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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 1,513 records · Page 84
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Magnetic properties of spin frustrated spinel ZnFe{sub 2}O{sub 4}/ZnCr{sub 2}O{sub 4} superlattices

Superlattice films composed of frustrated spin systems, [ZnFe{sub 2}O{sub 4}]{sub m}/[ZnCr{sub 2}O{sub 4}]{sub m}, are grown on MgAl{sub 2}O{sub 4} (111) substrates by pulsed laser deposition, and their frustrated magnetism is studied. The superlattice films show spin-glass behavior and the spin-glass transition temperature (T{sub g}) varies nonmonotonically as a function of the layer thickness m. T{sub g} increases with decreasing m due to an increase in the inhomogeneous exchange interaction between Cr{sup 3+} and Fe{sup 3+} at the interface. However, below m = 4, a decrease in T{sub g} is observed. Compared with the solid solution Zn(CrFe)O{sub 4} film and the other superlattices, the decrease in T{sub g} is considered to be a unique property of the periodically modulated short period superlattices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Physical mechanisms of SiN{sub x} layer structuring with ultrafast lasers by direct and confined laser ablation

In the production process of silicon microelectronic devices and high efficiency silicon solar cells, local contact openings in thin dielectric layers are required. Instead of photolithography, these openings can be selectively structured with ultra-short laser pulses by confined laser ablation in a fast and efficient lift off production step. Thereby, the ultrafast laser pulse is transmitted by the dielectric layer and absorbed at the substrate surface leading to a selective layer removal in the nanosecond time domain. Thermal damage in the substrate due to absorption is an unwanted side effect. The aim of this work is to obtain a deeper understanding of the physical laser-material interaction with the goal of finding a damage-free ablation mechanism. For this, thin silicon nitride (SiN{sub x}) layers on planar silicon (Si) wafers are processed with infrared fs-laser pulses. Two ablation types can be distinguished: The known confined ablation at fluences below 300 mJ/cm{sup 2} and a combined partial confined and partial direct ablation at higher fluences. The partial direct ablation process is caused by nonlinear absorption in the SiN{sub x} layer in the center of the applied Gaussian shaped laser pulses. Pump-probe investigations of the central area show ultra-fast reflectivity changes typical for direct laser ablation. Transmission electron microscopy results demonstrate that the Si surface under the remaining SiN{sub x} island is not damaged by the laser ablation process. At optimized process parameters, the method of direct laser ablation could be a good candidate for damage-free selective structuring of dielectric layers on absorbing substrates.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1978

Friction and wear of several compressor gas-path seal movements

Rub interaction experiments were conducted on a series of sintered and plasma sprayed compressor gas path seal materials in contact with Ti-6Al-4V blade tip and knife edge rotors. The most rub tolerant materials investigated were sintered Nichrome and plasma sprayed nickel 25 percent graphite. The effectiveness of providing a compliant substrate for dense seal material coatings was also demonstrated. In general, it was observed that rotor wear and high frictional energy generation rates accompanied smearing or surface densification of the materials investigated. The onset of smearing was sensitive to rub interaction parameters and seal geometry. Two complementary models were proposed to account for the smearing trends. One is based on thermal effects, the other on particulate escape effects. They were shown to be consistent with the experimental evidence at hand, and together they predict that smearing, with the onset of high energy rub conditions, is favored when incursion rates (radial motion) are low, incursion depths are high, the seal geometry is of a knife-edge character, and the seal particle size is small.

Bill, R. C.↗
DOE OSTI2016

A Structurally Dynamic Region of the HslU Intermediate Domain Controls Protein Degradation and ATP Hydrolysis

The I domain of HslU sits above the AAA+ ring and forms a funnel-like entry to the axial pore, where protein substrates are engaged, unfolded, and translocated into HslV for degradation. The L199Q I-domain substitution, which was originally reported as a loss-of-function mutation, resides in a segment that appears to adopt multiple conformations as electron density is not observed in HslU and HslUV crystal structures. The L199Q sequence change does not alter the structure of the AAA+ ring or its interactions with HslV but increases I-domain susceptibility to limited endoproteolysis. Notably, the L199Q mutation increases the rate of ATP hydrolysis substantially, results in slower degradation of some proteins but faster degradation of other substrates, and markedly changes the preference of HslUV for initiating degradation at the N or C terminus of model substrates. As such, a structurally dynamic region of the I domain plays a key role in controlling protein degradation by HslUV.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2011

