(A) study of compressive strength of two resins on the cavity forms

치의학과/석사[한글] 심미성 수복재료의 구치부용 복합레진은 점차 널리 사용되어지고 있는바, 교합압에 저항할 수 있는 적절한 형태의 와동을 형성하기 위하여 폭과 깊이에 따른 압축강도를 측정하여 다음과 같은 결과를 얻었다. Ⅰ. 각 와동형태에 따라 압축강도의 통계적 유의성이 있었다(P<0.05). Ⅱ. 두 종류의 복합레진의 와동형태에 따른 통계적 유의성은 없었다(P>0.05). Ⅲ. 깊이 3mm의 군에서 폭 증가시 통계적 유의성이 있었다(P<0.05). [영문] Composite resins has been widely used in dental clinics because of esthetic restoration. The aim of this study was to assess the effects of the cavity designs on the compressive stress of resin restoration. So, the author made the standardized specimen of four types(Type of speciemen are width 1.5mm, depth 2mm, width 1.5mm, depth 3mm, width 2mm, depth 2mm, width 2mm, depth 3mm). The compressive strength was measured by universal testing machine(Tong Kwang Co.) The results indicating following; 1. There was a statistic significance of compressive strength between four cavity forms. 2. There was no difference of significance of compressive strength between two resins. 3. There was a significance of compressive strength between depth 3mm width 1.5mm and depth 3mm width 2mm.restrictio

