Photocurable glycidoxypropyltrimethoxysilane based sol-gel hybrid materials

Hybrid sol-gel materials are promising candidates for electro/optical applications, combining the most important glass-like and polymer-like properties. Hybrid patternable materials produced by photopolymerisation processes have been mainly developed on 3-methacrloxypropyltrimethoxysilane based systems in which the polymerisable organic function is the CC bond of the methacrylic group. A new photosensitive hybrid material is described here, based on 3-glycidoxypropyltrimethoxysilane (GPTMS) and on the cationic photopolymerisation of the epoxide groups, which lead to the formation of a PEO organic interpenetrating network.     

Influence of the Host Matrix on the Microstructure of Sol-Gel Films Doped with CdS and PbS Q-Dots

The preparation of non-linear optical materials for integrated photonic devices needs the development of procedures which permit a very good control of the microstructure. Sol-gel is a good method for the preparation of glasses doped with semiconductor Q-Dots. However, the control on the microstructure and the properties of the material is related to many parameters (e.g., conditions of hydrolysis, precursors, heat treatments, etc.). In this work the effect of the matrix on the size and size distribution of the semiconductor nanoparticles was investigated. The films were characterized by UV-VIS-NIR spectrophotometry, Grazing Angle X-Ray Diffraction (GA-XRD), and High Resolution Transmission Electron Microscopy (HRTEM).     

Control of Semiconductor Particle Size in Sol-Gel Thin Films

Thin silica and silica-titania films containing CdS and PbS quantum size particles were obtained by separate preparation of the matrix and the colloidal sols and successive mixing. Sulfide particles were obtained by reaction of metal acetates with thioacetamide and control of particle size was achieved by surface capping agents. Powders and thin films deposited on soda-lime slides were prepared and characterized by XRD. Absorption spectra were recorded on films. The nonlinear refractive index was measured by anm-line technique on a CdS-doped sample. The nonlinear effect was found to be reversible and an ₂ value of −3 10⁻⁹ cm²/kW was measured.     

Computing breaking points in implicit delay differential equations

Systems of implicit delay differential equations, including state-dependent problems, neutral and differential-algebraic equations, singularly perturbed problems, and small or vanishing delays are considered. The numerical integration of such problems is very sensitive to jump discontinuities in the solution or in its derivatives (so-called breaking points). In this article we discuss a new strategy – peculiar to implicit schemes – that allows codes to detect automatically and then to compute very accurately those breaking points which have to be inserted into the mesh to guarantee the required accuracy. In particular for state-dependent delays, where breaking points are not known in advance, this treatment leads to a significant improvement in accuracy. As a theoretical result we obtain a general convergence theorem which was missing in the literature (see Bellen and Zennaro, Numerical Methods for Delay Differential Equations, Oxford University Press, Oxford, 2003). Furthermore, as a useful by-product, we design strategies that are able to detect points of non-uniqueness or non-existence of the solution so that the code can terminate when such a situation occurs. A new version of the code RADAR5 together with drivers for some real-life problems is available on the homepages of the authors. Supported by the Swiss National Science Foundation, project # 200020-101647.     

An algorithm for finding extremal polytope norms of matrix families

In this paper the problem of the computation of the joint spectral radius of a finite set of matrices is considered. We present an algorithm which, under some suitable assumptions, is able to check if a certain product in the multiplicative semigroup is spectrum maximizing. The algorithm proceeds by attempting to construct a suitable extremal norm for the family, namely a complex polytope norm. As examples for testing our technique, we first consider the set of two 2-dimensional matrices recently analyzed by Blondel, Nesterov and Theys to disprove the finiteness conjecture, and then a set of 3-dimensional matrices arising in the zero-stability analysis of the 4-step BDF formula for ordinary differential equations.     

On the fictitious nonlinearity of the surface impedance of the Earth’s crust

The observations of Alfvén oscillations of the magnetosphere are used to study the Earth’s crust and upper mantle by the magnetotelluric sounding method. The sounding procedure involves the measurement of the horizontal components of the electromagnetic field at a given point on the ground, the calculation of the surface impedance, and the determination of the conductivity of rocks from these data. It has been shown that the anharmonicity of the oscillations of the magnetosphere in combination with the nonlocality of the boundary condition on the ground gives rise to the amplitude dependence of the impedance calculated using the classical magnetotelluric sounding method. This apparent nonlinearity of the impedance can be manifested in the sounding of the Earth’s interior with intense electromagnetic pulsations, which appear when the Earth’s magnetosphere is embedded in the highspeed solar wind flow.     

Generalized Moment Theory and Bayesian Robustness Analysis for Hierarchical Mixture Models

In applications of Bayesian analysis one problem that arises is the evaluation of the sensitivity, or robustness, of the adopted inferential procedure with respect to the components of the formulated statistical model. In particular, it is of interest to study robustness with respect to the prior, when this latter cannot be uniquely elicitated, but a whole class Γ of probability measures, agreeing with the available information, can be identified. In this situation, the analysis of robustness consists of finding the extrema of posterior functionals under Γ. In this paper, we provide a theoretical framework for the treatment of a global robustness problem in the context of hierarchical mixture modeling, where the mixing distribution is a random probability whose law belongs to a generalized moment class Γ. Under suitable conditions on the functions describing the problem, the solution of this latter coincides with the solution of a linear semi-infinite programming problem.     

Hardron production and neutrino beams

The precise measurements of the neutrino mixing parameters in the oscillation experiments at accelerators require new high-intensity and high-purity neutrino beams. Ancillary hadron-production measurements are then needed as inputs to precise calculation of neutrino beams and of atmospheric neutrino fluxes. The text was submitted by the author in English.     

Precursors for sol-gel preparations

Precursors used for the synthesis of oxide systems by the sol-gel method are reviewed and their role in the various stages of the process is discussed. Emphasis is given to alkoxide precursors and to their physical and chemical properties. In particular, the following topics are discussed: degree of oligomerization, volatility, viscosity, reactions with alcohol, molecular association between alkoxides, hydrolysis, stabilization against hydrolysis. Some information about preparation methods, commercial products and availability is also given. Among non-alkoxide precursors, nitrates, carboxylates, acetylacetonates, chlorides and other inorganics are described from the point of view of their use in sol-gel preparations. They are compared, when possible, with the corresponding alkoxides.