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Coherent electromagnetic field imaging through Fourier transform heterodyne

Description: The authors present a detection process capable of directly imaging the transverse amplitude, phase, and if desired, Doppler shift of coherent electromagnetic fields. Based on coherent detection principles governing conventional heterodyned RADAR/LIDAR systems, Fourier Transform Heterodyne (FTH) incorporates transverse spatial encoding of the local oscillator for image capture. Appropriate selection of spatial encoding functions, or basis set, allows image retrieval by way of classic Fourier manipulations. Of practical interest: (1) imaging is accomplished on a single element detector requiring no additional scanning or moving components, and (2) a wide variety of appropriate spatial encoding functions exist that may be adaptively configured in real-time for applications requiring optimal detection. In this paper, they introduce the underlying principles governing FTH imaging, followed by demonstration of concept via a simple experimental setup based on a HeNe laser and a 69 element spatial phase modulator.
Date: December 1998
Creator: Cooke, B. J.; Laubscher, B. E.; Olivas, N. L.; Goeller, R. M.; Cafferty, M.; Briles, S. D. et al.
Partner: UNT Libraries Government Documents Department

Data analysis using wavelets

Description: This paper describes the use of wavelet transform techniques to analyze typical data found in industrial applications. A way of detecting system changes using wavelet transforms is described. The results of applying this method are described for several typical applications. The wavelet technique is compared with the use of Fourier transform methods.
Date: May 1, 1997
Creator: Fryer, M.O.
Partner: UNT Libraries Government Documents Department

Fast approximation of self-similar network traffic

Description: Recent network traffic studies argue that network arrival processes are much more faithfully modeled using statistically self-similar processes instead of traditional Poisson processes [LTWW94a, PF94]. One difficulty in dealing with self-similar models is how to efficiently synthesize traces (sample paths) corresponding to self-similar traffic. We present a fast Fourier transform method for synthesizing approximate self-similar sample paths and assess its performance and validity. We find that the method is as fast or faster than existing methods and appears to generate a closer approximation to true self-similar sample paths than the other known fast method (Random Midpoint Displacement). We then discuss issues in using such synthesized sample paths for simulating network traffic, and how an approximation used by our method can dramatically speed up evaluation of Whittle`s estimator for H, the Hurst parameter giving the strength of long-range dependence present in a self-similar time series.
Date: January 1, 1995
Creator: Paxson, V.
Partner: UNT Libraries Government Documents Department

Wavelet transforms as solutions of partial differential equations

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). Wavelet transforms are useful in representing transients whose time and frequency structure reflect the dynamics of an underlying physical system. Speech sound, pressure in turbulent fluid flow, or engine sound in automobiles are excellent candidates for wavelet analysis. This project focused on (1) methods for choosing the parent wavelet for a continuous wavelet transform in pattern recognition applications and (2) the more efficient computation of continuous wavelet transforms by understanding the relationship between discrete wavelet transforms and discretized continuous wavelet transforms. The most interesting result of this research is the finding that the generalized wave equation, on which the continuous wavelet transform is based, can be used to understand phenomena that relate to the process of hearing.
Date: October 1, 1997
Creator: Zweig, G.
Partner: UNT Libraries Government Documents Department

Sets of Fourier coefficients using numerical quadrature

Description: One approach to the calculation of Fourier trigonometric coefficients f(r) of a given function f(x) is to apply the trapezoidal quadrature rule to the integral representation f(r) = {line_integral}{sub 0}{sup 1} f(x)e{sup -2{pi}irx}dx. Some of the difficulties in this approach are discussed. A possible way of overcoming many of these is by means of a subtraction function. Thus, one sets f(x) = h{sub p-1}(x) + g{sub p}(x), where h{sub -1}(x) is an algebraic polynomial of degree p-1, specified in such a way that the Fourier series of g{sub p}(x) converges more rapidly than that of f(x). To obtain the Fourier coefficients of f(x), one uses an analytic expression for those of h{sub p-1}(x) and numerical quadrature to approximately those of g{sub p}(x).
Date: October 10, 2001
Creator: Lyness, J. N.
Partner: UNT Libraries Government Documents Department

