Science.gov

Sample records for aligning magnetic field

  1. Measurements of magnetic field alignment

    SciTech Connect

    Kuchnir, M.; Schmidt, E.E.

    1987-11-06

    The procedure for installing Superconducting Super Collider (SSC) dipoles in their respective cryostats involves aligning the average direction of their field with the vertical to an accuracy of 0.5 mrad. The equipment developed for carrying on these measurements is described and the measurements performed on the first few prototypes SSC magnets are presented. The field angle as a function of position in these 16.6 m long magnets is a characteristic of the individual magnet with possible feedback information to its manufacturing procedure. A comparison of this vertical alignment characteristic with a magnetic field intensity (by NMR) characteristic for one of the prototypes is also presented. 5 refs., 7 figs.

  2. Magnetic field alignment studies for the URAGAN-3 torsatron

    SciTech Connect

    Colchin, R.J.; Fedotov, S.I.; Harris, J.H.; Lee, D.K.; Ozherel'ev, F.I.; Pavlichenko, O.S.; Pogozhev, D.P.; Rome, J.A.; Treffert, J.D.; Zalkind, V.M.

    1986-02-01

    If the major axes of the helical and vertical field coils of a torsatron plasma confinement device are not aligned to within approx.1% of their major radii, the resulting error field can break up closed magnetic flux surfaces and reduce the effective plasma confinement volume. A novel technique for accurately locating the magnetic symmetry axes of torsatron helical and vertical coil sets to within approx.1 mm using magnetic field measurements near the device major axis (i.e., away from the confinement volume) is described and applied to the URAGAN-3 torsatron. The axis of the vertical field coil set was found to be shifted by approx.1 cm relative to the axis of the helical coil set; this shift could account for the reduced confinement volume observed in previous experiments. The magnetic measurements were repeated after coil repositioning to verify correct alignment. 10 refs., 13 figs.

  3. Generation of macroscopic magnetic-field-aligned electric fields by the convection surge ion acceleration mechanism

    NASA Technical Reports Server (NTRS)

    Mauk, B. H.

    1989-01-01

    The 'convection surge' model for ion acceleration, designed by Mauk (1986) to explain the observed ion distributions and the field-aligned character of middle magnetospheric ion distributions during the expansion phase of a substorm, was extended to include the self-consistent generation of magnetic-field-aligned electric fields. Results from the modified model show that the convection surge mechanism leads to the generation of dynamical macroscopic magnetic field-aligned electric fields that begin their strongest developments very near the magnetic equator and then propagate to higher latitudes. Potential drops as high as 1 to 10 kV might be expected, depending on the mass species of the ions and on the electron temperatures. It is speculated that the convection surge mechanism could be a key player in the transient field-aligned electromagnetic processes observed to operate within the middle magnetosphere.

  4. Alignment of Iron Nanoparticles in a Magnetic Field Due to Shape Anisotropy

    DOE PAGES

    Radhakrishnan, Balasubramaniam; Nicholson, Don M; Eisenbach, Markus; ...

    2015-07-09

    During high magnetic field processing there is evidence for alignment of non-spherical metallic particles above the Curie temperature in alloys with negligible magneto-crystalline anisotropy. The main driving force for alignment is the magnetic shape anisotropy. Current understanding of the phenomenon is not adequate to quantify the effect of particle size, aspect ratio, temperature and the magnetic field on particle alignment. We demonstrate a Monte Carlo approach coupled with size scaling to show the conditions under which alignment is possible.

  5. Alignment of Iron Nanoparticles in a Magnetic Field Due to Shape Anisotropy

    SciTech Connect

    Radhakrishnan, Balasubramaniam; Nicholson, Don M; Eisenbach, Markus; Ludtka, Gerard Michael; Rios, Orlando; Parish, Chad M

    2015-07-09

    During high magnetic field processing there is evidence for alignment of non-spherical metallic particles above the Curie temperature in alloys with negligible magneto-crystalline anisotropy. The main driving force for alignment is the magnetic shape anisotropy. Current understanding of the phenomenon is not adequate to quantify the effect of particle size, aspect ratio, temperature and the magnetic field on particle alignment. We demonstrate a Monte Carlo approach coupled with size scaling to show the conditions under which alignment is possible.

  6. Modeling magnetic perturbation fields associated with ionospheric and geomagnetic-field-aligned currents

    NASA Astrophysics Data System (ADS)

    Richmond, A. D.; Maute, A.

    2003-04-01

    The National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General-Circulation Model calculates ionospheric and geomagnetic-field-aligned electric currents produced by ionospheric wind dynamo action, taking into account magnetospheric sources at high latitudes. The associated magnetic perturbations at the ground and at low-Earth-orbit (LEO) satellite altitudes are calculated by representing the height-integrated horizontal ionospheric current as a current sheet at 110 km, connected to geomagnetic-field-aligned currents flowing into and out of the top. The horizontal sheet current can be divided into two components: a divergence-free equivalent current which, together with the associated induced Earth currents, is responsible for all of the magnetic perturbations below the current sheet, and a divergent (but not irrotational) current that closes the field-aligned currents above. We call the combination of the field-aligned currents and their closing ionospheric currents the ``nonequivalent'' currents. By definition, these produce no magnetic effect at the ground, but they do produce important magnetic effects at LEO altitudes, generally dominating the component of LEO magnetic perturbations perpendicular to the main geomagnetic field. At high magnetic latitudes the nonequivalent LEO magnetic perturbations are largely toroidal, and are associated with the strong field-aligned currents that couple the ionosphere with the outer magnetosphere. At middle and low magnetic latitudes the nonequivalent LEO magnetic perturbations are largely associated with field-aligned currents that flow between the northern and southern hemispheres, and that can produce east-west perturbations of tens of nanoteslas.

  7. Structural and magnetic properties of L10 -FePt nanoparticles aligned by external magnetic field

    NASA Astrophysics Data System (ADS)

    Tamada, Yoshinori; Yamamoto, Shinpei; Nasu, Saburo; Ono, Teruo

    2008-12-01

    We investigated structural and magnetic properties of the easy-axis aligned L10 -FePt nanoparticles by the combined use of x-ray diffraction (XRD), magnetization, and F57e Mössbauer measurements. The L10 -FePt nanoparticles were fixed in a polystyrene matrix by performing free radical polymerization of styrene under an aligning external magnetic field. Mössbauer spectrum of the L10 -FePt nanoparticles/polystyrene composite showed tremendous decrease in the second and fifth absorption lines under the condition that the incident γ ray was parallel to the aligning field. This result indicates that the easy axes of the L10 -FePt nanoparticles in the composite have a strong preferred orientation with a finite distribution. We estimated the distribution of easy-axis orientation by using the Mössbauer hyperfine parameters, which is in good agreement with that determined by the XRD rocking curve.

  8. Magnetic field alignment of randomly oriented, high aspect ratio silicon microwires into vertically oriented arrays.

    PubMed

    Beardslee, Joseph A; Sadtler, Bryce; Lewis, Nathan S

    2012-11-27

    External magnetic fields have been used to vertically align ensembles of silicon microwires coated with ferromagnetic nickel films. X-ray diffraction and image analysis techniques were used to quantify the degree of vertical orientation of the microwires. The degree of vertical alignment and the minimum field strength required for alignment were evaluated as a function of the wire length, coating thickness, magnetic history, and substrate surface properties. Nearly 100% of 100 μm long, 2 μm diameter, Si microwires that had been coated with 300 nm of Ni could be vertically aligned by a 300 G magnetic field. For wires ranging from 40 to 60 μm in length, as the length of the wire increased, a higher degree of alignment was observed at lower field strengths, consistent with an increase in the available magnetic torque. Microwires that had been exposed to a magnetic sweep up to 300 G remained magnetized and, therefore, aligned more readily during subsequent magnetic field alignment sweeps. Alignment of the Ni-coated Si microwires occurred at lower field strengths on hydrophilic Si substrates than on hydrophobic Si substrates. The magnetic field alignment approach provides a pathway for the directed assembly of solution-grown semiconductor wires into vertical arrays, with potential applications in solar cells as well as in other electronic devices that utilize nano- and microscale components as active elements.

  9. Alignment Behavior of Crystal with Magnetic Anisotropy of χc < χa under Rotating Magnetic Field

    NASA Astrophysics Data System (ADS)

    Iwai, Kazuhiko; Niimi, Masahiro; Kohama, Takenori

    2009-10-01

    The alignment behavior of a crystal has been investigated by numerical calculation and an in situ observation experiment with a process combining magnetic field imposition and sample rotation to form unidirectionally aligned crystals with a magnetic anisotropy of χc < χa. The experimentally observed alignment behavior of a polymeric fiber and its alignment time agreed with the numerically calculated ones. Crystal alignment under the out-of-step condition alternately repeats the alignment duration and the keeping of a constant duration, and finally the crystal aligns in a specific direction. The alignment time under the synchronous condition is longer than that under the out-of-step condition if the magnetic field intensity is constant. To reduce the alignment time, a strong magnetic field under the out-of-step condition is desirable in this process.

  10. ALIGNMENT OF THE SCALAR GRADIENT IN EVOLVING MAGNETIC FIELDS

    SciTech Connect

    Sur, Sharanya; Scannapieco, Evan; Pan, Liubin E-mail: evan.scannapieco@asu.edu

    2014-07-20

    We conduct simulations of turbulent mixing in the presence of a magnetic field, grown by the small-scale dynamo. We show that the scalar gradient field, ∇C, which must be large for diffusion to operate, is strongly biased perpendicular to the magnetic field, B. This is true both early on, when the magnetic field is negligible, and at late times, when the field is strong enough to back react on the flow. This occurs because ∇C increases within the plane of a compressive motion, but B increases perpendicular to it. At late times, the magnetic field resists compression, making it harder for scalar gradients to grow and likely slowing mixing.

  11. Cooperative ordering and kinetics of cellulose nanocrystal alignment in a magnetic field

    SciTech Connect

    De France, Kevin J.; Yager, Kevin G.; Hoare, Todd; Cranston, Emily D.

    2016-07-13

    Cellulose nanocrystals (CNCs) are emerging nanomaterials that form chiral nematic liquid crystals above a critical concentration (C*) and additionally orient within electromagnetic fields. The control over CNC alignment is significant for materials processing and end use; to date, magnetic alignment has been demonstrated using only strong fields over extended or arbitrary time scales. This work investigates the effects of comparatively weak magnetic fields (0–1.2 T) and CNC concentration (1.65–8.25 wt %) on the kinetics and degree of CNC ordering using small-angle X-ray scattering. Interparticle spacing, correlation length, and orientation order parameters (η and S) increased with time and field strength following a sigmoidal profile. In a 1.2 T magnetic field for CNC suspensions above C*, partial alignment occurred in under 2 min followed by slower cooperative ordering to achieve nearly perfect alignment in under 200 min (S = –0.499 where S = –0.5 indicates perfect antialignment). At 0.56 T, nearly perfect alignment was also achieved, yet the ordering was 36% slower. Outside of a magnetic field, the order parameter plateaued at 52% alignment (S = –0.26) after 5 h, showcasing the drastic effects of relatively weak magnetic fields on CNC alignment. For suspensions below C*, no magnetic alignment was detected.

  12. Cooperative ordering and kinetics of cellulose nanocrystal alignment in a magnetic field

    DOE PAGES

    De France, Kevin J.; Yager, Kevin G.; Hoare, Todd; ...

    2016-07-13

    Cellulose nanocrystals (CNCs) are emerging nanomaterials that form chiral nematic liquid crystals above a critical concentration (C*) and additionally orient within electromagnetic fields. The control over CNC alignment is significant for materials processing and end use; to date, magnetic alignment has been demonstrated using only strong fields over extended or arbitrary time scales. This work investigates the effects of comparatively weak magnetic fields (0–1.2 T) and CNC concentration (1.65–8.25 wt %) on the kinetics and degree of CNC ordering using small-angle X-ray scattering. Interparticle spacing, correlation length, and orientation order parameters (η and S) increased with time and field strengthmore » following a sigmoidal profile. In a 1.2 T magnetic field for CNC suspensions above C*, partial alignment occurred in under 2 min followed by slower cooperative ordering to achieve nearly perfect alignment in under 200 min (S = –0.499 where S = –0.5 indicates perfect antialignment). At 0.56 T, nearly perfect alignment was also achieved, yet the ordering was 36% slower. Outside of a magnetic field, the order parameter plateaued at 52% alignment (S = –0.26) after 5 h, showcasing the drastic effects of relatively weak magnetic fields on CNC alignment. For suspensions below C*, no magnetic alignment was detected.« less

  13. Cooperative ordering and kinetics of cellulose nanocrystal alignment in a magnetic field

    SciTech Connect

    De France, Kevin J.; Yager, Kevin G.; Hoare, Todd; Cranston, Emily D.

    2016-07-13

    Cellulose nanocrystals (CNCs) are emerging nanomaterials that form chiral nematic liquid crystals above a critical concentration (C*) and additionally orient within electromagnetic fields. The control over CNC alignment is significant for materials processing and end use; to date, magnetic alignment has been demonstrated using only strong fields over extended or arbitrary time scales. This work investigates the effects of comparatively weak magnetic fields (0–1.2 T) and CNC concentration (1.65–8.25 wt %) on the kinetics and degree of CNC ordering using small-angle X-ray scattering. Interparticle spacing, correlation length, and orientation order parameters (η and S) increased with time and field strength following a sigmoidal profile. In a 1.2 T magnetic field for CNC suspensions above C*, partial alignment occurred in under 2 min followed by slower cooperative ordering to achieve nearly perfect alignment in under 200 min (S = –0.499 where S = –0.5 indicates perfect antialignment). At 0.56 T, nearly perfect alignment was also achieved, yet the ordering was 36% slower. Outside of a magnetic field, the order parameter plateaued at 52% alignment (S = –0.26) after 5 h, showcasing the drastic effects of relatively weak magnetic fields on CNC alignment. For suspensions below C*, no magnetic alignment was detected.

  14. Aligned nanostructured polymers by magnetic-field-directed self-assembly of a polymerizable lyotropic mesophase.

    PubMed

    Tousley, Marissa E; Feng, Xunda; Elimelech, Menachem; Osuji, Chinedum O

    2014-11-26

    Magnetic-field-directed assembly of lyotropic surfactant mesophases provides a scalable approach for the fabrication of aligned nanoporous polymers by templated polymerization. We develop and characterize a lyotropic liquid crystalline system containing hexagonally packed cylindrical micelles of a polymerizable surfactant in a polymerizable solvent. The system exhibits negative magnetic anisotropy, resulting in the degenerate alignment of cylindrical micelles perpendicular to the magnetic field. Sample rotation during field alignment is used to effectively break this degeneracy and enable the production of uniformly well-aligned mesophases. High-fidelity retentions of the hexagonal structure and alignment were successfully achieved in polymer films produced upon UV exposure of the reactive system. The success of this effort provides a route for the fabrication of aligned nanoporous membranes suitable for highly selective separations, sensing, and templated nanomaterial synthesis.

  15. The aligned magnetic field with convective boundary conditions over a stretching sheet in a viscous fluid

    NASA Astrophysics Data System (ADS)

    Arifin, N. S.; Zokri, S. M.; Aziz, L. A.; Kasim, A. R. M.; Salleh, M. Z.; Mohammad, N. F.

    2017-05-01

    In this study, the aligned magnetic field on the flow of a viscous fluid over a stretching sheet with convective boundary conditions is analyzed. The governing nonlinear boundary layer equations is transformed into ordinary differential equations and then solved numerically by Keller-box method. The numerical solutions with different values of aligned angle, Prandtl number and magnetic field are presented graphically and tabular form. It is found that the velocity profile, skin friction coefficient and Nusselt number decreases with the increasing of aligned angle and magnetic field. Similarly, increment in Prandtl number decreases the temperature profile.

  16. Magnetic field-aligned electric field acceleration and the characteristics of the optical aurora

    NASA Technical Reports Server (NTRS)

    Christensen, A. B.; Lyons, L. R.; Hecht, J. H.; Sivjee, G. G.; Meier, R. R.

    1987-01-01

    The long-recognized association of brighter aurora with more deeply penetrating, and hence more energetic, electrons is examined. Using the Knight (1973) relation between the magnetic-field-aligned current density and potential drop (derived from the theory of single-particle motion in the presence of a magnetic-field-aligned electric field), an approximate expression relating the energy flux of the precipitating electrons over discrete aurora and the mean particle energy is derived. This expression is used in conjunction with an auroral optical excitation and emission model to specify the dependence of the red/blue ratio of auroral optical emissions on the brightness of the aurora. It is shown that the quantitative predictions of the discrete auroral theory are in accord with observations of the aurora.

  17. Magnetic field-aligned electric field acceleration and the characteristics of the optical aurora

    NASA Technical Reports Server (NTRS)

    Christensen, A. B.; Lyons, L. R.; Hecht, J. H.; Sivjee, G. G.; Meier, R. R.

    1987-01-01

    The long-recognized association of brighter aurora with more deeply penetrating, and hence more energetic, electrons is examined. Using the Knight (1973) relation between the magnetic-field-aligned current density and potential drop (derived from the theory of single-particle motion in the presence of a magnetic-field-aligned electric field), an approximate expression relating the energy flux of the precipitating electrons over discrete aurora and the mean particle energy is derived. This expression is used in conjunction with an auroral optical excitation and emission model to specify the dependence of the red/blue ratio of auroral optical emissions on the brightness of the aurora. It is shown that the quantitative predictions of the discrete auroral theory are in accord with observations of the aurora.

  18. Alignment of SWNTs by protein-ligand interaction of functionalized magnetic particles under low magnetic fields.

    PubMed

    Park, Tae Jung; Park, Jong Pil; Lee, Seok Jae; Jung, Dae-Hwan; Ko, Young Koan; Jung, Hee-Tae; Lee, Sang Yup

    2011-05-01

    Carbon nanotubes (CNTs) have attracted considerable attention for applications using their superior mechanical, thermal and electrical properties. A simple method to controllably align single-walled CNTs (SWNTs) by using magnetic particles embedded with superparamagnetic iron oxide as an accelerator under the magnetic field was developed. The functionalization of SWNTs using biotin, interacted with streptavidin-coupled magnetic particles (micro-to-nano in diameter), and layer-by-layer assembly were performed for the alignment of a particular direction onto the clean silicon and the gold substrate at very low magnetic forces (0.02-0.89 T) at room temperature. The successful alignment of the SWNTs with multi-layer film was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). By changing the orientation and location of the substrates, crossed-networks of SWNTs-magnetic particle complex could easily be fabricated. We suggest that this approach, which consists of a combination of biological interaction among streptavidin-biotin and magnetite particles, should be useful for lateral orientation of individual SWNTs with controllable direction.

  19. Magnetic and electric field alignments of cellulose chains for electro-active paper actuator

    NASA Astrophysics Data System (ADS)

    Yun, Sungryul; Chen, Yi; Lee, Sang Woo; Kim, Jaehwan; Kim, Heung Soo

    2008-03-01

    To improve the piezoelectricity of cellulose electro-active paper (EAPap), electrical field and magnetic field alignments were investigated. EAPap is made with cellulose by dissolving cotton pulp and regenerating cellulose with aligned cellulose fibers. EAPap made with cellulose has piezoelectric property due to its structural crystallinity. Noncentro-symmetric crystal structure of EAPap, which is mostly cellulose II, can exhibit piezoelectricity. However, EAPap has ordered crystal parts as well as disordered parts of cellulose. Thus, well alignment of cellulose chains in EAPap is important to improve its piezoelectricity. In this paper, uniaxial alignments of cellulose chains were investigated by applying electric field and magnetic field. As exposing different fields to EAPap samples, the changed characteristics were analyzed by X-Ray diffractometer (XRD) and Scanning electron microscopy (SEM). Finally, the piezoelectricity of EAPap samples was evaluated by comparing their piezoelectric charge constant [d 31]. As increasing applied electric field up to 40V/mm, d 31 value was gradually improved due to increased cellulose crystallinity as well as alignment of cellulose chains. Also the alignment of cellulose chains was improved with increasing the exposing time to magnetic field (5.3T) and well alignment was achieved by exposing EAPap sample on the magnetic field for 180min.

  20. Diffusive alignment of the magnetic field in active regions of plasmas

    PubMed

    Nunez

    2000-11-01

    Regions of high magnetic field within plasmas tend to keep this field aligned in a dominant direction. This occurs both in observed phenomena and in simulations of kinematic and nonlinear dynamos. Although most of this effect is due to the particular dynamics of each case, magnetic diffusion also plays an important role. It is shown here that the unitary magnetic field vector satisfies a certain estimate that bounds its possible variations. The dependence of the bound on the plasma parameters is analyzed.

  1. On the alignment of diamagnetic molecules in interstellar magnetic fields

    NASA Astrophysics Data System (ADS)

    Papoular, R.

    2017-01-01

    This paper reports the results of new chemical modeling measurements of the Faraday rotation braking mechanism operating on a diamagnetic molecule in a magnetic field (see Papoular 2016). The time length of the experiment is extended, more relevant variables are measured (rotation, vibration, drift energies; molecule orientation), and more accurately, as a function of time. The polarization of light by the moving molecule is computed. The observed behavior of the molecule may be understood, and the rotation damping time more accurately deduced by fitting a mathematical model built upon the classical equations of motion in a field. This model, meant to include the essential physics involved in the experiment, with the minimum number of parameters, also allows the chemical modeling experimental results to be extrapolated to other molecular structures, shapes and sizes, and other magnetic fields. For a given particle, the rotation damping time scales like 1/H and is independent on rotation frequency. As an example, we follow the motion of a rod of homogeneous material, 10-5 cm in length, moving in a field 5 10-6 G in intensity. Its angular rotation is found to decrease to 0, while its axis settles perpendicularly to the field within a few years. Molecular vibrations appear as an illustration of the fluctuation-dissipation theorem: they absorb friction heat and, at the same time, are the very cause of this friction.

  2. Dependence of the magnetic properties on the alignment magnetic field for NdFeB bonded magnets made from anisotropic HDDR powders

    NASA Astrophysics Data System (ADS)

    Gao, R. W.; Zhang, J. C.; Zhang, D. H.; Dai, Y. Y.; Meng, X. H.; Wang, Z. M.; Zhang, Y. J.; Liu, H. Q.

    1999-01-01

    The dependence of the hard magnetic properties on the alignment magnetic field for Nd(Fe,Co)B bonded magnets made from anisotropic HDDR powders is studied. The experimental results demonstrate that addition of a little Ga can induce a strong magnetic anisotropy in the HDDR magnetic powders. The application of an alignment magnetic field while the powders are bonded can increase the remanence, the coercivity and the maximum energy product in different degrees and the hard magnetic properties of the magnet are obviously improved with increasing alignment field.

  3. Feasibility study of cellulose nanofiber alignment by high DC magnetic field

    NASA Astrophysics Data System (ADS)

    Kim, Hyun Chan; Kang, Jinmo; Park, Jung Ho; Akther, Asma; Kim, Jaehwan

    2017-04-01

    Cellulose nanofiber (CNF) has taken center stage as a future material with high specific strength, specific modulus and environmentally friendly behavior. However, natural CNFs are so randomly oriented that once CNFs are used in composites, their mechanical properties are not the same as expected from the CNFs. Thus, CNF alignment is important in fabricating composites and fibers. Interestingly, CNFs have negative diamagnetic anisotropy. In the presence of high magnetic field, the fiber axis of CNF can be aligned perpendicular to the applied field. This paper reports a preliminary study of CNF alignment by high dc magnetic field. The CNF emulsion is prepared by aqueous counter collision method and centrifugation. The CNF emulsion is placed in the high dc magnet and cured for a certain time. The alignment of CNF is investigated by scanning electron microscopy, mechanical tensile test.

  4. The inhomogeneous ion temperature anisotropy instabilities of magnetic-field-aligned plasma sheared flow

    NASA Astrophysics Data System (ADS)

    Mikhailenko, V. V.; Mikhailenko, V. S.; Lee, Hae June

    2016-11-01

    The stability of the magnetic field aligned sheared flow with anisotropic ion temperatures, which have the anisotropic spatial inhomogeneities across the magnetic field and are comparable with or are above the electron temperature, is investigated numerically and analytically. The ion temperatures gradients across the magnetic field affect the instability development only when the inhomogeneous is the ion temperature along the magnetic field irrespective the inhomogeneity of the ion temperature across the magnetic field. In this case, the instability is developed due to the combined effect of the ion Landau damping, velocity shear, ion temperature anisotropy, and anisotropy of the ion temperature gradients. In the case when the ion temperature along the magnetic field is homogeneous, but the ion temperature across the magnetic field is inhomogeneous, the short wavelength instability develops with the wave length less than the thermal ion Larmor radius. This instability excites due to the coupled effect of the ion Landau damping, velocity shear and ion temperature anisotropy.

  5. Magnetic field aligned assembly of nonmagnetic composite dumbbells in nanoparticle-based aqueous ferrofluid.

    PubMed

    Takahashi, Hayato; Nagao, Daisuke; Watanabe, Kanako; Ishii, Haruyuki; Konno, Mikio

    2015-05-26

    Monodisperse, nonmagnetic, asymmetrical composite dumbbells in a suspension of magnetic nanoparticles (ferrofluid) were aligned by application of an external magnetic field to the ferrofluid. The asymmetrical composite dumbbells were prepared by two-step soap-free emulsion polymerization consisting of the first polymerization to coat spherical silica cores with cross-linked poly(methyl methacrylate) (PMMA) shell and the second polymerization to protrude a polystyrene (PSt) lobe from the core-shell particles. A chain structure of nonmagnetic dumbbells oriented to the applied magnetic field was observed at nanoparticle content of 2.0 vol % and field strengths higher than 1.0 mT. A similar chain structure of the dumbbells was observed under application of alternating electric field at strengths higher than 50 V/mm. Parallel and orthogonally combined applications of the electric and magnetic fields were also conducted to examine independence of the electric and magnetic applications as operational factors in the dumbbell assembling. Dumbbell chains stiffer than those in a single application of external field were formed in the parallel combined application of electric and magnetic fields. The orthogonal combination of the different applied fields could form a magnetically aligned chain structure of the nonmagnetic dumbbells oriented to the electric field. The present work experimentally indicated that the employment of inverse magnetorheological effect for nonmagnetic, anisotropic particles can be a useful method for the simultaneous controls over the orientation and the positon of anisotropic particles in their assembling.

  6. Polar cap field-aligned currents for southward interplanetary magnetic fields

    SciTech Connect

    Xu, D.; Kivelson, M.G.

    1994-04-01

    It has been common to suppose that polar region field-aligned currents for southward interplanetary magnetic fields (IMF) consist of two parts: region 1 and region 2 currents. It is often suggested that both of these current systems flow on closed field lines. In this pilot study the limited data available from the ISIS 2 satellite are used to examine region 1 currents with the objective of establishing whether or not they can exist partially on open field lines (i.e., inside the polar caps) for southward IMF. Magnetic field perturbations were used to identify the field-aligned currents (FACs). The absence of {ge}keV electrons but the presence of {le}200 eV electrons in the polar cap or background polar rain is considered as the signature of open field lines. On some passes, region 1 sense FACs appear to be composed of two parts. The poleward part of the current signature is accompanied by electron fluxes at energies {le}200 eV or occasionally by fluxes at background levels while the equatorward part of the interval is accompanied by electron fluxes at energies both {le}200 eV and {ge}keV. On other passes, region 1 sense currents are accompanied by both {le}200 eV and {ge}keV electron fluxes during the entire pass. The authors propose that region 1 sense FACs flow on both closed and open field lines for the first situation and on closed field lines for the second situation. In seeking to understand why region 1 currents sometimes flow only on closed field lines and sometimes flow on open as well as closed field lines, the authors suggest a control by the IMF B{sub y}. The IMF B{sub y} may also shift the region 1 currents on open field lines to one side (dawn or dusk) of the polar cap like the convection cells. Such a shift provides a consistent model of the data taken on the dayside and the authors discuss why night side observations may be different. 47 refs., 6 figs., 1 tab.

  7. The aligned magnetic field of a dusty fluid flow over a stretching sheet

    NASA Astrophysics Data System (ADS)

    Arifin, N. S.; Zokri, S. M.; Kasim, A. R. M.; Salleh, M. Z.; Mohammad, N. F.

    2017-08-01

    In this study, the aligned magnetic field on the flow of a dusty fluid over a stretching sheet is analyzed. The governing nonlinear boundary layer equations is transformed into ordinary differential equations and then solved numerically by the Runge-Kutta Fehlberg fourth-fifth method (RKF45). The numerical solutions with different values of aligned angle, fluid particle interaction parameter and Prandtl number are presented in graphical form. It is found that, increasing aligned angle lead to the decreasing velocity profile while increasing the temperature profile for both fluid and dust phases respectively.

  8. Magnetically Aligned Supramolecular Hydrogels

    PubMed Central

    Wallace, Matthew; Cardoso, Andre Zamith; Frith, William J; Iggo, Jonathan A; Adams, Dave J

    2014-01-01

    The magnetic-field-induced alignment of the fibrillar structures present in an aqueous solution of a dipeptide gelator, and the subsequent retention of this alignment upon transformation to a hydrogel upon the addition of CaCl2 or upon a reduction in solution pH is reported. Utilising the switchable nature of the magnetic field coupled with the slow diffusion of CaCl2, it is possible to precisely control the extent of anisotropy across a hydrogel, something that is generally very difficult to do using alternative methods. The approach is readily extended to other compounds that form viscous solutions at high pH. It is expected that this work will greatly expand the utility of such low-molecular-weight gelators (LMWG) in areas where alignment is key. PMID:25345918

  9. Dust Grain Alignment and Magnetic Field Strength in the Wall of the Local Bubble

    NASA Astrophysics Data System (ADS)

    Andersson, B.-G.; Medan, Ilija

    2017-01-01

    We use archival data on polarization (Berdyugin 2014) and extinction in the wall of the Local Bubble to study the grain alignment efficiency and the magnetic field strength. We find that the grain alignment efficiency variations can be directly tied to the location of the known OB-associations within 200pc from the Sun, strongly supporting modern, radiation-driven dust grain alignment. Based on the Davis-Chandrasekhar-Fermi method, we find a bimodal magnetic field-strength distribution, where the locations of the strongest fields correlate with the directions towards the near-by OB associations. We hypothesize that this strengthening is due to compression of the bubble wall by the opposing outflows in the Local Bubble and from the surrounding OB associations.

  10. Positioning and aligning CNTs by external magnetic field to assist localised epoxy cure

    NASA Astrophysics Data System (ADS)

    Ariu, G.; Hamerton, I.; Ivanov, D.

    2016-01-01

    This work focuses on the generation of conductive networks through the localised alignment of nano fillers, such as multi-walled carbon nanotubes (MWCNTs). The feasibility of alignment and positioning of functionalised MWCNTs by external DC magnetic fields was investigated. The aim of this manipulation is to enhance resin curing through AC induction heating due to hysteresis losses from the nanotubes. Experimental analyses focused on in-depth assessment of the nanotube functionalisation, processing and characterisation of magnetic, rheological and cure kinetics properties of the MWCNT solution. The study has shown that an external magnetic field has great potential for positioning and alignment of CNTs. The study demonstrated potential for creating well-ordered architectures with an unprecedented level of control of network geometry. Magnetic characterisation indicated cobalt-plated nanotubes to be the most suitable candidate for magnetic alignment due to their high magnetic sensitivity. Epoxy/metal-plated CNT nanocomposite systems were validated by thermal analysis as induction heating mediums. The curing process could therefore be optimised by the use of dielectric resins. This study offers a first step towards the proof of concept of this technique as a novel repair technology.

  11. Alignment and measurement of the magnetic field for the BESIII muon counter

    NASA Astrophysics Data System (ADS)

    Gao, Qing; Zhang, Jing-Zhi; Li, Chun-Hua; Yin, Jun-Hao

    2016-11-01

    Based on cosmic ray events without a magnetic field taken with the BESIII detector during the summer shutdown of BEPCII in 2012 and di-muon events from a data sample taken at center-of-mass energy of 3.686 GeV in 2009, we compare the coordinates of hits registered in the BESIII muon counter with the expected interaction point extrapolated from reconstructed tracks from the inner tracking system in the absence of a magnetic field. By minimizing the difference, we align the muon counter with the inner tracking system. Moreover, the strength of the magnetic field in the muon counter is measured for the first time with di-muon events from data taken at a center-of-mass energy of 3.686 GeV. After the alignment and the magnetic field strength measurement, the offsets in the reconstructed hit positions for muon tracks are reduced, which improves the muon identification. The alignment and magnetic field strength measurement have been adopted in the latest version of the BESIII offline software system. This addition to the software reduces the systematic uncertainty for the physics analysis in cases where the muon counter information is used. Supported by National Key Basic Research Program of China (2015CB856701), National Natural Science Foundation of China (NSFC) (11475187, 11575198, 11521505), 100 Talents Program of CAS (U-25)

  12. Implications of grain size variation in magnetic field alignment of block copolymer blends

    DOE PAGES

    Rokhlenko, Yekaterina; Majewski, Pawel W.; Larson, Steven R.; ...

    2017-03-28

    Recent experiments have highlighted the intrinsic magnetic anisotropy in coil–coil diblock copolymers, specifically in poly(styrene-block-4-vinylpyridine) (PS-b-P4VP), that enables magnetic field alignment at field strengths of a few tesla. We consider here the alignment response of two low molecular weight (MW) lamallae-forming PS-b-P4VP systems. Cooling across the disorder–order transition temperature (Todt) results in strong alignment for the higher MW sample (5.5K), whereas little alignment is discernible for the lower MW system (3.6K). This disparity under otherwise identical conditions of field strength and cooling rate suggests that different average grain sizes are produced during slow cooling of these materials, with larger grainsmore » formed in the higher MW material. Blending the block copolymers results in homogeneous samples which display Todt, d-spacings, and grain sizes that are intermediate between the two neat diblocks. Similarly, the alignment quality displays a smooth variation with the concentration of the higher MW diblock in the blends, and the size of grains likewise interpolates between limits set by the neat diblocks, with a factor of 3.5× difference in the grain size observed in high vs low MW neat diblocks. Finally, these results highlight the importance of grain growth kinetics in dictating the field response in block copolymers and suggests an unconventional route for the manipulation of such kinetics.« less

  13. Large magnetostrain in magnetic-field-aligned Mn0.965CoGe compound

    NASA Astrophysics Data System (ADS)

    Hu, Qiu-Bo; Hu, Yong; Fang, Yong; Wang, Dun-Hui; Cao, Qing-Qi; Yang, Yan-Ting; Li, Jing; Du, You-Wei

    2017-05-01

    By applying external stimulus (temperature or magnetic field), MnCoGe-based compounds undergo a martensitic transformation from hexagonal Ni2In-type to orthorhombic TiNiSi-type structure accompanied with a giant negative thermal expansion, which suggests a large magnetic-field-induced strain. However, these compounds naturally collapse into powders and are difficult to be oriented, which hinder their applications for magnetostrain. In this paper, a magnetic-field-aligned Mn0.965CoGe compound was prepared by bonding with epoxy resin and orientating in a magnetic field. The XRD patterns revealed the texture in this sample. By introducing vacancies of Mn element, the magnetostructural transformation temperature of Mn0.965CoGe compound was shifted down to 278 K. The magnetostrain was measured at some selected temperatures and the maximal strain could reach up to 925 ppm at 270 K.

  14. Correlation between magnetic and electric field perturbations in the field-aligned current regions deduced from DE 2 observations

    NASA Technical Reports Server (NTRS)

    Ishii, M.; Sugiura, M.; Iyemori, T.; Slavin, J. A.

    1992-01-01

    The satellite-observed high correlations between magnetic and electric field perturbations in the high-latitude field-aligned current regions are investigated by examining the dependence of the relationship between Delta-B and E on spatial scale, using the electric and magnetic field data obtained by DE 2 in the polar regions. The results are compared with the Pedersen conductivity inferred from the international reference ionosphere model and the Alfven wave velocity calculated from the in situ ion density and magnetic field measurements.

  15. Can primordial magnetic fields seeded by electroweak strings cause an alignment of quasar axes on cosmological scales?

    PubMed

    Poltis, Robert; Stojkovic, Dejan

    2010-10-15

    The decay of nontopological electroweak strings may leave an observable imprint in the Universe today in the form of primordial magnetic fields. Protogalaxies preferentially tend to form with their axis of rotation parallel to an external magnetic field, and, moreover, an external magnetic field produces torque which tends to align the galaxy axis with the magnetic field. We demonstrate that the shape of a magnetic field left over from two looped electroweak strings can explain the observed nontrivial alignment of quasar polarization vectors and make predictions for future observations.

  16. Multi-point Magnetic Field Observations of Field-Aligned Currents from Swarm Constellation Mission

    NASA Astrophysics Data System (ADS)

    Le, Guan; Chi, Peter; Lühr, Hermann; Gjerloev, Jesper; Stolle, Claudia; Park, Jaeheung; Rauberg, Jan

    2015-04-01

    In this paper, we report the results of case studies of multi-point magnetic field measurements of field-aligned currents (FACs) from Swarm constellation mission to understand their temporal characteristics and hemispheric asymmetry. For science operations (since April, 2014), the three spacecraft were placed in slightly different polar orbits: Swarm B spacecraft in a higher altitude orbit (507km x 512km) and Swarm A and C side-by-side in lower altitude orbits (459km x 462km). In the beginning of the science operational phase, the longitudinal separations of the orbital planes were small, and Swarm A/C pair and Swarm B were nearly out of phase in the orbit. This unique orbit configuration provides opportunities to study some new features of FACs. Specifically, the Swarm satellites make multiple crossings of a FAC region within a few hours. Such data enable us to study temporal variations in several time scales, from 1 minute up to about 3 hours. Furthermore, the three satellites make nearly simultaneous observations of FACs in northern and southern hemispheres, which provide us an opportunity to study the hemispheric asymmetry.

  17. Liquid Crystalline Block Copolymers with Brush Type Architecture: Toward Functional Membranes by Magnetic Field Alignment

    NASA Astrophysics Data System (ADS)

    Choo, Youngwoo; Gopinadhan, Manesh; Mahajan, Lalit; Kasi, Rajeswari; Osuji, Chinedum

    2015-03-01

    We introduce a novel liquid crystalline block copolymer with brush type architecture for membrane applications by magnetic field directed self-assembly. Ring-opening metathesis of n-alkyloxy cyanobiphenyl and polylactide (PLA) functionalized norbornene monomers provides efficient polymerization yielding low polydispersity block copolymers. The molecular weight of the PLA side chains, spacer length of the cyanobiphenyl mesogens are systematically varied to form well-ordered BCP morphologies at varying volume fractions. Interestingly, the system features morphology dependent anchoring condition where mesogens adopt planar anchoring on cylindrical interface while homeotropic anchoring was preferred on a planar block interface. The minority PLA domains from highly aligned materials can be readily degraded by hydrolysis to produce vertically aligned nanoporous polymer films which exhibit reversible thermal switching behavior. The polymers introduced here provide a versatile platform for scalable fabrication of aligned membranes and further functional materials based on such templates. This work was supported by NSF(CCMI-1246804).

  18. Influence of magnetic field alignment of cellulose whiskers on the mechanics of all-cellulose nanocomposites.

    PubMed

    Pullawan, Tanittha; Wilkinson, Arthur N; Eichhorn, Stephen J

    2012-08-13

    Orientation of cellulose nanowhiskers (CNWs) derived from tunicates, in an all-cellulose nanocomposite, is achieved through the application of a magnetic field. CNWs are incorporated into a dissolved cellulose matrix system and during solvent casting of the nanocomposite a magnetic field is applied to induce their alignment. Unoriented CNW samples, without the presence of a magnetic field, are also produced. The CNWs are found to orient under the action of the magnetic field, leading to enhanced stiffness and strength of the composites, but not to the level that is theoretically predicted for a fully aligned system. Lowering the volume fraction of the CNWs is shown to allow them to orient more readily in the magnetic field, leading to larger relative increases in the mechanical properties. It is shown, using polarized light microscopy, that the all-cellulose composites have a domain structure, with some domains showing pronounced orientation of CNWs and others where no preferred orientation occurs. Raman spectroscopy is used to both follow the position of bands located at ~1095 and ~895 cm(-1) with deformation and also their intensity as a function rotation angle of the specimens. It is shown that these approaches give valuable independent information on the respective molecular deformation and orientation of the CNWs, and the molecules in the matrix phase, in oriented and nonoriented domains of all-cellulose composites. These data are then related to an increase in the level of molecular deformation in the axial direction, as revealed by the Raman technique. Little orientation of the matrix phase is observed under the action of the magnetic field indicating the dominance of the stiff CNWs in governing mechanical properties.

  19. Particle trajectories in Weibel magnetic filaments with a flow-aligned magnetic field

    NASA Astrophysics Data System (ADS)

    Bret, Antoine

    2016-08-01

    > . In the absence of an external guiding magnetic field, these filaments can block the incoming flow, initiating the shock formation, if their size is larger than the Larmor radius of the incoming particles in the peak field. Here we show that this result still holds in the presence of an external magnetic field, provided it is not too high. Yet, for 0\\gtrsim Bf/2, the filaments become unable to stop any particle, regardless of its initial velocity.

  20. Short-term magnetic field alignment variations of equatorial ionospheric irregularities

    SciTech Connect

    Johnson, A.L.

    1988-06-01

    The ionospheric irregularities that cause equatorial scintillation are elongated along the north-south magnetic field lines. During a 1981 field campaign at Ascension Island, 250-MHz receivers were spaced from 300 m to 1.6 km along the field lines, and the signals received from the Marisat satellite were cross correlated. Data collected during eight nights of fading showed a linear relationship between fading rate and cross correlation. The alignment of the antennas was adjusted to give a zero time lag between the widely spaced receivers with a measurement accuracy of 0.03 s. Since the average irregularity velocity was 125 m/s, this time accuracy translated to an angular measurement accuracy of 0.1 deg. During a 4-hour period of nightly fading, occasional differences in time of arrival were noted that corresponded to a tilt in the north-south alignment of + or - 1 deg. Data from several nights of fading were analyzed, and each night exhibited the same variance in the north-south irregularity alignment. It is postulated that the shift in the measured peak correlation may have been caused by patches of irregularities at different altitudes where the magnetic field lines have a slightly different direction. 13 references.

  1. On the relationship between morning sector irregular magnetic pulsations and field aligned currents

    NASA Technical Reports Server (NTRS)

    Engebretson, M. J.; Cahill, L. J., Jr.; Potemra, T. A.; Zanetti, L. J.; Arnoldy, R. L.; Mende, S. B.; Rosenberg, T. J.

    1984-01-01

    For three magnetically disturbed days in early 1980, data from south polar masses of the Magsat satellite are compared with data from search coil magnetometer, riometer, and photometer instrumentation at Siple, Antarctica. It is found that during each Magsat polar pass in the morning sector, the level of Pi 1 activity correlates well with the intensities of three-dimensional current systems. Fine structure is often observed in the field-aligned currents during periods of intense Pi activity. Among the Birkeland currents are 2-s to 10-s (16-80 km) structured perturbations; these are evident in the transverse components of the field and are thought to indicate filamentary currents. Pi 1 amplitudes are found to be considerably larger when region 2 Birkeland currents are overhead than when they are not. In one case, detailed features are identified in the high-resolution Magsat magnetic field data that may be current fluctuations related to asymmetric Pi 1.

  2. Electron Weibel instability in relativistic counterstreaming plasmas with flow-aligned external magnetic fields.

    PubMed

    Grassi, A; Grech, M; Amiranoff, F; Pegoraro, F; Macchi, A; Riconda, C

    2017-02-01

    The Weibel instability driven by two symmetric counterstreaming relativistic electron plasmas, also referred to as current-filamentation instability, is studied in a constant and uniform external magnetic field aligned with the plasma flows. Both the linear and nonlinear stages of the instability are investigated using analytical modeling and particle-in-cell simulations. While previous studies have already described the stabilizing effect of the magnetic field, we show here that the saturation stage is only weakly affected. The different mechanisms responsible for the saturation are discussed in detail in the relativistic cold fluid framework considering a single unstable mode. The application of an external field leads to a slight increase of the saturation level for large wavelengths, while it does not affect the small wavelengths. Multimode and temperature effects are then investigated. While at high temperature the saturation level is independent of the external magnetic field, at low but finite temperature the competition between different modes in the presence of an external magnetic field leads to a saturation level lower with respect to the unmagnetized case.

  3. Electron Weibel instability in relativistic counterstreaming plasmas with flow-aligned external magnetic fields

    NASA Astrophysics Data System (ADS)

    Grassi, A.; Grech, M.; Amiranoff, F.; Pegoraro, F.; Macchi, A.; Riconda, C.

    2017-02-01

    The Weibel instability driven by two symmetric counterstreaming relativistic electron plasmas, also referred to as current-filamentation instability, is studied in a constant and uniform external magnetic field aligned with the plasma flows. Both the linear and nonlinear stages of the instability are investigated using analytical modeling and particle-in-cell simulations. While previous studies have already described the stabilizing effect of the magnetic field, we show here that the saturation stage is only weakly affected. The different mechanisms responsible for the saturation are discussed in detail in the relativistic cold fluid framework considering a single unstable mode. The application of an external field leads to a slight increase of the saturation level for large wavelengths, while it does not affect the small wavelengths. Multimode and temperature effects are then investigated. While at high temperature the saturation level is independent of the external magnetic field, at low but finite temperature the competition between different modes in the presence of an external magnetic field leads to a saturation level lower with respect to the unmagnetized case.

  4. Director alignment by crossed electric and magnetic fields: a deuterium NMR study.

    PubMed

    Hamasuna, D; Luckhurst, G R; Sugimura, A; Timimi, B A; Zimmermann, H

    2011-07-01

    The static director distribution in thin nematic liquid crystal cells, subject to both electric and magnetic fields, has been investigated using a combination of deuterium nuclear magnetic resonance (NMR) spectroscopy and continuum theory in terms of the director distribution function, which gives the probability density for finding the director at a given orientation. A series of deuterium NMR spectra for the nematic liquid crystal, 4-pentyl-d(2)-4'-cyanobiphenyl deuteriated in the α position of the pentyl chain were acquired as a function of the applied electric field. This powerful experimental technique allowed us to observe uniform and nonuniform director alignment depending on the angle between the two fields and their relative strength. On the basis of the detailed experimental results, we have explored the factors that influence the nature of both the uniform and the nonuniform director distributions. We have discussed the questions that are raised by our attempt to understand the static director distribution as a function of the angle between the two fields. We have discovered that the alignment of the director at the surface of the Teflon spacers is essential in addition to the random variation in the cell thickness in order to account for the static director distribution determined from the NMR spectra.

  5. Dynamics of the field-aligned current distribution during a magnetic storm: AMPERE

    NASA Astrophysics Data System (ADS)

    Vassiliadis, D.; Tepke, B. P.

    2015-12-01

    Field-aligned current density in the ionosphere can be used to identify the location and intensity of solar wind-magnetosphere-ionosphere coupling, and help identify the large-scale processes that contribute to this coupling. The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) mission effectively provides high-resolution spatial and temporal measurements of the radial current during magnetic storms. These in situ measurements are complementary to magnetic remote sensing from the ground using magnetometer arrays. Here we examine two storms, on May 29, 2010 and August 5, 2011, using AMPERE and solar wind data. We identify the regions whose radial current density has the greatest correlation with solar wind coupling functions and individual magnetic and plasma variables. We develop a statistical model of the radial current density from the magnetospheric and solar wind data which is then used to represent regions of outflowing and inflowing current in the two hemispheres. While the model is limited in representing high spatial resolution, time series of regional and global field-aligned current are reproduced with relatively large correlation coefficients (0.70-0.90) in each event.

  6. Numerical study of anomalous absorption of O mode waves on magnetic field-aligned striations

    NASA Astrophysics Data System (ADS)

    Eliasson, B.; Papadopoulos, K.

    2015-04-01

    Simple expressions that describe mode conversion and anomalous absorption of ordinary (O) mode waves injected at angles between the vertical and magnetic zenith to upper hybrid (UH) oscillations in the presence of field-aligned density striations are presented. The absorption takes place in a region above the UH resonance layer where the striations allow trapped eigenmodes, leading to excitation of large-amplitude UH waves. The derivation of the expressions is guided by dimensional analysis and numerical simulations. The results are relevant in interpreting high-latitude heating experiments where anomalous absorption due to striations plays a crucial role.

  7. Driven magnetic reconnection in three dimensions - Energy conversion and field-aligned current generation

    NASA Technical Reports Server (NTRS)

    Sato, T.; Walker, R. J.; Ashour-Abdalla, M.

    1984-01-01

    The energy conversion processes occurring in three-dimensional driven reconnection is analyzed. In particular, the energy conversion processes during localized reconnection in a taillike magnetic configuration are studied. It is found that three-dimensional driven reconnection is a powerful energy converter which transforms magnetic energy into plasma bulk flow and thermal energy. Three-dimensional driven reconnection is an even more powerful energy converter than two-dimensional reconnection, because in the three-dimensional case, plasmas were drawn into the reconnection region from the sides as well as from the top and bottom. Field-aligned currents are generated by three-dimensional driven reconnection. The physical mechanism responsible for these currents which flow from the tail toward the ionosphere on the dawnside of the reconnection region and from the ionosphere toward the tail on the duskside is identified. The field-aligned currents form as the neutral sheet current is diverted through the slow shocks which form on the outer edge of the reconnected field lines (outer edge of the plasma sheet).

  8. Magneto-plasmonic study of aligned Ni, Co and Ni/Co multilayer in polydimethylsiloxane as magnetic field sensor

    NASA Astrophysics Data System (ADS)

    Hamidi, Seyedeh Mehri; Mosaeii, Babak; Afsharnia, Mina; Aftabi, Ali; Najafi, Mojgan

    2016-11-01

    We report the magneto-optical properties of aligned cobalt, Nickel and nickel/ Cobalt multilayer nanowires embedded in polydimethylsiloxane matrix. The NWs prepared by electrodeposition method in anodic alumina template and then dispersed in ethanol and placed in a heater to evaporate the ethanol and finally dispersed in polydimethylsiloxane matrix to reach to the composite. The used external magnetic field arranges the nanowires and our aligned nanowires were investigated by magneto-optical surface plasmon resonance techniques in two easy and hard axis configurations. Our results show the sufficient sensitivity in magneto-optical surface plasmon resonance of Nickel and cobalt arrays nanowires and because the different modulation mechanism in Ni and Co nanodisks, in Ni/Co multilayer we see the magnetization modulation of the excitation angle in accordance with magnetic field modulation of the SPP wave vector in each nanodisk. Finally, we show that the Ni/Co multilayer aligned nanowires can be used as efficient magnetic field sensor.

  9. Static magnetic fields enhance skeletal muscle differentiation in vitro by improving myoblast alignment.

    PubMed

    Coletti, Dario; Teodori, Laura; Albertini, Maria C; Rocchi, Marco; Pristerà, Alessandro; Fini, Massimo; Molinaro, Mario; Adamo, Sergio

    2007-10-01

    Static magnetic field (SMF) interacts with mammal skeletal muscle; however, SMF effects on skeletal muscle cells are poorly investigated. The myogenic cell line L6, an in vitro model of muscle development, was used to investigate the effect of a 80 +/- mT SMF generated by a custom-made magnet. SMF promoted myogenic cell differentiation and hypertrophy, i.e., increased accumulation of actin and myosin and formation of large multinucleated myotubes. The elevated number of nuclei per myotube was derived from increased cell fusion efficiency, with no changes in cell proliferation upon SMF exposure. No alterations in myogenin expression, a modulator of myogenesis, occurred upon SMF exposure. SMF induced cells to align in parallel bundles, an orientation conserved throughout differentiation. SMF stimulated formation of actin stress-fiber like structures. SMF rescued muscle differentiation in the presence of TNF, a muscle differentiation inhibitor. We believe this is the first report showing that SMF promotes myogenic differentiation and cell alignment, in the absence of any invasive manipulation. SMF-enhanced parallel orientation of myotubes is relevant to tissue engineering of a highly organized tissue such as skeletal muscle. SMF rescue of muscle differentiation in the presence of TNF may have important therapeutic implications.

  10. Comparison of auroral ionospheric and field-aligned currents derived from Swarm and ground magnetic field measurements

    NASA Astrophysics Data System (ADS)

    Juusola, L.; Kauristie, K.; Vanhamäki, H.; Aikio, A.; Kamp, M.

    2016-09-01

    Derivation of the auroral ionospheric currents from magnetic field measurements can produce drastically different results depending on the data and method used. We have cross tested several methods for obtaining instantaneous field-aligned and horizontal currents from Swarm satellite and International Monitor for Auroral Geomagnetic Effects (IMAGE) ground magnetic field measurements. We found that Swarm can yield latitude profiles of the east-west component of the divergence-free current density at most at ˜200 km resolution, typically resolving the electrojets. The north-south divergence-free component, on the other hand, is not always well reproduced due to the small longitudinal distance between the side-by-side flying satellite pair. Swarm can yield the field-aligned and curl-free current density at a wider range of latitude resolutions (˜7.5-200 km) than the divergence-free current density. While 7.5 km is suitable for comparison with auroras, 200 km typically resolves the Regions 1 and 2 field-aligned currents. IMAGE can yield maps of the divergence-free current density at ˜50 km resolution. Induced telluric currents should be accounted for in the derivation. Not accounting for them in the Swarm analysis, however, does not appear to introduce significant errors. Ionospheric conductances can be estimated by combining the total horizontal current density, consisting of the curl-free and divergence-free components, with the electric field measurements. Our results indicate that Swarm can only yield these at ˜200 km scale size when there is no significant dependence on longitude. However, combining the divergence-free current from IMAGE with the curl-free current and electric field from Swarm could yield conductance maps at ˜50 km resolution.

  11. Filamentary field-aligned currents at the polar cap region during northward interplanetary magnetic field derived with the Swarm constellation

    NASA Astrophysics Data System (ADS)

    Lühr, Hermann; Huang, Tao; Wing, Simon; Kervalishvili, Guram; Rauberg, Jan; Korth, Haje

    2016-10-01

    ESA's Swarm constellation mission makes it possible for the first time to determine field-aligned currents (FACs) in the ionosphere uniquely. In particular at high latitudes, the dual-satellite approach can reliably detect some FAC structures which are missed by the traditional single-satellite technique. These FAC events occur preferentially poleward of the auroral oval and during times of northward interplanetary magnetic field (IMF) orientation. Most events appear on the nightside. They are not related to the typical FAC structures poleward of the cusp, commonly termed NBZ. Simultaneously observed precipitating particle spectrograms and auroral images from Defense Meteorological Satellite Program (DMSP) satellites are consistent with the detected FACs and indicate that they occur on closed field lines mostly adjacent to the auroral oval. We suggest that the FACs are associated with Sun-aligned filamentary auroral arcs. Here we introduce in an initial study features of the high-latitude FAC structures which have been observed during the early phase of the Swarm mission. A more systematic survey over longer times is required to fully characterize the so far undetected field aligned currents.

  12. Atomic barium and cesium alignment-to-orientation conversion in external electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Hilborn, Robert C.; Hunter, Larry R.; Johnson, Kent; Peck, Stephen K.; Spencer, Alison; Watson, John

    1994-09-01

    We present an alternative method for changing atomic alignment to orientation through interactions with orthogonal static electric and magnetic fields. Experimental results demonstrating this effect in the 5d6p 1P state of atomic barium and the F=4 hyperfine level of the ground state of atomic cesium are presented. The theory of this effect for a j=0 to j=1 electric dipole transition is discussed in detail. The tensor polarizability of the 5d6p 1P state of Ba is determined to be 1.31(15) MHz/(kV/cm)2, in good agreement with the results of van Leeuwen and Hogervorst [Z. Phys. A 310, 37 (1983)].

  13. Stability estimate for the aligned magnetic field in a periodic quantum waveguide from Dirichlet-to-Neumann map

    SciTech Connect

    Mejri, Youssef

    2016-06-15

    In this article, we study the boundary inverse problem of determining the aligned magnetic field appearing in the magnetic Schrödinger equation in a periodic quantum cylindrical waveguide, by knowledge of the Dirichlet-to-Neumann map. We prove a Hölder stability estimate with respect to the Dirichlet-to-Neumann map, by means of the geometrical optics solutions of the magnetic Schrödinger equation.

  14. Dust Particle Alignment in the Solar Magnetic Field: a Possible Cause of the Cometary Circular Polarization

    NASA Astrophysics Data System (ADS)

    Kolokolova, L.; Koenders, C.; Rosenbush, V.; Kiselev, N.; Ivanova, A.; Afanasiev, V.

    2015-12-01

    Circular polarization (CP) produced by scattering of sunlight on cometary dust has been observed in 11 comets, and showed the values from 0.01% to 0.8%. CP of both signs was observed, although negative (left-handed) CP dominates. Recent observations of several comets using SCORPIO-2 focal reducer at the 6-m BTA telescope of the Special Astrophysical Observatory (Russia) allowed producing maps of CP in the comet continuum filter at 684 nm and red wide-band filter. A gradual increase of the CP with the nucleocentric distance was usually observed. The most plausible reason why the light scattered by cometary dust becomes circularly polarized is alignment of the dust particles in the solar magnetic field. However, in-situ data for comet Halley, indicated that the solar magnetic field could not penetrate deep into the coma, limited by the diamagnetic cavity, and, thus, could not be responsible for the CP observed closer than ~4000 km from the nucleus. Advanced theoretical studies of interaction of the solar magnetic field with cometary ions led to reconsidering the diamagnetic cavity boundary - it is defined by the cometary ionopause, at which a balance is achieved between the magnetic pressure in the magnetic pile up region and the neutral friction force. The nucleocentric distance where this balance is achieved depends on the comet characteristics, increasing with the increase of the gas production rate, and local solar wind conditions, approximatively given by the comet location, specifically, its heliocentric distance. The size of diamagnetic cavity was calculated for the conditions of our CP observations. We found that it could be as small as dozens (comets 73P, 8P, 290P) or hundreds (comets Q4 NEAT, K1 PanSTARRS, Tago-Sato-Kosaka) kilometers. Thus, non-zero CP close to the nucleus can be easily explained by the interaction of the dust particles with the solar magnetic field. This mechanism also explains the observed increase in CP with the distance from the

  15. Interplanetary magnetic field control of mantle precipitation and associated field-aligned currents

    NASA Technical Reports Server (NTRS)

    Xu, Dingan; Kivelson, Margaret G.; Walker, Ray J.; Newell, Patrick T.; Meng, C.-I.

    1995-01-01

    Dayside reconnection, which is particularly effective for a southward interplanetary magnetic field (IMF), allows magnetosheath particles to enter the magnetosphere where they form the plasma mantle. The motions of the reconnected flux tube produce convective flows in the ionosphere. It is known that the convection patterns in the polar cap are skewed to the dawnside for a positive IMF B(sub y) (or duskside for a negative IMF B(sub y)) in the northern polar cap. Correspondingly, one would expect to find asymmetric distributions of mantle particle precipitation, but previous results have been unclear. In this paper the correlation between B(sub y) and the distribution of mantle particle precipitation is studied for steady IMF conditions with southward IMF. Ion and electron data from the Defense Meteorological Satellite Program (DMSP) F6 and F7 satellites are used to identify the mantle region and IMP 8 is used as a solar wind monitor to characterize the IMF. We study the local time extension of mantle precipitation in the prenoon and postnoon regions. We find that, in accordance with theoretical expectations for a positive (negative) IMF B(sub y), mantle particle precipitation mainly appears in the prenoon region of the northern (southern) hemisphere. The mantle particle precipitation can extend to as early as 0600 magnetic local time (MLT) in the prenoon region but extends over a smaller local time region in the postnoon sector (we did not find mantle plasma beyond 1600 MLT in our data set although coverage is scant in this area). Magnetometer data from F7 are used to determine whether part of the region 1 current flows on open field lines. We find that at times part of the region 1 sense current extends into the region of mantle particle precipitation, and is therefore on open field lines. In other cases, region 1 currents are absent on open field lines. Most of the observed features can be readily interpreted in terms of the open magnetosphere model.

  16. Interplanetary magnetic field control of mantle precipitation and associated field-aligned currents

    NASA Technical Reports Server (NTRS)

    Xu, Dingan; Kivelson, Margaret G.; Walker, Ray J.; Newell, Patrick T.; Meng, C.-I.

    1995-01-01

    Dayside reconnection, which is particularly effective for a southward interplanetary magnetic field (IMF), allows magnetosheath particles to enter the magnetosphere where they form the plasma mantle. The motions of the reconnected flux tube produce convective flows in the ionosphere. It is known that the convection patterns in the polar cap are skewed to the dawnside for a positive IMF B(sub y) (or duskside for a negative IMF B(sub y)) in the northern polar cap. Correspondingly, one would expect to find asymmetric distributions of mantle particle precipitation, but previous results have been unclear. In this paper the correlation between B(sub y) and the distribution of mantle particle precipitation is studied for steady IMF conditions with southward IMF. Ion and electron data from the Defense Meteorological Satellite Program (DMSP) F6 and F7 satellites are used to identify the mantle region and IMP 8 is used as a solar wind monitor to characterize the IMF. We study the local time extension of mantle precipitation in the prenoon and postnoon regions. We find that, in accordance with theoretical expectations for a positive (negative) IMF B(sub y), mantle particle precipitation mainly appears in the prenoon region of the northern (southern) hemisphere. The mantle particle precipitation can extend to as early as 0600 magnetic local time (MLT) in the prenoon region but extends over a smaller local time region in the postnoon sector (we did not find mantle plasma beyond 1600 MLT in our data set although coverage is scant in this area). Magnetometer data from F7 are used to determine whether part of the region 1 current flows on open field lines. We find that at times part of the region 1 sense current extends into the region of mantle particle precipitation, and is therefore on open field lines. In other cases, region 1 currents are absent on open field lines. Most of the observed features can be readily interpreted in terms of the open magnetosphere model.

  17. Numerical simulations of Hall-effect plasma accelerators on a magnetic-field-aligned mesh.

    PubMed

    Mikellides, Ioannis G; Katz, Ira

    2012-10-01

    The ionized gas in Hall-effect plasma accelerators spans a wide range of spatial and temporal scales, and exhibits diverse physics some of which remain elusive even after decades of research. Inside the acceleration channel a quasiradial applied magnetic field impedes the current of electrons perpendicular to it in favor of a significant component in the E×B direction. Ions are unmagnetized and, arguably, of wide collisional mean free paths. Collisions between the atomic species are rare. This paper reports on a computational approach that solves numerically the 2D axisymmetric vector form of Ohm's law with no assumptions regarding the resistance to classical electron transport in the parallel relative to the perpendicular direction. The numerical challenges related to the large disparity of the transport coefficients in the two directions are met by solving the equations on a computational mesh that is aligned with the applied magnetic field. This approach allows for a large physical domain that extends more than five times the thruster channel length in the axial direction and encompasses the cathode boundary where the lines of force can become nonisothermal. It also allows for the self-consistent solution of the plasma conservation laws near the anode boundary, and for simulations in accelerators with complex magnetic field topologies. Ions are treated as an isothermal, cold (relative to the electrons) fluid, accounting for the ion drag in the momentum equation due to ion-neutral (charge-exchange) and ion-ion collisions. The density of the atomic species is determined using an algorithm that eliminates the statistical noise associated with discrete-particle methods. Numerical simulations are presented that illustrate the impact of the above-mentioned features on our understanding of the plasma in these accelerators.

  18. Angle-dependent radiative grain alignment. Confirmation of a magnetic field - radiation anisotropy angle dependence on the efficiency of interstellar grain alignment

    NASA Astrophysics Data System (ADS)

    Andersson, B.-G.; Pintado, O.; Potter, S. B.; Straižys, V.; Charcos-Llorens, M.

    2011-10-01

    Context. Interstellar grain alignment studies are currently experiencing a renaissance due to the development of a new quantitative theory based on radiative alignment torques (RAT). One of the distinguishing predictions of this theory is a dependence of the grain alignment efficiency on the relative angle (Ψ) between the magnetic field and the anisotropy direction of the radiation field. In an earlier study we found observational evidence for such an effect from observations of the polarization around the star HD 97300 in the Chamaeleon I cloud. However, due to the large uncertainties in the measured visual extinctions, the result was uncertain. Aims: By acquiring explicit spectral classification of the polarization targets, we have sought to perform a more precise reanalysis of the existing polarimetry data. Methods: We have obtained new spectral types for the stars in our for our polarization sample, which we combine with photometric data from the literature to derive accurate visual extinctions for our sample of background field stars. This allows a high accuracy test of the grain alignment efficiency as a function of Ψ. Results: We confirm and improve the measured accuracy of the variability of the grain alignment efficiency with Ψ, seen in the earlier study. We note that the grain temperature (heating) also shows a dependence on Ψ which we interpret as a natural effect of the projection of the grain surface to the illuminating radiation source. This dependence also allows us to derive an estimate of the fraction of aligned grains in the cloud.

  19. Transport in a field aligned magnetized plasma/neutral gas boundary: the end of the plasma

    NASA Astrophysics Data System (ADS)

    Cooper, Christopher Michael

    The objective of this dissertation is to characterize the physics of a boundary layer between a magnetized plasma and a neutral gas along the direction of a confining magnetic field. A series of experiments are performed at the Enormous Toroidal Plasma Device (ETPD) at UCLA to study this field aligned Neutral Boundary Layer (NBL) at the end of the plasma. A Lanthanum Hexaboride (LaB6) cathode and semi-transparent anode creates a magnetized, current-free helium plasma which terminates on a neutral helium gas without touching any walls. Probes are inserted into the plasma to measure the basic plasma parameters and study the transport in the NBL. The experiment is performed in the weakly ionized limit where the plasma density (ne) is much less than the neutral density (nn) such that ne/nn < 5%. The NBL is characterized by a field-aligned electric field which begins at the point where the plasma pressure equilibrates with the neutral gas pressure. Beyond the pressure equilibration point the electrons and ions lose their momentum by collisions with the neutral gas and come to rest. An electric field is established self consistently to maintain a current-free termination through equilibration of the different species' stopping rates in the neutral gas. The electric field resembles a collisional quasineutral sheath with a length 10 times the electron-ion collision length, 100 times the neutral collision length, and 10,000 times the Debye length. Collisions with the neutral gas dominate the losses in the system. The measured plasma density loss rates are above the classical cross-field current-free ambipolar rate, but below the anomalous Bohm diffusion rate. The electron temperature is below the ionization threshold of the gas, 2.2 eV in helium. The ions are in thermal equilibrium with the neutral gas. A generalized theory of plasma termination in a Neutral Boundary Layer is applied to this case using a two-fluid, current-free, weakly ionized transport model. The electron

  20. Magnetopause Erosion During the 17 March 2015 Magnetic Storm: Combined Field-Aligned Currents, Auroral Oval, and Magnetopause Observations

    NASA Technical Reports Server (NTRS)

    Le, G.; Luehr, H.; Anderson, B. J.; Strangeway, R. J.; Russell, C. T.; Singer, H.; Slavin, J. A.; Zhang, Y.; Huang, T.; Bromund, K.; hide

    2016-01-01

    We present multimission observations of field-aligned currents, auroral oval, and magnetopause crossings during the 17 March 2015 magnetic storm. Dayside reconnection is expected to transport magnetic flux, strengthen field-aligned currents, lead to polar cap expansion and magnetopause erosion. Our multimission observations assemble evidence for all these manifestations. After a prolonged period of strongly southward interplanetary magnetic field, Swarm and AMPERE observe significant intensification of field-aligned currents .The dayside auroral oval, as seen by DMSP, appears as a thin arc associated with ongoing dayside reconnection. Both the field-aligned currents and the auroral arc move equatorward reaching as low as approx. 60 deg. magnetic latitude. Strong magnetopause erosion is evident in the in situ measurements of the magnetopause crossings by GOES 13/15 and MMS. The coordinated Swarm, AMPERE, DMSP, MMS and GOES observations, with both global and in situ coverage of the key regions, provide a clear demonstration of the effects of dayside reconnection on the entire magnetosphere.

