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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Determination of krypton diffusion coefficients in uranium dioxide using atomic scale calculations

We present a study of the diffusion of krypton in UO 2 using atomic scale calculations combined with diffusion models adapted to the system studied. The migration barriers of the elementary mechanisms for interstitial or vacancy assisted migration are calculated in the DFT + U framework using the nudged elastic band method. The attempt frequencies are obtained from the phonon modes of the defect at the initial and saddle points using empirical potential methods. The diffusion coefficients of Kr in UO 2 are then calculated by combining this data with diffusion models accounting for the concentration of vacancies and the interaction of vacancies with Kr atoms. We determined the preferred mechanism for Kr migration and the corresponding diffusion coefficient as a function of the oxygen chemical potential μ O or nonstoichiometry. For very hypostoichiometric (or U-rich) conditions, the most favorable mechanism is interstitial migration. For hypostoichiometric UO 2 , migration is assisted by the bound Schottky defect and the charged uranium vacancy, V U 4– . Around stoichiometry, migration assisted by the charged uranium–oxygen divacancy (V UO 2– ) and V U 4– is the favored mechanism. Finally, for hyperstoichiometric or O-rich conditions, the migration assisted by two V U 4– dominates. Kr migration is enhanced at higher μ O , and in this regime, the activation energy will be between 4.09 and 0.73 eV depending on nonstoichiometry. The experimental values available are in the latter interval. Since it is very probable that these values were obtained for at least slightly hyperstoichiometric samples, our activation energies are consistent with the experimental data, even if further experiments with precisely controlled stoichiometry are needed to confirm these results. Finally, the mechanisms and trends with nonstoichiometry established for Kr are similar to those found in previous studies of Xe.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Topography and canopy cover influence soil organic carbon composition and distribution across a forested hillslope in the discontinuous permafrost zone

This dataset contains data used for the paper "Topography and canopy cover influence soil organic carbon composition and distribution across a forested hillslope in the discontinuous permafrost zone". The Related References field will be updated with a full citation when available. Topography and canopy cover influence ground temperature in warming permafrost landscapes, yet soil temperature heterogeneity introduced by meso-topographic slope positions, microtopographic differences in vegetation cover, and the subsequent impact of contrasting temperature conditions to soil organic carbon (SOC) dynamics are understudied. Buffering of permafrost-affected soils against warming air temperatures in boreal forests can reflect surface soil characteristics (e.g., thickness of organic material) as well as the degree and type of canopy cover (e.g., open cover vs closed cover). Both landscape and soil properties interact to determine meso- and micro-scale heterogeneity of ground warming. We sampled a hillslope catena transect in a discontinuous permafrost zone near Fairbanks, Alaska to test the small-scale (1 to 3 meter) impacts of slope position and cover type on soil organic matter composition. Mineral active layer samples were collected from backslope, low backslope, and footslope positions at depths spanning 19 to 60 cm. We examined soil mineralogical composition, soil moisture, total carbon and nitrogen content, and organic mat thickness in conjunction with an assessment of SOC composition using Fourier-transform ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS). Soils in the footslope position had a higher relative contribution of lignin-like compounds while backslope soils had more aliphatic and condensed aromatic compounds as determined by FT-ICR-MS. The effect of open versus closed tree canopy cover varied with slope position. On the backslope, we found higher oxidation of molecules under open cover compared with closed cover, indicating an effect of warmer soil temperature on decomposition. Little to no effect of canopy was observed for soils at the footslope position, which we attributed, in part, to the strong impact of soil moisture content in SOC dynamics in the water-gathering footslope position. The thin organic mat under open cover on the backslope position may have contributed to differences in soil temperature and thus SOC oxidation under open and closed canopy. Here, the thinner organic mat did not appear to buffer the underlying soil against warm season air temperatures and thus increased SOC decomposition as indicated by higher oxidation of SOC molecules and a lower contribution of simple molecules under open cover compared with the closed canopy sites. Our findings suggest that the role of canopy cover in SOC dynamics varies as a function of landscape position and soil properties, namely organic mat thickness and soil moisture. Condition-specific heterogeneity of SOC composition under open and closed canopy cover highlights the protective effect of canopy cover for soils on backslope positions. This dataset contains a compressed (.zip) archive of the data and R scripts used for this manuscript. The dataset includes files in .csv format, which can be accessed and processed using MS Excel or R. This archive can also be accessed on GitHub at https://github.com/Erin-Rooney/Y1_fairbanks (DOI: 10.5281/zenodo.8071247).

