The Experts below are selected from a list of 201 Experts worldwide ranked by ideXlab platform
Velisa Vesovic - One of the best experts on this subject based on the ideXlab platform.
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Calculation of the relaxation properties of a dilute gas consisting of Lennard–Jones chains
Chemical Physics Letters, 2013Co-Authors: Robert Hellmann, Nicolas Riesco, Velisa VesovicAbstract:Abstract The relaxation properties in the dilute-gas limit have been calculated by the classical trajectory (CT) method for a gas consisting of chain-like molecules that are rigid and interact through site–site Lennard–Jones 12–6 potentials. Results are reported for Volume Viscosity η V , rotational collision number ζ rot and the ratio of the rotational to self-diffusion coefficient D rot / D . The results indicate that the Volume Viscosity increases with temperature and decreases with chain length. The rotational relaxation of chains is efficient, as it takes of the order of 1.75–2.7 collisions to attain equilibrium. The rotational collision number is only weakly temperature dependent.
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Calculation of the transport and relaxation properties of dilute water vapor.
The Journal of chemical physics, 2009Co-Authors: Robert Hellmann, Eckard Bich, Alan S. Dickinson, Eckhard Vogel, Velisa VesovicAbstract:Transport properties of dilute water vapor have been calculated in the rigid-rotor approximation using four different potential energy hypersurfaces and the classical-trajectory method. Results are reported for shear Viscosity, self-diffusion, thermal conductivity, and Volume Viscosity in the dilute-gas limit for the temperature range of 250–2500 K. Of these four surfaces the CC-pol surface of Bukowski et al. [J. Chem. Phys. 128, 094314 (2008)] is in best accord with the available measurements. Very good agreement is found with the most accurate results for Viscosity in the whole temperature range of the experiments. For thermal conductivity the deviations of the calculated values from the experimental data increase systematically with increasing temperature to around 5% at 1100 K. For both self-diffusion and Volume Viscosity, the much more limited number of available measurements are generally consistent with the calculated values, apart from the lower temperature isotopically labeled diffusion measurements.
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On the behavior of the Volume Viscosity of atom-molecule mixtures.
Journal of Chemical Physics, 2004Co-Authors: Alan S. Dickinson, Velisa VesovicAbstract:The behavior of the Volume Viscosity in atom-molecule gas mixtures is investigated in the framework of the first-order Enskog–Chapman expansion when the internal-energy relaxation cross section for atom-molecule collisions is small compared to that for molecule-molecule collisions. Two phenomena are analyzed: first, the sensitivity of the Volume Viscosity to this particular cross section allows the Volume Viscosity of the atom-molecule mixture to be significantly larger than that of the pure molecular gas; second, when this cross section is set to zero, the Volume Viscosity becomes discontinuous at the pure-atom limit.
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Calculation of the transport properties of carbon dioxide. III. Volume Viscosity, depolarized Rayleigh scattering, and nuclear spin relaxation
The Journal of chemical physics, 2004Co-Authors: S. Bock, Alan S. Dickinson, Eckard Bich, Eckhard Vogel, Velisa VesovicAbstract:Transport properties of pure carbon dioxide have been calculated from the intermolecular potential using the classical trajectory method. Results are reported in the dilute-gas limit for Volume Viscosity, depolarized Rayleigh scattering, and nuclear spin relaxation for temperatures ranging from 200 to 1000 K. Three recent carbon dioxide potential energy hypersurfaces have been investigated. Calculated values for the rotational collision number for all three intermolecular surfaces are consistent with the measurements and indicate that the temperature dependence of the Brau-Jonkman correlation is not applicable for carbon dioxide. The results for the depolarized Rayleigh scattering cross section and the nuclear spin relaxation cross section show that calculated values for the generally more successful potentials differ from the observations by 9% at about 290 K, although agreement is obtained for nuclear spin relaxation at about 400 K.
Pere Clave - One of the best experts on this subject based on the ideXlab platform.
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sensitivity and specificity of the eating assessment tool and the Volume Viscosity swallow test for clinical evaluation of oropharyngeal dysphagia
Neurogastroenterology and Motility, 2014Co-Authors: Laia Rofes, Viridiana Arreola, Pere Clave, R MukherjeeAbstract:Background Oropharyngeal dysphagia (OD) is an underdiagnosed digestive disorder that causes severe nutritional and respiratory complications. Our aim was to determine the accuracy of the Eating Assessment Tool (EAT-10) and the Volume-Viscosity Swallow Test (V-VST) for clinical evaluation of OD.
