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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Non-invasive characterization of complex coronary lesions

Conventional invasive diagnostic imaging techniques do not adequately resolve complex Type B and C coronary lesions, which present unique challenges, require personalized treatment and result in worsened patient outcomes. These lesions are often excluded from large-scale non-invasive clinical trials and there does not exist a validated approach to characterize hemodynamic quantities and guide percutaneous intervention for such lesions. This work identifies key biomarkers that differentiate complex Type B and C lesions from simple Type A lesions by introducing and validating a coronary angiography-based computational fluid dynamic (CFD-CA) framework for intracoronary assessment in complex lesions at ultrahigh resolution. Among 14 patients selected in this study, 7 patients with Type B and C lesions were included in the complex lesion group including ostial, bifurcation, serial lesions and lesion where flow was supplied by collateral bed. Simple lesion group included 7 patients with lesions that were discrete, <10mm long and readily accessible. Intracoronary assessment was performed using CFD-CA framework and validated by comparing to clinically measured pressure-based index, such as FFR. Local pressure, endothelial shear stress (ESS) and velocity profiles were derived for all patients. We validates the accuracy of our CFD-CA framework and report excellent agreement with invasive measurements (n=14,R 2 =0.6,p=0.0013). Ultra-high resolution achieved by the model enable physiological assessment in complex lesions and quantify hemodynamic metrics in all vessels up to 1mm in diameter. Importantly, we demonstrate that in contrast to traditional pressure-based metrics, there is a significant difference in the intracoronary hemodynamic forces, such as ESS, in complex lesions compared to simple lesions at both resting and hyperemic physiological states [n = 14, p=0.03]. Higher ESS was observed in the complex lesion group (7.0±4.7 Pa) than in simple lesion group (4.8±3.6 Pa). Complex coronary lesions have higher ESS compared to simple lesions, such differential hemodynamic evaluation can provide much the needed insight into the increase in adverse outcomes for such patients and has incremental prognostic value over traditional pressure-based indices, such as FFR.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Exploring 3D elastic-wave scattering at interfaces using high-resolution phased-array system

The elastic-wave scattering at interfaces, such as cracks, is essential for nondestructive inspections, and hence, understanding the phenomenon is crucial. However, the elastic-wave scattering at cracks is very complex in three dimensions since microscopic asperities of crack faces can be multiple scattering sources. We propose a method for exploring 3D elastic-wave scattering based on our previously developed high-resolution 3D phased-array system, the piezoelectric and laser ultrasonic system (PLUS). We describe the principle of PLUS, which combines a piezoelectric transmitter and a 2D mechanical scan of a laser Doppler vibrometer, enabling us to resolve a crack into a collection of scattring sources. Subsequently, we show how the 3D elastic-wave scattering in the vicinity of each response can be extracted. Here, we experimentally applied PLUS to a fatigue-crack specimen. We found that diverse 3D elastic-wave scattering occurred in a manner depending on the responses within the fatigue crack. This is significant because access to such information will be useful for optimizing inspection conditions, designing ultrasonic measurement systems, and characterizing cracks. More importantly, the described methodology is very general and can be applied to not only metals but also other materials such as composites, concrete, and rocks, leading to progress in many fields.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Extensive 3D mapping of dislocation structures in bulk aluminum

Abstract Thermomechanical processing such as annealing is one of the main methods to tailor the mechanical properties of materials, however, much is unknown about the reorganization of dislocation structures deep inside macroscopic crystals that give rise to those changes. Here, we demonstrate the self-organization of dislocation structures upon high-temperature annealing in a mm-sized single crystal of aluminum. We map a large embedded 3D volume ( $$100\times 300\times 300$$ 100 × 300 × 300 $$\upmu$$ μ m $$^3$$ 3 ) of dislocation structures using dark field X-ray microscopy (DFXM), a diffraction-based imaging technique. Over the wide field of view, DFXM’s high angular resolution allows us to identify subgrains, separated by dislocation boundaries, which we identify and characterize down to the single-dislocation level using computer-vision methods. We demonstrate how even after long annealing times at high temperatures, the remaining low density of dislocations still pack into well-defined, straight dislocation boundaries (DBs) that lie on specific crystallographic planes. In contrast to conventional grain growth models, our results show that the dihedral angles at the triple junctions are not the predicted 120 $$^{\circ }$$ ∘ , suggesting additional complexities in the boundary stabilization mechanisms. Mapping the local misorientation and lattice strain around these boundaries shows that the observed strain is shear, imparting an average misorientation around the DB of $$\approx$$ ≈ 0.003 to 0.006 $$^{\circ }$$ ∘ .

