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DOE OSTI2016

Isochronal annealing effects on local structure, crystalline fraction, and undamaged region size of radiation damage in Ga-stabilized δ-Pu

The effects on the local structure due to self-irradiation damage of Ga stabilized δ-Pu stored at cryogenic temperatures have been examined using extended x-ray absorption fine structure (EXAFS) experiments. Extensive damage, seen as a loss of local order, was evident after 72 days of storage below 15 K. The effect was observed from both the Pu and the Ga sites, although less pronounced around Ga. Isochronal annealing was performed on this sample to study the annealing processes that occur between cryogenic and room temperature storage conditions, where damage is mostly reversed. Damage fractions at various points along the annealing curve have been determined using an amplitude-ratio method, a standard EXAFS fitting, and a spherical crystallite model, and provide information complementary to the previous electrical resistivity- and susceptibility-based isochronal annealing studies. The use of a spherical crystallite model accounts for the changes in EXAFS spectra using just two parameters, namely, the crystalline fraction and the particle radius. Together, these results are discussed in terms of changes to the local structure around Ga and Pu throughout the annealing process and highlight the unusual role of Ga in the behavior of the lowest temperature anneals.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Improved inertial control for permanent magnet synchronous generator wind turbine generators

With increasing integrations of large‐scale systems based on permanent magnet synchronous generator wind turbine generators (PMSG‐WTGs), the overall inertial response of a power system will tend to deteriorate as a result of the decoupling of rotor speed and grid frequency through the power converter as well as the scheduled retirement of conventional synchronous generators. Thus, PMSG‐WTGs can provide value to an electric grid by contributing to the system's inertial response through the inherent kinetic energy stored in their rotating masses and fast power converter control. In this study, an improved inertial control method based on the maximum power point tracking operation curve is introduced to enhance the overall frequency support capability of PMSG‐WTGs in the case of large supply–demand imbalances. Moreover, this method is implemented in the CART2‐PMSG integrated model in MATLAB/Simulink to investigate its impact on the wind turbine's structural loads during the inertial response process. Simulation results indicate that the proposed method can effectively reduce the frequency nadir, arrest the rate of change of frequency, and alleviate the secondary frequency dip while imposing no negative impact on the major mechanical components of the wind turbine.

Wu, Ziping↗

NASA NTRS1992

Evaluation of human response to structural vibrations induced by sonic booms

The topic is addressed of building vibration response to sonic boom and the evaluation of the associated human response to this vibration. An attempt is made to reexamine some of the issues addressed previously and to offer fresh insight that may assist in reassessing the potential impact of sonic boom over populated areas. Human response to vibration is reviewed first and a new human vibration response criterion curve is developed as a function of frequency. The difference between response to steady state versus impulsive vibration is addressed and a 'vibration exposure' or 'vibration energy' descriptor is suggested as one possible way to evaluate duration effects on response to transient vibration from sonic booms. New data on the acoustic signature of rattling objects are presented along with a review of existing data on the occurrence of rattle. Structural response to sonic boom is reviewed and a new descriptor, 'Acceleration Exposure Level' is suggested which can be easily determined from the Fourier Spectrum of a sonic boom. A preliminary assessment of potential impact from sonic booms is provided in terms of human response to vibration and detection of rattle based on a synthesis of the preceding material.

Sutherland, Louis C.↗

DOE OSTI2018

Single fiber peel test to assess ultra high molecular weight polyethylene fiber mesostructure interactions

ABSTRACT In this work, a variable angle, single fiber peel test is developed to analyze the effects of fiber structure on the mixed mode failure within ultra high molecular weight polyethylene fibers. The Mode I and Mode II peel energy release rates are quantified and the effects of fiber meso/nanostructure on these modes are examined. Comparison of the load‐extension curves from the peel test with in‐situ video, and post‐mortem analysis using high‐resolution microscopy techniques indicates that Mode I and Mode II splitting are both significantly influenced by the deformation of nanoscale fibrils within a mesoscale network. The fibrils in the network are placed in tension across the peel/shear interface resulting in elevated values of peel energy release rates with an increasing number of engaged fibrils. The number of engaged fibrils is shown to increase with decreasing peel angle and increasing Mode II failure contribution. A bi‐linear mixed‐mode failure criterion is established. The results, and analysis of the fiber structure are discussed in context of their implications for load pathways in the fiber. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135 , 46156.

