Search NASA⌕ Search

SEARCH · Search NASA

Results for “Gap Formation”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Symmetric Nuclear Matter from the Strong Interaction

We study the equation of state of symmetric nuclear matter at zero temperature over a wide range of densities using two complementary theoretical approaches. At low densities, up to twice nuclear saturation density, we compute the energy per particle based on modern nucleon-nucleon and three-nucleon interactions derived within chiral effective field theory. For higher densities, we derive for the first time constraints in a Fierz-complete setting directly based on quantum chromodynamics using functional renormalization group techniques. Here, we find remarkable consistency of the results obtained from both approaches as they come together in density and the natural emergence of a maximum in the speed of sound 𝑐𝑆 at supranuclear densities. The presence of this maximum appears tightly connected to the formation of a diquark gap. Notably, this maximum is observed to exceed the asymptotic value 𝑐$^{2}_{𝑆}$ =1/3 while its exact position in terms of the density cannot yet be determined conclusively.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Kernel Buffer Volume Fraction Margin of the AGR Designed Fuel Particle

Modeling results used to assess the fuel performance of the TRISO-coated fuel particles as a function of kernel/buffer volume fraction include SiC tangential stress, formation of the buffer/IPyC gap, particle temperature profile, internal particle pressure, fission gas released from the kernel, probability of fuel particle failure, and fission product diffusion. These results were evaluated at two burnup levels and irradiation temperatures to bound expected steady-state irradiation conditions. In general, increasing the kernel/buffer volume fraction increases the SiC stress and subsequently the failure probability of a fuel particle when compared to the AGR designed particle. There was little impact on the fission product diffusion through the particle as the kernel/buffer volume fraction increased.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Apparatus and method for producing a crystalline film on a substrate surface

An apparatus and method is provided for coating a surface of a material with a film of porous coordination polymer. A first substrate having a first surface to be coated is positioned in a processing chamber such that the first surface is placed in a substantially opposing relationship to a second surface. In some embodiments, the second surface is provided by a wall of the processing chamber, and in other embodiments the second surface is provided by a second substrate to be coated. The first substrate is held such that a gap exists between the first and second surfaces, and the gap is filled with at least one reaction mixture comprising reagents sufficient to form the crystalline film on at least the first surface. A thin gap (e.g., having a thickness less than 2 mm) between the first and second surfaces is effective for producing a high quality film having a thickness less than 100 μm. Confining the volume of the reaction mixture to a thin layer adjacent the substrate surface significantly reduces problems with sedimentation and concentration control. In some embodiments, the size, shape, or average thickness of the gap is adjusted during formation of the film in response to feedback from at least one film growth monitor.

Britt, David K.↗
DOE OSTI2025

Discovery of an unconventional quantum echo by interference of Higgs coherence

Detecting photon echoes from superconducting Higgs modes is challenging due to the necessity of preserving and retrieving phase coherence encoded in multiple Higgs and quasiparticle (QP) excitations. Here, we demonstrate the emergence of a Higgs echo in niobium superconductors. This approach disentangles unique quantum pathways involving the Higgs mode and QP excitations. Using Higgs echo spectroscopy, we also uncover unconventional echo formation caused by inhomogeneous broadening and “soft” QP bands, which dynamically evolve under terahertz (THz) driving. Specifically, THz pulse pairs modulate the superconducting gap, imprinting coherence and forming a temporal “Higgs grating.” This grating produces echoes with distinctive characteristics: (i) echo rephasing spectral peaks at superconducting gap frequencies, (ii) asymmetric echo formation delays unlike those observed in atoms or semiconductors, and (iii) negative-time echo signals stemming from Higgs-QP anharmonic interactions. Combined with advanced time-frequency analysis, these findings distinguish Higgs from QP responses and clarify their intricate interactions in THz-driven superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Characterizing New Particle Formation and Growth (Field Campaign Report)

