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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Dissipation in open holography

We exploit the holographic realization of a conformal theory coupled to an external bath realized via a double trace deformation and its gravity dual in terms of transparent boundary conditions in order to map out some basic dissipative properties of this simple open holographic system. In particular, we determine the energy transmission coefficient across the boundary, discover a novel duality relating weak and strong coupling to the external bath, and quantify the dissipation in the system by working out the quasi normal modes.

AdS-CFT correspondence↗
DOE OSTI2016

Investigation of Iso-octane Ignition and Validation of a Multizone Modeling Method in an Ignition Quality Tester

An ignition quality tester was used to characterize the autoignition delay times of iso-octane. The experimental data were characterized between temperatures of 653 and 996 K, pressures of 1.0 and 1.5 MPa, and global equivalence ratios of 0.7 and 1.05. A clear negative temperature coefficient behavior was seen at both pressures in the experimental data. These data were used to characterize the effectiveness of three modeling methods: a single-zone homogeneous batch reactor, a multizone engine model, and a three-dimensional computational fluid dynamics (CFD) model. A detailed 874 species iso-octane ignition mechanism (Mehl, M.; Curran, H. J.; Pitz, W. J.; Westbrook, C. K.Chemical kinetic modeling of component mixtures relevant to gasoline. Proceedings of the European Combustion Meeting; Vienna, Austria, April 14-17, 2009) was reduced to 89 species for use in these models, and the predictions of the reduced mechanism were consistent with ignition delay times predicted by the detailed chemical mechanism across a broad range of temperatures, pressures, and equivalence ratios. The CFD model was also run without chemistry to characterize the extent of mixing of fuel and air in the chamber. The calculations predicted that the main part of the combustion chamber was fairly well-mixed at longer times (> ~30 ms), suggesting that the simpler models might be applicable in this quasi-homogeneous region. The multizone predictions, where the combustion chamber was divided into 20 zones of temperature and equivalence ratio, were quite close to the coupled CFD-kinetics results, but the calculation time was ~11 times faster than the coupled CFD-kinetics model. Although the coupled CFD-kinetics model captured the observed negative temperature coefficient behavior and pressure dependence, discrepancies remain between the predictions and the observed ignition time delays, suggesting improvements are still needed in the kinetic mechanism and/or the CFD model. This approach suggests a combined modeling approach, wherein the CFD calculations (without chemistry) can be used to examine the sensitivity of various model inputs to in-cylinder temperature and equivalence ratios. In conclusion, these values can be used as inputs to the multizone model to examine the impact on ignition delay. Additionally, the speed of the multizone model also makes it feasible to quickly test more detailed kinetic mechanisms for comparison to experimental data and sensitivity analysis.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2021

27 Al NMR diffusometry of Al 13 Keggin nanoclusters

Although nanometer-sized aluminum hydroxide clusters (i.e., ϵ-Al 13 , [Al 13 O 4 (OH) 24 (H 2 O) 12 ] 7+ ) command a central role in aluminum ion speciation and transformations between minerals, measurement of their translational diffusion is often limited to indirect methods. Here, in this work, 27 Al pulsed field gradient stimulated echo nuclear magnetic resonance (PFGSTE NMR) spectroscopy has been applied to the AlO 4 core of the ϵ-Al 13 cluster with complementary theoretical simulations of the diffusion coefficient and corresponding hydrodynamic radii from a boundary element-based calculation. The tetrahedral AlO 4 center of the ϵ-Al 13 cluster is symmetric and exhibits only weak quadrupolar coupling, which results in favorable T 1 and T 2 27 Al NMR relaxation coefficients for 27 Al PFGSTE NMR studies. Stokes–Einstein relationship was used to relate the 27 Al diffusion coefficient of the ϵ-Al 13 cluster to the hydrodynamic radius for comparison with theoretical simulations, dynamic light scattering from literature, and previously published 1 H PFGSTE NMR studies of chelated Keggin clusters. This first-of-its-kind observation proves that 27 Al PFGSTE NMR diffusometry can probe symmetric Al environments in polynuclear clusters of greater molecular weight than previously considered.

