Cellular instabilities of expanding hydrogen/propane spherical flames at elevated pressures: theory and experiment

An experimental and theoretical investigation of the onset of cellular instabilities on spherically expanding flames in mixtures of hydrogen and propane in air at elevated pressures was conducted. Critical conditions for the onset of instability were measured and mapped out over a range of pressures and mixture compositions. An asymptotic theory of hydrodynamic and diffusional-thermal cell development on flames in mixtures comprised of two scarce fuels burning in air was also formulated. Predicted values of Peclet number, defined as the flame radius at the onset of instability normalized by the flame thickness, were shown to compare favorably with the experimentally measured values.     

Application of gel-permeation chromatography to studies of the functionality distribution of carboxy- and hydroxy-polybutadienes

Separations of carboxy-polybutadienes and hydroxy-polybutadienes according to functionality have been effected using stepwise elution from silica gel. Recoveries in the 95–100% range have been achieved. Subjection of the fractions obtained from the silica gel separation to analysis via gel-permeation chromatography and infrared or near-infrared spectroscopy yields not only functionality distribution data, but also provides the relationship between molecular weight distribution and functional type. Analytical techniques and interpretation of data are discussed.     

The molecular potential energy surface and vibrational energy levels of methyl fluoride. Part II

New analytical bending and stretching, ground electronic state, potential energy surfaces for CH(3)F are reported. The surfaces are expressed in bond-length, bond-angle internal coordinates. The four-dimensional stretching surface is an accurate, least squares fit to over 2000 symmetrically unique ab initio points calculated at the CCSD(T) level. Similarly, the five-dimensional bending surface is a fit to over 1200 symmetrically unique ab initio points. This is an important first stage towards a full nine-dimensional potential energy surface for the prototype CH(3)F molecule. Using these surfaces, highly excited stretching and (separately) bending vibrational energy levels of CH(3)F are calculated variationally using a finite basis representation method. The method uses the exact vibrational kinetic energy operator derived for XY(3)Z systems by Manson and Law (preceding paper, Part I, Phys. Chem. Chem. Phys., 2006, 8, DOI: 10.1039/b603106d). We use the full C(3v) symmetry and the computer codes are designed to use an arbitrary potential energy function. Ultimately, these results will be used to design a compact basis for fully coupled stretch-bend calculations of the vibrational energy levels of the CH(3)F system.     

Quantum phase transition between a Luttinger liquid and a gas of cold molecules

We consider cold polar molecules confined in a helical optical lattice similar to those used in holographic microfabrication. An external electric field polarizes molecules along the axis of the helix. The large-distance intermolecular dipolar interaction is attractive but the short-scale interaction is repulsive due to geometric constraints and thus prevents collapse. The interaction strength depends on the electric field. We show that a zero-temperature second-order liquid-gas transition occurs at a critical field. It can be observed under experimentally accessible conditions.