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Articles 1 - 7 of 7

Full-Text Articles in Engineering

Development And Application Of Spread-Spectrum Ultrasonic Evaluation Technique , Jahangir Khan Kayani Jan 1996

Development And Application Of Spread-Spectrum Ultrasonic Evaluation Technique , Jahangir Khan Kayani

Retrospective Theses and Dissertations

A new approach to ultrasonic NDE called spread-spectrum ultrasonic evaluation (SSUE) is investigated. It regards the ultrasonic nondestructive evaluation as an acoustic-impulse-response estimation and characterization problem. This problem has been compared with the analogous problems of radio-detection-and-ranging from communications field and the seismic exploration problem of geophysics. Out of the various options for the impulse response estimation, the continuous pseudorandom signal correlation method has been shown to be the optimum for peak-power limited systems such as the ultrasonic NDE systems. The problem of self-noise and its consequences in pseudorandom correlation systems is investigated, followed by the development of various optimum ...


Invariance Transformations For Processing Nde Signals , Shreekanth Ammanji Mandayam Jan 1996

Invariance Transformations For Processing Nde Signals , Shreekanth Ammanji Mandayam

Retrospective Theses and Dissertations

The ultimate objective in nondestructive evaluation (NDE) is the characterization of materials, on the basis of information in the response from energy/material interactions. This is commonly referred to as the "inverse problem." Inverse problems are in general ill-posed and full analytical solutions to these problems are seldom tractable. Pragmatic approaches for solving them employ a constrained search technique by limiting the space of all possible solutions. A more modest goal is therefore to use the received signal for characterizing defects in objects in terms of the location, size and shape. However, the NDE signal received by the sensors is ...


Projection Based Edge Recovery In Low Bit Rate Vector Quantizers , Ajai Narayan Jan 1996

Projection Based Edge Recovery In Low Bit Rate Vector Quantizers , Ajai Narayan

Retrospective Theses and Dissertations

Data compression is probably the single most important factor in every information service that is being visualized and proposed by engineers. The effectiveness of such services are dependent upon achievable compression of real time speech and video signals. Several approaches to signal encoding have been proposed and realized, each with its unique advantages and costs. Large compression ratios can only be achieved through lossy source encoding methods. One such method is Vector Quantization (VQ);The lossy nature of such encoders imply that the process of encoding is non invertible. At low bit rates, lossy compression with conventional decoders (realized as ...


Pattern Recognition And Image Processing Of Infrared Astronomical Satellite Images , Lun Xiong He Jan 1996

Pattern Recognition And Image Processing Of Infrared Astronomical Satellite Images , Lun Xiong He

Retrospective Theses and Dissertations

The Infrared Astronomical Satellite (IRAS) images with wavelengths of 60 [mu] m and 100 [mu] m contain mainly information on both extra-galactic sources and low-temperature interstellar media. The low-temperature interstellar media in the Milky Way impose a "cirrus" screen of IRAS images, especially in images with 100 [mu] m wavelength. This dissertation deals with the techniques of removing the "cirrus" clouds from the 100 [mu] m band in order to achieve accurate determinations of point sources and their intensities (fluxes). We employ an image filtering process which utilizes mathematical morphology and wavelet analysis as the key tools in removing the ...


Signal Estimation Using H [Infinity Sign] Criteria , Sanjeev Tavathia Jan 1996

Signal Estimation Using H [Infinity Sign] Criteria , Sanjeev Tavathia

Retrospective Theses and Dissertations

In many signal processing and communication (SPC) applications we require to estimate signal corrupted by channel and additive noise. Optimal linear filters and predictors are used to recover signal from given observed (corrupted) signal. Kalman and Wiener filters are commonly used as optimal filters. These filters minimize the mean square error (MSE) or variance of the output error. The minimization require exact knowledge of input signal and noise power spectral density (PSD). Therefore, the performance of Kalman or Wiener filters degrade if the input signal and noise statistics is changing with time and is not known a priori. In many ...


Blind Adaptive Near-Far Resistant Receivers For Ds/Cdma Multi-User Communication Systems , Sang Chul Park Jan 1996

Blind Adaptive Near-Far Resistant Receivers For Ds/Cdma Multi-User Communication Systems , Sang Chul Park

Retrospective Theses and Dissertations

Code-division multiple-access (CDMA) systems have multiple users that simultaneously share a common channel using pre-assigned signature waveforms. The conventional receiver suffers from the near-far problem when the received signal power of the desired user is weaker than those of the other users. Optimum and suboptimum multi-user detectors outperform the conventional receiver at the expense of a significant increase in complexity and need for side-information about interfering users. Complexity of these detectors may not be acceptable for many practical applications and communication security may restrict the distribution of all users' signature waveforms to all the receivers;For a single-user receiver, the ...


Analysis And Synthesis Of Nonlinear Control Systems , Shan Lin Jan 1996

Analysis And Synthesis Of Nonlinear Control Systems , Shan Lin

Retrospective Theses and Dissertations

In this dissertation, regular nonlinear control systems of the form .x=X0(x)+[sigma]spi=1m uiXi(x) are considered. Necessary and sufficient conditions are given for a point to be reached from one of its entire neighborhoods in finite time by a piece-wise analytic feedback controller. Under such a feedback controller, the domain of attraction of the point is maximal. In particular, necessary and sufficient conditions on stabilization of a point or a periodic orbit in two dimension flat space are given. Moreover, practical examples are discussed and some interesting results are derived. Finally, when one dimensional systems are ...