  1. Magnetopause erosion during the 17 March 2015 magnetic storm: Combined field-aligned currents, auroral oval, and magnetopause observations

    NASA Astrophysics Data System (ADS)

    Le, G.; Lühr, H.; Anderson, B. J.; Strangeway, R. J.; Russell, C. T.; Singer, H.; Slavin, J. A.; Zhang, Y.; Huang, T.; Bromund, K.; Chi, P. J.; Lu, G.; Fischer, D.; Kepko, E. L.; Leinweber, H. K.; Magnes, W.; Nakamura, R.; Plaschke, F.; Park, J.; Rauberg, J.; Stolle, C.; Torbert, R. B.

    2016-03-01

    We present multimission observations of field-aligned currents, auroral oval, and magnetopause crossings during the 17 March 2015 magnetic storm. Dayside reconnection is expected to transport magnetic flux, strengthen field-aligned currents, lead to polar cap expansion and magnetopause erosion. Our multimission observations assemble evidence for all these manifestations. After a prolonged period of strongly southward interplanetary magnetic field, Swarm and AMPERE observe significant intensification of field-aligned currents. The dayside auroral oval, as seen by DMSP, appears as a thin arc associated with ongoing dayside reconnection. Both the field-aligned currents and the auroral arc move equatorward reaching as low as ~60° magnetic latitude. Strong magnetopause erosion is evident in the in situ measurements of the magnetopause crossings by GOES 13/15 and MMS. The coordinated Swarm, AMPERE, DMSP, MMS and GOES observations, with both global and in situ coverage of the key regions, provide a clear demonstration of the effects of dayside reconnection on the entire magnetosphere.

  2. Is the flow-aligned component of IMF really able to impact the magnetic field structure of Venusian magnetotail?

    NASA Astrophysics Data System (ADS)

    Rong, Z. J.; Stenberg, G.; Wei, Y.; Chai, L. H.; Futaana, Y.; Barabash, S.; Wan, W. X.; Shen, C.

    2016-11-01

    An earlier statistical survey suggested that the flow-aligned component of upstream interplanetary magnetic field (IMF) may play an important role in controlling the lobe asymmetries of the Venusian magnetotail. The tail current sheet would be displaced and the magnetic field configuration would show asymmetries with respect to the current sheet. The asymmetries are expected to be more evident when the flow-aligned component becomes dominant. Here with carefully selected cases as well as a statistical study based on Venus Express observations in the near-Venus tail, we show that the lobe asymmetries of the magnetic field as well as the displacement of the current sheet are common characteristics of the Venusian magnetotail. However, the asymmetries and the displacement of the current sheet do not show a significant dependence on the flow-aligned component of the IMF. Our results suggest that the flow-aligned component of IMF cannot penetrate into the near magnetotail to impact the magnetic field structure.

  3. Field-Aligned and Ionospheric Current Contributions to Ground Magnetic Perturbations

    NASA Astrophysics Data System (ADS)

    Connors, M. G.; McPherron, R. L.; Anderson, B. J.; Korth, H.; Russell, C. T.; Chu, X.

    2014-12-01

    AMPERE data provides global space-derived radial electric currents on temporal and spatial scales suited to studying magnetic fields at ULF frequencies. It responds little to ionspheric currents, which dominate ground-based measurements, so that AMPERE and ground datasets complement each other to give a comprehensive view of near-Earth electric currents. Connors et al. (GRL, 2014) found that a three-dimensional current system slightly modified from the original substorm current wedge (SCW) concept of McPherron et al. (JGR, 1973) represented substorm midnight sector perturbations well both in the auroral and subauroral regions, if a current equivalent to that found by integrating AMPERE downward current was used, located where clear SCW signatures were indicated by AMPERE, and featuring an ionospheric electrojet. The AMPERE upward current was found to exceed that in the SCW, at least in part since the evening sector electrojet fed into it. We extend these results with a more detailed accounting of field-aligned and ionospheric currents throughout the active period (including growth phase). Ionospheric currents for the study are obtained from ground perturbations through optimization of a simple forward model over regions or on a meridian chain. We also investigate the degree to which subauroral perturbations may be directly calculated from AMPERE results. We further find that auroral zone currents may be very localized, to the extent that the entire SCW ionospheric current flows in a very restricted latitudinal range near onset, possibly corresponding to a single auroral arc.

  4. Microstructures and rheological properties of tilapia fish-scale collagen hydrogels with aligned fibrils fabricated under magnetic fields.

    PubMed

    Chen, S; Hirota, N; Okuda, M; Takeguchi, M; Kobayashi, H; Hanagata, N; Ikoma, T

    2011-02-01

    Tilapia fish-scale type I atelocollagen hydrogels with aligned fibril structures were fabricated under a strong magnetic field of 6 or 12 T using two different methods. In the first method, a solution of acid-soluble collagen was neutralized with phosphate buffer saline and maintained in the magnetic field at 28°C for 3h. Under these conditions fibrogenesis occurs, and a hydrogel is formed. The hydrogel was subsequently crosslinked with ethyl-dimethylcarbodiimide (EDC). In the second method, the hydrogels were formed as described above, but in the absence of an applied magnetic field. Only after being crosslinked with EDC were these gels exposed to the magnetic field (28°C for 3h). Both methods led to alignment of the collagen fibrils perpendicular to the magnetic direction, the extent of which depended on the duration of magnetic treatment. Even after EDC treatment, collagen fibrils can align, indicating that crosslinking has taken place within fibrils. Both sorts of aligned hydrogels exhibited similar rheological properties with higher storage and loss moduli than were observed with unoriented gels. The hydrogels treated at 6 T had the best rheological properties. The decrease in tangent angle phase delta indicated that the ratio of elasticity to viscosity was greater in the crosslinked than in the non-crosslinked hydrogels. Atomic force microscopy images showed that magnetic treatment had no effect on the nanostructure of collagen fibrils. Differential scanning calorimetry measurements indicated that collagen hydrogels with and without magnetic treatment had the same denaturation temperature, 48°C, while EDC crosslinking increased the denaturation temperature to 62°C. Copyright © 2010. Published by Elsevier Ltd.

  5. Field-aligned current signatures during the March 13-14, 1989, great magnetic storm

    SciTech Connect

    Fujii, R. ); Fukunishi, H. ); Kokubun, S. ); Sugiura, M. ); Tohyama, F. ); Hayakawa, H.; Tsuruda, K. ); Okada, T. )

    1992-07-01

    Characteristics of field-aligned currents (FACs) in the evening and morning regions during the March 13-14, 1989, great magnetic storm have been determined using magnetic and electric field data obtained from the EXOS D spacecraft. This storm began with an SSC at 0128 UT on March 13, and the second SSC occurred at 0747 UT on the same day. The storm continued until March 14. The equatorward boundary of the FAC region began to move equatorward right after the first SSC in both the evening and morning sectors, but the poleward boundary did not immediately respond to the SSC. The equatorward boundary of the FAC system reached as low as below 48{degree} invariant latitude, which corresponds to L = 2.2, and the latitudinal width of the FAC region increased greatly, particularly in the morning sector ({approximately}33{degree} in invariant latitude). In the evening sector the conventional current system characterized by a pair of upward region 1 and downward region 2 FACs changed into complicated patterns consisting of many pairs of upward and downward FACs with the development of the storm, particularly around 22 UT on March 13 when an intense eastward electrojet was observed as low as 50{degree} invariant latitude on the ground. In the morning sector an additional large-scale upward FAC was observed poleward of the conventional downward region 1 and upward region 2 FAC system throughout the storm. In addition, a pair of FACs with a narrow latitudinal width ({approximately}1.5{degree}) was observed at the poleward boundary of the extra upward FAC.

  6. Self-propelled in-tube shuttle and control system for automated measurements of magnetic field alignment

    NASA Astrophysics Data System (ADS)

    Boroski, W. N.; Nicol, T. H.; Pidcoe, S. V.; Zink, R. A.

    1990-03-01

    A magnetic field alignment gauge is used to measure the field angle as a function of axial position in each of the magnets for the Superconducting Super Collider (SSC). Present measurements are made by manually pushing the gauge through the magnet bore tube and stopping at intervals to record field measurements. Gauge location is controlled through graduation marks and alignment pins on the push rods. Field measurements are recorded on a logging multimeter with tape output. Described is a computerized control system being developed to replace the manual procedure for field alignment measurements. The automated system employs a pneumatic walking device to move the measurement gauge through the bore tube. Movement of the device, called the Self-Propelled In-Tube Shuttle (SPITS), is accomplished through an integral, gas driven, double-acting cylinder. The motion of the SPITS is transferred to the bore tube by means of a pair of controlled, retractable support feet. Control of the SPITS is accomplished through an RS-422 interface from an IBM-compatible computer to a series of solenoid-actuated air valves. Direction of SPITS travel is determined by the air-valve sequence, and is managed through the control software. Precise axial position of the gauge within the magnet is returned to the control system through an optically-encoded digital position transducer attached to the shuttle. Discussed is the performance of the transport device and control system during preliminary testing of the first prototype shuttle.

  7. Phase alignment and crystal orientation of Al 3Ni in Al-Ni alloy by imposition of a uniform high magnetic field

    NASA Astrophysics Data System (ADS)

    Wang, Chunjiang; Wang, Qiang; Wang, Zhongying; Li, Hutian; Nakajima, Keiji; He, Jicheng

    2008-03-01

    Solidification experiments of aluminum-nickel binary alloys under uniform high magnetic fields have been conducted. The effects of high magnetic fields on the crystal orientation of Al 3Ni were investigated by XRD and the alignment of primary phases Al 3Ni were also analyzed. Experimental results showed that the easy magnetization axis of Al 3Ni crystal oriented parallel to the imposed magnetic fields and the primary phase Al 3Ni aligned perpendicular to the magnetic fields. Magnetic orientation of crystal was determined by magnetic anisotropy energy. Whereas the phase alignment should be contributed to the combined effects of magnetic orientation, crystal growth and the effects of magnetic fields on mass transport during solidification.

  8. Aligned magnetic field effects on water based metallic nanoparticles over a stretching sheet with PST and thermal radiation effects

    NASA Astrophysics Data System (ADS)

    Rashid, Irfan; Ul Haq, Rizwan; Al-Mdallal, Qasem M.

    2017-05-01

    This study deals the simultaneous effects of inclined magnetic field and prescribed surface temperature (PST) on boundary layer flow of nanofluid over a stretching sheet. In order to make this mechanism more feasible, we have further considered the velocity slip and thermal radiation effects. Moreover, this perusal is made to consider the two kinds of nanofluid namely: Cu -water and A l2O3-water. Inclined magnetic field is utilized to accompanying an aligned angle that varies from 0 to π / 2 . The exact solutions are acquired from the transformed non-dimensional momentum and energy equations in the form of confluent hypergeometric function. Lorentz forces and aligned magnetic field depicts the significant effects on nanofluid. We found that, due to the increase in the aligned angle provides the enhancement in local skin friction coefficient and a reduction in the local Nusselt number. The combined impacts of inclined magnetic field with other emerging parameters such as velocity slip, thermal radiation and nanoparticles volume fraction on velocity, temperature, local Nusselt number and skin friction coefficient are examined. Flow behavior of nanofluid is also determined via stream lines pattern.

  9. By-controlled convection and field-aligned currents near midnight auroral oval for northward interplanetary magnetic field

    NASA Technical Reports Server (NTRS)

    Taguchi, S.; Sugiura, M.; Iyemori, T.; Winningham, J. D.; Slavin, J. A.

    1994-01-01

    Using the Dynamics Explorer (DE) 2 magnetic and electric field and plasma data, B(sub y)- controlled convection and field-aligned currents in the midnight sector for northward interplanetary magnetic field (IMF) are examined. The results of an analysis of the electric field data show that when IMF is stable and when its magnitude is large, a coherent B(sub y)-controlled convection exists near the midnight auroral oval in the ionosphere having adequate conductivities. When B(sub y) is negative, the convection consists of a westward (eastward) plasma flow at the lower latitudes and an eastward (westward) plasma flow at the higher latitudes in the midnight sector in the northern (southern) ionosphere. When B(sub y) is positive, the flow directions are reversed. The distribution of the field-aligned currents associated with the B(sub y)-controlled convection, in most cases, shows a three-sheet structure. In accordance with the convection the directions of the three sheets are dependent on the sign of B(sub y). The location of disappearance of the precipitating intense electrons having energies of a few keV is close to the convection reversal surface. However, the more detailed relationship between the electron precipitation boundary and the convection reversal surface depends on the case. In some cases the precipitating electrons extend beyond the convection reversal surface, and in others the poleward boundary terminates at a latitude lower than the reversal surface. Previous studies suggest that the poleward boundary of the electrons having energies of a few keV is not necessarily coincident with an open/closed bounary. Thus the open/closed boundary may be at a latitude higher than the poleward boundary of the electron precipitation, or it may be at a latitude lower than the poleward boundary of the electron precipitation. We discuss relationships between the open/closed boundary and the convection reversal surface. When as a possible choice we adopt a view that the

  10. Field-aligned current associated with a distorted two-cell convection pattern during northward interplanetary magnetic field

    NASA Technical Reports Server (NTRS)

    Zhu, L.; Schunk, R. W.; Sojka, J. J.

    1991-01-01

    The influence of the ionospheric conductance on the field-aligned current associated with a distorted two-cell convection pattern during northward IMF was investigated using the Heppner-Maynard (1987) convection model and the Utah State University conductivity model described by Rasmussen and Schunk (1987). Results show that the variation of the ionospheric conductivity distribution can significantly affect the features of the field-aligned current for northward IMF, where matching or mismatching between the conductance gradient and the convection electric field plays a key role. It was found that the increase of the field-aligned current in the polar cap observed during summer is mainly due to the increasing contribution from the Pedersen current, and that the increase of the field-aligned current in both the oval region and the evening-midnight sector during the active aurora period is mainly due to the increasing contribution from the Hall current.

  11. Euler potentials for two layers with non-constant current densities in the ambient magnetic field aligned to the layers

    NASA Astrophysics Data System (ADS)

    Vandas, Marek; Romashets, Eugene P.

    2016-12-01

    The Euler potentials for two current layers aligned to an ambient homogeneous magnetic field are found. Previous treatment of such a system assumed constant current density in the layers. However, the magnetic field becomes infinite at the edges. The new approach eliminates this inconsistency by introducing an inhomogeneous current density. Euler potentials are constructed semi-analytically for such a system. Charged-particle motion and trapping in it are examined by this representation. Using Euler potentials, the influence of current sheets of zero and non-zero thicknesses on energetic-particle fluxes is investigated, and characteristic flux variations near the sheets are presented. The results can be applied to Birkeland currents.

  12. Avoiding Tokamak Disruptions by Applying Static Magnetic Fields That Align Locked Modes with Stabilizing Wave-Driven Currents.

    PubMed

    Volpe, F A; Hyatt, A; La Haye, R J; Lanctot, M J; Lohr, J; Prater, R; Strait, E J; Welander, A

    2015-10-23

    Nonrotating ("locked") magnetic islands often lead to complete losses of confinement in tokamak plasmas, called major disruptions. Here locked islands were suppressed for the first time, by a combination of applied three-dimensional magnetic fields and injected millimeter waves. The applied fields were used to control the phase of locking and so align the island O point with the region where the injected waves generated noninductive currents. This resulted in stabilization of the locked island, disruption avoidance, recovery of high confinement, and high pressure, in accordance with the expected dependencies upon wave power and relative phase between the O point and driven current.

  13. Transparency enhancement for photoinitiated polymerization (UV curing) through magnetic field alignment in a piezoresistive metal/polymer composite.

    PubMed

    Knaapila, Matti; Høyer, Henrik; Kjelstrup-Hansen, Jakob; Helgesen, Geir

    2014-03-12

    We use a magnetic field to align nickel particles into stringlike assemblies in urethane oligomer mixtures and create a semitransparent UV-curable nickel particle/polymer composite with anisotropic electrical conductivity and piezoresistive properties. When the particles are uniformly distributed in the oligourethane matrix, the mixture is moderately conductive at higher particle fractions but becomes insulating once the fraction is below about 5 vol %. With the particle fraction below this threshold and using an external magnetic field, the particles are aligned into continuous pathways through the oligomer mixtures following the magnetic flux lines. The matrix is subsequently cured by UV light. This results in conductivity and piezoresistivity along the alignment direction, while the material is not conducting perpendicular to the alignment direction. The lower particle fraction results in a lower number of absorbers for UV light: the decrease from 5 to 1 vol % increases optical transmission from 10% to 50% in the UV/vis region. This leads to a shorter photocuring time, typically from tens of seconds to seconds for 300-μm-thick films at a wavelength of 365 nm. We propose that this concept could be applied in areas such as pressure sensors.

  14. Studies of Westward Electrojets and Field-Aligned Currents in the Magnetotail during Substorms: Implications for Magnetic Field Models

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Our studies elucidated the relationship between the auroral arcs and magnetotail phenomena. One paper examined particle energization in the source region of the field-aligned currents that intensify at substorm onset when the arc brightens to form the westward electrojet. A second paper examined the relationship between the precipitating particles in the arcs, the location of the westward electrojet, and magnetospheric source regions. Two earlier papers also investigated the roles that field aligned currents and particle acceleration have during substorms.

  15. Field-Aligned Current Reconfiguration and Magnetospheric Response to an Impulse in the Interplanetary Magnetic Field BY Component

    NASA Astrophysics Data System (ADS)

    Wilder, F. D.; Eriksson, S.; Korth, H.; Hairston, M. R.; Baker, J. B.; Heinselman, C. J.

    2013-12-01

    When the interplanetary magnetic field (IMF) is dawnward or duskward, magnetic merging between the IMF and the geomagnetic field occurs near the cusp on the dayside flanks of the magnetosphere. During these intervals, flow channels in the ionosphere with velocities in excess of 2 km/s have been observed, which can deposit large amounts of energy into the high-latitude thermosphere. In this study, we analyze an interval on 5 April 2010 where there was a strong dawnward impulse in the IMF, followed by a gradual decay in IMF magnitude at constant clock angle. Data from the Sondrestrom incoherent scatter radar and the DMSP spacecraft were used to investigate ionospheric convection during this interval, and data from the Active Magnetospheric and Planetary Electrodynamics Response Experiment (AMPERE) were used to investigate the associated Field-Aligned Current (FAC) system. Additionally, data from AMPERE were used to investigate the time response of the dawn-side FAC pair. We find there is a delay of approximately 1.25 hours between the arrival of the dawnward IMF impulse at the magnetopause and strength of the dawnward FAC pair, which is comparable to substorm growth and expansion time scales under southward IMF. Additionally, we find at the time of the peak FAC, there is evidence of a reconfiguring four-sheet FAC system in the morning local time sector of the ionosphere. Additionally, we find an inverse correlation between the dawn FAC strength and both the solar wind Alfvénic Mach number and the SYM-H index. No statistically significant correlation between the FAC strength and the solar wind dynamic pressure was found.

  16. Field-aligned current reconfiguration and magnetospheric response to an impulse in the interplanetary magnetic field BY component

    NASA Astrophysics Data System (ADS)

    Wilder, F. D.; Eriksson, S.; Korth, H.; Baker, J. B. H.; Hairston, M. R.; Heinselman, C.; Anderson, B. J.

    2013-06-01

    the interplanetary magnetic field (IMF) is dawnward or duskward, magnetic merging between the IMF and the geomagnetic field occurs near the cusp on the dayside flanks of the magnetosphere. During these intervals, flow channels in the ionosphere with velocities in excess of 2 km/s have been observed, which can deposit large amounts of energy into the high-latitude thermosphere. In this study, we analyze an interval on 5 April 2010 where there was a strong dawnward impulse in the IMF, followed by a gradual decay in IMF magnitude at constant clock angle. Data from the Sondrestrom incoherent scatter radar and the Defense Meteorological Satellite Program spacecraft were used to investigate ionospheric convection during this interval, and data from the Active Magnetospheric and Planetary Electrodynamics Response Experiment (AMPERE) were used to investigate the associated Field-Aligned Current (FAC) system. Additionally, data from AMPERE were used to investigate the time response of the dawnside FAC pair. We find there is a delay of approximately 1.25 h between the arrival of the dawnward IMF impulse at the magnetopause and strength of the dawnward FAC pair, which is comparable to substorm growth and expansion time scales under southward IMF. Additionally, we find at the time of the peak FAC, there is evidence of a reconfiguring four-sheet FAC system in the morning local time sector of the ionosphere. Additionally, we find an inverse correlation between the dawn FAC strength and both the solar wind Alfvénic Mach number and the SYM-H index. No statistically significant correlation between the FAC strength and the solar wind dynamic pressure was found.

  17. Mesoscale Magnetosphere-Ionosphere Coupling along Open Magnetic Field Lines Associated with Airglow Patches: Field-aligned Currents and Precipitation

    NASA Astrophysics Data System (ADS)

    Zou, Y.; Nishimura, Y.; Lyons, L. R.; Shiokawa, K.; Burchill, J. K.; Knudsen, D. J.; Buchert, S. C.; Chen, S.; Nicolls, M. J.; Ruohoniemi, J. M.; McWilliams, K. A.; Nishitani, N.

    2016-12-01

    Although airglow patches are traditionally regarded as high-density plasma unrelated to local field-aligned currents (FACs) and precipitation, past observations were limited to storm-time conditions. Recent non-storm time observations show patches to be associated with azimuthally narrow ionospheric fast flow channels that substantially contribute to plasma transportation across the polar cap and connect dayside and nightside explosive disturbances. We examine whether non-storm time patches are related also to localized polar cap FACs and precipitation using Swarm- and FAST-imager-radar conjunctions. In Swarm data, we commonly (66%) identify substantial magnetic perturbations indicating FAC enhancements around patches. These FACs have substantial densities (0.1-0.2 μA/m-2) and can be approximated as infinite current sheets (typically 75 km wide) orientated roughly parallel to patches. They usually exhibit a Region-1 sense, i.e. a downward FAC lying eastward of an upward FAC, and can close through Pedersen currents in the ionosphere, implying that the locally enhanced dawn-dusk electric field across the patch is imposed by processes in the magnetosphere. In FAST data, we identify localized precipitation that is enhanced within patches in comparison to weak polar rain outside patches. The precipitation consists of structured or diffuse soft electron fluxes. While the latter resembles polar rain only with higher fluxes, the former consists of discrete fluxes enhanced by 1-2 orders of magnitude from several to several hundred eV. Although the precipitation is not a major contributor to patch ionization, it implies that newly reconnected flux tubes that retain electrons of magnetosheath origin can rapidly traverse the polar cap from the dayside. Therefore non-storm time patches should be regarded as part of a localized magnetosphere-ionosphere coupling system along open magnetic field lines, and their transpolar evolution as a reflection of reconnected flux tubes

  18. Influences of the interplanetary magnetic field clock angle and cone angle on the field-aligned currents in the magnetotail

    NASA Astrophysics Data System (ADS)

    Cheng, Z. W.; Shi, J. K.; Dunlop, M.; Liu, Z. X.

    2013-10-01

    The influences of the interplanetary magnetic field (IMF) cone angle θ and clock angle ϕ on the field-aligned currents (FACs) at the plasma sheet boundary layers (PSBLs) have been investigated using Cluster Data. The FAC occurrence increases monotonically with IMF cone angle and has two peaks at -90° and +110° clock angle, respectively. The peak at +110° is distinctly larger than that at -90°. Overall, there are more FACs between 0° < ϕ < 180°, indicating that FACs occurrence is closely associated with duskward IMF. More FACs occur when 90° < |ϕ| < 180°, implying that FAC is closely associated with southward IMF. The large FAC densities occur when 60° < |ϕ| < 120°. The density also has two peaks and the peak at +90° clock angle (duskward IMF) is larger than that at -90° (dawnward IMF). These results indicate that the IMF influence on the FACs is from all IMF components and not only from a single component.

  19. The interplanetary magnetic field B sub y -dependent field-aligned current in the dayside polar cap under quiet conditions

    SciTech Connect

    Yamauchi, M. Kyoto Univ. ); Araki, T. )

    1989-03-01

    Spatial distribution and temporal variation of the interplanetary magnetic field (IMF) B{sub y}-dependent cusp region field-aligned currents (FACs) during quiet periods were studied by use of magnetic data observed by Magsat. The analysis was made for 11 events (each event lasts more than one and a half days) when the IMF B{sub y} component was steadily large and B{sub x} was relatively small ({vert bar}B{sub z}{vert bar} < {vert bar}B{sub y}{vert bar}). Results of the analysis of total 62 half-day periods for the IMF B{sub y}-dependent cusp region FAC are summarized as follows: (1) the IMF B{sub y}-dependent cusp region FAC is located at around 86{degree}-87{degree} invariant latitude local noon, which is more poleward than the location of the IMF B{sub z}-dependent cusp region FAC; (2) the current density of this FAC is greater than previous studies ({ge} 4 {mu}A/m{sup 2} for IMF B{sub y} = 6 nT); (3) there are two time scales for the IMF B{sub y}-dependent cusp region FAC to appear: the initial rise of the current is on a short time scale, {approximately} 10 min, and it is followed by a gradual increase on a time scale of several hours to a half day; (4) the seasonal change of this FAC is greater than that of the nightside region 1 or region 2 FACs; (5) the IMF B{sub z}-dependent cusp region FAC is not well observed around the cusp when the IMF B{sub y}-dependent cusp region FAC is intense.

  20. Lateral Diffusion of PEG-Lipid in Magnetically Aligned Bicelles Measured Using Stimulated Echo Pulsed Field Gradient 1H NMR

    PubMed Central

    Soong, Ronald; Macdonald, Peter M.

    2005-01-01

    Lateral diffusion measurements of PEG-lipid incorporated into magnetically aligned bicelles are demonstrated using stimulated echo (STE) pulsed field gradient (PFG) proton (1H) nuclear magnetic resonance (NMR) spectroscopy. Bicelles were composed of dimyristoyl phosphatidylcholine (DMPC) plus dihexanoyl phosphatidylcholine (DHPC) (q = DMPC/DHPC molar ratio = 4.5) plus 1 mol % (relative to DMPC) dimyristoyl phosphatidylethanolamine-N-[methoxy(polyethylene glycol)-2000] (DMPE-PEG 2000) at 25 wt % lipid. 1H NMR STE spectra of perpendicular aligned bicelles contained only resonances assigned to residual HDO and to overlapping contributions from a DMPE-PEG 2000 ethoxy headgroup plus DHPC choline methyl protons. Decay of the latter's STE intensity in the STE PFG 1H NMR experiment (gz = 244 G cm−1) yielded a DMPE-PEG 2000 (1 mol %, 35°C) lateral diffusion coefficient D = 1.35 × 10−11 m2 s−1. Hence, below the “mushroom-to-brush” transition, DMPE-PEG 2000 lateral diffusion is dictated by its DMPE hydrophobic anchor. D was independent of the diffusion time, indicating unrestricted lateral diffusion over root mean-square diffusion distances of microns, supporting the “perforated lamellae” model of bicelle structure under these conditions. Overall, the results demonstrate the feasibility of lateral diffusion measurements in magnetically aligned bicelles using the STE PFG NMR technique. PMID:15475584

  1. Lateral diffusion of PEG-Lipid in magnetically aligned bicelles measured using stimulated echo pulsed field gradient 1H NMR.

    PubMed

    Soong, Ronald; Macdonald, Peter M

    2005-01-01

    Lateral diffusion measurements of PEG-lipid incorporated into magnetically aligned bicelles are demonstrated using stimulated echo (STE) pulsed field gradient (PFG) proton (1H) nuclear magnetic resonance (NMR) spectroscopy. Bicelles were composed of dimyristoyl phosphatidylcholine (DMPC) plus dihexanoyl phosphatidylcholine (DHPC) (q = DMPC/DHPC molar ratio = 4.5) plus 1 mol % (relative to DMPC) dimyristoyl phosphatidylethanolamine-N-[methoxy(polyethylene glycol)-2000] (DMPE-PEG 2000) at 25 wt % lipid. 1H NMR STE spectra of perpendicular aligned bicelles contained only resonances assigned to residual HDO and to overlapping contributions from a DMPE-PEG 2000 ethoxy headgroup plus DHPC choline methyl protons. Decay of the latter's STE intensity in the STE PFG 1H NMR experiment (g(z) = 244 G cm(-1)) yielded a DMPE-PEG 2000 (1 mol %, 35 degrees C) lateral diffusion coefficient D = 1.35 x 10(-11) m2 s(-1). Hence, below the "mushroom-to-brush" transition, DMPE-PEG 2000 lateral diffusion is dictated by its DMPE hydrophobic anchor. D was independent of the diffusion time, indicating unrestricted lateral diffusion over root mean-square diffusion distances of microns, supporting the "perforated lamellae" model of bicelle structure under these conditions. Overall, the results demonstrate the feasibility of lateral diffusion measurements in magnetically aligned bicelles using the STE PFG NMR technique.

  2. Grain Alignment and the Magnetic Field Geometry in the Filamentary Dark Cloud GF 9

    NASA Astrophysics Data System (ADS)

    Jones, Terry Jay

    2003-06-01

    We present measurements of the interstellar polarization at 1.65 μm of stars shining through the filamentary dark cloud GF 9. Unlike many dark clouds, the interstellar polarization through GF 9 increases significantly with increasing extinction through the cloud. We find the magnetic field geometry in GF 9-core is very smooth, in agreement with results from far-infrared polarimetry by Clemens, Kraemer, & Ciardi (published in 1999). Our much more limited results for GF 9-filament are consistent with a disordered field, also in agreement with the far-infrared polarimetry. Comparison of the near-infrared and far-infrared position angles suggests that there is a moderate rotation in the projected magnetic field direction from the exterior to the interior of GF 9-core.

  3. Observation of transient alignment-inversion walls in nematics of phenyl benzoates in the presence of a magnetic field.

    PubMed

    Hinov, Hristo P; Vistin', Leonard K; Marinov, Yordan G

    2014-04-17

    Formation of new transient walls by a constant magnetic field at the Fréedericsz critical value has been observed. They are oriented along the initial alignment of the nematic phase of phenyl benzoates and appeared only in relatively thick samples with a thickness between 50 and 100 μm of the cells. The excellent planarity of the liquid crystal orientation is considered to be the most important condition for their presence These magnetic walls are transient as they disappear either after a few seconds for 100 μm thick nematic cells or after parts of a second for thinner (50 μm) nematic cells. Nonregular stable magnetic walls, incorporating disclinations with core, appear immediately after the relaxation of the transient walls, when the planarity of the nematic orientation is not perfect. In thinner nematic cells of 20 μm or less, a Fréedericksz transition has only been observed. The formation of transient magnetic walls can be described by a model taking into account alignment-inversion, twisted along Y regions. The transient walls accompanied by a system of Becke lines relax by going through three-dimensional twist-splay-bend deformations.

  4. Using AMIENext Patterns Derived from AMPERE Data to Explore Hemispheric Asymmetries in Field Aligned Currents and Magnetic Potential

    NASA Astrophysics Data System (ADS)

    Shi, Y.; Knipp, D. J.; Matsuo, T.; Anderson, B. J.

    2016-12-01

    We report on the inter-hemispheric asymmetries that develop during a quiet time period on June 14, 2011 and an active interval on May 28 2011. Magnetic potential and field-aligned currents (FACs) patterns derived from Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) data using the new AMIENext procedure (Matsuo et al, 2015), allow us to do simultaneous northern/southern hemisphere comparisons. We generate empirical orthogonal functions (EOFs) from the data to describe the primary modes of variability in magnetic potential and field-aligned currents, which helps minimize the impact of difference in data coverage resulting from relative displacement of the geomagnetic pole from geographic poles in the two hemispheres. On the quiet day we observe that when the IMF By and Bz is positive, the expected mirror symmetry in magnetic potential patterns is only partially present (Fig. a and b). More symmetry appears when Bz turns south during the middle of the day (Fig. c and d). We attribute this to seasonal conductivity difference. We also see strong cusp and region 1 current in the sunlit hemisphere while the dark hemisphere lacks clear cusp current throughout the day and lacks symmetric region 1 current for most of the day. Our preliminary result for the active days suggests strong mirror symmetry even under different sunlit conditions. We will show results for solstice and equinox to compare and contrast the hemispheric asymmetries.

  5. Examining the Electric Fields of the Evening Equatorial Ionosphere When the Solar Terminator is Aligned and Not Aligned with the Magnetic Meridian

    NASA Astrophysics Data System (ADS)

    Eccles, J. V.

    2014-12-01

    The electric field structure of the equatorial ionosphere near sunset has implications on the development of plasma irregularities. The details of the development of the electric fields are examined using a global ionosphere-electrodynamics model. The results of simulations of simplified conditions show the influence of the arrangement of the solar terminator with the magnetic meridian. The relationships of the Curl-Free mechanism, the Hall Current Divergence mechanism, and the role of the Equatorial Electorjet region control the magnitude and timing of the Prereversal Enhancement of the zonal electric field as well as its altitude profile above the F region bottomside. Realistic conditions for 'equinox' and 'solstice' solar terminator arrangments are presented. The stability of the low-latitude ionosphere has a demonstrated relationship with the solar terminator alignment [Tsunoda, JGR, 1981]. The profile of the vertical and zonal electric field below the bottomside is then examined using the global model to explore the controlling elements of the electric field structure and the growth rates of the Rayleigh-Taylor instability and Collisional Shear instability.Tsunoda, R. T. (1985), Control of the seasonal and longitudinal occurrence of equatorial scintillations by the longitudinal gradient in integrated E region Pedersen conductivity, J. Geophys. Res., 90(A1),447-456, doi:10.1029/JA090iA01p00447.

  6. Aligned magnetic field and cross-diffusion effects of a nanofluid over an exponentially stretching surface in porous medium

    NASA Astrophysics Data System (ADS)

    Sulochana, C.; Sandeep, N.; Sugunamma, V.; Rushi Kumar, B.

    2016-06-01

    In this paper, we investigated the effects of aligned magnetic field, thermal radiation, heat generation/absorption, cross-diffusion, viscous dissipation, heat source and chemical reaction on the flow of a nanofluid past an exponentially stretching sheet in porous medium. The governing partial differential equations are transformed to set of ordinary differential equations using self-similarity transformation, which are then solved numerically using bvp4c Matlab package. Finally the effects of various non-dimensional parameters on velocity, temperature, concentration, skin friction, local Nusselt and Sherwood numbers are thoroughly investigated and presented through graphs and tables. We observed that an increase in the aligned angle strengthens the applied magnetic field and decreases the velocity profiles of the flow. Soret and Dufour numbers are helpful to enhance the heat transfer rate. An increase in the heat source parameter, radiation parameter and Eckert number increases the mass transfer rate. Mixed convection parameter has tendency to enhance the friction factor along with the heat and mass transfer rate.

  7. Interplay of dust alignment, grain growth, and magnetic fields in polarization: lessons from the emission-to-extinction ratio

    NASA Astrophysics Data System (ADS)

    Fanciullo, L.; Guillet, V.; Boulanger, F.; Jones, A. P.

    2017-06-01

    Context. Polarized extinction and emission from dust in the interstellar medium (ISM) are hard to interpret, as their dependence on dust optical properties, grain alignment, and magnetic field orientation is complex. This is particularly true in molecular clouds. The aforementioned phenomena are usually considered independently in polarization studies, while it is likely that they all contribute and their effects have yet to be disentangled. Aims: The data available today are not yet used to their full potential. The combination of emission and extinction, in particular, provides information not available from either of them alone. We combine data from the scientific literature on polarized dust extinction with Planck data on polarized emission, and we use them to constrain the possible variations in dust and environmental conditions inside molecular clouds, and especially translucent lines of sight, taking the magnetic field orientation into account. Methods: We focused on the dependence between λmax (the wavelength of maximum polarization in extinction) and other observables such as the extinction polarization, the emission polarization, and the ratio between the two. We set out to reproduce these correlations using Monte Carlo simulations in which we varied the relevant quantities in a dust model, which are grain alignment, size distribution, and magnetic field orientation, to mimic the diverse conditions that are expected inside molecular clouds. Results: None of the quantities we chose can explain the observational data on their own: the best results are obtained when all quantities vary significantly across and within clouds. However, some of the data, most notably the stars with a low ratio of polarization in emission to polarization in extinction, are not reproduced by our simulation. Conclusions: Our results suggest not only that dust evolution is necessary to explain polarization in molecular clouds, but that a simple change in size distribution is not

  8. Does the Earth's Magnetic Field Serve as a Reference for Alignment of the Honeybee Waggle Dance?

    PubMed Central

    Lambinet, Veronika; Hayden, Michael E.; Bieri, Marco; Gries, Gerhard

    2014-01-01

    The honeybee (Apis mellifera) waggle dance, which is performed inside the hive by forager bees, informs hive mates about a potent food source, and recruits them to its location. It consists of a repeated figure-8 pattern: two oppositely directed turns interspersed by a short straight segment, the “waggle run”. The waggle run consists of a single stride emphasized by lateral waggling motions of the abdomen. Directional information pointing to a food source relative to the sun's azimuth is encoded in the angle between the waggle run line and a reference line, which is generally thought to be established by gravity. Yet, there is tantalizing evidence that the local (ambient) geomagnetic field (LGMF) could play a role. We tested the effect of the LGMF on the recruitment success of forager bees by placing observation hives inside large Helmholtz coils, and then either reducing the LGMF to 2% or shifting its apparent declination. Neither of these treatments reduced the number of nest mates that waggle dancing forager bees recruited to a feeding station located 200 m north of the hive. These results indicate that the LGMF does not act as the reference for the alignment of waggle-dancing bees. PMID:25541731

  9. Does the Earth's magnetic field serve as a reference for alignment of the honeybee Waggle dance?

    PubMed

    Lambinet, Veronika; Hayden, Michael E; Bieri, Marco; Gries, Gerhard

    2014-01-01

    The honeybee (Apis mellifera) waggle dance, which is performed inside the hive by forager bees, informs hive mates about a potent food source, and recruits them to its location. It consists of a repeated figure-8 pattern: two oppositely directed turns interspersed by a short straight segment, the "waggle run". The waggle run consists of a single stride emphasized by lateral waggling motions of the abdomen. Directional information pointing to a food source relative to the sun's azimuth is encoded in the angle between the waggle run line and a reference line, which is generally thought to be established by gravity. Yet, there is tantalizing evidence that the local (ambient) geomagnetic field (LGMF) could play a role. We tested the effect of the LGMF on the recruitment success of forager bees by placing observation hives inside large Helmholtz coils, and then either reducing the LGMF to 2% or shifting its apparent declination. Neither of these treatments reduced the number of nest mates that waggle dancing forager bees recruited to a feeding station located 200 m north of the hive. These results indicate that the LGMF does not act as the reference for the alignment of waggle-dancing bees.

  10. A comparison of small-scale magnetic fluctuations in the Region 1 and 2 field-aligned current systems

    NASA Astrophysics Data System (ADS)

    Wu, J.; Bryant, M. S.; Ridley, C. G.; Shen, Y.; Yang, L.; Clausen, L. B. N.; McWilliams, K. A.; Murphy, K. R.; Mann, I. R.; Ozeke, L. G.; Korth, H.; Anderson, B. J.; Waters, C. L.

    2017-03-01

    By determining the location and size of the Region 1 (R1) and Region 2 (R2) large-scale field-aligned currents (FACs) from Active Magnetosphere and Planetary Electrodynamics Response Experiment data, we are able to study the small-scale magnetic fluctuations observed by the Swarm satellites embedded within the large-scale FACs. A statistical comparison of R1 and R2 high-frequency fluctuations is presented in terms of different solar wind conditions and geomagnetic activities. We find that (1) the amplitude of high-frequency fluctuations in both R1 and R2 increases as the large-scale R1 and R2 FACs intensify; (2) high-frequency fluctuations in R1 peak near dayside dawn and dusk, while those in R2 peak around noon; (3) the location of the largest high-frequency fluctuations in R1 shifts in local time in response to IMF By, indicating a connection between the R1 fluctuation and the driving solar wind most likely explained by magnetic reconnection; and (4) high-frequency fluctuations in R2 are enhanced in a small region near local noon and respond clearly to nightside drivers, as characterized by the auroral electrojet index. Our analysis shows that the intensity of R1 and R2 high-frequency magnetic fluctuations is directly connected to the intensity of FACs, which implies that the magnetic fluctuations are closely related to the magnetospheric processes that drive them.

  11. Energetic particle signatures of magnetic field-aligned potentials over Jupiter's polar regions

    NASA Astrophysics Data System (ADS)

    Clark, G.; Mauk, B. H.; Haggerty, D.; Paranicas, C.; Kollmann, P.; Rymer, A.; Bunce, E. J.; Cowley, S. W. H.; Mitchell, D. G.; Provan, G.; Ebert, R. W.; Allegrini, F.; Bagenal, F.; Bolton, S.; Connerney, J.; Kotsiaros, S.; Kurth, W. S.; Levin, S.; McComas, D. J.; Saur, J.; Valek, P.

    2017-09-01

    Recent results of the first ever orbit through Jupiter's auroral region by NASA's Juno spacecraft did not show evidence of coherent acceleration in the auroral or polar region. However, in this letter, we show energetic particle data from Juno's Jupiter Energetic-particle Detector Instrument instrument during the third auroral pass that exhibits conclusive evidence of downward parallel electric fields in portions of Jupiter's polar region. The energetic particle distributions show inverted-V ion and electron structures in a downward electric current region with accelerated peaked distributions in hundreds of keV to 1 MeV range. The origin of these large electric potential structures is investigated and discussed within the current theoretical framework of current-voltage relationships at both Earth and Jupiter. Parallel electric fields responsible for accelerating particles to maintain the aurora/magnetospheric circuit appear to be a common phenomenon among strongly magnetized planets with conducting ionospheres; however, their origin and generation mechanisms are subjects of ongoing research.

  12. Differential Heating of Magnetically Aligned Dust Grains

    NASA Astrophysics Data System (ADS)

    Vaillancourt, John E.; Andersson, B.

    2013-01-01

    We use far-infrared photometric maps from IRAS and Herschel to search for the differential heating of asymmetric dust grains aligned with respect to an interstellar magnetic field and heated by a localized radiation source. The grains are known to be asymmetric and have a net alignment of their axes from observations of background starlight polarization. Modern theories on grain alignment suggest that photons from stars embedded in the foreground cloud are a key ingredient of the physical mechanism responsible for alignment (i.e., radiative torques). This theory predicts a relation between the grain alignment efficiency and the angle between the magnetic field and the direction to the aligning radiation source. This effect has been tentatively observed in a source with a very simple geometry (Andersson et al. 2011): the aligning photons are primarily from a single localized source (i.e., a single star) and the local magnetic field direction is known to be fairly uniform. Such a region also has consequences for the distribution of grain heating. For example, asymmetric grains whose largest cross-sections are normal to the incident stellar radiation will reach warmer equilibrium temperatures compared to grains whose largest cross-section is parallel to that direction. This should be observed as an azimuthal dependence of the dust color temperature. We present evidence of such a dependence using IRAS data at 60 and 100 micron. We expect this effect to be stronger using longer wavelength (i.e., 160 micron) data better coupled to the "big-grain" dust population, grains which are also more efficiently aligned with the local magnetic field. Here we also present the results of our on-going work to search for this signal using Herschel maps towards three candidate stars.

  13. Time-Aligned Averaging and Comparison of Low Frequency Magnetic Fields Produced by In-Cloud Lightning Discharges

    NASA Astrophysics Data System (ADS)

    Weinert, J. L.; Cummer, S. A.

    2016-12-01

    Time-aligned epoch averaging is a powerful tool for analyzing small-magnitude features of similar lightning events which would normally be below the sensor operational noise levels. Through averaging, the noise level of the averaged signal decreases as the square root of the number of events. Previous work has demonstrated the value of averaging on magnetic field emissions from cloud-to-ground events, with a reduction from a single-event noise level of roughly 30 picotesla to an averaged noise level of only 40 femtotesla. Noise levels at this point allow for the detection of averaged lightning currents of just a few tens of amps at a distance of 1000 kilometers, making clear the charge motion and current in even relatively weak processes such as downward leader motion and continuing current in negative CG flashes. In this work, we apply time-aligned averaging procedures to a range of in-cloud (IC) flashes and processes in an effort to reveal fine details involved in events including narrow bipolar events, upward IC leaders, terrestrial gamma flashes, and others.

  14. Magnetic-Field-Aligned Characteristics of Plasma Bubbles in the Nighttime Equatorial Ionosphere.

    DTIC Science & Technology

    1979-07-01

    The best evidence published to date is that of Dyson and Benson [19781. Using topside ionograms taken from Alouette II and ISIS I satellites, they...inferred the existence of depleted magnetic flux tubes in the equatorial ionosphere by interpreting anomalous ionogram traces in terms of high-frequency

  15. The fabrication of single-walled carbon nanotube/polyelectrolyte multilayer composites by layer-by-layer assembly and magnetic field assisted alignment

    NASA Astrophysics Data System (ADS)

    Tian, Ying; Park, Jin Gyu; Cheng, Qunfeng; Liang, Zhiyong; Zhang, Chuck; Wang, Ben

    2009-08-01

    Single-walled carbon nanotube (SWNT)/polymer composites are widely studied because of their potential for high mechanical performance and multifunctional applications. In order to realize highly ordered multilayer nanostructures, we combined the layer-by-layer (LBL) assembly method with magnetic force-induced alignment to fabricate SWNT/poly(ethylamine) (PEI) multilayer composites. The SWNTs were functionalized with the anionic surfactant sodium dodecylbenzenesulfonate (NaDDBS) to realize negative charge at pH>7, while the PEI is positively charged at pH<7. The LBL method is based on the electrostatic absorption between the charged SWNTs and PEI resin to form multilayer composites on a solid substrate polydimethylsiloxane. Since the fabricated thickness of each SWNT-NaDDBS/PEI bilayer is uniform (~150 nm), the multilayer film thickness can be strictly controlled via the number of deposition cycles. A high magnetic field (8.5 Tesla) was used to align the SWNTs during the LBL process. The resultant LBL composite samples demonstrated high SWNT loading of approximately 50 wt% and uniform distribution of SWNTs in the multilayer structures, which was verified using a quartz crystal microbalance. Good alignment was also realized and observed through using high magnetic fields to align the nanotubes during the LBL deposition process. The results indicate that the LBL/magnetic alignment approach has potential for fabricating nanotube composites with highly ordered nanostructures for multifunctional materials and device applications.

  16. Ion-temperature-gradient sensitivity of the hydrodynamic instability caused by shear in the magnetic-field-aligned plasma flow

    SciTech Connect

    Mikhailenko, V. V.; Mikhailenko, V. S.; Lee, Hae June; Koepke, M. E.

    2014-07-15

    The cross-magnetic-field (i.e., perpendicular) profile of ion temperature and the perpendicular profile of the magnetic-field-aligned (parallel) plasma flow are sometimes inhomogeneous for space and laboratory plasma. Instability caused either by a gradient in the ion-temperature profile or by shear in the parallel flow has been discussed extensively in the literature. In this paper, (1) hydrodynamic plasma stability is investigated, (2) real and imaginary frequency are quantified over a range of the shear parameter, the normalized wavenumber, and the ratio of density-gradient and ion-temperature-gradient scale lengths, and (3) the role of inverse Landau damping is illustrated for the case of combined ion-temperature gradient and parallel-flow shear. We find that increasing the ion-temperature gradient reduces the instability threshold for the hydrodynamic parallel-flow shear instability, also known as the parallel Kelvin-Helmholtz instability or the D'Angelo instability. We also find that a kinetic instability arises from the coupled, reinforcing action of both free-energy sources. For the case of comparable electron and ion temperature, we illustrate analytically the transition of the D'Angelo instability to the kinetic instability as (a) the shear parameter, (b) the normalized wavenumber, and (c) the ratio of density-gradient and ion-temperature-gradient scale lengths are varied and we attribute the changes in stability to changes in the amount of inverse ion Landau damping. We show that near a normalized wavenumber k{sub ⊥}ρ{sub i} of order unity (i) the real and imaginary values of frequency become comparable and (ii) the imaginary frequency, i.e., the growth rate, peaks.

  17. Measurement of magnetic field aligned potential differences using high resolution conjugate photoelectron energy spectra

    NASA Technical Reports Server (NTRS)

    Peterson, W. K.; Doering, J. P.; Potemra, T. A.; Bostrom, C. O.; Brace, L. H.; Heelis, R. A.; Hanson, W. B.

    1977-01-01

    Simultaneous high-resolution observations of a distinctive feature in the energy spectrum of conjugate photoelectrons and spacecraft potential relative to the local ionosphere have allowed the net potential difference between magnetic conjugate points at latitudes below the region of low-energy (i.e., lower than 100 eV) auroral electron precipitation to be determined. Measurements made at 300 km from Atmosphere Explorer C show that there is normally no net potential difference between hemispheres in this region, which extended up to invariant latitudes as high as 74 deg. Two types of apparently related anomalous behavior were infrequently observed at high latitudes. During these periods the incident flux of conjugate photoelectrons was either decelerated by about 3 eV or was not detected.

  18. Renormalized theory of ion temperature gradient instability of the magnetic-field-aligned plasma shear flow with hot ions

    SciTech Connect

    Mikhailenko, V. V. Mikhailenko, V. S.; Lee, Hae June

    2015-10-15

    The developed kinetic theory for the stability of a magnetic-field-aligned (parallel) shear flow with inhomogeneous ion temperature [Mikhailenko et al., Phys. Plasmas 21, 072117 (2014)] predicted that a kinetic instability arises from the coupled reinforcing action of the flow velocity shear and ion temperature gradient in the cases where comparable ion and electron temperatures exist. In the present paper, the nonlinear theory was developed for the instability caused by the combined effects of ion-temperature-gradient and shear-flow (ITG–SF). The level of the electrostatic turbulence is determined for the saturation state of the instability on the basis of the nonlinear dispersion equation, which accounts for a nonlinear scattering of ions by the developed turbulence in a sheared flow. The renormalized quasilinear equation for the ion distribution function, which accounts for the turbulent scattering of ions by ITG–SF driven turbulence, was derived and employed for the estimation of the turbulent ion viscosity, the anomalous ion thermal conductivity, and anomalous ion heating rate at the saturation state of the instability.

  19. Contribution of Field-Aligned Currents to the Variations of Mid-Latitude Magnetic Field on the Ground: Dayside and Nightside are Compared.

    NASA Astrophysics Data System (ADS)

    Dubyagin, S.; Ganushkina, N. Y.

    2015-12-01

    Field-aligned currents (FACs) are believed to be the main contributors to the asymmetric variation of the magnetic field on the ground at mid-latitudes during geomagnetic storms. However, the contribution from the ionospheric currents can interfere with that from FACs on the dayside where ionospheric conductivity is higher and not concentrated along the auroral oval. We present the results of the comparison of the contribution from the large-scale FAC system with the observations at the mid-latitude observatories during 12 geomagnetic storms. The contribution from the FAC system is estimated using the 10 min resolution data of AMPERE system which provides 2D map of the FAC flowing in and out of the ionosphere reconstructed from the measurements onboard of ~70 Irridium satellites . To estimate the magnetic effect of FAC system, we performed Biot-Savart integration of these currents along IGRF field from the equator to the earth center. Although in reality the FACs close via ionosphere, we generally obtain a good quantitative agreement with observations at the ground observatories on the nighside. On the other hand the agreement is much worse on the dayside. The correlation coefficient between the D-component of the magnetic field measured on the ground and that computed using Biot-Savart integration varies between ~0.65 (21-03h MLT) and < 0.1 (12-18h MLT). In addition, we discuss the closure paths of the large scale FACs during storm periods and the sources of the north-south asymmetry of the ground magnetic field at mid-latitudes.

  20. The interplanetary magnetic field B[sub y] effects on large-scale field-aligned currents near local noon: Contributions from cusp part and noncusp part

    SciTech Connect

    Yamauchi, M.; Lundin, R.; Woch, J. )

    1993-04-01

    latitudinals develop a model to account for the effect of the interplanetary magnetic field (IMF) B[sub y] component on the dayside field-aligned currents (FACs). As part of the model the FACs are divided into a [open quotes]cusp part[close quotes] and a [open quotes]noncusp part[close quotes]. The authors then propose that the cusp part FACs shift in the longitudinal direction while the noncusplike part FACs shift in both longitudinal and latitudinal directions in response to the y component of the IMF. If combined, it is observed that the noncusp part FAC is found poleward of the cusp part FAC system when the y component of the IMF is large. These two FAC systems flow in the same direction. They reinforce one another, creating a strong FAC, termed the DPY-FAC. The model also predicts that the polewardmost part of the DPY-FAC flows on closed field lines, even in regions conventionally occupied by the polar cap. Results of the model are successfully compared with particle and magnetic field data from Viking missions.

  1. Studies of Westward Electrojets and Field-Aligned Currents in the Magnetotail During Substorms: Implications for Magnetic Field Models

    NASA Technical Reports Server (NTRS)

    Spence, Harlan E.

    1996-01-01

    This section outlines those tasks undertaken in the final year that contribute integrally to the overarching project goals. Fast, during the final year, it is important to note that the project benefited greatly with the addition of a Boston University graduate student, Ms. Karen Hirsch. Jointly, we made substantial progress on the development of and improvements to magnetotail magnetic field and plasma models. The ultimate aim of this specific task was to assess critically the utility of such models for mapping low-altitude phenomena into the magnetotail (and vice-versa). The bulk of this effort centered around the finite-width- magnetotail convection model developed by and described by Spence and Kivelson (J. Geophys. Res., 98, 15,487, 1993). This analytic, theoretical model specifies the bulk plasma characteristics of the magnetotail plasma sheet (number density, temperature, pressure) across the full width of the tail from the inner edge of the plasma sheet to lunar distances. Model outputs are specified by boundary conditions of the source particle populations as well as the magnetic and electric field configuration. During the reporting period, we modified this code such that it can be interfaced with the auroral particle precipitation model developed by Dr. Terry Onsager. Together, our models provide a simple analytic specification of the equatorial distribution of fields and plasma along with their low-altitude consequences. Specifically, we have built a simple, yet powerful tool which allows us to indirectly 'map' auroral precipitation signatures (VDIS, inverted-V's, etc.) measured by polar orbiting spacecraft in the ionosphere, to the magnetospheric equatorial plane. The combined models allow us to associate latitudinal gradients measured in the ion energy fluxes at low-altitudes with the large-scale pressure gradients in the equatorial plane. Given this global, quasi-static association, we can then make fairly strong statements regarding the location of

  2. Designing an optimum pulsed magnetic field by a resistance/self-inductance/capacitance discharge system and alignment of carbon nanotubes embedded in polypyrrole matrix.

    PubMed

    Kazemikia, Kaveh; Bonabi, Fahimeh; Asadpoorchallo, Ali; Shokrzadeh, Majid

    2015-02-01

    In this work, an optimized pulsed magnetic field production apparatus is designed based on a RLC (Resistance/Self-inductance/Capacitance) discharge circuit. An algorithm for designing an optimum magnetic coil is presented. The coil is designed to work at room temperature. With a minor physical reinforcement, the magnetic flux density can be set up to 12 Tesla with 2 ms duration time. In our design process, the magnitude and the length of the magnetic pulse are the desired parameters. The magnetic field magnitude in the RLC circuit is maximized on the basis of the optimal design of the coil. The variables which are used in the optimization process are wire diameter and the number of coil layers. The coil design ensures the critically damped response of the RLC circuit. The electrical, mechanical, and thermal constraints are applied to the design process. A locus of probable magnetic flux density values versus wire diameter and coil layer is provided to locate the optimum coil parameters. Another locus of magnetic flux density values versus capacitance and initial voltage of the RLC circuit is extracted to locate the optimum circuit parameters. Finally, the application of high magnetic fields on carbon nanotube-PolyPyrrole (CNT-PPy) nano-composite is presented. Scanning probe microscopy technique is used to observe the orientation of CNTs after exposure to a magnetic field. The result shows alignment of CNTs in a 10.3 Tesla, 1.5 ms magnetic pulse.

  3. Micromagnet structures for magnetic positioning and alignment

    NASA Astrophysics Data System (ADS)

    Zanini, L. F.; Osman, O.; Frenea-Robin, M.; Haddour, N.; Dempsey, N. M.; Reyne, G.; Dumas-Bouchiat, F.

    2012-04-01

    High performance hard magnetic films (NdFeB, SmCo) have been patterned at the micron scale using thermo-magnetic patterning. Both out-of-plane and in-plane magnetized structures have been prepared. These micromagnet arrays have been used for the precise positioning and alignment of superparamagnetic nano- and microparticles. The specific spatial arrangement achieved is shown to depend on both the particle size and the size and orientation of the micromagnets. These micromagnet arrays were used to trap cells magnetically functionalized by endocytosis of 100 nm superparamagnetic particles. These simple, compact, and autonomous structures, which need neither an external magnetic field source nor a power supply, have much potential for use in a wide range of biological applications.

  4. Magnetic alignment and the Poisson alignment reference system

    NASA Astrophysics Data System (ADS)

    Griffith, L. V.; Schenz, R. F.; Sommargren, G. E.

    1990-08-01

    Three distinct metrological operations are necessary to align a free-electron laser (FEL): the magnetic axis must be located, a straight line reference (SLR) must be generated, and the magnetic axis must be related to the SLR. This article begins with a review of the motivation for developing an alignment system that will assure better than 100-μm accuracy in the alignment of the magnetic axis throughout an FEL. The 100-μm accuracy is an error circle about an ideal axis for 300 m or more. The article describes techniques for identifying the magnetic axes of solenoids, quadrupoles, and wiggler poles. Propagation of a laser beam is described to the extent of revealing sources of nonlinearity in the beam. Development of a straight-line reference based on the Poisson line, a diffraction effect, is described in detail. Spheres in a large-diameter laser beam create Poisson lines and thus provide a necessary mechanism for gauging between the magnetic axis and the SLR. Procedures for installing FEL components and calibrating alignment fiducials to the magnetic axes of the components are also described. The Poisson alignment reference system should be accurate to 25 μm over 300 m, which is believed to be a factor-of-4 improvement over earlier techniques. An error budget shows that only 25% of the total budgeted tolerance is used for the alignment reference system, so the remaining tolerances should fall within the allowable range for FEL alignment.

  5. Aligned magnetic field of two-phase mixed convection flow in dusty Casson fluid over a stretching sheet with Newtonian heating

    NASA Astrophysics Data System (ADS)

    Arifin, N. S.; Zokri, S. M.; Kasim, A. R. M.; Salleh, M. Z.; Mohammad, N. F.; Yusoff, W. N. S. W.

    2017-09-01

    The effect of aligned magnetic field is numerically investigated for mixed convection flow of dusty Casson fluid over a stretching sheet. The governing equations of flow and heat transfer for the two-phase model (fluid and dust) with an appropriate thermal boundary condition which is Newtonian heating (NH) is presented. The similarity transformation is employed to transform the nonlinear governing equations for each phase into the ordinary differential equations which then solved numerically using Runge-Kutta Fehlberg (RKF45) method. Numerical solutions obtained for velocity and temperature distributions are illustrated through graph by varying several physical parameters. It is observed that the fluid velocity decreases with an increase in aligned magnetic field and particle-fluid interaction parameter.

  6. A self-consistent two-dimensional resistive fluid theory of field-aligned potential structures including charge separation and magnetic and velocity shear

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Birn, Joachim; Schindler, Karl

    1990-01-01

    A self-consistent two-fluid theory that includes the magnetic field and shear patterns is developed to model stationary electrostatic structures with field-aligned potential drops. Shear flow is also included in the theory since this seems to be a prominent feature of the structures of interest. In addition, Ohmic dissipation, a Hall term, and pressure gradients in a generalized Ohm's law, modified for cases without quasi-neutrality, are included. In the analytic theory, the electrostatic force is balanced by field-aligned pressure gradients (i.e., thermal effects in the direction of the magnetic field) and by pressure gradients and magnetic stresses in the perpendicular direction. Within this theory, simple examples of applications are presented to demonstrate the kind of solutions resulting from the model. The results show how the effects of charge separation and shear in the magnetic field and the velocity can be combined to form self-consistent structures such as are found to exist above the aurora, suggested also in association with solar flares.

  7. Magnetic axis alignment and the Poisson alignment reference system

    NASA Astrophysics Data System (ADS)

    Griffith, Lee V.; Schenz, Richard F.; Sommargren, Gary E.

    1989-01-01

    Three distinct metrological operations are necessary to align a free-electron laser (FEL): the magnetic axis must be located, a straight line reference (SLR) must be generated, and the magnetic axis must be related to the SLR. This paper begins with a review of the motivation for developing an alignment system that will assure better than 100 micrometer accuracy in the alignment of the magnetic axis throughout an FEL. The paper describes techniques for identifying the magnetic axis of solenoids, quadrupoles, and wiggler poles. Propagation of a laser beam is described to the extent of revealing sources of nonlinearity in the beam. Development and use of the Poisson line, a diffraction effect, is described in detail. Spheres in a large-diameter laser beam create Poisson lines and thus provide a necessary mechanism for gauging between the magnetic axis and the SLR. Procedures for installing FEL components and calibrating alignment fiducials to the magnetic axes of the components are also described. An error budget shows that the Poisson alignment reference system will make it possible to meet the alignment tolerances for an FEL.

  8. Simultaneous particle and field observations of field-aligned currents

    NASA Technical Reports Server (NTRS)

    Berko, F. W.; Hoffman, R. A.; Burton, R. K.; Holzer, R. E.

    1973-01-01

    Simultaneous measurements of low energy precipitating electrons and magnetic fluctuations from the low altitude polar orbiting satellite OGO-4 have been compared. Analysis of the two sets of experimental data for isolated events led to the classification of high latitude field-aligned currents as purely temporal or purely spatial variations. Magnetic field disturbances calculated using these simple current models and the measured particle fluxes were in good agreement with measured field values. While fluxes of greater than 1 keV electrons are detected primarily on the nightside, magnetometer disturbances indicative of field-aligned currents were seen at all local times, both in the visual auroral regions and dayside polar cusp. Thus electrons with energies less than approximately 1 keV are the prime charge carriers in high latitude dayside field-aligned currents. The satellite measurements are in good agreement with previously measured field-aligned current values and with values predicted from several models involving magnetospheric field-aligned currents.

  9. Studies on in situ magnetic alignment of bonded anisotropic Nd-Fe-B alloy powders

    DOE PAGES

    Nlebedim, I. C.; Ucar, Huseyin; Hatter, Christine B.; ...

    2016-08-30

    We presented some considerations for achieving high degree of alignment in polymer bonded permanent magnets via the results of a study on in situ magnetic alignment of anisotropic Nd-Fe-B magnet powders. Contributions from effect of the alignment temperature, alignment magnetic field and the properties of the polymer on the hard magnetic properties of the bonded magnet were considered. Moreover, the thermo-rheological properties of the polymer and the response of the magnet powders to the applied magnetic field indicate that hard magnetic properties were optimized at an alignment temperature just above the melting temperature of the EVA co-polymer. This agrees withmore » an observed correlation between the change in magnetization due to improved magnetic alignment of the anisotropic powders and the change in viscosity of the binder. Finally, manufacturing cost can be minimized by identifying optimum alignment temperatures and magnetic field strengths.« less

  10. Studies on in situ magnetic alignment of bonded anisotropic Nd-Fe-B alloy powders

    NASA Astrophysics Data System (ADS)

    Nlebedim, I. C.; Ucar, Huseyin; Hatter, Christine B.; McCallum, R. W.; McCall, Scott K.; Kramer, M. J.; Paranthaman, M. Parans

    2017-01-01

    Considerations for achieving high degree of alignment in polymer bonded permanent magnets are presented via the results of a study on in situ magnetic alignment of anisotropic Nd-Fe-B magnet powders. Contributions from effect of the alignment temperature, alignment magnetic field and the properties of the polymer on the hard magnetic properties of the bonded magnet were considered. The thermo-rheological properties of the polymer and the response of the magnet powders to the applied magnetic field indicate that hard magnetic properties were optimized at an alignment temperature just above the melting temperature of the EVA co-polymer. This agrees with an observed correlation between the change in magnetization due to improved magnetic alignment of the anisotropic powders and the change in viscosity of the binder. Manufacturing cost can be minimized by identifying optimum alignment temperatures and magnetic field strengths.

  11. Studies on in situ magnetic alignment of bonded anisotropic Nd-Fe-B alloy powders

    SciTech Connect

    Nlebedim, I. C.; Ucar, Huseyin; Hatter, Christine B.; McCallum, R. W.; McCall, Scott K.; Kramer, M. J.; Paranthaman, M. Parans

    2016-08-30

    We presented some considerations for achieving high degree of alignment in polymer bonded permanent magnets via the results of a study on in situ magnetic alignment of anisotropic Nd-Fe-B magnet powders. Contributions from effect of the alignment temperature, alignment magnetic field and the properties of the polymer on the hard magnetic properties of the bonded magnet were considered. Moreover, the thermo-rheological properties of the polymer and the response of the magnet powders to the applied magnetic field indicate that hard magnetic properties were optimized at an alignment temperature just above the melting temperature of the EVA co-polymer. This agrees with an observed correlation between the change in magnetization due to improved magnetic alignment of the anisotropic powders and the change in viscosity of the binder. Finally, manufacturing cost can be minimized by identifying optimum alignment temperatures and magnetic field strengths.

