외부 공격으로부터 자율 복원 가능한 제어 시스템: 센서 공격에 안전한 상태 추정 기법

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 전기·컴퓨터공학부, 2018. 2. 심형보.Recent advances in computer and communication technologies make control systems more connected thanks to the developments in networked actuation and sensing devices. As this connectivity increases, the resulting large scale networked control systems, or the cyber-physical systems (CPS), are exposed and can be vulnerable to malicious attacks. In response to the crisis by the malicious adversaries, this dissertation presents sophisticated control algorithms which are more reliable even when some components of the feedback control systems are corrupted. Focusing especially on sensor attacks, security related problems on CPS are carefully analyzed and an attack-resilient state estimation scheme is proposed. First, the notion of redundant observability is introduced that explains in a unified manner existing security notions such as dynamic security index, attack detectability, and observability under attacks. The redundant observability is a key concept in this dissertation, and a system is said to be q-redundant observable if it is observable even after eliminating any q measurements. It has been shown that any q-sparse sensor attack is detectable if and only if the given linear time invariant (LTI) system is q-redundant observable. It is also equivalent to the condition that the system is observable under ⌊q/2⌋-sparse sensor attacks. Moreover, the dynamic security index, which is defined by the minimum number of attacks to be undetectable, can be computed as q + 1. In addition, the redundant detectability (or, asymptotic redundant observability), which is a weaker notion than the redundant observability, is also introduced. While the redundant observability does not care about the magnitudes of sensor attacks and does not mind whether the attacks are disruptive or not, the redundant detectability only deals with attacks that do not converge to zero as time goes on, so that it is more practical in the sense that it can only detect and correct the attacks that are actually harmful to the system. Next, a resilient state estimation scheme is proposed under two assumptions: ⌊q/2⌋-sparsity of attack vector and q-redundant detectability of the system. The proposed estimator consists of a bank of partial observers operating based on Kalman detectability decomposition and a decoder exploiting error correction techniques. The partial observers are either constructed by Luenberger observers or Kalman filters. The Luenberger observer guarantees the robustness with bounded disturbances/noises, while the Kalman filter shows the suboptimality in the sense of minimum variance with Garussian disturbances/noises. In terms of time complexity, an ℓ0 minimization problem in the decoder alleviates the computational efforts by reducing the search space to a finite set and by combining a detection algorithm to the optimization process. On the other hand, in terms of space complexity, the required memory is linear with the number of sensors by means of the decomposition used for constructing a bank of partial observers. This resilient state estimation scheme proposed for LTI systems, is further extended for a class of uniformly observable nonlinear systems. Based on the uniform observability decomposition, a high gain observer is constructed for each single measurement to estimate the observable sub-state and it constitutes the partial observer. Finally, the decoder solves a nonlinear error correcting problem by collecting all the information from the high gain observers and by exploiting redundancy.1 Introduction 1 1.1 Background 1 1.2 Research Objective and Contributions 5 1.3 Outline of the Dissertation 8 2 Error Correction over Reals and its Extensions 11 2.1 Error Correction over Reals and Compressed Sensing 11 2.2 Extension to Stacked Vector Case 16 2.2.1 Error Detectability and Error Correctability 16 2.2.2 Error Detection and Correction Scheme for Noiseless Case 20 2.2.3 Error Detection and Correction Scheme for Noisy Case 23 3 On Redundant Observability 41 3.1 Redundant Observability 42 3.1.1 Definition and Characterization 42 3.1.2 Relationship with Strong Observability 45 3.1.3 Redundant Unobservable Subspace 47 3.1.4 Asymptotic Redundant Observability 49 3.2 Attack Detectability and Dynamic Security Index 56 3.3 Observability under Sparse Sensor Attacks 65 4 Attack-Resilient State Estimation for Linear Systems 69 4.1 Problem Formulation 70 4.2 Components of Attack-Resilient Estimator and Their Functions 73 4.2.1 Partial Observer: Kalman Detectability Decomposition 73 4.2.2 Decoder: Error Correction for Stacked Vector 77 4.3 Design of Attack-Resilient State Estimator 78 4.3.1 Deterministic Estimator with Bounded Disturbance and Noise 79 4.3.2 Suboptimal Estimator with Gaussian Disturbance and Noise 85 4.4 Remarks on Proposed Attack-Resilient Estimator 93 4.4.1 Comparison with Fault Detection and Isolation 93 4.4.2 Analysis of Time and Space Complexity 95 4.5 Simulation Results: Three-Inertia System 96 5 Attack-Resilient State Estimation for Nonlinear Systems 101 5.1 Problem Formulation and Preliminaries 102 5.1.1 Problem Formulation 102 5.1.2 Bi-Lipschitz Function and Lipschitz Left Inverse 103 5.1.3 Nonlinear Error Detectability and Error Correctability 105 5.2 Uniformly Observable Nonlinear Systems for Any Input 108 5.2.1 Uniform Observability Decomposition 108 5.2.2 Design of High Gain Observer 111 5.3 Redundant Observability for Nonlinear Systems 112 5.4 Attack Detection and Resilient Estimation for Nonlinear Systems 115 5.4.1 Detection of Sensor Attacks 115 5.4.2 Attack-Resilient State Estimation 119 5.5 Simulation Results: Numerical Example 121 6 Conclusion 125 6.1 Summary 125 6.2 Future Works 127 Bibliography 129 국문초록 141Docto

