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All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Modeling and analysis of cascade solar cells

A brief review is given of the present status of the development of cascade solar cells. It is known that photovoltaic efficiencies can be improved through this development. The designs and calculations of the multijunction cells, however, are quite complicated. The main goal is to find a method which is a compromise between accuracy and simplicity for modeling a cascade solar cell. Three approaches are presently under way, among them (1) equivalent circuit approach, (2) numerical approach, and (3) analytical approach. Here, the first and the second approaches are discussed. The equivalent circuit approach using SPICE (Simulation Program, Integrated Circuit Emphasis) to the cascade cells and the cascade-cell array is highlighted. The methods of extracting parameters for modeling are discussed.

Ho, F. D.↗
NASA NTRS1991

An overview of the halogen occultation experiment (HALOE)

The HALOE experiment will fly on the Upper Atmosphere Research Satellite (UARS) in the last quarter of 1991. The experiment uses the solar occultation limb sounding approach, in combination with gas filter and broadband radiometry to provide measurements of temperature profiles and key gases in the ClO(y), NO(y), and HO(y) chemical families of the middle atmosphere. The instrument has been characterized in great detail to determine gains, spectral response, noise, crosstalk, field-of-view, and thermal drift characteristics. A final end-to-end test using a gas cell to simulate the atmosphere demonstrated measurement repeatability to about 1 percent and agreement between measured and calculated signals to within about 1 percent to 3 percent. This latter agreement provides confidence in knowledge of both the hardware as well as the software.

Russell, James M., III↗
NASA NTRS2019

NuStar Hard X-Ray View of Low-Luminosity Active Galactic Nuclei: High-Energy Cutoff and Truncated Thin Disk

We report the analysis of simultaneous XMM-Newton+Nuclear Spectroscopic Telescope Array (NuSTAR) observations of two low-luminosity active galactic nuclei (LLAGNs), NGC3998 and NGC4579. We do not detect any significant variability in either source over the ∼3 day length of the NuSTAR observations. The broadband 0.5–60 keV spectrum of NGC3998 is best fit with a cutoff power law, while the one for NGC4579 is best fit with a combination of a hot thermal plasma model, a power law, and a blend of Gaussians to fit an Fe complex observed between 6 and 7 keV. Our main spectral results are the following: (1) neither source shows any reflection hump with 3σ reflection fraction upper limits of R < 0.3 and R < 0.18 for NGC3998 and NGC4579, respectively; (2) the 6–7 keV line complex in NGC4579 could be fit with either a narrow Fe K line at 6.4 keV and a moderately broad Fe XXV line or with three relatively narrow lines, which include contribution from Fe XXVI; (3) the NGC4579 flux is 60% brighter than previously detected with XMM-Newton, accompanied by a hardening in the spectrum; (4) we measure a cutoff energy = - E 107+ cut 18 27 keV in NGC3998, which represents the lowest and best constrained high-energy cutoff ever measured for an LLAGN; (5) the NGC3998 spectrum is consistent with a Comptonization model with either a sphere (τ ≈ 3 ± 1) or slab (τ ≈ 1.2 ± 0.6) geometry, corresponding to plasma temperatures between 20 and 150 keV. We discuss these results in the context of hard X-ray emission from bright AGNs, other LLAGNs, and hot accretion flow models.

Younes, George↗
NASA NTRS2012

Development of Field-Controlled Smart Optic Materials (ScN, AlN) with Rare Earth Dopants

