These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Probing Primordial Magnetic Fields Using Ly? Clouds  

NASA Astrophysics Data System (ADS)

From previous studies of the effect of primordial magnetic fields on early structure formation, we know that the presence of primordial magnetic fields during early structure formation could induce more perturbations at small scales (at present 1-10 h -1 Mpc) as compared to the usual ?CDM theory. Matter power spectra over these scales are effectively probed by cosmological observables such as shear correlation and Ly? clouds. In this paper we discuss the implications of primordial magnetic fields on the distribution of Ly? clouds. We simulate the line-of-sight density fluctuation including the contribution coming from the primordial magnetic fields. We compute the evolution of Ly? opacity for this case and compare our theoretical estimates of Ly? opacity with the existing data to constrain the parameters of the primordial magnetic fields. We also discuss the case when the two density fields are correlated. Our analysis yields an upper bound of roughly 0.3-0.6 nG on the magnetic field strength for a range of nearly scale-invariant models, corresponding to a magnetic field power spectrum index n ~= -3.

Pandey, Kanhaiya L.; Sethi, Shiv K.

2013-01-01

2

Probing strong magnetic fields with cyclotron lines  

NASA Astrophysics Data System (ADS)

The physics of accretion of X-ray pulsars are dominated by very strong magnetic fields of of the order of 1012 Gauss. The only direct measure of these magnetic fields is the spectral analysis of cyclotron resonance scattering features (CRSFs). Electron CRSFs can form as broad harmonic absorption features in the keV regime when X- ray photons resonantly scatter with quantized electrons in the strongly magnetized accretion plasma. Recently, also the detection of proton CRSFs for magnetars has been claimed, rendering the basic understanding of the formation of CRSFs an important factor also for another class of fascinating extreme objects. In both cases, the line positions are directly linked to the magnetic field strength of the neutron star. Using Monte Carlo simulations, we perform a detailed study of the line shapes and positions of electron cyclotron lines of accreting neutron stars. These are indicators not only of the magnetic field strength but also give insight into the geometry of accretion, the structure of the magnetic field and gravitational effects around the compact object. For the first time ever, we have build a simulation based XSPEC model application to quantitatively compare our theoretical results to real observed source data. Recent results and their meaning for the physical picture of accreting X-ray pulsars from a comparison of the Monte Carlo Model to a set of sources are presented.

Schönherr, Gabriele; Wilms, Jörn; Kretschmar, Peter; Kreykenbohm, Ingo; Pottschmidt, Katja; Suchy, Slawo; Rothschild, Rick; Caballero, Isabel

3

Field measuring probe for SSC (Superconducting Super Collider) magnets  

SciTech Connect

The field probe developed for measuring the field in SSC dipole magnets is an adaptation of the rotating tangential coil system in use at Brookhaven for several years. Also known as the MOLE, it is a self-contained room-temperature mechanism that is pulled through the aperture of the magnet with regular stops to measure the local field. Several minutes are required to measure the field at each point. The probe measures the multipole components of the field as well as the field angle relative to gravity. The sensitivity of the coil and electronics is such that the field up to the full 6.6 T excitation of the magnet as well as the field when warm with only 0.01 T excitation can be measured. Tethers are attached to both ends of the probe to carry electrical connections and to supply dry nitrogen to the air motors that rotate the tangential windings as well as the gravity sensor. A small computer is attached to the probe for control and for data collection, analysis and storage. Digital voltmeters are used to digitize the voltages from the rotating coil and several custom circuits control motor speeds in the probe. The overall diameter of the probe is approximately 2 cm and its length is 2.4 m; the field sensitive windings are 0.6 m in length.

Ganetis, G.; Herrera, J.; Hogue, R.; Skaritka, J.; Wanderer, P.; Willen, E.

1987-03-01

4

Scattering effects of electric and magnetic field probes  

NASA Astrophysics Data System (ADS)

Many electromagnetic measurements of electromagnetic pulse (EMP) interactions with electronic systems use B-dot and D-dot probes. The effect of the measurement probe on the field distribution being measured is considered. An infrared measurement technique is used to determine the field distributions with and without the presence of electric- or magnetic-field probes. Two-dimensional thermogram images of the scattered field patterns are measured. The scattering effects of various probes in the frequency range from 1 to 10 GHz are presented. This frequency range can be used to scale-model many EMP and high-power microwave (HPM) effects. It is shown that wide variations in the response of a probe can occur due to resonant frequency and mutual-coupling effects. These effects are due, in part, to the different measurement configurations of the probe relative to the direction of propagation and polarization of the incident electromagnetic wave to be measured. These differences can be significant at certain frequencies and separation distances for the various probe measurement configurations.

Norgard, John D.; Sega, Ronald M.; Harrison, Michael; Pesta, Anthony; Seifert, Mike

1989-12-01

5

Probing the internal solar magnetic field through g-modes  

E-print Network

The observation of g-mode candidates by the SoHO mission opens the possibility of probing the internal structure of the solar radiative zone (RZ) and the solar core more directly than possible via the use of the p-mode helioseismology data. We study the effect of rotation and RZ magnetic fields on g-mode frequencies. Using a self-consistent static MHD magnetic field model we show that a 1% g-mode frequency shift with respect to the Solar Seismic Model (SSeM) prediction, currently hinted in the GOLF data, can be obtained for magnetic fields as low as 300 kG, for current measured modes of radial order n=-20. On the other hand, we also argue that a similar shift for the case of the low order g-mode candidate (l=2, n=-3) frequencies can not result from rotation effects nor from central magnetic fields, unless these exceed 8 MG.

T. I. Rashba; V. B. Semikoz; S. Turck-Chieze; J. W. F. Valle

2007-04-11

6

Characterization of magnetic force microscopy probe tip remagnetization for measurements in external in-plane magnetic fields  

SciTech Connect

A quantitative analysis of magnetic force microscopy (MFM) images taken in external in-plane magnetic fields is difficult because of the influence of the magnetic field on the magnetization state of the magnetic probe tip. We prepared calibration samples by ion bombardment induced magnetic patterning with a topographically flat magnetic pattern magnetically stable in a certain external magnetic field range for a quantitative characterization of the MFM probe tip magnetization in point-dipole approximation.

Weis, Tanja; Engel, Dieter; Ehresmann, Arno [Institute of Physics and Centre for Interdisciplinary Nanostructure Science and Technology, University of Kassel, Heinrich-Plett-Str. 40, 34132 Kassel (Germany); Krug, Ingo [DSM IRAMIS SPCSI, CEA-Saclay, 91191 Gif sur Yvette (France); Hoeink, Volker; Schmalhorst, Jan; Reiss, Guenter [Department of Physics, Thin Films and Nanostructures, Bielefeld University, P.O. Box 100131, 33501 Bielefeld (Germany)

2008-12-15

7

Modified pulsar current analysis: probing magnetic field evolution  

NASA Astrophysics Data System (ADS)

We use a modified pulsar current analysis to study magnetic field decay in radio pulsars. In our approach, we analyse the flow not along the spin period axis as has been performed in previous studies, but study the flow along the direction of growing characteristic age, ? =P/(2dot{P}). We perform extensive tests of the method and find that in most of the cases it is able to uncover non-negligible magnetic field decay (more than a few tens of per cent during the studied range of ages) in normal radio pulsars for realistic initial properties of neutron stars. However, precise determination of the magnetic field decay time-scale is not possible at present. The estimated time-scale may differ by a factor of few for different sets of initial distributions of neutron star parameters. In addition, some combinations of initial distributions and/or selection effects can also mimic enhanced field decay. We apply our method to the observed sample of radio pulsars at distances <10 kpc in the range of characteristic ages 8 × 104 < ? < 106 yr where, according to our study, selection effects are minimized. By analysing pulsars in the Parkes Multibeam and Swinburne surveys, we find that, in this range, the field decays roughly by a factor of 2. With an exponential fit, this corresponds to the decay time-scale ˜4 × 105 yr. With larger statistics and better knowledge of the initial distribution of spin periods and magnetic field strength, this method can be a powerful tool to probe magnetic field decay in neutron stars.

Igoshev, A. P.; Popov, S. B.

2014-10-01

8

Probe measurements of the three-dimensional magnetic field structure in a rotating magnetic field sustained field-reversed configuration  

SciTech Connect

A translatable three-axis probe was constructed and installed on the translation, confinement, and sustainment upgrade (TCSU) experiment. With ninety windings, the probe can simultaneously measure B{sub r}, B{sub ?}, and B{sub z} at 30 radial positions, and can be placed at any desired axial position within the field reversed configuration (FRC) confinement chamber. Positioning the probe at multiple axial positions and taking multiple repeatable shots allows for a full r-z map of the magnetic field. Measurements were made for odd-parity rotating magnetic field (RMF) antennas and even-parity RMF. The steady state data from applying a 10?kHz low pass filter used in conjunction with data at the RMF frequency yields a map of the full 3D rotating field structure. Comparisons will be made to the 3D magnetic structure predicted by NIMROD simulations, with parameters adjusted to match that of the TCSU experiments. The probe provides sufficient data to utilize a Maxwell stress tensor approach to directly measure the torque applied to the FRC's electrons, which combined with a resistive torque model, yields an estimate of the average FRC resistivity.

Velas, K. M. [William E. Boeing Department of Aeronautics and Astronautics, University of Washington, Box 352250, Seattle, Washington 98195-2250 (United States)] [William E. Boeing Department of Aeronautics and Astronautics, University of Washington, Box 352250, Seattle, Washington 98195-2250 (United States); Milroy, R. D. [Plasma Science and Innovation-Center, William E. Boeing Department of Aeronautics and Astronautics, University of Washington, Box 352250, Seattle, Washington 98195-2250 (United States)] [Plasma Science and Innovation-Center, William E. Boeing Department of Aeronautics and Astronautics, University of Washington, Box 352250, Seattle, Washington 98195-2250 (United States)

2014-01-15

9

Probing electric field control of magnetism using ferromagnetic resonance.  

PubMed

Exchange coupled CoFe/BiFeO3 thin-film heterostructures show great promise for power-efficient electric field-induced 180° magnetization switching. However, the coupling mechanism and precise qualification of the exchange coupling in CoFe/BiFeO3 heterostructures have been elusive. Here we show direct evidence for electric field control of the magnetic state in exchange coupled CoFe/BiFeO3 through electric field-dependent ferromagnetic resonance spectroscopy and nanoscale spatially resolved magnetic imaging. Scanning electron microscopy with polarization analysis images reveal the coupling of the magnetization in the CoFe layer to the canted moment in the BiFeO3 layer. Electric field-dependent ferromagnetic resonance measurements quantify the exchange coupling strength and reveal that the CoFe magnetization is directly and reversibly modulated by the applied electric field through a ~180° switching of the canted moment in BiFeO3. This constitutes an important step towards robust repeatable and non-volatile voltage-induced 180° magnetization switching in thin-film multiferroic heterostructures and tunable RF/microwave devices. PMID:25631924

Zhou, Ziyao; Trassin, Morgan; Gao, Ya; Gao, Yuan; Qiu, Diana; Ashraf, Khalid; Nan, Tianxiang; Yang, Xi; Bowden, S R; Pierce, D T; Stiles, M D; Unguris, J; Liu, Ming; Howe, Brandon M; Brown, Gail J; Salahuddin, S; Ramesh, R; Sun, Nian X

2015-01-01

10

Probing Mars Crustal Magnetic Field and Ionosphere with the MGS Electron Reflectometer  

NASA Technical Reports Server (NTRS)

MGS Electron Reflectometer data are used to probe the shape and variability of Mars ionosphere and to identify weak crustal magnetic fields within the Hellas basin. Additional information is contained in the original extended abstract.

Mitchell, D. L.; Lin, R. P.; Reme, H.; Cloutier, P. A.; Connerney, J. E. P.; Acuna, M. H.; Ness, N. F.

2002-01-01

11

Probing correlations of early magnetic fields using mu-distortion  

E-print Network

The damping of a non-uniform magnetic field between the redshifts of about $10^4$ and $10^6$ injects energy into the photon-baryon plasma and causes the CMB to deviate from a perfect blackbody spectrum, producing a so-called $\\mu$-distortion. We can calculate the correlation $\\langle\\mu T\\rangle$ of this distortion with the temperature anisotropy $T$ of the CMB to search for a correlation $\\langle B^2\\zeta\\rangle$ between the magnetic field $B$ and the curvature perturbation $\\zeta$; knowing the $\\langle B^2\\zeta\\rangle$ correlation would help us distinguish between different models of magnetogenesis. Since the perturbations which produce the $\\mu$-distortion will be much smaller scale than the relevant density perturbations, the observation of this correlation is sensitive to the squeezed limit of $\\langle B^2\\zeta\\rangle$, which is naturally parameterized by $b_{\\text{NL}}$ (a parameter defined analogously to $f_{\\text{NL}}$). We find that a PIXIE-like CMB experiments has a signal to noise $S/N\\approx 1.0 \\times b_{\\text{NL}} (\\tilde B_\\mu/10\\text{ nG})^2$, where $\\tilde B_\\mu$ is the magnetic field's strength on $\\mu$-distortion scales normalized to today's redshift; thus, a 10 nG field would be detectable with $b_{\\text{NL}}=\\mathcal{O}(1)$. However, if the field is of inflationary origin, we generically expect it to be accompanied by a curvature bispectrum $\\langle\\zeta^3\\rangle$ induced by the magnetic field. For sufficiently small magnetic fields, the signal $\\langle B^2 \\zeta\\rangle$ will dominate, but for $\\tilde B_\\mu\\gtrsim 1$ nG, one would have to consider the specifics of the inflationary magnetogenesis model. We also discuss the potential post-magnetogenesis sources of a $\\langle B^2\\zeta\\rangle$ correlation and explain why there will be no contribution from the evolution of the magnetic field in response to the curvature perturbation.

Jonathan Ganc; Martin S. Sloth

2014-04-23

12

Magnetic Field Measurement in an Electromagnetic Shock Tube Using Large Area Probes  

Microsoft Academic Search

We examine the problem of measuring with a probe the magnetic field in a plasma which is moving with respect to the probe. It is shown that integration with respect to time is, in general, not proper and we develop correct expressions for the case of a current conducting plasma produced by a strong ionizing shock wave in an electromagnetically

Bennett Miller

1966-01-01

13

Radial magnetic field measurements with a Hall probe device in the muon (g-2) storage ring magnet at BNL  

Microsoft Academic Search

A Hall probe device has been built to measure the radial component of the magnetic field in the muon (g-2) storage ring at Brookhaven National Laboratory. The ultraprecise (g-2) magnet provides a dominantly vertical magnetic field of about 1.45T. In order to limit the vertical shift of the muon orbit, the average radial field component should be no more than

S. I. Redin; N. M. Ryskulov; G. V. Fedotovich; B. I. Khazin; G. M. Bunce; G. T. Danby; J. W. Jackson; W. M. Morse; R. Prigl; Y. K. Semertzidis; E. Efstathiadis; B. L. Roberts; A. Grossmann; K. Jungmann; G. zu Putlitz; P. von Walter; S. K. Dhawan; F. J. M. Farley; M. Grosse-Perdekamp; V. W. Hughes; D. Kawall

2001-01-01

14

Nanoscale magnetic field mapping with a single spin scanning probe magnetometer  

SciTech Connect

We demonstrate quantitative magnetic field mapping with nanoscale resolution, by applying a lock-in technique on the electron spin resonance frequency of a single nitrogen-vacancy defect placed at the apex of an atomic force microscope tip. In addition, we report an all-optical magnetic imaging technique which is sensitive to large off-axis magnetic fields, thus extending the operation range of diamond-based magnetometry. Both techniques are illustrated by using a magnetic hard disk as a test sample. Owing to the non-perturbing and quantitative nature of the magnetic probe, this work should open up numerous perspectives in nanomagnetism and spintronics.

Rondin, L.; Tetienne, J.-P.; Spinicelli, P.; Roch, J.-F.; Jacques, V. [Laboratoire de Photonique Quantique et Moleculaire, Ecole Normale Superieure de Cachan and CNRS UMR 8537, 94235 Cachan Cedex (France); Dal Savio, C.; Karrai, K. [Attocube systems AG, Koeniginstrasse 11A RGB, Munich 80539 (Germany); Dantelle, G. [Laboratoire de Physique de la Matiere Condensee, Ecole Polytechnique and CNRS UMR 7643, 91128 Palaiseau (France); Thiaville, A.; Rohart, S. [Laboratoire de Physique des Solides, Universite Paris-Sud and CNRS UMR 8502, 91405 Orsay (France)

2012-04-09

15

Probing Mars' crustal magnetic field and ionosphere with the MGS Electron Reflectometer  

Microsoft Academic Search

The Electron Reflectometer (ER) on board Mars Global Surveyor measures the energy and angular distributions of solar wind electrons and ionospheric photoelectrons. These data can be used in conjunction with magnetometer data to probe Mars' crustal magnetic field and to study Mars' ionosphere and solar wind interaction. During aerobraking, ionospheric measurements were obtained in the northern hemisphere at high solar

R. P. Lin; C. Mazelle; H. Rème; P. A. Cloutier; J. E. P. Connerney; M. H. Acuña; N. F. Ness

2001-01-01

16

Primary processing of magnetic field data aboard a space probe  

Microsoft Academic Search

The real-time processing of magnetometric data on a space probe is examined. The design and components of the three-component vector magnetometer used in this study are discussed. The on-board computer used to digitize the three signal components consists of: a processor; memory; and input, control, calibration, time, output, and interrupt ports. The functions of these components and the tasks of

D. Lenners; H. J. Linthe

1987-01-01

17

Rotating field eddy current probe for characterization of cracking in non-magnetic tubing  

SciTech Connect

A rotating field eddy current probe was built and tested for use in small diameter, non-magnetic tubing. The rotating field probe is a driver/pickup style with two orthogonally wound drive coils and a pancake pickup coil. The driver coils are excited by two sine waves 90{degree} out of phase with each other. The physical arrangement of the drive coils and the 90{degree} phase shift of the excitation waveforms creates a field which rotates in the test piece under the drive coils. Preliminary tests on electrical discharge machined (EDM) notches show that phased based estimates of notch depth are possible. Probes currently used for detection of cracks in tubing produce responses that have proven unreliable for estimating defect depths. This recently developed version of the rotating field eddy current probe produces a bipolar response in the presence of a crack or a notch. Typically, the phase angle of a bipolar eddy current response is easily identified and measured and is used extensively for estimating depths of volumetric defects. Data are shown relating the phase angle of the rotating field probe`s bipolar response to the depth of circumferential EDM notches.

Capobianco, T.E. [Lockheed Martin, Schenectady, NY (United States)

1998-07-01

18

Magnetic testing probe  

SciTech Connect

A cylindrical eddy current tube testing probe is disclosed. Current flow in dual electromagnetic coils separated by an eddy current sensing coil is so directed that magnetic fields of the electromagnet coils have components extending in opposite directions axially of the tested tube and components extending radially of the tube which add in the region of the eddy current sensing coil.

Scott, G.W.; Chitwood, L.D.

1981-07-07

19

Magnetically driven filament probe.  

PubMed

A radially movable probe has been developed for studies of filamentary transport in ASDEX Upgrade during edge localized modes (ELMs) by means of Langmuir tips and magnetic pickup coils. The probe is permanently installed at the low field side in the ASDEX Upgrade vacuum vessel and is not subject to limitations in probe size, as, for example, probes on a shared manipulator are. The probe is moved by a magnetic drive, which allows for easy installation in the vessel, and has moderate machine requirements, as it will only require an electric feedthrough and an external power supply. The drive gives a linear motion with a radial range of 5 cm within 50 ms, where range and velocity can be largely scaled according to experimental requirements. The probe has been installed in the outer midplane of the ASDEX Upgrade vessel, where ELM filaments are expected to have their maximum amplitude. Filaments are coherent substructures within an ELM, carrying a fraction of the ELM released energy towards the wall. The new probe allows to measure the structure of these filaments, in particular, parameters such as filament rotation (by time delay measurements) and size (by peak width analysis). Activating the drive moves the probe from a safe position behind the limiter to a position in front of the limiters, i.e., exposes the Langmuir pins to the scrape-off layer plasma. PMID:17552815

Schmid, A; Herrmann, A; Rohde, V; Maraschek, M; Müller, H W

2007-05-01

20

Lobe crossing events observed by the Van Allen Probes as tests of magnetic field line mapping  

NASA Astrophysics Data System (ADS)

In this paper we examine a series of lobe crossing events witnessed by the twin Van Allen Probes spacecraft between 0200 and 0515 on November 14th 2012. The events occurred on the flank between 0400 and 0635 local time and at altitudes between 5.6 and 6.2 RE. During the events Dst was less than 100nT with the IMF being strongly southward (Bz = - 15nT) and eastward (By = 20 nT). Other observations at geosynchronous orbit also show lobe crossings at dawn and dusk flanks. These events provide a chance to examine the magnetic field topology in detail and compare it with models. We will show that the spacecraft were in locations with access to the open field lines by comparison to the CRCM + BATS-RUS models as well as comparing spacecraft encounters with the lobe to the predicted magnetic field topology.

Dixon, P.; MacDonald, E.; Grande, M.; Glocer, A.

2014-04-01

21

Probing the Solar Magnetic Field with a Sun-Grazing Comet  

NASA Astrophysics Data System (ADS)

On 15 and 16 December 2011, Sun-grazing comet C/2011 W3 (Lovejoy) passed deep within the solar corona, effectively probing a region that has never been visited by spacecraft. Imaged from multiple perspectives, extreme ultraviolet observations of Lovejoy's tail showed substantial changes in direction, intensity, magnitude, and persistence. To understand this unique signature, we combined a state-of-the-art magnetohydrodynamic model of the solar corona and a model for the motion of emitting cometary tail ions in an embedded plasma. The observed tail motions reveal the inhomogeneous magnetic field of the solar corona. We show how these motions constrain field and plasma properties along the trajectory, and how they can be used to meaningfully distinguish between two classes of magnetic field models.

Downs, Cooper; Linker, Jon A.; Miki?, Zoran; Riley, Pete; Schrijver, Carolus J.; Saint-Hilaire, Pascal

2013-06-01

22

Probing the solar magnetic field with a Sun-grazing comet.  

PubMed

On 15 and 16 December 2011, Sun-grazing comet C/2011 W3 (Lovejoy) passed deep within the solar corona, effectively probing a region that has never been visited by spacecraft. Imaged from multiple perspectives, extreme ultraviolet observations of Lovejoy's tail showed substantial changes in direction, intensity, magnitude, and persistence. To understand this unique signature, we combined a state-of-the-art magnetohydrodynamic model of the solar corona and a model for the motion of emitting cometary tail ions in an embedded plasma. The observed tail motions reveal the inhomogeneous magnetic field of the solar corona. We show how these motions constrain field and plasma properties along the trajectory, and how they can be used to meaningfully distinguish between two classes of magnetic field models. PMID:23744941

Downs, Cooper; Linker, Jon A; Mikií, Zoran; Riley, Pete; Schrijver, Carolus J; Saint-Hilaire, Pascal

2013-06-01

23

Use of Langmuir probes in a weakly ionized, steady-state plasma with strong magnetic field  

SciTech Connect

This article describes the use of Langmuir probes to measure plasma parameters in low density, low temperature plasmas with a strong applied magnetic field. The experiment has been performed at the Physics Department of Milan{close_quote}s University on the steady-state toroidal machine {open_quotes}Thorello.{close_quotes} Results have been analyzed by taking into account instrumental and ionic sheath effects. Finally, experimental results have been compared with direct measurements of the electron distribution function in Thorello. {copyright} {ital 1997 American Institute of Physics.}

Batani, D.; Alba, S.; Lombardi, P.; Galassi, A. [Dipartimento di Fisica, Universita di Milano, and Istituto Nazionale di Fisica della Materia, Unita di Milano, Via Celoria 16, 20133 Milano (Italy)] [Dipartimento di Fisica, Universita di Milano, and Istituto Nazionale di Fisica della Materia, Unita di Milano, Via Celoria 16, 20133 Milano (Italy)

1997-11-01

24

Probing the Solar Magnetic Field With a Sun-Grazing Comet  

NASA Astrophysics Data System (ADS)

Observations of comets occupy a rich history within Solar and Heliospheric science. Cometary plasma tails probe the solar wind in the inner solar system 0.5-3 AU) and their observations led to its discovery more than half a century ago. Fast forwarding to today, recent observations of sun-grazing comets within the solar corona have opened up a whole new avenue to study the Sun with these striking celestial bodies. Here we present our recent study of the perihelion passage of comet C/2011 W3 (Lovejoy), which came within 140Mm of the solar surface. Imaged from multiple perspectives by SDO/AIA and the STEREO/EUVI, extreme ultraviolet (EUV) observations of Lovejoy's tail showed substantial changes in direction, intensity, magnitude, and persistence. To understand this unique signature, we combine a state-of-the-art magnetohydrodynamic (MHD) model of the solar corona and a prescription for the motion of emitting cometary tail ions in an embedded plasma. We show how the observed tail motions reveal the inhomogeneous magnetic field of the solar corona, and demonstrate how they constrain field and plasma properties in a region where the coronal plasma is normally not easily observed in EUV. We will also discuss our results in context of the upcoming perihelion passage of comet C/2012 S1 (ISON), expected by many to be a spectacular probe of the near-sun environment. Work supported by NASA and NSF.

Downs, Cooper; Linker, J. A.; Mikic, Z.; Riley, P.; Schrijver, C. J.; Saint-Hilaire, P.

2013-07-01

25

Probing the Intergalactic Magnetic Field with the Anisotropy of the Extragalactic Gamma-ray Background  

NASA Technical Reports Server (NTRS)

The intergalactic magnetic field (IGMF) may leave an imprint on the angular anisotropy of the extragalactic gamma-ray background through its effect on electromagnetic cascades triggered by interactions between very high energy photons and the extragalactic background light. A strong IGMF will deflect secondary particles produced in these cascades and will thus tend to isotropize lower energy cascade photons, thereby inducing a modulation in the anisotropy energy spectrum of the gamma-ray background. Here we present a simple, proof-of-concept calculation of the magnitude of this effect and demonstrate that current Fermi data already seem to prefer nonnegligible IGMF values. The anisotropy energy spectrum of the Fermi gamma-ray background could thus be used as a probe of the IGMF strength.

Venters, T. M.; Pavlidou, V.

2013-01-01

26

Spin dynamics in a diluted magnetic semiconductor quantum well studied by pump-probe absorption spectroscopy: Magnetic-field-induced suppression of electron-spin relaxation  

Microsoft Academic Search

Exciton spin dynamics is studied in a diluted magnetic semiconductor quantum well of Cd0.95Mn0.05Te by pump-probe absorption spectroscopy under magnetic fields. The time dependences of the saturated absorbance for the higher- and lower-energy spin states of heavy-hole (hh) excitons clarify the following exciton-spin relaxation process in magnetic fields: ultrafast hh-spin relaxation with the formation of dark excitons and subsequent electron-spin

A. Murayama; K. Seo; K. Nishibayashi; I. Souma; Y. Oka

2006-01-01

27

Relaxation of quasi-two-dimensional electrons in a quantizing magnetic field probed by time-resolved cyclotron resonance  

E-print Network

resonance of photogenerated transient carriers in undoped InSb/Al0.09In0.91Sb quantum wells by two-color pump-probe spectroscopy in a magnetic field. The strong conduction-band nonparabolicity of InSb causes study of photogenerated electrons in undoped InSb quantum wells QW's . TRCR is a recently developed

Kono, Junichiro

28

Probing Mars' crustal magnetic field and ionosphere with the MGS Electron Reflectometer  

Microsoft Academic Search

Mars' magnetic field is dominated by remanent magnetization of the crust, which is distributed non-uniformly over the surface. In the northern hemisphere, crustal magnetic fields are so weak that the solar wind interacts directly with the atmosphere and ionosphere in a manner similar to Venus and active comets. The Electron R flectometer (ER) onboard Mars Global Surveyor (MGS) detected ae

D. Mitchell; R. Lin; C. Lee; S. Chou; H. Reme; P. Cloutier; J. Connerney; M. Acuna; N. Ness

2002-01-01

29

Thermonuclear Supernovae: Probing Magnetic Fields by Positrons and Late-time IR Line Profiles  

NASA Astrophysics Data System (ADS)

We show the importance of ? and positron transport for the formation of late-time spectra in Type Ia supernovae (SNe Ia). The goal is to study the imprint of magnetic fields (B) on late-time IR line profiles, particularly the [Fe II] feature at 1.644 ?m, which becomes prominent two to three months after the explosion. As a benchmark, we use the explosion of a Chandrasekhar mass (M Ch) white dwarf (WD) and, specifically, a delayed detonation model that can reproduce the light curves and spectra for a Branch-normal SN Ia. We assume WDs with initial magnetic surface fields between 1 and 109 G. We discuss large-scale dipole and small-scale magnetic fields. We show that positron transport effects must be taken into account for the interpretation of emission features starting at about one to two years after maximum light, depending on the size of B. The [Fe II] line profile and its evolution with time can be understood in terms of the overall energy input by radioactive decay and the transition from a ?-ray to a positron-dominated regime. We find that the [Fe II] line at 1.644 ?m can be used to analyze the overall chemical and density structure of the exploding WD up to day 200 without considering B. At later times, positron transport and magnetic field effects become important. After about day 300, the line profile allows one to probe the size of the B-field. The profile becomes sensitive to the morphology of B at about day 500. In the presence of a large-scale dipole field, a broad line is produced in M Ch mass explosions that may appear flat-topped or rounded depending on the inclination at which the SN is observed. Small or no directional dependence of the spectra is found for small-scale B. We note that narrow-line profiles require central 56Ni as shown in our previous studies. Persistent broad-line, flat-topped profiles require high-density burning, which is the signature of a WD close to M Ch. Good time coverage is required to separate the effects of optical depth, the size and morphology of B, and the aspect angle of the observer. The spectra require a resolution of about 500 km s-1 and a signal-to-noise ratio of about 20%. Two other strong near-IR spectral features at about 1.5 and 1.8 ?m are used to demonstrate the importance of line blending, which may invalidate a kinematic interpretation of emission lines. Flat-topped line profiles between 300 and 400 days have been observed and reported in the literature. They lend support for M Ch mass explosions in at least some cases and require magnetic fields equal to or in excess of 106 G. We briefly discuss the effects of the size and morphology of B on light curves, as well as limitations. We argue that line profiles are a more direct measurement of B than light curves because they measure both the distribution of 56Ni and the redistribution of the energy input by positrons rather than the total energy input. Finally, we discuss possible mechanisms for the formation of high B-fields and the limitations of our analysis.

Penney, R.; Hoeflich, P.

2014-11-01

30

Using the morphology and magnetic fields of tailed radio galaxies as environmental probes  

E-print Network

Bent-tailed (BT) radio sources have long been known to trace over densities in the Universe up to z ~ 1 and there is increasing evidence this association persists out to redshifts of 2. The morphology of the jets in BT galaxies is primarily a function of the environment that they have resided in and so BTs provide invaluable clues as to their local conditions. Thus, not only can samples of BT galaxies be used as signposts of large-scale structure, but are also valuable for obtaining a statistical measurement of properties of the intra-cluster medium including the presence of cluster accretion shocks & winds, and as historical anemometers, preserving the dynamical history of their surroundings in their jets. We discuss the use of BTs to unveil large-scale structure and provide an example in which a BT was used to unlock the dynamical history of its host cluster. In addition to their use as density and dynamical indicators, BTs are useful probes of the magnetic field on their environment on scales which are...

Johnston-Hollitt, M; Pratley, L

2014-01-01

31

Proton probe measurement of fast advection of magnetic fields by hot electrons  

NASA Astrophysics Data System (ADS)

A laser generated proton beam was used to measure the megagauss strength self-generated magnetic fields from a nanosecond laser interaction with an aluminum target. At intensities of 1015 W cm-2, the significant hot electron production and strong heat fluxes result in non-local transport becoming important to describe the magnetic field dynamics. Two-dimensional implicit Vlasov-Fokker-Planck modeling shows that fast advection of the magnetic field from the focal region occurs via the Nernst effect at significantly higher velocities than the sound speed, vN/cs ? 10.

Willingale, L.; Thomas, A. G. R.; Nilson, P. M.; Kaluza, M. C.; Bandyopadhyay, S.; Dangor, A. E.; Evans, R. G.; Fernandes, P.; Haines, M. G.; Kamperidis, C.; Kingham, R. J.; Minardi, S.; Notley, M.; Ridgers, C. P.; Rozmus, W.; Sherlock, M.; Tatarakis, M.; Wei, M. S.; Najmudin, Z.; Krushelnick, K.

2011-12-01

32

Magnetic field effects on spectrally resolved lifetime of on-line oxygen monitoring using magneto-optic probes  

NASA Astrophysics Data System (ADS)

Multimodal agents that serve as both probes for contrast and light-activated effectors of cellular processes in diseased tissue were developed. These agents were introduced into multicellular tumor spheroids (3D tissue models) and in the chorioallantoic membrane (CAM) of a chicken embryo. The luminescence decay was examined using a novel technique involving a spectrally-resolved fluorescence lifetime apparatus integrated with a weak electromagnet. A spectrallyresolved lifetime setup was used to identify magneto-optic species sensitive to magnetic field effects and distinguish from background emissions. We demonstrate that the applied magnetic fields can alter reaction rates and product distribution of some dyes detected by time- and spectrally-resolved luminescence changes. We will discuss the use of exogenous magneto-optical probes taken up in tumors to both induce phototoxicity, a process that is governed by complex and dynamically evolving mechanisms involving reactive oxygen species, and monitor treatment progress. The magnetic field enhancement, measured over a range of weak fields (0-300 mT) is correlated to oxygenation and may be used to monitor dynamic changes occurring due to oxygen consumption over the course of photodynamic therapy. Such online measurements provide the possibility to derive real-time information about response to treatment via monitoring magnetic field enhancement/suppression of the time-resolved, spectrally-resolved luminescence of the probe at the site of the treatment directly. Magnetic perturbation of lifetime can serve as a status reporter, providing optical feedback of oxygen-mediated treatments in situ and allowing for real-time adjustment of a phototherapy treatment plan.

Mermut, O.; Gallant, P.; Le Bouch, N.; Leclair, S.; Noiseux, I.; Vernon, M.; Morin, J.-F.; Diamond, K.; Patterson, M. S.; Samkoe, K.; Pogue, B.

2009-02-01

33

Chiral Symmetry Breaking: To Probe Anisotropy and Magnetic Field in QGP  

E-print Network

We discuss the (spontaneous) chiral symmetry breaking in a strongly coupled anisotropic quark-gluon plasma (QGP) in the presence of the magnetic field, using holography. The physical quantities related to the chiral symmetry breaking (m;B_c) distinguish between the effects of the anisotropy and magnetic field on the plasma. Anisotropy affects the system similar to the temperature and for its larger values heavier quarks can live in the QGP without getting condensed. Raising the anisotropy in the system will also increase the value of the critical magnetic field, B_c, at which the spontaneous chiral symmetry breaking happens. Both of these growths are even more when the magnetic field is applied perpendicular to the anisotropy direction. Such behaviour persists in the high temperature limit where the temperature is kept fixed. However, when the entropy density is held fixed, as one increases the anisotropy, lighter mesons melt when the magnetic field is applied along the anisotropy direction, in contrast to when the magnetic field is perpendicular to the anisotropy direction.

Mohammad Ali-Akbari; Hajar Ebrahim

2014-03-08

34

Chiral symmetry breaking: To probe anisotropy and magnetic field in quark-gluon plasma  

NASA Astrophysics Data System (ADS)

We discuss the (spontaneous) chiral symmetry breaking in a strongly coupled anisotropic quark-gluon plasma (QGP) in the presence of the magnetic field, using holography. The physical quantities related to the chiral symmetry breaking (m ,Bc) distinguish between the effects of the anisotropy and magnetic field on the plasma. Anisotropy affects the system similar to the temperature and for its larger values heavier quarks can live in the QGP without getting condensed. Raising the anisotropy in the system will also increase the value of the critical magnetic field, Bc, at which the spontaneous chiral symmetry breaking happens. Both of these growths are even more when the magnetic field is applied perpendicular to the anisotropy direction. Such behavior persists in the high temperature limit where the temperature is kept fixed. However, when the entropy density is held fixed, as one increases the anisotropy, lighter mesons melt when the magnetic field is applied along the anisotropy direction, in contrast to when the magnetic field is perpendicular to the anisotropy direction.

Ali-Akbari, Mohammad; Ebrahim, Hajar

2014-03-01

35

Plasma resonance at low magnetic fields as a probe of vortex line meandering in layered superconductors  

E-print Network

We consider the magnetic field dependence of the plasma resonance frequency in pristine and in irradiated Bi$_2$Sr$_2$CaCu$_2$O$_8$ crystals near $T_c$. At low magnetic fields we relate linear in field corrections to the plasma frequency to the average distance between the pancake vortices in the neighboring layers (wandering length). We calculate the wandering length in the case of thermal wiggling of vortex lines, taking into account both Josephson and magnetic interlayer coupling of pancakes. Analyzing experimental data, we found that (i) the wandering length becomes comparable with the London penetration depth near T$_{c}$ and (ii) at small melting fields ($plasma resonance frequency near $T_c$.

L. N. Bulaevskii; A. E. Koshelev; V. M. Vinokur; M. P. Maley

1999-12-19

36

Magnetic Fields  

E-print Network

In this chapter, we give a brief introduction into the use of the Zeeman effect in astronomy and the general detection of magnetic fields in stars, concentrating on the use of FORS2 for longitudinal magnetic field measurements.

Schöller, Markus

2015-01-01

37

The Electric and Magnetic Field Instrument Suite with Integrated Science (EMFISIS) on the Radiation Belt Storm Probes  

NASA Astrophysics Data System (ADS)

The physics of the creation and loss of radiation belt particles is intimately connected to the electric and magnetic fields which mediate these processes. A large range of field dynamics and time scales are involved in this physics from ring current magnetic fields to microscopic kinetic interactions such as whistler-mode chorus waves with energetic electrons. To measure these key field interactions, NASA has selected the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on the Radiation Belt Storm Probes (RBSP). EMFISIS is an integrated set of instruments consisting of a tri-axial fluxgate magnetometer (MAG) and a Waves instrument which includes a tri-axial search coil magnetometer and measures AC electric and magnetic fields from 10 Hz to MHz frequencies. The broad frequency range of the Waves instrument enables the identification of resonances and cutoffs from Waves to achieve high cadence, accurate plasma density measurements that are essential to RBSP theory and modeling efforts. The instruments are integrated through a Central Data Processor Unit (CDPU) which provides for flexible instrument operations in both burst and survey telemetry modes that can be optimized to address the specific physics of the many radiation belt processes. The EMFISIS multi-institution team comprises a group of knowledgeable space physics investigators, both experimental and theoretical, with the requisite capability, desire, and experience to accomplish the goals of the RBSP mission to further our nation's space weather capability. In combination with the selected double probe electric field and particle investigations on RBSP, EMFISIS will provide the essential measurements necessary to open the frontier of predictive capability for the Earth's highly variable radiation belts.

Kletzing, C. A.; Kurth, W.; Acuna, M.; Torbert, R.; Thorne, R.; Jordanova, V.; Bounds, S.; Smith, C.; Santolik, O.; Pfaff, R.; Rowland, D.; Hospodarsky, G.; Baumjohann, W.; Nakamura, R.; Puhl-Quinn, P.

2006-12-01

38

Measurements of solar irradiance and effective temperature as a probe of solar interior magnetic fields  

E-print Network

We argue that a variety of solar data suggest that the activity-cycle timescale variability of the total irradiance, is produced by structural adjustments of the solar interior. Assuming these adjustments are induced by variations of internal magnetic fields, we use measurements of the total irradiance and effective temperature over the period from 1978 to 1992, to infer the magnitude and location of the magnetic field. Using an updated stellar evolution model, which includes magnetic fields, we find that the observations can be explained by fields whose peak values range from 120k to 2.3k gauss, located in the convection zone between $0.959R_{\\sun}$ and $0.997R_{\\sun}$, respectively. The corresponding maximal radius changes, are 17 km when the magnetic field is located at $0.959R_{\\sun}$ and 3 km when it is located at $0.997R_{\\sun}$. At these depths, the $W$ parameter(defined by $\\Delta \\ln R / \\Delta \\ln L$, where $R$ and $L$ are the radius and luminosity) ranges from 0.02 to 0.006. All these predictions are consistent with helioseismology and recent measurements carried out by the MDI experiment on SOHO.

L. H. Li; S. Sofia

2000-10-20

39

Local magnetic probes of superconductors  

NASA Astrophysics Data System (ADS)

Investigations of the magnetic properties of high temperature superconductors (HTSs) have revealed the existence of striking new vortex phenomena due, in part, to their strong crystalline anisotropy, very short coherence lengths and the much larger thermal energies available at high temperatures. Some of these phenomena, for example vortex lattice 'melting', pose serious problems for technological applications of the most anisotropic HTS materials and a fuller understanding of them is of considerable importance. The most direct information regarding vortex structures and dynamics is obtained through local measurement of the magnetic field within or at the surface of a superconducting sample. A detailed review of such local magnetic probes is presented here including Lorentz microscopy, magnetic force microscopy, Bitter decoration, scanning Hall probe microscopy, magneto-optical imaging, and scanning superconducting quantum interference device microscopy. In each case the principles underpinning the technique are described together with the factors that limit the magnetic field and the spatial and temporal resolution. A range of examples will be given, emphasizing applications in the area of HTSs. In addition the ways in which the existing techniques can be expected to develop over the next few years will be discussed and new approaches that seem likely to be successful described.

Bending, Simon J.

1999-07-01

40

THE INTERPLANETARY MAGNETIC FIELD  

Microsoft Academic Search

A new analysis of magnetic and concurrent plasma data collected from the ; space probes Pionecr 5, Explorer 10, and Mariner 2 yields a new model of the ; interplanetary magnetic field. It is hypothesized that the observed ; interplanetary field F\\/sub i\\/ is due to motion of the magnetometer relative to a ; negatively charged rotating sun from which

V. A. BAILEY

1963-01-01

41

Quantum oscillations as a probe of interaction effects in Weyl semimetals in a magnetic field  

E-print Network

The Weyl semimetal surface is modeled by applying the Bogolyubov boundary conditions, in which the quasiparticles have an infinite Dirac mass outside the semimetal. For a Weyl semimetal shaped as a slab of finite thickness, we derive an exact spectral equation for the quasiparticle states and obtain the spectrum of the bulk as well as surface Fermi arc modes. We also show that, in the presence of the magnetic field, the separation between Weyl nodes in momentum space and the length of the Fermi arcs in the reciprocal space are affected by the interactions. As a result, we find that the period of oscillations of the density of states related to closed magnetic orbits involving Fermi arcs has a nontrivial dependence on the orientation of the magnetic field projection in the plane of the semimetal surface. We conclude that the momentum space separation between Weyl nodes and its modification due the interaction effects in the magnetic field can be measured in the experimental studies of quantum oscillations.

E. V. Gorbar; V. A. Miransky; I. A. Shovkovy; P. O. Sukhachov

2014-09-18

42

Quantum oscillations as a probe of interaction effects in Weyl semimetals in a magnetic field  

NASA Astrophysics Data System (ADS)

The Weyl semimetal surface is modeled by applying the Bogolyubov boundary conditions, in which the quasiparticles have an infinite Dirac mass outside the semimetal. For a Weyl semimetal shaped as a slab of finite thickness, we derive an exact spectral equation for the quasiparticle states and obtain the spectrum of the bulk as well as surface Fermi arc modes. We also show that, in the presence of the magnetic field, the separation between Weyl nodes in momentum space and the length of the Fermi arcs in the reciprocal space are affected by the interactions. As a result, we find that the period of oscillations of the density of states related to closed magnetic orbits involving Fermi arcs has a nontrivial dependence on the orientation of the magnetic field projection in the plane of the semimetal surface. We conclude that the momentum-space separation between Weyl nodes and its modification due the interaction effects in the magnetic field can be measured in the experimental studies of quantum oscillations.

Gorbar, E. V.; Miransky, V. A.; Shovkovy, I. A.; Sukhachov, P. O.

2014-09-01

43

A biased probe analysis of potential well formation in an electron only, low beta Polywell magnetic field  

SciTech Connect

Orbital limited motion theory has been applied to two biased probes in a low beta Polywell. The cases studied include electron injection, magnetic field scaling, Polywell bias scaling, and radial position profiles. Langmuir's original orbital limited motion results for a monoenergetic electron beam are shown to be in excellent agreement for electron injection into the Polywell. A distribution function is proposed for the electron plasma characteristics in the centre of the magnetic null and confirmed with experimental results. A translational stage was used to measure the radial plasma potential profile. In other experiments, two probes were used to simultaneously measure the profiles in both the null and a position halfway along a corner cusp. The results confirm a radial potential well created by electron trapping in the device. In addition, we present preliminary results of the potential well scaling with the magnetic field, Polywell bias voltage, and the injected beam current. The electron population was found to maintain non-equilibrium in all cases studied.

Carr, Matthew; Khachan, Joe [Department of Plasma Physics, School of Physics A28, University of Sydney NSW 2006 (Australia)] [Department of Plasma Physics, School of Physics A28, University of Sydney NSW 2006 (Australia)

2013-05-15

44

A biased probe analysis of potential well formation in an electron only, low beta Polywell magnetic field  

NASA Astrophysics Data System (ADS)

Orbital limited motion theory has been applied to two biased probes in a low beta Polywell. The cases studied include electron injection, magnetic field scaling, Polywell bias scaling, and radial position profiles. Langmuir's original orbital limited motion results for a monoenergetic electron beam are shown to be in excellent agreement for electron injection into the Polywell. A distribution function is proposed for the electron plasma characteristics in the centre of the magnetic null and confirmed with experimental results. A translational stage was used to measure the radial plasma potential profile. In other experiments, two probes were used to simultaneously measure the profiles in both the null and a position halfway along a corner cusp. The results confirm a radial potential well created by electron trapping in the device. In addition, we present preliminary results of the potential well scaling with the magnetic field, Polywell bias voltage, and the injected beam current. The electron population was found to maintain non-equilibrium in all cases studied.

Carr, Matthew; Khachan, Joe

2013-05-01

45

Using Tailed Radio Galaxies to Probe the Environment and Magnetic Field of Galaxy Clusters in the SKA Era  

E-print Network

The morphology of tailed radio galaxies is an invaluable source of environmental information, in which a history of the past interactions in the intra-cluster medium, such as complex galaxy motions and cluster merger shocks, are preserved. In recent years, the use of tailed radio galaxies as environmental probes has gained momentum as a method for galaxy cluster detection, examining the dynamics of individual clusters, measuring the density and velocity flows in the intra-cluster medium, and for probing cluster magnetic fields. To date instrumental limitations in terms of resolution and sensitivity have confined this research to the local (z 50,000 and 100,000 tailed radio galaxies will be sufficiently polarized to a...

