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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 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

KINETIC STUDY OF RADIATION-REACTION-LIMITED PARTICLE ACCELERATION DURING THE RELAXATION OF UNSTABLE FORCE-FREE EQUILIBRIA

Many powerful and variable gamma-ray sources, including pulsar wind nebulae, active galactic nuclei and gamma-ray bursts, seem capable of accelerating particles to gamma-ray emitting energies efficiently over very short timescales. These are likely due to the rapid dissipation of electromagnetic energy in a highly magnetized, relativistic plasma. In order to understand the generic features of such processes, we have investigated simple models based on the relaxation of unstable force-free magnetostatic equilibria. In this work, we make the connection between the corresponding plasma dynamics and the expected radiation signal, using 2D particle-in-cell simulations that self-consistently include synchrotron radiation reactions. We focus on the lowest order unstable force-free equilibrium in a 2D periodic box. We find that rapid variability, with modest apparent radiation efficiency as perceived by a fixed observer, can be produced during the evolution of the instability. The “flares” are accompanied by an increased polarization degree in the high energy band, with rapid variation in the polarization angle. Furthermore, the separation between the acceleration sites and the synchrotron radiation sites for the highest energy particles facilitates acceleration beyond the synchrotron radiation reaction limit. We also discuss the dynamical consequences of the radiation reaction, and some astrophysical applications of this model. Our current simulations with numerically tractable parameters are not yet able to reproduce the most dramatic gamma-ray flares, e.g., from the Crab Nebula. Higher magnetization studies are promising and will be carried out in the future.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

Effects of discrete-source outgassing on motions of periodic comets and discontinuous orbital anomalies

Isoline maps of the Style II nongravitational parameters A1 and A2 of periodic comets are presented for a baseline model as functions of the parameters of the inertially fixed spin vector and the source's location-dependent thrust angle. The parameters A1 and A2 for a collection of sources are equal to the sum of their values for the individual contributors, thus depending on the source distribution. The model is consistent with even the most extreme among detected perturbations, including instances of rapid temporal changes in A2 and the discontinuous orbital anomalies, which are interpreted as products of a sudden redistribution of the transferred momentum due to episodic activation of short-lived sources. It is argued that the lifetimes of active regions vary considerably from case to case, and forced precession of the nucleus strongly influences the comet's activity pattern.

Sekanina, Zdenek↗
DOE OSTI2017

A submillimeter perspective on the goods fields. II. The high radio power population in the GOODS-N

We use ultradeep 20 cm data from the Karl G. Jansky Very Large Array and 850 μm data from SCUBA-2 and the Submillimeter Array of an 124 arcmin{sup 2} region of the Chandra Deep Field-north to analyze the high radio power (P{sub 20cm}>10{sup 31} erg s{sup −1} Hz{sup −1}) population. We find that 20 (42 ± 9%) of the spectroscopically identified z>0.8 sources have consistent star formation rates (SFRs) inferred from both submillimeter and radio observations, while the remaining sources have lower (mostly undetected) submillimeter fluxes, suggesting that active galactic nucleus (AGN) activity dominates the radio power in these sources. We develop a classification scheme based on the ratio of submillimeter flux to radio power versus radio power and find that it agrees with AGN and star-forming galaxy classifications from Very Long Baseline Interferometry. Our results provide support for an extremely rapid drop in the number of high SFR galaxies above about a thousand solar masses per year (Kroupa initial mass function) and for the locally determined relation between X-ray luminosity and radio power for star-forming galaxies applying at high redshifts and high radio powers. We measure far-infrared (FIR) luminosities and find that some AGNs lie on the FIR-radio correlation, while others scatter below. The AGNs that lie on the correlation appear to do so based on their emission from the AGN torus. We measure a median radio size of 1.″0 ± 0.3 for the star-forming galaxies. The radio sizes of the star-forming galaxies are generally larger than those of the AGNs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

GRB 110328A/SWIFT J164449.3+573451: THE TIDAL OBLITERATION OF A DEEPLY PLUNGING STAR?

