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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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Solution sensitivity and accuracy study of NASTRAN for large dynamic problems involving structural damping

Large dynamic problems involving NASTRAN SOLUTION 8 (i.e., the steady state dynamic response option wherein all response quantities vary as e sub i omega t, where omega is the driving frequency and t is time) are considered. Using a submerged steel plate with a viscoelastic layer layer as the bench mark sample, the solution sensitivity and solution accuracy are checked. The solution sensitivity is examined by running the same finite element model on different computers, different versions of NASTRAN, and different precision levels. The solution accuracy is evaluated for these same runs by comparing the NASTRAN results with the exact solution of the same problem.

Kalinowski, A. J.↗
NASA NTRS1995

Remotely sensed indicators of habitat heterogeneity and biological diversity: A preliminary report

The relationship between habitat area, spatial dynamics of the landscape, and species diversity is an important theme in population and conservation biology. Of particular interest is how populations of various species are affected by increasing habitat edges due to fragmentation. Over the last decade, assumptions regarding the effects of habitat edges on biodiversity have fluctuated wildly, from the belief that they have a positive effect to the belief that they have a clearly negative effect. This change in viewpoint has been brought about by an increasing recognition of the importance of geographic scale and a reinterpretation of natural history observations. In this preliminary report from an ongoing project, we explore the use of remote sensing technology and geographic information systems to further our understanding of how species diversity and population density are affected by habitat heterogeneity and landscape composition. A primary feature of this study is the investigation of SAR for making more rigorous investigations of habitat structure by exploiting the interaction between radar backscatter and vegetation structure and biomass. A major emphasis will be on the use of SAR data to define relative structural types based on measures of structural consolidation using the vegetation surface area to volume ratio (SA/V). Past research has shown that SAR may be sensitive to this form of structural expression which may affect biodiversity.

Imhoff, Marc↗
DOE OSTI2019

Electronic Structure and Optical Properties of Designed Photo-Efficient Indoline-Based Dye-Sensitizers with D–A–π–A Framework

Seven D–A–π–A-based indoline (IND) dyes that were designed via quantitative-structure–property relationship modeling have been comprehensively investigated using computational approaches to evaluate their prospect of application in future dye-sensitized solar cells (DSSCs). An array of optoelectronic properties of the isolated dye and dyes adsorbed on a TiO 2 cluster that simulates the semiconductor were explored by density functional theory (DFT) and time-dependent DFT methods. Light absorption spectra, vertical dipole moment, shift of the conduction band of semiconductor, excited state lifetime, driving force of electron injection, photostability of the excited state, and exciton binding energy were computed. Our study showed that the presence of an internal acceptor such as pyrido[3,4-b]pyrazine (pyrazine) would influence greater the open circuit voltage (VOC), compared to the benzothiadiazole moiety. Considering the balance between the VOC and J SC (short circuit current) along with the all calculated characteristics, the IND3, IND5, and IND10 are the most suited among the designed dyes to be used as potential candidates for the photo-efficient DSSCs. Finally, the present study provides the results of rational molecular design followed by exploration of photophysical properties to be used as a valuable reference for the synthesis of photo-efficient dyes for DSSCs.

14 SOLAR ENERGY↗
DOE OSTI2016

Microstructural, optical and ethanol sensing properties of sprayed Li-doped Mn{sub 3}O{sub 4} thin films