The purpose of this investigation is to develop the fundamental materials and fabrication technology for field-controlled spectrally active optics that are essential for industry, NASA, and DOD applications such as: membrane optics, filters for LIDARs, windows for sensors, telescopes, spectroscopes, cameras, flat-panel displays, etc. ScN and AlN thin films were fabricated on c-axis Sapphire (0001) or quartz substrate with the RF and DC magnetron sputtering. The crystal structure of AlN in fcc (rocksalt) and hcp (wurtzite) were controlled. Advanced electrical characterizations were performed, including I-V and Hall Effect Measurement. ScN film has a free carrier density of 5.8 x 10(exp 20)/per cubic centimeter and a conductivity of 1.1 x 10(exp 3) per centimeter. The background ntype conductivity of as-grown ScN has enough free electrons that can readily interact with the photons. The high density of free electrons and relatively low mobility indicate that these films contain a high level of shallow donors as well as deep levels. Also, the UV-Vis spectrum of ScN and AlN thin films with rare earth elements (Er or Ho) were measured at room temperature. Their optical band gaps were estimated to be about 2.33eV and 2.24eV, respectively, which are obviously smaller than that of undoped thin film ScN (2.4eV). The red-shifted absorption onset gives direct evidence for the decrease of band gap (Eg) and the energy broadening of valence band states are attributable to the doping. As the doped elements enter the ScN crystal lattices, the localized band edge states form at the doped sites with a reduction of Eg. Using a variable angle spectroscopic ellipsometer, the decrease in refractive index with applied field is observed with a smaller shift in absorption coefficient.

Kim, Hyun-Jung↗
DOE OSTI2020

Materials Data on Ho2Co12P7 by Materials Project

Ho2Co12P7 crystallizes in the hexagonal P-6 space group. The structure is three-dimensional. there are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six equivalent P3- atoms to form distorted HoP6 pentagonal pyramids that share corners with twelve CoP4 tetrahedra, corners with six equivalent CoP5 trigonal bipyramids, edges with nine CoP4 tetrahedra, edges with three equivalent CoP5 trigonal bipyramids, and faces with two equivalent HoP6 pentagonal pyramids. All Ho–P bond lengths are 2.82 Å. In the second Ho3+ site, Ho3+ is bonded to six equivalent P3- atoms to form distorted HoP6 pentagonal pyramids that share corners with twelve CoP4 tetrahedra, corners with six equivalent CoP5 trigonal bipyramids, edges with twelve CoP4 tetrahedra, and faces with two equivalent HoP6 pentagonal pyramids. All Ho–P bond lengths are 2.85 Å. There are four inequivalent Co+1.25+ sites. In the first Co+1.25+ site, Co+1.25+ is bonded to four P3- atoms to form CoP4 tetrahedra that share corners with four HoP6 pentagonal pyramids, corners with ten CoP4 tetrahedra, corners with two equivalent CoP5 trigonal bipyramids, an edgeedge with one HoP6 pentagonal pyramid, edges with three CoP4 tetrahedra, and edges with four equivalent CoP5 trigonal bipyramids. There are a spread of Co–P bond distances ranging from 2.13–2.27 Å. In the second Co+1.25+ site, Co+1.25+ is bonded to four P3- atoms to form CoP4 tetrahedra that share corners with two equivalent HoP6 pentagonal pyramids, corners with ten CoP4 tetrahedra, corners with four equivalent CoP5 trigonal bipyramids, edges with three HoP6 pentagonal pyramids, edges with four CoP4 tetrahedra, and an edgeedge with one CoP5 trigonal bipyramid. There are a spread of Co–P bond distances ranging from 2.24–2.31 Å. In the third Co+1.25+ site, Co+1.25+ is bonded to five P3- atoms to form distorted CoP5 trigonal bipyramids that share corners with four HoP6 pentagonal pyramids, corners with eight CoP4 tetrahedra, corners with four equivalent CoP5 trigonal bipyramids, an edgeedge with one HoP6 pentagonal pyramid, edges with seven CoP4 tetrahedra, and edges with four equivalent CoP5 trigonal bipyramids. There are a spread of Co–P bond distances ranging from 2.23–2.56 Å. In the fourth Co+1.25+ site, Co+1.25+ is bonded to four P3- atoms to form CoP4 tetrahedra that share corners with two equivalent HoP6 pentagonal pyramids, corners with twelve CoP4 tetrahedra, corners with two equivalent CoP5 trigonal bipyramids, edges with three HoP6 pentagonal pyramids, edges with three CoP4 tetrahedra, and edges with two equivalent CoP5 trigonal bipyramids. There are a spread of Co–P bond distances ranging from 2.24–2.29 Å. There are three inequivalent P3- sites. In the first P3- site, P3- is bonded in a 3-coordinate geometry to nine Co+1.25+ atoms. In the second P3- site, P3- is bonded in a 9-coordinate geometry to two equivalent Ho3+ and seven Co+1.25+ atoms. In the third P3- site, P3- is bonded in a 9-coordinate geometry to two equivalent Ho3+ and seven Co+1.25+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Multiple Tunable Hyperbolic Resonances in Broadband Infrared Carbon-Nanotube Metamaterials