We examine the tidal disruption event (TDE) scenario to explain Sw 1644+57, a powerful and persistent X-ray source which suddenly became active as GRB 110328A. The precise localization at the center of a z = 0.35 galaxy argues for activity of the central engine as the underlying cause. We look at the suggestion by Bloom et al. of the possibility of a TDE. We argue that Sw 1644+57 cannot be explained by the traditional TDE model in which the periastron distance is close to the tidal disruption radius-three independent lines of argument indicate the orbit must be deeply plunging or else the powerful jet we are observing could not be produced. These arguments stem from (1) comparing the early X-ray light curve to the expected theoretical fallback rate, (2) looking at the time of transition to disk-dominated decay, and (3) considering the TDE rate. Due to the extreme excess in the tidal force above that which would be required minimally to disrupt the star in a deeply plunging orbit at periastron, we suggest this scenario might be referred to more descriptively as a tidal obliteration event (TOE) rather than a TDE.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1988

The disks of T Tauri stars with flat infrared spectra

The energy distributions of T Tauri stars with flat infrared spectra is modeled by assuming that they have spatially thin disks with unorthodox radial gradients of temperature. Derived model parameters show that the disks associated with the flat-spectrum sources must contain intrinsic luminosity in addition to the energy intercepted and reprocessed from the central star, i.e., the disks must be active. Self-gravity may provide a possible source for this activity.

Adams, Fred C.↗
DOE OSTI2017

HOW TO FIND GRAVITATIONALLY LENSED TYPE Ia SUPERNOVAE

Type Ia supernovae (SNe Ia) that are multiply imaged by gravitational lensing can extend the SN Ia Hubble diagram to very high redshifts ( z ≳ 2), probe potential SN Ia evolution, and deliver high-precision constraints on H {sub 0}, w , and Ω{sub m} via time delays. However, only one, iPTF16geu, has been found to date, and many more are needed to achieve these goals. To increase the multiply imaged SN Ia discovery rate, we present a simple algorithm for identifying gravitationally lensed SN Ia candidates in cadenced, wide-field optical imaging surveys. The technique is to look for supernovae that appear to be hosted by elliptical galaxies, but that have absolute magnitudes implied by the apparent hosts’ photometric redshifts that are far brighter than the absolute magnitudes of normal SNe Ia (the brightest type of supernovae found in elliptical galaxies). Importantly, this purely photometric method does not require the ability to resolve the lensed images for discovery. Active galactic nuclei, the primary sources of contamination that affect the method, can be controlled using catalog cross-matches and color cuts. Highly magnified core-collapse SNe will also be discovered as a byproduct of the method. Using a Monte Carlo simulation, we forecast that the Large Synoptic Survey Telescope can discover up to 500 multiply imaged SNe Ia using this technique in a 10 year z -band search, more than an order of magnitude improvement over previous estimates. We also predict that the Zwicky Transient Facility should find up to 10 multiply imaged SNe Ia using this technique in a 3 year R -band search—despite the fact that this survey will not resolve a single system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Recovery of active recombinant EGFP from the excrement of transgenic mice: A possible source of recombinant protein

Transgenic animals provide attractive systems for the production of valuable recombinant proteins. Previous studies indicate that milk is a suitable source of secreted recombinant proteins. In the current study, we examine whether excrement can be another source of recombinant proteins by using transgenic mice ubiquitously-expressing green fluorescent protein (GFP) as a model. We found that the surface of excrement from GFP-transgenic mice was fluorescent, and the supernatant after centrifugation of an excrement suspension was rich in undegraded, actively fluorescing GFP. GFP was successfully purified from stool as a fluorescent 27 kDa protein by using a common procedure. Finally, we observed that the fluorescence of digested materials began in the ileum and persisted throughout the remainder of the digestive tract. Our results demonstrate that excrement, which is produced daily regardless of the sex or age of the animal, may be another feasible source of recombinant proteins. The preparation method is simple, economical, and noninvasive.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Active Layer Hydrology in an Arctic Tundra Ecosystem: Quantifying Water Sources and Cycling Using Water Stable Isotopes: Supporting Data

