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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Single-Polymer–Particle Growth Kinetics with Molecular Catalyst Speciation and Single-Turnover Imaging

The dynamics of the local environments surrounding molecular polymerization catalysts plausibly impact turnover kinetics, but the impact of and nature of such dynamics have previously been obscured by ensemble averaging. With Grubbs’ second generation ruthenium metathesis catalyst and a precipitation polymerization system, studies at the single-particle and -turnover level establish that (1) an inverse correlation exists between rate and duration of single-polymer–particle growth of aggregates, consistent with a local environment density model for the time-variable kinetics; (2) cross-linking additives produced a small, but detectible, reduction in overall monomer incorporation; (3) total ruthenium quantity within the polymer particles (as characterized by energy dispersive X-ray spectroscopy) is differentiable from the quantity that is catalytically active (as characterized by in situ fluorescence microscopy), providing catalyst speciation information; and (4) time-resolved enyne metathesis reactions can be imaged, corresponding to single turnovers at individual molecular catalysts during polymer growth under synthetically relevant conditions. Here, these findings identify and characterize reactivity distributions likely arising from the dynamics of local environments. As such, these data provide reactivity information that is unavailable through traditional ensemble analytical methods that obscure this type of information through averaging.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Minimum Fisher regularization of image reconstruction for infrared imaging bolometer on HL-2A

An infrared imaging bolometer diagnostic has been developed recently for the HL-2A tokamak to measure the temporal and spatial distribution of plasma radiation. The three-dimensional tomography, reduced to a two-dimensional problem by the assumption of plasma radiation toroidal symmetry, has been performed. A three-dimensional geometry matrix is calculated with the one-dimensional pencil beam approximation. The solid angles viewed by the detector elements are taken into account in defining the chord brightness. And the local plasma emission is obtained by inverting the measured brightness with the minimum Fisher regularization method. A typical HL-2A plasma radiation model was chosen to optimize a regularization parameter on the criterion of generalized cross validation. Finally, this method was applied to HL-2A experiments, demonstrating the plasma radiated power density distribution in limiter and divertor discharges.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Comparison of beam emission spectroscopy and gas puff imaging edge fluctuation measurements in National Spherical Torus Experiment

In this study, the close physical proximity of the Gas Puff Imaging (GPI) and Beam Emission Spectroscopy (BES) diagnostics on the National Spherical torus Experiment (NSTX) is leveraged to directly compare fluctuation measurements, and to study the local effects of the GPI neutral deuterium puff during H-mode plasmas without large Edge Localized Modes. The GPI and BES views on NSTX provide partially overlapping coverage of the edge and scrape-off layer (SOL) regions above the outboard midplane. The separation in the toroidal direction is 16°, and field lines passing through diagnostic views are separated by ∼20 cm in the direction perpendicular to the magnetic field. Strong cross-correlation is observed, and strong cross-coherence is seen for frequencies between 5 and 15 kHz. Also, probability distribution functions of fluctuations measured ∼3 cm inside the separatrix exhibit only minor deviations from a normal distribution for both diagnostics, and good agreement between correlation length estimates, decorrelation times, and structure velocities is found at the ±40% level. While the two instruments agree closely in many respects, some discrepancies are observed. Most notably, GPI normalized fluctuation levels exceed BES fluctuations by a factor of ∼9. BES mean intensity is found to be sensitive to the GPI neutral gas puff, and BES normalized fluctuation levels for frequencies between 1 and 10 kHz are observed to increase during the GPI puff.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Parabolic single-crystal diamond lenses for coherent x-ray imaging

We demonstrate parabolic single-crystal diamond compound refractive lenses designed for coherent x-ray imaging resilient to extreme thermal and radiation loading expected from next generation light sources. To ensure the preservation of coherence and resilience, the lenses are manufactured from the highest-quality single-crystalline synthetic diamond material grown by a high-pressure high-temperature technique. Picosecond laser milling is applied to machine lenses to parabolic with a similar or equal to 1 mu m precision and surface roughness. A compound refractive lens comprised of six lenses with a radius of curvature R = 200 mu m at the vertex of the parabola and a geometrical aperture A = 900 mu m focuses 10 keV x-ray photons from an undulator source at the Advanced Photon Source facility to a focal spot size of similar or equal to 20 x 90 mu m(2) with a gain factor of similar or equal to 50 - 100. (C) 2015 Author(s).

