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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Diagnosis of the ion density in two discharge modes generated in atmospheric pressure argon with pin-to-plate dielectric barrier geometry

In this study, the ion densities of an ac dielectric barrier discharge (DBD) (that is, a pin-to-plate DBD) as a function of the applied frequency in argon have been studied by means of the plasma radiation. The pin-to-plate DBD shows the characteristic of radiation oscillations with a low-frequency wave hidden in a high-frequency wave to form a mosaic structure, which reveals the coexistence of two discharge modes in the ac barrier discharge, i.e., the streamer mode and the corona mode. According to the oscillation frequencies, the ion densities are calculated. The results show that the ion density in streamer discharge is higher than that in corona discharge for about 1-2 magnitude orders.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Acoustic phonon dynamics in thin-films of the topological insulator Bi{sub 2}Se{sub 3}

Transient reflectivity traces measured for nanometer-sized films (6–40 nm) of the topological insulator Bi{sub 2}Se{sub 3} revealed GHz-range oscillations driven within the relaxation of hot carriers photoexcited with ultrashort (∼100 fs) laser pulses of 1.51 eV photon energy. These oscillations have been suggested to result from acoustic phonon dynamics, including coherent longitudinal acoustic phonons in the form of standing acoustic waves. An increase of oscillation frequency from ∼35 to ∼70 GHz with decreasing film thickness from 40 to 15 nm was attributed to the interplay between two different regimes employing traveling-acoustic-waves for films thicker than 40 nm and the film bulk acoustic wave resonator (FBAWR) modes for films thinner than 40 nm. The amplitude of oscillations decays rapidly for films below 15 nm thick when the indirect intersurface coupling in Bi{sub 2}Se{sub 3} films switches the FBAWR regime to that of the Lamb wave excitation. The frequency range of coherent longitudinal acoustic phonons is in good agreement with elastic properties of Bi{sub 2}Se{sub 3}.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

On the Ohmic-dominant heating mode of capacitively coupled plasma inverted by boundary electron emission

Electron emission from the boundary is ubiquitous in a capacitively coupled plasma (CCP) and precipitates nonnegligible influence on the discharge properties. Here, we present Particle-in-Cell/Monte Carlo Collision simulation of an Ohmic-dominant heating mode of the capacitively coupled plasma, where the stochastic heating vanishes and only Ohmic heating sustains the discharge due to sheath inversion by boundary electron emission. The inverted CCP features negative sheath potential without Bohm presheath, hence excluding plasma heating due to sheath edge oscillation. The particle and energy transport of the proposed heating mode is analyzed. The influence of boundary electron emission flux, source voltage, and neutral pressure on the transition between classic and Ohmic-dominant CCP heating modes is shown with designated simulation scans. Further, a modified inverse sheath–plasma coupling due to excessive ionization is discovered. In the end, key indicators of the proposed heating mode in plasma diagnostics are provided for future experimental verifications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Lifting of two-mode states in the D1-D5 CFT

We consider D1-D5-P states in the untwisted sector of the D1-D5 orbifold CFT where one copy of the seed CFT has been excited by a pair of oscillators, each being either bosonic or fermionic. While such states are BPS at the orbifold point, they will in general ‘lift’ as the theory is deformed towards general values of the couplings. We compute the expectation value of this lift at second order in the deformation parameter for the above mentioned states. We write this lift in terms of a fixed number of nested contour integrals on a given integrand; this integrand depends on the mode numbers of the oscillators in the state. We evaluate these integrals to obtain the explicit value of the lift for various subfamilies of states. At large mode numbers one observes a smooth increase of the lift with the dimension of the state h; this increase appears to follow a ~ √h behavior similar to that found analytically in earlier computations for other classes of states.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Plasmon oscillations in a linear cluster of spherical nanoparticles

