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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

Photoionization of iodine atoms: Angular distributions and relative partial photoionization cross-sections in the energy region 11.0-23.0 eV

Relative partial photoionization cross-sections and angular distribution parameters, {beta}, have been measured for the first, I{sup +}({sup 3}P{sub 2})<-I({sup 2}P{sub 3/2}), and fourth, I{sup +}({sup 1}D{sub 2})<-I({sup 2}P{sub 3/2}), (5p){sup -1} photoelectron (PE) bands of atomic iodine, by performing angle-resolved constant-ionic-state (CIS) measurements on these PE bands in the photon energy range 11.0-23.0 eV. Three Rydberg series, two ns and one nd series, which converge to the I{sup +} {sup 3}P{sub 1} limit at 11.33 eV and four Rydberg series, two ns and two nd series, which converge to the I{sup +} {sup 1}D{sub 2} limit at 12.15 eV were observed in the first PE band CIS spectra. The fourth band CIS spectrum showed structure in the 12.9-14.1eV photon energy range, which is also seen in the first band CIS spectra. This structure arises from excitation to ns and nd Rydberg states that are parts of series converging to the I{sup +} {sup 1}S{sub 0} limit we reported on earlier, as well as 5s{yields}5p excitations in the photon energy range 17.5-22.5 eV. These atomic iodine CIS spectra show reasonably good agreement with the equivalent spectra obtained for atomic bromine. The {beta}-plots for the first PE band recorded up to the I{sup +} {sup 3}P{sub 1} and I{sup +} {sup 1}D{sub 2} limits only show resonances corresponding to some of the 5p{yields}nd excitations observed in the first band CIS spectra scanned to the I{sup +} {sup 1}D{sub 2} limit (12.15 eV). These plots are interpreted in terms of an angular momentum transfer model with the positive values of {beta} obtained on resonances corresponding to parity allowed j{sub t}=1 and 3 channels and the off-resonance negative {beta} values corresponding to parity unfavored channels, where j{sub t} is the quantum number for angular momentum transfer between the molecule, and the ion and photoelectron. The {beta}-plots recorded for iodine are significantly different from those obtained for atomic bromine. Comparison of the experimental CIS spectra and {beta}-plots with available theoretical results highlights the need for higher level calculations which include factors such as configuration interaction in the initial and final states, relativistic effects including spin-orbit interaction, and autoionization via resonant Rydberg states.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2010

Alignments, additivity, and signature inversion in odd-odd {sup 170}Ta: A comprehensive high-spin study

High-spin states (I < or approx. 50(Planck constant/2pi)) of the odd-odd nucleus {sup 170}Ta have been investigated with the {sup 124}Sn({sup 51}V,5n) reaction. The resolving power of Gammasphere has allowed for the observation of eleven rotational bands (eight of which are new) and over 430 transitions (approx350 of which are new) in this nucleus. Many interband transitions have been observed such that the relative spins and excitation energies of the 11 bands have been established. This is an unusual circumstance in an odd-odd study. Configurations have been assigned to most of these bands based upon features such as alignment properties, band crossings, B(M1)/B(E2) ratios, and the additivity of Routhians. A systematic study of the frequency at which normal signature ordering occurs in the pih{sub 9/2}nui{sub 13/2} band has been performed and it is found that its trend is opposite to that observed in the pih{sub 11/2}nui{sub 13/2} bands. A possible interpretation of these trends is discussed based on a proton-neutron interaction.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Frustrated Heisenberg J 1 – J 2 model within the stretched diamond lattice of LiYbO 2

We investigate the magnetic properties of LiYbO 2 , containing a three-dimensionally frustrated, diamondlike lattice via neutron scattering, magnetization, and heat capacity measurements. The stretched diamond network of Yb 3+ ions in LiYbO 2 enters a long-range incommensurate, helical state with an ordering wave vector k = (0.384,±0.384,0) that “locks-in” to a commensurate k = (1/3,±1/3,0) phase under the application of a magnetic field. The spiral magnetic ground state of LiYbO 2 can be understood in the framework of a Heisenberg J 1 –J 2 Hamiltonian on a stretched diamond lattice, where the propagation vector of the spiral is uniquely determined by the ratio of J 2 /|J 1 |. Here, the pure Heisenberg model, however, fails to account for the relative phasing between the Yb moments on the two sites of the bipartite lattice, and this detail as well as the presence of an intermediate, partially disordered, magnetic state below 1 K suggests interactions beyond the classical Heisenberg description of this material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Astrophysical Equation-of-State Constraints on the Color-Superconducting Gap

