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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

The HST quasar absorption line key project. 4: HST faint-object spectrograph and ground-based observations of the unusual low-redshift broad absorption-line quasi-stellar object PG 0043+039

Hubble Space Telescope Faint Object Spectrograph (HST FOS) observations have shown that the spectrum of the low-redshift (z(sub em) approximately equal to 0.384) QSO PG 0043+039 exhibits weak broad absorption lines (BALs). The BALs were discovered during the course of UV spectrophotometry made for the HST Quasar Absorption Line Key Project. The HST data are analyzed along with ground-based optical and IUE spectrophotometry. The object is found to have a number of atypical properties relative to normal non-BAL QSOs. The observed continuum is atypical in the sense that it is much weaker than that of a normal optically selected QSO at rest wavelengths approximately less than 2200 A. Intrinsic reddening of E(B-V) approximately equal to 0.11 mag by dust similar to that found in the SMC at the redshift of PG 0043+039 conservatively accounts for the observed continuum shape moderately well. These observed characteristics are typical of low-ionization BAL QSOs, but convincing evidence for BALs due to low-ionization transitions of Mg II, Al III, Al II, or C II does not exist. Therefore, this object may be a misaligned BAL QSO having many of the characteristics of low-ionization BAL QSOs with the sight line passing through a putative dusty region, but evidently missing clouds of high enough column density to produce observable low-ionization BALs. If the intrinsic dust-extinction model is correct, the observations suggest that the dust is not confined to the presumably higher density, low-ionization BAL clouds, but that it has drifted to nearby high-ionization BAL regions. We also consider other possible mechanisms for producing the shape of the continuous energy distribution which cannot be ruled out. We compare the Fe II emission in PG 0043+039 with that in another Key Project QSO, NGC 2841-UB 3, which has optical Fe II emission comparable in strength to that in PG 0043+039, but has anomalously weak UV Fe II emission. In addition, from an analysis of UV and optical spectrophotometric data at 5 epochs over approximately 11 yr, there is tentative evidence that PG 0043+039 has varied in brightness by as much as 1.1 mag during this time interval. Two different interpretations of PG 0043+039 and the low-ionization BAL QSOs are considered. Various model scenarios for explaining the weak narrow-line (O III) emission are considered, but there is no definitive explanation.

Turnshek, David A.↗
NASA NTRS1997

Accurate universal parameterization of absorption cross sections II--neutron absorption cross sections

A recent parameterization (here after referred as paper I, Ref. [4]) of absorption cross sections for any system of charged ions collisions including proton -nucleus collisions, is extended for neutron-nucleus collisions valid from approximately 1 MeV to a few GeV, thus providing a comprehensive picture of absorption cross sections for any system of collision pair (charged and/or uncharged). The parameters are associated with the physics of the problem. At lower energies, the optical potential at the surface is important and the Pauli operator plays an increasingly important role at intermediate energies. The agreement between the calculated and experimental data is better than earlier published results.

NASA Discipline Radiation Health↗
DOE OSTI2018

A review of control methodologies for vapor compression and absorption heat pumps; Examen des méthodes de régulation des pompes à chaleur à compression et à absorption de vapeur

Here this paper presents an overview of control systems for heat pumps, and more specifically, a critical review of control methodologies for thermally activated absorption heat pumps. The objectives of a control system are identified and discussed, including optimal system operation, ability for continuous turndown, and fast response to changes in the operating conditions. Key details of different aspects of research and development such as steady-state and transient thermodynamic models, control algorithm development, and implementation are presented. Advanced multivariable feedback controls are able to perform better than individual feedback control loops and conventional on/off controls. The knowledge of the transient response of heat pump systems through models or experimental data is crucial for advanced control system design and implementation. Recently, data-based methods have also gained interest, but they are difficult to generalize. A general outlook with limitations and the potential of different approaches, and recommendations for future work are provided.

42 ENGINEERING↗
DOE OSTI2019

Combined Theoretical and Experimental Investigations of Atomic Doping To Enhance Photon Absorption and Carrier Transport of LaFeO 3 Photocathodes

Perovskite-type lanthanum iron oxide, LaFeO 3 , is a p-type semiconductor that can achieve overall water splitting using visible light while maintaining photostability. These features make LaFeO 3 a promising photocathode candidate for various photoelectrochemical cells. Currently, the photoelectrochemical performance of a LaFeO 3 photocathode is mainly limited by considerable bulk electron-hole recombination. This study reports a combined theoretical and experimental investigation on atomic doping of LaFeO 3 , in particular, substitutional doping of La 3+ with K + , to increase its charge transport properties and decrease electron-hole recombination. The computational results show that K doping enhances not only the charge transport properties but also photon absorption below the bandgap energy of the pristine LaFeO 3 . The effect of K doping was systematically investigated by comparing the electronic and atomic structures, majority carrier density, hole-polaron formation, and optical properties of pristine and K-doped LaFeO 3 . The computational results were then verified by experimentally characterizing the crystal structures, compositions, optical properties, and photoelectrochemical properties of LaFeO 3 and K-doped LaFeO 3 electrodes. For this purpose, pristine LaFeO 3 and K-doped LaFeO 3 were prepared as high-surface-area, high-purity photoelectrodes having the same morphology to accurately and unambiguously evaluate the effect of K doping. Here, the combined computational and experimental investigations presented in this study provide useful insights into the effect of composition tuning of LaFeO 3 and other p-type oxides with a perovskite structure.