New particle formation (NPF) and subsequent growth to sizes at which the aerosol particles can act as cloud condensation nuclei (CCN) is critical for understanding and modeling aerosol-climate interactions (Gordon et al. 2017, Dunne et al. 2016). While sulfuric acid is generally understood to play a central role in NPF and growth, measured sulfuric acid concentrations are insufficient to explain measured formation and growth rates in many locations even when stabilization by ammonia is considered (Kulmala et al. 2014, Riipinen et al. 2012). Extensive laboratory investigations have revealed that amines (Almeida et al. 2013), other reduced nitrogen compounds (Glasoe et al. 2015), and/or oxidized organic compounds (Kirkby et al. 2016) can enhance new particle formation rates and thus may explain, at least in part, the gap between our understanding of new particle formation and the measurements. Our knowledge, however, of the relative importance of these various pathways remains incomplete due to the limited number of ambient measurements, particularly in diverse ecosystems. Agricultural land use areas are particularly understudied despite accounting for ~41% of global land cover (Ellis et al. 2010). Improving our understanding of NPF requires measurements of NPF and the precursors to NPF and growth in a variety of ecosystems and ideally across seasons.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

CFD-Guided Evaluation of Spark-Assisted Gasoline Compression Ignition for Cold Idle Operation

A closed-cycle, three-dimensional (3D) computational fluid dynamics (CFD) analysis campaign was conducted to evaluate the performance of using spark plugs to assist gasoline compression ignition (GCI) combustion during cold idle operations. A conventional spark plug using single-sided J-strap design was put at a location on the cylinder head to facilitate spray-guided spark assistance. Ignition was modeled with an L-type energy distribution to depict the breakdown and the arc-to-glow phases during the energy discharge process. Several key design parameters were investigated, including injector clocking, number of nozzle holes, spray inclusion angle, number of fuel injections, fuel split ratio, and fuel injection timings. The study emphasized the region around the spark gap, focusing on flame kernel formation and development and local equivalence ratio distribution. Flame kernel development and the ignition process were found to correlate strongly with the fuel stratification and the flow velocity near the spark gap. The analysis results showed that the flame kernel development followed the direction of the local flow field. In addition, the local fuel stratification notably influenced early-stage flame kernel development due to varying injection spray patterns and the fuel injection strategies. Among these design parameters, the number of nozzle holes and fuel injection timing had the most significant effects on the engine combustion performance.

42 ENGINEERING↗
DOE OSTI2023

Giant Magnetic and Optical Anisotropy in Cerium-Substituted M-Type Strontium Hexaferrite Driven by $4f$ Electrons

By performing density-functional calculations, we find a giant magnetocrystalline anisotropy (MCA) constant in abundant element cerium $\mathrm{Ce}$ substituted M-type hexaferrite, in the energetically favorable strontium site, assisted by a quantum confined electron transfer from $\mathrm{Ce}$ to a specific iron $\mathrm{2a}$ site. Remarkably, the calculated electronic structure shows that the electron transfer leads to the formation of $\mathrm{Ce}^{3+}$ and $\mathrm{Fe}^{2+}$ at the $\mathrm{2a}$ site producing an occupied $\mathrm{Ce}$$(4f^1)$ state below the Fermi level that adds a significant contribution to MCA and magnetic moment. A half $\mathrm{Ce}$ substitution forms a metallic state, while a full substitution retains the semiconducting state of the strontium hexaferrite (host). In the latter, the band gap is reduced due to the formation of charge-transferred states in the gap region of the host. The optical absorption coefficient shows an enhanced anisotropy between light polarization in parallel and perpendicular directions. Calculated formation energies, including the analysis of probable competing phases, and elastic constants confirm that both compositions are chemically and mechanically stable. With successful synthesis, the $\mathrm{Ce}$ hexaferrite can be an alternative high-performing critical-element-free permanent magnet material adapted for use in devices such as automotive traction drive motors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Robust Surface States and Coherence Phenomena in Magnetically Alloyed SmB 6

Samarium hexaboride is a candidate for the topological Kondo insulator state, in which Kondo coherence is predicted to give rise to an insulating gap spanned by topological surface states. Here we investigate the surface and bulk electronic properties of magnetically alloyed Sm 1-x M x B 6 (M = Ce, Eu), using angle-resolved photoemission spectroscopy and complementary characterization techniques. Remarkably, topologically nontrivial bulk and surface band structures are found to persist in highly modified samples with up to 30% Sm substitution and with an antiferromagnetic ground state in the case of Eu doping. The results are interpreted in terms of a hierarchy of energy scales, in which surface state emergence is linked to the formation of a direct Kondo gap, while low-temperature transport trends depend on the indirect gap.

