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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 1,513 records · Page 84
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

An a priori model for the reduction of nutation observations: KSV(1994.3) nutation series

We discuss the formulation of a new nutation series to be used in the reduction of modern space geodetic data. The motivation for developing such a series is to develop a nutation series that has smaller short period errors than the IAU 1980 nutation series and to provide a series that can be used with techniques such as the Global Positioning System (GPS) that have sensitivity to nutations but can directly separate the effects of nutations from errors in the dynamical force models that effect the satellite orbits. A modern nutation series should allow the errors in the force models for GPS to be better understood. The series is constructed by convolving the Kinoshita and Souchay rigid Earth nutation series with an Earth response function whose parameters are partly based on geophysical models of the Earth and partly estimated from a long series (1979-1993) of very long baseline interferometry (VLBI) estimates of nutation angles. Secular rates of change of the nutation angles to represent corrections to the precession constant and a secular change of the obliquity of the ecliptic are included in the theory. Time dependent amplitudes of the Free Core Nutation (FCN) that is most likely excited by variations in atmospheric pressure are included when the geophysical parameters are estimated. The complex components of the prograde annual nutation are estimated simultaneously with the geophysical parameters because of the large contribution to the nutation from the S(sub 1) atmospheric tide. The weighted root mean square (WRMS) scatter of the nutation angle estimates about this new model are 0.32 mas and the largest correction to the series when the amplitudes of the ten largest nutations are estimated is 0.18 +/- 0.03 mas for the in phase component of the prograde 18. 6 year nutation.

Herring, T. A.↗
DOE OSTI2014

Interaction physics for the stimulated Brillouin scattering of a laser in laser driven fusion

Energy exchange between pump wave and ion-acoustic wave during the stimulated Brillouin Scattering process in relativistic laser-plasma interactions is studied, including the effect of damping coefficient of electron-ion collision by obeying the energy and momentum conservations. The variations of plasma density and damping coefficient of electron-ion collision change the amplitudes of the interacting wave. The relativistic mass effect modifies the dispersion relations of the interacting waves and consequently, the energy exchange during the stimulated Brillouin Scattering is affected. The collisional damping of electron-ion collision in the plasma is shown to have an important effect on the evolution of the interacting waves. (author)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1990

Multipole radiation in charged-particle scattering

This paper formulates the general problem of photon emission in particle scattering using a classical and quantum mechanical approach. The connection between the classical short collision time (SCT) and Born results is examined for various special classifications of problems. In the dipole case the two formulations yield results that can be expressed in the same form and for arbitrary scattering potential. For quadrupole emission the SCT and Born results are the same only for a short-range potential, however. The quadrupole problem is more sensitive to details in the process because the calculation requires an expansion of the total amplitude for the process to lowest order in the photon wave number or momentum. The special case of photon emission associated with spin-flip transitions during scattering is considered for spin-1/2 particles. Like classical magnetic dipole radiation, there is no infrared divergence feature for this type of emission.

Gould, Robert J.↗
DOE OSTI2017

The Correlation between Halo Mass and Stellar Mass for the Most Massive Galaxies in the Universe

We present measurements of the clustering of galaxies as a function of their stellar mass in the Baryon Oscillation Spectroscopic Survey. We compare the clustering of samples using 12 different methods for estimating stellar mass, isolating the method that has the smallest scatter at fixed halo mass. In this test, the stellar mass estimate with the smallest errors yields the highest amplitude of clustering at fixed number density. We find that the PCA stellar masses of Chen et al. clearly have the tightest correlation with halo mass. The PCA masses use the full galaxy spectrum, differentiating them from other estimates that only use optical photometric information. Using the PCA masses, we measure the large-scale bias as a function of M{sub ∗} for galaxies with logM{sub ∗}⩾11.4, correcting for incompleteness at the low-mass end of our measurements. Using the abundance matching ansatz to connect dark matter halo mass to stellar mass, we construct theoretical models of b(M{sub ∗}) that match the same stellar mass function but have different amounts of scatter in stellar mass at fixed halo mass, σ{sub logM∗}. Using this approach, we find σ{sub logM∗}=0.18{sub −0.02}{sup +0.01}. This value includes both intrinsic scatter as well as random errors in the stellar masses. To partially remove the latter, we use repeated spectra to estimate statistical errors on the stellar masses, yielding an upper limit to the intrinsic scatter of 0.16 dex.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1987

New main reflector, subreflector and dual chamber concepts for compact range applications