외란 관측기 이론 : 역동역학 기반 설계에 대한 새로운 관점

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 전기·컴퓨터공학부, 2018. 2. 심형보.The problem of compensating model uncertainty and external disturbance in control systems is one of long-standing and critical issues in academia and industry. Among several promising solutions to the problem, the disturbance observer approach has gained a particular attraction in the literature, due to its structural simplicity and powerful ability. This dissertation presents new theoretical results on the inverse-model based disturbance observers, in order to overcome the limitation of the existing disturbance observer approaches and to address several problems which modern control systems have encountered. Specific subjects dealt with in the dissertation are listed as follows: - The recovery of nominal performance is a key feature of the inverse model-based disturbance observers. It is remarkable that this property is generically an approximation, mainly because structural information of disturbance is not explicitly employed in the disturbance observer design. Motivated by the internal model principle, in the first part of this dissertation we propose a new disturbance observer into which a generating model of disturbance is embedded. Unlike those in the existing works, the proposed disturbance observer achieves “asymptotic” (rather than approximate) recovery of nominal performance in a sense of input-to-state stability. As a further research in this direction, we also find out that the asymptotic recovery of nominal performance is still possible even without exact knowledge on the frequencies of the sinusoidal disturbance, by realizing the internal model to be embedded in an adaptive fashion with a frequency identifier. - Modern control systems have often experienced not only persistent disturbances and model uncertainty, but also sudden faults of systems and actuators. Even though various fault-tolerant control schemes have been proposed to tackle the problem, guaranteeing satisfactory tracking performance under faults has been not fully studied yet. As another contribution of the dissertation, we propose a disturbance observer-based fault-tolerant controller that guarantees a “fault-free” tracking performance for the entire period (including the moment when an actuator fault occurs). By reminding that the disturbance observer approach is commonly applied to minimum phase systems, the underlying idea is to redefine a virtual input from the redundant control inputs such that the composite system from the virtual input to the output remains of minimum phase under any actuator faults. This work is in fact an extension of the disturbance observer for a larger class of systems that have more inputs than outputs, while the conventional disturbance observer scheme is mostly designed for “square” systems (that is, systems that have the same numbers of inputs and outputs). - While a physical plant is a continuous-time system, control schemes are usually implemented in discrete time. The mixture of continuous- and discrete-time components introduces some distinctive characteristics of the sampled-data systems, which possibly incurs unexpected situations when a discrete-time disturbance observer is employed for the sampled-data system. In the dissertation, a theoretical analysis of the discrete-time disturbance observer is newly provided in the sampled-data setting. In particular, by focusing on the limiting behavior of the overall system as the sampling period goes to zero, we obtain a “necessary and sufficient condition” for the robust stability under fast sampling. One important finding from our approach is that the discrete-time “sampling zeros” of the sampled-data model may hamper stability (even regardless of model uncertainty) when these zeros are not carefully taken into account in the disturbance observer design. Based on the stability analysis, we also present systematic design guidelines of the discrete-time disturbance observer to satisfy the stability constraint under arbitrarily large (but bounded) model uncertainty, and at the same time to embed a disturbance model (if available) into the discrete-time disturbance observer structure. - With increased interests in these days, the security of cyber-physical systems has been dealt with in the literature from a control-theoretical point of view. In the last part of this dissertation, we address the problem of constructing a “robust stealthy attack” that compromises uncertain cyber-physical systems having unstable zeros. It has been well known that the conventional zero-dynamics attack, a systematic stealthy attack to non-minimum phase systems, is easily detected as long as (even small) model uncertainty exists. Different from the conventional approach, our key idea is to isolate the real zero-dynamics from the plant’s input-output relation and to replace it with an auxiliary nominal zero-dynamicsas a result, this alternative attack does not require the exact model knowledge anymore. We show in this dissertation that all this can be realized by the disturbance observer, which now serves as an attack generator. This work explains the underlying principle of destabilizing phenomenon when the inverse model-based disturbance observer is applied to the non-minimum phase plants carelessly.1 Introduction 1 1.1 Research Background 1 1.1.1 Overview of Researches on Disturbance Observers 1 1.1.2 Motivating Questions on Inverse Model-based Designs 6 1.2 Contributions and Outline of Dissertation 6 2 Recovery of Nominal Performance in Asymptotic Sense: Part I - Embedding Internal Model into Disturbance Observer 11 2.1 Problem Formulation 13 2.2 Controller Design 17 2.2.1 Motivating Idea from Frequency Domain Analysis 18 2.2.2 Reduced-order Implementation of Disturbance Observer with Higher Order Numerator of Q-filter 21 2.2.3 Design of Disturbance Observer with Internal Model 24 2.3 Performance Analysis 29 2.3.1 Coordinate Transformation to Singular Perturbation Form 30 2.3.2 Lyapunov Analysis 42 2.4 Simulation: Mechanical Positioning Systems 49 3 Recovery of Nominal Performance in Asymptotic Sense: Part II - An Extension with Adaptive Internal Model 57 3.1 Problem Revisited: Mechanical System with Unknown Frequency of External Input 58 3.2 Disturbance Observer-based Controller Design with Adaptive Internal Model 60 3.3 Performance Analysis 64 3.3.1 Representation to Multiple-time Scaled Singular Perturbation Form 64 3.3.2 Convergence Analysis 70 3.4 Industrial Application: Optical Disk Drive 76 3.4.1 Simulation Results 78 3.4.2 Experimental Results 82 4 Guaranteeing Almost Fault-free Performance from Transient to Steady-state: Disturbance Observer-based Fault Tolerant Control 85 4.1 Problem Formulation 87 4.2 Design of Disturbance Observer-based Fault Tolerant Controller 91 4.2.1 Static Gain of Control Allocation Law 92 4.2.2 Representation to Byrnes-Isidori Normal Form 95 4.2.3 Disturbance Observer-based Controller 97 4.3 Performance Analysis 102 4.4 Simulation: Fault Tolerant Control of Boeing 747 112 5 Stability, Performance, and Designs of Discrete-time Disturbance Observers for Sampled-data Systems: A Fast Sampling Approach 117 5.1 Motivating Example: Stability Issue of Disturbance Observers in Sampled-data Frameworks 119 5.2 Basics on Sampled-data Systems 122 5.3 Generic Representation of Discrete-time Disturbance Observer 125 5.4 Almost Necessary and Sufficient Condition for Robust Internal Stability under Fast Sampling 129 5.4.1 Main Result 129 5.4.2 Issue 1: Exact vs. Approximate Discretization of Pn(s) 137 5.4.3 Issue 2: Importance of Q-filter Design 138 5.4.4 Issue 3: Indirect vs. Direct Designs of Discrete-time Disturbance Observers 140 5.5 Performance Analysis of Discrete-time Disturbance Observers in Frequency Domain 141 5.6 Direct Design Methods for Discrete-time Disturbance Observers 146 5.6.1 Design with Simplest Structure of Q-filter 147 5.6.2 Design to Embed Disturbance Model 148 5.7 Simulation Results: Two-mass-spring System Revisited 152 6 Robust Zero-dynamics Attack on Uncertain Cyber-physical Systems: Malicious Use of Disturbance Observer 161 6.1 Normal Form-based Interpretation of Zero-dynamics Attack 163 6.1.1 System Description 164 6.1.2 Performance of Zero-dynamics Attack 166 6.1.3 Limitation of Zero-dynamics Attack against Model Uncertainty 168 6.2 Robust Zero-dynamics Attack for Uncertain Cyber-Physical Systems 169 6.2.1 Problem Revisited with Model Uncertainty 169 6.2.2 Yet Another Attack Policy on Unstable Zero-dynamics: Ideal Strategy 173 6.2.3 Design of Robust Zero-dynamics Attack: Practical Implementation of New Attack Policy via Disturbance Observer 178 6.2.4 Proof of Main Result 180 6.3 Simulation: Power Generating Systems 185 7 Conclusion of Dissertation 191 APPENDIX 195 A.1 Design Guidelines of ai for CT-DOBs 195 A.1.1 Recursive Design Algorithm 195 A.1.2 Bilinear Matrix Inequality-based Design 199 A.2 Properties of δ in (3.3.19) 200 A.3 Derivation of Normal Form Representation (6.3.1) of Power Generating System 203 BIBLIOGRAPHY 207 국문초록 223Docto

