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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Bandgaps and directional properties of two-dimensional square beam-like zigzag lattices

In this paper we propose four kinds of two-dimensional square beam-like zigzag lattice structures and study their bandgaps and directional propagation of elastic waves. The band structures are calculated by using the finite element method. Both the in-plane and out-of-plane waves are investigated simultaneously via the three-dimensional Euler beam elements. The mechanism of the bandgap generation is analyzed by studying the vibration modes at the bandgap edges. The effects of the geometry parameters of the xy- and z-zigzag lattices on the bandgaps are investigated and discussed. Multiple complete bandgaps are found owing to the separation of the degeneracy by introducing bending arms. The bandgaps are sensitive to the geometry parameters of the periodic systems. The deformed displacement fields of the harmonic responses of a finite lattice structure subjected to harmonic loads at different positions are illustrated to show the directional wave propagation. An extension of the proposed concept to the hexagonal lattices is also presented. The research work in this paper is relevant to the practical design of cellular structures with enhanced vibro-acoustics performance.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Phase Formation and Electronic Structure Peculiarities in the Al{sub 1–} {sub x}Si{sub x} Film Composites under the Conditions of Magnetron and Ion-Beam Sputtering

The peculiarities of the phase composition and electronic structure of aluminum–silicon composite films near the Al{sub 0.75}Si{sub 0.25} composition obtained by the magnetron and ion-beam sputtering methods on a Si(100) silicon substrate are studied using the X-ray diffraction techniques and ultrasoft X-ray emission spectroscopy. In addition to silicon nanocrystals of about 25 nm in size, an ordered solid solution corresponding to the previously unknown Al{sub 3}Si phase is formed in magnetron sputtering on a polycrystalline Al matrix. Films obtained by ion-beam sputtering of the composite target are found to be monophasic and contained only one phase of an ordered solid solution of aluminum silicide Al{sub 3}Si of the Pm3m cubic system with the primitive cell parameter a = 4.085 Å. However, subsequent pulsed photon annealing of the composite with different radiation doses from 145 to 216 J/cm{sup 2} gives rise to the partial decomposition of the Al{sub 3}Si phase with the formation of free metallic aluminum and silicon nanocrystals with sizes in the range from 50 to 100 nm, depending on the pulsed photon radiation dose.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Cryo-FIB for TEM Investigation of Soft Matter and Beam Sensitive Energy Materials

Primarily driven by structural biology, the rapid advances in cryogenic electron microscopy techniques are now being adopted and applied by materials scientists. Samples that inherently have electron transparency can be rapidly frozen (vitrified) in amorphous ice and imaged directly on a cryogenic transmission electron microscopy (cryo-TEM), however this is not the case for many important materials systems, which can consist of layered structures, embedded architectures, or be contained within a device. Cryogenic focused ion beam (cryo-FIB) lift-out procedures have recently been developed to extract intact regions and interfaces of interest, that can then be thinned to electron transparency and transferred to the cryo-TEM for characterization. Several detailed studies have been reported demonstrating the cryo-FIB lift-out procedure, however due to its relative infancy in materials science improvements are still required to ensure the technique becomes more accessible and routinely successful. Here, we review recent results on the preparation of cryo-TEM lamellae using cryo-FIB and show that the technique is broadly applicable to a range of soft matter and beam sensitive energy materials. We then present a tutorial that can guide the materials scientist through the cryo-FIB lift-out process, highlighting recent methodological advances that address the most common failure points of the technique, such as needle attachment, lift-out and transfer, and final thinning.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Cryo-FIB for TEM Investigation of Soft Matter and Beam Sensitive Energy Materials

Primarily driven by structural biology, the rapid advances in cryogenic electron microscopy techniques are now being adopted and applied by materials scientists. Samples that inherently have electron transparency can be rapidly frozen (vitrified) in amorphous ice and imaged directly on a cryogenic transmission electron microscopy (cryo-TEM), however this is not the case for many important materials systems, which can consist of layered structures, embedded architectures, or be contained within a device. Cryogenic focused ion beam (cryo-FIB) lift-out procedures have recently been developed to extract intact regions and interfaces of interest, that can then be thinned to electron transparency and transferred to the cryo-TEM for characterization. Several detailed studies have been reported demonstrating the cryo-FIB lift-out procedure, however due to its relative infancy in materials science improvements are still required to ensure the technique becomes more accessible and routinely successful. Here, we review recent results on the preparation of cryo-TEM lamellae using cryo-FIB and show that the technique is broadly applicable to a range of soft matter and beam sensitive energy materials. We then present a tutorial that can guide the materials scientist through the cryo-FIB lift-out process, highlighting recent methodological advances that address the most common failure points of the technique, such as needle attachment, lift-out and transfer, and final thinning.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Ionizing-radiation beam monitoring system