36 MATERIALS SCIENCE↗
DOE OSTI2025

3D pattern formation of a protein–membrane suspension

Many essential cellular processes, including cell division and the establishment of cell polarity during embryogenesis, are regulated by pattern-forming proteins. These proteins often need to bind to a substrate, such as the cell membrane, onto which they interact and form two-dimensional (2D) patterns. It is unclear how the membrane’s continuity and dimensionality impact pattern formation. Here, we address this gap using the MinDE system, a prototypical example of pattern-forming membrane proteins. We show that when the lipid substrate is fragmented into submicrometer-sized diffusive liposomes, adenosine triphosphate-driven protein–protein interactions generate three-dimensional (3D) spatially extended patterns, despite the complete loss of membrane continuity. Remarkably, these 3D patterns emerge at scales four orders of magnitude larger than the individual liposomes. By systematically varying protein concentration, liposome size, and density, we observed and characterized a variety of 3D dynamical patterns not seen on continuous 2D membranes, including traveling waves, dynamical spirals, and a coexistence phase. Simulations and linear stability analysis of a coarse-grained model revealed that the physical properties of the dispersed membrane effectively rescale both the protein–membrane binding rates and diffusion, two key parameters governing pattern formation and wavelength selection. These findings highlight the robustness of Min’s pattern-forming ability, suggesting that protein–membrane suspensions could serve as an adaptable template for studying out-of-equilibrium self-organization in 3D, beyond in vivo contexts.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Giant Cloud Condensation Nuclei Facilitate Drizzle Formation in Stratocumulus—Insights From a Combined Observation‐Modeling Framework

The mechanism for initiating drizzle drop remains a gap in the current understanding of warm rain formation. One prevalent hypothesis suggests that the presence of Giant Cloud Condensation Nuclei (GCCN) generates drizzle‐sized drops necessary to trigger the Collision‐Coalescence (C‐C) process. Here, in this study, this hypothesis is investigated using a novel framework that integrates in situ observations, remote sensing measurements, and idealized models. Results show that GCCN can efficiently generate drizzle drops through condensation, producing a broad Droplet Size Distribution (DSD) comparable to in situ observations. The large drizzle drop and broad DSD strongly facilitate C‐C, further accelerating drizzle initiation. To compare with observation, the model‐generated DSDs are used to generate radar Doppler spectra where radar reflectivity and Doppler skewness is estimated. The simulated radar quantities correspond well with radar observations, providing critical evidence for the GCCN‐induced drizzle initiation mechanism.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Assessment of exchange-correlation functionals on oxygen vacancy formation energies of metal oxides

Oxygen vacancies are a common defect in oxides and play vital roles in many technological applications such as oxygen separation, catalytic reactors, solid oxide fuel cells, and solar thermochemical water splitting. The oxygen vacancy formation energy is directly related to the oxide reduction enthalpy and the vacancy concentration and, therefore, is a key quantity underlying these applications. The complexity of measuring oxygen vacancy formation energies experimentally suggests the utility of calculations based on density functional theory (DFT). However, the calculated results are strongly dependent on the exchange-correlation functionals and other parameters such as the Hubbard U . In this work, we compare the performance of the meta-GGA strongly constrained and appropriately normed (SCAN) functional and the commonly used semilocal generalized gradient approximation (GGA) functionals with experimental values of structural parameters, band gaps, magnetic structures, and oxygen vacancy formation energies for six representative oxides, i.e., CaMnO 3 , SrMnO 3 , LaMnO 3 , YMnO 3 , LaFeO 3 , and CeO 2 . Further, our results show that SCAN usually has better agreement with the experimental lattice constants and band gaps and larger magnetic moments than the commonly used GGA functionals. Although SCAN overestimates the oxygen vacancy formation energies of transition metal oxides and therefore requires unusually large Hubbard U values to reproduce the experimental reduction enthalpies, it does predict the correct oxygen vacancy formation energy of CeO 2 , which challenges the commonly used GGA and hybrid functionals. Our results underscore the challenges that exist in describing these complex oxides by DFT and may shed light on developing more accurate exchange-correlation functionals for oxygen vacancy formation energy calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Optical and photoemission investigation of structural and magnetic transitions in the iron-based superconductor Sr 0.67 Na 0.33 Fe 2 As 2