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2001

Evaluation Of The NASA Quality Surveillance System Pilot In Meeting Requirements For Contractor Surveillance Under Performance Based Contracting

The use of performance-based contracting at Kennedy Space Center has necessitated a shift from intrusive oversight of contractor activities to an insight surveillance role. This paper describes the results of a pilot implementation of the NASA Quality Surveillance System (NQSS) in the Space Shuttle Main Engines Processing Facility. The NQSS is a system to sample contractor activities using documented procedures, specifications, drawings and observations of work in progress to answer the question "Is the contractor doing what they said they would do?" The concepts of the NQSS are shown to be effective in providing assurance of contractor quality. Many of the concepts proven in the pilot are being considered for incorporation into an overall KSC Quality Surveillance System.

Schmahl, Karen E.↗
NASA NTRS2002

Evaluation of the NASA Quality Surveillance System Pilot in Meeting Requirements for Contractor Surveillance Under Performance Based Contracting

The use of performance-based contracting at Kennedy Space Center has necessitated a shift from intrusive oversight of contractor activities to an insight surveillance role. This paper describes the results of a pilot implementation of the NASA Quality Surveillance System (NQSS) in the Space Shuttle Main Engines Processing Facility. The NQSS is a system to sample contractor activities using documented procedures, specifications, drawings and observations of work in progress to answer the question "Is the contractor doing what they said they would do?" The concepts of the NQSS are shown to be effective in providing assurance of contractor quality. Many of the concepts proven in the pilot are being considered for incorporation into an overall KSC Quality Surveillance System.

Schmahl, Karen E.↗
DOE OSTI2023

Effects of presenilin-1 familial Alzheimer’s disease mutations on γ-secretase activation for cleavage of amyloid precursor protein

Presenilin-1 (PS1) is the catalytic subunit of γ-secretase which cleaves within the transmembrane domain of over 150 peptide substrates. Dominant missense mutations in PS1 cause early-onset familial Alzheimer’s disease (FAD); however, the exact pathogenic mechanism remains unknown. Here we combined Gaussian accelerated molecular dynamics (GaMD) simulations and biochemical experiments to determine the effects of six representative PS1 FAD mutations (P117L, I143T, L166P, G384A, L435F, and L286V) on the enzyme-substrate interactions between γ-secretase and amyloid precursor protein (APP). Biochemical experiments showed that all six PS1 FAD mutations rendered γ-secretase less active for the endoproteolytic (ε) cleavage of APP. Distinct low-energy conformational states were identified from the free energy profiles of wildtype and PS1 FAD-mutant γ-secretase. The P117L and L286V FAD mutants could still sample the “Active” state for substrate cleavage, but with noticeably reduced conformational space compared with the wildtype. The other mutants hardly visited the “Active” state. The PS1 FAD mutants were found to reduce γ-secretase proteolytic activity by hindering APP residue L49 from proper orientation in the active site and/or disrupting the distance between the catalytic aspartates. Therefore, our findings provide mechanistic insights into how PS1 FAD mutations affect structural dynamics and enzyme-substrate interactions of γ-secretase and APP.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Differences in halo-scale environments between type 1 and type 2 AGNs at low redshift

