Magnetic field effects on shear and normal stresses in magnetorheological finishing.

PubMed

Lambropoulos, John C; Miao, Chunlin; Jacobs, Stephen D

2010-09-13

We use a recent experimental technique to measure in situ shear and normal stresses during magnetorheological finishing (MRF) of a borosilicate glass over a range of magnetic fields. At low fields shear stresses increase with magnetic field, but become field-independent at higher magnetic fields. Micromechanical models of formation of magnetic particle chains suggest a complex behavior of magnetorheological (MR) fluids that combines fluid- and solid-like responses. We discuss the hypothesis that, at higher fields, slip occurs between magnetic particle chains and the immersed glass part, while the normal stress is governed by the MRF ribbon elasticity.

Iron chalcogenide superconductors at high magnetic fields

PubMed Central

Lei, Hechang; Wang, Kefeng; Hu, Rongwei; Ryu, Hyejin; Abeykoon, Milinda; Bozin, Emil S; Petrovic, Cedomir

2012-01-01

Iron chalcogenide superconductors have become one of the most investigated superconducting materials in recent years due to high upper critical fields, competing interactions and complex electronic and magnetic phase diagrams. The structural complexity, defects and atomic site occupancies significantly affect the normal and superconducting states in these compounds. In this work we review the vortex behavior, critical current density and high magnetic field pair-breaking mechanism in iron chalcogenide superconductors. We also point to relevant structural features and normal-state properties. PMID:27877518

EPR and magnetization studies on single crystals of a heterometallic (Cu II and Cr III) complex: Zero-field splitting determination

NASA Astrophysics Data System (ADS)

Novosel, Nikolina; Žilić, Dijana; Pajić, Damir; Jurić, Marijana; Perić, Berislav; Zadro, Krešo; Rakvin, Boris; Planinić, Pavica

2008-10-01

Magnetic properties of single crystals of the heterometallic complex [Cu(bpy) 3] 2[Cr(C 2O 4) 3]NO 3·9H 2O (bpy = 2,2'-bipyridine) have been investigated. From the recorded EPR spectra, the spin-Hamiltonian parameters have been determined. The magnetization measurements have shown magnetic anisotropy at low temperatures, which has been analysed as a result of the zero-field splitting of the Cr III ion. By fitting the exactly derived magnetization expression to the measured magnetization data, the axial zero-field splitting parameter, D, has been calculated. Comparing to the EPR measurements, it has been confirmed that D can be determined from the measurements of the macroscopic magnetization on the single crystals.

Magnetic Properties of Mononuclear Co(II) Complexes with Carborane Ligands.

PubMed

Alcoba, Diego R; Oña, Ofelia B; Massaccesi, Gustavo E; Torre, Alicia; Lain, Luis; Melo, Juan I; Peralta, Juan E; Oliva-Enrich, Josep M

2018-06-12

We analyze the magnetic properties of three mononuclear Co(II) coordination complexes using quantum chemical complete active space self-consistent field and N-electron valence perturbation theory approaches. The complexes are characterized by a distorted tetrahedral geometry in which the central ion is doubly chelated by the icosahedral ligands derived from 1,2-(HS) 2 -1,2-C 2 B 10 H 10 (complex I), from 1,2-(HS) 2 -1,2-C 2 B 10 H 10 and 9,12-(HS) 2 -1,2-C 2 B 10 H 10 (complex II), and from 9,12-(HS) 2 -1,2-C 2 B 10 H 10 (complex III), which are two positional isomers of dithiolated 1,2-dicarba- closo-dodecaborane (complex I). Complex I was realized experimentally recently (Tu, D.; Shao, D.; Yan, H.; Lu, C. Chem. Commun. 2016, 52, 14326) and served to validate the computational protocol employed in this work, while the remaining two proposed complexes can be considered positional isomers of I. Our calculations show that these complexes present different axial and rhombic zero-field splitting anisotropy parameters and different values of the most significant components of the g tensor. The predicted axial anisotropy D = -147.2 cm -1 for complex II is twice that observed experimentally for complex I, D = -72.8 cm -1 , suggesting that this complex may be of interest for practical applications. We also analyze the temperature dependence of the magnetic susceptibility and molar magnetization for these complexes when subject to an external magnetic field. Overall, our results suggest that o-carborane-incorporated Co(II) complexes are worthwhile candidates for experimental exploration as single-ion molecular magnets.

Chaos in Magnetic Flux Ropes

NASA Astrophysics Data System (ADS)

Gekelman, W. N.; DeHaas, T.; Van Compernolle, B.

2013-12-01

Magnetic Flux Ropes Immersed in a uniform magnetoplasma are observed to twist about themselves, writhe about each other and rotate about a central axis. They are kink unstable and smash into one another as they move. Full three dimensional magnetic field and flows are measured at thousands of time steps. Each collision results in magnetic field line generation and the generation of a quasi-seperatrix layer and induced electric fields. Three dimensional magnetic field lines are computed by conditionally averaging the data using correlation techniques. The permutation entropy1 ,which is related to the Lyapunov exponent, can be calculated from the the time series of the magnetic field data (this is also done with flows) and used to calculate the positions of the data on a Jensen Shannon complexity map2. The location of data on this map indicates if the magnetic fields are stochastic, or fall into regions of minimal or maximal complexity. The complexity is a function of space and time. The complexity map, and analysis will be explained in the course of the talk. Other types of chaotic dynamical models such as the Lorentz, Gissinger and Henon process also fall on the map and can give a clue to the nature of the flux rope turbulence. The ropes fall in the region of the C-H plane where chaotic systems lie. The entropy and complexity change in space and time which reflects the change and possibly type of chaos associated with the ropes. The maps give insight as to the type of chaos (deterministic chaos, fractional diffusion , Levi flights..) and underlying dynamical process. The power spectra of much of the magnetic and flow data is exponential and Lorentzian structures in the time domain are embedded in them. Other quantities such as the Hurst exponent are evaluated for both magnetic fields and plasma flow. Work Supported by a UC-LANL Lab fund and the Basic Plasma Science Facility which is funded by DOE and NSF. 1) C. Bandt, B. Pompe, Phys. Rev. Lett., 88,174102 (2007) 2) O. Russo et al., Phys. Rev. Lett., 99, 154102 (2007), J. Maggs, G.Morales, 55, 085015 (2013)

A six-coordinate ytterbium complex exhibiting easy-plane anisotropy and field-induced single-ion magnet behavior.

PubMed

Liu, Jun-Liang; Yuan, Kang; Leng, Ji-Dong; Ungur, Liviu; Wernsdorfer, Wolfgang; Guo, Fu-Sheng; Chibotaru, Liviu F; Tong, Ming-Liang

2012-08-06

The field-induced blockage of magnetization behavior was first observed in an Yb(III)-based molecule with a trigonally distorted octahedral coordination environment. Ab initio calculations and micro-SQUID measurements were performed to demonstrate the exhibition of easy-plane anisotropy, suggesting the investigated complex is the first pure lanthanide field-induced single-ion magnet (field-induced SIM) of this type. Furthermore, we found the relaxation time obeys a power law instead of an exponential law, indicating that the relaxation process should be involved a direct process rather than an Orbach process.

The complex magnetic field configuration of the Martian magnetotail as observed by MAVEN

NASA Astrophysics Data System (ADS)

DiBraccio, Gina A.; Luhmann, Janet; Curry, Shannon; Espley, Jared R.; Gruesbeck, Jacob; Xu, Shaosui; Mitchell, David; Soobiah, Yasir; Connerney, John E. P.; Dong, Chuanfei; Harada, Yuki; Ruhunusiri, Suranga; Halekas, Jasper; Hara, Takuya; Ma, Yingjuan; Brain, David; Jakosky, Bruce

2017-10-01

The Martian magnetosphere forms as the solar wind directly interacts with the planet’s upper atmosphere. During this interaction, the Sun’s interplanetary magnetic field (IMF) drapes around the planet and local crustal magnetic fields, creating a magnetosphere configuration that has attributes of both an induced magnetosphere like that of Venus, and a complex, small-scale magnetosphere like the Moon. In addition to the closed crustal fields and draped IMF at Mars, open magnetic fields are created when magnetic reconnection occurs between the planetary fields and the IMF. These various field topologies present a complex magnetotail structure that we are now able to explore using a combination of MAVEN observations and magnetohydrodynamic (MHD) simulations. Preliminary MHD results have suggested that the Martian magnetotail includes a dual-lobe component, composed of open crustal fields, enveloped by an induced comet-like tail. These simulated open-field lobes are twisted by roughly 45°, either clockwise or counterclockwise, from the ecliptic plane. This rotation depends on the east-west component of the IMF. We utilize MAVEN Magnetometer and Solar Wind Ion Analyzer (SWIA) measurements collected over two Earth years to analyze the tail magnetic field configuration as a function of IMF direction. Cross-tail views of the average measured magnetic field components directed toward and away from the planet are compared for a variety of solar wind parameters. We find that, in agreement with simulation results, the east-west IMF component strongly affects the magnetotail structure, twisting its sunward-antisunward polarity patterns in response to changing IMF orientation. Through a data-model comparison we are able to infer that regions of open magnetic fields in the tail are likely reconnected crustal fields. Futhermore, these open fields in the tail may contribute to atmospheric escape to space. From this investigation we are able to confirm that the Martian magnetotail is a hybrid configuration between intrinsic and induced magnetospheres, shifting the paradigm of Mars’ magnetosphere as we have understood it thus far.

Effect of Longitudinal Magnetic Field on Vibration Characteristics of Single-Walled Carbon Nanotubes in a Viscoelastic Medium

NASA Astrophysics Data System (ADS)

Zhang, D. P.; Lei, Y.; Shen, Z. B.

2017-12-01

The effect of longitudinal magnetic field on vibration response of a sing-walled carbon nanotube (SWCNT) embedded in viscoelastic medium is investigated. Based on nonlocal Euler-Bernoulli beam theory, Maxwell's relations, and Kelvin viscoelastic foundation model, the governing equations of motion for vibration analysis are established. The complex natural frequencies and corresponding mode shapes in closed form for the embedded SWCNT with arbitrary boundary conditions are obtained using transfer function method (TFM). The new analytical expressions for the complex natural frequencies are also derived for certain typical boundary conditions and Kelvin-Voigt model. Numerical results from the model are presented to show the effects of nonlocal parameter, viscoelastic parameter, boundary conditions, aspect ratio, and strength of the magnetic field on vibration characteristics for the embedded SWCNT in longitudinal magnetic field. The results demonstrate the efficiency of the proposed methods for vibration analysis of embedded SWCNTs under magnetic field.

Obtaining source current density related to irregularly structured electromagnetic target field inside human body using hybrid inverse/FDTD method.

PubMed

Han, Jijun; Yang, Deqiang; Sun, Houjun; Xin, Sherman Xuegang

2017-01-01

Inverse method is inherently suitable for calculating the distribution of source current density related with an irregularly structured electromagnetic target field. However, the present form of inverse method cannot calculate complex field-tissue interactions. A novel hybrid inverse/finite-difference time domain (FDTD) method that can calculate the complex field-tissue interactions for the inverse design of source current density related with an irregularly structured electromagnetic target field is proposed. A Huygens' equivalent surface is established as a bridge to combine the inverse and FDTD method. Distribution of the radiofrequency (RF) magnetic field on the Huygens' equivalent surface is obtained using the FDTD method by considering the complex field-tissue interactions within the human body model. The obtained magnetic field distributed on the Huygens' equivalent surface is regarded as the next target. The current density on the designated source surface is derived using the inverse method. The homogeneity of target magnetic field and specific energy absorption rate are calculated to verify the proposed method.

Single molecule magnet behaviour in robust dysprosium-biradical complexes.

PubMed

Bernot, Kevin; Pointillart, Fabrice; Rosa, Patrick; Etienne, Mael; Sessoli, Roberta; Gatteschi, Dante

2010-09-21

A Dy-biradical complex was synthesized and characterized down to very low temperature. ac magnetic measurements reveal single molecule magnet behaviour visible without any application of dc field. The transition to the quantum tunneling regime is evidenced. Photophysical and EPR measurements provide evidence of the excellent stability of these complexes in solution.

Complete magnetic field dependence of SABRE-derived polarization.

PubMed

Kiryutin, Alexey S; Yurkovskaya, Alexandra V; Zimmermann, Herbert; Vieth, Hans-Martin; Ivanov, Konstantin L

2018-07-01

Signal amplification by reversible exchange (SABRE) is a promising hyperpolarization technique, which makes use of spin-order transfer from parahydrogen (the H 2 molecule in its singlet spin state) to a to-be-polarized substrate in a transient organometallic complex, termed the SABRE complex. In this work, we present an experimental method for measuring the magnetic field dependence of the SABRE effect over an ultrawide field range, namely, from 10 nT to 10 T. This approach gives a way to determine the complete magnetic field dependence of SABRE-derived polarization. Here, we focus on SABRE polarization of spin-1/2 hetero-nuclei, such as 13 C and 15 N and measure their polarization in the entire accessible field range; experimental studies are supported by calculations of polarization. Features of the field dependence of polarization can be attributed to level anticrossings in the spin system of the SABRE complex. Features at magnetic fields of the order of 100 nT-1 μT correspond to "strong coupling" of protons and hetero-nuclei, whereas features found in the mT field range stem from "strong coupling" of the proton system. Our approach gives a way to measuring and analyzing the complete SABRE field dependence, to probing NMR parameters of SABRE complexes and to optimizing the polarization value. Copyright © 2017 John Wiley & Sons, Ltd.

Current systems of coronal loops in 3D MHD simulations

NASA Astrophysics Data System (ADS)

Warnecke, J.; Chen, F.; Bingert, S.; Peter, H.

2017-11-01

Aims: We study the magnetic field and current structure associated with a coronal loop. Through this we investigate to what extent the assumptions of a force-free magnetic field break down and where they might be justified. Methods: We analyze a three-dimensional (3D) magnetohydrodynamic (MHD) model of the solar corona in an emerging active region with the focus on the structure of the forming coronal loops. The lower boundary of this simulation is taken from a model of an emerging active region. As a consequence of the emerging magnetic flux and the horizontal motions at the surface a coronal loop forms self-consistently. We investigate the current density along magnetic field lines inside (and outside) this loop and study the magnetic and plasma properties in and around this loop. The loop is defined as the bundle of field lines that coincides with enhanced emission in extreme UV. Results: We find that the total current along the emerging loop changes its sign from being antiparallel to parallel to the magnetic field. This is caused by the inclination of the loop together with the footpoint motion. Around the loop, the currents form a complex non-force-free helical structure. This is directly related to a bipolar current structure at the loop footpoints at the base of the corona and a local reduction of the background magnetic field (I.e., outside the loop) caused by the plasma flow into and along the loop. Furthermore, the locally reduced magnetic pressure in the loop allows the loop to sustain a higher density, which is crucial for the emission in extreme UV. The action of the flow on the magnetic field hosting the loop turns out to also be responsible for the observed squashing of the loop. Conclusions: The complex magnetic field and current system surrounding it can only be modeled in 3D MHD models where the magnetic field has to balance the plasma pressure. A one-dimensional coronal loop model or a force-free extrapolation cannot capture the current system and the complex interaction of the plasma and the magnetic field in the coronal loop, despite the fact that the loop is under low-β conditions.

ARC-2012-ACD12-0020-001

NASA Image and Video Library

2012-02-02

Stein_Sun: Visualization of the complex magnetic field produced as magnetic flux rises toward the Sun¹s surface from the deep convection zone. The image shows a snapshot of how the magnetic field has evolved two days from the time uniform, untwisted, horizontal magnetic field started to be advected by inflows at the bottom (20 megameters deep). Axes are in megameters, and the color scale shows the log of the magnetic field strength. Credit: Robert Stein, Michigan State University; Tim Sandstrom, NASA/Ames

Sensed presence and mystical experiences are predicted by suggestibility, not by the application of transcranial weak complex magnetic fields.

PubMed

Granqvist, Pehr; Fredrikson, Mats; Unge, Patrik; Hagenfeldt, Andrea; Valind, Sven; Larhammar, Dan; Larsson, Marcus

2005-04-29

Transcranial magnetic stimulation (TMS) with weak (micro Tesla) complex waveform fields have been claimed to evoke the sensed presence of a sentient being in up to 80% in the general population. These findings have had a questionable neurophysiological foundation as the fields are approximately six orders of magnitude weaker than ordinary TMS fields. Also, no independent replication has been reported. To replicate and extend previous findings, we performed a double-blind experiment (N=89), with a sham-field control group. Personality characteristics indicating suggestibility (absorption, signs of abnormal temporal lobe activity, and a "new age"-lifestyle orientation) were used as predictors. Sensed presence, mystical, and other somatosensory experiences previously reported from the magnetic field stimulation were outcome measures. We found no evidence for any effects of the magnetic fields, neither in the entire group, nor in individuals high in suggestibility. Because the personality characteristics significantly predicted outcomes, suggestibility may account for previously reported effects. Our results strongly question the earlier claims of experiential effects of weak magnetic fields.

Spacetime algebra as a powerful tool for electromagnetism

NASA Astrophysics Data System (ADS)

Dressel, Justin; Bliokh, Konstantin Y.; Nori, Franco

2015-08-01

We present a comprehensive introduction to spacetime algebra that emphasizes its practicality and power as a tool for the study of electromagnetism. We carefully develop this natural (Clifford) algebra of the Minkowski spacetime geometry, with a particular focus on its intrinsic (and often overlooked) complex structure. Notably, the scalar imaginary that appears throughout the electromagnetic theory properly corresponds to the unit 4-volume of spacetime itself, and thus has physical meaning. The electric and magnetic fields are combined into a single complex and frame-independent bivector field, which generalizes the Riemann-Silberstein complex vector that has recently resurfaced in studies of the single photon wavefunction. The complex structure of spacetime also underpins the emergence of electromagnetic waves, circular polarizations, the normal variables for canonical quantization, the distinction between electric and magnetic charge, complex spinor representations of Lorentz transformations, and the dual (electric-magnetic field exchange) symmetry that produces helicity conservation in vacuum fields. This latter symmetry manifests as an arbitrary global phase of the complex field, motivating the use of a complex vector potential, along with an associated transverse and gauge-invariant bivector potential, as well as complex (bivector and scalar) Hertz potentials. Our detailed treatment aims to encourage the use of spacetime algebra as a readily available and mature extension to existing vector calculus and tensor methods that can greatly simplify the analysis of fundamentally relativistic objects like the electromagnetic field.

Orientational control of block copolymer microdomains by sub-tesla magnetic fields

NASA Astrophysics Data System (ADS)

Gopinadhan, Manesh; Choo, Youngwoo; Feng, Xunda; Kawabata, Kohsuke; di, Xiaojun; Osuji, Chinedum

Magnetic fields offer a versatile approach to controlling the orientation of block copolymer (BCP) microdomains during self-assembly. To date however, such control has required the imposition of large magnetic fields (>3T), necessitating the use of complex magnet systems - either superconducting or very large conventional resistive magnets. Here we demonstrate the ability to direct BCP self-assembly using considerably smaller fields (<1T) which are accessible using simple rare-earth permanent magnets. The low field alignment is enabled by the presence of small quantities of mesogenic species that are blended into, and co-assemble with the liquid crystalline (LC) mesophase of the side-chain LC BCP under study. In situ SAXS experiments reveal a pronounced dependence of the critical alignment field strength on the stoichiometry of the blend, and the ability to generate aligned microdomains with orientational distribution coefficients exceeding 0.95 at sub-1 T fields for appropriate stoichiometries. The alignment response overall can be rationalized in terms of increased mobility and grain size due to the presence of the mesogenic additive. We use a permanent magnet to fabricate films with aligned nanopores, and the utility of this approach to generate complex BCP microdomain patterns in thin films by local field screening are highlighted. NSF DMR-1410568 and DMR-0847534.

Effect of low frequency magnetic fields on the growth of MNP-treated HT29 colon cancer cells

NASA Astrophysics Data System (ADS)

Spyridopoulou, K.; Makridis, A.; Maniotis, N.; Karypidou, N.; Myrovali, E.; Samaras, T.; Angelakeris, M.; Chlichlia, K.; Kalogirou, O.

2018-04-01

Recent investigations have attempted to understand and exploit the impact of magnetic field-actuated internalized magnetic nanoparticles (MNPs) on the proliferation rate of cancer cells. Due to the complexity of the parameters governing magnetic field-exposure though, individual studies to date have raised contradictory results. In our approach we performed a comparative analysis of key parameters related to the cell exposure of cancer cells to magnetic field-actuated MNPs, and to the magnetic field, in order to better understand the factors affecting cellular responses to magnetic field-stimulated MNPs. We used magnetite MNPs with a hydrodynamic diameter of 100 nm and studied the proliferation rate of MNPs-treated versus untreated HT29 human colon cancer cells, exposed to either static or alternating low frequency magnetic fields with varying intensity (40-200 mT), frequency (0-8 Hz) and field gradient. All three parameters, field intensity, frequency, and field gradient affected the growth rate of cells, with or without internalized MNPs, as compared to control MNPs-untreated and magnetic field-untreated cells. We observed that the growth inhibitory effects induced by static and rotating magnetic fields were enhanced by pre-treating the cells with MNPs, while the growth promoting effects observed in alternating field-treated cells were weakened by MNPs. Compared to static, rotating magnetic fields of the same intensity induced a similar extend of cell growth inhibition, while alternating fields of varying intensity (70 or 100 mT) and frequency (0, 4 or 8 Hz) induced cell proliferation in a frequency-dependent manner. These results, highlighting the diverse effects of mode, intensity, and frequency of the magnetic field on cell growth, indicate that consistent and reproducible results can be achieved by controlling the complexity of the exposure of biological samples to MNPs and external magnetic fields, through monitoring crucial experimental parameters. We demonstrate that further research focusing on the accurate manipulation of the aforementioned magnetic field exposure parameters could lead to the development of successful non-invasive therapeutic anticancer approaches.

Magnetic blocking at 10 K and a dipolar-mediated avalanche in salts of the bis(η8-cyclooctatetraenide) complex [Er(COT)2]-.

PubMed

Meihaus, Katie R; Long, Jeffrey R

2013-11-27

The structures and magnetic properties of [K(18-crown-6)](+) (1) and [K(18-crown-6)(THF)2](+) (2) salts of the η(8)-cyclooctatetraenide sandwich complex [Er(COT)2](-) (COT(2-) = cyclooctatetraene dianion) are reported. Despite slight differences in symmetry, both compounds exhibit slow magnetic relaxation under zero applied dc field with relaxation barriers of ∼150 cm(-1) and waist-restricted magnetic hysteresis. Dc relaxation and dilution studies suggest that the drop in the magnetic hysteresis near zero field is influenced by a bulk magnetic avalanche effect coupled with tunneling of the magnetization. Through dilution with [K(18-crown-6)(THF)2][Y(COT)2] (3), these phenomena are substantially quenched, resulting in an open hysteresis loop to 10 K. Importantly, this represents the highest blocking temperature yet observed for a mononuclear complex and the second highest for any single-molecule magnet. A comprehensive comparative analysis of the magnetism of [K(18-crown-6)][Ln(COT)2] (Ln = Sm, Tb, Dy, Ho, Yb) reveals slow relaxation only for [K(18-crown-6)][Dy(COT)2] (4) with weak temperature dependence. Collectively, these results highlight the utility of an equatorial ligand field for facilitating slow magnetic relaxation in the prolate Er(III) ion.

Simultaneous identification of the low-field-induced tiny variation of complex refractive index for anisotropic and opaque magnetic-fluid thin film by a stable heterodyne Mach-Zehnder interferometer.

PubMed

Hong, Chin-Yih; Chieh, Jen-Jie; Yang, Shieh-Yueh; Yang, Hong-Chang; Horng, Herng-Er

2009-10-10

We use a heterodyne Mach-Zehnder interferometer to simultaneously and simply measure the complex refractive index by only normal incidence on the specimen, instead of using a complicated measurement procedure or instrument that only measures the real or imaginary part of the complex refractive index. To study the tiny variation of the complex refractive index, the small complex refractive-index variation of a rare-concentration magnetic-fluid thin film, due to a weak field of less than 200 Oe, was processed by this interferometer. We also present the wavelength trend of the complex refractive index of magnetic fluids to verify the appearance of the slight change in a small wavelength range.

High microwave attenuation performance of planar carbonyl iron particles with orientation of shape anisotropy field

NASA Astrophysics Data System (ADS)

Guo, Cheng; Yang, Zhihong; Shen, Shile; Liang, Juan; Xu, Guoyue

2018-05-01

Planar anisotropy carbonyl iron (PACI) particles were prepared from commercial spherical carbonyl iron particles through a high performance ball-milling technique. The paraffin composites with orientation of shape anisotropy field for these PACI particles were obtained by applying an external magnetic field during the fabrication process. The frequency-dependent complex permeability values of these prepared paraffin composites have been investigated in the frequency range of 1-18 GHz. The results demonstrate that the orientation of shape anisotropy field for these PACI particles can effectively increase the complex permeability and decrease the complex permittivity values. Benefit from the enhancement in the complex permeability and reduction in the complex permittivity, the better impedance matching condition can be obtained and thus the good microwave absorption performance can be achieved for the samples with enough magnetic field orientation time.

Interactions of Twisted Ω-loops in a Model Solar Convection Zone

NASA Astrophysics Data System (ADS)

Jouve, L.; Brun, A. S.; Aulanier, G.

2018-04-01

This study aims at investigating the ability of strong interactions between magnetic field concentrations during their rise through the convection zone to produce complex active regions at the solar surface. To do so, we perform numerical simulations of buoyant magnetic structures evolving and interacting in a model solar convection zone. We first produce a 3D model of rotating convection and then introduce idealized magnetic structures close to the bottom of the computational domain. These structures possess a certain degree of field line twist and they are made buoyant on a particular extension in longitude. The resulting twisted Ω-loops will thus evolve inside a spherical convective shell possessing large-scale mean flows. We present results on the interaction between two such loops with various initial parameters (mainly buoyancy and twist) and on the complexity of the emerging magnetic field. In agreement with analytical predictions, we find that if the loops are introduced with opposite handedness and same axial field direction or the same handedness but opposite axial field, they bounce against each other. The emerging region is then constituted of two separated bipolar structures. On the contrary, if the loops are introduced with the same direction of axial and peripheral magnetic fields and are sufficiently close, they merge while rising. This more interesting case produces complex magnetic structures with a high degree of non-neutralized currents, especially when the convective motions act significantly on the magnetic field. This indicates that those interactions could be good candidates to produce eruptive events like flares or CMEs.

Analysis of the vector magnetic fields of complex sunspots

NASA Technical Reports Server (NTRS)

Patty, S. R.

1981-01-01

An analysis of the vector magnetic field in the delta-configurations of two complex sunspot groups is presented, noting several characteristics identified in the delta-configurations. The observations of regions 2469 (S12E80) and 2470 (S21E83) took place in May, 1980 with a vector magnetograph, verified by optical viewing. Longitudinal magnetic field plots located the delta-configurations in relation to the transverse field neutral line. It is shown that data on the polarization yields qualitative information on the magnetic field strengths, while the azimuth of the transverse field can be obtained from the relative intensities of linear polarization measurements aligned with respect to the magnetograph analyses axis at 0 and 90 deg, and at the plus and minus 45 deg positions. Details of the longitudinal fields are discussed. A strong, sheared transverse field component is found to be a signature of strong delta. A weak delta is accompanied by a weak longitudinal gradient with an unsheared transverse component of variable strength.

Magnetic field structure and evolution features of selected stars. III.

NASA Astrophysics Data System (ADS)

Glagolevskij, Yu. V.

2016-01-01

We present the results of modeling for about a hundred magnetic stars. It is shown that the dipole representation of magnetic field structures describes the distribution of the magnetic field over stellar surfaces fairly well. We analyze some patterns which support the relic hypothesis of magnetic field formation.Arguments are given in favor of the assumption that themain properties ofmagnetic stars—slow rotation, predominant orientation of magnetic field lines along the plane of the rotation equator, complex internal structures of magnetic fields—are acquired in the process of gravitational collapse. There are no conditions for that in the non-stationary Hayashi phase and in the stage of a radiative young star.

FIRST ZEEMAN DOPPLER IMAGING OF A COOL STAR USING ALL FOUR STOKES PARAMETERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosén, L.; Kochukhov, O.; Wade, G. A.

Magnetic fields are ubiquitous in active cool stars, but they are in general complex and weak. Current Zeeman Doppler imaging (ZDI) studies of cool star magnetic fields chiefly employ circular polarization observations because linear polarization is difficult to detect and requires a more sophisticated radiative transfer modeling to interpret. But it has been shown in previous theoretical studies, and in the observational analyses of magnetic Ap stars, that including linear polarization in the magnetic inversion process makes it possible to correctly recover many otherwise lost or misinterpreted magnetic features. We have obtained phase-resolved observations in all four Stokes parameters ofmore » the RS CVn star II Peg at two separate epochs. Here we present temperature and magnetic field maps reconstructed for this star using all four Stokes parameters. This is the very first such ZDI study of a cool active star. Our magnetic inversions reveal a highly structured magnetic field topology for both epochs. The strength of some surface features is doubled or even quadrupled when linear polarization is taken into account. The total magnetic energy of the reconstructed field map also becomes about 2.1–3.5 times higher. The overall complexity is also increased as the field energy is shifted toward higher harmonic modes when four Stokes parameters are used. As a consequence, the potential field extrapolation of the four Stokes parameter ZDI results indicates that magnetic field becomes weaker at a distance of several stellar radii due to a decrease of the large-scale field component.« less

Fringe Field Effects on Bending Magnets, Derived for TRANSPORT/TURTLE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Molloy, Riley; Blitz, Sam

2013-08-05

A realistic magnetic dipole has complex effects on a charged particle near the entrance and exit of the magnet, even with a constant and uniform magnetic field deep within the interior of the magnet. To satisfy Maxwell's equations, the field lines near either end of a realistic magnet are significantly more complicated, yielding non-trivial forces. The effects of this fringe field are calculated to first order, applying both the paraxial and thin lens approximations. We find that, in addition to zeroth order effects, the position of a particle directly impacts the forces in the horizontal and vertical directions.

TWO NOVEL PARAMETERS TO EVALUATE THE GLOBAL COMPLEXITY OF THE SUN'S MAGNETIC FIELD AND TRACK THE SOLAR CYCLE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, L.; Landi, E.; Gibson, S. E., E-mail: lzh@umich.edu

2013-08-20

Since the unusually prolonged and weak solar minimum between solar cycles 23 and 24 (2008-2010), the sunspot number is smaller and the overall morphology of the Sun's magnetic field is more complicated (i.e., less of a dipole component and more of a tilted current sheet) compared with the same minimum and ascending phases of the previous cycle. Nearly 13 yr after the last solar maximum ({approx}2000), the monthly sunspot number is currently only at half the highest value of the past cycle's maximum, whereas the polar magnetic field of the Sun is reversing (north pole first). These circumstances make itmore » timely to consider alternatives to the sunspot number for tracking the Sun's magnetic cycle and measuring its complexity. In this study, we introduce two novel parameters, the standard deviation (SD) of the latitude of the heliospheric current sheet (HCS) and the integrated slope (SL) of the HCS, to evaluate the complexity of the Sun's magnetic field and track the solar cycle. SD and SL are obtained from the magnetic synoptic maps calculated by a potential field source surface model. We find that SD and SL are sensitive to the complexity of the HCS: (1) they have low values when the HCS is flat at solar minimum, and high values when the HCS is highly tilted at solar maximum; (2) they respond to the topology of the HCS differently, as a higher SD value indicates that a larger part of the HCS extends to higher latitude, while a higher SL value implies that the HCS is wavier; (3) they are good indicators of magnetically anomalous cycles. Based on the comparison between SD and SL with the normalized sunspot number in the most recent four solar cycles, we find that in 2011 the solar magnetic field had attained a similar complexity as compared to the previous maxima. In addition, in the ascending phase of cycle 24, SD and SL in the northern hemisphere were on the average much greater than in the southern hemisphere, indicating a more tilted and wavier HCS in the north than the south, associated with the early reversal of the polar magnetic field in the north relative to the south.« less

Dynamic response of a sensor element made of magnetic hybrid elastomer with controllable properties

NASA Astrophysics Data System (ADS)

Becker, T. I.; Zimmermann, K.; Borin, D. Yu.; Stepanov, G. V.; Storozhenko, P. A.

2018-03-01

Smart materials like magnetic hybrid elastomers (MHEs) are based on an elastic composite with a complex hybrid filler of magnetically hard and soft particles. Due to their unique magnetic field depending characteristics, these elastomers offer great potential for designing sensor systems with a complex adaptive behaviour and operating sensitivity. The present paper deals with investigations of the material properties and motion behaviour displayed by synthesised MHE beams in the presence of a uniform magnetic field. The distribution and structure formation of the magnetic components inside the elastic matrix depending on the manufacturing conditions are examined. The specific magnetic features of the MHE material during the magnetising process are revealed. Experimental investigations of the in-plane free vibrational behaviour displayed by the MHE beams with the fixed-free end conditions are performed for various magnitudes of an imposed uniform magnetic field. For the samples pre-magnetised along the length axis, it is demonstrated that the deflection of the beam can be identified unambiguously by magnetic field distortion measurements. It is shown that the material properties of the vibrating MHE element can be specifically adjusted by means of an external magnetic field control. The dependence of the first eigenfrequency of free bending vibrations of the MHE beams on the strength of an imposed uniform magnetic field is obtained. The results are aimed to assess the potential of MHEs to design acceleration sensor systems with an adaptive magnetically controllable sensitivity range.

Magnetic Doppler imaging of α2 Canum Venaticorum in all four Stokes parameters. Unveiling the hidden complexity of stellar magnetic fields

NASA Astrophysics Data System (ADS)

Kochukhov, O.; Wade, G. A.

2010-04-01

Context. Strong organized magnetic fields have been studied in the upper main sequence chemically peculiar stars for more than half a century. However, only recently have observational methods and numerical techniques become sufficiently mature to allow us to record and interpret high-resolution four Stokes parameter spectra, leading to the first assumption-free magnetic field models of these stars. Aims: Here we present a detailed magnetic Doppler imaging analysis of the spectropolarimetric observations of the prototypical magnetic Ap star α2 CVn. This is the second star for which the magnetic field topology and horizontal chemical abundance inhomogeneities have been inferred directly from phase-resolved observations of line profiles in all four Stokes parameters, free from the traditional assumption of a low-order multipolar field geometry. Methods: We interpret the rotational modulation of the circular and linear polarization profiles of the strong Fe II and Cr II lines in the spectra of α2 CVn recorded with the MuSiCoS spectropolarimeter. The surface abundance distributions of the two chemical elements and a full vector map of the stellar magnetic field are reconstructed in a self-consistent inversion using our state-of-the-art magnetic Doppler imaging code Invers10. Results: We succeeded in reproducing most of the details of the available spectropolarimetric observations of α2 CVn with a magnetic map which combines a global dipolar-like field topology with localized spots of higher field intensity. We demonstrate that these small-scale magnetic structures are inevitably required to fit the linear polarization spectra; however, their presence cannot be inferred from the Stokes I and V observations alone. We also found high-contrast surface distributions of Fe and Cr, with both elements showing abundance minima in the region of weaker and topologically simpler magnetic field. Conclusions: Our magnetic Doppler imaging analysis of α2 CVn and previous results for 53 Cam support the view that the upper main sequence stars can harbour fairly complex surface magnetic fields which resemble oblique dipoles only at the largest spatial scales. Spectra in all four Stokes parameters are absolutely essential to unveil and meaningfully characterize this field complexity in Ap stars. We therefore suggest that understanding magnetism of stars in other parts of the H-R diagram is similarly incomplete without investigation of their linear polarization spectra. Based on data obtained using the Télescope Bernard Lyot at Observatoire du Pic du Midi.

Thermoseeds for interstitial magnetic hyperthermia: from bioceramics to nanoparticles

NASA Astrophysics Data System (ADS)

Baeza, A.; Arcos, D.; Vallet-Regí, M.

2013-12-01

The development of magnetic materials for interstitial hyperthermia treatment of cancer is an ever evolving research field which provides new alternatives to antitumoral therapies. The development of biocompatible magnetic materials has resulted in new biomaterials with multifunctional properties, which are able to adapt to the complex scenario of tumoral processes. Once implanted or injected in the body, magnetic materials can behave as thermoseeds under the effect of AC magnetic fields. Magnetic bioceramics aimed to treat bone tumors and magnetic nanoparticles are among the most studied thermoseeds, and supply different solutions for the different scenarios in cancerous processes. This paper reviews some of the biomaterials used for bone cancer treatment and skeletal reinforcing, as well as the more complex topic of magnetic nanoparticles for intracellular targeting and hyperthermia.

Thermoseeds for interstitial magnetic hyperthermia: from bioceramics to nanoparticles.

PubMed

Baeza, A; Arcos, D; Vallet-Regí, M

2013-12-04

The development of magnetic materials for interstitial hyperthermia treatment of cancer is an ever evolving research field which provides new alternatives to antitumoral therapies. The development of biocompatible magnetic materials has resulted in new biomaterials with multifunctional properties, which are able to adapt to the complex scenario of tumoral processes. Once implanted or injected in the body, magnetic materials can behave as thermoseeds under the effect of AC magnetic fields. Magnetic bioceramics aimed to treat bone tumors and magnetic nanoparticles are among the most studied thermoseeds, and supply different solutions for the different scenarios in cancerous processes. This paper reviews some of the biomaterials used for bone cancer treatment and skeletal reinforcing, as well as the more complex topic of magnetic nanoparticles for intracellular targeting and hyperthermia.

Spin polarization transfer mechanisms of SABRE: A magnetic field dependent study.

PubMed

Pravdivtsev, Andrey N; Ivanov, Konstantin L; Yurkovskaya, Alexandra V; Petrov, Pavel A; Limbach, Hans-Heinrich; Kaptein, Robert; Vieth, Hans-Martin

2015-12-01

We have investigated the magnetic field dependence of Signal Amplification By Reversible Exchange (SABRE) arising from binding of para-hydrogen (p-H2) and a substrate to a suitable transition metal complex. The magnetic field dependence of the amplification of the (1)H Nuclear Magnetic Resonance (NMR) signals of the released substrates and dihydrogen, and the transient transition metal dihydride species shows characteristic patterns, which is explained using the theory presented here. The generation of SABRE is most efficient at low magnetic fields due to coherent spin mixing at nuclear spin Level Anti-Crossings (LACs) in the SABRE complexes. We studied two Ir-complexes and have shown that the presence of a (31)P atom in the SABRE complex doubles the number of LACs and, consequently, the number of peaks in the SABRE field dependence. Interestingly, the polarization of SABRE substrates is always accompanied by the para-to-ortho conversion in dihydride species that results in enhancement of the NMR signal of free (H2) and catalyst-bound H2 (Ir-HH). The field dependences of hyperpolarized H2 and Ir-HH by means of SABRE are studied here, for the first time, in detail. The field dependences depend on the chemical shifts and coupling constants of Ir-HH, in which the polarization transfer takes place. A negative coupling constant of -7Hz between the two chemically equivalent but magnetically inequivalent hydride nuclei is determined, which indicates that Ir-HH is a dihydride with an HH distance larger than 2Å. Finally, the field dependence of SABRE at high fields as found earlier has been investigated and attributed to polarization transfer to the substrate by cross-relaxation. The present study provides further evidence for the key role of LACs in the formation of SABRE-derived polarization. Understanding the spin dynamics behind the SABRE method opens the way to optimizing its performance and overcoming the main limitation of NMR, its notoriously low sensitivity. Copyright © 2015 Elsevier Inc. All rights reserved.

Spin polarization transfer mechanisms of SABRE: A magnetic field dependent study

NASA Astrophysics Data System (ADS)

Pravdivtsev, Andrey N.; Ivanov, Konstantin L.; Yurkovskaya, Alexandra V.; Petrov, Pavel A.; Limbach, Hans-Heinrich; Kaptein, Robert; Vieth, Hans-Martin

2015-12-01

We have investigated the magnetic field dependence of Signal Amplification By Reversible Exchange (SABRE) arising from binding of para-hydrogen (p-H2) and a substrate to a suitable transition metal complex. The magnetic field dependence of the amplification of the 1H Nuclear Magnetic Resonance (NMR) signals of the released substrates and dihydrogen, and the transient transition metal dihydride species shows characteristic patterns, which is explained using the theory presented here. The generation of SABRE is most efficient at low magnetic fields due to coherent spin mixing at nuclear spin Level Anti-Crossings (LACs) in the SABRE complexes. We studied two Ir-complexes and have shown that the presence of a 31P atom in the SABRE complex doubles the number of LACs and, consequently, the number of peaks in the SABRE field dependence. Interestingly, the polarization of SABRE substrates is always accompanied by the para-to-ortho conversion in dihydride species that results in enhancement of the NMR signal of free (H2) and catalyst-bound H2 (Ir-HH). The field dependences of hyperpolarized H2 and Ir-HH by means of SABRE are studied here, for the first time, in detail. The field dependences depend on the chemical shifts and coupling constants of Ir-HH, in which the polarization transfer takes place. A negative coupling constant of -7 Hz between the two chemically equivalent but magnetically inequivalent hydride nuclei is determined, which indicates that Ir-HH is a dihydride with an HH distance larger than 2 Å. Finally, the field dependence of SABRE at high fields as found earlier has been investigated and attributed to polarization transfer to the substrate by cross-relaxation. The present study provides further evidence for the key role of LACs in the formation of SABRE-derived polarization. Understanding the spin dynamics behind the SABRE method opens the way to optimizing its performance and overcoming the main limitation of NMR, its notoriously low sensitivity.

Effect of sample initial magnetic field on the metal magnetic memory NDT result

NASA Astrophysics Data System (ADS)

Moonesan, Mahdi; Kashefi, Mehrdad

2018-08-01

One of the major concerns regarding the use of Metal Magnetic Memory (MMM) technique is the complexity of residual magnetization effect on output signals. The present study investigates the influence of residual magnetic field on stress induced magnetization. To this end, various initial magnetic fields were induced on a low carbon steel sample, and for each level of residual magnetic field, the sample was subjected to a set of 4-point bending tests and, their corresponding MMM signals were collected from the surface of the bended sample using a tailored metal magnetic memory scanning device. Results showed a strong correlation between sample residual magnetic field and its corresponding level of stress induced magnetic field. It was observed that the sample magnetic field increases with applying the bending stress as long as the initial residual magnet field is low (i.e. <117 mG), but starts decreasing with higher levels of initial residual magnetic fields. Besides, effect of bending stress on the MMM output of a notched sample was investigated. The result, again, showed that MMM signals exhibit a drop at stress concentration zone when sample has high level of initial residual magnetic field.

Magnetic Doppler imaging of 53 Camelopardalis in all four Stokes parameters

NASA Astrophysics Data System (ADS)

Kochukhov, O.; Bagnulo, S.; Wade, G. A.; Sangalli, L.; Piskunov, N.; Landstreet, J. D.; Petit, P.; Sigut, T. A. A.

2004-02-01

We present the first investigation of the structure of the stellar surface magnetic field using line profiles in all four Stokes parameters. We extract the information about the magnetic field geometry and abundance distributions of the chemically peculiar star 53 Cam by modelling time-series of high-resolution spectropolarimetric observations with the help of a new magnetic Doppler imaging code. This combination of the unique four Stokes parameter data and state-of-the-art magnetic imaging technique makes it possible to infer the stellar magnetic field topology directly from the rotational variability of the Stokes spectra. In the magnetic imaging of 53 Cam we discard the traditional multipolar assumptions about the structure of magnetic fields in Ap stars and explore the stellar magnetic topology without introducing any global a priori constraints on the field structure. The complex magnetic model of 53 Cam derived with our magnetic Doppler imaging method achieves a good fit to the observed intensity, circular and linear polarization profiles of strong magnetically sensitive Fe II spectral lines. Such an agreement between observations and model predictions was not possible with any earlier multipolar magnetic models, based on modelling Stokes I spectra and fitting surface averaged magnetic observables (e.g., longitudinal field, magnetic field modulus, etc.). Furthermore, we demonstrate that even the direct inversion of the four Stokes parameters of 53 Cam assuming a low-order multipolar magnetic geometry is incapable of achieving an adequate fit to our spectropolarimetric observations. Thus, as a main result of our investigation, we discover that the magnetic field topology of 53 Cam is considerably more complex than any low-order multipolar expansion, raising a general question about the validity of the multipolar assumption in the studies of magnetic field structures of Ap stars. In addition to the analysis of the magnetic field of 53 Cam, we reconstruct surface abundance distributions of Si, Ca, Ti, Fe and Nd. These abundance maps confirm results of the previous studies of 53 Cam, in particular dramatic antiphase variation of Ca and Ti abundances. Based on observations obtained with the Bernard Lyot telescope of the Pic du Midi Observatory and Isaac Newton Telescope of the La Palma Observatory.

Polarization of seven MBM clouds at high Galactic latitude

NASA Astrophysics Data System (ADS)

Neha, S.; Maheswar, G.; Soam, A.; Lee, C. W.

2018-06-01

We made R-band polarization measurements of 234 stars towards the direction of the MBM 33-39 cloud complex. The distance of the MBM 33-39 complex was determined as 120 ± 10 pc using polarization results and near-infrared photometry from the 2MASS survey. The magnetic field geometry of the individual clouds inferred from our polarimetric results reveals that the field lines are in general consistent with the global magnetic field geometry of the region obtained from previous studies. This implies that the clouds in the complex are permeated by the interstellar magnetic field. Multi-wavelength polarization measurements of a few stars projected on to the complex suggest that the size of the dust grains in these clouds is similar to those found in the normal interstellar medium of the Milky Way. We studied a possible formation scenario of the MBM 33-39 complex by combining the polarization results from our study with those from the literature and by identifying the distribution of ionized, atomic and molecular (dust) components of material in the region.

Non-Maxwellian and magnetic field effects in complex plasma wakes★

NASA Astrophysics Data System (ADS)

Ludwig, Patrick; Jung, Hendrik; Kählert, Hanno; Joost, Jan-Philip; Greiner, Franko; Moldabekov, Zhandos; Carstensen, Jan; Sundar, Sita; Bonitz, Michael; Piel, Alexander

2018-05-01

In a streaming plasma, negatively charged dust particles create complex charge distributions on the downstream side of the particle, which are responsible for attractive forces between the like-charged particles. This wake phenomenon is studied by means of refined linear response theory and molecular dynamics simulations as well as in experiments. Particular attention is paid to non-Maxwellian velocity distributions that are found in the plasma sheath and to situations with strong magnetic fields, which are becoming increasingly important. Non-Maxwellian distributions and strong magnetic fields result in a substantial damping of the oscillatory wake potential. The interaction force in particle pairs is explored with the phase-resolved resonance method, which demonstrates the non-reciprocity of the interparticle forces in unmagnetized and magnetized systems.

The X-ray corona and the photospheric magnetic field.

NASA Technical Reports Server (NTRS)

Krieger, A. S.; Vaiana, G. S.; Van Speybroeck, L. P.

1971-01-01

Soft X-ray photographs of the solar corona have been obtained on four flights of a rocket-borne grazing incidence telescope having a resolution of a few arc sec. The configuration of the X-ray emitting structures in the corona has been compared to the magnetic field distribution measured by photospheric longitudinal magnetograms. The X-ray structures trace the three-dimensional configuration of the magnetic field through the lower corona. Active regions in the corona take the form of tubular structures connecting regions of opposite magnetic polarity within the same or adjacent chromospheric active regions. Higher, larger structures link widely separated active regions into complexes of activity covering substantial fractions of the disk. The complexes are separated by areas of low average field in the photosphere. Interconnections across the solar equator appear to originate over areas of preceding polarity.

MAVEN observations of complex magnetic field topology in the Martian magnetotail

NASA Astrophysics Data System (ADS)

DiBraccio, Gina A.; Espley, Jared R.; Luhmann, Janet G.; Curry, Shannon M.; Gruesbeck, Jacob R.; Connerney, John E. P.; Soobiah, Yasir; Xu, Shaosui; Mitchell, David M.; Harada, Yuki; Halekas, Jasper S.; Brain, David A.; Dong, Chuanfei; Hara, Takuya; Jakosky, Bruce M.

2017-04-01

MAVEN observations have revealed an unexpectedly complex magnetic field configuration in the magnetotail of Mars. This planetary magnetotail forms as the solar wind interacts with the Martian upper atmosphere and the interplanetary magnetic field (IMF) drapes around the planet. This interaction is classically defined as an induced magnetosphere similar to the plasma environments of Venus and comets. However, unlike at these induced magnetic environments, Mars is complicated by the existence of crustal magnetic fields, which are able to reconnect with the IMF to produce open magnetic fields. Preliminary magnetohydrodynamic simulation results have suggested that this magnetic reconnection may be responsible for creating a hybrid magnetotail configuration between intrinsic and induced magnetospheres. This hybrid tail is composed of the closed planetary fields, draped IMF, and two distinct lobes of open magnetic fields. More importantly, these open lobes appear to be twisted by roughly 45°, either clockwise or counterclockwise, from the ecliptic plane with a strong dependence on the east-west component of the IMF and negligible influence from crustal field orientation. To explore this unexpected twisted-tail configuration, we analyze MAVEN Magnetometer (MAG) and Solar Wind Ion Analyzer (SWIA) data to examine magnetic field topology in the Martian magnetotail. We compare the average magnetic field orientation, directed toward and away from the planet, for a variety of solar wind parameters at various downtail distances. We conclude that the east-west IMF component strongly affects the magnetotail structure, as predicted by simulations. Furthermore, these data reveal that the tail lobes are indeed twisted, which we infer based on model results, to be regions of open magnetic fields that are likely reconnected crustal fields. These MAVEN observations confirm that the Martian magnetotail has a hybrid configuration between an intrinsic and induced magnetosphere, shifting the paradigm of Mars as we have understood it thus far.

A Comparative Analysis of the Magnetic Field Signals over Impact Structures on the Earth, Mars and the Moon

NASA Technical Reports Server (NTRS)

Isac, Anca; Mandea, Mioara; Purucker, Michael; Langlais, Benoit

2015-01-01

An improved description of magnetic fields of terrestrial bodies has been obtained from recent space missions, leading to a better characterization of the internal fields including those of crustal origin. One of the striking differences in their crustal magnetic field is the signature of large impact craters. A comparative analysis of the magnetic characteristics of these structures can shed light on the history of their respective planetary-scale magnetic dynamos. This has motivated us to identify impact craters and basins, first by their quasi-circular features from the most recent and detailed topographic maps and then from available global magnetic field maps. We have examined the magnetic field observed above 27 complex craters on the Earth, 34 impact basins on Mars and 37 impact basins on the Moon. For the first time, systematic trends in the amplitude and frequency of the magnetic patterns, inside and outside of these structures are observed for all three bodies. The demagnetization effects due to the impact shock wave and excavation processes have been evaluated applying the Equivalent Source Dipole forward modeling approach. The main characteristics of the selected impact craters are shown. The trends in their magnetic signatures are indicated, which are related to the presence or absence of a planetary-scale dynamo at the time of their formation and to impact processes. The low magnetic field intensity at center can be accepted as the prime characteristic of a hypervelocity impact and strongly associated with the mechanics of impact crater formation. In the presence of an active internal field, the process of demagnetization due to the shock impact is associated with post-impact remagnetization processes, generating a more complex magnetic signature.

Interactions and reversal-field memory in complex magnetic nanowire arrays

NASA Astrophysics Data System (ADS)

Rotaru, Aurelian; Lim, Jin-Hee; Lenormand, Denny; Diaconu, Andrei; Wiley, John. B.; Postolache, Petronel; Stancu, Alexandru; Spinu, Leonard

2011-10-01

Interactions and magnetization reversal of Ni nanowire arrays have been investigated by the first-order reversal curve (FORC) method. Several series of samples with controlled spatial distribution were considered including simple wires of different lengths and diameters (70 and 110 nm) and complex wires with a single modulated diameter along their length. Subtle features of magnetic interactions are revealed through a quantitative analysis of the local interaction field profile distributions obtained from the FORC method. In addition, the FORC analysis indicates that the nanowire systems with a mean diameter of 70 nm appear to be organized in symmetric clusters indicative of a reversal-field memory effect.

Anomalous resistivity and the evolution of magnetic field topology

NASA Technical Reports Server (NTRS)

Parker, E. N.

1993-01-01

This paper explores the topological restructuring of a force-free magnetic field caused by the hypothetical sudden onset of a localized region of strong anomalous resistivity. It is shown that the topological complexity increases, with the primitive planar force-free field with straight field lines developing field lines that wrap half a turn around each other, evidently providing a surface of tangential discontinuity in the wraparound region. It is suggested that the topological restructuring contributes to the complexity of the geomagnetic substorm, the aurora, and perhaps some of the flare activity on the sun, or other star, and the Galactic halo.

Zonal harmonic model of Saturn's magnetic field from Voyager 1 and 2 observations

NASA Technical Reports Server (NTRS)

Connerney, J. E. P.; Ness, N. F.; Acuna, M. H.

1982-01-01

An analysis of the magnetic field of Saturn is presented which takes into account both the Voyager 1 and 2 vector magnetic field observations. The analysis is based on the traditional spherical harmonic expansion of a scale potential to derive the magnetic field within 8 Saturn radii. A third-order zonal harmonic model fitted to Voyager 1 and 2 observations is found to be capable of predicting the magnetic field characteristics at one encounter based on those observed at another, unlike models including dipole and quadrupole terms only. The third-order model is noted to lead to significantly enhanced polar surface field intensities with respect to dipole models, and probably represents the axisymmetric part of a complex dynamo field.

Effect of a magnetic field on the track structure of low-energy electrons: a Monte Carlo study

NASA Astrophysics Data System (ADS)

Bug, M. U.; Gargioni, E.; Guatelli, S.; Incerti, S.; Rabus, H.; Schulte, R.; Rosenfeld, A. B.

2010-10-01

The increasing use of MRI-guided radiation therapy evokes the necessity to investigate the potential impact of a magnetic field on the biological effectiveness of therapeutic radiation beams. While it is known that a magnetic field, applied during irradiation, can improve the macroscopic absorbed dose distribution of electrons in the tumor region, effects on the microscopic distribution of energy depositions and ionizations have not yet been investigated. An effect on the number of ionizations in a DNA segment, which is related to initial DNA damage in form of complex strand breaks, could be beneficial in radiation therapy. In this work we studied the effects of a magnetic field on the pattern of ionizations at nanometric level by means of Monte Carlo simulations using the Geant4-DNA toolkit. The track structure of low-energy electrons in the presence of a uniform static magnetic field of strength up to 14 T was calculated for a simplified DNA segment model in form of a water cylinder. In the case that no magnetic field is applied, nanodosimetric results obtained with Geant4-DNA were compared with those from the PTB track structure code. The obtained results suggest that any potential enhancement of complexity of DNA strand breaks induced by irradiation in a magnetic field is not related to modifications of the low-energy secondary electrons track structure.

Giant crystal-electric-field effect and complex magnetic behavior in single-crystalline CeRh3Si2

NASA Astrophysics Data System (ADS)

Pikul, A. P.; Kaczorowski, D.; Gajek, Z.; Stȩpień-Damm, J.; Ślebarski, A.; Werwiński, M.; Szajek, A.

2010-05-01

Single-crystalline CeRh3Si2 was investigated by means of x-ray diffraction, magnetic susceptibility, magnetization, electrical resistivity, and specific-heat measurements carried out in wide temperature and magnetic field ranges. Moreover, the electronic structure of the compound was studied at room temperature by cerium core-level x-ray photoemission spectroscopy (XPS). The physical properties were analyzed in terms of crystalline electric field and compared with results of ab initio band-structure calculations performed within the density-functional theory approach. The compound was found to crystallize in the orthorhombic unit cell of the ErRh3Si2 type (space group Imma No.74, Pearson symbol: oI24 ) with the lattice parameters a=7.1330(14)Å , b=9.7340(19)Å , and c=5.6040(11)Å . Analysis of the magnetic and XPS data revealed the presence of well-localized magnetic moments of trivalent cerium ions. All the physical properties were found to be highly anisotropic over the whole temperature range studied and influenced by exceptionally strong crystalline electric field with the overall splitting of the 4f1 ground multiplet exceeding 5700 K. Antiferromagnetic order of the cerium magnetic moments at TN=4.70(1)K and their subsequent spin rearrangement at Tt=4.48(1)K manifest themselves as distinct anomalies in the temperature characteristic of all the physical properties investigated and exhibit complex evolution in an external magnetic field. A tentative magnetic B-T phase diagram, constructed for B parallel to the b axis being the easy magnetization direction, shows very complex magnetic behavior of CeRh3Si2 , similar to that recently reported for an isostructural compound CeIr3Si2 . The electronic band-structure calculations corroborated the antiferromagnetic ordering of the cerium magnetic moments and well-reproduced the experimental XPS valence-band spectrum.

Magnetic field and dielectric environment effects on an exciton trapped by an ionized donor in a spherical quantum dot

NASA Astrophysics Data System (ADS)

Aghoutane, N.; Feddi, E.; El-Yadri, M.; Bosch Bailach, J.; Dujardin, F.; Duque, C. A.

2017-11-01

Magnetic field and host dielectric environment effects on the binding energy of an exciton trapped by an ionized donor in spherical quantum dot are investigated. In the framework of the effective mass approximation and by using a variational method, the calculations have been performed by developing a robust ten-terms wave function taking into account the different inter-particles correlations and the distortion of symmetry induced by the orientation of the applied magnetic field. The binding and the localization energies are determined as functions of dot size and magnetic field strength. It appears that the variation of magnetic shift obeys a quadratic law for low magnetic fields regime while, for strong magnetic fields, this shift tends to be linear versus the magnetic field strength. The stability of this complex subjected to a magnetic field is also discussed according to the electron-hole ratio and the dielectric constant of the surrounding medium. A last point to highlight is that the Haynes' rule remains valid even in the presence of an applied magnetic field.

On the measurement of magnetic viscosity

NASA Astrophysics Data System (ADS)

Serletis, C.; Efthimiadis, K. G.

2012-08-01

This work is an investigation of the experimental method used for measuring the magnetic viscosity in a hard ferromagnetic material, i.e. the recording of the magnetization under constant applied field and temperature, after the material has been magnetically saturated. It investigates how the experimental results are affected by the initial conditions of the method (saturation field, field change rate and field oscillation prior to its stabilization), and by minor variations of field and temperature during the recording. Based on the arising conclusions and the use of a more complex fitting function of measurements, the accuracy and repeatability of experimental results is improved.

Analysis of Magnetic Anisotropy and the Role of Magnetic Dilution in Triggering Single-Molecule Magnet (SMM) Behavior in a Family of CoII YIII Dinuclear Complexes with Easy-Plane Anisotropy.

PubMed

Palacios, María A; Nehrkorn, Joscha; Suturina, Elizaveta A; Ruiz, Eliseo; Gómez-Coca, Silvia; Holldack, Karsten; Schnegg, Alexander; Krzystek, Jurek; Moreno, José M; Colacio, Enrique

2017-08-25

Three new closely related Co II Y III complexes of general formula [Co(μ-L)(μ-X)Y(NO 3 ) 2 ] (X - =NO 3 - 1, benzoate 2, or 9-anthracenecarboxylato 3) have been prepared with the compartmental ligand N,N',N''-trimethyl-N,N''-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H 2 L). In these complexes, Co II and Y III are triply bridged by two phenoxide groups belonging to the di-deprotonated ligand (L 2- ) and one ancillary anion X - . The change of the ancillary bridging group connecting Co II and Y III ions induces small differences in the trigonally distorted CoN 3 O 3 coordination sphere with a concomitant tuning of the magnetic anisotropy and intermolecular interactions. Direct current magnetic, high-frequency and -field EPR (HFEPR), frequency domain Fourier transform THz electron paramagnetic resonance (FD-FT THz-EPR) measurements, and ab initio theoretical calculations demonstrate that Co II ions in compounds 1-3 have large and positive D values (≈50 cm -1 ), which decrease with increasing the distortion of the pseudo-octahedral Co II coordination sphere. Dynamic ac magnetic susceptibility measurements indicate that compound 1 exhibits field-induced single-molecule magnet (SMM) behavior, whereas compounds 2 and 3 only display this behavior when they are magnetically diluted with diamagnetic Zn II (Zn/Co=10:1). In view of this, it is always advisable to use magnetically diluted complexes, in which intermolecular interactions and quantum tunneling of magnetism (QTM) would be at least partly suppressed, so that "hidden single-ion magnet (SIM)" behavior could emerge. Field- and temperature-dependence of the relaxation times indicate the prevalence of the Raman process in all these complexes above approximately 3 K. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Unraveling the Complexity of the Evolution of the Sun's Photospheric Magnetic Field

NASA Astrophysics Data System (ADS)

Hathaway, David H.

2016-10-01

Given the emergence of tilted, bipolar active regions, surface flux transport has been shown to reproduce much of the complex evolution of the Sun's photospheric magnetic field. Surface flux is transported by flows in the surface shear layer - the axisymmetric differential rotation and meridional flow and the non-axisymmetric convective motions (granules, supergranules, and giant cells). We have measured these flows by correlation tracking of the magnetic elements themselves, correlation tracking of the Doppler features (supergranules), and by direct Doppler measurements using SDO/HMI data. These measurements fully constrain (with no free parameters) the flows used in our surface flux transport code - the Advective Flux Transport or AFT code. Here we show the up-to-date evolution of these flows, their impact on the detailed evolution of the Sun's photospheric magnetic field, and predictions for what the polar fields will be at the next minimum in 2020.

Influence of Magnetic Fields on Magneto-Aerotaxis

PubMed Central

Bennet, Mathieu; McCarthy, Aongus; Fix, Dmitri; Edwards, Matthew R.; Repp, Felix; Vach, Peter; Dunlop, John W. C.; Sitti, Metin; Buller, Gerald S.; Klumpp, Stefan; Faivre, Damien

2014-01-01

The response of cells to changes in their physico-chemical micro-environment is essential to their survival. For example, bacterial magnetotaxis uses the Earth's magnetic field together with chemical sensing to help microorganisms move towards favoured habitats. The studies of such complex responses are lacking a method that permits the simultaneous mapping of the chemical environment and the response of the organisms, and the ability to generate a controlled physiological magnetic field. We have thus developed a multi-modal microscopy platform that fulfils these requirements. Using simultaneous fluorescence and high-speed imaging in conjunction with diffusion and aerotactic models, we characterized the magneto- aerotaxis of Magnetospirillum gryphiswaldense. We assessed the influence of the magnetic field (orientation; strength) on the formation and the dynamic of a micro-aerotactic band (size, dynamic, position). As previously described by models of magnetotaxis, the application of a magnetic field pointing towards the anoxic zone of an oxygen gradient results in an enhanced aerotaxis even down to Earth's magnetic field strength. We found that neither a ten-fold increase of the field strength nor a tilt of 45° resulted in a significant change of the aerotactic efficiency. However, when the field strength is zeroed or when the field angle is tilted to 90°, the magneto-aerotaxis efficiency is drastically reduced. The classical model of magneto-aerotaxis assumes a response proportional to the cosine of the angle difference between the directions of the oxygen gradient and that of the magnetic field. Our experimental evidence however shows that this behaviour is more complex than assumed in this model, thus opening up new avenues for research. PMID:24983865

Field-induced reentrant magnetoelectric phase in LiNiPO 4

DOE PAGES

Toft-Petersen, Rasmus; Fogh, Ellen; Kihara, Takumi; ...

2017-02-21

Using pulsed magnetic fields up to 30 T we have measured the bulk magnetization and electrical polarization of LiNiPO 4 and have studied its magnetic structure by time-of-flight neutron Laue diffraction. Our data establish the existence of a reentrant magnetoelectric phase between 19 T and 21 T. We show that a magnetized version of the zero field commensurate structure explains the magnetoelectric response quantitatively. The stability of this structure suggests a field-dependent spin anisotropy. Above 21 T , a magnetoelectrically inactive, short-wavelength incommensurate structure is identified. Lastly, our results demonstrate the combination of pulsed fields with epithermal neutron Laue diffractionmore » as a powerful method to probe even complex phase diagrams in strong magnetic fields.« less

Time-resolved luminescence measurements of the magnetic field effect on paramagnetic photosensitizers in photodynamic reactions

NASA Astrophysics Data System (ADS)

Mermut, O.; Bouchard, J.-P.; Cormier, J.-F.; Desroches, P.; Diamond, K. R.; Fortin, M.; Gallant, P.; Leclair, S.; Marois, J.-S.; Noiseux, I.; Morin, J.-F.; Patterson, M. S.; Vernon, M.

2008-02-01

The development of multimodal molecular probes and photosensitizing agents for use in photodynamic therapy (PDT) is vital for optimizing and monitoring cytotoxic responses. We propose a combinatorial approach utilizing photosensitizing molecules that are both paramagnetic and luminescent with multimodal functionality to perturb, control, and monitor molecular-scale reaction pathways in PDT. To this end, a time-domain single photon counting lifetime apparatus with a 400 nm excitation source has been developed and integrated with a variable low field magnet (0- 350mT). The luminescence lifetime decay function was measured in the presence of a sweeping magnetic field for a custom designed photosensitizing molecule in which photoinduced electron transfer was studied The photosensitizer studied was a donor-acceptor complex synthesized using a porphyrin linked to a fullerene molecule. The magneto-optic properties were investigated for the free-base photosensitizer complex as well as those containing either diamagnetic (paired electron) or paramagnetic (unpaired electron) metal centers, Zn(II) and Cu(II). The magnetic field was employed to affect and modify the spin states of radical pairs of the photosensitizing agents via magnetically induced hyperfine and Zeeman effects. Since the Type 1 reaction pathway of an excited triplet state photosensitizer involves the production of radical species, lifetime measurements were conducted at low dissolved oxygen concentration (0.01ppm) to elucidate the dependence of the magnetic perturbation on the photosensitization mechanistic pathway. To optimize the magnetic response, a solvent study was performed examining the dependence of the emission properties on the magnetic field in solutions of varying dielectric constants. Lastly, the cytotoxicity in murine tumor cell suspensions was investigated for the novel porphyrin-fullerene complex by inducing photodynamic treatments and determining the associated cell survival.

Reading the Magnetic Patterns in Earth complex impact craters to detect similarities and cues from some Nectarian craters of the Moon

NASA Astrophysics Data System (ADS)

Isac, Anca; Mandea, Mioara; Purucker, Michael

2013-04-01

Most of the terrestrial impact craters have been obliterated by other terrestrial geological processes. Some examples however remain. Among them, complex craters such as Chicxculub, Vredefort, or the outsider Bangui structure (proposed but still unconfirmed as a result of an early Precambrian large impact) exert in the total magnetic field anomaly global map (WDMAM-B) circular shapes with positive anomalies which may suggest the circularity of a multiring structure. A similar pattern is observed from the newest available data (global spherical model of the internal magnetic field by Purucker and Nicolas, 2010) for some Nectarian basins as Moscovienese, Mendel-Rydberg or Crissium. As in the case of Earth's impacts, the positive anomalies appear near the basin center and inside the first ring, this distribution being strongly connected with crater-forming event. Detailed analysis of largest impact craters from Earth and Moon --using a forward modeling approach by means of the Equivalent Source Dipole method--evaluates the shock impact demagnetization effects--a magnetic low--by reducing the thickness of the pre-magnetized lithosphere due to the excavation process (the impact crater being shaped as a paraboloid of revolution). The magnetic signature of representative early Nectarian craters, Crissium, as well as Earth's complex craters, defined by stronger magnetic fields near the basin center and/or inside the first ring, might be a consequence of the shock remanent magnetization of the central uplift plus a thermoremanent magnetization of the impact melt in a steady magnetizing field generated by a former active dynamo. In this case, ESD method is not able to obtain a close fit of the forward model to the observation altitude map or model.

Field-controlled structures in ferromagnetic cholesteric liquid crystals.

PubMed

Medle Rupnik, Peter; Lisjak, Darja; Čopič, Martin; Čopar, Simon; Mertelj, Alenka

2017-10-01

One of the advantages of anisotropic soft materials is that their structures and, consequently, their properties can be controlled by moderate external fields. Whereas the control of materials with uniform orientational order is straightforward, manipulation of systems with complex orientational order is challenging. We show that a variety of structures of an interesting liquid material, which combine chiral orientational order with ferromagnetic one, can be controlled by a combination of small magnetic and electric fields. In the suspensions of magnetic nanoplatelets in chiral nematic liquid crystals, the platelet's magnetic moments orient along the orientation of the liquid crystal and, consequently, the material exhibits linear response to small magnetic fields. In the absence of external fields, orientations of the liquid crystal and magnetization have wound structure, which can be either homogeneously helical, disordered, or ordered in complex patterns, depending on the boundary condition at the surfaces and the history of the sample. We demonstrate that by using different combinations of small magnetic and electric fields, it is possible to control reversibly the formation of the structures in a layer of the material. In such a way, different periodic structures can be explored and some of them may be suitable for photonic applications. The material is also a convenient model system to study chiral magnetic structures, because it is a unique liquid analog of a solid helimagnet.

Magneto-Structural Correlations in Pseudotetrahedral Forms of the [Co(SPh)4]2- Complex Probed by Magnetometry, MCD Spectroscopy, Advanced EPR Techniques, and ab Initio Electronic Structure Calculations.

PubMed

Suturina, Elizaveta A; Nehrkorn, Joscha; Zadrozny, Joseph M; Liu, Junjie; Atanasov, Mihail; Weyhermüller, Thomas; Maganas, Dimitrios; Hill, Stephen; Schnegg, Alexander; Bill, Eckhard; Long, Jeffrey R; Neese, Frank

2017-03-06

The magnetic properties of pseudotetrahedral Co(II) complexes spawned intense interest after (PPh 4 ) 2 [Co(SPh) 4 ] was shown to be the first mononuclear transition-metal complex displaying slow relaxation of the magnetization in the absence of a direct current magnetic field. However, there are differing reports on its fundamental magnetic spin Hamiltonian (SH) parameters, which arise from inherent experimental challenges in detecting large zero-field splittings. There are also remarkable changes in the SH parameters of [Co(SPh) 4 ] 2- upon structural variations, depending on the counterion and crystallization conditions. In this work, four complementary experimental techniques are utilized to unambiguously determine the SH parameters for two different salts of [Co(SPh) 4 ] 2- : (PPh 4 ) 2 [Co(SPh) 4 ] (1) and (NEt 4 ) 2 [Co(SPh) 4 ] (2). The characterization methods employed include multifield SQUID magnetometry, high-field/high-frequency electron paramagnetic resonance (HF-EPR), variable-field variable-temperature magnetic circular dichroism (VTVH-MCD), and frequency domain Fourier transform THz-EPR (FD-FT THz-EPR). Notably, the paramagnetic Co(II) complex [Co(SPh) 4 ] 2- shows strong axial magnetic anisotropy in 1, with D = -55(1) cm -1 and E/D = 0.00(3), but rhombic anisotropy is seen for 2, with D = +11(1) cm -1 and E/D = 0.18(3). Multireference ab initio CASSCF/NEVPT2 calculations enable interpretation of the remarkable variation of D and its dependence on the electronic structure and geometry.

MAVEN observations of complex magnetic field configuration in the Martian magnetotail

NASA Astrophysics Data System (ADS)

DiBraccio, G. A.; Luhmann, J. G.; Curry, S.; Espley, J. R.; Gruesbeck, J.; Xu, S.; Mitchell, D. L.; Soobiah, Y. I. J.; Connerney, J. E. P.; Dong, C.; Harada, Y.; Ruhunusiri, S.; Halekas, J. S.; Hara, T.; Ma, Y.; Brain, D.; Jakosky, B. M.

2017-12-01

The magnetosphere of Mars has attributes of both induced and intrinsic magnetospheres, forming as a result of direct solar wind interaction with the planet's upper atmosphere and local crustal magnetic fields. Magnetic reconnection is able to occur between the draped interplanetary magnetic field (IMF) and closed crustal magnetic fields, creating an open field topology with one end attached to the planet and the other flowing in the solar wind. For this reason, the Martian magnetotail becomes a complex menagerie of various field topologies that may contribute to atmospheric escape to space. We explore these magnetic topologies in the Martian magnetotail using a combination of observations from the the Mars Atmosphere Volatile EvolutioN (MAVEN) spacecraft along with magnetohydrodynamic (MHD) simulations. Preliminary MHD results suggest that the central tail contains two lobes composed of open crustal fields, which are twisted by roughly 45°, either clockwise or counterclockwise from the ecliptic plane, in response to the east-west component of the IMF. These simulated open-field lobes are enveloped by an induced comet-like tail formed by the draped IMF. Using two Earth years of data, we analyze MAVEN Magnetometer and Solar Wind Ion Analyzer (SWIA) measurements to assess the tail magnetic field configuration as a function of IMF orientation. We infer, through data-model comparisons, that the open-field tail lobes are likely a result of reconnection between the crustal fields and the IMF. The open topology of these fields may in fact contribute to atmospheric loss to space. This investigation confirms that the Martian magnetotail is a hybrid configuration between intrinsic and induced magnetospheres, shifting the paradigm of Mars' magnetosphere as we have understood it thus far.

Occupational exposure to intermediate frequency and extremely low frequency magnetic fields among personnel working near electronic article surveillance systems.

