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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Long wavelength infrared detector

Long wavelength infrared detection is achieved by a detector made with layers of quantum well material bounded on each side by barrier material to form paired quantum wells, each quantum well having a single energy level. The width and depth of the paired quantum wells, and the spacing therebetween, are selected to split the single energy level with an upper energy level near the top of the energy wells. The spacing is selected for splitting the single energy level into two energy levels with a difference between levels sufficiently small for detection of infrared radiation of a desired wavelength.

Vasquez, Richard P.↗
DOE OSTI2016

Capacity Payments in Restructured Markets under Low and High Penetration Levels of Renewable Energy

Growing levels of variable renewable energy resources arguably create new challenges for capacity market designs, because variable renewable energy suppresses wholesale energy prices while providing relatively little capacity. This effect becomes more pronounced the higher the variable renewable energy penetration in a market. The purpose of this report is threefold. First, we provide a brief outline of the purpose and design of various capacity markets using administratively determined capacity demand curves. Second, we discuss some of the main challenges raised in existing literature and a set of interviews that we conducted with market participants, regulators, and observers. Third, we consider some of the challenges to capacity markets that arise with higher variable renewable energy penetration.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
NASA NTRS1991

A damage tolerance comparison of 7075-T6 aluminum alloy and IM7/977-2 carbon/epoxy

A comparison of low velocity impact damage between one of the strongest aluminum alloys, to a new, damage tolerant resin system as a matrix for high strength carbon fibers was examined in this study. The aluminum and composite materials were used as face sheets on a 0.13 g/cu cm aluminum honeycomb. Four levels of impact energy were used; 2.6 J, 5.3 J, 7.8 J and 9.9 J. The beams were compared for static strength and fatique life by use of the four-point bend flexure test. It was found that in the undamaged state the specific strength of the composite face sheets was about twice that of the aluminum face sheets. A sharp drop in strength was observed for the composite specimens impacted at the lowest (2.6J) energy level, but the overall specific strength was still higher than for the aluminum specimens. At all impact energy levels tested, the static specific strength of the composite face sheets were significantly higher than the aluminum face sheets. The fatigue life of the most severely damaged composite specimen was about 17 times greater than the undamaged aluminum specimens when cycled at 1 Hz between 20 percent and 85 percent of ultimate breaking load.

Nettles, Alan T.↗
DOE OSTI2013

On the interaction of the Dirac oscillator with the Aharonov–Casher system in topological defect backgrounds

In this paper, we study the influence of the Aharonov–Casher effect [Y. Aharonov, A. Casher, Phys. Rev. Lett. 53 (1984) 319] on the Dirac oscillator in three different scenarios of general relativity: the Minkowski spacetime, the cosmic string spacetime and the cosmic dislocation spacetime. In this way, we solve the Dirac equation and obtain the energy levels for bound states and the Dirac spinors for positive-energy solutions. We show that the relativistic energy levels depend on the Aharonov–Casher geometric phase. We also discuss the influence of curvature and torsion on the relativistic energy levels and the Dirac spinors due to the topology of the cosmic string and cosmic dislocation spacetimes. -- Highlights: •Influence of the Aharonov–Casher effect on the Dirac oscillator. •Exact solutions of the Dirac equation in topological defect spacetimes. •Dependence of the relativistic energy levels on the Aharonov–Casher geometric phase. •Influence of curvature and torsion on the relativistic energy levels and the Dirac spinors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Investigation on the upconversion luminescence in Ho3+/Yb3+ co-doped Ba3Sc4O9 phosphor