27Al↗
DOE OSTI2019

Self-dual ν = 1 bosonic quantum Hall state in mixed-dimensional QED

Here, we consider a (2 + 1)-dimensional Wilson-Fisher boson coupled to a (3 + 1)-dimensional U(1) gauge field. This theory possesses a strong-weak duality in terms of the coupling constant e and is self-dual at a particular value of $\mathcal{e}$. We derive exact relations between transport coefficients for a $\mathcal{ν}$ = 1 quantum Hall state at the self-dual point. Using boson-fermion duality, we map the $\mathcal{ν}$ = 1 bosonic quantum Hall state to a Fermi sea of the dual fermion and observe that the exact relationships between transport coefficients at the bosonic self-dual point are reproduced by a simple random-phase approximation (RPA), coupled with a Drude formula, in the fermionic theory. We explain this success of the RPA by pointing out a cancellation of a parity-breaking term in the fermion theory which occurs only at the self-dual point, resulting in the fermion self-dual theory explored previously. In addition, we argue that the equivalence of the self-dual structure can be understood in terms of electromagnetic duality or modular invariance, and these features are not inherited by the nonrelativistic cousins of the present model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Constraining the nonanalytic terms in the isospin-asymmetry expansion of the nuclear equation of state

In this report we examine the properties of the isospin-asymmetry expansion of the nuclear equation of state from chiral two- and three-body forces. We focus on extracting the high-order symmetry energy coefficients that consist of both normal terms (occurring with even powers of the isospin asymmetry) as well as terms involving the logarithm of the isospin asymmetry that are formally nonanalytic around the expansion point of isospin-symmetric nuclear matter. These coefficients are extracted from numerically precise perturbation theory calculations of the equation of state coupled with a new set of finite difference formulas that achieve stability by explicitly removing the effects of higher-order terms in the expansion. We consider contributions to the symmetry energy coefficients from both two- and three-body interactions. It is found that the coefficients of the logarithmic terms are generically larger in magnitude than those of the normal terms from second-order perturbation theory diagrams, but overall the normal terms give larger contributions to the ground state energy. The high-order isospin-asymmetry terms are especially relevant at large densities where they affect the proton fraction in β-equilibrium matter, and in particular we find that at twice saturation density they can reduce the proton fraction by up to 0.02.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Al and Zn Impurity Diffusion in Binary and Ternary Magnesium Solid-Solutions

Magnesium alloys are considered for implementation into structural components where energy-efficiency and light-weighting are important. Two of the most common alloying elements in magnesium alloys are Aluminum and Zinc. The present work examines impurity diffusion coefficients of Al and Zn in Mg(Zn) and Mg(Al) binary solid solutions, respectively. Experimental investigation is carried out with ternary diffusion couples with polycrystalline alloys. Concentration profiles were measured by electron microprobe micro-analysis and the impurity diffusion coefficients were determined by the Hall Method. Results of Al and Zn impurity diffusion in Mg solid solutions are reported, and examined as a function of composition of Mg solid solution.

aluminum↗
DOE OSTI2025

Sylvester-preconditioned adaptive-rank implicit time integrators for advection-diffusion equations with variable coefficients

Here, we consider the adaptive-rank integration of multi-dimensional time-dependent advection-diffusion partial differential equations (PDEs) with variable coefficients. We employ a standard finite-difference method for spatial discretization coupled with high-order diagonally implicit Runge-Kutta temporal schemes. The discrete equation is a generalized Sylvester equation (GSE), which we solve with a projection-based adaptive-rank algorithm structured around two key strategies: (i) constructing dimension-wise subspaces using a novel atypical extended Krylov strategy, and (ii) efficiently solving the basis coefficient matrix with a preconditioned GMRES solver. The low-rank decomposition is performed in 2D using SVD and with high-order SVD (HOSVD) in 3D to represent the tensor in a compressed Tucker format. For d-dimensional problems (here, d = 2 or 3), the computational complexity and memory storage of the approach are found numerically to scale as and $\mathscr{O}(Nr^2) + \mathscr{O} (r^{d+1})$ and $\mathscr{O}(Nr) + \mathscr{O} (r^{d})$, respectively, with the one-dimensional resolution and the maximal rank during the Krylov iteration (which we find to be largely independent of on our numerical examples). We present numerical examples that illustrate the advertised properties of the algorithm.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Modified algorithms for image inpainting in Fourier transform domain

