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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.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Radiative transfer with partial frequency redistribution in inhomogeneous atmospheres - Application to the Jovian aurora

A direct finite difference numerical solution for the equation of radiative transfer by the Feautrier method is developed for use in planetary atmospheres. The procedure described here uses a plane-parallel atmosphere, and can treat partial frequency redistribution, inhomogeneity, external or internal sources, and various boundary conditions. Isotropic scattering is assumed, but in the case of no frequency redistribution, Rayleigh scattering can also be handled. A program utilizing this method is tested in a variety of situations against more powerful and elaborate methods. The case of the Lyman alpha aurora on Jupiter is then considered, where the effects of partial frequency redistribution are shown to be of great importance. New results for the detailed line profiles for Lyman alpha in the Jovian aurora are presented. The method is quite versatile, and should be especially useful in studying a wide range of problems related to auroral or dayglow emissions in planetary atmospheres.

Gladstone, G. R.↗
NASA NTRS1981

Coding tradeoffs for improved performance of FH/MFSK systems in partial band noise

Partial band noise jamming can severely degrade the performance of frequency-hopped, M-ary frequency-shift keyed communciation systems. This paper illustrates the tradeoffs between channel coding, diversity, and block orthogonal (MFSK) modulation as a means of overcoming the advantage of worst case, non-adaptive (as opposed to repeat-back) partial band jamming. For ease of computation, the analysis relies on exponentially tight error bounds, and is based on a noncoherent detection metric that requires jamming state information for each hop. A more robust, less complex receiver structure which eliminates the jamming knowledge requirement is shown to degrade performance less than 2-1/2 dB. The coding tradeoffs discussed in this report are exemplified in the design of a hypothetical 32 kb/s military frequency-hopped communication link.

Levitt, B. K.↗
NASA NTRS1982

Boundary-fitted coordinate systems for numerical solution of partial differential equations - A review

A comprehensive review of methods of numerically generating curvilinear coordinate systems with coordinate lines coincident with all boundary segments is given. Some general mathematical framework and error analysis common to such coordinate systems is also included. The general categories of generating systems are those based on conformal mapping, orthogonal systems, nearly orthogonal systems, systems produced as the solution of elliptic and hyperbolic partial differential equations, and systems generated algebraically by interpolation among the boundaries. Also covered are the control of coordinate line spacing by functions embedded in the partial differential operators of the generating system and by subsequent stretching transformation. Dynamically adaptive coordinate systems, coupled with the physical solution, and time-dependent systems that follow moving boundaries are treated. References reporting experience using such coordinate systems are reviewed as well as those covering the system development.

Thompson, J. F.↗
NASA NTRS1984

Transfer Function Bounds for Partial-unit-memory Convolutional Codes Based on Reduced State Diagram

The performance of a coding system consisting of a convolutional encoder and a Viterbi decoder is analytically found by the well-known transfer function bounding technique. For the partial-unit-memory byte-oriented convolutional encoder with m sub 0 binary memory cells and (k sub 0 m sub 0) inputs, a state diagram of 2(K) (sub 0) was for the transfer function bound. A reduced state diagram of (2 (m sub 0) +1) is used for easy evaluation of transfer function bounds for partial-unit-memory codes.

Lee, P. J.↗
NASA NTRS1984

Area estimation using multiyear designs and partial crop identification

Statistical procedures were developed for large area assessments using both satellite and conventional data. Crop acreages, other ground cover indices, and measures of change were the principal characteristics of interest. These characteristics are capable of being estimated from samples collected possibly from several sources at varying times, with different levels of identification. Multiyear analysis techniques were extended to include partially identified samples; the best current year sampling design corresponding to a given sampling history was determined; weights reflecting the precision or confidence in each observation were identified and utilized, and the variation in estimates incorporating partially identified samples were quantified.

Sielken, R. L., Jr.↗
NASA NTRS1985

Film cooling on a convex wall: Heat transfer and hydrodynamic measurements for full and partial coverage

