcoding. Approximately 120 clonal isolates from 308 natural substratum samples were collected from the entire coastline of Kuwait. Amongst these isolates, 77 (64%) were identified through DNA barcoding using the nuclear ribosomal small subunit, RuBisCO spacer (ITS2, tufa, rbcL, psaA, and psbA) and sequencing. Twenty-six isolates (34%) were identified in the division Chlorophyta, 18 (23%) as Phaeophyceae, and 33 (43%) as Rhodophyta. For all DNA sequences in this study, species-level cut off applied was ≥98% homology which depend entirely on the markers used. Three putative new records of Chlorophyta new for the Arabian Gulf were made: Cladophora laetevirens (Dillwyn) Kützing, Ulva torta (Mertens) Trevisan and Ulvella leptochaete (Huber) R. Nielsen, C. J. O'Kelly & B. Wysor in Nielsen, while Cladophora gracilis Kützing and Ulva ohnoi M. Hiraoka & S. Shimada are new records for Kuwait. For Phaeophyceae, Ectocarpus subulatus Kützing and Elachista stellaris Areschoug were new records for the Gulf and Kuwait. In the Rhodophyta, Acrochaetium secundatum (Lyngbye) Nägeli in Nägeli & Cramer, Ceramium affine Setchell & N. L. Gardner, Gelidium pusillum var. pakistanicum Afaq-Husain & Shameel and Dasya caraibica Børgesen are new records for the Gulf and Kuwait, while the red alga Stylonema alsidii (Zanardini) K. Drew is a new record for Kuwait. Several isolates identified corresponded to genera not previously reported in Kuwait and / or the Arabian Gulf, such as Porphyrostromium Trevisan, a new genus from the Bangiales, and two unidentified species for the Planophilaceae Škaloud & Leliaert. The isolates cultivated from substrata enhance understanding of the marine macroalgal diversity in the region and confirmed that the Germling Emergence Method is suitable for determining the actual diversity of a given study area through isolation from cryptic life-history phases.

• 한국지형학회지
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• 제26권3호
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• pp.53-67
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• 2019

The purpose of this study is to identify the quality of landslide susceptibility in a landslide-prone area (Jinbu-myeon, Gangwon-do, South Korea) by spatial prediction modeling approach and compare the results obtained. For this goal, a landslide inventory map was prepared mainly based on past historical information and aerial photographs analysis (Daum Map, 2008), as well as some field observation. Altogether, 550 landslides were counted at the whole study area. Among them, 182 landslides are debris flow and each group of landslides was constructed in the inventory map separately. Then, the landslide inventory was randomly selected through Excel; 50% landslide was used for model analysis and the remaining 50% was used for validation purpose. Total 12 contributing factors, such as slope, aspect, curvature, topographic wetness index (TWI), elevation, forest type, forest timber diameter, forest crown density, geology, landuse, soil depth, and soil drainage were used in the analysis. Moreover, to find out the co-relation between landslide causative factors and incidents landslide, pixels were divided into several classes and frequency ratio for individual class was extracted. Eventually, six landslide susceptibility maps were constructed using the Bayesian Predictive Discriminant (BPD), Empirical Likelihood Ratio (ELR), and Linear Regression Method (LRM) models based on different category dada. Finally, in the cross validation process, landslide susceptibility map was plotted with a receiver operating characteristic (ROC) curve and calculated the area under the curve (AUC) and tried to extract success rate curve. The result showed that Bayesian, likelihood and linear models were of 85.52%, 85.23%, and 83.49% accuracy respectively for total data. Subsequently, in the category of debris flow landslide, results are little better compare with total data and its contained 86.33%, 85.53% and 84.17% accuracy. It means all three models were reasonable methods for landslide susceptibility analysis. The models have proved to produce reliable predictions for regional spatial planning or land-use planning.

• Advances in concrete construction
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• 제16권1호
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• pp.35-57
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• 2023

Majority of the plastic produced each year is being disposed in land after single-use, which becomes waste and takes up a lot of storage space. Therefore, there is an urgent need to find alternative solutions instead of disposal. Recycling and reusing the PET plastic waste as aggregate replacement and fiber in concrete production can be one of the eco- friendly methods as there is a great demand for concrete around the world, especially in developing countries by raising human awareness of the environment, the economy, and Carbon dioxide (CO2) emissions. Self-compacting concrete (SCC) is a key development in concrete technology that offers a number of attractive features over traditional concrete applications. Recently, in order to improve its durability and prevent such plastics from directly contacting the environment, various kinds of plastics have been added. This review article summarizes the latest evident on the performance of SCC containing recycled PET as eco-friendly aggregates and fiber. Moreover, it highlights the influence of substitution content, shape, length, and size on the fresh and properties of SCC incorporating PET plastic. Based on the findings of the articles that were reviewed for this study, it is observed that SCC made of PET plastic (PETSCC) can be employed in construction era owing to its acceptable mechanical and fresh properties. On the other hand, it is concluded that owing to the lightweight nature of plastic aggregate, Reusing PET waste in the construction application is an effective approach to reduces the earthquake risk of a building.