Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “DENSITY MATRIX”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Electroactive Polymers as Artificial Muscles: Capabilities, Potentials and Challenges

The low density and the relative ease of shaping made polymers highly attractive materials and they are increasingly being chosen for aerospace applications. Polymer matrix composite materials significantly impacted the construction of high performance aircraft components and structures. In recent years, the resilience characteristics of polymers made them attractive to the emerging field of inflatable structures. Balloons were used to cushion the deployment of the Mars Pathfinder lander on July 4, 1997, paving the way for the recent large number of related initiatives. Inflatable structures are now being used to construct a rover, aerial vehicles, telescopes, radar antennas, and others. Some of these applications have reached space flight experiments, whereas others are now at advanced stages of development.

Bar-Cohen, Yoseph↗
NASA NTRS1997

Orthorhombic Titanium Matrix Composite Subjected to Simulated Engine Mission Cycles

Titanium matrix composites (TMC's) are commonly made up of a titanium alloy matrix reinforced by silicon carbide fibers that are oriented parallel to the loading axis. These composites can provide high strength at lower densities than monolithic titanium alloys and superalloys in selected gas turbine engine applications. The use of TMC rings with unidirectional SiC fibers as reinforcing rings within compressor rotors could significantly reduce the weight of these components. In service, these TMC reinforcing rings would be subjected to complex service mission loading cycles, including fatigue and dwell excursions. Orthorhombic titanium aluminide alloys are of particular interest for such TMC applications because their tensile and creep strengths are high in comparison to those of other titanium alloys. The objective of this investigation was to assess, in simulated mission tests at the NASA Lewis Research Center, the durability of a SiC (SCS-6)/Ti-22Al-23Nb (at.%) TMC for compressor ring applications, in cooperation with the Allison Engine Company.

Gabb, Timothy P.↗
NASA NTRS2007

Atomic Data and Spectral Line Intensities for CA XVII

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ca XVII. The configurations used are 2s(sup 2), 2s2p, 2p(sup 2), 2l3l', 214l' and 2s5l', with l = s,p and l' = s,p, d giving rise to 92 fine-structure levels in intermediate coupling. Collision strengths are calculated at seven incident energies (15, 30, 75, 112.5, 150, 187.5 and 225 Ry) for the transitions within the three lowest configurations corresponding to the 10 lowest energy levels, and five incident energies (75, 112.5, 150, 187.5 and 225 Ry) for transitions between the lowest five levels and the n = 3,4,5 configurations. Calculations have been carried out using the distorted wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates of the present work, and R-Matrix results for the 2s2, 2s2p, 2p2 configurations available in the literature, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(exp 8)-10(exp 14)/cu cm at an electron temperature of log Te(K)=6.7, corresponding to the maximum abundance of Ca XVII. Spectral line intensities are calculated, and their diagnostic relevance L; discussed. This dataset will be made available in the next version of the CHIANTI database.

Bhatia, A.K.↗
DOE OSTI2023

Enhanced Hanford High-Fluoride Waste Glass Property Data Development: Phase 1

This study focused on investigating the effects of fluorine concentration on simulated high-level waste glass properties to eventually establish a fluorine limit (as a single-component or multiple-component constraint) for glass formulations for high-fluoride Hanford wastes. This is a first step to provide data to understand the impacts of changing flowsheets on the mission duration and extent. A test matrix of 20 high-fluoride glasses was generated, and the chemical compositions were measured. The following properties were measured and tested against current model predictions: crystal formation after centerline canister cooling, crystallinity as a function of temperature, density, viscosity, electrical conductivity, toxic leaching characteristics using the toxicity characteristic leach profile (TCLP), product consistency using the product consistency test (PCT), and SO 3 solubility. Overall, current models failed to adequately predict most of the properties, possibly due to differences in compositional space used to generate the models and the current test matrix. Additional work is needed to more accurately assess the impacts of high-fluoride wastes on Hanford processing, including additional data collection over a broader composition region and model development for the key models of interest such as PCT and TCLP.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS2008

