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Tamer A. Zaki - One of the best experts on this subject based on the ideXlab platform.

  • characterization of aerosol stokes number in 90 bends and idealized extrathoracic airways
    Journal of Aerosol Science, 2016
    Co-Authors: Laura Nicolaou, Tamer A. Zaki
    Abstract:

    Abstract Prediction of aerosol deposition in the respiratory system is important for improving the efficiency of inhaled drug delivery and for assessing the toxicity of airborne pollutants. Deposition is typically reported as a function of a global Stokes number which is based on a Reference Flow timescale, or the ratio of the characteristic Flow length and velocity scales. In reality, however, particles experience varying Flow timescales as they are advected through the airways, which motivates the use of an instantaneous Stokes number based on the local properties of the Flow field. We then define the effective Stokes number as the time-average of the instantaneous value. This effective Stokes number thus encapsulates the Flow history and geometric variability, and provides a more detailed account of the particle trajectory in the Flow. Laminar and turbulent Flows in a curved pipe are examined first and provide a simplified, or canonical, configuration of the Flow in the upper airways. They are followed by a study of turbulent Flow in an idealized mouth–throat geometry. Our results demonstrate that the effective Stokes number can deviate significantly from the traditional value based solely on the Reference Flow timescale. In addition, the effective Stokes number shows a clear correlation with deposition efficiency and can therefore be used to determine optimal aerosol release locations in order to minimize extrathoracic losses.

  • Characterization of aerosol Stokes number in 90° bends and idealized extrathoracic airways
    Journal of Aerosol Science, 2016
    Co-Authors: Laura Nicolaou, Tamer A. Zaki
    Abstract:

    Abstract Prediction of aerosol deposition in the respiratory system is important for improving the efficiency of inhaled drug delivery and for assessing the toxicity of airborne pollutants. Deposition is typically reported as a function of a global Stokes number which is based on a Reference Flow timescale, or the ratio of the characteristic Flow length and velocity scales. In reality, however, particles experience varying Flow timescales as they are advected through the airways, which motivates the use of an instantaneous Stokes number based on the local properties of the Flow field. We then define the effective Stokes number as the time-average of the instantaneous value. This effective Stokes number thus encapsulates the Flow history and geometric variability, and provides a more detailed account of the particle trajectory in the Flow. Laminar and turbulent Flows in a curved pipe are examined first and provide a simplified, or canonical, configuration of the Flow in the upper airways. They are followed by a study of turbulent Flow in an idealized mouth–throat geometry. Our results demonstrate that the effective Stokes number can deviate significantly from the traditional value based solely on the Reference Flow timescale. In addition, the effective Stokes number shows a clear correlation with deposition efficiency and can therefore be used to determine optimal aerosol release locations in order to minimize extrathoracic losses.

  • ON THE STOKES NUMBER AND CHARACTERIZATION OF AEROSOL DEPOSITION IN THE RESPIRATORY AIRWAYS
    2015
    Co-Authors: Laura Nicolaou, Tamer A. Zaki
    Abstract:

    SUMMARY Aerosol deposition in the respiratory airways has traditionally been examined in terms of the Stokes number based on the Reference Flow timescale. This choice leads to large scatter in deposition efficiency when plotted against the Reference Stokes number because the velocity and length scales experienced by advected particles deviate considerably from the Reference values. A time-average of the particle local Stokes number should be adopted instead. Our results demonstrate that this average, or effective, Stokes number can deviate significantly from the Reference value, in particular in the intermediate Stokes number range where variation across subjects is largest.

Laura Nicolaou - One of the best experts on this subject based on the ideXlab platform.