Using low-redshift (z<0.09) samples of active galactic nuclei (AGNs), normal galaxies and groups of galaxies selected from the Sloan Digital Sky Survey, we study the environments of Type 1 and Type 2 AGNs, both on small and large scales. Comparisons are made for galaxy samples matched in redshift, r-band luminosity, [O iii] luminosity, and also the position in groups (central or satellite). We find that Type 2 AGNs and normal galaxies reside in similar environments. Type 1 and Type 2 AGNs have similar clustering properties on large scales (≳1 h{sup −1} Mpc), but at scales smaller than 100 h{sup −1} kpc, Type 2s have significantly more neighbors than Type 1s (3.09 ± 0.69 times more for central AGNs at ≲30 h{sup −1} kpc). These results suggest that Type 1 and Type 2 AGNs are hosted by halos of similar masses, as can also be seen directly from the mass distributions of their host groups (∼10{sup 12} h{sup −1} M{sub ⊙} for centrals and ∼10{sup 13} h{sup −1} M{sub ⊙} for satellites). Type 2s have significantly more satellites around them, and the distribution of their satellites is also more centrally concentrated. The host galaxies of both types of AGNs have similar optical properties, but their infrared colors are significantly different. Our results suggest that the simple unified model based solely on torus orientation is not sufficient, but that galaxy interactions in dark matter halos must have played an important role in the formation of the dust structure, which obscures AGNs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Experiment Design and Preparation for a Shielding Benchmark Utilizing Godiva-IV

An experiment is currently being designed to provide a high-quality shielding benchmark for Criticality Accident Alarm System (CAAS) modeling. Previous benchmarks have suffered from uncertainty primarily due to two factors. The first factor is radiation that is not directly coming from the source, also known as room return. Room return is notoriously difficult to account for in experimental data and to model in benchmarks. The second factor is uncertainty associated with the source term itself. In order to reduce these two sources of uncertainty, this experiment will utilize a room return shield [1] that will reduce the effect of room return and previous work performed to ensure the reproducibility of the source term. The experiment will use the Godiva IV [2] assembly located at the National Criticality Experiments Research Center (NCERC) to provide a neutron source representative of a criticality accident. Previous experiments [3]-[4] have shown that Godiva IV is capable of producing both bursts and steady-state emissions of equal magnitude which will allow for reduced uncertainty in the source term. The room return shield will house and isolate the shielding samples, neutron activation foils, and other detectors. Data collected will provide a comparison of the neutron and gamma dose for shielded and unshielded configurations. This data will be used to validate shielding data used for modeling criticality accident alarm systems. Shielding samples included in this benchmark are C, Fe, NaCl, Pb, high density polyethylene, and SiO 2 . This paper details the design of the room return shield, the experimental plan, challenges, and mitigation strategies.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

Probing the Physics of Narrow-line Regions in Active Galaxies. IV. Full Data Release of the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7)

We present the second and final data release of the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7). Data are presented for 63 new galaxies not included in the first data release, and we provide 2D emission-line fitting products for the full S7 sample of 131 galaxies. The S7 uses the WiFeS instrument on the ANU 2.3 m telescope to obtain spectra with a spectral resolution of R = 7000 in the red (540–700 nm) and R = 3000 in the blue (350–570 nm), over an integral field of 25 × 38 arcsec{sup 2} with 1 × 1 arcsec{sup 2} spatial pixels. The S7 contains both the largest sample of active galaxies and the highest spectral resolution of any comparable integral field survey to date. The emission-line fitting products include line fluxes, velocities, and velocity dispersions across the WiFeS field of view, and an artificial neural network has been used to determine the optimal number of Gaussian kinematic components for emission-lines in each spaxel. Broad Balmer lines are subtracted from the spectra of nuclear spatial pixels in Seyfert 1 galaxies before fitting the narrow lines. We bin nuclear spectra and measure reddening-corrected nuclear fluxes of strong narrow lines for each galaxy. The nuclear spectra are classified on optical diagnostic diagrams, where the strength of the coronal line [Fe vii] λ 6087 is shown to be correlated with [O iii]/H β . Maps revealing gas excitation and kinematics are included for the entire sample, and we provide notes on the newly observed objects.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

New approach to precisely measure γ-ray intensities for long-lived fission products, with results for the decay of 95 Zr

