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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 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
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.↗
NASA NTRS1988

Measurement and modeling of land mobile satellite propagation at UHF and L-band

A propagation experiment is described in which a stratospheric balloon served as a transmitter platform at 870 and 1502 MHz in simulation of a land mobile satellite. A vehicle followed the drifting balloon along roads of western Texas and New Mexico, collecting at L-band amplitude and phase, and at UHF amplitude information only for elevation angles between 25 and 45 deg. The data obtained have been analyzed and are presented along with results from modeling of multipath scattering and roadside tree attenuation. The signal, with variations caused by multipath propagation and tree shadowing, was reduced by 3 dB at L-band and 2 dB at UHF for one percent of all locations. A median ratio of 3.9 was found between peak-to-peak phase (degrees) and power (dB) fluctuations. The ratio between L-band and UHF dB attenuation averages varied from 1.3 to 1.0 at fade levels from 6 to 23 dB. Optical sky brightness was measured and used to predict fade distribution with great accuracy. A single-scatterer multipath model is introduced. It is used to duplicate some of the measured data and to show the dependence of power variations on satellite elevation angle. Using Fresnel diffraction theory, the attenuation caused by a model tree was calculated to be near 10 dB and the maximum fade was found to increase by the logarithm of the number of branches.

Vogel, Wolfhard J.↗
NASA NTRS1995

Signal-to-noise enhancement in ground-based intensity observations of solar p modes

Intensity observations of solar p modes are needed to form a complete picture of wave propagation in the photosphere. Ground-based intensity observations are severely hampered by terrestrial atmospheric noise. Partial cancellation of the noise power can be achieved if two spectra having disparate signal-to- noise ratios, and based on time series acquired simultaneously at the same site, are combined. A method of combining the spectra is suggested in which one amplitude is scaled and subtracted from the other. The result is squared yielding a positive-definite power density. To test the method, the intensity of light scattered by the Earth's atmnosphere was recorded at fifteen- second intervals in two narrow bands centered on 0.5 microns and 1.6 microns. When the two resulting spectra were combined, the noise power was attenuated by a factor of 2.7. The scale factor was varied about its optimum value, revealing that noise peaks have a different siganture than signal peaks, and opening up the possibility of a new tool in discrimination against noise peaks. Maxima at symmetry-allowed frequencies and minima at symmetry- forbidden frequencies indicate that the possibility that these results are obtained by chance is only 6.1 x 10(exp -4). The positions of these maxima and minima also support the solar-cycle dependent frequency shifts found by Palle, Regulo, and Roca Cortes.

Germain, Marvin E.↗
NASA NTRS2011

Observation of Relativistic Electron Microbursts in Conjunction with Intense Radiation Belt Whistler-Mode Waves

We present multi-satellite observations of large amplitude radiation belt whistler-mode waves and relativistic electron precipitation. On separate occasions during the Wind petal orbits and STEREO phasing orbits, Wind and STEREO recorded intense whistler-mode waves in the outer nightside equatorial radiation belt with peak-to-peak amplitudes exceeding 300 mV/m. During these intervals of intense wave activity, SAMPEX recorded relativistic electron microbursts in near magnetic conjunction with Wind and STEREO. This evidence of microburst precipitation occurring at the same time and at nearly the same magnetic local time and L-shell with a bursty temporal structure similar to that of the observed large amplitude wave packets suggests a causal connection between the two phenomena. Simulation studies corroborate this idea, showing that nonlinear wave.particle interactions may result in rapid energization and scattering on timescales comparable to those of the impulsive relativistic electron precipitation.

