Search NASA⌕ Search

SEARCH · Search NASA

Results for “sample activation”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Unveiling User Behavior on Summit Login Nodes as a User

We observe and analyze usage of the login nodes of the leadership class Summit supercomputer from the perspective of an ordinary user—not a system administrator—by periodically sampling user activities (job queues, running processes, etc.) for two full years (2020–2021). Our findings unveil key usage patterns that evidence misuse of the system, including gaming the policies, impairing I/O performance, and using login nodes as a sole computing resource. Our analysis highlights observed patterns for the execution of complex computations (workflows), which are key for processing large-scale applications.

Wilkinson, Sean↗
DOE OSTI2016

A Chemical Separation Procedure Using Ionic Liquid Extraction for Fe-59 and Fe-55 Quantification

Quantitating iron (Fe) isotopes, Fe-55 and Fe-59, radiometrically can be difficult due to emission interferences or high spectral backgrounds due to the presence of other activation products or fission product contaminants. The purpose of this work was to demonstrate a separation procedure for Fe activation products from complex samples that contain either activated soil components or freshly produced fission products generated from highly enriched uranium. The developed procedure succesfully allowed for quantitative analysis of both the Fe-59 (by gamma spectroscopy) and Fe-55 (by low energy photon spectrsocopy) with > 90% elemental recovery.

Morrison, Samuel S.↗
DOE OSTI2020

Void coalescence and ductile failure in IN718 investigated via high-energy synchrotron X-ray tomography and diffraction

Ductile failure through the growth and coalescence of voids is of particular relevance for many engineering materials. Yet, the lack of experimental measurements of the mechanical state of the material at an appropriate length scale has limited further understanding of the regime of ductile failure. In this study, local grain-scale experimental measurements are used to determine their relevance for describing and predicting ductile failure. Additive manufactured materials, due to the presence of inherent porosity, as well as the ability to tailor internal porosity, provides a promising avenue to study ductile failure. Selective laser melting is used to manufacture a specially designed specimen with two large, internal voids, in addition to the natural porosity, which is characteristic to the production process. The initial porosity and its evolution upon tensile loading are characterized via micro tomography. Several locations of void coalescence are captured in the sample, revealing activity of multiple modes of failure. Finite element simulations, with a simplified J2 plasticity model, instantiated with the initial void structure, is deployed, in which geometric localizations of stress concentration corresponded with experimentally observed sites of coalescence but was inadequate in capturing the appropriate failure mechanism. Furthermore, from the experimental results of the far-field high-energy diffraction microscopy, the heterogeneous micromechanical state is identified and tracked around voids due to the local grain interactions. These experiments determine narrow bands of low stress triaxiality, at the onset of failure, which highlight the path of coalescence through intervoid shearing. Diffraction spot spreading analysis aided characterization of intragranular plasticity and strain heterogeneity, which can be coupled with high triaxiality to form the conditions inducive for coalescence through intervoid necking. In this study, the experimentally determined grain-scale description of the micromechanical state provides a physical basis that can accurately capture both the sites and the mechanism of void coalescence at the onset of ductile failure.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Facile fabrication of micro-floriated AgBr/Bi{sub 2}O{sub 3} as highly efficient visible-light photocatalyst

