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At least 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Leaf-level physiological strategies related to productivity and plasticity of Populus in the Southeastern United States

Introduction: Populus and its hybrids are attractive bioenergy crops and the southeastern United States has broad ability to supply bioenergy markets with woody biomass. Breeding and hybridization have led to superior eastern cottonwood (Populus deltoides W. Bartram ex Marshall) and hybrid poplars adapted to a wide variety of site types not suited for agricultural production. In order to maximize productivity and minimize inputs, genotypes need to efficiently use available site resources and tolerate environmental stresses. In addition, we need to determine plasticity of traits and their coordination across sites to select traits that will broadly characterize genotypes. Therefore, our study objectives were to determine (1) which leaf traits were correlated with growth, (2) if traits and genotypes exhibited significant plasticity across sites, and (3) how traits were coordinated within and across sites and Populus taxa. Methods: We measured trees at two sites in northeastern Mississippi, United States: one upland and one alluvial terrace site. Genotypes included eastern cottonwoods as well as F 1 crosses of eastern cottonwood and P. maximowiczii (Henry), P. nigra (L.) and P. trichocarpa (Torr. & Gray). Results: We found that sites differed in which leaf traits were correlated with productivity; with water use efficiency specifically being positively correlated with growth at an alluvial terrace site, but negatively correlated with growth at an upland site. Tree height growth, leaf isotope composition (δ 13 C and δ 15 N), as well as leaf mass per area (LMA) exhibited the least plasticity across sites, while physiological gas exchange parameters and leaf nitrogen concentration exhibited the highest plasticity. Broadly across taxa, leaf carbon isotope ratios were correlated with intrinsic water use efficiency, and stomatal conductance was positively correlated with photosynthetic nitrogen use efficiency across sites, while leaf nitrogen isotope ratios exhibited contrasting relationships with leaf nitrogen concentration. Discussion: Overall, these results allow us to refine selections of productive genotypes based on site conditions and site-specific relationships with physiological parameters to better match Populus taxa with sites and landowner objectives.

bioenergy feedstocks↗
NASA NTRS2003

Density Anomalies in the Mantle and the Gravitational Core-Mantle Interaction

Seismic studies suggest that the bulk of the mantle is heterogeneous, with density variations in depth as well as in horizontal directions (latitude and longitude). This density variation produces a three- dimensional gravity field throughout the Earth. On the other hand, the core density also varies in both time and space, due to convective core flow. Consequently, the fluid outer core and the solid mantle interact gravitationally due to the mass anomalies in both regions. This gravitational core-mantle interaction could play a significant role in exchange of angular momentum between the core and the mantle, and thus the change in Earth's rotation on time scales of decades and longer. Aiming at estimating the significance of the gravitational core-mantle interaction on Earth's rotation variation, we introduce in our MoSST core dynamics model a heterogeneous mantle, with a density distribution derived from seismic results. In this model, the core convection is driven by the buoyancy forces. And the density variation is determined dynamically with the convection. Numerical simulation is carried out with different parameter values, intending to extrapolate numerical results for geophysical implications.

Kuang, Weijia↗
NASA NTRS1995

Self-consistent solar wind-LISM interaction including neutrals: A 4-fluid model

We investigate the interaction between the heliosphere and local interstellar medium, including charge-exchange self-consistently between the neutral and ionized components. The system is modelled as consisting of neutral hydrogen, protons and electrons. The electrons are assumed to contribute to the dynamics via a pressure that is everywhere equal to the proton pressure. The fluid equations for the protons and hydrogen are solved self-consistently, assuming the two species interact only via charge exchange. The protons are treated as a single isotropic fluid. The hydrogen is decomposed into three isotropic fluids: hydrogen of interstellar origin with characteristic temperature of approximately 104 K, hydrogen produced via charge exchange in the post-shock solar wind, with characteristic temperature of approximately 105 K, and hydrogen produced via charge exchange in the supersonic solar wind, relatively cool but expanding radially outward with the solar wind speed. Two-Dimensional time-dependent numerical simulations of this system are performed to calculate the number density, temperature and bulk velocity of neutral hydrogen and plasma everywhere in the heliosphere. These quantities are compared to relevant solar wind observations. Implications for the pick-up process in the supersonic solar wind, as well as heating and deceleration of the wind, are addressed.

