• 대한불안의학회지
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• 제17권2호
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• pp.84-91
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• 2021

Objective : Mismatch negativity (MMN) is known to reflect several abnormalities of cognitive functioning. This study is aimed to investigate the differences in MMN among major depressive disorder (MDD) patients with or without suicidal ideation. Methods : Sixty-seven patients with MDD were recruited into this study. MMN was measured by a 64-channel electroencephalography (EEG) using oddball paradigm over the front-central area. Clinical characteristics were assessed using the Beck Anxiety Inventory (BAI), the Beck Depression Inventory-II (BDI-II), and the Beck Scale for Suicide ideation (SSI-BECK). Patients were divided into two groups, no suicidal ideation (N=12) and suicidal ideation (N=55), depending on the presence of suicide ideation in SSI-BECK questionnaires. Results : The MMN latencies were significantly longer in the MDD patients with suicidal ideation than in the MDD patents without suicidal ideation (p<0.05). The MMN amplitudes were not significantly different between the two groups. Conclusion : Suicidal ideation may be associated with longer MMN latencies, and it suggests that MMN may play a potential role in assessing the suicidal risk among MDD patients.

• 항공우주시스템공학회지
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• 제13권2호
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• pp.19-25
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• 2019

구조물의 충격 위치 검출을 위해 본 연구그룹에서는 압전 페인트 센서를 연구하고 있다. 압전 페인트는 고주파 신호 및 충격에 민감한 특성으로 인하여 충격 감지에 사용할 수 있다. 또한, 압전 페인트 센서는 세라믹 센서가 적용될 수 없는 곡선 또는 복잡한 구조에 코팅될 수 있으며 외부 전원을 필요로 하지 않는다. 충격을 검출하기 위해 모자이크 패턴 전극을 시험편 위에 코팅하였고, 충격 신호는 충격이 발생한 전극부에서 얻을 수 있었다. 보다 더 정확한 충격 위치 검출을 위해서는 전극을 더 많은 부분으로 나누어 해당 전극부로부터 충격 데이터 수집이 필요하다. 본 연구에서는, 데이터 수집을 위하여 가볍고 저렴한 간단한 멀티채널 데이터 수집 시스템을 개발하였다. ARM Cortex-M3의 UART 통신을 이용하여 총 4채널의 데이터를 수집하였다.

• 한국콘텐츠학회논문지
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• 제21권2호
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• pp.652-666
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• 2021

유튜브 채널에서 중국 관련 코로나19 정보의 확산과정을 네트워크 분석을 통해 알아봤다. 중국 관련 코로나19 정보를 사실 정보와 허위정보로 구분했고, 사실 정보는 긍정적, 부정적으로 분류했다. 네트워크 분석결과 부정적 정보와 허위정보가 많았고, 긍정적 정보는 가장 적었다. 허위정보 중에서 우한연구소 유출설 관련 동영상이 많았고, 유전자 조작설 관련 동영상의 조회 수와 매개 중심성 평균이 가장 컸다. 언론사 채널은 허위정보에 대한 팩트 체크보다 있는 그대로 전달하는데 그쳤다. 중국 관련 코로나19 동영상 중 부정적 정보와 허위정보가 많았다는 것은 중국 관련 비판적이거나 자극적인 내용이 유튜버의 관심을 끌었다는 것을 보여준다. 결론적으로 유튜브 채널의 허위정보는 이용자들이 유사한 주제의 동영상을 시청하게 하는 확산 효과를 가져왔다.

• 한국지형학회지
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• 제25권2호
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• pp.15-29
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• 2018

