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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

Role of Compressive Viscosity and Thermal Conductivity on the Damping of Slow Waves in Coronal Loops with and Without Heating–Cooling Imbalance

In the present article, we derive a new dispersion relation for slow magnetoacoustic waves invoking the effect of thermal conductivity, compressive viscosity, radiation, and an unknown heating term along with the consideration of heating–cooling imbalance from linearized MHD equations. We solve the general dispersion relation to understand the role of compressive viscosity and thermal conductivity in the damping of slow waves in coronal loops with and without heating–cooling imbalance. We have analyzed the wave damping for the range of loop length L=50--500 Mm, temperature T=5--30 MK, and density ρ=10^(−11)--10^(−9) kg/cu.m. It was found that the inclusion of compressive viscosity along with thermal conductivity significantly enhances the damping of the fundamental mode oscillations in shorter (e.g. L=50 Mm) and super-hot (T>10 MK) loops. However, the role of viscosity in the damping is insignificant in longer (e.g. L=500 Mm) and hot loops (T≤10 MK) where, instead, thermal conductivity along with the presence of heating–cooling imbalance plays a dominant role. For shorter loops at a super-hot regime of temperature, the increment in the loop density substantially enhances the damping of the fundamental modes due to thermal conductivity when viscosity is absent, however, when the compressive viscosity is added the increase in density substantially weakens the damping. Thermal conductivity alone is found to play a dominant role in longer loops at lower temperatures (T≤10 MK), while compressive viscosity dominates the damping at super-hot temperatures (T>10 MK) in shorter loops. The predicted scaling law between damping time (τ) and wave period (P) is found to better match the observed SUMER (Solar Ultraviolet Measurements of Emitted Radiation) oscillations when the heating–cooling imbalance is taken into account in addition to thermal conductivity and compressive viscosity for the damping of the fundamental slow mode oscillations.

Abhinav Prasad↗
DOE OSTI2020

Evidence for an edge supercurrent in the Weyl superconductor MoTe 2

Edge supercurrents in superconductors have long been an elusive target. Interest in them has reappeared in the context of topological superconductivity. We report evidence for the existence of a robust edge supercurrent in the Weyl superconductor molybdenum ditelluride (MoTe 2 ). In a magnetic field B , fluxoid quantization generates a periodic modulation of the edge condensate observable as a “fast-mode” oscillation of the critical current I c versus B . The fast-mode frequency is distinct from the conventional Fraunhofer oscillation displayed by the bulk supercurrent. We confirm that the fast-mode frequency increases with crystal area as expected for an edge supercurrent. In addition, weak excitation branches are resolved that display an unusual broken symmetry.

Science & Technology - Other Topics↗
NASA NTRS1988

Long-pulse generation with a stable-relaxation-oscillation Nd:YLF laser

A simple technique for long-pulse (0.2-2 microsec) generation with neodymium lasers has been demonstrated. Under the proper conditions, a normal-mode oscillator, operated in a single transverse mode, produces well-defined relaxation oscillations from which a single subpulse can be isolated for amplification. The characteristic subpulse temporal profile is ideal for saturated amplification without pulse shortening. Data are presented for a Nd:YLF system consisting of an oscillator followed by a 64-nm-long amplifier. Pulse energies in excess of 100 mJ were achieved with a small-signal gain of 630.

