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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Imaging Macromolecular Structural Dynamics with Low-Dose, Time-Resolved Transmission Electron Microscopy

All well-established experimental methods for investigating the structure of biological macromolecules have spatial and/or temporal limitations inherent to the technique that limit their applicability to studying macromolecular dynamics. The ability to measure macromolecular dynamics is key to gaining predictive mastery of biological systems. This work demonstrates that sufficient data can be acquired from low-Z soft materials using dynamic transmission electron microscopy (DTEM) to potentially allow measurements of macromolecular motion. While a dynamic measurement of macromolecular motion or structural change requires further effort, it is evident from this work that this is feasible under specific experimental conditions that can be achieved using low-dose, time-resolved transmission electron microscopy.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Development of Simplified Model Test Methods for Creep-Fatigue Evaluation

The Simplified Model Test (SMT) approach is an alternative creep-fatigue evaluation method that no longer requires the use of the damage interaction diagram, or D-diagram. The reason is that the combined effects of creep and fatigue are accounted for in the test data by means of a SMT specimen that is designed to replicate or bound the stress and strain redistribution that occurs in actual components when loaded in the creep regime. However, creep-fatigue experiments on SMT key feature articles are specialized and difficult to perform by the general research community. In this paper, two innovative SMT based creep-fatigue experimental methods are developed and implemented. These newly-developed SMT test methods have resolved all the critical challenges in the SMT key feature article testing and enable the potential of further development of the SMT based creep-fatigue evaluation method into a standard testing method. Scoping test results on Alloy 617 and SS 316H using the newly developed SMT methods are summarized and discussed. The concepts of the SMT methodology for creep-fatigue evaluation are explained.

Wang, Yanli↗
DOE OSTI2014

Preliminary Phase Field Computational Model Development

This interim report presents progress towards the development of meso-scale models of magnetic behavior that incorporate microstructural information. Modeling magnetic signatures in irradiated materials with complex microstructures (such as structural steels) is a significant challenge. The complexity is addressed incrementally, using the monocrystalline Fe (i.e., ferrite) film as model systems to develop and validate initial models, followed by polycrystalline Fe films, and by more complicated and representative alloys. In addition, the modeling incrementally addresses inclusion of other major phases (e.g., martensite, austenite), minor magnetic phases (e.g., carbides, FeCr precipitates), and minor nonmagnetic phases (e.g., Cu precipitates, voids). The focus of the magnetic modeling is on phase-field models. The models are based on the numerical solution to the Landau-Lifshitz-Gilbert equation. From the computational standpoint, phase-field modeling allows the simulation of large enough systems that relevant defect structures and their effects on functional properties like magnetism can be simulated. To date, two phase-field models have been generated in support of this work. First, a bulk iron model with periodic boundary conditions was generated as a proof-of-concept to investigate major loop effects of single versus polycrystalline bulk iron and effects of single non-magnetic defects. More recently, to support the experimental program herein using iron thin films, a new model was generated that uses finite boundary conditions representing surfaces and edges. This model has provided key insights into the domain structures observed in magnetic force microscopy (MFM) measurements. Simulation results for single crystal thin-film iron indicate the feasibility of the model for determining magnetic domain wall thickness and mobility in an externally applied field. Because the phase-field model dimensions are limited relative to the size of most specimens used in experiments, special experimental methods were devised to create similar boundary conditions in the iron films. Preliminary MFM studies conducted on single and polycrystalline iron films with small sub-areas created with focused ion beam have correlated quite well qualitatively with phase-field simulations. However, phase-field model dimensions are still small relative to experiments thus far. We are in the process of increasing the size of the models and decreasing specimen size so both have identical dimensions. Ongoing research is focused on validation of the phase-field model. Validation is being accomplished through comparison with experimentally obtained MFM images (in progress), and planned measurements of major hysteresis loops and first order reversal curves. Extrapolation of simulation sizes to represent a more stochastic bulk-like system will require sampling of various simulations (i.e., with single non-magnetic defect, single magnetic defect, single grain boundary, single dislocation, etc.) with distributions of input parameters. These outputs can then be compared to laboratory magnetic measurements and ultimately to simulate magnetic Barkhausen noise signals.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Directly Observing Micelle Fusion and Growth in Solution by Liquid-Cell Transmission Electron Microscopy

