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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

RX GEMINORUM: PHOTOMETRIC SOLUTIONS, (NEARLY UNIFORM) GAINER ROTATION, DONOR RADIAL VELOCITY SOLUTION, NON-LTE ACCRETION DISK MODELS OF Hα EMISSION PROFILES, AND SECULAR LIGHT CURVE CHANGES IN THE 20TH CENTURY

We obtained full-orbit Iybvu intermediate-band photometry and CCD spectroscopy of the long-period Algol eclipsing binary RX Geminorum. Photometric solutions using the Wilson–Devinney code give a gainer rotation (hotter, mass-accreting component) about 15 times the synchronous rate. We describe a simple technique to detect departures from uniform rotation of the hotter component. These binaries radiate double-peaked Hα emission from a low-mass accretion disk around the gainer. We used an approximate non-LTE disk code to predict models in fair agreement with observations, except in the far wings of the emission profile, where the star–inner disk boundary layer emits extra radiation. Variations in Hα emission derive from modulations in the transfer rate. A study of times of minima during the 20th century suggests that a perturbing third body is present near RX Gem.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

First-principles studies of the local structure and relaxor behavior of Pb ( Mg 1 / 3 Nb 2 / 3 ) O 3 – PbTiO 3 -derived ferroelectric perovskite solid solutions

We have investigated the effect of transition-metal dopants on the local structure of the prototypical 0.75Pb(Mg 1/3 Nb 2/3 )O 3 –0.25PbTiO 3 relaxor ferroelectric. We find that these dopants give rise to very different local structure and other physical properties. For example, when Mg is partially substituted by Cu or Zn, the displacement of Cu or Zn is much larger than that of Mg and is even comparable to that of Nb. The polarization of these systems is also increased, especially for the Cu-doped solution, due to the large polarizability of Cu and Zn. As a result, the predicted maximum dielectric constant temperatures T m are increased. On the other hand, the replacement of a Ti atom with a Mo or Tc atom dramatically decreases the displacements of the cations and the polarization, and thus, the T m values are also substantially decreased. Here, the higher T m cannot be explained by the conventional argument based on the ionic radii of the cations. Furthermore, we find that Cu, Mo, or Tc doping increases the cation displacement disorder. Here, the effect of the dopants on the temperature dispersion ΔT m , which is the change in T m for different frequencies, is also discussed. Our findings lay the foundation for further investigations of unexplored dopants.

25 ENERGY STORAGE↗
DOE OSTI2012

Entanglement-Controlled Subdiffusion of Nanoparticles within Concentrated Polymer Solutions

We describe x-ray photon correlation spectroscopy (XPCS) experiments tracking the motion of gold nanoparticles within solutions of high-molecular-weight polystyrene. Over displacements from nanometers to tens of nanometers, the particles undergo subdiffusive motion that is dictated by the temporal evolution of the entangled polymer mesh in the immediate vicinity of the particles. The results thus provide a novel microscopic dynamical characterization of this key structural property of polymers and more broadly demonstrate the capability of XPCS-based microrheology to interrogate heterogeneous mechanical environments in nanostructured soft materials.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Local correlated motions in aqueous solution of sodium chloride

Real-space motions of molecules and ions in an aqueous solution of sodium chloride are studied with high-resolution inelastic x-ray scattering. In this study, we focus on the correlated dynamics of water molecules and salt ions, instead of the instantaneous structure and the rotational and reorientation dynamics that have been studied using scattering techniques and optical spectroscopy, respectively. The real-space analysis in terms of the Van Hove function illustrates the effect of salt ions to slow down the local correlated dynamics of surrounding water in the hydration shells.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Crystal Viscoplasticity Model of Molybdenum Including the Influence of Silicon in Solid Solution [Crystal Viscoplasticity Model of Mo Including the Influence of Si in Solid Solution]

Molybdenum (Mo)-based alloys offer higher temperature capability than nickel-based superalloys. The challenge of designing these alloys is tailoring the chemistry and microstructure to achieve high-temperature strength, creep and fatigue resistance, and oxidation resistance while maintaining lower-temperature ductility and damage tolerance. Structure-properties modeling tools can be used to identify optimum microstructures. However, one missing element in this tool set is a constitutive model for the more ductile α-Mo phase over the entire temperature range from room temperature to 1,400°C. A crystal viscoplasticity model is developed for α-Mo, including the influence of varying amounts of silicon (Si) in solid solution. As a result, the temperature, strain rate, and Si dependence of the deformation behavior needed to determine the model parameters are obtained from new compression experiments.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Microbial Activity and Precipitation at Solution-Solution Mixing Zones in Porous Media (Final Report)

