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1

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.

2

An Extraordinary Magnetic Field Map of Mars  

NASA Technical Reports Server (NTRS)

The Mars Global Surveyor spacecraft has completed two Mars years in nearly circular polar orbit at a nominal altitude of 400 km. The Mars crust is at least an order of magnitude more intensely magnetized than that of the Earth [1], and intriguing in both its global distribution and geometric properties [2,3]. Measurements of the vector magnetic field have been used to map the magnetic field of crustal origin to high accuracy [4]. We present here a new map of the magnetic field with an order of magnitude increased sensitivity to crustal magnetization. The map is assembled from > 2 full years of MGS night-side observations, and uses along-track filtering to greatly reduce noise due to external field variations.

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

2004-01-01

3

Orbital mapping of the lunar magnetic field.  

NASA Technical Reports Server (NTRS)

Examination of the lunar magnetic field as deduced from the orbital magnetometer data, with major emphasis on the general mapping of the lunar field over the orbit track of the Apollo 15 subsatellite. A detailed analysis of the data from a series of overflights of the Van de Graaff region at two different altitudes is also presented. This latter set of data makes it possible to determine the scale size of the region and the contrast between the remanent magnetization associated with the magnetic feature and its surroundings. The low altitude data from the Apollo 16 subsatellite, just prior to its impact into the lunar surface, are then examined. Data obtained while the moon was in the solar wind are used to construct a map which shows the lunar limb regions associated with the detection of limb compressions. This map is used to make qualitative inferences concerning the lunar remanent field in regions not covered by the contour maps.

Sharp, L. R.; Coleman, P. J., Jr.; Lichtenstein, B. R.; Russell, C. T.; Schubert, G.

1973-01-01

4

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

5

Mapping the magnetic field vector in a fountain clock  

NASA Astrophysics Data System (ADS)

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

2011-12-01

6

Starspots Magnetic field by transit mapping  

NASA Astrophysics Data System (ADS)

Sunspots are important signatures of the global solar magnetic field cycle. It is believed that other stars also present these same phenomena. However, today it is not possible to observe directly star spots due to their very small sizes. The method applied here studies star spots by detecting small variations in the stellar light curve during a planetary transit. When the planet passes in front of its host star, there is a chance of it occulting, at least partially, a spot. This allows the determination of the spots physical characteristics, such as size, temperature, and location on the stellar surface. In the case of the Sun, there exists a relation between the magnetic field and the spot temperature. We estimate the magnetic field component along the line-of-sight and the intensity of sunspots using data from the MDI instrument on board of the SOHO satellite. Assuming that the same relation applies to other stars, we estimate spots magnetic fields of CoRoT-2 and Kepler-17 stars.

Válio, Adriana; Spagiari, Eduardo

2014-08-01

7

Robotic mapping assisted by local magnetic field anomalies  

Microsoft Academic Search

This paper presents a method to incorporate measurement of local magnetic field anomalies into the SLAM (Simultaneous Localization And Mapping) algorithm. One of the key problems of SLAM is loop closure, which means to map the same place into the same location on the generated map when the place is revisited by the robot. It is particularly important for large

Haiyang Zhang; Fred Martin

2011-01-01

8

Mapping magnetic near-field distributions of plasmonic nanoantennas.  

PubMed

We present direct experimental mapping of the lateral magnetic near-field distribution in plasmonic nanoantennas using aperture scanning near-field optical microscopy (SNOM). By means of full-field simulations it is demonstrated how the coupling of the hollow-pyramid aperture probe to the nanoantenna induces an effective magnetic dipole which efficiently excites surface plasmon resonances only at lateral magnetic field maxima. This excitation in turn affects the detected light intensity enabling the visualization of the lateral magnetic near-field distribution of multiple odd and even order plasmon modes with subwavelength spatial resolution. PMID:23464670

Denkova, Denitza; Verellen, Niels; Silhanek, Alejandro V; Valev, Ventsislav K; Van Dorpe, Pol; Moshchalkov, Victor V

2013-04-23

9

Vacuum Magnetic Field Mapping of the Compact Toroidal Hybrid (CTH)  

NASA Astrophysics Data System (ADS)

Vacuum magnetic field mapping experiments are performed on the CTH torsatron with a movable electron gun and phosphor-coated screen or movable wand at two different toroidal locations. These experiments compare the experimentally measured magnetic configuration produced by the as-built coil set, to the magnetic configuration simulated with the IFT Biot-Savart code using the measured coil set parameters. Efforts to minimize differences between the experimentally measured location of the magnetic axis and its predicted value utilizing a Singular Value Decomposition (SVD) process result in small modifications of the helical coil winding law used to model the vacuum magnetic field geometry of CTH. Because these studies are performed at relatively low fields B = 0.01 - 0.05 T, a uniform ambient magnetic field is included in the minimization procedure.

Peterson, J. T.; Hanson, J.; Hartwell, G. J.; Knowlton, S. F.; Montgomery, C.; Munoz, J.

2007-11-01

10

Large-scale solar magnetic field mapping: I.  

PubMed

This article focuses on mapping the Sun's large-scale magnetic fields. In particular, the model considers how photospheric fields evolve in time. Our solar field mapping method uses Netlogo's cellular automata software via algorithms to carry out the movement of magnetic field on the Sun via agents. This model's entities consist of two breeds: blue and red agents. The former carry a fixed amount of radially outward magnetic flux: 10(23) Mx, and the latter, the identical amount of inward directed flux. The individual agents are distinguished, for clarity, by various shades of blue and red arrows whose orientation indicates the direction the agents are moving, relative to the near-steady bulk fluid motions. The fluid motions generally advect the field with the well known meridional circulation and differential rotation. Our model predominantly focuses on spatial and temporal variations from the bulk fluid motions owing to magnetic interactions. There are but a few effects that agents have on each other: i) while at the poles, field agents are connected via the Babcock - Leighton (B - L) subsurface field to other latitudes. This allows them to undertake two duties there: A) the B - L subsurface field spawns the next generation of new magnetic field via new agents, and B) the B - L subsurface field attracts lower-latitude fields via the "long-range" magnetic stress tension; ii) nearby agents affect each other's motion by short-range interactions; and iii) through annihilation: when opposite field agents get too close to each other, they disappear in pairs. The behavior of the agents' long- and short-range magnetic forces is discussed within this paper as well as the model's use of internal boundary conditions. The workings of the model may be seen in the accompanying movies and/or by using the software available via SpringerPlus' website, or on the Netlogo (TM) community website, where help is readable available, and should all these fail, some help from the author. PMID:23518616

Schatten, Kenneth H

2013-12-01

11

Computation of flow pressure fields from magnetic resonance velocity mapping.  

PubMed

Magnetic resonance phase velocity mapping has unrivalled capacities for acquiring in vivo multi-directional blood flow information. In this study, the authors set out to derive both spatial and temporal components of acceleration, and hence differences of pressure in a flow field using cine magnetic resonance velocity data. An efficient numerical algorithm based on the Navier-Stokes equations for incompressible Newtonian fluid was used. The computational approach was validated with in vitro flow phantoms. This work aims to contribute to a better understanding of cardiovascular dynamics and to serve as a basis for investigating pulsatile pressure/flow relationships associated with normal and impaired cardiovascular function. PMID:8892202

Yang, G Z; Kilner, P J; Wood, N B; Underwood, S R; Firmin, D N

1996-10-01

12

New frontiers in magnetic field interpretation and modeling: Examples from the World Digital Magnetic Anomaly Map  

NASA Astrophysics Data System (ADS)

The World Digital Magnetic Anomaly Map is a joint effort on the part of the marine, airborne, and satellite magnetic communities to stitch together a unified map of the earth's lithospheric magnetic field. Several preliminary versions of this map will be exhibited during AGU, and this presentation will highlight interpretations of data that have gone into making this map. Examples to be discussed include 1) the Chicxulub impact structure, 2) geodynamical interpretations of dike swarms, 3) structural and tectonic interpretations of aeromagnetic maps over forearc basins with Cenozoic to Recent faulting, 4) heat flux beneath the Antarctic ice sheet, 5) the role of magnetic interpretations in identifying diamond-bearing kimberlites, and 6) structural inferences drawn from magnetic surveys over the West Siberian basin, and the Urengoy gas field.

Purucker, M.

2006-12-01

13

The spectra spectroheliograph system, section 1. [production of magnetic field maps direct from solar spectra  

NASA Technical Reports Server (NTRS)

A system capable of producing maps of the magnetic field straight from spectra was created. The theory of the extraction of magnetic field information by Fourier transform techniques is discussed. Contour maps of a high gradient magnetic field region are presented.

Title, A. M.

1974-01-01

14

Faraday rotation, stochastic magnetic fields, and CMB maps  

SciTech Connect

The high- and low-frequency descriptions of the predecoupling plasma are deduced from the Vlasov-Landau treatment generalized to curved space-times and in the presence of the relativistic fluctuations of the geometry. It is demonstrated that the interplay between one-fluid and two-fluid treatments is mandatory for a complete and reliable calculation of the polarization observables. The Einstein-Boltzmann hierarchy is generalized to handle the dispersive propagation of the electromagnetic disturbances in the predecoupling plasma. Given the improved physical and numerical framework, the polarization observables are computed within the magnetized {lambda}CDM paradigm (m{lambda}CDM). In particular, the Faraday-induced B-mode is consistently estimated by taking into account the effects of the magnetic fields on the initial conditions of the Boltzmann hierarchy, on the dynamical equations, and on the dispersion relations. The complete calculations of the angular power spectra constitute the first step for the derivation of magnetized maps of the CMB temperature and polarization which are here obtained for the first time and within the minimal m{lambda}CDM model. The obtained results set the ground for direct experimental scrutiny of large-scale magnetism via the low- and high-frequency instruments of the Planck explorer satellite.

Giovannini, Massimo [Section of Milan-Bicocca, INFN, 20126 Milan (Italy); Department of Physics, Theory Division, CERN, 1211 Geneva 23 (Switzerland); Kunze, Kerstin E. [Departamento de Fisica Fundamental, Universidad de Salamanca, Plaza de la Merced s/n, E-37008 Salamanca (Spain)

2008-07-15

15

Magnetic field of Mars: Summary of results from the aerobraking and mapping orbits  

Microsoft Academic Search

The Mars Global Surveyor (MGS) Magnetic Field Investigation was designed to provide fast vector measurements of the ambient magnetic field in the near-Mars environment and over a wide dynamic range. The fundamental objectives of this investigation were to (1) establish the nature of the magnetic field of Mars; (2) develop appropriate models for its representation; and (3) map the Martian

J. E. P. Connerney; P. Wasilewski; R. P. Lin; D. Mitchell; K. A. Anderson; C. W. Carlson; J. McFadden; H. Rème; C. Mazelle; D. Vignes; S. J. Bauer; P. Cloutier; N. F. Ness

2001-01-01

16

Mapping Weak Crustal Magnetic Fields on Mars with Electron Reflectometry  

NASA Technical Reports Server (NTRS)

One of the great surprises of the Mars Global Surveyor (MGS) mission was the discovery of intensely magnetized crust. These magnetic sources are at least ten times stronger than their terrestrial counterparts, probably requiring large volumes of coherently magnetized material, very strong remanence, or both. Perhaps the most intriguing aspect of these fields is their large scale coherence and organization into east-west stripes thousands of kilometers long. The anomalies were almost certainly created by thermoremanent magnetization (TRM) in the presence of a strong Martian dynamo. With few exceptions, the crustal fields are associated with the oldest terrain on Mars. Much of the northern lowlands appears to be non-magnetic, except for the relatively weak north polar anomalies and a few sources adja-cent to the dichotomy boundary, which appear to be associated with strongly magnetized crust south of the boundary. There is clear evidence for impact demagnetization of the Hellas, Argyre, and Isidis basins. Thus, Mars' crustal magnetic fields are among the oldest preserved geologic features on the planet.

Mitchell, D. L.; Lillis, R.; Lin, R. P.; Connerney, J. E. P.; Acuna, M. H.

2004-01-01

17

Mapping Gravitational and Magnetic Fields with Children 9-11: Relevance, Difficulties and Prospects  

ERIC Educational Resources Information Center

This paper presents an investigation centered on a guided conceptual path concerning magnetic and gravitational fields, proposed for children aged 9-11. The goal is to appreciate to what extent the idea of "mapping" two fields of interaction is accessible and fruitful for children of that age. The conceptual target is to link magnetic and…

Bradamante, F.; Viennot, L.

2007-01-01

18

BTA Magnet Field Map Archive and MAD Model  

SciTech Connect

This note publishes some and information that has resided in private files. The attached tables were provided by Joseph Skelly from his archives. They show magnetic field measurements versus excitation current for the Booster to AGS transfer line quadrupoles and dipoles based on field measurements [we believe] were done by the Magnet Division. Also given are Ed Blesser's fifth order fits of field versus current. The results are given in 'Tesla' or T-M/M. These tables are attached to provide an archive of this data. The MAD model of the BTA line does have the same values as shown in the attached fits so the transfer was correct. MAD uses as its 'gradient' for quads Tesla per meter normalized to rigidity [B-rho]. The model of the BTA line in use uses the T-M/M given in the tables divided by the length to give T M which is then normalized by Brho. Thus, the input to the model appears to be correct. The original model is also attached as part of a memo by Skelly describing it.

Glenn,J.W.