Highlights: • The optical properties of novel Ba{sub 3}Y{sub 4}O{sub 9}:Ho{sup 3+}/Yb{sup 3+} phosphor were investigated. • The luminescence color could be tuned from green to yellow-green light. • The energy transfer mechanisms of UC luminescence were investigated in detail. • The phosphor can be a good candidate for green UC material in display fields and fluorescent labeling. - Abstract: A series of Ba{sub 3}Sc{sub 4}O{sub 9}:Ho{sup 3+}/Yb{sup 3+} phosphors were synthesized by a high-temperature solid-state reaction method. The phase purity and upconversion luminescence were characterized by X-ray diffraction and photoluminescence spectroscopy. The sintering temperature and doping concentrations were optimized to obtain the strongest emission intensity. Under 980 nm laser diode excitation, the green (545 nm, {sup 5}F{sub 4}/{sup 5}S{sub 2} → {sup 5}I{sub 8}) and red (665 nm, {sup 5}F{sub 5} → {sup 5}I{sub 8}) emissions were observed. The cross-relaxation and back-energy-transfer processes play an important role to adjust the emission intensity ratio of Green/Red at different dopant concentrations. Based on the energy level diagrams, the energy transfer mechanisms are investigated in detail according to the analysis of pump power dependence and luminescence decay curves. The upconversion luminescence properties of the phosphor were evaluated and the results show good color monochromaticity and relatively high upconversion luminescence intensity. The Ba{sub 3}Sc{sub 4}O{sub 9}:Ho{sup 3+}/Yb{sup 3+} can be a good candidate for green upconversion material in display fields and fluorescent labeling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Tunable Semiconductors: Control over Carrier States and Excitations in Layered Hybrid Organic-Inorganic Perovskites

Here, for a class of 2D hybrid organic-inorganic perovskite semiconductors based on π-conjugated organic cations, we predict quantitatively how varying the organic and inorganic component allows control over the nature, energy, and localization of carrier states in a quantum-well-like fashion. Our first-principles predictions, based on large-scale hybrid density-functional theory with spin-orbit coupling, show that the interface between the organic and inorganic parts within a single hybrid can be modulated systematically, enabling us to select between different type-I and type-II energy level alignments. Lastly, energy levels, recombination properties, and transport behavior of electrons and holes thus become tunable by choosing specific organic functionalizations and juxtaposing them with suitable inorganic components.

36 MATERIALS SCIENCE↗
DOE OSTI2015

SU-D-BRA-06: Dual-Energy Chest CT: The Effects of Virtual Monochromatic Reconstructions On Texture Analysis Features

Purpose: To characterize the effect of virtual monochromatic reconstructions on several commonly used texture analysis features in DECT of the chest. Further, to assess the effect of monochromatic energy levels on the ability of these textural features to identify tissue types. Methods: 20 consecutive patients underwent chest CTs for evaluation of lung nodules using Siemens Somatom Definition Flash DECT. Virtual monochromatic images were constructed at 10keV intervals from 40–190keV. For each patient, an ROI delineated the lesion under investigation, and cylindrical ROI’s were placed within 5 different healthy tissues (blood, fat, muscle, lung, and liver). Several histogram- and Grey Level Cooccurrence Matrix (GLCM)-based texture features were then evaluated in each ROI at each energy level. As a means of validation, these feature values were then used in a random forest classifier to attempt to identify the tissue types present within each ROI. Their predictive accuracy at each energy level was recorded. Results: All textural features changed considerably with virtual monochromatic energy, particularly below 70keV. Most features exhibited a global minimum or maximum around 80keV, and while feature values changed with energy above this, patient ranking was generally unaffected. As expected, blood demonstrated the lowest inter-patient variability, for all features, while lung lesions (encompassing many different pathologies) exhibited the highest. The accuracy of these features in identifying tissues (76% accuracy) was highest at 80keV, but no clear relationship between energy and classification accuracy was found. Two common misclassifications (blood vs liver and muscle vs fat) accounted for the majority (24 of the 28) errors observed. Conclusion: All textural features were highly dependent on virtual monochromatic energy level, especially below 80keV, and were more stable above this energy. However, in a random forest model, these commonly used features were able to reliably differentiate between most tissues types regardless of energy level. Dr Godoy has received a dual-energy CT research grant from Siemens Healthcare. That grant did not directly fund this research.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Quinolyl functionalized spiro[fluorene-9,9'-xanthene] host materials with bipolar characteristics for green and red phosphorescent organic light-emitting diodes

