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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Motion and decay of vortex rings submerged in a rotational flow

The interaction between vortex rings of finite strength and an axisymmetric rotational background flow is studied by a singular perturbation method, because it is difficult to use a finite-difference method to analyze the viscous decay in the small core of a vortex ring. The analysis is carried out by combining a composite solution of a vortex ring and an unsteady Euler solution for the background rotational flow. Using the method of averaging, a numerical scheme is developed to obtain an Euler solution in which the grid and time-step sizes depend solely on the length and velocity scales of the background flow. Numerical results are presented to illustrate the interaction between the trajectories and decay rates of the vortex rings and the background rotational flow.

Ishii, K.↗
NASA NTRS1987

Decay of electrostatic hydrogen cyclotron waves into ion acoustic modes in auroral field lines

The coherent three-wave decay of a linearly unstable electrostatic hydrogen cyclotron (EHC) wave into stable EHC and ion acoustic modes is considered. The general problem of the three weakly interacting electrostatic normal modes in a Maxwellian plasma is discussed. EHC is examined in a fluid description, and the results are used to guide a similar study in a Vlasov plasma system intended to model the aurora acceleration region parameters. The time dependence of the decay in a simple three-wave interaction is presented in order to show how wave saturation can arise.

Bergmann, R.↗
NASA NTRS1987

Observation of nonlinear wave decay processes in the solar wind by the AMPTE IRM plasma wave experiment

Nonlinear wave decay processes have been detected in the solar wind by the plasma wave experiment aboard the Active Magnetospheric Particle Tracer Explorers (AMPTE) IRM spacecraft. The main process is the generation of ultralow-frequency ion acoustic waves from the decay of Langmuir waves near the electron plasma frequency. Frequently, this is accompanied by an enhancement of emissions near twice the plasma frequency. This enhancement is most likely due to the generation of electromagnetic waves from the coalescence of two Langmuir waves. These processes occur within the electron foreshock in front of the earth's bow shock.

Koons, H. C.↗
NASA NTRS1987

Alpha-decay-induced fracturing in zircon - The transition from the crystalline to the metamict state

Zonation due to alpha-decay damage in a natural single crystal of zircon from Sri Lanka is discussed. The zones vary in thickness on a scale from one to hundreds of microns. The uranium and thorium concentrations vary from zone to zone such that the alpha decay dose is between 0.2 x 10 to the 16th and 0.8 x 10 to the 16th alpha-events per milligram. The transition from the crystalline to the aperiodic metamict state occurs over this dose range. At doses greater than 0.8 x 10 to the 16th alpha events/mg there is no evidence for long-range order. This type of damage will accumulate in actinide-bearing, ceramic nuclear waste forms. The systematic pattern of fractures would occur in crystalline phases that are zoned with respect to actinide radionuclides.

Chakoumakos, Bryan C.↗
NASA NTRS1987

On the correlation of plume centerline velocity decay of turbulent acoustically excited jets

Acoustic excitation was shown to alter the velocity decay and spreading characteristics of jet plumes by modifying the large-scale structures in the plume shear layer. The present work consists of reviewing and analyzing available published and unpublished experimental data in order to determine the importance and magnitude of the several variables that contribute to plume modification by acoustic excitation. Included in the study were consideration of the effects of internal and external acoustic excitation, excitation Strouhal number, acoustic excitation level, nozzle size, and flow conditions. The last include jet Mach number and jet temperature. The effects of these factors on the plume centerline velocity decay are then summarized in an overall empirical correlation.

Vonglahn, Uwe H.↗
NASA NTRS1988

Evidence of the in situ decay of Al-26 in a Semarkona chondrule

A long-standing problem in the study of meteorites, with broad implications for the evolution of the solar system, is the source of heat for melting small planets. Meteorites, such as the eucrites, were obviously the result of a melting process on a small planet, yet the decay of the long-lived radionuclides present on the earth, K-40, U-235, U-238, and Th-232, could not have provided nearly enough heat to initiate melting approximately 4.5 aeons ago, even on bodies 1000 km in diameter. This problem addressed by H.C. Urey in 1955, who recognized that the presence of short-lived (and now extinct) radionuclides such as Al-26 (half-life of approximately 720,000 y) in the early solar system would have provided an abundant heat source for melting small asteroid-size bodies. Since any Al-26 initially present in the solar nebula would have completely decayed after only a few tens of millions of years, the problem became one of finding evidence of Al-26, in the form of excess Mg-26, in meteorites. The search for evidence of the Al-26 is briefly examined.

