Search NASA⌕ Search

SEARCH · Search NASA

Results for “matrix structures”

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 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Data-driven probability concentration and sampling on manifold

A new methodology is proposed for generating realizations of a random vector with values in a finite-dimensional Euclidean space that are statistically consistent with a dataset of observations of this vector. The probability distribution of this random vector, while a priori not known, is presumed to be concentrated on an unknown subset of the Euclidean space. A random matrix is introduced whose columns are independent copies of the random vector and for which the number of columns is the number of data points in the dataset. The approach is based on the use of (i) the multidimensional kernel-density estimation method for estimating the probability distribution of the random matrix, (ii) a MCMC method for generating realizations for the random matrix, (iii) the diffusion-maps approach for discovering and characterizing the geometry and the structure of the dataset, and (iv) a reduced-order representation of the random matrix, which is constructed using the diffusion-maps vectors associated with the first eigenvalues of the transition matrix relative to the given dataset. The convergence aspects of the proposed methodology are analyzed and a numerical validation is explored through three applications of increasing complexity. The proposed method is found to be robust to noise levels and data complexity as well as to the intrinsic dimension of data and the size of experimental datasets. Both the methodology and the underlying mathematical framework presented in this paper contribute new capabilities and perspectives at the interface of uncertainty quantification, statistical data analysis, stochastic modeling and associated statistical inverse problems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Evaluation of a Fluorochlorozirconate Glass-Ceramic Storage Phosphor Plate for Gamma-Ray Computed Radiography

In this paper, a fluorochlorozirconate (FCZ) glass-ceramic containing orthorhombic barium chloride crystals doped with divalent europium was evaluated for use as a storage phosphor in gamma-ray imaging. X-ray diffraction and phosphorimetry of the glass-ceramic sample showed the presence of a significant amount of orthorhombic barium chloride crystals in the glass matrix. Transmission electron microscopy and scanning electron microscopy were used to identify crystal size, structure, and morphology. The size of the orthorhombic barium chloride crystals in the FCZ glass matrix was very large, ~0.5–0.7 μm, which can limit image resolution. The FCZ glass-ceramic sample was exposed to 1 MeV gamma rays to determine its photostimulated emission characteristics at high energies, which were found to be suitable for imaging applications. Test images were made at 2 MeV energies using gap and step wedge phantoms. Gaps as small as 101.6 μm in a 440 stainless steel phantom were imaged using the sample imaging plate. Analysis of an image created using a depleted uranium step wedge phantom showed that emission is proportional to incident energy at the sample and the estimated absorbed dose. Finally, the results showed that the sample imaging plate has potential for gamma-ray-computed radiography and dosimetry applications.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Apparatus for forming a continuous lightweight multicell material

An apparatus is described for producing a lightweight structural material (12), by forming gas-filled shells (38) of molten material from a matrix of nozzles (22) that form shells of very uniform size at very uniform rates. The matrix of molten shells coalesce into a multi-cell material of controlled cellular structure. The shells can be of two different sizes (38, 44) that are interspersed, to form a multicell material that has a regular cell pattern but which avoids planes of weakness and localized voids. The gas (50) in the shells can be under a high pressure, and can be a fire extinguishing gas.

Wang, Taylor G.↗
DOE OSTI2011

Tracking a defined route for O[subscript 2] migration in a dioxygen-activating diiron enzyme

For numerous enzymes reactive toward small gaseous compounds, growing evidence indicates that these substrates diffuse into active site pockets through defined pathways in the protein matrix. Toluene/o-xylene monooxygenase hydroxylase is a dioxygen-activating enzyme. Structural analysis suggests two possible pathways for dioxygen access through the {alpha}-subunit to the diiron center: a channel or a series of hydrophobic cavities. To distinguish which is utilized as the O{sub 2} migration pathway, the dimensions of the cavities and the channel were independently varied by site-directed mutagenesis and confirmed by X-ray crystallography. The rate constants for dioxygen access to the diiron center were derived from the formation rates of a peroxodiiron(III) intermediate, generated upon treatment of the diiron(II) enzyme with O2. This reaction depends on the concentration of dioxygen to the first order. Altering the dimensions of the cavities, but not the channel, changed the rate of dioxygen reactivity with the enzyme. These results strongly suggest that voids comprising the cavities in toluene/o-xylene monooxygenase hydroxylase are not artifacts of protein packing/folding, but rather programmed routes for dioxygen migration through the protein matrix. Because the cavities are not fully connected into the diiron active center in the enzyme resting state, conformational changes will be required to facilitate dioxygen access to the diiron center. We propose that such temporary opening and closing of the cavities may occur in all bacterial multicomponent monooxygenases to control O{sub 2} consumption for efficient catalysis. Our findings suggest that other gas-utilizing enzymes may employ similar structural features to effect substrate passage through a protein matrix.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2006

