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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Connection between Emission and Absorption Outflows through the Study of Quasars with Extremely High Velocity Outflows

A recently discovered class of outflows, extremely high velocity outflows (EHVOs), may be key to understanding feedback processes, as it is likely the most powerful in terms of mass energy. These EHVOs have been observed at redshifts 1.052 < z em < 7.641, but the potential connection with outflows in emission has not been studied. We find that EHVOs, albeit their small numbers at the moment, appear to show distinct C IV and He II properties. In particular, EHVOs are more predominant in quasars with large blueshifts of the C IV emission line, suggesting a connection between emission and absorption outflowing signatures for these extreme outflows. We also find incipient trends with the maximum velocity of the outflows, which is similar to what has been previously found in BALQSOs but now extending previous studies to speeds up to ~0.2c. We find that the bolometric luminosities, Eddington ratios, and black hole masses of our sample are overall very similar to the general quasar population upon considering their C IV emission properties. This is close to the case for He II EW, as we observe a tentative upper limit to the He II strength for a quasar to host an EHVO. This study shows that extreme outflows such as EHVOs appear in quasars that are clearly a distinct class from the overall BALQSO population and solidify the relation between outflows observed in emission and absorption.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1965

Mariner-mars absorptance experiment.

Absorptivity standard instrument to investigate solar absorptance of four surfaces used for spacecraft temperature control for Mariner IV on Mars mission

ABSORPTIVE INDEX↗
NASA NTRS1966

Mariner-Mars absorptance experiment.

Absorptivity standard instrument to investigate solar absorptance of four surfaces used for spacecraft temperature control for Mariner IV on Mars mission

TEMPERATURE CONTROL↗
DOE OSTI2018

Low-Temperature Absorption, Photoluminescence, and Lifetime of CsPbX 3 (X = Cl, Br, I) Nanocrystals

The absorption and photoluminescence, both steady–state and time–resolved, of CsPbX 3 (X = Cl, Br, I) nanocrystals are reported at temperatures ranging from 3 to 300 K. These measurements offer a unique window into the fundamental properties of this class of materials which is considered promising for light–emitting and detection devices. The bandgaps are shown to increase from low to high temperature, and none of the examined cesium–based perovskite nanocrystals exhibit a bandgap discontinuity in this temperature range suggesting constant crystal phase. Time–resolved measurements show that the radiative lifetime of the band–edge emission depends strongly on the halide ion and increases with heating. The increasing lifetime at higher temperatures is attributed primarily to free carriers produced from exciton fission, corroborated by the prevalence of excitonic character in absorption. Furthermore, the results particularly highlight many of the similarities in physical properties, such as low exciton binding energy and long lifetime, between CsPbI 3 and hybrid organic–inorganic plumbotrihalide perovskites.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Revealing Parallel Inter‐ and Intra‐Ligand Charge Transfer Dynamics in [Ru(L) 2 (dppz)] 2+ Molecular Lightswitch with N K‐Edge X‐Ray Absorption Spectroscopy

In photoactive metal complexes the localization of photoexcited charges dictates the site of chemical reactivity, but few studies measure the charge redistribution in these systems with spatial precision. Herein, we track the inter- and intra-ligand charge transfer processes that underpin light-driven charge separation in the well-studied “molecular lightswitch” [Ru(bpy) 2 dppz] 2+ (aqueous [Ruthenium II (2,2′-bipyridine)2(dipyrido[3,2-a:2′,3′-c]phenazine)] 2+ [Cl − ] 2 ) by probing the electronic structure of ligand nitrogen atoms in real-time using ultrafast X-ray absorption spectroscopy and first principles calculations. We confirm the localization of excited electron density on the phenazine N atoms of dppz and we newly identify two parallel electron transfer pathways to populate this state. Sub-70 fs electron transfer to the phenazine portion of dppz is observed and attributed to intra-ligand electron transfer following Ru-to-dppz metal-to-ligand charge transfer (MLCT) excitation. This fast charge transfer was not reported in prior ultrafast studies. The slower (ca. 2 ps) charge transfer reported extensively in time-resolved optical absorption and emission studies is reassigned here to inter-ligand electron “hopping” between nearly isoenergetic ligand moieties following Ru-to-bpy MLCT excitation. In conclusion, the results demonstrate much faster charge separation than previously identified in this well-studied system, highlighting how extended azaacene ligand motifs promote the competitive charge transfer processes needed to drive light-driven electron transfer chemistry.

