Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “MAGNETIC DISPERSION”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Effects of Nd, Er Doping on the Structure and Magnetic Properties of YFeO{sub 3}

Nd, Er co-doped YFeO{sub 3} compounds were synthesized by sol-gel method. The prepared compounds were characterized by powder x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive x-ray (EDX), and vibrating sample magnetometer (VSM) integrated in a physical property measurement system (PPMS-9), respectively. The results show that the compounds possess orthorhombic perovskite structure. The Y{sub 0.5}Er{sub 0.1}Nd{sub 0.4}FeO{sub 3} compound mainly consists of five elements (Er, Nd, Y, Fe, and O) and atom ratio matched well with the formula. With the increase of Nd{sup 3+} doping content in Y{sub 0.5}Er{sub 0.5−x}Nd{sub x}FeO{sub 3} (x = 0, 0.1, 0.2, 0.3, and 0.4), the coercivity increases gradually while the saturation magnetization and remanent magnetization decrease at the same time. Introducing Nd{sup 3+} and Er{sup 3+} ions into YFeO{sub 3} will make a change on a structure distortion, resulting in the decrease of the Fe–O–Fe angle and the consequent reduction of superexchange effect. From our research results, the relationship between the r (R{sup 3+}) and the superexchange bond angle is different from pure-phase orthoferrites R FeO{sub 3}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Homogenization theory for the effective permittivity of a turbulent tokamak plasma in the scrape-off layer

We report that there has been a growing interest, over the past few years, on understanding the effect on radio frequency waves due to turbulence in the scrape-off layer of tokamak plasmas. While the far scrape-off layer density width is of the order of centimetres in contemporary tokamaks, in ITER (International Thermonuclear Experimental Reactor), and in future fusion reactors, the corresponding width will be of the order of tens of centimetres. As such, this could impact the spectral properties of the waves and, consequently, the transport of wave energy and momentum to the core plasma. The turbulence in the scrape-off layer spans a broad range of spatial scales and includes blobs and filaments that are elongated along the magnetic field lines. The propagation of radio frequency waves through this tenuous plasma is given by Maxwell’s equations. The characteristic properties of the plasma appear as a permittivity tensor in the expression for the current in Ampere’s equation. This paper develops a formalism for expressing the permittivity of a turbulent plasma using the homogenization technique. This technique has been extensively used to express the dielectric properties of composite materials that are spatially inhomogeneous, for example, due to the presence of micro-structures. In a similar vein, the turbulent plasma in the scrape-off layer is spatially inhomogeneous and can be considered as a composite material in which the micro-structures are filaments and blobs. The classical homogenization technique is not appropriate for the magnetized plasma in the scrape-off layer, as the radio frequency waves span a broad range of wavelengths and frequencies – from tens of megahertz to hundreds of gigahertz. The formalism in this paper makes use of the Fourier space components of the electric and magnetic fields of the radio frequency waves for the scattered fields and fields inside the filaments and blobs. These are the eigenvectors of the dispersion matrix which, using the Green’s function approach, lead to a homogenized dielectric tensor.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Silicon Solid Electrolyte Interphase (SEI) of Lithium Ion Battery Characterized by Microscopy and Spectroscopy

