Contribution à la mise au point d'une procédure de caractérisation quantitative des surfaces en béton en vue de travaux de réfection

Ce mémoire porte sur les surfaces préparées en béton en vue de travaux de réfection. L’objectif principal vise le développement d’une méthode de caractérisation quantitative des surfaces préparées. Le projet comporte également deux objectifs spécifiques : évaluer l’influence des méthodes de préparation sur l’intégrité des surfaces en béton et vérifier l’existence d’une corrélation entre la rugosité de surface et l’adhérence de réparations en béton. Afin d’atteindre ces objectifs, le projet a été divisé en trois principaux volets où plusieurs essais expérimentaux ont été réalisés, ainsi qu’une modélisation de l’essai d’adhérence. Le premier volet expérimental porte sur l’évaluation de l’intégrité des surfaces préparées. Les essais ont démontré que l’endommagement du béton réduit de manière significative la résistance de la surface préparée. Le second volet présente les résultats qui ont conduit au développement et à la validation d’une nouvelle méthode d’évaluation quantitative des surfaces préparées. La méthode permet de réaliser des essais de caractérisation rapidement (environ 2 heures) sur des surfaces tant horizontales, verticales qu’en surplombs. Le troisième volet expérimental comporte l’étude de la rugosité de surface et de l’adhérence des réparations en béton. Ce dernier volet inclut une partie expérimentale et une partie modélisation. Les résultats montrent que l’endommagement du substrat est beaucoup plus critique que la rugosité de surface. En effet, aucune corrélation entre la rugosité de surface et l’adhérence des réparations en béton n’a été observée à l’échelle d’observation étudiée. Pour terminer, des recommandations sont émises concernant les critères d’acceptation relatifs à la préparation de surface et à l’adhésion en place d’une réparation.The subject of this master is surface preparation of concrete for repair works. The main objective aims at developing a quantitative characterization method for the prepared surfaces. The project also includes two specific objectives: evaluate the influence of preparation methods on the integrity of concrete surfaces and verify the existence of a correlation between the surface roughness and the bond of the concrete repair. In order to achieve these goals, the project was divided into three parts where several experimental tests were carried out, as well as a modeling of the bond test. The first experimental part evaluates the integrity of the prepared surfaces. The tests revealed that damage in concrete decreases significantly the resistance of the prepared surface. The second part presents the results on the development and validation of a new quantitative evaluation method of prepared surfaces. The method makes it possible to quickly carry out characterization tests (approximately 2 hours) on prepared surfaces (horizontal, vertical or overhanging). The third experimental part deals with the study of the surface roughness and the bond of concrete repairs. This last segment includes an experimental and modeling part. The results show that substrate damage is more critical than surface roughness. In fact, no correlation between surface roughness and bond of concrete repairs was observed on the studied observation scale. Finally, recommendations are given for acceptance criteria relating to the surface preparation and adhesion of the in place repair

On positive solutions and the Omega limit set for a class of delay differential equations

This paper studies the positive solutions of a class of delay differential equations with two delays. These equations originate from the modeling of hematopoietic cell populations. We give a sufficient condition on the initial function for $t\leq 0$ such that the solution is positive for all time $t>0$. The condition is "optimal". We also discuss the long time behavior of these positive solutions through a dynamical system on the space of continuous functions. We give a characteristic description of the $\omega$ limit set of this dynamical system, which can provide informations about the long time behavior of positive solutions of the delay differential equation.Comment: 15 pages, 2 figure

Global exponential stability of nonautonomous neural network models with continuous distributed delays

For a family of non-autonomous differential equations with distributed delays, we give sufficient conditions for the global exponential stability of an equilibrium point. This family includes most of the delayed models of neural networks of Hopfield type, with time-varying coefficients and distributed delays. For these models, we establish sufficient conditions for their global exponential stability. The existence and global exponential stability of a periodic solution is also addressed. A comparison of results shows that these results are general, news, and add something new to some earlier publications.Fundação para a Ciência e a Tecnologia (FCT

Global asymptotic stability for neural network models with distributed delays

In this paper, we obtain the global asymptotic stability of the zero solution of a general n-dimensional delayed differential system, by imposing a condition of dominance of the nondelayed terms which cancels the delayed effect. We consider several delayed differential systems in general settings, which allow us to study, as subclasses, the well known neural network models of Hopfield, Cohn-Grossberg, bidirectional associative memory, and static with S-type distributed delays. For these systems, we establish sufficient conditions for the existence of a unique equilibrium and its global asymptotic stability, without using the Lyapunov functional technique. Our results improve and generalize some existing ones.Fundação para a Ciência e a Tecnologia (FCT

