Theoretical study of some structures of titanium(IV) complexes derived from 2-, 3- and 4-hydroxyl-benzoic acids

Complexes of fluoride titanium(IV) using hydroxyl benzoic acids as ligands are known for their great interest for care of the teeth, of the oral cavity or of dentures. Their activity is closely linked to the stability of their geometry. In this paper, we studied the structures of Ti(IV) complexes derived from hydroxyl-2-benzoic acid, hydroxyl-3-benzoic and hydroxyl-4-benzoic acids by molecular modelling. Calculations by molecular mechanics, Extended Huckel Theory (EHT) calculations have enabled access to the values of steric energy, bond lengths and bond angles, torsion angles, charges, coordinates of the atoms and the total energy values. The data obtained using molecular modelling are in the same range of those obtained in literature. Both data showed an octahedral structure around the metal ion of Ti(IV) complex with a small distortion.               KEY WORDS: Hydroxy benzoic acids, Ti(IV) complexes, Molecular modelling, Steric Energy, Stability Bull. Chem. Soc. Ethiop. 2018, 32(3), 571-577.DOI: https://dx.doi.org/10.4314/bcse.v32i3.1

Control of a flexible spacecraft using discrete IDA-PBC design

This paper has two objectives, first synthesize a discrete-time IDA-PBC for an underactuated port-Hamiltonian system, and second stabilize the angular position of an experimental testbed used in aerospace engineering. Based on the energetic integrator, the discrete-time methodology that exactly preserves the passivity property is presented for a linear Hamiltonian system with physical damping. A stability condition is given when taking the desired Hamiltonian as Lyapunov candidate function. The model of the spacecraft is composed of a rigid central body actuated by a torque motor around the vertical axis with two flexible appendages and a local mass at the tip of each appendage. Experiments are carried out to assess the validity of the more theoretical design methodology. The results show that the performances of our design results are better compared to an emulation controller obtained by sample and hold or Tustin transformation of the continuous-time controller

Optimizing the design of timber components under decay and climate variations

International audienceThe durability of timber structures can be affected by the isolated or combined actions of loading, moisture content, temperature, biological activity, etc. This work focuses on the optimal design of new timber structures subjected to deterioration. Since the deterioration processes and the structural behavior of timber structures are complex, nowadays the deterioration models are not able to account for all influencing factors. Consequently, this study is based on an empirical model that was derived based in-lab experimental studies for the decay growth of brown rot in pine sapwood under variant climate conditions. Such a model is divided into two processes: (i) activation process and (ii) mass loss process. On the other hand, there are significant uncertainties involved in the problem. The uncertainties inherent to materials properties, models and climate are considered throughout a time-dependent reliability based-design optimization (TD-RBDO) approach. The TD-RBDO aims to ensure a target reliability level during the operational life. This approach is applied to design optimization of a new timber component subjected to different French climates. The performance of the optimized solution is compared with a traditional cross-section designed according to the Eurocode 5 in terms of safety. The overall results indicate that an optimized solution ensures a target reliability level during the whole structural lifetime

Schémas d'intégration dédiés à l'étude, l'analyse et la synthèse dans le formalisme Hamiltonien à ports

This thesis work dealing with finite dimensional approximation of infinite dimension system. The class considered is that of Hamiltonian systems in ports. We study initially ordinary differential equations systems. Based on an energy integrator, we define a class of discrete passive dynamics is invariant interconnection. We obtain the stability conditions (LMI) for dynamic network in the presence of delays and uncertainties, and propose a method of stabilizing energy synthesis. These developments were experimentally validated by the implementation of an energy control a power converter (Buck). We then study the Hamiltonian formalism in infinite dimensions. We offer an approximation that combines a semi-discretization and an energy integrator. The mixed composability is studied and a method of synthesis IDA-PBC was developed. All the obtained results are numerically illustrated in the manuscript.Ces travaux de thèse traitent de l'approximation en dimension finie de système de dimension infinie. La classe considérée est celle des systèmes hamiltoniens à ports. Nous étudions dans un premier temps les systèmes d'équations différentielles ordinaires. Sur la base d'un intégrateur énergétique, nous définissons une classe de dynamiques passives discrètes qui est invariante par interconnexion. Nous obtenons alors des conditions de stabilité (LMI) pour des dynamiques en réseau en présence de retards et d'incertitudes, et proposons une méthode de synthèse énergétique stabilisante. Ces développements ont été validés expérimentalement par la mise en oeuvre d'une commande énergétique sur un convertisseur de puissance (Buck). Nous étudions ensuite le formalisme hamiltonien en dimension infinie. Nous proposons une approximation qui combine une semi-discrétisation et un intégrateur énergétique. La composabilité mixte est étudiée et une méthode de synthèse IDA-PBC a été développée. L'ensemble des résultats obtenus sont illustrés numériquement dans le manuscrit

Dactylifera L) on the biochemical indicators of lead poisoning in male Wistar rats

This study is conducted to examine the effect of the oral administration of pectin of dates on perturbation of the biochemical parameters induced by lead. Male rats were exposed to lead acetate at 350mg/Kg for one month, after this period, rats treated during one month with the pectin of date at 3%. Rats were sacrificed, the blood and urine are collected for the biochemical assays: glucose, total protein, phosphatase acide (PAC), alkaline phosphatase (PAL), aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatinine, urea and uric acid. The results showed that the exposure to lead has induced a disturbance in the biochemical parameters. Thus, the treatment by the pectin of dates reduced the high concentration of these parameters. Our results show that the pectins of dates may have a corrective effect on the biochemical disturbances induced by the lead.Keywords: Phoenix Dactylifera, Pectin, Lead, Biochemical parameter

Multiple solutions for flow mode−transition in an inclined cavity generated by natural convection