The sediment transport process in a river reflects the process of geomorphological change in the watershed, influencesthe river bed variation and the river channel migration, and is a parametric phenomenon that exhibits a dynamic self-adjusting process. Sediment load is divided into bedload and suspended load depending on the dominant mechanism. Quantitative sediment load is important information for solving river problems. Because it is difficult and time consuming to measure bedload, compared to that ofsuspended load, data on the sediment transport load and the research required for the gravel-bed rivers are insufficient. This study is to analyze the ratio of the bedload to the total sediment load in gravel-bed rivers. The sediment load ratio in gravel-bed rivers increases with the flow rate per unit width, and the rate of the bedload varies more rapidly than the suspended load. The sediment transport efficiency coefficient has been affected by the ratio of the flow depth to the mean diameter of particles and has been dependent on the shear velocity Reynolds number. So $A^{\ast}$ and $B^{\ast}$ are introduced to compensate for the uncertainties such as bed materials, sediment transport, and flow velocity distribution, and the coefficient of bedload ratio has been presented. For the sediment load data in experimental channels and rivers, A* was 3.1. The dominant variables of $B^{\ast}$ were $u_*d_m/{\nu}$ in the gravel-bed and h/dm in the sand-bed. When $B^{\ast}$ the is the same, in the experimental channels the coefficient of bedload ratio was affected by the bed forms, but in the rivers it was of little difference between the gravel-bed and sand-bed.

• 한국수자원학회논문집
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• 제55권7호
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• pp.557-563
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• 2022

수위-유량관계곡선식은 측정된 수위를 유량으로 변환하는 데 필요하며 유량측정 성과를 이용하여 개발된다. 수위-유량관계곡선식 개발에서 구간분리 위치는 수리적 특성과 하천단면 형상 등을 고려하여 결정되며 이 과정에서 개발자의 주관적인 판단이 개입되는 경우가 있다. 구간분리 위치는 수위-유량관계곡선식의 전체적인 형태를 결정할 정도로 중요하고 잘못된 구간분리는 수위-유량관계곡선식의 오류를 유발하게 되며 특히 외삽구간에서 큰 오류가 발생할 가능성이 높다. 또한 예산, 인력 등의 문제로 많지 않은 유량측정성과로 정확한 수위-유량관계곡선식을 개발하려면 하천의 단면형상 및 흐름 특성 등 수리적인 요소를 고려하여 구간을 분할해야 한다. 본 연구에서는 기존의 수위-평균유속, 수위-단면적, 수위-${\sqrt{Q}}$ 등 수리적 검토 방법을 살펴보고 이를 보완하여 구간분리 위치 결정에 있어서 주관성을 배제하고자 하였다. 구간분리 위치에 대한 적절성을 수위-유량관계곡선식 지수 (c)의 물리적인 의미를 고려하여 이를 검토하였다.

• 한국콘텐츠학회논문지
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• 제22권4호
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• pp.479-487
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• 2022

본 연구는 국내 대표적인 중국어 교육 관련 유튜브 채널들을 중심으로 유튜브 중국어 교육 채널에 속한 동영상 콘텐츠를 내적 구성요소와 외적 구성요소와 나누어 분석하였다. 분석 결과 유튜브 중국어 교육 채널 콘텐츠 들에서는 상호작용, 기타 이용의 편의성, 멀티미디어 자료 활용 등 외적 구성요소와 학습 목표 및 내용, 강의 방식, 강의 분량, 학습 자료, 학습 평가 및 연습, 교육과정의 연계 및 체계성 등 내적 구성요소가 다양한 형태로 나타나고 있었다. 유튜브 중국어 교육 채널 콘텐츠들에서는 전통적인 교실 수업이나 면대면 수업에서 나타나지 않는 웹 기반 교육 자료의 특징들을 보여 주었으며 이를 통하여 기존 교실 수업의 부족함을 채울 수 있는 새로운 교육 매체로써 역할을 할 수 있는 가능성을 보여 주었다. 그럼에도 불구하고 상당수의 유튜브 중국어 교육 채널 콘텐츠들의 내적 구성요소와 외적 구성요소에서는 여전히 개선해야 할 문제점이 나타났으며 이러한 문제점들은 동영상 콘텐츠를 제작하는 교수자 개인의 노력과 관심뿐만 아니라 인적, 물적 자원이 필요할 것으로 보인다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권3호
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• pp.1051-1077
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• 2021

The secure communication of information is a major concern over the internet. The information must be protected before transmitting over a communication channel to avoid security violations. In this paper, a new hybrid method called compressed encrypted data embedding (CEDE) is proposed. In CEDE, the secret information is first compressed with Lempel Ziv Welch (LZW) compression algorithm. Then, the compressed secret information is encrypted using the Advanced Encryption Standard (AES) symmetric block cipher. In the last step, the encrypted information is embedded into an image of size 512 × 512 pixels by using image steganography. In the steganographic technique, the compressed and encrypted secret data bits are divided into pairs of two bits and pixels of the cover image are also arranged in four pairs. The four pairs of secret data are compared with the respective four pairs of each cover pixel which leads to sixteen possibilities of matching in between secret data pairs and pairs of cover pixels. The least significant bits (LSBs) of current and imminent pixels are modified according to the matching case number. The proposed technique provides double-folded security and the results show that stego image carries a high capacity of secret data with adequate peak signal to noise ratio (PSNR) and lower mean square error (MSE) when compared with existing methods in the literature.