We demonstrate that astrophysical constraints on the dense-matter equation of state place an upper bound on the color-superconducting gap in dense matter above the transition from nuclear matter to quark matter. Pairing effects in the color-flavor locked quark matter phase increase the pressure at high density, and if this effect is sufficiently large then the requirements of causality and mechanical stability make it impossible to reach such a pressure in a way that is consistent with what is known at lower densities. The intermediate-density equation of state is inferred by considering extensions of chiral effective field theory to neutron star densities, and conditioning these using current astrophysical observations of neutron star radius, maximum mass, and tidal deformability (PSR J⁢0348+0432, PSR J1624-2230, PSR J⁢0740+6620, GW170817). At baryon number chemical potential μ = 2.6 GeV we find a 95% upper limit on the color-flavor locked pairing gap Δ of 457 MeV using overly conservative assumptions and 216 MeV with more reasonable assumptions. Furthermore, this constraint may be strengthened by future astrophysical measurements as well as by future advances in high-density QCD calculations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Method and apparatus for executing a shift in a hybrid transmission

A method for executing a transmission shift in a hybrid transmission including first and second electric machines includes executing a shift-through-neutral sequence from an initial transmission state to a target transmission state including executing an intermediate shift to neutral. Upon detecting a change in an output torque request while executing the shift-through-neutral sequence, possible recovery shift paths are identified. Available ones of the possible recovery shift paths are identified and a shift cost for each said available recovery shift path is evaluated. The available recovery shift path having a minimum shift cost is selected as a preferred recovery shift path and is executed to achieve a non-neutral transmission state.

47 OTHER INSTRUMENTATION↗
DOE OSTI2017

Numerical Study of Quantum Hall Bilayers at Total Filling ν T = 1 : A New Phase at Intermediate Layer Distances

We view the phase diagram of quantum Hall bilayer systems with total filing ν T = 1/2 + 1/2 of the lowest Landau level as a function of layer distances d . Based on numerical exact diagonalization calculations, we obtain three distinct phases, including an exciton superfluid phase with spontaneous interlayer coherence at small d , a composite Fermi liquid at large d , and an intermediate phase for 1.1 < d/l B < 1.8 (l B is the magnetic length). The transition from the exciton superfluid to the intermediate phase is identified by (i) a dramatic change in the Berry curvature of the ground state under twisted boundary conditions on the two layers and (ii) an energy level crossing of the first excited state. The transition from the intermediate phase to the composite Fermi liquid is identified by the vanishing of the exciton superfluid stiffness. Moreover, from our finite-size study, the energy cost of transferring one electron between the layers shows an even-odd effect and possibly extrapolates to a finite value in the thermodynamic limit, indicating the enhanced intralayer correlation. Our identification of an intermediate phase and its distinctive features shed new light on the theoretical understanding of the quantum Hall bilayer system at total filling ν T = 1 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Solid-state synthesis, structure and properties of a novel open-framework cadmium selenite bromide: [Cd{sub 10}(SeO{sub 3}){sub 8}Br{sub 4}]·HBr·H{sub 2}O

A novel open-framework cadmium selenite bromide, [Cd{sub 10}(SeO{sub 3}){sub 8}Br{sub 4}]·HBr·H{sub 2}O (1), has been obtained by a solid-state reaction at 450 °C, and the structure has been determined by single-crystal X-ray diffraction analysis. Compound 1 crystallizes in Pbcm of the orthorhombic system: a=10.882(3), b=16.275(5), c=18.728(6) Å, V=3317(2) Å{sup 3}, R1/wR2=0.0411/0.0659. Compound 1 is characteristic of a novel 3-D open-framework structure, composing {sub ∞}{sup 2}[CdSeO{sub 3}] layers and the pillars of edge-shared CdO{sub 3}Br{sub 2} square pyramids. The lattice water molecules and the HBr molecules locate in the voids of the framework. Optical absorption spectrum of 1 reveals the presence of an optical gap of 1.65 eV. Solid-state photoluminescent study indicates that compound 1 exhibits strong violet emission. TG–DSC measurement shows that compound 1 is thermally stable up to 200 °C. - Graphical abstract: A metal selenite halide has been synthesized and features a 3-D open-framework structure, composing edge-shared CdO{sub 8} decahedra and pillars of edge-sharing pentahedra. UV–vis, TG–DSC and luminescent measurements are also reported. Highlights: • This paper reports a novel cadmium selenite bromide obtained by an intermediate-temperature solid-state reaction. • The title compound is characteristic of a novel 3-D open-framework structure, composing {sub ∞}{sup 2}[CdSeO{sub 3}] layers and the pillars of edge-shared CdO{sub 3}Br{sub 2} square pyramids. • The title compound is thermally stable up to 200 °C. • The title compound has an optical gap of 1.65 eV and exhibits strong violet emission.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Phosphoserine Charge State Drives Ion Condensation and Spatial Polyamine Presentation in Multirepeat Silaffin