Donor-acceptor systems↗
DOE OSTI2021

Site-Selective Real-Time Observation of Bimolecular Electron Transfer in a Photocatalytic System Using L-Edge X-Ray Absorption Spectroscopy

Here, time-resolved X-ray absorption spectroscopy has been utilized to monitor the bimolecular electron transfer in a photocatalytic water splitting system. This has been possible by uniting the local probe and element specific character of X-ray transitions with insights from high-level ab initio calculations. The specific target has been a heteroleptic [Ir III (ppy) 2 (bpy)] + photosensitizer, in combination with triethylamine as a sacrificial reductant and Fe 3 (CO) 12 as a water reduction catalyst. The relevant molecular transitions have been characterized via high-resolution Ir L-edge X-ray absorption spectroscopy on the picosecond time scale and restricted active space self-consistent field calculations. The presented methods and results will enhance our understanding of functionally relevant bimolecular electron transfer reactions and thus will pave the road to rational optimization of photocatalytic performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

The Nature of the Long-Lived Excited State in a Ni II Phthalocyanine Complex Investigated by X-Ray Transient Absorption Spectroscopy

The nature of the photoexcited state of octabutoxy nickel(II) phthalocyanine (NiPcOBu8) with a 500ps lifetime was investigated by X-ray transient absorption (XTA) spectroscopy. Previous optical, vibrational, and computational studies have suggested that this photoexcited state has a ligand-to-metal charge transfer (LMCT) nature. By using XTA, which provides unambiguous information on the local electronic and nuclear configuration around the Ni center, the nature of the excited state of NiPcOBu8 was reassessed. Using X-ray probe pulses from a synchrotron source, the ground- and excited-state X-ray absorption spectra of NiPcOBu 8 were measured. Based on the results, we identified that the excited state exhibits spectral features that are characteristic of a Ni-1,Ni-3(3d(z2),3d(x2-y2)) state rather than a LMCT state with a transiently reduced Ni center. This state resembles the (d,d) state of nickel(II) tetramesitylphorphyrin. The XTA features are rationalized based on the inherent cavity sizes of the macrocycles. These results may provide useful guidance for the design of photocatalysts in the future.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Investigation of Magnetic and Microwave Absorption Properties of Ba{sub (1−2x)}La{sub x}Na{sub x}Fe{sub 10}CoTiO{sub 19} Hexaferrites in 18.0–26.5 GHz Band

A series of Ba{sub (1−2x)}La{sub x}Na{sub x}Fe{sub 10}CoTiO{sub 19} hexaferrite samples with x = 0.00–0.25 (step size 0.05) were prepared by using conventional solid-state reaction technique. The magnetic properties of the hexaferrites have been investigated at room temperature by employing a vibrating sample magnetometer. There is an overall decrease in saturation magnetization from 70.64 to 57.83 emu/g with an increase in doping concentration from x = 0.00–0.25. The microwave measurements were done utilizing vector network analyzer in the k-band (18.0–26.5 GHz) frequency range. The electromagnetic measurements revealed that the gross tangent loss is maximum for x = 0.10 sample. The microwave absorption measurements show that sample x = 0.10 with 1.4 mm thickness exhibits a reflection loss of − 26.59 dB (99.78% signal absorption) and 7.65 GHz bandwidth. Thus, it is considered for thin single-layer broadband microwave absorber applications in 18.0–26.5 GHz frequency range.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Identification of Natural and Synthetic Diamonds from Their Optical Absorption and Cathodoluminescence Spectra

The optical absorption and cathodoluminescence spectra of nine diamond specimens are investigated at the temperatures 295 K and 82–295 K, respectively. By the presence of an N3a electron-vibrational system with a phonon-free line at 2.68 eV, six of them are identified as natural diamonds. By the presence of the electron-vibrational system at 2.56 eV and a structureless band at 2.54 eV, associated with nickel in the optical absorption and luminescence spectra, two specimens are identified as synthetic diamonds grown at high pressures and temperatures. By the presence of exciton luminescence at 5.271 eV and the absence of any spectral, impurity-related peculiarities, one of the specimens is identified as a synthetic diamond grown by the chemical vapor deposition. Based on the data obtained, a procedure is proposed for identifying natural and synthetic diamonds and determining a model scheme of the radiation-thermal treatment of the specimens.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Monte Carlo Simulation of Hydrogen Absorption in Palladium and Palladium-Silver Alloy