• 한국농공학회논문집
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• 제64권3호
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• pp.63-73
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• 2022

A more accurate understanding of the irrigation water supply is necessary for efficient agricultural water management. Although we measure water levels in an irrigation canal using ultrasonic water level gauges, some errors occur due to malfunctions or the surrounding environment. This study aims to apply CNN (Convolutional Neural Network) Deep-learning-based image classification and segmentation models to the irrigation canal's CCTV (Closed-Circuit Television) images. The CCTV images were acquired from the irrigation canal of the agricultural reservoir in Cheorwon-gun, Gangwon-do. We used the ResNet-50 model for the image classification model and the U-Net model for the image segmentation model. Using the Natural Breaks algorithm, we divided water level data into 2, 4, and 8 groups for image classification models. The classification models of 2, 4, and 8 groups showed the accuracy of 1.000, 0.987, and 0.634, respectively. The image segmentation model showed a Dice score of 0.998 and predicted water levels showed R² of 0.97 and MAE (Mean Absolute Error) of 0.02 m. The image classification models can be applied to the automatic gate-controller at four divisions of water levels. Also, the image segmentation model results can be applied to the alternative measurement for ultrasonic water gauges. We expect that the results of this study can provide a more scientific and efficient approach for agricultural water management.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권4호
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• pp.1392-1413
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• 2022

In order to meet the rapid development of the unmanned aerial vehicle (UAV) communication needs, cooperative spectrum sensing (CSS) helps to identify unused spectrum for the primary users (PU). However, multi-UAV mode (MUM) requires the large communication resource in a cognitive UAV network, resulting in a severe decline of spectrum efficiency (SE) and energy efficiency (EE) and increase of energy consumption (EC). On this account, we extend the traditional 2D spectrum space to 3D spectrum space for the UAV network scenario and enable UAVs to proceed with spectrum sensing behaviors in this paper, and propose a novel multi-slot mode (MSM), in which the sensing slot is divided into multiple mini-slots within a UAV. Then, the CSS process is developed into a composite hypothesis testing problem. Furthermore, to improve SE and EE and reduce EC, we use the sequential detection to make a global decision about the PU channel status. Based on this, we also consider a truncation scenario of the sequential detection under the sensing delay constraint, and further derive a closed-form performance expression, in terms of the CSS performance and cooperative efficiency. At last, the simulation results verify that the performance and cooperative efficiency of MSM outperforms that of the traditional MUM in a low EC.

• 한국산업융합학회 논문집
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• 제26권4_2호
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• pp.623-628
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• 2023

The purpose of this study was to evaluate the fracture strength and removal torque value (RTV) of a conventional angled abutment and a newly developed angled abutment (Beauty up abutment) with an angulated screw access hole. Each abutment was divided into a control group and an experimental group (n = 20, respectively). To measure the fracture strength, the abutment was connected to the internal hex implant with 30 Ncm torque, and a load was applied at 30 degree angle with cross-head speed of 1 mm/min using a universal testing machine according to the ISO 14801:2016 standard. To measure RTV, each abutment was fastened to the implant with 30 Ncm torque. Retightening was performed after 10 minutes, and initial RTV was measured with a digital torque gauge. After retightening, a load of 250 N was applied to the abutment at a 30 degree angle using a chewing simulator. After a total of 100,000 repeated loads, RTV was measured. Statistical analysis was performed using Wilcoxon signed rank test and Mann-Whitney U test (α = .05). The fracture strength of the experimental group was statistically significantly lower than that of the control group (P = .009). There was no significant difference between initial RTV and post-loading RTV between the experimental group and the control group (P = .753, P = .527, respectively), and cyclic loading did not significantly affect RTV in both groups (P = .078).