진동 생성 메커니즘을 고려한 초기 결함 단계의 베어링 진단 연구

학위논문(박사) -- 서울대학교대학원 : 공과대학 기계항공공학부, 2023. 2. 윤병동.The failure of rolling element bearings is a common fault in rotating machines. These failures can have catastrophic consequences, including fatal injuries and significant financial losses. To mitigate these risks, researchers have explored various ways to detect and prevent bearing failures as early as possible. One promising approach is the use of condition monitoring data; in this approach, vibration data has been found to be particularly effective for identifying and preventing potential failures. However, the use of vibration signals to diagnose bearings at the incipient fault stage is a challenging task, in part due to the gap between the controlled conditions under which research data is often generated and the actual field conditions in which these bearings operate. In particular, fault-related signals are weak and nonstationary; further, they are usually obscured by noise that arises from environmental factors. Additionally, these signals may be complicated or modulated, making them difficult to discern. To properly address these research issues, this dissertation aims at advancing two research thrusts focused on developing techniques for modeling and analyzing vibration signals based on physical phenomena. In Research Thrust 1, a quasi-periodic impulse train model with an impact force function is suggested to brtidge the gap between theory and reality. In this research, a pseudo second-order cyclostationary signal is modeled using the quasi-periodic impulse train model. In order to simulate the dynamic response of a system, considering the physical behaviors in bearings, the impact force function that reflects the change in contact stress is used. Finally, the proposed model is validated by performing signal processing on the synthesized signal, including simulation of the proposed model. The result confirm that an appropriate preprocessing process is essential to diagnose bearing failure at the incipient failure stage, further, that finding the frequency band that contains the failure information is essential for performance improvement. In Research Thrust 2, a new feature extraction method is proposed for bearing diagnosis using vibration signals, namely the linear power normalized cepstral coefficients (LPNCC). The proposed approach is designed to enhance the bearing signal, which is buried in noise that arises from environmental effects, and which contains mechanical phenomena. The proposed method consists of two sequentially executed steps: 1) extraction of the LPNCC and 2) demodulation analysis that is performed by examining the squared envelope spectra (SES). Combined, this approach is called LPNCC-SES. The performance of the proposed method is examined by applying it to both simulation data and experimental cases. The results show a high level of accuracy and robustness in the diagnostic capabilities of the method, making it suitable for use in maintenance and diagnostic routines.구름 베어링은 회전 기계 및 왕복동 기계의 핵심적인 요소부품으로 회전하거나 진동하는 구조를 지지하며 구성품 간의 하중을 전달한다. 