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Results for “Structure elucidation”

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 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Origin and development of plasma membrane derived invaginations in Vinca rosea l.

The occurrence, morphology, and possible ontogeny of plasma-membrane-related structures are described which can develop into invaginations or intravacuolar formations. An underlying study of meristematic tissues from the shoot of Vinca rosea supports the interpretation that endocytosis does occur in plant cells and that it is appropriate to refer to these structures as endocytoses. The function of these invaginations or their content remains to be elucidated.

Mahlberg, P.↗
NASA NTRS1973

Experiments on confined turbulent jets in cross flow.

Results are reported of experiments on the effects of an opposite wall on the characteristics of turbulent jets injected into a cross flow, for unheated and heated jets. Longitudinal and transverse distributions of velocity and temperature are presented for single and multiple circular jets, and trajectories are presented for two-domensional jets. The opposite wall has relatively little effect on a single jet unless the ratio of jet to cross flow momentum flux is large enough for the jet to impinge on the opposite wall. For a row of jets aligned perpendicularly to the cross flow, the opposite wall exerts progressively larger influence as the spacing between jets decreases. Much of the effect of jet and wall proximity can be understood by considering the interaction of the vortex flow which is the major feature of the structure of a single jet in a cross flow. Smoke photographs are shown to elucidate some of the interaction patterns.

Kamotani, Y.↗
NASA NTRS1974

Experiments on confined turbulent jets in cross flow

Results are reported of experiments on the effects of an opposite wall on the characteristics of turbulent jets injected into a cross flow, for unheated and heated jets. Longitudinal and transverse distributions of velocity and temperature are presented for single and multiple circular jets, and trajectories are presented for two-dimensional jets. The opposite wall has relatively little effect on a single jet unless the ratio of jet to cross flow momentum flux is large enough for the jet to impinge on the opposite wall. For a row of jets aligned perpendicularly to the cross flow, the opposite wall exerts progressively larger influence as the spacing between jets decreases. Much of the effect of jet and wall proximity can be understood by considering the interaction of the vortex flow which is the major feature of the structure of a single jet in a cross flow. Smoke photographs are shown to elucidate some of the interaction patterns.

Kamotani, Y.↗
NASA NTRS1986

The tensile and fatigue deformation structures in a single crystal Ni-base superalloy

Dislocation structures produced in Rene N4 crystals of various orientations deformed in tension and low cycle fatigue (LCF) at 760 and 980 degrees C were examined in order to elucidate the observed differences in stress-strain behavior. Specimens tensile tested at 760 degrees C displayed significant crystallographic orientation dependences in mechanical response but comparable inhomogeneous dislocation structures. LCF specimens of various orientations had comparable cyclic stress-strain curves and generally similar somewhat more homogeneous dislocation structures. Tensile specimens at the higher temperature had comparable mechanical response and corresponding similar quite homogeneous dislocation structures with gamma' faulting; and LCF specimens had orientation-dependent mechanical response but comparable homogeneous loose dislocation networks.

Gabb, T. P.↗
NASA NTRS1991

Potential approaches to the spectroscopic characterization of high performance polymers exposed to energetic protons and heavy ions

A potential limitation to human activity on the lunar surface or in deep space is the exposure of the crew to unacceptably high levels of penetrating space radiations. The radiations of most concerns for such missions are high-energy protons emitted during solar flares, and galactic cosmic rays which are high-energy ions ranging from protons to iron. The development of materials for effective shielding from energetic space radiations will clearly require a greater understanding of the underlying mechanisms of radiation-induced damage in bulk materials. This can be accomplished in part by the detailed spectroscopic characterization of bulk materials that were exposed to simulated space radiations. An experimental data base thus created can then be used in conjunction with existing radiation transport codes in the design and fabrication of effective radiation shielding materials. Electron Paramagnetic Resonance Spectroscopy was proven very useful in elucidating radiation effects in polymers (high performance polymers are often an important components of structural composites).

