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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Correlation of the Structure with Performance in MEH-PPV/dPS Thin Films Illuminated during Processing

Thin films containing conjugated polymers have been used in a wide array of optoelectronic devices, and much research has focused on the conformation of the conjugated polymer as a key aspect to tuning the performance of the resulting devices. White light exposure has been studied as a post-processing method to alter the film’s morphology and photoluminescence (PL) in systems composed of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and polystyrene (PS). To date, there have been few studies that correlate the changes in the depth profile with the PL performance of MEH-PPV/PS films. This study is designed to address this gap in knowledge. Thin films of MEH-PPV/dPS annealed above the glass transition temperatures (T g ) in an illuminated environment led to lower PL than that found in annealed samples that are not illuminated. However, at higher MEH-PPV loading in the blend film, the extent of variation of PL with illumination diminished. Additionally, time-of-flight secondary ion mass spectrometry and small-angle neutron scattering document the three-dimensional morphology of the films under illumination conditions, which are correlated with the changes in PL. Illumination during annealing compressed MEH-PPV-rich layers in the thin film blends at low loadings of MEH-PPV (below 10 wt %) but resulted in significant in-plane phase separation at higher loadings (above 15 wt %). Both changes increase interchain interactions and lower the PL of the illuminated samples. The changes in the depth profile significantly alter the PL of the films, while the in-plane phase separation affected the optoelectronic properties to a lesser degree. This work, therefore, provides insights into how illumination and film composition can be utilized to predictably alter the structure and optoelectronic performance of conjugated polymer blend films.

36 MATERIALS SCIENCE↗
NASA NTRS2001

Three-dimensionally ordered array of air bubbles in a polymer film

We report the formation of a three-dimensionally ordered array of air bubbles of monodisperse pore size in a polymer film through a templating mechanism based on thermocapillary convection. Dilute solutions of a simple, coil-like polymer in a volatile solvent are cast on a glass slide in the presence of moist air flowing across the surface. Evaporative cooling and the generation of an ordered array of breath figures leads to the formation of multilayers of hexagonally packed water droplets that are preserved in the final, solid polymer film as spherical air bubbles. The dimensions of these bubbles can be controlled simply by changing the velocity of the airflow across the surface. When these three-dimensionally ordered macroporous materials have pore dimensions comparable to the wavelength of visible light, they are of interest as photonic band gaps and optical stop-bands.

Non-NASA Center↗
NASA NTRS2004

Dynamical Modeling of Mars' Paleoclimate

This report summarizes work undertaken under a one-year grant from the NASA Mars Fundamental Research Program. The goal of the project was to initiate studies of the response of the Martian climate to changes in planetary obliquity and orbital elements. This work was undertaken with a three-dimensional numerical climate model based on the Geophysical Fluid Dynamics Laboratory (GFDL) Skyhi General Circulation Model (GCM). The Mars GCM code was adapted to simulate various obliquity and orbital parameter states. Using a version of the model with a basic water cycle (ice caps, vapor, and clouds), we examined changes in atmospheric water abundances and in the distribution of water ice sheets on the surface. This work resulted in a paper published in the Journal of Geophysical Research - Planets. In addition, the project saw the initial incorporation of a regolith water transport and storage scheme into the model. This scheme allows for interaction between water in the pores of the near subsurface (<3m) and the atmosphere. This work was not complete by the end of the one-year grant, but is now continuing within the auspices of a three-year grant of the same title awarded by the Mars Fundamental Research Program in late 2003.

Richardson, Mark I.↗
NASA NTRS1994

Estimates of the changes in tropospheric chemistry which result from human activity and their dependence on NO(x) emissions and model resolution

As a consequence of the non-linear behavior of the chemistry of the atmosphere and because of the short lifetime of nitrogen oxides (NO(x)), two-dimensional models do not give an adequate description of the production and destruction rates of NO(x) and their effects on the distributions of the concentration of ozone and hydroxyl radical. In this study, we use a three-dimensional model to evaluate the contribution of increasing NO(x) emissions from industrial activity and biomass burning to changes in the chemical composition of the troposphere. By comparing results obtained from longitudinally-uniform and longitudinally-varying emissions of NO(x), we demonstrate that the geographical representation of the NO(x) emissions is crucial in simulating tropospheric chemistry.