Convergence of asymptotic systems of non-autonomous neural network models with infinite distributed delays

In this paper we investigate the global convergence of solutions of non-autonomous Hopfield neural network models with discrete time-varying delays, infinite distributed delays, and possible unbounded coefficient functions. Instead of using Lyapunov functionals, we explore intrinsic features between the non-autonomous systems and their asymptotic systems to ensure the boundedness and global convergence of the solutions of the studied models. Our results are new and complement known results in the literature. The theoretical analysis is illustrated with some examples and numerical simulations.The paper was supported by the Research Centre of Mathematics of the University of Minho with the Portuguese Funds from the "Fundacao para a Ciencia e a Tecnologia", through the Project PEstOE/MAT/UI0013/2014. The author thanks the referee for valuable comments.info:eu-repo/semantics/publishedVersio

Complex Dynamics and Multistability in a Damped Harmonic Oscillator with Delayed Negative Feedback

A center manifold reduction and numerical calculations are used to demonstrate the presence of limit cycles, two-tori, and multistability in the damped harmonic oscillator with delayed negative feedback. This model is the prototype of a mechanical system operating with delayed feedback. Complex dynamics are thus seen to arise in very plausible and commonly occurring mechanical and neuromechanical feedback systems

Cartoons kill: casualties in animated recreational theater in an objective observational new study of kids' introduction to loss of life.

Objectives To assess the risk of on-screen death of important characters in children’s animated films versus dramatic films for adults. Design Kaplan-Meier survival analysis with Cox regression comparing time to first on-screen death. Setting Authors’ television screens, with and without popcorn. Participants Important characters in 45 top grossing children’s animated films and a comparison group of 90 top grossing dramatic films for adults. Main outcome measures Time to first on-screen death. Results Important characters in children’s animated films were at an increased risk of death compared with characters in dramatic films for adults (hazard ratio 2.52, 95% confidence interval 1.30 to 4.90). Risk of on-screen murder of important characters was higher in children’s animated films than in comparison films (2.78, 1.02 to 7.58). Conclusions Rather than being the innocuous form of entertainment they are assumed to be, children’s animated films are rife with on-screen death and murder

Sustained IFN signaling is associated with delayed development of SARS-CoV-2-specific immunity.

Plasma RNAemia, delayed antibody responses and inflammation predict COVID-19 outcomes, but the mechanisms underlying these immunovirological patterns are poorly understood. We profile 782 longitudinal plasma samples from 318 hospitalized patients with COVID-19. Integrated analysis using k-means reveals four patient clusters in a discovery cohort: mechanically ventilated critically-ill cases are subdivided into good prognosis and high-fatality clusters (reproduced in a validation cohort), while non-critical survivors segregate into high and low early antibody responders. Only the high-fatality cluster is enriched for transcriptomic signatures associated with COVID-19 severity, and each cluster has distinct RBD-specific antibody elicitation kinetics. Both critical and non-critical clusters with delayed antibody responses exhibit sustained IFN signatures, which negatively correlate with contemporaneous RBD-specific IgG levels and absolute SARS-CoV-2-specific B and CD4 <sup>+</sup> T cell frequencies. These data suggest that the "Interferon paradox" previously described in murine LCMV models is operative in COVID-19, with excessive IFN signaling delaying development of adaptive virus-specific immunity

State-dependent distributed-delay model of orthogonal cutting

In this paper we present a model of turning operations with state-dependent distributed time delay. We apply the theory of regenerative machine tool chat- ter and describe the dynamics of the tool-workpiece sys- tem during cutting by delay-diferential equations. We model the cutting-force as the resultant of a force sys- tem distributed along the rake face of the tool, which results in a short distributed delay in the governing equation superimposed on the large regenerative de- lay. According to the literature on stress distribution along the rake face, the length of the chip-tool inter- face, where the distributed cutting-force system is act- ing, is function of the chip thickness, which depends on the vibrations of the tool-workpiece system due to the regenerative efect. Therefore, the additional short de- lay is state-dependent. It is shown that involving state- dependent delay in the model does not afect linear sta- bility properties, but does afect the nonlinear dynamics of the cutting process. Namely, the sense of the Hopf bi- furcation along the stability boundaries may turn from sub- to supercritical at certain spindle speed regions