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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Singular spectrum analysis in nonlinear dynamics, with applications to paleoclimatic time series

Two dimensions of a dynamical system given by experimental time series are distinguished. Statistical dimension gives a theoretical upper bound for the minimal number of degrees of freedom required to describe the attractor up to the accuracy of the data, taking into account sampling and noise problems. The dynamical dimension is the intrinsic dimension of the attractor and does not depend on the quality of the data. Singular Spectrum Analysis (SSA) provides estimates of the statistical dimension. SSA also describes the main physical phenomena reflected by the data. It gives adaptive spectral filters associated with the dominant oscillations of the system and clarifies the noise characteristics of the data. SSA is applied to four paleoclimatic records. The principal climatic oscillations and the regime changes in their amplitude are detected. About 10 degrees of freedom are statistically significant in the data. Large noise and insufficient sample length do not allow reliable estimates of the dynamical dimension.

Vautard, R.↗
NASA NTRS2009

Corona, Jet, and Relativistic Line Models for Suzaku/RXTE/Chandra-HETG Observations of the Cygnus X-1 Hard State

Using Suzaku and the Rossi X-ray Timing Explorer (RXTE), we have conducted a series of four simultaneous observations of the galactic black hole candidate Cyg X-1 in what were historically faint and spectrally hard "low states". Additionally, all of these observations occurred near superior conjunction with our line of sight to the X-ray source passing through the dense phases of the "focused wind" from the mass donating secondary. One of our observations was also simultaneous with observations by the Chandra-High Energy Transmission Grating (HETG). These latter spectra are crucial for revealing the ionized absorption due to the secondary s focused wind. Such absorption is present and must be accounted for in all four spectra. These simultaneous data give an unprecedented view of the 0.8-300 keV spectrum of Cyg X-1, and hence bear upon both corona and X-ray emitting jet models of black hole hard states. Three models fit the spectra well: coronae with thermal or mixed thermal/non-thermal electron populations, and jets. All three models require a soft component that we fit with a low temperature disk spectrum with an inner radius of only a few tens of GM/c2. All three models also agree that the known spectral break at 10 keV is not solely due to the presence of reflection, but each gives a different underlying explanation for the augmentation of this break. Thus whereas all three models require that there is a relativistically broadened Fe line, the strength and inner radius of such a line is dependent upon the specific model, thus making premature line-based estimates of the black hole spin in the Cyg X-1 system. We look at the relativistic line in detail, accounting for the narrow Fe emission and ionized absorption detected by HETG. Although the specific relativistic parameters of the line are continuum-dependent, none of the broad line fits allow for an inner disk radius that is > 40 GM/c(sup 2).

Nowak, Michael A.↗
DOE OSTI2018

Transverse momentum spectra at threshold for groomed heavy quark jets

We present the transverse momentum spectrum for a heavy hadron at threshold in a groomed jet initiated by a heavy quark. The cross section is doubly differential in the energy fraction of an identified heavy hadron in the jet and its transverse momentum measured with respect to the groomed (recoil free) jet axis. The grooming is implemented using a soft-drop grooming algorithm and helps us in mitigating the effects of Non-Global logarithms and pile up. For the particular case of a B meson, we identify two distinct regimes of the transverse momentum spectrum and develop an EFT within the formalisms of Soft Collinear Effective Theory (SCET) and Heavy Quark Effective Theory (HQET) for each of these regions. We show how each region can be matched smoothly into the other to provide a prediction for the perturbative transverse momentum spectrum. The EFT also predicts the scaling behavior of the leading non-perturbative power corrections and implements a simple shape function to account for hadronization. We work in the threshold region where the heavy hadron carries most of the energy of the jet since in this regime, we have a very good discriminating power between heavy quark and gluon initiated jets. We observe that the shape of the spectrum is independent of the energy of the jet over a large range of transverse momentum. We propose that this spectrum can be used as a probe of evolution for heavy quark TMD fragmentation function. At the same time, it can be treated as a jet substructure observable for probing Quark-Gluon Plasma (QGP).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

The Ground State of (CS) 4 Is Different from That of (CO) 4 : An Experimental Test of a Computational Prediction by Negative Ion Photoelectron Spectroscopy

