Synthesis of 1-phenyl- and 1-pyridyl-3-pyridoazepines by reductive cyclization of diarylacetonitriles

Several pyrido[2,3-d]azepines and pyrido[3,4-d]azepines, novel aza analogs of the pharmacologically relevant 1-aryl-3-benzazepines, were synthesized by assembling the azepine ring by reductive cyclization of (2-methoxyvinyl)pyridinyl(aryl)acetonitrile derivatives, which were easily derived from contiguously substituted bromo(2-methoxyvinyl)pyridines and the corresponding arylacetonitriles.     

On the feasibility of chemical reactions in the presence of siloxane-based surfactants

Siloxane-containing surfactants have been tested as stabilizers for the preparation of polymer nanoparticles by three types of chemical reactions. Two crosslinking reactions were used to obtain silicone elastomers particles: one involved HO-terminated polydimethylsiloxane and tetraethoxysilane, while the other one was a crosslinking via polyhydrosilylation. The third reaction was a linear polycondensation between a diamine and a siloxane dialdehyde. The monitoring of the reactions has been made by infrared spectroscopy and the resulting particles have been analyzed in dispersion by light scattering and in dry state by electron microscopy and atomic force microscopy. The particles size was of hundreds of nanometers and their spherical shape was generally maintained after drying. The spectral and microscopy data proved efficient stabilization, which allowed the reactions to evolve after the formation of the particles.     

Spurious Structures in Recurrence Plots Induced by Embedding

In this paper we show that delay embedding produces spurious structures in a recurrence plot (RP) that are not present in the real attractor. We analyze typical sets of simulated data, such as white noise and data from the chaotic R?ssler system to show the relevance of this effect. In the second part of the paper we show that the second order Rényi entropy and the correlation dimension are dynamical invariants that can be estimated from Recurrence Plots with arbitrary embedding dimension and delay.     

Improving the accuracy of BDF methods for index 3 differential-algebraic equations

Methods for solving index 3 DAEs based on BDFs suffer a loss of accuracy when there is a change of step size or a change of order of the method. A layer of nonuniform convergence is observed in these cases, andO(1) errors may appear in the algebraic variables. From the viewpoint of error control, it is beneficial to allow smooth changes of step size, and since most codes based on BDFs are of variable order, it is also of interest to avoid the inaccuracies caused by a change of order of the method. In the case of BDFs applied to index 3 DAEs in semi-explicit form, we present algorithms that correct toO(h) the inaccurate approximations to the algebraic variables when there are changes of step size in the backward Euler method. These algorithms can be included in an existing code at a very small cost. We have also described how to obtain formulas that correct theO(1) errors in the algebraic variables appearing after a change of order.This author thanks the Centro de Estadística y Software Matemático de la Universidad Simón Bolívar (CESMa) for permitting her free use of its research facilities.