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NASA NTRS2008

High-Altitude Emission from Pulsar Slot Gaps: The Crab Pulsar

We present results of a 3D model of optical to gamma-ray emission from the slot gap accelerator of a rotation-powered pulsar. Primary electrons accelerating to high-altitudes in the unscreened electric field of the slot gap reach radiation-reaction limited Lorentz factors of approx. 2 x 10(exp 7), while electron-positron pairs from lower-altitude cascades flow along field lines interior to the slot gap. The curvature, synchrotron and inverse Compton radiation of both primary electrons and pairs produce a broad spectrum of emission from infra-red to GeV energies. Both primaries and pairs undergo cyclotron resonant absorption of radio photons, allowing them to maintain significant pitch angles. Synchrotron radiation from pairs with a power-law energy spectrum from gamma = 10(exp 2) - 10(exp 5), dominate the spectrum up to approx. 10 MeV. Synchrotron and curvature radiation of primaries dominates from 10 MeV up to a few GeV. We examine the energy-dependent pulse profiles and phase-resolved spectra for parameters of the Crab pulsar as a function of magnetic inclination alpha and viewing angle zeta, comparing to broad-band data. In most cases, the pulse profiles are dominated by caustics on trailing field lines. We also explore the relation of the high-energy and the radio profiles, as well as the possibility of caustic formation in the radio cone emission. We find that the Crab pulsar profiles and spectrum can be reasonably well reproduced by a model with alpha = 45deg and zeta approx. 100deg or 80deg. This model predicts that the slot gap emission below 200 MeV will exhibit correlations in time and phase with the radio emission.

Harding, Alice K.↗

DOE OSTI2022

The photon content of the proton in the CT18 global analysis

Recently, two photon PDF sets based on implementations of the LUX ansatz into the CT18 global analysis were released. In CT18lux, the photon PDF is calculated directly using the LUX master formula for all scales, \mu μ . In an alternative realization, CT18qed, the photon PDF is initialized at the starting scale, \mu_0 μ 0 , using the LUX formulation and evolved to higher scales \mu(>\mu_0) μ ( > μ 0 ) with a combined QED+QCD kernel at \mathcal{O}(\alpha),~\mathcal{O}(\alpha\alpha_s) 𝒪 ( α ) , 𝒪 ( α α s ) and \mathcal{O}(\alpha^2) 𝒪 ( α 2 ) . In the small- x x region, the photon PDF uncertainty is mainly induced by the quark and gluon PDFs, through the perturbative DIS structure functions. In comparison, the large- x x photon uncertainty comes from various low-energy, nonperturbative contributions, including variations of the inelastic structure functions in the resonance and continuum regions, higher-twist and target-mass corrections, and elastic electromagnetic form factors of the proton. We take the production of doubly-charged Higgs pairs, (H^{++}H^{--}) ( H + + H − − ) , as an example of scenarios beyond the Standard Model to illustrate the phenomenological implications of these photon PDFs at the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS2002

Insulin secretion and sensitivity in space flight: diabetogenic effects

Nearly three decades of space flight research have suggested that there are subclinical diabetogenic changes that occur in microgravity. Alterations in insulin secretion, insulin sensitivity, glucose tolerance, and metabolism of protein and amino acids support the hypothesis that insulin plays an essential role in the maintenance of muscle mass in extended-duration space flight. Experiments in flight and after flight and ground-based bedrest studies have associated microgravity and its experimental paradigms with manifestations similar to those of diabetes, physical inactivity, and aging. We propose that these manifestations are characterized best by an etiology that falls into the clinical category of "other" causes of diabetes, including, but not restricted to, genetic beta-cell defects, insulin action defects, diseases of the endocrine pancreas, endocrinopathies, drug or chemically induced diabetes, infections, immune-mediated metabolic alteration, and a host of genetic related diseases. We present data showing alterations in tumor necrosis factor-alpha production, insulin secretion, and amino acid metabolism in pancreatic islets of Langerhans cultured in a ground-based cell culture bioreactor that mimics some of the effects of microgravity. Taken together, space flight research, ground-based studies, and bioreactor studies of pancreatic islets of Langerhans support the hypothesis that the pancreas is unable to overcome peripheral insulin resistance and amino acid dysregulation during space flight. We propose that measures of insulin secretion and insulin action will be necessary to design effective countermeasures against muscle loss, and we advance the "disposition index" as an essential model to be used in the clinical management of space flight-induced muscle loss.