  12. Studies on in situ magnetic alignment of bonded anisotropic Nd-Fe-B alloy powders

    SciTech Connect

    Nlebedim, I. C.; Ucar, Huseyin; Hatter, Christine B.; McCallum, R. W.; McCall, Scott K.; Kramer, M. J.; Paranthaman, M. Parans

    2016-08-30

    We presented some considerations for achieving high degree of alignment in polymer bonded permanent magnets via the results of a study on in situ magnetic alignment of anisotropic Nd-Fe-B magnet powders. Contributions from effect of the alignment temperature, alignment magnetic field and the properties of the polymer on the hard magnetic properties of the bonded magnet were considered. Moreover, the thermo-rheological properties of the polymer and the response of the magnet powders to the applied magnetic field indicate that hard magnetic properties were optimized at an alignment temperature just above the melting temperature of the EVA co-polymer. This agrees with an observed correlation between the change in magnetization due to improved magnetic alignment of the anisotropic powders and the change in viscosity of the binder. Finally, manufacturing cost can be minimized by identifying optimum alignment temperatures and magnetic field strengths.

  13. Studies on in situ magnetic alignment of bonded anisotropic Nd-Fe-B alloy powders

    DOE PAGES

    Nlebedim, I. C.; Ucar, Huseyin; Hatter, Christine B.; ...

    2016-08-30

    We presented some considerations for achieving high degree of alignment in polymer bonded permanent magnets via the results of a study on in situ magnetic alignment of anisotropic Nd-Fe-B magnet powders. Contributions from effect of the alignment temperature, alignment magnetic field and the properties of the polymer on the hard magnetic properties of the bonded magnet were considered. Moreover, the thermo-rheological properties of the polymer and the response of the magnet powders to the applied magnetic field indicate that hard magnetic properties were optimized at an alignment temperature just above the melting temperature of the EVA co-polymer. This agrees withmore » an observed correlation between the change in magnetization due to improved magnetic alignment of the anisotropic powders and the change in viscosity of the binder. Finally, manufacturing cost can be minimized by identifying optimum alignment temperatures and magnetic field strengths.« less

  14. Thermal characterization of magnetically aligned carbonyl iron/agar composites.

    PubMed

    Diaz-Bleis, D; Vales-Pinzón, C; Freile-Pelegrín, Y; Alvarado-Gil, J J

    2014-01-01

    Composites of magnetic particles into polymeric matrices have received increasing research interest due to their capacity to respond to external magnetic or electromagnetic fields. In this study, agar from Gelidium robustum has been chosen as natural biocompatible polymer to build the matrix of the magnetic carbonyl iron particles (CIP) for their uses in biomedical fields. Heat transfer behavior of the CIP-agar composites containing different concentrations (5, 10, 15, 20, 25 and 30% w/w) of magnetically aligned and non-aligned CIP in the agar matrix was studied using photothermal radiometry (PTR) in the back-propagation emission configuration. The morphology of the CIP-agar composites with aligned and non-aligned CIP under magnetic field was also evaluated by scanning electron microscopy (SEM). The results revealed a dominant effect of CIP concentration over the alignment patterns induced by the magnetic field, which agrees with the behavior of the thermal diffusivity and thermal conductivity. Agar served as a perfect matrix to be used with CIP, and CIP-agar composites magnetically aligned at 20% CIP concentration can be considered as promising 'smart' material for hyperthermia treatments in the biomedical field. Copyright © 2013 Elsevier Ltd. All rights reserved.

  15. Magnetic Fractionation and Alignment of Single Wall Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Islam, M. F.; Milkie, D. E.; Yodh, A. G.; Kikkawa, J. M.

    2004-03-01

    We study mechanisms of single wall carbon nanotube (SWNT) alignment in a magnetic field. Through magnetic fractionation, we create SWNT suspensions with varying quantities of magnetic catalyst particles. The degree of tube alignment in magnetic fields up to 9 Tesla is quantified using polarized optical absorbance anisotropy. Continuous measurements of the nematic order parameter of these suspensions in variable magnetic fields provides a way to identify the origin of magnetic torques giving rise to nanotube alignment. Initial data suggests a transition from catalyst-driven to nanotube-anisotropy driven orientation as the catalyst fraction is reduced. We relate these results to observations of nanotube aggregation. This work has been supported by NSF through DMR-0203378, DMR-079909 and DGE-0221664, NASA through NAG8-2172, DARPA/ONR through N00014-01-1-0831, and SENS.

  16. Spontaneous magnetic alignment behaviour in free-living lizards

    NASA Astrophysics Data System (ADS)

    Diego-Rasilla, Francisco J.; Pérez-Mellado, Valentín; Pérez-Cembranos, Ana

    2017-04-01

    Several species of vertebrates exhibit spontaneous longitudinal body axis alignment relative to the Earth's magnetic field (i.e., magnetic alignment) while they are performing different behavioural tasks. Since magnetoreception is still not fully understood, studying magnetic alignment provides evidence for magnetoreception and broadens current knowledge of magnetic sense in animals. Furthermore, magnetic alignment widens the roles of magnetic sensitivity in animals and may contribute to shed new light on magnetoreception. In this context, spontaneous alignment in two species of lacertid lizards ( Podarcis muralis and Podarcis lilfordi) during basking periods was monitored. Alignments in 255 P. muralis and 456 P. lilfordi were measured over a 5-year period. The possible influence of the sun's position (i.e., altitude and azimuth) and geomagnetic field values corresponding to the moment in which a particular lizard was observed on lizards' body axis orientation was evaluated. Both species exhibited a highly significant bimodal orientation along the north-northeast and south-southwest magnetic axis. The evidence from this study suggests that free-living lacertid lizards exhibit magnetic alignment behaviour, since their body alignments cannot be explained by an effect of the sun's position. On the contrary, lizard orientations were significantly correlated with geomagnetic field values at the time of each observation. We suggest that this behaviour might provide lizards with a constant directional reference while they are sun basking. This directional reference might improve their mental map of space to accomplish efficient escape behaviour. This study is the first to provide spontaneous magnetic alignment behaviour in free-living reptiles.

  17. Spontaneous magnetic alignment behaviour in free-living lizards.

    PubMed

    Diego-Rasilla, Francisco J; Pérez-Mellado, Valentín; Pérez-Cembranos, Ana

    2017-04-01

    Several species of vertebrates exhibit spontaneous longitudinal body axis alignment relative to the Earth's magnetic field (i.e., magnetic alignment) while they are performing different behavioural tasks. Since magnetoreception is still not fully understood, studying magnetic alignment provides evidence for magnetoreception and broadens current knowledge of magnetic sense in animals. Furthermore, magnetic alignment widens the roles of magnetic sensitivity in animals and may contribute to shed new light on magnetoreception. In this context, spontaneous alignment in two species of lacertid lizards (Podarcis muralis and Podarcis lilfordi) during basking periods was monitored. Alignments in 255 P. muralis and 456 P. lilfordi were measured over a 5-year period. The possible influence of the sun's position (i.e., altitude and azimuth) and geomagnetic field values corresponding to the moment in which a particular lizard was observed on lizards' body axis orientation was evaluated. Both species exhibited a highly significant bimodal orientation along the north-northeast and south-southwest magnetic axis. The evidence from this study suggests that free-living lacertid lizards exhibit magnetic alignment behaviour, since their body alignments cannot be explained by an effect of the sun's position. On the contrary, lizard orientations were significantly correlated with geomagnetic field values at the time of each observation. We suggest that this behaviour might provide lizards with a constant directional reference while they are sun basking. This directional reference might improve their mental map of space to accomplish efficient escape behaviour. This study is the first to provide spontaneous magnetic alignment behaviour in free-living reptiles.

  18. A Unified Model of Grain Alignment: Radiative Alignment of Interstellar Grains with Magnetic Inclusions

    NASA Astrophysics Data System (ADS)

    Hoang, Thiem; Lazarian, A.

    2016-11-01

    The radiative torque (RAT) alignment of interstellar grains with ordinary paramagnetic susceptibilities has been supported by earlier studies. The alignment of such grains depends on the so-called RAT parameter q max, which is determined by the grain shape. In this paper, we elaborate on our model of RAT alignment for grains with enhanced magnetic susceptibility due to iron inclusions, such that RAT alignment is magnetically enhanced, which we term the MRAT mechanism. Such grains can be aligned with high angular momentum at the so-called high-J attractor points, achieving a high degree of alignment. Using our analytical model of RATs, we derive the critical value of the magnetic relaxation parameter δ m to produce high-J attractor points as functions of q max and the anisotropic radiation angle relative to the magnetic field ψ. We find that if about 10% of the total iron abundance present in silicate grains is forming iron clusters, this is sufficient to produce high-J attractor points for all reasonable values of q max. To calculate the degree of grain alignment, we carry out numerical simulations of MRAT alignment by including stochastic excitations from gas collisions and magnetic fluctuations. We show that large grains can achieve perfect alignment when the high-J attractor point is present, regardless of the values of q max. Our obtained results pave the way for the physical modeling of polarized thermal dust emission as well as magnetic dipole emission. We also find that millimeter-sized grains in accretion disks may be aligned with the magnetic field if they are incorporated with iron nanoparticles.

  19. Field aligned current observations in the polar cusp ionosphere

    NASA Technical Reports Server (NTRS)

    Ledley, B. G.; Farthing, W. H.

    1973-01-01

    Vector magnetic field measurements made during a sounding rocket flight in the polar cusp ionosphere show field fluctuations in the lower F-region which are interpreted as being caused by the payload's passage through a structured field aligned current system. The field aligned currents have a characteristic horizontal scale size of one kilometer. Analysis of one large field fluctuation gives a current density of 0.0001 amp/m sq.

  20. Competition of magnetic and hydrodynamic forces on ellipsoidal particles under shear: Influence of the Earth's magnetic field on particle alignment in viscous media

    NASA Astrophysics Data System (ADS)

    Jezek, Josef; Gilder, Stuart A.

    2006-12-01

    We present a model that describes the rotation of ellipsoidal magnetic particles in a viscous fluid under the influence of hydrodynamic and magnetic forces, with an aim to better understand how sediments acquire their remanent magnetizations. Analyses of the governing equations elucidate how magnetic particles will rotate for different values of leading parameters including particle shape, remanent and induced magnetic intensity, magnetic field intensity and direction, strain rate, shear direction, and viscosity. Numerical solution of the governing equations makes it possible to visualize the rotation path and the magnetic direction of a particle through time. Thus the model can discern the timescales and trajectories of magnetic particles rotating due to torque of the magnetic field couple while simultaneously entrained in a velocity gradient. For example, in a layer of viscosity 104 Pa s, prolate magnetite starting at any initial orientation and subjected to simple shear with a strain rate of 3.17 × 10-8 s-1 needs 4 months to rotate within 3° of the Earth's field direction. Under the same conditions, hydrodynamic forces will govern the orientation of oblate hematite whose moment will be perpetually randomly oriented with respect to the magnetic field direction. When applied to laboratory experiments, the viscous model successfully matches the observed data, particularly after accounting for mechanical interaction and flocculation effects. Magnetic anisotropies calculated from multiparticle systems of hematite yield typical sedimentary fabrics with relatively low percentages of anisotropy (<5%) and maximum principal axes that lie in the sedimentation plane.

  1. Creeping flow of a conducting fluid past axisymmetric bodies in the presence of an aligned magnetic field

    NASA Technical Reports Server (NTRS)

    Kyrlidis, A.; Brown, R. A.; Walker, J. S.

    1990-01-01

    The use of strong magnetic fields for the control of particle settling in metallic systems is investigated by altering the fluid mechanics in the melt. The fluid mechanism of particle settling is analyzed for the motion around single, axisymmetric particles in the limit of creeping flow for a fluid with a large electrical conductivity. The drag is found to increase proportionately to the intensity of the magnetic field or the Hartmann number Ha. The flowfield forms boundary layers, which thin out with increasing Ha, along the surfaces parallel to the flow. For axisymmetric bodies, the boundary layer separates as the poles of the surface are approached and encloses regions of almost stagnant fluid. These regions spread upstream and downstream along the body with increasing Ha, thereby trapping the particle in a column of stagnant fluid.

  2. 'Fixed-axis' magnetic orientation by an amphibian: non-shoreward-directed compass orientation, misdirected homing or positioning a magnetite-based map detector in a consistent alignment relative to the magnetic field?

    PubMed

    Phillips, John B; Borland, S Chris; Freake, Michael J; Brassart, Jacques; Kirschvink, Joseph L

    2002-12-01

    suggestion that homing newts use the light-dependent magnetic compass to align a magnetite-based 'map detector' when obtaining the precise measurements necessary to derive map information from the magnetic field. However, aligning the putative map detector does not explain the fixed-axis response of newts tested under long-wavelength light. Preliminary evidence suggests that, in the absence of reliable directional information from the magnetic compass (caused by the 90 degrees rotation of the response of the magnetic compass under long-wavelength light), newts may resort to a systematic sampling strategy to identify alignment(s) of the map detector that yields reliable magnetic field measurements.

  3. Detecting Field-Aligned Current Signatures Using MAVEN Observations

    NASA Astrophysics Data System (ADS)

    Hanley, K.; Brain, D.; Weber, T. D.

    2016-12-01

    Currents aligned with magnetic field lines have been observed on multiple planets, including Mars, Mercury, Earth, Saturn, and Jupiter. As documented by Mars Global Surveyor, field-aligned currents occur at Mars near regions of moderate or strong crustal magnetic fields. These currents, identified by the magnetic field perturbations they cause, indicate the acceleration of charged particles toward the Martian atmosphere, which may result in atmospheric heating, ionization, and discrete aurora observed at ultraviolet wavelengths. It is likely that charged particles are removed from the atmosphere via these currents in magnetic cusp regions. At present, the locations and conditions for which field-aligned current systems can occur at Mars are not well understood. We use magnetic field measurements collected by MAVEN between December 2014 and September 2015 to investigate the incidence of low-altitude field-aligned currents on the nightside of the planet in regions of strong crustal fields. These currents have been found to cause perturbations in the magnetic field at magnitudes of 5 nT. We have automated the detection process in order to facilitate future study of field-aligned currents using MAVEN data. First, low-frequency signals caused by spacecraft motion are removed from the data, revealing short-term (1-5 seconds) perturbations. The disturbances due to field-aligned currents are recorded by finding areas where the filtered data exceeds a threshold value for multiple seconds. Current events are then mapped to the planet's surface. We report on the geographic distribution of field-aligned current signatures, as well as their distributions with respect to local time.

  4. Study of field-aligned current (FAC), interplanetary electric field component (Ey), interplanetary magnetic field component (Bz), and northward (x) and eastward (y) components of geomagnetic field during supersubstorm

    NASA Astrophysics Data System (ADS)

    Adhikari, Binod; Dahal, Subodh; Chapagain, Narayan P.

    2017-05-01

    A dominant process by which energy and momentum are transported from the magnetosphere to the ionosphere is known as field-aligned current (FAC). It is enhanced during magnetic reconnection and explosive energy release at a substorm. In this paper, we studied FAC, interplanetary electric field component (Ey), interplanetary magnetic field component (Bz), and northward (x) and eastward (y) components of geomagnetic field during three events of supersubstorm occurred on 24 November 2001, 21 January 2005, and 24 August 2005. Large-scale FAC, supposed to be produced during supersubstorm (SSS), has potentiality to cause blackout on Earth. We examined temporal variations of the x and y components of high-latitude geomagnetic field during SSS, which is attributed to the FACs. We shall report the characteristics of high-latitude northward and eastward components of geomagnetic field variation during the growth phase of SSS by the implementation of discrete wavelet transform (DWT) and cross-correlation analysis. Among three examples of SSS events, the highest peak value of FAC was estimated to be 19 μAm-2. This is shore up with the prediction made by Parks (1991) and Stasiewicz et al. (1998) that the FACs may vary from a few tens to several hundred μAm-2. Although this peak value of FACs for SSS event is much higher than the average FACs associated with regular substorms or magnetic storms, it is expedient and can be expect for SSS events which might be due to very high density solar wind plasma parcels (PPs) triggering the SSS events. In all events, during growth phase, the FAC increases to extremely high level and the geomagnetic northward component decreases to extremely low level. This represents a strong positive correlation between FAC and geomagnetic northward component. The DWT analysis accounts that the highest amplitude of the wavelet coefficients indicates singularities present in FAC during SSS event. But the amplitude of squared wavelet coefficient is found

  5. Transparent and through thickness conductive polystyrene films using external magnetic fields for ``Z'' alignment of nickel nanoparticles

    NASA Astrophysics Data System (ADS)

    Chen, Yuwei; Guo, Yuanhao; Batra, Saurabh; Wang, Enmin; Wang, Yanping; Liu, Xueqing; Wang, Yimin; Cakmak, Miko

    2015-08-01

    A combination of transparency, electrical conductivity and flexibility is desired in the emerging flexible electronics industry for current and future applications. In this paper, we report the development of through thickness electrical conductivity in polystyrene films filled with nickel nanopowder by external magnetic field application. This process leads to the formation of nanocolumns of nickel spanning across the thickness direction while generating nanoparticle depleted regions in between. This leads to directionally dependent enhancement in optical light transmission particularly in the normal direction of the films. With the use of as little as 2 wt% (0.22 vol%) nickel we were able to achieve high through thickness conductivity under the influence of a magnetic field. While these films exhibit high through thickness conductivity they remain non-conductive in their planes as a result of the unique nanomorphology created which eliminates potential side branch formations. These films are anticipated to be used as electrodes for touch screens, electric dissipative materials for electronic packaging and other sensors.A combination of transparency, electrical conductivity and flexibility is desired in the emerging flexible electronics industry for current and future applications. In this paper, we report the development of through thickness electrical conductivity in polystyrene films filled with nickel nanopowder by external magnetic field application. This process leads to the formation of nanocolumns of nickel spanning across the thickness direction while generating nanoparticle depleted regions in between. This leads to directionally dependent enhancement in optical light transmission particularly in the normal direction of the films. With the use of as little as 2 wt% (0.22 vol%) nickel we were able to achieve high through thickness conductivity under the influence of a magnetic field. While these films exhibit high through thickness conductivity they

  6. Transparent and through thickness conductive polystyrene films using external magnetic fields for "Z" alignment of nickel nanoparticles.

    PubMed

    Chen, Yuwei; Guo, Yuanhao; Batra, Saurabh; Wang, Enmin; Wang, Yanping; Liu, Xueqing; Wang, Yimin; Cakmak, Miko

    2015-09-21

    A combination of transparency, electrical conductivity and flexibility is desired in the emerging flexible electronics industry for current and future applications. In this paper, we report the development of through thickness electrical conductivity in polystyrene films filled with nickel nanopowder by external magnetic field application. This process leads to the formation of nanocolumns of nickel spanning across the thickness direction while generating nanoparticle depleted regions in between. This leads to directionally dependent enhancement in optical light transmission particularly in the normal direction of the films. With the use of as little as 2 wt% (0.22 vol%) nickel we were able to achieve high through thickness conductivity under the influence of a magnetic field. While these films exhibit high through thickness conductivity they remain non-conductive in their planes as a result of the unique nanomorphology created which eliminates potential side branch formations. These films are anticipated to be used as electrodes for touch screens, electric dissipative materials for electronic packaging and other sensors.

  7. Magnetic Alignment of Pulsed Solenoids Using the Pulsed Wire Method

    SciTech Connect

    Arbelaez, D.; Madur, A.; Lipton, T.M.; Waldron, W.L.; Kwan, J.W.

    2011-04-01

    A unique application of the pulsed-wire measurement method has been implemented for alignment of 2.5 T pulsed solenoid magnets. The magnetic axis measurement has been shown to have a resolution of better than 25 {micro}m. The accuracy of the technique allows for the identification of inherent field errors due to, for example, the winding layer transitions and the current leads. The alignment system is developed for the induction accelerator NDCX-II under construction at LBNL, an upgraded Neutralized Drift Compression experiment for research on warm dense matter and heavy ion fusion. Precise alignment is essential for NDCX-II, since the ion beam has a large energy spread associated with the rapid pulse compression such that misalignments lead to corkscrew deformation of the beam and reduced intensity at focus. The ability to align the magnetic axis of the pulsed solenoids to within 100 pm of the induction cell axis has been demonstrated.

  8. Biphenyl Bicelle Disks Align Perpendicular to Magnetic Fields on Large Temperature Scales: A Study Combining Synthesis, Solid-State NMR, TEM, and SAXS

    PubMed Central

    Loudet, Cécile; Manet, Sabine; Gineste, Stéphane; Oda, Reïko; Achard, Marie-France; Dufourc, Erick J.

    2007-01-01

    A phosphatidylcholine lipid (PC) containing a biphenyl group in one of its acyl chains (1-tetradecanoyl-2-(4-(4-biphenyl)butanoyl)-sn-glycero-3-PC, TBBPC) was successfully synthesized with high yield. Water mixtures of TBBPC with a short-chain C6 lipid, dicaproyl-PC (DCPC), lead to bicelle systems formation. Freeze-fracture electron microscopy evidenced the presence of flat bilayered disks of 800 Å diameter for adequate composition, hydration, and temperature conditions. Because of the presence of the biphenyl group, which confers to the molecule a positive magnetic anisotropy Δχ, the disks align with their normal, n, parallel to the magnetic field B0, as directly detected by 31P, 14N, 2H solid-state NMR and also using small-angle x-ray scattering after annealing in the field. Temperature-composition and temperature-hydration diagrams were established. Domains where disks of TBBPC/DCPC align with their normal parallel to the field were compared to chain-saturated lipid bicelles made of DMPC(dimyristoylPC)/DCPC, which orient with their normal perpendicular to B0. TBBPC/DCPC bicelles exist on a narrow range of long- versus short-chain lipid ratios (3%) but over a large temperature span around room temperature (10–75°C), whereas DMPC/DCPC bicelles exhibit the reverse situation, i.e., large compositional range (22%) and narrow temperature span (25–45°C). The two types of bicelles present orienting properties up to 95% dilution but with the peculiarity that water trapped in biphenyl bicelles exhibits ordering properties twice as large as those observed in the saturated-chains analog, which offers very interesting properties for structural studies on hydrophilic or hydrophobic embedded biomolecules. PMID:17307824

  9. Magnetic alignment of mesophase pitch-based carbon fibers

    NASA Astrophysics Data System (ADS)

    Matthews, M. J.; Dresselhaus, M. S.; Dresselhaus, G.; Endo, M.; Nishimura, Y.; Hiraoka, T.; Tamaki, N.

    1996-07-01

    Mesophase pitch-based carbon fibers (MPCFs) have recently been developed for use as high performance anode materials in Li ion secondary batteries, having a microscopic as well as macroscopic structure especially suitable for Li storage. Because of the highly anisotropic diamagnetic moment observed between 50 and 310 K in pristine milled MPCF segments, they can easily be oriented parallel to an applied magnetic field, as observed by scanning electron microscopy. A simple model is proposed to explain both the observed alignment of undoped fibers and the suppression of alignment in B-doped MPCFs for relatively small applied magnetic fields, because of their smaller diamagnetic moment.

  10. Magnetic Alignment of Block Copolymer Microdomains by Intrinsic Chain Anisotropy

    NASA Astrophysics Data System (ADS)

    Rokhlenko, Yekaterina; Gopinadhan, Manesh; Osuji, Chinedum O.; Zhang, Kai; O'Hern, Corey S.; Larson, Steven R.; Gopalan, Padma; Majewski, Paweł W.; Yager, Kevin G.

    2015-12-01

    We examine the role of intrinsic chain susceptibility anisotropy in magnetic field directed self-assembly of a block copolymer using in situ x-ray scattering. Alignment of a lamellar mesophase is observed on cooling across the disorder-order transition with the resulting orientational order inversely proportional to the cooling rate. We discuss the origin of the susceptibility anisotropy, Δ χ , that drives alignment and calculate its magnitude using coarse-grained molecular dynamics to sample conformations of surface-tethered chains, finding Δ χ ≈2 ×1 0-8. From field-dependent scattering data, we estimate that grains of ≈1.2 μ m are present during alignment. These results demonstrate that intrinsic anisotropy is sufficient to support strong field-induced mesophase alignment and suggest a versatile strategy for field control of orientational order in block copolymers.

  11. Magnetic alignment of block copolymer microdomains by intrinsic chain anisotropy

    SciTech Connect

    Rokhlenko, Yekaterina; Yager, Kevin G.; Gopinadhan, Manesh; Osuji, Chinedum O.; Zhang, Kai; O'Hern, Corey S.; Larson, Steven R.; Gopalan, Padma; Majewski, Pawel W.

    2015-12-18

    We examine the role of intrinsic chain susceptibility anisotropy in magnetic field directed self-assembly of a block copolymer using in situ x-ray scattering. Alignment of a lamellar mesophase is observed on cooling across the disorder-order transition with the resulting orientational order inversely proportional to the cooling rate. We discuss the origin of the susceptibility anisotropy, Δχ, that drives alignment and calculate its magnitude using coarse-grained molecular dynamics to sample conformations of surface-tethered chains, finding Δχ ≈ 2×10–8. From field-dependent scattering data, we estimate that grains of ≈ 1.2 μm are present during alignment. Furthermore, these results demonstrate that intrinsic anisotropy is sufficient to support strong field-induced mesophase alignment and suggest a versatile strategy for field control of orientational order in block copolymers.

  12. Magnetic alignment of block copolymer microdomains by intrinsic chain anisotropy

    DOE PAGES

    Rokhlenko, Yekaterina; Yager, Kevin G.; Gopinadhan, Manesh; ...

    2015-12-18

    We examine the role of intrinsic chain susceptibility anisotropy in magnetic field directed self-assembly of a block copolymer using in situ x-ray scattering. Alignment of a lamellar mesophase is observed on cooling across the disorder-order transition with the resulting orientational order inversely proportional to the cooling rate. We discuss the origin of the susceptibility anisotropy, Δχ, that drives alignment and calculate its magnitude using coarse-grained molecular dynamics to sample conformations of surface-tethered chains, finding Δχ ≈ 2×10–8. From field-dependent scattering data, we estimate that grains of ≈ 1.2 μm are present during alignment. Furthermore, these results demonstrate that intrinsic anisotropymore » is sufficient to support strong field-induced mesophase alignment and suggest a versatile strategy for field control of orientational order in block copolymers.« less

  13. Modeling of Field-Aligned Guided Echoes in the Plasmasphere

    NASA Technical Reports Server (NTRS)

    Fung, Shing F.; Green, James L.

    2004-01-01

    The conditions under which high frequency (f>>f(sub uh)) long-range extraordinary-mode discrete field-aligned echoes observed by the Radio Plasma Imager (RPI) on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite in the plasmasphere are investigated by ray tracing modeling. Field-aligned discrete echoes are most commonly observed by RPI in the plasmasphere although they are also observed over the polar cap region. The plasmasphere field-aligned echoes appearing as multiple echo traces at different virtual ranges are attributed to signals reflected successively between conjugate hemispheres that propagate along or nearly along closed geomagnetic field lines. The ray tracing simulations show that field-aligned ducts with as little as 1% density perturbations (depletions) and less than 10 wavelengths wide can guide nearly field-aligned propagating high frequency X mode waves. Effective guidance of wave at a given frequency and wave normal angle (Psi) depends on the cross-field density scale of the duct, such that ducts with stronger density depletions need to be wider in order to maintain the same gradient of refractive index across the magnetic field. While signal guidance by field aligned density gradient without ducting is possible only over the polar region, conjugate field-aligned echoes that have traversed through the equatorial region are most likely guided by ducting.

  14. Temporal variations in a four-sheet field-aligned current system and associated aurorae as observed during a Polar-ground magnetic conjunction in the midmorning sector

    NASA Astrophysics Data System (ADS)

    Farrugia, C. J.; Sandholt, P. E.; Maynard, N. C.; Torbert, R. B.; Ober, D. M.

    2003-06-01

    We relate measurements of temporarily varying field-aligned current systems (FACs) and their associated plasmas made by the Polar spacecraft at midmorning local times and likewise temporarily varying aurorae observed from Svalbard, Norway, when the magnetic footprint of the spacecraft passed across the field-of-view of the ground instruments on 3 December 1997. We combine the in situ observations of plasma and magnetic and electric fields with meridian scanning photometry and all-sky imagery from the ground site. The interplanetary magnetic field (IMF) pointed strongly east (By ≫ 0) and generally south. Descending from ˜7.5 to ˜5.5 RE and heading south, Polar traversed a four-sheet current system: a twin-sheet cusp current system C1-C2, spanning 80.6°-77.7° invariant latitudes (ILT), and then the traditional regions 1 (R1) and 2 (R2) currents, extending from 77.7° to 73.3° ILT. A convection reversal separated the C1-C2 from the R1-R2 FACs. Currents C1 and R2 flow out of the ionosphere, while C2 and R1 flow into the ionosphere. Within C1, Polar observed six bursts of ions of typically magnetosheath energies (≤2 keV) repeating every ˜5 min, accompanied by intensified field-aligned electron beams and magnetic field depressions. Auroral data, acquired later but under very similar IMF conditions and at the same latitudes as when Polar was within C1, suggest auroral forms which are pulsed in both red and green lines with a similar period to the plasma bursts observed earlier at Polar. Within C2, at Polar, the pulsing ceased, but magnetosheath plasma was still present, albeit at diminished intensity. This was in part also a temporal change as the IMF clock angle decreased to ˜60°. Equatorward of the cusp aurora we find a mixing region of magnetosheath and magnetospheric plasmas with spectral characteristics of the boundary plasma sheet (BPS) forming the source of the R1 current. Plasma inhomogeneities and bipolar current elements embedded therein were related

  15. Anisotropic structural and magnetic properties of the field-aligned superconducting system SmFeAsO1-xFx (x = 0, 0.1, 0.2, 0.25 and 0.3)

    NASA Astrophysics Data System (ADS)

    You, Y. B.; Hsiao, T. K.; Chang, B. C.; Tai, M. F.; Hsu, Y. Y.; Ku, H. C.; Wei, Z.; Ruan, K. Q.; Li, X. G.

    2011-01-01

    Anisotropic structural and magnetic properties of the field-aligned superconducting system SmFeAsO1-xFx (x = 0, 0.1, 0.2, 0.25 and 0.3) are reported. Due to the Fe spin-orbital related anisotropic exchange coupling, all the tetragonal microcrystalline powders in epoxy were aligned at room temperature using the field-rotation method where the tetragonal ab-plane is parallel to the magnetic alignment field Ba of 0.9 T and the c-axis parallels to the rotating axis. Anisotropic magnetic properties are studied through low temperature magnetic measurements along the c-axis and paralleled to the ab-plane of aligned samples in both zero-field-cooled (ZFC) and field-cooled (FC) modes. The under-doped compound (x = 0.1) is not superconducting with an antiferromagnetic Néel temperature TN ~ 40 K, while the two optimum-doped compounds (x = 0.2 and 0.25) show high superconducting transition temperatures Tc of 49K and 50K, respectively. The variation of anisotropic structural and magnetic properties for this system are discussed and compared with the previously reported 52 K anisotropic superconductor Sm0.95La0.05FeAsO0.85F0.15.

  16. Spin dynamics and magnetic field induced polarization of excitons in ultrathin GaAs/AlAs quantum wells with indirect band gap and type-II band alignment

    NASA Astrophysics Data System (ADS)

    Shamirzaev, T. S.; Rautert, J.; Yakovlev, D. R.; Debus, J.; Gornov, A. Yu.; Glazov, M. M.; Ivchenko, E. L.; Bayer, M.

    2017-07-01

    The exciton spin dynamics are investigated both experimentally and theoretically in two-monolayer-thick GaAs/AlAs quantum wells with an indirect band gap and a type-II band alignment. The magnetic field induced circular polarization of photoluminescence Pc is studied as function of the magnetic field strength and direction as well as sample temperature. The observed nonmonotonic behavior of these functions is provided by the interplay of bright and dark exciton states contributing to the emission. To interpret the experiment, we have developed a kinetic master equation model which accounts for the dynamics of the spin states in this exciton quartet, radiative and nonradiative recombination processes, and redistribution of excitons between these states as result of spin relaxation. The model offers quantitative agreement with experiment and allows us to evaluate, for the studied structure, the heavy-hole g factor, gh h=+3.5 , and the spin relaxation times of electron, τs e=33 μ s , and hole, τs h=3 μ s , bound in the exciton.

  17. Effect of alignment of easy axes on dynamic magnetization of immobilized magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Yoshida, Takashi; Matsugi, Yuki; Tsujimura, Naotaka; Sasayama, Teruyoshi; Enpuku, Keiji; Viereck, Thilo; Schilling, Meinhard; Ludwig, Frank

    2017-04-01

    In some biomedical applications of magnetic nanoparticles (MNPs), the particles are physically immobilized. In this study, we explore the effect of the alignment of the magnetic easy axes on the dynamic magnetization of immobilized MNPs under an AC excitation field. We prepared three immobilized MNP samples: (1) a sample in which easy axes are randomly oriented, (2) a parallel-aligned sample in which easy axes are parallel to the AC field, and (3) an orthogonally aligned sample in which easy axes are perpendicular to the AC field. First, we show that the parallel-aligned sample has the largest hysteresis in the magnetization curve and the largest harmonic magnetization spectra, followed by the randomly oriented and orthogonally aligned samples. For example, 1.6-fold increase was observed in the area of the hysteresis loop of the parallel-aligned sample compared to that of the randomly oriented sample. To quantitatively discuss the experimental results, we perform a numerical simulation based on a Fokker-Planck equation, in which probability distributions for the directions of the easy axes are taken into account in simulating the prepared MNP samples. We obtained quantitative agreement between experiment and simulation. These results indicate that the dynamic magnetization of immobilized MNPs is significantly affected by the alignment of the easy axes.

  18. Numerical Simulations of a 20-kW Class Hall Thruster Using the Magnetic-Field-Aligned-Mesh Code Hall2De

    NASA Technical Reports Server (NTRS)

    Mikellides, Ioannis G.; Katz, Ira; Kamhawi, Hani; Vannoord, Jonathan L.

    2011-01-01

    This paper reports on numerical simulations of the NASA-300M, a 20-kW class Hall thruster developed at the NASA Glenn Research Center (GRC). The numerical simulations have been performed with a 2-D axisymmetric, magnetic field-aligned-mesh (MFAM) plasma solver developed at the Jet Propulsion Laboratory (JPL). The main objective of the collaborative effort is to combine physics-based simulation, plasma diagnostics and recent findings on erosion physics to design and demonstrate a high-power, high-performance Hall thruster that exceeds the life of state-of-the-art Hall thrusters by more than one order of magnitude. The thruster simulations have been carried out at a discharge voltage of 500 V and discharge current of 40 A. The results indicate that although the impact energy of ions may attain values that are comparable to the discharge voltage along the downstream portions of the channel, a withdrawn ionization region and significant ion focusing combine to sustain erosion rates below 1 mm/kh. A more extensive evaluation of the baseline NASA-300M configuration and re-design of this thruster with magnetically shielded walls constitute the main focus of our work in the coming months.

  19. Numerical Simulations of a 20-kW Class Hall Thruster Using the Magnetic-Field-Aligned-Mesh Code Hall2De

    NASA Technical Reports Server (NTRS)

    Mikellides, Ioannis G.; Katz, Ira; Kamhawi, Hani; Vannoord, Jonathan L.

    2011-01-01

    This paper reports on numerical simulations of the NASA-300M, a 20-kW class Hall thruster developed at the NASA Glenn Research Center (GRC). The numerical simulations have been performed with a 2-D axisymmetric, magnetic field-aligned-mesh (MFAM) plasma solver developed at the Jet Propulsion Laboratory (JPL). The main objective of the collaborative effort is to combine physics-based simulation, plasma diagnostics and recent findings on erosion physics to design and demonstrate a high-power, high-performance Hall thruster that exceeds the life of state-of-the-art Hall thrusters by more than one order of magnitude. The thruster simulations have been carried out at a discharge voltage of 500 V and discharge current of 40 A. The results indicate that although the impact energy of ions may attain values that are comparable to the discharge voltage along the downstream portions of the channel, a withdrawn ionization region and significant ion focusing combine to sustain erosion rates below 1 mm/kh. A more extensive evaluation of the baseline NASA-300M configuration and re-design of this thruster with magnetically shielded walls constitute the main focus of our work in the coming months.

  20. Transient Sheets of Field-Aligned Current Observed by DMSP During the Main Phase of a Magnetic Superstorm

    DTIC Science & Technology

    2004-06-16

    ram direction. These are (1) ion traps to measure the total ion moved equatorward and stabilized at -53’ magnetic lati- densities, (2) ion drift meters...F12 and F15) were moving equatorward in the time magnetosphere, (2) applications of Ohm’s law in the morning (evening) sector above the northern...particle fluxes DMSP orbits are on the dusk side of the Earth. Thus the by four Los Alamos National Laboratory (LANL) satellites satellites move toward the

  1. Effect of frictional heating on radiative ferrofluid flow over a slendering stretching sheet with aligned magnetic field

    NASA Astrophysics Data System (ADS)

    Ramana Reddy, J. V.; Sugunamma, V.; Sandeep, N.

    2017-01-01

    The pivotal objective of this paper is to look into the flow of ferrofluids past a variable thickness surface with velocity slip. Magnetite (Fe3O4 nanoparticles are embedded to the regular fluid. The occurrence of frictional heating in the flow is also taken into account. So the flow equations will be coupled and nonlinear. These are remodelled into dimensionless form with the support of suitable transmutations. The solution of the transformed equations is determined with the support of an effective Runge-Kutta (RK)-based shooting technique. Ultimately, the effects of a few flow modulating quantities on fluid motion and heat transport were explored through plots which are procured using the MATLAB tool box. Owing to the engineering applications, we also calculated the friction factor and the heat transfer coefficient for the influencing parameters. The results are presented comparatively for both regular fluid (water) and water-based ferrofluid. This study enables us to deduce that inflation in the aligned angle or surface thickness reduces the fluid velocity. The radiation and dissipation parameters are capable of providing heat energy to the flow.

  2. Optimization of cross-polarization at low radiofrequency fields for sensitivity enhancement in solid-state NMR of membrane proteins reconstituted in magnetically aligned bicelles

    NASA Astrophysics Data System (ADS)

    Koroloff, Sophie N.; Nevzorov, Alexander A.

    2015-07-01

    Solid-state NMR (ssNMR) of oriented membrane proteins (MPs) is capable of providing structural and dynamic information at nearly physiological conditions. However, NMR experiments performed on oriented membrane proteins generally suffer from low sensitivity. Moreover, utilization of high-power radiofrequency (RF) irradiations for magnetization transfer may give rise to sample heating, thereby decreasing the efficiency of conventional cross-polarization schemes. Here we have optimized the recently developed repetitive cross-polarization (REP-CP) sequence (Tang et al., 2011) to further increase the magnetization transfer efficiency for membrane proteins reconstituted in magnetically aligned bicelles and compared its performance to single-contact Hartmann-Hahn cross-polarization (CP), CP-MOIST and the adiabatic transfer. It has been found that employing the REP-CP sequence at RF amplitudes of 19 kHz instead of the commonly used higher RF fields (>45 kHz) enhances the efficiency of REP-CP. An additional 30% signal can be obtained as compared to the previously published REP-CP, and 20% when compared to the re-optimized REP-CP at 50 kHz RF fields. Moreover, the 15N signal gain of low-power REP-CP was found to be 40% over the adiabatic CP and up to 80% over CP-MOIST. Thus, the low-power REP-CP sequence surpasses all of the previous CP schemes in addition of having the tremendous advantage of reducing the RF powers by a factor of seven, thereby preserving the liquid-like bicelle sample. By contrast, in purely static (NAL crystal) and semi-rigid systems (Pf1 phage), the adiabatic CP was found to be more effective. Periodic oscillations of the intensity profile (distinct from the transient oscillations) as a function of the CP contact time and B1 RF field strengths were observed during the REP-CP optimization with the oscillations becoming more pronounced with lower RF fields. Many-spin simulations were performed to explain the oscillations and their periodicity.

  3. Molecular focusing and alignment with plasmon fields.

    PubMed

    Artamonov, Maxim; Seideman, Tamar

    2010-12-08

    We show the possibility of simultaneously aligning molecules and focusing their center-of-mass motion near a metal nanoparticle in the field intensity gradient created by the surface plasmon enhancement of incident light. The rotational motion is described quantum mechanically while the translation is treated classically. The effects of the nanoparticle shape on the alignment and focusing are explored. Our results carry interesting implications to the field of molecular nanoplasmonics and suggest several potential applications in nanochemistry.

  4. The magnetic properties of aligned M hexa-ferrite fibres

    NASA Astrophysics Data System (ADS)

    Pullar, R. C.; Bhattacharya, A. K.

    2006-05-01

    Aligned and random fibres of strontium hexaferrite (SrM, SrFe 12O 19) and barium hexaferrite (BaM, BaFe 12O 19) were manufactured by blow spinning from an aqueous inorganic sol-gel precursor, which was then fired to give the hexagonal ferrite fibre. Their magnetic properties were studied by VSM, investigating the evolution of these properties with firing and measurement temperature, and in particular the effects of fibre alignment. It has been predicted that aligned ferrite fibres will demonstrate an enhanced magnetisation along the axis of alignment with respect to perpendicular to the axis, and this has been demonstrated here for the first time. The optimum firing temperature was 1000 °C, at which point they still had submicron grains. In BaM random fibres Ms=63.8 emu g -1 and Hc=428.1 kA m -1, and in SrM random fibres Ms=63.3 emu g -1 and Hc=452.8 kA m -1, high values for polycrystalline materials. Fibres aligned parallel to the applied field had saturation magnetisation ( Ms) values equal to those of the random fibres, whilst fibres aligned perpendicular to the field had Ms values 62% and 75% lower, for BaM and SrM, respectively. There was no change in coercivity ( Hc) between random or aligned fibres of any orientation, and fibres aligned 45° and parallel to H appeared identical. Therefore, properties along the axis of alignment were superior when compared to measurements perpendicular to the axis of alignment, giving a directionality to the magnetisation in an otherwise randomly oriented ferrite material.

  5. Beam based alignment of C-shaped quadrupole magnets

    SciTech Connect

    Portmann, G.; Robin, D.

    1998-06-01

    Many storage rings have implemented a method of finding the positional offset between the electrical center of the beam position monitors (BPM) and the magnetic center of the adjacent quadrupole magnets. The algorithm for accomplishing this is usually based on modulating the current in the quadrupole magnet and finding the beam position that minimizes the orbit perturbation. When the quadrupole magnet is C-shaped, as it is for many light sources, the modulation method can produce an erroneous measurement of the magnetic center in the horizontal plane. When the current in a C-shaped quadrupole is changed, there is an additional dipole component in the vertical field. Due to nonlinearities in the hysteresis cycle of the C-magnet geometry, the beam-based alignment technique at the Advanced Light Source (ALS) deviated horizontally by .5 mm from the actual magnetic center. By modifying the technique, the offsets were measured to an accuracy of better than 50 {micro}m.

  6. Magnetic alignment in grazing and resting cattle and deer.

    PubMed

    Begall, Sabine; Cerveny, Jaroslav; Neef, Julia; Vojtech, Oldrich; Burda, Hynek

    2008-09-09

    We demonstrate by means of simple, noninvasive methods (analysis of satellite images, field observations, and measuring "deer beds" in snow) that domestic cattle (n = 8,510 in 308 pastures) across the globe, and grazing and resting red and roe deer (n = 2,974 at 241 localities), align their body axes in roughly a north-south direction. Direct observations of roe deer revealed that animals orient their heads northward when grazing or resting. Amazingly, this ubiquitous phenomenon does not seem to have been noticed by herdsmen, ranchers, or hunters. Because wind and light conditions could be excluded as a common denominator determining the body axis orientation, magnetic alignment is the most parsimonious explanation. To test the hypothesis that cattle orient their body axes along the field lines of the Earth's magnetic field, we analyzed the body orientation of cattle from localities with high magnetic declination. Here, magnetic north was a better predictor than geographic north. This study reveals the magnetic alignment in large mammals based on statistically sufficient sample sizes. Our findings open horizons for the study of magnetoreception in general and are of potential significance for applied ethology (husbandry, animal welfare). They challenge neuroscientists and biophysics to explain the proximate mechanisms.

  7. Magnetic alignment in grazing and resting cattle and deer

    PubMed Central

    Begall, Sabine; Červený, Jaroslav; Neef, Julia; Vojtěch, Oldřich; Burda, Hynek

    2008-01-01

    We demonstrate by means of simple, noninvasive methods (analysis of satellite images, field observations, and measuring “deer beds” in snow) that domestic cattle (n = 8,510 in 308 pastures) across the globe, and grazing and resting red and roe deer (n = 2,974 at 241 localities), align their body axes in roughly a north–south direction. Direct observations of roe deer revealed that animals orient their heads northward when grazing or resting. Amazingly, this ubiquitous phenomenon does not seem to have been noticed by herdsmen, ranchers, or hunters. Because wind and light conditions could be excluded as a common denominator determining the body axis orientation, magnetic alignment is the most parsimonious explanation. To test the hypothesis that cattle orient their body axes along the field lines of the Earth's magnetic field, we analyzed the body orientation of cattle from localities with high magnetic declination. Here, magnetic north was a better predictor than geographic north. This study reveals the magnetic alignment in large mammals based on statistically sufficient sample sizes. Our findings open horizons for the study of magnetoreception in general and are of potential significance for applied ethology (husbandry, animal welfare). They challenge neuroscientists and biophysics to explain the proximate mechanisms. PMID:18725629

  8. Columnar-to-Equiaxed Transition and Equiaxed Grain Alignment in Directionally Solidified Ni3Al Alloy Under an Axial Magnetic Field

    NASA Astrophysics Data System (ADS)

    Liu, Huan; Xuan, Weidong; Xie, Xinliang; Li, Chuanjun; Wang, Jiang; Yu, Jianbo; Li, Xi; Zhong, Yunbo; Ren, Zhongming

    2017-09-01

    The effect of an axial magnetic field on the solidification structure in directionally solidified Ni-21.5Al-0.4Zr-0.1B (at. pct) alloy was investigated. The experimental results indicated that the application of a high magnetic field caused the deformation of dendrites and the occurrence of columnar-to-equiaxed transition (CET). The magnetic field tended to orient the 〈001〉 crystal direction of the equiaxed grains along the magnetic field direction. The bulk solidification experiment under a high magnetic field showed that the crystal exhibited magnetic crystalline anisotropy. Further, the thermoelectric (TE) magnetic force and TE magnetic convention were analyzed by three-dimensional (3-D) numerical simulations. The results showed that the maximum value of TE magnetic force localized in the vicinity of the secondary dendrite arm root, which should be responsible for the dendrite break and CET. Based on the high-temperature creep mechanism, a simple model was proposed to describe the magnetic field intensity needed for CET: B ≥ kG^{ - 1.5} R^{1.25} . The model is in good agreement with the experiment results. The experimental results should be attributed to the combined action of TE magnetic effects and the magnetic moment.

  9. Columnar-to-Equiaxed Transition and Equiaxed Grain Alignment in Directionally Solidified Ni3Al Alloy Under an Axial Magnetic Field

    NASA Astrophysics Data System (ADS)

    Liu, Huan; Xuan, Weidong; Xie, Xinliang; Li, Chuanjun; Wang, Jiang; Yu, Jianbo; Li, Xi; Zhong, Yunbo; Ren, Zhongming

    2017-06-01

    The effect of an axial magnetic field on the solidification structure in directionally solidified Ni-21.5Al-0.4Zr-0.1B (at. pct) alloy was investigated. The experimental results indicated that the application of a high magnetic field caused the deformation of dendrites and the occurrence of columnar-to-equiaxed transition (CET). The magnetic field tended to orient the <001> crystal direction of the equiaxed grains along the magnetic field direction. The bulk solidification experiment under a high magnetic field showed that the crystal exhibited magnetic crystalline anisotropy. Further, the thermoelectric (TE) magnetic force and TE magnetic convention were analyzed by three-dimensional (3-D) numerical simulations. The results showed that the maximum value of TE magnetic force localized in the vicinity of the secondary dendrite arm root, which should be responsible for the dendrite break and CET. Based on the high-temperature creep mechanism, a simple model was proposed to describe the magnetic field intensity needed for CET: B ≥ kG^{ - 1.5} R^{1.25} . The model is in good agreement with the experiment results. The experimental results should be attributed to the combined action of TE magnetic effects and the magnetic moment.

  10. Changes in collection efficiency in nylon net filter media through magnetic alignment of elongated aerosol particles.

    PubMed

    Lam, Christopher O; Finlay, W H

    2009-10-01

    Fiber aerosols tend to align parallel to surrounding fluid streamlines in shear flows, making their filtration more difficult. However, previous research indicates that composite particles made from cromoglycic acid fibers coated with small nanoscaled magnetite particles can align with an applied magnetic field. The present research explored the effect of magnetically aligning these fibers to increase their filtration. Nylon net filters were challenged with the aerosol fibers, and efficiency tests were performed with and without a magnetic field applied perpendicular to the flow direction. We investigated the effects of varying face velocities, the amount of magnetite material on the aerosol particles, and magnetic field strengths. Findings from the experiments, matched by supporting single-fiber theories, showed significant efficiency increases at the low face velocity of 1.5 cm s(-1) at all magnetite compositions, with efficiencies more than doubling due to magnetic field alignment in certain cases. At a higher face velocity of 5.12 cm s(-1), filtration efficiencies were less affected by the magnetic field alignment being, at most, 43% higher for magnetite weight compositions up to 30%, while at a face velocity of 10.23 cm s(-1) alignment effects were insignificant. In most cases, efficiencies became independent of magnetic field strength above 50 mT, suggesting full alignment of the fibers. The present data suggest that fiber alignment in a magnetic field may warrant applications in the filtration and detection of fibers, such as asbestos.

  11. A MODEL FOR THE WAVEFORM BEHAVIOR OF ACCRETING MILLISECOND X-RAY PULSARS: NEARLY ALIGNED MAGNETIC FIELDS AND MOVING EMISSION REGIONS

    SciTech Connect

    Lamb, Frederick K.; Boutloukos, Stratos; Van Wassenhove, Sandor; Chamberlain, Robert T.; Lo, Ka Ho; Clare, Alexander; Yu Wenfei; Miller, M. Coleman

    2009-11-20

    We investigate further a model of the accreting millisecond X-ray pulsars we proposed earlier. In this model, the X-ray-emitting regions of these pulsars are near their spin axes but move. This is to be expected if the magnetic poles of these stars are close to their spin axes, so that accreting gas is channeled there. As the accretion rate and the structure of the inner disk vary, gas is channeled along different field lines to different locations on the stellar surface, causing the X-ray-emitting areas to move. We show that this 'nearly aligned moving spot model' can explain many properties of the accreting millisecond X-ray pulsars, including their generally low oscillation amplitudes and nearly sinusoidal waveforms; the variability of their pulse amplitudes, shapes, and phases; the correlations in this variability; and the similarity of the accretion- and nuclear-powered pulse shapes and phases in some. It may also explain why accretion-powered millisecond pulsars are difficult to detect, why some are intermittent, and why all detected so far are transients. This model can be tested by comparing with observations the waveform changes it predicts, including the changes with accretion rate.

  12. Generation of field-aligned current in the auroral zone

    NASA Technical Reports Server (NTRS)

    Okuda, Hideo

    1991-01-01

    Generation of a magnetic field-aligned current in the auroral zone connecting the magnetospheric and ionospheric plasmas has been studied by means of a three dimensional particle simulation model. The model is of a magnetostatic variety appropriate for a low beta plasma in which the high frequency transverse displacement current has been eliminated. The simulation model is highly elongated along the magnetic field lines in order to model a highly elongated flux tube in the auroral zone. An enhanced field-aligned current was generated by injection of a magnetospheric plasma across the auroral zone magnetic field at the center of the model. Such a plasma injection may correspond to a plasmoid injection at the geomagnetic tail associated with magnetic reconnection during a substorm or a transverse plasma flow along the low latitude magnetopause boundary layer. The results of the simulations show that the field-aligned current can be enhanced over the thermal current by a factor of 5 - 10 via such injection. Associated with the enhanced current are the electrostatic ion cyclotron waves and shear Alfven waves excited in the auroral zone.

  13. Remanent magnetism of sediment governs magnetofossil alignment

    NASA Astrophysics Data System (ADS)

    Wendel, JoAnna

    2014-04-01

    Most bacteria navigate by reacting to different chemical signals in their surroundings, but some bacteria have another navigational tool in their arsenal—the Earth's magnetic field. Nestled inside these magnetotactic bacteria (MTB) are organelles called magnetosomes, filled with tiny magnetic crystals and arranged in chains, which form nano-sized compass needles. When MTB die and degrade, these tiny crystals can remain in sediment and eventually become magnetic fossils called magnetofossils.

  14. Field-Aligned Current Systems at Mercury

    NASA Astrophysics Data System (ADS)

    Heyner, Daniel; Exner, Willi

    2017-04-01

    Mercury exhibits a very dynamic magnetosphere, which is partially due to strong dayside reconnection and fast magnetospheric convection. It has been shown that dayside reconnection occurs even on low magnetic shear angles across the magnetopause. This drives quasi-steady region 1 field-aligned currents (FAC) that are observable in in-situ MESSENGER data. Here, the structure of the Hermean FAC-system is discussed and compared to the terrestrial counterpart. Due to the lack of a significant ionosphere at Mercury, it has to be examined how much of the poloidal FAC is reflected back to the magnetosphere, closed via toroidal currents in the planetary interior or via Pedersen currents in the tenuous exosphere. This investigation gives insights into the planetary conductivity structure as well as the exospheric plasma densities. Furthermore, it will be examined how much the only partially developed ring current at Mercury produces possible region 2 FAC signatures. We conclude with requirements to simulations that are needed to forecast the FAC structure on the southern hemisphere that will be closely studied with the upcoming BepiColombo mission.

  15. Laboratory simulation of field-aligned currents

    NASA Technical Reports Server (NTRS)

    Wessel, Frank J.; Rostoker, Norman

    1993-01-01

    A summary of progress during the period Apr. 1992 to Mar. 1993 is provided. Objectives of the research are (1) to simulate, via laboratory experiments, the three terms of the field-aligned current equation; (2) to simulate auroral-arc formation processes by configuring the boundary conditions of the experimental chamber and plasma parameters to produce highly localized return currents at the end of a field-aligned current system; and (3) to extrapolate these results, using theoretical and computational techniques, to the problem of magnetospheric-ionospheric coupling and to compare them with published literature signatures of auroral-arc phenomena.

  16. Enhanced method of magnetic powder alignment for production of PLP Nd-Fe-B magnets

    NASA Astrophysics Data System (ADS)

    Popov, A. G.; Golovnia, O. A.; Protasov, A. V.

    2017-04-01

    It is demonstrated how the high degree of powder alignment in PLP magnets can be achieved by loading the powder into a container placed in a magnetic field of moderate strength. The strip-cast alloy with a composition of 30.00 Nd, 1.95 Dy, 66.42 Fe, 0.99 B, 0.54 Co, 0.1 Ga (wt%) was subjected to hydrogen decrepitation and then milled in a vibratory mill in toluene to an average particle size of 2.9 μm determined by the FSSS method. The powder was compacted in the magnetic field of 0.2 - 1.2 T to the filling density 2.6 - 3.2×103 kg/m3. It is shown that loading the powder into a container placed in a magnetic field enhances the degree of powder alignment in sintered Nd-Fe-B magnets produced from non-pressed powder. At the filling density less than 3.2×103 kg/m3, the density of magnets is high but insufficient, because of the formation of magnetostatic chains of particles, which impedes the powder compaction. The simulation by the discrete-element method qualitatively proves that the magnetostatic interaction of the chains of particles that are formed in the course of loading in the magnetic field stimulates a decrease in the density of the sintered magnets and its non-uniform distribution over the sample. As a result of the optimization of the parameters of the alignment and compaction of the powder loaded in a magnetic field, PLP magnets with Br ≥1.34 T, Нc ≥950 kA/m, (BH)max ≥340 kJ/m3, and the degree of alignment exceeding 96% were produced.

  17. Terrestrial ionospheric signatures of field-aligned currents

    NASA Technical Reports Server (NTRS)

    Friis-Christensen, E.

    1990-01-01

    The occurrence of traveling field-aligned current filaments and twin-vortex patterns is suggested to be related to sudden changes in solar wind dynamic pressure and/or the IMF. Greenland magnetometer observations of the cleft region magnetic perturbations associated with small-scale twin-vortex patterns show that these events occur on both sides of the magnetic local noon, contradicting Glassmeier at al.'s (1989) statistical analysis of 82 twin-vortex subauroral-latitude events obtained by the Scandinavian Magnetometer Array; the stations are closer to the ionospheric projection of the cleft earlier in magnetic local time, relative to the across-the-cleft-located Greenland stations.

  18. Field-aligned currents and large scale magnetospheric electric fields

    NASA Technical Reports Server (NTRS)

    Dangelo, N.

    1980-01-01

    D'Angelo's model of polar cap electric fields (1977) was used to visualize how high-latitude field-aligned currents are driven by the solar wind generator. The region 1 and region 2 currents of Iijima and Potemra (1976) and the cusp field-aligned currents of Wilhjelm et al. (1978) and McDiarmid et al. (1978) are apparently driven by different generators, although in both cases the solar wind is their ultimate source.

  19. Magnetic field sensor

    NASA Astrophysics Data System (ADS)

    Silva, Nicolas

    2012-09-01

    Earlier papers1-3 in this journal have described experiments on measuring the magnetic fields of current-carrying wires and permanent magnets using magnetic field probes of various kinds. This paper explains how to use an iPad and the free app MagnetMeter-3D Vector Magnetometer and Accelerometer4 (compass HD) to measure the magnetic fields.

  20. Avoiding Tokamak Disruptions by Applying Static Magnetic Fields That Align Locked Modes with Stabilizing Wave-Driven Currents [Avoiding Tokamak Disruptions by Magnetically Aligning Locked Modes with Stabilizing Wave-Driven Currents

    DOE PAGES

    Volpe, F. A.; Hyatt, Alan; La Haye, Robert J.; ...

    2015-10-19

    The international ITER tokamak has the objective of demonstrating the scientific feasibility of magnetic confinement fusion as a source of energy. A concern towards the achievement of this goal is represented by major disruptions: complete losses of confinement often initiated by a non-rotating ('locked') magnetic island created by magnetic reconnection. During disruptions, energy and particles accumulated in the plasma volume over many seconds are lost in a few milliseconds and released on the plasma-facing materials. In addition, multi-MA level currents flowing in the tokamak plasma for its sustainment and confinement are lost, also in milliseconds, thus terminating the plasma dischargemore » and causing electromagnetic stresses that, if unmitigated, could lead to excessive device wear. Moreover it is shown that magnetic perturbations can be used to avoid disruptions by "guiding" the magnetic island to lock in a position where it is accessible to millimetre wave beams that fully stabilize it.« less

  1. Avoiding Tokamak Disruptions by Applying Static Magnetic Fields That Align Locked Modes with Stabilizing Wave-Driven Currents [Avoiding Tokamak Disruptions by Magnetically Aligning Locked Modes with Stabilizing Wave-Driven Currents

    SciTech Connect

    Volpe, F. A.; Hyatt, Alan; La Haye, Robert J.; Lanctot, Matthew J.; Lohr, John; Prater, Ronald; Strait, Edward J.; Welander, Anders

    2015-10-19

    The international ITER tokamak has the objective of demonstrating the scientific feasibility of magnetic confinement fusion as a source of energy. A concern towards the achievement of this goal is represented by major disruptions: complete losses of confinement often initiated by a non-rotating ('locked') magnetic island created by magnetic reconnection. During disruptions, energy and particles accumulated in the plasma volume over many seconds are lost in a few milliseconds and released on the plasma-facing materials. In addition, multi-MA level currents flowing in the tokamak plasma for its sustainment and confinement are lost, also in milliseconds, thus terminating the plasma discharge and causing electromagnetic stresses that, if unmitigated, could lead to excessive device wear. Moreover it is shown that magnetic perturbations can be used to avoid disruptions by "guiding" the magnetic island to lock in a position where it is accessible to millimetre wave beams that fully stabilize it.

  2. Magnetic Alignment and Charge Transport Improvement in Functional Soft Materials

    NASA Astrophysics Data System (ADS)

    Majewski, Pawel W.

    The realization of nanostructured functional materials by self-assembly in polymers and polymer nanocomposites is adversely affected by persisting structural defects which greatly diminish the performance of the material. The use of magnetic fields to impose long-range order is investigated in three distinct systems - ion-conducting block copolymers, semiconducting nanowire-polymer composites and lyotropic surfactant mesophases. The alignment process is quantitatively studied with X-ray scattering and microscopic methods. Time and temperature resolved data collected in situ during the magnetic experiments provide an insight into the thermodynamic and kinetic aspects of the process. These data together with simultaneous electrical conductivity measurements allow relating fundamental structural properties (e.g., morphology and long-range order) to transport properties (i.e., conductivity). In particular, it is demonstrated that magnetic fields offer a viable route for improvement of electric conductivity in these systems. More than an order of magnitude increase in conductivity is recorded in magnetically-annealed materials. The resulting aligned nanostructured systems are attractive for ordered solid polymer electrolyte membranes, heterojunction photovoltaic devices and generally help to understand charge transport mechanisms in anisotropic heterogeneous systems.

  3. Giant Magnetic Susceptibility of Gold Nanorods Detected by Magnetic Alignment

    NASA Astrophysics Data System (ADS)

    van Rhee, P. G.; Zijlstra, P.; Verhagen, T. G. A.; Aarts, J.; Katsnelson, M. I.; Maan, J. C.; Orrit, M.; Christianen, P. C. M.

    2013-09-01

    We have determined the magnetic properties of single-crystalline Au nanorods in solution using an optically detected magnetic alignment technique. The rods exhibit a large anisotropy in the magnetic volume susceptibility (ΔχV). ΔχV increases with decreasing rod size and increasing aspect ratio and corresponds to an average volume susceptibility (χV), which is drastically enhanced relative to bulk Au. This high value of χV is confirmed by SQUID magnetometry and is temperature independent (between 5 and 300 K). Given this peculiar size, shape, and temperature dependence, we speculate that the enhanced χV is the result of orbital magnetism due to mesoscopic electron trajectories within the nanorods.

  4. He I VECTOR MAGNETOMETRY OF FIELD-ALIGNED SUPERPENUMBRAL FIBRILS

    SciTech Connect

    Schad, T. A.; Penn, M. J.; Lin, H.

    2013-05-10

    Atomic-level polarization and Zeeman effect diagnostics in the neutral helium triplet at 10830 A in principle allow full vector magnetometry of fine-scaled chromospheric fibrils. We present high-resolution spectropolarimetric observations of superpenumbral fibrils in the He I triplet with sufficient polarimetric sensitivity to infer their full magnetic field geometry. He I observations from the Facility Infrared Spectropolarimeter are paired with high-resolution observations of the H{alpha} 6563 A and Ca II 8542 A spectral lines from the Interferometric Bidimensional Spectrometer from the Dunn Solar Telescope in New Mexico. Linear and circular polarization signatures in the He I triplet are measured and described, as well as analyzed with the advanced inversion capability of the ''Hanle and Zeeman Light'' modeling code. Our analysis provides direct evidence for the often assumed field alignment of fibril structures. The projected angle of the fibrils and the inferred magnetic field geometry align within an error of {+-}10 Degree-Sign . We describe changes in the inclination angle of these features that reflect their connectivity with the photospheric magnetic field. Evidence for an accelerated flow ({approx}40 m s{sup -2}) along an individual fibril anchored at its endpoints in the strong sunspot and weaker plage in part supports the magnetic siphon flow mechanism's role in the inverse Evershed effect. However, the connectivity of the outer endpoint of many of the fibrils cannot be established.

  5. Magnetically aligned H I fibers and the rolling hough transform

    SciTech Connect

    Clark, S. E.; Putman, M. E.; Peek, J. E. G.

    2014-07-01

    We present observations of a new group of structures in the diffuse Galactic interstellar medium (ISM): slender, linear H I features we dub 'fibers' that extend for many degrees at high Galactic latitude. To characterize and measure the extent and strength of these fibers, we present the Rolling Hough Transform, a new machine vision method for parameterizing the coherent linearity of structures in the image plane. With this powerful new tool we show that the fibers are oriented along the interstellar magnetic field as probed by starlight polarization. We find that these low column density (N{sub H} {sub I}≃5×10{sup 18} cm{sup –2}) fiber features are most likely a component of the local cavity wall, about 100 pc away. The H I data we use to demonstrate this alignment at high latitude are from the Galactic Arecibo L-Band Feed Array H I (GALFA-H I) Survey and the Parkes Galactic All Sky Survey. We find better alignment in the higher resolution GALFA-H I data, where the fibers are more visually evident. This trend continues in our investigation of magnetically aligned linear features in the Riegel-Crutcher H I cold cloud, detected in the Southern Galactic Plane Survey. We propose an application of the RHT for estimating the field strength in such a cloud, based on the Chandrasekhar-Fermi method. We conclude that data-driven, quantitative studies of ISM morphology can be very powerful predictors of underlying physical quantities.

  6. Magnetically Aligned H I Fibers and the Rolling Hough Transform

    NASA Astrophysics Data System (ADS)

    Clark, S. E.; Peek, J. E. G.; Putman, M. E.

    2014-07-01

    We present observations of a new group of structures in the diffuse Galactic interstellar medium (ISM): slender, linear H I features we dub "fibers" that extend for many degrees at high Galactic latitude. To characterize and measure the extent and strength of these fibers, we present the Rolling Hough Transform, a new machine vision method for parameterizing the coherent linearity of structures in the image plane. With this powerful new tool we show that the fibers are oriented along the interstellar magnetic field as probed by starlight polarization. We find that these low column density (NH \\scriptsize{I} ≃ 5 × 1018 cm-2) fiber features are most likely a component of the local cavity wall, about 100 pc away. The H I data we use to demonstrate this alignment at high latitude are from the Galactic Arecibo L-Band Feed Array H I (GALFA-H I) Survey and the Parkes Galactic All Sky Survey. We find better alignment in the higher resolution GALFA-H I data, where the fibers are more visually evident. This trend continues in our investigation of magnetically aligned linear features in the Riegel-Crutcher H I cold cloud, detected in the Southern Galactic Plane Survey. We propose an application of the RHT for estimating the field strength in such a cloud, based on the Chandrasekhar-Fermi method. We conclude that data-driven, quantitative studies of ISM morphology can be very powerful predictors of underlying physical quantities.

  7. Uniformly spaced field-aligned ionization ducts

    NASA Technical Reports Server (NTRS)

    Gross, S. H.; Muldrew, D. B.

