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At least 199 records · Page 11

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NASA NTRS1971

DALG: A program for test pattern generation in combinational logical circuits

A user's manual for a computer program DALG which generates test patterns for detecting faults in combinational logic circuits containing up to 200 logical gates is presented. The gates may be of logical types AND, OR, NAND, NOR, NOT, or Exclusive OR is presented. The faults may be any one gate or input struck at a fixed value (0 or 1). In addition to test pattern generation DALG will also determine whether or not the given test pattern will detect given faults in a circuit. Sample problems are given along with input data sheets and printed output to illustrate the capabilities of the program.

Source record↗

NASA NTRS1972

Mask and pattern characteristics

The use of the mask and pattern facility to include information on equipment accuracy, limitations, and pattern making capabilities is discussed. An insight is provided into potential areas of pattern applications, the sequence of mask making, as well as possible inputs and outputs available to the user.

Routh, D. E.↗

NASA NTRS1971

Directive gain of circular Taylor patterns.

The practicality of various classes of planar aperture distributions in high-gain antenna design is discussed, and optimal circular Taylor distributions are illustrated. In particular, the directive gain of circular Taylor patterns is determined. It is shown that so-called optimum patterns - i.e., uniform sidelobes in all planes, are severly limited for planar apertures because of excessive sidelobe power. The optimum directive gain of the circular Taylor pattern with a given sidelobe level can be obtained by appropriate design.

Rudduck, R. C.↗

NASA NTRS1973

Urban street patterns detectable from ERTS-1

The author has identified the following significant results. The major street patterns in Lincoln, Nebraska, are detectable on the January 24, 1973 ERTS MSS-4 image. To further study and identify the street patterns, a 3x Polaroid enlargement was made of the city from the image. An overlay of the enlargement was used to map the street patterns, with reference to the original image for clarity. The technique seems to be adaptable for updating standard road maps.

Morain, S. A.↗

NASA NTRS1973

Acoustic radiation patterns for a source in a hard-walled unflanged circular duct

Acoustic radiation patterns are measured over a 320 deg arc for a point source in a finite length, hard walled, unflanged circular duct. The measured results are compared with computed results which are based on the Wiener-Hopf solution for radiation from a semi-infinite unflanged duct. Measurements and computations are presented for frequencies slightly below and slightly above each of the first four higher order radial mode cutoff frequencies. It is found that the computed and measured patterns show better agreement below the mode cut-off frequencies than above and that the agreement is better at lower frequencies that at higher frequencies. The computed radiation patterns do not show fine lobes which are caused by diffraction from the back end of the duct.

Holm, R. G.↗

NASA NTRS1974

Fault pattern at the northern end of the Death Valley - Furnace Creek fault zone, California and Nevada

The author has identified the following significant results. The pattern of faulting associated with the termination of the Death Valley-Furnace Creek Fault Zone in northern Fish Lake Valley, Nevada was studied in ERTS-1 MSS color composite imagery and color IR U-2 photography. Imagery analysis was supported by field reconnaissance and low altitude aerial photography. The northwest-trending right-lateral Death Valley-Furnace Creek Fault Zone changes northward to a complex pattern of discontinuous dip slip and strike slip faults. This fault pattern terminates to the north against an east-northeast trending zone herein called the Montgomery Fault Zone. No evidence for continuation of the Death Valley-Furnace Creek Fault Zone is recognized north of the Montgomery Fault Zone. Penecontemporaneous displacement in the Death Valley-Furnace Creek Fault Zone, the complex transitional zone, and the Montgomery Fault Zone suggests that the systems are genetically related. Mercury mineralization appears to have been localized along faults recognizable in ERTS-1 imagery within the transitional zone and the Montgomery Fault Zone.

Liggett, M. A.↗

NASA NTRS1974

An integral equation formulation for predicting radiation patterns of a space shuttle annular slot antenna

An integral equation formulation is applied to predict pitch- and roll-plane radiation patterns of a thin VHF/UHF (very high frequency/ultra high frequency) annular slot communications antenna operating at several locations in the nose region of the space shuttle orbiter. Digital computer programs used to compute radiation patterns are given and the use of the programs is illustrated. Experimental verification of computed patterns is given from measurements made on 1/35-scale models of the orbiter.