A compact range is a facility used for the measurement of antenna radiation and target scattering problems. Most presently available parabolic reflectors do not produce ideal uniform plane waves in the target zone. Design improvements are suggested to reduce the amplitude taper, ripple and cross polarization errors. The ripple caused by diffractions from the reflector edges can be reduced by adding blended rolled edges and shaping the edge contour. Since the reflected edge continues smoothly from the parabola onto the rolled surface, rather than being abruptly terminated, the discontinuity in the reflected field is reduced which results in weaker diffracted fields. This is done by blending the rolled edges from the parabola into an ellipse. An algorithm which enables one to design optimum blended rolled edges was developed that is based on an analysis of the continuity of the surface radius of curvature and its derivatives across the junction. Futhermore, a concave edge contour results in a divergent diffracted ray pattern and hence less stray energy in the target zone. Design equations for three-dimensional reflectors are given. Various examples were analyzed using a new physical optics method which eliminates the effects of the false scattering centers on the incident shadow boundaries. A Gregorian subreflector system, in which both the subreflector and feed axes are tilted, results in a substantial reduction in the amplitude taper and cross polarization errors. A dual chamber configuration is proposed to eliminate the effects of diffraction from the subreflector and spillover from the feed. A computationally efficient technique, based on ray tracing and aperture integration, was developed to analyze the scattering from a lossy dielectric slab with a wedge termination.

Pistorius, C. W. I.↗
DOE OSTI2011

Diffusion Dynamics in a Tevatron Store

A separator failure during a store in 2002 led to a drop in luminosity, to increased emittance growth and to a drop in beam lifetimes. We show that a simple diffusion model can be used to explain the changes in beam lifetimes. Emittance growth of beams when they are in collision occurs due to many sources: beam-beam interactions, magnetic nonlinearities, intra-beam scattering, scattering off the residual gas and possibly others. The dynamics of the emittance growth is complicated and it depends strongly on the tunes. It is not always clear that the dynamics can be described by a diffusion process at all particle amplitudes in each beam. However in one store early in Run II, there was a sudden drop in a separator voltage in the Tevatron and the subsequent enhanced emittance growth and intensity lifetime drop could be described by a simple diffusion model. In this report we analyze the luminosity drop, compare the measured value with the expected drop and analyze the change in beam lifetimes. We show how a simple model of diffusive emittance growth and a change in physical aperture provides a quantitative explanation for the change in lifetimes.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Regulation of ion drifts and anisotropies by parametrically unstable finite-amplitude Alfvén-cyclotron waves in the fast solar wind

We study the preferential heating and differential acceleration of minor ions by dissipation of ion-acoustic waves (IAWs) generated by parametric instabilities of a finite-amplitude monochromatic Alfvén-cyclotron pump wave. We consider the associated kinetic effects of Landau damping and nonlinear pitch-angle scattering of protons and α particles in the tenuous plasma of coronal holes and the fast solar wind. Various data collected by Wind spacecraft show signatures for a local transverse heating of the minor ions, presumably by Alfvén-cyclotron wave dissipation, and an unexpected parallel heating by a so far unknown mechanism. Here, we present the results from a set of 1.5 dimensional hybrid simulations in search for a plausible explanation for the observed field-aligned kinetic features in the fast solar wind minor ions. We investigate the origin and regulation of ion relative drifts and temperature anisotropies in low plasma β, fast solar wind conditions. Depending on their initial drifts, both ion species can heat up not only transversely through cyclotron resonance and non-resonant wave-particle interactions, but also strongly in the parallel direction by Landau damping of the daughter IAWs. We discuss the dependence of the relative ion drifts and temperature anisotropies on the plasma β of the individual species and we describe the effect of the pump wave amplitude on the ion heating and acceleration.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Fermi monitoring of radio-loud narrow-line Seyfert 1 galaxies