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the Volume Viscosity swallow test for clinical screening of dysphagia and aspiration
Stepping stones to living well with dysphagia. 72nd Nestlé Nutrition Institute Workshop Barcelona Spain 5-6 May 2011, 2012Co-Authors: Laia Rofes, Viridiana Arreola, Pere ClaveAbstract:Background: Oropharyngeal dysphagia (OD) is a major complaint among many patients with neurological diseases and in the elderly, but is often underdiagnosed. The Volume-Viscosity swallow test (V-VST) is a bedside method to screen patients for dysphagia. Methods: The V-VST was designed to identify clinical signs of impaired efficacy (labial seal, oral and pharyngeal residue, and piecemeal deglutition) and impaired safety of swallow (voice changes, cough and decrease in oxygen saturation ≥3%). It starts with nectar Viscosity and increasing bolus Volume, then liquid and finally pudding Viscosity in a progression of increasing difficulty to protect patients from aspiration. Results: The V-VST allows quick, safe and accurate screening for OD in hospitalized and independently living patients with multiple etiologies. The V-VST presents a sensitivity of 88.2% and a specificity of 64.7% to detect clinical signs of impaired safety of swallow (aspiration or penetration). The test takes 5–10 min to complete. Discussion and Conclusion: The V-VST is an excellent tool to screen patients for OD. It combines good psychometric properties, a detailed and easy protocol designed to protect safety of patients, and valid end points to evaluate safety and efficacy of swallowing and detect silent aspirations.
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accuracy of the Volume Viscosity swallow test for clinical screening of oropharyngeal dysphagia and aspiration
Clinical Nutrition, 2008Co-Authors: Viridiana Arreola, Pere Clave, Maise Romea, Lucia Medina, Elisabet Palomera, Mateu SerrapratAbstract:Summary Aims: To determine the accuracy of the bedside VolumeeViscosity swallow test (V-VST) for clinical screening of impaired safety and efficacy of deglutition. Methods: We studied 85 patients with dysphagia and 12 healthy subjects. Series of 5e20 mL nectar (295.02 mPa.s), liquid (21.61 mPa.s) and pudding (3682.21 mPa.s) bolus were administered during the V-VST and videofluoroscopy. Cough, fall in oxygen saturation �3%, and voice changes were considered signs of impaired safety, and piecemeal deglutition and oropharyngeal residue, signs of impaired efficacy. Results: Videofluoroscopy showed patients had prolonged swallow response (�1064 ms); 52.1% had safe swallow at nectar, 32.9%, at liquid (p <0.05), and 80.6% at pudding Viscosity (p < 0.05); 29.4% had aspirations, and 45.8% oropharyngeal residue. The V-VST showed 83.7% sensitivity and 64.7% specificity for bolus penetration into the larynx and 100% sensitivity and 28.8% specificity for aspiration. Sensitivity of V-VST was 69.2% for residue, 88.4% for piecemeal deglutition, and 84.6% for identifying patients whose deglutition improved by enhancing bolus Viscosity. Specificity was 80.6%, 87.5%, and 73.7%, respectively.
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Accuracy of the Volume-Viscosity swallow test for clinical screening of oropharyngeal dysphagia and aspiration *
Clinical nutrition (Edinburgh Scotland), 2008Co-Authors: Pere Clave, Viridiana Arreola, Maise Romea, Lucia Medina, Elisabet Palomera, Mateu Serra-pratAbstract:Summary Aims: To determine the accuracy of the bedside VolumeeViscosity swallow test (V-VST) for clinical screening of impaired safety and efficacy of deglutition. Methods: We studied 85 patients with dysphagia and 12 healthy subjects. Series of 5e20 mL nectar (295.02 mPa.s), liquid (21.61 mPa.s) and pudding (3682.21 mPa.s) bolus were administered during the V-VST and videofluoroscopy. Cough, fall in oxygen saturation �3%, and voice changes were considered signs of impaired safety, and piecemeal deglutition and oropharyngeal residue, signs of impaired efficacy. Results: Videofluoroscopy showed patients had prolonged swallow response (�1064 ms); 52.1% had safe swallow at nectar, 32.9%, at liquid (p
Vincent Giovangigli - One of the best experts on this subject based on the ideXlab platform.
