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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Virtual strain gage size study

DIC is a non-linear low-pass spatial filtering operation; whether we consider the effect of the subset and shape function, the strain window used in the strain calculation, of other post-processing of the results, each decision will impact the spatial resolution, of the measurement. More fundamentally, the speckle size limits, the spatial resolution by dictating the smallest possible subset. After this decision the processing settings are controlled by the allowable noise level balanced by possible bias errors created by the data filtering. This article describes a process to determine optimum DIC software settings to determine if the peak displacements or strains are being found.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Introduction to a Virtual Issue on root traits

Plant traits – ‘morphological, anatomical, physiological, biochem-ical and phenological characteristics of plants and their organs’(Kattge et al., 2011) – are increasingly being harnessed byempiricists and modelers as a framework to understand patternsin the structure and function of specie s across the globe. Trait-basedecology, which emphasizes functional traits over the taxonomicalrelationships among organisms (Laliberte, 2017), promises toimprove generality, synthesis, and predictive ability across ecolog-ical scales (Shipley et al., 2016). Indeed, plant trait studies areincreasingly prominent in the literature: a simple Web of Sciencesearch on the term indicates a surge in publications from 2576during the three-year period from 1999 to 2001 to 13 234 in thethree-year period between 2014 and 2016. However, the mostcommon plant traits described in the literature relate to above -ground organs and their function, including leaf morphology,photosynthetic parameters, and above ground growth rate. Roottraits, particularly those of fine roots associated with criticalbelowground plant functions, are much less studied – they are, afterall, harder to measure and less likely to have a role in ecosystemmodels as they are encoded today. Although the TRY database ofplant traits (Kattge et al., 2011) has been a highly valuable resourcefor plant and ecosystem ecologists, < 1% of the data entries describefine-root functional traits. This glaring gap in our knowledge of thebelowground half of ecosystem function has led to a chorus of pleasin recent years for a stronger emphasis on the measurement andunderstanding of root traits (e.g . Bardgett et al., 2014).

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Optimizing cone beam CT scatter estimation in egs-cbct for a clinical and virtual chest phantom

Purpose: Cone beam computed tomography (CBCT) image quality suffers from contamination from scattered photons in the projection images. Monte Carlo simulations are a powerful tool to investigate the properties of scattered photons.egs-cbct, a recent EGSnrc user code, provides the ability of performing fast scatter calculations in CBCT projection images. This paper investigates how optimization of user inputs can provide the most efficient scatter calculations. Methods: Two simulation geometries with two different x-ray sources were simulated, while the user input parameters for the efficiency improving techniques (EITs) implemented inegs-cbct were varied. Simulation efficiencies were compared to analog simulations performed without using any EITs. Resulting scatter distributions were confirmed unbiased against the analog simulations. Results: The optimal EIT parameter selection depends on the simulation geometry and x-ray source. Forced detection improved the scatter calculation efficiency by 80%. Delta transport improved calculation efficiency by a further 34%, while particle splitting combined with Russian roulette improved the efficiency by a factor of 45 or more. Combining these variance reduction techniques with a built-in denoising algorithm, efficiency improvements of 4 orders of magnitude were achieved. Conclusions: Using the built-in EITs inegs-cbct can improve scatter calculation efficiencies by more than 4 orders of magnitude. To achieve this, the user must optimize the input parameters to the specific simulation geometry. Realizing the full potential of the denoising algorithm requires keeping the statistical uncertainty below a threshold value above which the efficiency drops exponentially.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

SU-G-IeP2-15: Virtual Insertion of Digital Kidney Stones Into Dual-Source, Dual- Energy CT Projection Data