Diatom silaffins direct silica biomineralization through heavily post-translationally modified repeat domains, yet how these modifications reshape the multirepeat conformational ensemble remains unknown. We report all-atom MD simulations of a 195-residue construct spanning repeats R1–R7 of Sil1p from Cylindrotheca fusiformis, carrying the full complement of native PTMs: phosphoserine (pSer), long-chain polyamines (LCPA), dimethyllysine (MLY), and trimethylhydroxylysine phosphate (TPL). We simulated three variants (Native, P1/singly deprotonated phosphate, and P2/doubly deprotonated phosphate) at two NaCl concentrations in triplicate for 500 ns each. All systems disorder from the AlphaFold 3 starting structure. Phosphate charge state, not ionic strength, is the dominant control of ensemble compaction and ion organization. Doubly deprotonated phosphate organizes an extensive Na + condensation shell (∼100 ions, 20% of box Na + ) and a heterogeneous bridging network that integrates both pSer and TPL phosphate groups. The resulting ensemble is compact with LCPA side chains exhibiting above-median solvent accessibility in 84% of simulation frames in P2 at 300 mM. This is higher than any other condition we simulated and indicates that polyamine groups are preferentially surface-presented in the most compact, ion-organized state. A charge-neutralization control confirms that this compact state is a structured intermediate maintained by the bridging network, not a simple collapsed globule. Here, this repeat-scale spatial organization is not captured by single-repeat peptide studies. Understanding the dynamics, mechanism, and spatial organization of PTM-rich silaffin at the repeat scale is a step closer to hierarchical biomimetic materials beyond simple silica morphologies.

Amines↗
DOE OSTI2022

13 C ENDOR Characterization of the Central Carbon within the Nitrogenase Catalytic Cofactor Indicates That the CFe 6 Core Is a Stabilizing “Heart of Steel”

Substrates and inhibitors of Mo-dependent nitrogenase bind and react at Fe ions of the active-site FeMo-cofactor [7Fe–9S–C–Mo–homocitrate] contained within the MoFe protein α-subunit. The cofactor contains a CFe 6 core, a carbon centered within a trigonal prism of six Fe, whose role in catalysis is unknown. Targeted 13 C labeling of the carbon enables electron-nuclear double resonance (ENDOR) spectroscopy to sensitively monitor the electronic properties of the Fe–C bonds and the spin-coupling scheme adopted by the FeMo-cofactor metal ions. Here this report compares 13 CFe 6 ENDOR measurements for (i) the wild-type protein resting state (E 0 ; α-Val 70 ) to those of (ii) α-Ile 70 , (iii) α-Ala 70 -substituted proteins; (iv) crystallographically characterized CO-inhibited “hi-CO” state; (v) E 4 (4H) Janus intermediate, activated for N 2 binding/reduction by accumulation of 4[ e– /H + ]; (vi) E 4 (2H)* state containing a doubly reduced FeMo-cofactor without Fe-bound substrates; and (vii) propargyl alcohol reduction intermediate having allyl alcohol bound as a ferracycle to FeMo-cofactor Fe6. All states examined, both S = 1/2 and 3/2 exhibited near-zero 13 C isotropic hyperfine coupling constants, $^Ca$ = [-1.3 ↔ +2.7] MHz. Density functional theory computations and natural bond orbital analysis of the Fe-C bonds show that this occurs because a (3 spin-up/3 spin-down) spin-exchange configuration of CFe 6 Fe-ion spins produces cancellation of large spin-transfers to carbon in each Fe–C bond. Previous X-ray diffraction and DFT both indicate that trigonal-prismatic geometry around carbon is maintained with high precision in all these states. The persistent structure and Fe–C bonding of the CFe 6 core indicate that it does not provide a functionally dynamic (hemilabile) “beating heart”-instead it acts as “a heart of steel”, stabilizing the structure of the FeMo-cofactor-active site during nitrogenase catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Hamiltonian constraint in polymer parametrized field theory

