Un modèle de particules à patchs pour l'étude numérique de la réponse mécanique des gels

In the current language, the term “gel” refers to a large number of materials that have intermediate behavior between solid and liquid. They generally have a low yield stress, and can be soft and ductile as well as hard and brittle. So, the term "gel" refers primarily to a type of macroscopic behavior. At the microscopic scale, these materials are formed by small elements, colloids or polymers, suspended in a liquid, which ensures a global incompressibility. Colloids, as well as polymers, are subject to thermal motion which gives them a certain ability to reorganize. This allows some gels to flow like liquids. Yet, by definition, gels also exhibit a yield stress which allows them to be stable in the absence of mechanical stress: this is possible because the colloids or polymers that compose them tend to stick together and form a network structure. It is thus essential that these elements develop mutually attractive interactions that are responsible for the formation of a weak, yet mechanically stable, network within the suspending fluid. The objective of this thesis is to build numerical tools, based on molecular dynamics, to study the formation and the mechanical behavior of gels. For this, we use a model of ``patchy'' particles taken from the literature. It consists of spherical objects at the surface of which are grafted small patches that attract each other. The interaction between patchy particles thus combine a central repulsion with attractive potentials between patches. Considering these particles as ``building blocks '' that form polymers, we have built and characterized a model of semi-flexible linear polymers of controlled rigidity; we have then studied the crosslinking kinetics of chemical gels and their mechanical (elastic) response under a constant strain. We were able to show that the network topology depends significantly of crosslinking conditions, and determines quite significantly the elastic response of the material. A preliminary study of colloïdal physical gels is also presented in the last part of the documentDans le langage courant, le terme « gel »réfère à un grand nombre de matériaux qui ont des comportements intermédiaires entre solides et liquides. Ils présentent en général une faible contrainte seuil, et peuvent aussi bien être mous et ductiles que durs et cassants. Le terme "gel" fait donc d'abord référence à un type de comportement macroscopique. A l'échelle microscopique, la matière dont ils sont formés, colloïdes ou polymères, est suspendue et diluée dans un liquide, qui assure un caractère essentiellement incompressible à l'ensemble. Les polymères, comme les colloïdes, sont soumis à l'agitation thermique qui leur confère une certaine capacité à se réorganiser. Cela permet à certains gels de s'écouler comme des liquides. Mais par définition, les gels présentent aussi une contrainte seuil qui leur permet d'être stables en l'absence de sollicitation mécanique : cela est possible parce que les colloïdes ou polymères qui les composent ont tendance à s'attacher entre eux de sorte à former une structure en réseau. Il est donc essentiel que ces éléments soient sujet à des interactions attractives, qui permettent la formation d'un réseau faible, mais mécaniquement stable, au sein du fluide porteur. L'objectif de cette thèse est de construire des outils numériques de type dynamique moléculaire pour étudier la formation et le comportement mécanique de gels. Pour cela, nous utilisons un modèle de ``particules à patchs'' tiré de la littérature. Les particules sont des objets de forme sphérique à la surface desquels sont greffés des sites ponctuels, les « patchs » qui s'attirent entre eux. Les interactions entre particules combinent une répulsion centrale aux efforts entre patchs. En considérant ces particules comme des « briques élémentaires » qui constituent des polymères, nous avons construit et caractérisé un modèle de polymères linéaires semi-flexibles de rigidité contrôlée. Puis, nous avons étudié la cinétique de réticulation de gels chimiques ainsi que sa réponse mécanique quand celui-ci est soumis à une déformation constante. Nous avons ainsi pu mettre en évidence que la topologie du réseau dépend très sensiblement des conditions de réticulation, et joue un rôle déterminant dans la réponse élastique du matériau. Ce même modèle de particules à patchs a aussi été utilisé pour construire un modèle de gels physiques colloïdaux, dont l'étude est restée cependant préliminair

Pull-out strength of four tibial fixation devices used in anterior cruciate ligament reconstruction

International audienceIntroduction: In reconstructions of the anterior cruciate ligament (ACL), tibial fixation can be the weak point in the assembly during the early postoperative period. The present study sought to compare pull-out strength between four tibial fixation systems used in ACL reconstruction.Hypothesis: The study hypothesis was that all four devices show ≥ 450 N pull-out strength with comparable biomechanical breakage characteristics. Material and methods: An experimental study used a mechanical model to perform axial traction on a synthetic ligament (polypropylene cord folded in four) implanted in an artificial tibia (Sawbones Proximal Tibia # 1116-2: model: normal anatomy; solid foam; size: medium) using four tibial fixation systems: Ligafix ® interference screw (SBM TM); Bio-Intrafix ® (Mitek TM); Translig ® (SBM TM); RIGIDfix ® (SBM TM). For each system, four models were tested using an Instron 5566 ® traction machine, allowing 100 mm/min stretching up to breakage. Study parameters comprised: pull-out strength, maximal whole assembly slippage, stiffness at breaking point, and type of break.Results: Mean pull-out strength was 450 ± 24 N (range, 421–488 N) for Ligafix ® , 415 ± 60 N (327–454 N) for Bio-Intrafix ® , 539 ± 66 N (449–636 N) for RigidFix and 1067 ± 211 N (736–1301 N) for Translig ® , and was significantly greater for Translig ® than for the other devices (p = 0.02), which did not significantly differ from one another. The expected maximal load of 450 N was reached in 100% of cases with Translig ® and RIGIDfix ® and in 50% of cases with Bio-Intrafix ® and Ligafix ®. There were no significant differences regarding stiffness. Ligafix ® showed significantly less slippage than the others (p = 0.006), with breakage caused by the ligament sliding between bone and implant.Discussion: In this in-vitro study, the Translig ® fixation device showed better pull-out strength than the other three devices tested. Type of study and level of evidence: Comparative laboratory study. Level II

