Non-linear dynamic phenomena in the behaviour of a railway wheelset model

A dicone moving on a pair of cylindrical rails can be considered as a simplified model of a railway wheelset. Taking into account the non-linear friction laws of rolling contact, the equations of motion for this non-linear mechanical system result in a set of differential-algebraic equations. Previous simulations performed with the differential-algebraic solver DASSL, [2], and experiments, [7], indicated non-linear phenomena such as limit-cycles, bifurcations as well as chaotic behaviour. In this paper the non-linear phenomena are investigated in more detail with the aid of special in-house software and the path-following algorithm PATH [10]. We apply Poincaré sections and Poincaré maps to describe the structure of periodic, quasiperiodic and chaotic motions. The analyses show that part of the chaotic behaviour of the non-linear system can be fully understood as a non-linear iterative process. The resulting stretching and folding processes are illustrated by series of Poincaré sections.     

Synthesis and Characterization of New Adhesion Promoter for Grafting Conducting Polymer on Oxide Substrate

For grafting polypyrrole layers on oxidic substrates, the synthesis and characterization of a new adhesion promoter 11‐(pyrrol‐3‐yl) undecyl trimethoxysilane (PyTMS) were described in this article. The oxidation potential of PyTMS was determined by cyclic voltammetry. The grafting behavior of such an adhesion promoter on oxidized surface and chemical deposition of polypyrrole over the modified oxidized surface were studied. The adsorbed layer on the oxidized substrates thus formed was determined by both contact angle measurements and X‐ray photoelectron spectroscopy. Chemical polymerization of terminal pyrrole moieties on such substrates yielded adhesive polypyrrole films, and SEM image showed that the morphology of the polypyrrole films was influenced by the experimental conditions.     

Hybrid nanoparticle design based on cationized gelatin and the polyanions dextran sulfate and chondroitin sulfate for ocular gene therapy

We describe the development of hybrid nanoparticles composed of cationized gelatin and the polyanions CS and DS for gene therapy in the ocular surface. The physicochemical properties of the nanoparticles that impact their bioperformance, such as average size and zeta potential, can be conveniently modulated by changing the ratio of polymers and the crosslinker. These systems associate plasmid DNA and are able to protect it from DNase I degradation. We corroborate that the introduction of CS or DS in the formulation decreases the in vitro toxicity of the nanoparticles to human corneal cells without compromising the transfection efficiency. These nanoparticles are potential candidates for the development of safer and more effective nanomedicines for ocular therapy.     

Light-Mediated Formal Radical Deoxyfluorination of Tertiary Alcohols through Selective Single-Electron Oxidation with TEDA2+.

The synthesis of tertiary alkyl fluorides through a formal radical deoxyfluorination process is described herein. This light-mediated, catalyst-free methodology is fast and broadly applicable allowing for the preparation of C−F bonds from (hetero)benzylic, propargylic, and non-activated tertiary alcohol derivatives. Preliminary mechanistic studies support that the key step of the reaction is the single-electron oxidation of cesium oxalates—which are readily available from the corresponding tertiary alcohols—with in situ generated TEDA^2+. (TEDA: N-(chloromethyl)triethylenediamine), a radical cation derived from Selectfluor®.     

One-dimensional SAMs of (12-pyrrol-1-yl-dodecyl)-phosphonic acid templated by polyelectrolyte molecules

We present a novel method for the fabrication of one-dimensional (1-D) self-assembled monolayers and multilayers (SAMs) of (12-pyrrol-1-yl-dodecyl)-phosphonic acid (Py-DPA) on various polar surfaces using polyelectrolyte nanostructures as positive templates. Particularly, we demonstrate that (i) patterns of aligned 1-D polycation structures on a poly(dimethylsiloxane) stamp can be prepared by moving a droplet of polycation solution along the surface; (ii) these patterns can be used as templates for the ordered assembly of Py-DPA in water where Py-DPA carries a charge opposite to the charge of the template; and (iii) Py-DPA SAMs can then be transferred onto mica or silicon wafers by a printing process. These nanostructures with a polymerizable pyrrole headgroup might be useful for the creation of electrically conductive patterns of conjugated polymers.     

Pyrrole-substituted alkyl silanes as new adhesion promoters on oxidic substrates

ω-(Pyrrol-1-yl alkyl) dimethylchlorosilanes with different chain length were synthesized and characterized with IR, NMR and elemental analysis. The growth of self-assembled monolayers of ω-(pyrrol-1-yl alkyl) dimethylchlorosilanes on oxide surfaces has been investigated. The order gradually improved with adsorption time and highly ordered SAMs were obtained for nearly 2 days adsorption time. Characterization of the films has been performed with contact angle measurements, ellipsometry, SPR and grazing incident FTIR. The chemical deposition of polypyrrole on the modified surface was investigated. The thickness of polypyrrole layer was influenced by the concentration of monomer, the deposition time, and the ratio of monomer to oxidant.