2008-04-01

19

Global Mapping of Near-Earth Magnetic Fields Measured by KITSAT-1 and KITSAT-2  

Microsoft Academic Search

The magnetic field measurements from the KitSat-1 and KitSat-2 were tested by comparing with the IGRF model. The magnetic data have been collected by a three-axis fluxgate magnetometer on each satellite at an altitude of 1,325km and 820km, respectively. To avoid highly variable magnetic disturbances at the polar region, the field map has been drawn within the limits of 50

Yoo-Surn Pyo; Dong-Hun Lee; Kyoung-Wook Min

1994-01-01

20

Statistical maps of geomagnetic perturbations as a function of the interplanetary magnetic field  

Microsoft Academic Search

Mappings of geomagnetic perturbations are shown for different combinations of the solar wind velocity, interplanetary magnetic field (IMF), and dipole tilt angle (season). Average maps were derived separately for the northward, eastward, and vertical (downward) components of the geomagnetic disturbances, using spherical cap harmonics in least error fits of sorted measurements. The source data are obtained from 104 ground-based magnetometer

D. R. Weimer; C. R. Clauer; M. J. Engebretson; T. L. Hansen; H. Gleisner; I. Mann; K. Yumoto

2010-01-01

21

Obtaining vector magnetic field maps from single-component measurements of geological samples  

NASA Astrophysics Data System (ADS)

Maxwell's equations can be used to demonstrate that the components of a static magnetic field in a region of space devoid of sources are not independent. This means that magnetometers that measure a single component of the magnetic field can potentially obtain all of three components of the field external to a source. Here we present an improved technique in the Fourier domain which can obtain the complete vector field planar map from just the planar map of one component. This technique is fast, robust, does not rely on any specific source type or configuration, and does not require the formulation of an inverse problem. An in-depth analysis of the advantages and shortcomings of the technique is presented, demonstrating that high-quality three-component field maps with virtually no information loss can be obtained when proper sensor and mapping configurations are used. Several results derived from both synthetic and experimental data are presented. In particular, practical cases are shown where vector maps can assist the analysis of magnetic properties of geological samples. MATLAB® routines implementing the basic vector map calculation algorithm are available as auxiliary materials and can be readily adapted for processing magnetic data obtained from a variety of magnetic sensors.

Lima, Eduardo A.; Weiss, Benjamin P.

2009-06-01

22

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

23

Nanoscale magnetic field mapping with a single spin scanning probe magnetometer  

NASA Astrophysics Data System (ADS)

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.; Dal Savio, C.; Karrai, K.; Dantelle, G.; Thiaville, A.; Rohart, S.; Roch, J.-F.; Jacques, V.

2012-04-01

24

Surface magnetic field mapping on high albedo marking areas of the moon  

NASA Astrophysics Data System (ADS)

The correlation between high albedo markings (HAM) on the surface of the moon and strong magnetic anomalies has been claimed since the early time of the lunar magnetic field study (Hood and Schubert, 1980). Hood et al. (1989) mapped the smoothed magnetic field over the Reiner Gamma region using Lunar Prospector magnetometer (LP-MAG) data, and showed that the position of them matches well. We have developed a method to recover the 3-d magnetic field from satellite field observations (EPR method which stands for Equivalent Pole Reduction; Toyoshima et al. 2008). Applying EPR to the several areas of strong magnetic anomalies, we calculated the magnetic anomaly maps of near surface regions, to see how the anomaly and the HAM correlate each other. The data used is of the Lunar Prospector magnetometer (LP-MAG). They are selected from low altitude observations performed in 1998 to 1999. The areas studied are Reiner Gamma, Airy, Descartes, Abel, and Crisium Antipode regions. The EPR determines a set of magnetic monopoles at the moon surface which produce the magnetic field of the observation. In each studied area, we put poles in 0.1° intervals of both latitude and longitude, then the magnetic field at 5km in altitude is calculated. The field distribution is superimposed with the albedo map made from Clementine data. The total force (Bf) maps indicate that the HMA occurs at the strong anomaly regions, but their shape does not quite overlie. However, taking horizontal component (Bh), not only position but the shape and size of the anomalies coincide with HMA regions. It is particularly true for the Reiner Gamma, and Descartes regions. The shape of HMA fits in a Bh contour. The HMA is argued to be formed by the reduction of solar wind particles which are shielded by the magnetic field. Since the deflection of the charged particle becomes large at large horizontal component, the Bh distribution showed here support the argument.

Shibuya, H.; Aikawa, K.; Tsunakawa, H.; Takahashi, F.; Shimizu, H.; Matsushima, M.

2009-12-01

25

Lorentz Mapping of Magnetic Fields in Hot Dense Plasmas  

E-print Network

Unique detection of electromagnetic fields and identification of field type and strength as a function of position were used to determine the nature of self-generated fields in a novel experiment with laser-generated plasma ...

Amendt, P. A.

26

High-Sensitivity Mapping of Crustal Magnetic Fields on Mars withElectron Reflectometry  

NASA Astrophysics Data System (ADS)

The Electron Reflectometer (ER) aboard Mars Global Surveyor (MGS) samples the local electron population's distribution in energy and pitch angle (the angle between an electron's instantaneous velocity and local magnetic field direction) at the mapping orbit altitude of ~400km. We have developed a single-particle model of an electron's interaction with the neutral atmosphere as it gyrates around open field lines connecting the solar wind to remnant crustal magnetic fields. Electrons that penetrate to lower altitudes before magnetically reflecting are more likely to be absorbed by the neutral atmosphere. By fitting measured electron pitch angle distributions with this model, we can determine the strength of the magnetic field at ~200km, which represents an eight-fold increase in sensitivity to isolated magnetic sources compared with Magnetometer measurements at 400 km. We have mapped selected regions using this technique and are working towards a global electron reflection map. Our electron reflection results show good agreement with Magnetometer measurements where the field is strong enough to be mapped with both techniques. Over the regions where low-altitude Magnetometer data (collected during aerobraking) are sparse or missing, the ER can be used to search for crustal magnetic sources that are too weak to be detected by the Magnetometer at 400 km. Initial results reveal weak and isolated crustal magnetic sources within the Hellas Basin. These sources are far too weak to account for a horizontal field over the basin with a strength of several nanotesla, which has been inferred from ionospheric perturbations observed by the ER using a separate technique (Lee et al., this conference). This horizontal field is thus likely to originate from magnetic sources around the basin perimeter.

Lillis, R. J.; Mitchell, D. L.; Lee, C. O.; Lin, R. P.; Reme, H.; Cloutier, P. A.; Acuna, M. H.

2003-04-01

27

Simultaneous mapping of chemical abundances and magnetic field structure in Ap stars  

NASA Astrophysics Data System (ADS)

Magnetic A stars represent about 5 highly ordered, very stable and often very strong magnetic fields. They frequently show variations in both brightness and spectral line profiles that are synchronised to stellar rotation. Those variations are believed to be produced by atomic diffusion operating in the stellar atmospheres which have become stabilized by multi-kG magnetic fields. In recent years, with the development and application of the Doppler and magnetic-Doppler imaging techniques and the availability of high-precision spectroscopic and spectropolarimetric data, it has became possible to map the chemical abundances and magnetic field structures of Ap stars simultaneously and in increasing detail, based on full Stokes vector observations. I review the state-of-the-art understanding pf Ap star spots and their relation to magnetic fields, the development of Doppler and magnetic-Doppler imaging into one of the most powerful remote sensing methods for astrophysics, and the physics of Ap stars atmospheres that we can deduce from simultaneous mapping of magnetic field structure and chemical abundances.

Lueftinger, T.

2014-11-01

28

The symmetric quartic map for trajectories of magnetic field lines in elongated divertor tokamak plasmas  

Microsoft Academic Search

The coordinates of the area-preserving map equations for integration of magnetic field line trajectories in divertor tokamaks can be any coordinates for which a transformation to (psit,theta,phi) coordinates exists [A. Punjabi, H. Ali, T. Evans, and A. Boozer, Phys. Lett. A 364, 140 (2007)]. psit is toroidal magnetic flux, theta is poloidal angle, and phi is toroidal angle. This freedom

Morgin Jones; Hasina Wadi; Halima Ali; Alkesh Punjabi

2009-01-01

29

Magnetic field map around a wall with a complete lightning protection system  

Microsoft Academic Search

This paper presents a lumped element model suitable for the evaluation of the electromagnetic interference generated by a lightning protection system during a transient. The protection system considered, consisting of several downlead and potential equalization conductors, is complete. The proposed model accounts for possible ionization effects caused by high lightning currents. A map of the magnetic field near the wall

G. Casinovi; A. Geri; G. M. Veca

1989-01-01

30

Results of SPARO 2003: Mapping Magnetic Fields in Giant Molecular Clouds  

NASA Astrophysics Data System (ADS)

We present results from the Austral Winter 2003 observing campaign of SPARO, a 450 ?m polarimeter used with a 2 m telescope at the South Pole. We mapped large-scale magnetic fields in four GMCs in the Galactic disk: NGC 6334, the Carina Nebula, G333.6-0.2, and G331.5-0.1. We find a statistically significant correlation of the inferred field directions with the orientation of the Galactic plane. Specifically, three of the four GMCs (NGC 6334 is the exception) have mean field directions that are within 15° of the plane. The simplest interpretation is that the field direction tends to be preserved during the process of GMC formation. We have also carried out an analysis of published optical polarimetry data. For the closest of the SPARO GMCs, NGC 6334, we can compare the field direction in the cloud as measured by SPARO with the field direction in a larger region surrounding the cloud, as determined from optical polarimetry. For purposes of comparison, we also use optical polarimetry to determine field directions for 9-10 other regions of similar size. We find that the region surrounding NGC 6334 is an outlier in the distribution of field directions determined from optical polarimetry, just as the NGC 6334 cloud is an outlier in the distribution of cloud field directions determined by SPARO. In both cases the field direction corresponding to NGC 6334 is rotated away from the direction of the plane by a large angle. This finding is consistent with our suggestion that field direction tends to be preserved during GMC formation. Finally, by comparing the disorder in our magnetic field maps with the disorder seen in magnetic field maps derived from MHD turbulence simulations, we conclude that the magnetic energy density in our clouds is comparable to the turbulent energy density.

Li, H.; Griffin, G. S.; Krejny, M.; Novak, G.; Loewenstein, R. F.; Newcomb, M. G.; Calisse, P. G.; Chuss, D. T.

2006-09-01

31

Detection of Magnetic Field Intensity Gradient by Homing Pigeons (Columba livia) in a Novel "Virtual Magnetic Map" Conditioning Paradigm  

PubMed Central

It has long been thought that birds may use the Earth's magnetic field not only as a compass for direction finding, but that it could also provide spatial information for position determination analogous to a map during navigation. Since magnetic field intensity varies systematically with latitude and theoretically could also provide longitudinal information during position determination, birds using a magnetic map should be able to discriminate magnetic field intensity cues in the laboratory. Here we demonstrate a novel behavioural paradigm requiring homing pigeons to identify the direction of a magnetic field intensity gradient in a “virtual magnetic map” during a spatial conditioning task. Not only were the pigeons able to detect the direction of the intensity gradient, but they were even able to discriminate upward versus downward movement on the gradient by differentiating between increasing and decreasing intensity values. Furthermore, the pigeons typically spent more than half of the 15 second sampling period in front of the feeder associated with the rewarded gradient direction indicating that they required only several seconds to make the correct choice. Our results therefore demonstrate for the first time that pigeons not only can detect the presence and absence of magnetic anomalies, as previous studies had shown, but are even able to detect and respond to changes in magnetic field intensity alone, including the directionality of such changes, in the context of spatial orientation within an experimental arena. This opens up the possibility for systematic and detailed studies of how pigeons could use magnetic intensity cues during position determination as well as how intensity is perceived and where it is processed in the brain. PMID:24039812

Mora, Cordula V.; Bingman, Verner P.

2013-01-01

32

Results of SPARO 2003: Mapping Magnetic Fields in Giant Molecular Clouds  

E-print Network

We present results from the Austral Winter 2003 observing campaign of SPARO, a 450 micron polarimeter used with a two-meter telescope at South Pole. We mapped large-scale magnetic fields in four Giant Molecular Clouds (GMCs) in the Galactic disk: NGC 6334, the Carina Nebula, G333.6-0.2 and G331.5-0.1. We find a statistically significant correlation of the inferred field directions with the orientation of the Galactic plane. Specifically, three of the four GMCs (NGC 6334 is the exception) have mean field directions that are within 15 degrees of the plane. The simplest interpretation is that the field direction tends to be preserved during the process of GMC formation. We have also carried out an analysis of published optical polarimetry data. For the closest of the SPARO GMCs, NGC 6334, we can compare the field direction in the cloud as measured by SPARO with the field direction in a larger region surrounding the cloud, as determined from optical polarimetry. For purposes of comparison, we also use optical polarimetry to determine field directions for other regions of similar size and distance. Overall, the results from this optical polarimetry analysis are consistent with our suggestion that field direction tends to be preserved during GMC formation. Finally, we compare the disorder in our magnetic field maps with the disorder seen in magnetic field maps derived from MHD turbulence simulations. We conclude from these comparisons that the magnetic energy density in our clouds is comparable to the turbulent energy density.

H. Li; G. S. Griffin; M. Krejny; G. Novak; R. F. Loewenstein; M. G. Newcomb; P. G. Calisse; D. T. Chuss

2006-02-21

33

Statistical maps of geomagnetic perturbations as a function of the interplanetary magnetic field  

NASA Astrophysics Data System (ADS)

Mappings of geomagnetic perturbations are shown for different combinations of the solar wind velocity, interplanetary magnetic field (IMF), and dipole tilt angle (season). Average maps were derived separately for the northward, eastward, and vertical (downward) components of the geomagnetic disturbances, using spherical cap harmonics in least error fits of sorted measurements. The source data are obtained from 104 ground-based magnetometer stations in the Northern Hemisphere at geomagnetic latitudes over 40° during the years 1998 through 2001. Contour maps of statistical fits are shown along-side scatter plots of individual measurements in corrected geomagnetic apex coordinates. The patterns are consistent with previous mappings of ionospheric electric potential. Interestingly, the vertical component of the magnetic perturbations closely resembles maps of the overhead, field-aligned currents, including the Northward IMF configuration. The maximum and minimum values from the statistical mappings are graphed to show their changes as a function of southward IMF magnitude, solar wind velocity, and seasons. It is expected that this work will lead to better advance predictions of the geomagnetic perturbations that are based on real-time IMF measurements.

Weimer, D. R.; Clauer, C. R.; Engebretson, M. J.; Hansen, T. L.; Gleisner, H.; Mann, I.; Yumoto, K.