Johnston-Hollitt, M; Pratley, L

2015-01-01

46

ANISOTROPY AS A PROBE OF THE GALACTIC COSMIC-RAY PROPAGATION AND HALO MAGNETIC FIELD  

SciTech Connect

The anisotropy of cosmic rays (CRs) in the solar vicinity is generally attributed to CR streaming due to the discrete distribution of CR sources or local magnetic field modulation. Recently, the two-dimensional large-scale CR anisotropy has been measured by many experiments in the TeV-PeV energy range in both hemispheres. The tail-in excess along the tangential direction of the local spiral arm and the loss cone deficit pointing to the north Galactic pole direction agree with what have been obtained in tens to hundreds of GeV. The persistence of the two large-scale anisotropy structures in such a wide energy range suggests that the anisotropy might be due to global streaming of the Galactic CRs (GCRs). This work tries to extend the observed CR anisotropy picture from the solar system to the whole galaxy. In such a case, we can find a new interesting signature, a loop of GCR streaming, of the GCR propagation. We further calculate the overall GCR streaming induced magnetic field, and find a qualitative consistency with the observed structure of the halo magnetic field.

Qu, Xiao-bo; Zhang, Yi; Liu, Cheng; Hu, Hong-bo [Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Xue, Liang, E-mail: zhangyi@mail.ihep.ac.cn [School of Physics, Shandong University, Ji'nan 250100 (China)

2012-05-01

47

SQUID readout and ultra-low magnetic fields for Gravity Probe-B (GP-B)  

NASA Technical Reports Server (NTRS)

The superconducting readout system to be used for resolving 0.001 arcsec changes in the gyroscope spin direction in the Relativity Gyroscope (GP-B) experiment is described. This system couples the London magnetic moment flux of the spinning gyro to a low noise superconducting quantum interference device (SQUID) detector. Resolution limits and noise performance of the detection system are discussed, and improvements obtained and expected with advanced SQUIDs are presented. Also described is the novel use of superconducting magnetic shielding techniques to obtain a 250 dB attenuation of the earth's magnetic field at the location of the gyroscopes. In this approach, expanded superconducting foil shields are coupled with fixed cylindrical superconducting shields and special geometric considerations to obtain the extremely high attenuation factor required. With these shielding techniques, it appears that the 0.5-Gauss earth field (which appears to the gyroscopes as an ac field at the satellite roll rate) can be reduced to the 10 to the -13th G level required by the experiment. Recent results concerning improvements in the performance of the superconducting foil techniques obtained with the use of a new computer-controlled cooling system are presented.

Lockhart, James M.

1986-01-01

48

Probing the Magnetic Fields in the Environment of Mg II Absorbers  

NASA Astrophysics Data System (ADS)

We present a rotation measure survey of radio luminous QSOs with known Mg II absorption line systems, the purpose of which is to measure the characteristics of magnetics fields in and around galaxies at intermediate redshift. A sample of 38 high Galactic latitude QSOs have been selected as our primary targets. Each QSO has a single absorption line system between a redshift of 0.38<0.65 and we have excellent photometry on the galaxies associated with each absorber. In addition we identify a statistically significant sample of QSOs without intervening Mg II absorbers as a control sample. We use the control sample to correct for both the Galactic foreground and the Faraday rotation internal to the background QSOs. With these data we plan to derive the mean strength of the coherent field in the intermediate redshift galaxies and correlate variations in the observed RM with galaxy color, Mg II equivalent width, and impact parameter. At this time, we present preliminary total intensity images and RMs of the target objects in our sample. Additionally, observed radio jets in a portion of the sample provide an interesting comparison between the RMs of the disks of the galaxies versus those measured in the jets. The ultimate goal for this study is to provide robust constraints on models of the origin and evolution of the global magnetic fields in galaxies like the Milky Way. This work was supported by the National Science Foundation's REU program through NSF Award AST-1004881.

Manning, Sinclaire; Williams, Anna; Wilcots, Eric M.; Gould Zweibel, Ellen

2015-01-01

49

Magnetic Fields  

NSDL National Science Digital Library

This page and its annex describes, in trivial terms, the physics of magnetic fields and the history of its discovery. Included is the work of Halley, Oersted, Ampere and Maxwell. It also describes a way of demonstrating it in the classroom, using a vu-graph projector. Later sections #5, #5a and #6 extend this to magnetic field lines and electromagnetism.

Stern, David

2005-01-04

50

Triaxial Probe Magnetic Data Analysis  

NASA Technical Reports Server (NTRS)

The Triaxial Magnetic Moment Analysis software uses measured magnetic field test data to compute dipole and quadrupole moment information from a hardware element. It is used to support JPL projects needing magnetic control and an understanding of the spacecraft-generated magnetic fields. Evaluation of the magnetic moment of an object consists of three steps: acquisition, conditioning, and analysis. This version of existing software was extensively rewritten for easier data acquisition, data analysis, and report presentation, including immediate feedback to the test operator during data acquisition. While prior JPL computer codes provided the same data content, this program has a better graphic display including original data overlaid with reconstructed results to show goodness of fit accuracy and better appearance of the report graphic page. Data are acquired using three magnetometers and two rotations of the device under test. A clean acquisition user interface presents required numeric data and graphic summaries, and the analysis module yields the best fit (least squares) for the magnetic dipole and/or quadrupole moment of a device. The acquisition module allows the user to record multiple data sets, selecting the best data to analyze, and is repeated three times for each of the z-axial and y-axial rotations. In this update, the y-axial rotation starting position has been changed to an option, allowing either the x- or z-axis to point towards the magnetometer. The code has been rewritten to use three simultaneous axes of magnetic data (three probes), now using two "rotations" of the device under test rather than the previous three rotations, thus reducing handling activities on the device under test. The present version of the software gathers data in one-degree increments, which permits much better accuracy of the fit ted data than the coarser data acquisition of the prior software. The data-conditioning module provides a clean data set for the analysis module. For multiple measurements at a given degree, the first measurement is used. For omitted measurements, the missing field is estimated by linear interpolation between the two nearest measurements. The analysis module was rewritten for the dual rotation, triaxial probe measurement process and now has better moment estimation accuracy, based on the finer one degree of data acquisition resolution. The magnetic moments thus computed are used as an input to summarize the total spacecraft field.

Shultz, Kimberly; Whittlesey, Albert; Narvaez, Pablo

2007-01-01

51

PROBING THE SHALLOW CONVECTION ZONE: RISING MOTION OF SUBSURFACE MAGNETIC FIELDS IN THE SOLAR ACTIVE REGION  

SciTech Connect

In this Letter, we present a seismological detection of a rising motion of magnetic flux in the shallow convection zone of the Sun, and show estimates of the emerging speed and its decelerating nature. In order to evaluate the speed of subsurface flux that creates an active region, we apply six Fourier filters to the Doppler data of NOAA AR 10488, observed with the Solar and Heliospheric Observatory/Michelson Doppler Imager, to detect the reduction of acoustic power at six different depths from -15 to -2 Mm. All the filtered acoustic powers show reductions, up to 2 hr before the magnetic flux first appears at the visible surface. The start times of these reductions show a rising trend with a gradual deceleration. The obtained velocity is first several km s{sup -1} in a depth range of 15-10 Mm, then {approx}1.5 km s{sup -1} at 10-5 Mm, and finally {approx}0.5 km s{sup -1} at 5-2 Mm. If we assume that the power reduction is actually caused by the magnetic field, the velocity of the order of 1 km s{sup -1} is well in accordance with previous observations and numerical studies. Moreover, the gradual deceleration strongly supports the theoretical model that the emerging flux slows down in the uppermost convection zone before it expands into the atmosphere to build an active region.

Toriumi, Shin; Yokoyama, Takaaki [Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Ilonidis, Stathis [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305-4085 (United States); Sekii, Takashi, E-mail: toriumi@eps.s.u-tokyo.ac.jp [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

2013-06-10

52

Theoretical investigation of dynamic properties of magnetic molecule systems as probed by NMR and pulsed fields experiments  

NASA Astrophysics Data System (ADS)

In this dissertation we theoretically investigate static and especially dynamic properties of magnetic molecules (MM's), as probed by the nuclear spin lattice relaxation rate 1/T1 (first part) and pulsed fields measurements of the magnetization M( t) (second part). In the first part, we provide a general first-principles account for 1/T1, which incorporates the decay of spin fluctuations and the corresponding "broadening" of the discrete magnetic energy levels of MM's. This is achieved by including the interaction of the electronic moments with the local deformation of the host lattice (phonons), in the Markovian regime and employing the quantum regression theorem. Within this framework, we provide a rigorous interpretation of a number of 1/ T1 experimental findings in MM's. We also provide an extensive account of the model spin-1/2 tetramer {V12} by analyzing magnetic susceptibility and 1/T1 data. The second part focuses on phenomena manifested in pulsed fields measurements of M(t), such as hysteresis loops and Landau-Zener-Stuckelberg (LZS) steps. First, we give a theoretical analysis of the low-T hysteresis loops and LZS steps at B ? 0 observed in the magnetic molecule {V6}. The loops are successfully reproduced by employing a generalization of the standard Bloch equation which in turn reveals the one-phonon acoustic processes as the dominant source of relaxation in this system. The origin of the US steps is attributed to the presence in {V 6} of a weak intra-molecular anisotropic exchange. The small deviation from the quantum-mechanical prediction of exact magnetization reversals at B ? 0 is attributed to the role of the phonon heat bath (dissipative US problem). Second, we provide a general, first-principles account of all dynamic phenomena manifested in pulsed fields experiments, by extending the standard spin-lattice relaxation theory to include time-dependent (pulsed) fields. This theory accounts for: (i) hysteresis effects (including the generalized Bloch equation used for {V6}), (ii) the effects associated with the dissipative US problem, in the adiabatic regime and in particular, (iii) the so-called magnetic Foehn effect. We also discuss how the phonon bottleneck effect (typically occurring at T ? 1 K) can give rise to an enhanced Foehn effect.

Rousochatzakis, Ioannis

53

Using Tailed Radio Galaxies to Probe the Environment and Magnetic Field of Galaxy Clusters in the SKA Era  

E-print Network

The morphology of tailed radio galaxies is an invaluable source of environmental information, in which a history of the past interactions in the intra-cluster medium, such as complex galaxy motions and cluster merger shocks, are preserved. In recent years, the use of tailed radio galaxies as environmental probes has gained momentum as a method for galaxy cluster detection, examining the dynamics of individual clusters, measuring the density and velocity flows in the intra-cluster medium, and for probing cluster magnetic fields. To date instrumental limitations in terms of resolution and sensitivity have confined this research to the local (z < 0.7) Universe. The advent of SKA1 surveys however will allow detection of roughly 1,000,000 tailed radio galaxies and their associated galaxy clusters out to redshifts of 2 or more. This is in fact ten times more than the current number of known clusters in the Universe. Additionally between 50,000 and 100,000 tailed radio galaxies will be sufficiently polarized to a...

Johnston-Hollitt, M; Pratley, L

2015-01-01

54

Magnetic Field Safety Magnetic Field Safety  

E-print Network

Magnetic Field Safety Training #12;Magnetic Field Safety Strong Magnetic Fields exist around energized magnets. High magnetic fields alone are a recognized hazard only for personnel with certain medical conditions such as pacemakers, magnetic implants, or embedded shrapnel. In addition, high magnetic

McQuade, D. Tyler

55

A new probe of magnetic fields during high-mass star formation: Zeeman splitting of 6.7 GHz methanol masers  

E-print Network

Context: The role of magnetic fields during high-mass star formation is a matter of fierce debate, yet only a few direct probes of magnetic field strengths are available. Aims: The magnetic field is detected in a number of massive star-forming regions through polarization observations of 6.7 GHz methanol masers. Although these masers are the most abundant of the maser species occurring during high-mass star formation, most magnetic field measurements in the high-density gas currently come from OH and H2 O maser observations. Methods: The 100-m Effelsberg telescope was used to measure the Zeeman splitting of 6.7 GHz methanol masers for the first time. The observations were performed on a sample of 24 bright northern maser sources. Results: Significant Zeeman splitting is detected in 17 of the sources with an average magnitude of 0.56 m/s . Using the current best estimate of the 6.7 GHz methanol maser Zeeman splitting coefficient and a geometrical correction, this corresponds to an absolute magnetic field strength of 23 mG in the methanol maser region. Conclusions: The magnetic field is dynamically important in the dense maser regions. No clear relation is found with the available OH maser magnetic field measurements. The general sense of direction of the magnetic field is consistent with other Galactic magnetic field measurements, although a few of the masers display a change of direction between different maser features. Due to the abundance of methanol masers, measuring their Zeeman splitting provides the opportunity to construct a comprehensive sample of magnetic fields in high-mass star-forming regions.

W. H. T. Vlemmings

2008-04-07

56

Polarization as a probe of magnetic field and plasma properties of compact radio sources - Simulation of relativistic jets  

Microsoft Academic Search

The relationship between linearly and circularly polarized synchrotron emission and the internal magnetic field and plasma properties of compact radio sources is explored through a large set of numerical simulations. The simulations involve approximate, divergent jet flows of relativistic plasma and turbulent magnetic fields. The results are compared to the observed properties of compact jets. The most severe constraint which

T. W. Jones

1988-01-01

57

Molecular diffusion in disordered interfacial media as probed by pulsed field gradients and nuclear magnetic relaxation dispersion  

NASA Astrophysics Data System (ADS)

We address the question of probing the fluid dynamics in disordered interfacial media by Pulsed field gradient (PFG) and Magnetic relaxation dispersion (MRD) techniques. We show that the PFG method is useful to separate the effects of morphology from the connectivity in disordered macroporous media. We propose simulations of molecular dynamics and spectral density functions, J(?), in a reconstructed mesoporous medium for different limiting conditions at the pore surface. An algebraic form is found for J(?) in presence of a surface diffusion and a local exploration of the pore network. A logarithmic form of J(?) is found in presence of a pure surface diffusion. We present magnetic relaxation dispersion experiments (MRD) for water and acetone in calibrated mesoporous media to support the main results of our simulations and theories. Nous présentons les avantages respectifs des méthodes de gradients de champs pulsés (PFG) et de relaxation magnétique nucléaire en champs cyclés (MRD) pour sonder la dynamique moléculaire dans les milieux interfaciaux désordonnés. La méthode PFG est utile pour séparer la morphologie et la connectivité dans des milieux macroporeux. Des simulations de diffusion moléculaire et de densité spectrale J(?) en milieux mésoporeux sont présentées dans différentes conditions limites aux interfaces des pores. Nous trouvons une forme de dispersion algébrique de J(?) pour une diffusion de surface assistée d'une exploration locale du réseau de pores et une forme logarithmique dans le cas d'une simple diffusion de surface. Les résultats expérimentaux de la méthode MRD pour de l'eau et de l'acétone dans des milieux mésoporeux calibrés supportent les résultats principaux de nos simulations et théories.

Levitz, P.; Korb, J.-P.; Bryant, R. G.

1999-10-01

58

Singlet and triplet states of trions in ZuSe-based quantum wells probed by magnetic fields to 50 Tesla  

SciTech Connect

Singlet and triplet states of positively (X{sup +}) and negatively (X{sup -}) charged excitons in ZnSe-based quantum wells have been studied by means of photoluminescence in pulsed magnetic fields up to 50 T. The binding energy of the X{sup -} singlet state shows a monotonic increase with magnetic field with a tendency to saturation, while that of the X{sup +} slightly decreases. The triplet X{sup +} and X{sup -} states, being unbound at zero magnetic field, noticeably increase their binding energy in high magnetic fields. The experimental evidence for the interaction between the triplet and singlet states of lTions leading to their anticrossing in magnetic fields has been found.

Astakhov, G. V.; Yakovlev, D. R.; Crooker, S. A. (Scott A.); Barrick, T. (Todd); Dzyubenko, A. B.; Sander, Thomas; Kochereshko, V. P.; Ossau, W.; Faschinger, W.; Waag, A.

2002-01-01

59

Negative Differential Velocity in Artificial Crystals Probed by High Magnetic Fields  

NASA Astrophysics Data System (ADS)

Progress in the synthesis and engineering of semiconductor materials has led to improved device performances and functionalities. In particular, in the last decade, there has been considerable interest in the physics and applications of highly-mismatched alloys in which small and highly-electronegative isovalent N-atoms are incorporated onto the anion sublattice of a III-V compound semiconductor.1 The most studied material is the GaAs1-xNx alloy. Our magnetotunnelling studies have shown that a small percentage of N (x < 1%) perturbs dramatically the electronic properties of the host GaAs crystal leading to a large increase of the electron effective mass and an unusual response of the energy-wavevector dispersions to hydrostatic pressure.2-6 These effects differ from the smoother variation of the energy band gap and electron effective mass with alloy composition observed in other semiconductor compounds, such as InyGa1-yAs. The incorporation of N in GaAs gives rise to a qualitatively different type of alloy phenomenon: N-impurities and N-clusters tend to localize the extended Bloch states of GaAs at resonant energies in the conduction band (CB), thus fragmenting the energy-wavevector dispersion relations. The possibility of tailoring the electronic properties of III-V compounds by N-incorporation has stimulated proposals for innovative devices in optoelectronics and high frequency (terahertz, THz) electronics.7 However, to date, the implementation of dilute nitrides in these technologies presents several challenges, including a degradation of the electron mobility. Also, despite a rapidly expanding body of work on the electronic properties of GaAs1-xNx, the range of N-concentrations over which this alloy behaves as a good conductor is not yet well established. Our magnetotransport experiments have revealed how the incorporation of N in GaAs affects the electrical conductivity. Our studies in n-type GaAs1-xNx epilayers revealed a large increase of the resistivity, ?, for x > 0.2%, which we have attributed to the emergence of defect states with deep (~ 0.3 eV) energy levels. Electron trapping onto these states was not observed at low x (x = 0.2%). In this ultra-dilute alloy regime and at low electric fields (F < 1 kV/cm) the electrical conductivity retains the characteristic features of transport through extended states, albeit with relatively low mobility (µ ~ 0.1 m2/Vs at RT) due to scattering of electrons by N-atoms. We have focused our research on this ultra-dilute regime and exploited the admixing of the localized single N-impurity level with the extended conduction band states of GaAs to realize an unusual type of negative differential velocity (NDV) effect: at large F (> 1 kV/cm), electrons gain sufficient energy to approach the energy of the resonant N-level, where they become spatially localized.7-10 This Resonant Electron Localization in Electric Field, to which we give the acronym RELIEF, leads to NDV and strongly non-linear current-voltage characteristics. We envisage that the RELIEF-effect could be observed in other III-N-V alloys, such as InP1-xNx and InAs1-xNx. In these compounds the nature of the resonant interaction between the N-level and the conduction band states of the host-crystal is still relatively unexplored. However, it is clear that the different energy positions of the N-level relative to the conduction band minimum of different materials could offer new degrees of freedom in the design of the electronic band structure and electron dynamics. The RELIEF-effect may open up prospects for future applications in fast electronics. We have shown that the maximum response frequency, fmax, of a RELIEF-diode can be tuned by the applied electric field in the THz frequency range.7 This is of potential technological significance for the development of detectors/sources in the 0.6-1 THz region, which is not currently attainable using conventional Transferred Electron Devices and Quantum Cascade Lasers. Our recent studies of GaAs1-xNx have also shown a fast response of the current in the sub-T

Patanè, A.

60

Design of a triple resonance magic angle sample spinning probe for high field solid state nuclear magnetic resonance  

NASA Astrophysics Data System (ADS)

Standard design and construction practices used in building nuclear magnetic resonance (NMR) probes for the study of solid state samples become difficult if not entirely impractical to implement as the 1H resonance frequency approaches the self resonance frequency of commercial capacitors. We describe an approach that utilizes short variable transmission line segments as tunable reactances. Such an approach effectively controls stray reactances and provides a higher Q alternative to ceramic chip capacitors. The particular probe described is built to accommodate a 2.5 mm magic angle spinning rotor system, and is triply tuned to 13C, 15N, and 1H frequencies for use at 18.8 T (200, 80, and 800 MHz, respectively). Isolation of the three radio frequency (rf) channels is achieved using both a rejection trap and a transmission line notch filter. The compact geometry of this design allows three channels with high power handling capability to fit in a medium bore (63 mm) magnet. Extended time variable temperature operation is integral to the mechanical design, enabling the temperature control necessary for investigation of biological macromolecules. Accurate measurement of the air temperature near the sample rotor is achieved using a fiber optic thermometer, which does not interfere with the rf electronics. We also demonstrate that acceptable line shapes are only readily achieved using zero magnetic susceptibility wire in construction of the sample coil. Computer simulation of the circuit aided in the physical design of the probe. Representative data illustrating the efficiency, rf homogeneity, and signal to noise factor of the probe are presented.

Martin, Rachel W.; Paulson, Eric K.; Zilm, Kurt W.

2003-06-01

61

Extending the distance range accessed with continuous wave EPR with Gd3+ spin probes at high magnetic fields†  

PubMed Central

Interspin distances between 0.8 nm and 2.0 nm can be measured through the dipolar broadening of the continuous wave (cw) EPR spectrum of nitroxide spin labels at X-band (9.4 GHz, 0.35 T). We introduce Gd3+ as a promising alternative spin label for distance measurements by cw EPR above 7 Tesla, where the |?1/2? to |1/2? transition narrows below 1 mT and becomes extremely sensitive to dipolar broadening. To estimate the distance limits of cw EPR with Gd3+, we have measured spectra of frozen solutions of GdCl3 at 8.6 T (240 GHz) and 10 K at concentrations ranging from 50 mM to 0.1 mM, covering a range of average interspin distances. These experiments show substantial dipolar broadening at distances where line broadening cannot be observed with nitroxides at X-band. This data, and its agreement with calculated dipolar-broadened lineshapes, show Gd3+ to be sensitive to distances as long as ~3.8 nm. Further, the linewidth of a bis-Gd3+ complex with a flexible ~1.6 nm bridge is strongly broadened as compared to the mono-Gd3+ complex, demonstrating the potential for application to pairwise distances. Gd-DOTA-based chelates that can be functionalized to protein surfaces display linewidths narrower than aqueous GdCl3, implying they should be even more sensitive to dipolar broadening. Therefore, we suggest that the combination of tailored Gd3+ labels and high magnetic fields can extend the longest interspin distances measurable by cw EPR from 2.0 nm to 3.8 nm. cw EPR data at 260 K demonstrate that the line broadening remains clear out to similar average interspin distances, offering Gd3+ probes as promising distance rulers at temperatures higher than possible with conventional pulsed EPR distance measurements. PMID:23732863

Edwards, Devin T.; Ma, Zhidong; Meade, Thomas J.; Goldfarb, Daniella; Han, Songi

2014-01-01

62

A novel magnetic field probing technique for determining state of health of sealed lead-acid batteries  

NASA Astrophysics Data System (ADS)

State of Health (SOH) is a critical index for a Sealed Lead-Acid (SLA) battery diagnostic which provides the information about battery replacement and aging effects. SOH is a complex function of chemical parameters of a battery such as stratification in electrolyte, electrode structure (sulfation and hard sulfation) in addition to electrical parameters of a battery. This paper describes a method of online determination of stratification, electrode structure, electrode polarization and current profile within the battery under the influence of a magnetic field. An AC magnetic field is used as a noninvasive tool during battery cycles. An induced emf in a secondary coil (SCV) is used as a measure of change in the magnetic field. The H+ proton density varies with change in sulfuric acid (electrolyte) concentration during battery cycles. The magnetic flux lines are affected by the density of H+ protons whose magnetic dipole moments try to align along the magnetic flux lines. The stratification is seen by a 12% decrease in magnetic flux linking from the top to the bottom of the electrolyte in a battery. Additional experimental results demonstrate the variation in magnetic flux linking which correlates with current profile across the electrode and electrode structure.

Khare, Neeta; Singh, Pritpal; Vassiliou, John K.

2012-11-01

63

Magnetic tape leads for probes in electromagnetic radiation  

SciTech Connect

Electrically conducting magnetic recording tape having a coating of gamma -fe2o3 particles on a polyester substrate is used as leads for probes in oven cavities and other microwave fields. The tape leads are flexible, have a high resistance per unit length, and are nearly transparent to electromagnetic waves. Electric diode-dipole probes with such leads are uniquely electric and a magnetic loop detector is uniquely magnetic.

Andrews, C.L.; Belden, L.H.

1981-07-28

64

Polarization as a probe of magnetic field and plasma properties of compact radio sources - simulation of relativistic jets  

Microsoft Academic Search

The relationship between polarized emission, both linear and circular, and the magnetic field and plasma properties is explored using a large set of numerical simulations. The results show that integrated polarization properties of compact jets seem to place rather severe constraints on the attributes of the plasma inside the sources. The absence of large circular polarization in such jets requires

T. W. Jones

1988-01-01

65

A new method of measuring the poloidal magnetic and radial electric fields in a tokamak using a laser-accelerated ion-beam trace probe  

SciTech Connect

Both the poloidal magnetic field (B{sub p}) and radial electric field (E{sub r}) are significant in magnetic confinement devices. In this paper, a new method was proposed to diagnose both B{sub p} and E{sub r} at the same time, which was named Laser-accelerated Ion-beam Trace Probe (LITP). This method based on the laser-accelerated ion beam, which has three properties: large energy spread, short pulse lengths, and multiple charge states. LITP can provide the 1D profiles, or 2D images of both B{sub p} and E{sub r}. In this paper, we present the basic principle and some preliminary theoretical results.

Yang, X. Y.; Chen, Y. H.; Lin, C.; Wang, X. G.; Xiao, C. J., E-mail: cjxiao@pku.edu.cn [State Key Labaratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China); Wang, L. [Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190 (China); Xu, M. [Center for Fusion Science of Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041 (China)

2014-11-15

66

Molecules as magnetic probes of starspots  

E-print Network

Stellar dynamo processes can be explored by measuring the magnetic field. This is usually obtained using the atomic and molecular Zeeman effect in spectral lines. While the atomic Zeeman effect can only access warmer regions, the use of molecular lines is of advantage for studying cool objects. The molecules MgH, TiO, CaH, and FeH are suited to probe stellar magnetic fields, each one for a different range of spectral types, by considering the signal that is obtained from modeling various spectral types. We have analyzed the usefulness of different molecules (MgH, TiO, CaH, and FeH) as diagnostic tools for studying stellar magnetism on active G-K-M dwarfs. We investigate the temperature range in which the selected molecules can serve as indicators for magnetic fields on highly active cool stars and present synthetic Stokes profiles for the modeled spectral type. We modeled a star with a spot size of 10% of the stellar disk and a spot comprising either only longitudinal or only transverse magnetic fields and es...

Afram, Nadine

2015-01-01

67

CORONAL MAGNETIC FIELD MEASUREMENTS THROUGH GYRORESONANCE EMISSION  

E-print Network

observations have provided a direct measurement of magnetic field strengths in the solar corona. It is a happy probes of the magnetic field strength above active regions, and this unique capability is one to a different magnetic field strength, the coronal structure can be "peeled away" by using different frequencies

White, Stephen

68

Exploring Magnetic Fields  

NSDL National Science Digital Library

In this activity, students investigate the presence of magnetic fields around magnets, the sun and the earth. They will explore magnetic field lines, understand that magnetic lines of force show the strength and direction of magnetic fields, determine how field lines interact between attracting and repelling magnetic poles, and discover that the earth and sun have magnetic properties. They will also discover that magnetic force is invisible and that a "field of force" is a region or space in which one object can attract or repel another.

69

Multi-element Magnetic ``B-dot'' Probe  

NASA Astrophysics Data System (ADS)

We describe a 24-element magnetic probe consisting of miniature commercial chip inductors that will be used to investigate the evolution of the magnetic field lines during a reconnection event. Eight clusters of three mutually orthogonal inductor coils mounted in a linear array provide dB/dt data in the x, y, and z directions with a spatial resolution of 0.5 cm. The probe will be part of the Reconnection Scaling Experiment (RSX) at Los Alamos National Laboratory, which creates multiple magnetic flux ropes of H^+ plasma. Using numerical integration, we expect to measure magnetic field strengths of 1-10 gauss. The plasma columns of RSX that undergo magnetic reconnection, merging, and bouncing evolve on a characteristic timescale of 1-10 ?s, which is well within the probe's expected time resolution.

Harrold, Samuel; Intrator, Tom; Sun, Xuan

2007-11-01

70

Contributions of the electronic spin and orbital current to the CoCl{sub 4}{sup 2-} magnetic field probed in polarised neutron diffraction experiments  

SciTech Connect

Polarised neutron diffraction experiments conducted at 4.2 K on Cs{sub 3}CoCl{sub 5} crystals have been analysed by using a four-dimensional model Hilbert space made of ab initio n-electron wave functions of the CoCl{sub 4}{sup 2-} molecular ion. Two spin-orbit mixing coefficients and several configuration interaction coefficients have been optimized by fitting calculated magnetic structure factors to experimental ones, to obtain the best ensemble density operator that is representable in the model space. A goodness of fit, {chi}{sup 2}, less then 1 has been obtained for the first time for the two experimental data sets available. In the present article, the optimized density operators are used to calculate the magnetic field densities that are the genuine observables probed in neutron diffraction experiments. Density maps of such observables are presented for the first time and numerical details are provided. The respective contributions of spin density and orbital current to the magnetic field density are analyzed.

Cassam-Chenaie, Patrick [Laboratoire J. A. Dieudonne, UMR 6621 du CNRS, Faculte des Sciences, Parc Valrose, 06108 Nice cedex 2 (France); Jayatilaka, Dylan [School of Chemistry and Biochemistry, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia)

2012-08-14

71

Visualizing Magnetic Field Lines  

NSDL National Science Digital Library

In this activity, students take the age old concept of etch-a-sketch a step further. Using iron filings, students begin visualizing magnetic field lines. To do so, students use a compass to read the direction of the magnet's magnetic field. Then, students observe the behavior of iron filings near that magnet as they rotate the filings about the magnet. Finally, students study the behavior of iron filings suspended in mineral oil which displays the magnetic field in three dimensions.

VU Bioengineering RET Program, School of Engineering,

72

What are Magnetic Fields?  

NSDL National Science Digital Library

This is an activity about magnetic fields. Using iron filings, learners will observe magnets in various arrangements to investigate the magnetic field lines of force. This information is then related to magnetic loops on the Sun's surface and the magnetic field of the Earth. This is the second activity in the Magnetic Math booklet; this booklet can be found on the Space Math@NASA website.

73

Magnetic field line Hamiltonian  

SciTech Connect

The basic properties of the Hamiltonian representation of magnetic fields in canonical form are reviewed. The theory of canonical magnetic perturbation theory is then developed and applied to the time evolution of a magnetic field embedded in a toroidal plasma. Finally, the extension of the energy principle to tearing modes, utilizing the magnetic field line Hamiltonian, is outlined.

Boozer, A.H.

1985-02-01

74

The magnetic-distortion probe: Velocimetry in conducting fluids  

NASA Astrophysics Data System (ADS)

A new type of velocimeter, capable of local velocity measurements in conducting fluids, is introduced. The principle of the "magnetic-distortion probe" is based on the measurement of the induced magnetic field by the flow of a conducting fluid in the vicinity of a localized magnetic field. The new velocimeter has no moving parts, and can be enclosed in a sealed cap, easing the implementation in harsh environments, such as liquid metals. The proposed method allows one to probe both the continuous part and fluctuations of the velocity, the temporal and spatial resolution being linked to the actual geometric configuration of the probe. A prototype probe has been tested in a gallinstan pipe flow and in a fully turbulent flow of liquid gallium generated by the counter rotation of two coaxial impellers in a cylinder. The signals have been compared to a reference potential probe and show very good agreement both for time-averaged velocities and turbulent fluctuations. The prototype is shown to detect motion from a few cm s-1 to a few m s-1. Moreover, the use of the magnetic-distortion probe with large-scale applied magnetic field is discussed.

Miralles, Sophie; Verhille, Gautier; Plihon, Nicolas; Pinton, Jean-François

2011-09-01

75

Essential properties of a D2+ molecular complex confined in ring-like nanostructures under external probes: Magnetic field and hydrostatic pressure  

NASA Astrophysics Data System (ADS)

A rigorous adiabatic approximation is used to investigate the energy states of the singly ionized double-donors D2+ complex formed by the coupling of a conduction band electron and two donor centers in a quantum ring with rectangular cross-section. The effects of changing the relative position between the Coulombic centers and the quantum ring geometry parameters, as well as the influence of external probes such as applied magnetic fields and hydrostatic pressure, are particularly studied, highlighting the important contribution of the repulsive inter-center interaction. The suppression of the Aharonov-Bohm ground state oscillations associated with the localization of the electron by the fixed donors is discussed. Comparison between the essential properties of an actual hydrogen ion H2+ and those of the D2+ complex trapped within a quantum ring shows that the strong electron confinement substantially increases the D2+ stability effects.

R-Fulla, M.; Marín, J. H.; Gutiérrez, W.; Mora-Ramos, M. E.; Duque, C. A.

2014-03-01

76

Probing Electric and Magnetic Vacuum Fluctuations with Quantum Dots  

NASA Astrophysics Data System (ADS)

The electromagnetic-vacuum-field fluctuations are intimately linked to the process of spontaneous emission of light. Atomic emitters cannot probe electric- and magnetic-field fluctuations simultaneously because electric and magnetic transitions correspond to different selection rules. In this Letter we show that semiconductor quantum dots are fundamentally different and are capable of mediating electric-dipole, magnetic-dipole, and electric-quadrupole transitions on a single electronic resonance. As a consequence, quantum dots can probe electric and magnetic fields simultaneously and can thus be applied for sensing the electromagnetic environment of complex photonic nanostructures. Our study opens the prospect of interfacing quantum dots with optical metamaterials for tailoring the electric and magnetic light-matter interaction at the single-emitter level.

Tighineanu, P.; Andersen, M. L.; Sørensen, A. S.; Stobbe, S.; Lodahl, P.

2014-07-01

77

Probing electric and magnetic vacuum fluctuations with quantum dots  

E-print Network

The electromagnetic-vacuum-field fluctuations are intimately linked to the process of spontaneous emission of light. Atomic emitters cannot probe electric- and magnetic-field fluctuations simultaneously because electric and magnetic transitions correspond to different selection rules. In this paper we show that semiconductor quantum dots are fundamentally different and are capable of mediating electric-dipole, magnetic-dipole, and electric-quadrupole transitions on a single electronic resonance. As a consequence, quantum dots can probe electric and magnetic fields simultaneously and can thus be applied for sensing the electromagnetic environment of complex photonic nanostructures. Our study opens the prospect of interfacing quantum dots with optical metamaterials for tailoring the electric and magnetic light-matter interaction at the single-emitter level.

Petru Tighineanu; Mads Lykke Andersen; Anders Søndberg Sørensen; Søren Stobbe; Peter Lodahl

2014-04-04

78

Probing electric and magnetic vacuum fluctuations with quantum dots.  

PubMed

The electromagnetic-vacuum-field fluctuations are intimately linked to the process of spontaneous emission of light. Atomic emitters cannot probe electric- and magnetic-field fluctuations simultaneously because electric and magnetic transitions correspond to different selection rules. In this Letter we show that semiconductor quantum dots are fundamentally different and are capable of mediating electric-dipole, magnetic-dipole, and electric-quadrupole transitions on a single electronic resonance. As a consequence, quantum dots can probe electric and magnetic fields simultaneously and can thus be applied for sensing the electromagnetic environment of complex photonic nanostructures. Our study opens the prospect of interfacing quantum dots with optical metamaterials for tailoring the electric and magnetic light-matter interaction at the single-emitter level. PMID:25105618

Tighineanu, P; Andersen, M L; Sørensen, A S; Stobbe, S; Lodahl, P

2014-07-25

79

Mapping Magnetic Fields  

NSDL National Science Digital Library

This is an activity about bar magnets and their invisible magnetic fields. Learners will experiment with magnets and a compass to detect and draw magnetic fields. This is Activity 1 of a larger resource, entitled Exploring the Sun. The NASA spacecraft missions represented by this material include SOHO, TRACE, STEREO, Hinode, and SDO.

2012-08-03

80

An emerging population of BL Lacs with extreme properties: towards a class of EBL and cosmic magnetic field probes?  

E-print Network

High energy observations of extreme BL Lac objects, such as 1ES 0229+200 or 1ES 0347-121, recently focused interest both for blazar and jet physics and for the implication on the extragalactic background light and intergalactic magnetic field estimate. However, the number of these extreme highly peaked BL Lac objects (EHBL) is still rather small. Aiming at increase their number, we selected a group of EHBL candidates starting from the BL Lac sample of Plotkin et al. (2011), considering those undetected (or only barely detected) by the Large Area Telescope onboard Fermi and characterized by a high X-ray vs. radio flux ratio. We assembled the multi-wavelength spectral energy distribution of the resulting 9 sources, profiting of publicly available archival observations performed by the Swift, Galex and Fermi satellites, confirming their nature. Through a simple one-zone synchrotron self-Compton model we estimate the expected VHE flux, finding that in the majority of cases it is within the reach of present genera...

Bonnoli, Giacomo; Ghisellini, Gabriele; Sbarrato, Tullia

2015-01-01

81

Probes for investigating the effect of magnetic field, field orientation, temperature and strain on the critical current density of anisotropic high-temperature superconducting tapes in a split-pair 15 T horizontal magnet  

NASA Astrophysics Data System (ADS)

We present the designs of probes for making critical current density (Jc) measurements on anisotropic high-temperature superconducting tapes as a function of field, field orientation, temperature and strain in our 40 mm bore, split-pair 15 T horizontal magnet. Emphasis is placed on the design of three components: the vapour-cooled current leads, the variable temperature enclosure, and the springboard-shaped bending beam sample holder. The vapour-cooled brass critical-current leads used superconducting tapes and in operation ran hot with a duty cycle (D) of ˜0.2. This work provides formulae for optimising cryogenic consumption and calculating cryogenic boil-off, associated with current leads used to make Jc measurements, made by uniformly ramping the current up to a maximum current (Imax) and then reducing the current very quickly to zero. They include consideration of the effects of duty cycle, static helium boil-off from the magnet and Dewar (b'), and the maximum safe temperature for the critical-current leads (Tmax). Our optimized critical-current leads have a boil-off that is about 30% less than leads optimized for magnet operation at the same maximum current. Numerical calculations show that the optimum cross-sectional area (A) for each current lead can be parameterized by LI_{max} /A = [1.46D^{ - 0.18} L^{0.4} (T_{max } - 300)^{0.25D^{ - 0.09} } + 750(b^' /I_{max })D^{10^{ - 3} I_{max } - 2.87b^' }] × 10^6 A m^{ - 1} where L is the current lead's length and the current lead is operated in liquid helium. An optimum A of 132 mm2 is obtained when Imax = 1000 A, Tmax = 400 K, D = 0.2, b' = 0.3 l h-1 and L = 1.0 m. The optimized helium consumption was found to be 0.7 l h-1. When the static boil-off is small, optimized leads have a boil-off that can be roughly parameterized by: b/Imax ? (1.35 × 10-3)D0.41 l h-1 A-1. A split-current-lead design is employed to minimize the rotation of the probes during the high current measurements in our high-field horizontal magnet. The variable-temperature system is based on the use of an inverted insulating cup that operates above 4.2 K in liquid helium and above 77.4 K in liquid nitrogen, with a stability of ±80 mK to ±150 mK. Uniaxial strains of -1.4% to 1.0% can be applied to the sample, with a total uncertainty of better than ±0.02%, using a modified bending beam apparatus which includes a copper beryllium springboard-shaped sample holder.

Sunwong, P.; Higgins, J. S.; Hampshire, D. P.

2014-06-01

82

Probes for investigating the effect of magnetic field, field orientation, temperature and strain on the critical current density of anisotropic high-temperature superconducting tapes in a split-pair 15 T horizontal magnet.  

PubMed

We present the designs of probes for making critical current density (Jc) measurements on anisotropic high-temperature superconducting tapes as a function of field, field orientation, temperature and strain in our 40 mm bore, split-pair 15 T horizontal magnet. Emphasis is placed on the design of three components: the vapour-cooled current leads, the variable temperature enclosure, and the springboard-shaped bending beam sample holder. The vapour-cooled brass critical-current leads used superconducting tapes and in operation ran hot with a duty cycle (D) of ~0.2. This work provides formulae for optimising cryogenic consumption and calculating cryogenic boil-off, associated with current leads used to make J(c) measurements, made by uniformly ramping the current up to a maximum current (I(max)) and then reducing the current very quickly to zero. They include consideration of the effects of duty cycle, static helium boil-off from the magnet and Dewar (b'), and the maximum safe temperature for the critical-current leads (T(max)). Our optimized critical-current leads have a boil-off that is about 30% less than leads optimized for magnet operation at the same maximum current. Numerical calculations show that the optimum cross-sectional area (A) for each current lead can be parameterized by LI(max)/A = [1.46D(-0.18)L(0.4)(T(max) - 300)(0.25D(-0.09)) + 750(b'/I(max))D(10(-3)I(max)-2.87b') × 10? A m?¹ where L is the current lead's length and the current lead is operated in liquid helium. An optimum A of 132 mm(2) is obtained when I(max) = 1000 A, T(max) = 400 K, D = 0.2, b' = 0.3 l?h(-1) and L = 1.0 m. The optimized helium consumption was found to be 0.7 l?h(-1). When the static boil-off is small, optimized leads have a boil-off that can be roughly parameterized by: b/I(max)? ? (1.35 × 10(-3))D(0.41) l?h(?1)?A(-1). A split-current-lead design is employed to minimize the rotation of the probes during the high current measurements in our high-field horizontal magnet. The variable-temperature system is based on the use of an inverted insulating cup that operates above 4.2 K in liquid helium and above 77.4 K in liquid nitrogen, with a stability of ±80 mK to ±150 mK. Uniaxial strains of -1.4% to 1.0% can be applied to the sample, with a total uncertainty of better than ±0.02%, using a modified bending beam apparatus which includes a copper beryllium springboard-shaped sample holder. PMID:24985856

Sunwong, P; Higgins, J S; Hampshire, D P

2014-06-01

83

Exploring Magnetic Fields in Your Environment  

NSDL National Science Digital Library

This is a lesson about measuring magnetic field directions of Earth and in the environment. First, learners go outside, far away from buildings, power lines, or anything electrical or metal, and use compasses to identify magnetic North. Next, they use the compasses to probe whether there are any sources of magnetic fields in the local environment, including around electronic equipment such as a CD player and speakers. This is the first lesson in the second session of the Exploring Magnetism teacher guide.

84

Introduction to Magnetic Fields  

NSDL National Science Digital Library

This is an activity about magnetic fields. Learners will use various magnets, magnetic film, and a compass to see and illustrate what magnetic fields look like. This is the fourth activity as part of the iMAGiNETICspace: Where Imagination, Magnetism, and Space Collide educator's guide. Instructions for downloading the iBook educator's guide and the associated Transmedia book student guide are available at the resource link.

2013-05-06

85

Drawing Magnetic Fields  

NSDL National Science Digital Library

Students use a compass and a permanent magnet to trace the magnetic field lines produced by the magnet. By positioning the compass in enough spots around the magnet, the overall magnet field will be evident from the collection of arrows representing the direction of the compass needle. In activities 3 and 4 of this unit, students will use this information to design a way to solve the grand challenge of separating metal for a recycling company.

2014-09-18

86

Electricity and Magnetic Fields  

NSDL National Science Digital Library

The grand challenge for this legacy cycle unit is for students to design a way to help a recycler separate aluminum from steel scrap metal. In previous lessons, they have looked at how magnetism might be utilized. In this lesson, students think about how they might use magnets and how they might confront the problem of turning the magnetic field off. Through the accompanying activity students explore the nature of an electrically induced magnetic field and its applicability to the needed magnet.

VU Bioengineering RET Program,

87

Circuits and Magnetic Fields  

NSDL National Science Digital Library

Students use the same method as in the activity from lesson 2 of this unit to explore the magnetism due to electric current instead of a permanent magnet. Students use a compass and circuit to trace the magnetic field lines induced by the electric current moving through the wire. Students develop an understanding of the effect of the electrical current on the compass needle through the induced magnetic field and understand the complexity of a three dimensional field system.

VU Bioengineering RET Program,

88

Magnetic fields at Neptune  

Microsoft Academic Search

The National Aeronautics and Space Administration Goddard Space Flight Center-University of Delaware Bartol Research Institute magnetic field experiment on the Voyager 2 spacecraft discovered a strong and complex intrinsic magnetic field of Neptune and an associated magnetosphere and magnetic tail. A maximum magnetic field of nearly 10,000 nanoteslas (1 nanotesla = 10⁻⁵ gauss) was observed near closest approach, at a

N. F. Ness; M. H. Acuna; L. F. Burlaga; J. E. P. Connerney; R. P. Lepping; F. M. Neubauer

1989-01-01

89

Second solar spectrum observed at the Pic-du-Midi: depth probing of the turbulent magnetic field intensity in a quiet region.  

NASA Astrophysics Data System (ADS)

The installation of a new polarimeter at the Turret Dome of the Pic-du-Midi has permitted new observations of the "second solar spectrum" (which is the spectrum of the linear polarization observed near the solar limb), having a spatial resolution. On 2003 October 25, we have observed a quiet region located at the East limb equator, in the resonance line of neutral strontium at 4607 Å. The slit was positioned perpendicular to the limb: recording various limb distances provides a depth probing of the solar atmosphere. The intensity of the turbulent magnetic field has been derived from the Hanle effect interpretation, which is actually the only method for vectorial weak field determination. The theoretical profiles to be compared to the observed ones have been obtained by applying the atomic density matrix formalism (Landi Degl'Innocenti E., Bommier V., & Sahal-Bréchot S., 1990). The various collisional coefficients have been computed by applying semi-classical methods that are accurate to 20% or better: the one from Seaton (1962) and Sahal-Bréchot (1969a, 1969b) for the collisions with electrons, responsible for the inelastic transitions, and the one developed by Anstee & O'Mara (1991, 1995) for line broadening computations, generalized to the collisional depolarization by Derouich et al. (2003; see also Derouich, 2004), for the elastic collisions with neutral hydrogen atoms. The results have been found in full agreement with those previously obtained with THEMIS without any spatial resolution (at 9 limb distances). With the spatial resolution that we have now at the Pic-du-Midi (1 arcsec, 138 limb distances), it appears that the turbulent magnetic field intensity does not vary with depth, in the line formation region that ranges from ~200 to ~300 km above the tau5000=1 level.

Derouich, M.; Malherbe, J. M.; Bommier, V.; Landi Degl'Innocenti, E.; Sahal-Bréchot, S.

2004-12-01

90

Quantitative magnetic force microscopy on permalloy dots using an iron filled carbon nanotube probe.  

