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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

Evidence for Systematic Changes in the Stratospheric Aerosol Size Following Volcanic Eruptions of Diverse Magnitudes Using Space-Based Instruments

An analysis of multiwavelength stratospheric aerosol extinction coefficient data from the Stratospheric Aerosol and Gas Experiment II and III/ISS instruments is used to demonstrate a coherent relationship between the perturbation in extinction coefficient in an eruption’s main aerosol layer and an apparent change in aerosol size distribution that spans multiple orders of magnitude in the stratospheric impact of an volcanic event. The relationship is measurement-based and does not rely on assumptions about the aerosol size distribution. In this respect, it may be a unique tool to verify the performance of interactive aerosol models used in GCMs and ESMs and may suggest an avenue for improving aerosol extinction coefficient measurements from single channel observations such the Optical Spectrograph and Infrared Imager System. We note limitations on this analysis including that the presence of significant amounts of ash in the main aerosol layer may significantly modulate these results.

Larry Thomason↗
DOE OSTI2020

Robustness of slow contraction to cosmic initial conditions

We present numerical relativity simulations of cosmological scenarios in which the universe is smoothed and flattened by undergoing a phase of slow contraction and test their sensitivity to a wide range of initial conditions. Our numerical scheme enables the variation of all freely specifiable physical quantities that characterize the initial spatial hypersurface, such as the initial shear and spatial curvature contributions as well as the initial field and velocity distributions of the scalar that drives the cosmological evolution. In particular, we include initial conditions that are far outside the perturbative regime of the well-known attractor scaling solution. We complement our numerical results by analytically performing a complete dynamical systems analysis and show that the two approaches yield consistent results.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Exploring the growth index γ L : Insights from different CMB dataset combinations and approaches

In this study we investigate the growth index γ L , which characterizes the growth of linear matter perturbations, while analysing different cosmological datasets. We compare the approaches implemented by two different patches of the cosmological solver : and __. In our analysis we uncover a deviation of the growth index from its expected Λ CDM value of 0.55 when utilizing the Planck dataset, both in the case and in the __ case, but in opposite directions. This deviation is accompanied by a change in the direction of correlations with derived cosmological parameters. However, the incorporation of cosmic microwave background lensing data helps reconcile γ L with its Λ -cold dark matter value in both cases. Conversely, the alternative ground-based telescopes Atacama Cosmology Telescope and South Pole Telescope consistently yield growth index values in agreement with γ L = 0.55 . We conclude that the presence of the A lens problem in the Planck dataset contributes to the observed deviations, underscoring the importance of additional datasets in resolving these discrepancies. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2020

θ -dependence of light nuclei and nucleosynthesis

We investigate the impact of the QCD vacuum at nonzero θ on the properties of light nuclei, Big Bang nucleosynthesis, and stellar nucleosynthesis. Our analysis starts with a calculation of the θ-dependence of the neutron-proton mass difference and neutron decay using chiral perturbation theory. We then discuss the θ-dependence of the nucleon-nucleon interaction using a one-boson-exchange model and compute the properties of the two-nucleon system. Using the universal properties of four-component fermions at large scattering length, we then deduce the binding energies of the three-nucleon and four-nucleon systems. Based on these results, we discuss the implications for primordial abundances of light nuclei, the production of nuclei in stellar environments, and implications for an anthropic view of the universe.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Xylan Is Critical for Proper Bundling and Alignment of Cellulose Microfibrils in Plant Secondary Cell Walls

