Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “DISTRIBUTION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Plume mass flow and optical damage distributions for an MMH/N2O4 RCS thruster

The data obtained from two recent experiments conducted in a continuing series of experiments at the Lewis Research Center into the contamination characteristics of a 5-pound thrust MMH/N2O4 engine are presented. The primary objectives of these experiments were to establish the angular distribution of condensible exhaust products within the plume and the corresponding optical damage angular distribution of transmitting optical elements attributable to this contaminant. The plume mass flow distribution was measured by five quartz crystal microbalances (QCM's) located at the engine axis evaluation. The fifth QCM was located above the engine and 15 deg behind the nozzle exit plane. The optical damage was determined by ex-situ transmittance measurements for the wavelength range from 0.2 to 0.6 microns on 2.54 cm diameter fused silica discs also located at engine centerline elevation. Both the mass deposition and optical damage angular distributions followed the expected trend of decreasing deposition and damage as the angle between sensor or sample and the nozzle axis increased. A simple plume gas flow equation predicted the deposition distribution reasonably well for angles of up to 55 degrees. The optical damage measurements also indicated significant effects at large angles.

Spisz, E. W.↗
NASA NTRS1972

Heat transfer and pressure distributions at M equals 8 on 0.029 scale models of the Viking entry vehicle

An investigation in the Langley Research Center Mach-8 Variable Density Hypersonic Tunnel was made of the pressure distributions and heat transfer rate distributions on two 0.029 scale Viking Entry Vehicle models. Comparable ranges of test Reynolds number were exercised for the two tests between run conditions around 4 million and conditions of about 1.6 million. At angles of attack less than 20 degrees the pressure ratio distribution referenced to stagnation pressure appeared invariant with Reynolds number. Increasing angle of attack results in a flatter distribution of both the windward and leeward pressure distributions; in addition, the stagnation point shifted into the windward plane. A subsequent rise in the heating rate profile on the leeward side with further increase in angle of attack is attributed to boundary layer natural transition to turbulent flow. Schlieren photographs were taken for flow field visualization and to correct model angle of attack.

Faye-Petersen, R.↗
NASA NTRS1973

Effect of photogrammetric reading error on slope-frequency distributions

The effect of reading error on two hypothetical slope frequency distributions and two slope frequency distributions from actual lunar data in order to ensure that these errors do not cause excessive overestimates of algebraic standard deviations for the slope frequency distributions. The errors introduced are insignificant when the reading error is small and the slope length is large. A method for correcting the errors in slope frequency distributions is presented and applied to 11 distributions obtained from Apollo 15, 16, and 17 panoramic camera photographs and Apollo 16 metric camera photographs.

Moore, H. J.↗
NASA NTRS1974

An extension of the Laplace transform to Schwartz distributions

A characterization of the Laplace transform is developed which extends the transform to the Schwartz distributions. The class of distributions includes the impulse functions and other singular functions which occur as solutions to ordinary and partial differential equations. The standard theorems on analyticity, uniqueness, and invertibility of the transform are proved by using the characterization as the definition of the Laplace transform. The definition uses sequences of linear transformations on the space of distributions which extends the Laplace transform to another class of generalized functions, the Mikusinski operators. It is shown that the sequential definition of the transform is equivalent to Schwartz' extension of the ordinary Laplace transform to distributions but, in contrast to Schwartz' definition, does not use the distributional Fourier transform. Several theorems concerning the particular linear transformations used to define the Laplace transforms are proved. All the results proved in one dimension are extended to the n-dimensional case, but proofs are presented only for those situations that require methods different from their one-dimensional analogs.

Price, D. R.↗
NASA NTRS1974

Behaviour of ion velocity distributions for a simple collision model

Calculation of the ion velocity distributions for a weakly ionized plasma subjected to crossed electric and magnetic fields. An exact solution to Boltzmann's equation has been obtained by replacing the Boltzmann collision integral with a simple relaxation model. At altitudes above about 150 km, where the ion collision frequency is much less than the ion cyclotron frequency, the ion distribution takes the shape of a torus in velocity space for electric fields greater than 40 mV/m. This shape persists for one to two hours after application of the electric field. At altitudes where the ion collision and cyclotron frequencies are approximately equal (about 120 km), the ion velocity distribution is shaped like a bean for large electric field strengths. This bean-shaped distribution persists throughout the lifetime of ionospheric electric fields. These highly non-Maxwellian ion velocity distributions may have an appreciable affect on the interpretation of ion temperature measurements.

St-Maurice, J.-P.↗
NASA NTRS1974

Efficient stream distributions in radiative transfer theory

This paper discusses a new, computationally-efficient method for approximating the integro-differential equation of radiative transfer with a finite set of coupled differential equations for discrete streams. The method uses recommended spatial distributions of streams that are quite different from those typically used in that they are based on the symmetry of several regular Platonic solids. To facilitate the use of such distributions, an explicit, one-parameter relationship between the physical radiance and the abstract stream is formulated. The parameter is used to determine the minimum number of streams required in the radiative transfer model. Accuracy and computational efficiency are shown to be served best by choosing a stream distribution that is invariant to a large number of three space rotations. For various values of the above-mentioned parameter, the resulting recommended stream distribution is shown to be more computationally efficient than more conventional stream distributions. Finally, the incorporation of polarization in the stream definition is described.