Current Computational Challenges for CMC Processes, Properties, and Structures

In comparison to current state-of-the-art metallic alloys, ceramic matrix composites (CMC) offer a variety of performance advantages, such as higher temperature capability (greater than the approx.2100 F capability for best metallic alloys), lower density (approx.30-50% metal density), and lower thermal expansion. In comparison to other competing high-temperature materials, CMC are also capable of providing significantly better static and dynamic toughness than un-reinforced monolithic ceramics and significantly better environmental resistance than carbon-fiber reinforced composites. Because of these advantages, NASA, the Air Force, and other U.S. government agencies and industries are currently seeking to implement these advanced materials into hot-section components of gas turbine engines for both propulsion and power generation. For applications such as these, CMC are expected to result in many important performance benefits, such as reduced component cooling air requirements, simpler component design, reduced weight, improved fuel efficiency, reduced emissions, higher blade frequencies, reduced blade clearances, and higher thrust. Although much progress has been made recently in the development of CMC constituent materials and fabrication processes, major challenges still remain for implementation of these advanced composite materials into viable engine components. The objective of this presentation is to briefly review some of those challenges that are generally related to the need to develop physics-based computational approaches to allow CMC fabricators and designers to model (1) CMC processes for fiber architecture formation and matrix infiltration, (2) CMC properties of high technical interest such as multidirectional creep, thermal conductivity, matrix cracking stress, damage accumulation, and degradation effects in aggressive environments, and (3) CMC component life times when all of these effects are interacting in a complex stress and service environment. To put these computational issues in perspective, the various modeling needs within these three areas are briefly discussed in terms of their technical importance and their key controlling mechanistic factors as we know them today. Emphasis is placed primarily on the SiC/SiC ceramic composite system because of its higher temperature capability and enhanced development within the CMC industry. A brief summary is then presented concerning on-going property studies aimed at addressing these CMC modeling needs within NASA in terms of their computational approaches and recent important results. Finally an overview perspective is presented on those key areas where further CMC computational studies are needed today to enhance the viability of CMC structural components for high-temperature applications.

DiCarlo, James↗
DOE OSTI2021

New sterically hindered polyvinylamine-containing membranes for CO 2 capture from flue gas

Amine-containing facilitated transport membranes can have both high permeability and selectivity due to the reversible reaction between CO 2 and amino groups for effective carbon capture from flue gas. In this study, we have developed an improved method for the synthesis of high-molecular-weight sterically hindered polyvinylamine (PVAm) as the new fixed-site carrier in thin-film composite membranes for CO 2 capture. Commercially available PVAm was N-monomethylated into poly-N-methyl-N-vinylamine (PVAm-CH 3 ) using the stepwise reductive amination with a highly polar fluorinated alcohol as the solvent to enhance the equilibrium shift to the formation of the imine intermediate. The method prevented over-alkylation, resulting in the increased yield of the target product. PVAm-CH 3 exhibited excellent CO 2 facilitation with a CO 2 permeability of 445.7 Barrer (1 Barrer = 3.349 x 10 –16 mol m m –2 s –1 Pa –1 ) and a CO 2 /N 2 selectivity of 70.3, which are above the Robeson 2008 upper bound. The PVAm-CH 3 solution retained a sufficiently high viscosity after incorporating the aminoacid salt, 2-(1-piperazinyl)ethylamine sarcosinate (PZEA-Sar), as the mobile carrier for the membrane coating on nanoporous polyethersulfone (PES) substrates without any penetration issues. The resultant thin-film composite PVAm-CH3/PZEA-Sar membrane with a thickness of approximately 170 nm exhibited a superior CO 2 performance of 1071 GPU (1 GPU = 3.349 x 10 –10 mol m –2 s –1 Pa –1 ) and a CO 2 /N 2 selectivity of 183 at 57°C and a feed gas pressure of 111.64 kPa (1.5 psig). This PVAm-CH 3 /PZEA-Sar membrane surpassed the latest redefined 2019 CO 2 /N 2 upper bound and outperformed other polymer-based membranes. Density functional theory calculations also demonstrated that PVAm-CH 3 showed a stronger preference, relative to PVAm, toward the more efficient bicarbonate pathway. Thus, the steric hindrance effect of PVAm-CH 3 enhanced the solubility of CO 2 in the polymer matrix and resulted in the higher CO 2 permeance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Surprisingly high irradiation-induced defect mobility in Fe 3 O 4 as revealed through in situ transmission electron microscopy