Recently, a generally covariant reformulation of two-dimensional flat spacetime free scalar field theory known as parametrized field theory was quantized using loop quantum gravity (LQG) type ''polymer'' representations. Physical states were constructed, without intermediate regularization structures, by averaging over the group of gauge transformations generated by the constraints, the constraint algebra being a Lie algebra. We consider classically equivalent combinations of these constraints corresponding to a diffeomorphism and a Hamiltonian constraint, which, as in gravity, define a Dirac algebra. Our treatment of the quantum constraints parallels that of LQG and obtains the following results, expected to be of use in the construction of the quantum dynamics of LQG: (i) the (triangulated) Hamiltonian constraint acts only on vertices, its construction involves some of the same ambiguities as in LQG and its action on diffeomorphism invariant states admits a continuum limit, (ii) if the regulating holonomies are in representations tailored to the edge labels of the state, all previously obtained physical states lie in the kernel of the Hamiltonian constraint, (iii) the commutator of two (density weight 1) Hamiltonian constraints as well as the operator correspondent of their classical Poisson bracket converge to zero in the continuum limit defined by diffeomorphism invariant states, and vanish on the Lewandowski-Marolf habitat, (iv) the rescaled density 2 Hamiltonian constraints and their commutator are ill-defined on the Lewandowski-Marolf habitat despite the well-definedness of the operator correspondent of their classical Poisson bracket there, (v) there is a new habitat which supports a nontrivial representation of the Poisson-Lie algebra of density 2 constraints.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Redox-Mediated Stabilization in Zinc Molybdenum Nitrides

We report on the theoretical prediction and experimental realization of new ternary zinc molybdenum nitride compounds. We used theory to identify previously unknown ternary compounds in the Zn-Mo-N systems, Zn 3 MoN 4 and ZnMoN 2 , and to analyze their bonding environment. Experiments show that Zn-Mo-N alloys can form in broad composition range from Zn 3 MoN 4 to ZnMoN 2 in the wurtzite-derived structure, accommodating very large off-stoichiometry. Interestingly, the measured wurtzite-derived structure of the alloys is metastable for the ZnMoN 2 stoichiometry, in contrast to the Zn 3 MoN 4 stoichiometry, where ordered wurtzite is predicted to be the ground state. The formation of Zn 3 MoN 4 -ZnMoN 2 alloy with wurtzite-derived crystal structure is enabled by the concomitant ability of Mo to change oxidation state from +VI in Zn 3 MoN 4 to +IV in ZnMoN 2 , and the capability of Zn to contribute to the bonding states of both compounds, an effect that we define as 'redox-mediated stabilization.' The stabilization of Mo in both the +VI and +IV oxidation states is due to the intermediate electronegativity of Zn, which enables significant polar covalent bonding in both Zn 3 MoN 4 and ZnMoN 2 compounds. The smooth change in the Mo oxidation state between Zn 3 MoN 4 and ZnMoN 2 stoichiometries leads to a continuous change in optoelectronic properties - from resistive and semitransparent Zn 3 MoN 4 to conductive and absorptive ZnMoN 2 . The reported redox-mediated stabilization in zinc molybdenum nitrides suggests there might be many undiscovered ternary compounds with one metal having an intermediate electronegativity, enabling significant covalent bonding, and another metal capable of accommodating multiple oxidation states, enabling stoichiometric flexibility.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Asymptotic-bound-state model for Feshbach resonances

We present an asymptotic-bound-state model which can be used to accurately describe all Feshbach resonance positions and widths in a two-body system. With this model we determine the coupled bound states of a particular two-body system. The model is based on analytic properties of the two-body Hamiltonian and on asymptotic properties of uncoupled bound states in the interaction potentials. In its most simple version, the only necessary parameters are the least bound state energies and actual potentials are not used. The complexity of the model can be stepwise increased by introducing threshold effects, multiple vibrational levels, and additional potential parameters. The model is extensively tested on the {sup 6}Li-{sup 40}K system and additional calculations on the {sup 40}K-{sup 87}Rb system are presented.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Raman spectroscopy and x-ray diffraction of sp 3 CaC O 3 at lower mantle pressures

The exceptional ability of carbon to form sp 2 and sp 3 bonding states leads to a great structural and chemical diversity of carbon-bearing phases at nonambient conditions. Here we use laser-heated diamond-anvil cells combined with synchrotron x-ray diffraction, Raman spectroscopy, and first-principles calculations to explore phase transitions in CaC O 3 at P > 40 GPa . We find that postaragonite CaC O 3 transforms to the previously predicted P 2 1 / c CaC O 3 with sp 3 -hybridized carbon at 105 GPa ( ~ 30 GPa higher than the theoretically predicted crossover pressure). The lowest-enthalpy transition path to P2 1 / c CaC O 3 includes reoccurring sp 2 and sp 3 CaC O 3 intermediate phases and transition states, as revealed by our variable-cell nudged-elastic-band simulation. Raman spectra of P 2 1 / c CaC O 3 show an intense band at 1025 c m -1 , which we assign to the symmetric C-O stretching vibration based on empirical and first-principles calculations. This Raman band has a frequency that is ~ 20 % low-ymmetric C-O stretching in sp 2 CaC O 3 due to the C-O bond length increase across the sp 2 ~ sp 3 transition and can be used as a fingerprint of tetrahedrally coordinated carbon in other carbonates.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Realizing a topological diode effect on the surface of a topological Kondo insulator