Cyclobutane-1,2,3,4-tetrathione, (CS)4, has recently been calculated to have a singlet ground state, 1A1g, in which the highest b2g MO is doubly occupied and the lowest a2u MO is empty. Thus, (CS)4 is predicted to have a different ground state than its lighter congener, (CO)4, which has a triplet ground state, 3B1u, in which these two MOs are each singly occupied. Here we report the results of a negative ion photoelectron spectroscopy (NIPES) study of the radical anion (CS)4∙-, designed to test the prediction that (CS)4 has a singlet ground state. The NIPE spectrum reveals that (CS)4 does, indeed, have a singlet ground state with electron affinity (EA) = 3.75 eV. The lowest triplet state is found to lie 0.31 eV higher in energy than the ground state, and the open-shell singlet is 0.14 eV higher in energy than the triplet state. Calculations at the (U)CCSD(T)/aug-cc-pVTZ//(U)B3LYP/6-311+G(2df) level support the spectral assignments, giving EA = 3.71 eV, EST = 0.44 eV. These calculated values are, respectively, 0.04 eV (0.9 kcal/mol) smaller, and 0.13 eV (3.0 kcal/mol) larger than the corresponding experimental values. In addition, RASPT2 calculations with various active spaces converge on a 1B1u-3B1u energy gap of 0.137 eV, in excellent agreement with the 0.14 eV energy difference obtained from the NIPE spectrum. Finally, calculations of the Franck-Condon factors for transitions from the ground state of (CS)4∙- to the ground (1A1g) and two excited states (3B1u, 1B1u) of (CS)4 account for all of the major spectral peaks, and nicely reproduce vibrational structure observed in each electronic transition. The close correspondence between the calculated and the observed features in the NIPE spectrum of (CS)4∙- provides unequivocal proof that (CS)4, unlike (CO)4, has a singlet ground state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Combining cluster number counts and galaxy clustering

The abundance of clusters and the clustering of galaxies are two of the important cosmological probes for current and future large scale surveys of galaxies, such as the Dark Energy Survey. In order to combine them one has to account for the fact that they are not independent quantities, since they probe the same density field. It is important to develop a good understanding of their correlation in order to extract parameter constraints. We present a detailed modelling of the joint covariance matrix between cluster number counts and the galaxy angular power spectrum. We employ the framework of the halo model complemented by a Halo Occupation Distribution model (HOD). We demonstrate the importance of accounting for non-Gaussianity to produce accurate covariance predictions. Indeed, we show that the non-Gaussian covariance becomes dominant at small scales, low redshifts or high cluster masses. We discuss in particular the case of the super-sample covariance (SSC), including the effects of galaxy shot-noise, halo second order bias and non-local bias. We demonstrate that the SSC obeys mathematical inequalities and positivity. Using the joint covariance matrix and a Fisher matrix methodology, we examine the prospects of combining these two probes to constrain cosmological and HOD parameters. We find that the combination indeed results in noticeably better constraints, with improvements of order 20% on cosmological parameters compared to the best single probe, and even greater improvement on HOD parameters, with reduction of error bars by a factor 1.4-4.8. This happens in particular because the cross-covariance introduces a synergy between the probes on small scales. We conclude that accounting for non-Gaussian effects is required for the joint analysis of these observables in galaxy surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Making Quality HPGe Gamma Ray Spectrum Measurements for Uranium: The Role of FRAM for Analysis, Quality Control and Enrichment Measurements, and Opportunities for Improved Quantification Documentation

