• 비파괴검사학회지
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• 제30권1호
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• pp.46-53
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• 2010

항공기용 복합재료 내부 여러 층에서 발생하는 박리를 정량적으로 평가하기 위한 X-ray 후방산란 검사장치를 개발하였다. 복합재료 두께방향으로의 역산란 밀도변화로부터 층간 박리를 검사하는 슬릿 방식의 카메라와 컴퓨터로 제어되는 X-ray 선원, 그리고 센서로 구성되는 X-ray 후방산란장치를 제작하여 그 성능을 충격하중에 의해 만들어진 인공결함시편을 이용해 검증하였다. 결함평가를 위해 복합재료내 산란장의 크기를 이론적으로 계산하는 수학적 해석 모델을 볼츠만 방정식을 이용하여 제안하였으며 적응필터 알고리즘을 사용하여 산란 노이즈를 최소화 하였다. 다중 박리 결함을 X-ray 후방산란장치를 통해 효과적으로 검출하였으며, 박리 위치와 박리 상태를 모두 정확하게 검사할 수 있음을 실험을 통해 확인하였다.

• 한국해양학회지
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• 제13권1호
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• pp.1-8
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• 1978

지층 속에 남아 있는 퇴적구조는 퇴적환경을 추정하는 중요한 지표가 된다. 암상이나 화석과는 달리 퇴적구조는 퇴적 현장에서 형성되고 외부로부터 전입될 수는 없기 때문이다. 퇴적구조는 기존 암석이나 퇴적층이 잘 노출되어 있는 노두에서는 쉽사리 연구될 수 있으나 지표면하에 존재하는 퇴적층 구조는 직접적인 방법으로서는 시추에 의해서만 연구될 수 있다. 그러나 지하층을 시추하기에는 시간적 경제적으로 많은 부담이 따르기 때문에 개략조사의 단계에서는 바람직하지 못하다. 탄성파 탐사 방법이 발전됨에 따라 비교적 장파장을 사용하여 얕은 지하층을 탐사할 때 대체적인 지층구조를 파악할 수가 있게 되었다. 이는 각 퇴적층이 Acoustic Impedance를 달리하기 때문에 나타나는 결과이다. 분해능이 50cm정도의 탄성파를 이용한 탄성파 탐사에서 얻어진 탄성파 반사 기록은 이 분해능 범위보다 큰 규모의 해저지층구조를 어느 정도 잘 반영해 준다.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2007년도 가을 학술발표논문집 Vol.34 No.2 (D)
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• pp.240-243
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• 2007

Geographic routing has been considered as an efficient simple, and scalable routing protocol for wireless sensor networks since it exploits pure location information instead of global topology information to route data packets. Geographic routing requires the sources nodes to be aware of the location of the sinks. In this paper, we propose a scheme named Sink Location Service for geographic routing in wireless Sensor Networks, in which the source nodes can get and update the location of sinks with low overhead. In this scheme, a source and a sink send data announcement and query messages along two paths respectively by geographic routing. The node located on the crossing point of the two paths informs the source about the location of the sink. Then the source can send data packet to the sink by geographic routing. How to guarantee that these two paths have at least one crossing point in any irregular profile of sensor network is the challenge of this paper.

• 지구물리와물리탐사
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• 제12권1호
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• pp.99-104
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• 2009

본 연구에서는 천부 토양층의 2차원 불균질 S파 단면을 결정하기 위해 천부 굴절법 탐사로부터 얻은 SH파 자료에 대한 파형역산 기법을 제안한다. 2차원 매질에서 SH파의 전파를 모사하기 위해 2.5차원 파동 방정식을 사용한다. 합성탄성파를 계산하기 위해 공간축으로 4차, 시간축으로 2차 근사한 staggered grid 유한차분법을 사용하여 파동 방정식을 푼다. 계산된 파형과 측정 파형의 잔여오차로 정의되는 목적함수를 하이브리드 발견적 탐색기법에 의해 최소화한다. 2차원 지하구조 모형은 각기 다른 심도 경계면을 갖는 블록과 블록 내부의 S파 속도에 의해 매개화한다. 수치실험은 암영층파 불규칙한 경계를 갖는 모델에 대해 백색잡음을 추가한 합성 SH파 자료를 이용하여 수행하였다. 지표 굴절법 자료로부터 암영층을 포함한 구조를 적절한 계산시간 내에 영상화할 수 있었다