McDaniel, Preston B.↗

NASA NTRS1993

Advanced composite fuselage technology

Boeing's ATCAS program has completed its third year and continues to progress towards a goal to demonstrate composite fuselage technology with cost and weight advantages over aluminum. Work on this program is performed by an integrated team that includes several groups within The Boeing Company, industrial and university subcontractors, and technical support from NASA. During the course of the program, the ATCAS team has continued to perform a critical review of composite developments by recognizing advances in metal fuselage technology. Despite recent material, structural design, and manufacturing advancements for metals, polymeric matrix composite designs studied in ATCAS still project significant cost and weight advantages for future applications. A critical path to demonstrating technology readiness for composite transport fuselage structures was created to summarize ATCAS tasks for Phases A, B, and C. This includes a global schedule and list of technical issues which will be addressed throughout the course of studies. Work performed in ATCAS since the last ACT conference is also summarized. Most activities relate to crown quadrant manufacturing scaleup and performance verification. The former was highlighted by fabricating a curved, 7 ft. by 10 ft. panel, with cocured hat-stiffeners and cobonded J-frames. In building to this scale, process developments were achieved for tow-placed skins, drape formed stiffeners, braided/RTM frames, and panel cure tooling. Over 700 tests and supporting analyses have been performed for crown material and design evaluation, including structural tests that demonstrated limit load requirements for severed stiffener/skin failsafe damage conditions. Analysis of tests for tow-placed hybrid laminates with large damage indicates a tensile fracture toughness that is higher than that observed for advanced aluminum alloys. Additional recent ATCAS achievements include crown supporting technology, keel quadrant design evaluation, and sandwich process development.

Ilcewicz, Larry B.↗

DOE OSTI2022

Pre-vaporized ignition behavior of ethyl- and propyl-terminated oxymethylene ethers

Oxymethylene ethers (OMEs) have been studied in recent years for use as compression ignition fuel blendstocks, but the methyl-terminated OMEs commonly studied exhibit properties that are poorly optimized for engine use and distribution. Recent work has shown that OMEs with larger (ethyl, propyl, or butyl) end groups may have superior properties for fuel usage/storage. In this work, we consider ignition of four OMEs - diethoxymethane (E-1-E), dipropoxymethane (P-1-P), ethoxy-(methoxy) 2 -ethane (E-2-E), and diisopropoxymethane (iP-1-iP) - as representatives of the possible effects of changes to OME structures. To our knowledge, ignition behaviors of the latter three fuels have not been studied prior to this work. Further, we find that all of the tested linear OMEs (E-1-E, P-1-P, and E-2-E) show two-stage ignition at low temperatures and nonlinear ignition behavior, consistent with literature on methyl-terminated OMEs and E-1-E. The nonlinear, branched OME (iP-1-iP) required higher pressure and temperature to ignite than the linear OMEs; further, this fuel experienced only single stage ignition and a linear ignition delay curve. By analogy to existing kinetic mechanisms for ethers and higher alcohols, the chemical basis for the observed trends are hypothesized. Faster ignition of E-2-E results from the additional oxymethylene group providing additional sites for ROO formation and more possible QOOH structures. Slower low temperature ignition of P-1-P is driven by lower H abstraction rates in comparison to E-1-E, however at high temperatures P-1-P ignites faster, driven by increasing abstraction from the additional H site on the propyl group that opens up additional QOOH formation pathways. iP-1-iP ignition is slowed significantly by preferential H abstraction from the central carbon of the isopropyl group, which is crowded and unlikely to bond with O 2 , however at high temperatures, abstraction from H sites on the methyl groups allows for the ROO cascade initiation and subsequent rapid ignition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

Structural properties of Bi{sub 2}Te{sub 3} topological insulator thin films grown by molecular beam epitaxy on (111) BaF{sub 2} substrates

Structural properties of topological insulator bismuth telluride films grown epitaxially on (111) BaF{sub 2} with a fixed Bi{sub 2}Te{sub 3} beam flux were systematically investigated as a function of substrate temperature and additional Te flux. A layer-by-layer growth mode is observed since the early stages of epitaxy and remains throughout the whole deposition. Composition of the epitaxial films produced here stays between Bi{sub 2}Te{sub 3} and Bi{sub 4}Te{sub 5}, as determined from the comparison of the measured x-ray diffraction curves with calculations. The substrate temperature region, where the growth rate remains constant, is found to be the most appropriate to obtain ordered Bi{sub 2}Te{sub 3} films. Line width of the L = 18 Bi{sub 2}Te{sub 3} diffraction peaks as low as 140 arcsec was obtained, indicating high crystalline quality. Twinning domains density rises with increasing growth temperature and reducing Te extra flux. X-ray reflectivity curves of pure Bi{sub 2}Te{sub 3} films with thickness from 165 to 8 nm exhibited well defined interference fringes, evidencing homogeneous layers with smooth surface. Our results demonstrate that Bi{sub 2}Te{sub 3} films with very well controlled structural parameters can be obtained. High structural quality Bi{sub 2}Te{sub 3} films as thin as only eight quintuple layers grown here are promising candidates for intrinsic topological insulator.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Efficient conversion from UV light to near-IR emission in Yb{sup 3+}-doped triple-layered perovskite CaLaNb{sub 3}O{sub 10}