Williams, L. L.↗
DOE OSTI2014

Exchange integrals in magnetoelectric hexagonal ferrite (SrCo{sub 2}Ti{sub 2}Fe{sub 8}O{sub 19}): A density functional study

The exchange integrals in magnetoelectric hexagonal ferrite SrCo{sub 2}Ti{sub 2}Fe{sub 8}O{sub 19} have been calculated by using density functional theory. To get 10 inter-sublattice and 3 intra-sublattice exchange integrals, the electronic structures and total energies of 20 spin arrangements have been calculated with General Gradient Approximation (GGA) + U method. The dependence of exchange integrals on U has been studied. The comparison between the exchange integrals in SrFe{sub 12}O{sub 19} and those in SrCo{sub 2}Ti{sub 2}Fe{sub 8}O{sub 19} shows that substitution of Co and Ti decreases the most interactions involving the 12 k sites. The investigation based on our exchange integrals indicates that magnetic interaction between R and S blocks reduces significantly in SrCo{sub 2}Ti{sub 2}Fe{sub 8}O{sub 19}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

A fusion of the Bacteroides fragilis ferrous iron import proteins reveals a role for FeoA in stabilizing GTP-bound FeoB

Iron is an essential element for nearly all organisms, and under anoxic and/or reducing conditions, Fe 2+ is the dominant form of iron available to bacteria. The ferrous iron transport (Feo) system is the primary prokaryotic Fe 2+ import machinery, and two constituent proteins (FeoA and FeoB) are conserved across most bacterial species. However, how FeoA and FeoB function relative to one another remains enigmatic. In this work, we explored the distribution of feoAB operons encoding a fusion of FeoA tethered to the N-terminal, G-protein domain of FeoB via a connecting linker region. We hypothesized that this fusion poises FeoA to interact with FeoB to affect function. To test this hypothesis, we characterized the soluble NFeoAB fusion protein from Bacteroides fragilis, a commensal organism implicated in drug-resistant infections. Using X-ray crystallography, we determined the 1.50-Å resolution structure of BfFeoA, which adopts an SH3-like fold implicated in protein–protein interactions. Using a combination of structural modeling, small-angle X-ray scattering, and hydrogen–deuterium exchange mass spectrometry, we show that FeoA and NFeoB interact in a nucleotide-dependent manner, and we mapped the protein–protein interaction interface. Finally, using guanosine triphosphate (GTP) hydrolysis assays, we demonstrate that BfNFeoAB exhibits one of the slowest known rates of Feo-mediated GTP hydrolysis that is not potassium-stimulated. Importantly, truncation of FeoA from this fusion demonstrates that FeoA–NFeoB interactions function to stabilize the GTP-bound form of FeoB. Taken together, our work reveals a role for FeoA function in the fused FeoAB system and suggests a function for FeoA among prokaryotes.

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

Observing and preventing rubidium runaway in a direct-infusion xenon-spin hyperpolarizer optimized for high-resolution hyper-CEST (chemical exchange saturation transfer using hyperpolarized nuclei) NMR

Xenon is well known to undergo host-guest interactions with proteins and synthetic molecules. As xenon can also be hyperpolarized by spin exchange optical pumping, allowing the investigation of highly dilute systems, it makes an ideal nuclear magnetic resonance probe for such host molecules. The utility of xenon as a probe can be further improved using Chemical Exchange Saturation Transfer using hyperpolarized nuclei (Hyper-CEST), but for highly accurate experiments requires a polarizer and xenon infusion system optimized for such measurements. We present the design of a hyperpolarizer and xenon infusion system specifically designed to meet the requirements of Hyper-CEST measurements. One key element of this design is preventing rubidium runaway, a chain reaction induced by laser heating that prevents efficient utilization of high photon densities. Using thermocouples positioned along the pumping cell we identify the sources of heating and conditions for rubidium runaway to occur. We then demonstrate the effectiveness of actively cooling the optical cell to prevent rubidium runaway in a compact setup. This results in a 2–3-fold higher polarization than without cooling, allowing us to achieve a polarization of 25% at continuous flow rates of 9 ml/min of {sup 129}Xe. The simplicity of this design also allows it to be retrofitted to many existing polarizers. Combined with a direction infusion system that reduces shot-to-shot noise down to 0.56% we have captured Hyper-CEST spectra in unprecedented detail, allowing us to completely resolve peaks separated by just 1.62 ppm. Due to its high polarization and excellent stability, our design allows the comparison of underlying theories of host-guest systems with experiment at low concentrations, something extremely difficult with previous polarizers.

