The Experts below are selected from a list of 125136 Experts worldwide ranked by ideXlab platform
Jeffrey R Errington - One of the best experts on this subject based on the ideXlab platform.
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comparing the use of gibbs ensemble and grand canonical Transition Matrix monte carlo methods to determine phase equilibria
Industrial & Engineering Chemistry Research, 2008Co-Authors: Andrew S Paluch, Vincent K Shen, Jeffrey R ErringtonAbstract:We present results from a computational study investigating the use of Gibbs ensemble and grand-canonical Transition-Matrix Monte Carlo (GC-TMMC) methods to determine the liquid−vapor phase coexistence properties of pure molecular fluids of varying degrees of complexity. The molecules used in this study were ethane, n-octane, cyclohexane, 2,5-dimethylhexane, 1-propanol, and water. We first show that the GC-TMMC method can reproduce Gibbs ensemble results found in the literature. Given the excellent agreement for each molecule, we then compare directly the performance of Gibbs ensemble and GC-TMMC simulations at both low and high reduced temperatures by monitoring the relative uncertainties in the saturation properties as a function of computational time. In general, we found that the GC-TMMC method yielded limiting uncertainties in the saturated vapor density and pressure that were significantly smaller, by an order of magnitude in some instances, than those of the Gibbs ensemble method. Limiting Gibbs en...
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computation of interfacial properties via grand canonical Transition Matrix monte carlo simulation
Journal of Chemical Physics, 2008Co-Authors: Eric M Grzelak, Jeffrey R ErringtonAbstract:We examine two free-energy-based methods for studying the wetting properties of a fluid in contact with a solid substrate. Application of the first approach involves examination of the adsorption behavior of a fluid at a single substrate, while the second technique requires investigation of the properties of a system confined between two parallel substrates. Both of the techniques rely upon computation and analysis of the density dependence of a system’s surface free energy and provide the contact angle and solid-vapor and solid-liquid interfacial tensions for substrate-fluid combinations within the partial wetting regime. Grand canonical Transition Matrix Monte Carlo simulation is used to obtain the required free-energy curves. The methods examined within this work are general and are applicable to a wide range of molecular systems. We probe the performance of the methods by computing the interfacial properties for two systems in which an atomistic fluid interacts with a fcc crystal. For both of the syst...
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computation of interfacial properties via grand canonical Transition Matrix monte carlo simulation
Journal of Chemical Physics, 2008Co-Authors: Eric M Grzelak, Jeffrey R ErringtonAbstract:We examine two free-energy-based methods for studying the wetting properties of a fluid in contact with a solid substrate. Application of the first approach involves examination of the adsorption behavior of a fluid at a single substrate, while the second technique requires investigation of the properties of a system confined between two parallel substrates. Both of the techniques rely upon computation and analysis of the density dependence of a system’s surface free energy and provide the contact angle and solid-vapor and solid-liquid interfacial tensions for substrate-fluid combinations within the partial wetting regime. Grand canonical Transition Matrix Monte Carlo simulation is used to obtain the required free-energy curves. The methods examined within this work are general and are applicable to a wide range of molecular systems. We probe the performance of the methods by computing the interfacial properties for two systems in which an atomistic fluid interacts with a fcc crystal. For both of the systems studied we find good agreement between our results and those obtained via the mechanical definition of the interfacial tension.
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determination of fluid phase behavior using Transition Matrix monte carlo binary lennard jones mixtures
Journal of Chemical Physics, 2005Co-Authors: Vincent K Shen, Jeffrey R ErringtonAbstract:We present a novel computational methodology for determining fluid-phase equilibria in binary mixtures. The method is based on a combination of highly efficient Transition-Matrix Monte Carlo and histogram reweighting. In particular, a directed grand-canonical Transition-Matrix Monte Carlo scheme is used to calculate the particle-number probability distribution, after which histogram reweighting is used as a postprocessing procedure to determine the conditions of phase equilibria. To validate the methodology, we have applied it to a number of model binary Lennard-Jones systems known to exhibit nontrivial fluid-phase behavior. Although we have focused on monatomic fluids in this work, the method presented here is general and can be easily extended to more complex molecular fluids. Finally, an important feature of this method is the capability to predict the entire fluid-phase diagram of a binary mixture at fixed temperature in a single simulation.