Aligned densely packed carbon-nanotube metamaterials prepared using vacuum filtration are an emerging infrared nanophotonic material. We report multiple hyperbolic plasmon resonances, together spanning the mid-infrared, in individual resonators made from aligned and densely packed carbon nanotubes. In a near-field scanning optical microscopy (NSOM) imaging study of nanotube metamaterial resonators, we observe distinct deeply subwavelength field profiles at the fundamental and higher-order resonant frequencies. The wafer-scale area of the nanotube metamaterials allows us to combine this near-field imaging with a systematic far-field spectroscopic study of the scaling properties of many resonator arrays. Thorough theoretical modeling agrees with these measurements and identifies the resonances as higher-order Fabry-Perot (FP) resonances of hyperbolic waveguide modes. Nanotube resonator arrays show broadband extinction from 1.5–10 µm and reversibly switchable extinction in the 3–5 µm atmospheric transparency window through the coexistence of multiple modes in individual ribbons. Broadband carbon-nanotube metamaterials supporting multiple resonant modes are a promising candidate for ultracompact absorbers, tunable thermal emitters, and broadband sensors in the mid-infrared.

36 MATERIALS SCIENCE↗
NASA NTRS2011

Mercury's Weather-Beaten Surface: Understanding Mercury in the Context of Lunar and Asteroid Space Weathering Studies

Understanding the composition of Mercury's crust is key to comprehending the formation of the planet. The regolith, derived from the crustal bedrock, has been altered via a set of space weathering processes. These processes are the same set of mechanisms that work to form Mercury's exosphere, and are moderated by the local space environment and the presence of an intrinsic planetary magnetic field. The alterations need to be understood in order to determine the initial crustal compositions. The complex interrelationships between Mercury's exospheric processes, the space environment, and surface composition are examined and reviewed. The processes are examined in the context of our understanding of these same processes on the lunar and asteroid regoliths. Keywords: Mercury (planet) Space weathering Surface processes Exosphere Surface composition Space environment 3

Dominque, Deborah L.↗
DOE OSTI2020

Materials Data on KHo2Cu(MoO4)4 by Materials Project

KHo2Cu(MoO4)4 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. K1+ is bonded in a 10-coordinate geometry to ten O2- atoms. There are a spread of K–O bond distances ranging from 2.69–3.23 Å. Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.27–2.49 Å. There are two inequivalent Mo6+ sites. In the first Mo6+ site, Mo6+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Mo–O bond distances ranging from 1.78–1.87 Å. In the second Mo6+ site, Mo6+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Mo–O bond distances ranging from 1.77–1.88 Å. Cu1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Cu–O bond distances ranging from 2.05–2.66 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Mo6+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Mo6+ atom. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Mo6+ atom. In the fourth O2- site, O2- is bonded in a 1-coordinate geometry to one K1+, one Mo6+, and one Cu1+ atom. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Mo6+, and one Cu1+ atom. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to one K1+, one Mo6+, and one Cu1+ atom. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Ho3+, and one Mo6+ atom. In the eighth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one K1+, one Ho3+, and one Mo6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na2HoTa5O15 by Materials Project