Kersten, K.↗
DOE OSTI2015

WE-EF-207-04: An Inter-Projection Sensor Fusion (IPSF) Approach to Estimate Missing Projection Signal in Synchronized Moving Grid (SMOG) System

Purpose: A synchronized moving grid (SMOG) has been proposed to reduce scatter and lag artifacts in cone beam computed tomography (CBCT). However, information is missing in each projection because certain areas are blocked by the grid. A previous solution to this issue is acquiring 2 complimentary projections at each position, which increases scanning time. This study reports our first Result using an inter-projection sensor fusion (IPSF) method to estimate missing projection in our prototype SMOG-based CBCT system. Methods: An in-house SMOG assembling with a 1:1 grid of 3 mm gap has been installed in a CBCT benchtop. The grid moves back and forth in a 3-mm amplitude and up-to 20-Hz frequency. A control program in LabView synchronizes the grid motion with the platform rotation and x-ray firing so that the grid patterns for any two neighboring projections are complimentary. A Catphan was scanned with 360 projections. After scatter correction, the IPSF algorithm was applied to estimate missing signal for each projection using the information from the 2 neighboring projections. Feldkamp-Davis-Kress (FDK) algorithm was applied to reconstruct CBCT images. The CBCTs were compared to those reconstructed using normal projections without applying the SMOG system. Results: The SMOG-IPSF method may reduce image dose by half due to the blocked radiation by the grid. The method almost completely removed scatter related artifacts, such as the cupping artifacts. The evaluation of line pair patterns in the CatPhan suggested that the spatial resolution degradation was minimal. Conclusion: The SMOG-IPSF is promising in reducing scatter artifacts and improving image quality while reducing radiation dose.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Reproducible emission from nonlinear random lasers

Multiple scattering of light serves as a mechanism for feedback in random lasers. Consequently, internal spatial mode patterns, lasing wavelengths, and output directionality can all be random. Strong mode interaction can occur in such devices due to spatially overlapping modes resulting in nonlinearity with respect to the pump input power. Nevertheless, temporal coherence and lasing mode amplitude can be fixed at a constant pumping rate. This is a property desirable for applications where unique randomness is exploited but expected to be reliable over time, such as physical unclonable functions. Random lasers can also be cheaply and easily fabricated, exhibit relatively low lasing thresholds and high emission intensity. However, the precise scattering properties of such structures and fluctuations in the pump field can make device emission irreproducible, thereby limiting random laser applications. Here, in this work, we directly compare the random lasing spectra from zinc oxide samples fabricated in four distinct ways: spin-coating, sputtering, solgel deposition, and atomic layer deposition. The particular method of fabrication has a strong impact. Samples made through atomic layer deposition here exhibit both reproducibility and strong nonlinearity desirable for applications. Randomness in emission spectra persists across hundreds of repeated and averaged measurements irrespective of spatial location and is demonstrably nonlinear with respect to input signal intensity.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Cyclotron resonance spectroscopy of a high-mobility two-dimensional electron gas from 0.4 to 100 K at high filling factors

We have studied the cyclotron mobility of a Landau-quantized two-dimensional electron gas as a function of temperature (0.4 --100 K) at a fixed magnetic field (1.25 T) using terahertz time-domain spectroscopy in a sample with a low frequency mobility of μ dc = 3.6 x 10 6 cm 2 V -1 s -1 and a carrier concentration of ns = 2 x 10 6 cm -2 . The low temperature mobility in this sample results from both impurity scattering and acoustic deformation potential scattering, with μ$-1\atop{CR}$ ≈ (2.1 x 10 5 cm 2 V -1 s -1 ) -1 + (3.8 x 10 -8 V sK -1 cm -2 x T) -1 at low temperatures. Above 50 K, the cyclotron oscillations show a strong reduction in both the oscillation amplitude and lifetime that is dominated by the contribution due to polar optical phonons. These results suggest that electron dephasing times as long as ~ 300 ps are possible even at this high lling factor (v = 6:6) in higher mobility samples (> 10 7 cm 2 V -1 s -1 ) that have lower impurity concentrations and where the cyclotron mobility at this carrier concentration would be limited by acoustic deformation potential scattering.