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Volume Viscosity and Internal Energy Relaxation: Error Estimates
Nonlinear Analysis: Real World Applications, 2018Co-Authors: Vincent Giovangigli, Wen YongAbstract:We investigate the fast relaxation of internal energy in nonequilibrium gas models derived from the kinetic theory of gases. We establish uniform a priori estimates and existence theorems for symmetric hyperbolic-parabolic systems of partial differential equations with small second order terms and stiff sources. We prove local in time error estimates between the out of equilibrium solution and the one-temperature equilibrium fluid solution for well prepared data and justify the apparition of Volume Viscosity terms.
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Volume Viscosity and Internal Energy Relaxation : Error Estimates
2014Co-Authors: Vincent Giovangigli, Wen-an YongAbstract:We investigate the fast relaxation of internal energy in nonequilibrium gas models derived from the kinetic theory of gases. We establish a priori estimates and existence theorems for symmetric hyperbolic-parabolic systems of partial differential equations with small second order terms and stiff sources. We also establish the stability of the corresponding equilibrium systems. We then prove local in time error estimates between the out of equilibrium solution and the one-temperature equilibrium fluid solution for well prepared data and justify the apparition of Volume Viscosity terms. The situation of ill prepared data with initial layers is also addressed.
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Volume Viscosity and Internal Energy Relaxation : Symmetrization and Chapman-Enskog Expansion
2014Co-Authors: Vincent Giovangigli, Wen-an YongAbstract:We analyze a mathematical model for the relaxation of translational and internal temperatures in a nonequilibrium gas. The system of partial differential equations---derived from the kinetic theory of gases---is recast in its natural entropic symmetric form as well as in a convenient hyperbolic-parabolic symmetric form. We investigate the Chapman-Enskog expansion in the fast relaxation limit and establish that the temperature difference become asymptotically proportional to the divergence of the velocity field. This asymptotic behavior yields the Volume Viscosity term of the limiting one-temperature fluid model.
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Relaxation of rotational-vibrational energy and Volume Viscosity in H-H2 mixtures.
The Journal of chemical physics, 2013Co-Authors: Domenico Bruno, F. Esposito, Vincent GiovangigliAbstract:We investigate a kinetic model for H–H2 mixtures in a regime where translational/rotational and vibrational-resonant energy exchanges are fast whereas vibrational energy variations are slow. In a relaxation regime, the effective Volume Viscosity is found to involve contributions from the rotational Volume Viscosity, the vibrational Volume Viscosity, the relaxation pressure, and the perturbed source term. In the thermodynamic equilibrium limit, the sum of these four terms converges toward the one-temperature two-mode Volume Viscosity. The theoretical results are applied to the calculation of the Volume viscosities of molecular hydrogen in the trace limit on the basis of a complete set of state-selected cross sections for the H + H2(v, j) system.
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Relaxation of internal temperature and Volume Viscosity
Physics of Fluids, 2011Co-Authors: Domenico Bruno, Vincent GiovangigliAbstract:We investigate the relaxation of internal temperature and the concept of Volume Viscosity in nonequilibrium gas models derived from the kinetic theory. We first investigate a nonequilibrium gas model with two temperatures—translational and internal—where the Volume Viscosity is absent. We establish that in a relaxation regime, the temperature difference becomes proportional to the divergence of the velocity fields and define a nonequilibrium, multitemperature, Volume Viscosity coefficient. We next analyze the convergence of the two temperature model towards the one temperature model when the relaxation is fast. We then investigate a nonequilibrium two temperature gas model with a fast and a slow internal energy mode. We establish that in a relaxation regime, there are four contributions to the Volume Viscosity, namely, the fast internal mode Volume Viscosity, the slow internal mode Volume Viscosity, the relaxation pressure, and the perturbed source term. In the thermodynamic equilibrium limit, the sum of ...
Alan S. Dickinson - One of the best experts on this subject based on the ideXlab platform.
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Calculation of the transport and relaxation properties of dilute water vapor.
The Journal of chemical physics, 2009Co-Authors: Robert Hellmann, Eckard Bich, Alan S. Dickinson, Eckhard Vogel, Velisa VesovicAbstract:Transport properties of dilute water vapor have been calculated in the rigid-rotor approximation using four different potential energy hypersurfaces and the classical-trajectory method. Results are reported for shear Viscosity, self-diffusion, thermal conductivity, and Volume Viscosity in the dilute-gas limit for the temperature range of 250–2500 K. Of these four surfaces the CC-pol surface of Bukowski et al. [J. Chem. Phys. 128, 094314 (2008)] is in best accord with the available measurements. Very good agreement is found with the most accurate results for Viscosity in the whole temperature range of the experiments. For thermal conductivity the deviations of the calculated values from the experimental data increase systematically with increasing temperature to around 5% at 1100 K. For both self-diffusion and Volume Viscosity, the much more limited number of available measurements are generally consistent with the calculated values, apart from the lower temperature isotopically labeled diffusion measurements.
