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Results for “DIFFRACTION MODELS”

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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Analytical solutions with Generalized Impedance Boundary Conditions (GIBC)

The diffraction by a material discontinuity in a thick dielectric/ferrite layer is considered by modeling the layer as a distributed current sheet obeying generalized sheet transition conditions (GSTC's). The sheet currents are then formulated and solved via the standard dual integral equation approach. This yields the diffracted field in terms of unknown constants which underscore the non-uniqueness of the GSTC current sheet representation. The constants are dependent on the geometry and properties of the discontinuity and are determined by enforcing field continuity across the material junction. This requires the field internal to the slab which are determined from the external ones via analytic continuity. Results are given which validate the solution and demonstrate the importance of the constants.

Ricoy, Mark A.↗
DOE OSTI2014

Temporal characteristics of polarization holographic gratings formed in a photosensitive polymeric film containing N-benzylideneaniline derivative side groups

A polarization holographic grating was recorded in a transparent thin film formed from polymethacrylate with N-benzylideneaniline (NBA) derivative side groups. We measured the real time diffraction properties. The data were analyzed based on a theoretical model that accounted for the distribution of optical anisotropy caused by molecular reorientation as well as for surface relief (SR) deformation caused by molecular motion. Optical anisotropy rapidly increased and then slowly decreased, with increasing recording time. This phenomenon was described based on photoisomerization and photocleavage reactions of the NBA side groups. SR deformation was also induced in the film by polarization holographic recording, without any subsequent processes. The photoinduced optical anisotropy and SR deformation were retained after the recording was turned off.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Status Report on Photothermal Radiometry Development

Thermal transport properties such as thermal conductivity and diffusivity, are critical parameters in the development of improved nuclear fuels and components. It is well known that thermal transport properties change temporally and spatially due to dynamic microstructural evolution as a result of neutron irradiation. Laser based photothermal techniques are an ideal candidate for thermal properties measurement of irradiated materials because they are non contact, non destructive and can be performed remotely. In this report, we present the progress in the development of a photothermal radiometry (PTR) system to measure the thermal diffusivity of solid samples. The PTR technique measures the local temperature response from a modulated heat source by detecting the sample radiation heat flux. Initially, a well developed thermal wave analytical model was fit to the data to obtain the thermal diffusivity. However, systematic errors from the diffraction effect and non linearity issues resulted in thermal diffusivity measurements higher than literature values. These effects have been studied, an improved analytical model has been developed, and the physics behind the phenomena are still under investigation. A procedure for optimizing measurements from the benchtop system has been provided.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2026

Validation Data for Benchmarking Wire Arc Additive Manufacturing Process Simulations

Residual stresses cause geometric distortion and affect mechanical performance of additively manufactured structures, yet they are notoriously difficult to assess and predict. Distortion (warpage) can drive parts outside dimensional tolerance limits, leading to part rejection or rework. For parts that meet tolerance, locked-in residual stress fields can affect structural integrity during operation, particularly subcritical cracking by fatigue, creep, or corrosion. This work develops benchmark data for a common additive manufacturing process (Wire Arc Additive Manufacturing) that can be applied for calibration and validation of physical process models that predict residual stress fields. The work includes design of two different samples of differing geometry, detailed manufacturing records for a set of physical samples, and an extensive set of residual stress measurement data developed using two diverse techniques (the contour method and neutron diffraction). An initial application of the work is also reported, where a modeling challenge was issued to secure residual stress model predictions from two independent laboratories that were blind to residual stress measurement data. These initial blind residual stress predictions show significant discrepancies relative to the measurement data, illustrating the potential value of the underlying validation data. An open repository for this work, including the sample designs, manufacturing process records, and the residual stress data, is also provided for future application in non-blind validation efforts.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Roles of Hydration and Magnetism on the Structure of Ferrihydrite from First Principles