Micromechanics and Piezo Enhancements of HyperSizer

The commercial HyperSizer aerospace-composite-material-structure-sizing software has been enhanced by incorporating capabilities for representing coupled thermal, piezoelectric, and piezomagnetic effects on the levels of plies, laminates, and stiffened panels. This enhancement is based on a formulation similar to that of the pre-existing HyperSizer capability for representing thermal effects. As a result of this enhancement, the electric and/or magnetic response of a material or structure to a mechanical or thermal load, or its mechanical response to an applied electric or magnetic field can be predicted. In another major enhancement, a capability for representing micromechanical effects has been added by establishment of a linkage between HyperSizer and Glenn Research Center s Micromechanics Analysis Code With Generalized Method of Cells (MAC/GMC) computer program, which was described in several prior NASA Tech Briefs articles. The linkage enables Hyper- Sizer to localize to the fiber and matrix level rather than only to the ply level, making it possible to predict local failures and to predict properties of plies from those of the component fiber and matrix materials. Advanced graphical user interfaces and database structures have been developed to support the new HyperSizer micromechanics capabilities.

Arnold, Steven M.↗
DOE OSTI2013

TEM study of {beta} Prime precipitate interaction mechanisms with dislocations and {beta} Prime interfaces with the aluminium matrix in Al-Mg-Si alloys

The interaction mechanisms between dislocations and semi-coherent, needle-shaped {beta} Prime precipitates in Al-Mg-Si alloys have been studied by High Resolution Transmission Electron Microscopy (HRTEM). Dislocation loops appearing as broad contrast rings around the precipitate cross-sections were identified in the Al matrix. A size dependency of the interaction mechanism was observed; the precipitates were sheared when the longest dimension of their cross-section was shorter than approximately 15 nm, and looped otherwise. A more narrow ring located between the Al matrix and bulk {beta} Prime indicates the presence of a transition interface layer. Together with the bulk {beta} Prime structure, this was further investigated by High Angle Annular Dark Field Scanning TEM (HAADF-STEM). In the bulk {beta} Prime a higher intensity could be correlated with a third of the Si-columns, as predicted from the published structure. The transition layer incorporates Si columns in the same arrangement as in bulk {beta} Prime , although it is structurally distinct from it. The Z-contrast information and arrangement of these Si-columns demonstrate that they are an extension of the Si-network known to structurally connect all the precipitate phases in the Al-Mg-Si(-Cu) system. The width of the interface layer was estimated to about 1 nm. - Highlights: Black-Right-Pointing-Pointer {beta} Prime is found to be looped at sizes larger than 15 nm (cross section diameter). Black-Right-Pointing-Pointer {beta} Prime is found to be sheared at sizes smaller than 15 nm (cross section diameter). Black-Right-Pointing-Pointer The recently determined crystal structure of {beta} Prime is confirmed by HAADF-STEM. Black-Right-Pointing-Pointer Between {beta} Prime and the Al-matrix a transition layer of about 1 nm is existent. Black-Right-Pointing-Pointer The {beta} Prime /matrix layer is structurally distinct from bulk {beta} Prime and the aluminium matrix.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Multisliced gausslet basis sets for electronic structure

