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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Advancing nuclear forensics competencies at the National Nuclear Center of the Republic of Kazakhstan and conceptual development of a National Nuclear Forensics Library

Since 2021, the National Nuclear Center (NNC) of the Republic of Kazakhstan has been successfully developing a project dedicated to nuclear forensics. The relevance of this project is underscored by Kazakhstan’s leading position in the global uranium mining and export market. The country operates research reactors and is involved in the production of experimental nuclear fuel. The nuclear forensics project is being implemented in several key areas: the project will develop competencies in laboratory research of samples, interpretation of results, and develop a prototype concept for the National Nuclear Forensics Library. In implementing these challenges, the NNC experts draw on the experience of colleagues from world-leading scientific and research centers. Designing a prototype National Nuclear Forensics Library (NNFL) is a challenging project. In conclusion, the solution to this task is based on the IAEA’s approaches, recommendations, and the experience gained from the construction of similar systems in other countries.

and nuclear chemistry↗
DOE OSTI2023

Aqueous buffer solution-induced crystallization competes with enzymatic depolymerization of pre-treated post-consumer poly (ethylene terephthalate) waste

In this paper, the complex relationship between kinetics and substrate morphology during enzymatic depolymerization of melt processed poly(ethylene terephthalate) (PET) is explored and the effects of competing transformations are analyzed. Extruded PET substrates from post-consumer recycled PET (RPET) bottles flakes subjected to enzymatic depolymerization are examined to reveal increases in crystallinity from ~10% post-extrusion to >30% after 3 days of depolymerization as well as increases in glass transition temperature (T g ) from ~66°C to > 80°C. Further investigation into this behavior shows that post-extrusion RPET substrates do not exhibit changes in crystallinity when subjected to dry annealing at 65°C in an oven over 7 days, but they do experience annealing in depolymerization buffer solution with no enzymes at 65°C within 3 days. This difference may be attributed to plasticization of PET in the presence of water, also known as solvent induced crystallization. The impact of this plasticized annealing behavior is demonstrated by subjecting RPET substrates to increasing enzyme-to-substrate loads. As enzyme load increases, overall conversion of substrates increases despite crystallinity also increasing to similar levels regardless of the initial enzyme loading. The competition between depolymerization and crystallization suggests that the rate at which PET substrates are depolymerized at the operational temperature is integral to achieving high conversion to monomeric product. This, in turn, also suggests that savings from lowered enzyme loadings may be more detrimental than helpful in pursuing the most cost-effective recycling systems.

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

Competing Radical and Molecular Channels in the Unimolecular Dissociation of Methylformate

The thermal dissociation of methylformate has been characterized by numerous experimental and theoretical studies that all seem to agree that the lowest energetically accessible process is a 3-center H-atom transfer that leads to the molecular products CH3OH 3 OH + CO. However, these literature studies seem to be at odds with regards to the role of other competing molecular eliminations and bond-fission processes and therefore a complete and resolved mechanistic picture of methylformate thermal dissociation still eludes us. In this work, we have performed high-level electronic structure theory calculations to characterize the energetics of other overlooked molecular and radical processes that can originate on the complex CH3OCHO 3 OCHO potential energy surface (PES). The present calculations do indeed confirm that the lowest energy process accessible on this PES is molecular elimination to form CH3OH 3 OH + CO. However, unlike prior theoretical studies, the present calculations reveal that the second lowest energy process is a 5-center concerted elimination process that leads to the direct formation of H2 2 + CH2O 2 O + CO. We also note that HCO2 2 from the lowest-lying bond fission has two energetically comparable electronic states (of 2 B 2 and 2 A 1 symmetry). Furthermore, the barrier for H-atom migration of CH3OCHO 3 OCHO to form the carbene (CH3OCOH) 3 OCOH) is similar to that for the direct 4-center elimination process leading to CH2O 2 O + CH2O 2 O characterized in prior literature studies. Radical and molecular pathways to CH3 3 + HOCO and CH4 4 + CO2 2 can also be facilitated from this carbene. Master equation calculations were performed to characterize the competition between the various molecular and radical processes on this more elaborate CH3OCHO 3 OCHO PES. The results of the present theoretical analyses were used to resolve outstanding questions on the role of secondary radical- initiated reactions in characterizing prior literature experimental studies.