The PROSAIC Laplace and Fourier Transform

Description: Integral Transform methods play an extremely important role in many branches of science and engineering. The ease with which many problems may be solved using these techniques is well known. In Electrical Engineering especially, Laplace and Fourier Transforms have been used for a long time as a way to change the solution of differential equations into trivial algebraic manipulations or to provide alternate representations of signals and data. These techniques, while seemingly overshadowed by today`s emphasis on digital analysis, still form an invaluable basis in the understanding of systems and circuits. A firm grasp of the practical aspects of these subjects provides valuable conceptual tools. This tutorial paper is a review of Laplace and Fourier Transforms from an applied perspective with an emphasis on engineering applications. The interrelationship of the time and frequency domains will be stressed, in an attempt to comfort those who, after living so much of their lives in the time domain, find thinking in the frequency domain disquieting.
Date: November 1, 1994
Creator: Smith, G. A.
Partner: UNT Libraries Government Documents Department

Power spectrum calculations using the fast Fourier transform

Description: In the analysis of turbulent flow, the evaluation of simulations is difficult because the results are three-dimensional and transient. We have found that analysis of the power spectra from the nodal time histories provides not only insight into the behavior of the flow, but it is a useful tool in determining the solution`s spatial (grid) and temporal (time step) convergence. We have developed a method and computer code for calculating the power spectrum for any set of equal-interval data. The code is called PWRSPEC. This report documents the method used to calculate the power spectrum, provides guidance on how to use the PWRSPEC code, and includes an example problem that was used for code validation.
Date: December 5, 1995
Creator: McCallen, R.
Partner: UNT Libraries Government Documents Department

Particle beam dynamics simulations using the POOMA framework

Description: A program for simulation of the dynamics of high intensity charged particle beams in linear particle accelerators has been developed in C++ using the POOMA Framework, for use on serial and parallel architectures. The code models the trajectories of charged particles through a sequence of different accelerator beamline elements such as drift chambers, quadrupole magnets, or RF cavities. An FFT-based particle-in-cell algorithm is used to solve the Poisson equation that models the Coulomb interactions of the particles. The code employs an object-oriented design with software abstractions for the particle beam, accelerator beamline, and beamline elements, using C++ templates to efficiently support both 2D and 3D capabilities in the same code base. The POOMA Framework, which encapsulates much of the effort required for parallel execution, provides particle and field classes, particle-field interaction capabilities, and parallel FFT algorithms. The performance of this application running serially and in parallel is compared to an existing HPF implementation, with the POOMA version seen to run four times faster than the HPF code.
Date: December 31, 1998
Creator: Humphrey, W.; Ryne, R.; Cleland, T.; Cummings, J.; Habib, S.; Mark, G. et al.
Partner: UNT Libraries Government Documents Department

Nonlinear spatio-temporal interactions and neural connections in human vision using transient and M-sequence stimuli

Description: Reciprocal connections, in essence, are the dynamic wiring (connections) of the neural network circuitry. Given the high complexity of the neural circuitry in the human brain, it is quite a challenge to study the dynamic wiring of highly parallel and widely distributed neural networks. The measurements of stimulus evoked coherent oscillations provide indirect evidence of dynamic wiring. In this study, in addition to the coherent oscillation measurements, two more techniques are discussed for testing possible dynamic wiring: measurements of spatio-temporal interactions beyond the classical receptive fields, and neural structural testing using nonlinear systems analysis.
Date: February 1, 1996
Creator: Chen, H.W.; Aine, C.J.; Flynn, E.R. & Wood, C.C.
Partner: UNT Libraries Government Documents Department

Numerical Time-Dependent Schroedinger Description of Charge-Exchange Collisions

Description: An implicit Fast Fourier Transform (FFT) algorithm is implemented to solve the time-dependent Schroedinger equation with application to charge-exchange collisions. Cross sections are calculated for He{sup 2} on H and compared with experiment and other theoretical results. A disagreement between previously published theoretical results is resolved.
Date: February 23, 1999
Creator: Riley, M.E. & Ritchie, B.
Partner: UNT Libraries Government Documents Department

Extended pseudo-screen migration with multiple reference velocities

Description: The pseudo-screen propagator is a kind of one way wave propagation based on the local Born approximation. The problem of the propagator is that it is difficult to calculate the scattered fields when the velocity perturbation is large; not to mention the accuracy of the propagator. We develop an extended pseudo-screen propagator by introducing different reference velocities in different regions of a medium to ensure the condition of small perturbation. The exploding reflector data for a 2D slice of the SEG/EAEG 3D salt model is generated by a finite difference scheme to test the feasibility of the method. The migration result demonstrates that the method can handle severe lateral velocity variations and provides high quality images for complex structures.
Date: November 1, 1997
Creator: Huang, Lian-Jie & Fehler, M.C.
Partner: UNT Libraries Government Documents Department

