The Experts below are selected from a list of 4380 Experts worldwide ranked by ideXlab platform
Lihong V Wang - One of the best experts on this subject based on the ideXlab platform.
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cuffing based photoacoustic flowmetry in humans at depths in the Diffusive Regime
Proceedings of SPIE, 2016Co-Authors: Yong Zhou, Jinyang Liang, Lihong V WangAbstract:Using a handheld photoacoustic probe, we proposed a cuffing-based method to quantify blood flow speed in humans. By cuffing and releasing the blood vessel, we can measure the blood flow speed downstream. In phantom experiments, we demonstrated that the minimum and maximum measurable flow speeds were 0.035 mm/s and 42 mm/s, respectively. In human experiments, flow speeds were measured in three different blood vessels: a radial artery in the right forearm, a radial artery in the index finger of the right hand, and a radial vein in the right forearm.
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in vivo photoacoustic flowmetry in the optical Diffusive Regime based on saline injection
Proceedings of SPIE, 2016Co-Authors: Yong Zhou, Joemini Poudel, Guo Li, Lihong V WangAbstract:We propose a saline-injection-based method to quantify blood flow velocity in vivo with acoustic-resolution photoacoustic tomography. By monitoring the saline-blood-interface propagating in the blood vessel, we can resolve the flow velocity. In phantom experiments, a root-mean-squared error of prediction of 0.29 mm/s was achieved. By injecting saline into a mouse tail vein covered with 1 mm chicken tissue, we showed that the flow velocity in the tail vein could be measured at depth, which is especially pertinent to monitoring blood flow velocity in patients undergoing intravenous infusion.
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cuffing based photoacoustic flowmetry in humans in the optical Diffusive Regime
Journal of Biophotonics, 2016Co-Authors: Yong Zhou, Jinyang Liang, Lihong V WangAbstract:Measuring blood flow speed in the optical Diffusive Regime in humans has been a long standing challenge for photoacoustic tomography. In this work, we proposed a cuffing-based method to quantify blood flow speed in humans with a handheld photoacoustic probe. By cuffing and releasing the blood vessel, we can measure the blood flow speed downstream. In phantom experiments, we demonstrated that the minimum and maximum measurable flow speeds were 0.035 mm/s and 42 mm/s, respectively. In human experiments, flow speeds were measured in three different blood vessels: a radial artery in the right forearm, a radial artery in the index finger of the right hand, and a radial vein in the right forearm. Taking advantage of the handheld probe, our method can potentially be used to monitor blood flow speed in the clinic and at the bedside.
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in vivo photoacoustic flowmetry at depths of the Diffusive Regime based on saline injection
Journal of Biomedical Optics, 2015Co-Authors: Yong Zhou, Joemini Poudel, Guo Li, Lihong V WangAbstract:We propose a saline injection-based method to quantify blood flow velocity in vivo with acoustic-resolution photoacoustic tomography. By monitoring the saline–blood interface propagating in the blood vessel, the flow velocity can be resolved. We first demonstrated our method in phantom experiments, where a root mean square error of prediction of 0.29 mm/s 0.29 mm/s was achieved. By injecting saline into a mouse tail vein covered with 1 mm chicken tissue, we showed that the flow velocity in the tail vein could be measured at depths, which is especially pertinent to monitoring blood flow velocity in patients undergoing intravenous infusion.
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Quantitative photoacoustic microscopy of optical absorption coefficients from acoustic spectra in the optical Diffusive Regime
Journal of Biomedical Optics, 2012Co-Authors: Christopher P Favazza, Alejandro Garcia-uribe, Lihong V WangAbstract:Photoacoustic (PA) microscopy (PAM) can image optical absorption contrast with ultrasonic spatial resolution in the optical Diffusive Regime. Conventionally, accurate quantification in PAM requires knowledge of the optical fluence attenuation, acoustic pressure attenuation, and detection bandwidth. We circumvent this requirement by quantifying the optical absorption coefficients from the acoustic spectra of PA signals acquired at multiple optical wavelengths. With the acoustic spectral method, the absorption coefficients of an oxygenated bovine blood phantom at 560, 565, 570, and 575 nm were quantified with errors of
Tzuming Lu - One of the best experts on this subject based on the ideXlab platform.
