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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Data associated with "Methane emissions from gathering and boosting compressor stations in the U.S. Supporting volume 1: Multi-day measurements of pneumatic controller emissions"

This study was part of a larger study (the Gathering Emission Factor, or "GEF") study [1] to develop activity and methane emission factors for EPA's Greenhouse Gas Inventory (EPA GHGI) using direct emission measurements at the device level on all classes of equipment found on gathering compressor stations. To accomplish this, Colorado State University (CSU) partnered with the engineering firm AECOM to assist with planning, logistics, field work and analysis. Nine midstream natural gas companies – Anadarko Petroleum, Equinor, DCP Midstream, Kinder Morgan, MarkWest Energy Partners, Pioneer Natural Resources, Southwestern Energy, Williams Companies Inc., and XTO Energy Inc. – acted as partners in the study, provided site access for measurements, and provided representatives to advisory committees. At all times, and with the encouragement of industry partners, CSU maintained control the sampling plan, analysis and reporting. This study documents one part of the larger study - emissions from pneumatic actuated valve controllers (PC).

03 NATURAL GAS↗
DOE OSTI2016

EMISSION SIGNATURES FROM SUB-PARSEC BINARY SUPERMASSIVE BLACK HOLES. I. DIAGNOSTIC POWER OF BROAD EMISSION LINES

Motivated by advances in observational searches for sub-parsec supermassive black hole binaries (SBHBs) made in the past few years, we develop a semi-analytic model to describe spectral emission-line signatures of these systems. The goal of this study is to aid the interpretation of spectroscopic searches for binaries and to help test one of the leading models of binary accretion flows in the literature: SBHB in a circumbinary disk. In this work, we present the methodology and a comparison of the preliminary model with the data. We model SBHB accretion flows as a set of three accretion disks: two mini-disks that are gravitationally bound to the individual black holes and a circumbinary disk. Given a physically motivated parameter space occupied by sub-parsec SBHBs, we calculate a synthetic database of nearly 15 million broad optical emission-line profiles and explore the dependence of the profile shapes on characteristic properties of SBHBs. We find that the modeled profiles show distinct statistical properties as a function of the semimajor axis, mass ratio, eccentricity of the binary, and the degree of alignment of the triple disk system. This suggests that the broad emission-line profiles from SBHB systems can in principle be used to infer the distribution of these parameters and as such merit further investigation. Calculated profiles are more morphologically heterogeneous than the broad emission lines in observed SBHB candidates and we discuss improved treatment of radiative transfer effects, which will allow a direct statistical comparison of the two groups.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

GAMMA-RAY EMISSION FROM PSR J0007+7303 USING SEVEN YEARS OF FERMI LARGE AREA TELESCOPE OBSERVATIONS

Based on more than seven years of Fermi Large Area Telescope Pass 8 data, we report on a detailed analysis of the bright gamma-ray pulsar (PSR) J0007+7303. We confirm that PSR J0007+7303 is significantly detected as a point source also during the off-peak phases with a test statistic value of 262 (∼16 σ ). In the description of the off-peak spectrum of PSR J0007+7303, a power law with an exponential cutoff at 2.7 ± 1.2 ± 1.3 GeV (the first/second uncertainties correspond to statistical/systematic errors) is preferred over a single power law at a level of 3.5 σ . The possible existence of a cutoff hints at a magnetospheric origin of the emission. In addition, no extended gamma-ray emission is detected that is compatible with either the supernova remnant (CTA 1) or the very high-energy (>100 GeV) pulsar wind nebula. A flux upper limit of 6.5 × 10{sup −12} erg cm{sup −2} s{sup −1} in the energy range 10–300 GeV is reported, for an extended source assuming the morphology of the VERITAS detection. During on-peak phases, a sub-exponential cutoff is significantly preferred (∼11 σ ) for representing the spectral energy distribution, in both the phase-averaged and phase-resolved spectra. Three glitches are detected during the observation period and we found no flux variability at the time of the glitches or in the long-term behavior. We also report the discovery of a previously unknown gamma-ray source in the vicinity of PSR J0007+7303, Fermi J0020+7328, which we associate with the z = 1.781 quasar S5 0016+73. A concurrent analysis of this source is needed to correctly characterize the behavior of CTA 1 and it is also presented in the paper.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Search for gamma-ray emission from AE Aquarii with seven years of Fermi LAT observations

