28,508 research outputs found
Errors in particle tracking velocimetry with high-speed cameras
Velocity errors in particle tracking velocimetry (PTV) are studied. When
using high-speed video cameras, the velocity error may increase at a high
camera frame rate. This increase in velocity error is due to particle-position
uncertainty, which is one of two sources of velocity errors studied here. The
other source of error is particle acceleration, which has the opposite trend of
diminishing at higher frame rates. Both kinds of errors can propagate into
quantities calculated from velocity, such as the kinetic temperature of
particles or correlation functions. As demonstrated in a dusty plasma
experiment, the kinetic temperature of particles has no unique value when
measured using PTV, but depends on the sampling time interval or frame rate. It
is also shown that an artifact appears in an autocorrelation function computed
from particle positions and velocities, and it becomes more severe when a small
sampling-time interval is used. Schemes to reduce these errors are
demonstrated.Comment: 6 pages, 5 figures, Review of Scientific Instruments, 2011 (In Press
Accurate particle position measurement from images
The moment method is an image analysis technique for sub-pixel estimation of
particle positions. The total error in the calculated particle position
includes effects of pixel locking and random noise in each pixel. Pixel
locking, also known as peak locking, is an artifact where calculated particle
positions are concentrated at certain locations relative to pixel edges. We
report simulations to gain an understanding of the sources of error and their
dependence on parameters the experimenter can control. We suggest an algorithm,
and we find optimal parameters an experimenter can use to minimize total error
and pixel locking. Simulating a dusty plasma experiment, we find that a
sub-pixel accuracy of 0.017 pixel or better can be attained. These results are
also useful for improving particle position measurement and particle tracking
velocimetry (PTV) using video microscopy, in fields including colloids,
biology, and fluid mechanics.Comment: 8 pages, 17 figure
Evolution of shear-induced melting in dusty plasma
The spatiotemporal development of melting is studied experimentally in a 2D
dusty plasma suspension. Starting with an ordered lattice, and then suddenly
applying localized shear, a pair of counter-propagating flow regions develop. A
transition between two melting stages is observed before a steady state is
reached. Melting spreads with a front that propagates at the transverse sound
speed. Unexpectedly, coherent longitudinal waves are excited in the flow
region.Comment: 5 pages text, 3 figures, in press Physical Review Letters 2010
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