Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “SCATTERING AMPLITUDES”

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 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Phased Microphone Array on Aircraft Fuselage

This paper studies some challenging features for phased microphone arrays on aircraft fuselage, including the effects of sound scattering such as refraction by nonuniform boundary layer flows, reflection by curved surfaces, and diffraction by sharp edges and smooth geometry. The objective is to show if and how source locations and source amplitudes can be accurately captured by the array data analysis, in the presence of these features. The study starts with canonical problems to separately examine the individual features, making use of their respective analytical solutions, which provide exact results for all quantities needed for the array data processing. To simulate realistic flight environments, a generic aircraft geometry is then utilized, involving multiple scattering mechanisms and multiple noise sources to model aircraft engine noise. For this application, numerical solutions are computed to provide noise propagation and scattering from the sources to the microphones, as well as the quantities needed for array data analysis. The study reveals the effects of various features on fuselage-mounted arrays and provides guidelines to account for these effects in array data analysis.

Yueping Guo↗
NASA NTRS1974

Flow tracing fidelity of scattering aerosol in laser Doppler velocimetry

An experimental method for determinating the flow tracing fidelity of a scattering aerosol used in laser Doppler velocimeters was developed with particular reference to the subsonic turbulence measurements. The method employs the measurement of the dynamic response of a flow seeding aerosol excited by acoustic waves. The amplitude and frequency of excitation were controlled to simulate the corresponding values of fluid turbulence components. Experimental results are presented on the dynamic response of aerosols over the size range from 0.1 to 2.0 microns in diameter and over the frequency range 100 Hz to 100 kHz. It was observed that unit density spherical scatterers with diameters of 0.2 microns followed subsonic air turbulence frequency components up to 100 kHz with 98 percent fidelity.

Mazumder, M. K.↗
DOE OSTI2013

Self-focusing and stimulated Brillouin back-scattering of a long intense laser pulse in a finite temperature relativistic plasma

The nonlinear dynamics of electromagnetic waves propagating through a plasma considering the effects of relativistic mass and ponderomotive nonlinearities is investigated. The modified electron density distribution, the dispersion relation, and the spatial profiles of electromagnetic wave amplitude in the plasma are obtained. It is shown that the cut-off frequency decreases, and there is an intensity range in which the ponderomotive self-focusing takes place. In the upper limit of this range, the laser beam is defocused due to the relativistic ponderomotive force. In addition, the stability of electromagnetic waves to stimulated Brillouin scattering is studied, and the backscattered wave resulting from decay of high power electromagnetic beam is resolved in relativistic regime. The study of effects of electron density and temperature on the growth rate of backscattered wave has been shown that by increasing these effects, the growth rate of instability increases.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Theory for time-resolved resonant inelastic x-ray scattering

Time-resolved measurements of materials provide a wealth of information on quasiparticle dynamics, and have been the focus of optical studies for decades. In this paper, we develop a theory for explicitly evaluating time-resolved resonant inelastic x-ray scattering (tr-RIXS). We apply the theory to a noninteracting electronic system and reveal the particle-hole spectrum and its evolution during the pump pulse. With a high-frequency pump, the frequency and amplitude dependence analysis of the spectra agrees well with the steady-state assumptions and Floquet excitations. When the pump frequency is low, the spectrum extracts real-time dynamics of the particle-hole continuum in momentum space. These results verify the correctness of our theory and demonstrate the breadth of physical problems that tr-RIXS could shed light on.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A high-resolution analytical scanning transmission electron microscopy study of the early stages of spinodal decomposition in binary Fe–Cr