Amphiphilic small molecules and polymers form commonplace nanoscale macromolecular compartments and bilayers, and as such are truly essential components in all cells and in many cellular processes. The nature of these architectures, including their formation, phase changes, and stimuli-response behaviors, is necessary for the most basic functions of life, and over the past half-century, these natural micellar structures have inspired a vast diversity of industrial products, from biomedicines to detergents, lubricants, and coatings. The importance of these materials and their ubiquity have made them the subject of intense investigation regarding their nanoscale dynamics with increasing interest in obtaining sufficient temporal and spatial resolution to directly observe nanoscale processes. However, the vast majority of experimental methods involve either bulk-averaging techniques including light, neutron, and X-ray scattering, or are static in nature including even the most advanced cryogenic transmission electron microscopy techniques. Here, we employ in situ liquid-cell transmission electron microscopy (LCTEM) to directly observe the evolution of individual amphiphilic block copolymer micellar nanoparticles in solution, in real time with nanometer spatial resolution. These observations, made on a proof-of-concept bioconjugate polymer amphiphile, revealed growth and evolution occurring by unimer addition processes and by particle-particle collision-and-fusion events. In conclusion, the experimental approach, combining direct LCTEM observation, quantitative analysis of LCTEM data, and correlated in silico simulations, provides a unique view of solvated soft matter nanoassemblies as they morph and evolve in time and space, enabling us to capture these phenomena in solution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems

Interacting multi-component spin systems are ubiquitous in nature and in the laboratory. As such, investigations of inter-species spin interactions are of vital importance. Traditionally, they are studied by experimental methods that are necessarily perturbative: e.g., by intentionally polarizing or depolarizing one spin species while detecting the response of the other(s). Here, we describe and demonstrate an alternative approach based on multi-probe spin noise spectroscopy , which can reveal inter-species spin interactions - under conditions of strict thermal equilibrium - by detecting and cross-correlating the stochastic fluctuation signals exhibited by each of the constituent spin species. Specifically, we consider a two-component spin ensemble that interacts via exchange coupling, and we determine cross-correlations between their intrinsic spin fluctuations. The model is experimentally confirmed using “two-color” optical spin noise spectroscopy on a mixture of interacting Rb and Cs vapors. Noise correlations directly reveal the presence of inter-species spin exchange, without ever perturbing the system away from thermal equilibrium. These non-invasive and noise-based techniques should be generally applicable to any heterogeneous spin system in which the fluctuations of the constituent components are detectable.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Accessing metal-specific orbital interactions in C–H activation with resonant inelastic X-ray scattering

Photochemically prepared transition-metal complexes are known to be effective at cleaving the strong C–H bonds of organic molecules in room temperature solutions. There is also ample theoretical evidence that the two-way, metal to ligand (MLCT) and ligand to metal (LMCT), charge-transfer between an incoming alkane C–H group and the transition metal is the decisive interaction in the C–H activation reaction. What is missing, however, are experimental methods to directly probe these interactions in order to reveal what determines reactivity of intermediates and the rate of the reaction. Here, using quantum chemical simulations we predict and propose future time-resolved valence-to-core resonant inelastic X-ray scattering (VtC-RIXS) experiments at the transition metal L-edge as a method to provide a full account of the evolution of metal–alkane interactions during transition-metal mediated C–H activation reactions. For the model system cyclopentadienyl rhodium dicarbonyl (CpRh(CO) 2 ), we demonstrate, by simulating the VtC-RIXS signatures of key intermediates in the C–H activation pathway, how the Rh-centered valence-excited states accessible through VtC-RIXS directly reflect changes in donation and back-donation between the alkane C–H group and the transition metal as the reaction proceeds via those intermediates. We benchmark and validate our quantum chemical simulations against experimental steady-state measurements of CpRh(CO) 2 and Rh(acac)(CO)2 (where acac is acetylacetonate). Our study constitutes the first step towards establishing VtC-RIXS as a new experimental observable for probing reactivity of C–H activation reactions. More generally, the study further motivates the use of time-resolved VtC-RIXS to follow the valence electronic structure evolution along photochemical, photoinitiated and photocatalytic reactions with transition metal complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Secondary particle emission from a ferromagnetic binary compound

