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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Topotactic Phase Transformation of Lithiated Spinel to Layered LiMn0.5Ni0.5O2: The Interaction of 3-D and 2-D Li-ion Diffusion

This study investigates the structural evolution of LiMn0.5Ni0.5O2 cathode materials for Li-ion batteries as a function of synthesis temperature and its effect on electrochemical performance. It is demonstrated that, as the synthesis temperature increases from 400 to 900 ?C, a gradual topotactic transformation occurs between a lithiated spinel structure, denoted herein as “lithium-excess spinel” LxS-LiMn0.5Ni0.5O2 (or LxS-LMNO), and the well-known layered LiMn0.5Ni0.5O2 structure prepared at high temperature, HT-LiMn0.5Ni0.5O2 (HT-LMNO). The electrochemical capacity of the LiMn0.5Ni0.5O2 electrodes follows a parabolic trend with increasing synthesis temperature, which is attributed primarily to the gradual transformation of 3-dimensional (3-D) to 2-dimensional (2-D) diffusion pathways for the Li ions. When synthesized at 400 °C, LxS-LiMn0.5Ni0.5O2 electrodes perform well, benefitting from the 3-D network of channels within the LxS structure. By contrast, when prepared at 500-700 °C, LiMn0.5Ni0.5O2 electrodes operate poorly, which is attributed to the formation of locally disordered structural arrangements that impede Li-ion diffusion. Such an increase in local disorder in the mid-temperature synthesis range is attributed to the structural frustration between the lithium-excess spinal and layered end-members. The transformation from the locally disordered to more ordered layered components between 700 °C and 900 °C enhances electrochemical performance. The study opens new avenues for designing next-generation Mn-rich cathode materials by fine-tuning the synthesis conditions as well as the composition and structure of LxS-LMNO electrodes.

energy storage↗
DOE OSTI2014

Competitive autocatalytic reactions in chaotic flows with diffusion: Prediction using finite-time Lyapunov exponents

We investigate chaotic advection and diffusion in autocatalytic reactions for time-periodic sine flow computationally using a mapping method with operator splitting. We specifically consider three different autocatalytic reaction schemes: a single autocatalytic reaction, competitive autocatalytic reactions, which can provide insight into problems of chiral symmetry breaking and homochirality, and competitive autocatalytic reactions with recycling. In competitive autocatalytic reactions, species B and C both undergo an autocatalytic reaction with species A such that A+B→2B and A+C→2C. Small amounts of initially spatially localized B and C and a large amount of spatially homogeneous A are advected by the velocity field, diffuse, and react until A is completely consumed and only B and C remain. We find that local finite-time Lyapunov exponents (FTLEs) can accurately predict the final average concentrations of B and C after the reaction completes. The species that starts in the region with the larger FTLE has, with high probability, the larger average concentration at the end of the reaction. If B and C start in regions with similar FTLEs, their average concentrations at the end of the reaction will also be similar. When a recycling reaction is added, the system evolves towards a single species state, with the FTLE often being useful in predicting which species fills the entire domain and which is depleted. The FTLE approach is also demonstrated for competitive autocatalytic reactions in journal bearing flow, an experimentally realizable flow that generates chaotic dynamics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

An AMR capable finite element diffusion solver for ALE hydrocodes [An AMR capable diffusion solver for ALE-AMR]

Here, we present a novel method for the solution of the diffusion equation on a composite AMR mesh. This approach is suitable for including diffusion based physics modules to hydrocodes that support ALE and AMR capabilities. To illustrate, we proffer our implementations of diffusion based radiation transport and heat conduction in a hydrocode called ALE-AMR. Numerical experiments conducted with the diffusion solver and associated physics packages yield 2nd order convergence in the L 2 norm.

