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NASA NTRS2001

April 1998 Asian dust event: A southern California perspective

In late April 1998 an extreme Asian dust episode reached the U.S. western seaboard. This event was observed by several in situ and remote sensing atmospheric measurement stations. Dramatic reductions in boundary layer visibility were recorded and the resultant peak backscatter coefficients exceeded prevailing upper tropospheric background conditions by at least 2 orders of magnitude. An analysis of this event is given using lidar vertical backscatter profilometry, concurrent Sun photometer opacity data, and transport modeling.

aerosol↗

DOE OSTI2023

The stability of FeH x and hydrogen transport at Earth’s core mantle boundary

Iron hydride in Earth’s interior can be formed by the reaction between hydrous minerals (water) and iron. Studying iron hydride improves our understanding of hydrogen transportation in Earth’s interior. Our high-pressure experiments found that face-centered cubic (fcc) FeH x (x≤1) is stable up to 165 GPa, and our ab initio molecular dynamics simulations predicted that fcc FeH x transforms to a superionic state under lower mantle conditions. In the superionic state, H-ions in fcc FeH become highly diffusive-like fluids with a high diffusion coefficient of ~3.7 × 10 -4 cm 2 s -1 , which is comparable to that in the liquid Fe-H phase. The densities and melting temperatures of fcc FeH x were systematically calculated. Similar to superionic ice, the extra entropy of diffusive H-ions increases the melting temperature of fcc FeH. Further, the wide stability field of fcc FeH enables hydrogen transport into the outer core to create a potential hydrogen reservoir in Earth’s interior, leaving oxygen-rich patches (ORP) above the core mantle boundary (CMB).

58 GEOSCIENCES↗

DOE OSTI2021

Voltage-Dependent Barrier Height of Electron Transport through Iron Porphyrin Molecular Junctions

Electron transport through iron porphyrin (FeP) molecules self-assembled on a gold (Au) substrate was investigated using conductive atomic force microscopy (AFM) to measure current–voltage (I–V) characteristics. In the direct tunneling region (|V| ≤ 0.1 V), the Simmons model was used to characterize the electron transport. Furthermore, the energy barrier between the Fermi energy level of Au and the highest occupied molecular orbital (HOMO) level of the FeP molecule was determined to be between 0.3 and 0.6 eV; the range of the electron attenuation coefficient was 0.6–0.8 Å–1. Instead of a constant barrier height, a voltage-dependent barrier height was adapted to simulate the experimental I–V curves over the entire voltage range (|V| ≤ 2 V) using the Simmons model for the intermediate case. The voltage-dependent barrier height is supported by a previously predicted response of molecular-projected self-consistent Hamiltonian orbitals. The dependence showed that the HOMO level relative to the Fermi energy level of the Au electrode decreased as the bias voltage increased. To verify the deposition of the FeP on the Au substrate, Raman spectroscopy and AFM analysis were performed.

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DOE OSTI2021

Effective Fragment Potential-Based Molecular Dynamics Studies of Diffusion in Acetone and Hexane

To facilitate more reliable descriptions of transport properties in liquids, molecular dynamics (MD) simulations are performed based on the effective fragment potential (EFP) method derived from first-principles quantum mechanics (in contrast to MD based upon empirically fitted potentials). The EFP method describes molecular interactions in terms of Coulomb, polarization/induction, dispersion, exchange-repulsion, and charge-transfer interactions. The EFP MD simulations described in this paper, performed on hexane and acetone, are able to track the mean-square displacement of molecules for sufficient time to reliably extract translational diffusion coefficients. Finally, the results reported here are in reasonable agreement with experiment.

