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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Cutting-edge issues of core-collapse supernova theory

Based on multi-dimensional neutrino-radiation hydrodynamic simulations, we report several cutting-edge issues about the long-veiled explosion mechanism of core-collapse supernovae (CCSNe). In this contribution, we pay particular attention to whether three-dimensional (3D) hydrodynamics and/or general relativity (GR) would or would not help the onset of explosions. By performing 3D simulations with spectral neutrino transport, we show that it is more difficult to obtain an explosion in 3D than in 2D. In addition, our results from the first generation of full general relativistic 3D simulations including approximate neutrino transport indicate that GR can foster the onset of neutrino-driven explosions. Based on our recent parametric studies using a light-bulb scheme, we discuss impacts of nuclear energy deposition behind the supernova shock and stellar rotation on the neutrino-driven mechanism, both of which have yet to be included in the self-consistent 3D supernova models. Finally we give an outlook with a summary of the most urgent tasks to extract the information about the explosion mechanisms from multi-messenger CCSN observables.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

X-ray diffraction on the X-cut of a Ca{sub 3}TaGa{sub 3}Si{sub 2}O{sub 14} single crystal modulated by a surface acoustic wave

The result of X-ray diffraction study on a single crystal of the calcium-gallogermanate family Ca{sub 3}TaGa{sub 3}Si{sub 2}O{sub 14} (CTGS) modulated by a surface acoustic wave (SAW) is presented. The power flow angle for SAW propagating along the X{sub 2} axis of the X-cut in CTGS was measured. The rocking curves for the CTGS crystal were recorded at different amplitudes of an input high frequency electric signal on interdigital transducer used to excite a SAW. Based on the data obtained, intensity dependence of diffraction satellites on the amplitude of electric signal exciting a SAW was built. Numerical simulation of the crystal rocking curves and dependence of diffraction satellite intensities on the SAW amplitude enabled the selection of a set of material constants at which the most complete coincidence of experimental and calculated results is observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Refractive index of r-cut sapphire under shock pressure range 5 to 65 GPa

High-pressure refractive index of optical window materials not only can provide information on electronic polarizability and band-gap structure, but also is important for velocity correction in particle-velocity measurement with laser interferometers. In this work, the refractive index of r-cut sapphire window at 1550 nm wavelength was measured under shock pressures of 5–65 GPa. The refractive index (n) decreases linearly with increasing shock density (ρ) for shock stress above the Hugoniot elastic limit (HEL): n = 2.0485 (± 0.0197) − 0.0729 (± 0.0043)ρ, while n remains nearly a constant for elastic shocks. This behavior is attributed to the transition from elastic (below HEL) to heterogeneous plastic deformation (above HEL). Based on the obtained refractive index-density relationship, polarizability of the shocked sapphire was also obtained.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

A cut cell method for the 3D simulation of Crookes radiometer

Devices involved in engineering applications, such as vacuum pumps or MEMS, may be made of several moving parts. This raise the issue of the simulation of rarefied gas flow around moving boundaries. We propose a simple process, known as cut cell method, to treat the motion of a solid body in the framework of the deterministic solving of a kinetic equation. Up to our knowledge, this is the first time that this approach has been used for this kind of simulations. The method is illustrated by the 2D and 3D simulations of a Crookes radiometer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Energy efficiency, human behavior, and economic growth: Challenges to cutting energy demand to sustainable levels

Increasing energy efficiency in households, transportation, industries, and services is an important strategy to reduce energy service demand to levels that allow the steep reduction of greenhouse gases, and a full fledged switch of energy systems to a renewable basis. Yet, technological efficiency improvements may generate so-called rebound effects, which may ‘eat up’ parts of the technical savings potential. This article provides a comprehensive review of existing research on these effects, raises critiques, and points out open questions. It introduces micro-economic rebound effect and suggests extending consumer-side analysis to incorporate potential ‘psychological rebound effects.’ It then discusses meso-economic rebound effects, i.e. producer-side and market-level rebounds, which so far have achieved little attention in the literature. Finally, the article critically reviews evidence for macro-economic rebound effects as energy efficiency-induced economic growth impacts. For all three categories, the article summarizes assessments of their potential quantitative scope, while pointing out remaining methodological weaknesses and open questions. As a rough “rule of thumb”, in the long term and on gross average, only half the technical savings potential of across-the-board efficiency improvements may actually be achieved in the real world. Policies that aim at cutting energy service demand to sustainable levels are well advised to take due note of detrimental behavioral and economic growth impacts, and should foster policies and measures that can contain them.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2015

Theoretical analysis of surface acoustic wave propagating properties of Y-cut nano lithium niobate film on silicon dioxide