따라서 구름 베어링의 고장은 시스템 전체의 고장으로 이어져 치명적인 인명 피해는 물론 막대한 재정적 손실을 초래할 수 있다. 이에 따라 조기에 베어링의 고장을 관측하고 진단하기 위해 상태관측 데이터를 활용한 많은 연구가 진행되어 왔으며 특히 진동신호를 활용한 진단이 널리 수행되었다. 베어링 초기 결함을 진단을 하는데 있어 어려움을 겪게 하는 이유로 환경 영향으로 인해 발생하는 잡음에 묻혀 있는 약한 결함 신호 및 베어링의 결함 관련 신호의 복잡한 변조를 들 수있다. 이러한 문제를 극복하기 위해 본 연구에서는 베어링 결함신호의 생성원리에에 기반한 신호 모델을 제안하였다. 베어링 신호는 본질적으로 비정상성을 띄며 또한 실제 현장에서 획득한 신호는 복잡하고 다양한 소스에서 발생하는 신호가 조합된다. 이론과 현실 사이의 격차를 해소하기 위해 해석적 신호 모델에 헤르츠 접촉 이론에 기반한 충격 메커니즘을 구현하였다. 시뮬레이션된 베어링 신호에 기어의 결정론적 신호, 회전축의 사인파 신호 및 가우시안 노이즈와 합성된 신호에 대한 전처리 분석을 통해 제안 모델의 타당성을 검증하였다. 이 후, 다양한 잡음 환경에서 여러 변조된 음성 신호를 효과적으로 판별하는 음성인식 방법을 기계시스템에 적용한 고장특징 추출 방법을 새로이 제안하여 캡스트럽에 기반한 특징인자를 추출하였다. 추출된 인자로부터 시간-주파수 영역에서 스펙트럼을 계산하여 효과적으로 베어링의 특성 주파수를 검출하였다. 제안된 방법의 검증을 위해 다양한 잡음 환경에서의 시뮬레이션 데이터와 실험데이터를 사용하였다. 또한 가속수명시험을 통한 데이터를 통하여 조기진단의 효과를 검증하였다.Chapter 1. Introduction 1 1.1 Motivation 1 1.2 Research Scope and Overview 3 1.3 Dissertation Layout 5 Chapter 2. Technical Background and Literature Review 6 2.1 Vibration Signals of Bearing Faults 6 2.1.1 Rolling Element Bearings 6 2.1.2 Failure of Rolling Element Bearings 7 2.1.3 Bearing Fault Signature and Its Frequencies 8 2.2 Vibration Techniques for Bearing Incipient Fault Diagnosis 10 2.2.1 Overview of Vibration Techniques for Bearings 10 2.2.2 Cepstrum-Based Fault Diagnosis Techniques 13 Chapter 3. Quasi Periodic Impulse Train Model with Impact Force Function 20 3.1 Vibration Modelling of Bearing Fault 21 3.1.1 General Mathematical Model 21 3.1.2 Quasi-periodic Model with Cyclostationary 22 3.1.3 Excitation Force Function in Dynamic Models 23 3.2 Quasi Period Impulse Model with Impact Function 26 3.2.1 Overall Process of Proposed Model 26 3.2.2 Modeling the Excitation Force 27 3.3 Numerical Results and Discussion 32 3.3.1 Necessity of Choosing an Appropriate Preprocessing Method 34 Chapter 4. Speech Recognition-Inspired Feature Engineering for Bearing Fault Diagnosis 48 4.1 Review of Power-Normalized Cepstral Coefficients (PNCC) 49 4.1.1 Basic Definition of Cepstrum 49 4.1.2 Characteristics of cepstrum in mechanical vibrations 50 4.1.3 Power-Normalized Cepstral Coefficients (PNCC) 52 4.2 Proposed Feature Extraction Method: Linear Power-Normalized Cepstral Coefficients (LPNCC) 55 4.3 Fault Diagnosis by Implementing LPNCC 57 4.3.1 Fault Diagnosis Method using LPNCC and Squared Envelope Spectrum (LPNCC-SES) 57 4.3.2 Effect of Linear Filter and Power-normalization 59 4.4 Experimental Application and Results 60 4.4.1 Case Study with Simulation Model 61 4.4.1.1. Simulation Data with White Gaussian Noise 61 4.4.1.2. Denoising Under Gaussian Noise 62 4.4.1.3. Reseults Under Non-gaussian Noise 66 4.4.2 Case Study with Experiment Data 67 4.4.2.1. Experimental Data: Case Western Reserve University Dataset 67 4.4.2.1.1. Compared Methods 67 4.4.2.1.2. Case 1: Impusive Noise 68 4.4.2.1.3. Case 2: Low Signal-to-noise Ratio (SNR) 69 4.4.2.1.4. Case 3: Multiple Defective Signals 71 4.4.2.2. Experimental Data: Naturally Degradation Data 72 Chapter 5. Conclusions 108 5.1 Summary of Dissertation 108 5.2 Contributions and Significance 110 5.3 Suggestions for Future Research 113 References 116 Abstract (Korean) 130박