Radiation-induced defects are expected to change the corrosion kinetics when a material is exposed to a corrosive environment. Characterization of the defects forming under irradiation and their ability to move/diffuse is therefore key to understanding how they impact the corrosion kinetics and possibly mechanisms. For that matter, Fe/Fe 3 O 4 interfaces were irradiated using 1 MeV Kr 2+ at temperatures of 273 K (25 °C), 573 K (300 °C) and 773 K (500 °C) to a maximum dose of 10 dpa (as measured in the Fe matrix) in situ in a transmission electron microscope. The evolution of the microstructure was followed as a function of the dose and temperature. The formation of defects was followed in the metal and the oxide as well as at the metal/oxide interface and characterized in terms of size and density. Additionally, the dynamic observation of the spatial distribution of the defects allowed for a qualitative assessment of the mobility of defects in the oxide as a function of temperature, revealing evidence for enhanced mobility even more so than in the Fe matrix. Mechanisms of induced defect mobility in the spinel are discussed to account for the observations.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Segmentation of RDX and TNT in X‐Ray Computed Tomography Reconstructions of Melt‐Cast Explosives

ABSTRACT Three‐dimensional mesoscale characterization of heterogeneous melt‐cast high explosives is challenging because of the difficulty differentiating binder from explosive crystals: two functionally different materials which are typically similar in density by design. Here, we report an algorithm which can differentiate hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) from 2,4,6‐trinitrotoluene (TNT) in x‐ray computed tomography (CT) volumes with tens of microns resolution. This method allows us to quantify RDX/TNT content, porosity, and RDX domain size. We calibrated the segmentation algorithm using simulated x‐ray CT volumes containing object models of RDX crystals within a TNT matrix. We then segmented and analyzed CT data for Composition B (Comp B), a 60/40 RDX/TNT mixture, and Cyclotol, a 75/25 RDX/TNT mixture. We examined melt‐cast samples fabricated with 100% theoretical maximum density (TMD) and 85% TMD. For the 100% TMD Comp B and Cyclotol samples, the RDX content values calculated by segmentation were 3% and 9% lower, respectively, than the values measured by high‐performance liquid chromatography on material from the same synthesis lots. This result is consistent with the expected underreporting of RDX content resulting from x‐ray CT resolution limits on RDX particles with diameters smaller than 25 µm. The 85% TMD samples were less accurately segmented with our algorithm due to the confounding presence of voids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1995

Cell shape, cytoskeletal mechanics, and cell cycle control in angiogenesis

Capillary endothelial cells can be switched between growth and differentiation by altering cell-extracellular matrix interactions and thereby, modulating cell shape. Studies were carried out to determine when cell shape exerts its growth-regulatory influence during cell cycle progression and to explore the role of cytoskeletal structure and mechanics in this control mechanism. When G0-synchronized cells were cultured in basic fibroblast growth factor (FGF)-containing defined medium on dishes coated with increasing densities of fibronectin or a synthetic integrin ligand (RGD-containing peptide), cell spreading, nuclear extension, and DNA synthesis all increased in parallel. To determine the minimum time cells must be adherent and spread on extracellular matrix (ECM) to gain entry into S phase, cells were removed with trypsin or induced to retract using cytochalasin D at different times after plating. Both approaches revealed that cells must remain extended for approximately 12-15 h and hence, most of G1, in order to enter S phase. After this restriction point was passed, normally 'anchorage-dependent' endothelial cells turned on DNA synthesis even when round and in suspension. The importance of actin-containing microfilaments in shape-dependent growth control was confirmed by culturing cells in the presence of cytochalasin D (25-1000 ng ml-1): dose-dependent inhibition of cell spreading, nuclear extension, and DNA synthesis resulted. In contrast, induction of microtubule disassembly using nocodazole had little effect on cell or nuclear spreading and only partially inhibited DNA synthesis. Interestingly, combination of nocodazole with a suboptimal dose of cytochalasin D (100 ng ml-1) resulted in potent inhibition of both spreading and growth, suggesting that microtubules are redundant structural elements which can provide critical load-bearing functions when microfilaments are partially compromised. Similar synergism between nocodazole and cytochalasin D was observed when cytoskeletal stiffness was measured directly in living cells using magnetic twisting cytometry. These results emphasize the importance of matrix-dependent changes in cell and nuclear shape as well as higher order structural interactions between different cytoskeletal filament systems for control of capillary cell growth during angiogenesis.

