Fault diagnosis in spacecraft attitude control system

This thesis presents a method for fault diagnosis in spacecraft attitude control system. The focus of this diagnosis problem will be on the actuator components. The considered actuator is assumed to be a reaction wheel. Since the attitude model of the spacecraft to be used is a coupled three-axis, three reaction wheels are required to provide actuation signals in this system. A high-fidelity model of the reaction wheel is considered which incorporates the effect of most disturbances involved in practice. A controller is designed to guarantee the stability of the signals in the system. This controller is designed according to nearly ideal model of the reaction wheel in a single axis system. The performance of this controller is validated for the three-axis nonlinear model of the spacecraft attitude control system using nonlinear model of the reaction whee

Modeling and control of angioplasty balloon deployment based on intravascular optical coherence tomography

Cardiovascular disease is the leading cause of death in industrialized nations. Angioplasty is performed on millions of patients every year. It is, therefore, essential to constantly explore and investigate new approaches to study and improve the outcomes of this minimally-invasive procedure. In this thesis, novel applications of intravascular optical coherence tomography (IVOCT) are proposed, namely, monitoring, characterization, simulation, and control of balloon inflation.High-resolution IVOCT images lead to a detailed assessment of microstructures. Using image analysis techniques, IVOCT characterization of balloon deformation is presented as a method to validate the performance of balloons. IVOCT characterization of the deformation of artery phantoms is proposed as a method to study the tissue's response to various balloon sizes, various balloon folding strategies and various inflation strategies.In addition, IVOCT characterization of deformation is proposed as a method to validate simulation results. This thesis provides a comparison between finite-element simulation results and experimental results for two case studies, which investigate the effects of variation of mechanical properties as well as balloon unfolding and inflation process.Finally, in this thesis, methods are proposed to control the balloon inflation. During balloon inflation, the luminal diameter of an artery could be estimated in real-time and used in a feedback loop to control the inflation. The experimental relevance of this method is demonstrated when the balloon is inflated in an artery phantom, in an artery of an excised porcine heart and in an artery of a beating porcine heart.The methods and the results, provided in this thesis, could benefit the developers of angioplasty devices, cardiovascular research, and clinical users.Les maladies cardiovasculaires sont la principale cause de décès dans les pays industrialisés. L'angioplastie est réalisée sur des millions de patients chaque année. Il est donc essentiel de constamment explorer et étudier de nouvelles approches pour étudier et améliorer les résultats de cette procédure peu invasive. Dans cette thèse, de nouvelles applications de la tomographie par cohérence optique intravasculaire (IVOCT) sont proposées, à savoir, la surveillance, la caractérisation, la simulation et le contrôle du gonflement du ballon.Des images haute résolution IVOCT mènent à une évaluation détaillée des microstructures. En utilisant des techniques d'analyse d'image, la caractérisation de la déformation du ballon est présentée comme une méthode pour valider la performance de ballons. La caractérisation de la déformation des fantômes est proposée comme une méthode pour étudier la réponse des tissus à des tailles différentes de ballons, et diverses stratégies de pliage et de gonflement du ballon. En outre, la caractérisation de la déformation est proposée pour valider les résultats de simulation. Une comparaison est fournie entre les résultats de la simulation par éléments finis et des résultats expérimentaux pour les deux études de cas, qui étudient les effets de la variation des propriétés mécaniques ainsi que le processus de déploiement et de gonflement du ballon. Enfin, dans cette thèse, des méthodes sont proposées pour contrôler le gonflement du ballon. Pendant le gonflement du ballon, le diamètre luminal de l'artère peut être estimé en temps réel et utilisé dans une boucle de rétroaction pour contrôler le gonflement. La pertinence expérimentale de cette méthode est démontrée lorsque le ballon est gonflé dans un fantôme, dans les artères porcines d'un cœur excisé et d'un cœur battant. Les méthodes et les résultats fournis dans cette thèse pourraient bénéficier aux développeurs de dispositifs d'angioplastie, à la recherche cardiovasculaire et aux utilisateurs cliniques

Angioplasty Balloon Deployment Control

Abstract-Application of control engineering methods is suggested for percutaneous coronary intervention. In particular, angioplasty balloon deployment control is discussed. A general control structure is proposed with the aim of reducing possible arterial damage during balloon deployment

Traveling patterns in a network of memristor-based oscillators with extreme multistability

The study of collective behaviors in the networks of memristive systems has achieved negligible attention. In this paper, a ring network of memristive based Wien-bridge oscillators is investigated. The Wien-bridge oscillator exhibits extreme multistability. Therefore, the initial conditions of the network can play an important role in the emergence of different spatiotemporal patterns. Here, the initial conditions are chosen in a small region, in which a single oscillator shows various attractors with similar topologies. It is observed that by varying the coupling strength and coupling range, various patterns are formed. In most of the appeared patterns, the traveling of coexistent coherent and incoherent oscillators is observed, whether in a part of the pattern or in the whole. It seems that the traveling patterns are formed due to the multistability of the oscillators and their time-scaled time series. Overall, by varying the coupling parameters, several patterns such as chimera state, traveling chimera and nonstationary chimera, are emerged in the network