Spinodal decomposition (SD) is an important phenomenon in materials science and engineering. For example, it is considered to be responsible for the 475 °C embrittlement of stainless steels comprising the bcc (ferrite) or bct (martensite) phases. Structural characterization of the evolving minute nano-scale concentration fluctuations during SD in the Fe–Cr system is, however, a notable challenge, and has mainly been considered accessible via atom probe tomography (APT) and small-angle neutron scattering. The standard tool for nanostructure characterization, viz. transmission electron microscopy (TEM), has only been successfully applied to late stages of SD when embrittlement is already severe. However, we here demonstrate that the structural evolution in the early stages of SD in binary Fe–Cr, and alloys based on the binary, are accessible via analytical scanning TEM. An Fe–36 wt% Cr alloy aged at 500 °C for 1, 10 and 100 h is investigated using an aberration-corrected microscope and it is found that highly coherent and interconnected Cr-rich regions develop. The wavelength of decomposition is rather insensitive to the sample thickness and it is quantified to 2, 3 and 6 nm after ageing for 1, 10 and 100 h, which is in reasonable agreement with prior APT analysis. The concentration amplitude is more sensitive to the sample thickness and acquisition parameters but the TEM analysis is in good agreement with APT analysis for the longest ageing time. These findings open up for combinatorial TEM studies where both local crystallography and chemistry is required. - Highlights: • STEM-EELS analysis was successfully applied to resolve early stage SD in Fe–Cr. • Compositional wavelength measured with STEM-EELS compares well to previous ATP studies. • Compositional amplitude measured with STEM-EELS is a function of experimental parameters. • STEM-EELS allows for combinatorial studies of SD using complementary techniques.

36 MATERIALS SCIENCE↗
DOE OSTI2019

EXAFS Spectroscopy of Fractional Mixed-Valence Charge Density Wave Systems

We present extended X-ray absorption fine structure (EXAFS) spectra and modeling of a series of structurally tunable quasi-one-dimensional mixed-valence platinum–halide linear chain materials, [Pt(en 2 )][Pt(en 2 )X 2 ](ClO 4 ) 4 with X = Cl, Br, I. The materials exhibit a commensurate charge density wave with fractional charge states on alternating platinum ions in the chain, as well as a Peierls distortion with alternating platinum–halide bond lengths. The amplitude of the charge density wave and, correspondingly, the extent of the Peierls distortion are controlled by the identity of the bridging halide ion. We have carried out ab initio multiple scattering calculations using the FEFF9 code to relate the oriented Pt L III EXAFS spectra to the tunable electronic and structural properties. The spectral modeling reveals distinct photoelectron threshold energy values for the two inequivalent platinum ions in each of the mixed-valence chains, with values that vary systematically with fractional valence state. The difference in the photoelectron threshold energies of the two inequivalent platinum ions within each material correlates directly with the amplitude of the charge density wave, reflecting the decrease in charge density wave strength through the halide series X = Cl, Br, and I. We use dynamical matrix modeling to relate the experimentally determined mean-square relative displacement parameters for the metal–halide bond distances to the chain–axis vibrational modes that modulate the charge density wave structure. In addition, we discuss the EXAFS fitting results for the Pt–I bond lengths in the [Pt(en 2 )][Pt(en 2 )I 2 ](ClO 4 ) 4 complex in comparison to previous, mutually inconsistent structural determinations for this material.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Electric field directed formation of aligned conjugated polymer fibers

Alternating current (AC) electric fields effectively align poly (3-alkylthiophene) (P3AT) fibers during a one-dimensional crystallization process. Structural, mechanical and electrical properties have been probed using microscopy, small angle neutron scattering (SANS), atomic force microscopy (AFM), x-ray diffraction (XRD), rheology, UV-vis spectroscopy, and dielectric spectroscopy. Optimum frequency and amplitudes were identified for specific P3AT concentrations and for variable solvent quality. Optical microscopy along with SANS and XRD demonstrate alignment persists over both micrometer and nanometer length scales. Small amplitude oscillatory shear rheology also showed that the shear modulus increased for aligned fibers. The structural changes were correlated to improvements in electric conductivity as probed by dielectric spectroscopy. XRD experiments performed with variable sample orientations also showed that the P3HT stacking direction was aligned parallel to the direction of the fiber axis. Electric field alignment was also possible for other alkyl-thiophene polymers and for polymers with simple backbone repeat units.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

The SRG/eROSITA All-Sky Survey: Dark Energy Survey year 3 weak gravitational lensing by eRASS1 selected galaxy clusters