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On the behavior of the Volume Viscosity of atom-molecule mixtures.
Journal of Chemical Physics, 2004Co-Authors: Alan S. Dickinson, Velisa VesovicAbstract:The behavior of the Volume Viscosity in atom-molecule gas mixtures is investigated in the framework of the first-order Enskog–Chapman expansion when the internal-energy relaxation cross section for atom-molecule collisions is small compared to that for molecule-molecule collisions. Two phenomena are analyzed: first, the sensitivity of the Volume Viscosity to this particular cross section allows the Volume Viscosity of the atom-molecule mixture to be significantly larger than that of the pure molecular gas; second, when this cross section is set to zero, the Volume Viscosity becomes discontinuous at the pure-atom limit.
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Calculation of the transport properties of carbon dioxide. III. Volume Viscosity, depolarized Rayleigh scattering, and nuclear spin relaxation
The Journal of chemical physics, 2004Co-Authors: S. Bock, Alan S. Dickinson, Eckard Bich, Eckhard Vogel, Velisa VesovicAbstract:Transport properties of pure carbon dioxide have been calculated from the intermolecular potential using the classical trajectory method. Results are reported in the dilute-gas limit for Volume Viscosity, depolarized Rayleigh scattering, and nuclear spin relaxation for temperatures ranging from 200 to 1000 K. Three recent carbon dioxide potential energy hypersurfaces have been investigated. Calculated values for the rotational collision number for all three intermolecular surfaces are consistent with the measurements and indicate that the temperature dependence of the Brau-Jonkman correlation is not applicable for carbon dioxide. The results for the depolarized Rayleigh scattering cross section and the nuclear spin relaxation cross section show that calculated values for the generally more successful potentials differ from the observations by 9% at about 290 K, although agreement is obtained for nuclear spin relaxation at about 400 K.
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Traditional transport properties of CO
Physica A-statistical Mechanics and Its Applications, 1995Co-Authors: E.l. Heck, Alan S. DickinsonAbstract:Abstract Classical trajectory rigid-rotor calculations using higher-order kinetic theory expressions for shear Viscosity, diffusion, Volume Viscosity and thermal conductivity have been performed using the anisotropic ab initio potential energy hypersurface of van der Pol et al. for the temperature range between 77 K and 1500 K. Comparison with experiment shows differences less than 1.2% with the best shear Viscosity measurements, consistency with the relative diffusion coefficient data, an underestimate by up to 30% of the Volume Viscosity values and agreement with the thermal conductivity data between 120 K and 200 K but differences increasing to 7% at 430 K.
Mateu Serraprat - One of the best experts on this subject based on the ideXlab platform.
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accuracy of the Volume Viscosity swallow test for clinical screening of oropharyngeal dysphagia and aspiration
Clinical Nutrition, 2008Co-Authors: Viridiana Arreola, Pere Clave, Maise Romea, Lucia Medina, Elisabet Palomera, Mateu SerrapratAbstract:Summary Aims: To determine the accuracy of the bedside VolumeeViscosity swallow test (V-VST) for clinical screening of impaired safety and efficacy of deglutition. Methods: We studied 85 patients with dysphagia and 12 healthy subjects. Series of 5e20 mL nectar (295.02 mPa.s), liquid (21.61 mPa.s) and pudding (3682.21 mPa.s) bolus were administered during the V-VST and videofluoroscopy. Cough, fall in oxygen saturation �3%, and voice changes were considered signs of impaired safety, and piecemeal deglutition and oropharyngeal residue, signs of impaired efficacy. Results: Videofluoroscopy showed patients had prolonged swallow response (�1064 ms); 52.1% had safe swallow at nectar, 32.9%, at liquid (p <0.05), and 80.6% at pudding Viscosity (p < 0.05); 29.4% had aspirations, and 45.8% oropharyngeal residue. The V-VST showed 83.7% sensitivity and 64.7% specificity for bolus penetration into the larynx and 100% sensitivity and 28.8% specificity for aspiration. Sensitivity of V-VST was 69.2% for residue, 88.4% for piecemeal deglutition, and 84.6% for identifying patients whose deglutition improved by enhancing bolus Viscosity. Specificity was 80.6%, 87.5%, and 73.7%, respectively.
