DSMC Dissociation Model Based on Two-Temperature Chemical Rate Constant

2007 ◽  
Author(s):  
Yevgeniy Bondar ◽  
Mikhail Ivanov
Keyword(s):  
Rate Constant ◽  
Model Based ◽  
Dissociation Model ◽  
Two Temperature ◽  
Chemical Rate

scholarly journals Impact of uncertainties in inorganic chemical rate constants on tropospheric composition and ozone radiative forcing

2017 ◽  
Author(s):  
Ben Newsome ◽  
Mat Evans
Keyword(s):  
Rate Constant ◽  
Atmospheric Chemistry ◽  
Rate Constants ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Transport Model ◽  
Surface Ozone ◽  
Photolysis Rates ◽  
The Impact ◽  
Chemical Rate

Abstract. Chemical rate constants determine the composition of the atmosphere and how this composition has changed over time. They are central to our understanding of climate change and air quality degradation. Atmospheric chemistry models, whether online or offline, box, regional or global use these rate constants. Expert panels synthesise laboratory measurements, making recommendations for the rate constants that should be used. This results in very similar or identical rate constants being used by all models. The inherent uncertainties in these recommendations are, in general, therefore ignored. We explore the impact of these uncertainties on the composition of the troposphere using the GEOS-Chem chemistry transport model. Based on the JPL and IUPAC evaluations we assess 50 mainly inorganic rate constants and 10 photolysis rates, through simulations where we increase the rate of the reactions to the 1σ upper value recommended by the expert panels. We assess the impact on 4 standard metrics: annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime. Uncertainty in the rate constants for NO2 + OH    M →  HNO3, OH + CH4 → CH3O2 + H2O and O3 + NO → NO2 + O2 are the three largest source of uncertainty in these metrics. We investigate two methods of assessing these uncertainties, addition in quadrature and a Monte Carlo approach, and conclude they give similar outcomes. Combining the uncertainties across the 60 reactions, gives overall uncertainties on the annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime of 11, 12, 17 and 17 % respectively. These are larger than the spread between models in recent model inter-comparisons. Remote regions such as the tropics, poles, and upper troposphere are most uncertain. This chemical uncertainty is sufficiently large to suggest that rate constant uncertainty should be considered when model results disagree with measurement. Calculations for the pre-industrial allow a tropospheric ozone radiative forcing to be calculated of 0.412 ± 0.062 Wm−2. This uncertainty (15 %) is comparable to the inter-model spread in ozone radiative forcing found in previous model-model inter-comparison studies where the rate constants used in the models are all identical or very similar. Thus the uncertainty of tropospheric ozone radiative forcing should expanded to include this additional source of uncertainty. These rate constant uncertainties are significant and suggest that refinement of supposedly well known chemical rate constants should be considered alongside other improvements to enhance our understanding of atmospheric processes.

Mechanism-based Pharmacokinetic–Pharmacodynamic Modeling of the Antinociceptive Effect of Buprenorphine in Healthy Volunteers

2006 ◽  
Vol 104 (6) ◽  
pp. 1232-1242 ◽  
Author(s):  
Ashraf Yassen ◽  
Erik Olofsen ◽  
Raymonda Romberg ◽  
Elise Sarton ◽  
Meindert Danhof ◽  
...  
Keyword(s):  
Confidence Interval ◽  
Healthy Volunteers ◽  
Rate Constant ◽  
Time Course ◽  
Antinociceptive Effect ◽  
Receptor Occupancy ◽  
Compartment Model ◽  
Effect Compartment ◽  
Effect Compartment Model ◽  
Dissociation Model

Background The objective of this investigation was to characterize the pharmacokinetic-pharmacodynamic relation of buprenorphine's antinociceptive effect in healthy volunteers. Methods Data on the time course of the antinociceptive effect after intravenous administration of 0.05-0.6 mg/70 kg buprenorphine in healthy volunteers was analyzed in conjunction with plasma concentrations by nonlinear mixed-effects analysis. Results A three-compartment pharmacokinetic model best described the concentration time course. Four structurally different pharmacokinetic-pharmacodynamic models were evaluated for their appropriateness to describe the time course of buprenorphine's antinociceptive effect: (1) E(max) model with an effect compartment model, (2) "power" model with an effect compartment model, (3) receptor association-dissociation model with a linear transduction function, and (4) combined biophase equilibration/receptor association-dissociation model with a linear transduction function. The latter pharmacokinetic-pharmacodynamic model described the time course of effect best and was used to explain time dependencies in buprenorphine's pharmacodynamics. The model converged, yielding precise estimation of the parameters characterizing hysteresis and the relation between relative receptor occupancy and antinociceptive effect. The rate constant describing biophase equilibration (k(eo)) was 0.00447 min(-1) (95% confidence interval, 0.00299-0.00595 min(-1)). The receptor dissociation rate constant (k(off)) was 0.0785 min(-1) (95% confidence interval, 0.0352-0.122 min(-1)), and k(on) was 0.0631 ml . ng(-1) . min(-1) (95% confidence interval, 0.0390-0.0872 ml . ng(-1) . min(-1)). Conclusion This is consistent with observations in rats, suggesting that the rate-limiting step in the onset and offset of the antinociceptive effect is biophase distribution rather than slow receptor association-dissociation. In the dose range studied, no saturation of receptor occupancy occurred explaining the lack of a ceiling effect for antinociception.