Review↗

NASA NTRS1993

A self-consistent model for the long-term gamma-ray spectral variability of Cygnus X-1

The long-term transitions of the black hole candidate Cygnus X-1 (between the states gamma-1, gamma-2, and gamma-3) include the occasional appearance of a strong nearly-MeV bump (gamma-1), whose strength appears to be anticorrelated with the continuum flux (below 400 keV) due to the Compton upscattering of cold disk photons by the inner, hot corona. We develop a self-consistent disk picture in which the bump is seen as due to the self-Comptonization of bremsstrahlung photons emitted predominantly near the plane of the corona itself. A decrease by a factor of about two in the viscosity parameter alpha is responsible for quenching this bump and driving the system to the gamma-2 state, whereas a transition from gamma-2 to gamma-3 appears to be induced by an increase of about 25 percent in the accretion rate M. In view of the fact that most of the transitions observed in this source seem to be of the gamma-2-gamma-3 variety, we conclude that much of the long-term gamma-ray spectral variability in Cygnus X-1 is due to these small fluctuations in M. The unusual appearance of the gamma-1 state apparently reflects a change in the dissipative processes within the disk.

Melia, Fulvio↗

DOE OSTI2026

Electromagnetic Transient Modeling of Large Data Centers for Grid-Level Studies: Beta Release

The magnitude and complexity of electricity usage patterns from large data centers are having significant impacts on the operation and dynamics of the power grid; grid operators and planners require a range of specialized data center models to properly evaluate these impacts and specify technical solutions as needed. Towards addressing this need, Pacific Northwest National Laboratory (PNNL) has developed a library of electromagnetic transient (EMT) models for grid-level studies of data centers called the data center model library (DML). This report describes how the DML was created and how it may properly be used. This report details the DML’s beta release, completed in July 2026. This is a revision and expansion of the alpha release, which was made available in January 2026 The models present in the DML are generic models; subject matter expertise and additional technical data are needed to modify these models before they can represent any real data center. However, they will significantly reduce the level of effort required to develop site-specific models and can serve as a common starting point to guide industry towards a more refined consensus. Most of the models within DML are dedicated to representing the power electronics interfaces commonly used in modern data centers, such as double-conversion uninterruptible power supplies and single-phase power factor correction converters. These models are intended for use in grid-level studies and are a simplified aggregation of many small components. That said, background material on the physical and electrical design of large data centers is provided as companion material so that users can be aware of many of the details which have been omitted or streamlined as a matter of practical necessity. Additionally, guidance on the application of EMT analysis for data center interconnection studies is provided, which aids users in identifying when the DML is necessary and what sort of additional model development may be necessary for conducting real-world studies.

electromagnetic transients↗

NASA NTRS2014

Confirmation of a Steep Luminosity Function for Ly alpha Emitters at z 5.7: a Major Component of Reionization

