The viscosity of triethylamine vapor at low densities and in the saturated vapor phase

For the first time, results of high-precision measurements of the viscosity coefficient of triethylamine vapor at low densities are reported. The relative measurements with an all-quartz oscillating-disk viscometer were carried out along seven isochores at densities from 0.002 to 0.009 mol m⁻³ in the temperature range between 298 and 498 K. The uncertainty is estimated to be ±$\pm$0.2% at ambient temperature, increasing up to ±$\pm$0.3% at higher temperatures. First isothermal values were recalculated from the original experimental data and then evaluated with a first-order expansion for the viscosity, in terms of density. In addition, viscosity values of the saturated vapor were determined at low temperatures. The results are utilized to model the viscosity coefficient of triethylamine vapor at moderately low densities. A so-called individual correlation on the basis of the extended theorem of corresponding states was employed to describe the zero-density viscosity coefficient, whereas the Rainwater–Friend theory was used to represent the initial density dependence expressed as second viscosity virial coefficient.     

Effects of shearing flow with inertia on monolayer mesoscale structure

In an experimental flow system capable of imparting a well-controlled shear-rate distribution with inertia to a monolayer consisting of coexisting phases, we have studied the resulting phase morphology and domain fragmentation. These evolve on distinct time scales: the viscous time associated with the viscosity in the bulk and the Marangoni stress and the fragmentation/relaxation time associated with the phase morphology. A relationship between the microstructure (line tension) and macroflow (shear rate) determining the meso length scale of the coexisting phase domains has been deduced from dimensional analysis and was found to correlate well with the quantitative experimental observations.     

Ion and polymer dynamics in polymer electrolytes PPO-LiClO4. II. 2H and 7Li NMR stimulated-echo experiments

We use 2H NMR stimulated-echo spectroscopy to measure two-time correlation functions characterizing the polymer segmental motion in polymer electrolytes PPO-LiClO4 near the glass transition temperature Tg. To investigate effects of the salt on the polymer dynamics, we compare results for different ether oxygen to lithium ratios, namely, 6:1, 15:1, 30:1, and infinity. For all compositions, we find nonexponential correlation functions, which can be described by a Kohlrausch function. The mean correlation times show quantitatively that an increase of the salt concentration results in a strong slowing down of the segmental motion. Consistently, for the high 6:1 salt concentration, a high apparent activation energy Ea=4.1 eV characterizes the temperature dependence of the mean correlation times at Tg相似文献   

Local search-based metaheuristics for the split delivery vehicle routing problem

The split delivery vehicle routing problem is a variant of the standard vehiclerouting problem where the single-visit assumption is waived and a customer mightbe served on more than one vehicle tour. In this article we report on a studywhere we have applied the standard local search-based metaheuristics usingadaptations of the most widely used inter-tour and intra-tour exchange operatorsfor solving the standard vehicle routing problem now allowing splitting andjoining of deliveries. As we will show we could find new best solutions for 51out of 57 benchmark instances, which have been defined for this problemclass.     

Complex Formation of the Tetracycline‐Binding Aptamer Investigated by Specific Cross‐Relaxation under DNP

While dynamic nuclear polarization (DNP) under magic‐angle spinning (MAS) is generally a powerful method capable of greatly enhancing the sensitivity of solid‐state NMR spectroscopy, hyperpolarization also gives rise to peculiar spin dynamics. Here, we elucidate how specific cross‐relaxation enhancement by active motions under DNP (SCREAM‐DNP) can be utilized to selectively obtain MAS‐NMR spectra of an RNA aptamer in a tightly bound complex with a methyl‐bearing ligand (tetracycline) due to the effective CH₃‐reorientation at an optimized sample temperature of approximately 160 K. SCREAM‐DNP can spectrally isolate the complex from non‐bound species in an RNA mixture. This selectivity allows for a competition assay between the aptamer and a mutant with compromised binding affinity. Variations in molecular structure and methyl dynamics, as observed by SCREAM‐DNP, between free tetracycline and RNA‐bound tetracycline are discussed.     

The Radical Anions of syn-1,6:8,13-Bridged [14] Annulenes. A Compilation of Hyperfine Data

Hyperfine coupling constants and g-factors determined by ESR and ENDOR spectroscopy are given for the radical anions of 21 syn-1,6:8,13-bridged [14]annulenes. The great majority of these values is reported for the first time. The hyperfine data are consistent with the single occupancy of an orbital which resembles a π-perimeter-LUMO of the same nodal properties. The sum of the coupling constants of the protons attached to the π-perimeter can be used as a planarity criterion for this perimeter.