2010-10-01

34

Magnetic Field Mapping and Biaxial Vector Operation for Biomagnetic Applications Using High-Sensitivity Optically Pumped Atomic Magnetometers  

NASA Astrophysics Data System (ADS)

Optically pumped alkali-metal atomic magnetometers are expected to be used not only for biomagnetic field measurements but also for magnetic resonance imaging because of their potential ultrahigh sensitivity. Here, we studied magnetic field mapping and biaxial vector operation using atomic magnetometers. A potassium atomic magnetometer was used in these measurements. First, we obtained sensor output signals by solving the Bloch equation. Next, we measured magnetic field distributions generated by a current dipole electrode that was placed in a spherical phantom, which simulated a group of simultaneously activated neurons in the human brain. We obtained vector contour maps of the magnetic field distributions from the dipoles oriented parallel and orthogonal to the pump laser beam and have found good agreement with theoretical magnetic field distributions. These results demonstrate practical applications of magnetic field mapping and biaxial vector operation using optically pumped atomic magnetometers.

Taue, Shuji; Sugihara, Yasuyuki; Kobayashi, Tetsuo; Ishikawa, Kiyoshi; Kamada, Keigo

2011-11-01

35

Mapping the conductivity tensor of disordered topological insulators in the presence of magnetic fields  

NASA Astrophysics Data System (ADS)

Transport measurements on topological insulators revealed extremely interesting effects and generated data that contain extremely valuable information. It is now possible to control the carriers' concentration using finely tuned gate voltages and to do the transport measurements under controlled applied magnetic fields. As such, accurate maps of the conductivity tensor are now available, as function of the Fermi level and the magnetic field strength. To extract useful information, we need a quantitative theory of charge transport for aperiodic systems in presence of magnetic fields. Such theory has been developed in the past using C*-Algebras and Non-Commutative calculus, the result being closed and exact formulas for the conductivity tensor. In this talk we explain how to manipulate the algebras and how to implement the non-commutative calculus on a computer, in order to compute the conductivity tensor of topological insulating materials in the presence of disorder and magnetic fields. Quantitative simulations of the transport experiments on 2D (and possibly 3D) topological insulators will be presented. Since the methodology can treat disorder and magnetic fields in the same time, it enable us to reproduce, for example, the quantization and the plateaus of the Hall conductance.

Prodan, Emil; Xue, Yu

2012-02-01

36

Generating Synthetic Magnetic Field Intermittency Using a Minimal Multiscale Lagrangian Mapping Approach  

NASA Astrophysics Data System (ADS)

The Minimal Multiscale Lagrangian Mapping procedure developed in the context of neutral fluid turbulence is a simple method for generating synthetic vector fields. Using a sequence of low-pass filtered fields, fluid particles are displaced at their rms speed for some scale-dependent time interval, and then interpolated back to a regular grid. Fields produced in this way are seen to possess certain properties of real turbulence. This paper extends the technique to plasmas by taking into account the coupling between the velocity and magnetic fields. We examine several possible applications to plasma systems. One use is as initial conditions for simulations, wherein these synthetic fields may efficiently produce a strongly intermittent cascade. The intermittency properties of the synthetic fields are also compared with those of the solar wind. Finally, studies of cosmic ray transport and modulation in the test particle approximation may benefit from improved realism in synthetic fields produced in this way.

Subedi, P.; Chhiber, R.; Tessein, J. A.; Wan, M.; Matthaeus, W. H.

2014-12-01

37

Nonlinear Regularization for Per Voxel Estimation of Magnetic Susceptibility Distributions from MRI Field Maps  

PubMed Central

Magnetic susceptibility is an important physical property of tissues, and can be used as a contrast mechanism in magnetic resonance imaging. Recently, targeting contrast agents by conjugation with signaling molecules and labeling stem cells with contrast agents have become feasible. These contrast agents are strongly paramagnetic, and the ability to quantify magnetic susceptibility could allow accurate measurement of signaling and cell localization. Presented here is a technique to estimate arbitrary magnetic susceptibility distributions by solving an ill-posed inversion problem from field maps obtained in an MRI scanner. Two regularization strategies are considered, conventional Tikhonov regularization, and a sparsity promoting nonlinear regularization using the ?1 norm. Proof of concept is demonstrated using numerical simulations, phantoms, and in a stroke model mouse. Initial experience indicates that the nonlinear regularization better suppresses noise and streaking artifacts common in susceptibility estimation. PMID:19502123

Kressler, Bryan; de Rochefort, Ludovic; Liu, Tian; Spincemaille, Pascal; Jiang, Quan; Wang, Yi

2010-01-01

38

Mapping of Ambient Magnetic Fields within Liquid Helium Dewar for Testing of a DC SQUID Magnetometer  

SciTech Connect

In an effort to explore the cavity lights phenomenon, Experimental Facilities Department at SLAC is testing a DC SQUID magnetometer. Due to the nature of the SQUID magnetometer and the intended tests, the earth's magnetic field must be negated. It is proposed to reduce ambient fields using bucking coils. First, however, an accurate map of the magnetic field inside the liquid helium Dewar where the experiment is going to take place needed to be made. This map was made using a three-axis fluxgate magnetometer mounted on a 3D positioning device made for this purpose. A ten inch tall volume within the Dewar was measured at data points approximately an inch from each other in all three axes. A LabVEIW program took readings from the magnetometer at 2 ms intervals for 1000 readings in such a way as to eliminate any ambient 60 Hz signals that may be present in the data. This data was stored in spreadsheet format and was analyzed to determine how the magnetic field within the Dewar was changing as a function of position.

Newhouse, Randal

2003-09-05

39

The Geopotential Research Mission - Mapping the near earth gravity and magnetic fields  

NASA Technical Reports Server (NTRS)

The Geopotential Research Mission (GRM), NASA's low-level satellite system designed to measure the gravity and magnetic fields of the earth, and its objectives are described. The GRM will consist of two, Shuttle launched, satellite systems (300 km apart) that will operate simultaneously at a 160 km circular-polar orbit for six months. Current mission goals include mapping the global geoid to 10 cm, measuring gravity-field anomalies to 2 mgal with a spatial resolution of 100 km, detecting crustal magnetic anomalies of 100 km wavelength with 1 nT accuracy, measuring the vectors components to + or - 5 arc sec and 5 nT, and computing the main dipole or core field to 5 nT with a 2 nT/year secular variation detection. Resource analysis and exploration geology are additional applications considered.

Taylor, P. T.; Keating, T.; Smith, D. E.; Langel, R. A.; Schnetzler, C. C.; Kahn, W. D.

1983-01-01

40

Results of SPARO 2003: Mapping Magnetic Fields in Giant Molecular Clouds  

NASA Astrophysics Data System (ADS)

We present results obtained in 2003 using the Submillimeter Polarimeter for Antarctic Remote Observations (SPARO). SPARO is an imaging polarimeter operating at 450 microns that is used together with the 2 meter Viper telescope at South Pole to map magnetic fields in the dense component of the Galactic ISM. In comparison with other submillimeter polarimeters currently in use, SPARO is especially sensitive to diffuse, extended submillimeter emission. SPARO observed four Giant Molecular Clouds (GMCs) during April-July 2003, obtaining polarimetric detections for about 150 sky positions covering a total sky area of about 0.5 square degrees. The inferred projected magnetic field directions show a tendency to be parallel to the Galactic Plane except where disturbed by expanding bubbles. The bubbles are revealed by Midcourse Space Experiment (MSX) Band A (7-11 microns) images, as well as (in some cases) by optical recombination line maps. In the vicinity of the bubbles, the projected magnetic field directions tend to run parallel to the bubbles' limb-brightened shells, as expected for formation of a highly compressed shell of gas under flux-freezing conditions. We discuss the implications of our results for future studies of magnetohydrodynamic turbulence in GMCs to be carried out using instruments now under development such as the polarimeter for SCUBA2 at the James Clerk Maxwell Telescope, and the SHARP polarimeter at the Caltech Submillimeter Observatory. SPARO is funded by the National Science Foundation's Office of Polar Programs.

Novak, G.; Griffin, G. S.; Krejny, M.; Li, H.; Loewenstein, R. F.; Newcomb, M. G.; Calisse, P. G.; Chuss, D. T.

2005-05-01

41

Cardiac magnetic field map topology quantified by Kullback-Leibler entropy identifies patients with hypertrophic cardiomyopathy  

NASA Astrophysics Data System (ADS)

Hypertrophic cardiomyopathy (HCM) is a common primary inherited cardiac muscle disorder, defined clinically by the presence of unexplained left ventricular hypertrophy. The detection of affected patients remains challenging. Genetic testing is limited because only in 50%-60% of all HCM diagnoses an underlying mutation can be found. Furthermore, the disease has a varied clinical course and outcome, with many patients having little or no discernible cardiovascular symptoms, whereas others develop profound exercise limitation and recurrent arrhythmias or sudden cardiac death. Therefore prospective screening of HCM family members is strongly recommended. According to the current guidelines this includes serial echocardiographic and electrocardiographic examinations. In this study we investigated the capability of cardiac magnetic field mapping (CMFM) to detect patients suffering from HCM. We introduce for the first time a combined diagnostic approach based on map topology quantification using Kullback-Leibler (KL) entropy and regional magnetic field strength parameters. The cardiac magnetic field was recorded over the anterior chest wall using a multichannel-LT-SQUID system. CMFM was calculated based on a regular 36 point grid. We analyzed CMFM in patients with confirmed diagnosis of HCM (HCM, n =33, 43.8±13 years, 13 women, 20 men), a control group of healthy subjects (NORMAL, n =57, 39.6±8.9 years; 22 women and 35 men), and patients with confirmed cardiac hypertrophy due to arterial hypertension (HYP, n =42, 49.7±7.9 years, 15 women and 27 men). A subgroup analysis was performed between HCM patients suffering from the obstructive (HOCM, n =19) and nonobstructive (HNCM, n =14) form of the disease. KL entropy based map topology quantification alone identified HCM patients with a sensitivity of 78.8% and specificity of 86.9% (overall classification rate 84.8%). The combination of the KL parameters with a regional field strength parameter improved the overall classification rate to 87.9% (sensitivity: 84.8%, specificity: 88.9%, area under ROC curve: 0.94). KL measures applied to discriminate between HOCM and HNCM patients showed a correct classification of 78.8%. The combination of one KL and one regional parameter again improved the overall classification rate to 97%. A preliminary prospective analysis in two HCM families showed the feasibility of this diagnostic approach with a correct diagnosis of all 22 screened family members (1 HOCM, 4 HNCM, 17 normal). In conclusion, Cardiac Magnetic Field Mapping including KL entropy based topology quantifications is a suitable tool for HCM screening.

Schirdewan, A.; Gapelyuk, A.; Fischer, R.; Koch, L.; Schütt, H.; Zacharzowsky, U.; Dietz, R.; Thierfelder, L.; Wessel, N.

2007-03-01

42

Mapping of drift surfaces in toroidal systems with chaotic magnetic fields  

NASA Astrophysics Data System (ADS)

Drift orbits of test particles are studied using a recently proposed Hamiltonian theory of guiding-center motion in toroidal systems. A symplectic mapping procedure in symmetric form is developed which allows a fast and accurate characterization of the Poincaré plots in poloidal cross sections. It is shown that the stochastic magnetic field acts differently on the onset of chaotic motion for co- and counterpassing particles, respectively. Resonant drift surfaces are shifted inward for the co-passing particles, and are shifted outward for the counterpassing particles, when compared with resonant magnetic surfaces. The overall result is an inward (outward) shift of chaotic zones of co-passing (counterpassing) particles with respect to the magnetic ergodic zone. The influence of a stationary radial electric field is discussed. It shifts the orbits farther inward for the co-passing particles and outward for the counterpassing particles, respectively. The shifts increase with the energies of the particles. A rotation of the magnetic field perturbations and its effect on drift motion is also investigated. Estimates for the local diffusion rates are presented. For applications, parameters of the dynamic ergodic divertor of the Torus Experiment for Technology-Oriented Research are used [Fusion Eng. Design 37, 337 (1997)].

Abdullaev, S. S.; Wingen, A.; Spatschek, K. H.

2006-04-01

43

Experimental Mapping and Benchmarking of Magnetic Field Codes on the LHD Ion Accelerator  

SciTech Connect

For the validation of the numerical models used for the design of the Neutral Beam Test Facility for ITER in Padua [1], an experimental benchmark against a full-size device has been sought. The LHD BL2 injector [2] has been chosen as a first benchmark, because the BL2 Negative Ion Source and Beam Accelerator are geometrically similar to SPIDER, even though BL2 does not include current bars and ferromagnetic materials. A comprehensive 3D magnetic field model of the LHD BL2 device has been developed based on the same assumptions used for SPIDER. In parallel, a detailed experimental magnetic map of the BL2 device has been obtained using a suitably designed 3D adjustable structure for the fine positioning of the magnetic sensors inside 27 of the 770 beamlet apertures. The calculated values have been compared to the experimental data. The work has confirmed the quality of the numerical model, and has also provided useful information on the magnetic non-uniformities due to the edge effects and to the tolerance on permanent magnet remanence.

Chitarin, G. [Consorzio RFX, Associazione EURATOM-ENEA, Corso Stati Uniti 4, 35127 Padova (Italy); University of Padova, Dept. of Management and Engineering, strad. S. Nicola, 36100 Vicenza (Italy); Agostinetti, P.; Gallo, A.; Marconato, N.; Serianni, G. [Consorzio RFX, Associazione EURATOM-ENEA, Corso Stati Uniti 4, 35127 Padova (Italy); Nakano, H.; Takeiri, Y.; Tsumori, K. [National Institute for Fusion Science, Particle Beam Heated Research Div, 322-6, Oroshi-cho, Toki, Gifu, 509-5292 (Japan)

2011-09-26

44

A model of the AGS based on stepwise ray-tracing through the measured field maps of the main magnets  

SciTech Connect

Two-dimensional mid-plane magnetic field maps of two of the main AGS magnets were produced, from Hall probe measurements, for a series of different current settings. The analysis of these data yielded the excitation functions [1] and the harmonic coefficients [2] of the main magnets which have been used so far in all the models of the AGS. The constant increase of the computation power makes it possible today to directly use a stepwise raytracing through these measured field maps with a reasonable computation time. We describe in detail how these field maps have allowed the generation of models of the 6 different types of AGS main magnets, and how they are being handled with the Zgoubi ray-tracing code [3]. We give and discuss a number of results obtained regarding both beam and spin dynamics in the AGS, and we provide comparisons with other numerical and analytical modelling methods.

Dutheil Y.; Meot, F.; Tsoupas, N.