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weak anti localization of two dimensional holes in germanium beyond the Diffusive Regime
Nanoscale, 2018Co-Authors: Chungtao Chou, Noah Tobias Jacobson, Jonathan E Moussa, Andrew Baczewski, Yen Chuang, Jiunyun Li, Tzuming LuAbstract:Gate-controllable spin–orbit coupling is often one requisite for spintronic devices. For practical spin field-effect transistors, another essential requirement is ballistic spin transport, where the spin precession length is shorter than the mean free path such that the gate-controlled spin precession is not randomized by disorder. In this letter, we report the observation of a gate-induced crossover from weak localization to weak anti-localization in the magneto-resistance of a high-mobility two-dimensional hole gas in a strained germanium quantum well. From the magneto-resistance, we extract the phase-coherence time, spin–orbit precession time, spin–orbit energy splitting, and cubic Rashba coefficient over a wide density range. The mobility and the mean free path increase with increasing hole density, while the spin precession length decreases due to increasingly stronger spin–orbit coupling. As the density becomes larger than ∼6 × 1011 cm−2, the spin precession length becomes shorter than the mean free path, and the system enters the ballistic spin transport Regime. We also report here the numerical methods and code developed for calculating the magneto-resistance in the ballistic Regime, where the commonly used HLN and ILP models for analyzing weak localization and anti-localization are not valid. These results pave the way toward silicon-compatible spintronic devices.
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weak anti localization of two dimensional holes in germanium beyond the Diffusive Regime
arXiv: Mesoscale and Nanoscale Physics, 2018Co-Authors: Chungtao Chou, Noah Tobias Jacobson, Jonathan E Moussa, Andrew Baczewski, Yen Chuang, Jiunyun Li, Tzuming LuAbstract:Gate-controllable spin-orbit coupling is often one requisite for spintronic devices. For practical spin field-effect transistors, another essential requirement is ballistic spin transport, where the spin precession length is shorter than the mean free path such that the gate-controlled spin precession is not randomized by disorder. In this letter, we report the observation of a gate-induced crossover from weak localization to weak anti-localization in the magneto-resistance of a high-mobility two-dimensional hole gas in a strained germanium quantum well. From the magneto-resistance, we extract the phase-coherence time, spin-orbit precession time, spin-orbit energy splitting, and cubic Rashba coefficient over a wide density range. The mobility and the mean free path increase with increasing hole density, while the spin precession length decreases due to increasingly stronger spin-orbit coupling. As the density becomes larger than $\sim6\times 10^{11}$cm$^{-2}$, the spin precession length becomes shorter than the mean free path, and the system enters the ballistic spin transport Regime. We also report here the numerical methods and code developed for calculating the magneto-resistance in the ballistic Regime, where the commonly used HLN and ILP models for analyzing weak localization and anti-localization are not valid. These results pave the way toward silicon-compatible spintronic devices.
Songze Chen - One of the best experts on this subject based on the ideXlab platform.
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radial thermal rectification in concentric silicon ring from ballistic to Diffusive Regime
International Journal of Heat and Mass Transfer, 2020Co-Authors: Chuang Zhang, Songze ChenAbstract:Abstract In this work, the radial thermal rectification in concentric silicon ring is studied based on the phonon Boltzmann transport equation. In the ballistic and Diffusive limits, the analytical solutions reveal no thermal rectification. In the ballistic-Diffusive Regime, numerical results show that the thermal conductivity is a nonseparable function of the spatial position and local temperature. In addition, the heat prefers to flow from the inner boundary to the outer one, which characterizes the thermal rectification. As the distance between two circular boundaries increases from tens of nanometers to tens of microns, the thermal rectification ratio increases first and then decreases gradually. Similar size-dependent thermal rectification phenomena can be observed with different reference temperatures and radius ratios. It is mainly attributed to the asymmetric phonon transport and rapidly changing thermal conductivity in the ballistic-Diffusive Regime.