36 MATERIALS SCIENCE↗
DOE OSTI2021

Direct visualization of radiation-induced transformations at alkali halide–air interfaces

Radiation driven reactions at mineral/air interfaces are important to the chemistry of the atmosphere, but experimental constraints (e.g. simultaneous irradiation, in situ observation, and environmental control) leave process understanding incomplete. Using a custom atomic force microscope equipped with an integrated X-ray source, transformation of potassium bromide surfaces to potassium nitrate by air radiolysis species was followed directly in situ at the nanoscale. Radiolysis initiates dynamic step edge dissolution, surface composition evolution, and ultimately nucleation and heteroepitaxial growth of potassium nitrate crystallites mediated by surface diffusion at rates controlled by adsorbed water. Finally, in contrast to in situ electron microscopy and synchrotron-based imaging techniques where high radiation doses are intrinsic, our approach illustrates the value of decoupling irradiation and the basis of observation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Femtosecond multimodal imaging with a laser-driven X-ray source

Laser-plasma accelerators are compact linear accelerators based on the interaction of high-power lasers with plasma to form accelerating structures up to 1000 times smaller than standard radiofrequency cavities, and they come with an embedded X-ray source, namely betatron source, with unique properties: small source size and femtosecond pulse duration. A still unexplored possibility to exploit the betatron source comes from combining it with imaging methods able to encode multiple information like transmission and phase into a single-shot acquisition approach. In this work, we combine edge illumination-beam tracking (EI-BT) with a betatron X-ray source and present the demonstration of multimodal imaging (transmission, refraction, and scattering) with a compact light source down to the femtosecond timescale. The advantage of EI-BT is that it allows multimodal X-ray imaging technique, granting access to transmission, refraction and scattering signals from standard low-coherence laboratory X-ray sources in a single shot.

43 PARTICLE ACCELERATORS↗
DOE OSTI2026

Regularization by denoising diffusion models for solving inverse PDE problems with application to full waveform inversion

Partial differential equation (PDE)-governed inverse problems are fundamental across various scientific and engineering applications; yet they face significant challenges due to nonlinearity, ill-posedness, and sensitivity to noise. Here, we introduce a computational framework, regularization by denoising using diffusion models for partial differential equations (RED-DiffEq), by integrating physics-driven inversion and data-driven learning. RED-DiffEq leverages pretrained diffusion models as a regularization mechanism for PDE-governed inverse problems. We apply RED-DiffEq to solve the full waveform inversion problem in geophysics, a challenging seismic imaging technique that seeks to reconstruct high-resolution subsurface velocity models from seismic measurement data. Our method shows enhanced accuracy and robustness compared to benchmark methods. Additionally, it exhibits strong generalization and domain decomposition capacity, enabling the inversion of more complex velocity models with larger domains than those used in training the diffusion model. Our framework can also be directly applied to diverse PDE-governed inverse problems.

Shan, Siming [Yale University, New Haven, CT (Unit↗
DOE OSTI2025

Generating multi-scale Li-ion battery cathode particles with radial grain architectures using stereological generative adversarial networks

Abstract Understanding structure-property relationships of Li-ion battery cathodes is crucial for optimizing rate-performance and cycle-life resilience. However, correlating the morphology of cathode particles, such as in LiNi0.8Mn0.1Co0.1O2 (NMC811), and their inner grain architecture with electrode performance is challenging, particularly, due to the significant length-scale difference between grain and particle sizes. Experimentally, it is not feasible to image such a high number of particles with full granular detail. A second challenge is that sufficiently high-resolution 3D imaging techniques remain expensive and are sparsely available at research institutions. Here, we present a stereological generative adversarial network-based model fitting approach to tackle this, that generates representative 3D information from 2D data, enabling characterization of materials in 3D using cost-effective 2D data. Once calibrated, this multi-scale model can rapidly generate virtual cathode particles that are statistically similar to experimental data, and thus is suitable for virtual characterization and materials testing through numerical simulations. A large dataset of simulated particles with inner grain architecture has been made publicly available.

25 ENERGY STORAGE↗
DOE OSTI2015

Control of plasmonic nanoantennas by reversible metal-insulator transition

We demonstrate dynamic reversible switching of VO 2 insulator-to-metal transition (IMT) locally on the scale of 15 nm or less and control of nanoantennas, observed for the first time in the near-field. Using polarization-selective near-field imaging techniques, we simultaneously monitor the IMT in VO 2 and the change of plasmons on gold infrared nanoantennas. Structured nanodomains of the metallic VO 2 locally and reversibly transform infrared plasmonic dipole nanoantennas to monopole nanoantennas. Fundamentally, the IMT in VO 2 can be triggered on femtosecond timescale to allow ultrafast nanoscale control of optical phenomena. In conclusion, these unique features open up promising novel applications in active nanophotonics.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Nondestructive volumetric 3-D chemical mapping of nickel-sulfur compounds at the nanoscale