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NASA NTRS2021

Intercomparison of the representations of the atmospheric chemistry of pre-industrial methane and ozone in earth system and other global chemistry-transport models

An intercomparison has been set up to study the representation of the atmospheric chemistry of the pre-industrial troposphere in earth system and other global tropospheric chemistry-transport models. The intercomparison employed a constrained box model and utilised tropospheric trace gas composition data for the pre-industrial times at ninety mid-latitude surface locations. Incremental additions of four organic compounds: methane, ethane, acetone and propane, were used to perturb the constrained box model and generate responses in hydroxyl radicals and tropospheric ozone at each location and with each chemical mechanism. Although the responses agreed well across the chemical mechanisms from the selected earth system and other global tropospheric chemistry-transport models, there were differences in the detailed responses between the chemical mechanisms that could be tracked down by sensitivity analysis to differences in the representation of C1–C3 chemistry. Inter-mechanism ranges in NOx compensation points were about 0.17 ± 0.12 when expressed relative to the inter-mechanism average. Monte Carlo uncertainty analysis carried out with a single chemical mechanism put the intra-mechanism range a factor of three higher at 0.50 ± 0.12. Similar differences between inter-mechanism and intra-mechanism ranges were found for hydroxyl radical depletion but were up to a factor of six wider for ozone formation from incremental additions of organic compounds. The cause of the discrepancies between the inter- and intra-mechanism ranges was found to be the large uncertainties that are present in the laboratory determinations of the rate coefficients and product channel branching ratios of some key chemical reactions involving organic peroxy radicals and hydroperoxides. Whilst these large uncertainties are present in the laboratory determinations, there will be irreducible uncertainties in the predictions from the earth system and other chemistry-transport models of methane and tropospheric ozone trends since pre-industrial times and hence their contributions to the radiative forcing of climate change. Further definitive laboratory studies of the reaction rates and product yields of the reactions of the simple organic peroxy radicals and hydroperoxides are required to resolve and reduce current uncertainties in earth system and chemistry-transport model predictions.

atmospheric chemistry↗

DOE OSTI2022

Current challenges in the physics of white dwarf stars

White dwarfs are a class of stars with unique physical properties. They present many challenging problems whose solution requires advanced theories of dense matter, state-of-the-art experimental techniques, and extensive computing efforts. New ground- and space-based observatories will soon provide an increasingly detailed view of white dwarf stars and reveal new phenomena that will challenge our models. This review is an introduction to the nature of white dwarfs, the physical processes that determine their structure and evolution, and the physical conditions they span. Here we discuss a wide variety of currently unsolved or partially resolved problems in their constitutive physics that are broadly related to equations of state, transport processes and opacities.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Two Polymorphs of BaZn 2 P 2 : Crystal Structures, Phase Transition, and Transport Properties

Here, the novel α-BaZn 2 P 2 structural polymorph has been synthesized and structurally characterized for the first time. Its structure, elu-cidated from single crystal X-ray diffraction, indicates that the compound crystallizes in the orthorhombic α-BaCu 2 S 2 structure type, with unit cell parameters a = 9.7567(14) Å, b = 4.1266(6) Å, and c = 10.6000(15) Å. With β-BaZn 2 P 2 being previously iden-tified as belonging to the ThCr 2 Si 2 family, and with the precedent of structural phase transitions between the α-BaCu 2 S 2 type and the ThCr 2 Si 2 type, the potential for the pattern to be extended to the two different structural forms of BaZn 2 P 2 was explored. Thermal analysis suggest that a first order phase transition occurs at ~1123 K, whereby the low-temperature orthorhombic α-phase transforms to a high-temperature tetragonal β-BaZn 2 P 2 ; the structure of which was also studied and confirmed by single-crystal X-ray diffraction. Preliminary transport properties and band structure calculations indicate that α-BaZn 2 P 2 is a p-type, narrow-gap semiconductor with a direct bandgap (Eg) of 0.5 eV. The Seebeck coefficient, S(T), for the material increases steadily from the room temperature value of 119 µV/K to 184 µV/K at 600 K. The electrical resistivity of α-BaZn 2 P 2 is relatively high, on the order of 40 mΩ·cm, and the ρ(T) dependence shows gradual decrease upon heating. Such behavior is comparable to those of the typical semimetals or degenerate semiconductors. Although the observed values of the as-synthesized samples are not optimal, the carrier concentration can apparently be tuned to fall between the values of metals and semiconductors, thus providing an open window for optimizing this phase towards achieving an enhanced thermoelectric figure of merit zT. The calculated indirect band gap for the β-BaZn 2 P 2 phase is Eg = 0.03 eV which is about an order of magnitude lower than that of α-BaZn 2 P 2 . It is expected that the cage-like structural motif and layered structure possessed by α-BaZn 2 P 2 and β-BaZn 2 P 2 phases, respectively, would promote the realiza-tion of a low thermal conductivity in both compounds.