PubMed

Roivainen, Päivi; Eskelinen, Tuomo; Jokela, Kari; Juutilainen, Jukka

2014-05-01

Cashiers are potentially exposed to intermediate frequency (IF) magnetic fields at their workplaces because of the electronic article surveillance (EAS) systems used in stores to protect merchandise against theft. This study aimed at investigating occupational exposure of cashiers to IF magnetic fields in Finnish stores. Exposure to extremely low frequency (ELF) magnetic fields was also evaluated because cashiers work near various devices operating with 50 Hz electric power. The peak magnetic flux density was measured for IF magnetic fields, and was found to vary from 0.2 to 4 µT at the cashier's seat. ELF magnetic fields from 0.03 to 4.5 µT were found at the cashier's seat. These values are much lower than exposure limits. However, according to the International Commission on Non-Ionizing Radiation Protection (ICNIRP) occupational reference levels for IF magnetic fields (141 µT for the peak field) were exceeded in some cases (maximum 189 µT) for short periods of time when cashiers walked through the EAS gates. As the ICNIRP reference levels do not define any minimum time for exposure, additional investigations are recommended to determine compliance with basic restrictions. Even if the basic restrictions are not exceeded, persons working near EAS devices represent an exceptional group of workers with respect to exposure to electromagnetic fields. This group could serve as a basis for epidemiological studies addressing possible health effects of IF magnetic fields. Compliance with the reference levels for IF fields was evaluated using both broadband measurement of peak fields and the ICNIRP summation rule for multiple frequencies. The latter was generally more conservative, and the difference between the two methods was large (>10-fold) for EAS systems using a 58 kHz signal with complex waveform. This indicates that the ICNIRP multiple frequency rule can be unnecessarily conservative when measuring complex waveforms. © 2014 Wiley Periodicals, Inc.

Geophysical variables and behavior: XCII. Experimental elicitation of the experience of a sentient being by right hemispheric, weak magnetic fields: interaction with temporal lobe sensitivity.

PubMed

Cook, C M; Persinger, M A

2001-04-01

We tested the hypothesis that proportionally more people with above average numbers of complex partial epileptic-like experiences before the experiment would report a proximal presence during applications of a weak (1 microTesla), frequency-modulated magnetic field over the right hemisphere. Each of 16 subjects sat in a darkened, quiet room and was exposed for 20 min. to complex fields, applied through a helmet, either along the right hemisphere or across both hemispheres. None of the 8 subjects with below average scores reported a presence during the applications of the magnetic fields while 75% and 60% of the 8 subjects with above average scores reported a presence during right hemispheric and bilateral stimulation, respectively.

Cryogenic STM in 3D vector magnetic fields realized through a rotatable insert.

PubMed

Trainer, C; Yim, C M; McLaren, M; Wahl, P

2017-09-01

Spin-polarized scanning tunneling microscopy (SP-STM) performed in vector magnetic fields promises atomic scale imaging of magnetic structure, providing complete information on the local spin texture of a sample in three dimensions. Here, we have designed and constructed a turntable system for a low temperature STM which in combination with a 2D vector magnet provides magnetic fields of up to 5 T in any direction relative to the tip-sample geometry. This enables STM imaging and spectroscopy to be performed at the same atomic-scale location and field-of-view on the sample, and most importantly, without experiencing any change on the tip apex before and after field switching. Combined with a ferromagnetic tip, this enables us to study the magnetization of complex magnetic orders in all three spatial directions.

Magnetic blocking in a linear iron(I) complex.

PubMed

Zadrozny, Joseph M; Xiao, Dianne J; Atanasov, Mihail; Long, Gary J; Grandjean, Fernande; Neese, Frank; Long, Jeffrey R

2013-07-01

Single-molecule magnets that contain one spin centre may represent the smallest possible unit for spin-based computational devices. Such applications, however, require the realization of molecules with a substantial energy barrier for spin inversion, achieved through a large axial magnetic anisotropy. Recently, significant progress has been made in this regard by using lanthanide centres such as terbium(III) and dysprosium(III), whose anisotropy can lead to extremely high relaxation barriers. We contend that similar effects should be achievable with transition metals by maintaining a low coordination number to restrict the magnitude of the d-orbital ligand-field splitting energy (which tends to hinder the development of large anisotropies). Herein we report the first two-coordinate complex of iron(I), [Fe(C(SiMe3)3)2](-), for which alternating current magnetic susceptibility measurements reveal slow magnetic relaxation below 29 K in a zero applied direct-current field. This S =  complex exhibits an effective spin-reversal barrier of Ueff = 226(4) cm(-1), the largest yet observed for a single-molecule magnet based on a transition metal, and displays magnetic blocking below 4.5 K.

Effect of angular momentum alignment and strong magnetic fields on the formation of protostellar discs

NASA Astrophysics Data System (ADS)

Gray, William J.; McKee, Christopher F.; Klein, Richard I.

2018-01-01

Star-forming molecular clouds are observed to be both highly magnetized and turbulent. Consequently, the formation of protostellar discs is largely dependent on the complex interaction between gravity, magnetic fields, and turbulence. Studies of non-turbulent protostellar disc formation with realistic magnetic fields have shown that these fields are efficient in removing angular momentum from the forming discs, preventing their formation. However, once turbulence is included, discs can form in even highly magnetized clouds, although the precise mechanism remains uncertain. Here, we present several high-resolution simulations of turbulent, realistically magnetized, high-mass molecular clouds with both aligned and random turbulence to study the role that turbulence, misalignment, and magnetic fields have on the formation of protostellar discs. We find that when the turbulence is artificially aligned so that the angular momentum is parallel to the initial uniform field, no rotationally supported discs are formed, regardless of the initial turbulent energy. We conclude that turbulence and the associated misalignment between the angular momentum and the magnetic field are crucial in the formation of protostellar discs in the presence of realistic magnetic fields.

Field-induced magnetic phase transitions and memory effect in bilayer ruthenate Ca 3Ru 2O 7 with Fe substitution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, M.; Hong, Tao; Peng, J.

Bilayer ruthenate Ca 3(Ru 1-xFe x) 2O 7 (x = 0.05) exhibits an incommensurate magnetic soliton lattice driven by the Dzyaloshinskii–Moriya interaction. Here, in this work, we report complex field-induced magnetic phase transitions and memory effect in this system via single-crystal neutron diffraction and magnetotransport measurements. We observe first-order incommensurate-to-commensurate magnetic transitions upon applying the magnetic field both along and perpendicular to the propagation axis of the incommensurate spin structure. Furthermore, we find that the metastable states formed upon decreasing the magnetic field depend on the temperature and the applied field orientation. Lastly, we suggest that the observed field-induced metastabilitymore » may be ascribable to the quenched kinetics at low temperature.« less

Field-induced magnetic phase transitions and memory effect in bilayer ruthenate Ca 3Ru 2O 7 with Fe substitution

DOE PAGES

Zhu, M.; Hong, Tao; Peng, J.; ...

2018-01-09

Bilayer ruthenate Ca 3(Ru 1-xFe x) 2O 7 (x = 0.05) exhibits an incommensurate magnetic soliton lattice driven by the Dzyaloshinskii–Moriya interaction. Here, in this work, we report complex field-induced magnetic phase transitions and memory effect in this system via single-crystal neutron diffraction and magnetotransport measurements. We observe first-order incommensurate-to-commensurate magnetic transitions upon applying the magnetic field both along and perpendicular to the propagation axis of the incommensurate spin structure. Furthermore, we find that the metastable states formed upon decreasing the magnetic field depend on the temperature and the applied field orientation. Lastly, we suggest that the observed field-induced metastabilitymore » may be ascribable to the quenched kinetics at low temperature.« less

Hazard zoning around electric substations of petrochemical industries by stimulation of extremely low-frequency magnetic fields.

PubMed

Hosseini, Monireh; Monazzam, Mohammad Reza; Farhang Matin, Laleh; Khosroabadi, Hossein

2015-05-01

Electromagnetic fields in recent years have been discussed as one of the occupational hazards at workplaces. Hence, control and assessment of these physical factors is very important to protect and promote the health of employees. The present study was conducted to determine hazard zones based on assessment of extremely low-frequency magnetic fields at electric substations of a petrochemical complex in southern Iran, using the single-axis HI-3604 device. In measurement of electromagnetic fields by the single-axis HI-3604 device, the sensor screen should be oriented in a way to be perpendicular to the field lines. Therefore, in places where power lines are located in different directions, it is required to keep the device towards three axes of x, y, and z. For further precision, the measurements should be repeated along each of the three axes. In this research, magnetic field was measured, for the first time, in three axes of x, y, and z whose resultant value was considered as the value of magnetic field. Measurements were done based on IEEE std 644-1994. Further, the spatial changes of the magnetic field surrounding electric substations were stimulated using MATLAB software. The obtained results indicated that the maximum magnetic flux density was 49.90 μT recorded from boiler substation, while the minimum magnetic flux density of 0.02 μT was measured at the control room of the complex. As the stimulation results suggest, the spaces around incoming panels, transformers, and cables were recognized as hazardous zones of indoor electric substations. Considering the health effects of chronic exposure to magnetic fields, it would be possible to minimize exposure to these contaminants at workplaces by identification of risky zones and observation of protective considerations.

Magnetic particles guided by ellipsoidal AC magnetic fields in a shallow viscous fluid: Controlling trajectories and chain lengths

NASA Astrophysics Data System (ADS)

Jorge, Guillermo A.; Llera, María; Bekeris, Victoria

2017-12-01

We study the propulsion of superparamagnetic particles dispersed in a viscous fluid upon the application of an elliptically polarized rotating magnetic field. Reducing the fluid surface tension the particles sediment due to density mismatch and rotate close to the low recipient confining plate. We study the net translational motion arising from the hydrodynamic coupling with the plate and find that, above a cross over magnetic field, magnetically assembled doublets move faster than single particles. In turn, particles are driven in complex highly controlled trajectories by rotating the plane containing the magnetic field vector. The effect of the field rotation on long self assembled chains is discussed and the alternating breakup and reformation of the particle chains is described.

The role of activity complexes in the distribution of solar magnetic fields.

NASA Astrophysics Data System (ADS)

García de La Rosa, J. I.; Reyes, R. C.

Using published data on the large-scale distribution of solar activity, the authors conclude that the longlived coronal holes are formed and maintained by the unbalanced magnetic flux which developes at both extremes of the complexes of activity.

Jovian magnetic fields is complex, Pioneer 11 shows

NASA Technical Reports Server (NTRS)

Panagakos, N.; Waller, P.

1975-01-01

An analysis of the magnetic field of the planet Jupiter is presented. The data are based on the information returned by Pioneer 11 space probe. It was determined that the magnetic field stretches across 9 million miles of space at some times and shrinks in volume by three-fourths or more at other times. It was also determined that electrons trapped in the magnetic field of Jupiter are 10,000 times more intense than those in the Van Allen radiation belts which circle the earth. Additional data were obtained on the polar regions, atmospheric circulation, and the nature of the moons.

Magnetic Protostars

NASA Astrophysics Data System (ADS)

Glagolevskij, Yu. V.

2015-09-01

A possible variant of the evolution of magnetic protostars "before the Hayashi phase" is discussed. Arguments are given in support of the following major properties of magnetic stars: (1) global magnetic dipole fields with predominant orientation of the magnetic lines of force in the plane of the equator of revolution; (2) slow rotation; (3) complex, two and three dipole structures of the magnetic field in a large part of the stars; (4) partition of stars into magnetic and normal in a proportion of 1:10 occurs during the period when the protostellar clouds undergo gravitational collapse "before the Hayashi phase."

Rapid and precise determination of zero-field splittings by terahertz time-domain electron paramagnetic resonance spectroscopy.

PubMed

Lu, Jian; Ozel, I Ozge; Belvin, Carina A; Li, Xian; Skorupskii, Grigorii; Sun, Lei; Ofori-Okai, Benjamin K; Dincă, Mircea; Gedik, Nuh; Nelson, Keith A

2017-11-01

Zero-field splitting (ZFS) parameters are fundamentally tied to the geometries of metal ion complexes. Despite their critical importance for understanding the magnetism and spectroscopy of metal complexes, they are not routinely available through general laboratory-based techniques, and are often inferred from magnetism data. Here we demonstrate a simple tabletop experimental approach that enables direct and reliable determination of ZFS parameters in the terahertz (THz) regime. We report time-domain measurements of electron paramagnetic resonance (EPR) signals associated with THz-frequency ZFSs in molecular complexes containing high-spin transition-metal ions. We measure the temporal profiles of the free-induction decays of spin resonances in the complexes at zero and nonzero external magnetic fields, and we derive the EPR spectra via numerical Fourier transformation of the time-domain signals. In most cases, absolute values of the ZFS parameters are extracted from the measured zero-field EPR frequencies, and the signs can be determined by zero-field measurements at two different temperatures. Field-dependent EPR measurements further allow refined determination of the ZFS parameters and access to the g -factor. The results show good agreement with those obtained by other methods. The simplicity of the method portends wide applicability in chemistry, biology and material science.

Real-time and quantitative isotropic spatial resolution susceptibility imaging for magnetic nanoparticles

NASA Astrophysics Data System (ADS)

Pi, Shiqiang; Liu, Wenzhong; Jiang, Tao

2018-03-01

The magnetic transparency of biological tissue allows the magnetic nanoparticle (MNP) to be a promising functional sensor and contrast agent. The complex susceptibility of MNPs, strongly influenced by particle concentration, excitation magnetic field and their surrounding microenvironment, provides significant implications for biomedical applications. Therefore, magnetic susceptibility imaging of high spatial resolution will give more detailed information during the process of MNP-aided diagnosis and therapy. In this study, we present a novel spatial magnetic susceptibility extraction method for MNPs under a gradient magnetic field, a low-frequency drive magnetic field, and a weak strength high-frequency magnetic field. Based on this novel method, a magnetic particle susceptibility imaging (MPSI) of millimeter-level spatial resolution (<3 mm) was achieved using our homemade imaging system. Corroborated by the experimental results, the MPSI shows real-time (1 s per frame acquisition) and quantitative abilities, and isotropic high resolution.

Study of multi-level atomic systems with the application of magnetic field

NASA Astrophysics Data System (ADS)

Hu, Jianping; Roy, Subhankar; Ummal Momeen, M.

2018-04-01

The complexity of multiple energy levels associated with each atomic system determines the various processes related to light- matter interactions. It is necessary to understand the influence of different levels in a given atomic system. In this work we focus on multi- level atomic schemes with the application of magnetic field. We analyze the different EIT windows which appears in the presence of moderately high magnetic field (∼ 10 G) strength.

Magnetic Reconnection at a Thin Current Sheet Separating Two Interlaced Flux Tubes at the Earth's Magnetopause

NASA Astrophysics Data System (ADS)

Kacem, I.; Jacquey, C.; Génot, V.; Lavraud, B.; Vernisse, Y.; Marchaudon, A.; Le Contel, O.; Breuillard, H.; Phan, T. D.; Hasegawa, H.; Oka, M.; Trattner, K. J.; Farrugia, C. J.; Paulson, K.; Eastwood, J. P.; Fuselier, S. A.; Turner, D.; Eriksson, S.; Wilder, F.; Russell, C. T.; Øieroset, M.; Burch, J.; Graham, D. B.; Sauvaud, J.-A.; Avanov, L.; Chandler, M.; Coffey, V.; Dorelli, J.; Gershman, D. J.; Giles, B. L.; Moore, T. E.; Saito, Y.; Chen, L.-J.; Penou, E.

2018-03-01

The occurrence of spatially and temporally variable reconnection at the Earth's magnetopause leads to the complex interaction of magnetic fields from the magnetosphere and magnetosheath. Flux transfer events (FTEs) constitute one such type of interaction. Their main characteristics are (1) an enhanced core magnetic field magnitude and (2) a bipolar magnetic field signature in the component normal to the magnetopause, reminiscent of a large-scale helicoidal flux tube magnetic configuration. However, other geometrical configurations which do not fit this classical picture have also been observed. Using high-resolution measurements from the Magnetospheric Multiscale mission, we investigate an event in the vicinity of the Earth's magnetopause on 7 November 2015. Despite signatures that, at first glance, appear consistent with a classic FTE, based on detailed geometrical and dynamical analyses as well as on topological signatures revealed by suprathermal electron properties, we demonstrate that this event is not consistent with a single, homogenous helicoidal structure. Our analysis rather suggests that it consists of the interaction of two separate sets of magnetic field lines with different connectivities. This complex three-dimensional interaction constructively conspires to produce signatures partially consistent with that of an FTE. We also show that, at the interface between the two sets of field lines, where the observed magnetic pileup occurs, a thin and strong current sheet forms with a large ion jet, which may be consistent with magnetic flux dissipation through magnetic reconnection in the interaction region.

Modeling magnetic field amplification in nonlinear diffusive shock acceleration

NASA Astrophysics Data System (ADS)

Vladimirov, Andrey

2009-02-01

This research was motivated by the recent observations indicating very strong magnetic fields at some supernova remnant shocks, which suggests in-situ generation of magnetic turbulence. The dissertation presents a numerical model of collisionless shocks with strong amplification of stochastic magnetic fields, self-consistently coupled to efficient shock acceleration of charged particles. Based on a Monte Carlo simulation of particle transport and acceleration in nonlinear shocks, the model describes magnetic field amplification using the state-of-the-art analytic models of instabilities in magnetized plasmas in the presence of non-thermal particle streaming. The results help one understand the complex nonlinear connections between the thermal plasma, the accelerated particles and the stochastic magnetic fields in strong collisionless shocks. Also, predictions regarding the efficiency of particle acceleration and magnetic field amplification, the impact of magnetic field amplification on the maximum energy of accelerated particles, and the compression and heating of the thermal plasma by the shocks are presented. Particle distribution functions and turbulence spectra derived with this model can be used to calculate the emission of observable nonthermal radiation.

Electric field effects on nuclear magnetic shielding of the 1:1 and 2:1 (homo and heterochiral) complexes of XOOX' (X, X' = H, CH3) with lithium cation and their chiral discrimination.

PubMed

Alkorta, Ibon; Elguero, José; Provasi, Patricio F; Pagola, Gabriel I; Ferraro, Marta B

2011-09-14

The set of 1:1 and 2:1 complexes of XOOX' (X, X' = H, CH(3)) with lithium cation has been studied to determine if they are suitable candidates for chiral discrimination in an isotropic medium via nuclear magnetic resonance spectroscopy. Conventional nuclear magnetic resonance is unable to distinguish between enantiomers in the absence of a chiral solvent. The criterion for experimental detection is valuated by the isotropic part of nuclear shielding polarisability tensors, related to a pseudoscalar of opposite sign for two enantiomers. The study includes calculations at coupled Hartree-Fock and density functional theory schemes for (17)O nucleus in each compound. Additional calculations for (1)H are also included for some compounds. A huge static homogeneous electric field, perpendicular to the magnetic field of the spectromer, as big as ≈1.7 × 10(8) V m(-1) should be applied to observe a shift of ≈1 ppm for (17)O magnetic shielding in the proposed set of complexes. © 2011 American Institute of Physics

D2+ Molecular complex in non-uniform height quantum ribbon under crossed electric and magnetic fields

NASA Astrophysics Data System (ADS)

Suaza, Y. A.; Laroze, D.; Fulla, M. R.; Marín, J. H.

2018-05-01

The D2+ molecular complex fundamental properties in a uniform and multi-hilled semiconductor quantum ribbon under orthogonal electric and magnetic fields are theoretically studied. The energy structure is calculated by using adiabatic approximation combined with diagonalization procedure. The D2+ energy structure is more strongly controlled by the geometrical structural hills than the Coulomb interaction. The formation of vibrational and rotational states is discussed. Aharanov-Bohm oscillation patterns linked to rotational states as well as the D2+ molecular complex stability are highly sensitive to the number of hills while electric field breaks the electron rotational symmetry and removes the energy degeneration between low-lying states.

Destabilizing effect of time-dependent oblique magnetic field on magnetic fluids streaming in porous media.

PubMed

El-Dib, Yusry O; Ghaly, Ahmed Y

2004-01-01

The present work studies Kelvin-Helmholtz waves propagating between two magnetic fluids. The system is composed of two semi-infinite magnetic fluids streaming throughout porous media. The system is influenced by an oblique magnetic field. The solution of the linearized equations of motion under the boundary conditions leads to deriving the Mathieu equation governing the interfacial displacement and having complex coefficients. The stability criteria are discussed theoretically and numerically, from which stability diagrams are obtained. Regions of stability and instability are identified for the magnetic fields versus the wavenumber. It is found that the increase of the fluid density ratio, the fluid velocity ratio, the upper viscosity, and the lower porous permeability play a stabilizing role in the stability behavior in the presence of an oscillating vertical magnetic field or in the presence of an oscillating tangential magnetic field. The increase of the fluid viscosity plays a stabilizing role and can be used to retard the destabilizing influence for the vertical magnetic field. Dual roles are observed for the fluid velocity in the stability criteria. It is found that the field frequency plays against the constant part for the magnetic field.

Complex-Spectrum Magnetic Environment enhances and/or modifies Bioeffects of Hypokinetic Stress Condition: an Animal Study

NASA Astrophysics Data System (ADS)

Temuriantz, N. A.; Martinyuk, V. S.; Ptitsyna, N. G.; Villoresi, G.; Iucci, N.; Tyasto, M. I.; Dorman, L. I.

During last decades it was shown by many authors that ultra-low and extremely low frequency electric and magnetic fields ULF 0-10 Hz ELF 10-1000 Hz may produce biological effects and consequently may be a possible source for health problems Spaceflight electric and magnetic environments are characterized by complex combination of static and time-varying components in ULF-ELF range and by high variability The objective of this study was to investigate the possible influence of such magnetic fields on rats to understand the pathway regarding functional state of cardiovascular system Magnetic field MF pattern with variable complex spectra in 0-150 Hz frequency range was simulated using 3-axial Helmholtz coils and special computer-based equipment The effect of the real world MF exposure on rats was also tested in combination with hypokinetic stress condition which is typical for spaceflights It was revealed that variable complex-spectrum MF acts as a weak or moderate stress-like factor which amplifies and or modifies the functional shifts caused by other stress-factors The value and direction of the functional shifts caused by MF exposure significantly depend on gender individual-typological constitutional features and also on the physiological state norm stress of organism Our results support the idea that variable complex-spectrum MF action involves sympathetic activation overload in cholesterol transport in blood and also secretor activation of tissue basophyls mast cells that can influence the regional haemodynamics These

Slow Magnetic Relaxations in Cobalt(II) Tetranitrate Complexes. Studies of Magnetic Anisotropy by Inelastic Neutron Scattering and High-Frequency and High-Field EPR Spectroscopy

DOE PAGES

Chen, Lei; Cui, Hui-Hui; Stavretis, Shelby E.; ...

2016-12-07

We synthesized and studied three mononuclear cobalt(II) tetranitrate complexes (A) 2[Co(NO 3) 4] with different countercations, Ph 4P + (1), MePh 3P + (2), and Ph 4As + (3), using X-ray single-crystal diffraction, magnetic measurements, inelastic neutron scattering (INS), high-frequency and high-field EPR (HF-EPR) spectroscopy, and theoretical calculations. Furthermore, the X-ray diffraction studies reveal that the structure of the tetranitrate cobalt anion varies with the countercation. 1 and 2 exhibit highly irregular seven-coordinate geometries, while the central Co(II) ion of 3 is in a distorted-dodecahedral configuration. The sole magnetic transition observed in the INS spectroscopy of 1–3 corresponds to themore » zero-field splitting (2(D 2 + 3E 2) 1/2) from 22.5(2) cm –1 in 1 to 26.6(3) cm –1 in 2 and 11.1(5) cm –1 in 3. The positive sign of the D value, and hence the easy-plane magnetic anisotropy, was demonstrated for 1 by INS studies under magnetic fields and HF-EPR spectroscopy. The combined analyses of INS and HF-EPR data yield the D values as +10.90(3), +12.74(3), and +4.50(3) cm –1 for 1–3, respectively. Frequency- and temperature-dependent alternating-current magnetic susceptibility measurements reveal the slow magnetization relaxation in 1 and 2 at an applied dc field of 600 Oe, which is a characteristic of field-induced single-molecule magnets (SMMs). Finally, the electronic structures and the origin of magnetic anisotropy of 1–3 were revealed by calculations at the CASPT2/NEVPT2 level.« less

Waves associated to COMPLEX EVENTS observed by STEREO

NASA Astrophysics Data System (ADS)

Siu Tapia, A. L.; Blanco-Cano, X.; Kajdic, P.; Aguilar-Rodriguez, E.; Russell, C. T.; Jian, L. K.; Luhmann, J. G.

2012-12-01

Complex Events are formed by two or more large-scale solar wind structures which interact in space. Typical cases are interactions of: (i) a Magnetic Cloud/Interplanetary Coronal Mass Ejection (MC/ICME) with another MC/ICME transient; and (ii) an ICME followed by a Stream Interaction Region (SIR). Complex Events are of importance for space weather studies and studying them can enhance our understanding of collisionless plasma physics. Some of these structures can produce or enhance southward magnetic fields, a key factor in geomagnetic storm generation. Using data from the STEREO mission during the years 2006-2011, we found 17 Complex Events preceded by a shock wave. We use magnetic field and plasma data to study the micro-scale structure of the shocks, and the waves associated to these shocks and within Complex Events structures. To determine wave characteristics we perform Power Spectra and Minimum Variance Analysis. We also use PLASTIC WAP protons data to study foreshock extensions and the relationship between Complex Regions and particle acceleration to suprathermal energies.

Space-based magnetometers

NASA Astrophysics Data System (ADS)

Acuña, Mario H.

2002-11-01

The general characteristics and system level concepts for space-based magnetometers are presented to illustrate the instruments, principles, and tools involved in making accurate magnetic field measurements in space. Special consideration is given to the most important practical problems that need to be solved to ensure the accuracy of the measurements and their overall impact on system design and mission costs. Several types of instruments used to measure magnetic fields aboard spacecraft and their capabilities and limitations are described according to whether they measure scalar or vector fields. The very large dynamic range associated with magnetic fields of natural origin generally dictates the use of optimized designs for each particular space mission although some wide-range, multimission magnetometers have been developed and used. Earth-field magnetic mapping missions are the most demanding in terms of absolute accuracy and resolution, approaching <1 part in 100 000 in magnitude and a few arcsec in direction. The difficulties of performing sensitive measurements aboard spacecraft, which may not be magnetically clean, represent a fundamental problem which must be addressed immediately at the planning stages of any space mission that includes these measurements. The use of long, deployable booms to separate the sensors from the sources of magnetic contamination, and their impact on system design are discussed. The dual magnetometer technique, which allows the separation of fields of external and spacecraft origin, represents an important space magnetometry tool which can result in significant savings in complex contemporary spacecraft built with minimum magnetic constraints. Techniques for in-flight estimation of magnetometer biases and sensor alignment are discussed briefly, and highlight some basic considerations within the scope and complexity of magnetic field data processing and reduction. The emerging field of space weather is also discussed, including the essential role that space-based magnetic field measurements play in this complex science, which is just in its infancy. Finally, some considerations for the future of space-based magnetometers are presented. Miniature, mass produced sensors based on magnetoresistance effects and micromachined structures have made significant advances in sensitivity but have yet to reach the performance level required for accurate space measurements. The miniaturization of spacecraft and instruments to reduce launch costs usually results in significantly increased magnetic contamination problems and degraded instrument performance parameters, a challenge that has yet to be solved satisfactorily for "world-class" science missions. The rapidly disappearing manufacturing capabilities for high-grade, low noise, soft magnetic materials of the Permalloy family is a cause of concern for the development of high performance fluxgate magnetometers for future space missions.

Improving the SMM and luminescence properties of lanthanide complexes with LnO9 cores in the presence of ZnII: an emissive Zn2Dy single ion magnet.

PubMed

Fondo, Matilde; Corredoira-Vázquez, Julio; Herrera-Lanzós, Antía; García-Deibe, Ana M; Sanmartín-Matalobos, Jesús; Herrera, Juan Manuel; Colacio, Enrique; Nuñez, Cristina

2017-12-12

Mononuclear complexes of stoichiometry [Ln(H 3 L)(H 2 O)(NO 3 )](NO 3 ) 2 (Ln = Tb, 1; Dy, 2, Er, 3), which crystallise with different solvates, and the heterotrinuclear compound [Zn 2 Dy(L)(NO 3 ) 3 (OH)] (4) can be obtained with the same H 3 L compartmental ligand. The single X-ray crystal structure of the mononuclear complexes shows a LnO 9 core with a muffin-like disposition while the geometry of the DyO 9 core in 4 seems to be closer to spherical capped square antiprism. The analysis of the magnetic properties of all the complexes demonstrates that the mononuclear lanthanide compounds do not show slow relaxation of the magnetization, even when the samples are diluted with a diamagnetic matrix and subjected to a dc applied field of 1000 Oe. Nevertheless, the heterotrinuclear dysprosium complex 4·3H 2 O is a field-induced single ion magnet, with an estimated U eff barrier of 59 K. The luminescence characterisation of all the metal complexes in methanol solution at 298 K also shows a notable increase in the fluorescence emission of the heterotrinuclear complex with respect to the mononuclear ones, in such a way that 4 can be defined as a fluorescent single ion magnet.

Magnetohydrodynamics of atmospheric transients. IV - Nonplane two-dimensional analyses of energy conversion and magnetic field evolution. [during corona following solar flare

NASA Technical Reports Server (NTRS)

Wu, S. T.; Nakagawa, Y.; Han, S. M.; Dryer, M.

1982-01-01

The evolution of the magnetic field and the manner of conversion of thermal energy into different forms in the corona following a solar flare are investigated by means of a nonplane magnetohydrodynamic (MHD) analysis. All three components of magnetic field and velocity are treated in a physically self-consistent manner, with all physical variables as functions of time (t) and two spatial coordinates (r, theta). The difference arising from the initial magnetic field, either twisted (force-free) or non-twisted (potential), is demonstrated. Consideration is given to two initial field topologies (open vs. closed). The results demonstrate that the conversion of magnetic energy is faster for the case of the initially twisted (force-free) field than for the initially untwisted (potential) field. In addition, the twisted field is found to produce a complex structure of the density enhancements.

Enhanced ferromagnetic resonance linewidth of the free layer in perpendicular magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Gopman, D. B.; Dennis, C. L.; McMichael, R. D.; Hao, X.; Wang, Z.; Wang, X.; Gan, H.; Zhou, Y.; Zhang, J.; Huai, Y.

2017-05-01

We report the frequency dependence of the ferromagnetic resonance linewidth of the free layer in magnetic tunnel junctions with all perpendicular-to-the-plane magnetized layers. While the magnetic-field-swept linewidth nominally shows a linear growth with frequency in agreement with Gilbert damping, an additional frequency-dependent linewidth broadening occurs that shows a strong asymmetry between the absorption spectra for increasing and decreasing external magnetic field. Inhomogeneous magnetic fields produced during reversal of the reference and pinned layer complex is demonstrated to be at the origin of the symmetry breaking and the linewidth enhancement. Consequentially, this linewidth enhancement provides indirect information on the magnetic coercivity of the reference and pinned layers. These results have important implications for the characterization of perpendicular magnetized magnetic random access memory bit cells.

Application of transcerebral, weak (1 microT) complex magnetic fields and mystical experiences: are they generated by field-induced dimethyltryptamine release from the pineal organ?

PubMed

Hill, D R; Persinger, M A

2003-12-01

During the last 15 years weak, complex magnetic fields have been applied across the two cerebral hemispheres at the level of the temporoparietal lobes of more than 500 volunteers. Most of these subjects have reported visual, vestibular, and proprioceptive sensations as well as experiences of detachment from the body of 'sentient beings'. Similar but more intense experiences were reported by Strassman in 2001 for volunteers who were injected with N,n-dimethyltryptamine, a compound Strassman hypothesized as the primary mediator of these experiences. If this speculation is valid, then subjects who are exposed to the very weak, complex fields known to elicit similar experiences should display significant increases in the metabolites of this compound within their blood.

Influence of clamping plate permeability and metal screen structures on three-dimensional magnetic field and eddy current loss in end region of a turbo-generator by numerical analysis

NASA Astrophysics Data System (ADS)

Likun, Wang; Weili, Li; Yi, Xue; Chunwei, Guan

2013-11-01

A significant problem of turbogenerators on complex end structures is overheating of local parts caused by end losses in the end region. Therefore, it is important to investigate the 3-D magnetic field and eddy current loss in the end. In end region of operating large turbogenerator at thermal power plants, magnetic leakage field distribution is complex. In this paper, a 3-D mathematical model used for the calculation of the electromagnetic field in the end region of large turbo-generators is given. The influence of spatial locations of end structures, the actual shape and material of end windings, clamping plate, and copper screen are considered. Adopting the time-step finite element (FE) method and taking the nonlinear characteristics of the core into consideration, a 3-D transient magnetic field is calculated. The objective of this paper is to investigate the influence of clamping plate permeability and metal screen structures on 3-D electromagnetic field distribution and eddy current loss in end region of a turbo-generator. To reduce the temperature of copper screen, a hollow metal screen is proposed. The eddy current loss, which is gained from the 3D transient magnetic field, is used as heat source for the thermal field of end region. The calculated temperatures are compared with test data.

Open-loop correction for an eddy current dominated beam-switching magnet.

PubMed

Koseki, K; Nakayama, H; Tawada, M

2014-04-01

A beam-switching magnet and the pulsed power supply it requires have been developed for the Japan Proton Accelerator Research Complex. To switch bunched proton beams, the dipole magnetic field must reach its maximum value within 40 ms. In addition, the field flatness should be less than 5 × 10(-4) to guide each bunched beam to the designed orbit. From a magnetic field measurement by using a long search coil, it was found that an eddy current in the thick endplates and laminated core disturbs the rise of the magnetic field. The eddy current also deteriorates the field flatness over the required flat-top period. The measured field flatness was 5 × 10(-3). By using a double-exponential equation to approximate the measured magnetic field, a compensation pattern for the eddy current was calculated. The integrated magnetic field was measured while using the newly developed open-loop compensation system. A field flatness of less than 5 × 10(-4), which is an acceptable value, was achieved.

Open-loop correction for an eddy current dominated beam-switching magnet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koseki, K., E-mail: kunio.koseki@kek.jp; Nakayama, H.; Tawada, M.

2014-04-15

A beam-switching magnet and the pulsed power supply it requires have been developed for the Japan Proton Accelerator Research Complex. To switch bunched proton beams, the dipole magnetic field must reach its maximum value within 40 ms. In addition, the field flatness should be less than 5 × 10{sup −4} to guide each bunched beam to the designed orbit. From a magnetic field measurement by using a long search coil, it was found that an eddy current in the thick endplates and laminated core disturbs the rise of the magnetic field. The eddy current also deteriorates the field flatness over the requiredmore » flat-top period. The measured field flatness was 5 × 10{sup −3}. By using a double-exponential equation to approximate the measured magnetic field, a compensation pattern for the eddy current was calculated. The integrated magnetic field was measured while using the newly developed open-loop compensation system. A field flatness of less than 5 × 10{sup −4}, which is an acceptable value, was achieved.« less

Exchange coupling and magnetic anisotropy of exchanged-biased quantum tunnelling single-molecule magnet Ni3Mn2 complexes using theoretical methods based on Density Functional Theory.

PubMed

Gómez-Coca, Silvia; Ruiz, Eliseo

2012-03-07

The magnetic properties of a new family of single-molecule magnet Ni(3)Mn(2) complexes were studied using theoretical methods based on Density Functional Theory (DFT). The first part of this study is devoted to analysing the exchange coupling constants, focusing on the intramolecular as well as the intermolecular interactions. The calculated intramolecular J values were in excellent agreement with the experimental data, which show that all the couplings are ferromagnetic, leading to an S = 7 ground state. The intermolecular interactions were investigated because the two complexes studied do not show tunnelling at zero magnetic field. Usually, this exchange-biased quantum tunnelling is attributed to the presence of intermolecular interactions calculated with the help of theoretical methods. The results indicate the presence of weak intermolecular antiferromagnetic couplings that cannot explain the ferromagnetic value found experimentally for one of the systems. In the second part, the goal is to analyse magnetic anisotropy through the calculation of the zero-field splitting parameters (D and E), using DFT methods including the spin-orbit effect.

Experimental observation of Bethe strings

NASA Astrophysics Data System (ADS)

Wang, Zhe; Wu, Jianda; Yang, Wang; Bera, Anup Kumar; Kamenskyi, Dmytro; Islam, A. T. M. Nazmul; Xu, Shenglong; Law, Joseph Matthew; Lake, Bella; Wu, Congjun; Loidl, Alois

2018-02-01

Almost a century ago, string states—complex bound states of magnetic excitations—were predicted to exist in one-dimensional quantum magnets. However, despite many theoretical studies, the experimental realization and identification of string states in a condensed-matter system have yet to be achieved. Here we use high-resolution terahertz spectroscopy to resolve string states in the antiferromagnetic Heisenberg-Ising chain SrCo2V2O8 in strong longitudinal magnetic fields. In the field-induced quantum-critical regime, we identify strings and fractional magnetic excitations that are accurately described by the Bethe ansatz. Close to quantum criticality, the string excitations govern the quantum spin dynamics, whereas the fractional excitations, which are dominant at low energies, reflect the antiferromagnetic quantum fluctuations. Today, Bethe’s result is important not only in the field of quantum magnetism but also more broadly, including in the study of cold atoms and in string theory; hence, we anticipate that our work will shed light on the study of complex many-body systems in general.

Twisted versus braided magnetic flux ropes in coronal geometry. II. Comparative behaviour

NASA Astrophysics Data System (ADS)

Prior, C.; Yeates, A. R.

2016-06-01

Aims: Sigmoidal structures in the solar corona are commonly associated with magnetic flux ropes whose magnetic field lines are twisted about a mutual axis. Their dynamical evolution is well studied, with sufficient twisting leading to large-scale rotation (writhing) and vertical expansion, possibly leading to ejection. Here, we investigate the behaviour of flux ropes whose field lines have more complex entangled/braided configurations. Our hypothesis is that this internal structure will inhibit the large-scale morphological changes. Additionally, we investigate the influence of the background field within which the rope is embedded. Methods: A technique for generating tubular magnetic fields with arbitrary axial geometry and internal structure, introduced in part I of this study, provides the initial conditions for resistive-MHD simulations. The tubular fields are embedded in a linear force-free background, and we consider various internal structures for the tubular field, including both twisted and braided topologies. These embedded flux ropes are then evolved using a 3D MHD code. Results: Firstly, in a background where twisted flux ropes evolve through the expected non-linear writhing and vertical expansion, we find that flux ropes with sufficiently braided/entangled interiors show no such large-scale changes. Secondly, embedding a twisted flux rope in a background field with a sigmoidal inversion line leads to eventual reversal of the large-scale rotation. Thirdly, in some cases a braided flux rope splits due to reconnection into two twisted flux ropes of opposing chirality - a phenomenon previously observed in cylindrical configurations. Conclusions: Sufficiently complex entanglement of the magnetic field lines within a flux rope can suppress large-scale morphological changes of its axis, with magnetic energy reduced instead through reconnection and expansion. The structure of the background magnetic field can significantly affect the changing morphology of a flux rope.

RF-SABRE: A Way to Continuous Spin Hyperpolarization at High Magnetic Fields.

PubMed

Pravdivtsev, Andrey N; Yurkovskaya, Alexandra V; Vieth, Hans-Martin; Ivanov, Konstantin L

2015-10-29

A new technique is developed that allows one to carry out the signal amplification by reversible exchange (SABRE) experiments at high magnetic field. SABRE is a hyperpolarization method, which utilizes transfer of spin order from para-hydrogen to the spins of a substrate in transient iridium complexes. Previously, it has been thought that such a transfer of spin order is only efficient at low magnetic fields, notably, at level anti-crossing (LAC) regions. Here it is demonstrated that LAC conditions can also be fulfilled at high fields under the action of a RF field. The high-field RF-SABRE experiment can be implemented using commercially available nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) machines and does not require technically demanding field-cycling. The achievable NMR enhancements are around 100 for several substrates as compared to their NMR signals at thermal equilibrium conditions at 4.7 T. The frequency dependence of RF-SABRE is comprised of well pronounced peaks and dips, whose position and amplitude are conditioned solely by the magnetic resonance parameters such as chemical shifts and scalar coupling of the spin system involved in the polarization transfer and by the amplitude of the RF field. Thus, the proposed method can serve as a new sensitive tool for probing transient complexes. Simulations of the dependence of magnetization transfer (i.e., NMR signal amplifications) on the frequency and amplitude of the RF field are in good agreement with the developed theoretical approach. Furthermore, the method enables continuous re-hyperpolarization of the SABRE substrate over a long period of time, giving a straightforward way to repetitive NMR experiments.

Recent advances in magnetofection and its potential to deliver siRNAs in vitro.

PubMed

Mykhaylyk, Olga; Zelphati, Olivier; Hammerschmid, Edelburga; Anton, Martina; Rosenecker, Joseph; Plank, Christian

2009-01-01

This chapter describes how to design and conduct experiments to deliver siRNA to adherent mammalian cells in vitro by magnetic force-assisted transfection using self-assembled complexes of small interfering RNA (siRNA) and cationic lipids or polymers that are associated with magnetic nanoparticles. These magnetic complexes are targeted to the cell surface by the application of a magnetic gradient field. In this chapter, first we describe the synthesis of magnetic nanoparticles for magnetofection and the association of siRNA with the magnetic components of the transfection complex. Second, a simple protocol is described in order to evaluate magnetic responsiveness of the magnetic siRNA transfection complexes and estimate the complex loading with magnetic nanoparticles. Third, protocols are provided for the preparation of magnetic lipoplexes and polyplexes of siRNA, magnetofection, downregulation of gene expression, and the determination of cell viability. The addition of INF-7 peptide, a fusogenic peptide, to the magnetic transfection triplexes improved gene silencing in HeLa cells. The described protocols are also valuable for screening vector compositions and novel magnetic nanoparticle preparations to optimize siRNA transfection by magnetofection in every cell type.

Heavy ligand atom induced large magnetic anisotropy in Mn(ii) complexes.

PubMed

Chowdhury, Sabyasachi Roy; Mishra, Sabyashachi

2017-06-28

In the search for single molecule magnets, metal ions are considered pivotal towards achieving large magnetic anisotropy barriers. In this context, the influence of ligands with heavy elements, showing large spin-orbit coupling, on magnetic anisotropy barriers was investigated using a series of Mn(ii)-based complexes, in which the metal ion did not have any orbital contribution. The mixing of metal and ligand orbitals was achieved by explicitly correlating the metal and ligand valence electrons with CASSCF calculations. The CASSCF wave functions were further used for evaluating spin-orbit coupling and zero-field splitting parameters for these complexes. For Mn(ii) complexes with heavy ligand atoms, such as Br and I, several interesting inter-state mixings occur via the spin-orbit operator, which results in large magnetic anisotropy in these Mn(ii) complexes.

Pre-eruptive Magnetic Reconnection within a Multi-flux-rope System in the Solar Corona

NASA Astrophysics Data System (ADS)

Awasthi, Arun Kumar; Liu, Rui; Wang, Haimin; Wang, Yuming; Shen, Chenglong

2018-04-01

The solar corona is frequently disrupted by coronal mass ejections (CMEs), whose core structure is believed to be a flux rope made of helical magnetic field. This has become a “standard” picture; though, it remains elusive how the flux rope forms and evolves toward eruption. While one-third of the ejecta passing through spacecraft demonstrate a flux-rope structure, the rest have complex magnetic fields. Are they originating from a coherent flux rope, too? Here we investigate the source region of a complex ejecta, focusing on a flare precursor with definitive signatures of magnetic reconnection, i.e., nonthermal electrons, flaring plasma, and bidirectional outflowing blobs. Aided by nonlinear force-free field modeling, we conclude that the reconnection occurs within a system of multiple braided flux ropes with different degrees of coherency. The observation signifies the importance of internal structure and dynamics in understanding CMEs and in predicting their impacts on Earth.

Analytic solutions for single and multiple cylinders of gravitating polytropes in magnetostatic equilibrium

NASA Technical Reports Server (NTRS)

Lerche, I.; Low, B. C.

1980-01-01

Exact analytic solutions for the static equilibrium of a gravitating plasma polytrope in the presence of magnetic fields are presented. The means of generating various equilibrium configurations to illustrate directly the complex physical relationships between pressure, magnetic fields, and gravity in self-gravitating systems is demonstrated. One of the solutions is used to model interstellar clouds suspended by magnetic fields against the galactic gravity such as may be formed by the Parker (1966) instability. It is concluded that the pinching effect of closed loops of magnetic fields in the clouds may be a dominant agent in further collapsing the clouds following their formation.

An initial physical mechanism in the treatment of neurologic disorders with externally applied pico Tesla magnetic fields.

PubMed

Jacobson, J I; Yamanashi, W S

1995-04-01

The recent clinical studies describing the treatment of some neurological disorders with an externally applied pico Tesla (10(-12) Tesla, or 10(-8) gauss) magnetic field are considered from a physical view point. An equation relating the intrinsic (or rest) energy of a charged particle of mass m with its energy of interaction in an externally applied magnetic field B is presented. The equation represents an initial basic physical interaction as a part of a more complex biological mechanism to explain the therapeutic effects of externally applied magnetic fields in these and other neurologic disorders.

A physical mechanism in the treatment of neurologic disorders with externally applied pico Tesla magnetic fields.

PubMed

Jacobson, J I; Yamanashi, W S

1995-06-01

The clinical studies describing the treatment of some neurological disorders with an externally applied pico Tesla (10R Tesla, or 10(-8) gauss) magnetic field are considered from a physical view point. An equation relating the intrinsic or "rest" energy of a charged particle of mass with its energy of interaction in an externally applied magnetic field B is presented. The equation is proposed to represent an initial basic physical interaction as a part of a more complex biological mechanism to explain the therapeutic effects of externally applied magnetic fields in these and other neurologic disorders.

The Effect of Combined Magnetic Geometries on Thermally Driven Winds. II. Dipolar, Quadrupolar, and Octupolar Topologies

NASA Astrophysics Data System (ADS)

Finley, Adam J.; Matt, Sean P.

2018-02-01

During the lifetime of Sun-like or low-mass stars a significant amount of angular momentum is removed through magnetized stellar winds. This process is often assumed to be governed by the dipolar component of the magnetic field. However, observed magnetic fields can host strong quadrupolar and/or octupolar components, which may influence the resulting spin-down torque on the star. In Paper I, we used the MHD code PLUTO to compute steady-state solutions for stellar winds containing a mixture of dipole and quadrupole geometries. We showed the combined winds to be more complex than a simple sum of winds with these individual components. This work follows the same method as Paper I, including the octupole geometry, which not only increases the field complexity but also, more fundamentally, looks for the first time at combining the same symmetry family of fields, with the field polarity of the dipole and octupole geometries reversing over the equator (unlike the symmetric quadrupole). We show, as in Paper I, that the lowest-order component typically dominates the spin-down torque. Specifically, the dipole component is the most significant in governing the spin-down torque for mixed geometries and under most conditions for real stars. We present a general torque formulation that includes the effects of complex, mixed fields, which predicts the torque for all the simulations to within 20% precision, and the majority to within ≈5%. This can be used as an input for rotational evolution calculations in cases where the individual magnetic components are known.

Electronic structures and magnetic/optical properties of metal phthalocyanine complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baba, Shintaro; Suzuki, Atsushi, E-mail: suzuki@mat.usp.ac.jp; Oku, Takeo

2016-02-01

Electronic structures and magnetic / optical properties of metal phthalocyanine complexes were studied by quantum calculations using density functional theory. Effects of central metal and expansion of π orbital on aromatic ring as conjugation system on the electronic structures, magnetic, optical properties and vibration modes of infrared and Raman spectra of metal phthalocyanines were investigated. Electron and charge density distribution and energy levels near frontier orbital and excited states were influenced by the deformed structures varied with central metal and charge. The magnetic parameters of chemical shifts in {sup 13}C-nuclear magnetic resonance ({sup 13}C-NMR), principle g-tensor, A-tensor, V-tensor of electricmore » field gradient and asymmetry parameters derived from the deformed structures with magnetic interaction of nuclear quadruple interaction based on electron and charge density distribution with a bias of charge near ligand under crystal field.« less

Electric-Field Control of Oxygen Vacancies and Magnetic Phase Transition in a Cobaltite/Manganite Bilayer

NASA Astrophysics Data System (ADS)

Cui, B.; Song, C.; Li, F.; Zhong, X. Y.; Wang, Z. C.; Werner, P.; Gu, Y. D.; Wu, H. Q.; Saleem, M. S.; Parkin, S. S. P.; Pan, F.

2017-10-01

Manipulation of oxygen vacancies (VO ) in single oxide layers by varying the electric field can result in significant modulation of the ground state. However, in many oxide multilayers with strong application potentials, e.g., ferroelectric tunnel junctions and solid-oxide fuel cells, understanding VO behavior in various layers under an applied electric field remains a challenge, owing to complex VO transport between different layers. By sweeping the external voltage, a reversible manipulation of VO and a corresponding fixed magnetic phase transition sequence in cobaltite/manganite (SrCoO3 -x/La0.45Sr0.55MnO3 -y ) heterostructures are reported. The magnetic phase transition sequence confirms that the priority of electric-field-induced VO formation or annihilation in the complex bilayer system is mainly determined by the VO formation energies and Gibbs free-energy differences, which is supported by theoretical analysis. We not only realize a reversible manipulation of the magnetic phase transition in an oxide bilayer but also provide insight into the electric-field control of VO engineering in heterostructures.

Effect of magnetic field on the phase transition in a dusty plasma

NASA Astrophysics Data System (ADS)

Jaiswal, S.; Hall, T.; LeBlanc, S.; Mukherjee, R.; Thomas, E.

2017-11-01

The formation of a self-consistent crystalline structure is a well-known phenomenon in complex plasmas. In most experiments, the pressure and rf power are the main controlling parameters in determining the phase of the system. We have studied the effect of the externally applied magnetic field on the configuration of plasma crystals, suspended in the sheath of a radio-frequency discharge using the Magnetized Dusty Plasma Experiment device. Experiments are performed at a fixed pressure and rf power where a crystalline structure is formed within a confining ring. The magnetic field is then increased from 0 to 1.28 T. We report on the breakdown of the crystalline structure with the increasing magnetic field. The magnetic field affects the dynamics of the plasma particles and first leads to a rotation of the crystal. At a higher magnetic field, there is a radial variation (shear) in the angular velocity of the moving particles which we believe to lead to the melting of the crystal. This melting is confirmed by evaluating the variation of the pair correlation function as a function of magnetic field.

VLA Zeeman Observations of the NGC 6334 Complex

NASA Astrophysics Data System (ADS)

Mayo, E. A.; Sarma, A. P.; Troland, T. H.

2004-05-01

We present OH 1665 and 1667 MHz observations of the NGC 6334 complex taken with the Very Large Array in the BnA configuration. We have combined our data with the lower resolution CnB data of Sarma et al (1999), in order to perform a detailed study of Source A, a compact continuum source in the SW region of the complex. Our observations reveal magnetic fields with peak values of the order of 700μ G toward Source A. Virial estimates presented indicate the significance of the magnetic field in the support of the molecular cloud against gravitational collapse.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, V.K.; Patel, A.S.; Sharma, A.

This paper presents the design of magnetic coil for relativistic magnetron (RM) for LIA (Linear Induction Accelerator)-400 systems. Vacuum improves the efficiency of RM for HPM generation. Magnetic field in RM is very critical parameter and should be nearly constant in the active region. Typical coils are helical in nature, which have multi turns of varying radius. Magnetic field calculation of such coils with basic equations of Helmholtz coils or solenoid with mean radius can only give estimation. Field computational softwares like CST require small mesh size and boundary at very far so consume large memory and take very muchmore » time. Helical coils are simplified such that the basic law of magnetic field calculation i.e. Bio-Savart law can be applied with less complexity. Pairs of spiral coils have been analyzed for magnetic field and Lorenz's force. The approach is field experimentally validated. (author)« less

Analytic solution of field distribution and demagnetization function of ideal hollow cylindrical field source

NASA Astrophysics Data System (ADS)

Xu, Xiaonong; Lu, Dingwei; Xu, Xibin; Yu, Yang; Gu, Min

2017-09-01

The Halbach type hollow cylindrical permanent magnet array (HCPMA) is a volume compact and energy conserved field source, which have attracted intense interests in many practical applications. Here, using the complex variable integration method based on the Biot-Savart Law (including current distributions inside the body and on the surfaces of magnet), we derive analytical field solutions to an ideal multipole HCPMA in entire space including the interior of magnet. The analytic field expression inside the array material is used to construct an analytic demagnetization function, with which we can explain the origin of demagnetization phenomena in HCPMA by taking into account an ideal magnetic hysteresis loop with finite coercivity. These analytical field expressions and demagnetization functions provide deeper insight into the nature of such permanent magnet array systems and offer guidance in designing optimized array system.

3-D RPIC Simulations of Relativistic Jets: Particle Acceleration, Magnetic Field Generation, and Emission

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Mizuno, Y.; Hardee, P.; Hededal, C. B.; Fishman, G. J.

2006-01-01

Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets into ambient plasmas show that acceleration occurs in relativistic shocks. The Weibel instability created in shocks is responsible for particle acceleration, and generation and amplification of highly inhomogeneous, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection in relativistic jets. The "jitter" radiation from deflected electrons has different properties than the synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understand the complex time evolution and spectral structure in relativistic jets and gamma-ray bursts. We will present recent PIC simulations which show particle acceleration and magnetic field generation. We will also calculate associated self-consistent emission from relativistic shocks.

A Study of Magnetic CP Stars in Open Clusters and Associations with the 6-m Telescope

NASA Astrophysics Data System (ADS)

Romanyuk, I. I.; Semenko, E. A.; Yakunin, I. A.; Kudryavtsev, D. O.

2017-06-01

The study of magnetic CP stars in groups of different ages allows us to obtain data on the origin and evolution of large-scale magnetic fields. We selected 17 groups for observation with the 6-m telescope. Here we draw first conclusions from the study of the Orion OB1 association. Six new magnetic stars in it are added to those seventeen that had been known earlier, ten more CP stars were suspected to have fields. A complex structure of the magnetic field in the star HD 34736 has been found, which is indicative of its fossil origin.

Magnetohydrodynamic Modeling of Solar Coronal Dynamics with an Initial Non-force-free Magnetic Field

NASA Astrophysics Data System (ADS)

Prasad, A.; Bhattacharyya, R.; Kumar, Sanjay

2017-05-01

The magnetic fields in the solar corona are generally neither force-free nor axisymmetric and have complex dynamics that are difficult to characterize. Here we simulate the topological evolution of solar coronal magnetic field lines (MFLs) using a magnetohydrodynamic model. The simulation is initialized with a non-axisymmetric non-force-free magnetic field that best correlates with the observed vector magnetograms of solar active regions (ARs). To focus on these ideas, simulations are performed for the flaring AR 11283 noted for its complexity and well-documented dynamics. The simulated dynamics develops as the initial Lorentz force pushes the plasma and facilitates successive magnetic reconnections at the two X-type null lines present in the initial field. Importantly, the simulation allows for the spontaneous development of mass flow, unique among contemporary works, that preferentially reconnects field lines at one of the X-type null lines. Consequently, a flux rope consisting of low-lying twisted MFLs, which approximately traces the major polarity inversion line, undergoes an asymmetric monotonic rise. The rise is attributed to a reduction in the magnetic tension force at the region overlying the rope, resulting from the reconnection. A monotonic rise of the rope is in conformity with the standard scenario of flares. Importantly, the simulated dynamics leads to bifurcations of the flux rope, which, being akin to the observed filament bifurcation in AR 11283, establishes the appropriateness of the initial field in describing ARs.

Magnetohydrodynamic Modeling of Solar Coronal Dynamics with an Initial Non-force-free Magnetic Field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prasad, A.; Bhattacharyya, R.; Kumar, Sanjay

The magnetic fields in the solar corona are generally neither force-free nor axisymmetric and have complex dynamics that are difficult to characterize. Here we simulate the topological evolution of solar coronal magnetic field lines (MFLs) using a magnetohydrodynamic model. The simulation is initialized with a non-axisymmetric non-force-free magnetic field that best correlates with the observed vector magnetograms of solar active regions (ARs). To focus on these ideas, simulations are performed for the flaring AR 11283 noted for its complexity and well-documented dynamics. The simulated dynamics develops as the initial Lorentz force pushes the plasma and facilitates successive magnetic reconnections atmore » the two X-type null lines present in the initial field. Importantly, the simulation allows for the spontaneous development of mass flow, unique among contemporary works, that preferentially reconnects field lines at one of the X-type null lines. Consequently, a flux rope consisting of low-lying twisted MFLs, which approximately traces the major polarity inversion line, undergoes an asymmetric monotonic rise. The rise is attributed to a reduction in the magnetic tension force at the region overlying the rope, resulting from the reconnection. A monotonic rise of the rope is in conformity with the standard scenario of flares. Importantly, the simulated dynamics leads to bifurcations of the flux rope, which, being akin to the observed filament bifurcation in AR 11283, establishes the appropriateness of the initial field in describing ARs.« less

Development of Numerical Methods to Estimate the Ohmic Breakdown Scenarios of a Tokamak

NASA Astrophysics Data System (ADS)

Yoo, Min-Gu; Kim, Jayhyun; An, Younghwa; Hwang, Yong-Seok; Shim, Seung Bo; Lee, Hae June; Na, Yong-Su

2011-10-01

The ohmic breakdown is a fundamental method to initiate the plasma in a tokamak. For the robust breakdown, ohmic breakdown scenarios have to be carefully designed by optimizing the magnetic field configurations to minimize the stray magnetic fields. This research focuses on development of numerical methods to estimate the ohmic breakdown scenarios by precise analysis of the magnetic field configurations. This is essential for the robust and optimal breakdown and start-up of fusion devices especially for ITER and its beyond equipped with low toroidal electric field (ET <= 0.3 V/m). A field-line-following analysis code based on the Townsend avalanche theory and a particle simulation code are developed to analyze the breakdown characteristics of actual complex magnetic field configurations including the stray magnetic fields in tokamaks. They are applied to the ohmic breakdown scenarios of tokamaks such as KSTAR and VEST and compared with experiments.

Investigation of complexity dynamics in a DC glow discharge magnetized plasma using recurrence quantification analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mitra, Vramori; Sarma, Bornali; Sarma, Arun

Recurrence is an ubiquitous feature which provides deep insights into the dynamics of real dynamical systems. A suitable tool for investigating recurrences is recurrence quantification analysis (RQA). It allows, e.g., the detection of regime transitions with respect to varying control parameters. We investigate the complexity of different coexisting nonlinear dynamical regimes of the plasma floating potential fluctuations at different magnetic fields and discharge voltages by using recurrence quantification variables, in particular, DET, L{sub max}, and Entropy. The recurrence analysis reveals that the predictability of the system strongly depends on discharge voltage. Furthermore, the persistent behaviour of the plasma time seriesmore » is characterized by the Detrended fluctuation analysis technique to explore the complexity in terms of long range correlation. The enhancement of the discharge voltage at constant magnetic field increases the nonlinear correlations; hence, the complexity of the system decreases, which corroborates the RQA analysis.« less

Magnetic Characterization of Direct-Write Free-Form Building Blocks for Artificial Magnetic 3D Lattices

PubMed Central

Al Mamoori, Mohanad K. I.; Keller, Lukas; Pieper, Jonathan; Winkler, Robert; Plank, Harald; Müller, Jens

2018-01-01

Three-dimensional (3D) nanomagnetism, where spin configurations extend into the vertical direction of a substrate plane allow for more complex, hierarchical systems and the design of novel magnetic effects. As an important step towards this goal, we have recently demonstrated the direct-write fabrication of freestanding ferromagnetic 3D nano-architectures of ferromagnetic CoFe in shapes of nano-tree and nano-cube structures by means of focused electron beam induced deposition. Here, we present a comprehensive characterization of the magnetic properties of these structures by local stray-field measurements using a high-resolution micro-Hall magnetometer. Measurements in a wide range of temperatures and different angles of the externally applied magnetic field with respect to the surface plane of the sensor are supported by corresponding micromagnetic simulations, which explain the overall switching behavior of in part rather complex magnetization configurations remarkably well. In particular, the simulations yield coercive and switching fields that are in good quantitative correspondence with the measured coercive and switching fields assuming a bulk metal content of 100 at % consisting of bcc Co3Fe. We show that thermally-unstable magnetization states can be repetitively prepared and their lifetime controlled at will, a prerequisite to realizing dynamic and thermally-active magnetic configurations if the building blocks are to be used in lattice structures. PMID:29439553

Extreme Material Physical Properties and Measurements above 100 tesla

NASA Astrophysics Data System (ADS)

Mielke, Charles

2011-03-01

The National High Magnetic Field Laboratory (NHMFL) Pulsed Field Facility (PFF) at Los Alamos National Laboratory (LANL) offers extreme environments of ultra high magnetic fields above 100 tesla by use of the Single Turn method as well as fields approaching 100 tesla with more complex methods. The challenge of metrology in the extreme magnetic field generating devices is complicated by the millions of amperes of current and tens of thousands of volts that are required to deliver the pulsed power needed for field generation. Methods of detecting physical properties of materials are essential parts of the science that seeks to understand and eventually control the fundamental functionality of materials in extreme environments. De-coupling the signal of the sample from the electro-magnetic interference associated with the magnet system is required to make these state-of-the-art magnetic fields useful to scientists studying materials in high magnetic fields. The cutting edge methods that are being used as well as methods in development will be presented with recent results in Graphene and High-Tc superconductors along with the methods and challenges. National Science Foundation DMR-Award 0654118.

Application of Wave Distribution Function Method to the ERG/PWE Data

NASA Astrophysics Data System (ADS)

Ota, M.; Kasahara, Y.; Matsuda, S.; Kojima, H.; Matsuoka, A.; Hikishima, M.; Kasaba, Y.; Ozaki, M.; Yagitani, S.; Tsuchiya, F.; Kumamoto, A.

2017-12-01

The ERG (Arase) satellite was launched on 20 December 2016 to study acceleration and loss mechanisms of relativistic electrons in the Earth's magnetosphere. The Plasma Wave Experiment (PWE), which is one of the science instruments on board the ERG satellite, measures electric field and magnetic field. The PWE consists of three sub-systems; EFD (Electric Field Detector), OFA/WFC (Onboard Frequency Analyzer and Waveform Capture), and HFA (High Frequency Analyzer).The OFA/WFC measures electromagnetic field spectra and raw waveforms in the frequency range from few Hz to 20 kHz. The OFA produces three kind of data; OFA-SPEC (power spectrum), OFA-MATRIX (spectral matrix), and OFA-COMPLEX (complex spectrum). The OFA-MATRIX measures ensemble averaged complex cross-spectra of two electric field components, and of three magnetic field components. The OFA-COMPLEX measures instantaneous complex spectra of electric and magnetic fields. These data are produced every 8 seconds in the nominal mode, and it can be used for polarization analysis and wave propagation direction finding.In general, spectral matrix composed by cross-spectra of observed signals is used for direction finding, and many algorithms have been proposed. For example, Means method and SVD method can be applied on the assumption that the spectral matrix is consists of a single plane wave, while wave distribution function (WDF) method is applicable even to the data in which multiple numbers of plane waves are simultaneously included. In this presentation, we introduce the results when the WDF method is applied to the ERG/PWE data.

Rapid and precise determination of zero-field splittings by terahertz time-domain electron paramagnetic resonance spectroscopy† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7sc00830a Click here for additional data file.

PubMed Central

Lu, Jian; Ozel, I. Ozge; Belvin, Carina A.; Li, Xian; Skorupskii, Grigorii; Sun, Lei; Ofori-Okai, Benjamin K.; Dincă, Mircea; Gedik, Nuh

2017-01-01

Zero-field splitting (ZFS) parameters are fundamentally tied to the geometries of metal ion complexes. Despite their critical importance for understanding the magnetism and spectroscopy of metal complexes, they are not routinely available through general laboratory-based techniques, and are often inferred from magnetism data. Here we demonstrate a simple tabletop experimental approach that enables direct and reliable determination of ZFS parameters in the terahertz (THz) regime. We report time-domain measurements of electron paramagnetic resonance (EPR) signals associated with THz-frequency ZFSs in molecular complexes containing high-spin transition-metal ions. We measure the temporal profiles of the free-induction decays of spin resonances in the complexes at zero and nonzero external magnetic fields, and we derive the EPR spectra via numerical Fourier transformation of the time-domain signals. In most cases, absolute values of the ZFS parameters are extracted from the measured zero-field EPR frequencies, and the signs can be determined by zero-field measurements at two different temperatures. Field-dependent EPR measurements further allow refined determination of the ZFS parameters and access to the g-factor. The results show good agreement with those obtained by other methods. The simplicity of the method portends wide applicability in chemistry, biology and material science. PMID:29163882

Field-Induced Magnetic Phase Transitions in a Triangular Lattice Antiferromagnet CuFeO 2 up to 14.5 T

NASA Astrophysics Data System (ADS)

Mitsuda, Setsuo; Mase, Motoshi; Prokes, K.; Kitazawa, Hideaki; Katori, H.

2000-11-01

Neutron diffraction studies on a frustrated triangular lattice antiferromagnet (TLA) CuFeO2 have been performed under an applied magnetic field up to 14.5 T. The first-field-induced state was found to be not the commensurate 5-sublattice (↑↑↑↓↓) magnetic state but rather an incommensurate complex helical state reflecting the Heisenberg spin character of orbital singlet Fe3+ magnetic ions. In contrast, the second-field-induced state was found to be the 5-sublattice (↑↑↑↓↓) magnetic state predicted by the two-dimensional (2D) Ising spin TLA model with competing exchange interactions up to the 3rd neighbors.

Electromagnetic Gun With Commutated Coils

NASA Technical Reports Server (NTRS)

Elliott, David G.

1991-01-01

Proposed electromagnetic gun includes electromagnet coil, turns of which commutated in sequence along barrel. Electrical current fed to two armatures by brushes sliding on bus bars in barrel. Interaction between armature currents and magnetic field from coil produces force accelerating armature, which in turn, pushes on projectile. Commutation scheme chosen so magnetic field approximately coincides and moves with cylindrical region defined by armatures. Scheme has disadvantage of complexity, but in return, enables designer to increase driving magnetic field without increasing armature current. Attainable muzzle velocity increased substantially.

Tuning of Magnetic Anisotropy in Hexairon(III) Rings by Host-Guest Interactions: An Investigation by High-Field Torque Magnetometry.

PubMed

Cornia; Affronte; Jansen; Abbati; Gatteschi

1999-08-01

Full chemical control of magnetic anisotropy in hexairon(III) rings can be achieved by varying the size of the guest alkali metal ion. Dramatically different anisotropies characterize the Li(I) and Na(I) complexes of [Fe(6)(OMe)(12)(L)(6)] (L=1,3-propanedione derivatives; a schematic representation of the Li(I) complex is shown), as revealed by high-field torque magnetometry-Iron: (g), oxygen: o, carbon: o, Li(+): plus sign in circle.

CAN WE PREDICT THE GLOBAL MAGNETIC TOPOLOGY OF A PRE-MAIN-SEQUENCE STAR FROM ITS POSITION IN THE HERTZSPRUNG-RUSSELL DIAGRAM?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gregory, S. G.; Hillenbrand, L. A.; Donati, J.-F.

2012-08-20

Zeeman-Doppler imaging studies have shown that the magnetic fields of T Tauri stars can be significantly more complex than a simple dipole and can vary markedly between sources. We collect and summarize the magnetic field topology information obtained to date and present Hertzsprung-Russell (H-R) diagrams for the stars in the sample. Intriguingly, the large-scale field topology of a given pre-main-sequence (PMS) star is strongly dependent upon the stellar internal structure, with the strength of the dipole component of its multipolar magnetic field decaying rapidly with the development of a radiative core. Using the observational data as a basis, we arguemore » that the general characteristics of the global magnetic field of a PMS star can be determined from its position in the H-R diagram. Moving from hotter and more luminous to cooler and less luminous stars across the PMS of the H-R diagram, we present evidence for four distinct magnetic topology regimes. Stars with large radiative cores, empirically estimated to be those with a core mass in excess of {approx}40% of the stellar mass, host highly complex and dominantly non-axisymmetric magnetic fields, while those with smaller radiative cores host axisymmetric fields with field modes of higher order than the dipole dominant (typically, but not always, the octupole). Fully convective stars above {approx}> 0.5 M{sub Sun} appear to host dominantly axisymmetric fields with strong (kilo-Gauss) dipole components. Based on similarities between the magnetic properties of PMS stars and main-sequence M-dwarfs with similar internal structures, we speculate that a bistable dynamo process operates for lower mass stars ({approx}< 0.5 M{sub Sun} at an age of a few Myr) and that they will be found to host a variety of magnetic field topologies. If the magnetic topology trends across the H-R diagram are confirmed, they may provide a new method of constraining PMS stellar evolution models.« less

Magnetic fields at neptune.

PubMed

Ness, N F; Acuña, M H; Burlaga, L F; Connerney, J E; Lepping, R P; Neubauer, F M

1989-12-15

The National Aeronautics and Space Administration Goddard Space Flight Center-University of Delaware Bartol Research Institute magnetic field experiment on the Voyager 2 spacecraft discovered a strong and complex intrinsic magnetic field of Neptune and an associated magnetosphere and magnetic tail. The detached bow shock wave in the supersonic solar wind flow was detected upstream at 34.9 Neptune radii (R(N)), and the magnetopause boundary was tentatively identified at 26.5 R(N) near the planet-sun line (1 R(N) = 24,765 kilometers). A maximum magnetic field of nearly 10,000 nanoteslas (1 nanotesla = 10(-5) gauss) was observed near closest approach, at a distance of 1.18 R(N). The planetary magnetic field between 4 and 15 R(N) can be well represented by an offset tilted magnetic dipole (OTD), displaced from the center of Neptune by the surprisingly large amount of 0.55 R(N) and inclined by 47 degrees with respect to the rotation axis. The OTD dipole moment is 0.133 gauss-R(N)(3). Within 4 R(N), the magnetic field representation must include localized sources or higher order magnetic multipoles, or both, which are not yet well determined. The obliquity of Neptune and the phase of its rotation at encounter combined serendipitously so that the spacecraft entered the magnetosphere at a time when the polar cusp region was directed almost precisely sunward. As the spacecraft exited the magnetosphere, the magnetic tail appeared to be monopolar, and no crossings of an imbedded magnetic field reversal or plasma neutral sheet were observed. The auroral zones are most likely located far from the rotation poles and may have a complicated geometry. The rings and all the known moons of Neptune are imbedded deep inside the magnetosphere, except for Nereid, which is outside when sunward of the planet. The radiation belts will have a complex structure owing to the absorption of energetic particles by the moons and rings of Neptune and losses associated with the significant changes in the diurnally varying magnetosphere configuration. In an astrophysical context, the magnetic field of Neptune, like that of Uranus, may be described as that of an "oblique" rotator.

Multiscale tomography of buried magnetic structures: its use in the localization and characterization of archaeological structures

NASA Astrophysics Data System (ADS)

Saracco, Ginette; Moreau, Frédérique; Mathé, Pierre-Etienne; Hermitte, Daniel; Michel, Jean-Marie

2007-10-01

We have previously developed a method for characterizing and localizing `homogeneous' buried sources, from the measure of potential anomalies at a fixed height above ground (magnetic, electric and gravity). This method is based on potential theory and uses the properties of the Poisson kernel (real by definition) and the continuous wavelet theory. Here, we relax the assumption on sources and introduce a method that we call the `multiscale tomography'. Our approach is based on the harmonic extension of the observed magnetic field to produce a complex source by use of a complex Poisson kernel solution of the Laplace equation for complex potential field. A phase and modulus are defined. We show that the phase provides additional information on the total magnetic inclination and the structure of sources, while the modulus allows us to characterize its spatial location, depth and `effective degree'. This method is compared to the `complex dipolar tomography', extension of the Patella method that we previously developed. We applied both methods and a classical electrical resistivity tomography to detect and localize buried archaeological structures like antique ovens from magnetic measurements on the Fox-Amphoux site (France). The estimates are then compared with the results of excavations.