• Restorative Dentistry and Endodontics
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• 제25권1호
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• pp.116-122
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• 2000

On the instrumented root canal wall, amorphous, irregular smear layer can be observed with Scanning Electron Microscope(SEM). The purpose of this study was to evaluate the effect of the presence or absence of smear layer on the adhesion of Staphylococcus aureus to the dentin of the root canal. Human incisors, extracted within 7 days, with no caries, no fracture, no calcification of canal, were selected. After cutting crown portion at cemento-enamel junction, root canal preparation was done by modified crown-down technique using Profile and Gates - Glidden Drill. During canal preparation, 10ml physiologic saline solution(group1&3) or 10ml 3.5% NaOCl(group2&4) was used as irrigation solution. And 10ml physiologic saline solution(group1&3) or 10ml 0.5M EDTA(group2&4) was applicated for final flush. After vertical sectioning and ethylene oxide gas sterilization, samples(group1&2) were immersed into BHIYHM broth inoculated with Staphylococcus aureus (ATCC 31153) and incubated for 3hrs at $37^{\circ}C$. All samples were prepared for and observed with SEM(JEOL JSM840S). The data were analyzed by Mann-Whitney rank sum test. The conclusions are as follows ; 1. Smear layer covers entire root canal surface after root canal preparation. 2. Smear layer has been removed away and the entrances of dentinal tubules have opened widely, when applying 0.5M EDTA and 3.5% NaOCl. 3. A significantly higher number of bacteria were adhered to the root canal dentin without smear layer(p<0.0001). 4. Smear layer produced during root canal preparation impedes bacterial adhesion and colonization to dentin matrix, therefore inhibits canal reinfection.

• 비파괴검사학회지
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• 제20권6호
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• pp.545-554
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• 2000

충격에 의해 복합 재료 내에 발생하는 층간 박리를 정량적으로 평가하기 위한 비파괴 방법중에서 Compton X-ray 역산란 기술은 초음파에 비해 비접촉식이며 박리 층간의 상호간섭이 없어 복합재료 판면의 박리 층의 위치와 크기를 검사하는데 효과적인 방법으로 사용되어 왔다. 그러나 X-ray역산란 기술에 있어서 복합재료의 박리 층과 같은 미세한 결함의 측정을 위해 측정 정도를 높이면 역산란 양의 감소로 인해 신호 대 잡음 비(SNR)가 급격히 감소하여 결함검출 가능성이 크게 저하된다. 본 논문에서는 복합재료의 특성을 고려한 X-ray 역산란 모델을 기초로 적응필터를 사용하여 결함신호를 비선형 감쇄, 빔 경화(X-ray hardening), 비균질 특성과 같은 잡음 신호로부터 분리, 추출하는 방법을 제시하였다. 이렇게 분리된 결함신호로부터 정량적인 결함(박리)의 위치와 크기를 수학적 산란 모델과의 비교를 통해 최소 자승법을 이용하여 결정하였다.

• 설비공학논문집
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• 제20권5호
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• pp.304-313
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• 2008

This paper investigates the indoor-air-quality (IAQ) characteristics of the interior space equipped with system air-conditioner. The behaviors of individual variables such as temperature, humidity and concentration of carbon dioxide ($CO_2$) that influence on IAQ of the interior space were characterized under various cooling conditions by numerical and experimental studies. The numerical analysis predicting the temperature behavior of the interior space was conducted, and its results showed a good agreement with the experimental ones. The $CO_2$ concentration and humidity were measured and their time dependent behaviors were monitored and analyzed. From the results, it was found that there existed the differences of the time-dependent behaviors of IAQ variables according to the locations. In addition, it is demonstrated that the large discharge angle of $45^{\circ}$ made the temperature profile more irregular and the high discharge flow of 5.34 m/s produced similar temperature profiles at three different sensing locations. Finally, the humidity of interior space was less sensitive to the changes of the air cooling conditions than the case of temperature and the $CO_2$ concentration increase mainly depended on the number of individuals inside the space.