Spiro[fluorene-9,9'-xanthene] (SFX) bipolar hosts bearing one, two and three quinolyl substituents, namely SFX-bPy, SFX-DbPy and SFX-TbPy, were designed and synthesized for phosphorescent organic light emitting diodes (PhOLEDs). The successive substitution of quinoline at 2', 2 and 7' positions of SFX results in reduced LUMO energy levels while leaving the HOMO energy levels nearly intact. The impact of quinoline substitution in these SFX-based hosts on PhOLED performance was investigated in detail through green and red model devices. For the green emitting devices, the device based on SFX-bPy host showed better performance (23.6 cd A -1 , 23.4 lm W -1 , 6.3%) due to high triplet energy level ( T 1 ) and balanced carriers-transporting ability. In contrast, for the red PhOLED devices, the device hosted by SFX-DbPy displayed higher performance (15.8 cd A -1 , 16.0 lm W -1 , 9.1%), attributable to the well matched T 1 and separated frontier molecular orbitals. This work thus sheds light on the rational design of SFX-based bipolar hosts for more efficient PhOLEDs.

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

Spectroscopy of a one-dimensional V-shaped quantum well with a point impurity

We consider the one-dimensional Hamiltonian with a V-shaped potential H{sub 0}=(1/2) [−((d{sup 2})/(dx{sup 2}))+|x|], decorated with a point impurity of either δ-type, or local δ{sup ′}-type or even nonlocal δ{sup ′}-type, thus yielding three exactly solvable models. We analyse the behaviour of the change in the energy levels when an interaction of the type −λ δ(x) or −λ δ(x−x{sub 0}) is switched on. In the first case, even energy levels, pertaining to antisymmetric bound states, remain invariant with respect to λ even though odd energy levels, pertaining to symmetric bound states, decrease as λ increases. In the second, all energy levels decrease when the factor λ increases. A similar study has been performed for the so-called nonlocal δ{sup ′} interaction, requiring a coupling constant renormalisation, which implies the replacement of the form factor λ by a renormalised form factor β. In terms of β, odd energy levels are unchanged. However, we show the existence of level crossings: after a fixed value of β the energy of each even level, with the natural exception of the first one, becomes lower than the constant energy of the previous odd level. Finally, we consider an interaction of the type −λδ(x)+μδ{sup ′}(x), and analyse in detail the discrete spectrum of the resulting self-adjoint Hamiltonian.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Evaluation and prediction of color-tunable organic light-emitting diodes based on carrier/exciton adjusting interlayer

A color tuning index (I{sub CT}) parameter for evaluating the color change capability of color-tunable organic light-emitting diodes (CT-OLEDs) was proposed and formulated. And a series of CT-OLEDs, consisting of five different carrier/exciton adjusting interlayers (C/EALs) inserted between two complementary emitting layers, were fabricated and applied to disclose the relationship between I{sub CT} and C/EALs. The result showed that the trend of electroluminescence spectra behavior in CT-OLEDs has good accordance with I{sub CT} values, indicating that the I{sub CT} parameter is feasible for the evaluation of color variation. Meanwhile, by changing energy level and C/EAL thickness, the optimized device with the widest color tuning range was based on N,N′-dicarbazolyl-3,5-benzene C/EAL, exhibiting the highest I{sub CT} value of 41.2%. Based on carrier quadratic hopping theory and exciton transfer model, two fitting I{sub CT} formulas derived from the highest occupied molecular orbital (HOMO) energy level and triplet energy level were simulated. Finally, a color tuning prediction (CTP) model was developed to deduce the I{sub CT} via C/EAL HOMO and triplet energy levels, and verified by the fabricated OLEDs with five different C/EALs. We believe that the CTP model assisted with I{sub CT} parameter will be helpful for fabricating high performance CT-OLEDs with a broad range of color tuning.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Towards monomaterial p-n junctions: Single-step fabrication of tin oxide films and their non-destructive characterisation by angle-dependent X-ray photoelectron spectroscopy

