Engineering Papers⌕ Search

SEARCH · Engineering Papers

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Orientation epitaxy of Ge 1–x Sn x films grown on single crystal CaF 2 substrates

Ge 1–x Sn x films were grown via physical vapor deposition below the crystallization temperature of Ge on single crystal (111) and (100) CaF 2 substrates to assess the role of Sn alloying in Ge crystallization. By studying samples grown at several growth temperatures ranging from 250 °C to 400 °C we report temperature-dependent trends in several of the films' properties. X-ray diffraction theta vs. two-theta (θ/2θ) scans indicate single orientation Ge 1–x Sn x (111) films are grown on CaF 2 (111) substrates at each temperature, while a temperature-dependent superposition of (111) and (100) orientations are exhibited in films grown on CaF2(100) above 250 °C. This is the first report of (111) oriented Ge 1–x Sn x grown on a (100) oriented CaF 2 substrate, which is successfully predicted by a superlattice area matching model. These results are confirmed by X-ray diffraction pole figure analysis. θ/2θ results indicate substitutional Sn alloying in each film of about 5%, corroborated by energy dispersive spectroscopy. In addition, morphological and electrical properties are measured by scanning electron microscopy, atomic force microscopy and Hall mobility measurements and are also shown to be dependent upon growth temperature.

36 MATERIALS SCIENCE↗
NASA NTRS1993

A prediction model of signal degradation in LMSS for urban areas

A prediction model of signal degradation in a Land Mobile Satellite Service (LMSS) for urban areas is proposed. This model treats shadowing effects caused by buildings statistically and can predict a Cumulative Distribution Function (CDF) of signal diffraction losses in urban areas as a function of system parameters such as frequency and elevation angle and environmental parameters such as number of building stories and so on. In order to examine the validity of the model, we compared the percentage of locations where diffraction losses were smaller than 6 dB obtained by the CDF with satellite visibility measured by a radiometer. As a result, it was found that this proposed model is useful for estimating the feasibility of providing LMSS in urban areas.

Matsudo, Takashi↗
DOE OSTI2014

S4: A spatial-spectral model for speckle suppression

High dynamic range imagers aim to block or eliminate light from a very bright primary star in order to make it possible to detect and measure far fainter companions; in real systems, a small fraction of the primary light is scattered, diffracted, and unocculted. We introduce S4, a flexible data-driven model for the unocculted (and highly speckled) light in the P1640 spectroscopic coronagraph. The model uses principal components analysis (PCA) to capture the spatial structure and wavelength dependence of the speckles, but not the signal produced by any companion. Consequently, the residual typically includes the companion signal. The companion can thus be found by filtering this error signal with a fixed companion model. The approach is sensitive to companions that are of the order of a percent of the brightness of the speckles, or up to 10{sup –7} times the brightness of the primary star. This outperforms existing methods by a factor of two to three and is close to the shot-noise physical limit.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Advanced 3D Characterization and Reconstruction of Reactor Materials FY16 Final Report

A coordinated effort to link advanced materials characterization methods and computational modeling approaches is critical to future success for understanding and predicting the behavior of reactor materials that operate at extreme conditions. The difficulty and expense of working with nuclear materials have inhibited the use of modern characterization techniques on this class of materials. Likewise, mesoscale simulation efforts have been impeded due to insufficient experimental data necessary for initialization and validation of the computer models. The objective of this research is to develop methods to integrate advanced materials characterization techniques developed for reactor materials with state-of-the-art mesoscale modeling and simulation tools. Research to develop broad-ion beam sample preparation, high-resolution electron backscatter diffraction, and digital microstructure reconstruction techniques; and methods for integration of these techniques into mesoscale modeling tools are detailed. Results for both irradiated and un-irradiated reactor materials are presented for FY14 - FY16 and final remarks are provided.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

Exploring the Links between Structural Distortions, Orbital Ordering, and Multipolar Magnetic Ordering in Double Perovskites Containing Re(VI) and Os(VII)