Enrichment measurements are used in uranium safeguards verification and accountancy as both an attribute signature and in the interpretation of other nondestructive assay information, such as active interrogation for mass. Accurate and reliable assessments require quality information. The practices used to collect the raw data are therefore the crucial first step in managing the overall quality and uncertainty of the enrichment determination. This report discusses several topics associated with gamma-ray spectrum measurements of uranium using HPGe detectors. First a discussion of good data acquisition practices including physical setup, detector types and configurations, detector shielding and filtering, spectrum stabilization, and data acquisition protocols. Next is a discussion of analysis options to obtain isotopic composition and/or enrichment centered on the FRAM gamma ray isotopic analysis software. The report discusses the results of the development of a FRAM parameter file to perform classical Enrichment Meter Principle (EMP) analysis. Possible analysis and data acquisition issues (random summing, x-ray fluorescence peaks, peak interferences, shielding) that can affect FRAM analyses are also discussed. There is also a brief discussion of FRAM measurements in the field. Under the topic of uncertainty propagation and quantification in FRAM, uncertainty propagation verification methods and gaps in available uncertainty quantification data for uranium is covered. Suggestions are made for areas where ORNL can contribute to closing the identified uncertainty quantification gaps, and also to contributing nuclear data quality spectra to the research community.

61 RADIATION PROTECTION AND DOSIMETRY↗
NASA NTRS1988

Modelling a C-type flare observed in microwaves and hard X-rays

Using the very large array (VLA) at 6 and 20 cm wavelength and the hard X-ray burst spectrometer on the Solar Maximum Mission, a two-ribbon flare was observed from the onset phase through the maximum and decline on November 14, 1981. Because of the extensive size of the microwave source and the gradual variations in hard X-rays whose spectrum becomes progressively flatter with time, the flare is classified as a C-type flare. Considering the hardening of the X-ray spectrum and its non-impulsive nature, a coronal trap model was invoked for the energetic electrons. The microwave emission is easily accounted for by gyrosynchronous radiation from mildly relativistic electrons. It was found that the source must be optically thick at 20 cm during the maximum phase, but as the source evolved toward an optically thin regime, the intensity decreased while the degree of circular polarization increased. In an initial homogeneous model, we found that the computed microwave spectrum was too narrow to match the patrol spectrum from 606 to 15400 MHz. In the model, the magnetic field consists of a dipolar arcade bridging the H alpha ribbons, and extending to heights of order 40,000 to 50,000 km. The variation of the magnetic field strength from footpoints to apex causes the gyrosynchrotron spectrum to be broader. Preliminary conclusions regarding the electron distributions producing the hard X-rays and the microwaves, and the suitability of this model for C-type flares is presented.

Schmahl, E. J.↗
DOE OSTI2015

Quasi-resonant enhancement of a grazing diffracted wave and deep suppression of specular reflection on shallow metal gratings in terahertz

We report on a previously unexamined anomaly at diffraction of THz radiation on metal gratings. This anomaly consists in a nearly complete redirection of energy to a non-specular homogeneous diffraction order propagating at a specific grazing angle and deep suppression of the specular reflection. We show that this anomaly is located far enough from the well-known one caused by the resonant excitation of the surface plasmon-polariton. The effect under consideration is of general nature and can exist in all spectrum regions; however, it is especially pronounced in THz region, where it should be taken into account when analyzing relevant experimental results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Cavitation erosion prediction based on analysis of flow dynamics and impact load spectra

Cavitation erosion is the consequence of repeated collapse-induced high pressure-loads on a material surface. The present paper assesses the prediction of impact load spectra of cavitating flows, i.e., the rate and intensity distribution of collapse events based on a detailed analysis of flow dynamics. Data are obtained from a numerical simulation which employs a density-based finite volume method, taking into account the compressibility of both phases, and resolves collapse-induced pressure waves. To determine the spectrum of collapse events in the fluid domain, we detect and quantify the collapse of isolated vapor structures. As reference configuration we consider the expansion of a liquid into a radially divergent gap which exhibits unsteady sheet and cloud cavitation. Analysis of simulation data shows that global cavitation dynamics and dominant flow events are well resolved, even though the spatial resolution is too coarse to resolve individual vapor bubbles. The inviscid flow model recovers increasingly fine-scale vapor structures and collapses with increasing resolution. We demonstrate that frequency and intensity of these collapse events scale with grid resolution. Scaling laws based on two reference lengths are introduced for this purpose. We show that upon applying these laws impact load spectra recorded on experimental and numerical pressure sensors agree with each other. Furthermore, correlation between experimental pitting rates and collapse-event rates is found. Locations of high maximum wall pressures and high densities of collapse events near walls obtained numerically agree well with areas of erosion damage in the experiment. The investigation shows that impact load spectra of cavitating flows can be inferred from flow data that captures the main vapor structures and wave dynamics without the need for resolving all flow scales.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Orbital spectrum analysis of non-axisymmetric perturbations of the guiding-center particle motion in axisymmetric equilibria