Ultra-robust high-field magnetization plateau and supersolidity in bond-frustrated MnCr2S4

PubMed Central

Tsurkan, Vladimir; Zherlitsyn, Sergei; Prodan, Lilian; Felea, Viorel; Cong, Pham Thanh; Skourski, Yurii; Wang, Zhe; Deisenhofer, Joachim; von Nidda, Hans-Albrecht Krug; Wosnitza, Joahim; Loidl, Alois

2017-01-01

Frustrated magnets provide a promising avenue for realizing exotic quantum states of matter, such as spin liquids and spin ice or complex spin molecules. Under an external magnetic field, frustrated magnets can exhibit fractional magnetization plateaus related to definite spin patterns stabilized by field-induced lattice distortions. Magnetization and ultrasound experiments in MnCr2S4 up to 60 T reveal two fascinating features: (i) an extremely robust magnetization plateau with an unusual spin structure and (ii) two intermediate phases, indicating possible realizations of supersolid phases. The magnetization plateau characterizes fully polarized chromium moments, without any contributions from manganese spins. At 40 T, the middle of the plateau, a regime evolves, where sound waves propagate almost without dissipation. The external magnetic field exactly compensates the Cr–Mn exchange field and decouples Mn and Cr sublattices. In analogy to predictions of quantum lattice-gas models, the changes of the spin order of the manganese ions at the phase boundaries of the magnetization plateau are interpreted as transitions to supersolid phases. PMID:28345038

Dynamics of multiple viscoelastic carbon nanotube based nanocomposites with axial magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karličić, Danilo; Cajić, Milan; Murmu, Tony

2014-06-21

Nanocomposites and magnetic field effects on nanostructures have received great attention in recent years. A large amount of research work was focused on developing the proper theoretical framework for describing many physical effects appearing in structures on nanoscale level. Great step in this direction was successful application of nonlocal continuum field theory of Eringen. In the present paper, the free transverse vibration analysis is carried out for the system composed of multiple single walled carbon nanotubes (MSWCNT) embedded in a polymer matrix and under the influence of an axial magnetic field. Equivalent nonlocal model of MSWCNT is adopted as viscoelasticallymore » coupled multi-nanobeam system (MNBS) under the influence of longitudinal magnetic field. Governing equations of motion are derived using the Newton second low and nonlocal Rayleigh beam theory, which take into account small-scale effects, the effect of nanobeam angular acceleration, internal damping and Maxwell relation. Explicit expressions for complex natural frequency are derived based on the method of separation of variables and trigonometric method for the “Clamped-Chain” system. In addition, an analytical method is proposed in order to obtain asymptotic damped natural frequency and the critical damping ratio, which are independent of boundary conditions and a number of nanobeams in MNBS. The validity of obtained results is confirmed by comparing the results obtained for complex frequencies via trigonometric method with the results obtained by using numerical methods. The influence of the longitudinal magnetic field on the free vibration response of viscoelastically coupled MNBS is discussed in detail. In addition, numerical results are presented to point out the effects of the nonlocal parameter, internal damping, and parameters of viscoelastic medium on complex natural frequencies of the system. The results demonstrate the efficiency of the suggested methodology to find the closed form solutions for the free vibration response of multiple nanostructure systems under the influence of magnetic field.« less

Delta-configurations - Flare activity and magnetic-field structure

NASA Technical Reports Server (NTRS)

Patty, S. R.; Hagyard, M. J.

1986-01-01

Complex sunspots in four active regions of April and May 1980, all exhibiting regions of magnetic classification delta, were studied using data from the NASA Marshall Space Flight Center vector magnetograph. The vector magnetic field structure in the vicinity of each delta was determined, and the location of the deltas in each active region was correlated with the locations and types of flare activity for the regions. Two types of delta-configuration were found to exist, active and inactive, as defined by the relationships between magnetic field structure and activity. The active delta exhibited high flare activity, strong horizontal gradients of the longitudinal (line-of-sight) magnetic field component, a strong transverse (perpendicular to line-of-sight) component, and a highly nonpotential orientation of the photospheric magnetic field, all indications of a highly sheared magnetic field. The inactive delta, on the other hand, exhibited little or no flare production, weaker horizontal gradients of the longitudinal component, weaker transverse components, and a nearly potential, nonsheared orientation of the magnetic field. It is concluded that the presence of such sheared fields is the primary signature by which the active delta may be distinguished, and that it is this shear which produces the flare activity of the active delta.

Topological Evolution of a Fast Magnetic Breakout CME in 3-Dimensions

NASA Technical Reports Server (NTRS)

Lynch, B. J.; Antiochos, S. K.; DeVore, C. R.; Luhmann, J. G.; Zurbuchen, T. H.

2008-01-01

W present the extension of the magnetic breakout model for CME initiation to a fully 3-dimensional, spherical geometry. Given the increased complexity of the dynamic magnetic field interactions in 3-dimensions, we first present a summary of the well known axisymmetric breakout scenario in terms of the topological evolution associated with the various phases of the eruptive process. In this context, we discuss the completely analogous topological evolution during the magnetic breakout CME initiation process in the simplest 3-dimensional multipolar system. We show that an extended bipolar active region embedded in an oppositely directed background dipole field has all the necessary topological features required for magnetic breakout, i.e. a fan separatrix surface between the two distinct flux systems, a pair of spine fieldlines, and a true 3-dimensional coronal null point at their intersection. We then present the results of a numerical MHD simulation of this 3-dimensional system where boundary shearing flows introduce free magnetic energy, eventually leading to a fast magnetic breakout CME. The eruptive flare reconnection facilitates the rapid conversion of this stored free magnetic energy into kinetic energy and the associated acceleration causes the erupting field and plasma structure to reach an asymptotic eruption velocity of greater than or approx. equal to 1100 km/s over an approx.15 minute time period. The simulation results are discussed using the topological insight developed to interpret the various phases of the eruption and the complex, dynamic, and interacting magnetic field structures.

3D print of polymer bonded rare-earth magnets, and 3D magnetic field scanning with an end-user 3D printer

NASA Astrophysics Data System (ADS)

Huber, C.; Abert, C.; Bruckner, F.; Groenefeld, M.; Muthsam, O.; Schuschnigg, S.; Sirak, K.; Thanhoffer, R.; Teliban, I.; Vogler, C.; Windl, R.; Suess, D.

2016-10-01

3D print is a recently developed technique, for single-unit production, and for structures that have been impossible to build previously. The current work presents a method to 3D print polymer bonded isotropic hard magnets with a low-cost, end-user 3D printer. Commercially available isotropic NdFeB powder inside a PA11 matrix is characterized, and prepared for the printing process. An example of a printed magnet with a complex shape that was designed to generate a specific stray field is presented, and compared with finite element simulation solving the macroscopic Maxwell equations. For magnetic characterization, and comparing 3D printed structures with injection molded parts, hysteresis measurements are performed. To measure the stray field outside the magnet, the printer is upgraded to a 3D magnetic flux density measurement system. To skip an elaborate adjusting of the sensor, a simulation is used to calibrate the angles, sensitivity, and the offset of the sensor. With this setup, a measurement resolution of 0.05 mm along the z-axes is achievable. The effectiveness of our calibration method is shown. With our setup, we are able to print polymer bonded magnetic systems with the freedom of having a specific complex shape with locally tailored magnetic properties. The 3D scanning setup is easy to mount, and with our calibration method we are able to get accurate measuring results of the stray field.

Excitonic magnet in external field: Complex order parameter and spin currents

NASA Astrophysics Data System (ADS)

Geffroy, D.; Hariki, A.; Kuneš, J.

2018-04-01

We investigate spin-triplet exciton condensation in the two-orbital Hubbard model close to half-filling by means of dynamical mean-field theory. Employing an impurity solver that handles complex off-diagonal hybridization functions, we study the behavior of excitonic condensate in stoichiometric and doped systems subject to external magnetic field. We find a general tendency of the triplet order parameter to lie perpendicular with the applied field and identify exceptions from this rule. For solutions exhibiting k -odd spin textures, we discuss the Bloch theorem, which, in the absence of spin-orbit coupling, forbids the appearance of spontaneous net spin current. We demonstrate that the Bloch theorem is not obeyed by the dynamical mean-field theory.

Laboratory Experiments on Propagating Plasma Bubbles into Vacuum, Vacuum Magnetic Field, and Background Plasmas

NASA Astrophysics Data System (ADS)

Lynn, Alan G.; Zhang, Yue; Gilmore, Mark; Hsu, Scott

2014-10-01

We discuss the dynamics of plasma ``bubbles'' as they propagate through a variety of background media. These bubbles are formed by a pulsed coaxial gun with an externally applied magnetic field. Bubble parameters are typically ne ~1020 m-3, Te ~ 5 - 10 eV, and Ti ~ 10 - 15 eV. The structure of the bubbles can range from unmagnetized jet-like structures to spheromak-like structures with complex magnetic flux surfaces. Some of the background media the bubbles interact with are vacuum, vacuum with magnetic field, and other magnetized plasmas. These bubbles exhibit different qualitative behavior depending on coaxial gun parameters such as gas species, gun current, and gun bias magnetic field. Their behavior also depends on the parameters of the background they propagate through. Multi-frame fast camera imaging and magnetic probe data are used to characterize the bubble evolution under various conditions.

Non-rigid precession of magnetic stars

NASA Astrophysics Data System (ADS)

Lander, S. K.; Jones, D. I.

2017-06-01

Stars are, generically, rotating and magnetized objects with a misalignment between their magnetic and rotation axes. Since a magnetic field induces a permanent distortion to its host, it provides effective rigidity even to a fluid star, leading to bulk stellar motion that resembles free precession. This bulk motion is, however, accompanied by induced interior velocity and magnetic field perturbations, which are oscillatory on the precession time-scale. Extending previous work, we show that these quantities are described by a set of second-order perturbation equations featuring cross-terms scaling with the product of the magnetic and centrifugal distortions to the star. For the case of a background toroidal field, we reduce these to a set of differential equations in radial functions, and find a method for their solution. The resulting magnetic field and velocity perturbations show complex multipolar structure and are strongest towards the centre of the star.

The Role of Magnetic Reconnection in Solar Activity

NASA Technical Reports Server (NTRS)

Antiochos, Spiro; DeVore, C. R.

2008-01-01

The central challenge in solar/heliospheric physics is to understand how the emergence and transport of magnetic flux at the photosphere drives the structure and dynamics that we observe in the corona and heliosphere. This presentation focuses on the role of magnetic reconnection in determining solar/heliospheric activity. We demonstrate that two generic properties of the photospheric magnetic and velocity fields are responsible for the ubiquitous reconnection in the corona. First, the photospheric velocities are complex, which leads to the injection of energy and helicity into the coronal magnetic fields and to the efficient, formation of small-scale structure. Second, the flux distribution at the photosphere is multi-polar, which implies that topological discontinuities and, consequently, current sheets, must be present in the coronal magnetic field. We: present numerical simulations showing that photospherically-driven reconnection is responsible for the heating and dynamics of coronal plasma, and for the topology of the coronal/heliospheric magnetic field.

Diamond-Based Magnetic Imaging with Fourier Optical Processing

NASA Astrophysics Data System (ADS)

Backlund, Mikael P.; Kehayias, Pauli; Walsworth, Ronald L.

2017-11-01

Diamond-based magnetic field sensors have attracted great interest in recent years. In particular, wide-field magnetic imaging using nitrogen-vacancy (NV) centers in diamond has been previously demonstrated in condensed matter, biological, and paleomagnetic applications. Vector magnetic imaging with NV ensembles typically requires a significant applied field (>10 G ) to resolve the contributions from four crystallographic orientations, hindering studies of magnetic samples that require measurement in low or independently specified bias fields. Here we model and measure the complex amplitude distribution of NV emission at the microscope's Fourier plane and show that by modulating this collected light at the Fourier plane, one can decompose the NV ensemble magnetic resonance spectrum into its constituent orientations by purely optical means. This decomposition effectively extends the dynamic range at a given bias field and enables wide-field vector magnetic imaging at arbitrarily low bias fields, thus broadening potential applications of NV imaging and sensing. Our results demonstrate that NV-based microscopy stands to benefit greatly from Fourier optical approaches, which have already found widespread utility in other branches of microscopy.

Pulsating Magnetic Reconnection Driven by Three-Dimensional Flux-Rope Interactions.

PubMed

Gekelman, W; De Haas, T; Daughton, W; Van Compernolle, B; Intrator, T; Vincena, S

2016-06-10

The dynamics of magnetic reconnection is investigated in a laboratory experiment consisting of two magnetic flux ropes, with currents slightly above the threshold for the kink instability. The evolution features periodic bursts of magnetic reconnection. To diagnose this complex evolution, volumetric three-dimensional data were acquired for both the magnetic and electric fields, allowing key field-line mapping quantities to be directly evaluated for the first time with experimental data. The ropes interact by rotating about each other and periodically bouncing at the kink frequency. During each reconnection event, the formation of a quasiseparatrix layer (QSL) is observed in the magnetic field between the flux ropes. Furthermore, a clear correlation is demonstrated between the quasiseparatrix layer and enhanced values of the quasipotential computed by integrating the parallel electric field along magnetic field lines. These results provide clear evidence that field lines passing through the quasiseparatrix layer are undergoing reconnection and give a direct measure of the nonlinear reconnection rate. The measurements suggest that the parallel electric field within the QSL is supported predominantly by electron pressure; however, resistivity may play a role.

High field hyperpolarization-EXSY experiment for fast determination of dissociation rates in SABRE complexes

NASA Astrophysics Data System (ADS)

Hermkens, Niels K. J.; Feiters, Martin C.; Rutjes, Floris P. J. T.; Wijmenga, Sybren S.; Tessari, Marco

2017-03-01

SABRE (Signal Amplification By Reversible Exchange) is a nuclear spin hyperpolarization technique based on the reversible concurrent binding of small molecules and para-hydrogen (p-H2) to an iridium metal complex in solution. At low magnetic field, spontaneous conversion of p-H2 spin order to enhanced longitudinal magnetization of the nuclear spins of the other ligands occurs. Subsequent complex dissociation results in hyperpolarized substrate molecules in solution. The lifetime of this complex plays a crucial role in attained SABRE NMR signal enhancements. Depending on the ligands, vastly different dissociation rates have been previously measured using EXSY or selective inversion experiments. However, both these approaches are generally time-consuming due to the long recycle delays (up to 2 min) necessary to reach thermal equilibrium for the nuclear spins of interest. In the cases of dilute solutions, signal averaging aggravates the problem, further extending the experimental time. Here, a new approach is proposed based on coherent hyperpolarization transfer to substrate protons in asymmetric complexes at high magnetic field. We have previously shown that such asymmetric complexes are important for application of SABRE to dilute substrates. Our results demonstrate that a series of high sensitivity EXSY spectra can be collected in a short experimental time thanks to the NMR signal enhancement and much shorter recycle delay.

Experimental investigation of the critical magnetic fields of transition metal superconductors

NASA Technical Reports Server (NTRS)

Mcevoy, J. P.

1973-01-01

The isothermal magnetic transitions of a type 2 superconductor have been studied by AC susceptibility techniques as a function of the amplitude and frequency of the exciting field. The field variation of the complex susceptibility was used to determine the critical fields. The research was planned to clarify the determination (both experimentally and theoretically) of the maximum field at which the superconductive phase spontaneously nucleates in the bulk and on the surface of the metal.

Simulation of Relativistic Shocks and Associated Radiation from Turbulent Magnetic Fields

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Mizuno, Y.; Niemiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Frederiksen, J.; Sol, H.; Pohl, M.; Hartmann, D. H.;

Weak arrest-like and field-driven first order magnetic phase transitions of itinerant Fe3Ga4 revealed by magnetization and magnetoresistance isotherms

NASA Astrophysics Data System (ADS)

Samatham, S. Shanmukharao; Suresh, K. G.

2017-01-01

The detailed magnetic study of complex 3d-electron based Fe3Ga4 is reported. It undergoes paramagnetic to antiferromagnetic (TN) and antiferromagnetic to ferromagnetic (TC) transitions respectively around 380 and 70 K. The thermal hysteresis of field-cooled cooling (FCC) and field-cooled warming (FCW) hints at first order phase transition below Curie temperature. A weak phase coexistence of ferro and antiferromagnetic phases is suggested by exploring the arrest-like first-order phenomenon. In the intermediate temperature range, field-driven metamagnetic transition from antiferro to ferromagnetic phase is confirmed. Further bringing the system very near to TN, field-induced transitions disappear and above TN predominant paramagnetic contribution is evident. The magnetic H-T phase diagram distinguishing different magnetic phases of Fe3Ga4 is obtained.

Multi-wavelength Observations and Modeling of Solar Flares: Magnetic Structures

NASA Astrophysics Data System (ADS)

Su, Y.

2017-12-01

We present a review of our recent investigations on multi-wavelength observations and magnetic field modeling of solar flares. High-resolution observations taken by NVST and BBSO/NST reveal unprecedented fine structures of the flaring regions. Observations by SDO, IRIS, and GOES provide the complementary information. The magnetic field models are constructed using either non-linear force free field extrapolations or flux rope insertion method. Our studies have shown that the flaring regions often consist of double or multiple flux ropes, which often exist at different heights. The fine flare ribbon structures may be due to the magnetic reconnection in the complex quasi separatrix layers. The magnetic field modeling of several large flares suggests that the so called hot-channel structure is corresponding to the erupting flux rope above the X-point in a magnetic configuration with Hyperbolic Flux Tube.

Anomalous Thermal Conductivity and Magnetic Torque Response in the Honeycomb Magnet α -RuCl3

NASA Astrophysics Data System (ADS)

Leahy, Ian A.; Pocs, Christopher A.; Siegfried, Peter E.; Graf, David; Do, S.-H.; Choi, Kwang-Yong; Normand, B.; Lee, Minhyea

2017-05-01

We report on the unusual behavior of the in-plane thermal conductivity κ and torque τ response in the Kitaev-Heisenberg material α -RuCl3 . κ shows a striking enhancement with linear growth beyond H =7 T , where magnetic order disappears, while τ for both of the in-plane symmetry directions shows an anomaly at the same field. The temperature and field dependence of κ are far more complex than conventional phonon and magnon contributions, and require us to invoke the presence of unconventional spin excitations whose properties are characteristic of a field-induced spin-liquid phase related to the enigmatic physics of the Kitaev model in an applied magnetic field.

Vacuum birefringence in strong magnetic fields: (II) Complex refractive index from the lowest Landau level

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hattori, Koichi, E-mail: khattori@yonsei.ac.kr; Itakura, Kazunori, E-mail: kazunori.itakura@kek.jp; Department of Particle and Nuclear Studies, Graduate University for Advanced Studies

2013-07-15

We compute the refractive indices of a photon propagating in strong magnetic fields on the basis of the analytic representation of the vacuum polarization tensor obtained in our previous paper. When the external magnetic field is strong enough for the fermion one-loop diagram of the polarization tensor to be approximated by the lowest Landau level, the propagating mode in parallel to the magnetic field is subject to modification: The refractive index deviates from unity and can be very large, and when the photon energy is large enough, the refractive index acquires an imaginary part indicating decay of a photon intomore » a fermion–antifermion pair. We study dependences of the refractive index on the propagating angle and the magnetic-field strength. It is also emphasized that a self-consistent treatment of the equation which defines the refractive index is indispensable for accurate description of the refractive index. This self-consistent treatment physically corresponds to consistently including the effects of back reactions of the distorted Dirac sea in response to the incident photon. -- Highlights: •Vacuum birefringence and photon decay are described by the complex refractive index. •Resummed photon vacuum polarization tensor in the lowest Landau level is used. •Back reactions from the distorted Dirac sea are self-consistently taken into account. •Self-consistent treatment drastically changes structure in photon energy dependence. •Dependences on photon propagation angle and magnetic-field strength are presented.« less

Magnetic field changes activate the trigeminal brainstem complex in a migratory bird

PubMed Central

Heyers, Dominik; Zapka, Manuela; Hoffmeister, Mara; Wild, John Martin; Mouritsen, Henrik

2010-01-01

The upper beak of birds, which contains putative magnetosensory ferro-magnetic structures, is innervated by the ophthalmic branch of the trigeminal nerve (V1). However, because of the absence of replicable neurobiological evidence, a general acceptance of the involvement of the trigeminal nerve in magnetoreception is lacking in birds. Using an antibody to ZENK protein to indicate neuronal activation, we here document reliable magnetic activation of neurons in and near the principal (PrV) and spinal tract (SpV) nuclei of the trigeminal brainstem complex, which represent the two brain regions known to receive primary input from the trigeminal nerve. Significantly more neurons were activated in PrV and in medial SpV when European robins (Erithacus rubecula) experienced a magnetic field changing every 30 seconds for a period of 3 h (CMF) than when robins experienced a compensated, zero magnetic field condition (ZMF). No such differences in numbers of activated neurons were found in comparison structures. Under CMF conditions, sectioning of V1 significantly reduced the number of activated neurons in and near PrV and medial SpV, but not in lateral SpV or in the optic tectum. Tract tracing of V1 showed spatial proximity and regional overlap of V1 nerve endings and ZENK-positive (activated) neurons in SpV, and partly in PrV, under CMF conditions. Together, these results suggest that magnetic field changes activate neurons in and near the trigeminal brainstem complex and that V1 is necessary for this activation. We therefore suggest that V1 transmits magnetic information to the brain in this migratory passerine bird. PMID:20439705

Source analysis of MEG activities during sleep (abstract)

NASA Astrophysics Data System (ADS)

Ueno, S.; Iramina, K.

1991-04-01

The present study focuses on magnetic fields of the brain activities during sleep, in particular on K-complexes, vertex waves, and sleep spindles in human subjects. We analyzed these waveforms based on both topographic EEG (electroencephalographic) maps and magnetic fields measurements, called MEGs (magnetoencephalograms). The components of magnetic fields perpendicular to the surface of the head were measured using a dc SQUID magnetometer with a second derivative gradiometer. In our computer simulation, the head is assumed to be a homogeneous spherical volume conductor, with electric sources of brain activity modeled as current dipoles. Comparison of computer simulations with the measured data, particularly the MEG, suggests that the source of K-complexes can be modeled by two current dipoles. A source for the vertex wave is modeled by a single current dipole which orients along the body axis out of the head. By again measuring the simultaneous MEG and EEG signals, it is possible to uniquely determine the orientation of this dipole, particularly when it is tilted slightly off-axis. In sleep stage 2, fast waves of magnetic fields consistently appeared, but EEG spindles appeared intermittently. The results suggest that there exist sources which are undetectable by electrical measurement but are detectable by magnetic-field measurement. Such source can be described by a pair of opposing dipoles of which directions are oppositely oriented.

Transition metal redox switches for reversible "on/off" and "slow/fast" single-molecule magnet behaviour in dysprosium and erbium bis-diamidoferrocene complexes.

PubMed

Dickie, Courtney M; Laughlin, Alexander L; Wofford, Joshua D; Bhuvanesh, Nattamai S; Nippe, Michael

2017-12-01

Single-molecule magnets (SMMs) are considered viable candidates for next-generation data storage and quantum computing. Systems featuring switchability of their magnetization dynamics are particularly interesting with respect to accessing more complex logic gates and device architectures. Here we show that transition metal based redox events can be exploited to enable reversible switchability of slow magnetic relaxation of magnetically anisotropic lanthanide ions. Specifically, we report anionic homoleptic bis-diamidoferrocene complexes of Dy 3+ (oblate) and Er 3+ (prolate) which can be reversibly oxidized by one electron to yield their respective charge neutral redox partners (Dy: [1] - , 1 ; Er: [2] - , 2 ). Importantly, compounds 1 and 2 are thermally stable which allowed for detailed studies of their magnetization dynamics. We show that the Dy 3+ [1] - / 1 system can function as an "on"/"off" or a "slow"/"fast" redox switchable SMM system in the absence or presence of applied dc fields, respectively. The Er 3+ based [2] - / 2 system features "on"/"off" switchability of SMM properties in the presence of applied fields. Results from electrochemical investigations, UV-vis-NIR spectroscopy, and 57 Fe Mössbauer spectroscopy indicate the presence of significant electronic communication between the mixed-valent Fe ions in 1 and 2 in both solution and solid state. This comparative evaluation of redox-switchable magnetization dynamics in low coordinate lanthanide complexes may be used as a potential blueprint toward the development of future switchable magnetic materials.

The evolution of the storm-time ring current in response to different characteristics of the plasma source

NASA Astrophysics Data System (ADS)

Lemon, C.; Chen, M.; O'Brien, T. P.; Toffoletto, F.; Sazykin, S.; Wolf, R.; Kumar, V.

2006-12-01

We present simulation results of the Rice Convection Model-Equilibrium (RCM-E) that test and compare the effect on the storm time ring current of varying the plasma sheet source population characteristics at 6.6 Re during magnetic storms. Previous work has shown that direct injection of ionospheric plasma into the ring current is not a significant source of ring current plasma, suggesting that the plasma sheet is the only source. However, storm time processes in the plasma sheet and inner magnetosphere are very complex, due in large part to the feedback interactions between the plasma distribution, magnetic field, and electric field. We are particularly interested in understanding the role of the plasma sheet entropy parameter (PV^{5/3}, where V=\\int ds/B) in determining the strength and distribution of the ring current in both the main and recovery phases of a storm. Plasma temperature and density can be measured from geosynchrorous orbiting satellites, and these are often used to provide boundary conditions for ring current simulations. However, magnetic field measurements in this region are less commonly available, and there is a relatively poor understanding of the interplay between the plasma and the magnetic field during magnetic storms. The entropy parameter is a quantity that incorporates both the plasma and the magnetic field, and understanding its role in the ring current injection and recovery is essential to describing the processes that are occuring during magnetic storms. The RCM-E includes the physics of feedback between the plasma and both the electric and magnetic fields, and is therefore a valuable tool for understanding these complex storm-time processes. By contrasting the effects of different plasma boundary conditions at geosynchronous orbit, we shed light on the physical processes involved in ring current injection and recovery.

Magnetic Fields in the Massive Dense Cores of the DR21 Filament: Weakly Magnetized Cores in a Strongly Magnetized Filament

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ching, Tao-Chung; Lai, Shih-Ping; Zhang, Qizhou

We present Submillimeter Array 880 μ m dust polarization observations of six massive dense cores in the DR21 filament. The dust polarization shows complex magnetic field structures in the massive dense cores with sizes of 0.1 pc, in contrast to the ordered magnetic fields of the parsec-scale filament. The major axes of the massive dense cores appear to be aligned either parallel or perpendicular to the magnetic fields of the filament, indicating that the parsec-scale magnetic fields play an important role in the formation of the massive dense cores. However, the correlation between the major axes of the cores andmore » the magnetic fields of the cores is less significant, suggesting that during the core formation, the magnetic fields below 0.1 pc scales become less important than the magnetic fields above 0.1 pc scales in supporting a core against gravity. Our analysis of the angular dispersion functions of the observed polarization segments yields a plane-of-sky magnetic field strength of 0.4–1.7 mG for the massive dense cores. We estimate the kinematic, magnetic, and gravitational virial parameters of the filament and the cores. The virial parameters show that the gravitational energy in the filament dominates magnetic and kinematic energies, while the kinematic energy dominates in the cores. Our work suggests that although magnetic fields may play an important role in a collapsing filament, the kinematics arising from gravitational collapse must become more important than magnetic fields during the evolution from filaments to massive dense cores.« less

Parametric Transformation Analysis

NASA Technical Reports Server (NTRS)

Gary, G. Allan

2003-01-01

Because twisted coronal features are important proxies for predicting solar eruptive events, and, yet not clearly understood, we present new results to resolve the complex, non-potential magnetic field configurations of active regions. This research uses free-form deformation mathematics to generate the associated coronal magnetic field. We use a parametric representation of the magnetic field lines such that the field lines can be manipulated to match the structure of EUV and SXR coronal loops. The objective is to derive sigmoidal magnetic field solutions which allows the beta greater than 1 regions to be included, aligned and non-aligned electric currents to be calculated, and the Lorentz force to be determined. The advantage of our technique is that the solution is independent of the unknown upper and side boundary conditions, allows non-vanishing magnetic forces, and provides a global magnetic field solution, which contains high- and low-beta regimes and is consistent with all the coronal images of the region. We show that the mathematical description is unique and physical.

Characteristics, location and origin of flare activity in a complex active region

NASA Technical Reports Server (NTRS)

Machado, M. E.; Gary, G. A.; Hagyard, M. J.; Hernandez, A. M.; Rovira, M. G.

1986-01-01

The observational characteristics of series of multiple-loop flares from a complex active region are summarized. The location of the highest observed photospheric magnetic shear is found to be the commonly observed site of flare onset, but not, in many cases, the magnetic region where the largest time-integrated energy release is observed. The observations thus reveal a consistent pattern of energy-release processes related to the magnetic-field topology.

Design of magnetic gene complexes as effective and serum resistant gene delivery systems for mesenchymal stem cells.

PubMed

Zhang, Tian-Yuan; Wu, Jia-He; Xu, Qian-Hao; Wang, Xia-Rong; Lu, Jingxiong; Hu, Ying; Jo, Jun-Ichiro; Yamamoto, Masaya; Ling, Daishun; Tabata, Yasuhiko; Gao, Jian-Qing

2017-03-30

Gene engineered mesenchymal stem cells (MSCs) have been proposed as promising tools for their various applications in biomedicine. Nevertheless, the lack of an effective and safe way to genetically modify these stem cells is still a major obstacle in the current studies. Herein, we designed novel magnetic complexes by assembling cationized pullulan derivatives with magnetic iron oxide nanoparticles for delivering target genes to MSCs. Results showed that this complexes achieved effective gene expression with the assistance of external magnetic field, and resisted the adverse effect induced by serum proteins on the gene delivery. Moreover, neither significant cytotoxicity nor the interference on the osteogenic differentiation to MSCs were observed after magnetofection. Further studies revealed that this effective and serum resistant gene transfection was partly due to the accelerated and enhanced intracellular uptake process driven by external magnetic field. To conclude, the current study presented a novel option for genetic modification of MSCs in an effective, relatively safe and serum compatible way. Copyright © 2017 Elsevier B.V. All rights reserved.

The complex magnetic field of Jupiter

NASA Technical Reports Server (NTRS)

Acuna, M. H.; Ness, N. F.

1975-01-01

An analysis of the characteristics of the magnetic field of the planet Jupiter is presented. The data were obtained during the flight of Pioneer 11 space probe, using a high field triaxial fluxgate magnetometer. The data are analyzed in terms of traditional Schmitt normalized spherical harmonic expansion fitted to the observations in a least squares sense. Tables of data and graphs are provided to summarize the findings.

Evaluation and characterization of fetal exposures to low frequency magnetic fields generated by laptop computers.

PubMed

Zoppetti, Nicola; Andreuccetti, Daniele; Bellieni, Carlo; Bogi, Andrea; Pinto, Iole

2011-12-01

Portable - or "laptop" - computers (LCs) are widely and increasingly used all over the world. Since LCs are often used in tight contact with the body even by pregnant women, fetal exposures to low frequency magnetic fields generated by these units can occur. LC emissions are usually characterized by complex waveforms and are often generated by the main AC power supply (when connected) and by the display power supply sub-system. In the present study, low frequency magnetic field emissions were measured for a set of five models of portable computers. For each of them, the magnetic flux density was characterized in terms not just of field amplitude, but also of the so called "weighted peak" (WP) index, introduced in the 2003 ICNIRP Statement on complex waveforms and confirmed in the 2010 ICNIRP Guidelines for low frequency fields. For the model of LC presenting the higher emission, a deeper analysis was also carried out, using numerical dosimetry techniques to calculate internal quantities (current density and in-situ electric field) with reference to a digital body model of a pregnant woman. Since internal quantities have complex waveforms too, the concept of WP index was extended to them, considering the ICNIRP basic restrictions defined in the 1998 Guidelines for the current density and in the 2010 Guidelines for the in-situ electric field. Induced quantities and WP indexes were computed using an appropriate original formulation of the well known Scalar Potential Finite Difference (SPFD) numerical method for electromagnetic dosimetry in quasi-static conditions. Copyright © 2011 Elsevier Ltd. All rights reserved.

[Mo2(CN)11]:5- A detailed description of ligand-field spectra and magnetic properties by first-principles calculations.

PubMed

Hendrickx, Marc F A; Clima, S; Chibotaru, L F; Ceulemans, A

2005-10-06

An ab initio multiconfigurational approach has been used to calculate the ligand-field spectrum and magnetic properties of the title cyano-bridged dinuclear molybdenum complex. The rather large magnetic coupling parameter J for a single cyano bridge, as derived experimentally for this complex by susceptibility measurements, is confirmed to a high degree of accuracy by our CASPT2 calculations. Its electronic structure is rationalized in terms of spin-spin coupling between the two constituent hexacyano-monomolybdate complexes. An in-depth analysis on the basis of Anderson's kinetic exchange theory provides a qualitative picture of the calculated CASSCF antiferromagnetic ground-state eigenvector in the Mo dimer. Dynamic electron correlations as incorporated into our first-principles calculations by means of the CASPT2 method are essential to obtain quantitative agreement between theory and experiment.

Effect of magnetic field on the phase transition in dusty plasma

NASA Astrophysics Data System (ADS)

Jaiswal, Surabhi; Thomas, Edward; Mukherjee, Rupak

2017-10-01

The formation of self-consistent crystalline structure is a well-known phenomenon in complex plasmas. In most experiments the pressure and rf power are the main controlling parameter in determining the phase of the system. We have studied the effect of externally applied magnetic field on the configuration of plasma crystals, suspended in the sheath of a radio-frequency discharge using the Magnetized Dusty Plasma Experiment (MDPX) device. Experiments are performed at a fixed pressure and rf power where a crystalline structure formed within the confining ring, but ramping the magnetic field up to 1.28 T. We report on the breakdown of the crystalline structure with increasing magnetic field. The magnetic field affects the dynamics of the plasma particles and first leads to a rotation of the crystal. At higher magnetic field, there is a radial variation (shear) in the angular velocity of the moving particles which we believe leads to the melting of the crystal. This melting is confirmed by evaluating the variation of the pair correlation function as a function of magnetic field. This work was supported by the US Dept. of Energy, DE - SC0010485.

Magnetic characterization of Daphnia resting eggs.

PubMed

Sakata, Masanobu; Kawasaki, Tamami; Shibue, Toshimichi; Takada, Atsushi; Yoshimura, Hideyuki; Namiki, Hideo

2006-12-15

This study characterized the magnetic materials found within Daphnia resting eggs by measuring static magnetization with a superconducting quantum interference device (SQUID) magnetometer, after forming two types of conditions, each of which consists of zero-field cooling (ZFC) and field cooling (FC). Magnetic ions, such as Fe(3+), contained in Daphnia resting eggs existed as (1) paramagnetic and superparamagnetic particles, demonstrated by a magnetization and temperature dependence of the magnetic moments under an applied magnetic field after ZFC and FC, and (2) ferromagnetic particles with definite magnetic moments, the content of which was estimated to be very low, demonstrated by the Moskowitz test. Conventionally, biomagnets have been directly detected by transmission electron microscopes (TEM). As demonstrated in this study, it is possible to nondestructively detect small biomagnets by magnetization measurement, especially after two types of ZFC and FC. This nondestructive method can be applied in detecting biomagnets in complex biological organisms.

HPTLC and magnetochromatography of new complexes of carboxylates with transition metals or rare earth elements and their ligands - study of lipophilicity.

PubMed

Malinowska, Irena; Wronka, Agnieszka; Ferenc, Wiesława

2017-05-01

Nineteen new complexes of carboxylates with transition and rare elements as central ions and their ligands were characterized by chromatographic analyses. The parameter of relative lipophilicity (R M0 ) of the tested compounds was determined experimentally by the reversed-phase high-performance thin layer chromatography method with mixtures of various organic modifiers (acetonitrile, acetone, dioxane) and water as a mobile phase. The extrapolated R M0 values were compared with the logP values calculated from the molecular structures of tested solutes. Similarities between the lipophilicity indices were analysed by principal component analysis and linear regression. Thin-layer chromatography combined with a magnetic field has been proposed as a complementary method for determination of lipophilicity of the investigated compounds. The chromatograms in the field and outside it were developed simultaneously in two identical chromatographic chambers. One of them was placed in the external magnetic field of 0.4 T inductivity. We proved that chelation causes a drastic change in compound lipophilicity, but all complexes did not exhibit enhanced activity as compared with the parent ligand. Also in the magnetic field the retention of some complexes changed, which means that the presence of the field influences the physicochemical properties of the compounds and their interactions with the stationary phase. Copyright © 2016 John Wiley & Sons, Ltd.

Dirac and non-Dirac conditions in the two-potential theory of magnetic charge

NASA Astrophysics Data System (ADS)

Scott, John; Evans, Timothy J.; Singleton, Douglas; Dzhunushaliev, Vladimir; Folomeev, Vladimir

2018-05-01

We investigate the Cabbibo-Ferrari, two-potential approach to magnetic charge coupled to two different complex scalar fields, Φ _1 and Φ _2, each having different electric and magnetic charges. The scalar field, Φ _1, is assumed to have a spontaneous symmetry breaking self-interaction potential which gives a mass to the "magnetic" gauge potential and "magnetic" photon, while the other "electric" gauge potential and "electric" photon remain massless. The magnetic photon is hidden until one reaches energies of the order of the magnetic photon rest mass. The second scalar field, Φ _2, is required in order to make the theory non-trivial. With only one field one can always use a duality rotation to rotate away either the electric or magnetic charge, and thus decouple either the associated electric or magnetic photon. In analyzing this system of two scalar fields in the Cabbibo-Ferrari approach we perform several duality and gauge transformations, which require introducing non-Dirac conditions on the initial electric and magnetic charges. We also find that due to the symmetry breaking the usual Dirac condition is altered to include the mass of the magnetic photon. We discuss the implications of these various conditions on the charges.

Formation of magnetic discontinuities through viscous relaxation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Sanjay; Bhattacharyya, R.; Smolarkiewicz, P. K.

2014-05-15

According to Parker's magnetostatic theorem, tangential discontinuities in magnetic field, or current sheets (CSs), are generally unavoidable in an equilibrium magnetofluid with infinite electrical conductivity and complex magnetic topology. These CSs are due to a failure of a magnetic field in achieving force-balance everywhere and preserving its topology while remaining in a spatially continuous state. A recent work [Kumar, Bhattacharyya, and Smolarkiewicz, Phys. Plasmas 20, 112903 (2013)] demonstrated this CS formation utilizing numerical simulations in terms of the vector magnetic field. The magnetohydrodynamic simulations presented here complement the above work by demonstrating CS formation by employing a novel approach ofmore » describing the magnetofluid evolution in terms of magnetic flux surfaces instead of the vector magnetic field. The magnetic flux surfaces being the possible sites on which CSs develop, this approach provides a direct visualization of the CS formation, helpful in understanding the governing dynamics. The simulations confirm development of tangential discontinuities through a favorable contortion of magnetic flux surfaces, as the magnetofluid undergoes a topology-preserving viscous relaxation from an initial non-equilibrium state with twisted magnetic field. A crucial finding of this work is in its demonstration of CS formation at spatial locations away from the magnetic nulls.« less

Externally driven magnetic granular layers at a liquid/air interface: self-organization, flows and magnetic order

NASA Astrophysics Data System (ADS)

Snezhko, Alexey

2007-03-01

Collective dynamics and pattern formation in ensembles of magnetic microparticles suspended at the liquid/air interface and subjected to an alternating magnetic field are studied. Experiments reveal a new type of nontrivially ordered dynamic self-assembled structures (``snakes'') emerging in such systems in a certain range of field magnitudes and frequencies. These remarkable structures are directly related to surface waves in the liquid generated by the collective response of magnetic microparticles to the alternating magnetic field. In addition, a large-scale vortex flows are induced in the vicinity of the dynamic structures. Some features of the self-localized snake structures can be understood in the framework of an amplitude equation for parametric waves coupled to the conservation law equation describing the evolution of the magnetic particle density. Self-assembled snakes have a complex magnetic order: the segments of the snake exhibit long-range antiferromagnetic ordering mediated by the surface wave, while each segment is composed of ferromagnetically aligned chains of microparticles. A phenomenological model describing magnetic behavior of the magnetic snakes in external magnetic fields is proposed.

Magnetic mapping of (carbonated) oceanic crust-mantle boundary: New insights from Linnajavri, northern Norway

NASA Astrophysics Data System (ADS)

Tominaga, M.; Beinlich, A.; Tivey, M.; Andrade Lima, E.; Weiss, B. P.

2012-12-01

The contribution of lower oceanic crust and upper mantle to marine magnetic anomalies has long been recognized, but the detailed magnetic character of this non-volcanic source layer remains to be fully defined. Here, we report preliminary results of a magnetic survey and source characterization of a "carbonated" oceanic Moho (petrological "Mohorovicic discontinuity") sequence observed at the Linnajavri Serpentinite Complex (LSC), northern Norway. The LSC is located at 67° 36'N and 16° 24'E within the upper Allochthon of the Norwegian Caledonides and represents a dismembered ophiolite. Particularly in the southern ("Ridoalggicohkka") area of the LSC, gabbro, serpentinite and its talc-carbonate (soapstone) and quartz-carbonate (listvenite) altered equivalents are extraordinarily well-exposed [1]. An intact oceanic Moho is exposed here, despite its complex tectonic setting. The small degree of arctic rock weathering (≤ 2 mm weathering surface) allowed for detailed regional-scale surface magnetic mapping across alteration fronts (serpentinite-soapstone; soapstone-listvenite) and lithological contacts (soapstone-gabbro). Magnetic mapping was conducted using a handheld 3-axis magnetometer, surface-towed resistivity meter and Teka surface magnetic susceptometer with sample spacing of 1 m. Geophysical field mapping was combined with petrological observations and scanning SQUID microscopy (SM) mapping conducted on thin sections from rock samples that were drilled along the survey lines. Regional scale magnetic mapping indicates that the total magnetic field across both the "carbonated" Moho and the soapstone-serpentinite interfaces show higher frequency changes in their magnetic anomaly character and amplitudes than the surface-towed resistivity data. SQUID microscopy mapping of both natural remanence magnetization (NRM) and anhysteretic remanence magnetization (ARM) on gabbro, serpentinite, soapstone, and listvenite samples, with a sensor-sample separation of ˜190 μm, show that the distribution of microscopically measurable ferromagnetic and possibly sulfide minerals produces a different bulk intensity for each of the rock types. SM vector magnetic field maps of these samples also reveal that the magnetization associated with these grains (observed as dipole-like fields in SM maps) is variable in direction from grain to grain, which may result from different alteration histories for each grain. These complex magnetization patterns acquired through thermal and chemical alteration history may explain the short wavelength magnetic anomalies observed along our traverse lines. [1] Beinlich, A., Plümper, O., Hövelmann, J., Austrheim, H. and Jamtveit, B. (2012), Terra Nova, in press.

Evaluation of human exposure to complex waveform magnetic fields generated by arc-welding equipment according to European safety standards.

PubMed

Zoppetti, Nicola; Bogi, Andrea; Pinto, Iole; Andreuccetti, Daniele

2015-02-01

In this paper, a procedure is described for the assessment of human exposure to magnetic fields with complex waveforms generated by arc-welding equipment. The work moves from the analysis of relevant guidelines and technical standards, underlining their strengths and their limits. Then, the procedure is described with particular attention to the techniques used to treat complex waveform fields. Finally, the procedure is applied to concrete cases encountered in the workplace. The discussion of the results highlights the critical points in the procedure, as well as those related to the evolution of the technical and exposure standards. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Ferromagnetic coupled mu-phenoxo-mu-carboxylato heterodinuclear complexes based on the Cr(salen) moiety: structural and magnetic characterization.

PubMed

Alborés, Pablo; Seeman, Johanna; Rentschler, Eva

2009-10-07

The synthesis, crystal structure, and magneto-chemical characterization of two new unprecedented -phenoxo--carboxylato heterodinuclear complexes based on the Cr(salen) moiety (salen = N,N-bis(salicylidene)ethylenediamine), [MII(O2C(CH3)3)(OH2)2(mu-O2C(CH3)3)(-salen)CrIII(O2C(CH3)3)], M = Ni (2), Co(3) are reported. The dinuclear complexes were obtained starting from the mononuclear trans-[Cr(salen)(CN)2]PPh4 (1), whose crystal structure is also reported. They show a trans arrangement of the Cr(salen) unit, bridging through the phenolate O atoms to a second metal center. An additional 2-O2-carboxylato bridge and a further monodentating carboxylate ligand complete the roughly octahedral Cr(III) coordination sphere. The highly distorted octahedral M(II) coordination environment is completed by two coordinated water molecules and an additional monodentating carboxylate. Variable-temperature solid-state DC magnetization studies were carried out in the 2.0-300 K range. Ferromagnetic isotropic pairwise exchange parameters were found with values of J = 4.1 cm-1 (2) and J = 2.1 cm-1 (3). Additionally, for complex 3, a ZFS parameter, D, was employed to properly fit the experimental data. Magnetization (M) vs. field (H) and temperature (T) data further support the presence of this anisotropic component and confirm ground states S = 5/2 and S = 3 for 2 and 3, respectively. Broken symmetry DFT calculations properly reproduce the experimental J values supporting the ferromagnetic exchange interaction experimentally observed. No out of phase susceptibility signal was observed in 0 DC magnetic field for both complexes. However, in the case of complex 3 a non-zero is observed when a small external field is applied below 3 K, suggesting slow relaxation of the magnetization which at 0 DC field is suppressed, probably due to efficient tunnelling relaxation pathways. The low symmetry of the Co(II) site in complex 3 may lead to the presence of transversal anisotropic components which could be responsible for the enhanced tunnelling pathway.

Numerical simulation of magnetic interactions in polycrystalline YFeO 3

NASA Astrophysics Data System (ADS)

Lima, E.; Martins, T. B.; Rechenberg, H. R.; Goya, G. F.; Cavelius, C.; Rapalaviciute, R.; Hao, S.; Mathur, S.

The magnetic behavior of polycrystalline yttrium orthoferrite was studied from the experimental and theoretical points of view. Magnetization measurements up to 170 kOe were carried out on a single-phase YFeO 3 sample synthesized from heterobimetallic alkoxides. The complex interplay between weak-ferromagnetic and antiferromagnetic interactions, observed in the experimental M( H) curves, was successfully simulated by locally minimizing the magnetic energy of two interacting Fe sublattices. The resulting values of exchange field ( HE=5590 kOe), anisotropy field ( HA=0.5 kOe) and Dzyaloshinsky-Moriya antisymmetric field ( HD=149 kOe) are in good agreement with previous reports on this system.

Dynamic magnetic hysteresis and nonlinear susceptibility of antiferromagnetic nanoparticles

NASA Astrophysics Data System (ADS)

Kalmykov, Yuri P.; Ouari, Bachir; Titov, Serguey V.

2016-08-01

The nonlinear ac stationary response of antiferromagnetic nanoparticles subjected to both external ac and dc fields of arbitrary strength and orientation is investigated using Brown's continuous diffusion model. The nonlinear complex susceptibility and dynamic magnetic hysteresis (DMH) loops of an individual antiferromagnetic nanoparticle are evaluated and compared with the linear regime for extensive ranges of the anisotropy, the ac and dc magnetic fields, damping, and the specific antiferromagnetic parameter. It is shown that the shape and area of the DMH loops of antiferromagnetic particles are substantially altered by applying a dc field that permits tuning of the specific magnetic power loss in the nanoparticles.

Knotty structures of the evolving heliospheric magnetic fields.

NASA Astrophysics Data System (ADS)

Roth, Ilan

2013-04-01

The analogy between MHD and knot theory is utilized in an analysis of structure, stability and evolution of complex magnetic heliospheric flux tubes. Planar projection of a three-dimensional magnetic configuration depicts the structure as a two-dimensional diagram with crossings, to which one may assign mathematical operations leading to robust topological invariants. These invariants enrich the topological information of magnetic configurations beyond helicity. It is conjectured that the field which emerges from the solar photosphere is structured as one of simplest knot invariants - unknot or prime knot, and these flux ropes are then stretched while carried by the solar wind into the interplanetary medium. Preservation of invariants for small diffusivity and large cross section of the emerging magnetic flux makes them impervious to large scale reconnection, allowing us to predict the observed structures at 1AU as elongated prime knots. Similar structures may be observed in magnetic clouds which got disconnected from their foot-points and in ion drop-out configurations from a compact flare source in solar impulsive solar events. Observation of small scale magnetic features consistent with prime knot may indicate spatial intermittency and non-Gaussian statistics in the turbulent cascade process. For flux tubes with higher resistivity, magnetic energy decay rate should decrease with increased knot complexity as the invariants are then harder to be violated. Future measurements are suggested for distinctly oriented magnetic fields with directionally varying suprathermal particle fluxes.

Pentacoordinate and Hexacoordinate Mn(III) Complexes of Tetradentate Schiff-Base Ligands Containing Tetracyanidoplatinate(II) Bridges and Revealing Uniaxial Magnetic Anisotropy.

PubMed

Nemec, Ivan; Herchel, Radovan; Trávníček, Zdeněk

2016-12-08

Crystal structures and magnetic properties of polymeric and trinuclear heterobimetallic Mn III ···Pt II ···Mn III coordination compounds, prepared from the Ba[Pt(CN)₄] and [Mn(L4A/B)(Cl)] ( 1a / b ) precursor complexes, are reported. The polymeric complex [{Mn(L4A)}₂{μ⁴-Pt(CN)₄}] n ( 2a ), where H₂L4A = N , N '-ethylene-bis(salicylideneiminate), comprises the {Mn(L4A)} moieties covalently connected through the [Pt(CN)₄] 2- bridges, thus forming a square-grid polymeric structure with the hexacoordinate Mn III atoms. The trinuclear complex [{Mn(L4B)}₂{μ-Pt(CN)₄}] ( 2b ), where H₂L4B = N , N '-benzene-bis(4-aminodiethylene-salicylideneiminate), consists of two [{Mn(L4B)} moieties, involving pentacoordinate Mn III atoms, bridged through the tetracyanidoplatinate (II) bridges to which they are coordinated in a trans fashion. Both complexes possess uniaxial type of magnetic anisotropy, with D (the axial parameter of zero-field splitting) = -3.7(1) in 2a and -2.2(1) cm -1 in 2b . Furthermore, the parameters of magnetic anisotropy 2a and 2b were also thoroughly studied by theoretical complete active space self-consistent field (CASSCF) methods, which revealed that the former is much more sensitive to the ligand field strength of the axial ligands.

Strong magnetic field generated by the extreme oxygen-rich red supergiant VY Canis Majoris

NASA Astrophysics Data System (ADS)

Shinnaga, Hiroko; Claussen, Mark J.; Yamamoto, Satoshi; Shimojo, Masumi

2017-12-01

Evolved stars experience high mass-loss rates forming thick circumstellar envelopes (CSEs). The circumstellar material is made of the result of stellar nucleosynthesis and, as such, plays a crucial role in the chemical evolution of galaxies and the universe. Since asymmetric geometries of CSEs are common, and with very complex structures for some cases, radiative pressure from the stars can explain only a small portion of the mass-loss processes; thus the essential driving mechanism is still unknown, particularly for high-mass stars. Here we report on magnetic field measurements associated with the well-known extreme red supergiant (RSG) VY Canis Majoris (VY CMa). We measured the linear polarization and the Zeeman splitting of the SiO v = 0, J = 1-0 transition using a sensitive radio interferometer. The measured magnetic field strengths are surprisingly high; their upper limits range between 150 and 650 G within 530 au (˜80 R*) of the star. The lower limit of the field strength is expected to be at least ˜10 G based on the high degree of linear polarization. Since the field strengths are very high, the magnetic field must be a key element in understanding the stellar evolution of VY CMa, as well as the dynamical and chemical evolution of the complex CSE of the star. M-type RSGs, with large stellar surface, were thought to be very slow rotators. This would seem to make a dynamo in operation difficult, and would also dilute any fossil magnetic field. At least for VY CMa, we expect that powerful dynamo processes must still be active to generate the intense magnetic field.

A mechanical characterisation on multiple timescales of electroconductive magnetorheological elastomers

NASA Astrophysics Data System (ADS)

Schümann, M.; Morich, J.; Kaufhold, T.; Böhm, V.; Zimmermann, K.; Odenbach, S.

2018-05-01

Magnetorheological elastomers are a type of smart hybrid material which combines elastic properties of a soft elastomer matrix with magnetic properties of magnetic micro particles. This leads to a material with magnetically controllable mechanical properties of which the magnetorheological effect is the best known. The addition of electroconductive particles to the polymer mix adds electrical properties to the material behaviour. The resulting electrical resistance of the sample can be manipulated by external magnetic fields and mechanical loads. This results in a distinct interplay of mechanical, electrical and magnetic effects with a highly complex time behaviour. In this paper a mechanical characterisation on multiple time scales was conducted to get an insight on the short and long-term electrical and mechanical behaviour of this novel material. The results show a complex resistivity behaviour on several timescales, sensitive to magnetic fields and strain velocity. The observed material exhibits fatigue and relaxation behaviour, whereas the magnetorheological effect appears not to interfere with the piezoresistive properties.

Self-replication with magnetic dipolar colloids

NASA Astrophysics Data System (ADS)

Dempster, Joshua M.; Zhang, Rui; Olvera de la Cruz, Monica

2015-10-01

Colloidal self-replication represents an exciting research frontier in soft matter physics. Currently, all reported self-replication schemes involve coating colloidal particles with stimuli-responsive molecules to allow switchable interactions. In this paper, we introduce a scheme using ferromagnetic dipolar colloids and preprogrammed external magnetic fields to create an autonomous self-replication system. Interparticle dipole-dipole forces and periodically varying weak-strong magnetic fields cooperate to drive colloid monomers from the solute onto templates, bind them into replicas, and dissolve template complexes. We present three general design principles for autonomous linear replicators, derived from a focused study of a minimalist sphere-dimer magnetic system in which single binding sites allow formation of dimeric templates. We show via statistical models and computer simulations that our system exhibits nonlinear growth of templates and produces nearly exponential growth (low error rate) upon adding an optimized competing electrostatic potential. We devise experimental strategies for constructing the required magnetic colloids based on documented laboratory techniques. We also present qualitative ideas about building more complex self-replicating structures utilizing magnetic colloids.

Magnetic structure of rare-earth dodecaborides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siemensmeyer, K.; Flachbart, K.; Gabani, S.

2006-09-15

We have investigated the magnetic structure of HoB{sub 12}, ErB{sub 12} and TmB{sub 12} by neutron diffraction on isotopically enriched single-crystalline samples. Results in zero field as well as in magnetic field up to 5T reveal modulated incommensurate magnetic structures in these compounds. The basic reflections can be indexed with q=(1/2+/-{delta}, 1/2+/-{delta}, 1/2+/-{delta}), where {delta}=0.035 both for HoB{sub 12} and TmB{sub 12} and with q=(3/2+/-{delta}, 1/2+/-{delta}, 1/2+/-{delta}), where {delta}=0.035, for ErB{sub 12}. In an applied magnetic field, new phases are observed. The complex magnetic structure of these materials seems to result from the interplay between the RKKY and dipole-dipole interaction.more » The role of frustration due to the fcc symmetry of dodecaborides and the crystalline electric field effect is also considered.« less

Triaxial fiber optic magnetic field sensor for MRI applications

NASA Astrophysics Data System (ADS)

Filograno, Massimo L.; Pisco, Marco; Catalano, Angelo; Forte, Ernesto; Aiello, Marco; Soricelli, Andrea; Davino, Daniele; Visone, Ciro; Cutolo, Antonello; Cusano, Andrea

2016-05-01

In this paper, we report a fiber-optic triaxial magnetic field sensor, based on Fiber Bragg Gratings (FBGs) integrated with giant magnetostrictive material, the Terfenol-D. The realized sensor has been designed and engineered for Magnetic Resonance Imaging (MRI) applications. A full magneto-optical characterization of the triaxial sensing probe has been carried out, providing the complex relationship among the FBGs wavelength shift and the applied magnetostatic field vector. Finally, the developed fiber optic sensors have been arranged in a sensor network composed of 20 triaxial sensors for mapping the magnetic field distribution in a MRI-room at a diagnostic center in Naples (SDN), equipped with Positron emission tomography/magnetic resonance (PET/MR) instrumentation. Experimental results reveal that the proposed sensor network can be efficiently used in MRI centers for performing quality assurance tests, paving the way for novel integrated tools to measure the magnetic dose accumulated day by day by MRI operators.

Review: Magnetic Fields of O-Type Stars

NASA Astrophysics Data System (ADS)

Wade, G. A.; MiMeS Collaboration

2015-04-01

Since 2002, strong, organized magnetic fields have been firmly detected at the surfaces of about 10 Galactic O-type stars. In this paper I will review the characteristics of the inferred fields of individual stars as well as the overall population. I will discuss the extension of the “magnetic desert,” first inferred among the A-type stars, to O stars up to 60 M⊙. I will discuss the interaction of the winds of the magnetic stars with the fields above their surfaces, generating complex “dynamical magnetosphere” structures detected in optical and UV lines, and in X-ray lines and continuum. Finally, I will discuss the detection of a small number of variable O stars in the LMC and SMC that exhibit spectral characteristics analogous to the known Galactic magnetic stars, and that almost certainly represent the first known examples of extragalactic magnetic stars.

Results from the GSFC fluxgate magnetometer on Pioneer 11

NASA Technical Reports Server (NTRS)

Acuna, M. H.; Ness, N. F.

1976-01-01

A high-field triaxial fluxgate magnetometer was mounted on Pioneer 11 to measure the main magnetic field of Jupiter. It is found that this planetary magnetic field is more complex than that indicated by the results of the Pioneer 10 vector helium magnetometer. At distances less than 3 Jupiter radii, the magnetic field is observed to increase more rapidly than an inverse-cubed distance law associated with any simple dipole model. Contributions from higher-order multipoles are significant, with the quadrupole and octupole being 24 and 21 percent of the dipole moment, respectively. Implications of the results for the study of trapped particles, planetary radio emission, and planetary interiors are discussed. Major conclusions are that the deviation of the main planetary magnetic field from a simple dipole leads to distortion of the L shells of the charged particles and to warping of the magnetic equator. Enhanced absorption effects associated with Amalthea and Io are predicted.

Magnetic reconnection in plasma under inertial confinement fusion conditions driven by heat flux effects in Ohm's law.

PubMed

Joglekar, A S; Thomas, A G R; Fox, W; Bhattacharjee, A

2014-03-14

In the interaction of high-power laser beams with solid density plasma there are a number of mechanisms that generate strong magnetic fields. Such fields subsequently inhibit or redirect electron flows, but can themselves be advected by heat fluxes, resulting in complex interplay between thermal transport and magnetic fields. We show that for heating by multiple laser spots reconnection of magnetic field lines can occur, mediated by these heat fluxes, using a fully implicit 2D Vlasov-Fokker-Planck code. Under such conditions, the reconnection rate is dictated by heat flows rather than Alfvènic flows. We find that this mechanism is only relevant in a high β plasma. However, the Hall parameter ωcτei can be large so that thermal transport is strongly modified by these magnetic fields, which can impact longer time scale temperature homogeneity and ion dynamics in the system.

Large-scale patterns formed by solar active regions during the ascending phase of cycle 21

NASA Astrophysics Data System (ADS)

Gaizauskas, V.; Harvey, K. L.; Harvey, J. W.; Zwaan, C.

1983-02-01

Synoptic maps of photospheric magnetic fields prepared at the Kitt Peak National Observatory are used in investigating large-scale patterns in the spatial and temporal distribution of solar active regions for 27 solar rotations between 1977 and 1979. The active regions are found to be distributed in 'complexes of activity' (Bumba and Howard, 1965). With the working definition of a complex of activity based on continuity and proximity of the constituent active regions, the phenomenology of complexes is explored. It is found that complexes of activity form within one month and that they are typically maintained for 3 to 6 solar rotations by fresh injections of magnetic flux. During the active lifetime of a complex of activity, the total magnetic flux in the complex remains steady to within a factor of 2. The magnetic polarities are closely balanced, and each complex rotates about the sun at its own special, constant rate. In certain cases, the complexes form two diverging branches.

Heating of the corona by magnetic singularities

NASA Technical Reports Server (NTRS)

Antiochos, Spiro K.

1990-01-01

Theoretical models of current-sheet formation and magnetic heating in the solar corona are examined analytically. The role of photospheric connectivity in determining the topology of the coronal magnetic field and its equilibrium properties is explored; nonequilibrium models of current-sheet formation (assuming an initially well connected field) are described; and particular attention is given to models with discontinuous connectivity, where magnetic singularities arise from smooth footpoint motions. It is shown that current sheets arise from connectivities in which the photospheric flux structure is complex, with three or more polarity regions and a magnetic null point within the corona.

Synergistic interactions between temporal coupling of complex light and magnetic pulses upon melanoma cell proliferation and planarian regeneration.

PubMed

Murugan, Nirosha J; Karbowski, Lukasz M; Persinger, Michael A

2017-01-01

Synergisms between a physiologically patterned magnetic field that is known to enhance planarian growth and suppress proliferation of malignant cells in culture and three light emitting diode (LED) generated visible wavelengths (blue, green, red) upon planarian regeneration and melanoma cell numbers were discerned. Five days of hourly exposures to either a physiologically patterned (2.5-5.0 μT) magnetic field, one of three wavelengths (3 kLux) or both treatments simultaneously indicated that red light (680 nm), blue light (470 nm) or the magnetic field significantly facilitated regeneration of planarian compared to sham field exposed planarian. Presentation of both light and magnetic field conditions enhanced the effect. Whereas the blue and red light diminished the growth of malignant (melanoma) cells, the effect was not as large as that produced by the magnetic field. Only the paired presentation of the blue light and magnetic field enhanced the suppression. On the other hand, the changes following green light (540 nm) exposure did not differ from the control condition and green light presented with the magnetic field eliminated its effects for both the planarian and melanoma cells. These results indicate specific colors affect positive adaptation that is similar to weak, physiologically patterned frequency modulated (8-24 Hz) magnetic fields and that the two forms of energy can synergistically summate or cancel.

The B-dot Earth Average Magnetic Field

NASA Technical Reports Server (NTRS)

Capo-Lugo, Pedro A.; Rakoczy, John; Sanders, Devon

2013-01-01

The average Earth's magnetic field is solved with complex mathematical models based on mean square integral. Depending on the selection of the Earth magnetic model, the average Earth's magnetic field can have different solutions. This paper presents a simple technique that takes advantage of the damping effects of the b-dot controller and is not dependent of the Earth magnetic model; but it is dependent on the magnetic torquers of the satellite which is not taken into consideration in the known mathematical models. Also the solution of this new technique can be implemented so easily that the flight software can be updated during flight, and the control system can have current gains for the magnetic torquers. Finally, this technique is verified and validated using flight data from a satellite that it has been in orbit for three years.

Ferroelastically and magnetically co-coupled resistive switching in Nd0.5Sr0.5MnO3/PMN-PT(011) multiferroic heterostructures

NASA Astrophysics Data System (ADS)

Zheng, Ming; Xu, Xiao-Ke; Ni, Hao; Qi, Ya-Ping; Li, Xiao-Min; Gao, Ju

2018-03-01

The phase separation, i.e., the competition between coexisting multi-phases, can be adjusted by external stimuli, such as magnetic field, electric field, current, light, and strain. Here, a multiferroic heterostructure composed of a charge-ordered Nd0.5Sr0.5MnO3 thin film and a ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal is fabricated to investigate the lattice strain and magnetic field co-control of phase separation in resistive switching. The stable and nonvolatile resistance tuning is realized at room temperature using the electric-field-induced reversible ferroelastic strain effect, which can be enhanced by 84% under the magnetic field. Moreover, the magnetoresistance can be effectively tuned by the electrically driven ferroelastic strain. These findings reveal that the ferroelastic strain and the magnetic field strongly correlate with each other and are mediated by phase separation. Our work provides an approach to design strain-engineered multifunctional memory devices based on complex oxides by introducing an extra magnetic field stimulus.

Field-induced magnetic phase transitions and metastable states in Tb3Ni

NASA Astrophysics Data System (ADS)

Gubkin, A. F.; Wu, L. S.; Nikitin, S. E.; Suslov, A. V.; Podlesnyak, A.; Prokhnenko, O.; Prokeš, K.; Yokaichiya, F.; Keller, L.; Baranov, N. V.

2018-04-01

In this paper we report the detailed study of magnetic phase diagrams, low-temperature magnetic structures, and the magnetic field effect on the electrical resistivity of the binary intermetallic compound Tb3Ni . The incommensurate magnetic structure of the spin-density-wave type described with magnetic superspace group P 1121/a 1'(a b 0 ) 0 s s and propagation vector kIC=[" close="]1/2 ,1/2 ,0 ]">0.506 ,0.299 ,0 was found to emerge just below Néel temperature TN=61 K. Further cooling below 58 K results in the appearance of multicomponent magnetic states: (i) a combination of k1=[1/2 ,0 ,0 ] below 48 K. An external magnetic field suppresses the complex low-temperature antiferromagnetic states and induces metamagnetic transitions towards a forced ferromagnetic state that are accompanied by a substantial magnetoresistance effect due to the magnetic superzone effect. The forced ferromagnetic state induced after application of an external magnetic field along the b and c crystallographic axes was found to be irreversible below 3 and 8 K, respectively.

The alignment of molecular cloud magnetic fields with the spiral arms in M33.

PubMed

Li, Hua-bai; Henning, Thomas

2011-11-16

The formation of molecular clouds, which serve as stellar nurseries in galaxies, is poorly understood. A class of cloud formation models suggests that a large-scale galactic magnetic field is irrelevant at the scale of individual clouds, because the turbulence and rotation of a cloud may randomize the orientation of its magnetic field. Alternatively, galactic fields could be strong enough to impose their direction upon individual clouds, thereby regulating cloud accumulation and fragmentation, and affecting the rate and efficiency of star formation. Our location in the disk of the Galaxy makes an assessment of the situation difficult. Here we report observations of the magnetic field orientation of six giant molecular cloud complexes in the nearby, almost face-on, galaxy M33. The fields are aligned with the spiral arms, suggesting that the large-scale field in M33 anchors the clouds. ©2011 Macmillan Publishers Limited. All rights reserved

Nanoscale magnetic characterization of tunneling magnetoresistance spin valve head by electron holography.

PubMed

Park, Hyun Soon; Hirata, Kei; Yanagisawa, Keiichi; Ishida, Yoichi; Matsuda, Tsuyoshi; Shindo, Daisuke; Tonomura, Akira

2012-12-07

Nanostructured magnetic materials play an important role in increasing miniaturized devices. For the studies of their magnetic properties and behaviors, nanoscale imaging of magnetic field is indispensible. Here, using electron holography, the magnetization distribution of a TMR spin valve head of commercial design is investigated without and with a magnetic field applied. Characterized is the magnetic flux distribution in complex hetero-nanostructures by averaging the phase images and separating their component magnetic vectors and electric potentials. The magnetic flux densities of the NiFe (shield and 5 nm-free layers) and the CoPt (20 nm-bias layer) are estimated to be 1.0 T and 0.9 T, respectively. The changes in the magnetization distribution of the shield, bias, and free layers are visualized in situ for an applied field of 14 kOe. This study demonstrates the promise of electron holography for characterizing the magnetic properties of hetero-interfaces, nanostructures, and catalysts. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Exploring the Influence of Diamagnetic Ions on the Mechanism of Magnetization Relaxation in {CoIII2LnIII2} (Ln = Dy, Tb, Ho) "Butterfly" Complexes.

PubMed

Vignesh, Kuduva R; Langley, Stuart K; Murray, Keith S; Rajaraman, Gopalan

2017-03-06

The synthesis and magnetic and theoretical studies of three isostructural heterometallic [Co III 2 Ln III 2 (μ 3 -OH) 2 (o-tol) 4 (mdea) 2 (NO 3 ) 2 ] (Ln = Dy (1), Tb (2), Ho (3)) "butterfly" complexes are reported (o-tol = o-toluate, (mdea) 2- = doubly deprotonated N-methyldiethanolamine). The Co III ions are diamagnetic in these complexes. Analysis of the dc magnetic susceptibility measurements reveal antiferromagnetic exchange coupling between the two Ln III ions for all three complexes. ac magnetic susceptibility measurements reveal single-molecule magnet (SMM) behavior for complex 1, in the absence of an external magnetic field, with an anisotropy barrier U eff of 81.2 cm -1 , while complexes 2 and 3 exhibit field induced SMM behavior, with a U eff value of 34.2 cm -1 for 2. The barrier height for 3 could not be quantified. To understand the experimental observations, we performed DFT and ab initio CASSCF+RASSI-SO calculations to probe the single-ion properties and the nature and magnitude of the Ln III -Ln III magnetic coupling and to develop an understanding of the role the diamagnetic Co III ion plays in the magnetization relaxation. The calculations were able to rationalize the experimental relaxation data for all complexes and strongly suggest that the Co III ion is integral to the observation of SMM behavior in these systems. Thus, we explored further the effect that the diamagnetic Co III ions have on the magnetization blocking of 1. We did this by modeling a dinuclear {Dy III 2 } complex (1a), with the removal of the diamagnetic ions, and three complexes of the types {K I 2 Dy III 2 } (1b), {Zn II 2 Dy III 2 } (1c), and {Ti IV 2 Dy III 2 } (1d), each containing a different diamagnetic ion. We found that the presence of the diamagnetic ions results in larger negative charges on the bridging hydroxides (1b > 1c > 1 > 1d), in comparison to 1a (no diamagnetic ion), which reduces quantum tunneling of magnetization effects, allowing for more desirable SMM characteristics. The results indicate very strong dependence of diamagnetic ions in the magnetization blocking and the magnitude of the energy barriers. Here we propose a synthetic strategy to enhance the energy barrier in lanthanide-based SMMs by incorporating s- and d-block diamagnetic ions. The presented strategy is likely to have implications beyond the single-molecule magnets studied here.

Shaping magnetic fields to direct therapy to ears and eyes.

PubMed

Shapiro, B; Kulkarni, S; Nacev, A; Sarwar, A; Preciado, D; Depireux, D A

2014-07-11

Magnetic fields have the potential to noninvasively direct and focus therapy to disease targets. External magnets can apply forces on drug-coated magnetic nanoparticles, or on living cells that contain particles, and can be used to manipulate them in vivo. Significant progress has been made in developing and testing safe and therapeutic magnetic constructs that can be manipulated by magnetic fields. However, we do not yet have the magnet systems that can then direct those constructs to the right places, in vivo, over human patient distances. We do not yet know where to put the external magnets, how to shape them, or when to turn them on and off to direct particles or magnetized cells-in blood, through tissue, and across barriers-to disease locations. In this article, we consider ear and eye disease targets. Ear and eye targets are too deep and complex to be targeted by a single external magnet, but they are shallow enough that a combination of magnets may be able to direct therapy to them. We focus on how magnetic fields should be shaped (in space and time) to direct magnetic constructs to ear and eye targets.

Picturing the Sun’s Magnetic Field

NASA Image and Video Library

2017-12-08

This illustration lays a depiction of the sun's magnetic fields over an image captured by NASA’s Solar Dynamics Observatory on March 12, 2016. The complex overlay of lines can teach scientists about the ways the sun's magnetism changes in response to the constant movement on and inside the sun. Note how the magnetic fields are densest near the bright spots visible on the sun – which are magnetically strong active regions – and many of the field lines link one active region to another. This magnetic map was created using the PFSS – Potential Field Source Surface – model, a model of the magnetic field in the sun’s atmosphere based on magnetic measurements of the solar surface. The underlying image was taken in extreme ultraviolet wavelengths of 171 angstroms. This type of light is invisible to our eyes, but is colorized here in gold. Credits: NASA/SDO/AIA/LMSAL NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Robust spin correlations at high magnetic fields in the harmonic honeycomb iridates

DOE PAGES

Modic, K. A.; Ramshaw, Brad J.; Betts, J. B.; ...

2017-08-01

Here, the complex antiferromagnetic orders observed in the honeycomb iridates are a double-edged sword in the search for a quantum spin-liquid: both attesting that the magnetic interactions provide many of the necessary ingredients, while simultaneously impeding access. Focus has naturally been drawn to the unusual magnetic orders that hint at the underlying spin correlations. However, the study of any particular broken symmetry state generally provides little clue about the possibility of other nearby ground states. Here we use magnetic fields approaching 100 Tesla to reveal the extent of the spin correlations in γ-lithium iridate. We find that a small componentmore » of field along the magnetic easy-axis melts long-range order, revealing a bistable, strongly correlated spin state. Far from the usual destruction of antiferromagnetism via spin polarization, the high-field state possesses only a small fraction of the total iridium moment, without evidence for long-range order up to the highest attainable magnetic fields.« less

Mapping magnetoelastic response of terfenol-D ring structure

NASA Astrophysics Data System (ADS)

Youssef, George; Newacheck, Scott; Lopez, Mario

2017-05-01

The magneto-elastic response of a Terfenol-D (Tb.3Dy.7Fe1.92) ring has been experimentally investigated and analyzed. Ring structures give rise to complex behavior based on the interaction of the magnetic field with the material, which is further compounded with anisotropies associated with mechanical and magnetic properties. Discrete strain measurements were used to construct magnetostriction maps, which are used to elucidate the non-uniformity of the strain distribution due to geometrical factors and magnetic field interactions, namely, magnetic shielding and stable onion state in the ring structure.

What we think we know and do not know about solar flares

NASA Technical Reports Server (NTRS)

Parker, E. N.

1973-01-01

Solar-terrestrial relations begin in the convective zone of the sun. A combination of nonuniform rotation and cyclonic convection generates magnetic fields in migratory waves, which can account for the observed 22-year solar magnetic cycle. The magnetic fields are the active agent in creating the active magnetic regions, with sunspots, prominences, and flares. The present status of knowledge regarding the solar flare phenomenon is reviewed, giving attention to the extraordinary complexity of the solar flare and the broad spectrum of theoretical ideas that have been generated to meet the challenge.

2D Potential Theory using Complex Algebra: New Perspectives for Interpretation of Marine Magnetic Anomaly

NASA Astrophysics Data System (ADS)

Le Maire, P.; Munschy, M.

2017-12-01

Interpretation of marine magnetic anomalies enable to perform accurate global kinematic models. Several methods have been proposed to compute the paleo-latitude of the oceanic crust as its formation. A model of the Earth's magnetic field is used to determine a relationship between the apparent inclination of the magnetization and the paleo-latitude. Usually, the estimation of the apparent inclination is qualitative, with the fit between magnetic data and forward models. We propose to apply a new method using complex algebra to obtain the apparent inclination of the magnetization of the oceanic crust. For two dimensional bodies, we rewrite Talwani's equations using complex algebra; the corresponding complex function of the complex variable, called CMA (complex magnetic anomaly) is easier to use for forward modelling and inversion of the magnetic data. This complex equation allows to visualize the data in the complex plane (Argand diagram) and offers a new way to interpret data (curves to the right of the figure (B), while the curves to the left represent the standard display of magnetic anomalies (A) for the model displayed (C) at the bottom of the figure). In the complex plane, the effect of the apparent inclination is to rotate the curves, while on the standard display the evolution of the shape of the anomaly is more complicated (figure). This innovative method gives the opportunity to study a set of magnetic profiles (provided by the Geological Survey of Norway) acquired in the Norwegian Sea, near the Jan Mayen fracture zone. In this area, the age of the oceanic crust ranges from 40 to 55 Ma and the apparent inclination of the magnetization is computed.