A combination of high-resolution powder diffraction techniques and solid-state NMR has been employed to explore the links between crystal structure, orbital ordering, and magnetism in three isostructural double perovskites containing transition metal ions with a 5d 1 configuration. In Ba 2 ZnReO 6 , both neutron and synchrotron X-ray powder diffraction data reveal a cubic-to-tetragonal transition at 23 K that breaks the degeneracy of the t 2g orbitals and leads to a pattern of orbital ordering that stabilizes magnetic ordering when the sample is cooled below 16 K. Similar behavior is observed in Ba 2 MgReO 6 , with an orbital ordering temperature of 33 K and a magnetic ordering temperature of 18 K. Prior theoretical works suggest that the pattern of orbital order seen in the P42/mnm space group is needed to stabilize the heavily canted antiferromagnetism of these compounds. Unfortunately, powder diffraction data is not sensitive enough to differentiate between the I4/mmm and P42/mnm structural models, as the distortions are too subtle to be unambiguously identified from either neutron or synchrotron X-ray powder diffraction methods. In contrast, both diffraction and 7 Li NMR data indicate that Ba 2 LiOsO 6 retains the cubic structure down to 1.7 K. The antiferromagnetic ground state and lack of any sign of orbital ordering in Ba 2 LiOsO 6 provide compelling evidence that the electronically driven tetragonal distortion seen in Ba2ZnReO6, and Ba2MgReO6 is intimately linked to the magnetic ordering seen in those compounds. The absence of magnetic reflections in high intensity neutron powder diffraction data collected on Ba 2 MgReO 6 strongly suggests ordering of multipolar moments on Re(VI), likely ferro-octupolar ordering.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Application of differential resonant high-energy X-ray diffraction to three-dimensional structure studies of nanosized materials: A case study of Pt–Pd nanoalloy catalysts

Atoms in many of the increasingly complex nanosized materials of interest to science and technology do not necessarily occupy the vertices of Bravais lattices. The atomic scale structure of such materials is difficult to determine by traditional X-ray diffraction and so their functional properties remain difficult to optimize by rational design. Here, the three-dimensional structure of Pt x Pd 100– x nanoalloy particles is determined, where x = 0, 14, 36, 47, 64 and 100, by a non-traditional technique involving differential resonant high-energy X-ray diffraction experiments conducted at the K edge of Pt and Pd. The technique is coupled with three-dimensional modeling guided by the experimental total and element-specific atomic pair distribution functions. Furthermore, using DFT (density functional theory) calculation based on the positions of atoms in the obtained three-dimensional structure models, the catalytic performance of Pt–Pd particles is explained. Furthermore, differential resonant high-energy X-ray diffraction is shown to be an excellent tool for three-dimensional structure studies of nanosized materials. The experimental and modeling procedures are described in good detail, to facilitate their wider usage.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Simulation of nonlinear propagation of biomedical ultrasound using PZFlex and the KZK Texas code

In biomedical ultrasound nonlinear acoustics can be important in both diagnostic and therapeutic applications and robust simulations tools are needed in the design process but also for day-to-day use such as treatment planning. For most biomedical application the ultrasound sources generate focused sound beams of finite amplitude. The KZK equation is a common model as it accounts for nonlinearity, absorption and paraxial diffraction and there are a number of solvers available, primarily developed by research groups. We compare the predictions of the KZK Texas code (a finite-difference time-domain algorithm) to an FEM-based commercial software, PZFlex. PZFlex solves the continuity equation and momentum conservation equation with a correction for nonlinearity in the equation of state incorporated using an incrementally linear, 2nd order accurate, explicit algorithm in time domain. Nonlinear ultrasound beams from two transducers driven at 1 MHz and 3.3 MHz respectively were simulated by both the KZK Texas code and PZFlex, and the pressure field was also measured by a fibre-optic hydrophone to validate the models. Further simulations were carried out a wide range of frequencies. The comparisons showed good agreement for the fundamental frequency for PZFlex, the KZK Texas code and the experiments. For the harmonic components, the KZK Texas code was in good agreement with measurements but PZFlex underestimated the amplitude: 32% for the 2nd harmonic and 66% for the 3rd harmonic. The underestimation of harmonics by PZFlex was more significant when the fundamental frequency increased. Furthermore non-physical oscillations in the axial profile of harmonics occurred in the PZFlex results when the amplitudes were relatively low. These results suggest that careful benchmarking of nonlinear simulations is important.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Quantum Bohm correction to polarization spectrum of graphene