PubMed

An iron filled carbon nanotube (FeCNT), a 10-40 nm ferromagnetic nanowire enclosed in a protective carbon tube, is an attractive candidate for a magnetic force microscopy (MFM) probe as it provides a mechanically and chemically robust, nanoscale probe. We demonstrate the probe's capabilities with images of the magnetic field gradients close to the surface of a Py dot in both the multi-domain and vortex states. We show the FeCNT probe is accurately described by a single magnetic monopole located at its tip. Its effective magnetic charge is determined by the diameter of the iron wire and its saturation magnetization 4?M(s) ? 2.2 × 10(4)G. A magnetic monopole probe is advantageous as it enables quantitative measurements of the magnetic field gradient close to the sample surface. The lateral resolution is defined by the diameter of the iron wire and the probe-sample separation. PMID:21864777

Wolny, F; Obukhov, Y; Mühl, T; Weissker, U; Philippi, S; Leonhardt, A; Banerjee, P; Reed, A; Xiang, G; Adur, R; Lee, I; Hauser, A J; Yang, F Y; Pelekhov, D V; Büchner, B; Hammel, P C

2011-07-01

91

The Square Kilometre Array: A new probe of cosmic magnetism  

E-print Network

Magnetic fields are a fundamental part of many astrophysical phenomena, but the evolution, structure and origin of magnetic fields are still unresolved problems in physics and astrophysics. When and how were the first fields generated? Are present-day magnetic fields the result of standard dynamo action, or do they represent rapid or recent field amplification through other processes? What role do magnetic fields play in turbulence, cosmic ray acceleration and structure formation? I explain how the Square Kilometre Array (SKA), a next-generation radio telescope, can deliver stunning new data-sets that will address these currently unanswered issues. The foundation for these experiments will be an all-sky survey of rotation measures, in which Faraday rotation toward >10^7 background sources will provide a dense grid for probing magnetism in the Milky Way, nearby galaxies, and in distant galaxies, clusters and protogalaxies. Using these data, we can map out the evolution of magnetized structures from redshifts z > 3 to the present, can distinguish between different origins for seed magnetic fields in galaxies, and can develop a detailed model of the magnetic field geometry of the intergalactic medium and of the overall Universe. In addition, the SKA will certainly discover new magnetic phenomena beyond what we can currently predict or imagine.

Bryan M. Gaensler

2006-03-02

92

The First Magnetic Fields  

E-print Network

We review current ideas on the origin of galactic and extragalactic magnetic fields. We begin by summarizing observations of magnetic fields at cosmological redshifts and on cosmological scales. These observations translate into constraints on the strength and scale magnetic fields must have during the early stages of galaxy formation in order to seed the galactic dynamo. We examine mechanisms for the generation of magnetic fields that operate prior during inflation and during subsequent phase transitions such as electroweak symmetry breaking and the quark-hadron phase transition. The implications of strong primordial magnetic fields for the reionization epoch as well as the first generation of stars is discussed in detail. The exotic, early-Universe mechanisms are contrasted with astrophysical processes that generate fields after recombination. For example, a Biermann-type battery can operate in a proto-galaxy during the early stages of structure formation. Moreover, magnetic fields in either an early genera...

Widrow, Lawrence M; Schleicher, Dominik; Subramanian, Kandaswamy; Tsagas, Christos G; Treumann, Rudolf A

2011-01-01

93

Solar magnetic fields - Extended.  

NASA Technical Reports Server (NTRS)

Spacecraft observations of the interplanetary magnetic field have revealed that almost always each solar rotation can be divided into sectors, within each of which the field has a predominant polarity toward the sun or away from the sun. Comparisons of this interplanetary magnetic sector pattern with observations of the photospheric magnetic field have revealed a similar solar magnetic pattern. The boundaries between solar magnetic sectors are approximately in the north-south direction over a wide range of latitudes on both sides of the equator. This solar magnetic sector structure can be described as a rotating dipole whose magnetic axis makes an angle of approximately 90 deg with the axis of rotation. Possible similarities between this solar-sector magnetism and the models derived from observations of stellar magnetism are discussed.

Wilcox, J. M.

1971-01-01

94

Magnetic microwire probes for the magnetic rod interfacial stress rheometer.  

PubMed

The magnetic needle interfacial shear rheometer is a valuable tool for the study of the mechanical properties of thin fluid films or monolayers. However, it is difficult to differentiate the interfacial and subphase contributions to the drag on the needle. In principle, the problem can be addressed by decreasing the needle diameter, which decreases the bulk contribution while the interfacial contribution remains essentially the same. Here we show the results obtained when using a new type of needle, that of magnetic microwires with diameter approximately 10 times thinner than for commercial needles. We show that the lower inertia of the microwires calls for a new calibration procedure. We propose such a new calibration procedure based on the flow field solution around the needle introduced in refs 1 and 2. By measuring thin silicone oil films with well-controlled interfacial viscosities as well as eicosanol (C20) and pentadecanoic acid (PDA, C15) Langmuir monolayers, we show that the new calibration method works well for standard needles as well as for the microwire probes. Moreover, we show that the analysis of the force terms contributing to the force on the needle helps to ascertain whether the measurements obtained are reliable for given surface shear viscosity values. We also show that the microwire probes have at least a 10-fold-lower resolution limit, allowing one to measure interfacial viscosities as low as 10(-7) N·m/s. PMID:25495270

Tajuelo, J; Pastor, J M; Martínez-Pedrero, F; Vázquez, M; Ortega, F; Rubio, R G; Rubio, M A

2015-02-01

95

Mapping Magnetic Field Lines  

NSDL National Science Digital Library

This is a lesson about the magnetic field of a bar magnet. The lesson begins with an introductory discussion with learners about magnetism to draw out any misconceptions that may be in their minds. Then, learners freely experiment with bar magnets and various materials, such as paper clips, rulers, copper or aluminum wire, and pencils, to discover that magnets attract metals containing iron, nickel, and/or cobalt but not most other materials. Next, learners experiment with using a magnetic compass to discover how it is affected by the magnet and then draw the magnetic field lines of the magnet by putting dots at the location of the compass arrow. This is the first lesson in the first session of the Exploring Magnetism teacher guide.

96

Cyclic Magnetic Field Reconnection  

NASA Astrophysics Data System (ADS)

Using a 2.5D electromagnetic particle-in-cell model, we study the magnetic field reconnection around the rotating plasma embedded in a magnetic field. Considering plasma rotation driven by an external electric field, it was found that during one rotational cycle, first the magnetic field energy increases and then decreases to its initial value. The magnetic reconnection occurring during this cycle plays two roles: first, it produces the closed magnetic islands and later on it reopens them to the initial form of magnetic field lines. Thus, the magnetic reconnection can be cyclically repeated in following plasma rotations. Simultaneously, the kinetic particle energy in the system increases due to dissipative processes in this externally driven plasma system. We think that this cyclic reconnection can operate around rapidly rotating stars and in the plasma vortices formed in unstable plasma flows.

Karlický, Marian

2009-02-01

97

Comparison of magnetic probe calibration at nano and millitesla magnitudes  

NASA Astrophysics Data System (ADS)

Magnetic field probes are invaluable diagnostics for pulsed inductive plasma devices where field magnitudes on the order of tenths of tesla or larger are common. Typical methods of providing a broadband calibration of dot{{B}} probes involve either a Helmholtz coil driven by a function generator or a network analyzer. Both calibration methods typically produce field magnitudes of tens of microtesla or less, at least three and as many as six orders of magnitude lower than their intended use. This calibration factor is then assumed constant regardless of magnetic field magnitude and the effects of experimental setup are ignored. This work quantifies the variation in calibration factor observed when calibrating magnetic field probes in low field magnitudes. Calibration of two dot{{B}} probe designs as functions of frequency and field magnitude are presented. The first dot{{B}} probe design is the most commonly used design and is constructed from two hand-wound inductors in a differential configuration. The second probe uses surface mounted inductors in a differential configuration with balanced shielding to further reduce common mode noise. Calibration factors are determined experimentally using an 80.4 mm radius Helmholtz coil in two separate configurations over a frequency range of 100-1000 kHz. A conventional low magnitude calibration using a vector network analyzer produced a field magnitude of 158 nT and yielded calibration factors of 15 663 ± 1.7% and 4920 ± 0.6% {T}/{V {s}} at 457 kHz for the surface mounted and hand-wound probes, respectively. A relevant magnitude calibration using a pulsed-power setup with field magnitudes of 8.7-354 mT yielded calibration factors of 14 615 ± 0.3% and 4507 ± 0.4% {T}/{V {s}} at 457 kHz for the surface mounted inductor and hand-wound probe, respectively. Low-magnitude calibration resulted in a larger calibration factor, with an average difference of 9.7% for the surface mounted probe and 12.0% for the hand-wound probe. The maximum difference between relevant and low magnitude tests was 21.5%.

Pahl, Ryan A.; Rovey, Joshua L.; Pommerenke, David J.

2014-01-01

98

The advantages of the magnetic structure in ferromagnetic-film-coated carbon nanotube probes  

NASA Astrophysics Data System (ADS)

The magnetic structures of ferromagnetic-film-coated carbon nanotube (CNT) probes and conventional pyramidal probes for a magnetic force microscope (MFM) were simulated using three-dimensional micromagnetic simulation. The CNT-MFM probes with a total probe diameter less than 60 nm are almost uniformly magnetized along the longitudinal direction of the CNT, which is the ideal magnetic structure for MFM observations. On the other hand, the pyramidal probes had a vortex structure around the point tip, which suggests that they require a greater thickness of the ferromagnetic film because only part of the magnetic moment participates in the detection of the z-component of the stray field from samples. The advantages of the CNT-MFM probe are uniform magnetization along the longitudinal direction and magnetic imaging ability using a smaller coating thickness.

Manago, T.; Asada, H.; Uzumaki, T.; Takano, F.; Akinaga, H.; Kuramochi, H.

2012-01-01

99

Magnetic field generator  

DOEpatents

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.

Krienin, Frank (Shoreham, NY)

1990-01-01

100

Cosmic Magnetic Fields  

Microsoft Academic Search

Most of the visible matter in the Universe is in a plasma state, or more specifically is composed of ionized or partially ionized gas permeated by magnetic fields. Thanks to recent advances on the theory and detection of cosmic magnetic fields there has been a worldwide growing interest in the study of their role on the formation of astrophysical sources

Elisabete M. de Gouveia Dal Pino; Dal Pino

2006-01-01

101

The solar magnetic field  

Microsoft Academic Search

The magnetic field of the Sun is the underlying cause of the many diverse phenomena combined under the heading of solar activity. Here we describe the magnetic field as it threads its way from the bottom of the convection zone, where it is built up by the solar dynamo, to the solar surface, where it manifests itself in the form

Sami K. Solanki; Bernd Inhester; Manfred Schüssler

2006-01-01

102

Dynamic optical probing of the magnetic anisotropy of nickelferrite nanoparticles  

Microsoft Academic Search

Field dependence of dynamic magneto-orientational birefringence in a ferrocolloid based on the nickel-ferrite nanoparticles is examined. The nanoparticles are electrostatically stabilized and suspended in glycerin at low-volume fractions Phi<=0.75%. The colloids are tested under crossed magnetic fields: an alternating weak (probing) and a constant strong (bias) one. By comparison to a theoretical model of the birefringence relaxation, an evaluation of

Yu. L. Raikher; V. I. Stepanov; J. Depeyrot; M. H. Sousa; F. A. Tourinho; E. Hasmonay; R. Perzynski

2004-01-01

103

Local magnetic probes of superconductors  

Microsoft Academic Search

Investigations of the magnetic properties of high temperature superconductors (HTSs) have revealed the existence of striking new vortex phenomena due, in part, to their strong crystalline anisotropy, very short coherence lengths and the much larger thermal energies available at high temperatures. Some of these phenomena, for example vortex lattice 'melting', pose serious problems for technological applications of the most anisotropic

Simon J. Bending

1999-01-01

104

Interplanetary Magnetic Field Lines  

NSDL National Science Digital Library

This web page provides information and a graphical exercise for students regarding the interaction between magnetic field lines and a plasma. The activity involves tracing a typical interplanetary magnetic field line, dragged out of a location on the Sun by the radial flow of the solar wind. This illustrates the way magnetic field lines are "frozen to the plasma" and the wrapping of field lines due to the rotation of the sun. This is part of the work "The Exploration of the Earth's Magnetosphere". A Spanish translation is available.

Stern, David

2005-04-27

105

Solar polar magnetic field  

NASA Astrophysics Data System (ADS)

The solar polar magnetic field has attracted the attention of researchers since the polar magnetic field reversal was revealed in the middle of the last century (Babcock and Livingston, 1958). The polar magnetic field has regularly reversed because the magnetic flux is transported from the sunspot formation zone owing to differential rotation, meridional circulation, and turbulent diffusion. However, modeling of these processes leads to ambiguous conclusions, as a result of which it is sometimes unclear whether a transport model is actual. Thus, according to the last Hinode data, the problem of a standard transport model (Shiota et al., 2012) consists in that a decrease in the polar magnetic flux in the Southern Hemisphere lags behind such a decrease in the flux in the Northern Hemisphere (from 2008 to June 2012). On the other hand, Svalgaard and Kamide (2012) consider that the asymmetry in the sign reversal simply results from the asymmetry in the emerging flux in the sunspot formation region. A detailed study of the polar magnetic flux evolution according to the Solar Dynamics Observatory (SDO) data for May 2010-December 2012 is illustrated in the present work. Helioseismic & Magnetic Imager (HMI) magnetic data in the form of a magnetic field component along the line of sight (the time resolution is 720 s) are used here. The magnetic fluxes in sunspot formation regions and at high latitudes have been compared.

Benevolenskaya, E. E.

2013-12-01

106

Magnetic Probe Construction using Thick-film Technology  

SciTech Connect

Thick-film technology has been successfully adapted for the design and fabrication of magnetic probes of a new type suitable for use in the simultaneous ultra-high vacuum and high-temperature environment of a nuclear fusion device. The maximum usable temperature is expected to be around 900 degrees C. This new probe has a specific sensitivity (coupling area per unit volume) an order of magnitude higher than a conventional coil. The new probe in one implementation is capable of simultaneously measuring magnetic field in three orthogonal directions about a single spatial point and in two frequency ranges. Low-frequency coils have a measured coupling area of 296-323 cm squared and a frequency response of about 300 kHz. High-frequency coils have a design coupling area of 12-15 cm squared.

Takahashi, H.; Sakakibara, S.; Kubota, Y.; and Yamada, H.

2001-02-02

107

Detecting Exoplanetary Magnetic Fields  

NASA Astrophysics Data System (ADS)

Asymmetries in exoplanet transits are proving to be a useful tool for furthering our understanding of magnetic activity on both stars and planets outside our Solar System.Near-UV observations of the WASP-12 system have revealed asymmetries in the timing of the transit when compared with the optical light curve. A number of possible explanations have been suggested for this variation, including the presence of a magnetospheric bow shock arising from the interaction of the planet's magnetic field with the stellar wind from it's host star. Such observations provide the first method for directly detecting the presence of a magnetic field on exoplanets.The shape and size of such asymmetries is highly dependent on the structure of the host stars magnetic field at the time of observation. This implies we may observe highly varying near-UV transit light curves for the same system. These variations can then be used to learn about the geometry of the host star's magnetic field.In this presentation I will show modelling a bow shock around an exoplanet can help us to not only detect, but also also place constraints on the magnetic field strength of hot Jupiters. For some systems, such as HD 189733, we have maps of the surface magnetic field of the star at various epochs. I will also show how incorporating these maps into a stellar wind model, I can model the formation of a bow shock around the planet and hence demonstrate the variability of the near-UV transits.

Llama, Joe

2015-01-01

108

Magnetic probing of the spatial development of discharges in a pulsed coaxial lamp  

Microsoft Academic Search

Results are presented in [2, 3] for experimental investigations of the magnetic field created by the pulsed coaxial lamps with discharge times of about 120 #sec. The results using the magnetic probe were compared with the results of high-speed motion pictures. It was established that maximal values of mag-netic fields correspond to nonuniform filling of the lamp discharge cavity. In

V. A. Alekseev; V. V. Gusev; B. V. Kalachev; V. N. Makarov; A. I. Sopin

1976-01-01

109

Eruptive solar magnetic fields  

Microsoft Academic Search

This paper considers the quasi-steady evolution of solar magnetic fields in response to gradual photospheric changes. Special interest is taken in the threshold of a sudden eruption in the solar atmosphere. The formal model of an evolving, force-free field dependent on two Cartesian coordinates has been treated previously, and we extend it to a field which is not force free

B. C. Low

1981-01-01

110

Mapping Magnetic Field Lines  

NSDL National Science Digital Library

This is an activity about electromagnetism. Learners will use a compass to map the magnetic field lines surrounding a coil of wire that is connected to a battery. This activity requires a large coil or spool of wire, a source of electricity such as 3 D-cell batteries or an AC to DC power adapter, alligator-clipped wire, and magnetic compasses. This is the third lesson in the second session of the Exploring Magnetism teachers guide.

111

The FIELDS experiment for Solar Probe Plus  

NASA Astrophysics Data System (ADS)

Many of our basic ideas on the plasma physics of acceleration, energy flow, and dissipation, and structure of the solar wind have never been rigorously confronted by direct experimental measurements in the region where these processes are actually occurring. Although Alfven waves, shocks, and magnetic reconnection are often invoked as heating mechanisms, there have never been any direct measurements of Alfvenic waves nor the associated Poynting flux nor any measurements of ion or electron kinetic energy flux in the region from 10 R_s to 30 R_s where the final stages of wind acceleration are believed to occur. The radial profiles of both slow and fast solar wind acceleration are based on remote-sensing measurements and have been obtained for only a few selected events. Thus, the spatial radial and perpendicular scales of the acceleration process have been averaged by line-of-sight effects and the possibility of intense localized acceleration cannot be ruled out. The Solar Probe Plus (SPP) mission calls for the high quality fields and particles measurements required to solve the coronal heating and wind acceleration problem. The SPP 'FIELDS' experiment measures the electric and magnetic fields fundamental to the plasma physics of the structured and turbulent solar wind, flux ropes, collisionless shocks, and magnetic reconnection. FIELDS will make the first-ever measurements of the DC/Low-Frequency electric field inside of 1 AU allowing for in situ, high cadence measurements of the Poynting vector, the Elsasser variables, and E/B diagnostics of the wave spectrum to fce in the solar wind. SPP/FIELDS measures the radio wave (type III and II) signatures of microflares, energized electrons, and CME propagation. SPP/ FIELDS measures the plasma electron density to ~2% accuracy and the core electron temperature to ~5-10% accuracy more than 90% of the time at perihelion. FIELDS will also measure the in situ density fluctuation spectrum and structures at a very high cadence (? 10 kHz) and provide definitive signatures of the turbulent nature and heating of the solar wind plasma. Furthermore, SPP/FIELDS measures the impact rate and sig- natures of dust from micron- to nano-scales, by measuring the voltage signature of dust impacts on the spacecraft. FIELDS will also measure the floating potential of the SPP spacecraft, which is essential for correcting in situ electron data. The SPP/FIELDS experiment combines four (4) deployable electric antennas, fluxgate and search coil magnetometers and the associated signal processing electronics into a scientifically and technically integrated package. SPP/FIELDS makes very high cadence measurements of fields and density and employs an internal burst memory for intelligent data selection. FIELDS is required to measure very large plasma potentials and electric fields (~10V) and uses floating ground (+/- 100V) power preamplifiers. The SPP/FIELDS team has performed 3D plasma simulations of the SPP spacecraft plasma environ- ment, which reveal enormous voltage fluctuation levels in the plasma wake behind the spacecraft. This voltage noise dominates the true signal by orders of magnitude in the critical DC/LF frequency range. Therefore, we are proposing a design which places the four (4) electric antennas in front of the spacecraft ahead of the heat shield.

Bale, S.; Spp/Fields Team

2010-12-01

112

Properties of electromagnetic field focusing probe.  

PubMed

The electromagnetic field focusing (EFF) apparatus consists of a radio frequency generator, solenoidal coil, and a hand-held or catheter probe. Applications such as aneurysm treatment, angioplasty, and neurosurgery in various models have been reported. The probe is operated in the near field (within one wavelength of an electromagnetic field source) of a coil inducing eddy currents in biological tissues, producing maximal convergence of the induced current at the probe tip. The probe produces very high temperatures depending on the wattage selected for the given radio frequency of output power. The high temperature can be used in cutting, cauterizing, or vaporizing. The EFF probe is comparable to different types of lasers and to bipolar and monopolar cautery. The EFF probe can be used with catheters or endoscopes. Objectives of this study were to determine what the thermal properties of the EFF probe are and how instrument parameters can be varied to obtain different temperatures in the tissue near the probe tip. In this study an F2 catheter was used as an insulated sheath and the tip of the guide wire was used as the probe tip. Different powers, wave forms, coil-to-probe distances, and probe-tip lengths were tested on a phantom that simulates tissue electrical properties. Some of the experiments were conducted under normal saline to simulate treatment of tissue with body fluids such as blood vessels or brain tissue under normal physiologic conditions. It is concluded that the EFF probe has the advantages of easy manipulation, relative safety, cost effectiveness, and a high degree of spatial control.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:3177961

Yamanashi, W S; Yassa, N A; Hill, D L; Patil, A A; Lester, P D

1988-11-01

113

Magnetic field dosimeter development  

SciTech Connect

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.

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

1980-09-01

114

Solar magnetic fields  

Microsoft Academic Search

Since the structuring and variability of the Sun and other stars are governed by magnetic fields, much of present-day stellar\\u000a physics centers around the measurement and understanding of the magnetic fields and their interactions. The Sun, being a prototypical\\u000a star, plays a unique role in astrophysics, since its proximity allows the fundamental processes to be explored in detail.\\u000a The PRL

J. O. Stenflo

2008-01-01

115

Solar magnetic fields  

Microsoft Academic Search

This paper is a review of our observational knowledge on solar magnetic fields. In Section 1 we make an attempt to summarize all observations of the general magnetic field (m.f.) of the Sun. Section 2 deals with the local m.f. at low latitudes and their connection with some features on the disk. The m.f. of sunspots and their peculiar character

A. Severny

1964-01-01

116

Mapping the magnetic field vector in a fountain clock  

SciTech Connect

We show how the mapping of the magnetic field vector components can be achieved in a fountain clock by measuring the Larmor transition frequency in atoms that are used as a spatial probe. We control two vector components of the magnetic field and apply audio frequency magnetic pulses to localize and measure the field vector through Zeeman spectroscopy.

Gertsvolf, Marina; Marmet, Louis [National Research Council of Canada, Ottawa, Ontario K1A 0R6 (Canada)

2011-12-15

117

Probes of strong-field gravity  

E-print Network

In this thesis, I investigate several ways to probe gravity in the strong-field regime. These investigations focus on observables from the gravitational dynamics, i.e. when time derivatives are large: thus I focus on sources ...

Stein, Leo Chaim

2012-01-01

118

Magnetic and Langmuir Probe Measurements on the Plasmoid Thruster Experiment (PTX)  

NASA Technical Reports Server (NTRS)

The Plasmoid Thruster Experiment (PTX) operates by inductively producing plasmoids in a conical theta-pinch coil and ejecting them at high velocity. A plasmoid is a plasma with an imbedded closed magnetic field structure. The shape and magnetic field structure of the translating plasmoids have been measured with of an array of magnetic field probes. Six sets of two B-dot probes were constructed for measuring B(sub z) and B(sub theta), the axial and azimuthal components of the magnetic field. The probes are wound on a square G10 form, and have an average (calibrated) NA of 9.37 x l0(exp -5) square meters, where N is the number of turns and A is the cross-sectional area. The probes were calibrated with a Helmholtz coil, driven by a high-voltage pulser to measure NA, and by a signal generator to determine the probe's frequency response. The plasmoid electron number density n(sub e) electron temperature T(sub e), and velocity ratio v/c(sub m), (where v is the bulk plasma flow velocity and c(sub m), is the ion thermal speed) have also been measured with a quadruple Langmuir probe. The Langmuir probe tips are 10 mm long, 20-mil diameter stainless steel wire, housed in a 6-inch long 4-bore aluminum rod. Measurements on PTX with argon and hydrogen from the magnetic field probes and quadruple Langmuir probe will be presented in this paper.

Koelfgen, Syri J.; Eskridge, Richard; Lee, Michael H.; Martin, Adam; Hawk, Clark W.; Fimognan, Peter

2004-01-01

119

Magnetic Probe to Study Plasma Jets for Magneto-Inertial Fusion  

SciTech Connect

A probe has been constructed to measure the magnetic field of a plasma jet generated by a pulsed plasma rail-gun. The probe consists of two sets of three orthogonally-oriented commercial chip inductors to measure the three-dimensional magnetic field vector at two separate positions in order to give information about the magnetic field evolution within the jet. The strength and evolution of the magnetic field is one of many factors important in evaluating the use of supersonic plasma jets for forming imploding spherical plasma liners as a standoff driver for magneto-inertial fusion.

Martens, Daniel [Los Alamos National Laboratory; Hsu, Scott C. [Los Alamos National Laboratory

2012-08-16

120

Magnetic Field Problem: Current  

NSDL National Science Digital Library

A cross section of a circular wire loop carrying an unknown current is shown above. The arrows represent the direction of the magnetic field. The color of the arrows represents the magnitude of the field with magnitude increasing as the color changes from blue to green to red to black. You can double-click in the animation to add magnetic field lines, click-drag the center of the loop to reposition it, and click-drag the top or bottom of the loop to change its size.

Wolfgang Christian

121

Magnetic Field Solver  

NASA Technical Reports Server (NTRS)

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.

Ilin, Andrew V.

2006-01-01

122

Probes for High Field Solid-state NMR of Lossy Biological Samples  

PubMed Central

In solid-state NMR exphydrated samples biopolymers are susceptible to radio-frequency heating and have a significant impact on probe tuning frequency and performance parameters such as sensitivity. These considerations are increasingly important as magnetic field strengths increase with improved magnet technology. Recent developments in the design, construction, and performance of probes for solid-state NMR experiments on stationary lossy biological samples at high magnetic fields are reviewed. PMID:20435493

Grant, Christopher V.; Wu, Chin H.; Opella, Stanley J.

2010-01-01

123

Electrically silent magnetic fields.  

PubMed Central

There has been a significant controversy over the past decade regarding the relative information content of bioelectric and biomagnetic signals. In this paper we present a new, theoretical example of an electrically-silent magnetic field, based on a bidomain model of a cylindrical strand of tissue generalized to include off-diagonal components in the conductivity tensors. The physical interpretation of the off-diagonal components is explained, and analytic expressions for the electrical potential and the magnetic field are found. These expressions show that information not obtainable from electrical potential measurements can be obtained from measurements of the magnetic field in systems with conductivity tensors more complicated than those previously examined. PMID:3779008

Roth, B J; Wikswo, J P

1986-01-01

124

Field Mapping System for Solenoid Magnet  

NASA Astrophysics Data System (ADS)

A three-dimensional Hall probe mapping system for measuring the solenoid magnet of PLS photo-cathode RF e-gun has been developed. It can map the solenoid field either in Cartesian or in cylindrical coordinate system with a measurement reproducibility better than 5 × 10-5 T. The system has three axis motors: one for the azimuthal direction and the other two for the x and z direction. This architecture makes the measuring system simple in fabrication. The magnetic center was calculated using the measured axial component of magnetic field Bz in Cartesian coordinate system because the accuracy of magnetic axis measurement could be improved significantly by using Bz, instead of the radial component of magnetic field Br. This paper describes the measurement system and summarizes the measurement results for the solenoid magnetic of PLS photo-cathode RF e-gun.

Park, K. H.; Jung, Y. K.; Kim, D. E.; Lee, H. G.; Park, S. J.; Chung, C. W.; Kang, B. K.

2007-01-01

125

Magnetic Fields in Galaxies  

NASA Astrophysics Data System (ADS)

The origin and evolution of cosmic magnetic fields, their strength and structure in intergalactic space, their first occurrence in young galaxies, and their dynamical importance for galaxy evolution remain widely unknown. Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized radio synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30 ?G) and in central starburst regions (50-100 ?G). Such fields are dynamically important; they can affect gas flows and drive gas inflows in central regions. Polarized radio emission traces ordered fields which can be regular or anisotropic turbulent, generated from isotropic turbulent fields by compression or shear. The strongest ordered fields of 10-15 ?G strength are generally found in interarm regions and follow the orientation of adjacent gas spiral arms. In galaxies with strong density waves, ordered (anisotropic turbulent) fields are also observed at the inner edges of the spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions of starburst galaxies. Ordered fields in interacting galaxies have asymmetric distributions and are an excellent tracer of past interactions between galaxies or with the intergalactic medium. Irregular galaxies host isotropic turbulent fields often of similar strength as in spiral galaxies, but only weak ordered fields. Faraday rotation measures (RM) of the diffuse polarized radio emission from the disks of several galaxies reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by a mean-field ? -? dynamo. So far no indications were found in external galaxies of large-scale field reversals, like the one in the Milky Way. Ordered magnetic fields are also observed in radio halos around edge-on galaxies out to large distances from the plane, with X-shaped patterns. In the outflow cone above a starburst region of NGC 253, RM data indicate a helical magnetic field.

Beck, Rainer

126

Magnetic probing of the solar interior  

NASA Technical Reports Server (NTRS)

The magnetic field patterns in the region beneath the solar photosphere is determined. An approximate method for downward extrapolation of line of sight magnetic field measurements taken at the solar photosphere was developed. It utilizes the mean field theory of electromagnetism in a form thought to be appropriate for the solar convection zone. A way to test that theory is proposed. The straightforward application of the lowest order theory with the complete model fit to these data does not indicate the existence of any reasonable depth at which flux conservation is achieved.

Benton, E. R.; Estes, R. H.

1985-01-01

127

Solar magnetic fields and convection. IX - A primordial magnetic field  

Microsoft Academic Search

Observational evidence is reviewed in an attempt to decide between a reversing (dynamo) and a nonreversing primordial solar poloidal magnetic field. The data examined include Zeeman-effect measurements, measurements of gross magnetic fluxes in individual magnetic elements, determinations of average field strength, observations of polar-cap magnetic fields, eclipse observations of coronal structure, and observations of interplanetary-magnetic-field polarity reversals. It is suggested

J. H. Piddington

1977-01-01

128

Designing magnets with prescribed magnetic fields  

NASA Astrophysics Data System (ADS)

We present a novel design method capable of finding the magnetization densities that generate prescribed magnetic fields. The method is based on the solution to a simple variational inequality and the resulting designs have simple piecewise-constant magnetization densities. By this method, we obtain new designs of magnets that generate commonly used magnetic fields: uniform magnetic fields, self-shielding fields, quadrupole fields and sextupole fields. Further, it is worth noting that this method is not limited to the presented examples, and in particular, three-dimensional designs can be constructed in a similar manner. In conclusion, this novel design method is anticipated to have broad applications where specific magnetic fields are important for the performance of the devices.

Liu, Liping

2011-03-01

129

A versatile variable field module for field and angular dependent scanning probe microscopy measurements  

E-print Network

We demonstrate a versatile variable field module (VFM) with capability of both field and angular dependent measurements up to 1800 Oe for scanning probe system. The magnetic field strength is changed by adjusting the distance between a rare earth magnet and the probe tip and is monitored in-situ by a built-in Hall sensor. Rotating the magnet allows the field vector to change from the horizontal to vertical direction and makes it possible to do angular dependent measurements. The capability of the VFM system is demonstrated by degaussing a floppy disk media with increasing magnetic field. Angular dependent measurements clearly show the evolution of magnetic domain structures, with a completely reversible magnetic force microscopy phase contrast observed when the magnetic field is rotated by 180{\\deg}. A further demonstration of out-of-plane and in-plane magnetic switching of CoFe2O4 pillars in CoFe2O4-BiFeO3 nanocomposites was presented and discussed.

Liu, Hongxue; Lu, Jiwei; Wolf, Stuart; Hodgson, Jim; Rutgers, Maarten

2013-01-01

130

High field superconducting magnets  

NASA Technical Reports Server (NTRS)

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.

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

2011-01-01

131

Nuclear Magnetic Resonance and Magnetic Field Measurements  

NSDL National Science Digital Library

This laboratory is designed for students to become familiar with the principles and detection techniques of Nuclear Magnetic Resonance (NMR), examine the relationship between current and magnetic field in an electromagnet, and gain experience in the use of magnetic field measurement techniques.

2012-01-04

132

Probing latitudinal variations of the solar magnetic field in cycles 21-23 by Parker's Two-Layer Dynamo Model with meridional circulation  

NASA Astrophysics Data System (ADS)

Principle component analysis (PCA) of the solar background magnetic field (SBMF) measured from Wilcox Solar Observatory (WSO) magnetograms revealed the following principal components (PCs) in latitudes: two main symmetric components, which are the same for all cycles 21-23, and three pairs of asymmetric components, which are unique for each cycle. These SBMF variations are assumed to be those of poloidal magnetic field travelling slightly off-phase from pole to pole while crossing the equator. They are assumed to be caused by a joint action of dipole and quadruple magnetic sources in the Sun. In the current paper, we make the first attempt to interpret these latitudinal variations in the surface magnetic field with Parker's two-layer dynamo model. The latitudinal distributions of such waves are simulated for cycles 21-23 by the modified Parker's dynamo model taking into account both ? and ? effects operating simultaneously in the two (upper and lower) layers of the solar convective zone (SCZ) and having opposite directions of meridional circulation. The simulations are carried out for both dipole and quadruple magnetic sources with the dynamo parameters specifically selected to provide the curves fitting closely the PCs derived from SBMF variations in cycles 21-23. The simulations are optimised for matching the positions of maximums in latitude, the number of equator crossings and the phase difference between the two dynamo waves operating in the two layers. The dominant pair of PCs present in each cycle is found to be fully asymmetric with respect to the magnetic poles and produced by a magnetic dipole. This pair is found to account for the two main dynamo waves operating between the two magnetic poles. There are also three further pairs of waves unique to each cycle and associated with multiple magnetic sources in the Sun. For the odd cycle 21 the simulated poloidal field fits the observed PCs, only if they are produced by magnetic sources with a quadruple symmetry in both layers, while for the even cycle 22 the fit to the observed PCs is achieved only in the case of quadruple magnetic sources in the upper layer and dipole sources in the inner layer. For the other odd cycle 23 the fit to observation is obtained for the quadruple magnetic sources in the inner layer and the dipole sources in the upper layer. The magnitudes of dynamo numbers D defining the conditions (depth and latitude) of a magnetic flux formation and the numbers N of zeros (equator crossings by the waves) are found to increase and the meridional circulation speed to decrease with a cycle number increase (D = -700, N = 3 for cycle 21 and D = -104, N = 9 for cycle 23). The phase delays between the waves in each unique pairs are also found to increase with the cycle number from ~9° in cycle 21 to ~13° in cycle 23.

Popova, E.; Zharkova, V.; Zharkov, S.

2013-11-01

133

Field Directed Ordering in Magnetic Nanocrystal Structures  

NASA Astrophysics Data System (ADS)

Iron oxide nanocrystals (NCs) have been the focus of intense research owing to the observation of tunable magnetic properties which could lead to advances in many fields including magnetic storage devices and medicine. We have been targeting the use of iron oxide NCs as magnetoresistance (MR) based sensors using ordered NC arrays. In this work, we will present our efforts toward using external magnetic fields to induce intraparticle ordering in iron oxide NC drop cast films. We use x-ray diffraction to analyze effects of the external fields on the NC array structure, while using SQUID magnetometry to probe the effects of NC interactions on the magnetic properties of iron oxide NCs ranging from 5 - 20 nm in diameter. MR measurements suggest large changes in the MR ratio can be achieved using the directed ordering approach for NC arrays. Our work could provide new avenues towards the fabrication of new magnetic devices.

Lawson, Stuart; Meulenberg, Robert

2013-03-01

134

The Earth's Magnetic Field  

NSDL National Science Digital Library

This section of the Windows to the Universe website provides information and images about Earth's magnetic field (the magnetosphere), including detailed information about the aurora borealis, magnets, and solar wind. Windows to the Universe is a user-friendly learning system pertaining to the Earth and Space sciences. The objective of this project is to develop an innovative and engaging website that includes a rich array of documents, including images, movies, animations, and data sets that explore the Earth and Space sciences and the historical and cultural ties between science, exploration and the human experience. Links at the top of each page allow users to navigate between beginner, intermediate and advanced levels.

Johnson, Roberta

2000-07-01

135

Heat Capacity Measurements in Pulsed Magnetic Fields  

SciTech Connect

The new NHMFL 60T quasi-continuous magnet produces a flat-top field for a period of 100 ms at 60 Tesla, and for longer time at lower fields, e.g. 0.5 s at 45 Tesla. We have developed for the first time the capability to measure heat capacity at very high magnetic fields in the NHMFL 60T quasi-continuous magnet at LANL, using a probe built out of various plastic materials. The field plateau allows us to utilize a heat-pulse method to obtain heat capacity data. Proof-of-principle heat capacity experiments were performed on a variety of correlated electron systems. Both magnet performance characteristics and physical properties of various materials studied hold out a promise of wide application of this new tool.

Jaime, M.; Movshovich, R.; Sarrao, J.L.; Kim, J.; Stewart, G.; Beyermann, W.P.; Canfield, P.C.

1998-10-23

136

Antenna Near-Field Probe Station Scanner  

NASA Technical Reports Server (NTRS)

A miniaturized antenna system is characterized non-destructively through the use of a scanner that measures its near-field radiated power performance. When taking measurements, the scanner can be moved linearly along the x, y and z axis, as well as rotationally relative to the antenna. The data obtained from the characterization are processed to determine the far-field properties of the system and to optimize the system. Each antenna is excited using a probe station system while a scanning probe scans the space above the antenna to measure the near field signals. Upon completion of the scan, the near-field patterns are transformed into far-field patterns. Along with taking data, this system also allows for extensive graphing and analysis of both the near-field and far-field data. The details of the probe station as well as the procedures for setting up a test, conducting a test, and analyzing the resulting data are also described.

Zaman, Afroz J. (Inventor); Lee, Richard Q. (Inventor); Darby, William G. (Inventor); Barr, Philip J. (Inventor); Lambert, Kevin M (Inventor); Miranda, Felix A. (Inventor)

2011-01-01

137

Review of MFTF yin-yang magnet displacement and magnetic field measurements and calculations  

SciTech Connect

During the recent testing of the MFTF yin-yang magnet, measurements of coil position, structural case strain, and magnetic field were made to verify calculated values. Measurements to detect magnet movement were taken throughout cooldown and during the operation of the magnet. The magnetic field at the mirror points was measured by Hall-effect probes. The magnet position, structural case strain, and magnetic field measurements indicated a reasonably close correlation with calculated values. Information obtained from the yin-yang test has been very useful in setting realistic mechanical alignment values for the new MFTF-B magnet system.

Hanson, C.L.; Myall, J.O.; Wohlwend, J.W.

1983-11-21

138

Plasmonic concentrator of magnetic field of light  

NASA Astrophysics Data System (ADS)

We propose an efficient concentrator of the magnetic component of evanescent field of light for measuring magnetic responses of nanostructures. It is in the form of a tapered fiber probe, which in its final part has corrugations along the angular dimension and is coated with metal except for the aperture at the tip. Internal, azimuthally polarized illumination is concentrated into a subwavelength spot with a strong longitudinal magnetic component Hz. Within the visual range of wavelengths 400-700 nm, the energy density of Hz is up to 50 times larger than that of the azimuthal electric E? one. This dominant Hz contribution may be used for magnetic excitation of elementary cells of metamaterials with a single probe guiding a wide spectrum of generated plasmons.

Wróbel, Piotr; Antosiewicz, Tomasz J.; Stefaniuk, Tomasz; Szoplik, Tomasz

2012-10-01

139

High sensitivity piezomagnetic force microscopy for quantitative probing of magnetic materials at the nanoscale.  

PubMed

Accurate scanning probing of magnetic materials at the nanoscale is essential for developing and characterizing magnetic nanostructures, yet quantitative analysis is difficult using the state of the art magnetic force microscopy, and has limited spatial resolution and sensitivity. In this communication, we develop a novel piezomagnetic force microscopy (PmFM) technique, with the imaging principle based on the detection of magnetostrictive response excited by an external magnetic field. In combination with the dual AC resonance tracking (DART) technique, the contact stiffness and energy dissipation of the samples can be simultaneously mapped along with the PmFM phase and amplitude, enabling quantitative probing of magnetic materials and structures at the nanoscale with high sensitivity and spatial resolution. PmFM has been applied to probe magnetic soft discs and cobalt ferrite thin films, demonstrating it as a powerful tool for a wide range of magnetic materials. PMID:23720016

Chen, Qian Nataly; Ma, Feiyue; Xie, Shuhong; Liu, Yuanming; Proksch, Roger; Li, Jiangyu

2013-07-01

140

The CMS Magnetic Field Map Performance  

E-print Network

The Compact Muon Solenoid (CMS) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive featuresinclude a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10000-ton return yoke made of construction steel. Accurate characterization of the magnetic field everywhere in the CMS detector is required. During two major tests of the CMS magnet the magnetic flux density was measured inside the coil in a cylinder of 3.448 m diameter and 7 m length with a specially designed field-mapping pneumatic machine as well as in 140 discrete regions of the CMS yoke with NMR probes, 3-D Hall sensors and flux-loops. A TOSCA 3-D model of the CMS magnet has been developed to describe the magnetic field everywhere outside the tracking volume measured with the field-mapping machine. A volume based representation of the magnetic field is used to provide the CMS simulation and reconstruction software with the magnetic field values. The value of the field at a given point of a volume is obtained by interpolation from a regular grid of values resulting from a TOSCA calculation or, when available, from a parameterization. The results of the measurements and calculations are presented, compared and discussed.

V. I. Klyukhin; N. Amapane; V. Andreev; A. Ball; B. Curé; A. Hervé; A. Gaddi; H. Gerwig; V. Karimaki; R. Loveless; M. Mulders; S. Popescu; L. I. Sarycheva; T. Virdee

2011-10-04

141

Mars Observer magnetic fields investigation  

Microsoft Academic Search

The magnetic fields experiment designed for the Mars Observer mission will provide definitive measurements of the Martian magnetic field from the transition and mapping orbits planned for the Mars Observer. The paper describes the instruments (which include a classical magnetometer and an electron reflection magnetometer) and techniques designed to investigate the nature of the Martian magnetic field and the Mars-solar

J. E. P. Connerney; P. Wasilewski; R. P. Lin; K. A. Anderson; C. W. Carlson; J. McFadden; D. W. Curtis; H. Reme; A. Cros; J. L. Médale; J. A. Sauvaud; C. d'Uston; S. J. Bauer; P. Cloutier; Michael Mayhew; N. F. Ness

1992-01-01

142

The WIND magnetic field investigation  

Microsoft Academic Search

The magnetic field experiment on WIND will provide data for studies of a broad range of scales of structures and fluctuation characteristics of the interplanetary magnetic field throughout the mission, and, where appropriate, relate them to the statics and dynamics of the magnetosphere. The basic instrument of the Magnetic Field Investigation (MFI) is a boom-mounted dual triaxial fluxgate magnetometer and

R. P. Lepping; M. H. Ac?na; L. F. Burlaga; W. M. Farrell; J. A. Slavin; K. H. Schatten; F. Mariani; N. F. Ness; F. M. Neubauer; Y. C. Whang; J. B. Byrnes; R. S. Kennon; P. V. Panetta; J. Scheifele; E. M. Worley

1995-01-01

143

Magnetic field switchable dry adhesives.  

PubMed

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. PMID:25588470

Krahn, Jeffrey; Bovero, Enrico; Menon, Carlo

2015-02-01

144

Study of interplanetary magnetic field with Ground State Alignment  

NASA Astrophysics Data System (ADS)

We demonstrate a new way of studying interplanetary magnetic field—Ground State Alignment (GSA). Instead of sending thousands of space probes, GSA allows magnetic mapping with any ground telescope facilities equipped with spectropolarimeter. The polarization of spectral lines that are pumped by the anisotropic radiation from the Sun is influenced by the magnetic realignment, which happens for magnetic field (<1 G). As a result, the linear polarization becomes an excellent tracer of the embedded magnetic field. The method is illustrated by our synthetic observations of the Jupiter's Io and comet Halley. Polarization at each point was constructed according to the local magnetic field detected by spacecrafts. Both spatial and temporal variations of turbulent magnetic field can be traced with this technique as well. The influence of magnetic field on the polarization of scattered light is discussed in detail. For remote regions like the IBEX ribbons discovered at the boundary of interstellar medium, GSA provides a unique diagnostics of magnetic field.

Shangguan, Jinyi; Yan, Huirong

2013-01-01

145

Spin Polarized Electron Probes and Magnetic Nanostructures  

SciTech Connect

OAK B188 This report summarizes progress to date in our theoretical research program, for the period from July 1, 2002 to November 1, 2003. In addition, our research priorities for the coming year are set forth. The reporting period has been a most exciting and significant one. For the past several years, one of our principal thrust areas has been development of the theory of spin dynamics in magnetic nanostructures with emphasis on the use of spin polarized electrons as probes of short wavelength spin dynamics in such entities. Our program stimulated the first experiment which detected large wave vector spin waves in ultrathin films in 1999 through spin polarized electron loss spectroscopy (SPEELS); the publication which announced this discovery was a joint publication between a group in Halle (Germany) with our theory effort. The continued collaboration has led to the design and implementation of the new SPEELS spectrometer and we now have in hand the first detailed measurements of spin wave dispersion in an ultrathin film. A second such spectrometer is now operational in the laboratory of Prof. H. Hopster, at UC Irvine. We are thus entering a most exciting new era in the spectroscopy of spin excitations in magnetic nanostructures. During the reporting period, we have completed very important new analyses which predict key aspects of the spectra which will be uncovered by these new instruments, and the calculations continue to be developed and to expand our understanding. In addition, we have initiated a new series of theoretical studies directed toward spin dynamics of single magnetic adatoms on metal surfaces, with STM based studies of this area n mind. In the near future, these studies will continue, and we will expand our effort into new areas of spin dynamics in magnetic nanostructures.

D.L. Mills

2003-10-15

146

Analysis and measurement of the 3D magnetic field in a rotating magnetic field driven FRC  

NASA Astrophysics Data System (ADS)

A translatable three-axis probe was installed on TCSU shortly before its shutdown. The probe has 90 windings that simultaneously measure Br, B?, and Bz at 30 radial positions. Positioning the probe at multiple axial positions and taking multiple repeatable shots allows for a full r-z map of the magnetic field. Probe measurements are used to calculate the end-shorting torque and the rotating magnetic field (RMF) torque. The torque applied to the plasma is the RMF torque reduced by the shorting torque. An estimate of the plasma resistivity is made based on the steady state balance between the applied torque and the resistive torque. The steady state data from applying a 10 kHz low pass filter used in conjunction with data at the RMF frequency yields a map of the full 3D rotating field structure. Data from even- and odd-parity experiments will be presented. The NIMROD code has been adapted to simulate the TCSU experiment using boundary conditions adjusted to match both even- and odd-parity experimental conditions. A comparison of the n=0 components of the calculated fields to the 3-axis probe measurements shows agreement in the magnetic field structure of the FRC as well as in the jet region.

Velas, K. M.; Milroy, R. D.