Secondary ion emission from an ion-bombarded binary compound in the ferro- and paramagnetic states has been studied using experimental methods and molecular dynamics simulations. The experiments were performed with a widely used NiPd binary compound, which was bombarded by obliquely incident 10-keV Ar ions. It is established that the intensity of Ni{sup +} and Pd{sup +} ion emission from a polycrystalline NiPd sample decreases significantly when it passes from the ferromagnetic to paramagnetic state. This effect is explained by a change in the surface binding energy and density of surface states at the Fermi level and by a cumulative process related to sputtering. The energies and directions of emission of secondary particles from poly- and single-crystalline NiPd samples in the ferromagnetic state have been jointly studied. It is established that the maximum of the polar angular distribution of secondary particles deviates toward the normal to the irradiated surface with a decrease in their energy. A difference in the azimuthal distribution of emitted Ni and Pd particles has been observed during the bombardment of a (001)NiPd crystal face and explained by specific features of correlated collisions. The best agreement of experimental data with the results of molecular dynamics simulations is obtained if the calculations are performed with allowance for an experimentally established modified composition of the three uppermost surface layers [39].

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Systematic Molecular Engineering of a Series of Aniline-Based Squaraine Dyes and Their Structure-Related Properties

With the objective of developing new near-infrared fluorescent probes and understanding the effect molecular structure exerts on physical properties, a series of aniline-based squaraine dyes with different number and position of methoxy substituents adjacent to the squaraine core were synthesized and investigated. Using both computational and experimental methods, we found that the subtle changes of the number or position of the methoxy substituents influenced the twisting angle of the structure and led to significant variations in optical properties. Moreover, the methoxy substituent also affected aggregation behavior due to steric effects. The X-ray crystal structure of one of the key members of the series, SD-2a, clearly demonstrates the distortion between the four-membered squaraine core and the adjacent aniline ring due to methoxy substitution. Structure-related fast relaxation processes were investigated by femtosecond pump–probe experiments and transient absorption spectra. Quantum chemical calculations and essential state models were exploited to analyze the primary experimental results. Here, the comprehensive investigation of structure-related properties of dihydroxylaniline-based squaraine dyes, with systematic substitution of OH by OCH 3 functional groups, serves as a guide for the design of novel squaraine dyes for photonics applications.

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

Effects of Downstream Vortex Generators on Film Cooling a Flat Plate Fed by Crossflow

Counter-rotating vortices, formed by the interaction of film-cooling jets and the hot gas flow, adversely affect the performance of conventional film-cooling designs. Downstream vortex generators have been shown to improve cooling effectiveness by mitigating the effects of the counter-rotating vortices and by deflecting the cooling jet laterally. In this study, computational and experimental methods were used to examine how cylindrical film-cooling holes (D = 3.2 mm, L/D = 6, p/D = 3, α = 30 deg) with and without downstream vortex generators perform when the coolant supply channel is perpendicular to the direction of the hot gas. For this study, the hot gas had a temperature of 650 K and an average Mach number of 0.23. Here, the hot-gas-to-coolant temperature ratio was 1.9, and two blowing ratios (0.75 and 1.0) were studied. Results from the computational fluid dynamics study show how crossflow affects the interaction between the film-cooling jet and hot gas flow with and without downstream vortex generators. The experimental measurements were based on infrared thermography in a conjugate heat transfer environment. Results were obtained for film-cooling performance in terms of overall effectiveness, film effectiveness, and local heat transfer coefficients. The downstream vortex generators can increase the laterally averaged effectiveness by a factor of 1.5 relative to cylindrical holes, but this higher performance is restricted to low crossflow velocities and higher blowing ratios.

17 WIND ENERGY↗
DOE OSTI2013

Discovery of difference in the diffuse scattering from nonstoichiometric Ca{sub 0.87}La{sub 0.13}F{sub 2.13} and Ca{sub 0.92}Er{sub 0.08}F{sub 2.08} crystals with different types of clusters of structural defects

A new approach to application of diffuse scattering (DS) for studying the defect structure of crystals on laboratory radiation sources is implemented. The basic principles of this approach are as follows: (i) choice of crystals with a high concentration of structural defects (highly nonstoichiometric Ca{sub 1-x}R{sub x}F{sub 2+x} phases), (ii) application of intermeasurement minimization method (experimental comparison) to select a weak desired DS signal from a superposition of signals of different nature, and (iii) choice of the basic model proceeding from the reliable information provided by accurate analysis of the contribution of structural defects to Bragg reflections. Significantly different DS diffraction patterns have been recorded for Ca{sub 0.87}La{sub 0.13}F{sub 2.13} and Ca{sub 0.92}Er{sub 0.08}F{sub 2.08} crystals, characterized by different types of structural-defect clusters, determined from the Bragg diffraction data. Experiments performed at 90-100 K proved that DS is caused by clusters with stable atomic configurations rather than cooperative thermal atomic vibrations. A set of methods is proposed which can efficiently be used in diagnostics of nanomaterials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Time-domain terahertz emission spectroscopy on van der Waals materials