    1984-01-01

    A number of interesting cases of combination mode ducted echoes for mid- and low-latitude regions are presented that show nearly uniformly spaced multiple combination mode traces on the ionograms in the frequency range above 1 MHz. These traces suggest that a parallel system of field-aligned ducts is present. Ray tracing studies are made to determine the structure that would explain the observations using the electron density profile derivable from the vertical trace and assuming field-aligned ducts. Spacing perpendicular to the ducts is found to be as much as 70 km. Some of these parallel duct structures are found to extend to the conjugate hemisphere, possibly to the F peak.

  8. Swarm Observations of Field Aligned Currents during Geomagnetic Storms

    NASA Astrophysics Data System (ADS)

    Le, G.; Luhr, H.; Anderson, B. J.; Strangeway, R. J.; Russell, C. T.; Slavin, J. A.; Bromund, K. R.; Plaschke, F.; Magnes, W.; Fischer, D.; Nakamura, R.; Leinweber, H. K.; Torbert, R. B.; Le Contel, O.; Oliveira, D. M.; Raeder, J.; Kepko, L.

    2015-12-01

    Field-aligned currents connect the Earth's magnetosphere to the high latitude ionosphere, and provide a main channel for energy transfer from the magnetosphere to the ionosphere. They are driven by solar wind-magnetosphere interactions and respond dynamically to changes in the solar wind and interplanetary magnetic field. Enhanced interaction during geomagnetic storms significantly intensifies their strength and variability. In this paper, we review our recent observations of field-aligned currents (FACs) during geomagnetic storms using observations from polar orbiting Swarm constellation as well as the Active Magnetosphere and Polar Electrodynamics Response Experiment (AMPERE). Both temporal resolutions and spatial coverage of these observations provide new insights in understanding the FACs and the magnetosphere-ionosphere coupling. We will discuss their spatial and temporal evolutions, ionospheric closure currents, and hemispheric asymmetry during storms.

  9. Magnetic alignment of Ni-coated single wall carbon nanotubes in heat transfer nanofluids

    NASA Astrophysics Data System (ADS)

    Horton, Mark; Hong, Haiping; Li, Chen; Shi, Bo; Peterson, G. P.; Jin, Sungho

    2010-05-01

    Thermal conductivity (TC) of heat transfer nanofluids containing magnetic-metal-coated carbon nanotubes can be significantly enhanced (>60%) by applied magnetic field. In this paper, we report the observed real images of Ni-coated single wall carbon nanotubes in water and oils (polyalphaolefin, polyol ester) under magnetic field by high speed microscopy, and correlate them with TC measurements. Initially, the nanotubes are randomly dispersed in the fluid, however, on longer holding in magnetic field the nanotubes gradually stretch and are finally aligned. The chain length in the images is found to be around 30˜150 μm, which is much longer than the real length of individual nanotubes (5˜40 μm), indicating that nanotubes are aligned and form some chains and clusters. Because of the semicontinuous nature of Ni magnetic nanoparticles, as well as the viscosity resistance of the fluid itself, it takes some time for the Ni-coated nanotubes to respond to the applied magnetic field and align. Time dependent TC experiments indicate that alignment process dominates the TC enhancement rather than microconvection. Finally, scanning electron microscopy images also show that the Ni coated nanotubes are aligned well under the influence of a magnetic field. Transmission electron microscopy images indicate that nickel remains stable and attached onto the nanotubes after the magnetic field exposure and movements.

  10. Cosmological magnetic fields

    NASA Astrophysics Data System (ADS)

    Kunze, Kerstin E.

    2013-12-01

    Magnetic fields are observed on nearly all scales in the Universe, from stars and galaxies up to galaxy clusters and even beyond. The origin of cosmic magnetic fields is still an open question, however a large class of models puts its origin in the very early Universe. A magnetic dynamo amplifying an initial seed magnetic field could explain the present day strength of the galactic magnetic field. However, it is still an open problem how and when this initial magnetic field was created. Observations of the cosmic microwave background (CMB) provide a window to the early Universe and might therefore be able to tell us whether cosmic magnetic fields are of a primordial cosmological origin and at the same time constrain its parameters. We will give an overview of the observational evidence of large-scale magnetic fields, describe generation mechanisms of primordial magnetic fields and possible imprints in the CMB.

  11. Shifted magnetic alignment in vertebrates: Evidence for neural lateralization?

    PubMed

    Malkemper, E Pascal; Painter, Michael S; Landler, Lukas

    2016-06-21

    A wealth of evidence provides support for magnetic alignment (MA) behavior in a variety of disparate species within the animal kingdom, in which an animal, or a group of animals, show a tendency to align the body axis in a consistent orientation relative to the geomagnetic field lines. Interestingly, among vertebrates, MA typically coincides with the north-south magnetic axis, however, the mean directional preferences of an individual or group of organisms is often rotated clockwise from the north-south axis. We hypothesize that this shift is not a coincidence, and future studies of this subtle, yet consistent phenomenon may help to reveal some properties of the underlying sensory or processing mechanisms, that, to date, are not well understood. Furthermore, characterizing the fine structure exhibited in MA behaviors may provide key insights to the biophysical substrates mediating magnetoreception in vertebrates. Therefore, in order to determine if a consistent shift is exhibited in taxonomically diverse vertebrates, we performed a meta-analysis on published MA datasets from 23 vertebrate species that exhibited an axial north-south preference. This analysis revealed a significant clockwise shift from the north-south magnetic axis. We summarize and discuss possible competing hypotheses regarding the proximate mechanisms underlying the clockwise shifted MA and conclude that the most likely cause of such a shift would be a lateralization in central processing of magnetic information. Copyright © 2016 Elsevier Ltd. All rights reserved.

  12. Structural anisotropy of magnetically aligned single wall carbon nanotube films

    SciTech Connect

    Smith, B. W.; Benes, Z.; Luzzi, D. E.; Fischer, J. E.; Walters, D. A.; Casavant, M. J.; Schmidt, J.; Smalley, R. E.

    2000-07-31

    Thick films of aligned single wall carbon nanotubes and ropes have been produced by filtration/deposition from suspension in strong magnetic fields. We measured mosaic distributions of rope orientations in the film plane, for samples of different thicknesses. For an {approx}1 {mu}m film the full width at half maximum (FWHM) derived from electron diffraction is 25 degree sign -28 degree sign . The FWHM of a thicker film ({approx}7 {mu}m) measured by x-ray diffraction is slightly broader, 35{+-}3 degree sign . Aligned films are denser than ordinary filter-deposited ones, and much denser than as-grown material. Optimization of the process is expected to yield smaller FWHMs and higher densities. (c) 2000 American Institute of Physics.

  13. Magnetic Alignment of Cellulose Nanowhiskers in an All-Cellulose Composite

    SciTech Connect

    Li, Dongsheng; Liu, Zuyan; Al-Haik, Marwan; Tehrani, Mehran; Murray, Frank; Tennenbaum, Rina; Garmestani, Hamid

    2010-08-01

    Unidirectional reinforced nanocomposite paper was fabricated from cellulose nanowhiskers and wood pulp under an externally-applied magnetic field. A 1.2 Tesla magnetic field was applied in order to align the nanowhiskers in the pulp as it was being formed into a sheet of paper. The magnetic alignment was driven by the characteristic negative diamagnetic anisotropy of the cellulose nanowhiskers. ESEM micrographs demonstrated unidirectional alignment of the nanowhiskers in the all-cellulose composite paper. Comparing with control paper sheets made from wood pulp only, the storage modulus in the all-cellulose nanocomposites increased dramatically. The storage modulus along the direction perpendicular to the magnetic field was much stronger than that parallel to the magnetic field. This new nanocomposite, which contains preferentially-oriented microstructures and has improved mechanical properties, demonstrates the possibility of expanding the functionality of paper products and constitutes a promising alternative to hydrocarbon based materials and fibers.

  14. Facility Measures Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Honess, Shawn B.; Narvaez, Pablo; Mcauley, James M.

    1991-01-01

    Partly automated facility measures and computes steady near magnetic field produced by object. Designed to determine magnetic fields of equipment to be installed on spacecraft including sensitive magnetometers, with view toward application of compensating fields to reduce interfernece with spacecraft-magnetometer readings. Because of its convenient operating features and sensitivity of its measurements, facility serves as prototype for similar facilities devoted to magnetic characterization of medical equipment, magnets for high-energy particle accelerators, and magnetic materials.

  15. Magnetic alignment of high-aspect ratio microwires into vertical arrays

    NASA Astrophysics Data System (ADS)

    Beardslee, Joseph

    Fundamental studies of magnetic alignment of highly anisotropic mesostructures can enable the clean-room-free fabrication of flexible, array-based solar and electronic devices, in which preferential orientation of nano- or microwire-type objects is desired. In this study, ensembles of 100 micron long Si microwires with ferromagnetic Ni and Co coatings are oriented vertically in the presence of magnetic fields. The degree of vertical alignment and threshold field strength depend on geometric factors, such as microwire length and ferromagnetic coating thickness, as well as interfacial interactions, which are modulated by varying solvent and substrate surface chemistry. Microwire ensembles with vertical alignment over 97% within 10 degrees of normal, as measured by X-ray diffraction, are achieved over square cm scale areas and set into flexible polymer films. A force balance model has been developed as a predictive tool for magnetic alignment, incorporating magnetic torque and empirically derived surface adhesion parameters. As supported by these calculations, microwires are shown to detach from the surface and align vertically in the presence of magnetic fields on the order of 100 gauss. Microwires aligned in this manner are set into a polydimethylsiloxane film where they retain their vertical alignment after the field has been removed and can subsequently be used as a flexible solar absorber layer. Finally, these microwires arrays can be protected for use in electrochemical cells by the conformal deposition of a graphene layer.

  16. Biaxial magnetic alignment in twinned REBa2Cu3Oy superconductors

    NASA Astrophysics Data System (ADS)

    Horii, S.; Nishioka, T.; Arimoto, I.; Fujioka, S.; Doi, T.

    2016-12-01

    Biaxial magnetic alignment of REBa2Cu3O y (RE123, RE = Y, Nd, Sm, Dy, and Er) superconductor powders containing twin microstructures was demonstrated. Appropriate choice of RE effectively improved the degrees of in-plane and c-axis orientation in RE123 powder samples aligned under modulated rotating magnetic fields at room temperature. From the relationship between the magnetic field strength and the degrees of orientation, it is concluded that heavy RE ions induced the improvement of the in-plane magnetic anisotropies in RE123 grains with twin microstructures.

  17. Dynamic Behavior Analysis of Crystal with Magnetic Anisotropy under Imposition of Rotating Magnetic Field

    NASA Astrophysics Data System (ADS)

    Iwai, Kazuhiko

    2010-12-01

    The alignment behavior of a crystal with a magnetic anisotropy of χc < χa under the imposition of a rotating magnetic field has been investigated by numerical calculation. The promotion of the crystal alignment when the projection of the magnetically hard axis on the magnetic field rotating plane is parallel to the magnetic field direction and its suppression when the magnetically hard axis is perpendicular to the magnetic field direction can be explained by the fact that the direction of the driving torque acting on the crystal minimizes the magnetic energy. Non dimensional alignment time normalized by the alignment time under the imposition of a static field is constant in the out-of-step region where the crystal cannot follow the magnetic field rotation during its alignment. The initial phase difference between the projection of the magnetically hard axis on the magnetic field rotating plane and its direction hardly affects the alignment time in the out-of-step region but strongly affects that in the synchronous region where the crystal rotation synchronous with the magnetic field rotation. A crystal aligns quickly if the initial phase difference is between 0 and 90° in the synchronous region. The minimum alignment time is the same as that under the imposition of a static field.

  18. Net field-aligned currents observed by Triad

    NASA Technical Reports Server (NTRS)

    Sugiura, M.; Potemra, T. A.

    1975-01-01

    From the Triad magnetometer observation of a step-like level shift in the east-west component of the magnetic field at 800 km altitude, the existence of a net current flowing into or away from the ionosphere in a current layer was inferred. The current direction is toward the ionosphere on the morning side and away from it on the afternoon side. The field aligned currents observed by Triad are considered as being an important element in the electro-dynamical coupling between the distant magnetosphere and the ionosphere. The current density integrated over the thickness of the layer increases with increasing magnetic activity, but the relation between the current density and Kp in individual cases is not a simple linear relation. An extrapolation of the statistical relation to Kp = 0 indicates existence of a sheet current of order 0.1 amp/m even at extremely quiet times. During periods of higher magnetic activity an integrated current of approximately 1 amp/m and average current density of order 0.000001 amp/sq m are observed. The location and the latitudinal width of the field aligned current layer carrying the net current very roughly agree with those of the region of high electron intensities in the trapping boundary.

  19. Magnetoconvection in sheared magnetic fields

    SciTech Connect

    Bian, N. H.; Garcia, O. E.

    2008-10-15

    The development of magnetoconvection in a sheared magnetic field is investigated. The equilibrium magnetic field B{sub 0} is horizontal and its orientation varies linearly along the vertical axis. Preliminary consideration of the transition from the inertial to the viscous regime of the gravitational resistive interchange instability, reveals that the latter is characterized by the existence of viscoresistive boundary layers of vertical width which scales as Q{sup -1/6}, where Q is the Chandrasekhar number. The situation is analogous to the one encountered in magnetically confined laboratory plasmas, where convective flows are constrained by the magnetic shear to develop in boundary layers located around resonant magnetic surfaces in order to fulfill the 'interchange condition'k{center_dot}B{sub 0}=0, where k is the wave vector of the magnetic perturbation. It follows that when the effect of thermal diffusion is taken into account in the process, convection can only occur above a certain critical value of the Rayleigh number which scales as Q{sup 2/3} for large Q. At the onset, the convection pattern is a superposition of identically thin convective rolls everywhere aligned with the local magnetic field lines and which therefore adopt the magnetic field geometry, a situation also reminiscent of the penumbra of sunspots. Using this degeneracy, equations describing the weakly nonlinear state are obtained and discussed. A reduced magnetohydrodynamic description of magnetoconvection is introduced. Since it is valid for arbitrary magnetic field configurations, it allows a simple extension to the case where there exists an inclination between the direction of gravity and the plane spanned by the equilibrium magnetic field. These reduced magnetohydrodynamic equations are proposed as a powerful tool for further investigations of magnetoconvection in more complex field line geometries.

  20. Relationships between field-aligned currents, electric fields and particle precipitation as observed by dynamics Explorer-2

    NASA Technical Reports Server (NTRS)

    Sugiura, M.; Iyemori, T.; Hoffman, R. A.; Maynard, N. C.; Burch, J. L.; Winningham, J. D.

    1983-01-01

    The relationships between field-aligned currents, electric fields, and particle fluxes are determined using observations from the polar orbiting low-altitude satellite Dynamics Explorer-2. It is shown that the north-south electric field and the east-west magnetic field components are usually highly correlated in the field-aligned current regions. This proportionality observationally proves that the field-aligned current equals the divergence of the height-integrated ionospheric Pedersen current in the meridional plane to a high degree of approximation. As a general rule, in the evening sector the upward field-aligned currents flow in the boundary plasma sheet region and the downward currents flow in the central plasma sheet region. The current densities determined independently from the plasma and magnetic field measurements are compared. Although the current densities deduced from the two methods are in general agreement, the degree and extent of the agreement vary in individual cases.

  1. Relationships between field-aligned currents, electric fields, and particle precipitation as observed by Dynamics Explorer-2

    NASA Technical Reports Server (NTRS)

    Sugiura, M.; Iyemori, T.; Hoffman, R. A.; Maynard, N. C.; Burch, J. L.; Winningham, J. D.

    1984-01-01

    The relationships between field-aligned currents, electric fields, and particle fluxes are determined using observations from the polar orbiting low-altitude satellite Dynamics Explorer-2. It is shown that the north-south electric field and the east-west magnetic field components are usually highly correlated in the field-aligned current regions. This proportionality observationally proves that the field-aligned current equals the divergence of the height-integrated ionospheric Pedersen current in the meridional plane to a high degree of approximation. As a general rule, in the evening sector the upward field-aligned currents flow in the boundary plasma sheet region and the downward currents flow in the central plasma sheet region. The current densities determined independently from the plasma and magnetic field measurements are compared. Although the current densities deduced from the two methods are in general agreement, the degree and extent of the agreement vary in individual cases.

  2. Relationships between Geomagnetic Induced Currents and Field Aligned Currents

    NASA Astrophysics Data System (ADS)

    Waters, C. L.; Barnett, R.; Anderson, B. J.; Gjerloev, J. W.; Korth, H.; Barnes, R. J.

    2015-12-01

    Geomagnetic Induced Currents (GICs) appear in the ground due to time varying magnetic fields that occur during periods of enhanced geomagnetic activity. The resultant time varying electric fields at Earth's surface drive very low frequency, currents through electricity supply transformers which reduces transforming capacity. In extreme cases, electricity supply grids can collapse as multiple transformers are affected. GICs have larger magnitudes at auroral latitudes and should be related to the field aligned current (FAC) and auroral ionosphere currents systems. At ground locations under the regions between upward and downward FACs, the GIC related fields show a direct relationship with the time derivative of the FACs. This allows a conversion factor between FAC and GIC magnitudes. Examples of the relationship between FAC and GIC related fields are presented using data derived from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) and SuperMAG.

  3. Field-aligned current response to solar indices

    NASA Astrophysics Data System (ADS)

    Edwards, Thom R.; Weimer, D. R.; Tobiska, W. K.; Olsen, Nils

    2017-05-01

    Magnetometer data from three satellite missions have been used to analyze and identify the effects of varying solar radiation on the magnitudes and locations of field-aligned currents in the Earth's upper atmosphere. Data from the CHAMP, Ørsted, and Swarm satellite missions have been brought together to provide a database spanning a 15 year period. The extensive time frame has been augmented by data from the ACE satellite, as well as a number of indices of solar radiation. This data set has been sorted by a number of solar wind, interplanetary magnetic field, and solar radiation indices to provide measurements for the field-aligned current structures in both hemispheres for arbitrary seasonal tilts. In addition, routines have been developed to extract the total current for different regions of the current structures, including regions 0, 1, and 2. Results from this study have been used to evaluate the effects of variations in four different solar indices on the total current in different regions of the polar cap. While the solar indices do not have major influence on the total current of the polar cap when compared to solar wind and interplanetary magnetic field parameters, it does appear that there is a nonlinear response to increasing F10.7, M10.7, and S10.7 solar indices. Surprisingly, there appears to be a very linear response as Y10.7 solar index increases.

  4. Field-aligned currents and ionospheric electric fields

    NASA Technical Reports Server (NTRS)

    Yasuhara, F.; Akasofu, S.-I.

    1977-01-01

    It is shown that the observed distribution of the ionospheric electric field can be deduced from an equation combining Ohm's law with the current continuity equation by using the 'observed' distribution of field-aligned currents as the boundary condition for two models of the ionosphere. The first model has one conductive annular ring representing the quiet-time auroral precipitation belt; the second has two conductive annular rings that simulate the discrete and diffuse auroral regions. An analysis is performed to determine how well the electric-field distribution can be reproduced. The results indicate that the first model reproduces the Sq(p)-type distribution, the second model reproduces reasonably well a substorm-type potential and ionospheric current patterns together with the Harang discontinuity, and that the distribution of field-aligned currents is the same for both models.

  5. Photospheric magnetic fields

    NASA Technical Reports Server (NTRS)

    Howard, R.

    1972-01-01

    Knowledge on the nature of magnetic fields on the solar surface is reviewed. At least a large part of the magnetic flux in the solar surface is confined to small bundles of lines of force within which the field strength is of the order of 500 gauss. Magnetic fields are closely associated with all types of solar activity. Magnetic flux appears at the surface at the clearly defined birth or regeneration of activity of an active region. As the region ages, the magnetic flux migrates to form large-scale patterns and the polar fields. Some manifestations of the large-scale distribution are discussed.

  6. Dynamics of field-aligned currents reconstructed by the ground-based and satellite data

    NASA Astrophysics Data System (ADS)

    Nikolaeva, V. D.; Kotikov, A. L.; Sergienko, T. I.

    2014-09-01

    Parameters of field-aligned currents reconstructed by ground-based measurements of magnetic field in the Scandinavian countries (IMAGE) and ionospheric conductivity for specific events of the 6 and 8 December 2004 are represented here. Ionospheric conductivity was calculated from precipitating electron flux measured at DMSP-13 satellite and electron density EISCAT incoherent scattering radar direct measurements. There is a high correlation between field-aligned currents, calculated from DMSP-13 satellite data and field-aligned currents calculated from radar measurements for the December 6, 2004 in the presence of developed ionospheric current system. The comparison of field-aligned currents, reconstructed by the proposed method, with the currents calculated by the variation of magnetic field on the DMSP satellites, confirms correctness of the offered algorithm.

  7. Field-aligned current and the auroral electrojets in the post-noon quadrant

    NASA Astrophysics Data System (ADS)

    Rostoker, G.; Mareschal, M.

    1982-11-01

    It is shown that in the post-noon quadrant, the combination of field-aligned currents associated with the eastward auroral electrojet and polar cap currents produces a magnetic field perturbation pattern on the ground and at TRIAD altitude (800 km) in good agreement with observations. This model permits downward net field-aligned current flow across the post-noon sector auroral oval while at the same time replicating the observation of a sharp level shift in the east-west component of the magnetic perturbation field at 800-km altitude attributed, until now, to net upward field-aligned current. These results reconcile the contentions of Hughes and Rostoker (1977, 1979) that there is net downward field-aligned current across the post-noon auroral oval and of Sugiura and Potemra (1976) that the net current flow in the post-noon quadrant is upward.

  8. Final Technical Report: Global Field Aligned Mesh and Gyrokinetic Field Solver in a Tokamak Edge Geometry

    SciTech Connect

    Cummings, Julian C.

    2013-05-15

    This project was a collaboration between researchers at the California Institute of Technology and the University of California, Irvine to investigate the utility of a global field-aligned mesh and gyrokinetic field solver for simulations of the tokamak plasma edge region. Mesh generation software from UC Irvine was tested with specific tokamak edge magnetic geometry scenarios and the quality of the meshes and the solutions to the gyrokinetic Poisson equation were evaluated.

  9. Field line twist and field-aligned currents in an axially symmetric equilibrium magnetosphere. [of Uranus

    NASA Technical Reports Server (NTRS)

    Voigt, Gerd-Hannes

    1986-01-01

    Field-aligned Birkeland currents and the angle of the magnetic line twist were calculated for an axially symmetric pole-on magnetosphere (assumed to be in MHD equilibrium). The angle of the field line twist was shown to have a strong radial dependence on the axisymmetric magnetotail as well as on the ionospheric conductivity and the amount of thermal plasma contained in closed magnetotail flux tubes. The field line twist results from the planetary rotation, which leads to the development of a toroidal magnetic B-sub-phi component and to differentially rotating magnetic field lines. It was shown that the time development of the toroidal magnetic B-sub-phi component and the rotation frequency are related through an induction equation.

  10. Influence of the electron source distribution on field-aligned currents

    NASA Astrophysics Data System (ADS)

    Bruening, K.; Goertz, C. K.

    1985-01-01

    The field-aligned current density above a discrete auroral arc has been deduced from the downward electron flux and magnetic field measurements onboard the rocket Porcupine flight 4. Both measurements show that the field-aligned current density is, in spite of decreasing peak energies towards the edge of the arc, about 4 times higher there than in the center of the arc. This can be explained by using the single particle description for an anisotropic electron source distribution.

  11. Magnetic Fields in Stars

    NASA Astrophysics Data System (ADS)

    Landstreet, J.; Murdin, P.

    2000-11-01

    Magnetism—the force that deflects the needle of a compass—and magnetic fields have been found in some hundreds of stars during the past 50 yr. Magnetic fields have been detected in T Tauri stars and other pre-main-sequence stars, several types of main sequence stars, white dwarfs and neutron stars. We now know a number of methods by which such magnetic fields may be detected, we are in the proces...

  12. Organic magnetic field sensor

    DOEpatents

    McCamey, Dane; Boehme, Christoph

    2017-01-24

    An organic, spin-dependent magnetic field sensor (10) includes an active stack (12) having an organic material with a spin-dependence. The sensor (10) also includes a back electrical contact (14) electrically coupled to a back of the active stack (12) and a front electrical contact (16) electrically coupled to a front of the active stack (12). A magnetic field generator (18) is oriented so as to provide an oscillating magnetic field which penetrates the active stack (12).

  13. Fabrication of Tri-axially Oriented RE-Ba-Cu-O Ceramics by Magnetic Alignment

    NASA Astrophysics Data System (ADS)

    Yamaki, M.; Furuta, M.; Doi, T.; Shimoyama, J.; Horii, S.

    Magnetic alignment is a new crystal alignment process which enables tri-axial orientation without epitaxial growth at room temperature. In order to investigate the effectiveness of this magnetic tri-axial alignment process, we attempted to fabricate tri-axially oriented ErBa2Cu4O8 (Er124) ceramics by a slip-casting technique under two different modulated rotation magnetic fields (MRFs); uni-directional rotation type and oscillation type. For improvement of the degrees of tri-axial orientation in the Er124 green compacts slip-casted under MRFs, appropriate choice of sample-rotation method, magnetic field condition, control of mean diameter of source powders, and viscosity of slurry was found to be important in the case of MRFs induced by the sample-rotation. At the current stage, the degree of inplane orientation with ∼10̊ in Er124 was achieved.

  14. How are static magnetic fields detected biologically?

    NASA Astrophysics Data System (ADS)

    Finegold, Leonard

    2009-03-01

    There is overwhelming evidence that life, from bacteria to birds to bats, detects magnetic fields, using the fields for orientation or navigation. Indeed there are recent reports (based on Google Earth imagery) that cattle and deer align themselves with the earth's magnetic field. [1]. The development of frog and insect eggs are changed by high magnetic fields, probably through known physical mechanisms. However, the mechanisms for eukaryotic navigation and alignment are not clear. Persuasive published models will be discussed. Evidence, that static magnetic fields might produce therapeutic effects, will be updated [2]. [4pt] [1] S. Begall, et al., Proc Natl Acad Sci USA, 105:13451 (2008). [0pt] [2] L. Finegold and B.L. Flamm, BMJ, 332:4 (2006).

  15. Pulsed taut-wire measurement of the magnetic alignment of the ITS induction cells

    SciTech Connect

    Melton, J.G.; Burns, M.J.; Honaberger, D.J.

    1993-06-01

    The mechanical and magnetic alignment of the first eight induction-cell, solenoid magnets of the Integrated Test Stand (ITS) for the Dual-Axis Radiographic Hydrodynamic Test (DARHT) facility were measured by observing the deflection of a fine, taut wire carrying a pulsed current. To achieve the required alignment (less than 0.25 mm offset and less than 5 mrad tilt), the magnet design uses quadrufilar windings and iron field-smoothing rings. After detailed measurements of each solenoid magnet, the cells are assembled and then mechanically aligned using a laser and an alignment target moved along the cell centerline. After the cells are in final position, the pulsed wire method is used to verify the magnetic alignment. The measurements show an average offset of the magnetic axes from the mechanical axis of 0. 15 mm, with a maximum offset of 0.3 mm. The average tilt of the magnetic axis was 0.7 mrad with a maximum tilt of 1.4 mrad. Tilts are corrected to less than 0.3 mrad, using dipole trim magnets assembled into each cell. Correction is limited noise.

  16. Magnetic field generator

    DOEpatents

    Krienin, Frank

    1990-01-01

    A magnetic field generating device provides a useful magnetic field within a specific retgion, while keeping nearby surrounding regions virtually field free. By placing an appropriate current density along a flux line of the source, the stray field effects of the generator may be contained. One current carrying structure may support a truncated cosine distribution, and it may be surrounded by a current structure which follows a flux line that would occur in a full coaxial double cosine distribution. Strong magnetic fields may be generated and contained using superconducting cables to approximate required current surfaces.

  17. Space Technology 5 observations of auroral field-aligned currents

    NASA Astrophysics Data System (ADS)

    Slavin, James

    During its three month long technology validation mission, Space Technology 5 (ST-5) returned high quality multi-point measurements of the near-Earth magnetic field. Its three micro-satellites were launched into a 300 x 4500 km, dawn - dusk, sun synchronous orbit (inclination = 105.6o) orbit with a period of 138 min by a Pegasus launch vehicle on March 22, 2006. The spacecraft were maintained in a "pearls on a sting" constellation with controlled spacings ranging from just over 5000 km down to under 50 km. The individual micro-satellites were 48 cm tall octagons with diameters of 50 cm. They were spin-stabilized at approximately 20 rpm at deployment and slowly spun-down to about 15 rpm by the end of the mission. Each spacecraft carried a miniature tri-axial fluxgate magnetometer (MAG) provided by the University of California at Los Angeles mounted at the end of a ultra-low mass 72 cm boom. These data allow, for the first time, the separation of temporal and spatial variations in field-aligned current (FAC) perturbations measured in low-Earth orbit on time scales of 10 sec to 10 min. The constellation measurements are used to directly determine field-aligned current sheet motion, thickness, and current density. Two multi-point methods for the inference of FAC current density that have not previously been possible in low-Earth orbit are demonstrated: 1) the "standard method," based upon s/c velocity, but corrected for FAC current sheet motion, and 2) the "gradiometer method" which uses simultaneous magnetic field measurements at two points with known separation. Future studies will apply these methods to the entire ST-5 data set and expand to include horizontal ionospheric currents, ULF waves and geomagnetic field gradient analyses.

  18. Space Technology 5 Observations of Auroral Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Slavin, James

    2008-01-01

    During its three month long technology validation mission, Space Technology 5 (ST-5) returned high quality multi-point measurements of the near-Earth magnetic field. Its three micro-satellites were launched into a 300 x 4500 km, dawn - dusk, sun synchronous orbit (inclination = 105.60) orbit with a period of 138 min by a Pegasus launch vehicle on March 22, 2006. The spacecraft were maintained in a "pearls on a sting" constellation with controlled spacings ranging from just over 5000 km down to under 50 km. The individual micro-satellites were 48 cm tall octagons with diameters of 50 cm. They were spin-stabilized at approximately 20 rpm at deployment and slowly spun-down to about 15 rpm by the end of the mission. Each spacecraft carried a miniature tri-axial fluxgate magnetometer (MAG) provided by the University of California at Los Angeles mounted at the end of a ultra-low mass 72 cm boom. These data allow, for the first time, the separation of temporal and spatial variations in field-aligned current (FAC) perturbations measured in low-Earth orbit on time scales of 10 sec to 10 min. The constellation measurements are used to directly determine field-aligned current sheet motion, thickness. and current density. Two multi-point methods for the inference of FAC current density that have not previously been possible in low-Earth orbit are demonstrated: 1) the -standard method." based upon s/c velocity, but corrected for FAC current sheet motion. and 2) the "gradiometer method" which uses simultaneous magnetic field measurements at two points with known separation. Future studies will apply these methods to the entire ST-5 data sct and expand to include horizontal ionospheric currents. ULF waves and geomagnetic field gradient analyses.

  19. Assessment of a field-aligned ICRF antenna

    NASA Astrophysics Data System (ADS)

    Wukitch, S. J.; Brunner, D.; Ennever, P.; Garrett, M. L.; Hubbard, A.; Labombard, B.; Lau, C.; Lin, Y.; Lipschultz, B.; Miller, D.; Ochoukov, R.; Porkolab, M.; Reinke, M. L.; Terry, J. L.

    2014-02-01

    Impurity contamination and localized heat loads associated with ion cyclotron range of frequency (ICRF) antenna operation are among the most challenging issues for ICRF utilization.. Another challenge is maintaining maximum coupled power through plasma variations including edge localized modes (ELMs) and confinement transitions. Here, we report on an experimental assessment of a field aligned (FA) antenna with respect to impurity contamination, impurity sources, RF enhanced heat flux and load tolerance. In addition, we compare the modification of the scrape of layer (SOL) plasma potential of the FA antenna to a conventional, toroidally aligned (TA) antenna, in order to explore the underlying physics governing impurity contamination linked to ICRF heating. The FA antenna is a 4-strap ICRF antenna where the current straps and antenna enclosure sides are perpendicular to and the Faraday screen rods are parallel to the total magnetic field. In principle, alignment with respect to the total magnetic field minimizes integrated E∥ (electric field along a magnetic field line) via symmetry. Consistent with expectations, we observed that the impurity contamination and impurity source at the FA antenna are reduced compared to the TA antenna. In both L and H-mode discharges, the radiated power is 20-30% lower for a FA-antenna heated discharge than a discharge heated with the TA-antennas. Further we observe that the fraction of RF energy deposited upon the antenna is less than 0.4 % of the total injected RF energy in dipole phasing. The total deposited energy increases significantly when the FA antenna is operated in monopole phasing. The FA antenna also exhibits an unexpected load tolerance for ELMs and confinement transitions compared to the TA antennas. However, inconsistent with expectations, we observe RF induced plasma potentials to be nearly identical for FA and TA antennas when operated in dipole phasing. In monopole phasing, the FA antenna has the highest plasma

  20. Assessment of a field-aligned ICRF antenna

    SciTech Connect

    Wukitch, S. J.; Brunner, D.; Ennever, P.; Garrett, M. L.; Hubbard, A.; Labombard, B.; Lau, C.; Lin, Y.; Lipschultz, B.; Miller, D.; Ochoukov, R.; Porkolab, M.; Reinke, M. L.; Terry, J. L.

    2014-02-12

    Impurity contamination and localized heat loads associated with ion cyclotron range of frequency (ICRF) antenna operation are among the most challenging issues for ICRF utilization.. Another challenge is maintaining maximum coupled power through plasma variations including edge localized modes (ELMs) and confinement transitions. Here, we report on an experimental assessment of a field aligned (FA) antenna with respect to impurity contamination, impurity sources, RF enhanced heat flux and load tolerance. In addition, we compare the modification of the scrape of layer (SOL) plasma potential of the FA antenna to a conventional, toroidally aligned (TA) antenna, in order to explore the underlying physics governing impurity contamination linked to ICRF heating. The FA antenna is a 4-strap ICRF antenna where the current straps and antenna enclosure sides are perpendicular to and the Faraday screen rods are parallel to the total magnetic field. In principle, alignment with respect to the total magnetic field minimizes integrated E∥ (electric field along a magnetic field line) via symmetry. Consistent with expectations, we observed that the impurity contamination and impurity source at the FA antenna are reduced compared to the TA antenna. In both L and H-mode discharges, the radiated power is 20–30% lower for a FA-antenna heated discharge than a discharge heated with the TA-antennas. Further we observe that the fraction of RF energy deposited upon the antenna is less than 0.4 % of the total injected RF energy in dipole phasing. The total deposited energy increases significantly when the FA antenna is operated in monopole phasing. The FA antenna also exhibits an unexpected load tolerance for ELMs and confinement transitions compared to the TA antennas. However, inconsistent with expectations, we observe RF induced plasma potentials to be nearly identical for FA and TA antennas when operated in dipole phasing. In monopole phasing, the FA antenna has the highest plasma

  1. Creation of helical vortices during magnetization of aligned carbon nanotubes filled with Fe: theory and experiment.

    PubMed

    López-Urías, F; Muñoz-Sandoval, E; Reyes-Reyes, M; Romero, A H; Terrones, M; Morán-López, J L

    2005-06-03

    We report a novel magnetic phenomenon consisting of the formation of helical spin configurations during the magnetization of densely packed ferromagnetic nanowires encapsulated inside carbon nanotubes. We studied the hysteresis loops when the magnetic fields are applied parallel and perpendicular to the nanotubes axes. We also performed theoretical calculations on aligned nanowire arrays that clearly indicate the creation of helical spin vortices in the hysteresis loops. The latter are caused by the presence of strong dipolar interactions among neighboring wires.

  2. Investigation of the Possibility of Using Nuclear Magnetic Spin Alignment

    NASA Technical Reports Server (NTRS)

    Dent, William V., Jr.

    1998-01-01

    The goal of the program to investigate a "Gasdynamic fusion propulsion system for space exploration" is to develop a fusion propulsion system for a manned mission to the planet mars. A study using Deuterium and Tritium atoms are currently in progress. When these atoms under-go fusion, the resulting neutrons and alpha particles are emitted in random directions (isotropically). The probable direction of emission is equal for all directions, thus resulting in wasted energy, massive shielding and cooling requirements, and serious problems with the physics of achieving fusion. If the nuclear magnetic spin moments of the deuterium and tritium nuclei could be precisely aligned at the moment of fusion, the stream of emitted neutrons could be directed out the rear of the spacecraft for thrust and the alpha particles directed forward into an electromagnet ot produce electricity to continue operating the fusion engine. The following supporting topics are discussed: nuclear magnetic moments and spin precession in magnetic field, nuclear spin quantum mechanics, kinematics of nuclear reactions, and angular distribution of particles.

  3. NdFeB Magnets Aligned in a 9-T Superconducting Solenoid (asterisk)

    NASA Astrophysics Data System (ADS)

    Mulcahy, T. M.; Hull, J. R.

    2002-08-01

    Commercial-grade magnet powder (Magnequench UG) was uniaxial die-pressed into cylindrical compacts, while being aligned in the 1-T to 8-T DC field of a superconducting solenoid at Argonne National Laboratory. Then, the compacts were added to normal Magnequench UG production batches for sintering and annealing. The variations in magnet properties for different strengths of alignment fields are reported for 15.88-mm (5/8-in.) diameter compacts made with length-to-diameter (L/D) ratios in the range 3 0.25 and L 1. The best magnets were produced when the powder-filled die was inserted into the active field of the solenoid and then pressed. Improvements in the residual flux density of 8% and in the energy product of 16% were achieved by increasing the alignment field beyond the typical 2-T capabilities of electromagnets. The most improvement was achieved for the compacts with the smallest L/D ratio. The ability to make very strong magnets with small L/D, where self-demagnetization effects during alignment are greatest, would benefit most the production of near-final-shape magnets. Compaction of the magnet powder using a horizontal die and a continuously active superconducting solenoid was not a problem. Although the press was operated in the batch mode for this proof-of-concept study, its design is intended to enable automated production.

  4. Swarm Observations of Field-Aligned Currents: Case Studies

    NASA Astrophysics Data System (ADS)

    Le, G.; Chi, P. J.; Gjerloev, J. W.; Stolle, C.; Luhr, H.; Park, J.; Rauberg, J.

    2014-12-01

    In this paper, we report the results of a few case studies of multi-point magnetic field measurements of field-aligned currents (FACs) from Swarm constellation mission to understand their temporal and spatial characteristics. During the commissioning phase, the three Swarm spacecraft were in an identical polar orbit with a string-of-pearl configuration with small separations. During the science operational phase (since April, 2014), the three spacecraft were placed in slightly different polar orbits: one spacecraft in a higher altitude orbit (507km x 512km) and two side-by-side in lower altitude orbits (459km x 462km). We analyze a few FAC events in both orbital phases and during periods of active geomagnetic conditions. The multi-point observations enable us to examine the FACs' temporal evolution and separate their temporal and spatial variations.

  5. Permanent Magnet Ecr Plasma Source With Magnetic Field Optimization

    DOEpatents

    Doughty, Frank C.; Spencer, John E.

    2000-12-19

    In a plasma-producing device, an optimized magnet field for electron cyclotron resonance plasma generation is provided by a shaped pole piece. The shaped pole piece adjusts spacing between the magnet and the resonance zone, creates a convex or concave resonance zone, and decreases stray fields between the resonance zone and the workpiece. For a cylindrical permanent magnet, the pole piece includes a disk adjacent the magnet together with an annular cylindrical sidewall structure axially aligned with the magnet and extending from the base around the permanent magnet. The pole piece directs magnetic field lines into the resonance zone, moving the resonance zone further from the face of the magnet. Additional permanent magnets or magnet arrays may be utilized to control field contours on a local scale. Rather than a permeable material, the sidewall structure may be composed of an annular cylindrical magnetic material having a polarity opposite that of the permanent magnet, creating convex regions in the resonance zone. An annular disk-shaped recurve section at the end of the sidewall structure forms magnetic mirrors keeping the plasma off the pole piece. A recurve section composed of magnetic material having a radial polarity forms convex regions and/or magnetic mirrors within the resonance zone.

  6. Exploring the Potential of Starch/Polycaprolactone Aligned Magnetic Responsive Scaffolds for Tendon Regeneration.

    PubMed

    Gonçalves, Ana I; Rodrigues, Márcia T; Carvalho, Pedro P; Bañobre-López, Manuel; Paz, Elvira; Freitas, Paulo; Gomes, Manuela E

    2016-01-21

    The application of magnetic nanoparticles (MNPs) in tissue engineering (TE) approaches opens several new research possibilities in this field, enabling a new generation of multifunctional constructs for tissue regeneration. This study describes the development of sophisticated magnetic polymer scaffolds with aligned structural features aimed at applications in tendon tissue engineering (TTE). Tissue engineering magnetic scaffolds are prepared by incorporating iron oxide MNPs into a 3D structure of aligned SPCL (starch and polycaprolactone) fibers fabricated by rapid prototyping (RP) technology. The 3D architecture, composition, and magnetic properties are characterized. Furthermore, the effect of an externally applied magnetic field is investigated on the tenogenic differentiation of adipose stem cells (ASCs) cultured onto the developed magnetic scaffolds, demonstrating that ASCs undergo tenogenic differentiation synthesizing a Tenascin C and Collagen type I rich matrix under magneto-stimulation conditions. Finally, the developed magnetic scaffolds were implanted in an ectopic rat model, evidencing good biocompatibility and integration within the surrounding tissues. Together, these results suggest that the effect of the magnetic aligned scaffolds structure combined with magnetic stimulation has a significant potential to impact the field of tendon tissue engineering toward the development of more efficient regeneration therapies.

  7. Field-aligned ICRF antenna design for EAST

    NASA Astrophysics Data System (ADS)

    Wukitch, S. J.; Lin, Y.; Qin, C.; Zhang, X.; Beck, W.; Koert, P.; Zhou, L.

    2015-12-01

    For ion cyclotron range of frequency (ICRF), a number of physics and technological challenges remain for steady state, toroidal devices. Among the most critical is maintaining good coupling and maximizing the coupled power through plasma variations including edge localized modes (ELMs) and confinement transitions. As pulse length increases, enhanced localized heat loads associated with antenna operation can challenge antenna integrity. In addition, ICRF impurity sources and contamination need to be minimized to enable effective plasma heating. Here, we report on a four strap field aligned (FA) antenna design for the EAST tokamak. A FA antenna is an antenna where the current straps and antenna side enclosure are perpendicular to the total magnetic field while the Faraday screen rods are parallel to the total magnetic field. In C-Mod, a FA antenna has been shown to be inherently load tolerant which allows for robust power delivery to the plasma. Furthermore, the RF enhanced heat flux and antenna impurity source were nearly eliminated. For both L and H-mode discharges, the core impurity contamination is 20-30% lower but not eliminated. The emerging physics understanding is that the local RF impurity sources and RF enhanced heat flux is reduced due to the geometric alignment of the FA antenna while impurity contamination is a result of far field sheaths. An important aspect of antenna design is to identify a core absorption scenario that is characterized by strong single pass absorption for a broad range of target discharges. To maximize power coupling, the antenna spectrum needs to balance the k|| needed for strong single pass absorption and high coupling efficiency through evanescent layer. The latest design for a FA four strap adapted to EAST device is balance between geometrical constraints and physics requirements.

  8. Magnetic Alignment Theory and the Interpretation of Polarization

    NASA Technical Reports Server (NTRS)

    Cugnon, P.

    1984-01-01

    The theory of magnetic spinning alignment is outlined. It is shown that a classical enhanced thermal Davis and Greenstein mechanism may be considered as a limiting case of Purcell's suprathermal spinning alignment theory when the number of active sites on a given grain becomes very important and/or for very short lived suprathermal sites. The results are applied to the interstellar medium and some problems in which it may be important are discussed.

  9. Magnetic Trapping of Bacteria at Low Magnetic Fields

    PubMed Central

    Wang, Z. M.; Wu, R. G.; Wang, Z. P.; Ramanujan, R. V.

    2016-01-01

    A suspension of non-magnetic entities in a ferrofluid is referred to as an inverse ferrofluid. Current research to trap non-magnetic entities in an inverse ferrofluid focuses on using large permanent magnets to generate high magnetic field gradients, which seriously limits Lab-on-a-Chip applications. On the other hand, in this work, trapping of non-magnetic entities, e.g., bacteria in a uniform external magnetic field was studied with a novel chip design. An inverse ferrofluid flows in a channel and a non-magnetic island is placed in the middle of this channel. The magnetic field was distorted by this island due to the magnetic susceptibility difference between this island and the surrounding ferrofluid, resulting in magnetic forces applied on the non-magnetic entities. Both the ferromagnetic particles and the non-magnetic entities, e.g., bacteria were attracted towards the island, and subsequently accumulate in different regions. The alignment of the ferrimagnetic particles and optical transparency of the ferrofluid was greatly enhanced by the bacteria at low applied magnetic fields. This work is applicable to lab-on-a-chip based detection and trapping of non-magnetic entities bacteria and cells. PMID:27254771

  10. Magnetic Trapping of Bacteria at Low Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Wang, Z. M.; Wu, R. G.; Wang, Z. P.; Ramanujan, R. V.

    2016-06-01

    A suspension of non-magnetic entities in a ferrofluid is referred to as an inverse ferrofluid. Current research to trap non-magnetic entities in an inverse ferrofluid focuses on using large permanent magnets to generate high magnetic field gradients, which seriously limits Lab-on-a-Chip applications. On the other hand, in this work, trapping of non-magnetic entities, e.g., bacteria in a uniform external magnetic field was studied with a novel chip design. An inverse ferrofluid flows in a channel and a non-magnetic island is placed in the middle of this channel. The magnetic field was distorted by this island due to the magnetic susceptibility difference between this island and the surrounding ferrofluid, resulting in magnetic forces applied on the non-magnetic entities. Both the ferromagnetic particles and the non-magnetic entities, e.g., bacteria were attracted towards the island, and subsequently accumulate in different regions. The alignment of the ferrimagnetic particles and optical transparency of the ferrofluid was greatly enhanced by the bacteria at low applied magnetic fields. This work is applicable to lab-on-a-chip based detection and trapping of non-magnetic entities bacteria and cells.

  11. Sources of field-aligned currents in the auroral plasma

    SciTech Connect

    Marshall, J.A.; Burch, J.L. ); Kan, J.R. ); Reiff, P.H. ); Slavin, J.A. )

    1991-01-01

    Data from the Dynamics Explorer 1 High Altitude Plasma Instrument (HAPI) and magnetometer are used to investigate the sources of field-aligned currents in the nightside auroral zone. It is found that the formula developed by S. Knight predicts the field-aligned current density fairly accurately in regions where a significant potential drop can be inferred from the HAPI data; there are, however, regions in which the proportionality between potential drop and field-aligned current does not hold. In particular, the authors note occurrences of strong upward field-aligned current associated not with inverted-V events but instead with suprathermal bursts. In addition, upward field-aligned currents are often observed to peak near the edges of inverted-V events, rather than in the center as would be predicted by Knight.

  12. Sources of field-aligned currents in the auroral plasma

    NASA Astrophysics Data System (ADS)

    Marshall, J. A.; Burch, J. L.; Kan, J. R.; Reiff, P. H.; Slavin, J. A.

    1991-01-01

    Data from the Dynamics Explorer 1 High Altitude Plasma Instrument (HAPI) and magnetometer are used to investigate the sources of field-aligned currents in the nightside auroral zone. It is found that the formula developed by S. Knight predicts the field-aligned current density fairly accurately in regions where a significant potential drop can be inferred from the HAPI data; there are, however, regions in which the proportionality between potential drop and field-aligned current does not hold. In particular, occurrences of strong upward field-aligned current associated not with inverted-V events but instead with suprathermal bursts are noted. In addition, upward field-aligned currents are often observed to peak near the edges of inverted-V events, rather than in the center as would be predicted by Knight.

  13. Mode conversion of Langmuir to electromagnetic waves at magnetic field-aligned density inhomogeneities: Simulations, theory, and applications to the solar wind and the corona

    SciTech Connect

    Kim, Eun-Hwa; Cairns, Iver H.; Robinson, Peter A.

    2008-10-15

    Linear mode conversion of Langmuir waves to radiation near the plasma frequency at density gradients is potentially relevant to multiple solar radio emissions, ionospheric radar experiments, laboratory plasma devices, and pulsars. Here we study mode conversion in warm magnetized plasmas using a numerical electron fluid simulation code with the density gradient parallel to the ambient magnetic field B{sub 0} for a range of incident Langmuir wavevectors. Our results include: (1) both o- and x-mode waves are produced for {omega}=({omega}L/c){sup 1/3}({omega}{sub c}/{omega})(less-or-similar sign)1, contrary to previous ideas. Only the o mode is produced for {omega}(greater-or-similar sign)1.5. Here {omega}{sub c} is the (angular) electron cyclotron frequency, {omega} is the angular wave frequency, L is the length scale of the (linear) density gradient, and c is the speed of light. A WKB-style analysis accounts semiquantitatively for the production and relative conversion efficiencies of the o and x modes in the simulations. (2) In the unmagnetized limit, equal amounts of o- and x-mode radiation are produced. (3) The mode conversion window narrows as {omega} increases. (4) As {omega} increases the total electromagnetic field changes from linear to circular polarization, with the o- and x-mode signals remaining circularly polarized. (5) The conversion efficiency to the x mode decreases monotonically as {omega} increases while the o-mode conversion efficiency oscillates due to an interference phenomenon between incoming and reflected Langmuir/z modes. (6) The maximum total conversion efficiencies for wave power from the Langmuir/z mode to radiation are of order 50%-70%. They depend strongly on the wave frequency when close to the background plasma frequency but weakly on the electron temperature T{sub 0} and {beta}=T{sub 0}/mc{sup 2}. The corresponding energy conversion efficiencies are favored since they allow separation into o and x modes, use directly measured

  14. FAST/Polar Conjunction Study of Field-Aligned Auroral Acceleration and Corresponding Magnetotail Drivers

    NASA Technical Reports Server (NTRS)

    Schriver, D.; Ashour-Abdalla, M.; Strangeway, R. J.; Richard, R. L.; Klezting, C.; Dotan, Y.; Wygant, J.

    2003-01-01

    The discrete aurora results when energized electrons bombard the Earth's atmosphere at high latitudes. This paper examines the physical processes that can cause field-aligned acceleration of plasma particles in the auroral region. A data and theoretical study has been carried out to examine the acceleration mechanisms that operate in the auroral zone and to identi@ the magnetospheric drivers of these acceleration mechanisms. The observations used in the study were collected by the Fast Auroral Snapshot (FAST) and Polar satellites when the two satellites were in approximate magnetic conjunction in the auroral region. During these events FAST was in the middle of the auroral zone and Polar was above the auroral zone in the near-Earth plasma sheet. Polar data were used to determine the conditions in the magnetotail at the time field-aligned acceleration was measured by FAST in the auroral zone. For each of the magnetotail drivers identified in the data study, the physics of field-aligned acceleration in the auroral region was examined using existing theoretical efforts and/or a long-system particle in cell simulation to model the magnetically connected region between the two satellites. Results from the study indicate that there are three main drivers of auroral acceleration: (1) field-aligned currents that lead to quasistatic parallel potential drops (parallel electric fields), (2) earthward flow of high-energy plasma beams from the magnetotail into the auroral zone that lead to quasistatic parallel potential drops, and (3) large-amplitude Alfven waves that propagate into the auroral region from the magnetotail. The events examined thus far confm the previously established invariant latitudinal dependence of the drivers and show a strong dependence on magnetic activity. Alfven waves tend to occur primarily at the poleward edge of the auroral region during more magnetically active times and are correlated with intense electron precipitation. At lower latitudes away

  15. FAST/Polar Conjunction Study of Field-Aligned Auroral Acceleration and Corresponding Magnetotail Drivers

    NASA Technical Reports Server (NTRS)

    Schriver, D.; Ashour-Abdalla, M.; Strangeway, R. J.; Richard, R. L.; Klezting, C.; Dotan, Y.; Wygant, J.

    2003-01-01

    The discrete aurora results when energized electrons bombard the Earth's atmosphere at high latitudes. This paper examines the physical processes that can cause field-aligned acceleration of plasma particles in the auroral region. A data and theoretical study has been carried out to examine the acceleration mechanisms that operate in the auroral zone and to identi@ the magnetospheric drivers of these acceleration mechanisms. The observations used in the study were collected by the Fast Auroral Snapshot (FAST) and Polar satellites when the two satellites were in approximate magnetic conjunction in the auroral region. During these events FAST was in the middle of the auroral zone and Polar was above the auroral zone in the near-Earth plasma sheet. Polar data were used to determine the conditions in the magnetotail at the time field-aligned acceleration was measured by FAST in the auroral zone. For each of the magnetotail drivers identified in the data study, the physics of field-aligned acceleration in the auroral region was examined using existing theoretical efforts and/or a long-system particle in cell simulation to model the magnetically connected region between the two satellites. Results from the study indicate that there are three main drivers of auroral acceleration: (1) field-aligned currents that lead to quasistatic parallel potential drops (parallel electric fields), (2) earthward flow of high-energy plasma beams from the magnetotail into the auroral zone that lead to quasistatic parallel potential drops, and (3) large-amplitude Alfven waves that propagate into the auroral region from the magnetotail. The events examined thus far confm the previously established invariant latitudinal dependence of the drivers and show a strong dependence on magnetic activity. Alfven waves tend to occur primarily at the poleward edge of the auroral region during more magnetically active times and are correlated with intense electron precipitation. At lower latitudes away

  16. Formation of magnetically anisotropic composite films at low magnetic fields

    NASA Astrophysics Data System (ADS)

    Ghazi Zahedi, Maryam; Ennen, Inga; Marchi, Sophie; Barthel, Markus J.; Hütten, Andreas; Athanassiou, Athanassia; Fragouli, Despina

    2017-04-01

    We present a straightforward two-step technique for the fabrication of poly (methyl methacrylate) composites with embedded aligned magnetic chains. First, ferromagnetic microwires are realized in a poly (methyl methacrylate) solution by assembling iron nanoparticles in a methyl methacrylate solution under heat in an external magnetic field of 160 mT. The simultaneous thermal polymerization of the monomer throughout the wires is responsible for their permanent linkage and stability. Next, the polymer solution containing the randomly dispersed microwires is casted on a solid substrate in the presence of a low magnetic field (20-40 mT) which induces the final alignment of the microwires into long magnetic chains upon evaporation of the solvent. We prove that the presence of the nanoparticles assembled in the form of microwires is a key factor for the formation of the anisotropic films under low magnetic fields. In fact, such low fields are not capable of driving and assembling dispersed magnetic nanoparticles in the same type of polymer solutions. Hence, this innovative approach can be utilized for the synthesis of magnetically anisotropic nanocomposite films at low magnetic fields.

  17. Method for alignment of microwires

    DOEpatents

    Beardslee, Joseph A.; Lewis, Nathan S.; Sadtler, Bryce

    2017-01-24

    A method of aligning microwires includes modifying the microwires so they are more responsive to a magnetic field. The method also includes using a magnetic field so as to magnetically align the microwires. The method can further include capturing the microwires in a solid support structure that retains the longitudinal alignment of the microwires when the magnetic field is not applied to the microwires.

  18. Magnetic fields in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Chiba, Masashi

    The magnetic-field characteristics in spiral galaxies are investigated, with emphasis on the Milky Way. The dynamo theory is considered, and axisymmetric spiral (ASS) and bisymmetric spiral (BSS) magnetic fields are analyzed. Toroidal and poloidal magnetic fields are discussed.

  19. Dynamical formation of spatially localized arrays of aligned nanowires in plastic films with magnetic anisotropy.

    PubMed

    Fragouli, Despina; Buonsanti, Raffaella; Bertoni, Giovanni; Sangregorio, Claudio; Innocenti, Claudia; Falqui, Andrea; Gatteschi, Dante; Cozzoli, Pantaleo Davide; Athanassiou, Athanassia; Cingolani, Roberto

    2010-04-27

    We present a simple technique for magnetic-field-induced formation, assembling, and positioning of magnetic nanowires in a polymer film. Starting from a polymer/iron oxide nanoparticle casted solution that is allowed to dry along with the application of a weak magnetic field, nanocomposite films incorporating aligned nanocrystal-built nanowire arrays are obtained. The control of the dimensions of the nanowires and of their localization across the polymer matrix is achieved by varying the duration of the applied magnetic field, in combination with the evaporation dynamics. These multifunctional anisotropic free-standing nanocomposite films, which demonstrate high magnetic anisotropy, can be used in a wide field of technological applications, ranging from sensors to microfluidics and magnetic devices.

  20. Magnetic field dosimeter development

    SciTech Connect

    Lemon, D.K.; Skorpik, J.R.; Eick, J.L.

    1980-09-01

    In recent years there has been increased concern over potential health hazards related to exposure of personnel to magnetic fields. If exposure standards are to be established, then a means for measuring magnetic field dose must be available. To meet this need, the Department of Energy has funded development of prototype dosimeters at the Battelle Pacific Northwest Laboratory. This manual reviews the principle of operation of the dosimeter and also contains step-by-step instructions for its operation.

  1. Magnetosheath magnetic field variability

    NASA Technical Reports Server (NTRS)

    Sibeck, D. G.

    1994-01-01

    A case study using simulations IRM and CCE observations demonstrates that transient magnetospheric events correspond to pressure pulses in the magnetosheath, inward bow shock motion, and magnetopause compression. Statistical surveys indicate that the magnetosheath magnetic field orientation rarely remains constant during periods of magnetopause and bow shock motion (both characterized by periods of 1 to 10 min). There is no tendency for bow shock motion to occur for southward interplanetary magnetic field (IMF) orientations.

  2. Solar Wind Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Smith, E. J.

    1995-01-01

    The magnetic fields originate as coronal fields that are converted into space by the supersonic, infinitely conducting, solar wind. On average, the sun's rotation causes the field to wind up and form an Archimedes Spiral. However, the field direction changes almost continuously on a variety of scales and the irregular nature of these changes is often interpreted as evidence that the solar wind flow is turbulent.

  3. Solar Wind Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Smith, E. J.

    1995-01-01

    The magnetic fields originate as coronal fields that are converted into space by the supersonic, infinitely conducting, solar wind. On average, the sun's rotation causes the field to wind up and form an Archimedes Spiral. However, the field direction changes almost continuously on a variety of scales and the irregular nature of these changes is often interpreted as evidence that the solar wind flow is turbulent.

  4. Magnetic Field Illuminated

    NASA Image and Video Library

    2016-06-16

    Each day NASA solar scientists produce overlays (in white lines) that show their estimation of how the magnetic field lines above the sun are configured (June16, 2016). In the video clip we show the sun in a wavelength of extreme ultraviolet light, then reveal the magnetic field line configuration in the same wavelength. Notice how the lines are tightly bundled near the lighter-toned active regions, which are magnetically intense regions. The magnetic lines from the darker areas, called coronal holes, open out into space and the extended lines show that. Our magnetically active sun is a dynamic body that changes all the time. Movie are also available at the Photojournal. http://photojournal.jpl.nasa.gov/catalog/PIA20881

  5. Magnetic Control of MOF Crystal Orientation and Alignment.

    PubMed

    Cheng, Fei; Marshall, Ellis S; Young, Adam J; Robinson, Peter J; Bouillard, Jean-Sebastien G; Adawi, Ali M; Vermeulen, Nicolaas A; Farha, Omar K; Reithofer, Michael R; Chin, Jia Min

    2017-09-14

    Most MOFs possess anisotropic properties, the full exploitation of which necessitates a general strategy for the controllable orientation of such MOF crystals. Current methods largely rely upon layer-by-layer MOF epitaxy or tuning of MOF crystal growth on appropriate substrates, yielding MOFs with fixed crystal orientations. Here, the dynamic magnetic alignment of different MOF crystals (NH2-MIL-53(Al) and NU-1000) is shown. The MOFs were magnetized by electrostatic adsorption of iron oxide nanoparticles, dispersed in curable polymer resins (Formlabs 1+ clear resin / Sylgard® 184), magnetically oriented and fixed by resin curing. The importance of crystal orientation on MOF functionality was demonstrated whereby magnetically aligned NU-1000/Sylgard® 184 composite was excited with linearly polarized 405 nm light, affording an anisotropic fluorescence response dependent on the polarization angle of the excitation beam relative to NU-1000 crystal orientation. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Orienting Paramecium with intense static magnetic fields

    NASA Astrophysics Data System (ADS)

    Valles, James M., Jr.; Guevorkian, Karine; Quindel, Carl

    2004-03-01

    Recent experiments on cell division suggest the application of intense static magnetic fields as a novel tool for the manipulation of biological systems [1]. The magnetic field appears to couple to the intrinsic anisotropies in the diamagnetic components of the cells. Here, we present measurements of the intrinsic average diamagnetic anisotropy of the whole single celled ciliate, Paramecium Caudatum. Magnetic fields, 2.5 T < B < 8 T were applied to immobilized (non-swimming) Paramecium Caudatum that were suspended in a density matched medium. The organisms align with their long axis parallel to the applied magnetic field. Their intrinsic diamagnetic anisotropy is 3x10-11 in cgs units. We will discuss the implications of these results for employing magnetic fields to probe the behavior of swimming Paramecium. [1] J. M. Valles, Jr. et al., Expt. Cell Res.274, 112-118 (2002).

  7. Molecules in Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Berdyugina, Svetlana

    2015-08-01

    Molecules probe cool matter in the Universe and various astrophysical objects. Their ability to sense magnetic fields provides new insights into magnetic properties of these objects. During the past fifteen years we have carried out a theoretical study of molecular magnetic effects such as the Zeeman, Paschen-Back and Hanle effects and their applications for inferring magnetic structures and spatial inhomogeneities on the Sun, cool stars, brown dwarfs, and exoplanets from molecular spectro-polarimetry (e.g., Berdyugina 2011). Here, we present an overview of this study and compare our theoretical predictions with recent laboratory measurements of magnetic properties of some molecules. We present also a new web-based tool to compute molecular magnetic effects and polarized spectra which is supported by the ERC Advanced Grant HotMol.

  8. Fantastic Striations and Where to Find Them: The Origin of Magnetically Aligned Striations in Interstellar Clouds

    NASA Astrophysics Data System (ADS)

    Chen, Che-Yu; Li, Zhi-Yun; King, Patrick K.; Fissel, Laura M.

    2017-10-01

    Thin, magnetically aligned striations of relatively moderate contrast with the background are commonly observed in both atomic and molecular clouds. They are also prominent in MHD simulations with turbulent converging shocks. The simulated striations develop within a dense, stagnated sheet in the midplane of the post-shock region where magnetically induced converging flows collide. We show analytically that the secondary flows are an inevitable consequence of the jump conditions of oblique MHD shocks. They produce the stagnated, sheet-like sub-layer through a secondary shock when, roughly speaking, the Alfvénic speed in the primary converging flows is supersonic, a condition that is relatively easy to satisfy in interstellar clouds. The dense sub-layer is naturally threaded by a strong magnetic field that lies close to the plane of the sub-layer. The substantial magnetic field makes the sheet highly anisotropic, which is the key to the striation formation. Specifically, perturbations of the primary inflow that vary spatially perpendicular to the magnetic field can easily roll up the sheet around the field lines without bending them, creating corrugations that appear as magnetically aligned striations in column density maps. On the other hand, perturbations that vary spatially along the field lines curve the sub-layer and alter its orientation relative to the magnetic field locally, seeding special locations that become slanted overdense filaments and prestellar cores through enhanced mass accumulation along field lines. In our scenario, the dense sub-layer, which is unique to magnetized oblique shocks, is the birthplace for both magnetically aligned diffuse striations and massive star-forming structures.

  9. Magnetic Fields in Massive Filaments

    NASA Astrophysics Data System (ADS)

    Pillai, Thushara

    Magnetic fields pervade galaxies, shaping them from the largest scales to the smallest star forming scales. A firm understanding of their role is crucial to our understanding of the physics of ISM. A dominant phase of the ISM that has received considerable attention is that of filaments which are ubiquitous and dominate the mass reservoir in molecular clouds. Enormous progress has been made recently towards understanding filament properties. The next major step should be to understand the role of magnetic fields in filaments. We propose to take advantage of HAWC+ dust emission polarimeter now available on SOFIA to launch a pilot polarization study towards three major classes of filaments: (i) Pristine (ii) Hub-Filament systems and (iii) Perturbed. HAWC+ will trace the connection between the star forming cores and the filaments enveloping them. By covering a vast range in parameter space from quiescent to active filaments, we will be constraining the initial conditions prior to star formation, during star formation and after star formation (feedback from newly formed stars on their parent clouds.) The interpretation of observations will be supported by extensive custom-made numerical simulations of magnetized clouds and subsequent dust radiative transfer with various grain alignment mechanisms, as provided by collaborators. Combined, these observations will provide the first panoramic view of the magnetized nature of massive filaments in the ISM.

  10. Magnetic Fields in Massive Filaments

    NASA Astrophysics Data System (ADS)

    Pillai, G. S. Thushara

    2015-10-01

    Magnetic fields pervade galaxies, shaping them from the largest scales to the smallest star forming scales. A firm understanding of their role is crucial to our understanding of the physics of ISM. A dominant phase of the ISM that has received considerable attention is that of filaments which are ubiquitous and dominate the mass reservoir in molecular clouds. Enormous progress has been made recently towards understanding filament properties. The next major step should be to understand the role of magnetic fields in filaments. We propose to take advantage of HAWC+ dust emission polarimeter now available on SOFIA to launch a pilot polarization study towards three major classes of filaments: (i) Pristine (ii) Hub-Filament systems and (iii) Perturbed. HAWC+ will trace the connection between the star forming cores and the filaments enveloping them. By covering a vast range in parameter space from quiescent to active filaments, we will be constraining the initial conditions prior to star formation, during star formation and after star formation (feedback from newly formed stars on their parent clouds.) The interpretation of observations will be supported by extensive custom--made numerical simulations of magnetized clouds and subsequent dust radiative transfer with various grain alignment mechanisms, as provided by collaborators. Combined, these observations will provide the first panoramic view of the magnetized nature of massive filaments in the ISM.

  11. Influence of the long-chain/short-chain amphiphile ratio on lateral diffusion of PEG-lipid in magnetically aligned lipid bilayers as measured via pulsed-field-gradient NMR.