Nano-structures of nickel (Ni) and nickel subsulfide (Ni{sub 3}S{sub 2}) materials were studied and mapped in 3D with high-resolution x-ray nanotomography combined with full field XANES spectroscopy. This method for characterizing these phases in complex microstructures is an important new analytical imaging technique, applicable to a wide range of nanoscale and mesoscale electrochemical systems.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Impact of chain microstructure on solution and thin film self-assembly of PCHD-based semi-flexible/flexible diblock copolymers

We examine self-assembly of semi-flexible/flexible block copolymers in a selective solvent iusing a set of diblock copolymers where the chain microstructure of the semi-flexible block is manipulated in order to tune chain stiffness. The reduced conformational space of the semi-flexible block is anticipated to alter the way the chains pack, potentially changing the structure of self-assembled aggregates in comparison to flexible diblock copolymer analogs. Semi-flexible/flexible diblock copolymers comprised of poly(styrene)-block-poly(1,3-cyclohexadiene) (PS-b-PCHD) having systematic changes in chain microstructure, as captured by the ratio of 1,4/1,2-linkages between cyclohexenyl repeat units, and molecular weight of the PCHD blocks were synthesized using anionic polymerization. Moreover, these diblocks were dissolved in tetrahydrofuran (THF), which is a preferential solvent for PS, and the structures formed were examined using laser light scattering and complementary imaging techniques. Results show that PS-b-PCHD copolymers with a chain microstructure of 90% 1,4/10% 1,2 linkages between cyclohexenyl repeat units (referred to simply as 90/10) are able to micellize, forming spherical structures, while diblocks of 70/30 and 50/50 1,4-to-1,2 ratios remain as single chains and ill-defined aggregates, respectively, when dissolved in THF. With inferences drawn from simple structural models, we speculate that this self-assembly behavior arises due to the change in the chain configuration with increasing content of 1,2-links in the backbone. Finally, this renders the chain with higher 1,2 content incapable of swelling in response to solvent and unable to pack into well-defined self-assembled structures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Imaging H abstraction dynamics in crossed molecular beams: O( 3 P) + propanol isomers

The crossed beam reaction dynamics of ground state O( 3 P) atoms with propanol isomers (1-propanol and 2-propanol) have been studied for the first time using the velocity map imaging technique. The hydroxypropyl radical products, generated from H-abstraction of the secondary and tertiary C–H groups of propanol isomers, were detected via single photon ionization at 157 nm under single collision conditions with collision energies of 8 and 10 kcal mol –1 . Direct rebound dynamics were suggested by the angular distributions, which show overall sideways-backward scattering but more pronounced backward scattering for both isomer reactions under all collision energies studied here. All the translational energy distributions peak at low energy, on average 20–40% of the total available energy. This indicates high internal excitation in the products that is treated by various models of energy release. As a result, we infer that most of the total available energy is partitioned into rotational excitation due to the long-rang dipole–dipole interaction between the dipolar OH and hydroxypropyl radicals.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Tuning the bandgap of Cs 2 AgBiBr 6 through dilute tin alloying

The promise of lead halide hybrid perovskites for optoelectronic applications makes finding less-toxic alternatives a priority. The double perovskite Cs 2 AgBiBr 6 ( 1 ) represents one such alternative, offering long carrier lifetimes and greater stability under ambient conditions. However, the large and indirect 1.95 eV bandgap hinders its potential as a solar absorber. Here we report that alloying crystals of 1 with up to 1 atom% Sn results in a bandgap reduction of up to ca. 0.5 eV while maintaining low toxicity. Crystals can be alloyed with up to 1 atom% Sn and the predominant substitution pathway appears to be a ~2 : 1 substitution of Sn 2+ and Sn 4+ for Ag + and Bi 3+ , respectively, with Ag + vacancies providing charge compensation. Spincoated films of 1 accommodate a higher Sn loading, up to 4 atom% Sn, where we see mostly Sn 2+ substitution for both Ag + and Bi 3+ . Density functional theory (DFT) calculations ascribe the bandgap redshift to the introduction of Sn impurity bands below the conduction band minimum of the host lattice. Using optical absorption spectroscopy, photothermal deflection spectroscopy, X-ray absorption spectroscopy, 119 Sn NMR, redox titration, single-crystal and powder X-ray diffraction, multiple elemental analysis and imaging techniques, and DFT calculations, we provide a detailed analysis of the Sn content and oxidation state, dominant substitution sites, and charge-compensating defects in Sn-alloyed Cs 2 AgBiBr 6 ( 1:Sn ) crystals and films. An understanding of heterovalent alloying in halide double perovskites opens the door to a wider breadth of potential alloying agents for manipulating their band structures in a predictable manner.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

ZTF SN Ia DR2: An environmental study of Type Ia supernovae using host galaxy image decomposition