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

First Observation of 𝑃-odd 𝛾 Asymmetry in Polarized Neutron Capture on Hydrogen

Here, we report the first observation of the parity-violating gamma-ray asymmetry 𝐴$^{𝑛⁢𝑝}_{𝛾}$ in neutron-proton capture using polarized cold neutrons incident on a liquid parahydrogen target at the Spallation Neutron Source at Oak Ridge National Laboratory. 𝐴$^{𝑛⁢𝑝}_{𝛾}$ isolates the Δ⁢𝐼 =1, 3 𝑆 1 → 3 𝑃 1 component of the weak nucleon-nucleon interaction, which is dominated by pion exchange and can be directly related to a single coupling constant in either the DDH meson exchange model or pionless effective field theory. We measured 𝐴$^{𝑛⁢𝑝}_{𝛾}$=[−3.0±1.4⁢(stat)±0.2⁢(syst)]×10 −8 , which implies a DDH weak 𝜋⁢𝑁⁢𝑁 coupling of ℎ$^1_𝜋$=[2.6±1.2⁢(stat)±0.2⁢(syst)]×10 −7 and a pionless EFT constant of 𝐶 3 𝑆 1 → 3 𝑃 1 /𝐶 0 =[−7.4±3.5⁢(stat)±0.5⁢(syst)]×10 −11 MeV −1 . We describe the experiment, data analysis, systematic uncertainties, and implications of the result.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Benchmarking the performance of density functional theory and point charge force fields in their description of sI methane hydrate against diffusion Monte Carlo

High quality reference data from diffusion Monte Carlo calculations are presented for bulk sI methane hydrate, a complex crystal exhibiting both hydrogen-bond and dispersion dominated interactions. The performance of some commonly used exchange-correlation functionals and all-atom point charge force fields is evaluated. Our results show that none of the exchange-correlation functionals tested are sufficient to describe both the energetics and the structure of methane hydrate accurately, while the point charge force fields perform badly in their description of the cohesive energy but fair well for the dissociation energetics. By comparing to ice I{sub h}, we show that a good prediction of the volume and cohesive energies for the hydrate relies primarily on an accurate description of the hydrogen bonded water framework, but that to correctly predict stability of the hydrate with respect to dissociation to ice I{sub h} and methane gas, accuracy in the water-methane interaction is also required. Our results highlight the difficulty that density functional theory faces in describing both the hydrogen bonded water framework and the dispersion bound methane.

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

Covariant Spectator Theory of np scattering: Isoscalar interaction currents

Using the Covariant Spectator Theory (CST), one boson exchange (OBE) models have been found that give precision fits to low energy $np$ scattering and the deuteron binding energy. The boson-nucleon vertices used in these models contain a momentum dependence that requires a new class of interaction currents for use with electromagnetic interactions. Current conservation requires that these new interaction currents satisfy a two-body Ward-Takahashi (WT), and using principals of {\it simplicity\/} and {\it picture independence\/}, these currents can be uniquely determined. The results lead to general formulae for a two-body current that can be expressed in terms of relativistic $np$ wave functions, ${\it \Psi}$, and two convenient truncated wave functions, ${\it \Psi}^{(2)}$ and $\widehat {\it \Psi}$, which contain all of the information needed for the explicit evaluation of the contributions from the interaction current. These three wave functions can be calculated from the CST bound or scattering state equations (and their off-shell extrapolations). A companion paper uses this formalism to evaluate the deuteron magnetic moment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Effect of intervalley interaction on band topology of commensurate graphene/EuO heterostructures

Recent experiments demonstrating proximity induced ferromagnetism in graphene motivate this study of commensurate graphene/EuO heterostructures. Due to the commensurability of graphene with the (111)-EuO layer, graphene’s Dirac points are mapped to the Γ point of the commensurate Brillouin zone. The Eu atoms not only induce proximity exchange on the graphene layer, but they also introduce intervalley interactions resulting in a nonlinear dispersion at Γ. Here, we develop a model Hamiltonian, consistent with the lattice symmetries, that includes proximity induced exchange splitting, spin-orbit coupling, and intervalley interactions with parameters fitted to ab initio calculations. The intervalley interaction opens up a trivial gap preventing the system from crossing into a nontrivial state. The model Hamiltonian is analyzed to determine the conditions under which the heterostructures can exhibit topologically nontrivial bands.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Report on the Joint EU-US Workshop on Microbial Community Dynamics: Cooperation and Competition