We report the temperature-dependent optical conductivity and angle-resolved photoemission spectroscopy (ARPES) studies of the multiband iron-based superconductor Sr 0.67 Na 0.33 Fe 2 As 2 . Measurements were made in the high-temperature tetragonal paramagnetic phase, below the structural and magnetic transitions at $T_N$ $≃$ 125 K in the orthorhombic spin-density-wave (SDW)-like phase and $T_r$ $≃$42 K in the reentrant tetragonal double-Q magnetic phase where both charge and SDWorder exist, and below the superconducting transition at $T_c$ $≃$ 10 K. The free-carrier component in the optical conductivity is described by two Drude contributions: one strong and broad and the other weak and narrow. The broad Drude component decreases dramatically below TN and Tr , with much of its strength being transferred to a bound excitation in the midinfrared, while the narrow Drude component shows no anomalies at either of the transitions, actually increasing in strength at low temperature while narrowing dramatically. The behavior of an infrared-active mode suggests zone folding below Tr. Below Tc the dramatic decrease in the low-frequency optical conductivity signals the formation of a superconducting energy gap. ARPES reveals holelike bands at the center of the Brillouin zone (BZ), with both electron- and holelike bands at the corners. Below $T_N$, the hole pockets at the center of the BZ decrease in size, consistent with the behavior of the broad Drude component; however, below $T_r$ the electronlike bands shift and split, giving rise to a low-energy excitation in the optical conductivity at $≃$20 meV. The $C_2$ and $C_4$ magnetic states, with resulting spin-density-wave and charge-SDW order, respectively, lead to a significant reconstruction of the Fermi surface that has profound implications for the transport originating from the electron and hole pockets but appears to have relatively little impact on the superconductivity in this material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Ingredients for enhanced thermoelectric power at cryotemperatures in the correlated semiconductor CoSbS revealed by its optical response

The semiconducting CoSbS is well-known for its thermoelectric performance at high-temperatures but it is also of interest because of its colossal low-temperature thermopower. Here, we address the temperature dependence of its optical response over a broad spectral range, from which we reveal several ingredients determining the thermoelectric properties at cryo-temperatures. Furthermore, we discover co- herent phonon modes and with the additional support of scanning transmission electron microscopy investigations we provide evidences for in-gap impurity states driving the formation of correlated electrons in the valence band. Their implications, with respect to the high thermoelectric power at low temperatures, are discussed within the framework of the phonon-drag transport of low-mobility heavy quasiparticles.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

A High-Quality Workflow for Multi-Resolution Scientific Data Reduction and Visualization

Multi-resolution methods such as Adaptive Mesh Refinement (AMR) can enhance storage efficiency for HPC applications generating vast volumes of data. However, their applicability is limited and cannot be universally deployed across all applications. Furthermore, integrating lossy compression with multi-resolution techniques to further boost storage efficiency encounters significant barriers. To this end, we introduce an innovative workflow that facilitates high-quality multi-resolution data compression for both uniform and AMR simulations. Initially, to extend the usability of multi-resolution techniques, our workflow employs a compression-oriented Region of Interest (ROI) extraction method, transforming uniform data into a multi-resolution format. Subsequently, to bridge the gap between multi-resolution techniques and lossy compressors, we optimize three distinct compressors, ensuring their optimal performance on multi-resolution data. These optimizations can improve the compression ratio of SOTA approaches by up to 3.3× under the same data quality loss. Lastly, we incorporate an advanced uncertainty visualization method into our workflow to understand the potential impacts of lossy compression. Experimental evaluation demonstrates that our workflow achieves significant compression quality improvements.

