Über einige bei einem Polystyren-Film beobachtete Erscheinungen und die daraus gefolgerten Betrachtungen

Zusammenfassung Die Autoren beschreiben verschiedene Versuche mit Streifen, welche in der Walzenrichtung und senkrecht dazu aus einem Polystyrenfilm geschnitten wurden. Die Streifen wurden in unbelastetem Zustand und auch bei verschiedenen Belastungen auf Temperaturen dicht oberhalb 90° C erhitzt. Sie zeigten dabei eine Verkürzung („Racking“), eine Verl?ngerung, oder auch erst eine Verkürzung und danach eine Verl?ngerung. Die ?nderungen der Abmessungen wurden festgelegt, w?hrend auch die Doppelbrechung vor und nach der Erhitzung gemessen wurde. Für die merkwürdigen Erscheinungen wurde eine theoretische Deutung gegeben auf Grund einer Auffassung von dem Bau der Gele, welche als eine Synthese einer erweiterten „Fransentheorie“ und einer „kinetischen Theorie“ von diesem Bau zu betrachten ist.     

Cycloisomerization of γ- and δ-acetylenic acids catalyzed by gold(I) chloride

We have developed a gold(I)-catalyzed intramolecular cyclization of γ- and δ-alkyne acids in mild conditions yielding various alkylidene lactones. Whereas a slight electronic effect of the R group was observed on the regioselectivity, bulky substituents on the R group bearing the alkyne strongly modify the reactivity. The cycloisomerization of o-alkynylbenzoic methyl esters was achieved rather with AuCl₃ as catalyst owing the presence of water affording exclusively the isocoumarins.     

On the mechanism of the copper-mediated C-S bond formation in the intramolecular disproportionation of imine disulfides

The mechanism of the copper-mediated disproportionation of aromatic imine disulfides to benzothiazoles in the gas phase is investigated by experimental and theoretical methods. Application of infrared multiphoton dissociation and hydrogen/deuterium exchange experiments combined with density functional theory (DFT) calculations of the relevant molecular structures and the associated infrared spectra allows the identification of the observed ionic intermediates. The theoretical investigation of the possible reaction pathways supported by collision-induced dissociation experiments provides a consistent mechanistic picture of the reaction catalyzed by a single copper(I) ion. Activation of the substrate proceeds via homolytic sulfur-sulfur bond cleavage, yielding metal complexes in the formal +3 oxidation state; carbon-sulfur coupling and hydrogen-atom transfer complete the transformation to the products. Exploratory studies demonstrate that in the gas phase, the disproportionation of the imine disulfide can also be mediated by other metal ions via different either homo- or heterolytic mechanisms without involving high-valent intermediates.     

FeIII(tmdta)]--twist-boat/half-chair conformer ratio reliably deduced from DFT-calculated Raman spectra

The equilibrium between the twist-boat (tb) and half-chair (hc) conformers of the central diamine chelate ring of [Fe(III)(tmdta)]- in solids and aqueous solution has been studied by Raman spectroscopy, supported by calculated Raman spectra using Density Functional Theory.     

3D Model compression using Connectivity-Guided Adaptive Wavelet Transform built into 2D SPIHT

Connectivity-Guided Adaptive Wavelet Transform based mesh compression framework is proposed. The transformation uses the connectivity information of the 3D model to exploit the inter-pixel correlations. Orthographic projection is used for converting the 3D mesh into a 2D image-like representation. The proposed conversion method does not change the connectivity among the vertices of the 3D model. There is a correlation between the pixels of the composed image due to the connectivity of the 3D mesh. The proposed wavelet transform uses an adaptive predictor that exploits the connectivity information of the 3D model. Known image compression tools cannot take advantage of the correlations between the samples. The wavelet transformed data is then encoded using a zero-tree wavelet based method. Since the encoder creates a hierarchical bitstream, the proposed technique is a progressive mesh compression technique. Experimental results show that the proposed method has a better rate distortion performance than MPEG-3DGC/MPEG-4 mesh coder.     

Monitoring powder blending by NIR spectroscopy

A strategy is proposed for the monitoring of powder blending. Samples are taken throughout the blender vessel and scanned by diffuse reflectance spectroscopy in the NIR range. The NIR spectra are first subjected to the Standard Normal Variate transformation (SNV). The first approach consists of overlaying the transformed spectra taken from different locations at each time. To quantify the differences between the spectra, the standard deviation spectrum at each time is calculated and the mean standard deviation value is plotted as a function of time. This plot indicates the time at which the blend is most homogeneous. Each individual spectrum can be compared with the mixture spectrum, which is an approximation of the spectrum of a true homogeneous sample. For that purpose several approaches, i.e. determination of the dissimilarity, Principal Component Analysis, are proposed. As an alternative approach to monitoring the blending the use of SIMPLISMA is recommended.Dedicated to Professor Dr. h.c. mult. J.F.K. Huber on the occasion of his 70th birthday     

Depletion-flocculation in oil-in-water emulsions using fibrillar protein assemblies

This paper shows that low concentrations of beta-lactoglobulin fibrils can induce depletion-flocculation in beta-lactoglobulin-stabilized oil-in-water emulsions. The minimum required fibril concentration for flocculation was determined experimentally for fibril lengths of about 3 and 0.1 microm. The minimum fibril concentration for flocculation is two orders of magnitude higher for the short fibrils than for the long ones. These experimental results correspond well with a theoretical prediction based on a model of spinodal decomposition. In addition, rheological measurements were performed, verifying that flocculation was induced by a depletion mechanism. The results of this study show that the minimum concentration required for depletion-flocculation can be tuned by varying the length of the fibrils.     

Incomplete vibrational relaxation of pyrene in its first excited singlet state in the vapour phase

The non-exponential fluorescence decay of pyrene is assigned to incomplete vibrational relaxation in the first excited singlet state. The increasing rate of this fluorescence decay with increasing vibrational energy is mainly attributed to an increase of the intersystem-crossing rate and to a smaller extent to a temperature dependence of the radiative rate constant.