Na2HoTa5O15 crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. Na1+ is bonded in a 6-coordinate geometry to nine O2- atoms. There are a spread of Na–O bond distances ranging from 2.70–3.13 Å. Ho3+ is bonded to twelve O2- atoms to form HoO12 cuboctahedra that share faces with two equivalent HoO12 cuboctahedra and faces with eight equivalent TaO6 octahedra. There are four shorter (2.56 Å) and eight longer (2.66 Å) Ho–O bond lengths. There are two inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 0–33°. There is two shorter (1.96 Å) and four longer (2.00 Å) Ta–O bond length. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and faces with two equivalent HoO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 12–42°. There are a spread of Ta–O bond distances ranging from 1.92–2.05 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Na1+ and two Ta5+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Na1+, one Ho3+, and two equivalent Ta5+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Na1+ and two equivalent Ta5+ atoms. In the fourth O2- site, O2- is bonded in a linear geometry to two equivalent Na1+ and two equivalent Ta5+ atoms. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ho3+ and two equivalent Ta5+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Ni12P7 by Materials Project

Ho2Ni12P7 crystallizes in the hexagonal P-6 space group. The structure is three-dimensional. there are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six equivalent P3- atoms to form distorted HoP6 pentagonal pyramids that share corners with six equivalent NiP5 square pyramids, corners with twelve NiP4 tetrahedra, edges with twelve NiP4 tetrahedra, and faces with two equivalent HoP6 pentagonal pyramids. All Ho–P bond lengths are 2.87 Å. In the second Ho3+ site, Ho3+ is bonded to six equivalent P3- atoms to form distorted HoP6 pentagonal pyramids that share corners with six equivalent NiP5 square pyramids, corners with twelve NiP4 tetrahedra, edges with three equivalent NiP5 square pyramids, edges with nine NiP4 tetrahedra, and faces with two equivalent HoP6 pentagonal pyramids. All Ho–P bond lengths are 2.85 Å. There are four inequivalent Ni+1.25+ sites. In the first Ni+1.25+ site, Ni+1.25+ is bonded to four P3- atoms to form NiP4 tetrahedra that share corners with two equivalent HoP6 pentagonal pyramids, corners with four equivalent NiP5 square pyramids, corners with ten NiP4 tetrahedra, edges with three HoP6 pentagonal pyramids, an edgeedge with one NiP5 square pyramid, and edges with four NiP4 tetrahedra. There are a spread of Ni–P bond distances ranging from 2.25–2.34 Å. In the second Ni+1.25+ site, Ni+1.25+ is bonded to four P3- atoms to form NiP4 tetrahedra that share corners with four HoP6 pentagonal pyramids, corners with two equivalent NiP5 square pyramids, corners with ten NiP4 tetrahedra, an edgeedge with one HoP6 pentagonal pyramid, edges with four equivalent NiP5 square pyramids, and edges with three NiP4 tetrahedra. There are a spread of Ni–P bond distances ranging from 2.15–2.31 Å. In the third Ni+1.25+ site, Ni+1.25+ is bonded to five P3- atoms to form distorted NiP5 square pyramids that share corners with four HoP6 pentagonal pyramids, corners with four equivalent NiP5 square pyramids, corners with eight NiP4 tetrahedra, an edgeedge with one HoP6 pentagonal pyramid, edges with four equivalent NiP5 square pyramids, and edges with seven NiP4 tetrahedra. There are a spread of Ni–P bond distances ranging from 2.29–2.56 Å. In the fourth Ni+1.25+ site, Ni+1.25+ is bonded to four P3- atoms to form NiP4 tetrahedra that share corners with two equivalent HoP6 pentagonal pyramids, corners with two equivalent NiP5 square pyramids, corners with twelve NiP4 tetrahedra, edges with three HoP6 pentagonal pyramids, edges with two equivalent NiP5 square pyramids, and edges with three NiP4 tetrahedra. There are a spread of Ni–P bond distances ranging from 2.23–2.33 Å. There are three inequivalent P3- sites. In the first P3- site, P3- is bonded in a 3-coordinate geometry to nine Ni+1.25+ atoms. In the second P3- site, P3- is bonded in a 9-coordinate geometry to two equivalent Ho3+ and seven Ni+1.25+ atoms. In the third P3- site, P3- is bonded in a 9-coordinate geometry to two equivalent Ho3+ and seven Ni+1.25+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Chilled water temperature set-point reset based on outdoor air temperature and its cooling energy performance in an office building

