The authors have developed a method to reduce noise in three-dimensional (3D) phase-contrast magnetic resonance (MR) velocity measurements by exploiting the property that blood is incompressible and, therefore, the velocity field describing its flow must be divergence-free. The divergence-free condition is incorporated by a projection operation in Hilbert space. The velocity field obtained with 3D phase-contrast MR imaging is projected onto the space of divergence-free velocity fields. The reduction of noise is achieved because the projection operation eliminates the noise component that is not divergence-free. Signal-to-noise ratio (S/N) gains on the order of 15%-25% were observed. The immediate effect of this noise reduction manifests itself in higher-quality phase-contrast MR angiograms. Alternatively, the S/N gain can be traded for a reduction in imaging time and/or improved spatial resolution.

The product branching ratio of [NH2 + NO → N2H + OH]:[NH2 + NO → N2 + H2O] has been determined in the temperature range of 1340−1670 K in a shock tube study with laser photolytic generation of the NH2 radicals. Sensitive frequency-modulation detection of the NH2 radical enables experiments with very low initial radical concentrations and, hence, virtually no interference from secondary reactions or dependence on the overall rate coefficient of the reaction. The branching ratio, α, defined as α = k 1a/(k 1a+k 1b), increases from 0.42 at 1340 K to 0.53 at 1670 K. Over this temperature range our results can be expressed as α = 0.5 + (3.36 × 10-4)(T/K − 1600). A detailed error analysis yields an uncertainty in the values of α of ±0.02 near 1500 K, increasing to ±0.05 at the temperature extremes.

The rate coefficient of the reaction NH 2 + NO → products (R1) was determined in shock tube experiments using frequency-modulation absorption spectroscopy for detection of NH 2 . Because of the sensitivity of the diagnostic system, very low reactant concentrations could be employed in order to reduce the influence of secondary reactions on the NH 2 profiles. Benzylamine, C 6 H 5 CH 2 NH 2 , was used as a thermal source of the NH 2 radicals in the experiments. To determine the reaction rate, a perturbation strategy was employed that is based on changes in the NH 2 profiles when NO is added to the C 6 H 5 CH 2 NH 2 /Ar mixtures. The measured NH 2 profiles were interpreted by detailed kinetic modeling to obtain the overall reaction rate of R1 in the temperature range 1262-1726 K. The lower temperature limit of the present study is in the middle of the Thermal De-NOx temperature window. The present rate measurements are consistent with both our previous determination of the rate at higher temperatures and lower temperature data. A rate expression obtained by combining our higher temperature data and lower temperature data isfor the temperature range 200-2500 K. The estimated uncertainty of the rate coefficient is ±20%.

For the pyrolysis of refuse plastic fuel (RPF), the typical particle size is large and the time required for pyrolysis is long. Therefore, the rate-limiting mechanisms of gas diffusion and chemical reaction might be important. In this paper, the kinetics of RPF pyrolysis was investigated through a thermogravimetry analysis under isothermal conditions between 300 and 600 °C. A kinetic model was used to examine the effects of the surface chemical reaction and gas diffusion on the rate-limiting steps of RPF pyrolysis. The results show that the rate was controlled by a combination of the surface chemical reaction and gas diffusion through the solid product layer. The activation energies for the surface chemical reaction and gas diffusion were determined to be 70.2 and 65.9 kJ mol-1, respectively. The weight loss of RPF pyrolysis occurred mainly at temperatures higher than 400 °C and increased with temperatures. Concentrations of pyrolysis gases including H2, CO, and hydrocarbons were analyzed through a real-time gas analyzer. Gas yields from pyrolysis were sensitive to temperatures higher than 300 °C, while a very small amount of gas was released at 300 °C.