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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
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Comparison of Acoustic Models and Trajectory Generation Methods for an Acoustically-Aware Aircraft

Motivation - Noise management is one of the major barriers to Urban Air Mobility - Approaches to noise mitigation (non-exhaustive) - Vehicle configuration - Directivity control via propeller phase synchronization - Trajectory optimization Objective - Create framework for trajectory generation integrating location-based acoustic metrics and vehicle performance limitations - Multiple trajectory optimization methods and acoustic noise models - Mission-relevant constraints - Mission duration, airspace restrictions, ... - Vehicle dynamic constraints - Aircraft structural limitations, min/max airspeed, ... - Vehicle separation/obstacle avoidance - Acoustic constraints at a number of discrete observer locations

Kasey A Ackerman↗
DOE OSTI2013

Mitigation of two-plasmon decay in direct-drive inertial confinement fusion through the manipulation of ion-acoustic and Langmuir wave damping

The extended Zakharov model of the two-plasmon decay instability in an inhomogeneous plasma [D. F. DuBois et al., Phys. Rev. Lett. 74, 3983 (1995); D. A. Russell and D. F. DuBois, Phys. Rev. Lett. 86, 428 (2001)] is further generalized to include the evolution of the electron distribution function in the quasi-linear approximation [cf., e.g., K. Y. Sanbonmatsu et al. Phys. Plasmas 7, 2824 (2000); D. A. Russell et al., paper presented at the Workshop on SRS/SBS Saturation, Wente Vineyards, Livermore, CA, 2–5 April 2002]. This makes it possible to investigate anomalous absorption of laser light and hot electron production due to the two-plasmon decay instability of multiple overlapping electromagnetic waves. Scalings of hot-electron production in the (stationary) nonlinearly saturated regime relevant to recent experiments [B. Yaakobi et al., Phys. Plasmas 19, 012704 (2012); D. H. Froula et al., Phys. Rev. Lett. 108, 165003 (2012)] have been obtained. They indicate a sensitivity to ion-acoustic wave (IAW) damping and to the collisional absorption of Langmuir waves. Such a sensitivity might be exploited in inertial confinement fusion target design by the use of mid-Z ablators.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Switchable and tunable film bulk acoustic resonator fabricated using barium strontium titanate active layer and Ta{sub 2}O{sub 5}/SiO{sub 2} acoustic reflector

A solidly mounted acoustic resonator was fabricated using a Ba{sub 0.60}Sr{sub 0.40}TiO{sub 3} (BST) film deposited by metal organic chemical vapor deposition. The device was acoustically isolated from the substrate using a Bragg reflector consisting of three pairs of Ta{sub 2}O{sub 5}/SiO{sub 2} layers deposited by chemical solution deposition. Transmission electron microscopy verified that the Bragg reflector was not affected by the high temperatures and oxidizing conditions necessary to process high quality BST films. Electrical characterization of the resonator demonstrated a quality factor (Q) of 320 and an electromechanical coupling coefficient (K{sub t}{sup 2}) of 7.0% at 11 V.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Heat-induced drift reduction of time of flight in fused quartz acoustic waveguides via annealing process

High temperature structural acoustic sensors play an important role in many applications. Fused quartz waveguide is a popular choice due to its resistance to harsh environments and its convenience of modification. However, time of flight between pulse and echo, which is widely used in these sensors, tends to encounter drifts in fast temperature changing process even after temperature returns to initial value. In this article, different annealing process are performed for a special modified fused quartz waveguide with a sensor node. Annealing treatment is found able to reduce the drift when the waveguide undergoes a sudden temperature spike to 1000 °C at 500 kHz operating acoustic frequency, and the best annealing condition could make the drift one magnitude smaller. A following temperature test up to 1000 °C shows consistent measurement readings.

Hileman, Zachary (ORCID:0000000226529274)↗
DOE OSTI2017

Electron-acoustic solitons and double layers in the inner magnetosphere: ELECTRON-ACOUSTIC SOLITONS

The Van Allen Probes observe generally two types of electrostatic solitary waves (ESW) contributing to the broadband electrostatic wave activity in the nightside inner magnetosphere. ESW with symmetric bipolar parallel electric field are electron phase space holes. The nature of ESW with asymmetric bipolar (and almost unipolar) parallel electric field has remained puzzling. To address their nature, we consider a particular event observed by Van Allen Probes to argue that during the broadband wave activity electrons with energy above 200 eV provide the dominant contribution to the total electron density, while the density of cold electrons (below a few eV) is less than a few tenths of the total electron density. We show that velocities of the asymmetric ESW are close to velocity of electron-acoustic waves (existing due to the presence of cold and hot electrons) and follow the Korteweg-de Vries (KdV) dispersion relation derived for the observed plasma conditions (electron energy spectrum is a power law between about 100 eV and 10 keV and Maxwellian above 10 keV). The ESW spatial scales are in general agreement with the KdV theory. We interpret the asymmetric ESW in terms of electron-acoustic solitons and double layers (shocks waves).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Mechanism of acoustically induced diffusional structuring of surface adatoms

Physical mechanisms of time-averaged structuring of adatoms induced by a standing surface acoustic wave (SAW) on a solid substrate are studied. Despite some similarity with conventional mechanisms based on averaging of fast oscillation-type motion or radiation-pressure effects, we demonstrate that, for diffusional (i.e., strongly damped) adatom motion, the origin of time-averaged structuring is essentially different. The proposed analytical model and kinetic Monte–Carlo (kMC) simulations reveal several distinct structuring regimes and directly relate them to the transient modification of diffusion barriers and adiabatic temperature variations induced by SAW strains.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Acoustically determined linear piezoelectric response of lithium niobate up to 1100 V