Suleman, Naushadalli K.↗
NASA NTRS2005

A Preliminary Investigation of the E-Beam Induced Polymerization of Maleimide and Norbornene End-capped Polyimides

A research area of high activity in connection with aerospace engineering has been the development of polymer thermosetting resins that can resist temperature as high as 300 C while maintaining adequate toughness, and providing ease of processing to enable low temperature and low cost composite fabrication methods. In order to meet such requirements, sequential interpenetrating polymer networks (IPNs) based on bismaleimide (BMI) and cyanate ester (CE) monomers were investigated. In these systems, a polycyanurate network is first formed in the presence of BMI and appropriate reactive diluent monomers and in a second step, a network based on the BMI is created in the presence of a fully formed polycyanurate network. The materials developed can be processed at relatively low temperature (less than 150 C) and with the aid of electron beam (EB) curing. Of major importance to the success of this work was the identification of a reactive diluent that improves ease of processing and has tailored reactivity to allow for the controlled synthesis of CE-BMI sequential IPNs. Based on solubility and reactivity of a number of reactive diluents, N-acryloylmorpholine (AMP) was selected as a comonomer for BMI copolymerization. A donor-acceptoreaction mechanism was suggested to explain the relative reactivity of a variety of reactive diluents towards maleimide functionality. The optimum processing parameters for the formation of the first network were determined through the study of metal catalyzed cure and hydrolysis of cyanate esters, whereas the reaction behavior for second network formation in terms of the influence of EB dose rate and temperature was elucidated through an in-situ kinetics study of maleimide and AMP copolymerization. Structure-property relationships were developed which allowed for the design of improved resin systems. In particular, appropriate network coupler possessing cyanate ester and maleimide functionality was synthesized to link the polycyanurate first network to the BMI/AMP second network and thus form linked sequential IPNs (LIPNs). Consequently, Tg as high as 370 C was achieved and a fracture toughness of 120 Joules per square meters was obtained for resin systems that possess adequately low viscosity for processing using liquid molding techniques at low temperature.

Palmese, Giuseppe R.↗
NASA NTRS2011

A Snapshot of the Sun Near Solar Minimum: The Whole Heliosphere Interval

We present an overview of the data and models collected for the Whole Heliosphere Interval, an international campaign to study the three-dimensional solar heliospheric planetary connected system near solar minimum. The data and models correspond to solar Carrington Rotation 2068 (20 March 16 April 2008) extending from below the solar photosphere, through interplanetary space, and down to Earth's mesosphere. Nearly 200 people participated in aspects of WHI studies, analyzing and interpreting data from nearly 100 instruments and models in order to elucidate the physics of fundamental heliophysical processes. The solar and inner heliospheric data showed structure consistent with the declining phase of the solar cycle. A closely spaced cluster of low-latitude active regions was responsible for an increased level of magnetic activity, while a highly warped current sheet dominated heliospheric structure. The geospace data revealed an unusually high level of activity, driven primarily by the periodic impingement of high-speed streams. The WHI studies traced the solar activity and structure into the heliosphere and geospace, and provided new insight into the nature of the interconnected heliophysical system near solar minimum.

Thompson, Barbara J.↗
DOE OSTI2021

In Situ ATR-FTIR Study of the Cathode–Electrolyte Interphase: Electrolyte Solution Structure, Transition Metal Redox, and Surface Layer Evolution

We present a study of the lithium nickel manganese cobalt oxide (LiNi 0.6 Mn 0.2 Co 0.2 O 2 , NMC622) cathode-electrolyte interphase (CEI) during galvanostatic charging and discharging using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) methods to investigate the voltage dependent electrolyte solution structure changes at the interface, transition metal (TM) redox chemistry, and cathode/electrolyte interfacial layer evolution. Furthermore, our in situ cell design provides both reliable electrochemical device testing and strong FTIR vibrational absorption signals near the cathode surface. Specifically, advanced spectral analysis elucidates changes of near-surface Li+ ion (de)solvation by solvent molecules during galvanostatic cycling. Moreover, cathode metal-oxygen vibrational absorptions, sensitive to TM redox behaviors and subsequent local structural variations, were correlated to cathode de-lithiation (and lithiation) and electrolyte solution structure changes. In addition, we have detected the formation and evolution of a CEI surface layer on the NMC622 cathode that contributes to the cell's capacity fade.