We report the first direct and robust measurement of the faint-end slope of the Ly-alpha emitter (LAE) luminosity function at z = 5.7. Candidate LAEs from a low-spectral-resolution blind search with IMACS on Magellan- Baade were targeted at higher resolution to distinguish high redshift LAEs from foreground galaxies. All but 2 of our 42 single-emission-line systems are fainter than F = 2.0×10(exp−17) ergs s(exp−1) cm(exp−2), making these the faintest emission-lines observed for a z = 5.7 sample with known completeness, an essential property for determining the faint end slope of the LAE luminosity function. We find 13 LAEs as compared to 29 foreground galaxies, in very good agreement with the modeled foreground counts predicted in Dressler et al. (2011a) that had been used to estimate a faint-end slope of alpha = −2.0 for the LAE luminosity function. A 32% LAE fraction, LAE/(LAE+foreground) within the flux interval F = 2−20 × 10(exp−18) ergs s(exp−1) cm(exp−2) constrains the faint end slope of the luminosity function to −1.95 greater than alpha greater than −2.35 (1 delta). We show how this steep LF should provide, to the limit of our observations, more than 20% of the flux necessary to maintain ionization at z = 5.7, with a factor-of-ten extrapolation in flux reaching more than 55%. We suggest that this bodes well for a comparable contribution by similar, low-mass star forming galaxies at higher-redshift - within the reionization epoch at z greater than approximately 7, only 250 Myr earlier - and that such systems provide a substantial, if not dominant, contribution to the late-stage reionization of the IGM.

STEEP↗

NASA NTRS1985

X-ray spectrum and variability of 3C 120

The X-ray luminosity of 3C 120 is variable by a factor of 2.5 on time scales of days to months. The spectral slope of the 2-10 keV X-rays changes systematically in the sense that the higher intensity states are steeper. Simple power laws fitted to the data are consistent with an energy index alpha of 0.51 + or - 0.13 at minimum intensity and 0.83 + or - 0.03 at maximum, with a continuous variation in between. A more complicated spectral shape cannot be ruled out, but changes in absorbing column density alone cannot explain the data. The results are interpreted in terms of beamed synchrotron emission from a relativistic jet, a model which has been invoked previously for the spectra of BL Lac objects. The spectral variability is in marked contrast to the behavior of 3C 273, another superluminal source in which the X-ray spectral index is constant to a high degree of accuracy despite variability in time scales and amplitudes which are quite similar to those of 3C 120. The difference may be due to the degree of beaming of the respective core components. Another model which is consistent with the data involves thermal emission from isothermal shocks in a hot (approximately 10 to the 8th K) medium. Thermal Compton and spherical accretion X-ray source models do not reproduce the correct behavior of alpha versus flux.

Halpern, J. P.↗

NASA NTRS1986

Altitude variation of EUV emissions and evidence for proton precipitation at low latitudes in the Saturnian atmosphere

Extreme ultraviolet observations of Saturn from Voyager 1 and 2 are analyzed. The Lyman alpha and H2 band emissions extend throughout the upper atmosphere, from the hydrocarbon homopause to well above the exobase. Analysis of the Lyman alpha emissions with a radiative transfer model indicates that the Lyman alpha source temperature is very high. This suggests that energetic protons or hydrogen atoms are responsible for a fraction of the emissions. Calculation of the solar-scattered component of the emissions based on the neutral atmosphere of Smith et al. (1983) reveals that only 1-2 kR out of a total of 3.5 kR of the observed Lyman alpha intensity is due to solar scatter for the Voyager 2 disk observations; the remainder of the Lyman alpha emissions are collisionally excited. The Lyman alpha and H2 bands are constant in longitude but decrease in local time by a factor of 2 from dawn to dusk. This correlation of the Lyman alpha and H2 band intensities is further evidence that most of the Lyman alpha is collisionally excited.

Yelle, R. V.↗

NASA NTRS1986

The 4 micron spectra of compact infrared sources

High resolution 5 arcsec spectra in the 4 micron region are presented of the central 5 arcsec of the compact near infrared sources K3-50, W51-IRS2 East, and G333.6-0.2. From measured Br-alpha/Pf-beta line ratios and previously published infrared and radio maps, it is concluded that standard recombination theory fails to explain our observations in at least two cases. It is demonstrated that the data are consistent with thermal excitation of the hydrogen lines in strong stellar winds. The Pf-beta Hu-epsilon line ratio, which is completely insensitive to differential extinction, confirms the need for the stellar wind model for the core of G333.6-0.2. From the (K III) line it is estimated that the potassium abundance in G333.6-0.2 is at least equal to the solar value, and possibly enhanced by a factor up to 10.

