The hydroxyl radical reaction rate constant and products of cyclohexanol

The gas phase reaction of the hydroxyl radical (OH) with cyclohexanol (COL) has been studied. The rate coefficient was determined to be (19.0 ± 4.8) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ (at 297 ± 3 K and 1 atmosphere total pressure) using the relative rate technique with pentanal, decane, and tridecane as the reference compounds. Assuming an average OH concentration of 1 × 10⁶ molecules cm⁻³, an atmospheric lifetime of 15 h is calculated for cyclohexanol. Products of the OH + COL reaction were determined to more clearly define COL's atmospheric degradation mechanism. The observed products and their formation yields were: cyclohexanone (0.55 ± 0.06), hexanedial (0.32 ± 0.15), 3‐hydroxycyclohexanone (0.31 ± 0.14), and 4‐hydroxycyclohexanone (0.08 ± 0.04). Consideration of the potential reaction pathways suggests that each of these products is formed via hydrogen abstraction at a different site on the COL ring. The products and their relative amounts are discussed in light of the predicted yields for each reaction channel. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 108–117, 2001     

Dilute limit of a strongly-interacting model of spinless fermions and hardcore bosons on the square lattice

In our model, spinless fermions (or hardcore bosons) on a square lattice hop to nearest neighbor sites, and also experience a hard-core repulsion at the nearest neighbor separation. This is the simplest model of correlated electrons and is more tractable for exact diagonalization than the Hubbard model. We study systematically the dilute limit of this model by a combination of analytical and several numerical approaches: the two-particle problem using lattice Green functions and the t-matrix, the few-fermion problem using a modified t-matrix (demonstrating that the interaction energy is well captured by pairwise terms), and for bosons the fitting of the energy as a function of density to Schicks analytical result for dilute hard disks. We present the first systematic study for a strongly-interacting lattice model of the t-matrix, which appears as the central object in older theories of the existence of a two-dimensional Fermi liquid for dilute fermions with strong interactions. For our model, we can (Lanczos) diagonalize the 7 x 7 system at all fillings and the 20 x 20 system with four particles, thus going far beyond previous diagonalization works on the Hubbard model.Received: 8 May 2003, Published online: 28 May 2004PACS: 71.10.Fd Lattice fermion models (Hubbard model, etc.) - 71.10.Pm Fermions in reduced dimensions (anyons, composite fermions, Luttinger liquid, etc.) - 05.30.Jp Boson systems - 74.20.Mn Nonconventional mechanisms (spin fluctuations, polarons and bipolarons, resonating valence bond model, anyon mechanism, marginal Fermi liquid, Luttinger liquid, etc.)N.G. Zhang: Present address: Dept. of Physics, George Washington University, Washington, DC 20052     

Computational electrochemistry: finite element simulation of a disk electrode with ultrasonic acoustic streaming

Computer simulations using the finite element method (FEM) are used to predict the correlation between the transport limiting current (I(lim)) and parameters such as diffusion coefficient, source to electrode separation, source power, and medium viscosity for a sonicated disk electrode in "face on" mode. The fluid dynamics and diffusion layer are modeled directly using FEM and predict that the electrode is uniformly accessible, I(lim) is proportional to the diffusion coefficient to the 2/3 power and I(lim) is proportional to the square root of the source power. Curves are also calculated relating I(lim) to the source to electrode separation and liquid viscosity.     

Parity violation in electron-deuteron scattering. II. Break-up channels

Parity violation in electron-deuteron inelastic scattering is decribed. An impulse approximation, modified to incorporate gauge invariance, is employed. Additional meson-exchange currents are included. Normal-parity and abnormal-parity wave function components are generated numerically with a Reid soft-core potential for the former and a general parity-violating weak potential with adjustable coupling constants for the latter. Numerical results for parity-conserving differential cross sections are in good agreement with existing data. For low n?p excitation energies and medium-energy electrons, we find that parity-violating asymmetries are dominated by contributions from neutral weak currents so that the Weinberg-Salam theory can be tested. For low-energy electrons, 5 MeV ? E_e ? 50 MeV, our results indicate that the asymmetry caused by nuclear parity violation is roughly as important as that due to neutral weak currents. The pion-nucleon parity-violating coupling, f_π, as well as the rho- and omega-nucleon parity-violating couplings, may be determinable from such experiments. Further, it is possible to check the experiment of Lobashov et al., which detects circular polarization in the thermal-neutron capture reaction.     

Two improved methods of surface-displacement measurements by holographic interferometry

This paper describes two new methods for measuring surface-displacements. The first method is an improvement of Ennos' scheme in that multiple object beams are used instead of multiple hologram plates. This arrangement enables the three fringe patterns required for calculating displacement components to be viewed from the same direction, i.e., normal view. Thus the necessity of laborious fringe reprojection is eliminated. The second method involves making three holograms, one situated on each of the three coordinate axes assigned to the surface. Each hologram picks up one component of displacement. Hence no separation of displacement components is required. An experimental demonstration is presented which utilizes the first technique and checks with theoretical predictions.     

Simultaneous measurement of vapor diffusion and solubility coefficients in polymers by frequency response techniques

An experimental technique for the simultaneous measurement of solubility and diffusion coefficients in polymers by frequency response techniques has been developed. A sample of polymer suspended from an electrobalance is exposed to a permeating gas whose pressure is being varied sinusoidally at ultra-low frequencies. The phase angle and amplitude of the weight changes are measured as a function of the frequency of the pressure wave. It is shown that in the linear range the diffusivity coefficient for polyethylene–ethane calculated from the phase angle lag and the Henry's law solubility and the diffusivity obtained from the amplitude ratios are in excellent internal agreement and also agree with values obtained from transient measurements.