Study on the Microstructure and Surface Morphology of BST Thin Films Prepared by Off-axis Sputtering

Maste

Design of Nonlinear Disturbance Observer with Higher Order Numerator of Q-filter

학위논문 (석사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2013. 2. 심형보.외란 관측기는 외란을 제거하기 위해 널리 사용되는 제어기들 중 하나로, 비교적 간편하게 설계할 수 있고 제어 대상이 되는 시스템의 불확실성에 강인하다는 장점들이 있다. 외란 관측기의 성능과 전체 시스템의 안정도는 외란 관측기를 구성하는 저역 통과 필터인 Q-필터에 의해 결정된다. 그러므로 외란 관측기의 성능을 향상시키면서 전체 시스템을 안정하게 하는 Q-필터를 설계하는 방법들이 끊임없이 연구되어 왔다. 이러한 흐름 속에서 선형 외란 관측기의 구조에 특정한 외란의 모델이 포함되도록 Q-필터를 설계하는 방법이 제안되었다. 일반적으로 외란 관측기는 외란의 모델을 고려하지 않고 설계되어 외란의 영향을 근사적으로 약화시킨다. 반면 위의 방법으로 설계한 외란 관측기는 포함하고 있는 외란의 영향을 점근적으로 제거하기 때문에 외란의 모델을 고려하지 않고 설계된 외란 관측기보다 더 좋은 성능을 낼 수 있다. 하지만 선형 외란 관측기와는 달리 지금까지 제안된 비선형 외란 관측기들은 모두 Q-필터의 분자가 상수였기 때문에 비선형 외란 관측기의 구조에 내부 모델로 포함될 수 있는 외란은 상수 외란들뿐이었다. 따라서 비선형 외란 관측기의 구조에 계단파, 정현파 등 다양한 형태의 외란들을 내부 모델로 포함시키기 위해 임의의 분자 차수를 가지는 Q-필터를 설계하는 것이 필요하였다. 본 논문에서는 Q-필터의 분자 차수를 높인 비선형 외란 관측기를 설계한다. 또한 제안한 외란 관측기를 이론적으로 분석하기 위해 전체 시스템의 상태 방정식을 특이 섭동 모델로 표현하는 Q-필터 상태 변수의 좌표 변환을 소개한다. 이를 이용하여 전체 시스템의 강인 안정도 조건을 찾고 이 조건을 만족하는 Q-필터를 설계하는 방법을 제안한다.제 1 장. 서론 1 제 2 장. 문제 설정 7 제 3 장. 비선형 외란 관측기의 설계와 특이 섭동 모델로의 표현 11 제 1 절. 비선형 외란 관측기의 설계 11 제 2 절. 새로운 좌표 변환을 통한 특이 섭동 모델로의 표현 17 제 4 장. 전체 시스템의 강인 안정도 조건 및 Q-필터의 설계 23 제 1 절. 준 정상상태 시스템과 경계층 시스템의 안정도 조건 23 제 2 절. 전체 폐루프 시스템의 강인 안정도 조건 31 제 3 절. 전체 폐루프 시스템을 안정하게 하는 Q-필터를 설계하는 방법 48 제 5 장. 결론. 부록 A. 세부적인 증명 57 제 1 절. 보조 정리 2.2.1의 증명 57 제 2 절. 보조 정리 2.3.1의 증명 63 제 3 절. 따름 정리 2.4.1의 증명 67 참고 문헌 71 ABSTRACT 77Maste

