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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 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Human cytochrome P450 17A1 structures with metabolites of prostate cancer drug abiraterone reveal substrate-binding plasticity and a second binding site

Abiraterone acetate is a first-line therapy for castration-resistant prostate cancer. This prodrug is deacetylated in vivo to abiraterone, which is a potent and specific inhibitor of cytochrome P450 17A1 (CYP17A1). CYP17A1 performs two sequential steps that are required for the biosynthesis of androgens that drive prostate cancer proliferation, analogous to estrogens in breast cancer. Abiraterone can be further metabolized in vivo on the steroid A ring to multiple metabolites that also inhibit CYP17A1. Despite its design as an active-site-directed substrate analog, abiraterone and its metabolites demonstrate mixed competitive/noncompetitive inhibition. To understand their binding, we solved the X-ray structures of CYP17A1 with three primary abiraterone metabolites. Despite different conformations of the steroid A ring and substituents, all three bound in the CYP17A1 active site with the steroid core packed against the I helix and the A ring C3 keto or hydroxyl oxygen forming a hydrogen bond with N202 similar to abiraterone itself. The structure of CYP17A1 with 3-keto, 5α-abiraterone was solved to 2.0 Å, the highest resolution to date for a CYP17A1 complex. This structure had additional electron density near the F/G loop, which is likely a second molecule of the inhibitor and which may explain the noncompetitive inhibition. Mutation of the adjacent Asn52 to Tyr positions its side chain in this space, maintains enzyme activity, and prevents binding of the peripheral ligand. Collectively, our findings provide further insight into abiraterone metabolite binding and CYP17A1 function.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Bismuth as a Reactive Solvent in the Synthesis of Multicomponent Transition-Metal-Bearing Bismuthides

Employment of liquid bismuth (Bi) allows the facile single-crystal growth of compounds containing elements with high melting points, provided that these elements have reasonably high solubility in Bi. Utilization of the Bi flux approach yielded two new ternary bismuthides, SrNi 0.17(1) Bi 2 [a defect variant of the BaCuSn 2 type, space group Cmcm , α = 4.879(2) Å, b = 17.580(6) Å, and c = 4.696(2) Å] and CaTi 3 Bi 4 [NdTi 3 (Sn 0.1 Sb 0.9 ) 4 structure type, space group Fmmm , a = 5.6295(7) Å, b = 9.8389(1) Å, and c = 23.905(3) Å]. In addition, the ternary antimonide CaV3Sb4, isostructural with CaTi 3 Bi 4 , was synthesized from antimony (Sb) flux, and analyzed with the goal of validating structural assessment of the bismuthide analogue, where the X-ray crystallographic work proved to be very challenging. All synthesized compounds exhibit complex crystal structures featuring quasi-two-dimensional building blocks of different topologies. First-principle calculations reveal hypervalent bonding in the homoatomic Bi subunits. Lastly, physical property measurements indicate metallic conductivity and the absence of localized magnetism in the studied compounds.

36 MATERIALS SCIENCE↗
NASA NTRS1986

Synchronously Deployable Truss Structures

Structure lightweight, readily deployed, and has reliable joints. New truss concept, designated as "pac truss," developed. Features easy deployment without need for complex mechanisms. Structures of this type deployed in free flight by controlled release of stored energy in torsional springs at selected hinges located throughout structure. Double-folding technique used in beam model applicable to flat planar trusses, allowing structures of large expanse to fold into compact packages and be deployed for space-platform applications.

Rhodes, M. D.↗
NASA NTRS2013

Three Dimensional Numerical Simulation and Characterization of Crack Growth in the Weld Region of a Friction Stir Welded Structure

Friction stir welding (FSW) fabrication technology is being adopted in aerospace applications. The use of this technology can reduce production cost, lead-times, reduce structural weight and need for fasteners and lap joints, which are typically the primary locations of crack initiation and multi-site fatigue damage in aerospace structures. FSW is a solid state welding process that is well-suited for joining aluminum alloy components; however, the process introduces residual stresses (both tensile and compressive) in joined components. The propagation of fatigue cracks in a residual stress field and the resulting redistribution of the residual stress field and its effect on crack closure have to be estimated. To insure the safe insertion of complex integral structures, an accurate understanding of the fatigue crack growth behavior and the complex crack path process must be understood. A life prediction methodology for fatigue crack growth through the weld under the influence of residual stresses in aluminum alloy structures fabricated using FSW will be detailed. The effects and significance of the magnitude of residual stress at a crack tip on the estimated crack tip driving force are highlighted. The location of the crack tip relative to the FSW and the effect of microstructure on fatigue crack growth are considered. A damage tolerant life prediction methodology accounting for microstructural variation in the weld zone and residual stress field will lead to the design of lighter and more reliable aerospace structures

Seshadri, Banavara R.↗
NASA NTRS1989

Dynamic analysis of space structures including elastic, multibody, and control behavior

The problem is to develop analysis methods, modeling stategies, and simulation tools to predict with assurance the on-orbit performance and integrity of large complex space structures that cannot be verified on the ground. The problem must incorporate large reliable structural models, multi-body flexible dynamics, multi-tier controller interaction, environmental models including 1g and atmosphere, various on-board disturbances, and linkage to mission-level performance codes. All areas are in serious need of work, but the weakest link is multi-body flexible dynamics.