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metastability and instability in the lennard jones fluid investigated by Transition Matrix monte carlo
Journal of Physical Chemistry B, 2004Co-Authors: Vincent K Shen, Jeffrey R ErringtonAbstract:Grand canonical Transition-Matrix Monte Carlo is used to investigate kinetic and thermodynamic stability limits of the liquid and vapor in the Lennard-Jones fluid. Kinetic spinodals are associated with a vanishing of the free-energy barrier between metastable and stable states, and thermodynamic spinodals are related to diverging thermodynamic response functions. We show that the kinetically and thermodynamically defined spinodals are conceptually equivalent viewpoints in the case of the liquid−vapor Transition. In agreement with the work of others, we find that the properties of the supersaturated vapor at its limit of stability approach their saturation values with increasing system size. We also find an analogous trend in the case of the superheated liquid. Finally, the computational algorithm and manipulation of data outlined in this work provide an intuitive and efficient method for determining thermophysical properties of stable and metastable fluids via molecular simulation.
Vincent K Shen - One of the best experts on this subject based on the ideXlab platform.
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comparing the use of gibbs ensemble and grand canonical Transition Matrix monte carlo methods to determine phase equilibria
Industrial & Engineering Chemistry Research, 2008Co-Authors: Andrew S Paluch, Vincent K Shen, Jeffrey R ErringtonAbstract:We present results from a computational study investigating the use of Gibbs ensemble and grand-canonical Transition-Matrix Monte Carlo (GC-TMMC) methods to determine the liquid−vapor phase coexistence properties of pure molecular fluids of varying degrees of complexity. The molecules used in this study were ethane, n-octane, cyclohexane, 2,5-dimethylhexane, 1-propanol, and water. We first show that the GC-TMMC method can reproduce Gibbs ensemble results found in the literature. Given the excellent agreement for each molecule, we then compare directly the performance of Gibbs ensemble and GC-TMMC simulations at both low and high reduced temperatures by monitoring the relative uncertainties in the saturation properties as a function of computational time. In general, we found that the GC-TMMC method yielded limiting uncertainties in the saturated vapor density and pressure that were significantly smaller, by an order of magnitude in some instances, than those of the Gibbs ensemble method. Limiting Gibbs en...
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determination of fluid phase behavior using Transition Matrix monte carlo binary lennard jones mixtures
Journal of Chemical Physics, 2005Co-Authors: Vincent K Shen, Jeffrey R ErringtonAbstract:We present a novel computational methodology for determining fluid-phase equilibria in binary mixtures. The method is based on a combination of highly efficient Transition-Matrix Monte Carlo and histogram reweighting. In particular, a directed grand-canonical Transition-Matrix Monte Carlo scheme is used to calculate the particle-number probability distribution, after which histogram reweighting is used as a postprocessing procedure to determine the conditions of phase equilibria. To validate the methodology, we have applied it to a number of model binary Lennard-Jones systems known to exhibit nontrivial fluid-phase behavior. Although we have focused on monatomic fluids in this work, the method presented here is general and can be easily extended to more complex molecular fluids. Finally, an important feature of this method is the capability to predict the entire fluid-phase diagram of a binary mixture at fixed temperature in a single simulation.