Energetic deposition of carbon in a cathodic vacuum arc with a biased mesh

Carbon films were deposited in a filtered cathodic vacuum arc with a bias potential applied to a conducting mesh mounted in the plasma stream between the source and the substrate. We determined the stress and microstructural properties of the resulting carbon films and compared the results with those obtained using direct substrate bias with no mesh. Since the relationship between deposition energy and the stress, sp{sup 2} fraction and density of carbon are well known, measuring these film properties enabled us to investigate the effect of the mesh on the energy and composition of the depositing flux. When a mesh was used, the film stress showed a monotonic decrease for negative mesh bias voltages greater than 400V, even though the floating potential of the substrate did not vary. We explain this result by the neutralization of some ions when they are near to or passing through the negatively biased mesh. The microstructure of the films showed a change from amorphous to glassy carbonlike with increasing bias. Potential applications for this method include the deposition of carbon films with controlled stress on low conductivity substrates to form rectifying or ohmic contacts.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

High-Performance CO 2 Capture from Air by Harnessing the Power of CaO- and Superbase-Ionic-Liquid-Engineered Sorbents

Direct air capture (DAC) of CO 2 by solid porous materials represents an attractive “negative emission” technology. However, state-of-the-art sorbents based on supported amines still suffer from unsolved high energy consumption and stability issues. For this work, taking clues from the CO 2 interaction with superbase-derived ionic liquids (SILs), high-performance and tunable sorbents in DAC of CO 2 was developed by harnessing the power of CaO- and SIL-engineered sorbents. Deploying mesoporous silica as the substrate, a thin CaO layer was first introduced to consume the surface-OH groups, and then active sites with different basicities (e. g., triazolate and imidazolate) were introduced as a uniformly distributed thin layer. The as-obtained sorbents displayed high CO 2 uptake capacity via volumetric (at 0.4 mbar) and breakthrough test (400 ppm CO 2 source), rapid interaction kinetics, facile CO 2 releasing, and stable sorption/desorption cycles. Operando diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS) analysis under simulated air atmosphere and solid-state NMR under 13 CO 2 atmosphere demonstrated the critical roles of the SIL species in low-concentration CO 2 capture. The fundamental insights obtained in this work provide guidance on the development of high-performance sorbents in DAC of CO 2 by leveraging the combined advantages of porous solid scaffolds and the unique features of CO 2 -philic ionic liquids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Nanoscale ferroelastic twins formed in strained LaCoO 3 films

The coexistence and coupling of ferroelasticity and magnetic ordering in a single material offers a great opportunity to realize novel devices with multiple tuning knobs. Complex oxides are a particularly promising class of materials to find multiferroic interactions due to their rich phase diagrams, and are sensitive to external perturbations. Still, there are very few examples of these systems. Here, we report the observation of twin domains in ferroelastic LaCoO 3 epitaxial films and their geometric control of structural symmetry intimately linked to the material’s electronic and magnetic states. A unidirectional structural modulation is achieved by selective choice of substrates having twofold rotational symmetry. This modulation perturbs the crystal field–splitting energy, leading to unexpected in-plane anisotropy of orbital configuration and magnetization. These findings demonstrate the use of structural modulation to control multiferroic interactions and may enable a great potential for stimulation of exotic phenomena through artificial domain engineering.

36 MATERIALS SCIENCE↗
DOE OSTI2015

USP22 acts as an oncogene by regulating the stability of cyclooxygenase-2 in non-small cell lung cancer

The histone ubiquitin hydrolase ubiquitin-specific protease 22 (USP22) is an epigenetic modifier and an oncogene that is upregulated in many types of cancer. In non-small cell lung cancer (NSCLC), aberrant expression of USP22 is a predictor of poor survival, as is high expression of cyclooxygenase-2 (COX-2). Despite its oncogenic role, few substrates of USP22 have been identified and its mechanism of action in cancer remains unclear. Here, we identified COX-2 as a direct substrate of USP22 and showed that its levels are modulated by USP22 mediated deubiquitination. Silencing of USP22 downregulated COX-2, decreased its half-life, and inhibited lung carcinoma cell proliferation by directly interacting with and modulating the stability and activity of COX-2 through the regulation of its ubiquitination status. The findings of the present study suggest a potential mechanism underlying the oncogenic role of USP22 mediated by the modulation of the stability and activity of COX-2. - Highlights: • USP22 interacts with COX-2. • USP22 deubiquitinates and stabilizes COX-2. • USP22 is required for COX-2-mediated upregulation of prostaglandin E2.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2026

Substrate-Directed Dimensional and Phase Control of Peptide Assemblies on Two-Dimensional van der Waals Materials

