Photoinitiated cationic polymerisation of multifunctional systems

Different types of tridimensional polymer networks have been synthetised by photoinitiated cationic polymerisation of vinyl ether and epoxy-functionalised oligomers and polymers. The polymerisation kinetics was followed by real-time infrared (RTIR) spectroscopy, a technique that records directly conversion versus time profiles in a timescale as short as 1 s. The addition of a diacrylate monomer was shown to accelerate the ring-opening polymerisation of epoxidized polyisoprene, with formation of interpenetrating polymer networks having well contrasted properties. A dual polymer network has been generated by photocrosslinking of a polyisoprene functionalised with both epoxy and acrylate groups.     

Data assimilation and pollution forecasting in Burgers' equation with model error function

This article presents a correction method for a better resolution of the problem of estimating and predicting pollution, governed by Burgers' equations. The originality of the method consists in the introduction of an error function into the system's equations of state to model uncertainty in the model. The initial conditions and diffusion coefficients, present in the equations for pollution and concentration, and also those in the model error equations, are estimated by solving a data assimilation problem. The efficiency of the correction method is compared with that produced by the traditional method without introduction of an error function.Three test cases are presented in this study in order to compare the performances of the proposed methods. In the first two tests, the reference is the analytical solution and the last test is formulated as part of the “twin experiment”.The numerical results obtained confirm the important role of the model error equation for improving the prediction capability of the system, in terms of both accuracy and speed of convergence.     

The interior proximal extragradient method for solving equilibrium problems

In this article we present a new and efficient method for solving equilibrium problems on polyhedra. The method is based on an interior-quadratic proximal term which replaces the usual quadratic proximal term. This leads to an interior proximal type algorithm. Each iteration consists in a prediction step followed by a correction step as in the extragradient method. In a first algorithm each of these steps is obtained by solving an unconstrained minimization problem, while in a second algorithm the correction step is replaced by an Armijo-backtracking linesearch followed by an hyperplane projection step. We prove that our algorithms are convergent under mild assumptions: pseudomonotonicity for the two algorithms and a Lipschitz property for the first one. Finally we present some numerical experiments to illustrate the behavior of the proposed algorithms.     

Synthesis of cation-exchanged laponite suspensions by laser ablation of microsized-metal particles in liquid

Laser ablation in the liquid technique has been used to synthesize cation-exchanged laponite suspensions. In summary, laser ablation of the microsize-metal powder (Co, Al, and Cu) dispersed in an aqueous solution containing deionized water laponite crystals was carried out using laser beam generated by a single-mode, Q-switched Nd-Yag laser operating at 532 nm with a pulse duration of 5.5 ns and 10 Hz repetition rate. Laser fluence was 0.265 J/cm² for all tests. For all samples, the mass fraction of laponite was 1%. General observations of the prepared samples indicated that an aqueous suspension of 1 wt% laponite retained its free flowing liquid phase characteristics even after aging for several weeks. When bivalent cationic metals (Cu, Co, Al) were ablated in it for about 1 h, even with a small amount of the metal (0.025% and 0.050%) were generated, the suspension became highly viscous and behaved as a shear-thinning and thixotropic material. That is, the suspension gelled strongly when it was allowed to rest. The gels, however, could easily be reverted to a low viscosity liquid with simple shaking. Information from TEM and XRD analysis indicated that such a sol-gel transformation might be due to the charge exchange between the cationic species produced during the laser ablation and the sodium ions in the interlayers of the clay sheets.     

Fourier transform and smoothness of solutions of a class of semilinear elliptic degenerate equations with double characteristics

This paper is a continuation of our earlier note [V. T. T. Hien and N. M. Tri, “Analyticity of Solutions of Semililnear Equations with Double Characteristics,” J. Math. Anal. Appl. 337, 1249–1260 (2008)]. Here we prove the analyticity of solutions of a class of semilinear elliptic degenerate equations with double characteristics by using the Fourier transform.     

Solution to the Neumann problem exterior to a prolate spheroid by radial basis functions

We consider the exterior Neumann problem of the Laplacian with boundary condition on a prolate spheroid. We propose to use spherical radial basis functions in the solution of the boundary integral equation arising from the Dirichlet–to–Neumann map. Our approach is particularly suitable for handling of scattered data, e.g. satellite data. We also propose a preconditioning technique based on domain decomposition method to deal with ill-conditioned matrices arising from the approximation problem.     

Determination of neutron temperature in irradiation channels of reactor

The neutron temperature is a characteristic parameter in irradiation channels of reactor. For nuclides which have resonances in the thermal neutron energy range, their Westcott g-factors are different from unity. The values of g-factors and cross-sections of (n, γ) reaction of these nuclides are temperature dependence. The standard energy for tabulation of thermal neutron cross-section (σ₀) is that of room temperature (293.59 K or 20.43 °C), corresponding to a neutron energy 0.0253 eV or to a neutron velocity of 2200 m/s. However, in the irradiation channels of reactor, the temperature is not exact at 20.43 °C. Thus, the temperature at the irradiation position must be known to convert σ₀ to σ(T). A method for determination of the neutron temperature in irradiation channels of Dalat reactor is presented by fitting the thermal neutron spectrum obtained from the calculation using MCNP code.     

Drop deposition of thin nanostructured coatings of lead telluride

The current-voltage relationships of deposited structures are measured for cluster structures consisting of nanoparticles of lead telluride. Variation in the value of the tunnel current is shown. Optimum conditions for the possible emergence of quantum-hopping conductivity due to carrier tunneling (the characteristic sizes of the nanoclusters and the distances between them) are determined.