The eigenfrequencies and eigenfunctions of plasmon oscillations in an infinite linear cluster of spherical nanoparticles are found analytically within the framework of the quasi-static approach and numerically within the framework of the finite element method. It is shown that the spectrum of plasmon oscillations is complex and contains previously unknown, highly localised modes in a high-frequency region of the spectrum. The results obtained can be used in designing plasmon nanowaveguides and nanolasers. (nanostructures)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Preheating after multifield inflation with nonminimal couplings. III. Dynamical spacetime results

This paper concludes our semianalytic study of preheating in inflationary models comprised of multiple scalar fields coupled nonminimally to gravity. Using the covariant framework of paper I in this series, we extend here the rigid-spacetime results of paper II by considering both the expansion of the Universe during preheating, as well as the effect of the coupled metric perturbations on particle production. The adiabatic and isocurvature perturbations are governed by different effective masses that scale differently with the nonminimal couplings and evolve differently in time. The effective mass for the adiabatic modes is dominated by contributions from the coupled metric perturbations immediately after inflation. The metric perturbations contribute an oscillating tachyonic term that enhances an early period of significant particle production for the adiabatic modes, which ceases on a time scale governed by the nonminimal couplings ${{\xi}}_{I}$. The effective mass of the isocurvature perturbations, on the other hand, is dominated by contributions from the fields' potential and from the curvature of the field-space manifold (in the Einstein frame), the balance between which shifts on a time scale governed by ${{\xi}}_{I}$. As in papers I and II, we identify distinct behavior depending on whether the nonminimal couplings are small [${{\xi}}_{I}{\lesssim}\mathcal{O}(1)$], intermediate [${{\xi}}_{I}{\sim}\mathcal{O}(1{-}10)$], or large (${{\xi}}_{I}{\ge}100$).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Torsional Vibration in the National Wind Technology Center’s 2.5-Megawatt Dynamometer

This report documents the torsional drivetrain dynamics of the NWTC's 2.5-megawatt dynamometer as identified experimentally and as calculated using lumped parameter models using known inertia and stiffness parameters. The report is presented in two parts beginning with the identification of the primary torsional modes followed by the investigation of approaches to damp the torsional vibrations. The key mechanical parameters for the lumped parameter models and justification for the element grouping used in the derivation of the torsional modes are presented. The sensitivities of the torsional modes to different test article properties are discussed. The oscillations observed from the low-speed and generator torque measurements were used to identify the extent of damping inherently achieved through active and passive compensation techniques. A simplified Simulink model of the dynamometer test article integrating the electro-mechanical power conversion and control features was established to emulate the torque behavior that was observed during testing. The torque response in the high-speed, low-speed, and generator shafts were tested and validated against experimental measurements involving step changes in load with the dynamometer operating under speed-regulation mode. The Simulink model serves as a ready reference to identify the torque sensitivities to various system parameters and to explore opportunities to improve torsional damping under different conditions.

17 WIND ENERGY↗
DOE OSTI2020

Dimensional crossover in spin Hall oscillators

Auto-oscillations of magnetization driven by direct spin current have been previously observed in multiple quasi-zero-dimensional (0D) ferromagnetic systems such as nanomagnets and nanocontacts. Recently, it was shown that pure spin Hall current can excite coherent auto-oscillatory dynamics in quasi-one-dimensional (1D) ferromagnetic nanowires but not in quasi-two-dimensional (2D) ferromagnetic films. Here we study the 1D to 2D dimensional crossover of current-driven magnetization dynamics in wire-based Pt/Ni 80 Fe 20 bilayer spin Hall oscillators via varying the wire width. We find that increasing the wire width results in an increase of the number of excited auto-oscillatory modes accompanied by a decrease of the amplitude and coherence of each mode. We also observe a crossover from a hard to a soft onset of the auto-oscillations with increasing wire width. The amplitude of auto-oscillations rapidly decreases with increasing temperature suggesting that interactions of the phase-coherent auto-oscillatory modes with incoherent thermal magnons play an important role in suppression of the auto-oscillatory dynamics. Our measurements in this work set the upper limit on the dimensions of an individual spin Hall oscillator and elucidate the mechanisms leading to suppression of coherent auto-oscillations with increasing oscillator size.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Aeroelastic oscillations of a cantilever with structural nonlinearities: theory and numerical simulation.

