205 research outputs found
Quantification of uncertainty in a stereoscopic particle image velocimetry measurement
In Stereoscopic Particle Image Velocimetry (Stereo-PIV), the three velocity components are obtained by illuminating a planar region in the flow field and recording the region of interest using two cameras at an angle. Calibration, planar velocity estimation, and velocity reconstruction are the three essential steps involved in the process. Earlier efforts to quantify the accuracy in a Stereo-PIV measurement process have shown higher error in out of plane motion. However, a detailed analysis of the measurement uncertainty involved in a Stereo-PIV calibration-based reconstruction process has yet to be presented. This analysis provides a detailed framework to specify the uncertainty in the coefficients of the calibration mapping function and the uncertainty involved in self-calibration step for correction of the registration error. Using Taylor series expansion for uncertainty propagation the contribution of the calibration step uncertainties are combined with planar field uncertainties to predict the overall uncertainty in the reconstructed velocity components. The analysis is tested using simulated random field images and experimental vortex ring images. The results emphasize the sensitivity and interdependence of the individual uncertainties involved in each step of a Stereo-PIV measurement process
Electronic Service Quality In Mobile Internet Music Services: Comparing Different Second-Order Measurement Specifications
Construct misspecification is deleterious in that it leads to Type I and Type II errors. In this study we empirically demonstrate that different measurement conceptualizations can lead to different conclusions concerning the relative importance of beliefs in predicting electronic service quality. Specifically we test three second-order measurement conceptualizations of the electronic service quality construct in the context of a mobile internet music service. We find that there is poor convergence between the three models highlighting the need for more careful measurement specification of IS constructs even at a higher-order hierarchical measurement level
Volumetric Particle Tracking Velocimetry (PTV) Uncertainty Quantification
We introduce the first comprehensive approach to determine the uncertainty in
volumetric Particle Tracking Velocimetry (PTV) measurements. Volumetric PTV is
a state-of-the-art non-invasive flow measurement technique, which measures the
velocity field by recording successive snapshots of the tracer particle motion
using a multi-camera set-up. The measurement chain involves reconstructing the
three-dimensional particle positions by a triangulation process using the
calibrated camera mapping functions. The non-linear combination of the
elemental error sources during the iterative self-calibration correction and
particle reconstruction steps increases the complexity of the task. Here, we
first estimate the uncertainty in the particle image location, which we model
as a combination of the particle position estimation uncertainty and the
reprojection error uncertainty. The latter is obtained by a gaussian fit to the
histogram of disparity estimates within a sub-volume. Next, we determine the
uncertainty in the camera calibration coefficients. As a final step the
previous two uncertainties are combined using an uncertainty propagation
through the volumetric reconstruction process. The uncertainty in the velocity
vector is directly obtained as a function of the reconstructed particle
position uncertainty. The framework is tested with synthetic vortex ring
images. The results show good agreement between the predicted and the expected
RMS uncertainty values. The prediction is consistent for seeding densities
tested in the range of 0.01 to 0.1 particles per pixel. Finally, the
methodology is also successfully validated for an experimental test case of
laminar pipe flow velocity profile measurement where the predicted uncertainty
is within 17% of the RMS error value
Hemodynamics of Stent Implantation Procedures in Coronary Bifurcations: an in vitro study
Stent implantation in coronary bifurcations presents unique challenges and
currently there is no universally accepted stent deployment approach. Despite
clinical and computational studies, to date, the effect of each stent
implantation method on the coronary artery hemodynamics is not well understood.
In this study the hemodynamics of stented coronary bifurcations under pulsatile
flow conditions were investigated experimentally. Three implantation methods,
provisional side branch (PSB), culotte (CUL), and crush (CRU), were
investigated using time-resolved particle image velocimetry (PIV) to measure
the velocity fields. Subsequently, hemodynamic parameters including wall shear
stress (WSS), oscillatory shear index (OSI), and relative residence time (RRT)
were calculated and the pressure field through the vessel was non-invasively
quantified. The effects of each stented case were evaluated and compared
against an un-stented case. CRU provided the lowest compliance mismatch, but
demonstrated detrimental stent interactions. PSB, the clinically preferred
method, and CUL maintained many normal flow conditions. However, PSB provided
about a 300% increase in both OSI and RRT. CUL yielded a 10% and 85% increase
in OSI and RRT, respectively. The results of this study support the concept
that different bifurcation stenting techniques result in hemodynamic
environments that deviate from that of un-stented bifurcations, to varying
degrees.Comment: 33 pages, 8 figures, 3 table
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