The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Yusuke Takahashi - One of the best experts on this subject based on the ideXlab platform.
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reentry blackout prediction for atmospheric reentry demonstrator mission considering uncertainty in Chemical Reaction Rate model
Physics of Plasmas, 2018Co-Authors: Minseok Jung, Hisashi Kihara, Yusuke TakahashiAbstract:A numerical simulation model of plasma flows and electromagnetic waves around a vehicle was developed to predict a radio frequency blackout. Plasma flows in the shock layer and the wake region were calculated using a computational fluid dynamics technique with a three-dimensional model. A finite-catalytic wall condition known to affect plasma properties, such as the number density of electrons, was considered for accuRate prediction. A parametric study was performed to investigate the effect of uncertainty in the Chemical Reaction Rate model on evaluating a radio frequency blackout. The behavior of electromagnetic waves in plasma was investigated using a frequency-dependent finite-difference time-domain method. Numerical simulations of reentry blackout were performed for the Atmospheric Reentry Demonstrator mission at various altitudes. The plasma flows and the complex movement of electromagnetic waves around the Atmospheric Reentry Demonstrator vehicle were clarified. The predicted signal loss profile wa...
Maksym Kryvohuz - One of the best experts on this subject based on the ideXlab platform.
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calculation of Chemical Reaction Rate constants using on the fly high level electronic structure computations with account of multidimensional tunneling
Journal of Chemical Physics, 2012Co-Authors: Maksym KryvohuzAbstract:The semiclassical instanton approach to the calculation of Reaction Rate constants at arbitrary temperatures in multiatomic systems is combined with high-level ab initio calculations of reactive potential energy surface (PES). The number of required ab initio calculations weakly depends on system size and allows on-the-fly evaluations of PES with high accuracy. The approach can be efficiently parallelized and provides a practical way of calculating quantum Reaction Rate constants with account of nuclear quantum effects such as multidimensional tunneling and zero point energies, which are rigorously incorpoRated in the theory. An algorithm for the search of instanton trajectories is explained. Application of the approach is illustRated for H + H2 → H2 + H and D + D2 → D2 + D bimolecular Reactions in the wide temperature range with on-the-fly evaluation of PES at the ab initio full configuration interaction (FCI), coupled-cluster single double (CCSD), and single and double excitation configuration interacti...
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semiclassical instanton approach to calculation of Reaction Rate constants in multidimensional Chemical systems
Journal of Chemical Physics, 2011Co-Authors: Maksym KryvohuzAbstract:The semiclassical instanton approximation is revisited in the context of its application to the calculation of Chemical Reaction Rate constants. An analytical expression for the quantum canonical Reaction Rate constants of multidimensional systems is derived for all temperatures from the deep tunneling to high-temperature regimes. The connection of the derived semiclassical instanton theory with several previously developed Reaction Rate theories is shown and the numerical procedure for the search of instanton trajectories is provided. The theory is tested on seven different collinear symmetric and asymmetric atom transfer Reactions including heavy-light-heavy, light-heavy-light and light-light-heavy systems. The obtained thermal Rate constants agree within a factor of 1.5–2 with the exact quantum results in the wide range of temperatures from 200 to 1500 K.
Minseok Jung - One of the best experts on this subject based on the ideXlab platform.
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reentry blackout prediction for atmospheric reentry demonstrator mission considering uncertainty in Chemical Reaction Rate model
Physics of Plasmas, 2018Co-Authors: Minseok Jung, Hisashi Kihara, Yusuke TakahashiAbstract:A numerical simulation model of plasma flows and electromagnetic waves around a vehicle was developed to predict a radio frequency blackout. Plasma flows in the shock layer and the wake region were calculated using a computational fluid dynamics technique with a three-dimensional model. A finite-catalytic wall condition known to affect plasma properties, such as the number density of electrons, was considered for accuRate prediction. A parametric study was performed to investigate the effect of uncertainty in the Chemical Reaction Rate model on evaluating a radio frequency blackout. The behavior of electromagnetic waves in plasma was investigated using a frequency-dependent finite-difference time-domain method. Numerical simulations of reentry blackout were performed for the Atmospheric Reentry Demonstrator mission at various altitudes. The plasma flows and the complex movement of electromagnetic waves around the Atmospheric Reentry Demonstrator vehicle were clarified. The predicted signal loss profile wa...
Andreas Jess - One of the best experts on this subject based on the ideXlab platform.
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influence of Chemical Reaction Rate diffusion and pore structure on the regeneration of a coked al2o3 catalyst
Applied Catalysis A-general, 2004Co-Authors: Dahai Tang, Christoph Kern, Andreas JessAbstract:Abstract As a contribution to a better basic understanding and an accuRate modelling of the regeneration of coked catalyst particles, the following investigations were done with pure Al 2 O 3 as a model catalyst: (1) determination of the intrinsic and effective kinetics of coke burn-off; (2) characterisation of the catalyst’s morphology with respect to the influence of the carbon load on the surface area, porosity, pore diameter, and tortuosity; (3) measurement of radial coke profiles within partly regeneRated particles; (4) numerical simulation of the regeneration within coked particles and comparison with experimental data of radial coke profiles and the time needed for a certain degree of burn-off. For the modelling of coke burn-off within single particles, the Chemical Reaction Rate, pore diffusion, radial gradients of the O 2 - and the carbon-concentration, and the influence of the carbon load on the porosity and tortuosity have to be considered. Only the resistances of external heat and mass transfer and of intraparticle heat conduction can be neglected, at least for particle sizes and temperatures of technical relevance for fixed beds ( The results show that temperatures above about 400 °C are needed to achieve regeneration within an acceptable timeframe. On the other hand, a temperature of more than about 500 °C will not anymore acceleRate the burn-off, at least in case of fixed bed reactors with particles in the region of mm. This effect can be attributed to the increasing strength of pore diffusion resistance, and eventually the complete resistance is confined to the outer carbon-free shell.
Craig C. Martens - One of the best experts on this subject based on the ideXlab platform.
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Toward a quantum trajectory-based Rate theory
Theoretical Chemistry Accounts, 2014Co-Authors: Brittany L. Hyland, Craig C. MartensAbstract:We describe a new approach to incorporating quantum effects into Chemical Reaction Rate theory using quantum trajectories. Our development is based on the entangled trajectory molecular dynamics method for simulating quantum processes using trajectory integration and ensemble averaging. By making dynamical approximations similar to those underlying classical transition state theory, quantum corrections are incorpoRated analytically into the quantum Rate expression. We focus on a simple model of quantum decay in a metastable system and consider the deep tunneling limit where the classical Rate vanishes and the process is entirely quantum mechanical. We compare our approximate estimate with the well-known WKB tunneling Rate and find qualitative agreement.