We present detailed analysis of the γ-ray flux variability and spectral properties of the five radio-loud narrow line Seyfert 1 (RL-NLSy1) galaxies, detected by the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope, namely 1H 0323+342, SBS 0846+513, PMN J0948+0022, PKS 1502+036, and PKS 2004−447. The first three sources show significant flux variations, including the rapid variability of a few hours by 1H 0323+342. The average γ-ray spectrum of 1H 0323+342 and PMN J0948+0022 shows deviation from a simple power-law (PL) behavior, whereas the PL model gives a better fit for the other three sources. The spectra of 1H 0323+342, SBS 0846+513, and PMN J0948+0022, which are in low, flaring, and moderately active states, respectively, show significant curvature. Such curvature in the γ-ray spectrum of 1H 0323+342 and PMN J0948+0022 could be due to the emission region located inside the broad line region (BLR) where the primary mechanism of the γ-ray emission is inverse-Compton (IC) scattering of BLR photons occurring in the Klein–Nishina regime. The γ-ray emission of SBS 0846+513 is explained by IC scattering of dusty torus photons, which puts the emission region outside the BLR and thus under the Thomson regime. Therefore, the observed curvature of SBS 0846+513 could be intrinsic to the particle energy distribution. The presence of curvature in the γ-ray spectrum and flux variability amplitudes of some of the RL-NLSy1 galaxies suggests that these sources could be akin to low/moderate jet power flat spectrum radio quasars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

TEMPORAL EVOLUTION OF THE SCATTERING POLARIZATION OF THE Ca II IR TRIPLET IN HYDRODYNAMICAL MODELS OF THE SOLAR CHROMOSPHERE

Velocity gradients in a stellar atmospheric plasma have an effect on the anisotropy of the radiation field that illuminates each point within the medium, and this may in principle influence the scattering line polarization that results from the induced atomic level polarization. Here, we analyze the emergent linear polarization profiles of the Ca II infrared triplet after solving the radiative transfer problem of scattering polarization in time-dependent hydrodynamical models of the solar chromosphere, taking into account the effect of the plasma macroscopic velocity on the atomic level polarization. We discuss the influence that the velocity and temperature shocks in the considered chromospheric models have on the temporal evolution of the scattering polarization signals of the Ca II infrared lines as well as on the temporally averaged profiles. Our results indicate that the increase of the linear polarization amplitudes caused by macroscopic velocity gradients may be significant in realistic situations. We also study the effect of the integration time, the microturbulent velocity, and the photospheric dynamical conditions, and discuss the feasibility of observing with large-aperture telescopes the temporal variation of the scattering polarization profiles. Finally, we explore the possibility of using a Hanle effect line-ratio technique in the IR triplet of Ca II to facilitate magnetic field diagnostics in dynamic situations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Direct observation of the two-plasmon-decay common plasma wave using ultraviolet Thomson scattering

A 263-nm Thomson-scattering beam was used to directly probe two-plasmon-decay (TPD) excited electron plasma waves (EPWs) driven by between two and five 351-nm beams on the OMEGA Laser System. The amplitude of these waves was nearly independent of the number of drive beams at constant overlapped intensity, showing that the observed EPWs are common to the multiple beams. In an experimental configuration where the Thomson-scattering diagnostic was not wave matched to the common TPD EPWs, a broad spectrum of TPD-driven EPWs was observed, indicative of nonlinear effects associated with TPD saturation. Electron plasma waves corresponding to Langmuir decay of TPD EPWs were observed in both Thomson-scattering spectra, suggesting the Langmuir decay instability as a TPD saturation mechanism. Simulated Thomson-scattering spectra from three-dimensional numerical solutions of the extended Zakharov equations of TPD are in excellent agreement with the experimental spectra and verify the presence of the Langmuir decay instability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

CARMA MEASUREMENTS OF THE SUNYAEV-ZEL'DOVICH EFFECT IN RX J1347.5-1145

We demonstrate the Sunyaev-Zel'dovich (SZ) effect imaging capabilities of the Combined Array for Research in Millimeter-wave Astronomy (CARMA) by presenting an SZ map of the galaxy cluster RX J1347.5-1145. By combining data from multiple CARMA bands and configurations, we are able to capture the structure of this cluster over a wide range of angular scales, from its bulk properties to its core morphology. We find that roughly 9% of this cluster's thermal energy is associated with sub-arcminute-scale structure imparted by a merger, illustrating the value of high-resolution SZ measurements for pursuing cluster astrophysics and for understanding the scatter in SZ scaling relations. We also find that the cluster's SZ signal is lower in amplitude than suggested by a spherically symmetric model derived from X-ray data, consistent with compression along the line of sight relative to the plane of the sky. Finally, we discuss the impact of upgrades currently in progress that will further enhance CARMA's power as an SZ imaging instrument.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Entanglement, trace anomaly, and confinement in QCD