For many fission products, the rays emitted following decay provide an easily-detectable signature that can be used to identify their quantities and distributions in a sample. As a result, γ-ray spectroscopy is often exploited to study fission-product yields, provided sufficiently accurate information on the γ-ray intensity is available. However, in many cases, the uncertainties in the existing nuclear data are large enough that they compromise the precision achievable for modern experiments and applications. To address this need, we have developed a new experimental method that is well suited to precisely measure absolute γ-ray intensities in the β decay of long-lived fission products. The approach involves the production of a radiopure sample by implantation of a mass-separated ion beam from the CAlifornium Rare Isotope Breeder Upgrade (CARIBU) facility on a thin carbon foil. The emitted β-decay radiation is detected with a 4π gas proportional counter and a meticulously efficiency-calibrated high-purity germanium (HPGe) detector. As a first measurement to demonstrate the approach, we studied the absolute γ-ray intensities of the strongest transitions following the β decay of 95 Zr and its decay-daughter 95 Nb, and determined them to fractional precisions of better than 1–2%. In addition, with a larger sample of activity produced through neutron irradiation of an isotopically-enriched Zr foil, we performed a high-precision measurement of the relative γ-ray intensities following the decay of 95 Zr with just the HPGe detector. Here, the sample-production method at CARIBU and the coincidence detection approach demonstrated here can be applied to study fission products with half-lives longer than a day, which includes isotopes important not only for nuclear-energy and national-security applications, but also for medical-isotope research and environmental monitoring.

4π↗
DOE OSTI2012

CONTEMPORANEOUS VLBA 5 GHz OBSERVATIONS OF LARGE AREA TELESCOPE DETECTED BLAZARS

The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long Baseline Array (VLBA). In total, 232 sources were observed with the VLBA. Ninety sources that were previously observed as part of the VLBA Imaging and Polarimetry Survey (VIPS) have been included in the sample, as well as 142 sources not found in VIPS. This very large, 5 GHz flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong {gamma}-ray emission. In particular, we see that {gamma}-ray emission is related to strong, uniform magnetic fields in the cores of the host AGN. Included in this sample are non-blazar AGNs such as 3C84, M82, and NGC 6251. For the blazars, the total VLBA radio flux density at 5 GHz correlates strongly with {gamma}-ray flux. The LAT BL Lac objects tend to be similar to the non-LAT BL Lac objects, but the LAT flat-spectrum radio quasars (FSRQs) are significantly different from the non-LAT FSRQs. Strong core polarization is significantly more common among the LAT sources, and core fractional polarization appears to increase during LAT detection.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Characterization of Oxygen Containing Functional Groups on Carbon Materials with Oxygen K-edge X-ray Absorption Near Edge Structure Spectroscopy

Surface functional groups on carbon materials are critical to their surface properties and related applications. Many characterization techniques have been used to identify and quantify the surface functional groups, but none is completely satisfactory especially for quantification. In this work, we used oxygen K-edge X-ray absorption near edge structure (XANES) spectroscopy to identify and quantify the oxygen containing surface functional groups on carbon materials. XANES spectra were collected in fluorescence yield mode to minimize charging effect due to poor sample conductivity which can potentially distort XANES spectra. The surface functional groups are grouped into three types, namely carboxyl-type, carbonyl-type, and hydroxyl-type. XANES spectra of the same type are very similar while spectra of different types are significantly different. Two activated carbon samples were analyzed by XANES. The total oxygen contents of the samples were estimated from the edge step of their XANES spectra, and the identity and abundance of different functional groups were determined by fitting of the sample XANES spectrum to a linear combination of spectra of the reference compounds. It is concluded that oxygen K-edge XANES spectroscopy is a reliable characterization technique for the identification and quantification of surface functional groups on carbon materials.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Hanford Waste Treatment Plant Low Activity Waste Facility Stack Effluent Monitoring: Sampling Probe Location Qualification Evaluation (Rev.1)

The Hanford Tank Waste Treatment and Immobilization Plant Low Activity Waste (LAW) facility stack monitor locations were qualified using scale model stacks to mitigate the risk of discovering that sampling locations do not meet the qualification criteria on the full-scale stacks. As required by the American National Standards Institute/Health Physics Society (ANSI/HPS) N13.1-1999 standard, the scale model and its sampling location were geometrically similar to the actual stack and the Reynolds numbers for both the actual and model stacks were >10,000. An additional criterion is that the product of the hydraulic diameter and mean velocity (DV) of the full-scale stack must be between 1/6 DV and 6 DV of the scale model stack tests. Verification tests of the LAW stacks were performed at normal operating conditions. The minimum 1/6 DV value, along with the maximum 6 DV value from the scale model testing, determines the range of stack flow rates for which the full-scale stack may be operated and remain in compliance with the stack verification criterion. For this analysis, the range of qualified flow rates listed is conservatively based on the average DV through 6 DV for LV-S1, LV-S2, and LV-C2, and 1/3 DV to 3 DV for LV-S3. Table S1 lists the operating flow rates along with the conservative lower and upper qualified stack flow rates for each of the LAW facility stacks. For each stack, the operating flow is below the upper qualified stack.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