The paper presents Monte Carlo simulation of the hydrogen absorption in palladium and palladium-silver alloy of the composition Pd{sub x}Ag{sub 1–x} (x = 0.7–0.9) at 293–373 K temperature and 0.1 MPa pressure. Hydrogen atoms in palladium lattice locate mostly in octahedral holes in a face-centered cubic unit cell. In palladiumsilver alloy with the increased Ag content, the absorption energy distribution of hydrogen becomes wider. The interatomic Ag–H distance is shorter than Pd–H distance that means that when contacting with Ag atoms, H atoms occupy less stable tetrahedral holes. When the amount of silver in the alloy grows up to 30 аt.% H atoms are more likely to locate in tetrahedral vacancies resulting in the stability decrease of the system with hydrogen dissolved in the bulk of the material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Near-Edge Soft X-ray Absorption Mass Spectrometry of Protonated Melittin

We have investigated the photoionization and photofragmentation yields of gas-phase multiply protonated melittin cations for photon energies at the K-shell absorption edges of carbon, nitrogen, and oxygen. Two similar experimental approaches were employed. In both experiments, mass selected [melittin+qH]{sup q+} (q=2–4) ions were accumulated in radiofrequency ion traps. The trap content was exposed to intense beams of monochromatic soft X-ray photons from synchrotron beamlines and photoproducts were analyzed by means of time-of-flight mass spectrometry. Mass spectra were recorded for fixed photon energies, and partial ion yield spectra were recorded as a function of photon energy. The combination of mass spectrometry and soft X-ray spectroscopy allows for a direct correlation of protein electronic structure with various photoionization channels. Non-dissociative single and double ionization are used as a reference. The contribution of both channels to various backbone scission channels is quantified and related to activation energies and protonation sites. Soft X-ray absorption mass spectrometry combines fast energy deposition with single and double ionization and could complement established activation techniques. .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

High compressive energy absorption and shape recovery behavior of additively manufactured textile-inspired cylindrical braided metamaterials

Mechanical metamaterials (MMs) are engineered structures with unique mechanical properties that arise from their unique spatial arrangement or lattice-like structure. The most commonly designed MMs such as honeycomb and re-entrant auxetics are prone to failure at the sharp corners and weak joints due to the increased stress concentration under deformation. To mitigate this challenge, braided MM structures involving intertwining threads of nylon—forming curved unit cells—have been studied. These textile-inspired cylindrical braided metamaterials (CBMMs) with contrasting unit cells, namely diamond and regular CBMMs, were fabricated by 3D printing. The layer-by-layer deposited structure built by fused filament fabrication delivered an assembly of overlapped threads that are fused at the contact point. To understand deformation behavior of these MMs, finite element models were developed for various load scenarios including quasi-static compression, cyclic and creep loads at room temperature. Stress distribution, deformation mechanisms, and failure modes were analyzed and validated by experiments to analyze the geometries and associated performance. The diamond CBMMs showed stress softening at 30 % compressive strain, withstanding a load of ∼440 N, whereas the regular CBMMs at 50 % strain experienced ∼250 N. The diamond CBMMs delivered higher creep resistance under sustained load and better energy absorption under cyclic loading than the regular CBMMs. The latter, however, exhibited 94 % shape recovery in contrast to 88 % recovery in former prototype during their first cyclic load. In conclusion, this study helps design mechanical lightweight devices that endure significant sustained load and exhibit enhanced energy absorption and shape recovery characteristics in cyclic loading.

Creep↗
DOE OSTI2017

Ionic liquid-based hybrid absorption cycle for water heating, dehumidification, and cooling

Water heating, dehumidification and space cooling are responsible for significant energy consumption in buildings. A potential energy saving measure is to develop hybrid systems that can utilize the sensible and latent heats removed in space cooling to heat water. In this paper, we present experimental results on a hybrid system that utilizes the latent heat released in the dehumidification process for water heating. This system absorbs water vapor from the air and transfers the heat of phase change into the process water. The absorbed water vapor is then liberated in a desorber and subsequently condensed in a condenser, while its latent heat is transferred to the process water. The condensed water vapor can then be either drained (if dehumidification is desired), or utilized in an evaporative cooling process (if sensible space cooling is desired). In essence, the system can exchange both sensible and latent heats with its ambient. The main innovations implemented in the system are (1) a semi-open absorption system architecture to lower the system cost, (2) a membrane-based absorber to alleviate the liquid entrainment issue encountered in the conventional packed bed absorbers and (3) an ionic liquid that eliminates the crystallization risks and minimizes corrosion issues normally associated with LiBr-based absorption systems. Furthermore, a water heating thermal COP of 1.4 is achieved at 30°C, 70% RH ambient conditions.