The second data release of Type Ia supernovae (SNe Ia) observed by the Zwicky Transient Facility has provided a homogeneous sample of 3628 SNe Ia with photometric and spectral information. This unprecedented sample size enables us to better explore our currently tentative understanding of the dependence of the host environment on SN Ia properties. In this paper, we make use of two-dimensional image decomposition to model the host galaxies of SNe Ia. We model elliptical galaxies as well as disc and spiral galaxies with or without central bulges and bars. This allows for the categorisation of SN Ia based on their morphological host environment, as well as the extraction of intrinsic galaxy properties corrected for both cosmological and atmospheric effects, through point-spread-function (PSF) convolution. We find that although this image decomposition technique leads to a significant bias towards elliptical galaxies in our final sample of processed galaxies, the overall results are still robust. By successfully modelling 728 host galaxies, we find that the photometric properties of SNe Ia found in discs and in elliptical galaxies correlate fundamentally differently with their host environment. We identified strong linear relations between light-curve stretch and our model-derived galaxy colour for both the elliptical (16.8σ) and disc (5.1σ) subpopulations of SNe Ia. Lower-stretch SNe Ia are found in redder environments, which we identify as an age and/or metallicity effect. Within the subpopulation of SNe Ia found in disc-containing galaxies, we find a significant linear trend (6.1σ) between light-curve stretch and model-derived local r-band surface brightness, which we link to the age and metallicity gradients found in disc galaxies. SN Ia colour shows little correlation with the host environment, as is seen in the literature. We do identify a possible dust effect in our model-derived surface brightness (3.3σ) for SNe Ia in disc galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Competitive ionization processes of anthracene excited with a femtosecond pulse in the multi-photon ionization regime

To clarify the ionization mechanism of large molecules under multi-photon ionization conditions, photo-electron spectroscopic studies on anthracene have been performed with electron imaging technique. Electron kinetic energy distributions below a few eV reveal that three kinds of ionization channels coexist, viz., vertical ionization, ionization from Rydberg states, and thermionic hot electron emission. Their relative yield is determined by the characteristic of the laser pulse. The duration in particular influences the ratio between the first two processes, while for higher intensities the last process dominates. Our results provide strong evidence that internal conversion plays an important role for the ionization of the molecule.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Real-Space Microscopic Electrical Imaging of n+-p Junction Beneath Front-Side Ag Contact of Multicrystalline Si Solar Cells

We investigated the quality of the n+-p diffused junction beneath the front-side Ag contact of multicrystalline Si solar cells by characterizing the uniformities of electrostatic potential and doping concentration across the junction using the atomic force microscopy-based electrical imaging techniques of scanning Kelvin probe force microscopy and scanning capacitance microscopy. We found that Ag screen-printing metallization fired at the over-fire temperature significantly degrades the junction uniformity beneath the Ag contact grid, whereas metallization at the optimal- and under-fire temperatures does not cause degradation. Ag crystallites with widely distributed sizes were found at the Ag-grid/emitter-Si interface of the over-fired cell, which is associated with the junction damage beneath the Ag grid. Large crystallites protrude into Si deeper than the junction depth. However, the junction was not broken down; instead, it was reformed on the entire front of the crystallite/Si interface. We propose a mechanism of junction-quality degradation, based on emitter Si melting at the temperature around the Ag-Si eutectic point during firing, and subsequent re-crystallization with incorporation of Ag and other impurities and with formation of crystallographic defects during quenching. The effect of this junction damage on solar cell performance is discussed.

14 SOLAR ENERGY↗
DOE OSTI2012

Angular and energy distribution of fragment ions in dissociative double photoionization of acetylene molecules at 39 eV

The two-body dissociation reactions of the dication, C{sub 2}H{sub 2}{sup 2+}, produced by 39.0 eV double photoionization of acetylene molecules, have been studied by coupling photoelectron-photoion-photoion coincidence and ion imaging techniques. The results provide the kinetic energy and angular distributions of product ions. The analysis of the results indicates that the dissociation leading to C{sub 2}H{sup +}+H{sup +} products occurs through a metastable dication with a lifetime of 108 {+-} 22 ns, and a kinetic energy release (KER) distribution exhibiting a maximum at {approx}4.3 eV with a full width at half maximum (FWHM) of about 60%. The reaction leading to CH{sub 2}{sup +}+C{sup +} occurs in a time shorter than the typical rotational period of the acetylene molecules (of the order of 10{sup -12} s). The KER distribution of product ions for this reaction, exhibits a maximum at {approx}4.5 eV with a FWHM of about 28%. The symmetric dissociation, leading to CH{sup +} + CH{sup +}, exhibits a KER distribution with a maximum at {approx}5.2 eV with a FWHM of 44%. For the first two reactions the angular distributions of ion products also indicate that the double photoionization of acetylene occurs when the neutral molecule is mainly oriented perpendicularly to the light polarization vector.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