2012-05-20

45

Development of magnetic field mapping via heavy ion beam spectral imaging  

SciTech Connect

Mapping magnetic fields via heavy ion beam spectral imaging relies upon establishing a high quality ion beam, identifying beam emission at wavelengths favorable for imaging, and designing an appropriate imaging configuration. Identifying emission lines suitable for imaging is difficult due to intense, broadband radiation of the target reversed field pinch plasma. To compensate, we have worked to raise the beam emission intensity. Simulations of the beam optics and characteristics have led to a technique that achieves a narrower beam and increased ion current at the plasma. Additionally, we are developing computer vision tools to reconstruct beam trajectories based on various camera and system configurations. We simulate charge coupled device images of the vessel interior and beam trajectories, and reconstruct three dimensional trajectories from image pairs. Analysis of the simulated images will guide the system specifications. We present results of the beam optics and camera simulations, surveys of radiation, and status of the diagnostic.

Demers, D.R.; Connor, K.A.; Schoch, P.M.; Radke, R.J.; Anderson, J.K.; Craig, D.; Hartog, D.J. den [Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); University of Wisconsin, Madison, Wisconsin 53706 (United States)

2004-10-01

46

Inner Magnetosphere Modeling at the CCMC: Ring Current, Radiation Belt and Magnetic Field Mapping  

NASA Astrophysics Data System (ADS)

Modeling of the inner magnetosphere has entered center stage with the launch of the Van Allen Probes (RBSP) in 2012. The Community Coordinated Modeling Center (CCMC) has drastically improved its offerings of inner magnetosphere models that cover energetic particles in the Earth's ring current and radiation belts. Models added to the CCMC include the stand-alone Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model by M.C. Fok, the Rice Convection Model (RCM) by R. Wolf and S. Sazykin and numerous versions of the Tsyganenko magnetic field model (T89, T96, T01quiet, TS05). These models join the LANL* model by Y. Yu hat was offered for instant run earlier in the year. In addition to these stand-alone models, the Comprehensive Ring Current Model (CRCM) by M.C. Fok and N. Buzulukova joined as a component of the Space Weather Modeling Framework (SWMF) in the magnetosphere model run-on-request category. We present modeling results of the ring current and radiation belt models and demonstrate tracking of satellites such as RBSP. Calculations using the magnetic field models include mappings to the magnetic equator or to minimum-B positions and the determination of foot points in the ionosphere.

Rastaetter, L.; Mendoza, A. M.; Chulaki, A.; Kuznetsova, M. M.; Zheng, Y.

2013-12-01

47

Results of SPARO 2003: Mapping Magnetic Fields in Giant Molecular Clouds  

E-print Network

We present results from the Austral Winter 2003 observing campaign of SPARO, a 450 micron polarimeter used with a two-meter telescope at South Pole. We mapped large-scale magnetic fields in four Giant Molecular Clouds (GMCs) in the Galactic disk: NGC 6334, the Carina Nebula, G333.6-0.2 and G331.5-0.1. We find a statistically significant correlation of the inferred field directions with the orientation of the Galactic plane. Specifically, three of the four GMCs (NGC 6334 is the exception) have mean field directions that are within 15 of the plane. The simplest interpretation is that the field direction tends to be preserved during the process of GMC formation. We have also carried out an analysis of published optical polarimetry data. For the closest of the SPARO GMCs, NGC 6334, we can compare the field direction in the cloud as measured by SPARO with the field direction in a larger region surrounding the cloud, as determined from optical polarimetry. For purposes of comparison, we also use optical polarimetry...

Li, H; Chuss, D T; Griffin, G S; Krejny, M; Loewenstein, R F; Newcomb, M G; Novak, G

2006-01-01

48

INTERPRETING THE ROLE OF THE MAGNETIC FIELD FROM DUST POLARIZATION MAPS  

SciTech Connect

Dust polarization observations from the Submillimeter Array (SMA) and the Caltech Submillimeter Observatory (CSO) are analyzed with the goal of providing a general tool to interpret the role of the magnetic field in molecular clouds. Magnetic field and dust emission gradient orientations are observed to show distinct patterns and features. The angle ? between these two orientations can be interpreted as a magnetic field alignment deviation, assuming the emission gradient orientation to coincide with the density gradient orientation in the magnetohydrodynamics force equation. In SMA high-resolution (collapsing) cores, additional symmetry properties in ? can reveal accretion and outflow zones. All these observational findings suggest the angle ? to be a relevant quantity that can assess the role of the magnetic field. Indeed, when comparing this angle with the (projection-free) magnetic field significance ?{sub B} (introduced by Koch and coworkers in 2012), it is demonstrated that |?| yields an approximation to the change in ?{sub B}. Thus, changes in the magnetic field alignment deviation ? trace changes in the role of the magnetic field. The angle ? is observationally straightforward to determine, providing a tool to distinguish between zones of minor or significant magnetic field impact. This is exemplified by the CSO M+0.25 + 0.01, Mon R2, CO+0.02 – 0.02, M–0.02 – 0.07 sources and by the SMA high-resolution data from W51 e2, W51 North, Orion BN/KL and g5.89. Additional CSO sources are analyzed, providing further support of this result. Finally, based on the different features found in our sample of 31 sources in total, covering sizes from large-scale complexes to collapsing cores, a schematic evolutionary scenario is proposed. Here, the significance of the magnetic field evolves both with position and scale, and can be assessed with the angle ?.

Koch, Patrick M.; Tang, Ya-Wen; Ho, Paul T. P., E-mail: pmkoch@asiaa.sinica.edu.tw [Academia Sinica, Institute of Astronomy and Astrophysics, Taipei, Taiwan (China)

2013-09-20

49

Mapping the earth's magnetic and gravity fields from space Current status and future prospects  

NASA Technical Reports Server (NTRS)

The principal magnetic fields encountered by earth orbiting spacecraft include the main (core) field, external fields produced by electrical currents within the ionosphere and magnetosphere, and the crustal (anomaly) field generated by variations in the magnetization of the outermost portions of the earth. The first orbital field measurements which proved to be of use for global studies of crustal magnetization were obtained by a series of three satellites launched and operated from 1965 to 1971. Each of the satellites, known as a Polar Orbiting Geophysical Observatory (POGO), carried a rubidium vapor magnetometer. Attention is also given to Magsat launched in 1979, the scalar anomaly field derived from the Magsat measurements, satellite tracking studies in connection with gravity field surveys, radar altimetry, the belt of positive free air gravity anomalies situated along the edge of the Pacific Ocean basin, future technological capabilities, and information concerning data availability.

Settle, M.; Taranik, J. V.

1983-01-01

50

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

51

Obtaining vector magnetic field maps from single-component measurements of geological samples  

E-print Network

Maxwell's equations can be used to demonstrate that the components of a static magnetic field in a region of space devoid of sources are not independent. This means that magnetometers that measure a single component of the ...

Andrade Lima, Eduardo

52

Precisely mapping the magnetic field gradient in vacuum with an atom interferometer  

SciTech Connect

The magnetic field gradient has been measured with an atom interferometer using the magnetic sublevels of {sup 87}Rb atoms. The Doppler-insensitive measurement effectively eliminates the contribution from gravity and background vibration noise, and the differential measurement also can reject some systematic errors. A resolution of 300 pT/mm has been demonstrated with a 90-s integration time and a spatial resolution of 1.4 mm. The gradiometer was then used to measure the magnetic field gradient in an ultrahigh-vacuum environment. The technique will also be very useful to subtract the systematic error arising from the magnetic field inhomogeneity in precision atom-interferometry experiments, such as gravity measurement.

Zhou Minkang; Hu Zhongkun; Duan Xiaochun; Sun Buliang; Zhao Jinbo; Luo Jun [School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)

2010-12-15

53

MAGNETIC FIELD STRENGTH MAPS FOR MOLECULAR CLOUDS: A NEW METHOD BASED ON A POLARIZATION-INTENSITY GRADIENT RELATION  

SciTech Connect

Dust polarization orientations in molecular clouds often tend to be close to tangential to the Stokes I dust continuum emission contours. The magnetic field and the emission gradient orientations, therefore, show some correlation. A method is proposed, which-in the framework of ideal magnetohydrodynamics (MHD)-connects the measured angle between magnetic field and emission gradient orientations to the total field strength. The approach is based on the assumption that a change in emission intensity (gradient) is a measure for the resulting direction of motion in the MHD force equation. In particular, this new method leads to maps of position-dependent magnetic field strength estimates. When evaluating the field curvature and the gravity direction locally on a map, the method can be generalized to arbitrary cloud shapes. The technique is applied to high-resolution ({approx}0.''7) Submillimeter Array polarization data of the collapsing core W51 e2. A tentative {approx}7.7 mG field strength is found when averaging over the entire core. The analysis further reveals some structures and an azimuthally averaged radial profile {approx}r{sup -1/2} for the field strength. Maximum values close to the center are around 19 mG. The currently available observations lack higher resolution data to probe the innermost part of the core where the largest field strength is expected from the method. Application regime and limitations of the method are discussed. As a further important outcome of this technique, the local significance of the magnetic field force compared to the other forces can be quantified in a model-independent way, from measured angles only. Finally, the method can potentially also be expanded and applied to other objects (besides molecular clouds) with measurements that reveal the field morphology, as, e.g., Faraday rotation measurements in galaxies.

Koch, Patrick M.; Tang, Ya-Wen; Ho, Paul T. P., E-mail: pmkoch@asiaa.sinica.edu.tw [Academia Sinica, Institute of Astronomy and Astrophysics, Taipei, Taiwan (China)

2012-03-01

54

Magnetic Field Mapping and Integral Transfer Function Matching of the Prototype Dipoles for the NSLS-II at BNL  

SciTech Connect

The National Synchrotron Light Source-II (NSLS-II) storage ring at Brookhaven National Laboratory (BNL) will be equipped with 54 dipole magnets having a gap of 35 mm, and 6 dipoles having a gap of 90 mm. Each dipole has a field of 0.4 T and provides 6 degrees of bending for a 3 GeV electron beam. The large aperture magnets are necessary to allow the extraction of long-wavelength light from the dipole magnet to serve a growing number of users of low energy radiation. The dipoles must not only have good field homogeneity (0.015% over a 40 mm x 20 mm region), but the integral transfer functions and integral end harmonics of the two types of magnets must also be matched. The 35 mm aperture dipole has a novel design where the yoke ends are extended up to the outside dimension of the coil using magnetic steel nose pieces. This design increases the effective length of the dipole without increasing the physical length. These nose pieces can be tailored to adjust the integral transfer function as well as the homogeneity of the integrated field. One prototype of each dipole type has been fabricated to validate the designs and to study matching of the two dipoles. A Hall probe mapping system has been built with three Group 3 Hall probes mounted on a 2-D translation stage. The probes are arranged with one probe in the midplane of the magnet and the others vertically offset by {+-}10 mm. The field is mapped around a nominal 25 m radius beam trajectory. The results of measurements in the as-received magnets, and with modifications made to the nose pieces are presented.

He, P.; Jain, A., Gupta, R., Skaritka, J., Spataro, C., Joshi, P., Ganetis, G., Anerella, M., Wanderer, P.

2011-03-28

55

High-Resolution Mapping of Lunar Crustal Magnetic Fields: Correlations with Albedo Markings of the Reiner Gamma Class  

NASA Astrophysics Data System (ADS)

During the last eight months of the Lunar Prospector mission (December 1999-July 1999), the spacecraft was placed in a relatively low-altitude (15-30-km perapsis), near-polar orbit that allowed high-resolution mapping of crustal magnetic fields. We report here initial studies of the correlation of locally strong magnetic anomalies with unusual, swirl-like albedo markings of the Reiner Gamma class. Based on this correlation, which is known from earlier studies of Apollo subsatellite magnetometer data, it has been proposed that the swirls represent regions whose higher albedos have been preserved via deflection of the solar-wind ion bombardment by strong crustal fields. This model in turn depends on the hypothesis that solar-wind implanted H is at least one component of the process that optically matures exposed silicate surfaces in the inner solar system . Specifically, it is hypothesized that implanted H acts as an effective reducing agent to enhance the rate of production of nanophase metallic Fe particles from preexisting silicates during micrometeoroid impacts. According to the model, the curvilinear shapes of these albedo markings are caused, at least in part, by the geometry of ion deflections in a magnetic field. The improved resolution and coverage of the Prospector data allow more detailed mapping of the fields, especially on the lunar farside. This permits a more quantitative test of whether all albedo markings of this class are associated with strong local magnetic fields.Only if the latter condition is met can the solar-wind deflection hypothesis he valid. The basic procedure for mapping crustal magnetic fields using Lunar Prospector magnetometer data follows that developed for analysis of Apollo subsatellite magnetometer data. The specific mapping steps are (1) selection of mission time intervals suitable for mapping crustal fields; these are limited essentially either to times when the Moon is in a lobe of the geomagnetic tail or to times when the Moon is in the solar wind but the spacecraft is in the lunar wake; the data are transformed to a radial, east, and north coordinate system with measurements given as a function of spacecraft latitude, longitude, and altitude; (2) visual editing of individual orbit segments selected for minimal external field disturbances; (3) minimization of remaining low-frequency external fields for individual orbit data segments by quadratic detrending; and (4) two-dimensional filtering of individual orbit segments to produce a vector field map along the slightly curved surface defined by the spacecraft altitude; maps of the three field components (radial, east, and north), the field magnitude, and the spacecraft altitude are constructed. For data obtained at low to middle latitudes, the horizontal resolution of the field maps is limited by the orbit-track separation (about 30 km at the equator). Maps of the field magnitude have been constructed within limited selenographic regions based mainly on data acquired in March, April, and May of 1999. This was a time period when the orbit plane was nearly aligned with the Sun-Moon line so that field mapping was possible at times when the Moon was in the solar wind as well as when the Moon was in the geomagnetic tail. Most of the coverage is across the lunar farside. However, a shows an example of a field map produced from solar-wind wake data for a region including Reiner Gamm on western Oceanus Procellarum (location: 58.5W, 7.5N). The contour interval is 3 nT and the mean spacecraft altitude is 18 km to within the accuracy allowed by the resolution of the map (30 km or about 1 deg.); strong magnetic anomalies correlate closely with swirl locations. Individual orbit profiles (whose resolution along the orbit track is comparable to the spacecraft altitude of 18 km) also demonstrate a good correlation of field magnitude with surface albedo. In order to investigate the correlation of magnetic fields with the location of swirl features, we have reexamined available lunar imagery (Lunar Orbiter, Apollo, and Clementine) to identify and map s

Hood, L. L.; Yingst, A.; Mitchell, D. L.; Lin, R. P.; Acuna, M.; Binder, A.