We report density functional theory calculations aimed at predicting thermodynamically stable structures for ferrihydrite across a range of possible compositions determined by the amount of structural water. Based on an assumed formula unit of Fe5O8H + nH2O, we performed ab initio calculations with evolutionary searching to find the lowest enthalpy structures as a function of the water content up to n = 2. This is the most exhaustive search for the ferrihydrite structure conducted so far; more than 5000 unique configurations were generated and evaluated over five states of hydration. Among them, the Michel akdaliate model was generated, along with several energetically comparable new structures at higher states of hydration. However, a direct comparison between calculated and experimental pair distribution function and X-ray diffraction patterns for the 50 lowest energy structures shows that none beyond the Michel model could be associated with ferrihydrite. Nevertheless, this energetically comparable structure set provides a novel basis for analyzing and understanding the effects of hydration and magnetism on the topology of ferrihydrite, from which we conclude that any tetrahedral Fe should be viewed as a metastable structural defect, created either as a result of the rapid kinetics of crystal growth or to accommodate a local magnetic stress between neighboring Fe atoms.

composition, density functional theory, ferrihydri↗
DOE OSTI2019

A study of defect structures in Fe-alloyed ZnO: Morphology, magnetism, and hyperfine interactions

In order to study the effect of Fe cation substitution on the local structure, defect formation, and hyperfine interactions in ZnO, Mössbauer spectroscopy measurements of the microwave processed Zn 1 - x Fe x O (x = 0.05, 0.10, 0.15, and 0.20) nanoparticles, together with ab initio calculations, were performed. Complementary information on the distribution of particle size and morphology, as well as magnetic properties, were obtained by X-ray diffraction, transmission electron microscopy, and squid-magnetometry. The selected model for analyzing the Mössbauer spectra of our samples is a distribution of quadrupole splittings. The fitting model with two Lorentz doublets was rejected due to its failure to include larger doublets. The Fe 3 + ions do not yield magnetic ordering in the samples at room temperature. The results from first-principles calculations confirm that the major component of the Mössbauer spectra corresponds to the Fe-alloyed ZnO with Zn vacancy in the next nearest neighbor environment. The magnetic measurements are consistent with the description of the distribution of iron ions over the randomly formed clusters in the ZnO host lattice. While at room temperature all the samples are paramagnetic, magnetic interactions cause a transition into a cluster spin-glass state at low temperatures. © 2019 Author(s).

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Rolling hills on the core-mantle boundary

Recent results suggest that an iron-rich oxide may have fractionally crystallized from a primordial magma ocean and settled on the core–mantle boundary (CMB). Based on experimental results, the presence of only a few percent of Fe-rich oxide could slow seismic waves down by several percent. This heavy layer can become highly undulating as predicted from dynamic modeling but can remain as a distinct structure with uniform velocity reductions. Here, we use the large USArray seismic network to search for such structures. Strong constraints on D" are provided by the core-phase SKS where it bifurcates, containing a short segment of P-wave diffractions (P d ) when crossing the CMB, called SKS d . Synthetics from models with moderate velocity drops (less than 10%) involving a layer with variable thickness, perhaps a composite of sharp small structures, with strong variation in thickness can explain both the observed SKS d waveforms and large scatter in differential times between SKKS and SKS. A smooth 3D image is obtained from inverting SKS d waveforms displaying rolling-hills with elongated dome-like structures sitting on the CMB. The most prominent one has an 80-km height, ~8° length, and ~4° width, thus adding still more structural complexity to the lower mantle. We suggest that these results can be explained by a dynamically-stabilized material containing small amounts (~5%) iron-rich (Mg,Fe)O providing a self-consistent physical interpretation.

Sun, Daoyuan↗
DOE OSTI2014

Resonant diffraction gratings for spatial differentiation of optical beams

Diffraction of a two-dimensional optical beam from a resonant diffraction grating is considered. It is shown that at certain resonance parameters the diffraction grating allows for spatial differentiation and integration of the incident beam. The parameters of the diffraction grating for spatial differentiation of optical beams in the transmission geometry are calculated. It is shown that the differentiating diffraction grating allows the conversion of the two-dimensional beam into the two-dimensional Hermite – Gaussian mode. The presented results of numerical modelling are in good agreement with the proposed theoretical description. The use of the considered resonant diffraction gratings is promising for solving the problems of all-optical data processing. (laser applications and other topics in quantum electronics)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Anisotropic broadening of XRD peaks of α′-Fe: Williamson-Hall and Warren-Averbach analysis using full width at half maximum (FWHM) and integral breadth (IB)