Curtis, Jeremy A.↗
DOE OSTI2010

Photon parton distributions in nuclei and the EMC effect

Photons, as well as quarks and gluons, are constituents of the infinite momentum frame (IMF) wave function of an energetic particle. They are mostly equivalent photons whose amplitude follows from the Lorentz transformation of the particle rest frame Coulomb field into the IMF and from the conservation of the electromagnetic current. We evaluate in a model independent way the dominant photon contribution {proportional_to}{alpha}{sub em}(Z{sup 2}/A{sup 4/3})ln(1/R{sub A}m{sub N}x) to the nuclear structure functions as well as the term {proportional_to}{alpha}{sub em}Z/A. In addition we show that the definition of x consistent with the exact kinematics of eA scattering (with exact sum rules) works in the same direction as the nucleus field of equivalent photons. Combined, these effects account for the bulk of the hadronic European Muon Collaboration (EMC) effect for x{<=}0.5 where Fermi motion effects are small. In particular, for these x the hadronic mechanism contribution to the EMC effect does not exceed {approx}3% for all nuclei. Also, the A dependence of the hadronic mechanism of the EMC effect for x>0.5 is significantly modified.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

A subleading operator basis and matching for gg → H

The Soft Collinear Effective Theory (SCET) is a powerful framework for studying factorization of amplitudes and cross sections in QCD. While factorization at leading power has been well studied, much less is known at subleading powers in the λ << 1 expansion. In SCET subleading soft and collinear corrections to a hard scattering process are described by power suppressed operators, which must be fixed case by case, and by well established power suppressed Lagrangians, which correct the leading power dynamics of soft and collinear radiation. Here we present a complete basis of power suppressed operators for gg → H, classifying all operators which contribute to the cross section at O(λ 2 ), and showing how helicity selection rules significantly simplify the construction of the operator basis. We perform matching calculations to determine the tree level Wilson coefficients of our operators. These results are useful for studies of power corrections in both resummed and fixed order perturbation theory, and for understanding the factorization properties of gauge theory amplitudes and cross sections at subleading power. As one example, our basis of operators can be used to analytically compute power corrections for N -jettiness subtractions for gg induced color singlet production at the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Low momentum transfer measurements of pion electroproduction and virtual Compton scattering at the Delta resonance

Non-spherical components of the nucleon wave function are measured through p(e,e'p)π 0 experiment at the Δ + (1232) resonance for Q 2 = 0.04, 0.09, and 0.13 (GeV=c) 2 utilizing the Jefferson National Accelerator Facility (JLab) pulsed beam and Hall A spectrometers. The new data extend the measurements of the Coulomb quadrupole amplitude to the lowest momentum transfer ever reached. The results disagree with predictions of constituent quark models and are in reasonable agreement with dynamical calculations that include pion cloud effects, chiral effective field theory and lattice calculations. The reported measurements indicate that improvement is required to the theoretical calculations and provide valuable input that will allow their refinements. The Coulomb to magnetic multipole ratio (CMR) and generalized polarizability (GP) of the nucleon are also measured through virtual Compton scattering (VCS) for Q 2 = 0.2(GeV=c) 2 utilizing the Mainz Microtron (MAMI) continuous beam and A1 spectrometers. This data represents the first low Q 2 GP measurement at the Δ + (1232) resonance. The GP measurement explores a region where previous data and theoretical calculations disagree. The CMR measurement will be the first VCS extraction to compare with world data generated through pion electroproduction. The Dispersion Relation (DR) model used for the VCS extraction provides a new theoretical framework for the data signal and backgrounds that is largely independent from the pion electroproduction models. The independence of the DR from the traditional models provides a strong crosscheck on the ability of the models to isolate the data signal.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Resonant interaction between phonons and PbTe/PbSe (001) misfit dislocation networks

