A Near-Optimal Decentralized Servomechanism Controller for Hierarchical Interconnected Systems

This paper is concerned with decentralized output regulation of hierarchical systems subject to input and output disturbances. It is assumed that the disturbance can be represented as the output of an autonomous LTI system with unknown initial state. The primary objective is to design a decentralized controller with the property that not only does it reject the degrading effect of the disturbance on the output (for a satisfactory steady-state performance), it also results in a small LQ cost function (implying a good transient behavior). To this end, the underlying problem is treated in two phases. In the first step, a number of modified systems are defined in terms of the original system. The problem of designing a LQ centralized controller which stabilizes all the modified systems and rejects the disturbance in the original system is considered, and it is shown that this centralized controller can be efficiently found by solving a LMI problem. In the second step, a method recently presented in the literature is exploited to decentralize the designed centralized controller. It is proved that the obtained controller satisfies the pre-determined design specifications including disturbance rejection. Simulation results elucidate the efficacy of the proposed control law

Decentralized control of uncertain interconnected time-delay systems

In this thesis, novel stability analysis and control synthesis methodologies are proposed for uncertain interconnected time-delay systems. It is known that numerous real-world systems such as multi-vehicle flight formation, automated highway systems, communication networks and power systems can be modeled as the interconnection of a number of subsystems. Due to the complex and distributed structure of this type of systems, they are subject to propagation and processing delays, which cannot be ignored in the modeling process. On the other hand, in a practical environment the parameters of the system are not known exactly, and usually the nominal model is used for controller design. It is important, however, to ensure that robust stability and performance are achieved, that is, the overall closed-loop system remains stable and performs satisfactorily in the presence of uncertainty. To address the underlying problem, the notion of decentralized fixed modes is extended to the class of linear time-invariant (LTI) time-delay systems, and a necessary and sufficient condition is proposed for stabilizability of this type of systems by means of a finite-dimensional decentralized LTI output feedback controller. A near-optimal decentralized servomechanism control design method and a cooperative predictive control scheme are then presented for uncertain LTI hierarchical interconnected systems. A H {592} decentralized overlapping control design technique is provided consequently which guarantees closed-loop stability and disturbance attenuation in the presence of delay. In particular, for the case of highly uncertain time-delay systems, an adaptive switching control methodology is proposed to achieve output tracking and disturbance rejection. Simulation results are provided throughout the thesis to support the theoretical finding

Sufficient conditions for the convergence of a class of nonlinear distributed consensus algorithms

This paper is concerned with the convergence of a class of continuous-time nonlinear consensus algorithms for single integrator agents. In the consensus algorithms studied here, the control input of each agent is assumed to be a state-dependent combination of the relative positions of its neighbors in the information flow graph. Using a novel approach based on the smallest order of the nonzero derivative, it is shown that under some mild conditions the convex hull of the agents has a contracting property. A set-valued LaSalle-like approach is subsequently employed to show the convergence of the agents to a common point. The results are shown to be more general than the ones reported in the literature in some cases. An illustrative example demonstrates how the proposed convergence conditions can be verifie

Effect of Fluoxetine Consumption on Orthodontic Tooth Movement in Rats

Objectives: Fluoxetine is a selective serotonin re-uptake inhibitor (SSRI) widely used for depression, bipolar disorder, anxiety and obsessive-compulsive disorder. The aim of this study was to assess the effect of fluoxetine on orthodontic tooth movement (OTM) in rats. Materials and Methods: Forty-five male Wistar rats were randomly divided into three groups namely the control group (no medication), saline and fluoxetine dissolved in saline. In all groups, nickel titanium closed-coil spring was used between the left maxillary central incisor and first molar to exert 60g force at 2mm activation. Radiographs were taken at one and 21 days. After 21 days, the rats were sacrificed. The distance between the first and second molar teeth, optical density of bone, periodontal ligament (PDL) width, lacuna length and depth and number of osteoclasts were measured and compared among the groups. Results: Tooth movement significantly increased in the fluoxetine group (P=0.005). No significant differences were found in osteoclast count (P=0.069). The PDL width in the mesioapical region of root was significantly different among the groups (P=0.015). Statistical analysis did not show significant differences in depth or length of lacunae in any examined part of the root (P>0.05). Bone densitometry results showed that in fluoxetine group, density of bone in all four areas (alveolar bone, hard palate, skull and mandibular bone) significantly decreased from day one to day 21 (P< 0.05). Conclusion: This study indicated that fluoxetine decreased bone density, which resulted in subsequently greater tooth movement in rats; however, further studies are needed on humans

Effect of Long-Term Captopril Administration on Bone Density and Orthodontic Tooth Movement

Background and Aim: Captopril is an oral angiotensin-converting-enzyme (ACE) inhibitor extensively used in the treatment of hypertension and heart failure. ACE has been suggested to function in bone cells and might therefore impact orthodontic tooth movement (OTM). Considering the controversy surrounding the effects of ACE and its inhibitors on osseous tissues, we aimed to evaluate the effect of captopril on OTM for the first time in a rat model. Materials and Methods: Orthodontic appliances were fixed between the left first molars and incisors of 30 rats divided into three groups (n=10) receiving captopril, saline or no treatment. Following sacrifice on day 21, the amount of tooth movement was measured as the distance created between the first and second molars. Bone density was assessed by lateral cephalograms on days 1 and 21 and osteoclast number, root resorption and periodontal ligament (PDL) width were analyzed histologically. One-way ANOVA followed by post-hoc test were used for statistical analysis (P<0.05) Results: OTM significantly increased in the captopril group compared to the saline and no-treatment groups (P<0.05). Bone density significantly decreased in the mandible of the captopril group from day 1 to 21 (P<0.05). No significant differences were found in the histological variables except for the significant increase in PDL width at the mesioapical aspect in the captopril group. Conclusion: The present study showed that captopril administration could lead to increased OTM and decreased bone density in rats. Further studies are suggested to clarify its exact role at the cellular and molecular levels. Key Words: Captopril, Tooth Movement Techniques, Rat