Highlights: • We successfully fabricate micro-floriated AgBr/Bi{sub 2}O{sub 3} composites by one simple hydrothermal react with precusor BiOBr. This micro-floriated Bi{sub 2}O{sub 3} heterojunction composite is rarely reported by others. • Heterojunction AgBr/Bi{sub 2}O{sub 3} composite exhibits highly efficient photocatalytic activity to decompose pollutant. • The enhanced photocatalytic activity was attributed to the improved visible light harvesting ability and higher separation efficiency of photogenerated electron–hole pairs by the introduction of AgBr. • This composite is beneficial to industrial applications to eliminate the organic pollutants from waste water. - Abstract: Semiconductor with photocatalytic property is the potential solution to solve the problem about water pollution. Novel floriated AgBr/Bi{sub 2}O{sub 3} fabricated through a facile simple two-step hydrothermal method is an efficient photocatalyst. The eminent performance for degradation of methyl orange (MO) was evaluated under visible light irradiation. Many characterization methods, including XPS, XRD, FT-IR, SEM, TEM and UV–vis diffuse reflection spectroscopy, were used to investigate the structure, elemental composition, morphology and catalytic activity. Broad contact between AgBr and Bi{sub 2}O{sub 3} interface enabled hybrid materials possess superior efficiency for the decomposition of MO under visible light irradiation. The optimum photocatalytic activity of samples was approximately 11.7 times higher than pure Bi{sub 2}O{sub 3}. In addition, the photo-generated reactive species were identified based on free radicals trapping experiments, which revealed that superoxide radical is the key factor to the photocatalytic process.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Activity of titania and zeolite samples dosed with triethylamine

Certain properties of titania and the ammonium- and proton-form of Y zeolites (silica/alumina ratio of 5.2) were explored before and after treatment by triethylamine (TEA). The effect of the triethylamine upon the physical and chemical properties of both titania and the zeolite were characterized by physical and chemical adsorption methods. BET surface area data showed enhanced surface area of the TEA-treated nanotitania over the untreated nanotitania whereas the TEA-treated zeolite showed a considerable decrease in surface area compared to the untreated zeolite. TPD of the TEA-treated Y zeolite showed that weakly adsorbed TEA left the surface between 150 and 300 oC; strongly adsorbed TEA decomposed to ethylene and ammonia at higher temperatures. XPS, IR, and Raman spectroscopies, powder XRD, and 27Al MAS-NMR spectroscopy were used to further characterize the changes introduced by in-situ nitridation. Pre-adsorbed triethylamine decorated acid sites so as to neutralize these sites for the reaction of methanol to dimethylether. Carbon monoxide and ormaldehyde, products of the methanol probe reaction, were observed-- suggesting that basic sites are present in this treated zeolite and titania.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2025

DNA viruses from different stages of a wastewater treatment plant in southwest Ohio

Wastewater treatment plants (WWTPs) house diverse populations of microbial communities that are dynamic across treatment stages. Although viruses, especially non-pathogenic ones are relatively less studied compared to their bacterial counterparts, they are equally important players in WWTP microbiomes. In this study, we sampled influent, activated sludge, and effluent stages of a WWTP in southwest Ohio to sequence their viral population using multiple displacement amplification (MDA) and metagenomic approaches. We recovered 1003 viral genomes, the majority of which were ssDNA (single-stranded DNA) viruses that formed distinct clusters representing novel species and phylogenetic groups not closely related to known human gut or terrestrial viruses. Additionally, tracking viruses across treatment stages showed several persisted across multiple treatment stages. These results suggest that further studies are needed to understand the persistence of viral populations, particularly non-pathogenic ones, across different stages of WWTPs.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Surface-Enhanced Raman Detection of the CO 2 Moisture Swing

The development of scalable, energy-efficient carbon dioxide (CO 2 ) capture technologies is critical for achieving net-zero emissions. Moisture swing (MS) sorbents offer a promising alternative to traditional thermal regeneration methods by enabling reversible CO 2 binding through humidity-driven ion hydrolysis. In this study, we investigate the anion speciation dynamics in two classes of MS materials─an anion-exchange resin with a bicarbonate anion and activated carbon impregnated with potassium bicarbonate salt─using both sorption measurements and in situ surface-enhanced Raman spectroscopy (SERS). Ni-coated Ag nanowires were employed as SERS substrates to enhance signal intensity and enable the real-time detection of carbonate (CO 3 2– ), bicarbonate (HCO 3 – ), and hydroxide (OH – ) species under controlled humidity conditions in both air and nitrogen atmospheres. The results reveal humidity-dependent interconversion between anionic species with significant spectral shifts confirming the reversible hydrolysis reactions that drive the MS mechanism. Under humid conditions, we observed the depletion of bicarbonate signals and a concurrent increase in carbonate species, consistent with moisture-induced desorption of CO 2 . With the activated carbon samples, we further observed the formation of hydroxide. These findings not only validate the mechanistic models of humidity-driven anion exchange in MS sorbents but also demonstrate the practical potential of SERS as an operando diagnostic tool for monitoring CO 2 capture media. The ability to resolve and semiquantitatively evaluate the reversible transformation of carbonate, bicarbonate, and hydroxide ions under realistic environmental conditions provides valuable insight for the rational design, performance optimization, and quality control of next-generation sorbent materials for direct air capture applications.