We introduce highly local basis sets for electronic structure which are very efficient for correlation calculations near the complete basis set limit. Our approach is based on gausslets, recently introduced waveletlike smooth orthogonal functions. We adapt the gausslets to particular systems using one-dimensional (1D) coordinate transformations, putting more basis functions near the nuclei, while maintaining orthogonality. Furthermore, three-dimensional basis functions are composed out of products of the 1D functions in an efficient way called multislicing. We demonstrate these bases with both Hartree-Fock and density matrix renormalization group calculations on hydrogen chain systems. With both methods, we can go to higher accuracy in the complete basis set limit than is practical for conventional Gaussian basis sets, with errors near 0.1 mH per atom.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2003

Polymer Matrix Composites for Propulsion Systems

The Access-to-Space study identified the requirement for lightweight structures to achieve orbit with a single-stage vehicle. Thus a task was undertaken to examine the use of polymer matrix composites for propulsion components. It was determined that the effort of this task would be to extend previous efforts with polymer matrix composite feedlines and demonstrate the feasibility of manufacturing large diameter feedlines with a complex shape and integral flanges, (i.e. all one piece with a 90 deg bend), and assess their performance under a cryogenic atmosphere.

Nettles, Alan T.↗
DOE OSTI2012

Crystal Structure of the C-terminal Region of Streptococcus mutans Antigen I/II and Characterization of Salivary Agglutinin Adherence Domains

The Streptococcus mutans antigen I/II (AgI/II) is a cell surface-localized protein that adheres to salivary components and extracellular matrix molecules. Here we report the 2.5 {angstrom} resolution crystal structure of the complete C-terminal region of AgI/II. The C-terminal region is comprised of three major domains: C{sub 1}, C{sub 2}, and C{sub 3}. Each domain adopts a DE-variant IgG fold, with two {beta}-sheets whose A and F strands are linked through an intramolecular isopeptide bond. The adherence of the C-terminal AgI/II fragments to the putative tooth surface receptor salivary agglutinin (SAG), as monitored by surface plasmon resonance, indicated that the minimal region of binding was contained within the first and second DE-variant-IgG domains (C{sub 1} and C{sub 2}) of the C terminus. The minimal C-terminal region that could inhibit S. mutans adherence to SAG was also confirmed to be within the C{sub 1} and C{sub 2} domains. Competition experiments demonstrated that the C- and N-terminal regions of AgI/II adhere to distinct sites on SAG. A cleft formed at the intersection between these C{sub 1} and C{sub 2} domains bound glucose molecules from the cryo-protectant solution, revealing a putative binding site for its highly glycosylated receptor SAG. Finally, electron microscopy images confirmed the elongated structure of AgI/II and enabled building a composite tertiary model that encompasses its two distinct binding regions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2010

Quantifying the nucleon's pion cloud with transverse charge densities

The transverse densities in a fast-moving nucleon offer a model-independent framework for analyzing the spatial structure of the pion cloud and its role in current matrix elements. We calculate the chiral large-distance component of the charge density in a dispersion representation of the form factor and discuss its partonic interpretation. It dominates over the nonchiral density only at surprisingly large distances above {approx}2 fm. The chiral component can be probed in precision low-Q{sup 2} elastic eN scattering or in peripheral deep-inelastic processes that resolve its quark/gluon content.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Soft network composite materials with deterministic and bio-inspired designs

Hard and soft structural composites found in biology provide inspiration for the design of advanced synthetic materials. Many examples of bio-inspired hard materials can be found in the literature; far less attention has been devoted to soft systems. Here we introduce deterministic routes to low-modulus thin film materials with stress/strain responses that can be tailored precisely to match the non-linear properties of biological tissues, with application opportunities that range from soft biomedical devices to constructs for tissue engineering. The approach combines a low-modulus matrix with an open, stretchable network as a structural reinforcement that can yield classes of composites with a wide range of desired mechanical responses, including anisotropic, spatially heterogeneous, hierarchical and self-similar designs. Demonstrative application examples in thin, skin-mounted electrophysiological sensors with mechanics precisely matched to the human epidermis and in soft, hydrogel-based vehicles for triggered drug release suggest their broad potential uses in biomedical devices.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Electron Paramagnetic Resonance of Cr{sup 3+} Ions in Single Crystals of Yttrium Aluminum Borate YAl{sub 3}(BO{sub 3}){sub 4}