The Degree of the Islamic Education Teachers’ Practices of Information Technology and Communication Applications and the Obstacles of Practice from Their Perspectives

This study aimed at studying the degree of the Islamic education teachers’ practices of Information technology and communication applications and the obstacles of practice from their point view. To achieve the purpose of the study a validated questionnaire was developed  and was applied on a sample of (225)male and female teachers .The study revealed that the degree of the Islamic Education teachers’ application of the information technology and communication  in Tabouk schools was moderate and the purposes of using the information technology and communication practices was high. The results of the study also revealed that there  were no statistical significant differences (0.05??) of degree that Islamic Education teachers’ application of the information technology and communication in Tabouk district due to gender and qualification. Whereas , the results showed that there were statistical significant differences attributed to experience in favor of  (6-10) years. Key Words:Islamic Education, Teachers Practices ,Information Technology ,Communication, Obstacles

El pompón rojo : opera cómica ent tres actos

Copia digital. España : Ministerio de Cultura. Subdirección General de Coordinación Bibliotecaria, d2024Rústica.Registro de la Propiedad Intelectual, Ley de 1847: 19388; n. de solicitud de ingreso: "1220"; fecha y datos del ingreso: "19 Nove. 77", "Regº fº 186 lib. 29

Photochemical versus Thermal Synthesis of Cobalt Oxyhydroxide Nanocrystals

Photochemical methods facilitate the generation, isolation, and study of metastable nanomaterials having unusual size, composition, and morphology. These harder-to-isolate and highly reactive phases, inaccessible using conventional high-temperature pyrolysis, are likely to possess enhanced and unprecedented chemical, electromagnetic, and catalytic properties. We report a fast, low-temperature and scalable photochemical route to synthesize very small (~3 nm) monodisperse cobalt oxyhydroxide (Co(O)OH) nanocrystals. This method uses readily and commercially available pentaamminechlorocobalt(III) chloride, [Co(NH3) 5Cl]Cl2, under acidic or neutral pH and proceeds under either near-UV (350 nm) or Vis (575 nm) illumination. Control experiments showed that the reaction proceeds at competent rates only in the presence of light, does not involve a free radical mechanism, is insensitive to O 2, and proceeds in two steps: (1) Aquation of [Co(NH3) 5Cl] 2+ to yield [Co(NH3) 5(H2O)] 3+, followed by (2) slow photoinduced release of NH3 from the aqua complex. This reaction is slow enough for Co(O)OH to form but fast enough so that nanocrystals are small (ca. 3 nm). The alternative dark thermal reaction proceeds much more slowly and produces much larger (~250 nm) polydisperse Co(O)OH aggregates. UV-Vis absorption measurements and ab initio calculations yield a Co(O)OH band gap of 1.7 eV. Fast thermal annealing of Co(O)OH nanocrystals leads to Co3O4 nanocrystals with overall retention of nanoparticle size and morphology. Thermogravimetric analysis shows that oxyhydroxide to mixed-oxide phase transition occurs at significantly lower temperatures (up to T = 64 degrees C) for small nanocrystals compared with the bulk

Lessons Learned After 760 Neurointerventions via the Upper Extremity Vasculature: Pearls and Pitfalls.

BACKGROUND: The radial approach has been gaining more widespread use by neurointerventionalists fueled by data from the cardiology literature showing better safety and overall reduced morbidity. OBJECTIVE: To present our institution\u27s experience with the radial approach for neuroendovascular interventions in 614 consecutive patients who underwent a cumulative of 760 procedures. METHODS: A retrospective analysis was performed and identified neuroendovascular procedures performed via the upper extremity vasculature access site. RESULTS: Amongst 760 procedures, 34.2% (260) were therapeutic, and 65.7% (500) were nontherapeutic angiograms. Access sites were 71.5% (544) via a conventional radial artery, 27.8% (211) via a distal radial artery, 0.5% (4) via an ulnar artery, and 0.1% (1) via the brachial artery. Most of the procedures (96.9%) were performed via the right-sided (737), 2.9% (22) via the left-sided, and 0.1% (1) via a bilateral approach. Major access site complications occurred at a rate of 0.9% (7). The rate of transfemoral conversion was 4.7% (36). There was a statistically higher incidence of transfemoral conversion when repeat procedures were performed using the same access site. Also, there was no significant difference between nontherapeutic procedures performed using the right and left radial access, and conventional versus distal radial access. Procedural metrics improved after completion of 14 procedures, indicating a learning curve that should be surpassed by operators to reach optimal outcomes. CONCLUSION: Radial artery catheterization is a safe and effective means of carrying out a wide range of neuroendovascular procedures associated with excellent clinical outcomes and an overall low rate of periprocedural complications