332 research outputs found
Taylor's (1935) dissipation surrogate reinterpreted
New results from direct numerical simulation of decaying isotropic turbulence show that Taylor’s expression for the viscous dissipation rate ε = CεU3/L is more appropriately interpreted as a surrogate for the inertial energy flux. As a consequence, the well known dependence of the Taylor prefactor Cε on Reynolds number Cε(RL)→Cε,∞ can be understood as corresponding to the onset of an inertial range
Non-local modulation of the energy cascade in broad-band forced turbulence
Classically, large-scale forced turbulence is characterized by a transfer of
energy from large to small scales via nonlinear interactions. We have
investigated the changes in this energy transfer process in broad-band forced
turbulence where an additional perturbation of flow at smaller scales is
introduced. The modulation of the energy dynamics via the introduction of
forcing at smaller scales occurs not only in the forced region but also in a
broad range of length-scales outside the forced bands due to non-local triad
interactions. Broad-band forcing changes the energy distribution and energy
transfer function in a characteristic manner leading to a significant
modulation of the turbulence. We studied the changes in this transfer of energy
when changing the strength and location of the small-scale forcing support. The
energy content in the larger scales was observed to decrease, while the energy
transport power for scales in between the large and small scale forcing regions
was enhanced. This was investigated further in terms of the detailed transfer
function between the triad contributions and observing the long-time statistics
of the flow. The energy is transferred toward smaller scales not only by
wavenumbers of similar size as in the case of large-scale forced turbulence,
but by a much wider extent of scales that can be externally controlled.Comment: submitted to Phys. Rev. E, 15 pages, 18 figures, uses revtex4.cl
Phase imaging in scanning transmission electron microscopy using bright-field balanced divergency method
We introduce a phase imaging mechanism for scanning transmission electron
microscopy that exploits the complementary intensity changes of transmitted
disks at different scattering angles. For scanning transmission electron
microscopy, this method provides a straightforward, dose-efficient, and
noise-robust phase imaging, from atomic resolution to intermediate length
scales, as a function of scattering angles and probe defocus. At atomic
resolution, we demonstrate that the phase imaging using the method can detect
both light and heavy atomic columns. Furthermore, we experimentally apply the
method to the imaging of nanoscale magnetic phases in FeGe samples. Compared
with conventional methods, phase retrieval using the new method has higher
effective spatial resolution and robustness to non-phase background contrast.
Our method complements traditional phase imaging modalities in electron
microscopy and has the potential to be extended to other scanning transmission
techniques and to characterize many emerging material systems.Comment: Updated link to codes; Fixed wrong labeling in Figures 3; Updated
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A single trapped ion in a finite range trap
This paper presents a method to describe dynamics of an ion confined in a
realistic finite range trap. We model this realistic potential with a solvable
one and we obtain dynamical variables (raising and lowering operators) of this
potential. We consider coherent interaction of this confined ion in a finite
range trap and we show that its center-of-mass motion steady state is a special
kind of nonlinear coherent states. Physical properties of this state and their
dependence on the finite range of potential are studied
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