Kanakidou, Maria↗
DOE OSTI2022

Exploring the roles of microbes in facilitating plant adaptation to climate change

Plants benefit from their close association with soil microbes which assist in their response to abiotic and biotic stressors. Yet much of what we know about plant stress responses is based on studies where the microbial partners were uncontrolled and unknown. Under climate change, the soil microbial community will also be sensitive to and respond to abiotic and biotic stressors. Thus, facilitating plant adaptation to climate change will require a systems-based approach that accounts for the multi-dimensional nature of plant–microbe–environment interactions. In this perspective, we highlight some of the key factors influencing plant–microbe interactions under stress as well as new tools to facilitate the controlled study of their molecular complexity, such as fabricated ecosystems and synthetic communities. When paired with genomic and biochemical methods, these tools provide researchers with more precision, reproducibility, and manipulability for exploring plant–microbe–environment interactions under a changing climate.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Substance P in the Gas Phase: Conformational Changes and Dissociations Induced by Collisional Activation in a Drift Tube

The work presented below is related to our companion paper in this issue, entitled: Substance P in solution: trans-to-cis configurational changes of penultimate prolines initiate non-enzymatic peptide bond cleavages. Two-dimensional ion mobility spectrometry (IMS-IMS) and mass spectrometry techniques are used to investigate structural transitions for [M+3H]{sup 3+} ions of substance P (subP) upon collisional activation (CA) in the gas phase. In this approach, different conformations of ions having a specified mobility are selected after an initial IMS separation, collisionally activated to produce new conformers, and these product structures are separated again using a second IMS region. In this way, it is possible to follow folding and unfolding transitions of different conformations. The analysis shows evidence for five conformations. Unlike other systems, every transition is irreversible. Studies as a function of activation voltage are used to discern pathways of structural changes prior to reaching the energy required for dissociation. Thresholds associated with the onsets of transitions are calibrated to obtain estimates of the energetic barriers between different structures and semi-quantitative potential energy diagrams are presented. Overall, barriers associated with structural transitions of [subP+3H]{sup 3+} in the absence of solvent are on the order of ~ 40 kJ mol{sup −1}, substantially lower than the ~ 90 kJ mol{sup −1} required for some similar structural transitions in solutions of ethanol. Comparisons of the transition energies in the gas phase with thermochemistry for similar transitions in solution provide clues about why reverse transitions are prohibited. .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1981

Application of a Laser Interferometer Skin-Friction Meter in Complex Flows

A nonintrusive skin-friction meter has been found useful for a variety of complex wind-tunnel flows. This meter measures skin friction with a remotely located laser interferometer that monitors the thickness change of a thin oil film. Its accuracy has been proven in a low-speed flat-plate flow. The wind-tunnel flows described here include sub-sonic separated and reattached flow over a rearward-facing step, supersonic flow over a flat plate at high Reynolds numbers, and supersonic three - dimensional vortical flow over the lee of a delta wing at angle of attack. The data-reduction analysis was extended to apply to three-dimensional flows with unknown flow direction, large pressure and shear gradients, and large oil viscosity changes with time. The skin friction measurements were verified, where possible, with results from more conventional techniques and also from theoretical computations.

Monson, D. J.↗
NASA NTRS1992

The three-dimensional evolution of a plane mixing layer. Part 2: Pairing and transition to turbulence

The evolution of three-dimensional temporally evolving plane mixing layers through as many as three pairings was simulated numerically. Initial conditions for all simulations consisted of a few low-wavenumber disturbances, usually derived from linear stability theory, in addition to the mean velocity. Three-dimensional perturbations were used with amplitudes ranging from infinitesimal to large enough to trigger a rapid transition to turbulence. Pairing is found both to inhibit the growth of infinitesimal three-dimensional disturbances and to trigger the transition to turbulence in highly three dimensional flows. The mechanisms responsible for the growth of three-dimensionality as well as the initial phases of the transition to turbulence are described. The transition to turbulence is accompanied by the formation of thin sheets of span wise vorticity, which undergo a secondary roll up. Transition also produces an increase in the degree of scalar mixing, in agreement with experimental observations of mixing transition. Simulations were also conducted to investigate changes in span wise length scale that may occur in response to the change in stream wise length scale during a pairing. The linear mechanism for this process was found to be very slow, requiring roughly three pairings to complete a doubling of the span wise scale. Stronger three-dimensionality can produce more rapid scale changes but is also likely to trigger transition to turbulence. No evidence was found for a change from an organized array of rib vortices at one span wise scale to a similar array at a larger span wise scale.