Highlights: • Li doped Mn{sub 3}O{sub 4} was grown on glass substrate via the low cost effective spray pyrolysis technique. • Li doping notably tuned the optical band gap of Mn{sub 3}O{sub 4} thin film. • The incorporation of Li ions was found to provide an enhancement of ethanol sensitivity. - Abstract: Lithium-doped manganese oxide thin films have been deposited onto glass substrate by the spray pyrolysis technique. The effect on structural, morphological, optical and ethanol sensitivity properties of the films with different Li concentrations was investigated. The X-ray diffraction (XRD) studies of Li doped Mn{sub 3}O{sub 4} thin films revealed polycrystalline tetragonal structure with lattice parameters: a = 5.73 Å and c = 9.46 Å. The most intense band at 653.26 cm{sup −1} observed in room temperature Raman spectrum of all films corresponds to the tetragonal crystal structure of Mn{sub 3}O{sub 4}. Optical band gap energy was found to vary in the range of 2.23–2.82 eV by an increase in Li-doping concentration up to 15%. The resistance based gas sensing measurements showed a clear response already at a low ethanol concentration of 0.1%. The films showed promising ethanol sensing behavior; especially the sample doped with 3% of lithium exhibits the most excellent sensing performance.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Interfacial Octahedral Manipulation Imparts Hysteresis-Free Metal to Insulator Transition in Ultrathin Nickelate Heterostructure

Much like epitaxial strain, engineering oxygen octahedral rotations (OORs) in perovskite oxide thin films can be a powerful means of manipulating their physical and chemical properties. Here, it is demonstrated that the fundamental character of the metal-insulator transition (MIT) can be sensitively controlled by the structure of the oxygen sublattice for NdNiO 3 thin films grown epitaxially on NdGaO 3 (110) substrates. The MIT is sharp and hysteretic for a Ni-O-Ni bond angle of 154.0° (6 nm thick film) like the bulk behavior, while it is diffuse and largely nonhysteretic for a bond angle of 149.5° (3 nm thick film), stemming from the smaller bond angle of the NdGaO 3 substrate. Using synchrotron X-ray diffraction to quantify the geometric framework of the oxygen sublattice, it is found that the influence of the substrate OORs propagates and decays after a few nanometers into the ultrathin film. The sublattice structure in the 6 nm thick film is similar to that for bulk NdNiO 3 , leading to the sharp and hysteretic MIT.

36 MATERIALS SCIENCE↗
DOE OSTI2023

When Is a Bond Broken? The Polarizability Perspective.

Abstract The question of when a chemical bond can be said to be broken is of fundamental chemical interest but has not been widely studied. Herein we propose that the maxima of static polarizability along bond dissociation coordinates naturally define cutoff points for bond rupture, as they represent the onset of localization of shared electron density into constituent fragments. Examples of computed polarizability maxima over the course of bond cleavage in main‐group and transition metal compounds are provided, across covalent, dative and charge‐shift bonds. The behavior along reaction paths is also considered. Overall, the static polarizability is found to be a sensitive reporter of electronic structure reorganization associated with bond stretching, and thus can serve as a metric for describing bond cleavage (or diagnose the absence of a chemical bond).

Hait, Diptarka↗
DOE OSTI2023

When Is a Bond Broken? The Polarizability Perspective.

Abstract The question of when a chemical bond can be said to be broken is of fundamental chemical interest but has not been widely studied. Herein we propose that the maxima of static polarizability along bond dissociation coordinates naturally define cutoff points for bond rupture, as they represent the onset of localization of shared electron density into constituent fragments. Examples of computed polarizability maxima over the course of bond cleavage in main‐group and transition metal compounds are provided, across covalent, dative and charge‐shift bonds. The behavior along reaction paths is also considered. Overall, the static polarizability is found to be a sensitive reporter of electronic structure reorganization associated with bond stretching, and thus can serve as a metric for describing bond cleavage (or diagnose the absence of a chemical bond).