42 ENGINEERING↗
DOE OSTI2016

Radio galaxies dominate the high-energy diffuse gamma-ray background

It has been suggested that unresolved radio galaxies and radio quasars (sometimes referred to as misaligned active galactic nuclei) could be responsible for a significant fraction of the observed diffuse gamma-ray background. In this study, we use the latest data from the Fermi Gamma-Ray Space Telescope to characterize the gamma-ray emission from a sample of 51 radio galaxies. In addition to those sources that had previously been detected using Fermi data, we report here the first statistically significant detection of gamma-ray emission from the radio galaxies 3C 212, 3C 411, and B3 0309+411B. Combining this information with the radio fluxes, radio luminosity function, and redshift distribution of this source class, we find that radio galaxies dominate the diffuse gamma-ray background, generating 77.2(+25.4)(-9.4)% of this emission at energies above ~1 GeV . We discuss the implications of this result and point out that it provides support for scenarios in which IceCube's high-energy astrophysical neutrinos also originate from the same population of radio galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Decoupling Li out-diffusion and surface diffusion in the lithiation-assisted epitaxial growth of lithium tungstate

Lithiation-assisted epitaxy offers a flexible and robust approach for synthesizing high-quality Li-containing materials and interfaces with precise control. Here, in this study, we use lithium tungstate (Li x WO 3+x/2 , where x = 0 to 2) as a model system to investigate the intertwined effects of Li out-diffusion-induced compositional changes and surface-diffusion-induced morphological changes. By systematically varying synthesis and processing conditions, we uncover their impact on lithium tungstate film formation. Comprehensive characterizations, including X-ray diffraction, atomic force microscopy, X-ray photoemission spectroscopy and time-of-flight secondary ion mass spectrometry, reveal that low-temperature growth (< 300 °C) followed by high-temperature annealing yields continuous lithium tungstate films with significantly reduced surface roughness. In contrast, high-temperature deposition (≥ 300 °C) accelerates surface diffusion and Li out-diffusion, leading to island formation. Furthermore, in situ scanning transmission electron microscopy demonstrates the beam sensitivity of Li 2 WO 4 and reveals a phase transition from Li 2 WO 4 to LiWO 3.5 under prolonged electron beam exposure. These findings deepen our understanding of how to control composition and morphology of Li-containing films, providing valuable insights for the design and integration of energy materials.

Shi, Jueli [Pacific Northwest National Laboratory ↗
DOE OSTI2026

Direct Measurement of Diffusion Coefficients: Evidence for Diffusive Stochastic Heating in Collisionless Plasmas

Open questions in collisionless plasma dissipation can be addressed using space-based observations in different astrophysical environments, with implications for both astrophysical and laboratory plasma systems. We study a low-𝛽, highly imbalanced, sub-Alfvénic stream observed by Parker Solar Probe (PSP) to identify and distinguish between signatures of stochastic heating (SH) and resonant heating (RH) by parallel ion cyclotron waves (∥-ICWs). Prior work studying this stream [Trevor A. Bowen et al., Stochastic heating in the sub-Alfvénic solar wind, Phys. Rev. Lett. 135, 255201 (2025)] showed that the SH rate, accounting for intermittency, matched the amplitude of the local energy transfer (LET) rate, while the RH rate did not. This comparison relied on a number of assumptions regarding the nature of the diffusive process and the calculation of the LET rate. We introduce a novel technique of inverting the proton guiding center equation to empirically measure velocity-space diffusion coefficients using three-dimensional proton velocity distribution functions, from the ion electrostatic analyzer (the Solar Probe Analyzer for Ions) on PSP. Measured diffusion coefficients are used to determine phase-space heating rates, leading to a calculation of a fully kinetic heating rate independent of assumptions made in prior work. We show that scale-dependent analytic expressions for SH via noncoherent fluctuations match the empirical measurements from PSP data, provided that we account for intermittency in the heating calculation. In contrast, the derived heating rates for SH that accounts for the effects of the helicity barrier and heating rates for RH via ∥-ICWs do not peak in the same region of velocity space as the empirical measurements, nor do they reach the required magnitude. Our approach provides novel methodology to uniquely identify and constrain heating processes in collisionless plasmas and shows evidence of a Fokker-Planck-like diffusive process in the near-Sun solar wind.