Clinical Comparison between Microsurgical Decompression and Lumbar Interbody Fusion with Instrumentation for Lumbar Stenosis

Objective：We report clinical results of the patients who received microsurgical decompression procedure(bilateral partial laminectomy and medial facetectomy：Group A) compared with lumbar interbody fusion with instrumentation(total laminectomy, interbody fusion and pedicle screw fixation：Group B). Methods：From March 1996 to December 2000, twenty patients with symptomatic lumbar stenosis underwent microsurgical decompression and twenty-five patients underwent lumbar interbody fusion by two operators. Two groups of patients were compared retrospectively in respect to the mechanical back pain, leg pain, motor weakness, sensory hypesthesia(numbness) and clinical outcomes. The mean follow-up period was 30 months. Results：In Group A, mechanical back pain, leg pain, motor weakness, and sensory hypesthesia were improved in 72.2%, 69%, 80%, 44.4% and 70%, 71%, 83.3%, 50% respectively in Group B. Clinical outcomes was excellent or good in 80% in Group A and 84% in Group B and no differences in clinical parameters between Groups were demonstrated. Conclusion：We recommend microsurgical decompression for the patients suffering from symptomatic lumbar stenosis with stable spine because microsurgical decompression provided a satisfactory clinical results equivalent to lumbar interbody fusion with instrumentation.ope

Long-term Effects on the Cervical Spine after Anterior Locking Plate Fixation

Objective：Anterior cervical locking plates are the devices for achieving anterior cervical spinal fusion. This study was conducted to evaluate the locking plate system regarding its long-term advantages and disadvantages in the view of interbody fusion rate, hardware-related failures, vertebral change close to the fusion segment and postoperative complications. Method：Eight-six patients, operated from Jan., 1996 to Jun. 1998, were followed-up for more than two years. All of the cases were fused with iliac bone graft and ORION locking plate(Sofamor Danek USA, Inc., Memphis, TN) fixation. The patients were discharged or transferred to rehabilitation department 2-7 days after operation. A comprehensive evaluation of the interbody fusion state, instrument failure, vertebral change and postoperative complications were made by direct interview and cervical flexion-extension lateral plain films. Results：There were 55 male and 31 female with a mean age of 45 years(18-75 years). The mean follow-up period was 29 months(24-43 months). Various disorders that were operated were 40 cervical discs, 6 cervical stenosis including OPLL, 2 infections, and 38 traumas. Fusion level was single in 59 cases, two levels of each disc space in 15 cases, and two levels after one corpectomy in 12 cases. There was no instrument failure. Pseudoarthrosis was observed in two cases(2%) without radiological instability. The other patients(98%) showed complete cervical fusion with stable instrument. Mild settling of interbody graft with upward migration of screws was found in 12 cases(14%). Anterior bony growth at the upper segment was found in 5 cases(6%). Postoperative foreign body sensation or dysphagia was observed in 12 cases(4%), and disappeared within one month in 7 cases and within six months in 4 cases. One patient complained for more than six months and required reoperation to remove paraesophageal granulation tissue. Conclusion：The results show that Orion cervical locking plate has some disadvantages of upward migration of screws, anterior bony growth at the upper segment, or possibility of esophageal compression even though it has advantages of high interbody fusion rate or low instrument failure. Author believe that anterior cervical locking plate in the future should be thinner, and should have short end from the screw hole, and movable screw with adequate stability.ope

Results of microsurgical anterolateral tunnel approach for cervical disc herniation

Objective：The authors report the microsurgical anterolateral tunnel approach for the treatment of the cervical disc diseases and its postoperative surgical results. Methods：All surgical procedures followed the method of classical microsurgical anterior discectomy. Small tunnel(7-8mm) was made on the disc space reaching to the posterior longitudinal ligament. The disc materials and bony spurs were removed through this tunnel. Thirty-one patients of cervical disc herniation(24 cases with pure disc herniation, 7 cases with combined cervical spondylosis) were evaluated on the symptoms, conformation in plain X-ray, C-T, and MRI. The follow up time was over 2 years . Results：Postoperatively the result(following the out come scale) was excellent and good in Twenty-nine patients. One with fair result showed remnant disc particle and spur and another one is combined with cord contusion. One patient with lesion in C 3-4 space and two cervicothoracic junction showed excellent result. Two patients with osteoporosis also showed good results. Cervical spine curvature and disc space height were not changed on the plain X-ray and MRI in all patients. Twenty-nine patients were discharged within 3 days after surgery without any postoperative complications. Conclusions：The microsurgical anterolateral tunnel approach could be indicated for the treatment of patients with cervical disc diseases and with difficulty in achieving interbody fusion(the higher cervical level and cervicothoracic junction, osteoporosis etc.).ope