1999-01-01

56

CDC field mapping device - ''ROTOTRACK''  

SciTech Connect

A field mapping device for the magnet of the Collider Detector at Fermilab (CDF) was constructed. The device was used for extensive study of the CDF magnetic field distribution. The mechanical and electrical features of the device, as well as the data acquisition system and software, are described. The mechanical system was designed so that the errors on the position and angle of the probe were +-0.75 mm and +-1 mrad, respectively.

Yamada, R.; Hawtree, J.; Kaczar, K.; Leverence, R.; McGuire, K.; Newman-Holmes, C.; Schmidt, E.E.; Shallenberger, J.

1985-10-01

57

Mapping Solar Open Magnetic Fields With Near-Relativistic Electron Beams  

NASA Astrophysics Data System (ADS)

We used a combination of heliospheric and solar data to identify a set of open fields for which both the solar and near-Earth positions are known. The purpose is to test existing and developing models of magnetic field topology. The models are provided by other members of the Living With a Star Targeted Research & Technology Heliospheric Magnetic Field Focus Team. For our part, we concentrated on the solar phenomena associated with near-relativistic electron energization and transport, because near-relativistic electrons emit or excite many forms of detectable electromagnetic (EM) radiation. The EM radiations help us identify the solar end or `origin' of individual open field lines, and the near-Earth ends can be identified by their association with electron beam events at 1 AU, using the EPAM instrument on the ACE spacecraft. The total number of events that met our criteria for inclusion in the study is about 200. For each event, we used the measured solar wind speed to estimate the curvature of the field line, from which we could infer the Carrington longitude of the open field on the `source surface' at 2.5 solar radii. Potential field source surface calculations supplied by I.-M. Wang and N. R. Sheeley allowed us to trace the open fields from their intersection with the heliospheric field at 2.5 solar radii down to the base of the corona. Our study was specifically designed to test two contrasting open field models: (1) a model with widely distributed open fields and (2) a model with open fields only in well- defined coronal holes. We will present the preliminary results of the study and several case studies. This work was supported by NASA TR&T grant NNG05GM69G.

Rust, D. M.; Haggerty, D. K.

2006-12-01

58

Planck intermediate results. XXXIII. Signature of the magnetic field geometry of interstellar filaments in dust polarization maps  

E-print Network

Planck observations at 353GHz provide the first fully-sampled maps of the polarized dust emission of interstellar filaments, offering unprecedented information on the structure of the magnetic field. We present the polarization properties of three nearby filaments, Musca, B211, and L1506. These three filaments have similar total intensities (Stokes I), while the variations of the Stokes Q and U are all different: the Musca filament is visible in the Q and U maps, B211 and L1506 are seen in the Q map but are not distinguishable in the U map, and the Q increase for L1506 is not spatially coincident with that of I. They all offer 3pc segments, along which both the filament and the background Stokes parameters are almost uniform. In all three cases, the polarization fraction (p) towards the filaments is smaller than that of their background. The polarized emission results from the combination of the magnetic field (B) structure and the dust polarization properties. We model the variations of the Stokes parameters...

Ade, P A R; Alves, M I R; Arnaud, M; Arzoumanian, D; Aumont, J; Baccigalupi, C; Banday, A J; Barreiro, R B; Bartolo, N; Battaner, E; Benabed, K; Benoit-Lévy, A; Bernard, J -P; Berné, O; Bersanelli, M; Bielewicz, P; Bonaldi, A; Bonavera, L; Bond, J R; Borrill, J; Bouchet, F R; Boulanger, F; Bracco, A; Burigana, C; Calabrese, E; Cardoso, J -F; Catalano, A; Chamballu, A; Chiang, H C; Christensen, P R; Clements, D L; Colombi, S; Combet, C; Couchot, F; Crill, B P; Curto, A; Cuttaia, F; Danese, L; Davies, R D; Davis, R J; de Bernardis, P; de Rosa, A; de Zotti, G; Delabrouille, J; Dickinson, C; Diego, J M; Donzelli, S; Doré, O; Douspis, M; Ducout, A; Dupac, X; Elsner, F; Enßlin, T A; Eriksen, H K; Falgarone, E; Ferrière, K; Forni, O; Frailis, M; Fraisse, A A; Franceschi, E; Frejsel, A; Galeotta, S; Galli, S; Ganga, K; Ghosh, T; Giard, M; Giraud-Héraud, Y; Gjerløw, E; González-Nuevo, J; Gregorio, A; Gruppuso, A; Guillet, V; Hansen, F K; Hanson, D; Harrison, D L; Hernández-Monteagudo, C; Herranz, D; Hildebrandt, S R; Hivon, E; Hobson, M; Holmes, W A; Huffenberger, K M; Hurier, G; Jaffe, A H; Jaffe, T R; Jones, W C; Juvela, M; Keskitalo, R; Kisner, T S; Knoche, J; Kunz, M; Kurki-Suonio, H; Lagache, G; Lamarre, J -M; Lasenby, A; Lawrence, C R; Leonardi, R; Levrier, F; Liguori, M; Lilje, P B; Linden-Vørnle, M; López-Caniego, M; Lubin, P M; Macías-Pérez, J F; Maffei, B; Mandolesi, N; Mangilli, A; Maris, M; Martin, P G; Martínez-González, E; Masi, S; Matarrese, S; Mazzotta, P; Melchiorri, A; Mendes, L; Mennella, A; Migliaccio, M; Mitra, S; Miville-Deschênes, M -A; Moneti, A; Montier, L; Morgante, G; Mortlock, D; Munshi, D; Murphy, J A; Naselsky, P; Nati, F; Natoli, P; Nørgaard-Nielsen, H U; Noviello, F; Novikov, D; Novikov, I; Oppermann, N; Pagano, L; Pajot, F; Paladini, R; Paoletti, D; Pasian, F; Perrotta, F; Pettorino, V; Piacentini, F; Piat, M; Pierpaoli, E; Pietrobon, D; Plaszczynski, S; Pointecouteau, E; Polenta, G; Pratt, G W; Puget, J -L; Rachen, J P; Rebolo, R; Reinecke, M; Remazeilles, M; Renault, C; Renzi, A; Ricciardi, S; Ristorcelli, I; Rocha, G; Rosset, C; Rossetti, M; Roudier, G; Rubiño-Martín, J A; Rusholme, B; Sandri, M; Savelainen, M; Savini, G; Scott, D; Soler, J D; Stolyarov, V; Sutton, D; Suur-Uski, A -S; Sygnet, J -F; Tauber, J A; Terenzi, L; Toffolatti, L; Tomasi, M; Tristram, M; Tucci, M; Valenziano, L; Valiviita, J; Van Tent, B; Vielva, P; Villa, F; Wade, L A; Wandelt, B D; Yvon, D; Zacchei, A; Zonca, A

2014-01-01

59

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

60

Interferometric Mapping of Magnetic Fields in Star-forming Regions I. W51 e1/e2 Molecular Cores  

E-print Network

We present the first interferometric polarization map of the W51 e1/e2 molecular cores obtained with the BIMA array at 1.3 mm wavelength with approximately 3 arcsecond resolution. The polarization angle varies smoothly across the double cores with an average position angle of 23+-5 degrees for W51 e1 and 15+-7 degrees for W51 e2. The inferred magnetic field direction is parallel to the minor axis of the double cores, which is consistent with the theoretical picture that clouds collapse along the field lines. However, the magnetic field may not determine the axis of angular momentum of these two cores as the field directions of the two cores significantly differ with the previously measured directions of rotational axes. The polarization percentage decreases toward regions with high intensity, suggesting that the dust alignment efficiency decreases toward high density regions. The field directions are highly ordered, and the small dispersion of the polarization angles implies that magnetic fields are strong ($\\gtrsim$ 1 mG) and perhaps dominate turbulence in W51 e1/e2.

Shih-Ping Lai; Richard M. Crutcher; Jose M. Girart; Ramprasad Rao

2001-07-17

61

Optical Auroral Observations at High Latitudes to Investigate Processes at the Foot of Magnetic Field Lines That Map Into the Interplanetary Medium  

Microsoft Academic Search

At high magnetic latitudes the magnetic field lines, are open and they map from the ground into the interplanetary medium. Due to the larger offset between the geographic and geomagnetic poles in the Southern hemisphere the Antarctic Continent is especially suitable for making visible wavelength optical observations of the foot of such field lines. Near the Austral winter solstice the

S. B. Mende

2005-01-01

62

Generalized Gauss maps and integrals for three-component links: Toward higher helicities for magnetic fields and fluid flows  

NASA Astrophysics Data System (ADS)

To each three-component link in the 3-sphere we associate a generalized Gauss map from the 3-torus to the 2-sphere, and show that the pairwise linking numbers and Milnor triple linking number that classify the link up to link homotopy correspond to the Pontryagin invariants that classify its generalized Gauss map up to homotopy. We view this as a natural extension of the familiar situation for two-component links in 3-space, where the linking number is the degree of the classical Gauss map from the 2-torus to the 2-sphere. The generalized Gauss map, like its prototype, is geometrically natural in the sense that it is equivariant with respect to orientation-preserving isometries of the ambient space, thus positioning it for application to physical situations. When the pairwise linking numbers of a three-component link are all zero, we give an integral formula for the triple linking number analogous to the Gauss integral for the pairwise linking numbers. This new integral is also geometrically natural, like its prototype, in the sense that the integrand is invariant under orientation-preserving isometries of the ambient space. Versions of this integral have been applied by Komendarczyk in special cases to problems of higher order helicity and derivation of lower bounds for the energy of magnetic fields. We have set this entire paper in the 3-sphere because our generalized Gauss map is easiest to present here, but in a subsequent paper we will give the corresponding maps and integral formulas in Euclidean 3-space.

DeTurck, Dennis; Gluck, Herman; Komendarczyk, Rafal; Melvin, Paul; Shonkwiler, Clayton; Vela-Vick, David Shea

2013-01-01

63

Robotic mapping assisted by local magnetic field Haiyang Zhang, Fred Martin  

E-print Network

is revisited by the robot. It is particularly important for large area map consistency. Steel structures, such as average range, number of clusters, etc. Then, in an unknown environment, it compares the current laser-generated map to improve localization and mapping accuracy. The algorithm is designed to explore unknown area

64

Synoptic maps of polar caps for stable interplanetary magnetic field intervals during January 1992 geospace environment modeling campaign  

NASA Astrophysics Data System (ADS)

Observations from January 27-28, 1992, when four polar-orbiting DMSP satellites were in operation, are used to construct synoptic maps of convective flows and particle regions within the polar ionosphere. We chose periods of relative steady interplanetary magnetic field (IMF) and use data from multiple satellite passes during each period to obtain unprecedented two-dimensional coverage. For strongly negative IMF By, convection patterns are similar to those that have been previously obtained but also show significant. IMF Bz effects. For Bz>>|By|, we see strong sunward flow near the pole, but antisunward convection on open field lines at lower latitudes on the nightside. The particle observations reveal the two-dimensional structure of the cusp/mantle region and the existence of a strong polar arc within the circular convection cell that has a negative electric field divergence on open field lines. The particle observations also readily identify the magnetic separatrix when a satellite crosses the inner edge of the cusp or the boundary between the plasma sheet and polar rain. However, on the morningside and often on the afternoonside, we find a distinct and well-defined region of soft-electron and magnetosheath-like ion precipitation [(the ``soft- electron zone'' (SEZ)] lying between the plasma sheet and the region of polar rain. Separatrix identification is uncertain at local times where the SEZ is present; however, it appears that large portions of the SEZ are on open field lines. Dawn-dusk displacements of the open field line regions in the two polar caps are seen that are consistent with IMF By effects. Additionally, the dayside separatrix is observed to be further poleward for positive than for negative IMF Bz, whereas Bz is not observed to have a significant effect on the location of the nightside separatrix. Also, we consistently find larger cross polar-cap potential drops in the southern hemisphere than in the northern hemisphere. This suggests that there are significant (tens of kV) magnetic-field-aligned potential drops along high-altitude regions of open field lines where the magnetic field is weak and particle motion strongly violates the guiding center approximation.

Lyons, L. R.; Lu, G.; de la Beaujardière, O.; Rich, F. J.

1996-12-01

65

Mars Observer magnetic fields investigation  

NASA Technical Reports Server (NTRS)

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 wind interaction, the mapping of crustal magnetic fields, and studies of the Martian ionosphere, which are activities included in the Mars Observer mission objectives. Attention is also given to the flight software incorporated in the on-board data processor, and the procedures of data processing and analysis.

Acuna, M. H.; Connerney, J. E. P.; Wasilewski, P.; Lin, R. P.; Anderson, K. A.; Carlson, C. W.; Mcfadden, J.; Curtis, D. W.; Reme, H.; Cros, A.

1992-01-01

66

THE EFFECT OF LIMITED SPATIAL RESOLUTION OF STELLAR SURFACE MAGNETIC FIELD MAPS ON MAGNETOHYDRODYNAMIC WIND AND CORONAL X-RAY EMISSION MODELS  

SciTech Connect

We study the influence of the spatial resolution on scales of 5 Degree-Sign and smaller of solar surface magnetic field maps on global magnetohydrodynamic solar wind models, and on a model of coronal heating and X-ray emission. We compare the solutions driven by a low-resolution Wilcox Solar Observatory magnetic map, the same map with spatial resolution artificially increased by a refinement algorithm, and a high-resolution Solar and Heliospheric Observatory Michelson Doppler Imager map. We find that both the wind structure and the X-ray morphology are affected by the fine-scale surface magnetic structure. Moreover, the X-ray morphology is dominated by the closed loop structure between mixed polarities on smaller scales and shows significant changes between high- and low-resolution maps. We conclude that three-dimensional modeling of coronal X-ray emission has greater surface magnetic field spatial resolution requirements than wind modeling, and can be unreliable unless the dominant mixed polarity magnetic flux is properly resolved.