A transmissive ionizing-radiation beam monitoring system includes an enclosure structure with at least one ultra-thin window to an incident ionizing-radiation beam, where the ultra-thin window is highly transmissive to ionizing-radiation. Embodiments include at least one thin or ultra-thin scintillator within the enclosure structure that is substantially directly in an incident ionizing-radiation beam path and transmissive to the incident radiation beam, and at least one ultraviolet (UV) illumination source within the enclosure structure facing the scintillator. Embodiments include at least one machine vision camera within the enclosure structure located out of an incident ionizing-radiation beam path and including a camera body and lens having a projection of its optical axis oriented at an angle of incidence of 45±35 degrees to a surface of the scintillator.

Friedman, Peter S.↗
DOE OSTI2026

Nanometer-scale prebunched electron beams generated from all-optical plasma-based acceleration

High-quality and prebunched electron beams can produce coherent x-rays with high intensity and narrow bandwidth, which are essential for modern light sources. An all-optical scheme based on plasma-based acceleration for producing bright electron beams that are prebunched on the nanometer scale is proposed. By using a density modulation created by two low intensity counterpropagating lasers, the phase velocity of the plasma wake excited by an intense driver laser in a uniform plasma can be modulated at a frequency twice that of the colliding lasers, thus turning the injection on and off. The injected electrons are microbunched at the Doppler-shifted modulated wavelength, corresponding to the phase velocity of the gradually expanding wakefield. It is demonstrated that by controlling the properties of the drive and colliding lasers, beams with exotic prebunched structures can be produced, which may have critical applications in ultrafast high power x-rays. This extremely compact, all-optical scheme for producing ultrabright prebunched electron beams may therefore enable novel applications for ultrafast x-ray users and arouse general interest in various fields.

Beam injection, extraction & transport↗
DOE OSTI2015

Efficient Coupling and Transport of a Surface Plasmon at 780 nm in a Gold Nanostructure

We studied plasmonic nanostructures in single-crystal gold with scanning electron and femtosecond photoemission electron microscopies. We designed an integrated laser coupling and nanowire waveguide structure by focused ion beam lithography in single-crystal gold flakes. The photoemission results show that the laser field is efficiently coupled into a propagating surface plasmon by a simple hole structure and propagates efficiently in an adjacent nano-bar waveguide. A strong local field is created by the propagating surface plasmon at the nano-bar tip. A similar structure, with a decreased waveguide width and thickness, displayed significantly more intense photoemission indicating enhanced local electric field at the sharper tip.

Gong, Yu↗
DOE OSTI2018

Casting of Reinforced Concrete Beam: Project Progress

Aging concrete structures in nuclear power plants undergo mechanical, physical, chemical, and radioactive degradation. One of the chemical degradation mechanisms that is investigated in the research project under the Plant Modernization Pathway of the Light Water Reactor Sustainability Program is the alkali-silica reaction (ASR). The ASR is a chemical process that over time, causes expansion of calcium silicate hydrate gel. To date, the research project has studied the ASR gel formation and expansion in non-reinforced concrete specimens using vibro-acoustic modulation (VAM) technique. However, nuclear plant concrete structures are reinforced, and it might influence the application of VAM technique on reinforced concrete specimens compared to non-reinforced specimens. A research activity is initiated between Idaho National Laboratory, Vanderbilt University, and University of Nebraska - Lincoln to study the impact of reinforcement in concrete structures on the application of the VAM technique. To support this activity, University of Nebraska - Lincoln is casting and curing four reinforced concrete samples that at the end of the curing period will be transferred to Vanderbilt University to perform experimental VAM study. Vanderbilt University and Idaho National Laboratory will perform the data analysis and enhance the developed structural health monitoring framework. In this report, a progress on casting and curing of reinforced concrete samples at University of Nebraska – Lincoln is provided.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRSDate not supplied

Lightweight Thrust Chamber Assemblies using Multi-Alloy Additive Manufacturing and Composite Overwrap