25 ENERGY STORAGE↗
DOE OSTI2023

Asymmetric nanoparticle oxidation observed in-situ by the evolution of diffraction contrast

Abstract The use of transmission electron microscopy (TEM) to observe real-time structural and compositional changes has proven to be a valuable tool for understanding the dynamic behavior of nanomaterials. However, identifying the nanoparticles of interest typically require an obvious change in position, size, or structure, as compositional changes may not be noticeable during the experiment. Oxidation or reduction can often result in subtle volume changes only, so elucidating mechanisms in real-time requires atomic-scale resolution or in-situ electron energy loss spectroscopy, which may not be widely accessible. Here, by monitoring the evolution of diffraction contrast, we can observe both structural and compositional changes in iron oxide nanoparticles, specifically the oxidation from a wüstite-magnetite (FeO@Fe 3 O 4 ) core – shell nanoparticle to single crystalline magnetite, Fe 3 O 4 nanoparticle. The in-situ TEM images reveal a distinctive light and dark contrast known as the ‘Ashby-Brown contrast’, which is a result of coherent strain across the core – shell interface. As the nanoparticles fully oxidize to Fe 3 O 4 , the diffraction contrast evolves and then disappears completely, which is then confirmed by modeling and simulation of TEM images. This represents a new, simplified approach to tracking the oxidation or reduction mechanisms of nanoparticles using in-situ TEM experiments.

36 MATERIALS SCIENCE↗
NASA NTRSDate not supplied

Structural Requirements and Scaling Analysis of a Fluidic Mirror Space Telescope Support Structure

The NASA FLUTE project proposes large-scale (50m) fluidic telescopes for astronomy applications. To continue to explore the universe, astronomers require larger and larger telescope apertures. The highest priority astrophysics targets such as exoplanets and early galaxies are extremely faint, motivating larger telescope apertures. However, mission costs depend on aperture diameter, and scaling apertures beyond 10-m apertures faces economic and technological viability challenges. An unsegmented primary mirror made in space via fluidic microgravity shaping would provide a scalable and cost-effective method to scale apertures to 50-m scale while achieving sub-nanometer (root mean square) surface quality. Such microgravity fluidic shaping has been demonstrated in laboratory neutral buoyance environments, parabolic microgravity experiments, as well aboard the International Space Station. One of the main components of a fluidic observatory is the mirror frame. The frame must provide a stable bounding circular ring which the edges of the fluid mirror surface can wet. The frame can optionally provide a ‘floor’ surface on the interior of the ring to provide additional fluid support and reduce required fluid volume. In this work, we evaluate several classes of structural frame architectures potentially suitable for a fluidic telescope support structure. We start by estimating stability requirements, orbital, station keeping, and slew loads based on a notional CONOPS. The scaling of overall fluid mass required for each architecture is evaluated. Preliminary results elucidate the importance of a support floor for overall mission viability above 10-m diameter. We then investigate the scaling of a tetrahedral truss frame support structure. We show that segmented solid shell support surfaces can provide sufficient stability at modest mass fractions. We estimate that the total fluid and frame mass for a 50-m telescope could be on the order of 15,000 kg. Finally, implementation considerations are discussed, including deployment/assembly methodologies. The results of this study establish feasibility of a large-scale fluidic telescope and will guide further architecture development and detailed structural design.