Garraffo, C.; Cohen, O.; Drake, J. J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St. Cambridge, MA 02138 (United States)] [Harvard-Smithsonian Center for Astrophysics, 60 Garden St. Cambridge, MA 02138 (United States); Downs, C. [Institute for Astronomy, University of Hawaii at Manoa, 2680 Woodlawn Dr., Honolulu, HI 96822 (United States)] [Institute for Astronomy, University of Hawaii at Manoa, 2680 Woodlawn Dr., Honolulu, HI 96822 (United States)

2013-02-10

67

Magnetic fields in astrophysics  

Microsoft Academic Search

The evidence of cosmic magnetism is examined, taking into account the Zeeman effect, beats in atomic transitions, the Hanle effect, Faraday rotation, gyro-lines, and the strength and scale of magnetic fields in astrophysics. The origin of magnetic fields is considered along with dynamos, the conditions for magnetic field generation, the topology of flows, magnetic fields in stationary flows, kinematic turbulent

Ia. B. Zeldovich; A. A. Ruzmaikin; D. D. Sokolov

1983-01-01

68

Unambiguous identification of superparamagnetic iron oxide (SPIO) particles through quantitative susceptibility mapping of the nonlinear response to magnetic fields  

PubMed Central

Superparamagnetic iron oxide (SPIO) particles generate signal void regions on gradient echo images due to their strong magnetization. In practice, the signal void region might be indistinguishable from that generated by air. However, the response of SPIO to an externally applied magnetic field is non-linear. Magnetization of SPIO saturates at around 1 Tesla while magnetization of water and air increase linearly with field strength. Phantom experiment and mice experiments demonstrated the feasibility of a non-ambiguous identification of superparamagnetic contrast agents. PMID:20688448

Liu, Tian; Spincemaille, Pascal; de Rochefort, Ludovic; Wong, Richard; Prince, Martin; Wang, Yi

2010-01-01

69

Magnetic field sensor  

NASA Astrophysics Data System (ADS)

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

Silva, Nicolas

2012-09-01

70

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.

71

Magnetic fields of galaxies  

Microsoft Academic Search

The current state of the understanding of the magnetic fields of galaxies is reviewed. A simple model of the turbulent dynamo is developed which explains the main observational features of the global magnetic fields of spiral galaxies. The generation of small-scale chaotic magnetic fields in the interstellar medium is also examined. Attention is also given to the role of magnetic

Aleksandr A. Ruzmaikin; Dmitrii D. Sokolov; Anvar M. Shukurov

1988-01-01

72

High-Field (9.4 T) MRI of Brain Dysmyelination by Quantitative Mapping of Magnetic Susceptibility  

PubMed Central

The multilayered myelin sheath wrapping around nerve axons is essential for proper functioning of the central nervous system. Abnormal myelination leads to a wide range of neurological diseases and developmental disorders. Non-invasive imaging of myelin content is of great clinical importance. The present work demonstrated that loss of myelin in the central nervous system of the shiverer mouse results in a dramatic reduction of magnetic susceptibility in white matter axons. The reduction resulted in a near extinction of susceptibility contrast between gray and white matter. Quantitative magnetic susceptibility imaging and diffusion tensor imaging were conducted on a group of control and shiverer mice at 9.4 T. We measured the resonance frequency distribution of the whole brain for each mouse. Magnetic susceptibility maps were computed and compared between the two groups. It was shown that the susceptibility contrast between gray and white matter was reduced by 96% in the shiverer compared to the controls. Diffusion measurements further confirmed intact fiber pathways in the shiverer mice, ruling out the possibility of axonal injury and its potential contribution to the altered susceptibility. As an autosomal recessive mutation, shiverer is characterized by an almost total lack of central nervous system myelin. Our data provides new evidences indicating that myelin is the predominant source of susceptibility differences between deep gray and white matter observed in magnetic resonance imaging. More importantly, the present study suggests that quantitative magnetic susceptibility is a potential endogenous biomarker for myelination. PMID:21320606

Liu, Chunlei; Li, Wei; Johnson, G. Allan; Wu, Bing

2011-01-01

73

Facility Measures Magnetic Fields  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

74

Earths magnetic field  

Microsoft Academic Search

Recent studies of the Paleosecular Variation of lavas (PSVL) by the authors and others, shows that the variability of Earth's magnetic field over the last several million years is less than the variability of the present Earth's magnetic field. The present magnetic field is asymmetric between the northern and southern hemispheres. The dispersion in the southern hemisphere being much greater

N. Opdyke; V. Mejia

2003-01-01

75

The Magnetic Field  

NSDL National Science Digital Library

This demonstration of the magnetic field lines of Earth uses a bar magnet, iron filings, and a compass. The site explains how to measure the magnetic field of the Earth by measuring the direction a compass points from various points on the surface. There is also an explanation of why the north magnetic pole on Earth is actually, by definition, the south pole of a magnet.

Barker, Jeffrey

76

Magnetic Fields Analogous to electric field, a magnet  

E-print Network

Magnetic Fields Analogous to electric field, a magnet produces a magnetic field, B Set up a B field two ways: Moving electrically charged particles Current in a wire Intrinsic magnetic field Basic characteristic of elementary particles such as an electron #12;Magnetic Fields Magnetic field lines Direction

Bertulani, Carlos A. - Department of Physics and Astronomy, Texas A&M University

77

The Magnetic Field  

NSDL National Science Digital Library

This webpage is part of the University Corporation for Atmospheric Research (UCAR) "Windows to the Universe" program. It describes the nature and configuration of magnetic fields, which are the result of moving electric charges, including how they cause magnetic objects to orient themselves along the direction of the magnetic force points, which are illustrated as lines. Magnetic field lines by convention point outwards at the north magnetic pole and inward at the south magnetic pole. The site features text, scientific illustrations and an animation. Text and vocabulary are selectable for the beginning, intermediate, or advanced reader.

78

Magnetic Field Example 1  

NSDL National Science Digital Library

Clicking on the different links below will produce different magnetic fields in the box above. The wires (perpendicular to the screen) or coils (in and out of the screen) are not visible, but you can determine what they are from the field. You can also click on a point to read off the magnetic field at that place.

Christian, Wolfgang; Belloni, Mario

2008-02-19

79

The DYNAMO Orbiter Project: High Resolution Mapping of Gravity/Magnetic Fields and In Situ Investigation of Mars Atmospheric Escape  

NASA Technical Reports Server (NTRS)

Dynamo is a small Mars orbiter planned to be launched in 2005 or 2007, in the frame of the NASA/CNES Mars exploration program. It is aimed at improving gravity and magnetic field resolution, in order to better understand the magnetic, geologic and thermal history of Mars, and at characterizing current atmospheric escape, which is still poorly constrained. These objectives are achieved by using a low periapsis orbit, similar to the one used by the Mars Global Surveyor spacecraft during its aerobraking phases. The proposed periapsis altitude for Dynamo of 120-130 km, coupled with the global distribution of periapses to be obtained during one Martian year of operation, through about 5000 low passes, will produce a magnetic/gravity field data set with approximately five times the spatial resolution of MGS. Low periapsis provides a unique opportunity to investigate the chemical and dynamical properties of the deep ionosphere, thermosphere, and the interaction between the atmosphere and the solar wind, therefore atmospheric escape, which may have played a crucial role in removing atmosphere, and water, from the planet. There is much room for debate on the importance of current atmosphere escape processes in the evolution of the Martian atmosphere, as early "exotic" processes including hydrodynamic escape and impact erosion are traditionally invoked to explain the apparent sparse inventory of present-day volatiles. Yet, the combination of low surface gravity and the absence of a substantial internally generated magnetic field have undeniable effects on what we observe today. In addition to the current losses in the forms of Jeans and photochemical escape of neutrals, there are solar wind interaction-related erosion mechanisms because the upper atmosphere is directly exposed to the solar wind. The solar wind related loss rates, while now comparable to those of a modest comet, nonetheless occur continuously, with the intriguing possibility of important cumulative and/or enhanced effects over the several billion years of the solar system's life. If the detailed history of the Martian internal field could be traced back, and the current escape processes could be understood well enough to model the expected stronger losses under early Sun conditions, one could go a long way toward constraining this part of the mysterious history of Mars' atmosphere.

Smrekar, S.; Chassefiere, E.; Forget, F.; Reme, H.; Mazelle, C.; Blelly, P. -L.; Acuna, M.; Connerney, J.; Purucker, M.; Lin, R.

2000-01-01

80

USGS Topographic Mapping Field Camp  

USGS Multimedia Gallery

USGS topographic mapping field camp in the early 1900s. Note the USGS "pick and hammer" flag flying below the United States flag. It was common practice to fly both flags in USGS field camps. Also note the "US" on the tents. Much of the USGS field gear was obtained from army surplus....

2009-11-23

81

Design, construction, and field mapping of the HISTRAP prototype dipole  

SciTech Connect

HISTRAP is a proposed 2.67 T-m synchrotron-cooler-storage ring having eight 45/degree/, C-design dipole magnets. A prototype dipole has been designed, fabricated, and mapped. The magnet design utilizes curved and angled coil ends to compensate for end effects in the field. Construction of the prototype dipole has been completed by the FNAL magnet factory. The magnetic field has been mapped using a Hall-effect probe afixed to a newly constructed, PC-based, horizontal positioning system. Results of the field mapping are presented. 6 refs., 7 figs., 1 tabs.

Tatum, B.A.; Dowling, D.T.; Lord, R.S.; Mosko, S.W.; Olsen, D.K.

1989-01-01

82

Magnetic Field Distribution of Permanent Magnet Magnetized by Static Magnetic Field Generated by HTS Bulk Magnet  

Microsoft Academic Search

Demagnetized rare earth magnets (Nd-Fe-B) can be fully magnetized by scanning them in the intense static fields over 3 T of a HTS bulk magnet which was cooled to the temperature range lower than 77K with use of cryo-coolers and activated by the field of 5 T. We precisely examined the magnetic field distributions of magnetized permanent magnets. The magnetic

Tetsuo Oka; Nobutaka Kawasaki; Satoshi Fukui; Jun Ogawa; Takao Sato; Toshihisa Terasawa; Yoshitaka Itoh; Ryohei Yabuno

2012-01-01

83

Abstract: Quasistatic magnetic fields  

Microsoft Academic Search

A prototype switching system has been developed which can switch 20 kA at 230 V for short periods of time through inductive loads. High power silicon controlled rectifiers are used to switch the National Magnet Laboratory dc generators on and off into a liquid N2 cooled, low impedance high field magnet so that high fields can be generated for a

H. C. Praddaude; S. Foner

1979-01-01

84

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

85

Magnetic Fields in Galaxies  

NASA Astrophysics Data System (ADS)

Magnetic fields are a major agent in the interstellar medium. They contribute significantly to the total pressure which balances the gas disk against gravitation. They affect the gas flows in spiral arms (Gómez and Cox, 2002). The effective sound speed of the gas is increased by the presence of strong fields which reduce the shock strength. The interstellar fields are closely connected to gas clouds. They affect the dynamics of the gas clouds (Elmegreen, 1981; de Avillez and Breitschwerdt, 2004). The stability and evolution of gas clouds are also influenced by magnetic fields, but it is not understood how (Crutcher, 1999; see Chap. 7). Magnetic fields are essential for the onset of star formation as they enable the removal of angular momentum from the protostellar cloud during its collapse (magnetic braking, Mouschovias, 1990). Strong fields may shift the stellar mass spectrum towards the more massive stars (Mestel, 1990). MHD turbulence distributes energy from supernova explosions within the ISM (Subramanian, 1998) and regenerates the field via the dynamo process (Wielebinski, R., Krause, 1993, Beck et al., 1996; Sect. 6). Magnetic reconnection is a possible heating source for the ISM and halo gas (Birk et al., 1998). Magnetic fields also control the density and distribution of cosmic rays in the ISM. A realistic model for any process in the ISM needs basic information about the magnetic field which has to be provided by observations.

Beck, Rainer

86

A global magnetic anomaly map. [obtained from POGO satellite data  

NASA Technical Reports Server (NTRS)

A subset of POGO satellite magnetometer data has been formed that is suitable for analysis of crustal magnetic anomalies. Using a thirteenth order field model, fit to these data, magnetic residuals have been calculated over the world to latitude limits of plus 50 deg. These residuals averaged over one degree latitude-longitude blocks represent a detailed global magnetic anomaly map derived solely from satellite data. Preliminary analysis of the map indicates that the anomalies are real and of geological origin.

Regan, R. D.; Davis, W. M.; Cain, J. C.

1974-01-01

87

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

88

Magnetic Fields on the Surface of the Sun  

NSDL National Science Digital Library

This is a lesson about magnetism in solar flares. Learners will map magnetic fields around bar magnets and investigate how this configuration relates to magnetic fields of sunspots. This activity requires compasses, bar magnets, and a equipment for the instructor to project a PowerPoint or pdf lecture presentation. This is Activity 1 in the Exploring Magnetism in Solar Flares teachers guide.

89

Magnetic Bar Field Model  

NSDL National Science Digital Library

The EJS Magnetic Bar Field Model shows the field of a bar magnet and has a movable compass that reports the magnetic field values. The bar magnet model is built by placing a group of magnetic dipoles along the bar magnet. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. The Magnetic Bar Field model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_em_MagneticBarField.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Christian, Wolfgang; Franciscouembre; Cox, Anne

2009-09-18

90

Magnetic Fields, Flares & Forecasts  

Microsoft Academic Search

A 2D wavelet transform modulus maxima (WTMM) method is used to characterise the complexity of the distribution of the photospheric magnetic field of active regions. The WTMM method offers increased accuracy and reliability over previous fractal and multifractal methods. The multifractal spectrum of both quiet Sun and active region magnetic features are presented. It is shown that the multifractal nature

Paul A. Conlon; P. Kestener; R. McAteer; P. Gallagher

2009-01-01

91

Opening the cusp. [using magnetic field topology  

NASA Technical Reports Server (NTRS)

This paper discusses the magnetic field topology (determined by the superposition of dipole, image, and uniform fields) for mapping the cusp to the ionosphere. The model results are compared to both new and published observations and are then used to map the footprint of a flux transfer event caused by a time variation in the merging rate. It is shown that the cusp geometry distorts the field lines mapped from the magnetopause to yield footprints with dawn and dusk protrusions into the region of closed magnetic flux.