Moser, Robert D.↗
DOE OSTI2018

Entropy Signatures of Topological Phase Transitions

We review the behavior of the entropy per particle in various two-dimensional electronic systems. The entropy per particle is an important characteristic of any many-body system that tells how the entropy of the ensemble of electrons changes if one adds one more electron. Recently, it has been demonstrated how the entropy per particle of a two-dimensional electron gas can be extracted from the recharging current dynamics in a planar capacitor geometry. These experiments pave the way to the systematic studies of entropy in various crystal systems including novel two-dimensional crystals such as gapped graphene, germanene, and silicene. Theoretically, the entropy per particle is linked to the temperature derivative of the chemical potential of the electron gas by the Maxwell relation. Using this relation, we calculate the entropy per particle in the vicinity of topological transitions in various two-dimensional electronic systems. We show that the entropy experiences quantized steps at the points of Lifshitz transitions in a two-dimensional electron gas with a parabolic energy spectrum. In contrast, in doubled-gapped Dirac materials, the entropy per particle demonstrates characteristic spikes once the chemical potential passes through the band edges. The transition from a topological to trivial insulator phase in germanene is manifested by the disappearance of a strong zero-energy resonance in the entropy per particle dependence on the chemical potential. We conclude that studies of the entropy per particle shed light on multiple otherwise hidden peculiarities of the electronic band structure of novel two-dimensional crystals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Δ133p53 coordinates ECM-driven morphogenesis and gene expression in 3-dimensional mammary epithelial acini

Growing evidence indicates that p53 has a crucial role in normal tissue development. The role of the canonical p53 (p53α) and its 12± isoforms in development and homeostasis of healthy tissue remains poorly understood. Here we demonstrate that Δ133p53, three short isoforms of p53 isoform, responds specifically to laminin-111 and plays an important regulatory role in formation of mammary organoids in concert with p53α. We demonstrate that down-modulation of Δ133p53 isoforms leads to changes in gene expression of extracellular matrix molecules: fibronectin (FN), EDA+-FN, laminin α5, and laminin α3 in human breast epithelial cells. These changes resulted in increased actin stress fibers and enhanced migratory behavior of cells in 2-dimensional culture. We found that α5β1-integrin coupled with the extracellularly deposited EDA+-FN activates Akt signaling pathway in 3-dimensional (3D) culture when Δ133p53 is dysregulated. Cells that do not express detectable Δ133p53 isoforms or express low levels of these isoforms failed to form polarized structures in 3D. These results uncover that Δ133p53 isoforms coordinate expression and deposition of organ-specific ECM molecules that are critical for maintenance of tissue architecture and function.

Lee, Sun-Young (ORCID:000000034970241X)↗
DOE OSTI2022

Metallurgical alloy approach to two-dimensional supramolecular materials

Alloys are normally mixtures of metallic elements used to search for superior functional properties compared with their individual components. Although a quintessential approach to better materials in metallurgy, the concept of alloying has been expanded to other inorganic materials and covalent polymers. In this work, we report on alloy formation of small organic molecules structured as amphiphilic chromophores in water. Using X-ray scattering, microscopy, and optical spectroscopy, we unambiguously demonstrate the formation of supramolecular alloys with changes in physical, photophysical, and mechanical properties. Additionally, we identify single-crystalline, two-dimensional supramolecular polymers containing multiple molecular species, analogous to intermetallic compounds. The mechanism of alloy formation suggests the possibility of controlled growth in these supramolecular assemblies to create emergent functional structures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Compressional wave velocity and effective stress in unsaturated soil: Potential application for monitoring moisture conditions in vadose zone sediments

Compressional seismic (P-wave) velocities were measured experimentally at different water potentials and confining pressure states using a variety of sediments collected from the US Department of Energy Hanford Site in southeastern Washington State. P-wave velocity was measured in variably saturated sediments using ultrasonic piezoelectric transducers and water potential was measured with a heat dissipation sensor. We propose a model to relate changes in P-wave velocity to soil stress conditions using an effective stress formulation that includes capillary stress as well as adsorptive stress. We show that compressional wave velocities can be related to water potential and confining stress using a model with five fitted parameters. A single set of parameters provides an excellent fit to data acquired from all of the sediment samples. Under very dry conditions, corresponding to low water potentials, water flow occurs in adsorptive thin films associated with very low unsaturated hydraulic conductivities. The results presented here suggest the utility of seismic methods for establishing low water potential and flow conditions within variably saturated Hanford formation sediments and providing feedback on the performance of mitigation efforts such as soil desiccation and surface infiltration barriers. Seismic methods can provide minimally invasive, three-dimensional information on relevant flow conditions in vadose zone sediments as well as changes that occur over time.

