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At least 1,135 records · Page 63

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NASA NTRS1987

Hypersonic structures and materials - A progress report

The weight of a hypersonic, airbreathing SSTO vehicle may be more critical than for any previous aerospacecraft; an evaluation is accordingly made of the development status and applicability of intermetallic compounds, metal-matrix composites, carbon-carbon composites, ceramics, and ceramic-matrix composites applicable to SSTO craft primary structures. Aerothermal, aerothermoelastic, and acoustic loads are high because the airbreathing SSTO vehicle must follow a high dynamic pressure trajectory in order to achieve the requisite propulsive efficiency. Attention is given to the prospects for integral cryogenic tankage and actively hydrogen-cooled airframe and engine structures.

Jackson, L. Robert↗

DOE OSTI2015

Seeding for sirtuins: microseed matrix seeding to obtain crystals of human Sirt3 and Sirt2 suitable for soaking

In the present study, microseed matrix seeding was successfully applied to obtain a large number of crystals of the human sirtuin isotypes Sirt2 and Sirt3. These crystals appeared predictably in diverse crystallization conditions, diffracted to a higher resolution than reported in the literature and were subsequently used to study the protein–ligand interactions of two indole inhibitors. Sirtuins constitute a family of NAD{sup +}-dependent enzymes that catalyse the cleavage of various acyl groups from the ∊-amino group of lysines. They regulate a series of cellular processes and their misregulation has been implicated in various diseases, making sirtuins attractive drug targets. To date, only a few sirtuin modulators have been reported that are suitable for cellular research and their development has been hampered by a lack of structural information. In this work, microseed matrix seeding (MMS) was used to obtain crystals of human Sirt3 in its apo form and of human Sirt2 in complex with ADP ribose (ADPR). Crystal formation using MMS was predictable, less error-prone and yielded a higher number of crystals per drop than using conventional crystallization screening methods. The crystals were used to solve the crystal structures of apo Sirt3 and of Sirt2 in complex with ADPR at an improved resolution, as well as the crystal structures of Sirt2 in complex with ADPR and the indoles EX527 and CHIC35. These Sirt2–ADPR–indole complexes unexpectedly contain two indole molecules and provide novel insights into selective Sirt2 inhibition. The MMS approach for Sirt2 and Sirt3 may be used as the basis for structure-based optimization of Sirt2/3 inhibitors in the future.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2021

Determination of oxidation rates and volatile oxidation products for HTGR graphite matrix material exposed to steam atmospheres

High-temperature gas-cooled reactors (HTGRs) in operation use tristructural isotropic (TRISO) particles embedded in graphite and carbonized resin matrix to form the fuel element. This graphite matrix material serves as a supportive structural element, heat transfer medium, and neutron moderator. In HTGR designs, fuel compacts are exposed to helium coolant, which facilitates high outlet temperatures (750°C 2 O, 800°C 2 , and H 2 , are quantified in varied oxidant atmospheres using a coupled thermogravimetric analyzer and mass spectrometer. Furthermore, oxidation rates reported here for varied steam (H 2 O [g]) atmospheres are predominantly linear and comparable with literature values in the range of tested temperatures (800–1200°C). Changes in dominant matrix oxidation products from primarily CO to a mixture of CO, CO 2 , and H 2 were observed at higher temperatures (≥1000°C) and steam atmospheres (≥5 kPa pH 2 O). Kinetic data indicates that there was no shift in oxidation regime with chemical oxidation occurring at all temperatures and H2O (g) atmospheres tested. These data provide insight into the oxidation behavior of graphite matrix material and will inform future testing conditions, notably mixed atmospheric conditions, of HTGR fuel elements.

36 MATERIALS SCIENCE↗

DOE OSTI2011

A new model to simulate the elastic properties of mineralized collagen fibril.