Pinson, Larry↗
NASA NTRS1992

Observation of a solar flare at the limb with the Yohkoh Soft X-ray Telescope

A long-enduring soft X-ray flare at the solar limb was well observed by the Soft X-ray Telescope aboard the Yohkoh spacecraft from the preflare stage through the postflare phase. A 'helmet streamer' arch appears several hours prior to the flare, in association with a continuous expansion and restructuring of the active-region magnetic structure. This arch then starts to flare, and increases its height and footpoint separation at v = 10-30 km/s. The arch has a complex temperature structure in the rising phase, whereas the outer arches have systematically higher temperatures in the decay phase. Magnetic reconnection in a neutral sheet at the loop top, created by preflare magnetic restructuring, would explain this type of flare.

Tsuneta, Saku↗
NASA NTRS2015

Solar Proton Transport within an ICRU Sphere Surrounded by a Complex Shield: Combinatorial Geometry

The 3DHZETRN code, with improved neutron and light ion (Z (is) less than 2) transport procedures, was recently developed and compared to Monte Carlo (MC) simulations using simplified spherical geometries. It was shown that 3DHZETRN agrees with the MC codes to the extent they agree with each other. In the present report, the 3DHZETRN code is extended to enable analysis in general combinatorial geometry. A more complex shielding structure with internal parts surrounding a tissue sphere is considered and compared against MC simulations. It is shown that even in the more complex geometry, 3DHZETRN agrees well with the MC codes and maintains a high degree of computational efficiency.

Wilson, John W.↗
NASA NTRS1994

A new stochastic systems approach to structural integrity

This paper develops improved stochastic models for the description of a large variety of fatigue crack growth phenomena that occur in components of considerable importance to the functionality and reliability of complex engineering structures. In essence, the models are based on the McGill-Markov and Closure-Lognormal stochastic processes. Not only do these models have the capability of predicting the statistical dispersion of crack growth rates, they also, by incorporating the concept of crack closure, have the capability of transferring stochastic crack growth properties measured under ideal laboratory conditions to situations of industrial significance, such as those occurring under adverse loading and/or environmental conditions. The primary data required in order to be in a position to estimate the pertinent parameters of these stochastic models are obtained from a statistically significant number of replicate tests. In this paper, both the theory and the experimental technique are illustrated using a Ti-6Al-4V alloy. Finally, important structural integrity, reliability, availability and maintainability concepts are developed and illustrated.

Provan, James W.↗
DOE OSTI2022

Chemical and Morphological Structure of Transgenic Switchgrass Organosolv Lignin Extracted by Ethanol, Tetrahydrofuran, and $\mathcal{γ}$-Valerolactone Pretreatments

We report the recalcitrance of lignocellulosic biomass is a challenge in biological-based biorefinery systems due to the complex physicochemical structure of plant cell walls. Pretreatment and genetic modification are two approaches in biomass conversion that have succeeded in modifying the structure of lignocellulose to enable better enzymatic deconstruction. However, the structural differences among pretreatment-solubilized lignin isolated from switchgrass genotypes have not been extensively investigated. Here, three organosolv pretreatment systems-ethanol (EtOH), tetrahydrofuran (THF), and γ-valerolactone (GVL)-were used on wild-type (WT) and two transgenic switchgrasses. All organosolv pretreatments caused a significant reduction in the molecular mass of lignins; particularly, up to ~90% decrease was observed in EtOH-pretreated lignin compared to untreated lignin. The WT EtOH lignin also presented the smallest particle size among all WT lignins. THF pretreated transgenic lignins showed a higher molecular mass, β-O-4 linkages, and aliphatic hydroxyl content compared to EtOH and GVL pretreated lignin. The number of hydrogen bonds between lignin and the organic solvents calculated from the molecular dynamics simulations followed the same trend as the experimentally determined reduction in lignin molecular mass. The results revealed the structural changes of solubilized lignin isolated from wild-type and transgenic switchgrass after different organosolv pretreatments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Impact of surface hydrophilicity on the ordering and transport properties of bicontinuous microemulsions

