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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Constrained Chebyshev approximations to some elementary functions suitable for evaluation with floating point arithmetic

Approximations which can be evaluated with precision using floating-point arithmetic are presented. The particular set of approximations thus far developed are for the function TAN and the functions of USASI FORTRAN excepting SQRT and EXPONENTIATION. These approximations are, furthermore, specialized to particular forms which are especially suited to a computer with a small memory, in that all of the approximations can share one general purpose subroutine for the evaluation of a polynomial in the square of the working argument.

Manos, P.↗
NASA NTRS1972

Production of fibers by a floating zone fiber drawing technique

A CO2 laser heated, floating zone fiber growth process was developed. The resulting Al2O3 fibers exhibited the high room temperature strengths for large diameter fibers as well as high specific creep rupture strengths observed at 1093 C and 1316 C (2000 F and 2400 F). Single crystal fibers of TiC and Y2O3 were also grown. An optical system was developed to focus four CO2 laser beams onto the surface of a feed rod permitting the formation of highly controllable molten zones. The optical system permitted energy densities and angle of incidence of the beams to be adjusted over wide ranges. This optical system was incorporated into a controlled atmosphere, fiber growth furnace. The two principal advantages of a CO2 laser heat source are that ambient atmospheres may be freely selected to optimize fiber properties and the laser has no inherent temperature limit, so extremely high melting point materials can be melted. Both advantages were demonstrated.

Haggerty, J. S.↗
NASA NTRS1972

Instabilities caused by floating-point arithmetic quantization.

It is shown that an otherwise stable digital control system can be made unstable by signal quantization when the controller operates on floating-point arithmetic. Sufficient conditions of instability are determined, and an example of loss of stability is treated when only one quantizer is operated.

Phillips, C. L.↗
NASA NTRS1972

Area influences and floating potentials in Langmuir probe measurements.

Analysis of the influence of a relatively small reference electrode on a Langmuir probe measurement of plasma density and temperature. The analysis employs the collisionless theory of Laframboise for spherical and cylindrical probes and in a completely general way includes a broad range of electron densities and temperatures, as well as all possible values of ion mass and multiplicity of ionization. It is shown that a ratio alpha of reference-electrode area to probe area of 10,000 will guarantee no distortion of the measurement as a result of a shifting reference-electrode potential. It is further shown that the constraint on alpha can be relaxed by approximately two orders of magnitude when the charge-normalized ion mass is decreased from 200 to 1 amu and the ratio of reference-electrode radius to Debye length is decreased from 100 to 0. An additional result of the analysis is the dependence of a probe's floating potential on its geometry and radius, as well as on the properties of the plasma. A discussion of the latter result reveals in a striking manner the significant differences between the ion-current responses of spherical and cylindrical probes.

Szuszczewicz, E. P.↗
NASA NTRS1973

Floating baffle to improve efficiency of liquid transfer from tanks

When liquid tank is full, baffle is held up against a stop on top of shaft to prevent restriction of flow from outlet. As tank is being emptied, baffle, floating on top of liquid surface, descends with liquid level toward outlet until it reaches its bottom stop. Baffle prevents gas pull-through until practically all liquid is emptied from tank.

Howard, F. S.↗
NASA NTRS1973

Application of the floating-potential probe for studies of low frequency oscillations in a plasma

The proper interpretation of the results obtained from measurements of the floating potential of an electrostatic probe may cause difficulties in time varying plasmas. The following limitations of the method are considered: the charge separation in the plasma, the influence of the input capacity of the measuring circuit, and the influence of the layer capacity near the probe. A detailed analysis is carried out in the cases of moving striations and ion acoustic waves. A simple measuring technique is suggested for ion acoustic studies, giving detailed information about ion density oscillations.

Dzhakov, B. Y.↗
NASA NTRS1973

Floating baffle to improve efficiency of liquid transfer from tanks

A floating baffle is described which rides up and down on a vertical shaft over a drain in a tank as the liquid level within the tank varies. When the baffle is in the raised position, the liquid is allowed to flow out of the drain at an unrestricted rate. When the baffle is in the lowered position, pull-through of air or gas that is above the liquid is presented, which would interfere and reduce the flow of liquid from the tank.

Howard, F. S.↗
NASA NTRS1973

Floating-point system quantization errors in digital control systems

The results are reported of research into the effects on system operation of signal quantization in a digital control system. The investigation considered digital controllers (filters) operating in floating-point arithmetic in either open-loop or closed-loop systems. An error analysis technique is developed, and is implemented by a digital computer program that is based on a digital simulation of the system. As an output the program gives the programing form required for minimum system quantization errors (either maximum of rms errors), and the maximum and rms errors that appear in the system output for a given bit configuration. The program can be integrated into existing digital simulations of a system.

Phillips, C. L.↗
NASA NTRS1973

Double floating probe measurements on S3-A.

Model calculations are made to explain the behavior of the potential of a pair of symmetrical floating probes used for the measurement of dc electric fields inside the plasmapause on the S3-A satellite launched on Nov. 15, 1971, into an eccentric orbit. Data representing the behavior of three regions of the plasmapause on and around Dec. 17, 1971, are discussed. The behavior of the plasmapause is found to be generally similar to that determined by previous observations involving variable magnetic activity.

Maynard, N. C.↗
NASA NTRS1973

Sink-float ferrofluid separator applicable to full scale nonferrous scrap separation

Design and performance of a ferrofluid levitation separator for recovering nonferrous metals from shredded automobiles are reported. The scrap separator uses an electromagnet to generate a region of constant density within a pool of ferrofluid held between the magnetic poles; a saturated kerosene base ferrofluid as able to float all common industrial metals of interest. Conveyors move the scrap into the ferrofluid for separation according to density. Results of scrap mixture separation studies establish the technical feasibility of relatively pure aluminum alloy and zinc alloy fractions from shredded automobile scrap by this ferrofluid levitation process. Economic projections indicate profitable operation for shredders handling more than 300 cars per day.

Source record↗
NASA NTRS1974

Float zone processing in a weightless environment

Results are given for investigations into: (1) the physical limits which set the maximum practical diameters of Si crystals that can be processed by the float-zone method in a near weightless environment, and (2) the economic impact of large, space-produced Si crystals on the electronics industry. The stability of the melt is evaluated. Heat transfer and fluid flow within the melt as dependent on the crystal size and the degree and type of rotation imparted to the melt are studied. Methods of utilizing the weightless environment for the production of large, stress-free Si crystals of uniform composition are proposed. The economic effect of large size Si crystals, their potential applications, likely utilization and cost advantages in LSI, integrated circuits, and power devices are also evaluated. Foreseeable advantages of larger diameter wafers of good characteristics and the possibilities seen for greater perfection resulting from stress-free growth are discussed.

Fowle, A. A.↗
NASA NTRS1974

San Francisco Floating Stolport Study

The report describes a cooperative transaction concerning the study of the feasibility of a floating STOLport on the San Francisco Bay.

Source record↗