The possibly important role played by Ga{sub 2}O{sub 3} during the activation of GaN photocathode

Three different chemical solutions are used to remove the possible contamination on GaN surface, while Ga{sub 2}O{sub 3} is still found at the surface. After thermal annealing at 710 °C in the ultrahigh vacuum (UHV) chamber and activated with Cs/O, all the GaN samples are successfully activated to the effective negative electron affinity (NEA) photocathodes. Among all samples, the GaN sample with the highest content of Ga{sub 2}O{sub 3} after chemical cleaning obtains the highest quantum efficiency. By analyzing the property of Ga{sub 2}O{sub 3}, the surface processing results, and electron affinity variations during Cs and Cs/O{sub 2} deposition on GaN of other groups, it is suggested that before the adsorption of Cs, Ga{sub 2}O{sub 3} is not completely removed from GaN surface in our samples, which will combine with Cs and lead to a large decrease in electron affinity. Furthermore, the effective NEA is formed for GaN photocathode, along with the surface downward band bending. Based on this assumption, a new dipole model Ga{sub 2}O{sub 3}-Cs is suggested, and the experimental effects are explained and discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Leverage Score Sampling for Parametric PDEs (Final Technical Report)

This final technical report summarizes the accomplishments of work performed under DOE Office of Science Award DE-SC0022266, which is titled “Leverage Score Sampling for Parametric PDEs”. The goal of the project was to extend methods from Randomized Numerical Linear Algebra (RandNLA) to tackle central computational challenges in model order reduction and uncertainty quantification (UQ) for parametric partial differential equations (PDEs). In particular, we sought to use importance sampling methods originally developed for RandNLA to develop sample efficient active learning algorithms for approximating high-dimensional scalar functions, e.g. by polynomials, Gaussian process models, and simple neural networks. Such methods can be immediately applied to developing surrogate models or to approximating quantity of interest (QoI) surfaces. In the context of PDEs, each sample used for learning equates to the solution of the differential equation for a particular set of parameters, so sample efficiency translates to improved computational efficiency for a variety of downstream tasks.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1982

Solar and late-type dwarfs

The Einstein Observatory's and the IUE's contributions to knowledge of coronal formation in late-type stars are discussed. The HR diagram of stars seen as X-ray sources by these observatories is presented, and the influence of rotation on X-ray emission is reviewed. Emission from the Alpha Cen system and from active stars with quiescent coronae is examined, and the extent of the contribution of emission from normal stars to the soft X-ray background is addressed. The quiescent and flare emission from Alpha Cen, the temporal variability of X-ray emission from a sample of active chromosphere stars, and the predicted contribution of chromospheric emission to the diffuse soft X-ray background are depicted. Chromospheric indicators of activity are discussed, the connection between surface magnetic fields and X-ray emission in the chromosphere is briefly reviewed, and the quantitative links between X-ray data and magnetic fields is summarily presented.

Golub, L.↗
DOE OSTI2017

Chromospherically active stars in the RAVE survey. II. Young dwarfs in the solar neighborhood