Highlights: • There is a limited increase in the dislocation density in the martensite from the center to the surface of the specimen. • Both FWHM and Integral Breadth (IB) follows Conventional-WH model for undeformed material. • Significant perturbation from linearity observed for higher order peaks in deformed material • Between FWHM and IB-approach, the modified-WH model provides a better response with the FWHM-approach than IB-approach. - Abstract: The anisotropic broadening of the X-ray diffraction (XRD) peaks of shear deformed martensite (α′-Fe), using both full-width at half-maximum (FWHM) and integral breadth (IB), has been studied following conventional and modified Williamson-Hall (WH) and Warren-Averbach (WA) analysis. The crystallographic study reveals limited plastic deformation of martensite (α′) within a shallow depth from the shear surface, as indicated by marginal change in the character and density of dislocation, showing the inability of the α′-phase to accommodate the strain energy of shear deformation. More importantly, the study reveals significant perturbation of modified-WH and WA model, when IB is considered for size and strain analysis, especially for higher order peaks, whereas, FWHM shows reasonably good agreement with the above mentioned models for the range of diffraction spectrum considered.

36 MATERIALS SCIENCE↗
DOE OSTI2018

MS–STEM–FEM: A parallelized multi-slice fluctuation TEM simulation tool

Atomic configurations of glassy or amorphous materials containing medium-range order (MRO) may be identified by comparing fluctuation transmission electron microscopy (FTEM) measurements to FTEM simulations obtained using model configurations. Candidate model sizes have traditionally been much thinner than the samples measured experimentally, and publicly available FTEM simulation software has until now omitted microscope parameters, dynamical scattering, and the phase of the diffracted electron wave. We introduce MS–STEM–FEM, an open-source software package for simulating FTEM experiments using established multi-slice TEM simulation techniques to emulate experiment more closely by incorporating microscope parameters and simulating electron scattering and propagation as a complex valued wave. Simulations using established models are compared with results of experimental STEM–FEM to validate the software. Several statistical measures of diffraction are implemented and their responses to model features are compared. Dynamical scattering is found to be less influential than the variety of crystallite orientations which occur in thicker models. Simulations of variable resolution microscopy confirm that cumulative intensity of the FTEM signal decreases with reduced model MRO and increased coherence volume. In conclusion, advantageous model scaling characteristics and efficient processor performance scaling are demonstrated, along with a study of convergence with respect to pertinent simulation parameters to identify accuracy requirements.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Electron- and light-induced stimulated Raman spectroscopy for nanoscale molecular mapping

We propose and theoretically analyze a new vibrational spectroscopy, termed electron- and light-induced stimulated Raman (ELISR) scattering, that combines the high spatial resolution of elec-tron microscopy with the molecular sensitivity of surface-enhanced Raman spectroscopy. WithELISR, electron-beam excitation of plasmonic nanoparticles is utilized as a spectrally-broadband butspatially-confined Stokes beam in the presence of a diffraction-limited pump laser. To characterizethis technique, we develop a numerical model and conduct full-field electromagnetic simulations toinvestigate two distinct nanoparticle geometries, nanorods and nanospheres, coated with a Raman-active material. Our results show the significant (10 6 -10 7 ) stimulated Raman enhancement that isachieved with dual electron and optical excitation of thesenanoparticle geometries. Importantly,the spatial resolution of this vibrational spectroscopy for electron microscopy is solely determinedby the nanoparticle geometry and the plasmon mode volume. Our results highlight the promiseof ELISR for simultaneous high-resolution electron microscopy with sub-diffraction-limited Ramanspectroscopy, complementing advances in superresolutionmicroscopy, correlated light and electronmicroscopy, and vibrational electron energy loss spectroscopy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Effect of thickness and Ti interlayers on stresses and texture transformations in thin Ag films during thermal cycling

The driving forces for the (111) to (100) texture transformation often observed during annealing of thin face-centered cubic metal films were investigated. Thin passivated silver films were produced with and without Ti adhesion layers. Stresses were measured in situ during heating to induce the texture transformation, and the texture was characterized using x-ray diffraction. Sufficiently thin films did not transform and sufficiently thick films transformed fully. Intermediate thickness films transformed to an extent dependent on thickness, leading to stable mixed textures. In the prevailing thermodynamic model, texture transformation is attributed to minimization of strain and interface energies. However, calculations using the measured stresses, known elastic constants, and estimated interface energies in this model reveal that the stresses are not sufficient to cause the texture transformation and, furthermore, that variations in interface energy cannot lead to the observed behavior. The results suggest that neither the interface energy nor the stress plays decisive roles in the texture transformation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Cu site differentiation in tetracopper(I) sulfide clusters enables biomimetic N 2 O reduction