Plant biomass represents an abundant and increasingly important natural resource and it mainly consists of a number of cell types that have undergone extensive secondary cell wall (SCW) formation. These cell types are abundant in the stems of Arabidopsis, a well-studied model system for hardwood, the wood of eudicot plants. The main constituents of hardwood include cellulose, lignin, and xylan, the latter in the form of glucuronoxylan (GX). The binding of GX to cellulose in the eudicot SCW represents one of the best-understood molecular interactions within plant cell walls. The evenly spaced acetylation and 4-O-methyl glucuronic acid (MeGlcA) substitutions of the xylan polymer backbone facilitates binding in a linear two-fold screw conformation to the hydrophilic side of cellulose and signifies a high level of molecular specificity. However, the wider implications of GX–cellulose interactions for cellulose network formation and SCW architecture have remained less explored. In this study, we seek to expand our knowledge on this by characterizing the cellulose microfibril organization in three well-characterized GX mutants. The selected mutants display a range of GX deficiency from mild to severe, with findings indicating even the weakest mutant having significant perturbations of the cellulose network, as visualized by both scanning electron microscopy (SEM) and atomic force microscopy (AFM). We show by image analysis that microfibril width is increased by as much as three times in the severe mutants compared to the wild type and that the degree of directional dispersion of the fibrils is approximately doubled in all the three mutants. Further, we find that these changes correlate with both altered nanomechanical properties of the SCW, as observed by AFM, and with increases in enzymatic hydrolysis. Results from this study indicate the critical role that normal GX composition has on cellulose bundle formation and cellulose organization as a whole within the SCWs.

09 BIOMASS FUELS↗
NASA NTRS1972

Effect of environmental torques on short-term attitude prediction for a rolling-wheel spacecraft in a sun-synchronous orbit

A numerical evaluation and an analysis of the effects of environmental disturbance torques on the attitude of a hexagonal cylinder rolling wheel spacecraft were performed. The resulting perturbations caused by five such torques were found to be very small and exhibited linearity such that linearized equations of motion yielded accurate results over short periods and the separate perturbations contributed by each torque were additive in the sense of superposition. Linearity of the torque perturbations was not affected by moderate system design changes and persisted for torque-to-angular momentum ratios up to 100 times the nominal expected value. As these conditions include many possible applications, similar linear behavior might be anticipated for other rolling-wheel spacecraft.

Hodge, W. F.↗
NASA NTRS1975

General verification description

A brief general description of the ASTP flight program verification was presented. The total program verification effort assures the accuracy and adequacy of the LVDC flight program and verifies that the final program meets mission requirements and conforms to program documentation. The flight program's functional requirements to integrate the guidance and control system with the launch vehicle sequencing system are verified directly by analysis of many special logic checks designed for this purpose and indirectly by the correct overall program response to nominal and numerous perturbed conditions. Verification of the interaction of function requirements is accomplished on every case run during the verification effort.

Source record↗
NASA NTRS1976

Influence of finite-beta effects on the lower-hybrid-drift instability in post-implosion theta pinches

The influence of finite values of the plasma parameter beta on the lower-hybrid-drift instability is investigated, with particular emphasis on the post-implosion theta-pinch configurations. The analysis is carried out in a fully self-consistent manner and includes the finite-beta effects associated with transverse electromagnetic perturbations as well as with resonant and nonresonant electron-orbit modifications. Except in the limit where the ratio of electron and ion temperatures approaches zero, it is found that there is a critical value for the local beta such that the lower-hybrid-drift instability is completely stabilized. For typical post-implosion theta pinches, it is concluded that if the magnetic-field depression is sufficiently large, the interior region of the pinch will be stable to the examined instability but the exterior region will be unstable.

Davidson, R. C.↗
NASA NTRS1982

High-intensity sound in air saturated fibrous bulk porous materials

The interaction high-intensity sound with bulk porous materials in porous materials including Kevlar 29 is reported. The nonlinear behavior of the materials was described by dc flow resistivity tests. Then acoustic propagation and reflection were measured and small signal broadband measurements of phase speed and attenuation were carried out. High-intensity tests were made with 1, 2, and 3 kHz tone bursts to measure harmonic generation and extra attenuation of the fundamental. Small signal standing wave tests measured impedence between 0.1 and 3.5 kHz. High level tests with single cycle tone bursts at 1 to 4 kHz show that impedance increases with intensity. A theoretical analysis is presented for high-porosity, rigid-frame, isothermal materials. One dimensional equations of motion are derived and solved by perturbation. The experiments show that there is excess attenuation of the fundamental component and in some cases a close approach to saturation. A separate theoretical model, developed to explain the excess attenuation, yields predictions that are in good agreement with the measurements. Impedance and attenuation at high intensities are modeled.