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radial thermal rectification in the concentric silicon ring from ballistic to Diffusive Regime
arXiv: Mesoscale and Nanoscale Physics, 2019Co-Authors: Chuang Zhang, Songze ChenAbstract:The radial thermal rectification in the concentric silicon ring from ballistic to Diffusive Regime is investigated based on the phonon Boltzmann transport equation. In the ballistic and Diffusive limits, the analytical solutions prove that there is no thermal rectification. In the ballistic-Diffusive Regime, the heat flux prefers to flow from the inner boundary to the outer boundary. Furthermore, as the characteristic length (the distance between two circular boundaries) increases from tens of nanometers to tens of microns, the thermal rectification ratio enhances first and then fades away gradually. It attributes to that as the direction of the temperature gradient changes, the average phonon mean free path changes. The difference of the average phonon mean free path finally leads to the change of the heat flux or thermal conductivity. As the temperature decreases, the maximum thermal rectification ratio decreases. In addition, as the radius ratio between the inner and outer boundary increases, the thermal rectification ratio decreases for a given characteristic length.
Rodrigo Soto - One of the best experts on this subject based on the ideXlab platform.
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run and tumble bacteria slowly approaching the Diffusive Regime
Physical Review E, 2020Co-Authors: Andrea Villatorrealba, Cristobal Chavezraby, Pablo De Castro, Rodrigo SotoAbstract:The run-and-tumble (RT) dynamics followed by bacterial swimmers gives rise first to a ballistic motion due to their persistence and later, through consecutive tumbles, to a Diffusive process. Here we investigate how long it takes for a dilute swimmer suspension to reach the Diffusive Regime as well as what is the amplitude of the deviations from the Diffusive dynamics. A linear time dependence of the mean-squared displacement (MSD) is insufficient to characterize diffusion and thus we also focus on the excess kurtosis of the displacement distribution. Four swimming strategies are considered: (i) the conventional RT model with complete reorientation after tumbling; (ii) the case of partial reorientation, characterized by a distribution of tumbling angles; (iii) a run-and-reverse model with rotational diffusion; and (iv) a RT particle where the tumbling rate depends on the stochastic concentration of an internal protein. By analyzing the associated kinetic equations for the probability density function and simulating the models, we find that for models (ii), (iii), and (iv) the relaxation to diffusion can take much longer than the mean time between tumble events, evidencing the existence of large tails in the particle displacements. Moreover, the excess kurtosis can assume large positive values. In model (ii) it is possible for some distributions of tumbling angles that the MSD reaches a linear time dependence but, still, the dynamics remains non-Gaussian for long times. This is also the case in model (iii) for small rotational diffusivity. For all models, the long-time diffusion coefficients are also obtained. The theoretical approach, which relies on eigenvalue and angular Fourier expansions of the van Hove function, is in excellent agreement with the simulations.
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how slowly do run and tumble bacteria approach the Diffusive Regime
arXiv: Soft Condensed Matter, 2020Co-Authors: Andrea Villatorrealba, Pablo De Castro, Cristobal Chavez Raby, Rodrigo SotoAbstract:The run-and-tumble (RT) dynamics followed by bacterial swimmers gives rise first to a ballistic motion due to their persistence, and later, through consecutive tumbles, to a Diffusive process. Here we investigate how long it takes for a dilute swimmer suspension to reach the Diffusive Regime as well as what is the amplitude of the deviations from the Diffusive dynamics, which we characterize by the excess kurtosis of the displacement distribution. Four swimming strategies are considered: (i) the conventional RT model with complete reorientation after tumbling, (ii) the case of partial reorientation, characterized by a distribution of tumbling angles, (iii) a run-and-reverse model with rotational diffusion, and (iv) a RT particle where the tumbling rate depends on the stochastic concentration of an internal protein. By analyzing the associated kinetic equations for the probability density function and simulating the models, we find that for models (ii), (iii), and (iv) the relaxation to diffusion can take much longer than the mean time between tumble events, evidencing the existence of large tails in the particle displacements. Moreover, the kurtosis can assume large positive values. In model (ii) it is possible for some distributions of tumbling angles that the mean-squared displacement increases linearly with time but, still, the dynamics remains non-Gaussian for long times. For all models, the long-time diffusion coefficients are also obtained. The theoretical approach, which relies on eigenvalue expansions of the van Hove function, is in excellent agreement with the simulations.
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SubDiffusive behavior of a dilute non-Brownian suspension under shear.