Hofmann, R.↗

NASA NTRS1994

Inverse Compton X-ray emission from the superluminal quasar 3C 345

In quasars with strong radio cores, the inverse-Compton process is believed to be the dominant source X-ray emission. For objects with parsec-scale radio jets, simple models have predicted that components in the jet emerging from the quasar nucleus generate the observed X-ray emission. We have tested this hypothesis in detail for the quasar 3C 345 using a ROSAT X-ray observation in 1990 July, together with quasi-simultaneous very long base interferometry (VLBI) imaging of the parsec-scale jet at five frequencies. The ROSAT spectrum is well fitted by a power law with index alpha = -0.96 +/- -0.13, consistent with models in which the X-ray emission results from inverse-Compton scattering of radio radiation from high-energy electrons in compact components. We show that the radio properties of brightest `knot' in the jet (`C5') can be fitted with a homogeneous sphere model whose parameters require bulk relativistic motion of the emitting material; otherwise the predicted model whose parameters require bulk relativistic motion of the emitting material; otherwise the predicted inverse-Compton X-ray emission exceeds the observed flux. If C5 is the origin of the X-ray emission, then it has a Doppler factor delta = 7.5((sup +3 sub -2)). If the nucleus or other components contribute to the X-ray emission, then this becomes a firm lower limit to delta. The inhomogeneous jet model of Koenigl is a good fit both to the barely resolved (less than 1 pc) flat-spectrum nucleus in the radio, and also to the ROSAT X-ray spectrum. The synchrotron and inverse-Compton emitting fluid moves down a narrow cone (opening angle 2 phi approximately 5 deg) nucleus relativistically, with delta approximately 4.6. Doppler factors for the nucleus and C5, derived from our ROSAT observation, provide evidence for bulk relativistic motion in the jet. By combining these constraints with well-known superluminal motion of jet components, we can deduce geometry. For epoch 1990.5 we infer the Lorentz factor gamma = 7.5 ((sup +1.0 sub -1.5)) and angle to the line of sight theta = 8((sup +2 deg sub -3 deg)) for H(sub 0) = 100 km/s/Mpc. These values are the most reliable yet derived using this method, because of the near-simultaneity of our X-ray and VLBI observations and the quality of the multifrequency of VLBI images and component radio spectra.

Unwin, S. C.↗

NASA NTRS1999

Thermal Emission Spectroscopy of 1 Ceres: Evidence for Olivine

Thermal emission spectra of the largest asteroid 1 Ceres obtained from the Kuiper Airborne Observatory display features that may provide information on its surface mineralogy. A plot of the Ceres spectrum (calibrated using alpha Boo as a standard) divided by a standard thermal model (STM) is shown. Also shown is the emissivity spectrum deduced from reflectivity measurements for olivine grains <5 microns in diameter. The general shape of the Ceres and the olivine curves agree in essential details, such as the maxima from 8 to 12 microns, the minimum between 12 and 14 microns, the broad peak near 17.5 micron, and the slope beyond 22 micron. (Use of the 10 to 15-micron grain reflectivities provides a better match to the 12- to 14-micron dip. We used a value of unity for beta, the beaming factor associated with small-scale surface roughness in our STM. Adjustment of beta to a lower value raises the long-wavelength side of the Ceres spectrum, providing an even better match to the olivine curve.) The emissivity behavior roughly matches the emission coefficients which were calculated for olivine particles with a particle radius of 3 microns. Their calculations show not only the negative slope from 23 to 25 pm, but a continued decrease past 30 micron. The Ceres emissivity is thus similar to that of small olivine grains from 8 to 30 micron, but olivine's emissivity is lower from 5 to 8 pm.