Here this work aims at a quantitative and mechanistic understanding of the dynamic process of the phonon-dislocation interaction in PbTe/PbSe (001) heterostructures using the Concurrent Atomistic-Continuum (CAC) method as the simulation tool. The misfit dislocation network and the atomic-scale dislocation core structure obtained in the simulations are found to agree reasonably well with the experimental observations of the PbTe/PbSe (001) interface. Through visualizing the dynamic interaction between phonons and dislocations, as well as quantifying the dislocation vibration amplitude, the phonon energy transmission, and the thermal resistance of the misfit interfaces, this work has illustrated and quantified two mechanisms for phonon-dislocation interaction: (1) phonon scattering by the strain field of dislocations, and (2) phonon scattering by dislocations that vibrate via the local modes of a dislocation network; the latter, leads to resonant phonon-dislocation interaction, which is manifested as local maxima of out-of-phase vibration of the atoms on the two sides of the slip plane, leading to local minima of the energy transmission in the heterostructure that contains one interface. The local vibrational modes are found to be excited only by shear stress induced by transverse phonons. Among various resonant modes, the one with the lowest frequency has the strongest effect. This work has also demonstrated the collective motion of dislocations under ultrafast phonon pulses. In addition, the dynamic properties of the misfit dislocation network localized within one interface are found to be significantly altered by the presence of misfit dislocations at other interfaces, thus further confirming the cooperative dynamic nature of the motion of dislocations and phonons.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Friedel oscillation effects on the elastic collision in degenerate quantum collisional plasmas

The Friedel oscillation effects on the elastic electron-ion collisions are investigated in degenerate quantum collisional plasmas. The eikonal analysis and effective interaction model including the far-field terms caused by the quantum screening and Kohn singularities are employed to obtain the eikonal scattering phase shift and eikonal cross section as functions of the collision energy, impact parameter, collision frequency, Fermi wave number, and collision energy. The results show that the amplitude of the eikonal phase shift decreases with an increase of the collision frequency. It is found that the Friedel oscillation causes the oscillatory behavior of the differential cross section in the small-frequency domain. It is also found that the quantum oscillating behavior suddenly vanishes with an increase of the collision frequency. In addition, the collision effect of the differential cross section decreases with increasing impact parameter. It is also found that the oscillating amplitude of the differential cross section decreases with an increase of the Fermi wave number.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Transient crystalline superlattice generated by a photoacoustic transducer

Designing an efficient and simple method for modulating the intensity of x-ray radiation on a picosecond time-scale has the potential to produce ultrafast pulses of hard x-rays. In this work, we generate a tunable transient superlattice, in an otherwise perfect crystal, by photoexciting a metal film on a crystalline substrate. The resulting transient strain has amplitudes approaching 1%, wavevectors greater than 0.002 Å−1, and lifetimes approaching 1 ns. This method has the potential to generate isolated picosecond x-ray bursts with scattering efficiencies in excess of 10%.

Loether, A.↗
DOE OSTI2016

Mean flows and blob velocities in scrape-off layer (SOLT) simulations of an L-mode discharge on Alcator C-Mod

Two-dimensional scrape-off layer turbulence (SOLT) code simulations are compared with an L-mode discharge on the Alcator C-Mod tokamak [M. Greenwald, et al., Phys. Plasmas 21, 110501 (2014)]. Density and temperature profiles for the simulations were obtained by smoothly fitting Thomson scattering and mirror Langmuir probe (MLP) data from the shot. Simulations differing in turbulence intensity were obtained by varying a dissipation parameter. Mean flow profiles and density fluctuation amplitudes are consistent with those measured by MLP in the experiment and with a Fourier space diagnostic designed to measure poloidal phase velocity. Blob velocities in the simulations were determined from the correlation function for density fluctuations, as in the analysis of gas-puff-imaging (GPI) blobs in the experiment. In the simulations, it was found that larger blobs moved poloidally with the ExB flow velocity, v E , in the near-SOL, while smaller fluctuations moved with the group velocity of the dominant linear (interchange) mode, v E + 1/2 v di , where v di is the ion diamagnetic drift velocity. Comparisons are made with the measured GPI correlation velocity for the discharge. The saturation mechanisms operative in the simulation of the discharge are also discussed. In conclusion, it is found that neither sheared flow nor pressure gradient modification can be excluded as saturation mechanisms.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Feynman Amplitude Approach to study the Passage of a Jet in a Medium

In the Feynman amplitude approach for coherent collisions of a jet with medium partons, the Bose-Einstein symmetry with respect to the interchange of the exchanged bosons leads to a destructive interference of the amplitudes in most regions of the phase space but a constructive interference in some other regions. As a consequence, there is a collective longitudinal momentum transfer to the scatterers along the jet direction, each scatterer carrying a substantial fraction of the incident jet longitudinal momentum. The manifestation of the Bose-Einstein interference may have been observed in angular correlations of hadrons associated with a high-pT trigger in high-energy collisions at RHIC and LHC.

