Various columnar phases formed by bent-core mesogens

Two new compounds containing bent-core mesogens are presented in which a flexible central methyleneoxycarbonyl unit acts as the bent fragment. The compounds form different two-dimensional columnar ('B 1 ') phases both with a rectangular lattice but different in the angle of the director of the molecules with respect to the a -axis of the lattice. Based on X-ray diffraction measurements structural models are proposed which cannot be described with the common model of p 2 mg symmetry for B 1 phases of bent-shaped molecules. The new models are of layer group symmetry ( p 11 n and pm 2 1 n ) and are discussed as a new common model for two-dimensional columnar phases of bent-shaped mesogens.     

Structural characterization of the new polymorphic mesophases formed by bent-core molecules

A new achiral banana-shaped five-ring 2-methylresorcinol derivative fluorinated on the outer rings has been synthesized. This compound exhibits four antiferroelectric smectic phases characteristic for bent-core molecules (B 2 , B' 2 , B' 2 , B 5 ). In addition, a highly viscous solid-like phase has been detected which also shows electro-optical switching. This is the first switchable highly ordered B phase. The characterization of the mesophases was made by X-ray diffraction, electro-optical measurements and dielectric spectroscopy.     

Heat Transfer Experiments in a Rotary Drum for a Variety of Granular Materials

The influence of material properties on the contact heat transfer coefficient between the covered wall surface and the solid bed was investigated. The contact heat transfer coefficients were calculated from the measured radial and circumferential temperature profiles. Experiments were carried out with six different materials, including steel spheres, animal powder, cement clinker, quartz sand, glass beads, and expanded clay. The rotational speeds were varied from 1 to 6 rpm to evaluate the influence of rotational speed on the contact heat transfer coefficient. The measured contact heat transfer coefficients were compared with four models from the literature.     

The first liquid crystalline dimers consisting of two banana-shaped mesogenic units: a new way for switching between ferroelectricity and antiferroelectricity with bent-core molecules

Depending on the number of dimethylsiloxane units in the spacer connecting two banana-shaped molecules either ferroelectric or antiferroelectric switchable polar smectic C phases have been obtained.     

Fractional Calculus via Functional Calculus: Theory and Applications

This paper demonstrates the power of the functional-calculus definition oflinear fractional (pseudo-)differential operators via generalised Fouriertransforms.Firstly, we describe in detail how to get global causal solutions of linearfractional differential equations via this calculus. The solutions arerepresented as convolutions of the input functions with the related impulseresponses. The suggested method via residue calculus separates an impulseresponse automatically into an exponentially damped (possibly oscillatory)part and a `slow' relaxation. If an impulse response is stable it becomesautomatically causal, otherwise one has to add a homogeneous solution to getcausality.Secondly, we present examples and, moreover, verify the approach alongexperiments on viscolelastic rods. The quality of the method as an effectivefew-parameter model is impressively demonstrated: the chosen referenceexample PTFE (Teflon) shows that in contrast to standard classical modelsour model describes the behaviour in a wide frequency range within theaccuracy of the measurement. Even dispersion effects are included.Thirdly, we conclude the paper with a survey of the required theory. Therethe attention is directed to the extension from the L ₂-approachon the space of distributions .     

A study of the effect of different catalysts for the efficient CVD growth of carbon nanotubes on silicon substrates

We report on the identification of efficient combinations of catalyst, carbon feedstock, and temperature for the ethanol chemical vapour deposition (CVD) growth of single-wall carbon nanotubes (SWCNTs) onto silicon substrates.Different catalyst preparations, based on organometallic salts (Co, Fe, Mo, Ni acetate, and bimetallic mixtures), have been spin coated onto thermally grown silicon dioxide on silicon chips to perform tests in a temperature range between 500 and 900 °C.The samples have been then characterized by Raman spectroscopy, atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. Assuming the growth of high-quality isolated nanotubes as target, the ratio in Raman spectra between the intensity of the G peak and of the D peak has been used as the main parameter to evaluate the performance of the catalytic process. A comparison made for both single metals and bimetallic mixtures points out best conditions to achieve efficient CVD growth of SWCNTs.     

Strukturbildung von homologen Lecithin-Monohydraten in Abhängigkeit von Temperatur und Vorgeschichte der Lecithine

The influence of temperature and crystallization of homologous lecithinmonohydrates on the phase transitions was studied. The structural differences between various samples of dimyristoyl-phosphatidyl-choline-monohydrate, di-palmitoyl-phosphatidyl-choline-monohydrate and di-stearoyl-phosphatidyl-choline-monohydrate were discussed and their lattice parameters compared. The results show that the polymorphism of the lecithin-monohydrates, similar to the polymorphism of the water free lecithins, depends on the chain length and the conditions of crystallization.