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At least 559 records · Page 31

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NASA NTRS1982

Behavioral study of ultradian activity periods of mice enclosed in experimental cages of different dimensions

Male mice are enclosed in cages of different dimensions (cage A - 23x8x8 cm., cage B - 36x27x17 cm.), in an alternating light/dark regimen, at an ambient temperature of 22 to 23 C. The successions of the behavioral sequences of ultradian activity periods are noticed by direct observation during 11 consecutive hours in light. The experimental situation modifies the mean duration time and the behavioral organization of each activity period. However, the comparison of the overall activity time lengths and the comparison of the overall behavioral frequencies suggest that the energy spent per mouse is constant.

Guillot, A.↗

NASA NTRS1981

Review of analysis methods for rotating systems with periodic coefficients

Two of the more common procedures for analyzing the stability and forced response of equations with periodic coefficients are reviewed: the use of Floquet methods, and the use of multiblade coordinate and harmonic balance methods. The analysis procedures of these periodic coefficient systems are compared with those of the more familiar constant coefficient systems.

Dugundji, J.↗

NASA NTRS1982

GRID3C: Computer program for generation of C type multilevel, three dimensional and boundary conforming periodic grids

A fast computer program, GRID3C, was developed for accurately generating periodic, boundary conforming, three dimensional, consecutively refined computational grids applicable to realistic axial turbomachinery geometries. The method is based on using two functions to generate two dimensional grids on a number of coaxial axisymmetric surfaces positioned between the centerbody and the outer radial boundary. These boundary fitted grids are of the C type and are characterized by quasi-orthogonality and geometric periodicity. The built in nonorthogonal coordinate stretchings and shearings cause the grid clustering in the regions of interest. The stretching parameters are part of the input to GRID3C. In its present version GRID3C can generate and store a maximum of four consecutively refined three dimensional grids. The output grid coordinates can be calculated either in the Cartesian or in the cylindrical coordinate system.

Dulikravich, D. S.↗

NASA NTRS1982

The ultraviolet spectrum of periodic comet Encke

A comparison of the ultraviolet spectrum of periodic comet Encke, recorded by the IUE between 1980 October 24 and November 5, with similar spectra of short and long period comets shows the gaseous composition of P/Encke to be virtually identical to that of the other comets. If P/Encke is indeed the remains of a once giant comet, this similarity implies a homogeneous structure for the cometary ice nucleus. The OH brightness distribution shows a spatial variation similar to the visible fan shaped image of the comet. The total derived water production rate is a factor of five higher than that derived from HI Lyman alpha observations during the 1970 apparition and shows a variation with heliocentric distance (r) as r to the -33 power over the range from 0.81 to 1.02 AU.

Feldman, P. D.↗

NASA NTRS1981

ISEE 1 observations of thermal plasma in the vicinity of the plasmasphere during periods of quieting magnetic activity

An investigation of thermal plasma behavior in the vicinity of the plasmasphere during periods of quieting magnetic activity was conducted by combining thermal ion observations made with the plasma composition experiment on ISEE 1 with plasma density profiles obtained from plasma frequency measurements made with the same satellite's plasma wave experiment. During periods in which the magnetic activity quiets, the two regions characterized by H(+):He(+):O(+) (isotropic) and H(+):O(+):He(+) (field-aligned) ion species distributions (in order of dominance) are separated by a new region in which low-energy H(+) and He(+) are found flowing along the magnetic field lines. At other times, following quieting magnetic activity, distributions having peak fluxes at 90 deg pitch angle are observed in this region.

Horwitz, J. L.↗

NASA NTRS1981

Effects of low temperature periodic annealing on the deep-level defects in 200 keV proton irradiated AlGaAs-GaAs solar cells

The GaAs solar cell has shown good potential for space applications. However, degradation in performance occurred when the cells were irradiated by high energy electrons and protons in the space environment. The considered investigation is concerned with the effect of periodic thermal annealing on the deep-level defects induced by the 200 keV protons in the AlGaAs-GaAs solar cells. Protons at a fluence of 10 to the 11th P/sq cm were used in the irradiation cycle, while annealing temperatures of 200 C (for 24 hours), 300 C (six hours), and 400 C (six hours) were employed. The most likely candidate for the E(c) -0.71 eV electron trap observed in the 200 keV proton irradiated samples may be due to GaAs antisite, while the observed E(v) +0.18 eV hole trap has been attributed to the gallium vacancy related defect. The obtained results show that periodic annealing in the considered case does not offer any advantages over the one time annealing process.