Bone, because of its hierarchical composite structure, exhibits an excellent combination of stiffness and toughness, which is due substantially to the structural order and deformation at the smaller length scales. Here, we focus on the mineralized collagen fibril, consisting of hydroxyapatite plates with nanometric dimensions aligned within a protein matrix, and emphasize the relationship between the structure and elastic properties of a mineralized collagen fibril. We create two- and three-dimensional representative volume elements to represent the structure of the fibril and evaluate the importance of the parameters defining its structure and properties of the constituent mineral and collagen phase. Elastic stiffnesses are calculated by the finite element method and compared with experimental data obtained by synchrotron X-ray diffraction. The computational results match the experimental data well, and provide insight into the role of the phases and morphology on the elastic deformation characteristics. Also, the effects of water, imperfections in the mineral phase and mineral content outside the mineralized collagen fibril upon its elastic properties are discussed.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2018

Transdermal Delivery of Nicotine Using Pectin Isolated from Durian Fruit-Hulls-Based Polymer Blends as a Matrix Layer

Many natural polymers with various chemical structures are used to prepare transdermal patches. Pectin is a one interesting type of polymer because it can control drug release when used in transdermal patches. In Thailand, the waste from durian fruit-hulls is a major problem for the environment. However, the pectin from it can be isolated under acid conditions and used to prepare transdermal patches for nicotine delivery which has not yet been reported. As the isolated pectin is a natural polymer, the film made from isolated pectin is a brittle; therefore, adding a low protein natural rubber latex (LPNRL) polymer was needed to increase its flexibility. The transdermal patches were amorphous and had T{sub g} values ranging from 81.0 to 93.3 °C. Moisture uptake, swelling ratio, and erosion values of the patches were significantly decreased after addition of LPNRL, which resulted in low hydrophilicity. The in vitro release and permeation of nicotine depends on the hydrophilicity of the patches. The kinetic models for in vitro release and permeation of nicotine were Higuchi model and zero order, respectively. In conclusion, pectin isolated from fruit-hulls of Mon Thong durians is an effective polymer to control the release of nicotine. It also is an option that could solve the environmental problems caused by durian fruit-hulls waste.

36 MATERIALS SCIENCE↗

NASA NTRS1969

A description of the computer program STIFEIG for structural dynamic analysis

FORTRAN computer program for stiffness matrix eigenvalue calculation

Hou, S. N.↗

DOE OSTI2012

A new model to simulate the elastic properties of mineralized collagen fibril

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2011

Reactions between chlorine atom and acetylene in solid para-hydrogen: Infrared spectrum of the 1-chloroethyl radical

We applied infrared matrix isolation spectroscopy to investigate the reactions between Cl atom and acetylene (C{sub 2}H{sub 2}) in a para-hydrogen (p-H{sub 2}) matrix at 3.2 K; Cl was produced via photodissociation at 365 nm of matrix-isolated Cl{sub 2} in situ. The 1-chloroethyl radical ({center_dot}CHClCH{sub 3}) and chloroethene (C{sub 2}H{sub 3}Cl) are identified as the main products of the reaction Cl + C{sub 2}H{sub 2} in solid p-H{sub 2}. IR absorption lines at 738.2, 1027.6, 1283.4, 1377.1, 1426.6, 1442.6, and 2861.2 cm{sup -1} are assigned to the 1-chloroethyl radical. For the reaction of Cl + C{sub 2}D{sub 2}, lines due to the {center_dot}CDClCH{sub 2}D radical and trans-CHDCDCl are observed; the former likely has a syn-conformation. These assignments are based on comparison of observed vibrational wavenumbers and {sup 13}C- and D-isotopic shifts with those predicted with the B3LYP/aug-cc-pVDZ and MP2/aug-cc-pVDZ methods. Our observation indicates that the primary addition product of Cl + C{sub 2}H{sub 2}, 2-chlorovinyl ({center_dot}CHCHCl) reacts readily with a neighboring p-H{sub 2} molecule to form {center_dot}CHClCH{sub 3} and C{sub 2}H{sub 3}Cl. Observation of {center_dot}CDClCH{sub 2}D and trans-CHDCDCl from Cl + C{sub 2}D{sub 2} further supports this conclusion. Although the reactivity of p-H{sub 2} appears to be a disadvantage for making highly reactive free radicals in solid p-H{sub 2}, the formation of 1-chloroethyl radical indicates that this secondary reaction might be advantageous in producing radicals that are difficult to prepare from simple photolysis or bimolecular reactions in situ.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2011

Blackbody radiation shift, multipole polarizabilities, oscillator strengths, lifetimes, hyperfine constants, and excitation energies in Ca{sup +}