Trace water vapor determination in nitrogen and corrosive gases using infrared spectroscopy

Description: The generation of particles in gas handling systems as a result of corrosion is a major concern in the microelectronics industry. The corrosion can be caused by the presence of trace quantities of water in corrosive gases such as HCl or HBr. FTIR spectroscopy has been shown to be a method that can be made compatible with corrosive gases and is capable of detecting low ppb levels of water vapor. In this report, the application of FTIR spectroscopy combined with classical least squares multivariate calibration to detect trace H{sub 2}O in N{sub 2}, HCl and HBr is discussed. Chapter 2 discusses the gas handling system and instrumentation required to handle corrosive gases. A method of generating a background spectrum useful to the measurements discussed in this report, as well as in other application areas such as gas phase environmental monitoring, is discussed in Chapter 3. Experimental results obtained with the first system are presented in Chapter 4. Those results made it possible to optimize the design options for the construction of a dedicate system for low ppb water vapor determination. These designs options are discussed in Chapter 5. An FTIR prototype accessory was built. In addition, a commercially available evacuable FTIR system was obtained for evaluation. Test results obtained with both systems are discussed in Chapter 6. Experiments dealing with the interaction between H{sub 2}O-HCl and potential improvements to the detection system are discussed in Chapter 7.
Date: June 1, 1997
Creator: Espinoza, L.H.; Niemczyk, T.M.; Stallard, B.R. & Garcia, M.J.
Partner: UNT Libraries Government Documents Department

Turbulence and turbulence spectra in complex fluid flows

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). Our objective was to develop a theoretical model of fluid turbulence in parallel with a series of direct numerical simulations of increasingly complex test environments to establish limits of error and regimes of applicability, and to guide improvements. The aim is to produce methods of tested accuracy, with tractable numerical approximations, for turbulent fluids of constant density, and then for variable densities and multimaterial flows. We proceed from a recent spectral model that describes turbulent energy and stress densities in terms of a range of length scales. This should lead not only to improved engineering models, but also to a basic conceptual improvement because the spectral approach accounts for the variation of evolution rates with turbulence length scales.
Date: November 1, 1997
Creator: Clark, T.T.; Chen, Shi-Yi; Turner, L. & Zemach, C.
Partner: UNT Libraries Government Documents Department

Pillared clays as superior catalysts for selective catalytic reduction of nitric oxide. Second semiannual report, 1996

Description: During the first six months of the program, the work has progressed as planned. We have constructed a reactor system and assembled all laboratory essentials for conducting the three-year project. First, the catalytic activities of the Cu(2+) ion exchanged alumina-pillared clay for the selective catalytic reduction of NO by ethylene were measured. The temperature range was 250-500{degrees}C. The activities of this catalyst were substantially higher than the catalyst that has been extensively studied in the literature, Cu-ZSM-5. Fourier Transform Infrared Spectroscopy (FTIR) was used to study the acidity of the catalyst. The second part of the work was an in-depth FTIR study of the NO decomposition mechanism on the catalyst. This was planned as the first and the key step to obtain an understanding of the reaction mechanism. Key surface intermediates were identified from the FTIR spectra, and a redox type Eley-Rideal mechanism was proposed for the NO decomposition on this catalyst. This report will be divided into two parts. In Part One, we report results on the catalytic activities of the Cu-alumina-pillared clay and a direct comparison with other known catalysts. In Part two, we focus on the FTIR study and from the results, we propose a NO decomposition mechanism on this new catalyst. Plans for the next six months include tests of different pillared clays as well as the catalytic mechanism. The micro reactor will continue to be the key equipment for measuring the catalytic activities. FTIR will continue to be the major technique for identifying surface species and hence understanding the reaction mechanism.
Date: August 1, 1997
Creator: Yang, R.T.; Li, W.B.; Sirilumpen, M. & Tharapiwattananon, N.
Partner: UNT Libraries Government Documents Department

Instantaneous phasor method under severely unbalanced situations

Description: The new instantaneous phasor method originated by the author for obtaining instantaneous balanced fundamental components is further studied under severely unbalanced situations. Selection of the initial and synchronization phasors becomes important. An example is presented. This technique may substitute for the fast Fourier transformation (FFT) plus symmetrical component method for active power quality control and for continuous diagnostics. The influence of high magnitudes of harmonics will be discussed in a separate paper.
Date: December 1, 1997
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department