Wong, Cheuk-Yin↗
DOE OSTI2017

Beam normal spin asymmetry for the e p → e Δ ( 1232 ) process

Here, we calculate the single spin asymmetry for the $e p \to e \Delta(1232)$ process, for an electron beam polarized normal to the scattering plane. Such single spin asymmetries vanish in the one-photon exchange approximation, and are directly proportional to the absorptive part of a two-photon exchange amplitude. As the intermediate state in such two-photon exchange process is on its mass shell, the asymmetry allows one to access for the first time the on-shell $\Delta \to \Delta$ as well as $N^\ast \to \Delta$ electromagnetic transitions. We present the general formalism to describe the $e p \to e \Delta$ beam normal spin asymmetry, and provide a numerical estimate of its value using the nucleon, $\Delta(1232)$, $S_{11}(1535)$, and $D_{13}(1520)$ intermediate states. We compare our results with the first data from the Qweak@JLab experiment and give predictions for the A4@MAMI experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Blazar Jets Perturbed by Magneto-gravitational Stresses in Supermassive Binaries

We study particle acceleration and radiative processes in blazar jets under recurring conditions set by gravitational perturbations in supermassive binary systems. We consider the action from a companion orbiting a primary black hole of ∼10{sup 8} M{sub ⊙}, and perturbing its relativistic jet. We discuss how such conditions induce repetitive magneto-hydrodynamic stresses along the jet, and affect its inner electron acceleration and radiative processes. Specifically, we study how macroscopic perturbations related to increased jet “magnetization” end up in higher radiative outputs in the optical, X-ray, and gamma-ray bands. We first find an increase in magnetic field strength, as gauged in the optical band from the synchrotron emission of electrons accelerated in kinetic processes stimulated by reconnecting magnetic lines. The energetic electrons then proceed to up-scatter the synchrotron photons to GeV energies after the canonical synchrotron self-Compton radiation process. Our model implies a specific recurring pattern in the optical to gamma-ray emissions, made of high peaks and wide troughs. Progressing accelerations caused by spreading reconnections will produce an additional synchrotron keV component. Such outbursts provide a diagnostics for enhanced acceleration of electrons, which can up-scatter photons into the TeV range. We discuss how our model applies to the BL Lac object PG 1553+113, arguably the best candidate to now for high amplitude, recurring modulations in its gamma-ray emissions. We also consider other BL Lacs showing correlated keV–TeV radiations such as Mrk 421.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Mean flows and blob velocities in scrape-off layer (SOLT) simulations of an L-mode discharge on Alcator C-Mod

Two-dimensional scrape-off layer turbulence (SOLT) code simulations are compared with an L-mode discharge on the Alcator C-Mod tokamak [M. Greenwald, et al., Phys. Plasmas 21, 110501 (2014)]. Density and temperature profiles for the simulations were obtained by smoothly fitting Thomson scattering and mirror Langmuir probe (MLP) data from the shot. Simulations differing in turbulence intensity were obtained by varying a dissipation parameter. Mean flow profiles and density fluctuation amplitudes are consistent with those measured by MLP in the experiment and with a Fourier space diagnostic designed to measure poloidal phase velocity. Blob velocities in the simulations were determined from the correlation function for density fluctuations, as in the analysis of gas-puff-imaging (GPI) blobs in the experiment. In the simulations, it was found that larger blobs moved poloidally with the ExB flow velocity, vE , in the near-SOL, while smaller fluctuations moved with the group velocity of the dominant linear (interchange) mode, vE + 1/2 vdi, where vdi is the ion diamagnetic drift velocity. Comparisons are made with the measured GPI correlation velocity for the discharge. The saturation mechanisms operative in the simulation of the discharge are also discussed. It is found that neither sheared flow nor pressure gradient modification can be excluded as saturation mechanisms.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