Linneman, Dorothy C.↗
NASA NTRS1998

Total Lightning and Radar Storm Characteristics Associated with Severe Storms in Central Florida

This paper examines the three dimensional characteristics of lightning flashes and severe storms observed in Central Florida during 1997-1998. The lightning time history of severe and tornadic storms were captured during the on-going ground validation campaign supporting the Lightning Imaging Sensor (LIS) experiment on the Tropical Rainfall Measuring Mission (TRMM). The ground validation campaign is a collaborative experiment that began in 1997 and involves scientists at the Global Hydrology and Climate Center, MIT/Lincoln Laboratories, and the NWS Forecast Office at Melbourne, FL. Lightning signatures that may provide potential early warning of severe storms are being evaluated by the forecasters at the NWS/MLB office. Severe storms with extreme flash rates sometimes exceeding 300 per minute and accompanying rapid increases in flash rate prior to the onset of the severe weather (hall, damaging winds, tornadoes) have been reported by Hodanish et al. and Williams et al. (1998-this conference). We examine the co-evolving changes in storm structure (mass, echo top, shear, latent heat release) and kinematics associated with these extreme and rapid flash rate changes over time. The flash frequency and density are compared with the three dimensional radar reflectivity structure of the storm to help interpret the possible mechanisms producing the extreme and rapidly increasing flash rates. For two tornadic storms examined thus far, we find the burst of lightning is associated with the development of upper level rotation in the storm. In one case, the lightning burst follows the formation of a bounded weak echo region (BWER). The flash rates diminish with time as the rotation develops to the ground in conjunction with the decent of the reflectivity core. Our initial findings suggest the dramatic increase of flash rates is associated with a sudden and dramatic increase in storm updraft intensity which we hypothesize is stretching vertical vorticity as well as enhancing the development of the mixed phase region of the storm. We discuss the importance of these factors in producing both the observed extreme flash rates and the severe weather that follows in these storms and others to be presented.

Goodman, Steven J↗
DOE OSTI2022

Application of Poly(ether sulfone)‐Based Membranes in Clean Energy Technology

Abstract Poly(ether sulfone) (PES) is a kind of polymer materials with excellent electrical insulation and acid/alkali stability. PES can be operated at high temperature continuously for a long time and still maintain excellent property stability in the environments with rapidly changed temperature, namely, great thermostability. Moreover, PES has low molding shrinkage, good dimensional stability and excellent film‐forming characteristics. Compared with inorganic membranes, PES‐based membranes have lower cost, which have received more attention and wide recognition in the field of clean energy technologies in recent years, such as flow batteries, fuel cells, water treatment, and gas separation. Therefore, this review summarizes the research status and prospect of the utilization of PES‐based membranes in clean energy fields, in order to further promote their development and application.

Chemistry↗
DOE OSTI2019

Reservoir scale reactive-transport modeling of a buoyancy-controlled CO 2 plume with impurities (SO 2 , NO 2 , O 2 )

We present that a demonstration project for the geological storage of CO 2 is currently being considered in the deep Precipice Sandstone formation of the Surat Basin, Queensland, Australia. Because of the presence of potential fresh water resources in this formation, a reservoir-scale two-dimensional reactive-transport model was developed to assess temporal and spatial changes in water quality imposed by co-injecting CO 2 with SO 2 , NO 2 , and O 2 at this location. The model shows that because the injection rate is relatively low (60,000 tons/year), flow is buoyancy-dominated and under these conditions the predicted CO 2 flow pattern is quite sensitive to fine-scale heterogeneities and the resolution of the numerical mesh. The model also shows that SO 2 and NO 2 readily partition into the aqueous phase in close vicinity of their injection point, lowering pH somewhat beyond the acidification from CO 2 dissolution. Only O 2 under redox disequilibrium conditions is modeled to persist in the CO 2 plume away from the injection point, however at sub-ppm levels. In conclusion, this modeling effort demonstrates acidification near the wellbore due to the preferential stripping of gas impurities, and accumulation of CO 2 around a lithostratigraphic boundary above the target formation, where relatively rapid mineral dissolution (muscovite, chlorite and calcite) and precipitation (ankerite, kaolinite and chalcedony) occur.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