Plasma kinetic theory↗
DOE OSTI2014

Messages Do Diffuse Faster than Messengers: Reconciling Disparate Estimates of the Morphogen Bicoid Diffusion Coefficient

The gradient of Bicoid (Bcd) is key for the establishment of the anterior-posterior axis in Drosophila embryos. The gradient properties are compatible with the SDD model in which Bcd is synthesized at the anterior pole and then diffuses into the embryo and is degraded with a characteristic time. Within this model, the Bcd diffusion coefficient is critical to set the timescale of gradient formation. This coefficient has been measured using two optical techniques, Fluorescence Recovery After Photobleaching (FRAP) and Fluorescence Correlation Spectroscopy (FCS), obtaining estimates in which the FCS value is an order of magnitude larger than the FRAP one. This discrepancy raises the following questions: which estimate is "correct’’; what is the reason for the disparity; and can the SDD model explain Bcd gradient formation within the experimentally observed times? In this paper, we use a simple biophysical model in which Bcd diffuses and interacts with binding sites to show that both the FRAP and the FCS estimates may be correct and compatible with the observed timescale of gradient formation. The discrepancy arises from the fact that FCS and FRAP report on different effective (concentration dependent) diffusion coefficients, one of which describes the spreading rate of the individual Bcd molecules (the messengers) and the other one that of their concentration (the message). The latter is the one that is more relevant for the gradient establishment and is compatible with its formation within the experimentally observed times.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Derivation of effective fission gas diffusivities in UO2 from lower length scale simulations and implementation of fission gas diffusion models in BISON

This report summarizes the development of new fission gas diffusion models from lower length scale simulations and assessment of these models in terms of annealing experiments and fission gas release simulations using the BISON fuel performance code. Based on the mechanisms established from density functional theory (DFT) and empirical potential calculations, continuum models for diffusion of xenon (Xe) in UO 2 were derived for both intrinsic conditions and under irradiation. The importance of the large X eU 3 O cluster (a Xe atom in a uranium + oxygen vacancy trap site with two bound uranium vacancies) is emphasized, which is a consequence of its high mobility and stability. These models were implemented in the MARMOT phase field code, which is used to calculate effective Xe diffusivities for various irradiation conditions. The effective diffusivities were used in BISON to calculate fission gas release for a number of test cases. The results are assessed against experimental data and future directions for research are outlined based on the conclusions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Probing Galactic Diffuse TeV Gamma-Ray Emission with the HAWC Observatory

Galactic diffuse TeV gamma-ray emission is produced by the interaction of high-energy cosmic- ray particles with matter and radiation in our Galaxy. The measurement of Galactic diffuse TeV gamma-ray emission would provide strong constraints on the acceleration and propagation of Galactic cosmic rays. The High Altitude Water Cherenkov (HAWC) Observatory, located in central Mexico at 4100 m above sea level, is sensitive to gamma rays between a few hundreds GeV and ~100 TeV. Thanks to its large field of view of 2 steradians and excellent background estimation, HAWC has a unique capability to observe large extended sources such as Galactic diffuse emission. We present the analysis strategy to detect the Galactic diffuse emission with HAWC, including techniques to remove contaminations from localized sources.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Technical Note: Isotopic corrections for the radiocarbon composition of CO 2 in the soil gas environment must account for diffusion and diffusive mixing