Li, S. S.↗

NASA NTRS1982

Power series expansions for the frequency and period of the limit cycle of the van der Pol equation

An equation reported by van der Pol (1926) in connection with relaxation-oscillations studies is considered. The equation contains the factor epsilon which can assume values in the range from zero to infinity. The period T(epsilon), or equivalently the frequency nu(epsilon) of the limit cycle has been studied. However, to date there has been little success in discovering the analytical structure of T(epsilon) as a function of epsilon. The present investigation has the objectives to present the Taylor series expansion of nu(epsilon), to locate the singularities which determine the radius of convergence of that expansion, to introduce a new damping variable in terms of which the expansion converges for all epsilon, to form a new expansion for the period T(epsilon) which improves the rate of convergence of the series, to attempt to 'complete' the series, and to compare the obtained results with the numerically determined values of T(epsilon) and with the asymptotic approximation valid for large epsilon.

Andersen, C. M.↗

NASA NTRS1982

The light curve of periodic comet Halley 1910 II

Photometric parameters for periodic comet Halley 1910 II have been derived from 144 total visual magnitude estimates. The pre-perihelion data are best represented by an absolute magnitude of 5.47 and a power-law exponent of 4.44; post-perihelion results show that the absolute magnitude brightened to 4.94, and the exponent decreased to 3.07. Only small fluctuations in brightness about the power-law solutions are noted. Based on these results, a forecast of the visual brightness of periodic comet Halley's 1985-1987 apparition is presented.

Morris, C. S.↗

NASA NTRS1981

Effect of the fluid core on changes in the length of day due to long period tides

The long period luni-solar tidal potential is known to cause periodic changes in the earth's rotation rate. It is found that the effect of a dissipationless fluid outer core is to reduce the amplitudes of these tidal perturbations by about 11 percent. When the fluid core effect is added to Agnew and Farrell's (1978) estimate of the effect of an equilibrium ocean, the result is in accord with observation. The effects of dissipative processes within the fluid core are also examined. Out-of-phase perturbations are found which could be as large as about 10 ms at 18.6 yr. It is concluded, however, that the poorly understood decade fluctuations in the earth's rotation rate will prohibit observation of this effect.

Wahr, J. M.↗

NASA NTRS1981

Modification of average coronal properties in the presence of periodic temperature and density variations near the base

Conductive damping of the transient motion of the solar corona, and the consequences on the average flow field of conductively re-distributed energy are discussed. A particular example is treated. First, a steady solution for solar wind flow is found for a given set of steady boundary conditions, between 1.4 and 28 solar radii. These boundary conditions are that the density is 1.6xEO6 cm-3 and the temperature is 1.6xEO6 degrees. The flow profiles for this initial state are those shown at t=0 in the figures. Then, at t=0, periodic, in phase, sinusoidal variations in temperature and density are initiated and continued indefinitely. The amplitudes of the variations are 5 percent and 7.5 percent for the temperature and density respectively, imposed at 1.4 solar radii. The variations have a period of 1 hour shorter than a coronal transit time, but sufficiently long for the disturbances to propagate for small distances (2 to 3 solar radii). These oscillations are like those that might occur for acoustic oscillations, although no explanation is offered as to how an acoustic oscillation might extend to this radius in the first place.

Suess, S. T.↗

NASA NTRS1982

Infrared photometry of periodic comets Encke, Chernykh, Kearns-Kwee, Stephan-Oterma, and Tuttle

Nearly simultaneous photometry of the reflected and thermal infrared spectra of periodic comets Encke, Chernykh, Kearns-Kwee, Stephan-Oterma, and Tuttle are presented. The 10-micron silicate emission feature has been detected for the first time in periodic comets and was observed in three of these objects. The albedo of the dust particles in the comae of these comets is calculated and compared to that of Comet Kohoutek. The peculiar behavior of the dust in Comet Encke is discussed.

Campins, H.↗

NASA NTRS1982

Implicit numerical integration for periodic solutions of autonomous nonlinear systems

A change of variables that stabilizes numerical computations for periodic solutions of autonomous systems is derived. Computation of the period is decoupled from the rest of the problem for conservative systems of any order and for any second-order system. Numerical results are included for a second-order conservative system under a suddenly applied constant load. Near the critical load for the system, a small increment in load amplitude results in a large increase in amplitude of the response.