2012-10-01

147

Muon g-2 Measurement: Determination of the Magnetic Field  

Microsoft Academic Search

Determination of the magnetic field B in the muon storage ring of the muon g-2 experiment (E821) in Brookhaven National Laboratory is obtained from NMR measurements[1] with probes in a hermetically sealed trolley which can be moved around the storage ring in vacuum. Each of 17 probes inside the trolley has a precision of 0.04ppm(rms) in a constant magnetic field

Huaizhang Deng; Ralf Prigl

2001-01-01

148

The CMS Magnetic Field Map Performance  

E-print Network

The Compact Muon Solenoid (CMS) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive featuresinclude a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10000-ton return yoke made of construction steel. Accurate characterization of the magnetic field everywhere in the CMS detector is required. During two major tests of the CMS magnet the magnetic flux density was measured inside the coil in a cylinder of 3.448 m diameter and 7 m length with a specially designed field-mapping pneumatic machine as well as in 140 discrete regions of the CMS yoke with NMR probes, 3-D Hall sensors and flux-loops. A TOSCA 3-D model of the CMS magnet has been developed to describe the magnetic field everywhere outside the tracking volume measured with the field-mapping machine. A volume based representation of the magnetic field is used to provide the CMS simulation and reconstruction software with the magnetic field ...

Klyukhin, VI; Sarycheva, L I; Klyukhin, V I; Ball, A; Gaddi, A; Amapane, N; Gerwig, H; Andreev, V; Cure, B; Mulders, M; Loveless, R; Karimaki, V; Popescu, S; Herve, A

2010-01-01

149

Suppression of probe background signals via B(1) field inhomogeneity.  

PubMed

A new approach combining a long pulse with the DEPTH sequence (Cory and Ritchey, Journal of Magnetic Resonance, 1988) greatly improves the efficiency for suppressing probe background signals arising from spinning modules. By applying a long initial excitation pulse in the DEPTH sequence, instead of a ?/2 pulse, the inhomogeneous B(1) fields outside the coil can dephase the background coherence in the nutation frame. The initial long pulse and the following two consecutive EXORCYCLE ? pulses function complementarily and prove most effective in removing background signals from both strong and weak B? fields. Experimentally, the length of the long pulse can be optimized around odd multiples of the ?/2 pulse, depending on the individual probe design, to preserve signals inside the coil while minimizing those from probe hardware. This method extends the applicability of the DEPTH sequence to probes with small differences in B? field strength between the inside and outside of the coil, and can readily combine with well-developed double resonance experiments for quantitative measurement. In general, spin systems with weak internal interactions are required to attain efficient and uniform excitation for powder samples, and the principles to determine the applicability are discussed qualitatively in terms of the relative strength of spin interactions, r.f. power and spinning rate. PMID:21349751

Feng, Jian; Reimer, Jeffrey A

2011-04-01

150

Fast superconducting magnetic field switch  

SciTech Connect

The superconducting magnetic switch or fast kicker magnet is employed with an 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 than 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. Magnetic switches and particularly fast kicker magnets are used in the accelerator industry to quickly deflect particle beams into and out of various transport lines, storage rings, dumps, and specifically to differentially route individual bunches of particles from a train of bunches which are injected or ejected from a given ring.

Goren, Y.; Mahale, N.K.

1995-12-31

151

Baryon magnetic moments in the background field method [rapid communication  

NASA Astrophysics Data System (ADS)

We present a calculation of the magnetic moments for the baryon octet and decuplet using the background-field method and standard Wilson gauge and fermion actions in the quenched approximation of lattice QCD. Progressively smaller static magnetic fields are introduced on a 244 lattice at beta = 6.0 and the pion mass is probed down to about 500 MeV. Magnetic moments are extracted from the linear response of the masses to the background field.

Lee, F. X.; Kelly, R.; Zhou, L.; Wilcox, W.

2005-10-01

152

Baryon magnetic moments in the external field method  

NASA Astrophysics Data System (ADS)

We present a calculation of the magnetic moments of the baryon octet and decuplet using the external field method and standard Wilson gauge and fermion actions in the quenched approximation. Progressively smaller static magnetic fields are introduced on a 24 4 lattice at beta=6.0 and the pion mass is probed down to about 500 MeV. Magnetic moments are extracted from the linear response of the masses to the external field.

Lee, F. X.; Kelly, R.; Zhou, L.; Wilcox, W.

2005-03-01

153

Baryon magnetic moments in the external field method  

E-print Network

We present a calculation of the magnetic moments of the baryon octet and decuplet using the external field method and standard Wilson gauge and fermion actions in the quenched approximation. Progressively smaller static magnetic fields are introduced on a $24^4$ latticeat beta=6.0 and the pion mass is probed down to about 500 MeV. Magnetic moments are extracted from the linear response of the masses to the external field.

F. X. Lee; R. Kelly; L. Zhou; W. Wilcox

2004-10-25

154

Modeling and Measurements by Hall probes of Magnetic Structures of Undulators HU256  

NASA Astrophysics Data System (ADS)

The magnetic calculations of the individual dipoles and dipoles in "undulator environment" were executed by means of Mermaid 3D Code and these results were confirmed by magnetic measurements of the individual dipoles and the assembled undulators. The magnetic parameters of all dipoles were estimated on basis of the mechanical measurement of the dipole characteristics (pole gap, yoke width, coil position) and the main dependences obtained from magnetic calculations and measurements. These parameters were used for optimal placing of the dipoles in undulators (sorting). The special Hall probe system was designed and manufactured for magnetic measurements of the undulators. It allowed us to observe the inner structure of the magnetic fields. At a magnetic field measurement accuracy of ± 15 ?T the accuracy of the 1st integral calculated on the basis of the measured magnetic fields is ˜ 50 ?Tm. All three undulators were magnetically measured at BINP and are being re-measured at Soleil after transportation.

Batrakov, A.; Briquez, F.; Chubar, O.; Dael, A.; Churkin, I.; Ilyin, I.; Roux, G.; Steshov, A.; Valleau, M.; Vobly, P.

2007-01-01

155

Modeling and Measurements by Hall probes of Magnetic Structures of Undulators HU256  

SciTech Connect

The magnetic calculations of the individual dipoles and dipoles in 'undulator environment' were executed by means of Mermaid 3D Code and these results were confirmed by magnetic measurements of the individual dipoles and the assembled undulators. The magnetic parameters of all dipoles were estimated on basis of the mechanical measurement of the dipole characteristics (pole gap, yoke width, coil position) and the main dependences obtained from magnetic calculations and measurements. These parameters were used for optimal placing of the dipoles in undulators (sorting). The special Hall probe system was designed and manufactured for magnetic measurements of the undulators. It allowed us to observe the inner structure of the magnetic fields. At a magnetic field measurement accuracy of {+-} 15 {mu}T the accuracy of the 1st integral calculated on the basis of the measured magnetic fields is {approx} 50 {mu}Tm. All three undulators were magnetically measured at BINP and are being re-measured at Soleil after transportation.

Batrakov, A.; Churkin, I.; Ilyin, I.; Steshov, A.; Vobly, P. [Budker Institute of Nuclear Physics, Lavrenteva 11, Novosibirsk, 630090 (Russian Federation); Briquez, F.; Chubar, O.; Dael, A.; Roux, G.; Valleau, M. [Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48-F91192, GIF-sur-YVETTE Cedex (France)

2007-01-19

156

Evidence for the Reversal of Magnetic Field Polarity in Coronal Streamers  

NASA Technical Reports Server (NTRS)

Faraday rotation observations are unique amongst radio occultation measurements in that they respond to magnetic field in addition to electron density, making it possible to probe the coronal magnetic field.

Woo, Richard

1996-01-01

157

Photonic Magnetic Field Sensor  

NASA Astrophysics Data System (ADS)

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.

Wyntjes, Geert

2002-02-01

158

The Heliospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

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.

Owens, Mathew J.; Forsyth, Robert J.

2013-11-01

159

Magnetic Resonance Imaging of time-varying magnetic fields from therapeutic devices  

PubMed Central

While magnetic resonance imaging of static magnetic fields generated by external probes has been previously demonstrated, there is an unmet need to image time-varying magnetic fields, such as those generated by transcranial magnetic stimulators or radiofrequency hyperthermia probes. A method to image such time-varying magnetic fields is introduced in this work. This article presents the theory behind the method and provides proof of concept by imaging time-varying magnetic fields generated by a figure-eight coil inside simple phantoms over a range of frequencies and intensities, using a 7T small animal MRI scanner. The method is able to reconstruct the three-dimensional components of the oscillating magnetic field vector. PMID:23355446

Hernandez-Garcia, Luis; Bhatia, Vivek; Prem-Kumar, Krishan; Ulfarsson, Magnus

2013-01-01

160

Magnetic Propeller for Uniform Magnetic Field Levitation  

E-print Network

Three new approaches to generating thrust in uniform magnetic fields are proposed. The first direction is based on employing Lorentz force acting on partial magnetically shielded 8-shaped loop with current in external magnetic field, whereby a net force rather than a torque origins. Another approach, called a Virtual Wire System, is based on creating a magnetic field having an energetic symmetry (a virtual wire), with further superposition of external field. The external field breaks the symmetry causing origination of a net force. Unlike a wire with current, having radial energetic symmetry, the symmetry of the Virtual Wire System is closer to an axial wire. The third approach refers to the first two. It is based on creation of developed surface system, comprising the elements of the first two types. The developed surface approach is a way to drastically increase a thrust-to-weight ratio. The conducted experiments have confirmed feasibility of the proposed approaches.

Mark Krinker; Alexander Bolonkin

2008-07-12

161

Magnetic and Langmuir Probe Measurements on the Plasmoid Thruster Experiment (PTX)  

NASA Technical Reports Server (NTRS)

The Plasmoid Thruster Experiment (PTX) operates by inductively producing plasmoids in a conical theta-pinch coil and subsequently ejecting them at high velocity. An overview of PTX is described in a companion paper. The shape and magnetic field structure of the translating plasmoids will be measured with of an array of inductive magnetic field probes. Six sets of two B-dot probes (for a total of twelve probes) have been constructed for measuring B(sub z) and B(sub theta), the axial and azimuthal components of the magnetic field. The probes were calibrated with a Helmholtz coil, driven alternately by a high-voltage pulser or a signal generator. The probes are wound on a G-10 form, and have an average (calibrated) NA of 9.37 x 10(exp -5) square meters, where N is the number of turns and A is cross-sectional area. The frequency response of the probes was measured over the range from 1 kHz to 10 MHZ. The electron number density n(sub e), electron temperature T(sub e) and velocity v will be determined from measurements taken with a quadruple Langmuir probe, situated in the exhaust chamber. Three of the four probes on the quadruple probe sample the current-voltage characteristic, and from this yield measurements of T(sub e) and n(sub e). The fourth probe provides a measurement of plasma flow velocity. A 6-inch long alumina rod, hollowed with four holes to house the probe wires, is being used to construct the quadruple probe. A variety of propellants will be used, including hydrogen, nitrogen and argon. From the measurements of the plasmoid mass, density, temperature, and velocity, the basic propulsion characteristics of PTX will be evaluated.

Koelfgen, Syri J.; Eskridge, Richard; Fimognari, Peter; Hawk, Clark W.; Lee, Mike; Martin, Adam

2004-01-01

162

Using Coordinated Observations in Polarised White Light and Faraday Rotation to Probe the Spatial Position and Magnetic Field of an Interplanetary Sheath  

E-print Network

Coronal mass ejections (CMEs) can be continuously tracked through a large portion of the inner heliosphere by direct imaging in visible and radio wavebands. White-light (WL) signatures of solar wind transients, such as CMEs, result from Thomson scattering of sunlight by free electrons, and therefore depend on both the viewing geometry and the electron density. The Faraday rotation (FR) of radio waves from extragalactic pulsars and quasars, which arises due to the presence of such solar wind features, depends on the line-of-sight magnetic field component $B_\\parallel$, and the electron density. To understand coordinated WL and FR observations of CMEs, we perform forward magnetohydrodynamic modelling of an Earth-directed shock and synthesise the signatures that would be remotely sensed at a number of widely distributed vantage points in the inner heliosphere. Removal of the background solar wind contribution reveals the shock-associated enhancements in WL and FR. While the efficiency of Thomson scattering depen...

Xiong, Ming; Feng, Xueshang; Owens, Mathew J; Harrison, Richard A; Davis, Chris J; Liu, Ying D

2013-01-01

163

Fast superconducting magnetic field switch  

DOEpatents

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.

Goren, Yehuda (Mountain View, CA); Mahale, Narayan K. (The Woodlands, TX)

1996-01-01

164

Fast superconducting magnetic field switch  

DOEpatents

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.

Goren, Y.; Mahale, N.K.

1996-08-06

165

USING COORDINATED OBSERVATIONS IN POLARIZED WHITE LIGHT AND FARADAY ROTATION TO PROBE THE SPATIAL POSITION AND MAGNETIC FIELD OF AN INTERPLANETARY SHEATH  

SciTech Connect

Coronal mass ejections (CMEs) can be continuously tracked through a large portion of the inner heliosphere by direct imaging in visible and radio wavebands. White light (WL) signatures of solar wind transients, such as CMEs, result from Thomson scattering of sunlight by free electrons and therefore depend on both viewing geometry and electron density. The Faraday rotation (FR) of radio waves from extragalactic pulsars and quasars, which arises due to the presence of such solar wind features, depends on the line-of-sight magnetic field component B{sub ?} and the electron density. To understand coordinated WL and FR observations of CMEs, we perform forward magnetohydrodynamic modeling of an Earth-directed shock and synthesize the signatures that would be remotely sensed at a number of widely distributed vantage points in the inner heliosphere. Removal of the background solar wind contribution reveals the shock-associated enhancements in WL and FR. While the efficiency of Thomson scattering depends on scattering angle, WL radiance I decreases with heliocentric distance r roughly according to the expression I?r {sup –3}. The sheath region downstream of the Earth-directed shock is well viewed from the L4 and L5 Lagrangian points, demonstrating the benefits of these points in terms of space weather forecasting. The spatial position of the main scattering site r{sub sheath} and the mass of plasma at that position M{sub sheath} can be inferred from the polarization of the shock-associated enhancement in WL radiance. From the FR measurements, the local B{sub ?sheath} at r{sub sheath} can then be estimated. Simultaneous observations in polarized WL and FR can not only be used to detect CMEs, but also to diagnose their plasma and magnetic field properties.

Xiong, Ming; Feng, Xueshang; Liu, Ying D. [State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing (China); Davies, Jackie A.; Harrison, Richard A. [Rutherford-Appleton Laboratory (RAL) Space, Harwell Oxford (United Kingdom); Owens, Mathew J.; Davis, Chris J., E-mail: mxiong@spacweather.ac.cn [Reading University, Reading (United Kingdom)

2013-11-01

166

Magnetic field coupled velocimeters - year one  

NASA Astrophysics Data System (ADS)

The major elements of the theoretical analysis and numerical simulation phase of a multi-year research program to demonstrate the viability of a totally nonintrusive, magnetically coupled velocimeter has been completed. The velocimeter R/D program was undertaken to yield a device capable of accurately measuring the mean and the turbulent velocity structure of flow-fields typical of rocket combustion chambers and exhaust nozzles. A drive dipole magnetic field array was designed to produce a harmonically varying, spatially localized and controlled field which penetrates flow-fields to produce eddy and motional currents. A probe array has been designed to differentiate those currents from each other and the drive array currents by analytically inverting the measured fields to yield the spatial structure of flow velocity and conductivity. An experimental test of the basic approach (using a electrolytic test chamber) has verified key elements in the analysis. A small, bench scale combustor test of the approach has begun.

Spight, C.

1981-01-01

167

[Magnetic fields and fish behavior].  

PubMed

In the review, contemporary data on the influence of natural and artificial magnetic fields on fish behavior are considered. In this regard, elasmobranchs and teleosts appear to be studied most exhaustively. Elasmobranchs and some teleosts are able to perceive magnetic fields via electroreceptors. A number of teleosts can sense magnetic fields via sensory cells containing crystals of biogenic magnetite. Laboratory experiments and field observations indicate the influence of magnetic fields on fish locomotor activity and spatial distribution. The geomagnetic field can be used by fish for navigation. Besides, artificial magnetic fields and natural fluctuations of the geomagnetic field can affect fish embryos leading to alterations in their development. It is suggested that, afterwards, these alterations can have an effect on fish behavior. PMID:25508098

2013-01-01

168

[Magnetic fields and fish behavior].  

PubMed

In the review, contemporary data on the influence of natural and artificial magnetic fields on fish behavior are considered. In this regard, elasmobranchs and teleosts appear to be studied most exhaustively. Elasmobranchs and some teleosts are able to perceive magnetic fields via electroreceptors. A number of teleosts can sense magnetic fields via sensory cells containing crystals of biogenic magnetite. Laboratory experiments and field observations indicate the influence of magnetic fields on fish locomotor activity and spatial distribution. The geomagnetic field can be used by fish for navigation. Besides, artificial magnetic fields and natural fluctuations of the geomagnetic field can affect fish embryos leading to alterations in their development. It is suggested that, afterwards, these alterations can have an effect on fish behavior. PMID:25438567

Krylov, V V; Iziumov, Iu G; Izvekov, E I; Nepomniashchikh, V A

2013-01-01

169

Exposure guidelines for magnetic fields  

SciTech Connect

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.

Miller, G.

1987-12-01

170

Magnetic-field-dosimetry system  

DOEpatents

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.

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

1981-01-21

171

Magnetic fields in massive stars  

E-print Network

Although indirect evidence for the presence of magnetic fields in high-mass stars is regularly reported in the literature, the detection of these fields remains an extremely challenging observational problem. We review the recent discoveries of magnetic fields in different types of massive stars and briefly discuss strategies for spectropolarimetric observations to be carried out in the future.

S. Hubrig

2007-03-09

172

Ion beam probing of electrostatic fields  

Microsoft Academic Search

The determination of a cylindrically symmetric, time-independent electrostatic potential V in a magnetic field B with the same symmetry by measurements of the deflection of a primary beam of ions is analyzed and substantiated by examples. Special attention is given to the requirements on canonical angular momentum and total energy set by an arbitrary, nonmonotone V, to scaling laws obtained

H. Persson

1979-01-01

173

A platform for designing hyperpolarized magnetic resonance chemical probes  

PubMed Central

Hyperpolarization is a highly promising technique for improving the sensitivity of magnetic resonance chemical probes. Here we report [15N, D9]trimethylphenylammonium as a platform for designing a variety of hyperpolarized magnetic resonance chemical probes. The platform structure shows a remarkably long 15N spin–lattice relaxation value (816?s, 14.1 T) for retaining its hyperpolarized spin state. The extended lifetime enables the detection of the hyperpolarized 15N signal of the platform for several tens of minutes and thus overcomes the intrinsic short analysis time of hyperpolarized probes. Versatility of the platform is demonstrated by applying it to three types of hyperpolarized chemical probes: one each for sensing calcium ions, reactive oxygen species (hydrogen peroxide) and enzyme activity (carboxyl esterase). All of the designed probes achieve high sensitivity with rapid reactions and chemical shift changes, which are sufficient to allow sensitive and real-time monitoring of target molecules by 15N magnetic resonance. PMID:24022444

Nonaka, Hiroshi; Hata, Ryunosuke; Doura, Tomohiro; Nishihara, Tatsuya; Kumagai, Keiko; Akakabe, Mai; Tsuda, Masashi; Ichikawa, Kazuhiro; Sando, Shinsuke

2013-01-01

174

Probe compensation in cylindrical near-field scanning: A novel simulation methodology  

NASA Technical Reports Server (NTRS)

Probe pattern compensation is essential in near-field scanning geometry, where there is a great need to accurately know far-field patterns at wide angular range. This paper focuses on a novel formulation and computer simulation to determine the precise need for and effect of probe compensation in cylindrical near-field scanning. The methodology is applied to a linear test array antenna and the NASA scatterometer radar antenna. The formulation is based on representing the probe by its equivalent tangential magnetic currents. The interaction between the probe equivalent aperture currents and the test antenna fields is obtained with the application of a reciprocity theorem. This allows us to obtain the probe vector output pickup integral which is proportional to the amplitude and phase of the electric field induced in the probe aperture with respect to its position to the test antenna. The integral is evaluated for each probe position on the required sampling point on a cylindrical near-field surface enclosing the antenna. The use of a hypothetical circular-aperture probe with a different radius permits us to derive closed-form expressions for its far-field radiation patterns. These results, together with the probe vector output pickup, allow us to perform computer simulated synthetic measurements. The far-field patterns of the test antenna are formulated based on cylindrical wave expansions of both the probe and test antenna fields. In the limit as the probe radius becomes very small, the probe vector output is the direct response of the near-field at a point, and no probe compensation is needed. Useful results are generated to compare the far-field pattern of the test antenna constructed from the knowledge of the simulated near-field with and without probe pattern compensation and the exact results. These results are important since they clearly illustrate the angular range over which probe compensation is needed. It has been found that a probe with an aperture radius of 0.25(lambda), 0.5(lambda), and 1(lambda) needs a little probe compensation, if any, near the test antenna main beam. In addition, a probe with low directivity may provide a better signal-to-noise ratio than a highly directive one. This is evident in test antenna patterns without probe compensation at wide angles.

Hussein, Ziad A.; Rahmat-Samii, Yahya

1993-01-01

175

Detecting solar axions using Earth's magnetic field  

E-print Network

We show that solar axion conversion to photons in the Earth's magnetosphere can produce an x-ray flux, with average energy \\sim 4 keV, which is measurable on the dark side of the Earth. The smallness of the Earth's magnetic field is compensated by a large magnetized volume. For axion masses solar core, can probe the photon-axion coupling down to 10^{-11} GeV^{-1}, in one year. Thus, the sensitivity of this new approach will be an order of magnitude beyond current laboratory limits.

Hooman Davoudiasl; Patrick Huber

2005-10-20

176

Ferrofilm in a magnetic field  

NASA Astrophysics Data System (ADS)

A vertically draining thin ferrofilm under the influence of gravity and a nonuniform magnetic field is considered. It is observed experimentally that the presence of the magnetic field greatly alters the drainage of the film. A mathematical model is developed to describe the behavior. Experiments are conducted for multiple magnetic field configurations. The model is solved for two different sets of boundary conditions and results are compared to experiments. It is shown that the magnetic field structure, the concentration of magnetite in the solution, and the boundary conditions all have noticeable affects on the evolution of the thinning film. Good qualitative agreement between the model and the experiments is observed.

Back, Randy; Beckham, J. Regan

2012-10-01

177

Acoustic ringing effects in pulsed nuclear magnetic resonance probes  

Microsoft Academic Search

The troublesome spurious ringing phenomenon found in pulsed nuclear magnetic resonance probes is explained in terms of the electromagnetic generation and detection of ultrasonic waves. A few techniques for eliminating this problem are discussed.

M. L. Buess; G. L. Petersen

1978-01-01

178

Acoustic ringing effects in pulsed nuclear magnetic resonance probes.  

PubMed

The troublesome spurious ringing phenomenon found in pulsed nuclear magnetic resonance probes is explained in terms of the electromagnetic generation and detection of ultrasonic waves. A few techniques for eliminating this problem are discussed. PMID:18699271

Buess, M L; Petersen, G L

1978-08-01

179

Study of magnetic properties of magnetic force microscopy probes using micronscale current rings  

E-print Network

Study of magnetic properties of magnetic force microscopy probes using micronscale current rings, fabricated using electron-beam lithography, were used to calibrate magnetic force microscopy MFM . A MFM tip magnetic force microscopy MFM is an essential tool for characterizing magnetic ma- terials in submicron

180

Master equations for pulsed magnetic fields: Application to magnetic molecules  

NASA Astrophysics Data System (ADS)

We extend spin-lattice relaxation theory to incorporate the use of pulsed magnetic fields for probing the hysteresis effects and magnetization steps and plateaus exhibited, at low temperatures, by the dynamical magnetization of magnetic molecules. The main assumption made is that the lattice degrees of freedom equilibrate in times much shorter than both the experimental time scale (determined by the sweep rate) and the typical spin-lattice relaxation time. We first consider the isotropic case (a magnetic molecule with a ground state of spin S well separated from the excited levels and also the general isotropic Heisenberg-Hamiltonian where all energy levels are relevant) and then we include small off-diagonal terms in the spin Hamiltonian to take into account the Landau-Zener-Stückelberg (LZS) effect. In the first case, and for an S=1/2 magnetic molecule we arrive at the generalized Bloch equation recently used for the magnetic molecule {V6} in [Phys. Rev. Lett. 94, 147204 (2005)]. An analogous equation is derived for the magnetization, at low temperatures, of antiferromagnetic ring systems. The LZS effect is discussed for magnetic molecules with a low spin ground state, for which we arrive at a very convenient set of equations that take into account the combined effects of LZS and thermal transitions. In particular, these equations explain the deviation from exact magnetization reversal at B?0 observed in {V6} . They also account for the small magnetization plateaus (“magnetic Foehn effect”), following the LZS steps that have been observed in several magnetic molecules. Finally, we discuss the role of the phonon bottleneck effect at low temperatures and specifically we indicate how this can give rise to a pronounced Foehn effect.

Rousochatzakis, Ioannis; Luban, Marshall

2005-10-01

181

Theory of fossil magnetic field  

NASA Astrophysics Data System (ADS)

Theory of fossil magnetic field is based on the observations, analytical estimations and numerical simulations of magnetic flux evolution during star formation in the magnetized cores of molecular clouds. Basic goals, main features of the theory and manifestations of MHD effects in young stellar objects are discussed.

Dudorov, Alexander E.; Khaibrakhmanov, Sergey A.

2015-02-01

182

Estimation of fluctuating magnetic fields by an atomic magnetometer  

SciTech Connect

We present a theoretical procedure to estimate with an atomic magnetometer the time dependence of a magnetic field that fluctuates according to an Ornstein-Uhlenbeck process. The magnetometer applies the detected polarization rotation of an optical probe to measure a collective atomic spin, which precesses due to the magnetic field. Based on the noisy optical detection record, our consistent Gaussian update formalism provides an estimator for the magnetic fields, and we identify analytically the steady-state performance of this estimator. We show that the estimate of the current value of the magnetic field is further improved if noisy measurement data obtained also at later times are taken into account.

Petersen, Vivi; Moelmer, Klaus [QUANTOP--Danish National Research Foundation Center for Quantum Optics, Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark)

2006-10-15

183

Cosmic Magnetic Fields - An Overview  

NASA Astrophysics Data System (ADS)

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.

Wielebinski, Richard; Beck, Rainer

184

Measurements of magnetic field alignment  

SciTech Connect

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.

Kuchnir, M.; Schmidt, E.E.

1987-11-06

185

CHAPTER 3. STRUCTURE OF MAGNETIC FIELDS 1 Structure of Magnetic  

E-print Network

CHAPTER 3. STRUCTURE OF MAGNETIC FIELDS 1 Chapter 3 Structure of Magnetic Fields Many of the most interesting plasmas are permeated by or imbedded in magnetic fields.1 As shown in Fig. 3.1, the magnetic field properties of magnetic fields in plasmas can be discussed without specifying a model for the plasma

Callen, James D.

186

Magnetic Field Problem: Measuring Current  

NSDL National Science Digital Library

A cross section of two circular wire loops carrying the exact same current is shown above (position given in centimeters and magnetic field given in milli-Tesla). You can click-drag to read the magnitude of the magnetic field.

Christian, Wolfgang; Belloni, Mario

2007-03-03

187

Studies of solar magnetic fields  

Microsoft Academic Search

An estimate of the average magnetic field strength at the poles of the Sun from Mount Wilson measurements is made by comparing low latitude magnetic measurements in the same regions made near the center of the disk and near the limb. There is still some uncertainty because the orientation angle of the field lines in the meridional plane is unknown,

Robert Howard

1977-01-01

188

Magnetic Compton scattering: A reliable probe to investigate magnetic properties  

NASA Astrophysics Data System (ADS)

Magnetic Compton scattering (MCS) is an ideal technique for the study of magnetic properties of ferro/ferrimagnetic materials because this method reveals the spin-polarized electron momentum density and yields the absolute and site dependent spin moments. The quantity measured in the MCS, so called magnetic Compton profile, is defined as the difference in the one-dimensional projection of the spin-polarized electron momentum density for majority and minority spin bands. In MCS, the Doppler broadening of the scattered radiation provides information on the correlation between the spin moment and the spin-polarized electron states of the valence electrons. It can also distinguish the spin polarization of itinerant electrons, because their momentum is narrow around the center of the profile. In this paper, temperature and field dependent spin momentum densities in Zn doped Ni ferrite namely, Ni1-xZnxFe2O4(x = 0.0,0.1,0.2), hole doped manganites like La0.7Ca0.3Mn1-xAlxO3(x = 0,0.02and0.06) and half Heusler alloys Cu1-xNixMnSb(x = 0.17,0.22) are reviewed. The decomposition of profiles in terms of site specific magnetic moments and their role in the formation of total spin moment is also discussed.

Ahuja, B. L.

2013-02-01

189

A 4 K cryogenic probe for use in magnetic resonance force microscopy experiments  

NASA Astrophysics Data System (ADS)

The detailed design of a mechanically detected nuclear magnetic resonance probe using the SPAM (Springiness Preservation by Aligning Magnetization) geometry, operating at 4 K, in vacuum, and a several-Tesla magnetic field is described. The probe head is vibration-isolated well enough from the environment by a three-spring suspension system that the cantilever achieves thermal equilibrium with the environment without the aid of eddy current damping. The probe uses an ultra-soft Si cantilever with a Ni sphere attached to its tip, and magnetic resonance is registered as a change in the resonant frequency of the driven cantilever. The RF system uses frequency sweeps for adiabatic rapid passage using a 500 ?m diameter RF coil wound around a sapphire rod. The RF coil and optical fiber of the interferometer used to sense the cantilever's position are both located with respect to the cantilever using a Garbini micropositioner, and the sample stage is mounted on an Attocube nanopositioner.

Smith, Doran D.; Alexson, Dimitri A.; Garbini, Joseph L.

2013-09-01

190

A 4 K cryogenic probe for use in magnetic resonance force microscopy experiments  

SciTech Connect

The detailed design of a mechanically detected nuclear magnetic resonance probe using the SPAM (Springiness Preservation by Aligning Magnetization) geometry, operating at 4 K, in vacuum, and a several-Tesla magnetic field is described. The probe head is vibration-isolated well enough from the environment by a three-spring suspension system that the cantilever achieves thermal equilibrium with the environment without the aid of eddy current damping. The probe uses an ultra-soft Si cantilever with a Ni sphere attached to its tip, and magnetic resonance is registered as a change in the resonant frequency of the driven cantilever. The RF system uses frequency sweeps for adiabatic rapid passage using a 500 ?m diameter RF coil wound around a sapphire rod. The RF coil and optical fiber of the interferometer used to sense the cantilever's position are both located with respect to the cantilever using a Garbini micropositioner, and the sample stage is mounted on an Attocube nanopositioner.

Smith, Doran D.; Alexson, Dimitri A. [U.S. Army Research Laboratory, 2800 Powder Mill Road, Adelphi, Maryland 20783 (United States)] [U.S. Army Research Laboratory, 2800 Powder Mill Road, Adelphi, Maryland 20783 (United States); Garbini, Joseph L. [Mechanical Engineering, University of Washington, Seattle, Washington 98195 (United States)] [Mechanical Engineering, University of Washington, Seattle, Washington 98195 (United States)

2013-09-15

191

Depth-resolved studies of layered magnetic nanostructures using 57Fe probe layers and Mössbauer spectroscopy  

NASA Astrophysics Data System (ADS)

An atomic-scale quantitative analysis of the structural and magnetic properties of surfaces, interfaces and complex nanostructures is of fundamental relevance for the development of new materials for spintronics. Studies of buried magnetic interfaces and depth-resolved measurements in layered magnetic nanostructures are particularly challenging, and the combination of conversion electron Mössbauer spectroscopy and/or nuclear resonant scattering of synchrotron radiation with isotope-enriched probe layers can be a powerful tool in this field. The potential offered by the application of isotope-selective measurements for the study of Fe-based layered magnetic nanostructures is illustrated with our recent results on the investigation of depth-dependent spin structures and interfacial interdiffusion in exchange-biased ferromagnetic/antiferromagnetic bilayer systems and of an epitaxial magnetic system with perpendicular magnetic anisotropy, obtained from samples prepared with ultrathin 57Fe probe layers placed at different depths during the growth processes, via molecular beam epitaxy or sputtering deposition.

Macedo, Waldemar A. A.

2014-11-01

192

High frequency umbilical magnetic probe array for SSX wind tunnel  

NASA Astrophysics Data System (ADS)

The Swarthmore Spheromak Experiment (SSX) wind tunnel consists of a high velocity plume of magnetized plasma injected into a copper flux conserver with dimensions L = 1 m and R = 0.08 m (aspect ratio 10:1). The plasma spheromaks in this wind tunnel typically have densities on the order of 1 - 5 x10^15 cm-3 and flow speeds of 50 km/s. In the past, fluctuations and turbulence in the SSX plasma wind tunnel during magnetic reconnection have been examined by means of two high resolution (16 position at 0.46 cm spacing) radial magnetic probes. Results from the radial probes show high frequency magnetic fluctuations at the site of reconnection. Four more probes have been design to help detect magnetic fluctuations and reconnection activity along the axial direction of the wind tunnel. The four new probes have 8 positions at 0.95 cm spacing and have a flexible bellow in vacuum and a quartz jacket. The bellows act as an umbilical giving the probe excellent flexibility and versatility. The flexibility allows the probe to be bent so it lies along the axis of the flux conserver.

Werth, A. M.; Gray, T.; Brown, M. R.

2012-10-01

193

MANUFACTURING OF MAGNETIC PROBE COILS FOR DIII-D  

SciTech Connect

OAK-B135 The magnetic diagnostics program at DIII-D adds to its in-vessel installations of induction-type loops and coils almost every year. The current design of toroidal and poloidal magnetic field coils (45-50 kHz, N {center_dot} A = 0.06 m{sup 2}) has been in existence since 1987. Many coils were installed in DIII-D during that year and are still operating and reliable today. The high reliability of the coils is owing to the use of a continuous length of mineral-insulated cable, eliminating any electrical connections inside the vacuum vessel. The geometry of the probes was designed to achieve a bandwidth of 50 kHz, despite the conducting shell formed by the stainless steel sheath of the mineral-insulated cable. The bandwidth is sensitive to the details of the cable dimensions and winding technique, and care must be taken in the fabrication in order to maintain this specification. With possible future magnetic diagnostics installations IN ITER and other long-pulse machines requiring large numbers of coils and/or multiple layers per coil, the manufacturing scale-up, quality control, and the development of layered coils should all be investigated in addition to the obvious issues such as irradiation effects.

BOZEK,A.S; STRAIT,E.J

2003-10-01

194

Solar magnetic fields and convection  

Microsoft Academic Search

The solar magnetic fields observed in active regions and their residues are thought to be parts of toroidal field systems renewed every 11-yr cycle from a poloidal field. The latter may be either a reversing (dynamo) field or a non-reversing, primordial field. The latter view was held for some 70 yr, but the apparent reversals of the polar-cap fields in

J. H. Piddington

1977-01-01

195

Field quality measurements of a 2-Tesla transmission line magnet  

SciTech Connect

A prototype 2-Tesla superconducting transmission line magnet for future hadron colliders was designed, built and tested at Fermilab. The 1.5 m long, combined-function gradient-dipole magnet has a vertical pole aperture of 20 mm. To measure the magnetic field quality in such a small magnet aperture, a specialized rotating coil of 15.2 mm diameter, 0.69 m long was fabricated. Using this probe, a program of magnetic field quality measurements was successfully performed. Results of the measurements are presented and discussed.

Velev, G.V.; Foster, W.; Kashikhin, V.; Mazur, P.; Oleck, A.; Piekarz, H.; Schlabach, P.; Sylvester, C.; /Fermilab; Wake, M.; /KEK, Tsukuba

2005-09-01

196

Observation of low magnetic field density peaks in helicon plasma  

SciTech Connect

Single density peak has been commonly observed in low magnetic field (<100 G) helicon discharges. In this paper, we report the observations of multiple density peaks in low magnetic field (<100 G) helicon discharges produced in the linear helicon plasma device [Barada et al., Rev. Sci. Instrum. 83, 063501 (2012)]. Experiments are carried out using argon gas with m = +1 right helical antenna operating at 13.56 MHz by varying the magnetic field from 0 G to 100 G. The plasma density varies with varying the magnetic field at constant input power and gas pressure and reaches to its peak value at a magnetic field value of {approx}25 G. Another peak of smaller magnitude in density has been observed near 50 G. Measurement of amplitude and phase of the axial component of the wave using magnetic probes for two magnetic field values corresponding to the observed density peaks indicated the existence of radial modes. Measured parallel wave number together with the estimated perpendicular wave number suggests oblique mode propagation of helicon waves along the resonance cone boundary for these magnetic field values. Further, the observations of larger floating potential fluctuations measured with Langmuir probes at those magnetic field values indicate that near resonance cone boundary; these electrostatic fluctuations take energy from helicon wave and dump power to the plasma causing density peaks.

Barada, Kshitish K.; Chattopadhyay, P. K.; Ghosh, J.; Kumar, Sunil; Saxena, Y. C. [Institute for Plasma Research, Bhat, Gandhinagar 382428 (India)

2013-04-15

197

Catheter based magnetic resonance compatible perfusion probe  

E-print Network

Neurosurgeons are using a thermal based technique to quantify brain perfusion. The thermal diffusion probe (TDP) technology measures perfusion in a relatively small volume of brain tissue. The neurosurgeon chooses the ...

Toretta, Cara Lynne

2007-01-01

198

PREPROCESSING MAGNETIC FIELDS WITH CHROMOSPHERIC LONGITUDINAL FIELDS  

SciTech Connect

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.

Yamamoto, Tetsuya T. [Solar-Terrestrial Environment Laboratory, Nagoya University, Chikusa-ku, Nagoya 464-8601 (Japan); Kusano, K., E-mail: tyamamot@stelab.nagoya-u.ac.jp [Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Kanagawa 236-0001 (Japan)

2012-06-20

199

Improved tapered tubular optical waveguide probe for magnetic focusing immunosensors  

NASA Astrophysics Data System (ADS)

Based on a non-sequential raytrace simulation, a previously developed tubular optical waveguide probe for magnetic- focusing immunosensors has been redesigned and tested. The design features a tubular waveguide tapered at both ends with a tapered magnet embedded inside of the waveguide. For reducing background, the excitation light is directly projected into the sample solution via a fiber against the cuvette wall adjacent to the waveguide. The fluorescent signal is collected by the probe and is coupled into a transmission fiber at the distal end of probe. Simulated antigen samples (paramagnetic microspheres of 5-micron diameter with immobilized antibodies that are labeled with Cy5 dye) have been prepared for testing magnetic signal enhancement and fluorescent signal collection. Typical results show that the sensitivity of the tubular probe is one order of magnitude higher than that of a similar dual- fiber probe. With the improved excitation and transmission scheme, the new tubular probe reduces background noise to one-third that of a previously reported tubular probe and is less sensitive to the interference of ambient light.

Cao, He; Baqaen, Hazem; Letcher, Stephen V.

2000-08-01

200

Thermometers in Low Magnetic Fields  

NASA Astrophysics Data System (ADS)

In this article the effect of low amplitude DC magnetic fields on different types of thermometers is discussed. By means of a precision water-cooled electromagnet, the effect of a magnetic field on platinum resistance thermometers, thermistors, and type T, J, and K thermocouples was investigated, while thermometers were thermally stabilized in thermostatic baths. Four different baths were used for temperatures from 77 K (-196 °C) to 353 K (80 °C): liquid nitrogen bath (nitrogen boiling point at atmospheric pressure), ice-point bath, room-temperature air bath, and hot-water bath. The generated DC magnetic field of high relative precision (2 × 10-4 at 1 T, 4 × 10-5 short-term stability) and high relative uniformity (2 × 10-5 over 1 cm2, 10 mm gap) had a magnetic flux density of 1 T in the center of the gap between the magnet pole caps. The results indicate a magnetic effect of up to 100 mK due to a 1 T magnetic field for the types of thermocouples composed of ferromagnetic materials (Fe, Cr, Ni). For platinum resistance thermometers, thermistors, and non-magnetic type T thermocouples, the detected magnetic effect was weaker, i.e., under 10 mK.

Geršak, G.; Beguš, S.

2010-09-01

201

Low-Magnetic-Field Magnetars  

NASA Astrophysics Data System (ADS)

It is now widely accepted that soft gamma repeaters and anomalous X-ray pulsars are the observational manifestations of magnetars, i.e. sources powered by their own magnetic energy. This view was supported by the fact that these "magnetar candidates" exhibited, without exception, a surface dipole magnetic field (as inferred from the spin-down rate) in excess of the electron critical field (? 4.4×1013 G). The recent discovery of fully qualified magnetars, SGR 0418+5729 and Swift J1822.3-1606, with dipole magnetic field well in the range of ordinary radio pulsars posed a challenge to the standard picture, showing that a very strong field is not necessary for the onset of magnetar activity (chiefly bursts and outbursts). Here we summarize the observational status of the low-magnetic-field magnetars and discuss their properties in the context of the mainstream magnetar model and its main alternatives.

Turolla, Roberto; Esposito, Paolo

2013-11-01

202

Resonant magnetic fields from inflation  

SciTech Connect

We propose a novel scenario to generate primordial magnetic fields during inflation induced by an oscillating coupling of the electromagnetic field to the inflaton. This resonant mechanism has two key advantages over previous proposals. First of all, it generates a narrow band of magnetic fields at any required wavelength, thereby allaying the usual problem of a strongly blue spectrum and its associated backreaction. Secondly, it avoids the need for a strong coupling as the coupling is oscillating rather than growing or decaying exponentially. Despite these major advantages, we find that the backreaction is still far too large during inflation if the generated magnetic fields are required to have a strength of O(10{sup ?15} Gauss) today on observationally interesting scales. We provide a more general no-go argument, proving that this problem will apply to any model in which the magnetic fields are generated on subhorizon scales and freeze after horizon crossing.

Byrnes, Christian T. [CERN, PH-TH Division, CH-1211, Genève 23 (Switzerland); Hollenstein, Lukas; Jain, Rajeev Kumar [Département de Physique Théorique and Center for Astroparticle Physics, Université de Genève, 24, Quai Ernest Ansermet, CH-1211 Genève 4 (Switzerland); Urban, Federico R., E-mail: cbyrnes@cern.ch, E-mail: lukas.hollenstein@unige.ch, E-mail: rajeev.jain@unige.ch, E-mail: urban@phas.ubc.ca [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, B.C. V6T 1Z1 (Canada)

2012-03-01

203

condensate in constant magnetic fields  

Microsoft Academic Search

We solve the Dirac equation in the presence of a constant magnetic field in (3+1) and (2+1) dimensions. Quantizing the fermion field, we calculate the condensate from first principles for parity conserving and violating Lagrangians for arbitrary field strength. We make a comparison with the results already known in the literature for some particular cases and point out the relevance

M. de J Anguiano-Galicia; A. Bashir; A. Raya

2007-01-01

204

Investigating Magnetic Force Fields  

NSDL National Science Digital Library

In this classroom activity, the students will investigate the magnetic pull of a bar magnet at varying distances with the use of paper clips. Students will hypothesize, conduct the experiment, collect the data, and draw conclusions that support their data. Each student will record the experiment and their findings in their science journals. As a class, students will compare each groups' data and their interpretation of the results.

Daryl ("Tish") Monjeau, Bancroft Elementary School, Minneapolis, MN

2012-03-18

205

Preface: Cosmic magnetic fields  

NASA Astrophysics Data System (ADS)

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.

Kosovichev, Alexander

2015-02-01

206

Holographic non-Fermi liquid in a background magnetic field  

SciTech Connect

We study the effects of a nonzero magnetic field on a class of 2+1 dimensional non-Fermi liquids, recently found in [Hong Liu, John McGreevy, and David Vegh, arXiv:0903.2477.] by considering properties of a Fermionic probe in an extremal AdS{sup 4} black hole background. Introducing a similar fermionic probe in a dyonic AdS{sup 4} black hole geometry, we find that the effect of a magnetic field could be incorporated in a rescaling of the probe fermion's charge. From this simple fact, we observe interesting effects like gradual disappearance of the Fermi surface and quasiparticle peaks at large magnetic fields and changes in other properties of the system. We also find Landau level like structures and oscillatory phenomena similar to the de-Haas-van Alphen effect.

Basu, Pallab; He Jianyang; Mukherjee, Anindya; Shieh, Hsien-Hang [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, B.C. V6T 1Z1 (Canada)

2010-08-15

207

Magnetically insulated baffled probe for real-time monitoring of equilibrium and fluctuating values of space potentials, electron and ion temperatures, and densities  

SciTech Connect

By restricting the electron-collection area of a cold Langmuir probe compared to the ion-collection area, the probe floating potential can become equal to the space potential, and thus conveniently monitored, rather than to a value shifted from the space potential by an electron-temperature-dependent offset, i.e., the case with an equal-collection-area probe. This design goal is achieved by combining an ambient magnetic field in the plasma with baffles, or shields, on the probe, resulting in species-selective magnetic insulation of the probe collection area. This permits the elimination of electron current to the probe by further adjustment of magnetic insulation which results in an ion-temperature-dependent offset when the probe is electrically floating. Subtracting the floating potential of two magnetically insulated baffled probes, each with a different degree of magnetic insulation, enables the electron or ion temperature to be measured in real time.

Demidov, V. I.; Koepke, M. E. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States); Raitses, Y. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

2010-10-15

208

Magnetic field in holographic superconductor with dark matter sector  

E-print Network

Based on the analytical technique the effect of the static magnetic field on the s-wave holographic superconductor with dark matter sector of U(1)-gauge field type coupled to the Maxwell field has been examined. In the probe limit, we obtained the mean value of the condensation operator. The nature of the condensate in an external magnetic field as well as the behaviour of the critical field close to the transition temperature has been revealed. The obtained upturn of the critical field curves as a function of temperature, both in four and five spacetime dimensions, is a fingerprint of the strong coupling approach.

Nakonieczny, L; Wysokinski, K I

2015-01-01

209

The magnetic field of Canopus  

Microsoft Academic Search

Zeeman spectrograms taken at the ESO in 1978 for Canopus (F0 Ib-II) confirm the presence of the weak magnetic field detected by Schermann (1977) and Rakosch et al. (1977), and a new period of 6.90 days for the Canopus magnetic field variation is proposed. It is noted that with the MSHIFT-technique (Weiss et al., 1978) the plate-mean Zeeman shifts can

W. W. Weiss

1986-01-01

210

Solar magnetic fields and convection  

Microsoft Academic Search

The flux-rope model of solar magnetic fields is developed further by the use of a variety of observational results.(i)It is confirmed that magnetic fields emerging to form active regions are already in the form of helically twisted flux ropes.(ii)A flux rope is not a homogeneous structure but is made up of hundreds or thousands of flux fibres. These are individually

J. H. Piddington

1976-01-01

211

Ion beam probing of electrostatic fields  

NASA Technical Reports Server (NTRS)

The determination of a cylindrically symmetric, time-independent electrostatic potential V in a magnetic field B with the same symmetry by measurements of the deflection of a primary beam of ions is analyzed and substantiated by examples. Special attention is given to the requirements on canonical angular momentum and total energy set by an arbitrary, nonmonotone V, to scaling laws obtained by normalization, and to the analogy with ionospheric sounding. The inversion procedure with the Abel analysis of an equivalent problem with a one-dimensional fictitious potential is used in a numerical experiment with application to the NASA Lewis Modified Penning Discharge. The determination of V from a study of secondary beams of ions with increased charge produced by hot plasma electrons is also analyzed, both from a general point of view and with application to the NASA Lewis SUMMA experiment. Simple formulas and geometrical constructions are given for the minimum energy necessary to reach the axis, the whole plasma, and any point in the magnetic field. The common, simplifying assumption that V is a small perturbation is critically and constructively analyzed; an iteration scheme for successively correcting the orbits and points of ionization for the electrostatic potential is suggested.

