The chiroptical properties of a new liquid-crystalline polymer: (trityl)(pentyl)cellulose

The chiroptical properties of a new liquid crystalline polymer, trityl pentyl cellulose (TPeC), are discussed. This polymer forms lyotropic liquid-crystalline phases in tetrahydrofuran and chloroform. The cholesteric twist sense is right handed in both solvents. The dilute solution optical activity of the phenyl chromophores, measured by circular dichroism (CD), showed no evidence of the exciton splitting expected for a helical arrangement of chromophores. The sign and magnitude of the CD signals were found to change considerably upon mesophase formation.     

Acoustic double layers in multispecies plasma

Particle simulation in a one-dimensional bounded system is used to examine the formation of acoustic double layers in the presence of two ion species. Double-layer formation depends critically on the details of the distribution functions of the supporting ion populations, and their relative drifts with respect to the electrons. The effect of having two ion components, an H⁺ and an O⁺ beam, on double-layer evolution from ion acoustic turbulence driven by an electron drift relative to the H⁺ beam of ≈0.5u _e, where uu_e is the electron thermal speed, is examined. The ratio of ion drifts is taken to be consistent with acceleration by a quasi-static auroral potential drop (i.e. V _H/V_O=√M_O/ M_H=4.0). Acoustic double layers form in either ion species on the time scale τ≈100ω_ps^-1, where ω_ps is the ion plasma frequency for species `s' and s=H or O, and for drifts relative to the electrons lower than that required for double layer formation in simulations of single ion component plasma     

Thermometrie

Ohne Zusammenfassung     

Complexity of a modelling exercise: A discussion of the role of computer simulation in complex system science

Shifting the emphasis from a model to a modeling task, which involves both a computer model and a modeler, we ask what makes a problem complex. We propose that a modeling task can be seen as a set of questions‐and‐answers, nested at multiple levels. The role of the modeler then lies in posing the questions and choosing the best procedure to answer them, while the role of the model lies in answering the questions, via algorithmic, thus logically simple, procedures. Within this framework, complexity is broadly related to the number of question‐answer levels involved in the process and the nature of the questions posed. Addressing this complexity depends crucially on the ingenuity and creativity of the modeler. This may lead to a view of complexity, which is no more observer‐independent, but rather accounts for both historical and cultural development, that is the context of the problem at hand. © 2008 Wiley Periodicals, Inc. Complexity, 2008.     

High-temperature ignition of propane with MTBE as an additive: Shock tube experiments and modeling

Ignition of propane has been studied in a shock tube and by computational modeling to determine the effect of methyl tert-butyl ether (MTBE) as a fuel additive. MTBE and isobutene were added in amounts up to 25% of the fuel to propane-oxygen-argon mixtures in shock tube experiments covering a range of temperatures between 1450 and 1800 K. Ignition delays were measured from chemiluminescence at 432 nm due to excited CH radicals. The temperature dependence of the ignition rates was analyzed to yield Arrhenius parameters of E_a ca. 40 kcal/mol and A ca. 10⁹ s^?1 for the overall propane reaction and E_a ca. 34 kcal/mol and A ca. 10^8.3 s^?1 for the overall propane/MTBE reaction. Reactions involving MTBE and its decomposition products were combined with an established propane mechanism in a numerical model to describe the kinetic interaction of this additive with a typical hydrocarbon fuel. The experiments and the kinetic model both show that MTBE and isobutene retard propane ignition with nearly equal efficiency. The kinetic model demonstrates that isobutene kinetics are responsible for inhibition by both MTBE and isobutene, and the specific elementary reactions that produce this behavior are identified. © 1994 John Wiley & Sons, Inc.     

Information theory of line-shape in collision-induced absorption

Information theory is used to interpret the line-shape of collision-induced absorption spectra of rare-gas mixtures. Numerical results and comparison with experiment are given for low-density XeAr gas mixtures at 295 K.