The surface reactions of electrolytes with a silicon anode in lithium ion cells have been investigated. The investigation utilizes two novel techniques that are enabled by the use of binder-free silicon (BF-Si) nanoparticle anodes. The first method, transmission electron microscopy with energy dispersive X-ray spectroscopy, allows straightforward analysis of the BF-Si solid electrolyte interphase (SEI). The second method utilizes multi-nuclear magnetic resonance spectroscopy of D2O extracts from the cycled anodes. The TEM and NMR data are complemented by XPS and FTIR data, which are routinely used for SEI studies. Coin cells (BF-Si/Li) were cycled in electrolytes containing LiPF6 salt and ethylene carbonate or fluoroethylene carbonate solvent. Capacity retention was significantly better for cells cycled with LiPF6/FEC electrolyte than for cells cycled with LiPF6/EC electrolyte. Our unique combination of techniques establishes that for LiPF6/EC electrolyte the BF-Si SEI continuously grows during the first 20 cycles and the SEI becomes integrated with the BF-Si nanoparticles. The SEI predominantly contains lithium ethylene dicarbonate, LiF, and LixSiOy. BF-Si electrodes cycled with LiPF6/FEC electrolyte have a different behavior; the BF-Si nanoparticles remain relatively distinct from the SEI. The SEI predominantly contains LiF, LixSiOy, and an insoluble polymeric species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Reactive instabilities of lower hybrid-like waves in regions with parallel currents

The dispersion and reactive instabilities of obliquely propagating waves near the lower hybrid (LH) frequency are studied in plasma carrying a current parallel to the magnetic field. Possible applications of these instabilities include magnetic reconnection regions, where LH-like waves may accelerate and heat both ions and electrons. In plasmas with a bulk drift of electrons relative to the ions at speed v{sub d} along the magnetic field, the forward and backward propagating LH modes are shown to be replaced by four LH-like modes. Reactive instabilities are discovered here for a forward propagating mode with Re({omega}){approx_equal}k{sub ||}v{sub d}/2 and a backward propagating mode with Re({omega})<{approx}5{Omega}{sub i}. Numerical warm, fully electromagnetic, kinetic calculations are compared with cold plasma calculations and agree well, confirming that the discovered instabilities are reactive. In the cold plasma limit, the forward and backward propagating instabilities occur for v{sub d} below and above some thresholds, respectively.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

ON THE DISPERSION AND SCATTERING OF MAGNETOHYDRODYNAMIC WAVES BY LONGITUDINALLY STRATIFIED FLUX TUBES

We provide a fairly general analytic theory for the dispersion and scattering of magnetohydrodynamic waves by longitudinally stratified flux tubes. The theory provides a common framework for, and synthesis of, many previous studies of flux tube oscillations that were carried out under various simplifying assumptions. The present theory focuses on making only a minimal number of assumptions. As a result it thus provides an analytical treatment of several generalizations of existing tube oscillation models. The most important practical cases are inclusion of plasma pressure and possibly buoyancy effects in models of straight non-diverging tubes as applied in coronal seismology, and relaxation of the 'thin tube' approximation in oscillation models of diverging tubes as applied both in the context of p-mode scattering and coronal seismology. In particular, it illustrates the unifying theoretical framework underlying both the description of waves scattered by flux tubes and the dispersion of waves carried along flux tubes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Homogenization theory for the effective permittivity of a turbulent tokamak plasma in the scrape-off layer

There has been a growing interest, over the past few years, on understanding the effect on radio frequency waves due to turbulence in the scrape-off layer of tokamak plasmas. While the far scrape-off layer density width is of the order of centimeters in contemporary tokamaks, in ITER, and in future fusion reactors, the corresponding width will be of the order of tens of centimeters. As such, this could impact the spectral properties of the waves and, consequently, the transport of wave energy and momentum to the core plasma. The turbulence in the scrape-off layer spans a broad range of spatial scales and includes blob and filaments that are elongated along the magnetic field lines. The propagation of radio frequency waves through this tenuous plasma is given by Maxwell's equations. The characteristic properties of the plasma appear as a permittivity tensor in the expression for the current in Ampere's equation. This paper develops a formalism for expressing the permittivity of a turbulent plasma using the homogenization technique. This technique has been extensively used to express the dielectric properties of composite materials that are spatially inhomogeneous, for example, due to the presence of micro-structures. In a similar vein, the turbulent plasma in the scrape-off layer is spatially inhomogeneous and can be considered as a composite material in which the micro-structures are filaments and blobs. The classical homogenization technique is not appropriate for the magnetized plasma in the scrape-off layer, as the radio frequency waves span a broad range of wavelengths and frequencies -- from tens of megahertz to hundreds of gigahertz. The formalism in this paper makes use of the Fourier space components of the electric and magnetic fields of the radio frequency waves for the scattered fields and fields inside the filaments and blobs. These are the eigenvectors of the dispersion matrix which, using the Green's function approach, lead to a homogenized dielectric tensor.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1976