Context. Number counts of galaxy clusters across redshift are a powerful cosmological probe if a precise and accurate reconstruction of the underlying mass distribution is performed – a challenge called mass calibration. With the advent of wide and deep photometric surveys, weak gravitational lensing (WL) by clusters has become the method of choice for this measurement. Aims. We measured and validated the WL signature in the shape of galaxies observed in the first three years of the Dark Energy Survey (DES Y3) caused by galaxy clusters and groups selected in the first all-sky survey performed by SRG (Spectrum Roentgen Gamma)/eROSITA (eRASS1). These data were then used to determine the scaling between the X-ray photon count rate of the clusters and their halo mass and redshift. Methods. We empirically determined the degree of cluster member contamination in our background source sample. The individual cluster shear profiles were then analyzed with a Bayesian population model that self-consistently accounts for the lens sample selection and contamination and includes marginalization over a host of instrumental and astrophysical systematics. To quantify the accuracy of the mass extraction of that model, we performed mass measurements on mock cluster catalogs with realistic synthetic shear profiles. This allowed us to establish that hydrodynamical modeling uncertainties at low lens redshifts (z < 0.6) are the dominant systematic limitation. At high lens redshift, the uncertainties of the sources’ photometric redshift calibration dominate. Results. With regard to the X-ray count rate to halo mass relation, we determined its amplitude, its mass trend, the redshift evolution of the mass trend, the deviation from self-similar redshift evolution, and the intrinsic scatter around this relation. Conclusions. The mass calibration analysis performed here sets the stage for a joint analysis with the number counts of eRASS1 clusters to constrain a host of cosmological parameters. We demonstrate that WL mass calibration of galaxy clusters can be performed successfully with source galaxies whose calibration was performed primarily for cosmic shear experiments, opening the way for the cluster cosmological exploitation of future optical and NIR surveys like Euclid and LSST.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Low-frequency whistler waves in quiescent runaway electron plasmas

In quiescent runaway electron plasmas in the DIII-D tokamak, whistler waves with frequencies between 90 and 200 MHz are driven unstable in plasmas with appreciable hard x-ray and non-thermal electron cyclotron emission (ECE). Narrow (δf < 50 kHz) discrete modes with erratically spaced frequencies are observed. Unstable modes often extend over a range Δf ≃ 50 MHz but lower frequency unstable modes are usually most intense. The dependency of the frequency on field and density implies a wavenumber k ≃ 150 m -1 with parallel wavenumber k ∥ < k. Results show that reducing the gap between the plasma and the wall increases the number of detected modes. Lowering the magnetic field promotes instability. Nonlinear limit-cycle-like oscillations in the whistler amplitude occur on a 10 ms timescale. The ECE signals often jump at whistler bursts, suggesting that the modes pitch-angle scatter the runaways. Additionally, sawteeth cause transient stabilization of the whistlers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

A Physical Basis for M s -Yield Scaling in Hard Rock and Implications for Late-Time Damage of the Source Medium

Surface wave magnitude M s for a compilation of 72 nuclear tests detonated in hard rock media for which yields and burial depths have been reported in the literature is shown to scale with yield W as a + b × log[W], where a = 2.50 ± 0.08 and b = 0.80 ± 0.05. While the exponent b is consistent with an M s scaling model for fully coupled, normal containment-depth explosions, the intercept a is offset 0.45 magnitude units lower than the model. The cause of offset is important to understand in terms of the explosion source. Hard rock explosions conducted in extensional and compressional stress regimes show similar offsets, an indication that the tectonic setting in which an explosion occurs plays no role causing the offset. The scaling model accounts for the effects of source medium material properties on the generation of 20-s period Rayleigh wave amplitudes. Aided by thorough characterizations of the explosion and tectonic release sources, an extensive analysis of the 1963 October 26 Shoal nuclear test detonated in granite 27 miles southeast of Fallon NV shows that the offset is consistent with the predictions of a material damage source model related to non-linear stress wave interactions with the free surface. This source emits Rayleigh waves with polarity opposite to waves emitted by the explosion. The Shoal results were extended to analyse surface waves from the 1962 February 15 Hardhat nuclear test, the 1988 September 14 Soviet Joint Verification Experiment, and the anomalous 1979 August 18 northeast Balapan explosion which exhibits opposite polarity, azimuth-independent source component U1 compared to an explosion. Modelling these tests shows that Rayleigh wave amplitudes generated by the damage source are nearly as large as or larger than amplitudes from the explosion. As such, destructive interference can be drastic, introducing metastable conditions due to the sensitivity of reduced amplitudes to Rayleigh wave initial phase angles of the explosion and damage sources. This meta-stability is a likely source of scatter in M s -yield scaling observations. The agreement of observed scaling exponent b with the model suggests that the damage source strength does not vary much with yield, in contrast to explosions conducted in weak media where Ms scaling rates are greater than the model predicts, and the yield dependence of the damage source strength is significant. This difference in scaling behaviour is a consequence of source medium material properties.

