Predicting the onset of delamination in layered fiber-reinforced composites

In this paper, composite structures are considered which consist of several layers of carbon fiber reinforced plastics (CFRP). For such layered composite structures, delamination constitutes one of the major failure modes and hence predicting its initiation is essential for their design. Evaluating stress-strength relation based onset criteria requires an accurate representation of the through-the-thickness stress distribution, which can be particularly delicate in the case of shell-like structures. Thus, in this paper, a solid-shell finite element is utilized, which allows for incorporating a fully three-dimensional material model, still being suited for application to thin structures. Moreover, locking phenomena are cured by using both the EAS and the ANS concept, and numerical efficiency is ensured through reduced integration. The proposed anisotropic material model accounts for the material's micro-structure by using the concept of structural tensors. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Molecular Tagging Velocimetry (MTV) measurements in gas phase flows

 Recent developments in Molecular Tagging Velocimetry (MTV) using the phosphorescence of biacetyl are described for gas-phase flows. With improvements in tagging, detection, and processing schemes, whole-field measurements of two components of the velocity vector are obtained simultaneously, typically at more than 300 points over a plane. Application of this measurement approach is demonstrated in mapping the velocity and vorticity fields of the intake flow into a “steady flow rig” model of an internal combustion engine. Received: 29 August 1997/Accepted: 16 September 1998     

Influence of the reaction mechanism on the time course of the entropy production during reversible polymerization

The paper shows the influence of the reaction mechanism on the time course of the entropy production sigma in a closed system during reversible polymerization. We consider two different reaction mechanisms with (a) being a polycondensation and (b) a chain growth mechanism. For both mechanisms explicit expressions for the entropy production sigma as a function of time t are derived. To demonstrate the application of these general expressions we consider two different polymerization experiments where the reaction starts (i) from monomer molecules polymerizing to a defined number average chain length x(n,eq) and (ii) from monodisperse polymer molecules reacting with each other under the constraint that x(n) is the same at the beginning and the end of the reaction. In both cases we treat the system to be ideal and describe the kinetics of the reversible polymerization reactions using two kinetic constants for the forward and backward reactions, respectively. Under these assumptions the difference in the curvature of the entropy production sigma between a polycondensation and a chain growth mechanism is only marginal if the reaction starts from monomer molecules polymerizing to a defined number average chain length x(n,eq).     

The preparation of optically active α-amino 4H-[1,2,4]oxadiazol-5-ones from optically active α-amino acids

Optically active α-amino 4H-[1,2,4]oxadiazol-5-ones (oxadiazolones) were prepared from optically active α-amino acids in five synthetic steps. The oxadiazolone moiety serves as a bioisosteric replacement for the carboxylic acid. Incorporation of an α-amino oxadiazolone into a representative dipeptide mimic is described.     

Inducible nitric oxide synthase, <Emphasis Type="Italic">Nos2</Emphasis>, does not mediate optic neuropathy and retinopathy in the DBA/2J glaucoma model

Background  

Nitric oxide synthase 2 (NOS2) contributes to neural death in some settings, but its role in glaucoma remains controversial. NOS2 is implicated in retinal ganglion cell degeneration in a rat glaucoma model in which intraocular pressure (IOP) is experimentally elevated by blood vessel cauterization, but not in a rat glaucoma model where IOP was elevated by injection of hypertonic saline. To test the importance of NOS2 for an inherited glaucoma, in this study we both genetically and pharmacologically decreased NOS2 activity in the DBA/2J mouse glaucoma model.     

The origin and elimination of spurious peaks in threshold electron photoionization spectra

Autoionization electrons in threshold photoionization spectra are known to occur. The effect of such electrons on the interpretation of threshold electron spectra is discussed and a new method is described which enables one to discriminate between zero kinetic energy electrons and energetic electrons in photoionization experiments with little ambiguity. The method largely overcomes the main problem present in some previously described threshold electron studies; namely, the line-of-sight transmission of energetic electrons which gives rise to non-threshold electron peaks. A rejection ratio of 25 is readily obtained for 0.038 eV electrons compared with threshold (zero kinetic energy) electrons and the (small) transition probability for energetic electrons falls off more rapidly than for analysers previously described. Design parameters based on electron trajectory calculations are given for the analyser used, and photoionization results on argon are presented.     

Z4-Kerdock Codes, Orthogonal Spreads, and Extremal Euclidean Line-Sets

When m is odd, spreads in an orthogonal vector space of type⁺(2m + 2,2) are related to binary Kerdock codes and extremalline-sets in 2^{m + 1} with prescribed angles. Spreads in a 2m-dimensionalbinary symplectic vector space are related to Kerdock codesover Z₄ and extremal line-sets in with prescribed angles. These connections involve binary, realand complex geometry associated with extraspecial 2-groups.A geometric map from symplectic to orthogonal spreads is shownto induce the Gray map from a corresponding Z₄-Kerdock codeto its binary image. These geometric considerations lead tothe construction, for any odd composite m, of large numbersof Z₄-Kerdock codes. They also produce new Z₄-linear Kerdockand Preparata codes. 1991 Mathematics Subject Classification:primary 94B60; secondary 51M15, 20C99.     

Phonon-assisted polar exciton–transitions in self-organized InAs/GaAs quantum dots

Phonon-assisted exciton transitions are investigated for self-organized InAs/GaAs quantum dots (QDs) using selectively excited photoluminescence (PL) and PL excitation spectroscopy. The results unambiguously demonstrate intrinsic recombination in the coherent InAs/GaAs QDs and the absence of a Stokes shift between ground state absorption and emission. Phonon-sidebands corresponding to a phonon energy of 34 meV are resolved and Huang–Rhys parameters of 0.015 and 0.08 are found for phonon-assisted emission and absorption, respectively, which are about one order of magnitude larger than in bulk InAs. Calculations of the exciton–LO–phonon interaction based on an adiabatic approximation and realistic wave functions for ideal pyramidal InAs/GaAs QDs show this enhanced polar coupling to result from the particular confinement and the strain-induced piezoelectric potential in such strained low-symmetry QDs.