The European Commission (EC)-United States (US) Task Force on Biotechnology Research has a longstanding joint Working Group on Biotechnology for the Environment whose mission is to foster collaborations between researchers in the European Union (EU) and US in the field of environmental biotechnology. A special focus of the Working Group is to increase scientific interchange between early career scientists in the US and EU. Such interactions initiate a foundation of respect and trust needed to develop long-term collaborations. In order to realize the full potential for the application of modern technologies to obtain a sustainable biosphere, it is vital to create conduits for knowledge exchange among scientists worldwide engaged in environmental microbial biotechnology research. Since its formation in 1994, the Working Group has organized many activities for early career scientists designed to promote this scientific exchange, including two week courses with hands-on research experience, intensive workshops of two or three days, and research scholar exchanges of one to six months. These interactions are focused on environmental problems that respect no international boundaries.

09 BIOMASS FUELS↗
DOE OSTI2021

Magnetic Materials: Chiral Spin Textures in Amorphous Iron–Germanium Thick Films (Adv. Mater. 8/2021)

Topological solitary fields, such as magnetic and polar skyrmions, are envisioned to revolutionize microelectronics. These configurations have been stabilized in solid-state materials with a global inversion symmetry breaking, which translates in magnetic materials into a vector spin exchange known as the Dzyaloshinskii–Moriya interaction (DMI), as well as spin chirality selection and isotropic solitons. This work reports experimental evidence of 3D chiral spin textures, such as helical spins and skyrmions with different chirality and topological charge, stabilized in amorphous Fe–Ge thick films. These results demonstrate that structurally and chemically disordered materials with a random DMI can resemble inversion symmetry broken systems with similar magnetic properties, moments, and states. In conclusion, disordered systems are distinguished from systems with global inversion symmetry breaking by their degenerate spin chirality that allows for forming isotropic and anisotropic topological spin textures at remanence, while offering greater flexibility in materials synthesis, voltage, and strain manipulation.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Current‐Driven Switching of Néel Vector of an Antiferromagnetic Insulator Thin Film

Manipulation of antiferromagnetic (AFM) materials as active elements provides a crucial combination of electrical, thermal, and magnetic properties for spintronics. This study shows how the spin current generated in heavy metal is induced by spin‐orbit torque into an adjacent AFM insulator. The bulk unpinned spins of the AFM layer drive a spin current that is transmitted to the top ferromagnet. This mechanism allows the electrical control of the exchange bias, coercive field, and blocking temperature of the system. Further support is provided by a model calculation that quantitatively describes the effect of the spin current injection into the AFM.

antiferromagnetism↗
DOE OSTI2014

Two-dimensional lattice gauge theories with superconducting quantum circuits

A quantum simulator of U(1) lattice gauge theories can be implemented with superconducting circuits. This allows the investigation of confined and deconfined phases in quantum link models, and of valence bond solid and spin liquid phases in quantum dimer models. Fractionalized confining strings and the real-time dynamics of quantum phase transitions are accessible as well. Here we show how state-of-the-art superconducting technology allows us to simulate these phenomena in relatively small circuit lattices. By exploiting the strong non-linear couplings between quantized excitations emerging when superconducting qubits are coupled, we show how to engineer gauge invariant Hamiltonians, including ring-exchange and four-body Ising interactions. We demonstrate that, despite decoherence and disorder effects, minimal circuit instances allow us to investigate properties such as the dynamics of electric flux strings, signaling confinement in gauge invariant field theories. The experimental realization of these models in larger superconducting circuits could address open questions beyond current computational capability.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