Persson, H.

1979-01-01

212

Broadband calibration for magnetic probes for use in the Maryland spheromak  

SciTech Connect

Magnetic probes are commonly used in plasma experiments to measure the magnetic and plasma properties of the configuration. Probes consisting of coils of copper wire encased in one or more layers of stainless-steel tubing are used both inside and outside the plasma to measure the magnetic field in the Maryland spheromak. A technique has been developed to calibrate the probes over a large frequency bandwidth using digital computer signal processing. The frequency-dependent effects of the stainless-steel tubing and the self-inductance of the coils on the recorded signal are taken into account over the entire bandwidth. This technique may also be used to take into account the eddy currents present in the metal vessel walls.

Shaw, R.S.; Booske, J.H.; McCarrick, M.J.

1987-07-01

213

A magnetically driven reciprocating probe for tokamak scrape-off layer measurements.  

PubMed

A new in situ reciprocating probe system has been developed to provide scrape-off layer measurements in the Tore Supra tokamak. The probe motion is provided by the rotation of an energized coil in the tokamak magnetic field. Simple analytic approximations to the exact numerical model were used to identify the important parameters that govern the dynamics of the system, and optimize the coil geometry, the electrical circuit, and the stiffness of the retaining spring. The linear speed of the probe is directly proportional to the current induced by the coil's rotation; its integral gives the coil position, providing a means to implement real-time feedback control of the probe motion. Two probes were recently mounted on a movable outboard antenna protection limiter in Tore Supra and provided automatic measurements during the 2011 experimental campaign. PMID:22225216

Gunn, J P; Pascal, J-Y

2011-12-01

214

Probing Ganymede's Magnetosphere with Field Line Resonances  

NASA Technical Reports Server (NTRS)

We report on the spectrum of field line resonances identified in data acquired by the Galileo spacecraft within Ganymede's magnetosphere on a relatively low latitude pass. We infer properties of the plasma distribution and its transport from the observed spectrum. The harmonic structure in the spectrum of the magnetometer data agrees very well with the frequencies predicted for resonances of a dipole field. The spectrum implies a density of 2 amu per cubic centimeter near the equator on closed field lines of Ganymede's magnetic field inside of 2 RG (Ganymede radii). This density is significantly reduced relative to the local density of the Jovian plasma sheet near Ganymede (less than or equal to 8 electrons per cubic centimeter, or approximately equal to 100 amu per cubic centimeter for an average ion mass per charge of 20 amu and average charge of 1.5 electron charges). A shadowing effect of Ganymede for the flow of particles injected at a reconnection layer on the side of the moon downstream relative to the direction of torus plasma flow accounts for the marked density depletion. Implications for conducting paths near Ganymede's surface are considered.

Volwerk, M.; Kivelson, M. G.; Khurana, K. K.; McPherron, R. L.

1999-01-01

215

Extraordinary optical transmission brightens near-field fiber probe.  

PubMed

Near-field scanning optical microscopy (NSOM) offers high optical resolution beyond the diffraction limit for various applications in imaging, sensing, and lithography; however, for many applications the very low brightness of NSOM aperture probes is a major constraint. Here, we report a novel NSOM aperture probe that gives a 100× higher throughput and 40× increased damage threshold than conventional near-field aperture probes. These brighter probes facilitate near-field imaging of single molecules with apertures as small as 45 nm in diameter. We achieve this improvement by nanostructuring the probe and by employing a novel variant of extraordinary optical transmission, relying solely on a single aperture and a coupled waveguide. Comprehensive electromagnetic simulations show good agreement with the measured transmission spectra. Due to their significantly increased throughput and damage threshold, these resonant configuration probes provide an important step forward for near-field applications. PMID:21175134

Neumann, Lars; Pang, Yuanjie; Houyou, Amel; Juan, Mathieu L; Gordon, Reuven; van Hulst, Niek F

2011-02-01

216

A Review of Maser Polarization and Magnetic Fields  

E-print Network

Through polarization observations masers are unique probes of the magnetic field in a variety of different astronomical objects, with the different maser species tracing different physical conditions. In recent years maser polarization observations have provided insights in the magnetic field strength and morphology in, among others, the envelopes around evolved stars, Planetary Nebulae (PNe), massive star forming regions and supernova remnants. More recently, maser observations have even been used to determine the magnetic field in megamaser galaxies. This review will present an overview of maser polarization observations and magnetic field determinations of the last several years and discuss the implications of the magnetic field measurements for several important fields of study, such as aspherical PNe creation and massive star formation.

W. H. T. Vlemmings

2007-05-07

217

Magnetic field induced dynamical chaos  

SciTech Connect

In this article, we have studied the dynamics of a particle having charge in the presence of a magnetic field. The motion of the particle is confined in the x–y plane under a two dimensional nonlinear potential. We have shown that constant magnetic field induced dynamical chaos is possible even for a force which is derived from a simple potential. For a given strength of the magnetic field, initial position, and velocity of the particle, the dynamics may be regular, but it may become chaotic when the field is time dependent. Chaotic dynamics is very often if the field is time dependent. Origin of chaos has been explored using the Hamiltonian function of the dynamics in terms of action and angle variables. Applicability of the present study has been discussed with a few examples.

Ray, Somrita; Baura, Alendu; Bag, Bidhan Chandra, E-mail: bidhanchandra.bag@visva-bharati.ac.in [Department of Chemistry, Visva-Bharati, Santiniketan 731 235 (India)

2013-12-15

218

Analysis of the Distribution of Magnetic Fluid inside Tumors by a Giant Magnetoresistance Probe  

PubMed Central

Magnetic fluid hyperthermia (MFH) therapy uses the magnetic component of electromagnetic fields in the radiofrequency spectrum to couple energy to magnetic nanoparticles inside tumors. In MFH therapy, magnetic fluid is injected into tumors and an alternating current (AC) magnetic flux is applied to heat the magnetic fluid- filled tumor. If the temperature can be maintained at the therapeutic threshold of 42°C for 30 minutes or more, the tumor cells can be destroyed. Analyzing the distribution of the magnetic fluid injected into tumors prior to the heating step in MFH therapy is an essential criterion for homogenous heating of tumors, since a decision can then be taken on the strength and localization of the applied external AC magnetic flux density needed to destroy the tumor without affecting healthy cells. This paper proposes a methodology for analyzing the distribution of magnetic fluid in a tumor by a specifically designed giant magnetoresistance (GMR) probe prior to MFH heat treatment. Experimental results analyzing the distribution of magnetic fluid suggest that different magnetic fluid weight densities could be estimated inside a single tumor by the GMR probe. PMID:24312280

Gooneratne, Chinthaka P.; Kurnicki, Adam; Yamada, Sotoshi; Mukhopadhyay, Subhas C.; Kosel, Jürgen

2013-01-01

219

Ultracold plasma dynamics in a magnetic field  

NASA Astrophysics Data System (ADS)

Plasmas, often called the fourth state of matter and the most common one in the universe, have parameters varying by many orders of magnitude, from temperature of a few hundred kelvin in the Earth's ionosphere to 10 16 K in the magnetosphere of a pulsar. Ultracold plasmas, produced by photoionizing a sample of laser-cooled and trapped atoms near the ionization limit, have extended traditional neutral plasma parameters by many orders of magnitude, to electron temperatures below 1 K and ion temperatures in the tens of muK to a few Kelvin, and densities of 105 cm -3 to 1010 cm-3. These plasmas thus provide a testing ground to study basic plasma theory in a clean and simple system with or without a magnetic field. Previous studies of ultracold plasmas have primarily concentrated on temperature measurements, collective modes and expansion dynamics in the absence of magnetic fields. This thesis presents the first study of ultracold plasma dynamics in a magnetic field. The presence of a magnetic field during the expansion can initiate various phenomena, such as plasma confinement and plasma instabilities. While the electron temperatures are very low in ultracold plasmas, we need only tens of Gauss of magnetic field to observe significant effects on the expansion dynamics. To probe the ultraocold plasma dynamics in a magnetic field, we developed a new diagnostic - projection imaging, which images the ion distribution by extracting the ions with a high voltage pulse onto a position-sensitive detector. Early in the lifetime of the plasma (< 20 mus), the size of the image is dominated by the time-of-flight Coulomb explosion of the dense ion cloud. For later times, we measure the 2-D Gaussian width of the ion image, obtaining the transverse expansion velocity as a function of magnetic field (up to 70 G), and observe that the transverse expansion velocity scales as B-1/2, explained by a nonlinear ambipolar diffusion model that involes anisotropic diffusion in two different directions. We also present the first observation of a plasma instability in an expanding ultracold plasma. We observe periodic emission of electrons from an ultracold plasma in weak, crossed magnetic and electric fields, and a strong perturbed electron density distribution in electron time-of-flight projection images. We identify this instability as a high-frequency electron drift instability due to the coupling between the electron drift wave and electron cyclotron harmonic, which has large wavenumbers corresponding to wavelengths close to the electron gyroradius.

Zhang, Xianli

220

Damping of cosmic magnetic fields  

SciTech Connect

We examine the evolution of magnetic fields in an expanding fluid composed of matter and radiation with particular interest in the evolution of cosmic magnetic fields. We derive the propagation velocities and damping rates for relativistic and non-relativistic fast and slow magnetosonic and Alfv{acute e}n waves in the presence of viscous and heat conducting processes. The analysis covers all magnetohydrodynamics modes in the radiation diffusion and the free-streaming regimes. When our results are applied to the evolution of magnetic fields in the early universe, we find that cosmic magnetic fields are damped from prior to the epoch of neutrino decoupling up to recombination. Similar to the case of sound waves propagating in a demagnetized plasma, fast magnetosonic waves are damped by radiation diffusion on all scales smaller than the radiation diffusion length. The characteristic damping scales are the horizon scale at neutrino decoupling (M{sub {nu}}{approx}10{sup {minus}4}M{sub {circle_dot}} in baryons) and the Silk mass at recombination (M{sub {gamma}}{approx}10{sup 13}M{sub {circle_dot}} in baryons). In contrast, the oscillations of slow magnetosonic and Alfv{acute e}n waves get overdamped in the radiation diffusion regime, resulting in frozen-in magnetic field perturbations. Further damping of these perturbations is possible only if before recombination the wave enters a regime in which radiation free-streams on the scale of the perturbation. The maximum damping scale of slow magnetosonic and Alfv{acute e}n modes is always smaller than or equal to the damping scale of fast magnetosonic waves, and depends on the magnetic field strength and its direction relative to the wave vector. Our findings have multifold implications for cosmology. The dissipation of magnetic field energy into heat during the epoch of neutrino decoupling ensures that most magnetic field configurations generated in the very early universe satisfy big bang nucleosynthesis constraints. Further dissipation before recombination constrains models in which primordial magnetic fields give rise to galactic magnetic fields or density perturbations. Finally, the survival of Alfv{acute e}n and slow magnetosonic modes on scales well below the Silk mass may be of significance for the formation of structure on small scales. {copyright} {ital 1998} {ital The American Physical Society}

Jedamzik, K. [Max-Planck-Institut fuer Astrophysik, 85748 Garching bei Muenchen (Germany)] [Max-Planck-Institut fuer Astrophysik, 85748 Garching bei Muenchen (Germany); Katalinic, V.; Olinto, A.V. [Department of Astronomy and Astrophysics and Enrico Fermi Institute, University of Chicago, 5640 S. Ellis Ave., Chicago, Illinois 60637 (United States)] [Department of Astronomy and Astrophysics and Enrico Fermi Institute, University of Chicago, 5640 S. Ellis Ave., Chicago, Illinois 60637 (United States)

1998-03-01

221

Damping of cosmic magnetic fields  

NASA Astrophysics Data System (ADS)

We examine the evolution of magnetic fields in an expanding fluid composed of matter and radiation with particular interest in the evolution of cosmic magnetic fields. We derive the propagation velocities and damping rates for relativistic and non-relativistic fast and slow magnetosonic and Alfvén waves in the presence of viscous and heat conducting processes. The analysis covers all magnetohydrodynamics modes in the radiation diffusion and the free-streaming regimes. When our results are applied to the evolution of magnetic fields in the early universe, we find that cosmic magnetic fields are damped from prior to the epoch of neutrino decoupling up to recombination. Similar to the case of sound waves propagating in a demagnetized plasma, fast magnetosonic waves are damped by radiation diffusion on all scales smaller than the radiation diffusion length. The characteristic damping scales are the horizon scale at neutrino decoupling (M?~10-4Msolar in baryons) and the Silk mass at recombination (M?~1013Msolar in baryons). In contrast, the oscillations of slow magnetosonic and Alfvén waves get overdamped in the radiation diffusion regime, resulting in frozen-in magnetic field perturbations. Further damping of these perturbations is possible only if before recombination the wave enters a regime in which radiation free-streams on the scale of the perturbation. The maximum damping scale of slow magnetosonic and Alfvén modes is always smaller than or equal to the damping scale of fast magnetosonic waves, and depends on the magnetic field strength and its direction relative to the wave vector. Our findings have multifold implications for cosmology. The dissipation of magnetic field energy into heat during the epoch of neutrino decoupling ensures that most magnetic field configurations generated in the very early universe satisfy big bang nucleosynthesis constraints. Further dissipation before recombination constrains models in which primordial magnetic fields give rise to galactic magnetic fields or density perturbations. Finally, the survival of Alfvén and slow magnetosonic modes on scales well below the Silk mass may be of significance for the formation of structure on small scales.

Jedamzik, Karsten; Katalini?, Višnja; Olinto, Angela V.

1998-03-01

222

Magnetic fields in protoplanetary disks  

E-print Network

Magnetic fields likely play a key role in the dynamics and evolution of protoplanetary discs. They have the potential to efficiently transport angular momentum by MHD turbulence or via the magnetocentrifugal acceleration of outflows from the disk surface, and magnetically-driven mixing has implications for disk chemistry and evolution of the grain population. However, the weak ionisation of protoplanetary discs means that magnetic fields may not be able to effectively couple to the matter. I present calculations of the ionisation equilibrium and magnetic diffusivity as a function of height from the disk midplane at radii of 1 and 5 AU. Dust grains tend to suppress magnetic coupling by soaking up electrons and ions from the gas phase and reducing the conductivity of the gas by many orders of magnitude. However, once grains have grown to a few microns in size their effect starts to wane and magnetic fields can begin to couple to the gas even at the disk midplane. Because ions are generally decoupled from the magnetic field by neutral collisions while electrons are not, the Hall effect tends to dominate the diffusion of the magnetic field when it is able to partially couple to the gas. For a standard population of 0.1 micron grains the active surface layers have a combined column of about 2 g/cm^2 at 1 AU; by the time grains have aggregated to 3 microns the active surface density is 80 g/cm^2. In the absence of grains, x-rays maintain magnetic coupling to 10% of the disk material at 1 AU (150 g/cm^2). At 5 AU the entire disk thickness becomes active once grains have aggregated to 1 micron in size.

Mark Wardle

2007-04-07

223

Whistler wave propagation in plasma with magnetic field duct  

NASA Astrophysics Data System (ADS)

Propagation of whistler waves in ducts field-aligned plasma irregularities plays a principal role in VLF signals transmission through magnetosphere Traditionally only plasma density ducts are under investigation but propagation of whistler waves can be strongly affected by duct-like magnetic field nonuniformities In this paper we describe the first experiments performed on Krot facility in which whistler propagation in appearance of magnetic field duct was modeled The experiments were conducted in low-temperature 0 2 eV uniform plasma with external magnetic field B 35 G to produce the duct-like magnetic irregularity we use compact wire solenoid 7 loops 40 cm long 7 5 cm in diameter carrying current up to 100 A Probe waves at frequencies f 20 - 50 MHz were radiated and received from plasma by loop antennas located in different sections of vacuum chamber The experiments show trapping of a whistler wave in duct with increased magnetic field It is essential that at frequencies close to the half of the electron cyclotron frequency approximately 50 MHz in our experiment trapping is very effective even in case of week about 10 magnetic field perturbation Detailed researches of RF field spatial structure versus frequency plasma density magnetic field and current in solenoid were carried out the results are presented The qualitative theoretical model is proposed some mechanisms of magnetic field ducts formation in magnetosphere are discussed Several principal distinctions between whistler wave trapping by density ducts and magnetic field

Starodubtsev, M.; Guschin, M.; Korobkov, S.; Kostrov, A.; Strikovsky, A.; Zaboronkova, T.

224

In situ magnetic compensation for potassium spin-exchange relaxation-free magnetometer considering probe beam pumping effect.  

PubMed

A novel method to compensate the residual magnetic field for an atomic magnetometer consisting of two perpendicular beams of polarizations was demonstrated in this paper. The method can realize magnetic compensation in the case where the pumping rate of the probe beam cannot be ignored. In the experiment, the probe beam is always linearly polarized, whereas, the probe beam contains a residual circular component due to the imperfection of the polarizer, which leads to the pumping effect of the probe beam. A simulation of the probe beam's optical rotation and pumping rate was demonstrated. At the optimized points, the wavelength of the probe beam was optimized to achieve the largest optical rotation. Although, there is a small circular component in the linearly polarized probe beam, the pumping rate of the probe beam was non-negligible at the optimized wavelength which if ignored would lead to inaccuracies in the magnetic field compensation. Therefore, the dynamic equation of spin evolution was solved by considering the pumping effect of the probe beam. Based on the quasi-static solution, a novel magnetic compensation method was proposed, which contains two main steps: (1) the non-pumping compensation and (2) the sequence compensation with a very specific sequence. After these two main steps, a three-axis in situ magnetic compensation was achieved. The compensation method was suitable to design closed-loop spin-exchange relaxation-free magnetometer. By a combination of the magnetic compensation and the optimization, the magnetic field sensitivity was approximately 4 fT/Hz(1/2), which was mainly dominated by the noise of the magnetic shield. PMID:24985800

Fang, Jiancheng; Wang, Tao; Quan, Wei; Yuan, Heng; Zhang, Hong; Li, Yang; Zou, Sheng

2014-06-01

225

Smallscale Solar Magnetic Fields - an Overview  

Microsoft Academic Search

An overview is given of the observational and the theoretical methods used to investigate solar magnetic fields. It includes an introduction to the Stokes parameters, their radiative transfer in the presence of a magnetic field, and empirical techniques used to measure various properties of solar magnetic features, such as the strength and direction of the magnetic field, magnetic flux, temperature,

Sami K. Solanki

1993-01-01

226

Helical Magnetic Fields from Sphaleron Decay and Baryogenesis  

SciTech Connect

Many models of baryogenesis rely on anomalous particle physics processes to give baryon number violation. By numerically evolving the electroweak equations on a lattice, we show that baryogenesis in these models creates helical cosmic magnetic fields, though the helicity created is smaller than earlier analytical estimates. After a transitory period, electroweak dynamics is found to conserve the Chern-Simons number and the total electromagnetic helicity. We argue that baryogenesis could lead to magnetic fields of nano-Gauss strength today on astrophysical length scales. In addition to being astrophysically relevant, such helical magnetic fields can provide an independent probe of baryogenesis and CP violation in particle physics.

Copi, Craig J. [CERCA, Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106-7079 (United States); Ferrer, Francesc [CERCA, Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106-7079 (United States); Department of Physics, Washington University, St. Louis, Missouri 63130 (United States); Vachaspati, Tanmay [CERCA, Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106-7079 (United States); Institute for Advanced Study, Princeton, New Jersey 08540 (United States); Achucarro, Ana [Instituut-Lorentz for Theoretical Physics, Leiden (Netherlands); Department of Theoretical Physics, The University of the Basque Country UPV-EHU, 48940 Bilbao (Spain)

2008-10-24

227

Jovian magnetic fields is complex, Pioneer 11 shows  

NASA Technical Reports Server (NTRS)

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

Panagakos, N.; Waller, P.

1975-01-01

228

Helical magnetic fields from sphaleron decay and baryogenesis.  

PubMed

Many models of baryogenesis rely on anomalous particle physics processes to give baryon number violation. By numerically evolving the electroweak equations on a lattice, we show that baryogenesis in these models creates helical cosmic magnetic fields, though the helicity created is smaller than earlier analytical estimates. After a transitory period, electroweak dynamics is found to conserve the Chern-Simons number and the total electromagnetic helicity. We argue that baryogenesis could lead to magnetic fields of nano-Gauss strength today on astrophysical length scales. In addition to being astrophysically relevant, such helical magnetic fields can provide an independent probe of baryogenesis and CP violation in particle physics. PMID:18999736

Copi, Craig J; Ferrer, Francesc; Vachaspati, Tanmay; Achúcarro, Ana

2008-10-24

229

Time-Resolved X-Ray Magnetic Circular Dichroism - A Selective Probe of Magnetization Dynamics on Nanosecond Timescales  

NASA Astrophysics Data System (ADS)

Many synchrotron radiation techniques have been developed in the last 15 years for studying the magnetic properties of thin-film materials. The most attractive properties of synchrotron radiation are its energy tunability and its time structure. The first property allows measurements in resonant conditions at an absorption edge of each of the magnetic elements constituting the probed sample, and the latter allows time-resolved measurements on subnanosecond timescales. In this review, we introduce some of the synchrotron-based techniques used for magnetic investigations. We then describe in detail X-ray magnetic circular dichroism (XMCD) and how time-resolved XMCD studies can be carried out in the pump-probe mode. Finally, we illustrate some applications to magnetization reversal dynamics in spin valves and tunnel junctions, using fast magnetic field pulses applied along the easy magnetization axis of the samples. Thanks to the element-selectivity of X-ray absorption spectroscopy, the magnetization dynamics of the soft (Permalloy) and the hard (cobalt) layers can be studied independently. In the case of spin valves, this allowed us to show that two magnetic layers that are strongly coupled in a static regime can become uncoupled on nanosecond timescales.Present address: Universidade Federal do Paraná, Centro Politécnico CP 19011, Curitiba - PR CEP 81531-990, Brazil

Pizzini, Stefania; Vogel, Jan; Bonfim, Marlio; Fontaine, Alain

230

Distinguishing magnetic and electrostatic interactions by a Kelvin probe force microscopy–magnetic force microscopy combination  

PubMed Central

Summary The most outstanding feature of scanning force microscopy (SFM) is its capability to detect various different short and long range interactions. In particular, magnetic force microscopy (MFM) is used to characterize the domain configuration in ferromagnetic materials such as thin films grown by physical techniques or ferromagnetic nanostructures. It is a usual procedure to separate the topography and the magnetic signal by scanning at a lift distance of 25–50 nm such that the long range tip–sample interactions dominate. Nowadays, MFM is becoming a valuable technique to detect weak magnetic fields arising from low dimensional complex systems such as organic nanomagnets, superparamagnetic nanoparticles, carbon-based materials, etc. In all these cases, the magnetic nanocomponents and the substrate supporting them present quite different electronic behavior, i.e., they exhibit large surface potential differences causing heterogeneous electrostatic interaction between the tip and the sample that could be interpreted as a magnetic interaction. To distinguish clearly the origin of the tip–sample forces we propose to use a combination of Kelvin probe force microscopy (KPFM) and MFM. The KPFM technique allows us to compensate in real time the electrostatic forces between the tip and the sample by minimizing the electrostatic contribution to the frequency shift signal. This is a great challenge in samples with low magnetic moment. In this work we studied an array of Co nanostructures that exhibit high electrostatic interaction with the MFM tip. Thanks to the use of the KPFM/MFM system we were able to separate the electric and magnetic interactions between the tip and the sample. PMID:22003461

Jaafar, Miriam; Iglesias-Freire, Oscar; Serrano-Ramón, Luis; Ibarra, Manuel Ricardo; de Teresa, Jose Maria

2011-01-01

231

Probing Gravitational Sensitivity in Biological Systems Using Magnetic Body Forces  

NASA Technical Reports Server (NTRS)

At Brown University, we are developing the use of magnetic body forces as a means to simulate variable gravity body forces on biological systems. This tool promises new means to probe gravi-sensing and the gravi-response of biological systems. It also has the potential as a technique for screening future systems for space flight experiments.

Guevorkian, Karine; Wurzel, Sam; Mihalusova, Mariana; Valles, Jim

2003-01-01

232

Analytical Methods for Characterizing Magnetic Resonance Probes  

PubMed Central

SUMMARY The efficiency of Gd(III) contrast agents in magnetic resonance image enhancement is governed by a set of tunable structural parameters. Understanding and measuring these parameters requires specific analytical techniques. This Feature describes strategies to optimize each of the critical Gd(III) relaxation parameters for molecular imaging applications and the methods employed for their evaluation. PMID:22624599

Manus, Lisa M.; Strauch, Renee C.; Hung, Andy H.; Eckermann, Amanda L.; Meade, Thomas J.

2012-01-01

233

X-Ray Detected Magnetic Resonance: A Unique Probe of the Precession Dynamics of Orbital Magnetization Components  

PubMed Central

X-ray Detected Magnetic Resonance (XDMR) is a novel spectroscopy in which X-ray Magnetic Circular Dichroism (XMCD) is used to probe the resonant precession of local magnetization components in a strong microwave pump field. We review the conceptual bases of XDMR and recast them in the general framework of the linear and nonlinear theories of ferromagnetic resonance (FMR). Emphasis is laid on the information content of XDMR spectra which offer a unique opportunity to disentangle the precession dynamics of spin and orbital magnetization components at given absorbing sites. For the sake of illustration, we focus on selected examples in which marked differences were found between FMR and XDMR spectra simultaneously recorded on ferrimagnetically ordered iron garnets. With pumping capabilities extended up to sub-THz frequencies, high-field XDMR should allow us to probe the precession of orbital magnetization components in paramagnetic organometallic complexes with large zero-field splitting. Even more challenging, we suggest that XDMR spectra might be recorded on selected antiferromagnetic crystals for which orbital magnetism is most often ignored in the absence of any supporting experimental evidence. PMID:22272105

Goulon, Jo?e; Rogalev, Andrei; Goujon, Gérard; Wilhelm, Fabrice; Ben Youssef, Jamal; Gros, Claude; Barbe, Jean-Michel; Guilard, Roger

2011-01-01

234

Observations of Mercury's magnetic field  

NASA Technical Reports Server (NTRS)

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.

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

1975-01-01

235

Three axis vector magnet set-up for cryogenic scanning probe microscopy  

NASA Astrophysics Data System (ADS)

We describe a three axis vector magnet system for cryogenic scanning probe microscopy measurements. We discuss the magnet support system and the power supply, consisting of a compact three way 100 A current source. We obtain tilted magnetic fields in all directions with maximum value of 5T along z-axis and of 1.2T for XY-plane magnetic fields. We describe a scanning tunneling microscopy-spectroscopy (STM-STS) set-up, operating in a dilution refrigerator, which includes a new high voltage ultralow noise piezodrive electronics and discuss the noise level due to vibrations. STM images and STS maps show atomic resolution and the tilted vortex lattice at 150 mK in the superconductor ?-Bi2Pd. We observe a strongly elongated hexagonal lattice, which corresponds to the projection of the tilted hexagonal vortex lattice on the surface. We also discuss Magnetic Force Microscopy images in a variable temperature insert.

Galvis, J. A.; Herrera, E.; Guillamón, I.; Azpeitia, J.; Luccas, R. F.; Munuera, C.; Cuenca, M.; Higuera, J. A.; Díaz, N.; Pazos, M.; García-Hernandez, M.; Buendía, A.; Vieira, S.; Suderow, H.

2015-01-01

236

Three axis vector magnet set-up for cryogenic scanning probe microscopy.  

PubMed

We describe a three axis vector magnet system for cryogenic scanning probe microscopy measurements. We discuss the magnet support system and the power supply, consisting of a compact three way 100 A current source. We obtain tilted magnetic fields in all directions with maximum value of 5T along z-axis and of 1.2T for XY-plane magnetic fields. We describe a scanning tunneling microscopy-spectroscopy (STM-STS) set-up, operating in a dilution refrigerator, which includes a new high voltage ultralow noise piezodrive electronics and discuss the noise level due to vibrations. STM images and STS maps show atomic resolution and the tilted vortex lattice at 150 mK in the superconductor ?-Bi2Pd. We observe a strongly elongated hexagonal lattice, which corresponds to the projection of the tilted hexagonal vortex lattice on the surface. We also discuss Magnetic Force Microscopy images in a variable temperature insert. PMID:25638089

Galvis, J A; Herrera, E; Guillamón, I; Azpeitia, J; Luccas, R F; Munuera, C; Cuenca, M; Higuera, J A; Díaz, N; Pazos, M; García-Hernandez, M; Buendía, A; Vieira, S; Suderow, H

2015-01-01

237

Nano-magnetic probing on magnetite (110)  

Microsoft Academic Search

In this study, magnetite Fe3O4(110) thin films were grown epitaxially on MgO substrates. Scanning tunneling microscopy (STM) was used to observe surface structure after annealing the films in UHV at 1000 K. The conductivity character of the films was analyzed by means of scanning tunneling spectroscopy (STS). Nanometer scale magnetism of magnetite film was also observed from the STS data.

G. A. Maris; L. C. Jdira; J. G. H. Hermsen; S. Murphy; I. Shvets; S. Speller

2006-01-01

238

Magnetic Forces and Field Line Density  

NSDL National Science Digital Library

This is an activity about depicting the relative strength of magnetic fields using field line density. Learners will use the magnetic field line drawing of six magnetic poles created in a previous activity and identify the areas of strong, weak, and medium magnetic intensity using the density of magnetic field lines. This is the fifth activity in the Magnetic Math booklet; this booklet can be found on the Space Math@NASA website. How to Draw Magnetic Fields - II in the Magnetic Math booklet must be completed prior to this activity.

239

Photospheric and coronal magnetic fields  

SciTech Connect

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.

Sheeley, N.R., Jr. (USAF, Geophysics Laboratory, Hanscom AFB, MA (United States))

1991-01-01

240

Magnetic field sensing based on magneto-volume variation of magnetic fluids investigated by air-gap Fabry-Pérot fiber interferometers  

NASA Astrophysics Data System (ADS)

A compact air-gap Fabry-Pérot fiber interferometer using magnetic fluids as the constituent material is constructed. The proposed structure possesses high sensitivity to magnetic field and is eligible for probing the tiny magnetic-field-induced volume variation of magnetic fluids. The underlying physical mechanisms for the magneto-volume variation are clarified in detail. The shift of the interference spectrum with magnetic field is employed for the magnetic field sensing applications. The highest sensitivity of magnetic field sensing for our experimental structure can reach 117.3 pm/mT when the sensing head is set at 45° azimuthal angle (with respect to the magnetic field direction).

Dong, Shaohua; Pu, Shengli; Huang, Juan

2013-09-01

241

EXPLORER 10 MAGNETIC FIELD MEASUREMENTS  

Microsoft Academic Search

Magnetic field measurements made by means of Explorer 10 over geocentric ; distances of 1.8 to 42.6R\\/sub e\\/ on March 25experiment on the same satellite are ; referenced in interpretations. The close-in data are consistent with the ; existence of a very weak ring current below 3R\\/sub e\\/ along the trajectory, but ; alternative explanations for the field deviations are

J. P. Heppner; N. F. Ness; C. S. Scearce; T. L. Skillman

1963-01-01

242

COLLIMATION OF COSMIC RAYS BY THE INTERPLANETARY MAGNETIC FIELD  

Microsoft Academic Search

a portion of the cosmic-ray and magnetic data observed during one of these flare events and lo demonstrate specific particle guidance properties of the interplanetary magnetic field. The data were obtained at a time when the spacecraft was 2.8 X 106 km from earth and at a sun-earth probe angle of 90 ø east of the sun and arc, therefore,

K. G. McCracken; N. F. Ness

1966-01-01

243

Large-scale solar magnetic fields  

Microsoft Academic Search

Topics discussed in this review of large-scale solar magnetic fields include large-scale magnetic surface features, the solar activity cycle and the large-scale patterns, and magnetic fields in the corona. Features considered include the decay of active regions, the background field pattern, the polar fields, giant regular structures, expansion of the field in surface harmonics, and the average inclination of magnetic-field

R. Howard

1977-01-01

244

Magnetic Field - Stellar Winds Interaction  

NASA Astrophysics Data System (ADS)

As per the recent study by the MiMeS collaboration, only about 10% of massive stars possess organized global magnetic fields, typically dipolar in nature. The competition between such magnetic fields and highly non-linear radiative forces that drive the stellar winds leads to a highly complex interaction. Such an interplay can lead to a number of observable phenomena, e.g. X-ray, wind confinement, rapid stellar spindown. However, due to its complexity, such an interaction cannot usually be modeled analytically, instead numerical modeling becomes a necessary tool. In this talk, I will discuss how numerical magnetohydrodynamic (MHD) simulations are employed to understand the nature of such magnetized massive star winds.

ud-Doula, Asif

2015-01-01

245

How to Draw Magnetic Fields - I  

NSDL National Science Digital Library

This is an activity about depicting magnetic fields. Learners will observe two provided drawings of magnetic field line patterns for bar magnets in simple orientations of like and unlike polarities and carefully draw the field lines for both orientations. This is the third activity in the Magnetic Math booklet; this booklet can be found on the Space Math@NASA website.

246

Crystal field and magnetic properties  

NASA Technical Reports Server (NTRS)

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.

Flood, D. J.

1977-01-01

247

Studies of solar magnetic fields  

Microsoft Academic Search

The telescope, spectrograph, and magnetograph at the 150-ft Tower Telescope are described, and a chronology of changes in the instrumentation is given. The average magnetic field strengths over the last seven years are discussed. The changes in polarity at the poles of the Sun are described. The characteristics of these polarity reversals at both poles are similar. A reversal is

Robert Howard

1974-01-01

248

Quantum probe and design for a chemical compass with magnetic nanostructures  

E-print Network

Magnetic fields as weak as Earth's may affect the outcome of certain photochemical reactions that go through a radical pair intermediate. When the reaction environment is anisotropic, this phenomenon can form the basis of a chemical compass and has been proposed as a mechanism for animal magnetoreception. Here, we demonstrate how to optimize the design of a chemical compass with a much better directional sensitivity simply by a gradient field, e.g. from a magnetic nanostructure. We propose an experimental test of these predictions, and suggest design principles for a hybrid metallic-organic chemical compass. In addition to the practical interest in designing a biomimetic weak magnetic field sensor, our result shows that gradient fields can server as powerful tools to probe spin correlations in radical pair reactions.

Jianming Cai

2010-11-24

249

Dynamic Pressure Probes Developed for Supersonic Flow-Field Measurements  

NASA Technical Reports Server (NTRS)

A series of dynamic flow-field pressure probes were developed for use in large-scale supersonic wind tunnels at the NASA Glenn Research Center. These flow-field probes include pitot and static pressure probes that can capture fast-acting flow-field pressure transients occurring on a millisecond timescale. The pitot and static probes can be used to determine local Mach number time histories during a transient event. The flow-field pressure probe contains four major components: 1) Static pressure aerodynamic tip; 2) Pressure-sensing cartridge assembly; 3) Pitot pressure aerodynamic tip; 4) Mounting stem. This modular design allows for a variety of probe tips to be used for a specific application. Here, the focus is on flow-field pressure measurements in supersonic flows, so we developed a cone-cylinder static pressure tip and a pitot pressure tip. Alternatively, probe tips optimized for subsonic and transonic flows could be used with this design. The pressure-sensing cartridge assembly allows the simultaneous measurement of steady-state and transient pressure which allows continuous calibration of the dynamic pressure transducer.

Porro, A. Robert

2001-01-01

250

Testing a sheath-compensated Langmuir probe in geometrically and magnetically expanding plasmas  

NASA Astrophysics Data System (ADS)

A sheath expansion around the Langmuir probe is known to give a significantly overestimated plasma density. Here, the sheath expansion effect suggested by Sheridan [Phys. Plasmas 7, 3084 (2000)] is successfully incorporated with no cumbersome analysis of the current–voltage (I–V) characteristics of the planar probe by measuring local plasma potential, floating potential, and ion saturation current. The probe consists of an emissive probe and two planar Langmuir probes, and is tested in low-pressure geometrically and magnetically expanding plasmas. The electron temperature estimated from the difference between the local plasma and floating potentials in the geometrically expanding plasma is in good agreement with that obtained from a classical analysis of the I–V characteristics. The plasma density computed with taking into account the sheath expansion effect shows significantly lower values than that obtained from the classical density estimation. The measurements in the magnetically expanding plasma successfully reproduce both the presence of the high-temperature population of electrons near the last field lines intersecting the radial wall at the open source exit and the presence of cold electrons outside the last field lines. The presently proposed method will lead to easy access to the two- and/or three-dimensional diagnoses of the low-pressure plasma structures.

Takahashi, Kazunori; Higashiyama, Hiroki; Takaki, Koichi; Ando, Akira

2015-01-01

251

Probe Compensation Characterization in Cylindrical Near-Field Scanning  

NASA Technical Reports Server (NTRS)

This paper presents a useful computer simulation methodology to properly characterize the role of probe compensation in cylindrical near-field scanning. The methodology is applied to a linear test array antenna and has been applied to other antenna configurations.

Hussein, Ziad A.; Rahmat-Samii, Yahya

1993-01-01

252

Internal Magnetic Field Measurements in STX Generated FRCs  

NASA Astrophysics Data System (ADS)

The internal magnetic field probes installed in the STX experiment at the Redmond Plasma Physics laboratory are designed to provide a one dimensional internal magnetic field profile of a 25 eV 10^19 m-3 FRC. The probe consists of 24 1cm × 1mm 8 turn coils interconnected like a chain to provide information on the RMF field components. This probe can be swept through the vacuum chamber to provide field information for different points throughout the FRC. The coils themselves are made with one mil magnet wire (half mil insulation). Structural and thermal support for the field coils is provided by a 53 mil ID × 78 mil OD berylium oxide tube capped with a boron nitride tip. Berylium oxide is an insulator with good thermal diffusivity/ablation properties. Calculations and test results indicate minimal perturbations to the plasma caused by the probe. Information on the construction methods employed as well as physical and external electrical design will be presented along with representative experimental results. This work is funded by the USDOE. www.aa.washington.edu/AERP/RPPL

Andreason, Samuel; Miller, Ken; Slough, John

1999-11-01

253

A silicon metal-oxide-semiconductor field-effect transistor Hall bar for scanning Hall probe microscopy.  

PubMed

We demonstrate successful operation of a scanning Hall probe microscope with a few micron-size resolution by using a silicon metal-oxide semiconductor field-effect transistor (Si-MOSFET) Hall bar, which is designed to improve not only the mechanical strength but also the temperature stability. The Si-MOSFET micro-Hall probe is cheaper than the current micro-Hall probes and is found to be as sensitive as a micro-Hall probe with GaAs/AlGaAs heterostructure or an epitaxial InSb two-dimensional electron gas. This was used to magnetically image the surface of a Sm(2)Co(17) permanent magnet during the magnetization reversal process as a function of an external magnetic field below 1.5 T. This revealed firm evidence of the presence of the inverse magnetic seed as theoretically predicted earlier. Magnetically pinned centers, with a typical size 80 mum, are observed to persist even under a high magnetic field, clearly indicating the robustness of the Si Hall probe against the field application as well as the repetition of the measurement. PMID:19044353

Yamaguchi, Akinobu; Saito, Hiromasa; Shimizu, Masayoshi; Miyajima, Hideki; Matsumoto, Satoru; Nakamura, Yoshiharu; Hirohata, Atsufumi

2008-08-01

254

Novel rotating field probe for inspection of tubes  

SciTech Connect

Inspection of steam generator tubes in nuclear power plants is extremely critical for safe operation of the power plant. In the nuclear industry, steam generator tube inspection using eddy current techniques has evolved over the years from a single bobbin coil, to rotating probe coil (RPC) and array probe, in an attempt to improve the speed and reliability of inspection. The RPC probe offers the accurate spatial resolution but involves complex mechanical rotation. This paper presents a novel design of eddy current probes based on rotating fields produced by three identical coils excited by a balanced three-phase supply. The sensor thereby achieves rotating probe functionality by electronic means and eliminates the need for mechanical rotation. The field generated by the probe is largely radial that result in induced currents that flow circularly around the radial axis and rotating around the tube at a synchronous speed effectively producing induced eddy currents that are multidirectional. The probe will consequently be sensitive to cracks of all orientations in the tube wall. The finite element model (FEM) results of the rotating fields and induced currents are presented. A prototype probe is being built to validate simulation results.

Xin, J.; Tarkleson, E.; Lei, N.; Udpa, L.; Udpa, S. S. [Nondestructive Evaluation Laboratory, Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI, 48824 (United States)

2012-05-17

255

Magnetic field of the Earth  

NASA Astrophysics Data System (ADS)

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 of electromagnetism. According to a rule of the left hand: if the magnetic field in a kernel is directed to drawing, electric current are directed to an axis of rotation of the Earth, - a action of force clockwise (to West). Definition of the force causing drift a kernel according to the law of Ampere F = IBlsin. Powerful force 3,5 × 1012 Nyton, what makes drift of the central part of a kernel of the Earth on 0,2 the longitude in year to West, and also it is engine of the mechanism of movement of slabs together with continents. Movement of a core of the Earth carry out around of a terrestrial axis one circulation in the western direction in 2000 of years. Linear speed of rotation of a kernel concerning a mantle on border the mantle a kernel: V = × 3,471 × 10 = 3,818 × 10 m/s = 33 m/day = 12 km/years. Considering greater viscosity of a mantle, the powerful energy at rotation of a kernel seize a mantle and lithospheric slabs and makes their collisions as a result of which there are earthquakes and volcano. Continents Northern and Southern America every year separate from the Europe and Africa on several centimeters. Atlantic ocean as a result of movement of these slabs with such speed was formed for 200 million years, that in comparison with the age of the Earth - several billions years, not so long time. Drift of a kernel in the western direction is a principal cause of delay of speed of rotation of the Earth. Flow of radial electric currents allot according to the law of Joule - Lenz, the quantity of warmth : Q = I2Rt = IUt, of thermal energy 6,92 × 1017 calories/year. This defines heating of a kernel and the Earth as a whole. In the valley of the median-Atlantic ridge having numerous volcanos, the lava flow constantly thus warm up waters of Atlantic ocean. It is a fact the warm current Gulf Stream. Thawing of a permafrost and ices of Arctic ocean, of glaciers of Greenland and Antarctica is acknowledgement: the warmth of earth defines character of thawing of glaciers and a permafrost. This is a global warming. The version of the author: the period

Popov, Aleksey

2013-04-01

256

Near-field Optical Measurement using Nano-Prism Probes  

NASA Astrophysics Data System (ADS)

Recently, a nano-prism (NP) structure has drawn attention as an optical nano-antenna due to its exotic optical properties, while it has been extremely difficult to prepare a probe terminated with a NP for near-field optical measurement. Herein, we report a method to mass-produce pristine NP-probes. Our fabrication process allowed us to prepare NPs with sharp edge at the end of the probes, which significantly enhanced the electric fields around the probes and made the NP-probes ideal for nano-optical applications. We performed the apertureless near-field scanning optical microscopy on gold nanoparticles using a NP-probe, revealing the field localization at the vertices of the NP. We also achieved high resolution topographic imaging on carbon nanotubes and successfully performed the tip-enhanced Raman spectroscopy (TERS) experiment on brilliant cresyl blue (BCB) molecules, revealing a significant field localization at the sharp edge of the NP. This method could be a major breakthrough and provide tremendous flexibility for near-field optical applications.

Kim, Taekyeong; Lee, Byung Yang; Heo, Kwang; Hong, Seunghun; Jeon, Ki Seok; Kim, Hyung Min; Suh, Yung Doug; Kim, Deok Soo; Kim, Zee Hwan

2010-03-01

257

Optical probe, local fields, and Lorentz factor in ferroelectrics  

NASA Astrophysics Data System (ADS)

An optical probe is suggested that allows measurements of the local field and Lorentz factor ( L) in ferroelectric medium. The copolymer poly (vinylidene fluoride/trifluoroethylene) is mixed with Pd-tetraphenylporphyrin (TPP-Pd) that has a very narrow absorption band. Thus, TPP-Pd serves as a molecular optical probe of the local field. During the switching of the electric field lower than the coercive one the factor L of an unpolarized ferroelectric mixture is found to be of about 1/3 that corresponds to the random distribution of molecular dipoles in the ferroelectric. With increasing field, the dipole orientation acquires a lower symmetry and L tends to zero as predicted by lattice sum calculations for vinylidene fluoride. The knowledge of the field dependence of L and the usage of the optical probe makes it possible to measure directly the local and macroscopic fields in the individual elements of various ferroelectric-dielectric heterostructures.

Blinov, L. M.; Lazarev, V. V.; Palto, S. P.; Yudin, S. G.

2014-06-01

258

Field induced anisotropic cooperativity in a magnetic colloidal glass  

E-print Network

The translational dynamics in a repulsive colloidal glass-former is probed by time-resolved X-ray Photon Correlation Spectroscopy. In this dense dispersion of charge-stabilized and magnetic nanoparticles, the interaction potential can be tuned, from quasi-isotropic to anisotropic by applying an external magnetic field. Structural and dynamical anisotropies are reported on interparticle lengthscales associated with highly anisotropic cooperativity, almost two orders of magnitude larger in the field direction than in the perpendicular direction and in zero field.

E Wandersman; Y Chushkin; E Dubois; V Dupuis; A Robert; R Perzynski

2015-02-03

259

Magnetic Field Effects on High Quality Factor Superconducting Coplanar Resonators  

NASA Astrophysics Data System (ADS)

Superconducting coplanar waveguide resonators have proven to be invaluable tools in studying some of the same decoherence mechanisms as those found in superconducting qubits. Prior improvements in fabrication led to resonator internal quality factors (Qi's) in excess of 10 million at high power, enabling us to sensitively probe environmental effects on the resonance frequency and Qi. We have found these resonators to be very susceptible to applied and stray magnetic fields, with measurable changes in the resonator's Qi and resonance frequency from fields as small as a few milligauss. I will present more recent measurements of resonators in magnetic fields.

Megrant, Anthony; Neill, Charles; Barends, Rami; Chen, Yu; Chiaro, Ben; Kelly, Julian; Mariantoni, Matteo; Mutus, Josh; O'Malley, Peter; Sank, Daniel; Vainsencher, Amit; Wenner, James; White, Ted; Low, David; Ohya, Shinobu; Palmstrom, Christopher; Martinis, John; Cleland, Andrew

2013-03-01

260

Stripline probes for nuclear magnetic resonance.  