The application of a non-destructive method for characterization of electronic structure of an ultra-thin SnO{sub 1<x<2} layer synthesized by spin coating on Si wafers was demonstrated. Utilizing angle dependent XPS, we quantified stoichiometry changes inside the SnO{sub 1<x<2} layers of thickness comparable with the electron attenuation length. The O/Sn concentration varied from 1.25 near the SnO{sub x} surface to 1.10 near the substrate/overlayer interface. Deviations from ideal stoichiometry are caused by defects, and defect levels affect the band structure of the SnO{sub x} layers. By investigation of the valence band region, followed by main core level position tracking, changes of electronic parameters like energy levels shift were identified. The results indicated a downward energy levels shift by 0.45 eV in SnO{sub x} layers at the SiO{sub 2}/SnO{sub x} interface. In combination with the detected upward energy levels shift in the substrate's electronic structure, these results suggest a negative charge displacement across the SiO{sub 2} layer. As a consequence, there is a significant carrier concentration gradient in the layer, from a nearly insulating oxide at the SnO{sub x} surface to a semiconducting one at the bottom of the SnO{sub x} film. The results showed that the application of a simple and cost-effective method allows tuning the materials' properties towards the one-step fabrication of materials with ambipolar doping.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Breit–Pauli atomic structure calculations for Fe XI

Energy levels, oscillator strengths, and transition probabilities are calculated for the lowest-lying 165 energy levels of Fe XI using configuration-interaction wavefunctions. The calculations include all the major correlation effects. Relativistic effects are included in the Breit–Pauli approximation by adding mass-correction, Darwin, and spin–orbit interaction terms to the non-relativistic Hamiltonian. For comparison with the calculated ab initio energy levels, we have also calculated the energy levels by using the fully relativistic multiconfiguration Dirac–Fock method. The calculated results are in close agreement with the National Institute of Standards and Technology compilation and other available results. New results are predicted for many of the levels belonging to the 3s3p{sup 4}3d and 3s3p{sup 3}3d{sup 2} configurations, which are very important in astrophysics, relevant, for example, to the recent observations by the Hinode spacecraft. We expect that our extensive calculations will be useful to experimentalists in identifying the fine structure levels in their future work.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Slater transition methods for core-level electron binding energies

Methods for computing core-level ionization energies using self-consistent field (SCF) calculations are evaluated and benchmarked. These include a “full core hole” (or “ΔSCF”) approach that fully accounts for orbital relaxation upon ionization, but also methods based on Slater’s transition concept in which the binding energy is estimated from an orbital energy level that is obtained from a fractional-occupancy SCF calculation. A generalization that uses two different fractional-occupancy SCF calculations is also considered. The best of the Slater-type methods afford mean errors of 0.3–0.4 eV with respect to experiment for a dataset of K-shell ionization energies, a level of accuracy that is competitive with more expensive many-body techniques. An empirical shifting procedure with one adjustable parameter reduces the average error below 0.2 eV. Here, this shifted Slater transition method is a simple and practical way to compute core-level binding energies using only initial-state Kohn–Sham eigenvalues. It requires no more computational effort than ΔSCF and may be especially useful for simulating transient x-ray experiments where core-level spectroscopy is used to probe an excited electronic state, for which the ΔSCF approach requires a tedious state-by-state calculation of the spectrum. As an example, we use Slater-type methods to model x-ray emission spectroscopy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Modeling the effect of climate change on U.S. state-level buildings energy demands in an integrated assessment framework