Analysis of Hierarchical CdS/CdTe Nanowire Heterostructure

학위논문 (석사)-- 서울대학교 대학원 : 재료공학부, 2012. 8. 김미영.CdS와 CdTe는 상용화된 CdTe 태양전지를 구성하는 물질로서 약 30%에 이르는 이론적 효율에 비해 실제 효율은 약 17%에 머무르고 있다. 이러한 이론적 효율과 실제 효율의 차이점의 원인 중 하나로 박막형태로 제작되는 태양전지의 구조적 한계를 꼽는다. Hierarchical Structure를 형성하였을 경우 박막 태양전지와는 다르게 태양광의 흡수 방향과 소수캐리어의 수집 방향을 수직으로 형성할 수 있기 때문에 태양전지 효율 향상을 기대할 수 있다. Hierarchical Structure는 성장하는 System에 따라 형태와 특성이 다르게 나타나며, 특히, CdS / CdTe Nanowire Hetero structure에 대한 성장과 특성에 대한 연구보고가 많지 않다. 따라서 연구보고에 기본적인 특성 측정이 수반되어야 한다. 샘플은 CdS는 Au 촉매를 사용하여, CdTe는 Au와 Bi를 촉매로 사용하여 VLS 메커니즘을 통해 진공분위기인 Tubular Furnace 내에서 성장하였다. SEM을 이용하여 나무 형태를 이루고 기둥과 가지가 특정한 각도를 가지고 자라있음을 확인하였으며, XRD를 통하여 각 물질의 결정구조가 모두 Hexagonal임을 확인하였다. 기둥의 성장 방향은 [0002], [11-20] 두 가지가 확인되었으며, [0002] 성장시 가지는 [11-20]으로, [11-20] 성장시 가지는 [-12-13]방향으로 성장하였다. TEM으로 [0002] 성장은 명확한 Core-shell 구조가 [11-20] 성장에서는 Core가 한 쪽으로 치우친 형상을 EDS와 Moire Fringe를 통하여 확인하였다. 기둥과 가지의 EELS에서의 Peak의 차이점은 12eV에 해당하는 Interband Transition Peak Excitation이 기둥에서 더 명확하게 확인되고, 이는 기둥을 형성하는 CdS와 CdTe간의 Interaction에 의하여 Peak의 Intensity가 향상된 것이라 판단하였다. 저온 PL을 이용하여 광학적 특성을 확인하였다. 각 물질의 Energy Band Gap에 해당하는 peak인 2.42eV(CdS), 1.44eV(CdTe) 뿐 아니라, Intersititial로 작용하여 Donor State를 형성할 때 발생하는 2.05eV Peak이 더욱 Dominant함을 확인하여 Yellow emittion에 대한 특성을 확인하였다. 본 연구를 통해 CdS와 CdTe의 새로운 이종접합구조 성장을 확인하였으며, 다양한 분석방법을 통하여 신구조의 결정구조 및 관계, 광학적 특성, 전자 구조차이 등을 확인하였다. 이를 통하여 3차원 빌딩 구조 형성에 대한 가능성을 확인함으로서 태양전지 또는 나노소자 적용과 효율 향상을 위한 연구에 도움이 될 것으로 기대한다.Commercial CdTe solar cells, comprised of CdS and CdTe, have a theoretical efficiency of 30%. However, the actual efficiency is limited to 17%. Structural limitation of thin film solar cell is one of the main reason for the efficiency difference. When hierarchical structure is made of two materials as a heterojuction, it makes a perpendicular relationship between the direction of light and the direction of the collected minority carrier. Hierarchical structure has attracted great attention because its structural interests and potential applications in 3-D building block for improving efficiency and functionality. Characterization is essential for this structure because Hierarchical structure has various morphology (shape or crystal structure) and properties according to the growth system. We have synthesized a hierarchical CdS / CdTe nanowire heterojuction by CSS(Close Space Sublimation) method, where the Au nanoparticle works as a catalysts in a VLS(Vapor Liquid Solid) process for CdS growth, and Au and Bi was used for CdTe growth by a tulbular furnace at 10-3 torr. SEM images of this structure show the branch growth from backbones with directional relationship. The X-ray diffraction pattern reveals the hexagonal structure of CdS and CdTe. HRTEM images show the two types of growth direction which are [0002], [11-20]. When the stem growth directions are [0002], [11-20], the branches are [11-20], [-12-13]. In the line profile EDS spectum & Moire fringe, while [0002] stem has correct core-shell structure, [11-20] stem has off-center CdS Core in CdS / CdTe Heterostructure. In the EELS spectrum of stem and branch, the stem has more interband transition intensity at 12eV than bulk plasmon peak at 16eV occasionally. But branch does not show this phenomenon, where only 16eV peak is dominant. By result of low temperature PL, we found the dominant peak 2.05eV, 2.42eV, 1.44eV, 2.36eV. Dominant peak correspond to donor state induced by Cd interstitial, 2.05eV and 2.42eV are energy band gap for each material CdS, CdTe. An unknown peak at 2.36eV was observed. In conclusion, we have confirmed the new structure growth and properties about hierarchical CdS / CdTe nanowire heterojuction by various measurements.초 록 i 목 차 iii List of Figures v List of Tables vii 1.서 론 1 2.문헌연구 3 2.1 Hierarchical 나노구조 및 응용 3 2.1.1 Hierarchical 나노구조 3 2.1.2 나노와이어 성장(VLS mechanism) 6 2.1.3 Hierarchical Nanostructure의 기둥과 가지의 관계(Epitaxial Relationship) 8 2.1.4 Hierarchical Nanostructure의 응용 10 2.2 CdTe, CdS의 물성 및 접합 12 2.2.1 CdTe의 물성 12 2.2.2 CdS의 물성 및 나노와이어 성장 14 2.2.3 CdTe / CdS 접합 및 태양전지 응용의 한계 17 2.2.4 CdS / CdTe 나노구조의 응용 21 3.실험방법 23 3.1시편의 성장 23 3.2 SEM, XRD, PL, CL의 측정 25 3.3 TEM 측정 27 3.3.1 TEM sample 제작 27 3.3.2 TEM 기본 관찰 27 3.3.3 EELS 관찰 29 4.실험결과 30 4.1 CdS / CdTe 기본 구조 및 성분 분석 30 4.1.1 Mophology 분석(SEM,TEM) 30 4.1.2 XRD 결정구조 분석 34 4.1.3 회절패턴을 이용한 구조 분석 35 4.1.4 EDS 성분 분석 37 4.2 결정성장 방향에 따른 기둥과 가지의 관계 40 4.2.1 [1120] 결정성장 방향 41 4.2.2 [0002] 결정성장 방향 42 4.3 기둥과 가지의 EELS 분석 44 5.결 론 49 6.참고문헌 51 Abstract 53Maste