PubMed

A novel route towards chip integrated NMR analysis is evaluated. The basic element in the design is a stripline RF 'coil' which can be defined in a single layer lithographic process and which is fully scalable to smaller dimensions. The sensitivity of such a planar structure can be superior to that of a conventional 3D helix. The basic properties, such as RF field strength, homogeneity and susceptibility broadening are discussed in detail. Secondary effects related to the thermal characteristics are discussed in simplified models. Preliminary NMR tests of basic solid and liquid samples measured at 600 MHz confirm the central findings of the design study. It is concluded that the stripline structure can be a valuable addition to the NMR toolbox; it combines high sensitivity with low susceptibility broadening and high power handling capabilities in a simple scalable design. PMID:17890116

van Bentum, P J M; Janssen, J W G; Kentgens, A P M; Bart, J; Gardeniers, J G E

2007-11-01

261

Fast Advection of Magnetic Fields by Hot Electrons  

NASA Astrophysics Data System (ADS)

Experiments where a laser-generated proton beam is used to probe the megagauss strength self-generated magnetic fields from a nanosecond laser interaction with an aluminum target are presented. At intensities of 1015Wcm-2 and under conditions of significant fast electron production and strong heat fluxes, the electron mean-free-path is long compared with the temperature gradient scale length and hence nonlocal transport is important for the dynamics of the magnetic field in the plasma. The hot electron flux transports self-generated magnetic fields away from the focal region through the Nernst effect [A. Nishiguchi , Phys. Rev. Lett. 53, 262 (1984)PRLTAO0031-900710.1103/PhysRevLett.53.262] at significantly higher velocities than the fluid velocity. Two-dimensional implicit Vlasov-Fokker-Planck modeling shows that the Nernst effect allows advection and self-generation transports magnetic fields at significantly faster than the ion fluid velocity, vN/cs?10.

Willingale, L.; Thomas, A. G. R.; Nilson, P. M.; Kaluza, M. C.; Bandyopadhyay, S.; Dangor, A. E.; Evans, R. G.; Fernandes, P.; Haines, M. G.; Kamperidis, C.; Kingham, R. J.; Minardi, S.; Notley, M.; Ridgers, C. P.; Rozmus, W.; Sherlock, M.; Tatarakis, M.; Wei, M. S.; Najmudin, Z.; Krushelnick, K.

2010-08-01

262

Fast advection of magnetic fields by hot electrons  

NASA Astrophysics Data System (ADS)

Experiments where a laser generated proton beam is used to probe the megagauss strength self-generated magnetic fields from a nanosecond laser interaction with an aluminum target are presented. At intensities of 10^15 ; Wcm-2 and under conditions of significant fast electron production and strong heat fluxes, the electron mean-free-path is long compared with the temperature gradient scale-length and hence non-local transport is important for the dynamics of the magnetic field in the plasma. The hot electron flux transports self-generated magnetic fields away from the focal region through the Nernst effect [1] at significantly higher velocities than the fluid velocity. Two-dimensional implicit Vlasov-Fokker-Planck modeling shows that the Nernst effect allows advection and self-generation transports magnetic fields at significantly faster than the ion fluid velocity, vN/cs 10.[4pt] [1] A. Nishiguchi et al., Phys. Rev. Lett., 53, 262 (1984).

Willingale, L.; Thomas, A. G. R.; Krushelnick, K.; Nilson, P. M.; Kaluza, M. C.; Dangor, A. E.; Evans, R. G.; Fernandes, P.; Haines, M. G.; Kamperidis, C.; Kingham, R. J.; Ridgers, C. P.; Sherlock, M.; Wei, M.-S.; Najmudin, Z.; Bandyopadyay, S.; Notley, M.; Minardi, S.; Tatarakis, M.; Rozmus, W.

2010-11-01

263

Field errors in superconducting magnets  

SciTech Connect

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.

Barton, M.Q.

1982-01-01

264

Ground state alignment as a tracer of interplanetary magnetic field  

NASA Astrophysics Data System (ADS)

We demonstrate a new way of studying interplanetary magnetic field -- spectropolarimetry based on ground state alignment. Ground state alignment is a new promising way of sub-gausian magnetic fields in radiation-dominated environment. The polarization of spectral lines that are pumped by the anisotropic radiation from the sun is influenced by the magnetic alignment, which happens for sub-gausian magnetic field. As a result, the linear polarization becomes an excellent tracer of the embedded magnetic field. The method is illustrated by our synthetic obser- vation of the Jupiter's Io and comet Halley. A uniform density distribution of Na was considered and polar- ization at each point was then constructed. Both spa- tial and temporal variations of turbulent magnetic field can be traced with this technique as well. Instead of sending thousands of space probes, ground state alignment allows magnetic mapping with any ground telescope facilities equipped with spectrometer and polarimeter. For remote regions like the the boundary of interstellar medium, ground state alignment provides a unique diagnostics of magnetic field, which is crucial for understanding the physical processes such as the IBEX ribbons.

Yan, H.

2012-12-01

265

Development Trends in High Field Magnet Technology  

Microsoft Academic Search

The production of high magnetic fields using low temperature superconductors (LTS) has become common place. However, large magnet sizes and associated high cooling costs have often precluded the full utilization of these research capabilities. Recent advances in internal Sn superconductors and cryogen free technology have opened up a new era in superconducting magnet development. Ultra-compact, laboratory sized magnets producing fields

R. Harrison; R. Bateman; J. Brown; F. Domptail; C. M. Friend; P. Ghoshal; C. King; A. Van der Linden; Z. Melhem; P. Noonan; A. Twin; M. Field; S. Hong; J. Parrell; Y. Zhang

2008-01-01

266

Variability in Martian Magnetic Field Topology  

NASA Astrophysics Data System (ADS)

We have determined the locations of open and closed magnetic field lines at Mars as a function of four different controlling influences: solar wind magnetic field direction, solar wind pressure, martian season, and solar EUV flux.

Brain, D. A.; Halekas, J. S.; Eastwood, J. P.; Ulusen, D.; Lillis, R. J.

2014-07-01

267

Plasma stability in a dipole magnetic field  

E-print Network

The MHD and kinetic stability of an axially symmetric plasma, confined by a poloidal magnetic field with closed lines, is considered. In such a system the stabilizing effects of plasma compression and magnetic field ...

Simakov, Andrei N., 1974-

2001-01-01

268

Measurements of Solar Vector Magnetic Fields  

NASA Technical Reports Server (NTRS)

Various aspects of the measurement of solar magnetic fields are presented. The four major subdivisions of the study are: (1) theoretical understanding of solar vector magnetic fields; (3) techniques for interpretation of observational data; and (4) techniques for data display.

Hagyard, M. J. (editor)

1985-01-01

269

Dynamics of positive probes in underdense, strongly magnetized, E×B drifting plasma: Particle-in-cell simulations  

SciTech Connect

Electron trapping, electron heating, space-charge wings, wake eddies, and current collection by a positive probe in E×B drifting plasma were studied in three-dimensional electromagnetic particle-in-cell simulations. In these simulations, electrons and ions were magnetized with respect to the probe and the plasma was underdense (?{sub pe}probe was created with background electric and magnetic fields. Four distinct regions developed in the presences of the positive probe: a quasi-trapped electron region, an electron-depletion wing, an ion-rich wing, and a wake region. We report on the observations of strong electron heating mechanisms, space-charge wings, ion cyclotron charge-density eddies in the wake, electron acceleration due to a magnetic presheath, and the current-voltage relationship.

Heinrich, Jonathon R.; Cooke, David L. [Air Force Research Laboratory, Kirtland Air Force Base, New Mexico 87117 (United States)] [Air Force Research Laboratory, Kirtland Air Force Base, New Mexico 87117 (United States)

2013-09-15

270

Topological constraints in magnetic field relaxation  

NASA Astrophysics Data System (ADS)

Stability and reconnection of magnetic fields play a fundamental role in natural and manmade plasma. In these applications the field's topology determines the stability of the magnetic field. Here I will describe the importance of one topology quantifier, the magnetic helicity, which impedes any free decay of the magnetic energy. Further constraints come from the fixed point index which hinders the field to relax into the Taylor state.

Candelaresi, S.

2014-10-01

271

Magnetically engineered semiconductor quantum dots as multimodal imaging probes.  

PubMed

Light-emitting semiconductor quantum dots (QDs) combined with magnetic resonance imaging contrast agents within a single nanoparticle platform are considered to perform as multimodal imaging probes in biomedical research and related clinical applications. The principles of their rational design are outlined and contemporary synthetic strategies are reviewed (heterocrystalline growth; co-encapsulation or assembly of preformed QDs and magnetic nanoparticles; conjugation of magnetic chelates onto QDs; and doping of QDs with transition metal ions), identifying the strengths and weaknesses of different approaches. Some of the opportunities and benefits that arise through in vivo imaging using these dual-mode probes are highlighted where tumor location and delineation is demonstrated in both MRI and fluorescence modality. Work on the toxicological assessments of QD/magnetic nanoparticles is also reviewed, along with progress in reducing their toxicological side effects for eventual clinical use. The review concludes with an outlook for future biomedical imaging and the identification of key challenges in reaching clinical applications. PMID:25178258

Jing, Lihong; Ding, Ke; Kershaw, Stephen V; Kempson, Ivan M; Rogach, Andrey L; Gao, Mingyuan

2014-10-01

272

High-field magnetic force microscopy as susceptibility imaging Casey Israel, Weida Wu, and Alex de Lozannea  

E-print Network

High-field magnetic force microscopy as susceptibility imaging Casey Israel, Weida Wu, and Alex de an extension of variable-temperature magnetic force microscopy MFM that allows spatial discrimination between.1063/1.2221916 Magnetic force microscopy MFM was developed as a scanning probe technique for mapping out magnetic field

Wu, Weida

273

Anomalous global strings and primordial magnetic fields  

SciTech Connect

We propose a new mechanism for the generation of primordial magnetic fields, making use of the magnetic fields which are induced by anomalous global strings, such as pion and axion strings, which couple to electromagnetism via Wess-Zumino type interactions. We calculate the magnitude and coherence length of these fields. They are seen to depend on the string dynamics. With optimistic assumptions, both the magnitude and coherence scale of the induced magnetic fields can be large enough to explain the seed magnetic fields of greater than 10{sup {minus}23} G necessary to produce the observed galactic magnetic fields via the galactic dynamo mechanism. {copyright} {ital 1999} {ital The American Physical Society}

Brandenberger, R.H. [Department of Physics, Brown University, Providence, Rhode Island 02912 (United States)] [Department of Physics, Brown University, Providence, Rhode Island 02912 (United States); Zhang, X. [CCAST (World Laboratory), P.O. Box 8730, Beijing 100080, Peoples Republic of (China)] [CCAST (World Laboratory), P.O. Box 8730, Beijing 100080, Peoples Republic of (China); [Institute of High Energy Physics, Academia Sinica, Beijing 100039, Peoples Republic of (China)

1999-04-01

274

Development of internal magnetic probe for current density profile measurement in Versatile Experiment Spherical Torusa)  

NASA Astrophysics Data System (ADS)

An internal magnetic probe using Hall sensors to measure a current density profile directly with perturbation of less than 10% to the plasma current is successfully operated for the first time in Versatile Experiment Spherical Torus (VEST). An appropriate Hall sensor is chosen to produce sufficient signals for VEST magnetic field while maintaining the small size of 10 mm in outer diameter. Temperature around the Hall sensor in a typical VEST plasma is regulated by blown air of 2 bars. First measurement of 60 kA VEST ohmic discharge shows a reasonable agreement with the total plasma current measured by Rogowski coil in VEST.

Yang, J.; Lee, J. W.; Jung, B. K.; Chung, K. J.; Hwang, Y. S.

2014-11-01

275

A new approach for highly accurate, remote temperature probing using magnetic nanoparticles  

PubMed Central

In this study, we report on a new approach for remote temperature probing that provides accuracy as good as 0.017°C (0.0055% accuracy) by measuring the magnetisation curve of magnetic nanoparticles. We included here the theoretical model construction and the inverse calculation method, and explored the impact caused by the temperature dependence of the saturation magnetisation and the applied magnetic field range. The reported results are of great significance in the establishment of safer protocols for the hyperthermia therapy and for the thermal assisted drug delivery technology. Likewise, our approach potentially impacts basic science as it provides a robust thermodynamic tool for noninvasive investigation of cell metabolism. PMID:25315470

Zhong, Jing; Liu, Wenzhong; Kong, Li; Morais, Paulo Cesar

2014-01-01

276

Probing magnetic anisotropy effects in epitaxial CrO2 thin films  

NASA Astrophysics Data System (ADS)

The magnetic anisotropy in ferromagnetic chromium dioxide thin films (Tc~393 K) grown epitaxially on (100) TiO2 substrates, is probed using precise rf transverse susceptibility (?T) measurements. Singular peaks in ?T are observed that are associated with the anisotropy (+/-HK) and switching (+/-Hs) fields in CrO2. Theoretical calculations of ?T based on a simple coherent rotation model display remarkable agreement with the experimental data, indicating that these thin films behave like single-domain magnetic particles. Magnetoelastic contributions to the total anisotropy energy are needed to describe the evolution of ?T peaks at lower temperatures.

Spinu, L.; Srikanth, H.; Gupta, A.; Li, X. W.; Xiao, Gang

2000-10-01

277

Applied Magnetic Field Enhances Arc Vapor Deposition  

NASA Technical Reports Server (NTRS)

Applied magnetic field enhances performance of vaporization part of arc vapor deposition apparatus. When no magnetic field applied by external means, arc wonders semirandomly over cathode, with net motion toward electrical feedthrough. When magnetic field applied arc moves circumferentially around cathode, and downward motion suppressed.

Miller, T. A.; Loutfy, R. O.; Withers, J. C.

1993-01-01

278

Mars: a magnetic field due to thermoremanence?  

Microsoft Academic Search

Presently available magnetic field data suggest a dipole moment of Mars of less than 10?4 times the Earth's dipole moment. Presumably, Mars does not have an active dynamo at present which could give rise to a significant magnetic field. Nevertheless, the presently available data do not rule out a minor intrinsic field which may originate from a magnetized lithosphere. The

Martin Leweling; Tilman Spohn

1997-01-01

279

MAXWELLIAN FIELD EXPANSION OF HELICAL MAGNET  

Microsoft Academic Search

Three dimensional (3D) magnetic field calculated by the computer code TOSCA was analyzed including the fring- ing field region. The magnetic field in the median plane was well simulated by a simple function. Off median plane, contributions from the coils should be taken into account. Superconducting helical dipole magnets will be used in RHIC as Siberian snakes and rotators(1). Extensive

K. Hatanaka; T. Katayama; T. Tominaka

1998-01-01

280

Prediction of the interplanetary magnetic field strength  

Microsoft Academic Search

A new model of the coronal and interplanetary magnetic field can predict both the interplanetary magnetic field strength and its polarity from measurements of the photospheric magnetic field. The model includes the effects of the large-scale horizontal electric currents flowing in the inner corona, of the warped heliospheric current sheet in the upper corona, and of volume currents flowing in

Xuepu Zhao; J. Todd Hoeksema

1995-01-01

281

The resonant radio-frequency magnetic probe tuned by coaxial cable.  

PubMed

In this paper, the resonant rf magnetic probe is upgraded by replacing the rotary capacitor in the old version with the series-connected coaxial cable. The numerical calculation and the measurement with the prototype probe show that the rf magnetic probe can achieve resonance at a middle length of the series-connected coaxial cable. The good electrical symmetry of the new rf magnetic probe is ensured by both the identity of series-connected coaxial cables and the new structure of the primary winding. Practical measurements conduced on an rf inductively coupled plasma source demonstrate that performances of the new rf magnetic probe are good. PMID:22938337

Sun, B; Huo, W G; Ding, Z F

2012-08-01

282

The resonant radio-frequency magnetic probe tuned by coaxial cable  

NASA Astrophysics Data System (ADS)

In this paper, the resonant rf magnetic probe is upgraded by replacing the rotary capacitor in the old version with the series-connected coaxial cable. The numerical calculation and the measurement with the prototype probe show that the rf magnetic probe can achieve resonance at a middle length of the series-connected coaxial cable. The good electrical symmetry of the new rf magnetic probe is ensured by both the identity of series-connected coaxial cables and the new structure of the primary winding. Practical measurements conduced on an rf inductively coupled plasma source demonstrate that performances of the new rf magnetic probe are good.

Sun, B.; Huo, W. G.; Ding, Z. F.

2012-08-01

283

Lightning-Driven Electric and Magnetic Fields Measured in the Stratosphere: Implications for Sprites  

E-print Network

Lightning-Driven Electric and Magnetic Fields Measured in the Stratosphere: Implications made from microform." Signature Date #12;#12;University of Washington Abstract Lightning impedance, dou- ble Langmuir probe instrument is designed specifically for measuring these large lightning

Thomas, Jeremy N.

284

Phosphate vibrations probe local electric fields and hydration in biomolecules  

PubMed Central

The role of electric fields in important biological processes like binding and catalysis has been studied almost exclusively by computational methods. Experimental measurements of the local electric field in macromolecules are possible using suitably calibrated vibrational probes. Here we demonstrate that the vibrational transitions of phosphate groups are highly sensitive to an electric field and quantify that sensitivity, allowing local electric field measurements to be made in phosphate-containing biological systems without chemical modification. PMID:21809829

Levinson, Nicholas M.; Bolte, Erin E.; Miller, Carrie S.

2011-01-01

285

Development of flexible array eddy current probes for complex geometries and inspection of magnetic parts using magnetic sensors  

NASA Astrophysics Data System (ADS)

Eddy Current Technique is a powerful method of inspection of metal parts. When size of flaws decreases, inspection areas become hardly accessible or material is magnetic, traditional winding coil probes are less efficient. Thanks to new CIVA simulation tools, we have designed and optimized advanced EC probes: flexible EC probe based on micro-coil arrays and EC probe with magnetic sensors, including specific electronics.

Marchand, B.; Decitre, J.-M.; Sergeeva-Chollet, N.; Skarlatos, A.

2013-01-01

286

Cross-duct electric field perturbation void fraction probe  

SciTech Connect

An advanced probe has been developed for transient and time-averaged measurement of the void fraction under various thermal-hydraulic conditions. The Electric Field Perturbation (EFP) probe operates by measuring the electrical properties of a two-phase mixture which are related to the void fraction by a theoretical electromagnetic field model. Qualification tests were performed in both air-water and high pressure steam-water facilities. In the former set of experiments, the EFP measurements were compared to void fractions obtained with fast-acting valves and a hot-film anemometer. For high-pressure experiments in a pool boiling configuration, simultaneous void fraction time traces from the EFP probe and differential pressure cell indicated that the EFP probe responds well to overall void fraction fluctuations.

Duncan, D.; Trabold, T.A. [Lockheed Martin Corp., Schenectady, NY (United States)] [Lockheed Martin Corp., Schenectady, NY (United States)

1997-03-01

287

A multichannel magnetic probe system for analysing magnetic fluctuations in helical axis plasmas  

SciTech Connect

The need to understand the structure of magnetic fluctuations in H-1NF heliac [S. Hamberger et al., Fusion Technol. 17, 123 (1990)] plasmas has motivated the installation of a sixteen former, tri-axis helical magnetic probe Mirnov array (HMA). The new array complements two existing poloidal Mirnov arrays by providing polarisation information, higher frequency response, and improved toroidal resolution. The helical placement is ideal for helical axis plasmas because it positions the array as close as possible to the plasma in regions of varying degrees of favourable curvature in the magnetohydrodynamic sense, but almost constant magnetic angle. This makes phase variation with probe position near linear, greatly simplifying the analysis of the data. Several of the issues involved in the design, installation, data analysis, and calibration of this unique array are presented including probe coil design, frequency response measurements, mode number identification, orientation calculations, and mapping probe coil positions to magnetic coordinates. Details of specially designed digitally programmable pre-amplifiers, which allow gains and filters to be changed as part of the data acquisition initialisation sequence and stored with the probe signals, are also presented. The low shear heliac geometry [R. Jiménez-Gómez et al., Nucl. Fusion 51, 033001 (2011)], flexibility of the H-1NF heliac, and wealth of information provided by the HMA create a unique opportunity for detailed study of Alfvén eigenmodes, which could be a serious issue for future fusion reactors.

Haskey, S. R.; Blackwell, B. D.; Seiwald, B.; Hole, M. J.; Pretty, D. G.; Howard, J.; Wach, J. [Plasma Research Laboratory, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 0200 (Australia)] [Plasma Research Laboratory, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 0200 (Australia)

2013-09-15

288

Magnetic monopole and the nature of the static magnetic field  

E-print Network

We investigate the factuality of the hypothetical magnetic monopole and the nature of the static magnetic field. It is shown from many aspects that the concept of the massive magnetic monopoles clearly is physically untrue. We argue that the static magnetic field of a bar magnet, in fact, is the static electric field of the periodically quasi-one-dimensional electric-dipole superlattice, which can be well established in some transition metals with the localized d-electron. This research may shed light on the perfect unification of magnetic and electrical phenomena.

Xiuqing Huang

2008-12-10

289

Quantitative stray field imaging of a magnetic vortex core  

NASA Astrophysics Data System (ADS)

Thin-film ferromagnetic disks present a vortex spin structure whose dynamics, added to the small size (?10 nm) of their core, has earned them intensive study. Here we use a scanning nitrogen-vacancy (NV) center microscope to quantitatively map the stray magnetic field above a 1-?m-diameter disk of permalloy, unambiguously revealing the vortex core. Analysis of both probe-to-sample distance and tip motion effects through stroboscopic measurements allows us to compare directly our quantitative images to micromagnetic simulations of an ideal structure. Slight perturbations with respect to the perfect vortex structure are clearly detected either due to an applied in-plane magnetic field or imperfections of the magnetic structures. This work demonstrates the potential of scanning NV microscopy to map tiny stray field variations from nanostructures, providing a nanoscale, nonperturbative detection of their magnetic texture.

Tetienne, J.-P.; Hingant, T.; Rondin, L.; Rohart, S.; Thiaville, A.; Roch, J.-F.; Jacques, V.

2013-12-01

290

Magnetic field sources and their threat to magnetic media  

NASA Technical Reports Server (NTRS)

Magnetic storage media (tapes, disks, cards, etc.) may be damaged by external magnetic fields. The potential for such damage has been researched, but no objective standard exists for the protection of such media. This paper summarizes a magnetic storage facility standard, Publication 933, that ensures magnetic protection of data storage media.

Jewell, Steve

1993-01-01

291

Design and calibration of high-frequency magnetic probes for the SUNIST spherical tokamaka)  

NASA Astrophysics Data System (ADS)

A new high-frequency magnetic diagnostic system is designed, installed, and calibrated in the Sino-United Spherical Tokamak (SUNIST) to investigate Alfvén waves (AWs). The system consists of a fixed toroidal array and a movable radial array of high-frequency magnetic probes (HFMPs) with 21 and 60 probes, respectively. Based on the method of vacuum enameled wire wound on ceramic bobbins, the fixed toroidal array is located as near as possible to the plasma and carefully shielded to reduce the attenuation of high-frequency magnetic field. Meanwhile, by using the technology of commercial chip inductors mounted on printed circuit boards, the movable radial array is inserted into a thin quartz tube that allows positioning along radial direction. A Helmholtz coil is utilized to calibrate the effective areas as well as the frequency response of each HFMP. The calibration results are consistent with the calculated results of an equivalent probe-and-cable circuit model. High-frequency magnetic signals related to AW are detected with these HFMPs. These HFMPs are expected to play a key role in analyzing Alfvén eigenmodes excited by AW antenna in the SUNIST.

Liu, Yangqing; Tan, Yi; Pan, Ou; Ke, Rui; Wang, Wenhao; Gao, Zhe

2014-11-01

292

Thinned fiber Bragg grating magnetic field sensor with magnetic fluid  

Microsoft Academic Search

The refractive index of magnetic fluid may be changed by external magnetic field. Therefore, through measuring its refractive index, the intensity of the magnetic field can be obtained. Fiber Bragg grating (FBG) is sensitive to the refractive index surrounding its cladding when the diameter of cladding is reduced to a certain degree. In order to prove the sensitivity of the

Ciming Zhou; Li Ding; Dongli Wang; Yaqi Kuang; Desheng Jiang

2011-01-01

293

Harmonic undulator radiations with constant magnetic field  

NASA Astrophysics Data System (ADS)

Harmonic undulators has been analysed in the presence of constant magnetic field along the direction of main undulator field. The spectrum modifications in harmonic undulator radiations and intensity degradation as a function of constant magnetic field magnitude at fundamental and third harmonics have been evaluated with a numerical integration method and generalised Bessel function. The role of harmonic field to overcome the intensity reduction due to constant magnetic field and energy spread in electron beam has also been demonstrated.

Jeevakhan, Hussain; Mishra, G.

2015-01-01

294

Features of the Martian Magnetic Field Structure  

Microsoft Academic Search

Based on the single-fluid MHD model of Mars space simulation, this paper has studied the magnetic field structure in the near-Mars space and investigated the influence of Martian crustal magnetic anomalies on the magnetic field structure. In the process of the solar wind interaction with Mars, the bow shock and magnetic pile-up region are produced. The interplanetary magnetic lines are

Yi-Teng Zhang; Lei Li

2009-01-01

295

How to Draw Magnetic Fields - II  

NSDL National Science Digital Library

This is an activity about depicting magnetic polarity. Learners will observe several provided drawings of magnetic field line patterns for bar magnets in simple orientations of like and unlike polarities and carefully draw the field lines and depict the polarities for several orientations, including an arrangement of six magnetic poles. This is the fourth activity in the Magnetic Math booklet; this booklet can be found on the Space Math@NASA website.

296

Probing Brownian relaxation in water-glycerol mixtures using magnetic hyperthermia  

NASA Astrophysics Data System (ADS)

Generation of heat by magnetic nanoparticles in the presence of an external oscillating magnetic field is known as magnetic hyperthermia (MHT). This heat is generated by two mechanisms: the Neel relaxation and Brownian relaxation. While the internal spin relaxation of the nanoparticles known as Neel relaxation is largely dependent on the magnetic properties of the nanoparticles, the physical motion of the particle or the Brownian relaxation is largely dependent on the viscous properties of the carrier liquid. The MHT properties of dextran coated iron oxide nanoparticles have been investigated at a frequency of 400KHz. To understand the influence of Brownian relaxation on heating, we probe the MHT properties of these ferrofluids in water-glycerol mixtures of varying viscosities. The heat generation is quantified using the specific absorption rate (SAR) and its maximum at a particular temperature is discussed with reference to the viscosity.

Nemala, Humeshkar; Milgie, Michael; Wadehra, Anshu; Thakur, Jagdish; Naik, Vaman; Naik, Ratna

2013-03-01

297

Permanent Magnet Ecr Plasma Source With Magnetic Field Optimization  

DOEpatents

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.

Doughty, Frank C. (Plano, TX); Spencer, John E. (Plano, TX)

2000-12-19

298

Graphene in high magnetic fields  

NASA Astrophysics Data System (ADS)

Carbon-based nano-materials, such as graphene and carbon nanotubes, represent a fascinating research area aiming at exploring their remarkable physical and electronic properties. These materials not only constitute a playground for physicists, they are also very promising for practical applications and are envisioned as elementary bricks of the future of the nano-electronics. As for graphene, its potential already lies in the domain of opto-electronics where its unique electronic and optical properties can be fully exploited. Indeed, recent technological advances have demonstrated its effectiveness in the fabrication of solar cells and ultra-fast lasers, as well as touch-screens and sensitive photo-detectors. Although the photo-voltaic technology is now dominated by silicon-based devices, the use of graphene could very well provide higher efficiency. However, before the applied research to take place, one must first demonstrates the operativeness of carbon-based nano-materials, and this is where the fundamental research comes into play. In this context, the use of magnetic field has been proven extremely useful for addressing their fundamental properties as it provides an external and adjustable parameter which drastically modifies their electronic band structure. In order to induce some significant changes, very high magnetic fields are required and can be provided using both DC and pulsed technology, depending of the experimental constraints. In this article, we review some of the challenging experiments on single nano-objects performed in high magnetic and low temperature. We shall mainly focus on the high-field magneto-optical and magneto-transport experiments which provided comprehensive understanding of the peculiar Landau level quantization of the Dirac-type charge carriers in graphene and thin graphite.

Orlita, Milan; Escoffier, Walter; Plochocka, Paulina; Raquet, Bertrand; Zeitler, Uli

2013-01-01

299

Vlasov Equation In Magnetic Field  

E-print Network

The linearized Vlasov equation for a plasma system in a uniform magnetic field and the corresponding linear Vlasov operator are studied. The spectrum and the corresponding eigenfunctions of the Vlasov operator are found. The spectrum of this operator consists of two parts: one is continuous and real; the other is discrete and complex. Interestingly, the real eigenvalues are infinitely degenerate, which causes difficulty solving this initial value problem by using the conventional eigenfunction expansion method. Finally, the Vlasov equation is solved by the resolvent method.

Biao Wu

1999-09-07

300

An analytic solar magnetic field model  

Microsoft Academic Search

We describe a simple analytic model for the magnetic field in the solar corona and interplanetary space which is appropriate to solar minimum conditions. The model combines an azimuthal current sheet in the equatorial plane with an axisymmetric multipole field representing the internal magnetic field of the Sun. The radial component of the field filling interplanetary space is approximately monopolar

M. Banaszkiewicz; W. I. Axford; J. F. McKenzie

1998-01-01

301

On the origin of solar magnetic fields  

Microsoft Academic Search

A fresh approach to the theoretical problems raised by observations of solar magnetic fields is outlined. Tentative conclusions are made that the large-scale magnetic field from which Cowling's (1953) hypothetical toroidal field is generated by differential rotation is not itself regenerated by diffusive processes in the sun's outer layers and that this field enters the differentially rotating layer from below

D. Layzer; R. Rosner; H. T. Doyle

1979-01-01

302

Magnetic field effects on microwave absorbing materials  

NASA Technical Reports Server (NTRS)

The objective of this program was to gather information to formulate a microwave absorber that can work in the presence of strong constant direct current (DC) magnetic fields. The program was conducted in four steps. The first step was to investigate the electrical and magnetic properties of magnetic and ferrite microwave absorbers in the presence of strong magnetic fields. This included both experimental measurements and a literature survey of properties that may be applicable to finding an appropriate absorbing material. The second step was to identify those material properties that will produce desirable absorptive properties in the presence of intense magnetic fields and determine the range of magnetic field in which the absorbers remain effective. The third step was to establish ferrite absorber designs that will produce low reflection and adequate absorption in the presence of intense inhomogeneous static magnetic fields. The fourth and final step was to prepare and test samples of such magnetic microwave absorbers if such designs seem practical.

Goldberg, Ira; Hollingsworth, Charles S.; Mckinney, Ted M.

1991-01-01

303

Full 180° magnetization reversal with electric fields.  

PubMed

Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals. PMID:25512070

Wang, J J; Hu, J M; Ma, J; Zhang, J X; Chen, L Q; Nan, C W

2014-01-01

304

Full 180° Magnetization Reversal with Electric Fields  

NASA Astrophysics Data System (ADS)

Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals.

Wang, J. J.; Hu, J. M.; Ma, J.; Zhang, J. X.; Chen, L. Q.; Nan, C. W.

2014-12-01

305

Full 180° Magnetization Reversal with Electric Fields  

PubMed Central

Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals. PMID:25512070

Wang, J. J.; Hu, J. M.; Ma, J.; Zhang, J. X.; Chen, L. Q.; Nan, C. W.

2014-01-01

306

Sub arcsec evolution of solar magnetic fields  

Microsoft Academic Search

Context: .The evolution of the concentrated magnetic field in flux tubes is one challenge of the nowadays Solar physics which requires time sequence with high spatial resolution. Aims: .Our objective is to follow the properties of the magnetic concentrations during their life, in intensity (continuum and line core), magnetic field and Doppler velocity. Methods: .We have observed solar region NOAA

Th. Roudier; J. M. Malherbe; J. Moity; S. Rondi; P. Mein; Ch. Coutard

2006-01-01

307

Exploring Magnetic Fields with a Compass  

ERIC Educational Resources Information Center

A compass is an excellent classroom tool for the exploration of magnetic fields. Any student can tell you that a compass is used to determine which direction is north, but when paired with some basic trigonometry, the compass can be used to actually measure the strength of the magnetic field due to a nearby magnet or current-carrying wire. In this…

Lunk, Brandon; Beichner, Robert

2011-01-01

308

Probing Magnetic Configurations in Buried Cobalt/Copper Multilayered Nanowires  

NASA Astrophysics Data System (ADS)

Multilayered magnetic nanowires have been a model system for heterostructured junctions that exhibit a host of fascinating perpendicular spin transport phenomena, such as giant and tunneling magnetoresistance (MR), and spin-transfer torque effects. Due to the extremely small physical dimensions the magnetic components in these nanowires or junctions often exhibit complex magnetization reversal behaviors, which are difficult to probe by magnetic imaging since the entities are buried deep inside a matrix. Conventional hysteresis loop measurement alone cannot reliably distinguish the reversal mechanisms either. In this work we have captured magnetic and MR ``fingerprints'' of Co nanodiscs in Co/Cu multilayered nanowires as they undergo a single domain to vortex state transition, using a first-order reversal curve (FORC) method [1]. The nanowires have been electrochemically deposited into nanoporous polycarbonate membranes. In 50 nm diameter [Co(5nm)/Cu(8nm)]400 nanowires, a 10% MR effect is observed at 300 K. In 200 nm diameter nanowires, the magnetic configurations can be tuned by adjusting the Co nanodisc aspect ratio. Nanowires with thinnest Co exhibit single domain behavior. Those with thicker Co exhibit vortex states, where the irreversible nucleation and annihilation of the vortices are manifested as butterfly-like features in the FORC distributions, similar to those observed in arrays of Fe nanodots [2]. They also show a superposition of giant and anisotropic magnetoresistance, which corresponds to the specific magnetic configurations of the Co nanodiscs. [4pt] [1] J. E. Davies, et al, Phys. Rev. B 70, 224434 (2004); Appl. Phys. Lett. 86, 262503 (2005); Phys. Rev. B 77, 014421 (2008).[0pt] [2] R. K. Dumas, et al, Phys. Rev. B 75, 134405 (2007); Appl. Phys. Lett. 91, 202501 (2007).

Liu, Kai

2009-03-01

309

Discovery of Magnetic Fields in CPNs  

NASA Astrophysics Data System (ADS)

For the first time we have directly detected magnetic fields in central stars of planetary nebulae by means of spectro-polarimetry with FORS1 at the VLT. In all four objects of our sample we found kilogauss magnetic fields, in NGC 1360 and LSS 1362 with very high significance, while in Abell 36 and EGB 5 the existence of a magnetic field is probable but with less certainty. This discovery supports the hypothesis that the non-spherical symmetry of most planetary nebulae is caused by magnetic fields in AGB stars. Our high discovery rate demands mechanisms to prevent full conservation of magnetic flux during the transition to white dwarfs.

Jordan, S.; Werner, K.; O'Toole, S. J.

2005-07-01

310

Neutrino Conversions in Solar Random Magnetic Fields  

E-print Network

We consider the effect of a random magnetic field in the convective zone of the Sun superimposed to a regular magnetic field on resonant neutrino spin-flavour oscillations. We argue for the existence of a field of strongly chaotic nature at the bottom of the convective zone. In contrast to previous attempts we employ in addition a model motivated regular twisting magnetic field profile. In this scenario electron antineutrinos are produced through cascades like $\

V. B Semikoz; E. Torrente-Lujan

1998-09-16

311

Differential rotation of solar magnetic fields  

Microsoft Academic Search

The connection of the differential rotation of solar magnetic fields with the field sign and strength is studied. The synoptic\\u000a maps of magnetic fields over the last three solar cycles taken at the Kitt Peak Observatory served as input data for the study.\\u000a The algorithm of magnetic field filtering over 14 chosen strengt intervals and successive 5-degree latitude zones was

O. A. Andreyeva; Ya. I. Zyelyk; N. N. Stepanian

2008-01-01

312

Probing the quality of Ni filled nanoporous alumina templates by magnetic techniques.  

PubMed

Pulsed electrodeposition prepared porous alumina templates with Ni nanowires pore filling ranged from 1 to 100%, depending on the alumina barrier-layer thickness, were probed by continuous wave ferromagnetic resonance at room temperature. For completely filled samples, a single resonance peak was observed in the whole range of angles between the applied magnetic field and normal to the sample plane. Its position was described by Kittel formula that takes into account shape anisotropy of individual Ni wires and dipolar interactions between them. For the samples with lower pore filling the effective anisotropy field decreased and the resonance linewidth in the perpendicular configuration increased. Also a quite intense second peak was observed at lower fields for these samples. These changes are associated with reduction of pore filling percentage that can lead to decrease of dipolar interactions between nanowires and to appearance of magnetic inhomogeneities inside wires. PMID:23035501

Sousa, C T; Leitão, D C; Proença, M P; Apolinário, A; Azevedo, A M; Sobolev, N A; Bunyaev, S A; Pogorelov, Yu G; Ventura, J; Araújo, J P; Kakazei, G N

2012-09-01

313

Magnetic field waves at Uranus  

NASA Technical Reports Server (NTRS)

The research efforts funded by the Uranus Data Analysis Program (UDAP) grant to the Bartol Research Institute (BRI) involved the study of magnetic field waves associated with the Uranian bow shock. Upstream wave studies are motivated as a study of the physics of collisionless shocks. Collisionless shocks in plasmas are capable of 'reflecting' a fraction of the incoming thermal particle distribution and directing the resulting energetic particle motion back into the upstream region. Once within the upstream region, the backward streaming energetic particles convey information of the approaching shock to the supersonic flow. This particle population is responsible for the generation of upstream magnetic and electrostatic fluctuations known as 'upstream waves', for slowing the incoming wind prior to the formation of the shock ramp, and for heating of the upstream plasma. The waves produced at Uranus not only differed in several regards from the observations at other planetary bow shocks, but also gave new information regarding the nature of the reflected particle populations which were largely unmeasurable by the particle instruments. Four distinct magnetic field wave types were observed upstream of the Uranian bow shock: low-frequency Alfven or fast magnetosonic waves excited by energetic protons originating at or behind the bow shock; whistler wave bursts driven by gyrating ion distributions within the shock ramp; and two whistler wave types simultaneously observed upstream of the flanks of the shock and argued to arise from resonance with energetic electrons. In addition, observations of energetic particle distributions by the LECP experiment, thermal particle populations observed by the PLS experiment, and electron plasma oscillations recorded by the PWS experiment proved instrumental to this study and are included to some degree in the papers and presentations supported by this grant.

Smith, Charles W.; Goldstein, Melvyn L.; Lepping, Ronald P.; Mish, William H.; Wong, Hung K.

1994-01-01

314

Bipolar pulse field for magnetic refrigeration  

DOEpatents

A magnetic refrigeration apparatus includes first and second steady state magnets, each having a field of substantially equal strength and opposite polarity, first and second bodies made of magnetocaloric material disposed respectively in the influence of the fields of the first and second steady state magnets, and a pulsed magnet, concentric with the first and second steady state magnets, and having a field which cycles between the fields of the first and second steady state magnets, thereby cyclically magnetizing and demagnetizing and thus heating and cooling the first and second bodies. Heat exchange apparatus of suitable design can be used to expose a working fluid to the first and second bodies of magnetocaloric material. A controller is provided to synchronize the flow of working fluid with the changing states of magnetization of the first and second bodies.

Lubell, Martin S. (Oak Ridge, TN)

1994-01-01

315

Atom probe field ion microscopy of high resistivity materials  

SciTech Connect

Over the last 30 years the atom probe has proved to be a powerful tool for studying nanometer-sized compositional fluctuations in a wide range of metallic alloys but has had only limited applications to semiconductors and ceramics. One of the primary reasons for this difference is the higher resistivity of semiconducting and ceramic specimens. Because of this high resistivity, the high voltage field evaporation pulse is attenuated before it reaches the apex of the specimen thereby making the pulse ineffective for field evaporation. Experiments have demonstrated that both variants of the voltage-pulsed atom probe (i.e., those instruments in which the field evaporation pulse is applied directly to the specimen and those in which the negative pulse is applied to a counter electrode in front of the specimen) are equally affected. In this overview, the limits of applicability of the voltage-pulsed atom probe to high resistivity materials are examined. In this study, a wide range of materials have been examined to determine whether field ion microscopy and voltage-pulsed field evaporation can be achieved and the results are summarized in the report. Field ion microscopy including dc field evaporation was possible for all materials except bulk ceramic insulators and glasses. Field ion microscopy requires some conductivity both to achieve a high electric field at the apex of the specimen, and also to support the field ion current. In contrast, voltage-pulsed field evaporation requires transmission of the pulse to the apex of the specimen. All metallic alloys including high resistance alloys and metallic glasses were successfully field evaporated with a voltage pulse. Specimens that were produced from bulk material of several conducting ceramics including MoSi, TiB and TiC were also successfully field evaporated with a voltage pulse.

Sibrandij, S.J.; Larson, D.J.; Miller, M.K.

1998-02-01

316

Polar magnetic field reversals on the Sun  

NASA Astrophysics Data System (ADS)

The polar magnetic fields on the Sun have been an attractive subject for solar researches since Babcock measured them in solar cycle 19. One of the remarkable features of the polar magnetic fields is their reversal during the maxima of 11-year sunspot cycles. I have present results of the investigations of the polar magnetic field using SOHO-mdi data. It is found, that the polar magnetic field reversal is detected with mdi data for polar region within 78° 88°. The North Pole has changed polarity in CR1975 (April 2001). The South reversed later in CR1980 (September 2001). The total unsigned magnetic flux does not show the dramatic decreasing during the polar reversals due to omnipresent bi-polar small-scale magnetic elements. The observational and theoretical aspects of the polar magnetic field reversals are discussed.

Benevolenskaya, Elena E.

2007-08-01

317

Probe Station and Near-Field Scanner for Testing Antennas  

NASA Technical Reports Server (NTRS)

A facility that includes a probe station and a scanning open-ended waveguide probe for measuring near electromagnetic fields has been added to Glenn Research Center's suite of antenna-testing facilities, at a small fraction of the cost of the other facilities. This facility is designed specifically for nondestructive characterization of the radiation patterns of miniaturized microwave antennas fabricated on semiconductor and dielectric wafer substrates, including active antennas that are difficult to test in traditional antenna-testing ranges because of fragility, smallness, or severity of DC-bias or test-fixture requirements. By virtue of the simple fact that a greater fraction of radiated power can be captured in a near-field measurement than in a conventional far-field measurement, this near-field facility is convenient for testing miniaturized antennas with low gains.

Zaman, Afroz; Lee, Richard Q.; Darby, William G.; Barr, Philip J.; Miranda, Felix A.; Lambert, Kevin

2006-01-01

318

Pulsed beams as field probes for precision measurement  

E-print Network

We describe a technique for mapping the spatial variation of static electric, static magnetic, and rf magnetic fields using a pulsed atomic or molecular beam. The method is demonstrated using a beam designed to measure the electric dipole moment of the electron. We present maps of the interaction region, showing sensitivity to (i) electric field variation of 1.5 V/cm at 3.3 kV/cm with a spatial resolution of 15 mm; (ii) magnetic field variation of 5 nT with 25 mm resolution; (iii) radio-frequency magnetic field amplitude with 15 mm resolution. This new diagnostic technique is very powerful in the context of high-precision atomic and molecular physics experiments, where pulsed beams have not hitherto found widespread application.

Hudson, J J; Kara, D M; Tarbutt, M R; Sauer, B E; Hinds, E A

2007-01-01

319

Cosmological Magnetic Fields and CMBR Polarization  

E-print Network

A simple introduction to physics of CMBR polarization and the Faraday rotation of the latter in cosmic magnetic field is presented. The content of the lecture is the following: 1. Description of polarization of photons. 2. Polarization field of CMBR. 3. Faraday effect. 4. Cosmic magnetic fields. 5. Faraday rotation of CMBR polarization.

A. D. Dolgov

2005-03-21

320

Representation of magnetic fields in space  

NASA Technical Reports Server (NTRS)

Several methods by which a magnetic field in space can be represented are reviewed with particular attention to problems of the observed geomagnetic field. Time dependence is assumed to be negligible, and five main classes of representation are described by vector potential, scalar potential, orthogonal vectors, Euler potentials, and expanded magnetic field.

Stern, D. P.

1975-01-01

321

Fiber Bragg Grating Magnetic Field Sensor  

Microsoft Academic Search

In this paper we demonstrate experimentally a magnetic field sensor using a fiber Bragg grating. The shift in the Bragg condition as a result of strain applied on the fiber mounted on a nickel base by the magnetic field gives an indirect measure of the field. The proposed method overcomes the need for long fiber lengths required in methods such

K. V. Madhav; K. Ravi Kumar; T. Srinivas; S. Asokan

2006-01-01

322

Gravity field information from Gravity Probe-B  

NASA Technical Reports Server (NTRS)

The Gravity Probe-B Mission will carry the Stanford Gyroscope relativity experiment into orbit in the mid 1990's, as well as a Global Positioning System (GPS) receiver whose tracking data will be used to study the earth gravity field. Estimates of the likely quality of a gravity field model to be derived from the GPS data are presented, and the significance of this experiment to geodesy and geophysics are discussed.

Smith, D. E.; Lerch, F. J.; Colombo, O. L.; Everitt, C. W. F.

1989-01-01

323

Static uniform magnetic fields and amoebae  

SciTech Connect

Three species of potentially pathogenic amoebae were exposed to 71 and 106.5 mT from constant homogeneous magnetic fields and examined for inhibition of population growth. The number of amoebae for three species was significantly less than controls after a 72 h exposure to the magnetic fields when the temperature was 20 C or above. Axenic cultures, i.e., cultures grown without bacteria, were significantly affected after only 24 h. In 20 of 21 tests using the three species, the magnetic field significantly inhibited the growth of amoebae. In one test in which the temperature was 20 C for 48 h, exposure to the magnetic field was not inhibitory. Final numbers of magnetic field-exposed amoebae ranged from 9 to 72% lower than the final numbers of unexposed controls, depending on the species. This research may lead to disinfection strategies utilizing magnetic fields for surfaces on which pathogenic amoebae may proliferate.

Berk, S.G.; Srikanth, S.; Mahajan, S.M.; Ventrice, C.A. [Tennessee Technological Univ., Cookeville, TN (United States)] [Tennessee Technological Univ., Cookeville, TN (United States)

1997-03-01

324

Magnetic field sensor for isotropically sensing an incident magnetic field in a sensor plane  

NASA Technical Reports Server (NTRS)

A magnetic field sensor that isotropically senses an incident magnetic field. This is preferably accomplished by providing a magnetic field sensor device that has one or more circular shaped magnetoresistive sensor elements for sensing the incident magnetic field. The magnetoresistive material used is preferably isotropic, and may be a CMR material or some form of a GMR material. Because the sensor elements are circular in shape, shape anisotropy is eliminated. Thus, the resulting magnetic field sensor device provides an output that is relatively independent of the direction of the incident magnetic field in the sensor plane.