42 ENGINEERING↗
DOE OSTI2022

Synthesis and characterization of UiO-66-NH 2 incorporated graphene aerogel composites and their utilization for absorption of organic liquids

This work details the synthesis, materials characterization and absorption capacity of graphene aerogel (GA) loaded with UiO-66-NH 2 metal organic framework (MOF). Throughout the study, a series of density-tunable MOF/GA composites were synthesized by adjusting the MOF/graphene oxide (GO) mass ratio of the precursors before hydrothermal reduction and subsequent critical point drying to achieve MOF-x%/GA composites, with x, ranging from 0 to 100, denoting the weight percent ratio of MOF to GO in the starting solution. Scanning electron microscopy (SEM) images and Barrett-Joyner-Halenda (BJH) pore size calculations supported that MOF loading enlarged the macroporous (>50 nm) structure of the GA framework but had no influence on the mesoporous (2–50 nm) structure of GA. The degree of MOF loading first decreased and then increased the density of resulting composites, exhibiting a minimum for the 10–30% samples. Such behavior with respect to MOF loading has not been reported previously. MOF-x%/GA samples were further investigated for absorption capacity using various organic liquids. MOF-30%/GA proved to be the best absorbent sample for all solvents tested, achieving the highest capacity for chloroform at 147.0 ± 10.0 mg/mg. The behavior is attributed to the structural changes induced by the MOF incorporation as well as the interactions between the organic molecules and the MOF.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Experimental study of ethanol oxidation behind reflected shock waves: Ignition delay time and H 2 O laser-absorption measurements

The oxidation of ethanol was investigated in shock tubes by measuring ignition delay times and water time history profiles. A laser absorption technique was used in the latter case. Ignition delay times were investigated for three equivalence ratios, 0.5, 1.0, and 2.0, and for pressures ranging from 1.3 to 53 atm. The fuel concentration and the type of diluent used were also varied. The ignition delay times were in very good agreement with results from the literature for the very few overlapping conditions, and most of the experimental conditions have never been studied before. A high level of accuracy was observed for the predictions of the ignition delay times from detailed kinetics mechanisms. Inhomogeneous ignition events were observed in some specific conditions, validating the notions of thermal diffusivity and flame thickness developed in the literature for the reasons behind such inhomogeneous ignition. The water time-history profiles showed the formation of water in two stages. These profiles were also modeled using well-known detailed kinetic mechanisms from the literature. Severe discrepancies were often observed for laser-absorption measurements, and this was the case with most of the models. A numerical analysis (sensitivity and rate-of-production) was conducted using the two best-performing literature mechanisms (namely, AramcoMech3.0 and CRECK).

42 ENGINEERING↗
DOE OSTI2020

Experimental study on a novel three-phase absorption thermal battery with high energy density applied to buildings

Buildings contribute to 75% of total electricity consumption and 80% of peak electricity demand in the United States. A significant portion of building electricity consumption goes to space conditioning. Therefore, using thermal energy storage (TES) to decouple the building electricity consumption and the fluctuating space-conditioning load has significant potential to shift peak electricity demand and improve the stability of the grid. To provide effective TES within the spatial constraints in buildings, a three-phase absorption thermal battery (TATB) system with very high energy storage density was designed and studied. The TATB stores low-temperature heat in hydrate crystals of salts and supports space conditioning through absorption systems. In this study, a benchtop TATB using lithium chloride (LiCl) hydrate crystals as the storage material was tested under practical operating conditions for its energy storage density and discharge rate. We report the TATB successfully generated LiCl hydrate crystals during charging mode and then dissolved the crystals during discharging mode. A material-based energy storage density of 300 kWh/m 3 (specific energy of 903 kJ/kg) was achieved with a discharge rate of up to 1.3 kW thermal energy. The test results verified the high performance of the TATB and encouraged further development of this technology.

25 ENERGY STORAGE↗