A systematic study of Ca{sup +} atomic properties is carried out using a high-precision relativistic all-order method where all single, double, and partial triple excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. Reduced matrix elements, oscillator strengths, transition rates, and lifetimes are determined for the levels up to n=7. Recommended values and estimates of their uncertainties are provided for a large number of electric-dipole transitions. Electric-dipole scalar polarizabilities for the 5s, 6s, 7s, 8s, 4p{sub j}, 5p{sub j}, 3d{sub j}, and 4d{sub j} states and tensor polarizabilities for the 4p{sub 3/2}, 5p{sub 3/2}, 3d{sub j}, and 4d{sub j} states in Ca{sup +} are calculated. Methods are developed to accurately treat the contributions from highly excited states, resulting in significant (factor of 3) improvement in the accuracy of the 3d{sub 5/2} static polarizability value, 31.8(3)a{sub 0}{sup 3}, in comparison with the previous calculation [Arora et al., Phys. Rev. A 76, 064501 (2007).]. The blackbody radiation shift of the 4s-3d{sub 5/2} clock transition in Ca{sup +} is calculated to be 0.381(4) Hz at room temperature, T=300 K. Electric-quadrupole 4s-nd and electric-octupole 4s-nf matrix elements are calculated to obtain the ground-state multipole E2 and E3 static polarizabilities. Excitation energies of the ns, np, nd, nf, and ng states with n{<=} 7 in are evaluated and compared with experiment. Recommended values are provided for the 7p{sub 1/2}, 7p{sub 3/2}, 8p{sub 1/2}, and 8p{sub 3/2} removal energies for which experimental measurements are not available. The hyperfine constants A are determined for the low-lying levels up to n=7. The quadratic Stark effect on hyperfine structure levels of {sup 43}Ca{sup +} ground state is investigated. These calculations provide recommended values critically evaluated for their accuracy for a number of Ca{sup +} atomic properties for use in planning and analysis of various experiments as well as theoretical modeling.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2016

Multidimensional solid-state NMR spectroscopy of plant cell walls

Plant biomass has become an important source of bio-renewable energy in modern society. The molecular structure of plant cell walls is difficult to characterize by most atomic-resolution techniques due to the insoluble and disordered nature of the cell wall. Solid-state NMR (SSNMR) spectroscopy is uniquely suited for studying native hydrated plant cell walls at the molecular level with chemical resolution. Significant progress has been made in the last five years to elucidate the molecular structures and interactions of cellulose and matrix polysaccharides in plant cell walls. These studies have focused on primary cell walls of growing plants in both the dicotyledonous and grass families, as represented by the model plants Arabidopsis thaliana, Brachypodium distachyon, and Zea mays. To date, these SSNMR results have shown that 1) cellulose, hemicellulose, and pectins form a single network in the primary cell wall; 2) in dicot cell walls, the protein expansin targets the hemicellulose-enriched region of the cellulose microfibril for its wall-loosening function; and 3) primary wall cellulose has polymorphic structures that are distinct from the microbial cellulose structures. This article summarizes these key findings, and points out future directions of investigation to advance our fundamental understanding of plant cell wall structure and function.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2018

Size Dependences of the Magnetic Properties of Superconducting Lead–Porous Glass Nanostructures

Superconducting structures Pb–PG formed by filling a porous glass matrix with the lead from melt under pressure have been investigated. Samples with characteristic pore structure diameters of d ≈ 7, 3, and 2 nm have been studied. It has been found that the critical temperature of the superconducting transition in the samples under study is similar to the corresponding value T{sub c} ≈ 7.2 K for bulk lead. At the same time, it has been observed that the critical magnetic field of the nanocomposites, which attains H{sub c}(T = 0 K) ≈ 165 kOe for Pb–PG (3 nm), exceeds several times the value H{sub c}(0) = 803 Oe for bulk lead. The low-temperature magnetic- field dependences of magnetic moment M(H) contain quasi-periodic flux jumps, which vanish with a decrease in the lead nanostructure diameter. A qualitative model of the observed effects is considered.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2025

Microstructure of Neutron-Irradiated Al 3 Hf-Al Thermal Neutron Absorber Materials