Our study details the derivation of the nonlinear equations of motion for the axial, biaxial bending and torsional vibrations of an aeroelastic cantilever undergoing rigid body (pitch) rotation at the base. The primary attenstion is focussed on the geometric nonlinearities of the system, whereby the aeroelastic load is modeled by the theory of linear quasisteady aerodynamics. This modelling effort is intended to mimic the wind-tunnel experimental setup at the Royal Military College of Canada. While the derivation closely follows the work of Hodges and Dowell [1] for rotor blades, this aeroelastic system contains new inertial terms which stem from the fundamentally different kinematics than those exhibited by helicopter or wind turbine blades. Using the Hamilton’s principle, a set of coupled nonlinear partial differential equations (PDEs) and an ordinary differential equation (ODE) are derived which describes the coupled axial-bending-bending-torsion-pitch motion of the aeroelastic cantilever with the pitch rotation. The finite dimensional approximation of the coupled system of PDEs are obtained using the Galerkin projection, leading to a coupled system of ODEs. Subsequently, these nonlinear ODEs are solved numerically using the built-in MATLAB implicit ODE solver and the associated numerical results are compared with those obtained using Houbolt’s method. It is demonstrated that the system undergoes coalescence flutter, leading to a limit cycle oscillation (LCO) due to coupling between the rigid body pitching mode and teh flexible mode arising from the flapwise bending motion.

42 ENGINEERING↗
DOE OSTI2022

Quantum states of cylindrical surface charge density for modeling plasmonic circuit elements: Nanowires, nanorods, cavities, and waveguides

Nanostructures in the form of ellipsoids, prolate spheroids, rings, and cylinders are known to exhibit resonant surface and cavity modes with applications in nanophotonics and plasmonics and, more recently, in novel quantum experiments, in which control of plasmons and their interactions with plasmons, photons, phonons, excitons, and quantum emitters are desired. Nanorods and nanowires are examples of plasmonic structures with spectral properties of potential use as interconnects and circuit components. Additionally, estimates of the surface properties of these components are needed in circuit design and integrated systems. Here, we present a quantum Hamiltonian for the cylindrical surface charge density. We then study the photon excitation of plasmons on the cylindrical surface and calculate their scattering and radiative decay rate. Nonradiative decay of plasmons induces an efficient heating of the nanoparticle and can photoacoustically excite mechanical oscillations. Computational calculations are also presented for the plasmonic modes and the ensuing excitations of nanomechanical eigenmodes of nanoparticles with near-cylindrical symmetries.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Resonant Cascaded Downconversion

We analyze an optical parametric oscillator (OPO) in which cascaded down-conversion occurs inside a cavity resonant for all modes but the initial pump. Due to the resonant cascade design, the OPO presents two {chi}{sup (2)}-level oscillation thresholds that are therefore much lower than for a {chi}{sup (3)} OPO. This is promising for reaching the regime of an effective third-order nonlinearity well above both thresholds. Such a {chi}{sup (2)} cascaded device also has potential applications in frequency conversion to far-infrared regimes. But, most importantly, it can generate novel multipartite quantum correlations in the output radiation, which represent a step beyond squeezed or entangled light. The output can be highly non-Gaussian and therefore not describable by any semiclassical model. In this paper, we derive quantum stochastic equations in the positive-P representation and undertake an analysis of steady-state and dynamical properties of this system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Plasma shape and position control development for NSTX-U using the GSEvolve plasma simulator