gain fitting method for a hearing aid

본 발명은 난청자의 음향 인지 특성에 따라 보청기의 주파수 대역별 증폭도를 조정하는 방법에 관한 것이다.본 발명에 따른 보청기의 증폭도 맞춤 방법은, 가청주파수대역을 인간의 음향 인지 특성을 고려하여 다수의 임계대역(critical band)으로 나누고, 가청 소리 크기를 인간이 느끼는 음감의 정도에 따라 다수의 레벨로 나누고, 청력 정상인들과 난청인을 대상으로 상기 다수의 임계대역별로 다수의 레벨에 대한 청감값을 획득하여 상기 난청인의 보청기 증폭도를 설정하는 보청기 증폭도 맞춤 시스템에서의 보청기 증폭도 맞춤 방법에 있어서,상기 청력 정상인들을 대상으로 상기 다수의 임계대역별로 상기 다수의 레벨에 대한 청감값을 입력받아 저장하는 제 1 단계와; 상기 제 1 단계에서 청력 정상인들로부터 얻어진 상기 다수의 임계대역 및 레벨별 청감값들의 평균인 청감 평균값을 계산하여 저장하는 제 2 단계와; 상기 난청자를 대상으로 상기 다수의 임계대역별로 상기 다수의 레벨에 대한 청감값을 입력받아 저장하는 제 3 단계와; 상기 청력 정상인들로부터 얻어진 다수의 임계대역 및 레벨별 청감 평균값과 상기 난청자로부터 얻어진 다수의 임계대역 및 레벨별 청감값과의 차이값을 계산하여, 상기 난청자의 보청기의 다수의 임계대역 및 레벨별 목표이득을 설정하는 제 4 단계를 포함한다

A study on the psychoacoustic fitting of digital hearing aids using the modified critical bands

학위논문(석사) - 한국과학기술원 : 기계공학전공, 2004.2, [ x, 108 p. ]한국과학기술원 : 기계공학전공

An Experimental Study on UNDEX Characteristics of Airbag Inflators

This paper deals with an experimental study of the dynamics of an underwater bubbles and shock waves, generated by rapid underwater release of highly compressed gas. Aribag inflators, which are used for automobile’s airbag system, are used to generate the extremely-rapid underwater gas release. Experimental studies of the complex underwater bubble dynamics as well as underwater shock wave were carried out in a specifically designed cylindrical water tank. The water tank is equipped with a high-speed camera and pressure sensors. The high-speed camera was used to capture the expansion and collapse of the gas bubble created by inflators, while pressure sensors was used to measure the underwater shock propagation and magnitudes. The experimental results were compared against the results of explosion of pentolite explosive. Several physical phenomena that has been observed and discussed, which are different from the explosive underwater explosion.