Crooker, N. U.; Toffoletto, F. R.; Gussenhoven, M. S.

1991-01-01

92

The First Magnetic Fields  

E-print Network

We demonstrate that the Biermann battery mechanism for the creation of large scale magnetic fields can arise in a simple model protogalaxy. Analytic calculations and numerical simulations follow explicitly the generation of vorticity (and hence magnetic field) at the outward-moving shock that develops as the protogalactic perturbation collapses. Shear angular momentum then distorts this field into a dipole-like configuration. The magnitude of the field created in the fully formed disk galaxy is estimated to be 10^(-17) Gauss, approximately what is needed as a seed for the galactic dynamo.

George Davies; Lawrence M. Widrow

1999-12-14

93

Mars Crustal Magnetic Field Remnants  

NASA Technical Reports Server (NTRS)

The radial magnetic field measured is color coded on a global perspective view that shows measurements derived from spacecraft tracks below 200 km overlain on a monochrome shaded relief map of the topography.

This image shows especially strong Martian magnetic fields in the southern highlands near the Terra Cimmeria and Terra Sirenum regions, centered around 180 degrees longitude from the equator to the pole. It is where magnetic stripes possibly resulting from crustal movement are most prominent. The bands are oriented approximately east - west and are about 100 miles wide and 600 miles long, although the longest band stretches more than 1200 miles.

The false blue and red colors represent invisible magnetic fields in the Martian crust that point in opposite directions. The magnetic fields appear to be organized in bands, with adjacent bands pointing in opposite directions, giving these stripes a striking similarity to patterns seen in the Earth's crust at the mid-oceanic ridges.

These data were compiled by the MGS Magnetometer Team led by Mario Acuna at the Goddard Space Flight Center in Greenbelt, MD.

2001-01-01

94

Solar Wind Magnetic Fields  

NASA Technical Reports Server (NTRS)

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

Smith, E. J.

1995-01-01

95

Unique topological characterization of braided magnetic fields  

SciTech Connect

We introduce a topological flux function to quantify the topology of magnetic braids: non-zero, line-tied magnetic fields whose field lines all connect between two boundaries. This scalar function is an ideal invariant defined on a cross-section of the magnetic field, and measures the average poloidal magnetic flux around any given field line, or the average pairwise crossing number between a given field line and all others. Moreover, its integral over the cross-section yields the relative magnetic helicity. Using the fact that the flux function is also an action in the Hamiltonian formulation of the field line equations, we prove that it uniquely characterizes the field line mapping and hence the magnetic topology.

Yeates, A. R. [Department of Mathematical Sciences, Durham University, Durham DH1 3LE (United Kingdom); Hornig, G. [Division of Mathematics, University of Dundee, Dundee DD1 4HN (United Kingdom)

2013-01-15

96

Planetary magnetic fields  

Microsoft Academic Search

The past several years have seen dramatic developments in the study of planetary magnetic fields, including a wealth of new data, mainly from the Galilean satellites and Mars, together with major improvements in our theoretical modeling effort of the dynamo process believed responsible for large planetary fields. These dynamos arise from thermal or compositional convection in fluid regions of large

David J. Stevenson

2003-01-01

97

Prediction of DC magnetic fields for magnetic cleanliness on spacecraft  

Microsoft Academic Search

Magnetometry is among the most used techniques in space exploration, e.g. to study complex plasma interactions between the solar wind and the Earth's magnetosphere, to map the planetary or interplanetary magnetic fields, or to retrieve information about the structural composition of planets. The success of each mission relies on the attainment of an adequate level of magnetic cleanliness at the

Axel Junge; Filippo Marliani

2011-01-01

98

Indoor localization using magnetic fields  

NASA Astrophysics Data System (ADS)

Indoor localization consists of locating oneself inside new buildings. GPS does not work indoors due to multipath reflection and signal blockage. WiFi based systems assume ubiquitous availability and infrastructure based systems require expensive installations, hence making indoor localization an open problem. This dissertation consists of solving the problem of indoor localization by thoroughly exploiting the indoor ambient magnetic fields comprising mainly of disturbances termed as anomalies in the Earth's magnetic field caused by pillars, doors and elevators in hallways which are ferromagnetic in nature. By observing uniqueness in magnetic signatures collected from different campus buildings, the work presents the identification of landmarks and guideposts from these signatures and further develops magnetic maps of buildings - all of which can be used to locate and navigate people indoors. To understand the reason behind these anomalies, first a comparison between the measured and model generated Earth's magnetic field is made, verifying the presence of a constant field without any disturbances. Then by modeling the magnetic field behavior of different pillars such as steel reinforced concrete, solid steel, and other structures like doors and elevators, the interaction of the Earth's field with the ferromagnetic fields is described thereby explaining the causes of the uniqueness in the signatures that comprise these disturbances. Next, by employing the dynamic time warping algorithm to account for time differences in signatures obtained from users walking at different speeds, an indoor localization application capable of classifying locations using the magnetic signatures is developed solely on the smart phone. The application required users to walk short distances of 3-6 m anywhere in hallway to be located with accuracies of 80-99%. The classification framework was further validated with over 90% accuracies using model generated magnetic signatures representing hallways with different kinds of pillars, doors and elevators. All in all, this dissertation contributes the following: 1) provides a framework for understanding the presence of ambient magnetic fields indoors and utilizing them to solve the indoor localization problem; 2) develops an application that is independent of the user and the smart phones and 3) requires no other infrastructure since it is deployed on a device that encapsulates the sensing, computing and inferring functionalities, thereby making it a novel contribution to the mobile and pervasive computing domain.

Pathapati Subbu, Kalyan Sasidhar

99

Graphene Magnetic Field Sensors  

Microsoft Academic Search

Graphene extraordinary magnetoresistance (EMR) devices have been fabricated and characterized in varying magnetic fields at room temperature. The atomic thickness, high carrier mobility and high current carrying capabilities of graphene are ideally suited for the detection of nanoscale sized magnetic domains. The device sensitivity can reach 10 mV\\/Oe, larger than state of the art InAs 2DEG devices of comparable size

Simone Pisana; Patrick M. Braganca; Ernesto E. Marinero; Bruce A. Gurney

2010-01-01

100

Magnetic Field and Life  

NSDL National Science Digital Library

This is a lesson where learners explore magnetic forces, fields, and the relationship between electricity. Learners will use this information to infer how the Earth generates a protective magnetic field. The lesson models scientific inquiry using the 5E instructional model and includes teacher notes, prerequisite concepts, common misconceptions, student journal and reading. This is lesson seven in the Astro-Venture Geology Training Unit that were developed to increase students' awareness of and interest in astrobiology and the many career opportunities that utilize science, math and technology skills. The lessons are designed for educators to use with with the Astro-Venture multimedia modules.

101

Ground Vehicle Navigation Using Magnetic Field Variation  

NASA Astrophysics Data System (ADS)

The Earth's magnetic field has been the bedrock of navigation for centuries. The latest research highlights the uniqueness of magnetic field measurements based on position due to large scale variations as well as localized perturbations. These observable changes in the Earth's magnetic field as a function of position provide distinct information which can be used for navigation. This dissertation describes ground vehicle navigation exploiting variation in Earth's magnetic field using a self-contained navigation system consisting of only a magnetometer and magnetic field maps. In order to achieve navigation, effective calibration enables repeatable magnetic field measurements from different vehicles and facilitates mapping of the observable magnetic field as a function of position. A new modified ellipsoid calibration technique for strapdown magnetometers in large vehicles is described, as well as analysis of position measurement generation comparing a multitude of measurement compositions using existing and newly developed likelihood techniques. Finally, navigation solutions are presented using both a position measurement and direct incorporation of the magnetometer measurements via a particle filter to demonstrate road navigation in three different environments. Emphatically, the results affirm that navigation using magnetic field variation in ground vehicles is viable and achieves adequate performance for road level navigation.

Shockley, Jeremiah A.

102

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

103

The next generation Antarctic digital magnetic anomaly map  

USGS Publications Warehouse

S (Golynsky et al., 2001). This map synthesized over 7.1 million line-kms of survey data available up through 1999 from marine, airborne and Magsat satellite observations. Since the production of the initial map, a large number of new marine and airborne surveys and improved magnetic observations from the Ørsted and CHAMP satellite missions have become available. In addition, an improved core field model for the Antarctic has been developed to better isolate crustal anomalies in these data. The next generation compilation also will likely represent the magnetic survey observations of the region in terms of a high-resolution spherical cap harmonic model. In this paper, we review the progress and problems of developing an improved magnetic anomaly map to facilitate studies of the Antarctic crustal magnetic field

von Frese, R.R.B; Golynsky, A.V.; Kim, H.R.; Gaya-Piqué, L.; Thébault, E.; Chiappinii, M.; Ghidella, M.; Grunow, A.; ADMAP Working Group

2007-01-01

104

Mappings of stochastic field lines in poloidal divertor tokamaks  

NASA Astrophysics Data System (ADS)

Two mapping methods to study magnetic field lines near the separatrix of poloidal divertor tokamaks in the presence of external non-axisymmetric magnetic perturbations are proposed. The first mapping method is based on the Hamiltonian formulation of field line equations in the Boozer coordinates and solving it by the canonical transformation of variables (Abdullaev et al 1999 Phys. Plasmas 6 153). The second mapping is a canonical mapping near the separatrix which is constructed using the recently developed method (Abdullaev 2004 Phys. Rev. E 70 064202, Abdullaev 2005 Phys. Rev. E 72 064202). We construct the corresponding mappings for magnetic field lines in divertor tokamaks in the presence of non-axisymmetric magnetic perturbations. The mappings are applied to study the properties of open stochastic field lines near the separatrix for the wire model of the plasma. Poincaré sections, the so-called laminar and magnetic footprint plot (a contour plot of wall to wall connections lengths) in the plasma region and on the divertor plates are obtained. The quasilinear diffusion coefficients of field lines are also estimated.

Abdullaev, S. S.; Finken, K. H.; Jakubowski, M.; Lehnen, M.

2006-04-01

105

Mapping the energy spectrum of the spin states of mixed-valent [Fe8]n- via pulsed field magnetization  

SciTech Connect

The electronic structure of a family of octanuclear Fe{sup III}-complexes of the general formula [Fe{sub 8}({mu}{sub 4}-O)4({mu}-{sub r}-R-pz){sub 12}X{sub 4}] ([Fe{sub 8}]{sup 0}) and its redox-modified, mixed-valence [Fe{sub 8}]{sup n-} derivatives, where R = H, Me, Et, F, CI, Sr, I, etc. and X = F, CI, Sr, NCS, NCO, N{sub 3}, has recently been modeled by a an effective Hamiltonian consisting of two dominant exchange interactions [1]. The ground state properties (from S{sub tot} = 0 to 7) and magnetic energy level spacing of the Hamiltonian, and hence predicted magnetic properties, are widely tunable via choice of J's. The corresponding [Fe{sub 8}]{sup n-} anionic complexes with n = 1 - 4 are accessible electrochemically, allowing their in situ spectroelectrochemical characterization. The singly-reduced anions [Fe{sub 8}]{sup 1-} of the R = H, Cl and X = Cl species have also been prepared chemically via reduction with a stoichiometric amount of [BH{sub 4}]-, and characterized crystallographically; the structure of the Fe{sub 8}-cluster remains unaffected by the reduction, with most bond lengths differences within experimental error. Their Moessbauer spectroscopic analysis has pointed to the reduction taking place primarily within the Fe{sub 4}O{sub 4}-cubane, with charges delocalized over the four Fe{sub c} sites in the Moessbauer timescale. In contrast, the [Fe{sub 8}]{sup 1-} and [Fe{sub 8}]{sup 2-} species with R = Cl and X = NCS show a reduction at the outer, Fe{sub o}-sites, generating one or two localized Fe{sub o}-centers.

Mcdonald, Ross D [Los Alamos National Laboratory; Singleton, John [Los Alamos National Laboratory; Raptis, Raphel G [UNIV OF PUERTO RICO

2011-01-14

106

On magnetic field ``reconstruction''  

NASA Astrophysics Data System (ADS)

Context: Solanki and colleagues have presented intriguing 3D “reconstructions” of magnetic fields from the vector polarimetry of the He I 1083 nm multiplet. Aims: In this Research Note I re-examine the reconstruction technique used. Methods: Using a simple dipole field, I examine the reconstruction technique as applied to the theoretical fields. I assume that the He line forms in two locations, (1) along the magnetic loops and (2) in a horizontal plane. Results: The planar interpretation can account for all aspects of the data, but the loop interpretation has geometrical and physical problems. Conclusions: The data by themselves are not sufficient to determine which picture is more applicable. Nevertheless I argue that the planar interpretation makes more physical sense and that the early reconstructions lead to spurious results. I suggest additional tests that might help constrain the problem further.

Judge, P. G.

2009-01-01

107

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

108

Radio frequency magnetic field mapping of a 3 Tesla birdcage coil: Experimental and theoretical dependence on sample properties  

Microsoft Academic Search

The RF B1 distribution was studied, theoretically and experi- mentally, in phantoms and in the head of volunteers usin ga3T MRI system equipped with a birdcage coil. Agreement between numerical simulation and experiment demonstrates that B1 dis- tortion at high field can be explained with 3D full-Maxwell cal- culations. It was found that the B1 distribution in the transverse plane

Marcello Alecci; Christopher M. Collins; Michael B. Smith; Peter Jezzard

2001-01-01

109

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

110

The Heliospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

The Heliospheric Magnetic Field (HMF) is the physical framework in which energetic particles and cosmic rays propagate. Changes in the large scale structure of the magnetic field lead to short- and long term changes in cosmic ray intensities, in particular in anti-phase with solar activity. The origin of the HMF in the corona is well understood and inner heliospheric observations can generally be linked to their coronal sources. The structure of heliospheric magnetic polarities and the heliospheric current sheet separating the dominant solar polarities are reviewed here over longer than a solar cycle, using the three dimensional heliospheric observations by Ulysses. The dynamics of the HMF around solar minimum activity is reviewed and the development of stream interaction regions following the stable flow patterns of fast and slow solar wind in the inner heliosphere is described. The complex dynamics that affects the evolution of the stream interaction regions leads to a more chaotic structure of the HMF in the outer heliosphere is described and discussed on the basis of the Voyager observations. Around solar maximum, solar activity is dominated by frequent transients, resulting in the interplanetary counterparts of Coronal Mass Ejections (ICMEs). These produce a complex aperiodic pattern of structures in the inner heliosphere, at all heliolatitudes. These structures continue to interact and evolve as they travel to the outer heliosphere. However, linking the observations in the inner and outer heliospheres is possible in the case of the largest solar transients that, despite their evolutions, remain recognizably large structures and lead to the formation of Merged Interaction Regions (MIRs) that may well form a quasi-spherical, "global" shell of enhanced magnetic fields around the Sun at large distances. For the transport of energetic particles and cosmic rays, the fluctuations in the magnetic field and their description in alternative turbulent models remains a very important research topic. These are also briefly reviewed in this paper.

