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At least 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Origin of the High CO Oxidation Activity on CeO 2 Supported Pt Nanoparticles: Weaker Binding of CO or Facile Oxygen Transfer from the Support?

Pt clusters supported on CeO 2 are highly active for low temperature CO oxidation. The enhanced reactivity could be caused by weakening of the CO binding on Pt, allowing adsorbed oxygen to more effectively compete for sites. An alternative explanation is that interfacial sites allow adsorbed CO on Pt to react with lattice oxygen in the ceria. Here we explore the origins of enhanced CO oxidation reactivity on Pt/CeO 2 using in-situ/operando infrared and x-ray spectroscopies, microcalorimetry, and reaction kinetics. Iin this work we show that CO adsorbs strongly (~110–120 kJ/mol) on Pt clusters (~1.5 nm) and Pt is almost fully covered by CO during reaction, indicating that the high activity can be related to reactive interfacial O* species. Using in-situ infrared spectroscopy we show that when the reaction mixture of CO and O 2 stops flowing over the catalyst, the adsorbed CO on Pt is lost since it reacts with interfacial O*, but if this O* is depleted, the CO band does not disappear. The role of CeO 2 is not to alter the binding of CO, but rather to enhance the reactivity of the interfacial metal-support lattice oxygens. The reaction mechanism involving the interfacial Pt–CeO 2 sites (two-site mechanism) is further confirmed by kinetic measurements which show near zero order dependence on CO and O 2 partial pressures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Ab initio exploration of low–lying electronic states of linear and bent MNX + (M = Ca, Sr, Ba, Ra; X = O, S, Se, Te, Po) and their origins

High-level multireference and coupled cluster quantum calculations were employed to analyze low-lying electronic states of linear-MNX + and side-bonded-M[NX] + (M = Ca, Sr, Ba, Ra; X = O, S, Se, Te, Po) species. Their full potential energy curves (PECs), dissociation energies (D e s), geometric parameters, excitation energies (T e s), and harmonic vibrational frequencies (ω e s) are reported. The first three chemically bound electronic states of MNX + and M[NX] + are 3 Σ – , 1 Δ, 1 Σ + and 3 A", 1 A', 1 A", respectively. The 3 Σ – , 1 Δ, 1 Σ + of MNX + originate from the M + ( 2 D) + NX( 2 Π) fragments, whereas the 3 A", 1 A', 1A" states of M[NX] + dissociate to M + ( 2 S) + NX( 2 Π) as a result of avoided crossings. The MNX + and M[NX] + are real minima on the potential energy surface and their interconversions are possible. The M 2+ NX – /M 2+ [NX] – ionic structure is an accurate representation for their low-lying electronic states. The D e s of MNX + species were found to depend on the dipole moment (μ) of the corresponding NX ligands and a linear relationship between these two parameters was observed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Efficacy of a Short-Term Captive Broodstock Program Compared with Hatchery-Origin Spring Chinook Salmon Derived from the Same Population

Abstract We examined the efficacy of a one-generation (five brood years: 1997–2001) captive broodstock program for spring Chinook Salmon Oncorhynchus tshawytscha by comparing survival rates of captive broodstock progeny (CBP; F2) with that of hatchery-origin fish (HOR) from a conservation hatchery supplementation program in which both groups were derived from the Tucannon River (Washington State) population for the 2000–2006 brood years. Survival rates compared were egg to fry, fry to smolt, egg to smolt, total (ages 3–5) and adult (ages 4+) smolt-to-adult-return (SAR) survival, and total (ages 3–5) and adult (ages 4+) progeny-to-parent (P:P) ratio. Total escapement and adult P:P ratios were also examined to determine if observed demographic benefits to the population continued after the captive broodstock program ended. The CBP group had lower within-hatchery survival than the HOR group, with significant differences in survival at the egg-to-fry and egg-to-smolt stages due to poor egg viability. Mean untransformed total and adult SARs for the CBP were half those of the HOR group; however, SARs did not differ significantly. The CBP also had significantly lower total and adult P:P ratios than the HOR group and were below replacement for six of the seven brood years. While the captive broodstock provided additional fish for release that would not have been available otherwise, overall the CBP performed poorly and below expectations compared with the HOR group, both within the hatchery and after release. The captive broodstock program provided a short-term demographic boost, most notable in the 2008–2010 return years, but the benefit did not carry over after the program ended.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Preserved and variable spatial‐chemical changes of lipids across tomato leaves in response to central vein wounding reveals potential origin of linolenic acid in signal transduction cascade