Whitney, C.↗
NASA NTRS1973

The abundance and age distributions of 500 F stars in the solar neighbourhood

The uvby catalog of Perry has been used, in conjunction with theoretical uvby colors and stellar evolutionary tracks, to obtain the metal abundance distribution and age distribution of F and G type dwarf stars within 100 pc of the sun. Eighty-three per cent of stars with spectral type F5-G2 have metal content within a factor of 2.5 of the solar abundance, and only 2% have less than one-quarter the solar abundance. The metal abundance distribution, which contains more metal-rich stars than found in previous investigations of F and G dwarfs, has also been compared with the observed metal abundance distribution of G and K giants and the model galaxy calculations of Truran and Cameron (1971). A comparison of the age distribution with evolutionary calculations implies that the rate of star formation in the galaxy may not have decreased by a large factor in the last 10 billion years.

Clegg, R. E. S.↗
NASA NTRS1975

A study of lunar impact crater size-distributions

In view of the discrepancies in published crater frequency data, effects modifying production size distributions of impact craters are discussed. The resulting criteria are applied to the determination of the size distributions of unmodified impact crater populations in selected lunar regions of different ages. The measured cumulative crater frequencies are used to obtain a general calibration size distribution curve by a normalization procedure. Deviations of measured size distributions from the calibration distribution are strongly suggestive of the existence of processes having modified the primary impact crater population.

Neukum, G.↗
NASA NTRS1976

The period-pulse-width distribution of pulsars and their division into three classes

The period-pulse-width (P-W) distribution of sample of 41 pulsars has been reanalyzed under two versions of a model where radiation is beamed from magnetic polar caps which are isotropically oriented with respect to the rotation axis of the neutron stars (IOPC models). It is found that neither IOPC model can explain the P-W distribution of the entire sample. Pulsars with simple unimodal (U) or complicated multimodal (M) pulse shapes show significantly different P-W distributions. Class M pulsars have a narrower P-W distribution than do class U pulsars and, taken separately, are compatible with either IOPC model. Class U pulsars divide into two subgroups, those with relatively narrower pulses (UN) and those with relatively wider pulses (UW), each of which is compatible with either IOPC model. One interpretation of these results is that the pulsars in classes UN, M, and UW have different intrinsic beam sizes, roughly in the ratios 1:2:4, respectively. The possible origins of the three classes are discussed in terms of the force-balance magnetosphere model (Roberts et al., 1972, 1973), where the differences may be attributed to different-mass neutron stars and the structure of the polar caps. An alternative interpretation is that the angle between the rotation and emission axes is not isotropically distributed, but can take only certain preferred values.

Roberts, D. H.↗
NASA NTRS1976

Classical trajectory study of internal energy distributions in unimolecular processes

Energy flow in a molecular system such as CD3Cl or CD3H representing a chemical activation experiment is studied by the method of classical trajectories. A correlation function method is used to obtain energy distributions before and after the breakup of the activated molecule. The energy distribution in the final product is found to be randomly distributed for a surface with no exit channel barrier or strong intermode couplings. Nonrandom energy distributions result when these special forces are present. Product channel barriers result in an excess of translational energy and exit channel intermode couplings result in nonrandom vibrational distributions.

Mcdonald, J. D.↗
NASA NTRS1977

An estimate of field size distributions for selected sites in the major grain producing countries

The field size distributions for the major grain producing countries of the World were estimated. LANDSAT-1 and 2 images were evaluated for two areas each in the United States, People's Republic of China, and the USSR. One scene each was evaluated for France, Canada, and India. Grid sampling was done for representative sub-samples of each image, measuring the long and short axes of each field; area was then calculated. Each of the resulting data sets was computer analyzed for their frequency distributions. Nearly all frequency distributions were highly peaked and skewed (shifted) towards small values, approaching that of either a Poisson or log-normal distribution. The data were normalized by a log transformation, creating a Gaussian distribution which has moments readily interpretable and useful for estimating the total population of fields. Resultant predictors of the field size estimates are discussed.

Podwysocki, M. H.↗
NASA NTRS1977

Departures of the electron energy distribution from a Maxwellian in hydrogen. I - Formulation and solution of the electron kinetic equation. II - Consequences

The problem of calculating the steady-state free-electron energy distribution in a hydrogen gas is considered in order to study departures of that distribution from a Maxwellian at sufficiently low degrees of ionization. A model kinetic equation is formulated and solved analytically for the one-particle electron distribution function in a steady-state partially ionized hydrogen gas, and it is shown that the formal solution can be accurately approximated by using the WKB method. The solutions obtained indicate that the high-energy tail of the distribution is susceptible to distortion by imbalanced inelastic collisions for ionization fractions not exceeding about 0.1 and that such departures from a Maxwellian can lead to significant changes in the collisional excitation and ionization rates of ground-state hydrogen atoms. Expressions for the electron-hydrogen collision rates are derived which explicitly display their dependence on the hydrogen departure coefficients. The results are applied in order to compare self-consistent predictions with those based on the a priori assumption of a Maxwellian distribution for models of the thermal ionization equilibrium of hydrogen in the optically thin limit, spectral-line formation by a gas consisting of two-level atoms, and radiative transfer in finite slabs by a gas of four-level hydrogen atoms.