Hutcheon, I. D.↗
NASA NTRS1987

On the correlation of plume centerline velocity decay of turbulent acoustically excited jets

Acoustic excitation has been shown to alter the velocity decay and spreading characteristics of jet plumes by modifying the large-scale structures in the plume shear layer. The present work consists of reviewing and analyzing available published and unpublished experimental data in order to determine the importance and magnitude of the several variables that contribute to plume modification by acoustic excitation. Included in the study were consideration of the effects of internal or external acoustic excitation, excitation Strouhal number, acoustic excitation level, nozzle size and flow conditions. The last include jet Mach number and jet temperature. The effects of these factors on the plume centerline velocity decay are then summarized in an overall empirical correlation.

Von Glahn, Uwe H.↗
NASA NTRS1987

The effect of decay of the amplitude of oscillation on random process models for QPO X-ray stars

Random process models provide a useful mathematical framework for analysis of the quasi-periodic oscillations (QPO) recently discovered in the X-ray emission from certain luminous Galactic X-ray stars. In this paper, consideration is given to the effects of the power spectrum of the decay of the amplitude of oscillation that is expected in some physical models for the QPO phenomena. The resulting changes in the power spectrum depend on the ratio of the decay time of the amplitude of oscillation to the lifetime of the shot envelope. For values of this ratio less than about 10, it is found that incoherent QPO peaks in the power spectrum are significantly reduced in height and total power and are broadened in width, making them more difficult to detect. Coherent terms in the power spectrum, if present, are reduced in height and total power, but their width is unaffected. The red noise component remains unchanged. The present results are applied to the beat-frequency modulated accretion model in order to set constraints on the physical properties of the boundary layer between the inner edge of the accretion disk and the neutron star magnetosphere.

Shibazaki, N.↗
NASA NTRS1988

Assessment of the hydrogen external tank pressure decay anomaly on Space Transportation System (STS) 51-L

Following the Challenger tragedy, an evaluation of the integrated main propulsion system flight data revealed a premature decay in the hydrogen external tank ullage pressure. A reconstruction of predicted ullage pressure versus time indicated an inconsistency between predicted and measured ullage pressure starting at approximately 65.5 seconds into the flight and reaching a maximum value between 72 and 72.9 seconds. This discrepancy could have been caused by a hydrogen gas leak or by a liquied hydrogen leak that occurred either in the pressurization system or in the external tank. The corresponding leak rates over the time interval from 65.5 to 72.9 seconds were estimated to range from 0.28 kg/s (0.62 lbm/s) + or - 41 percent to between 0.43 and 0.51kg/s (0.94 and 1.12lbs/s) + or - 1 percent for a gas leak and from 72.9 kg/s (160.5 lbs/s) + or - 41 percent to between 111.6 and 133.2 kg/s (245.8 and 293.3 lbs/s) + or - 1 percent for a liquid leak. No speculation is made to ascertain whether the leak is liquid or gas, as this cannot be determined from the analysis performed. Four structural failures in the hydrogen external tank were considered to explain the leak rates. A break in the 5-cm (2 in) pressurization line, in the 13-cm (5 in) vent line, or in the 43-cm (17 in) feedline is not likely. A break in the 10-cm (4 in) recirculation line with a larger structural failure occurring in the 72 to 73-second time period, the time of the visibly identified premature pressure decay, does seem plausible and the most likely of the four modes considered. These modes are not all-inclusive and do not preclude the possibility of a leak elsewhere in the tank.

Buckley, Theresa M.↗
NASA NTRS1988

EUVE/XTE orbit decay study

The Explorer Platform (EP) program currently comprises two missions, the Extreme Ultraviolet Explorer (EUVE) and the X-ray Timing Explorer (XTE), each of which consists of a scientific payload mounted to the EP. The EP has no orbit maintenance capability. The EP with the EUVE payload will be launched first. At the end of the EUVE mission, the spacecraft will be serviced by the Space Transportation System (STS), and the EUVE instrument will be exchanged for the XTE. The XTE mission will continue until reentry or reservicing by the STS. Because the missions will be using the EP sequentially, the orbit requirements are unusually constrained by orbit decay rates. The initial altitude must be selected so that, by the end of the EUVE mission (2.5 years), the spacecraft will have decayed to an altitude within the STS capabilities. In addition, the payload exchange must occur at an altitude that ensures meeting the minimum XTE mission lifetime (3 years) because no STS reboost will be available. Studies were performed using the Goddard Mission Analysis System to estimate the effects of mass, cross-sectional area, and solar flux on the fulfillment of mission requirements. In addition to results from these studies, conclusions are presented as to the accuracy of the Marshall Space Flight Center solar flux predictions.