Graphical abstract: CaRNb{sub 3}O{sub 10} is a self-activated oxide due to charge transfer transition in octahedral NbO{sub 6} groups. CaLaNb{sub 3}O{sub 10}:Yb{sup 3+} presents intense IR emission due to the cooperative energy transfer from host (NbO{sub 6}) to Yb{sup 3+} is responsible. It could be expected to be potentially applicable for enhancing photovoltaic conversion efficiency of Si-based solar cells. - Abstract: Yb{sup 3+}-doped triple-layered perovskite CaLaNb{sub 3}O{sub 10} micro-particles were synthesized via the solid-state reaction method. The crystal structure and morphology of the polycrystalline samples were investigated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) measurements, respectively. The reflectance spectra, photoluminescence (PL) excitation and emission spectra, the decay curves, and the absolute quantum efficiency (QE) of the near-infrared (NIR) emission (910–1100 nm) were measured. Under excitation of UV light, Yb{sup 3+}-doped perovskite shows an intense NIR emission attributed to the {sup 2}F{sub 5/2} → {sup 2}F{sub 7/2} transitions of Yb{sup 3+} ions, which could match maximum spectral response of a Si-based solar cell. This is beneficial for its possible application in an enhancement of the photovoltaic conversion efficiency of solar energy utilization. The efficient energy transfer in Yb{sup 3+}-doped CaLaNb{sub 3}O{sub 10} from NbO{sub 6} groups into Yb{sup 3+} ions was confirmed by the spectra and fluorescent decay measurements. Cooperative energy transfer (CET) was supposed to be the NIR emission mechanism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1961

Semi-Annual Report: October 15, 1961

Investigations are proposed involving an experimental and theoretical program designed to investigate various properties of the structure of helium both in its atomic form and in the aggregates of the liquid and solid states. The key to the possibilities of performing the experiments lies in the relatively weak electric fields existing in liquid and solid helium and the possibility of producing external fields almost comparable with the internal fields. It is proposed to examine a) the melting pressure curve for helium as a function of electric field b) the dielectric constant of helium as a function of pressure and electric field c) in future, the effect of electric fields on the lambda transition. From the results of these experiments one would expect to be able to gather at least corroborative evidence on a) the crystal structure of solid helium on b) the effect of the Van der Waal interaction of the electric polarizability of helium, c) the possibility of producing helium molecules d) the effective volume available to helium atoms in the liquid and possibly e) the effect of particle interactions on the Bose-Einstein condensation.

HELIUM↗

DOE OSTI2016

Frequency Support of PMSG-WTG Based on Improved Inertial Control

With increasing integrations of large-scale systems based on permanent magnet synchronous generator wind turbine generators (PMSG-WTGs), the overall inertial response of a power system will tend to deteriorate as a result of the decoupling of rotor speed and grid frequency through the power converter as well as the scheduled retirement of conventional synchronous generators. Thus, PMSG-WTGs can provide value to an electric grid by contributing to the system's inertial response by utilizing the inherent kinetic energy stored in their rotating masses and fast power control. In this work, an improved inertial control method based on the maximum power point tracking operation curve is introduced to enhance the overall frequency support capability of PMSG-WTGs in the case of large supply-demand imbalances. Moreover, this method is implemented in the CART2-PMSG integrated model in MATLAB/Simulink to investigate its impact on the wind turbine's structural loads during the inertial response process. Simulation results indicate that the proposed method can effectively reduce the frequency nadir, arrest the rate of change of frequency, and mitigate the secondary frequency drop while imposing no negative impact on the major mechanical components of the wind turbine.

