Specific power input and local micromixing times in turbulent Taylor–Couette flow

In the present work, the distribution of the local dissipation rate of turbulent kinetic energy in Taylor–Couette flow was studied with the help of the particle image velocimetry (PIV). The experimental values of dissipation rate are strongly affected by spatial resolution of PIV measurements. Therefore, a reference value of the average specific power input is needed. Such a value was achieved from an independent torque measurement. Using these values it was possible to quantify the true local values of the dissipation rate. The distribution of mixing times in the gap could thus be calculated and was found to become more homogeneous with increasing turbulence intensity.     

Hydrodynamic Activation of the Batch-Polymerization of Methyl methacrylate in a Taylor-Couette Reactor

Summary: In this work, the free radical batch polymerization of methyl methacrylate (MMA) premixed with xylene as a solvent, in the presence of an initiator, 2,2-azoisobutyronitrile (AIBN), in the Taylor-Couette reactor was studied. We observed an unexpected influence of hydrodynamic process parameters, i.e. angular velocity ω, on the polymer conversion, molecular weight and viscosity of the produced polymer. The polymerization process seems to be activated by hydrodynamic process parameters. Hydrodynamic activation is a promoting effect of process parameters on polymer product properties. The hydrodynamic activation is found to depend on the reaction time and the angular velocity of the inner cylinder. In addition, our results highlight both the reaction kinetics and the hydrodynamics during the polymerization. The conversion exhibits a significant difference between tests with and without the angular velocity of the inner cylinder. The conversion and the molecular weight strongly increase with the increase of the angular velocity of the inner cylinder, whereas the viscosity is less strongly dependent. There is more increase with decreasing solvent concentration. The radial Reynolds number decreases with increasing conversion. The polymerization is faster with a low solvent concentration, and the molecular weight is higher compared to the case of high solvent concentration.     

Phase transitions and lattice dynamics in Ag2H3IO6 and (NH4)2H3IO6

The investigation of thermal, optical and dielectric properties of Ag₂H₃IO₆ and (NH₄)₂H₃IO₆ revealed phase transitions in two steps with unknown intermediate phases. Reflectivity measurements in the far infrared region confirm that the main step is caused by a freezing in of the proton tunnelling modes. From the results of NMR-NQR-spectroscopy the low temperature structures for both compounds are deduced. The complete group analysis of lattice vibrations and proton ordering modes of the room temperature phases is performed. In the case of Ag₂H₃IO₆ the transitions can be discussed in the frame-work of the Landau theory, starting with a condensation of an antiphase vibration of the silver atoms in theF point of the trigonal Brillouin zone, whereas in the case of (NH₄)₂H₃IO₆ a simultaneous ordering of protons inZ, F, andL-points of the Brillouin zone is proposed for the first step. A new definition of antiferroelectric transitions is suggested which is based on symmetry arguments only. The proton-ordering transitions in both compounds can then be classified as antiferroelectric.     

14N and35Cl nuclear quadrupole double resonance study of the structural phase transitions in N-octylammoniumchloride

The structural phase transitions between the non-intercalated phases of the layer structure compound N-octylammoniumchloride have been studied via proton-¹⁴N and proton-³⁵Cl nuclear quadrupole double resonance. The results have been related to an order-disorder model of the octylammonium chains. The temperature dependence of the order parameters of the –NH₃ head groups has been determined.     

Sequential fractionation procedure for the identification of potentially cytochrome P4501A-inducing compounds

A multistep fractionation procedure for the separation of nonpolar aromatic compounds with respect to cytochrome P4501A induction is presented. Normal-phase HPLC on nitrophenylpropyl silica and cyanopropyl silica was tested for group-specific separation as a first fractionation step. Subsequent individual compound-specific PAH fractionation was done by means of reversed-phase HPLC. Electron-donor-acceptor HPLC and size-exclusion chromatography were applied to separate PAHs, PCBs, PCNs and PCDD/Fs according to their number of aromatic carbon atoms, their hydrophobicity, their degree of chlorination, their planarity and their molecular size. The method was validated for complex environmental mixtures on the basis of two sediment extracts.     

NMR self-diffusion study of organic glasses: COANP,MBANP, PNP,NPP

A pulsed field gradient proton spin-echo NMR self-diffusion study of organic glasses COANP, MBANP, PNP and NPP in their liquid and weakly supercooled states was performed. The NMR phase diagrams, based on the proton NMR transverse relaxation time (T ₂) temperature hysteresis data of these materials, clearly give evidence of the onset of a glass phase on cooling the isotropic liquids below their respective melting temperatures. The self-diffusion data exhibit in the supercooled glassy state a non-Arrhenius behaviour and can be described in terms of the Vogel-Fulcher modification of the Arrhenius law,D=D exp{–E _a /[k _B (T–T _VF )]}. The activation energiesE _a and Vogel-Fulcher temperaturesT _VF are 83.2 meV and 239 K for COANP, 66 meV and 249 K for MBANP, and 85 meV and 245 K for PNP, respectively. The flow viscosity data obtained for COANP in the same temperature region as well conform to the Vogel-Fulcher behaviour, exp{E _a ⁽⁾ /[k _B (T–T _VF )]}, withE _a ⁽⁾ =80.4 meV andT _VF =239 K. In case of COANPD was found to increase with decreasing diffusion time in the supercooled (glassy) melt just belowT _M whereas no such behaviour was found aboveT _M .     

Drying,film formation and open time of aqueous polymer dispersions

Industry has invested significant time and effort to develop water-based paints and varnishes, that show a drying behaviour comparable to that of established solvent-based polymer solutions. To further improve the application properties - open time, film quality and compound distribution - of water-based formulations, it requires a fundamental understanding of the drying and film formation mechanism from colloidal dispersions. This is where this work wants to make a contribution using experimental data and model calculations.     

Einbettungen in konvexe Hyperflächen des Rn

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