We formulate confinement in quantum chromodynamics (QCD) as an entropic surface phenomenon. Quark and gluon quantum information is localized on a transverse, entangling two-sphere of radius 𝑅 𝐸⁢𝐸 ; at this radius the QCD vacuum—partitioned by a hadron into interior and exterior regions—reaches its maximal entanglement entropy. Lattice-QCD determinations of the scalar (trace) gravitational form factors fix both 𝑅 𝐸⁢𝐸 and the transverse trace-anomaly density 𝜌 ℎ ⁡(𝑅 𝐸⁢𝐸 ), yielding a parameter-free slope 𝑐 ℎ = 8⁢𝜋 2 ⁢𝑅𝑆$^2_{𝐸⁢𝐸}$𝜌 ℎ ⁡(𝑅 𝐸⁢𝐸 ) and a mechanical entropy 𝑆 𝐸⁢𝐸 ⁡(𝑦) = 𝑐 ℎ ⁢𝑦 that grows linearly with rapidity 𝑦. The entropy gradient ∂ 𝑅 𝑆 𝐸⁢𝐸 changes sign at 𝑅 𝐸⁢𝐸 : it pushes colored degrees of freedom outward for 𝑟 <𝑅 𝐸⁢𝐸 and pulls them inward for 𝑟 >𝑅 𝐸⁢𝐸 , thereby localizing them on the codimension-2 entangling two-sphere Σ ⊥ = 𝑆$^2_{𝑅_{𝐸⁢𝐸}}$ (which, in the infinite-momentum frame (IMF), projects onto the transverse plane)—the “information wall.” This provides a high-energy (large-𝑦) entropic confinement diagnostic that complements—rather than replaces—Wilson’s area-law criterion, which probes long-distance dynamics near the rest frame (𝑦 → 0). Imposing unitarity on an entropic ansatz for the amplitude yields 𝜎⁡(𝑠) ∝ 𝑦 𝛿 . World data favor 𝛿 = 2 for elastic 𝑝⁡𝑝⁡($𝑝\bar{⁡𝑝}$) scattering and heavy-quark photoproduction, whereas 𝜙 photoproduction favors a softer 𝛿 = 0.387. All extracted cross sections remain well below the Froissart-Martin bound. These results provide a confinement criterion quantified directly from nonperturbative QCD inputs, unifying the trace anomaly, entanglement entropy, and high-energy scattering within a single quantitative framework.

Color confinement↗
DOE OSTI2012

Incoherent photoproduction of pseudoscalar mesons off nuclei at forward angles

Recent advances in the photon tagging facilities together with the novel, high-resolution fast calorimetry make it possible to perform photoproduction cross section measurements of pseudoscalar mesons on nuclei with a percent level accuracy. The extraction of the radiative decay widths, needed for testing the symmetry breaking effects in QCD, from these measurements at small angles is done by the Primakoff method. This method requires theoretical treatment of all processes participating in these reactions at the same percent level. The most updated description of general processes, including the nuclear coherent amplitude, is done in our previous paper. In this work, in the framework of the Glauber multiple scattering theory, we obtain analytical expressions for the incoherent cross section of the photoproduction of pseudoscalar mesons off nuclei accounting for the mesons absorption in nuclei and the Pauli suppression at forward production angles. As illustrations of the obtained formulas, we calculate the incoherent cross section for photoproduction from a closed shell nucleus, {sup 16}O, and from an unclosed shell nucleus, {sup 12}C. These calculations allow one to compare different approaches and estimate their impact on the incoherent cross section of the processes under consideration.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Ghost Images in DECam [Slides]

This presentation concludes that ghost images are all understood. Amplitude is about what is expected for CCDs with 10%-15% reflectivity, filters with 1%-1.5% reflectivity. Scattered light from bright stars off the field has multiple causes: a) Unblocked edges of filters. We definitely want to add baffles to all filters to block light around edges. b) Inside shutter wall. We want to either paint the wall with aeroglaze black (or equivalent) or add some baffles. c) Filter cage or some other surface located above u/Y filter cassette. Probably need to examine visually before deciding on a course of action.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1990

Faraday rotation measure variations in the Cygnus region and the spectrum of interstellar plasma turbulence

Linear polarization observations were made of eight double-lobed radio galaxies viewed through the galactic plane in the Cygnus region. These observations have been used to determine intra- and intersource rotation measure differences; in some cases, unambiguous rotation measures have been extracted. The rotation measures are dominated by foreground magnetoionic material. The differences in rotation measure between pairs of sources correlate with angular separation for separations from 10 arcsec to 1.5 deg. These rotation measure fluctuations are consistent with a model in which the electron density varies on roughly 0.1-200 pc scales. The amplitudes of these variations are, in turn, consistent with those electron density variations that cause diffractive interstellar scattering on scales less than 10 to the 11th cm.