Chemical Kinetics↗
DOE OSTI2021

Competing endogenous RNA network associated with oxygen-induced retinopathy: Expression of the network and identification of the MALAT1/miR-124–3p/EGR1 regulatory axis

Retinopathy of prematurity (ROP) is a severe retinal dysfunction in prematurely born babies. The relationship between non-coding RNAs and retinopathy of prematurity (ROP) remain unclear. Microarray analysis of lncRNAs, miRNAs, and mRNAs was conducted in a mouse model of ROP. A competing endogenous RNA (ceRNA) network was constructed. The relationship among MALAT1, miR-124–3p, and Early growth response protein 1 (EGR1) was assessed in hypoxia-induced primary human umbilical vein endothelial cells (HUVECs) and ROP mouse model. In the study, we found 2252 lncRNAs, 1239 mRNAs, and 36 miRNAs were differentially regulated. ceRNA network consisting of 21 lncRNAs, 10 miRNAs, and 19 mRNAs was established. Of the most down-regulated miRNAs, miR-124–3p was selected for additional study. miR-124–3p ceased the migration and proliferation of primary HUVECs in hypoxic conditions, and directly suppressed EGR1. Additionally, MALAT1 directly sponged miR-124–3p. Knockdown of MALAT1 decreased EGR1 expression and inhibited the migration and proliferation of primary HUVECs in hypoxia. Furthermore, these changes were rescued by depletion of miR-124–3p. In vivo, intravitreal injection of miR-124–3p, shMALAT1 decreased EGR1 expression and markedly suppressed retinal neovascularization in OIR models. Intravitreal injection of shMALAT1 and miR-124–3p antagomir at the same time can promote retinal neovascularization, which reversed the suppression of retinal neovascularization functioned by shMALAT1. In conclusion, the expression profiles of lncRNAs and miRNAs and the ceRNA network in a mouse model of ROP may be indicative of the underlying mechanisms of retinal angiogenesis and neural activity. The MALAT1/miR-124–3p/EGR1 regulatory axis is partly responsible for retinal neovascularization, which may provide a novel theoretical basis for the pathogenesis of ROP.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Competing Magnetic Interactions and the Role of Unpaired 4 f Electrons in Oxygen-Deficient Perovskites Ba 3 R Fe 2 O 7.5 ( R = Y, Dy)

Oxygen-deficient perovskite compounds with the general formula Ba 3 RFe 2 O 7.5 present a good opportunity to study competing magnetic interactions between Fe 3+ 3d cations with and without the involvement of unpaired 4f electrons on R 3+ cations. From analysis of neutron powder diffraction data, complemented by ab initio density functional theory calculations, we determined the magnetic ground states when R 3+ = Y 3+ (non-magnetic) and Dy 3+ (4f 9 ). They both adopt complex long-range ordered antiferromagnetic structures below T N = 6.6 and 14.5 K, respectively, with the same magnetic space group C a 2/c (BNS #15.91). However, the dominant influence of f-electron magnetism is clear in temperature dependence and differences between the size of the ordered moments on the two crystallographically independent Fe sites, one of which is enhanced by R–O–Fe superexchange in the Dy compound, while the other is frustrated by it. We report the Dy compound also shows evidence for temperature- and field-dependent transitions with hysteresis, indicating a field-induced ferromagnetic component below TN.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Competing Effects of Network Architecture and Composition on Polydomain Liquid Crystal Elastomers

Main-chain liquid crystal elastomers (LCEs) are synthesized to investigate the interplay of the composition and network structure on LCE nematic-to-isotropic (N–I) transitions. We focus on networks synthesized from liquid crystalline oligomers reacted with tri- or tetrafunctional nonmesogenic cross-linker molecules. We find that coupling between mesogens and the polymer backbone increases with the degree of cross-linking. However, this enhanced coupling competes with mesogenic dilution arising from the cross-linker molecules to determine the N–I transition temperature (T NI ). When cross-linker molecules are dilute, the degree of cross-linking directly correlates to the change in T NI from the oligomer to LCE (ΔT NI ) through mesogen–backbone coupling. In this regime, ΔT NI ranges from 2.9 to 12.2 °C and 2.9–13.9 °C for tri- and tetrafunctional cross-linkers, respectively. At high cross-linker concentrations, deviations from this linear relationship appear. Further, the fractional mesogen content within an oligomer chain induces molecular weight-dependent mesogenic dilution effects arising from the flexible spacer molecules. Analysis of the N–I transition peak reveals a maximum latent heat per gram of mesogen (ΔH NI,mes ) for this system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Tunable Multisite Proton-Coupled Electron Transfer Mediators: Distinct Pathways for Substrate Reduction Versus Competing Hydrogen Evolution