CO2 capture↗
DOE OSTI2019

Moisture outgassing from siloxane elastomers containing surface-treated-silica fillers

Abstract The outgassing kinetics from siloxane elastomers is dominated by moisture desorption from the reinforcing silica filler and can be detrimental in moisture-sensitive applications. In this study, a custom 3D printable siloxane rubber (LL50) was analyzed in three different states: after a high temperature vacuum heat treatment, limited re-exposure to moisture after vacuum heat treatment, and in the as-received condition. The outgassing kinetics were extracted using isoconversional and iterative regression analyses. Moisture release by physisorbed and chemisorbed water from the samples have activation energies in the range of 50 kJ/mol (physisorbed type) to 220 kJ/mol (chemisorbed type). Overall, moisture outgassing from LL50 was 10 times lower than that from traditionally prepared siloxane rubbers. The vastly diminished moisture content in LL50 is attributed to the existence of a finite low level of silanol groups that remain on the fumed silica surface even after hydrophobic treatment.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Photoluminescence properties and energy levels of RE (RE = Pr, Sm, Er, Tm) in layered-CaZnOS oxysulfide

RE{sup 3+} (RE = Pr, Sm, Er, Tm)-activated CaZnOS samples were prepared by a solid-state reaction method at high temperature, and their photoluminescence properties were investigated. Doping with RE{sup 3+} (RE = Pr, Sm, Er, Tm) into layered-CaZnOS resulted in typical RE{sup 3+} (RE = Pr, Sm, Er, Tm) f-f line absorptions and emissions, as well as the charge transfer band of Sm{sup 3+} at about 3.3 eV. The energy level scheme containing the position of the 4f and 5d levels of all divalent and trivalent lanthanide ions with respect to the valence and conduction bands of CaZnOS has been constructed based on the new data presented in this work, together with the data from literature on Ce{sup 3+} and Eu{sup 2+} doping in CaZnOS. The detailed energy level scheme provides a platform for interpreting the optical spectra and could be used to comment on the valence stability of the lanthanide ions in CaZnOS.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Tunable atomic termination in nano-necklace BiFeO{sub 3}

We investigate the growth kinetics of BiFeO{sub 3} (BFO) nano-necklace based on first principles modeling and electrospinning experiments. A two-step layered growth mechanism is proposed to control the atomic termination of each nano-necklace. X-ray diffraction (XRD) results agree well with our model predictions; (1) samples calcined at 500 and 550 °C consist of FeO{sub 2} (F-F) terminated nano-necklace, (2) samples calcined at 650 °C consist of either BiO (B-B) or BiO and FeO{sub 2} (B-F) terminated ones. The XRD diffraction peaks are located at lower 2θ values with a magnetic moment of 3.0 emu/g for the former and at higher 2θ values with a decrease in the magnetic moment to 0.4 emu/g for the later samples. The activation energy associated with the growth of the nano-necklaces was experimentally determined to be 0.37 eV/atom. This study provides fundamental understanding for the long-sought layer-by-layer assembly of BFO nanostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Half-life determination for {sup 108}Ag and {sup 110}Ag