A thermal neutron-absorbing metal matrix composite (MMC) comprised of Al 3 Hf particles in an aluminum matrix was developed to filter out thermal neutrons and create a fast flux environment for material testing in a mixed-spectrum nuclear reactor. Intermetallic Al 3 Hf particles capture thermal neutrons and are embedded in a highly conductive aluminum matrix that provides conductive cooling of the heat generated due to thermal neutron capture by the hafnium. These Al 3 Hf-Al MMCs were fabricated using powder metallurgy via hot pressing. The specimens were neutron-irradiated to between 1.12 and 5.38 dpa and temperatures ranging from 286 °C to 400 °C. The post-irradiation examination included microstructure characterization using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy. This study reports the microstructural observations of four irradiated samples and one unirradiated control sample. All the samples showed the presence of oxide at the particle–matrix interface. The irradiated specimens revealed needle-like structures that extended from the surface of the Al 3 Hf particles into the Al matrix. An automated segmentation tool was implemented based on a YOLO11 computer vision-based approach to identify dislocation lines and loops in TEM images of the irradiated Al-Al 3 Hf MMCs. This work provides insight into the microstructural stability of Al 3 Hf-Al MMCs under irradiation, supporting their consideration as a novel neutron absorber that enables advanced spectral tailoring.

36 MATERIALS SCIENCE↗

NASA NTRS1985

Free-Vibration Analysis of Structures

Improved numerical procedure more than twice as fast as previous methods. Unified numerical algorithm efficiently solves free-vibration problems of stationary or spinning structures with or without viscous or structural damping. Algorithm used to solve static problems involving multiple loads and to solve quadratic matrix eigenvalue problems associated with finite-dynamic-element structural discretization.

Gupta, K. K.↗

NASA NTRS2018

Implementation of a Matrix Crack Spacing Parameter in a Continuum Damage Mechanics Finite Element Model

Continuum Damage Mechanics (CDM) based progressive damage and failure analysis (PDFA) methods have demonstrated success in a variety of finite element analysis (FEA) implementations. However, the technical maturity of CDM codes has not yet been proven for the full design space of composite materials in aerospace applications. CDM-based approaches represent the presence of damage by changing the local material stiffness definitions and without updating the original mesh or element integration schemes. Without discretely representing cracks and their paths through the mesh, damage in models with CDM-based materials is often distributed in a region of partially damaged elements ahead of stress concentrations. Having a series of discrete matrix cracks represented by a softened region may affect predictions of damage propagation and, thus, structural failure. This issue can be mitigated by restricting matrix damage development to discrete, fiber-aligned rows of elements; hence CDM-based matrix cracks can be implemented to be more representative of discrete matrix cracks. This paper evaluates the effect of restricting CDM matrix crack development to discrete, fiber-aligned rows where the spacing of these rows is controlled by a user-defined crack spacing parameter. Initially, the effect of incrementally increasing matrix crack spacing in a unidirectional center notch coupon is evaluated. Then, the lessons learned from the center notch specimen are applied to open-hole compression finite element models. Results are compared to test data, and the limitations, successes, and potential of the matrix crack spacing approach are discussed.

Hyder, Imran↗

DOE OSTI2012

Very High Efficiency, Hybrid Organic-Inorganic Photovoltaic Cells

This SETP project focuses on developing highly efficient, hybrid organic inorganic photovoltaic (OIPV) cells. The goal is to greatly enhance the power conversion efficiency of hybrid OIPV cells using several innovative approaches. The specific objectives are: (i) to develop new inorganic nanocrystals along with conjugated oligomers and polymers to improve their matching with the solar spectrum; (ii) to engineer the interfacial electronic structures at the hybrid interface to minimize energy and carrier losses during charge transfer; (iii) to understand the assembly of hybrid polymer/nanorod composites and demonstrate hybrid nanostructures that facilitate carrier transport and collection; and (iv) to demonstrate high efficiency hybrid OIPV cells by effectively incorporating materials absorbing in different spectral regions. Through this project, the research team at the University of Florida synthesized a series of new functional organic materials and colloidal nanocrystals with optical absorption covering the near-ultraviolet, visible, and near-infrared regions of the solar spectrum. The team also demonstrated improved understandings on how to control the morphological structure of the organic/inorganic hybrid active layer as well as on the orientation of anisotropic nanostructures in the organic matrix. With the demonstration of several innovative device structures, the efficiency of such hybrid photovoltaic cells was drastically increased. The introduction of proper chemical treatment of the nanocrystal/organic interface and the demonstration of a new light trapping technique (which can also be easily scaled up for large area device fabrication) also contributed to the significant increase in device efficiency. The new knowledge on material synthesis, material processing, device physics, and optical design gained from this project will greatly contribute to the further development of this low-cost PV technology.