One of the aims of image inpainting is recovering an image some of which Fourier transform coefficients are lost. In this area, the algorithm of iterative coupled transform domain (ICTDI) has been given by Li and Zeng (SIAM J Imaging Sci 9:24–51, 2016). In this paper, we present some modified algorithms of ICTDI and prove their convergence. In fact, we consider the effect of spectrum and phase angle of the Fourier transform, separately. Therefore, in comparison with ICTDI, one more regularization parameter is generated, and hence, we have more degree of freedom, and therefore, in general, we expect a more appropriate solution.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

Temporal variability in urinary levels of drinking water disinfection byproducts dichloroacetic acid and trichloroacetic acid among men

Urinary haloacetic acids (HAAs), such as dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), have been suggested as potential biomarkers of exposure to drinking water disinfection byproducts (DBPs). However, variable exposure to and the short elimination half-lives of these biomarkers can result in considerable variability in urinary measurements, leading to exposure misclassification. Here we examined the variability of DCAA and TCAA levels in the urine among eleven men who provided urine samples on 8 days over 3 months. The urinary concentrations of DCAA and TCAA were measured by gas chromatography coupled with electron capture detection. We calculated the intraclass correlation coefficients (ICCs) to characterize the within-person and between-person variances and computed the sensitivity and specificity to assess how well single or multiple urine collections accurately determined personal 3-month average DCAA and TCAA levels. The within-person variance was much higher than the between-person variance for all three sample types (spot, first morning, and 24-h urine samples) for DCAA (ICC=0.08–0.37) and TCAA (ICC=0.09–0.23), regardless of the sampling interval. A single-spot urinary sample predicted high (top 33%) 3-month average DCAA and TCAA levels with high specificity (0.79 and 0.78, respectively) but relatively low sensitivity (0.47 and 0.50, respectively). Collecting two or three urine samples from each participant improved the classification. The poor reproducibility of the measured urinary DCAA and TCAA concentrations indicate that a single measurement may not accurately reflect individual long-term exposure. Collection of multiple urine samples from one person is an option for reducing exposure classification errors in studies exploring the effects of DBP exposure on reproductive health. - Highlights: • We evaluated the variability of DCAA and TCAA levels in the urine among men. • Urinary DCAA and TCAA levels varied greatly over a 3-month period. • Single measurement may not accurately reflect personal long-term exposure levels. • Collecting multiple samples from one person improved the exposure classification.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Observation of VVZ production at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search for the production of three massive vector bosons, VVZ(V = W, Z) , in proton-proton collisions at $\sqrt{s}$ = 13 TeV is performed using data with an integrated luminosity of 140 fb -1 recorded by the ATLAS detector at the Large Hadron Collider. Events produced in the leptonic final states WWZ → ℓvℓvℓℓ (ℓ = e,μ), WZZ → ℓvℓℓℓℓ, ZZZ → ℓℓℓℓℓ, and the semileptonic final states WWZ → qq ℓvℓℓ and WZZ → ℓv qq ℓℓ, are analysed. The measured cross section for the pp → VVZ process is 660$^{+93}_{-90}$(stat.)$^{+80}_{-81}$(syst.) fb, and the observed (expected) significance is 6.4 (4.7) standard deviations, representing the observation of VVZ production. In addition, the measured cross section for the pp → WWZ process is 442 ± 94(stat.)$^{+60}_{-52}$(syst.) fb, and the observed (expected) significance is 4.4 (3.6) standard deviations, representing evidence of WWZ production. The measured cross sections are consistent with the Standard Model predictions. Constraints on physics beyond the Standard Model are also derived in the effective field theory framework by setting limits on Wilson coefficients for dimension-8 operators describing anomalous quartic gauge boson couplings.