  • characterization of aerosol stokes number in 90 bends and idealized extrathoracic airways
    Journal of Aerosol Science, 2016
    Co-Authors: Laura Nicolaou, Tamer A. Zaki
    Abstract:

    Abstract Prediction of aerosol deposition in the respiratory system is important for improving the efficiency of inhaled drug delivery and for assessing the toxicity of airborne pollutants. Deposition is typically reported as a function of a global Stokes number which is based on a Reference Flow timescale, or the ratio of the characteristic Flow length and velocity scales. In reality, however, particles experience varying Flow timescales as they are advected through the airways, which motivates the use of an instantaneous Stokes number based on the local properties of the Flow field. We then define the effective Stokes number as the time-average of the instantaneous value. This effective Stokes number thus encapsulates the Flow history and geometric variability, and provides a more detailed account of the particle trajectory in the Flow. Laminar and turbulent Flows in a curved pipe are examined first and provide a simplified, or canonical, configuration of the Flow in the upper airways. They are followed by a study of turbulent Flow in an idealized mouth–throat geometry. Our results demonstrate that the effective Stokes number can deviate significantly from the traditional value based solely on the Reference Flow timescale. In addition, the effective Stokes number shows a clear correlation with deposition efficiency and can therefore be used to determine optimal aerosol release locations in order to minimize extrathoracic losses.

  • Characterization of aerosol Stokes number in 90° bends and idealized extrathoracic airways
    Journal of Aerosol Science, 2016
    Co-Authors: Laura Nicolaou, Tamer A. Zaki
    Abstract:

    Abstract Prediction of aerosol deposition in the respiratory system is important for improving the efficiency of inhaled drug delivery and for assessing the toxicity of airborne pollutants. Deposition is typically reported as a function of a global Stokes number which is based on a Reference Flow timescale, or the ratio of the characteristic Flow length and velocity scales. In reality, however, particles experience varying Flow timescales as they are advected through the airways, which motivates the use of an instantaneous Stokes number based on the local properties of the Flow field. We then define the effective Stokes number as the time-average of the instantaneous value. This effective Stokes number thus encapsulates the Flow history and geometric variability, and provides a more detailed account of the particle trajectory in the Flow. Laminar and turbulent Flows in a curved pipe are examined first and provide a simplified, or canonical, configuration of the Flow in the upper airways. They are followed by a study of turbulent Flow in an idealized mouth–throat geometry. Our results demonstrate that the effective Stokes number can deviate significantly from the traditional value based solely on the Reference Flow timescale. In addition, the effective Stokes number shows a clear correlation with deposition efficiency and can therefore be used to determine optimal aerosol release locations in order to minimize extrathoracic losses.

  • ON THE STOKES NUMBER AND CHARACTERIZATION OF AEROSOL DEPOSITION IN THE RESPIRATORY AIRWAYS
    2015
    Co-Authors: Laura Nicolaou, Tamer A. Zaki
    Abstract:

    SUMMARY Aerosol deposition in the respiratory airways has traditionally been examined in terms of the Stokes number based on the Reference Flow timescale. This choice leads to large scatter in deposition efficiency when plotted against the Reference Stokes number because the velocity and length scales experienced by advected particles deviate considerably from the Reference values. A time-average of the particle local Stokes number should be adopted instead. Our results demonstrate that this average, or effective, Stokes number can deviate significantly from the Reference value, in particular in the intermediate Stokes number range where variation across subjects is largest.

Stephen Wiggins - One of the best experts on this subject based on the ideXlab platform.

  • The role of variability in transport for large-scale Flow dynamics
    Communications in Nonlinear Science and Numerical Simulation, 2015
    Co-Authors: Kayo Ide, Stephen Wiggins
    Abstract:

    Abstract We develop a framework to study the role of variability in transport across a kinematically-defined boundary defined as a streamline in a Reference Flow. Two complementary schemes are presented: a graphical approach appropriate for analyzing specific cases of variability, and an analytical approach for analyzing the effect of general fluid properties on variability. Spatio-temporal nonlinear interaction between dynamic variability and the Reference Flow leads to flux variability that governs the transport processes. A characteristic length-scale of dynamic and flux variability can be expressed with the units of time using the flight time of the trajectory along the kinematically defined boundary. The characteristic time-scale of the flux variability is that of dynamic variability with the units of time. The non-dimensional ratio of the two characteristic scales is shown to be a critical parameter for evaluating the effectiveness of variability on transport. The pseudo-lobe sequence along the Reference streamline describes spatial coherency of transport. The emergence of the pseudo-lobe sequence is likely to be synchronous with the flux variability. Once a pseudo-lobe sequence is formed, the characteristic length-scale of the flux variability regulates the width of the pseudo-lobes. In contrast, for transport over a fixed time interval and spatial segment, the characteristic time-scale of the dynamic variability regulates the width of the pseudo-lobes. Using a kinematic model, we demonstrate the framework for two types of transports in a blocked Flow of the mid-latitude atmosphere: across the meandering jet axis and between the jet and recirculation cell.