In this paper, by using a quantum hydrodynamic plasma model which incorporates the important quantum statistical pressure and electron diffraction force, we present the corrected plasmon dispersion relation for graphene which includes a k{sup 4} quantum term arising from the collective electron density wave interference effects. This correction may well describe the shortcoming of the previous results based on the classical hydrodynamics and confirms that the quantum hydrodynamic model may be as effective as the random phase approximation in successful description of the collective density excitations in quantum plasmas. It is clearly observed that the quantum correction due to the collective interaction of electron waves gives rise to significant contribution in the dispersion behavior of the collective plasmon density waves in a wide range of wavelength, as a fundamental property of the monolayer atom-thick graphene. It is revealed that the plasmon density-perturbation linear phase-speed in graphene possesses some universal minimum characteristic value, in the absence of an external magnetic field. It is further remarked that such correction also has important effect on the dielectric function, hence on the impurity screening, in graphene.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2016

A Computationally-Efficient, Multi-Mechanism Based Framework for the Comprehensive Modeling of the Evolutionary Behavior of Shape Memory Alloys

The report summarizes the accomplishments made during the 4-year duration of the project. Here, the major emphasis is placed on the different tasks performed by the two research teams; i.e., the modeling activities by the University of Akron (UA) team and the experimental and neutron diffraction studies conducted by the University of Central Florida (UCF) team, during this 4-year period. Further technical details are given in the upcoming sections by UA and UCF for each of the milestones/years (together with the corresponding figures and captions).The project majorly involved the development, validation, and application of a general theoretical model that is capable of capturing the nonlinear hysteretic responses, including pseudoelasticity, shape memory effect, rate-dependency, multi-axiality, asymmetry in tension versus compression response of shape memory alloys. Among the targeted goals for the SMA model was its ability to account for the evolutionary character response (including transient and long term behavior under sustained cycles) for both conventional and high temperature (HT) SMAs, as well as being able to simulate some of the devices which exploit these unique material systems. This required extensive (uniaxial and multi-axial) experiments needed to guide us in calibrating and characterizing the model. Moreover, since the model is formulated on the theoretical notion of internal state variables (ISVs), neutron diffraction experiments were needed to establish the linkage between the micromechanical changes and these ISVs. In addition, the design of the model should allow easy implementation in large scale finite element application to study the behavior of devices making use of these SMA materials under different loading controls. Summary of the activities, progress/achievements made during this period is given below in details for the University of Akron and the University (Section 2.0) of Central Florida (Section 3.0).

Alloys↗
DOE OSTI2016

Calculation of Debye-Scherrer diffraction patterns from highly stressed polycrystalline materials

Calculations of Debye-Scherrer diffraction patterns from polycrystalline materials have typically been done in the limit of small deviatoric stresses. Although these methods are well suited for experiments conducted near hydrostatic conditions, more robust models are required to diagnose the large strain anisotropies present in dynamic compression experiments. A method to predict Debye-Scherrer diffraction patterns for arbitrary strains has been presented in the Voigt (iso-strain) limit [Higginbotham, J. Appl. Phys. 115, 174906 (2014)]. Here, we present a method to calculate Debye-Scherrer diffraction patterns from highly stressed polycrystalline samples in the Reuss (iso-stress) limit. This analysis uses elastic constants to calculate lattice strains for all initial crystallite orientations, enabling elastic anisotropy and sample texture effects to be modeled directly. The effects of probing geometry, deviatoric stresses, and sample texture are demonstrated and compared to Voigt limit predictions. An example of shock-compressed polycrystalline diamond is presented to illustrate how this model can be applied and demonstrates the importance of including material strength when interpreting diffraction in dynamic compression experiments.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