AE Aquarii (AE Aqr) is a cataclysmic binary hosting one of the fastest rotating (P{sub spin} = 33.08 s) white dwarfs (WDs) known. Based on seven years of Fermi Large Area Telescope (LAT) Pass 8 data, we report on a deep search for gamma-ray emission from AE Aqr. Using X-ray observations from ASCA, XMM-Newton, Chandra, Swift, Suzaku, and NuSTAR, spanning 20 years, we substantially extend and improve the spin ephemeris of AE Aqr. Using this ephemeris, we searched for gamma-ray pulsations at the spin period of the WD. No gamma-ray pulsations were detected above 3σ significance. Neither phase-averaged gamma-ray emission nor gamma-ray variability of AE Aqr is detected by Fermi LAT. We impose the most restrictive upper limit to the gamma-ray flux from AE Aqr to date: 1.3×10{sup −12} erg cm{sup −2} s{sup −1} in the 100 MeV–300 GeV energy range, providing constraints on models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Polarization Signatures of Kink Instabilities in the Blazar Emission Region from Relativistic Magnetohydrodynamic Simulations

Kink instabilities are likely to occur in the current-carrying magnetized plasma jets. Recent observations of the blazar radiation and polarization signatures suggest that the blazar emission region may be considerably magnetized. While the kink instability has been studied with first-principle magnetohydrodynamic (MHD) simulations, the corresponding time-dependent radiation and polarization signatures have not been investigated. In this paper, we perform comprehensive polarization-dependent radiation modeling of the kink instability in the blazar emission region based on relativistic MHD (RMHD) simulations. We find that the kink instability may give rise to strong flares with polarization angle (PA) swings or weak flares with polarization fluctuations, depending on the initial magnetic topology and magnetization. These findings are consistent with observations. Compared with the shock model, the kink model generates polarization signatures that are in better agreement with the general polarization observations. Therefore, we suggest that kink instabilities may widely exist in the jet environment and provide an efficient way to convert the magnetic energy and produce multiwavelength flares and polarization variations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Presupernova Neutrinos: Realistic Emissivities from Stellar Evolution

We present a new calculation of neutrino emissivities and energy spectra from a massive star going through the advanced stages of nuclear burning (presupernova) in the months before becoming a supernova. The contributions from β decay and electron capture, pair annihilation, plasmon decay, and the photoneutrino process are modeled in detail, using updated tabulated nuclear rates. We also use realistic conditions of temperature, density, electron fraction, and nuclear isotopic composition of the star from the state-of-the-art stellar evolution code MESA. Results are presented for a set of progenitor stars with mass between 15 M{sub ⊙} and 30 M{sub ⊙}. It is found that β processes contribute substantially to the neutrino emissivity above realistic detection thresholds of few MeV, at selected positions and times in the evolution of the star.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

FIRST CONNECTION BETWEEN COLD GAS IN EMISSION AND ABSORPTION: CO EMISSION FROM A GALAXY–QUASAR PAIR

We present the first detection of molecular emission from a galaxy selected to be near a projected background quasar using the Atacama Large Millimeter/submillimeter Array (ALMA). The ALMA detection of CO(1−0) emission from the z = 0.101 galaxy toward quasar PKS 0439–433 is coincident with its stellar disk and yields a molecular gas mass of M{sub mol} ≈ 4.2 × 10{sup 9} M{sub ⊙} (for a Galactic CO-to-H{sub 2} conversion factor), larger than the upper limit on its atomic gas mass. We resolve the CO velocity field, obtaining a rotational velocity of 134 ± 11 km s{sup −1} and a resultant dynamical mass of ≥4 × 10{sup 10} M{sub ⊙}. Despite its high metallicity and large molecular mass, the z = 0.101 galaxy has a low star formation rate, implying a large gas consumption timescale, larger than that typical of late-type galaxies. Most of the molecular gas is hence likely to be in a diffuse extended phase, rather than in dense molecular clouds. By combining the results of emission and absorption studies, we find that the strongest molecular absorption component toward the quasar cannot arise from the molecular disk, but is likely to arise from diffuse gas in the galaxy’s circumgalactic medium. Our results emphasize the potential of combining molecular and stellar emission line studies with optical absorption line studies to achieve a more complete picture of the gas within and surrounding high-redshift galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

International Assistance for Low-Emission Development Planning: Coordinated Low Emissions Assistance Network (CLEAN) Inventory of Activities and Tools--Preliminary Trends