Richon, K.↗
NASA NTRS1988

Lower bound on e+e- decay of massive neutrinos

Astronomical observations of SN1987A, such as the light curve, spectral intensities of lines, the X-ray emissions, etc., constrain the lifetime for the decay of a heavy neutrino 1 MeV less than or equivalent to m sub nu H less than or equal to 50 MeV through nu sub H yields nu sub 1+e(+)+e(-) exceeds 4 x 10 to the 15th exp(-m sub nuH/5MeV) seconds. Otherwise. resulting ionization energy deposits and stronger X-ray emission would have been observed. This coupled with traditional cosmological considerations argues that the lifetime of tau-neutrinos probably exceeds the age of the universe. This in turn would imply the standard cosmological mass bound does apply to nu sub tau, namely m sub nu sub tau less than or equivalent to 100 h squared eV (where h is the Hubble constant in units of 100 km/sec/mpc). The only significant loophole for these latter arguments would be if nu sub tau primarily decays rapidly into particles having very weak interactions.

Cowsik, R.↗
NASA NTRS1988

Cosmic string catalysis of skyrmion decay

The Callan-Witten picture is developed for monopole catalyzed skyrmion decay in order to analyze the corresponding cosmic string scenario. It is discovered that cosmic strings (both ordinary and superconducting) can catalyze proton decay, but that this catalysis only occurs on the scale of the core of the string. In order to do this we have to develop a vortex model for the superconducting string. An argument is also given for the difference in the enhancement factors for monopoles and strings.

Gregory, Ruth↗
NASA NTRS1988

Trajectory analysis for low thrust maneuvers and drag decay in low earth orbit operations

In the 1990s low earth orbit operations are anticipated which will include the Space Station and orbital maneuver vehicle (OMV) serviceable satellites requiring reboost and coordination despite drag decay and oblateness effects. A low thrust targeting algorithm is described applicable to Space Station and the OMV. Tests were made with Space Station reboost requirements and an oblate gravity model. The reboost requirements were determined based on projected station growth, atmospheric models and anticipated flight profiles. The targeting algorithm as well as the algorithm for predicting orbital decay are perturbation formulations of more 'transcendental' systems and are used in interactive personal computer simulations. Performance results and a discussion for the Space Station problems are provided.

Kelly, W. D.↗
NASA NTRS1989

Cosmic strings and baryon decay catalysis

Cosmic strings, like monopoles, can catalyze proton decay. For integer charged fermions, the cross section for catalysis is not amplified, unlike in the case of monopoles. The catalysis processes are reviewed both in the free quark and skyrmion pictures and the implications for baryogenesis are discussed. A computation of the cross section for monopole catalyzed skyrmion decay is presented using classical physics. Also discussed are some effects which can screen catalysis processes.

Gregory, Ruth↗
NASA NTRS1990

Cosmic strings and baryon decay

The current literature is reviewed on baryon decay catalysis by cosmic string. A summary is presented of the main arguments for decay catalysis.

Gregory, Ruth↗
NASA NTRS1989

Does mass accretion lead to field decay in neutron stars?

Adopting the hypothesis of accretion-induced magnetic field decay in neutron stars, the consequent evolution of a neutron star's spin and magnetic field are calculated. The results are consistent with observations of binary and millisecond radio pulsars. Thermomagnetic effects could provide a possible physical mechanism for such accretion-induced field decay.

Shibazaki, N.↗
NASA NTRS1990

Solar neutron decay proton observations in cycle 21

Measurement of the flux and energy spectrum of the protons resulting from the decay of solar flare neutrons gives unique information on the spectrum of neutrons from 5 to 200 MeV. Neutrons from three flares have been observed in this manner during solar cycle 21. The use of the decay protons to determine neutron energy spectra is reviewed, and new and definitive energy spectra are presented for the two large flares on June 3, 1982 and April 25, 1984.

Evenson, Paul↗