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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Phases of 2D massless QCD with qubit regularization

We investigate the possibility of reproducing the continuum physics of 2D S U ( N ) gauge theory coupled to a single flavor of massless Dirac fermion using qubit regularization. The continuum theory is described by N free fermions in the ultraviolet (UV) and a coset Wess-Zumino-Witten (WZW) model in the infrared (IR). In this work, we first explore how well these features can be reproduced using the Kogut-Susskind (KS) Hamiltonian with a finite-dimensional link Hilbert space and a generalized Hubbard coupling. We do this by analyzing the renormalization group (RG) flow diagram of the continuum theory and identifying important phases of the theory. Using strong coupling expansions, we show that our lattice model exhibits a gapped dimer phase and a spin-chain phase. Furthermore, for N = 2 , using tensor network methods, we show that there is a second-order phase transition between these two phases, which we identify as the critical surface of the continuum theory that connects the IR and UV fixed points. In the IR, we identify the critical theory at the transition as the expected S U ( 2 ) 1 WZW model. Lastly, we argue that modifications of our model may allow the study of the UV physics of free fermions. Published by the American Physical Society 2025

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Deviations from the Isobaric Multiplet Mass Equation due to Threshold States

Recent studies have completed the A=16 isospin quintets for states with J π =0 + and 2 + . The dependence of their masses as a function of isospin projection shows evidence for deviations from quadratic behavior indicating isospin violation beyond the expectation from two-body forces. The deviation is most pronounced for the 2 + states. Predictions from the shell model embedded in the continuum (SMEC) allow us to explain that this isospin violation is associated with a modification of the nuclear structure due to the open-quantum-system nature of the proton-rich members of the quintet. In particular, the 0 + and 2 + states in 16 Ne and the 2 + state in 16 F are threshold resonances located just above a proton-decay threshold where s-wave coupling to the continuum is expected. The measured deviations of these threshold states from the quadratic behavior of the remaining members of the multiplets makes it possible to obtain information on the magnitude and the energy dependence of the continuum-coupling energy correction. Finally, continuum coupling is also indicated for the ground state of 8 C, but this time through p-wave coupling

coulomb energies & analogue states↗
DOE OSTI2022

A novel post-processing method for progressive failure analysis of brittle composite compression

Finite element analysis of brittle materials in axial compression typically uses element deletion to allow continued global deformation post-element-failure. However, element deletion produces cyclic load-displacement curves that underestimate energy absorption and are not representative of a continuum system. Two key observations support the conclusion that results from an appropriately discretized model can be an adequate representation of a continuum system. Specifically, the frequency of the oscillations in the load-displacement curve is directly dependent upon element length in the loading direction, and the peak amplitudes of oscillations are mesh size independent. A method of post-processing the analysis results, by connecting the peak amplitudes of oscillations, is proposed and applied to a series of continuous carbon fiber composite crush tubes. The load-displacement curve, stable crushing load, and specific energy absorption of the post-processed results compare well to an experimental study of crush tubes with similar layups.

Materials Science↗
DOE OSTI2020

A thermodynamics-based damage model for the non-linear mechanical behavior of SiC/SiC ceramic matrix composites in irradiation and thermal environments

A damage model is developed and validated with experimental data for the non-linear mechanical behavior of SiC/SiC composite materials in nuclear applications. Cyclic thermal and mechanical loading associated with neutron irradiation effects of these composites leads to wide-spread and progressive micro-cracking that leads to loss of thermal conductivity and further enhancement of thermo-mechanical damage. A physics-based model of wide-spread micro-cracking is developed within the thermodynamic framework of continuum damage mechanics. Evolution equations for damage parameters that describe the growth of continuum damage are developed, where the material variables are obtained from experiments. The model novelty is in coupling mechanical, thermal, and irradiation damage through a consistent thermodynamic framework, including loss of thermal conductivity due to the evolution of mechanically induced micro-cracks. A number of thermo-mechanical experiments were conducted to confirm model assumptions. The model is shown to be validated with out-of-pile experiments, and then implemented using commercial finite element code COMSOL to the fuel cladding problem with normal and high radiation dose cases.