Here, in this study, the cooling energy performance of two strategies for controlling ChWT (chilled water temperature) are compared: the conventional control strategy of constantly fixing ChWT and the OAT (outdoor air temperature) compensation control strategy that adjusts ChWT according to the changes in OAT. OAT compensation control strategy was modeled and realized based on Appendix G of ASHRAE Standard 90.1. It was confirmed that applying OAT compensation control strategy can significantly reduce chiller energy consumption, which accounts for the largest portion of total cooling energy consumption. It was found that the difference in total cooling energy consumption between applying the conventional control of constantly fixing ChWT to 6 °C and applying the OAT compensation control was approximately 8 % and 3 % during spring (March to May) and summer (June to August), respectively. Additionally, during the fall (September–November) period, about 7 % of total cooling energy consumption could be saved.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2020

Mechanoadaptive strain and functional osseointegration of dental implants in rats

Spatiotemporal implant-bone biomechanics and mechanoadaptive strains in peri-implant tissue are poorly understood. Physical and chemical characteristics of an implant-bone complex (IBC) were correlated in three-dimensional space (along the length and around a dental implant) to gather insights into time related integration of the implant with the cortical portion of a jaw bone in a rat. Rats (N = 9) were divided into three experimental groups with three rats per time point; 3-, 11-, and 24-day. All rats were fed crumbled hard pellets mixed with water (soft-food diet) for the first 3 days followed by a hard-food diet with intact hard-food pellets (groups of 11- and 24-day only). Biomechanics of the IBCs harvested from rats at each time point was evaluated by performing mechanical testing in situ in tandem with X-ray imaging. The effect of physical association (contact area) of a loaded implant with adapting peri-implant tissue, and resulting strain within was mapped by using digital volume correlation (DVC) technique. The IBC stiffness at respective time points was correlated with mechanical strain in peri-implant tissue. Results illustrated that IBC stiffness at 11-day was lower than that observed at 3-day. However, at 24-day, IBC stiffness recovered to that which was observed at 3-day. Furthermore, correlative microscopy and spectroscopy illustrated that the lower IBC stiffness was constituted by softer and less mineralized peri-implant tissue that contained varying expressions of osteoconductive elements. Lower IBC stiffness observed at 11-day was constituted by less mineralized peri-implant tissue with osteoconductive elements that included phosphorus (P) which was co-localized with higher expression of zinc (Zn), and lower expression of calcium (Ca). Higher IBC stiffness at 24-day was constituted by mineralized peri-implant tissue with higher expressions of osteoconductive elements including Ca and P, and lower expressions of Zn. These spatiotemporal correlative maps of peri-implant tissue architecture, heterogeneous distribution of mineral density, and elemental colocalization underscore mechanoadaptive physicochemical properties of peri-implant tissue that facilitate functional osseointegration of an implant. These results provided insights into 1) plausible "prescription" of mechanical loads as an osteoinductive "therapeutic dose" to encourage osteoconductive elements in the peri-implant tissue that would facilitate functional osseointegration of the implant; 2) a "critical temporal window" between 3 and 11 days, and perhaps it is this acute phase during which key candidate regenerative molecules can be harnessed to accelerate osseointegration of an implant under load.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Photoemission and dynamical mean field theory study of electronic correlations in a t 2 g 5 metal SrRhO 3 thin film