Shoub, E. C.↗
NASA NTRS1978

Low cost data distribution

The paper examines some of the technology developments which are needed to bridge the gap between research and development and the operational data distribution needs of the user community. In the short term (1978-1985), the data distribution technology activities will be concerned with the distribution needs of the user spacecraft, the central ground facility, the regional data center, and the user terminals. In the long term (1985-2000), the data distribution activities will place emphasis on those technology areas which are required for the user community to interact directly with a spacecraft to obtain processed data. User applications by government and private organizations are discussed, as are future low-cost distribution scenarios.

Catoe, C. E.↗
NASA NTRS1978

Continuous distributions of specific ventilation recovered from inert gas washout

A new technique is described for recovering continuous distributions of ventilation as a function of tidal ventilation/volume ratio from the nitrogen washout. The analysis yields a continuous distribution of ventilation as a function of tidal ventilation/volume ratio represented as fractional ventilations of 50 compartments plus dead space. The procedure was verified by recovering known distributions from data to which noise had been added. Using an apparatus to control the subject's tidal volume and FRC, mixed expired N2 data gave the following results: (a) the distributions of young, normal subjects were narrow and unimodal; (b) those of subjects over age 40 were broader with more poorly ventilated units; (c) patients with pulmonary disease of all descriptions showed enlarged dead space; (d) patients with cystic fibrosis showed multimodal distributions with the bulk of the ventilation going to overventilated units; and (e) patients with obstructive lung disease fell into several classes, three of which are illustrated.

Lewis, S. M.↗
NASA NTRS1977

Air traffic control by distributed management in a MLS environment

The microwave landing system (MLS) is a technically feasible means for increasing runway capacity since it could support curved approaches to a short final. The shorter the final segment of the approach, the wider the variety of speed mixes possible so that theoretically, capacity would ultimately be limited by runway occupance time only. An experiment contrasted air traffic control in a MLS environment under a centralized form of management and under distributed management which was supported by a traffic situation display in each of the 3 piloted simulators. Objective flight data, verbal communication and subjective responses were recorded on 18 trial runs lasting about 20 minutes each. The results were in general agreement with previous distributed management research. In particular, distributed management permitted a smaller spread of intercrossing times and both pilots and controllers perceived distributed management as the more 'ideal' system in this task. It is concluded from this and previous research that distributed management offers a viable alternative to centralized management with definite potential for dealing with dense traffic in a safe, orderly and expeditious manner.

Kreifeldt, J. G.↗
NASA NTRS1978

Remote sensing of environmental particulate pollutants - Optical methods for determinations of size distribution and complex refractive index

A unifying approach, based on a generalization of Pearson's differential equation of statistical theory, is proposed for both the representation of particulate size distribution and the interpretation of radiometric measurements in terms of this parameter. A single-parameter gamma-type distribution is introduced, and it is shown that inversion can only provide the dimensionless parameter, r/ab (where r = particle radius, a = effective radius, b = effective variance), at least when the distribution vanishes at both ends. The basic inversion problem in reconstructing the particle size distribution is analyzed, and the existing methods are reviewed (with emphasis on their capabilities) and classified. A two-step strategy is proposed for simultaneously determining the complex refractive index and reconstructing the size distribution of atmospheric particulates.

Fymat, A. L.↗
NASA NTRS1978

Distribution of atmospheric ozone and how it is measured

The total amount of ozone in a vertical column has been measured spectroscopically at near ultraviolet and visible wavelengths, using ground- and satellite-based instruments. The vertical distribution of ozone from the surface up to approximately 100 km has been measured by a variety of techniques - chemical and optical - and from a number of observing platforms, including balloon, rocket, and satellite platforms. The various methods presently used for determining the atmospheric ozone distribution are reviewed, along with a discussion of their advantages and disadvantages. The observed average distribution of total ozone for the period 1958-1975 shows the expected geographic and seasonal variations. The variations of total ozone, including hemispheric differences, are clearly associated with large-scale circulation processes in the lower stratosphere. Approximately ten years of observations of the vertical ozone distribution, up through the ozone maximum, also show geographic and seasonal variations strongly related to the lower stratosphere circulation. The distribution above the maximum, however, results from the interaction of photochemistry and stratospheric motions.

London, J.↗
NASA NTRS1979

Galactic distribution models of gamma-ray burst sources

The log N-log S relationships for several galactic distribution models of gamma-ray burst sources are derived. The resulting curves are substantially different from the galactic curves usually assumed (slope = -1). There is a relatively weak dependence on the radial distribution assumed but a strong dependence on scale height. Available observational data from several experiments appear to rule out both thin disk distributions and extended halo distributions which have a strong radial density dependence. The prospects are good for obtaining self-consistent distribution data from future large-area detectors.

Fishman, G. J.↗