• 한국의학물리학회지:의학물리
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• 제30권1호
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• pp.32-38
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• 2019

Purpose: The objective of this study is to evaluate the geometrical accuracy of a patient-specific bolus based on a three-dimensional (3D) printed mold and casting method. Materials and Methods: Three breast cancer patients undergoing treatment for a superficial region were scanned using computed tomography (CT) and a designed bolus structure through a treatment planning system (TPS). For the fabrication of patient-specific bolus, we cast harmless certified silicone into 3D printed molds. The produced bolus was also imaged using CT under the same conditions as the patient CT to acquire its geometrical shape. We compared the shapes of the produced bolus with the planned bolus structure from the TPS by measuring the average distance between two structures after a surface registration. Results and Conclusions: The result of the average difference in distance was within 1 mm and, as the worst case, the absolute difference did not exceed ${\pm}2mm$. The result of the geometric difference in the cross-section profile of each bolus was approximately 1 mm, which is a similar property of the average difference in distance. This discrepancy was negligible in affecting the dose reduction. The proposed fabrication of patient-specific bolus is useful for radiation therapy in the treatment of superficial regions, particularly those with an irregular shape.

• Steel and Composite Structures
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• 제39권1호
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• pp.65-80
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• 2021

Irregularities of a building in plan and elevation, which results in the change in stiffness on different floors highly affect the seismic performance and resistance of a structure. This study motivated to investigate the seismic responses of high-rise steel-frame buildings of twelve stories with various stiffness irregularities. The building has five spans of 3200 mm distance in both X- and Z-directions in the plan. The design package SAP2000 was adopted for the design of beams and columns and resulted in the profile IPE500 for the beams of all floors and box sections for columns. The column cross-section dimensions vary concerning the number of the story; one to three: 0.50×0.50×0.05m, four to seven: 0.45×0.45×0.05 m, and eight to twelve: 0.40×0.40×0.05 m. Real recorded ground accelerations obtained from the Vrancea earthquake in Romania together with dead and live loads corresponding to each story were considered for the applied load. The model was validated by comparing the results of the current method and literature considering a three-bay steel moment-resisting frame of eight-story height subject to seismic load. To investigate the seismic performance of the buildings, the time-history analysis was performed using ABAQUS. Deformed shapes corresponding to negative and positive peaks were provided followed by the story drifts and fragility curves which were used to examine the probability of collapse of the building. From the results, it was concluded that regular buildings provided a seismic performance much better than irregular buildings. Furthermore, it was observed that building with torsional irregularity was more vulnerable to seismic failure.

• Journal of Periodontal and Implant Science
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• 제42권3호
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• pp.88-94
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• 2012

Purpose: The use of appropriate instruments to clean surfaces with minimal change, is critical for the successful maintenance of a dental implant. However, there is no consensus about the type and methodology for such instruments. The aim of this study was to characterize changes in the roughness of titanium surfaces treated by various scaling instruments. Methods: Thirty-seven identical disks (5 mm in diameter) were investigated in this study. The specimens were divided into eight groups according to the types of instrumentation and the angle of application. Ultrasonic scaling systems were applied on a titanium disk to simulate standard clinical conditions. The equipment included a piezoelectric ultrasonic scaler with a newly developed metallic tip (NS group), a piezoelectric ultrasonic scaler with a conventional tip (CS group), a piezoelectric root planer ultrasonic scaler with a conventional tip (PR group), and a plastic hand curette (PH group). In addition, the sites treated using piezoelectric ultrasonic scaler systems were divided two sub-groups: 15 and 45 degrees. The treated titanium surfaces were observed by scanning electron microscopy (SEM), and the average surface roughness (Ra) and mean roughness profile depth (Rz) were measured with a profilometer. Results: SEM no significant changes in the titanium surfaces in the NS group, regardless of the angle of application. The PH group also showed no marked changes to the titanium surface, although some smoothening was observed. All CS and PR sites lost their original texture and showed irregular surfaces in SEM analysis. The profilometer analysis demonstrated that the roughness values (Ra and Rz) of the titanium surfaces increased in all, except the PH and NS groups, which showed roughness decreases relative to the untreated control group. The Ra value differed significantly between the NS and PR groups (P<0.05). Conclusions: The results of this study indicated that changes in or damage to titanium surfaces might be more affected by the hardness of the scaler tip than by the application method. Within the limitations of this study, the newly developed metallic scaler tip might be especially suitable for peri-implant surface decontamination, due to its limited effects on the titanium surface.