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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 289 records · Page 16
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NASA NTRS1972

The mass-zero spin-two field and gravitational theory.

Demonstration that the conventional theory of the mass-zero spin-two field with sources introduces extraneous nonspin-two field components in source regions and fails to be covariant under the full or restricted conformal group. A modified theory is given, expressed in terms of the physical components of mass-zero spin-two field rather than in terms of 'potentials,' which has no extraneous components inside or outside sources, and which is covariant under the full conformal group. For a proper choice of source term, this modified theory has the correct Newtonian limit and automatically implies that a symmetric second-rank source tensor has zero divergence. It is shown that possibly a generally covariant form of the spin-two theory derived here can be constructed to agree with general relativity in all currently accessible experimental situations.

Coulter, C. A.↗
NASA NTRS1972

A new theory of gravity

A new relativistic theory of gravity is presented. This theory agrees with all experiments to date. It is a metric theory, it is Lagrangian-based, and it possesses a preferred frame with conformally-flat space slices. With an appropriate choice of certain adjustable functions and parameters, this theory possesses precisely the same post-Newtonian limit as general relativity.

Ni, W.↗
NASA NTRS1973

New aspects of subsonic aerodynamic noise theory

A theory of aerodynamic noise is presented which differs from Lighthill's theory primarily in the way in which convection of the noise sources is treated. The sound directivity pattern obtained from the present theory agrees better with jet-noise directivity data than does that obtained from Lighthill's theory. The results imply that the shear-noise contribution to jet noise is smaller than previously expected.

Goldstein, M. E.↗
NASA NTRS1972

An analysis of the Belinfante-Swihart theory of gravity

The Belinfante-Swihart (BS) theory is reformulated in a representation in which uncharged matter responds to gravity in the same way as in metric theories. The BS gravitationally modified Maxwell equations are also put into metric form to first order in the deviations of the physical metric from flat space, but not to second order; consequently the theory is nonmetric except in first order. Also shown is that the theory violates the high precision Eotvos-Dicke experiment, but cannot be ruled out by the gravitational precession of gyroscopes.

Lee, D. L.↗
NASA NTRS1972

Gravitation theory - Empirical status from solar system experiments.

Review of historical and recent experiments which speak in favor of a post-Newtonian relativistic gravitational theory. The topics include the foundational experiments, metric theories of gravity, experiments designed to differentiate among the metric theories, and tests of Machian concepts of gravity. It is shown that the metric field for any metric theory can be specified by a series of potential terms with several parameters. It is pointed out that empirical results available up to date yield values of the parameters which are consistent with the prediction of Einstein's general relativity.

Nordtvedt, K. L., Jr.↗
NASA NTRS1973

A new theory of gravity.

A new relativistic theory of gravity is presented. This theory agrees with all experiments to date. It is a metric theory; it is Lagrangian-based; and it possesses a preferred frame with conformally flat space slices. With an appropriate choice of certain adjustable functions and parameters and of the cosmological model, this theory possesses precisely the same post-Newtonian limit as general relativity.

Ni, W.-T.↗
NASA NTRS1973

On the improper neglect of certain terms in random function theory

This paper presents some exact solutions of problems in random function theory for the purpose of testing the validity of an approximate method known variously in the many different fields of its application as first order smoothing theory, first order cumulant discard, quasilinear theory, or the adiabatic approximation. The hydromagnetic dynamo equations are used here, as particularly appropriate for such an investigation. The calculations show that in one case the exact and approximate solutions agree. In the other case the approximate solution is wrong. Hence, in the absence of a general criterion for validity, a result based on first order smoothing theory is a conjecture rather than a fact. This impacts strongly on much of the recent work on hydromagnetic dynamos.

Lerche, I.↗
NASA NTRS1976

Use of dynamic theory to describe experimental results from volume holography

The general applicability of dynamic theory to the description of the recording and readout characteristics of volume (thick) hologram gratings is indicated. In dynamic theory (as opposed to static theory), the volume nature of the thick holographic grating allows the interference of an incident light beam with its own diffracted beam inside the recording medium. This effect causes the continuous recording of another grating that alters the initial one, producing a resultant grating that is not uniform through the thickness of the recording material and a grating whose writing and reading characteristics may vary dramatically, depending on the recording material and the experimental conditions. A large number of diverse types of writing, reading, and angular-selectivity behavior have been reported. The dynamic theory of thick-hologram writing and reading is shown to predict qualitatively all of these various types of experimental behavior.

Magnusson, R.↗
NASA NTRS1976

Adequacy of classical inverse bremsstrahlung theory for low-temperature plasmas

The authors examine those plasma heating conditions under which a theory more accurate than the classical inverse bremsstrahlung theory should be used to predict absorption coefficients when laser energy is injected into the plasma. A correlation plot for measured absorption coefficients at three laser wavelengths versus those calculated by quantum mechanical theory yields a correlation coefficient for the least-squares fit of 0.994. A plot of the ratio of the quantum-mechanically corrected electron ion inverse bremsstrahlung absorption coefficient to that calculated by classical methods versus plasma temperature shows that at around 20 eV and above the differences between classical and quantum predictions are negligible, but significant errors could arise from application of classical theories to lower-temperature plasmas. Some recent experiments in the literature are shown to be worthy of reinterpretation in this light.

