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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

A simple method to incorporate water vapor absorption in the 15 microns remote temperature sounding

The water vapor absorption in the 15 micron CO2 band, which can affect the remotely sensed temperatures near the surface, are estimated with the help of an empirical method. This method is based on the differential absorption properties of the water vapor in the 11-13 micron window region and does not require a detailed knowledge of the water vapor profile. With this approach Nimbus 4 IRIS radiance measurements are inverted to obtain temperature profiles. These calculated profiles agree with radiosonde data within about 2 C.

Dallu, G.↗
NASA NTRS1975

A counter example in linear feature selection theory

The linear feature selection problem in multi-class pattern recognition is described as that of linearly transforming statistical information from n-dimensional (real Euclidean) space into k-dimensional space, while requiring that average interclass divergence in the transformed space decrease as little as possible. Divergence is the expected interclass divergence derived from Hajek two-class divergence; it is known that there always exists a k x n matrix B such that the transformation determined by B maximizes the divergence in k-dimensional space. It is known that, if Q is any k x k invertible matrix, and B is as defined above, then QB again maximizes the divergence in k-space. It is shown that the converse of this result is false: two matrices exist, B sub 1 and B sub 2, each of which maximizes transformed divergence, which are not related in the fashion B sub 2 = QB sub 1 for any k x k matrix Q.

Brown, D. R.↗
NASA NTRS1975

Power processing for electric propulsion

The inclusion of electric thruster systems in spacecraft design is considered. The propulsion requirements of such spacecraft dictate a wide range of thruster power levels and operational lifetimes, which must be matched by lightweight, efficient, and reliable thruster power processing systems. Electron bombardment ion thruster requirements are presented, and the performance characteristics of present power processing systems are reviewed. Design philosophies and alternatives in areas such as inverter type, arc protection, and control methods are discussed along with future performance potentials for meeting goals in the areas of power process or weight (10 kg/kW), efficiency (approaching 92 percent), reliability (0.96 for 15,000 hr), and thermal control capability (0.3 to 5 AU).

Finke, R. C.↗
NASA NTRS1974

Anisotropic proton instability magnetospheric /APIM/ hiss - An introduction

Plasmaspheric hiss is broadband ELF noise between 100 and 2000 Hz generally occurring inside the plasmasphere. It is proposed that some plasmaspheric ELF hiss is generated by ring current protons. The mechanism by which waves are generated is the anisotropic proton instability magnetospheric (APIM) hiss mechanism. APIM hiss (with a frequency close to the lower hybrid resonance frequency) is a loss-cone, flute instability arising from proton velocity space anisotropies. The energy driving the waves comes from the free energy of the 'inverted population' of the proton loss-cone distribution. The APIM hiss mechanism predicts the bandwidth, center frequency, source location, and wave normal angle of some types of plasmaspheric hiss. APIM hiss is suggested as a possible additional loss mechanism for ring current protons.

Parady, B. K.↗
NASA NTRS1974

The non-existence of the Oort cometary shell

The procedures adopted as theory for a shell of comets are shown to be invalid. Any plot of numbers of long-period comets against 1/a will automatically exhibit a peak at small values of this parameter, and cannot be inverted to demonstrate a high volume-density of aphelia in space. The positions of actual aphelion-points show no sign of any concentration at any range. Further, the aphelion-distance undergoes large almost random changes owing to planetary perturbations at each return, and present values can yield no indication of original positions. A recent attempt to save the shell-theory by making use solely of comets with large perihelion-distance is shown to rest on exactly the same errors as have done all the earlier presentations. The plain conclusions emerge that the shell-theory is devoid of any support by facts, and that the alleged shell of comets is non-existent.

Lyttleton, R. A.↗
NASA NTRS1975

On the Laplace transform for distributions

A new characterization of the Laplace transform for Schwartz distributions is developed, using sequences of linear transformations on the space of distributions. The standard theorems on analyticity, uniqueness and invertibility of the transform are proved, using the new characterization as the definition of the Laplace transform. It is shown that this sequential definition is equivalent to Schwartz's extension of the ordinary Laplace transform to distributions which he obtained from the Fourier transform.

Price, D. B.↗
NASA NTRS1975

Influence of head orientation on visually induced pitch and roll sensation

Observers viewing rotating scenes in their periphery frequently experience self-motion in the opposite direction. A full field flight simulator projection system was used to investigate the sensations resulting from pitch, roll, and yaw stimuli at various head orientations. Steady yaw rate (circularvection) and development of a constant roll tilt angle, for the head erect and constant velocity yaw and roll stimuli, confirmed previous reports. Pitch stimuli also were found to produce a sensation of tilting to a steady pitch angle, which was much stronger for pitch forward than backward. Pitch and roll effects were strongly dependent on head position, increasing for the head rolled 90 deg to the side or inverted, and decreasing for the head pitched 25 deg forward. These results support a hypothesis that visually induced tilt is limited by conflict with otolith information.

Young, L. R.↗
NASA NTRS1974

Wide range multi-channel analog switch

A ten-channel analog switch has been developed as a sample and shape circuit for signals used as inputs to a logarithmic pulse height recording system. The circuit employs a field effect transistor as the switching element. Switching transients are reduced to approximately 2 mV by adding to the gated signal an inverted transient generated by an identical circuit with no signal applied. The circuit is linear to 2% from 3 mV to 10 V.