The surface acoustic wave (SAW) propagating characteristics of Y-cut nano LiNbO{sub 3} (LN) film on SiO{sub 2}/LN substrate have been theoretically calculated. The simulated results showed a shear horizontal (SH) SAW with enhanced electromechanical coupling factor K{sup 2} owing to a dimensional effect of the nanoscale LN film. However, a Rayleigh SAW and two other resonances related to thickness vibrations caused spurious responses for wideband SAW devices. These spurious waves could be fully suppressed by properly controlling structural parameters including the electrode layer height, thickness, and the Euler angle (θ) of the LN thin film. Finally, a pure SH SAW was obtained with a wide θ range, from 0° to 5° and 165° to 180°. The largest K{sup 2} achieved for the pure SH SAW was about 35.1%. The calculated results demonstrate the promising application of nano LN film to the realization of ultra-wideband SAW devices.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Bessel beam transformation in c-cuts of uniaxial crystals by varying the source wavelength

Transformation of Bessel beam of a zero order to Bessel beam of the second order in c-cut of CaCO{sub 3} crystal is experimentally investigated. Possibility of output beam control at changing of wavelength and using of a diffraction axicon is shown. Full transformation of beams at changing of wavelength Δλ=1.5 nanometers is received at initial wavelength λ=637.5 nanometers for a crystal of CaCO{sub 3} with 15 mm long and a diffraction axicon with period of 2 microns. The theoretical value of necessary wavelength changing is Δλ=1.7 nanometers that is according with experimental results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Second harmonic microscopy of poled x-cut thin film lithium niobate: Understanding the contrast mechanism

Thin film lithium niobate has been of great interest recently, and an understanding of periodically poled thin films is crucial for both fundamental physics and device developments. Second-harmonic (SH) microscopy allows for the noninvasive visualization and analysis of ferroelectric domain structures and walls. While the technique is well understood in bulk lithium niobate, SH microscopy in thin films is largely influenced by interfacial reflections and resonant enhancements, which depend on film thicknesses and substrate materials. We present a comprehensive analysis of SH microscopy in x-cut lithium niobate thin films, based on a full three-dimensional focus calculation and accounting for interface reflections. We show that the dominant signal in backreflection originates from a copropagating phase-matched process observed through reflections, rather than direct detection of the counterpropagating signal as in bulk samples. We simulate the SH signatures of domain structures by a simple model of the domain wall as an extensionless transition from a −χ(2) to a +χ(2) region. This allows us to explain the main observation of domain structures in the thin-film geometry, and, in particular, we show that the SH signal from thin poled films allows to unambiguously distinguish areas, which are completely or only partly inverted in depth.

Rüsing, M. (ORCID:0000000346824577)↗
DOE OSTI2020

Poling thin-film x-cut lithium niobate for quasi-phase matching with sub-micrometer periodicity

Quasi-phase-matched grating structures in lithium niobate waveguides with sub-micrometer periodicities will benefit the development of short-wavelength nonlinear optical devices. Here, we report on the reproducible formation of periodically poled domains in x-cut single-crystalline thin-film lithium niobate with periodicities as short as 600 nm. Shaped single-voltage poling pulses were applied to electrode structures that were fabricated by a combination of electron-beam and direct-writing laser lithography. Evidence of successful poling with good quality was obtained through second-harmonic microscopy and piezoresponse force microscopy imaging. For the sub-micrometer period structures, we observed patterns with a double periodicity formed by domain interactions and features with sizes <200 nm.

Zhao, Jie (ORCID:0000000306230125)↗
DOE OSTI2017

Spectral and power characteristics of a 5% Tm : KLu(WO{sub 4}){sub 2}N{sub m}-cut minislab laser passively Q-switched by a Cr{sup 2+} : ZnSe crystal

Laser characteristics of a 5%Tm : KLu(WO{sub 4}){sub 2} N{sub m}-cut minislab laser passively Q-switched by a Cr{sup 2+} : ZnSe saturable absorber are presented. At a pump power of 21 W, the average laser power at a wavelength of 1.91 μm was 3.2 W (pulse duration 35 ns, pulse energy 0.3 mJ). The maximum slope efficiency of the laser in the Q-switched regime was 31%; the loss in power with respect to the cw regime did not exceed 17%. At pump powers above 15 W, the dependence of the output power in the Q-switched regime on the pump power considerably differed from linear, which was explained by the formation of a thermal lens in the saturable absorber volume. The experimental energies and durations of laser pulses well agree with the values calculated from rate equations. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Cutting edge research and new technologies in heat and mass transfer processes of refrigeration and air conditioning systems

