HyBra1, a Brachyury homologue, acts during head formation in Hydra

A homologue of the T-box gene, Brachyury, has been isolated from hydra. The gene, termed HyBra1, is expressed in the endoderm and is associated with the formation of the hypostome, the apical part of the head in four different developmental situations. In adults, which are continuously undergoing patterning, HyBra1 is continuously expressed in the hypostome. During budding, hydra's asexual form of reproduction, the gene is expressed in a small area that will eventually form the hypostome of the developing bud before any morphological sign of budding is apparent. The gene is also expressed very early during head regeneration and is confined to the region that will form the hypostome. During embryogenesis, HyBra1 is expressed shortly before hatching in the region that will form the apical end of the animal, the hypostome. The absence of expression at the apical end of decapitated animals of reg-16, a head formation-deficient mutant, provides additional evidence for a role of HyBra1 during head formation. Further, treatments that alter the head activation gradient have no effect on HyBra1 expression indicating the role of the gene is confined to head formation. Transplantation experiments indicate that the expression occurs before head determination has occurred, but expression does not irreversibly commit tissue to forming a head. A comparison of the function of the Brachyury homologues suggests an evolutionary conservation of a molecular mechanism that has been co-opted for a number of developmental processes throughout evolution.     

Long-term behaviour of tungsten oxide hydrate gels in an alkali containing aqueous environment

The room temperature ageing process of tungsten oxide dihydrate grains (H₂WO₄·H₂O) prepared by the methods of Zocher and Jacobson (Kolloidchem. Beih. 28 (1929) 167) and Freedman (J. Am. Chem. Soc. 81 (1959) 3834) has been studied. A comparison between these two preparation methods and the ageing characteristics is reported. Zocher and Jacobson-type grains, spindle like in shape, have a strong tendency to morphological conversion depending on the pH value of the surrounding aqueous solution. Under the same conditions the Freedman-type irregularly shaped particles preserve their morphology. Scanning electron microscopy and Fourier transform infrared spectroscopy studies have shown that this structural and morphological stability of Freedman-type grains can be altered by the presence of alkaline (Li⁺, Na⁺, K⁺) and NH₄⁺ ions. A limited incorporation of cations into the tungstate structure was observed.     

Bestimmung von Ausgas- und Desorptionsraten mittels Restgasanalysator

Determination of Outgassing and Desorption Rates by Means of Residual Gas Analysis Especially when using plastic materials in vacuum chambers it is essential to know the amount of gases outgassing from the surface of those materials. Depending on the so-called outgassing or desorption rate one can decide if the proposed plastic material is suited for the desired application and how the vacuum system has to be configured, so that the use of the particular material makes sense. The article will demonstrate by means of 2 examples that there exist temperature-dependent outgassing behaviors of different materials. It also gives an overview of the measuring equipment set up to determine the outgassing rates.     

Physical characterization of a self‐healing dental restorative material

The objectives of this study were to determine the efficacy of self‐healing a highly filled composite and to investigate the physical properties of a model dental compound formulated to autonomically heal cracks. A visible light cured model resin consisting of TEGMA : UDMA : BisGMA (1 : 1 : 1) at 45% w/w with silane 0.7 μ glass was formulated with a self‐healing system consisting of encapsulated dicyclopentadiene and Grubbs' catalyst. The base resin was also formulated and characterized with the microcapsules alone, Grubbs' catalyst alone, and no healing additives. Fracture toughness (K_Ic) was assessed using single edge notch specimens in three‐point bend (n = 12). Data was analyzed with ANOVA/Tukey's at p ≤ 0.05. DMA was performed from ?140 to 250°C at 2°/min and 1 Hz. Storage and loss modulus, T_g and tan δ, was recorded for each material. The self‐healing material was loaded to failure, was left to sit for 7 days and then loaded a second time to failure to determine healing in the material. These specimens had a K_Ic = 0.69 ± 0.072 for a 57% average recovery rate of the original fracture toughness. The fracture toughness of the self‐healing material was statistically similar to the control. The modulus decreased in the composites with encapsulated dicyclopentadiene. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of water-soluble cellulose esters applying carboxylic acid imidazolides