As long-term socioeconomic transformation and energy service expansion show large spatial heterogeneity, advanced understanding of climate impact on building energy use at the sub-national level will offer useful insights into climate policy and regional energy system planning. In this study, we presented a detailed building energy model with a U.S. state-level representation, nested in the GCAM integrated assessment framework. We projected state-level building energy demand and its spatial pattern over the century, considering the impact of climate change based on the estimates of heating and cooling degree days derived from downscaled USGS CASCaDE temperature data. The result indicates that climate change has a large impact on heating and cooling building energy and fuel use at the state level, exhibiting large spatial heterogeneity across states (ranges from -10% to +10%). The sensitivity analysis reveals that the building energy demand is subject to multiple key factors, such as the magnitude of climate change, the choice of climate models, and the growth of population and GDP, and that their relative contributions vary greatly across the space. The scale impact in building energy use modeling highlights the importance of constructing a building energy model with the spatially-explicit representation of socioeconomics, energy system development, and climate change. These findings will help the climate-based policy decision and energy system, especially utility planning related to building sector at the U.S. state and regional level facing the potential climate change.

Building Energy Demand, Climate Change Impact, Sta↗
DOE OSTI2015

Interfacial electronic structure at the CH{sub 3}NH{sub 3}PbI{sub 3}/MoO{sub x} interface

Interfacial electronic properties of the CH{sub 3}NH{sub 3}PbI{sub 3} (MAPbI{sub 3})/MoO{sub x} interface are investigated using ultraviolet photoemission spectroscopy and X-ray photoemission spectroscopy. It is found that the pristine MAPbI{sub 3} film coated onto the substrate of poly (3,4-ethylenedioxythiophene) poly(styrenesulfonate)/indium tin oxide by two-step method behaves as an n-type semiconductor, with a band gap of ∼1.7 eV and a valence band edge of 1.40 eV below the Fermi energy (E{sub F}). With the MoO{sub x} deposition of 64 Å upon MAPbI{sub 3}, the energy levels of MAPbI{sub 3} shift toward higher binding energy by 0.25 eV due to electron transfer from MAPbI{sub 3} to MoO{sub x}. Its conduction band edge is observed to almost pin to the E{sub F}, indicating a significant enhancement of conductivity. Meanwhile, the energy levels of MoO{sub x} shift toward lower binding energy by ∼0.30 eV, and an interface dipole of 2.13 eV is observed at the interface of MAPbI{sub 3}/MoO{sub x}. Most importantly, the chemical reaction taking place at this interface results in unfavorable interface energy level alignment for hole extraction. A potential barrier of ∼1.36 eV observed for hole transport will impede the hole extraction from MAPbI{sub 3} to MoO{sub x}. On the other hand, a potential barrier of ∼0.14 eV for electron extraction is too small to efficiently suppress electrons extracted from MAPbI{sub 3} to MoO{sub x}. Therefore, such an interface is not an ideal choice for hole extraction in organic photovoltaic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Excited state management

Arrangements and techniques for providing organic emissive layers are provided, in which the emissive layer includes a first dopant having a dissociative energy level. A second dopant in the emissive layer provides a solid state sink energy level, to which doubly excited excitons and/or polarons may transition instead of to the dissociative energy level, thereby decreasing the undesirable effects of transitions to the dissociative energy level.

Forrest, Stephen R.↗
DOE OSTI2019

Excited state management

Arrangements and techniques for providing organic emissive layers are provided, in which the emissive layer includes a first dopant having a dissociative energy level. A second dopant in the emissive layer provides a solid state sink energy level, to which doubly excited excitons and/or polarons may transition instead of to the dissociative energy level, thereby decreasing the undesirable effects of transitions to the dissociative energy level.

Forrest, Stephen R.↗
DOE OSTI2021

Excited state management

Arrangements and techniques for providing organic emissive layers are provided, in which the emissive layer includes a first dopant having a dissociative energy level. A second dopant in the emissive layer provides a solid state sink energy level, to which doubly excited excitons and/or polarons may transition instead of to the dissociative energy level, thereby decreasing the undesirable effects of transitions to the dissociative energy level.

Forrest, Stephen R.↗