A large sample of over 38,000 chromospherically active candidate solar-like stars and cooler dwarfs from the RAVE survey is addressed in this paper. An improved activity identification with respect to the previous study was introduced to build a catalog of field stars in the solar neighborhood with an excess emission flux in the calcium infrared triplet wavelength region. The central result of this work is the calibration of the age–activity relation for main-sequence dwarfs in a range from a few 10 Myr up to a few Gyr. It enabled an order of magnitude age estimation of the entire active sample. Almost 15,000 stars are shown to be younger than 1 Gyr and ∼2000 younger than 100 Myr. The young age of the most active stars is confirmed by their position off the main sequence in the J − K versus N{sub UV}−V diagram showing strong ultraviolet excess, mid-infrared excess in the J − K versus W{sub 1}−W{sub 2} diagram, and very cool temperatures (J−K>0.7). They overlap with the reference pre-main-sequence RAVE stars often displaying X-ray emission. The activity level increasing with the color reveals their different nature from the solar-like stars and probably represents an underlying dynamo-generating magnetic fields in cool stars. Of the RAVE objects from DR5, 50% are found in the TGAS catalog and supplemented with accurate parallaxes and proper motions by Gaia. This makes the database of a large number of young stars in a combination with RAVE’s radial velocities directly useful as a tracer of the very recent large-scale star formation history in the solar neighborhood. The data are available online in the Vizier database.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Magnetic and electric modulus properties of In substituted Mg–Mn–Cu ferrites

Highlights: • Ferrite of composition Mg{sub 1−y}Cu{sub y}Mn{sub 0.1}In{sub x}Fe{sub 1.9−x}O{sub 4} with (0.0 ≤ x ≤ 0.4; y = 0.0; 0.1) has been synthesized. • Electric, magnetic and Mössbauer studies have been investigated. • The real and imaginary parts of electric modulus follow the Arrhenius law. • Saturation magnetization increases up to x = 0.2 and thereafter it decreases. • Good agreement between the magnetic and Mössbauer effect studies. - Abstract: Ferrite of composition Mg{sub (1−y)}Cu{sub (y)}Mn{sub (0.1)}In{sub (x)}Fe{sub (1.9−x)}O{sub 4} with (0.0 ≤ x ≤ 0.4; y = 0.0 and y = 0.1) has been synthesized by solid state reaction technique. X-ray diffraction (XRD) patterns of the samples indicated the formation of single-phase cubic spinel structure up to 0.2 and mixed phase for samples x ≥ 0.3. Vibrating sample magnetometer (VSM) measurements indicated that the saturation magnetization increases up to x = 0.2 and thereafter it decreases. Electric modulus analysis was used as a tool to analyze the electrical behavior of the samples. The activation energies extracted from real M′ (ω) and imaginary M″ (ω) peaks were found to follow the Arrhenius law. The area ratio of Fe{sup 3+} at the tetrahedral A- and octahedral B-sites was deduced from the spectral analysis of Mössbauer measurements. The results give evidence that In{sup 3+} replaces Fe{sup 3+} at A-site in the range (0.0 < x ≤ 0.2). As the In{sup 3+} content increases; it replaces Fe at B-site.

36 MATERIALS SCIENCE↗
DOE OSTI2013

A PHYSICAL LINK BETWEEN JET FORMATION AND HOT PLASMA IN ACTIVE GALACTIC NUCLEI

Recent observations suggest that in black hole X-ray binaries jet/outflow formation is related to the hot plasma in the vicinity of the black hole, either in the form of an advection-dominated accretion flow at low accretion rates or in a disk corona at high accretion rates. We test the viability of this scenario for supermassive black holes using two samples of active galactic nuclei distinguished by the presence (radio-strong) and absence (radio-weak) of well-collimated, relativistic jets. Each is centered on a narrow range of black hole mass but spans a very broad range of Eddington ratios, effectively simulating in a statistical manner the behavior of a single black hole evolving across a wide spread in accretion states. Unlike the relationship between the radio and optical luminosity, which shows an abrupt break between high- and low-luminosity sources at an Eddington ratio of {approx}1%, the radio emission-a measure of the jet power-varies continuously with the hard X-ray (2-10 keV) luminosity, roughly as L{sub R} {proportional_to} L{sub X}{sup 0.6-0.75}. This relation, which holds for both radio-weak and radio-strong active galaxies, is similar to the one seen in X-ray binaries. Jet/outflow formation appears to be closely linked to the conditions that give rise to the hot, optically thin coronal emission associated with accretion flows, both in the regime of low and high accretion rates.

79 ASTRONOMY AND ASTROPHYSICS↗