Abstract Membrane lipids serve as substrates for the generation of numerous signaling lipids when plants are exposed to environmental stresses, and jasmonic acid, an oxidized product of 18‐carbon unsaturated fatty acids (e.g., linolenic acid), has been recognized as the essential signal in wound‐induced gene expression. Yet, the contribution of individual membrane lipids in linolenic acid generation is ill‐defined. In this work, we performed spatial lipidomic experiments to track lipid changes that occur locally at the sight of leaf injury to better understand the potential origin of linolenic and linoleic acids from individual membrane lipids. The central veins of tomato leaflets were crushed using surgical forceps, leaves were cryosectioned and analyzed by two orthogonal matrix‐assisted laser desorption/ionization mass spectrometry imaging platforms for insight into lipid spatial distribution. Significant changes in lipid composition are only observed 30 min after wounding, while after 60 min lipidome homeostasis has been re‐established. Phosphatidylcholines exhibit a variable pattern of spatial behavior in individual plants. Among lysolipids, lysophosphatidylcholines strongly co‐localize with the injured zone of wounded leaflets, while, for example, lysophosphatidylglycerol (LPG) (16:1) accumulated preferentially toward the apex in the injured zone of wounded leaflets. In contrast, two other LPGs (LPG [18:3] and LPG [18:2]) are depleted in the injured zone. Our high‐resolution co‐localization imaging analyses suggest that linolenic acids are predominantly released from PCs with 16_18 fatty acid composition along the entire leaf, while it seems that in the apex zone PG (16:1_18:3) significantly contributes to the linolenic acid pool. These results also indicate distinct localization and/or substrate preferences of phospholipase isoforms in leaf tissue.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

The N‐terminal intrinsically disordered region of Ncb5or docks with the cytochrome b 5 core to form a helical motif that is of ancient origin

Abstract NADH cytochromeb 5 oxidoreductase (Ncb5or) is a cytosolic ferric reductase implicated in diabetes and neurological conditions. Ncb5or comprises cytochromeb 5 (b 5 ) and cytochromeb 5 reductase (b 5 R) domains separated by a CHORD‐Sgt1 (CS) linker domain. Ncb5or redox activity depends on proper inter‐domain interactions to mediate electron transfer from NADH or NADPH via FAD to heme. While full‐length human Ncb5or has proven resistant to crystallization, we have succeeded in obtaining high‐resolution atomic structures of theb 5 domain and a construct containing the CS andb 5 R domains (CS/b 5 R). Ncb5or also contains an N‐terminal intrinsically disordered region of 50 residues that has no homologs in other protein families in animals but features a distinctive, conserved L 34 MDWIRL 40 motif also present in reduced lateral root formation (RLF) protein in rice and increased recombination center 21 in baker's yeast, all attaching to ab 5 domain. After unsuccessful attempts at crystallizing a human Ncb5or construct comprising the N‐terminal region naturally fused to theb 5 domain, we were able to obtain a high‐resolution atomic structure of a recombinant rice RLF construct corresponding to residues 25–129 of human Ncb5or (52% sequence identity; 74% similarity). The structure reveals Trp 120 (corresponding to invariant Trp 37 in Ncb5or) to be part of an 11‐residue α‐helix (S 116 QMDWLKLTRT 126 ) packing against two of the four helices in theb 5 domain that surround heme (α2 and α5). The Trp 120 side chain forms a network of interactions with the side chains of four highly conserved residues corresponding to Tyr 85 and Tyr 88 (α2), Cys 124 (α5), and Leu 47 in Ncb5or. Circular dichroism measurements of human Ncb5or fragments further support a key role of Trp 37 in nucleating the formation of the N‐terminal helix, whose location in the N/b 5 module suggests a role in regulating the function of this multi‐domain redox enzyme. This study revealed for the first time an ancient origin of a helical motif in the N/b 5 module as reflected by its existence in a class of cytochromeb 5 proteins from three kingdoms among eukaryotes.