The presence of non-axisymmetric perturbations in an axisymmetric magnetic field equilibrium renders the Guiding Center (GC) particle motion non-integrable and may result in particle, energy, and momentum redistribution, due to resonance mechanisms. We analyse these perturbations in terms of their spectrum, as observed by the particles in the frame of unperturbed GC motion. We calculate semi-analytically the exact locations and strength of resonant spectral components of multiple perturbations. The presented Orbital Spectrum Analysis method is based on an exact Action-Angle transform that fully takes into account Finite Orbit Width effects. The method provides insight into the particle dynamics and enables the prediction of the effect of any perturbation to all different types of particles and orbits in a given, analytically or numerically calculated, axisymmetric equilibrium.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Nonlinear structure formation in the cubic Galileon gravity model

We model the linear and nonlinear growth of large scale structure in the Cubic Galileon gravity model, by running a suite of N-body cosmological simulations using the ECOSMOG code. Our simulations include the Vainshtein screening effect, which reconciles the Cubic Galileon model with local tests of gravity. In the linear regime, the amplitude of the matter power spectrum increases by ∼ 20% with respect to the standard ΛCDM model today. The modified expansion rate accounts for ∼ 15% of this enhancement, while the fifth force is responsible for only ∼ 5%. This is because the effective unscreened gravitational strength deviates from standard gravity only at late times, even though it can be twice as large today. In the nonlinear regime (k∼>0.1h Mpc{sup −1}), the fifth force leads to only a modest increase (∼<8%) in the clustering power on all scales due to the very efficient operation of the Vainshtein mechanism. Such a strong effect is typically not seen in other models with the same screening mechanism. The screening also results in the fifth force increasing the number density of halos by less than 10%, on all mass scales. Our results show that the screening does not ruin the validity of linear theory on large scales which anticipates very strong constraints from galaxy clustering data. We also show that, whilst the model gives an excellent match to CMB data on small angular scales (l∼>50), the predicted integrated Sachs-Wolfe effect is in tension with Planck/WMAP results.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A separate universe view of the asymmetric sky

We provide a unified description of the hemispherical asymmetry in the cosmic microwave background generated by the mechanism proposed by Erickcek, Kamionkowski, and Carroll, using a δ N formalism that consistently accounts for the asymmetry-generating mode throughout. We derive a general form for the power spectrum which explicitly exhibits the broken translational invariance. This can be directly compared to cosmic microwave background observables, including the observed quadrupole and f{sub NL} values, automatically incorporating the Grishchuk-Zel'dovich effect. Our calculation unifies and extends previous calculations in the literature, in particular giving the full dependence of observables on the phase of our location in the super-horizon mode that generates the asymmetry. We demonstrate how the apparently different results obtained by previous authors arise as different limiting cases. We confirm the existence of non-linear contributions to the microwave background quadrupole from the super-horizon mode identified by Erickcek et al. and further explored by Kanno et al., and show that those contributions are always significant in parameter regimes capable of explaining the observed asymmetry. We indicate example parameter values capable of explaining the observed power asymmetry without violating other observational bounds.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Critical Fluorescence of a Transmon at the Schmid Transition

Here, we investigate inelastic microwave photon scattering by a transmon qubit embedded in a high-impedance circuit. The transmon undergoes a charge-localization (Schmid) transition upon the impedance reaching the critical value. Due to the unique transmon level structure, the fluorescence spectrum carries a signature of the transition point. At higher circuit impedance, quasielastic photon scattering may account for the main part of the inelastic scattering cross-section; we find its dependence on the qubit and circuit parameters.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Superradiance and Subradiance due to Quantum Interference of Entangled Free Electrons