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DOE OSTI2020

Enhanced Low-Temperature Thermoelectric Performance in (PbSe) 1+δ (VSe 2 ) 1 Heterostructures due to Highly Correlated Electrons in Charge Density Waves

We explore the effect of charge density wave (CDW) on the in-plane thermoelectric transport properties of (PbSe) 1+δ (VSe 2 ) 1 and (PbSe) 1+δ (VSe 2 ) 2 heterostructures. In (PbSe) 1+δ (VSe 2 ) 1 we observe an abrupt 86% increase in the Seebeck coefficient, 245% increase in the power factor, and a slight decrease in resistivity over the CDW transition. This behavior is not observed in (PbSe) 1+δ (VSe 2 ) 2 and is rather unusual compared to the general trend observed in other materials. The abrupt transition causes a deviation from the Mott relationship through correlated electron states. Raman spectra of the (PbSe) 1+δ (VSe 2 ) 1 material show the emergence of additional peaks below the CDW transition temperature associated with VSe 2 material. Temperature-dependent in-plane X-ray diffraction (XRD) spectra show a change in the in-plane thermal expansion of VSe 2 in (PbSe) 1+δ (VSe 2 ) 1 due to lattice distortion. Here, the increase in the power factor and decrease in the resistivity due to CDW suggest a potential mechanism for enhancing the thermoelectric performance at the low temperature region.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Efficient calculation of carrier scattering rates from first principles

Abstract The electronic transport behaviour of materials determines their suitability for technological applications. We develop a computationally efficient method for calculating carrier scattering rates of solid-state semiconductors and insulators from first principles inputs. The present method extends existing polar and non-polar electron-phonon coupling, ionized impurity, and piezoelectric scattering mechanisms formulated for isotropic band structures to support highly anisotropic materials. We test the formalism by calculating the electronic transport properties of 23 semiconductors, including the large 48 atom CH 3 NH 3 PbI 3 hybrid perovskite, and comparing the results against experimental measurements and more detailed scattering simulations. The Spearman rank coefficient of mobility against experiment ( r s = 0.93) improves significantly on results obtained using a constant relaxation time approximation ( r s = 0.52). We find our approach offers similar accuracy to state-of-the art methods at approximately 1/500th the computational cost, thus enabling its use in high-throughput computational workflows for the accurate screening of carrier mobilities, lifetimes, and thermoelectric power.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2021

TOUGHREACT V4.12

TOUGHREACT V4.12 is a 3-D reactive transport code that handles to non-isothermal, multiphase/multicomponent fluid flow, heat transport, aqueous and gaseous species advection-diffusion, and equilibrium/kinetic water-gas-rock-biological reactions. TOUGHREACT V4.12 is based on TOUGHREACT V3.3, with several new features including: an option to compute activity coefficients using the Pitzer ion interaction model; implementation of ECO2N V2.0 for temperatures up to 300 C; options to simulate forward and reverse osmosis, including 2D Poiseuille flow; addition of EOS8 and revisions for EOS5 and EWASG with H2(g); addition of gas species decay, various new output formats and time step control options; many bug fixes.