Perovskite rhodates are characterized by intermediate strengths of both electronic correlation as well as spin-orbit coupling (SOC) and usually behave as moderately correlated metals. A recent publication on epitaxial SrRhO 3 thin films reported a bad-metallic behavior and suggested the occurrence of antiferromagnetism below 100 K. In this work, we have further studied this SrRhO 3 thin film by hard x-ray photoemission spectroscopy and found a very small density of states (DOS) at the Fermi level $(E_F)$, which is consistent with the previously reported bad-metallic behavior. However, the absence of DOS persists up to room temperature, which contradicts the explanation of antiferromagnetic transition at ~100 K. We also employed electronic structure calculations within the framework of density functional theory and dynamical mean-field theory. In contrast to the photoemission results, our calculations indicate metallic behaviors of both bulk SrRhO 3 and the SrRhO 3 thin film, and a stronger correlation effect was observed in the thin film than that in the bulk. The calculated uniform magnetic susceptibility is substantially larger in the thin film than that in the bulk. We also investigated the role of SOC and found only a moderate modulation of the band structure. Hence SOC is not expected to significantly affect the electronic correlation in SrRhO 3 . Extrinsic effects of finite-thickness effects beyond our calculations and localization effects may play important roles to induce the negligible spectral weight at $(E_F)$.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na3HoTi2Nb2O12 by Materials Project

Na3HoTi2Nb2O12 is Orthorhombic Perovskite-derived structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are three inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a 3-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.34–2.91 Å. In the second Na1+ site, Na1+ is bonded in a 3-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.37–2.80 Å. In the third Na1+ site, Na1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.37–2.69 Å. Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.29–2.54 Å. There are two inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with six NbO6 octahedra. The corner-sharing octahedra tilt angles range from 25–33°. There are a spread of Ti–O bond distances ranging from 1.87–2.17 Å. In the second Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with six NbO6 octahedra. The corner-sharing octahedra tilt angles range from 25–31°. There are a spread of Ti–O bond distances ranging from 1.87–2.15 Å. There are two inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six TiO6 octahedra. The corner-sharing octahedra tilt angles range from 25–31°. There are a spread of Nb–O bond distances ranging from 1.92–2.16 Å. In the second Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six TiO6 octahedra. The corner-sharing octahedra tilt angles range from 25–33°. There are a spread of Nb–O bond distances ranging from 1.90–2.15 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+, one Ti4+, and one Nb5+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+, one Ti4+, and one Nb5+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to one Na1+, one Ho3+, one Ti4+, and one Nb5+ atom. In the fourth O2- site, O2- is bonded in a distorted tetrahedral geometry to one Na1+, one Ho3+, one Ti4+, and one Nb5+ atom. In the fifth O2- site, O2- is bonded in a 5-coordinate geometry to two Na1+, one Ho3+, one Ti4+, and one Nb5+ atom. In the sixth O2- site, O2- is bonded in a 5-coordinate geometry to three Na1+, one Ti4+, and one Nb5+ atom. In the seventh O2- site, O2- is bonded in a 5-coordinate geometry to two Na1+, one Ho3+, one Ti4+, and one Nb5+ atom. In the eighth O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+, one Ho3+, one Ti4+, and one Nb5+ atom. In the ninth O2- site, O2- is bonded in a 5-coordinate geometry to two Na1+, one Ho3+, one Ti4+, and one Nb5+ atom. In the tenth O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+, one Ho3+, one Ti4+, and one Nb5+ atom. In the eleventh O2- site, O2- is bonded in a 5-coordinate geometry to two Na1+, one Ho3+, one Ti4+, and one Nb5+ atom. In the twelfth O2- site, O2- is bonded in a 5-coordinate geometry to three Na1+, one Ti4+, and one Nb5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Initial Characterization of Active Transitioning Centaur, P/2019 LD{sub 2} (ATLAS), Using Hubble, Spitzer, ZTF, Keck, Apache Point Observatory, and GROWTH Visible and Infrared Imaging and Spectroscopy