17 WIND ENERGY↗

DOE OSTI2018

Inositol phosphates are assembly co-factors for HIV-1

A short, 14-amino-acid segment called SP1, located in the Gag structural protein, has a critical role during the formation of the HIV-1 virus particle. During virus assembly, the SP1 peptide and seven preceding residues fold into a six-helix bundle, which holds together the Gag hexamer and facilitates the formation of a curved immature hexagonal lattice underneath the viral membrane. Upon completion of assembly and budding, proteolytic cleavage of Gag leads to virus maturation, in which the immature lattice is broken down; the liberated CA domain of Gag then re-assembles into the mature conical capsid that encloses the viral genome and associated enzymes. Folding and proteolysis of the six-helix bundle are crucial rate-limiting steps of both Gag assembly and disassembly, and the six-helix bundle is an established target of HIV-1 inhibitors. Here, using a combination of structural and functional analyses, we show that inositol hexakisphosphate (InsP6, also known as IP 6 ) facilitates the formation of the six-helix bundle and assembly of the immature HIV-1 Gag lattice. IP 6 makes ionic contacts with two rings of lysine residues at the centre of the Gag hexamer. Proteolytic cleavage then unmasks an alternative binding site, where IP 6 interaction promotes the assembly of the mature capsid lattice. Furthermore, these studies identify IP6 as a naturally occurring small molecule that promotes both assembly and maturation of HIV-1.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2016

Mode shape combination in a two-dimensional vibration energy harvester through mass loading structural modification

Mode shapes in the design of mechanical energy harvesters, as a means of performance increase, have been largely overlooked. Currently, the vast majority of energy harvester designs employ some variation of a single-degree-of-freedom cantilever, and the mode shapes of such beams are well known. This is especially true for the first bending mode, which is almost exclusively the chosen vibration mode for energy harvesting. Two-dimensional beam shapes (those which curve, meander, spiral, etc., in a plane) have recently gained research interest, as they offer freedom to modify the vibration characteristics of the harvester beam for achieving higher power density. In this study, the second bending mode shape of the “Elephant” two-dimensional beam shape is examined, and its interaction with the first bending mode is evaluated. A combinatory mode shape created by using mass loading structural modification to lower the second bending modal frequency was found to interact with the first bending mode. This is possible since the first two bending modes do not share common areas of displacement. The combined mode shape is shown to produce the most power of any of the considered mode shapes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2018

Defect Structure of GaAs Layers Implanted with Nitrogen Ions

Structural defects formed in epitaxial GaAs layers as a result of 250-keV N{sup +} ion implantation to doses within 5 × 10{sup 14}–5 × 10{sup 16} cm{sup –2} have been studied by the X-ray diffraction (XRD) and transmission electron microscopy techniques. No amorphization of the ion-implanted layer took place in the entire dose range studied. The implantation to doses of 5 × 10{sup 14} and 5 × 10{sup 15} cm{sup –2} led to the appearance of an additional peak on XRD curves, which was related to the formation of a stressed GaAs layer with positive deformation arising due to the formation of point-defect clusters. The implantation to a dose of 5 × 10{sup 16} cm{sup –2} led to the formation of a dense structure of extended defects in the implanted layer, which was accompanied by the relaxation of macrostresses to the initial state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Evidence for Sub-Chandrasekhar Mass Type Ia Supernovae from an Extensive Survey of Radiative Transfer Models

There exists two classes of viable progenitors for normal Type Ia supernovae (SNe Ia): systems in which a white dwarf explodes at the Chandrasekhar mass (${M}_{\mathrm{ch}}$), and systems in which a white dwarf explodes below the Chandrasekhar mass (sub-${M}_{\mathrm{ch}}$). It is not clear which of these channels is dominant; observations and light-curve modeling have provided evidence for both. In this work we use an extensive grid of 4500 time-dependent, multiwavelength radiation transport simulations to show that the sub-${M}_{\mathrm{ch}}$ model can reproduce the entirety of the width–luminosity relation, while the ${M}_{\mathrm{ch}}$ model can only produce the brighter events $(0.8\lt {\rm{\Delta }}{M}_{15}(B)\lt 1.55)$, implying that fast-declining SNe Ia come from sub-${M}_{\mathrm{ch}}$ explosions. We do not assume a particular theoretical paradigm for the progenitor or explosion mechanism, but instead construct parameterized models that vary the mass, kinetic energy, and compositional structure of the ejecta, thereby realizing a broad range of possible outcomes of white dwarf explosions. We provide fitting functions based on our large grid of detailed simulations that map observable properties of SNe Ia, such as peak brightness and light-curve width, to physical parameters such as ${}^{56}\mathrm{Ni}$ and total ejected mass. These can be used to estimate the physical properties of observed SNe Ia.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Type II string theory on Calabi-Yau manifolds with torsion and non-Abelian discrete gauge symmetries