NSTX-U discharges have been reproduced using the GSEvolve plasma simulator in order to improve their control and reduce oscillations during the plasma current (Ip) ramp-up phase, and with the ultimate goal of enabling reliable H-mode access with a double-null shape at high elongation, low internal inductance, and high plasma performance. The control objective is to eliminate undesired oscillations in the plasma shape and vertical position that start when the plasma diverts during the Ip ramp-up phase, and that happened recurrently during the first NSTX-U experimental campaign. Model-based control solutions have been developed, including alternative H-mode access recipes and a Multi-Input Multi-Output (MIMO) decoupling controller. These solutions have demonstrated their capability to reduce or eliminate the aforementioned oscillations in GSEvolve simulations, enabling reproducible H-mode access. The results of this work aim to inform NSTX-U experimental operations on potential control developments to maximize its scientific output, and highlight the powerful capabilities of high-fidelity control-simulation frameworks like GSEvolve.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Evaluation of atmospheric precipitable water from reanalysis products using homogenized radiosonde observations over China

Many multidecadal atmospheric reanalysis products are available now, but their consistencies and reliability are far from perfect. In this work, atmospheric precipitable water (PW) from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), NCEP/Department of Energy (DOE), Modern Era Retrospective-Analysis for Research and Applications (MERRA), Japanese 55 year Reanalysis (JRA-55), JRA-25, ERA-Interim, ERA-40, Climate Forecast System Reanalysis (CFSR), and 20th Century Reanalysis version 2 is evaluated against homogenized radiosonde observations over China during 1979–2012 (1979–2001 for ERA-40). Results suggest that the PW biases in the reanalyses are within ~20% for most of northern and eastern China, but the reanalyses underestimate the observed PW by 20%–40% over western China and by ~60% over the southwestern Tibetan Plateau. The newer-generation reanalyses (e.g., JRA25, JRA55, CFSR, and ERA-Interim) have smaller root-mean-sq uare error than the older-generation ones (NCEP/NCAR, NCEP/DOE, and ERA-40). Most of the reanalyses reproduce well the observed PW climatology and interannual variations over China. However, few reanalyses capture the observed long-term PW changes, primarily because they show spurious wet biases before about 2002. This deficiency results mainly from the discontinuities contained in reanalysis relative humidity fields in the middle-lower troposphere due to the wet bias in older radiosonde records that are assimilated into the reanalyses. An empirical orthogonal function (EOF) analysis revealed two leading modes that represent the long-term PW changes and El Niño–Southern Oscillation-related interannual variations with robust spatial patterns. The reanalysis products, especially the MERRA and JRA-25, roughly capture these EOF modes, which acco unt for over 50% of the total variance. The results show that even during the post-1979 satellite era, discontinuities in radiosonde data can still induce large spurious long-term changes in reanalysis PW and other related fields. Thus, more efforts are needed to remove spurious changes in input data for future long-term reanalyses.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Lead(II) complex formation with l -cysteine in aqueous solution

The lead(II) complexes formed with the multidentate chelator l-cysteine (H 2 Cys) in an alkaline aqueous solution were studied using 207 Pb, 13 C, and 1 H NMR, Pb L III -edge X-ray absorption, and UV–vis spectroscopic techniques, complemented by electrospray ion mass spectrometry (ESI-MS). The H 2 Cys/Pb II mole ratios were varied from 2.1 to 10.0 for two sets of solutions with C Pb II = 0.01 and 0.1 M, respectively, prepared at pH values (9.1–10.4) for which precipitates of lead(II) cysteine dissolved. At low H 2 Cys/Pb II mole ratios (2.1–3.0), a mixture of the dithiolate [Pb(S,N-Cys) 2 ] 2– and [Pb(S,N,O-Cys)(S-HCys)] – complexes with average Pb–(N/O) and Pb–S distances of 2.42 ± 0.04 and 2.64 ± 0.04 Å, respectively, was found to dominate. At high concentration of free cysteinate (>0.7 M), a significant amount converts to the trithiolate [Pb(S,N-Cys)(S-HCys) 2 ] 2– , including a minor amount of a PbS 3 -coordinated [Pb(S-HCys) 3 ] – complex. The coordination mode was evaluated by fitting linear combinations of EXAFS oscillations to the experimental spectra and by examining the 207 Pb NMR signals in the chemical shift range δ Pb = 2006–2507 ppm, which became increasingly deshielded with increasing free cysteinate concentration. One-pulse magic-angle-spinning (MAS) 207 Pb NMR spectra of crystalline Pb(aet) 2 (Haet = 2-aminoethanethiol or cysteamine) with PbS 2 N 2 coordination were measured for comparison (δ iso = 2105 ppm). The UV–vis spectra displayed absorption maxima at 298–300 nm (S – → Pb II charge transfer) for the dithiolate PbS 2 N(N/O) species; with increasing ligand excess, a shoulder appeared at ~330 nm for the trithiolate PbS 3 N and PbS 3 (minor) complexes. Finally, the results provide spectroscopic fingerprints for structural models for lead(II) coordination modes to proteins and enzymes.