This special edition of the Science and Technology for the Built Environment (STBE) presents eight selected articles originally presented at the 17th International Refrigeration and Air Conditioning Conference held at Purdue University, West Lafayette, IN, USA, during July 9–12, 2018. All eight articles were significantly expanded with additional technical content and received full peer review before being finally accepted for publication in this special issue of the STBE. The eight articles in this special issue cover a wide range of topics from condensation and evaporation of low global warming potential (LGWP) refrigerants to phase change material storage for personal cooling systems, from frosting on hydrophilic and hydrophobic coated surfaces to geometry optimization of heat exchanger fins. Furthermore, these articles describe cutting-edge research and feasibility studies of new technologies that were recently investigated for refrigeration and air conditioning applications.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2017

Sequential computation of elementary modes and minimal cut sets in genome-scale metabolic networks using alternate integer linear programming

Elementary (flux) modes (EMs) have served as a valuable tool for investigating structural and functional properties of metabolic networks. Identification of the full set of EMs in genome-scale networks remains challenging due to combinatorial explosion of EMs in complex networks. It is often, however, that only a small subset of relevant EMs needs to be known, for which optimization-based sequential computation is a useful alternative. Most of the currently available methods along this line are based on the iterative use of mixed integer linear programming (MILP), the effectiveness of which significantly deteriorates as the number of iterations builds up. To alleviate the computational burden associated with the MILP implementation, we here present a novel optimization algorithm termed alternate integer linear programming (AILP). Results: Our algorithm was designed to iteratively solve a pair of integer programming (IP) and linear programming (LP) to compute EMs in a sequential manner. In each step, the IP identifies a minimal subset of reactions, the deletion of which disables all previously identified EMs. Thus, a subsequent LP solution subject to this reaction deletion constraint becomes a distinct EM. In cases where no feasible LP solution is available, IP-derived reaction deletion sets represent minimal cut sets (MCSs). Despite the additional computation of MCSs, AILP achieved significant time reduction in computing EMs by orders of magnitude. The proposed AILP algorithm not only offers a computational advantage in the EM analysis of genome-scale networks, but also improves the understanding of the linkage between EMs and MCSs.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Investigation of oscillations above the acoustic cut-off frequency for a sample of Kepler stars. II. Identifying temporal frequency shifts

ABSTRACT Stellar oscillations with frequencies greater than the acoustic cut-off frequency are not trapped within the star’s interior. Geometric interference between these high-frequency waves produces a peak-like structure in the power spectrum of the star, known as the pseudo-modes. In this study, we aim to analyse 51 stars previously identified (from a sample of 91 Kepler stars) to contain statistically significant evidence for pseudo-modes, to determine if the pseudo-mode frequencies vary in time. We obtained these frequency variations and the uncertainty by the resampled periodogram approach, where periodogram realisations were created from successive, overlapping 90-d time segments, and a cross-correlation function was generated between them. The computed shifts were compared against temporal p-mode frequency shifts and a stellar magnetic activity proxy, $S_{\mathrm{ph}}$. We found that for 16 per cent of the stars pseudo-mode frequency shifts were significantly anticorrelated with p-mode shifts, as is the case for the Sun. However, we also found pseudo-mode and p-mode shifts to be significantly correlated in-phase in 8 per cent of our sample. The remainder showed no significant correlation. We also searched for trends between the maximum variation of pseudo-mode frequency shifts and stellar parameters. Whilst we found no correlation between the maximum variation and stellar photospheric and chromospheric proxies, we found frequency variations to have a greater amplitude for cooler and slower rotating stars, which is in opposition to p-mode frequency shift variation. Temporal changes to pseudo-mode frequencies may be attributable to variations in stellar magnetic activity, and therefore can contribute to our understanding of stellar activity cycles.

Millson, L. J. (ORCID:0009000342542676)↗
DOE OSTI2020

Twinned nanostructure of VO 2 thin films grown on r-cut sapphire

Due to strong electron-phonon interactions, strain engineering is a powerful tool to control quantum critical phenomena in strongly correlated oxides. Exploring this possibility requires understanding the nanoscale structure of quantum materials and the role it plays in forming the strain landscape. In this work, we used a combination of x-ray nanoimaging and reciprocal space mapping to study the nanostructure of the archetypal Mott insulator VO 2 featuring an insulator-to-metal and structural phase transitions. We found that VO 2 thin films grown on r-cut sapphire consist of two intertwined crystal lattices, permanently inclined with respect to each other. This persistent pattern of twin domains stands out from the symmetry breaking induced by the structural phase transition and conceivably originates from the post-growth strain relaxation process. We propose a model explaining the formation of twin domains and the emergence of anisotropy in the film nanostructure. Our work suggests using miscut substrates to suppress either one or the other twin that can serve as a new tool to control strain in VO 2 films.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Burton-Cabrera-Frank theory for the influence of off-cut direction on the growth of hcp crystals