Thickness of magnetic structures associated with the earth's bow shock

The thickness of magnetic structures associated with quasi-perpendicular bow shocks has been observed to vary over more than 2 orders of magnitude. In this paper, a criterion is employed which states that the magnetic structure of perpendicular shocks adjusts itself to keep electrostatic waves excited by the relative drift of electrons and ions at marginal stability. The marginal stability boundary and measured plasma parameters are used to calculate the expected thickness of bow-shock magnetic structures. The calculated and measured thicknesses are compared and found to be in good agreement over a range from less than 10 km to greater than 500 km. The conclusion is that the thickness of magnetic structures associated with quasi-perpendicular bow shocks is determined primarily by dissipation due to electron-ion streaming instabilities rather than by dispersive effects.

Morse, D. L.↗
DOE OSTI2019

Study of the Effect of Pr Doping on Structural, Morphological and Magnetic Properties of Nickel Ferrite

Praseodymium rare earth ion (Pr{sup 3+}) doped nickel ferrite (NiFe{sub 2−x}Pr{sub x}O{sub 4}, 0 < x< 0.1) nanocrystals (NFPO) were synthesized by hydrothermal method. The structural, morphological and magnetic properties of the prepared samples have been studied. The x-ray diffraction (XRD) and fourier transform infrared (FTIR) techniques confirmed the phase formation of the NFPO nanocrystals. The average crystallite size of NFPO nanoparticles found to be in the range 39 to 44 nm. The presence of Pr ions in NFPO was confirmed by energy-dispersive x-ray (EDX) analysis. It has been observed that after a certain amount of Pr doping, the morphology of the nanocrystals starts changing from nano-octahedrons to nanorods shape, as confirmed by transmission electron microscopy (TEM). Also, the magnetic properties of the prepared nanocrystals were measured using physical properties measurement system (PPMS) at 10 K and 300 K. The saturation magnetization (Ms) first decreases with the increasing loading amount of Pr ions up to (x = 0.025) and later it increases at both the temperatures. However, the value of coercivity shows an increasing trend with the increasing amount of Pr ions in NFPO at room temperature.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Dispersion relation for hadronic light-by-light scattering: two-pion contributions

In our third paper of a series dedicated to a dispersive treatment of the hadronic light-by-light (HLbL) tensor, we derive a partial-wave formulation for two-pion intermediate states in the HLbL contribution to the anomalous magnetic moment of the muon (g - 2) μ , including a detailed discussion of the unitarity relation for arbitrary partial waves. We show that obtaining a final expression free from unphysical helicity partial waves is a subtle issue, which we thoroughly clarify. As a by-product, we obtain a set of sum rules that could be used to constrain future calculations of γ*γ* → ππ. We validate the formalism extensively using the pion-box contribution, defined by two-pion intermediate states with a pion-pole left-hand cut, and demonstrate how the full known result is reproduced when resumming the partial waves. Using dispersive fits to high-statistics data for the pion vector form factor, we provide an evaluation of the full pion box, a$π-box\atop{μ}$ =-15.9(2) × 10 -11 . As an application of the partial-wave formalism, we present a first calculation of ππ-rescattering effects in HLbL scattering, with γ*γ* → ππ helicity partial waves constructed dispersively using ππ phase shifts derived from the inverse-amplitude method. In this way, the isospin-0 part of our calculation can be interpreted as the contribution of the f0(500) to HLbL scattering in (g - 2) μ . We also argue that the contribution due to charged-pion rescattering implements corrections related to the corresponding pion polarizability and show that these are moderate. Our final result for the sum of pion-box contribution and its S-wave rescattering corrections reads a$π-box\atop{μ}$ + a$ππ, π-pole LHC\atop{μ, J=0}$ = -24(1) × 10 -11 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Supercurrent decay in ballistic magnetic Josephson junctions