Biochemistry & Molecular Biology↗
DOE OSTI2020

Origin of Suppression of Proximity-Induced Superconductivity in Bi/Bi 2 Sr 2 CaCu 2 O 8+δ Heterostructures

Mixing of topological states with superconductivity could result in topological superconductivity with the elusive Majorana fermions potentially applicable in fault-tolerant quantum computing. One possible candidate considered for realization of topological superconductivity is thin bismuth films on Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212). Here, we present angle-resolved and core-level photoemission spectroscopy studies of thin Bi films grown in-situ on as-grown Bi2212 that show the absence of proximity effect. We find that the electron transfer from the film to the substrate and the resulting severe underdoping of Bi2212 at the interface is a likely origin for the absence of proximity effect. We also propose a possible way of preventing a total loss of proximity effect in this system. Our results offer a better and more universal understanding of the film/cuprate interface and resolve many issues related to the proximity effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Signal Origin of Electrochemical Strain Microscopy and Link to Local Chemical Distribution in Solid State Electrolytes

Electrochemical strain microscopy (ESM) is a distinguished method to characterize Li-ion mobility in energy materials with extremely high spatial resolution. The exact origin of the cantilever deflection when the technique is applied on solid state electrolytes (SSEs) is currently discussed in the literature. Under-standing local properties and influences on ion mobility in SSEs is of utmost importance to improve such materials for next generation batteries. Here, the exact signal formation process of ESM when applied on sodium super ionic conductor (NASICON)-type SSE containing Na- and Li-ions is investigated. Changes in the dielectric properties, which are linked to the local chemical composition, are found to be responsible for the observed contrast in the deflection of the cantilever instead of a physical volume change as a result of Vegard´s Law. The cantilever response is strongly reduced in areas of high sodium content which is attributed to a reduction of the tip-sample capacitance in comparison to areas with high lithium content. This is the first time a direct link between electrostatic forces in contact mode and local chemical information is demonstrated on SSEs. Furthermore, the results open up new possibilities in information gain since dielectric proper-ties are sensitive to subtle changes in local chemical composition.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Tracing the origin of azimuthal gluon correlations in the color glass condensate

Here we examine the origins of azimuthal correlations observed in high energy proton-nucleus collisions by considering the simple example of the scattering of uncorrelated partons off color fields in a large nucleus. We demonstrate how the physics of fluctuating color fields in the color glass condensate (CGC) effective theory generates these azimuthal multiparticle correlations and compute the corresponding Fourier coefficients v n within different CGC approximation schemes. We discuss in detail the qualitative and quantitative differences between the different schemes. Lastly, we will show how a recently introduced color field domain model that captures key features of the observed azimuthal correlations can be understood in the CGC effective theory as a model of non-Gaussian correlations in the target nucleus.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

A common origin for the QCD axion and sterile neutrinos from SU(5) strong dynamics

We identify the QCD axion and right-handed (sterile) neutrinos as bound states of an SU(5) chiral gauge theory with Peccei-Quinn (PQ) symmetry arising as a global symmetry of the strong dynamics. The strong dynamics is assumed to spontaneously break the PQ symmetry, producing a high-quality axion and naturally generating Majorana masses for the right-handed neutrinos at the PQ scale. The composite sterile neutrinos can directly couple to the left-handed (active) neutrinos, realizing a standard see-saw mechanism. Alternatively, the sterile neutrinos can couple to the active neutrinos via a naturally small mass mixing with additional elementary states, leading to light sterile neutrino eigenstates. The SU(5) strong dynamics therefore provides a common origin for a high-quality QCD axion and sterile neutrinos.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Perspective on the Origin of Hadron Masses