The precise direction of the off-cut of a vicinal crystal surface determines the azimuth (in-plane angle) of the surface steps and thus their kink density. Here we develop a Burton-Cabrera-Frank (BCF) theory for step-flow crystal growth that includes the effects of step azimuth. We focus on the basal-plane surfaces of hexagonal close-packed (hcp) and related crystal structures, for which surface steps have alternating properties that depend on azimuth. We build on a previous treatment that considered only a single-step azimuth, 𝜙 = 0, that gives alternating steps of pure A and B type. As 𝜙 increases from zero, the density of kinks on the steps increases. For hcp-type crystals, in addition the structural difference between alternating steps decreases, until they become equivalent at 𝜙 = 30°. We consider the azimuth dependence of the step transparency, attachment, and repulsion parameters of the BCF model, including the effects of both geometrically required and thermally generated kinks. Example calculations are presented that demonstrate the overall effect of step azimuth on BCF predictions for step spacings during steady-state growth and for their dynamics during growth transients. Effects of symmetric and asymmetric step-step repulsion are discussed.

Ju, Guangxu↗
DOE OSTI2016

Vortex cutting in superconductors

Vortex cutting and reconnection is an intriguing and still-unsolved problem central to many areas of classical and quantum physics, including hydrodynamics, astrophysics, and superconductivity. Here, in this paper, we describe a comprehensive investigation of the crossing of magnetic vortices in superconductors using time dependent Ginsburg-Landau modeling. Within a macroscopic volume, we simulate initial magnetization of an anisotropic high temperature superconductor followed by subsequent remagnetization with perpendicular magnetic fields, creating the crossing of the initial and newly generated vortices. The time resolved evolution of vortex lines as they approach each other, contort, locally conjoin, and detach, elucidates the fine details of the vortex-crossing scenario under practical situations with many interacting vortices in the presence of weak pinning. Finally, our simulations also reveal left-handed helical vortex instabilities that accompany the remagnetization process and participate in the vortex crossing events.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Analyzer-based X-ray phase contrast imaging using the forward-diffracted o-beam in a few-millimetre-thick Bragg-case asymmetrically cut crystal

An analyzer-based X-ray phase contrast imaging experiment employing the forward-diffracted o-beam in a few-millimetre-thick Bragg-case asymmetrically cut analyzer crystal has been implemented and tested in a geometry similar to that used in conventional radiography. The high angular stability requirements were overcome using specially designed crystals and a closed-loop feedback intensity system, monitoring the intensity of the diffracted h-beam. Analyzer-based images (ABis) taken at different angular positions on the forward-diffracted o-beam rocking curve show different contrasts, as expected. However, the ABis did not show sharp borders. This was closely investigated by X-ray topography and Δ d / d mapping and was attributed to the stresses caused by the analyzer crystal's own weight in the bulk. Further investigation of the crystal design using finite element analysis coupled with dynamical theory of X-ray diffraction is envisaged.

Honnicke, Marcelo Goncalves (ORCID:000000033276432↗
DOE OSTI2025

Temperature and Strain Sensing Characteristics of a 128° YX-Cut LiNbO 3 Rayleigh-Mode SAW Sensor From Room to Cryogenic Temperatures

Accurate, passive, and wireless monitoring of cryogenic hardware is essential for high-energy physics, space propulsion, and biomedical instrumentation. Here, this study quantifies the coupled temperature-strain behavior of Rayleigh-mode surface acoustic-wave (SAW) delay-line sensors fabricated on 128° YX-cut LiNbO 3 . A nonlinear finite element (FE) model incorporating Varshni-based elastic constants, higher-order thermal expansion, and temperature-dependent piezo- and dielectric coefficients was developed and validated experimentally between 280K and 80K. Free-standing (first test condition) and bonded/wired (second test condition) devices exhibited indistinguishable thermal responses; the average temperature coefficient of delay (TCD) in the critical cryogenic range from 130K down to 80K differed by only 0.15 ppm/K (0.32%), confirming that bonding-induced stress is negligible. Over 280-80K the measured TCD was 61.77 ppm/K, while the FE model predicted an equivalent temperature coefficient of frequency (TCF) of −62.74 ppm/K with an overall coefficient of determination R2 = 0.998. In the critical cryogenic interval 130-80K the TCD fell to 47.66 ppm/K, indicating improved thermal stability at low temperature. Controlled loading (0-300 με) revealed a strain coefficient of delay (SCD) that rises from 0.53 ± 0.02 ppm/με at 300K to 1.05 ± 0.02 ppm/με at 80K. This modest sensitivity confirms that, for temperature sensing, strain is a second-order perturbation above 135K but must be compensated at deeper cryogenic levels. Overall, this work establishes a predictive multiphysics model together with repeatable wired measurements that confirm the suitability of SAW sensors for temperature and strain monitoring in extreme cryogenic environments, while also providing a baseline for future wireless implementations.

25 ENERGY STORAGE↗