• Advances in aircraft and spacecraft science
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• 제4권1호
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• pp.53-64
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• 2017

Aerospace Launch Vehicles (ALV) are generally designed with high reliability to operate in complete security through fault avoidance practices. However, in spite of such precaution, fault occurring is inevitable. Hence, there is a requirement for on-board fault recovery without significant degradation in the ALV performance. The present study develops an advanced fault recovery strategy to improve the reliability of an Aerospace Launch Vehicle (ALV) navigation system. The proposed strategy contains fault detection features and can reconfigure the system against common faults in the ALV navigation system. For this purpose, fault recovery system is constructed to detect and reconfigure normal navigation faults based on the sliding mode observer (SMO) theory. In the face of pitch channel sensor failure, the original gyro faults are reconstructed using SMO theory and by correcting the faulty measurement, the pitch-rate gyroscope output is constructed to provide fault tolerant navigation solution. The novel aspect of the paper is employing SMO as an online tuning of analytical fault recovery solution against unforeseen variations due to its hardware/software property. In this regard, a nonlinear model of the ALV is simulated using specific navigation failures and the results verified the feasibility of the proposed system. Simulation results and sensitivity analysis show that the proposed techniques can produce more effective estimation results than those of the previous techniques, against sensor failures.

• 한국정보과학회논문지:컴퓨팅의 실제 및 레터
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• 제16권7호
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• pp.804-808
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• 2010

본 논문에서는 네트워크에 분포된 센서 노드의 밀도와 노드의 제한된 에너지를 고려하여 데이터를 전송하는 Restricted Angle-control Flooding기법을 제안한다. 제안하는 기법은 특히 목적지에 가까워질수록 데이터 전송에 참여하는 노드의 수를 효율적으로 줄임으로써 불필요한 Broadcast 메시지를 제한하여 에너지 효율성을 높일 수 있으며, 노드의 Failure나 네트워크의 장애로 인한 Hole 발생시 Hole의 판단 기준에 따라 기존의 Flooding 방식 혹은 Forwarding area를 넓히는 Hole-Detection을 통하여 메시지 전송의 효율성을 높인다. 성능 평가를 통하여 노드 수가 증가할수록 기존의 Flooding에 비하여 메시지 전송시 소비되는 노드의 에너지와 전송률, 네트워크의 Lifetime면에서 우수하다는 것을 보여준다.

• Design & Manufacturing
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• 제15권4호
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• pp.51-56
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• 2021

Piercing is the process of shearing a circular hole in sheet metal, whose high shear force makes it difficult to secure the durability of tools. In addition, uneven clearance between tools due to poor alignment of the piercing punch causes accelerated die wear and breakage of the tool. This study reviewed the feasibility of in-situ determining alignment failure during the piercing process by analyzing the signal deviation of a bolt-type piezo sensor installed inside the tool whose alignment level was controlled. Finite element analysis was performed to select the optimal sensor location on the piercing tool for sensitive detection of process signals. A well-aligned piercing process results in uniform deformation in the circumferential direction, and shearing is completed at a stroke similar to the sheet thickness. Afterward, a sharp decrease in shear load is observed. The misaligned piecing punch leads to a gradual decrease in the load after the maximum shear load. This gradual decrease is due to the progressive shear deformation that proceeds in the circumferential direction after the initial crack occurs at the narrow clearance site. Therefore, analyzing the stroke at which the maximum shear load occurs and the load reduction rate after that could detect the misalignment of the piercing punch in real-time.

• 한국정보통신학회논문지
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• 제21권10호
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• pp.1892-1897
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• 2017

본 논문은 붙어 있는 손가락들을 가진 손을 대상으로 한 손가락 개수 알고리즘을 제안하고 있다. 제안된 알고리즘은 손가락 사이에 필연적으로 직선형 그림자가 발생한다는 사실을 기반으로 한다. 이 알고리즘은 효율적인 그림자 검출을 위해 손 영역을 엄지손가락 영역과 네 손가락 영역으로 구분하고, 각 영역에서 경계 영상을 생성한다. 각 경계 영상에 직선 검출과 투영 기법을 적용하므로 투영 곡선들이 생성되고, 곡선들의 피크들은 손가락 그림자의 후보들로 검출된다. 그러고는 검출된 피크들에서 손가락 그림자에 의한 피크들만 추출되고 개수된다. 붙어 있는 손가락으로 다양한 형상을 표현하는 손 영상들을 대상으로 한 손가락 개수 실험에서 손가락 수에 따른 개수 성공률이 83.3%에서 100%이고, 전체적으로 93.1%이다. 또한 통제된 조건하에서 손 영상이 생성된다면 실패한 경우들이 충분히 개선될 수 있음을 보여주고 있다.

• 해양환경안전학회지
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• 제29권2호
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• pp.139-146
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• 2023

양식장 부표 등과 같은 해상의 소형 장애물을 탐지하고 거리와 방위를 시각화시켜 주는 해상물체탐지시스템은 선체운동으로 인한 오차를 보정하기 위해 3축 짐벌이 장착되어 있지만, 파도 등에 의한 카메라와 해상물체의 상하운동으로 발생하는 거리오차를 보정하지 못하는 한계가 있다. 이에 본 연구에서는 외부환경에 따른 수면의 움직임으로 발생하는 해상물체탐지시스템의 거리오차를 분석하고, 이를 평균필터와 이동평균필터로 보정하고자 한다. 가우시안 표준정규분포를 따르는 난수를 이미지 좌표에 가감하여 불규칙파에 의한 부표의 상승 또는 하강을 재현하였다. 이미지 좌표의 변화에 따른 계산거리, 평균필터와 이동평균필터를 통한 예측거리 그리고 레이저 거리측정기에 의한 실측거리를 비교하였다. phase 1,2에서 불규칙파에 의한 이미지 좌표의 변화로 오차율이 최대 98.5%로 증가하였지만, 이동평균필터를 사용함으로써 오차율은 16.3%로 감소하였다. 오차보정 능력은 평균필터가 더 좋았지만 거리변화에 반응하지 못하는 한계가 있었다. 따라서 해상물체탐지시스템 거리오차 보정을 위해 이동평균필터를 사용함으로써 실시간 거리변화에 반응하고 오차율을 크게 개선할 수 있을 것으로 판단된다.