Billman, K. W.↗
NASA NTRS1976

Recent advances in shell theory

The results reviewed are divided into two categories: those that relate two-dimensional shell theory to three-dimensional elasticity theory and those concerned with shell theory per se. In the second category results for general elastic systems that carry over, by specialization or analogy, to shells and results that are unique to shell theory itself are considered.

Simmonds, J. G.↗
NASA NTRS1977

Pure field theories and MACSYMA algorithms

A pure field theory attempts to describe physical phenomena through singularity-free solutions of field equations resulting from an action principle. The physics goes into forming the action principle and interpreting specific results. Algorithms for the intervening mathematical steps are sketched. Vacuum general relativity is a pure field theory, serving as model and providing checks for generalizations. The fields of general relativity are the 10 components of a symmetric Riemannian metric tensor; those of the Einstein-Straus generalization are the 16 components of a nonsymmetric. Algebraic properties are exploited in top level MACSYMA commands toward performing some of the algorithms of that generalization. The light cone for the theory as left by Einstein and Straus is found and simplifications of that theory are discussed.

Ament, W. S.↗
NASA NTRS1977

Microwave backscattering theory and active remote sensing of the ocean surface

The status is reviewed of electromagnetic scattering theory relative to the interpretation of microwave remote sensing data acquired from spaceborne platforms over the ocean surface. Particular emphasis is given to the assumptions which are either implicit or explicit in the theory. The multiple scale scattering theory developed during this investigation is extended to non-Gaussian surface statistics. It is shown that the important statistic for the case is the probability density function of the small scale heights conditioned on the large scale slopes; this dependence may explain the anisotropic scattering measurements recently obtained with the AAFE Radscat. It is noted that present surface measurements are inadequate to verify or reject the existing scattering theories. Surface measurements are recommended for qualifying sensor data from radar altimeters and scatterometers. Additional scattering investigations are suggested for imaging type radars employing synthetically generated apertures.

Brown, G. S.↗
NASA NTRS1976

Scalar-tensor theory of gravitation with negative coupling constant

The possibility of a Brans-Dicke scalar-tensor gravitation theory with a negative coupling constant is considered. The admissibility of a negative-coupling theory is investigated, and a simplified cosmological solution is obtained which allows a negative derivative of the gravitation constant. It is concluded that a Brans-Dicke theory with a negative coupling constant can be a viable alternative to general relativity and that a large negative value for the coupling constant seems to bring the original scalar-tensor theory into close agreement with perihelion-precession results in view of recent observations of small solar oblateness.

Smalley, L. L.↗
NASA NTRS1976

Can Malin's gravitational-field equations be modified to obtain a viable theory of gravity

Malin's (1975) gravitational theory, which was recently shown by Lindblom and Nester (1975) to be incorrect, is modified by means of a recently proposed method for obtaining viable gravitational theories. The resulting self-consistent theory, which is in effect a Rastall-type modification of the Einstein theory, exhibits nonconservation of momentum, yet agrees with all experimental limits known to date within the post-Newtonian approximation framework.

Smalley, L. L.↗
NASA NTRS1977

Theory of motion of Jupiter's Galilean satellites

Final results are presented for a theory enabling one to calculate the positions of the Galilean satellites and their partial derivatives. Extensive use of algebraic manipulation software on a digital computer is made to generate the final expressions. The theory is, in effect, a revitalization of Sampson's (1921) theory. Algebraic and mathematical errors existing in Sampson's work are removed, some neglected effects due to solar interactions and the 3-7 commensurability are introduced, allowance is made for nonzero amplitude and phase of the free libration, and the final results are expressed as analytic functions of variations in 49 arbitrary constants of integration and physical parameters. The theory is constructed in a manner which readily allows for future revision, and analytic expressions are provided for the partial derivatives with respect to the 49 parameters.

Lieske, J. H.↗
NASA NTRS1977

An Integrated Theory for Predicting the Hydrothermomechanical Response of Advanced Composite Structural Components

An integrated theory is developed for predicting the hydrothermomechanical (HDTM) response of fiber composite components. The integrated theory is based on a combined theoretical and experimental investigation. In addition to predicting the HDTM response of components, the theory is structured to assess the combined hydrothermal effects on the mechanical properties of unidirectional composites loaded along the material axis and off-axis, and those of angleplied laminates. The theory developed predicts values which are in good agreement with measured data at the micromechanics, macromechanics, laminate analysis and structural analysis levels.

Chamis, C. C.↗
NASA NTRS1976

Comparison of aerodynamic theory and experiment for jet-flap wings

Aerodynamic theory predictions made for a jet flapped wing were compared with experimental data obtained in a fairly extensive series of tests in the Langley V/STOL tunnel. The tests were made on a straight, rectangular wing and investigated two types of jet flap concepts: a pure jet flap with high jet deflection and a wing with blowing at the knee of a plain trailing edge flap. The tests investigated full and partial span blowing for wing aspect ratios of 8.0 and 5.5 and momentum coefficients from 0 to about 4. The total lift, drag, and pitching moment coefficients predicted by the theory were in excellent agreement with experimental values for the pure jet flap, even with the high jet deflection. The pressure coefficients on the wing, and hence the circulation lift coefficients, were underpredicted, however, because of the linearizing assumptions of the planar theory. The lift, drag, and pitching moment coefficients, as well as pressure coefficients, were underpredicted for the wing with blowing over the flap because of the failure of the theory to account for the interaction effect of the high velocity jet passing over the flap.

Gainer, T. G.↗