Witteborn, F. C.↗

NASA NTRS1989

Far-ultraviolet spectrophotometry of Spica

A spectrum of the star Spica (Alpha Virginis) from 960 to 1270 A was recorded by a rocket-borne spectrograph March 13, 1988. The spectrum, which has 3.4 A resolution, shows a much sharper drop-off in intensity near 1050 A than similar measurements made by the Voyager UVS, but is in good agreement with the spectrum obtained by Brune et al. in a 1977 sounding rocket. The disagreement with Voyager is a factor of 1.5 at 1100 A and grows to a factor of 5.7 at 960 A. This implies that the photometric standards between 912 and 1100 A may need some revision, and that the standard photospheric models for hot stars may err significantly near the Lyman limit.

Cook, Timothy A.↗

NASA NTRS1998

The Effects of Impurities on Protein Crystal Growth and Nucleation: A Preliminary Study

Kubota and Mullin (1995) devised a simple model to account for the effects of impurities on crystal growth of small inorganic and organic molecules in aqueous solutions. Experimentally, the relative step velocity and crystal growth of these molecules asymptotically approach zero or non-zero values with increasing concentrations of impurities. Alternatively, the step velocity and crystal growth can linearly approach zero as the impurity concentration increases. The Kubota-Mullin model assumes that the impurity exhibits Langmuirian adsorption onto the crystal surface. Decreases in step velocities and subsequent growth rates are related to the fractional coverage (theta) of the crystal surface by adsorbed impurities; theta = Kx / (I +Kx), x = mole fraction of impurity in solution. In the presence of impurities, the relative step velocity, V/Vo, and the relative growth rate of a crystal face, G/Go, are proposed to conform to the following equations: V/Vo approx. = G/Go = 1 - (alpha)(theta). The adsorption of impurity is assumed to be rapid and in quasi-equilibrium with the crystal surface sites available. When the value of alpha, an effectiveness factor, is one the growth will asymptotically approach zero with increasing concentrations of impurity. At values less than one, growth approaches a non-zero value asymptotically. When alpha is much greater than one, there will be a linear relationship between impurity concentration and growth rates. Kubota and Mullin expect alpha to decrease with increasing supersaturation and shrinking size of a two dimensional nucleus. It is expected that impurity effects on protein crystal growth will exhibit behavior similar to that of impurities in small molecule growth. A number of proteins were added to purified chicken egg white lysozyme, the effect on crystal nucleation and growth assessed.

Schall, Constance A.↗

NASA NTRS2005

Calculated X-ray Intensities Using Monte Carlo Algorithms: A Comparison to Experimental EPMA Data

Monte Carlo (MC) modeling has been used extensively to simulate electron scattering and x-ray emission from complex geometries. Here are presented comparisons between MC results and experimental electron-probe microanalysis (EPMA) measurements as well as phi(rhoz) correction algorithms. Experimental EPMA measurements made on NIST SRM 481 (AgAu) and 482 (CuAu) alloys, at a range of accelerating potential and instrument take-off angles, represent a formal microanalysis data set that has been widely used to develop phi(rhoz) correction algorithms. X-ray intensity data produced by MC simulations represents an independent test of both experimental and phi(rhoz) correction algorithms. The alpha-factor method has previously been used to evaluate systematic errors in the analysis of semiconductor and silicate minerals, and is used here to compare the accuracy of experimental and MC-calculated x-ray data. X-ray intensities calculated by MC are used to generate a-factors using the certificated compositions in the CuAu binary relative to pure Cu and Au standards. MC simulations are obtained using the NIST, WinCasino, and WinXray algorithms; derived x-ray intensities have a built-in atomic number correction, and are further corrected for absorption and characteristic fluorescence using the PAP phi(rhoz) correction algorithm. The Penelope code additionally simulates both characteristic and continuum x-ray fluorescence and thus requires no further correction for use in calculating alpha-factors.