The Coordinated Low Emissions Assistance Network (CLEAN) is a voluntary network of international practitioners supporting low-emission planning in developing countries. The network seeks to improve quality of support through sharing project information, tools, best practices and lessons, and by fostering harmonized assistance. CLEAN has developed an inventory to track and analyze internationaltechnical support and tools for low-carbon planning activities in developing countries. This paper presents a preliminary analysis of the inventory to help identify trends in assistance activities and tools available to support developing countries with low-emission planning.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2015

CO₂ emission mitigation and fossil fuel markets: Dynamic and international aspects of climate policies

This paper explores a multi-model scenario ensemble to assess the impacts of idealized and non-idealized climate change stabilization policies on fossil fuel markets. Under idealized conditions climate policies significantly reduce coal use in the short- and long-term. Reductions in oil and gas use are much smaller, particularly until 2030, but revenues decrease much more because oil and gas prices are higher than coal prices. A first deviation from optimal transition pathways is delayed action that relaxes global emission targets until 2030 in accordance with the Copenhagen pledges. Fossil fuel markets revert back to the no-policy case: though coal use increases strongest, revenue gains are higher for oil and gas. To balance the carbon budget over the 21st century, the long-term reallocation of fossil fuels is significantly larger—twice and more—than the short-term distortion. This amplifying effect results from coal lock-in and inter-fuel substitution effects to balance the full-century carbon budget. The second deviation from the optimal transition pathway relaxes the global participation assumption. The result here is less clear-cut across models, as we find carbon leakage effects ranging from positive to negative because trade and substitution patterns of coal, oil, and gas differ across models. In summary, distortions of fossil fuel markets resulting from relaxed short-term global emission targets are more important and less uncertain than the issue of carbon leakage from early mover action.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2015

Simultaneous detection of electronic structure changes from two elements of a bifunctional catalyst using wavelength-dispersive X-ray emission spectroscopy and in situ electrochemistry.

Multielectron catalytic reactions, such as water oxidation, nitrogen reduction, or hydrogen production in enzymes and inorganic catalysts often involve multimetallic clusters. In these systems, the reaction takes place between metals or metals and ligands to facilitate charge transfer, bond formation/breaking, substrate binding, and release of products. In this study, we present a method to detect X-ray emission signals from multiple elements simultaneously, which allows for the study of charge transfer and the sequential chemistry occurring between elements. Kβ X-ray emission spectroscopy (XES) probes charge and spin states of metals as well as their ligand environment. A wavelength-dispersive spectrometer based on the von Hamos geometry was used to disperse Kβ signals of multiple elements onto a position detector, enabling an XES spectrum to be measured in a single-shot mode. This overcomes the scanning needs of the scanning spectrometers, providing data free from temporal and normalization errors and therefore ideal to follow sequential chemistry at multiple sites. We have applied this method to study MnOx-based bifunctional electrocatalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). In particular, we investigated the effects of adding a secondary element, Ni, to form MnNiOx and its impact on the chemical states and catalytic activity, by tracking the redox characteristics of each element upon sweeping the electrode potential. The detection scheme we describe here is general and can be applied to time-resolved studies of materials consisting of multiple elements, to follow the dynamics of catalytic and electron transfer reactions.

Gul, Sheraz↗
DOE OSTI2013

Excitation dependent two-component spontaneous emission and ultrafast amplified spontaneous emission in dislocation-free InGaN nanowires

Amplified spontaneous emission (ASE) at 456 nm from In{sub 0.2}Ga{sub 0.8}N nanowires grown on (001) silicon by catalyst-free molecular beam epitaxy was observed at room temperature under femtosecond excitation. The photoluminescence spectra below ASE threshold consist of two spontaneous emission bands centered at {approx}555 nm and {approx}480 nm, respectively, revealing the co-existence of deeply and shallowly localized exciton states in the nanowires. The ASE peak emerges from the 480 nm spontaneous emission band when the excitation density exceeds {approx}120 {mu}J/cm{sup 2}, indicating that optical gain arises from the radiative recombination of shallowly localized excitons in the nanowires. Time-resolved photoluminescence measurements revealed that the ASE process completes within 1.5 ps, suggesting a remarkably high stimulated emission recombination rate in one-dimensional InGaN nanowires.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Shape controlled Sn doped ZnO nanostructures for tunable optical emission and transport properties