Physical Review E, 2013Co-Authors: Francisca Guzmán-lastra, Rodrigo SotoAbstract:: Shear-induced self-diffusion in a dilute suspension of non-Brownian spheres under a simple shear flow is studied in the limit of zero Reynolds number, for different volume fractions φ. Particles are simulated considering the first term in the multipolar expansion to take into account the long-range hydrodynamic interactions, and a repulsive force is added to avoid interpenetration. The final Diffusive Regime is established after a long time (t(diffusion)~φ(-1.5)), and the diffusion coefficient is proportional to φ(2), as expected in the presence of the short-range repulsive force. Before the Diffusive Regime is established, there is a rich subDiffusive behavior, particularly in the gradient direction. Each pairwise hydrodynamic interaction is reversible, not leading to streamline migration. Due to the incoherence of the different pair interactions, a plateau in the mean square displacement is first observed, lasting for a period that increases as φ is decreased. Then, a first Diffusive Regime is established due to three-particle interactions, with a diffusion coefficient of D((1))~φ(2.4). At longer times, a phenomenon similar to caging is observed. Particles diffuse for long times in the vicinity of some positions, and eventually large displacements are produced, moving the particle to a new position and resulting in transient large values of the kurtosis of the displacement distribution. This migration is produced by collisions through the repulsive potential. After several of those large displacements, the final Diffusive Regime is established.
Chungtao Chou - One of the best experts on this subject based on the ideXlab platform.
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weak anti localization of two dimensional holes in germanium beyond the Diffusive Regime
Nanoscale, 2018Co-Authors: Chungtao Chou, Noah Tobias Jacobson, Jonathan E Moussa, Andrew Baczewski, Yen Chuang, Jiunyun Li, Tzuming LuAbstract:Gate-controllable spin–orbit coupling is often one requisite for spintronic devices. For practical spin field-effect transistors, another essential requirement is ballistic spin transport, where the spin precession length is shorter than the mean free path such that the gate-controlled spin precession is not randomized by disorder. In this letter, we report the observation of a gate-induced crossover from weak localization to weak anti-localization in the magneto-resistance of a high-mobility two-dimensional hole gas in a strained germanium quantum well. From the magneto-resistance, we extract the phase-coherence time, spin–orbit precession time, spin–orbit energy splitting, and cubic Rashba coefficient over a wide density range. The mobility and the mean free path increase with increasing hole density, while the spin precession length decreases due to increasingly stronger spin–orbit coupling. As the density becomes larger than ∼6 × 1011 cm−2, the spin precession length becomes shorter than the mean free path, and the system enters the ballistic spin transport Regime. We also report here the numerical methods and code developed for calculating the magneto-resistance in the ballistic Regime, where the commonly used HLN and ILP models for analyzing weak localization and anti-localization are not valid. These results pave the way toward silicon-compatible spintronic devices.
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weak anti localization of two dimensional holes in germanium beyond the Diffusive Regime
arXiv: Mesoscale and Nanoscale Physics, 2018Co-Authors: Chungtao Chou, Noah Tobias Jacobson, Jonathan E Moussa, Andrew Baczewski, Yen Chuang, Jiunyun Li, Tzuming LuAbstract:Gate-controllable spin-orbit coupling is often one requisite for spintronic devices. For practical spin field-effect transistors, another essential requirement is ballistic spin transport, where the spin precession length is shorter than the mean free path such that the gate-controlled spin precession is not randomized by disorder. In this letter, we report the observation of a gate-induced crossover from weak localization to weak anti-localization in the magneto-resistance of a high-mobility two-dimensional hole gas in a strained germanium quantum well. From the magneto-resistance, we extract the phase-coherence time, spin-orbit precession time, spin-orbit energy splitting, and cubic Rashba coefficient over a wide density range. The mobility and the mean free path increase with increasing hole density, while the spin precession length decreases due to increasingly stronger spin-orbit coupling. As the density becomes larger than $\sim6\times 10^{11}$cm$^{-2}$, the spin precession length becomes shorter than the mean free path, and the system enters the ballistic spin transport Regime. We also report here the numerical methods and code developed for calculating the magneto-resistance in the ballistic Regime, where the commonly used HLN and ILP models for analyzing weak localization and anti-localization are not valid. These results pave the way toward silicon-compatible spintronic devices.