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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Standard deviation of vertical two-point longitudinal velocity differences in the atmospheric boundary layer.

Statistical estimates of wind shear in the planetary boundary layer are important in the design of V/STOL aircraft, and for the design of the Space Shuttle. The data analyzed in this study consist of eleven sets of longitudinal turbulent velocity fluctuation time histories digitized at 0.2 sec intervals with approximately 18,000 data points per time history. The longitudinal velocity fluctuations were calculated with horizontal wind and direction data collected at the 18-, 30-, 60-, 90-, 120-, and 150-m levels. The data obtained confirm the result that Eulerian time spectra transformed to wave-number spectra with Taylor's frozen eddy hypothesis possess inertial-like behavior at wave-numbers well out of the inertial subrange.

Fichtl, G. H.↗
NASA NTRS1972

Properties of white light flares. I - Association with H-alpha flares and sudden frequency deviations.

All four large EUV bursts for which there were available concurrent white light observations of at least fair quality, were detected as white light flares. The rise times and maxima of the white light emissions coincided with rise times and maxima of the EUV bursts. The frequency of strong EUV bursts suggests that white light flares may occur at the rate of five or six per year near sunspot maximum. All of the white light flare areas coincided with intense bright areas of the H-alpha flares. These small areas appeared to be sources of high velocity ejecta in H-alpha. The white light flares occurred as several knots or patches of 2 to 15 arc-sec diameter, with bright cores perhaps less than 2 arc-sec diameter (1500 km). They preferred the outer penumbral borders of strong sunspots within 10 arc-sec of a longitudinal neutral line in the magnetic field.

Mcintosh, P. S.↗
NASA NTRS1974

Wide deviation phase modulator

Modulator produces phase-modulated waveform having high modulating linearity. Technique is inherently wideband with respect to carrier frequency and can operate over decade carrier frequency range without adjustments. Circuit performance is both mathematically predictable and highly reproducible.

Couch, R. H.↗
NASA NTRS1975

Axial-flow pump blade-element loss and deviation angle prediction

Determination of blade row fluid flow total-pressure loss and turning distributions in an axial-flow pump over a range of operating conditions is discussed. Included are a review of related research, correlations of pump rotor data and the results obtained using these data correlations with a computer program for pump off-design performance prediction. A number of the important problems related to determining fluid loss and turning information in a turbomachine and some of the consequences of imprecise prediction are pointed out.

Okiishi, T. H.↗
NASA NTRS1977

FM oscillator has improved deviation linearity

Device can be obtained by driving basic circuit through nonlinear FET input stage. Frequency of VCO is linearized with FET and total variance is varactor controlled. Experimental device exhibited linearity of better than plus or minus one percent for total frequency of plus or minus 10 millihertz.

Honnell, M. A.↗
NASA NTRS1981

Deviation-free Bragg cell frequency-shifting

A method is described of applying a variable frequency-shift to a laser beam, by means of Bragg cells, in which the direction of the output diffracted beam is unaffected by the magnitude of the applied shift. Applications of the technique to reference-beam and Doppler-difference forms of laser anemometry are discussed together with methods of obtaining increased dynamic range.

Abbiss, J. B.↗
NASA NTRS1981

The predicted deviation from the Z-sq dependence of the ion chamber and the Cerenkov counter response on the HEAO-3 experiment

The influence of the Mott cross section in producing a departure from a Z-sq dependence in the Heavy Nuclei Experiment instrument on board the HEAO-3 satellite is examined, along with the related problem of secondary electron energy transport through the instrument. A Monte Carlo method of electron transport and a modification of the Laulainen and Bichsel (1972) method were used to calculate energy deposition in the chamber, and corrections to the Cerenkov counter response were made. A maximum correction of a change of Z values of a -4 at Z equals 78 was found, and further calculations to determine the Mott cross sections for Z between 26-50 are indicated.

Derrickson, J. H.↗
NASA NTRS1986

Calculating Flow-Angle Deviation in Rotary Pumps

New mathematical formula calculates difference between angle of impeller blade and angle of flow. Formula used for inducers of mixed-flow pumps. With formula, calculations made more quickly and accurately than previously available formulas.

Meng, S. Y.↗
NASA NTRS1992

Noise-optimal control of HEMT LNA's for compensation of temperature deviations

Noise-optimal control of high-electron mobility transistor low noise amplifier (HEMT LNA) bias voltage and current values was achieved at room temperature. The performance metric maximized was the amplifier gain divided by the amplifier input noise temperature, G/T(sub e). Additionally, the feasibility of automating the initial determination of bias settings was demonstrated in the laboratory. Simulation models of an HEMT were developed from available measurement data, installed on a Sun SPARC 1 workstation, and used in investigating several optimization algorithms. Simple tracking-type algorithms, which follow changes in optimum settings if started at or near the global optimum point, produced the best performance. Implementation of the optimization algorithms was performed using a three-stage Field Effect Transistor (FET) LNA and an existing test apparatus. Software was written to control the bias settings of the first stage of the LNA and to perform noise and gain measurements by using the test apparatus. The optimization control was then integrated with existing test software to create a master test and optimization program for test apparatus use.