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

Machine Learning of Factors Influencing Damping and Frequency of Dominant Inter-area Modes in the WECC Interconnect

The stability of inter-area electromechanical oscillations are critical to power system reliability. Due to the complexities of power systems, relationships between system conditions and oscillation characteristics, such as damping and frequency, tend to be expressed only in generalities. In this study, a list of influential factors on Western Electricity Coordinating Council (WECC) interconnect modal characteristics are identified and evaluated with advanced machine learning techniques including principal component analysis, analysis of variance, random forest feature selection, support vector machine, and artificial neural network approaches.

Hou, Zhangshuan↗
DOE OSTI2012

Hybrid Alfven resonant mode generation in the magnetosphere-ionosphere coupling system

Feedback unstable Alfven waves involving global field-line oscillations and the ionospheric Alfven resonator (IAR) were comprehensively studied to clarify their properties of frequency dispersion, growth rate, and eigenfunctions. It is discovered that a new mode called here the hybrid Alfven resonant (HAR) mode can be destabilized in the magnetosphere-ionosphere coupling system with a realistic Alfven velocity profile. The HAR mode found in a high frequency range over 0.3 Hz is caused by coupling of IAR modes with strong dispersion and magnetospheric cavity resonances. The harmonic relation of HAR eigenfrequencies is characterized by a constant frequency shift from those of IAR modes. The three modes are robustly found even if effects of two-fluid process and ionospheric collision are taken into account and thus are anticipated to be detected by magnetic field observations in a frequency range of 0.3-1 Hz in auroral and polar-cap regions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

A stable snow–atmosphere coupled mode

Snow is both an important lower boundary forcing of the atmosphere and a response to atmospheric forcing in the extratropics. It is still unclear whether a stable snow–atmosphere coupled mode exists in the extratropics, like the ENSO in the tropics. Using Sliding Correlation analysis over Any Window, the present study quantitatively evaluates the stability of coupling relationships between the major modes of winter snow over the Northern Hemisphere and the winter atmospheric Arctic Oscillation (AO), the Antarctic Oscillation (AAO) and the Siberian High over the period 1872–2010, and discusses their possible relationships for different seasons. Results show that the first mode of the winter snow cover fraction and the winter AO together constitute a stable snow–atmosphere coupled mode, the SNAO. The coupled mode is stronger during recent decades than before. The snow anomaly over Europe is one key factor of the SNAO mode due to the high stability there, and the polar vortex anomaly in the atmosphere is its other key factor. The continuity of signals in the SNAO between autumn and winter is weaker than that between winter and spring. The second winter snow mode is generally stably correlated with the winter AAO and was more stable before the 1970s. The AAO signal with boreal snow has a strong continuity in seasonal transition. Generally, through these coupled modes, snow and atmosphere can interact in the same season or between different seasons: autumn snow can influence the winter atmosphere; the winter atmosphere can influence spring snow.

Meteorology & Atmospheric Sciences↗
DOE OSTI2017

QML-generation dynamics of a solid-state laser with an acousto-optic travelling wave modulator

The features of the generation dynamics of a laser with an acousto-optic modulator are studied. The light field injection with a frequency shift from the previous mode to the subsequent one ensures mode locking, and in many cases contributes to the instability and self-oscillations at the laser relaxation frequency. The amplitude and frequency characteristics of the emerging regime, along with the features of the regimes realised under external modulation of the diffraction coupling coefficient, are analysed. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