The Experts below are selected from a list of 123 Experts worldwide ranked by ideXlab platform
John R Rhoads - One of the best experts on this subject based on the ideXlab platform.
-
effects of magnetic field on the turbulent wake of a cylinder in free surface magnetohydrodynamic channel flow
Journal of Fluid Mechanics, 2014Co-Authors: John R Rhoads, Eric EdlundAbstract:Results from a free-surface magnetohydrodynamic (MHD) flow experiment are presented detailing the modification of vortices in the wake of a circular cylinder with its axis parallel to the applied magnetic field. Experiments were performed at Reynolds numbers of the order of as the interaction parameter , representing the ratio of electromagnetic forces to inertial forces, was increased through unity. The von Karman Vortex street in the wake of the cylinder was observed by simultaneously sampling the gradient of the induced electric potential, , at 16 cross-stream locations as a proxy for the streamwise fluid Velocity. An ensemble of Vortex Velocity profiles was measured as a function of the applied magnetic field strength. Results indicate a significant change in the circulation of vortices and the deviations from the average profile as was increased. By sampling the fluctuations in at three locations in the wake, the decay of the vortices was examined and the effective viscosity was found to decrease as . Using temperature as a passive tracer, qualitative observations were made with an infrared (IR) camera that showed significant changes in the wake, including the absence of small-scale structures at high magnetic field strengths. Collectively, the results suggest that the reduction in effective viscosity was due to the suppression of the small-scale eddies by the magnetic field. The slope of the power spectrum was observed to change from a power law at low to a power law for . Together, these results suggest the flow smoothly transitioned from a hydrodynamic state to a magnetohydrodynamic regime over the range of .
-
effects of magnetic field on the turbulent wake of a cylinder in free surface magnetohydrodynamic channel flow
Journal of Fluid Mechanics, 2014Co-Authors: John R Rhoads, E M Edlund, H JiAbstract:Results from a free-surface magnetohydrodynamic (MHD) flow experiment are presented detailing the modification of vortices in the wake of a circular cylinder with its axis parallel to the applied magnetic field. Experiments were performed at Reynolds numbers of the order of ${\mathit{Re}}\sim 10^4$ as the interaction parameter ${\mathit{N}}$ , representing the ratio of electromagnetic forces to inertial forces, was increased through unity. The von Karman Vortex street in the wake of the cylinder was observed by simultaneously sampling the gradient of the induced electric potential, $ \boldsymbol {\nabla }{\phi }$ , at 16 cross-stream locations as a proxy for the streamwise fluid Velocity. An ensemble of Vortex Velocity profiles was measured as a function of the applied magnetic field strength. Results indicate a significant change in the circulation of vortices and the deviations from the average profile as ${\mathit{N}}$ was increased. By sampling the fluctuations in $\boldsymbol {\nabla }{\phi }$ at three locations in the wake, the decay of the vortices was examined and the effective viscosity was found to decrease as ${\mathit{N}}^{-0.49 \pm 0.04}$ . Using temperature as a passive tracer, qualitative observations were made with an infrared (IR) camera that showed significant changes in the wake, including the absence of small-scale structures at high magnetic field strengths. Collectively, the results suggest that the reduction in effective viscosity was due to the suppression of the small-scale eddies by the magnetic field. The slope of the power spectrum was observed to change from a $k^{-1.8}$ power law at low ${\mathit{N}}$ to a $k^{-3.5}$ power law for ${\mathit{N}}> 1$ . Together, these results suggest the flow smoothly transitioned from a hydrodynamic state to a magnetohydrodynamic regime over the range of $0 < {\mathit{N}}< 1$ .
Gisela Schutz - One of the best experts on this subject based on the ideXlab platform.
-
x ray imaging of the dynamic magnetic Vortex core deformation
Nature Physics, 2009Co-Authors: Arne Vansteenkiste, Markus Weigand, Kang Wei Chou, Michael Curcic, Vitalij Sackmann, Hermann Stoll, T Tyliszczak, Georg Woltersdorf, C H Back, Gisela SchutzAbstract:The creation and annihilation of magnetic Vortex–antiVortex pairs has been predicted to have a role in magnetic switching in permalloy nanostructures, but has never previously been observed. High-speed X-ray microscopy now enables the evolution and dynamics of this process to be studied in detail. Magnetic thin-film square- or disc-shaped nanostructures with adequate dimensions exhibit a magnetic Vortex state: the magnetization vectors lie in the film plane and curl around the structure centre. At the very centre of the Vortex, a small, stable core exists where the magnetization points either up or down1,2. The discovery of an easy core reversal mechanism3 did not only open the possibility of using such systems as magnetic memories, but also initiated the fundamental investigation of the core switching mechanism itself4,5,6,7,8,9,10,11,12,13,14,15. Theoretical modelling predicted that the reversal is mediated by the creation and annihilation of a Vortex–antiVortex pair3,4,16, but experimental support has been lacking until now. We used high-resolution time-resolved magnetic X-ray microscopy to experimentally reveal the first step of the reversal process: the dynamic deformation of the Vortex core. In addition, we have measured a critical Vortex Velocity above which reversal must occur5,17. Both observations support the previously proposed reversal mechanism.
Eric Edlund - One of the best experts on this subject based on the ideXlab platform.
