Issue 10 Volume 41 May 16, 2003

estimate of the location of the velocity vector acquired through the use of tracer techniques, such as PIV, is at the midpoint
of the displacement vector. Thus, unless special care is taken, PIV data also are initially obtained on an irregular grid. This
study considered the use of 2nd, 3rd, or 4th order polynomials to remap the velocity field by performing a local least-squares
fit of the irregularly spaced data within region of radius R. Four approaches were assessed for computing the out-of-plane
vorticity field from the in-plane velocity measurements: direct differentiation of the polynomial fits used in the remapping
process, lst and 2nd order finite difference techniques (2nd and 4th order accurate, respectively), and an 8-point circulation
method on the regular data. Results show that the most accurate vorticity results are achieved by either directly differentiating
the 3rd order polynomial fit to the original irregular data, or by the 2nd order finite difference technique. (5 refs.)
DTIC
Velocity Measurement; Vorticity; Interpolation; Computational Grids; Marking; Mathematical Models; Algorithms; Vortices;
Laser Applications
20030034717 Universidad Nacional Autonoma de Mexico, Mexico City
Magnetic Resonance Image Wavelet Enhancer
Rodriguez, A. O.; Mansfield, P.; Azpiroz, J.; Oct 2001; 4 pp.; In English; Original contains color illustrations
Report No.(s): AD-A410347; No Copyright; Avail: CASI; A01, Hardcopy
Echo-Planar Imaging is able to generate images in less than 80 ms, however, images have poor quality since they have
an intrinsic poor Signal-to-Noise ratio. Filtering techniques can be applied to enhance the image quality such as Fourier
transform. Another natural tool is the so-called wavelet transform, this is an analytical tool capable of generating an analysis
in time and frequency simultaneously. The two-dimensional wavelet transform is applied to blood flow maps produced with
a flow encoding Echo-Planar Imaging sequence to improve the image Signal-to-Noise ratio. Enhanced flow maps and contour
maps are presented. The wavelet transform shows that flow magnetic resonance images can be improved without detriment
of the spatial resolution and unmasking the relevant anatomical and physiological information.
DTIC
Blood Flow; Image Resolution; Imaging Techniques; Magnetic Resonance
65
STATISTICS AND PROBABILITY
Includes data sampling and smoothing; Monte Carlo method; time series analysis; and stochastic processes.
20030032922 City Univ., London
Virtues and Vices of Source Separation Using Linear Independent Component Analysis for Blind Source Separation
of Non-Linearly Coupled and Synchronised Fetal and Mother ECGs
Sabry-Rizk, M.; Zgallai, W.; McLean, A.; Carson, E. R.; Grattan, K. T.; Oct 2001; 6 pp.; In English
Report No.(s): AD-A410440; No Copyright; Avail: CASI; A02, Hardcopy
In this paper, we address the imminent problem which arises when researchers unjudiciously use a linear and
instantaneous (memoryless) model for the source mixing structures of independent component analysis (ICA), also known as
blind source separation (BSS), in pursuit of separating noisy and frequently non stationary combined mother and fetal
electrocardiogram (ECG) signals from cutaneous measurements under the following false assumptions. (1) Sensors
(electrodes) are instantaneous linear mixtures of mother and fetal source signals. (2) Noise is an additive Gaussian
perturbation. (3) Mother and fetal ECG signals are assumed to be stationary and linear, mutually statistically independent and
statistically independent from noise. (4) Most of the second-order (SO) and fourth-order (FO) blind source separation (BSS)
methods developed this last decade assume that third-order cumulants vanish hence the need to use FO. All these assumptions
are not valid and will be challenged. We will expose these vices without providing any significant contributions for
overcoming them. Rather, we provide a framework for investigations which are based on conformal mapping of nonlinear
mixtures and novel dynamic nonlinear structures with time-variant memory to cater for quadratic coupling between mother
and fetal which is quasi-periodical and the concomitant (quasi) cyclostationarity. Results given here show linear ICA shortfalls
in non stationary environment which is precipitated by quadratic coupling between mother and fetal ECGs during events of
synchronised QRS complexes and P-waves and account for more than 20\% of the 100,000 maternal cardiac cycles obtained
from several clinical trials.
DTIC
Electrocardiography; Signal Processing; Statistical Analysis
179