Variation Of Rate Coefficient Research Articles

Effects of CH−NO Interactions on Kinetics of Prompt NO in High-Pressure Counterflow Flames

Laser-induced fluorescence (LIF) measurements of nitric oxide (NO) and methylidyne (CH), previously reported for prompt-dominated laminar, counterflow, methane−air non-premixed flames at a global strain rate of 20 s−1 and pressures from 1 to 6 atm, are analyzed by considering three important aspects of complex CH−NO kinetics. First, net reaction rates are studied as a function of pressure so as to understand the observed peaks in maximum [CH] and [NO] between 2 and 4 atm. Second, key elementary reactions are compared for two detailed chemical kinetic mechanisms, GRI 3.0 and Lindstedt, in order to investigate differences in computed [CH] and [NO]. Third, variations in rate coefficients are studied for those elementary reactions involving CH that strongly influence NO concentrations in these non-premixed flames. Rate coefficients are also considered for reaction steps which directly affect the formation and destruction of NO. On the basis of all three inquiries, rate coefficients for controlling elementary ...

Transition Event Statistics in Genetics and Disordered Kinetics. Theoretical Approaches for Extracting Rate Distributions from Experimental Data

We study the analogies between the theory of rate processes in disordered systems and the overdispersed molecular clocks in evolutionary biology. A biological "molecular clock" expresses the statistics of the number of amino acid or nucleotide substitutions during evolution. Random variations of the evolution rates lead to statistical (overdispersed) molecular clocks which are described by random point processes with random substitution rates. We find that the models for overdispersed molecular clocks are equivalent to those of the random-rate or random channel models used in disordered kinetics. The number of transport (reaction) events in disordered kinetics plays the same role as the number of substitution events in molecular biology. We study the connections between the (observed) statistics of the transition events and the statistics of random rate coefficients and random channels; a unified approach is developed which is valid both in molecular biology and in disordered kinetics. We develop methods for extracting statistical information about the variations of rate coefficients from experimental or observed data regarding the fluctuations of the numbers of substitution, reaction, or transport events. For systems with static disorder, the observed statistics of the number of reaction events, expressed in terms of probabilities at a given time or by the cumulants of the number of transition events at a given time, contains the information necessary for evaluating the cumulants or the probability density of the rate coefficients or the density of states for random channel kinetics. For dynamic disorder this is not possible; further information about multitime probability distributions of the reaction events is needed.

Ultrasonic degradation of polybutadiene and isotactic polypropylene

The ultrasonic degradation of polybutadiene and isotactic polypropylene in solution was studied at different temperatures and in different solvents. The time evolution of molecular weight distribution was determined experimentally through gel permeation chromatography. Degradation rate coefficients were determined from a model based on continuous distribution kinetics and assuming mid-point chain scission. The variation of rate coefficients with vapour pressure and kinematic viscosity was also investigated.

Variations of Rate Coefficients and Termination Mechanism During the After-Effects of a Light- Induced Polymerization of a Dimethacrylate Monomer

Variations of Rate Coefficients and Termination Mechanism During the After-Effects of a Light- Induced Polymerization of a Dimethacrylate Monomer

Continuous distribution kinetics for ultrasonic degradation of poly(methyl methacrylate)

AbstractUltrasonic degradation of poly(methyl methacrylate) (PMMA) was carried out in several solvents and some mixtures of solvents. The time evolution of molecular weight distribution (MWD), determined by gel permeation chromatography, is analysed by continuous distribution kinetics. The rate coefficients for polymer degradation are determined for each solvent. The variation of rate coefficients is correlated with the vapour pressure of the solvent, kinematic viscosity of the solution and solvent–polymer interaction parameters. The vapour pressure and the kinematic viscosity of the solution are found to be more critical than other parameters (such as the Huggins and Flory–Huggins constants) in determining the degradation rates.© 2001 Society of Chemical Industry

Effect of solvent on the ultrasonic degradation of poly(vinyl acetate)

The ultrasonic degradation of poly(vinyl acetate) was carried out in six different solvents and two mixtures of solvents. The evolution of molecular weight distribution (MWD) with time was determined with gel permeation chromatography. The observed MWDs were analyzed by continuous distribution kinetics. A stoichiometric kernel that accounts for preferential mid-point breakage of the polymer chains was used. The degradation rate coefficient of the polymer in each solvent was determined from the model. The variations of rate coefficients were correlated with vapor pressure of the solvent, the Flory–Huggins polymer–solvent interaction parameter and the kinematic viscosity of the solution. A lower saturation vapor pressure resulted in higher degradation rates of the polymer. The degradation rate increased with increasing kinematic viscosity.