The use of biological and chemical processes that degrade or immobilize contaminants in subsurface environments is a cornerstone of remediation technology. The enhancement of biological and chemical processes in situ, involves the transport, displacement, distribution and mixing of one or more reactive agents. Biological and chemical reactions all require diffusive transport of solutes to reaction sites at the molecular scale and accordingly, the success of processes at the meter-scale and larger is dictated by the success of phenomena that occur at the micron-scale. However, current understanding of scaling effects on the mixing and delivery of nutrients in biogeochemically dynamic porous media systems is limited, despite the limitations this imposes on the efficiency and effectiveness of the remediation challenges at hand. We therefore proposed to experimentally characterize and computationally describe the growth, evolution, and distribution of microbial activity and mineral formation as well as changes in transport processes in porous media that receive two or more reactive amendments. The model system chosen for this project was based on a method for immobilizing 90 Sr, which involves stimulating microbial urea hydrolysis with ensuing mineral precipitation (CaCO 3 ), and co-precipitation of Sr. Studies at different laboratory scales were used to visualize and quantitatively describe the spatial relationships between amendment transport and consumption that stimulate the production of biomass and mineral phases that subsequently modify the permeability and heterogeneity of porous media. Biomass growth, activity, and mass deposition in mixing zones was investigated using two-dimensional micro-model flow cells as well as flow cells that could be analyzed using synchrotron-based x-ray tomography. Larger-scale flow-cell experiments were conducted where the spatial distribution of media properties, flow, segregation of biological activity and impact on ancillary constituents (i.e., Sr) was determined. Model simulations accompanied the experimental efforts. The research contributed towards defining the key physical, chemical, and biological processes influencing the form and mobility of DOE priority contaminants (e.g., 60 Co, 90 Sr, U) in the subsurface. The work conducted and reported herein, will in the future (i) contribute to controlling the juxtaposition of microbial activity, contaminants and amendments, (ii) promote new strategies for delivering amendments, and (iii) allow new approaches for modifying permeability and flow in porous media. We feel that the work has already translated directly to improving the efficiency of amendment based remediation strategies. The results of the project have been published in a number of peer reviewed journal articles. The abstracts and citations to those articles, given in section 2.0 below, make up the bulk of this final report.

42 ENGINEERING↗
DOE OSTI2017

K-ε Turbulence Model Parameter Estimates Using an Approximate Self-similar Jet-in-Crossflow Solution

The k-ε turbulence model has been described as perhaps “the most widely used complete turbulence model.” This family of heuristic Reynolds Averaged Navier-Stokes (RANS) turbulence closures is supported by a suite of model parameters that have been estimated by demanding the satisfaction of well-established canonical flows such as homogeneous shear flow, log-law behavior, etc. While this procedure does yield a set of so-called nominal parameters, it is abundantly clear that they do not provide a universally satisfactory turbulence model that is capable of simulating complex flows. Recent work on the Bayesian calibration of the k-ε model using jet-in-crossflow wind tunnel data has yielded parameter estimates that are far more predictive than nominal parameter values. In this paper, we develop a self-similar asymptotic solution for axisymmetric jet-in-crossflow interactions and derive analytical estimates of the parameters that were inferred using Bayesian calibration. The self-similar method utilizes a near field approach to estimate the turbulence model parameters while retaining the classical far-field scaling to model flow field quantities. Our parameter values are seen to be far more predictive than the nominal values, as checked using RANS simulations and experimental measurements. They are also closer to the Bayesian estimates than the nominal parameters. A traditional simplified jet trajectory model is explicitly related to the turbulence model parameters and is shown to yield good agreement with measurement when utilizing the analytical derived turbulence model coefficients. Finally, the close agreement between the turbulence model coefficients obtained via Bayesian calibration and the analytically estimated coefficients derived in this paper is consistent with the contention that the Bayesian calibration approach is firmly rooted in the underlying physical description.

42 ENGINEERING↗
NASA NTRS1986

Transonic Navier-Stokes wing solution using a zonal approach. Part 1: Solution methodology and code validation

A fast diagonalized Beam-Warming algorithm is coupled with a zonal approach to solve the three-dimensional Euler/Navier-Stokes equations. The computer code, called Transonic Navier-Stokes (TNS), uses a total of four zones for wing configurations (or can be extended to complete aircraft configurations by adding zones). In the inner blocks near the wing surface, the thin-layer Navier-Stokes equations are solved, while in the outer two blocks the Euler equations are solved. The diagonal algorithm yields a speedup of as much as a factor of 40 over the original algorithm/zonal method code. The TNS code, in addition, has the capability to model wind tunnel walls. Transonic viscous solutions are obtained on a 150,000-point mesh for a NACA 0012 wing. A three-order-of-magnitude drop in the L2-norm of the residual requires approximately 500 iterations, which takes about 45 min of CPU time on a Cray-XMP processor. Simulations are also conducted for a different geometrical wing called WING C. All cases show good agreement with experimental data.

Flores, J.↗
NASA NTRS1986

Transonic Navier-Stokes wing solution using a zonal approach. Part 1: Solution methodology and code validation

A fast diagonalized Beam-Warming algorithm is coupled with a zonal approach to solve the three dimensional Euler/Navier-Stokes equations. The computer code, called Transonic Navier-Stokes (TNS), uses a total of four zones for wing configurations (or can be extended to complete aircraft configurations by adding zones). In the inner blocks near the wing surface, the thin-layer Navier-Stokes equations are solved, while in the outer two blocks the Euler equations are solved. The diagonal algorithm yields a speedup of as much as a factor of 40 over the original algorithm/zonal method code. The TNS code, in addition, has the capability to model wind tunnel walls. Transonic viscous solutions are obtained on a 150,000-point mesh for a NACA 0012 wing. A three-order-of-magnitude drop in the L2-norm of the residual requires approximately 500 iterations, which takes about 45 min of CPU time on a Cray-XMP processor. Simulations are also conducted for a different geometrical wing called WING C. All cases show good agreement with experimental data.

Flores, J.↗
NASA NTRS1987

Elastic interaction of a crack with a microcrack array. I - Formulation of the problem and general form of the solution. II - Elastic solution for two crack configurations (piecewise constant and linear approximations)

The elastic interactions of a two-dimensional configuration consisting of a crack with an array of microcracks located near the tip are studied. The general form of the solution is based on the potential representations and approximations of tractions on the microcracks by polynomials. In the second part, the technique is applied to two simple two-dimensional configurations involving one and two microcracks. The problems of stress shielding and stress amplification (the reduction or increase of the effective stress intensity factor due to the presence of microcracks) are discussed, and the refinements introduced by higher order polynomial approximations are illustrated.

Chudnovsky, A.↗