Awareness and apgar score in elective Cesarean section under general anesthesia with propofol or Isoflurane: A prospective, randomized, double-blinded clinical trial study

Background: Awareness is a postoperative recall of events experienced under general anesthesia. In this study, we compared the incidence of awareness between two routine methods used, inhalation (Isoflurane) and intravenous protocol (Propofol), in elective Cesarean section, and also evaluated the effect of these two different methods on the apgar score of newborns. Materials and Methods: In this prospective, clinical trial study, 90 pregnant women candidates for elective Cesarean section were randomly enrolled, after taking written consent. Induction of anesthesia in both groups was provided by propofol and succinylcholine in the same manner, and maintenance of anesthesia in Group 1 was provided by propofol 100 μg/kg/minute and in Group 2 with isoflurane 1 MAC, to maintain the bispectral index (BIS) between 45 and 60. Blood pressure, heart rate, electrocardiography (ECG), and also Etco2 and o2sat were recorded throughout the surgery and finally analyzed and compared. Results: From 90 patients, four cases of confirmed awareness were found in the propofol group and three cases in the Isoflurane group (8/9% vs. 6/7%), but the apgar scores were comparable between the two groups. Meanwhile there were no significant differences between the two groups in basic information, neonatal apgar scores, hemodynamic changes, and BIS, Electromyography (EMG), and signal quality index (SQI) values. Conclusion: According to the patient′s state, diagnosis of the anesthesiologist, and other criteria like price and its availability, we could use these drugs in general anesthesia during Cesarean section, although it is recommended that more studies be done to compare the effect of these two drugs in larger groups

Toward better treatment of clogged arteries

Real-time detailed monitoring of angioplasty balloon deformation may lead to improved medical devices to treat hardened artery walls.Peer reviewed: YesNRC publication: Ye

Detecting chimeras by eigenvalue decomposition of the bivariate local order parameter

It has been shown that the eigenvalue decomposition of the matrix of the bivariate phase synchronization measure can be used for the detection of cluster synchronization. It has also been shown that other measures, such as the strength of incoherence and various local order parameters, can be used to quantitatively characterize chimeras, or chimera states. Here we bridge these two domains by showing that the eigenvalue decomposition method can also be used for the detection of chimeras. We compute the local order parameter for all oscillator pairs and apply the eigenvalue decomposition on the bivariate matrix. We show that, in contrast to cluster synchronization, there are more eigenvalues above one than the number of synchronized clusters in the network. The corresponding eigenvectors correspond to synchronized groups, while the oscillators that are not represented by the eigenvectors form the chimeras. We demonstrate our approach on coupled Liénard equations and FitzHugh-Nagumo neurons

Prevention of postoperative nausea and vomiting with a subhypnotic dose of Propofol in patients undergoing lower abdominal surgery: A prospective, randomized, double-blind study

Background: Postoperative nausea and vomiting (PONV) is a common complication after general anesthesia in patients undergoing elective lower abdominal surgery. We aimed to compare the effect of a sub hypnotic dose of Propofol in the prevention of PONV after lower abdominal surgery with that of the conventional antiemetic drug Metoclopramide. Materials and Methods: In this prospective, randomized, double-blind, placebo-controlled study, 104 patients with American Society of Anesthesiologists (ASA) class I or II status, aged 18-65 years, and undergoing elective lower abdominal surgery were randomized to one of four groups (n = 26 each). The patients in the four groups were administered intravenously Propofol 20 mg (G1), Propofol 30 mg (G2), Metoclopramide 10 mg (G3), and placebo (G4), 15 min before skin closure. All episodes of PONV during the first 24 h after anesthesia were recorded by an investigator who was blinded to treatment assignment. Results: There were no significant differences between the treatment groups with regard to their gender, age, ASA class, duration of surgery, duration of recovery time and hospital stay, and also body mass index (BMI) (P > 0.05). The prevalence of PONV 0-6 h after anesthesia was 23.08% with Propofol 20 mg (P = 0.005), 15.38% with Propofol 30 mg (P = 0.016), 15.38% with Metoclopramide 10 mg (P = 0.016), compared to 30.77% with placebo (P = 0.005). Conclusions: Administration of a subhypnotic dose of Propofol (30 mg) was found to be as effective as 10 mg Metoclopramide in reducing the incidence and severity of PONV in adult patients undergoing elective lower abdominal surgeries under Isoflurane-based anesthesia in the early postoperative period