• Journal of Radiation Protection and Research
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• 제44권3호
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• pp.97-102
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• 2019

Background: Dose rate meters are the most widely used, and perhaps one of the most important tools for the measurement of ionising radiation. They are often the first, or only, device available to a user for an instant check of radiation dose at a certain location. Throughout the world, radiation safety practices rely strongly on the output of these dose rate meters. But how well do we know the quality of their output? Materials and Methods: This review is based on the measurements 1,158 commercially available dose rate meters of 116 different makes and models. Expected versus the displayed dose patterns and consistency was checked at various dose rates between $5{\mu}Gy{\cdot}h^{-1}$ and $2mGy{\cdot}h^{-1}$. Samples of these meters were then selected for further investigation and were exposed to radiation sources covering photon energies from 50 keV to 1.5 MeV. The effect of detector orientation on its reading was also investigated. Rather than focusing on the angular response distribution that is often reported by the manufacturer of the device, this study focussed on the design ergonomics i.e. the angles that the operator will realistically use to measure a dose rate. Results and Discussion: This review shows the scope and boundaries of the ionising radiation dose rate estimations that are made using commonly available meters. Observations showed both inter and intra make and model variations, occasional cases of instrument failure, instrument walk away, and erroneous response. Conclusion: The results indicate the significance of selecting and maintaining suitable monitors for specific applications in radiation safety.

• 대한의용생체공학회:의공학회지
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• 제37권1호
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• pp.31-38
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• 2016

For the patients with bladder dysfunction, measurement of urine volume inside the bladder is very critical to avoid bladder failure. In measuring urine volume inside a bladder, low-resolution 3D ultrasound images are widely used. However, urine volume estimation from 3D ultrasound images is prone to big errors and inconsistency because of low spatial resolution and low signal-to-noise ratio of ultrasound images. We developed a new robust volume estimation algorithm which is not computationally expensive. We tested the algorithm on a lab-built ultrasound bladder phantom and volunteers. The average error rate of the human bladder volume estimation was 5.9% which was better than the commercial machine.

• 디지털산업정보학회논문지
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• 제7권4호
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• pp.31-37
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• 2011

Recently, MANET(Mobile Ad-hoc Network) is developing increasingly in the wireless network. MANET has weakness because phases change frequently and MANET doesn't have middle management system. Every node which consists of MANET has to perform data forwarding, but traceback is not reliable if these nodes do malicious action owing to attack. It also is not easy to find location of attacker when it is attacked as moving of nodes. In this paper, we propose a hierarchical-based traceback method that reduce waste of memory and can manage path information efficiently. In order to manage trace path information and reduce using resource in the cluster head after network is formed to cluster, method which recomposes the path efficiently is proposed. Proposed method in this paper can reduce path trace failure rate remarkably due to moving of nodes. It can also reduce the cost for traceback and time it takes to collect information.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권8호
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• pp.343-349
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• 2005

The gas in oil analysis of transformer is the most widely used technology for diagnosis of transformer in the world. It has brought excellent results to prevention of transformer failure. The criteria for maintenance and judgement, however, is still required continuous supplement to improve the accuracy of the diagnosis on the basis of accumulated data of gas analysis and investigations in the transformer In this study, the relationship between the detection rate of the defects and the source of troubles are analyzed according to the investigation in the transformer, which was conducted by KEPCO in 2004. As a result, the validity of the criteria being used at present was examined thoroughly.

• Journal of Cardiovascular Imaging
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• 제31권4호
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• pp.169-177
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• 2023

BACKGROUND: Acute worsening of cardiac function frequently leads to kidney dysfunction. This study aimed to identify clinical and imaging parameters associated with impaired kidney function in patients with acute decompensated heart failure with reduced ejection fraction (HFrEF). METHODS: Data from 131 patients hospitalized with acute decompensated HFrEF (left ventricular ejection fraction, < 40%) were analyzed. Patients were divided into two groups according to the glomerular filtration rate (GFR) at admission (those with preserved kidney function [GFR ≥ 60 mL/min/1.73 m²] and those with reduced kidney function [GFR < 60 mL/min/1.73 m²]). Various echocardiographic parameters and perirenal fat thicknesses were assessed by computed tomography. RESULTS: There were 71 patients with preserved kidney function and 60 patients with reduced kidney function. Increased age (odds ratio [OR], 1.07; 95% confidence interval [CI], 1.04-1.12; p = 0.005), increased log N-terminal pro b-type natriuretic peptide (OR, 1.74; 95% CI, 1.14-2.66; p = 0.010), and increased perirenal fat thickness (OR, 1.19; 95% CI, 1.10-1.29; p < 0.001) were independently associated with reduced kidney function, even after adjusting for variable clinical and echocardiographic parameters. The optimal average perirenal fat thickness cut-off value of > 12 mm had a sensitivity of 55% and specificity of 83% for kidney dysfunction prediction. CONCLUSIONS: Thick perirenal fat was independently associated with impaired kidney function in patients hospitalized for acute decompensated HFrEF. Measurement of perirenal fat thickness may be a promising imaging marker for the detection of HFrEF patients who are more susceptible to kidney dysfunction.