  • The Role of Variability in Transport for Large-Scale Flow Dynamics
    arXiv: Fluid Dynamics, 2014
    Co-Authors: Kayo Ide, Stephen Wiggins
    Abstract:

    We develop a framework to study the role of variability in transport across a streamline of a Reference Flow. Two complementary schemes are presented: a graphical approach for individual cases, and an analytical approach for general properties. The spatially nonlinear interaction of dynamic variability and the Reference Flow results in flux variability. The characteristic time-scale of the dynamic variability and the length-scale of the flux variability in a unit of flight-time govern the spatio-temporal interaction that leads to transport. The non-dimensional ratio of the two characteristic scales is shown to be a a critical parameter. The pseudo-lobe sequence along the Reference streamline describes spatial coherency and temporal evolution of transport. For finite-time transport from an initial time up to the present, the characteristic length-scale of the flux variability regulates the width of the pseudo-lobes. The phase speed of pseudo-lobe propagation averages the Reference Flow and the flux variability. In contrast, for definite transport over a fixed time interval and spatial segment, the characteristic time-scale of the dynamic variability regulates the width of the pseudo-lobes. Generation of the pseudo-lobe sequence appears to be synchronous with the dynamic variability, although it propagates with the Reference Flow. In either case, the critical characteristic ratio is found to be one, corresponding to a resonance of the flux variability with the Reference Flow. Using a kinematic model, we demonstrate the framework for two types of transport in a blocked Flow of the mid-latitude atmosphere: across the meandering jet axis and between the jet and recirculating cell.

Jeanette Schulz-menger - One of the best experts on this subject based on the ideXlab platform.

  • Effects of heart valve prostheses on phase contrast Flow measurements in Cardiovascular Magnetic Resonance – a phantom study
    Journal of Cardiovascular Magnetic Resonance, 2017
    Co-Authors: Johanna Richau, Matthias A. Dieringer, Julius Traber, Florian Von Knobelsdorff-brenkenhoff, Andreas Greiser, Carsten Schwenke, Jeanette Schulz-menger
    Abstract:

    Background Cardiovascular Magnetic Resonance is often used to evaluate patients after heart valve replacement. This study systematically analyses the influence of heart valve prostheses on phase contrast measurements in a phantom trial. Methods Two biological and one mechanical aortic valve prostheses were integrated in a Flow phantom. B_0 maps and phase contrast measurements were acquired at a 1.5 T MR scanner using conventional gradient-echo sequences in predefined distances to the prostheses. Results were compared to measurements with a synthetic metal-free aortic valve. Results The Flow results at the level of the prosthesis differed significantly from the Reference Flow acquired before the level of the prosthesis. The maximum Flow miscalculation was 154 ml/s for one of the biological prostheses and 140 ml/s for the mechanical prosthesis. Measurements with the synthetic aortic valve did not show significant deviations. Flow values measured approximately 20 mm distal to the level of the prosthesis agreed with the Reference Flow for all tested all prostheses. Conclusions The tested heart valve prostheses lead to a significant deviation of the measured Flow rates compared to a Reference. A distance of 20 mm was effective in our setting to avoid this influence.