Non-London electrodynamics in a multiband London model: Anisotropy-induced nonlocalities and multiple magnetic field penetration lengths

NASA Astrophysics Data System (ADS)

Silaev, Mihail; Winyard, Thomas; Babaev, Egor

2018-05-01

The London model describes strongly type-2 superconductors as massive vector field theories, where the magnetic field decays exponentially at the length scale of the London penetration length. This also holds for isotropic multiband extensions, where the presence of multiple bands merely renormalizes the London penetration length. We show that, by contrast, the magnetic properties of anisotropic multiband London models are not this simple, and the anisotropy leads to the interband phase differences becoming coupled to the magnetic field. This results in the magnetic field in such systems having N +1 penetration lengths, where N is the number of field components or bands. That is, in a given direction, the magnetic field decay is described by N +1 modes with different amplitudes and different decay length scales. For certain anisotropies we obtain magnetic modes with complex masses. That means that magnetic field decay is not described by a monotonic exponential increment set by a real penetration length but instead is oscillating. Some of the penetration lengths are shown to diverge away from the superconducting phase transition when the mass of the phase-difference mode vanishes. Finally the anisotropy-driven hybridization of the London mode with the Leggett modes can provide an effectively nonlocal magnetic response in the nominally local London model. Focusing on the two-component model, we discuss the magnetic field inversion that results from the effective nonlocality, both near the surface of the superconductor and around vortices. In the regime where the magnetic field decay becomes nonmonotonic, the multiband London superconductor is shown to form weakly-bound states of vortices.

VLA OH Zeeman Observations of the NGC 6334 Complex Source A

NASA Astrophysics Data System (ADS)

Mayo, E. A.; Sarma, A. P.; Troland, T. H.; Abel, N. P.

2004-12-01

We present a detailed analysis of the NGC 6334 complex source A, a compact continuum source in the SW region of the complex. Our intent is to determine the significance of the magnetic field in the support of the surrounding molecular cloud against gravitational collapse. We have performed OH 1665 and 1667 MHz observations taken with the Very Large Array in the BnA configuration and combined these data with the lower resolution CnB data of Sarma et al. (2000). These observations reveal magnetic fields with values of the order of 350 μ G toward source A, with maximum fields reaching 500 μ G. We have also theoretically modeled the molecular cloud surrounding source A using Cloudy, with the constraints to the model based on observation. This model provides significant information on the density of H2 through the cloud and also the relative density of H2 to OH which is important to our analysis of the region. We will combine the knowledge gained through the Cloudy modeling with Virial estimates to determine the significance of the magnetic field to the dynamics and evolution of source A.

High field hyperpolarization-EXSY experiment for fast determination of dissociation rates in SABRE complexes.

PubMed

Hermkens, Niels K J; Feiters, Martin C; Rutjes, Floris P J T; Wijmenga, Sybren S; Tessari, Marco

2017-03-01

SABRE (Signal Amplification By Reversible Exchange) is a nuclear spin hyperpolarization technique based on the reversible concurrent binding of small molecules and para-hydrogen (p-H 2 ) to an iridium metal complex in solution. At low magnetic field, spontaneous conversion of p-H 2 spin order to enhanced longitudinal magnetization of the nuclear spins of the other ligands occurs. Subsequent complex dissociation results in hyperpolarized substrate molecules in solution. The lifetime of this complex plays a crucial role in attained SABRE NMR signal enhancements. Depending on the ligands, vastly different dissociation rates have been previously measured using EXSY or selective inversion experiments. However, both these approaches are generally time-consuming due to the long recycle delays (up to 2min) necessary to reach thermal equilibrium for the nuclear spins of interest. In the cases of dilute solutions, signal averaging aggravates the problem, further extending the experimental time. Here, a new approach is proposed based on coherent hyperpolarization transfer to substrate protons in asymmetric complexes at high magnetic field. We have previously shown that such asymmetric complexes are important for application of SABRE to dilute substrates. Our results demonstrate that a series of high sensitivity EXSY spectra can be collected in a short experimental time thanks to the NMR signal enhancement and much shorter recycle delay. Copyright © 2017 Elsevier Inc. All rights reserved.

Space-weather Parameters for 1,000 Active Regions Observed by SDO/HMI

NASA Astrophysics Data System (ADS)

Bobra, M.; Liu, Y.; Hoeksema, J. T.; Sun, X.

2013-12-01

We present statistical studies of several space-weather parameters, derived from observations of the photospheric vector magnetic field by the Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics Observatory, for a thousand active regions. Each active region has been observed every twelve minutes during the entirety of its disk passage. Some of these parameters, such as energy density and shear angle, indicate the deviation of the photospheric magnetic field from that of a potential field. Other parameters include flux, helicity, field gradients, polarity inversion line properties, and measures of complexity. We show that some of these parameters are useful for event prediction.

Activity and magnetic field structure of the Sun-like planet-hosting star HD 1237

NASA Astrophysics Data System (ADS)

Alvarado-Gómez, J. D.; Hussain, G. A. J.; Grunhut, J.; Fares, R.; Donati, J.-F.; Alecian, E.; Kochukhov, O.; Oksala, M.; Morin, J.; Redfield, S.; Cohen, O.; Drake, J. J.; Jardine, M.; Matt, S.; Petit, P.; Walter, F. M.

2015-10-01

We analyse the magnetic activity characteristics of the planet-hosting Sun-like star, HD 1237, using HARPS spectro-polarimetric time-series data. We find evidence of rotational modulation of the magnetic longitudinal field measurements that is consistent with our ZDI analysis with a period of 7 days. We investigate the effect of customising the LSD mask to the line depths of the observed spectrum and find that it has a minimal effect on the shape of the extracted Stokes V profile but does result in a small increase in the S/N (~7%). We find that using a Milne-Eddington solution to describe the local line profile provides a better fit to the LSD profiles in this slowly rotating star, which also affects the recovered ZDI field distribution. We also introduce a fit-stopping criterion based on the information content (entropy) of the ZDI map solution set. The recovered magnetic field maps show a strong (+90 G) ring-like azimuthal field distribution and a complex radial field dominating at mid latitudes (~45 degrees). Similar magnetic field maps are recovered from data acquired five months apart. Future work will investigate how this surface magnetic field distribution affeccts the coronal magnetic field and extended environment around this planet-hosting star.

Magnetic information affects the stellar orientation of young bird migrants

NASA Astrophysics Data System (ADS)

Weindler, Peter; Wiltschko, Roswitha; Wiltschko, Wolfgang

1996-09-01

WHEN young birds leave on their first migration, they are guided by innate information about their direction of migration. It is generally assumed that this direction is represented twice, namely with respect to celestial rotation and with respect to the Earth's magnetic field1,2. The interactions between the two cue systems have been analysed by exposing hand-raised young birds during the premigratory period to cue-conflict situations, in which celestial rotation and the magnetic field provided different information. Celestial rotation altered the course with respect to the magnetic field3-7, whereas conflicting magnetic information did not seem to affect the course with respect to the stars8,9. Celestial information thus seemed to dominate over magnetic information. Here we report that the interaction between the two cue systems is far more complex than this. Celestial rotation alone seems to provide only a tendency to move away from its centre (towards geographical south), which is then modified by information from the magnetic field to establish the distinctive, population-specific migratory direction.

Spectroscopic and Magnetic Investigations of Rhenium(i)chlorine(carbon MONOXIDE)(3)(ALPHA, - Complexes and Group (1B, 8B) Bimetallic Complexes.

NASA Astrophysics Data System (ADS)

Striplin, Durwin Ray

Complexes with the generic formula, Re(I)Cl(CO) _3(alpha,alpha-diimine), where alpha,alpha-diimine = 2,2^'-bipyridine, 1,10 -phenanthroline, or methyl-substituted analogs, were subjected to detailed optical investigations in the 77-4 K range, both in rigid glasses and in PMMA plastics. Excitation spectra, absorption spectra, and decay kinetics of the phosphorescing manifolds were complemented by detailed measurements of polarization ratios to arrive at a coherent picture of the emitting manifolds. Symmetry assignments and energy orderings of the ^3MLCT (metal-to-ligand charge transfer) spin sublevels were made. Analogous assignments for the ^3MLCT spin -sublevels of Ru(alpha, alpha -diimine)_3^{2+} and Os(alpha,alpha-diimine) _{3}^{2+} ions are implied by this analysis. Increases in luminescence decay rates and emission intensities with increasing external magnetic field strength were observed at 4 K. The decay rates were found to be non-quadratic with respect to magnetic field strength. A simple parametric model that includes spin-orbit coupling and a magnetic field perturbation was developed to describe the MLCT excited states. The energies, symmetry assignments, and magnetic field mixing of the ^3MLCT states were rationalized by the model. Fluorescence, phosphorescence, and excitation spectra were measured on a series of mu -bridged bis(diphenylphosphinomethane) homo- and heterobimetallic compounds of Rh(I), Ir(I), Pt(II), and Au(I). These results were augmented with polarization ratios obtained at 77 K and detailed studies of the temperature dependence of the phosphorescence in the 77-4 K range. The triplet manifold is split by spin-orbit coupling into a forbidden state lying lowest in energy followed by a quasi-degenerate pair lying a few wavenumbers higher that decays two orders of magnitude faster. A quadratic dependence of the decay rate on magnetic field strength was recorded at 4 K for ail complexes. The results are consistent with a rm d_{sigma*}to p_sigma orbital promotion, and the direction of charge-transfer for heterobimetallic complexes was unambiguously assigned. Electronic structural models based on D_{rm 4h}, D_{rm 2h}, and C _{rm 2v} micro-symmetries about the axial chromophore were employed to make explicit symmetry assignments of the excited states.

Magnetic hyperthermia with hard-magnetic nanoparticles

NASA Astrophysics Data System (ADS)

Kashevsky, Bronislav E.; Kashevsky, Sergey B.; Korenkov, Victor S.; Istomin, Yuri P.; Terpinskaya, Tatyana I.; Ulashchik, Vladimir S.

2015-04-01

Recent clinical trials of magnetic hyperthermia have proved, and even hardened, the Ankinson-Brezovich restriction as upon magnetic field conditions applicable to any site of human body. Subject to this restriction, which is harshly violated in numerous laboratory and small animal studies, magnetic hyperthermia can relay on rather moderate heat source, so that optimization of the whole hyperthermia system remains, after all, the basic problem predetermining its clinical perspectives. We present short account of our complex (theoretical, laboratory and small animal) studies to demonstrate that such perspectives should be related with the hyperthermia system based on hard-magnetic (Stoner-Wohlfarth type) nanoparticles and strong low-frequency fields rather than with superparamagnetic (Brownian or Neél) nanoparticles and weak high-frequency fields. This conclusion is backed by an analytical evaluation of the maximum absorption rates possible under the field restriction in the ideal hard-magnetic (Stoner-Wohlarth) and the ideal superparamagnetic (single relaxation time) systems, by theoretical and experimental studies of the dynamic magnetic hysteresis in suspensions of movable hard-magnetic particles, by producing nanoparticles with adjusted coercivity and suspensions of such particles capable of effective energy absorption and intratumoral penetration, and finally, by successful treatment of a mice model tumor under field conditions acceptable for whole human body.

Influence of the interaction between the inter- and intragranular magnetic responses in the analysis of the ac susceptibility of a granular FeSe0.5Te0.5 superconductor

NASA Astrophysics Data System (ADS)

Mancusi, D.; Polichetti, M.; Cimberle, M. R.; Pace, S.

2015-09-01

The temperature-dependent fundamental ac susceptibility of a granular superconductor in the absence of dc fields has been analyzed by developing a phenomenological model for effective magnetic fields, taking into account the influence of the magnetic interaction between the intergranular and the intragranular magnetizations due to demagnetizing effects. For this purpose a policrystal Fe-based superconductor FeSe0.5Te0.5 sample has been studied. By the frequency dependence of the peaks of the temperature-dependent imaginary part of the fundamental complex susceptibility, the dependence on temperature of the characteristic times both for intergranular and intragranular relaxations of magnetic flux are derived, and the corresponding relaxation processes due to combinations of the flux creep, the flux flow and the thermally activated flux flow regimes are identified on the basis of the effective magnetic fields both at the sample surface and at the grains’ surfaces. Such characteristic times, through the Havriliak-Negami function, determine the temperature and the frequency dependences of the complex susceptibility. The comparison of the numerically obtained curves with the experimental ones confirms the relevance, for identifying the intergranular and intragranular contributions to the ac magnetic response and the corresponding flux dynamical regimes, of the interaction between the intergranular and intragranular magnetizations due to demagnetizing effects.

Magnetic field-assisted gene delivery: achievements and therapeutic potential.

PubMed

Schwerdt, Jose I; Goya, Gerardo F; Calatayud, M Pilar; Hereñú, Claudia B; Reggiani, Paula C; Goya, Rodolfo G

2012-04-01

The discovery in the early 2000's that magnetic nanoparticles (MNPs) complexed to nonviral or viral vectors can, in the presence of an external magnetic field, greatly enhance gene transfer into cells has raised much interest. This technique, called magnetofection, was initially developed mainly to improve gene transfer in cell cultures, a simpler and more easily controllable scenario than in vivo models. These studies provided evidence for some unique capabilities of magnetofection. Progressively, the interest in magnetofection expanded to its application in animal models and led to the association of this technique with another technology, magnetic drug targeting (MDT). This combination offers the possibility to develop more efficient and less invasive gene therapy strategies for a number of major pathologies like cancer, neurodegeneration and myocardial infarction. The goal of MDT is to concentrate MNPs functionalized with therapeutic drugs, in target areas of the body by means of properly focused external magnetic fields. The availability of stable, nontoxic MNP-gene vector complexes now offers the opportunity to develop magnetic gene targeting (MGT), a variant of MDT in which the gene coding for a therapeutic molecule, rather than the molecule itself, is delivered to a therapeutic target area in the body. This article will first outline the principle of magnetofection, subsequently describing the properties of the magnetic fields and MNPs used in this technique. Next, it will review the results achieved by magnetofection in cell cultures. Last, the potential of MGT for implementing minimally invasive gene therapy will be discussed.

Slow magnetic relaxation in a dimeric Mn2Ca2 complex enabled by the large Mn(iii) rhombicity.

PubMed

Arauzo, Ana; Bartolomé, Elena; Benniston, Andrew C; Melnic, Silvia; Shova, Sergiu; Luzón, Javier; Alonso, Pablo J; Barra, Anne-Laure; Bartolomé, Juan

2017-01-17

In this paper we present the characterization of a complex with the formula [Mn 2 Ca 2 (hmp) 6 (H 2 O) 4 (CH 3 CN) 2 ](ClO 4 ) 4 (1), where hmp-H = 2-(hydroxymethyl)pyridine. Compound 1 crystallizes in the monoclinic space group C2/c with the cation lying on an inversion centre. Static magnetic susceptibility, magnetization and heat capacity measurements reflect a unique Mn(iii) valence state, and single-ion ligand field parameters with remarkable large rhombic distortion (D/k B = -6.4 K, E/k B = -2.1 K), in good agreement with the high-field electron paramagnetic resonance experiments. At low temperature Mn 2 Ca 2 cluster behaves as a system of ferromagnetically coupled (J/k B = 1.1 K) Mn dimers with a S T = 4 and m T = ±4 ground state doublet. Frequency dependent ac susceptibility measurements reveal the slow magnetic relaxation characteristic of a single molecule magnet (SMM) below T = 4 K. At zero magnetic field, an Orbach-type spin relaxation process (τ ∼ 10 -5 s) with an activation energy E a = 5.6 K is observed, enabled by the large E/D rhombicity of the Mn(iii) ions. Upon the application of a magnetic field, a second, very slow process (τ ∼ 0.2 s) is observed, attributed to a direct relaxation mechanism with enhanced relaxation time owing to the phonon bottleneck effect.

LIGHT-SABRE enables efficient in-magnet catalytic hyperpolarization

NASA Astrophysics Data System (ADS)

Theis, Thomas; Truong, Milton; Coffey, Aaron M.; Chekmenev, Eduard Y.; Warren, Warren S.

2014-11-01

Nuclear spin hyperpolarization overcomes the sensitivity limitations of traditional NMR and MRI, but the most general method demonstrated to date (dynamic nuclear polarization) has significant limitations in scalability, cost, and complex apparatus design. As an alternative, signal amplification by reversible exchange (SABRE) of parahydrogen on transition metal catalysts can hyperpolarize a variety of substrates, but to date this scheme has required transfer of the sample to low magnetic field or very strong RF irradiation. Here we demonstrate "Low-Irradiation Generation of High Tesla-SABRE" (LIGHT-SABRE) which works with simple pulse sequences and low power deposition; it should be usable at any magnetic field and for hyperpolarization of many different nuclei. This approach could drastically reduce the cost and complexity of producing hyperpolarized molecules.

Understanding magnetotransport signatures in networks of connected permalloy nanowires

NASA Astrophysics Data System (ADS)

Le, B. L.; Park, J.; Sklenar, J.; Chern, G.-W.; Nisoli, C.; Watts, J. D.; Manno, M.; Rench, D. W.; Samarth, N.; Leighton, C.; Schiffer, P.

2017-02-01

The change in electrical resistance associated with the application of an external magnetic field is known as the magnetoresistance (MR). The measured MR is quite complex in the class of connected networks of single-domain ferromagnetic nanowires, known as "artificial spin ice," due to the geometrically induced collective behavior of the nanowire moments. We have conducted a thorough experimental study of the MR of a connected honeycomb artificial spin ice, and we present a simulation methodology for understanding the detailed behavior of this complex correlated magnetic system. Our results demonstrate that the behavior, even at low magnetic fields, can be well described only by including significant contributions from the vertices at which the legs meet, opening the door to new geometrically induced MR phenomena.

MAGNETIC FLUX TUBE INTERCHANGE AT THE HELIOPAUSE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Florinski, V., E-mail: vaf0001@uah.edu

2015-11-01

The magnetic field measured by Voyager 1 prior to its heliocliff encounter on 2012.65 showed an unexpectedly complex transition from the primarily azimuthal inner-heliosheath field to the draped interstellar field tilted by some 20° to the nominal azimuthal direction. Most prominent were two regions of enhanced magnetic field strength depleted in energetic charged particles of heliospheric origin. These regions were interpreted as magnetic flux tubes connected to the outer heliosheath that provided a path for the particles to escape. Despite large increases in strength, the field’s direction did not change appreciably at the boundaries of these flux tubes. Rather, themore » field’s direction changed gradually over several months prior to the heliocliff crossing. It is shown theoretically that the heliopause, as a pressure equilibrium layer, can become unstable to interchange of magnetic fields between the inner and the outer heliosheaths. The curvature of magnetic field lines and the anti-sunward gradient in plasma kinetic pressure provide conditions favorable for an interchange. Magnetic shear between the heliosheath and the interstellar fields reduces the growth rates, but does not fully stabilize the heliopause against perturbations propagating in the latitudinal direction. The instability could create a transition layer permeated by magnetic flux tubes, oriented parallel to each other and alternately connected to the heliosheath or the interstellar regions.« less

Large Solar Flares and Sheared Magnetic Field Configuration

NASA Technical Reports Server (NTRS)

Choudhary, Debi Prasad

2001-01-01

This Comment gives additional information about the nature of flaring locations on the Sun described in the article "Sun unleashes Halloween storm", by R. E. Lopez, et al. What causes the large explosions from solar active regions that unleash huge magnetic storms and adverse space weather? It is now beyond doubt that the magnetic field in solar active regions harbors free energy that is released during these events. Direct measurements of the longitudinal and transverse components of active region magnetic fields with the vector magnetograph at NASA Marshall Space Flight Center (MSFC), taken on a regular basis for the last 30 years, have found key signatures of the locations of powerful flares. A vector magnetograph detects and measures the magnetic shear, which is the deviation of the observed transverse magnetic field direction from the potential field. The sheared locations possess abundant free magnetic energy for solar flares. In addition to active region NOAA 10486, the one that produced the largest flares last October, the NASA/MSFC vector magnetograph has observed several other such complex super active regions, including NOAA 6555 and 6659.

Electric Current Filamentation Induced by 3D Plasma Flows in the Solar Corona

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nickeler, Dieter H.; Karlický, Marian; Kraus, Michaela

Many magnetic structures in the solar atmosphere evolve rather slowly, so they can be assumed as (quasi-)static or (quasi-)stationary and represented via magnetohydrostatic (MHS) or stationary magnetohydrodynamic (MHD) equilibria, respectively. While exact 3D solutions would be desired, they are extremely difficult to find in stationary MHD. We construct solutions with magnetic and flow vector fields that have three components depending on all three coordinates. We show that the noncanonical transformation method produces quasi-3D solutions of stationary MHD by mapping 2D or 2.5D MHS equilibria to corresponding stationary MHD states, that is, states that display the same field-line structure as themore » original MHS equilibria. These stationary MHD states exist on magnetic flux surfaces of the original 2D MHS states. Although the flux surfaces and therefore also the equilibria have a 2D character, these stationary MHD states depend on all three coordinates and display highly complex currents. The existence of geometrically complex 3D currents within symmetric field-line structures provides the basis for efficient dissipation of the magnetic energy in the solar corona by ohmic heating. We also discuss the possibility of maintaining an important subset of nonlinear MHS states, namely force-free fields, by stationary flows. We find that force-free fields with nonlinear flows only arise under severe restrictions of the field-line geometry and of the magnetic flux density distribution.« less

On the feasibility of real-time mapping of the geoelectric field across North America

USGS Publications Warehouse

Love, Jeffrey J.; Rigler, E. Joshua; Kelbert, Anna; Finn, Carol A.; Bedrosian, Paul A.; Balch, Christopher C.

2018-06-08

A review is given of the present feasibility for accurately mapping geoelectric fields across North America in near-realtime by modeling geomagnetic monitoring and magnetotelluric survey data. Should this capability be successfully developed, it could inform utility companies of magnetic-storm interference on electric-power-grid systems. That real-time mapping of geoelectric fields is a challenge is reflective of (1) the spatiotemporal complexity of geomagnetic variation, especially during magnetic storms, (2) the sparse distribution of ground-based geomagnetic monitoring stations that report data in realtime, (3) the spatial complexity of three-dimensional solid-Earth impedance, and (4) the geographically incomplete state of continental-scale magnetotelluric surveys.

Resonant Magnetic Field Sensors Based On MEMS Technology.

PubMed

Herrera-May, Agustín L; Aguilera-Cortés, Luz A; García-Ramírez, Pedro J; Manjarrez, Elías

2009-01-01

Microelectromechanical systems (MEMS) technology allows the integration of magnetic field sensors with electronic components, which presents important advantages such as small size, light weight, minimum power consumption, low cost, better sensitivity and high resolution. We present a discussion and review of resonant magnetic field sensors based on MEMS technology. In practice, these sensors exploit the Lorentz force in order to detect external magnetic fields through the displacement of resonant structures, which are measured with optical, capacitive, and piezoresistive sensing techniques. From these, the optical sensing presents immunity to electromagnetic interference (EMI) and reduces the read-out electronic complexity. Moreover, piezoresistive sensing requires an easy fabrication process as well as a standard packaging. A description of the operation mechanisms, advantages and drawbacks of each sensor is considered. MEMS magnetic field sensors are a potential alternative for numerous applications, including the automotive industry, military, medical, telecommunications, oceanographic, spatial, and environment science. In addition, future markets will need the development of several sensors on a single chip for measuring different parameters such as the magnetic field, pressure, temperature and acceleration.

Resonant Magnetic Field Sensors Based On MEMS Technology

PubMed Central

Herrera-May, Agustín L.; Aguilera-Cortés, Luz A.; García-Ramírez, Pedro J.; Manjarrez, Elías

2009-01-01

Microelectromechanical systems (MEMS) technology allows the integration of magnetic field sensors with electronic components, which presents important advantages such as small size, light weight, minimum power consumption, low cost, better sensitivity and high resolution. We present a discussion and review of resonant magnetic field sensors based on MEMS technology. In practice, these sensors exploit the Lorentz force in order to detect external magnetic fields through the displacement of resonant structures, which are measured with optical, capacitive, and piezoresistive sensing techniques. From these, the optical sensing presents immunity to electromagnetic interference (EMI) and reduces the read-out electronic complexity. Moreover, piezoresistive sensing requires an easy fabrication process as well as a standard packaging. A description of the operation mechanisms, advantages and drawbacks of each sensor is considered. MEMS magnetic field sensors are a potential alternative for numerous applications, including the automotive industry, military, medical, telecommunications, oceanographic, spatial, and environment science. In addition, future markets will need the development of several sensors on a single chip for measuring different parameters such as the magnetic field, pressure, temperature and acceleration. PMID:22408480

THE EFFECT OF RECONNECTION ON THE STRUCTURE OF THE SUN’S OPEN–CLOSED FLUX BOUNDARY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pontin, D. I.; Wyper, P. F., E-mail: dpontin@maths.dundee.ac.uk, E-mail: peter.f.wyper@nasa.gov

2015-05-20

Global magnetic field extrapolations are now revealing the huge complexity of the Sun's corona, and in particular the structure of the boundary between open and closed magnetic flux. Moreover, recent developments indicate that magnetic reconnection in the corona likely occurs in highly fragmented current layers, and that this typically leads to a dramatic increase in the topological complexity beyond that of the equilibrium field. In this paper we use static models to investigate the consequences of reconnection at the open–closed flux boundary (“interchange reconnection”) in a fragmented current layer. We demonstrate that it leads to efficient mixing of magnetic fluxmore » (and therefore plasma) from open and closed field regions. This corresponds to an increase in the length and complexity of the open–closed boundary. Thus, whenever reconnection occurs at a null point or separator of this open–closed boundary, the associated separatrix arc of the so-called S-web in the high corona becomes not a single line but a band of finite thickness within which the open–closed boundary is highly structured. This has significant implications for the acceleration of the slow solar wind, for which the interaction of open and closed field is thought to be important, and may also explain the coronal origins of certain solar energetic particles. The topological structures examined contain magnetic null points, separatrices and separators, and include a model for a pseudo-streamer. The potential for understanding both the large scale morphology and fine structure observed in flare ribbons associated with coronal nulls is also discussed.« less

Large-scale Organized Magnetic Fields in O, B and A Stars

NASA Astrophysics Data System (ADS)

Mathys, G.

2009-06-01

The status of our current knowledge of magnetic fields in stars of spectral types ranging from early F to O is reviewed. Fields with large-scale organised structure have now been detected and measured throughout this range. These fields are consistent with the oblique rotator model. In early F to late B stars, their occurrence is restricted to the subgroup of the Ap stars, which have the best studied fields among the early-type stars. Presence of fields with more complex topologies in other A and late B stars has been suggested, but is not firmly established. Magnetic fields have not been studied in a sufficient number of OB stars yet so as to establish whether they occur in all or only in some subset of these stars.

Many-body calculations of low energy eigenstates in magnetic and periodic systems with self healing diffusion Monte Carlo: steps beyond the fixed-phase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reboredo, Fernando A.

The self-healing diffusion Monte Carlo algorithm (SHDMC) [Reboredo, Hood and Kent, Phys. Rev. B {\\bf 79}, 195117 (2009), Reboredo, {\\it ibid.} {\\bf 80}, 125110 (2009)] is extended to study the ground and excited states of magnetic and periodic systems. A recursive optimization algorithm is derived from the time evolution of the mixed probability density. The mixed probability density is given by an ensemble of electronic configurations (walkers) with complex weight. This complex weigh allows the amplitude of the fix-node wave function to move away from the trial wave function phase. This novel approach is both a generalization of SHDMC andmore » the fixed-phase approximation [Ortiz, Ceperley and Martin Phys Rev. Lett. {\\bf 71}, 2777 (1993)]. When used recursively it improves simultaneously the node and phase. The algorithm is demonstrated to converge to the nearly exact solutions of model systems with periodic boundary conditions or applied magnetic fields. The method is also applied to obtain low energy excitations with magnetic field or periodic boundary conditions. The potential applications of this new method to study periodic, magnetic, and complex Hamiltonians are discussed.« less

Magnetic Microhelix Coil Structures

NASA Astrophysics Data System (ADS)

Smith, Elliot J.; Makarov, Denys; Sanchez, Samuel; Fomin, Vladimir M.; Schmidt, Oliver G.

2011-08-01

Together with the well-known ferro- and antiferromagnetic ordering, nature has created a variety of complex helical magnetic configurations. Here, we design and investigate three-dimensional microhelix coil structures that are radial-, corkscrew-, and hollow-bar-magnetized. The magnetization configurations of the differently magnetized coils are experimentally revealed by probing their specific dynamic response to an external magnetic field. Helix coils offer an opportunity to realize microscale geometries of the magnetic toroidal moment, observed so far only in bulk multiferroic materials.

Understanding the Mechanism of Magnetic Relaxation in Pentanuclear {MnIVMnIII2LnIII2} Single-Molecule Magnets.

PubMed

Vignesh, Kuduva R; Langley, Stuart K; Moubaraki, Boujemaa; Murray, Keith S; Rajaraman, Gopalan

2018-02-05

A new family of heterometallic pentanuclear complexes of formulas [Mn IV Mn III 2 Ln III 2 O 2 (benz) 4 (mdea) 3 (NO 3 ) 2 (MeOH)] (Ln = Dy (1-Dy), Tb (2-Tb), Gd (3-Gd), Eu (4-Eu), Sm (5-Sm), Nd (6-Nd), Pr (7-Pr); benz(H) = benzoic acid; mdeaH 2 = N-methyldiethanolamine) and [Mn IV Mn III 2 Ln III 2 O 2 (o-tol) 4 (mdea) 3 (NO 3 ) 2 (MeOH)] (Ln = Gd (8-Gd), Eu (9-Eu); o-tol(H) = o-toluic acid) have been isolated and structurally, magnetically, and theoretically characterized. dc magnetic susceptibility measurements reveal dominant antiferromagnetic magnetic interactions for each complex, except for 2-Tb and 3-Gd, which reveal an upturn in the χ M T product at low temperatures. The magnetic interactions between the spin centers in the Gd derivatives, 3-Gd and 8-Gd, which display markedly different χ M T vs T profiles, were found to be due to the interactions of the Gd III -Gd III ions which change from ferromagnetic (3-Gd) to antiferromagnetic (8-Gd) due to structural differences. ac magnetic susceptibility measurements reveal a nonzero out-of-phase component for 1-Dy and 7-Pr, but no maxima were observed above 2 K (H dc = 0 Oe), which suggests single-molecule magnet (SMM) behavior. Out-of-phase signals were observed for complexes 2-Tb, 4-Eu, 8-Gd, and 9-Eu, in the presence of a static dc field (H dc = 2000, 3000 Oe). The anisotropic nature of the lanthanide ions in the benzoate series (1-Dy, 2-Tb, 5-Sm, 6-Nd, and 7-Pr) were thoroughly investigated using ab initio methods. CASSCF calculations predict that the origin of SMM behavior in 1-Dy and 7-Pr and the applied field SMM behavior in 2-Tb does not solely originate from the single-ion anisotropy of the lanthanide ions. To fully understand the relaxation mechanism, we have employed the Lines model to fit the susceptibility data using the POLY_ANISO program, which suggests that the zero-field SMM behavior observed in complexes 1-Dy and 7-Pr is due to weak Mn III/IV -Ln III and Ln III -Ln III couplings and an unfavorable Ln III /Mn III /Mn IV anisotropy. In complexes 4-Eu, 8-Gd, and 9-Eu ab initio calculations indicate that the anisotropy of the Mn III ions solely gives rise to the possibility of SMM behavior. Complex 7-Pr is a Pr(III)-containing complex that displays zero-field SMM behavior, which is rare, and our study suggests the possibility of coupling weak SOC lanthanide metal ions to anisotropic transition-metal ions to derive SMM characteristics; however, enhancing the exchange coupling in {3d-4f} complexes is still a stubborn hurdle in harnessing new generation {3d-4f} SMMs.

Resonant alteration of propagation in guiding structures with complex Robin parameter and its magnetic-field-induced restoration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Olendski, O., E-mail: oolendski@ksu.edu.sa

2011-06-15

Highlights: > Solutions of the wave equation are analyzed for the confined circular geometry with complex Robin boundary conditions. > Sharp extremum is found in the energy dependence on the imaginary part of the extrapolation length. > Nonzero real part of the Robin length or/and magnetic field wipe out the resonance. - Abstract: Solutions of the scalar Helmholtz wave equation are derived for the analysis of the transport and thermodynamic properties of the two-dimensional disk and three-dimensional infinitely long straight wire in the external uniform longitudinal magnetic field B under the assumption that the Robin boundary condition contains extrapolation lengthmore » {Lambda} with nonzero imaginary part {Lambda}{sub i}. As a result of this complexity, the self-adjointness of the Hamiltonian is lost, its eigenvalues E become complex too and the discrete bound states of the disk characteristic for the real {Lambda} turn into the corresponding quasibound states with their lifetime defined by the eigenenergies imaginary parts E{sub i}. Accordingly, the longitudinal flux undergoes an alteration as it flows along the wire with its attenuation/amplification being E{sub i}-dependent too. It is shown that, for zero magnetic field, the component E{sub i} as a function of the Robin imaginary part exhibits a pronounced sharp extremum with its magnitude being the largest for the zero real part {Lambda}{sub r} of the extrapolation length. Increasing magnitude of {Lambda}{sub r} quenches the E{sub i} - {Lambda}{sub i} resonance and at very large {Lambda}{sub r} the eigenenergies E approach the asymptotic real values independent of {Lambda}{sub i}. The extremum is also wiped out by the magnetic field when, for the large B, the energies tend to the Landau levels. Mathematical and physical interpretations of the obtained results are provided; in particular, it is shown that the finite lifetime of the disk quasibound states stems from the {Lambda}{sub i}-induced currents flowing through the sample boundary. Possible experimental tests of the calculated effect are discussed; namely, it is argued that it can be observed in superconductors by applying to them the external electric field E normal to the surface.« less

Quantum oscillator on CP{sup n} in a constant magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bellucci, Stefano; Nersessian, Armen; Yerevan Physics Institute, Alikhanian Brothers St., 2, Yerevan, 375036

2004-10-15

We construct the quantum oscillator interacting with a constant magnetic field on complex projective spaces CP{sup N}, as well as on their noncompact counterparts, i.e., the N-dimensional Lobachewski spaces L{sub N}. We find the spectrum of this system and the complete basis of wave functions. Surprisingly, the inclusion of a magnetic field does not yield any qualitative change in the energy spectrum. For N>1 the magnetic field does not break the superintegrability of the system, whereas for N=1 it preserves the exact solvability of the system. We extend these results to the cones constructed over CP{sup N} and L{sub N},more » and perform the Kustaanheimo-Stiefel transformation of these systems to the three dimensional Coulomb-like systems.« less

Jupiter, Tether, and Lenz's Law

NASA Technical Reports Server (NTRS)

Lee, Russell

1999-01-01

Jupiter has a large, complex, and intense magnetic field that is thought to arise from electrical currents in the rapidly spinning metallic hydrogen interior. The strong magnetic field can induce currents when the conductive tether is directed toward or away from Jupiter. The currents can be stored and used for both propulsion and power generation. Therefore, our spacecraft might be able to visit several Jovian moons or maintain in the orbit around Jupiter. In our future space traveling, we also can use this technical skill to travel to other planets without any fuel. First-year physics textbooks describe Lenz's Law in which current is induced in a conductor moving through a stationary magnetic field. A demonstration of induced current in a stationary conductor and moving magnetic field is described, which may have space-tether application.

Defect control of conventional and anomalous electron transport at complex oxide interfaces

DOE PAGES

Gunkel, F.; Bell, Chris; Inoue, Hisashi; ...

2016-08-30

Using low-temperature electrical measurements, the interrelation between electron transport, magnetic properties, and ionic defect structure in complex oxide interface systems is investigated, focusing on NdGaO 3/SrTiO 3 (100) interfaces. Field-dependent Hall characteristics (2–300 K) are obtained for samples grown at various growth pressures. In addition to multiple electron transport, interfacial magnetism is tracked exploiting the anomalous Hall effect (AHE). These two properties both contribute to a nonlinearity in the field dependence of the Hall resistance, with multiple carrier conduction evident below 30 K and AHE at temperatures ≲10 K. Considering these two sources of nonlinearity, we suggest a phenomenological modelmore » capturing the complex field dependence of the Hall characteristics in the low-temperature regime. Our model allows the extraction of the conventional transport parameters and a qualitative analysis of the magnetization. The electron mobility is found to decrease systematically with increasing growth pressure. This suggests dominant electron scattering by acceptor-type strontium vacancies incorporated during growth. The AHE scales with growth pressure. In conclusion, the most pronounced AHE is found at increased growth pressure and, thus, in the most defective, low-mobility samples, indicating a correlation between transport, magnetism, and cation defect concentration.« less

Remanent and induced contributions of the Earth's magnetization

NASA Astrophysics Data System (ADS)

Vervelidou, Foteini; Lesur, Vincent; Thébault, Erwan; Dyment, Jérôme; Holschneider, Matthias

2016-04-01

Inverting the magnetic field of crustal origin for the magnetization distribution that generates it suffers from non-uniqueness. The reason for this is the so-called annihilators, i.e. structures that produce no visible magnetic field outside the sources. Gubbins et al., 2011 uses the complex vector Spherical Harmonics notation in order to separate the Vertical Integrated Magnetization (VIM) distribution into the parts that do and do not contribute to the magnetic field measured in source free regions. We use their formalism and convert a crustal SH model based on the WDMAM into a model for the equivalent magnetization. However, we extend their formalism and assume that the magnetization is confined within a layer of finite thickness. A different thickness is considered for the oceanic crust than for the continental one. It is well known that the large scales of the crustal field are entirely masked by the Earth's main field. Therefore, we complement the WDMAM based magnetization map (SH degrees 16 to 800) with the magnetization map for the large wavelengths (SH degrees 1-15) that was recently derived by Vervelidou and Thébault (2015) from a series of regional statistical analyses of the World Digital Magnetic Anomaly Map. Finally we propose a tentative separation of this magnetization map into induced and remanent contributions on a regional scale. We do so based on the direction of the core magnetic field. We discuss the implications of these results in terms of the tectonic history of the Earth.

In Situ Observation of Chymotrypsin Catalytic Activity Change Actuated by Nonheating Low-Frequency Magnetic Field.

PubMed

Efremova, Maria V; Veselov, Maxim M; Barulin, Alexander V; Gribanovsky, Sergey L; Le-Deygen, Irina M; Uporov, Igor V; Kudryashova, Elena V; Sokolsky-Papkov, Marina; Majouga, Alexander G; Golovin, Yuri I; Kabanov, Alexander V; Klyachko, Natalia L

2018-04-24

Magnetomechanical modulation of biochemical processes is a promising instrument for bioengineering and nanomedicine. This work demonstrates two approaches to control activity of an enzyme, α-chymotrypsin immobilized on the surface of gold-coated magnetite magnetic nanoparticles (GM-MNPs) using a nonheating low-frequency magnetic field (LF MF). The measurement of the enzyme reaction rate was carried out in situ during exposure to the magnetic field. The first approach involves α-chymotrypsin-GM-MNPs conjugates, in which the enzyme undergoes mechanical deformations with the reorientation of the MNPs under LF MF (16-410 Hz frequency, 88 mT flux density). Such mechanical deformations result in conformational changes in α-chymotrypsin structure, as confirmed by infrared spectroscopy and molecular modeling, and lead to a 63% decrease of enzyme initial activity. The second approach involves an α-chymotrypsin-GM-MNPs/trypsin inhibitor-GM-MNPs complex, in which the activity of the enzyme is partially inhibited. In this case the reorientation of MNPs in the field leads to disruption of the enzyme-inhibitor complex and an almost 2-fold increase of enzyme activity. The results further demonstrate the utility of magnetomechanical actuation at the nanoscale for the remote modulation of biochemical reactions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Modic, K. A.; Ramshaw, Brad J.; Betts, J. B.

Here, the complex antiferromagnetic orders observed in the honeycomb iridates are a double-edged sword in the search for a quantum spin-liquid: both attesting that the magnetic interactions provide many of the necessary ingredients, while simultaneously impeding access. Focus has naturally been drawn to the unusual magnetic orders that hint at the underlying spin correlations. However, the study of any particular broken symmetry state generally provides little clue about the possibility of other nearby ground states. Here we use magnetic fields approaching 100 Tesla to reveal the extent of the spin correlations in γ-lithium iridate. We find that a small componentmore » of field along the magnetic easy-axis melts long-range order, revealing a bistable, strongly correlated spin state. Far from the usual destruction of antiferromagnetism via spin polarization, the high-field state possesses only a small fraction of the total iridium moment, without evidence for long-range order up to the highest attainable magnetic fields.« less

Effect of head motion on MRI B0 field distribution.

PubMed

Liu, Jiaen; de Zwart, Jacco A; van Gelderen, Peter; Murphy-Boesch, Joseph; Duyn, Jeff H

2018-05-16

To identify and characterize the sources of B 0 field changes due to head motion, to reduce motion sensitivity in human brain MRI. B 0 fields were measured in 5 healthy human volunteers at various head poses. After measurement of the total field, the field originating from the subject was calculated by subtracting the external field generated by the magnet and shims. A subject-specific susceptibility model was created to quantify the contribution of the head and torso. The spatial complexity of the field changes was analyzed using spherical harmonic expansion. Minor head pose changes can cause substantial and spatially complex field changes in the brain. For rotations and translations of approximately 5 º and 5 mm, respectively, at 7 T, the field change that is associated with the subject's magnetization generates a standard deviation (SD) of about 10 Hz over the brain. The stationary torso contributes to this subject-associated field change significantly with a SD of about 5 Hz. The subject-associated change leads to image-corrupting phase errors in multi-shot T2*-weighted acquisitions. The B 0 field changes arising from head motion are problematic for multishot T2*-weighted imaging. Characterization of the underlying sources provides new insights into mitigation strategies, which may benefit from individualized predictive field models in addition to real-time field monitoring and correction strategies. © 2018 International Society for Magnetic Resonance in Medicine.

Effect of electron reflection on magnetized plasma sheath in an oblique magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Ting-Ting; Ma, J. X., E-mail: jxma@ustc.edu.cn; Wei, Zi-An

Magnetized plasma sheaths in an oblique magnetic field were extensively investigated by conventionally assuming Boltzmann relation for electron density. This article presents the study of the magnetized sheath without using the Boltzmann relation but by considering the electron reflection along the magnetic field lines caused by the negative sheath potential. A generalized Bohm criterion is analytically derived, and sheath profiles are numerically obtained, which are compared with the results of the conventional model. The results show that the ion Mach number at the sheath edge normal to the wall has a strong dependence on the wall potential, which differs significantlymore » from the conventional model in which the Mach number is independent of the wall potential. The floating wall potential is lower in the present model than that in the conventional model. Furthermore, the sheath profiles are appreciably narrower in the present model when the wall bias is low, but approach the result of the conventional model when the wall bias is high. The sheath thickness decreases with the increase of ion-to-electron temperature ratio and magnetic field strength but has a complex relationship with the angle of the magnetic field.« less

Switching of chiral magnetic skyrmions by picosecond magnetic field pulses via transient topological states

PubMed Central

Heo, Changhoon; Kiselev, Nikolai S.; Nandy, Ashis Kumar; Blügel, Stefan; Rasing, Theo

2016-01-01

Magnetic chiral skyrmions are vortex like spin structures that appear as stable or meta-stable states in magnetic materials due to the interplay between the symmetric and antisymmetric exchange interactions, applied magnetic field and/or uniaxial anisotropy. Their small size and internal stability make them prospective objects for data storage but for this, the controlled switching between skyrmion states of opposite polarity and topological charge is essential. Here we present a study of magnetic skyrmion switching by an applied magnetic field pulse based on a discrete model of classical spins and atomistic spin dynamics. We found a finite range of coupling parameters corresponding to the coexistence of two degenerate isolated skyrmions characterized by mutually inverted spin structures with opposite polarity and topological charge. We demonstrate how for a wide range of material parameters a short inclined magnetic field pulse can initiate the reliable switching between these states at GHz rates. Detailed analysis of the switching mechanism revealed the complex path of the system accompanied with the excitation of a chiral-achiral meron pair and the formation of an achiral skyrmion. PMID:27273157

Switching of chiral magnetic skyrmions by picosecond magnetic field pulses via transient topological states.

PubMed

Heo, Changhoon; Kiselev, Nikolai S; Nandy, Ashis Kumar; Blügel, Stefan; Rasing, Theo

2016-06-08

Magnetic chiral skyrmions are vortex like spin structures that appear as stable or meta-stable states in magnetic materials due to the interplay between the symmetric and antisymmetric exchange interactions, applied magnetic field and/or uniaxial anisotropy. Their small size and internal stability make them prospective objects for data storage but for this, the controlled switching between skyrmion states of opposite polarity and topological charge is essential. Here we present a study of magnetic skyrmion switching by an applied magnetic field pulse based on a discrete model of classical spins and atomistic spin dynamics. We found a finite range of coupling parameters corresponding to the coexistence of two degenerate isolated skyrmions characterized by mutually inverted spin structures with opposite polarity and topological charge. We demonstrate how for a wide range of material parameters a short inclined magnetic field pulse can initiate the reliable switching between these states at GHz rates. Detailed analysis of the switching mechanism revealed the complex path of the system accompanied with the excitation of a chiral-achiral meron pair and the formation of an achiral skyrmion.

Magnetic and optoelectronic properties of gold nanocluster-thiophene assembly.

PubMed

Qin, Wei; Lohrman, Jessica; Ren, Shenqiang

2014-07-07

Nanohybrids consisting of Au nanocluster and polythiophene nanowire assemblies exhibit unique thermal-responsive optical behaviors and charge-transfer controlled magnetic and optoelectronic properties. The ultrasmall Au nanocluster enhanced photoabsorption and conductivity effectively improves the photocurrent of nanohybrid based photovoltaics, leading to an increase of power conversion efficiency by 14 % under AM 1.5 illumination. In addition, nanohybrids exhibit electric field controlled spin resonance and magnetic field sensing behaviors, which open up the potential of charge-transfer complex system where the magnetism and optoelectronics interact. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Element specific determination of the magnetic properties of two macrocyclic tetranuclear 3d-4f complexes with a Cu3Tb core by means of X-ray magnetic circular dichroism (XMCD).

PubMed

Balinski, K; Schneider, L; Wöllermann, J; Buling, A; Joly, L; Piamonteze, C; Feltham, H L C; Brooker, S; Powell, A K; Delley, B; Kuepper, K

2018-06-20

We apply X-ray magnetic circular dichroism to study the internal magnetic structure of two very promising star shaped macrocyclic complexes with a CuII3TbIII core. These complexes are rare examples prepared with a macrocyclic ligand that show indications of SMM (Single Molecule Magnet) behavior, and they differ only in ring size: one has a propylene linked macrocycle, [CuII3TbIII(LPr)(NO3)2(MeOH)(H2O)2](NO3)·3H2O (nickname: Cu3Tb(LPr)), and the other has the butylene linked analogue, [CuII3TbIII(LBu)(NO3)2(MeOH)(H2O)](NO3)·3H2O (nickname: Cu3Tb(LBu)). We analyze the orbital and spin contributions to the Cu and Tb ions quantitatively by applying the spin and orbital sum rules concerning the L2 (M4)/L3 (M5) edges. In combination with appropriate ligand field simulations, we demonstrate that the Tb(iii) ions contribute with high orbital magnetic moments to the magnetic anisotropy, whereas the ligand field determines the easy axis of magnetization. Furthermore, we confirm that the Cu(ii) ions in both molecules are in a divalent valence state, the magnetic moments of the three Cu ions appear to be canted due to 3d-3d intramolecular magnetic interactions. For Cu3Tb(LPr), the corresponding element specific magnetization loops reflect that the Cu(ii) contribution to the overall magnetic picture becomes more important as the temperature is lowered. This implies a low value for the 3d-4f coupling.

Stability Analysis of Flow Induced by the Traveling Magnetic Field

NASA Technical Reports Server (NTRS)

Mazuruk, Konstantin

2003-01-01

Re-circulating flow in molten metal columns can be conveniently induced by the axisymmetric traveling magnetic field. A number of applications can benefit from this technique, such as mixing under microgravity environment, or.crysta1 growth from metallic melts. For small magnetic field excitations, the flow is laminar and stationary. As the imposed field increases, a more complex flow will set up in the cylindrical column. Conditions for stable laminar flow are of importance for practical applications. In this work, a linear stability analysis is performed in order to determine the onset of the bifurcation in the system. Here the analysis is restricted to the axisymmetric modes and the low-frequency regime.

Stability Analysis of Flow Induced by the Traveling Magnetic Field

NASA Technical Reports Server (NTRS)

Mazuruk, Konstantin

2003-01-01

Re-circulating flow in molten metal columns can be conveniently induced by the axisymmetric traveling magnetic field. A number of applications can benefit from this technique, such as mixing under microgravity environment, or crysta1 growth from metallic melts. For small magnetic field excitations, the flow is laminar and stationary. As the imposed field increases, a more complex flow will set up in the cylindrical column. Conditions for stable laminar flow are of importance for practical applications. In this work, a linear stability analysis is performed in order to determine the onset of the bifurcation in the system. Here the analysis is restricted to the axisymmetric modes and the low-frequency regime.

Interfacial Magnetism in Complex Oxide Heterostructures Probed by Neutrons and X-rays

DOE PAGES

Liu, Yaohua; Ke, Xianglin

2015-09-02

Magnetic complex-oxide heterostructures are of keen interest because a wealth of phenomena at the interface of dissimilar materials can give rise to fundamentally new physics and potentially valuable functionalities. Altered magnetization, novel magnetic coupling and emergent interfacial magnetism at the epitaxial layered-oxide interfaces have all been intensively investigated, which shapes our understanding on how to utilize those materials, particularly for spintronics. Neutron and x-ray based techniques have played a decisive role in characterizing interfacial magnetic structures and clarifying the underlying physics in this rapidly developing field. Here we review some recent experimental results, with an emphasis on those studied viamore » polarized neutron reflectometery and polarized x-ray absorption spectroscopy. We conclude with some perspectives.« less

Interfacial magnetism in complex oxide heterostructures probed by neutrons and x-rays.

PubMed

Liu, Yaohua; Ke, Xianglin

2015-09-23

Magnetic complex-oxide heterostructures are of keen interest because a wealth of phenomena at the interface of dissimilar materials can give rise to fundamentally new physics and potentially valuable functionalities. Altered magnetization, novel magnetic coupling and emergent interfacial magnetism at the epitaxial layered-oxide interfaces are under intensive investigation, which shapes our understanding on how to utilize those materials, particularly for spintronics. Neutron and x-ray based techniques have played a decisive role in characterizing interfacial magnetic structures and clarifying the underlying physics in this rapidly developing field. Here we review some recent experimental results, with an emphasis on those studied via polarized neutron reflectometery and polarized x-ray absorption spectroscopy. We conclude with some perspectives.

The mechanisms of the effects of magnetic fields on cells

NASA Astrophysics Data System (ADS)

Kondrachuk, A.

The evolution of organisms in conditions of the Earth magnetism results in close dependence of their functioning on the properties of the Earth magnetic field. The magnetic conditions in space flight differ from those on the Earth (e.g. much smaller values of magnetic filed) that effect various processes in living organisms. Meanwhile the mechanisms of interaction of magnetic fields with cell structures are poorly understood and systemized. The goal of the present work is to analyze and estimate the main established mechanisms of "magnetic fields - cell" interaction. Due to variety and complexity of the effects the analysis is mainly restricted to biological effects of the static magnetic field at a cellular level. 1) Magnetic induction. Static magnetic fields exert forces on moving ions in solution (e.g., electrolytes), giving rise to induced electric fields and currents. This effect may be especially important when the currents changed due to the magnetic field application are participating in some receptor functions of cells (e.g. plant cells). 2) Magneto-mechanical effect of reorientation. Uniform static magnetic fields produce torques on certain molecules with anisotropic magnetic properties, which results in their reorientation and spatial ordering. Since the structures of biological cells are magnetically and mechanically inhomogeneous, the application of a homogeneous magnetic field may cause redistribution of stresses within cells, deformation of intracellular structures, change of membrane permeability, etc. 3) Ponderomotive effects. Spatially non-uniform magnetic field exerts ponderomotive force on magnetically non-uniform cell structures. This force is proportional to the gradient of the square of magnetic field and the difference of magnetic susceptibilities of the component of the cell and its environment. 4) Biomagnetic effects. Magnetic fields can exert torques and translational forces on ferromagnetic structures, such as magnetite and ferritins presented in the cells. 5) Electronic interactions. Static magnetic fields can alter energy levels and spin orientation of electrons. Similar interactions can also occur with nuclear spins, but these are very weak compared to electron interactions. 6) Free radicals. Magnetic fields alter the spin states of the radicals, which, in turn, changes the relative probabilities of recombination and other interactions, possibly with biological consequences. 7) Non-linear effects. A number of non-linear mechanisms of magnetic effects on cells were recently proposed to explain how the cell could extract a weak magnetic signal from noise (e.g. stochastic non-linear resonance, self-tuned Hopf bifurcations). These new models need further experimental testing.

Controlling the motion of solitons in 1-D magnonic crystal

NASA Astrophysics Data System (ADS)

Giridharan, D.; Sabareesan, P.; Daniel, M.

2018-04-01

We investigate nonlinear localized magnetic excitations in a simple form of one dimensional magnonic crystal by considering a ferromagnetic medium under periodic applied magnetic field of spatially varying strength. The governing Landau-Lifshitz equation is transformed into nonlinear evolution equation of a complex function through stereographic projection technique. The associated evolution equation numerically solved by using split-step Fourier method (SSFM). From the obtained results it is observed that the excitations appear in the form of solitons and the periodic magnetic field of spatially varying strength perturbs the soliton propagation. Bright and dark soliton solutions are constructed and studied the effect of tuning the strength of spatially periodic applied magnetic field on the nonlinear excitation of magnetization. The results show that the amplitude and velocity of the soliton can be effectively managed by varying the strength of spatially periodic applied magnetic field and it act as periodic potential which provides an additional degree of freedom to control the nature of soliton propagation in a ferromagnetic medium.

Efficient enhancement of magnetic anisotropy by optimizing the ligand-field in a typically tetranuclear dysprosium cluster.

PubMed

Liu, Jiang; Chen, Yan-Cong; Jiang, Zhong-Xia; Liu, Jun-Liang; Jia, Jian-Hua; Wang, Long-Fei; Li, Quan-Wen; Tong, Ming-Liang

2015-05-07

The perturbation to the ligand field around the lanthanide ion may significantly contribute to the magnetic dynamics of single molecule magnets. This can be demonstrated by two typical Dy4 cluster-based single molecular magnets (SMMs), [Dy4X2(μ3-OH)2(μ-OH)2(2,2-bpt)4(H2O)4]X2·2H2O·4EtOH (X = Cl and Br for and , respectively), which were constructed by using 3,5-bis(pyridin-2-yl)-1,2,4-triazole (2,2-bptH) as the polynuclear-chelating ligand. Alternating-current (ac) magnetic susceptibility measurements show that the energy barriers in complexes and were immensely enhanced by comparing with our previous work due to the optimization of the ligand field around Dy(III) ions. Remarkably, their high thermal active barriers at 190 K () and 197 K () under a zero applied external dc magnetic field are also among the highest within the reported tetranuclear lanthanide-based SMMs.

Effective Lagrangian in nonlinear electrodynamics and its properties of causality and unitarity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shabad, Anatoly E.; Usov, Vladimir V.

2011-05-15

In nonlinear electrodynamics, by implementing the causality principle as the requirement that the group velocity of elementary excitations over a background field should not exceed the speed of light in the vacuum c=1, and the unitarity principle as the requirement that the residue of the propagator should be nonnegative, we establish the positive convexity of the effective Lagrangian on the class of constant fields, also the positivity of all characteristic dielectric and magnetic permittivity constants that are derivatives of the effective Lagrangian with respect to the field invariants. Violation of the general principles by the one-loop approximation in QED atmore » exponentially large magnetic field is analyzed, resulting in complex energy ghosts that signal the instability of the magnetized vacuum. Superluminal excitations (tachyons) appear, too, but for the magnetic field exceeding its instability threshold. Also other popular Lagrangians are tested to establish that the ones leading to spontaneous vacuum magnetization possess wrong convexity.« less

The Strongest Magnetic Field in Sunspots

NASA Astrophysics Data System (ADS)

Okamoto, J.; Sakurai, T.

2017-12-01

Sunspots are concentrations of magnetic fields on the solar surface. Generally, the strongest magnetic field in each sunspot is located in the dark umbra in most cases. A typical field strength in sunspots is around 3,000 G. On the other hand, some exceptions also have been found in complex sunspots with bright regions such as light bridges that separate opposite polarity umbrae, for instance with a strength of 4,300 G. However, the formation mechanism of such strong fields outside umbrae is still puzzling. Here we report an extremely strong magnetic field in a sunspot, which was located in a bright region sandwiched by two opposite-polarity umbrae. The strength is 6,250 G, which is the largest ever observed since the discovery of magnetic field on the Sun in 1908 by Hale. We obtained 31 scanned maps of the active region observed by Hinode/SOT/SP with a cadence of 3 hours over 5 days (February 1-6, 2014). Considering the spatial and temporal evolution of the vector magnetic field and the Doppler velocity in the bright region, we suggested that this strong field region was generated as a result of compression of one umbra pushed by the outward flow from the other umbra (Evershed flow), like the subduction of the Earth's crust in plate tectonics.

Studying the Transfer of Magnetic Helicity in Solar Active Regions with the Connectivity-based Helicity Flux Density Method

NASA Astrophysics Data System (ADS)

Dalmasse, K.; Pariat, É.; Valori, G.; Jing, J.; Démoulin, P.

2018-01-01

In the solar corona, magnetic helicity slowly and continuously accumulates in response to plasma flows tangential to the photosphere and magnetic flux emergence through it. Analyzing this transfer of magnetic helicity is key for identifying its role in the dynamics of active regions (ARs). The connectivity-based helicity flux density method was recently developed for studying the 2D and 3D transfer of magnetic helicity in ARs. The method takes into account the 3D nature of magnetic helicity by explicitly using knowledge of the magnetic field connectivity, which allows it to faithfully track the photospheric flux of magnetic helicity. Because the magnetic field is not measured in the solar corona, modeled 3D solutions obtained from force-free magnetic field extrapolations must be used to derive the magnetic connectivity. Different extrapolation methods can lead to markedly different 3D magnetic field connectivities, thus questioning the reliability of the connectivity-based approach in observational applications. We address these concerns by applying this method to the isolated and internally complex AR 11158 with different magnetic field extrapolation models. We show that the connectivity-based calculations are robust to different extrapolation methods, in particular with regard to identifying regions of opposite magnetic helicity flux. We conclude that the connectivity-based approach can be reliably used in observational analyses and is a promising tool for studying the transfer of magnetic helicity in ARs and relating it to their flaring activity.

A Low Spin Manganese(IV) Nitride Single Molecule Magnet

PubMed Central

Ding, Mei; Cutsail, George E.; Aravena, Daniel; Amoza, Martín; Rouzières, Mathieu; Dechambenoit, Pierre; Losovyj, Yaroslav; Pink, Maren

2016-01-01

Structural, spectroscopic and magnetic methods have been used to characterize the tris(carbene)borate compound PhB(MesIm)3Mn≡N as a four-coordinate manganese(IV) complex with a low spin (S = 1/2) configuration. The slow relaxation of the magnetization in this complex, i.e. its single-molecule magnet (SMM) properties, is revealed under an applied dc field. Multireference quantum mechanical calculations indicate that this SMM behavior originates from an anisotropic ground doublet stabilized by spin-orbit coupling. Consistent theoretical and experiment data show that the resulting magnetization dynamics in this system is dominated by ground state quantum tunneling, while its temperature dependence is influenced by Raman relaxation. PMID:27746891

Polyethylenimine functionalized magnetic nanoparticles as a potential non-viral vector for gene delivery.

PubMed

Zhou, Yangbo; Tang, Zhaomin; Shi, Chunli; Shi, Shuai; Qian, Zhiyong; Zhou, Shaobing

2012-11-01

Polyethylenimine (PEI) functionalized magnetic nanoparticles were synthesized as a potential non-viral vector for gene delivery. The nanoparticles could provide the magnetic-targeting, and the cationic polymer PEI could condense DNA and avoid in vitro barriers. The magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy, X-ray powder diffraction, dynamic light scattering measurements, transmission electron microscopy, vibrating sample magnetometer and atomic force microscopy. Agarose gel electrophoresis was used to asses DNA binding and perform a DNase I protection assay. The Alamar blue assay was used to evaluate negative effects on the metabolic activity of cells incubated with PEI modified magnetic nanoparticles and their complexes with DNA both in the presence or absence of an external magnetic field. Flow cytometry and fluorescent microscopy were also performed to investigate the transfection efficiency of the DNA-loaded magnetic nanoparticles in A549 and B16-F10 tumor cells with (+M) or without (-M) the magnetic field. The in vitro transfection efficiency of magnetic nanoparticles was improved obviously in a permanent magnetic field. Therefore, the magnetic nanoparticles show considerable potential as nanocarriers for gene delivery.

Melt Stabilization of PbSnTe in a Magnetic Field

NASA Technical Reports Server (NTRS)

Fripp, Archibald L.; Debnam, William J.; Rosch, William; Chait, Arnon; Yao, Minwu; Szofran, Frank R.

1999-01-01

Both the experimental observation and numerical simulation indicate that the Bridgman growth of PbSnTe under the microgravity environment in space is still greatly influenced by buoyancy-induced convection. The application of a magnetic field during the semiconductor growth can dampen the convective flow in the metal-like melt. However, for Bridgman growth of PbSnTe on earth (with either vertical or horizontal configuration), both experimental observation and numerical modeling suggest that even with a strong magnetic furnace (5-Tesla constant axial magnetic field), the convective flow in the melt still cannot be sufficiently suppressed to reach the diffusion-controlled level. In order to completely dampen the buoyancy-induced convection on earth, estimates based on scaling analysis indicate that for common experimental conditions, an extremely high magnetic field is required, far beyond the capacity of the experimental apparatus currently available. Therefore, it is proposed that only the combination of microgravity environment and magnetic damping will produce the desired diffusion-controlled growth state for this particular material. The primary objectives of this study are to provide a quantitative understanding of the complex transport phenomena during solidification of non-dilute binarys, to furnish a numerical tool for furnace design and growth condition optimization, to provide estimates of the required magnetic field strength for low gravity growth, and to assess the role of magnetic damping for space and earth control of the double-diffusive convection. As an integral part of a NASA research program, our numerical simulation supports both the flight and ground-based experiments in an effort to bring together a complete picture of the complex physical phenomena involved in the crystal growth process. For Bridgman growth of PbSnTe under microgravity (with both vertical and horizontal configurations), the simulations suggest that a moderate axial magnetic field of only a few kilo-Gauss in strength could effectively eliminate buoyancy-induced convection in the melt and control solute segregation. Therefore, this work confirms the idea that the combination of microgravity environment and the magnetic damping will indeed be sufficient to produce the desired diffusion-controlled growth state for PbSnTe.

Emergent magnetic anisotropy in the cubic heavy-fermion metal CeIn3

DOE PAGES

Moll, Philip J. W.; Helm, Toni; Zhang, Shang-Shun; ...

2017-08-21

Metals containing cerium exhibit a diverse range of fascinating phenomena including heavy fermion behavior, quantum criticality, and novel states of matter such as unconventional superconductivity. The cubic system CeIn3 has attracted significant attention as a structurally isotropic Kondo lattice material possessing the minimum required complexity to still reveal this rich physics. By using magnetic fields with strengths comparable to the crystal field energy scale, we illustrate a strong field-induced anisotropy as a consequence of non-spherically symmetric spin interactions in the prototypical heavy fermion material CeIn3. We demonstrate the importance of magnetic anisotropy in modeling f-electron materials when the orbital charactermore » of the 4f wavefunction changes (e.g., with pressure or composition). Additionally, magnetic fields are shown to tune the effective hybridization and exchange interactions potentially leading to new exotic field tuned effects in f-based materials.« less

Emergent magnetic anisotropy in the cubic heavy-fermion metal CeIn3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moll, Philip J. W.; Helm, Toni; Zhang, Shang-Shun

Metals containing cerium exhibit a diverse range of fascinating phenomena including heavy fermion behavior, quantum criticality, and novel states of matter such as unconventional superconductivity. The cubic system CeIn3 has attracted significant attention as a structurally isotropic Kondo lattice material possessing the minimum required complexity to still reveal this rich physics. By using magnetic fields with strengths comparable to the crystal field energy scale, we illustrate a strong field-induced anisotropy as a consequence of non-spherically symmetric spin interactions in the prototypical heavy fermion material CeIn3. We demonstrate the importance of magnetic anisotropy in modeling f-electron materials when the orbital charactermore » of the 4f wavefunction changes (e.g., with pressure or composition). Additionally, magnetic fields are shown to tune the effective hybridization and exchange interactions potentially leading to new exotic field tuned effects in f-based materials.« less

LIGHT-SABRE enables efficient in-magnet catalytic hyperpolarization.

PubMed

Theis, Thomas; Truong, Milton; Coffey, Aaron M; Chekmenev, Eduard Y; Warren, Warren S

2014-11-01

Nuclear spin hyperpolarization overcomes the sensitivity limitations of traditional NMR and MRI, but the most general method demonstrated to date (dynamic nuclear polarization) has significant limitations in scalability, cost, and complex apparatus design. As an alternative, signal amplification by reversible exchange (SABRE) of parahydrogen on transition metal catalysts can hyperpolarize a variety of substrates, but to date this scheme has required transfer of the sample to low magnetic field or very strong RF irradiation. Here we demonstrate "Low-Irradiation Generation of High Tesla-SABRE" (LIGHT-SABRE) which works with simple pulse sequences and low power deposition; it should be usable at any magnetic field and for hyperpolarization of many different nuclei. This approach could drastically reduce the cost and complexity of producing hyperpolarized molecules. Copyright © 2014 Elsevier Inc. All rights reserved.

A DFT based ligand field model for magnetic exchange coupling in transition metal dimer complexes:. (ii) application to magnetic systems with more than one unpaired electron per site

NASA Astrophysics Data System (ADS)

Atanasov, M.; Daul, C. A.

2003-11-01

The DFT based ligand field model for magnetic exchange coupling proposed recently, has been extended to systems containing more than one unpaired electron per site. The guidelines for this extension are described using a model example - the complex (NH 3) 3Cr III(OH) 3Cr III (NH 3) 33+. The exchange Hamiltonian, H ex=-J 12S1S2 has been simplified using symmetry principles, i.e. utilizing the D 3h(C 3v) Cr III - dimer(site) symmetry. Both antiferro- and ferromagnetic exchange coupling constants are found to yield important contributions to the value of the (negative, antiferromagnetic) exchange coupling constant in good agreement with experiment.

The mean coronal magnetic field determined from Helios Faraday rotation measurements

NASA Technical Reports Server (NTRS)

Patzold, M.; Bird, M. K.; Volland, H.; Levy, G. S.; Seidel, B. L.; Stelzried, C. T.

1987-01-01

Coronal Faraday rotation of the linearly polarized carrier signals of the Helios spacecraft was recorded during the regularly occurring solar occultations over almost a complete solar cycle from 1975 to 1984. These measurements are used to determine the average strength and radial variation of the coronal magnetic field at solar minimum at solar distances from 3-10 solar radii, i.e., the range over which the complex fields at the coronal base are transformed into the interplanetary spiral. The mean coronal magnetic field in 1975-1976 was found to decrease with radial distance according to r exp-alpha, where alpha = 2.7 + or - 0.2. The mean field magnitude was 1.0 + or - 0.5 x 10 to the -5th tesla at a nominal solar distance of 5 solar radii. Possibly higher magnetic field strengths were indicated at solar maximum, but a lack of data prevented a statistical determination of the mean coronal field during this epoch.

Nonlinear magnetoelectric effects in a composite ferromagnetic-piezoelectric structure under harmonic and noise magnetic pumping

NASA Astrophysics Data System (ADS)

Burdin, D. A.; Chashin, D. V.; Ekonomov, N. A.; Fetisov, Y. K.; Stashkevich, A.

2018-03-01

Low-frequency nonlinear magnetoelectric effects in a composite structure comprised of a piezoelectric langatate slab sandwiched between two Metglas amorphous alloy magnetostrictive layers under simultaneous harmonic and noise magnetic pumping have been investigated. It is shown that the frequency fp of harmonic pumping is linearly reproduced in the piezoelectric voltage spectrum accompanied by its higher harmonics. Similarly, narrow-band magnetic noise with a central frequency fN is present in the output piezoelectric voltage along with two noise peaks in the vicinity of a double 2fN and zero frequency. Simultaneous application of harmonic and noise magnetic fields produces a noticeably more complex output voltage spectrum containing additional noise satellite lines at frequencies fp ±fN , 2fp ±fN etc. as well as a noise "pedestal". Amplitudes of voltage spectral components depend on the applied constant bias magnetic field, scaling as magnetostriction derivatives with respect to this field. The effects observed are well described by the theory of magnetic field mixing in magnetoelectric composites with nonlinear dependence of magnetostriction on applied fields.

Chevrons, filaments, spinning clusters and phase coexistence: emergent dynamics of 2- and 3-d particle suspensions driven by multiaxial magnetic fields

DOE PAGES

Solis, Kyle J.; Martin, James E.

2017-07-06

In recent years a rich variety of emergent phenomena have been observed when suspensions of magnetic particles are subjected to alternating magnetic fields. These particle assemblies often exhibit vigorous dynamics due to the injection of energy from the field. These include surface and interface phenomena, such as highly organized, segmented “snakes” that can be induced to swim by structural symmetry breaking, and “asters” and “anti-asters,” particle assemblies that can be manipulated to capture and transport cargo. In bulk suspensions of magnetic platelets subjected to multiaxial alternating fields, advection lattices and even vortex lattices have been created, and a variety ofmore » biomimetic dynamics – serpents, bees and amoebas – have been discovered in magnetic fluids suspended in an immiscible liquid. In this paper several new driven phases are presented, including flying chevrons, dense spinning clusters, filaments, and examples of phase coexistence in driven phases. These observations broaden the growing field of driven magnetic suspensions and present new challenges to those interested in simulating the dynamics of these complex systems.« less

Lodestone: Nature's own permanent magnet

NASA Technical Reports Server (NTRS)

Wasilewski, P.

1976-01-01

Magnetic hysteresis and microstructural details are presented which explain why the class of magnetic iron ores defined as proto-lodestones, can behave as permanent magnets, i.e. lodestones. Certain of these proto-lodestones which are not permanent magnets can be made into permanent magnets by charging in a field greater than 1000 oersted. This fact, other experimental observations, and field evidence from antiquity and the middle ages, which seems to indicate that lodestones are found as localized patches within massive ore bodies, suggests that lightning might be responsible for the charging of lodestones. The large remanent magnetization, high values of coercive force, and good time stability for the remanent magnetization are all characteristics of proto-lodestone iron ores which behave magnetically as fine scale ( 10 micrometer) intergrowths when subjected to magnetic hysteresis analysis. The magnetic results are easily understood by analysis of the complex proto lodestone microstructural patterns observable at the micrometer scale and less.

External Magnetic Field Reduction Techniques for the Advanced Stirling Radioisotope Generator

NASA Technical Reports Server (NTRS)

Niedra, Janis M.; Geng, Steven M.

2013-01-01

Linear alternators coupled to high efficiency Stirling engines are strong candidates for thermal-to-electric power conversion in space. However, the magnetic field emissions, both AC and DC, of these permanent magnet excited alternators can interfere with sensitive instrumentation onboard a spacecraft. Effective methods to mitigate the AC and DC electromagnetic interference (EMI) from solenoidal type linear alternators (like that used in the Advanced Stirling Convertor) have been developed for potential use in the Advanced Stirling Radioisotope Generator. The methods developed avoid the complexity and extra mass inherent in data extraction from multiple sensors or the use of shielding. This paper discusses these methods, and also provides experimental data obtained during breadboard testing of both AC and DC external magnetic field devices.

Development status of a next generation ECRIS: MARS-D at LBNL

DOE PAGES

Xie, D. Z.; Benitez, J. Y.; Hodgkinson, A.; ...

2015-09-29

To demonstrate a Mixed Axial and Radial field System (MARS) as the best magnet scheme for future ECRISs, MARS-D, a demonstrative ECRIS using a NbTi MARS magnet is progressing at Lawrence Berkeley National Laboratory. An optimized MARS design can use either NbTi or Nb 3Sn coils with reduced engineering complexities to construct the needed high-field magnets. The optimized magnet design could enhance MARS-D to a next generation ECRIS by producing minimum-B field maxima of 5.6 T axially and 3.2 T radially for operating frequencies up to 45 GHz. Lastly, in-progress test winding has achieved a milestone demonstrating the fabrication feasibilitymore » of a MARS closed-loop coil.« less

Development status of a next generation ECRIS: MARS-D at LBNL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, D. Z.; Benitez, J. Y.; Hodgkinson, A.

