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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

The measurement of pulsar periods.

The method used for determining the pulsar period is discussed. In connection with the computation of the time of arrival of a pulse the right ascension and declination of the earth relative to the barycenter, the center of mass of the solar system, are calculated. The data obtained together with the position of the pulsar are used to calculate what the time of arrival would have been had the antenna been at the barycenter. A matrix approach is used for series observations. Pulsar positions obtained are listed in a table. A graph is presented showing the rate of change of the period as a function of the period for several sources.

Downs, G. S.↗
NASA NTRS1972

Periodic solutions of a forced system with hysteresis.

Hysteresis damping arising in an oscillatory system due to the phenomenon of slip damping analyzed by Goodman and Klumpp (1956) is considered. An idealized physical model is proposed, and the existence of certain periodic motions is investigated in a system with small forcing which are near the largest periodic motion in a corresponding unforced system. Periodic solutions of the forced system are obtained.-

Drew, J. H.↗
NASA NTRS1972

Dipole antenna in space - Time periodic media.

Study and solution of the problem of dipole radiation in sinusoidally space-time periodic media. The space-time periodicity can be considered as due to a strong pump wave and is expressed as a traveling-wave type change in the dielectric constant or the plasma density. The solution also covers the limit case of a sinusoidally stratified medium. The solution is formulated in a matrix form such that the basic results and diagrams apply, with minor changes, to the different cases studied: electric and magnetic dipole in a dielectric, plasma, and uniaxial plasma. The wave-vector diagram is used extensively in studying and presenting the different properties of the solution: caustics, effect of the disturbance (pump wave) motion, harmonics, radiation outside the allowed cone in a uniaxial plasma. Many dipole radiation patterns are given, and their features are explained physically. Finally, the solution and results obtained are extended to certain generally space-time periodic media.

Elachi, C.↗
NASA NTRS1973

Coincidence degree and periodic solutions of neutral equations

The problem of existence of periodic solutions for some nonautonomous neutral functional differential equations is examined. It is an application of a basic theorem on the Fredholm alternative for periodic solutions of some linear neutral equations and of a generalized Leray-Schauder theory. Although proofs are simple, the results are nontrivial extensions to the neutral case of existence theorems for periodic solutions of functional differential equations.

Hale, J. K.↗
NASA NTRS1973

A search for periodic structure in solar 2 cm microwave radiation

A power spectral analysis of 285 hr of 2 cm microwave intensity data showed no statistically significant ( 96% confidence) periodicities in the frequency range 1 to 15 mHz. No correlation was found between 2 cm periodicities and solar activity in H alpha, X-ray, and several microwave frequencies. A small shift of power toward higher frequencies in the power spectrum of the 2 cm data was found to be correlated with solar H alpha and X-ray activity. Using the statistical properties of power spectra, an expression for the ratio of the minimum detectable peak-to-peak to ambient temperature at chromospheric heights may be derived. Applied to a model for oscillation bursts in quiescent supergranules, and using the most significant results of experiments to detect the microwave periodicities, this expression yields an upper limit of approximately .0015.

Sentman, D. D.↗
NASA NTRS1973

Lunar gravity derived from long-period satellite motion - A proposed method.

A new method has been devised to determine the spherical harmonic coefficients of the lunar gravity field. This method consists of a two-step data reduction and estimation process. In the first step, a weighted least-squares empirical orbit determination scheme is applied to Doppler tracking data from lunar orbits to estimate long-period Kepler elements and rates. Each of the Kepler elements is represented by an independent function of time. The long-period perturbing effects of the earth, sun, and solar radiation are explicitly modeled in this scheme. Kepler element variations estimated by this empirical processor are then ascribed to the non-central lunar gravitation features. Doppler data are reduced in this manner for as many orbits as are available. In the second step, the Kepler element rates are used as input to a second least-squares processor that estimates lunar gravity coefficients using the long-period Lagrange perturbation equations.

Ferrari, A. J.↗
NASA NTRS1973

Periodic insolation variations on Mars.

Previously unrecognized insolation variations on Mars are a consequence of periodic variations in eccentricity, first established by the theory of Brouwer and Van Woerkom (1950). Such annual insolation variations, characterized by both 95,000-year and 2,000,000-year periodicities, may actually be recorded in newly discovered layered deposits in the polar regions of Mars. An additional north-south variation in seasonal insolation, but not average annual insolation, exists with 51,000-year and 2,000,000-year periodicities.

Murray, B. C.↗
NASA NTRS1974

Coincidence degree and periodic solutions of neutral equations

A study is made of the problem of existence of periodic solutions for some nonautonomous neutral functional differential equations. It is essentially an application of a basic theorem on the Fredholm alternative for periodic solutions of some linear neutral equations recently obtained by Hale (1973) and of a generalized Leray-Schauder theory developed by Mawhin (1972, and to appear). Although their proofs are surprisingly simple, the obtained results are nontrivial extensions to the neutral case of a number of recent existence theorems for periodic solutions of functional differential equations.

Hale, J. K.↗
NASA NTRS1974

Periodic Trojan-type orbits in the earth-sun system

Periodic orbits about the triangular equilibrium points are found for the planar restricted three-body problem using the earth-sun system. The maximum semimajor axis for tadpole orbits ranges from the infinitesimal orbit at 1.000 AU to the near-limiting orbit at 1.00285 AU. Horseshoe orbits are found for 1.0029 to 1.0080 AU, larger horseshoes being unstable because of close approaches to the earth. Using stability tests devised by Rabe (1961, 1962), the limit of stability for nonperiodic orbits is found to occur for maximum semimajor axes near 1.0020 AU. In addition, near-periodic tadpole orbits appear to be stable against perturbations by Jupiter and Venus for periods of at least 10,000 yr. The possibility that minor planets actually exist in such orbits is considered.