Data include results from water isotope analyses (one *.csv file) for samples collected in Utqiagvik (Barrow), Alaska during August and September 2012. Samples were from surface and soil pore waters from 17 drainages that could be interlake (basins with polygonal terrain), different-aged drain thaw lake basins (young, medium, old, or ancient), or a combination of different aged basins. Samples taken in different drainage flow types at three different depths at each location in and around the Barrow Environmental Observatory. Precipitation stable isotope data are also included (added in October 2019 with no changes to previously released data). This dataset used in Throckmorton, et.al. 2016.The Next-Generation Ecosystem Experiments: Arctic (NGEE Arctic), was a 10-year research effort (2012-2022) to reduce uncertainty in Earth System Models by developing a predictive understanding of carbon-rich Arctic ecosystems and feedbacks to climate. NGEE Arctic was supported by the Department of Energy's Office of Biological and Environmental Research. The NGEE Arctic project had two field research sites: 1) located within the Arctic polygonal tundra coastal region on the Barrow Environmental Observatory (BEO) and the North Slope near Utqiagvik (Barrow), Alaska and 2) multiple areas on the discontinuous permafrost region of the Seward Peninsula north of Nome, Alaska. Through observations, experiments, and synthesis with existing datasets, NGEE Arctic provided an enhanced knowledge base for multi-scale modeling and contributed to improved process representation at global pan-Arctic scales within the Department of Energy's Earth system Model (the Energy Exascale Earth System Model, or E3SM), and specifically within the E3SM Land Model component (ELM).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

SNS Sample Activation Calculator Flux Recommendations and Validation

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) uses the Sample Activation Calculator (SAC) to calculate the activation of a sample after the sample has been exposed to the neutron beam in one of the SNS beamlines. The SAC webpage takes user inputs (choice of beamline, the mass, composition and area of the sample, irradiation time, decay time, etc.) and calculates the activation for the sample. In recent years, the SAC has been incorporated into the user proposal and sample handling process, and instrument teams and users have noticed discrepancies in the predicted activation of their samples. The Neutronics Analysis Team validated SAC by performing measurements on select beamlines and confirmed the discrepancies seen by the instrument teams and users. The conclusions were that the discrepancies were a result of a combination of faulty neutron flux spectra for the instruments, improper inputs supplied by SAC (1.12), and a mishandling of cross section data in the Sample Activation Program for Easy Use (SAPEU) (1.1.2). This report focuses on the conclusion that the SAPEU (1.1.2) beamline neutron flux spectra have errors and are a significant contributor to the activation discrepancies. The results of the analysis of the SAPEU (1.1.2) flux spectra for all beamlines will be discussed in detail. The recommendations for the implementation of improved neutron flux spectra in SAPEU (1.1.3) are also discussed.

43 PARTICLE ACCELERATORS↗
NASA NTRS2019

Temporal Characterization of Dust Activity in the Central Patagonia Desert (years 1964-2017)

Like a peninsula into the Southern Ocean, the vast Patagonia desert in the southern tip of South America is exposed to extreme winds. Dust blown from this region has important impacts thousands of kilometers away, but these impacts are very difficult to assess. Questions such as the sources of dust found in snow in East Antarctica as well as the provenance of nutrients in the Southern Ocean remain unanswered. While the Patagonia desert is the likely source of dust, there is a dearth of observational records of dust activity from this desert. This study fills the gap in observations by providing a record of 50 years of surface and satellite observations of the largest and most active dust source in Patagonia: lake Colhu Huapi. The seasonality, frequency and periods of major dust activity are identified from meteorological records at a station located 100km downwind from the lake. Collocated satellite observations confirmed the major periods of dust activity in the last 30 years. This dataset provides information on how to interpret records of recent dust found in East Antarctica snow as well as help to understand the CO2 cycle in the Southern Ocean.

Patagonia↗
DOE OSTI2014

SNS Sample Activation Calculator Experimental Validation - Paper 79

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) uses the Sample Activation Calculator (SAC) to calculate the activation of all samples after they have been exposed to the neutron beam in any of the neutron scattering instruments at the SNS beamlines. The SAC web page takes user inputs (choice of beamline, the mass, composition and area of the sample, irradiation time, decay time, etc.) and then calculates the activation for the sample. In recent years, the SAC has been incorporated into the user proposal and sample handling process, and beamline scientists and users have noticed discrepancies in the predicted activation of their samples. As a part of the Neutronics Analysis Group at SNS, we were tasked with validating the SAC tool and diagnosing the origin of the discrepancies seen by the beamline scientists and the users. In the process of performing these measurements, we additionally found that several aspects of realistic neutron scattering operations, and thus sample exposure, cannot be captured with current configuration of the SAC tool. Typical neutron scattering samples are irradiated for multiple periods with different neutron energy ranges; the realities of accelerator operation indicate that not all of those periods will be at the same accelerator power, and scattering samples are frequently not fully illuminated by the well-collimated neutron beam. Finally, we will explore whether neutron beams, as modified by neutron guide systems with energy-dependent intensity modifications and by precise energy-band defining mechanical choppers, are suitably analyzed with multigroup cross section libraries in which there are typically very few energy groups below one eV. (authors)