14 SOLAR ENERGY↗
DOE OSTI2018

Ab Initio Study of Covalency in the Ground versus Core-Excited States and X-ray Absorption Spectra of Actinide Complexes

Relativistic multireference ab initio wave function calculations within the restricted active space (RAS) framework were performed to calculate metal and ligand X-ray absorption (XAS) near-edge spectroscopy (XANES) intensities for the metal M 4,5 edges of [PuO 2 (H 2 O) 5 ] 2+ , [An VI O 2 ] 2+ (An = U, Np, Pu), and [AmCl 6 ] 3– and the Cl K edge of the Am complex. The extent of An(5f)–ligand bonding was determined via natural localized molecular orbital analyses of the relevant spin–orbit coupled multireference states. The calculated spectra are in good agreement with experiments and allow a detailed assignment of the observed spectral features. The XANES M 4,5 -edge spectra are representative of the actinide orbital covalency in the probed core-excited states, which may be different from the ground-state covalency. Furthermore, an assignment of ground-state An orbital covalency based on XAS spectra should therefore be made with caution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1996

Absorption of Sunlight by Water Vapor in Cloudy Conditions: A Partial Explaination for the Cloud Absorption Anomaly

The atmospheric radiative transfer algorithms used in most global general circulation models underestimate the globally-averaged solar energy absorbed by cloudy atmospheres by up to 25 Wm(sup -2)...Here, a sophisticated atmospheric radiative transfer model was used to provide a more comprehensive description of the physical processes that contribute to the absorption of solar radiation by the Earth's atmosphere.

absorption transfer algorithms circulation models ↗
DOE OSTI2018

Contact ion-pair structure in concentrated cesium chloride aqueous solutions: An extended X-ray absorption fine structure study

The hydration and ion pair structure of Cl- ion in aqueous cesium chloride solutions at 0.5, 6 and 11 mol/kg (H2O) has been studied using Extended X-ray Absorption Fine Structure (EXAFS) at the Cl K-edge. The co-refinement of multiple EXAFS datasets shows the hydration structure of the free Cl- ion is consistent with previously reported studies. In concentrated solution the Cl- ion is strongly associated with the cation forming contact ion pairs with 1.6 and 2.8 Cs ions in 6 and 11 mol/kg aqueous CsCl, respectively. The fact that the degree of ion pairing of Cs-Cl is higher than that of both aqueous RbCl and RbBr at the same concentration is an interesting result as it deviates from the Collins’s law of matching water affinities. The reported Cs-Cl ion-pair structure provides a basis for the development and testing of improved interaction potentials leading to more realistic structures from molecular dynamics (MD) simulations. ACKNOWLEDGEMENT VTP was supported by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 103.99-2013.19. Work by JLF was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. The PNC/XSD facilities at the Advanced Photon Source, and research at these facilities, are supported by DOE/BES, the Canadian Light Source and its funding partners, the University of Washington, and the Advanced Photon Source. Use of the Advanced Photon Source, an Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory, was supported by the DOE under Contract No. DE-AC02-06CH11357.

Pham, Van-Thai↗
DOE OSTI2018

Investigation of Solid Electrolyte Interphase Layer Formation and Electrochemical Reversibility of Magnetite, Fe 3 O 4 , Electrodes: A Combined X-ray Absorption Spectroscopy and X-ray Photoelectron Spectroscopy Study

Magnetite (Fe 3 O 4 ) is a promising electrode material for the next generation of Li-ion batteries with multiple electron transfers per metal center and a theoretical capacity of 924 mAh/g. However, multiple phase conversions during (de)lithiation of Fe 3 O 4 and formation of a surface electrolyte interphase (SEI) contribute to capacity fade. In this study, X-ray Absorption Spectroscopy (XAS), and X-ray Photoelectron Spectroscopy (XPS) were used to determine the surface chemistry, redox chemistry, and the impact on the electrochemical reversibility in the presence and absence of fluoroethylene carbonate (FEC) solvent. With FEC improved capacity retention and enhanced reversibility are observed. In contrast, electrodes cycled with no FEC exhibit decreased reversibility where the active material remains as reduced Fe 0 . XPS results reveal LiF and lower quantities of oxygen containing species, especially carbonates at the electrode surface tested in FEC. The improvement in electrochemical reversibility with FEC is attributed to the formation of a solid electrolyte interphase which forms prior to initiation of the conversion reaction limiting SEI growth on the reduced products, Fe0 and Li 2 O. In contrast, EC-based carbonate electrolyte forms SEI at a potential where formation of Fe0 and Li 2 O has already initiated resulting in SEI formation on Fe 0 nanograins.

25 ENERGY STORAGE↗
DOE OSTI2024

Quasiparticle Poisoning of Superconducting Qubits from Resonant Absorption of Pair-Breaking Photons

The ideal superconductor provides a pristine environment for the delicate states of a quantum computer: because there is an energy gap to excitations, there are no spurious modes with which the qubits can interact, causing irreversible decay of the quantum state. As a practical matter, however, there exists a high density of excitations out of the superconducting ground state even at ultralow temperature; these are known as quasiparticles. Observed quasiparticle densities are of order 1 μ m - 3 , tens of orders of magnitude greater than the equilibrium density expected from theory. Nonequilibrium quasiparticles extract energy from the qubit mode and can induce dephasing. Here we show that a dominant mechanism for quasiparticle poisoning is direct absorption of high-energy photons at the qubit junction. We use a Josephson junction-based photon source to controllably dose qubit circuits with millimeter-wave radiation, and we use an interferometric quantum gate sequence to reconstruct the charge parity of the qubit. We find that the structure of the qubit itself acts as a resonant antenna for millimeter-wave radiation, providing an efficient path for photons to generate quasiparticles. A deep understanding of this physics will pave the way to realization of next-generation superconducting qubits that are robust against quasiparticle poisoning.

Liu, Chuan-Hong↗