We investigate transport properties of ballistic magnetic Josephson junctions and establish that suppression of supercurrent is an intrinsic property of the junctions, even in absence of disorder. By studying the role of ferromagnet thickness, magnetization, and crystal orientation we show how the supercurrent decays exponentially with thickness and identify two mechanisms responsible for the effect: (i) large exchange splitting may gap out minority or majority carriers leading to the suppression of Andreev reflection in the junction, (ii) loss of synchronization between different modes due to the significant dispersion of the quasiparticle velocity with the transverse momentum. Our results for Nb/Ni/Nb junctions are in good agreement with recent experimental studies. Our approach combines density functional theory and the Bogoliubov-de Gennes model and opens a path for material composition optimization in magnetic Josephson junctions and superconducting magnetic spin valves.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Investigation of structure and magnetoresistance in Co/ZnO films

Co/ZnO films were deposited on glass substrates by magnetron sputtering at room temperature. The structure of the as-deposited films is studied by means of x-ray diffraction, x-ray photoelectron spectroscopy, and the zero-field-cooled and field-cooled magnetization curves. It is shown that the as-deposited samples consist of a mixture of regions of metallic Co and semiconducting ZnO. Large negative magnetoresistance of 26% and 11.9% are observed in the as-deposited Co/ZnO film with Co concentration of 50.7 at. % at 10 K and room temperature, respectively. Structural analysis, the temperature dependence of the conductivity and magnetoresistance reveal that the magnetoresistance is induced by spin-dependent tunneling between regions of conducting magnetic Co through the ZnO semiconducting barriers. The enhanced magnetoresistance in the low temperature regime may be related to the existence of higher-order tunneling processes between large Co regions mediated by small Co particles.

36 MATERIALS SCIENCE↗
DOE OSTI2011

The parametric decay of dust ion acoustic waves in non-uniform quantum dusty magnetoplasmas

The parametric decay instability of a dust ion acoustic wave into low-frequency electrostatic dust-lower-hybrid and electromagnetic shear Alfven waves has been investigated in detail in an inhomogeneous cold quantum dusty plasma in the presence of external/ambient uniform magnetic field. The quantum magnetohydrodynamic model of plasmas with quantum effect arising through the Bohm potential and Fermi degenerate pressure has been employed in order to find the linear and nonlinear responses of the plasma particles for three-wave nonlinear coupling in a dusty magnetoplasma. A relatively high frequency electrostatic dust ion acoustic wave has been taken as the pump wave. It couples with two other low-frequency internal possible modes of the dusty magnetoplasma, viz., the dust-lower-hybrid and shear Alfven waves. The nonlinear dispersion relation of the dust-lower-hybrid wave has been solved to obtain the growth rate of the parametric decay instability. The growth rate is at a maximum for a small value of the external magnetic field B{sub 0}. It is noted that the growth rate is proportional to the unperturbed electron number density n{sub oe} and is independent of inhomogeneity beyond L{sub e}=2 cm. An extraordinary growth rate is observed with the quantum effect.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