Introducing the concept of topology into material science has sparked a revolution from classic electronic and optoelectronic devices to topological quantum devices. The latter has potential for transferring energy and information with unprecedented efficiency. Here, we demonstrate a topological diode effect on the surface of a three-dimensional material, SmB 6 , a candidate topological Kondo insulator. The diode effect is evidenced by pronounced rectification and photogalvanic effects under electromagnetic modulation and radiation at radio frequency. Our experimental results and modeling suggest that these prominent effects are intimately tied to the spatially inhomogeneous formation of topological surface states (TSS) at the intermediate temperature. This work provides a manner of breaking the mirror symmetry (in addition to the inversion symmetry), resulting in the formation of pn-junctions between puddles of metallic TSS. Further, this effect paves the way for efficient current rectifiers or energy-harvesting devices working down to radio frequency range at low temperature, which could be extended to high temperatures using other topological insulators with large bulk gap.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Spin density wave instability in a ferromagnet

Due to its cooperative nature, magnetic ordering involves a complex interplay between spin, charge, and lattice degrees of freedom, which can lead to strong competition between magnetic states. Binary Fe 3 Ga 4 is one such material that exhibits competing orders having a ferromagnetic (FM) ground state, an antiferromagnetic (AFM) behavior at intermediate temperatures, and a conspicuous re-entrance of the FM state at high temperature. Through a combination of neutron diffraction experiments and simulations, we have discovered that the AFM state is an incommensurate spin-density wave (ISDW) ordering generated by nesting in the spin polarized Fermi surface. These two magnetic states, FM and ISDW, are seldom observed in the same material without application of a polarizing magnetic field. To date, this unusual mechanism has never been observed and its elemental origins could have far reaching implications in many other magnetic systems that contain strong competition between these types of magnetic order. Furthermore, the competition between magnetic states results in a susceptibility to external perturbations allowing the magnetic transitions in Fe 3 Ga 4 to be controlled via temperature, magnetic field, disorder, and pressure. Thus, Fe 3 Ga 4 has potential for application in novel magnetic memory devices, such as the magnetic components of tunneling magnetoresistance spintronics devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Stochastic and mixed density functional theory within the projector augmented wave formalism for simulation of warm dense matter

Stochastic density functional theory (DFT) and mixed stochastic-deterministic DFT are burgeoning approaches for the calculation of the equation of state and transport properties in materials under extreme conditions. In the intermediate warm dense matter regime, a state between correlated condensed matter and kinetic plasma, electrons can range from being highly localized around nuclei to delocalized over the whole simulation cell. The plane-wave basis pseudopotential approach is thus the typical tool of choice for modeling such systems at the DFT level. Unfortunately, stochastic DFT methods scale as the square of the maximum plane-wave energy in this basis. To reduce the effect of this scaling and improve the overall description of the electrons within the pseudopotential approximation, we present stochastic and mixed DFT approaches developed and implemented within the projector augmented wave formalism. In conclusion, we compare results between the different DFT approaches for both single-point and molecular dynamics trajectories and present calculations of self-diffusion coefficients of solid density carbon from 1 to 50 eV.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Clogging and depinning of ballistic active matter systems in disordered media

We numerically examine ballistic active disks driven through a random obstacle array. Formation of a pinned or clogged state occurs at much lower obstacle densities for the active disks than for passive disks. As a function of obstacle density, we identify several distinct phases including a depinned fluctuating cluster state, a pinned single-cluster or jammed state, a pinned multicluster state, a pinned gel state, and a pinned disordered state. At lower active disk densities, a drifting uniform liquid forms in the absence of obstacles, but when even a small number of obstacles are introduced, the disks organize into a pinned phase-separated cluster state in which clusters nucleate around the obstacles, similar to a wetting phenomenon. Here in this paper, we examine how the depinning threshold changes as a function of disk or obstacle density and find a crossover from a collectively pinned cluster state to a disordered plastic depinning transition as a function of increasing obstacle density. We compare this to the behavior of nonballistic active particles and show that as we vary the activity from completely passive to completely ballistic, a clogged phase-separated state appears in both the active and passive limits, while for intermediate activity, a readily flowing liquid state appears and there is an optimal activity level that maximizes the flux through the sample.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