Harisson, J.↗
DOE OSTI2011

ON THE FLARE-INDUCED SEISMICITY IN THE ACTIVE REGION NOAA 10930 AND RELATED ENHANCEMENT OF GLOBAL WAVES IN THE SUN

A major flare (of class X3.4) occurred on 2006 December 13 in the active region NOAA 10930. This flare event has remained interesting to solar researchers for studies related to particle acceleration during the flare process and the reconfiguration of magnetic fields as well as fine-scale features in the active region. The energy released during flares is also known to induce acoustic oscillations in the Sun. Here, we analyze the line-of-sight velocity patterns in this active region during the X3.4 flare using the Dopplergrams obtained by the Global Oscillation Network Group (GONG) instrument. We have also analyzed the disk-integrated velocity observations of the Sun obtained by the Global Oscillation at Low Frequency (GOLF) instrument on board the Solar and Heliospheric Observatory spacecraft as well as full-disk collapsed velocity signals from GONG observations during this flare to study any possible connection between the flare-related changes seen in the local and global velocity oscillations in the Sun. We apply wavelet transform to the time series of the localized velocity oscillations as well as the global velocity oscillations in the Sun spanning the flare event. The line-of-sight velocity shows significant enhancement in some localized regions of the penumbra of this active region during the flare. The affected region is seen to be away from the locations of the flare ribbons and the hard X-ray footpoints. The sudden enhancement of this velocity seems to be caused by the Lorentz force driven by the 'magnetic jerk' in the localized penumbral region. Application of wavelet analysis to these flare-induced localized seismic signals shows significant enhancement in the high-frequency domain (5 <{nu} < 8 mHz) and a feeble enhancement in the p-mode oscillations (2 <{nu} < 5 mHz) during the flare. On the other hand, the wavelet analysis of GOLF velocity data and the full-disk collapsed GONG velocity data spanning the flare event indicates significant post-flare enhancements in the high-frequency global velocity oscillations in the Sun, as evident from the wavelet power spectrum and the corresponding scale-average variance. The present observations of the flare-induced seismic signals in the active region in context of the driving force are different as compared to previous reports on such cases. We also find indications of a connection between flare-induced localized seismic signals and the excitation of global high-frequency oscillations in the Sun.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1984

Observations of Intermediate-degree Solar Oscillations

A progress report on observations of intermediate degree oscillations is presented. Frequencies of zonal p-mode oscillations with amplitudes in excess of approx are found. 2 cm/s. These frequencies show systematic disagreement with recent theoretical calculations. The frequencies with asymptotic formula estimates are examined. Small scatter is obtained for low degree modes but large scatter at large degree. A first look at sectoral harmonic observations shows that magnetic active regions provide a major signal at low frequencies.

Harvey, J. W.↗
DOE OSTI2014

Exact methods for self interacting neutrinos

The effective many-body Hamiltonian which describes vacuum oscillations and self interactions of neutrinos in a two flavor mixing scheme under the single angle approximation has the same dynamical symmetries as the well known BCS pairing Hamiltonian. These dynamical symmetries manifest themselves in terms of a set of constants of motion and can be useful in formulating the collective oscillation modes in an intuitive way. In particular, we show that a neutrino spectral split can be simply viewed as an avoided level crossing between the eigenstates of a mean field Hamiltonian which includes a Lagrange multiplier in order to fix the value of an exact many-body constant of motion. We show that the same dynamical symmetries also exist in the three neutrino mixing scheme by explicitly writing down the corresponding constants of motion.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Formation of nickel magnetic nanoparticles and modification of nickel phthalocyanine matrix by sodium doping

Data for the vapor-phase doping (300°C) of nickel phthalocyanine (NiPc) by sodium taken in different concentrations (x), as well as structural analysis data for Na{sub x=0.2}NiPc, Na{sub x=1}NiPc, and Na{sub x=3}NiPc samples, have been reported. The structure of the samples and their atomic configuration versus the doping level have been studied by transmission electron microscopy, Raman scattering, X-ray diffraction, X-ray absorption spectroscopy, and extended X-ray absorption fine structure (EXAFS) spectroscopy. The structural parameters of Ni–N, Ni–C, and Ni–Ni bonds have been determined, and it has been found that, at a low level of doping by sodium, local structural distortions are observed in some molecules of the NiPc matrix near nickel atoms. The fraction of these molecules grows as the doping level rises from x = 0.2 to x = 1.0. It has been shown that doping changes the oscillation mode of light atoms, which indicates a rise in the electron concentration on five- and six-membered rings. At a high level of sodium doping (x = 3.0), nickel nanoparticles with a mean size of 20 nm and molecule decomposition products have been observed in the NiPc matrix. It has been found that the fraction of nickel atoms in the Na{sub x=3}NiPc nanoparticles as estimated from EXAFS data is sufficient for the room-temperature magnetic properties of the samples to persist for a long time.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1995