Pant, Bharat B. (Inventor); Wan, Hong (Inventor)

2001-01-01

325

Properties of a hairpin probe in a strongly magnetized plasma  

NASA Astrophysics Data System (ADS)

Understanding of the physics in the filter field region of a neutral beam injection source for ITER under development is very important, as this region is where the negative ions are generated and extracted. For accurately determining electron densities in this complex plasma, a floating hairpin probe is applied on the KAMABOKO III ion source, at the MANTIS test bed at CEA Cadarache. The technique is based on measuring the probes resonance frequency (few GHz) shift in plasma with respect to that obtained in vacuum. The resonance frequency is proportional to the permittivity of the medium filling the space between the wires of the hairpin resonator. Using this technique we obtained the electron density variation as function of discharge power and on the external grid bias in front of the plasma grid.

Karkari, S. K.; Gogna, G. S.; Boilson, D.

2009-10-01

326

Beyond Solar-B: MTRAP, the Magnetic Transition Region Probe  

NASA Technical Reports Server (NTRS)

The next generation of solar missions will reveal and measure fine-scale solar magnetic fields and their effects in the solar atmosphere at heights, small scales, sensitivities, and fields of view well beyond the reach of Solar-B. The necessity for, and potential of, such observations for understanding solar magnetic fields, their generation in and below the photosphere, and their control of the solar atmosphere and heliosphere, were the focus of a science definition workshop, 'High-Resolution Solar Magnetography from Space: Beyond Solar-B,' held in Huntsville Alabama in April 2001. Forty internationally prominent scientists active in solar research involving fine-scale solar magnetism participated in this Workshop and reached consensus that the key science objective to be pursued beyond Solar-B is a physical understanding of the fine-scale magnetic structure and activity in the magnetic transition region, defined as the region between the photosphere and corona where neither the plasma nor the magnetic field strongly dominates the other. The observational objective requires high cadence (less than 10s) vector magnetic field maps, and spatially resolved spectra from the IR, visible, vacuum UV, to the EUV at high resolution (less than 50km) over a large FOV (approximately 140,000 km). A polarimetric resolution of one part in ten thousand is required to measure transverse magnetic fields of less than 30G. The latest SEC Roadmap includes a mission identified as MTRAP to meet these requirements. Enabling technology development requirements include large, lightweight, reflecting optics, large format sensors (16K x 16K pixels) with high QE at 150 nm, and extendable spacecraft structures. The Science Organizing Committee of the Beyond Solar-B Workshop recommends that: (1) Science and Technology Definition Teams should be established in FY04 to finalize the science requirements and to define technology development efforts needed to ensure the practicality of MTRAP's observational goals; (2) The necessary technology development funding should be included in Code S budgets for FY06 and beyond to prepare MTRAP for a new start no later than the nominal end of the Solar-B mission, around 2010.

Davis, John M.; Moore, Ronald L.; Hathaway, David H.

2003-01-01

327

Magnetic field waves at Uranus  

NASA Technical Reports Server (NTRS)

The proposed research efforts funded by the UDAP grant to the BRI involve the study of magnetic field waves associated with the Uranian bow shock. This is a collaborative venture bringing together investigators at the BRI, Southwest Research Institute (SwRI), and Goddard Space Flight Center (GSFC). In addition, other collaborations have been formed with investigators granted UDAP funds for similar studies and with investigators affiliated with other Voyager experiments. These investigations and the corresponding collaborations are included in the report. The proposed effort as originally conceived included an examination of waves downstream from the shock within the magnetosheath. However, the observations of unexpected complexity and diversity within the upstream region have necessitated that we confine our efforts to those observations recorded upstream of the bow shock on the inbound and outbound legs of the encounter by the Voyager 2 spacecraft.

Smith, Charles W.; Goldstein, Melvyn L.; Lepping, Ronald P.; Mish, William H.; Wong, Hung K.

1991-01-01

328

Lattice distortions in magnetic fields  

NASA Astrophysics Data System (ADS)

A study is made of the stability of the possible lattice structures which result from the magnetic-field-induced lattice deformation introduced by Araujo and Khmelnitskii. The deformed lattice may either be the result of a single distortion occurring along a particular direction or of a superposition of distortions in different directions. In a noninteracting electron model the energy variation of the electron system will determine which final lattice structure is the most stable. When electron interactions are considered in the Hartree approximation we find that the energy variation of the electron system alone will not determine which final structure is the most stable. The latter is then imposed by the lattice itself. If the distortion turns out to be unidirectional then the corresponding charge-density wave should be weakly pinned even in the absence of impurities.

Araujo, Miguel A. N.

1996-09-01

329

Extraterrestrial Magnetic Fields: Achievements and Opportunities  

Microsoft Academic Search

The major scientific achievements associated with the measurement of magnetic fields in space over the past decade and a half are reviewed. Aspects of space technology relevant to magnetic-field observations are discussed, including the different types of magnetometers used and how they operate, problems arising from spacecraft-generated magnetic fields and the appropriate countermeasures that have been developed and on-board processing

EDWARD J. SMITHAND; Charles Sonett

1976-01-01

330

Femtotesla Magnetic Field Measurement with Magnetoresistive Sensors  

Microsoft Academic Search

The measurement of magnetic fields in the femtotesla (fT, 10-15 tesla) range is important for applications such as magnetometry, quantum computing, solid-state nuclear magnetic resonance, and magnetoencephalography. The only sensors capable of detecting these very small fields have been based on low-temperature superconducting quantum interference devices operating at 4.2 kelvin. We present a magnetic field sensor that combines a superconducting

Myriam Pannetier; Claude Fermon; Gerald Le Goff; Juha Simola; Emma Kerr

2004-01-01

331

Dynamics of solar magnetic fields. VI  

Microsoft Academic Search

A mathematical model is developed to consider the evolution of force-free magnetic fields in relation to the displacements of their foot-points. For a magnetic field depending on only two Cartesian coordinates and time, the problem reduces to solving a nonlinear elliptic partial differential equation. As illustration of the physical process, two specific examples of evolving force-free magnetic fields are examined

B. C. Low; Y. Nakagawa

1975-01-01

332

Modeling solar force-free magnetic fields  

Microsoft Academic Search

A class of nonlinear force-free magnetic fields is presented, described in terms of the solutions to a second-order, nonlinear ordinary differential equation. These magnetic fields are three-dimensional, filling the infinite half-space above a plane where the lines of force are anchored. They model the magnetic fields of the sun over active regions with a striking geometric realism. The total energy

B. C. Low; Y. Q. Lou

1990-01-01

333

Fractal properties of solar magnetic fields  

Microsoft Academic Search

We study the spatial properties of solar magnetic fields using data from the Solar Vector Magnetograph of the Marshall Space\\u000a Flight Center (MSFC) (FeI 5250.2 Å) and SOHO\\/MDI longitudinal magnetic field measurements (Ni 6767.8 Å) (96-min full-disk\\u000a maps). Our study is focused on two objects: the fractal properties of sunspots and the fractal properties of the spatial magnetic\\u000a field distribution

B. A. Ioshpa; V. N. Obridko; E. A. Rudenchik

2008-01-01

334

Fractal properties of solar magnetic fields  

Microsoft Academic Search

We study the spatial properties of solar magnetic fields using data from the Solar Vector Magnetograph of the Marshall Space Flight Center (MSFC) (FeI 5250.2 Å) and SOHO\\/MDI longitudinal magnetic field measurements (Ni 6767.8 Å) (96-min full-disk maps). Our study is focused on two objects: the fractal properties of sunspots and the fractal properties of the spatial magnetic field distribution

B. A. Ioshpa; V. N. Obridko; E. A. Rudenchik

2008-01-01

335

Site and probe dependence of hyperfine magnetic field in L2 1 Heusler alloys X 2 MnZ (X=Ni, Cu, Rh, Pd and Z=Ga, Ge, In, Sn, Pb)  

Microsoft Academic Search

Results of TDPAC and Mössbauer measurements of hyperfine magnetic fields in L21 Heusler alloys X2MnZ are given. TDPAC utilized Cd-111 from In-111 at the Z site and Ag-111 at the X site, and Ru-99 from Rh-99 at the X site. Mössbauer studies utilized Sn-119 at the Z site or at the Mn site. A compilation of hmf values is presented,

S. Jha; H. M. Seyoum; M. Demarco; G. M. Julian; D. A. Stubbs; J. W. Blue; M. T. X. Silva; A. Vasquez

1983-01-01

336

Ferroelectric Cathodes in Transverse Magnetic Fields  

SciTech Connect

Experimental investigations of a planar ferroelectric cathode in a transverse magnetic field up to 3 kGs are presented. It is shown that the transverse magnetic field affects differently the operation of ferroelectric plasma cathodes in ''bright'' and ''dark'' modes in vacuum. In the ''bright'' mode, when the surface plasma is formed, the application of the transverse magnetic field leads to an increase of the surface plasma density. In the ''dark'' mode, the magnetic field inhibits the development of electron avalanches along the surface, as it does similarly in other kinds of surface discharges in the pre-breakdown mode.

Alexander Dunaevsky; Yevgeny Raitses; Nathaniel J. Fisch

2002-07-29

337

Magnetic field measurements in tokamak plasmas  

SciTech Connect

The measurement of the poloidal magnetic field in a tokamak plasma from the Zeeman splitting and polarization of the magnetic dipole radiation from heavy ions is discussed. When viewed from a direction perpendicular to the toroidal field, the effect of the poloidal field on the circularly polarized radiation is detectable using a photoelectric polarimeter. The Zeeman splittings for a number of magnetic dipole transitions with wavelengths in the range 2300--9300 A are presented. An imaging polarimeter is proposed that can measure the poloidal magnetic field with space and time resolution.

Feldman, U.; Seely, J.F.; Sheeley,Jr., N.R.; Suckewer, S.; Title, A.M.

1984-11-01

338

Magnetic fields in anisotropic relativistic stars  

E-print Network

Relativistic, spherically symmetric configurations consisting of a gravitating magnetized anisotropic fluid are studied. For such configurations, we obtain static equilibrium solutions with an axisymmetric, poloidal magnetic field produced by toroidal electric currents. The presence of such a field results in small deviations of the shape of the configuration from spherical symmetry. This in turn leads to the modification of an equation for the current and correspondingly to changes in the structure of the internal magnetic field for the systems supported by the anisotropic fluid, in contrast to the case of an isotropic fluid, where such deviations do not affect the magnetic field.

Vladimir Folomeev; Vladimir Dzhunushaliev

2015-01-26

339

Five years of magnetic field management  

SciTech Connect

The extensive publicity of epidemiological studies inferring correlation between 60 Hz magnetic fields and childhood leukemia prompted world wide research programs that have as a goal to determine if low frequency magnetic fields represent any risk for the general population, children or utility workers. While supporting this research effort through EPRI, Con Edison embarked on a technical research program aimed to: characterize magnetic fields as to intensity and variation in time; and investigate practical means to manage these magnetic fields through currently known methods. The final goal of these research projects is to establish viable methods to reduce magnetic field intensity to desired values at reasonable distances from the sources. This goal was pursued step by step, starting with an inventory of the main sources of magnetic fields in substations, distribution and transmission facilities and generating plants. The characterization of the sources helped to identify typical cases and select specific cases, far practical applications. The next step was to analyze the specific cases and develop design criteria for managing the magnetic fields in new installations. These criteria included physical arrangement of equipment based oil calculation of magnetic fields, cancellation effect, desired maximum field intensity at specific points and shielding with high magnetic permeability metals (mu-metal and steel). This paper summarizes the authors` experiences and shows the results of the specific projects completed in recent years.

Durkin, C.J.; Fogarty, R.P.; Halleran, T.M.; Mark, Dr. D.A.; Mukhopadhyay, A.

1995-01-01

340

Studies of strong magnetic field produced by permanent magnet array for magnetic refrigeration  

NASA Astrophysics Data System (ADS)

The success of a room temperature magnetic refrigerator (RTMR) depends critically on two essential parts: a high magnetic field and a magnetic refrigerant material with large magnetocaloric effect. A carefully designed hollow cylindrical permanent magnet array (HCPMA) can be used to provide strong magnetic field in the cavity, the magnitude of the resulting static field can be even greater than the remanence magnetization of the magnets comprising a HCPMA. A thorough understanding of the magnetic field distribution will provide an invaluable insight into the design and optimization of HCPMA in the reciprocating and rotary RTMR systems. Here, we show a construction of a 16 piece HCPMA with realistic dimensions and we illustrate the mechanism of generating a high magnetic field in such device. We present an effective way to calculate the field distribution of a permanent magnet array with finite size and an unsymmetrical geometry. Furthermore, detailed numerical results of the magnetic field distribution and its dependence on device dimensions are presented.

Xu, X. N.; Lu, D. W.; Yuan, G. Q.; Han, Y. S.; Jin, X.

2004-06-01

341

Magnetic monopole field exposed by electrons  

NASA Astrophysics Data System (ADS)

The experimental search for magnetic monopole particles has, so far, been in vain. Nevertheless, these elusive particles of magnetic charge have fuelled a rich field of theoretical study. Here, we created an approximation of a magnetic monopole in free space at the end of a long, nanoscopically thin magnetic needle. We experimentally demonstrate that the interaction of this approximate magnetic monopole field with a beam of electrons produces an electron vortex state, as theoretically predicted for a true magnetic monopole. This fundamental quantum mechanical scattering experiment is independent of the speed of the electrons and has consequences for all situations where electrons meet such monopole magnetic fields, as, for example, in solids. The set-up not only shows an attractive way to produce electron vortex states but also provides a unique insight into monopole fields and shows that electron vortices might well occur in unexplored solid-state physics situations.

Béché, Armand; van Boxem, Ruben; van Tendeloo, Gustaaf; Verbeeck, Jo

2014-01-01

342

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in fall 2012. The objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution using a constellation of three identical satellites. The mission shall deliver data that allow access to new insights into the Earth system by improved scientific understanding of the Earth's interior and near-Earth electromagnetic environment. After launch and triple satellite release at an initial altitude of about 490 km, a pair of the satellites will fly side-by-side with slowly decaying altitude, while the third satellite will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission science goals are to provide a unique view into Earth's core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently in the final stage of the development phase, will be addressed. A consortium of European scientific institutes is developing a distributed processing system to produce geophysical (Level 2) data products for the Swarm user community. The setup of the Swarm ground segment and the contents of the data products will be addressed. In case the Swarm satellites are already in orbit, a summary of the on-going mission operations activities will be given.

Plank, G.; Floberghagen, R.; Menard, Y.; Haagmans, R.

2012-12-01

343

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in 2013. The objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution using a constellation of 3 identical satellites. The Mission shall deliver data that allow access to new insights into the Earth system by improved scientific understanding of the Earth's interior and near-Earth electromagnetic environment. After launch and triple satellite release at an initial altitude of about 490 km, a pair of the satellites will fly side-by-side with slowly decaying altitude, while the third satellite will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission science goals are to provide a unique view into Earth's core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently in the final stage of the development phase, will be addressed. A consortium of European scientific institutes is developing a distributed processing system to produce geophysical (Level 2) data products for the Swarm user community. The setup of the Swarm ground segment and the contents of the data products will be addressed. More information on Swarm can be found at www.esa.int/esaLP/LPswarm.html.

Plank, Gernot; Haagmans, Roger; Floberghagen, Rune; Menard, Yvon

2013-04-01

344

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in fall 2013. The objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution using a constellation of three identical satellites. The mission shall deliver data that allow access to new insights into the Earth system by improved scientific understanding of the Earth's interior and near-Earth electromagnetic environment. After launch and triple satellite release at an initial altitude of about 490 km, a pair of the satellites will fly side-by-side with slowly decaying altitude, while the third satellite will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission science goals are to provide a unique view into Earth's core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently in the final stage of the development phase, will be addressed. A consortium of European scientific institutes is developing a distributed processing system to produce geophysical (Level 2) data products for the Swarm user community. The setup of the Swarm ground segment and the contents of the data products will be addressed. In case the Swarm satellites are already in orbit, a summary of the on-going mission operations activities will be given. More information on Swarm can be found at www.esa.int/esaLP/LPswarm.html.

Plank, G.; Floberghagen, R.; Menard, Y.; Haagmans, R.

2013-12-01

345

Gold nanocone near-field scanning optical microscopy probes.  

PubMed

Near-field scanning optical microscopy enables the simultaneous topographical and subdiffraction limited optical imaging of surfaces. A process is presented for the implementation of single individually engineered gold cones at the tips of atomic force microscopy cantilevers. These cantilevers act as novel high-performance optical near-field probes. In the fabrication, thin-film metallization, electron beam induced deposition of etch masks, and Ar ion milling are combined. The cone constitutes a well-defined highly efficient optical antenna with a tip radius on the order of 10 nm and an adjustable plasmon resonance frequency. The sharp tip enables high resolution topographical imaging. By controllably varying the cone size, the resonance frequency can be adapted to the application of choice. Structural properties of these sharp-tipped probes are presented together with topographical images recorded with a cone probe. The antenna functionality is demonstrated by gathering the near-field enhanced Raman signature of individual carbon nanotubes with a gold cone scanning probe. PMID:21401116

Fleischer, Monika; Weber-Bargioni, Alexander; Altoe, M Virginia P; Schwartzberg, Adam M; Schuck, P James; Cabrini, Stefano; Kern, Dieter P

2011-04-26

346

Attenuation of surface-enhanced Raman scattering of magnetic-plasmonic FePt@Ag core-shell nanoparticles due to an external magnetic field  

NASA Astrophysics Data System (ADS)

The surface-enhanced Raman scattering (SERS) activities of Ag and FePt@Ag nanoparticle probes were examined using thiophenol as a Raman reporter molecule in the absence and presence of a magnetic field. Under external magnetic fields of different field strength, the SERS activities of both types of nanoparticles (NPs) were weakened as a function of magnetic field strength. The attenuation degree of SERS activity by the magnetic field in the case of FePt@Ag NPs is found to be two times higher than for Ag NPs, because the superparamagnetic FePt cores enhance the local magnetic field at the area of the Ag shells.

Trang, Nguyen T. T.; Thuy, Trinh T.; Mott, Derrick M.; Koyano, Mikio; Maenosono, Shinya

2013-06-01

347

Magnetization measurements reveal the local shear stiffness of hydrogels probed by ferromagnetic nanorods  

NASA Astrophysics Data System (ADS)

The local mechanical coupling of ferromagnetic nanorods in hydrogels was characterized by magnetization measurements. Nickel nanorods were synthesized by the AAO-template method and embedded in gelatine hydrogels with mechanically soft or hard matrix properties determined by the gelatine weight fraction. By applying a homogeneous magnetic field during gelation the nanorods were aligned along the field resulting in uniaxially textured ferrogels. The magnetization curves of the soft ferrogel exhibited not only important similarities but also characteristic differences as compared to the hard ferrogel. The hystereses measured in a field parallel to the texture axis were almost identical for both samples indicating effective coupling of the nanorods with the polymer network. By contrast, measurements in a magnetic field perpendicular to the texture axis revealed a much higher initial susceptibility of the soft as compared to the hard ferrogel. This difference was attributed to the additional rotation of the nanorods allowed by the reduced shear modulus in the soft ferrogel matrix. Two methods for data analysis were presented which enabled us to determine the shear modulus of the gelatine matrix which was interpreted as a local rather than macroscopic quantity in consideration of the nanoscale of the probe particles.

Bender, P.; Tschöpe, A.; Birringer, R.

2014-12-01

348

Magnetic field optimization of permanent magnet undulators for arbitrary polarization  

NASA Astrophysics Data System (ADS)

Techniques for improving the magnetic field quality of APPLE II undulators are discussed. Individual block characterization including the inhomogeneities of the magnetization permits a precise prediction of field integrals as required for sorting. Specific shimming procedures adapted to the magnetic design of APPLE II undulators have to be employed in order to meet the stringent requirements of insertion devices in third generation synchrotron radiation sources as demonstrated for BESSY.

Bahrdt, J.; Frentrup, W.; Gaupp, A.; Scheer, M.; Englisch, U.

2004-01-01

349

SIMULATING MAGNETIC FIELDS IN THE ANTENNAE GALAXIES  

SciTech Connect

We present self-consistent high-resolution simulations of NGC 4038/4039 (the 'Antennae galaxies') including star formation, supernova feedback, and magnetic fields performed with the N-body/smoothed particle hydrodynamic (SPH) code GADGET, in which magnetohydrodynamics are followed with the SPH method. We vary the initial magnetic field in the progenitor disks from 10{sup -9} to 10{sup -4} G. At the time of the best match with the central region of the Antennae system, the magnetic field has been amplified by compression and shear flows to an equilibrium field value of {approx}10 {mu}G, independent of the initial seed field. These simulations are a proof of the principle that galaxy mergers are efficient drivers for the cosmic evolution of magnetic fields. We present a detailed analysis of the magnetic field structure in the central overlap region. Simulated radio and polarization maps are in good morphological and quantitative agreement with the observations. In particular, the two cores with the highest synchrotron intensity and ridges of regular magnetic fields between the cores and at the root of the southern tidal arm develop naturally in our simulations. This indicates that the simulations are capable of realistically following the evolution of the magnetic fields in a highly nonlinear environment. We also discuss the relevance of the amplification effect for present-day magnetic fields in the context of hierarchical structure formation.

Kotarba, H.; Karl, S. J.; Naab, T.; Johansson, P. H.; Lesch, H. [University Observatory Munich, Scheinerstr. 1, D-81679 Munich (Germany); Dolag, K.; Stasyszyn, F. A., E-mail: kotarba@usm.lmu.d [Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85741 Garching (Germany)

2010-06-20

350

Fine structure of solar magnetic fields  

Microsoft Academic Search

The deduction of magnetic fields from chromospheric structure is extended to active regions and transverse fields. Fields independently predicted by these rules from a high resolution Ha filtergram are compared with a high resolution magnetogram. The Ha method has the advantage over conventional magnetograms that it shows transverse fields and relates the fields to the real Sun. It has the

Harold Zirin

1972-01-01

351

Magnetic-field effects in non-magnetic glasses  

NASA Astrophysics Data System (ADS)

Recently, it was found that the multi-component glass a-BaO-Al2O3-SiO2 exhibits unusual magnetic properties at very low temperatures. Thus the question arises whether this is a specialty of that particular glass or a more general phenomenon. We report here on our studies of the magnetic-field dependence of the dielectric properties of the borosilicate glass BK7 which contains only a negligible amount of magnetic impurities. Since this glass also responds sensitively to magnetic fields, our investigations demonstrate that the reaction of glasses to magnetic fields is not caused by magnetic impurities but reflects a more general phenomenon. In addition, we have observed that the variation of the dielectric constant and the loss angle with magnetic field depend on the amplitude of the electric field that is used to measure the glass capacitance. We present the data and discuss possible origins of the magnetic-field phenomena in non-magnetic glasses.

Wohlfahrt, M.; Strehlow, P.; Enss, C.; Hunklinger, S.

2001-12-01

352

Thinned fiber Bragg grating magnetic field sensor with magnetic fluid  

NASA Astrophysics Data System (ADS)

The refractive index of magnetic fluid may be changed by external magnetic field. Therefore, through measuring its refractive index, the intensity of the magnetic field can be obtained. Fiber Bragg grating (FBG) is sensitive to the refractive index surrounding its cladding when the diameter of cladding is reduced to a certain degree. In order to prove the sensitivity of the thinned fiber Bragg grating to refractive index, series of experiments, such as the fabrication of thinned FBG, tuning magnetic field and obtaining spectral characterizations, are carried out. After the FBG is etched for 193 minutes by HF solution at 22%, the FBG starts to be sensitive to the surrounding refractive index and the Bragg wavelength decreases sharply with the etching process. The thinned FBG has been packaged to a container filled with MF. Using a tunable magnetic field the refractive index of magnetic fluid could be changed and the Bragg wavelength of FBG shifts correspondingly. Both the wavelength and the light power are sensitive to magnetic field and the sensitivity of wavelength is 2.3 pm/mT at least in the condition of proposed experiment. The obtained results show that the thinned FBG sensor with magnetic fluid could be applicable for magnetic field and current sensing.

Zhou, Ciming; Ding, Li; Wang, Dongli; Kuang, Yaqi; Jiang, Desheng

2011-05-01

353

Non-linear magnetization dynamics probed with X-rays: 1. Broken cylindrical symmetry of uniform modes  

NASA Astrophysics Data System (ADS)

We discuss how X-ray magnetic circular dichroism (XMCD) and X-ray magnetic linear dichroism (XMLD) may complement each other to probe the nonlinear nature of the resonant precession of either spin or orbital magnetization components in aligned ferro-, ferri- or even antiferro-magnets. The Landau-Lifshitz-Gilbert (LLG) equation is solved in a rotating frame locked to the microwave pump field, while treating as time-dependent perturbations the terms which, in the formulation of the free energy density, break down the cylindrical symmetry of precession. Concretely, we analyze the time-oscillating deviations of the magnetization from the steady-state solutions of the LLG equation hereafter called SS-modes. At any perturbation order, one may derive magnetic dipole components which oscillate at harmonic frequencies of the pump frequency and could be probed with XMCD. Under bichromatic pumping, frequency mixing arises from a time-dependent Zeeman coupling between two rotating frames locked to each individual pump field. Similarly, we expect magnetic quadrupole components to oscillate at the same frequencies. For consistency, their derivation requires a perturbation calculation up to second order. The latter time-reversal even, rank-2 magnetic tensor components can be probed only with XMLD. Beyond the (reciprocal) linear dichroism classically measured in ferri- or antiferromagnetic samples, a non-reciprocal XMLD signal is to be expected when space parity is lost. Nonlinear effects strongly depend upon the relative orientations of the external bias field and of the pump field with respect to the symmetry axes of the magnetic system. This holds true for the foldover lineshape distortions, harmonic generation, frequency mixing or multiquanta excitations.

Goulon, J.; Brouder, Ch.; Rogalev, A.; Goujon, G.; Wilhelm, F.

2014-10-01

354

Structure and evolution of the heliospheric magnetic field  

NASA Astrophysics Data System (ADS)

Global structure of the heliospheric magnetic field is investigated through several solar cycles. The study includes magnetic field measurements by space probes located in various spaces in the heliosphere. The latitudinal extent of the heliospheric current sheet is determined from the off-ecliptic observation by Ulysses during the declining phase of solar cycles 22 and 23. The results are compared to the latitudinal excursion of the neutral line on the source surface maps, the deviations are interpreted in relation with the characteristics of the solar cycles. The open magnetic flux of the sun, as determined from interplanetary measurements is best characterized by the radial component of the magnetic field. It is shown that the distribution of the radial component is a complex function of the location in the heliosphere, of the type of solar wind (i.e., slow or fast), and of the phase of the solar cycle. We demonstrate that this complexity is due to fluctuations of the magnetic field, the effect of which can be largely reduced by exploiting the symmetry features of the waves. Two methods are presented for the corrections of the interplanetary flux measurements. It is shown that the corrected magnetic flux density measured by the Ulysses around its solar polar orbit from 1990 to 2009 matches that calculated from the OMNI in-ecliptic, 1 AU data set over the same interval. This result shows that the sun's magnetic flux is generally distributed uniformly in the heliosphere and depends only on the total open magnetic flux of the sun. We calculate the open magnetic flux of the sun from the OMNI data base covering four solar cycles and the values are compared to the total open magnetic flux of the sun as determined from source surface models. The match is fairly good except for the raising phase of the solar cycles. The possible reasons are discussed.

Erdos, Geza

355

Atom probe analysis of sputtered Co Cr magnetic thin films  

NASA Astrophysics Data System (ADS)

Both Co-22at%Cr bulk alloy and its thin films were analyzed by an atom probe field ion microscope. While no compositional inhomogeneity was found in the bulk sample, a significant compositional fluctuation was found in the Co-Cr thin film sample which was deposited on a tungsten tip surface at 200°C. The concentration of the Cr enriched region was in the range of 30-40 at% Cr, while that of the Cr depleted region was in the range of 5-10 at% Cr.

Hono, K.; Maeda, Y.; Li, J.-L.; Sakurai, T.

1993-04-01

356

Estimation of fluctuating magnetic fields by an atomic magnetometer  

E-print Network

We present a theoretical analysis of the ability of atomic magnetometers to estimate a fluctuating magnetic field. Our analysis makes use of a Gaussian state description of the atoms and the probing field, and it presents the estimator of the field and a measure of its uncertainty which coincides in the appropriate limit with the achievements for a static field. We show by simulations that the estimator for the current value of the field systematically lags behind the actual value of the field, and we suggest a more complete theory, where measurement results at any time are used to update and improve both the estimate of the current value and the estimate of past values of the B-field.

Vivi Petersen; Klaus Molmer

2006-05-29

357

Preliminary Results of Performance Measurements on a Cylindrical Hall-Effect Thruster with Magnetic Field Generated by Permanent Magnets  

NASA Technical Reports Server (NTRS)

The performance of a low-power cylindrical Hall thruster, which more readily lends itself to miniaturization and low-power operation than a conventional (annular) Hall thruster, was measured using a planar plasma probe and a thrust stand. The field in the cylindrical thruster was produced using permanent magnets, promising a power reduction over previous cylindrical thruster iterations that employed electromagnets to generate the required magnetic field topology. Two sets of ring-shaped permanent magnets are used, and two different field configurations can be produced by reorienting the poles of one magnet relative to the other. A plasma probe measuring ion flux in the plume is used to estimate the current utilization for the two magnetic configurations. The measurements indicate that electron transport is impeded much more effectively in one configuration, implying a higher thrust efficiency. Preliminary thruster performance measurements on this configuration were obtained over a power range of 100-250 W. The thrust levels over this power range were 3.5-6.5 mN, with anode efficiencies and specific impulses spanning 14-19% and 875- 1425 s, respectively. The magnetic field in the thruster was lower for the thrust measurements than the plasma probe measurements due to heating and weakening of the permanent magnets, reducing the maximum field strength from 2 kG to roughly 750-800 G. The discharge current levels observed during thrust stand testing were anomalously high compared to those levels measured in previous experiments with this thruster.

Polzin, K. A.; Raitses, Y.; Merino, E.; Fisch, N. J.

2008-01-01

358

Videomagnetograph studies of solar magnetic fields  

Microsoft Academic Search

Observations of magnetic field diffusion in weak plage regions have been made using the analog videomagnetograph at the California Institute of Technology. Points of magnetic flux, usually described as ‘vertex points’ of the magnetic network, were found to have a mean lifetime of three to four days, and to disperse primarily by means of two mechanisms: a random walk with

Robert C. Smithson

1973-01-01

359

The Moessbauer effect in homogeneous magnetic field  

E-print Network

We derive the probability of the Moessbauer effect realized by the charged particle moving in the homogeneous magnetic field, or, in accelerating field. The submitted approach represents new deal of the Moessbauer physics. Key

Miroslav Pardy

2014-03-20

360

Magnetic field decay in model SSC dipoles  

SciTech Connect

We have observed that some of our model SSC dipoles have long time constant decays of the magnetic field harmonics with amplitudes large enough to result in significant beam loss, if they are not corrected. The magnets were run at constant current at the SSC injection field level of 0.3 tesla for one to three hours and changes in the magnetic field were observed. One explanation for the observed field decay is time dependent superconductor magnetization. Another explanation involves flux creep or flux flow. Data are presented on how the decay changes with previous flux history. Similar magnets with different Nb-Ti filament spacings and matrix materials have different long time field decay. A theoretical model using proximity coupling and flux creep for the observed field decay is discussed. 10 refs., 5 figs., 2 tabs.

Gilbert, W.S.; Althaus, R.F.; Barale, P.J.; Benjegerdes, R.W.; Green, M.A.; Green, M.I.; Scanlan, R.M.

1988-08-01

361

Low Energy Plasma Measurements of the Van Allen Probes Crossing Open Field Lines  

NASA Astrophysics Data System (ADS)

The Van Allen Probes encountered unusual low-latitude flank-side open field lines during the Nov. 14 2012 geomagnetic storm. Both spacecraft entered the lobes five times over several hours in the main phase of the storm. Four of the ~ five minute events were seen by both probes nearly simultaneously despite being 45 minutes apart in orbit (less than one L shell). The more tailward satellite always saw the boundary crossing first. We present the HOPE low energy plasma observations during these encounters. Adjacent to the lobe intervals, HOPE observed a hot electron plasma sheet leading to significant spacecraft charging. The electron and ion fluxes were significantly diminished during the lobe crossings coincident with a stronger, more highly stretched magnetic field. Significant accelerated field aligned oxygen signatures were measured on both closed and apparently open field lines, along with strong Alfvenic waves. Using the multipoint measurements we will examine the source of this acceleration and its role in inner magnetosphere ion dynamics. This event also represents the chance to constrain and assess magnetic field models and we will examine the topological location of the field lobes relative to the spacecraft for multiple models.

Larsen, B.; MacDonald, E.; Skoug, R. M.; Dixon, P.; Henderson, M. G.; Chaston, C. C.; Grande, M.; Funsten, H. O.; Thomsen, M.; Wygant, J. R.; Reeves, G. D.

2013-12-01

362

Magnetic Field Seeding through Supernova Feedback  

NASA Astrophysics Data System (ADS)

Stellar feedback occurring at small-scales can significantly impact the evolution of galaxies at much larger scales. For example, an appropriate feedback mechanism, including thermal and radiative components, can help regulate star formation, particularly in low-mass galaxies. While feedback models are generally prevalent in numerical simulations, the magnetic component is often neglected. However, measurements of galaxies indicate the presence of fields with a strength on the order of µG. Previous studies have demonstrated the formation of these fields through the amplification of a primordial magnetic field. Here, we describe a self-consistent prescription where magnetic fields are injected in supernova injections, calibrated by observations of magnetic fields in supernova remnants. These fields will then become seeds that evolve by way of mixing and turbulence to result in galactic-scale magnetic fields. As a proof of concept, we apply this method to model the supernova of a single Population III star and trace the evolution of the injected magnetic field. Future studies will apply this prescription to study not only the effects of magnetic fields on galaxy formation and evolution, but also the growth of the magnetized bubbles that form in the IGM.

Koh, Daegene; Wise, John

2015-01-01

363

Probing spin frustration in high-symmetry magnetic nanomolecules by inelastic neutron V. O. Garlea,1,  

E-print Network

Probing spin frustration in high-symmetry magnetic nanomolecules by inelastic neutron scattering V cluster features spin frustration and is one of the largest discrete magnetic molecules studied to date energy magnetic excitation spectrum of the magnetic nanomolecule Mo72Fe30 . This unique highly symmetric

Vakni, David

364

Graphene Nanoribbon in Sharply Localized Magnetic Fields  

E-print Network

We study the effect of a sharply localized magnetic field on the electron transport in a strip (ribbon) of graphene sheet, which allows to give results for the transmission and reflection probability through magnetic barriers. The magnetic field is taken as a single and double delta type localized functions, which are treated later as the zero width limit of gaussian fields. For both field configurations, we evaluate analytically and numerically their transmission and reflection coefficients. The possibility of spacial confinement due to the inhomogeneous field configuration is also investigated.

Abdulaziz D. Alhaidari; Hocine Bahlouli; Abderrahim El Mouhafid; Ahmed Jellal

2011-03-21

365

Interferometric methods for mapping static electric and magnetic fields  

NASA Astrophysics Data System (ADS)

The mapping of static electric and magnetic fields using electron probes with a resolution and sensitivity that are sufficient to reveal nanoscale features in materials requires the use of phase-sensitive methods such as the shadow technique, coherent Foucault imaging and the Transport of Intensity Equation. Among these approaches, image-plane off-axis electron holography in the transmission electron microscope has acquired a prominent role thanks to its quantitative capabilities and broad range of applicability. After a brief overview of the main ideas and methods behind field mapping, we focus on theoretical models that form the basis of the quantitative interpretation of electron holographic data. We review the application of electron holography to a variety of samples (including electric fields associated with p-n junctions in semiconductors, quantized magnetic flux in superconductors and magnetization topographies in nanoparticles and other magnetic materials) and electron-optical geometries (including multiple biprism, amplitude and mixed-type set-ups). We conclude by highlighting the emerging perspectives of (i) three-dimensional field mapping using electron holographic tomography and (ii) the model-independent determination of the locations and magnitudes of field sources (electric charges and magnetic dipoles) directly from electron holographic data.

Pozzi, Giulio; Beleggia, Marco; Kasama, Takeshi; Dunin-Borkowski, Rafal E.

2014-02-01

366

Bashful ballerina unveiled: Multipole analysis of the coronal magnetic field  

NASA Astrophysics Data System (ADS)

Heliospheric current sheet (HCS) is the continuum of the coronal magnetic equator, dividing the heliospheric magnetic field (HMF) into two sectors (polarities). Because of its wavy structure, the HCS is often called the ballerina skirt. Several studies have proven that the HCS is southward shifted during about three years in the solar declining phase. This persistent phenomenon, called the bashful ballerina, has been verified by geomagnetic indices since 1930s, by OMNI data base since 1960s, by the WSO PFSS model since mid-1970s and by the Ulysses probe measurements during the fast latitude scans in 1994-1995 and 2007. We study here the Wilcox Solar Observatory measurements of the photospheric magnetic field and the PFSS extrapolation of the coronal magnetic field. We show that the quadrupole moment of the photospheric magnetic field, which is important for the HCS asymmetry (bashful ballerina), mainly arises from the difference between northern and southern polar field strengths. According to the WSO data the minimum time quadrupole is mainly due to the difference between the highest northern and southern latitude bins. Related studies imply that the southward shift of the HCS is related to the delayed development of southern coronal holes. We also discuss the suggested connection of the HCS asymmetry to sunspot hemispheric asymmetry.

Virtanen, I.; Mursula, K.

2012-12-01

367

Polarized Radiation Observables for Probing the Magnetism of the Outer Solar Atmosphere  

NASA Astrophysics Data System (ADS)

The basic idea of optical pumping, for which Alfred Kastler received the 1966 Nobel Prize in Physics, is that the absorption and scattering of anisotropic radiation can produce population imbalances and quantum coherence among the magnetic substates of atomic levels. The degree of this radiatively-induced atomic level polarization, which is very sensitive to the presence of magnetic fields, can be determined by observing the polarization of the scattered or transmitted spectral line radiation. The most important point for solar physics is that the outer solar atmosphere is an optically pumped vapor and that the polarization of the emergent spectral line radiation can be exploited to obtain quantitative information on the strength and/or geometry of magnetic fields within the chromosphere, transition region, and corona. Here we review some recent investigations of the polarization produced by optical pumping in selected IR, FUV, and EUV spectral lines, showing that their magnetic sensitivity is suitable for probing the magnetism of the outer solar atmosphere.

Trujillo Bueno, J.

2014-10-01

368

Parker's magnetic field and relativistic jets  

NASA Astrophysics Data System (ADS)

We consider the motion of high-energy charged particles (cosmic rays) in Parker's spiral magnetic field. We show that under radial particle ejection from a sphere outside which there is Parker's magnetic field, all of the particles escaping from the sphere are focused either along the field symmetry axis or in the equatorial plane, depending on the field polarity. Based on the results obtained, we propose a possible model that explains the origin of relativistic jets.

Kichigin, G. N.

2014-10-01

369

Magnetic isotope and magnetic field effects on the DNA synthesis  

PubMed Central

Magnetic isotope and magnetic field effects on the rate of DNA synthesis catalysed by polymerases ? with isotopic ions 24Mg2+, 25Mg2+ and 26Mg2+ in the catalytic sites were detected. No difference in enzymatic activity was found between polymerases ? carrying 24Mg2+ and 26Mg2+ ions with spinless, non-magnetic nuclei 24Mg and 26Mg. However, 25Mg2+ ions with magnetic nucleus 25Mg were shown to suppress enzymatic activity by two to three times with respect to the enzymatic activity of polymerases ? with 24Mg2+ and 26Mg2+ ions. Such an isotopic dependence directly indicates that in the DNA synthesis magnetic mass-independent isotope effect functions. Similar effect is exhibited by polymerases ? with Zn2+ ions carrying magnetic 67Zn and non-magnetic 64Zn nuclei, respectively. A new, ion–radical mechanism of the DNA synthesis is suggested to explain these effects. Magnetic field dependence of the magnesium-catalysed DNA synthesis is in a perfect agreement with the proposed ion–radical mechanism. It is pointed out that the magnetic isotope and magnetic field effects may be used for medicinal purposes (trans-cranial magnetic treatment of cognitive deceases, cell proliferation, control of the cancer cells, etc). PMID:23851636

Buchachenko, Anatoly L.; Orlov, Alexei P.; Kuznetsov, Dmitry A.; Breslavskaya, Natalia N.

2013-01-01

370

Imaging and Probe Techniques for Wave Dispersion Estimates in Magnetized Plasmas  

NASA Astrophysics Data System (ADS)

Fluctuations in magnetized laboratory plasmas are ubiquitous and complex. In addition to deleterious effects, like increasing heat and particle transport in magnetic fusion energy devices, fluctuations also provide a diagnostic opportunity. Identification of a fluctuation with a particular wave or instability gives detailed information about the properties of the underlying plasma. In this work, diagnostics and spectral analysis techniques for fluctuations are developed and applied to two different laboratory plasma experiments. The first part of this dissertation discusses imaging measurements of coherent waves in the Controlled Shear Decorrelation Experiment (CSDX) at the University of California, San Diego. Visible light from ArII line emission is collected at high frame rates using an intensified digital camera. A cross-spectral phase technique allows direct visualization of dominant phase structures as a function of frequency, as well as identification of azimuthal asymmetries present in the system. Experimental dispersion estimates are constructed from imaging data alone. Drift-like waves are identified by comparison with theoretical dispersion curves, and a tentative match of a low- frequency spectral feature to Kelvin-Helmholtz-driven waves is presented. Imaging measurements are consistent with previous results, and provide non-invasive, single-shot measurements across the entire plasma cross-section. Relationships between imaging and electrostatic probe measurements are explored. The second part of this dissertation discusses the design and construction of diagnostics for the Colorado Field-Reversed Configuration (CFRC), as well as preliminary results. A triple probe, a Mach probe, a multi-chord heterodyne interferometer, Rogowski coils, a single-point, three-axis magnetic probe, and a 16-point, three-axis magnetic probe have been constructed. Each diagnostic is designed for fluctuation measurements up to the data acquisition Nyquist frequency of 20 MHz. A histogram cross-spectral analysis technique allows experimental dispersion estimates to be made from multi-channel magnetic measurements. Hints of waves in the range of ion-cyclotron frequency harmonics are observed, but lack of global information about the plasma objects formed in CFRC prevents definitive interpretation.

Light, A. D.

371

The gravitomagnetic field of a sphere, Gravity Probe B and the LAGEOS satellites  

E-print Network

The gravitomagnetic field generated by a rotating sphere is usually calculated from the ideal dipole model. However, for a sphere with a homogeneous mass density, this model is not generally valid. Trying to obtain a more accurate value of the gravitomagnetic field inside and outside the sphere, series expansions for this field are presented in this paper. The calculated polar gravitomagnetic field of the sphere and that from the ideal dipole model appear to coincide, but the field in the vicinity of the sphere may deviate. The deduced field within the sphere strongly deviates from the ideal dipole result. As an illustration, the gravitomagnetic precession rate (or frame-dragging effect) of a gyroscope moving in the gravitomagnetic field from a large rotating sphere is calculated. For the Gravity Probe B experiment the result may coincide with the prediction from the ideal dipole model and in fair agreement with observations. In addition, the obtained Lense-Thirring precession rate for the LAGEOS satellites probably coincides with the standard prediction. For both experiments alternative predictions are calculated, when the gravitomagnetic field and the magnetic field from moving charge are equivalent. Theoretical and observational indications for such an equivalence are summarized. The obtained series expansions for the gravitomagnetic field of a sphere can also be applied to the calculation of the magnetic field, generated by a rotating sphere with a homogeneous charge density. Results for this case are also discussed.

Jacob Biemond

2008-02-22

372

MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. I. FORCE-FREE MAGNETIC FIELDS B. Fornberg,2  

E-print Network

MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. I. FORCE-FREE MAGNETIC FIELDS N. Flyer,1 B Axisymmetric force-free magnetic fields external to a unit sphere are studied as solutions to boundary value against expansion into the unbounded space. This property as a basic mechanism for solar coronal mass

Fornberg, Bengt

373

Single core-shell nanoparticle probes for non-invasive magnetic force microscopy.  

PubMed

We present an easy, fast and reliable method for the preparation of magnetic force microscopy (MFM) probes based on single Co nanoparticles (NPs). Due to their dipolar character, these magnetic probes open up a new approach for quantitative and non-invasive MFM measurements on the nanometer length scale. To guarantee long-term stability of these tips under ambient conditions, an ultrathin protecting Au shell was grown around the Co NPs through photochemical deposition. Single magnetic particles were firmly attached to standard silicon AFM tips using bifunctional self-assembling molecules. Such probes were tested on longitudinal magnetic recording media and compared to the results as recorded with conventional thin-film MFM tips. Easy data interpretation of the magnetic nanoparticle probes in a point dipole model is shown. Our nanoparticle tips provide excellent endurance for MFM recording, enable non-invasive probing while maintaining a high sensitivity, resolution, and reproducibility. PMID:24896585

Uhlig, Tino; Wiedwald, Ulf; Seidenstücker, Axel; Ziemann, Paul; Eng, Lukas M

2014-06-27

374

The magnetic field of ? Ori A  

NASA Astrophysics Data System (ADS)

Magnetic fields play a significant role in the evolution of massive stars. About 7% of massive stars are found to be magnetic at a level detectable with current instrumentation (Wade et al. 2013) and only a few magnetic O stars are known. Detecting magnetic field in O stars is particularly challenging because they only have few, often broad, lines to measure the field, which leads to a deficit in the knowledge of the basic magnetic properties of O stars. We present new spectropolarimetric Narval observations of ? Ori A. We also provide a new analysis of both the new and older data taking binarity into account. The aim of this study was to confirm the presence of a magnetic field in ? Ori A. We identify that it belongs to ? Ori Aa and characterize it.

Blazère, A.; Neiner, C.; Bouret, J.-C.; Tkachenko, A.

2015-01-01

375

High concentration ferronematics in low magnetic fields  

E-print Network

We investigated experimentally the magneto-optical and dielectric properties of magnetic-nanoparticle-doped nematic liquid crystals (ferronematics). Our studies focus on the effect of the very small orienting bias magnetic field $B_{bias}$, and that of the nematic director pretilt at the boundary surfaces in our systems sensitive to low magnetic fields. Based on the results we assert that $B_{bias}$ is not necessarily required for a detectable response to low magnetic fields, and that the initial pretilt, as well as the aggregation of the nanoparticles play an important (though not yet explored enough) role.

T. Tóth-Katona; P. Salamon; N. Éber; N. Tomašovi?ová; Z. Mitróová; P. Kop?anský

2014-09-05

376

Interplanetary stream magnetism: Kinematic effects. [solar magnetic fields and wind  

NASA Technical Reports Server (NTRS)

The particle density, and the magnetic field intensity and direction are calculated in corotating streams of the solar wind, assuming that the solar wind velocity is constant and radial and that its azimuthal variations are not two rapid. The effects of the radial velocity profile in corotating streams on the magnetic fields were examined using kinematic approximation and a variety of field configurations on the inner boundary. Kinematic and dynamic effects are discussed.

Burlaga, L. F.; Barouch, E.

1974-01-01

377

Fluctuating magnetic field induced resonant activation.  