Thurston, G. A.↗

NASA NTRS1983

A large-amplitude photometric periodicity on a T Tauri star

B, V, and R light curvea are presented for the years 1970-1972, during whith the T Tauri star SY Chamaeleontis was observed to undergo precisely periodic brightness oscillations with a 1.6 mag B amplitude and a 6.129-day period. While SY Cha has shown small amplitude irregular variability since 1901, and in 1971 exhibited a sinusoidal light curve in the 13.4-14.2 mag range, this range was found to increase during 1971-1972 to 12.76-14.34 mag. Between 1973 and 1978, the odd behavior pattern was resumed. It is suggested that a localized bright spot formed on, or near, the surface of SY Cha, and that stellar rotation has caused the spot to appear and disapear from the vantage point of the earth.

Schaefer, B. E.↗

NASA NTRS1983

One-dimensional periodic flows with a shock transition - Application to the density wave theory of spiral structure

The problem of one-dimensional gas flow through a sinusoidal gravitational potential with a series of equally spaced shock fronts is considered. For time-independent and spatially periodic flows, an integral equation relates the flow velocity to the gravitational potential and source functions of energy and momentum densities. It is suggested that this problem simulates some of the dynamical effects of the azimuthal flow on a parcel of gas at a fixed radius in a galactic disk that supports a spiral density wave structure. It omits the radial motions. In this context, a typical azimuthal velocity across a spiral arm is specified and the resultant source functions are obtained. The implications of this calculation suggest heating of the gaseous disk by O and B stars behind the shock front, and subsequent interarm cooling is a plausible mechanism for maintaining the periodic cycling of the gaseous component of the galactic disk.

Bogdan, T. J.↗

NASA NTRS1983

The rupture process and asperity distribution of three great earthquakes from long-period diffracted P-waves

The variation of maximum earthquake size along the subduction zones has been interpreted as a variation in the seismic coupling ostensibly related to the mechanical conditions of the fault zone. Great differences are noted between the seismographs of the three great earthquakes whose rupture processes are presently considered: in the Kurile Islands (1963), The Rat Islands (1965) and Alaska (1964). On-scale long period P waves were recorded in all cases. Source time functions are deconvolved from the observed periods. It is concluded that maximum earthquake size is related to the asperity distribution on the fault. The subduction zones with the largest earthquakes have very large asperities, as in the Alaskan case, while the zones with the smaller great earthquakes, such as the Kurile Islands, have smaller scattered asperities.

Ruff, L.↗

NASA NTRS1983

Some analysis methods for rotating systems with periodic coefficients

Dugundji, J.↗

NASA NTRS1983

Orbital period changes in Centaurus X-3

Two new times of mid-X-ray eclipse for Cen X-3 are presented on the basis of pulse arrival time analyses of pointed observations with SAS 3. When combined with all other published eclipse times based on Doppler delay measurements, the results show that the 2.1d binary period is decreasing at an average rate of 1.8 x 10 to the -6th/yr. The decrease, however, is seen as having significant fluctuations about a smooth, linear decrease. The changes observed in the orbital period can be accounted for by mass loss from the system through the L2 point, although the rates required are implausibly high. It is also shown that the long-term overall orbital decay can readily be interpreted as the result of torques exerted by the tidally distorted companion star (Krzeminski's star) on the orbiting neutron star. It is noted that the inferred asynchronism between the orbital frequency and the rotation frequency of the companion star may be maintained by mass and angular momentum loss in a stellar wind or by a tidal instability related to the Darwin effect. However, this would not provide a natural explanation for any short-term deviations from a constant rate of orbital decay.

Kelley, R. L.↗

NASA NTRS1983

On searches for periodic pulsed emission - The Rayleigh test compared to epoch folding

The Rayleigh test has been recently invoked as a method of searching a time series for periodic pulsations. In this paper, this technique is discussed and compared to epoch folding, a technique which has had widespread use in X-ray astronomy. It is found that the Rayleigh test provides a more sensitive approach to the search for periodic pulsations when the pulses are sinusoidal or of broad duty cycle, such as those typical of the pulsing X-ray sources. Epoch folding, on the other hand, is more sensitive to the narrow pulses typical of radio pulsars.

Leahy, D. A.↗