Terentyev, Sergey↗
DOE OSTI2018

Dynamic compaction of nickel powder examined by x-ray phase contrast imaging

Understanding the shock response of porous, granular materials is important for many scientific applications. In this work, a propagation-based x-ray phase contrast imaging technique was used to examine the shock compaction response of Ni powder (particle size: 30 and 45 µm), encapsulated in PMMA cylinders, in situ and in real time. The propagating shock wave in the PMMA cylinder and the deformation of the Ni powder column were recorded, but the compaction wave in the Ni powder could not be observed due to insufficient penetration of x-ray photons through the sample. The overall shape of the deformed Ni column downstream of the PMMA shock looked qualitatively similar for both particle sizes: it deformed inward and then outward similar to a converging-diverging nozzle, followed by a ‘mushroom’-like structure at the impact face. A preliminary analysis of our data using shock-polar method provided insight into the observed shock and flow deflection angles at the PMMA/Ni interface, and permitted evaluation of the Ni powder EOS used in this work.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Developing a robust sensor for infrared imaging bolometers

A new type of large area sensor for infrared imaging bolometers has been developed. It replaces the thin and fragile free-standing metal foils, which typically have been used, with a multi-layer coated sapphire (or diamond) substrate. Sapphire is transparent to mid-infrared wavelengths, is robust against transients, and can be thick enough to even be the vacuum window. The primary radiation absorber is still a thin deposited metal layer, but now it is partially insulated from the supporting sapphire substrate by a black (carbon-based) layer, which also acts as a blackbody remitter. Test results indicate 6× more noise equivalent power density (estimated NEPD = 23 W/m 2 at 5 ms camera exposure time, foil temperature decay time 60 ms) for a 2 μm gold-coated sapphire disk compared to estimated NEP = 4 W/m 2 at 1.8 ms exposure time, with foil decay time 420 ms, for a nominal 2.5 μm thick platinum-free-standing foil.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

High-resolution images of diffuse neutral clouds in the milky way. I. Observations, imaging, and basic cloud properties

A set of diffuse interstellar clouds in the inner Galaxy within a few hundred parsecs of the Galactic plane has been observed at an angular resolution of ≈1 and farcm;0 combining data from the NRAO Green Bank Telescope and the Very Large Array. At the distance of the clouds, the linear resolution ranges from ∼1.9 to ∼2.8 pc. These clouds have been selected to be somewhat outside of the Galactic plane, and thus are not confused with unrelated emission, but in other respects they are a Galactic population. They are located near the tangent points in the inner Galaxy, and thus at a quantifiable distance: 2.3⩽R⩽6.0 kpc from the Galactic Center and −1000⩽z⩽+610 pc from the Galactic plane. These are the first images of the diffuse neutral H i clouds that may constitute a considerable fraction of the interstellar medium (ISM). Peak H i column densities lie in the range N{sub H i} = 0.8–2.9 × 10{sup 20} cm{sup −2}. Cloud diameters vary between about 10 and 100 pc, and their H i mass spans the range from less than a hundred to a few thousands M{sub ⊙}. The clouds show no morphological consistency of any kind, except that their shapes are highly irregular. One cloud may lie within the hot wind from the nucleus of the Galaxy, and some clouds show evidence of two distinct thermal phases as would be expected from equilibrium models of the ISM.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

POLARIZED LIGHT IMAGING OF THE HD 142527 TRANSITION DISK WITH THE GEMINI PLANET IMAGER: DUST AROUND THE CLOSE-IN COMPANION

When giant planets form, they grow by accreting gas and dust. HD 142527 is a young star that offers a scaled-up view of this process. It has a broad, asymmetric ring of gas and dust beyond ∼100 AU and a wide inner gap. Within the gap, a low-mass stellar companion orbits the primary star at just ∼12 AU, and both the primary and secondary are accreting gas. In an attempt to directly detect the dusty counterpart to this accreted gas, we have observed HD 142527 with the Gemini Planet Imager in polarized light at Y band (0.95-1.14 μm). We clearly detect the companion in total intensity and show that its position and photometry are generally consistent with the expected values. We also detect a point source in polarized light that may be spatially separated by ∼ a few AU from the location of the companion in total intensity. This suggests that dust is likely falling onto or orbiting the companion. Given the possible contribution of scattered light from this dust to previously reported photometry of the companion, the current mass limits should be viewed as upper limits only. If the dust near the companion is eventually confirmed to be spatially separated, this system would resemble a scaled-up version of the young planetary system inside the gap of the transition disk around LkCa 15.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