Microemulsions (MEs) have many industrial applications, where recent developments have shown that MEs can be utilized for electrochemical applications, including potentially in redox flow batteries. However, understanding the structure and dynamics of these systems, including at a surface, is needed to direct and rationally control their electrochemical behavior. While bulk solution measurements have provided insight into their structure, their assembly at an interface also impacts the electron (to the electrode) and ion (across the surfactant) charge transfer processes in the system. To address this shortcoming, neutron reflectivity experiments and molecular simulations have been completed that document the near surface structure of a series of deuterated water (D 2 O)/polysorbate-20/toluene MEs on hydrophilic and amphiphilic surfaces. These results show that the microemulsions form complex layered structures near a hard electrode surface, where most layers are not purely one component. Decreasing the D 2 O concentration in the ME increases the number of and purity of the layers established on the solid surface. These lamellar-type layers transition from the surface to the bulk microemulsion as a series of mixed layers (i.e., containing oil, water, and surfactant) that are consistent with perforated lamellae. Additionally, these mixed lamellae appear to become more perforated with oil and water pathways on an amphiphilic surface. Furthermore, the purity and thickness of these layers will influence the accessibility of an electrode by redox active species, as well as ion transport required to satisfy the electroneutrality condition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Direct functionalization of C-H bonds by electrophilic anions

Bond formation between two of the most inert molecules, alkanes and [B12X12]2- (X = Cl, Br), is performed in a two step process. Fragmentation of [B12X12]2- in the gas phase generates highly reactive [B12X11]- ions which spontaneously react with alkanes. The reaction mechanism was investigated using tandem mass spectrometry and gas-phase vibrational spectroscopy combined with electronic structure calculations. This effort revealed the unprecedented and counterintuitive electrophilic substitution of a proton in an alkane by a negatively charged ion resulting in a B-C bond formation. The product is a dianionic [B12X11CnH2n+1]2- species, in which H+ is electrostatically bound to the dianion. High flux ion soft-landing was performed to co-deposit [B12X11]- and complex organic molecules (phthalates) in thin layers on surfaces. Molecular structure analysis of the product films revealed that C-H functionalization by [B12X11]- occured in the presence of other more reactive functional groups. This observation demonstrates the utility of highly reactive fragment ions for defined bond formation processes and may pave the way to the use of gas phase ion chemistry for chemical synthesis in the condensed phase.

Warneke, Jonas↗
DOE OSTI2018

Structural basis for the second step of group II intron splicing

The group II intron and the spliceosome share a common active site architecture and are thought to be evolutionarily related. Here we report the 3.7 Å crystal structure of a eukaryotic group II intron in the lariat-3' exon form, immediately preceding the second step of splicing, analogous to the spliceosomal P complex. This structure reveals the location of the intact 3' splice site within the catalytic core of the group II intron. The 3'-OH of the 5' exon is positioned in close proximity to the 3' splice site for nucleophilic attack and exon ligation. The active site undergoes conformational rearrangements with the catalytic triplex having different configurations before and after the second step of splicing. We describe a complete model for the second step of group II intron splicing that incorporates a dynamic catalytic triplex being responsible for creating the binding pocket for 3' splice site capture.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Embedded Sensor Development in Metallic Structures for the Transformational Challenge Reactor

The ability to make minimally intrusive measurements of process conditions has tremendous potential for improving system performance and control in applications such as nuclear power generation. Towards this end, emerging and evolving advanced manufacturing methods, such as additive manufacturing, present new opportunities for more seamlessly integrating sensing with structure. This technical report summarizes the progress of work performed to assess the feasibility of embedding commercial off-the-shelf (COTS) sensors in a metallic reactor core using advanced manufacturing methods. The progress of four research and development tasks are documented: 1) A survey of COTS sensors for nuclear applications that are candidates for embedded fabrication, 2) Development of a conceptual framework for investigating the feasibility of sensor embedment, 3) Definition of structural geometries and other characteristics that will represent compelling proof-of-concept, and 4) Preliminary prototyping of embedded sensors. For the purposes of this initial study, nuclear grade K-type thermocouples were selected for investigation of embedment methodologies. This sensor was selected as an initial candidate because it represents one of the simplest sensor configurations that can provide useful process information. A selective laser melting (SLM) additive manufacturing process was used to fabricate structures with complexity representative of the core design of the transformational challenge reactor (TCR) and methods were developed to embed a thermocouple with a complex two-dimensional routing path. There are many challenges associated with embedding sensors during the additive manufacturing process including securing the sensor in the structure, relocating the part in the additive machine if using a “pick and place” sensor placement method, mitigating the potential for powder contamination, optimizing energy deposition parameters to build as closely as possible around the sensor path and improve structural integrity of the part, and tuning energy deposition to mitigate thermally induced warpage of the sensor and part as well as potential for damaging the sensing device. Preliminary results indicate that it is feasible to integrate the sensor while minimally compromising the structural integrity of the part and preserving sensor performance. This first phase of this work focused on developing a workflow for embedding sensors and controlling energy deposition during the additive manufacturing process to better understand the build characteristics around the sensor. Future work will perform more in-depth characterization of prototype parts using X-ray computed tomography and scanning electron microscopy to better understand fabricated structures, performance testing of embedded sensors in high temperature environments, adding new embedded measurement modalities, embedding devices with dissimilar materials in contact with additive powders, and the development of methods for embedding sensors with three-dimensional routing paths.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1978