  • Effects of heart valve prostheses on phase contrast Flow measurements in cardiovascular magnetic resonance - a phantom study
    Journal of cardiovascular magnetic resonance : official journal of the Society for Cardiovascular Magnetic Resonance, 2017
    Co-Authors: Johanna Richau, Matthias A. Dieringer, Julius Traber, Florian Von Knobelsdorff-brenkenhoff, Andreas Greiser, Carsten Schwenke, Jeanette Schulz-menger
    Abstract:

    Cardiovascular Magnetic Resonance is often used to evaluate patients after heart valve replacement. This study systematically analyses the influence of heart valve prostheses on phase contrast measurements in a phantom trial. Two biological and one mechanical aortic valve prostheses were integrated in a Flow phantom. B0 maps and phase contrast measurements were acquired at a 1.5 T MR scanner using conventional gradient-echo sequences in predefined distances to the prostheses. Results were compared to measurements with a synthetic metal-free aortic valve. The Flow results at the level of the prosthesis differed significantly from the Reference Flow acquired before the level of the prosthesis. The maximum Flow miscalculation was 154 ml/s for one of the biological prostheses and 140 ml/s for the mechanical prosthesis. Measurements with the synthetic aortic valve did not show significant deviations. Flow values measured approximately 20 mm distal to the level of the prosthesis agreed with the Reference Flow for all tested all prostheses. The tested heart valve prostheses lead to a significant deviation of the measured Flow rates compared to a Reference. A distance of 20 mm was effective in our setting to avoid this influence.

Kayo Ide - One of the best experts on this subject based on the ideXlab platform.

  • The role of variability in transport for large-scale Flow dynamics
    Communications in Nonlinear Science and Numerical Simulation, 2015
    Co-Authors: Kayo Ide, Stephen Wiggins
    Abstract:

    Abstract We develop a framework to study the role of variability in transport across a kinematically-defined boundary defined as a streamline in a Reference Flow. Two complementary schemes are presented: a graphical approach appropriate for analyzing specific cases of variability, and an analytical approach for analyzing the effect of general fluid properties on variability. Spatio-temporal nonlinear interaction between dynamic variability and the Reference Flow leads to flux variability that governs the transport processes. A characteristic length-scale of dynamic and flux variability can be expressed with the units of time using the flight time of the trajectory along the kinematically defined boundary. The characteristic time-scale of the flux variability is that of dynamic variability with the units of time. The non-dimensional ratio of the two characteristic scales is shown to be a critical parameter for evaluating the effectiveness of variability on transport. The pseudo-lobe sequence along the Reference streamline describes spatial coherency of transport. The emergence of the pseudo-lobe sequence is likely to be synchronous with the flux variability. Once a pseudo-lobe sequence is formed, the characteristic length-scale of the flux variability regulates the width of the pseudo-lobes. In contrast, for transport over a fixed time interval and spatial segment, the characteristic time-scale of the dynamic variability regulates the width of the pseudo-lobes. Using a kinematic model, we demonstrate the framework for two types of transports in a blocked Flow of the mid-latitude atmosphere: across the meandering jet axis and between the jet and recirculation cell.

  • The Role of Variability in Transport for Large-Scale Flow Dynamics
    arXiv: Fluid Dynamics, 2014
    Co-Authors: Kayo Ide, Stephen Wiggins
    Abstract:

    We develop a framework to study the role of variability in transport across a streamline of a Reference Flow. Two complementary schemes are presented: a graphical approach for individual cases, and an analytical approach for general properties. The spatially nonlinear interaction of dynamic variability and the Reference Flow results in flux variability. The characteristic time-scale of the dynamic variability and the length-scale of the flux variability in a unit of flight-time govern the spatio-temporal interaction that leads to transport. The non-dimensional ratio of the two characteristic scales is shown to be a a critical parameter. The pseudo-lobe sequence along the Reference streamline describes spatial coherency and temporal evolution of transport. For finite-time transport from an initial time up to the present, the characteristic length-scale of the flux variability regulates the width of the pseudo-lobes. The phase speed of pseudo-lobe propagation averages the Reference Flow and the flux variability. In contrast, for definite transport over a fixed time interval and spatial segment, the characteristic time-scale of the dynamic variability regulates the width of the pseudo-lobes. Generation of the pseudo-lobe sequence appears to be synchronous with the dynamic variability, although it propagates with the Reference Flow. In either case, the critical characteristic ratio is found to be one, corresponding to a resonance of the flux variability with the Reference Flow. Using a kinematic model, we demonstrate the framework for two types of transport in a blocked Flow of the mid-latitude atmosphere: across the meandering jet axis and between the jet and recirculating cell.