When multiple quantum emitters radiate, their emission rate may be enhanced or suppressed due to collective interference in a process known as super- or subradiance. Such processes are well known to occur also in light emission from free electrons, known as coherent cathodoluminescence. Unlike atomic systems, free electrons have an unbounded energy spectrum, and, thus, all their emission mechanisms rely on electron recoil, in addition to the classical properties of the dielectric medium. To date, all experimental and theoretical studies of super- and subradiance from free electrons assumed only classical correlations between particles. However, dependence on quantum correlations, such as entanglement between free electrons, has not been studied. Recent advances in coherent shaping of free-electron wave functions motivate the investigation of such quantum regimes of super- and subradiance. In this Letter, we show how a pair of coincident path-entangled electrons can demonstrate either super- or subradiant light emission, depending on the two-particle wave function. By choosing different free-electron Bell states, the spectrum and emission pattern of the light can be reshaped, in a manner that cannot be accounted for by a classical mixed state. We show these results for light emission in any optical medium and discuss their generalization to many-body quantum states. Furthermore, our findings suggest that light emission can be sensitive to the explicit quantum state of the emitting matter wave and possibly serve as a nondestructive measurement scheme for measuring the quantum state of many-body systems.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Optical spectroscopy of a resonant Bragg structure with InGaN/GaN quantum wells

The optical reflectance and transmittance spectra of a periodic InGaN/GaN semiconductor heterostructure with 60 quantum wells are studied at room temperature. The period of the structure was chosen such that, at some angles of incidence of light, the energy of a photon resonantly reflected from the Bragg structure coincides with the excitation energy for quantum-well excitons in quantum wells. The parameters of these excitons are determined by fitting the spectra measured at two different angles of incidence, 30° and 60°. We take into account the resonant exciton transitions in quantum wells as well as the transitions into the continuous spectrum. The radiative decay parameter is determined to be (0.20 ± 0.02) meV.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Gas-phase absorptions of C{sup +}{sub 60}: a new comparison with astronomical measurements

Campbell et al. recently revised, by a few tenths of an Å, the wavelengths for their low-temperature laboratory measurements of fullerene C{sub 60}{sup +} bands. This accounts for the perturbation caused by the He atom to the C{sub 60}{sup +}--He spectrum. Here, we demonstrate that the revised laboratory wavelengths improve coincidence with the 9632, 9577, 9428, 9365, and 9348 diffuse interstellar bands detected towards the stars HD 46711, HD 169454, and HD 183143.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Broadband Photon Spectrum and its Radial Profile of Pulsar Wind Nebulae

The observed radial profiles of the X-ray emission from pulsar wind nebulae (PWNe) have been claimed to contradict the standard 1D steady model. However, the 1D model has not been tested to simultaneously reproduce the volume-integrated spectrum and the radial profile of the surface brightness. We revisit the 1D steady model and apply it to PWNe 3C 58 and G21.5−0.9. We find that the parameters of the pulsar wind, the radius of the termination shock r{sub s}, and magnetization σ greatly affect both the photon spectrum and radial profile of the emission. We have shown that the parameters constrained by the entire spectrum lead to an X-ray nebula smaller than the observed nebula. We have also tested the case that reproduces only the observations in X- and gamma-rays, ignoring the radio and optical components. In this case, there are parameter sets that reproduce both the spectrum and emission profile, but the advection time to the edge of the nebula becomes much smaller than the age. Our detailed discussion clarifies that the standard 1D steady model has severe difficulty to simultaneously reproduce both the volume-integrated spectrum and the surface brightness. This implies that the model should be improved by taking into account extra physical processes such as spatial diffusion of particles. Additionally, we calculate the surface brightness profile of the radio, optical, and TeV gamma-rays. The future observations in these wavelengths are also important to probe the spatial distributions of the relativistic plasma and the magnetic field of PWNe.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1975

The variation of solar proton energy spectra and size distribution with heliolongitude

A statistical study of the initial phases of a large number of solar particle events provides an approach for an investigation of the variability in the production process and coronal diffusion. A description is given of the procedures which are suitable for identifying the parent flare of an event, taking into account the heliocentric distribution of the flare-associated events. The determination of the proton energy spectrum at the sun is discussed along with the variation of the spectral index with the associated flare heliocentric longitude, questions concerning the source spectra and the acceleration process, and the size distribution of flare associated particle events.

Van Hollebeke, M. A. I.↗