An optimized method for mouse liver sinusoidal endothelial cell isolation

The objective of the present study was to develop an accurate and reproducible method for liver sinusoidal endothelial cell (LSEC) isolation in mice. Non-parenchymal cells were isolated using a modified two-step collagenase digestion combined with Optiprep density gradient centrifugation. LSEC were further purified using two prevalent methods, short-term selective adherence and CD146+ magnetic-activated cell sorting (MACS), and compared in terms of cell yield, viability and purity to our purification technique using CD11b cell depletion combined with long-term selective adherence. LSEC purification using our technique allowed to obtain 7.07±3.80 million LSEC per liver, while CD146+ MACS and short-term selective adherence yielded 2.94±1.28 and 0.99±0.66 million LSEC, respectively. Purity of the final cell preparation reached 95.10±2.58% when using our method. In contrast, CD146+ MACS and short-term selective adherence gave purities of 86.75±3.26% and 47.95±9.82%, respectively. Similarly, contamination by non-LSEC was the lowest when purification was performed using our technique, with a proportion of contaminating macrophages of only 1.87±0.77%. Further, isolated cells analysed by scanning electron microscopy presented typical LSEC fenestrations organized in sieve plates, demonstrating that the technique allowed to isolate bona fide LSEC. In conclusion, we described a reliable and reproducible technique for the isolation of high yields of pure LSEC in mice. This protocol provides an efficient method to prepare LSEC for studying their biological functions. - Highlights: • This protocol provides an efficient method to prepare primary mouse LSEC for studying their biological functions. • The liver cell dispersion step was improved by performing a retrograde cannulation of the liver. • The cell yield and the purity obtained were higher than comparative techniques in mice. • Contaminating macrophages were removed by introducing a CD11b- magnetic –activated cell sorting step.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Fermi level pinning in Fe-doped PbTe under pressure

We synthesize an iron-doped PbTe single-crystal ingot and investigate the phase and the elemental composition as well as galvanomagnetic properties in weak magnetic fields (4.2 K≤T≤300 K, B ≤ 0.07 T) of Pb{sub 1−y}Fe{sub y}Te alloys upon varying the iron content, at atmospheric pressure and under hydrostatic compression up to 10 kilobars. We find an increase of iron concentration along the length of the ingot and the appearance of microscopic inclusions enriched with iron in the heavily doped samples. Lightly doped alloys are characterized by the p-type metal conductivity. An increase of the iron impurity content leads to a decrease in the free hole concentration, a stabilization of galvanomagnetic parameters, indicating the pinning of the Fermi energy by the iron resonant impurity level lying under the bottom of the valence band, and to the p-n inversion of the conductivity type. Under pressure, the free hole concentration in the sample, in which the stabilization of galvanomagnetic parameters takes place, increases by approximately a factor of four due to the flow of electrons from the valence band to the iron-induced resonant level. Using the two-band Kane and the six-band Dimmock dispersion relations, the pressure dependence of the Fermi energy is calculated. The model of the electronic structure rearrangement of Pb{sub 1−y}Fe{sub y}Te under pressure is proposed. The energy position and the pressure coefficient of the resonant iron impurity level are determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The generation of sub-millimeter lithium granules from liquid Jet for magnetic fusion applications

This paper is a report on using a liquid jet to generate spherical lithium granules which can be used in fusion devices. The liquid jet uses liquid lithium as the continuous phase and liquid paraffin as the dispersed phase which can effectively prevent the lithium granule from oxidation and carbonization considering the active chemical property of lithium. The liquid lithium flows through a nozzle and breaks up into globules that have diverse diameters. A deeper investigation indicates that the temperature and pressure difference, which directly influence the flow velocity, have impacts on the distribution of granule size. The increases of temperature and pressure result in the granule size approaches the orifice diameter. Thus, suggesting a method to generate small spherical lithium granules that are controllable in size by adjusting the orifice size, temperature and pressure difference.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1977

Effects of finite plasma beta on the lower-hybrid-drift instability

The local dispersion relation for the lower-hybrid-drift (LHD) instability is derived and analyzed, taking into account the finite-beta effects associated with transverse electromagnetic perturbations as well as with resonant and nonresonant electron-orbit modifications due to magnetic-field gradients. The influence of finite-beta effects on the LHD instability is calculated in a fully self-consistent manner for arbitrary values of electron-ion temperature ratio, local beta, cross-field ExB velocity/ion thermal speed ratio, and other plasma parameters. Stability properties are investigated analytically for the case of cold electrons, and the local dispersion relation is solved numerically in the parameter regime of most interest for high-density plasma pinches. The results show that for all parameter regimes studied, the net effect of finite plasma beta is to reduce the maximum growth rate of the LHD instability, although the details can vary, depending on the plasma parameters. Except in the limit where the electron/ion temperature ratio tends to zero, it is found that there is a critical value of plasma beta above which the LHD instability is completely stabilized.