Aad, G. (ORCID:0000000266654934)↗
DOE OSTI2015

Effects of spin diffusion on electron spin relaxation time measured with a time-resolved microscopic photoluminescence technique

We performed measurements at room temperature for a GaAs/AlGaAs multiple quantum well grown on GaAs(110) using a time-resolved microscopic photoluminescence (micro-PL) technique to find what effects spin diffusion had on the measured electron spin relaxation time, τ{sub s}, and developed a method of estimating the spin diffusion coefficient, D{sub s}, using the measured data and the coupled drift-diffusion equations for spin polarized electrons. The spatial nonuniformities of τ{sub s} and the initial degree of electron spin polarization caused by the pump intensity distribution inside the focal spot were taken into account to explain the dependence of τ{sub s} on the measured spot size, i.e., a longer τ{sub s} for a smaller spot size. We estimated D{sub s} as ∼100 cm{sup 2}/s, which is similar to a value reported in the literature. We also provided a qualitative understanding on how spin diffusion lengthens τ{sub s} in micro-PL measurements.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Energy spectrum and current-phase relation of a nanowire Josephson junction close to the topological transition

A semiconducting nanowire proximitized by an $\textit{s}$-wave superconductor can be tuned into a topological state by an applied magnetic field. This quantum phase transition is marked by the emergence of Majorana zero modes at the ends of the wire. The fusion of Majorana modes at a junction between two nanowires results in a 4π-periodic Josephson effect. Here, we elucidate how the 4π periodicity arises across the topological phase transition in a highly-transparent short nanowire junction. Owing to a high transmission coefficient, Majorana zero modes coming from different wires are strongly coupled, with an energy scale set by the proximity-induced, field-independent pairing potential. At the same time, the topological spectral gap—defined by competition between superconducting correlations and Zeeman splitting—becomes narrow in the vicinity of the transition point. The resulting hybridization of the fused Majorana states with the spectral continuum strongly affects the electron density of states at the junction and its Josephson energy. We study the manifestations of this hybridization in the energy spectrum and phase dependence of the Josephson current. We pinpoint the experimentally observable signatures of the topological phase transition, focusing on junctions with weak backscattering.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Correlation and transport properties for mixtures at constant pressure and temperature

Transport properties of mixtures of elements in the dense plasma regime play an important role in natural astrophysical and experimental systems, e.g., inertial confinement fusion. In this paper, we present a series of orbital-free molecular dynamics simulations on dense plasma mixtures with comparison to a global pseudo ion in jellium model. Hydrogen is mixed with elements of increasingly high atomic number (lithium, carbon, aluminum, copper, and silver) at a fixed temperature of 100 eV and constant pressure set by pure hydrogen at 2g/cm 3 , namely, 370 Mbars. We compute ionic transport coefficients, such as self-diffusion, mutual diffusion, and viscosity for various concentrations. Small concentrations of the heavy atoms significantly change the density of the plasma and decrease the transport coefficients. The structure of the mixture evidences a strong Coulomb coupling between heavy ions and the appearance of a broad correlation peak at short distances between hydrogen atoms. Finally, the concept of an effective one component plasma is used to quantify the overcorrelation of the light element induced by the admixture of a heavy element.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

The THz Spectrum of Density Fluctuations of Water: The Viscoelastic Regime

Relevant advances in the knowledge of the water dynamics at mesoscopic scales are reviewed, while mainly focusing on the contribution provided by high resolution inelastic X-ray scattering (IXS). In particular it is discussed how the use of IXS has improved our understanding of viscoelastic properties of water at THz frequencies. This specifically involves some solid-like features such as the onset of shear wave propagation, a sound velocity surprisingly similar to the one of ice, and an anomalously low sound absorption coefficient. All these properties can be explained by assuming the coupling of THz density fluctuations with a structural relaxation process connected to the breaking and forming of hydrogen bonds (HBs). This review also includes more recent IXS results demonstrating that, upon approaching supercritical conditions, relaxation phenomena in water gradually lose their structural character becoming essentially collisional in character. Furthermore, GHz spectroscopy results on supercooled water, suggesting the occurrence of a structural arrest, are discussed. An overview of the new opportunities offered by next generation IXS spectrometers finally concludes this review.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Development of a robust modeling tool for radiation-induced segregation in austenitic stainless steels

Irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels in Light Water Reactor (LWR) components has been linked to changes in grain boundary composition due to irradiation induced segregation (RIS). This work developed a robust RIS modeling tool to account for thermodynamics and kinetics of the atom and defect transportation under combined thermal and radiation conditions. The diffusion flux equations were based on the Perks model formulated through the linear theory of the thermodynamics of irreversible processes. Both cross and non-cross phenomenological diffusion coefficients in the flux equations were considered and correlated to tracer diffusion coefficients through Manning’s relation. The preferential atom-vacancy coupling was described by the mobility model, whereas the preferential atom-interstitial coupling was described by the interstitial binding model. The composition dependence of the thermodynamic factor was modeled using the CALPHAD approach. Detailed analysis on the diffusion fluxes near and at grain boundaries of irradiated austenitic stainless steels suggested the dominant diffusion mechanism for chromium and iron is via vacancy, while that for nickel can swing from the vacancy to the interstitial dominant mechanism. The diffusion flux in the vicinity of a grain boundary was found to be greatly influenced by the composition gradient formed from the transient state, leading to the oscillatory behavior of alloy compositions in this region. This work confirms that both vacancy and interstitial diffusion, and segregation itself, have important roles in determining the microchemistry of Fe, Cr, and Ni at irradiated grain boundaries in austenitic stainless steels.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2017

Compositional evolution of particle-phase reaction products and water in the heterogeneous OH oxidation of model aqueous organic aerosols

Organic compounds present at or near the surface of aqueous droplets can be efficiently oxidized by gas-phase OH radicals, which alter the molecular distribution of the reaction products within the droplet. A change in aerosol composition affects the hygroscopicity and leads to a concomitant response in the equilibrium amount of particle-phase water. The variation in the aerosol water content affects the aerosol size and physicochemical properties, which in turn governs the oxidation kinetics and chemistry. To attain better knowledge of the compositional evolution of aqueous organic droplets during oxidation, this work investigates the heterogeneous OH-radical-initiated oxidation of aqueous methylsuccinic acid (C 5 H 8 O 4 ) droplets, a model compound for small branched dicarboxylic acids found in atmospheric aerosols, at a high relative humidity of 85 % through experimental and modeling approaches. Aerosol mass spectra measured by a soft atmospheric pressure ionization source (Direct Analysis in Real Time, DART) coupled with a high-resolution mass spectrometer reveal two major products: a five carbon atom (C 5 ) hydroxyl functionalization product (C 5 H 8 O 5 ) and a C 4 fragmentation product (C 4 H 6 O 3 ). These two products likely originate from the formation and subsequent reactions (intermolecular hydrogen abstraction and carbon–carbon bond scission) of tertiary alkoxy radicals resulting from the OH abstraction occurring at the methyl-substituted carbon site. Based on the identification of the reaction products, a kinetic model of oxidation (a two-product model) coupled with the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients (AIOMFAC) model is built to simulate the size and compositional changes of aqueous methylsuccinic acid droplets during oxidation. Model results show that at the maximum OH exposure, the droplets become slightly more hygroscopic after oxidation, as the mass fraction of water is predicted to increase from 0.362 to 0.424; however, the diameter of the droplets decreases by 6.1 %. This can be attributed to the formation of volatile fragmentation products that partition to the gas phase, leading to a net loss of organic species and associated particle-phase water, and thus a smaller droplet size. Overall, fragmentation and volatilization processes play a larger role than the functionalization process in determining the evolution of aerosol water content and droplet size at high-oxidation stages.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Free vibration analysis of a multiple rotating nano-beams system based on the Eringen nonlocal elasticity theory

The free vibration analysis of a multiple rotating nanobeams' system applying the nonlocal Eringen elasticity theory is presented. Multiple nanobeams' systems are of great importance in nano-optomechanical applications. At nanoscale, the nonlocal effects become non-negligible. According to the nonlocal Euler-Bernoulli beam theory, the governing partial differential equations are derived by incorporating the nonlocal scale effects. Assuming a structure of n parallel nanobeams, the vibration of the system is described by a coupled set of n partial differential equations. The method involves a change of variables to uncouple the equations and the differential transform method as an efficient mathematical technique to solve the nonlocal governing differential equations. Then a number of parametric studies are conducted to assess the effect of the nonlocal scaling parameter, rotational speed, boundary conditions, hub radius, and the stiffness coefficients of the elastic interlayer media on the vibration behavior of the coupled rotating multiple-carbon-nanotube-beam system. It is revealed that the bending vibration of the system is significantly influenced by the rotational speed, elastic mediums, and the nonlocal scaling parameters. This model is validated by comparing the results with those available in the literature. The natural frequencies are in a reasonably good agreement with the reported results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