Physical measurements of Cu{sup 2+}-complexes of bilirubin

Description: Copper is known to form complexes with bilirubin (H{sub 2}BR). Such complexes have received increased attention due to their clinical significance as free-radical scavengers. The purpose of this study was to examine a series of Cu{sup 2+}BR complexes to ascertain the nature of the binding between Cu{sup 2+} and BR. Several physical measurements of the salts were made, such as Fourier Transform Infrared (FT-IR), Fourier Transform Raman spectroscopy (FT-R), and Electron Paramagnetic Resonance (EPR). The complexes were prepared by dissolving protonated BR in NaOH, and adding different ratios of aqueous CuCl{sub 2}. At ratios of Cu{sup 2+}:H{sub 2}BR of 1:1 and 2:1, soluble complexes were formed. In solution EPR spectra demonstrated 9 hyperfine peaks, which from the splitting, is indicative of Cu{sup 2+} coordinated to 4 nitrogen atoms coming from 2 molecules of BR.
Date: December 31, 1995
Creator: Ferraro, J.R.; Wu, J.G.; Li, W.H.; Xu, Y.Z.; Xu, D.F.; Shen, G.R. et al.
Partner: UNT Libraries Government Documents Department

Subtask 1.12 - Solid-Phase Microextraction (SPME) Coupled with Optical Spectroscopy for Near-Real-Time Determination of Fuel and Related Pollutants in Water Samples: Semi-annual report, July 1--December 31, 1996

Description: The measurement of organic pollutants in water requires that samples be collected, transported to a laboratory, extracted (usually with large volumes of hazardous chlorinated solvents), and analyzed using chromatographic techniques. Such limitations make rapid determinations in the field (e.g., for emergency response and/or for survey investigations) very expensive with analytical turnaround times requiring several days. Similar limitations exist for the collection and analysis of organic pollutants in air. An alternative approach is being developed at the Energy {ampersand} Environmental Research Center (EERC) that has been demonstrated to yield good sensitivities (ppb to ppm) and be easily adapted for rapid (less than 30 minutes) and inexpensive field surveys. This new approach is based on the preconcentration of organic pollutants in optically clear sorbent media followed by measurement with either ultraviolet (UV) spectroscopy or Fourier transform infrared spectrometry (FT-IR). Investigations using sorbent media including methylsilicone gums (for UV spectroscopy) and `Parafilm` (for FT-IR) have shown that quantitative determinations of aromatic fuel components, such as benzene and alkylbenzenes (BTEX), can be achieved using UV spectrometry, and of common solvents (e.g., chloroform and other chlorinated solvents) can be achieved using FT-IR. Sample concentration and spectroscopic steps can be performed in a few minutes using the combination of solid-phase sorption followed by spectroscopic measurements. This work has demonstrated that the approach can yield low-ppm to low-ppb detection limits for organic pollutants in water without the negative influences of water matrix components (e.g., dissolved humic material) that prohibit the use of direct spectroscopic measurements.
Date: December 31, 1997
Creator: Hawthorne, S.B.
Partner: UNT Libraries Government Documents Department

An Introduction to Wavelet Theory and Analysis

Description: This report reviews the history, theory and mathematics of wavelet analysis. Examination of the Fourier Transform and Short-time Fourier Transform methods provides tiormation about the evolution of the wavelet analysis technique. This overview is intended to provide readers with a basic understanding of wavelet analysis, define common wavelet terminology and describe wavelet amdysis algorithms. The most common algorithms for performing efficient, discrete wavelet transforms for signal analysis and inverse discrete wavelet transforms for signal reconstruction are presented. This report is intended to be approachable by non- mathematicians, although a basic understanding of engineering mathematics is necessary.
Date: October 1, 1998
Creator: Miner, N.E.
Partner: UNT Libraries Government Documents Department

Spatial frequency tuning functions and contrast sensitivity at different eccentricities in the visual field

Description: The human luminance spatial frequency contrast sensitivity function (CSF) has been well studied using psychophysical measurements by detecting spatial frequency (SF) grating patterns at threshold. Threshold CSFs at different eccentricities have proven to be quite useful in both basic and clinical vision research. However, near threshold, the CSF is measured at a linear area of the saturating contrast-response curve. In contrast, most of our everyday vision may be at suprathreshold levels, and thus may function most of the time at the nonlinear area of the contrast-response curve. In this study, in order to better characterize the CSF at normal contrast levels, we measured the SF tuning functions as well as the CR functions at different suprathreshold contrast levels and different eccentricities of the visual field using noninvasive MEG techniques. In this study, in addition to peak analysis, we have developed more reliable averaged power analysis methods where the average power can be calculated from the entire waveforms.
Date: July 1, 1996
Creator: Chen, H.W.; Aine, C.J.; Flynn, E.R. & Wood, C.C.
Partner: UNT Libraries Government Documents Department

