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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Derivation of linearized transfer functions for switching-mode regulations. Phase A: Current step-up and voltage step-up converters

Small-signal models are derived for the power stage of the voltage step-up (boost) and the current step-up (buck) converters. The modeling covers operation in both the continuous-mmf mode and the discontinuous-mmf mode. The power stage in the regulated current step-up converter on board the Dynamics Explorer Satellite is used as an example to illustrate the procedures in obtaining the small-signal functions characterizing a regulated converter.

Wong, R. C.↗
NASA NTRS1984

LANDSAT-4 Thematic Mapper Modulation Transfer Function (MTF) evaluation

Results of MTF analysis of imagery of the San Mateo Bridge are consistent on two TM image dates for bands 4,5, and 7. There are indications that bands 1, 2, and 3 suffer from low image contrast, and consequently low signal to noise in the derived MTFs. The two image analysis produced reasonable results along +45 deg and -45 deg azimuths in the 2-D MTF, but poor results along the 0 deg and 90 deg azimuths. The effective instantaneous field of view is given for each band, and the image contrast for water and the bridge are compared. Graphs show overall TM system MTFs.

Schowengerdt, R.↗
NASA NTRS1984

LANDSAT-4 Thematic Mapper Modulation Transfer Function (MFT) evaluation

The techniques used in the two-image comparison of TM data and 7-meter aerial data acquired over San Francisco on August 12, 1983 during LANDSAT 4 operation were refined. Analysis of one area is complete and reported herein; analysis of a second area is in progress. A large test target for measurement of the LANDSAT 5 MTF at the White Sands Missile Range, New Mexico was constructed.

Schowengerdt, R.↗
NASA NTRS1985

Forward and reverse transfer function model synthesis

A process for synthesizing a mathematical model for a linear mechanical system using the forward and reverse Fourier transform functions is described. The differential equation for a system model is given. The Bode conversion of the differential equation, and the frequency and time-domain optimization matching of the model to the forward and reverse transform functions using the geometric simplex method of Nelder and Mead (1965) are examined. The effect of the window function on the linear mechanical system is analyzed. The model is applied to two examples; in one the signal damps down before the end of the time window and in the second the signal has significant energy at the end of the time window.

Houghton, J. R.↗
NASA NTRS1988

Threshold computations for detection of failures in SISO systems with transfer function errors

The author considers the problem of detecting failures in SISO systems using analytic redundancy concepts. Since the models used are subject to error, a method of determining the detection thresholds that account for these errors is sought. The methodology presented utilizes a straightforward application of Parseval's relation to develop a threshold computation that is performed online as a function of the input signal. The threshold is set at a quiescent value to account for sensor noise and is adjusted (upward) according to the activity of the input signal. An application to detection of actuator failures is presented.

Weiss, Jerold L.↗
NASA NTRS1990

Thermospheric gravity waves - Observations and interpretation using the transfer function model (TFM)

This paper presents some numerical experiments performed with the TFM to study the various wave components excited in the auroral regions that propagate through the thermosphere and lower atmosphere, and to demonstrate the properties of realistic source geometries. The model is applied to the interpretation of satellite measurements, and gravity waves seen in the thermosphere of Venus are discussed. Gravity waves are prominent in the terrestrial thermosphere polar region and can be excited by perturbations in Joule heating and Lorentz force due to magnetospheric processes. Observations from the Dynamics Explorer-2 satellite are used to illustrate the complexity of the phenomenon and to review the TFM that is utilized.

Mayr, H. G.↗
NASA NTRS1992

Users manual for program ADMIT: Admittance and pressure transfer function developed for use on a PC computer

The piping in a liquid rocket can assume complex configurations due to multiple tanks, multiple engines, and structures that must be piped around. The capability to handle some of these complex configurations have been incorporated into the ADMIT code. The capability to modify the input on line has been implemented. The configurations allowed include multiple tanks, multiple engines, the splitting of a pipe into unequal segments going to different (or the same) engines. This program will handle the following type elements: straight pipes, bends, inline accumulators, tuned stub accumulators, Helmholtz resonators, parallel resonators, pumps, split pipes, multiple tanks, and multiple engines.

Armstrong, Wilbur C.↗
NASA NTRS1954

Application of several methods for determining transfer functions and frequency response of aircraft from flight data

In the process of analyzing the longitudinal frequency-response characteristics of aircraft, information on some of the methods of analysis has been obtained by the Langley Aeronautical Laboratory of the National Advisory Committee for Aeronautics. In the investigation of these methods, the practical applications and limitations were stressed. In general, the methods considered may be classed as: (1) analysis of sinusoidal response, (2) analysis of transient response as to harmonic content through determination of the Fourier integral by manual or machine methods, and (3) analysis of the transient through the use of least-squares solutions of the coefficients of an assumed equation for either the transient time response or frequency response (sometimes referred to as curve-fitting methods). (author)

Eggleston, John M↗
NASA NTRS1992

Head related transfer function pseudo-stereophony

An apparatus for producing pseudo-stereophonic sound from a monaural signal is discussed. The apparatus includes a monaural source that has a speaker placed in an anechoic room and has a sound output generated by the monaural signal. The second, third, fourth, and fifth speakers are placed in the anechoic room symmetrically about a listener. The monaural signal from the source is processed to output processed signals to each of the second, third, fourth, and fifth speakers, each speaker producing a sound output corresponding to the received processed signal. A pair of microphones is placed in the ears of the listener for receiving the sound outputs of the first, second, third, fourth, and fifth speakers and producing two differentiated audio channels.

Begault, Durand R.↗