Understanding and controlling biomolecular self-assembly on van der Waals (vdW) materials has the potential to advance hybrid bioelectronic devices by enabling precise tuning of the interface and modulation of the resulting electronic properties of the biomolecule-vdW heterostructure. However, how surface properties of vdW materials direct biomolecule assembly remains poorly understood. To fill this knowledge gap, we investigated the assembly of a peptide known to assemble into two-dimensional (2D) crystalline films on MoS 2 on three representative vdW surfaces: WS 2 , MoS 2 , and highly oriented pyrolytic graphite (HOPG). Using in situ atomic force microscopy (AFM), we find that assembly is substrate-dependent, resulting in multilayers on WS 2 , monolayers on MoS 2 , and multiple coexisting phases on HOPG. WS 2 exhibits a higher negative charge, strong long-range electrostatic interactions, and extensive hydration layering that may promote multilayer stacking. In contrast, MoS 2 has stronger short-range interactions with the peptides but much weaker long-range interactions and hydration structure, which may favor monolayer formation. Molecular dynamics simulations predict a corresponding switch from monolayer to multilayer aggregates of the adsorbed monomers, reflected in their relative mobilities. On hydrophobic HOPG, the peptides bind most strongly and remain as monomers with high surface mobility. The peptide dimers comprising the basic unit of the crystals are more compact on HOPG, which has a smaller lattice constant than WS 2 or MoS 2 , suggesting strain contributes to stabilizing multiple phases. Our results provide mechanistic insights into how surface charge and hydration structure, and the lattice structure of the substrates governs peptide assembly on vdW materials, offering a framework to rationally control the 2D peptide-vdW heterostructures.

Molecular dynamics simulations↗
DOE OSTI2012

Charged Amino Acids (R83, E567, D617, E625, R669, and K678) of CusA Are Required for Metal Ion Transport in the Cus Efflux System

Gram-negative bacteria expel various toxic chemicals via tripartite efflux pumps belonging to the resistance-nodulation-cell division superfamily. These pumps span both the inner and outer membranes of the cell. The three components of these tripartite systems are an inner-membrane, substrate-binding transporter (or pump); a periplasmic membrane fusion protein (or adaptor); and an outer-membrane-anchored channel. These three efflux proteins interact in the periplasmic space to form the three-part complexes. We previously presented the crystal structures of both the inner-membrane transporter CusA and membrane fusion protein CusB of the CusCBA tripartite efflux system from Escherichia coli. We also described the co-crystal structure of the CusBA adaptor-transporter, revealing that the trimeric CusA efflux pump assembles with six CusB protein molecules to form the complex CusB{sub 6}-CusA{sub 3}. We here report three different conformers of the crystal structures of CusBA-Cu(I), suggesting a mechanism on how Cu(I) binding initiates a sequence of conformational transitions in the transport cycle. Genetic analysis and transport assays indicate that charged residues, in addition to the methionine pairs and clusters, are essential for extruding metal ions out of the cell.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

The role of cardiac energy metabolism in cardiac hypertrophy and failure

In mammalian heart, incessant production of cellular energy is vital for maintaining continuous mechanical pumping function providing the body for oxygen and nutrients. To ensure this essential function, cardiac muscle adapt to increased energy demand or compromised energy supply by reprogramming the network of genes whose products are necessary to match the production of energy to consumption. Failure in this regulation leads to severe cardiac dysfunction and has been associated with cardiac pathogenesis including cardiac hypertrophy, failure and diabetes. Metabolic adaptations are induced by network of transcriptional pathways that are activated by a variety of factors such as hormones, nutrients, second messengers and oxygen. The metabolic phenotype of the heart is maintained by pathways controlling transcriptional regulators, which include peroxisome proliferator-activated receptors, estrogen-related receptors and nuclear respiratory factors, as well as their common coactivator protein peroxisome proliferator-activated receptor γ coactivator 1. These central regulators of gene expression are complemented with factors such as hypoxia inducible factor 1, which is activated in insufficient oxygenation of the tissue. Here, we discuss how these pathways relate to the cardiac metabolism and how they interact with pathways controlling the contractile phenotype of the heart. - Highlights: • Energy metabolic changes are associated with cardiac adaptation and pathogenesis. • Cardiac energy substrate utilisation is controlled by complex transcriptional networks. • Transcriptional pathways controlling heart metabolic and contractile phenotype overlap.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Interaction of cesium adatoms with free-standing graphene and graphene-veiled SiO 2 surfaces

In this study, the interaction of Cs adatoms with mono- or bi-layered graphene (MLG and BLG), either free-standing or on a SiO 2 substrate, was investigated using density functional theory. The most stable adsorption sites for Cs are found to be hollow sites on both graphene sheets and graphene-veiled SiO 2 (0001). In addition, larger dipole moments are created when a MLG-veiled SiO 2 (0001) substrate is used for adsorption of Cs atoms compared to the adsorption on free-standing MLG, due to charge transfer occurring between the MLG and the SiO 2 substrate. For the adsorption of Cs on BLG-veiled SiO 2 (0001) substrate, these differences are smoothed out and the binding energies corresponding to different sites are nearly degenerate; smaller dipole moments created by the Cs adatoms on BLG compared to MLG are also predicted.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