Additive Manufacturing (AM) has brought significant design and fabrication opportunities for complex components with internal features such as liquid rocket engine thrust chambers not previously possible. This technology allows for significant cost savings and schedule reductions in addition to new performance optimization through weight reduction and increased margins. Specific to regeneratively-cooled combustion chambers and nozzles for liquid rocket engines, additive manufacturing offers the ability to form the complex internal coolant channels and the closeout of the channels to contain the high pressure liquid propellants with a single operation. Much of additive manufacturing development has focused on monolithic alloys using Laser Powder Bed Fusion (L-PBF), which do not allow for complete optimization of the structure. The National Aeronautics and Space Administration (NASA) completed feasibility of an AM bimetallic L-PBF GRCop-84 copper-alloy combustion chamber with an AM electron beam freeform Inconel 625 structural jacket under the Low Cost Upper Stage Propulsion (LCUSP) Project. A follow-on project called Rapid Analysis and Manufacturing Propulsion Technology (RAMPT) is under development to further expand large-scale multi-alloy thrust chambers while maturing composite overwrap technology for significant weight savings opportunities. The RAMPT project has three primary objectives: 1) Advancing blown powder Directed Energy Deposition (DED) to fabricate integral-channel large scale nozzles, 2) Develop composite overwrap technology to reduce weight and provide structural capability for thrust chamber assemblies, and 3) Develop bimetallic and multi-metallic additively manufactured radial and axial joints to optimize material performance. In addition to these primary manufacturing developments, analytical modeling efforts compliment the process development to simulate the AM processes to reduce build failures and distortions. The RAMPT project is also maturing the supply chain for various manufacturing processes described above in addition to L-PBF of GRCop-42. This paper will present an overview of the RAMPT project, the process development and hardware progress to date, material and hot-fire testing results, along with future developments.

Additive Manufacturing↗
DOE OSTI2014

Measuring size dependent electrical properties from nanoneedle structures: Pt/ZnO Schottky diodes

This work reports the fabrication and testing of nanoneedle devices with well-defined interfaces that are amenable to a variety of structural and electrical characterization, including transmission electron microscopy. Single Pt/ZnO nanoneedle Schottky diodes were fabricated by a top down method using a combination of electro-polishing, sputtering, and focused ion beam milling. The resulting structures contained nanoscale planar heterojunctions with low ideality factors, the dimensions of which were tuned to study size-dependent electrical properties. The diameter dependence of the Pt/ZnO diode barrier height is explained by a joule heating effect and/or electronic inhomogeneity in the Pt/ZnO contact area.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Neutron spin structure with polarized deuterons and spectator proton tagging at EIC

The neutron's deep-inelastic structure functions provide essential information for the flavor separation of the nucleon parton densities, the nucleon spin decomposition, and precision studies of QCD phenomena in the flavor-singlet and nonsinglet sectors. Thus, traditional inclusive measurements on nuclear targets are limited by dilution from scattering on protons, Fermi motion and binding effects, final-state interactions, and nuclear shadowing at x << 0.1. An Electron-Ion Collider (EIC) would enable next-generation measurements of neutron structure with polarized deuteron beams and detection of forward-moving spectator protons over a wide range of recoil momenta (0 < pR << several 100 MeV in the nucleus rest frame). The free neutron structure functions could be obtained by extrapolating the measured recoil momentum distributions to the on-shell point. The method eliminates nuclear modifications and can be applied to polarized scattering, as well as to semi-inclusive and exclusive final states. We review the prospects for neutron structure measurements with spectator tagging at EIC, the status of R&D efforts, and the accelerator and detector requirements.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1992

Progressive fracture of polymer matrix composite structures: A new approach

A new approach independent of stress intensity factors and fracture toughness parameters has been developed and is described for the computational simulation of progressive fracture of polymer matrix composite structures. The damage stages are quantified based on physics via composite mechanics while the degradation of the structural behavior is quantified via the finite element method. The approach account for all types of composite behavior, structures, load conditions, and fracture processes starting from damage initiation, to unstable propagation and to global structural collapse. Results of structural fracture in composite beams, panels, plates, and shells are presented to demonstrate the effectiveness and versatility of this new approach. Parameters and guidelines are identified which can be used as criteria for structural fracture, inspection intervals, and retirement for cause. Generalization to structures made of monolithic metallic materials are outlined and lessons learned in undertaking the development of new approaches, in general, are summarized.