To demonstrate a Mixed Axial and Radial field System (MARS) as the best magnet scheme for future ECRISs, MARS-D, a demonstrative ECRIS using a NbTi MARS magnet is progressing at Lawrence Berkeley National Laboratory. An optimized MARS design can use either NbTi or Nb 3Sn coils with reduced engineering complexities to construct the needed high-field magnets. The optimized magnet design could enhance MARS-D to a next generation ECRIS by producing minimum-B field maxima of 5.6 T axially and 3.2 T radially for operating frequencies up to 45 GHz. Lastly, in-progress test winding has achieved a milestone demonstrating the fabrication feasibilitymore » of a MARS closed-loop coil.« less

The structure of rotational discontinuities. [in solar wind

NASA Technical Reports Server (NTRS)

Neugebauer, M.

1989-01-01

This study examines the structures of a set of rotational discontinuities detected in the solar wind by the ISEE-3 spacecraft. It is found that the complexity of the structure increases as the angle theta between the propagation vector k and the magnetic field decreases. For rotational discontinuities that propagate at a large angle to the field with an ion (left-hand) sense of rotation, the magnetic hodograms tend to be flattened, in agreement with prior numerical simulations. When theta is large, angular 'overshoots' are often observed at one or both ends of the discontinuity. When the propagation is nearly parallel to the field (when theta is small), many different types of structure are seen, ranging from straight lines, to S-shaped curves, to complex, disorganized shapes.

Knots in electromagnetism

NASA Astrophysics Data System (ADS)

Arrayás, M.; Bouwmeester, D.; Trueba, J. L.

2017-01-01

Maxwell equations in vacuum allow for solutions with a non-trivial topology in the electric and magnetic field line configurations at any given moment in time. One example is a space filling congruence of electric and magnetic field lines forming circles lying on the surfaces of nested tori. In this example the electric, magnetic and Poynting vector fields are orthogonal everywhere. As time evolves the electric and magnetic fields expand and deform without changing the topology and energy, while the Poynting vector structure remains unchanged while propagating with the speed of light. The topology is characterized by the concept of helicity of the field configuration. Helicity is an important fundamental concept and for massless fields it is a conserved quantity under conformal transformations. We will review several methods by which linked and knotted electromagnetic (spin-1) fields can be derived. A first method, introduced by A. Rañada, uses the formulation of the Maxwell equations in terms of differential forms combined with the Hopf map from the three-sphere S3 to the two-sphere S2. A second method is based on spinor and twistor theory developed by R. Penrose in which elementary twistor functions correspond to the family of electromagnetic torus knots. A third method uses the Bateman construction of generating null solutions from complex Euler potentials. And a fourth method uses special conformal transformations, in particular conformal inversion, to generate new linked and knotted field configurations from existing ones. This fourth method is often accompanied by shifting singularities in the field to complex space-time points. Of course the various methods must be closely related to one another although they have been developed largely independently and they suggest different directions in which to expand the study of topologically non-trivial field configurations. It will be shown how the twistor formulation allows for a direct extension to massless fields of other spin values, such as spin-2 fields satisfying the linearized Einstein vacuum equation, and how the formulation by A. Rañada can be extended to fields for which the electric and magnetic fields are not orthogonal everywhere. Underlying the various methods is the fact that electric and magnetic field lines can be described as the level curves of complex functions. Compactification of R3 naturally leads to finite energy solutions because the fields at infinity in all directions should all converge towards zero. An intriguing question that is raised by the finite energy is whether there is a connection to the quantization of the classical electromagnetic field. We will review some issues related to this question. Another interesting question is why the general formulation of topologically non-trivial solutions uses the electric and magnetic fields instead of the electromagnetic vector potentials. This leads to a discussion of the Clebsch representation of the electromagnetic field strength 2-form. Finally, a topic of great interest is the possibility of experimentally generating and investigating linked and knotted field configurations. Since the non-trivial topological field solutions exploit the special conformal symmetry of the underlying vacuum wave-equations it will only be possible to approximate the solutions in an experiment, which necessarily introduces material objects that will break the special conformal symmetry. We will review the research on plasma configurations in which the magnetic field-line configuration approximates plasma torus knots leading to the prediction of topological solitons in plasma.

Exchange bias in bulk layered hydroxylammonium fluorocobaltate (NH₃OH)₂CoF₄.

PubMed

Jagličić, Z; Zentková, M; Mihalik, M; Arnold, Z; Drofenik, M; Kristl, M; Dojer, B; Kasunič, M; Golobič, A; Jagodič, M

2012-02-08

The magnetic properties of layered hydroxylammonium fluorocobaltate (NH(3)OH)(2)CoF(4) were investigated by measuring its dc magnetic susceptibility in zero-field-cooled (ZFC) and field-cooled (FC) regimes, its frequency dependent ac susceptibility, its isothermal magnetization curves after ZFC and FC regimes, and its heat capacity. Effects of pressure and magnetic field on magnetic phase transitions were studied by susceptibility and heat capacity measurements, respectively. The system undergoes a magnetic phase transition from a paramagnetic state to a canted antiferromagnetic state exhibiting a weak ferromagnetic behavior at T(C) = 46.5 K and an antiferromagnetic transition at T(N) = 2.9 K. The most spectacular manifestation of the complex magnetic behavior in this system is a shift of the isothermal magnetization hysteresis loop in a temperature range below 20 K after the FC regime-an exchange bias phenomenon. We investigated the exchange bias as a function of the magnetic field during cooling and as a function of temperature. The observed exchange bias was attributed to the large exchange anisotropy which exists due to the quasi-2D structure of the layered (NH(3)OH)(2)CoF(4) material.

Simulation of Relativistic Shocks and Associated Self-Consistent Radiation

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Niemiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Mizuno, Y.; Nordlund, A.; Frederiksen, J.; Sol, H.; Pohl, M.;

Nuclear relaxation in an electric field enables the determination of isotropic magnetic shielding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garbacz, Piotr, E-mail: pgarbacz@chem.uw.edu.pl

2016-08-14

It is shown that in contrast to the case of nuclear relaxation in a magnetic field B, simultaneous application of the magnetic field B and an additional electric field E causes transverse relaxation of a spin-1/2 nucleus with the rate proportional to the square of the isotropic part of the magnetic shielding tensor. This effect can contribute noticeably to the transverse relaxation rate of heavy nuclei in molecules that possess permanent electric dipole moments. Relativistic quantum mechanical computations indicate that for {sup 205}Tl nucleus in a Pt-Tl bonded complex, Pt(CN){sub 5}Tl, the transverse relaxation rate induced by the electric fieldmore » is of the order of 1 s{sup −1} at E = 5 kV/mm and B = 10 T.« less

Determination of crystal-field energy levels and temperature dependence of magnetic susceptibility for Dy3+ in [Dy2Pd] heterometallic complex.

PubMed

Karbowiak, Mirosław; Rudowicz, Czesław; Ishida, Takayuki

2013-11-18

This study is the first in a series of experimental and theoretical investigations of the crystal-field (CF) energy levels obtained from optical electronic spectra for selected heterometallic 4f-3d compounds intensively studied for the development of novel single-molecule magnets (SMMs). An intriguing question is why the [{Dy(III)(hfac)3}2Cu(II)(dpk)2] (abbreviated as [Dy2Cu]; Hhfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione, Hdpk = di-2-pyridyl ketoxime) has antiferromagnetic coupling, whereas [Gd2Cu] and heavy [Ln2Cu] systems usually show ferromagnetic coupling. As the first step to explain this peculiarity, the recently synthesized complex, [Dy2Pd], is investigated. This complex is isostructural with [Dy2Cu] yet contains the diamagnetic Pd ion instead of the magnetic Cu(II) ion. Experimental energy levels of Dy(3+) ions in the powder [Dy2Pd] sample were determined from the 4.2 K absorption spectra. CF analysis was performed yielding the fitted free ion and CF parameters. The number of freely varied parameters was restricted using the superposition model. The fittings yield very satisfactory agreement between the experimental and the calculated energy levels (rms = 12.0 cm(-1)). The energies and exact composition of the state vector for the ground multiplet (6)H(15/2) of Dy(3+) are determined. These results are used for the simulation of the temperature dependence of the magnetic susceptibility, which enables the theoretical interpretation of the experimentally measured magnetic susceptibility in the range 1.8-300 K for the [Dy2Pd] complex. This study provides background for the subsequent investigation of the magnetic exchange interactions in the pertinent heterometallic complexes.

Magnetic fields, stellar feedback, and the geometry of H II regions

NASA Astrophysics Data System (ADS)

Ferland, Gary J.

2009-04-01

Magnetic pressure has long been known to dominate over gas pressure in atomic and molecular regions of the interstellar medium. Here I review several recent observational studies of the relationships between the H+, H0 and H2 regions in M42 (the Orion complex) and M17. A simple picture results. When stars form they push back surrounding material, mainly through the outward momentum of starlight acting on grains, and field lines are dragged with the gas due to flux freezing. The magnetic field is compressed and the magnetic pressure increases until it is able to resist further expansion and the system comes into approximate magnetostatic equilibrium. Magnetic field lines can be preferentially aligned perpendicular to the long axis of quiescent cloud before stars form. After star formation and pushback occurs ionized gas will be constrained to flow along field lines and escape from the system along directions perpendicular to the long axis. The magnetic field may play other roles in the physics of the H II region and associated PDR. Cosmic rays may be enhanced along with the field and provide additional heating of atomic and molecular material. Wave motions may be associated with the field and contribute a component of turbulence to observed line profiles.

Finite Element Modeling of Magnetically-Damped Convection during Solidification

NASA Technical Reports Server (NTRS)

deGroh, H. C.; Li, B. Q.; Lu, X.

1998-01-01

A fully 3-D, transient finite element model is developed to represent the magnetic damping effects on complex fluid flow, heat transfer and electromagnetic field distributions in a Sn- 35.5%Pb melt undergoing unidirectional solidification. The model is developed based on our in- house finite element code for the fluid flow, heat transfer and electromagnetic field calculations. The numerical model is tested against numerical and experimental results for water as reported in literature. Various numerical simulations are carried out for the melt convection and temperature distribution with and without the presence of a transverse magnetic field. Numerical results show that magnetic damping can be effectively applied to stabilize melt flow, reduce turbulence and flow levels in the melt and over a certain threshold value a higher magnetic field resulted in a greater reduction in velocity. Also, for the study of melt flow instability, a long enough running time is needed to ensure the final fluid flow recirculation pattern. Moreover, numerical results suggest that there seems to exist a threshold value of applied magnetic field, above which magnetic damping becomes possible and below which the 0 convection in the melt is actually enhanced.

Distribution of the Crustal Magnetic Field in Sichuan-Yunnan Region, Southwest China

PubMed Central

Bai, Chunhua; Kang, Guofa; Gao, Guoming

2014-01-01

Based on the new and higher degree geomagnetic model NGDC-720-V3, we have investigated the spatial distribution, the altitude decay characteristics of the crustal magnetic anomaly, the contributions from different wavelength bands to the anomaly, and the relationship among the anomaly, the geological structure, and the geophysical field in Sichuan-Yunnan region of China. It is noted that the most outstanding feature in this area is the strong positive magnetic anomaly in Sichuan Basin, a geologically stable block. Contrasting with this feature, a strong negative anomaly can be seen nearby in Longmen Mountain block, an active block. This contradiction implies a possible relationship between the magnetic field and the geological activity. Completely different feature in magnetic field distribution is seen in the central Yunnan block, another active region, where positive and negative anomalies distribute alternatively, showing a complex magnetic anomaly map. Some fault belts, such as the Longmen Mountain fault, Lijiang-Xiaojinhe fault, and the Red River fault, are the transitional zones of strong and weak or negative and positive anomalies. The corresponding relationship between the magnetic anomaly and the geophysical fields was confirmed. PMID:25243232

Lanthanides in molecular magnetism: old tools in a new field.

PubMed

Sorace, Lorenzo; Benelli, Cristiano; Gatteschi, Dante

2011-06-01

In this tutorial review we discuss some basic aspects concerning the magnetic properties of rare-earth ions, which are currently the subject of a renovated interest in the field of molecular magnetism, after the discovery that slow relaxation of the magnetization at liquid nitrogen temperature can occur in mononuclear complexes of these ions. Focusing on Dy(III) derivatives a tutorial discussion is given of the relation of the crystal field parameters, which determine the anisotropy of these systems and consequently their interesting magnetic properties, with the geometry of the coordination sphere around the lanthanide centre and with the pattern of f orbitals. The problem of systems of low point symmetry is also addressed by showing how detailed single crystal investigation, coupled to more sophisticated calculation procedures, is an absolute necessity to obtain meaningful structure-property relationships in these systems.

Spin mixing at level anti-crossings in the rotating frame makes high-field SABRE feasible.

PubMed

Pravdivtsev, Andrey N; Yurkovskaya, Alexandra V; Vieth, Hans-Martin; Ivanov, Konstantin L

2014-12-07

A new technique is proposed to carry out Signal Amplification By Reversible Exchange (SABRE) experiments at high magnetic fields. SABRE is a method, which utilizes spin order transfer from para-hydrogen to the spins of a substrate in transient complexes using suitable catalysts. Such a transfer of spin order is efficient at low magnetic fields, notably, in the Level Anti-Crossing (LAC) regions. Here it is demonstrated that LAC conditions can also be fulfilled at high fields in the rotating reference frame under the action of an RF-field. Spin mixing at LACs allows one to polarize substrates at high fields as well; the achievable NMR enhancements are around 360 for the ortho-protons of partially deuterated pyridine used as a substrate and around 700 for H2 and substrate in the active complex with the catalyst. High-field SABRE effects have also been found for several other molecules containing a nitrogen atom in the aromatic ring.

High-resolution measurements of the spatial and temporal evolution of megagauss magnetic fields created in intense short-pulse laser-plasma interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chatterjee, Gourab, E-mail: gourab@tifr.res.in; Singh, Prashant Kumar; Adak, Amitava

A pump-probe polarimetric technique is demonstrated, which provides a complete, temporally and spatially resolved mapping of the megagauss magnetic fields generated in intense short-pulse laser-plasma interactions. A normally incident time-delayed probe pulse reflected from its critical surface undergoes a change in its ellipticity according to the magneto-optic Cotton-Mouton effect due to the azimuthal nature of the ambient self-generated megagauss magnetic fields. The temporal resolution of the magnetic field mapping is typically of the order of the pulsewidth, limited by the laser intensity contrast, whereas a spatial resolution of a few μm is achieved by this optical technique. High-harmonics of themore » probe can be employed to penetrate deeper into the plasma to even near-solid densities. The spatial and temporal evolution of the megagauss magnetic fields at the target front as well as at the target rear are presented. The μm-scale resolution of the magnetic field mapping provides valuable information on the filamentary instabilities at the target front, whereas probing the target rear mirrors the highly complex fast electron transport in intense laser-plasma interactions.« less

Central Arctic Crustal Modeling Constrained by Potential Field data and recent ECS Seismic Data

NASA Astrophysics Data System (ADS)

Evangelatos, John; Oakey, Gordon; Saltus, Rick

2017-04-01

2-D gravity and magnetic models have been generated for several transects across the Alpha-Mendeleev ridge complex to study the regional variability of the crustal structure and identify large scale lateral changes. The geometry and density parameters for the models have been constrained using recently acquired seismic reflection and refraction data collected jointly by Canada and the United States as part of their collaborative Arctic ECS programs. A total of fifteen models have been generated perpendicular to the ridge complex, typically 50 to 150 km apart. A minimalist approach to modeling involved maintaining a simple, laterally continuous density structure for the crust while varying the model geometry to fit the observed gravity field. This approach is justified because low amplitude residual Bouguer anomalies suggest a relatively homogenous density structure within the ridge complex. These models have provided a new measure of the regional variability in crustal thickness. Typically, models with thinner crust correspond with deeper bathymetric depths of the ridge which is consistent with regional isostatic equilibrium. Complex "chaotic" magnetic anomalies are associated with the Alpha-Mendeleev ridge complex, which extends beneath the surrounding sedimentary basins. Pseudogravity inversion (magnetic potential) of the magnetic field provides a quantifiable areal extent of ˜1.3 x106 km2. Forward modeling confirms that the magnetic anomalies are not solely the result of magnetized bathymetric highs, but are caused to a great extent by mid- and lower crustal sources. The magnetization of the crust inferred from modeling is significantly higher than available lab measurements of onshore volcanic rocks. Although the 2-D models cannot uniquely identify whether the crustal protolith was continental or oceanic, there is a necessity for a significant content of high density and highly magnetic (ultramafic) material. Based on the crustal thickness estimates from our regional 2-D gravity models and the two possible protoliths, we determine volumetric estimates of the volcanic composition to ˜ 6 × 106 km3 for the mid- and upper-crust and between 10 × 106 and 14 × 106 km3 within the lower crust — for a total of at least ˜16 × 106 km3. This exceeds any estimates for the onshore circum-Arctic HALIP by more than an order of magnitude.

Guided and magnetic self-assembly of tunable magnetoceptive gels

NASA Astrophysics Data System (ADS)

Tasoglu, S.; Yu, C. H.; Gungordu, H. I.; Guven, S.; Vural, T.; Demirci, U.

2014-09-01

Self-assembly of components into complex functional patterns at microscale is common in nature, and used increasingly in numerous disciplines such as optoelectronics, microfabrication, sensors, tissue engineering and computation. Here, we describe the use of stable radicals to guide the self-assembly of magnetically tunable gels, which we call ‘magnetoceptive’ materials at the scale of hundreds of microns to a millimeter, each can be programmed by shape and composition, into heterogeneous complex structures. Using paramagnetism of free radicals as a driving mechanism, complex heterogeneous structures are built in the magnetic field generated by permanent magnets. The overall magnetic signature of final structure is erased via an antioxidant vitamin E, subsequent to guided self-assembly. We demonstrate unique capabilities of radicals and antioxidants in fabrication of soft systems with heterogeneity in material properties, such as porosity, elastic modulus and mass density; then in bottom-up tissue engineering and finally, levitational and selective assembly of microcomponents.

Slow Magnetic Relaxation and Single-Molecule Toroidal Behaviour in a Family of Heptanuclear {CrIII LnIII6 } (Ln=Tb, Ho, Er) Complexes.

PubMed

Vignesh, Kuduva R; Langley, Stuart K; Swain, Abinash; Moubaraki, Boujemaa; Damjanović, Marko; Wernsdorfer, Wolfgang; Rajaraman, Gopalan; Murray, Keith S

2018-01-15

The synthesis, magnetic properties, and theoretical studies of three heterometallic {Cr III Ln III 6 } (Ln=Tb, Ho, Er) complexes, each containing a metal topology consisting of two Ln 3 triangles connected via a Cr III linker, are reported. The {CrTb 6 } and {CrEr 6 } analogues display slow relaxation of magnetization in a 3000 Oe static magnetic field. Single-crystal measurements reveal opening up of the hysteresis loop for {CrTb 6 } and {CrHo 6 } molecules at low temperatures. Ab initio calculations predict toroidal magnetic moments in the two Ln 3 triangles, which are found to couple, stabilizing a con-rotating ferrotoroidal ground state in Tb and Ho examples and extend the possibility of observing toroidal behaviour in non Dy III complexes for the first time. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Guided and magnetic self-assembly of tunable magnetoceptive gels

PubMed Central

Tasoglu, S.; Yu, C.H.; Gungordu, H.I.; Guven, S.; Vural, T.; Demirci, U.

2014-01-01

Self-assembly of components into complex functional patterns at microscale is common in nature, and used increasingly in numerous disciplines such as optoelectronics, microfabrication, sensors, tissue engineering and computation. Here, we describe the use of stable radicals to guide the self-assembly of magnetically tunable gels, which we call ‘magnetoceptive’ materials at the scale of hundreds of microns to a millimeter, each can be programmed by shape and composition, into heterogeneous complex structures. Using paramagnetism of free radicals as a driving mechanism, complex heterogeneous structures are built in the magnetic field generated by permanent magnets. The overall magnetic signature of final structure is erased via an antioxidant vitamin E, subsequent to guided self-assembly. We demonstrate unique capabilities of radicals and antioxidants in fabrication of soft systems with heterogeneity in material properties, such as porosity, elastic modulus and mass density; then in bottom-up tissue engineering and finally, levitational and selective assembly of microcomponents. PMID:25175148

Dynamic Multi-Coil Shimming of the Human Brain at 7 Tesla

PubMed Central

Juchem, Christoph; Nixon, Terence W.; McIntyre, Scott; Boer, Vincent O.; Rothman, Douglas L.; de Graaf, Robin A.

2011-01-01

High quality magnetic field homogenization of the human brain (i.e. shimming) for MR imaging and spectroscopy is a demanding task. The susceptibility differences between air and tissue are a longstanding problem as they induce complex field distortions in the prefrontal cortex and the temporal lobes. To date, the theoretical gains of high field MR have only been realized partially in the human brain due to limited magnetic field homogeneity. A novel shimming technique for the human brain is presented that is based on the combination of non-orthogonal basis fields from 48 individual, circular coils. Custom-built amplifier electronics enabled the dynamic application of the multi-coil shim fields in a slice-specific fashion. Dynamic multi-coil (DMC) shimming is shown to eliminate most of the magnetic field inhomogeneity apparent in the human brain at 7 Tesla and provided improved performance compared to state-of-the-art dynamic shim updating with zero through third order spherical harmonic functions. The novel technique paves the way for high field MR applications of the human brain for which excellent magnetic field homogeneity is a prerequisite. PMID:21824794

A study of solar magnetic fields below the surface, at the surface, and in the solar atmosphere - understanding the cause of major solar activity

NASA Astrophysics Data System (ADS)

Chintzoglou, Georgios

2016-04-01

Magnetic fields govern all aspects of solar activity from the 11-year solar cycle to the most energetic events in the solar system, such as solar flares and Coronal Mass Ejections (CMEs). As seen on the surface of the sun, this activity emanates from localized concentrations of magnetic fields emerging sporadically from the solar interior. These locations are called solar Active Regions (ARs). However, the fundamental processes regarding the origin, emergence and evolution of solar magnetic fields as well as the generation of solar activity are largely unknown or remain controversial. In this dissertation, multiple important issues regarding solar magnetism and activities are addressed, based on advanced observations obtained by AIA and HMI instruments aboard the SDO spacecraft. First, this work investigates the formation of coronal magnetic flux ropes (MFRs), structures associated with major solar activity such as CMEs. In the past, several theories have been proposed to explain the cause of this major activity, which can be categorized in two contrasting groups (a) the MFR is formed in the eruption, and (b) the MFR pre-exists the eruption. This remains a topic of heated debate in modern solar physics. This dissertation provides a complete treatment of the role of MFRs from their genesis all the way to their eruption and even destruction. The study has uncovered the pre-existence of two weakly twisted MFRs, which formed during confined flaring 12 hours before their associated CMEs. Thus, it provides unambiguous evidence for MFRs truly existing before the CME eruptions, resolving the pre-existing MFR controversy. Second, this dissertation addresses the 3-D magnetic structure of complex emerging ARs. In ARs the photospheric fields might show all aspects of complexity, from simple bipolar regions to extremely complex multi-polar surface magnetic distributions. In this thesis, we introduce a novel technique to infer the subphotospheric configuration of emerging magnetic flux tubes while forming ARs on the surface. Using advanced 3D visualization tools and applying this technique on a complex flare and CME productive AR, we found that the magnetic flux tubes involved in forming the complex AR may originate from a single progenitor flux tube in the SCZ. The complexity can be explained as a result of vertical and horizontal bifurcations that occurred on the progenitor flux tube. Third, this dissertation proposes a new scenario on the origin of major solar activity. When more than one flux tubes are in close proximity to each other while they break through the photospheric surface, collision and shearing may occur as they emerge. Once this collisional shearing occurs between nonconjugated sunspots (opposite polarities not belonging to the same bipole), major solar activity is triggered. The collision and the shearing occur due to the natural separation of polarities in emerging bipoles. This is forcing changes in the connectivity close to the photosphere (up to a few local pressure scale heights above the surface) by means of photospheric reconnection and subsequent submergence of small bipoles at the collision interface (polarity inversion line; PIL). In this continuous collision, more poloidal flux is added to the system effectively creating an expanding MFR into the corona, explaining the observation of filament formation above the PIL together with flare activity and CMEs. Our results reject two popular scenarios on the possible cause of solar eruptions (1) eruption occurs due to shearing motion between conjugate polarities, and, (2) bodily emergence of an MFR.

Very Large Array H I Zeeman Observations of the Cygnus X Region: DR 22 and ON 2

NASA Astrophysics Data System (ADS)

Mayo, E. A.; Troland, T. H.

2012-02-01

We have used the Very Large Array to study the Zeeman effect in 21 cm H I absorption lines from two star-forming regions in the Cygnus X complex, DR 22 and ON 2. We measure the line-of-sight magnetic field toward these regions, finding B los = -84 ± 11 μG toward the DR 22 H II region and B los < 50 μG toward each of the two H II regions in ON 2. We interpret these results in terms of two different models. In one model, we assume that the H I Zeeman effect is a measure of magnetic fields in the associated molecular clouds. If so, then the DR 22 molecular cloud is magnetically subcritical, that is, magnetically dominated. The ON 2 molecular clouds are magnetically supercritical. In a second model, we assume that the H I Zeeman effect is a measure of magnetic fields in photon-dominated regions where the gas has been compressed (and the field amplified) by absorption of stellar radiation. We find that this second model, where the measured field strength has been affected by star formation, accounts well for the DR 22 H I Zeeman effect. This same model, however, overpredicts the magnetic field in ON 2. ON 2 may be a region where the magnetic field is energetically insignificant or where the field happens to lie nearly in the plane of the sky.

A broadband microwave Corbino spectrometer at ³He temperatures and high magnetic fields.

PubMed

Liu, Wei; Pan, LiDong; Armitage, N P

2014-09-01

We present the technical details of a broadband microwave spectrometer for measuring the complex conductance of thin films covering the range from 50 MHz up to 16 GHz in the temperature range 300 mK-6 K and at applied magnetic fields up to 8 T. We measure the complex reflection from a sample terminating a coaxial transmission line and calibrate the signals with three standards with known reflection coefficients. Thermal isolation of the heat load from the inner conductor is accomplished by including a section of NbTi superconducting cable (transition temperature around 8-9 K) and hermetic seal glass bead adapters. This enables us to stabilize the base temperature of the sample stage at 300 mK. However, the inclusion of this superconducting cable complicates the calibration procedure. We document the effects of the superconducting cable on our calibration procedure and the effects of applied magnetic fields and how we control the temperature with great repeatability for each measurement. We have successfully extracted reliable data in this frequency, temperature, and field range for thin superconducting films and highly resistive graphene samples.

A broadband microwave Corbino spectrometer at 3He temperatures and high magnetic fields

NASA Astrophysics Data System (ADS)

Liu, Wei; Pan, LiDong; Armitage, N. P.

2014-09-01

We present the technical details of a broadband microwave spectrometer for measuring the complex conductance of thin films covering the range from 50 MHz up to 16 GHz in the temperature range 300 mK-6 K and at applied magnetic fields up to 8 T. We measure the complex reflection from a sample terminating a coaxial transmission line and calibrate the signals with three standards with known reflection coefficients. Thermal isolation of the heat load from the inner conductor is accomplished by including a section of NbTi superconducting cable (transition temperature around 8-9 K) and hermetic seal glass bead adapters. This enables us to stabilize the base temperature of the sample stage at 300 mK. However, the inclusion of this superconducting cable complicates the calibration procedure. We document the effects of the superconducting cable on our calibration procedure and the effects of applied magnetic fields and how we control the temperature with great repeatability for each measurement. We have successfully extracted reliable data in this frequency, temperature, and field range for thin superconducting films and highly resistive graphene samples.

Magnetic field evolution in white dwarfs: The hall effect and complexity of the field

NASA Technical Reports Server (NTRS)

Muslimov, A. G.; Van Horn, H. M.; Wood, M. A.

1995-01-01

We calculate the evolution of the magnetic fields in white dwarfs, taking into account the Hall effect. Because this effect depends nonlinearly upon the magnetic field strength B, the time dependences of the various multipole field components are coupled. The evolution of the field is thus significantly more complicated than has been indicated by previous investigations. Our calculations employ recent white dwarf evolutionary sequences computed for stars with masses 0.4, 0.6, 0.8, and 1.0 solar mass. We show that in the presence of a strong (up to approximately 10(exp 9) G) internal toroidal magnetic field; the evolution of even the lowest order poloidal modes can be substantially changed by the Hall effect. As an example, we compute the evolution of an initially weak quadrupole component, which we take arbitrarily to be approximately 0.1%-1% of the strength of a dominant dipole field. We find that coupling provided by the Hall effect can produce growth of the ratio of the quadrupole to the dipole component of the surface value of the magnetic field strength by more than a factor of 10 over the 10(exp 9) to 10(exp 10) year cooling lifetime of the white dwarf. Some consequences of these results for the process of magnetic-field evolution in white dwarfs are briefly discussed.

Exotic magnetic states in Pauli-limited superconductors.

PubMed

Kenzelmann, M

2017-03-01

Magnetism and superconductivity compete or interact in complex and intricate ways. Here we review the special case where novel magnetic phenomena appear due to superconductivity, but do not exist without it. Such states have recently been identified in unconventional superconductors. They are different from the mere coexistence of magnetic order and superconductivity in conventional superconductors, or from competing magnetic and superconducting phases in many materials. We describe the recent progress in the study of such exotic magnetic phases, and articulate the many open questions in this field.

Study of Equatorial Ionospheric irregularities and Mapping of Electron Density Profiles and Ionograms

DTIC Science & Technology

2012-03-09

equation is a product of a complex basis vector in Jackson and a linear combination of plane wave functions. We convert both the amplitudes and the...wave function arguments from complex scalars to complex vectors . This conversion allows us to separate the electric field vector and the imaginary...magnetic field vector , because exponentials of imaginary scalars convert vectors to imaginary vectors and vice versa, while ex- ponentials of imaginary

Massive star winds interacting with magnetic fields on various scales

NASA Astrophysics Data System (ADS)

David-Uraz, A.; Petit, V.; Erba, C.; Fullerton, A.; Walborn, N.; MacInnis, R.

2018-01-01

One of the defining processes which govern massive star evolution is their continuous mass loss via dense, supersonic line-driven winds. In the case of those OB stars which also host a surface magnetic field, the interaction between that field and the ionized outflow leads to complex circumstellar structures known as magnetospheres. In this contribution, we review recent developments in the field of massive star magnetospheres, including current efforts to characterize the largest magnetosphere surrounding an O star: that of NGC 1624-2. We also discuss the potential of the "analytic dynamical magnetosphere" (ADM) model to interpret multi-wavelength observations. Finally, we examine the possible effects of — heretofore undetected — small-scale magnetic fields on massive star winds and compare their hypothetical consequences to existing, unexplained observations.

Self-assembly with orthogonal-imposed stimuli to impart structure and confer magnetic function to electrodeposited hydrogels.

PubMed

Li, Ying; Liu, Yi; Gao, Tieren; Zhang, Boce; Song, Yingying; Terrell, Jessica L; Barber, Nathan; Bentley, William E; Takeuchi, Ichiro; Payne, Gregory F; Wang, Qin

2015-05-20

A magnetic nanocomposite film with the capability of reversibly collecting functionalized magnetic particles was fabricated by simultaneously imposing two orthogonal stimuli (electrical and magnetic). We demonstrate that cathodic codeposition of chitosan and Fe3O4 nanoparticles while simultaneously applying a magnetic field during codeposition can (i) organize structure, (ii) confer magnetic properties, and (iii) yield magnetic films that can perform reversible collection/assembly functions. The magnetic field triggered the self-assembly of Fe3O4 nanoparticles into hierarchical "chains" and "fibers" in the chitosan film. For controlled magnetic properties, the Fe3O4-chitosan film was electrodeposited in the presence of various strength magnetic fields and different deposition times. The magnetic properties of the resulting films should enable broad applications in complex devices. As a proof of concept, we demonstrate the reversible capture and release of green fluorescent protein (EGFP)-conjugated magnetic microparticles by the magnetic chitosan film. Moreover, antibody-functionalized magnetic microparticles were applied to capture cells from a sample, and these cells were collected, analyzed, and released by the magnetic chitosan film, paving the way for applications such as reusable biosensor interfaces (e.g., for pathogen detection). To our knowledge, this is the first report to apply a magnetic field during the electrodeposition of a hydrogel to generate magnetic soft matter. Importantly, the simple, rapid, and reagentless fabrication methodologies demonstrated here are valuable features for creating a magnetic device interface.

Possible disruption of remote viewing by complex weak magnetic fields around the stimulus site and the possibility of accessing real phase space: a pilot study.

PubMed

Koren, S A; Persinger, M A

2002-12-01

In 2002 Persinger, Roll, Tiller, Koren, and Cook considered whether there are physical processes by which recondite information exists within the space and time of objects or events. The stimuli that compose this information might be directly detected within the whole brain without being processed by the typical sensory modalities. We tested the artist Ingo Swann who can reliably draw and describe randomly selected photographs sealed in envelopes in another room. In the present experiment the photographs were immersed continuously in repeated presentations (5 times per sec.) of one of two types of computer-generated complex magnetic field patterns whose intensities were less than 20 nT over most of the area. WINDOWS-generated but not DOS-generated patterns were associated with a marked decrease in Mr. Swann's accuracy. Whereas the DOS software generated exactly the same pattern, WINDOWS software phase-modulated the actual wave form resulting in an infinite bandwidth and complexity. We suggest that information obtained by processes attributed to "paranormal" phenomena have physical correlates that can be masked by weak, infinitely variable magnetic fields.

Biological effects due to weak magnetic field on plants

NASA Astrophysics Data System (ADS)

Belyavskaya, N. A.

2004-01-01

Throughout the evolution process, Earth's magnetic field (MF, about 50 μT) was a natural component of the environment for living organisms. Biological objects, flying on planned long-term interplanetary missions, would experience much weaker magnetic fields, since galactic MF is known to be 0.1-1 nT. However, the role of weak magnetic fields and their influence on functioning of biological organisms are still insufficiently understood, and is actively studied. Numerous experiments with seedlings of different plant species placed in weak magnetic field have shown that the growth of their primary roots is inhibited during early germination stages in comparison with control. The proliferative activity and cell reproduction in meristem of plant roots are reduced in weak magnetic field. Cell reproductive cycle slows down due to the expansion of G 1 phase in many plant species (and of G 2 phase in flax and lentil roots), while other phases of cell cycle remain relatively stabile. In plant cells exposed to weak magnetic field, the functional activity of genome at early pre-replicate period is shown to decrease. Weak magnetic field causes intensification of protein synthesis and disintegration in plant roots. At ultrastructural level, changes in distribution of condensed chromatin and nucleolus compactization in nuclei, noticeable accumulation of lipid bodies, development of a lytic compartment (vacuoles, cytosegresomes and paramural bodies), and reduction of phytoferritin in plastids in meristem cells were observed in pea roots exposed to weak magnetic field. Mitochondria were found to be very sensitive to weak magnetic field: their size and relative volume in cells increase, matrix becomes electron-transparent, and cristae reduce. Cytochemical studies indicate that cells of plant roots exposed to weak magnetic field show Ca 2+ over-saturation in all organelles and in cytoplasm unlike the control ones. The data presented suggest that prolonged exposures of plants to weak magnetic field may cause different biological effects at the cellular, tissue and organ levels. They may be functionally related to systems that regulate plant metabolism including the intracellular Ca 2+ homeostasis. However, our understanding of very complex fundamental mechanisms and sites of interactions between weak magnetic fields and biological systems is still incomplete and still deserve strong research efforts.

Quantifying the motion of magnetic particles in excised tissue: Effect of particle properties and applied magnetic field

NASA Astrophysics Data System (ADS)

Kulkarni, Sandip; Ramaswamy, Bharath; Horton, Emily; Gangapuram, Sruthi; Nacev, Alek; Depireux, Didier; Shimoji, Mika; Shapiro, Benjamin

2015-11-01

This article presents a method to investigate how magnetic particle characteristics affect their motion inside tissues under the influence of an applied magnetic field. Particles are placed on top of freshly excised tissue samples, a calibrated magnetic field is applied by a magnet underneath each tissue sample, and we image and quantify particle penetration depth by quantitative metrics to assess how particle sizes, their surface coatings, and tissue resistance affect particle motion. Using this method, we tested available fluorescent particles from Chemicell of four sizes (100 nm, 300 nm, 500 nm, and 1 μm diameter) with four different coatings (starch, chitosan, lipid, and PEG/P) and quantified their motion through freshly excised rat liver, kidney, and brain tissues. In broad terms, we found that the applied magnetic field moved chitosan particles most effectively through all three tissue types (as compared to starch, lipid, and PEG/P coated particles). However, the relationship between particle properties and their resulting motion was found to be complex. Hence, it will likely require substantial further study to elucidate the nuances of transport mechanisms and to select and engineer optimal particle properties to enable the most effective transport through various tissue types under applied magnetic fields.

Is magnetic topology important for heating the solar atmosphere?

PubMed

Parnell, Clare E; Stevenson, Julie E H; Threlfall, James; Edwards, Sarah J

2015-05-28

Magnetic fields permeate the entire solar atmosphere weaving an extremely complex pattern on both local and global scales. In order to understand the nature of this tangled web of magnetic fields, its magnetic skeleton, which forms the boundaries between topologically distinct flux domains, may be determined. The magnetic skeleton consists of null points, separatrix surfaces, spines and separators. The skeleton is often used to clearly visualize key elements of the magnetic configuration, but parts of the skeleton are also locations where currents and waves may collect and dissipate. In this review, the nature of the magnetic skeleton on both global and local scales, over solar cycle time scales, is explained. The behaviour of wave pulses in the vicinity of both nulls and separators is discussed and so too is the formation of current layers and reconnection at the same features. Each of these processes leads to heating of the solar atmosphere, but collectively do they provide enough heat, spread over a wide enough area, to explain the energy losses throughout the solar atmosphere? Here, we consider this question for the three different solar regions: active regions, open-field regions and the quiet Sun. We find that the heating of active regions and open-field regions is highly unlikely to be due to reconnection or wave dissipation at topological features, but it is possible that these may play a role in the heating of the quiet Sun. In active regions, the absence of a complex topology may play an important role in allowing large energies to build up and then, subsequently, be explosively released in the form of a solar flare. Additionally, knowledge of the intricate boundaries of open-field regions (which the magnetic skeleton provides) could be very important in determining the main acceleration mechanism(s) of the solar wind. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Numerical study of plasma generation process and internal antenna heat loadings in J-PARC RF negative ion source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shibata, T., E-mail: shibat@post.j-parc.jp; Ueno, A.; Oguri, H.

A numerical model of plasma transport and electromagnetic field in the J-PARC (Japan Proton Accelerator Research Complex) radio frequency ion source has been developed to understand the relation between antenna coil heat loadings and plasma production/transport processes. From the calculation, the local plasma density increase is observed in the region close to the antenna coil. Electrons are magnetized by the magnetic field line with absolute magnetic flux density 30–120 Gauss which leads to high local ionization rate. The results suggest that modification of magnetic configuration can be made to reduce plasma heat flux onto the antenna.

Spatial Transport of Magnetic Flux Surfaces in Strongly Anisotropic Turbulence

NASA Astrophysics Data System (ADS)

Matthaeus, W. H.; Servidio, S.; Wan, M.; Ruffolo, D. J.; Rappazzo, A. F.; Oughton, S.

2013-12-01

Magnetic flux surfaces afford familiar descriptions of spatial structure, dynamics, and connectivity of magnetic fields, with particular relevance in contexts such as solar coronal flux tubes, magnetic field connectivity in the interplanetary and interstellar medium, as well as in laboratory plasmas and dynamo problems [1-4]. Typical models assume that field-lines are orderly, and flux tubes remain identifiable over macroscopic distances; however, a previous study has shown that flux tubes shred in the presence of fluctuations, typically losing identity after several correlation scales [5]. Here, the structure of magnetic flux surfaces is numerically investigated in a reduced magnetohydrodynamic (RMHD) model of homogeneous turbulence. Short and long-wavelength behavior is studied statistically by propagating magnetic surfaces along the mean field. At small scales magnetic surfaces become complex, experiencing an exponential thinning. At large scales, instead, the magnetic flux undergoes a diffusive behavior. The link between the diffusion of the coarse-grained flux and field-line random walk is established by means of a multiple scale analysis. Both large and small scales limits are controlled by the Kubo number. These results have consequences for understanding and interpreting processes such as magnetic reconnection and field-line diffusion in plasmas [6]. [1] E. N. Parker, Cosmical Magnetic Fields (Oxford Univ. Press, New York, 1979). [2] J. R. Jokipii and E. N. Parker, Phys. Rev. Lett. 21, 44 (1968). [3] R. Bruno et al., Planet. Space Sci. 49, 1201 (2001). [4] M. N. Rosenbluth et al., Nuclear Fusion 6, 297 (1966). [5] W. H. Matthaeus et al., Phys. Rev. Lett. 75, 2136 (1995). [6] S. Servidio et al., submitted (2013).

Shorter Life Span of Microorganisms and Plants as a Consequence of Shielded Magnetic Environment

NASA Astrophysics Data System (ADS)

Dobrota, C.; Piso, I. M.; Bathory, D.

The geomagnetic field is an essential environmental factor for life and health on this planet. In order to survey how magnetic fields affect the life span and the nitrogenase (an iron-sulphur enzyme) activity of Azotobacter chroococcum as well as the life span, the main organic synthesis and the water balance of plants (22 species), the biological tests were incubated under shielded magnetic field and also in normal geo-magnetic environment. The shielding level was about 10-6 of the terrestrial magnetic field.Life cycles of all organisms require the co-ordinated control of a complex set of interlocked physiological processes and metabolic pathways. Such processes are likely to be regulated by a large number of genes. Our researches suggest that the main point in biological structures, which seems to be affected by the low magnetic environment, is the water molecule. Magnetic field induces a molecular alignment. Under shielded conditions, unstructured water molecules with fewer hydrogen bonds, which are producing a more reactive environment, are occurring. As compared to control, the life span of both microorganisms and plants was shorter in shielded environment. A higher nitrogenase affinity for the substrate was recorded in normal geo-magnetic field compared to low magnetic field. The synthesis of carbohydrates, lipids, proteins and enzymes was modified under experimental conditions. The stomatal conductance was higher between 158 and 300% in shielded environment indicating an important water loss from the plant cells.Our results support the idea that the shielded magnetic environment induces different reactions depending on the time of exposure and on the main metabolic pathways of the cells.

Broadband complex permeability characterization of magnetic thin films using shorted microstrip transmission-line perturbation

NASA Astrophysics Data System (ADS)

Liu, Yan; Chen, Linfeng; Tan, C. Y.; Liu, H. J.; Ong, C. K.

2005-06-01

A brief review of the methods used for broadband complex permeability measurement of magnetic thin films up to microwave frequencies is given. In particular, the working principles of the transmission-line perturbation methods for the characterization of magnetic thin films are discussed, with emphasis on short-circuited planar transmission-line perturbation methods. The algorithms for calculating the complex permeability of magnetic thin films for short-circuited planar transmission-line perturbation methods are analyzed. A shorted microstrip line is designed and fabricated as a prototype measurement fixture. The structure of the microstrip fixture and the corresponding measurement procedure are discussed in detail. A piece of 340 nm thick FeTaN thin film deposited on Si substrate using sputtering method is characterized using the microstrip fixture. An improved technique for obtaining permeability by using a saturation magnetization field is demonstrated here, and the results fit well with the Landau-Lifchitz-Gilbert theory. Approaches to extending this method to other aspects in the investigation of magnetic thin film are also discussed.

A preliminary study of extended magnetic field structures in the ionosphere

NASA Technical Reports Server (NTRS)

Sullivan, James D.; Lane, Barton G.; Post, Richard S.

1987-01-01

Several plasma phenomena which are to be expected around a magnet in LEO were identified and analyzed qualitatively. The ASTROMAG cusp magnet will create an extended field whose strength drops to the ambient level over a scale length of approx. 15 m; the combined field has a complex topology with ring nulls and open and closed field lines. The entire configuration is moving through the partially ionized F-layer of the ionosphere at a speed slow compared to the local Alfven speed but fast compared to the ion sound speed. The ambient plasma crosses the extended field structure in a time short compared to the ion Larmor period yet long relative to the electron Larmor period. Thus, electrons behave as a magnetized fluid while ions move ballistically until reflected from higher fields near the cusp. Since the Debye length is short compared to the field scale length, an electrostatic shock-like structure forms to equilibrate the flows and achieve quasi-neutrality. The ambient plasma will be excluded from a cavity near the magnet. The size and nature of the strong interaction region in which the magnet significantly perturbs the ambient flow were determined by studying ion orbits numerically. Lecture viewgraphs summarizing these results are presented.

Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system

PubMed Central

Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng

2015-01-01

We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices. PMID:26687638

Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system.

PubMed

Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng

2015-12-21

We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices.

Working principle and application of magnetic separation for biomedical diagnostic at high- and low-field gradients.

PubMed

Leong, Sim Siong; Yeap, Swee Pin; Lim, JitKang

2016-12-06

Magnetic separation is a versatile technique used in sample preparation for diagnostic purpose. For such application, an external magnetic field is applied to drive the separation of target entity (e.g. bacteria, viruses, parasites and cancer cells) from a complex raw sample in order to ease the subsequent task(s) for disease diagnosis. This separation process not only can be achieved via the utilization of high magnetic field gradient, but also, in most cases, low magnetic field gradient with magnitude less than 100 T m -1 is equally feasible. It is the aim of this review paper to summarize the usage of both high gradient magnetic separation and low gradient magnetic separation (LGMS) techniques in this area of research. It is noteworthy that effectiveness of the magnetic separation process not only determines the outcome of a diagnosis but also directly influences its accuracy as well as sensing time involved. Therefore, understanding the factors that simultaneously influence the efficiency of both magnetic separation process and target detection is necessary. Moreover, for LGMS, there are several important considerations that should be taken into account in order to ensure its successful implementation. Hence, this review paper aims to provide an overview to relate all this crucial information by linking the magnetic separation theory to biomedical diagnostic applications.

Magnetic to magnetic and kinetic to magnetic energy transfers at the top of the Earth's core

NASA Astrophysics Data System (ADS)

Huguet, Ludovic; Amit, Hagay; Alboussière, Thierry

2016-11-01

We develop the theory for the magnetic to magnetic and kinetic to magnetic energy transfer between different spherical harmonic degrees due to the interaction of fluid flow and radial magnetic field at the top of the Earth's core. We show that non-zero secular variation of the total magnetic energy could be significant and may provide evidence for the existence of stretching secular variation, which suggests the existence of radial motions at the top of the Earth's core-whole core convection or MAC waves. However, the uncertainties of the small scales of the geomagnetic field prevent a definite conclusion. Combining core field and flow models we calculate the detailed magnetic to magnetic and kinetic to magnetic energy transfer matrices. The magnetic to magnetic energy transfer shows a complex behaviour with local and non-local transfers. The spectra of magnetic to magnetic energy transfers show clear maxima and minima, suggesting an energy cascade. The kinetic to magnetic energy transfers, which are much weaker due to the weak poloidal flow, are either local or non-local between degree one and higher degrees. The patterns observed in the matrices resemble energy transfer patterns that are typically found in 3-D MHD numerical simulations.

Direct Observation of Very Large Zero-Field Splitting in a Tetrahedral Ni(II)Se4 Coordination Complex.

PubMed

Jiang, Shang-Da; Maganas, Dimitrios; Levesanos, Nikolaos; Ferentinos, Eleftherios; Haas, Sabrina; Thirunavukkuarasu, Komalavalli; Krzystek, J; Dressel, Martin; Bogani, Lapo; Neese, Frank; Kyritsis, Panayotis

2015-10-14

The high-spin (S = 1) tetrahedral Ni(II) complex [Ni{(i)Pr2P(Se)NP(Se)(i)Pr2}2] was investigated by magnetometry, spectroscopic, and quantum chemical methods. Angle-resolved magnetometry studies revealed the orientation of the magnetization principal axes. The very large zero-field splitting (zfs), D = 45.40(2) cm(-1), E = 1.91(2) cm(-1), of the complex was accurately determined by far-infrared magnetic spectroscopy, directly observing transitions between the spin sublevels of the triplet ground state. These are the largest zfs values ever determined--directly--for a high-spin Ni(II) complex. Ab initio calculations further probed the electronic structure of the system, elucidating the factors controlling the sign and magnitude of D. The latter is dominated by spin-orbit coupling contributions of the Ni ions, whereas the corresponding effects of the Se atoms are remarkably smaller.

Extracting, Tracking, and Visualizing Magnetic Flux Vortices in 3D Complex-Valued Superconductor Simulation Data.

PubMed

Guo, Hanqi; Phillips, Carolyn L; Peterka, Tom; Karpeyev, Dmitry; Glatz, Andreas

2016-01-01

We propose a method for the vortex extraction and tracking of superconducting magnetic flux vortices for both structured and unstructured mesh data. In the Ginzburg-Landau theory, magnetic flux vortices are well-defined features in a complex-valued order parameter field, and their dynamics determine electromagnetic properties in type-II superconductors. Our method represents each vortex line (a 1D curve embedded in 3D space) as a connected graph extracted from the discretized field in both space and time. For a time-varying discrete dataset, our vortex extraction and tracking method is as accurate as the data discretization. We then apply 3D visualization and 2D event diagrams to the extraction and tracking results to help scientists understand vortex dynamics and macroscale superconductor behavior in greater detail than previously possible.

The Large Scale Structure of the Galactic Magnetic Field and High Energy Cosmic Ray Anisotropy

NASA Astrophysics Data System (ADS)

Alvarez-Muñiz, Jaime; Stanev, Todor

2006-10-01

Measurements of the magnetic field in our Galaxy are complex and usually difficult to interpret. A spiral regular field in the disk is favored by observations, however the number of field reversals is still under debate. Measurements of the parity of the field across the Galactic plane are also very difficult due to the presence of the disk field itself. In this work we demonstrate that cosmic ray protons in the energy range 1018 to 1019eV, if accelerated near the center of the Galaxy, are sensitive to the large scale structure of the Galactic Magnetic Field (GMF). In particular if the field is of even parity, and the spiral field is bi-symmetric (BSS), ultra high energy protons will predominantly come from the Southern Galactic hemisphere, and predominantly from the Northern Galactic hemisphere if the field is of even parity and axi-symmetric (ASS). There is no sensitivity to the BSS or ASS configurations if the field is of odd parity.

Magnetic Field Observations near Mercury: Preliminary Results from Mariner 10.

PubMed

Ness, N F; Behannon, K W; Lepping, R P; Whang, Y C; Schatten, K H

1974-07-12

Results are presented from a preliminary analysis of data obtained near Mercury on 29 March 1974 by the NASA-GSFC magnetic field experiment on Mariner 10. Rather unexpectedly, a very well-developed, detached bow shock wave, which develops as the super-Alfvénic solar wind interacts with the planet, has been observed. In addition, a magnetosphere-like region, with maximum field strength of 98 gammas at closest approach (704 kilometers altitude), has been observed, contained within boundaries similar to the terrestrial magnetopause. The obstacle deflecting the solar wind flow is global in size, but the origin of the enhanced magnetic field has not yet been uniquely established. The field may be intrinsic to the planet and distorted by interaction with the solar wind. It may also be associated with a complex induction process whereby the planetary interior-atmosphere-ionosphere interacts with the solar wind flow to generate the observed field by a dynamo action. The complete body of data favors the preliminary conclusion that Mercury has an intrinsic magnetic field. If this is correct, it represents a major scientific discovery in planetary magnetism and will have considerable impact on studies of the origin of the solar system.

Can we explain atypical solar flares?

NASA Astrophysics Data System (ADS)

Dalmasse, K.; Chandra, R.; Schmieder, B.; Aulanier, G.

2015-02-01

Context. We used multiwavelength high-resolution data from ARIES, THEMIS, and SDO instruments to analyze a non-standard, C3.3 class flare produced within the active region NOAA 11589 on 2012 October 16. Magnetic flux emergence and cancellation were continuously detected within the active region, the latter leading to the formation of two filaments. Aims: Our aim is to identify the origins of the flare taking the complex dynamics of its close surroundings into account. Methods: We analyzed the magnetic topology of the active region using a linear force-free field extrapolation to derive its 3D magnetic configuration and the location of quasi-separatrix layers (QSLs), which are preferred sites for flaring activity. Because the active region's magnetic field was nonlinear force-free, we completed a parametric study using different linear force-free field extrapolations to demonstrate the robustness of the derived QSLs. Results: The topological analysis shows that the active region presented a complex magnetic configuration comprising several QSLs. The considered data set suggests that an emerging flux episode played a key role in triggering the flare. The emerging flux probably activated the complex system of QSLs, leading to multiple coronal magnetic reconnections within the QSLs. This scenario accounts for the observed signatures: the two extended flare ribbons developed at locations matched by the photospheric footprints of the QSLs and were accompanied with flare loops that formed above the two filaments, which played no important role in the flare dynamics. Conclusions: This is a typical example of a complex flare that can a priori show standard flare signatures that are nevertheless impossible to interpret with any standard model of eruptive or confined flare. We find that a topological analysis, however, permitted us to unveil the development of such complex sets of flare signatures. Movies associated to Figs. 1, 3, and 9 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/574/A37

Magnetomechanical effect in silicon (Cz-Si) surface layers

NASA Astrophysics Data System (ADS)

Koplak, O. V.; Dmitriev, A. I.; Morgunov, R. B.

2012-07-01

The mechanical properties of near-surface layers of Czochralski-grown silicon crystals Cz- n-Si(111) have been found to undergo changes in response to an external constant magnetic field ( B ˜ 0.1 T). A magnetically induced variation in the microhardness, Young's modulus, and coefficient of plasticity of silicon crystals correlates with the change in the lattice parameter and internal stresses of the sample. The growth of an oxide film under exposure to a magnetic field plays the principal role in the magnetomechanical effect due to a decrease in the concentration of oxygen complexes in the near-surface layers of the sample. In microstructured silicon, where the surface is considerably more developed, the magnetic field induces more profound changes in the internal stresses as compared to single crystals.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solis, Kyle J.; Martin, James E.

In recent years a rich variety of emergent phenomena have been observed when suspensions of magnetic particles are subjected to alternating magnetic fields. These particle assemblies often exhibit vigorous dynamics due to the injection of energy from the field. These include surface and interface phenomena, such as highly organized, segmented “snakes” that can be induced to swim by structural symmetry breaking, and “asters” and “anti-asters,” particle assemblies that can be manipulated to capture and transport cargo. In bulk suspensions of magnetic platelets subjected to multiaxial alternating fields, advection lattices and even vortex lattices have been created, and a variety ofmore » biomimetic dynamics – serpents, bees and amoebas – have been discovered in magnetic fluids suspended in an immiscible liquid. In this paper several new driven phases are presented, including flying chevrons, dense spinning clusters, filaments, and examples of phase coexistence in driven phases. These observations broaden the growing field of driven magnetic suspensions and present new challenges to those interested in simulating the dynamics of these complex systems.« less

Magnetically tunable bidirectional locomotion of a self-assembled nanorod-sphere propeller.

PubMed

García-Torres, José; Calero, Carles; Sagués, Francesc; Pagonabarraga, Ignacio; Tierno, Pietro

2018-04-25

Field-driven direct assembly of nanoscale matter has impact in disparate fields of science. In microscale systems, such concept has been recently exploited to optimize propulsion in viscous fluids. Despite the great potential offered by miniaturization, using self-assembly to achieve transport at the nanoscale remains an elusive task. Here we show that a hybrid propeller, composed by a ferromagnetic nanorod and a paramagnetic microsphere, can be steered in a fluid in a variety of modes, from pusher to puller, when the pair is dynamically actuated by a simple oscillating magnetic field. We exploit this unique design to build more complex structures capable of carrying several colloidal cargos as microscopic trains that quickly disassemble at will under magnetic command. In addition, our prototype can be extended to smaller nanorods below the diffraction limit, but still dynamically reconfigurable by the applied magnetic field.

Magnetic field effects on electrochemical metal depositions.

PubMed

Bund, Andreas; Ispas, Adriana; Mutschke, Gerd

2008-04-01

This paper discusses recent experimental and numerical results from the authors' labs on the effects of moderate magnetic (B) fields in electrochemical reactions. The probably best understood effect of B fields during electrochemical reactions is the magnetohydrodynamic (MHD) effect. In the majority of cases it manifests itself in increased mass transport rates which are a direct consequence of Lorentz forces in the bulk of the electrolyte. This enhanced mass transport can directly affect the electrocrystallization. The partial currents for the nucleation of nickel in magnetic fields were determined using an in situ micro-gravimetric technique and are discussed on the basis of the nucleation model of Heerman and Tarallo. Another focus of the paper is the numerical simulation of MHD effects on electrochemical metal depositions. A careful analysis of the governing equations shows that many MHD problems must be treated in a 3D geometry. In most cases there is a complex interplay of natural and magnetically driven convection.

Dynamic cross correlation studies of wave particle interactions in ULF phenomena

NASA Technical Reports Server (NTRS)

Mcpherron, R. L.

1979-01-01

Magnetic field observations made by satellites in the earth's magnetic field reveal a wide variety of ULF waves. These waves interact with the ambient particle populations in complex ways, causing modulation of the observed particle fluxes. This modulation is found to be a function of species, pitch angle, energy and time. The characteristics of this modulation provide information concerning the wave mode and interaction process. One important characteristic of wave-particle interactions is the phase of the particle flux modulation relative to the magnetic field variations. To display this phase as a function of time a dynamic cross spectrum program has been developed. The program produces contour maps in the frequency time plane of the cross correlation coefficient between any particle flux time series and the magnetic field vector. This program has been utilized in several studies of ULF wave-particle interactions at synchronous orbit.

Three isostructural one-dimensional Ln(III) chains with distorted cubane motifs showing dual fluorescence and slow magnetic relaxation/magnetocaloric effect.

PubMed

Li, Yan; Yu, Jia-Wen; Liu, Zhong-Yi; Yang, En-Cui; Zhao, Xiao-Jun

2015-01-05

Three new homometallic lanthanide complexes with mixed carboxylate-modified rigid ligands, [Ln(μ3-OH)(na)(pyzc)]n (na(-) = 1-naphtholate, pyzc(-) = 2-pyrazinecarboxylate, Ln = Dy (1), Yb (2), and Gd (3)), were solvothermally synthesized, and their structures and magnetic as well as photophysical properties were completely investigated. Complexes 1-3 are crystallographically isostructural, exhibiting linear chains with four bidentate bridging μ-COO(-) moieties encapsulated cubic {Ln4(μ3-OH)4}(8+) clusters repeatedly extended by 4-fold chelating-bridging-pyzc(-) connectors. Magnetically, the former two complexes with highly anisotropic Dy(III) and weak anisotropic Yb(III) ions in the distorted NO7 triangular dodecahedron coordination environment display field-induced slow relaxation of magnetization. Fitting the dynamic magnetic data to the Arrhenius law gives energy barrier ΔE/kB = 39.6 K and pre-exponential factor τo = 1.52 × 10(-8) s for 1 and ΔE/kB = 14.1 K and τo = 2.13 × 10(-7) s for 2. By contrast, complex 3 with isotropic Gd(III) ion and weak intracluster antiferromagnetic coupling shows a significant cryogenic magnetocaloric effect, with a maximum -ΔSm value of 30.0 J kg(-1) K(-1) at 2.5 K and 70 kOe. Additionally, the chromophoric na(-) and pyzc(-) ligands can serve as antenna groups, selectively sensitizing the Dy(III)- and Yb(III)-based luminescence of 1 and 2 in the UV-visible region by an intramolecular energy transfer process. Thus, complexes 1-3, incorporating field-induced slow magnetic magnetization and interesting luminescence together, can be used as composite magneto-optical materials. More importantly, these interesting results further demonstrate that the mixed-ligand system with rigid carboxylate-functionalized chromophores can be excellent candidates for the preparations of new bifunctional magneto-optical materials.

Magnetic resonance signal moment determination using the Earth's magnetic field.

PubMed

Fridjonsson, E O; Creber, S A; Vrouwenvelder, J S; Johns, M L

2015-03-01

We demonstrate a method to manipulate magnetic resonance data such that the moments of the signal spatial distribution are readily accessible. Usually, magnetic resonance imaging relies on data acquired in so-called k-space which is subsequently Fourier transformed to render an image. Here, via analysis of the complex signal in the vicinity of the centre of k-space we are able to access the first three moments of the signal spatial distribution, ultimately in multiple directions. This is demonstrated for biofouling of a reverse osmosis (RO) membrane module, rendering unique information and an early warning of the onset of fouling. The analysis is particularly applicable for the use of mobile magnetic resonance spectrometers; here we demonstrate it using an Earth's magnetic field system. Copyright © 2015 Elsevier Inc. All rights reserved.

Sub-millitesla magnetic field effects on the recombination reaction of flavin and ascorbic acid radicals

NASA Astrophysics Data System (ADS)

Evans, Emrys W.; Kattnig, Daniel R.; Henbest, Kevin B.; Hore, P. J.; Mackenzie, Stuart R.; Timmel, Christiane R.

2016-08-01

Even though the interaction of a <1 mT magnetic field with an electron spin is less than a millionth of the thermal energy at room temperature (kBT), it still can have a profound effect on the quantum yields of radical pair reactions. We present a study of the effects of sub-millitesla magnetic fields on the photoreaction of flavin mononucleotide with ascorbic acid. Direct control of the reaction pathway is achieved by varying the rate of electron transfer from ascorbic acid to the photo-excited flavin. At pH 7.0, we verify the theoretical prediction that, apart from a sign change, the form of the magnetic field effect is independent of the initial spin configuration of the radical pair. The data agree well with model calculations based on a Green's function approach that allows multinuclear spin systems to be treated including the diffusive motion of the radicals, their spin-selective recombination reactions, and the effects of the inter-radical exchange interaction. The protonation states of the radicals are uniquely determined from the form of the magnetic field-dependence. At pH 3.0, the effects of two chemically distinct radical pair complexes combine to produce a pronounced response to ˜500 μT magnetic fields. These findings are relevant to the magnetic responses of cryptochromes (flavin-containing proteins proposed as magnetoreceptors in birds) and may aid the evaluation of effects of weak magnetic fields on other biologically relevant electron transfer processes.

Magnetofection™ of NMDA Receptor Subunits GluN1 and GluN2A Expression Vectors in Non-Neuronal Host Cells.

PubMed

Bruneau, Nadine; Szepetowski, Pierre

2017-01-01

The functional study of reconstituted NMDA receptors (NMDARs) in host cells requires that the corresponding vectors for the expression of the NMDAR subunits are co-transfected with high efficiency. Magnetofection™ is a technology used to deliver nucleic acids to cells. It is driven and site-specifically guided by the attractive forces of magnetic fields acting on magnetic nanoparticles that are associated with nucleic acid vectors. In magnetofection™, cationic lipids form self-assembled complexes with the nucleic acid vectors of interest. Those complexes are then associated with magnetic nanoparticles that are concentrated at the surface of cultured cells by applying a permanent magnetic field. Magnetofection™ is a simple method to transfect cultured cells with high transfection rates. Satisfactory expression levels are obtained with very low amounts of nucleic acid vector. Moreover, incubation time with host cells is less than 1 h, as compared with the several hours needed with standard transfection assays.

Dilution-triggered SMM behavior under zero field in a luminescent Zn2Dy2 tetranuclear complex incorporating carbonato-bridging ligands derived from atmospheric CO2 fixation.

PubMed

Titos-Padilla, Silvia; Ruiz, José; Herrera, Juan Manuel; Brechin, Euan K; Wersndorfer, Wolfgang; Lloret, Francesc; Colacio, Enrique

2013-08-19

The synthesis, structure, magnetic, and luminescence properties of the Zn2Dy2 tetranuclear complex of formula {(μ3-CO3)2[Zn(μ-L)Dy(NO3)]2}·4CH3OH (1), where H2L is the compartmental ligand N,N',N″-trimethyl-N,N″-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine, are reported. The carbonate anions that bridge two Zn(μ-L)Dy units come from the atmospheric CO2 fixation in a basic medium. Fast quantum tunneling relaxation of the magnetization (QTM) is very effective in this compound, so that single-molecule magnet (SMM) behavior is only observed in the presence of an applied dc field of 1000 Oe, which is able to partly suppress the QTM relaxation process. At variance, a 1:10 Dy:Y magnetic diluted sample, namely, 1', exhibits SMM behavior at zero applied direct-current (dc) field with about 3 times higher thermal energy barrier than that in 1 (U(eff) = 68 K), thus demonstrating the important role of intermolecular dipolar interactions in favoring the fast QTM relaxation process. When a dc field of 1000 Oe is applied to 1', the QTM is almost fully suppressed, the reversal of the magnetization slightly slows, and U(eff) increases to 78 K. The dilution results combined with micro-SQUID magnetization measurements clearly indicate that the SMM behavior comes from single-ion relaxation of the Dy(3+) ions. Analysis of the relaxation data points out that a Raman relaxation process could significantly affect the Orbach relaxation process, reducing the thermal energy barrier U(eff) for slow relaxation of the magnetization.

Magnetic domain wall creep and depinning: A scalar field model approach

NASA Astrophysics Data System (ADS)

Caballero, Nirvana B.; Ferrero, Ezequiel E.; Kolton, Alejandro B.; Curiale, Javier; Jeudy, Vincent; Bustingorry, Sebastian

2018-06-01

Magnetic domain wall motion is at the heart of new magnetoelectronic technologies and hence the need for a deeper understanding of domain wall dynamics in magnetic systems. In this context, numerical simulations using simple models can capture the main ingredients responsible for the complex observed domain wall behavior. We present a scalar field model for the magnetization dynamics of quasi-two-dimensional systems with a perpendicular easy axis of magnetization which allows a direct comparison with typical experimental protocols, used in polar magneto-optical Kerr effect microscopy experiments. We show that the thermally activated creep and depinning regimes of domain wall motion can be reached and the effect of different quenched disorder implementations can be assessed with the model. In particular, we show that the depinning field increases with the mean grain size of a Voronoi tessellation model for the disorder.

Numerical modeling of Bridgman growth of PbSnTe in a magnetic field

NASA Technical Reports Server (NTRS)

Yao, Minwu; Chait, Arnon; Fripp, Archibald L.; Debnam, William J.

1995-01-01

In this work we study heat and mass transport, fluid motion, and solid/liquid phase change in the process of steady Bridgman growth of Pb(.8)Sn(.2)Te (LTT) in an axially-imposed uniform magnetic field under terrestrial and microgravity conditions. In particular, this research is concerned with the interrelationships among segregation, buoyancy-driven convection, and magnetic damping in the LTT melt. The main objectives are to provide a quantitative understanding of the complex transport phenomena during solidification of the nondilute binary of LTT, to provide estimates of the strength of magnetic field required to achieve the desired diffusion-dominated growth, and to assess the role of magnetic damping for space and earth based control of the buoyancy-induced convection. The problem was solved by using FIDAP and numerical results for both vertical and horizontal growth configurations with respect to the acceleration of gravity vector are presented.

Spatial encoding using the nonlinear field perturbations from magnetic materials.

PubMed

Karimi, Hirad; Dominguez-Viqueira, William; Cunningham, Charles H

2014-08-01

A proof-of-concept study was performed to assess the technical feasibility of using magnetic materials to generate spatial encoding fields. Spatially varying magnetic fields were generated by the placement of markers with different volume susceptibilities within the imaging volume. No linear gradients were used for spatial encoding during the signal acquisition. A signal-encoding model is described for reconstructing the images encoded with these field perturbations. Simulation and proof-of-concept experimental results are presented. Experiments were performed using field perturbations from a cylindrical marker as an example of the new encoding fields. Based on this experimental setup, annular rings were reconstructed from signals encoded with the new fields. Simulation results were presented for different acquisition parameters. Proof-of-concept was supported by the correspondence of regions in an image reconstructed from experimental data compared to those in a conventional gradient-echo image. Experimental results showed that inclusions of dimensions 1.5 mm in size could be resolved with the experimental setup. This study shows the technical feasibility of using magnetic markers to produce encoding fields. Magnetic materials will allow generating spatial encoding fields, which can be tailored to an imaging application with less complexity and at lower cost compared to the use of gradient inserts. Copyright © 2013 Wiley Periodicals, Inc.

Origin and Evolution of Magnetic Field in PMS Stars: Influence of Rotation and Structural Changes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Emeriau-Viard, Constance; Brun, Allan Sacha, E-mail: constance.emeriau@cea.fr, E-mail: sacha.brun@cea.fr

During stellar evolution, especially in the pre-main-sequence phase, stellar structure and rotation evolve significantly, causing major changes in the dynamics and global flows of the star. We wish to assess the consequences of these changes on stellar dynamo, internal magnetic field topology, and activity level. To do so, we have performed a series of 3D HD and MHD simulations with the ASH code. We choose five different models characterized by the radius of their radiative zone following an evolutionary track computed by a 1D stellar evolution code. These models characterized stellar evolution from 1 to 50 Myr. By introducing amore » seed magnetic field in the fully convective model and spreading its evolved state through all four remaining cases, we observe systematic variations in the dynamical properties and magnetic field amplitude and topology of the models. The five MHD simulations develop a strong dynamo field that can reach an equipartition state between the kinetic and magnetic energies and even superequipartition levels in the faster-rotating cases. We find that the magnetic field amplitude increases as it evolves toward the zero-age main sequence. Moreover, the magnetic field topology becomes more complex, with a decreasing axisymmetric component and a nonaxisymmetric one becoming predominant. The dipolar components decrease as the rotation rate and the size of the radiative core increase. The magnetic fields possess a mixed poloidal-toroidal topology with no obvious dominant component. Moreover, the relaxation of the vestige dynamo magnetic field within the radiative core is found to satisfy MHD stability criteria. Hence, it does not experience a global reconfiguration but slowly relaxes by retaining its mixed stable poloidal-toroidal topology.« less

On the Support of Solar Prominence Material by the Dips of a Coronal Flux Tube

NASA Astrophysics Data System (ADS)

Hillier, Andrew; van Ballegooijen, Adriaan

2013-04-01

The dense prominence material is believed to be supported against gravity through the magnetic tension of dipped coronal magnetic field. For quiescent prominences, which exhibit many gravity-driven flows, hydrodynamic forces are likely to play an important role in the determination of both the large- and small-scale magnetic field distributions. In this study, we present the first steps toward creating a three-dimensional magneto-hydrostatic prominence model where the prominence is formed in the dips of a coronal flux tube. Here 2.5D equilibria are created by adding mass to an initially force-free magnetic field, then performing a secondary magnetohydrodynamic relaxation. Two inverse polarity magnetic field configurations are studied in detail, a simple o-point configuration with a ratio of the horizontal field (Bx ) to the axial field (By ) of 1:2 and a more complex model that also has an x-point with a ratio of 1:11. The models show that support against gravity is either by total pressure or tension, with only tension support resembling observed quiescent prominences. The o-point of the coronal flux tube was pulled down by the prominence material, leading to compression of the magnetic field at the base of the prominence. Therefore, tension support comes from the small curvature of the compressed magnetic field at the bottom and the larger curvature of the stretched magnetic field at the top of the prominence. It was found that this method does not guarantee convergence to a prominence-like equilibrium in the case where an x-point exists below the prominence flux tube. The results imply that a plasma β of ~0.1 is necessary to support prominences through magnetic tension.

Generation Mechanism for Interlinked Flux Tubes on the Magnetopause

NASA Astrophysics Data System (ADS)

Farinas Perez, G.; Cardoso, F. R.; Sibeck, D.; Gonzalez, W. D.; Facskó, G.; Coxon, J. C.; Pembroke, A. D.

2018-02-01

We use a global magnetohydrodynamics simulation to analyze transient magnetic reconnection processes at the magnetopause. The solar wind conditions have been kept constant, and an interplanetary magnetic field with large duskward BY and southward BZ components has been imposed. Five flux transfer events (FTEs) with clear bipolar magnetic field signatures have been observed. We observed a peculiar structure defined as interlinked flux tubes (IFTs) in the first and fourth FTE, which had very different generation mechanisms. The first FTE originates as an IFTs and remains with this configuration until its final moment. However, the fourth FTE develops as a classical flux rope but changes its 3-D magnetic configuration to that of IFTs. This work studies the mechanism for generating IFTs. The growth of the resistive tearing instability has been identified as the cause for the first IFTs formation. We believe that the instability has been triggered by the accumulation of interplanetary magnetic field at the subsolar point where the grid resolution is very high. The evidence shows that two new reconnection lines form northward and southward of the subsolar region. The IFTs have been generated with all the classical signatures of a single flux rope. The other IFTs detected in the fourth FTE developed as a result of magnetic reconnection inside its complex and twisted magnetic fields, which leads to a change in the magnetic configuration from a flux rope of twisted magnetic field lines to IFTs.

Transverse susceptibility as a probe of the magnetocrystalline anisotropy-driven phase transition in Pr0.5Sr0.5CoO3

NASA Astrophysics Data System (ADS)

Frey Huls, N. A.; Bingham, N. S.; Phan, M. H.; Srikanth, H.; Stauffer, D. D.; Leighton, C.