Some recent advances in numerical methods in structural dynamics

The purpose of this paper is to present some recent developments in the area of numerical dynamic analysis of large structural systems. The first part of the paper is devoted to the finite dynamic element method, a new concept in the discretization of a continuum, the adoption of which effects considerable reduction in the number of degrees of freedom for a required solution accuracy, when compared with the usual finite element method. This is followed by a brief description of eigenproblem solution techniques, for the free vibration analysis of both rotating and nonrotating structures, that fully exploit the associated matrix sparsity. Together, these techniques constitute a powerful tool for the free vibration and subsequent dynamic response analysis of complex practical structures.

Gupta, K. K.↗
NASA NTRS1989

Recent developments in deployment analysis simulation using a multi-body computer code

Deployment is a candidate mode for construction of structural space systems components. By its very nature, deployment is a dynamic event, often involving large angle unfolding of flexible beam members. Validation of proposed designs and conceptual deployment mechanisms is enhanced through analysis. Analysis may be used to determine member loads thus helping to establish deployment rates and deployment control requirements for a given concept. Futhermore, member flexibility, joint free-play, manufacturing tolerances, and imperfections can affect the reliability of deployment. Analyses which include these effects can aid in reducing risks associated with a particular concept. Ground tests which can play a similar role to that of analyses are difficult and expensive to perform. Suspension systems just for vibration ground tests of large space structures in a 1 g environment present many challenges. Suspension of a structure which spatially expands is even more challenging. Analysis validation through experimental confirmation on relatively small simple models would permit analytical extrapolation to larger more complex space structures.

Housner, Jerrold M.↗
NASA NTRS1992

A high performance, ad-hoc, fuzzy query processing system for relational databases

Database queries involving imprecise or fuzzy predicates are currently an evolving area of academic and industrial research. Such queries place severe stress on the indexing and I/O subsystems of conventional database environments since they involve the search of large numbers of records. The Datacycle architecture and research prototype is a database environment that uses filtering technology to perform an efficient, exhaustive search of an entire database. It has recently been modified to include fuzzy predicates in its query processing. The approach obviates the need for complex index structures, provides unlimited query throughput, permits the use of ad-hoc fuzzy membership functions, and provides a deterministic response time largely independent of query complexity and load. This paper describes the Datacycle prototype implementation of fuzzy queries and some recent performance results.

Mansfield, William H., Jr.↗
DOE OSTI2019

Electric Form Factor of the Neutron from Asymmetry Measurements

The overwhelming majority of visible mass in the universe is composed of protons and neutrons, collectively known as nucleons, which are arguably the most important strongly interacting systems to study. A nucleon may naively be thought of as a composite object built out of three non-interacting sub-objects, known as quarks, in the large energy limit; however, the structure of the nucleon is much more complicated, and consequently far richer, than a simple valence-quark picture. There are sea quarks in addition to valence quarks that interact strongly via the exchange of gluons resulting in a complex vacuum structure, and the collective system must give rise to the observed properties of the nucleon, e.g. the radius and mass. The nucleon is the most well-studied hadron and yet there are still unresolved complexities in the calculation of properties from first principles of QCD; this represents a central problem in nuclear physics. The theoretical difficulty with the nucleon requires experimentation, which is steadily increasing the knowledge of nucleon structure and the strong interaction. The subject of this thesis pertains to nucleon electromagnetic form factors which are fundamental quantities containing information on the spatial and momentum distributions of charge and current within the nucleon. Nucleon form factors may be accessed through well-understood leading order electromagnetic processes with a leptonic probe, and provide strong constraints on testing non-perturbative QCD and nuclear structure models. The form factor ratio of the neutron has been extracted via a beam-target helicity asymmetry measurement. The Jefferson Lab Hall A experiment E02-013 ran in 2006 utilizing the 6 GeV CEBAF for its high-duty, longitudinally polarized electron beam. The double-arm coincidence experiment detected the quasielastically scattered electrons in a large angular and momentum acceptance spectrometer. The recoiling nucleons were detected and momentum analyzed in a large scintillator-iron based neutron detector. The analysis of a previously unpublished extraction of the electric form factor of the neutron is presented.

Obrecht, Richard↗