An N$\cdots$H$\cdots$N low-barrier hydrogen bond preorganizes the catalytic site of aspartate aminotransferase to facilitate the second half-reaction

Pyridoxal 5'-phosphate (PLP)-dependent enzymes have been extensively studied for their ability to fine-tune PLP cofactor electronics to promote a wide array of chemistries. Neutron crystallography offers a straightforward approach to studying the electronic states of PLP and the electrostatics of enzyme active sites, responsible for the reaction specificities, by enabling direct visualization of hydrogen atom positions. Here we report a room-temperature joint X-ray/neutron structure of aspartate aminotransferase (AAT) with pyridoxamine 5'-phosphate (PMP), the cofactor product of the first half reaction catalyzed by the enzyme. Between PMP N SB and catalytic Lys258 Nζ amino groups an equally shared deuterium is observed in an apparent low-barrier hydrogen bond (LBHB). Density functional theory calculations were performed to provide further evidence of this LBHB interaction. The structural arrangement and the juxtaposition of PMP and Lys258, facilitated by the LBHB, suggests active site preorganization for the incoming ketoacid substrate that initiates the second half-reaction.

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

Divertor heat load estimates on NSTX and DIII-D using new and open-source 2D inversion analysis code

A thermography inversion algorithm has been developed in the open-source Python-based computer code, HYPERION, to calculate the heat flux incident on plasma-facing components (PFCs) in axisymmetric tokamaks. The chosen mesh size at the surface significantly affects the calculated transient heat flux results. The calculated transient heat flux will exceed the real value when the mesh size tends to zero but will underestimate the real value when the mesh size is large. A criterion for determining the appropriate mesh size for the transient heat flux calculation will be discussed. The numerical scheme for HYPERION uses a 2D fully implicit finite-difference approach, allowing temperature-dependent thermal properties of PFC materials. The inversion algorithm is benchmarked against established heat flux calculation codes, TACO and THEODOR, based on thermography data from NSTX and DIII-D respectively. The primary benefits of HYPERION compared to TACO and THEODOR are that it is open-source and it allows for the optimization of mesh thickness along the substrate. The algorithm also accounts for the thermal properties of thin surface layers that characteristically form on PFCs due to plasma-material interactions. The agreement between HYPERION and THEODOR is excellent, as the percent difference between the codes is ~5% on average in the case of the DIII-D data for moderate to high heat flux. Verification tests with TACO show slightly higher average percent differences of 8% and 12%. In using HYPERION to study filaments in heat flux, the initial results indicate that small ELMs filaments significantly broaden the divertor heat flux, and decrease divertor peak flux. Compared to the inter-ELM, the small ELM filaments decrease the divertor peak surface temperature. With intermittent divertor filaments, the divertor heat flux width is comparable with that found in L-mode.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Hopping crossover and high-temperature superspin glass behavior in Ni films deposited on MoS 2

Realizing the potential of MoS 2 and other two-dimensional semiconductors in spintronic devices requires a fundamental understanding of their interaction with ferromagnetic metals. We have investigated the transport and magnetic properties of thin Ni films grown on single-crystal MoS 2 substrates. The Ni is found to have a granular morphology with an average grain size of approximately 2 nm. Like previously investigated granular Ni/insulator composites below the percolation threshold, transport is found to proceed via hopping. However, our Ni/MoS 2 sample exhibits a dual crossover: activated hopping to 𝑇−1/2 variable-range hopping at a higher temperature and then a transition to power-law behavior at a lower temperature. The magnetoresistance was used as a novel probe for uncovering superspin-glass-like behavior above room temperature in the Ni/MoS 2 nanostructure, which also exhibits a collective ferromagnetic state at very low temperatures, reminiscent of superferromagnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Pattern formation and flocking for particles near the jamming transition on resource gradient substrates

Here, we numerically examine a bidisperse system of active and passive particles coupled to a resource substrate. The active particles deplete the resource at a fixed rate and move toward regions with higher resources, while all of the particles interact sterically with each other. We show that at high densities, this system exhibits a rich variety of pattern-forming phases along with directed motion or flocking as a function of the relative rates of resource absorption and consumption as well as the active to passive particle ratio. These include partial phase separation into rivers of active particles flowing through passive clusters, strongly phase separated states where the active particles induce crystallization of the passive particles, mixed jammed states, and fluctuating mixed fluid phases. For higher resource recovery rates, we demonstrate that the active particles can undergo motility-induced phase separation, while at high densities, there can be a coherent flock containing only active particles or a solid mixture of active and passive particles. The directed flocking motion typically shows a transient in which the flow switches among different directions before settling into one direction, and there is a critical density below which flocking does not occur. We map out the different phases as function of system density, resource absorption and recovery rates, and the ratio of active to passive particles.

97 MATHEMATICS AND COMPUTING↗