A global uncertainty analysis is performed for three current mechanisms describing the low temperature oxidation of dimethyl ether (Aramco Mech 1.3, Zheng et al. 2005, Liu et al. 2013) with application to simulations of species concentrations (CH 2 , H 2 O 2 , CH 3 OCHO) corresponding to existing data from an atmospheric pressure flow reactor, and high pressure ignition delays. When incorporating uncertainties in reaction rates within a global sampling approach, the distributions of predicted targets can span several orders of magnitude. The experimental profiles however, fall within the predictive uncertainty limits. A variance based sensitivity analysis is then undertaken using high dimensional model representations. The main contributions to predictive uncertainties come from the CH 3 OCH 2 +O 2 system, with isomerisation, propagation, chain-branching, secondary OH formation and peroxy-peroxy reactions all playing a role. The response surface describing the relationship between sampled reaction rates and predicted outputs is complex in all cases. Higher-order interactions between parameters contribute significantly to output variance, and no single reaction channel dominates for any of the conditions studied. Sensitivity scatter plots illustrate that many different parameter combinations could lead to good agreement with specific sets of experimental data. The Aramco scheme is then updated based on data from a recent study by Eskola et al. which presents quite different temperature and pressure dependencies for the rates of CH 3 OCH 2 O 2 CH 2 OCH 2 O 2 H and CH 2 OCH 2 O 2 H OH+2CH 2 O compared with currently used values, and includes well skipping channels. The updates from Eskola worsen the agreement with experiments when used in isolation. However, if the rate of the CH 2 OCH 2 O 2 H+O 2 channel is subsequently reduced, very good agreement can be achieved. Due to the complex nature of the response surface, the tuning of this channel remains speculative. Further detailed studies of the temperature and pressure dependence of the CH 3 OCH 2 O 2 +O 2 , CH 2 OCH 2 O 2 H+O 2 system are recommended in order to reduce uncertainties within current DME mechanisms for low temperature conditions.
Abstract. The availability of reliable modeling tools and input data required for the prediction of surface removal rate from the lithium fl uoride targets irradiated by the intense photon beams is essential for many practical aspects. This study is motivated by the practical implementation of soft X-ray (SXR) or extreme ultraviolet (XUV) lasers for the pulsed ablation and thin fi lm deposition. Specifi cally, it is focused on quantitative description of XUV laser-induced desorption/ablation from lithium fl uoride, which is a reference large band-gap dielectric material with ionic crystalline structure. Computational framework was proposed and employed here for the reconstruction of plume expansion dynamics induced by the irradiation of lithium fl uoride targets. The morphology of experimentally observed desorption/ablation craters were reproduced using idealized representation (two-zone approximation) of the laser fl uence profi le. The calculation of desorption/ablation rate was performed using one-dimensional thermomechanic model (XUV-ABLATOR code) taking into account laser heating and surface evaporation of the lithium fl uoride target occurring on a nanosecond timescale. This step was followed by the application of two-dimensional hydrodynamic solver for description of laser-produced plasma plume expansion dynamics. The calculated plume lengths determined by numerical simulations were compared with a simple adiabatic expansion (blast-wave) model.
An effective communication among authorities, citizens and industry is crucial to ensure good awareness of risk and knowledge of adequate reactions in preparedness to major industrial accidents. The present risk communication system in Czech Republic was evaluated by a nationwide survey. The main research was focused on the level of knowledge about risks and appropriate reactions to an accident and on the attitudes towards existing risk communication system. The results of survey indicate that the current system is insufficient and has to be improved to fulfill the requirements of the new Seveso III directive (2012/18/EU) and to secure safety of the citizens.
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