Christine Gregg↗
DOE OSTI2024

Emerging Functionality in Transition-Metal Compounds Driven by Spatial Confinement and Broken Symmetry

This research project investigates the emerging functionality in transition-metal-compounds (TMCs) driven by spatial confinement and broken symmetry. It combines advanced growth capabilities with cutting-edge characterization and first principles theory to probe and control the properties of TMC interfaces, including the utilization and development of state-of-the-art atomically resolved electron microscopy and spectroscopy to determine the structure, composition, and bonding at TMC interfaces. The proposed research will focus on four challenging areas: 1) manipulate interfaces to design new material phases such as magnetic metals with unique polar structure (net dipole) to achieve multiple functionality; 2) explore electronic mismatch or screening at interfaces of insulating/poor metal TMCs to produce novel electronic and magnetic properties; 3) elucidate and exploit the role of defects, both point and extended, on the functionality of interfaces; 4) develop advanced electron microscopy/spectroscopy techniques to explore temperature dependent phase transitions and couple these structural tools with new nonlinear optical probes of the electronic structure. The research team aims to close the materials-by-design loop of make, measure, model, and modify. The program promises to enhance our ability to engineer the desired physical properties at interfaces, superlattices (periodic arrays of films of different compounds), and heterostructures of TMCs.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Novel and effective surface passivation for high efficiency n- and p-type Silicon solar cell

The project objective was to develop a novel Si surface passivation method using chalcogens, sulfur (S) and/or selenium (Se), as passivating elements, to withstand industry-standard high temperature contacting and metallization schemes for p-type Si based passivated emitter and rear contact (p-PERC) solar cells. The back surface passivation of PERC cells has been improved drastically with the invention and successful application of an Al 2 O 3 passivation layer. However, the front n + diffused junction surface is still poorly passivated by the standard amorphous silicon nitride (SiNx) anti-reflection coating (ARC) layer. This project sought to address the passivation challenges of both front n+ emitter and undiffused p-Si back surface. Improved p-PERC solar cell performance with open circuit voltage (V OC ) > 680 mV and efficiency of 22% were targeted to validate superior defect passivation properties as compared to standard SiO 2 / Al 2 O 3 passivation. During this project, we systematically investigated process-structure-properties-performance relationships of this novel advanced defect passivation approach. The S/Se passivation was carried out by reacting industrial Czochralski (Cz) Si wafers in H 2 S and H 2 Se gases in a chemical vapor deposition (CVD) reactor at temperatures up to 700°C. After an exhaustive optimization of the process parameters (temperature, time, and gas concentration), we established an optimized process and demonstrated extremely low surface recombination velocities (SRVs) of 1.5 cm/s and 8 cm/s on n-type and p-type Si, respectively, by S-passivation. In-depth surface and interface characterization were performed using soft x-ray and photoelectron spectroscopies (XPS, UPS, XES), combined with capacitance-voltage-frequency (C-V-f) measurements, to decipher the surface chemical/electronic structure and interface defect state densities. These measurements provided critical understanding of the defect passivation mechanism and elucidated the presence of surface S-Si bonds, a reduction of surface dipoles, and low interface state densities (D it ) < 10 11 cm -2 ev -1 . We also found that the Se-passivation is inferior to the S-passivation (by at least one order of magnitude in SRV). Application of the optimized S-passivation to the n+ diffused emitter surface led to a low surface recombination current density, J0 ≈ 40 fA/cm 2 (~ 1/4 of the industry-standard SiNx-passivation), and high implied V OC (686 mV) in p-PERC solar cell structures. The S-passivation process also was found to improve the bulk quality of the p-type Si, better than the SiO 2 or Al 2 O 3 passivation processes. After successful demonstration of efficient passivation of Si surface defects by S, we extensively studied the air, thermal, and illumination stability of the passivation structure. S-passivation itself degrades in air due to competing reactions with moisture and oxygen to form oxides, which can be eliminated by a SiNx capping layer (also acting as a anti-reflective coating). After SiNx process optimization, we demonstrated illumination and thermally stable S-passivation with SRV < 5 cm/s and J 0 < 80 fA/cm 2 . These enhancements in Si passivation, incorporated into p-PERC cells, achieved an efficiency of 19.93% with V OC = 649 mV, using manufacturing metallization and contacting schemes. The low cell performance (cell V OC is much less than the implied V OC = 686 mV, anticipated from surface passivation) was identified due to degradation of S-passivation during the metal firing step (out-diffusion of S from the Si interface to the SiNx surface). The S-passivation of Si surfaces shows significant promise with excellent passivation quality, essential for high performance (high V OC , high efficiency) solar cells. Integration of this innovative defect passivation into devices, however, demands further development of the capping layer, low temperature (<700°C) metallization process, and/or engineering of advanced device structures. Surface passivation-dominated advanced Si solar cells, such as tunnel oxide passivated contacts and Si heterojunctions, are increasingly of interest due to their high-performance potential and will have a growing photovoltaic market share in the near future.