A finite element formulation for deformation twinning induced strain localization in polycrystal magnesium alloys

Deformation twinning induces shear strain localization in hexagonal close-packed crystals and is critical for the material’s ductility and failure. Cracks often occur at twin-twin or twin-grain boundary intersections and propagate along twin bands. However, most crystal plasticity models for deformation twinning are based on a “pseudo-slip” approach and do not capture the localized deformation associated with the formation of each discrete twin band. The few exceptions are discrete twin models that involve very complex numerical algorithms and are often compromised in accuracy due to the numerical convergence. These factors make the discrete twin models hard to adopt. This paper proposes a modification to the conventional finite element weak form, to fully incorporate a twin-induced heterogeneous deformation that does not depend on the “pseudo-slip” assumption. The model starts by splitting the deformation gradient into elastic-slip-twinning components. The twin-induced deformation gradient component is computed separately by solving a microstructural evolution problem and then implemented into finite element weak form by constructing a global “twin-force” vector. The constitutive update (e.g., in the user-defined material subroutine, or UMAT, for ABAQUS) therefore avoids dealing with the twinning and recovers to the form of a regular slip-based crystal plasticity model. The results presented here indicate that the twin-induced strain localization and the associated stress-reversal phenomena near the twin band were naturally captured in the model, which was validated against an in-situ synchrotron X-ray micro-diffraction experiment.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Anisotropic lattice thermal expansion of PbFeBO{sub 4}: A study by X-ray and neutron diffraction, Raman spectroscopy and DFT calculations

Highlights: • Mullite-type PbFeBO{sub 4} shows uni-axial negative coefficient of thermal expansion. • Anisotropic thermal expansion of the metric parameters was modeled using modified Grüneisen approximation. • The model includes harmonic, quasi-harmonic and intrinsic anharmonic contributions to the internal energy. • DFT calculation, temperature- and pressure-dependent Raman spectra help understand the phonon decay and associated anharmonicity. - Abstract: The lattice thermal expansion of mullite-type PbFeBO{sub 4} is presented in this study. The thermal expansion coefficients of the metric parameters were obtained from composite data collected from temperature-dependent neutron and X-ray powder diffraction between 10 K and 700 K. The volume thermal expansion was modeled using extended Grüneisen first-order approximation to the zero-pressure equation of state. The additive frame of the model includes harmonic, quasi-harmonic and intrinsic anharmonic potentials to describe the change of the internal energy as a function of temperature. The unit-cell volume at zero-pressure and 0 K was optimized during the DFT simulations. Harmonic frequencies of the optical Raman modes at the Γ-point of the Brillouin zone at 0 K were also calculated by DFT, which help to assign and crosscheck the experimental frequencies. The low-temperature Raman spectra showed significant anomaly in the antiferromagnetic regions, leading to softening or hardening of some phonons. Selected modes were analyzed using a modified Klemens model. The shift of the frequencies and the broadening of the line-widths helped to understand the anharmonic vibrational behaviors of the PbO{sub 4}, FeO{sub 6} and BO{sub 3} polyhedra as a function of temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Application of a modified method of ultrasonic measurements for determination of elastic moduli of rocks

The velocities of elastic waves with quasi-longitudinal and quasi-transverse polarizations in a spherical rock sample have been measured. The experimental values of velocities are used to calculate 21 elastic moduli of the sample. For comparison, the effective elastic properties of the sample are simulated based on the data on the crystallographic textures of rock-forming minerals obtained by neutron diffraction. It is shown that the largest discrepancy between the model predictions and experimental velocity values is observed for transversely polarized waves.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effects of Low Concentrations of Docosahexaenoic Acid on the Structure and Phase Behavior of Model Lipid Membranes