In this work, the half-life of the short-lived silver radionuclides {sup 108}Ag and {sup 110}Ag were measured by following the activity of samples after they were irradiated in the IEA-R1 reactor. The results were then fitted using a non-paralizable dead time correction to the regular exponential decay and the individual half-life values obtained were then analyzed using both the Normalized Residuals and the Rajeval techniques, in order to reach the most exact and precise final values. To check the validity of dead-time correction, a second correction method was also employed by means of counting a long-lived {sup 60}Co radioactive source together with the samples as a livetime chronometer. The final half-live values obtained using both dead-time correction methods were in good agreement, showing that the correction was properly assessed. The results obtained are partially compatible with the literature values, but with a lower uncertainty, and allow a discussion on the last ENSDF compilations' values.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Simultaneous ambient pressure x-ray photoelectron spectroscopy and grazing incidence x-ray scattering in gas environments

We have developed an experimental system to simultaneously measure surface structure, morphology, composition, chemical state, and chemical activity for samples in gas phase environments. This is accomplished by simultaneously measuring x-ray photoelectron spectroscopy (XPS) and grazing incidence x-ray scattering in gas pressures as high as the multi-Torr regime while also recording mass spectrometry. Scattering patterns reflect near-surface sample structures from the nano-scale to the meso-scale, and the grazing incidence geometry provides tunable depth sensitivity of structural measurements. Scattered x rays are detected across a broad range of angles using a newly designed pivoting-UHV-manipulator for detector positioning. At the same time, XPS and mass spectrometry can be measured, all from the same sample spot and under ambient conditions. To demonstrate the capabilities of this system, we measured the chemical state, composition, and structure of Ag-behenate on a Si(001) wafer in vacuum and in O 2 atmosphere at various temperatures. These simultaneous structural, chemical, and gas phase product probes enable detailed insights into the interplay between the structure and chemical state for samples in gas phase environments. The compact size of our pivoting-UHV-manipulator makes it possible to retrofit this technique into existing spectroscopic instruments installed at synchrotron beamlines. Because many synchrotron facilities are planning or undergoing upgrades to diffraction limited storage rings with transversely coherent beams, a newly emerging set of coherent x-ray scattering experiments can greatly benefit from the concepts we present here.

47 OTHER INSTRUMENTATION↗
DOE OSTI2017

Vacuum System and Modeling for the Materials Plasma Exposure Experiment

Understanding the science of plasma-material interactions (PMI) is essential for the future development of fusion facilities. The design of divertors and first walls for the next generation of long-pulse fusion facilities, such as a Fusion Nuclear Science Facility (FNSF) or a DEMO, requires significant PMI research and development. In order to meet this need, a new linear plasma facility, the Materials Plasma Exposure Experiment (MPEX) is proposed, which will produce divertor relevant plasma conditions for these next generation facilities. The device will be capable of handling low activation irradiated samples and be able to remove and replace samples without breaking vacuum. A Target Exchange Chamber (TEC) which can be disconnected from the high field environment in order to perform in-situ diagnostics is planned for the facility as well. The vacuum system for MPEX must be carefully designed in order to meet the requirements of the different heating systems, and to provide conditions at the target similar to those expected in a divertor. An automated coupling-decoupling (“autocoupler”) system is designed to create a high vacuum seal, and will allow the TEC to be disconnected without breaking vacuum in either the TEC or the primary plasma materials interaction chamber. This autocoupler, which can be actuated remotely in the presence of the high magnetic fields, has been designed and prototyped, and shows robustness in a variety of conditions. The vacuum system has been modeled using a simplified finite element analysis, and indicates that the design goals for the pressures in key regions of the facility are achievable.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