동맥경화증과 종양마우스모델에서 페리틴을 이용한 세포추적자기공명영상

Dept. of Medicine/박사Molecular imaging is a type of innovative medical imaging that provides detailed images of the in vivo occurrences at a molecular or cellular level through real-time imaging. Among the various molecular imaging modalities, magnetic resonance imaging(MRI) can use in detection of cell movement, proliferation, and division through cell labeling, and diagnose and evaluate the treatment effectiveness of tumors or inflammations depending the labeling cell type. MRI provides high tissue contrast and superior resolution but it has relatively low sensitivity, and therefore, contrast agents are used to overcome this challenge. However, problems such as dilution of contrast agents within the body, instability of cell labeling, and cytotoxicity suggest that there is a need for a more safe and efficient cell labeling technique. The reporter-gene based technique is being proposed as a method to overcome these problems. Ferritin is an intracellular, iron-binding protein that accumulates extracellular iron entering the cell and exhibits magnetic properties, allowing T2 contrast effects under MRI. This makes it a good candidate as an MR contrast agent for cell tracking. This study aims to understand the effectiveness of ferritin as a contrast agent and also a potential reporter gene, by tracking macrophages and tumor cells using ferritin in arteriosclerosis and tumor mouse models. In a comparison experiment with the currently used T2 contrast agent Feridex, ferritin showed 50% lower relaxivity (Feridex vs ferritin = 0.00298 ml/µg Fe∙1/sec vs 0.00159 ml/µg Fe∙1/sec), which was sufficient to act as the MR contrast agent for cellular imaging. Macrophage cell line Raw264.7, labeled with ferritin, showed T1 and T2 contrast effects in cell pellet imaging. In vivo imaging of ApoE knockout (ApoE-/-) mice 24 hr after intravenous injection of the cells revealed negative contrast effects in the aortic arch walls. Therefore, ferritin can be used to diagnose inflammations by tracking ferritin-labeled macrophages. Since the contrast effects of ferritin were confirmed, the use of ferritin as a reporter gene and its use as an adenovirus-based expression system were assessed in this experiment. First, a Mock (control group) and an adenoviral human ferritin heavy chain ([Ad-FTH] experimental group) were injected into the subcutaneous tumor models made using the colorectal cancer cell line HCT116. T1 and T2 -weighted images were obtained every two days after injection. Day 2 post-injection images showed negative contrast areas within the tumor, and by day 4 post-injection, the enhanced contrast areas were clearly observed. The results of the Prussian blue staining performed using the same tissue samples demonstrated overlapping of the negative contrast-enhanced region and iron absorption region, thereby confirming that the contrast effects were due to ferritin gene expression. Considering the fact that the iron concentration increases within the tumor, a glioma cell line U87MG was infected with Ad-FTH and ferritin expression was induced. Then, cell-pellet MRI was performed using cells cultured with 1mM FeCl3 and 3mM FeCl3; cells cultured under higher iron concentration were confirmed to show stronger negative contrast enhancing effects. In order to validate the negative contrast effects of ferritin through T2*-weighted images, brain tumor models were established by injecting U87MG cells into mouse brain and Ad-FTH was injected into the tumor; T1, T2 and T2*- weighted images were simultaneously obtained from days 1 through 6. Day 2 post-injection, T2 and T2*- images showed negative contrast effects at the tumor margins, and maintained until day 6. In conclusion, through cellular level investigation and in vivo experiments using animal models, this study strongly suggests the effectiveness of ferritin as an endogenous MR contrast agent and a potential reporter gene, which is capable of maintaining cell labeling stability and cellular safety.ope