    PubMed

    Soong, Ronald; Macdonald, Peter M

    2005-09-01

    Lateral diffusion measurements of polyethylene glycol(PEG)-lipid incorporated into magnetically aligned lipid bilayers, composed of dimyristoyl phosphatidylcholine (DMPC) plus dihexanoyl phosphatidylcholine (DHPC) plus 1 mol % (relative to DMPC) dimyristoyl phosphatidylethanolamine-n-[methoxy(polyethylene glycol)-2000] (DMPE-PEG 2000), were performed using stimulated-echo pulsed-field-gradient proton ((1)H) nuclear magnetic resonance spectroscopy. The DMPE-PEG 2000 (1 mol %, 35 degrees C) lateral diffusion coefficient D varied directly with the mole fraction of DMPC, X(DMPC) = q/(1+q) where q = DMPC/DHPC molar ratio, decreasing progressively from D = 1.65 x 10(-11) m(2) s(-1) at q approximately 4.7 to D = 0.65 x 10(-11) m(2) s(-1) at q approximately 2.5. Possible sources of this dependence, including orientational disorder, obstruction, and PEG-lipid sequestration, were simulated using, respectively, a diffusion-in-a-cone model, percolation theory, and a two-phase PEG distribution model. Orientational disorder alone was not capable of reproducing the observations, but in combination with either obstruction or PEG-lipid two-phase distribution models did so satisfactorily. A combination of all three models yielded the most reasonable fit to the observed dependence of lateral diffusion on q. These same effects would be expected to influence lateral diffusion of any bilayer-associating species in such systems.

  12. Influence of the Long-Chain/Short-Chain Amphiphile Ratio on Lateral Diffusion of PEG-Lipid in Magnetically Aligned Lipid Bilayers as Measured via Pulsed-Field-Gradient NMR

    PubMed Central

    Soong, Ronald; Macdonald, Peter M.

    2005-01-01

    Lateral diffusion measurements of polyethylene glycol(PEG)-lipid incorporated into magnetically aligned lipid bilayers, composed of dimyristoyl phosphatidylcholine (DMPC) plus dihexanoyl phosphatidylcholine (DHPC) plus 1 mol % (relative to DMPC) dimyristoyl phosphatidylethanolamine-n-[methoxy(polyethylene glycol)-2000] (DMPE-PEG 2000), were performed using stimulated-echo pulsed-field-gradient proton (1H) nuclear magnetic resonance spectroscopy. The DMPE-PEG 2000 (1 mol %, 35°C) lateral diffusion coefficient D varied directly with the mole fraction of DMPC, XDMPC = q/(1+q) where q = DMPC/DHPC molar ratio, decreasing progressively from D = 1.65 × 10−11 m2 s−1 at q ≈ 4.7 to D = 0.65 × 10−11 m2 s−1 at q ≈ 2.5. Possible sources of this dependence, including orientational disorder, obstruction, and PEG-lipid sequestration, were simulated using, respectively, a diffusion-in-a-cone model, percolation theory, and a two-phase PEG distribution model. Orientational disorder alone was not capable of reproducing the observations, but in combination with either obstruction or PEG-lipid two-phase distribution models did so satisfactorily. A combination of all three models yielded the most reasonable fit to the observed dependence of lateral diffusion on q. These same effects would be expected to influence lateral diffusion of any bilayer-associating species in such systems. PMID:15994903

  13. Cluster Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Carilli, C. L.; Taylor, G. B.

    Magnetic fields in the intercluster medium have been measured using a variety of techniques, including studies of synchrotron relic and halo radio sources within clusters, studies of inverse Compton X-ray emission from clusters, surveys of Faraday rotation measures of polarized radio sources both within and behind clusters, and studies of cluster cold fronts in X-ray images. These measurements imply that most cluster atmospheres are substantially magnetized, with typical field strengths of order 1 μGauss with high areal filling factors out to Mpc radii. There is likely to be considerable variation in field strengths and topologies both within and between clusters, especially when comparing dynamically relaxed clusters to those that have recently undergone a merger. In some locations, such as the cores of cooling flow clusters, the magnetic fields reach levels of 10-40 μG and may be dynamically important. In all clusters the magnetic fields have a significant effect on energy transport in the intracluster medium. We also review current theories on the origin of cluster magnetic fields.

  14. The electric field alignment of ice particles in thunderstorms

    NASA Technical Reports Server (NTRS)

    Weinheimer, Andrew J.; Few, Arthur A.

    1987-01-01

    Electrical and aerodynamic torques on atmospheric ice particles are calculaed in order to assess the degree of alignment of these particles with the electric fields in thunderstorms. In such clouds fields of many tens of kilovolts per meter are commonly measured, and values of 100 to 200 kV/m are not rare. For E = 100 kV/m the calculations indicate that electric field alignment occurs for crystals with major dimensions up to maximum values in the range from 200 microns to 1 mm, depending upon crystal type. Columns are aligned more easily than platelike crystals, except for dendrites which, by virtue of their smaller assumed density, have smaller fall velocities thereby experiencing weaker aerodynamic torques. Thus a substantial degree of alignment is expected for E = 100 kV/m. For E = 10 kV/m only much smaller crystals will be aligned, probably only ones with major dimensions of less than 50 microns or so.

  15. The electric field alignment of ice particles in thunderstorms

    NASA Technical Reports Server (NTRS)

    Weinheimer, Andrew J.; Few, Arthur A.

    1987-01-01

    Electrical and aerodynamic torques on atmospheric ice particles are calculaed in order to assess the degree of alignment of these particles with the electric fields in thunderstorms. In such clouds fields of many tens of kilovolts per meter are commonly measured, and values of 100 to 200 kV/m are not rare. For E = 100 kV/m the calculations indicate that electric field alignment occurs for crystals with major dimensions up to maximum values in the range from 200 microns to 1 mm, depending upon crystal type. Columns are aligned more easily than platelike crystals, except for dendrites which, by virtue of their smaller assumed density, have smaller fall velocities thereby experiencing weaker aerodynamic torques. Thus a substantial degree of alignment is expected for E = 100 kV/m. For E = 10 kV/m only much smaller crystals will be aligned, probably only ones with major dimensions of less than 50 microns or so.

  16. Magnetic Field Solver

    NASA Technical Reports Server (NTRS)

    Ilin, Andrew V.

    2006-01-01

    The Magnetic Field Solver computer program calculates the magnetic field generated by a group of collinear, cylindrical axisymmetric electromagnet coils. Given the current flowing in, and the number of turns, axial position, and axial and radial dimensions of each coil, the program calculates matrix coefficients for a finite-difference system of equations that approximates a two-dimensional partial differential equation for the magnetic potential contributed by the coil. The program iteratively solves these finite-difference equations by use of the modified incomplete Cholesky preconditioned-conjugate-gradient method. The total magnetic potential as a function of axial (z) and radial (r) position is then calculated as a sum of the magnetic potentials of the individual coils, using a high-accuracy interpolation scheme. Then the r and z components of the magnetic field as functions of r and z are calculated from the total magnetic potential by use of a high-accuracy finite-difference scheme. Notably, for the finite-difference calculations, the program generates nonuniform two-dimensional computational meshes from nonuniform one-dimensional meshes. Each mesh is generated in such a way as to minimize the numerical error for a benchmark one-dimensional magnetostatic problem.

  17. X-ray study of aligned magnetic stripe domains in perpendicular multilayers

    SciTech Connect

    Hellwig, O.; Denbeaux, G.P.; Kortright, J.B.; Fullerton, Eric E.

    2003-03-03

    We have investigated the stripe domain structure and the magnetic reversal of perpendicular Co/Pt based multilayers at room temperature using magnetometry, magnetic imaging and magnetic x-ray scattering. In-plane field cycling aligns the stripe domains along the field direction. In magnetic x-ray scattering the parallel stripe domains act as a magnetic grating resulting in observed Bragg reflections up to 5th order. We model the scattering profile to extract and quantify the domain as well as domain wall widths. Applying fields up to {approx}1.2 kOe perpendicular to the film reversibly changes the relative width of up versus down domains while maintaining the overall stripe periodicity. Fields above 1.2 kOe introduce irreversible changes into the domain structure by contracting and finally annihilating individual stripe domains. We compare the current results with modeling and previous measurements of films with perpendicular anisotropy.

  18. Imaging the antiparallel magnetic alignment of adjacent Fe and MnAs thin films

    NASA Astrophysics Data System (ADS)

    Breitwieser, R.; Marangolo, M.; Lüning, J.; Jaouen, N.; Joly, L.; Eddrief, M.; Etgens, V. H.; Sacchi, M.

    2008-09-01

    The magnetic coupling between iron and α-MnAs in the epitaxial system Fe/MnAs/GaAs(001) has been studied at the submicron scale, using element-selective x-ray photoemission electron microscopy. At room temperature, MnAs layers display ridges and grooves, alternating α (magnetic) and β (nonmagnetic) phases. The self-organized microstructure of MnAs and the stray fields that it generates govern the local alignment between the Fe and α-MnAs magnetization directions, which is mostly antiparallel with a marked dependence upon the magnetic domain size.

  19. Magnetic fields at uranus.

    PubMed

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

    1986-07-04

    The magnetic field experiment on the Voyager 2 spacecraft revealed a strong planetary magnetic field of Uranus and an associated magnetosphere and fully developed bipolar masnetic tail. The detached bow shock wave in the solar wind supersonic flow was observed upstream at 23.7 Uranus radii (1 R(U) = 25,600 km) and the magnetopause boundary at 18.0 R(U), near the planet-sun line. A miaximum magnetic field of 413 nanotesla was observed at 4.19 R(U ), just before closest approach. Initial analyses reveal that the planetary magnetic field is well represented by that of a dipole offset from the center of the planet by 0.3 R(U). The angle between Uranus' angular momentum vector and the dipole moment vector has the surprisingly large value of 60 degrees. Thus, in an astrophysical context, the field of Uranus may be described as that of an oblique rotator. The dipole moment of 0.23 gauss R(3)(U), combined with the large spatial offset, leads to minimum and maximum magnetic fields on the surface of the planet of approximately 0.1 and 1.1 gauss, respectively. The rotation period of the magnetic field and hence that of the interior of the planet is estimated to be 17.29+/- 0.10 hours; the magnetotail rotates about the planet-sun line with the same period. Thelarge offset and tilt lead to auroral zones far from the planetary rotation axis poles. The rings and the moons are embedded deep within the magnetosphere, and, because of the large dipole tilt, they will have a profound and diurnally varying influence as absorbers of the trapped radiation belt particles.

  20. Direct-write 3D printing of composite materials with magnetically aligned discontinuous reinforcement

    NASA Astrophysics Data System (ADS)

    Martin, Joshua J.; Caunter, Andrew; Dendulk, Amy; Goodrich, Scott; Pembroke, Ryan; Shores, Dan; Erb, Randall M.

    2017-05-01

    Three-dimensional (3D) printing of fiber reinforced composites represents an enabling technology that may bring toughness and specific strength to complex parts. Recently, direct-write 3D printing has been offered as a promising route to manufacturing fiber reinforced composites that show high specific strength. These approaches primarily rely on the use of shear-alignment during the extrusion process to align fibers along the printing direction. Shear alignment prevents fibers from being oriented along principle stress directions of the final designed part. This paper describes a new direct-write style 3D printing system that incorporates magnetic fields to actively control the orientation of reinforcing fibers during the printing of fiber reinforced composites. Such a manufacturing system is fraught with complications from the high shear dominated alignment experienced by the fibers during extrusion to the slow magnetic alignment dynamics of fibers in viscous media. Here we characterize these issues and suggest effective operating windows in which magnetic alignment is a viable approach to orienting reinforcing particles during direct-write 3D printing.

  1. Localized field-aligned currents and 4-min TEC and ground magnetic oscillations during the 2015 eruption of Chile's Calbuco volcano

    NASA Astrophysics Data System (ADS)

    Aoyama, Tadashi; Iyemori, Toshihiko; Nakanishi, Kunihito; Nishioka, Michi; Rosales, Domingo; Veliz, Oscar; Safor, Erick Vidal

    2016-08-01

    The Calbuco volcano in southern Chile erupted on April 22, 2015. About 2 h after the first eruption, a Swarm satellite passed above the volcano and observed enhancement of small-amplitude (~0.5 nT) magnetic fluctuations with wave-packet structure which extends 15° in latitude. Similar wave packet is seen at the geomagnetic conjugate point of the volcano. Just after the eruption, geomagnetic fluctuations with the spectral peaks around the vertical acoustic resonance periods, 215 and 260 s, were also observed at Huancayo Geomagnetic Observatory located on the magnetic equator. Besides these observations, around 4-min, i.e., 175, 205 and 260 s, oscillations of total electron content (TEC) were observed at global positioning system stations near the volcano. The horizontal propagation velocity and the spatial scale of the TEC oscillation are estimated to be 720 m/s and 1600 km, respectively. These observations strongly suggest that the atmospheric waves induced by explosive volcanic eruption generate TEC variation and electric currents. The Swarm observation may be explained as a manifestation of their magnetic effects observed in the topside ionosphere.

  2. Mercury's Magnetic Field

    NASA Astrophysics Data System (ADS)

    Johnson, C. L.

    2014-12-01

    Mercury is the only inner solar system body other than Earth to possess an active core dynamo-driven magnetic field and the only planet with a small, highly dynamic magnetosphere. Measurements made by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft have provided a wealth of data on Mercury's magnetic field environment. Mercury's weak magnetic field was discovered 40 years ago by the Mariner 10 spacecraft, but its large-scale geometry, strength and origin could not be definitively established. MESSENGER data have shown that the field is dynamo-generated and can be described as an offset axisymmetric dipole field (hereafter OAD): the magnetic equator lies ~0.2 RM (RM = 2440 km) north of the geographic equator and the dipole moment is 2.8 x1019 Am2 (~0.03% that of Earth's). The weak internal field and the high, but variable, solar wind ram pressure drive vigorous magnetospheric dynamics and result in an average distance from the planet center to the sub-solar magnetopause of only 1.42 RM. Magnetospheric models developed with MESSENGER data have allowed re-analysis of the Mariner 10 observations, establishing that there has been no measureable secular variation in the internal field over 40 years. Together with spatial power spectra for the OAD, this provides critical constraints for viable dynamo models. Time-varying magnetopause fields induce secondary core fields, the magnitudes of which confirm the core radius estimated from MESSENGER gravity and Earth-based radar data. After accounting for large-scale magnetospheric fields, residual signatures are dominated by additional external fields that are organized in the local time frame and that vary with magnetospheric activity. Birkeland currents have been identified, which likely close in the planetary interior at depths below the base of the crust. Near-periapsis magnetic field measurements at altitudes greater than 200 km have tantalizing hints of crustal fields, but crustal

  3. Magnetic field evolution in tidal disruption events

    NASA Astrophysics Data System (ADS)

    Bonnerot, Clément; Price, Daniel J.; Lodato, Giuseppe; Rossi, Elena M.

    2017-08-01

    When a star gets tidally disrupted by a supermassive black hole, its magnetic field is expected to pervade its debris. In this paper, we study this process via smoothed particle magnetohydrodynamical simulations of the disruption and early debris evolution including the stellar magnetic field. As the gas stretches into a stream, we show that the magnetic field evolution is strongly dependent on its orientation with respect to the stretching direction. In particular, an alignment of the field lines with the direction of stretching induces an increase of the magnetic energy. For disruptions happening well within the tidal radius, the star compression causes the magnetic field strength to sharply increase by an order of magnitude at the time of pericentre passage. If the disruption is partial, we find evidence for a dynamo process occurring inside the surviving core due to the formation of vortices. This causes an amplification of the magnetic field strength by a factor of ˜10. However, this value represents a lower limit since it increases with numerical resolution. For an initial field strength of 1 G, the magnetic field never becomes dynamically important. Instead, the disruption of a star with a strong 1 MG magnetic field produces a debris stream within which magnetic pressure becomes similar to gas pressure a few tens of hours after disruption. If the remnant of one or multiple partial disruptions is eventually fully disrupted, its magnetic field could be large enough to magnetically power the relativistic jet detected from Swift J1644+57. Magnetized streams could also be significantly thickened by magnetic pressure when it overcomes the confining effect of self-gravity.

  4. Magnetic Field Arches

    NASA Image and Video Library

    2016-09-28

    When an active region rotated into a profile view, SDO was able to capture the magnificent loops arching above an active region (Sept. 28-29, 2016). Active region are areas of strong magnetic fields. The magnetic field lines above these regions are illuminated by charged particles spiraling along them. The images were taken in a wavelength of extreme ultraviolet light. The video covers 12 hours of activity. The Earth was inset to give a sense of the scale of these towering arches. Movies are available at http://photojournal.jpl.nasa.gov/catalog/PIA21101

  5. The evolution of arguments regarding the existence of field-aligned currents

    NASA Technical Reports Server (NTRS)

    Dessler, A. J.

    1984-01-01

    The present understanding of Birkeland (magnetically-field-aligned) currents was not obtained by a direct, logical course. The story is rather more complex. Starting at the end of the 19th century, the Norwegian scientist Kristian Birkeland laid out a compelling case, supported by both theory and experiment, for the existence of field-aligned currents that cause both the aurora and polar geomagnetic disturbances. Sydney Chapman, the British geophysicist, became the acknowledged leader and opinion maker in the field in the decades following Birkeland's death. Chapman proposed, in contradistinction to Birkeland's ideas, equivalent currents that were restricted to flow in the ionosphere with no vertical or field-aligned components. Birkeland's ideas may have faded completely if it had not been for Hannes Alfven, who became involved well after Chapman's ideas gained predominance. Alfven kept insisting that Birkeland's current system made more sense because field-aligned currents were required to drive most of the ionospheric currents. The author became personally involved when Zmuda et al. (1966) submitted to the Journal of Geophysical Research a paper reporting satellite data showing magnetic disturbances above the ionosphere that were consistent with field-aligned Birkeland currents, but which they did not interpret as being due to such currents.

  6. Magnetic fields from inflation?

    SciTech Connect

    Demozzi, Vittoria; Mukhanov, Viatcheslav; Rubinstein, Hector E-mail: viatcheslav.mukhanov@physik.uni-muenchen.de

    2009-08-01

    We consider the possibility of generation of the primordial magnetic field on inflation and show that the effect of the back reaction of this field can be very important. Assuming that the back reaction does not spoil inflation we find a rather strong restriction on the amplitude of the primordial field which could be generated on inflation. Namely, this amplitude recalculated to the present epoch cannot exceed 10{sup −32}G in Mpc scales. This field seems to be too small to be amplified to the observable values by a possible dynamo mechanism.

  7. Simulations of the equatorial thermosphere anomaly: Field-aligned ion drag effect

    NASA Astrophysics Data System (ADS)

    Lei, Jiuhou; Thayer, Jeffrey P.; Wang, Wenbin; Richmond, Arthur D.; Roble, Raymond; Luan, Xiaoli; Dou, Xiankang; Xue, Xianghui; Li, Tao

    2012-01-01

    In this paper the impact of the field-aligned ion drag on equatorial thermosphere temperature and density is quantitatively investigated on the basis of the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model (NCAR TIEGCM) simulations under high solar activity (F107 = 180). The increase of upward vertical winds over the magnetic equator associated with the additional divergence of meridional winds, caused by the inclusion of field-aligned ion drag, leads to a reduction in thermosphere temperature and density at the magnetic equator through enhanced adiabatic cooling. We found that the field-aligned ion drag has an obvious impact on the thermosphere only over the magnetic equatorial region in the daytime and evening sectors, whereas it has less effect on the equatorial thermosphere anomaly (ETA) crests. The daytime neutral temperature over the magnetic equator is reduced by about 30 K, for altitudes above 250 km without significant altitudinal variations, when field-aligned ion drag is included in the simulation. The thermosphere density in the magnetic equatorial region starts to change slightly at 300 km and depletes by about 5% at 400 km, while experiencing a greater decrease with altitude. Furthermore, the trough produced in the neutral temperature and density corresponds well with the magnetic dip equator. The ETA features during 12:00-18:00 LT become obvious as a result of the inclusion of the field-aligned ion drag. Specifically, our results show that at 400 km the crest-trough differences in neutral temperature are about 30-60 K, and the crest-trough ratios in thermosphere density are 1.03-1.06, comparable with observations.

  8. Magnetic dipole in a nonuniform magnetic field

    NASA Astrophysics Data System (ADS)

    Kraftmakher, Yaakov

    2017-05-01

    The magnetic moment of a permanent magnet is determined from forces acting on the magnet in nonuniform magnetic fields produced by two coaxial current-carrying coils. Therefore, the measurements are performed under well controllable and reproducible conditions. With a data-acquisition system, the experiments can be done in a reasonably short time. The magnetic moment of the magnet is in good agreement with values obtained by other experimental techniques. The experiment is well suited for undergraduate laboratories.

  9. Alfven Wave - DC Dualism in Description of Stationary Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Khazanov, George V.

    2009-01-01

    In many cases, the field-aligned currents (FACs) in the Earth's magnetosphere and heliosphere may be described in terms of both DC currents and the currents of a propagating Alfven wave. The simplest example is when a propagating Alfven wave transports a potential hop along the magnetic fieid: between the source of the wave and its front, the problem is well stationary and includes the stationary field-aligned currents, transporting the electric charges along the magnetic field, which may be described as a DC problem, and only at the front of the wave there are the polarization (inertial) currents, closing across the magnetic field. In some cases, the Alfven wave approach brings better understanding to many problems. We will consider here the results of the applications of this approach to two long-staying problems: the effect of saturation of the transpolar voltage in the Earth's magnetosphere, and the experimentally-observed existence of the strong field-aligned currents in the subtle Mercury's magnetosphere which is not able tc close the measured field-aligned currents.

  10. Alfven Wave - DC Dualism in Description of Stationary Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Khazanov, George V.

    2009-01-01

    In many cases, the field-aligned currents (FACs) in the Earth's magnetosphere and heliosphere may be described in terms of both DC currents and the currents of a propagating Alfven wave. The simplest example is when a propagating Alfven wave transports a potential hop along the magnetic fieid: between the source of the wave and its front, the problem is well stationary and includes the stationary field-aligned currents, transporting the electric charges along the magnetic field, which may be described as a DC problem, and only at the front of the wave there are the polarization (inertial) currents, closing across the magnetic field. In some cases, the Alfven wave approach brings better understanding to many problems. We will consider here the results of the applications of this approach to two long-staying problems: the effect of saturation of the transpolar voltage in the Earth's magnetosphere, and the experimentally-observed existence of the strong field-aligned currents in the subtle Mercury's magnetosphere which is not able tc close the measured field-aligned currents.

  11. High field superconducting magnets

    NASA Technical Reports Server (NTRS)

    Hait, Thomas P. (Inventor); Shirron, Peter J. (Inventor)

    2011-01-01

    A superconducting magnet includes an insulating layer disposed about the surface of a mandrel; a superconducting wire wound in adjacent turns about the mandrel to form the superconducting magnet, wherein the superconducting wire is in thermal communication with the mandrel, and the superconducting magnet has a field-to-current ratio equal to or greater than 1.1 Tesla per Ampere; a thermally conductive potting material configured to fill interstices between the adjacent turns, wherein the thermally conductive potting material and the superconducting wire provide a path for dissipation of heat; and a voltage limiting device disposed across each end of the superconducting wire, wherein the voltage limiting device is configured to prevent a voltage excursion across the superconducting wire during quench of the superconducting magnet.

  12. 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.

  13. The interplanetary magnetic field

    NASA Technical Reports Server (NTRS)

    Davis, L., Jr.

    1972-01-01

    Large-scale properties of the interplanetary magnetic field as determined by the solar wind velocity structure are examined. The various ways in which magnetic fields affect phenomena in the solar wind are summarized. The dominant role of high and low velocity solar wind streams that persist, with fluctuations and evolution, for weeks or months is emphasized. It is suggested that for most purposes the sector structure is better identified with the stream structure than with the magnetic polarity and that the polarity does not necessarily change from one velocity sector to the next. Several mechanisms that might produce the stream structure are considered. The interaction of the high and low velocity streams is analyzed in a model that is steady state when viewed in a frame that corotates with the sun.

  14. The Sun Magnetic Field

    NASA Image and Video Library

    2011-12-16

    This frame from an animation shows how the magnetic field lines emanating from our sun spiral out into the solar system as the sun rotates. NASA Voyager 1 is in an area scientists are calling the stagnation region, at the outer layer of the heliosphere.

  15. Field-aligned currents calculated based on the upgraded Prairie View Magnetosphere- ionosphere Coupling Model

    NASA Astrophysics Data System (ADS)

    Romashets, E.; Huang, T.

    2006-12-01

    Using the experimental magnetic field and the newly defined Eular Potentials, we upgraded Prairie View Magnetosphere-ionosphere Coupling Model that was originally created in the frame of IGRF. The electric fields in the ionosphere and the field-aligned currents in the magnetosphere are calculated with the upgraded magnetosphere-ionosphere coupling model, and a preliminary comparison of the calculations with the measurements from ST5 will be presented.

  16. Magnetic Alignment in Carps: Evidence from the Czech Christmas Fish Market

    PubMed Central

    Hart, Vlastimil; Kušta, Tomáš; Němec, Pavel; Bláhová, Veronika; Ježek, Miloš; Nováková, Petra; Begall, Sabine; Červený, Jaroslav; Hanzal, Vladimír; Malkemper, Erich Pascal; Štípek, Kamil; Vole, Christiane; Burda, Hynek

    2012-01-01

    While magnetoreception in birds has been studied intensively, the literature on magnetoreception in bony fish, and particularly in non-migratory fish, is quite scarce. We examined alignment of common carps (Cyprinus carpio) at traditional Christmas sale in the Czech Republic. The sample comprised measurements of the directional bearings in 14,537 individual fish, distributed among 80 large circular plastic tubs, at 25 localities in the Czech Republic, during 817 sampling sessions, on seven subsequent days in December 2011. We found that carps displayed a statistically highly significant spontaneous preference to align their bodies along the North-South axis. In the absence of any other common orientation cues which could explain this directional preference, we attribute the alignment of the fish to the geomagnetic field lines. It is apparent that the display of magnetic alignment is a simple experimental paradigm of great heuristic potential. PMID:23227241

  17. Magnetic alignment in carps: evidence from the Czech christmas fish market.

    PubMed

    Hart, Vlastimil; Kušta, Tomáš; Němec, Pavel; Bláhová, Veronika; Ježek, Miloš; Nováková, Petra; Begall, Sabine; Cervený, Jaroslav; Hanzal, Vladimír; Malkemper, Erich Pascal; Stípek, Kamil; Vole, Christiane; Burda, Hynek

    2012-01-01

    While magnetoreception in birds has been studied intensively, the literature on magnetoreception in bony fish, and particularly in non-migratory fish, is quite scarce. We examined alignment of common carps (Cyprinus carpio) at traditional Christmas sale in the Czech Republic. The sample comprised measurements of the directional bearings in 14,537 individual fish, distributed among 80 large circular plastic tubs, at 25 localities in the Czech Republic, during 817 sampling sessions, on seven subsequent days in December 2011. We found that carps displayed a statistically highly significant spontaneous preference to align their bodies along the North-South axis. In the absence of any other common orientation cues which could explain this directional preference, we attribute the alignment of the fish to the geomagnetic field lines. It is apparent that the display of magnetic alignment is a simple experimental paradigm of great heuristic potential.

  18. Mid-latitude field-aligned ionospheric irregularities and its impact on GPS

    NASA Astrophysics Data System (ADS)

    Yasyukevich, Yury; Afraimovich, Edward; Ishin, Artem; Tinin, Mikhail

    2010-05-01

    Strong scintillations of amplitude and phase of transionospheric radio signals occur due to signal scattering on intensive small scale irregularities. Scintillation can have an adverse effect on GPS signals and cause a GPS receiver to lose lock on the signal in some extreme cases. Although the plasma bubble is a common phenomenon and it has been studied for years, precise observed data of ionospheric scintillations and loss of lock to GPS receivers due to plasma bubble at mid-latitude are still limited. In most papers there are no data regarding the space geometry of field-aligned irregularities. For the first time, we propose a GPS method to detect mid-latitude field-aligned irregularities (FAIs) by line-of-sight angular scanning regarding the local magnetic field vector. We show that total GPS L2 phase slips over Japan during the recovery phase of the 12 February, 2000 geomagnetic storm (Ma and Maruyama, 2006, doi:10.1029/2006GL027512) were caused by GPS signal scattering on FAIs for the line-of-sight of both aligned to magnetic field line (the field of aligned scattering, FALS), and across it or at large angles to magnetic field line (the field of across scattering, FACS). Our FALS results confirm well with data of investigation of magnetic field orientation control of GPS occultation observations of equatorial scintillation during detailed LEO CHAMP, SAC-C and PICOSat measurements, realized by Anderson and Strauss (2005, doi:10.1029/2005GL023781). The role of large-angle scattering almost along the normal to the magnetic field line in GPS scintillation is determined by attenuation of the irregularity anisotropy factor as compared with the other factors. The work was supported by the Fundamental Research Program of RAS Physical Science Department (Project IV.12 "Modern problems of radiophysics").

  19. Field-free alignment in repetitively kicked nitrogen gas

    SciTech Connect

    Cryan, James P.; Bucksbaum, Philip H.; Coffee, Ryan N.

    2009-12-15

    We demonstrate a high level of laser-induced transient alignment in room temperature and density N{sub 2} with a technique that avoids laser field ionization. Our measured alignment shows an improvement over previous one-pulse or two-pulse experimental alignment results and approaches the theoretical maximum value. We employ eight equally spaced ultrafast laser pulses with a separation that takes advantage of the periodic revivals for the ensemble of quantum rotors. Each successive pulse increases the transient alignment [(t)] and also moves the rotational population away from thermal equilibrium. These measurements are combined with simulations to determine the value of , the J-state distributions, and the functional dependencies of the alignment features.

  20. Field-aligned currents observed in the vicinity of a moving auroral arc

    NASA Astrophysics Data System (ADS)

    Goertz, C. K.; Bruening, K.

    1984-09-01

    The sounding rocket Porcupine F4 was launched into an auroral arc and the field aligned currents were independently deduced from magnetic field measurements; the horizontal current deduced from the electric field measurements and height integrated conductivity calculations; and measurements of electron fluxes. Above the arc the different methods agree. The magnetosphere acts as generator and the ionosphere as load. North of the arc, the first two methods disagree, possibly due to an Alfven wave carrying the observed magnetic field perturbation. The energy flow is out of the ionosphere. Here the ionosphere acts as generator and the magnetosphere as load.

  1. Field-aligned currents observed in the vicinity of a moving auroral arc

    NASA Technical Reports Server (NTRS)

    Goertz, C. K.; Bruening, K.

    1984-01-01

    The sounding rocket Porcupine F4 was launched into an auroral arc and the field aligned currents were independently deduced from magnetic field measurements; the horizontal current deduced from the electric field measurements and height integrated conductivity calculations; and measurements of electron fluxes. Above the arc the different methods agree. The magnetosphere acts as generator and the ionosphere as load. North of the arc, the first two methods disagree, possibly due to an Alfven wave carrying the observed magnetic field perturbation. The energy flow is out of the ionosphere. Here the ionosphere acts as generator and the magnetosphere as load.

  2. Unusual 5 m E region field-aligned irregularities observed from Northern Germany during the magnetic storm of 17 March 2015

    NASA Astrophysics Data System (ADS)

    Chau, Jorge L.; St.-Maurice, Jean-Pierre

    2016-10-01

    Coherent E region echoes were observed during the 17 March 2015 storm at midlatitudes by multistatic wide field of view radars operating in northern Germany. Two of the stations operated in a monostatic configuration, while one link was set in bistatic mode. Interferometry made it feasible to locate the targets. While the radars were built to measure mesospheric winds from specular meteor echoes, the storm was so intense that it allowed them to observe auroral E region echoes for more than 4 h. All stations detected numerous examples of narrow spectra with slow (≈180 m/s) and fast (up to 1600 m/s) Doppler velocities. The target speeds were much faster than the Doppler velocities for the slow narrow echoes (more than 800 m/s versus 180 m/s) but comparable to the observed Doppler shift for the 1500 m/s narrow fast types. The narrow types came from localized horizontal structures 50 to 80 km wide in range. The fast narrow types came from the upper part of the altitudes associated with Farley-Buneman waves. The slow narrow structures were typically from altitudes lower than 100 km. Unexpectedly, the great majority of the echoes associated with more ordinary ion acoustic turbulence had a positive Doppler shift and came from the east. A companion paper uses these new observations to reevaluate the origin of the narrow echoes and of the asymmetry in the counts. Irrespective of the generation mechanisms, our observations indicate that a combination of unusually large electric field and strong precipitation is needed to produce the unusual echoes.

  3. Observations of field-aligned currents, waves, and electric fields at substorm onset

    NASA Technical Reports Server (NTRS)

    Smits, D. P.; Hughes, W. J.; Cattell, C. A.; Russell, C. T.

    1986-01-01

    Substorm onsets, identified Pi 2 pulsations observed on the Air Force Geophysics Laboratory Magnetometer Network, are studied using magnetometer and electric field data from ISEE 1 as well as magnetometer data from the geosynchronous satellites GOES 2 and 3. The mid-latitude magnetometer data provides the means of both timing and locating the substorm onset so that the spacecraft locations with respect to the substorm current systems are known. During two intervals, each containing several onsets or intensifications, ISEE 1 observed field-aligned current signatures beginning simultaneously with the mid-latitude Pi 2 pulsation. Close to the earth broadband bursts of wave noise were observed in the electric field data whenever field-aligned currents were detected. One onset occurred when ISEE 1 and GOES 2 were on the same field line but in opposite hemispheres. During this onset ISEE 1 and GOES 2 saw magnetic signatures which appear to be due to conjugate field-aligned currents flowing out of the western end of the westward auroral electrojets. The ISEE 1 signature is of a line current moving westward past the spacecraft. During the other interval, ISEE 1 was in the near-tail region near the midnight meridian. Plasma data confirms that the plasma sheet thinned and subsequently expanded at onset. Electric field data shows that the plasma moved in the opposite direction to the plasma sheet boundary as the boundary expanded which implies that there must have been an abundant source of hot plasma present. The plasma motion was towards the center of the plasma sheet and earthwards and consisted of a series of pulses rather than a steady flow.

  4. Block Copolymer Nanocomposites in Electric Fields: Kinetics of Alignment

    SciTech Connect

    Liedel, Clemens; Pester, Christian; Ruppel, Markus A; Lewin, Christian; Pavan, Mariela J.; Urban, Volker S; Shenhar, Roy; Bosecke, Peter; Boker, Alexander

    2013-01-01

    We investigate the kinetics of block copolymer/nanoparticle composite alignment in an electric field using in situ transmission small-angle X-ray scattering. As a model system, we employ a lamellae forming polystyrene-block-poly(2-vinyl pyridine) block copolymer with different contents of gold nanoparticles in thick films under solvent vapor annealing. While the alignment improves with increasing nanoparticle fraction, the kinetics slows down. This is explained by changes in the degree of phase separation and viscosity. Our findings provide extended insights into the basics of nanocomposite alignment.

  5. Magnetic-Field-Assisted Assembly of Anisotropic Superstructures by Iron Oxide Nanoparticles and Their Enhanced Magnetism.

    PubMed

    Jiang, Chengpeng; Leung, Chi Wah; Pong, Philip W T

    2016-12-01

    Magnetic nanoparticle superstructures with controlled magnetic alignment and desired structural anisotropy hold promise for applications in data storage and energy storage. Assembly of monodisperse magnetic nanoparticles under a magnetic field could lead to highly ordered superstructures, providing distinctive magnetic properties. In this work, a low-cost fabrication technique was demonstrated to assemble sub-20-nm iron oxide nanoparticles into crystalline superstructures under an in-plane magnetic field. The gradient of the applied magnetic field contributes to the anisotropic formation of micron-sized superstructures. The magnitude of the applied magnetic field promotes the alignment of magnetic moments of the nanoparticles. The strong dipole-dipole interactions between the neighboring nanoparticles lead to a close-packed pattern as an energetically favorable configuration. Rod-shaped and spindle-shaped superstructures with uniform size and controlled spacing were obtained using spherical and polyhedral nanoparticles, respectively. The arrangement and alignment of the superstructures can be tuned by changing the experimental conditions. The two types of superstructures both show enhancement of coercivity and saturation magnetization along the applied field direction, which is presumably associated with the magnetic anisotropy and magnetic dipole interactions of the constituent nanoparticles and the increased shape anisotropy of the superstructures. Our results show that the magnetic-field-assisted assembly technique could be used for fabricating nanomaterial-based structures with controlled geometric dimensions and enhanced magnetic properties for magnetic and energy storage applications.

  6. Observations of Field-Aligned Current Spatial and Temporal Variations by Space Technology 5

    NASA Astrophysics Data System (ADS)

    Le, G.; Slavin, J. A.; Strangeway, R. J.; Wang, Y.

    2013-12-01

    In this paper, we report the results of magnetic field measurements of field-aligned currents (FACs) using multi-point magnetic field data from Space Technology 5 (ST-5) mission. ST-5 is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, sun synchronous polar orbit. The spacecraft were maintained in a 'pearls on a sting' constellation with controlled spacings ranging from just over 5000 km down to under 50 km. During the three-month mission duration, the constellation mission returned high quality multi-point measurements of the magnetic field through Earth's dynamic ionospheric current systems over a range of inter-satellite spacing. In this study, we use the ST-5 magnetic field measurements to separate spatial and temporal variations of FACs and to quantify the imbalance between the region 1 (R1) and the region 2 (R2) currents.

  7. A statistical simulation of magnetic particle alignment in sediments

    NASA Astrophysics Data System (ADS)

    Heslop, David; Roberts, Andrew P.; Hawkins, Rhys

    2014-05-01

    Sedimentary magnetizations are fundamental to palaeomagnetism, but the mechanisms that control remanence acquisition remain poorly constrained. Observed sedimentary natural remanent magnetizations are often orders of magnitude smaller than the saturation remanent magnetization of the same sediment, which indicates inefficient remanence acquisition. We present a statistical model, based on the von Mises-Fisher distribution, in which magnetic particle reorientations towards an ambient field are considered, without representing the physics of the magnetization acquisition process. The results provide insights into the nature of sedimentary magnetizations. Specifically, an assemblage of randomly oriented magnetic particles can acquire a high-fidelity palaeomagnetic signal with only small rotations (in some cases <1°) of particles towards the ambient field direction. This demonstrates that the action of a geomagnetic torque on individual magnetic mineral particle orientation may be minor, and that a weak directional bias on an assemblage of particles could be responsible for the typically observed inefficiency of sedimentary remanence acquisition. Additionally, we demonstrate that weak fields produce sedimentary magnetizations with larger directional uncertainties. For natural sediments, however, these uncertainties appear to be small enough to allow reliable recording of directional geomagnetic field behaviour during periods with weak fields, such as palaeomagnetic reversals and excursions.

  8. Reinforcement of epoxy-based composites by magnetically aligned multi walled carbon nanotube

    NASA Astrophysics Data System (ADS)

    Xu, Xianjuan; Lin, Song; Li, Moyu; Li, Wusheng; Jia, Xiaolong; Cai, Qing; Yang, Xiaoping

    2015-07-01

    Multi walled carbon nanotubes decorated with ferriferrous oxide nanoparticle (MWCNTs-Fe3O4) complex was used as an effective reinforcement in the polymer composites. The MWCNTs-Fe3O4 with various grafting contents of Fe3O4 nanoparticles were successfully prepared by combining in situ atom transfer radical polymerization (ATRP) and coprecipitation process, which was characterized with Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscope (TEM). The MWCNTs-Fe3O4 complex showed the strong magnetic response behavior, which could be easily aligned in an external magnetic field. The alignment state of MWCNTs-Fe3O4 complex could be modulated by adjusting the intensity of external magnetic field, grafting content of Fe3O4 nanoparticles and viscosity of the solvent. Moreover, with the addition of MWCNTs-Fe3O4, tensile strength and modulus of epoxy composites were enhanced by 12.3 and 10.9%, respectively, which was due to the reinforcing effect of the aligned MWCNTs-Fe3O4 within magnetic field.

  9. Magnetic fields and cancer

    SciTech Connect

    Jones, T.L.

    1993-10-01

    This letter is a response to an article by Savitz and Kaune, EHP 101:76-80. W-L wire code was applied to data from a 1988 Denver study, and an association was reported between high W-L wire code and childhood cancer. This author discusses several studies and provides explanations which weakens the argument that classification error resulted in an appreciable reduction in the association between W-L high wire code and childhood cancer. In conclusion, the fact that new wire code is only weakly correlated with magnetic field measurements (in the same manner as the original W-L wire code) suggests that the newly reported stronger association with childhood cancer is likely due to factors other than magnetic fields. Differential residential mobility and differential residential age are two possible explanations and are suggestive that the reported association may be false.

  10. First evidence of anisotropy of GPS phase slips caused by the mid-latitude field-aligned ionospheric irregularities

    NASA Astrophysics Data System (ADS)

    Afraimovich, E. L.; Ishin, A. B.; Tinin, M. V.; Yasyukevich, Yu. V.; Jin, S. G.

    2011-05-01

    The mid-latitude field-aligned irregularity (FAI) along the magnetic field line is a common phenomenon in the ionosphere. However, few data reveal the field-aligned ionospheric irregularities. They are insufficient to identify FAIs effects so far, particularly effect on global positioning system (GPS) signals. In this paper, the mid-latitude FAIs by line-of-sight angular scanning relative to the local magnetic field vector are investigated using the denser GPS network observations in Japan. It has been the first found that total GPS L2 phase slips over Japan, during the recovery phase of the 12 Feb 2000 geomagnetic storm were caused by GPS signal scattering on FAIs both for the lines-of-sight aligned to the magnetic field line (the field of aligned scattering, FALS) and across the magnetic field line (the field of across scattering, FACS). The FALS results are also in a good agreement with the data of the magnetic field orientation control of GPS occultation observations of equatorial scintillation during thorough low earth orbit (LEO) satellites measurements, e.g. Challenging Minisatellite Payload (CHAMP) and Satellite de Aplicaciones Cientificas-C (SAC-C). The role of large-angle scattering almost along the normal to the magnetic field line in GPS scintillation is determined by attenuation of the irregularity anisotropy factor as compared with the other factors.

  11. A seasonal change in the effect of field-aligned currents at synchronous orbit

    NASA Technical Reports Server (NTRS)

    Mcpherron, R. L.; Barfield, J. N.

    1980-01-01

    The expected signature of substorm field-aligned currents is described for synchronous satellites near 10 deg magnetic latitude. The main effect is a positive D perturbation premidnight and a negative D perturbation postmidnight. This behavior is illustrated for two substorms near the fall equinox. A second pair of substorms taken from winter solstice do not show the expected behavior. The absence of this effect in winter observations is verified statistically by superposed epoch analysis. A simple explanation of this behavior based on the geometry of the plane of magnetic symmetry is presented. During disturbed times at winter solstice a synchronous satellite nominally at 10 deg magnetic latitude is effectively at the magnetic equator. This distortion of the magnetic equator must be considered in future models of the disturbed magnetospheric magnetic field.

  12. Photonic Magnetic Field Sensor

    DTIC Science & Technology

    2007-11-02

    reduce feedback in fiber optic links can be the basis for excellent magnetic field sensors. Based on the giant magneto-optical ( GMO ) or Faraday...Squids are those based upon the giant magneto-optical ( GMO ) effect in ferrimagnetic materials or YIG garnets and the giant magneto-resistance (GMR...effect in manganese based compounds. The development of the GMO material was mostly motivated by the need for compact, in-line fiber optical

  13. Magnetic field reconnection

    NASA Astrophysics Data System (ADS)

    Axford, W. I.

    The fundamental principles of particle acceleration by magnetic reconnection in cosmic plasmas are reviewed. The history of reconnection models is traced, and consideration is given to the Kelvin-Helmholtz theorem, the frozen-field theorem, the application of the Kelvin-Helmholtz theorem to a collisionless plasma, solutions to specific reconnection problems, and configurational instability. Diagrams and graphs are provided, and the objections raised by critics of the reconnection theory and/or its astrophysical applications are discussed.

  14. Coronal Magnetic Field Models

    NASA Astrophysics Data System (ADS)

    Wiegelmann, Thomas; Petrie, Gordon J. D.; Riley, Pete

    2017-09-01

    Coronal magnetic field models use photospheric field measurements as boundary condition to model the solar corona. We review in this paper the most common model assumptions, starting from MHD-models, magnetohydrostatics, force-free and finally potential field models. Each model in this list is somewhat less complex than the previous one and makes more restrictive assumptions by neglecting physical effects. The magnetohydrostatic approach neglects time-dependent phenomena and plasma flows, the force-free approach neglects additionally the gradient of the plasma pressure and the gravity force. This leads to the assumption of a vanishing Lorentz force and electric currents are parallel (or anti-parallel) to the magnetic field lines. Finally, the potential field approach neglects also these currents. We outline the main assumptions, benefits and limitations of these models both from a theoretical (how realistic are the models?) and a practical viewpoint (which computer resources to we need?). Finally we address the important problem of noisy and inconsistent photospheric boundary conditions and the possibility of using chromospheric and coronal observations to improve the models.

  15. Spontaneous magnetic alignment by yearling snapping turtles: rapid association of radio frequency dependent pattern of magnetic input with novel surroundings.

    PubMed

    Landler, Lukas; Painter, Michael S; Youmans, Paul W; Hopkins, William A; Phillips, John B

    2015-01-01

    We investigated spontaneous magnetic alignment (SMA) by juvenile snapping turtles using exposure to low-level radio frequency (RF) fields at the Larmor frequency to help characterize the underlying sensory mechanism. Turtles, first introduced to the testing environment without the presence of RF aligned consistently towards magnetic north when subsequent magnetic testing conditions were also free of RF ('RF off → RF off'), but were disoriented when subsequently exposed to RF ('RF off → RF on'). In contrast, animals initially introduced to the testing environment with RF present were disoriented when tested without RF ('RF on → RF off'), but aligned towards magnetic south when tested with RF ('RF on → RF on'). Sensitivity of the SMA response of yearling turtles to RF is consistent with the involvement of a radical pair mechanism. Furthermore, the effect of RF appears to result from a change in the pattern of magnetic input, rather than elimination of magnetic input altogether, as proposed to explain similar effects in other systems/organisms. The findings show that turtles first exposed to a novel environment form a lasting association between the pattern of magnetic input and their surroundings. However, under natural conditions turtles would never experience a change in the pattern of magnetic input. Therefore, if turtles form a similar association of magnetic cues with the surroundings each time they encounter unfamiliar habitat, as seems likely, the same pattern of magnetic input would be associated with multiple sites/localities. This would be expected from a sensory input that functions as a global reference frame, helping to place multiple locales (i.e., multiple local landmark arrays) into register to form a global map of familiar space.

  16. Spontaneous Magnetic Alignment by Yearling Snapping Turtles: Rapid Association of Radio Frequency Dependent Pattern of Magnetic Input with Novel Surroundings

    PubMed Central

    Landler, Lukas; Painter, Michael S.; Youmans, Paul W.; Hopkins, William A.; Phillips, John B.

    2015-01-01

    We investigated spontaneous magnetic alignment (SMA) by juvenile snapping turtles using exposure to low-level radio frequency (RF) fields at the Larmor frequency to help characterize the underlying sensory mechanism. Turtles, first introduced to the testing environment without the presence of RF aligned consistently towards magnetic north when subsequent magnetic testing conditions were also free of RF (‘RF off → RF off’), but were disoriented when subsequently exposed to RF (‘RF off → RF on’). In contrast, animals initially introduced to the testing environment with RF present were disoriented when tested without RF (‘RF on → RF off’), but aligned towards magnetic south when tested with RF (‘RF on → RF on’). Sensitivity of the SMA response of yearling turtles to RF is consistent with the involvement of a radical pair mechanism. Furthermore, the effect of RF appears to result from a change in the pattern of magnetic input, rather than elimination of magnetic input altogether, as proposed to explain similar effects in other systems/organisms. The findings show that turtles first exposed to a novel environment form a lasting association between the pattern of magnetic input and their surroundings. However, under natural conditions turtles would never experience a change in the pattern of magnetic input. Therefore, if turtles form a similar association of magnetic cues with the surroundings each time they encounter unfamiliar habitat, as seems likely, the same pattern of magnetic input would be associated with multiple sites/localities. This would be expected from a sensory input that functions as a global reference frame, helping to place multiple locales (i.e., multiple local landmark arrays) into register to form a global map of familiar space. PMID:25978736

  17. An MHD simulation of By-dependent magnetospheric convection and field-aligned currents during northward IMF

    NASA Technical Reports Server (NTRS)

    Ogino, T.; Walker, R. J.; Ashour-Abdalla, M.; Dawson, J. M.

    1985-01-01

    A three-dimensional MHD simulation code is used to model the magnetospheric configuration when the IMF has both a northward B(z) component and a B(y) component in the east-west direction. Projections of the plasma pressure, the field-aligned velocity, the field-aligned vorticity, and the field-aligned current along the magnetic field lines into the northern ionosphere are shown and discussed. Cross-sectional patterns of these parameters are shown. The results demonstrate that the B(y) component of the IMF strongly influences the plasma sheet configuration and the magnetospheric convection pattern.

  18. Magnetospheric Multiscale analysis of intense field-aligned Poynting flux near the Earth's plasma sheet boundary

    NASA Astrophysics Data System (ADS)

    Stawarz, J. E.; Eastwood, J. P.; Varsani, A.; Ergun, R. E.; Shay, M. A.; Nakamura, R.; Phan, T. D.; Burch, J. L.; Gershman, D. J.; Giles, B. L.; Goodrich, K. A.; Khotyaintsev, Y. V.; Lindqvist, P.-A.; Russell, C. T.; Strangeway, R. J.; Torbert, R. B.

    2017-07-01

    The Magnetospheric Multiscale mission is employed to examine intense Poynting flux directed along the background magnetic field toward Earth, which reaches amplitudes of nearly 2 mW/m2. The event is located within the plasma sheet but likely near the boundary at a geocentric distance of 9 RE in association with bulk flow signatures. The fluctuations have wavelengths perpendicular to the magnetic field of 124-264 km (compared to an ion gyroradius of 280 km), consistent with highly kinetic Alfvén waves. While the wave vector remains highly perpendicular to the magnetic field, there is substantial variation of the direction in the perpendicular plane. The field-aligned Poynting flux may be associated with kinetic Alfvén waves released along the separatrix by magnetotail reconnection and/or the radiation of waves excited by bursty bulk flow braking and may provide a means through which energy released by magnetic reconnection is transferred to the auroral region.

  19. Synthetic Observations of Magnetic Fields in Protostellar Cores

    NASA Astrophysics Data System (ADS)

    Lee, Joyce W. Y.; Hull, Charles L. H.; Offner, Stella S. R.

    2017-01-01

    The role of magnetic fields in the early stages of star formation is not well constrained. In order to discriminate between different star formation models, we analyze 3D magnetohydrodynamic simulations of low-mass cores and explore the correlation between magnetic field orientation and outflow orientation over time. We produce synthetic observations of dust polarization at resolutions comparable to millimeter-wave dust polarization maps observed by the Combined Array for Research in Millimeter-wave Astronomy and compare these with 2D visualizations of projected magnetic field and column density. Cumulative distribution functions of the projected angle between the magnetic field and outflow show different degrees of alignment in simulations with differing mass-to-flux ratios. The distribution function for the less magnetized core agrees with observations finding random alignment between outflow and field orientations, while the more magnetized core exhibits stronger alignment. We find that fractional polarization increases when the system is viewed such that the magnetic field is close to the plane of the sky, and the values of fractional polarization are consistent with observational measurements. The simulation outflow, which reflects the underlying angular momentum of the accreted gas, changes direction significantly over over the first ∼0.1 Myr of evolution. This movement could lead to the observed random alignment between outflows and the magnetic fields in protostellar cores.

  20. Magnetically Aligned HI and Dust: New insights into the physical properties of the diffuse ISM

    NASA Astrophysics Data System (ADS)

    Clark, Susan E.; Peek, Joshua E. G.; Hill, J. Colin; Putman, Mary; Schudel, Lowell E.

    2015-08-01

    Sensitive, high resolution observations of Galactic HI reveal an intricate network of slender linear features, much as sensitive surveys of dust in Galactic molecular clouds reveal ubiquitous filamentary structure. Across the high Galactic latitude sky, diffuse HI structures are aligned with the interstellar magnetic field, as revealed by background starlight polarization (Clark, Peek, Putman 2014). We present the discovery that the orientation of HI structures traces the Planck 353 GHz polarization angle measurements with extraordinary accuracy. We explore the physical properties of the HI structures, and the physical mechanisms responsible for their alignment, by examining the HI structures across a range of densities and environments. We discuss the insights that may be gained from a deeper understanding of the interplay between gas, dust, and magnetic fields in the ISM.

  1. Magnetic Field Topology in Jets

    NASA Technical Reports Server (NTRS)

    Gardiner, T. A.; Frank, A.

    2000-01-01

    We present results on the magnetic field topology in a pulsed radiative. jet. For initially helical magnetic fields and periodic velocity variations, we find that the magnetic field alternates along the, length of the jet from toroidally dominated in the knots to possibly poloidally dominated in the intervening regions.

  2. Low field magnetic resonance imaging

    DOEpatents

    Pines, Alexander; Sakellariou, Dimitrios; Meriles, Carlos A.; Trabesinger, Andreas H.

    2010-07-13

    A method and system of magnetic resonance imaging does not need a large homogenous field to truncate a gradient field. Spatial information is encoded into the spin magnetization by allowing the magnetization to evolve in a non-truncated gradient field and inducing a set of 180 degree rotations prior to signal acquisition.

  3. Magnetic Field Topology in Jets

    NASA Technical Reports Server (NTRS)

    Gardiner, T. A.; Frank, A.

    2000-01-01

    We present results on the magnetic field topology in a pulsed radiative. jet. For initially helical magnetic fields and periodic velocity variations, we find that the magnetic field alternates along the, length of the jet from toroidally dominated in the knots to possibly poloidally dominated in the intervening regions.

  4. Alignment induced aberration fields of next generation telescopes

    NASA Astrophysics Data System (ADS)

    Schmid, Tobias; Thompson, Kevin; Rolland, Jannick

    2008-08-01

    There is a long list of new ground-based optical telescopes being considered around the world. While many are conventional Cassegrain and Ritchey-Chretien designs, some are from a family of three mirror anastigmatic (TMA) telescopes that are configured with an offset field (but still obscured) that trace back to designs developed in the 1970s for military applications. The nodal theory of aberrations, developed in the late 1970s, provides valuable insights into the response of TMA telescopes to alignment errors. Here it is shown for the first time that the alignment limiting aberration in any TMA telescope is a 3rd order astigmatism term with a new field dependence, termed field-asymmetric, field-linear 3rd order astigmatism. It is also shown that a TMA telescope under assembly that is only measured to have excellent/perfect performance onaxis is not aligned in any significant way. This is because the new astigmatic term is always zero on-axis, even though it is large over the field of view. Knowledge of this intrinsic misalignment aberration field for any TMA telescope aids greatly in ensuring it can be aligned successfully. The James Webb Space Telescope (JWST), is used an example of a relevant TMA system.

  5. Magnetic field switchable dry adhesives.

    PubMed

    Krahn, Jeffrey; Bovero, Enrico; Menon, Carlo

    2015-02-04

    A magnetic field controllable dry adhesive device is manufactured. The normal adhesion force can be increased or decreased depending on the presence of an applied magnetic field. If the magnetic field is present during the entire normal adhesion test cycle which includes both applying a preloading force and measuring the pulloff pressure, a decrease in adhesion is observed when compared to when there is no applied magnetic field. Similarly, if the magnetic field is present only during the preload portion of the normal adhesion test cycle, a decrease in adhesion is observed because of an increased stiffness of the magnetically controlled dry adhesive device. When the applied magnetic field is present during only the pulloff portion of the normal adhesion test cycle, either an increase or a decrease in normal adhesion is observed depending on the direction of the applied magnetic field.

  6. The Martian magnetic field

    NASA Technical Reports Server (NTRS)

    Russell, C. T.

    1979-01-01

    The paper presents an overview of the Martian magnetic field measurements and the criticisms made of them. The measurements of the Mars 2, 3, and 5 spacecraft were interpreted by Dolginov et al. (1976, 1978) to be consistent with an intrinsic planetary magnetic moment of 2.5 times 10 to the 22nd power gauss cu cm, basing this result on the apparent size of the obstacle responsible for deflecting the solar wind and an apparent encounter of the spacecraft with the planetary field. It is shown that if the dependence of the Martian magnetic moment on the rotation rate was linear, the estimate of the moment would be far larger than reported by Dolginov et al. An upper limit of 250 km is calculated for the dynamo radius using the similarity law, compared with 500 km obtained by Dolginov et al. It is concluded that the possible strength of a Martian dynamo is below expectations, and it is likely that the Mars dynamo is not presently operative.

  7. Superhorizon magnetic fields

    NASA Astrophysics Data System (ADS)

    Campanelli, Leonardo

    2016-03-01

    We analyze the evolution of superhorizon-scale magnetic fields from the end of inflation till today. Whatever is the mechanism responsible for their generation during inflation, we find that a given magnetic mode with wave number k evolves, after inflation, according to the values of k ηe , nk , and Ωk , where ηe is the conformal time at the end of inflation, nk is the number density spectrum of inflation-produced photons, and Ωk is the phase difference between the two Bogoliubov coefficients which characterize the state of that mode at the end of inflation. For any realistic inflationary magnetogenesis scenario, we find that nk-1≪|k ηe|≪1 , and three evolutionary scenarios are possible: (i) |Ωk∓π |=O (1 ) , in which case the evolution of the magnetic spectrum Bk(η ) is adiabatic, a2Bk(η )=const , with a being the expansion parameter; (ii) |Ωk∓π |≪|k ηe| , in which case the evolution is superadiabatic, a2Bk(η )∝η ; (iii) |k ηe|≪|Ωk∓π |≪1 or |k ηe|˜|Ωk∓π |≪1 , in which case an early phase of adiabatic evolution is followed, after a time η⋆˜|Ωk∓π |/k , by a superadiabatic evolution. Once a given mode reenters the horizon, it remains frozen into the plasma and then evolves adiabatically till today. As a corollary of our results, we find that inflation-generated magnetic fields evolve adiabatically on all scales and for all times in conformal-invariant free Maxwell theory, while they evolve superadiabatically after inflation on superhorizon scales in the nonconformal-invariant Ratra model, where the inflaton is kinematically coupled to the electromagnetic field. The latter result supports and, somehow, clarifies our recent claim that the Ratra model can account for the presence of cosmic magnetic fields without suffering from both backreaction and strong-coupling problems.

  8. Electric and magnetic fields

    NASA Technical Reports Server (NTRS)

    Kaufman, H. R.; Robinson, R. S.; Etters, R. D.

    1982-01-01

    A number of energy momentum anomalies are described that result from the use of Abraham-Lorentz electromagnetic theory. These anomalies have in common the motion of charged bodies or current carrying conductors relative to the observer. The anomalies can be avoided by using the nonflow approach, based on internal energy of the electromagnetic field. The anomalies can also be avoided by using the flow approach, if all contributions to flow work are included. The general objective of this research is a fundamental physical understanding of electric and magnetic fields which, in turn, might promote the development of new concepts in electric space propulsion. The approach taken is to investigate quantum representations of these fields.

  9. Dark Field Technology - A Practical Approach To Local Alignment

    NASA Astrophysics Data System (ADS)

    Beaulieu, David R.; Hellebrekers, Paul P.

    1987-01-01

    A fully automated direct reticle reference alignment system for use in step and repeat camera systems is described. The technique, first outlined by Janus S. Wilczynski, ("Optical Step and Repeat Camera with Dark Field Alignment", J. Vac. Technol., 16(6), Nov./Dec. 1979), has been implemented on GCA Corporation's DSW Wafer Stepper. Results from various process levels covering the typical CMOS process have shown that better than ±0.2μm alignment accuracy can be obtained with minimal process sensitivity. The technique employs fixed illumination and microscope optics to achieve excellent registration stability and maintenance-free operation. Latent image techniques can be exploited for intra-field, grid and focus characterization.

  10. Reconnection of Magnetic Fields

    NASA Technical Reports Server (NTRS)

    1984-01-01

    Spacecraft observations of steady and nonsteady reconnection at the magnetopause are reviewed. Computer simulations of three-dimensional reconnection in the geomagnetic tail are discussed. Theoretical aspects of the energization of particles in current sheets and of the microprocesses in the diffusion region are presented. Terrella experiments in which magnetospheric reconnection is simulated at both the magnetopause and in the tail are described. The possible role of reconnection in the evolution of solar magnetic fields and solar flares is discussed. A two-dimensional magnetohydrodynamic computer simulation of turbulent reconnection is examined. Results concerning reconnection in Tokamak devices are also presented.

  11. Orbital alignment in photodissociation probed using strong field ionization

    SciTech Connect

    Lin Yunfei; Yan Lu; Lee, Suk Kyoung; Herath, Thushani; Li Wen

    2011-12-21

    The photodissociation of molecules often produces atomic fragments with polarized electronic angular momentum, and the atomic alignment, for example, can provide valuable information on the dynamical pathways of chemical reactions unavailable by other means. In this work, we demonstrate for the first time that orbital polarization in chemical reactions can be measured with great sensitivity using strong field ionization by exploiting its extreme nonlinearity.

  12. Space Technology 5 Multipoint Observations of Temporal and Spatial Variability of Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Le, G.; Wang, Y.; Slavin, J. A.; Strangeway, R. L.

    2009-01-01

    Space Technology 5 (ST5) is a constellation mission consisting of three microsatellites. It provides the first multipoint magnetic field measurements in low Earth orbit, which enables us to separate spatial and temporal variations. In this paper, we present a study of the temporal variability of field-aligned currents using the ST5 data. We examine the field-aligned current observations during and after a geomagnetic storm and compare the magnetic field profiles at the three spacecraft. The multipoint data demonstrate that mesoscale current structures, commonly embedded within large-scale current sheets, are very dynamic with highly variable current density and/or polarity in approx.10 min time scales. On the other hand, the data also show that the time scales for the currents to be relatively stable are approx.1 min for mesoscale currents and approx.10 min for large-scale currents. These temporal features are very likely associated with dynamic variations of their charge carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of mesoscale field-aligned currents are found to be consistent with those of auroral parallel electric field.

  13. Dissipation in magnetic reconnection with a guide magnetic field

    SciTech Connect

    Hesse, Michael

    2006-12-15

    A combination of numerical simulation results and analytical theory is applied to the problem of magnetic reconnection in a guide magnetic field. An investigation of electron distribution functions within the electron diffusion region leads to a picture of mixing of particles with different acceleration histories on electron Larmor scales. Based on an apparent average loss of accelerated particles by field-aligned and ExB transport, it is proposed that the role of the reconnection electric field is to replenish this loss by acceleration of particles that enter the electron diffusion region. Analytic theory is employed to verify this model, and an equation is derived, which balances the average electric field force density by a diffusion term applied to the electron momentum density. The diffusion coefficient contains explicitly the electron Larmor spatial scale and a poloidal transport time scale.

  14. Dependence of field-aligned electron precipitation occurrence on season and altitude

    NASA Technical Reports Server (NTRS)

    Berko, F. W.; Hoffman, R. A.

    1974-01-01

    An examination of factors affecting the occurrence of field-aligned 2.3-keV electron precipitation has been performed by using data from more than 7500 orbits of the polar-orbiting satellite Ogo 4. Both season and altitude were found to be parameters that are directly related to the probability of occurrence. The highest probabilities occurred when the measurements were made at altitudes from 800 km to apogee (914 km), except during summer. In this altitude interval, the electron precipitation was more likely to be field-aligned during winter than during any other season. The analysis suggests the establishment by electrostatic charge layers of localized electric fields parallel to the magnetic field. The resulting potential distribution focuses the electron beam along the field lines in the region between the charge layers but destroys the focused beam below the lower layer, and thus an altitude dependence is created.

  15. The Heliospheric Magnetic Field

    NASA Astrophysics Data System (ADS)

    Owens, Mathew J.; Forsyth, Robert J.

    2013-12-01

    The heliospheric magnetic field (HMF) is the extension of the coronal magnetic field carried out into the solar system by the solar wind. It is the means by which the Sun interacts with planetary magnetospheres and channels charged particles propagating through the heliosphere. As the HMF remains rooted at the solar photosphere as the Sun rotates, the large-scale HMF traces out an Archimedean spiral. This pattern is distorted by the interaction of fast and slow solar wind streams, as well as the interplanetary manifestations of transient solar eruptions called coronal mass ejections. On the smaller scale, the HMF exhibits an array of waves, discontinuities, and turbulence, which give hints to the solar wind formation process. This review aims to summarise observations and theory of the small- and large-scale structure of the HMF. Solar-cycle and cycle-to-cycle evolution of the HMF is discussed in terms of recent spacecraft observations and pre-spaceage proxies for the HMF in geomagnetic and galactic cosmic ray records.

  16. Polar Magnetic Field Experiment

    NASA Technical Reports Server (NTRS)

    Russell, C. T.

    1999-01-01

    This grant covers the initial data reduction and analysis of the magnetic field measurements of the Polar spacecraft. At this writing data for the first three years of the mission have been processed and deposited in the key parameter database. These data are also available in a variety of time resolutions and coordinate systems via a webserver at UCLA that provides both plots and digital data. The flight software has twice been reprogrammed: once to remove a glitch in the data where there were rare collisions between commands in the central processing unit and once to provide burst mode data at 100 samples per second on a regular basis. The instrument continues to function as described in the instrument paper (1.1 in the bibliography attached below). The early observations were compared with observations on the same field lines at lower altitude. The polar magnetic measurements also proved to be most useful for testing the accuracy of MHD models. WE also made important contributions to study of waves and turbulence.

  17. Photonic Magnetic Field Sensor

    NASA Astrophysics Data System (ADS)

    Wyntjes, Geert

    2002-02-01

    Small, in-line polarization rotators or isolators to reduce feedback in fiber optic links can be the basis for excellent magnetic field sensors. Based on the giant magneto-optical (GMO) or Faraday effect in iron garnets, they with a magnetic field of a few hundred Gauss, (20 mT) for an interaction length for an optical beam of a few millimeters achieve a polarization rotation or phase shift of 45 deg (1/8 cycle). When powered by a small laser diode, with the induced linear phase shift recovered at the shot noise limit, we have demonstrated sensitivities at the 3.3 nT/Hz1/2 level for frequencies from less than 1 Hz to frequencies into the high kHz range. Through further improvements; an increase in interaction length, better materials and by far the greatest factor, the addition of a flux concentrator, sensitivities at the pT/Hz1/2 level appear to be within reach. We will detail such a design and discuss the issues that may limit achieving these goals.

  18. Magnetic Fields: Visible and Permanent.

    ERIC Educational Resources Information Center

    Winkeljohn, Dorothy R.; Earl, Robert D.