Pure and Sn doped ZnO nanostructures have been grown on SiO{sub 2}/Si substrates by vapor-solid technique without using any catalysts. It has been found that the morphology of the nanostructures depend strongly on the growth temperature and doping concentration. By proper tuning of the growth temperature, morphology of pure ZnO can be changed from tetrapods to multipods. On the other hand, by varying the doping concentration of Sn in ZnO, the morphology can be tuned from tetrapods to flower-like multipods to nanowires. X-ray diffraction pattern reveals that the nanostructures have a preferred (0002) growth orientation, and they are tensile strained with the increase of Sn doping in ZnO. Temperature-dependent photoluminescence characteristics of these nanostructures have been investigated in the range from 10 to 300 K. Pure ZnO tetrapods exhibited less defect state emissions than that of pure ZnO multipods. The defect emission is reduced with low concentration of Sn doping, but again increases at higher concentration of doping because of increased defects. Transport properties of pure and Sn doped ZnO tetrapods have been studied using complex-plane impedance spectroscopy. The contribution from the arms and junctions of a tetrapod could be distinguished. Sn doped ZnO samples showed lower conductivity but higher relaxation time than that of pure ZnO tetrapods.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Cryogenic operation of planar ultrananocrystalline diamond field emission source in SRF injector

Here, we report a demonstration of electron beam generation in a superconducting radio frequency (SRF) Teraelectronvolt Energy Superconducting Linear Accelerator 1.3 GHz gun equipped with a field emission cathode and operated at 2 K. The cathode is a submicrometer film of nitrogen-incorporated ultrananocrystalline diamond [(N)UNCD] deposited atop a Nb RRR300 cathode plug that is 4 mm in diameter. Measurements of the output current showed that it increased exponentially as a function of the gun gradient. Our results demonstrate a feasible path toward simplified fully cryogenic SRF injector technology. At a maximal gradient of 0.9 MV/m, a current density of 22 μA/cm2 was obtained [calculated as a 2.75 μA current over the total cathode surface area of π(2 mm)2]. One important finding is that the electron emitter made of (N)UNCD, a material long been known as a highly efficient field emission material, demonstrated a record low turn-on gradient of 0.6 MV/m. A hypothesis explaining this behavior is proposed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

NuSTAR OBSERVATIONS OF GRB 130427A ESTABLISH A SINGLE COMPONENT SYNCHROTRON AFTERGLOW ORIGIN FOR THE LATE OPTICAL TO MULTI-GEV EMISSION

GRB 130427A occurred in a relatively nearby galaxy; its prompt emission had the largest GRB fluence ever recorded. The afterglow of GRB 130427A was bright enough for the Nuclear Spectroscopic Telescope ARray (NuSTAR) to observe it in the 3-79 keV energy range long after its prompt emission (∼1.5 and 5 days). This range, where afterglow observations were previously not possible, bridges an important spectral gap. Combined with Swift, Fermi, and ground-based optical data, NuSTAR observations unambiguously establish a single afterglow spectral component from optical to multi-GeV energies a day after the event, which is almost certainly synchrotron radiation. Such an origin of the late-time Fermi/Large Area Telescope >10 GeV photons requires revisions in our understanding of collisionless relativistic shock physics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

X-ray emission of the radio-loud quasar SDSS J121426.52+140258.9: independent variations between optical/UV and X-ray emission

To understand the X-ray emission of active galactic nuclei (AGNs), we explored the optical-to-X-ray variation correlation of a radio-loud quasar (RLQ) SDSS J121426.52+140258.9 (hereafter J1214+1402) with multi-epoch observations by the Swift and XMM–Newton telescopes. With the historical multiband data, we found that the infrared-to-X-ray flux of RLQ J1214+1402 should not be dominated by the beamed-jet emission. The Swift optical/UV and X-ray light curves showed that J1214+1402 has two optical states, with low flux before 2014 April 8 and high flux after 2014 June 11, but has no significant X-ray variations during the time range between 2007 March 9 and 2014 August 4. This result was supported by the XMM–Newton observations in the time overlapping with Swift. Interestingly, the early XMM–Newton data prior to the Swift time present two unusual emission epochs when J1214+1402 has relatively low optical fluxes but has the brightest X-ray fluxes. The overall independence of optical-to-X-ray variation seems hard to describe by the disc–corona model. With the X-ray spectral fitting, we find that the soft X-ray excess in J1214+1402 appears only during the high optical state when the X-ray emission is at a low state. The soft X-ray excess in J1214+1402 is difficult to explain by an ionized accretion disc; instead, it may be related to the warm corona.

79 ASTRONOMY AND ASTROPHYSICS↗