Follow-up Comparison of Two Different Types of Anterior Thoracolumbar Instrumentations in Trauma Cases : Z-plate vs. Kaneda Device

Objective：In a variety of thoracolumbar diseases, corpectomy followed by interbody bone graft and anterior instrumentation has allowed direct neural decompression and reconstruction of the weight-bearing column by short segments fusion. In this study, we compared spinal stability of the two different anterior thoracolumbar instruments : Z-plate and Kaneda device representing plate and two-rods type, respectively. Methods：A retrospective review was performed for all the patients with thoracolumbar diseases or traumas treated with anterior corpectomy, autologous iliac bone graft, and fixation with instruments from 1996 to 2000. For the anterior instrumentation, Z-plate or Kaneda device was used for 24 (M:F=5:9, average age=37) and 12 (M:F=9:3, average age=41) patients, respectively. The plain AP and lateral flexion-extension films were taken immediately after surgery and at each follow-up. The sagittal and coronal Cobb's angles at the operation segments were used to observe the change of initial fixation status. The surgical time length and bleeding amount of the two groups were compared. Intra-operative and post-operative instrument-associated complications were evaluated. Student t-test was used for statistical analysis and p-value less than 0.05 was considered to be significant. Results：Mean follow-up durations for Z-plate and Kaneda device were 24 and 21 months, respectively. The fusion rate was 91% for Z-plate and 100% for Kaneda device. Two cases of Z-plate group showed instrumentation failure during the follow-up period, in which additional surgery was necessary. The mean differences of sagittal Cobb's angles among the AP images immediate after surgery and at follow-up were 7 and 2 degrees for Z-plate and Kaneda device, respectively (p<0.05). The mean differences of coronal Cobb's angles were 5 and 2 degrees for Z-plate and Kaneda device, respectively (p<0.05). No intra-operative complication has occurred in both groups. There was no difference in surgery time and bleeding amount between two groups. Conclusion：We think that Kaneda device (rod type) is stronger than Z-plate (plate type) to keep the spinal stability after anterior thoracolumbar surgery.ope

Chronic Spinal Epidural Abscess after Epidural Analgesia: Case Report

Three cases of chronic spinal epidural abscess following spinal epidural analgesia are presented. Spinal epidural abscess is a relatively rare infectious disease. It has recently increased in frequency due to the increased use of epidural steroid injections and epidural analgesia. It is very difficult to detect the spinal epidural abscess from its variable symptoms. So, it is important in making a diagnosis of epidural abscess to take into account the previous history of epidural analgesia.ope