Non-NASA Center↗
DOE OSTI2025

Xenon–metal pair formation in UO 2 investigated using DFT + U

A recent experimental study on a spent uranium dioxide (UO 2 ) fuel sample from Belgium Reactor 3 identified a unique pair structure formed by the noble metal phase (NMP) and fission gas [xenon (Xe)] precipitate. However, the fundamental mechanism behind this structure remains unclear. The present study aims to provide an understanding of the interaction between five different metal precipitates [molybdenum (Mo), ruthenium (Ru), palladium (Pd), technetium (Tc), and rhodium (Rh)] and the Xe fission gas atoms in UO 2 , by using density functional theory (DFT) in combination with the Hubbard U correction to compute the formation energies involved. All DFT + U calculations were performed with occupation matrix control to ensure antiferromagnetic ordering of UO 2 . The calculated formation and binding energies of the Xe and solid fission products in the NMP reveal that these metal precipitates form stable pair structures with Xe. Notably, the formation energy of Xe–metal pairs is lower than that of the isolated single defects in all instances, with Pd and Mo showing the most favorable binding energy, likely accounting for the observed pair structure formation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Form factors and spectral densities from Lightcone Conformal Truncation

We use the method of Lightcone Conformal Truncation (LCT) to obtain form factors and spectral densities of local operators $\mathcal{O}$ in $\phi^4$ theory in two dimensions. We show how to use the Hamiltonian eigenstates from LCT to obtain form factors that are matrix elements of a local operator $\mathcal{O}$ between single-particle bra and ket states, and we develop methods that significantly reduce errors resulting from the finite truncation of the Hilbert space. We extrapolate these form factors as a function of momentum to the regime where, by crossing symmetry, they are form factors of $\mathcal{O}$ between the vacuum and a two-particle asymptotic scattering state. We also compute the momentum-space time-ordered two-point functions of local operators in LCT. These converge quickly at momenta away from branch cuts, allowing us to indirectly obtain the time-ordered correlator and the spectral density at the branch cuts. We focus on the case where the local operator $\mathcal{O}$ is the trace Θ of the stress tensor.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2013

A Patch Density Recommendation based on Convergence Studies for Vehicle Panel Vibration Response resulting from Excitation by a Diffuse Acoustic Field

Producing fluid structural interaction estimates of panel vibration from an applied pressure field excitation are quite dependent on the spatial correlation of the pressure field. There is a danger of either over estimating a low frequency response or under predicting broad band panel response in the more modally dense bands if the pressure field spatial correlation is not accounted for adequately. It is a useful practice to simulate the spatial correlation of the applied pressure field over a 2d surface using a matrix of small patch area regions on a finite element model (FEM). Use of a fitted function for the spatial correlation between patch centers can result in an error if the choice of patch density is not fine enough to represent the more continuous spatial correlation function throughout the intended frequency range of interest. Several patch density assumptions to approximate the fitted spatial correlation function are first evaluated using both qualitative and quantitative illustrations. The actual response of a typical vehicle panel system FEM is then examined in a convergence study where the patch density assumptions are varied over the same model. The convergence study results illustrate the impacts possible from a poor choice of patch density on the analytical response estimate. The fitted correlation function used in this study represents a diffuse acoustic field (DAF) excitation of the panel to produce vibration response.

Smith, Andrew↗
DOE OSTI2023

Impact of artificial topological changes on flow and transport through fractured media due to mesh resolution

Abstract We performed a set of numerical simulations to characterize the interplay of fracture network topology, upscaling, and mesh refinement on flow and transport properties in fractured porous media. We generated a set of generic three-dimensional discrete fracture networks at various densities, where the radii of the fractures were sampled from a truncated power-law distribution, and whose parameters were loosely based on field site characterizations. We also considered five network densities, which were defined using a dimensionless version of density based on percolation theory. Once the networks were generated, we upscaled them into a single continuum model using the upscaled discrete fracture matrix model presented by Sweeney et al. (2019). We considered steady, isothermal pressure-driven flow through each domain and then simulated conservative, decaying, and adsorbing tracers using a pulse injection into the domain. For each simulation, we calculated the effective permeability and solute breakthrough curves as quantities of interest to compare between network realizations. We found that selecting a mesh resolution such that the global topology of the upscaled mesh matches the fracture network is essential. If the upscaled mesh has a connected pathway of fracture (higher permeability) cells but the fracture network does not, then the estimates for effective permeability and solute breakthrough will be incorrect. False connections cannot be eliminated entirely, but they can be managed by choosing appropriate mesh resolution and refinement for a given network. Adopting octree meshing to obtain sufficient levels of refinement leads to fewer computational cells (up to a 90% reduction in overall cell count) when compared to using a uniform resolution grid and can result in a more accurate continuum representation of the true fracture network.