Purpose: In order to investigate novel methods to more accurately estimate the mineral composition of kidney stones using dual energy CT, it is desirable to be able to combine digital stones of known composition with actual phantom and patient scan data. In this work, we developed and validated a method to insert digital kidney stones into projection data acquired on a dual-source, dual-energy CT system. Methods: Attenuation properties of stones of different mineral composition were computed using tabulated mass attenuation coefficients, the chemical formula for each stone type, and the effective beam energy at each evaluated tube potential. A previously developed method to insert lesions into x-ray CT projection data was extended to include simultaneous dual-energy CT projections acquired on a dual-source gantry (Siemens Somatom Flash). Digital stones were forward projected onto both detectors and the resulting projections added to the physically acquired sinogram data. To validate the accuracy of the technique, digital stones were inserted into different locations in the ACR CT accreditation phantom; low and high contrast resolution, CT number accuracy and noise properties were compared before and after stone insertion. The procedure was repeated for two dual-energy tube potential pairs in clinical use on the scanner, 80/Sn140 kV and 100/Sn140 kV, respectively. Results: The images reconstructed after the insertion of digital kidney stones were consistent with the images reconstructed from the scanner. The largest average CT number difference for the 4 insert in the CT number accuracy module of the phantom was 3 HU. Conclusion: A framework was developed and validated for the creation of digital kidney stones of known mineral composition, and their projection-domain insertion into commercial dual-source, dual-energy CT projection data. This will allow a systematic investigation of the impact of scan and reconstruction parameters on stone attenuation and dual-energy behavior under rigorously controlled conditions. Dr. McCollough receives research support from Siemens Healthcare.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Silicon as a virtual plasmonic material: Acquisition of its transient optical constants and the ultrafast surface plasmon-polariton excitation

Ultrafast intense photoexcitation of a silicon surface is complementarily studied experimentally and theoretically, with its prompt optical dielectric function obtained by means of time-resolved optical reflection microscopy and the underlying electron-hole plasma dynamics modeled numerically, using a quantum kinetic approach. The corresponding transient surface plasmon-polariton (SPP) dispersion curves of the photo-excited material were simulated as a function of the electron-hole plasma density, using the derived optical dielectric function model, and directly mapped at several laser photon energies, measuring spatial periods of the corresponding SPP-mediated surface relief nanogratings. The unusual spectral dynamics of the surface plasmon resonance, initially increasing with the increase in the electron-hole plasma density but damped at high interband absorption losses induced by the high-density electron-hole plasma through instantaneous bandgap renormalization, was envisioned through the multi-color mapping.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Nuclear vertex constants for the virtual decay {sup 7}Be {yields} {sup 3}He + {sup 4}He of the 7Be bound states from a phase-shift analysis in the effective-range theory

The phase-shift-analysis data for the {sup 3}He{sup 4}He scattering are analyzed using the effective-range theory, with the Coulomb interaction taken into account. We find both the renormalized nuclear vertex constants for the vertex {sup 7}Be {yields} {sup 3}He + {sup 4}He in the ground (3/2{sup -}) and in the first excited (1/2{sup -}) bound states of {sup 7}Be, and the corresponding asymptotic normalization constants of the radial wave functions in these states. The results obtained can be used in an astrophysical S-factor calculation for radiative capture reaction {sup 4}He({sup 3}He, {gamma}){sup 7}Be.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

Configuration splitting of the Gamow-Teller resonance in antimony isotopes: Is this a real or a virtual effect?

The Gamow-Teller strength functions for a number of antimony isotopes were calculated within a semimicroscopic approach based on the continuum version of the charge-exchange quasiparticle random-phase approximation and on phenomenologically taking into account the fragmentation effect. The structural effect of splitting of the main maximum of the Gamow-Teller resonance in these isotopes was confirmed. Experimental data on the excitation of this resonance in a direct and a resonance reaction for the {sup 118}Sn parent nucleus were analyzed with allowance for this effect.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Virtual Compton scattering measurements in the nucleon resonance region

We report on new measurements of the electric Generalized Polarizability (GP) of the proton \( \alpha_{E}\) in a kinematic region where a puzzling dependence on momentum transfer has been observed, and we have found that \( \alpha_E = (5.3 \pm 0.6_{stat} \pm 1.3_{sys}) 10^{-4}\) fm 3 at \( Q^{2}=0.20\) (GeV/ c ) 2 . The new measurements, when considered along with the rest of the world data, suggest that \( \alpha_E\) can be described by either a local plateau or by an enhancement in the region \( Q^2=0.20\) (GeV/ c ) 2 to 0.33 (GeV/ c ) 2 . The experiment also provides the first measurement of the Coulomb quadrupole amplitude in the \( N \rightarrow \Delta\) transition through the exploration of the \( p(e,e'p)\gamma\) reaction. The new measurement gives \( CMR = (-4.4 \pm 0.8_{stat} \pm 0.6_{sys})\%\) at \( Q^2=0.20\) (GeV/ c ) 2 and is consistent with the results from the pion electroproduction world data. It has been obtained using a completely different extraction method, and therefore represents a strong validation test of the world data model uncertainties.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