Angiographic analysis of the intracranial aneurysms

의학과/석사[한글] 파열전의 뇌동맥류는 거의 증상을 나타내지 않고 임상적으로 문제를 일으키지 않으나, 일단 파열되면 높은 유병률 및 사망률을 초래하게 되므로 파열전 적극적인 치료가 중요하다. 따라서 파열위험을 예측할 수 있는 기준이 필요한데, 뇌동맥류의 파열에 관여하는 인자들 즉, 뇌동맥류 모혈관의 혈류역동학적 변화, 뇌동맥류벽의 병태, 뇌동맥류의 크기 및 위치, 환자의 나이, 성별 및 혈압 등의 여러 가지 중뇌동맥류의 크기가 가장 중요하다고 알려져 왔다. 이에 저자는 뇌혈관조영술소견을 분석하여 파열된 뇌동맥류의 크기를 측정함으로써 파열위험의 기준이 되는 임계치를 알아보고자 하였고, 뇌동맥류의 위치별 분포 및 그에 따른 크기의 차이가 있는가, 뇌동맥류의 모양을 보아 파열여부를 예측할 수 있는가를 보았으며, 전산화단층촬영을 함께 비교 분석하였다. 1989년 7월부터 1991년 12월까지 임상적으로 뇌동맥류 파열에 의한 지주막하출혈을 의심하여 전산화단층촬영 및 뇌혈관조영술을 시행하고 영상 검사 등 기록을 확인할 수 있었던 100명의 판자를 대상으로 하였다. 뇌혈관조영술상 뇌동맥류 크기의 최대치를 측정하였고, 뇌동맥류의 위치 ,숫자 및 모양을 보았으며, 위치 분포에 따른 크기의 차이를 분석하였다. 전산화단층촬영을 참고하여 지주막하출혈분포로 파열 뇌동맥류의 위치를 예측해 보았고, 지주막하출혈의 정도와 뇌동맥류 크기사이의 상관관계, 뇌실질내 혈종 및 뇌실출혈의 동반빈도를 보았으며, 이들이 지주막하출혈의 정도와 관계가 있는지를 살펴본 결과 다음과 같은 결과를 얻었다. 1. 연령은 23세에서 15세 사이로 평균 52.2세로 50대에서 그 빈도가 가장 높았고, 성별은 남녀비가 45:55로 여자가 약간 많았다. 2. 동맥류의 수는 단일성 동맥류가 78예였고, 다발성 동맥류는 22예로서 2개의 동맥류는 14예, 3개 이상은 8예에서 관찰되었다. 3. 파열된 동맥류의 크기는 2-l8mm 사이였고 평균 7.9±3.2mm로 나타났으며, 파열되지 않은 뇌동맥류의 크기는 2-9mm로 평균 4.0±1.5mm 로서, 파열된 동맥류의 크기가 컸다(t=0.677, p < 0.001). 4. 동맥류의 위치별 분포는 전대뇌동맥이 34%였고 이 중 전교통동맥이 29.6%였으며, 내경동맥은 35.5%, 그 중 후교통동맥 22.2%로 나타났고, 중대뇌동맥은 28.2%를 차지하였으며, 각 위치에 따른 동맥류 크기의 차이는 없었다. 5. 뇌혈관조영술상의 뇌동맥류 모양을 기준으로 68.9%에서 파열여부를 예측할 수 있었다. 6. 전산화 단층촬영상 지주막하 출혈의 분포, 뇌실질내혈종의 위치 및 조영증강된 소결절로 나타나는 동맥류 자체의 음영을 토대로 47%에서 파열 뇌동맥류의 위치를 추정할 수 있었다. 7. 전산화단층촬영상 86%에서 지주막하출혈을 진단할 수 있었고, 15.3%에서 동맥류 자체를 관찰할 수 있었으며, 뇌실질내혈종은 11%에서 뇌실출혈은 10%에서 동반되었다. 8. 전산화단층촬영상 지주막하출혈의 정도와 실제 뇌동맥류의 크기 및 뇌실확장 동반빈도는 무관하였고, 지주막하출혈이 심할수록 뇌실출혈의 동반빈도는 높게 나타났다. 이상의 결과로 보아 뇌동맥류의 파열임계치를 특정수치로 확정지을 수는 없으나 뇌혈관조영술상 5-lOmm 크기의 파열동맥류가 가장 빈도가 놓으므로, 5mm이상의 최대직경을 갖는 동맥류 발견시 수술 등의 적극적 치료를 하는 것이 바람직하리라 사료된다. 그러나 본 연구만으로 정착한 파열임계치의 특정간을 결정지을 수는 없고, 더우기 동맥류파열이 단순히 뇌동맥류의 크기만으로 결정되지는 않으므로 추후 동맥류파열에 영향을 끼치는 다른 중요인자에 관한 연구가 필요하리라 생각된다. [영문] Intracranial aneurysms do not cause significant symptoms or present serious clinical problems when unruptured, but once rupture occurs, it is associated with a high morbidity and mortality rate, and therefore active management before rupture and methods to predict are necessary. Factors predisposing to aneurysm rupture such as hemodynamic changes in the parent vessel, pathophysiology of the aneurysm wall, size and location of the aneurysm, age, sex aid blood pressure of the patient are thought to be important contributing factors. The authors analysed the angiograms along with CTs in order to evaluate the size of ruptured aneurysms and to obtain the critical size that an aneurysm becomes hazardous, and to observe if there is any significant difference in the distribution of the location and size of aneurysms, and to see if