58 GEOSCIENCES↗
DOE OSTI2024

Searching for parity violation in SDSS DR16 Lyman-α forest data

The four-point correlation function is the lowest order correlation function for scalar fields that can be used to probe statistical parity invariance in an isotropic universe. There are intriguing claims of detection of parity violation in the 4-point function of BOSS galaxy clustering data. We apply the same estimator to the public SDSS Data Release 16 Lyman-α forest data. Lyman-α forest data probes a different redshift range and is sensitive to a different density regime using a completely different technique. A detection would therefore be a strong indication of new physics. We identify an accurate covariance matrix as a crucial impediment to performing this measurement accurately, consistent with existing literature on galaxy 4-point function. Here, we discuss several approaches to estimating the covariance matrix, several of which produce spurious detection. Using a robust, but very suboptimal, covariance matrix derived from subsample bootstrapping, we find no evidence for parity violation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2003

Calculation of Free-Free Opacities

Free-free absorption is an important contribution to the opacity for radiation transport through hot materials Temperatures can be as high as several keV, such that it becomes a computational challenge to solve the Schrodinger equation efficiently for rapidly oscillating continuum functions for high angular momenta. Several groups\footnots, including ours, have studied the phase amplitude solution (PAS) of the Schrodinger equation, in which one solves equations for the wave function amplitude and phase, which are: smooth functions of the electron energy. It is also important to have an accurate Schroudinger benchmark for the development of the PAS method. We present results for dipole matrix elements, Gaunt factors, and cross sections for the absorption of radiation at various energies for Cs XIX at temperature=100 eV and density=0.187 g/cc for our newly developed PAS and Schrodinger benchmark.

Bhatia, A. K.↗
NASA NTRS2005

THERMAL INSULATION SYSTEMS

Thermal insulation systems and with methods of their production. The thermal insulation systems incorporate at least one reflection layer and at least one spacer layer in an alternating pattern. Each spacer layer includes a fill layer and a carrier layer. The fill layer may be separate from the carrier layer, or it may be a part of the carrier layer, i.e., mechanically injected into the carrier layer or chemically formed in the carrier layer. Fill layers contain a powder having a high surface area and low bulk density. Movement of powder within a fill layer is restricted by electrostatic effects with the reflection layer combined with the presence of a carrier layer, or by containing the powder in the carrier layer. The powder in the spacer layer may be compressed from its bulk density. The thermal insulation systems may further contain an outer casing. Thermal insulation systems may further include strips and seams to form a matrix of sections. Such sections serve to limit loss of powder from a fill layer to a single section and reduce heat losses along the reflection layer.

Augustynowicz, Stanislaw D.↗
NASA NTRS2004

Photoionization of Benzene and Small Polycyclic Aromatic Hydrocarbons in Ultraviolet-Processed Astrophysical Ices: A Computational Study

We employed density functional theory (DFT) calculations to model the photoionization behavior of benzene and small polycyclic aromatic hydrocarbons when they are embedded in a matrix of water ice in order to investigate issues raised by recent experimental work by Gudipati and Allamandola. The ionization energies of benzene, naphthalene, anthracene, and pyrene were found to be lowered by 1.5-2.1 eV in water ice. Low-lying vertical electronic excitation energies were computed with time-dependent DFT for both neutral and ionized species and are found in both cases to be remarkably unaffected by the ice matrix. Chemical behavior in ultraviolet-photoprocessed ices is also discussed, with a focus on electron recombination and pathways leading to phenol and analogous products.

Woon, D. E.↗
DOE OSTI2020

General Bayesian Inference over the Stiefel Manifold via the Givens Transform

We introduce here an approach based on the Givens representation for posterior inference in statistical models with orthogonal matrix parameters, such as factor models and probabilistic principal component analysis (PPCA). We show how the Givens representation can be used to develop practical methods for transforming densities over the Stiefel manifold into densities over subsets of Euclidean space. We demonstrate how to deal with issues arising from the topology of the Stiefel manifold and how to inexpensively compute the change-of-measure terms. We introduce an auxiliary parameter approach that limits the impact of topological issues. We provide both analysis of our methods and numerical examples demonstrating the effectiveness of the approach. We also discuss how our Givens representation can be used to define general classes of distributions over the space of orthogonal matrices. We then give demonstrations on several examples showing how the Givens approach performs in practice in comparison with other methods.

97 MATHEMATICS AND COMPUTING↗