2011-01-01

Half-doped Pr1-xSrxCoO3 (x=0.5) displays anomalous magnetism, most notably manifest in the field-cooled magnetization versus temperature curves under different applied cooling fields. Recently, an explanation was advanced that a magnetocrystalline anisotropy transition driven by a structural transition at 120 K is the origin of this behavior. In this paper, we further elucidate the nature of the magnetic anisotropy across the low-temperature phase transition in this material by means of transverse susceptibility (TS) measurements performed using a self-resonant tunnel diode oscillator. TS probes magnetic materials by means of a small radio frequency oriented transverse to a dc field that sweeps from positive to negative saturation. TS scans as a function of field clearly reveal peaks associated with the anisotropy (HK) and switching fields (HS). When peak position is examined as a function of temperature, ˜120 K the signature of a ferromagnetic-to-ferromagnetic phase transition is evident as a sharp feature in HK and a corresponding cusp in HS. A third TS peak (not previously observed in other classes of magnetic oxides such as manganites and spinel ferrites) is found to be correlated with the crossover field (Hcr) in the unconventional magnetization versus temperature [M(T)] behavior. We observe a strong temperature dependence of Hcr at ˜120 K using this technique, which suggests the magnetic-field-influenced magnetocrystalline anisotropy transition. We show the switching between the high-field magnetization state and the low-field magnetization state associated with the magnetocrystalline anisotropy transition is irreversible when the magnetic field is recycled. Finally, we demonstrate that the TS peak magnitude indicates easy axis switching associated with this phase transition, even in these polycrystalline samples. Our results further confirm that TS provides new insights into the magnetic behavior of complex oxides.

Differential numbers of foci of lymphocytes within the brains of Lewis rats exposed to weak complex nocturnal magnetic fields during development of experimental allergic encephalomyelitis.

PubMed

Persinger, Michael A

2009-01-01

To discern if specific structures of the rat brain contained more foci of lymphocytes following induction of experimental allergic encephalomyelitis and exposures to weak, amplitude-modulated magnetic fields for 6 min once per hour during the scotophase, the residuals between the observed and predicted values for the numbers of foci for 320 structures were obtained. Compared to the brains of sham-field exposed rats, the brains of rats exposed to 7-Hz 50 nT (0.5 mG) amplitude-modulated fields showed more foci within hippocampal structures and the dorsal central grey of the midbrain while those exposed to 7-Hz 500 nT (5 mG) fields showed greater densities within the hypothalamus and optic chiasm. The brains of rats exposed to either the 50 nT or 500 nT amplitude-modulated 40-Hz fields displayed greater densities of foci within the midbrain structures related to rapid eye movement. Most of the enhancements of infiltrations within the magnetic field-exposed rats occurred in structures within periventricular or periaqueductal regions and were both frequency- and intensity-dependent. The specificity and complexity of the configurations of the residuals of the numbers of infiltrated foci following exposures to the different fields suggest that the brain itself may be a "sensory organ" for the detection of these stimuli.

New self-magnetically insulated connection of multilevel accelerators to a common load

DOE PAGES

VanDevender, J. Pace; Langston, William L.; Pasik, Michael F.; ...

2015-03-04

A new way to connect pulsed-power modules to a common load is presented. Unlike previous connectors, the clam shell magnetically insulated transmission line (CSMITL) has magnetic nulls only at large radius where the cathode electric field is kept below the threshold for emission, has only a simply connected magnetic topology to avoid plasma motion along magnetic field lines into highly stressed gaps, and has electron injectors that ensure efficient electron flow even in the limiting case of self-limited MITLs. Multilevel magnetically insulated transmission lines with a posthole convolute are the standard solution but associated losses limit the performance of state-of-the-artmore » accelerators. Mitigating these losses is critical for the next generation of pulsed-power accelerators. A CSMITL has been successfully implemented on the Saturn accelerator. A reference design for the Z accelerator is derived and presented. The design conservatively meets the design requirements and shows excellent transport efficiency in three simulations of increasing complexity: circuit simulations, electromagnetic fields only with Emphasis, fields plus electron and ion emission with Quicksilver.« less

Spatial characterization of the edge barrier in wide superconducting films

NASA Astrophysics Data System (ADS)

Sivakov, A. G.; Turutanov, O. G.; Kolinko, A. E.; Pokhila, A. S.

2018-03-01

The current-induced destruction of superconductivity is discussed in wide superconducting thin films, whose width is greater than the magnetic field penetration depth, in weak magnetic fields. Particular attention is paid to the role of the boundary potential barrier (the Bin-Livingston barrier) in critical state formation and detection of the edge responsible for this critical state with different mutual orientations of external perpendicular magnetic field and transport current. Critical and resistive states of the film were visualized using the space-resolving low-temperature laser scanning microscopy (LTLSM) method, which enables detection of critical current-determining areas on the film edges. Based on these observations, a simple technique was developed for investigation of the critical state separately at each film edge, and for the estimation of residual magnetic fields in cryostats. The proposed method only requires recording of the current-voltage characteristics of the film in a weak magnetic field, thus circumventing the need for complex LTLSM techniques. Information thus obtained is particularly important for interpretation of studies of superconducting film single-photon light emission detectors.

Strong Nonvolatile Magnon-Driven Magnetoelectric Coupling in Single-Crystal Co /[PbMg1/3Nb2/3O3] 0.71[PbTiO3]0.29 Heterostructures

NASA Astrophysics Data System (ADS)

Zhou, Cai; Shen, Lvkang; Liu, Ming; Gao, Cunxu; Jia, Chenglong; Jiang, Changjun

2018-01-01

The ability to manipulate the magnetism on interfacing ferromagnetic and ferroelectric materials via electric fields to achieve an emergent multiferroic response has enormous potential for nanoscale devices with novel functionalities. Herein, a strong electric-field control of the magnetism modulation is reported for a single-crystal Co (14 nm )/(001 )Pb (Mg1/3Nb2/3) 0.7Ti0.3O3 (PMN-PT) heterostructure by fabricating an epitaxial Co layer on a PMN-PT substrate. Electric-field-tuned ferromagnetic resonance exhibits a large resonance field shift, with a 120-Oe difference between that under positive and negative remanent polarizations, which demonstrates nonvolatile electric-field control of the magnetism. Further, considering the complexity of the twofold symmetry magnetic anisotropy, the linear change of the fourfold symmetry magnetic anisotropy, relating to the single-crystal cubic magnetocrystal anisotropy of the Co thin film, is resolved and quantified to exert a magnon-driven, strong direct magnetoelectric effect on the Co /PMN -PT interface. These results are promising for future multiferroic devices.

Measurement of eddy-current distribution in the vacuum vessel of the Sino-UNIted Spherical Tokamak.

PubMed

Li, G; Tan, Y; Liu, Y Q

2015-08-01

Eddy currents have an important effect on tokamak plasma equilibrium and control of magneto hydrodynamic activity. The vacuum vessel of the Sino-UNIted Spherical Tokamak is separated into two hemispherical sections by a toroidal insulating barrier. Consequently, the characteristics of eddy currents are more complex than those found in a standard tokamak. Thus, it is necessary to measure and analyze the eddy-current distribution. In this study, we propose an experimental method for measuring the eddy-current distribution in a vacuum vessel. By placing a flexible printed circuit board with magnetic probes onto the external surface of the vacuum vessel to measure the magnetic field parallel to the surface and then subtracting the magnetic field generated by the vertical-field coils, the magnetic field due to the eddy current can be obtained, and its distribution can be determined. We successfully applied this method to the Sino-UNIted Spherical Tokamak, and thus, we obtained the eddy-current distribution despite the presence of the magnetic field generated by the external coils.

A Magnetoresistive Heat Switch for the Continuous ADR

NASA Technical Reports Server (NTRS)

Canavan, E. R.; Dipirro, M. J.; Jackson, M.; Panek, J.; Shirron, P. J.; Tuttle, J. G.; Krebs, C. (Technical Monitor)

2001-01-01

In compensated elemental metals at low temperature, a several Tesla field can suppress electronic heat conduction so thoroughly that heat is effectively carried by phonons alone. In approximately one mm diameter single crystal samples with impurity concentrations low enough that electron conduction is limited by surface scattering, the ratio of zerofield to high-field thermal conductivity can exceed ten thousand. We have used this phenomenon to build a compact, solid-state heat switch with no moving parts and no enclosed fluids. The time scale for switching states is limited by time scale for charging the magnet that supplies the controlling field. Our design and fabrication techniques overcome the difficulties associated with manufacturing and assembling parts from single crystal tungsten. A clear disadvantage of the magnetoresistive switch is the mass and complexity of the magnet system for the controlling field. We have discovered a technique of minimizing this mass and complexity, applicable to the continuous adiabatic demagnetization refrigerator.

Forced- and Self-Rotation of Magnetic Nanorods Assembly at the Cell Membrane: A Biomagnetic Torsion Pendulum.

PubMed

Mazuel, François; Mathieu, Samuel; Di Corato, Riccardo; Bacri, Jean-Claude; Meylheuc, Thierry; Pellegrino, Teresa; Reffay, Myriam; Wilhelm, Claire

2017-08-01

In order to provide insight into how anisotropic nano-objects interact with living cell membranes, and possibly self-assemble, magnetic nanorods with an average size of around 100 nm × 1 µm are designed by assembling iron oxide nanocubes within a polymeric matrix under a magnetic field. The nano-bio interface at the cell membrane under the influence of a rotating magnetic field is then explored. A complex structuration of the nanorods intertwined with the membranes is observed. Unexpectedly, after a magnetic rotating stimulation, the resulting macrorods are able to rotate freely for multiple rotations, revealing the creation of a biomagnetic torsion pendulum. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A current filamentation mechanism for breaking magnetic field lines during reconnection

NASA Astrophysics Data System (ADS)

Che, H.; Drake, J. F.; Swisdak, M.

2011-06-01

During magnetic reconnection, the field lines must break and reconnect to release the energy that drives solar and stellar flares and other explosive events in space and in the laboratory. Exactly how this happens has been unclear, because dissipation is needed to break magnetic field lines and classical collisions are typically weak. Ion-electron drag arising from turbulence, dubbed `anomalous resistivity', and thermal momentum transport are two mechanisms that have been widely invoked. Measurements of enhanced turbulence near reconnection sites in space and in the laboratory support the anomalous resistivity idea but there has been no demonstration from measurements that this turbulence produces the necessary enhanced drag. Here we report computer simulations that show that neither of the two previously favoured mechanisms controls how magnetic field lines reconnect in the plasmas of greatest interest, those in which the magnetic field dominates the energy budget. Rather, we find that when the current layers that form during magnetic reconnection become too intense, they disintegrate and spread into a complex web of filaments that causes the rate of reconnection to increase abruptly. This filamentary web can be explored in the laboratory or in space with satellites that can measure the resulting electromagnetic turbulence.

Global Simulations of Dynamo and Magnetorotational Instability in Madison Plasma Experiments and Astrophysical Disks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ebrahimi, Fatima

2014-07-31

Large-scale magnetic fields have been observed in widely different types of astrophysical objects. These magnetic fields are believed to be caused by the so-called dynamo effect. Could a large-scale magnetic field grow out of turbulence (i.e. the alpha dynamo effect)? How could the topological properties and the complexity of magnetic field as a global quantity, the so called magnetic helicity, be important in the dynamo effect? In addition to understanding the dynamo mechanism in astrophysical accretion disks, anomalous angular momentum transport has also been a longstanding problem in accretion disks and laboratory plasmas. To investigate both dynamo and momentum transport,more » we have performed both numerical modeling of laboratory experiments that are intended to simulate nature and modeling of configurations with direct relevance to astrophysical disks. Our simulations use fluid approximations (Magnetohydrodynamics - MHD model), where plasma is treated as a single fluid, or two fluids, in the presence of electromagnetic forces. Our major physics objective is to study the possibility of magnetic field generation (so called MRI small-scale and large-scale dynamos) and its role in Magneto-rotational Instability (MRI) saturation through nonlinear simulations in both MHD and Hall regimes.« less

Enhancing the magnetic anisotropy of maghemite nanoparticles via the surface coordination of molecular complexes

NASA Astrophysics Data System (ADS)

Prado, Yoann; Daffé, Niéli; Michel, Aude; Georgelin, Thomas; Yaacoub, Nader; Grenèche, Jean-Marc; Choueikani, Fadi; Otero, Edwige; Ohresser, Philippe; Arrio, Marie-Anne; Cartier-Dit-Moulin, Christophe; Sainctavit, Philippe; Fleury, Benoit; Dupuis, Vincent; Lisnard, Laurent; Fresnais, Jérôme

2015-12-01

Superparamagnetic nanoparticles are promising objects for data storage or medical applications. In the smallest--and more attractive--systems, the properties are governed by the magnetic anisotropy. Here we report a molecule-based synthetic strategy to enhance this anisotropy in sub-10-nm nanoparticles. It consists of the fabrication of composite materials where anisotropic molecular complexes are coordinated to the surface of the nanoparticles. Reacting 5 nm γ-Fe2O3 nanoparticles with the [CoII(TPMA)Cl2] complex (TPMA: tris(2-pyridylmethyl)amine) leads to the desired composite materials and the characterization of the functionalized nanoparticles evidences the successful coordination--without nanoparticle aggregation and without complex dissociation--of the molecular complexes to the nanoparticles surface. Magnetic measurements indicate the significant enhancement of the anisotropy in the final objects. Indeed, the functionalized nanoparticles show a threefold increase of the blocking temperature and a coercive field increased by one order of magnitude.

Planetary Magnetic Fields

NASA Astrophysics Data System (ADS)

Christensen, Ulrich R.

2017-06-01

The Earth's magnetic field has been known for centuries. Since the mid-20th century space missions carrying vector magnetometers showed that most, but not all, solar system planets have a global magnetic field of internal origin. They also revealed a surprising diversity in terms of field strength and morphology. While Jupiter's field, like that of Earth, is dominated by a dipole moderately tilted relative to the planet's spin axis, with multipole components being subordinate but not negligible, the fields of Uranus and Neptune are multipole-dominated, whereas those of Saturn und Mercury are highly symmetric relative to the rotation axis. Planetary magnetism originates from a dynamo process, which requires a fluid and electrically conducting region in the interior with sufficiently rapid and complex flow. The magnetic fields are of interest for three reasons: (1) They provide ground truth for dynamo theory, which is a fundamental and not completely solved physical problem; (2) the magnetic field controls how the planet interacts with its space environment, for example, the solar wind; and (3) the existence (or nonexistence) and the properties of the field allow us to draw inferences on the constitution, dynamics, and thermal evolution of the planet's interior. For example, the lack of global magnetic fields at Mars and Venus can be explained if their iron cores, although liquid, are stably stratified. Numerical simulations of the geodynamo—in which convective flow in a rapidly rotating spherical shell representing the outer liquid iron core of the Earth leads to induction of electric currents and the associated magnetic field—have successfully reproduced many observed properties of the geomagnetic field. They have also provided guidelines on the factors controlling magnetic field strength and, tentatively, their morphology. For numerical reasons the simulations must employ viscosities far greater than those inside planets, and it is debatable whether they truly capture the correct physics of planetary dynamo processes. Nonetheless, such models have been adapted to test concepts for explaining magnetic field properties of other planets. For example, they show that a stable stratified conducting layer above the dynamo region is a plausible cause for the strongly axisymmetric magnetic fields of Mercury or Saturn.

Scanning tunnelling spectroscopy as a probe of multi-Q magnetic states of itinerant magnets

DOE PAGES

Gastiasoro, Maria N.; Eremin, Ilya; Fernandes, Rafael M.; ...

2017-02-08

The combination of electronic correlations and Fermi surfaces with multiple nesting vectors can lead to the appearance of complex multi-Q magnetic ground states, hosting unusual states such as chiral density waves and quantum Hall insulators. Distinguishing single-Q and multi-Q magnetic phases is however a notoriously difficult experimental problem. Here we propose theoretically that the local density of states (LDOS) near a magnetic impurity, whose orientation may be controlled by an external magnetic field, can be used to map out the detailed magnetic configuration of an itinerant system and distinguish unambiguously between single-Q and multi-Q phases. We demonstrate this concept bymore » computing and contrasting the LDOS near a magnetic impurity embedded in three different magnetic ground states relevant to iron-based superconductors—one single-Q and two double-Q phases. Our results open a promising avenue to investigate the complex magnetic configurations in itinerant systems via standard scanning tunnelling spectroscopy, without requiring spin-resolved capability.« less

Dynamo action and magnetic activity during the pre-main sequence: Influence of rotation and structural changes

NASA Astrophysics Data System (ADS)

Emeriau-Viard, Constance; Brun, Allan Sacha

2017-10-01

During the PMS, structure and rotation rate of stars evolve significantly. We wish to assess the consequences of these drastic changes on stellar dynamo, internal magnetic field topology and activity level by mean of HPC simulations with the ASH code. To answer this question, we develop 3D MHD simulations that represent specific stages of stellar evolution along the PMS. We choose five different models characterized by the radius of their radiative zone following an evolutionary track, from 1 Myr to 50 Myr, computed by a 1D stellar evolution code. We introduce a seed magnetic field in the youngest model and then we spread it through all simulations. First of all, we study the consequences that the increase of rotation rate and the change of geometry of the convective zone have on the dynamo field that exists in the convective envelop. The magnetic energy increases, the topology of the magnetic field becomes more complex and the axisymmetric magnetic field becomes less predominant as the star ages. The computation of the fully convective MHD model shows that a strong dynamo develops with a ratio of magnetic to kinetic energy reaching equipartition and even super-equipartition states in the faster rotating cases. Magnetic fields resulting from our MHD simulations possess a mixed poloidal-toroidal topology with no obvious dominant component. We also study the relaxation of the vestige dynamo magnetic field within the radiative core and found that it satisfies stability criteria. Hence it does not experience a global reconfiguration and instead slowly relaxes by retaining its mixed poloidal-toroidal topology.

ELF field in the proximity of complex power line configuration measurement procedures.

PubMed

Benes, M; Comelli, M; Villalta, R

2006-01-01

The issue of how to measure magnetic induction fields generated by various power line configurations, when there are several power lines that run across the same exposure area, has become a matter of interest and study within the Regional Environment Protection Agency of Friuli Venezia Giulia. In classifying the various power line typologies the definition of double circuit line was given: in this instance the magnetic field is determined by knowing the electrical and geometric parameters of the line. In the case of independent lines instead, the field is undetermined. It is therefore pointed out how, in the latter case, extracting previsional information from a set of measurements of the magnetic field alone is impossible. Making measurements throughout the territory of service has in several cases offered the opportunity to define standard operational procedures.

Ultrahigh field NMR and MRI: Science at a crossroads. Report on a jointly-funded NSF, NIH and DOE workshop, held on November 12-13, 2015 in Bethesda, Maryland, USA

NASA Astrophysics Data System (ADS)

Polenova, Tatyana; Budinger, Thomas F.

2016-05-01

Magnetic resonance plays a central role in academic, industrial and medical research. NMR is widely used for characterizing the structure, chemistry and dynamic properties of new materials, chemicals and pharmaceuticals, in both the liquid and solid phases. NMR also provides detailed functional information on biological macromolecules and their assemblies, in vitro, in membranes and even in whole cells. In vivo, MRI/S are used for clinical diagnosis and prognosis of disease, for non-invasive studies of human physiology and metabolism in general, and for evaluating brain function, in particular. MRI/S is also a key technology for imaging small organisms at the cellular level, monitoring catalysis in chemical reactors and other scientific areas where non-destructive characterizations of structure and dynamics in complex systems are needed. At the heart of all the MR methods are strong, stable and homogeneous magnets built from low-temperature superconductors (LTS), which are essential to these experiments. Further developments in NMR/MRI are hampered because the ultimate limit of the attainable field strengths of persistent LTS magnets has now been reached. Fortunately, recent breakthroughs in new high-temperature superconductors (HTS) and hybrid LTS/HTS magnet technologies promise to greatly increase the achievable field strength of NMR magnets and to decrease the operational complexity of high field human MRI infrastructures, thereby enabling new applications at the forefront of modern multidisciplinary research.

Random walk study of electron motion in helium in crossed electromagnetic fields

NASA Technical Reports Server (NTRS)

Englert, G. W.

1972-01-01

Random walk theory, previously adapted to electron motion in the presence of an electric field, is extended to include a transverse magnetic field. In principle, the random walk approach avoids mathematical complexity and concomitant simplifying assumptions and permits determination of energy distributions and transport coefficients within the accuracy of available collisional cross section data. Application is made to a weakly ionized helium gas. Time of relaxation of electron energy distribution, determined by the random walk, is described by simple expressions based on energy exchange between the electron and an effective electric field. The restrictive effect of the magnetic field on electron motion, which increases the required number of collisions per walk to reach a terminal steady state condition, as well as the effect of the magnetic field on electron transport coefficients and mean energy can be quite adequately described by expressions involving only the Hall parameter.

Continuous spectra of atomic hydrogen in a strong magnetic field

NASA Astrophysics Data System (ADS)

Zhao, L. B.; Zatsarinny, O.; Bartschat, K.

2016-09-01

We describe a theoretical method, developed in the coupled-channel formalism, to study photoionization of H atoms in a strong magnetic field of a size that is typical for magnetic white dwarfs. The coupled Schrödinger equations are solved numerically using the renormalized Numerov method proposed by Johnson [B. R. Johnson, J. Chem. Phys. 67, 4086 (1977), 10.1063/1.435384; B. R. Johnson, J. Chem. Phys. 69, 4678 (1978), 10.1063/1.436421]. The distinct advantage of this method is the fact that no overflow problems are encountered in the classically forbidden region, and hence the method exhibits excellent numerical stability. Photoionization cross sections are presented for magnetized H atoms in the ground and 2 p excited states. The calculated results are compared with those obtained by other theories. The present method is particularly useful for explaining the complex features of continuous spectra in a strong magnetic field and hence provides an efficient tool for modeling photoionization spectra observed in the atmosphere of magnetic white dwarfs.

Origin of the magnetic-field controlled polarization reversal in multiferroic TbMn2 O 5

NASA Astrophysics Data System (ADS)

Leo, N.; Meier, D.; Pisarev, R. V.; Park, S.; Cheong, S.-W.; Fiebig, M.

2011-03-01

The interplay of multi-dimensional complex magnetic order parameters leads to interesting effects like magnetically induced ferroelectricity. A particular interesting example is TbMn 2 O5 because of the associated magnetic-field controllable electric polarization. By optical second harmonic generation we show that the gigantic magnetoelectric effect originates in three independent ferroelectric contributions. Two of these are manganese-generated. The third contribution is related to the magnetism of the Tb 3+ sublattice and has not been identified so far. It mediates the remarkable magnetic-field induced polarization reversal. This model is verified by experiments on the isostructural YMn 2 O5 where Y3+ ions are nonmagnetic and only two polarization contributions are present and no magnetoelectric coupling is observed. These results underline the importance of the 3 d - 4 f -interaction for the intricate magnetoelectric coupling in the class of isostructural RMn 2 O5 compounds. This work was supported by the DFG through SFB 608.

An investigation into the vector ellipticity of extremely low frequency magnetic fields from appliances in UK homes

NASA Astrophysics Data System (ADS)

Ainsbury, Elizabeth A.; Conein, Emma; Henshaw, Denis L.

2005-07-01

Elliptically polarized magnetic fields induce higher currents in the body compared with their plane polarized counterparts. This investigation examines the degree of vector ellipticity of extremely low frequency magnetic fields (ELF-MFs) in the home, with regard to the adverse health effects reportedly associated with ELF-MFs, for instance childhood leukaemia. Tri-axial measurements of the magnitude and phase of the 0-3000 Hz magnetic fields, produced by 226 domestic mains-fed appliances of 32 different types, were carried out in 16 homes in Worcestershire in the summer of 2004. Magnetic field strengths were low, with average (RMS) values of 0.03 ± 0.02 µT across all residences. In contrast, background field ellipticities were high, on average 47 ± 11%. Microwave and electric ovens produced the highest ellipticities: mean respective values of 21 ± 21% and 21 ± 17% were observed 20 cm away from these appliances. There was a negative correlation between field strength and field polarization, which we attribute to the higher relative field contribution close to each individual (single-phase) appliance. The measurements demonstrate that domestic magnetic fields are extremely complex and cannot simply be characterized by traditional measurements such as time-weighted average or peak exposure levels. We conclude that ellipticity should become a relevant metric for future epidemiological studies of health and ELF-MF exposure. This work is supported by the charity CHILDREN with LEUKAEMIA, registered charity number 298405.

Cholesterol-diethylenetriaminepentaacetate complexed with thulium ions integrated into bicelles to increase their magnetic alignability.

PubMed

Liebi, Marianne; Kuster, Simon; Kohlbrecher, Joachim; Ishikawa, Takashi; Fischer, Peter; Walde, Peter; Windhab, Erich J

2013-11-27

Lanthanides have been used for several decades to increase the magnetic alignability of bicelles. DMPE-DTPA (1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylenetriaminepentaacetate) is commonly applied to anchor the lanthanides into the bicelles. However, because DMPE-DTPA has the tendency to accumulate at the highly curved edge region of the bicelles and if located there does not contribute to the magnetic orientation energy, we have tested cholesterol-DTPA complexed with thulium ions (Tm(3+)) as an alternative chelator to increase the magnetic alignability. Differential scanning calorimetric (DSC) measurements indicate the successful integration of cholesterol-DTPA into a DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) bilayer. Cryo transmission electron microscopy and small-angle neutron scattering (SANS) measurements show that the disklike structure, that is, bicelles, is maintained if cholesterol-DTPA·Tm(3+) is integrated into a mixture of DMPC, cholesterol, and DMPE-DTPA·Tm(3+). The size of the bicelles is increased compared to the size of the bicelles obtained from mixtures without cholesterol-DTPA·Tm(3+). Magnetic-field-induced birefringence and SANS measurements in a magnetic field show that with addition of cholesterol-DTPA·Tm(3+) the magnetic alignability of these bicelles is significantly increased compared to bicelles composed of DMPC, cholesterol, and DMPE-DTPA·Tm(3+) only.

Size-driven magnetic transitions in La1/3Ca2/3MnO3 nanoparticles

NASA Astrophysics Data System (ADS)

Markovich, V.; Fita, I.; Wisniewski, A.; Mogilyansky, D.; Puzniak, R.; Titelman, L.; Gorodetsky, G.

2010-09-01

Magnetic properties of electron-doped La1/3Ca2/3MnO3 manganite nanoparticles with average particle size ranging from 12 to 42 nm, prepared by the glycine-nitrate method, have been investigated in temperature range 5-300 K and in magnetic fields up to 90 kOe. Reduction in the particle size suppresses antiferromagnetism and decreases the Néel temperature. In contrast to bulk crystals, the charge ordering does not occur in all studied nanoparticles, while a weak ferromagnetism appears above 200 K. Low temperature magnetic hysteresis loops indicate upon exchange bias effect displayed by horizontal and vertical shifts in field cooled processes. The spontaneous and remanent magnetization at low temperature shows a relatively complex variation with particle size. The size-induced structural/magnetic disorder drives the La1/3Ca2/3MnO3 nanoparticles to a pronounced glassy behavior for the smallest 12 nm particles, as evidenced by large difference between zero field cooled and field cooled magnetization, frequency dependent ac-susceptibility, as well as characteristic slowing down in the spin dynamics. Time evolution of magnetization recorded in magnetic fields after field cooling to low temperatures exhibits pronounced relaxation and a very noisy behavior that may be caused by formation of some collective states. Magnetic properties of the nanoparticle samples are compared with those of La0.2Ca0.8MnO3 nanoparticles. These results shed some light on the coupling between charges and spin degrees of freedom in antiferromagnetic manganite nanoparticles.

Polarization ellipse and Stokes parameters in geometric algebra.

PubMed

Santos, Adler G; Sugon, Quirino M; McNamara, Daniel J

2012-01-01

In this paper, we use geometric algebra to describe the polarization ellipse and Stokes parameters. We show that a solution to Maxwell's equation is a product of a complex basis vector in Jackson and a linear combination of plane wave functions. We convert both the amplitudes and the wave function arguments from complex scalars to complex vectors. This conversion allows us to separate the electric field vector and the imaginary magnetic field vector, because exponentials of imaginary scalars convert vectors to imaginary vectors and vice versa, while exponentials of imaginary vectors only rotate the vector or imaginary vector they are multiplied to. We convert this expression for polarized light into two other representations: the Cartesian representation and the rotated ellipse representation. We compute the conversion relations among the representation parameters and their corresponding Stokes parameters. And finally, we propose a set of geometric relations between the electric and magnetic fields that satisfy an equation similar to the Poincaré sphere equation.

Short-Term Forecasting of Radiation Belt and Ring Current

NASA Technical Reports Server (NTRS)

Fok, Mei-Ching

2007-01-01

A computer program implements a mathematical model of the radiation-belt and ring-current plasmas resulting from interactions between the solar wind and the Earth s magnetic field, for the purpose of predicting fluxes of energetic electrons (10 keV to 5 MeV) and protons (10 keV to 1 MeV), which are hazardous to humans and spacecraft. Given solar-wind and interplanetary-magnetic-field data as inputs, the program solves the convection-diffusion equations of plasma distribution functions in the range of 2 to 10 Earth radii. Phenomena represented in the model include particle drifts resulting from the gradient and curvature of the magnetic field; electric fields associated with the rotation of the Earth, convection, and temporal variation of the magnetic field; and losses along particle-drift paths. The model can readily accommodate new magnetic- and electric-field submodels and new information regarding physical processes that drive the radiation-belt and ring-current plasmas. Despite the complexity of the model, the program can be run in real time on ordinary computers. At present, the program can calculate present electron and proton fluxes; after further development, it should be able to predict the fluxes 24 hours in advance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shrestha, K.; Antonio, D.; Jaime, M.

Uranium nitride (UN) is one of the most studied actinide materials as it is a promising fuel for the next generation of nuclear reactors. Despite large experimental and theoretical efforts, some of the fundamental questions such as degree of 5 f–electron localization/delocalization and its relationship to magneto-vibrational properties are not resolved yet. We show that the magnetostriction of UN measured in pulsed magnetic fields up to 65 T and below the Néel temperature is large and exhibits complex behavior with two transitions. While the high field anomaly is a field-induced metamagnetic-like transition and affects both magnetisation and magnetostriction, the lowmore » field anomaly does not contribute to the magnetic susceptibility. Our data suggest a change in the nature of the metamagnetic transition from first to second order-like at a tricritical point at T tri ~24 K and H tri ~52 T. The induced magnetic moment at 60 T might suggest that only one subset of magnetic moments has aligned along the field direction. Using the results obtained here we have constructed a magnetic phase diagram of UN. Our studies demonstrate that dilatometry in high fields is an effective method to investigate the magneto-structural coupling in actinide materials.« less

[Review of the active locomotion system for capsule endoscope].

PubMed

Zhao, Dechun; Guo, Yijun; Peng, Chenglin

2010-02-01

This review summarized the progress of researches on the active locomotion system for capsule endoscope, analyzed the moving and controlling principles in different locomotion systems, and compared their merits and shortcomings. Owing to the complexity of human intestines and the limits to the size and consumption of locomotion system from the capsule endoscope, there is not yet one kind of active locomotion system currently used in clinical practice. The locomotive system driven by an outer rotational magnetic field could improve the commercial endoscope capsule, while its magnetic field controlling moving is complex. Active locomotion system driven by shape memory alloys will be the orientated development and the point of research in the future.

A search for weak or complex magnetic fields in the B3V star ι Herculis

NASA Astrophysics Data System (ADS)

Wade, G. A.; Folsom, C. P.; Petit, P.; Petit, V.; Lignières, F.; Aurière, M.; Böhm, T.

2014-11-01

We obtained 128 high signal-to-noise ratio Stokes V spectra of the B3V star ι Her on five consecutive nights in 2012 with the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope, with the aim of searching for the presence of weak and/or complex magnetic fields. Least-squares deconvolution (LSD) mean profiles were computed from individual spectra, averaged over individual nights and over the entire run. No Zeeman signatures are detected in any of the profiles. The longitudinal magnetic field in the grand average profile was measured to be -0.24 ± 0.32 G, as compared to -0.22 ± 0.32 G in the null profile. Our observations therefore provide no evidence for the presence of Zeeman signatures analogous to those observed in the A0V star Vega by Lignières et al. We interpret these observations in three ways. First, we compare the LSD profiles with synthetic Stokes V profiles corresponding to organized (dipolar) magnetic fields, for which we find an upper limit of about 8 G on the polar strength of any surface dipole present. Secondly, we compare the grand average profile with calculations corresponding to the random magnetic spot topologies of Kochukhov & Sudnik, inferring that spots, if present, of 2° radius with strengths of 2-4 G and a filling factor of 50 per cent should have been detected in our data. Finally, we compare the observations with synthetic V profiles corresponding to the surface magnetic maps of Vega (Petit et al.) computed for the spectral characteristics of ι Her. We conclude that while it is unlikely we would have detected a magnetic field identical to Vega's, we would have likely detected one with a peak strength of about 30 G, i.e. approximately four times as strong as that of Vega.

Deriving the Coronal Magnetic Field Using Parametric Transformation Analysis

NASA Technical Reports Server (NTRS)

Gary, G. Allen; Rose, M. Franklin (Technical Monitor)

2001-01-01

When plasma-beta greater than 1 then the gas pressure dominates over the magnetic pressure. This ratio as a function along the coronal magnetic field lines varies from beta greater than 1 in the photosphere at the base of the field lines, to beta much less than 1 in the mid-corona, to beta greater than 1 in the upper corona. Almost all magnetic field extrapolations do not or cannot take into account the full range of beta. They essentially assume beta much less than 1, since the full boundary conditions do not exist in the beta greater than 1 regions. We use a basic parametric representation of the magnetic field lines such that the field lines can be manipulated to match linear features in the EUV and SXR coronal images in a least squares sense. This research employs free-form deformation mathematics to generate the associated coronal magnetic field. In our research program, the complex magnetic field topology uses Parametric Transformation Analysis (PTA) which is a new and innovative method to describe the coronal fields that we are developing. In this technique the field lines can be viewed as being embedded in a plastic medium, the frozen-in-field-line concept. As the medium is deformed the field lines are similarly deformed. However the advantage of the PTA method is that the field line movement represents a transformation of one magnetic field solution into another magnetic field solution. When fully implemented, this method will allow the resulting magnetic field solution to fully match the magnetic field lines with EUV/SXR coronal loops by minimizing the differences in direction and dispersion of a collection of PTA magnetic field lines and observed field lines. The derived magnetic field will then allow beta greater than 1 regions to be included, the electric currents to be calculated, and the Lorentz force to be determined. The advantage of this technique is that the solution is: (1) independent of the upper and side boundary conditions, (2) allows non-vanishing magnetic forces, and (3) provides a global magnetic field solution, which contains high- and low-beta regimes and maximizes the similarity between the field lines structure and all the coronal images of the region. The coronal image analysis is crucial to the investigation and for the first time these images can be exploited to derive the coronal magnetic field in a well-posed mathematical formulation. This program is an outgrowth of an investigation in which an extrapolated potential field was required to be "inflated" in order to have the field lines match the Yohkoh/SXT images. The field lines were radially stretched resulting in a better match to the coronal loops of an active region. The PTA method of radial and non-radial deformations of field lines to provide a match to the EUV/SXR images will be presented.

Gradient-induced Longitudinal Relaxation of Hyperpolarized Noble Gases in the Fringe Fields of Superconducting Magnets Used for Magnetic Resonance

PubMed Central

Zheng, Wangzhi; Cleveland, Zackary I.; Möller, Harald E.; Driehuys, Bastiaan

2010-01-01

When hyperpolarized noble gases are brought into the bore of a superconducting magnet for magnetic resonance imaging (MRI) or spectroscopy studies, the gases must pass through substantial field gradients, which can cause rapid longitudinal relaxation. In this communication, we present a means of calculating this spatially dependent relaxation rate in the fringe field of typical magnets. We then compare these predictions to experimental measurements of 3He relaxation at various positions near a medium-bore 2-T small animal MRI system. The calculated and measured relaxation rates on the central axis of the magnet agree well and show a maximum 3He relaxation rate of 3.83 × 10−3 s−1 (T1 = 4.4 min) at a distance of 47 cm from the magnet isocenter. We also show that if this magnet were self-shielded, its minimum T1 would drop to 1.2 min. In contrast, a typical self-shielded 1.5-T clinical MRI scanner will induce a minimum on-axis T1 of 12 min. Additionally, we show that the cylindrically symmetric fields of these magnets enable gradient-induced relaxation to be calculated using only knowledge of the on-axis longitudinal field, which can either be measured directly or calculated from a simple field model. Thus, while most MRI magnets employ complex and proprietary current configurations, we show that their fringe fields and the resulting gradient induced relaxation are well approximated by simple solenoid models. Finally, our modeling also demonstrates that relaxation rates can increase by nearly an order of magnitude at radial distances equivalent to the solenoid radius. PMID:21134771

Gradient-induced longitudinal relaxation of hyperpolarized noble gases in the fringe fields of superconducting magnets used for magnetic resonance.

PubMed

Zheng, Wangzhi; Cleveland, Zackary I; Möller, Harald E; Driehuys, Bastiaan

2011-02-01

When hyperpolarized noble gases are brought into the bore of a superconducting magnet for magnetic resonance imaging (MRI) or spectroscopy studies, the gases must pass through substantial field gradients, which can cause rapid longitudinal relaxation. In this communication, we present a means of calculating this spatially dependent relaxation rate in the fringe field of typical magnets. We then compare these predictions to experimental measurements of (3)He relaxation at various positions near a medium-bore 2-T small animal MRI system. The calculated and measured relaxation rates on the central axis of the magnet agree well and show a maximum (3)He relaxation rate of 3.83×10(-3) s(-1) (T(1)=4.4 min) at a distance of 47 cm from the magnet isocenter. We also show that if this magnet were self-shielded, its minimum T(1) would drop to 1.2 min. In contrast, a typical self-shielded 1.5-T clinical MRI scanner will induce a minimum on-axis T(1) of 12 min. Additionally, we show that the cylindrically symmetric fields of these magnets enable gradient-induced relaxation to be calculated using only knowledge of the on-axis longitudinal field, which can either be measured directly or calculated from a simple field model. Thus, while most MRI magnets employ complex and proprietary current configurations, we show that their fringe fields and the resulting gradient-induced relaxation are well approximated by simple solenoid models. Finally, our modeling also demonstrates that relaxation rates can increase by nearly an order of magnitude at radial distances equivalent to the solenoid radius. Copyright © 2010 Elsevier Inc. All rights reserved.

Reconciling solar and stellar magnetic cycles with nonlinear dynamo simulations.

PubMed

Strugarek, A; Beaudoin, P; Charbonneau, P; Brun, A S; do Nascimento, J-D

2017-07-14

The magnetic fields of solar-type stars are observed to cycle over decadal periods-11 years in the case of the Sun. The fields originate in the turbulent convective layers of stars and have a complex dependency upon stellar rotation rate. We have performed a set of turbulent global simulations that exhibit magnetic cycles varying systematically with stellar rotation and luminosity. We find that the magnetic cycle period is inversely proportional to the Rossby number, which quantifies the influence of rotation on turbulent convection. The trend relies on a fundamentally nonlinear dynamo process and is compatible with the Sun's cycle and those of other solar-type stars. Copyright © 2017, American Association for the Advancement of Science.

Simulation of the formation of nonequilibrium structures in magnetorheological fluids subject to an external magnetic field

NASA Astrophysics Data System (ADS)

Mohebi, M.; Jamasbi, N.; Liu, Jing

1996-11-01

We developed a computer model to understand the nonequilibrium structures induced in a magnetorheological (MR) fluid by rapidly applying an external magnetic field. MR fluids consist of particles suspended in a liquid where particles interact through dipole moments induced by the external magnetic field. We have simulated these induced structures in both directions, parallel and perpendicular to the field, in the limit of fastest response, by neglecting thermal motion and applying the field instantaneously. Our results show that the process of structure formation starts with particles forming chains aligned with the external field. The chains then coalesce to form columns and wall-like structures (``worms'' as viewed from the top). The complexity of this pattern is found to depend on the concentration of particles and the confinement of the cell in the direction of the external field. These results are consistent with experimental observations [G.A. Flores et al., in Proceedings of the Fifth International Conference on ER Fluids, MR Suspensions, and Associate Technology, University of Sheffield, Sheffield, 1995, edited by W. Bullough (World Scientific, Singapore, 1996), p. 140]. We have also used this model to study the interaction of two chains. The results of this study help in the understanding of the connection between the thickness of the sample and the increased complexity of the observed lateral pattern.

Surprises in low dimensional spin 1/2 magnets - from crystal chemistry to microscopic magnetic models of complex oxides

NASA Astrophysics Data System (ADS)

Rosner, Helge

2011-03-01

A microscopic understanding of the structure-properties relation in crystalline materials is a main goal of modern solid state chemistry and physics. Due to their peculiar magnetism, low dimensional spin 1/2 systems are often highly sensitive to structural details. Seemingly unimportant structural details can be crucial for the magnetic ground state of a compound, especially in the case of competing interactions, frustration and near-degeneracy. Here, we present for selected, complex Cu 2+ systems that a first principles based approach can reliably provide the correct magnetic model, especially in cases where the interpretation of experimental data meets serious difficulties or fails. We demonstrate that the magnetism of low dimensional insulators crucially depends on the magnetically active orbitals which are determined by details of the ligand field of the magnetic cation. Our theoretical results are in very good agreement with thermodynamic and spectroscopic data and provide deep microscopic insight into topical low dimensional magnets.

Magnetocapacitance and the physics of solid state interfaces

NASA Astrophysics Data System (ADS)

Hebard, Arthur

2008-10-01

When Herbert Kroemer stated in his Nobel address [1] that ``the interface is the device,'' he was implicitly acknowledging the importance of understanding the physics of interfaces. If interfaces are to have character traits, then ``impedance'' (or complex capacitance) would be a commonly used descriptor. In this talk I will discuss the use of magnetic fields to probe the ``character'' of a variety of interfaces including planar capacitor structures with magnetic electrodes, simple metal/semiconductor contacts (Schottky barriers) and the interface-dominated competition on microscopic length scales between ferromagnetic metallic and charge-ordered insulating phases in complex oxides. I will show that seeking experimental answers to surprisingly simple questions often leads to striking results that seriously challenge theoretical understanding. Perhaps Herbert Kroemer should have said, ``the interface is the device with a magnetic personality that continually surprises.'' [3pt] [1] Herbert Kroemer, ``Quasielectric fields and band offsets: teaching electron s new tricks,'' Nobel Lecture, December 8, 2000:

High-Resolution and Frequency, Printed Miniature Magnetic Probes

NASA Astrophysics Data System (ADS)

Prager, James; Ziemba, Timothy; Miller, Kenneth; Picard, Julian

2013-10-01

Eagle Harbor Technologies, Inc. (EHT) is developing a technique to significantly reduce the cost and development time of producing magnetic field diagnostics. EHT is designing probes that can be printed on flexible PCBs thereby allowing for extremely small coils to be produced while essentially eliminating the time to wind the coils. The coil size can be extremely small when coupled with the EHT Hybrid Integrator, which is capable of high bandwidth measurements over short and long pulse durations. This integrator is currently being commercialized with the support of a DOE SBIR. Additionally, the flexible PCBs allow probes to be attached to complex surface and/or probes that have a complex 3D structure to be designed and fabricated. During the Phase I, EHT will design and construct magnetic field probes on flexible PCBs, which will be tested at the University of Washington's HIT-SI experiment and in EHT's material science plasma reactor. Funding provided by DOE SBIR/STTR Program.

CAWSES November 7-8, 2004, Superstorm: Complex Solar and Interplanetary Features in the Post-Solar Maximum Phase

NASA Technical Reports Server (NTRS)

Tsurutani, Bruce T.; Echer, Ezequiel; Guarnieri, Fernando L.; Kozyra, J. U.

2008-01-01

The complex interplanetary structures during 7 to 8 Nov 2004 are analyzed to identify their properties as well as resultant geomagnetic effects and the solar origins. Three fast forward shocks, three directional discontinuities and two reverse waves were detected and analyzed in detail. The three fast forward shocks 'pump' up the interplanetary magnetic field from a value of approx.4 nT to 44 nT. However, the fields after the shocks were northward, and magnetic storms did not result. The three ram pressure increases were associated with major sudden impulses (SI + s) at Earth. A magnetic cloud followed the third forward shock and the southward Bz associated with the latter was responsible for the superstorm. Two reverse waves were detected, one at the edge and one near the center of the magnetic cloud (MC). It is suspected that these 'waves' were once reverse shocks which were becoming evanescent when they propagated into the low plasma beta MC. The second reverse wave caused a decrease in the southward component of the IMF and initiated the storm recovery phase. It is determined that flares located at large longitudinal distances from the subsolar point were the most likely causes of the first two shocks without associated magnetic clouds. It is thus unlikely that the shocks were 'blast waves' or that magnetic reconnection eroded away the two associated MCs. This interplanetary/solar event is an example of the extremely complex magnetic storms which can occur in the post-solar maximum phase.

The Effect of Combined Magnetic Geometries on Thermally Driven Winds. I. Interaction of Dipolar and Quadrupolar Fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Finley, Adam J.; Matt, Sean P., E-mail: af472@exeter.ac.uk

Cool stars with outer convective envelopes are observed to have magnetic fields with a variety of geometries, which on large scales are dominated by a combination of the lowest-order fields such as the dipole, quadrupole, and octupole modes. Magnetized stellar wind outflows are primarily responsible for the loss of angular momentum from these objects during the main sequence. Previous works have shown the reduced effectiveness of the stellar wind braking mechanism with increasingly complex but singular magnetic field geometries. In this paper, we quantify the impact of mixed dipolar and quadrupolar fields on the spin-down torque using 50 MHD simulationsmore » with mixed fields, along with 10 each of the pure geometries. The simulated winds include a wide range of magnetic field strength and reside in the slow-rotator regime. We find that the stellar wind braking torque from our combined geometry cases is well described by a broken power-law behavior, where the torque scaling with field strength can be predicted by the dipole component alone or the quadrupolar scaling utilizing the total field strength. The simulation results can be scaled and apply to all main-sequence cool stars. For solar parameters, the lowest-order component of the field (dipole in this paper) is the most significant in determining the angular momentum loss.« less

Satellite Attitude Control Utilizing the Earth's Magnetic Field

NASA Technical Reports Server (NTRS)

White, John S.; Shigemoto, Fred H.; Bourquin, Kent

1961-01-01

A study was conducted to determine the feasibility of a satellite attitude fine-control system using the interaction of the earth's magnetic field with current-carrying coils to produce torque. The approximate intensity of the earth's magnetic field was determined as a function of the satellite coordinates. Components of the magnetic field were found to vary essentially sinusoidally at approximately twice orbital frequency. Amplitude and distortion of the sinusoidal components were a function of satellite orbit. Two systems for two-axis attitude control evolved from this study, one using three coils and the other using two coils. The torques developed by the two systems differ only when the component of magnetic field along the tracking line is zero. For this case the two-coil system develops no torque whereas the three-coil system develops some effective torque which allows partial control. The equations which describe the three-coil system are complex in comparison to those of the two-coil system and require the measurement of all three components of the magnetic field as compared with only one for the two-coil case. Intermittent three-axis torquing can also be achieved. This torquing can be used for coarse attitude control, or for dumping the stored momentum of inertia reaction wheels. Such a system has the advantage of requiring no fuel aboard the satellite. For any of these magnetic torquing schemes the power required to produce the magnetic moment and the weight of the coil seem reasonable.

Microfluidic magnetic bead conveyor belt.

PubMed

van Pelt, Stijn; Frijns, Arjan; den Toonder, Jaap

2017-11-07

Magnetic beads play an important role in the miniaturization of clinical diagnostics systems. In lab-on-chip platforms, beads can be made to link to a target species and can then be used for the manipulation and detection of this species. Current bead actuation systems utilize complex on-chip coil systems that offer low field strengths and little versatility. We demonstrate a novel system based on an external rotating magnetic field and on-chip soft-magnetic structures to focus the field locally. These structures were designed and optimized using finite element simulations in order to create a number of local flux density maxima. These maxima, to which the magnetic beads are attracted, move over the chip surface in a continuous way together with the rotation of the external field, resulting in a mechanism similar to that of a conveyor belt. A prototype was fabricated using PDMS molding techniques mixed with iron powder for the magnetic structures. In the subsequent experiments, a quadrupole electromagnet was used to create the rotating external field. We observed that beads formed agglomerates that rolled over the chip surface, just above the magnetic structures. Field rotation frequencies between 0.1-50 Hz were tested resulting in magnetic bead speeds of over 1 mm s -1 for the highest frequency. With this, we have shown that our novel concept works, combining a simple design and simple operation with a powerful and versatile method for bead actuation. This makes it a promising method for further research and utilization in lab-on-chip systems.

Working principle and application of magnetic separation for biomedical diagnostic at high- and low-field gradients

PubMed Central

Yeap, Swee Pin; Lim, JitKang

2016-01-01

Magnetic separation is a versatile technique used in sample preparation for diagnostic purpose. For such application, an external magnetic field is applied to drive the separation of target entity (e.g. bacteria, viruses, parasites and cancer cells) from a complex raw sample in order to ease the subsequent task(s) for disease diagnosis. This separation process not only can be achieved via the utilization of high magnetic field gradient, but also, in most cases, low magnetic field gradient with magnitude less than 100 T m−1 is equally feasible. It is the aim of this review paper to summarize the usage of both high gradient magnetic separation and low gradient magnetic separation (LGMS) techniques in this area of research. It is noteworthy that effectiveness of the magnetic separation process not only determines the outcome of a diagnosis but also directly influences its accuracy as well as sensing time involved. Therefore, understanding the factors that simultaneously influence the efficiency of both magnetic separation process and target detection is necessary. Moreover, for LGMS, there are several important considerations that should be taken into account in order to ensure its successful implementation. Hence, this review paper aims to provide an overview to relate all this crucial information by linking the magnetic separation theory to biomedical diagnostic applications. PMID:27920891

Enhancing Mechanical and Thermal Properties of Epoxy Nanocomposites via Alignment of Magnetized SiC Whiskers.

PubMed

Townsend, James; Burtovyy, Ruslan; Aprelev, Pavel; Kornev, Konstantin G; Luzinov, Igor

2017-07-12

This research is focused on the fabrication and properties of epoxy nanocomposites containing magnetized SiC whiskers (MSiCWs). To this end, we report an original strategy for fabrication of magnetically active SiCWs by decorating the whiskers with magnetic (iron oxide) nanoparticles via polymer-polymer (poly(acrylic acid)/poly(2-vinyl pyridine)) complexation. The obtained whiskers demonstrated a substantial magnetic response in the polymerizing epoxy resin, with application of only a 20 mT (200 G) magnetic field. We also found that the whiskers chemically reacted with the epoxy resin, causing formation of an extended interphase near the boundary of the whiskers. The SiC whiskers oriented with the magnetic field demonstrated positive effects on the behavior of epoxy-based nanocomposites. Namely, the aligned MSiCWs enhanced the thermomechanical properties of the materials significantly above that of the neat epoxy and epoxy nanocomposite, with randomly oriented whiskers.

Theory of magnetic reconnection in solar and astrophysical plasmas.

PubMed

Pontin, David I

2012-07-13

Magnetic reconnection is a fundamental process in a plasma that facilitates the release of energy stored in the magnetic field by permitting a change in the magnetic topology. In this paper, we present a review of the current state of understanding of magnetic reconnection. We discuss theoretical results regarding the formation of current sheets in complex three-dimensional magnetic fields and describe the fundamental differences between reconnection in two and three dimensions. We go on to outline recent developments in modelling of reconnection with kinetic theory, as well as in the magnetohydrodynamic framework where a number of new three-dimensional reconnection regimes have been identified. We discuss evidence from observations and simulations of Solar System plasmas that support this theory and summarize some prominent locations in which this new reconnection theory is relevant in astrophysical plasmas.

Magnetic interactions and magnetic anisotropy in exchange coupled 4f-3d systems: a case study of a heterodinuclear Ce3+-Fe3+ cyanide-bridged complex.

PubMed

Sorace, Lorenzo; Sangregorio, Claudio; Figuerola, Albert; Benelli, Cristiano; Gatteschi, Dante

2009-01-01

We report here a detailed single-crystal EPR and magnetic study of a homologous series of complexes of the type Ln-M (Ln = La(III), Ce(III); M = Fe(III), Co(III)). We were able to obtain a detailed picture of the low-lying levels of Ce(III) and Fe(III) centres through the combined use of single-crystal EPR and magnetic susceptibility data. We show that classical ligand field theory can be of great help in rationalising the energies of the low-lying levels of both the transition-metal and rare-earth ions. The combined analysis of single-crystal EPR and magnetic data of the coupled system Ce-Fe confirmed the great complexity of the interactions involving rare-earth elements. With little uncertainty, it turned out clearly that the description of the interaction involving the lowest lying spin levels requires the introduction of the isotropic, anisotropic and antisymmetric terms.

Research on magnetic separation for complex nickel deep removal and magnetic seed recycling.

PubMed

Qiu, Yiqin; Xiao, Xiao; Ye, Ziwei; Guan, Zhijie; Sun, Shuiyu; Ren, Jie; Yan, Pingfan

2017-04-01

This study investigated the deep removal of complex nickel from simulated wastewater using magnetic separation and magnetic seed recycling. Nano-magnetite (Fe 3 O 4 ) was used as the magnetic seed. The flocculant applied was N,N-bis-(dithiocarboxy) ethanediamine (EDTC), a highly efficient heavy metal chelating agent included in dithiocarbamate (DTC). Important investigated parameters included hydraulic retention time, magnetic seed dosage, and magnetic field strength. The study also explored the magnetic flocculation mechanism involved in the reaction. The result indicated that the residual Ni concentration was reduced to less than 0.1 mg/L from the initial concentration of 50 mg/L under optimal conditions. Magnetic seed recovery reached 76.42% after a 3-h stirring period; recycled magnetic seeds were analyzed using scanning electron microscope (SEM) and X-ray diffraction (XRD). The zeta potential results illustrated that magnetic seeds firmly combined with flocs when the pH ranged from 6.5 to 7.5 due to the electrostatic attraction. When the pH was less than 7, magnetic seeds and EDTC were also combined due to electrostatic attraction. Particle size did affect microfloc size; it decreased microfloc size and increased floc volume through magnetic seed loading. The effective binding sites between flocs and magnetic seeds increased when adding the magnetic seeds. This led the majority of magnetic flocs to be integrated with the magnetic seeds, which served as a nucleus to enhance the flocculation property and ultimately improve the nickel complex removal rate.

The topology of intrasector reversals of the interplanetary magnetic field

NASA Astrophysics Data System (ADS)

Kahler, S. W.; Crooker, N. U.; Gosling, J. T.

1996-11-01

A technique has been developed recently to determine the polarities of interplanetary magnetic fields relative to their origins at the Sun by comparing energetic electron flow directions with local magnetic field directions. Here we use heat flux electrons from the Los Alamos National Laboratory (LANL) plasma detector on the ISEE 3 spacecraft to determine the field polarities. We examine periods within well-defined magnetic sectors when the field directions appear to be reversed from the normal spiral direction of the sector. About half of these intrasector field reversals (IFRs) are cases in which the polarities match those of the surrounding sectors, indicating that those fields have been folded back toward the Sun. The more interesting cases are those with polarity reversals. We find no clear cases of isolated reverse polarity fields, which suggests that islands of reverse polarity in the solar source dipole field probably do not exist. The IFRs with polarity reversals are strongly associated with periods of bidirectional electron flows, suggesting that those fields occur only in conjunction with closed fields. We propose that both those IFRs and the bidirectional flows are signatures of coronal mass ejections (CMEs). In that case, many interplanetary CMEs are larger and more complex than previously thought, consisting of both open and closed field components.

Ultra-high field magnets for whole-body MRI

NASA Astrophysics Data System (ADS)

Warner, Rory

2016-09-01

For whole-body MRI, an ultra-high field (UHF) magnet is currently defined as a system operating at 7 T or above. Over 70 UHF magnets have been built, all with the same technical approach originally developed by Magnex Scientific Ltd. The preferred coil configuration is a compensated solenoid. In this case, the majority of the field is generated by a simple long solenoid that stretches the entire length of the magnet. Additional coils are wound on a separate former outside the main windings with the purpose of balancing the homogeneity. Most of the magnets currently in operation are passively shielded systems where the magnet is surrounded by a steel box of 200-870 tonnes of carbon steel. More recently actively shielded magnets have been built for operation at 7 T; in this case the stray field is controlled by with reverse turns wound on a separate former outside the primary coils. Protection against quench damage is much more complex with an actively shielded magnet design due to the requirement to prevent the stray field from increasing during a quench. In the case of the 7 T 900 magnet this controlled by combining some of the screening coils into each section of the protection circuit. Correction of the field variations caused by manufacturing tolerances and environmental effects are made with a combination of superconducting shims and passive shims. Modern UHF magnets operate in zero boil-off mode with the use of cryocoolers with cooling capacity at 4.2 K. Although there are no cryogen costs associated with normal operation UHF magnets require a significant volume (10 000-20 000 l) of liquid helium for the cool-down. Liquid helium is expensive therefore new methods of cool-down using high-power cryocoolers are being implemented to reduce the requirement.

Three-dimensional printed magnetophoretic system for the continuous flow separation of avian influenza H5N1 viruses.

PubMed

Wang, Yuhe; Li, Yanbin; Wang, Ronghui; Wang, Maohua; Lin, Jianhan

2017-04-01

As a result of the low concentration of avian influenza viruses in samples for routine screening, the separation and concentration of these viruses are vital for their sensitive detection. We present a novel three-dimensional printed magnetophoretic system for the continuous flow separation of the viruses using aptamer-modified magnetic nanoparticles, a magnetophoretic chip, a magnetic field, and a fluidic controller. The magnetic field was designed based on finite element magnetic simulation and developed using neodymium magnets with a maximum intensity of 0.65 T and a gradient of 32 T/m for dragging the nanoparticle-virus complexes. The magnetophoretic chip was designed by SOLIDWORKS and fabricated by a three-dimensional printer with a magnetophoretic channel for the continuous flow separation of the viruses using phosphate-buffered saline as carrier flow. The fluidic controller was developed using a microcontroller and peristaltic pumps to inject the carrier flow and the viruses. The trajectory of the virus-nanoparticle complexes was simulated using COMSOL for optimization of the carrier flow and the magnetic field, respectively. The results showed that the H5N1 viruses could be captured, separated, and concentrated using the proposed magnetophoretic system with the separation efficiency up to 88% in a continuous flow separation time of 2 min for a sample volume of 200 μL. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jadav, Mudra; Patel, Rajesh, E-mail: rjp@mkbhavuni.edu.in, E-mail: rpat7@yahoo.co

Here we present a technique using magnetic nanofluid to induce bidispersed suspension of nonmagnetic particles to assemble into colloidal chain, triangle, rectangle, ring-flower configurations. By changing the amplitude and direction of the magnetic field, we could tune the structure of nonmagnetic particles in magnetic nanofluid. The structures are assembled using magneto static interactions between effectively nonmagnetic particles dispersed in magnetizable magnetic nanofluid. The assembly of complex structures out of simple colloidal building blocks is of practical interest in photonic crystals and DNA biosensors.

Magnetic field dependence of high- T c interface superconductivity in L a 1.55 S r 0.45 Cu O 4 / L a 2 Cu O 4 heterostructures

DOE PAGES

Gasparov, V. A.; Drigo, L.; Audouard, A.; ...

2016-07-11

Heterostructures made of a layer of a cuprate insulator La 2CuO 4 on the top of a layer of a nonsuperconducting cuprate metal La 1.55Sr 0.45CuO 4 show high-T c interface superconductivity confined within a single CuO 2 plane. Given this extreme quasi-two-dimensional quantum confinement, it is of interest to find out how interface superconductivity behaves when exposed to an external magnetic field. With this motivation, we have performed contactless tunnel-diode-oscillator-based measurements in pulsed magnetic fields up to 56 T as well as measurements of the complex mutual inductance between a spiral coil and the film in static fields upmore » to 3 T. Remarkably, we observe that interface superconductivity survives up to very high perpendicular fields, in excess of 40 T. Additionally, the critical magnetic field H m(T) reveals an upward divergence with decreasing temperature, in line with vortex melting as in bulk superconducting cuprates.« less

Noncollinear magnetic ordering in the Shastry-Sutherland Kondo lattice model: Insulating regime and the role of Dzyaloshinskii-Moriya interaction

NASA Astrophysics Data System (ADS)

Shahzad, Munir; Sengupta, Pinaki

2017-12-01

We investigate the necessary conditions for the emergence of complex, noncoplanar magnetic configurations in a Kondo lattice model with classical local moments on the geometrically frustrated Shastry-Sutherland lattice and their evolution in an external magnetic field. We demonstrate that topologically nontrivial spin textures, including a new canted flux state, with nonzero scalar chirality arise dynamically from realistic short-range interactions. Our results establish that a finite Dzyaloshinskii-Moriya (DM) interaction is necessary for the emergence of these novel magnetic states when the system is at half filling, for which the ground state is insulating. We identify the minimal set of DM vectors that are necessary for the stabilization of chiral magnetic phases. The noncoplanarity of such structures can be tuned continually by applying an external magnetic field. This is the first part in a series of two papers; in the following paper the effects of frustration, thermal fluctuations, and magnetic field on the emergence of novel noncollinear states at metallic filling of itinerant electrons are discussed. Our results are crucial in understanding the magnetic and electronic properties of the rare-earth tetraboride family of frustrated magnets with separate spin and charge degrees of freedom.

Role of atomic spin-mechanical coupling in the problem of a magnetic biocompass

NASA Astrophysics Data System (ADS)

Cao, Yunshan; Yan, Peng

2018-04-01

It is a well established notion that animals can detect the Earth's magnetic field, while the biophysical origin of such magnetoreception is still elusive. Recently, a magnetic receptor Drosophila CG8198 (MagR) with a rodlike protein complex is reported [S. Qin et al., Nat. Mater. 15, 217 (2016), 10.1038/nmat4484] to act like a compass needle to guide the magnetic orientation of animals. This view, however, is challenged [M. Meister, Elife 5, e17210 (2016), 10.7554/eLife.17210] by arguing that thermal fluctuations beat the Zeeman coupling of the proteins's magnetic moment with the rather weak geomagnetic field (˜25 -65 μ T ). In this work, we show that the spin-mechanical interaction at the atomic scale gives rise to a high blocking temperature which allows a good alignment of the protein's magnetic moment with the Earth's magnetic field at room temperature. Our results provide a promising route to resolve the debate on the thermal behaviors of MagR, and may stimulate a broad interest in spin-mechanical couplings down to atomistic levels.

Enhancement of TbIII–CuII Single‐Molecule Magnet Performance through Structural Modification

PubMed Central

Heras Ojea, María José; Milway, Victoria A.; Velmurugan, Gunasekaran; Thomas, Lynne H.; Coles, Simon J.; Wilson, Claire; Wernsdorfer, Wolfgang

2016-01-01

Abstract We report a series of 3d–4f complexes {Ln2Cu3(H3L)2Xn} (X=OAc−, Ln=Gd, Tb or X=NO3 −, Ln=Gd, Tb, Dy, Ho, Er) using the 2,2′‐(propane‐1,3‐diyldiimino)bis[2‐(hydroxylmethyl)propane‐1,3‐diol] (H6L) pro‐ligand. All complexes, except that in which Ln=Gd, show slow magnetic relaxation in zero applied dc field. A remarkable improvement of the energy barrier to reorientation of the magnetisation in the {Tb2Cu3(H3L)2Xn} complexes is seen by changing the auxiliary ligands (X=OAc− for NO3 −). This leads to the largest reported relaxation barrier in zero applied dc field for a Tb/Cu‐based single‐molecule magnet. Ab initio CASSCF calculations performed on mononuclear TbIII models are employed to understand the increase in energy barrier and the calculations suggest that the difference stems from a change in the TbIII coordination environment (C 4v versus Cs). PMID:27484259

Monitoring and modelling of white dwarfs with extremely weak magnetic fields. WD 2047+372 and WD 2359-434

NASA Astrophysics Data System (ADS)

Landstreet, J. D.; Bagnulo, S.; Valyavin, G.; Valeev, A. F.

2017-11-01

Magnetic fields are detected in a few percent of white dwarfs. The number of such magnetic white dwarfs known is now some hundreds. Fields range in strength from a few kG to several hundred MG. Almost all the known magnetic white dwarfs have a mean field modulus ≥1 MG. We are trying to fill a major gap in observational knowledge at the low field limit (≤200 kG) using circular spectro-polarimetry. In this paper we report the discovery and monitoring of strong, periodic magnetic variability in two previously discovered "super-weak field" magnetic white dwarfs, WD 2047+372 and WD 2359-434. WD 2047+372 has a mean longitudinal field that reverses between about -12 and + 15 kG, with a period of 0.243 d, while its mean field modulus appears nearly constant at 60 kG. The observations can be interpreted in terms of a dipolar field tilted with respect to the stellar rotation axis. WD 2359-434 always shows a weak positive longitudinal field with values between about 0 and + 12 kG, varying only weakly with stellar rotation, while the mean field modulus varies between about 50 and 100 kG. The rotation period is found to be 0.112 d using the variable shape of the Hα line core, consistent with available photometry. The field of this star appears to be much more complex than a dipole, and is probably not axisymmetric. Available photometry shows that WD 2359-434 is a light variable with an amplitude of only 0.005 mag; our own photometry shows that if WD 2047+372 is photometrically variable, the amplitude is below about 0.01 mag. These are the first models for magnetic white dwarfs with fields below about 100 kG based on magnetic measurements through the full stellar rotation. They reveal two very different magnetic surface configurations, and that, contrary to simple ohmic decay theory, WD 2359-434 has a much more complex surface field than the much younger WD 2047+372. Based, in part, on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under observing programmes 095.D-0264 and 097.D-0264, and obtained from the ESO/ST-ECF Science Archive Facility; in part, on observations made with the William Herschel Telescope, operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias; and in part on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

Interstellar Matters: Neutral Hydrogen and the Galactic Magnetic Field

NASA Astrophysics Data System (ADS)

Verschuur, Gerrit; Schmelz, Joan T.; Asgari-Targhi asgari-Targhi, M.

2018-01-01

The physics of the interstellar medium was revolutionized by the observations of the Galactic Arecibo L-Band Feed Array (GALFA) HI survey done at the Arecibo Observatory. The high-resolution, high-sensitivity, high-dynamic- range images show complex, tangled, extended filaments, and reveal that the fabric of the neutral interstellar medium is deeply tied to the structure of the ambient magnetic field. This discovery prompts an obvious question – how exactly is the interstellar {\\it neutral} hydrogen being affected by the galactic magnetic field? We look into this question by examining a set of GALFA-HI data in great detail. We have chosen a long, straight filament in the southern galactic sky. This structure is both close by and isolated in velocity space. Gaussian analysis of profiles both along and across the filament reveal internal structure – braided strands that can be traced through the simplest part, but become tangled in more complex segments. These braids do not resemble in any way the old spherical HI clouds and rudimentary pressure balance models that were used to explain the pre-GALFA- HI interstellar medium. It is clear that these structures are created, constrained, and dominated by magnetic fields. Like many subfields of astronomy before it, e.g., physics of the solar coronal, extragalactic radio jets, and pulsar environment, scientists are confronted with observations that simply cannot be explained by simple hydrodynamics and are forced to consider magneto-hydrodynamics.

Sub-millitesla magnetic field effects on the recombination reaction of flavin and ascorbic acid radicals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Evans, Emrys W.; Henbest, Kevin B.; Timmel, Christiane R., E-mail: christiane.timmel@chem.ox.ac.uk, E-mail: stuart.mackenzie@chem.ox.ac.uk

Even though the interaction of a <1 mT magnetic field with an electron spin is less than a millionth of the thermal energy at room temperature (k{sub B}T), it still can have a profound effect on the quantum yields of radical pair reactions. We present a study of the effects of sub-millitesla magnetic fields on the photoreaction of flavin mononucleotide with ascorbic acid. Direct control of the reaction pathway is achieved by varying the rate of electron transfer from ascorbic acid to the photo-excited flavin. At pH 7.0, we verify the theoretical prediction that, apart from a sign change, themore » form of the magnetic field effect is independent of the initial spin configuration of the radical pair. The data agree well with model calculations based on a Green’s function approach that allows multinuclear spin systems to be treated including the diffusive motion of the radicals, their spin-selective recombination reactions, and the effects of the inter-radical exchange interaction. The protonation states of the radicals are uniquely determined from the form of the magnetic field-dependence. At pH 3.0, the effects of two chemically distinct radical pair complexes combine to produce a pronounced response to ∼500 μT magnetic fields. These findings are relevant to the magnetic responses of cryptochromes (flavin-containing proteins proposed as magnetoreceptors in birds) and may aid the evaluation of effects of weak magnetic fields on other biologically relevant electron transfer processes.« less

Laboratory studies of magnetic anomaly effects on electric potential distributions near the lunar surface

NASA Astrophysics Data System (ADS)

Wang, X.; Robertson, S. H.; Horanyi, M.; NASA Lunar Science Institute: Colorado CenterLunar Dust; Atmospheric Studies

2011-12-01

The Moon does not have a global magnetic field, unlike the Earth, rather it has strong crustal magnetic anomalies. Data from Lunar Prospector and SELENE (Kaguya) observed strong interactions between the solar wind and these localized magnetic fields. In the laboratory, a configuration of a horseshoe permanent magnet below an insulating surface is used as an analogue of lunar crustal magnetic anomalies. Plasmas are created above the surface by a hot filament discharge. Potential distributions are measured with an emissive probe and show complex spatial structures. In our experiments, electrons are magnetized with gyro-radii r smaller than the distance from the surface d (r < d) and ions are un-magnetized with r > d. Unlike negative charging on surfaces with no magnetic fields, the surface potential at the center of the magnetic dipole is found close to the plasma bulk potential. The surface charging is dominated by the cold unmagnetized ions, while the electrons are shielded away. A potential minimum is formed between the center of the surface and the bulk plasma, most likely caused by the trapped electrons between the two magnetic mirrors at the cusps. The value of the potential minimum with respect to the bulk plasma potential decreases with increasing plasma density and neutral pressure, indicating that the mirror-trapped electrons are scattered by electron-electron and electron-neutral collisions. The potential at the two cusps are found to be more negative due to the electrons following the magnetic field lines onto the surface.

Geomagnetic Cutoff Rigidity Computer Program: Theory, Software Description and Example

NASA Technical Reports Server (NTRS)

Smart, D. F.; Shea, M. A.

2001-01-01

The access of charged particles to the earth from space through the geomagnetic field has been of interest since the discovery of the cosmic radiation. The early cosmic ray measurements found that cosmic ray intensity was ordered by the magnetic latitude and the concept of cutoff rigidity was developed. The pioneering work of Stoermer resulted in the theory of particle motion in the geomagnetic field, but the fundamental mathematical equations developed have 'no solution in closed form'. This difficulty has forced researchers to use the 'brute force' technique of numerical integration of individual trajectories to ascertain the behavior of trajectory families or groups. This requires that many of the trajectories must be traced in order to determine what energy (or rigidity) a charged particle must have to penetrate the magnetic field and arrive at a specified position. It turned out the cutoff rigidity was not a simple quantity but had many unanticipated complexities that required many hundreds if not thousands of individual trajectory calculations to solve. The accurate calculation of particle trajectories in the earth's magnetic field is a fundamental problem that limited the efficient utilization of cosmic ray measurements during the early years of cosmic ray research. As the power of computers has improved over the decades, the numerical integration procedure has grown more tractable, and magnetic field models of increasing accuracy and complexity have been utilized. This report is documentation of a general FORTRAN computer program to trace the trajectory of a charged particle of a specified rigidity from a specified position and direction through a model of the geomagnetic field.

Tricritical point from high-field magnetoelastic and metamagnetic effects in UN.

PubMed

Shrestha, K; Antonio, D; Jaime, M; Harrison, N; Mast, D S; Safarik, D; Durakiewicz, T; Griveau, J-C; Gofryk, K

2017-07-26

Uranium nitride (UN) is one of the most studied actinide materials as it is a promising fuel for the next generation of nuclear reactors. Despite large experimental and theoretical efforts, some of the fundamental questions such as degree of 5 f-electron localization/delocalization and its relationship to magneto-vibrational properties are not resolved yet. Here we show that the magnetostriction of UN measured in pulsed magnetic fields up to 65 T and below the Néel temperature is large and exhibits complex behavior with two transitions. While the high field anomaly is a field-induced metamagnetic-like transition and affects both magnetisation and magnetostriction, the low field anomaly does not contribute to the magnetic susceptibility. Our data suggest a change in the nature of the metamagnetic transition from first to second order-like at a tricritical point at T tri  ∼ 24 K and H tri  ∼ 52 T. The induced magnetic moment at 60 T might suggest that only one subset of magnetic moments has aligned along the field direction. Using the results obtained here we have constructed a magnetic phase diagram of UN. These studies demonstrate that dilatometry in high fields is an effective method to investigate the magneto-structural coupling in actinide materials.

Magnetic Flux Transport at the Solar Surface

NASA Astrophysics Data System (ADS)

Jiang, J.; Hathaway, D. H.; Cameron, R. H.; Solanki, S. K.; Gizon, L.; Upton, L.

