Geometric synthesis of a hybrid limit cycle for the stabilizing control of a class of nonlinear switched dynamical systems

International audienceThis paper proposes a new constructive method for synthesizing a hybrid limit cycle for the stabilizing control of a class of switched dynamical systems in IR 2 , switching between two discrete modes and without state discontinuity. For each mode, the system is continuous, linear or nonlinear. This method is based on a geometric approach. The first part of this paper demonstrates a necessary and sufficient condition of the existence and stability of a hybrid limit cycle consisting of a sequence of two operating modes in IR 2 which respects the technological constraints (minimum duration between two successive switchings, boundedness of the real valued state variables). It outlines the established method for reaching this hybrid limit cycle from an initial state, and then stablizing it, taking into account the constraints on the continuous variables. This is then illustrated on a Buck electrical energy converter and a nonlinear switched system in IR 2. The second part of the paper proposes and demonstrates an extension to IR n for a class of systems, which is then illustrated on a nonlinear switched system in IR 3

Computational Laser Spectroscopy in a Biological Tissue

We present a numerical spectroscopic study of visible and infrared laser radiation in a biological tissue. We derive a solution of a general two-dimensional time dependent radiative transfer equation in a tissue-like medium. The used model is suitable for many situations especially when the external source is time-dependent or continuous. We use a control volume-discrete ordinate method associated with an implicit three-level second-order time differencing scheme. We consider a very thin rectangular biological-tissue-like medium submitted to a visible or a near infrared light sources. The RTE is solved for a set of different wavelength source. All sources are assumed to be monochromatic and collimated. The energetic fluence rate is computed at a set of detector points on the boundaries. According to the source type, we investigate either the steady-state or transient response of the medium. The used model is validated in the case of a heterogeneous tissue-like medium using referencing experimental results from the literature. Also, the developed model is used to study changes on transmitted light in a rat-liver tissue-like medium. Optical properties depend on the source wavelength and they are taken from the literature. In particular, light-transmission in the medium is studied for continuous wave and for short pulse

Neurocognitive outcome after preterm birth: Interest of the follow-up and the systematic evaluation

ObjectivePreterm children can experience cognitive and behavioral difficulties being able to be responsible for school difficulties going to the academic failure. The aim of this study was to assess the cognitive process while insisting on the early screening from the preschool age.MethodsThe data arise from the study of files and from the neuropsychological evaluations realized with the premature children followed in a regular way to the service. The premature children with or without motor disabilities more 4 and a half-years, old deficit integrated pre-school and ordinary school were included. The children with severe disabilities in upper limbs and the children having a mental deficiency were excluded.Results30 middle-aged children 7 years 5 months have been included. The prematurity is between 27–34. The born term has an effect on the performances in particular on attention and visuo-spatial capacities.ConclusionThe prematurity is a risk factor of the school future of the child. There is specially a negative impact on visuo-spatial and visuo-motor processes and those children present social and behavioral difficulties. It is mandatory to include the neuropsychological evaluation in any follow-up of premature child thanks to tests validated in the Tunisian context. It remains of great importance to identify effective interventions to improve the long-term neurocognitive outcomes