Chamis, C. C.↗
DOE OSTI2014

Polarized light ions and spectator nucleon tagging at EIC

The neutron's deep-inelastic structure functions provide essential information for the flavor separation of the nucleon parton densities, the nucleon spin decomposition, and precision studies of QCD phenomena in the flavor-singlet and nonsinglet sectors. Traditional inclusive measurements on nuclear targets are limited by dilution from scattering on protons, Fermi motion and binding effects, final-state interactions, and nuclear shadowing at x ll 0.1. An Electron-Ion Collider (EIC) would enable next-generation measurements of neutron structure with polarized deuteron beams and detection of forward-moving spectator protons over a wide range of recoil momenta (0 < p(R) < several 100MeV in the nucleus rest frame). The free neutron structure functions could be obtained by extrapolating the measured recoil momentum distributions to the on-shell point. The method eliminates nuclear modifications and can be applied to polarized scattering, as well as to semi-inclusive and exclusive final states. We review the prospects for neutron structure measurements with spectator tagging at EIC, the status of R&D efforts, and the accelerator and detector requirements.

Guzey, Vadim↗
DOE OSTI2015

Evaluation of the radiation doses in newborn patients submitted to CT examinations

The number of computed tomography (CT) scans available to the population is increasing, as well as the complexity of such exams. As a result, the radiation doses are increasing as well. Considering the population exposed to CT exams, pediatric patients are considerably more sensitive to radiation than adults. They have a longer life expectancy than adults, and may receive a higher radiation dose than necessary if the CT scan settings are not adjusted for their smaller body size. As a result of these considerations, the risk of developing cancer is of great concern when newborn patients are involved. The objective of this work was to study the radiation doses on radiosensitive organs of newborn patients undergoing a whole body CT examination, utilizing Monte Carlo simulations. The novelty of this work is the use of pediatric virtual anthropomorphic phantoms, developed at the Department of Nuclear Energy at the Federal University of Pernambuco (DEN/UFPE). The CT equipment utilized during the simulations was a Discovery VCT GE PET/CT system, with a tube voltage of 140 kVp. The X-ray spectrum of this CT scanner was generated by the SRS-78 software, which takes into account the X-ray beam energy used in PET/CT procedures. The absorbed organ doses were computed employing the F6 tally (MeV/g). The results were converted to dose coefficients (mGy/100 mA) for all the structures, considering all employed beams. The highest dose coefficients values were obtained for the brain and the thyroid. This work provides useful information regarding the risks involving ionizing radiation in newborn patients, employing a new and reliable technique. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Aberration‐Corrected Transmission Electron Microscopy and In Situ XAFS Structural Characterization of Pt/γ‐Al 2 O 3 Nanoparticles

Abstract Aberration‐corrected (AC) STEM, AC TEM and in situ X‐ray absorption fine structure spectroscopy (XAFS) were used to characterize the Pt clusters present on a 0.35 wt % Pt on γ‐alumina support after reduction in hydrogen at 700 °C. STEM high‐angle annular dark field imaging shows that cluster formation takes place at temperatures up to approximately 350 °C, and this is followed by gradual growth in cluster size for heat treatments in hydrogen up to 700 °C. The STEM data show that after 700 °C reduction the Pt clusters are present in a narrow size distribution centered at 0.88 nm, and using a method involving a redistribution of the Pt atoms using a high electron dosage in the STEM, it is shown that the clusters are present in two‐dimensional morphology. This conclusion is verified using intensity line scans. The in situ extended X‐ray absorption fine structure data are in good agreement with these observations. High‐resolution AC–TEM, which uses a broad coherent electron beam, and can thus offer advantages relative to STEM for structure determination of fine clusters, supported by image simulations of through‐focus series, were used to analyze the structures of Pt particles. The structures determined by using AC–TEM are consistent with STEM and EXAFS data in having a flat two‐dimensional morphology. Comparison of AC–STEM and AC TEM data for the same 700 °C reduced sample suggests that parallel‐beam TEM mode of imaging may be advantageous because of the less pronounced beam‐induced structural rearrangements that occur when imaging with a fine STEM probe.

Sinkler, Wharton↗
NASA NTRS1979

Analysis of beam-like lattice trusses

A simple procedure is presented for predicting the thermoelastic and free vibration responses of large repetitive beam-like trusses. The procedure is based on replacing the original lattice structure by an equivalent continuum beam model and obtaining closed-form (exact) solutions for the beam model. The equivalent beam model accounts for warping and shear deformation in the plane of the cross-section and is characterized by its thermoelastic strain and kinetic energies, from which the equations of motion and constitutive relations can be derived. The high accuracy of the results obtained by the proposed approach is demonstrated by means of numerical examples.

Noor, K.↗