2014-12-01

After emerging to the solar surface, the Sun's magnetic field displays a complex and intricate evolution. The evolution of the surface field is important for several reasons. One is that the surface field, and its dynamics, sets the boundary condition for the coronal and heliospheric magnetic fields. Another is that the surface evolution gives us insight into the dynamo process. In particular, it plays an essential role in the Babcock-Leighton model of the solar dynamo. Describing this evolution is the aim of the surface flux transport model. The model starts from the emergence of magnetic bipoles. Thereafter, the model is based on the induction equation and the fact that after emergence the magnetic field is observed to evolve as if it were purely radial. The induction equation then describes how the surface flows—differential rotation, meridional circulation, granular, supergranular flows, and active region inflows—determine the evolution of the field (now taken to be purely radial). In this paper, we review the modeling of the various processes that determine the evolution of the surface field. We restrict our attention to their role in the surface flux transport model. We also discuss the success of the model and some of the results that have been obtained using this model.

Tricritical point from high-field magnetoelastic and metamagnetic effects in UN

DOE PAGES

Shrestha, K.; Antonio, D.; Jaime, M.; ...

2017-07-26

Uranium nitride (UN) is one of the most studied actinide materials as it is a promising fuel for the next generation of nuclear reactors. Despite large experimental and theoretical efforts, some of the fundamental questions such as degree of 5 f–electron localization/delocalization and its relationship to magneto-vibrational properties are not resolved yet. We show that the magnetostriction of UN measured in pulsed magnetic fields up to 65 T and below the Néel temperature is large and exhibits complex behavior with two transitions. While the high field anomaly is a field-induced metamagnetic-like transition and affects both magnetisation and magnetostriction, the lowmore » field anomaly does not contribute to the magnetic susceptibility. Our data suggest a change in the nature of the metamagnetic transition from first to second order-like at a tricritical point at T tri ~24 K and H tri ~52 T. The induced magnetic moment at 60 T might suggest that only one subset of magnetic moments has aligned along the field direction. Using the results obtained here we have constructed a magnetic phase diagram of UN. Our studies demonstrate that dilatometry in high fields is an effective method to investigate the magneto-structural coupling in actinide materials.« less

Reducing the Viscosity of Blood by Pulsed Magnetic Field

NASA Astrophysics Data System (ADS)

Tao, R.; Huang, K.

2010-03-01

Blood viscosity is a major player in heart disease. When blood is viscous, in addition to a high blood pressure required for the blood circulation, blood vessel walls are also easy to be damaged. While this issue is very important, currently the only method to reduce the blood viscosity is to take medicine, such as aspirin. Here we report our new finding that the blood viscosity can be reduced by pulsed magnetic field. Blood is a suspension of red blood cells (erythrocytes), white blood cells (leukocytes) and platelets in plasma, a complex solution of gases, salts, proteins, carbohydrates, and lipids. The base liquid, plasma, has low viscosity. The effective viscosity of whole blood increases mainly due to the red blood cells, which have a volume fraction about 40% or above. Red blood cells contain iron and are sensitive to magnetic field. Therefore, when we apply a strong magnetic field, the red cells make their diameters align in the field direction to form short chains. This change in rheology reduces the effective viscosity as high as 20-30%. While this reduction is not permanent, it lasts for several hours and repeatable. The reduction rate can be controlled by selecting suitable magnetic field and duration of field application to make blood viscosity within the normal range.

Hydrothermal synthesis, crystal structure, luminescent and magnetic properties of a new mononuclear GdIII coordination complex

NASA Astrophysics Data System (ADS)

Coban, Mustafa Burak

2018-06-01

A new GdIII coordination complex, {[Gd(2-stp)2(H2O)6].2(4,4'-bipy).4(H2O)}, complex 1, (2-stp = 2-sulfoterephthalate anion and 4,4'-bipy = 4,4'-bipyridine), has been synthesized by hydrothermal method and characterized by elemental analysis, solid state UV-Vis and FT-IR spectroscopy, single-crystal X-ray diffraction, solid state photoluminescence and variable-temperature magnetic measurements. The crystal structure determination shows that GdIII ions are eight coordinated and adopt a distorted square-antiprismatic geometry. Molecules interacting through intra- and intermolecular (O-H⋯O, O-H⋯N) hydrogen bonds in complex 1, give rise to 3D hydrogen bonded structure and the discrete lattice 4,4'-bipy molecules occupy the channel of the 3D structure. π-π stacking interactions also exist 4,4'-bipy-4,4'-bipy and 4,4'-bipy-2-stp molecule rings in 3D structures. Additionally, solid state photoluminescence properties of complex 1 at room temperature have been investigated. Under the excitation of UV light (at 349 nm), the complex 1 exhibited green emissions (at 505 nm) of GdIII ion in the visible region. Furthermore, Variable-temperature magnetic susceptibility and isothermal magnetization as function of external magnetic field studies reveal that complex 1 displays possible antiferromagnetic interaction.

Preliminary Phase Field Computational Model Development

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yulan; Hu, Shenyang Y.; Xu, Ke

2014-12-15

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 ofmore » 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.« less

Single molecule magnet behavior of a pentanuclear Mn-based metallacrown complex: solid state and solution magnetic studies.

PubMed

Zaleski, Curtis M; Tricard, Simon; Depperman, Ezra C; Wernsdorfer, Wolfgang; Mallah, Talal; Kirk, Martin L; Pecoraro, Vincent L

2011-11-21

The magnetic behavior of the pentanuclear complex of formula Mn(II)(O(2)CCH(3))(2)[12-MC(Mn(III)(N)shi)-4](DMF)(6), 1, was investigated using magnetization and magnetic susceptibility measurements both in the solid state and in solution. Complex 1 has a nearly planar structure, made of a central Mn(II) ion surrounded by four peripheral Mn(III) ions. Solid state variable-field dc magnetic susceptibility experiments demonstrate that 1 possesses a low value for the total spin in the ground state; fitting appropriate expressions to the data results in antiferromangetic coupling both between the peripheral Mn(III) ions (J = -6.3 cm(-1)) and between the central Mn(II) ion and the Mn(III) ones (J' = -4.2 cm(-1)). In order to obtain a reasonable fit, a relatively large single ion magnetic anisotropy (D) value of 1 cm(-1) was necessary for the central Mn(II) ion. The single crystal magnetization measurements using a microsquid array display a very slight opening of the hysteresis loop but only at a very low temperature (0.04 K), which is in line with the ac susceptibility data where a slow relaxation of the magnetization occurs just around 2 K. In frozen solution, complex 1 displays a frequency dependent ac magnetic susceptibility signal with an energy barrier to magnetization reorientation (E) and relaxation time at an infinite temperature (τ(o)) of 14.7 cm(-1) and 1.4 × 10(-7) s, respectively, demonstrating the single molecule magnetic behavior in solution.

Simulation of therapeutic electron beam tracking through a non-uniform magnetic field using finite element method

PubMed Central

Tahmasebibirgani, Mohammad Javad; Maskani, Reza; Behrooz, Mohammad Ali; Zabihzadeh, Mansour; Shahbazian, Hojatollah; Fatahiasl, Jafar; Chegeni, Nahid

2017-01-01

Introduction In radiotherapy, megaelectron volt (MeV) electrons are employed for treatment of superficial cancers. Magnetic fields can be used for deflection and deformation of the electron flow. A magnetic field is composed of non-uniform permanent magnets. The primary electrons are not mono-energetic and completely parallel. Calculation of electron beam deflection requires using complex mathematical methods. In this study, a device was made to apply a magnetic field to an electron beam and the path of electrons was simulated in the magnetic field using finite element method. Methods A mini-applicator equipped with two neodymium permanent magnets was designed that enables tuning the distance between magnets. This device was placed in a standard applicator of Varian 2100 CD linear accelerator. The mini-applicator was simulated in CST Studio finite element software. Deflection angle and displacement of the electron beam was calculated after passing through the magnetic field. By determining a 2 to 5cm distance between two poles, various intensities of transverse magnetic field was created. The accelerator head was turned so that the deflected electrons became vertical to the water surface. To measure the displacement of the electron beam, EBT2 GafChromic films were employed. After being exposed, the films were scanned using HP G3010 reflection scanner and their optical density was extracted using programming in MATLAB environment. Displacement of the electron beam was compared with results of simulation after applying the magnetic field. Results Simulation results of the magnetic field showed good agreement with measured values. Maximum deflection angle for a 12 MeV beam was 32.9° and minimum deflection for 15 MeV was 12.1°. Measurement with the film showed precision of simulation in predicting the amount of displacement in the electron beam. Conclusion A magnetic mini-applicator was made and simulated using finite element method. Deflection angle and displacement of electron beam were calculated. With the method used in this study, a good prediction of the path of high-energy electrons was made before they entered the body. PMID:28607652

Self-assembly of smallest magnetic particles

PubMed Central

Mehdizadeh Taheri, Sara; Michaelis, Maria; Friedrich, Thomas; Förster, Beate; Drechsler, Markus; Römer, Florian M.; Bösecke, Peter; Narayanan, Theyencheri; Weber, Birgit; Rehberg, Ingo; Rosenfeldt, Sabine; Förster, Stephan

2015-01-01

The assembly of tiny magnetic particles in external magnetic fields is important for many applications ranging from data storage to medical technologies. The development of ever smaller magnetic structures is restricted by a size limit, where the particles are just barely magnetic. For such particles we report the discovery of a kind of solution assembly hitherto unobserved, to our knowledge. The fact that the assembly occurs in solution is very relevant for applications, where magnetic nanoparticles are either solution-processed or are used in liquid biological environments. Induced by an external magnetic field, nanocubes spontaneously assemble into 1D chains, 2D monolayer sheets, and large 3D cuboids with almost perfect internal ordering. The self-assembly of the nanocubes can be elucidated considering the dipole–dipole interaction of small superparamagnetic particles. Complex 3D geometrical arrangements of the nanodipoles are obtained under the assumption that the orientation of magnetization is freely adjustable within the superlattice and tends to minimize the binding energy. On that basis the magnetic moment of the cuboids can be explained. PMID:26554000

Magnetic field, frequency and temperature dependence of complex conductance of ultrathin La 1.65Sr 0.45CuO 4/La 2CuO 4 films and the organic superconductors κ-(BEDT-TTF) 2Cu[N(CN) 2]Br

DOE PAGES

V. A. Gasparov; Bozovic, I.; He, Xi; ...

2015-09-01

In this study, we used atomic-layer molecular beam epitaxy (ALL-MBE) to synthesize bilayer films of a cuprate metal (La 1.65Sr 0.45CuO 4) and a cuprate insulator (La 2CuO 4), in which interface superconductivity occurs in a layer that is just one-half unit cell thick. We have studied the magnetic field and temperature dependence of the complex sheet conductance, σ(ω), of these films, and compared them to κκ-(BEDT-TTF) 2Cu[N(CN) 2]Br single crystals. The magnetic field H was applied both parallel and perpendicular to the 2D conducting layers. Experiments have been carried out at frequencies between 23 kHz and 50 MHz usingmore » either two-coil mutual inductance technique, or the LC resonators with spiral or rectangular coils. The real and the imaginary parts of the mutual-inductance M(T,ω) between the coil and the sample were measured and converted to complex conductivity. For H perpendicular to the conducting layers, we observed almost identical behavior in both films and κ-Br single crystals: (i) the transition onset in the inductive response, L k –1(T) occurs at a temperature lower by 2 K than in Re σ(T), (ii) this shift is almost constant with magnetic field up to 8 T; (iii) the vortex diffusion constant D(T) is exponential due to pinning of vortex cores. These results can be described by the extended dynamic theory of the Berezinski–Kosterlitz–Thouless (BKT) transition and dynamics of bound vortex–antivortex pairs with short separation lengths.« less

Coronal holes, large-scale magnetic field, and activity complexes in solar cycle 23

NASA Astrophysics Data System (ADS)

Tavastsherna, K. S.; Polyakow, E. V.

2014-12-01

A correlation among coronal holes (CH), a large-scale magnetic field (LMF), and activity complexes (AC) is studied in this work for 1997-2007 with the use of a coronal hole series obtained from observations at the Kitt Peak Observatory in the HeI 10830 Å line in 1975-2003 and SOHO/EIT-195 Å in 1996-2012 (Tlatov et al., 2014), synoptic Hα charts from Kislovodsk Mountain Astonomical Station, and the catalog of AC cores (Yazev, 2012). From the imposition of CH boundaries on Hα charts, which characterize the positions of neutral lines of the radial components of a large-scale solar magnetic field, it turns out that 70% of CH are located in unipolar regions of their sign during the above period, 10% are in the region of an opposite sign, and 20% are mainly very large CH, which are often crossed by the neutral lines of several unipolar regions. Data on mutual arrangement of CH and AC cores were obtained. It was shown that only some activity comples cores have genetic relationships with CH.

Present understanding of MHD and heat transfer phenomena for liquid metal blankets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirillov, I.R.; Barleon, L.; Reed, C.B.

1994-07-01

A review of experimental work on magnetohydrodynamic (MHD) and heat transfer (HT) characteristics of liquid metal flows in fusion relevant conditions is presented. Experimental data on MHD flow pressure drop in straight channels of round and rectangular cross-section with electroconducting walls in a transverse magnetic field show good agreement with theoretical predictions, and simple engineering formulas are confirmed. Less data are available on velocity distribution and HT characteristics, and even less data are available for channels with electroinsulating walls or artificially made self-heating electroinsulating coatings. Some experiments show an interesting phenomena of HT increase in the presence of a transversemore » or axial magnetic field. For channels of complex geometry -- expansions, contractions, bends, and manifolds -- few experimental data are available. Future efforts should be directed toward investigation of MHD/HT in straight channels with perfect and nonperfect electroinsulated walls, including walls with controlled imperfections, and in channels of complex geometry. International cooperation in manufacturing and operating experimental facilities with magnetic fields at, or even higher than, 5--7 T with comparatively large volumes may be of great help.« less

Reversed-polarity regions

NASA Technical Reports Server (NTRS)

Tang, F.

1980-01-01

The 58 RPRS studied have a lifespan comparable to normal active regions and have no tendency to rotate toward a more normal alignment. They seem to have stable configurations with no apparent evidence suggesting stress due to their anomalous magnetic alignment. Magnetic complexity in RPRs is the key to flare productivity just as it is in normal regions - weak field RPRs produced no flares and regions with complex spots produced more flares than regions with noncomplex spots by a factor of 5. The RPRs however, differ from normal regions in the frequency of having complex spots, particularly the long lived complex spots, in them. Less than 17 percent of normal ARs have complex spots; less than 1.8 percent have long lived complex spots. In contrast, 41 percent of RPRs have complex spots and 24 percent have long lived complex spots.

The Global and Small-scale Magnetic Fields of Fully Convective, Rapidly Spinning M Dwarf Pair GJ65 A and B

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kochukhov, Oleg; Lavail, Alexis

2017-01-20

The nearby M dwarf binary GJ65 AB, also known as BL Cet and UV Cet, is a unique benchmark for investigation of dynamo-driven activity of low-mass stars. Magnetic activity of GJ65 was repeatedly assessed by indirect means, such as studies of flares, photometric variability, X-ray, and radio emission. Here, we present a direct analysis of large-scale and local surface magnetic fields in both components. Interpreting high-resolution circular polarization spectra (sensitive to a large-scale field geometry) we uncovered a remarkable difference of the global stellar field topologies. Despite nearly identical masses and rotation rates, the secondary exhibits an axisymmetric, dipolar-like globalmore » field with an average strength of 1.3 kG while the primary has a much weaker, more complex, and non-axisymmetric 0.3 kG field. On the other hand, an analysis of the differential Zeeman intensification (sensitive to the total magnetic flux) shows the two stars having similar magnetic fluxes of 5.2 and 6.7 kG for GJ65 A and B, respectively, although there is evidence that the field strength distribution in GJ65 B is shifted toward a higher field strength compared to GJ65 A. Based on these complementary magnetic field diagnostic results, we suggest that the dissimilar radio and X-ray variability of GJ65 A and B is linked to their different global magnetic field topologies. However, this difference appears to be restricted to the upper atmospheric layers but does not encompass the bulk of the stars and has no influence on the fundamental stellar properties.« less

Climatology of the Auroral Electrojets Derived From the Along-Track Gradient of Magnetic Field Intensity Measured by POGO, Magsat, CHAMP, and Swarm

NASA Astrophysics Data System (ADS)

Smith, A. R. A.; Beggan, C. D.; Macmillan, S.; Whaler, K. A.

2017-10-01

The auroral electrojets (AEJs) are complex and dynamic horizontal ionospheric electric currents which form ovals around Earth's poles, being controlled by the morphology of the main magnetic field and the energy input from the solar wind interaction with the magnetosphere. The strength and location of the AEJ varies with solar wind conditions and the solar cycle but should also be controlled on decadal timescales by main field secular variation. To determine the AEJ climatology, we use data from four polar Low Earth Orbit magnetic satellite missions: POGO, Magsat, CHAMP, and Swarm. A simple estimation of the AEJ strength and latitude is made from each pass of the satellites, from peaks in the along-track gradient of the magnetic field intensity after subtracting a core and crustal magnetic field model. This measure of the AEJ activity is used to study the response in different sectors of magnetic local time (MLT) during different seasons and directions of the interplanetary magnetic field (IMF). We find a season-dependent hemispherical asymmetry in the AEJ response to IMF By, with a tendency toward stronger (weaker) AEJ currents in the north than the south during By>0 (By<0) around local winter. This effect disappears during local summer when we find a tendency toward stronger currents in the south than the north. The solar cycle modulation of the AEJ and the long-term shifting of its position and strength due to the core field variation are presented as challenges to internal field modeling.

Circularly polarized attosecond pulse generation and applications to ultrafast magnetism

NASA Astrophysics Data System (ADS)

Bandrauk, André D.; Guo, Jing; Yuan, Kai-Jun

2017-12-01

Attosecond science is a growing new field of research and potential applications which relies on the development of attosecond light sources. Achievements in the generation and application of attosecond pulses enable to investigate electron dynamics in the nonlinear nonperturbative regime of laser-matter interactions on the electron’s natural time scale, the attosecond. In this review, we describe the generation of circularly polarized attosecond pulses and their applications to induce attosecond magnetic fields, new tools for ultrafast magnetism. Simulations are performed on aligned one-electron molecular ions by using nonperturbative nonlinear solutions of the time-dependent Schrödinger equation. We discuss how bichromatic circularly polarized laser pulses with co-rotating or counter-rotating components induce electron-parent ion recollisions, thus producing circularly polarized high-order harmonic generation, the source of circularly polarized attosecond pulses. Ultrafast quantum electron currents created by the generated attosecond pulses give rise to attosecond magnetic field pulses. The results provide a guiding principle for producing circularly polarized attosecond pulses and ultrafast magnetic fields in complex molecular systems for future research in ultrafast magneto-optics.

Dynamics of plasma−dust structures formed in a trap created in the narrowing of a current channel in a magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dzlieva, E. S., E-mail: plasmadust@yandex.ru; Karasev, V. Yu., E-mail: v.karasev@spbu.ru; Pavlov, S. I.

The geometry and dynamics of plasma−dust structures in a longitudinal magnetic field is studied experimentally. The structures are formed in a glow-discharge trap created in the double electric layer produced as a result of discharge narrowing by means of a dielectric insert introduced in the discharge tube. Studies of structures formed in the new type of glow-discharge trap are of interest from the standpoint of future experiments with complex plasmas in superstrong magnetic fields in which the dust component is magnetized. Different types of dielectric inserts were used: conical and plane ones with symmetric and asymmetric apertures. Conditions for themore » existence of stable dust structures are determined for dust grains of different density and different dispersity. According to the experimental results, the angular velocity of dust rotation is ≥10 s{sup –1}, which is the fastest type of dust motion for all types of discharges in a magnetic field. The rotation is interpreted by analyzing the dynamics of individual dust grains.« less

The Origins of Magnetic Structure in the Corona and Wind

NASA Technical Reports Server (NTRS)

Antiochos, Spiro K.

2010-01-01

One of the most important and most puzzling features of the coronal magnetic field is that it appears to have smooth magnetic structure with little evidence for non-potentiality except at two special locations: photospheric polarity inversions lines. (non-potentiality observed as a filament channel) and coronal hole boundaries, (observed as the slow solar wind). This characteristic feature of the closed-field corona is highly unexpected given that its magnetic field is continuously tangled by photospheric motions. Although reconnection can eliminate some of the injected structure, it cannot destroy the helicity, which should build up to produce observable complexity. I propose that an inverse cascade process transports the injected helicity from the interior of closed flux regions to their boundaries inversion lines and coronal holes, creating both filament channels and the slow wind. We describe how the helicity is injected and transported and calculate the relevant rates. I argue that one process, helicity transport, can explain both the observed lack and presence of structure in the coronal magnetic field. This work has been supported by the NASA HTP, SR&T, and LWS programs.

Evaluation of the exchange interaction and crystal fields in a prototype Dy2 SMM

NASA Astrophysics Data System (ADS)

Zhang, Qing; Sarachik, Myriam; Baker, Michael; Chen, Yizhang; Kent, Andrew; Pineda, Eufemio; McInnes, Eric

In order to gain an understanding of the INS and magnetization data obtained for Dy2, the simplest member of a newly synthesized family of dysprosium-based molecular magnets, we report on calculations of the magnetic behavior of a Dy2 cluster with the formula [hqH2][Dy2(hq)4(NO3)3].MeOH. The molecular complex contains one high symmetry Dy(III) ion and one low symmetry Dy(III) ion. Our calculations suggest that exchange coupling between the two ions controls the behavior of the magnetization at low temperature, while the crystal field of the low symmetry Dy(III) ion controls the behavior at higher temperature. A point charge electrostatic model, based on crystallographic coordinates, provides a starting point for the determination of the crystal field. Parameters in these calculations are adjusted to provide best fits to inelastic neutron scattering data (INS) and low temperature magnetometry: the INS measurements access crystal field energies and low temperature magnetization probes the Dy-Dy exchange interaction. Work supported by ARO W911NF-13-1-1025 (CCNY) and NSF-DMR-1309202 (NYU).

The solar magnetic field: from complexity to simplicity (and back)

NASA Astrophysics Data System (ADS)

Schüssler, Manfred

2017-06-01

The Sun is the only astrophysical object that permits a detailed study of the basic processes governing its magnetic field. Observations reveal stunning complexity due to the interaction with turbulent convection. Numerical simulations and observations strongly suggest that most of the small-scale field is generated by a process called small-scale dynamo action. The fundamental nature of this process makes it a candidate for magnetic field generation in a broad variety of astrophysical settings.On the other hand, the global nature of the 11-year cycle (as exhibited, for instance, by the polarity laws of sunspot groups and the regularly reversing axial dipole field) reveals a surprising simplicity. This suggests a description of the global dynamo process underlying the solar cycle in terms of relatively simple concepts. Insufficient knowledge about the structure of magnetic field and flows in the convection zone requires the introduction of a variety of free parameters (or even free functions), which severely impairs the explanatory power of most such models. However, during the last decades, surface observations of plasma flows and magnetic flux emergence, together with studies of magnetic flux transport, provided crucial information aboutthe workings of the dynamo process. They confirm the visionary approach proposed already in the 1960s by Babcock and Leighton. A recent update of their model permits a full study of the space spanned by the few remaining parameters in order to identify the regions with solar-like solutions.Observations of other cool stars show that the magnetic activity level decreases strongly with stellar rotation rate. The relatively slow rotation of the Sun puts it near to the threshold at which global dynamo action ceases. This suggests a further simplification of the dynamo model in terms of a generic normal form for a weakly nonlinear system. Including the inherent randomness brought about by the flux emergence process leads to a stochastic model whose parameters are fixed by observations. The model results explain the variability of the solar cycle amplitudes from decadal to millennial time scales.

RESEARCH ACTIVITIES IN THE FIELD OF MATERIALS SCIENCE.

DTIC Science & Technology

MAGNETIC RESONANCE, COMPLEX COMPOUNDS, CRYSTAL STRUCTURE, ELECTROCHEMISTRY, CHEMILUMINESCENCE, PHOTOCHEMICAL REACTIONS, PHOSPHORUS HETEROCYCLIC COMPOUNDS...RADIATION CHEMISTRY, POLYMERS, ROCK, SUPERCONDUCTORS, POSITRONS , DAMAGE, RADIATION EFFECTS, HALIDES

Thermo-magneto-elastoplastic coupling model of metal magnetic memory testing method for ferromagnetic materials

NASA Astrophysics Data System (ADS)

Shi, Pengpeng; Zhang, Pengcheng; Jin, Ke; Chen, Zhenmao; Zheng, Xiaojing

2018-04-01

Metal magnetic memory (MMM) testing (also known as micro-magnetic testing) is a new non-destructive electromagnetic testing method that can diagnose ferromagnetic materials at an early stage by measuring the MMM signal directly on the material surface. Previous experiments have shown that many factors affect MMM signals, in particular, the temperature, the elastoplastic state, and the complex environmental magnetic field. However, the fact that there have been only a few studies of either how these factors affect the signals or the physical coupling mechanisms among them seriously limits the industrial applications of MMM testing. In this paper, a nonlinear constitutive relation for a ferromagnetic material considering the influences of temperature and elastoplastic state is established under a weak magnetic field and is used to establish a nonlinear thermo-magneto-elastoplastic coupling model of MMM testing. Comparing with experimental data verifies that the proposed theoretical model can accurately describe the thermo-magneto-elastoplastic coupling influence on MMM signals. The proposed theoretical model can predict the MMM signals in a complex environment and so is expected to provide a theoretical basis for improving the degree of quantification in MMM testing.

Numerical assessment of low-frequency dosimetry from sampled magnetic fields

NASA Astrophysics Data System (ADS)

Freschi, Fabio; Giaccone, Luca; Cirimele, Vincenzo; Canova, Aldo

2018-01-01

Low-frequency dosimetry is commonly assessed by evaluating the electric field in the human body using the scalar potential finite difference method. This method is effective only when the sources of the magnetic field are completely known and the magnetic vector potential can be analytically computed. The aim of the paper is to present a rigorous method to characterize the source term when only the magnetic flux density is available at discrete points, e.g. in case of field measurements. The method is based on the solution of the discrete magnetic curl equation. The system is restricted to the independent set of magnetic fluxes and circulations of magnetic vector potential using the topological information of the computational mesh. The solenoidality of the magnetic flux density is preserved using a divergence-free interpolator based on vector radial basis functions. The analysis of a benchmark problem shows that the complexity of the proposed algorithm is linearly dependent on the number of elements with a controllable accuracy. The method proposed in this paper also proves to be useful and effective when applied to a real world scenario, where the magnetic flux density is measured in proximity of a power transformer. A 8 million voxel body model is then used for the numerical dosimetric analysis. The complete assessment is completed in less than 5 min, that is more than acceptable for these problems.

Numerical assessment of low-frequency dosimetry from sampled magnetic fields.

PubMed

Freschi, Fabio; Giaccone, Luca; Cirimele, Vincenzo; Canova, Aldo

2017-12-29

Low-frequency dosimetry is commonly assessed by evaluating the electric field in the human body using the scalar potential finite difference method. This method is effective only when the sources of the magnetic field are completely known and the magnetic vector potential can be analytically computed. The aim of the paper is to present a rigorous method to characterize the source term when only the magnetic flux density is available at discrete points, e.g. in case of field measurements. The method is based on the solution of the discrete magnetic curl equation. The system is restricted to the independent set of magnetic fluxes and circulations of magnetic vector potential using the topological information of the computational mesh. The solenoidality of the magnetic flux density is preserved using a divergence-free interpolator based on vector radial basis functions. The analysis of a benchmark problem shows that the complexity of the proposed algorithm is linearly dependent on the number of elements with a controllable accuracy. The method proposed in this paper also proves to be useful and effective when applied to a real world scenario, where the magnetic flux density is measured in proximity of a power transformer. A 8 million voxel body model is then used for the numerical dosimetric analysis. The complete assessment is completed in less than 5 min, that is more than acceptable for these problems.

Detailed ADM-based Modeling of Shock Retreat and X-ray Emission of τ Sco

NASA Astrophysics Data System (ADS)

Fletcher, C. L.; Petit, V.; Cohen, D. H.; Townsend, R. H.; Wade, G. A.

2018-01-01

Leveraging the improvement of spectropolarimeters over the past few decades, surveys have found that about 10% of OB-type stars host strong (˜ kG) and mostly dipolar surface magnetic fields. One B-type star, τ Sco, has a more complex surface magnetic field than the general population of OB stars. Interestingly, its X-ray luminosity is an order of magnitude higher than predicted from analytical models of magnetized winds. Previous studies of τ Sco's magnetosphere have predicted that the region of closed field loops should be located close to the stellar surface. However, the lack of X-ray variability and the location of the shock-heated plasma measured from forbidden-to-intercombination X-ray line ratios suggest that the hot plasma, and hence the closed magnetic loops, extend considerably farther from the stellar surface, implying a significantly lower mass loss rate than initially assumed. We present an adaptation of the Analytic Dynamical Magnetosphere model, describing the magnetic confinement of the stellar wind, for an arbitrary field loop configuration. This model is used to predict the shock-heated plasma temperatures for individual field loops, which are then compared to high resolution grating spectra from the Chandra X-ray Observatory. This comparison shows that larger closed magnetic loops are needed.

Magnetic properties of the Fe{sup II} spin crossover complex in emulsion polymerization of trifluoroethylmethacrylate using poly(vinyl alcohol)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suzuki, Atsushi, E-mail: suzuki@mat.usp.ac.j; Iguchi, Motoi; Oku, Takeo

2010-04-15

Influence of chemical substitution in the Fe{sup II} spin crossover complex on magnetic properties in emulsion polymerization of trifluoroethylmethacrylate using poly(vinyl alcohol) as a protective colloid was investigated near its high spin/low spin (HS/LS) phase transition. The obvious bi-stability of the HS/LS phase transition was considered by the identification of multiple spin states between the quintet (S=2) states to single state (S=0) across the excited triplet state (S=1). Magnetic parameters of gradual shifts of anisotropy g-tensor supported by the molecular distortion of the spin crossover complex would arise from a Jahn-Teller effect regarding ligand field theory on the basis ofmore » a B3LYP density functional theory using electron spin resonance (ESR) spectrum and X-ray powder diffraction. - Graphical abstract: AFM surface image of the emulsion particles with the spin crossover complex.« less

Particle acceleration magnetic field generation, and emission in Relativistic pair jets

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Ramirez-Ruiz, E.; Hardee, P.; Hededal, C.; Kouveliotou, C.; Fishman, G. J.

2005-01-01

Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) are responsible for particle acceleration in relativistic pair jets. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic pair jet propagating through a pair plasma. Simulations show that the Weibel instability created in the collisionless shock accelerates particles perpendicular and parallel to the jet propagation direction. Simulation results show that this instability generates and amplifies highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The "jitter' I radiation from deflected electrons can have different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. The growth rate of the Weibel instability and the resulting particle acceleration depend on the magnetic field strength and orientation, and on the initial particle distribution function. In this presentation we explore some of the dependencies of the Weibel instability and resulting particle acceleration on the magnetic field strength and orientation, and the particle distribution function.

Evolution of heliospheric magnetized configurations via topological invariants

NASA Astrophysics Data System (ADS)

Roth, Ilan

2013-07-01

The analogy between magnetohydrodynamics (MHD) and knot theory is utilized in presenting a new method for an analysis of stability and evolution of complex magnetic heliospheric flux tubes. Planar projection of a three-dimensional magnetic configuration depicts the structure as a two-dimensional diagram with crossings, to which one may assign mathematical operations leading to robust topological invariants. These invariants enrich the topological information of magnetic configurations beyond helicity. It is conjectured that the field which emerges from the solar photosphere is structured as one of the simplest knots-unknot or prime knot-and these flux ropes are then stretched while carried by the solar wind into the interplanetary medium. Preservation of invariants for small diffusivity and large cross section of the emerging magnetic flux makes them impervious to large scale reconnection, allowing us to predict the observed structures at 1 AU as elongated prime knots. Similar structures may be observed in magnetic clouds which got disconnected from their footpoints and in ion drop-out configurations from a compact flare source in solar impulsive solar events. Observation of small scale magnetic features consistent with prime knots may indicate spatial intermittency and non-Gaussian statistics in the turbulent cascade process. For flux tubes with higher resistivity, magnetic energy decay rate should decrease with increased knot complexity as the invariants are then harder to be violated. These observations could be confirmed if adjacent satellites happen to measure distinctly oriented magnetic fields with directionally varying suprathermal particle fluxes.

Understanding the Internal Magnetic Field Configurations of ICMEs Using More than 20 Years of Wind Observations

NASA Astrophysics Data System (ADS)

Nieves-Chinchilla, T.; Vourlidas, A.; Raymond, J. C.; Linton, M. G.; Al-haddad, N.; Savani, N. P.; Szabo, A.; Hidalgo, M. A.

2018-02-01

The magnetic topology, structure, and geometry of the magnetic obstacles embedded within interplanetary coronal mass ejections (ICMEs) are not yet fully and consistently described by in situ models and reconstruction techniques. The main goal of this work is to better understand the status of the internal magnetic field of ICMEs and to explore in situ signatures to identify clues to develop a more accurate and reliable in situ analytical models. We take advantage of more than 20 years of Wind observations of transients at 1 AU to compile a comprehensive database of ICMEs through three solar cycles, from 1995 to 2015. The catalog is publicly available at wind.gsfc.nasa.gov and is fully described in this article. We identify and collect the properties of 337 ICMEs, of which 298 show organized magnetic field signatures. To allow for departures from idealized magnetic configurations, we introduce the term "magnetic obstacle" (MO) to signify the possibility of more complex configurations. To quantify the asymmetry of the magnetic field strength profile within these events, we introduce the distortion parameter (DiP) and calculate the expansion velocity within the magnetic obstacle. Circular-cylindrical geometry is assumed when the magnetic field strength displays a symmetric profile. We perform a statistical study of these two parameters and find that only 35% of the events show symmetric magnetic profiles and a low enough expansion velocity to be compatible with the assumption of an idealized cylindrical static flux rope, and that 41% of the events do not show the expected relationship between expansion and magnetic field compression in the front, with the maximum magnetic field closer to the first encounter of the spacecraft with the magnetic obstacle; 18% show contractions ( i.e. apparent negative expansion velocity), and 30% show magnetic field compression in the back. We derive an empirical relation between DiP and expansion velocity that is the first step toward improving reconstructions with possible applications to space weather studies. In summary, our main results demonstrate that the assumed correlation between expanding structure and asymmetric magnetic field is not always valid. Although 59% of the cases could be described by circular-cylindrical geometry, with or without expansion, the remaining cases show significant in situ signatures of departures from circular-cylindrical geometry. These results will aid in the development of more accurate in situ models to reconcile image.

Shape-programmable magnetic soft matter

PubMed Central

Lum, Guo Zhan; Ye, Zhou; Dong, Xiaoguang; Marvi, Hamid; Erin, Onder; Hu, Wenqi; Sitti, Metin

2016-01-01

Shape-programmable matter is a class of active materials whose geometry can be controlled to potentially achieve mechanical functionalities beyond those of traditional machines. Among these materials, magnetically actuated matter is particularly promising for achieving complex time-varying shapes at small scale (overall dimensions smaller than 1 cm). However, previous work can only program these materials for limited applications, as they rely solely on human intuition to approximate the required magnetization profile and actuating magnetic fields for their materials. Here, we propose a universal programming methodology that can automatically generate the required magnetization profile and actuating fields for soft matter to achieve new time-varying shapes. The universality of the proposed method can therefore inspire a vast number of miniature soft devices that are critical in robotics, smart engineering surfaces and materials, and biomedical devices. Our proposed method includes theoretical formulations, computational strategies, and fabrication procedures for programming magnetic soft matter. The presented theory and computational method are universal for programming 2D or 3D time-varying shapes, whereas the fabrication technique is generic only for creating planar beams. Based on the proposed programming method, we created a jellyfish-like robot, a spermatozoid-like undulating swimmer, and an artificial cilium that could mimic the complex beating patterns of its biological counterpart. PMID:27671658

Shape-programmable magnetic soft matter.

PubMed

Lum, Guo Zhan; Ye, Zhou; Dong, Xiaoguang; Marvi, Hamid; Erin, Onder; Hu, Wenqi; Sitti, Metin

2016-10-11

Shape-programmable matter is a class of active materials whose geometry can be controlled to potentially achieve mechanical functionalities beyond those of traditional machines. Among these materials, magnetically actuated matter is particularly promising for achieving complex time-varying shapes at small scale (overall dimensions smaller than 1 cm). However, previous work can only program these materials for limited applications, as they rely solely on human intuition to approximate the required magnetization profile and actuating magnetic fields for their materials. Here, we propose a universal programming methodology that can automatically generate the required magnetization profile and actuating fields for soft matter to achieve new time-varying shapes. The universality of the proposed method can therefore inspire a vast number of miniature soft devices that are critical in robotics, smart engineering surfaces and materials, and biomedical devices. Our proposed method includes theoretical formulations, computational strategies, and fabrication procedures for programming magnetic soft matter. The presented theory and computational method are universal for programming 2D or 3D time-varying shapes, whereas the fabrication technique is generic only for creating planar beams. Based on the proposed programming method, we created a jellyfish-like robot, a spermatozoid-like undulating swimmer, and an artificial cilium that could mimic the complex beating patterns of its biological counterpart.

Shape-programmable magnetic soft matter

NASA Astrophysics Data System (ADS)

Zhan Lum, Guo; Ye, Zhou; Dong, Xiaoguang; Marvi, Hamid; Erin, Onder; Hu, Wenqi; Sitti, Metin

2016-10-01

Shape-programmable matter is a class of active materials whose geometry can be controlled to potentially achieve mechanical functionalities beyond those of traditional machines. Among these materials, magnetically actuated matter is particularly promising for achieving complex time-varying shapes at small scale (overall dimensions smaller than 1 cm). However, previous work can only program these materials for limited applications, as they rely solely on human intuition to approximate the required magnetization profile and actuating magnetic fields for their materials. Here, we propose a universal programming methodology that can automatically generate the required magnetization profile and actuating fields for soft matter to achieve new time-varying shapes. The universality of the proposed method can therefore inspire a vast number of miniature soft devices that are critical in robotics, smart engineering surfaces and materials, and biomedical devices. Our proposed method includes theoretical formulations, computational strategies, and fabrication procedures for programming magnetic soft matter. The presented theory and computational method are universal for programming 2D or 3D time-varying shapes, whereas the fabrication technique is generic only for creating planar beams. Based on the proposed programming method, we created a jellyfish-like robot, a spermatozoid-like undulating swimmer, and an artificial cilium that could mimic the complex beating patterns of its biological counterpart.

AC transport in p-Ge/GeSi quantum well in high magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Drichko, I. L.; Malysh, V. A.; Smirnov, I. Yu.

2014-08-20

The contactless surface acoustic wave technique is implemented to probe the high-frequency conductivity of a high-mobility p-Ge/GeSi quantum well structure in the regime of integer quantum Hall effect (IQHE) at temperatures 0.3–5.8 K and magnetic fields up to 18 T. It is shown that, in the IQHE regime at the minima of conductivity, holes are localized and ac conductivity is of hopping nature and can be described within the “two-site” model. The analysis of the temperature and magnetic-field-orientation dependence of the ac conductivity at odd filing factors enables us to determine the effective hole g-factor, |g{sub zz}|≈4.5. It is shownmore » that the in-plane component of the magnetic field leads to a decrease in the g-factor as well as increase in the cyclotron mass, which is explained by orbital effects in the complex valence band of germanium.« less

The local time dependence of the anisotropic solar cosmic ray flux.

PubMed

Smart, D F; Shea, M A

2003-01-01

The distribution of the solar cosmic radiation flux over the earth is not uniform, but the result of complex phenomena involving the interplanetary magnetic field, the geomagnetic field and latitude and longitude of locations on the earth. The latitude effect relates to the geomagnetic shield; the longitude effect relates to local time. For anisotropic solar cosmic ray events the maximum particle flux is always along the interplanetary magnetic field direction, sometimes called the Archimedean spiral path from the sun to the earth. During anisotropic solar cosmic ray event, the locations on the earth viewing "sunward" into the interplanetary magnetic field direction will observe the largest flux (when adjustments are made for the magnetic latitude effect). To relate this phenomena to aircraft routes, for anisotropic solar cosmic ray events that occur during "normal quiescent" conditions, the maximum solar cosmic ray flux (and corresponding solar particle radiation dose) will be observed in the dawn quadrant, ideally at about 06 hours local time. Published by Elsevier Ltd on behalf of COSPAR.

A case study of magnetotail current sheet disruption and diversion

NASA Technical Reports Server (NTRS)

Lui, A. T. Y.; Lopez, R. E.; Krimigis, S. M.; Mcentire, R. W.; Zanetti, L. J.

1988-01-01

On June 1, 1985 the AMPTE/CCE spacecraft (at a geocentric distance of about 8.8 earth radii at the midnight neutral sheet region) observed a dispersionless energetic particle injection and an increase in magnetic field magnitude, which are features commonly attributed to disruption of the near-earth cross-tail current sheet during substorm expansion onsets. An analysis based on high time-resolution measurements from the magnetometer and the energetic particle detector indicates that the current sheet disruption region exhibited localized (less than 1 earth radius) and transient (less than 1 min) particle intensity enhancements, accompanied by complex magnetic field changes with occasional development of a southward magnetic field component. Similar features are seen in other current disruption/diversion events observed by the CCE. The present analysis suggests that the current disruption region is quite turbulent, similar to laboratory experiments on current sheet disruption, with signatures unlike those expected from an X-type neutral line configuration. No clear indication of periodicity in any magnetic field parameter is discernible for this current disruption event.

Radiation from Relativistic Jets

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Mizuno, Y.; Hardee, P.; Sol, H.; Medvedev, M.; Zhang, B.; Nordlund, A.; Frederiksen, J. T.; Fishman, G. J.; Preece, R.

2008-01-01

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., gamma-ray bursts (GRBs), active galactic nuclei (AGNs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations of relativistic electron-ion (electron-positron) jets injected into a stationary medium show that particle acceleration occurs within the downstream jet. In the presence of relativistic jets, instabilities such as the Buneman instability, other two-streaming instability, and the Weibel (filamentation) instability create collisionless shocks, which are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The 'jitter' radiation from deflected electrons in small-scale magnetic fields has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation, a case of diffusive synchrotron radiation, may be important to understand the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

Inferred flows of electric currents in solar active regions

NASA Technical Reports Server (NTRS)

Ding, Y. J.; Hong, Q. F.; Hagyard, M. J.; Deloach, A. C.

1985-01-01

Techniques to identify sources of major current systems in active regions and their channels of flow are explored. Measured photospheric vector magnetic fields together with high resolution white light and H-alpha photographs provide the data base to derive the current systems in the photosphere and chromosphere of a solar active region. Simple mathematical constructions of active region fields and currents are used to interpret these data under the assumptions that the fields in the lower atmosphere (below 200 km) may not be force free but those in the chromosphere and higher are. The results obtained for the complex active region AR 2372 are: (1) Spots exhibiting significant spiral structure in the penumbral filaments were the source of vertical currents at the photospheric surface; (2) Magnetic neutral lines where the transverse magnetic field was strongly sheared were channels along which a strong current system flowed; (3) The inferred current systems produced a neutral sheet and oppositely-flowing currents in the area of the magnetic delta configuration that was the site of flaring.

Particle Acceleration, Magnetic Field Generation, and Associated Emission in Collisionless Relativistic Jets

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.

2007-01-01

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electro-positron)jets show that acceleration occurs within the downstream jet. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

Particle acceleration, magnetic field generation, and emission in relativistic pair jets

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Ramirez-Ruiz, E.; Hardee, P.; Hededal, C.; Kouveliotou, C.; Fishman, G. J.; Mizuno, Y.

2005-01-01

Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Recent simulations show that the Weibel instability created by relativistic pair jets is responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet propagating through an ambient plasma with and without initial magnetic fields. The growth rates of the Weibel instability depends on the distribution of pair jets. The Weibel instability created in the collisionless shock accelerates particles perpendicular and parallel to the jet propagation direction. This instability is also responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron s transverse deflection behind the jet head. The jitter radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

Particle Acceleration, Magnetic Field Generation and Associated Emission in Collisionless Relativistic Jets

NASA Technical Reports Server (NTRS)

Nishikawa, K. I.; Ramirez-Ruiz, E.; Hardee, P.; Mizuno, Y.; Fishman. G. J.

2007-01-01

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that acceleration occurs within the downstream jet. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

Mu2e Solenoid Field Mapping System Design

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feher, Sandor; DeLurgio, Patrick M.; Elementi, Luciano

The Mu2e experiment at Fermilab plans to search for charged-lepton flavor violation by looking for neutrino-less muon to electron conversion in the field of the nucleus. A complex solenoid system and precise knowledge of its magnetic field play a major role in the experimental approach Mu2e has chosen. It is essential to map the solenoid field up to 10 -4 accuracy. This article describes the design of the Field Mapping System Mu2e will use to measure the magnetic field. Two different mechanical mapper systems, a survey based position determination of the in-house calibrated 3D Hall probes, a motion control system,more » and a data acquisition and readout system are presented.« less

Mu2e Solenoid Field Mapping System Design

DOE PAGES

Feher, Sandor; DeLurgio, Patrick M.; Elementi, Luciano; ...

2018-01-11

The Mu2e experiment at Fermilab plans to search for charged-lepton flavor violation by looking for neutrino-less muon to electron conversion in the field of the nucleus. A complex solenoid system and precise knowledge of its magnetic field play a major role in the experimental approach Mu2e has chosen. It is essential to map the solenoid field up to 10 -4 accuracy. This article describes the design of the Field Mapping System Mu2e will use to measure the magnetic field. Two different mechanical mapper systems, a survey based position determination of the in-house calibrated 3D Hall probes, a motion control system,more » and a data acquisition and readout system are presented.« less

The Maximum Entropy Limit of Small-scale Magnetic Field Fluctuations in the Quiet Sun

NASA Astrophysics Data System (ADS)

Gorobets, A. Y.; Berdyugina, S. V.; Riethmüller, T. L.; Blanco Rodríguez, J.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; van Noort, M.; Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.

2017-11-01

The observed magnetic field on the solar surface is characterized by a very complex spatial and temporal behavior. Although feature-tracking algorithms have allowed us to deepen our understanding of this behavior, subjectivity plays an important role in the identification and tracking of such features. In this paper, we continue studies of the temporal stochasticity of the magnetic field on the solar surface without relying either on the concept of magnetic features or on subjective assumptions about their identification and interaction. We propose a data analysis method to quantify fluctuations of the line-of-sight magnetic field by means of reducing the temporal field’s evolution to the regular Markov process. We build a representative model of fluctuations converging to the unique stationary (equilibrium) distribution in the long time limit with maximum entropy. We obtained different rates of convergence to the equilibrium at fixed noise cutoff for two sets of data. This indicates a strong influence of the data spatial resolution and mixing-polarity fluctuations on the relaxation process. The analysis is applied to observations of magnetic fields of the relatively quiet areas around an active region carried out during the second flight of the Sunrise/IMaX and quiet Sun areas at the disk center from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory satellite.

Dynamics of the magnetization of single domain particles having triaxial anisotropy subjected to a uniform dc magnetic field

NASA Astrophysics Data System (ADS)

Ouari, Bachir; Kalmykov, Yury P.

2006-12-01

Thermally induced relaxation of the magnetization of single domain ferromagnetic particles with triaxial (orthorhombic) anisotropy in the presence of a uniform external magnetic field H0 is considered in the context of Brown's continuous diffusion model. Simple analytic equations, which allow one to describe qualitatively the field effects in the relaxation behavior of the system for wide ranges of the field strength and damping parameters are derived. It is shown that these formulas are in complete agreement with the exact matrix continued fraction solution of the infinite hierarchy of linear differential-recurrence equations for the statistical moments, which governs the magnetization dynamics of an individual particle (this hierarchy is derived by averaging the underlying stochastic Landau-Lifshitz-Gilbert equation over its realizations). It is also demonstrated that in strong fields the longitudinal relaxation of the magnetization is essentially modified by the contribution of the high-frequency "intrawell" modes to the relaxation process. This effect discovered for uniaxial particles by Coffey et al. [Phys. Rev. B 51, 15947 (1995)] is the natural consequence of the depletion of population of the shallow potential well. However, in contrast to uniaxial anisotropy, for orthorhombic crystals there is an inherent geometric dependence of the complex magnetic susceptibility and the relaxation time on the damping parameter α arising from the coupling of longitudinal and transverse relaxation modes.

Magnetically induced ferroelectricity in Bi2CuO4

NASA Astrophysics Data System (ADS)

Zhao, L.; Guo, H.; Schmidt, W.; Nemkovski, K.; Mostovoy, M.; Komarek, A. C.

2017-08-01

The tetragonal copper oxide Bi2CuO4 has an unusual crystal structure with a three-dimensional network of well separated CuO4 plaquettes. The spin structure of Bi2CuO4 in the magnetically ordered state below TN˜43 K remains controversial. Here we present the results of detailed studies of specific heat, magnetic, and dielectric properties of Bi2CuO4 single crystals grown by the floating zone technique, combined with the polarized neutron scattering and high-resolution x-ray measurements. Down to 3.5 K our polarized neutron scattering measurements reveal ordered magnetic Cu moments which are aligned within the a b plane. Below the onset of the long range antiferromagnetic ordering we observe an electric polarization induced by an applied magnetic field, which indicates inversion symmetry breaking by the ordered state of Cu spins. For the magnetic field applied perpendicular to the tetragonal axis, the spin-induced ferroelectricity is explained in terms of the linear magnetoelectric effect that occurs in a metastable magnetic state. A relatively small electric polarization induced by the field parallel to the tetragonal axis may indicate a more complex magnetic ordering in Bi2CuO4 .

Evolution of a Gaussian laser beam in warm collisional magnetoplasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jafari, M. J.; Jafari Milani, M. R., E-mail: mrj.milani@gmail.com; Niknam, A. R.

2016-07-15

In this paper, the spatial evolution of an intense circularly polarized Gaussian laser beam propagated through a warm plasma is investigated, taking into account the ponderomotive force, Ohmic heating, external magnetic field, and collisional effects. Using the momentum transfer and energy equations, both modified electron temperature and electron density in plasma are obtained. By introducing the complex dielectric permittivity of warm magnetized plasma and using the complex eikonal function, coupled differential equations for beam width parameter are established and solved numerically. The effects of polarization state of laser and magnetic field on the laser spot size evolution are studied. Itmore » is observed that in case of the right-handed polarization, an increase in the value of external magnetic field causes an increase in the strength of the self-focusing, especially in the higher values, and consequently, the self-focusing occurs in shorter distance of propagation. Moreover, the results demonstrate the existence of laser intensity and electron temperature ranges where self-focusing can occur, while the beam diverges outside of these regions; meanwhile, in these intervals, there exists a turning point for each of intensity and temperature in which the self-focusing process has its strongest strength. Finally, it is found that the self-focusing effect can be enhanced by increasing the plasma frequency (plasma density).« less

Temperature and magnetic field effects on electron transport through DNA molecules in a two-dimensional four-channel system.

PubMed

Joe, Yong S; Lee, Sun H; Hedin, Eric R; Kim, Young D

2013-06-01

We utilize a two-dimensional four-channel DNA model, with a tight-binding (TB) Hamiltonian, and investigate the temperature and the magnetic field dependence of the transport behavior of a short DNA molecule. Random variation of the hopping integrals due to the thermal structural disorder, which partially destroy phase coherence of electrons and reduce quantum interference, leads to a reduction of the localization length and causes suppressed overall transmission. We also incorporate a variation of magnetic field flux density into the hopping integrals as a phase factor and observe Aharonov-Bohm (AB) oscillations in the transmission. It is shown that for non-zero magnetic flux, the transmission zero leaves the real-energy axis and moves up into the complex-energy plane. We also point out that the hydrogen bonds between the base pair with flux variations play a role to determine the periodicity of AB oscillations in the transmission.

Residual Field Correction of Pulsed Bending Magnet

NASA Astrophysics Data System (ADS)

Takano, Junpei; Igarashi, Susumu; Kamikubota, Norihiko; Meigo, Shin-ichiro; Sato, Kenichi; Shirakata, Masashi; Yamada, Shuei

The Japan Proton Accelerator Research Complex (J-PARC) has an accelerator chain, Linac, Rapid Cycling Synchrotron (RCS), and Main Ring (MR). The RCS accelerates the proton beam up to 3 GeV every 40 msec. After the beam is extracted from the RCS, it is delivered to a beam transport line, which is 3NBT for the Material and Life Science Experimental Facility (MLF). Some bunches of the proton beam are bended from the 3NBT to another beam transport line, which is 3-50BT for the MR, by using a pulsed bending magnet (PB) [1]. However, the beam orbit in the 3NBT is kicked by the residual magnetic field of the PB. In order to correct the residual magnetic field, additional coils had been wound on the PB poles. As a result of scanning the current pattern of the correction coils, the orbit distortion in the 3NBT has been reduced.

Effects of Mn-doping on the giant magnetocaloric effect of EuTiO3 compound

NASA Astrophysics Data System (ADS)

Mo, Zhao-Jun; Sun, Qi-Lei; Han, Sheng; Zhao, Yun; Chen, Xing; Li, Lan; Liu, Guo-Dong; Meng, Fan-Bin; Shen, Jun

2018-06-01

The magnetic properties and magnetocaloric effect of EuTi1-xMnxO3 (x = 0-0.1) compounds are investigated. When the Ti4+ was substituted by Mn2+, the lattice constants were changed, the Eu3+ state and the oxygen vacancy generated. The exchange mechanisms were more complex among the Mn2+ 3d, the Eu 5d and Eu2+ 4f. The FM phase was dominant between AFM and FM as Mn substitute for Ti, which improve the MCE under low magnetic field. The values of -ΔSMmax are evaluated to 11.7 and 11.1 J/kg K for EuTi0.975Mn0.025O3 and EuTi0.95Mn0.05O3 compounds, under a magnetic field change of 1 T. And, the values of RC were obviously enhanced under the magnetic field changes of 1 and 2 T. Therefore, the giant reversible MCE makes these compounds promising candidates for magnetic refrigeration.

Morphology-controlled synthesis and novel microwave electromagnetic properties of hollow urchin-like chain Fe-doped MnO 2 under 10 T high magnetic field

NASA Astrophysics Data System (ADS)

Yuping, Duan; Jia, Zhang; Hui, Jing; Shunhua, Liu

2011-05-01

Fe-doped MnO 2 with a hollow sea urchin-like ball chain shape was first synthesized under a high magnetic field of 10 T. The formation mechanism was investigated and discussed in detail. The synthesized samples were characterized by XRD, SEM, TEM, EMPA, and vector network analysis. By doping MnO 2 with Fe, the relative complex permittivity of MnO 2 and its corresponding loss tangent clearly decreases, but its relative complex permeability and its corresponding loss tangent markedly increases. Moreover, the theoretically calculated values of reflection loss show that with increasing the Fe content, the as-prepared Fe-doped MnO 2 exhibits good microwave absorption capability.

Pulse-driven magnetoimpedance sensor detection of cardiac magnetic activity.

PubMed

Nakayama, Shinsuke; Sawamura, Kenta; Mohri, Kaneo; Uchiyama, Tsuyoshi

2011-01-01

This study sought to establish a convenient method for detecting biomagnetic activity in the heart. Electrical activity of the heart simultaneously induces a magnetic field. Detection of this magnetic activity will enable non-contact, noninvasive evaluation to be made. We improved the sensitivity of a pulse-driven magnetoimpedance (PMI) sensor, which is used as an electric compass in mobile phones and as a motion sensor of the operation handle in computer games, toward a pico-Tesla (pT) level, and measured magnetic fields on the surface of the thoracic wall in humans. The changes in magnetic field detected by this sensor synchronized with the electric activity of the electrocardiogram (ECG). The shape of the magnetic wave was largely altered by shifting the sensor position within 20 mm in parallel and/or perpendicular to the thoracic wall. The magnetic activity was maximal in the 4th intercostals near the center of the sterna. Furthermore, averaging the magnetic activity at 15 mm in the distance between the thoracic wall and the sensor demonstrated magnetic waves mimicking the P wave and QRS complex. The present study shows the application of PMI sensor in detecting cardiac magnetic activity in several healthy subjects, and suggests future applications of this technology in medicine and biology.

Dynamical Model for Spindown of Solar-type Stars

NASA Astrophysics Data System (ADS)

Sood, Aditi; Kim, Eun-jin; Hollerbach, Rainer

2016-12-01

After their formation, stars slow down their rotation rates by the removal of angular momentum from their surfaces, e.g., via stellar winds. Explaining how this rotation of solar-type stars evolves in time is currently an interesting but difficult problem in astrophysics. Despite the complexity of the processes involved, a traditional model, where the removal of angular momentum by magnetic fields is prescribed, has provided a useful framework to understand observational relations between stellar rotation, age, and magnetic field strength. Here, for the first time, a spindown model is proposed where loss of angular momentum by magnetic fields evolves dynamically, instead of being prescibed kinematically. To this end, we evolve the stellar rotation and magnetic field simultaneously over stellar evolution time by extending our previous work on a dynamo model which incorporates nonlinear feedback mechanisms on rotation and magnetic fields. We show that our extended model reproduces key observations and is capable of explaining the presence of the two branches of (fast and slow rotating) stars which have different relations between rotation rate Ω versus time (age), magnetic field strength | B| versus rotation rate, and frequency of magnetic field {ω }{cyc} versus rotation rate. For fast rotating stars we find that: (I) there is an exponential spindown {{Ω }}\\propto {e}-1.35t, with t measured in Gyr; (II) magnetic activity saturates for higher rotation rate; (III) {ω }{cyc}\\propto {{{Ω }}}0.83. For slow rotating stars we find: (I) a power-law spindown {{Ω }}\\propto {t}-0.52; (II) that magnetic activity scales roughly linearly with rotation rate; (III) {ω }{cyc}\\propto {{{Ω }}}1.16. The results obtained from our investigations are in good agreement with observations. The Vaughan-Preston gap is consistently explained in our model by the shortest spindown timescale in this transition from fast to slow rotators. Our results highlight the importance of self-regulation of magnetic fields and rotation by direct and indirect interactions involving nonlinear feedback in stellar evolution.

Narrow Scale Flow and a Weak Field by the Top of Earth's Core: Evidence from Orsted, Magsat and Secular Variation

NASA Technical Reports Server (NTRS)

Voorhies, Coerte V.

2004-01-01

As Earth's main magnetic field weakens, our magnetic shield against the onslaught of the solar wind thins. And the field strength needed to fend off battering by solar coronal mass ejections is decreasing, just when the delicate complexity of modem, vulnerable, electro-technological systems is increasing at an unprecedented rate. Recently, a working group of distinguished scientist from across the nation has asked NASA's Solid Earth and Natural Hazards program a key question: What are the dynamics of Earth s magnetic field and its interactions with the Earth system? Paleomagnetic studies of crustal rocks magnetized in the geologic past reveal that polarity reversals have occurred many times during Earth s history. Networked super-computer simulations of core field and flow, including effects of gravitational, pressure, rotational Coriolis, magnetic and viscous forces, suggest how this might happen in detail. And space-based measurements of the real, time-varying magnetic field help constrain estimates of the speed and direction of fluid iron flowing near the top of the core and enable tests of some hypotheses about such flow. Now scientists at NASA s Goddard Space Flight Center have developed and applied methods to test the hypotheses of narrow scale flow and of a dynamically weak magnetic field near the top of Earth s core. Using two completely different methods, C. V. Voorhies has shown these hypotheses lead to specific theoretical forms for the "spectrum" of Earth s main magnetic field and the spectrum of its rate of change. Much as solar physicists use a prism to separate sunlight into its spectrum, from long wavelength red to short wavelength blue light, geophysicists use a digital prism, spherical harmonic analysis, to separate the measured geomagnetic field into its spectrum, from long to short wavelength fields. They do this for the rate of change of the field as well.

The Magnetohydrodynamic Kelvin-Helmholtz Instability. III. The Role of Sheared Magnetic Field in Planar Flows

NASA Astrophysics Data System (ADS)

Jeong, Hyunju; Ryu, Dongsu; Jones, T. W.; Frank, Adam

2000-01-01

We have carried out simulations of the nonlinear evolution of the magnetohydrodynamic (MHD) Kelvin-Helmholtz (KH) instability for compressible fluids in 2.5 dimensions, extending our previous work by Frank et al. and Jones et al. In the present work we have simulated flows in the x-y plane in which a ``sheared'' magnetic field of uniform strength smoothly rotates across a thin velocity shear layer from the z-direction to the x-direction, aligned with the flow field. The sonic Mach number of the velocity transition is unity. Such flows containing a uniform field in the x-direction are linearly stable if the magnetic field strength is great enough that the Alfvénic Mach number MA=U0/cA<2. That limit does not apply directly to sheared magnetic fields, however, since the z-field component has almost no influence on the linear stability. Thus, if the magnetic shear layer is contained within the velocity shear layer, the KH instability may still grow, even when the field strength is quite large. So, here we consider a wide range of sheared field strengths covering Alfvénic Mach numbers, MA=142.9 to 2. We focus on dynamical evolution of fluid features, kinetic energy dissipation, and mixing of the fluid between the two layers, considering their dependence on magnetic field strength for this geometry. There are a number of differences from our earlier simulations with uniform magnetic fields in the x-y plane. For the latter, simpler case we found a clear sequence of behaviors with increasing field strength ranging from nearly hydrodynamic flows in which the instability evolves to an almost steady cat's eye vortex with enhanced dissipation, to flows in which the magnetic field disrupts the cat's eye once it forms, to, finally, flows that evolve very little before field-line stretching stabilizes the velocity shear layer. The introduction of magnetic shear can allow a cat's eye-like vortex to form, even when the field is stronger than the nominal linear instability limit given above. For strong fields that vortex is asymmetric with respect to the preliminary shear layer, however, so the subsequent dissipation is enhanced over the uniform field cases of comparable field strength. In fact, so long as the magnetic field achieves some level of dynamical importance during an eddy turnover time, the asymmetries introduced through the magnetic shear will increase flow complexity and, with that, dissipation and mixing. The degree of the fluid mixing between the two layers is strongly influenced by the magnetic field strength. Mixing of the fluid is most effective when the vortex is disrupted by magnetic tension during transient reconnection, through local chaotic behavior that follows.

Convection and magnetic field generation in the interior of planets (August Love Medal Lecture)

NASA Astrophysics Data System (ADS)

Christensen, U. R.

2009-04-01

Thermal convection driven by internal energy plays a role of paramount importance in planetary bodies. Its numerical modeling has been an essential tool for understanding how the internal engine of a planet works. Solid state convection in the silicate or icy mantles is the cause of endogenic tectonic activity, volcanism and, in the case of Earth, of plate motion. It also regulates the energy budget of the entire planet, including that of its core, and controls the presence or absence of a dynamo. The complex rheology of solid minerals, effects of phase transitions, and chemical heterogeneity are important issues in mantle convection. Examples discussed here are the convection pattern in Mars and the complex morphology of subducted slabs that are observed by seismic tomography in the Earth's mantle. Internally driven convection in the deep gas envelopes of the giant planets is possibly the cause for the strong jet streams at the surfaces that give rise to their banded appearance. Modeling of the magnetohydrodynamic flow in the conducting liquid core of the Earth has been remarkably successful in reproducing the primary properties of the geomagnetic field. As an examplefor attempts to explain also secondary properties, I will discuss dynamo models that account for the thermal coupling to the mantle. The understanding of the somewhat enigmatic magnetic fields of some other planets is less advanced. Here I will show that dynamos that operate below a stable conducting layer in the upper part of the planetary core can explain the unusual magnetic field properties of Mercury and Saturn. The question what determines the strength of a dynamo-generated magnetic field has been a matter of debate. From a large set of numerical dynamo simulations that cover a fair range of control parameters, we find a rule that relates magnetic field strength to the part of the energy flux that is thermodynamically available to be transformed into other forms of energy. This rules predicts correctly not only the magnetic field strength of planets with sufficiently simple dynamos (Earth and Jupiter), but also that of rapidly rotating stars.

Saturn's Magnetic Field Model: Birotor Dipole From Cassini RPWS and MAG Experiments

NASA Astrophysics Data System (ADS)

Galopeau, P. H. M.

2016-12-01

The radio and plasma wave science (RPWS) experiment on board the Cassini spacecraft, orbiting around Saturn since July 2004, revealed the presence of two distinct and variable rotation periods in the Saturnian kilometric radiation (SKR) which were attributed to the northern and southern hemispheres respectively. We believe that the periodic time modulations present in the SKR are mainly due to the rotation of Saturn's inner magnetic field. The existence of a double period implies that the inner field is not only limited to a simple rotation dipole but displays more complex structures having the same time periodicities than the radio emission. In order to build a model of this complex magnetic field, it is absolutely necessary to know the accurate phases of rotation linked with the two periods. The radio observations from the RPWS experiment allow a continuous and accurate follow-up of these rotation phases, since the SKR emission is permanently observable and produced very close to the planetary surface. A wavelet transform analysis of the intensity of the SKR signal received at 290 kHz between July 2004 and June 2012 was performed in order to calculate in the same time the different periodicities and phases. A dipole model was proposed for Saturn's inner magnetic field: this dipole presents the particularity to have North and South poles rotating around Saturn's axis at two different angular velocities; this dipole is tilted and not centered. 57 Cassini's revolutions, the periapsis of which is less than 5 Saturnian radii, have been selected for this study. For each of these chosen orbits, it is possible to fit with high precision the measurements of the MAG data experiment given by the magnetometers embarked on board Cassini. A nonrotating external magnetic field completes the model. This study suggests that Saturn's inner magnetic field is neither stationary nor fully axisymmetric. These results can be used as a boundary condition for modelling and constraining the planetary dynamo and they can be a starting point for the study of Saturn's inner structure and the comparison with the interior of Jupiter.

A model for metastable magnetism in the hidden-order phase of URu2Si2

NASA Astrophysics Data System (ADS)

Boyer, Lance; Yakovenko, Victor M.

2018-01-01

We propose an explanation for the experiment by Schemm et al. (2015) where the polar Kerr effect (PKE), indicating time-reversal symmetry (TRS) breaking, was observed in the hidden-order (HO) phase of URu2Si2. The PKE signal on warmup was seen only if a training magnetic field was present on cool-down. Using a Ginzburg-Landau model for a complex order parameter, we show that the system can have a metastable ferromagnetic state producing the PKE, even if the HO ground state respects TRS. We predict that a strong reversed magnetic field should reset the PKE to zero.

Controlling the spins angular momentum in ferromagnets with sequences of picosecond acoustic pulses.

PubMed

Kim, Ji-Wan; Vomir, Mircea; Bigot, Jean-Yves

2015-02-17

Controlling the angular momentum of spins with very short external perturbations is a key issue in modern magnetism. For example it allows manipulating the magnetization for recording purposes or for inducing high frequency spin torque oscillations. Towards that purpose it is essential to modify and control the angular momentum of the magnetization which precesses around the resultant effective magnetic field. That can be achieved with very short external magnetic field pulses or using intrinsically coupled magnetic structures, resulting in a transfer of spin torque. Here we show that using picosecond acoustic pulses is a versatile and efficient way of controlling the spin angular momentum in ferromagnets. Two or three acoustic pulses, generated by femtosecond laser pulses, allow suppressing or enhancing the magnetic precession at any arbitrary time by precisely controlling the delays and amplitudes of the optical pulses. A formal analogy with a two dimensional pendulum allows us explaining the complex trajectory of the magnetic vector perturbed by the acoustic pulses.

Investigating Jupiter's Deep Flow Structure using the Juno Magnetic and Gravity Measurements

NASA Astrophysics Data System (ADS)

Duer, K.; Galanti, E.; Cao, H.; Kaspi, Y.

2017-12-01

Jupiter's flow below its cloud-level is still largely unknown. The gravity measurements from Juno provide now an initial insight into the depth of the flow via the relation between the gravity field and the flow field. Furthermore, additional constraints could be put on the flow if the expected Juno magnetic measurements are also used. Specifically, the gravity and magnetic measurements can be combined to allow a more robust estimate of the deep flow structure. However, a complexity comes from the fact that both the radial profile of the flow, and it's connection to the induced magnetic field, might vary with latitude. In this study we propose a method for using the expected Juno's high-precision measurements of both the magnetic and gravity fields, together with latitude dependent models that relate the measurements to the structure of the internal flow. We simulate possible measurements by setting-up specific deep wind profiles and forward calculate the resulting anomalies in both the magnetic and gravity fields. We allow these profiles to include also latitude dependency. The relation of the flow field to the gravity field is based on thermal wind balance, and it's relation to the magnetic field is via a mean-field electrodynamics balance. The latter includes an alpha-effect, describing the mean magnetic effect of turbulent rotating convection, which might also vary with latitude. Using an adjoint based optimization process, we examine the ability of the combined magnetic-gravity model to decipher the flow structure under the different potential Juno measurements. We investigate the effect of different latitude dependencies on the derived solutions and their associated uncertainties. The novelty of this study is the combination of two independent Juno measurements for the calculation of a latitudinal dependent interior flow profile. This method might lead to a better constraint of Jupiter's flow structure.

Nanocluster building blocks of artificial square spin ice: Stray-field studies of thermal dynamics

NASA Astrophysics Data System (ADS)

Pohlit, Merlin; Porrati, Fabrizio; Huth, Michael; Ohno, Yuzo; Ohno, Hideo; Müller, Jens

2015-05-01

We present measurements of the thermal dynamics of a Co-based single building block of an artificial square spin ice fabricated by focused electron-beam-induced deposition. We employ micro-Hall magnetometry, an ultra-sensitive tool to study the stray field emanating from magnetic nanostructures, as a new technique to access the dynamical properties during the magnetization reversal of the spin-ice nanocluster. The obtained hysteresis loop exhibits distinct steps, displaying a reduction of their "coercive field" with increasing temperature. Therefore, thermally unstable states could be repetitively prepared by relatively simple temperature and field protocols allowing one to investigate the statistics of their switching behavior within experimentally accessible timescales. For a selected switching event, we find a strong reduction of the so-prepared states' "survival time" with increasing temperature and magnetic field. Besides the possibility to control the lifetime of selected switching events at will, we find evidence for a more complex behavior caused by the special spin ice arrangement of the macrospins, i.e., that the magnetic reversal statistically follows distinct "paths" most likely driven by thermal perturbation.

Enhancing the magnetic anisotropy of maghemite nanoparticles via the surface coordination of molecular complexes

PubMed Central

Prado, Yoann; Daffé, Niéli; Michel, Aude; Georgelin, Thomas; Yaacoub, Nader; Grenèche, Jean-Marc; Choueikani, Fadi; Otero, Edwige; Ohresser, Philippe; Arrio, Marie-Anne; Cartier-dit-Moulin, Christophe; Sainctavit, Philippe; Fleury, Benoit; Dupuis, Vincent; Lisnard, Laurent; Fresnais, Jérôme

2015-01-01

Superparamagnetic nanoparticles are promising objects for data storage or medical applications. In the smallest—and more attractive—systems, the properties are governed by the magnetic anisotropy. Here we report a molecule-based synthetic strategy to enhance this anisotropy in sub-10-nm nanoparticles. It consists of the fabrication of composite materials where anisotropic molecular complexes are coordinated to the surface of the nanoparticles. Reacting 5 nm γ-Fe2O3 nanoparticles with the [CoII(TPMA)Cl2] complex (TPMA: tris(2-pyridylmethyl)amine) leads to the desired composite materials and the characterization of the functionalized nanoparticles evidences the successful coordination—without nanoparticle aggregation and without complex dissociation—of the molecular complexes to the nanoparticles surface. Magnetic measurements indicate the significant enhancement of the anisotropy in the final objects. Indeed, the functionalized nanoparticles show a threefold increase of the blocking temperature and a coercive field increased by one order of magnitude. PMID:26634987

Magnetic anisotropy of [Mo(CN)7]4- anions and fragments of cyano-bridged magnetic networks.

PubMed

Chibotaru, Liviu F; Hendrickx, Marc F A; Clima, Sergiu; Larionova, Joulia; Ceulemans, Arnout

2005-08-18

Quantum chemistry calculations of CASSCF/CASPT2 level together with ligand field analysis are used for the investigation of magnetic anisotropy of [Mo(CN)7]4- complexes. We have considered three types of heptacyano environments: two ideal geometries, a pentagonal bipyramid and a capped trigonal prism, and the heptacyanomolybdate fragment of the cyano-bridged magnetic network K2[Mn(H2O)2]3[Mo(CN)7]2.6H2O. At all geometries the first excited Kramers doublet is found remarkably close to the ground one due to a small orbital energy gap in the ligand field spectrum, which ranges between a maximal value in the capped trigonal prism (800 cm(-1)) and zero in the pentagonal bipyramid. The small value of this gap explains (i) the axial form of the g tensor and (ii) the strong magnetic anisotropy even in strongly distorted complexes. Comparison with available experimental data for the g tensor of the mononuclear precursors reveals good agreement with the present calculations for the capped trigonal prismatic complex and a significant discrepancy for the pentagonal bipyramidal one. The calculations for the heptacyanomolybdate fragment of K2[Mn(H2O)2]3[Mo(CN)7]2.6H2O give g(perpendicular)/g(parallel) approximately 0.5 and the orientation of the local anisotropy axis close to the symmetry axis of an idealized pentagonal bipyramid. These findings are expected to be important for the understanding of the magnetism of anisotropic Mo(III)-Mn(II) cyano-bridged networks based on the [Mo(CN)7]4- building block.