Here, we provide the first explicit example of Type IIB string theory compactication on a globally defined Calabi-Yau threefold with torsion which results in a fourdimensional effective theory with a non-Abelian discrete gauge symmetry. Our example is based on a particular Calabi-Yau manifold, the quotient of a product of three elliptic curves by a fixed point free action of Z 2 X Z 2 . Its cohomology contains torsion classes in various degrees. The main technical novelty is in determining the multiplicative structure of the (torsion part of) the cohomology ring, and in particular showing that the cup product of second cohomology torsion elements goes non-trivially to the fourth cohomology. This specifies a non-Abelian, Heisenberg-type discrete symmetry group of the four-dimensional theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

DNA-binding induced conformational change of c-Myb R2R3 analyzed using diffracted X-ray tracking

Highlights: • DNA-binding protein, c-Myb R2R3, largely fluctuates in solution. • We evaluated structural dynamics of R2R3 using diffracted X-ray tracking (DXT). • The flexibility of R2R3 is decreased upon the DNA binding. • We could determine the DNA-binding energies of R2R3 using DXT. Previous structural analyses have shown that R2R3, the minimum unit of the DNA-binding domain of the transcriptional factor c-Myb, is largely flexible in solution, and changes to a more rigid structure upon DNA binding. In this study, we evaluated the structural dynamics using the diffracted X-ray tracking method, in correlation with DNA-binding abilities under different salt conditions, and compared them with the previous results. The resultant curve of the mean square angular displacements (MSD) clearly showed that the flexibility of R2R3 was decreased upon DNA binding, and the DNA-binding energies determined using the angular diffusion coefficients were in good agreement with those determined using isothermal titration calorimetry. The results of the MSD curves also indicate that the translational length reduces by approximately half upon DNA binding.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2018

Propagation of a stable gaseous detonation in a circular arc configuration

Here, we examine numerically the effect that detonation wavefront curvature has on gaseous detonation cellular structure in a circular arc geometry with rigid walls. For the model considered, a planar detonation is weakly unstable. The detonation curvature is induced by diffraction and flow divergence as the wave sweeps around the arc. We examine the effect of arc thickness, inner arc radius and activation energy on the cellular pattern. A combination of pseudo-Schlieren, pseudo-soot foil records and detonation shock and sonic flow loci are used to explore the observed detonation structures. We find that for sufficiently wide arcs, the detonation wavefront curvature renders the detonation hydrodynamically stable, i.e. laminar flow with no cells. The stable configuration consists of a broadly curved wave originating from the inner arc surface, which is typically connected to the outer arc boundary by a stable Mach stem. The stable detonation is driven by a small region of subsonic flow attached to the inner arc surface, outside of which the flow is supersonic. The initiation dynamics of a stable propagating wave case are explored. The evolution dynamics between an unstable (cellular) and stable arc thickness are also examined. Finally, smaller inner arc radii and lower activation energies increase the range of stable solutions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Quantification of Coexisting Inner- and Outer-Sphere Complexation of Sulfate on Hematite Surfaces

Sulfate adsorption on hematite surfaces controls sulfate mobility and environmental behavior but whether sulfate forms both inner- and outer-sphere complexes and the type of the inner-sphere complexes remain contentious. With ionic strength tests and S K-edge X-ray absorption near-edge structure spectroscopy, we show that sulfate forms both outer- and inner-sphere complexes on hematite surfaces. Both S K-edge extended X-ray absorption fine structure spectroscopy and the differential pair distribution function analyses determine the S–Fe interatomic distance (~3.24 Å) of the inner-sphere complex, suggesting bidentate-binuclear complexation. A multivariate curve resolution (MCR) analysis of the attenuated total reflection–Fourier-transform infrared spectra of adsorption envelope samples shows that increasing ionic strength does not affect the inner-sphere but decreases the outer-sphere complex adsorption loading, consistent with the ionic strength effect. The extended triple layer model directly and successfully models the MCR-derived inner- and outer-sphere surface loadings at various ionic strengths, indicating weaker sulfate inner-sphere complexation on hematite than on ferrihydrite surfaces. Results also show that sample drying, lower pH, and higher ionic strength all favor sulfate inner-sphere complexation, but the hematite particle size does not affect the relative proportions of the two types of complexes. Sulfate adsorption kinetics show increasing ratio of exchanged OH– to adsorbed sulfate with time, attributed to inner- and outer-sphere complexation dominating at different adsorption stages and to the changes of the relative abundance of surface OH – and H 2 O groups with time. This work clarifies sulfate adsorption mechanisms on hematite and has implications for understanding sulfate availability, behavior and fate in the environment. Our work suggests that the simple macroscopic ionic strength test correlates well with directly measured outer-sphere complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