Kuntz, H. L., II↗
NASA NTRS1983

The effect of solar-wind convection on charged particle transport in interplanetary space

In the formulation of focused transport without convection, approximate solutions of the Boltzmann equation are described in terms of small perturbations of its two fundamental steady-state solutions. In the presence of convection, the same approach is applicable, provided that the analysis is carried out in a system moving with the solar wind. The approximate transport equations that apply in this system are very similar to those that apply in the absence of convection. The new equations assume that the wind blows in the direction of the guiding field and is constant in space and time. Nevertheless, these equations are more general than existing formulations, for they retain their validity when the solar wind velocity is large, and they describe the coherent modes of transport that appear when the mean free path is greater than 1 AU. An interesting implication of the new formulation is that coherent disturbances are swept along with the wind. In this respect, they differ from truly scatter-free modes, which are not affected by the wind.

Earl, J. A.↗
NASA NTRS1986

The Comet Halley ephemeris development effort

Nongravitational forces affecting Comet Halley's motion are discussed. Analysis of the comet's orbit since 1982 is described. The astrometry network of the International Halley Watch is introduced. Ephemeris (with perturbations) from 1 January 1985 through 30 June 1986 are listed.

Yeomans, D. K.↗
NASA NTRS1987

Analysis of eccentric annular incompressible seals. II - Effects of eccentricity on rotordynamic coefficients

A new analysis procedure has been presented which solves for the flow variables of an annular pressure seal in which the rotor has a large static displacement (eccentricity) from the centered position. The present paper incorporates the solutions to investigate the effect of eccentricity on the rotordynamic coefficients. The analysis begins with a set of governing equations based on a turbulent bulk-flow model and Moody's friction factor equation. Perturbations of the flow variables yields a set of zeroth- and first-order equations. After integration of the zeroth-order equations, the resulting zeroth-order flow variables are used as input in the solution of the first-order equations. Further integration of the first order pressures yields the eccentric rotordynamic coefficients. The results from this procedure compare well with available experimental and theoretical data, with accuracy just as good or slightly better than the predictions based on a finite-element model.

Nelson, C. C.↗
NASA NTRS1988

The origin of broad emission line clouds in active galactic nuclei

Numerous arguments suggest that the broad emission lines characteristic of many types of active galactic nuclei are formed in comparatively cool clouds embedded in a much hotter medium of roughly equal pressure. Here it is shown that a cycle exists in which cooler condensations form within the hot medium via a finite-amplitude thermal instability, drop to temperatures characteristic of photoionization equilibrium, are destroyed by hydrodynamic processes, and then return their material to the hot medium. Clouds of characteristic pressure about 10 to the 14th K/cu cm and thickness about 10 to the 23rd/sq cm are produced by this mechanism, in agreement with the pressure and thickness inferred from photoionization model analysis of observed emission-line ratios. Only a fraction of the hot medium's mass must encounter a finite-amplitude perturbation in order to produce the observed mass in clouds.

Krolik, Julian H.↗
NASA NTRS1950

The calculation of downwash behind supersonic wings with an application to triangular plan forms

A method is developed consistent with the assumptions of small perturbation theory which provides a means of determining the downwash behind a wing in supersonic flow for a known load distribution. The analysis is based upon the use of supersonic doublets which are distributed over the plan form and wake of the wing in a manner determined from the wing loading. The equivalence in subsonic and supersonic flow of the downwash at infinity corresponding to a given load distribution is proved.