Spycher, Nicolas↗

DOE OSTI2025

Summer Aerosol and Trace Gas Observations in Houston, Texas Using an Adaptable Mobile Facility

An aerosol container featuring a shared inlet system was deployed to Houston, Texas in July 2022, enabling direct, high-time-resolution in situ measurements of aerosols and trace gases. The internal rack system and floorplan was designed for adaptable modularity to elucidate aerosol physicochemical processes at fine scales. The design allowed for the deployment of a core instrument suite and additional customized research grade instruments. A heterogeneous mixture of aerosols was observed during three regimes: (1) intermittent black carbon (BC) and diurnal variations in aerosol chemical composition, (2) observed particle growth associated with SO 2 , (3) transported supermicron dust. The high variability of observed particles and gases in high time resolution indicated a complex urban area with multiple local and regional sources and processes. Particle growth rates of 7–16 nm/hr were observed for submicron particles during periods when SO 2 was >0.5 ppbv. Two periods of multi-day long-range transport events of dust from the African Sahara were observed in the supermicron and submicron particle modes with total mass concentrations up to 30 μg m −3 . Aerosol scattering angstrom exponents and extinction coefficients (B ext ) increased with humidity as a function of particle composition. The measurements demonstrate collaborative capabilities that can be used to increase observations of aerosol processing, microphysical and optical properties, internal mixing state, and supermicron aerosol that are not parameterized or missing in global Earth energy system models.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2023

Beam Energy Dependence of the Linear and Mode-Coupled Flow Harmonics Using the a Multi-Phase Transport Model

In the framework of the A Multi-Phase Transport (AMPT) model, the multi-particle azimuthal cumulant method is used to calculate the linear and mode-coupled contributions to the quadrangular flow harmonic (v4) and the mode-coupled response coefficient as functions of centrality in Au+Au collisions at sNN = 200, 39, 27 and 19.6 GeV. This study indicates that the linear and mode-coupled contributions to v4 are sensitive to beam energy change. Nevertheless, the correlations between different-order flow symmetry planes and the mode-coupled response coefficients show weak beam energy dependence. In addition, the presented results suggest that the experimental measurements that span a broad range of beam energies can be an additional constraint for the theoretical model calculations.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1972

Riding and handling qualities of light aircraft: A review and analysis

Design procedures and supporting data necessary for configuring light aircraft to obtain desired responses to pilot commands and gusts are presented. The procedures employ specializations of modern military and jet transport practice where these provide an improvement over earlier practice. General criteria for riding and handling qualities are discussed in terms of the airframe dynamics. Methods available in the literature for calculating the coefficients required for a linearized analysis of the airframe dynamics are reviewed in detail. The review also treats the relation of spin and stall to airframe geometry. Root locus analysis is used to indicate the sensitivity of airframe dynamics to variations in individual stability derivatives and to variations in geometric parameters. Computer programs are given for finding the frequencies, damping ratios, and time constants of all rigid body modes and for generating time histories of aircraft motions in response to control inputs. Appendices are included presenting the derivation of the linearized equations of motion; the stability derivatives; the transfer functions; approximate solutions for the frequency, damping ratio, and time constants; an indication of methods to be used when linear analysis is inadequate; sample calculations; and an explanation of the use of root locus diagrams and Bode plots.

Smetana, F. O.↗

NASA NTRS1979

Mathematical model investigation of long-term transport of ocean-dumped sewage sludge related to remote sensing

An existing, three-dimensional, Eulerian-Lagrangian finite-difference model was modified and used to examine the transport processes of dumped sewage sludge in the New York Bight. Both in situ and laboratory data were utilized in an attempt to approximate model inputs such as mean current speed, horizontal diffusion coefficients, particle size distributions, and specific gravities. The results presented are a quantitative description of the fate of a negatively buoyant sewage sludge plume resulting from continuous and instantaneous barge releases. Concentrations of the sludge near the surface were compared qualitatively with those remotely sensed. Laboratory study was performed to investigate the behavior of sewage sludge dumping in various ambient density conditions.

Kuo, C. Y.↗

NASA NTRS1981

Transport properties for a mixture of the ablation products C, C2, and C3

The ablation of carbon-phenolic heat shields upon entry into the atmosphere of one of the outer planets leads to the injection of large amounts of C, C2, and C3 into the shock layer. These species must be included in the calculation of transport properties in the shock layer. The kinetic theory of gases has been used to obtain accurate results for the transport properties of monatomic carbon. The Hulburt-Hirschelder potential, the most accurate general purpose atom-atom potential for states with an attractive minimum, was used to represent such states and repulsive states were represented by fitting quantum mechanical potential energy curves with the exponential repulsive potential. These results were orientation averaged according to the peripheral force model to obtain transport collision integrals for the C-C2 and C2-C2 interaction. Results for C3 were obtained by ignoring the presence of the central carbon atom. The thermal conductivity, viscosity, and diffusion coefficients for pure C, C2, and C3, and for mixtures of these gases, were then calculated from 1000 K - 25,000 K.