Hait, Diptarka↗
DOE OSTI2020

Jet substructure from dark sector showers

We examine the robustness of collider phenomenology predictions for a dark sector scenario with QCD-like properties. Pair production of dark quarks at the LHC can result in a wide variety of signatures, depending on the details of the new physics model. A particularly challenging signal results when prompt production induces a parton shower that yields a high multiplicity of collimated dark hadrons with subsequent decays to Standard Model hadrons. The final states contain jets whose substructure encodes their non-QCD origin. This is a relatively subtle signature of strongly coupled beyond the Standard Model dynamics, and thus it is crucial that analyses incorporate systematic errors to account for the approximations that are being made when modeling the signal. We estimate theoretical uncertainties for a canonical substructure observable designed to be sensitive to the gauge structure of the underlying object, the two-point energy correlator $ {e}_2^{\left(\beta \right)} $ , by computing envelopes between resummed analytic distributions and numerical results from Pythia. We explore the separability against the QCD background as the confinement scale, number of colors, number of flavors, and dark quark masses are varied. Additionally, we investigate the uncertainties inherent to modeling dark sector hadronization. Simple estimates are provided that quantify one’s ability to distinguish these dark sector jets from the overwhelming QCD background. Such a search would benefit from theory advances to improve the predictions, and the increase in statistics using the data to be collected at the high luminosity LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Laser-induced selective local patterning of vanadium oxide phases

The same elements can form different compounds with widely different physical properties. Synthesis of a single-phase material is commonly achieved by controlling experimental conditions. Synthesizing materials that incorporate multiple specific spatially distributed chemical phases is often challenging, especially if different phases must be organized into well-defined spatial patterns. Here, we present an efficient solid reaction laser annealing (SRLA) approach to directly write regions of different local chemical compositions. We demonstrate the practical utility of our approach by locally writing microscale patterns of distinct chemical phases in vanadium oxide thin films. Specifically, we achieved the controlled local recrystallization of a uniform V 2 O 3 matrix into VO 2 , V 3 O 5 , and V 4 O 7 regions exhibiting sharp 1st- and 2nd-order metal–insulator phase transitions over a wide range of critical temperatures, i.e., a characteristic feature of select vanadium oxides that is extremely sensitive to even minute structural or compositional imperfections. We utilized the local chemical phase writing to pattern spiking oscillators with distinct electrical behavior directly in the thin film sample without employing elaborate lithography fabrication. Our laser tuning local chemical composition opens a pathway to synthesize a wide range of artificially micropatterned composite materials, with precision and control unattainable in conventional material synthesis methods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Low-frequency and Moiré–Floquet engineering: A review

Highlights: • Review of theoretical and experimental advances in Floquet engineering. • Review of theories to derive effective Floquet Hamiltonians, with a focus on the low-frequency regime. • Review of the theoretical effects of light in Moiré materials. We review recent work on low-frequency Floquet engineering and its application to quantum materials driven by light, focusing on van der Waals systems hosting Moiré superlattices. These non-equilibrium systems combine the twist-angle sensitivity of the band structure with the flexibility of light drives. The frequency, amplitude, and polarization of light can be tuned in experimental setups, leading to platforms with on-demand properties. First, we review recent theoretical developments to derive effective Floquet Hamiltonians, emphasizing the low-frequency regime. We then review applications of some of these theories to study twisted graphene and transition metal dichalcogenide systems irradiated by light in free space and inside a waveguide. We study the changes induced in the quasienergies and steady-states, which can lead to topological transitions. Next, we consider van der Waals magnetic materials driven by low-frequency light pulses in resonance with the phonons. We discuss the phonon dynamics induced by the light and the resulting magnetic transitions from a Floquet perspective. We finish by outlining new directions for Moiré–Floquet engineering in the low-frequency regime and their relevance for technological applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Assessing the ability of $\mathrm{MODIS}$ $\mathrm{EVI}$ to estimate terrestrial ecosystem gross primary production of multiple land cover types

