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LOW FREQUENCY AMPLIFIER IH-130-1

Description: The design of a transistorized d-c coupled amplifier having very good gain stability and low drift of the output d-c level is described. Low-frequency input signals from a low-impedance source are amplified by the system to an approximate peak-to-peak amplitude of 4 v. (J.R.D.)
Date: October 23, 1961
Creator: Llacer, J.
Partner: UNT Libraries Government Documents Department

The Crosscorrelation Method of Measuring System Dynamic Response

Description: The basic relations of the crosscorrelation method are presented; and variations of the method for dealing with practical cases for which the idealized relations are inaccurate due to finite experiment length, finite bandwidth of the input signal, and uncorrelated noise in the system response signal are discussed and demonstrated. (D.C.W.)
Date: November 1, 1963
Creator: Balcomb, J. D.
Partner: UNT Libraries Government Documents Department

INFORMATION, COMMUNICATION, AND LANGUAGE

Description: A lecture delivered at Sandia Corp., Albuquerque, N. Mex., June 18, 1958. A discussion of information exchange theory is presented. Semantics in communications are examined, and the use of symbols in thinking and presentaion are discussed in some detail. (J.R.D.)
Date: July 1, 1959
Creator: Hammer, P.C.
Partner: UNT Libraries Government Documents Department

SERVOMECHANISMS WITH FORCE FEEDBACK

Description: A class of linear proportional servomechanisms is examined in which an electrical signal proportional to output force is used to improve performance. The effect of this "force feedback" on a positional servomechanism is analyzed as well as the effect on a special type of servomechanism which reflects load forces back to the input. This latter type of servomechanism is called "force reflecting." Laboratory models of these servormechanisms were designed and constructed, and experimental data are presented in support of the analysis. (auth)
Date: May 1, 1960
Creator: Arzbaecher, R.C.
Partner: UNT Libraries Government Documents Department

Privacy Preserving EEG-based Authentication Using Perceptual Hashing

Description: The use of electroencephalogram (EEG), an electrophysiological monitoring method for recording the brain activity, for authentication has attracted the interest of researchers for over a decade. In addition to exhibiting qualities of biometric-based authentication, they are revocable, impossible to mimic, and resistant to coercion attacks. However, EEG signals carry a wealth of information about an individual and can reveal private information about the user. This brings significant privacy issues to EEG-based authentication systems as they have access to raw EEG signals. This thesis proposes a privacy-preserving EEG-based authentication system that preserves the privacy of the user by not revealing the raw EEG signals while allowing the system to authenticate the user accurately. In that, perceptual hashing is utilized and instead of raw EEG signals, their perceptually hashed values are used in the authentication process. In addition to describing the authentication process, algorithms to compute the perceptual hash are developed based on two feature extraction techniques. Experimental results show that an authentication system using perceptual hashing can achieve performance comparable to a system that has access to raw EEG signals if enough EEG channels are used in the process. This thesis also presents a security analysis to show that perceptual hashing can prevent information leakage.
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Date: December 2016
Creator: Koppikar, Samir Dilip
Partner: UNT Libraries

From shock response spectrum to temporal moments and vice-versa

Description: Temporal momerils have been used in engineering mechanics to condense the information contained in the shock response spectrum into a few scalar quantities. This paper presents an application of temporal moments to the propagation of an explosive-driven shock wave through an assembly of metallic parts. For this particular application, it is shown that temporal moments characterize the response of the system better than other features traditionally used in the analysis of nonlinear, transient events, such as the peak response or 10% duration of event. The inverse problem is also illustrated: the original, time-domain signals and their shock response spectra can be reconstructed from the temporal moments. This property makes temporal moments features of choice for the analysis of experimental data or the development of numerical models because they are low-dimensional quantities; they capture transient dynamics well; and they can be used to re-generate the original time signals.
Date: January 1, 2002
Creator: Hemez, F. M. (Fran├žois M.) & Doebling, S. W. (Scott W.)
Partner: UNT Libraries Government Documents Department

Evaluation of signal processing techniques for the analysis of large civil structures.

