• ETRI Journal
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• v.45 no.2
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• pp.226-239
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• 2023

Challenges in cognitive radio and tactical communications include recognizing anonymously received signals and estimating parameters in a blind or semi-blind manner. In this paper, we examine this issue for orthogonal frequency division multiplexing (OFDM) signaling. There are several parameters in OFDM signaling, and the blind receiver must extract and consider the synchronization issue. We assume that the blind receiver is aware of modulation type, OFDM, and not aware of chip duration and the length of cyclic prefix. First, we present new criteria based on kurtosis to estimate these parameters and compare their performance at different levels of additive white Gaussian noise with methods based on correlation, kurtosis, maximum likelihood, and matched filter. Then, we perform synchronization and estimate the start time based on these criteria and several new criteria in two steps: fine and coarse synchronization. Finally, in a more practical setup, we present the idea of jointly estimating the mentioned parameters and the signal start time as coarse synchronization. We compare different criteria and show that one of the proposed criteria has the highest efficiency.

• Prospectives of Industrial Chemistry
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• v.20 no.6
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• pp.40-53
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• 2017

나노전달체 관련 기술은 다양한 질병 치료에 사용되어 단위세포 수준의 치료를 가능하게 할 뿐 아니라 영상 진단과 접목되어 질병의 진단 및 치료가 동시에 가능한 기술로 진화하고 있다. 본지에서는 이러한 연구 중 하나로 생체모사 나노전달체에 대해 다룬다. 다양한 면역세포 및 백혈구, 적혈구 등의 살아있는 세포의 기능을 나노전달체에 부여하여 전달효율 및 치료효과를 높이고자 하는 기술이다. 지금까지의 나노전달체 연구 및 개발 동향에 대하여 간략하게 살펴보고 특별히 최근 주목 받고 있는 생체모사 나노전달체의 개념, 제조 방법, 응용 및 앞으로의 전망에 대하여 논하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2023.05a
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• pp.363-365
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• 2023

본 논문에서는 어텐션(Attention) 메커니즘을 이미지 처리에 적용한 연구가 진행되면서 등장한 비전 트랜스포머 (Vision Transformer, ViT)의 한계를 극복하기 위해 ViT 기반의 딥 클러스터링(Deep Clustering) 기법을 제안한다. ViT는 완전히 트랜스포머(Transformer)만을 사용하여 입력 이미지의 패치(patch)들을 벡터로 변환하여 학습하는 모델로, 합성곱 신경망(Convolutional Neural Network, CNN)을 사용하지 않으므로 입력 이미지의 크기에 대한 제한이 없으며 높은 성능을 보인다. 그러나 작은 데이터셋에서는 학습이 어렵다는 단점이 있다. 제안하는 딥 클러스터링 기법은 처음에는 입력 이미지를 임베딩 모델에 통과시켜 임베딩 벡터를 추출하여 클러스터링을 수행한 뒤, 클러스터링 결과를 임베딩 벡터에 반영하도록 업데이트하여 클러스터링을 개선하고, 이를 반복하는 방식이다. 이를 통해 ViT 모델의 일반적인 패턴 파악 능력을 개선하고 더욱 정확한 클러스터링 결과를 얻을 수 있다는 것을 실험을 통해 확인하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2023.11a
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• pp.718-721
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• 2023

이미지 내 글꼴을 파악하는 것은 디자인 자료 제작, 저작권 확인 등 다양한 곳에서 중요한 문제이다. 하지만 이미지 내 한글 글꼴을 자동으로 식별하는 시스템은 아직 존재하지 않으며, 수동으로 한글 글꼴을 파악하는 것은 시간과 정확도 측면에서 매우 비효율적이다. 따라서 본 논문에서는 이미지 내 한글 글꼴을 자동으로 인식하는 시스템을 개발한다. 본 논문에서 개발한 시스템은 크게 두 가지 기법을 사용한다: (1) 한글의 기하학적인 특성을 활용하여 글자 단위로 텍스트를 인식하며, (2) 단어가 아닌 글자 단위로 글꼴을 분류하고 각 글자에 대한 글꼴 분류 결과를 종합하여 최종적인 글꼴 분류 결과를 얻는다. 10가지 한글 글꼴이 나타나는 직접 제작한 이미지를 사용하여 시스템의 성능을 평가한 결과 제안 방법은 비교 방법에 비해 더욱 정확히 한글 글꼴을 분류함을 확인하였다.

• International Journal of Computer Science & Network Security
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• v.24 no.4
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• pp.1-10
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• 2024

In the era of big data, the growth of e-commerce transactions brings forth both opportunities and risks, including the threat of data theft and fraud. To address these challenges, an automated real-time fraud detection system leveraging machine learning was developed. Four algorithms (Decision Tree, Naïve Bayes, XGBoost, and Neural Network) underwent comparison using a dataset from a clothing website that encompassed both legitimate and fraudulent transactions. The dataset exhibited an imbalance, with 9.3% representing fraud and 90.07% legitimate transactions. Performance evaluation metrics, including Recall, Precision, F1 Score, and AUC ROC, were employed to assess the effectiveness of each algorithm. XGBoost emerged as the top-performing model, achieving an impressive accuracy score of 95.85%. The proposed system proves to be a robust defense mechanism against fraudulent activities in e-commerce, thereby enhancing security and instilling trust in online transactions.