Terrestrial ecosystem gross primary production (GPP) is the largest component in the global carbon cycle. The enhanced vegetation index (EVI) has been proven to be strongly correlated with annual GPP within several biomes. However, the annual GPP-EVI relationship and associated environmental regulations have not yet been comprehensively investigated across biomes at the global scale. In this report we explored relationships between annual integrated EVI (iEVI) and annual GPP observed at 155 flux sites, where GPP was predicted with a log-log model: 1n(GPP) = a x 1n(iEVI) + b. iEVI was computed from MODIS monthly EVI products following removal of values affected by snow or cold temperature and without calculating growing season duration. Through categorisation of flux sites into 12 land cover types, the ability of iEVI to estimate GPP was considerably improved (R 2 from 0.62 to 0.74, RMSE from 454.7 to 368.2 g C m -2 yr -1 ). The biome-specific GPP-iEVI formulae generally showed a consistent performance in comparison to a global benchmarking dataset (R 2 = 0.79, RMSE = 387.8 g C m -2 yr -1 ). Specifically, iEVI performed better in cropland regions with high productivity but poorer in forests. The ability of iEVI in estimating GPP was better in deciduous biomes (except deciduous broadleaf forest) than in evergreen due to the large seasonal signal in iEVI in deciduous biomes. Likewise, GPP estimated from iEVI was in a closer agreement to global benchmarks at mid and high-latitudes, where deciduous biomes are more common and cloud cover has a smaller effect on remote sensing retrievals. Across biomes, a significant and negative correlation (R 2 = 0.37, p < 0.05) was observed between the strength (R 2 ) of GPP-iEVI relationships and mean annual maximum leaf area index (LAI max ), and the relationship between the strength and mean annual precipitation followed a similar trend. LAI max also revealed a scaling effect on GPP-iEVI relationships. Our results suggest that iEVI provides a very simple but robust approach to estimate spatial patterns of global annual GPP whereas its effect is comparable to various light-use-efficiency and data-driven models. The impact of vegetation structure on accuracy and sensitivity of EVI in estimating spatial GPP provides valuable clues to improve EVI-based models.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

A comprehensive review of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) techniques in protonic ceramic cells (PCCs): Current status and future perspective

Protonic ceramic cells (PCCs) have emerged as a promising technology for power generation, energy storage, and value-added chemical synthesis, offering benefits such as fuel flexibility, low emissions, and efficient operation at intermediate temperatures (300–600 ​°C). Recently, significant breakthroughs in materials and manufacturing methods have markedly enhanced the performance of PCCs. However, establishing a fundamental understanding of their electrocatalytic reactions has gained less attention. As a fast and cost-effective method for physicochemical fingerprinting, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) has proven to be a surface-sensitive analytical tool for structural and functional studies. This review critically examines the most up-to-date applications of DRIFTS for characterizing key components of PCCs, including oxygen electrodes, protonic electrolytes, and hydrogen electrodes for different applications, with a focus on revealing hydration properties and catalytic reactions, and guiding rational material design. The challenges for advancing DRIFTS, including quantitative capabilities and operando applications for PCC investigations, are highlighted and strategies to tackle these challenges are discussed. Ultimately, this review underscores the critical role of DRIFTS in accelerating the development of high-performance and durable PCCs for next-generation energy solutions, offering methodologies and insights broadly applicable to a wide range of electrochemical energy conversion and storage technologies.

Diffuse Reflectance Infrared Fourier Transform Spe↗
DOE OSTI2022

Enhancement of effective thermal conductivity of rGO/Mg nanocomposite packed beds

Engineering thermophysical properties of metal hydrides nanocomposites is crucial for effective thermal management during hydrogen storage reactions; however, the effect of microstructure on thermal transport mechanisms is still unclear. Here, we employed an integrated experiment-modeling approach to investigate microstructural factors that determine the effective thermal conductivity of individual reduced graphene oxide-magnesium (rGO/Mg) nanocomposites and their packed bed. Here the effective thermal conductivity of the rGO/Mg nanocomposite packed bed was measured by using guarded hot-plate method under various atmospheric conditions (i.e., vacuum, Ar and He). A microstructure-aware mesoscopic modeling revealed that anisotropy of the effective thermal conductivity of individual rGO/Mg nanocomposites plays an important role in determining the effective thermal conductivity of their packed bed. The validated mesoscopic model also disclosed a nontrivial interplay between the intrinsic rGO properties and the extrinsic composite structural features. Finally, quantitative sensitivity analysis based on the modeling framework is used to provide practical engineering guidance for controlling the thermal transport within nanocomposite packed beds.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Coupling of TIGRESS and EMMA with Auxiliary Array TIP at TRIUMF