Materials Science↗
DOE OSTI2021

Exotic symmetries, duality, and fractons in 2+1-dimensional quantum field theory

We discuss nonstandard continuum quantum field theories in 2+1 dimensions. They exhibit exotic global symmetries, a subtle spectrum of charged excitations, and dualities similar to dualities of systems in 1+1 dimensions. These continuum models represent the low-energy limits of certain known lattice systems. One key aspect of these continuum field theories is the important role played by discontinuous field configurations. In two companion papers, we will present 3+1-dimensional versions of these systems. In particular, we will discuss continuum quantum field theories of some models of fractons.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

The Changing-look Blazar B2 1420+32

Abstract Blazars are active galactic nuclei with their relativistic jets pointing toward the observer, comprising two major subclasses, flat-spectrum radio quasars (FSRQs) and BL Lac objects. We present multiwavelength photometric and spectroscopic monitoring observations of the blazar B2 1420+32, focusing on its outbursts in 2018–2020. Multiepoch spectra show that the blazar exhibited large-scale spectral variability in both its continuum and line emission, accompanied by dramatic gamma-ray and optical variability by factors of up to 40 and 15, respectively, on week to month timescales. Over the last decade, the gamma-ray and optical fluxes increased by factors of 1500 and 100, respectively. B2 1420+32 was an FSRQ with broad emission lines in 1995. Following a series of flares starting in 2018, it transitioned between BL Lac and FSRQ states multiple times, with the emergence of a strong Fe pseudocontinuum. Two spectra also contain components that can be modeled as single-temperature blackbodies of 12,000 and 5200 K. Such a collection of “changing-look” features has never been observed previously in a blazar. We measure gamma-ray–optical and interband optical lags implying emission-region separations of less than 800 and 130 gravitational radii, respectively. Since most emission-line flux variations, except the Fe continuum, are within a factor of 2–3, the transitions between FSRQ and BL Lac classifications are mainly caused by the continuum variability. The large Fe continuum flux increase suggests the occurrence of dust sublimation releasing more Fe ions in the central engine and an energy transfer from the relativistic jet to subrelativistic emission components.

Astronomy & Astrophysics↗
NASA NTRS1975

Decameter storm radiation. II

The height, size, directivity, and lifetime of decametric storm sources are investigated. The height of the continuum sources is determined from the rotation rate, and the gradient of electron density for the regions of storm origin is computed by assuming that the radiation originates at the plasma frequency. The mean angular size of the sources is found to be quite large (increasing with decreasing frequency), the storm continuum is strongly directive toward the disk center, and east-west asymmetry is observed at decameter wavelengths. Two distinct classes of type III bursts are observed during storms: 'off-fringe' (displaced in position from the continuum source) and 'on-fringe' (coinciding in position with the continuum). A model of the storm region is proposed in which the 'on-fringe' bursts originate in regions of diverging field lines above closed magnetic loops and the 'off-fringe' bursts are excited by energetic electron streams having access to open field lines at the base of the loops.

Gergely, T. E.↗
NASA NTRS1976

The solar XUV spectrum of He II

OSO-7 observations of the first five Lyman lines and the Lyman continuum of He II are given for the quiet sun, a coronal hole, prominences, filaments, and the flare of August 7, 1972. These data are calibrated and given in specific intensity units together with color and brightness temperatures for the He II continuum. It is found that He II is overionized in all features except the flare and that the continuum is formed at temperatures near 14,000 K. The He II-He III ionization equilibrium appears to be dominated by photoionizations and radiative recombinations. Schematic calculations for realistic chromosphere and transition-region models can account for the observed intensities of Ly-beta through Ly-epsilon, the Lyman continuum, and its color temperature. To account for the intensity of Ly-alpha, either an implausible 100-km plateau at temperatures near 80,000 K is needed or, more likely, the diffusion-enhanced collisional excitation should be incorporated into the models.

Linsky, J. L.↗
NASA NTRS1976

A Comparison of the Composition of New and Evolved Comets

The intensity ratio of the continuum to the molecular emissions was estimated in the spectra of eight-five comets. Four conclusions are drawn: (1) There is no readily apparent difference in continuum to emission intensity ratio between new and more evolved comets; (2) an intrinsic distribution of this characteristic does occur; (3) periodic comets with weak continua are derived from new comets with the same property; and (4) no weakening of the continuum in general occurs following perihelion passage. The infrared evidence for comet Encke suggests that the faintness of its continuum may be caused by a size distribution containing only particles larger than about 10 um.