• Journal of Energy Engineering
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• v.17 no.1
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• pp.15-22
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• 2008

This study was carried out to investigate physical and chemical characteristics of the distillates and residue of Athabasca oilsand bitumen obtained from Canada, using a vacuum distillation unit. The distillates and residue produced from the vacuum distillation were characterized through atomic analysis, SARA analysis, and measurement of boiling point distribution, molecular weight, and API gravity. The vacuum distillation equipment consisted of a 6-litter volume vessel, a glass-packed column, a condenser, a reflux device, a flask fer collecting distillates, and a temperature controller. The cutting of distillates was performed with four steps under the condition of full vacuum and maximum temperature of $320^{\circ}C$. The results showed that the sulfur amount and average molecular weight of the distillates were significantly reduced compared to those of oilsand bitumen. As the cutting temperature increased, the hydrogen amount decreased but the sulfur amount and average molecular weight increased in the distillates.

• Journal of Energy Engineering
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• v.17 no.1
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• pp.38-45
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• 2008

In this work, we investigated the variation of physical and chemical characteristics of solvent-insolubles and solvent-solubles in Canada's Athabasca oil sands by solvent-insolubles experiments. N-Heptane, n-Hexane, and n-Pentane were tested for solvents and asphaltenes were separated from maltenes by using a modified ASTM D 3279 method. Elemental analysis, boiling point distribution (SIMDIS), molecular weight distribution, heavy metal contents, API gravity, viscosity and SARA fractions were measured for thorough samples. The asphaltenes-removed maltenes contained less sulfur and heavy metal amounts and had lower molecular weight than the original bitumen. N-Pentane solvent could lower sulfur and heavy metal amounts, molecular weight, and viscosity of maltenes compared to the other solvents. Eventually, we confirmed that the obtained experimental data could be used as basic informations of bitumen upgrading processes for the production of SCO (synthetic crude oil).

• Applied Chemistry for Engineering
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• v.30 no.5
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• pp.556-561
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• 2019

In this study, the physical and chemical analyses of petroleum residues (pyrolized fuel oil, PFO) were conducted and major components were selected to investigate their fire and explosion characteristics. Major component distribution areas of the PFO were identified via the GC-SIMDIS and MALDI-TOF analyses. In addition, the qualitative analysis of major component distribution areas was performed by GC-MS analysis. Major components of pyrolysis residue were selected based on the results of various analyses such as EA, SARA and TGA. As a result, benzene, toluene and xylene were selected as major components. Finally, the process hazard analysis software tool (PHAST) analysis was performed to investigate the range of maximum damage effect in case of fire and explosion. Toluene presented the highest risk due to the radiation effect of $227kW/m^2$ and 118 m in the case of jet fire. Xylene and benzene showed the maximum radiant heat values of 114 and $151kW/m^2$, respectively. It was also confirmed from the analysis of pasquill stability and wind speed that the radiant heat increased up to 55% according to wind speed in benzene, which was considered to be a main factor increasing the influence range.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.7
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• pp.864-872
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• 2020

In accordance with the sulfur regulations of the International Maritime Organization (IMO), very low sulfur fuel oil (VLSFO) shows various production-dependent physico-chemical properties. This study aims to use as basic data for oil spill response according to study of physico-chemical characteristics of VLSFO and mixed fuel oil of VLSFO-HSFO. The mixed fuel oil was prepared by mixing 25, 50, 75 mass% of HSFO with VLSFO containing 0.46 and 0.36 mass% of sulfur. The physico-chemical properties such as the kinematic viscosity, pour point and distribution of Saturates, Aromatics, Resins, and Asphaltenes (SARA) were studied in the laboratory. As mixed of 75 mass% of HSFO with high the kinematic viscosity and low pour point in VLSFO, the kinematic viscosity of the mixed fuel oil increased to 350.2 %, and VLSFO with pour point of 23℃ and -11℃ lowered or raised to -3℃ and -6℃ respectively. As HSFO was mixed in VLSFO with a small Asphaltenes distribution, the Saturates distribution decreased to 68.8% and Asphaltenes distribution increased to 1,417 % dramatically.

• Journal of the Korean Society of Clothing and Textiles
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• v.27 no.12
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• pp.1405-1411
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• 2003

본 연구의 목적은 기계에 의한 객관적 오염제거 평가와 육안에 의한 주관적 오염제거 평가를 비교하기 위한 것이다. 본 연구를 위해 백색의 순면직물과 65%/35% 폴리에스테르/면직물 시료에 9가지의 오염을 각각 처리한 오염포를 제작한 후, 세탁 실험을 하였다. 주관적 오염제거의 평가는 오염시키지 않은 포를 기준시료로 하여 오염포와 같은 조건으로 세탁한 후, 오염제거도를 AATCC Gray Scale for Staining으로 평가하였다. 세탁 후 오염제거도를 객관적으로 평가하기 위해서 각 시료의 K/S values, CIELAB, CMC, ASTM E313 Whiteness Index(WI), ASTM E313 Yellowness Index, and CIE tristimulus values를 구하였고. 세탁에 의한 control 시료의 반사율 변화에 대한 오염포의 반사율 변화를 비교한 오염제거율(PSR)을 구하였다 육안에 의한 주관적 평가 결과와 기계에 의한 객관적 평가의 결과와의 관계를 파악하고자 상관분석을 실시하였다. 본 연구 결과, 주관적 평가와 객관적 평가사이에 유의적인 상관관계가 확인되었으며, 주관적 평가 결과 중 WI가 주관적 평가 결과와 가장 상관관계가 높았으며, PSR과 주관적 평가 결과와의 상관이 상대적으로 가장 낮은 것으로 나타났다. 따라서 백색포의 오염 판정이 필요한 산업체에서 현재 많이 사용하고있는 PSR보다는 WI나 다른 색차를 이용하여 객관적 오염 평가를 하는 것이 주관적인 오염평가 결과에 더 근접할 수 있음을 알 수 있었다.