Lomax, Harvard↗
NASA NTRS2000

Viscous and Thermal Effects on Hydrodynamic Instability in Liquid-Propellant Combustion

A pulsating form of hydrodynamic instability has recently been shown to arise during the deflagration of liquid propellants in those parameter regimes where the pressure-dependent burning rate is characterized by a negative pressure sensitivity. This type of instability can coexist with the classical cellular, or Landau, form of hydrodynamic instability, with the occurrence of either dependent on whether the pressure sensitivity is sufficiently large or small in magnitude. For the inviscid problem, it has been shown that when the burning rate is realistically allowed to depend on temperature as well as pressure, that sufficiently large values of the temperature sensitivity relative to the pressure sensitivity causes the pulsating form of hydrodynamic instability to become dominant. In that regime, steady, planar burning becomes intrinsically unstable to pulsating disturbances whose wavenumbers are sufficiently small. In the present work, this analysis is extended to the fully viscous case, where it is shown that although viscosity is stabilizing for intermediate and larger wavenumber perturbations, the intrinsic pulsating instability for small wavenumbers remains. Under these conditions, liquid-propellant combustion is predicted to be characterized by large unsteady cells along the liquid/gas interface.

Margolis, Stephen B.↗
NASA NTRS2012

New Approaches to Quantifying Transport Model Error in Atmospheric CO2 Simulations

In recent years, much progress has been made in observing CO2 distributions from space. However, the use of these observations to infer source/sink distributions in inversion studies continues to be complicated by difficulty in quantifying atmospheric transport model errors. We will present results from several different experiments designed to quantify different aspects of transport error using the Goddard Earth Observing System, Version 5 (GEOS-5) Atmospheric General Circulation Model (AGCM). In the first set of experiments, an ensemble of simulations is constructed using perturbations to parameters in the model s moist physics and turbulence parameterizations that control sub-grid scale transport of trace gases. Analysis of the ensemble spread and scales of temporal and spatial variability among the simulations allows insight into how parameterized, small-scale transport processes influence simulated CO2 distributions. In the second set of experiments, atmospheric tracers representing model error are constructed using observation minus analysis statistics from NASA's Modern-Era Retrospective Analysis for Research and Applications (MERRA). The goal of these simulations is to understand how errors in large scale dynamics are distributed, and how they propagate in space and time, affecting trace gas distributions. These simulations will also be compared to results from NASA's Carbon Monitoring System Flux Pilot Project that quantified the impact of uncertainty in satellite constrained CO2 flux estimates on atmospheric mixing ratios to assess the major factors governing uncertainty in global and regional trace gas distributions.

Ott, L.↗
DOE OSTI2021

Probabilistic Voltage Sensitivity Analysis to Quantify Impact of High PV Penetration on Unbalanced Distribution System

From an operational and planning perspective, it is important to quantify the impact of increasing penetration of photovoltaics on the distribution system. Most existing impact assessment studies are scenario-based where derived results are scenario specific and not generalizable. Moreover, stochasticity in the temporal behavior of spatially distributed PVs requires a large number of scenarios that increase with the size of the network and the level of penetration. Therefore, we propose a new computationally efficient analytical framework of voltage sensitivity analysis that allows for stochastic analysis of voltage change due to random changes in PV generation. We first derive an analytical approximation for voltage change at any node of the network due to change in power at other nodes in an unbalanced distribution network. The quality of this approximation is reinforced via bounds on the approximation error. Then, we derive the probability distribution of voltage change at a certain node due to random changes in power injections/consumptions at multiple locations of the network. The accuracy of the proposed PVSA is illustrated using a modified version of the IEEE 37 bus test system. As a result, the proposed PVSA can serve as a powerful tool for proactive monitoring/control and ease the computational burden associated with perturbation based cybersecurity mechanisms.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS1987

Analysis of eccentric annular incompressible seals. I - A new solution using fast Fourier transforms for determining hydrodynamic force

A new analysis procedure is presented which solves for the flow variables of an incompressible-flow annular pressure seal in which the rotor has a large static displacement from the centered position. The analysis begins with a set of governing equations based on a turbulent bulk-flow model and Moody's friction equation. No simplification of these bulk-flow equations is required for the solution procedure. Perturbation of the flow variables yields a set of zeroth and first-order equations. The zeroth-order equations (which model the large static displacement) are integrated by means of an efficient new method which employs fast Fourier transforms. Further integration of the zeroth-order pressures yields the hydrodynamic reactive force. Predictions for the hydrodynamic forces from this analysis procedure are in excellent agreement with available experimental results.

Nelson, C. C.↗