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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

The Ehrlich–Schwoebel barrier on an oxide surface: a combined Monte-Carlo and in situ scanning tunneling microscopy approach

The controlled growth of epitaxial films of complex oxides requires an atomistic understanding of key parameters determining final film morphology, such as termination dependence on adatom diffusion, and height of the Ehrlich–Schwoebel (ES) barrier. In this study, through an in situ scanning tunneling microscopy study of mixed-terminated La 5/8 Ca 3/8 MnO 3 (LCMO) films, we image adatoms and observe pile-up at island edges. Image analysis allows determination of the population of adatoms at the edge of islands and fractions on A-site and B-site terminations. A simple Monte-Carlo model, simulating the random walk of adatoms on a sinusoidal potential landscape using Boltzmann statistics is used to reproduce the experimental data, and provides an estimate of the ES barrier as ~0.18 ± 0.04 eV at T = 1023 K, similar to those of metal adatoms on metallic surfaces. In conclusion, these studies highlight the utility of in situ imaging, in combination with basic Monte-Carlo methods, in elucidating the factors which control the final film growth in complex oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Imaging the spatial form of a superconducting order parameter via Josephson scanning tunneling spectroscopy

Motivated by recent experiments, we investigate Josephson scanning tunneling spectroscopy in an s-wave superconductor. Here, we demonstrate that the spatial oscillations in the superconducting order parameter induced by defects can be spatially imaged through local measurements of the critical Josephson current, providing unprecedented insight into the nature of superconductivity. The spatial form of the Josephson current reflects the nature of the defects, and can be used to probe defect-induced phase transitions from an S = 0 to an S = 1/2 ground state.

Graham, Martin↗
DOE OSTI2019

Building and exploring libraries of atomic defects in graphene: Scanning transmission electron and scanning tunneling microscopy study

The presence and configurations of defects are primary components determining materials functionality. Their population and distribution are often nonergodic and dependent on synthesis history, and therefore rarely amenable to direct theoretical prediction. Here, dynamic electron beam–induced transformations in Si deposited on a graphene monolayer are used to create libraries of possible Si and carbon vacancy defects. Deep learning networks are developed for automated image analysis and recognition of the defects, creating a library of (meta) stable defect configurations. Density functional theory is used to estimate atomically resolved scanning tunneling microscopy (STM) signatures of the classified defects from the created library, allowing identification of several defect types across imaging platforms. This approach allows automatic creation of defect libraries in solids, exploring the metastable configurations always present in real materials, and correlative studies with other atomically resolved techniques, providing comprehensive insight into defect functionalities.

36 MATERIALS SCIENCE↗
DOE OSTI2015

W-Band Scanning ARM Cloud Radar (WSACR) Multiple Elevation PPI Scan (a1-level)

The wsacr PCM process executed by the sacr3 binary reads in wsacr.00 data and produces CF/Radial compliant NetCDF files for each of the radar operational scanning modes. This incorporates raw data from the radar, as well as scientifically important base derived parameters that affect interpretation of the data.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Directed flow of quarks from the RHIC Beam Energy Scan measured by STAR

Directed flow (ν 1 ) is a good probe of the early-stage dynamics of collision systems, and the ν 1 slope at midrapidity ( dv 1 /dy| y=0 ) is sensitive to the system's equation of state. STAR has published ν 1 (y) measurements for ten particle species (π ± ,$p, \bar{p},Λ,\bar{Λ},ϕ,K^± and K_S^0$) in Au+Au collisions at eight beam energies from $ \sqrt{s_{NN}}$ = 7.7 GeV to 200 GeV. In this study, we employ a simple coalescence idea to decompose ν 1 of hadrons into ν 1 of constituent quarks. The dv 1 /dy values of $\bar{p},\bar{K},$ and $\bar{Λ}$ are used to test the coalescence sum rule for produced quarks. Data involving produced quarks support the coalescence picture at $ \sqrt{s_{NN}}$ =11.5 GeV to 200 GeV, and a sharp deviation from this picture is observed at 7.7 GeV. The dv 1 /dy of transported quarks is studied via net particles (net p and net Λ). In these proceedings, we further extract the ν 1 slopes of produced and transported quarks, assuming that the coalescence sum rule is valid.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Comparison of image noise and image quality between full-dose abdominal computed tomography scans reconstructed with weighted filtered back projection and half-dose scans reconstructed with improved sinogram-affirmed iterative reconstruction (SAFIRE*)

Purpose: To retrospectively compare the image noise, signal-to-noise ratio (SNR), and subjective image quality between CT images acquired with a dual-source, split-dose imaging protocol reconstructed at full and half doses with weighted filtered back projection (wFBP) and an improved sinogram-affirmed iterative reconstruction algorithm (SAFIRE*). Methods: Fifty-three consecutive patients underwent contrast-enhanced CT of the abdomen using a standardized dual-source, single energy CT protocol. Half-dose images were retrospectively generated using data from one detector only. Full-dose datasets were reconstructed with wFBP, while half-dose datasets were reconstructed with wFBP and SAFIRE* strengths 1–5. Region of interest analysis was performed to assess SNR and noise. Diagnostic acceptability, subjective noise, and spatial resolution were graded on a 10-point scale by two readers. Statistical analysis was carried out with repeated measures analysis of variance, Wilcoxon signed rank test, and Cohen’s κ test. Results: With the increasing strengths of SAFIRE*, a progressive reduction in noise and increase in SNR (p < 0.01) was observed. There was a statistically significant decrease in objective noise and increase in SNR in half-dose SAFIRE* strength 4 and 5 reconstructions compared to full-dose reconstructions using wFBP (p < 0.01). Qualitative analysis revealed a progressive increase in diagnostic acceptability, decrease in subjective noise and increase in spatial resolution for half-dose images reconstructed with the increasing strengths of SAFIRE* (p < 0.01). Conclusions: Half-dose CT images reconstructed with SAFIRE* at strength 4 and 5 have superior image quality compared to full-dose images reconstructed with wFBP. SAFIRE* potentially allows dose reductions in the order of 50% over wFBP.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Metal hydride differential scanning calorimetry as an approach to compositional determination of mixtures of hydrogen isotopologues and helium

Gaseous mixtures of diatomic hydrogen isotopologues and helium are often encountered in the nuclear energy industry and in analytical chemistry. Compositions of stored mixtures can vary due to interactions with storage and handling materials. When tritium is present, it decays to form ions and helium-3, both of which can lead to further compositional variation. Monitoring of composition is typically achieved by mass spectrometry, a method that is bulky and energy-intensive. Mass spectrometers disperse sample material through vacuum pumps, which is especially troublesome if tritium is present. Moreover, our ultimate goal is to create a compact, fast, low-power sensor that can determine composition with minimal gas consumption and waste generation, as a complement to mass spectrometry that can be instantiated more widely. We propose calorimetry of metal hydrides as an approach to this, due to the strong isotope effect on gas absorption, and demonstrate the sensitivity of measured heat flow to atomic composition of the gas. Peak shifts are discernible when mole fractions change by at least 1%. A mass flow restriction results in a unique dependence of the measurement on helium concentration. We present a mathematical model as a first step toward prediction of the peak shapes and positions. The model includes a useful method to compute estimates of phase diagrams for palladium in the presence of arbitrary mixtures of hydrogen isotopologues. As a result, we expect that this approach can be used to deduce unknown atomic compositions from measured calorimetric data over a useful range of partial pressures of each component.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