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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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NASA NTRS1973

Gauge invariance, current conservation, and GIAO's.

The well-known relationship between gauge invariance and current conservation is exhibited within the usual quantum mechanical formalism. It is then shown that the use of Gauge Invariant Atomic Orbitals does not necessarily lead to the expected current conservation. The reason is found to lie in the constrained nature of the gauge invariance which is provided by the use of GIAO's. It is concluded that this invariance is, of itself, no argument in favor of their use.

Epstein, S. T.↗
NASA NTRS1973

An inverse theorem about the magnetic field line velocity.

It is shown that every field line velocity is associated with a set of Euler potentials (alpha prime, beta prime) such that particles moving with this velocity observe constant values of alpha prime and beta prime. The field line and flux preservation properties of the motion follow immediately, and a short independent proof of the Helmholtz-Zorawski criterion for field line preservation is also given. Arguments are given to show that in general it is not possible to single out one 'basic' field line velocity when only the time dependent magnetic field configuration is given.

Stern, D. P.↗
NASA NTRS1972

Comments on lunar origin.

Consideration of the tidal evolution of the earth-moon system in the light of recent published studies of lunar origin. The subjects include the factors of orbital evolution, the auxiliary Model Zero, orbital evolution along the outgoing branch, capture models, capture probability, capture with break-up, the tidal evolution of circular and elliptical fragmented rings, and precession and collisions in a ring of fragments. A numerical integration of precessions is performed for the actual nonzero mass of the moon and for a lunar distance of about 22 earth radii. A simplified Model Zero is found to compare well with Goldreich's solution (1968). It is concluded that the moon must have become freely yielding to tidal deformation at distances less than about 8 earth radii. Arguments are given in favor of the capture theory as a basis for the genesis of the moon.

Opik, E. J.↗
NASA NTRS1973

On the distances to transient X-ray sources.

Estimation of the distance of three transient X-ray sources characterized by a rapid increase to a flux comparable with the strongest galactic X-ray sources, followed by a slower decay over a time scale of three to four months. A simple argument based only on X-ray data is presented, which yields a typical distance estimate on the order of a few kiloparsecs. In particular, it is demonstrated that it is most unlikely that the transient X-ray sources can be extragalactic in nature and produced by supernova events in nearby galaxies.

Silk, J.↗
NASA NTRS1973

Effects of motion of the equatorial plane on the orbital elements of an earth satellite.

Exact differential equations relating the perturbations to satellite orbital elements by the motion of the earth's equatorial plane are derived, and they are solved to second order in precession. The system proposed in a previous paper (Kozai, 1960), in which the inclination and the argument of perigee are referred to the equator of date and the longitude of the ascending node is measured from a fixed point along a fixed plane and then along the equator of date, can still be recommended for precise studies of satellite motion even when the second-order perturbations are taken into account.

Kozai, Y.↗
NASA NTRS1973

Can the ionosphere regulate magnetospheric convection.

A simple model is outlined that relates the dayside magnetopause displacement to the currents feeding the polar cap ionosphere, from which the ionospheric electric field and the flux return rate may be estimated as a function of magnetopause displacement. Then, flux conservation arguments make possible an estimate of the time scale on which convection increases.

Coroniti, F. V.↗
NASA NTRS1973

Cometary exploration - A case for Encke.

A specific case is made for beginning small body exploration at the short-period comet Encke. The arguments review science rationale, interest, and selection criteria. Against this background, aspects of mission execution are considered including phasing, mission modes, and funding. Technology status and contending concepts round out the discussion and lead to recommendations for action.

Atkins, K. L.↗
NASA NTRS1973

A hex on MPASK.

A class of multiple-phase amplitude-shift-keying (MPASK) signal sets based upon a hexagonal design is presented. The sets give slightly improved error probability performance over any other MPASK set thus far reported in the literature. The hexagonal signal set designs presented are motivated by a sphere-packing argument. Gray codes for binary data are considered, giving attention to questions regarding the 'best' impure Gray code that can be constructed for hexagonal signal sets.

Simon, M. K.↗
NASA NTRS1973

Minor planets and related objects. XIII - Long-term orbital evolution of /1685/ Toro.

The orbital evolution of (1685) Toro has been investigated over 5000 yr. The asteroid exhibits a locked resonance through an 8:5 commensurability with the earth for the first 3400 yr of integration and a locked resonance with Venus through a 13:5 commensurability for the last 1000 yr. Control of these resonances passes from the earth to Venus as the distance from the earth's orbit gets greater and the distance to Venus' orbit gets closer as a consequence of the precession of the argument of perihelion. The double resonance may give Toro the ability to avoid collisions with the earth and Venus at the present time but this is still uncertain. Mars perturbations could remove Toro from the deepest part of the resonance in about 3,000,000 yrs.

Williams, J. G.↗
NASA NTRS1973

Classification and distribution of WR stars and an interpretation of the WN sequence.

New observational data for Wolf-Rayet stars are interpreted in areas of atmospheric abundances, absolute magnitudes, Galactic distribution, distribution in M33, and bolometric luminosities. The observational data are used in support of arguments (1) that WN stars are helium stars of eight to fourteen solar masses with atmospheres which contain only a very low proportion of hydrogen, (2) that the properties of the stars are very sensitive to this very small amount of hydrogen, and (3) that consequently this structure explains many of the general properties of the subclasses.

Smith, L. F.↗
NASA NTRS1973

Further aspects of weak shock theory applied to the solar chromosphere.