Hybrid propulsion for launch vehicle boosters: A program status update

Results obtained in studying the origin and suppression of large-amplitude pressure oscillations in a 24 in. diameter hybrid motor using a liquid oxygen/hydroxylterminated polybutadiene/polycyclopentadiene propellant system are discussed. Tests conducted with liquid oxygen flow rates varying from 10 to 40 lbm/sec were designed to gauge the effectiveness of various vaporization chamber flow fields, injector designs, and levels of heat addition in suppressing high-frequency longitudinal mode oscillations. Longitudinal acoustic modes did not arise in any tests. However, initial testing revealed the presence of high-amplitude, sinusoidal, nonacoustic oscillations persisting throughout the burn durations. Analysis showed this to be analogous to chug mode instability in liquid rocket engines brought about by a coupling of motor combustion processes and the liquid oxygen feed system. Analytical models were developed and verified by test data to predict the amplitude and frequency of feed-system-coupled combustion pressure oscillations. Subsequent testing showed that increasing the feed system impedance eliminated the bulk mode instability. This paper documents the work completed to date in performance of the Hybrid Propulsion Technology for Launch Vehicle Boosters Program (NAS8-39942) sponsored by NASA's George C. Marshall Space Flight Center.

Carpenter, R. L.↗
DOE OSTI2011

Gamma-ray strength functions and their relation to astrophysics

The nuclear {gamma}-ray strength function is one of the indispensable inputs needed for reaction-rate calculations, and is particularly important for the neutron-capture cross section. The nuclear physics group at the Oslo Cyclotron Laboratory has developed a method to extract simultaneously nuclear level density and {gamma}-ray strength function from particle-{gamma} coincidence measurements. Data on the strength functions of Sn nuclei as well as for lighter elements are presented. The Sn isotopes all display a resonance-like structure close to the neutron threshold, that could possibly be due to the neutron-skin oscillation mode. This so-called pygmy dipole resonance greatly influences the neutron-capture rates. In the lighter nuclei, an enhancement of the strength function at low {gamma} energies is observed. The possible impact of this increase on Maxwellian-averaged reaction rates has been investigated.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Charge carrier dynamics and surface plasmon interaction in gold nanorod-blended organic solar cell

The inclusion of plasmonic nanoparticles into organic solar cell enhances the light harvesting properties that lead to higher power conversion efficiency without altering the device configuration. This work defines the consequences of the nanoparticle overloading amount and energy transfer process between gold nanorod and polymer (active matrix) in organic solar cells. We have studied the hole population decay dynamics coupled with gold nanorods loading amount which provides better understanding about device performance limiting factors. The exciton and plasmon together act as an interacting dipole; however, the energy exchange between these two has been elucidated via plasmon resonance energy transfer (PRET) mechanism. Further, the charge species have been identified specifically with respect to their energy levels appearing in ultrafast time domain. The specific interaction of these charge species with respective surface plasmon resonance mode, i.e., exciton to transverse mode of oscillation and polaron pair to longitudinal mode of oscillations, has been explained. Thus, our analysis reveals that PRET enhances the carrier population density in polymer via non-radiative process beyond the concurrence of a particular plasmon resonance oscillation mode and polymer absorption range. These findings give new insight and reveal specifically the factors that enhance and control the performance of gold nanorods blended organic solar cells. This work would lead in the emergence of future plasmon based efficient organic electronic devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1993

Acoustic oscillations of Jupiter

We calculate low-degree l acoustic (p-mode) oscillations of the giant planet Jupiter. We use two Jupiter models, both of which contain a rocky core, an ice mantle, and a hydrogen-rich envelope. One of the models incorporates the 'plasma phase transition' of hydrogen, a first-order phase transition that yields a density discontinuity in the hydrogen-rich envelope. Our calculations of the acoustic oscillation spectrum of Jupiter have taken account of the effects of the rapid rotation of the planet: the Coriolis force, centrifugal force, and deformation of the equilibrium state. The p-mode frequency spectra of the Jupiter models are summarized in several echelle diagrams. We show that the frequency spectra of the low-degree p-modes are strongly affected by the existence of the rocky core and by avoided crossings among high radial-order p-modes with different l's.