Copper clusters feature prominently in both metalloenzymes and synthetic nanoclusters that mediate catalytic redox transformations of gaseous small molecules. Such reactions are critical to biological energy conversion and are expected to be crucial parts of renewable energy economies. However, the precise roles of individual metal atoms within clusters are difficult to elucidate, particularly for cluster systems that are dynamic under operating conditions. Here, we present a metal site-specific analysis of synthetic Cu 4 (μ 4 -S) clusters that mimic the Cu Z active site of the nitrous oxide reductase enzyme. Leveraging the ability to obtain structural snapshots of both inactive and active forms of the synthetic model system, we analyzed both states using resonant X-ray diffraction anomalous fine structure (DAFS), a technique that enables X-ray absorption profiles of individual metal sites within a cluster to be extracted independently. Using DAFS, we found that a change in cluster geometry between the inactive and active states is correlated to Cu site differentiation that is presumably required for efficient activation of N 2 O gas. More precisely, we hypothesize that the Cu δ+ ∙∙∙Cu δ- pairs produced upon site differentiation are poised for N 2 O activation, as supported by computational modeling. These results provide an unprecedented level of detail on the roles of individual metal sites within the synthetic cluster system and how those roles interplay with cluster geometry to impact the reactivity function. We expect this fundamental knowledge to inform understanding of metal clusters in settings ranging from (bio)molecular to nanocluster to extended solid systems involved in energy conversion.

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

Disorder and hydrogenation in graphene nanopowder revealed by complementary X-ray and neutron scattering

Functionalization of graphene's two-dimensional sheets can be used to modify the physical properties of graphene, such as changing its conductivity or inducing ferromagnetism, which is of broad interest for a myriad of applications. However, functionalized graphene can possess significant structural disorder that is often overlooked and is difficult to characterize quantitatively. Here we investigate hydrogenated graphene nanopowder (H-Gr) produced by Birch reduction of graphene oxide. By combining complementary x-ray and neutron diffraction, we show how to quantitatively characterize the H-Gr nanostructure, including the hydrogen content. Further, we show that the majority of the H-Gr consists of highly disordered molecular-scale carbon while a small portion of the sample contains few-layered graphene having an expanded interlayer spacing. Modeling the coherent diffuse scattering for both x-ray and neutron diffraction, and comparing it with the incoherent neutron scattering, the hydrogen to carbon ratio was measured and it was determined that most of the hydrogen resides within the disordered carbon rather than in the graphene. Evidence is presented for hydrogen clustering as well as for hydrogen bonded perpendicular to the plane of molecular-carbon bonds. Our quantitative approach to characterizing carbon nanopowders has broad relevance to understanding disorder and bonding of hydrogen in graphitic carbons and other nanomaterials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Complete the Design of Benchtop Fiber-Optic Based Photo-Thermal Radiometry System

Thermal transport properties of nuclear fuels, i.e., thermal conductivity and diffusivity, are critical parameters in the thermal design of a nuclear reactor. It is well known that thermal transport properties change temporally and spatially due to dynamic microstructural evolution as a result of neutron irradiation. A real-time instrument to monitor the local thermal property change, which can survive the harsh in-pile environment, will give researchers unprecedented access to fuel behavior during irradiation. Laser-based photothermal techniques are an ideal candidate to accomplish this specific task, because of the remote, non-contact, and non-destructive features. In this report, we present the progress in the development of a bench-top photothermal radiometry (PTR) system to measure the thermal diffusivity of solid samples, and the preliminary design of a fiber-based PTR instrument to measure the real-time, in-pile thermal diffusivity of nuclear fuels. The PTR technique measures the local temperature response from a modulated heat source by detecting the sample radiation heat flux. Initially a well-developed thermal wave analytical model was fit to the data to obtain the thermal diffusivity. However, systematic errors from the diffraction effect and non-linearity issues resulted in thermal diffusivity measurements higher than literature values. These effects have been studied and an improved analytical model has been developed, and the physics behind the phenomena are still under investigation. A procedure for optimizing measurements from the bench-top system has been provided. The experiences from the bench top measurement were then used to guide the fiber-based system.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