Carpenter, P. K.↗

DOE OSTI2024

Cosmology before noon with multiple galaxy populations

Near-future facilities observing the high-redshift universe (2 < z < 5) will have an opportunity to take advantage of "multi-tracer" cosmology by observing multiple tracers of the matter density field: Lyman alpha emitters (LAE), Lyman break galaxies (LBG), and CMB lensing κ. Here, in this work we use Fisher forecasts to investigate the effect of multi-tracers on next-generation facilities. In agreement with previous work, we show that multiple tracers improve constraints primarily from degeneracy breaking, instead of the traditional intuition of sample variance cancellation. Then, we forecast that for both BBN and CMB primary priors, the addition of lensing and LAEs onto a LBG-only sample will gain 25% or more in many parameters, with the largest gains being factor of ~ 10 improvement for f EDE . We include a preliminary approach towards modelling the impact of radiative transfer (RT) on forecasts involving LAEs by introducing a simplified model at linear theory level. Our results, albeit preliminary, show that while RT influences LAE-only forecasts strongly, its effect on composite multi-tracer forecasts is limited.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1984

Observational evidence for chromospheric footpoint penetration of nonthermal electrons during two well-observed flares

Recent advances have enabled simultaneous H-alpha and X-ray observations with substantially improved spatial, spectral, and temporal resolution. In this paper a study is conducted of two events observed as part of a coordinated observing program between the Solar Maximum Mission and Sacramento Peak Observatory: the flares of 1456 UT, 7 May 1980 and 1522 UT, 24 June 1980. Using recently developed physical models of static flare chromospheres, and corresponding theoretical H-alpha line profiles, effects of intense nonthermal electron heating can be distinguished from those of high conduction and pressure from the overlying flare corona. Both flares show the signature of intense chromospheric heating by fast electrons, temporally correlated with X-ray light curves at E greater than 27keV, and spatially associated with X-ray emission sites at E greater than 16 keV. Interpreting the H-alpha line profile observations using the theoretical H-alpha line profiles, values of the thick-target input power contained in nonthermal electrons that are observationally indistinguishable (within a factor of 2-3) from those inferred from the X-ray data are inferred. Although these events are small, the energy flux values are large: of order 10 to the 11th ergs per sq cm per s above 20 keV.

Canfield, R. C.↗

NASA NTRS1991

Relativistic enhancement of the Compton-reflected component in active galactic nuclei

Compton reflection may be an important process in AGNs, since it provides an improvement over power-law fits to AGN spectra observed by Ginga and can also explain the spectrum of the cosmic X-ray background. The fraction of the total X-ray luminosity which is incident upon a thin steady alpha-disk if the X-rays are produced by inverse-Compton scattering of soft, disk photons off relativistic electrons located above the disk is calculated. This fraction is called the Compton reflection covering factor, f, and it is found that it can range between 0.5 and 0.88. This large range in f, due to a relativistic kinematic effect first calculated in this connection by Ghisellini et al (1991) is sufficient to explain the typical covering (about 0.5) observed in bright AGNs by Ginga as well as the large covering factor (about 0.9) required to explain the cosmic X-ray background in the Compton reflection model.

Rogers, R. D.↗

NASA NTRS1982

Mass loss from alpha Cyg /A2Ia/ derived from the profiles of low excitation Fe II lines

The low-excitation Fe II lines in the spectral region 2000-3000 A are studied in the spectrum of alpha-Cyg. The profiles of the resonance lines are described by four representative parameters, and a preliminary model is derived from the dependence of these parameters on theoretical line strength, taking into account the influence of blending photospheric lines in an overall and qualitative way. At least 11% of all iron in the wind is once ionized, unless a non-thermal heating source enhances the fraction Fe(++) without destroying much Al(+). It is shown that the contribution of blending photospheric absorption lines to weaker P Cygni profiles has been previously largely underestimated. The mass loss rate corresponding to the model is derived, and is smaller by a factor of 500 than the one derived from the infrared excess by Barlow and Cohen (1977).

Hensberge, H.↗