rupture of the aneurysms can be predicted according to its shape. From July 1989 to Dec. 1991, 100 patients who underwent cerebral angiograhy and CT due to clinically ruptured aneufsm leading to SAH were studied. The maximum size of the aneurysms was measured on the angiograms, and the location, number and shape of each aneurysm was noted. The difference in size according to differing locations, the correlation between the size of aneurysm and degree of SAH, the rate of combined presence of intracerebral hematoma and initraventricular hemorrhage were all analysed with respect to degree of SAH, and the following results were obtained. 1. The mean age of the subject was 52.2 years (range 23-75 years), the 6th decade being the most common, and the ratio of males and females was 45:55. 2. Single aneurysms were present in 78 cases, and multiple aneurysms were present in 22 cases, of which 14 cases had 2 aneurysms, and 8 cases had 3 or more. 3, The size of the ruptured aneurysms were between 2-l8mm (mean 7.9±3.2mm),and for the unruptured aneurysm the sine was 2-9mm (mean 4.0± 1.5mm), showing that ruptured aneurysm were significantly larger. 4. The locations of aneurysms were anterior cerebral artery (34%) among which A-COM was 29.6%, internal carotid artery (35.5%) among which P-COM was 22.2% and MCA (28.2%), which showed no significant difference in size. 5. According to the shape of aneurysm, rupture was predicted in more than 68.9% of the cases studied. 6. The location of 47% of the ruptured aneurysms could be assumed by studying the distribution of SAH on CT, and by the density of the aneurysm itself representing as enhancing nodules and the site of the ICH. 7. Diagnesis of the SAH could be made in 86% by CT, and 15.3% of the aneurysms could be detected. Intracerebral hematomas were present in 11 %and IVH was present in 10% of the cases. 8. There was no correlation between the degree of SAH and size of the aneurysms, but the severity of SAH correlated with the incidence of IVH. In conclusion, the exact relationship between the size of unruptured aneurysm and liklihood of bleeding remains poorly defined. However, our data revealed the average longest diameter was 5-lOmm in the most cases of reptured aneurysm. Therefore, intact sacs less than 10mm in diameter cannot be considered innocuous. Until further information is available, we recommended surgical correction of the aneurysms greater than 5mm in longest diameter. However, further study regarding attributing factors of aneurysmal rupture other than aneurysmal size should be taken into consideration.restrictio

이산 시간 외란 관측기의 해석과 설계

Thesis(masters) --서울대학교 대학원 :전기. 컴퓨터공학부,2010.2.Maste