Biolsi, L.↗

NASA NTRS1995

HZETRN: Description of a free-space ion and nucleon transport and shielding computer program

The high-charge-and energy (HZE) transport computer program HZETRN is developed to address the problems of free-space radiation transport and shielding. The HZETRN program is intended specifically for the design engineer who is interested in obtaining fast and accurate dosimetric information for the design and construction of space modules and devices. The program is based on a one-dimensional space-marching formulation of the Boltzmann transport equation with a straight-ahead approximation. The effect of the long-range Coulomb force and electron interaction is treated as a continuous slowing-down process. Atomic (electronic) stopping power coefficients with energies above a few A MeV are calculated by using Bethe's theory including Bragg's rule, Ziegler's shell corrections, and effective charge. Nuclear absorption cross sections are obtained from fits to quantum calculations and total cross sections are obtained with a Ramsauer formalism. Nuclear fragmentation cross sections are calculated with a semiempirical abrasion-ablation fragmentation model. The relation of the final computer code to the Boltzmann equation is discussed in the context of simplifying assumptions. A detailed description of the flow of the computer code, input requirements, sample output, and compatibility requirements for non-VAX platforms are provided.

Wilson, John W.↗

DOE OSTI2026

Diameter-dependent multiple proton jumps dictate hydronium and hydroxide transport in carbon nanotubes

Nanofluidic channels impose extreme confinement on water, giving rise to unusual transport phenomena of the liquid. However, how the transport of hydroxide and hydronium ions is influenced by such confinement is still not fully understood. This study employs machine learning-accelerated simulations, based on the SCAN density functional, to investigate proton transfer dynamics in CNTs of varying diameters (0.8 nm to 2.8 nm). The extreme confinement of water inside a 0.8 nm CNT not only enhances the probability of multiple consecutive proton jumps, but also reverses the relative diffusion coefficient of hydronium and hydroxide ions in bulk water. In CNTs with diameters larger than 0.8 nm, hydronium diffuses slightly faster than in bulk water, whereas hydroxide diffusion slows because of its localization near CNT walls, hindering multiple proton jumps. This work highlights the significant impact of nanoscale confinement on proton transfer dynamics, with implications for designing nanoscale systems with controlled proton transport.

Chemistry↗

DOE OSTI2025

Global Simulations of Phase State and Equilibration Time Scales of Secondary Organic Aerosols with GEOS-Chem

The phase state of secondary organic aerosols (SOA) can range from liquid through amorphous semisolid to glassy solid, which is important to consider as it influences various multiphase processes including SOA formation and partitioning, multiphase chemistry, and cloud activation. In this study, we simulate the glass transition temperature and viscosity of SOA over the globe using the global chemical transport model, GEOS-Chem. The simulated spatial distributions show that SOA at the surface exist as liquid over equatorial regions and oceans, semisolid in the midlatitude continental regions, and glassy solid over lands with low relative humidity. The predicted SOA viscosities are mostly consistent with the available measurements. In the free troposphere, SOA particles are mostly predicted to be semisolid at 850 hPa and glassy solid at 500 hPa, except over tropical regions including Amazonia, where SOA are predicted to be low viscous. Phase state also exhibits seasonal variation with a higher frequency of semisolid and solid particles in winter compared to warmer seasons. We calculate equilibration time scales of SOA partitioning (τ eq ) and effective mass accommodation coefficient (α eff ), indicating that τ eq is shorter than the chemical time step of GEOS-Chem of 20 min and αeff is close to unity for most locations at the surface level, supporting the application of equilibrium SOA partitioning. However, τ eq is prolonged and α eff is lowered over drylands and most regions in the upper troposphere, suggesting that kinetically limited growth would need to be considered for these regions in future large-scale model studies.

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