Time-domain terahertz (THz) emission spectroscopy provides a direct method to probe transient photo-currents by recording the emitted terahertz electric field. Although the basic principles of THz surface emission have been understood for more than 30 years, the constant progress in ultrafast laser science to ever shorter pulses, the development of new materials and enhanced sensitivity promote THz emission spectroscopy as a reliable method to gain insights into charge carrier dynamics with unprecedented precision. It provides a versatile tool to study ultrafast processes, such as plasmon-driven hot carriers, dynamics of Dirac fermions, interfacial charge transfer, coherent phonon emission and quantum beating, to name only a few. However, despite the rapidly growing body of research on van der Waals materials, especially in their low-dimensional limit, THz emission spectroscopy has only been applied to a limited extent in these material systems. In this prospective, we review time-domain THz emission spectroscopy as a complementary approach to probe ultrafast charge carrier dynamics and the material’s nonlinear response. After a description of the experimental method, we report on THz emission spectroscopy of bulk and 2D van der Waals materials with special focus on graphene and transition metal dichalcogenide layers.

2D materials↗
DOE OSTI2012

Dissociative electron attachment to C{sub 2}F{sub 5} radicals

Dissociative electron attachment to the reactive C{sub 2}F{sub 5} molecular radical has been investigated with two complimentary experimental methods; a single collision beam experiment and a new flowing afterglow Langmuir probe technique. The beam results show that F{sup -} is formed close to zero electron energy in dissociative electron attachment to C{sub 2}F{sub 5}. The afterglow measurements also show that F{sup -} is formed in collisions between electrons and C{sub 2}F{sub 5} molecules with rate constants of 3.7 Multiplication-Sign 10{sup -9} cm{sup 3} s{sup -1} to 4.7 Multiplication-Sign 10{sup -9} cm{sup 3} s{sup -1} at temperatures of 300-600 K. The rate constant increases slowly with increasing temperature, but the rise observed is smaller than the experimental uncertainty of 35%.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Structure determination of the intermediate phase of PbSe using experiments and calculations

The pressure-induced structure transitions of PbSe were investigated at pressures up to 50 GPa in diamond anvil cells using synchrotron powder and single-crystal X-ray diffraction methods. A phase transition from the initial NaCl-type structure to an intermediate phase was observed at 4.8 GPa, followed by another phase transition to a CsCl-type structure at 19.5 GPa, which is in agreement with previous reports. In addition, the NaCl-type, Pnma, Cmcm, and CsCl-type structures of PbSe were investigated using density functional theory calculations. Based on the experiments and calculations, the intermediate phase has Pnma symmetry rather than Cmcm symmetry, as has been previously suggested. Some of the diffraction peaks of the Pnma phase were broad in the high-pressure experiments, but were determined to be single diffraction peaks rather than the overlap of multiple peaks by different experimental methods. The Pnma and Cmcm structures of PbSe were compared. It was found that two structures were very similar, and it was difficult to distinguish one power diffraction pattern from the other.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

On stability of self-sustained volume discharge in working mixtures of non-chain electrochemical HF laser

Burning voltage of a self-sustained volume discharge (SSVD) is studied as a function of the specific energy deposition in SF{sub 5} with C{sub 2}-H{sub 6} and H{sub 2} mixtures, which are working media of a non-chain electrochemical HF laser. It is established that the voltage rises linearly with increasing the specific energy deposition, the relative voltage rise in the SF{sub 6}-C{sub 2}H{sub 6} mixtures being noticeably higher than in pure SF{sub 6} and SF{sub 6}-H{sub 2} mixtures. An assumption is suggested and substantiated on determining the role of molecule dissociation by the electron impact leading to the observed voltage rise. From experimental data we have found approximate energy expenditures of producing dissociation fragments including atomic fluorine in a discharge in pure SF{sub 6}: E-tilde {sub d}(F)= 5{+-}1 eV. The values of E{sub d} well agree with literature data obtained by other experimental methods. A conclusion is drawn that the dissociation process is the main mechanism limiting the current density, which implies SSVD realisation without preliminary gas ionisation in working mixtures of a non-chain HF laser and determines a higher stability of the volume discharge in mixtures of SF{sub 6} with hydrocarbons (deuterocarbons) as compared to mixtures with hydrogen (deuterium). A method is suggested and substantiated for numerical estimation of the limitation effect of the current density and its influence on the SSVD stability. (control of radiation parameters)