58 GEOSCIENCES↗
DOE OSTI2020

Angle-resolved nonresonant two-photon single ionization of argon using 9.3-eV photons produced via high-order harmonic generation

Here we present an experimental study on the photoionization dynamics of nonresonant one-color two-photon single valence ionization of neutral argon atoms. Using 9.3-eV photons produced via high harmonic generation and a three-dimensional momentum imaging spectrometer, we detect the photoelectrons and ions produced from nonresonant two-photon ionization in coincidence. Photoionization from the $3p$ orbital produces a photoelectron scattering wave function with $p$- and $f$-partial-wave components, which interfere and result in a photoelectron angular distribution with peak amplitude perpendicular to the vacuum ultraviolet polarization. The comparison between the present results and the two previous sets of theoretical calculations [Phys. Rev. A 44, 324 (1991), and J. Phys. B: At. Mol. Phys. 16, 2737 (1983)] indicates that electron-electron correlation contributes appreciably to the two-photon ionization dynamics.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1972

Observations of sunspot umbral velocity oscillations.

Review of sunspot umbral velocity measurements obtained free from any cross talk introduced by photospheric and penumbral scattered light by using lines formed only in the sunspot umbrae and showing no Zeeman effect. The maximum peak-to-peak amplitude of the umbral oscillatory velocity component is found to be of the order of 0.5 km per sec.

Bhatnagar, A.↗
NASA NTRS1983

EXOS-B/Siple station VLF wave-particle interaction experiments. II - Transmitter signals and associated emissions

New observations in the magnetosphere of coherent VLF waves from the Siple Station, Antarctica, transmitter and associated VLF emissions triggered by the transmitter signals are reported. The data analyzed were acquired on the EXOS-B high-altitude satellite during the period July 15-September 7, 1979, during joint VLF wave-injection experiments involving scientists from Kyoto, Tokyo, and Stanford universities. The experiments were carried out to gain a deeper understanding of the interactions between coherent VLF waves and energetic particles in the magnetosphere, in particular, the whistler-mode instability through which both natural and stimulated VLF emissions are produced. Analysis of the emission-triggering events provides strong evidence that the triggering took place inside whistler-mode ducts and that the emissions reached the satellite only after being scattered at one end of the ducts by ionospheric irregularities. It is concluded that in the noon sector of the magnetosphere, the amplitude of nonducted signals from the Siple transmitter is generally less than the threshold level necessary for triggering in the nonducted mode.

Bell, T. F.↗
NASA NTRS1987

Interferogram analysis using Fourier transform techniques

A method of interferogram analysis is described in which Fourier transform techniques are used to map the complex fringe visibility in several types of interferograms. Algorithms are developed for estimation of both the amplitude and the phase of the fringes (yielding the modulus and the phase of the holographically recorded object Fourier transform). The algorithms were applied to the reduction of interferometric seeing measurements (i.e., the estimation of the fringe amplitude only), and the reduction of interferometric tests (i.e., estimation of the fringe phase only). The method was used to analyze scatter-plate interferograms obtained at NOAO.

Roddier, Claude↗
NASA NTRS1999

Fatigue Failure Criteria for Single Crystal Nickel Superalloys

High Cycle Fatigue (HCF) induced failures in aircraft gas-turbine and rocket engine turbopump blades is a pervasive problem. Single crystal turbine blades are being utilized in rocket engine turbopumps and jet engines throughout industry and NASA because of their superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys. Single-crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the pan geometry a significant factor in the overall analysis. The failure modes of single crystal turbine blades is complicated to predict due to the material orthotropy and variations in crystal orientations. A fatigue failure criteria based on the maximum shear stress amplitude [delta t max] on the 30 slip systems, is presented for single crystal nickel superalloys (FCC crystal). This criteria reduces the scatter in uniaxial LCF test data, for four different specimen orientations, for PWA 1484 at 1200 F in air, quite well. A power law curve fit of the failure parameter, delta t max, vs. cycles to failure is presented.

