Some Evidence on the Polymerization of Phenylglycidylether Using AIP/ZnCl2 as Initiator System

Abstract

The influence of the composition of the initiator system used in the polymerization of PGE is studied. Structural studies of intermediate species by NMR and IR spectroscopies are made which allow confirmation of some characteristics on the previously proposed mechanism and clarification of the mechanism leading to the chlorinated insoluble polymer fraction. This can be explained by the formation of halogenated oligomers in the first stage of the reaction which interchange with different aluminum alkoxides to give another type of initiator system.     

On the “Hidden” Harmonics Associated to Best Approximants Due to Quasi-periodicity in Splitting Phenomena

The effects of quasi-periodicity on the splitting of invariant manifolds are examined. We have found that some harmonics that could be expected to be dominant in some ranges of the perturbation parameter actually are nondominant. It is proved that, under reasonable conditions, this is due to the arithmetic properties of the frequencies.     

Structural studies of metal ligand complexes by ion mobility-mass spectrometry

Collision cross sections (CCS) have been measured for three salen ligands, and their complexes with copper and zinc using travelling-wave ion mobility-mass spectrometry (TWIMS) and drift tube ion mobility-mass spectrometry (DTIMS), allowing a comparative size evaluation of the ligands and complexes. CCS measurements using TWIMS were determined using peptide and TAAH calibration standards. TWIMS measurements gave significantly larger CCS than DTIMS in helium, by 9 % for TAAH standards and 3 % for peptide standards, indicating that the choice of calibration standards is important in ensuring the accuracy of TWIMS-derived CCS measurements. Repeatability data for TWIMS was obtained for inter- and intra-day studies with mean RSDs of 1.1 % and 0.7 %, respectively. The CCS data obtained from IM-MS measurements are compared to CCS values obtained via the projection approximation, the exact hard spheres method and the trajectory method from X-ray coordinates and modelled structures using density functional theory (DFT) based methods.     

Finite Time Extinction for Nonlinear Schrödinger Equation in 1D and 2D

We consider a nonlinear Schrödinger equation with power nonlinearity, either on a compact manifold without boundary, or on the whole space in the presence of harmonic confinement, in space dimension one and two. Up to introducing an extra superlinear damping to prevent finite time blow up, we show that the presence of a sublinear damping always leads to finite time extinction of the solution in 1D, and that the same phenomenon is present in the case of small mass initial data in 2D.     

In-Situ Synthesis and Characterization of Nanocomposites in the Si-Ti-N and Si-Ti-C Systems

The pyrolysis (1000 °C) of a liquid poly(vinylmethyl-co-methyl)silazane modified by tetrakis(dimethylamido)titanium in flowing ammonia, nitrogen and argon followed by the annealing (1000–1800 °C) of as-pyrolyzed ceramic powders have been investigated in detail. We first provide a comprehensive mechanistic study of the polymer-to-ceramic conversion based on TG experiments coupled with in-situ mass spectrometry and ex-situ solid-state NMR and FTIR spectroscopies of both the chemically modified polymer and the pyrolysis intermediates. The pyrolysis leads to X-ray amorphous materials with chemical bonding and ceramic yields controlled by the nature of the atmosphere. Then, the structural evolution of the amorphous network of ammonia-, nitrogen- and argon-treated ceramics has been studied above 1000 °C under nitrogen and argon by X-ray diffraction and electron microscopy. HRTEM images coupled with XRD confirm the formation of nanocomposites after annealing at 1400 °C. Their unique nanostructural feature appears to be the result of both the molecular origin of the materials and the nature of the atmosphere used during pyrolysis. Samples are composed of an amorphous Si-based ceramic matrix in which TiN_xC_y nanocrystals (x + y = 1) are homogeneously formed “in situ” in the matrix during the process and evolve toward fully crystallized compounds as TiN/Si₃N₄, TiN_xC_y (x + y = 1)/SiC and TiC/SiC nanocomposites after annealing to 1800 °C as a function of the atmosphere.     

Catalytic Effect of Electric Fields on the Kemp Elimination Reactions with Neutral Bases

The effect of solvent reaction fields and oriented electric fields on the Kemp elimination reaction between methylamine or imidazole and 5-nitrobenzisoxazole has been theoretically studied. The Kemp reaction is the most widely used for the design of new enzymes. Our results, using the SMD continuous model for solvents, are in quite good agreement with the experimental fact that the rate of the analogous reaction with butylamine is one order of magnitude smaller in water than in acetonitrile. In the case of external electric fields, our results show that they can increase or decrease the energy barrier depending on the magnitude and orientation of the field. A duly oriented electric field may have a notable catalytic effect on the reaction. So, external electric fields and reaction fields due to the medium can contribute to the design of new enzymes. Several factors that must be taken into account to increase the catalytic effect are discussed.     

Quantification of the effect of nonphotochemical quenching on the determination of in vivo chl a from phytoplankton along the water column of a freshwater reservoir

Nonphotochemical quenching (NPQ) is a well-known collection of different photoprotective mechanisms of plants and algae to avoid photodamage under an excess of light energy. In order to evaluate the overall effect of NPQ processes on the fluorometric determination of in vivo Chl a from a phytoplankton community dominated by diatoms, we compared the results obtained by two different fluorometric field devices with the total concentration of extracted Chl a measured by HPLC ( in vitro Chl a ). A different set of measurements were made to assess the performance of these fluorometers at high, moderate and low irradiance conditions. The Fbbe fluorometer, which is capable of distinguishing different algal groups according to their pigment content, allowed a better determination of in vivo Chl a under high irradiance conditions, with only a 10% mean difference from the in vitro Chl a concentration. In turn, the FMII fluorometer underestimated by as much as 50% the in vitro Chl a concentration under the same light conditions. As data from both fluorometers were in accordance with the in vitro Chl a values at moderate irradiance levels, the differences observed at high irradiances were attributed to the decrease in the yield of Chl a fluorescence caused by photoprotective NPQ processes. Accordingly, we estimated the effect of NPQ processes on the in vivo Chl a determination and the results allow us to provide an equation to correct this effect when in situ fluorometric measurements are carried out under high irradiance regimes. Our results demonstrate that under certain circumstances NPQ seriously compromises the results obtained by in situ fluorometric probes and highlight the need for a cautious interpretation of field data under such environmental conditions.     

Secret Sharing Schemes with Detection of Cheaters for a General Access Structure

In a secret sharing scheme, some participants can lie about the value of their shares when reconstructing the secret in order to obtain some illicit benefit. We present in this paper two methods to modify any linear secret sharing scheme in order to obtain schemes that are unconditionally secure against that kind of attack. The schemes obtained by the first method are robust, that is, cheaters are detected with high probability even if they know the value of the secret. The second method provides secure schemes, in which cheaters that do not know the secret are detected with high probability. When applied to ideal linear secret sharing schemes, our methods provide robust and secure schemes whose relation between the probability of cheating and the information rate is almost optimal. Besides, those methods make it possible to construct robust and secure schemes for any access structure.