Davidson, R. C.↗
DOE OSTI2015

Investigation of dielectric relaxation, Jahn-Teller distortion, and magnetic ordering in Y substituted Pr{sub 1−x}Y{sub x}MnO{sub 3} (0.1 ≤ x ≤ 0.4)

We report structural, magnetic, and dielectric properties of the perovskite compound Pr{sub 1−x}Y{sub x}MnO{sub 3} (0.1 ≤ x ≤ 0.4) studied using dc magnetization, ac susceptibility, neutron powder diffraction, and dielectric techniques. These compounds crystallize in orthorhombic space group (Pnma) in the temperature range 5–300 K. The Mn-O-Mn bond angle decreases with the Y substitution along with an increase in the Jahn-Teller distortion. The Jahn-Teller distortion for Pr{sub 0.9}Y{sub 0.1}MnO{sub 3} shows an anomalous change near 50 K, below which it falls sharply. Neutron powder diffraction patterns of all reported compositions at low temperature constitute additional magnetic Bragg peaks that suggest magnetic ordering. Magnetic reflections were indexed in the nuclear lattice with the propagation vector k = (0, 0, 0). Rietveld refinement of powder patterns conform to A type antiferromagnetic ordering where moments are aligned ferromagnetically in a–c plane and coupled nearly antiferromagnetically along b-axis resulting in a net ferromagnetic component along the b-direction. The antiferromagnetic transition temperature was deduced from dc magnetization and ac susceptibility data. The transition temperature decreases by nearly 22 K (from 81 K to 59 K) as yttrium content (x) increases from 0.1 to 0.4. Measurements reveal strong frequency dispersion in dielectric constant and dielectric loss. Activation energy and relaxation time are estimated from the Arrhenius plot. It is further shown that relaxation behaviour is altered with yttrium doping concentration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Nuclear magnetic relaxation by the dipolar EMOR mechanism: Three-spin systems

In aqueous systems with immobilized macromolecules, including biological tissue, the longitudinal spin relaxation of water protons is primarily induced by exchange-mediated orientational randomization (EMOR) of intra- and intermolecular magnetic dipole-dipole couplings. Starting from the stochastic Liouville equation, we have developed a non-perturbative theory that can describe relaxation by the dipolar EMOR mechanism over the full range of exchange rates, dipole couplings, and Larmor frequencies. Here, we implement the general dipolar EMOR theory for a macromolecule-bound three-spin system, where one, two, or all three spins exchange with the bulk solution phase. In contrast to the previously studied two-spin system with a single dipole coupling, there are now three dipole couplings, so relaxation is affected by distinct correlations as well as by self-correlations. Moreover, relaxation can now couple the magnetizations with three-spin modes and, in the presence of a static dipole coupling, with two-spin modes. As a result of this complexity, three secondary dispersion steps with different physical origins can appear in the longitudinal relaxation dispersion profile, in addition to the primary dispersion step at the Larmor frequency matching the exchange rate. Furthermore, and in contrast to the two-spin system, longitudinal relaxation can be significantly affected by chemical shifts and by the odd-valued (“imaginary”) part of the spectral density function. We anticipate that the detailed studies of two-spin and three-spin systems that have now been completed will provide the foundation for developing an approximate multi-spin dipolar EMOR theory sufficiently accurate and computationally efficient to allow quantitative molecular-level interpretation of frequency-dependent water-proton longitudinal relaxation data from biophysical model systems and soft biological tissue.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