Description: Several new methods of determining change in the data signature of a large Cable-Stayed bridge are examined and compared. Two sets of data, one taken in September 1995, and the second in June 2000 are studied. Structural changes are investigated using several techniques; (1) Modal behavior in the .3 to 3 Hz range is investisated using Transmissibility FRFs and the Random Decrement Method, (2) Quasi Periodic behavior in the 3 to 30 Hz frequency range is observed in several tests. Potential causes and characteristics of this behavior are investigated. (3) Some methods of non-linear analysis are applied to the bridge data and changes in behavior are evaluated. Capability and concerns with each method are addressed in conjunction with physical ambient excitation data and its signal properties.
Date: January 1, 2001
Creator: Hunter, N. F. (Norman F.) & Schultze, J. F. (John F.)
Partner: UNT Libraries Government Documents Department

Optimal dynamic detection of explosives

Description: The detection of explosives is a notoriously difficult problem, especially at stand-off distances, due to their (generally) low vapor pressure, environmental and matrix interferences, and packaging. We are exploring optimal dynamic detection to exploit the best capabilities of recent advances in laser technology and recent discoveries in optimal shaping of laser pulses for control of molecular processes to significantly enhance the standoff detection of explosives. The core of the ODD-Ex technique is the introduction of optimally shaped laser pulses to simultaneously enhance sensitivity of explosives signatures while reducing the influence of noise and the signals from background interferents in the field (increase selectivity). These goals are being addressed by operating in an optimal nonlinear fashion, typically with a single shaped laser pulse inherently containing within it coherently locked control and probe sub-pulses. With sufficient bandwidth, the technique is capable of intrinsically providing orthogonal broad spectral information for data fusion, all from a single optimal pulse.
Date: January 1, 2009
Creator: Moore, David Steven; Mcgrane, Shawn D; Greenfield, Margo T; Scharff, R J; Rabitz, Herschel A & Roslund, J
Partner: UNT Libraries Government Documents Department

Empirical constraints on the first stars and quasars

Description: Empirical studies of the first generation of stars and quasars in the Universe will likely become feasible over the next decade. The Next Generation Space Telescope will provide direct imaging and photometry of sub-galactic objects at z approximately greater than 10, while microwave anisotropy experiments, such as MAP or Planck, will set constraints on the ionization history of the intergalactic medium due to these sources. We describe the expected signals that will be detectable with these future instruments.
Date: December 1, 1998
Creator: Loeb, Zoltan Haiman and Avi
Partner: UNT Libraries Government Documents Department

Implementation guidance for industrial-level security systems using radio frequency alarm links

Description: Spread spectrum (SS) RF transmission technologies have properties that make the transmitted signal difficult to intercept, interpret, and jam. The digital code used in the modulation process results in a signal that has high reception reliability and supports multiple use of frequency bands and selective addressing. These attributes and the relatively low installation cost of RF systems make SSRF technologies candidate for communications links in security systems used for industrial sites, remote locations, and where trenching or other disturbances of soil or structures may not be desirable or may be costly. This guide provides a description of such a system and presents implementation methods that may be of engineering benefit.
Date: July 12, 1996
Creator: Swank, R.G.
Partner: UNT Libraries Government Documents Department

Event identification from seismic/magnetic feature vectors: a comparative study

Description: The event identification problem plays a large role in the application of unattended ground sensors to the monitoring of borders and checkpoints. The choice of features and methods for classifying features affects how accurately these classifications are made. Finding features which reliably distinguish events of interest may require measurements based on separate physical phenomena. Classification methods include neural net versus fuzzy logic approaches, and within the neural category, different architectures and transfer functions for reaching decisions. This study examines ways of optimizing feature sets and surveys common techniques for classifying feature vectors corresponding to physical events. We apply each technique to samples of existing data, and compare discrimination attributes. Specifically, we calculate the confusion matrices for each technique applied to each sample dataset, and reduce them statistically to scalar scores. In addition, we gauge how the accuracy of each method is degraded by reducing the feature vector length by one element. Finally, we gather rough estimates of the relative cpu performance of the forward prediction algorithms.
Date: April 1, 1997
Creator: Wolford, J. K.
Partner: UNT Libraries Government Documents Department

Propagation analysis of a 900 MHz spread spectrum centralized traffic signal control system.

Description: The objective of this research is to investigate different propagation models to determine if specified models accurately predict received signal levels for short path 900 MHz spread spectrum radio systems. The City of Denton, Texas provided data and physical facilities used in the course of this study. The literature review indicates that propagation models have not been studied specifically for short path spread spectrum radio systems. This work should provide guidelines and be a useful example for planning and implementing such radio systems. The propagation model involves the following considerations: analysis of intervening terrain, path length, and fixed system gains and losses.
Date: May 2006
Creator: Urban, Brian L.
Partner: UNT Libraries

Technique for reduction of coherence function bias error

Description: The bias error in the coherence function is found to arise from the calculation of the square magnitude of the cross-power spectral density when the real and imaginary components are not converged. Therefore, the bias error of the coherence function can be decreased significantly without averaging more data blocks if the variance of the real and imaginary components are reduced by fitting the spectra of these separate components to an appropriate model.
Date: January 1, 1984
Creator: King, W.T.
Partner: UNT Libraries Government Documents Department