14 SOLAR ENERGY↗

DOE OSTI2013

Effect of re-melting on particle distribution and interface formation in SiC reinforced 2124Al matrix composite

The interface between metal matrix and ceramic reinforcement particles plays an important role in improving properties of the metal matrix composites. Hence, it is important to find out the interface structure of composite after re-melting. In the present investigation, the 2124Al matrix with 10 wt.% SiC particle reinforced composite was re-melted at 800 °C and 900 °C for 10 min followed by pouring into a permanent mould. The microstructures reveal that the SiC particles are distributed throughout the Al-matrix. The volume fraction of SiC particles varies from top to bottom of the composite plate and the difference increases with the decrease of re-melting temperature. The interfacial structure of re-melted 2124Al–10 wt.%SiC composite was investigated using scanning electron microscopy, an electron probe micro-analyzer, a scanning transmission electron detector fitted with scanning electron microscopy and an X-ray energy dispersive spectrometer. It is found that a thick layer of reaction product is formed at the interface of composite after re-melting. The experimental results show that the reaction products at the interface are associated with high concentration of Cu, Mg, Si and C. At re-melting temperature, liquid Al reacts with SiC to form Al{sub 4}C{sub 3} and Al–Si eutectic phase or elemental Si at the interface. High concentration of Si at the interface indicates that SiC is dissociated during re-melting. The X-ray energy dispersive spectrometer analyses confirm that Mg- and Cu-enrich phases are formed at the interface region. The Mg is segregated at the interface region and formed MgAl{sub 2}O{sub 4} in the presence of oxygen. The several elements identified at the interface region indicate that different types of interfaces are formed in between Al matrix and SiC particles. The Al–Si eutectic phase is formed around SiC particles during re-melting which restricts the SiC dissolution. - Highlights: • Re-melted composite shows homogeneous particle distribution • Thick reaction products are observed at the interface • Carbide is identified at interface due to SiC dissolution at high temperature • Reaction products are also Si enrich phase • Mg and Cu segregated and formed MgAl{sub 2}O{sub 4}, CuMgAl{sub 2} phase at grain boundary.

36 MATERIALS SCIENCE↗

NASA NTRS1993

A study of strength evaluations of EDNi/EDCu/NARloy-Z bonded joints

Dissimilar material interfaces can be found in many materials and structural bonds such as composite materials, welded parts, inclusion in matrix, bond between metallic and ceramic materials, and so forth. One of such structural bonds can be seen in the main combustion chamber (MCC) of the Space Shuttle Main Engine (SSME). In this study, from a practical sense, the primary concern is to understand the systems response of EDNi/EDCu/NARloy-Z bonded joints using stress values approximated by the finite element method to determine an influence of the variation of structural bond parameters on the bonded joints, and consequently main combustion chamber of the Space Shuttle Main Engine. The results presented in this study could be an appropriate indicator for a good bond of EDNi/DECu/NARloy-Z layers with the desired thickness of copper deposition in the SSME MCC manufacturing process. Furthermore, the results from this study appear to be applicable to any bonded joints that can be characterized by the parameters and assumptions used in this analysis.

Min, J. B.↗

DOE OSTI2014

Quasi-periodic Fibonacci and periodic one-dimensional hypersonic phononic crystals of porous silicon: Experiment and simulation

A one-dimensional Fibonacci phononic crystal and a distributed Bragg reflector were constructed from porous silicon. The structures had the same number of layers and similar acoustic impedance mismatch, and were electrochemically etched in highly boron doped silicon wafers. The thickness of the individual layers in the stacks was approximately 2 μm. Both types of hypersonic band gap structure were studied by direct measurement of the transmittance of longitudinal acoustic waves in the 0.1–2.6 GHz range. Acoustic band gaps deeper than 50 dB were detected in both structures. The experimental results were compared with model calculations employing the transfer matrix method. The acoustic properties of periodic and quasi-periodic structures in which half-wave retarding bi-layers do not consist of two quarter-wave retarding layers are discussed. The strong correlation between width and depth of gaps in the transmission spectra is demonstrated. The dominant mechanisms of acoustic losses in porous multilayer structures are discussed. The elastic constants remain proportional over our range of porosity, and hence, the Grüneisen parameter is constant. This simplifies the expression for the porosity dependence of the Akhiezer damping.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