Maccarley, C.↗
NASA NTRS1991

An improved offset generator developed for Allan deviation measurement of ultra stable frequency standards

Measuring the performance of ultra stable frequency standards such as the Superconducting Cavity Maser Oscillator (SCMO) necessitates improvement of some test instrumentation. The frequency stability test equipment used at JPL includes a 1 Hz Offset Generator to generate a beat frequency between a pair of 100 MHz signals that are being compared. The noise floor of the measurement system using the current Offset Generator is adequate to characterize stability of hydrogen masers, but it is not adequate for the SCMO. A new Offset Generator with improved stability was designed and tested at JPL. With this Offset Generator and a new Zero Crossing Detector, recently developed at JPL, the measurement flow was reduced by a factor of 5.5 at 1 second tau, 3.0 at 1000 seconds, and 9.4 at 10,000 seconds, compared against the previous design. In addition to the new circuit designs of the Offset Generator and Zero Crossing Detector, tighter control of the measurement equipment environment was required to achieve this improvement. The design of this new Offset Generator are described, along with details of the environment control methods used.

R. L. Hamell↗
NASA NTRS1993

The cosmic-ray path length (age) distribution in the Galaxy - Experimental limits on the deviation from an exponential

A systematic examination is presented of the observational effects that can provide information on the departure of the cosmic-ray path length distribution (PLD) for propagation in the Galaxy from a simple exponential distribution. The possible physical causes for this departure are examined in order to set realistic limits on how well a simple exponential PLD actually describes the distribution of sources and propagation of cosmic rays in the galaxy. From the findings, it is argued that the cosmic ray source distribution must be quite uniform, probably on a scale of about 50 pc or less near the sun. Extending this uniformity to the Galaxy as a whole would imply more than 100,000 active sources. The cosmic-ray propagation can be described quite well by a leaky box model which is equivalent to observing the particles through a dense fog.

Webber, W. R.↗
NASA NTRS1993

Deviations from the straight line: Bumps (and grinds) in the collisionally evolved size distribution of asteroids

Dohnanyi established that the size distribution of a collisionally relaxed population is a power-law with a -3.5 slope (incremental diameter), provided that: (1) collisional parameters are independent of size and (2) there is no lower limit on the population size for shattering impacts. In the course of studying collisional effects over a wide range of asteroid sizes (cm up to hundreds of km range), we have investigated the consequences of relaxing the second condition, while maintaining the first one.

Davis, D. R.↗
NASA NTRS1998

Simple Refractometers for Index Measurements by Minimum Deviation Method from Far-ultraviolet to Near Infrared

The focal shift of an optical filter used in non-collimated light depends directly on substrate thickness and index of refraction. The HST Advanced Camera for Surveys (ACS) requires a set of filters whose focal shifts are tightly matched. Knowing the index of refraction for substrate glasses allows precise substrate thicknesses to be specified. Two refractometers have been developed at the Goddard Space Flight Center (GSFC) to determine the indices of refraction of materials from which ACS filters are made. Modem imaging detectors for the near infrared, visible, and far ultraviolet spectral regions make these simple yet sophisticated refractometers possible. A new technology, high accuracy, angular encoder also developed at GSFC makes high precision index measurement possible in the vacuum ultraviolet.

Leviton, Douglas B.↗
NASA NTRS1998

The Impact of Deviation from Michaelis-Menten Saturation on Mathematical Model Stability Properties

Based on purely abstract ecological theory, it has been argued that a system composed of two or more consumers competing for the same resource cannot persist. By analysis on a Monod format mathematical model, Hubble and others demonstrated that this assertion is true for all but very special cases of such competing organisms which are determined by an index formed by a grouping of. the parameters which characterize the biological processes of the competing organisms. In the laboratory, using a bioreactor, Hansen and Hubble obtained confirmatory results for several cases of two competing species, and they characterized it as "qualitative confirmation" of the assertion. This result is amazing, since the analysis required the exact equality of the hey index, and it seems certain that no pair of organism species could have exactly equal values. It is quite plausible, however, that pairs of organism species could have approximately equal indices, and the question of how different they could be and still have coexistence of the two (or more) presents itself. In this paper, the pursuit of this question and a compatible resolution is presented.

Blackwell, Charles↗