We present visible and mid-infrared imagery and photometry of temporary Jovian co-orbital comet P/2019 LD{sub 2} taken with Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3), Spitzer Space Telescope/Infrared Array Camera (Spitzer/IRAC), and the GROWTH telescope network, visible spectroscopy from Keck/Low-Resolution Imaging Spectrometer (LRIS), and archival Zwicky Transient Facility observations taken between 2019 April and 2020 August. Our observations indicate that the nucleus of LD{sub 2} has a radius between 0.2 and 1.8 km assuming a 0.08 albedo and a coma dominated by ∼100 μm-scale dust ejected at ∼1 m s{sup −1} speeds with a ∼1′ jet pointing in the southwest direction. LD{sub 2} experienced a total dust mass loss of ∼10{sup 8} kg at a loss rate of ∼6 kg s{sup −1} with Afρ/cross section varying between ∼85 cm/125 km{sup 2} and ∼200 cm/310 km{sup 2} from 2019 April 9 to 2019 November 8. If the increase in Afρ/cross section remained constant, it implies LD{sub 2}'s activity began ∼2018 November when within 4.8 au of the Sun, implying the onset of H{sub 2}O sublimation. We measure CO/CO{sub 2} gas production of ≲10{sup 27} mol s{sup −1}/≲10{sup 26} mol s{sup −1} from our 4.5 μm Spitzer observations; g–r = 0.59 ± 0.03, r–i = 0.18 ± 0.05, and i–z = 0.01 ± 0.07 from GROWTH observations; and H{sub 2}O gas production of ≲80 kg s{sup −1} scaling from our estimated C {sub 2} production of Q{sub C{sub 2}}≲7.5×10{sup 24} mol s{sup −1} from Keck/LRIS spectroscopy. We determine that the long-term orbit of LD{sub 2} is similar to Jupiter-family comets having close encounters with Jupiter within ∼0.5 Hill radius in the last ∼3 y and within 0.8 Hill radius in ∼9 y. Additionally, 78.8% of our orbital clones are ejected from the solar system within 1 × 10{sup 6} yr, having a dynamical half-life of 3.4 × 10{sup 5} yr.

47 OTHER INSTRUMENTATION↗
NASA NTRS1988

Ground-based column abundance measurements of atmospheric hydroxyl

The preliminary results of ground-based OH column abundance measurements from Truk, Federated States of Micronesia, are contained. These are the first OH column measurements from the tropics, and constitute a signficcant contribution to the OH data base. Comparisons of tropical OH behavior with the extensive mid-latitude observations serve as a critical test of the current understanding of the HO (sub x) photochemistry and its relationship to the other major chemical families. The quasi-biennial oscillation (QBO) in tropical stratospheric winds exerts a major influence on the Hadley cell vertical transport. Related QBOs in total O3 and in stratospheric H2O were identified, but QBO effects on other stratospheric species are still unknown. The solar tide in the tropics produces a diurnal surface pressure variation of 2 to 3 mb; its effect on OH photochemistry in the stratosphere may be significant.

Burnett, Clyde R.↗
DOE OSTI2021

SNS Warm Linac Circulator Breakdown Considerations for the PPU Project

Multipacting in accelerating structures is a complex phenomenon about which there is much to be understood. While multipacting research efforts have primarily been focused on superconducting radio frequency (SRF) systems, normal conducting accelerating structures which have a higher thermal capacity, and a greater vacuum pressure tolerance could benefit from additional investigation. This research details multipacting simulation methods and the results of 3-D electromagnetic simulations of RF vacuum windows used on normal conducting linac (NCL) cavities. Benchmarking of the peak electric fields in these structures, benefits of material processing and possible techniques for reducing or eliminating multipacting activities are discussed.

Toby, George↗