Proton-coupled electron transfer (PCET) reagents have emerged as powerful tools for transferring net H atoms to organic substrates from relatively weak X–H bonds. One advantage of employing PCET reagents is the tunability of the X–H bond strength by independently varying their redox potential and/or p K a for selective substrate reductions; however, the rational development of modular catalytic PCET reagents based on these features remains underdeveloped. In this work, we address important mechanistic questions relevant to a dimethylaniline-appended cobaltocene PCET mediator that our lab has previously introduced. Specifically, we examine where protonation occurs within the reactive Co(II, NH) + intermediate of a Brønsted-base modified cobaltocene mediator, whether substrate reduction and hydrogen evolution reaction (HER) proceed by a common or bifurcated mechanistic pathway, and how the redox, acid–base, and structural properties of PCET mediators can dictate their reactivity and selectivity. We show that substrate compatibility can be tuned and, via a model study with N -aryl imine substrates, provide data pointing to a multisite PCET (MS-PCET) pathway. Moreover, we rigorously characterize the site of protonation in the reactive reduced, protonated form of the mediator, and through kinetic analysis establish that the pathway for undesired competing HER is fundamentally different and involves Cp-ring protonation. Our findings point to a high degree of flexibility in the design of reductive PCET mediators.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Emergence of high piezoelectricity from competing local polar order-disorder in relaxor ferroelectrics

Relaxor ferroelectrics are known for outstanding piezoelectric properties, finding a broad range of applications in advanced electromechanical devices. Decoding the origins of the enhanced properties, however, have long been complicated by the heterogeneous local structures. Here, we employ the advanced big-box refinement method by fitting neutron-, X-ray-based total scattering, and X-ray absorption spectrum simultaneously, to extract local atomic polar displacements and construct 3D polar configurations in the classical relaxor ferroelectric Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 . Our results demonstrate that prevailing order-disorder character accompanied by the continuous rotation of local polar displacements commands the composition-driven global structure evolution. The omnidirectional local polar disordering appears as an indication of macroscopic relaxor characteristics. Combined with phase-field simulations, it demonstrates that the competing local polar order-disorder between different states with balanced local polar length and direction randomness leads to a flattening free-energy profile over a wide polar length, thus giving rise to high piezoelectricity. Our work clarifies that the critical structural feature required for high piezoelectricity is the competition states of local polar rather than relaxor.

42 ENGINEERING↗
DOE OSTI2025

Pressure tuning of competing interactions on a honeycomb lattice

Exchange interactions are mediated via orbital overlaps across chemical bonds. Thus, modifying the bond angles by physical pressure or strain can tune the relative strength of competing interactions. Here we present a remarkable case of such tuning between the Heisenberg (J) and Kitaev (K) exchange, which respectively establish magnetically ordered and spin liquid phases on a honeycomb lattice. We observe a rapid suppression of the Néel temperature (T N ) with pressure in Ag 3 LiRh 2 O 6 , a spin-1/2 honeycomb lattice with both J and K couplings. Using a combined analysis of x-ray data and first-principles calculations, we find that pressure modifies the bond angles in a way that increases the ∣K/J∣ ratio and thereby suppresses T N . Consistent with this picture, we observe a spontaneous onset of muon spin relaxation (μSR) oscillations below T N at low pressure, whereas in the high pressure phase, oscillations appear only when T < T N /2. Unlike other candidate Kitaev materials, Ag 3 LiRh 2 O 6 is tuned toward a quantum critical point by pressure while avoiding a structural dimerization in the relevant pressure range.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Complex magnetic properties associated with competing local and itinerant magnetism in \({\text {Pr}}_2 {\text {Co}}_{0.86} {\text {Si}}_{2.88}\)