-
effects of magnetic field on the turbulent wake of a cylinder in free surface magnetohydrodynamic channel flow
Journal of Fluid Mechanics, 2014Co-Authors: John R Rhoads, Eric EdlundAbstract:Results from a free-surface magnetohydrodynamic (MHD) flow experiment are presented detailing the modification of vortices in the wake of a circular cylinder with its axis parallel to the applied magnetic field. Experiments were performed at Reynolds numbers of the order of as the interaction parameter , representing the ratio of electromagnetic forces to inertial forces, was increased through unity. The von Karman Vortex street in the wake of the cylinder was observed by simultaneously sampling the gradient of the induced electric potential, , at 16 cross-stream locations as a proxy for the streamwise fluid Velocity. An ensemble of Vortex Velocity profiles was measured as a function of the applied magnetic field strength. Results indicate a significant change in the circulation of vortices and the deviations from the average profile as was increased. By sampling the fluctuations in at three locations in the wake, the decay of the vortices was examined and the effective viscosity was found to decrease as . Using temperature as a passive tracer, qualitative observations were made with an infrared (IR) camera that showed significant changes in the wake, including the absence of small-scale structures at high magnetic field strengths. Collectively, the results suggest that the reduction in effective viscosity was due to the suppression of the small-scale eddies by the magnetic field. The slope of the power spectrum was observed to change from a power law at low to a power law for . Together, these results suggest the flow smoothly transitioned from a hydrodynamic state to a magnetohydrodynamic regime over the range of .
Markus Weigand - One of the best experts on this subject based on the ideXlab platform.
-
local modification of the magnetic Vortex core Velocity by gallium implantation
Journal of Applied Physics, 2014Co-Authors: Hauke H Langner, Andreas Vogel, Bjorn Beyersdorff, Markus Weigand, Robert Fromter, H P Oepen, Guido MeierAbstract:The dynamics of magnetic vortices in microsquares with local modifications of magnetic parameters and thickness are investigated. By implanting gallium ions with focussed ion beam into permalloy thin-film elements, we have locally tailored their magnetic properties and the layer thickness. The Vortex of the Landau domain pattern of a square is resonantly excited to a gyrotropic motion and crosses regions with and without implantation. With time-resolved scanning transmission x-ray microscopy, we observe an abrupt change in the Vortex Velocity close to the borders between the two regions.
-
x ray imaging of the dynamic magnetic Vortex core deformation
Nature Physics, 2009Co-Authors: Arne Vansteenkiste, Markus Weigand, Kang Wei Chou, Michael Curcic, Vitalij Sackmann, Hermann Stoll, T Tyliszczak, Georg Woltersdorf, C H Back, Gisela SchutzAbstract:The creation and annihilation of magnetic Vortex–antiVortex pairs has been predicted to have a role in magnetic switching in permalloy nanostructures, but has never previously been observed. High-speed X-ray microscopy now enables the evolution and dynamics of this process to be studied in detail. Magnetic thin-film square- or disc-shaped nanostructures with adequate dimensions exhibit a magnetic Vortex state: the magnetization vectors lie in the film plane and curl around the structure centre. At the very centre of the Vortex, a small, stable core exists where the magnetization points either up or down1,2. The discovery of an easy core reversal mechanism3 did not only open the possibility of using such systems as magnetic memories, but also initiated the fundamental investigation of the core switching mechanism itself4,5,6,7,8,9,10,11,12,13,14,15. Theoretical modelling predicted that the reversal is mediated by the creation and annihilation of a Vortex–antiVortex pair3,4,16, but experimental support has been lacking until now. We used high-resolution time-resolved magnetic X-ray microscopy to experimentally reveal the first step of the reversal process: the dynamic deformation of the Vortex core. In addition, we have measured a critical Vortex Velocity above which reversal must occur5,17. Both observations support the previously proposed reversal mechanism.
H Ji - One of the best experts on this subject based on the ideXlab platform.
-
effects of magnetic field on the turbulent wake of a cylinder in free surface magnetohydrodynamic channel flow
Journal of Fluid Mechanics, 2014Co-Authors: John R Rhoads, E M Edlund, H JiAbstract:Results from a free-surface magnetohydrodynamic (MHD) flow experiment are presented detailing the modification of vortices in the wake of a circular cylinder with its axis parallel to the applied magnetic field. Experiments were performed at Reynolds numbers of the order of ${\mathit{Re}}\sim 10^4$ as the interaction parameter ${\mathit{N}}$ , representing the ratio of electromagnetic forces to inertial forces, was increased through unity. The von Karman Vortex street in the wake of the cylinder was observed by simultaneously sampling the gradient of the induced electric potential, $ \boldsymbol {\nabla }{\phi }$ , at 16 cross-stream locations as a proxy for the streamwise fluid Velocity. An ensemble of Vortex Velocity profiles was measured as a function of the applied magnetic field strength. Results indicate a significant change in the circulation of vortices and the deviations from the average profile as ${\mathit{N}}$ was increased. By sampling the fluctuations in $\boldsymbol {\nabla }{\phi }$ at three locations in the wake, the decay of the vortices was examined and the effective viscosity was found to decrease as ${\mathit{N}}^{-0.49 \pm 0.04}$ . Using temperature as a passive tracer, qualitative observations were made with an infrared (IR) camera that showed significant changes in the wake, including the absence of small-scale structures at high magnetic field strengths. Collectively, the results suggest that the reduction in effective viscosity was due to the suppression of the small-scale eddies by the magnetic field. The slope of the power spectrum was observed to change from a $k^{-1.8}$ power law at low ${\mathit{N}}$ to a $k^{-3.5}$ power law for ${\mathit{N}}> 1$ . Together, these results suggest the flow smoothly transitioned from a hydrodynamic state to a magnetohydrodynamic regime over the range of $0 < {\mathit{N}}< 1$ .