14 SOLAR ENERGY↗
DOE OSTI2024

Elucidating mechanisms of Photosystem I assembly and repair (Final Technical Report)

Oxygenic photosynthesis generates the carbohydrates and oxygen that support life on earth. Central to this process are photosystems I and II (PSI and PSII), large protein-pigment complexes that are among the most complex macromolecular structures in nature. Impressive advances have been made in understanding the structure and photochemical mechanisms of PSI and PSII. However, less is known about the mechanisms underlying their biogenesis. The overarching goal of this project was to elucidate mechanisms of photosystem assembly. Several proteins that are not found in mature PSI or PSII are essential for their assembly, but the assembly pathways and the role of each assembly factor are just starting to emerge. During the course of this project, we advanced understanding of this problem in several ways. First, we addressed the spatial organization of photosystem assembly by localizing many known assembly factors to specific subdomains of thylakoid membranes in plant chloroplasts. This work revealed that the "curvature" domain - the highly curved periphery of stacked granal membrane disks - is a center of photosystem assembly. However, whereas some PSI assembly factors localized exclusively to the curvature domain, another was found exclusively in granal margins and unstacked membranes. This spatial partitioning suggests an assembly line along which different assembly intermediates are physically segregated. Most assembly factors localized similarly in dark-adapted and illuminated plants, but one PSII assembly factor shifted from the curvature domain to unstacked membranes upon illumination, suggesting an unanticipated role in the repair of light-induced PSII damage. Whereas most PSII subunits were found primarily in grana stacks (as expected), one PSII subunit, PsbP, was prominent also in the curvature fraction, suggesting that PsbP has functions beyond its role in mature PSII, possibly in biogenesis or repair.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Small Molecule Sorting: A Fluorescence Study of Microemulsions

The application of microemulsions to a wide range of industries relies on their ability to solubilize small molecules with vastly different structures. Herein, we use multiple fluorescence techniques to probe ionic (rhodamine 6g, r6g), polar (coumarin 153, c153), nonpolar (diphenylanthracene, DPA), and amphiphilic (laurdan) small molecules in a nonionic, bicontinuous microemulsion of varying hydration. All fluorophores investigated were found to associate with the surfactant region despite their different structures and properties. The hydration of the surfactant layer was found to increase linearly with water addition, but while this initially increases the fluidity of the surfactant layer, fluorescence anisotropy of c153 and r6g indicates a stiffening of the surfactant at water content >60%. This stiffening of the surfactant layer at higher water content correlates with a morphological change in the microemulsion from a bicontinuous structure to droplets. In contrast, the nonpolar DPA shows a change in partitioning as hydration changes, increasing its association with the oil domain. Altogether, these studies elucidate not only the capability of these microemulsions to host a range of small molecules in the surfactant layer with tunable position but also the ability to probe the driving force of bulk structural changes in these heterogeneous fluids.