The complete Brans–Dicke theories

Given that the simple wave equation of Brans–Dicke theory for the scalar field is preserved, we have investigated, through exhaustively analyzing the Bianchi identities, the consistent theories which violate the exact energy conservation equation. It is found that only three theories exist which are unambiguously determined from consistency, without imposing arbitrary functions by hand. Each of these theories possesses a specific interaction term which controls the energy exchange between the scalar field and ordinary matter. The theories contain new parameters (integration constants from the integration procedure) and when these are switched-off, Brans–Dicke theory emerges. As usually, the vacuum theories can be defined from the complete Brans–Dicke theories when the matter energy–momentum tensor vanishes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Effects of spatial variability in vegetation phenology, climate, landcover, biodiversity, topography, and soil property on soil respiration across a coastal ecosystem

Coastal terrestrial-aquatic interfaces (TAIs) are crucial contributors to global biogeochemical cycles and carbon exchange. A systematic evaluation of the interaction between coastal catchment properties and carbon dioxide (CO2) emission by soil respiration is significant for assessing carbon dynamics and predicting the future trajectory of atmospheric CO2 concentrations in coastal TAIs. The soil CO2 efflux in these transition zones is however poorly understood due to the high spatiotemporal dynamics of TAIs, as various sub-ecosystems in this region are compressed and expanded by complex influences of tides, changes in river levels, climate, and land use. We focus on the Chesapeake Bay region to (i) investigate the spatial heterogeneity of the coastal ecosystem and identify spatial zones with similar environmental characteristics based on the spatial data layers, including vegetation index (kNDVI), climate, landcover, diversity, topography, soil property, and relative tidal elevation; (ii) understand the primary driving factors affecting soil respiration within sub-ecosystems of the coastal ecosystem. Specifically, we employed hierarchical clustering analysis to identify spatial regions with distinct environmental characteristics, followed by the determination of main driving factors using Random Forest regression and SHapley Additive exPlanations. Maximum and minimum temperature are the main drivers common to all sub-ecosystems, while each region also has additional unique major drivers that differentiate them from one another. Precipitation exerts an influence on vegetated lands, while soil pH value holds importance specifically in forested lands. In croplands characterized by high clay content and low sand content, the significant role is attributed to bulk density. Wetlands demonstrate the importance of both elevation and sand content, with clay content being more relevant in non-inundated wetlands than in inundated wetlands. The topographic wetness index significantly contributes to the mixed vegetation areas, including shrub, grass, pasture, and forest. Additionally, our research reveals that dense vegetation land covers and urban/developed areas exhibit distinct soil property drivers. Overall, there is no one-size-fits-all approach to modeling carbon fluxes in coastal TAIs, and our study highlights the importance of further research and monitoring practices to improve our understanding of carbon dynamics and promote the sustainable management of coastal TAIs.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2013

Nanostructured dimagnesium manganese oxide (Spinel): Control of size, shape and their magnetic and electro catalytic properties

Tetravalent Mn based ternary oxides are of interest as they are important electrode materials. Dimagnesium manganate (Mg{sub 2}MnO{sub 4}) is one Mn(IV) containing oxide which has been of interest. Nanostructures of the above oxide (spinel) have been obtained by the thermal decomposition of nanostructured metal oxalate precursor at 500 Degree-Sign C. The size and anisotropy of the oxide nanostructures was controlled by choosing appropriate decomposition temperature of the oxalate precursor. Mg{sub 2}MnO{sub 4} nanorods were obtained at low temperature (500 Degree-Sign C), formed by aligned nanoparticles of size{approx}8-10 nm. These nanoparticles show Curie-Weiss behavior with Weiss constant (14 K). Below {approx}50 K there is a small deviation resulting in a negative Weiss constant (-7.36 K) indicating exchange cross over (from ferromagnetic like interactions to antiferromagnetic interactions). The high temperature magnetic moment corresponds to Mn (IV). Electrochemical experiments show that nanostructured Mg{sub 2}MnO{sub 4} is an efficient anode material for oxygen evolution reaction with a current density of 14 mA/cm{sup 2}. The stability of the anode over several cycles of oxidation and reduction is highly encouraging. - Graphical abstract: Nanostructured dimagnesium manganese with efficient electrocatalytic property synthesized by reverse micellar route. Highlights: Black-Right-Pointing-Pointer Mg{sub 2}MnO{sub 4} nanorods were synthesized by reverse micellar route. Black-Right-Pointing-Pointer Anisotropy of oxalate rods retained in oxides nanorods. Black-Right-Pointing-Pointer Nanorods show good catalytic behavior towards oxygen evolution reaction.

36 MATERIALS SCIENCE↗