Molecular mobility interpretation of the dielectric relaxor behavior in fluorinated copolymers and terpolymers

Thermo Stimulated Current and Dynamic Dielectric Spectroscopy have been applied to investigate dielectric relaxation modes of poly(vinylidene-fluoride trifluoroethylene) copolymer and poly(vinylidene-fluoridetrifluoroethylene-chlorofluoroethylene) terpolymer. The aim of this work is to check the molecular origin of the ferroelectric relaxor behavior of the terpolymer. The combination of data obtained by both dielectricmethods allows us to describe themolecular mobility of the amorphous phase and the cooperativity of the order/disorder dipolar transition in the crystalline phase. The introduction of 1,1-chlorofluoroethylene units in the main chain induces an increase of the Cooperative Rearranging Region size associatedwith less ordered and smaller crystallites. This morphological evolution is responsible of a lack of cooperativity and it explains the dielectric relaxor behavior of the poly(vinylidene-fluoride-trifluoroethylene-chloroethylene) terpolymer

Expertise or Experience: What Raises Pay?

An equilibrium job search model with on-the-job-search is presented and solved, in which we allow firms to implement optimal wage posting strategies in the sense that they leave no rent to their employees and counter the offers received by their employees from competing firms. Cross-firm productivity dispersion arises endogenously in equilibrium. The model delivers a hump-shaped aggregate earnings distribution that reflects both firm- and worker-heterogeneity. The model also generates plausible individual career paths on the basis of which it is estimated, using a French panel of wages over the period 1994-96.

Dynamic modeling of Terahertz Quantum cascade lasers

In this paper, the influence of the simplifications made in the four-equation-based set of rate equations describing the dynamic behavior of a Quantum Cascade Laser (QCL) is studied. Numerical simulations based on the set of four rate equations has been developed, enabling the theoretical study of the influence of different parameters on the direct modulation response of the laser. These equations have been then linearized in order to deduce a set of state system equations, which was written in a matrix formalism. Finally, an approximate second order transfer function has been derived with the linearized dependence of its times constant

Electroactive influence of ferroelectric nanofillers on polyamide 11 matrix properties

Barium titanate ceramic powders have been incorporated in polyamide 11 to form homogeneous dispersion of particles in the matrix. Barium titanate/polyamide 11 nanocomposites have been synthesized using a solvent casting method with ultrasonic stirring to homogeneously disperse inclusions in the matrix. Composites with volume fraction of barium titanate / ranging from 0.01 to 0.4 were elaborated. Films were fabricated using a hot press method. Only the inclusions were poled in the matrix to form a ferroelectric particles/ unpoled matrix composite. Interactions between the particles and the matrix, pyroelectric and piezoelectric response were studied as a function of / by dynamic dielectric spectroscopy. Composites show interesting pyro-piezoelectric activity. Pyroelectric merit factor increases linearly and it reaches a limit value of 0.3 for a volume fraction / = 0.1

Physical structure of P(VDF-TrFE)/barium titanate submicron composites

Dynamic Dielectric Spectroscopy and Thermo Stimulated Current were used to investigate of the dielectric relaxation of hybrid Poly(vinylidene-fluoride-trifluoroethylene)/barium titanate 700 nm composites with 0–3 connectivity. The results obtained by this method allow us to describe the physical structure of these composites in the glassy state at a nanometric scale. The decrease of the activation enthalpies and activation entropies involved in the dynamics of the α relaxation is attributed to: the decrease of Cooperative Rearranging Region sizes and an increase of intra/inter macromolecular interactions in the amorphous phase with the volume fraction

Piezoelectric sensing coating for real time impact detection and location on aircraft structures

Flexible, light weight and low cost electroactive coating has been fabricated by the dispersion of inorganic ferroelectric submicron particles in a polyurethane matrix. BaTiO3 particles have a mean diameter of 300 nm. The poling process and the influence of volume fraction of BaTiO3 on the piezoelectric activity of the coating have been reported. This spray coating has been realized on 1.6 * 1.6 m2 poly(epoxy)/carbon fiber reinforced composite. Impact detection has been also performed. A well-known cross correlated algorithm has been successfully employed to localize impact in a 90 * 90 cm2 area of the composite

Molecular mobility in piezoelectric hybrid nanocomposites with 0-3 connectivity: Particles size influence

Polyamide 11/barium titanate nanocomposites have been studied by a combination of dynamic dielectric spectroscopy, thermo stimulated current and differential scanning calorimetry. The correlation between results obtained by dielectric and calorimetric methods allows us to describe the evolution of the physical structure of the hybrid nanocomposites. The molecular mobility of 0-3 connectivity nanocomposites has been explored. The influence of the nanoparticles size is specifically studied. The smaller sized fillers produce a shift of the relaxation modes observed above the glass transition temperature of polyamide 11 towards lower frequency. The increase of the organic/inorganic interface induces an increase of the ratio rigid amorphous phase/soft amorphous phase. The interfaces favour local ordering stabilized by hydrogen bonds at a nanometric scale

La philosophie politique républicaine aujourd’hui. Un état des lieux

Ce texte d’introduction propose un état des lieux de la philosophie politique républicaine contemporaine. L’auteur étudie les apports des deux principaux représentants de ce courant de pensée, Philip Pettit et Quentin Skinner. Ces derniers se démarquent à la fois du libéralisme, par l’attention qu’ils portent aux phénomènes de domination et de dépendance, et du communautarisme, en demeurant fermement attachés à la notion d’indépendance individuelle. Bien que les thèmes de la liberté et de l’égalité soient au coeur du républicanisme contemporain, ces deux auteurs doutent de la possibilité de pleinement réaliser l’une ou l’autre dans une société où la notion d'auto-gouvernement perd son sens.This introductory text offers an overview of contemporary republican political philosophy. The author analyses the contribution made to republicanism by two of its most prominent theorists, Philip Pettit and Quentin Skinner. He identifies what distinguishes them from liberalism and from communitarianism: the focus on phenomena of domination and dependency on one hand, the unfaltering commitment to individual independence on the other. Although contemporary republicanism is foremost a discourse on liberty and equality, the two theorists discussed in this article strongly doubt that either one can be realized fully in a society in which the notion of self-government is losing its meaning

Converting DAE models to ODE models: application to reactive Rayleigh distillation

This paper illustrates the application of an index reduction method to some differential algebraic equations (DAE) modelling the reactive Rayleigh distillation. After two deflation steps, this DAE is converted to an equivalent first-order explicit ordinary differential equation (ODE). This ODE involves a reduced number of dependent variables, and some evaluations of implicit functions defined, either from the original algebraic constraints, or from the hidden ones. Consistent initial conditions are no longer to be computed; at the opposite of some other index reduction methods, which generate a drift-off effect, the algebraic constraints remain satisfied at any time; and, finally, the computational effort to solve the ODE may be less than the one associated to the original DAE