25 ENERGY STORAGE↗
DOE OSTI2021

Omics Approaches for Understanding Biogenesis, Composition and Functions of Fungal Extracellular Vesicles

Extracellular vesicles (EVs) are lipid bilayer structures released by organisms from all kingdoms of life. The diverse biogenesis pathways of EVs result in a wide variety of physical properties and functions across different organisms. Fungal EVs were first described in 2007 and different omics approaches have been fundamental to understand their composition, biogenesis, and function. In this review, we discuss the role of omics in elucidating fungal EVs biology. Transcriptomics, proteomics, metabolomics, and lipidomics have each enabled the molecular characterization of fungal EVs, providing evidence that these structures serve a wide array of functions, ranging from key carriers of cell wall biosynthetic machinery to virulence factors. Omics in combination with genetic approaches have been instrumental in determining both biogenesis and cargo loading into EVs. We also discuss how omics technologies are being employed to elucidate the role of EVs in antifungal resistance, disease biomarkers, and their potential use as vaccines. Finally, we review recent advances in analytical technology and multi-omic integration tools, which will help to address key knowledge gaps in EVs biology and translate basic research information into urgently needed clinical applications such as diagnostics, and immuno- and chemotherapies to fungal infections.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Microstructural evolutions, phase transformations and hard magnetic properties in polycrystalline Ce–Co–Fe–Cu alloys

This work focuses on systematic studies of Ce–Co based 1:5 permanent magnet alloys of CeCo 4.4-x Fe x Cu 0.6 and CeCo 3.9-x Fe x Cu 1.2 (x = 0, 0.3, 0.6, 0.9, 1.2, 1.8) by varying Co:Fe. The overarching aim of this manuscript is to elucidate the hard-magnetic properties through a better understanding of phase formation by the structural, microstructural, and magnetic properties in these materials. Improved mutual solubility of Fe in the 1:5 phase has been observed with an extended homogeneity range by Cu substitution. For both composition series, Fe contents of x ≤ 0.6 show a homogeneous microstructure with a single 1:5 phase and good magnetic properties. The composition region 0.6 < x ≤ 0.9 appears to be near the boundary of solubility and evolution of other phases. At x = 1.8, it is found that the homogeneous 1:5 phase and magnetic hardness deteriorated due to the evolution of secondary phases such as 2:17, 2:7, and Fe–Co. Furthermore, the addition of Fe improved both the magnetization and Curie temperature via increased effective exchange interactions, while an increase in Cu content enhanced coercivity.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2020

Abnormally Low Activation Energy in Cubic Na3SbS4 Superionic Conductor

Inorganic Na-ion superionic conductors play a vital role in all-solid-state Na batteries that operate at room temperature. Sodium thioantimonate (Na3SbS4), a popular sulfide-based solid electrolyte, has attracted serious attention due to its advantages of high ionic conductivity at room temperature and impressive chemical stability under ambient conditions. Much research detailing Na3SbS4 focused on its synthetic approaches and interfacial stability against Na metal, yet, there is limited information elucidating a fundamental understanding of the Na- ion diffusion mechanisms in Na3SbS4 with different crystal structures (e.g., tetragonal and cubic). Herein, we combine real-time electrochemical impedance measurements with theoretical simulations based on density functional theory and in situ quasi-elastic neutron scattering to study the Na-ion conductive properties of Na3SbS4 during its phase transition from a tetragonal to cubic structure. Although there is a slight change in the lattice parameters, the energy barrier for Na-ion diffusion in the tetragonal structure was determined to be much larger (5-10 times) than that in the cubic structure from both theoretical and experimental perspectives. The high degree of symmetry in cubic Na3SbS4 leads to less interatomic correlations between Na and S(Sb) atoms, a shorter jump distance (2.85 angstrom), and a larger diffusion coefficient. This research provides insight into understanding the Na-ion diffusion in solid electrolytes with phase transitions and provides fundamental guidance for designing novel solid-state Na-ion conductors.

Zhang, Qian↗