THE ACTIVE ASTEROIDS

Some asteroids eject dust, unexpectedly producing transient, comet-like comae and tails. First ascribed to the sublimation of near-surface water ice, mass-losing asteroids (also called 'main-belt comets') can in fact be driven by a surprising diversity of mechanisms. In this paper, we consider 11 dynamical asteroids losing mass, in nine of which the ejected material is spatially resolved. We address mechanisms for producing mass loss including rotational instability, impact ejection, electrostatic repulsion, radiation pressure sweeping, dehydration stresses, and thermal fracture, in addition to the sublimation of ice. In two objects (133P and 238P) the repetitive nature of the observed activity leaves ice sublimation as the only reasonable explanation, while in a third ((596) Scheila), a recent impact is the cause. Another impact may account for activity in P/2010 A2, but this tiny object can also be explained as having shed mass after reaching rotational instability. Mass loss from (3200) Phaethon is probably due to cracking or dehydration at extreme ({approx}1000 K) perihelion temperatures, perhaps aided by radiation pressure sweeping. For the other bodies, the mass-loss mechanisms remain unidentified, pending the acquisition of more and better data. While the active asteroid sample size remains small, the evidence for an astonishing diversity of mass-loss processes in these bodies is clear.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The spectral variability of the GHZ-Peaked spectrum radio source PKS 1718-649 and a comparison of absorption models

Using the new wideband capabilities of the ATCA, we obtain spectra for PKS 1718-649, a well-known gigahertz-peaked spectrum radio source. The observations, between approximately 1 and 10 GHz over 3 epochs spanning approximately 21 months, reveal variability both above the spectral peak at ∼3 GHz and below the peak. The combination of the low- and high-frequency variability cannot be easily explained using a single absorption mechanism, such as free–free absorption or synchrotron self-absorption. We find that the PKS 1718-649 spectrum and its variability are best explained by variations in the free–free optical depth on our line of sight to the radio source at low frequencies (below the spectral peak) and the adiabatic expansion of the radio source itself at high frequencies (above the spectral peak). The optical depth variations are found to be plausible when X-ray continuum absorption variability seen in samples of active galactic nuclei is considered. We find that the cause of the peaked spectrum in PKS 1718-649 is most likely due to free–free absorption. In agreement with previous studies, we find that the spectrum at each epoch of observation is best fit by a free–free absorption model characterized by a power-law distribution of free–free absorbing clouds. This agreement is extended to frequencies below the 1 GHz lower limit of the ATCA by considering new observations with Parkes at 725 MHz and 199 MHz observations with the newly operational Murchison Widefield Array. These lower frequency observations argue against families of absorption models (both free–free and synchrotron self-absorption) that are based on simple homogenous structures.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

CHARACTERISTICS OF GAMMA-RAY LOUD BLAZARS IN THE VLBA IMAGING AND POLARIMETRY SURVEY

The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed as part of the VLBA Imaging and Polarimetry Survey. This large, flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong {gamma}-ray emission. At lower flux levels, radio flux density does not directly correlate with {gamma}-ray flux. We find that the LAT-detected BL Lac objects tend to be similar to the non-LAT BL Lac objects, but that the LAT-detected FSRQs are often significantly different from the non-LAT FSRQs. The differences between the {gamma}-ray loud and quiet FSRQs can be explained by Doppler boosting; these objects appear to require larger Doppler factors than those of the BL Lac objects. It is possible that the {gamma}-ray loud FSRQs are fundamentally different from the {gamma}-ray quiet FSRQs. Strong polarization at the base of the jet appears to be a signature for {gamma}-ray loud AGNs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

TESTING A SCALE-INDEPENDENT METHOD TO MEASURE THE MASS OF BLACK HOLES

Estimating the black hole mass at the center of galaxies is a fundamental step not only for understanding the physics of accretion, but also for the cosmological evolution of galaxies. Recently, a new method, based solely on X-ray data, was successfully applied to determine the black hole mass in Galactic systems. Since X-rays are thought to be produced via Comptonization process both in stellar and supermassive black holes, in principle, the same method may be applied to estimate the mass in supermassive black holes. In this work we test this hypothesis by performing a systematic analysis of a sample of active galactic nuclei, whose black hole mass has been already determined via reverberation mapping and which possess high-quality XMM-Newton archival data. The good agreement obtained between the black hole masses derived with this novel scaling technique and the reverberation mapping values suggests that this method is robust and works equally well on stellar and supermassive black holes, making it a truly scale-independent technique for black hole determination.

79 ASTRONOMY AND ASTROPHYSICS↗