Wang, Daoce↗
DOE OSTI2021

Development of Standardized Property Requirements, Measurement Methods, and Reporting Guidance for Coatings

The diverse research programs presently in progress around the world have advanced a large number of coated cladding concepts to various stages of maturity. Industry teams have developed leading coating compositions and geometries, but significant disparity exists in the importance placed on different coating properties, as well as the applicability and standardization of the various methods used to measure these properties. This milestone report provides an initial assessment of the most important coating properties and the experimental methods available for their determination to lay the foundation for standardized reporting and development of comprehensive datasets for modeling efforts. This report has determined that the residual stress of the coating is the most crucial property to investigate, yet it has received minimal attention to date due to a knowledge gap about the growth and formation of the brittle Laves phase under reactor conditions. The significance of residual stress of the coating is further enhanced by its connection and interdependence with other important properties like creep and coating failure mechanisms. This milestone proposes an importance rating for residual stress properties and their associated measurement techniques to fill in knowledge. Furthermore, techniques to investigate the outlined properties are discussed, and their capabilities and limitations are illustrated to provide guidance on their use.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

Method for producing a crystalline film

A method is provided for coating a surface of a material with a film of porous coordination polymer. A first substrate having a first surface to be coated is positioned in a processing chamber such that the first surface is placed in an opposing relationship to a second surface. The second surface may be provided by a wall of the processing chamber, or in some cases the second surface may be provided by a second substrate to be coated. The first substrate is held such that a gap exists between the first and second surfaces, and the gap is filled with at least one reaction mixture comprising reagents sufficient to form the crystalline film on at least the first surface. A thin gap (e.g., less than 2 mm) between the first and second surfaces is effective for producing a high quality film having a thickness less than 100 μm. Confining the volume of the reaction mixture to a thin layer adjacent the substrate surface significantly reduces problems with sedimentation and concentration control. The size, shape, or average thickness of the gap may be adjusted during formation of the film in response to feedback from at least one film growth monitor.

Britt, David K.↗
DOE OSTI2025

Community Dynamics Drive Calcium Carbonate Production in an Enriched Consortium of Soil Microbes

Recently, there has been a focus on using soil microbes as a means to store carbon in the soil in the form of calcium carbonate, outcomes of which include soil stabilization and biocementation. The molecular processes involved in microbially induced calcium carbonate formation are known, but there is still a significant knowledge gap regarding how community interactions, emergent processes that are distinct from the roles of individual members, may drive the formation of carbonate. To answer these questions, we describe the development and application of a consortium of soil microbes consisting of one species each of the Rhodococcus , Microbacterium , and Curtobacterium genera and two species from the Bacillus genus. We term these five species cultivated together carbon storing consortium A (CSC-A). Growth assays show that only a subset of CSC-A members produces CaCO 3 with Rhodococcus producing the most CaCO 3 but the complete CSC-A produces significantly higher amounts of CaCO 3 compared to the sum total carbonate produced by all member species. The development of CSC-A shows that CaCO 3 production may be as much a community process as it is the contribution of individual species, requiring us to move beyond single species analysis to fully understand carbonate formation by microbial communities in nature. CSC-A will allow the scientific community to ask and answer key questions about the molecular interactions surrounding inorganic carbon formation in soil, an important knowledge gap that must be filled if we wish to stabilize soils and harness microbial processes for materials production.

calcium carbonate↗
DOE OSTI2021

Excited Rydberg states in MoSe 2 /WSe 2 heterostructures

The functional form of Coulomb interactions in the transition metal dichalcogenides (TDMs) and other van der Waals solids is critical to many of their unique properties, e.g. strongly-correlated electron states, superconductivity and emergent ferromagnetism. This paper presents measurements of key excitonic energy levels in MoSe 2 /WSe 2 heterostructures. These measurements are obtained from resonance Raman experiments on specific Raman peaks only observed at excited states of the excitons. This data is used to validate a model of the Coulomb potential in these structures which predicts the exciton energies to within ~5 meV. This model is used to determine the effect of heterostructure formation on the single-particle band gaps of the layers and will have a wide applicability in designing the next generation of more complex TDM structures.

Materials Science↗