Ternary intermetallic compound \({\text {Pr}}_2 {\text {Co}}_{0.86} {\text {Si}}_{2.88}\) has been synthesized in single phase and characterized by x-ray diffraction, scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDX) analysis, magnetization, heat capacity, neutron diffraction and muon spin rotation/relaxation ( \(\mu\) SR) measurements. The polycrystalline compound was synthesized in single phase by introducing necessary vacancies in Co/Si sites. Magnetic, heat capacity, and zero-field neutron diffraction studies reveal that the system undergoes magnetic transition below \(\sim\) 4 K. Neutron diffraction measurement further reveals that the magnetic ordering is antiferromagnetic in nature with an weak ordered moment. The high temperature magnetic phase has been attributed to glassy in nature consisting of ferromagnetic clusters of itinerant (3 d ) Co moments as evident by the development of internal field in zero-field \(\mu\) SR below 50 K. The density-functional theory (DFT) calculations suggest that the low temperature magnetic transition is associated with antiferromagnetic coupling between Pr 4 f and Co 3 d spins. Pr moments show spin fluctuation along with unconventional orbital moment quenching due to crystal field. The evolution of the symmetry and the crystalline electric field environment of Pr-ions are also studied and compared theoretically between the elemental Pr and when it is coupled with other elements such as Co. The localized moment of Pr 4 f and itinerant moment of Co 3 d compete with each other below \(\sim\) 20 K resulting in an unusual temperature dependence of magnetic coercivity in the system.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Chemical control of competing electron transfer pathways in iron tetracyano-polypyridyl photosensitizers

Photoinduced intramolecular electron transfer dynamics following metal-to-ligand charge-transfer (MLCT) excitation of [Fe(CN) 4 (2,2'-bipyridine)] 2- (1), [Fe(CN) 4 (2,3-bis(2-pyridyl)pyrazine)] 2- (2) and [Fe(CN) 4 (2,2'-bipyrimidine)] 2- (3) were investigated in various solvents with static and time-resolved UV-Visible absorption spectroscopy and Fe 2p3d resonant inelastic X-ray scattering (RIXS). This series of polypyridyl ligands, combined with the strong solvatochromism of the complexes, enables the 1 MLCT vertical energy to be varied from 1.64 eV to 2.64 eV and the 3 MLCT lifetime to range from 180 fs to 67 ps. The 3 MLCT lifetimes in 1 and 2 decrease exponentially as the MLCT energy increases, consistent with electron transfer to the lowest energy triplet metal-centred ( 3 MC) excited state, as established by the Tanabe–Sugano analysis of the Fe 2p3d RIXS data. In contrast, the 3 MLCT lifetime in 3 changes non-monotonically with MLCT energy, exhibiting a maximum. This qualitatively distinct behaviour results from a competing 3 MLCT → ground state (GS) electron transfer pathway that exhibits energy gap law behaviour. The 3 MLCT → GS pathway involves nuclear tunnelling for the high-frequency polypyridyl breathing mode (hν = 1530 cm -1 ), which is most displaced for complex 3, making this pathway significantly more efficient. Our study demonstrates that the excited state relaxation mechanism of Fe polypyridyl photosensitizers can be readily tuned by ligand and solvent environment. Furthermore, our study reveals that extending charge transfer lifetimes requires control of the relative energies of the 3 MLCT and the 3 MC states and suppression of the intramolecular distortion of the acceptor ligand in the 3 MLCT excited state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

LaMer's 1950 model of particle formation: a review and critical analysis of its classical nucleation and fluctuation theory basis, of competing models and mechanisms for phase-changes and particle formation, and then of its application to silver halide, semiconductor, metal, and metal-oxide nanoparticles

Are classical nucleation theory and the 1950 LaMer model of particle formation supported for a wide range of particle formations, or do competing models in the form of chemical reaction mechanisms have better experimental support? Read on to find out.

Whitehead, Christopher B.↗
DOE OSTI2022

NaCo 2 (SeO 3 ) 2 (OH): competing magnetic ground states of a new sawtooth structure with 3d 7 Co 2+ ions