Turbine-blade cooling is an important issue for high-efficiency turbine engines, and discrete-hole injection is widely used as a cooling method. In the present study, detailed measurements were made of the heat transfer and hydrodynamics of a film-cooled flow on a convex wall, both for full and partial coverage. Two important parameters were altered: the blowing ratio, m, and the number of rows of injection holes. Three values of m were tested: m = 0.2, 0.4, and 0.6. In the blown region, m = 0.4 results in the lowest Stanton numbers of the three blowing ratios tested. This indicates that the value of m = 0.4 is near optimum on the convex wall from the point of view of cooling effect by injection. In the recovery region, Stanton numbers gradually approach the no injection values. Although the heat-transfer behavior during recovery from injection looks relatively complicated, the behavior of Stanton number can be explained in terms of two mechanisms: recovery from the thermal effect of injection and recovery from the turbulence augmentation. This interpretation of the data is supported by the hydrodynamic and temperture-profile measurements. For partial blowing cases, the data follow the full-coverage values inside the blown region. In the unblown region, both in the curved and in the flat plate, the effect of the number of blown rows is clearly seen. Hydrodynamic boundary-layer profiles were measured with the aid of a triple hot-water probe. Three mean-velocity components and six turbulence quantities were simultaneously measured, and inside the blown region strong three-dimensionality was observed.

Furuhama, K.↗
NASA NTRS1985

Small, two-stage, partial-admission turbine

The Rocketdyne Orbital Transfer Vehicle (OTV) cryogenic, rocket engine system, high pressure, liquid hydrogen turbopump was designed with a two-stage, partial-admission axial turbine. The turbine is basically two single-stage, partial-admission, subsonic impulse stages designed so the kinetic energy leaving the first-stage rotor is discharged directly into the second-stage nozzle at nominal operation to minimize staging losses. Very little data were available in the literature for this type of turbine design. Therefore, it was decided to test a full-size model of the turbine design using ambient-temperature gaseous nitrogen as the working fluid. The tester design features a variable orientation second-stage nozzle to determine the optimum circumferential location for highest performance. The tester also features the capability to vary the nozzle arcs of admission and incorporates quartz windows to study the flowfield upstream of the second-stage nozzle using a laser velocimeter. The test operations will probe the efficiency and flow characteristics for three arcs of admission and the effects of second-stage nozzle circumferential orientations over wide ranges of speed and pressure ratios as well as the interstage pressure distributions.

Sutton, R. F.↗
NASA NTRS1985

Strategies for FH/MFSK signaling with diversity in worst-case partial-band noise

Optimum diversity and worst-case partial-band noise jamming conditions have been derived for noncoherent energy detection of frequency-hopped (FH) M-ary frequency-shift keyed (MFSK) signals using a soft-chip decision suboptimum linear combining metric with perfect jamming-state side information. However, the assumption implicit in previous publications is that the error is first maximized over the jammer's partial-band duty factor for arbitrary diversity, and the result is then minimized over the amount of diversity. This paper shows that if the order of optimization is reversed, different conditions and performance are produced; that is, the previous solution is not a saddlepoint. This introduces some game-theoretic considerations for the communicator and the jammer, the risks and advantages of which are explored.

Levitt, B. K.↗
NASA NTRS1986

Analytic computation of energy derivatives - Relationships among partial derivatives of a variationally determined function

Formulas are presented relating Taylor series expansion coefficients of three functions of several variables, the energy of the trial wave function (W), the energy computed using the optimized variational wave function (E), and the response function (lambda), under certain conditions. Partial derivatives of lambda are obtained through solution of a recursive system of linear equations, and solution through order n yields derivatives of E through order 2n + 1, extending Puley's application of Wigner's 2n + 1 rule to partial derivatives in couple perturbation theory. An examination of numerical accuracy shows that the usual two-term second derivative formula is less stable than an alternative four-term formula, and that previous claims that energy derivatives are stationary properties of the wave function are fallacious. The results have application to quantum theoretical methods for the computation of derivative properties such as infrared frequencies and intensities.

King, H. F.↗
NASA NTRS1986

Partial redistribution effects in the formation of hydrogen lines in quiescent prominences

Departures from complete frequency redistribution (CRD) in hydrogen lines are investigated for solar prominences. Partial redistribution effects (PRD) are found both in the wings (their already known lowering) and in the central part of the L alpha line; a new feature is evidenced here: the partially coherent scattering in the near wings of the line leads to a double-peaked profile mirroring the incident solar radiation. With a low density model, we obtain a good agreement with OSO 8 observed profiles. On the contrary, the PRD computed L beta profile (lower density, no reversal) departs from the observed one, a result which calls for more progress in terms of non-LTE transfer and modelling.