The combination of a germanium detector array and recoil mass spectrometer allows for high-sensitivity experiments in nuclear structure and astrophysics by enabling high-energy-resolution -ray spectroscopy and reaction measurements of weak fusion-evaporation, transfer or radiative-capture reactions in the presence of dominant background reaction channels. The TIGRESS -ray spectrometer with an upgraded data acquisition system has been coupled with the EMMA mass spectrometer alongside a suite of auxiliary detectors housed within TIGRESS such as TIP. This paper reviews the unique combination of radioactive beams at TRIUMF with the capabilities of TIGRESS and EMMA in the context of fusion-evaporation with TIP and radiative-capture reactions without an auxiliary array.

A/Q identification↗
DOE OSTI2025

Implications of a weakening N = 126 shell closure away from stability for r -process astrophysical conditions

The formation of the third r-process abundance peak near A ∼ 195 is highly sensitive to both nuclear structure far from stability and the astrophysical conditions that produce the heaviest elements. In particular, the N = 126 shell closure plays a crucial role in shaping this peak. Experimental data hints that the shell weakens as proton number departs from Z = 82, a trend largely missed by global mass models. To investigate its impact on r-process nucleosynthesis, we employ both standard global models with strong closures and modified Duflo-Zuker (DZ) models that reproduce the weakening, combined with three sets of β − -decay rates. Strong shell closures generate sharply peaked abundances, whereas weakened closures consistent with the experimental trend produce broader, flatter patterns. Accurately reproducing the solar third peak under weakened shell strength requires sufficiently neutron-rich conditions that significant fission occurs, and slower decay rates. These results demonstrate that a weakening N = 126 shell closure away from stability imposes significant constraints on the astrophysical environments of the r-process and underscores the need for precise mass measurements and improved characterization of β − -decay properties in this region.

N = 126 closed shells↗
DOE OSTI2020

Formulation and solution approach for calibrating activity-based travel demand model-system via microsimulation

This study addresses the problem of calibrating utility-maximizing nested logit activity-based travel demand model-systems. After estimation, it is common practice to use aggregate measurements to calibrate the estimated model-system’s parameters prior to their application in transportation planning, policy making, and operations. However, calibration of activity-based model-systems has received much less attention. Existing calibration approaches are myopic heuristics in the sense that they do not consider the fundamental inter-dependencies among choice-models and do not have a systematic way to adjust model parameters. Also, other purely simulation-based approaches do not perform well in large-scale applications. In this study, we focus on utility-maximizing nested logit activity-based model-systems and calibrating aggregate statistics such as activity shares, mode shares, time-dependent & mode-specific OD flows, and time-dependent & mode-specific sensor counts. We formulate the calibration problem as a simulation-based optimization problem and propose a stochastic gradient-based solution procedure to solve it. The solution procedure relies on microsimulation to calculate expectations of the aggregate statistics of interest to the calibration problem. Additionally, we derive approximate analytical expressions for the gradient of the objective function —that are evaluated through microsimulation on mini-batches of the population. The proposed solution procedure is sensitive to the fundamental structure of the activity-based model-system and is non-myopic in considering the dependencies across its model components. The formulated optimization problem is non-convex, highly nonlinear, and potentially has multiple-minima. Lastly, we show —through a real-world application— that the proposed solution procedure outperforms other state-of-the-art purely simulation-based optimization approaches in terms of computational efficiency, stability, and convergence. We also compare various gradient-based solution algorithms to determine the best algorithm to update the parameters. This work has the potential to facilitate wider and easier application of activity-based model-systems.

97 MATHEMATICS AND COMPUTING↗