Peroxy radical isomerization in the oxidation of isoprene

We report experimental evidence for the formation of C(5)-hydroperoxyaldehydes (HPALDs) from 1,6-H-shift isomerizations in peroxy radicals formed from the hydroxyl radical (OH) oxidation of 2-methyl-1,3-butadiene (isoprene). At 295 K, the isomerization rate of isoprene peroxy radicals (ISO2?) relative to the rate of reaction of ISO2? + HO2 is k(isom)(295)/(k(ISO2?+HO2)(295)) = (1.2 ± 0.6) x 10(8) mol cm(-3), or k(isom)(295) ? 0.002 s(-1). The temperature dependence of this rate was determined through experiments conducted at 295, 310 and 318 K and is well described by k(isom)(T)/(k(ISO2?+HO2)(T)) = 2.0 x 10(21) exp(-9000/T) mol cm(-3). The overall uncertainty in the isomerization rate (relative to k(ISO2?+HO2)) is estimated to be 50%. Peroxy radicals from the oxidation of the fully deuterated isoprene analog isomerize at a rate ～15 times slower than non-deuterated isoprene. The fraction of isoprene peroxy radicals reacting by 1,6-H-shift isomerization is estimated to be 8-11% globally, with values up to 20% in tropical regions.     

Numerical modeling of guided wave interaction with non-axisymmetric cracks in elastic cylinders

A three dimensional (3D) hybrid method combining the classical finite element (FE) method with the semi-analytical finite element (SAFE) technique is developed. This hybrid method is employed to study the interaction of guided waves with non-axisymmetric damages in cylinders. The near field surrounding the damage is analysed with the 3D FE method. The solution is expanded into sums of guided modes on both inlet and outlet cross-sections. Such eigenmode expansions enable separation into ingoing and outgoing waves, i.e., incident, reflected and transmitted waves. Using the SAFE method, elastic guided modes are then computed at the aforementioned cross-sections thus reducing the analysis to two dimensions (2D). The amplitudes of the incident modes are imposed, whereas those of the scattered modes are determined by solving the global system of the 3D hybrid FE-SAFE model. In this paper, a formula is proposed for the calculation of eigenforces and modal power flows from eigendisplacements and SAFE matrices. This has the advantage of simplifying the post-process of load eigenvectors in hybrid FE-SAFE methods. Results obtained for a vertical free-end cylinder are in good agreement with those published in the literature. Moreover, first results of the interaction of the fundamental compressional, flexural and torsional Pochhammer–Chree modes with non-axisymmetric vertical cracks are obtained and discussed. Then, the interactions of the fundamental compressional mode with oblique free-ends and cracks are briefly addressed. The power balance is shown to be satisfied with a good accuracy.     

Das Atomgewicht des Mangans

Analytical and Bioanalytical Chemistry -     

Delicious not siliceous: expanded carbohydrates as renewable separation media for column chromatography

Expansion of native corn starch produces a high surface area mesoporous material capable of acting as a novel stationary phase for separating various mixtures of compounds.     

Necessary and Sufficient Conditions to be an Eigenvalue for Linearly Recurrent Dynamical Cantor Systems

Necessary and sufficient conditions are given for linearly recurrentCantor dynamical systems to have measurable and continuous eigenfunctions.Also an example of a linearly recurrent system with a nontrivialKronecker factor and a trivial maximal equicontinuous factoris constructed explicitly.     

Exchange and correlation effects in electronic excitations of Cu(2)O

State-of-the-art theoretical methods fail in describing the optical absorption spectrum, band gap, and optical onset of Cu(2)O. We have extended a recently proposed self-consistent quasiparticle approach, based on the GW approximation, to the calculation of optical spectra, including excitonic effects. The band structure compares favorably with our present angle-resolved photoemission measurements. The excitonic effects based on these realistic band structure and screening provide a reliable optical absorption spectrum, which allows for a revised interpretation of its main structures.     

Signatures of short-range many-body effects in the dielectric function of silicon for finite momentum transfer

We present an investigation of the dynamic structure factor and of the dielectric function epsilonM(Q,omega) of the prototypical semiconductor silicon for finite momentum transfer, combining inelastic x-ray scattering experiments and ab initio calculations. In contrast with optical spectra, for finite momentum transfer time-dependent density-functional theory in the adiabatic local-density approximation together with lifetime broadening describes the physics of valence excitations correctly. Major structures in the spectra, governed by short-range crystal and exchange-correlation local-field effects, are strongly influenced by a mixing of transitions of positive and negative energies, in striking difference to spectra for vanishing momentum transfer. This mixing gives rise to a pronounced Fano asymmetry.