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Statistical analysis of MMS observations of energetic electron escape observed at/beyond the dayside magnetopause

Here, observations from the Energetic Particle Detector (EPD) instrument suite aboard the Magnetospheric Multiscale (MMS) spacecraft show that energetic (greater than tens of keV) magnetospheric particle escape into the magnetosheath occurs commonly across the dayside. This includes the surprisingly frequent observation of magnetospheric electrons in the duskside magnetosheath, an unexpected result given assumptions regarding magnetic drift shadowing. The 238 events identified in the 40 keV electron energy channel during the first MMS dayside season that exhibit strongly anisotropic pitch angle distributions indicating monohemispheric field-aligned streaming away from the magnetopause. A review of the extremely rich literature of energetic electron observations beyond the magnetopause is provided to place these new observations into historical context. Despite the extensive history of such research, these new observations provide a more comprehensive data set that includes unprecedented magnetic local time (MLT) coverage of the dayside equatorial magnetopause/magnetosheath. These data clearly highlight the common escape of energetic electrons along magnetic field lines concluded to have been reconnected across the magnetopause. While these streaming escape events agree with prior studies which show strong correlation with geomagnetic activity (suggesting a magnetotail source) and occur most frequently during periods of southward IMF, the high number of duskside events is unexpected and previously unobserved. Although the lowest electron energy channel was the focus of this study, the events reported here exhibit pitch angle anisotropies indicative of streaming up to 200 keV, which could represent the magnetopause loss of >1 MeV electrons from the outer radiation belt.

58 GEOSCIENCES↗
DOE OSTI2012

Strength, Hardening, and Failure Observed by In Situ TEM Tensile Testing: Strength, Hardening, and Failure Observed by In Situ TEM Tensile Testing

We present in situ transmission electron microscope tensile tests on focused ion beam fabricated single and multiple slip oriented Cu tensile samples with thicknesses in the range of 100–200 nm. Both crystal orientations fail by localized shear. While failure occurs after a few percent plastic strain and limited hardening in the single slip case, the multiple slip samples exhibit extended homogenous deformation and necking due to the activation of multiple dislocation sources in conjunction with significant hardening. The hardening behavior at 1% plastic strain is even more pronounced compared to compression samples of the same orientation due to the absence of sample taper and the interface to the compression platen. Moreover, we show for the first time that the strain rate sensitivity of such FIB prepared samples is an order of magnitude higher than that of bulk Cu.

36 MATERIALS SCIENCE↗
DOE OSTI2018

How to tackle the stringent sulfate removal requirements in mine water treatment—A review of potential methods

Highlights: • Gypsum precipitation can reach 1500 ppm SO{sub 4}{sup 2-} but many mines have stricter limits. • Several technologies for attaining low SO{sub 4}{sup 2-} level (even near 0 ppm) are available. • Sulfur chemicals can be recovered from sulfate. Sulfate (SO{sub 4}{sup 2-}) is a ubiquitous anion in natural waters. It is not considered toxic, but it may be detrimental to freshwater species at elevated concentrations. Mining activities are one significant source of anthropogenic sulfate into natural waters, mainly due to the exposure of sulfide mineral ores to weathering. There are several strategies for mitigating sulfate release, starting from preventing sulfate formation in the first place and ending at several end-of-pipe treatment options. Currently, the most widely used sulfate-removal process is precipitation as gypsum (CaSO{sub 4}·2H{sub 2}O). However, the lowest reachable concentration is theoretically 1500 mg L{sup −1} SO{sub 4}{sup 2-} due to gypsum's solubility. At the same time, several mines worldwide have significantly more stringent sulfate discharge limits. The purpose of this review is to examine the process options to reach low sulfate levels (< 1500 mg L{sup −1}) in mine effluents. Examples of such processes include alternative chemical precipitation methods, membrane technology, biological treatment, ion exchange, and adsorption. In addition, aqueous chemistry and current effluent standards concerning sulfate together with concentrate treatment and sulfur recovery are discussed.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Monte Carlo investigation of a high-efficiency, two-plane Compton camera for long-range localization of radioactive materials