Lee, Umin↗
NASA NTRS1990

Depth and latitude dependence of the solar internal angular velocity

One of the design goals for the dedicated helioseismology observing state located at Mount Wilson Observatory was the measurement of the internal solar rotation using solar p-mode oscillations. In this paper, the first p-mode splittings obtained from Mount Wilson are reported and compared with those from several previously published studies. It is demonstrated that the present splittings agree quite well with composite frequency splittings obtained from the comparisons. The splittings suggest that the angular velocity in the solar equatorial plane is a function of depth below the photosphere. The latitudinal differential rotation pattern visible at the surface appears to persist at least throughout the solar convection zone.

Rhodes, Edward J., Jr.↗
NASA NTRS1986

Oscillations of a viscous compound drop

The effect of viscosity on normal mode oscillations of a compound drop is determined for a range of values of the viscosity, and the effect of a host medium is considered. The general form of the dispersion relation is derived, and numerical values are obtained for the case of an annular liquid region composed of silicon oil and with the core and host regions taken to be air. Results indicate that the sloshing mode of the compound drop is more damped than the bubble mode.

Lyell, M. J.↗
NASA NTRS1983

Frequencies, amplitudes and linewidths of solar oscillations from total irradiance observations

Ten months of solar total irradiance data from the Solar Maximum Mission satellite have generated accurate frequencies, amplitudes and linewidths for individual about 5-min solar p-mode oscillations of low degree. The modes can be described as independent and chaotically excited oscillators, and provide no evidence for the fine structure taken to imply rapid internal rotation of the sun.

Woodard, M.↗
NASA NTRS1995

Measurement of high-degree solar oscillation frequencies

We present m-averaged solar p- and f-mode oscillation frequencies over the frequency range nu greater than 1.8 and less than 5.0 mHz and the spherical harmonic degree range l greater than or equal to 100 and less than or equal to 1200 from full-disk, 1000 x 1024 pixel, Ca II intensity images collected 1993 June 22-25 with a temporal cadence of 60 s. We itemize the sources and magnitudes of statistical and systematic uncertainties and of small frequency corrections, and we show that our frequencies represent an improvement in accuracy and coverage over previous measurements. Our frequencies agree at the 2 micro Hz level with Mount Wilson frequencies determined for l less than or equal to 600 from full-disk images, and we find systematic offsets of 10-20 micro Hz with respect to frequencies measured from Big Bear and La Palma observations. We give evidence that these latter offsets are indicative of spatial scaling uncertainties associated with the analysis of partial-disk images. In comparison with theory, our p-mode frequencies agree within 10 micro Hz of frequencies predicted by the Los Alamos model but are as much as 100 micro Hz smaller than frequencies predicted by the Denmark and Yale models at degrees near 1000. We also find systematic differences between our n = 0 frequencies and the frequencies closely agreed upon by all three models.

Bachmann, K. T.↗
NASA NTRS1991

Nonradial oscillations of Saturn

The planetary interior-state sensitivity of the f-mode oscillations of Saturn, which may be detected through their gravitational signature in the rings, are presently studied in light of the results of mode-period calculations for various interior models, envelope compositions, and hydrogen phase-transition pressures. It is established that the low-degree f modes exhibit the highest sensitivity to the size of the planetary core, while higher-degree modes exhibit greater sensitivity to the rotation state of the Saturn's outer layers.

Marley, Mark S.↗