    1983-01-01

    Children will be able to see the concept of a magnetic field translated into a visible reality using the simple method outlined. Standard shelf paper, magnets, iron filings, and paint in a spray can are used to prepare a permanent and well-detailed picture of the magnetic field. (Author/JN)

  19. Artificial field-aligned irregularities in the nightside auroral ionosphere

    NASA Astrophysics Data System (ADS)

    Blagoveshchenskaya, N.; Borisova, T.; Kornienko, V.; Leyser, T.; Rietveld, M.; Thide', B.

    The properties and behaviors of the artificial field-aligned small-scale irregularities (striations) in the nightside high latitudinal F-region in course of the Tromso ionospheric modification experiments are examined. Bistatic scatter measurements of HF diagnostic signals were carried out on the London-Tromso-St.Petersburg and Pori-Tromso-St.Petersburg paths using a Doppler spectral method. Striations act as an artificially produced target for the diagnostic HF radio waves and they are responsible for back-scattered signals. The main attention was paid to the aspect angle dependence of striations. It was found that the spectral features of the scattered signals are strongly dependent on the elevation angles of the HF heater antenna beam. The spectral power, broadening of the Doppler spectra, and median values of Doppler shift were maximal during the field-aligned direction of the HF heater antenna beam, whereas they were minimal during the vertical pointing of the HF beam. Simultaneous measurements from the EISCAT UHF incoherent scatter radar showed also the strongest heating effects in the field-aligned position. Electron temperature increases of up to 3000K (300%) induced by powerful HF pumping waves have been measured. Associated with them are the field-aligned ion outflows. Further observations of striations have been made using a narrower HF heater beam (sometimes termed "superheater"). The comparison between two HF heating experiments in a superheater mode, performed under the same geophysical conditions, also shows the strongest striations in the field-aligned position of the HF heater beam. The possible mechanisms for the directional dependence of striations are discussed.

  20. Magnetic fields and massive star formation

    SciTech Connect

    Zhang, Qizhou; Keto, Eric; Ho, Paul T. P.; Ching, Tao-Chung; Chen, How-Huan; Qiu, Keping; Girart, Josep M.; Juárez, Carmen; Liu, Hauyu; Tang, Ya-Wen; Koch, Patrick M.; Rao, Ramprasad; Lai, Shih-Ping; Li, Zhi-Yun; Frau, Pau; Li, Hua-Bai; Padovani, Marco; Bontemps, Sylvain

    2014-09-10

    Massive stars (M > 8 M {sub ☉}) typically form in parsec-scale molecular clumps that collapse and fragment, leading to the birth of a cluster of stellar objects. We investigate the role of magnetic fields in this process through dust polarization at 870 μm obtained with the Submillimeter Array (SMA). The SMA observations reveal polarization at scales of ≲0.1 pc. The polarization pattern in these objects ranges from ordered hour-glass configurations to more chaotic distributions. By comparing the SMA data with the single dish data at parsec scales, we found that magnetic fields at dense core scales are either aligned within 40° of or perpendicular to the parsec-scale magnetic fields. This finding indicates that magnetic fields play an important role during the collapse and fragmentation of massive molecular clumps and the formation of dense cores. We further compare magnetic fields in dense cores with the major axis of molecular outflows. Despite a limited number of outflows, we found that the outflow axis appears to be randomly oriented with respect to the magnetic field in the core. This result suggests that at the scale of accretion disks (≲ 10{sup 3} AU), angular momentum and dynamic interactions possibly due to close binary or multiple systems dominate over magnetic fields. With this unprecedentedly large sample of massive clumps, we argue on a statistical basis that magnetic fields play an important role during the formation of dense cores at spatial scales of 0.01-0.1 pc in the context of massive star and cluster star formation.

  1. Magnetically aligned graphite electrodes for high-rate performance Li-ion batteries

    NASA Astrophysics Data System (ADS)

    Billaud, Juliette; Bouville, Florian; Magrini, Tommaso; Villevieille, Claire; Studart, André R.

    2016-08-01

    As lithium-ion batteries become ubiquitous, the energy storage market is striving for better performance, longer lifetime and better safety of the devices. This race for performance is often focused on the search for new materials, whereas less effort has been dedicated to the electrode engineering. Enhancing the power density by increasing the amount of active material remains impractical since it impinges the transport of ions across the electrode during the charging and discharging processes. Here, we show that the electrochemical performance of a battery containing a thick (about 200 μm), highly loaded (about 10 mg cm-2) graphite electrode can be remarkably enhanced by fabricating anodes with an out-of-plane aligned architecture using a low external magnetic field. The lower tortuosity resulting from such a simple and scalable magnetic alignment approach leads to a specific charge up to three times higher than that of non-architectured electrodes at a rate of 1C.

  2. Joule heating and field-aligned currents: Preliminary results from DE-2

    NASA Technical Reports Server (NTRS)

    Sugiura, M.

    1986-01-01

    There are three main processes by which energy is transferred from the magnetosphere to the thermosphere: (1) charge exchange of the ring current particles; (2) precipitation of charged particles; and (3) joule dissipation by the magnetosphere-ionosphere current systems. The importance of this last process has been recognized and the rate of joule heating has been estimated by many workers. Observations of the electric (E) and magnetic (B) fields from Dynamics Explorer Satellite 2 are providing a new set of data on field-aligned currents. One of the remarkable features found in these observations is the high correlation between an orthogonal pair of the E and B field components. In recent years, observational data have accrued concerning the relationship between the interplanetary magnetic field and the size of the polar cap and also about the evolution of a substorm or a magnetic storm. It is suggested that these findings be incorporated in future model calculations.

  3. A numerical model of ionospheric convection derived from field-aligned currents and the corresponding conductivity

    NASA Astrophysics Data System (ADS)

    Blomberg, L. G.; Marklund, G. T.

    1988-03-01

    A numerical model for the calculation of ionospheric convection patterns from given distributions of field-aligned current and ionospheric conductivity is described. The model includes a coupling between the conductivity and the field-aligned current, so that the conductivity peaks in regions of upward current, as usually observed by measurements. The model is very flexible in that the input distributions, the field-aligned current, and the conductivity are parameterized in a convenient way. From the primary model output, namely the ionospheric electrostatic potential (or convection) in the corotating frame, a number of other quantities can be computed. These include: the potential in a Sun-fixed frame (the transformation takes into account the nonalignment of the Earth's magnetic and geographic axes); the potential in the magnetospheric equatorial plane (projected using either a dipole magnetic field model or the Tsyganenko-Usmanov model, and the assumption of vanishing parallel electric field); the distribution of ionospheric (horizontal) current; and Joule heating in the ionosphere. The model was used with input data inferred from satellite measurements to calculate the high-latitude potential distribution prevailing during a particular event. The model potential variation along the satellite orbit is found to be in excellent agreement with the measured electric field.

  4. Magnetic field satellite /MAGSAT/ spacecraft vector magnetometer calibration

    NASA Technical Reports Server (NTRS)

    Hinkal, S. W.

    1980-01-01

    The low-flying MAGSAT spacecraft, launched October 30, 1979, included a Vector Magnetometer to accurately map the magnitude and direction of the magnetic field of the earth. Calibration of the magnetometer included arc-second precision determination of the relative orientations of the three sensor axes in a coordinate system defined by optical references. This determination began with laboratory measurements of the relative alignments of optical components mounted with the magnetometer. The actual calibration procedure then consisted basically of accurate and repeatable positioning of the Vector Magnetometer within a unique magnetic test facility which nulls the earth's magnetic field, then generates magnetic fields of various orientations and strengths. Analysis of the magnetometer sensor outputs together with the position and alignment data then gave the axes orientations. We used precision theodolites and methods related to surveying techniques to achieve the accurate positioning and optical component alignment measurements. The final calibration accuracy exceeded results previously achieved in the facility.

  5. Alignment of Velocity and Magnetic Fluctuations in Simulations of Anisotropic MHD Turbulence

    NASA Astrophysics Data System (ADS)

    Ng, C. S.; Bhattacharjee, A.

    2007-11-01

    There has been recent theoretical interest in the effect of the alignment of velocity and magnetic fluctuations in three-dimensional (3D) MHD turbulence with a large-scale magnetic field [Boldyrev 2005, 2006]. This theory predicts that the angle θ between the velocity and magnetic fluctuation vectors has a scaling of θ&1/4circ;, where λ is the spatial scale of the fluctuations. There have also been simulations on 3D forced MHD turbulence that supports this prediction [Mason et al. 2006, 2007]. The scaling has also been tested against observations of solar wind turbulence [Podesta et al. 2007]. We report here simulation results based on decaying 2D turbulence. The scaling of θ&1/4circ; and Iroshnikov-Kraichnan scaling has also been observed within a range of time interval and spatial scales, despite the fact that Boldyrev's theory was developed for fully 3D turbulence in the presence of a strong external field. As the external field is reduced in magnitude and becomes comparable to the magnitude of magnetic fluctuations or lower, the scale-dependent alignment is weakened. Implications for observations of solar wind turbulence will be discussed.

  6. Fast superconducting magnetic field switch

    DOEpatents

    Goren, Y.; Mahale, N.K.

    1996-08-06

    The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater that the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles. 6 figs.

  7. Fast superconducting magnetic field switch

    DOEpatents

    Goren, Yehuda; Mahale, Narayan K.

    1996-01-01

    The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater that the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles.

  8. Martian external magnetic field proxies

    NASA Astrophysics Data System (ADS)

    Langlais, Benoit; Civet, Francois

    2015-04-01

    Mars possesses no dynamic magnetic field of internal origin as it is the case for the Earth or for Mercury. Instead Mars is characterized by an intense and localized magnetic field of crustal origin. This field is the result of past magnetization and demagnetization processes, and reflects its evolution. The Interplanetary Magnetic Field (IMF) interacts with Mars' ionized environment to create an external magnetic field. This external field is weak compared to lithospheric one but very dynamic, and may hamper the detailed analysis of the internal magnetic field at some places or times. Because there are currently no magnetic field measurements made at Mars' surface, it is not possible to directly monitor the external field temporal variability as it is done in Earth's ground magnetic observatories. In this study we examine to indirect ways of quantifying this external field. First we use the Advanced Composition Explorer (ACE) mission which measures the solar wind about one hour upstream of the bow-shock resulting from the interaction between the solar wind and the Earth's internal magnetic field. These measurements are extrapolated to Mars' position taking into account the orbital configurations of the Mars-Earth system and the velocity of particles carrying the IMF. Second we directly use Mars Global Surveyor magnetic field measurements to quantify the level of variability of the external field. We subtract from the measurements the internal field which is otherwise modeled, and bin the residuals first on a spatial and then on a temporal mesh. This allows to compute daily or semi daily index. We present a comparison of these two proxies and demonstrate their complementarity. We also illustrate our analysis by comparing our Martian external field proxies to terrestrial index at epochs of known strong activity. These proxies will especially be useful for upcoming magnetic field measurements made around or at the surface of Mars.

  9. Magnetic Fields in Irregular Galaxies

    NASA Astrophysics Data System (ADS)

    Kepley, Amanda A.; Muehle, S.; Robishaw, T.; Everett, J.; Wilcots, E.; Zweibel, E.; Heiles, C.

    2007-12-01

    Magnetic fields are an important component of the interstellar medium (ISM). They provide a source of pressure support, transfer energy from supernovae, are a possible heating mechanism for the ISM, and channel gas flows. Despite the importance of magnetic fields in the ISM, what generates and sustains galactic magnetic fields or how magnetic fields, gas, and stars interact in galaxies is not well understood. The magnetic fields may be especially important in low-mass galaxies like irregulars where the magnetic pressure may be great enough for the field to be dynamically important. Only three irregular galaxies besides the LMC and the SMC have previously observed magnetic field structures. NGC 4449 (Chyzy et al. 2000) and the LMC (Gaensler et al. 2005) both have large-scale fields, while IC 10 and NGC 6822 have mostly random fields (Chyzy et al. 2003). Our goal is to determine what mechanisms generate and sustain large-scale magnetic fields in irregular galaxies and what causes the range of magnetic field structure in irregular galaxies. We have observed the polarized radio continuum emission of four irregular galaxies with the VLA, GBT, and ATCA. Our observations double the number of irregular galaxies with observed magnetic field structure. Here we present results from two of our galaxies: NGC 4214 and NGC 1569. We find that NGC 4214 has a mostly random magnetic field structure, which is not surprising given its weak bar, small size, and high star formation rate. The magnetic field of NGC 1569 has large-scale structure which has been shaped not by a dynamo, but by an outflow generated by the massive star formation rate in this galaxy. Support for this research has been provided by a GBT Student Support Award, a Wisconsin Space Grant Consortium Graduate Fellowship, and an NSF Graduate Research Fellowship.

  10. Magnetospheric Multiscale Observations of Field-aligned Currents at the Magnetopause

    NASA Astrophysics Data System (ADS)

    Strangeway, R. J.; Russell, C. T.; Zhao, C.; Magnes, W.; Bromund, K. R.; Plaschke, F.; Fischer, D.; Anderson, B. J.; Le, G.; Chutter, M.; Slavin, J. A.; Nakamura, R.; Baumjohann, W.; Paterson, W. R.; Torbert, R. B.; Burch, J. L.

    2016-12-01

    Magnetospheric Multiscale (MMS) has demonstrated that the dayside magnetopause is usually highly structured, with multiple layers. Within these layers currents are observed to be flowing both parallel and perpendicular to the magnetic field. The parallel currents primarily act to bend or shear the magnetic field, while the perpendicular currents mainly change the field strength. We note that within the magnetopause MMS observes current densities that can be of the order of 100s of nAm-2. If these currents were to map to the ionosphere, then they would correspond to field-aligned current densities of the order of 100s of μAm-2, orders of magnitude larger than the observed low altitude field-aligned currents. A survey of several magnetopause crossings shows that the field-aligned currents on the magnetosphere side of the current layers can be flowing either parallel or anti-parallel to the magnetic field. On the magnetospheric side of the magnetopause current layers the plasma flows are generally in the -z direction (in GSM coordinates) for the events studied, suggesting that the observations are to the south of the reconnection site. If the currents were to correspond to Region-1 sense currents flowing into and out of the southern ionosphere, then the polarity of the currents would be ordered by local time, flowing parallel to the local magnetic field on the dusk-side of noon, and anti-parallel on the dawn-side of noon. But the current signatures are mixed, and sometimes the field-aligned currents reverse polarity within one crossing of the magnetopause. The issue is therefore how do we reconcile the local magnetopause field-aligned current signatures with what would be expected for the large-scale Region-1 currents that are typically associated with flow shears introduced through reconnection? Given the strength of the currents and their structure much of the current may be closed locally, with only a residual contributing to the large-scale currents.

  11. Inertial range spectrum of field-aligned whistler turbulence

    NASA Astrophysics Data System (ADS)

    Dwivedi, Navin Kumar; Singh, Shobhana

    2017-03-01

    An analytical model to study the whistler turbulence spectrum and inertial range spectral scalings related with the electric and magnetic field spectra in a weakly non-collisional magnetized plasma is developed. In the present model, the dispersion relation of whistler wave propagating along the background magnetic field is exploited to derive the inertial range scaling laws corresponding to the electric field and magnetic field fluctuations. The model is based on the concept of Iroshnikov–Kraichnan inertial range magnetohydrodynamic turbulence. The present phenomenological turbulence scaling model suggests the energy spectra associated with the whistler wave electric field fluctuations and magnetic field fluctuations pursue ‑1 and ‑3 power-laws, respectively. Moreover, the results obtained by the present analytical model reasonably able to explain and compare the observational energy spectra in the wave number domain. The observational and analytical results support the whistler dominated turbulence with the similar spectral index ‑1 of the electric field spectra, whereas, the magnetic field spectral indices in the wave number domain are found -13/3 and ‑3 for the observational and analytical approach, respectively.

  12. Evolution of twisted magnetic fields

    SciTech Connect

    Zweibel, E.G.; Boozer, A.H.

    1985-02-01

    The magnetic field of the solar corona evolves quasistatically in response to slowly changing photospheric boundary conditions. The magnetic topology is preserved by the low resistivity of the solar atmosphere. We show that a magnetic flux coordinate system simplifies the problem of calculating field evolution with invariant topology. As an example, we calculate the equilibrium of a thin magnetic flux tube with small twist per unit length.

  13. SOFIA/HAWC+: Mapping the Galactic Center Magnetic Field

    NASA Technical Reports Server (NTRS)

    Werner, Michael W.; Dowell, C. Darren; Chuss, D. T.; Morris, M. R.; Novak, G.

    2013-01-01

    Polarimetry of the far infrared emission from magnetically-aligned interstellar grains is one of the best ways of studying the magnetic field at the Galactic Center. We describe the HAWC+ instrument, under development for flight on SOFIA starting in 2015, which will provide a major advance in capability for these critically important measurements.

  14. SOFIA/HAWC+: Mapping the Galactic Center Magnetic Field

    NASA Technical Reports Server (NTRS)

    Werner, Michael W.; Dowell, C. Darren; Chuss, D. T.; Morris, M. R.; Novak, G.

    2013-01-01

    Polarimetry of the far infrared emission from magnetically-aligned interstellar grains is one of the best ways of studying the magnetic field at the Galactic Center. We describe the HAWC+ instrument, under development for flight on SOFIA starting in 2015, which will provide a major advance in capability for these critically important measurements.

  15. Protein Crystal Growth in Gels and Stationary Magnetic Fields

    SciTech Connect

    Moreno,A.; Quiroz-Garcia, B.; Yokaichiya, F.; Stojanoff, V.; Rudolph, P.

    2007-01-01

    Thaumatin, lysozyme, and ferritin single crystals were grown in solutions and gels without and with surrounding strong stationary magnetic fields. The crystal size, number and alignment in dependence on the induction force were analyzed. The crystal quality, like mosaicity, as function of the magnetic force is discussed by using synchrotron X-ray diffraction analysis.

  16. Field-aligned currents, convection electric fields, and ULF-ELF waves in the cusp

    NASA Technical Reports Server (NTRS)

    Saflekos, N. A.; Potemra, T. A.; Kintner, P. M., Jr.; Green, J. L.

    1979-01-01

    Nearly simultaneous observations from the Triad and Hawkeye satellites over the Southern Hemisphere, at low altitudes near the noon meridian and close to the usual polar cusp latitudes, show that in and near the polar cusp there exist several relationships between field-aligned currents (FACs), convection electric fields, ULF-ELF magnetic noise, broadband electrostatic noise and interplanetary magnetic fields. The most important findings are (1) the FACs directed into the ionosphere in the noon-to-dusk local time sector and directed away from the ionosphere in the noon-to-dawn local time sector and identified as region-1 permanent FACs (Iijima and Potemra, 1976a) and are located equatorward of the regions of antisunward (westward) convection; (2) the observations are consistent with a two-cell convection pattern symmetric in one case (throat positioned at noon) and asymmetric in another (throat located in a sector on the forenoon side in juxtaposition to the region of strong convection on the afternoon side); and (3) fine-structure FACs are responsible for the generation of ULF-ELF noise in the polar cusp.

  17. Controlled electrode magnetization alignment in planar elliptical ferromagnetic break junction devices

    NASA Astrophysics Data System (ADS)

    Scott, Gavin D.; Hu, Ting-Chen

    2016-10-01

    Controlling the magnetization reversal process of magnetic elements is important for a wide range of applications that make use of magnetoresistive effects but is difficult to achieve for devices that require adjacent thin film structures capable of contacting an individual molecule or quantum dot. We report on the fabrication and measurement of ferromagnetic break junction devices with planar, elliptical leads, to address the particular challenge of controlling the relative magnetization alignment between neighboring electrodes. Low temperature transport measurements, supported by finite-element micromagnetic simulations, are used to characterize the magnetoresistance response across a range of conductance levels. We demonstrate that an in-plane external field applied parallel to the hard axis of the ellipses may be used to controllably switch the magnetization of the source and drain electrodes between monodomain-like parallel and antiparallel configurations for devices in the tunneling regime.

  18. Exposure guidelines for magnetic fields

    SciTech Connect

    Miller, G.

    1987-12-01

    The powerful magnetic fields produced by a controlled fusion experiment at Lawrence Livermore National Laboratory (LLNL) necessitated the development of personnel-exposure guidelines for steady magnetic fields. A literature search and conversations with active researchers showed that it is currently possible to develop preliminary exposure guidelines for steady magnetic fields. An overview of the results of past research into the bioeffects of magnetic fields was compiled, along with a discussion of hazards that may be encountered by people with sickle-cell anemia or medical electronic and prosthetic implants. The LLNL steady magnetic-field exposure guidelines along with a review of developments concerning the safety of time-varying fields were also presented in this compilation. Guidelines developed elsewhere for time varying fields were also given. Further research is needed to develop exposure standards for both steady or time-varying fields.

  19. Exposure guidelines for magnetic fields.

    PubMed

    Miller, G

    1987-12-01

    The powerful magnetic fields produced by a controlled fusion experiment at Lawrence Livermore National Laboratory (LLNL) necessitated the development of personnel-exposure guidelines for steady magnetic fields. A literature search and conversations with active researchers showed that it is currently possible to develop preliminary exposure guidelines for steady magnetic fields. An overview of the results of past research into the bioeffects of magnetic fields was compiled, along with a discussion of hazards that may be encountered by people with sickle-cell anemia or medical electronic and prosthetic implants. The LLNL steady magnetic-field exposure guidelines along with a review of developments concerning the safety of time-varying fields were also presented in this compilation. Guidelines developed elsewhere for time varying fields were also given. Further research is needed to develop exposure standards for both steady or time-varying fields.

  20. Magnetic-field-dosimetry system

    DOEpatents

    Lemon, D.K.; Skorpik, J.R.; Eick, J.L.

    1981-01-21

    A device is provided for measuring the magnetic field dose and peak field exposure. The device includes three Hall-effect sensors all perpendicular to each other, sensing the three dimensional magnetic field and associated electronics for data storage, calculating, retrieving and display.

  1. Magnetic-field-dosimetry system

    SciTech Connect

    Lemon, D.K.; Skorpik, J.R.; Eick, J.L.

    1981-01-21

    A device is provided for measuring the magnetic field dose and peak field exposure. The device includes three Hall-effect sensors all perpendicular to each other, sensing the three dimensional magnetic field and associated electronics for data storage, calculating, retrieving and display.

  2. Direction dependent diffusion of aligned magnetic rods by means of x-ray photon correlation spectroscopy.

    PubMed

    Wagner, Joachim; Märkert, Christian; Fischer, Birgit; Müller, Leonard

    2013-01-25

    Rodlike hematite particles in suspension align perpendicular to an external magnetic field due to a negative anisotropy of their magnetic susceptibility Δχ. The diffusion tensor consists of two principal constants D(∥) and D(⊥) for the diffusion parallel and perpendicular to the long particle axis. X-ray photon correlation spectroscopy is capable of probing the diffusive motion in optically opaque suspensions of rodlike hematite particles parallel to the direction of the scattering vector Q. Choosing Q parallel or perpendicular to the direction of an external magnetic field H the direction dependent intermediate scattering function is measured by means of x-ray photon correlation spectroscopy. From the intermediate scattering function in both directions the principal diffusion constants D(∥) and D(⊥) are determined. The ratio D(∥)/D(⊥) increases with increasing aspect ratio of the particles and can be described via a rescaled theoretical approach for prolate ellipsoids of revolution.

  3. Phase-dependent field-free molecular alignment and orientation

    NASA Astrophysics Data System (ADS)

    Qin, Chaochao; Liu, Yuzhu; Zhang, Xianzhou; Gerber, Thomas

    2014-11-01

    We investigated the temporal behavior of alignment and orientation of LiH following a femtosecond laser pulse excitation comprising two fields at center frequencies ω and 2 ω (e.g., E (t )=E [cos(ω t )+cos(2 ω t +Φ ) ] ) shifted by a phase Φ . The effects of repopulations and rephasing of rotational states on the resulting alignment and orientation were evaluated. The population distribution of rotational states is only changed during the exciting pulse. Afterwards the established rotational state distribution is maintained in the absence of collisions. The phases of rotational states play the most crucial role in determining the time evolution of molecular alignment and orientation. Equal alignment and rotational populations are obtained when the phases are chosen Φ =0 and Φ =π . However, orientation is different due to the fact that in the case Φ =π the mutual phases of even rotation states are not changed but the phases of odd rotational states are shifted by π , comparing with that of Φ =0 . The effect of temperature on molecular orientation was also addressed. It was shown that an efficient field-free molecular orientation can be observed even at room temperature.

  4. A general approach to controlled alignment of filamentous supra-biomolecular assemblies into centimeter-scale highly-ordered patterns through nature-inspired magnetic guidance

    PubMed Central

    Cao, Binrui; Zhu, Ye; Wang, Lin

    2013-01-01

    We took the advantage of the capability of magnetic nanoparticles (MNPs) being aligned along a magnetic field and reproducibly generated large scale bio-nanofiber assemblies with the orientation of the constituent bio-nanofibers defined by the applied magnetic field. When decorated by MNPs, bio-nanofibers could be guided by the external magnetic field to become oriented either horizontally or vertically, forming single- and multi-orientation layered assemblies. PMID:24115320

  5. Thermal electron acceleration by electric field spikes in the outer radiation belt: generation of field-aligned pitch angle distributions

    NASA Astrophysics Data System (ADS)

    Vasko, I.; Agapitov, O. V.; Mozer, F.; Artemyev, A.

    2015-12-01

    Van Allen Probes observations in the outer radiation belt have demonstrated an abundance non-linear electrostatic stucture called Time Domain Structures (TDS). One of the type of TDS is electrostatic electron-acoustic double layers (DL). Observed DLs are frequently accompanied by field-aligned (bi-directional) pitch angle distributions (PAD) of electrons with energies from hundred eVs up to several keV (rarely up to tens of keV). We perform numerical simulations of the DL interaction with thermal electrons making use of the test particle approach. DL parameters assumed in the simulations are adopted from observations. We show that DLs accelerate thermal electrons parallel to the magnetic field via the electrostatic Fermi mechanism, i.e. due to reflections from DL potential humps. Due to this interaction some fraction of electrons is scattered into the loss cone. The electron energy gain is larger for larger DL scalar potential amplitudes and higher propagation velocities. In addition to the Fermi mechanism electrons can be trapped by DLs in their generation region and accelerated due to transport to higher latitudes. Both mechanisms result in formation of field-aligned PADs for electrons with energies comparable to those found in observations. The Fermi mechanism provides field-aligned PADs for <1 keV electrons, while the trapping mechanism extends field-aligned PADs to higher energy electrons.

  6. Thermal electron acceleration by electric field spikes in the outer radiation belt: Generation of field-aligned pitch angle distributions

    NASA Astrophysics Data System (ADS)

    Vasko, I. Y.; Agapitov, O. V.; Mozer, F. S.; Artemyev, A. V.

    2015-10-01

    Van Allen Probes observations in the outer radiation belt have demonstrated an abundance of electrostatic electron-acoustic double layers (DL). DLs are frequently accompanied by field-aligned (bidirectional) pitch angle distributions (PAD) of electrons with energies from hundred eVs up to several keV. We perform numerical simulations of the DL interaction with thermal electrons making use of the test particle approach. DL parameters assumed in the simulations are adopted from observations. We show that DLs accelerate thermal electrons parallel to the magnetic field via the electrostatic Fermi mechanism, i.e., due to reflections from DL potential humps. The electron energy gain is larger for larger DL scalar potential amplitudes and higher propagation velocities. In addition to the Fermi mechanism, electrons can be trapped by DLs in their generation region and accelerated due to transport to higher latitudes. Both mechanisms result in formation of field-aligned PADs for electrons with energies comparable to those found in observations. The Fermi mechanism provides field-aligned PADs for <1 keV electrons, while the trapping mechanism extends field-aligned PADs to higher-energy electrons. It is shown that the Fermi mechanism can result in scattering into the loss cone of up to several tenths of percent of electrons with flux peaking at energies up to several hundred eVs.

  7. Permanent Magnet Spiral Motor for Magnetic Gradient Energy Utilization: Axial Magnetic Field

    NASA Astrophysics Data System (ADS)

    Valone, Thomas F.

    2010-01-01

    The Spiral Magnetic Motor, which can accelerate a magnetized rotor through 90% of its cycle with only permanent magnets, was an energy milestone for the 20th century patents by Kure Tekkosho in the 1970's. However, the Japanese company used old ferrite magnets which are relatively weak and an electrically-powered coil to jump start every cycle, which defeated the primary benefit of the permanent magnet motor design. The principle of applying an inhomogeneous, anisotropic magnetic field gradient force Fz = μ cos φ dB/dz, with permanent magnets is well-known in physics, e.g., Stern-Gerlach experiment, which exploits the interaction of a magnetic moment with the aligned electron spins of magnetic domains. In this case, it is applied to dB/dθ in polar coordinates, where the force Fθ depends equally on the magnetic moment, the cosine of the angle between the magnetic moment and the field gradient. The radial magnetic field increases in strength (in the attractive mode) or decreases in strength (in the repulsive mode) as the rotor turns through one complete cycle. An electromagnetic pulsed switching has been historically used to help the rotor traverse the gap (detent) between the end of the magnetic stator arc and the beginning (Kure Tekko, 1980). However, alternative magnetic pulse and switching designs have been developed, as well as strategic eddy current creation. This work focuses on the switching mechanism, novel magnetic pulse methods and advantageous angular momentum improvements. For example, a collaborative effort has begun with Toshiyuki Ueno (University of Tokyo) who has invented an extremely low power, combination magnetostrictive-piezoelectric (MS-PZT) device for generating low frequency magnetic fields and consumes "zero power" for static magnetic field production (Ueno, 2004 and 2007a). Utilizing a pickup coil such as an ultra-miniature millihenry inductor with a piezoelectric actuator or simply Wiegand wire geometry, it is shown that the necessary

  8. A High-resolution Model of Field-aligned Currents Through Empirical Orthogonal Functions Analysis (MFACE)

    NASA Technical Reports Server (NTRS)

    He, Maosheng; Vogt, Joachim; Luehr, Hermann; Sorbalo, Eugen; Blagau, Adrian; Le, Guan; Lu, Gang

    2012-01-01

    Ten years of CHAMP magnetic field measurements are integrated into MFACE, a model of field-aligned currents (FACs) using empirical orthogonal functions (EOFs). EOF1 gives the basic Region-1/Region-2 pattern varying mainly with the interplanetary magnetic field Bz component. EOF2 captures separately the cusp current signature and By-related variability. Compared to existing models, MFACE yields significantly better spatial resolution, reproduces typically observed FAC thickness and intensity, improves on the magnetic local time (MLT) distribution, and gives the seasonal dependence of FAC latitudes and the NBZ current signature. MFACE further reveals systematic dependences on By, including 1) Region-1/Region-2 topology modifications around noon; 2) imbalance between upward and downward maximum current density; 3) MLT location of the Harang discontinuity. Furthermore, our procedure allows quantifying response times of FACs to solar wind driving at the bow shock nose: we obtain 20 minutes and 35-40 minutes lags for the FAC density and latitude, respectively.

  9. A new angle for probing field-aligned irregularities with the Murchison Widefield Array

    NASA Astrophysics Data System (ADS)

    Loi, Shyeh Tjing; Murphy, Tara; Cairns, Iver H.; Trott, Cathryn M.; Hurley-Walker, Natasha; Feng, Lu; Hancock, Paul J.; Kaplan, David L.

    2016-06-01

    Electron density irregularities in the ionosphere are known to be magnetically anisotropic, preferentially elongated along the lines of force. While many studies of their morphology have been undertaken by topside sounding and whistler measurements, it is only recently that detailed regional-scale reconstructions have become possible, enabled by the advent of widefield radio telescopes. Here we present a new approach for visualizing and studying field-aligned irregularities (FAIs), which involves transforming interferometric measurements of total electron content gradients onto a magnetic shell tangent plane. This removes the perspective distortion associated with the oblique viewing angle of the irregularities from the ground, facilitating the decomposition of dynamics along and across magnetic field lines. We apply this transformation to the data set of Loi et al. (2015a), obtained on 15 October 2013 by the Murchison Widefield Array (MWA) radio telescope and displaying prominent FAIs. We study these FAIs in the new reference frame, quantifying field-aligned and field-transverse behavior, examining time and altitude dependencies, and extending the analysis to FAIs on subarray scales. We show that the inclination of the plane can be derived solely from the data and verify that the best fit value is consistent with the known magnetic inclination. The ability of the model to concentrate the fluctuations along a single spatial direction may find practical application to future calibration strategies for widefield interferometry, by providing a compact representation of FAI-induced distortions.

  10. The link between magnetic field orientations and star formation rates

    NASA Astrophysics Data System (ADS)

    Li, Hua-Bai; Jiang, Hangjin; Fan, Xiaodan; Gu, Qilao; Zhang, Yapeng

    2017-08-01

    Understanding star formation rates (SFRs) is a central goal of modern star formation models, which mainly involve gravity, turbulence and, in some cases, magnetic fields (B-fields)1,2. However, a connection between B-fields and SFRs has never been observed. Here, a comparison between the surveys of SFRs3,4 and a study of cloud-field alignment5—which revealed a bimodal (parallel or perpendicular) alignment—shows consistently lower SFRs per solar mass for clouds almost perpendicular to the B-fields. This is evidence of B-fields being a primary regulator of SFRs. The perpendicular alignment possesses a significantly higher magnetic flux than the parallel alignment and thus a stronger support of the gas against self-gravity. This results in overall lower masses of the fragmented components, which are in agreement with lower SFRs.

  11. Mixed Brownian alignment and Néel rotations in superparamagnetic iron oxide nanoparticle suspensions driven by an ac field

    PubMed Central

    Shah, Saqlain A.; Reeves, Daniel B.; Ferguson, R. Matthew; Weaver, John B.

    2015-01-01

    Superparamagnetic iron oxide nanoparticles with highly nonlinear magnetic behavior are attractive for biomedical applications like magnetic particle imaging and magnetic fluid hyperthermia. Such particles display interesting magnetic properties in alternating magnetic fields and here we document experiments that show differences between the magnetization dynamics of certain particles in frozen and melted states. This effect goes beyond the small temperature difference (ΔT ~ 20 °C) and we show the dynamics to be a mixture of Brownian alignment of the particles and Néel rotation of their moments occurring in liquid particle suspensions. These phenomena can be modeled in a stochastic differential equation approach by postulating log-normal distributions and partial Brownian alignment of an effective anisotropy axis. We emphasize that precise particle-specific characterization through experiments and nonlinear simulations is necessary to predict dynamics in solution and optimize their behavior for emerging biomedical applications including magnetic particle imaging. PMID:26504371

  12. Mixed Brownian alignment and Néel rotations in superparamagnetic iron oxide nanoparticle suspensions driven by an ac field

    NASA Astrophysics Data System (ADS)

    Shah, Saqlain A.; Reeves, Daniel B.; Ferguson, R. Matthew; Weaver, John B.; Krishnan, Kannan M.

    2015-09-01

    Superparamagnetic iron oxide nanoparticles with highly nonlinear magnetic behavior are attractive for biomedical applications like magnetic particle imaging and magnetic fluid hyperthermia. Such particles display interesting magnetic properties in alternating magnetic fields and here we document experiments that show differences between the magnetization dynamics of certain particles in frozen and melted states. This effect goes beyond the small temperature difference (Δ T ˜20 ∘C ) and we show the dynamics to be a mixture of Brownian alignment of the particles and Néel rotation of their moments occurring in liquid particle suspensions. These phenomena can be modeled in a stochastic differential equation approach by postulating log-normal distributions and partial Brownian alignment of an effective anisotropy axis. We emphasize that precise particle-specific characterization through experiments and nonlinear simulations is necessary to predict dynamics in solution and optimize their behavior for emerging biomedical applications including magnetic particle imaging.

  13. Mixed Brownian alignment and Néel rotations in superparamagnetic iron oxide nanoparticle suspensions driven by an ac field.

    PubMed

    Shah, Saqlain A; Reeves, Daniel B; Ferguson, R Matthew; Weaver, John B; Krishnan, Kannan M

    Superparamagnetic iron oxide nanoparticles with highly nonlinear magnetic behavior are attractive for biomedical applications like magnetic particle imaging and magnetic fluid hyperthermia. Such particles display interesting magnetic properties in alternating magnetic fields and here we document experiments that show differences between the magnetization dynamics of certain particles in frozen and melted states. This effect goes beyond the small temperature difference (ΔT ~ 20 °C) and we show the dynamics to be a mixture of Brownian alignment of the particles and Néel rotation of their moments occurring in liquid particle suspensions. These phenomena can be modeled in a stochastic differential equation approach by postulating log-normal distributions and partial Brownian alignment of an effective anisotropy axis. We emphasize that precise particle-specific characterization through experiments and nonlinear simulations is necessary to predict dynamics in solution and optimize their behavior for emerging biomedical applications including magnetic particle imaging.

  14. Vestibular stimulation by magnetic fields

    PubMed Central

    Ward, Bryan K.; Roberts, Dale C.; Della Santina, Charles C.; Carey, John P.; Zee, David S.

    2015-01-01

    Individuals working next to strong static magnetic fields occasionally report disorientation and vertigo. With the increasing strength of magnetic fields used for magnetic resonance imaging (MRI) studies, these reports have become more common. It was recently learned that humans, mice and zebrafish all demonstrate behaviors consistent with constant peripheral vestibular stimulation while inside a strong, static magnetic field. The proposed mechanism for this effect involves a Lorentz force resulting from the interaction of a strong static magnetic field with naturally occurring ionic currents flowing through the inner ear endolymph into vestibular hair cells. The resulting force within the endolymph is strong enough to displace the lateral semicircular canal cupula, inducing vertigo and the horizontal nystagmus seen in normal mice and in humans. This review explores the evidence for interactions of magnetic fields with the vestibular system. PMID:25735662

  15. Monitoring the effect of magnetically aligned collagen scaffolds on tendon tissue engineering by PSOCT

    NASA Astrophysics Data System (ADS)

    Yang, Ying; Ahearne, Mark; Wimpenny, Ian; Torbet, Jim

    2009-02-01

    As the repair of injured or degenerated tendon is often compromised by the shortage of suitable donor tissue, other procedures need to be developed. The application of a functional tissue engineered tendon could prove to be a promising alternative therapy. Due to their good biocompatibility, collagen hydrogel based scaffolds have been considered to be potentially suitable for engineering tendon tissue in vitro. One of the major limitations of collagen hydrogels for engineering tissues is the difficulty in controlling their architecture and collagen concentration which results in poor mechanical strength. This study aims to overcome these limitations by creating a highly biocompatible scaffold that is both mechanically robust and aligned. Collagen fibers were pre-aligned under a high magnetic field then concentrated using plastic compression. Primary tenocytes cultured from rats were seeded on the aligned scaffolds. Following a protocol in public domain, thick cultured collagen constructs were rolled up into a spiral after undergoing plastic compressed. Both a light microscopy and a polarization sensitive optical coherence tomography (PSOCT) with central beam at 1300 nm were used to monitor the birefringence in the constructs. Conventional light microscopy showed that the tenocytes aligned along the pre-organized collagen bundles in contrast to the random distributed observed on unaligned scaffolds. PSOCT only revealed weak birefringence from aligned but uncompressed constructs. However, PSOCT images showed contrast band structures in the spiral constructs which suggests that the birefringence signal depends on the density of aligned collagen fibers. The effect of aligned cells, neo-formed matrix and the plastic compression on the birefringence signals are discussed in this paper briefly.

  16. Magnetic fields around evolved stars

    NASA Astrophysics Data System (ADS)

    Leal-Ferreira, M.; Vlemmings, W.; Kemball, A.; Amiri, N.; Maercker, M.; Ramstedt, S.; Olofsson, G.

    2014-04-01

    A number of mechanisms, such as magnetic fields, (binary) companions and circumstellar disks have been suggested to be the cause of non-spherical PNe and in particular collimated outflows. This work investigates one of these mechanisms: the magnetic fields. While MHD simulations show that the fields can indeed be important, few observations of magnetic fields have been done so far. We used the VLBA to observe five evolved stars, with the goal of detecting the magnetic field by means of water maser polarization. The sample consists in four AGB stars (IK Tau, RT Vir, IRC+60370 and AP Lyn) and one pPN (OH231.8+4.2). In four of the five sources, several strong maser features were detected allowing us to measure the linear and/or circular polarization. Based on the circular polarization detections, we infer the strength of the component of the field along the line of sight to be between ~30 mG and ~330 mG in the water maser regions of these four sources. When extrapolated to the surface of the stars, the magnetic field strength would be between a few hundred mG and a few Gauss when assuming a toroidal field geometry and higher when assuming more complex magnetic fields. We conclude that the magnetic energy we derived in the water maser regions is higher than the thermal and kinetic energy, leading to the conclusion that, indeed, magnetic fields probably play an important role in shaping Planetary Nebulae.

  17. Three-dimensional structure of ionospheric currents produced by field-aligned currents

    NASA Astrophysics Data System (ADS)

    Takeda, M.

    1982-08-01

    Ionospheric currents caused by field-aligned currents are calculated three-dimensionally under quiet conditions at the equinox, using a magnetic field line coordinate system and with the assumption of infinite parallel conductivity. Input field-aligned currents are assumed to be distributed only in the daytime and the whole system is assumed to be symmetric about the equator. Calculated currents are comparable with those of the ionospheric dynamo in higher latitudes, but much weaker in lower latitudes including the equatorial electrojet region. Hence, if the model is valid these currents may have a considerable effect on the day-to-day variation of Sq currents in higher latitudes, but little effect on those in lower latitudes such as the counter-electrojet.

  18. Composite Materials with Magnetically Aligned Carbon Nanoparticles Having Enhanced Electrical Properties and Methods of Preparation

    NASA Technical Reports Server (NTRS)

    Hong, Haiping (Inventor); Peterson, G.P. (Bud) (Inventor); Salem, David R. (Inventor)

    2016-01-01

    Magnetically aligned carbon nanoparticle composites have enhanced electrical properties. The composites comprise carbon nanoparticles, a host material, magnetically sensitive nanoparticles and a surfactant. In addition to enhanced electrical properties, the composites can have enhanced mechanical and thermal properties.

  19. Magnetic Fields in the Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Clark, Susan

    2017-01-01

    The Milky Way is magnetized. Invisible magnetic fields thread the Galaxy on all scales and play a vital but still poorly understood role in regulating flows of gas in the interstellar medium and the formation of stars. I will present highlights from my thesis work on magnetic fields in the diffuse interstellar gas and in accretion disks. At high Galactic latitudes, diffuse neutral hydrogen is organized into an intricate network of slender linear features. I will show that these neutral hydrogen “fibers” are extremely well aligned with the ambient magnetic field as traced by both starlight polarization (Clark et al. 2014) and Planck 353 GHz polarized dust emission (Clark et al. 2015). The structure of the neutral interstellar medium is more tightly coupled to the magnetic field than previously known. Because the orientation of neutral hydrogen is an independent predictor of the local dust polarization angle, our work provides a new tool in the search for inflationary gravitational wave B-mode polarization in the cosmic microwave background, which is currently limited by dust foreground contamination. Magnetic fields also drive accretion in astrophysical disks via the magnetorotational instability (MRI). I analytically derive the behavior of this instability in the weakly nonlinear regime and show that the saturated state of the instability depends on the geometry of the background magnetic field. The analytical model describes the behavior of the MRI in a Taylor-Couette flow, a set-up used by experimentalists in the ongoing quest to observe MRI in the laboratory (Clark & Oishi 2016a, 2016b).

  20. The Capacitive Magnetic Field Sensor

    NASA Astrophysics Data System (ADS)

    Zyatkov, D. O.; Yurchenko, A. V.; Balashov, V. B.; Yurchenko, V. I.

    2016-01-01

    The results of a study of sensitive element magnetic field sensor are represented in this paper. The sensor is based on the change of the capacitance with an active dielectric (ferrofluid) due to the magnitude of magnetic field. To prepare the ferrofluid magnetic particles are used, which have a followingdispersion equal to 50 < Ø < 56, 45 < Ø < 50, 40 < Ø < 45 and Ø < 40micron of nanocrystalline alloy of brand 5BDSR. The dependence of the sensitivity of the capacitive element from the ferrofluid with different dispersion of magnetic particles is considered. The threshold of sensitivity and sensitivity of a measuring cell with ferrofluid by a magnetic field was determined. The experimental graphs of capacitance change of the magnitude of magnetic field are presented.

  1. High magnetic field test of bismuth Hall sensors for ITER steady state magnetic diagnostic

    NASA Astrophysics Data System (ADS)

    Duran, I.; Entler, S.; Kohout, M.; Kočan, M.; Vayakis, G.

    2016-11-01

    Performance of bismuth Hall sensors developed for the ITER steady state magnetic diagnostic was investigated for high magnetic fields in the range ±7 T. Response of the sensors to the magnetic field was found to be nonlinear particularly within the range ±1 T. Significant contribution of the planar Hall effect to the sensors output voltage causing undesirable cross field sensitivity was identified. It was demonstrated that this effect can be minimized by the optimization of the sensor geometry and alignment with the magnetic field and by the application of "current-spinning technique."

  2. High magnetic field test of bismuth Hall sensors for ITER steady state magnetic diagnostic.

    PubMed

    Ďuran, I; Entler, S; Kohout, M; Kočan, M; Vayakis, G

    2016-11-01

    Performance of bismuth Hall sensors developed for the ITER steady state magnetic diagnostic was investigated for high magnetic fields in the range ±7 T. Response of the sensors to the magnetic field was found to be nonlinear particularly within the range ±1 T. Significant contribution of the planar Hall effect to the sensors output voltage causing undesirable cross field sensitivity was identified. It was demonstrated that this effect can be minimized by the optimization of the sensor geometry and alignment with the magnetic field and by the application of "current-spinning technique."

  3. The MAVEN Magnetic Field Investigation

    NASA Technical Reports Server (NTRS)

    Connerney, J. E. P.; Espley, J.; Lawton, P.; Murphy, S.; Odom, J.; Oliversen, R.; Sheppard, D.

    2014-01-01

    The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions ("boomlets"). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a quantization uncertainty of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05%. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers - multiple rotations about the spacecraft x and z axes - to characterize spacecraft fields and/or instrument offsets in flight.

  4. The MAVEN Magnetic Field Investigation

    NASA Astrophysics Data System (ADS)

    Connerney, J. E. P.; Espley, J.; Lawton, P.; Murphy, S.; Odom, J.; Oliversen, R.; Sheppard, D.

    2015-12-01

    The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions ("boomlets"). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a resolution of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05 %. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers—multiple rotations about the spacecraft x and z axes—to characterize spacecraft fields and/or instrument offsets in flight.

  5. Ultralow field magnetization reversal of two-body magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Li, Fei; Lu, Jincheng; Lu, Xiaofeng; Tang, Rujun; Sun, Z. Z.

    2016-08-01

    Field induced magnetization reversal was investigated in a system of two magnetic nanoparticles with uniaxial anisotropies and magnetostatic interaction. By using the micromagnetic simulation, ultralow switching field strength was found when the separation distance between the two particles reaches a critical small value (on nanometer scale) in the perpendicular configuration where the anisotropic axes of the two particles are perpendicular to the separation line. The switching field increases sharply when the separation is away from the critical distance. The ultralow field switching phenomenon was missed in the parallel configuration where both the anisotropic axes are aligned along the separation line of the two particles. The micromagnetic results are consistent with the previous theoretical prediction [J. Appl. Phys. 109, 104303 (2011)] where dipolar interaction between two single-domain magnetic particles was considered. Our present simulations offered further proofs and possibilities for the low-power applications of information storage as the two-body magnetic nanoparticles might be implemented as a composite information bit.

  6. Cosmic Magnetic Fields - An Overview

    NASA Astrophysics Data System (ADS)

    Wielebinski, Richard; Beck, Rainer

    Magnetic fields have been known in antiquity. Aristotle attributes the first of what could be called a scientific discussion on magnetism to Thales, who lived from about 625 BC. In China “magnetic carts” were in use to help the Emperor in his journeys of inspection. Plinius comments that in the Asia Minor province of Magnesia shepherds' staffs get at times “glued” to a stone, a alodestone. In Europe the magnetic compass came through the Arab sailors who met the Portuguese explorers. The first scientific treatise on magnetism, “De Magnete”, was published by William Gilbert who in 1600 described his experiments and suggested that the Earth was a huge magnet. Johannes Kepler was a correspondent of Gilbert and at times suggested that planetary motion was due to magnetic forces. Alas, this concept was demolished by Isaac Newton,who seeing the falling apple decided that gravity was enough. This concept of dealing with gravitational forces only remains en vogue even today. The explanations why magnetic effects must be neglected go from “magnetic energy is only 1% of gravitation” to “magnetic fields only complicate the beautiful computer solutions”. What is disregarded is the fact that magnetic effects are very directional(not omni-directional as gravity) and also the fact that magnetic fields are seen every where in our cosmic universe.

  7. A novel flexible field-aligned coordinate system for tokamak edge plasma simulation

    NASA Astrophysics Data System (ADS)

    Leddy, J.; Dudson, B.; Romanelli, M.; Shanahan, B.; Walkden, N.

    2017-03-01

    Tokamak plasmas are confined by a magnetic field that limits the particle and heat transport perpendicular to the field. Parallel to the field the ionised particles can move freely, so to obtain confinement the field lines are ;closed; (i.e. form closed surfaces of constant poloidal flux) in the core of a tokamak. Towards, the edge, however, the field lines intersect physical surfaces, leading to interaction between neutral and ionised particles, and the potential melting of the material surface. Simulation of this interaction is important for predicting the performance and lifetime of future tokamak devices such as ITER. Field-aligned coordinates are commonly used in the simulation of tokamak plasmas due to the geometry and magnetic topology of the system. However, these coordinates are limited in the geometry they allow in the poloidal plane due to orthogonality requirements. A novel 3D coordinate system is proposed herein that relaxes this constraint so that any arbitrary, smoothly varying geometry can be matched in the poloidal plane while maintaining a field-aligned coordinate. This system is implemented in BOUT++ and tested for accuracy using the method of manufactured solutions. A MAST edge cross-section is simulated using a fluid plasma model and the results show expected behaviour for density, temperature, and velocity. Finally, simulations of an isolated divertor leg are conducted with and without neutrals to demonstrate the ion-neutral interaction near the divertor plate and the corresponding beneficial decrease in plasma temperature.

  8. Magnetic Fields of Nondegenerate Stars

    NASA Astrophysics Data System (ADS)

    Donati, J.-F.; Landstreet, J. D.

    2009-09-01

    Magnetic fields are present in a wide variety of stars throughout the HR diagram and play a role at basically all evolutionary stages, from very-low-mass dwarfs to very massive stars, and from young star-forming molecular clouds and protostellar accretion discs to evolved giants/supergiants and magnetic white dwarfs/neutron stars. These fields range from a few μG (e.g., in molecular clouds) to TG and more (e.g., in magnetic neutron stars); in nondegenerate stars in particular, they feature large-scale topologies varying from simple nearly axisymmetric dipoles to complex nonaxsymmetric structures, and from mainly poloidal to mainly toroidal topologies. After recalling the main techniques of detecting and modeling stellar magnetic fields, we review the existing properties of magnetic fields reported in cool, hot, and young nondegenerate stars and protostars, and discuss our understanding of the origin of these fields and their impact on the birth and life of stars.

  9. Hierarchical nanostructure control in rod-coil block copolymers with magnetic fields.

    PubMed

    Tao, Yuefei; Zohar, Hagar; Olsen, Bradley D; Segalman, Rachel A

    2007-09-01

    Magnetic field alignment of rod-coil block copolymers is shown to proceed through coupling to the diamagnetic moment of individual rod blocks. Block copolymer self-assembly then leads to alignment of the interfaces perpendicular to the field lines and long range order on a 10 nm lengthscale. This is in contrast to previously demonstrated alignment techniques, which couple to the block copolymer interfaces rather than individual molecules. Furthermore, alignment occurs without direct physical contact to samples millimeters in size.

  10. Anisotropic magnetic particles in a magnetic field

    PubMed Central

    Martchenko, Ilya; Mihut, Adriana M.; Bialik, Erik; Hirt, Ann M.; Rufier, Chantal; Menzel, Andreas; Dietsch, Hervé; Linse, Per

    2016-01-01

    We characterize the structural properties of magnetic ellipsoidal hematite colloids with an aspect ratio ρ ≈ 2.3 using a combination of small-angle X-ray scattering and computer simulations. The evolution of the phase diagram with packing fraction φ and the strength of an applied magnetic field B is described, and the coupling between orientational order of magnetic ellipsoids and the bulk magnetic behavior of their suspension addressed. We establish quantitative structural criteria for the different phase and arrest transitions and map distinct isotropic, polarized non-nematic, and nematic phases over an extended range in the φ–B coordinates. We show that upon a rotational arrest of the ellipsoids around φ = 0.59, the bulk magnetic behavior of their suspension switches from superparamagnetic to ordered weakly ferromagnetic. If densely packed and arrested, these magnetic particles thus provide persisting remanent magnetization of the suspension. By exploring structural and magnetic properties together, we extend the often used colloid-atom analogy to the case of magnetic spins. PMID:27722439

  11. Polar Rain Gradients and Field-Aligned Polar Cap Potentials

    NASA Technical Reports Server (NTRS)

    Fairfield, D. H.; Wing, S.; Newell, P. T.; Ruohoniemi, J. M.; Gosling, J. T.; Skoug, R. M.

    2008-01-01

    ACE SWEPAM measurements of solar wind field-aligned electrons have been compared with simultaneous measurements of polar rain electrons precipitating over the polar cap and detected by DMSP spacecraft. Such comparisons allow investigation of cross-polarcap gradients in the intensity of otherwise-steady polar rain. The generally good agreement of the distribution functions, f, from the two data sources confirms that direct entry of solar electrons along open field lines is indeed the cause of polar rain. The agreement between the data sets is typically best on the side of the polar cap with most intense polar rain but the DMSP f's in less intense regions can be brought into agreement with ACE measurements by shifting all energies by a fixed amounts that range from tens to several hundred eV. In most cases these shifts are positive which implies that field-aligned potentials of these amounts exist on polar cap field lines which tend to retard the entry of electrons and produce the observed gradients. These retarding potentials undoubtedly appear in order to prevent the entry of low-energy electrons and maintain charge quasi-neutrality that would otherwise be violated since most tailward flowing magnetosheath ions are unable to follow polar rain electrons down to the polar cap. In more limited regions near the boundary of the polar cap there is sometimes evidence for field-aligned potentials of the opposite sign that accelerate polar rain electrons. A solar electron burst is also studied and it is concluded that electrons from such bursts can enter the magnetotail and precipitate in the same manner as polar rain.

  12. Space Technology 5 Multi-Point Observations of Temporal Variability of Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Le, Guan; Wang, Yongli; Slavin, James A.; Strangeway, Robert J.

    2008-01-01

    Space Technology 5 (ST5) is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, sun-synchronous polar orbit from March 22 to June 21, 2006, for technology validations. In this paper, we present a study of the temporal variability of field-aligned currents using multi-point magnetic field measurements from ST5. The data demonstrate that meso-scale current structures are commonly embedded within large-scale field-aligned current sheets. The meso-scale current structures are very dynamic with highly variable current density and/or polarity in time scales of approximately 10 min. They exhibit large temporal variations during both quiet and disturbed times in such time scales. On the other hand, the data also shown that the time scales for the currents to be relatively stable are approximately 1 min for meso-scale currents and approximately 10 min for large scale current sheets. These temporal features are obviously associated with dynamic variations of their particle carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of meso-scale field-aligned currents are found to be consistent with those of auroral parallel electric field.

  13. Space Technology 5 (ST-5) Observations of Field-Aligned Currents: Temporal Variability

    NASA Technical Reports Server (NTRS)

    Le, Guan

    2010-01-01

    Space Technology 5 (ST-5) is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, sun-synchronous polar orbit from March 22 to June 21, 2006, for technology validations. In this paper, we present a study of the temporal variability of field-aligned currents using multi-point magnetic field measurements from STS. The data demonstrate that masoscale current structures are commonly embedded within large-scale field-aligned current sheets. The meso-scale current structures are very dynamic with highly variable current density and/or polarity in time scales of about 10 min. They exhibit large temporal variations during both quiet and disturbed times in such time scales. On the other hand, the data also shown that the time scales for the currents to be relatively stable are about I min for meso-scale currents and about 10 min for large scale current sheets. These temporal features are obviously associated with dynamic variations of their particle carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of meso-scale field-aligned currents are found to be consistent with those of auroral parallel electric field.

  14. Space Technology 5 Multi-Point Observations of Temporal Variability of Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Le, Guan; Wang, Yongli; Slavin, James A.; Strangeway, Robert J.

    2008-01-01

    Space Technology 5 (ST5) is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, sun-synchronous polar orbit from March 22 to June 21, 2006, for technology validations. In this paper, we present a study of the temporal variability of field-aligned currents using multi-point magnetic field measurements from ST5. The data demonstrate that meso-scale current structures are commonly embedded within large-scale field-aligned current sheets. The meso-scale current structures are very dynamic with highly variable current density and/or polarity in time scales of approximately 10 min. They exhibit large temporal variations during both quiet and disturbed times in such time scales. On the other hand, the data also shown that the time scales for the currents to be relatively stable are approximately 1 min for meso-scale currents and approximately 10 min for large scale current sheets. These temporal features are obviously associated with dynamic variations of their particle carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of meso-scale field-aligned currents are found to be consistent with those of auroral parallel electric field.

  15. 3D model of small-scale density cavities in the auroral magnetosphere with field-aligned current

    NASA Astrophysics Data System (ADS)

    Bespalov, P. A.; Misonova, V. G.; Savina, O. N.

    2016-09-01

    We propose a 3D model of small-scale density cavities stimulated by an auroral field-aligned current and an oscillating field-aligned current of kinetic Alfvén waves. It is shown that when the field-aligned current increases so that the electron drift velocity exceeds a value of the order of the electron thermal velocity, the plasma becomes unstable to the formation of cavities with low density and strong electric field. The condition of instability is associated with the value of the background magnetic field. In the case of a relatively weak magnetic field (where the electron gyro-radius is greater than the ion acoustic wavelength), the current instability can lead to the formation of one-dimensional cavities along the magnetic field. In the case of a stronger magnetic field (where the ion acoustic wavelength is greater than the electron gyro-radius, but still is less than the ion gyro-radius), the instability can lead to the formation of 3D density cavities. In this case, the spatial scales of the cavity, both along and across the background magnetic field, can be comparable, and at the earlier stage of the cavity formation they are of the order of the ion acoustic wavelength. Rarefactions of the cavity density are accompanied by an increase in the electric field and are limited by the pressure of bipolar electric fields that occur within them. The estimates of typical density cavity characteristics and the results of numerical solutions agree with known experimental data: small-scale structures with a sufficiently strong electric field are observed in the auroral regions with strong field-aligned current.

  16. FAST/Polar Conjunction Study of Field-Aligned Auroral Acceleration and Corresponding Magnetotail Drivers

    NASA Technical Reports Server (NTRS)

    Schriver, D.; Ashour-Abdalla, M.; Strangeway, R. J.; Richard, R. L.; Klezting, C.; Dotan, Y.; Wygant, J.

    2002-01-01

    The discrete aurora results when energized electrons bombard the Earth's atmosphere at high latitudes. This paper examines the physical processes that can cause field-aligned acceleration of plasma particles in the auroral region. A data and theoretical study has been carried out to examine the acceleration mechanisms that operate in the auroral zone and to identity the magnetospheric drivers of these acceleration mechanisms. The observations used in the study were collected by the Fast Auroral SnapshoT (FAST) and Polar satellites when the two satellites were in approximate magnetic conjunction in the auroral region. During these events FAST was in the middle of the auroral zone and Polar was above the auroral zone in the near-Earth plasma sheet. Polar data was used to determine the conditions in the magnetotail at the time field-aligned acceleration was measured by FAST in the auroral zone. For each of the magnetotail drivers identified in the data study, the physics of field-aligned acceleration in the auroral region was examined using existing theoretical efforts and a long-system particle-in-cell simulation to model the magnetically connected region between the two satellites.

  17. Magnetic field synthesis for microwave magnetics

    NASA Astrophysics Data System (ADS)

    Morgenthaler, F. R.

    1982-04-01

    The Microwave and Quantum Magnetics Group of the M.I.T. Department of Electrical Engineering and Computer Science undertook a two-year research program directed at developing synthesis procedures that allow magnetostatic and/or magnetoelastic modes to be specially tailored for microwave signal processing applications that include magnetically tunable filters and limiters as well as delay lines that are either linearly dispersive or nondispersive over prescribed bandwidths. Special emphasis was given to devices employing thin films of yttrium iron garnet (YIG) that are blessed with spatially nonuniform dc magnetic fields.

  18. Nematic order of model goethite nanorods in a magnetic field

    NASA Astrophysics Data System (ADS)

    Wensink, H. H.; Vroege, G. J.

    2005-09-01

    We explore the nematic order of model goethite nanorods in an external magnetic field within Onsager-Parsons density functional theory. The goethite rods are represented by monodisperse, charged spherocylinders with a permanent magnetic moment along the rod main axis, forcing the particles to align parallel to the magnetic field at low field strength. The intrinsic diamagnetic susceptibility anisometry of the rods is negative, which leads to a preferred perpendicular orientation at higher field strength. It is shown that these competing effects may give rise to intricate phase behavior, including a pronounced stability of biaxial nematic order and the presence of reentrant phase transitions and demixing phenomena.

  19. Field-aligned currents and magnetospheric convection - A comparison between MHD simulations and observations

    NASA Technical Reports Server (NTRS)

    Walker, Raymond J.; Ogino, Tatsuki

    1988-01-01

    A time-dependent three-dimensional MHD model was used to investigate the magnetospheric configuration as a function of the interplanetary magnetic field direction when it was in the y-z plane in geocentric solar magnetospheric coordinates. The model results show large global convection cells, tail lobe cells, high-latitude polarcap cells, and low latitude cells. The field-aligned currents generated in the model magnetosphere and the model convection system are compared with observations from low-altitude polar orbiting satellites.

  20. HSX: Engineering Design and Fabrication of the main Magnet Coils, Vacuum Vessel and Support/Alignment Structure

    NASA Astrophysics Data System (ADS)

    Anderson, F. Simon B.; Anderson, D. T.; Almagri, A. F.; Matthews, P. G.; Probert, P. H.; Shohet, J. L.; Talmadge, J. N.

    1996-11-01

    The HSX device, with a magnetic field consisting of a SINGLE dominant HELICAL component, has a set of 48 twisted main magnetic field coils. Engineering analysis (ANSYS) has resulted in a set of construction and alignment constraints and goals for field accuracy and coil structural strength. Close proximity of the main coil set to the magnetic separatrix imposes space restrictions on the vacuum vessel. Fabrication of the vessel using explosive techniques, and the structural analysis for the stresses in the vacuum chamber will be discussed. Crucial to the integrity of the quasihelical magnetic field is the accurate positioning of the magnet coils and maintenance of the position during operation. The design and construct- ion of the completed support structure for HSX coils will also be presented. *** Work supported by U.S Dept. of Energy Grant DE-FG02-93ER54222

  1. Thermodynamics of the HMF model with a magnetic field

    NASA Astrophysics Data System (ADS)

    Chavanis, P. H.

    2011-04-01

    We study the thermodynamics of the Hamiltonian mean field (HMF) model with an external potential playing the role of a "magnetic field". If we consider only fully stable states, the caloric curve does not present any phase transition. However, if we take into account metastable states (for a restricted class of perturbations), we find a very rich phenomenology. In particular, the caloric curve displays a region of negative specific heat in the microcanonical ensemble in which the temperature decreases as the energy increases. This leads to ensembles inequivalence and to zeroth order phase transitions similar to the "gravothermal catastrophe" and to the "isothermal collapse" of self-gravitating systems. In the present case, they correspond to the reorganization of the system from an "anti-aligned" phase (magnetization pointing in the direction opposite to the magnetic field) to an "aligned" phase (magnetization pointing in the same direction as the magnetic field). We also find that the magnetic susceptibility can be negative in the microcanonical ensemble so that the magnetization decreases as the magnetic field increases. The magnetic curves can take various shapes depending on the values of energy or temperature. We describe first order phase transitions and hysteretic cycles involving positive or negative susceptibilities. We also show that this model exhibits gaps in the magnetization at fixed energy, resulting in ergodicity breaking.

  2. Ground Observations of Artificial E Region Field-Aligned Irregularities Over HAARP

    NASA Astrophysics Data System (ADS)

    Nossa, E.; Hysell, D. L.

    2008-12-01

    Heating experiments were performed at HAARP intended to create E region field aligned plasma irregularities (FAIs) at midday in July of 2008 when the critical frequency of the E layer is a maximum. Field-aligned backscatter was observed using a 30 MHz imaging coherent scatter radar located close to Homer, Alaska. Three experiment modes were used, involving 1) heating alternately at zenith and magnetic zenith, 2) heating using triangular power modulation, and 3) heating slightly above and below the second electron gyroharmonic. Strong echoes were observed in all cases. Radar imaging and other diagnostic methods are used to examine the degree to which irregularities can be observed outside the Spitze angle, the possible effects of predonditioning on thermal parametric instability, and the effects of the double resonance on backscatter intensity and irregularity formation.

  3. Tracing magnetic fields and identifying star formation with velocity gradients

    NASA Astrophysics Data System (ADS)

    Lazarian, Alex; Gonzalez Casanova, Diego; Yuen, Ka Ho

    2017-01-01

    We are presenting a new technique of tracing magnetic fields utilizing Doppler broadened spectral lines. We demonstrate that for subAlfvenic turbulence, i.e. for regions with turbulence velocities less than Alfven speed, the velocity gradients (VGs) are well aligned with magnetic fields both in 3D data cubes and in synthetic observations. For the latter case the VGs are calculated using velocity centroids and their alignment with the projected magnetic field is studied. We demonstraed this by comparing the HI data with the PLANCK polarization maps. We conclude that velocity gradients present a new promissing way of studying magnetic fields in diffuse media. We also explored the properties of VGs in dense gas and found that starting with a particular density threshold value the VGs tend to be perpendicular to magnetic fields. We also compare the alignment of VGs and the density gradients (DGs) and find that these measures are well aligned in the absense of self-gravity, although in diffuse regions the VGs trace magnetic field better than the DGs. The advantage of VGs for tracing magnetic fields gets more obvious as the Mach number increases. Self-gravity acts differently on the VGs and the DGs. For self-gravitating regions the VGs and the DGs tend to get orthogonal to each other, revealing the the regions of ongoing star formation. This misalignment of the VGs and DGs is also evident in synthetic observations. We conclude that the VGs present(a) a new promising way of tracing magnetic field in diffuse media, (b) in combination with polarimety they reveal shocked gas,(c) in combination with the DGs they reveal star forming regions.