Arakere, Nagaraj K.↗
DOE OSTI2021

Detection, monitoring, and determination of location of changes in metallic structures using multimode acoustic signals

Acoustic transducers generate and receive acoustic signals at multiple locations along a surface of rigid structure, wherein longitudinal spacing between transducer locations define measurement zones. Acoustic signals with chosen amplitude-time-frequency characteristics excite multiple vibration modes in the structure within each zone. Small mechanical changes in inspection zones lead to scattering and attenuation of broadband acoustic signals, which are detectable as changes in received signal characteristics as part of a through-transmission technique. Additional use of short, narrowband pulse acoustic signals as part of a pulse-echo technique allows determination of the relative location of the mechanical change within each zone based on the differential delay profiles. For accurate acoustic modeling and simulation, the mesh size, time step, time delay, and time-window size are optimized. Frequency normalization of the Short-Time Fourier Transform of acoustic response output improves experiment-simulation cross-validation. Applications of the method to structures with arbitrarily complex geometries are also demonstrated.

Findikoglu, Alp Tugrul↗
DOE OSTI2022

Preparation for a Measurement of Charge Asymmetry in the Bethe-Heitler Process

We have prepared a measurement of the energy asymmetry in wide- and medium-angle electron/positron pair production off protons and heavy targets. This asymmetry is caused by the interference between the first- and second-order Born diagrams and the Compton scattering diagram. It directly probes aspects of QED, as well as providing a direct measurement of the real part of the Compton amplitude. It will be conducted at the HI??S facility at Duke University, using a 60 MeV photon beam. This dissertation serves as documentation of the preparation stage of the Bethe-Heitler experiment. The major was the recommissioning of the vertical drift chambers previously used in the Q-weak experiment at the Jefferson Lab. Cosmic test runs were conducted, drift time data were collected and efficiency plateaus were measured. We made modifications to the JLAB Hall A analyzer to suit the geometry and drift characteristics of these wire chambers. The analyzer was used for the reconstruction of the trajectories of cosmic ray test runs with the results confirmed by direct measurement of trigger geometry. Spatial and angular resolution is estimated to ~300?? and 0.17° respectively. Geant 4 simulations with generated Bethe-Heitler pairs satisfying theoretical differential cross sections. It was used to check detector acceptance, optimize apparatus layout, and estimate measurable energy asymmetry. The measurable asymmetries from electron/positron pairs with polar angles around between approximately 5° and 8°, azimuthal angles differing by 180°, and energy differing by approximately 9 MeV to 15 MeV are predicted to be above 10%. The kinematics of primary vertices are reconstructed using the data from wire chambers in the simulation. The energy resolution is determined to be better than 1MeV.

Chen, Haoyu↗
DOE OSTI2017

Study of the grazing-incidence X-ray scattering of strongly disturbed fractal surfaces

The applicability of different approaches to the description of hard X-ray scattering from rough surfaces is generally limited by a maximum surface roughness height of no more than 1 nm. Meanwhile, this value is several times larger for the surfaces of different materials subjected to treatment, especially in the initial treatment stages. To control the roughness parameters in all stages of surface treatment, a new approach has been developed, which is based on a series expansion of wavefield over the plane eigenstate-function waves describing the small-angle scattering of incident X-rays in terms of plane q-waves propagating through the interface between two media with a random function of relief heights. To determine the amplitudes of reflected and transmitted plane q-waves, a system of two linked integral equations was derived. The solutions to these equations correspond (in zero order) to the well-known Fresnel expressions for a smooth plane interface. Based on these solutions, a statistical fractal model of an isotropic rough interface is built in terms of root-mean-square roughness σ, two-point correlation length l, and fractal surface index h. The model is used to interpret X-ray scattering data for polished surfaces of single-crystal cadmium telluride samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