In this paper we report an X-ray diffraction study on the phase behavior of binary lipid mixtures of 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphoethanolamine (DHA-PE) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) at low concentrations below 5.0 mol% DHA-PE. Our results show that DHA-PE induces phase separation into a DHA rich liquid crystalline (L α ) phase and a DHA poor gel (L β' ) phase at overall DHA-PE concentrations as low as 0.1 mol%. In addition, we find that the structure of the L β' phase, from which the DHA-PE molecules are largely excluded, is modified in the phase separated state at low DHA-PE concentrations, with a decrease in bilayer thickness of 1.34 nm for 0.1 mol% at room temperature, compared to pure DPPC bilayers. This result is contrary to that seen in similar studies on mono-unsaturated lipids where an increase in bilayer thickness is observed. The surprising effect of such low DHA-PE concentrations on membrane structure may be important in understanding the role of highly polyunsaturated lipids in biological membrane-based structures and similar artificial surfactant systems.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Effects of MnO doping on the electronic properties of zinc oxide: 406 GHz electron paramagnetic resonance spectroscopy and Newman superposition model analysis

MnO-doped ZnO ceramics have been synthesized through the conventional ceramic processing route. Mn{sup 2+} ions have been incorporated into the ZnO lattice within the limits of solid solubility. By using X-band-frequency and high-field electron paramagnetic resonance (EPR), we have resolved some of the main electronic transitions for the S = 5/2, I = 5/2 high-spin system and have determined accurately the EPR spin-Hamiltonian parameters. By combining data from crystallographic X-ray diffraction and EPR with the semi-empirical Newman superposition model, we have found the local configurational position of Mn{sup 2+} and have confirmed the symmetry of the lattice. The results presented in this contribution indicate that Mn ions substitute at Zn sites in ZnO. The effect of Mn{sup 2+} ions on the intrinsic defects becomes remarkable, thus the vacancy related intrinsic defect signals cannot be visible in the EPR spectrum. MnO doping affects the band gap energy of ZnO system which was confirmed via UV-Vis spectroscopy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Fidelity-preserving enhancement of ptychography with foundational text-to-image models

Ptychographic phase retrieval enables high-resolution imaging of complex samples but often suffers from artifacts such as grid pathology and multislice crosstalk, which degrade reconstructed images. We propose a plug-and-play (PnP) framework that integrates physics model-based phase retrieval with text-guided image editing using foundational diffusion models. By employing the alternating direction method of multipliers, our approach ensures consensus between data fidelity and artifact removal subproblems, maintaining physical consistency while enhancing image quality. Artifact removal is achieved using a text-guided diffusion image editing method (LEDITS++) with a pre-trained foundational diffusion model, allowing users to specify artifacts for removal in natural language. Demonstrations on simulated and experimental datasets show significant improvements in artifact suppression and structural fidelity, validated by metrics such as peak signal-to-noise ratio and diffraction pattern consistency. This work highlights the combination of text-guided generative models and model-based phase retrieval algorithms as a transferable and fidelity-preserving method for high-quality diffraction imaging.

image editing↗
NASA NTRS1987

Experiments on the applicability of MAE techniques for predicting sound diffraction by irregular terrains

The sound field diffracted by a single smooth hill of finite impedance is studied both analytically, within the context of the theory of Matched Asymptotic Expansions (MAE), and experimentally, under laboratory scale modeling conditions. Special attention is given to the sound field on the diffracting surface and throughout the transition region between the illuminated and the shadow zones. The MAE theory yields integral equations that are amenable to numerical computations. Experimental results are obtained with a spark source producing a pulse of 42 microsec duration and about 130 Pa at 1 m. The insertion loss of the hill is inferred from measurements of the acoustic signals at two locations in the field, with subsequent Fourier analysis on an IBM PC/AT. In general, experimental results support the predictions of the MAE theory, and provide a basis for the analysis of more complicated geometries.

Berthelot, Yves H.↗