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metastability and instability in the lennard jones fluid investigated by Transition Matrix monte carlo
Journal of Physical Chemistry B, 2004Co-Authors: Vincent K Shen, Jeffrey R ErringtonAbstract:Grand canonical Transition-Matrix Monte Carlo is used to investigate kinetic and thermodynamic stability limits of the liquid and vapor in the Lennard-Jones fluid. Kinetic spinodals are associated with a vanishing of the free-energy barrier between metastable and stable states, and thermodynamic spinodals are related to diverging thermodynamic response functions. We show that the kinetically and thermodynamically defined spinodals are conceptually equivalent viewpoints in the case of the liquid−vapor Transition. In agreement with the work of others, we find that the properties of the supersaturated vapor at its limit of stability approach their saturation values with increasing system size. We also find an analogous trend in the case of the superheated liquid. Finally, the computational algorithm and manipulation of data outlined in this work provide an intuitive and efficient method for determining thermophysical properties of stable and metastable fluids via molecular simulation.
Eric M Grzelak - One of the best experts on this subject based on the ideXlab platform.
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computation of interfacial properties via grand canonical Transition Matrix monte carlo simulation
Journal of Chemical Physics, 2008Co-Authors: Eric M Grzelak, Jeffrey R ErringtonAbstract:We examine two free-energy-based methods for studying the wetting properties of a fluid in contact with a solid substrate. Application of the first approach involves examination of the adsorption behavior of a fluid at a single substrate, while the second technique requires investigation of the properties of a system confined between two parallel substrates. Both of the techniques rely upon computation and analysis of the density dependence of a system’s surface free energy and provide the contact angle and solid-vapor and solid-liquid interfacial tensions for substrate-fluid combinations within the partial wetting regime. Grand canonical Transition Matrix Monte Carlo simulation is used to obtain the required free-energy curves. The methods examined within this work are general and are applicable to a wide range of molecular systems. We probe the performance of the methods by computing the interfacial properties for two systems in which an atomistic fluid interacts with a fcc crystal. For both of the syst...
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computation of interfacial properties via grand canonical Transition Matrix monte carlo simulation
Journal of Chemical Physics, 2008Co-Authors: Eric M Grzelak, Jeffrey R ErringtonAbstract:We examine two free-energy-based methods for studying the wetting properties of a fluid in contact with a solid substrate. Application of the first approach involves examination of the adsorption behavior of a fluid at a single substrate, while the second technique requires investigation of the properties of a system confined between two parallel substrates. Both of the techniques rely upon computation and analysis of the density dependence of a system’s surface free energy and provide the contact angle and solid-vapor and solid-liquid interfacial tensions for substrate-fluid combinations within the partial wetting regime. Grand canonical Transition Matrix Monte Carlo simulation is used to obtain the required free-energy curves. The methods examined within this work are general and are applicable to a wide range of molecular systems. We probe the performance of the methods by computing the interfacial properties for two systems in which an atomistic fluid interacts with a fcc crystal. For both of the systems studied we find good agreement between our results and those obtained via the mechanical definition of the interfacial tension.
M S Safronova - One of the best experts on this subject based on the ideXlab platform.
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precision measurement of Transition Matrix elements via light shift cancellation
Physical Review Letters, 2012Co-Authors: Creston Herold, Varun Vaidya, S L Rolston, J V Porto, M S SafronovaAbstract:Abstract : We present a method for accurate determination of atomic Transition Matrix elements at the 103 level. Measurements of the ac Stark (light) shift around magic-zero wavelengths, where the light shift vanishes, provide precise constraints on the Matrix elements. We make the first measurement of the 5s-6p Matrix elements in rubidium by measuring the light shift around the 421 and 423 nm zeros through diffraction of a condensate off a sequence of standing wave pulses. In conjunction with existing theoretical and experimental data, we find 0.3235(9) ea0 and 0.5230(8) ea0 for the 5s-6p1/2 and 5s-6p3/2 elements, respectively, an order of magnitude more accurate than the best theoretical values. This technique can provide needed, accurate Matrix elements for many atoms, including those used in atomic clocks, tests of fundamental symmetries, and quantum information.