Levit, L. B.↗
NASA NTRS1975

Observations of angular distributions of low energy electron intensities over the auroral zones with Ariel 4

The electron intensities considered are within the energy range from 244 eV to 10.8 keV. The measurements were made at an altitude of about 570 km over the local-evening sector of the auroral zone. Aspects of instrumentation are discussed along with details regarding the observations, energy-time spectrograms, the signature of the plasma sheet, and inverted V events. The initial results reported provide new information concerning auroral acceleration mechanisms.

Craven, J. D.↗
NASA NTRS1975

On the controversy about the direction of electrotransport in thin gold films

Annealed 'pure' gold films exhibit electromigration against the electron flow. In contrast, gold films deposited on a transition metal underlayer show mass flow in the same direction as the electron flow. Diffusion of the transition metal from the underlayer into the gold film, deduced from Auger analyses presented herein, is believed to be responsible for this reversal. A new experiment, utilizing an 'inverted temperature profile' gives unambiguous results on the direction of electrotransport.

Hummel, R. E.↗
NASA NTRS1974

Quaternion wave equations in curved space-time

The quaternion formulation of relativistic quantum theory is extended to include curvilinear coordinates and curved space-time in order to provide a framework for a unified quantum/gravity theory. Six basic quaternion fields are identified in curved space-time, the four-vector basis quaternions are identified, and the necessary covariant derivatives are obtained. Invariant field equations are derived, and a general invertable coordinate transformation is developed. The results yield a way of writing quaternion wave equations in curvilinear coordinates and curved space-time as well as a natural framework for solving the problem of second quantization for gravity.

Edmonds, J. D., Jr.↗
NASA NTRS1975

Effect of the Jovian oblateness on Pioneer 10/11 radio occultations

The oblateness of Jupiter, which was neglected in the standard inversion technique for radio occultation data, has a substantial effect on the refractivity profiles of the neutral Jovian atmosphere derived from the Pioneer 10/11 occultations. The geometry of the Pioneer 10 entry and exit occultations has the effect that oblateness should account for much of the discrepancy of the results with plausible atmospheric models. The effect of the oblateness on Pioneer 11 entry is smaller, where much of the discrepancy could be due to other effects, such as cycle-slip in the spacecraft transponder. Theory indicates that the Pioneer 11 exit occultation should be affected by the oblateness in the opposite sense from the first three occultations; and, indeed, the data which had not been invertible under the spherical assumption produced reasonable results when an oblateness correction was applied.

Hubbard, W. B.↗
NASA NTRS1975

Magnetospheric and auroral plasmas - A short survey of progress

Important milestones in our researches of auroral and magnetospheric plasmas for the past quadrennium 1971-1975 are reviewed. Many exciting findings, including those of the polar cusp, the polar wind, the explosive disruptions of the magnetotail, the interactions of hot plasmas with the plasmapause, the auroral field-aligned currents, and the striking inverted V electron precipitation events, were reported during this period. Solutions to major questions concerning the origins and acceleration of these plasmas appear possible in the near future. A comprehensive bibliography of current research is appended to this brief survey of auroral and magnetospheric plasmas.

Frank, L. A.↗
NASA NTRS1975

Feasibility of coherent X-ray production by X-ray pumping

It is suggested that coherent soft X rays can be produced by inverting the electron population in a suitable target, such as Li, through irradiation with X rays generated by fast electrons traversing an electromagnetic field (as in a storage ring). Conditions to be satisfied by target and radiation parameters are stated, and examples given.

Csonka, P. L.↗
NASA NTRS1975

Power transistor performance tradeoffs

Recent advances in the understanding of bipolar device physics permit the derivation of a number of quantitative relationships which are useful for improving existing designs and also for assessing the feasibility of proposed devices. This paper describes three important tradeoffs which apply to the design and performance of high-voltage transistors in inverter circuits.

Hower, P. L.↗
NASA NTRS1975

Derivation of phase functions from multiply scattered sunlight transmitted through a hazy atmosphere

The intensity of sunlight multiply scattered in model atmospheres is derived from the equation of radiative transfer by an analytical small-angle approximation. The approximate analytical solutions are compared to rigorous numerical solutions of the same problem. Results obtained from an aerosol-laden model atmosphere are presented. Agreement between the rigorous and the approximate solutions is found to be within a few per cent. The analytical solution to the problem which considers an aerosol-laden atmosphere is then inverted to yield a phase function which describes a single scattering event at small angles. The effect of noisy data on the derived phase function is discussed.

Weinman, J. A.↗
NASA NTRS1975

Wavefront-error evaluation by mathematical analysis of experimental Foucault-test data

The diffraction theory of the Foucault test provides an integral formula expressing the complex amplitude and irradiance distribution in the Foucault pattern of a test mirror (lens) as a function of wavefront error. Recent literature presents methods of inverting this formula to express wavefront error in terms of irradiance in the Foucault pattern. The present paper describes a study in which the inversion formulation was applied to photometric Foucault-test measurements on a nearly diffraction-limited mirror to determine wavefront errors for direct comparison with ones determined from scatter-plate interferometer measurements. The results affirm the practicability of the Foucault test for quantitative wavefront analysis of very small errors, and they reveal the fallacy of the prevalent belief that the test is limited to qualitative use only. Implications of the results with regard to optical testing and the potential use of the Foucault test for wavefront analysis in orbital space telescopes are discussed.

Wilson, R. G.↗
NASA NTRS1976

Growing crystals from eutectic melts

Inverted Bridgman Method yields crystals of higher homogeneity and better structure than those grown by ordinary Bridgman method. Process controls thermotransport by holding molten alloy in known temperature for known period of time. Rapid cooling quenches in state of segregation. Method is applicable to other eutectiferous systems where thermotransport is appreciable.

Bhat, B. N.↗