Compton cameras have become an instrument of interest for long-range localization of radioactive materials in nuclear-nonproliferation applications. In this work, a specialized simulation tool was developed for the optimization of a Compton camera through realistic Monte Carlo simulations. This tool can be used for Compton cameras with different geometries. The MCNPX-PoliMi code was used to simulate Compton scatters and photoelectric absorptions in the camera's detectors. The imaging capability is derived from the physics of Compton scattering and the full-energy information obtained in photoelectric absorptions. The simulated system is a 1 1 m2 Compton camera consisting of two planar arrays of photon detectors. Several scintillators were evaluated: LaBr3, CaF2, and NaI(Tl) (all inorganic scintillators), and C9H10 (plastic organic scintillator). The investigation was carried out with a 137Cs source. A minimum detectable activity (MDA) was defined and used to assess the performance of cameras based on different detectors. The simulation results show that C9H10 is a reliable, low-cost, scatter-plane material, increasing the MDA by ~0.2 mCi when compared to a CaF2 scatter plane. On the other hand, the intrinsic background of LaBr3 undermines its above-average energy resolution as the MDA increased by ~0.5 mCi when compared to a NaI(Tl) absorption plane.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Solute effects on interfacial dislocation emission in nanomaterials: Nucleation site competition and neutralization

Solutes added to stabilize nano-crystalline metals against grain growth, may segregate to grain boundaries and triple junctions where they can affect the process of the dislocation emission. Here, we demonstrate that this effect can be very complex due to different rates of segregation at different interfaces. Moreover, at large concentrations, when the solutes form clusters, the interfaces between these clusters and the matrix can introduce new dislocation emission sources, which can be activated under lower applied stress. Thus, the strength maximum can occur at a certain solute concentration: adding solutes beyond this optimal concentration can reduce the strength of the material.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Time course of systemic oxidative stress and inflammatory response induced by an acute exposure to Residual Oil Fly Ash

It is suggested that systemic oxidative stress and inflammation play a central role in the onset and progression of cardiovascular diseases associated with the exposure to particulate matter (PM). The aim of this work was to evaluate the time changes of systemic markers of oxidative stress and inflammation, after an acute exposure to Residual Oil Fly Ash (ROFA). Female Swiss mice were intranasally instilled with a ROFA suspension (1.0 mg/kg body weight) or saline solution, and plasma levels of oxidative damage markers [thiobarbituric acid reactive substances (TBARSs) and protein carbonyls], antioxidant status [reduced (GSH) and oxidized (GSSG) glutathione, ascorbic acid levels, and superoxide dismutase (SOD) activity], cytokines levels, and intravascular leukocyte activation were evaluated after 1, 3 or 5 h of exposure. Oxidative damage to lipids and decreased GSH/GSSG ratio were observed in ROFA-exposed mice as early as 1 h. Afterwards, increased protein oxidation, decreased ascorbic acid content and SOD activity were found in this group at 3 h. The onset of an adaptive response was observed at 5 h after the ROFA exposure, as indicated by decreased TBARS plasma content and increased SOD activity. The observed increase in oxidative damage to plasma macromolecules, together with systemic antioxidants depletion, may be a consequence of a systemic inflammatory response triggered by the ROFA exposure, since increased TNF-α and IL-6 plasma levels and polymorphonuclear leukocytes activation was found at every evaluated time point. These findings contribute to the understanding of the increase in cardiovascular morbidity and mortality, in association with environmental PM inhalation. - Highlights: • An acute exposure to ROFA triggers the occurrence of systemic oxidative stress. • Changes in plasmatic oxidative stress markers appear as early as 1 h after exposure. • ROFA induces proinflammatory cytokines release and intravascular leukocyte activation. • PMN activation is a relevant source of reactive oxygen species in this model. • These findings may account for previously described cardiopulmonary alterations.

60 APPLIED LIFE SCIENCES↗