  4. Rotating superconductor magnet for producing rotating lobed magnetic field lines

    DOEpatents

    Hilal, Sadek K.; Sampson, William B.; Leonard, Edward F.

    1978-01-01

    This invention provides a rotating superconductor magnet for producing a rotating lobed magnetic field, comprising a cryostat; a superconducting magnet in the cryostat having a collar for producing a lobed magnetic field having oppositely directed adjacent field lines; rotatable support means for selectively rotating the superconductor magnet; and means for energizing the superconductor magnet.

  5. Quantifying the Magnetic Alignment of Hi and Dust in the Diffuse ISM

    NASA Astrophysics Data System (ADS)

    Clark, S. E.; Peek, J. E. G.; Hill, J. Colin; Putman, M. E.

    Sensitive, high resolution observations of Galactic neutral hydrogen (Hi) reveal an intricate network of slender linear features, much as sensitive surveys of dust in Galactic molecular clouds reveal ubiquitous filamentary structure. Across the high Galactic latitude sky, diffuse Histructures are aligned with the interstellar magnetic field, as revealed by background starlight polarization (Clark, Peek, & Putman 2014) and by Planck 353 GHz polarized dust emission (Clark et al. 2015). These discoveries were enabled by the Rolling Hough Transform, a recently developed, open source machine vision algorithm.

  6. The Effects of GPS Signal Propagation Paths Alignment with Low-Latitude Ionospheric Field-Aligned Plasma Bubble Structures on Scintillation

    NASA Astrophysics Data System (ADS)

    Paula, E. R.; Moraes, A. D. O.; Costa, E.; Vani, B. C.; Abdu, M. A.; Galera Monico, J. F.

    2016-12-01

    This work analyzes GPS scintillation data recorded during five months (Nov/2014 to Mar/2015) at São José dos Campos, Brazil, located near the southern crest of the equatorial ionization anomaly. Analysis has been performed aiming at relating amplitude and phase scintillation indices with the orientation of the propagation path through the ionospheric irregularities and then evaluating its effects on receiver positioning and GPS availability. Based on the analysis of an extensive set with 311,369 samples, it was noted that there is a dominance of intense scintillation events around the azimuth angle of 345º (geographic northwest but nearly aligned with geomagnetic field lines). In view of the large westward magnetic declination (21.4ºW) of this region and of the nature of the plasma bubble irregularity distribution with respect to the geomagnetic field configuration, this result strongly suggests that such GPS signal propagation paths were close to being end-on through magnetic field aligned plasma bubbles. This work will show that during this alignment, the extensive propagation path length through the bubbles can result in larger scintillation intensity cases. Further analysis based on calculation of the propagation angles with respect to the magnetic field line (in elevation and azimuth) clearly support the interpretation that cases of loss of phase lock are most likely to occur for small values of these angles and that those cases are distributed around the value of the scintillation index S4 = 1. Thus, the present work provides for the first time a quantitative verification and confirmation of such effect of scintillation enhancement due to nearly magnetic longitudinal satellite-to-receiver propagation paths. Additionally, this work will show the consequences of such alignment on precise pointing positioning, highlighting the threat that this type of scenario could represent to users of such application.

  7. PREPROCESSING MAGNETIC FIELDS WITH CHROMOSPHERIC LONGITUDINAL FIELDS

    SciTech Connect

    Yamamoto, Tetsuya T.; Kusano, K.

    2012-06-20

    Nonlinear force-free field (NLFFF) extrapolation is a powerful tool for the modeling of the magnetic field in the solar corona. However, since the photospheric magnetic field does not in general satisfy the force-free condition, some kind of processing is required to assimilate data into the model. In this paper, we report the results of new preprocessing for the NLFFF extrapolation. Through this preprocessing, we expect to obtain magnetic field data similar to those in the chromosphere. In our preprocessing, we add a new term concerning chromospheric longitudinal fields into the optimization function proposed by Wiegelmann et al. We perform a parameter survey of six free parameters to find minimum force- and torque-freeness with the simulated-annealing method. Analyzed data are a photospheric vector magnetogram of AR 10953 observed with the Hinode spectropolarimeter and a chromospheric longitudinal magnetogram observed with SOLIS spectropolarimeter. It is found that some preprocessed fields show the smallest force- and torque-freeness and are very similar to the chromospheric longitudinal fields. On the other hand, other preprocessed fields show noisy maps, although the force- and torque-freeness are of the same order. By analyzing preprocessed noisy maps in the wave number space, we found that small and large wave number components balance out on the force-free index. We also discuss our iteration limit of the simulated-annealing method and magnetic structure broadening in the chromosphere.

  8. Microscopic observation of magnetic bacteria in the magnetic field of a rotating permanent magnet

    NASA Astrophysics Data System (ADS)

    Smid, Pieter; Shcherbakov, Valeriy; Petersen, Nikolai

    2015-09-01

    Magnetotactic bacteria are ubiquitous and can be found in both freshwater and marine environments. Due to intracellular chains of magnetic single domain particles, they behave like swimming compass needles. In external magnetic fields like the Earth's magnetic field, a torque is acting on the chain. This will cause the bacterium to be rotated and aligned with the external field. The swimming direction of magnetotactic bacteria can be controlled with external magnetic fields, which makes it convenient to study them under a light microscope. Usually, a special set of coils arranged around a light microscope is used to control the swimming magnetotactic bacteria. Here, we present a simple mechanical system with a permanent magnet, which produces a rotating magnetic field of nearly constant amplitude in the focal plane of a light microscope. The device is placed beside the light microscope and easily adaptable to almost any microscope and thus convenient for field experiments. To describe the trajectories qualitatively, a theoretical model of the trajectories is presented. This device can be used to control the swimming direction of magnetotactic bacteria and also for studying their magnetic and hydrodynamic properties.

  9. Microscopic observation of magnetic bacteria in the magnetic field of a rotating permanent magnet.

    PubMed

    Smid, Pieter; Shcherbakov, Valeriy; Petersen, Nikolai

    2015-09-01

    Magnetotactic bacteria are ubiquitous and can be found in both freshwater and marine environments. Due to intracellular chains of magnetic single domain particles, they behave like swimming compass needles. In external magnetic fields like the Earth's magnetic field, a torque is acting on the chain. This will cause the bacterium to be rotated and aligned with the external field. The swimming direction of magnetotactic bacteria can be controlled with external magnetic fields, which makes it convenient to study them under a light microscope. Usually, a special set of coils arranged around a light microscope is used to control the swimming magnetotactic bacteria. Here, we present a simple mechanical system with a permanent magnet, which produces a rotating magnetic field of nearly constant amplitude in the focal plane of a light microscope. The device is placed beside the light microscope and easily adaptable to almost any microscope and thus convenient for field experiments. To describe the trajectories qualitatively, a theoretical model of the trajectories is presented. This device can be used to control the swimming direction of magnetotactic bacteria and also for studying their magnetic and hydrodynamic properties.

  10. Misalignment of Magnetic Fields and Outflows in Protostellar Cores

    NASA Astrophysics Data System (ADS)

    Hull, Charles L. H.; Plambeck, Richard L.; Bolatto, Alberto D.; Bower, Geoffrey C.; Carpenter, John M.; Crutcher, Richard M.; Fiege, Jason D.; Franzmann, Erica; Hakobian, Nicholas S.; Heiles, Carl; Houde, Martin; Hughes, A. Meredith; Jameson, Katherine; Kwon, Woojin; Lamb, James W.; Looney, Leslie W.; Matthews, Brenda C.; Mundy, Lee; Pillai, Thushara; Pound, Marc W.; Stephens, Ian W.; Tobin, John J.; Vaillancourt, John E.; Volgenau, N. H.; Wright, Melvyn C. H.

    2013-05-01

    We present results of λ1.3 mm dust-polarization observations toward 16 nearby, low-mass protostars, mapped with ~2.''5 resolution at CARMA. The results show that magnetic fields in protostellar cores on scales of ~1000 AU are not tightly aligned with outflows from the protostars. Rather, the data are consistent with scenarios where outflows and magnetic fields are preferentially misaligned (perpendicular), or where they are randomly aligned. If one assumes that outflows emerge along the rotation axes of circumstellar disks, and that the outflows have not disrupted the fields in the surrounding material, then our results imply that the disks are not aligned with the fields in the cores from which they formed.

  11. Preflare magnetic and velocity fields

    NASA Technical Reports Server (NTRS)

    Hagyard, M. J.; Gaizauskas, V.; Chapman, G. A.; Deloach, A. C.; Gary, G. A.; Jones, H. P.; Karpen, J. T.; Martres, M.-J.; Porter, J. G.; Schmeider, B.

    1986-01-01

    A characterization is given of the preflare magnetic field, using theoretical models of force free fields together with observed field structure to determine the general morphology. Direct observational evidence for sheared magnetic fields is presented. The role of this magnetic shear in the flare process is considered within the context of a MHD model that describes the buildup of magnetic energy, and the concept of a critical value of shear is explored. The related subject of electric currents in the preflare state is discussed next, with emphasis on new insights provided by direct calculations of the vertical electric current density from vector magnetograph data and on the role of these currents in producing preflare brightenings. Results from investigations concerning velocity fields in flaring active regions, describing observations and analyses of preflare ejecta, sheared velocities, and vortical motions near flaring sites are given. This is followed by a critical review of prevalent concepts concerning the association of flux emergence with flares

  12. Complexities of determining the Field-Aligned current density from LEO satellites.

    NASA Astrophysics Data System (ADS)

    Gjerloev, J. W.; Friel, M. M.; Ohtani, S.; Muhleisen, M.; Gjerloev, A. W.; Martin, P.; Barnes, R. J.

    2015-12-01

    We show results from a study of the field-aligned currents (FAC) as derived from SWARM magnetic field perturbations. We calculate the FAC density using four different techniques and explain why they provide different results. Theoretical work, simulations and data are used to show that widely used techniques can provide current density estimates with errors of 1000%. These errors can be explained by spatial gradients in the currents and temporal variability of the currents as well as a breakdown of other fundamental assumptions. We apply the techniques to auroral crossings with THEMIS ASI coverage and use the SWARM magnetic field observations to calculate the current density. Finally, we show how to estimate the errors in the current density calculations.

  13. Toroidal and poloidal magnetic fields at Venus. Venus Express observations

    NASA Astrophysics Data System (ADS)

    Dubinin, E.; Fraenz, M.; Woch, J.; Zhang, T. L.; Wei, Y.; Fedorov, A.; Barabash, S.; Lundin, R.

    2013-10-01

    Magnetic field and plasma measurements carried out onboard Venus Express during solar minimum conditions suggest the existence of two kinds of magnetic field configuration in the Venusian ionosphere. We interpret these as the manifestation of two different types of generation mechanisms for the induced magnetosphere. A different magnetic field topology (toroidal and poloidal) arises if the induced currents are driven either by the solar wind motional electric field or by the Faraday electric field—a conducting ionosphere sees the magnetic field carried by solar wind as a time-varying field. At the dayside, both driving agents produce a similar draping pattern of the magnetic field. However, different magnetic field signatures inherent to both induction mechanisms appear at lower altitudes in the terminator region. The conditions at low solar EUV flux when the ionosphere of Venus becomes magnetized seem to be favorable to distinguish between two different types of the induced fields. We present cases of both types of the magnetic field topology. The cases when the effects of the Faraday induction become well noticeable are especially interesting since they provide us with an example of solar wind interaction with a tiny induced dipole field immersed into the ionosphere. Another interesting case when poloidal magnetic fields are evidently displayed is observed when the IMF vector is almost aligned with the solar wind velocity. In general case, both mechanisms of induction probably complement each other.

  14. Aligned Single Wall Carbon Nanotube Polymer Composites Using an Electric Field

    NASA Technical Reports Server (NTRS)

    Park, Cheol; Wiklinson, John; Banda, Sumanth; Ounaies, Zoubeida; Wise, Kristopher E.; Sauti, Godfrey; Lillehei, Peter T.; Harrison, Joycelyn S.

    2005-01-01

    While high shear alignment has been shown to improve the mechanical properties of single wall carbon nanotubes (SWNT)-polymer composites, it is difficult to control and often results in degradation of the electrical and dielectric properties of the composite. Here, we report a novel method to actively align SWNTs in a polymer matrix, which allows for control over the degree of alignment of SWNTs without the side effects of shear alignment. In this process, SWNTs are aligned via field-induced dipolar interactions among the nanotubes under an AC electric field in a liquid matrix followed by immobilization by photopolymerization while maintaining the electric field. Alignment of SWNTs was controlled as a function of magnitude, frequency, and application time of the applied electric field. The degree of SWNT alignment was assessed using optical microscopy and polarized Raman spectroscopy and the morphology of the aligned nanocomposites was investigated by high resolution scanning electron microscopy. The structure of the field induced aligned SWNTs is intrinsically different from that of shear aligned SWNTs. In the present work, SWNTs are not only aligned along the field, but also migrate laterally to form thick, aligned SWNT percolative columns between the electrodes. The actively aligned SWNTs amplify the electrical and dielectric properties in addition to improving the mechanical properties of the composite. All of these properties of the aligned nanocomposites exhibited anisotropic characteristics, which were controllable by tuning the applied field conditions.

  15. AC photovoltaic module magnetic fields

    SciTech Connect

    Jennings, C.; Chang, G.J.; Reyes, A.B.; Whitaker, C.M.

    1997-12-31

    Implementation of alternating current (AC) photovoltaic (PV) modules, particularly for distributed applications such as PV rooftops and facades, may be slowed by public concern about electric and magnetic fields (EMF). This paper documents magnetic field measurements on an AC PV module, complementing EMF research on direct-current PV modules conducted by PG and E in 1993. Although not comprehensive, the PV EMF data indicate that 60 Hz magnetic fields (the EMF type of greatest public concern) from PV modules are comparable to, or significantly less than, those from household appliances. Given the present EMF research knowledge, AC PV module EMF may not merit considerable concern.

  16. Magnetic Field of Strange Dwarfs

    NASA Astrophysics Data System (ADS)

    Baghdasaryan, D. S.

    2016-03-01

    The generation of a magnetic field in a strange quark star owing to differential rotation of the superfluid and superconducting quark core relative to the normal electron-nuclear crust of the star is examined. The maximum possible magnetic field on the surface is estimated for various models of strange dwarfs. Depending on the configuration parameters, i.e., the mass M and radius R of the star, a range of 103-105 G is found. These values of the magnetic field may be an additional condition for identification of strange dwarfs among the extensive class of observed white dwarfs.

  17. Preface: Cosmic magnetic fields

    NASA Astrophysics Data System (ADS)

    Kosovichev, Alexander

    2015-02-01

    Recent advances in observations and modeling have opened new perspectives for the understanding of fundamental dynamical processes of cosmic magnetism, and associated magnetic activity on the Sun, stars and galaxies. The goal of the Special Issue is to discuss the progress in solar physics and astrophysics, similarities and differences in phenomenology and physics of magnetic phenomena on the Sun and other stars. Space observatories, ground-based telescopes, and new observational methods have provided tremendous amount of data that need to be analyzed and understood. The solar observations discovered multi-scale organization of solar activity, dramatically changing current paradigms of solar variability. On the other side, stellar observations discovered new regimes of dynamics and magnetism that are different from the corresponding solar phenomena, but described by the same physics. Stars represent an astrophysical laboratory for studying the dynamical, magnetic and radiation processes across a broad range of stellar masses and ages. These studies allow us to look at the origin and evolution of our Sun, whereas detailed investigations of the solar magnetism give us a fundamental basis for interpretation and understanding of unresolved stellar data.

  18. Magnetic fields during galaxy mergers

    NASA Astrophysics Data System (ADS)

    Rodenbeck, Kai; Schleicher, Dominik R. G.

    2016-09-01

    Galaxy mergers are expected to play a central role for the evolution of galaxies and may have a strong effect on their magnetic fields. We present the first grid-based 3D magnetohydrodynamical simulations investigating the evolution of magnetic fields during merger events. For this purpose, we employed a simplified model considering the merger event of magnetized gaseous disks in the absence of stellar feedback and without a stellar or dark matter component. We show that our model naturally leads to the production of two peaks in the evolution of the average magnetic field strength within 5 kpc, within 25 kpc, and on scales in between 5 and 25 kpc. The latter is consistent with the peak in the magnetic field strength previously reported in a merger sequence of observed galaxies. We show that the peak on the galactic scale and in the outer regions is most likely due to geometrical effects, as the core of one galaxy enters the outskirts of the other one. In addition, the magnetic field within the central ~5 kpc is physically enhanced, which reflects the enhancement in density that is due to efficient angular momentum transport. We conclude that high-resolution observations of the central regions will be particularly relevant for probing the evolution of magnetic field structures during merger events.

  19. FOREWORD: Focus on Materials Analysis and Processing in Magnetic Fields Focus on Materials Analysis and Processing in Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Sakka, Yoshio; Hirota, Noriyuki; Horii, Shigeru; Ando, Tsutomu

    2009-03-01

    Recently, interest in the applications of feeble (diamagnetic and paramagnetic) magnetic materials has grown, whereas the popularity of ferromagnetic materials remains steady and high. This trend is due to the progress of superconducting magnet technology, particularly liquid-helium-free superconducting magnets that can generate magnetic fields of 10 T and higher. As the magnetic energy is proportional to the square of the applied magnetic field, the magnetic energy of such 10 T magnets is in excess of 10 000 times that of conventional 0.1 T permanent magnets. Consequently, many interesting phenomena have been observed over the last decade, such as the Moses effect, magnetic levitation and the alignment of feeble magnetic materials. Researchers in this area are widely spread around the world, but their number in Japan is relatively high, which might explain the success of magnetic field science and technology in Japan. Processing in magnetic fields is a rapidly expanding research area with a wide range of promising applications in materials science. The 3rd International Workshop on Materials Analysis and Processing in Magnetic Fields (MAP3), which was held on 14-16 May 2008 at the University of Tokyo, Japan, focused on various topics including magnetic field effects on chemical, physical, biological, electrochemical, thermodynamic and hydrodynamic phenomena; magnetic field effects on the crystal growth and processing of materials; diamagnetic levitation, the magneto-Archimedes effect, spin chemistry, magnetic orientation, control of structure by magnetic fields, magnetic separation and purification, magnetic-field-induced phase transitions, properties of materials in high magnetic fields, the development of NMR and MRI, medical applications of magnetic fields, novel magnetic phenomena, physical property measurement by magnetic fields, and the generation of high magnetic fields. This focus issue compiles 13 key papers selected from the proceedings of MAP3. Other

  20. Shock aurora: Field-aligned discrete structures moving along the dawnside oval

    NASA Astrophysics Data System (ADS)

    Zhou, Xiaoyan; Haerendel, Gerhard; Moen, Jøran I.; Trondsen, Espen; Clausen, Lasse; Strangeway, Robert J.; Lybekk, Bjørn; Lorentzen, Dag A.

    2017-03-01

    Generated by interplanetary shocks or solar wind pressure pulses, shock aurora has transient, global, and dynamic significances and provides a direct manifestation of the solar wind-magnetosphere-ionosphere interaction. As a part of a series of studies of the shock aurora, this paper focuses on the interaction at the morning magnetopause and its auroral manifestation at 06 magnetic local time, where the velocity and magnetic field shears dominate the interaction. Flow shears can generate wave-like structures inside a viscous boundary layer or even larger-scale vortices. These structures couple to the ionosphere via quasi-static field-aligned currents or via kinetic Alfvén waves. Potential drops along field-aligned filaments may be generated accelerating electrons to form auroral manifestations of the structures. A shock aurora event at dawnside is used to test this scenario. The findings include moving auroral streaks/rays that have a vertical profile from red (at 250 km altitude) to purple (at 100 km). The streaks moved antisunward along the poleward boundary of the oval at an ionospheric speed of 3 km s-1. It was mapped to the magnetopause flank at 133 km s-1, which was consistent with the observed speed of the magnetopause surface waves generated by the Kelvin-Helmholtz instability. The calculated field-aligned potential drop using Haerendel's analytic model was 5 kV that reasonably explained the observations. The results support the above scenario and reveal that magnetic and velocity shears at the flanks of the magnetospause may be the main cause of the fast moving shock aurora streaks.

  1. Field-aligned currents observed by the OGO 5 and Triad satellites

    NASA Technical Reports Server (NTRS)

    Sugiura, M.

    1975-01-01

    The existence of field-aligned currents in the polar cap boundary layer as a permanent feature of the magnetosphere is investigated. Magnetic field observations from Triad at 800 km altitude and from OGO 5 in the high-altitude magnetosphere are examined. Results indicate that in the morning half of the boundary layer, currents flow into the ionosphere, and that the current direction is reversed in the afternoon half of the layer. The Triad data further indicate that the net current is a maximum near 1500 MLT and that there may be a secondary maximum during early morning hours. According to the Isis 2 electron observations, the locations of these maximums of field-aligned net current roughly match those of two maximums in the isointensity contours for 150 ev electrons. It is proposed that the polar cap boundary current is driven by a current generator in the magnetotail, or ultimately in the solar wind. It is suggested that the large scale field-aligned currents in the polar cap boundary layer are associated with the dominance of protons on the morning side and of electrons on the afternoon side near the poleward edge of the precipitation zone along the auroral oval.

  2. High-latitude convection patterns for various large-scale field-aligned current configurations

    SciTech Connect

    Blomberg, L.G.; Marklund, G.T. )

    1991-04-01

    The large-scale field-aligned current system for persistent northward interplanetary magnetic field (IMF) is typically different from that for persistent southward IMF. One characteristic difference is that for northward IMF there is often a large-scale field-aligned current system poleward of the main auroral oval. This current system (the NBZ current) typically occupies a large function of the region poleward of the region 1 and 2 currents. The present paper models the high-latitude convection as a function of the large-scale field-aligned currents. In particular, a possible evolution of the convection pattern as the current system changes from a typical configuration for southward IMF to a configuration representing northward IMF (or vice versa) is presented. Depending on additional assumptions, for example about the y-component of the IMF, the convection pattern could either turn directly from a two-cell type to a four-cell type, or a three-cell type pattern could show up as an intermediate state. An interesting although rather surprising result of this study is that different ways of balancing the NBZ currents has a minor influence on the large-scale convection pattern.

  3. Field-induced alignment of a smectic-A phase: a time-resolved x-ray diffraction investigation.

    PubMed

    Bras, W; Emsley, J W; Levine, Y K; Luckhurst, G R; Seddon, J M; Timimi, B A

    2004-09-01

    The field-induced alignment of a smectic-A phase is, in principle, a complicated process involving the director rotation via the interaction with the field and the layer rotation via the molecular interactions. Time-resolved nuclear magnetic resonance spectroscopy has revealed this complexity in the case of the director alignment, but provides no direct information on the motion of the layers. Here we describe a time-resolved x-ray diffraction experiment using synchrotron radiation to solve the challenging problem of capturing the diffraction pattern on a time scale which is fast in comparison with that for the alignment of the smectic layers. We have investigated the alignment of the smectic-A phase of 4-octyl-4(')-cyanobiphenyl by a magnetic field. The experiment consists of creating a monodomain sample of the smectic-A phase by slow cooling from the nematic phase in a magnetic field with a flux density of 7 T. The sample is then turned quickly through an angle phi(0) about an axis parallel to the x-ray beam direction but orthogonal to the field. A sequence of two-dimensional small angle x-ray diffraction patterns are then collected at short time intervals. Experiments were carried out for different values of phi(0), and at different temperatures. The results show that the alignment behavior changes fundamentally when phi(0) exceeds 45 degrees, and that there is a sharp change in the alignment process when the temperature is less than 3 degrees C below the smectic-A-nematic transition. The results of the x-ray experiments are in broad agreement with the NMR results, but reveal major phenomena concerning the maintenance of the integrity of the smectic-A layer structure during the alignment process. (c) 2004 American Institute of Physics

  4. Magnetic fields from phase transitions

    NASA Astrophysics Data System (ADS)

    Hindmarsh, Mark; Everett, Allen

    1998-11-01

    The generation of primordial magnetic fields from cosmological phase transitions is discussed, paying particular attention to the electroweak transition and to the various definitions of the ``average'' field that have been put forward. It is emphasized that only the volume average has dynamical significance as a seed for galactic dynamos. On rather general grounds of causality and energy conservation, it is shown that, in the absence of MHD effects that transfer power in the magnetic field from small to large scales, processes occurring at the electroweak transition cannot generate fields stronger than 10-20 G on a scale of 0.5 Mpc. However, it is implausible that this upper bound could ever be reached, as it would require all the energy in the Universe to be turned into a magnetic field coherent at the horizon scale. Non-linear MHD effects seem therefore to be necessary if the electroweak transition is to create a primordial seed field.

  5. Measuring Earth's Magnetic Field Simply.

    ERIC Educational Resources Information Center

    Stewart, Gay B.

    2000-01-01

    Describes a method for measuring the earth's magnetic field using an empty toilet paper tube, copper wire, clear tape, a battery, a linear variable resistor, a small compass, cardboard, a protractor, and an ammeter. (WRM)

  6. Measuring Earth's Magnetic Field Simply.

    ERIC Educational Resources Information Center

    Stewart, Gay B.

    2000-01-01

    Describes a method for measuring the earth's magnetic field using an empty toilet paper tube, copper wire, clear tape, a battery, a linear variable resistor, a small compass, cardboard, a protractor, and an ammeter. (WRM)

  7. Field-Aligned ICRF Antenna Characterization and Performance in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Wukitch, Stephen

    2012-10-01

    Impurity contamination associated with ion cyclotron range of frequency (ICRF) heating remains a major challenge to ICRF utilization in magnetic confinement devices, particularly with metallic plasma facing components. Here, we report results on an experimental investigation of a high power, magnetic field-aligned (FA) antenna, designed to reduce parallel electric (E||) field through symmetry and thereby reduce RF related impurity contamination. Using the standard non-field aligned antennas (ST) as a reference, the impurity contamination and sources on the antenna are significantly lower for the FA-antenna than the ST antennas. In addition, the radiated power is reduced for given injected power for the FA-antenna compared to the ST-antennas in L and H-mode discharges. The improved performance is consistent with simulations indicating that the FA-antenna has reduced integrated E|| relative to the non-aligned antennas. However, the simulation also predicts that so-called monopole phasing, where antenna strap current has [0,0,0,0] phase, should have the lowest integrated E||. The initial results suggest that monopole phasing has a stronger impact on the plasma potential and higher core impurity contamination and sources at the antenna. Utilizing gas puff imaging, the radial electric field profile in the scrape-off-layer (SOL) is readily measured. For the ST and FA-antennas, fine structure (variations of order ˜0.5 cm) in the radial electric field is observed and radial penetration of the rectified potential structures is ˜10 times greater than the skin depth. This anomalous penetration appears to be consistent with including cross-field RF polarization currents in the sheath model. Further comparisons of the FA- and ST-antennas are being carried out with an extensive array of boundary plasma diagnostics to characterize the impurity behavior and impact on the SOL transport and SOL density profiles; the latest results will be presented.

  8. The Juno Magnetic Field Investigation

    NASA Astrophysics Data System (ADS)

    Connerney, J. E. P.; Benn, M.; Bjarno, J. B.; Denver, T.; Espley, J.; Jorgensen, J. L.; Jorgensen, P. S.; Lawton, P.; Malinnikova, A.; Merayo, J. M.; Murphy, S.; Odom, J.; Oliversen, R.; Schnurr, R.; Sheppard, D.; Smith, E. J.

    2017-02-01

    The Juno Magnetic Field investigation (MAG) characterizes Jupiter's planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor suites, each consisting of a tri-axial Fluxgate Magnetometer (FGM) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. The imaging system sensors are part of a subsystem that provides accurate attitude information (to ˜20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. The two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long magnetometer boom affixed to the outer end of one of 's three solar array assemblies. The magnetometer sensors are controlled by independent and functionally identical electronics boards within the magnetometer electronics package mounted inside Juno's massive radiation shielded vault. The imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. Each magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 Gauss = 1.6 × 106 nT per axis) with a resolution of ˜0.05 nT in the most sensitive dynamic range (±1600 nT per axis). Both magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. The magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. The attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. The system tracks and catalogs objects that pass through the imager field of

  9. The Juno Magnetic Field Investigation

    NASA Technical Reports Server (NTRS)

    Connerney, J. E. P.; Benna, M.; Bjarno, J. B.; Denver, T.; Espley, J.; Jorgensen, J. L.; Jorgensen, P. S.; Lawton, P.; Malinnikova, A.; Merayo, J. M.; hide

    2017-01-01

    The Juno Magnetic Field investigation (MAG) characterizes Jupiter's planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor suites, each consisting of a tri-axial Fluxgate Magnetometer (FGM) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. The imaging system sensors are part of a subsystem that provides accurate attitude information (to approx. 20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. The two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long magnetometer boom affixed to the outer end of one of 's three solar array assemblies. The magnetometer sensors are controlled by independent and functionally identical electronics boards within the magnetometer electronics package mounted inside Juno's massive radiation shielded vault. The imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. Each magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 Gauss = 1.6 x 10(exp. 6) nT per axis) with a resolution of approx. 0.05 nT in the most sensitive dynamic range (+/-1600 nT per axis). Both magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. The magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. The attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. The system tracks and catalogs objects that pass through

  10. Warm Magnetic Field Measurements of LARP HQ Magnet

    SciTech Connect

    Caspi, S; Cheng, D; Deitderich, D; Felice, H; Ferracin, P; Hafalia, R; Joseph, J; Lizarazo, J; Martchevskii, M; Nash, C; Sabbi, G L; Vu, C; Schmalzle, J; Ambrosio, G; Bossert, R; Chlachidze, G; DiMarco, J; Kashikhin, V

    2011-03-28

    The US-LHC Accelerator Research Program is developing and testing a high-gradient quadrupole (HQ) magnet, aiming at demonstrating the feasibility of Nb{sub 3}Sn technologies for the LHC luminosity upgrade. The 1 m long HQ magnet has a 120 mm bore with a conductor-limited gradient of 219 T/m at 1.9 K and a peak field of 15 T. HQ includes accelerator features such as alignment and field quality. Here we present the magnetic measurement results obtained at LBNL with a constant current of 30 A. A 100 mm long circuit-board rotating coil developed by FNAL was used and the induced voltage and flux increment were acquired. The measured b{sub 6} ranges from 0.3 to 0.5 units in the magnet straight section at a reference radius of 21.55 mm. The data reduced from the numerical integration of the raw voltage agree with those from the fast digital integrators.

  11. Investigation of Magnetic Field Measurements.

    DTIC Science & Technology

    1983-02-28

    the magnetic field in space by cancelling the ambient magnetic field. An observatory-quality, proton - precession magnetometer is available to monitor...test and calibrate the fluxgate magnetometers . Changes in design of the induction-coil magnetometere should enhance their reliability. The value of...Report) Ill. SUPPLEMENTARY NOTES IS. KEY WORDS (CoEntnue on revere side I necoseer mnd Identify by block mamber) AFGL Magnetometer Network Fluxgate

  12. Magnetic-Field Hazards Bibliography.

    DTIC Science & Technology

    1985-09-01

    Puchalska, I. B., Influence of magnetic fields on frog sciatic nerve , Biochem. Biophys. Res. Comm. 91:118 (1979). 35. Fardon, 3. C., "Effect of magnetic...fields, Bioelectromagnetic 2:357 (1981). 41. Gaffey, C. T. and Tenforde, T. S., Bioelectric properties of frog sciatic nerves during exposure to...available from: U.S. Dept. of Energy, Bonneville Power Administration, Portland, Oregon 97208 (1982). 29. Levy , R. H., and Jones, G. S., "Plasma

  13. On the Field-Aligned Beam Thermal Energy

    NASA Astrophysics Data System (ADS)

    Meziane, K.; Hamza, A. M.; Wilber, M.; Mazelle, C.; Lee, M. A.

    2013-11-01

    The parallel and perpendicular reduced distribution functions of field-aligned beams (FABs) observed upstream of the Earth's bow shock using the Cluster spacecrafts are examined. A previous study revealed that FABs, observed in oblique shock geometries, exhibit reduced distribution functions with high-energy tails. A selection of FABs with weak-energy tails are considered, and the associated reduced distributions are fit with Maxwellians. First, we have found that the FABs full width at half maximum (FWHM), σ∥ and σ⊥ derived from the fit, are linearly correlated with the solar wind speed (or equivalently to solar wind temperature). Moreover, the parallel beam σ∥ has a very weak dependence upon the beam parallel speed which reflects the shock geometry; we have found that σ∥˜0.23Vsw. In contrast, we have found that the perpendicular beam σ⊥, in the range of beam speeds investigated, depends on the shock geometry. These new results indicate that the parallel σ∥ is essentially controlled by the solar wind while the shock geometry plays, along with the solar wind, a role in the perpendicular σ⊥. These results also put some strong constraints on theoretical models as far as field-aligned beam production mechanisms are concerned. One potential explanation for the significant perpendicular broadening of the FAB distribution reported in this study could be the presence of kinetic Alfvèn (or/and whistler) turbulence at the shock.

  14. Optical sensor of magnetic fields

    DOEpatents

    Butler, M.A.; Martin, S.J.

    1986-03-25

    An optical magnetic field strength sensor for measuring the field strength of a magnetic field comprising a dilute magnetic semi-conductor probe having first and second ends, longitudinally positioned in the magnetic field for providing Faraday polarization rotation of light passing therethrough relative to the strength of the magnetic field. Light provided by a remote light source is propagated through an optical fiber coupler and a single optical fiber strand between the probe and the light source for providing a light path therebetween. A polarizer and an apparatus for rotating the polarization of the light is provided in the light path and a reflector is carried by the second end of the probe for reflecting the light back through the probe and thence through the polarizer to the optical coupler. A photo detector apparatus is operably connected to the optical coupler for detecting and measuring the intensity of the reflected light and comparing same to the light source intensity whereby the magnetic field strength may be calculated.

  15. Connecting the Sun and Earth: Field ALigned Connections Constellation

    NASA Astrophysics Data System (ADS)

    Stoneback, R.

    2016-12-01

    As the solar wind flows past the Earth power flows along geomagnetic field lines into the Earth's ionosphere, driving high latitude convection and plasma motions throughout the magnetosphere. Complete understanding of this energy flux has been limited by the availability of measurements. The presented Field ALigned CONnections constellation concept is designed to measure the energy flux as well as the energy deposited into the polar ionosphere. In collaboration with the ground based SuperDARN, measurements from both platforms may be assimilated into a cohesive system to better understand energy flow. The assimilation of DMSP and SuperDARN high-latitude convection measurements using Data Interpolating Empirical Orthogonal Functions (DINEOFs) will be shown.

  16. PROTOSTELLAR DISK FORMATION ENABLED BY WEAK, MISALIGNED MAGNETIC FIELDS

    SciTech Connect

    Krumholz, Mark R.; Crutcher, Richard M.; Hull, Charles L. H.

    2013-04-10

    The gas from which stars form is magnetized, and strong magnetic fields can efficiently transport angular momentum. Most theoretical models of this phenomenon find that it should prevent formation of large (>100 AU), rotationally supported disks around most protostars, even when non-ideal magnetohydrodynamic (MHD) effects that allow the field and gas to decouple are taken into account. Using recent observations of magnetic field strengths and orientations in protostellar cores, we show that this conclusion is incorrect. The distribution of magnetic field strengths is very broad, and alignments between fields and angular momentum vectors within protostellar cores are essentially random. By combining the field strength and misalignment data with MHD simulations showing that disk formation is expected for both weak and misaligned fields, we show that these observations imply that we should expect disk fractions of {approx}10%-50% even when protostars are still deeply embedded in their parent cores, and even if the gas is governed by ideal MHD.

  17. Statistical relationship between large-scale upward field-aligned currents and electron precipitation

    NASA Astrophysics Data System (ADS)

    Korth, Haje; Zhang, Yongliang; Anderson, Brian J.; Sotirelis, Thomas; Waters, Colin L.

    2014-08-01

    Simultaneous observations of Birkeland currents by the constellation of Iridium satellites and N2 Lyman-Birge-Hopfield (LBH) auroral emissions measured by the Global Ultraviolet Imager (GUVI) onboard the Thermosphere, Ionosphere, and Mesosphere Energetics and Dynamics (TIMED) satellite are used to establish relationships between large-scale upward field-aligned currents and electron precipitation during stable current configurations. The electron precipitation was inferred from GUVI data using a statistical relationship between LBH intensity and electron energy flux. LBH emissions with >5% contribution from protons, identified by Lyman-alpha intensity, were excluded from the analysis. The Birkeland currents were derived with a spatial resolution of 3° in latitude and 2 h in local time. For southward interplanetary magnetic field (IMF), the electron precipitation occurred primarily within and near large-scale upward currents. The correspondence was less evident for northward IMF, presumably because the spatial variability is large compared to the areas of interest so that the number of events identified is smaller and the derived statistical distributions are less reliable. At dusk, the correlation between upward current and precipitation was especially high, where a larger fraction of the electron precipitation is accelerated downward by a field-aligned potential difference. Unaccelerated electron precipitation dominated in the morning sector, presumably induced by scattering of eastward-drifting energetic electrons into the loss cone through interaction with whistler-mode waves (diffuse precipitation) rather than by field-aligned acceleration. In the upward Region 1 on the dayside, where the electron precipitation is almost exclusively due to field-aligned acceleration, a quadratic relationship between current density and electron energy flux was observed, implying a linear current-voltage relationship in this region. Current density and electron energy flux in

  18. Quantum oscillations without magnetic field

    NASA Astrophysics Data System (ADS)

    Liu, Tianyu; Pikulin, D. I.; Franz, M.

    2017-01-01

    When the magnetic field B is applied to a metal, nearly all observable quantities exhibit oscillations periodic in 1 /B . Such quantum oscillations reflect the fundamental reorganization of electron states into Landau levels as a canonical response of the metal to the applied magnetic field. We predict here that, remarkably, in the recently discovered Dirac and Weyl semimetals, quantum oscillations can occur in the complete absence of magnetic field. These zero-field quantum oscillations are driven by elastic strain which, in the space of the low-energy Dirac fermions, acts as a chiral gauge potential. We propose an experimental setup in which the strain in a thin film (or nanowire) can generate a pseudomagnetic field b as large as 15 T and demonstrate the resulting de Haas-van Alphen and Shubnikov-de Haas oscillations periodic in 1 /b .

  19. Magnetic fields in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Beck, Rainer

    2015-12-01

    Radio synchrotron emission, its polarization and Faraday rotation of the polarization angle are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30 \\upmu G) and in central starburst regions (50-100 \\upmu G). Such fields are dynamically important; they affect gas flows and drive gas inflows in central regions. Polarized emission traces ordered fields, which can be regular or anisotropic turbulent, where the latter originates from isotropic turbulent fields by the action of compression or shear. The strongest ordered fields (10-15 \\upmu G) are generally found in interarm regions. In galaxies with strong density waves, ordered fields are also observed at the inner edges of spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies and in central regions. Ordered fields in interacting galaxies have asymmetric distributions and are a tracer of past interactions between galaxies or with the intergalactic medium.—Faraday rotation measures of the diffuse polarized radio emission from galaxy disks reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by mean-field dynamos. "Magnetic arms" between gaseous spiral arms may also be products of dynamo action, but need a stable spiral pattern to develop. Helically twisted field loops winding around spiral arms were found in two galaxies so far. Large-scale field reversals, like the one found in the Milky Way, could not yet be detected in external galaxies. In radio halos around edge-on galaxies, ordered magnetic fields with X-shaped patterns are observed. The origin and evolution of cosmic magnetic fields, in particular their first occurrence in young galaxies and their dynamical importance during galaxy evolution, will be studied with

  20. MRFalign: protein homology detection through alignment of Markov random fields.

    PubMed

    Ma, Jianzhu; Wang, Sheng; Wang, Zhiyong; Xu, Jinbo

    2014-03-01

    Sequence-based protein homology detection has been extensively studied and so far the most sensitive method is based upon comparison of protein sequence profiles, which are derived from multiple sequence alignment (MSA) of sequence homologs in a protein family. A sequence profile is usually represented as a position-specific scoring matrix (PSSM) or an HMM (Hidden Markov Model) and accordingly PSSM-PSSM or HMM-HMM comparison is used for homolog detection. This paper presents a new homology detection method MRFalign, consisting of three key components: 1) a Markov Random Fields (MRF) representation of a protein family; 2) a scoring function measuring similarity of two MRFs; and 3) an efficient ADMM (Alternating Direction Method of Multipliers) algorithm aligning two MRFs. Compared to HMM that can only model very short-range residue correlation, MRFs can model long-range residue interaction pattern and thus, encode information for the global 3D structure of a protein family. Consequently, MRF-MRF comparison for remote homology detection shall be much more sensitive than HMM-HMM or PSSM-PSSM comparison. Experiments confirm that MRFalign outperforms several popular HMM or PSSM-based methods in terms of both alignment accuracy and remote homology detection and that MRFalign works particularly well for mainly beta proteins. For example, tested on the benchmark SCOP40 (8353 proteins) for homology detection, PSSM-PSSM and HMM-HMM succeed on 48% and 52% of proteins, respectively, at superfamily level, and on 15% and 27% of proteins, respectively, at fold level. In contrast, MRFalign succeeds on 57.3% and 42.5% of proteins at superfamily and fold level, respectively. This study implies that long-range residue interaction patterns are very helpful for sequence-based homology detection. The software is available for download at http://raptorx.uchicago.edu/download/. A summary of this paper appears in the proceedings of the RECOMB 2014 conference, April 2-5.

  1. MRFalign: Protein Homology Detection through Alignment of Markov Random Fields

    PubMed Central

    Ma, Jianzhu; Wang, Sheng; Wang, Zhiyong; Xu, Jinbo

    2014-01-01

    Sequence-based protein homology detection has been extensively studied and so far the most sensitive method is based upon comparison of protein sequence profiles, which are derived from multiple sequence alignment (MSA) of sequence homologs in a protein family. A sequence profile is usually represented as a position-specific scoring matrix (PSSM) or an HMM (Hidden Markov Model) and accordingly PSSM-PSSM or HMM-HMM comparison is used for homolog detection. This paper presents a new homology detection method MRFalign, consisting of three key components: 1) a Markov Random Fields (MRF) representation of a protein family; 2) a scoring function measuring similarity of two MRFs; and 3) an efficient ADMM (Alternating Direction Method of Multipliers) algorithm aligning two MRFs. Compared to HMM that can only model very short-range residue correlation, MRFs can model long-range residue interaction pattern and thus, encode information for the global 3D structure of a protein family. Consequently, MRF-MRF comparison for remote homology detection shall be much more sensitive than HMM-HMM or PSSM-PSSM comparison. Experiments confirm that MRFalign outperforms several popular HMM or PSSM-based methods in terms of both alignment accuracy and remote homology detection and that MRFalign works particularly well for mainly beta proteins. For example, tested on the benchmark SCOP40 (8353 proteins) for homology detection, PSSM-PSSM and HMM-HMM succeed on 48% and 52% of proteins, respectively, at superfamily level, and on 15% and 27% of proteins, respectively, at fold level. In contrast, MRFalign succeeds on 57.3% and 42.5% of proteins at superfamily and fold level, respectively. This study implies that long-range residue interaction patterns are very helpful for sequence-based homology detection. The software is available for download at http://raptorx.uchicago.edu/download/. A summary of this paper appears in the proceedings of the RECOMB 2014 conference, April 2–5. PMID:24675572

  2. Nanometric alternating magnetic field generator.

    PubMed

    Espejo, A P; Tejo, F; Vidal-Silva, N; Escrig, J

    2017-07-05

    In this work we introduce an alternating magnetic field generator in a cylindrical nanostructure. This field appears due to the rotation of a magnetic domain wall located at some position, generating a magnetic region that varies its direction of magnetization alternately, thus inducing an alternating magnetic flux in its vicinity. This phenomenon occurs due to the competition between a spin-polarized current and a magnetic field, which allows to control both the angular velocity and the pinning position of the domain wall. As proof of concept, we study the particular case of a diameter-modulated nanowire with a spin-polarized current along its axis and the demagnetizing field produced by its modulation. This inhomogeneous field allows one to control the angular velocity of the domain wall as a function of its position along the nanowire allowing frequencies in the GHz range to be achieved. This generator could be used in telecommunications for devices in the range of radiofrequencies or, following Faraday's induction law, could also induce an electromotive force and be used as a movable alternate voltage source in future nanodevices.

  3. Strong Magnetic Field Characterisation

    DTIC Science & Technology

    2012-04-01

    coils were driven by a pulsed-power system to generate the fields. All the sources were characterised through a series of measurements and modelling... generated for the coils. Options for further investigation were provided. UNCLASSIFIED UNCLASSIFIED This...investigation. The desired field strength was based on assessments [1] from preliminary magnetohydrodynamic ( MHD ) modelling and while not achievable by

  4. Electro-magnetic properties of composites with aligned Fe-Co hollow fibers

    NASA Astrophysics Data System (ADS)

    Cho, Seungchan; Choi, Jae Ryung; Jung, Byung Mun; Choi, U. Hyeok; Lee, Sang-Kwan; Kim, Ki Hyeon; Lee, Sang-Bok

    2016-05-01

    A novel Fe-Co binary hollow fiber was synthesized by electroless plating using hydrolyzed polyester fiber and its anisotropy characteristic was investigated for electromagnetic wave absorbing materials. The hollow fibers in parallel with magnetic field show higher saturated magnetization of 202 emu/g at the applied magnetic field of 10 kOe and lower coercivity (27.658 Oe), compared with the random and vertical oriented hollow fibers. From complex permittivity measurement, the Fe-Co hollow fiber composites clearly display a single dielectric resonance, located at ˜14 GHz. The Fe-Co hollow fibers not only provide excellent EM properties in GHz frequency ranges, resulting mainly from the strong resonance, but also adjust the soft magnetic properties through fiber alignments. The cavitary structure of the Fe-Co hollow fibers, not only giving rise to a dielectric loss resonance and also adjusting its peak frequency, may be a pathway to useful EM wave absorptive devices in GHz frequency ranges.

  5. Microbially assisted recording of the Earth's magnetic field in sediment

    PubMed Central

    Zhao, Xiangyu; Egli, Ramon; Gilder, Stuart A.; Müller, Sebastian

    2016-01-01

    Sediments continuously record variations of the Earth's magnetic field and thus provide an important archive for studying the geodynamo. The recording process occurs as magnetic grains partially align with the geomagnetic field during and after sediment deposition, generating a depositional remanent magnetization (DRM) or post-DRM (PDRM). (P)DRM acquisition mechanisms have been investigated for over 50 years, yet many aspects remain unclear. A key issue concerns the controversial role of bioturbation, that is, the mechanical disturbance of sediment by benthic organisms, during PDRM acquisition. A recent theory on bioturbation-driven PDRM appears to solve many inconsistencies between laboratory experiments and palaeomagnetic records, yet it lacks experimental proof. Here we fill this gap by documenting the important role of bioturbation-induced rotational diffusion for (P)DRM acquisition, including the control exerted on the recorded inclination and intensity, as determined by the equilibrium between aligning and perturbing torques acting on magnetic particles. PMID:26864428

  6. Microbially assisted recording of the Earth's magnetic field in sediment.

    PubMed

    Zhao, Xiangyu; Egli, Ramon; Gilder, Stuart A; Müller, Sebastian

    2016-02-11

    Sediments continuously record variations of the Earth's magnetic field and thus provide an important archive for studying the geodynamo. The recording process occurs as magnetic grains partially align with the geomagnetic field during and after sediment deposition, generating a depositional remanent magnetization (DRM) or post-DRM (PDRM). (P)DRM acquisition mechanisms have been investigated for over 50 years, yet many aspects remain unclear. A key issue concerns the controversial role of bioturbation, that is, the mechanical disturbance of sediment by benthic organisms, during PDRM acquisition. A recent theory on bioturbation-driven PDRM appears to solve many inconsistencies between laboratory experiments and palaeomagnetic records, yet it lacks experimental proof. Here we fill this gap by documenting the important role of bioturbation-induced rotational diffusion for (P)DRM acquisition, including the control exerted on the recorded inclination and intensity, as determined by the equilibrium between aligning and perturbing torques acting on magnetic particles.

  7. Magnetic field geometry of the large globule CB 34

    NASA Astrophysics Data System (ADS)

    Das, A.; Das, H. S.; Medhi, Biman J.; Wolf, S.

    2016-12-01

    We report the results of optical polarimetric observations of a Bok globule CB34 to study magnetic field structure on large scales (105-106 AU), which is combined with archival sub-mm observations to characterize the magnetic field structure of CB34 on small scales (104-105 AU). The optical polarization measurements indicate that the magnetic field in the globule is constrained to a maximum radius of 105 AU around the core, out to densities not smaller than 104 cm^{-3}. Our study is mainly concentrated on two submillimeter cores C1 and C2 of CB34. The direction of magnetic field of core C2 is found to be nearly perpendicular to the CO outflow direction of the globule. The magnetic field of core C1 is almost aligned with the minor axis of the core which is typical for magnetically dominated star formation models. The mean value of offset between the minor axis of core C2 and the outflow direction is found to be 14° which suggests that the direct ion of the outflow is almost aligned with the minor axis of core C2. The magnetic field strength in the plane-of-sky for cores C1 and C2 is estimated to be ≈ 34 μG and ≈ 70 μG.

  8. The effect of magnetic field induced aggregates on ultrasound propagation in aqueous magnetic fluid

    NASA Astrophysics Data System (ADS)

    Parekh, Kinnari; Upadhyay, R. V.

    2017-06-01

    Ultrasonic wave propagation in the aqueous magnetic fluid is investigated for different particle concentrations. The sound velocity decreases while acoustic impedance increases with increasing concentrations. The velocity anisotropy is observed upon application of magnetic field. The velocity anisotropy fits with Tarapov's theory suggests the presence of aggregates in the system. We report that these aggregates are thermodynamically unstable and the length of aggregate changes continuously with increasing concentration and, or magnetic field and resulted in a decrease in effective magnetic moment. The Taketomi's theory fits well with the experimental data suggesting that the particle clusters are aligned in the direction of the magnetic field. The radius of cluster found to increase with increasing concentration, and then decreases whereas the elastic force constant increases and then becomes constant. The increase in cluster radius indicates elongation of aggregate length due to tip-to-tip interaction of aggregates whereas for higher concentration, the lateral alignment is more favorable than tip-to-tip alignment of aggregates which reduces the cluster radius making elastic force constant to raise. Optical images show that the chains are fluctuating and confirming the lateral alignment of chains at higher fields.

  9. MAGNETIC FIELD MEASUREMENTS FOR FAST-CHANGING MAGNETIC FIELDS.

    SciTech Connect

    JAIN, A.; ESCALLIER, J.; GANETIS, G.; LOUIE, W.; MARONE, A.; THOMAS. R.; WANDERER, P.

    2004-10-03

    Several recent applications for fast ramped magnets have been found that require rapid measurement of the field quality during the ramp. (In one instance, accelerator dipoles will be ramped at 1 T/sec, with measurements needed to the accuracy typically required for accelerators.) We have built and tested a new type of magnetic field measuring system to meet this need. The system consists of 16 stationary pickup windings mounted on a cylinder. The signals induced in the windings in a changing magnetic field are sampled and analyzed to obtain the field harmonics. To minimize costs, printed circuit boards were used for the pickup windings and a combination of amplifiers and ADPs used for the voltage readout system. New software was developed for the analysis. Magnetic field measurements of a model dipole developed for the SIS200 accelerator at GSI are presented. The measurements are needed to insure that eddy currents induced by the fast ramps do not impact the field quality needed for successful accelerator operation.

  10. Saturn's auroral morphology and field-aligned currents during a solar wind compression

    NASA Astrophysics Data System (ADS)

    Badman, S. V.; Provan, G.; Bunce, E. J.; Mitchell, D. G.; Melin, H.; Nichols, J. D.; Jinks, S. L.; Cowley, S. W. H.; Stallard, T.; Radioti, A.; Pryor, W. R.; Kurth, W. S.; Brown, R. H.; Baines, K. H.; Dougherty, M. K.

    2014-04-01

    During the 2013 auroral observing campaign, instruments onboard Cassini and the Hubble Space Telescope observed Saturn's aurora while Cassini traversed the high latitude auroral field lines. Signatures of upward and downward field-aligned currents were detected on the nightside in the magnetic field and plasma measurements. The location of the upward current corresponded to the bright auroral arc seen in the auroral images, and the downward current region was located poleward of the upward current in an aurorally dark region. A solar wind compression region impacted Saturn's magnetosphere at the start of 2013-112 with the following sequence of effects: (1) intensification and extension to lower frequencies of the Saturn Kilometric Radiation; (2) intensification and spatial expansion of the auroral field-aligned current regions; (3) appearance of a localised, intense bulge in the dawnside aurora while the nightside aurora remained fainter and narrow; (4) latitudinal broadening and poleward contraction of the nightside aurora, where the poleward motion in this sector is opposite to that expected from a model of the auroral oval's usual oscillation. These observations are interpreted as the response to tail reconnection events, initially involving Vasyliunas-type reconnection of closed, mass-loaded magnetotail field lines, and then proceeding onto open lobe field lines, causing the contraction of the polar cap region.

  11. Magnetic field signatures of substorms on high latitudes field lines in the nighttime magnetosphere

    NASA Technical Reports Server (NTRS)

    Fairfield, D. H.

    1972-01-01

    Two types of magnetic field changes are repeatedly observed in the high latitude nightside magnetosphere in association with magnetic substorms. One type is characterized by sudden decrease in the field strength, accompanied by an abrupt perturbation in the field declination angle. These changes are attributed to field aligned-sheet currents flowing on the high latitude boundary of an expanding plasma sheet following substorms. Single sheets of field-aligned currents on this boundary tend to flow toward the earth in the morning quadrant and away in the evening. Multiple sheets of current may also occur, with the direction of the high latitude sheet generally being the same as for a single sheet. A second type of field change is a decrease in field inclination during substorms. This is regarded as a manifestation of the changing field configuration during substorms and can be described in terms of azimuthal currents.

  12. Field-aligned fluxes in the geomagnetic equator

    NASA Technical Reports Server (NTRS)

    Semar, C. L.; Konradi, A.

    1976-01-01

    During 12 electron injection events observed by Explorer 45 during the December, 1971, and February, 1972, in magnetic storms it was found that the lowest observable pitch angle particles (down to 7 degrees in one case) arrived first. Pitch angle dispersion and shell-splitting effects are shown to be inadequate explanations for most of these pitch angle distributions. It is suggested that parallel electric fields may be supplying 1- to 5-keV electrons to the magnetosphere from the ionosphere. Various models of parallel electric fields are discussed.

  13. Mechanical alignment of particles for use in fabricating superconducting and permanent magnetic materials

    DOEpatents

    Nellis, William J.; Maple, M. Brian

    1992-01-01

    A method for mechanically aligning oriented superconducting or permanently magnetic materials for further processing into constructs. This pretreatment optimizes the final crystallographic orientation and, thus, properties in these constructs. Such materials as superconducting fibers, needles and platelets are utilized.

  14. Specification and R and D Program on Magnet Alignment Tolerances for NSLS-II

    SciTech Connect

    Kramer,S.L.; Jain, A. K.

    2009-05-04

    The NSLS-II light source is a proposed 3 GeV storage ring, with the potential for ultra-low emittance. Despite the reduced emittance goal for the bare lattice, the closed orbit amplification factors are on average >55 in both planes, for random quadrupole alignment errors. The high chromaticity will also require strong sextupoles and the low 3 GeV energy will require large dynamic and momentum aperture to insure adequate lifetime. This will require tight alignment tolerances ({approx} 30{micro}m) on the multipole magnets during installation. By specifying tight alignment tolerances of the magnets on the support girders, the random alignment tolerances of the girders in the tunnel can be significantly relaxed. Using beam based alignment to find the golden orbit through the quadrupole centers, the closed orbit offsets in the multipole magnets will then be reduced to essentially the alignment errors of the magnets, restoring much of the dynamic aperture and lifetime of the bare lattice. Our R&D program to achieve these tight alignment tolerances of the magnets on the girders using a vibrating wire technique, will be discussed and initial results presented.

  15. Indoor localization using magnetic fields

    NASA Astrophysics Data System (ADS)

    Pathapati Subbu, Kalyan Sasidhar

    Indoor localization consists of locating oneself inside new buildings. GPS does not work indoors due to multipath reflection and signal blockage. WiFi based systems assume ubiquitous availability and infrastructure based systems require expensive installations, hence making indoor localization an open problem. This dissertation consists of solving the problem of indoor localization by thoroughly exploiting the indoor ambient magnetic fields comprising mainly of disturbances termed as anomalies in the Earth's magnetic field caused by pillars, doors and elevators in hallways which are ferromagnetic in nature. By observing uniqueness in magnetic signatures collected from different campus buildings, the work presents the identification of landmarks and guideposts from these signatures and further develops magnetic maps of buildings - all of which can be used to locate and navigate people indoors. To understand the reason behind these anomalies, first a comparison between the measured and model generated Earth's magnetic field is made, verifying the presence of a constant field without any disturbances. Then by modeling the magnetic field behavior of different pillars such as steel reinforced concrete, solid steel, and other structures like doors and elevators, the interaction of the Earth's field with the ferromagnetic fields is described thereby explaining the causes of the uniqueness in the signatures that comprise these disturbances. Next, by employing the dynamic time warping algorithm to account for time differences in signatures obtained from users walking at different speeds, an indoor localization application capable of classifying locations using the magnetic signatures is developed solely on the smart phone. The application required users to walk short distances of 3-6 m anywhere in hallway to be located with accuracies of 80-99%. The classification framework was further validated with over 90% accuracies using model generated magnetic signatures representing

  16. Magnetic field of the Earth

    NASA Astrophysics Data System (ADS)

    Popov, Aleksey

    2013-04-01

    The magnetic field of the Earth has global meaning for a life on the Earth. The world geophysical science explains: - occurrence of a magnetic field of the Earth it is transformation of kinetic energy of movements of the fused iron in the liquid core of Earth - into the magnetic energy; - the warming up of a kernel of the Earth occurs due to radioactive disintegration of elements, with excretion of thermal energy. The world science does not define the reasons: - drift of a magnetic dipole on 0,2 a year to the West; - drift of lithospheric slabs and continents. The author offers: an alternative variant existing in a world science the theories "Geodynamo" - it is the theory « the Magnetic field of the Earth », created on the basis of physical laws. Education of a magnetic field of the Earth occurs at moving the electric charge located in a liquid kernel, at rotation of the Earth. At calculation of a magnetic field is used law the Bio Savara for a ring electric current: dB = . Magnetic induction in a kernel of the Earth: B = 2,58 Gs. According to the law of electromagnetic induction the Faradey, rotation of a iron kernel of the Earth in magnetic field causes occurrence of an electric field Emf which moves electrons from the center of a kernel towards the mantle. So of arise the radial electric currents. The magnetic field amplifies the iron of mantle and a kernel of the Earth. As a result of action of a radial electric field the electrons will flow from the center of a kernel in a layer of an electric charge. The central part of a kernel represents the field with a positive electric charge, which creates inverse magnetic field Binv and Emfinv When ?mfinv = ?mf ; ?inv = B, there will be an inversion a magnetic field of the Earth. It is a fact: drift of a magnetic dipole of the Earth in the western direction approximately 0,2 longitude, into a year. Radial electric currents a actions with the basic magnetic field of a Earth - it turn a kernel. It coincides with laws

  17. High Latitude Precipitating Energy Flux and Joule Heating During Geomagnetic Storms Determined from AMPERE Field-aligned Currents

    NASA Astrophysics Data System (ADS)

    Robinson, R. M.; Zanetti, L. J.; Anderson, B. J.; Korth, H.; Samara, M.; Michell, R.; Grubbs, G. A., II; Hampton, D. L.; Dropulic, A.

    2016-12-01

    A high latitude conductivity model based on field-aligned currents measured by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) provides the means for complete specification of electric fields and currents at high latitudes. Based on coordinated measurements made by AMPERE and the Poker Flat Incoherent Scatter Radar, the model determines the most likely value of the ionospheric conductance from the direction, magnitude, and magnetic local time of the field-aligned current. A conductance model driven by field-aligned currents ensures spatial and temporal consistency between the calculated electrodynamic parameters. To validate the results, the Pedersen and Hall conductances were used to calculate the energy flux associated with the energetic particle precipitation. When integrated over the entire hemisphere, the total energy flux compares well with the Hemispheric Power Index derived from the OVATION-PRIME model. The conductances were also combined with the field-aligned currents to calculate the self-consistent electric field, which was then used to compute horizontal currents and Joule heating. The magnetic perturbations derived from the currents replicate most of the variations observed in ground-based magnetograms. The model was used to study high latitude particle precipitation, currents, and Joule heating for 24 magnetic storms. In most cases, the total energy input from precipitating particles and Joule heating exhibits a sharply-peaked maximum at the times of local minima in Dst, suggesting a close coupling between the ring current and the high latitude currents driven by the Region 2 field-aligned currents. The rapid increase and decrease of the high latitude energy deposition suggests an explosive transfer of energy from the magnetosphere to the ionosphere just prior to storm recovery.

  18. Rotating magnetic field induced oscillation of magnetic particles for in vivo mechanical destruction of malignant glioma.

    PubMed

    Cheng, Yu; Muroski, Megan E; Petit, Dorothée C M C; Mansell, Rhodri; Vemulkar, Tarun; Morshed, Ramin A; Han, Yu; Balyasnikova, Irina V; Horbinski, Craig M; Huang, Xinlei; Zhang, Lingjiao; Cowburn, Russell P; Lesniak, Maciej S

    2016-02-10

    Magnetic particles that can be precisely controlled under a magnetic field and transduce energy from the applied field open the way for innovative cancer treatment. Although these particles represent an area of active development for drug delivery and magnetic hyperthermia, the in vivo anti-tumor effect under a low-frequency magnetic field using magnetic particles has not yet been demonstrated. To-date, induced cancer cell death via the oscillation of nanoparticles under a low-frequency magnetic field has only been observed in vitro. In this report, we demonstrate the successful use of spin-vortex, disk-shaped permalloy magnetic particles in a low-frequency, rotating magnetic field for the in vitro and in vivo destruction of glioma cells. The internalized nanomagnets align themselves to the plane of the rotating magnetic field, creating a strong mechanical force which damages the cancer cell structure inducing programmed cell death. In vivo, the magnetic field treatment successfully reduces brain tumor size and increases the survival rate of mice bearing intracranial glioma xenografts, without adverse side effects. This study demonstrates a novel approach of controlling magnetic particles for treating malignant glioma that should be applicable to treat a wide range of cancers.

  19. Saturn's auroral morphology and field-aligned currents during a solar wind compression

    NASA Astrophysics Data System (ADS)

    Badman, S. V.; Provan, G.; Bunce, E. J.; Mitchell, D. G.; Melin, H.; Cowley, S. W. H.; Radioti, A.; Kurth, W. S.; Pryor, W. R.; Nichols, J. D.; Jinks, S. L.; Stallard, T. S.; Brown, R. H.; Baines, K. H.; Dougherty, M. K.

    2016-01-01

    On 21-22 April 2013, during a coordinated auroral observing campaign, instruments onboard Cassini and the Hubble Space Telescope observed Saturn's aurora while Cassini traversed Saturn's high latitude auroral field lines. Signatures of upward and downward field-aligned currents were detected in the nightside magnetosphere in the magnetic field and plasma measurements. The location of the upward current corresponded to the bright ultraviolet auroral arc seen in the auroral images, and the downward current region was located poleward of the upward current in an aurorally dark region. Within the polar cap magnetic field and plasma fluctuations were identified with periods of ∼20 and ∼60 min. The northern and southern auroral ovals were observed to rock in latitude in phase with the respective northern and southern planetary period oscillations. A solar wind compression impacted Saturn's magnetosphere at the start of 22 April 2013, identified by an intensification and extension to lower frequencies of the Saturn kilometric radiation, with the following sequence of effects: (1) intensification of the auroral field-aligned currents; (2) appearance of a localised, intense bulge in the dawnside (04-06 LT) aurora while the midnight sector aurora remained fainter and narrow; and (3) latitudinal broadening and poleward contraction of the nightside aurora, where the poleward motion in this sector is opposite to that expected from a model of the auroral oval's usual oscillation. These observations are interpreted as the response to tail reconnection events, initially involving Vasyliunas-type reconnection of closed mass-loaded magnetotail field lines, and then proceeding onto open lobe field lines, causing the contraction of the polar cap region on the night side.

  20. Plasma Sheet Response to the Ionosphere's Demand for Field-Aligned Current

    NASA Astrophysics Data System (ADS)

    Coroniti, F. V.; Pritchett, P. L.

    2007-12-01

    Magnetospheric convection electric fields and plasma stresses are transmitted to the ionosphere by Alfvén wave electric fields and field-aligned currents (FACs). The closure of the FACs by ionospheric Hall and Pedersen currents drives the ionospheric convection system. However, the ionospheric system does not necessarily mesh smoothly with the magnetospheric drivers, and the magnetosphere must respond by altering its convection and plasma stress configuration, thereby creating self-consistent closure paths for the complete coupled system of currents and electric potentials. Three-dimensional particle-in-cell plasma kinetic simulations are used to determine the plasma sheet response to various current systems imposed as boundary conditions at the near-Earth boundary. These systems consist of separate downward and upward tubes of FAC and a substorm current wedge configuration. The results demonstrate that the creation of closure paths for ionospheric FACs can result in large configuration changes within the near-Earth plasma sheet. The plasma sheet is forced to establish polarization electric fields that locally increase the cross-tail current by producing a duskward Hall electron current; this results in the formation of thin (in z), spatially localized (in y) electron-dominated Hall current sheets. The observed complex magnetic field configuration with opposite polarity Bz fields in close proximity separated by electron scale thin current sheets is reminiscent of the turbulent magnetic fields that are observed within the near-Earth current disruption region at substorm breakup [ Lui et al., 1988, 1992].

  1. Observations of Mercury's magnetic field

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

    Magnetic field data obtained by Mariner 10 during the third and final encounter with the planet Mercury on 16 March 1975 were studied. A well developed bow shock and modest magnetosphere, previously observed at first encounter on 29 March 1974, were again observed. In addition, a much stronger magnetic field near closest approach, 400 gamma versus 98 gamma, was observed at an altitude of 327 km and approximately 70 deg north Mercurian latitude. Spherical harmonic analysis of the data provide an estimate of the centered planetary magnetic dipole of 4.7 x 10 to the 22nd power Gauss/cu cm with the axis tilted 12 deg to the rotation axis and in the same sense as Earth's. The interplanetary field was sufficiently different between first and third encounters that in addition to the very large field magnitude observed, it argues strongly against a complex induction process generating the observed planetary field. While a possibility exists that Mercury possesses a remanent field due to magnetization early in its formation, a present day active dynamo seems to be a more likely candidate for its origin.