An investigation of natural convection in a rectangular cavity (AR = 4) filled with air (Pr = 0.71) heated from the side with adiabatic horizontal walls is carried out numerically. To describe the flow regime, we propose a description of the influence of the angle of inclination and Rayleigh number on the flow patterns likely to develop in this configuration. The numerical analysis of the governing equations of the problem is based on finite volume method with non-staggered grids arrangement and is solved through the iterative SIMPLEC algorithm. Results indicate that the angle of inclination has a significant effect on flow mode transition. The existence of multi-steady solutions closely depends on the value of the Rayleigh number. For that the Hysteresis phenomenon (multi−steady solutions) for Ra ≥ 2000 are demonstrated and parameter maps of Ra vs. φ are proposed

Theoretical analysis of the spatial variability in tillage forces for fatigue analysis of tillage machines

This paper presents a new theoretical model to describe the spatial variability in tillage forces for the purpose of fatigue analysis of tillage machines. The proposed model took into account both the variability in tillage system parameters (soil engineering properties, tool design parameters and operational conditions) and the cyclic effects of mechanical behavior of the soil during failure ahead of tillage tools on the spatial variability in tillage forces. The stress-based fatigue life approach was used to determine the life time of tillage machines, based on the fact that the applied stress on tillage machines is primarily within the elastic range of the material. Stress cycles with their mean values and amplitudes were determined by the rainflow algorithm. The damage friction caused by each cycle of stress was computed according to the Soderberg criterion and the total damage was calculated by the Miner's law. The proposed model was applied to determine the spatial variability in tillage forces on the shank of a chisel plough. The equivalent stress history resulted from these forces were calculated by means of a finite element model and the Von misses criterion. The histograms of mean stress and stress amplitude obtained by the rainflow algorithm showed significant dispersions. Although the equivalent stress is smaller than the yield stress of the material, the failure by fatigue will occur after a certain travel distance. The expected distance to failure was found to be df=0.825×106km. It is concluded that the spatial variability in tillage forces has significant effect on the life time of tillage machines and should be considered in the design analysis of tillage machines to predict the life time. Further investigations are required to correlate the results achieved by the proposed model with field tests and to validate the proposed assumptions to model the spatial variability in tillage force

Modeling and Control of a Rotating Flexible Spacecraft: A Port-Hamiltonian Approach

In this brief, we develop a mathematical model of a flexible spacecraft system composed of a hub and two symmetrical beams using the port-Hamiltonian framework. This class of system has favorable properties, such as passivity for controller synthesis and stability analysis, where the global Hamiltonian plays the role of a Lyapunov function candidate. The spacecraft model is viewed as a power-conserving interconnection between an infinite (beam) and finite (hub) dimensional system. We show that the interconnection result has a port-Hamiltonian structure and is passive. The introduction of a nonlinear feedback term, which takes into account the beam’s flexibility, is developed using the control by an interconnection approach. The closed-loop stability is proven; then, through explicitly solving the partial differential equations of the system, asymptotic stability is obtained. Finally, the experimental results are carried out to assess the validity of the proposed design methodology

Temporal analysis of the performance of an elevated concrete tank considering the corrosion of the steel reinforcement

Reinforced concrete water storage tanks are civil engineering structures subject to very aggressive atmospheric conditions that expose them to harmful corrosion risk. This dangerous phenomenon caused by the penetration of chloride ions causes pitting corrosion and leads to the reduction of the section of the reinforcements and consequently to the loss of strength and the structure performance. In this study, we are interested in analyzing the performance of an elevated storage tank, taking into account the corrosion of the reinforcements subjected to tensile stress, by considering environments with different rates of aggressiveness. A method based on Housner's model is used to evaluate the tension stresses in the reinforced concrete (RC) pedestal (supporting system) of the tank, subjected to the seismic actions. A pitting corrosion model is developed in order to determine the evolution in time of the reinforcements section in different environments. Several parameters influencing corrosion are taken into account, such as concrete cover and the concentration of chlorides ions

BEHAVIOR AND GLUTAMATE TRANSAMINASE CHANGES IN RAT EXPOSED TO LEAD AND TREATED BY WORMWOOD EXTRACT

Objective: Lead poisoning induced severe behavioral abnormalities and impaired cognitive functions in experimental animals. The aim of the present study is to investigate the detrimental effects of lead exposure on the behavior of rats and its association with altered neurochemistry.Methods: Twenty-four young male Wistar rats were divided into 4 groups: G1: a control group receiving drinking water. G2: intoxicated group (Pb) exposed to lead acetate (1000 ppm in drinking water). G3: receives Wormwood aqueous (A. Ab) extract at a dose of 300 mg/l in drinking water. G4: rats are receiving Pb+A. Ab mixture for 4 additional weeks after intoxication for 8 w. In the present study, locomotors activity in rats was assessed by open field test (OFT) while anxiety and depressive behavior were monitored by elevated plus maze (EPM) and the forced swim test (FST), the evaluation of glutamate metabolizing enzymes in whole brain and lipid peroxidation was carried out in all groups.Results: our results showed that lead acetate intoxication increased the level of lipid peroxidation in brain, decreased brain glutamate oxaloacetate transaminase activities and increased glutamate pyruvate transaminase. Also, lead (pb) exposure resulted in increased anxiety and fear-related behavior in both elevated plus maze and light dark box tests, showed hyperactivity in open field test presented by increased horizontal locomotion. However, A. Ab extract reduced the TBARS level by preventing oxidative stress induced by lead and increased glutamate pyruvate transaminase activity.Conclusion: The wormwood extract administration reduced anxiety, fear and locomotion and improved learning ability and memories. Therefore, these results indicated that wormwood is ameliorating the deleterious effects of lead and it appeared to be a protective agent against lead-induced toxicity.Â