Single crystal of yttrium aluminum borate YAl{sub 3}(BO{sub 3}){sub 4} doped with chromium ions (1 at %) was studied using electron paramagnetic resonance spectroscopy. It is shown that chromium ions introduced into the sample occupy yttrium ion sites in the crystal structure. The parameters of the spin Hamiltonian of Cr{sup 3+} ions in the YAl{sub 3}(BO{sub 3}){sub 4} matrix are determined at different temperatures. The sign of the fine structure parameter D allows the conclusion that the chromium ions in YA1{sub 3}(BO{sub 3}){sub 4} single crystals have an easy-plane anisotropy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1990

Evaluation of thermal and mechanical loading effects on the structural behavior of a SIC/titanium composite

Composite specimens of titanium-15-3 matrix reinforced with continuous SCS-6 silicon carbide fibers were tested under a variety of thermal and mechanical loadings. A combined experimental/finite element approach was used to estimate the effective in situ modulus of the matrix material and to evaluate changes in modulus due to the applied loads. Several fiber orientations were tested. Results indicate that the effect of thermal loads on composite stiffness varies with fiber orientation. Applications of this method to test specimens damaged by uniaxial tension, thermal cycling, and isothermal fatigue loadings are used to illustrate that by monitoring overall structural behavior, changes in stiffness caused by thermomechanical loading can be detected.

Grady, J. E.↗
DOE OSTI2017

Influence of surface morphology and UFG on damping and mechanical properties of composite reinforced with spinel MgAl{sub 2}O{sub 4}-SiC core-shell microcomposites

Interface between ceramic particulate and matrix is known to control the response of the materials and functionality of the composite. Among numerous physical properties, grain structure of the materials has also played a significant role in defining the behaviour of metal matrix composites. Usually, silicon carbide (SiC) particles show poor interfacial wettability in aluminium melt. Herein, we were successfully synthesized magnesium oxide (MgO) and nanocrystalline magnesium aluminate (MgAl{sub 2}O{sub 4}) spinel coated silicon carbide (SiC) core-shell micro-composites through sol-gel technique to improve the wettability of dispersoids. Core-shell structures of submicron size were thoroughly investigated by various characterization techniques. Further, aluminium matrix composites incorporated with pristine SiC, MgO grafted SiC and MgAl{sub 2}O{sub 4} grafted SiC particles were fabricated by stir casting technique, respectively. Additionally, as-cast composites were processed via friction stir processing (FSP) technique to observe the influence of grain refinement on mechanical and damping properties. Electron back scattered diffraction (EBSD), Field emission scanning electron microscopy (FE-SEM) and X-ray energy dispersion spectroscopy (EDX) analysis were conducted for investigating grain size refinement, adequate dispersion, stability and de-agglomeration of encapsulated SiC particles in aluminium matrix. The mechanical as well as thermal cyclic (from − 100 to 400 °C) damping performance of the as-cast and friction stir processed composites were studied, respectively. Finally, the enhanced properties were attributable to reduced agglomeration, stabilization and proper dispersion of the tailored SiC particles Al matrix. - Highlights: •Synthesizing a novel coating layer of MgO and MgAl{sub 2}O{sub 4} spinel onto SiC particles •Significant improvement in UTS and hardness by reinforcing tailored SiC in Al •Significant grain refinements were obtained through FSP •SiC/MgAl{sub 2}O{sub 4}/Al exhibits ~ 61% higher storage modulus as compare to pure Al after FSP.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Theoretical uncertainties in the nuclear matrix elements of neutrinoless double beta decay: The transition operator

We explore the theoretical uncertainties related to the transition operator of neutrinoless double-beta (0νββ) decay. The transition operator used in standard calculations is a product of one-body currents, that can be obtained phenomenologically as in Tomoda [1] or Šimkovic et al. [2]. However, corrections to the operator are hard to obtain in the phenomenological approach. Instead, we calculate the 0νββ decay operator in the framework of chiral effective theory (EFT), which gives a systematic order-by-order expansion of the transition currents. At leading orders in chiral EFT we reproduce the standard one-body currents of Refs. [1] and [2]. Corrections appear as two-body (2b) currents predicted by chiral EFT. We compute the effects of the leading 2b currents to the nuclear matrix elements of 0νββ decay for several transition candidates. The 2b current contributions are related to the quenching of Gamow-Teller transitions found in nuclear structure calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