Weissman, P. R.↗
NASA NTRS1974

A search for 5 min periodic structure in solar 2 cm emission

Two hundred and eighty-five hours of solar data obtained from a 2 cm radiometer during 1968-1969 were analyzed for evidence of periodic structure related to the 5 min periodic chromospheric oscillations detected in optical line emissions. A power spectral analysis of the data failed to show any statistically significant periodic activity in the frequency range 1-15 mHz for data organized according to solar activity in H-alpha, soft solar X-rays (2-12 A), and several microwave frequencies (3-15 GHz). A small shift in power from low to higher frequencies in the power spectrum of the 2 cm data was found to be correlated with H-alpha and X-ray activity. This power shift is attributed to a relative increase in chromospheric turbulence at altitudes common to H-alpha, X-ray, and 2 cm emission.

Sentman, D. D.↗
NASA NTRS1975

Tracking and data system support for the Pioneer project. Volume 3: Pioneer 10 from 1 April 1972 through the Jupiter encounter period, January 1974

The Tracking and Data Systems support of the Pioneer 10 mission from April 1, 1972 through the Jupiter encounter period which ended January 5, 1974 is described. The period covered involves operations in the interplanetary environment from the time of completion of the second trajectory correction to the start of Jupiter encounter; the implementation, planning, and testing that lead to the Jupiter encounter; and the operations during the 60 day encounter period.

Miller, R. B.↗
NASA NTRS1974

The small-scale, quasi-periodic, disk component of solar radio radiation

Interferometric observations of the sun at wavelengths of 3.7 and 11 cm show that small-scale, quasi-periodic radio emission is coming from the sun. The periods occur in a band of periods with a midband frequency of 3.75 mHz and a bandwidth of 2.5 mHz. The peak-to-peak fluctuations in brightness temperature, lie between 4,000 and 500,000 K. The radio emission is less than about 10% linearly or circularly polarized; the angular size of the emitting regions is of the order of 10 seconds. The radio emission originates at the base of the chromosphere-corona transition region at approximately 2200 km above the level at which the optical depth at 5000 A is unity.

Lang, K. R.↗
NASA NTRS1974

First-order reactant in homogeneous turbulence before the final period of decay

A method is described for studying theoretically the concentration fluctuations of a dilute contaminate undergoing a first-order chemical reaction. The method is based on Deissler's (1958) theory for homogeneous turbulence for times before the final period, and it follows the approach used by Loeffler and Deissler (1961) to study temperature fluctuations in homogeneous turbulence. Four-point correlation equations are obtained; it is assumed that terms containing fifth-order correlation are very small in comparison with those containing fourth-order correlations, and can therefore be neglected. A spectrum equation is obtained in a form which can be solved numerically, yielding the decay law for the concentration fluctuations in homogeneous turbulence for the period much before the final period of decay.

Kumar, P.↗
NASA NTRS1974

Periodic solutions in a class of nonlinear dual-mass systems

A class of nonlinear spring-mass systems with two degrees of freedom is studied. A numerical method is developed for determining the periodic solutions in such systems. The method grows out of a recent paper of Yen (1974a) in which properties of such periodic solutions have been investigated theoretically. Numerical results, obtained for some example systems involving linear, cubic and quintic spring forces, support the findings of Yen and reveal further details of the properties of such periodic solutions.

Yen, D. H. Y.↗
NASA NTRS1975

Short-periodic variations and second-order numerical averaging

The principal disadvantage of the method of numerical averaging is that it provides only the average time history of the orbital elements and yields no information about the high-frequency or short-periodic variations that occur inside the averaging interval. This paper contains a description of a technique for recovering the short-periodic variations by minor modifications to the averaging process so as to permit the construction of a Fourier series for the osculating elements. The availability of this series permits the extension of the averaging technique to higher order and allows us to account for short-periodic coupling of the perturbations. Comparisons of the results with numerically integrated solutions are presented for three distinct orbit prediction problems.

Lutzky, D.↗
NASA NTRS1975

Mercury rotation period determined from Mariner 10 photography

The rotation period of Mercury has been determined to be 58.661 days by using high-resolution photography from the Mariner 10 mission. This value matches the period required for 3/2 synchronism with the orbital period (58.6462 days) within the 1-sigma errors assigned and is consistent with the latest values derived from radar and earth-based telescopic observations.

Klaasen, K. P.↗
NASA NTRS1975

Quantization and symmetry in periodic coverage patterns with applications to earth observation

Analytical approaches based on an idealized physical model and concepts from number theory show that in periodic coverage patterns, uniquely defined by their revolution numbers R (orbital) and N (rotational), the subnodal points are earth-fixed, and they divide the equator into R equal segments of length s. The ascending subsatellite trace crosses each point once (only) each period. The descending subnodal points coincide with the ascending points if the integers N and R have like parity, and bisect the intervals between them if opposite. The interval between consecutive unidirectional crossings is Ns. Symmetries extend the equatorial results to all parallels of latitude. Complete periodic patterns of traces exhibit an overall symmetry, with trace intersections confined to discrete coordinate values which are quantized in longitude (basic s-unit) and symmetric in latitude.

King, J. C.↗
NASA NTRS1976

Long period coupling terms for Lagrange's equations

A generalization of that portion of the work of Berger, which deals with the long period coupling effect of certain pairs of zonal harmonics. Long period terms arising from the short short period coupling of zonal harmonics are derived for Lagrange's equations. The formulation is general so that the results are valid for any pairs of zonal harmonics. Formulas are given to generate the various functions and integrals needed for the results given. Checks have been made against the work of Kozai.

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