The low chromosphere now seems definitely to require mechanical heating, and dissipation of initially acoustic waves by shocking is one of the most promising possibilities. Results of recent calculations indicate that the weak shock theory may be applicable in this case, but discrepancies exist among various applications of this theory, and the explanations offered to date are not completely satisfactory. It is shown that the different approximations used by different authors to evaluate the mechanical flux integral play an important role in producing these discrepancies, in addition to the already well-known effects of the density scale heights and the wave periods. Arguments are presented favoring Ulmschneider's (1970, 1971) method for evaluation of this flux integral.

Jordan, S. D.↗
NASA NTRS1973

On local inflexional instability in boundary-layer flows.

Development of a linearized theory of the two- and three-dimensional incompressible viscous flows ensuing from locally unstable velocity profiles. Indications of the theory with respect to the instability of the two-dimensional separation bubble and the mechanisms underlying formation of the turbulence wedge behind a fixed roughness element are pointed out. In connection with the aforementioned mechanisms, a theoretically based argument is advanced that, as a result of local inflectional instability of the velocity profile in a succession of skewed planes, a corresponding succession of stationary vortices is induced, the induction process terminating at the boundaries of the turbulence wedge when the velocity profiles along the boundaries themselves become unstable. It is suggested that a rational method of predicting the occurrence of roughness-induced turbulence wedges might be possible if a theory were available for the steady laminar flow caused by the roughness at a stage just prior to transition.

Tobak, M.↗
NASA NTRS1972

The present thermal state of the terrestrial planets

The thermal state of bodies is discussed as an aspect of their internal dynamics for bodies of roughly meteoritic composition in the range of sizes of planetary objects. The rheological behaviour of planetary material is assumed to be represented by a Newtonian viscosity varying exponentially with temperature, and only the consistency of this assumption with the elastic view of the planets is considered. It is shown that for the whole range of physically plausible values of the material parameters, the temperature distribution associated with a solution to the problem of internal dynamics for bodies with external radii larger than about 800 km departs significantly from that predicted on conduction theory arguments. For bodies in the range of sizes of the terrestrial planets, the viscosity-temperature relationship plays a dominant role in setting the absolute temperature of the central regions.

Tozer, D. C.↗
NASA NTRS1972

Viscous stratification of the earth and convection

The shallow model of the earth's mantle is discussed along with a variety of geophysical arguments for its correctness and against the existence of deep convection. The main agrument is summarized in the proposal that the astheno sphere is less viscous (by a factor of 10 to 100) than has generally been assumed. In this shallow model, the return flow is essentially through the asthenosphere. The dynamical agent is the steep temperature gradient in the upper mantle. Speculations as to the historical variation of this gradient are advanced. The effects on the model of a nonuniform earth aggregation are considered and shown to favor shallow convection as well as a top convective layer (lithosphere plus asthenosphere) whose depth increases slowly over the earth's life, leading to a tectonic activity that increases gradually with time.

Elsasser, W. M.↗
NASA NTRS1972

Transport properties of liquid metal hydrogen under high pressures

A theory is developed for the compressibility and transport properties of liquid metallic hydrogen, near to its melting point and under high pressure. The interionic force law is assumed to be of the screened Coulomb type, because hydrogen has no core electrons. The random phase approximation is used to obtain the structure factor S(k) of the system in terms of the Fourier transform of this force law. The long wavelenth limit of the structure factor S(o) is related to the compressibility, which is much lower than that of alkali metals at their melting points. The diffusion constant at the melting point is obtained in terms of the Debye frequency, using a frequency spectrum analogous with the phonon spectrum of a solid. A similar argument is used to obtain the combined shear and bulk viscosities, but these depend also on S(o). The transport coefficients are found to be about the same size as those of alkali metals at their melting points.

Brown, R. C.↗
NASA NTRS1973

Reflection and interference of electromagnetic waves in inhomogeneous media

Solutions were obtained of the wave equation for a plane horizontally polarized electro-magnetic wave incident on a semi infinite two dimensional inhomogeneous medium. Two problems were considered: An inhomogeneous half space, and an inhomogeneous layer of arbitrary thickness. Solutions of the wave equation were obtained in terms of Hankel functions with complex arguments. Numerical calculations were made of the reflection coefficient R at the interface of the homogeneous medium. The startling results show that the reflection coefficient for a complex dielectric constant with gradient, can be less than that of the same medium with zero gradient.

Geiger, F. E.↗
NASA NTRS1973

Apollo 17 site selection

The scientific arguments and recommendations concerning the selection of the Apollo 17 landing site are presented. The final selection was influenced by the accomplishments and circumstances of previous Apollo flights and by the proposed experiments for Apollo 17. The decisive factors in selecting the Taurus-Littrow landing area were: (1) certainty of acquiring highlands lunar samples, (2) superior orbital coverage, and (3) better use of the lunar roving vehicle capabilities.

Hinners, N. W.↗
NASA NTRS1973

The Environmental Heat Flux Routine, Version 4 (EHFR-4) and Multiple Reflections Routine (MRR). Volume 2: Programmers reference manual

The EHFR program reference information which is presented consists of the following subprogram detailed data: purpose-description of the routine, a list of the calling programs, an argument list description, nomenclature definition, flow charts, and a compilation listing of each subprogram. Each of the EHFR subprograms were developed specifically for this routine and do not have an applicability of a general nature. Single precision accuracy available on the Univac 1108 is used exclusively in all but two of the 31 EHFR subprograms. The double precision variables required are identified in the nomenclature definition of the two subprograms that require them. A concise definition of the purpose, function, and capabilities is made in the subprogram description. The description references the appropriate Volume 1 sections of the report which contain the applicable detailed definitions, governing equations, and assumptions used. The compilation listing of each subprogram defines the program/data storage requirements, identifies the labeled block common data required, and identifies other subprograms called during execution. For Vol. 1, see N73-31842.

Dietz, J. B.↗