Fading channel simulator

Description: This invention relates to high frequency (HF) radio signal propagation through fading channels and, more particularly, to simulation of fading channels in order to characterize HF radio system performance in transmitting and receiving signals through such fading channels. Fading channel effects on a transmitted communication signal are simulated with both frequency and time variations using a channel scattering function to affect the transmitted signal. A conventional channel scattering function is converted to a series of channel realizations by multiplying the square root of the channel scattering function by a complex number of which the real and imaginary parts are each independent variables. The two-dimensional inverse-FFT of this complex-valued channel realization yields a matrix of channel coefficients that provide a complete frequency-time description of the channel. The transmitted radio signal is segmented to provide a series of transmitted signal and each segment is subject to FFT to generate a series of signal coefficient matrices. The channel coefficient matrices and signal coefficient matrices are then multiplied and subjected to inverse-FFT to output a signal representing the received affected radio signal. A variety of channel scattering functions can be used to characterize the response of a transmitter-receiver system to such atmospheric effects.
Date: December 31, 1991
Creator: Argo, P.E. & Fitzgerald, T.J.
Partner: UNT Libraries Government Documents Department

Electron yield XAFS study of evaporated Co/Pd multilayers with various thickness ratios of Co to Pd sublayers: Simulations of the Co K-edge XAFS and fourier transforms

Description: Electron-yield XAFS measurements using the NSLS were made on e-beam evaporated Co/Pd multilayers with various sublayer thicknesses and different thickness ratios of Co to Pd sublayers. The Co K-edge and the Pd K-edge XAFS data were obtained for the Co/Pd multilayers with sublayer thicknesses of 3{Angstrom}/ 4{Angstrom}, 15{Angstrom}/4{Angstrom}, 3{Angstrom}/15{Angstrom}, 2.1{Angstrom}/13.5{Angstrom}, and 2.2{Angstrom}/4.5{Angstrom}. Fourier transforms of Co K XAFS for most samples show a splitting of major peak, and the magnitude ratio of these split peaks varies systematically with the thickness ratio of the Pd sublayer to the Co sublayer, whereas the Fourier transforms of the Pd K XAFS for the same samples do not show a splitting of peaks. As a preliminary analysis, the Co K XAFS and the split peaks in the Fourier transform for the Co/Pd(3{Angstrom}/4{Angstrom}) case were simulated by using the FEFF calculations, and the Co K XAFS and the major peak in the fourier transform for the Co/Pd(15{Angstrom}/4{Angstrom}) case were also simulated consistently.
Date: November 1, 1992
Creator: Choi, M.; Joo, J. H.; Kim, S. K.; Kang, J. S.; Lee, Y. P.; Shin, S. C. et al.
Partner: UNT Libraries Government Documents Department

High-resolution signal synthesis for time-frequency distributions

Description: Bilinear time-frequency distributions (TFDs) offer improved resolution over linear nine-frequency representations (TFRs), but many TFDs are costly to evaluate and are not associated with signal synthesis algorithms. Recently, the spectrogram (SP) decomposition and weighted reversal correlator decomposition have been used to define low-cost, high-resolution TFDs. In this paper, we show that the vector-valued ``square-root`` of a TFD (VVTFR) provides a representational underpinning for the TFD. By synthesizing signals from modified VVTFRs, we define high-resolution signal synthesis algorithms associated with TFDs. The signal analysis and synthesis packages can be implemented as weighted sums of SP/short-time Fourier Transform signal analysis and synthesis packages, which are widely available, allowing the interested non-specialist easy access to high-resolution methods.
Date: March 1, 1993
Creator: Cunningham, G. S. & Williams, W. J.
Partner: UNT Libraries Government Documents Department

Blind deconvolution of two-dimensional complex data

Description: Inspired by the work of Lane and Bates on automatic multidimensional deconvolution, the authors have developed a systematic approach and an operational code for performing the deconvolution of multiply-convolved two-dimensional complex data sets in the absence of noise. They explain, in some detail, the major algorithmic steps, where noise or numerical errors can cause problems, their approach in dealing with numerical rounding errors, and where special noise-mitigating techniques can be used toward making blind deconvolution practical. Several examples of deconvolved imagery are presented, and future research directions are noted.
Date: January 1, 1994
Creator: Ghiglia, D. C. & Romero, L. A.
Partner: UNT Libraries Government Documents Department