200 MeV proton irradiation of the oxide-dispersion-strengthened copper alloy (GlidCop-Al15)

In search to identify extremely stable materials to perform the collimation function of the 7-TeV proton beam halo at the Large Hadron Collider (LHC), oxide dispersion strengthened (DS) copper alloys were explored. These internally oxidized copper alloys known as GlidCop are also leading candidates for high heat flux applications in fusion reactors and as divertor and first wall structure in ITER. These considerations have led to an extensive body of research on neutron-induced changes in the microstructure and physio-mechanical properties. This study focused primarily on the damage induced by 200 MeV protons on as wrought and cold-worked GlidCop Al15 DS copper ally selected as a candidate material of the LHC beam collimation structure to damage levels up to ~10 displacements-per-atom (dpa) and irradiation temperatures up to ~600 °C. For reference, low dose spallation neutron damage at sub-zero irradiation temperature was included in the study. Proton irradiation effects on dimensional stability, mechanical behavior, electrical resistivity and X-ray diffraction-based microstructural changes are presented in the paper. GlidCop Al15 exhibited excellent thermal stability and superior to pure Cu resistance to conductivity loss. Proton irradiation-induced hardening and embrittlement at distinct irradiation temperature regimes were shown to follow similar trends to what was reported under neutron exposure to even higher dpa damage. At T irr ~600 ± 20 °C the cold-worked DS copper alloy exhibited softening accompanied by elongation reduction while at T irr ~200 ± 10 °C the as-wrought experienced hardening with elongation increase. Furthermore, high resolution X-ray diffraction revealed that even low-dose neutron irradiation has a strong influence on the size and distribution of dispersed Al 2 O 3 particles.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Local Distortions and Metal–Semiconductor–Metal Transition in Quasi-One-Dimensional Nanowire Compounds AV 3 Q 3 O δ (A = K, Rb, Cs and Q = Se, Te)

Metal cluster compounds have garnered renewed interest in the search for novel superconductors and topological semimetals owing to structural instabilities of metal-cluster geometries and broken symmetries. Here we synthesized needle-like crystals of the V-cluster-based quasi-one-dimensional (Q1D) materials AV 3 Q 3 O δ (A = K, Rb, Cs, Q= Se, Te) which can also be viewed as being composed of parallel nanowires. We examine how changes in their average and local structure control their electronic properties. All compounds crystallize in the TIFe 3 Te 3 -type structure (P6 3 /m space group) with infinite (V 3 )Q 3 ) - double-walled columnar chains separated by A + cations. Our single-crystal and synchrotron powder diffraction studies indicate oxygen atoms partially occupy the center site of the V 6 octahedral metal cluster cages in KV 3 Te 3 O 0.33 , RbV 3 Te 3 O 0.32 , and CsV 3 Te 3 O 0.35 , whereas KV 3 Se 3 is structurally oxygen-free. Our synchrotron X-ray pair distribution function (PDF) analyses indicate that the oxygen-free V 6 cluster octahedra in KV 3 Se 3 are highly distorted perpendicular to the chain direction even at room temperature, reducing the symmetry of the average structure from hexagonal P6 3 /m to monoclinic P2 1 /m. Our theoretical calculation supports this P2 1 /m distortion and suggests the structure further distorts to P2 1 or P2 1 /c at lower temperatures. In contrast, the oxygen-centered V-cluster in KV 3 Te 3 O 0.33 exhibits a V-3-triangle-trimerization along the chain direction. This feature is discernible from the local PDF and is consistent with lattice dynamical calculations based on density functional theory. Resistivity measurements indicate that KV 3 Se 3 exhibits metallic behavior, whereas a dramatic metal-semiconductor-metal transition emerges in KV 3 Te 3 O 6.33 , RbV 3 Te 3 O 0.32 , and CsV 3 Te 3 O 0.35 because of oxygen disorder and changes in local structure captured from our electronic structure analyses of the Fermi surface. Our investigation of the AV 3 Q 3 O 6 family demonstrates the importance of understanding local changes in structure driven by electronic instabilities, which can guide the search for new quantum materials in other low-dimensional cluster-compound materials.

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

Optimization Modeling for Advanced Syngas to Olefin Reactive Systems

Reactor designs with mixed catalysts play an important role in transforming a multiple reactor system to single-shot reactors. In addition to savings in capital and ease of implementation, single-shot reactors are useful to break equilibrium limitations, thereby increasing the yield and selectivity of desired product as shown in previous studies. However, the nonlinear and highly exothermic nature of mixed-catalyst systems makes it difficult for commercial process simulation and optimization tools to optimize these systems. This study describes the development and application of optimization strategies for mixed-catalyst, single-shot reactors for syngas to olefin (STO) processes. Finding the optimal catalyst distribution is challenging and requires advanced solution strategies for singular optimal control problems, which are poorly conditioned and often lead to flat response surfaces. The graded bed and partial-moving finite-element approaches are used to find the optimal catalyst distribution that maximizes the olefins yield. A 1.3% increase in the yield is observed from one zone to three zones. The yield further improves from three zones to the exact infinite dimensional solution by 0.2%. This improvement can be realized in practice by changing only the catalyst distribution, without any extra investment. Lastly, the results suggest that a mixed-catalyst single shot reactor bed can be applied to other reaction mechanisms to increase reactor performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