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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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Fatty acid foams for nonselective physical removal of microplastics from aqueous solutions

Microplastics (MPs) are pervasive environmental contaminants whose removal from water remains a major challenge due to their small size, chemical diversity, and dynamic surface properties arising from environmental aging/weathering. Here, we present a concept of foam-based separation method that physically traps MPs in the foam phase using microtubular assemblies of 12-hydroxystearic acid. These foams are stabilized by anisotropic fatty acid microtubules formed in the presence of ethanolamine, which jam within the foam channels and suppress fluid drainage thereby enhancing MP retention and foam stability. MPs of different sizes, polymer compositions (including polystyrene, polypropylene, polyethylene terephthalate, and polytetrafluoroethylene), and weathered states were retained in the foam phase without requiring chemical modification or relying on chemical interactions between the fatty acid and MPs. Thermally induced transition of the fatty acid microtubules into nanomicelles above the characteristic phase transition temperature (∼35 °C) enables controlled foam collapse and recovery of trapped MPs. The cumulative removal efficiency can exceed 85% through multiple foaming cycles, matching predictions from a probabilistic retention model. This work shows that foams can provide a simple platform to trap MPs, thus providing a new physical-removal strategy that does not rely on the particles’ chemistry.

Guillot, Kennedy A. [Louisiana State Univ., Baton ↗
DOE OSTI2013

Non-destructive Faraday imaging of dynamically controlled ultracold atoms

We describe an easily implementable method for non-destructive measurements of ultracold atomic clouds based on dark field imaging of spatially resolved Faraday rotation. The signal-to-noise ratio is analyzed theoretically and, in the absence of experimental imperfections, the sensitivity limit is found to be identical to other conventional dispersive imaging techniques. The dependence on laser detuning, atomic density, and temperature is characterized in a detailed comparison with theory. Due to low destructiveness, spatially resolved images of the same cloud can be acquired up to 2000 times. The technique is applied to avoid the effect of shot-to-shot fluctuations in atom number calibration, to demonstrate single-run vector magnetic field imaging and single-run spatial imaging of the system's dynamic behavior. This demonstrates that the method is a useful tool for the characterization of static and dynamically changing properties of ultracold atomic clouds.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Electric field controlled reversible magnetic anisotropy switching studied by spin rectification

In this letter, spin rectification was used to study the electric field controlled dynamic magnetic properties of the multiferroic composite which is a Co stripe with induced in-plane anisotropy deposited onto a Pb(Mg{sub 1∕3}Nb{sub 2∕3})O{sub 3}-PbTiO{sub 3} substrate. Due to the coupling between piezoelectric and magnetoelastic effects, a reversible in-plane anisotropy switching has been realized by varying the history of the applied electric field. This merit results from the electric hysteresis of the polarization in the nonlinear piezoelectric regime, which has been proved by a butterfly type electric field dependence of the in-plane anisotropy field. Moreover, the electric field dependent effective demagnetization field and linewidth have been observed at the same time.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Impacts of surface spins and inter-particle interactions on the magnetism of hollow γ-Fe{sub 2}O{sub 3} nanoparticles

A comparative study of the static and dynamic magnetic properties of polycrystalline hollow γ-Fe{sub 2}O{sub 3} nanoparticles with two distinctly different sizes of 10.3 ± 1.3 nm and 14.8 ± 0.5 nm has been performed. High-resolution TEM images confirmed the crystalline structure and the presence of the shell thickness of 2.17 ± 0.28 nm and 3.25 ± 0.24 nm for the 10 nm and 15 nm particles, respectively. Quantitative fits of the frequency dependent ac susceptibility to the Vogel-Fulcher model, τ = τ{sub o} exp[E{sub a}/k(T − T{sub o})], show stronger inter-particle interactions in the 15 nm nanoparticles than in the 10 nm nanoparticles. A systematic analysis of the room-temperature magnetic loops using the modified Langevin function indicates a stronger effect of disordered surface spins in the 10 nm hollow particles as compared to the 15 nm hollow particles. Our study suggests that while the effect of disordered surface spins dominates the magnetic behavior of the 10 nm hollow particles, both the disordered surface spins and inter-particle interactions contribute to the magnetism of the 15 nm hollow particles.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Laser induced spin precession in highly anisotropic granular L1{sub 0} FePt

The dynamic magnetic properties of a highly anisotropic, granular L1{sub 0} FePt thin film in magnetic fields up to 7 T are investigated using time-resolved magneto-optical Kerr effect measurements. We find that ultrashort laser pulses induce coherent spin precession in the granular FePt sample. Frequencies of spin precession up to over 400 GHz are observed, which are strongly field and temperature dependent. The high frequencies can be ascribed to the high value of the magnetocrystalline anisotropy constant K{sub u} leading to large anisotropy fields H{sub a} of up to 10.7 T at 170 K. A Gilbert damping parameter of α ∼ 0.1 was derived from the lifetimes of the oscillations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Universal tight binding model for chemical reactions in solution and at surfaces. I. Organic molecules

As is now well established, a first order expansion of the Hohenberg–Kohn total energy density functional about a trial input density, namely, the Harris–Foulkes functional, can be used to rationalize a non self consistent tight binding model. If the expansion is taken to second order then the energy and electron density matrix need to be calculated self consistently and from this functional one can derive a charge self consistent tight binding theory. In this paper we have used this to describe a polarizable ion tight binding model which has the benefit of treating charge transfer in point multipoles. This admits a ready description of ionic polarizability and crystal field splitting. It is necessary in constructing such a model to find a number of parameters that mimic their more exact counterparts in the density functional theory. We describe in detail how this is done using a combination of intuition, exact analytical fitting, and a genetic optimization algorithm. Having obtained model parameters we show that this constitutes a transferable scheme that can be applied rather universally to small and medium sized organic molecules. We have shown that the model gives a good account of static structural and dynamic vibrational properties of a library of molecules, and finally we demonstrate the model's capability by showing a real time simulation of an enolization reaction in aqueous solution. In two subsequent papers, we show that the model is a great deal more general in that it will describe solvents and solid substrates and that therefore we have created a self consistent quantum mechanical scheme that may be applied to simulations in heterogeneous catalysis.

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

A single-molecule approach to ZnO defect studies: Single photons and single defects

Investigations that probe defects one at a time offer a unique opportunity to observe properties and dynamics that are washed out of ensemble measurements. Here, we present confocal fluorescence measurements of individual defects in ZnO nanoparticles and sputtered films that are excited with sub-bandgap energy light. Photon correlation measurements yield both antibunching and bunching, indicative of single-photon emission from isolated defects that possess a metastable shelving state. The single-photon emission is in the range of ∼560–720 nm and typically exhibits two broad spectral peaks separated by ∼150 meV. The excited state lifetimes range from 1 to 13 ns, consistent with the finite-size and surface effects of nanoparticles and small grains. We also observe discrete jumps in the fluorescence intensity between a bright state and a dark state. The dwell times in each state are exponentially distributed and the average dwell time in the bright (dark) state does (may) depend on the power of the exciting laser. Taken together, our measurements demonstrate the utility of a single-molecule approach to semiconductor defect studies and highlight ZnO as a potential host material for single-defect based applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Dependence of dynamic magnetization and magneto-transport properties of FeAlSi films with oblique sputtering studied via spin rectification effect

FeAlSi (Sendust) is known to possess excellent soft magnetic properties comparable to traditional soft magnetic alloys such as NiFe (Permalloy), while having a relatively higher resistance for lower eddy current losses. However, their dynamic magnetic and magneto-transport properties are not well-studied. Via the spin rectification effect, we electrically characterize a series of obliquely sputtered FeAlSi films at ferromagnetic resonance. The variations of the anisotropy fields and damping with oblique angle are extracted and discussed. In particular, two-magnon scattering is found to dominate the damping behavior at high oblique angles. An analysis of the results shows large anomalous Hall effect and anisotropic magneto-resistance across all samples, which decreases sharply with increasing oblique incidence.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Ab initio molecular orbital-configuration interaction based quantum master equation (MOQME) approach to the dynamic first hyperpolarizabilities of asymmetric π-conjugated systems

In this study, we apply the ab initio molecular orbital - configuration interaction based quantum master equation (MOQME) approach to the calculation and analysis of the dynamic first hyperpolarizabilities (β) of asymmetric π-conjugated molecules. In this approach, we construct the excited state models by the ab initio configuration interaction singles method. Then, time evolutions of system reduced density matrix ρ(t) and system polarization p(t) are calculated by the QME approach. Dynamic β in the second harmonic generation is calculated based on the nonperturbative definition of nonlinear optical susceptibility, using the frequency domain system polarization p(ω). Spatial contributions of electrons to β are analyzed based on the dynamic hyperpolarizability density map, which visualizes the second-order response of charge density oscillating with a frequency of 2ω. We apply the present method to the calculation of the dynamic β of a series of donor/acceptor substituted polyene oligomers, and then discuss the applicability of the MOQME method to the calculation and analysis of dynamic NLO properties of molecular systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Terahertz probes of magnetic field induced spin reorientation in YFeO{sub 3} single crystal

Using the terahertz time-domain spectroscopy, we demonstrate the spin reorientation of a canted antiferromagnetic YFeO{sub 3} single crystal, by evaluating the temperature and magnetic field dependence of resonant frequency and amplitude for the quasi-ferromagnetic (FM) and quasi-antiferromagnetic modes (AFM), a deeper insight into the dynamics of spin reorientation in rare-earth orthoferrites is established. Due to the absence of 4f-electrons in Y ion, the spin reorientation of Fe sublattices can only be induced by the applied magnetic field, rather than temperature. In agreement with the theoretical predication, the frequency of FM mode decreases with magnetic field. In addition, an obvious step of spin reorientation phase transition occurs with a relatively large applied magnetic field of 4 T. By comparison with the family members of RFeO{sub 3} (R = Y{sup 3+} or rare-earth ions), our results suggest that the chosen of R would tailor the dynamical rotation properties of Fe ions, leading to the designable spin switching in the orthoferrite antiferromagnetic systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Toward broad-band x-ray detected ferromagnetic resonance in longitudinal geometry

An ultrahigh-vacuum-compatible setup for broad-band X-ray detected ferromagnetic resonance (XFMR) in longitudinal geometry is introduced which relies on a low-power, continuous-wave excitation of the ferromagnetic sample. A simultaneous detection of the conventional ferromagnetic resonance via measuring the reflected microwave power and the XFMR signal of the X-ray absorption is possible. First experiments on the Fe and Co L{sub 3}-edges of a permalloy film covered with Co nanostripes as well as the Fe and Ni K-edges of a permalloy film are presented and discussed. Two different XFMR signals are found, one of which is independent of the photon energy and therefore does not provide element-selective information. The other much weaker signal is element-selective, and the dynamic magnetic properties could be detected for Fe and Co separately. The dependence of the latter XFMR signal on the photon helicity of the synchrotron light is found to be distinct from the usual x-ray magnetic circular dichroism effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Spin dynamics, electronic, and thermal transport properties of two-dimensional CrPS{sub 4} single crystal

2-Dimensional (2D) CrPS{sub 4} single crystals have been grown by the chemical vapor transport method. The crystallographic, magnetic, electronic, and thermal transport properties of the single crystals were investigated by the room-temperature X-ray diffraction, electrical resistivity ρ(T), specific heat C{sub P}(T), and the electronic spin response (ESR) measurements. CrPS{sub 4} crystals crystallize into a monoclinic structure. The electrical resistivity ρ(T) shows a semiconducting behavior with an energy gap E{sub a} = 0.166 eV. The antiferromagnetic transition temperature is about T{sub N} = 36 K. The spin flipping induced by the applied magnetic field is observed along the c axis. The magnetic phase diagram of CrPS{sub 4} single crystal has been discussed. The extracted magnetic entropy at T{sub N} is about 10.8 J/mol K, which is consistent with the theoretical value R ln(2S + 1) for S = 3/2 of the Cr{sup 3+} ion. Based on the mean-field theory, the magnetic exchange constants J{sub 1} and J{sub c} corresponding to the interactions of the intralayer and between layers are about 0.143 meV and −0.955 meV are obtained based on the fitting of the susceptibility above T{sub N}, which agree with the results obtained from the ESR measurements. With the help of the strain for tuning the magnetic properties, monolayer CrPS{sub 4} may be a promising candidate to explore 2D magnetic semiconductors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Magnetic spectra and Richter aftereffect relaxation in Ce{sub x}Y{sub 3−x}Fe{sub 5}O{sub 12} ferrites

The static and dynamic magnetic properties of cerium (Ce) doped yttrium iron garnet Ce{sub x}Y{sub 3−x}Fe{sub 5}O{sub 12} (x=0, 0.05, 0.1, 0.15, 0.2) ferrites (YIG) have been reported in this work. The ferrites were fabricated by the traditional solid-state reaction method. All ferrite samples reveal pure garnet structure identified by x-ray diffraction (XRD). The substitution of cerium not only enhances the saturation magnetization of the samples, but also regulates the magnetocrystalline anisotropy constant K{sub 1}. Obvious differences in permeability spectra over a frequency of 1 MHz - 1 GHz can be observed. It is verified that the permeability dispersion and magnetic losses of Ce-doped YIG ferrite contain the contribution of Richter aftereffect relaxation due to the existence of Fe{sup 2+} ions. The fitting results of the permeability spectra applied three-mechanism model is in good agreement with experimental data, which successfully explains the mechanisms of magnetic losses observed at 1 MHz to 1 GHz for Ce-doped YIG ferrite. In addition, the frequency shift of Richter aftereffect has also been discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Temperature dependence of dynamic deformation in FCC metals, aluminum and invar

Laser-driven shock experiments were performed on fcc metals, aluminum and invar, at a range of initial temperatures from approximately 120-800 K to explore the effect of initial temperature on dynamic strength properties at strain rates reaching up to 10 7 s -1 . In aluminum, velocimetry data demonstrated an increase of peak stress of the elastic wave, σ E , with initial temperature. Alternatively, for invar, σ E exhibits little-to-no decrease over the same initial temperature range. Aluminum’s unusual deformation behavior is found to primarily be due to anharmonic vibrational effects. Differences in the magnetic structure of aluminum and invar can account for discrepancies in high rate deformation behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The electro-thermal stability of tantalum relative to aluminum and titanium in cylindrical liner ablation experiments at 550 kA

Presented are the results from the liner ablation experiments conducted at 550 kA on the Michigan Accelerator for Inductive Z-Pinch Experiments. These experiments were performed to evaluate a hypothesis that the electrothermal instability (ETI) is responsible for the seeding of magnetohydrodynamic instabilities and that the cumulative growth of ETI is primarily dependent on the material-specific ratio of critical temperature to melting temperature. This ratio is lower in refractory metals (e.g., tantalum) than in non-refractory metals (e.g., aluminum or titanium). The experimental observations presented herein reveal that the plasma-vacuum interface is remarkably stable in tantalum liner ablations. This stability is particularly evident when contrasted with the observations from aluminum and titanium experiments. These results are important to various programs in pulsed-power-driven plasma physics that depend on liner implosion stability. Furthermore, examples include the magnetized liner inertial fusion (MagLIF) program and the cylindrical dynamic material properties program at Sandia National Laboratories, where liner experiments are conducted on the 27-MA Z facility.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Uncertainties in cylindrical anode current inferences on pulsed power drivers

For over a decade, velocimetry based techniques have been used to infer the electrical current delivered to dynamic materials properties experiments on pulsed power drivers such as the Z Machine. Though originally developed for planar load geometries, in recent years, inferring the current delivered to cylindrical coaxial loads has become a valuable diagnostic tool for numerous platforms. Presented is a summary of uncertainties that can propagate through the current inference technique when applied to expanding cylindrical anodes. An equation representing quantitative uncertainty is developed which shows the unfold method to be accurate to a few percent above 10 MA of load current.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

An approximate inertial manifold (AIM) based closure for turbulent flows

A closure model for turbulent flows is developed based on a dynamical system theory. An appropriately discretized formulation of the governing equations is considered for this process. The key ingredient is an approximation of the system’s attractor, where all the trajectories in phase space are confined. This approximate inertial manifold based approach provides a path to track trajectories of the system in a lower-dimensional subspace. Unlike conventional coarse-graining approaches, the turbulent field is decomposed into resolved and unresolved dynamics using the properties of the governing equations. The novelty of the approach relies on the reconstruction of the unresolved field constrained by the governing equations. A posteriori tests for homogeneous isotropic turbulence and the Kuramoto–Sivashinsky equation show promising results for considerable dimension reduction with strong convergence properties. The proposed model outperforms the dynamic Smagorinsky model, and the computational overhead is competitive with similar approaches.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Delineating magnetization dynamics in solution-processed doped yttrium iron garnet thin films

Here, in this work, thin films of ruthenium-doped and cerium-doped yttrium iron garnet were deposited on silicon using solgel chemistry. Doped YIG could be produced in phase pure form up to a precursor stoichiometry of Y 3 Ru 0.1 Fe 4.9 O 12 and Ce 0.7 Y 2.3 Fe 5 O 12 . Both dopants significantly increase the coercivity and anisotropy field of the materials either due to domain wall pinning or increased spin–orbit coupling from the dopant. To delineate these two effects, the dynamic magnetic properties were studied using strip line ferromagnetic resonance (FMR). The FMR linewidth was separated into intrinsic loss and inhomogeneous line broadening. Inhomogeneous line broadening was found to dominate the magnetic losses in all the films likely due to magnon scattering off grain boundaries, but the Gilbert damping remained fairly low. By comparing the two dopants, it was found that Gilbert damping increased more in Ce:YIG films than in Ru:YIG films. This finding was corroborated by changes in the anisotropy field of the films, indicating a larger contribution from spin–orbit coupling from cerium than from ruthenium. Surprisingly, while magnetic loss globally increased with higher substitution, adding a small amount of dopant actually reduced the inhomogeneous line broadening in both sets of films. This was corroborated by crystallite size. The damping in Ru:YIG also decreased with a small amount of the dopant, which has been predicted by Kittel for doped garnets. Thus, it follows that there is an ideal doping regime where solgel YIG can be doped at low levels without increasing magnetic loss.

36 MATERIALS SCIENCE↗