Donn, B.↗
NASA NTRS1977

A comparison of the composition of new and evolved comets

The continuum to molecular emission intensity ratio in cometary spectra is examined as an indicator of initial composition of the comets. This ratio presumably measures the dust to gas ratio in comets, or the component of gas yielding visible emissions. The spectral relationships and compositions of new comets and more evolved ones are compared. No significant difference in the continuum to emission ratio was noted between new and more evolved comets, which is in contradiction to Oort's conclusion. This suggests that no systematic change occurs in the continuum to emission ratio as comets evolve from new to periodic. Perihelion passage does not seem to produce a general weakening of the continuum, although it occurs in individual cases.

Donn, B.↗
NASA NTRS1980

HEAO 1 observations of gamma-ray lines from a solar flare

HEAO 1 observed gamma radiation, including the 2.223 MeV line of deuterium and the 4.43 MeV line of C-12, from a white-light solar flare of 1978 July 11. Line strengths over a 4 minute integration were 1.00 + or - 0.29 and 0.18 + or - 0.07 photons/sq cm s, respectively, and the continuum in the 1-5 MeV range fitted a spectrum 10 E to the -3rd photons/sq cm s keV. The 2.2 MeV line lagged 94 + or - 30 s behind the gamma-ray continuum, which itself was delayed about 20 s from the hard X-ray (not less than 40 keV) and microwave fluxes. This is the second flare for which both MeV-range lines and continuum have been observed, and the first for which simultaneous white-light observations exist. The prompt gamma-ray line (4.43 MeV) can be directly interpreted as an energy deposition of not greater than 7 x 10 to the 26th ergs per sec by energetic protons at photospheric depths. This is insufficient to maintain the white-light continuum by normal photospheric emission mechanisms.

Hudson, H. S.↗
NASA NTRS1981

IUE observations of two late-type stars Bx Mon (M + pec) and TV Gem (M1 Iab)

The IUE observations of two late type stars BX Mon and TV Gem that reveal the emission properties in the ultraviolet of subluminous companions are discussed. Analysis of the continuum emission observed from BX Mon suggests the companion, is a middle A III star. High excitation emission lines observed between 1200 A and 2000 A that generally do not typify emission observed in either late M type variables or A type stars are also detected. It is suggested that these strong high excitation lines arise in a large volume of gas heated by nonradiation processes that could be the result of tidal interaction and mass exchange in the binary system. In contrast to stars such as BX Mon, the luminous M1 supergiant TV Gem shows unexpected intense UV continuum throughout the sensitivity range of IUE. The UV spectrum of TV Gem is characterized by intense continuum with broad absorption features detected in the short wavelength range. The analysis shows that the companion could be a B9 or A1 III-IV star. Alternate suggestions are presented for explaining the UV continuum in terms of an accretion disk in association with TV Gem.

Michalitsianos, A. G.↗
NASA NTRS1981

The ultraviolet spectrum of Herbig-Haro Object 1

Continuum and emission line fluxes for HH 1 in the range of 1200-1300 A have been determined using IUE spectra, and it is found that the luminosity of HH 1 in this wavelength interval is slightly larger than 1 solar luminosity, or 20 times greater than for the wavelength range 3200-11,000 A. If averaged over intervals of 100 A, it is shown that the UV continuum rises almost monotonically toward shorter wavelengths over the entire interval 1300-3000 A. The UV continuum energy distribution cannot be explained by a T Tauri stellar continuum that is scattered by dust. Emission line identifications and flux measurements strongly confirm the statement that the high-ionization emission lines are too strong to be explained by shock-wave models derived from the emission line spectrum in the interval 3700-11,000 A. A possible explanation for this fact is discussed.