The energy-momentum tensor in chiral QCD, T-mu nu, exhibits an anomaly, viz. Theta(0) := T-mu mu not equal 0. Measured in the proton, this anomaly yields m(p)(2), where m(p) is the proton's mass; but, at the same time, when computed in the pion, the answer is m(pi)(2) = 0. Any attempt to understand the origin and nature of mass, and identify observable expressions thereof, must explain and unify these two apparently contradictory results, which are fundamental to the nature of our Universe. Given the importance of Poincare-invariance in modern physics, the utility of a frame-dependent approach to this problem seems limited. That is especially true of any approach tied to a rest-frame decomposition of T-mu nu because a massless particle does not possess a rest-frame. On the other hand, the dynamical chiral symmetry breaking paradigm, connected with a Poincare-covariant treatment of the continuum bound-state problem, provides a straightforward, simultaneous explanation of both these identities, and also a diverse array of predictions, testable at existing and proposed facilities. From this perspective, = 0 owing to exact, symmetry-driven cancellations which occur between one-body dressing effects and two-body-irreducible binding interactions in any well-defined computation of the forward scattering amplitude that defines this expectation value in the pseudoscalar meson. The cancellation is incomplete in any other hadronic bound state, with a remainder whose scale is set by the size of one-body dressing effects.

Roberts, Craig D.↗
DOE OSTI2017

Entrainment in Superfluid Neutron-Star Crusts: Hydrodynamic Description and Microscopic Origin

In spite of the absence of viscous drag, the neutron superfluid permeating the inner crust of a neutron star cannot flow freely and is entrained by the nuclear lattice similarly to laboratory superfluid atomic gases in optical lattices. The role of entrainment on the neutron superfluid dynamics is reviewed. For this purpose, a minimal hydrodynamical model of superfluidity in neutron-star crusts is presented. This model relies on a fully 4-dimensionally covariant action principle. The equivalence of this formulation with the more traditional approach is demonstrated. In addition, the different treatments of entrainment in terms of dynamical effective masses or superfluid density are clarified. The nuclear energy density functional theory employed for the calculations of all the necessary microscopic inputs is also reviewed, focusing on superfluid properties. In particular, the microscopic origin of entrainment and the different methods to estimate its importance are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

On the Origin of a Small Hole Pocket in the Fermi Surface of Underdoped YBa{sub 2}Cu{sub 3}O{sub y}

The comprehensive experimental studies of the quantum oscillations (QOs) in YBa{sub 2}Cu{sub 3}O{sub y} (YBCO) lead N. Doiron-Leyraud et al. (Nature Communications 6:6034, 2015) to detection of small hole pockets below the transition into the charge-ordered (CO) phase. Their interpretation of the observed energy spectrum imposes serious constraints for the possible origin of electron and hole pockets—both of them should be due to the Fermi surface (FS) reconstruction at charge ordering with biaxial order parameter. However, the results of recent X-ray experiments which reveal the uniaxial CO in the underdoped YBCO make such interpretation questionable. We show that uniaxial CO parameter in combination with preexisting electron pocket at the Γ-point of Brillouin zone suggests a plausible interpretation of QOs associated with small hole pockets in YBCO.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Origin of the Magnetism in Undoped and Mn-Doped In{sub 2}O{sub 3}: A First-Principles Study