Jones, J. E.↗

NASA NTRS1974

Application of an integral equation formulation to the prediction of space shuttle annular slot antenna radiation patterns

Pitch and roll plane radiation patterns computed by use of an integral equation formulation are presented for a space shuttle annular slot communications antenna. The excellent agreement between computed patterns and experimental patterns obtained from 1/35 scale models supports the use of this method as a design tool for similar spacecraft/aircraft antenna applications.

Jones, J. E.↗

NASA NTRS1974

Experimental investigation of the cornering characteristics of 18 by 5.5, type 7, aircraft tires with different tread patterns

The characteristics, which include the cornering-force and drag-force friction coefficients and self-alining torque, were obtained on dry, damp, and flooded runway surfaces over a range of yaw angles from 0 deg to 12 deg and at ground speeds from approximately 5 to 90 knots. The results indicate that a tread pattern with pinholes in the ribs reduces the tire cornering capability at high yaw angles on a damp surface but improves cornering on a dry surface. A tread pattern which has transverse grooves across the entire width of the tread improves the tire cornering performance slightly at high speeds on the flooded runway surface. The cornering capability of all the tires is degraded at high ground speeds by thin film lubrication and/or tire hydroplaning effects. Alterations to the conventional tread pattern provide only marginal improvements in the tire cornering capability which suggests that runway surface treatments may be a more effective way of improving aircraft ground performance during wet operations.

Dreher, R. C.↗

NASA NTRS1975

Antenna pattern corrections to microwave radiometer temperature calculations

In making microwave radiometer calculations of sea surface temperature, it is necessary to consider the errors resulting from the antenna radiation pattern. This is especially true for antennas with high sidelobes that are scanned in viewing angle and for antennas with high cross-polarized components. It is concluded that the plane wave brightness temperature is not by itself sufficient to describe the true radiometer temperature of the sea surface. This discrepancy can be attributed to one or more of the following: failure to use the total radiation pattern, error in determining the sea surface dielectric constant, error in sky model profile, or radiation pattern spillover onto water surroundings.

Beck, F. B.↗

NASA NTRS1976

Investigation of environmental change pattern in Japan: Investigation of variations in the prominent oceanic current, Kuroshio

The author has identified the following significant results. In the print of MSS band 4 of Shiono Misaki and Ise taken by LANDSAT on 11 September 1975, different water masses can be recognized distinctly. At 35 miles off Shiono Misaki, a vortex pattern is found which has an ellipsoidal shape with a diameter of 30 miles and appears to rotate counterclockwise. In Ise, water masses were found spreading widely along the coast from the mouth of Ise Bay. The temperature of sea surface obtained from sea truth shows almost a uniform pattern. The distribution of surface salinity and transparency shows a distinct pattern.

Maruyasu, T.↗

NASA NTRS1976

Analysis of aircraft wing-mounted antenna patterns

High frequency radiation patterns of aircraft wing mounted antennas are analyzed. Basic antenna types using ray optical techniques are studied. The aircraft is modelled in its most basic form so that this study is applicable to general type aircraft. The fuselage is modelled as a perfectly conducting finite elliptic cylinder. The wings and horizontal and vertical stabilizers are modelled as perfectly conducting "n" sided flat plates that can be arbitrarily attached to the fuselage or to themselves. The antenna locations are assumed to be on the surfaces of the wings at locations removed from engines and stores such that these effects are negligible. Volumetric patterns are calculated for several aircraft. The validity of the solution is shown by comparing the results against scale model measurements. The application of this solution to practical airborne antenna problems has shown its versatility in designing antennas and predicting their radiation patterns in an accurate and efficient manner.