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Analysis of isothermal and cooling-rate-dependent immersion freezing by a unifying stochastic ice nucleation model

Immersion freezing is an important ice nucleation pathway involved in the formation of cirrus and mixed-phase clouds. Laboratory immersion freezing experiments are necessary to determine the range in temperature, T , and relative humidity, RH, at which ice nucleation occurs and to quantify the associated nucleation kinetics. Typically, isothermal (applying a constant temperature) and cooling-rate-dependent immersion freezing experiments are conducted. In these experiments it is usually assumed that the droplets containing ice nucleating particles (INPs) all have the same INP surface area (ISA); however, the validity of this assumption or the impact it may have on analysis and interpretation of the experimental data is rarely questioned. Descriptions of ice active sites and variability of contact angles have been successfully formulated to describe ice nucleation experimental data in previous research; however, we consider the ability of a stochastic freezing model founded on classical nucleation theory to reproduce previous results and to explain experimental uncertainties and data scatter. A stochastic immersion freezing model based on first principles of statistics is presented, which accounts for variable ISA per droplet and uses parameters including the total number of droplets, N tot , and the heterogeneous ice nucleation rate coefficient, J het ( T ). This model is applied to address if (i) a time and ISA-dependent stochastic immersion freezing process can explain laboratory immersion freezing data for different experimental methods and (ii) the assumption that all droplets contain identical ISA is a valid conjecture with subsequent consequences for analysis and interpretation of immersion freezing. The simple stochastic model can reproduce the observed time and surface area dependence in immersion freezing experiments for a variety of methods such as: droplets on a cold-stage exposed to air or surrounded by an oil matrix, wind and acoustically levitated droplets, droplets in a continuous-flow diffusion chamber (CFDC), the Leipzig aerosol cloud interaction simulator (LACIS), and the aerosol interaction and dynamics in the atmosphere (AIDA) cloud chamber. Observed time-dependent isothermal frozen fractions exhibiting non-exponential behavior can be readily explained by this model considering varying ISA. An apparent cooling-rate dependence of J het is explained by assuming identical ISA in each droplet. When accounting for ISA variability, the cooling-rate dependence of ice nucleation kinetics vanishes as expected from classical nucleation theory. Finally, the model simulations allow for a quantitative experimental uncertainty analysis for parameters N tot , T , RH, and the ISA variability. We discuss the implications of our results for experimental analysis and interpretation of the immersion freezing process.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

FCRD Transmutation Fuels Handbook 2015

Transmutation of minor actinides such as Np, Am, and Cm in spent nuclear fuel is of international interest because of its potential for reducing the long-term health and safety hazards caused by the radioactivity of the spent fuel. One important approach to transmutation (currently being pursued by the DOE Fuel Cycle Research & Development Advanced Fuels Campaign) involves incorporating the minor actinides into U-Pu-Zr alloys, which can be used as fuel in fast reactors. It is, therefore, important to understand the properties of U-Pu-Zr alloys, both with and without minor actinide additions. In addition to requiring extensive safety precautions, alloys containing U and Pu are difficult to study for numerous reasons, including their complex phase transformations, characteristically sluggish phase-transformation kinetics, tendency to produce experimental results that vary depending on the histories of individual samples, and sensitivity to contaminants such as oxygen in concentrations below a hundred parts per million. Many of the experimental measurements were made before 1980, and the level of documentation for experimental methods and results varies widely. It is, therefore, not surprising that little is known with certainty about U-Pu-Zr alloys, and that general acceptance of results sometimes indicates that there is only a single measurement for a particular property. This handbook summarizes currently available information about U, Pu, Zr, and alloys of two or three of these elements. It contains information about phase diagrams and related information (including phases and phase transformations); heat capacity, entropy, and enthalpy; thermal expansion; and thermal conductivity and diffusivity. In addition to presenting information about materials properties, it attempts to provide information about how well the property is known and how much variation exists between measurements. Although the handbook includes some references to publications about modeling, its primary focus is experimental data. Most of the data has been published elsewhere (although scattered throughout numerous references, some quite obscure); however, some data is presented here for the first time.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