The magnetism of undoped and Mn-doped In{sub 2}O{sub 3} has been investigated by employing density functional calculations. For undoped In{sub 2}O{sub 3}, a neutral In vacancy in In{sub 2}O{sub 3} leads to the formation of a net moment of 3 μ{sub B}, which originates from the strong spin polarization of 2p orbitals of O atoms. While, Mn-doped In{sub 2}O{sub 3} system shows robust ferromagnetism which can be attributed to the p-d hybridization between Mn and their neighboring O atoms. In addition, because two O atoms between the two Mn atoms are removed, the ground state of the system have a transformation from the ferromagnetic to the antiferromagnetic state, which further demonstrates that the ferromagnetism is mediated through the p-d interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Origin of Interfacial Magnetic Anisotropy in Ta/CoFeB/MgO and Pt/CoFeB/MgO Multilayer Thin Film Stacks

Interfacial perpendicular magnetic anisotropy (PMA) in Pt/Co{sub 40}Fe{sub 40}B{sub 20}/MgO and Ta/Co{sub 40}Fe{sub 40}B{sub 20}/MgO multilayer structures has been researched at various CoFeB layer thicknesses. Magneto-optical Kerr effect (MOKE) and vibrating sample magnetometer (VSM) measurements show that while strong PMA is achieved in Ta/Co{sub 40}Fe{sub 40}B{sub 20}/MgO structure for the thickness of Co{sub 40}Fe{sub 40}B{sub 20} range from 0.5 to 1.0 nm, a very weak PMA is observed in Pt/Co{sub 40}Fe{sub 40}B{sub 20}/MgO film stack for the same Co{sub 40}Fe{sub 40}B{sub 20} thicknesses. Based on the experimental results, the interfacial anisotropy energy in Ta/Co{sub 40}Fe{sub 40}B{sub 20}/MgO (1.17 erg/cm{sup 2}) was found to be almost 2.5× larger than that in Pt/Co{sub 40}Fe{sub 40}B{sub 20}/MgO (0.43 erg/cm{sup 2}). It is accepted that the PMA comes from the seed/ferromagnetic and ferromagnetic/oxide layer interfaces. Thus, the origin of interfacial magnetic anisotropy can be hybridization and/or crystallinity properties at the interfaces in Ta- and Pt-seeded stacks. While the PMA is strong in Pt/Co/MgO structure, it becomes in-plane in Fe-rich Pt/CoFeB/MgO structure. It is deduced that hybridization between 3d-5d (Co-Pt) orbitals is more dominant in Pt/CoFeB interface than 2p-3d (O-Fe) hybridization at CoFeB/MgO interface in Pt-seeded stacks. In addition, the crystallinity was studied by performing high-resolution x-ray diffraction (HR-XRD) technique. The crystal orientations of Ta and Pt are found as (002) and (111), respectively. The ferromagnetic layer might be induced out-of-plane orientation in Ta-seeded stack due to observing highly crystallized MgO (001). Thus, another reason for in-plane magnetic anisotropy in Pt/Co{sub 40}Fe{sub 40}B{sub 20}/MgO might be the absence of MgO crystallization because Pt is crystallized fcc (111) orientation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Observational Study of Clogging Specimens from the Tundish Well Showing Origin and Growth of a Clog in an Al-Killed Ti-Alloyed Steel Cast

Post-mortem tundish skull samples of Ti-alloyed, Al-killed IF steel have been studied regarding the formation of clogging. By using modern characterization equipment and applied methods, we performed a detailed characterization of microstructures found in the tundish well. Aside from the primary metallographic examination, newly developed methods of particle size distribution analysis based on population density functions (PDF) and newly developed electron microscope EDS template mapping have been applied, allowing differentiation of complex particles according to phases and interphase contact relationships. Furthermore, detailed EDS analyses of individual inclusions with complex substructure regarding minor and trace elements within the alumina networks have been performed. These composite data on carefully selected clog microstructures allowed us to observe the presence of layering microstructures throughout the clog: “Coarse” layers (abundant microbubbles and internally complex alumina aggregates) and “Fine” layers (no microbubbles and complex alumina aggregates). Two populations of particles: Population I (2 to 5 µm) and a Population II (5 to 20 µm) build up the layers, both having lognormal PDF, in contrast to power-law PDF of secondary metallurgy inclusions. Coarse layers are further distinguished by selective concentrations of spinel with lognormal PDF as well as the occurrence of complex alumina particles with metal sub-inclusions often with elevated Cr, V, and Si content. Based on these observations, we derive a model for the origin and accumulation of the inclusions making up the clog, which suggests that the NMI of the two dominant populations do not come from the bulk steel, although secondary metallurgy-derived inclusions can be traced in the clog. Overall, microstructures show that the clog behaves as a coherent solid, and is able to displace and fracture.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Sintering Temperature on Density and Mechanical Properties of Solid-State Sintered Silicon Carbide Ceramics and Evaluation of Failure Origin