PubMed

In this paper, we have studied the properties of a Brownian particle at stationary state in the presence of a fluctuating magnetic field. Time dependence of the field makes the system thermodynamically open. As a signature of that the steady state distribution function becomes function of damping strength, intensity of fluctuations and constant parts of the applied magnetic field. It also depends on the correlation time of the fluctuating magnetic field. Our another observation is that the random magnetic field can induce the resonant activation phenomenon. Here correlation time is increased under the fixed variance of the fluctuating field. But if the correlation time (?) increases under the fixed field strength then the mean first passage time rapidly grows at low ? and it almost converges at other limit. This is sharp contrast to the usual colored noise driven open system case where the mean first passage time diverges exponentially. We have also observed that a giant enhancement of barrier crossing rate occurs particularly at large strength of constant parts of the applied magnetic field even for very weak fluctuating magnetic field. Finally, break down of the Arrhenius result and disappearance of the Kramers' turn over phenomenon may occur in the presence of a fluctuating magnetic field. PMID:25494726

Mondal, Shrabani; Das, Sudip; Baura, Alendu; Bag, Bidhan Chandra

2014-12-14

378

Fluctuating magnetic field induced resonant activation  

NASA Astrophysics Data System (ADS)

In this paper, we have studied the properties of a Brownian particle at stationary state in the presence of a fluctuating magnetic field. Time dependence of the field makes the system thermodynamically open. As a signature of that the steady state distribution function becomes function of damping strength, intensity of fluctuations and constant parts of the applied magnetic field. It also depends on the correlation time of the fluctuating magnetic field. Our another observation is that the random magnetic field can induce the resonant activation phenomenon. Here correlation time is increased under the fixed variance of the fluctuating field. But if the correlation time (?) increases under the fixed field strength then the mean first passage time rapidly grows at low ? and it almost converges at other limit. This is sharp contrast to the usual colored noise driven open system case where the mean first passage time diverges exponentially. We have also observed that a giant enhancement of barrier crossing rate occurs particularly at large strength of constant parts of the applied magnetic field even for very weak fluctuating magnetic field. Finally, break down of the Arrhenius result and disappearance of the Kramers' turn over phenomenon may occur in the presence of a fluctuating magnetic field.

Mondal, Shrabani; Das, Sudip; Baura, Alendu; Bag, Bidhan Chandra

2014-12-01

379

Probing the Magnetized Interstellar Medium Surrounding the Planetary Nebula Sh 2-216  

E-print Network

We present 1420 MHz polarization images of a 2.5 X 2.5 degree region around the planetary nebula (PN) Sh 2-216. The images are taken from the Canadian Galactic Plane Survey (CGPS). An arc of low polarized intensity appears prominently in the north-east portion of the visible disk of Sh 2-216, coincident with the optically identified interaction region between the PN and the interstellar medium (ISM). The arc contains structural variations down to the ~1 arcminute resolution limit in both polarized intensity and polarization angle. Several polarization-angle "knots" appear along the arc. By comparison of the polarization angles at the centers of the knots and the mean polarization angle outside Sh 2-216, we estimate the rotation measure (RM) through the knots to be -43 +/- 10 rad/m^2. Using this estimate for the RM and an estimate of the electron density in the shell of Sh 2-216, we derive a line-of-sight magnetic field in the interaction region of 5.0 +/- 2.0 microG. We believe it more likely the observed magnetic field is interstellar than stellar, though we cannot completely dismiss the latter possibility. We interpret our observations via a simple model which describes the ISM magnetic field around Sh 2-216, and comment on the potential use of old PNe as probes of the magnetized ISM.

Ryan Ransom; Bulent Uyaniker; Roland Kothes; Tom Landecker

2008-06-09

380

Homogenization of nanostructured media in magnetic field  

NASA Astrophysics Data System (ADS)

Problem of homogenization of nanostructured media in magnetic field has been considered. Possibility of introduction of effective material parameters dielectric permittivity and magnetic permeability for three classes of media such as magnetic metal nanostructures, film metal-dielectric composite media and 3D-nanocomposites on the base of opal matrices has been investigated. It has been stated that the introduction of effective parameters far from magnetic resonance conditions is possible at millimeter waveband frequencies. Strict introduction of effective magnetic permeability of nanostructured media near magnetic resonance is not possible.

Rinkevich, A. B.; Perov, D. V.

2014-11-01

381

Two-axis magnetic field sensor  

NASA Technical Reports Server (NTRS)

A ferromagnetic thin-film based magnetic field sensor with first and second sensitive direction sensing structures each having a nonmagnetic intermediate layer with two major surfaces on opposite sides thereof having a magnetization reference layer on one and an anisotropic ferromagnetic material sensing layer on the other having a length in a selected length direction and a smaller width perpendicular thereto and parallel to the relatively fixed magnetization direction. The relatively fixed magnetization direction of said magnetization reference layer in each is oriented in substantially parallel to the substrate but substantially perpendicular to that of the other. An annealing process is used to form the desired magnetization directions.

Jander, Albrecht (Inventor); Nordman, Catherine A. (Inventor); Qian, Zhenghong (Inventor); Smith, Carl H. (Inventor)

2006-01-01

382

Orientation effects in pulsed magnetic field treatment  

Microsoft Academic Search

This paper presents the orientation effects on residual stress release by pulsed magnetic field treatment. Specimens are produced by tungsten inert gas (TIG) welding and the initial residual stresses in them are measured by the hole-drilling method. With different orientations these specimens are treated in the same magnetic field and the residual stresses are measured for the second time. By

Cai Zhipeng; Lin Jian; Zhao Haiyan; Lu Anli

2005-01-01

383

A search for weak stellar magnetic fields  

Microsoft Academic Search

The magnetic fields of normal main sequence stars, supergiants, and mercury-manganese stars were measured in metal lines with the magnetometer of the main stellar spectrograph and in hydrogen lines with the spectropolarimeter at the 6-meter telescope. These data were analyzed statistically with data obtained by other authors. It is concluded that the dipole magnetic fields of the stars studied hardly

Yu. V. Glagolevskij; I. I. Romanyuk; I. D. Najdenov; V. G. Shtol

1991-01-01

384

Magnetic Fields at the Center of Coils  

ERIC Educational Resources Information Center

In this note we synthesize and extend expressions for the magnetic field at the center of very short and very long current-carrying coils. Elementary physics textbooks present the following equation for the magnetic field inside a very long current-carrying coil (solenoid): B[subscript sol] = µ[subscript 0] (N/L) I, (1) where I is the current, N…

Binder, Philippe; Hui, Kaleonui; Goldman, Jesse

2014-01-01

385

Space Quantization in a Gyrating Magnetic Field  

Microsoft Academic Search

The nonadiabatic transitions which a system with angular momentum J makes in a magnetic field which is rotating about an axis inclined with respect to the field are calculated. It is shown that the effects depend on the sign of the magnetic moment of the system. We therefore have an absolute method for measuring the sign and magnitude of the

I. I. Rabi

1937-01-01

386

The magnetic field of an infinite solenoid  

NASA Astrophysics Data System (ADS)

We use the Biot-Savart law for filamentary currents to show that the magnetic field produced by an infinitely long straight strip of infinitesimal width carrying a uniform transverse surface current can be written in simple geometrical terms. We use this result to calculate the magnetic field of an infinite solenoid of arbitrary but uniform cross-sectional shape.

Espinosa, Olivier; Slusarenko, Viktor

2003-09-01

387

Coulomb crystals in the magnetic field.  

PubMed

The body-centered-cubic Coulomb crystal of ions in the presence of a uniform magnetic field is studied using the rigid electron background approximation. The phonon mode spectra are calculated for a wide range of magnetic-field strengths and for several orientations of the field in the crystal. The phonon spectra are used to calculate the phonon contribution to the crystal energy, entropy, specific heat, Debye-Waller factor of ions, and the rms ion displacements from the lattice nodes for a broad range of densities, temperatures, chemical compositions, and magnetic fields. Strong magnetic field dramatically alters the properties of quantum crystals. The phonon specific heat increases by many orders of magnitude. The ion displacements from their equilibrium positions become strongly anisotropic. The results can be relevant for dusty plasmas, ion plasmas in Penning traps, and especially for the crust of magnetars (neutron stars with superstrong magnetic fields B > or approximately equal 10(14) G ). The effect of the magnetic field on ion displacements in a strongly magnetized neutron star crust can suppress the nuclear reaction rates and make them extremely sensitive to the magnetic-field direction. PMID:19905459

Baiko, D A

2009-10-01

388

Does the solar magnetic field increase?  

Microsoft Academic Search

We consider measurements of the general magnetic field (GMF) of the Sun as a star at four world observatories from 1968 until\\u000a 1999. We show that, within the error limits, the mean strength of the photospheric magnetic field H (of its longitudinal component, in magnitude) has not changed over the last 32 years. This is in conflict with the recent

V. A. Kotov; I. V. Kotova

2001-01-01

389

Using Experiment and Computer Modeling to Determine the Off-Axis Magnetic Field of a Solenoid  

ERIC Educational Resources Information Center

The study of the ideal solenoid is a common topic among introductory-based physics textbooks and a typical current arrangement in laboratory hands-on experiences where the magnetic field inside a solenoid is determined at different currents and at different distances from its center using a magnetic probe. It additionally provides a very simple…

Lietor-Santos, Juan Jose

2014-01-01

390

Permanent magnet edge-field quadrupole  

DOEpatents

Planar permanent magnet edge-field quadrupoles for use in particle accelerating machines and in insertion devices designed to generate spontaneous or coherent radiation from moving charged particles are disclosed. The invention comprises four magnetized rectangular pieces of permanent magnet material with substantially similar dimensions arranged into two planar arrays situated to generate a field with a substantially dominant quadrupole component in regions close to the device axis. 10 figs.

Tatchyn, R.O.

1997-01-21

391

Permanent magnet edge-field quadrupole  

DOEpatents

Planar permanent magnet edge-field quadrupoles for use in particle accelerating machines and in insertion devices designed to generate spontaneous or coherent radiation from moving charged particles are disclosed. The invention comprises four magnetized rectangular pieces of permanent magnet material with substantially similar dimensions arranged into two planar arrays situated to generate a field with a substantially dominant quadrupole component in regions close to the device axis.

Tatchyn, Roman O. (Mountain View, CA)

1997-01-01

392

Solar magnetic fields and the dynamo theory  

Microsoft Academic Search

Unlike Earth’s dipolar magnetic fields, solar magnetic fields consist of wide ranges of length-scales and strengths, and interestingly, they evolve in a cyclic fashion with a 22-year periodicity. A magnetohydrodynamic dynamo operating in the Sun is most likely responsible for producing the solar magnetic activity cycle. While the first solar dynamo models were built half a century ago, recent views

M. Dikpati

2005-01-01

393

Fields from a relativistic magnetic explosion  

NASA Astrophysics Data System (ADS)

Following Prendergast, we study the relativistically expanding electromagnetic fields generated by an axisymmetric explosion of magnetic energy in a small volume. The magnetic field expands uniformly either within a cone or in all directions and it is therefore accompanied by an electric field. In the highly conducting plasma, the charges move to annul the electric field in the frame of the moving plasma. The solutions presented are analytical and semi-analytical. We find that the time-scale for the winding up of the initial magnetic field is crucial, as short time-scales lead to strong radiant fields. Assuming a magnetic field of 1013G emerging from a magnetosphere of 109cm, we end with a jet when confined by a pressure environment that falls more slowly than r-4. The jet carries energy of 1051erg, which is mostly due to differential rotation at the base.

Gourgouliatos, K. N.; Lynden-Bell, D.

2008-11-01

394

Magnetic field amplification in supernova shock precursor  

NASA Astrophysics Data System (ADS)

Galactic cosmic rays are believed to be mostly accelerated at supernova shocks. However, the interstellar magnetic field is too weak to efficiently accelerate galactic cosmic rays up to the highest energies. A stronger magnetic field in the preshock region could provide the efficiency required. Cosmic ray streaming instability has been claimed to be responsible for the amplification of precursor magnetic fields. An alternative mechanism has been proposed in which the cosmic ray pressure gradient forms the shock precursor and drives turbulence, amplifying the magnetic field via the small-scale dynamo. We explore this last scenario through 3-D MHD numerical simulations. We show under which conditions an efficient amplification of the magnetic field is achieved.

Del Valle, Maria Victoria; Lazarian, Alex

395

Chaotic magnetic fields: Particle motion and energization  

SciTech Connect

Magnetic field line equations correspond to a Hamiltonian dynamical system, so the features of a Hamiltonian systems can easily be adopted for discussing some essential features of magnetic field lines. The integrability of the magnetic field line equations are discussed by various authors and it can be shown that these equations are, in general, not integrable. We demonstrate several examples of realistic chaotic magnetic fields, produced by asymmetric current configurations. Particular examples of chaotic force-free field and non force-free fields are shown. We have studied, for the first time, the motion of a charged particle in chaotic magnetic fields. It is found that the motion of a charged particle in a chaotic magnetic field is not necessarily chaotic. We also showed that charged particles moving in a time-dependent chaotic magnetic field are energized. Such energization processes could play a dominant role in particle energization in several astrophysical environments including solar corona, solar flares and cosmic ray propagation in space.

Dasgupta, Brahmananda [CSPAR, University of Alabama in Huntsville, Huntsville, AL 35805 (United States); Ram, Abhay K. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Li, Gang [Department of Physics, University of Alabama in Huntsville, Huntsville, AL 35899 and CSPAR, University of Alabama in Huntsville, Huntsville, AL 35805 (United States); Li, Xiaocan [Department of Physics, University of Alabama in Huntsville, Huntsville, AL 35899 (United States)

2014-02-11

396

Subnanosecond magnetization dynamics induced by a pulsed magnetic field in diluted magnetic semiconductor quantum wells  

NASA Astrophysics Data System (ADS)

The magnetization dynamics induced by a pulsed magnetic field is investigated by time- and polarization-resolved photoluminescene measurements in (Cd,Mn)Te/(Cd,Mg)Te quantum wells. The magnetization dynamics of Mn2+ ions is found to be strongly dependent on the external static magnetic field. A dynamical response of the magnetization on a subnanosecond time scale is observed at zero static magnetic field, while it drastically slows down and approaches the spin-lattice relaxation time constant for a nonzero static field. Theoretical calculations emphasize the importance of local spin interactions that interplay with the Zeeman interaction for the observed magnetization dynamics.

Chen, Y. S.; Wiater, M.; Karczewski, G.; Wojtowicz, T.; Bacher, G.

2013-04-01

397

Warm inflation in presence of magnetic fields  

SciTech Connect

We present preliminary results on the possible effects that primordial magnetic fields can have for a warm inflation scenario, based on global supersymmetry, with a new-inflation-type potential. This work is motivated by two considerations: first, magnetic fields seem to be present in the universe on all scales which rises de possibility that they could also permeate the early universe; second, the recent emergence of inflationary models where the inflaton is not assumed to be isolated but instead it is taken as an interacting field, even during the inflationary expansion. The effects of magnetic fields are included resorting to Schwinger's proper time method.

Piccinelli, Gabriella [Centro Tecnológico, FES Aragón, Universidad Nacional Autónoma de México, Avenida Rancho Seco S/N, Bosques de Aragón, Nezahualcóyotl, Estado de México 57130 (Mexico)] [Centro Tecnológico, FES Aragón, Universidad Nacional Autónoma de México, Avenida Rancho Seco S/N, Bosques de Aragón, Nezahualcóyotl, Estado de México 57130 (Mexico); Sánchez, Ángel [Department of Physics, University of Texas at El Paso, El Paso, Texas 79968 (United States)] [Department of Physics, University of Texas at El Paso, El Paso, Texas 79968 (United States); Ayala, Alejandro; Mizher, Ana Julia [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Apartado Postal 70-543, México Distrito Federal 04510 (Mexico)] [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Apartado Postal 70-543, México Distrito Federal 04510 (Mexico)

2013-07-23

398

Probing boundary magnetization through exchange bias in heterostructures with competing anisotropy  

NASA Astrophysics Data System (ADS)

Cr2O3 (chromia) is a magnetoelectric antiferromagnet with a bulk TN of 307 K. It has been utilized for electrically controlled exchange bias (EB) by taking advantage of voltage-controllable boundary magnetization (BM) occurring as a generic property in magnetoelectric single domain antiferromagnets.footnotetextXi He, et al., Nature Mater.9, 579-585 (2010) In the perpendicular Cr2O3(0001)/CoPd EB system the EB-field shows an order parameter type T-dependence close to TN reflecting the T-dependence of the BM. At about 150 K a decrease of the EB-field sets in with decreasing temperature suggesting canting of the BM. To evidence this mechanism we use EB as a probe. Specifically, we investigate EB in Permalloy(5nm)/Cr2O3 (0001)(100nm) with Permalloy and chromia having competing anisotropies. We measure easy axis magnetic hysteresis loops via longitudinal magneto-optical Kerr effect for various temperatures after perpendicular and in-plane magnetic field-cooling. The T-dependence of the EB field supports the canting mechanism. In addition to the all thin film EB system, we explore a Permalloy(10nm)/Cr2O3(0001 single crystal) heterostructure where magnetoelectric annealing allows selecting Cr2O3 single domain states. Here the effect of T-dependent canting of the BM is compared with findings in the complementary perpendicular EB system.

Wang, Yi; Binek, Christian

2013-03-01

399

Behavior of multi-component magnetic colloidal systems in tunable magnetic fields and applications in biosensing  

NASA Astrophysics Data System (ADS)

A system consisting of multiple-component beads, such as superparamagnetic beads, nonmagnetic beads and magnetorheological (MR) fluid, can display some very amazing and special properties when subjected to an external magnetic field because the MR fluid can act on both types of beads synchronously as a magnetic medium. Some novel structures and phenomena were discovered and are discussed in our work, including 'ring-structures', 'small-ring' and 'ring-chains' in static or rotational magnetic fields. If both probe and target molecules are attached consisting of functionalized superparamagnetic beads and non-magnetic beads, respectively, the ring-structure could be maintained due to biomolecular bonding, even after removing the external magnetic field. Using these remnant rings, we raised two protocols for biosensing: a two-dimensional biosensor using a magnetic self-assembled colloidal ring-structure, and an improved magneto-optical transmittance (MT) method. In the former protocol, we define the small nonmagnetic particles as "petals" because the whole structure looks like a flower. It was proved that the number of remnant ring petals was a function of the concentration of the target molecules', with a concentration range from 0.0768 ng/mL ~ 3.8419 ng/mL, making it a promising technology for applications involving biosensing. In the latter protocol, the use of larger individual units made the magnetic particle chain longer, which was considered to be a promising way of improving the sensitivity of the MT method.

Yang, Ye; Li, Zhengcao; Ko, Pil Ju; Sandhu, Adarsh

2012-03-01

400

Evolution of Magnetic Fields in Supernova Remnants  

E-print Network

Supernova remnants (SNR) are now widely believed to be a source of cosmic rays (CRs) up to an energy of 1 PeV. The magnetic fields required to accelerate CRs to sufficiently high energies need to be much higher than can result from compression of the circumstellar medium (CSM) by a factor 4, as is the case in strong shocks. Non-thermal synchrotron maps of these regions indicate that indeed the magnetic field is much stronger, and for young SNRs has a dominant radial component while for old SNRs it is mainly toroidal. How these magnetic fields get enhanced, or why the field orientation is mainly radial for young remnants, is not yet fully understood. We use an adaptive mesh refinement MHD code, AMRVAC, to simulate the evolution of supernova remnants and to see if we can reproduce a mainly radial magnetic field in early stages of evolution. We follow the evolution of the SNR with three different configurations of the initial magnetic field in the CSM: an initially mainly toroidal field, a turbulent magnetic field, and a field parallel to the symmetry axis. Although for the latter two topologies a significant radial field component arises at the contact discontinuity due to the Rayleigh-Taylor instability, no radial component can be seen out to the forward shock. Ideal MHD appears not sufficient to explain observations. Possibly a higher compression ratio and additional turbulence due to dominant presence of CRs can help us to better reproduce the observations in future studies.

K. M. Schure; J. Vink; A. Achterberg; R. Keppens

2008-10-28

401

A Large Volume Double Channel 1H-X RF Probe for Hyperpolarized Magnetic Resonance at 0.0475 Tesla  

PubMed Central

In this work we describe a large volume 340 mL 1H-X magnetic resonance (MR) probe for studies of hyperpolarized compounds at 0.0475 T. 1H/13C and 1H/15N probe configurations are demonstrated with the potential for extension to 1H/129Xe. The primary applications of this probe are preparation and quality assurance of 13C and 15N hyperpolarized contrast agents using PASADENA (parahydrogen and synthesis allow dramatically enhanced nuclear alignment) and other parahydrogen-based methods of hyperpolarization. The probe is efficient and permits 62 ?s 13C excitation pulses at 5.3 Watts, making it suitable for portable operation. The sensitivity and detection limits of this probe, tuned to 13C, are compared with a commercial radio frequency (RF) coil operating at 4.7 T. We demonstrate that low field MR of hyperpolarized contrast agents could be as sensitive as conventional high field detection and outline potential improvements and optimization of the probe design for preclinical in vivo MRI. PASADENA application of this low-power probe is exemplified with 13C hyperpolarized 2-hydroxyethyl propionate-1-13C,2,3,3-d3. PMID:22706029

Coffey, Aaron M.; Shchepin, Roman V.; Wilkens, Ken; Waddell, Kevin W.; Chekmenev, Eduard Y.

2012-01-01

402

Magnetic fields in noninvasive brain stimulation.  

PubMed

The idea that magnetic fields could be used therapeutically arose 2000 years ago. These therapeutic possibilities were expanded after the discovery of electromagnetic induction by the Englishman Michael Faraday and the American Joseph Henry. In 1896, Arsène d'Arsonval reported his experience with noninvasive brain magnetic stimulation to the scientific French community. In the second half of the 20th century, changing magnetic fields emerged as a noninvasive tool to study the nervous system and to modulate neural function. In 1985, Barker, Jalinous, and Freeston presented transcranial magnetic stimulation, a relatively focal and painless technique. Transcranial magnetic stimulation has been proposed as a clinical neurophysiology tool and as a potential adjuvant treatment for psychiatric and neurologic conditions. This article aims to contextualize the progress of use of magnetic fields in the history of neuroscience and medical sciences, until 1985. PMID:23787954

Vidal-Dourado, Marcos; Conforto, Adriana Bastos; Caboclo, Luis Otávio Sales Ferreira; Scaff, Milberto; Guilhoto, Laura Maria de Figueiredo Ferreira; Yacubian, Elza Márcia Targas

2014-04-01

403

Origin of magnetic fields in galaxies  

SciTech Connect

Microgauss magnetic fields are observed in all galaxies at low and high redshifts. The origin of these intense magnetic fields is a challenging question in astrophysics. We show here that the natural plasma fluctuations in the primordial Universe (assumed to be random), predicted by the fluctuation -dissipation theorem, predicts {approx}0.034 {mu}G fields over {approx}0.3 kpc regions in galaxies. If the dipole magnetic fields predicted by the fluctuation-dissipation theorem are not completely random, microgauss fields over regions > or approx. 0.34 kpc are easily obtained. The model is thus a strong candidate for resolving the problem of the origin of magnetic fields in < or approx. 10{sup 9} years in high redshift galaxies.

Souza, Rafael S. de; Opher, Reuven [IAG, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, CEP 05508-900, Sao Paulo, SP (Brazil)

2010-03-15

404

Magnetic-field-controlled reconfigurable semiconductor logic.  

PubMed

Logic devices based on magnetism show promise for increasing computational efficiency while decreasing consumed power. They offer zero quiescent power and yet combine novel functions such as programmable logic operation and non-volatile built-in memory. However, practical efforts to adapt a magnetic device to logic suffer from a low signal-to-noise ratio and other performance attributes that are not adequate for logic gates. Rather than exploiting magnetoresistive effects that result from spin-dependent transport of carriers, we have approached the development of a magnetic logic device in a different way: we use the phenomenon of large magnetoresistance found in non-magnetic semiconductors in high electric fields. Here we report a device showing a strong diode characteristic that is highly sensitive to both the sign and the magnitude of an external magnetic field, offering a reversible change between two different characteristic states by the application of a magnetic field. This feature results from magnetic control of carrier generation and recombination in an InSb p-n bilayer channel. Simple circuits combining such elementary devices are fabricated and tested, and Boolean logic functions including AND, OR, NAND and NOR are performed. They are programmed dynamically by external electric or magnetic signals, demonstrating magnetic-field-controlled semiconductor reconfigurable logic at room temperature. This magnetic technology permits a new kind of spintronic device, characterized as a current switch rather than a voltage switch, and provides a simple and compact platform for non-volatile reconfigurable logic devices. PMID:23364687

Joo, Sungjung; Kim, Taeyueb; Shin, Sang Hoon; Lim, Ju Young; Hong, Jinki; Song, Jin Dong; Chang, Joonyeon; Lee, Hyun-Woo; Rhie, Kungwon; Han, Suk Hee; Shin, Kyung-Ho; Johnson, Mark

2013-02-01

405

Optical probing of sample heating in scanning near-field experiments with apertured probes  

SciTech Connect

We have used the inherent thermochromism of conjugated polymers to investigate substrate heating effects in scanning near-field experiments with metal-coated 'apertured' probes. Chemically etched and pulled fibers were used to provide near-field excitation of fully converted films of poly(p-phenylene vinylene), PPV, and of poly(4,4{sup '}-diphenylene diphenylvinylene). We detect no significant blueshift of the photoluminescence spectra generated with near-field excitation, in comparison to those collected with far-field excitation. We conclude that polymer heating in the region contributing to the luminescence is less than 40 K. We also demonstrate that thermolithography of the PPV precursor is not significant by comparing UV (325 nm) and red (670 nm) illumination.

Latini, G.; Downes, A.; Fenwick, O.; Ambrosio, A.; Allegrini, M.; Daniel, C.; Silva, C.; Gucciardi, P.G.; Patane, S.; Daik, R.; Feast, W.J.; Cacialli, F. [Department of Physics and Astronomy and London Centre for Nanotechnology, University College London, Gower Street, WC1E 6BT, London (United Kingdom); INFM and Dipartimento di Fisica, Universita di Pisa, Via F. Buonarroti 2, 5612, Pisa (Italy); Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 0HE (United Kingdom); CNR-Istituto per i Processi Chimico-Fisici, sez. Messina, Via La Farina 237, 98123, Messina (Italy); INFM and Dipartimento di Fisica MTFA, Universita di Messina, Salita Sperone 31, 98166, Messina (Italy); IRC Polymer Science and Technology, Durham University, South Road, Durham DH1 3LE (United Kingdom); Department of Physics and Astronomy and London Centre for Nanotechnology, University College London, Gower Street, WC1E 6BT, London (United Kingdom)

2005-01-03

406

The Electric Field and Waves Instruments on the Radiation Belt Storm Probes Mission  

NASA Astrophysics Data System (ADS)

The Electric Fields and Waves (EFW) Instruments on the two Radiation Belt Storm Probe (RBSP) spacecraft (recently renamed the Van Allen Probes) are designed to measure three dimensional quasi-static and low frequency electric fields and waves associated with the major mechanisms responsible for the acceleration of energetic charged particles in the inner magnetosphere of the Earth. For this measurement, the instrument uses two pairs of spherical double probe sensors at the ends of orthogonal centripetally deployed booms in the spin plane with tip-to-tip separations of 100 meters. The third component of the electric field is measured by two spherical sensors separated by ˜15 m, deployed at the ends of two stacer booms oppositely directed along the spin axis of the spacecraft. The instrument provides a continuous stream of measurements over the entire orbit of the low frequency electric field vector at 32 samples/s in a survey mode. This survey mode also includes measurements of spacecraft potential to provide information on thermal electron plasma variations and structure. Survey mode spectral information allows the continuous evaluation of the peak value and spectral power in electric, magnetic and density fluctuations from several Hz to 6.5 kHz. On-board cross-spectral data allows the calculation of field-aligned wave Poynting flux along the magnetic field. For higher frequency waveform information, two different programmable burst memories are used with nominal sampling rates of 512 samples/s and 16 k samples/s. The EFW burst modes provide targeted measurements over brief time intervals of 3-d electric fields, 3-d wave magnetic fields (from the EMFISIS magnetic search coil sensors), and spacecraft potential. In the burst modes all six sensor-spacecraft potential measurements are telemetered enabling interferometric timing of small-scale plasma structures. In the first burst mode, the instrument stores all or a substantial fraction of the high frequency measurements in a 32 gigabyte burst memory. The sub-intervals to be downloaded are uplinked by ground command after inspection of instrument survey data and other information available on the ground. The second burst mode involves autonomous storing and playback of data controlled by flight software algorithms, which assess the "highest quality" events on the basis of instrument measurements and information from other instruments available on orbit. The EFW instrument provides 3-d wave electric field signals with a frequency response up to 400 kHz to the EMFISIS instrument for analysis and telemetry (Kletzing et al. Space Sci. Rev. 2013).

Wygant, J. R.; Bonnell, J. W.; Goetz, K.; Ergun, R. E.; Mozer, F. S.; Bale, S. D.; Ludlam, M.; Turin, P.; Harvey, P. R.; Hochmann, R.; Harps, K.; Dalton, G.; McCauley, J.; Rachelson, W.; Gordon, D.; Donakowski, B.; Shultz, C.; Smith, C.; Diaz-Aguado, M.; Fischer, J.; Heavner, S.; Berg, P.; Malsapina, D. M.; Bolton, M. K.; Hudson, M.; Strangeway, R. J.; Baker, D. N.; Li, X.; Albert, J.; Foster, J. C.; Chaston, C. C.; Mann, I.; Donovan, E.; Cully, C. M.; Cattell, C. A.; Krasnoselskikh, V.; Kersten, K.; Brenneman, A.; Tao, J. B.

2013-11-01

407

Near field optical probe for critical dimension measurements  

DOEpatents

A resonant planar optical waveguide probe for measuring critical dimensions on an object in the range of 100 nm and below. The optical waveguide includes a central resonant cavity flanked by Bragg reflector layers with input and output means at either end. Light is supplied by a narrow bandwidth laser source. Light resonating in the cavity creates an evanescent electrical field. The object with the structures to be measured is translated past the resonant cavity. The refractive index contrasts presented by the structures perturb the field and cause variations in the intensity of the light in the cavity. The topography of the structures is determined from these variations.

Stallard, Brian R. (Albuquerque, NM); Kaushik, Sumanth (Cambridge, MA)

1999-01-01

408

Near field optical probe for critical dimension measurements  

DOEpatents

A resonant planar optical waveguide probe for measuring critical dimensions on an object in the range of 100 nm and below is disclosed. The optical waveguide includes a central resonant cavity flanked by Bragg reflector layers with input and output means at either end. Light is supplied by a narrow bandwidth laser source. Light resonating in the cavity creates an evanescent electrical field. The object with the structures to be measured is translated past the resonant cavity. The refractive index contrasts presented by the structures perturb the field and cause variations in the intensity of the light in the cavity. The topography of the structures is determined from these variations. 8 figs.

Stallard, B.R.; Kaushik, S.

1999-05-18

409

External-field-free magnetic biosensor  

SciTech Connect

In this paper, we report a magnetic nanoparticle (MNP) detection scheme without the presence of any external magnetic field. The proposed magnetic sensor uses a patterned groove structure within the sensor so that no external magnetic field is needed to magnetize the MNPs. An example is given based on a giant magnetoresistance (GMR) sensing device with a spin valve structure. For this structure, the detection of MNPs located inside the groove and near the free layer is demonstrated under no external magnetic field. Micromagnetic simulations are performed to calculate the signal to noise level of this detection scheme. A maximum signal to noise ratio (SNR) of 18.6?dB from one iron oxide magnetic nanoparticle with 8?nm radius is achieved. As proof of concept, this external-field-free GMR sensor with groove structure of 200?nm?×?200?nm is fabricated using a photo and an electron beam integrated lithography process. Using this sensor, the feasibility demonstration of the detection SNR of 9.3?dB is achieved for 30??l magnetic nanoparticles suspension (30?nm iron oxide particles, 1?mg/ml). This proposed external-field-free sensor structure is not limited to GMR devices and could be applicable to other magnetic biosensing devices.

Li, Yuanpeng; Wang, Yi; Klein, Todd; Wang, Jian-Ping, E-mail: jpwang@umn.edu [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

2014-03-24

410

External-field-free magnetic biosensor  

NASA Astrophysics Data System (ADS)

In this paper, we report a magnetic nanoparticle (MNP) detection scheme without the presence of any external magnetic field. The proposed magnetic sensor uses a patterned groove structure within the sensor so that no external magnetic field is needed to magnetize the MNPs. An example is given based on a giant magnetoresistance (GMR) sensing device with a spin valve structure. For this structure, the detection of MNPs located inside the groove and near the free layer is demonstrated under no external magnetic field. Micromagnetic simulations are performed to calculate the signal to noise level of this detection scheme. A maximum signal to noise ratio (SNR) of 18.6 dB from one iron oxide magnetic nanoparticle with 8 nm radius is achieved. As proof of concept, this external-field-free GMR sensor with groove structure of 200 nm × 200 nm is fabricated using a photo and an electron beam integrated lithography process. Using this sensor, the feasibility demonstration of the detection SNR of 9.3 dB is achieved for 30 ?l magnetic nanoparticles suspension (30 nm iron oxide particles, 1 mg/ml). This proposed external-field-free sensor structure is not limited to GMR devices and could be applicable to other magnetic biosensing devices.

Li, Yuanpeng; Wang, Yi; Klein, Todd; Wang, Jian-Ping

2014-03-01

411

Compact low field magnetic resonance imaging magnet: Design and optimization  

NASA Astrophysics Data System (ADS)

Magnetic resonance imaging (MRI) is performed with a very large instrument that allows the patient to be inserted into a region of uniform magnetic field. The field is generated either by an electromagnet (resistive or superconductive) or by a permanent magnet. Electromagnets are designed as air cored solenoids of cylindrical symmetry, with an inner bore of 80-100 cm in diameter. In clinical analysis of peripheral regions of the body (legs, arms, foot, knee, etc.) it would be better to adopt much less expensive magnets leaving the most expensive instruments to applications that require the insertion of the patient in the magnet (head, thorax, abdomen, etc.). These "dedicated" apparati could be smaller and based on resistive magnets that are manufactured and operated at very low cost, particularly if they utilize an iron yoke to reduce power requirements. In order to obtain good field uniformity without the use of a set of shimming coils, we propose both particular construction of a dedicated magnet, using four independently controlled pairs of coils, and an optimization-based strategy for computing, a posteriori, the optimal current values. The optimization phase could be viewed as a low-cost shimming procedure for obtaining the desired magnetic field configuration. Some experimental measurements, confirming the effectiveness of the proposed approach (construction and optimization), have also been reported. In particular, it has been shown that the adoption of the proposed optimization based strategy has allowed the achievement of good uniformity of the magnetic field in about one fourth of the magnet length and about one half of its bore. On the basis of the good experimental results, the dedicated magnet can be used for MRI of peripheral regions of the body and for animal experimentation at very low cost.

Sciandrone, M.; Placidi, G.; Testa, L.; Sotgiu, A.

2000-03-01

412

Magnetic field corrections to solar oscillation frequencies  

NASA Technical Reports Server (NTRS)

It is argued that the frequencies of both the solar p- and g-modes of oscillation are modified by a magnetic field. In particular, the decrease in p-mode frequencies is attributed to a magnetic field within the solar interior evolving over the solar cycle. Field strengths at the base of the convection zone of at least 500,000 G are required.

Roberts, B.; Campbell, W. R.

1986-01-01

413

Vector Magnetic Field in Emerging Flux Regions  

NASA Astrophysics Data System (ADS)

A crucial phase in magnetic flux emergence is the rise of magnetic flux tubes through the solar photosphere, which represents a severe transition between the very different environments of the solar interior and corona. Multi-wavelength observations with Flare Genesis, TRACE, SoHO, and more recently with the vector magnetographs at THEMIS and Hida (DST) led to the following conclusions. The fragmented magnetic field in the emergence region - with dipped field lines or bald patches - is directly related with Ellerman bombs, arch filament systems, and overlying coronal loops. Measurements of vector magnetic fields have given evidence that undulating "serpentine" fields are present while magnetic flux tubes cross the photosphere. See the sketch below, and for more detail see Pariat et al. (2004, 2007); Watanabe et al. (2008):

Schmieder, B.; Pariat, E.

414

Advanced magnetic calculations for high magnetic field compact ion source  

NASA Astrophysics Data System (ADS)

The design of the advanced electronic cyclotronic resonance ion source (ECRIS) requires relatively high axial and radial magnetic inductions to allow the ECR frequency increase and to take advantage of the subsequent density increase (scaling laws). The last improvements of the commercial rare-earth magnet characteristics open new opportunities for ECRIS and enable the design of very high hexapolar magnetic fields for next generation compact ECRIS. Moreover, the high temperature superconducting (HTS) wires allow designing reliable and compact axial field coils (30 K cooled) at a very effective cost. It is thus very relevant to study a compact hybrid ECRIS using high remanence magnet and HTS technologies. In such a design, the volume of the plasma chamber is a free parameter that can be adjusted to the user requirement. It can be dedicated to very high ionic current production or high charge state production, pulsed, or cw operations. This paper presents the three-dimensional overall simulation of a 3 T axial magnetic field compact ECRIS with a high radial field sextupole composed with several magnet types and reaching ˜1.9 T in front of the radially magnetized magnets. This design study will lead to the building of the 28-40 GHz A-PHOENIX source at the laboratory which will deliver its first beam by the end of 2004.

Thuillier, T.; Curdy, J.-C.; Lamy, T.; Sole, P.; Sortais, P.; Vieux-Rochaz, J.-L.; Voulot, D.

2004-05-01

415

Magnetic reconnection at the edge of Uranus's magnetic field  

NASA Astrophysics Data System (ADS)

A new modeling study sheds light on how the magnetosphere of Uranus compares to those of other planets. Magnetospheres around the inner planets Mercury and Earth are primarily driven by the solar wind—the charged particles spewed out from the Sun—through magnetic reconnection, in which the planet's magnetic field lines break and reconnect, releasing energy in the process.

Balcerak, Ernie

2014-09-01

416

Anisotropy of magnetic susceptibility measured in variable weak magnetic fields  

NASA Astrophysics Data System (ADS)

Theory of the low-field anisotropy of magnetic susceptibility (AMS) of rocks is based on the assumption of the linear relationship between magnetization and magnetizing field, resulting in field independent susceptibility. This relationship is by definition valid in diamagnetic and paramagnetic minerals, while in ferrimagnetic and antiferromagnetic minerals this relationship is in general non-linear (represented by hysteresis loop), being linear only in very weak fields in which the initial susceptibility is measured. Among these minerals, magnetite shows no field variation of susceptibility and its anisotropy in the low fields used in common AMS meters. In pyrrhotite, hematite and titanomagnetite bearing rocks, in which these minerals are very fine-grained, the field variation of susceptibility is insignificant. Using linear theory in calculating the AMS is fully legitimate in all these cases. In pyrrhotite, hematite, and titanomagnetite bearing rocks, in which these minerals are relatively coarse-grained (typically hundreds of micrometers), clear field variation of magnetic susceptibility may exist even in the low fields used in common AMS meters, often resulting in bad fit of the susceptibility tensor to the measured data. Strictly speaking, linear theory in calculating the AMS is in general incorrect in this case. The KLY-3S Kappabridge has been modified in such a way to enable AMS measurement also in the fields down to 3 A/m. Examples are shown of the effect of this field decrease on the measured data.

Pokorny, J.; Suza, P.; Hrouda, F.

2003-04-01

417

Atom probe field ion microscopy and related topics: A bibliography 1991  

SciTech Connect

This report contains a bibliography for 1991 on the following topics: Atom probe field ion microscopy; field desorption mass spectrometry; field emission; field ion microscopy; and field emission theory.

Russell, K.F.; Miller, M.K.

1993-01-01

418

Particle Transport in Therapeutic Magnetic Fields  

NASA Astrophysics Data System (ADS)

Iron oxide magnetic nanoparticles, in ferrofluids or as magnetic microspheres, offer magnetic maneuverability, biochemical surface functionalization, and magnetic relaxation under the influence of an alternating field. The use of these properties for clinical applications requires an understanding of particles, forces, and scalar transport at various length scales. This review explains the behavior of magnetic nano- and microparticles during magnetic drug targeting and magnetic fluid hyperthermia, and the microfluidic transport of these particles in bioMEMS (biomedical microelectromechanical systems) devices for ex vivo therapeutic and diagnostic applications. Magnetic particle transport, the momentum interaction of these particles with a host fluid in a flow, and thermal transport in a particle-infused tissue are characterized through the governing electrodynamic, hydrodynamic, and scalar transport equations.

Puri, Ishwar K.; Ganguly, Ranjan

2014-01-01

419

The Measurement of Magnetic Fields  

ERIC Educational Resources Information Center

Discusses five experimental methods used by senior high school students to provide an accurate calibration curve of magnet current against the magnetic flux density produced by an electromagnet. Compares the relative merits of the five methods, both as measurements and from an educational viewpoint. (JR)

Berridge, H. J. J.

1973-01-01

420

Faraday's Magnetic Field Induction Experiment  

NSDL National Science Digital Library

This java simulation illustrates magnetic induction in a wire coil. The user can move a magnet in and out along the axis of a coil while a galvanometer shows the current induced in the coil. The deflection depends on the speed at which the coil moves.

Davidson, Michael

2010-12-29

421

Generation of high magnetic fields using superconducting magnets  

Microsoft Academic Search

High-field superconducting magnets have opened new frontiers for several kinds of applications, such as fusion reactors, particle accelerators, and nuclear magnetic resonance (NMR) spectrometers. The present record for the highest field in a fully superconducting state is 23.4T. It was achieved with a combination of NbTi, Nb3Sn, and Bi-2212 conductors in 1999. Since high Tc (critical temperature) superconductors (HTS) have

T. Kiyoshi; A. Otsuka; M. Kosuge; M. Yuyama; H. Nagai; F. Matsumoto

2006-01-01

422

Magnetic Field Measurement with Ground State Alignment  

NASA Astrophysics Data System (ADS)

Observational studies of magnetic fields are crucial. We introduce a process "ground state alignment" as a new way to determine the magnetic field direction in diffuse medium. The alignment is due to anisotropic radiation impinging on the atom/ion. The consequence of the process is the polarization of spectral lines resulting from scattering and absorption from aligned atomic/ionic species with fine or hyperfine structure. The magnetic field induces precession and realign the atom/ion and therefore the polarization of the emitted or absorbed radiation reflects the direction of the magnetic field. The atoms get aligned at their low levels and, as the life-time of the atoms/ions we deal with is long, the alignment induced by anisotropic radiation is susceptible to extremely weak magnetic fields (1 G ? B ? 10^{-15} G). In fact, the effects of atomic/ionic alignment were studied in the laboratory decades ago, mostly in relation to the maser research. Recently, the atomic effect has been already detected in observations from circumstellar medium and this is a harbinger of future extensive magnetic field studies. A unique feature of the atomic realignment is that they can reveal the 3D orientation of magnetic field. In this chapter, we shall review the basic physical processes involved in atomic realignment. We shall also discuss its applications to interplanetary, circumstellar and interstellar magnetic fields. In addition, our research reveals that the polarization of the radiation arising from the transitions between fine and hyperfine states of the ground level can provide a unique diagnostics of magnetic fields in the Epoch of Reionization.

Yan, Huirong; Lazarian, A.

423

Magnetic Fields from Heterotic Cosmic Strings  

E-print Network

Large-scale magnetic fields are observed today to be coherent on galactic scales. While there exists an explanation for their amplification and their specific configuration in spiral galaxies -- the dynamo mechanism -- a satisfying explanation for the original seed fields required is still lacking. Cosmic strings are compelling candidates because of their scaling properties, which would guarantee the coherence on cosmological scales of any resultant magnetic fields at the time of galaxy formation. We present a mechanism for the production of primordial seed magnetic fields from heterotic cosmic strings arising from M theory. More specifically, we make use of heterotic cosmic strings stemming from M5--branes wrapped around four of the compact internal dimensions. These objects are stable on cosmological time scales and carry charged zero modes. Therefore a scaling solution of such defects will generate seed magnetic fields which are coherent on galactic scales today.

Gwyn, Rhiannon; Brandenberger, Robert H; Dasgupta, Keshav

2008-01-01

424

Magnetic fields from heterotic cosmic strings  

SciTech Connect

Large-scale magnetic fields are observed today to be coherent on galactic scales. While there exists an explanation for their amplification and their specific configuration in spiral galaxies--the dynamo mechanism--a satisfying explanation for the original seed fields required is still lacking. Cosmic strings are compelling candidates because of their scaling properties, which would guarantee the coherence on cosmological scales of any resultant magnetic fields at the time of galaxy formation. We present a mechanism for the production of primordial seed magnetic fields from heterotic cosmic strings arising from M theory. More specifically, we make use of heterotic cosmic strings stemming from M5-branes wrapped around four of the compact internal dimensions. These objects are stable on cosmological time scales and carry charged zero modes. Therefore a scaling solution of such defects will generate seed magnetic fields which are coherent on galactic scales today.

Gwyn, Rhiannon; Alexander, Stephon H.; Brandenberger, Robert H.; Dasgupta, Keshav [Department of Physics, McGill University, Montreal, Quebec, H3A 2T8 (Canada); Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802-6300 (United States); Department of Physics and Astronomy, Koshland Center for Integrated Sciences, Haverford College, Haverford, Pennsylvania 19041 (United States); Department of Physics, McGill University, Montreal, Quebec, H3A 2T8 (Canada)

2009-04-15

425

The magnetic field of Mercury, part 1  

NASA Technical Reports Server (NTRS)

An updated analysis and interpretation is presented of the magnetic field observations obtained during the Mariner 10 encounter with the planet Mercury. The combination of data relating to position of the detached bow shock wave and magnetopause, and the geometry and magnitude of the magnetic field within the magnetosphere-like region surrounding Mercury, lead to the conclusion that an internal planetary field exists with dipole moment approximately 5.1 x 10 the 22nd power Gauss sq cm. The dipole axis has a polarity sense similar to earth's and is tilted 7 deg from the normal to Mercury's orbital plane. The magnetic field observations reveal a significant distortion of the modest Hermean field (350 Gamma at the equator) by the solar wind flow and the formation of a magnetic tail and neutral sheet which begins close to the planet on the night side. The composite data is not consistent with a complex induction process driven by the solar wind flow.

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

1974-01-01

426

Magnetic field induced optical vortex beam rotation  

E-print Network

Light with orbital angular momentum (OAM) has drawn a great deal of attention for its important applications in the fields of precise optical measurements and high capacity optical communications. Here we adopt a method to study the rotation of a light beam, which is based on magnetic field induced circular birefringence in warm 87Rb atomic vapor. The dependence of the rotation angle to the intensity of the magnetic field makes it appropriate for weak magnetic field measurement. We derive a detail theoretical description that is in well agreement with the experimental observations. The experiment shows here provides a new method for precise measurement of magnetic field intensity and expands the application of OAM-carrying light.

Shi, Shuai; Zhou, Zhi-Yuan; Li, Yan; Zhang, Wei; Shi, Bao-Sen

2015-01-01

427