Lazio, T. Joseph↗
NASA NTRS1993

Measuring rapid ocean tidal earth orientation variations with very long baseline interferometry

Ocean tidal effects on universal time and polar motion (UTPM) are investigated at four nearly diurnal (K(sub 1), P(sub 1), O(sub 1), and Q(sub 1)) and four nearly semidiurnal (K(sub 2), S(sub 2), M(sub 2), and N(sub 2)) frequencies by analyzing very long baseline interferometry (VLBI) data extending from 1978 to 1992. We discuss limitations of comparisons between experiment and theory for the retograde nearly diurnal polar motion components due to their degeneracy with prograde components of the nutation model. Estimating amplitudes of contributions to the modeled VLBI observables at these eight frequencies produces a statistically highly significant improvement of 7 mm to the residuals of a fit to the observed delays. Use of such an improved UTPM model also reduces the 14-30 mm scatter of baseline lengths about a time-linear model of tectonic motion by 3-14 mm, also withhigh significance levels. A total of 28 UTPM ocean tidal amplitudes can be unambiguously estimated from the data, with resulting UTI and PM magnitudes as large as 21 micro secs and 270 microarc seconds and formal uncertainties of the order of 0.3 micro secs and 5 microarc secs for UTI and PM, respectively. Empirically determined UTPM amplitudes and phases are com1pared to values calculated theoretically by Gross from Seiler's global ocean tide model. The discrepancy between theory and experiment is larger by a factor of 3 for UTI amplitudes (9 micro secs) than for prograde PM amplitudes (42 microarc secs). The 14-year VLBI data span strongly attenuates the influence of mismodeled effects on estimated UTPM amplitudes and phases that are not coherent with the eight frequencies of interest. Magnitudes of coherent and quasi-coherent systematic errors are quantified by means of internal consistency tests. We conclude that coherent systematic effects are many times larger than the formal uncertainties and can be as large as 4 micro secs for UTI and 60 microarc secs for polar motion. On the basis of such ealistic error estimates, 22 of the 31 fitted UTPM ocean tidal amplitudes differ from zero by more than 2 sigma.

Sovers, O. J.↗
DOE OSTI2026

Theory of stimulated and spontaneous axion scattering.

We present a theory for nonlinear, resonant excitation of dynamical axions by counterpropagating electromagnetic waves in materials that break both 𝒫 and 𝒯 symmetries. We show that dynamical axions can mediate an exponential growth in the amplitude of the lower frequency (Stokes) beam. We also discuss spontaneous generation of a counterpropagating Stokes mode, enabled by resonant amplification of quantum and thermal fluctuations in the presence of a single pump laser. Remarkably, the amplification can be orders of magnitude larger than that obtained via stimulated Brillouin and Raman scattering processes, and can be modulated with the application of external magnetic fields, making stimulated axion scattering promising for optoelectronics applications.

Smith, M.↗
DOE OSTI2015

Relativistic Eulerian Vlasov simulations of the amplification of seed pulses by Brillouin backscattering in plasmas

We apply an Eulerian Vlasov code to study the amplification by Brillouin scattering of a short seed laser pulse by a long pump laser pulse in an underdense plasma. The stimulated Brillouin backscattering interaction is the coupling of the pump and seed electromagnetic waves propagating in opposite directions, and the ion plasma wave. The code solves the one-dimensional relativistic Vlasov-Maxwell set of equations. Large amplitude ion waves are generated. In the simulations we present, the density plateau of the plasma is n{sub e}=0.3 n{sub c} (n{sub c} is the critical density), which excludes spurious stimulated Raman scattering amplification (which can occur only if n{sub e}<n{sub c}/4). We also varied the duration and/or amplitude of the short input seed pulse to study how these influence its subsequent behaviour. An initially broad pulse grows more rapidly than an initially narrow pulse. Furthermore, for an initially broader seed pulse, towards the end of the simulation, it is seen to become narrower and to gradually detach from the trailing signal. On the contrary, initially very narrow seed pulses are seen to broaden. The absence of noise in the Vlasov simulations allows to simulate long plasma amplifier lengths, and to follow the evolution of the system with a fully kinetic description and with an accurate representation of the phase-space structures of distribution function.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