STABLE ADAPTIVE CONTROL FOR A CLASS OF NONLINEAR SYSTEMS WITHOUT USE OF A SUPERVISORY TERM IN THE CONTROL LAW

In this paper, a direct adaptive control scheme for a class of nonlinear systems is proposed. The architecture employs a Gaussian radial basis function (RBF) network to construct an adaptive controller. The parameters of the adaptive controller are adapted and changed according to a law derived using Lyapunov stability theory. The centres of the RBF network are adapted on line using the k-means algorithm. Asymptotic Lyapunov stability is established without the use of a supervisory (compensatory) term in the control law and with the tracking errors converging to a neighbourhood of the origin. Finally, a simulation is provided to explore the feasibility of the proposed neuronal controller design method

Neural feedback linearization adaptive control for affine nonlinear systems based on neural network estimator

In this work, we introduce an adaptive neural network controller for a class of nonlinear systems. The approach uses two Radial Basis Functions, RBF networks. The first RBF network is used to approximate the ideal control law which cannot be implemented since the dynamics of the system are unknown. The second RBF network is used for on-line estimating the control gain which is a nonlinear and unknown function of the states. The updating laws for the combined estimator and controller are derived through Lyapunov analysis. Asymptotic stability is established with the tracking errors converging to a neighborhood of the origin. Finally, the proposed method is applied to control and stabilize the inverted pendulum system

A Mixed Binary-Real NSGA II Algorithm Ensuring Both Accuracy and Interpretability of a Neuro-Fuzzy Controller

In this work, a Neuro-Fuzzy Controller network, called NFC that implements a Mamdani fuzzy inference system is proposed. This network includes neurons able to perform fundamental fuzzy operations. Connections between neurons are weighted through binary and real weights. Then a mixed binary-real Non dominated Sorting Genetic Algorithm II (NSGA II) is used to perform both accuracy and interpretability of the NFC by minimizing two objective functions; one objective relates to the number of rules, for compactness, while the second is the mean square error, for accuracy. In order to preserve interpretability of fuzzy rules during the optimization process, some constraints are imposed. The  approach  is  tested  on  two  control examples:  a single  input  single  output (SISO) system  and  a  multivariable (MIMO) system

Infinite horizon fuzzy optimal control: optimality does not imply asymptotic stability

In this paper, novel stability result for discrete-time infinite horizon optimal control using fuzzy objective functions is presented. For this class of control, the fuzzy goals and the fuzzy constraints introduced in the fuzzy objective function handle the constraints placed on both the state and the control vectors. We analyze the asymptotic stability of the equilibrium for the infinite horizon fuzzy optimal control law using the minimum aggregation operator. We show that the infinite horizon control with the minimum aggregation operator does not guarantee the asymptotic stability of the equilibrium in general. This is done by deriving an analytical solution of the control law for a simple linear system using a fuzzy dynamic programming approach. An example that shows the novel asymptotic stability result of the equilibrium for discrete-time infinite horizon optimal control with fuzzy objective function problem is given

MULTI-OBJECTIVE PREDICTIVE CONTROL: A SOLUTION USING METAHEURISTICS

ABSTRACT KEYWORDS Model predictive control, Metaheuristcis, Multiobjective Optimization

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Transistors en couches minces de silicium microcristallin fabriqués à T<180 C (stabilité et mobilité)

e travail de thèse porte sur la réalisation de transistors en couches minces (Thin film transistors) de silicium microcristallin fabriqués à une température inférieure à 180C. Cette thèse permet d envisager diverses applications allant de la technologie des écrans OLED jusqu à l électronique flexible associée au textile intelligent. Pour le bon fonctionnement de ces applications, il est nécessaire de produire des transistors performants. C est pourquoi ces travaux de thèse visent la fabrication de transistors respectant les conditions pour un bon fonctionnement des applications attendues, c'est-à-dire une dualité mobilité-stabilité satisfaisante. Les premiers transistors en structure Top-Gate utilisant l oxyde de silicium comme isolant de grille ont abouti à d excellentes performances (40 cm /Vs). Ces derniers s avérèrent ne pas être fiable en terme de stabilité. Beaucoup de questions se sont alors posées pour remédier à cette instabilité. Des techniques telles que les mesures électriques (énergie d activation de la conductivité) et physiques (SIMS) ont permis de comprendre d où venait le problème. Il s avère que lors du dépôt de l isolant, une importante incorporation d oxygène pénètre dans la structure colonnaire du silicium microcristallin. La première solution consistait donc à utiliser une couche fine de silicium microcristallin. Les transistors ainsi fabriqués ne dérivent que faiblement. La deuxième solution consistait à l élaboration d un isolant autre que l oxygène lors du dépôt. Par le biais du nitrure de silicium, les transistors en structure Top-Gate de type N montrent une mobilité de (2 cm /Vs) et une bonne stabilité. Enfin, des transistors de type P ont été également fabriqués rendant possible la mise au point d une technologie de type CMOS avec le silicium microcristallin.This work deals with the achievement of microcrystalline silicon transistors (Thin film transistors) produced at a temperature below 180C. This thesis can lead to multiple applications such as OLED flat panel technology, flexible electronics used on intelligent textile. To fit with these applications, it is necessary to produce high performance transistors. This is why, present thesis aims to the production of transistors that follow the good functioning of the expected applications, that is to say a satisfactory mobility and stability. The first top gate transistors using silicon dioxide as gate insulator brought about great performances (40 cm /Vs). These transistors are not reliable in terms of stability. A lot of questions raised regarding the instability issues. Characterization techniques such as electrical measurements (thermal activation of the conductivity) and physical analysis (SIMS) were useful to determine the origin of the instability. During the insulator deposition, strong diffusion of oxygen goes into the column boundaries of the microcrystalline silicon. The first option was to use a dense structure of microcrystalline silicon. By this way, the threshold voltage shift of the transistors decreased highly. The second option was to develop an insulator, which do not need the use of oxygen during its deposition. Through the use of silicon nitride, N type top gate transistors show a mobility of (2 cm /Vs) and a good stability. P type transistors were also produced allowing the conception of the CMOS technology with microcrystalline silicon.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF