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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

On the validation of magnetic resonance velocimetry in single-phase turbulent pipe flows

A nuclear magnetic resonance imaging technique is used to measure velocity distributions in turbulent pipe flows up to Re = 24580. While turbulent intensity is usually determined from signal attenuation, we deduce turbulent intensity from velocity distribution with no need to suppose a Gaussian distribution for velocity fluctuations. Skewness and flatness measurements are also presented in this paper. Comparison with DNS show good agreement and we show that NMR data is sufficiently accurate to provide turbulent viscosity profile. The low field system used in this study allow the suppression of susceptibility artifacts and thus open its use for studying two-phase flows. We postulate that the method used here could be applied to two-phase flows and would thus provide valuable information on turbulent viscosity models. (authors)

42 ENGINEERING↗
DOE OSTI2015

Water dynamics on ice and hydrate lattices studied by second-order central-line stimulated-echo oxygen-17 nuclear magnetic resonance

Oxygen-17 stimulated-echo spectroscopy is a novel nuclear magnetic resonance (NMR) technique that allows one to investigate the time scale and geometry of ultraslow molecular motions in materials containing oxygen. The method is based on detecting orientationally encoded frequency changes within oxygen’s central-transition NMR line that are caused by second-order quadrupolar interactions. In addition to the latter, the present theoretical analysis of various two-pulse echo and stimulated-echo pulse sequences takes also heteronuclear dipolar interactions into account. As an experimental example, the ultraslow water motion in polycrystals of tetrahydrofuran clathrate hydrate is studied via two-time oxygen-17 stimulated-echo correlation functions. The resulting correlation times and those of hexagonal ice are similar to those from previous deuteron NMR measurements. Calculations of the echo functions’ final-state correlations for various motional models are compared with the experimental data of the clathrate hydrate. It is found that a six-site model including the oxygen-proton dipolar interaction describes the present results.

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

Dynamics of asymmetric binary glass formers. II. Results from nuclear magnetic resonance spectroscopy

Various {sup 2}H and {sup 31}P nuclear magnetic resonance (NMR) spectroscopy techniques are applied to probe the component dynamics of the binary glass former tripropyl phosphate (TPP)/polystyrene-d{sub 3} (PS) over the full concentration range. The results are quantitatively compared to those of a dielectric spectroscopy (DS) study on the same system previously published [R. Kahlau, D. Bock, B. Schmidtke, and E. A. Rössler, J. Chem. Phys. 140, 044509 (2014)]. While the PS dynamics does not significantly change in the mixtures compared to that of neat PS, two fractions of TPP molecules are identified, one joining the glass transition of PS in the mixture (α{sub 1}-process), the second reorienting isotropically (α{sub 2}-process) even in the rigid matrix of PS, although at low concentration resembling a secondary process regarding its manifestation in the DS spectra. Pronounced dynamical heterogeneities are found for the TPP α{sub 2}-process, showing up in extremely stretched, quasi-logarithmic stimulated echo decays. While the time window of NMR is insufficient for recording the full correlation functions, DS results, covering a larger dynamical range, provide a satisfactory interpolation of the NMR data. Two-dimensional {sup 31}P NMR spectra prove exchange within the broadly distributed α{sub 2}-process. As demonstrated by {sup 2}H NMR, the PS matrix reflects the faster α{sub 2}-process of TPP by performing a spatially highly hindered motion on the same timescale.

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

Structural properties of mixed (NH{sub 4}){sub 2−x}Rb{sub x}ZnCl{sub 4} (x=0, 1, and 2) crystals studied by {sup 1}H and {sup 87}Rb nuclear magnetic resonance

The structures of mixed (NH{sub 4}){sub 2−x}Rb{sub x}ZnCl{sub 4} (x=0, 1, and 2) single crystals were determined by x-ray diffraction. In addition, the nuclear magnetic resonance (NMR) spectra and spin–lattice relaxation times of the {sup 1}H and {sup 87}Rb nuclei in the three crystals were determined using NMR spectroscopy. We analyzed the crystallographic structures of these crystals by considering the occupation probabilities (NH{sub 4} or Rb) of the two cationic sites. Our NMR results confirm that there are two crystallographically inequivalent NH{sub 4} sites, NH{sub 4}(1) and NH{sub 4}(2), in (NH{sub 4}){sub 2}ZnCl{sub 4}, and two crystallographically inequivalent Rb sites, Rb(1) and Rb(2), in Rb{sub 2}ZnCl{sub 4}. However, only one NH{sub 4} site and two Rb sites were observed in NH{sub 4}RbZnCl{sub 4}. The NH{sub 4} and Rb occupation rates of each of the two available sites, A{sub 1} and A{sub 2}, were determined from the NMR signals. - Graphical abstract: The structures of mixed (NH{sub 4}){sub 2−x}Rb{sub x}ZnCl{sub 4} (x=0, 1, and 2) single crystals were determined by x-ray diffraction. In addition, the nuclear magnetic resonance (NMR) spectra and spin–lattice relaxation times of the {sup 1}H and {sup 87}Rb nuclei in the three crystals were determined using NMR spectroscopy. Highlights: ► Mixed (NH{sub 4}){sub 2−x}Rb{sub x}ZnCl{sub 4} (x=0, 1, and 2) crystals. ► The crystallographic structures by occupation probabilities. ► The NH{sub 4} and Rb occupation rates.

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

Inhomogeneous broadening of optically detected magnetic resonance of the ensembles of nitrogen-vacancy centers in diamond by interstitial carbon atoms

We study the impact of the negatively charged nitrogen-vacancy (NV{sup –}) center density on the lattice strain resulting in the splitting of the optically detected magnetic resonance of HPHT diamond. A simple model, taking into account the presence of the interstitial carbon atoms, acting like a wedge force on the crystal lattice, explains the broadening and splitting of the optically detected magnetic resonance of the ensemble of NV{sup –} centers at densities within the range of 10{sup 13} ÷ 10{sup 14 }cm{sup −3}. This model uses a complete generalized spin Hamiltonian, takes into account the strain-effect of each center in the ensemble and gives good agreement with experimental data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

High resolution detection and excitation of resonant magnetic perturbations in a wall-stabilized tokamak

We report high-resolution detection of the 3D plasma magnetic response of wall-stabilized tokamak discharges in the High Beta Tokamak-Extended Pulse [T. H. Ivers et al., Phys. Plasmas 3, 1926 (1996)] device. A new adjustable conducting wall has been installed on HBT-EP made up of 20 independent, movable, wall segments instrumented with three distinct sets of 40 modular coils that can be independently driven to generate a wide variety of magnetic perturbations. High-resolution detection of the plasma response is made with 216 poloidal and radial magnetic sensors that have been located and calibrated with high-accuracy. Static and dynamic plasma responses to resonant and non-resonant magnetic perturbations are observed through measurement of the step-response following a rapid change in the toroidal phase of the applied perturbations. Biorthogonal decomposition of the full set of magnetic sensors clearly defines the structures of naturally occurring external kinks as being composed of independent m/n = 3/1 and 6/2 modes. Resonant magnetic perturbations were applied to discharges with pre-existing, saturated m/n = 3/1 external kink mode activity. This m/n = 3/1 kink mode was observed to lock to the applied perturbation field. During this kink mode locked period, the plasma resonant response is characterized by a linear, a saturated, and a disruptive plasma regime dependent on the magnitude of the applied field and value of the edge safety factor and plasma rotation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

Neutrino spectral split in core-collapse supernovae: A magnetic resonance phenomenon

A variety of neutrino flavor conversion phenomena occur in core-collapse supernova, due to the large neutrino density close to the neutrinosphere, and the importance of the neutrino-neutrino interaction. Three different regimes have been identified so far, usually called the synchronization, the bipolar oscillations, and the spectral split. Using the formalism of polarization vectors, within two flavors, we focus on the spectral split phenomenon and we show for the first time that the physical mechanism underlying the neutrino spectral split is a magnetic resonance phenomenon. In particular, we show that the precession frequencies fulfill the magnetic resonance conditions. Our numerical calculations show that the neutrino energies and the location at which the resonance takes place in the supernova coincide well with the neutrino energies at which a spectral swap occurs. The corresponding adiabaticity parameters present spikes at the resonance location.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Comparative study of magnetic ordering in bulk and nanoparticles of Sm{sub 0.65}Ca{sub 0.35}MnO{sub 3}: Magnetization and electron magnetic resonance measurements

To explore the effect of size reduction to nanoscale on the hole doped Sm{sub 0.65}Ca{sub 0.35}MnO{sub 3} compound, dc magnetic measurements and electron magnetic resonance (EMR) were done on bulk and nanoparticle samples in the temperature range 10 ≤ T ≤ 300 K. Magnetization measurement showed that the bulk sample undergoes a charge ordering transition at 240 K and shows a mixed magnetic phase at low temperature. However, the nanosample underwent a ferromagnetic transition at 75 K, and the charge ordered state was destabilized on size reduction down to nanoscale. The low-temperature ferromagnetic component is found to be enhanced in nanoparticles as compared to their bulk counterpart. Interestingly around room temperature, bulk particles show higher magnetization where as at low temperature nanoparticles show higher magnetization. Ferromagnetism in the bulk is due to super exchange where as ferromagnetism in nanoparticles is due to uncompensated spins of the surface layer. Temperature variation of EMR parameters correlates well with the results of magnetic measurements. The magnetic behaviour of the nanoparticles is understood in terms of the core shell scenario.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Experimental cell for molecular beam deposition and magnetic resonance studies of matrix isolated radicals at temperatures below 1 K

We present the design and performance of an experimental cell constructed for matrix isolation studies of H and D atoms in solid H{sub 2}/D{sub 2} films, which are created by molecular beam deposition at temperatures below 1 K. The sample cell allows sensitive weighing of the films by a quartz microbalance (QM) and their studies by magnetic resonance techniques in a strong magnetic field of 4.6 T. We are able to regulate the deposition rate in the range from 0.01 to 10 molecular layers/s, and measure the thickness with ≈0.2 monolayer resolution. The upper QM electrode serves as a mirror for a 128 GHz Fabry-Perot resonator connected to an electron spin resonance (ESR) spectrometer. H and D atoms were created by RF discharge in situ in the sample cell, and characterized by ESR and electron-nuclear double resonance. From the magnetic resonance measurements we conclude that the films are smooth and provide homogeneous trapping conditions for embedded atoms. The current sample cell design also makes it possible to calibrate the ESR signal and estimate the average and local concentrations of H and D radicals in the film.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

The onset of rare earth metallosis begins with renal gadolinium-rich nanoparticles from magnetic resonance imaging contrast agent exposure

The leitmotifs of magnetic resonance imaging (MRI) contrast agent-induced complications range from acute kidney injury, symptoms associated with gadolinium exposure (SAGE)/gadolinium deposition disease, potentially fatal gadolinium encephalopathy, and irreversible systemic fibrosis. Gadolinium is the active ingredient of these contrast agents, a non-physiologic lanthanide metal. The mechanisms of MRI contrast agent-induced diseases are unknown. Mice were treated with a MRI contrast agent. Human kidney tissues from contrast-naïve and MRI contrast agent-treated patients were obtained and analyzed. Kidneys (human and mouse) were assessed with transmission electron microscopy and scanning transmission electron microscopy with X-ray energy-dispersive spectroscopy. MRI contrast agent treatment resulted in unilamellar vesicles and mitochondriopathy in renal epithelium. Electron-dense intracellular precipitates and the outer rim of lipid droplets were rich in gadolinium and phosphorus. We conclude that MRI contrast agents are not physiologically inert. The long-term safety of these synthetic metal–ligand complexes, especially with repeated use, should be studied further.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Coherence of magnetic resonators in a metamaterial

The coherence of periodic magnetic resonators (MRs) under oblique incidence is studied using simulations. The correlated phase of interaction including both the retardation effect and relative phase difference between two MRs is defined, and it plays a key role in the MR interaction. The correlated phase is anisotropic, as is the coherence condition. The coherence condition is the same as the Wood's anomaly and verified by the Fano resonance. This study shows that the applications of the Fano resonance of periodic MRs will become widespread owing to achieving the Fano resonance simply by tuning the incident angle.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Optical readout of singlet fission biexcitons in a heteroacene with photoluminescence detected magnetic resonance

Molecular spin systems based on photoexcited triplet pairs formed via singlet fission (SF) are attractive as carriers of quantum information because of their potentially pure and controllable spin polarization, but developing systems that offer optical routes to readout as well as initialization is challenging. Herein, we characterize the electron spin magnetic resonance change in the photoluminescence intensity for a tailored organic molecular crystal while sweeping a microwave drive up to 10 GHz in a broadband loop structure. We observe resonant transitions for both triplet and quintet spin sublevel populations showing their optical sensitivity and revealing the zero-field parameters for each. We map the evolution of these spectra in both microwave frequency and magnetic field, producing a pattern of optically detected magnetic resonance (ODMR) peaks. Fits to these data using a suitable model suggest significant spin polarization in this system with orientation selectivity. Unusual excitation intensity dependence is also observed, which inverts the sign of the ODMR signal for the triplet features, but not for the quintet. These observations demonstrate optical detection of the spin sublevel population dictated by SF and intermolecular geometry, and highlight anisotropic and multi-scale dynamics of triplet pairs.

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

Neoclassical transport due to resonant magnetic perturbations in DIII-D

In this work, the role of neoclassical physics in the particle and energy transport during the application of resonant magnetic perturbations (RMPs) to suppress the edge localised modes in a tokamak is analysed. The neoclassical fluxes in non-axisymmetric DIII-D equilibria with applied RMPs are calculated using the NEO code. The magnetic field provided to NEO as an input is calculated using M3D-C1 and includes the nonlinear one-fluid plasma response. Neoclassical fluxes obtained in this study are found to dramatically increase in the presence of applied resonant magnetic perturbations, and are in same range as the total radial particle fluxes calculated in comparable RMP discharges in DIII-D. This suggests that neoclassical transport plays a significant role in edge transport when RMPs are present. An increase in neoclassical fluxes during the ELM suppressed phase in DIII-D plasmas is calculated and is strongly correlated with the observation of density pump-out in the experiment.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Locally advanced rectal cancer: qualitative and quantitative evaluation of diffusion-weighted magnetic resonance imaging in restaging after neoadjuvant chemo-radiotherapy

Purpose: To determine the added value of qualitative and quantitative evaluation of diffusion-weighted magnetic resonance imaging (DWI) in locally advanced rectal cancer (LARC) restaging after neoadjuvant chemo-radiotherapy (CRT). Materials and Methods: A retrospective study was performed of 21 patients with LARC treated with CRT. All patients were evaluated with 1.5 T conventional magnetic resonance imaging (MRI) and DWI (0–1000 s/mm²) before starting therapy and after neoadjuvant CRT. All included patients underwent surgery after CRT: the histopathological evaluation of surgical specimens represented the reference standard for local staging after neoadjuvant therapy. The qualitative analysis was carried out by two operators in consensus, who reviewed the conventional MR image set [T1-weighted and T2-weighted morphological sequences + dynamic contrast-enhanced sequences (DCE)] and the combined set of conventional and DW images. For the quantitative analysis, the apparent diffusion coefficient (ADC) values were measured at each examination. For each lesion, the mean ADC value (ADCpre and ADCpost) and the ΔADC (ADCpost – ADCpre) were calculated, and values of the three groups of response [complete response (pCR), partial response (pPR), stable disease (pSD)] were compared. Results: In LARC restaging, conventional MRI showed a sensitivity of 80% and a specificity of 50%, with a total diagnostic capacity of 71.40%, while by adding DWI sensitivity increased to 100%, specificity to 67%, and total diagnostic capacity to 90.40%. ΔADC correlates with treatment response and a cutoff of 1.35 × 10{sup −3} mm²/s predicts the pCR with a sensitivity of 93.3% and a specificity of 83.3%. Conclusions: Adding DWI to conventional sequences may improve MRI capability to evaluate tumor response to CRT. The quantitative DWI assessment is promising, but larger studies are required.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
NASA NTRS2000

Magnetic resonance imaging of convection in laser-polarized xenon

We demonstrate nuclear magnetic resonance (NMR) imaging of the flow and diffusion of laser-polarized xenon (129Xe) gas undergoing convection above evaporating laser-polarized liquid xenon. The large xenon NMR signal provided by the laser-polarization technique allows more rapid imaging than one can achieve with thermally polarized gas-liquid systems, permitting shorter time-scale events such as rapid gas flow and gas-liquid dynamics to be observed. Two-dimensional velocity-encoded imaging shows convective gas flow above the evaporating liquid xenon, and also permits the measurement of enhanced gas diffusion near regions of large velocity variation.

Non-NASA Center↗