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precision measurement of Transition Matrix elements via light shift cancellation
Physical Review Letters, 2012Co-Authors: Creston Herold, Varun Vaidya, S L Rolston, J V Porto, M S SafronovaAbstract:We present a method for accurate determination of atomic Transition Matrix elements at the ${10}^{\ensuremath{-}3}$ level. Measurements of the ac Stark (light) shift around ``magic-zero'' wavelengths, where the light shift vanishes, provide precise constraints on the Matrix elements. We make the first measurement of the $5s\ensuremath{-}6p$ Matrix elements in rubidium by measuring the light shift around the 421 and 423 nm zeros through diffraction of a condensate off a sequence of standing wave pulses. In conjunction with existing theoretical and experimental data, we find $0.3235(9)e{a}_{0}$ and $0.5230(8)e{a}_{0}$ for the $5s\ensuremath{-}6{p}_{1/2}$ and $5s\ensuremath{-}6{p}_{3/2}$ elements, respectively, an order of magnitude more accurate than the best theoretical values. This technique can provide needed, accurate Matrix elements for many atoms, including those used in atomic clocks, tests of fundamental symmetries, and quantum information.
Raul Gonzalez Lima - One of the best experts on this subject based on the ideXlab platform.
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dynamic imaging in electrical impedance tomography of the human chest with online Transition Matrix identification
IEEE Transactions on Biomedical Engineering, 2010Co-Authors: Fernando Silva De Moura, Julio C C Aya, Agenor De Toledo Fleury, Marcelo Brito Passos Amato, Raul Gonzalez LimaAbstract:One of the electrical impedance tomography objectives is to estimate the electrical resistivity distribution in a domain based only on electrical potential measurements at its boundary generated by an imposed electrical current distribution into the boundary. One of the methods used in dynamic estimation is the Kalman filter. In biomedical applications, the random walk model is frequently used as evolution model and, under this conditions, poor tracking ability of the extended Kalman filter (EKF) is achieved. An analytically developed evolution model is not feasible at this moment. The paper investigates the identification of the evolution model in parallel to the EKF and updating the evolution model with certain periodicity. The evolution model Transition Matrix is identified using the history of the estimated resistivity distribution obtained by a sensitivity Matrix based algorithm and a Newton-Raphson algorithm. To numerically identify the linear evolution model, the Ibrahim time-domain method is used. The investigation is performed by numerical simulations of a domain with time-varying resistivity and by experimental data collected from the boundary of a human chest during normal breathing. The obtained dynamic resistivity values lie within the expected values for the tissues of a human chest. The EKF results suggest that the tracking ability is significantly improved with this approach.
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online Transition Matrix identification of the state evolution model for the extended kalman filter in electrical impedance tomography
Journal of Physics: Conference Series, 2008Co-Authors: Fernando Silva De Moura, Julio C C Aya, Raul Gonzalez Lima, Agenor De Toledo FleuryAbstract:One of the electrical impedance tomography objectives is to estimate the electrical resistivity distribution in a domain based only on contour electrical potential measurements caused by an imposed electrical current distribution into the boundary. In biomedical applications, the random walk model is frequently used as evolution model and, under this conditions, it is observed poor tracking ability of the Extended Kalman Filter (EKF). An analytically developed evolution model is not feasible at this moment. The present work investigates the possibility of identifying the evolution model in parallel to the EKF and updating the evolution model with certain periodicity. The evolution model is identified using the history of resistivity distribution obtained by a sensitivity Matrix based algorithm. To numerically identify the linear evolution model, it is used the Ibrahim Time Domain Method, normally used to identify the Transition Matrix on structural dynamics. The investigation was performed by numerical simulations of a time varying domain with the addition of noise. Numerical dificulties to compute the Transition Matrix were solved using a Tikhonov regularization. The EKF numerical simulations suggest that the tracking ability is significantly improved.
