NASA Scientific and Technical Aerospace Reports

20040073805 Naval Postgraduate School, Monterey, CA
Signal Enhancement Using Time-Frequency Based Denoising
Hughes, John B.; Mar. 2003; 125 pp.; In English; Original contains color illustrations
Report No.(s): AD-A422822; No Copyright; Avail: CASI; A06, Hardcopy
This thesis investigates and compares time and wavelet-domain denoising techniques where received signals contain
broadband noise. We consider how time and wavelet- domain denoising schemes and their combinations compare in the mean
squared error sense. This work applies Wiener prediction and Median filtering as they do not require any prior signal
knowledge. In the wavelet-domain we use soft or hard thresholding on the detail coefficients. In addition, we explore the effect
of these wavelet-domain thresholding techniques on the coefficients associated with cycle-spinning and the newly proposed
recursive cycle-spinning scheme. Finally, we note that thresholding does not make an attempt to de-noise coefficients that
remain after thresholding; therefore we apply time domain techniques to the remaining detail coefficients from the first level
of decomposition in an attempt to de-noise them further prior to reconstruction. This thesis applies and compares these
techniques using a mean squared error criterion to identify the best performing in a robust test signal environment. We find
that soft thresholding with Stein’s Unbiased Risk Estimate (SURE) thresholding produces the best mean squared error results
in each test case and that the addition of Wiener prediction to the first level of decomposition coefficients leads to a slightly
enhanced performance. Finally, we illustrate the effects of denoising algorithms on longer data segments.
DTIC
Algorithms; Augmentation; Frequencies
70
PHYSICS (GENERAL)
Includes general research topics related to mechanics, kinetics, magnetism, and electrodynamics. For specific areas of physics see
categories 71 through 77. For related instrumentation see 35 Instrumentation and Photography; for geophysics, astrophysics, or solar
physics see 46 Geophysics, 90 Astrophysics, or92 Solar Physics.
20040068234 Lockheed Martin Corp., Syracuse, NY, USA
Experimental and Numerical Investigation of Impinging Jet Flow in Square Ducts Intersecting at 90 degrees
Corson, D.; Vassallo, P.; Oct. 2003; 54 pp.; In English
Report No.(s): DE2004-822274; LM-03K110; No Copyright; Avail: Department of Energy Information Bridge
An experimental and numerical investigation has been conducted on flow through two square ducts with a 2:1 hydraulic
diameter ratio joined at a right angle. Measurements of the velocity field were acquired using a laser Doppler velocimeter at
various planar locations throughout the ducts at a nominal Reynolds number of 68, 000. Pressure drop measurements were
taken for 3 Reynolds numbers between 46,000 and 93,000. Computational fluid dynamics (CFD) analyses were performed
using STAR-CD to determine how well the experimental data could be predicted using the k-(var-epsilon), k-(var-epsilon)
RNG, k-(var-epsilon)Chen, k-(var-epsilon) quadratic, k-(omega), and Spalart-Allmaras models. The results show that there are
distinct differences in the CDF results. The standard k-(var-epsilon) model overpredicted the loss coefficient by 4% and
underpredicted the exit swirl magnitude by 43%. The best predictor of the swirl decay was found to be the k-(omega) model,
which adequately followed the data throughout the entire geometry and underpredicted the exit swirl by 16%. The best overall
model was found to be Spalart-Allmaras, which overpredicted the loss coefficient by 2% and underpredicted the exit swirl
magnitude by 40%.
NTIS
Decay; Hydraulics; Ducts
20040068235 Lockheed Martin Corp., Syracuse, NY, USA
Ohmic Contacts to n-type GaSb and n-type GaInAsSb
Huang, R. K.; Wang, C. A.; Harris, C. T.; Connors, M. K.; Shiau, D. A.; Jun. 2003; 22 pp.; In English
Report No.(s): DE2004-822096; LM-03K059; No Copyright; Avail: Department of Energy Information Bridge
No abstract available
Gallium Arsenides; N-Type Semiconductors
20040068241 Lawrence Livermore National Lab., Livermore, CA
Thick Liquid-Walled Spheromak Magnetic Fusion Power Plant. Revision 1
Moir, R. W.; Bulmer, R. H.; Fowler, T. K.; Rognlien, T. D.; Youssef, M. Z.; Oct. 03, 2002; In English
Report No.(s): DE2003-15004532; UCRL-ID-148021-R1; No Copyright; Avail: National Technical Information Service
(NTIS)
231