In-situ TEM을 이용한 기판의 전도성에 따른 금속 입 거동의 동역학적 분석 : 하전 효과

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 재료공학부, 2018. 2. 김미영.나노 구조체의 형성은 고전적으로 원자나 이온, 분자에 의한 소립자의 적층으로 성장한다는 것이 일반적인 메커니즘으로 받아들여져 왔다. 다양한 분야의 나노 구조체의 응용이 가능하게 된 오늘날 다양한 연구에서 고전적인 성장 메커니즘으로 설명할 수 없는 기하학적인 구조들이 생성 또는 합성이 되고 있다. 이는 비 고전적 결정 성장 (Non-classical Crystallization)로 명명 되는 새로운 학문 분야로서 나노 구조체의 조합이 나노 입자 단위로 생성된다는 새로운 접근 방법을 제공한다. 이 새로운 학문 분야의 정립은 대부분 액상에서 합성된 물질을 관찰 및 보고를 통하여 되고 있으나, 일찍이 본 실험실에서는 액상 뿐만 아니라 기상에서 또한 이 현상이 일어남을 간접적으로 증명해왔다. 다만, 이를 해석하는데 있어서 독창적으로 적용되는 것이 하전에 대한 효과로, 기상에서 생성되는 나노 입자가 하전을 가질 때 Liquid-like한 성질을 가져 이것이 나노 구조체를 형성하는 기본 단위가 된다는 것이 핵심이고, 이것을 하전된 나노 입자 이론(Theory of Charged Nanoparticle) 로 명명해왔다. 앞선 비 고전적 결정 성장방법에 대한 메커니즘은 아직 명확하게 정립되지 않는 영역으로, 다만, 중간 단계는 Oriented attachment가 일어나는 것은 잘 알려져 있다. 이런 나노입자에 의한 성장의 주도니 원동력은 표면 에너지의 감소를 위한 것으로 이를 예측하기 위한 다양한 모델들이 제시되고 있다. 이에 맞춰 제공되는 핵심 증거는 직접적인 육안 관찰이 가능한 투과전자현미경(TEM)을 이용한 실시간 관찰을 통하여 다양한 주장들이 제기되고 있다. 논의 되고 있는 다양한 메커니즘 속에서 투과전자현미경을 사용했을 때에 높은 에너지를 가지는 가속된 전자에 의한 타켓 물질과의 상호 작용에서 발생할 수 있는 하전의 영향을 간과하고 있는바, 본 학위논문에서는 하전에 초점을 두고 이것이 시스템 내에 존재했을 때 나노 구조체에 어떠한 영향을 미치는지에 대해서 체계적인 실험을 진행하였다. 일차적으로 타켓으로 삼은 금 입자를 기판의 전도성에 따라 입자의 거동 차이를 확인하였다. 인위적으로 하전을 띠고 있는 비 전도성 기판 위에서의 금 입자는 매우 불안정한 거동을 띠고 있음을 확인하였으나 대조군인 전도성 기판에서는 긴 시간동안에도 안정적인 형태를 띰을 확인하였다. 이에 더해, 비 전도성 기판 위의 금 입자가 기판에서 탈락됨을 통하여 척력, 즉 정전기적 반발력이 입자와 기판 사이에 작용하는 것이 관찰됨에 따라 시스템 내 입자에 하전을 인위적으로 구현할 수 있었다. 이에 더 나아가 하전 유무에 따른 나노 입자들간의 상관관계를 2개 이상의 입자가 존재하였을 때 관찰하였다. 나노 입자의 표면 에너지를 줄이기 위한 방법 중 하나인 coalescence가 일어나는 시스템 내에서, 하전이 존재할 때 약 15배 정도의 시간적인 빠르기를 가지고 이 메커니즘이 작용함을 확인함에 따라 나노 구조체를 형성하는데 있어서 하전은 나노 입자의 불안정성을 야기 시킴과 동시에 동역학적인 장벽을 낮추는 효과까지 가짐을 확인하였다. 마지막으로 이러한 관찰을 TEM을 이용하여 진행할 때에 제기될 수 있는 온도 상승, Hydrocarbon 오염, 다양한 기판을 사용함에 따른 타켓 물질이 처한 환경적 차이에 따른 논란을 해결하는데 중점을 두었다. 온도 상승은 관찰하는 환경의 전체적인 온도를 액체 질소 온도 까지 내림으로서 활성 장벽을 높였음에도 불구하고 coalescence가 일어나 이 것에 대한 온도 영향을 배제하려고 하였고, 전도성과 비전도성 물질의 관찰간 발생하는 시간적인 간극에 따른 TEM의 환경과 샘플의 변화를 배제 하기 위하여 이를 하나의 TEM Grid 위에 하전이 존재할 수 있는 환경과 존재할 수 없는 환경을 한 번에 구현함으로서 해결하고자 하였다. 동일한 물질을 사용한 Floating & Ground 시스템은 명확하게 하전만 변수로 삼을 수 있는 환경을 제공하였으며, 관찰 전 후의 명확한 차이를 통하여 나노 구조체를 형성하는 환경 내에서 하전이 중요변수로 작용할 수 있음을 보였다. 