scholarly journals Impact of uncertainties in inorganic chemical rate constants on tropospheric composition and ozone radiative forcing

2017 ◽  
Vol 17 (23) ◽  
pp. 14333-14352 ◽  
Author(s):  
Ben Newsome ◽  
Mat Evans
Keyword(s):  
Rate Constant ◽  
Atmospheric Chemistry ◽  
Rate Constants ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Transport Model ◽  
Surface Ozone ◽  
Chemistry Transport Model ◽  
The Impact ◽  
Chemical Rate

Abstract. Chemical rate constants determine the composition of the atmosphere and how this composition has changed over time. They are central to our understanding of climate change and air quality degradation. Atmospheric chemistry models, whether online or offline, box, regional or global, use these rate constants. Expert panels evaluate laboratory measurements, making recommendations for the rate constants that should be used. This results in very similar or identical rate constants being used by all models. The inherent uncertainties in these recommendations are, in general, therefore ignored. We explore the impact of these uncertainties on the composition of the troposphere using the GEOS-Chem chemistry transport model. Based on the Jet Propulsion Laboratory (JPL) and International Union of Pure and Applied Chemistry (IUPAC) evaluations we assess the influence of 50 mainly inorganic rate constants and 10 photolysis rates on tropospheric composition through the use of the GEOS-Chem chemistry transport model. We assess the impact on four standard metrics: annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime. Uncertainty in the rate constants for NO2 + OH →M  HNO3 and O3 + NO  →  NO2 + O2 are the two largest sources of uncertainty in these metrics. The absolute magnitude of the change in the metrics is similar if rate constants are increased or decreased by their σ values. We investigate two methods of assessing these uncertainties, addition in quadrature and a Monte Carlo approach, and conclude they give similar outcomes. Combining the uncertainties across the 60 reactions gives overall uncertainties on the annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime of 10, 11, 16 and 16 %, respectively. These are larger than the spread between models in recent model intercomparisons. Remote regions such as the tropics, poles and upper troposphere are most uncertain. This chemical uncertainty is sufficiently large to suggest that rate constant uncertainty should be considered alongside other processes when model results disagree with measurement. Calculations for the pre-industrial simulation allow a tropospheric ozone radiative forcing to be calculated of 0.412 ± 0.062 W m−2. This uncertainty (13 %) is comparable to the inter-model spread in ozone radiative forcing found in previous model–model intercomparison studies where the rate constants used in the models are all identical or very similar. Thus, the uncertainty of tropospheric ozone radiative forcing should expanded to include this additional source of uncertainty. These rate constant uncertainties are significant and suggest that refinement of supposedly well-known chemical rate constants should be considered alongside other improvements to enhance our understanding of atmospheric processes.

New two-temperature dissociation model for reacting flows

10.2514/3.478 ◽  
1993 ◽  
Vol 7 (4) ◽  
pp. 687-696 ◽  
Author(s):  
David P. Olynick ◽  
H. A. Hassan
Keyword(s):  
Reacting Flows ◽  
Dissociation Model ◽  
Two Temperature

Studies of the Chaotic Behaviour in the Peroxidase-Oxidase Reaction

1979 ◽  
Vol 34 (12) ◽  
pp. 1544-1546 ◽  
Author(s):  
Lars F. Olsen
Keyword(s):  
Rate Constant ◽  
Enzyme Concentration ◽  
Chaotic Behaviour ◽  
Experimental Results ◽  
Elementary Reaction ◽  
Model Based ◽  
Catalysed Reaction ◽  
Periodic Behaviour ◽  
Behaviour Changes ◽  
Oxidase Reaction

Abstract This note presents experimental results with an enzyme-catalysed reaction with a continuous supply of the substrates in which we observe a transition from periodic behaviour to apparently nonperiodic behaviour by decreasing the enzyme concentration. A model of the reaction is also described. This model, based only on elementary reaction steps, can simulate the periodic behaviour observed experimentally. By changing only one rate constant the behaviour changes from periodic to quasi-periodic behaviour. The work of earlier investigators suggests that such quasiperiodic behaviour (toroidal oscillations) is a step towards chaotic behaviour.

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