Densified silicon carbide (SiC) is prepared through dry pressing of SiC powder followed by pressureless sintering in the presence of boron carbide and carbon as the additives. Sintering of SiC parts shows the increase in density with the increase in temperature (1950-2180 °C) by resulting in higher than 98% relative density (RD) at 2150 °C and above for 1 h. Sintered specimens are evaluated concerning the phase, microstructure and mechanical properties including hardness and flexural strength. The machined surface of SiC parts with about 98% RD is studied for the origin of failure. The estimated size of critical flaws (32-110 µm) based on flexural strength and fracture toughness indicates that machining defects are one of the primary reasons for failure in SiC ceramics. The order of magnitude of defects on machined surfaces of sintered SiC by SEM studies is found to be comparable with the estimated size of critical flaws. The failure behavior of SiC is discussed with the help of Weibull statistics with respect to the variation of four-point flexural strength.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Origin of the {111}〈112〉 Cold Rolling Texture Development in a Soft Magnetic Fe-27%Co Alloy

Plastic deformation of Fe-27%Co alloy at room temperature was investigated. The present alloy, usually delivered with a low-texture component for the magnetic core in rotating machines, develops a rather high intensity of Goss texture after recrystallization, when a suitable manufacturing process is applied. Thanks to this texture and its magnetic properties, this material can replace the grain-oriented Fe-3%Si alloy in electric transformer application. The intensity of the recrystallization Goss component depends directly on the sharpness of the {111}〈112〉 orientation developed during cold rolling. Thus, the origin of this {111}〈112〉 deformation texture has been studied using visco-plastic self-consistent (VPSC) simulations. This model showed that only the {110}〈111〉 slip systems allow developing the {111}〈112〉 texture. The predominance of this slip system has been effectively identified from slip markings on the deformed sample by EBSD. More, this simulation has shown that a Goss texture at the hot-rolled state favors the {111}〈112〉 development during cold rolling, as observed experimentally.

36 MATERIALS SCIENCE↗
DOE OSTI2017

An origin of functional fatigue of shape memory alloys

Functional fatigue (FF) during thermal and mechanical cycling, which leads to the generation of macroscopic irrecoverable strain and the loss of dimensional stability, is a critical issue that limits the service life of shape memory alloys (SMAs). Although it has been demonstrated experimentally that such a phenomenon is related to microstructural changes, a fundamental understanding of the physical origin of FF is still lacking, especially from a crystallographic point of view. In this study, we show that in addition to the normal martensitic phase transformation pathway (PTP), there is a symmetry-dictated non-phase-transformation pathway (SDNPTP) during phase transformation cycling, whose activation could play a key role in leading to FF. By investigating crystal symmetry changes along both the PTPs and SDNPTPs, the characteristic types of defects (e.g., dislocations and grain boundaries) generated during transformation cycling can be predicted systematically, and agree well with those observed experimentally in NiTi. By analyzing key materials parameters that could suppress the SDNPTPs, strategies to develop high performance SMAs with much improved FF resistance through crystallographic design and transformation pathway engineering are suggested.

36 MATERIALS SCIENCE↗