Heinzel, P.↗
NASA NTRS1987

Stigmatically focusing partial pressure analyzer with dual chamber ion source

The partial pressure analyzer developed has a high absolute sensitivity and high resolution. Interaction effects, as they occur in conventional partial pressure analyzers between the heating filament for the emission of electrons and the residual gas, are suppressed by removing the heating filament from the measurement area. The electron beam is generated in an auxiliary vacuum compartment, and passes subsequently through an aperture into the ionization compartment. The probability is small, therefore, that the presence of substances produced at the heating filament by chemical reactions and thermal decompositions will have disturbing effects. The high sensitivity and resolution of the instrument are obtained with the aid of an electron path configuration of unconventional characteristics.

Rasskopf, Klaus F.↗
NASA NTRS1987

Observation model and parameter partials for the JPL VLBI parameter estimation software MASTERFIT-1987

This report is a revision of the document of the same title (1986), dated August 1, which it supersedes. Model changes during 1986 and 1987 included corrections for antenna feed rotation, refraction in modelling antenna axis offsets, and an option to employ improved values of the semiannual and annual nutation amplitudes. Partial derivatives of the observables with respect to an additional parameter (surface temperature) are now available. New versions of two figures representing the geometric delay are incorporated. The expressions for the partial derivatives with respect to the nutation parameters have been corrected to include contributions from the dependence of UTI on nutation. The authors hope to publish revisions of this document in the future, as modeling improvements warrant.

Sovers, O. J.↗
NASA NTRS1987

Partial redistribution in high-density, highly ionized plasmas

The conditions for which partial redistribution functions must be used for radiation transport in high-Z, high-density, laser-produced plasmas are examined. A previously developed two-photon formalism based on the model microfield method is used to calculate redistribution functions including electron and ion Stark broadening with ion dynamic effects. The competition between the relaxation rates and spontaneous emission is shown to determine the conditions for partial redistribution. The discussion makes use of microfield fluctuation rates and broadening coefficients which can be determined from simulation calculations. The redistribution function for the Ly-alpha transition of Ar XVIII is presented for typical plasma conditions.

Talin, B.↗
NASA NTRS1987

Textural evolution of partially-molten planetary materials in microgravity

Recent Earth-based experiments examining the textural evolution of partially-molten rocks have revealed two important ways in which surface energy considerations affect magma. An initial experimental program addressing surface-energy effects on partially-molten materials in microgravity would involve simple, isothermal treatment of natural samples (meteorites, perioditic komatiite) at preselected temperatures in the melting range. Textural evolution would be assessed by time studies in which the only experiment variable would be run duration. Textural characterization of each sample would be done by quenching, recover, and sectioning for generally later, computer-aided interpretation of features.

Watson, E. B.↗
NASA NTRS1987

Nested hierarchical controller with partial autonomy

The problem of computer architecture for intelligent robots with partial autonomy is addressed. A robot with partial autonomy is considered a degenerated case of a fully autonomous robot. Thus, the problem of man-machine communication is formulated, and the conditions are determined for generating a language for such a communication. The duties of the master are determined.

Meystel, A.↗
NASA NTRS1989

Magnetic reconnection in partially ionized gases

Magnetic field lines in a plasma reconnect at a rate scaled by the Alfven speed. In a partially ionized gas there are two natural Alfven speeds: one determined by the ionized mass density alone, which applies when ion-neutral friction is negligible, and one determined by the total mass density, which applies when ion-neutral friction is strong. When the ionization fraction is low, as in a dense molecular cloud, these two speeds differ by several orders of magnitude. Both time-dependent tearing modes and steady-state magnetic reconnection in partially ionized gas are considered, and the regimes in which the charged and neutral components are strongly, intermediately, and weakly coupled are delineated. Molecular clouds are probably in the intermediate regime, while reconnection in solar prominences probably has strong ion-neutral coupling. Reconnection proceeds more rapidly when coupling is not strong.

Zweibel, Ellen G.↗
NASA NTRS1989

Biological nitrogen fixation under primordial Martian partial pressures of dinitrogen

One of the most striking differences between the conditions on early Mars and earth was a low (18 mb) partial pressure of N2 (pN2) on early Mars, as opposed to 780 mb N2 on earth. To investigate the possibility of biological nitrogen fixation under conditions of early Mars, experiments were carried out on the growth of Azotobacter vinelandii and Azomonas agilis in nitrogen-free synthetic medium under various partial pressures of N2 (ranging from 780 to 0 mb). It was found that, although the biomass, cell number, and growth rate of these bacteria decreased with decreasing pN2 values below pN2 of 400 mb, both microorganisms were capable of growing at pN2 as low as 5 mb (but not at of below 1 mb), indicating that biological fixation of nitrogen could have occurred on primordial Mars.

Klingler, J. M.↗