Earth system scientists working with radiocarbon in organic samples use a stable carbon isotope ( δ 13 C ) correction to account for mass-dependent fractionation, but it has not been evaluated for the soil gas environment, wherein both diffusive gas transport and diffusive mixing are important. Using theory and an analytical soil gas transport model, we demonstrate that the conventional correction is inappropriate for interpreting the radioisotopic composition of CO 2 from biological production because it does not account for important gas transport mechanisms. Based on theory used to interpret δ 13 C of soil production from soil CO 2 , we propose a new solution for radiocarbon applications in the soil gas environment that fully accounts for both mass-dependent diffusion and mass-independent diffusive mixing.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1975

Cosmic ray diffusion: Report of the Workshop in Cosmic Ray Diffusion Theory

A workshop in cosmic ray diffusion theory was held at Goddard Space Flight Center on May 16-17, 1974. Topics discussed and summarized are: (1) cosmic ray measurements as related to diffusion theory; (2) quasi-linear theory, nonlinear theory, and computer simulation of cosmic ray pitch-angle diffusion; and (3) magnetic field fluctuation measurements as related to diffusion theory.

Birmingham, T. J.↗
NASA NTRS1987

Predicting diffusion paths and interface motion in gamma/gamma + beta, Ni-Cr-Al diffusion couples

A simplified model has been developed to predict Beta recession and diffusion paths in ternary gamma/gamma + beta diffusion couples (gamma:fcc, beta: NiAl structure). The model was tested by predicting beta recession and diffusion paths for four gamma/gamma + beta, Ni-Cr-Al couples annealed for 100 hours at 1200 C. The model predicted beta recession within 20 percent of that measured for each of the couples. The model also predicted shifts in the concentration of the gamma phase at the gamma/gamma + beta interface within 2 at. pct Al and 6 at. pct Cr of that measured in each of the couples. A qualitative explanation based on simple kinetic and mass balance arguments has been given which demonstrates the necessity for diffusion in the two-phase region of certain gamma/gamma + beta, Ni-Cr-Al couples.

Nesbitt, J. A.↗
NASA NTRS1990

NASA/DOD Aerospace Knowledge Diffusion Research Project. Paper 8: The role of the information intermediary in the diffusion of aerospace knowledge

The United States aerospace industry is experiencing profound changes created by a combination of domestic actions and circumstances such as airline deregulation. Other changes result from external trends such as emerging foreign competition. These circumstances intensify the need to understand the production, transfer, and utilization of knowledge as a precursor to the rapid diffusion of technology. Presented here is a conceptual framework for understanding the diffusion of technology. A conceptual framework is given for understanding the diffusion of aerospace knowledge. The framework focuses on the information channels and members of the social system associated with the aerospace knowledge diffusion process, placing particular emphasis on aerospace librarians as information intermediaries.

Pinelli, Thomas E.↗
NASA NTRS1991

NASA/DOD Aerospace Knowledge Diffusion Research Project. Paper 12: The diffusion of federally funded aerospace Research and Development (R&D) and the information seeking behavior of US aerospace engineers and scientists

The present exploration of the diffusion of federally-funded R&D via the information-seeking behavior of scientists and engineers proceeds under three assumptions: (1) that knowledge transfer and utilization is as important as knowledge production; (2) that the diffusion of knowledge obtained through federally-funded R&D is necessary for the maintenance of U.S. preeminence in the aerospace field; and (3) that federally-funded NASA and DoD technical reports play an important, albeit as-yet undefined, role in aerospace R&D diffusion. A conceptual model is presented for the process of knowledge diffusion that stresses the role of U.S. government-funded technical reports.

Pinelli, Thomas E.↗
NASA NTRS1991

NASA/DOD Aerospace Knowledge Diffusion Research Project. Paper 12: The diffusion of federally funded aerospace research and development (R/D) and the information seeking behavior of US aerospace engineers and scientists

In this paper, the diffusion of federally funded aerospace R&D is explored from the perspective of the information-seeking behavior of U.S. aerospace engineers and scientists. The following three assumptions frame this exploration: (1) knowledge production, transfer, and utilization are equally important components of the aerospace R&D process; (2) the diffusion of knowledge resulting from federally funded aerospace R&D is indispensable for the U.S. to remain a world leader in aerospace; and (3) U.S. government technical reports, produced by NASA and DOD, play an important, but as yet undefined, role in the diffusion of federally funded aerospace R&D. A conceptual model for federally funded aerospace knowledge diffusion, one that emphasizes U.S. goverment technical reports, is presented. Data regarding three research questions concerning the information-seeking behavior of U.S. aerospace engineers and scientists are also presented.

