1,937 research outputs found

    2-D Non-Fickian Dispersion Model for the Initial Period of River Mixing

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    Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchive

    Periodic shedding of vortex dipoles from a moving penetrable obstacle in a Bose-Einstein condensate

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    We investigate vortex shedding from a moving penetrable obstacle in a highly oblate Bose-Einstein condensate. The penetrable obstacle is formed by a repulsive Gaussian laser beam that has the potential barrier height lower than the chemical potential of the condensate. The moving obstacle periodically generates vortex dipoles and the vortex shedding frequency fvf_v linearly increases with the obstacle velocity vv as fv=a(vvc)f_v=a(v-v_c), where vcv_c is a critical velocity. Based on periodic shedding behavior, we demonstrate deterministic generation of a single vortex dipole by applying a short linear sweep of a laser beam. This method will allow further controlled vortex experiments such as dipole-dipole collisions.Comment: 6 pages, 7 figure

    Behavior of Longitudinal and Transverse Dispersion Coefficient in Three-Dimensional Open Channels

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    Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

    The Vertical Profile of Transverse Velocity of Secondary Flow in Meandering Channels

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    Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

    Observation of wall-vortex composite defects in a spinor Bose-Einstein condensate

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    We report the observation of spin domain walls bounded by half-quantum vortices (HQVs) in a spin-1 Bose-Einstein condensate with antiferromagnetic interactions. A spinor condensate is initially prepared in the easy-plane polar phase, and then, suddenly quenched into the easy-axis polar phase. Domain walls are created via the spontaneous Z2\mathbb{Z}_2 symmetry breaking in the phase transition and the walls dynamically split into composite defects due to snake instability. The end points of the defects are identified as HQVs for the polar order parameter and the mass supercurrent in their proximity is demonstrated using Bragg scattering. In a strong quench regime, we observe that singly charged quantum vortices are formed with the relaxation of free wall-vortex composite defects. Our results demonstrate a nucleation mechanism for composite defects via phase transition dynamics.Comment: 10 pages, 11 figures, reference update

    Analysis of Transverse Mixing Using Natural Tracers Continuously Introduced from Tributaries

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    Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchive

    A Particle Dispersion Model For Analysis Of Two-Dimensional Mixing In Open Channels

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    Pollutant mixing in natural rivers is analyzed by using the two-dimensional depth-averaged advection-dispersion model (2D ADE) for rapid completion of the vertical mixing. The dispersion term in the 2D ADE follows Taylor’s assumption (Taylor, 1954; Fischer et al., 1979) which can be applied in the Taylor period. However, most open channel flow has long initial period which makes the skewed concentration distribution due to the unbalance between the shear flow advection and the vertical mixing (Chatwin, 1970). Therefore, the non-Fickian dispersion model is necessary to compensate the limitations of the 2D ADE model. In this research, the two-dimensional particle dispersion model (2D PDM) was developed to analyze the pollutant mixing both in the initial and the Taylor period without determination of the dispersion coefficient. In the 2D PDM, pollutant particles were introduced to visualize physical mixing process according to the complicate flow variation in open channels. The 2D PDM is based on the shear flow dispersion theory and adopted the operator split method which divides the shear advection stage and the turbulent diffusion stage. In the shear advection stage, particles were separated by the vertical velocity deviations in the longitudinal and transverse directions. The separated particles according to the shear flow were mixed across the vertical in the turbulent diffusion stage. After the particle mixing, the particle distribution in each time step was converted to the concentration field for various analysis. The 2D PDM was applied to the straight channel and the meandering channel for analysis of the conservative pollutant mixing. In the straight channel, concentration curves from the 2D PDM showed skewed distribution in the initial period and then turned into the Gaussian distribution in the Taylor period. And, the concentration distributions in the meandering channel showed good agreement with the tracer test results
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