Marhefka, R. J.↗

NASA NTRS1975

Signatures analysis and recognition of severe weather patterns

The feasibility of designing a prediction and warning system for severe weather conditions on the basis of time series analysis and pattern recognition is examined. Data accumulated by Taylor (1972) on the rate of atmospherics produced by severe, tornado-producing storms that struck Oklahoma City during April 1970 are analyzed by time series analysis and pattern recognition. Power spectra, cross-power spectra, coherence functions, and time-varying patterns are analyzed.

Wang, P. P.↗

NASA NTRS1976

A method of distortion pattern synthesis for high response data screening

An empirically derived method of estimating maximum levels of instantaneous inlet total pressure distortion from steady state measurements is presented. The estimation procedure uses steady state total pressure and root mean square turbulent pressure data measurements to synthesize instantaneous distortion patterns. The synthesis method is tailored to intensify distortion patterns in a manner consistent with the characteristics of the particular index to be used in evaluating inlet/engine compatability. The maximum expected value of distortion, a statistically determined function of the length of time of inlet operation, is used to constrain the amount of pattern intensification. Comparison with an independent set of data is presented for verification of the synthesis method.

King, R. W.↗

NASA NTRS1977

Multimodal far-field acoustic radiation pattern: An approximate equation

The far-field sound radiation theory for a circular duct was studied for both single mode and multimodal inputs. The investigation was intended to develop a method to determine the acoustic power produced by turbofans as a function of mode cut-off ratio. With reasonable simplifying assumptions the single mode radiation pattern was shown to be reducible to a function of mode cut-off ratio only. With modal cut-off ratio as the dominant variable, multimodal radiation patterns can be reduced to a simple explicit expression. This approximate expression provides excellent agreement with an exact calculation of the sound radiation pattern using equal acoustic power per mode.

Rice, E. J.↗

NASA NTRS1977

Structural lineament and pattern analysis of Missouri, using LANDSAT imagery

The author has identified the following significant results. Major linear, circular, and arcuate traces were observed on LANDSAT imagery of Missouri. Lineaments plotted within the state boundaries range from 20 to nearly 500 km in length. Several extend into adjoining states. Lineaments plots indicate a distinct pattern and in general reflect structural features of the Precambrian basement of the platform. Coincidence of lineaments traced from the imagery and known structural features in Missouri is high, thus supporting a causative relation between them. The lineament pattern apparently reveals a fundamental style of the deformation of the intracontinental craton. Dozens of heretofore unknown linear features related to epirogenic movements and deformation of this segment of the continental crust were delineated. Lineaments and mineralization are interrelated in a geometrically classifiable pattern.

Martin, J. A.↗

NASA NTRS1976

Interference in astronomical speckle patterns

Astronomical speckle patterns are examined in an atmospheric-optics context in order to determine what kind of image quality is to be expected from several different imaging techniques. The model used to describe the instantaneous complex field distribution across the pupil of a large telescope regards the pupil as a deep phase grating with a periodicity given by the size of the cell of uniform phase or the refractive index structure function. This model is used along with an empirical formula derived purely from the physical appearance of the speckle patterns to discuss the orders of interference in astronomical speckle patterns.

Breckinridge, J. B.↗

NASA NTRS1976

Concept and analytical basis for revistas - A fast, flexible computer/graphic system for generating periodic satellite coverage patterns

The generation of satellite coverage patterns is facilitated by three basic strategies: use of a simplified physical model, permitting rapid closed-form calculation; separation of earth rotation and nodal precession from initial geometric analyses; and use of symmetries to construct traces of indefinite length by repetitive transposition of basic one-quadrant elements. The complete coverage patterns generated consist of a basic nadir trace plus a number of associated off-nadir traces, one for each sensor swath edge to be delineated. Each trace is generated by transposing one or two of the basic quadrant elements into a circle on a nonrotating earth model sphere, after which the circle is expanded into the actual 'helical' pattern by adding rotational displacements to the longitude coordinates. The procedure adapts to the important periodic coverage cases by direct insertion of the characteristic integers N and R (days and orbital revolutions, respectively, per coverage period).

King, J. C.↗