Pinelli, Thomas E.↗
DOE OSTI2016

Identification of the Diffusion Parameter in Nonlocal Steady Diffusion Problems

The problem of identifying the diffusion parameter appearing in a nonlocal steady diffusion equation is considered. The identification problem is formulated as an optimal control problem having a matching functional as the objective of the control and the parameter function as the control variable. The analysis makes use of a nonlocal vector calculus that allows one to define a variational formulation of the nonlocal problem. In a manner analogous to the local partial differential equations counterpart, we demonstrate, for certain kernel functions, the existence of at least one optimal solution in the space of admissible parameters. We introduce a Galerkin finite element discretization of the optimal control problem and derive a priori error estimates for the approximate state and control variables. Using one-dimensional numerical experiments, we illustrate the theoretical results and show that by using nonlocal models it is possible to estimate non-smooth and discontinuous diffusion parameters.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Second-order accurate interface- and discontinuity-aware diffusion solvers in two and three dimensions

A numerical scheme is developed for two- and three-dimensional time-dependent diffusion equations in numerical simulations involving mixed cells. The focus of the development is on the formulations for both transient and steady states, the property for large time steps, second-order accuracy in both space and time, the correct treatment of the discontinuity in material properties, and the handling of mixed cells. For a mixed cell, interfaces between materials are reconstructed within the cell so that each of resulting sub-cells contains only one material and the material properties of each sub-cell are known. Diffusion equations are solved on the resulting polyhedral mesh even if the original mesh is structured. The discontinuity of material properties between different materials is correctly treated based on governing physics principles. The treatment is exact for arbitrarily strong discontinuity. The formulae for effective diffusion coefficients across interfaces between materials are derived for general polyhedral meshes. The scheme is general in two and three dimensions. Since the scheme to be developed in this paper is intended for multi-physics code with adaptive mesh refinement (AMR), we present the scheme on mesh generated from AMR. The correctness and features of the scheme are demonstrated for transient problems and steady states in one-, two-, and three-dimensional simulations for heat conduction and radiation heat transfer. The test problems involve dramatically different materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Understanding the Different Diffusion Mechanisms of Hydrated Protons and Potassium Ions in Titanium Carbide MXene

The high intercalation capacitance of MXenes is attractive, but their performance as electrodes in supercapacitors is limited by mass transport when increasing the thickness and mass loading of the electrodes. Here, we report a combined experimental and computational study, through which we reveal the diffusion of hydrated ionic species at the interlayer spaces. We find that the cyclic voltammetry curves for the delaminated Ti 3 C 2 T x exhibit distinct features in acid (H 2 SO 4 ) and alkaline (KOH) electrolytes. The DFT-calculated migration profile of K + and H + , in the presence and absence of water, suggests that the intercalated water molecules stabilize the charged ions, facilitating their diffusion from two dimension to three dimension manifested by the reduced activation barriers and movement pathways. In addition, we show that the diffusion of low and high concentrations of protons is significantly different. That is, protons of high concentrations can adsorb at both sides of the interlayer spaces, and water drives frequent proton hopping between stable adsorption sites as shown in the ab initio molecular dynamics simulations. The calculations can thus explain the varied capacitance and distorted CV curves when the experiments are conducted in acid and alkaline electrolytes. Furthermore, these results can provide the guidance to improve the fast transport of ions and electrons in MXenes with high mass loading.

25 ENERGY STORAGE↗