3D Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Parnell, Clare E.; Maclean, Rhona C.; Haynes, Andrew L.; Galsgaard, Klaus

2011-08-01

Magnetic reconnection is an important process that is prevalent in a wide range of astrophysical bodies. It is the mechanism that permits magnetic fields to relax to a lower energy state through the global restructuring of the magnetic field and is thus associated with a range of dynamic phenomena such as solar flares and CMEs. The characteristics of three-dimensional reconnection are reviewed revealing how much more diverse it is than reconnection in two dimensions. For instance, three-dimensional reconnection can occur both in the vicinity of null points, as well as in the absence of them. It occurs continuously and continually throughout a diffusion volume, as opposed to at a single point, as it does in two dimensions. This means that in three-dimensions field lines do not reconnect in pairs of lines making the visualisation and interpretation of three-dimensional reconnection difficult. By considering particular numerical 3D magnetohydrodynamic models of reconnection, we consider how magnetic reconnection can lead to complex magnetic topologies and current sheet formation. Indeed, it has been found that even simple interactions, such as the emergence of a flux tube, can naturally give rise to `turbulent-like' reconnection regions.

Numerical Simulations of Flare-productive Active Regions: δ-sunspots, Sheared Polarity Inversion Lines, Energy Storage, and Predictions

NASA Astrophysics Data System (ADS)

Toriumi, Shin; Takasao, Shinsuke

2017-11-01

Solar active regions (ARs) that produce strong flares and coronal mass ejections (CMEs) are known to have a relatively high non-potentiality and are characterized by δ-sunspots and sheared magnetic structures. In this study, we conduct a series of flux emergence simulations from the convection zone to the corona and model four types of active regions that have been observationally suggested to cause strong flares, namely the spot-spot, spot-satellite, quadrupole, and inter-AR cases. As a result, we confirm that δ-spot formation is due to the complex geometry and interaction of emerging magnetic fields, and we find that the strong-field, high-gradient, highly sheared polarity inversion line (PIL) is created by the combined effect of the advection, stretching, and compression of magnetic fields. We show that free magnetic energy builds up in the form of a current sheet above the PIL. It is also revealed that photospheric magnetic parameters that predict flare eruptions reflect the stored free energy with high accuracy, while CME-predicting parameters indicate the magnetic relationship between flaring zones and entire ARs.

Determination of the magnetization scaling exponent for single-crystal La0.8Sr0.2MnO3 by broadband microwave surface impedance measurements

NASA Astrophysics Data System (ADS)

Schwartz, Andrew; Scheffler, Marc; Anlage, Steven M.

2000-01-01

Employing a broadband microwave reflection configuration, we have measured the complex surface impedance, ZS(ω,T), of single-crystal La0.8Sr0.2MnO3, as a function of frequency (0.045-45 GHz) and temperature (250-325 K). Through the dependence of the microwave surface impedance on the magnetic permeability, μ⁁(ω,T), we have studied the local magnetic behavior of this material, and have extracted the spontaneous magnetization, M0(T), in zero applied field. The broadband nature of these measurements and the fact that no external field is applied to the material provide a unique opportunity to analyze the critical behavior of the spontaneous magnetization at temperatures very close to the ferromagnetic phase transition. We find a Curie temperature TC=305.5+/-0.5 K and scaling exponent β=0.45+/-0.05, in agreement with the prediction of mean-field theory. We also discuss other recent determinations of the magnetization critical exponent in this and similar materials and show why our results are more definitive.

Enhancement of magnetic anisotropy in a Mn-Bi heterobimetallic complex.

PubMed

Pearson, Tyler J; Fataftah, Majed S; Freedman, Danna E

2016-09-15

A novel Mn 2+ Bi 3+ heterobimetallic complex, featuring the closest MnBi interaction for a paramagnetic molecular species, exhibits unusually large axial zero-field splitting. We attribute this enhancement to the proximity of Mn 2+ to a heavy main group element, namely, bismuth.

Close temporal correspondence between geomagnetic anomalies and earthquakes during the 2002-2003 eruption of Etna volcano

USGS Publications Warehouse

Currenti, G.; Del, Negro C.; Johnston, M.; Sasai, Y.

2007-01-01

The early stages of the 2002-2003 lateral eruption at Mount Etna were accompanied by slow changes (over some hours) and some rapid step offsets in the local magnetic field. At five monitoring locations, the total magnetic field intensity has been measured using continuously operating Overhauser magnetometers at a sampling rate of 10 s. The very unique aspect of these observations is the close temporal correspondence between magnetic field offsets and earthquakes that occurred in the upper northern flank of the volcano on 27 October 2002 prior to a primary eruption. Rapid coseismic changes of the magnetic field were clearly identified for three of the most energetic earthquakes, which were concentrated along the Northeast Rift at a depth of about 1 km below sea level. Coseismic magnetic signals, with amplitudes from 0.5 to 2.5 nT, have been detected for three of the largest seismic events located roughly midway between the magnetic stations. We quantitatively examine possible geophysical mechanisms, which could cause the magnetic anomalies. The comparison between magnetic data, seismicity and surface phenomena implies that piezomagnetic effects are the primary physical mechanism responsible for the observed magnetic anomalies although the detailed cause of the rapid high stress change required is not clear. The modeling of the observed coseismic magnetic changes in terms of piezomagnetic mechanism provides further evidence of the complex interaction between volcanic and tectonic processes during dike propagation along the Northeast Rift. Copyright 2007 by the American Geophysical Union.

Plasma convection in Saturn's magnetosphere: A diagnosis using Cassini observations of the magnetic field spiral

NASA Astrophysics Data System (ADS)

Smith, Edward; Dougherty, Michele K.

The global distribution of plasma and its flows inside Saturn's magnetosphere is complex. The large satellites in the inner magnetosphere are a persistent source of plasma that must make its way into the outer magnetosphere and exit through the magnetotail. The mass loaded into the magnetic field stretches the field lines outward resulting in the formation of the equatorial current sheet. The outward radial flow causes the closed stretched fields to spiral out of magnetic meridian planes. The angle associated with the spiralling is given by the ratio of the azimuthal field component, B , to the radial component Br : tan = B / Br . The magnetic spiral is directly related to the corresponding components of plasma velocity, v and v r, provided the conductivity of the ionosphere, , is high enough to enforce co-rotation of the field lines. If, as has been inferred, the conductivity is low, the field and plasma do not co-rotate and the conductivity also enters the expression for . Conditions are more uncertain further out in the magnetosphere where convective motions associated with magnetic reconnection between planetary and interplanetary fields and the motion of the shocked solar wind become dominant. The prevailing model is a superposition of two modes of plasma circulation inside the magnetosphere and magnetotail, the Dungey and Vasyliunas cycles, that depend on radial distance and local time with an x-line in the midnight sector that separates the two cycles. The measured spiral angle will be affected by this complexity and holds the promise of distinguishing the relative influences of v ,v r and . The two field components that define the spiral angle are also involved in the transfer of angular momentum from the ionosphere to the magnetospheric plasma and the outward mass flux. The spiral should also contain evidence, especially at high latitudes, of the return of the current to the ionosphere from the current sheet. Our major objective, therefore, is to characterize as a function of radius, latitude and local time using the global coverage provided by Cassini and apply the findings to the topics listed above.

Combined analysis of magnetic and gravity anomalies using normalized source strength (NSS)

NASA Astrophysics Data System (ADS)

Li, L.; Wu, Y.

2017-12-01

Gravity field and magnetic field belong to potential fields which lead inherent multi-solution. Combined analysis of magnetic and gravity anomalies based on Poisson's relation is used to determinate homology gravity and magnetic anomalies and decrease the ambiguity. The traditional combined analysis uses the linear regression of the reduction to pole (RTP) magnetic anomaly to the first order vertical derivative of the gravity anomaly, and provides the quantitative or semi-quantitative interpretation by calculating the correlation coefficient, slope and intercept. In the calculation process, due to the effect of remanent magnetization, the RTP anomaly still contains the effect of oblique magnetization. In this case the homology gravity and magnetic anomalies display irrelevant results in the linear regression calculation. The normalized source strength (NSS) can be transformed from the magnetic tensor matrix, which is insensitive to the remanence. Here we present a new combined analysis using NSS. Based on the Poisson's relation, the gravity tensor matrix can be transformed into the pseudomagnetic tensor matrix of the direction of geomagnetic field magnetization under the homologous condition. The NSS of pseudomagnetic tensor matrix and original magnetic tensor matrix are calculated and linear regression analysis is carried out. The calculated correlation coefficient, slope and intercept indicate the homology level, Poisson's ratio and the distribution of remanent respectively. We test the approach using synthetic model under complex magnetization, the results show that it can still distinguish the same source under the condition of strong remanence, and establish the Poisson's ratio. Finally, this approach is applied in China. The results demonstrated that our approach is feasible.

Complex monitoring and alert network for electromagnetic, infrasound, acoustic seismotectonic phenomena

NASA Astrophysics Data System (ADS)

-Emilian Toader, Victorin; Moldovan, Iren-Adelina; Constantin, Ionescu

2014-05-01

The Romanian seismicity recorded in 2013 three important events: the largest seismic "silence", the shortest sequence of two earthquakes greater than 4.8R in less than 14 days after the "Romanian National Institute for Earth Physics" (NIEP) developed a digital network, and a very high crustal activity in Galati area. We analyze the variations of the telluric currents and local magnetic field, variations of the atmospheric electrostatic field, infrasound, temperature, humidity, wind speed and direction, atmospheric pressure, variations in the earth crust with inclinometers and animal behavior. The general effect is the first high seismic energy discontinuity that could be a precursor factor. Since 1977 Romania did not register any important earthquake that would generate a sense of fear among the population. In parallel with the seismic network NIEP developed a magneto-telluric, bioseismic, VLF and acoustic network. A large frequency spectrum is covered for mechanical vibration, magnetic and electric field with ground and air sensors. Special software was designed for acquisition, analysis and real time alert using internet direct connection, web page, email and SMS. Many examples show the sensitivity of telluric current, infrasound, acoustic records (from air-ground), and the effect of tectonic stress on the magnetic field or ground deformation. The next update of the multidisciplinary monitoring network will include measurement of ionization, radon emission, sky color, solar radiation and extension of infrasound and VL/LF equipment. NOAA Space Weather satellites transmit solar activity magnetic field data, X ray flux, electron, and proton flux information useful for complex analysis.

Heterometallic Zn3 Ln3 Ensembles Containing (μ6 -CO3 ) Ligand and Triangular Disposition of Ln3+ ions: Analysis of Single-Molecule Toroic (SMT) and Single-Molecule Magnet (SMM) Behavior.

PubMed

Goura, Joydeb; Colacio, Enrique; Herrera, Juan Manuel; Suturina, Elizaveta A; Kuprov, Ilya; Lan, Yanhua; Wernsdorfer, Wolfgang; Chandrasekhar, Vadapalli

2017-11-21

Two new heterometallic Zn 3 Ln 3 (Ln 3+ =Dy, Tb) complexes, with a double triangular topology of the metal ions, have been assembled from the polytopic Mannich base ligand 6,6'-{[2-(dimethylamino)ethylazanediyl]bis(methylene)}bis(2-methoxy-4-methylphenol) (H 2 L) with the aid of an in situ generated carbonate ligand from atmospheric CO 2 fixation. Theoretical calculations indicate axial ground states for the Ln 3+ ions in these complexes, with their local magnetic moments being almost coplanar and tangential to the Ln 3+ atoms that define the equilateral triangle. Therefore, they can be considered as single-molecule toroics (SMTs) with almost zero total magnetic moment. Micro-SQUID measurements on the Dy 3+ counterpart show hysteresis loops below 3 K that have an S-shape, with large coercive fields opening upon cooling. This behavior is typical of a single molecule magnet (SMM) with very slow zero-field relaxation. At around ±0.35 T, the loops have a broad step, which is due to a direct relaxation process and corresponds to an acceleration of the relaxation of the magnetization, also observed at this magnetic field from ac susceptibility measurements. Simulations suggest that the broad step corresponds to two level avoidance of crossing points where the spin chiral Kramers doublet meets excited states of the coupled manifold, whose position is defined by exchange and dipole interactions. The Tb 3+ counterpart does not exhibit SMM behavior, which is due to the fact that the degeneracy of the ground state of the exchange coupled system is lifted at zero field, thus favoring quantum tunneling of magnetization (QTM). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

3D magnetic nanostructures grown by focused electron and ion beam induced deposition

NASA Astrophysics Data System (ADS)

Fernandez-Pacheco, Amalio

Three-dimensional nanomagnetism is an emerging research area, where magnetic nanostructures extend along the whole space, presenting novel functionalities not limited to the substrate plane. The development of this field could have a revolutionary impact in fields such as electronics, the Internet of Things or bio-applications. In this contribution, I will show our recent work on 3D magnetic nanostructures grown by focused electron and ion beam induced deposition. This 3D nano-printing techniques, based on the local chemical vapor deposition of a gas via the interaction with electrons and ions, makes the fabrication of complex 3D magnetic nanostructures possible. First, I will show how by exploiting different growth regimes, suspended Cobalt nanowires with modulated diameter can be patterned, with potential as domain wall devices. Afterwards, I will show recent results where the synthesis of Iron-Gallium alloys can be exploited in the field of artificial multiferroics. Moreover, we are developing novel methodologies combining physical vapor deposition and 3D nano-printing, creating Permalloy 3D nanostrips with controllable widths and lengths up to a few microns. This approach has been extended to more complex geometries by exploiting advanced simulation growth techniques combining Monte Carlo and continuum model methods. Throughout the talk, I will show the methodology we are following to characterize 3D magnetic nanostructures, by combining magneto-optical Kerr effect, scanning probe microscopy and electron and X-R magnetic imaging, and I will highlight some of the challenges and opportunities when studying these structures. I acknowledge funding from EPSRC and the Winton Foundation.

Gravitropic mechanisms derived from space experiments and magnetic gradients.

NASA Astrophysics Data System (ADS)

Hasenstein, Karl H.; Park, Myoung Ryoul

2016-07-01

Gravitropism is the result of a complex sequence of events that begins with the movement of dense particles, typically starch-filled amyloplasts in response to reorientation. Although these organelles change positions, it is not clear whether the critical signal is derived from sedimentation or dynamic interactions of amyloplasts with relevant membranes. Substituting gravity by high-gradient magnetic fields (HGMF) provides a localized stimulus for diamagnetic starch that is specific for amyloplasts and comparable to gravity without affecting other organelles. Experiments with Brassica rapa showed induction of root curvature by HGMF when roots moved sufficiently close to the magnetic gradient-inducing foci. The focused and short-range effectiveness of HGMFs provided a gravity-like stimulus and affected related gene expression. Root curvature was sensitive to the mutual alignment between roots and HGMF direction. Unrelated to any HGMF effects, the size of amyloplasts in space-grown roots increased by 30% compared to ground controls and suggests enhanced sensitivity in a gravity-reduced environment. Accompanying gene transcription studies showed greater differences between HGMF-exposed and space controls than between space and ground controls. This observation may lead to the identification of gravitropism-relevant genes. However, space grown roots showed stronger transcription of common reference genes such as actin and ubiquitin in magnetic fields than in non-magnetic conditions. In contrast, α-amylase, glucokinase and PIN encoding genes were transcribed stronger under non-magnetic conditions than under HGMF. The large number of comparisons between space, ground, and HGMF prompted the assessment of transcription differences between root segments, root-shoot junction, and seeds. Because presumed transcription of reference genes varied more than genes of interest, changes in gene expression cannot be based on reference genes. The data provide an example of complex and different responses to microgravity conditions, induced curvature, ground controls, clinorotation, and magnetic field exposure.

Excitons, trions, and biexcitons in transition-metal dichalcogenides: Magnetic-field dependence

NASA Astrophysics Data System (ADS)

Van der Donck, M.; Zarenia, M.; Peeters, F. M.

2018-05-01

The influence of a perpendicular magnetic field on the binding energy and structural properties of excitons, trions, and biexcitons in monolayers of semiconducting transition metal dichalcogenides (TMDs) is investigated. The stochastic variational method (SVM) with a correlated Gaussian basis is used to calculate the different properties of these few-particle systems. In addition, we present a simplified variational approach which supports the SVM results for excitons as a function of magnetic field. The exciton diamagnetic shift is compared with recent experimental results, and we extend this concept to trions and biexcitons. The effect of a local potential fluctuation, which we model by a circular potential well, on the binding energy of trions and biexcitons is investigated and found to significantly increase the binding of those excitonic complexes.

Temperature dependence dynamical permeability characterization of magnetic thin film using near-field microwave microscopy

NASA Astrophysics Data System (ADS)

Hung, Le Thanh; Phuoc, Nguyen N.; Wang, Xuan-Cong; Ong, C. K.

2011-08-01

A temperature dependence characterization system of microwave permeability of magnetic thin film up to 5 GHz in the temperature range from room temperature up to 423 K is designed and fabricated as a prototype measurement fixture. It is based on the near field microwave microscopy technique (NFMM). The scaling coefficient of the fixture can be determined by (i) calibrating the NFMM with a standard sample whose permeability is known; (ii) by calibrating the NFMM with an established dynamic permeability measurement technique such as shorted microstrip transmission line perturbation method; (iii) adjusting the real part of the complex permeability at low frequency to fit the value of initial permeability. The algorithms for calculating the complex permeability of magnetic thin films are analyzed. A 100 nm thick FeTaN thin film deposited on Si substrate by sputtering method is characterized using the fixture. The room temperature permeability results of the FeTaN film agree well with results obtained from the established short-circuited microstrip perturbation method. Temperature dependence permeability results fit well with the Landau-Lifshitz-Gilbert equation. The temperature dependence of the static magnetic anisotropy H_K^{sta}, the dynamic magnetic anisotropy H_K^{dyn}, the rotational anisotropy Hrot, together with the effective damping coefficient αeff, ferromagnetic resonance fFMR, and frequency linewidth Δf of the thin film are investigated. These temperature dependent magnetic properties of the magnetic thin film are important to the high frequency applications of magnetic devices at high temperatures.

Synthesis, characterisation and computational studies on a novel one-dimensional arrangement of Schiff-base Mn3 single-molecule magnet.

PubMed

Lin, Po-Heng; Gorelsky, Serge; Savard, Didier; Burchell, Tara J; Wernsdorfer, Wolfgang; Clérac, Rodolphe; Murugesu, Muralee

2010-09-07

The syntheses, structures and magnetic properties are reported for three new manganese complexes containing the Schiff-base ((2-hydroxy-3-methoxyphenyl)methylene)isonicotinohydrazine (H(2)hmi) ligand. Complex [Mn(II)(H(2)hmi)(2)(MeOH)(2)Cl(2)] (1) was obtained from the reaction of H(2)hmi with MnCl(2) in a MeOH-MeCN mixture. Addition of triethylamine to the previous reaction mixture followed by diethyl ether diffusion yielded a dinuclear manganese [Mn(III)(2)(hmi)(2)(OMe)(2)](infinity).2MeCN.2OEt(2) (2) compound. Upon increasing the MnCl(2)/H(2)hmi ratio, the mixed valence complex [Mn(III)(2)Mn(II)(hmi)(2)(OMe)(2)Cl(2)](infinity).MeOH (3) was obtained. Dc and ac magnetic measurements were carried out on all three samples. The ac susceptibility and field dependence of the magnetisation measurements confirmed that complex 3 exhibits a single-molecule magnet behaviour with an effective energy barrier of 8.1 K and an Arrhenius pre-exponential factor of 3 x 10(-9) s.

Transformable ferroelectric control of dynamic magnetic permeability

NASA Astrophysics Data System (ADS)

Jiang, Changjun; Jia, Chenglong; Wang, Fenglong; Zhou, Cai; Xue, Desheng

2018-02-01

Magnetic permeability, which measures the response of a material to an applied magnetic field, is crucial to the performance of magnetic devices and related technologies. Its dynamic value is usually a complex number with real and imaginary parts that describe, respectively, how much magnetic power can be stored and lost in the material. Control of permeability is therefore closely related to energy redistribution within a magnetic system or energy exchange between magnetic and other degrees of freedom via certain spin-dependent interactions. To avoid a high power consumption, direct manipulation of the permeability with an electric field through magnetoelectric coupling leads to high efficiency and simple operation, but remains a big challenge in both the fundamental physics and material science. Here we report unambiguous evidence of ferroelectric control of dynamic magnetic permeability in a Co /Pb (Mg1/3Nb2/3) 0.7Ti0.3O3 (Co/PMN-PT) heterostructure, in which the ferroelectric PMN-PT acts as an energy source for the ferromagnetic Co film via an interfacial linear magnetoelectric interaction. The electric field tuning of the magnitude and line shape of the permeability offers a highly localized means of controlling magnetization with ultralow power consumption. Additionally, the emergence of negative permeability promises a new way of realizing functional nanoscale metamaterials with adjustable refraction index.

Superconductor disks and cylinders in an axial magnetic field: II. Nonlinear and linear ac susceptibilities

NASA Astrophysics Data System (ADS)

Brandt, Ernst Helmut

1998-09-01

The ac susceptibility χ=χ'-iχ'' of superconductor cylinders of finite length in a magnetic field applied along the cylinder axis is calculated using the method developed in the preceding paper, part I. This method does not require any approximation of the infinitely extended magnetic field outside the cylinder or disk but directly computes the current density J inside the superconductor. The material is characterized by a general current-voltage law E(J), e.g., E(J)=Ec[J/Jc(B)]n(B), where E is the electric field, B=μ0H the magnetic induction, Ec a prefactor, Jc the critical current density, and n>=1 the creep exponent. For n>1, the nonlinear ac susceptibility is calculated from the hysteresis loops of the magnetic moment of the cylinder, which is obtained by time integration of the equation for J(r,t). For n>>1 these results go over into the Bean critical state model. For n=1, and for any linear complex resistivity ρac(ω)=E/J, the linear ac susceptibility is calculated from an eigenvalue problem which depends on the aspect ratio b/a of the cylinder or disk. In the limits b/a<<1 and b/a>>1, the known results for thin disks in a perpendicular field and long cylinders in a parallel field are reproduced. For thin disks in a perpendicular field, at large frequencies χ(ω) crosses over to the behavior of slabs in parallel geometry since the magnetic field lines are expelled and have to flow around the disk. The results presented may be used to obtain the nonlinear or linear resistivity from contact-free magnetic measurements on superconductors of realistic shape.

Fast solver for large scale eddy current non-destructive evaluation problems

NASA Astrophysics Data System (ADS)

Lei, Naiguang

Eddy current testing plays a very important role in non-destructive evaluations of conducting test samples. Based on Faraday's law, an alternating magnetic field source generates induced currents, called eddy currents, in an electrically conducting test specimen. The eddy currents generate induced magnetic fields that oppose the direction of the inducing magnetic field in accordance with Lenz's law. In the presence of discontinuities in material property or defects in the test specimen, the induced eddy current paths are perturbed and the associated magnetic fields can be detected by coils or magnetic field sensors, such as Hall elements or magneto-resistance sensors. Due to the complexity of the test specimen and the inspection environments, the availability of theoretical simulation models is extremely valuable for studying the basic field/flaw interactions in order to obtain a fuller understanding of non-destructive testing phenomena. Theoretical models of the forward problem are also useful for training and validation of automated defect detection systems. Theoretical models generate defect signatures that are expensive to replicate experimentally. In general, modelling methods can be classified into two categories: analytical and numerical. Although analytical approaches offer closed form solution, it is generally not possible to obtain largely due to the complex sample and defect geometries, especially in three-dimensional space. Numerical modelling has become popular with advances in computer technology and computational methods. However, due to the huge time consumption in the case of large scale problems, accelerations/fast solvers are needed to enhance numerical models. This dissertation describes a numerical simulation model for eddy current problems using finite element analysis. Validation of the accuracy of this model is demonstrated via comparison with experimental measurements of steam generator tube wall defects. These simulations generating two-dimension raster scan data typically takes one to two days on a dedicated eight-core PC. A novel direct integral solver for eddy current problems and GPU-based implementation is also investigated in this research to reduce the computational time.

Estimating the Geoelectric Field Using Precomputed EMTFs: Effect of Magnetometer Cadence

NASA Astrophysics Data System (ADS)

Grawe, M.; Butala, M.; Makela, J. J.; Kamalabadi, F.

2017-12-01

Studies that make use of electromagnetic transfer functions (EMTFs) to calculate the surface electric field from a specified surface magnetic field often use historical magnetometer information for validation and comparison purposes. Depending on the data source, the magnetometer cadence is typically between 1 and 60 seconds. It is often implied that a 60 (and sometimes 10) second cadence is acceptable for purposes of geoelectric field calculation using a geophysical model. Here, we quantitatively assess this claim under different geological settings and using models of varying complexity (using uniform/1D/3D EMTFs) across several different space weather events. Conclusions are made about sampling rate sufficiency as a function of local geology and the spectral content of the surface magnetic field.

Wide-field Infrared Polarimetry of the ρ Ophiuchi Cloud Core

NASA Astrophysics Data System (ADS)

Kwon, Jungmi; Tamura, Motohide; Hough, James H.; Nakajima, Yasushi; Nishiyama, Shogo; Kusakabe, Nobuhiko; Nagata, Tetsuya; Kandori, Ryo

2015-09-01

We conducted wide and deep simultaneous JHKs-band imaging polarimetry of the ρ Ophiuchi cloud complex. Aperture polarimetry in the JHKs band was conducted for 2136 sources in all three bands, of which 322 sources have significant polarizations in all the JHKs bands and have been used for a discussion of the core magnetic fields. There is a positive correlation between degrees of polarization and H - Ks color up to H - Ks ≈ 3.5. The magnetic field structures in the core region are revealed up to at least AV ≈ 47 mag and are unambiguously defined in each sub-region (core) of Oph-A, Oph-B, Oph-C, Oph-E, Oph-F, and Oph-AC. Their directions, degrees of polarization, and polarization efficiencies differ but their changes are gradual; thus, the magnetic fields appear to be connected from core to core, rather than as a simple overlap of the different cloud core components. Comparing our results with the large-scale field structures obtained from previous optical polarimetric studies, we suggest that the magnetic field structures in the core were distorted by the cluster formation in this region, which may have been induced by shock compression due to wind/radiation from the Scorpius-Centaurus association.

Observation of the magnetic flux and three-dimensional structure of skyrmion lattices by electron holography.

PubMed

Park, Hyun Soon; Yu, Xiuzhen; Aizawa, Shinji; Tanigaki, Toshiaki; Akashi, Tetsuya; Takahashi, Yoshio; Matsuda, Tsuyoshi; Kanazawa, Naoya; Onose, Yoshinori; Shindo, Daisuke; Tonomura, Akira; Tokura, Yoshinori

2014-05-01

Skyrmions are nanoscale spin textures that are viewed as promising candidates as information carriers in future spintronic devices. Skyrmions have been observed using neutron scattering and microscopy techniques. Real-space imaging using electrons is a straightforward way to interpret spin configurations by detecting the phase shifts due to electromagnetic fields. Here, we report the first observation by electron holography of the magnetic flux and the three-dimensional spin configuration of a skyrmion lattice in Fe(0.5)Co(0.5)Si thin samples. The magnetic flux inside and outside a skyrmion was directly visualized and the handedness of the magnetic flux flow was found to be dependent on the direction of the applied magnetic field. The electron phase shifts φ in the helical and skyrmion phases were determined using samples with a stepped thickness t (from 55 nm to 510 nm), revealing a linear relationship (φ = 0.00173 t). The phase measurements were used to estimate the three-dimensional structures of both the helical and skyrmion phases, demonstrating that electron holography is a useful tool for studying complex magnetic structures and for three-dimensional, real-space mapping of magnetic fields.

Thrust and efficiency model for electron-driven magnetic nozzles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Little, Justin M.; Choueiri, Edgar Y.

2013-10-15

A performance model is presented for magnetic nozzle plasmas driven by electron thermal expansion to investigate how the thrust coefficient and beam divergence efficiency scale with the incoming plasma flow and magnetic field geometry. Using a transformation from cylindrical to magnetic coordinates, an approximate analytical solution is derived to the axisymmetric two-fluid equations for a collisionless plasma flow along an applied magnetic field. This solution yields an expression for the half-width at half-maximum of the plasma density profile in the far-downstream region, from which simple scaling relations for the thrust coefficient and beam divergence efficiency are derived. It is foundmore » that the beam divergence efficiency is most sensitive to the density profile of the flow into the nozzle throat, with the highest efficiencies occurring for plasmas concentrated along the nozzle axis. Increasing the expansion ratio of the magnetic field leads to efficiency improvements that are more pronounced for incoming plasmas that are not concentrated along the axis. This implies that the additional magnet required to increase the expansion ratio may be worth the added complexity for plasma sources that exhibit poor confinement.« less

Numerical Study of Magnetic Damping During Unidirectional Solidification

NASA Technical Reports Server (NTRS)

Li, Ben Q.

1997-01-01

A fully 3-D numerical model is developed to represent magnetic damping of complex fluid flow, heat transfer and electromagnetic field distributions in a melt cavity. The model is developed based on our in-house finite element code for the fluid flow, heat transfer and electromagnetic field calculations. The computer code has been tested against benchmark test problems that are solved by other commercial codes as well as analytical solutions whenever available. The numerical model is tested against numerical and experimental results for water reported in literature. With the model so tested, various numerical simulations are carried out for the Sn-35.5% Pb melt convection and temperature distribution in a cylindrical cavity with and without the presence of a transverse magnetic field. Numerical results show that magnetic damping can be effectively applied to reduce turbulence and flow levels in the melt undergoing solidification and over a certain threshold value a higher magnetic field resulted in a higher velocity reduction. It is found also that for a fully 3-D representation of the magnetic damping effects, the electric field induced in the melt by the applied DC magnetic field does not vanish, as some researchers suggested, and must be included even for molten metal and semiconductors. Also, for the study of the melt flow instability, a long enough time has to be applied to ensure the final fluid flow recirculation pattern. Moreover, our numerical results suggested that there seems to exist a threshold value of applied magnetic field, above which magnetic damping becomes possible and below which the convection in the melt is actually enhanced. Because of the limited financial resource allocated for the project, we are unable to carry out extensive study on this effect, which should warrant further theoretical and experimental study. In that endeavor, the developed numerical model should be very useful; and the model should serve as a useful tool for exploring necessary design parameters for planning magnetic damping experiments and interpreting the experimental results.

MAVEN Observations of Magnetic Reconnection on the Dayside Martian Magnetosphere

NASA Astrophysics Data System (ADS)

DiBraccio, Gina A.; Espley, Jared R.; Connerney, John E. P.; Brain, David A.; Halekas, Jasper S.; Mitchell, David L.; Harada, Yuki; Hara, Takuya

2015-04-01

The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission offers a unique opportunity to investigate the complex solar wind-planetary interaction at Mars. The Martian magnetosphere is formed as the interplanetary magnetic field (IMF) drapes around the planet's ionosphere and localized crustal magnetic fields. As the solar wind interacts with this induced magnetosphere, magnetic reconnection can occur at any location where a magnetic shear is present. Reconnection between the IMF and the induced and crustal fields facilitates a direct plasma exchange between the solar wind and the Martian ionosphere. Here we address the occurrence of magnetic reconnection on the dayside magnetosphere of Mars using MAVEN magnetic field and plasma data. When reconnection occurs on the dayside, a non-zero magnetic field component normal to the obstacle, B_N, will result. Using minimum variance analysis, we measure BN by transforming Magnetometer data into boundary-normal coordinates. Selected events are then further examined to identify plasma heating and energization, in the form of Alfvénic outflow jets, using Solar Wind Ion Analyzer measurements. Additionally, the topology of the crustal fields is validated from electron pitch angle distributions provided by the Solar Wind Electron Analyzer. To understand which parameters are responsible for the onset of reconnection, we test the dependency of the dimensionless reconnection rate, calculated from BN measurements, on magnetic field shear angle and plasma beta (the ratio of plasma pressure to magnetic pressure). We assess the global impact of reconnection on Mars' induced magnetosphere by combining analytical models with MAVEN observations to predict the regions where reconnection may occur. Using this approach we examine how IMF orientation and magnetosheath parameters affect reconnection on a global scale. With the aid of analytical models we are able to assess the role of reconnection on a global scale to better understand which factors drive these dynamics in the space environment of Mars.

Polar Field Reversals and Active Region Decay

NASA Astrophysics Data System (ADS)

Petrie, Gordon; Ettinger, Sophie

2017-09-01

We study the relationship between polar field reversals and decayed active region magnetic flux. Photospheric active region flux is dispersed by differential rotation and turbulent diffusion, and is transported poleward by meridional flows and diffusion. We summarize the published evidence from observation and modeling of the influence of meridional flow variations and decaying active region flux's spatial distribution, such as the Joy's law tilt angle. Using NSO Kitt Peak synoptic magnetograms covering cycles 21-24, we investigate in detail the relationship between the transport of decayed active region flux to high latitudes and changes in the polar field strength, including reversals in the magnetic polarity at the poles. By means of stack plots of low- and high-latitude slices of the synoptic magnetograms, the dispersal of flux from low to high latitudes is tracked, and the timing of this dispersal is compared to the polar field changes. In the most abrupt cases of polar field reversal, a few activity complexes (systems of active regions) are identified as the main cause. The poleward transport of large quantities of decayed trailing-polarity flux from these complexes is found to correlate well in time with the abrupt polar field changes. In each case, significant latitudinal displacements were found between the positive and negative flux centroids of the complexes, consistent with Joy's law bipole tilt with trailing-polarity flux located poleward of leading-polarity flux. The activity complexes of the cycle 21 and 22 maxima were larger and longer-lived than those of the cycle 23 and 24 maxima, and the poleward surges were stronger and more unipolar and the polar field changes larger and faster. The cycle 21 and 22 polar reversals were dominated by only a few long-lived complexes whereas the cycle 23 and 24 reversals were the cumulative effects of more numerous, shorter-lived regions. We conclude that sizes and lifetimes of activity complexes are key to understanding the diversity of polar reversals.

Design principles and theory of paramagnetic fluorine-labelled lanthanide complexes as probes for (19)F magnetic resonance: a proof-of-concept study.

PubMed

Chalmers, Kirsten H; De Luca, Elena; Hogg, Naomi H M; Kenwright, Alan M; Kuprov, Ilya; Parker, David; Botta, Mauro; Wilson, J Ian; Blamire, Andrew M

2010-01-04

The synthesis and spectroscopic properties of a series of CF(3)-labelled lanthanide(III) complexes (Ln=Gd, Tb, Dy, Ho, Er, Tm) with amide-substituted ligands based on 1,4,7,10-tetraazacyclododecane are described. The theoretical contributions of the (19)F magnetic relaxation processes in these systems are critically assessed and selected volumetric plots are presented. These plots allow an accurate estimation of the increase in the rates of longitudinal and transverse relaxation as a function of the distance between the Ln(III) ion and the fluorine nucleus, the applied magnetic field, and the re-rotational correlation time of the complex, for a given Ln(III) ion. Selected complexes exhibit pH-dependent chemical shift behaviour, and a pK(a) of 7.0 was determined in one example based on the holmium complex of an ortho-cyano DO3A-monoamide ligand, which allowed the pH to be assessed by measuring the difference in chemical shift (varying by over 14 ppm) between two (19)F resonances. Relaxation analyses of variable-temperature and variable-field (19)F, (17)O and (1)H NMR spectroscopy experiments are reported, aided by identification of salient low-energy conformers by using density functional theory. The study of fluorine relaxation rates, over a field range of 4.7 to 16.5 T allowed precise computation of the distance between the Ln(III) ion and the CF(3) reporter group by using global fitting methods. The sensitivity benefits of using such paramagnetic fluorinated probes in (19)F NMR spectroscopic studies are quantified in preliminary spectroscopic and imaging experiments with respect to a diamagnetic yttrium(III) analogue.

Standardized UXO Technology Demonstration Site, Scoring Record No. 928

DTIC Science & Technology

2011-03-01

magnetic permittivity (possibly complex and frequency dependent), ω is radian frequency, Vrx is the voltage at the receiver coil, txn̂ and rxn̂ are the...voltage induced in the receiver coil Vrx due to the induced target dipole moment m  is related to magnetic field uxoH  at the target due to a

Stereo Science Results at Solar Minimum

NASA Technical Reports Server (NTRS)

Christian, Eric R.; Kaiser, Michael L.; Kucera Therese A.; St. Cyr, O. C.; van Driel-Gesztelyi, Lidia; Mandrini, Cristina H.

2009-01-01

The magnetic fields that drive solar activity are complex and inherently three-dimensional structures. Twisted flux ropes, magnetic reconnection and the initiation of solar storms, as well as space weather propagation through the heliosphere, are just a few of the topics that cannot properly be observed or modeled in only two dimensions. Examination of this three-dimensional complex has been hampered by the fact that solar remote sensing observations have occurred only from the Earth-Sun line, and in situ observations, while available from a greater variety of locations, have been sparse throughout the heliosphere.

Ferrotoroidic ground state in a heterometallic {CrIIIDyIII6} complex displaying slow magnetic relaxation.

PubMed

Vignesh, Kuduva R; Soncini, Alessandro; Langley, Stuart K; Wernsdorfer, Wolfgang; Murray, Keith S; Rajaraman, Gopalan

2017-10-18

Toroidal quantum states are most promising for building quantum computing and information storage devices, as they are insensitive to homogeneous magnetic fields, but interact with charge and spin currents, allowing this moment to be manipulated purely by electrical means. Coupling molecular toroids into larger toroidal moments via ferrotoroidic interactions can be pivotal not only to enhance ground state toroidicity, but also to develop materials displaying ferrotoroidic ordered phases, which sustain linear magneto-electric coupling and multiferroic behavior. However, engineering ferrotoroidic coupling is known to be a challenging task. Here we have isolated a {Cr III Dy III 6 } complex that exhibits the much sought-after ferrotoroidic ground state with an enhanced toroidal moment, solely arising from intramolecular dipolar interactions. Moreover, a theoretical analysis of the observed sub-Kelvin zero-field hysteretic spin dynamics of {Cr III Dy III 6 } reveals the pivotal role played by ferrotoroidic states in slowing down the magnetic relaxation, in spite of large calculated single-ion quantum tunneling rates.

Acceleration during magnetic reconnection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beresnyak, Andrey; Li, Hui

2015-07-16

The presentation begins with colorful depictions of solar x-ray flares and references to pulsar phenomena. Plasma reconnection is complex, could be x-point dominated or turbulent, field lines could break due to either resistivity or non-ideal effects, such as electron pressure anisotropy. Electron acceleration is sometimes observed, and sometimes not. One way to study this complex problem is to have many examples of the process (reconnection) and compare them; the other way is to simplify and come to something robust. Ideal MHD (E=0) turbulence driven by magnetic energy is assumed, and the first-order acceleration is sought. It is found that dissipationmore » in big (length >100 ion skin depths) current sheets is universal and independent on microscopic resistivity and the mean imposed field; particles are regularly accelerated while experiencing curvature drift in flows driven by magnetic tension. One example of such flow is spontaneous reconnection. This explains hot electrons with a power-law tail in solar flares, as well as ultrashort time variability in some astrophysical sources.« less

Hall Probe Calibration System Design for the Mu2e Solenoid Field Mapping System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Orozco, Charles; Elementi, Luciano; Feher, Sandor

The goal of the Mu2e experiment at Fermilab is to search for charged-lepton flavor violation by looking for neutrino-less muon to electron conversion in the field of the nucleus. The Mu2e experimental apparatus utilizes a complex magnetic field in the muon generation and momentum and charge selection process. Precise knowledge of the magnetic field is crucial. It is planned to map the solenoid field with calibrated 3D Hall probes up to 10 -5 accuracy. Here, this article describes a new design of a Hall probe calibration system that will be used to calibrate 3D Hall probes to better than 10more » -5 accuracy for the Mu2e Solenoid Field Mapping System.« less

Hall Probe Calibration System Design for the Mu2e Solenoid Field Mapping System

DOE PAGES

Orozco, Charles; Elementi, Luciano; Feher, Sandor; ...

2018-02-22

The goal of the Mu2e experiment at Fermilab is to search for charged-lepton flavor violation by looking for neutrino-less muon to electron conversion in the field of the nucleus. The Mu2e experimental apparatus utilizes a complex magnetic field in the muon generation and momentum and charge selection process. Precise knowledge of the magnetic field is crucial. It is planned to map the solenoid field with calibrated 3D Hall probes up to 10 -5 accuracy. Here, this article describes a new design of a Hall probe calibration system that will be used to calibrate 3D Hall probes to better than 10more » -5 accuracy for the Mu2e Solenoid Field Mapping System.« less

Soliton switching in a site-dependent ferromagnet

NASA Astrophysics Data System (ADS)

Senjudarvannan, R.; Sathishkumar, P.; Vijayalakshmi, S.

2017-02-01

Switching of soliton in a ferromagnetic medium offers the possibility of developing a new innovative approach for information storage technologies. The nonlinear spin dynamics of a site-dependent Heisenberg ferromagnetic spin chain with Gilbert damping under the influence of external magnetic field is expressed in the form of the Landau-Lifshitz-Gilbert equation in the classical continuum limit. The corresponding evolution equation is developed through stereographic projection technique by projecting the unit sphere of spin onto a complex plane. The exact soliton solutions are constructed by solving the associated evolution equation through the modified extended tanh-function method. The impact of damping and external magnetic field on the magnetic soliton under the invariant inhomogeneity is investigated and finally, the magnetization switching in the form of shape changing solitons are demonstrated.

Gradient magnetometer system balloons

NASA Astrophysics Data System (ADS)

Korepanov, Valery; Tsvetkov, Yury

2005-08-01

Earth's magnetic field study still remains one of the leading edges of experimental geophysics. Thus study is executed on the Earth surface, including ocean bottom, and on satellite heights using component, mostly flux-gate magnetometers. But balloon experiments with component magnetometers are very seldom, first of all because of great complexity of data interpretation. This niche still waits for new experimental ideology, which will allow to get the measurements results with high accuracy, especially in gradient mode. The great importance of precise balloon-borne component magnetic field gradient study is obvious. Its technical realization is based both on the available at the marked high-precision non-magnetic tiltmeters and on recent achievements of flux-gate magnetometry. The scientific goals of balloon-borne magnetic gradiometric experiment are discussed and its practical realization is proposed.

Moessbauer studies in zinc-manganese ferrites for use in measuring small velocities and accelerations with great precision

NASA Technical Reports Server (NTRS)

Escue, W. T.; Gupta, R. G.; Mendiratta, R. G.

1975-01-01

Mossbauer spectroscopy was used for a systematic study of the magnetic behavior of manganese and zinc in mixed ferrites. It was observed that Zn2+ has preference to substitute Mn2+ at interstitial sites where the metal ions are tetrahedrally coordinated with four oxygen neighbors. The internal magnetic hyperfine field at the tetrahedral iron site is larger than that at the octahedral site. The relaxation effects were observed to play an important role as the zinc contents were increased, while the spin-correlation time and the magnetic field were observed to decrease in strength. It is concluded that Mossbauer effect data on complex materials, when used in conjunction with other data, can provide useful insight into the origin of the microscopic properties of magnetic materials.

Galactic neutral hydrogen and the magnetic ISM foreground

NASA Astrophysics Data System (ADS)

Clark, S. E.

2018-05-01

The interstellar medium is suffused with magnetic fields, which inform the shape of structures in the diffuse gas. Recent high-dynamic range observations of Galactic neutral hydrogen, combined with novel data analysis techniques, have revealed a deep link between the morphology of neutral gas and the ambient magnetic field. At the same time, an observational revolution is underway in low-frequency radio polarimetry, driven in part by the need to characterize foregrounds to the cosmological 21-cm signal. A new generation of experiments, capable of high angular and Faraday depth resolution, are revealing complex filamentary structures in diffuse polarization. The relationship between filamentary structures observed in radio-polarimetric data and those observed in atomic hydrogen is not yet well understood. Multiwavelength observations will enable new insights into the magnetic interstellar medium across phases.

The relation between the column density structures and the magnetic field orientation in the Vela C molecular complex

NASA Astrophysics Data System (ADS)

Soler, J. D.; Ade, P. A. R.; Angilè, F. E.; Ashton, P.; Benton, S. J.; Devlin, M. J.; Dober, B.; Fissel, L. M.; Fukui, Y.; Galitzki, N.; Gandilo, N. N.; Hennebelle, P.; Klein, J.; Li, Z.-Y.; Korotkov, A. L.; Martin, P. G.; Matthews, T. G.; Moncelsi, L.; Netterfield, C. B.; Novak, G.; Pascale, E.; Poidevin, F.; Santos, F. P.; Savini, G.; Scott, D.; Shariff, J. A.; Thomas, N. E.; Tucker, C. E.; Tucker, G. S.; Ward-Thompson, D.

2017-07-01

We statistically evaluated the relative orientation between gas column density structures, inferred from Herschel submillimetre observations, and the magnetic field projected on the plane of sky, inferred from polarized thermal emission of Galactic dust observed by the Balloon-borne Large-Aperture Submillimetre Telescope for Polarimetry (BLASTPol) at 250, 350, and 500 μm, towards the Vela C molecular complex. First, we find very good agreement between the polarization orientations in the three wavelength-bands, suggesting that, at the considered common angular resolution of 3.´0 that corresponds to a physical scale of approximately 0.61 pc, the inferred magnetic field orientation is not significantly affected by temperature or dust grain alignment effects. Second, we find that the relative orientation between gas column density structures and the magnetic field changes progressively with increasing gas column density, from mostly parallel or having no preferred orientation at low column densities to mostly perpendicular at the highest column densities. This observation is in agreement with previous studies by the Planck collaboration towards more nearby molecular clouds. Finally, we find a correspondencebetween (a) the trends in relative orientation between the column density structures and the projected magnetic field; and (b) the shape of the column density probability distribution functions (PDFs). In the sub-regions of Vela C dominated by one clear filamentary structure, or "ridges", where the high-column density tails of the PDFs are flatter, we find a sharp transition from preferentially parallel or having no preferred relative orientation at low column densities to preferentially perpendicular at highest column densities. In the sub-regions of Vela C dominated by several filamentary structures with multiple orientations, or "nests", where the maximum values of the column density are smaller than in the ridge-like sub-regions and the high-column density tails of the PDFs are steeper, such a transition is also present, but it is clearly less sharp than in the ridge-like sub-regions. Both of these results suggest that the magnetic field is dynamically important for the formation of density structures in this region.

Assessing Exposures to Magnetic Resonance Imaging's Complex Mixture of Magnetic Fields for In Vivo, In Vitro, and Epidemiologic Studies of Health Effects for Staff and Patients.

PubMed

Frankel, Jennifer; Wilén, Jonna; Hansson Mild, Kjell

2018-01-01

A complex mixture of electromagnetic fields is used in magnetic resonance imaging (MRI): static, low-frequency, and radio frequency magnetic fields. Commonly, the static magnetic field ranges from one to three Tesla. The low-frequency field can reach several millitesla and with a time derivative of the order of some Tesla per second. The radiofrequency (RF) field has a magnitude in the microtesla range giving rise to specific absorption rate values of a few Watts per kilogram. Very little attention has been paid to the case where there is a combined exposure to several different fields at the same time. Some studies have shown genotoxic effects in cells after exposure to an MRI scan while others have not demonstrated any effects. A typical MRI exam includes muliple imaging sequences of varying length and intensity, to produce different types of images. Each sequence is designed with a particular purpose in mind, so one sequence can, for example, be optimized for clearly showing fat water contrast, while another is optimized for high-resolution detail. It is of the utmost importance that future experimental studies give a thorough description of the exposure they are using, and not just a statement such as "An ordinary MRI sequence was used." Even if the sequence is specified, it can differ substantially between manufacturers on, e.g., RF pulse height, width, and duty cycle. In the latest SCENIHR opinion, it is stated that there is very little information regarding the health effects of occupational exposure to MRI fields, and long-term prospective or retrospective cohort studies on workers are recommended as a high priority. They also state that MRI is increasingly used in pediatric diagnostic imaging, and a cohort study into the effects of MRI exposure on children is recommended as a high priority. For the exposure assessment in epidemiological studies, there is a clear difference between patients and staff and further work is needed on this. Studies that explore the possible differences between MRI scan sequences and compare them in terms of exposure level are warranted.

Imprints of magnetic power and helicity spectra on radio polarimetry statistics

NASA Astrophysics Data System (ADS)

Junklewitz, H.; Enßlin, T. A.

2011-06-01

The statistical properties of turbulent magnetic fields in radio-synchrotron sources should be imprinted on the statistics of polarimetric observables. In search of these imprints, i.e. characteristic modifications of the polarimetry statistics caused by magnetic field properties, we calculate correlation and cross-correlation functions from a set of observables that contain total intensity I, polarized intensity P, and Faraday depth φ. The correlation functions are evaluated for all combinations of observables up to fourth order in magnetic field B. We derive these analytically as far as possible and from first principles using only some basic assumptions, such as Gaussian statistics for the underlying magnetic field in the observed region and statistical homogeneity. We further assume some simplifications to reduce the complexity of the calculations, because for a start we were interested in a proof of concept. Using this statistical approach, we show that it is possible to gain information about the helical part of the magnetic power spectrum via the correlation functions < P(kperp) φ(k'_{perp)φ(k''perp)>B} and < I(kperp) φ(k'_{perp)φ(k''perp)>B}. Using this insight, we construct an easy-to-use test for helicity called LITMUS (Local Inference Test for Magnetic fields which Uncovers heliceS), which gives a spectrally integrated measure of helicity. For now, all calculations are given in a Faraday-free case, but set up so that Faraday rotational effects can be included later.

Joint SDO and IRIS Observations of a Novel, Hybrid Prominence-Coronal Rain Complex

NASA Astrophysics Data System (ADS)

Liu, Wei; Antolin, Patrick; Sun, Xudong; Gao, Lijia; Vial, Jean-Claude; Gibson, Sarah; Okamoto, Takenori; Berger, Thomas; Uitenbroek, Han; De Pontieu, Bart

2016-10-01

Solar prominences and coronal rain are intimately related phenomena, both involving cool material at chromospheric temperatures within the hot corona and both playing important roles as part of the return flow of the chromosphere-corona mass cycle. At the same time, they exhibit distinct morphologies and dynamics not yet well understood. Quiescent prominences consist of numerous long-lasting, filamentary downflow threads, while coronal rain is more transient and falls comparably faster along well-defined curved paths. We report here a novel, hybrid prominence-coronal rain complex in an arcade-fan geometry observed by SDO/AIA and IRIS, which provides new insights to the underlying physics of such contrasting behaviors. We found that the supra-arcade fan region hosts a prominence sheet consisting of meandering threads with broad line widths. As the prominence material descends to the arcade, it turns into coronal rain sliding down coronal loops with line widths 2-3 times narrower. This contrast suggests that distinct local plasma and magnetic conditions determine the fate of the cool material, a scenario supported by our magnetic field extrapolations from SDO/HMI. Specifically, the supra-arcade fan (similar to those in solar flares; e.g., McKenzie 2013) is likely situated in a current sheet, where the magnetic field is weak and the plasma-beta could be close to unity, thus favoring turbulent flows like those prominence threads. In contrast, the underlying arcade has a stronger magnetic field and most likely a low-beta environment, such that the material is guided along magnetic field lines to appear as coronal rain. We will discuss the physical implications of these observations beyond prominence and coronal rain.

Study of Magnetic Damping Effect on Convection and Solidification Under G-Jitter Conditions

NASA Technical Reports Server (NTRS)

Li, Ben Q.; deGroh, H. C.

2001-01-01

As shown in space flight experiments, g-jitter is a critical issue affecting solidification processing of materials in microgravity. This study aims to provide, through extensive numerical simulations and ground based experiments, an assessment of the use of magnetic fields in combination with microgravity to reduce the g-jitter induced convective flows in space processing systems. Analytical solutions and 2-D and 3-D numerical models for g-jitter driven flows in simple solidification systems with and without the presence of an applied magnetic field have been developed and extensive analyses were carried out. A physical model was also constructed and PIV measurements compared reasonably well with predictions from numerical models. Some key points may be summarized as follows: (1) the amplitude of the oscillating velocity decreases at a rate inversely proportional to the g-jitter frequency and with an increase in the applied magnetic field; (2) the induced flow oscillates at approximately the same frequency as the affecting g-jitter, but out of a phase angle; (3) the phase angle is a complicated function of geometry, applied magnetic field, temperature gradient and frequency; (4) g-jitter driven flows exhibit a complex fluid flow pattern evolving in time; (5) the damping effect is more effective for low frequency flows; and (6) the applied magnetic field helps to reduce the variation of solutal distribution along the solid-liquid interface. Work in progress includes developing numerical models for solidification phenomena with the presence of both g-jitter and magnetic fields and developing a ground-based physical model to verify numerical predictions.

Angular dependence of the magnetic properties of permalloy and nickel nanowires as a function of their diameters

NASA Astrophysics Data System (ADS)

Raviolo, Sofía; Tejo, Felipe; Bajales, Noelia; Escrig, Juan

2018-01-01

In this paper we have compared the angular dependence of the magnetic properties of permalloy (Ni80Fe20) and nickel nanowires by means of micromagnetic simulations. For each material we have chosen two diameters, 40 and 100 nm. Permalloy nanowires with smaller diameters (d = 40 nm) exhibit greater coercivity than nickel nanowires, regardless of the angle at which the external magnetic field is applied. In addition, both Py and Ni nanowires exhibit the same remanence values. However, the nanowires of larger diameters (d = 100 nm) exhibit a more complex behavior, noting that for small angles, nickel nanowires are those that now exhibit a greater coercivity in comparison to those of permalloy. The magnetization reversal modes vary as a function of the angle at which the external field is applied. When the field is applied parallel to the wire axis, it reverts through nucleation and propagation of domain walls, whereas when the field is applied perpendicular to the axis, it reverts by a pseudo-coherent rotation. These results may provide a guide to control the magnetic properties of nanowires for use in potential applications.

Directed transport of active magnetotactic bacteria in porous media flow

NASA Astrophysics Data System (ADS)

Waisbord, Nicolas; Dehkharghani, Amin; Coons, Thomas; Guasto, Jeffrey S.

2017-11-01

Swimming cell migration through porous media is a topic of ecological and technical relevance for understanding sediment ecosystems and bioremediation of soil for decontamination. We focus on magnetotactic bacteria - which align passively with Earth's magnetic field and migrate in such sediment environments - as a model system. The transport properties of magnetotactic bacteria are measured in a 2D microfluidic porous medium as a function of the porous microstructure geometry and under a variety of environmental conditions. In a quiescent fluid and in the absence of an external, guiding magnetic field, the effective diffusion of cells' random walk is unsurprisingly hindered with decreasing porosity due to cell-surface interactions. When guided by a magnetic field, cell trajectories acquire a net direction and form lanes, a behavior that is enhanced with increasing magnetic field. When the directed motility is coupled with an opposing fluid flow through the porous medium, convective cells form and locally trap the swimming bacteria. These results, which are corroborated by Langevin Simulations are an important step toward understanding magnetotactic bacterial ecology as well as for the magnetic guidance of microrobots in complex environments. Supported by NSF Grant CBET-1511340.

A critical shock mach number for particle acceleration in the absence of pre-existing cosmic rays: M=√5

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vink, Jacco; Yamazaki, Ryo, E-mail: j.vink@uva.nl

2014-01-10

It is shown that, under some generic assumptions, shocks cannot accelerate particles unless the overall shock Mach number exceeds a critical value M>√5. The reason is that for M≤√5 the work done to compress the flow in a particle precursor requires more enthalpy flux than the system can sustain. This lower limit applies to situations without significant magnetic field pressure. In case that the magnetic field pressure dominates the pressure in the unshocked medium, i.e., for low plasma beta, the resistivity of the magnetic field makes it even more difficult to fulfill the energetic requirements for the formation of shockmore » with an accelerated particle precursor and associated compression of the upstream plasma. We illustrate the effects of magnetic fields for the extreme situation of a purely perpendicular magnetic field configuration with plasma beta β = 0, which gives a minimum Mach number of M = 5/2. The situation becomes more complex, if we incorporate the effects of pre-existing cosmic rays, indicating that the additional degree of freedom allows for less strict Mach number limits on acceleration. We discuss the implications of this result for low Mach number shock acceleration as found in solar system shocks, and shocks in clusters of galaxies.« less

Particle Acceleration and Radiation associated with Magnetic Field Generation from Relativistic Collisionless Shocks

NASA Technical Reports Server (NTRS)

Nishikawa, K.; Hardee, P. E.; Richardson, G. A.; Preece, R. D.; Sol, H.; Fishman, G. J.

2003-01-01

Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. While some Fermi acceleration may occur at the jet front, the majority of electron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that this instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron s transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

M-dwarf stellar winds: the effects of realistic magnetic geometry on rotational evolution and planets

NASA Astrophysics Data System (ADS)

Vidotto, A. A.; Jardine, M.; Morin, J.; Donati, J. F.; Opher, M.; Gombosi, T. I.

2014-02-01

We perform three-dimensional numerical simulations of stellar winds of early-M-dwarf stars. Our simulations incorporate observationally reconstructed large-scale surface magnetic maps, suggesting that the complexity of the magnetic field can play an important role in the angular momentum evolution of the star, possibly explaining the large distribution of periods in field dM stars, as reported in recent works. In spite of the diversity of the magnetic field topologies among the stars in our sample, we find that stellar wind flowing near the (rotational) equatorial plane carries most of the stellar angular momentum, but there is no preferred colatitude contributing to mass-loss, as the mass flux is maximum at different colatitudes for different stars. We find that more non-axisymmetric magnetic fields result in more asymmetric mass fluxes and wind total pressures ptot (defined as the sum of thermal, magnetic and ram pressures). Because planetary magnetospheric sizes are set by pressure equilibrium between the planet's magnetic field and ptot, variations of up to a factor of 3 in ptot (as found in the case of a planet orbiting at several stellar radii away from the star) lead to variations in magnetospheric radii of about 20 per cent along the planetary orbital path. In analogy to the flux of cosmic rays that impact the Earth, which is inversely modulated with the non-axisymmetric component of the total open solar magnetic flux, we conclude that planets orbiting M-dwarf stars like DT Vir, DS Leo and GJ 182, which have significant non-axisymmetric field components, should be the more efficiently shielded from galactic cosmic rays, even if the planets lack a protective thick atmosphere/large magnetosphere of their own.

Magnetic structure of an activated filament in a flaring active region

NASA Astrophysics Data System (ADS)

Sasso, C.; Lagg, A.; Solanki, S. K.

2014-01-01

Aims: While the magnetic field in quiescent prominences has been widely investigated, less is known about the field in activated prominences. We report observational results on the magnetic field structure of an activated filament in a flaring active region. In particular, we studied its magnetic structure and line-of-sight flows during its early activated phase, shortly before it displayed signs of rotation. Methods: We inverted the Stokes profiles of the chromospheric He i 10 830 Å triplet and the photospheric Si i 10 827 Å line observed in this filament by the Vacuum Tower Telescope on Tenerife. Using these inversion results, we present and interpret the first maps of the velocity and magnetic field obtained in an activated filament, both in the photosphere and the chromosphere. Results: Up to five different magnetic components are found in the chromospheric layers of the filament, while outside the filament a single component is sufficient to reproduce the observations. Magnetic components displaying an upflow are preferentially located towards the centre of the filament, while the downflows are concentrated along its periphery. Moreover, the upflowing gas is associated with an opposite-polarity magnetic configuration with respect to the photosphere, while the downflowing gas is associated with a same-polarity configuration. Conclusions: The activated filament has a very complex structure. Nonetheless, it is compatible with a flux rope, albeit a distorted one, in the normal configuration. The observations are best explained by a rising flux rope in which part of the filament material is still stably stored (upflowing material, rising with the field), while the rest is no longer stably stored and flows down along the field lines. The movie is available in electronic form at http://www.aanda.org

Complexity methods applied to turbulence in plasma astrophysics

NASA Astrophysics Data System (ADS)

Vlahos, L.; Isliker, H.

2016-09-01

In this review many of the well known tools for the analysis of Complex systems are used in order to study the global coupling of the turbulent convection zone with the solar atmosphere where the magnetic energy is dissipated explosively. Several well documented observations are not easy to interpret with the use of Magnetohydrodynamic (MHD) and/or Kinetic numerical codes. Such observations are: (1) The size distribution of the Active Regions (AR) on the solar surface, (2) The fractal and multi fractal characteristics of the observed magnetograms, (3) The Self-Organised characteristics of the explosive magnetic energy release and (4) the very efficient acceleration of particles during the flaring periods in the solar corona. We review briefly the work published the last twenty five years on the above issues and propose solutions by using methods borrowed from the analysis of complex systems. The scenario which emerged is as follows: (a) The fully developed turbulence in the convection zone generates and transports magnetic flux tubes to the solar surface. Using probabilistic percolation models we were able to reproduce the size distribution and the fractal properties of the emerged and randomly moving magnetic flux tubes. (b) Using a Non Linear Force Free (NLFF) magnetic extrapolation numerical code we can explore how the emerged magnetic flux tubes interact nonlinearly and form thin and Unstable Current Sheets (UCS) inside the coronal part of the AR. (c) The fragmentation of the UCS and the redistribution of the magnetic field locally, when the local current exceeds a Critical threshold, is a key process which drives avalanches and forms coherent structures. This local reorganization of the magnetic field enhances the energy dissipation and influences the global evolution of the complex magnetic topology. Using a Cellular Automaton and following the simple rules of Self Organized Criticality (SOC), we were able to reproduce the statistical characteristics of the observed time series of the explosive events, (d) finally, when the AR reaches the turbulently reconnecting state (in the language of the SOC theory this is called SOC state) it is densely populated by UCS which can act as local scatterers (replacing the magnetic clouds in the Fermi scenario) and enhance dramatically the heating and acceleration of charged particles.

Vacuum Polarization by a Magnetic Flux Tube at Finite Temperature in the Cosmic String Space-Time

NASA Astrophysics Data System (ADS)

Spinelly, J.; Bezerra de Mello, E. R.

In this paper, we analyze the effect produced by the temperature in the vacuum polarization associated with a charged massless scalar field in the presence of a magnetic flux tube in the cosmic string space-time. Three different configurations of magnetic fields are taken into account: (i) a homogeneous field inside the tube, (ii) a field proportional to 1/r, and (iii) a cylindrical shell with δ-function. In these three cases, the axis of the infinitely long tube of radius R coincides with the cosmic string. Because of the complexity of this analysis in the region inside the tube, we consider the thermal effect in the region outside. In order to develop this analysis, we construct the thermal Green function associated with this system for the three above-mentioned situations considering points in the region outside the tube. We explicitly calculate, in the high-temperature limit, the thermal average of the field square and the energy-momentum tensor.

Exploring the prominence-corona connection and its expansion into the outer corona using total solar eclipse observations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Habbal, Shadia Rifai; Morgan, Huw; Druckmüller, Miloslav, E-mail: shadia@ifa.hawaii.edu

Prominences constitute the most complex magnetic structures in the solar corona. The ubiquitous presence of their seemingly confined dense and cool plasma in an otherwise million-degree environment remains a puzzle. Using a decade of white light total solar eclipse observations, we show how these images reveal an intricate relationship between prominences and coronal structures both in their immediate vicinity, known as coronal cavities, and in the extended corona out to several solar radii. Observations of suspended prominences and twisted helical structures spanning several solar radii are central to these findings. The different manifestations of the prominence-corona interface that emerge frommore » this study underscore the fundamental role played by prominences in defining and controlling the complex expansion and dynamic behavior of the solar magnetic field in the neighborhood of magnetic polarity reversal regions. This study suggests that the unraveling of prominences and the outward expansion of the helical twisted field lines linked to them could be the solar origin of twisted magnetic flux ropes detected in interplanetary space, and of the mechanism by which the Sun sheds its magnetic helicity. This work also underscores the likely role of the prominence-corona interface as a source of the slow solar wind.« less

The Last Word: Magnetic Storm-Still an Adequate Name?

NASA Astrophysics Data System (ADS)

Daglis, Ioannis A.

The magnetic storm is the principal and most complex collective phenomenon in geospace. It involves the magnetic fields of the Sun and the Earth, as well as plasma originating in the solar and terrestrial atmosphere. Magnetic storms involve more than just the geomagnetic field, as the original perception suggests. They involve a variety of dynamic processes among which charged particle acceleration and electric current intensification are the most important. Is the name still adequate, or should we switch to something more general and wide-ranging, such as ``space storms,'' or ``geospace storms''? The oldest printed record of ``magnetic storms'' that I was able to find appears in a letter published in Annalen der Physik written by the famous explorer Alexander von Humboldt to Paul Erman. I located this paper in the amazingly rich library of the Air Force Research Laboratory at Hanscom Air Force Base in Massachusetts with the kind help of Mike Heinemann.

Frequency domain and full waveform time domain inversion of ground based magnetometer, electrometer and incoherent scattering radar arrays to image strongly heterogenous 3-D Earth structure, ionospheric structure, and to predict the intensity of GICs in the power grid

NASA Astrophysics Data System (ADS)

Schultz, A.; Imamura, N.; Bonner, L. R., IV; Cosgrove, R. B.

2016-12-01

Ground-based magnetometer and electrometer arrays provide the means to probe the structure of the Earth's interior, the interactions of space weather with the ionosphere, and to anticipate the intensity of geomagnetically induced currents (GICs) in power grids. We present a local-to-continental scale view of a heterogeneous 3-D crust and mantle as determined from magnetotelluric (MT) observations across arrays of ground-based electric and magnetic field sensors. MT impedance tensors describe the relationship between electric and magnetic fields at a given site, thus implicitly they contain all known information on the 3-D electrical resistivity structure beneath and surrounding that site. By using multivariate transfer functions to project real-time magnetic observatory network data to areas surrounding electric power grids, and by projecting those magnetic fields through MT impedance tensors, the projected magnetic field can be transformed into predictions of electric fields along the path of the transmission lines, an essential element of predicting the intensity of GICs in the grid. Finally, we explore GICs, i.e. Earth-ionosphere coupling directly in the time-domain. We consider the fully coupled EM system, where we allow for a non-stationary ionospheric source field of arbitrary complexity above a 3-D Earth. We solve the simultaneous inverse problem for 3-D Earth conductivity and source field structure directly in the time domain. In the present work, we apply this method to magnetotelluric data obtained from a synchronously operating array of 25 MT stations that collected continuous MT waveform data in the interior of Alaska during the autumn and winter of 2015 under the footprint of the Poker Flat (Alaska) Incoherent Scattering Radar (PFISR). PFISR data yield functionals of the ionospheric electric field and ionospheric conductivity that constrain the MT source field. We show that in this region conventional robust MT processing methods struggle to produce reliable MT response functions at periods much greater than about 2,000 s, a consequence, we believe, of the complexity of the ionospheric source fields in this high latitude setting. This provides impetus for direct waveform inversion methods that dispense with typical parametric assumptions made about the MT source fields.

Magnetic measurement of soft magnetic composites material under 3D SVPWM excitation

NASA Astrophysics Data System (ADS)

Zhang, Changgeng; Jiang, Baolin; Li, Yongjian; Yang, Qingxin

2018-05-01

The magnetic properties measurement and analysis of soft magnetic material under the rotational space-vector pulse width modulation (SVPWM) excitation are key factors in design and optimization of the adjustable speed motor. In this paper, a three-dimensional (3D) magnetic properties testing system fit for SVPWM excitation is built, which includes symmetrical orthogonal excitation magnetic circuit and cubic field-metric sensor. Base on the testing system, the vector B and H loci of soft magnetic composite (SMC) material under SVPWM excitation are measured and analyzed by proposed 3D SVPWM control method. Alternating and rotating core losses under various complex excitation with different magnitude modulation ratio are calculated and compared.

The Evolution of the Solar Magnetic Field: A Comparative Analysis of Two Models

NASA Astrophysics Data System (ADS)

McMichael, K. D.; Karak, B. B.; Upton, L.; Miesch, M. S.; Vierkens, O.

2017-12-01

Understanding the complexity of the solar magnetic cycle is a task that has plagued scientists for decades. However, with the help of computer simulations, we have begun to gain more insight into possible solutions to the plethora of questions inside the Sun. STABLE (Surface Transport and Babcock Leighton) is a newly developed 3D dynamo model that can reproduce features of the solar cycle. In this model, the tilted bipolar sunspots are formed on the surface (based on the toroidal field at the bottom of the convection zone) and then decay and disperse, producing the poloidal field. Since STABLE is a 3D model, it is able to solve the full induction equation in the entirety of the solar convection zone as well as incorporate many free parameters (such as spot depth and turbulent diffusion) which are difficult to observe. In an attempt to constrain some of these free parameters, we compare STABLE to a surface flux transport model called AFT (Advective Flux Transport) which solves the radial component of the magnetic field on the solar surface. AFT is a state-of-the-art surface flux transport model that has a proven record of being able to reproduce solar observations with great accuracy. In this project, we implement synthetic bipolar sunspots into both models, using identical surface parameters, and run the models for comparison. We demonstrate that the 3D structure of the sunspots in the interior and the vertical diffusion of the sunspot magnetic field play an important role in establishing the surface magnetic field in STABLE. We found that when a sufficient amount of downward magnetic pumping is included in STABLE, the surface magnetic field from this model becomes insensitive to the internal structure of the sunspot and more consistent with that of AFT.

FLASH hydrodynamic simulations of experiments to explore the generation of cosmological magnetic fields

NASA Astrophysics Data System (ADS)

Scopatz, A.; Fatenejad, M.; Flocke, N.; Gregori, G.; Koenig, M.; Lamb, D. Q.; Lee, D.; Meinecke, J.; Ravasio, A.; Tzeferacos, P.; Weide, K.; Yurchak, R.

2013-03-01

We report the results of FLASH hydrodynamic simulations of the experiments conducted by the University of Oxford High Energy Density Laboratory Astrophysics group and its collaborators at the Laboratoire pour l'Utilisation de Lasers Intenses (LULI). In these experiments, a long-pulse laser illuminates a target in a chamber filled with Argon gas, producing shock waves that generate magnetic fields via the Biermann battery mechanism. The simulations show that the result of the laser illuminating the target is a series of complex hydrodynamic phenomena.

Magnetron magnetic priming for rapid startup and noise reduction

NASA Astrophysics Data System (ADS)

Neculaes, Vasile Bogdan

The magnetron is a vacuum electronics crossed-field device: perpendicular electric and magnetic fields determine the electron dynamics. Compactness, efficiency and reliability make magnetrons suitable for a wide range of military and civilian applications: radar, industrial heating, plasma sources, and medical accelerators. The most ubiquitous use of magnetrons is as the microwave power source in microwave ovens, operating at 2.45 GHz and delivering about 800--1000 W. University of Michigan and several other research programs are actively pursuing the development of GW range relativistic magnetrons. This dissertation presents experimental and computational results concerning innovative techniques to improve magnetron noise, startup and mode stability. The DC-operated oven magnetron studies performed at University of Michigan opened new directions by utilizing azimuthally varying magnetic fields (magnetic priming). Magnetic priming for rapid startup in an N-cavity magnetron operating in the pi-mode is based on implementation of an axial magnetic field with N/2 azimuthal periods, to prebunch the electrons in the desired number of spokes (N/2). Experiments with magnetic priming on DC oven magnetrons using perturbing magnets added on the upper existing magnet of the magnetron showed rapid startup (pi-mode oscillation observed at low currents) and up to 35 dB noise reduction (close to the carrier and in sidebands). A complex 3-dimensional (3D) ICEPIC computational model recovered the oven magnetron magnetic priming experimental results: rapid electron prebunching due to presence of perturbing magnets, fast startup and tendency towards a lower noise state. Simulations in 6-cavity relativistic magnetrons show that ideal magnetic priming causes fast startup, rapid mode growth (with radial electron diffusion) and suppression of mode competition. A highly idealized model (planar, crossed-field, non-resonant, non-relativistic structure) using single particle dynamics showed that magnetic priming causes rapid electron prebunching, specific symmetries in the electron cloud and an orbital parametric instability (radial exponential growth).

Angular distribution and polarization of atomic radiative emission in electric and magnetic fields

NASA Astrophysics Data System (ADS)

Jacobs, V. L.; Filuk, A. B.

1999-09-01

A density-matrix approach has been developed for the angular distribution and polarization of radiative emission during single-photon atomic transitions for a general set of steady-state excitation processes in an arbitrary arrangement of static (or quasistatic) electric and magnetic fields. Particular attention has been directed at spectroscopic observations in the intense fields of the high-power ion diodes on the Particle Beam Fusion Accelerator II (PBFA II) and SABRE devices at Sandia National Laboratories and at magnetic-field measurements in tokamak plasmas. The field-dependent atomic eigenstates are represented as expansions in a complete basis set of field-free bound and continuum eigenstates. Particular emphasis has been given to directed-electron collisional excitations, which may be produced by an anisotropic incident-electron velocity distribution. We have allowed for the possibility of the coherent excitation of the nearly degenerate field-dependent atomic substates, which can give rise to a complex spectral pattern of overlapping Stark-Zeeman components. Coherent excitations may be produced by a beam of electrons that are spin-polarized at an angle with respect to the propagation direction or by nonparallel electric and magnetic fields. Our main result is a general expression for the matrix elements of the photon-polarization density operator representing the total intensity, angular distribution, and polarization of the atomic radiative emission. For the observation of radiative emission in the direction of the magnetic field, the detection of linearly polarized emission, in addition to the usual circularly polarized radiation, can reveal the presence of a perpendicular electric field or a coherent excitation mechanism.