WE-AB-BRA-09: Sensitivity of Plan Re-Optimization to Errors in Deformable Image Registration in Online Adaptive Image-Guided Radiation Therapy

Purpose: Online adaptive therapy (ART) relies on auto-contouring using deformable image registration (DIR). DIR’s inherent uncertainties require user intervention and manual edits while the patient is on the table. We investigated the dosimetric impact of DIR errors on the quality of re-optimized plans, and used the findings to establish regions for focusing manual edits to where DIR errors can Result in clinically relevant dose differences. Methods: Our clinical implementation of online adaptive MR-IGRT involves using DIR to transfer contours from CT to daily MR, followed by a physicians’ edits. The plan is then re-optimized to meet the organs at risk (OARs) constraints. Re-optimized abdomen and pelvis plans generated based on physician edited OARs were selected as the baseline for evaluation. Plans were then re-optimized on auto-deformed contours with manual edits limited to pre-defined uniform rings (0 to 5cm) around the PTV. A 0cm ring indicates that the auto-deformed OARs were used without editing. The magnitude of the variations caused by the non-deterministic optimizer was quantified by repeat re-optimizations on the same geometry to determine the mean and standard deviation (STD). For each re-optimized plan, various volumetric parameters for the PTV, the OARs were extracted along with DVH and isodose evaluation. A plan was deemed acceptable if the variation from the baseline plan was within one STD. Results: Initial results show that for abdomen and pancreas cases, a minimum of 5cm margin around the PTV is required for contour corrections, while for pelvic and liver cases a 2–3 cm margin is sufficient. Conclusion: Focusing manual contour edits to regions of dosimetric relevance can reduce contouring time in the online ART process while maintaining a clinically comparable plan. Future work will further refine the contouring region by evaluating the path along the beams, dose gradients near the target and OAR dose metrics.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Chemical Imaging of Ambient Aerosol Particles: Observational Constraints on Mixing State Parameterization

A new parameterization for quantifying the mixing state of aerosol populations has been applied for the first time to samples of ambient particles analyzed using spectro-microscopy techniques. Scanning transmission x-ray microscopy/near edge x-ray absorption fine structure (STXM/NEXAFS) and computer controlled scanning electron microscopy/energy dispersive x-ray spectroscopy (CCSEM/EDX) were used to probe the composition of the organic and inorganic fraction of individual particles collected on June 27th and 28th during the 2010 Carbonaceous Aerosols and Radiative Effects (CARES) study in the Central Valley, California. The first field site, T0, was located in downtown Sacramento, while T1 was located near the Sierra Nevada Mountains. Mass estimates of the aerosol particle components were used to calculate mixing state metrics, such as the particle-specific diversity, bulk population diversity, and mixing state index, for each sample. Both microscopy imaging techniques showed more changes over these two days in the mixing state at the T0 site than at the T1 site. The STXM data showed evidence of changes in the mixing state associated with a build-up of organic matter confirmed by collocated measurements and the largest impact on the mixing state was due to an increase in soot dominant particles during this build-up. The CCSEM/EDX analysis showed the presence of two types of particle populations; the first was dominated by aged sea salt particles and had a higher mixing state index (indicating a more homogeneous population), the second was dominated by carbonaceous particles and had a lower mixing state index.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2017

Review of cardiovascular imaging in the journal of nuclear cardiology in 2016: Part 2 of 2—myocardial perfusion imaging

In 2016, the Journal of Nuclear Cardiology published many high-quality articles. Similar to previous years, we will summarize here a selection of the articles that were published in the Journal in 2016 to provide a concise review of the main advancements that have recently occurred in the field. In the first article of this two-part series we focused on publications dealing with positron emission tomography, computed tomography, and magnetic resonance. This review will place emphasis on myocardial perfusion imaging using single-photon emission-computed tomography summarizing advances in the field including in diagnosis, prognosis, and appropriate use.

62 RADIOLOGY AND NUCLEAR MEDICINE↗