While certain magnetic sublattices have long been known theoretically to give rise to emergent physics via competing magnetic interactions and quantum effects, finding such configurations in real materials is often deeply challenging. Here we report the synthesis and characterization of a new such material, NaCo 2 (SeO 3 ) 2 (OH) which crystallizes with a highly frustrated sublattice of sawtooth Co 2+ chains. Single crystals of NaCo 2 (SeO 3 ) 2 (OH) were synthesized using a low-temperature hydrothermal method. X-ray single crystal structure analysis reveals that the material crystallizes in orthorhombic space group of Pnma (no. 62). Its crystal structure exhibits one-dimensional chains of corner-sharing isosceles triangles that are made of two crystallographically distinct 3d 7 Co 2+ sites (Co(1) and Co(2)). The chains run along the b-axis and are interconnected via [SeO 3 ] groups to form a three-dimensional structure mediating super-exchange interactions. The temperature dependent magnetization data show a ferromagnetic-like (FM) transition at 11 K (T 1 ) followed by an antiferromagnetic (AFM) transition at about 6 K (T 2 ). Neutron-powder diffraction measurements reveal that at T 1 = 11 K only the Co(2) site orders magnetically, forming ferromagnetic zigzag chains along the b-axis. Below T 2 = 6 K, both Co(1) and Co(2) sites order in a nearly orthogonal configuration, with Co(1) moments lying inside the plane of the sawtooth chain while Co(2) moments cant out of the plane. The canting of the magnetic moments leads to a net ferromagnetic component along b-axis, parallel to the chain direction. The ordered moments are fully compensated in the ac-plane. Inelastic neutron scattering measurements reveal crystal field excitations that are consistent with the presence of a spin–orbital entangled pseudo-spin state J eff = 1/2 for the Co 2+ ions. Low-energy spin-wave excitations are observed below the second magnetic transition. The analysis of powder excitation spectrum suggests complex exchange interactions that go beyond a Heisenberg Hamiltonian model with nearest neighbor couplings. Our results demonstrate the richness of the magnetic properties of sawtooth-type structures and encourage the study of similar structures with different oxyanion groups.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Laning transitions in pattern-forming driven binary systems with competing interactions

A binary system of particles that move in opposite directions under an applied field can exhibit disordered states as well as laned states where the particles organize into oppositely moving high-mobility lanes to reduce collisions. Previous studies of laning transitions generally focused on particles with purely repulsive interactions. Here, in this study, we examine laning transitions for oppositely moving pattern-forming systems of particles with competing attractive and repulsive interactions, which in equilibrium form crystal, stripe, and bubble states. In addition to multiple types of laned states, we find jammed crystals, stripes, and bubbles, and generally observe a much richer variety of phases compared to the purely repulsive system. In the stripe-forming regime, the system can dynamically reorder into oppositely moving stripes that are aligned in the direction of the drive. The bubble phase can produce strongly polarized jammed states of elongated bubbles where particles in the individual bubbles segregate to opposite sides of the bubbles. We also find disordered states, segregated laned bubble states where the bubbles pass each other in lanes, and segregated bubbles that move through one another. In the compact bubble regime, we obtain a plastic bubble state in which the oppositely driven particles remain trapped in the bubbles but the bubbles move past each other at a slow velocity due to a net imbalance in the bubble population. At higher drives, individual particles begin to jump from bubble to bubble. We show that the different phases and the transitions between them produce signatures in the velocity-force and differential mobility curves. We demonstrate that the force for escaping from the jammed state is nonmonotonic, with stripes exhibiting the lowest unjamming force.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ratchet effects in cyclic pattern formation systems with competing interactions

Ratchet effects can appear for particles interacting with an asymmetric potential under ac driving or for a thermal system in which a substrate is periodically flashed. Here, we show that a different type of collective ratchet effect can arise for a pattern-forming system coupled to an asymmetric substrate when the interaction potential between the particles is periodically oscillated in order to cycle the system through different patterns. We consider particles with competing short-range attraction and long-range repulsion subjected to time-dependent oscillations of the ratio between the attractive and repulsive interaction terms, which causes the system to cycle periodically between crystal and bubble states. In the presence of the substrate, this system exhibits both a positive and a reversed ratchet effect, and we show that there is a maximum in the ratchet efficiency as a function of interaction strength, ac drive frequency, and particle density. In conclusion, our results could be realized for a variety of pattern-forming systems on asymmetric substrates where the pattern type or particle interactions can be oscillated.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Emergence of a competing stripe phase near the Mott transition in Ti-doped bilayer calcium ruthenates

We report the nanoscale imaging of Ti-doped bilayer calcium ruthenates during the Mott metal-insulator transition by microwave impedance microscopy. Different from a typical first-order phase transition where coexistence of the two terminal phases takes place, a new metallic stripe phase oriented along the in-plane crystalline axes emerges inside both the G-type antiferromagnetic insulating state and the paramagnetic metallic state. The effect of this electronic state can be observed in macroscopic measurements, allowing us to construct a phase diagram that takes into account the energetically competing phases. Our work provides a model approach to correlate the macroscopic properties and mesoscopic phase separation in complex oxide materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