Boehm, K. H.↗
NASA NTRS1984

Shear deformation plate continua of large double-layered space structures

The energy equivalence to construct equivalent continua for the actual lattice structure is described. An energy equivalent continuum is defined as that which has the same amount of strain and kinetic energies stored in it as the original lattice structure when both are subjected to the same loading conditions. The equivalent continuum is characterized by its strain and kinetic energies from which the constitutive relations and the equations of motion can be derived. A simple method to model large rigid jointed lattices as continuous media with couple stresses is presented. The transition from the discrete system to the continuous medium is achieved by expanding the displacements and the rotations of the nodal points in a Taylor series about a suitable chosen origin. Basic kinematic assumptions are introduced to insure that the assumptions used in deriving the governing equations of the modeled continuum are satisfied. The number of terms retained in the Taylor series expansion will depend upon the properties to be evaluated. This implies that the kind of continuum needed to model from the discrete lattice, before the actual properties are derived was to predetermined.

Hefzy, M. S.↗
NASA NTRS1986

High angular resolution infrared mapping of the compact H II regions W51 and DR 21/W75

Far-infrared maps of W51/G49.5-0.4, W51/G49.4-0.3, and the DR 21 W75 S regions are presented. The simultaneous 50 and 100 micron maps enable a determination of the dust temperature and density structure in these areas. In G49.5-0.4 a luminosity and dust column-density peak at the position of the W51-Main maser is found, suggesting that this is the dominant luminosity source in W51. In G49.4-0.3 three components associated with the three known 2.7 GHz sources are resolved. A comparison of the total far-infrared luminosity with the radio continuum brightness in both G49.5-0.4 and G49.4-0.3 shows that the ratio of Lyman continuum to total luminosity of the exciting stars in not consistent with excitation by a single ZAMS star if most of the Lyman continuum photons are being absorbed bay gas rather than dust. In DR 21 micron far-infrared data and some new 2-20 micron results reveal a region of hot dust associated with the 2 micron H2 emission to the east and west of DR 21. Finally, a new 1.5-100 micron 'protostellar' source 2 deg north of W75 S at the position of a 1 mm continuum peak is reported.

Harvey, P. M.↗
NASA NTRS1987

Broad, variable absorption lines in the Seyfert Galaxy NGC 3516 - Probing the structure of the emission-line regions

Nineteen short-wavelength IUE archive images were analyzed in order to probe the structure of the active nucleus in NGC 3516, an SB0 Seyfert I galaxy. The measurements of these features are presented, and the strength, variability, and morphology of the emission and absorption lines and their relation to the continuum are analyzed. It is shown that the absorption must arise within 10 pc of the nonthermal continuum source and that its variability must stem from changes in the velocity space coverage of clouds optically thin to the Lyman continuum. Two possible sites of absorption are discussed: dense clouds in the narrow-line region and optically thin clouds in the broad-line region. A theoretical model that explains the anticorrelation of C IV absorption with continuum flux is described.

Voit, G. Mark↗
NASA NTRS1989

How to unveil a T Tauri star

A method for separating the 'veiling' continuum often present in T Tauri stars from the underlying photospheric spectrum is described. Echelle observations from 5100 to 6800 A of the partially veiled T Tauri star BP Tau were analyzed to determine the shape of the veiling spectrum. The residuals of the fit indicate the deviation of the veiling spectrum from a simple continuum and identify the location and strength of any emission-line components. It is shown, by means of goodness-of-fit tests, that the spectrum of BP Tau can be decomposed into a normal stellar spectrum plus a smooth veiling continuum with only a few emission lines superposed. The continuum dominates the veiling spectrum in this spectral region; the veiling does not arise from numerous deep photospheric absorption lines that are filled in by weak emission.

Hartigan, Patrick↗
NASA NTRS1990

Emission-line variations and broad-line region kinematics of NGC 5548

Sixteen spectroscopic observations of the Seyfert galaxy NGC 5548 were made between March 1979 and June 1984 at Palomar and Steward Observatories. Broad-line flux variations correlated with nonstellar continuum changes were measured. H-beta, H-gamma, and He II 4686A all respond rapidly to continuum variations providing strong evidence for photoionization by a central continuum source. Additionally, H-beta profile variations have occurred during the 1900 day monitoring period. These profile variations also correlate with changes in the continuum, but lag behind by about 90 days or less. A kinematic model that incorporates radial outflow and an internal line opacity source is proposed to explain qualitatively the observed H-beta profile variations.

Rosenblatt, Edward I.↗