또한, 이를 은 입자에 적용함으로서 금 입자로 구성된 앞의 실험을 넘어 하전 효과를 다른 물질로 적용하여 일반화 시킬 수 있는 작은 단서를 같이 제공하였다.Non-classical crystallization is a remarkable phenomenon in the nanostructure fabrication, which suggests that nanoparticle is the smallest unit as building block in crystal growth. In-situ transmission electron microscopy (in-situ TEM) provides crucial clues in understanding its mechanism. However, many mechanisms still remain unclear, especially the lack of understanding the charge effect caused by inelastic collision of the electron beam with sample in TEM. Here, we report that the structural instability and coalescence are promoted by charging through real-time observation of Au particles on substrates with difference conductivity. From a kinetic point view, this difference implies that the charge enhanced diffusion. This investigation broadens current knowledge of non-classical crystallization that grows by nanoparticles, sheds light on a potential factor to control the nanostructure fabrication. In this thesis, I carefully pay attention to the charge effect caused by the interaction between injected electron beam with high energy and sample during real-time TEM observation. In order to clarify the effect of charging in TEM, first, we clearly reproduced the difference in structure stability of a nanoparticle according to the substrate conductivity. Furthermore, the coalescence of multi-particles according to the degree of activation by charge was confirmed from the viewpoint of dynamics. Finally, we attempted to exclude various interpretations occurring within in-situ TEM by constructing a well-established artificial charging systemCh. 1 Introduction 1 1.1 Non-classical Crystallization 2 1.2 In-situ TEM Observation of Non-classical crystallization 9 1.3 Theory of Charged Nanoparticle 12 1.4 Charged Particle in Transmission Electron Microscope (TEM) 19 Ch. 2 An isolated Nanoparticle Observation 25 2.1 Structure instability of Nanoparticle 25 2.2 Experiment 27 2.3 Result & Discussion 31 2.4 Conclusion 41 Ch. 3 Two or more Nanoparticles Observation 43 3.1 Aggregation and Coalescence of Nanoparticles 44 3.2 Experiment 48 3.3 Result & Discussion 52 3.4 Conclusion 60 Ch. 4 Artificial current path systems : Floating & Ground environment formed simultaneously in a TEM grid 61 4.1 Controversy over the observation of charged nanoparticles using in-situ TEM 62 4.2 Experiment 65 4.3 Result & discussion 69 4.4 Behavior of Ag Nanoparticles in Floating & Ground systems 79 4.5 Conclusion 81 Ch.5 Summary 82 Reference 85 국문 초록 91Docto