Water-soluble, non-ionic cellulose esters with a degree of substitution in the range from 0.11 to 3.0 were synthesized homogeneously using ionic liquids (1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, and 1-allyl-3-methylimidazolium chloride) as reaction medium. Highly substituted 3,6,9-trioxadecanoic acid esters and 3,6-dioxaheptanoic acid esters of cellulose were obtained via the activation of the carboxylic acids with N,N’-carbonyldiimidazole. The products were characterized by the means of FTIR-, ¹H- and ¹³C NMR spectroscopy.     

Transport and reaction in catalytic wall-flow filters

Diesel particulate filters composed of so-called wall-flow monoliths are well established devices for diesel particulate abatement. Recent improvements in production technology allow implementation of full-featured catalyst functionality in the filter walls.

From a reactor engineering point of view such wall-flow reactors with wall-integrated catalyst show fundamental differences compared to conventional flow-through monoliths. The complex interactions of convection, diffusion and reaction in the wall-flow monolith are studied by means of numerical simulation. A two-dimensional model for the flow in one pair of inlet/outlet channels with a generic first order reaction in the catalytic filter wall is developed. Concentration profiles in the reactor and a conventional flow-through catalyst are compared.

It is found that in the range of moderate reactor conversion concentration gradients along the inlet channel of the filter are small. Thus the reactor can be described by an approximate one-dimensional model, taking into account only the radial flux through the filter wall and assuming a constant inlet concentration in axial direction along the inlet channel.

Light-off curves are computed for the wall-flow and for the conventional flow-through monolith. Significantly better conversion is found for the wall-flow configuration. This can be explained by mass transfer limitation in the conventional flow-through monolith.     

Thin‐Film Catalytic Coating of a Microreactor for Preferential CO Oxidation over Pt Catalysts

Different Pt‐based catalyst layers have been prepared and tested in a stacked foil microreactor for CO oxidation and preferential oxidation of CO in presence of hydrogen. The reactions were performed on Pt without support by impregnation of a pre‐oxidized microstructured metal plate, Pt/Al₂O₃ and Pt/CeO₂ based on sol methods as well as Pt/nano‐Al₂O₃, a combined method of sol‐gel and nanoparticle slurry coating. The ceria based sol‐gel catalyst was much more active for CO oxidation than alumina based sol‐gel catalysts at low temperature. However, total oxidation was only obtained at higher temperature on the alumina based catalysts. The combined method seems to have advantages in terms of less internal mass transfer limitation when trying to increase the catalyst coating thickness based on sol‐gel approaches due to no reduction of CO selectivity up to 300 °C reaction temperature. Experiments on CO oxidation with the Pt/CeO₂ catalyst have been conducted in an oxygen supply microreactor to evaluate the catalyst performance under sequential oxygen supply to reaction zone (CO excess).     

Influence of laminate thickness reduction on the deformation mechanism of coextruded multilayered PC/PMMA films

The influence of the morphology of multilayered composites of poly(methyl‐methacrylate) (PMMA) and polycarbonate (PC) fabricated by layer multiplying coextrusion technique on their mechanical and especially their micromechanical deformation behavior was investigated. Electron microscopic studies revealed that the PC/PMMA multilayered composites have a well‐oriented, uniform, and continuous layered architecture. With decreasing layer thickness of each polymer in the composite, the elongation at break of the films was found to increase significantly which was correlated with a transition from a two‐component behavior (for single‐layer thickness of ≥8 μm) to an one‐component behavior (for single‐layer thickness of ≤250 nm). Rheo‐optical measurements using FTIR spectroscopy revealed that the molecular orientation during stretching of the PMMA phase remains unchanged for all the investigated films, whereas the PC orientation function decreases with decreasing layer thickness. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013