We present a method to measure high voltages using the piezoelectric crystal lithium niobate without using voltage dividers. A 36° Y-X cut lithium niobate crystal was coupled to two acoustic transducers, where direct current voltages were applied from 128–1100 V. The time-of-flight through the crystal was determined to be linearly dependent on the applied voltage. A model was developed to predict the time-delay in response to the applied voltage. The results show a sensitivity of 17 fs/V with a measurement error of 1 fs/V was achievable using this method. The sensitivity of this method can be increased by measuring the acoustic wave after multiple passes through the crystal. This method has many advantages over traditional techniques such as: favorable scalability for larger voltages, ease of use, cost effectiveness, and compactness.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Subwavelength acoustic focusing by surface-wave-resonance enhanced transmission in doubly negative acoustic metamaterials

We present analytical and numerical analyses of a yet unseen lensing paradigm that is based on a solid metamaterial slab in which the wave excitation source is attached. We propose and demonstrate sub-diffraction-limited acoustic focusing induced by surface resonant states in doubly negative metamaterials. The enhancement of evanescent waves across the metamaterial slab produced by their resonant coupling to surface waves is evidenced and quantitatively determined. The effect of metamaterial parameters on surface states, transmission, and wavenumber bandwidth is clearly identified. Based on this concept consisting of a wave source attached on the metamaterial, a high resolution of λ/28.4 is obtained with the optimum effective physical parameters, opening then an exciting way to design acoustic metamaterials for ultrasonic focused imaging.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Ion acoustic and dust acoustic waves at finite size of plasma particles

We consider the influence of the finite size of ions on the properties of classic plasmas. We focus our attention at the ion acoustic waves for electron-ion plasmas. We also consider the dusty plasmas where we account the finite size of ions and particles of dust and consider the dispersion of dust acoustic waves. The finite size of particles is a classical effect as well as the Coulomb interaction. The finite size of particles considerably contributes to the properties of the dense plasmas in the small wavelength limit. Low temperature dense plasmas, revealing the quantum effects, are also affected by the finite size of plasma particles. Consequently, it is important to consider the finite size of ions in the quantum plasmas as well.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Gyrokinetic particle simulation of beta-induced Alfven-acoustic eigenmode

The beta-induced Alfven-acoustic eigenmode (BAAE) in toroidal plasmas is verified and studied by global gyrokinetic particle simulations. When ion temperature is much lower than electron temperature, the existence of the weakly damped BAAE is verified in the simulations using initial perturbation, antenna excitation, and energetic particle excitation, respectively. When the ion temperature is comparable to the electron temperature, the unstable BAAE can be excited by realistic energetic particle density gradient, even though the stable BAAE (in the absence of energetic particles) is heavily damped by the thermal ions. In the simulations with reversed magnetic shear, BAAE frequency sweeping is observed and poloidal mode structure has a triangle shape with a poloidal direction similar to that observed in tokamak experiments. Here, the triangle shape changes the poloidal direction, and no frequency sweeping is found in the simulations with normal magnetic shear.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

DIASCoPE: Directly integrated acoustic system combined with pressure experiments—A new method for fast acoustic velocity measurements at high pressure

A novel experimental system to measure elastic wave velocities in samples in situ under extreme conditions of pressure and temperature in a multi-anvil apparatus has been installed at Beamline 6-BM-B of the Advanced Photon Source at Argonne National Laboratory. This system allows for measurement of acoustic velocities via ultrasonic interferometry, and makes use of the synchrotron beam to measure sample densities via X-ray diffraction and sample lengths using X-radiographic imaging. This system is fully integrated into the automated software controls of the beamline and is capable of collecting robust data on elastic wave travel times in less than 1 s, which is an improvement of more than one to two orders of magnitude over existing systems. Moreover, this fast data collection time has been shown to have no effect on the obtained travel time results. This allows for more careful study of time-dependent phenomena with tighter snapshots in time of processes that would otherwise be lost or averaged out in other acoustic measurement systems.

Whitaker, Matthew L.↗
DOE OSTI2018

Constraints on dark energy dynamics and spatial curvature from Hubble parameter and baryon acoustic oscillation data

We use all available baryon acoustic oscillation distance measurements and Hubble parameter data to constrain the cosmological constant Λ, dynamical dark energy, and spatial curvature in simple cosmological models. Here, we find that the consensus spatially flat ΛCDM (Λ cold dark matter) model provides a reasonable fit to the data, but depending on the Hubble constant prior and cosmological model, it can be a little more than 1σ away from the best-fitting model, which can favour mild dark energy dynamics or non-flat spatial hypersurfaces.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Baryon acoustic oscillation, Hubble parameter, and angular size measurement constraints on the Hubble constant, dark energy dynamics, and spatial curvature

ABSTRACT In this paper, we use all available baryon acoustic oscillation, Hubble parameter, and quasar angular size data to constrain six dark energy cosmological models, both spatially flat and non-flat. Depending on the model and data combination considered, these data mildly favour closed spatial hypersurfaces (by as much as 1.7σ) and dark energy dynamics (up to a little over 2σ) over a cosmological constant Λ. The data also favour, at 1.8σ to 3.4σ, depending on the model and data combination, a lower Hubble constant than what is measured from the local expansion rate.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Bispectrum as baryon acoustic oscillation interferometer

The galaxy bispectrum, measuring excess clustering of galaxy triplets, offers a probe of dark energy via baryon acoustic oscillations (BAOs). However up to now it has been severely underused due to the combinatorically explosive number of triangles. Here we exploit interference in the bispectrum to identify triangles that amplify BAOs. Here, this approach reduces the computational cost of estimating covariance matrices, offers an improvement in BAO constraints equivalent to lengthening BOSS by 30% and simplifies adding bispectrum BAO information to future large-scale redshift survey analyses.

47 OTHER INSTRUMENTATION↗