Extradural thoracic spinal meningioma arising from a nerve root -case report-

Extradural meningiomas are relatively rare and those arising from spinal root are even rarer. Recently, a case of extradural meningioma arising from a spinal nerve root was surgically treated in our institution. This patient was a 19-year-old female presented with paraparesis and paresthesia. The mass was compressing the spinal cord at the level of fourth thoracic spine, and it was extended to the nerve root. At operation it was found to be originated from the fourth thoracic spinal nerve root. After removal of the tumor, the neurologic symptom and sign were recovered completely. Histoligic examination of tumor revealed as transitional type of meningioma.ope

The Usefulness of 3D-Surface Rendering of the MRI in Surgical Treatment of Patients with Intractable Neocortical Epilepsy

BACKGROUND: This study is designed to indicate the role of 3D-surface rendering of the MRI in defining and resect-ing the epileptogenic zone.0aMETHODS: 25 healthy volunteers and 55 patients were studied. Conventional MRI and 3D-surface rendering were performed. Sulcal and gyral patterns were assesed by a neuroradiologist and a neurologist with-out the clinical informations. Chronic video-EEG monitoring with surface and subdural grid electrodes, and PET were done. Resection was performed based on data of the EEG recordings and 3D-surface rendering.0aRESULTS: Conventional MRI identified structural abnormality ("MRI-identifiable lesion") in 20 patients. 20 of 35 patients without structural abnormality in conventional MRI revealed abnormal sulcal and gyral patterns in 3D-surface rendering of MRI ("3D-identifiable lesion"). Subdural grid EEGs recorded focal or diffuse ictal EEG onset from the region of "3D-identifiable lesion". Histopathologic findings revealed cortical dysplasia in 48 and neocortical gliosis in seven. Overall surgical out-come, at the average follow up period of 32.5 months, showed class I in 63.6%, class II in 25.5%, and class III in 10.9%. Among 20 patients with "MRI-identifiable lesion", 80% were in class I and 20% were in class II. Among 35 patients without "MRI-identifiable lesion", 54.3% were in class I, 28.6% were class II, and 17.1% were in class III. 80% of 20 patients with "3D-identifiable lesion" showed class I and 20% of 15 patients without "3D-identifiable lesion" showed class I.0aCONCLUSIONS: Identification of "MRI-identifiable lesion" or "3D-identifiable lesion" was of value in defining the epileptogenic zone. Resection of "MRI-identifiable lesion" or "3D-identifiable lesion", which were epilep-togenic in EEGs, promised a good surgical outcome.ope