  2. Satellite to study earth's magnetic field

    NASA Technical Reports Server (NTRS)

    1979-01-01

    The Magnetic Field Satellite (Magsat) designed to measure the near earth magnetic field and crustal anomalies is briefly described. A scalar magnetometer to measure the magnitude of the earth's crustal magnetic field and a vector magnetometer to measure magnetic field direction as well as magnitude are included. The mission and its objectives are summarized along with the data collection and processing system.

  3. Galactic and Intergalactic Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Klein, U.; Fletcher, A.

    This course-tested textbook conveys the fundamentals of magnetic fields and relativistic plasma in diffuse cosmic media, with a primary focus on phenomena that have been observed at different wavelengths. Theoretical concepts are addressed wherever necessary, with derivations presented in sufficient detail to be generally accessible. In the first few chapters the authors present an introduction to various astrophysical phenomena related to cosmic magnetism, with scales ranging from molecular clouds in star-forming regions and supernova remnants in the Milky Way, to clusters of galaxies. Later chapters address the role of magnetic fields in the evolution of the interstellar medium, galaxies and galaxy clusters. The book is intended for advanced undergraduate and postgraduate students in astronomy and physics and will serve as an entry point for those starting their first research projects in the field.

  4. The effect of Birkeland currents on magnetic field topology

    NASA Technical Reports Server (NTRS)

    Peroomian, Vahe; Lyons, Larry R.; Schulz, Michael

    1996-01-01

    A technique was developed for the inclusion of large scale magnetospheric current systems in magnetic field models. The region 1 and 2 Birkeland current systems are included in the source surface model of the terrestrial magnetosphere. The region 1 and 2 Birkeland currents are placed in the model using a series of field aligned, infinitely thin wire segments. The normal component of the magnetic field from these currents is calculated on the surface of the magnetopause and shielded using image current carrying wires placed outside of the magnetosphere. It is found that the inclusion of the Birkeland currents in the model results in a northward magnetic field in the near-midnight tail, leading to the closure of previously open flux in the tail, and a southward magnetic field in the flanks. A sunward shift in the separatrix is observed.

  5. Improved field free line magnetic particle imaging using saddle coils.

    PubMed

    Erbe, Marlitt; Sattel, Timo F; Buzug, Thorsten M

    2013-12-01

    Magnetic particle imaging (MPI) is a novel tracer-based imaging method detecting the distribution of superparamagnetic iron oxide (SPIO) nanoparticles in vivo in three dimensions and in real time. Conventionally, MPI uses the signal emitted by SPIO tracer material located at a field free point (FFP). To increase the sensitivity of MPI, however, an alternative encoding scheme collecting the particle signal along a field free line (FFL) was proposed. To provide the magnetic fields needed for line imaging in MPI, a very efficient scanner setup regarding electrical power consumption is needed. At the same time, the scanner needs to provide a high magnetic field homogeneity along the FFL as well as parallel to its alignment to prevent the appearance of artifacts, using efficient radon-based reconstruction methods arising for a line encoding scheme. This work presents a dynamic FFL scanner setup for MPI that outperforms all previously presented setups in electrical power consumption as well as magnetic field quality.

  6. Expectations for the Martian core magnetic field

    NASA Technical Reports Server (NTRS)

    Stevenson, D. J.

    1993-01-01

    In the traditional view of planetary magnetism, a planet either has a core dynamo (Earth, Jupiter, Saturn, Uranus, Neptune, maybe Mercury) or does not (Mars, Venus, Moon...) I argue that this view is simplistic in two respects. First, mantle convection in terrestrial planets is invariably ata high enough Rayleigh number that it is time variable; this leads to the intermittent arrival of mantle 'cold fingers' at the core-mantle boundary promoting at least local core convection and dynamo action even when the planetary core is stably stratified on average. Thus, I predict an intermittent dynamo regime in addition to the simple dynamo-on (Earth) and dynamo-off regimes. Second, the mantle convection-driven horizontal temperature gradients just below the core-mantle boundary can lead to unstable flows that will convert thermoelectric or electrochemical toroidal fields into externally detectable poloidal fields, even when a dynamo is not possible. It is likely that Mars possesses an interesting core magnetic field of the latter kind, complex but with a dipole that might be approximately aligned with the rotation axis and a surface field of a few to tens of gammas.

  7. THE OUTER MAGNETIC FIELD OF L183

    SciTech Connect

    Clemens, Dan P.

    2012-03-20

    The L183 (= L134N) dark molecular cloud has been probed using deep near-infrared imaging polarimetry of stars to beyond 14 mag in H band (1.6 {mu}m), using the Mimir instrument on the 1.83 m Perkins Telescope. Nearly 400 arcmin{sup 2} were surveyed, including the dense core in L183, as seen in WISE Band 3 (12 {mu}m) extinction, and the near surroundings, revealing 35 stars with either detected polarizations or significant upper limits. Stars with detected polarizations are reddened if closer than 8 arcmin (0.25 pc at the 110 pc cloud distance) and unreddened beyond. The polarimetric sample probes as close to the core as 3 arcmin (0.1 pc), where A{sub V} {approx} 14 mag. Compared to the relatively unextincted surrounding stars, the reddened stars show no increase in polarization with extinction, suggesting that all of the polarization is induced in the outer layers of the cloud. This 0.25 pc radius envelope magnetic field does show a strong interaction with the L183 dark cloud. The envelope field is also virtually perpendicular, on the plane of the sky, to the field seen at 850 {mu}m, though more closely aligned with the rotation axis of the dense gas core. The physical size scale at which the envelope and the core magnetic fields either decouple from each other or strongly modify their directions must be inside the 0.1 pc region probed here.

  8. Radar observations of field-aligned plasma propagations associated with NASA's PMG experiment

    NASA Astrophysics Data System (ADS)

    Olson, Darren M.

    1994-09-01

    NASA's Plasma Motor Generator (PMG) tethered satellite mission was launched in June 1993 to verify the ability of hollow cathode plasma sources to couple electric currents from an electrodynamic tether into the ambient ionospheric plasma. This large-scale coupling process resulted in turbulent plasma signatures associated with the orbiting plasma generator, which propagated over great distances along the earth's geomagnetic field lines. VHF radars in Hilo, Hawaii and Jicamarca, Peru recorded observations of these field-aligned disturbances as part of the experiment. Based on analysis of these radar observations and tracking data of PMG's orbit, the effective propagation velocity of these traveling plasma waveforms was calculated to be of the order of 1000 meters per second. Detection of these disturbances, associated with PMG's passage overhead, supports the existence of a phantom current loop allowing current flow along the magnetic field lines of the earth and into the lower ionosphere from either end of an electrodynamic tether.

  9. Study on the scale distribution of the field-aligned irregularities in E-region

    NASA Astrophysics Data System (ADS)

    Gong, Wanlin; Qi, Hao

    2016-12-01

    The field-aligned backscattering region in the ionospheric E-region is considered to contain many small irregularities, which are arrayed along the magnetic lines. The scale and number of these irregularities in the backscattering region are different. The irregularities of a certain scale can reflect the radio wave of the corresponding wavelength on the basis of the Bragg scattering theory. The more the irregularities of a scale, the stronger is the backscattered power. Thus, the scale distribution can be estimated by the function relationship between the scale and the echo amplitude, while the incidence direction of the wave path is perpendicular to the geomagnetic field. Moreover, the echoes with oblique incidence direction can also be used to estimate the scale distribution, considering the factor of the angle between the wave path and the perpendicular field direction.

  10. Radar observations of field-aligned plasma propagations associated with nasa's PMG experiment. Master's thesis

    SciTech Connect

    Olson, D.M.

    1994-09-01

    NASA's Plasma Motor Generator (PMG) tethered satellite mission was launched in June 1993 to verify the ability of hollow cathode plasma sources to couple electric currents from an electrodynamic tether into the ambient ionospheric plasma. This large-scale coupling process resulted in turbulent plasma signatures associated with the orbiting plasma generator, which propagated over great distances along the earth's geomagnetic field lines. VHF radars in Hilo, Hawaii and Jicamarca, Peru recorded observations of these field-aligned disturbances as part of the experiment. Based on analysis of these radar observations and tracking data of PMG's orbit, the effective propagation velocity of these traveling plasma waveforms was calculated to be of the order of 1000 meters per second. Detection of these disturbances, associated with PMG's passage overhead, supports the existence of a phantom current loop allowing current flow along the magnetic field lines of the earth and into the lower ionosphere from either end of an electrodynamic tether.

  11. Coils of Magnetic Field Lines

    NASA Image and Video Library

    2017-06-27

    A smallish solar filament looks like it collapsed into the sun and set off a minor eruption that hurled plasma into space (June 20, 2017). Then, the disrupted magnetic field immediately began to reorganize itself, hence the bright series of spirals coiling up over that area. The magnetic field lines are made visible in extreme ultraviolet light as charged particles spin along them. Also of interest are the darker, cooler strands of plasma being pulled and twisted at the edge of the sun just below the active region. The activity here is in a 21-hour period. Movies are available at https://photojournal.jpl.nasa.gov/catalog/PIA21764

  12. Interplanetary magnetic field effects on high latitude ionospheric convection

    NASA Technical Reports Server (NTRS)

    Heelis, R. A.

    1985-01-01

    Relations between the electric field and the electric current in the ionosphere can be established on the basis of a system of mathematical and physical equations provided by the equations of current continuity and Ohm's law. For this reason, much of the synthesis of electric field and plasma velocity data in the F-region is made with the aid of similar data sets derived from field-aligned current and horizontal current measurements. During the past decade, the development of a self-consistent picture of the distribution and behavior of these measurements has proceeded almost in parallel. The present paper is concerned with the picture as it applies to the electric field and plasma drift velocity and its dependence on the interplanetary magnetic field. Attention is given to the southward interplanetary magnetic field and the northward interplanetary magnetic field.

  13. Dynamics of magnetic particles suspended in Newtonian fluids under magnetic field

    NASA Astrophysics Data System (ADS)

    Tan, Mingyang; Walker, Travis

    2016-11-01

    Anisotropic structures are commonly found in natural materials. Researchers are committed to developing meta-materials that mimic natural materials by introducing anisotropic filler particles. These materials can exhibit enhanced magnetic, mechanical, optical, and diffusive properties. In this study, a magnetic field is used to align magnetic oblate spheroids. We present an analytic solution based on a single-particle Stokes-flow model that describes the planar alignment of the particle in a rotating magnetic field. The analytic solution covers the full range of the magnetic field frequency agreeing well with our experimental results. Asymptotic solutions are also developed at both the high-frequency and the low-frequency limits of the field. The induced dipole of each particle can create its own magnetic field that can interact with neighboring particles, causing particles to aggregate. Different structures of particles are formed depending on the characteristics of the field, i.e., one-dimensional columns of particles in a constant field and two-dimensional sheets of particles in a rotating field. To simulate the realistic dynamics of the phenomena, we include hydrodynamic interactions between the particles via Stokesian dynamics.

  14. Photospheric and coronal magnetic fields

    SciTech Connect

    Sheeley, N.R., Jr. )

    1991-01-01

    Research on small-scale and large-scale photospheric and coronal magnetic fields during 1987-1990 is reviewed, focusing on observational studies. Particular attention is given to the new techniques, which include the correlation tracking of granules, the use of highly Zeeman-sensitive infrared spectral lines and multiple lines to deduce small-scale field strength, the application of long integration times coupled with good seeing conditions to study weak fields, and the use of high-resolution CCD detectors together with computer image-processing techniques to obtain images with unsurpassed spatial resolution. Synoptic observations of large-scale fields during the sunspot cycle are also discussed. 101 refs.

  15. Generation and Suppression of E Region Artificial Field Aligned Irregularities

    NASA Astrophysics Data System (ADS)

    Miceli, R. J.; Hysell, D. L.; Munk, J.; Han, S.

    2012-12-01

    Artificial field-aligned plasma density irregularities (FAIs) were generated in the E region of the ionosphere above the High Frequency Active Auroral Research Program (HAARP) facility during campaigns in May and August of 2012 and were quantified using a 30 MHz coherent scatter radar in Homer, Alaska. The purpose of the experiment was to analyze the X-mode suppression of FAIs generated from O-mode heating and to measure the threshold required to excite thermal parametric instabilities. The irregularities were excited by gradually increasing the power of a zenith pointing O-mode emission transmitted at a frequency of 2.75 MHz. To suppress the irregularities, a second X-mode emission at a higher frequency was added on alternating power cycles. The Homer radar measured the signal-to-noise ratio, Doppler shift, and spectral width of echoes reflected from the irregularities. We will calculate the threshold electric field required to excite the irregularities and compare with similar experiments in order to better understand the thermal parametric instability.

  16. Field-aligned Transport and Acceleration of Solar Energetic Particles

    NASA Astrophysics Data System (ADS)

    Borovikov, D.; Sokolov, I.; Tenishev, V.; Gombosi, T. I.

    2015-12-01

    Solar Energetic Particle (SEP) phenomena represent one of the major components of space weather. Often, but not exclusively associated with Coronal Mass Ejections (CMEs), they pose a significant scientific as well as practical interest. As these particles originate at such explosive events, they have energies up to several GeV. SEP may cause disruptions in operations of space instruments and spacecrafts and are dangerous to astronauts. For this reason, studies of SEP events and predictions of their impact are of great importance. The motion and acceleration of SEP, though kinetic in nature, is governed by Interplanetary Magnetic Field (IMF) and its disturbances. Therefore, a consistent and accurate simulation and predictive tool must include a realistic MHD model of IMF. At the same time, transport of SEP is essentially one-dimensional as at high energies particles are tied to magnetic field lines. This allows building a model that can effectively map active regions on the solar surface onto various regions of the Solar System thus predicting the affected regions of the at any distance from the Sun. We present the first attempt to construct a model that employs coupling of MHD and kinetic models. The former describes the evolution of IMF disturbed by CME, while the latter simulates particles moving along the field lines extracted from MHD model. The first results are provided.

  17. Large aperture laser beam alignment system based on far field sampling technique

    NASA Astrophysics Data System (ADS)

    Zhang, J. C.; Liu, D. Z.; Ouyang, X. P.; Kang, J.; Xie, X. L.; Zhou, J.; Gong, L.; Zhu, B. Q.

    2016-11-01

    Laser beam alignment is very important for high-power laser facility. Long laser path and large-aperture lens for alignment are generally used, while the proposed alignment system with a wedge by far-field sampling technique reduces both space and cost requirements. General alignment system for large-aperture laser beam is long in distance and large in volum because of taking near-field sampling technique. With the development of laser fusion facilities, the space for alignment system is limited. A new alignment system for large-aperture laser beam is designed to save space and reduce operating costs. The new alignment for large-aperture laser beam with a wedge is based on far-field sampling technique. The wedge is placed behind the spatial filter to reflect some laser beam as signal light for alignment. Therefore, laser beam diameter in alignment system is small, which can save space for the laser facility. Comparing to general alignment system for large-aperture laser beam, large-aperture lenses for near-field and far-field sampling, long distance laser path are unnecessary for proposed alignment system, which saves cost and space greatly. This alignment system for large-aperture laser beam has been demonstrated well on the Muliti-PW Facility which uses the 7th beam of the SG-Ⅱ Facility as pump source. The experimental results indicate that the average near-field alignment error is less than 1% of reference, and the average far-filed alignment error is less than 5% of spatial filter pinhole diameter, which meet the alignment system requirements for laser beam of Multi-PW Facility.

  18. Observations of Interstellar Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Crutcher, R.; Heiles, C.; Troland, T.

    This article describes how interstellar magnetic fields are detected, measured, and mapped, the results of such observations, and the role played by interstellar magnetic fields in the physics of the interstellar medium. A goal of the observations is the measurement of the morphology and strengths of the uniform (Bu) and random (Br) components of magnetic fields. Observational techniques probe either the component of B parallel to the line of sight (B_parallel) or in the plane of the sky (B_⊥). Tracers of B_parallel are Faraday rotation of the position angle of linearly polarized radiation and Zeeman splitting of spectral lines. Tracers of B_⊥ are the strength of synchrotron radiation and linear polarization of syn chrotron radiation and of emission or absorption from dust and spectral lines. Starlight polarization shows that on large spatial scales the Galactic magnetic field is not heavily tangled (B_u/B_r ≈ 0.7 - 1.0), that the field is generally parallel to the Galactic plane near the plane, that the local field points approximately along the local spiral arm (pitch angle 9.4(°) , center of curvature 7.8 kpc distant towards ℓ ≈ -15.4(°) ), and that off the Galactic plane there is considerable small-scale structure to the field. Galactic synchrotron emission shows magnetic spiral arms with a total strength B_t ≈ 6 #55G and B_u ≈ 4 #55G. Pulsar data show evidence for reversals of the field direction with Galactic radius and yield B_r ≈ 5 #55G and B_u ≈ 1.5 #55G; the morphology of the large-scale mean field is consistent with dynamo generation. H I Zeeman detections for diffuse clouds yield B_parallel char 126 5 - 20 #55G with many limits B_parallel #55G. A recent survey of Galactic H I in absorption against extragalactic sources confirms the result that the fields in diffuse clouds are often quite weak. The critical parameter for evaluating the importance of magnetic fields in star formation is the ratio of the mass to the magnetic flux, M

  19. Magnetic fields around black holes

    NASA Astrophysics Data System (ADS)

    Garofalo, David A. G.

    Active Galactic Nuclei are the most powerful long-lived objects in the universe. They are thought to harbor supermassive black holes that range from 1 million solar masses to 1000 times that value and possibly greater. Theory and observation are converging on a model for these objects that involves the conversion of gravitational potential energy of accreting gas to radiation as well as Poynting flux produced by the interaction of the rotating spacetime and the electromagnetic fields originating in the ionized accretion flow. The presence of black holes in astrophysics is taking center stage, with the output from AGN in various forms such as winds and jets influencing the formation and evolution of the host galaxy. This dissertation addresses some of the basic unanswered questions that plague our current understanding of how rotating black holes interact with their surrounding magnetized accretion disks to produce the enormous observed energy. Two magnetic configurations are examined. The first involves magnetic fields connecting the black hole with the inner accretion disk and the other involves large scale magnetic fields threading the disk and the hole. We study the effects of the former type by establishing the consequences that magnetic torques between the black hole and the inner accretion disk have on the energy dissipation profile. We attempt a plausible explanation to the observed "Deep Minimum" state in the Seyfert galaxy MCG-6- 30-15. For the latter type of magnetic geometry, we study the effects of the strength of the magnetic field threading the black hole within the context of the cherished Blandford & Znajek mechanism for black hole spin energy extraction. We begin by addressing the problem in the non-relativistic regime where we find that the black hole-threading magnetic field is stronger for greater disk thickness, larger magnetic Prandtl number, and for a larger accretion disk. We then study the problem in full relativity where we show that our

  20. Majorana neutrinos and magnetic fields

    NASA Astrophysics Data System (ADS)

    Schechter, J.; Valle, J. W. F.

    1981-10-01

    It is stressed that if neutrinos are massive they are probably of "Majorana" type. This implies that their magnetic-moment form factor vanishes identically so that the previously discussed phenomenon of spin rotation in a magnetic field would not appear to take place. We point out that Majorana neutrinos can, however, have transition moments. This enables an inhomogeneous magnetic field to rotate both spin and "flavor" of a neutrino. In this case the spin rotation changes particle to antiparticle. The spin-flavor-rotation effect is worked out in detail. We also discuss the parametrization and calculation of the electromagnetic form factors of Majorana neutrinos. Our discussion takes into account the somewhat unusual quantum theory of massive Majorana particles.

  1. The Effect of Extremely Low Frequency Alternating Magnetic Field on the Behavior of Animals in the Presence of the Geomagnetic Field

    PubMed Central

    Belova, Natalia A.; Acosta-Avalos, Daniel

    2015-01-01

    It is known that the geomagnetic field can influence animal migration and homing. The magnetic field detection by animals is known as magnetoreception and it is possible due to two different transduction mechanisms: the first one through magnetic nanoparticles able to respond to the geomagnetic field and the second one through chemical reactions influenced by magnetic fields. Another behavior is the magnetic alignment where animals align their bodies to the geomagnetic field. It has been observed that magnetic alignment of cattle can be disrupted near electric power lines around the world. Experimentally, it is known that alternating magnetic fields can influence living beings, but the exact mechanism is unknown. The parametric resonance model proposes a mechanism to explain that effect on living beings and establishes that, in the presence of a constant magnetic field, molecules associated with biochemical reactions inside cells can absorb resonantly alternating magnetic fields with specific frequencies. In the present paper, a review is made about animal magnetoreception and the effects of alternating magnetic fields in living beings. It is suggested how alternating magnetic fields can interfere in the magnetic alignment of animals and a general conclusion is obtained: alternating magnetic field pollution can affect the magnetic sensibility of animals. PMID:26823664

  2. The Effect of Extremely Low Frequency Alternating Magnetic Field on the Behavior of Animals in the Presence of the Geomagnetic Field.

    PubMed

    Belova, Natalia A; Acosta-Avalos, Daniel

    2015-01-01

    It is known that the geomagnetic field can influence animal migration and homing. The magnetic field detection by animals is known as magnetoreception and it is possible due to two different transduction mechanisms: the first one through magnetic nanoparticles able to respond to the geomagnetic field and the second one through chemical reactions influenced by magnetic fields. Another behavior is the magnetic alignment where animals align their bodies to the geomagnetic field. It has been observed that magnetic alignment of cattle can be disrupted near electric power lines around the world. Experimentally, it is known that alternating magnetic fields can influence living beings, but the exact mechanism is unknown. The parametric resonance model proposes a mechanism to explain that effect on living beings and establishes that, in the presence of a constant magnetic field, molecules associated with biochemical reactions inside cells can absorb resonantly alternating magnetic fields with specific frequencies. In the present paper, a review is made about animal magnetoreception and the effects of alternating magnetic fields in living beings. It is suggested how alternating magnetic fields can interfere in the magnetic alignment of animals and a general conclusion is obtained: alternating magnetic field pollution can affect the magnetic sensibility of animals.

  3. Magnetic Fields of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Konar, Sushan

    2017-09-01

    This article briefly reviews our current understanding of the evolution of magnetic fields in neutron stars, which basically defines the evolutionary pathways between different observational classes of neutron stars. The emphasis here is on the evolution in binary systems and the newly emergent classes of millisecond pulsars.

  4. Transverse Magnetic Field Propellant Isolator

    NASA Technical Reports Server (NTRS)

    Foster, John E.

    2000-01-01

    An alternative high voltage isolator for electric propulsion and ground-based ion source applications has been designed and tested. This design employs a transverse magnetic field that increases the breakdown voltage. The design can greatly enhance the operating range of laboratory isolators used for high voltage applications.

  5. Crystal field and magnetic properties

    NASA Technical Reports Server (NTRS)

    Flood, D. J.

    1977-01-01

    Magnetization and magnetic susceptibility measurements have been made in the temperature range 1.3 to 4.2 K on powdered samples of ErH3. The susceptibility exhibits Curie-Weiss behavior from 4.2 to 2 K, and intercepts the negative temperature axis at theta = 1.05 + or - 0.05 K, indicating that the material is antiferromagnetic. The low field effective moment is 6.77 + or - 0.27 Bohr magnetons per ion. The magnetization exhibits a temperature independent contribution, the slope of which is (5 + or - 1.2) x 10 to the -6th Weber m/kg Tesla. The saturation moment is 3.84 + or - 1 - 0.15 Bohr magnetons per ion. The results can be qualitatively explained by the effects of crystal fields on the magnetic ions. No definitive assignment of a crystal field ground state can be given, nor can a clear choice between cubically or hexagonally symmetric crystal fields be made. For hexagonal symmetry, the first excited state is estimated to be 86 to 100 K above the ground state. For cubic symmetry, the splitting is on the order of 160 to 180 K.

  6. Magnetic Field Statistics in Saturn's Magnetosphere

    NASA Astrophysics Data System (ADS)

    Guio, P.; Achilleos, N.; Santolik, O.; Masters, A.; Arridge, C.

    2012-04-01

    We present a statistical study of the fluctuations of the magnetic field for different regions of Saturn's magnetosphere as measured by the magnetometer instrument (MAG) on board the Cassini spacecraft. The magnetometer data, for a set of illustrative orbits during the prime mission, are used to construct probability distribution functions (PDFs) of magnetic fluctuations, in both the field-aligned and perpendicular directions. This technique is often used to look for intermittent plasma turbulence and non-self-similar properties in the fluctuations. Here we investigate the possibility to successfully characterise a region and/or regime of the magnetosphere in the signature of these PDFs. We construct PDFs from first principles, and we also consolidate our analysis by using an on-line data analysis tool ``Demonstrator for Multi-dimensional Spectral Analysis of Electromagnetic Fields'' developed under the Europlanet Joint Research Activity 3. We determine polarisation and propagation properties of the observed fluctuations as a function of frequency. We also comment on the applicability of these methods to identifying different characteristic frequencies and directions of boundary waves, such as Kelvin-Helmholtz disturbances.

  7. Magnetic Field Statistics in Saturn's Magnetosphere

    NASA Astrophysics Data System (ADS)

    Guio, P.; Achilleos, N. A.; Santolik, O.; Masters, A.; Arridge, C. S.

    2011-12-01

    We present a statistical study of the fluctuations of the magnetic field for different regions of Saturn's magnetosphere as measured by the magnetometer instrument (MAG) on board the Cassini spacecraft. The magnetometer data, for a set of illustrative orbits during the prime mission, are used to construct probability distribution functions (PDFs) of magnetic fluctuations, in both the field-aligned and perpendicular directions. This technique is often used to look for intermittent plasma turbulence and non-self-similar properties in the fluctuations. Here we investigate the possibility to successfully characterise a region and/or regime of the magnetosphere in the signature of these PDFs. We construct PDFs from first principles, and we also consolidate our analysis by using an on line data analysis tool "Demonstrator for Multi-dimensional Spectral Analysis of Electromagnetic Fields" developed under the Europlanet Joint Research Activity 3. We determine polarisation and propagation properties of the observed fluctuations as a function of frequency. We also comment on the applicability of these methods to identifying different characteristic frequencies and directions of boundary waves, such as Kelvin-Helmholtz disturbances.

  8. Collision-induced stimulated photon echo in magnetic field

    NASA Astrophysics Data System (ADS)

    Reshetov, V. A.

    2015-12-01

    The action of the longitudinal magnetic field on the collision-induced stimulated photon echo formed on the transition with the angular momentum change {{J}a}=0\\to {{J}b}=1 is studied theoretically. It is shown that this action depends essentially on the sign of the difference in the orientation Γb(1) and alignment Γb(2) relaxation rates of the excited level b. If Γb(2)>Γb(1) , then the echo intensity in a weak magnetic field increases with the increase in the magnetic field strength, while in the alternative case Γb(2)<Γb(1) it decreases up to zero value. The formulae enabling the determination of the magnitude of the difference Γb(1)-Γb(2) from the experimental study of the oscillations of the echo intensity with the increase in the magnetic field strength are obtained.

  9. The Global Magnetic Field of Mercury from MESSENGER Orbital Observations

    NASA Astrophysics Data System (ADS)

    Anderson, Brian J.; Johnson, Catherine L.; Korth, Haje; Purucker, Michael E.; Winslow, Reka M.; Slavin, James A.; Solomon, Sean C.; McNutt, Ralph L.; Raines, Jim M.; Zurbuchen, Thomas H.

    2011-09-01

    Magnetometer data acquired by the MESSENGER spacecraft in orbit about Mercury permit the separation of internal and external magnetic field contributions. The global planetary field is represented as a southward-directed, spin-aligned, offset dipole centered on the spin axis. Positions where the cylindrical radial magnetic field component vanishes were used to map the magnetic equator and reveal an offset of 484 ± 11 kilometers northward of the geographic equator. The magnetic axis is tilted by less than 3° from the rotation axis. A magnetopause and tail-current model was defined by using 332 magnetopause crossing locations. Residuals of the net external and offset-dipole fields from observations north of 30°N yield a best-fit planetary moment of 195 ± 10 nanotesla-RM3, where RM is Mercury’s mean radius.

  10. The Magnetic Field of Solar Chromospheric Spicules

    NASA Astrophysics Data System (ADS)

    Trujillo Bueno, J.; Ramelli, R.; Merenda, L.; Bianda, M.

    2007-05-01

    A suitable diagnostic tool for investigating the magnetism of the solar chromosphere is the observation and theoretical modeling of the Hanle and Zeeman effects in solar spicules. In our presentation we highlighted the great scientific interest of this new diagnostic window by showing how the magnetic field vector can be inferred from spectropolarimetric observations of solar chromospheric spicules in several spectral lines, such as those of the 10830 Å and 5876 Å multiplets of neutral helium. Our off-limb spectropolarimetric observations of the He I 10830 Å multiplet were obtained with the Tenerife Infrared Polarimeter (TIP) attached to the Vacuum Tower Telescope at the Observatorio del Teide (Tenerife), while those of the 5876 Å multiplet resulted from observations with the Zurich Imaging Polarimeter (ZIMPOL) at the Gregory Coudé Telescope of the Istituto Ricerche Solari Locarno. The application of a Stokes profiles inversion technique led to the following conclusion. In quiet Sun spicules the magnetic field vector at a height of about 2000 km above the solar visible ``surface" has a typical strength of the order to 10 G and is inclined by approximately 35° with respect to the solar local vertical direction. In spicules observed close to active regions the strength of the magnetic field was of the order of 50 G. The two figures below show the off-limb Stokes profiles of the He I 5876 Å multiplet observed in a quiet region (upper figure) and close to an active region (lower figure). Note that in both cases Stokes U is non-zero, which is the observational signature of the Hanle effect of an inclined magnetic field. The change of sign in Stokes U along the spatial direction of the spectrograph's slit can be explained by variations in the azimuth of the magnetic field vector. Interestingly, while the Stokes V profiles corresponding to the observed quiet region are caused by the alignment-to-orientation transfer mechanism (see, e.g., page 607 of Landi Degl

  11. Field-aligned currents onboard the Intercosmos Bulgaria-1300 satellite in comparison with modeled FAC

    NASA Astrophysics Data System (ADS)

    Danov, Dimitar

    2008-02-01

    The statistical field-aligned current (FAC) distribution has been demonstrated by [Iijima, T., Potemra, T.A., 1976. The amplitude distribution of field-aligned currents at northern high latitudes observed by Triad. Journal of Geophysical Research 81(13), 2165-2174] and many other authors. The large-scale (LS) FACs have been described by different empirical/statistical models [Feldstein, Ya. I., Levitin, A.E., 1986. Solar wind control of electric fields and currents in the ionosphere. Journal of Geomagnetism and Geoelectricity 38, 1143; Papitashvili, V.O., Rich, F.J., Heinemann, M.A., Hairston, M.R., 1999. Parameterization of the Defense Meteorological Satellite Program ionospheric electrostatic potentials by the interplanetary magnetic field strength and direction. Journal of Geophysical Research 104, 177-184; Papitashvili, V.O., Christiansen, F., Neubert, T., 2002. A new model of field-aligned currents derived from high-precision satellite magnetic field data. Geophysical Research Letters, 29(14), 1683, doi:10.1029/2001GL014207; Tsyganenko, N.A., 2001. A model of the near magnetosphere with a dawn-dusk asymetry (I. Mathematical structure). Journal of Geophysical Research 107(A8), doi:10.1029/2001JA000219; Weimer, D.R., 1996a. A new model for prediction of ionospheric electric potentials as a function of the IMF. In: Snowmass'96 Online Poster Session; Weimer, D.R., 1996b. Substorm influence on the ionospheric convection patterns. In: Snowmass'96 Online Poster Session; Weimer, D.R., 2001. Maps of ionospheric field-aligned currents as a function of the interplanetary magnetic field derived from Dynamic Explorer 2 data. Journal of Geophysical Research 106, 12,889-12,902; Weimer, D.R., 2005. Improved ionospheric electrodynamic models and application to calculating Joule heating rates. Journal of Geophysical Research 110, A05306, doi:10.1029/2004JA010884]. In the present work, we compare two cases of LS FAC obtained from magnetic field measurements onboard the

  12. Separation of magnetic field lines

    SciTech Connect

    Boozer, Allen H.

    2012-11-15

    The field lines of magnetic fields that depend on three spatial coordinates are shown to have a fundamentally different behavior from those that depend on two coordinates. Unlike two-coordinate cases, a flux tube in a magnetic field that depends on all three spatial coordinates that has a circular cross section at one location along the tube characteristically has a highly distorted cross section at other locations. In an ideal evolution of a magnetic field, the current densities typically increase. Crudely stated, if the current densities increase by a factor {sigma}, the ratio of the long to the short distance across a cross section of a flux tube characteristically increases by e{sup 2{sigma}}, and the ratio of the longer distance to the initial radius increases as e{sup {sigma}}. Electron inertia prevents a plasma from isolating two magnetic field structures on a distance scale shorter than c/{omega}{sub pe}, which is about 10 cm in the solar corona, and reconnection must be triggered if {sigma} becomes sufficiently large. The radius of the sun, R{sub Circled-Dot-Operator }=7 Multiplication-Sign 10{sup 10}cm is about e{sup 23} times larger, so when {sigma} Greater-Than-Or-Equivalent-To 23, two lines separated by c/{omega}{sub pe} at one location can be separated by the full scale of any magnetic structures in the corona at another. The conditions for achieving a large exponentiation, {sigma}, are derived, and the importance of exponentiation is discussed.

  13. Magnetic fields in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Krause, Marita

    2015-03-01

    The magnetic field structure in edge-on galaxies observed so far shows a plane-parallel magnetic field component in the disk of the galaxy and an X-shaped field in its halo. The plane-parallel field is thought to be the projected axisymmetric (ASS) disk field as observed in face-on galaxies. Some galaxies addionionally exhibit strong vertical magnetic fields in the halo right above and below the central region of the disk. The mean-field dynamo theory in the disk cannot explain these observed fields without the action of a wind, which also probably plays an important role to keep the vertical scale heights constant in galaxies of different Hubble types and star formation activities, as has been observed in the radio continuum: At λ6 cm the vertical scale heights of the thin disk and the thick disk/halo in a sample of five edge-on galaxies are similar with a mean value of 300 +/- 50 pc for the thin disk and 1.8 +/- 0.2 kpc for the thick disk (a table and references are given in Krause 2011) with our sample including the brightest halo observed so far, NGC 253, with strong star formation, as well as one of the weakest halos, NGC 4565, with weak star formation. If synchrotron emission is the dominant loss process of the relativistic electrons the outer shape of the radio emission should be dumbbell-like as has been observed in several edge-on galaxies like e.g. NGC 253 (Heesen et al. 2009) and NGC 4565. As the synchrotron lifetime t syn at a single frequency is proportional to the total magnetic field strength B t -1.5, a cosmic ray bulk speed (velocity of a galactic wind) can be defined as v CR = h CR /t syn = 2 h z /t syn , where h CR and h z are the scale heights of the cosmic rays and the observed radio emission at this freqnency. Similar observed radio scale heights imply a self regulation mechanism between the galactic wind velocity, the total magnetic field strength and the star formation rate SFR in the disk: v CR ~ B t 1.5 ~ SFR ~ 0.5 (Niklas & Beck 1997).

  14. Magnetic fields in the sun

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.

    1974-01-01

    The observed properties of solar magnetic fields are reviewed, with particular reference to the complexities imposed on the field by motions of the highly conducting gas. Turbulent interactions between gas and field lead to heating or cooling of the gas according to whether the field energy density is less or greater than the maximum kinetic energy density in the convection zone. The field strength above which cooling sets in is 700 gauss. A weak solar dipole field may be primeval, but dynamo action is also important in generating new flux. The dynamo is probably not confined to the convection zone, but extends throughout most of the volume of the sun. Planetary tides appear to play a role in driving the dynamo.

  15. The magnetic field of Jupiter

    NASA Technical Reports Server (NTRS)

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

    1976-01-01

    The paper is concerned mainly with the intrinsic planetary field which dominates the inner magnetosphere up to a distance of 10 to 12 Jovian radii where other phenomena, such as ring currents and diamagnetic effects of trapped charged particles, become significant. The main magnetic field of Jupiter as determined by in-situ observations by Pioner 10 and 11 is found to be relatively more complex than a simple offset tilted dipole. Deviations from a simple dipole geometry lead to distortions of the charged particle L shells and warping of the magnetic equator. Enhanced absorption effects associated with Io and Amalthea are predicted. The results are consistent with the conclusions derived from extensive radio observations at decimetric and decametric wavelengths for the planetary field.

  16. STUDYING THE INTERSTELLAR MAGNETIC FIELD FROM ANISOTROPIES IN VELOCITY CHANNELS

    SciTech Connect

    Esquivel, A.; Lazarian, A.; Pogosyan, D. E-mail: lazarian@astro.wisc.edu

    2015-11-20

    Turbulence in the interstellar medium is anisotropic due to the ubiquitous magnetic fields. This anisotropy depends on the strength of the magnetic field and leaves an imprint on observations of spectral line maps. We use a grid of ideal magnetohydrodynamic simulations of driven turbulence and produce synthetic position–position–velocity maps to study the turbulence anisotropy in velocity channels of various resolutions. We found that the average structure function of velocity channels is aligned with the projection of the magnetic field on the plane of the sky. We also found that the degree of such anisotropy increases with the magnitude of the magnetic field. For thick velocity channels (low velocity resolution), the anisotropy is dominated by density, and the degree of anisotropy in these maps allows one to distinguish sub-Alfvénic and super-Alfvénic turbulence regimes, but it also depends strongly on the sonic Mach number. For thin channels (high velocity resolution), we find that the anisotropy depends less on the sonic Mach number. An important limitation of this technique is that it only gives a lower limit on the magnetic field strength because the anisotropy is related only to the magnetic field component on the plane of the sky. It can, and should, be used in combination with other techniques to estimate the magnetic field, such as the Fermi-Chandrasekhar method, anisotropies in centroids, Faraday rotation measurements, or direct line-of-sight determinations of the field from Zeeman effect observations.

  17. Anomalous foreshock field-aligned beams observed by Cluster

    NASA Astrophysics Data System (ADS)

    Meziane, K.; Hamza, A. M.; Wilber, M.; Mazelle, C.; Lee, M. A.

    2011-10-01

    We report occasional observations of two simultaneously distinct ion foreshock components recorded by the Cluster spacecraft upstream of the Earth's bow shock. In most occurrences, the lower-energy population originates as a field-aligned beam (FAB) associated with quasi-perpendicular regions, which loses energy as the IMF rotates into oblique geometries. A second beam, with energies in excess of ~10 keV, appears sometimes in association with the onset of ultra-low frequency (ULF) waves, and sometimes ahead of the appearance of the latter. Measurements from the mass spectrometer indicate that both beams consist of protons. While the lower-speed beam is well-accounted for by a known reflection mechanism, the non-radial IMF orientations as well as other arguments seem to rule out magnetosheath or magnetospheric sources for the higher energy component. The wave characteristics are typical of the oblique foreshock and we have found that they are in cyclotron-resonance with the low speed beam (FAB). These observations constitute a theoretical challenge since conventional mechanisms described in the literature cannot account for the production of beams at two different energies.

  18. Oxide superconductors under magnetic field

    NASA Technical Reports Server (NTRS)

    Kitazawa, K.

    1990-01-01

    One of the current most serious problems for the oxide superconductors from the standpoint of practical application is the various novel features derived mainly from their extremely short coherence. In particular, the coherence length so far observed in the cuprate superconductors is in the range of 0.1 nm perpendicular to the CuO2 plane. This seems to be creating most of the difficulties in the device fabrication and in the performance under the magnetic field. Some of the superconducting properties under the magnetic field will be discussed in terms of the short coherence length. A model will be presented based on the gradual strengthening of the pinning force with decrease in temperature and the weak coupling at the grain boundaries. Secondly, the broadening of the superconducting transition under the magnetic field is discussed. This is observed significantly only when the field is applied perpendicular to the basal plane and the relative orientation of the current to the field is insignificant in determining the extent of the broadening. Besides, the change in the strength of the pinning force does not affect the width of the broadening. From these observations discussions will be made on a model based on the giant fluctuation. Based on this model, it is predicted that the coherence length along the c-axis will be the single most important material parameter to determine the performance of the superconductor under a strong magnetic field. It seems that BYCO is superior in this regard to Bi- or Tl-systems as far as the performance at 77 K is considered, although another material with the coherence length slightly longer along the c-axis is still highly desired.

  19. Oxide superconductors under magnetic field

    NASA Technical Reports Server (NTRS)

    Kitazawa, K.

    1991-01-01

    One of the current most serious problems for the oxide superconductors from the standpoint of practical application is the various novel features derived mainly from their extremely short coherence. In particular, the coherence length so far observed in the cuprate superconductors is in the range of 0.1 nm perpendicular to the CuO2 plane. This seems to be creating most of the difficulties in the device fabrication and in the performance under the magnetic field. Some of the superconducting properties under the magnetic field will be discussed in terms of the short coherence length. A model will be presented based on the gradual strengthening of the pinning force with decrease in temperature and the weak coupling at the grain boundaries. Secondly, the broadening of the superconducting transition under the magnetic field is discussed. This is observed significantly only when the field is applied perpendicular to the basal plane and the relative orientation of the current to the field is insignificant in determining the extent of broadening. Besides, the change in the strength of the pinning force does not affect the width of the broadening. From these observations discussions will be made on a model based on the giant fluctuation. Based on this model, it is predicted that the coherence length along the c-axis will be the single most important material parameter to determine the performance of the superconductor under a strong magnetic field. It seems that BYCO is superior in this regard to Bi- or Tl-systems as far as the performance at 77 K is considered, although another material with the coherence length slightly longer along the c-axis is still highly desired.

  20. Comparison of field-aligned currents at ionospheric and magnetospheric altitudes

    NASA Technical Reports Server (NTRS)

    Spence, H. E.; Kivelson, M. G.; Walker, R. J.

    1988-01-01

    Using the empirical terrestrial magnetospheric magnetic field models of Tsyganenko and Usmanov (1982) and Tsyganenko (1987) the average field-aligned currents (FACs) in the magnetosphere were determined as a function of the Kp index. Three major model FAC systems were identified, namely, the dayside region 1, the nightside region 1, and the nightside polar cap. The models provide information about the sources of the current systems. Mapped ionospheric model FACs are compared with low-altitude measurements obtained by the spacecraft. It is found that low-altitude data can reveal either classic region 1/2 or more highly structured FAC patterns. Therefore, statistical results either obtained from observations or inferred from models are expected to be averages over temporally and spatially shifting patterns.

  1. Generation of large scale field-aligned density irregularities in ionospheric heating experiments. [electromagnetic wave decay

    NASA Technical Reports Server (NTRS)

    Fejer, J. A.

    1974-01-01

    Threshold and growth rate for stimulated Brillouin scattering are calculated for a uniform magnetoplasma. These are then compared with the threshold and growth rate of a new thermal instability in which the nonlinear Lorentz force felt by the electrons at the beat frequency of the two electromagnetic waves is replaced by a pressure force due to differential heating in the interference pattern of the pump wave and the generated electromagnetic wave. This thermal instability, which is still essentially stimulated Brillouin scattering, has a threshold which is especially low when the propagation vector of the beat wave is almost normal to the magnetic field. The threshold is then considerably lower than the threshold for normal stimulated Brillouin scattering and therefore this new instability is probably responsible for the generation of large scale field aligned irregularities and ionospheric spread F.

  2. Evaluating the diffusive equilibrium models: Comparison with the IMAGE RPI field-aligned electron density measurements

    NASA Astrophysics Data System (ADS)

    Ozhogin, P.; Song, P.; Tu, J.; Reinisch, B. W.

    2014-06-01

    The diffusive equilibrium models that are widely used by the space physics community to describe the plasma densities in the plasmasphere are evaluated with field-aligned electron density measurements from the radio plasma imager (RPI) instrument onboard the IMAGE satellite. The original mathematical form of the diffusive equilibrium model was based on the hydrostatic equilibrium along the magnetic field line with the centrifugal force and the field-aligned electrostatic force as well as a large number of simplifying approximations. Six free parameters in the mathematical form have been conventionally determined from observations. We evaluate four sets of the parameters that have been reported in the literature. The evaluation is made according to the equatorial radial distance dependence, latitudinal dependence at a given radial distance, and the combined radial and latitudinal dependences. We find that the mathematical form given in the diffusive equilibrium model is intrinsically incompatible with the measurements unless another large number of free parameters are artificially introduced, which essentially changes the nature of a theoretical model to an empirical model.

  3. Space Technology 5 Multi-Point Field-Aligned Current Measurements (Invited)

    NASA Astrophysics Data System (ADS)

    Slavin, J. A.; Le, G.; Gjerloev, J. W.

    2013-12-01

    NASA's Space Technology 5 (ST 5) microsatellite constellation technology mission was launched by a Pegasus launch vehicle on March 22, 2006. The three small (48 cm tall, 50 cm diameter, 25 kg mass, spin stabilized at 20 rpm) satellites were placid in a 300 x 4500 km, dawn to dusk, sun synchronous orbit (inclination = 105.6 deg) orbit with a period of 138 min. They were maintained in this 'pearls on a sting' formation with inter-satellite spacings ranging from over 5000 km to under 50 km. Each satellite carried a miniature tri-axial fluxgate magnetometer (MAG) provided by the University of California at Los Angeles. Field aligned currents (FACs) form in response to the stress exerted on the magnetosphere by the solar wind and act as the primary mechanism for dissipating solar wind energy into the ionosphere and upper atmosphere during the solar wind magnetosphere ionosphere coupling process. ST 5 returned the first direct, simultaneous, multipoint measurements of FAC motion, thickness, and temporal variability. Current density was measured using both 1) the 'standard method' based upon s/c velocity, but corrected for FAC current sheet motion, with the assumption of a time-stationary current density profile, and 2) for the first time at low altitudes, the 'gradiometer method' which uses simultaneous magnetic field measurements at two points with known separation. Here we review the ST 5 scientific results concerning FACs and discuss their implications for future investigations of field aligned currents systems using distributed systems of spaceborne magnetometers.

  4. Validation of a new plasmapause model derived from CHAMP field-aligned current signatures

    NASA Astrophysics Data System (ADS)

    Heilig, Balázs; Darrouzet, Fabien; Vellante, Massimo; Lichtenberger, János; Lühr, Hermann

    2014-05-01

    Recently a new model for the plasmapause location in the equatorial plane was introduced based on magnetic field observations made by the CHAMP satellite in the topside ionosphere (Heilig and Lühr, 2013). Related signals are medium-scale field-aligned currents (MSFAC) (some 10km scale size). An empirical model for the MSFAC boundary was developed as a function of Kp and MLT. The MSFAC model then was compared to in situ plasmapause observations of IMAGE RPI. By considering this systematic displacement resulting from this comparison and by taking into account the diurnal variation and Kp-dependence of the residuals an empirical model of the plasmapause location that is based on MSFAC measurements from CHAMP was constructed. As a first step toward validation of the new plasmapause model we used in-situ (Van Allen Probes/EMFISIS, Cluster/WHISPER) and ground based (EMMA) plasma density observations. Preliminary results show a good agreement in general between the model and observations. Some observed differences stem from the different definitions of the plasmapause. A more detailed validation of the method can take place as soon as SWARM and VAP data become available. Heilig, B., and H. Lühr (2013) New plasmapause model derived from CHAMP field-aligned current signatures, Ann. Geophys., 31, 529-539, doi:10.5194/angeo-31-529-2013

  5. The behavior of a magnetic filament in flow under the influence of an external magnetic field

    NASA Astrophysics Data System (ADS)

    Lüsebrink, Daniel; Cerdà, Joan J.; Sánchez, Pedro A.; Kantorovich, Sofia S.; Sintes, Tomás

    2016-12-01

    We present an extensive numerical study of the behaviour of a filament made of ferromagnetic colloidal particles subjected to the simultaneous action of a fluid flow and a stationary external magnetic field perpendicular to the flow lines. We found that in the presence of a shear flow, the tumbling motion observed at zero field is strongly inhibited when the external magnetic field is applied. The field is able to stabilise the filament with a well defined degree of alignment that depends on the balance between hydrodynamic and magnetic torques. In addition, for a Poiseuille flow, it has been found that the initial position has a long lasting influence on the behaviour of the magnetic filament when the external field is applied.

  6. A New Feature of Field-Aligned Auroral Ion Beams Observed by Cluster

    NASA Astrophysics Data System (ADS)

    Parks, George; lee, Ensang; Suiyan, Fu; Fillingim, Matt; Cui, Yanbon; Hong, Jinhy; Dandouras, Iaonnis; reme, henri; Canu, Patrick; Lin, Naiguo

    2015-04-01

    Cluster measures 3D distributions in one spin of the spacecraft (4s). Field-aligned ion beams (H+, He+ and O+) are often observed accelerated out of the ionosphere. The escaping beams can be narrow in velocity space or more extended with a continuous range of velocities. Narrow velocity beams indicate the particles have been accelerated by a potential structure localized in space and beams with a wider velocity range indicate the potential structure is extended and distributed along the magnetic field. The Cluster ion composition experiment has now revealed a new feature showing some H+, He+ and O+ field-aligned beams are broken into many discrete beams each with its own velocity covering a wide velocity range. To interpret the discrete beams, the potential model requires existence of many narrow isolated potential structures along a magnetic field but there are currently no U-shaped theories or models that can explain how the discrete potential structures are formed or maintained. Our interpretation is that Cluster SC have actually crossed an auroral arc structure at a height of 3.5 RE and the discrete beams represent particles accelerated on different equi-potential contours of an aurora. While similar beams are observed in three of the four SC, the detailed features are not identical, indicating the beams have limited spatial scales and/or the dynamics include temporal variations. The distance between two discrete beams is estimated to be as small as ~145-290 meters at the SC position. This dimension mapped to the ionosphere is ~72-145 meters, which is a typical thickness of an auroral arc (Maggs and Davis, PSS 16, 205, 1968). The velocity of the beam increases as the SC moves toward the equator indicating that the auroral potential is higher at lower latitudes. This talk will discuss the new discrete beams and their interesting properties.

  7. Magnetically aligned phospholipid bilayers with positive ordering: a new model membrane system.

    PubMed Central

    Prosser, R S; Hwang, J S; Vold, R R

    1998-01-01

    A stable smectic phospholipid bilayer phase aligned with the director parallel to the magnetic field can be generated by the addition of certain trivalent paramagnetic lanthanide ions to a bicellar solution of dimyristoylphosphatidylcholine (DMPC) and dihexanoylphosphatidylcholine (DHPC) in water. Suitable lanthanide ions are those with positive anisotropy of their magnetic susceptibility, namely Eu3+, Er3+, Tm3+, and Yb3+. For samples doped with Tm3+, this phase extends over a wide range of Tm3+ concentrations (6-40 mM) and temperatures (35-90 degrees C) and appears to undergo a transition from a fluid nematic discotic to a fluid, but highly ordered, smectic phase at a temperature that depends on the thulium concentration. As a membrane mimetic, these new, positively ordered phospholipid phases have high potential for structural studies using a variety of techniques such as magnetic resonance (EMR and NMR), small-angle x-ray and neutron diffraction, as well as optical and infrared spectroscopy. PMID:9591667

  8. The HMI Magnetic Field Pipeline

    NASA Astrophysics Data System (ADS)

    Hoeksema, Jon Todd; Liu, Y.; Schou, J.; Scherrer, P.; HMI Science Team

    2009-05-01

    The Helioseismic and Magnetic Imager (HMI) will provide frequent full-disk magnetic field data after launch of the Solar Dynamics Observatory (SDO), currently scheduled for fall 2009. 16 megapixel line-of-sight magnetograms (Blos) will be recorded every 45 seconds. A full set of polarized filtergrams needed to determine the vector magnetic field requires 90 seconds. Quick-look data will be available within a few minutes of observation. Quick-look space weather and browse products must have identified users, and the list currently includes full disk magnetograms, feature identification and movies, 12-minute disambiguated vector fields in active region patches, time evolution of AR indices, synoptic synchronic frames, potential and MHD model results, and 1 AU predictions. A more complete set of definitive science data products will be offered about a day later and come in three types. "Pipeline” products, such as full disk vector magnetograms, will be computed for all data on an appropriate cadence. A larger menu of "On Demand” products, such as Non-Linear Force Free Field snapshots of an evolving active region, will be produced whenever a user wants them. Less commonly needed "On Request” products that require significant project resources, such as a high resolution MHD simulation of the global corona, will be created subject to availability of resources. Further information can be found at the SDO Joint Science Operations Center web page, jsoc.stanford.edu

  9. Explaining Mercury's peculiar magnetic field

    NASA Astrophysics Data System (ADS)

    Wicht, Johannes; Cao, Hao; Heyner, Daniel; Dietrich, Wieland; Christensen, Ulrich R.

    2014-05-01

    MESSENGER magnetometer data revealed that Mercury's magnetic field is not only particularly weak but also has a peculiar geometry. The MESSENGER team finds that the location of the magnetic equator always lies significantly north of the geographic equator, is largely independent of the distance to the planet, and also varies only weakly with longitude. The field is best described by an axial dipole that is offset to the north by about 20% of the planetary radius. In terms of classical Gauss coefficients, this translates into a low axial dipole component of g10= -190 nT but a relatively large axial quadrupole contribution that amounts to roughly 40% of this value. The axial octupole is also sizable while higher harmonic contributions are much weaker. Very remarkable is also the fact that the equatorial dipole contribution is very small, consistent with a dipole tilt below 0.8 degree, and this is also true for the other non-axisymmetic field contributions. We analyze several numerical dynamos concerning their capability of explaining Mercury's magnetic field. Classical schemes geared to model the geomagnetic field typically show a much weaker quadrupole component and thus a smaller offset. The onset only becomes larger when the dynamo operates in the multipolar regime at higher Rayleigh numbers. However, since the more complex dynamics generally promotes all higher multipole contributions the location of the magnetic equator varies strongly with longitude and distance to the planet. The situation improves when introducing a stably stratified outer layer in the dynamo region, representing either a rigid FeS layer or a sub-adiabatic core-mantle boundary heat flux. This layer filters out the higher harmonic contributions and the field not only becomes sufficiently weak but also assumes a Mercury like offset geometry during a few percent of the simulation time. To increase the likelihood for the offset configuration, the north-south symmetry must be permanently broken

  10. The susceptibility of pure tubulin to high magnetic fields: a magnetic birefringence and x-ray fiber diffraction study.

    PubMed Central

    Bras, W; Diakun, G P; Díaz, J F; Maret, G; Kramer, H; Bordas, J; Medrano, F J

    1998-01-01

    The orientational behavior of microtubules assembled in strong magnetic fields has been studied. It is shown that when microtubules are assembled in a magnetic field, they align with their long axis parallel to the magnetic field. The effect of several parameters known to affect the microtubule assembly are investigated with respect to their effect on the final degree of alignment. Aligned samples of hydrated microtubules suitable for low-resolution x-ray fiber diffraction experiments have been produced, and the results obtained from the fiber diffraction experiments have been compared with the magnetic birefringence experiments. Comparisons with earlier fiber diffraction work and small-angle x-ray solution scattering experiments have been made. PMID:9512047

  11. Electric-Field-Induced Alignment of Block Copolymer/Nanoparticle Blends

    SciTech Connect

    Liedel, Clemens; Schindler, Kerstin; Pavan, Mariela J.; Lewin, Christian; Pester, Christian W; Ruppel, Markus A; Urban, Volker S; Shenhar, Roy; Boker, Alexander

    2013-01-01

    External electric fi elds readily align birefringent block-copolymer mesophases. In this study the effect of gold nanoparticles on the electric-fi eld-induced alignment of a lamellae-forming polystyrene- block -poly(2-vinylpyridine) copolymer is assessed. Nanoparticles are homogeneously dispersed in the styrenic phase and promote the quantitative alignment of lamellar domains by substantially lowering the critical field strength above which alignment proceeds. The results suggest that the electric-fi eldassisted alignment of nanostructured block copolymer/nanoparticle composites may offer a simple way to greatly mitigate structural and orientational defects of such fi lms under benign experimental conditions.

  12. Field errors in superconducting magnets

    SciTech Connect

    Barton, M. Q.

    1982-01-01

    The mission of this workshop is a discussion of the techniques for tracking particles through arbitrary accelerator field configurations to look for dynamical effects that are suggested by various theoretical models but are not amenable to detailed analysis. A major motivation for this type of study is that many of our accelerator projects are based on the use of superconducting magnets which have field imperfections that are larger and of a more complex nature than those of conventional magnets. Questions such as resonances, uncorrectable closed orbit effects, coupling between planes, and diffusion mechanisms all assume new importance. Since, simultaneously, we are trying to do sophisticated beam manipulations such as stacking, high current accelerator, long life storage, and low loss extraction, we clearly need efficient and accurate tracking programs to proceed with confidence.

  13. DOES MAGNETIC-FIELD-ROTATION MISALIGNMENT SOLVE THE MAGNETIC BRAKING CATASTROPHE IN PROTOSTELLAR DISK FORMATION?

    SciTech Connect

    Li Zhiyun; Krasnopolsky, Ruben; Shang, Hsien

    2013-09-01

    Stars form in dense cores of molecular clouds that are observed to be significantly magnetized. In the simplest case of a laminar (non-turbulent) core with the magnetic field aligned with the rotation axis, both analytic considerations and numerical simulations have shown that the formation of a large, 10{sup 2} AU scale, rotationally supported protostellar disk is suppressed by magnetic braking in the ideal MHD limit for a realistic level of core magnetization. This theoretical difficulty in forming protostellar disks is termed the ''magnetic braking catastrophe''. A possible resolution to this problem, proposed by Hennebelle and Ciardi and Joos et al., is that misalignment between the magnetic field and rotation axis may weaken the magnetic braking enough to enable disk formation. We evaluate this possibility quantitatively through numerical simulations. We confirm the basic result of Joos et al. that the misalignment is indeed conducive to disk formation. In relatively weakly magnetized cores with dimensionless mass-to-flux ratio {approx}> 4, it enabled the formation of rotationally supported disks that would otherwise be suppressed if the magnetic field and rotation axis are aligned. For more strongly magnetized cores, disk formation remains suppressed, however, even for the maximum tilt angle of 90 Degree-Sign . If dense cores are as strongly magnetized as indicated by OH Zeeman observations (with a mean dimensionless mass-to-flux ratio {approx}2), it would be difficult for the misalignment alone to enable disk formation in the majority of them. We conclude that, while beneficial to disk formation, especially for the relatively weak field case, misalignment does not completely solve the problem of catastrophic magnetic braking in general.

  14. Does Magnetic-field-Rotation Misalignment Solve the Magnetic Braking Catastrophe in Protostellar Disk Formation?

    NASA Astrophysics Data System (ADS)

    Li, Zhi-Yun; Krasnopolsky, Ruben; Shang, Hsien

    2013-09-01

    Stars form in dense cores of molecular clouds that are observed to be significantly magnetized. In the simplest case of a laminar (non-turbulent) core with the magnetic field aligned with the rotation axis, both analytic considerations and numerical simulations have shown that the formation of a large, 102 AU scale, rotationally supported protostellar disk is suppressed by magnetic braking in the ideal MHD limit for a realistic level of core magnetization. This theoretical difficulty in forming protostellar disks is termed the "magnetic braking catastrophe." A possible resolution to this problem, proposed by Hennebelle & Ciardi and Joos et al., is that misalignment between the magnetic field and rotation axis may weaken the magnetic braking enough to enable disk formation. We evaluate this possibility quantitatively through numerical simulations. We confirm the basic result of Joos et al. that the misalignment is indeed conducive to disk formation. In relatively weakly magnetized cores with dimensionless mass-to-flux ratio >~ 4, it enabled the formation of rotationally supported disks that would otherwise be suppressed if the magnetic field and rotation axis are aligned. For more strongly magnetized cores, disk formation remains suppressed, however, even for the maximum tilt angle of 90°. If dense cores are as strongly magnetized as indicated by OH Zeeman observations (with a mean dimensionless mass-to-flux ratio ~2), it would be difficult for the misalignment alone to enable disk formation in the majority of them. We conclude that, while beneficial to disk formation, especially for the relatively weak field case, misalignment does not completely solve the problem of catastrophic magnetic braking in general.

  15. Magnetic fields for fluid motion.

    PubMed

    Weston, Melissa C; Gerner, Matthew D; Fritsch, Ingrid

    2010-05-01

    Three forces induced by magnetic fields offer unique control of fluid motion and new opportunities in microfluidics. This article describes magnetoconvective phenomena in terms of the theory and controversy, tuning by redox processes at electrodes, early-stage applications in analytical chemistry, mature applications in disciplines far afield, and future directions for micro total analysis systems. (To listen to a podcast about this article, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html .).

  16. The Role of Magnetic Fields in Structuring Clouds and Forming Stars

    NASA Astrophysics Data System (ADS)

    Li, Zhi-Yun; Chen, C.-Y.; Fissel, L.; King, P.

    2017-06-01

    I will discuss the role of magnetic fields in structuring diffuse ISM and molecular clouds and in forming stars, with emphasis on the distribution of the relative orientation between the field direction as traced by dust polarization and cloud structures and the origin of the magnetically aligned striations.

  17. Magnetic fields from domestic appliances in the UK

    NASA Astrophysics Data System (ADS)

    Preece, A. W.; Kaune, W.; Grainger, P.; Preece, S.; Golding, J.

    1997-01-01

    In a survey of 50 UK homes the 50 Hz fundamental and harmonic magnetic fields generated by 806 domestic appliances found in the homes, and used regularly by mothers, were measured. Measurements were made in the direction of most likely access, and from the surface of the appliances. Mothers completed a questionnaire on the use of appliances and were monitored for 24 h so that acquired exposure could be compared with the measured ambient fields in the home. Appliances were measured at standard distances and an algorithm was used to calculate fields at 100 and 50 cm to remove room background contributions. A few appliances generated fields in excess of ALIGN="TOP"/> at 1 m: microwave cookers ALIGN="TOP"/>; washing machines ALIGN="TOP"/>; dishwashers ALIGN="TOP"/>; some electric showers ALIGN="TOP"/> and can openers ALIGN="TOP"/>. Of continuously operating devices, only central heating pumps (ALIGN="TOP"/>), central heating boilers (ALIGN="TOP"/>) and fish-tank air pumps (ALIGN="TOP"/>) produced significant fields at 0.5 m. There were no obvious ways to group different types of appliances as high- or low-strength sources. Mothers spent on average about 4.5 h per day in the kitchen, where the strongest sources of magnetic field were located.

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

    NASA Astrophysics Data System (ADS)

    Ching, Tao-Chung; Lai, Shih-Ping; Zhang, Qizhou; Girart, Josep M.; Qiu, Keping; Liu, Hauyu B.

    2017-04-01

    We present Submillimeter Array 880 μm 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 and 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.

  19. Asymmetric field-aligned currents in the conjugate hemispheres

    NASA Astrophysics Data System (ADS)

    Reistad, J. P.; Ostgaard, N.; Oksavik, K.; Laundal, K. M.

    2012-12-01

    Earlier studies using simultaneous imaging from space of the Aurora Borealis (Northern Hemisphere) and Aurora Australis (Southern Hemisphere) have revealed that the aurora can experience a high degree of asymmetry between the two hemispheres. Using 19 hours of simultaneous global imaging from both hemispheres (IMAGE satellite in north and Polar satellite in south) in conjunction with the entire IMAGE WIC database, we investigate the importance of various mechanisms thought to generate the asymmetries seen in global imaging. In terms of asymmetric or interhemispheric field-aligned currents, three candidate mechanisms have been suggested: 1) Hemispheric differences in solar wind dynamo efficiency mainly controlled by IMF Bx leading to asymmetric region 1 currents; 2) conductivity differences in conjugate areas; and 3) penetration of IMF By into the closed magnetosphere possibly generating a pair of oppositely directed interhemispheric currents. From the 19 hour conjugate dataset we find that the solar wind dynamo is likely to be the most important controlling mechanism for asymmetric bright aurora in the polar part of the nightside oval. Here we present statistical analyses of candidates 1) and 3). Using the entire IMAGE WIC database, a statistical analysis of the auroral brightness distribution along and across the Northern Hemisphere oval is carried out. For each candidate, two extreme cases (+/- IMF Bx for 1) and +/- IMF By for 3)) are compared during times non-favorable for the other two mechanisms. Our results indicate that solar wind dynamo induced currents play an important role for the nightside auroral brightness in an average sense. Also, signatures of interhemispheric currents due to IMF By penetration are seen in our statistics, although this effect is somehow weaker.

  20. Climatology of the inter-hemispheric field-aligned currents system over the Nigeria ionosphere

    NASA Astrophysics Data System (ADS)

    Bolaji, O. S.; Rabiu, A. B.; Oyeyemi, E. O.; Yumoto, K.

    2012-11-01

    Records of the declination (D) magnetic field data for the year 2009 from the Magnetic Data Acquisition System (MAGDAS) facilities at University of Ilorin were employed for this work. From the minutes value of the D-component, the deduced hourly values of the D-component (Sq(QD)) were used to estimate its diurnal (Sq(D)) values with the most five quietest days identified. The monthly mean (MSq(D)) of the most five quietest days and their seasonal (SSq(D)) variabilities were investigated. The inter-hemispheric field aligned currents (IHFACs) exhibit downward and upward inter-hemispheric field-aligned sheet current that appears as a pair at all local times of the Sq(D), MSq(D), and SSq(D) variations. From these variabilities, the IHFACs were observed to flow from the winter to summer hemisphere during noon and dusk sector and flowing in opposite direction during the dawn sector. The Sq(D) variability patterns that were observed in May, June, August September are gentle compared to the disturbed variabilities in January, February, March and November. The highest positive (˜1.7 arc-min) and negative (˜-2.7 arc min) MSq(D) maxima values were observed in August during the dawn and noon sectors respectively. These values indicated that the IHFACs flow in August is strongly southbound (positive) and northbound (negative) in the dawn and noon sectors respectively. Dusk-side IHFACs as can be observed by MAGDAS are weakly northbound in all the seasons. The direction of IHFACs does not flip at the equinoxes but in June and November and does not become largest at solstices but in August. The IHFACs was observed to exhibit longitudinal variability, which indicated that larger amplitude of winter-to-summer IHFACs is observed to be greater in June solstice (northbound/negative IHFACs) than in the December solstice (southbound/positive IHFACs) during the noon sector.