The Interplay of Binary and Quantitative Structure on the Stability of Mutualistic Networks

Synopsis Understanding how the structure of biological systems impacts their resilience (broadly defined) is a recurring question across multiple levels of biological organization. In ecology, considerable effort has been devoted to understanding how the structure of interactions between species in ecological networks is linked to different broad resilience outcomes, especially local stability. Still, nearly all of that work has focused on interaction structure in presence-absence terms and has not investigated quantitative structure, i.e., the arrangement of interaction strengths in ecological networks. We investigated how the interplay between binary and quantitative structure impacts stability in mutualistic interaction networks (those in which species interactions are mutually beneficial), using community matrix approaches. We additionally examined the effects of network complexity and within-guild competition for context. In terms of structure, we focused on understanding the stability impacts of nestedness, a structure in which more-specialized species interact with smaller subsets of the same species that more-generalized species interact with. Most mutualistic networks in nature display binary nestedness, which is puzzling because both binary and quantitative nestedness are known to be destabilizing on their own. We found that quantitative network structure has important consequences for local stability. In more-complex networks, binary-nested structures were the most stable configurations, depending on the quantitative structures, but which quantitative structure was stabilizing depended on network complexity and competitive context. As complexity increases and in the absence of within-guild competition, the most stable configurations have a nested binary structure with a complementary (i.e., anti-nested) quantitative structure. In the presence of within-guild competition, however, the most stable networks are those with a nested binary structure and a nested quantitative structure. In other words, the impact of interaction overlap on community persistence is dependent on the competitive context. These results help to explain the prevalence of binary-nested structures in nature and underscore the need for future empirical work on quantitative structure.

Zoology↗
NASA NTRS1990

Evaluation of thermal and mechanical loading effects on the structural behavior of a SiC/titanium composite

Composite specimens of titanium-15-3 matrix reinforced with continuous SCS-6 silicon carbide fibers were tested under a variety of thermal and mechanical loadings. A combined experimental/finite element approach was used to estimate the effective in-situ modulus of the matrix material and to evaluate changes in modulus due to the applied loads. Several fiber orientations were tested. Results indicate that the effect of the thermal loads on composite stiffness varies with fiber orientation. Applications of this method to test specimens damaged by uniaxial tension, thermal cycling, and isothermal fatigue loadings are used to illustrate that by monitoring overall structural behavior, changes in stiffness caused by thermomechanical loading can be detected.

Grady, Joseph E.↗
DOE OSTI2017

High pressure synthesis and thermoelectric properties of micro/nano structures CoSb{sub 3}

Nano-particle and defect have been proved to be effective in depressing the lattice thermal conductivity and improving the performance of thermoelectric materials. In this work, In{sub 0.5}Sn{sub x}Co{sub 4}Sb{sub 12} were prepared using a high pressure and high temperature (HPHT) method, In and Sn was assumed that In plays the role of a filler and occupies the Sb-icosahedron voids. Doping of In and Sn results in the defects, nanostructuring, and mesoscale structuring were all combined into a single skutterudite matrix. The thermoelectric properties were measured in the temperature range of 321–710 K. As expected, with the synthetic pressures increased，the thermal conductivity of samples improved significantly. The minimum value of In{sub 0.5}Sn{sub 0.4}Co{sub 4}Sb{sub 12} synthesized at 3.8 GPa is 1.79 Wm{sup −1} K{sup −1} and the highest Seebeck coefficient of sample In{sub 0.5}Sn{sub 0.2}Co{sub 4}Sb{sub 12} synthesized at 2.8 GPa reached 222 μV K{sup −1} finally. - Graphical abstract: Micro/nano structures CoSb{sub 3} could be quickly prepared by HPHT method, the defects, nanostructuring and mesoscale structuring are uniformly distributed in the whole sample. Display Omitted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