Balogh, André; Erdõs, Géza

2013-06-01

111

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

112

Magnetic Fields, Flares & Forecasts  

NASA Astrophysics Data System (ADS)

A 2D wavelet transform modulus maxima (WTMM) method is used to characterise the complexity of the distribution of the photospheric magnetic field of active regions. The WTMM method offers increased accuracy and reliability over previous fractal and multifractal methods. The multifractal spectrum of both quiet Sun and active region magnetic features are presented. It is shown that the multifractal nature of the quiet Sun is significantly different from that of an active region. As such, a method is proposed to seperate the information corresponding to the multifractal spectrum of an active region from the surrounding quite Sun texture. The WTMM method and segmentation procedure are shown to detect the internal restructuring of active region magnetic features prior to flaring. We detect two thresholds (Haussdorf dimension > 1.2 and Holder Exponent > -0.7) as possible indicators for conditions favourable to flaring.

Conlon, Paul A.; Kestener, P.; McAteer, R.; Gallagher, P.

2009-05-01

113

The 3-dimensional radio mapping experiment /SBH/ on ISEE-C. [interplanetary magnetic field structure for solar wind flow studies using type 3 bursts  

NASA Technical Reports Server (NTRS)

The SBH experiment on ISEE-C will provide maps of the large scale structure of the interplanetary magnetic field from ten solar radii altitude to the earth orbit, in and out of the ecliptic. The SBH instrument will track type III solar radio bursts at 24 frequencies in the range 30 kHz-2 MHz thus providing the positions of 24 points along the line of force which guides the electrons producing the radio radiation. The antennas are two dipoles: one (90 m long) in the spin plane, the other (15 m long) along the spin axis. The receiver was designed for high sensitivity (0.3 microV in 3 kHz BW), high intermodulation rejection (80 dB/1 microV input for order 2 products), large dynamic range (70 dB), high selectivity (-30-dB response 6.5 kHz away from the center frequency of 10.7 MHz for the 3 kHz BW channels), and high reliability (expected orbital life: 3 years).

Knoll, R.; Epstein, G.; Hoang, S.; Huntzinger, G.; Steinberg, J. L.; Fainberg, J.; Grena, F.; Stone, R. G.; Mosier, S. R.

1978-01-01

114

Magnetic fields and cancer  

SciTech Connect

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

Jones, T.L.

1993-10-01

115

Magnetic Field of the Earth  

NSDL National Science Digital Library

Students can learn about how the magnetic field of the earth is similar to magnets. Go to the following link: Magnetic Field of the Earth 1. What makes the earth like a magnet? 2. How do we measure magnetism? Be sure to check out the fun games and activities on this web site too!! Now click on the following link and listen to a 2 minute presentation about magnetism: Pulse Planet Next go to ...

Merritt, Mrs.

2005-10-18

116

Visual field map clusters in human cortex  

PubMed Central

We describe the location and general properties of nine human visual field maps. The cortical location of each map, as well as many examples of the eccentricity and angular representations within these maps, are shown in a series of images that summarize a large set of functional MRI data. The organization and properties of these maps are compared and contrasted with descriptions by other investigators. We hypothesize that the human visual field maps are arranged in several clusters, each comprising a group of maps that share a common foveal representation and semicircular eccentricity map. The spatial organization of these clusters suggests that the perceptual processing within each cluster serves related functions. PMID:15937008

Wandell, Brian A; Brewer, Alyssa A; Dougherty, Robert F

2005-01-01

117

Magnetic nanoparticle density mapping from the magnetically induced displacement data: a simulation study  

PubMed Central

Background Magnetic nanoparticles are gaining great roles in biomedical applications as targeted drug delivery agents or targeted imaging contrast agents. In the magnetic nanoparticle applications, quantification of the nanoparticle density deposited in a specified region is of great importance for evaluating the delivery of the drugs or the contrast agents to the targeted tissues. We introduce a method for estimating the nanoparticle density from the displacement of tissues caused by the external magnetic field. Methods We can exert magnetic force to the magnetic nanoparticles residing in a living subject by applying magnetic gradient field to them. The nanoparticles under the external magnetic field then exert force to the nearby tissues causing displacement of the tissues. The displacement field induced by the nanoparticles under the external magnetic field is governed by the Navier's equation. We use an approximation method to get the inverse solution of the Navier's equation which represents the magnetic nanoparticle density map when the magnetic nanoparticles are mechanically coupled with the surrounding tissues. To produce the external magnetic field inside a living subject, we propose a coil configuration, the Helmholtz and Maxwell coil pair, that is capable of generating uniform magnetic gradient field. We have estimated the coil currents that can induce measurable displacement in soft tissues through finite element method (FEM) analysis. Results From the displacement data obtained from FEM analysis of a soft-tissue-mimicking phantom, we have calculated nanoparticle density maps. We obtained the magnetic nanoparticle density maps by approximating the Navier's equation to the Laplacian of the displacement field. The calculated density maps match well to the original density maps, but with some halo artifacts around the high density area. To induce measurable displacement in the living tissues with the proposed coil configuration, we need to apply the coil currents as big as 104A. Conclusions We can obtain magnetic nanoparticle maps from the magnetically induced displacement data by approximating the Navier's equation under the assumption of uniform-gradient of the external magnetic field. However, developing a coil driving system with the capacity of up to 104A should be a great technical challenge. PMID:22394477

2012-01-01

118

Autonomous Underwater Vehicle Magnetic Mapping System  

NASA Astrophysics Data System (ADS)

An Autonomous Underwater Vehicle (AUV) Magnetic Mapping (MM) System has been developed and tested for military munitions detection as well as pipeline locating, wreck searches, and geologic surveys in underwater environments. The system is comprised of a high sensitivity Geometrics G-880AUV cesium vapor magnetometer integrated with a Teledyne-Gavia AUV and associated Doppler enabled inertial navigation further utilizing traditional acoustic bathymetric and side scan imaging. All onboard sensors and associated electronics are managed through customized crew members to autonomously operate through the vehicles primary control module. Total field magnetic measurements are recorded with asynchronous time-stamped data logs which include position, altitude, heading, pitch, roll, and electrical current usage. Pre-planned mission information can be uploaded to the system operators to define data collection metrics including speed, height above seafloor, and lane or transect spacing specifically designed to meet data quality objectives for the survey. As a result of the AUVs modular design, autonomous navigation and rapid deployment capabilities, the AUV MM System provides cost savings over current surface vessel surveys by reducing the mobilization/demobilization effort, thus requiring less manpower for operation and reducing or eliminating the need for a surface support vessel altogether. When the system completes its mission, data can be remotely downloaded via W-LAN and exported for use in advanced signal processing platforms. Magnetic compensation software has been concurrently developed to accept electrical current measurements directly from the AUV to address distortions from permanent and induced magnetization effects on the magnetometer. Maneuver and electrical current compensation terms can be extracted from the magnetic survey missions to perform automated post-process corrections. Considerable suppression of system noise has been observed over traditional compensation methods that do not use electrical current terms. Recent demonstrations of the AUV MM System conducted at test plots seeded with inert munitions show reliable detection of 75mm and larger projectiles at altitudes of over 2 meters above the seafloor. Improvement ratios between 11 and 12.4 were observed in the survey data after magnetic compensation, reducing system noise to approximately ±0.25 nano-Tesla. Co-registered side scan sonar images were acquired with the magnetic data to augment target analysis and interpretation. No net drift of the navigation solution was observed during survey missions thus confirming target positional accuracy to better than 1 meter.;

Steigerwalt, R.; Johnson, R. M.; Trembanis, A. C.; Schmidt, V. E.; Tait, G.

2012-12-01

119

Mapping the magnetic mayhem in the heliosheath  

NASA Astrophysics Data System (ADS)

When Voyager 1 passed into the heliosheath in 2004, it became the first human-made object to explore the remote edge of the Sun's magnetic influence. The heliosheath, between 1.5 and 15 billion kilometers thick and starting roughly 14 billion kilometers from the Sun, is where the outgoing flows of solar wind start to be pushed back by interstellar particles and magnetic fields that are heading toward the solar system. While passing through the heliosheath, Voyager 1 experienced many sudden and drastic changes in the surrounding magnetic field driven by structures called current sheets. Using Voyager 1's ongoing measurements of the magnetic field, Burlaga and Ness identified three distinct types of current sheets. The structures, appearing as proton boundary layers (PBLs), magnetic holes or humps, or sector boundaries, were identified by characteristic fluctuations in either magnetic field strength or direction as the spacecraft crossed nearly 500 million kilometers of heliosheath in 2009. PBLs are defined by a rapid jump in magnetic field strength, with one observed event resulting in a doubling of the field strength in just half an hour. Passing through a sector boundary led to a sudden change in direction of the magnetic field. Magnetic holes saw the field strength drop to near zero before returning to the original background strength. Magnetic humps consisted of a sudden spike in strength and then a return to initial levels. (Journal of Geophysical Research-Space Physics, doi:10.1029/ 2010JA016309, 2011)

Schultz, Colin

2011-07-01

120

AC Magnetic Field Survey Report  

E-print Network

AC Magnetic Field Survey Report of Literature Building - 3000 University of California San Diego:..........................................................................................................2 ELF OR AC MAGNETIC FIELD CHARACTERISTICS:...............................................2 UNITS of California San Diego La Jolla, California PROJECT: AC Magnetic Field Survey SCOPE: The scope of this project

Krstic, Miroslav

121

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

122

Magnetic Field Topology in Jets  

NASA Technical Reports Server (NTRS)

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

Gardiner, T. A.; Frank, A.

2000-01-01

123

Low field magnetic resonance imaging  

DOEpatents

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

Pines, Alexander (Berkeley, CA); Sakellariou, Dimitrios (Billancourt, FR); Meriles, Carlos A. (Fort Lee, NJ); Trabesinger, Andreas H. (London, GB)

2010-07-13

124

Atoms in Crossed Electric and Magnetic Fields  

NASA Astrophysics Data System (ADS)

In this dissertation, extensive experimental and theoretical work pertaining to three interesting aspects of the interaction of atoms with crossed electric and magnetic fields is presented. The first experiment discussed deals with the effects of weak crossed fields on sodium atoms. A fluorescence spectrum of laser excited sodium n = 11 states in an electric field of 2560 V/cm perpendicular to a magnetic field of 4.4 kG is presented, along with a comparison to theory. The data show the important effects of m-mixing and residual degeneracies which remain in the crossed fields. The next topic presented is the theoretical prediction of novel resonances, termed "quasi-Penning resonances," corresponding to electron states localized away from the nucleus at the Stark saddlepoint in strong crossed electric and magnetic fields. The stability and possibility for observation of these resonances is explored. Finally, extensive experimental maps of data are presented which compare laser induced ionization spectra of sodium atoms in crossed electric and magnetic fields to spectra in an electric field atone. The experiment explores the energy region of the electric field saddlepoint, where quasi-Penning resonances are predicted to occur. The magnetic field is too weak for the observation of these resonances, but the experiment provides important groundwork for the understanding of future experiments in strong crossed fields. The magnetic field is seen to cause splitting of some transitions due to the interaction of the electron spin with the magnetic field. Also, magnetic field induced state mixing causes a redistribution of oscillator strengths leading to changes in peak heights and auto-ionizing line widths. On the whole, however, the effect of the weak crossed magnetic field on the sodium Stark spectra remains small.

Korevaar, Eric John

1987-09-01

125

NMR at low magnetic fields  

NASA Astrophysics Data System (ADS)

NMR provides outstanding information in chemistry and in medicine. But the equipment is expensive as high-field magnets are employed. Low-field NMR works with inexpensive permanent magnets. Until recently these did not provide fields sufficiently homogeneous for spectroscopy and were mostly used for relaxation measurements. Relaxation can also be measured outside the magnet, and small mobile NMR devices have been developed for non-destructive testing of large objects. Today small stray-field magnets and small magnets with homogeneous fields are available for relaxation analysis, imaging, and spectroscopy. Their availability is believed to be essential for shifting NMR analysis from a specialist's tool to a convenience tool.

Blümich, Bernhard; Casanova, Federico; Appelt, Stephan

2009-08-01

126

Magnetic Fields in Irregular Galaxies  

E-print Network

Magnetic fields are an important component of the interstellar medium, especially in low-mass galaxies like irregulars where the magnetic pressure may be significant. However, few irregular galaxies have observed magnetic field structures. Using the VLA, the GBT, and the ATCA, we have observed several irregular galaxies in the radio continuum to determine their magnetic field structures. Here we report on our results for the galaxies NGC 4214 and NGC 1569.

Amanda A. Kepley; Stefanie Muehle; Eric M. Wilcots; John Everett; Ellen Zweibel; Timothy Robishaw; Carl Heiles

2007-08-24

127

Measurement of AC magnetic field distribution using magnetic resonance imaging.  

PubMed

Electric currents are applied to body in numerous applications in medicine such as electrical impedance tomography, cardiac defibrillation, electrocautery, and physiotherapy. If the magnetic field within a region is measured, the currents generating these fields can be calculated using the curl operator. In this study, magnetic fields generated within a phantom by currents passing through an external wire is measured using a magnetic resonance imaging (MRI) system. A pulse sequence that is originally designed for mapping static magnetic field inhomogeneity is adapted. AC current in the form of a burst sine wave is applied synchronously with the pulse sequence. The frequency of the applied current is in the audio range with an amplitude of 175-mA rms. It is shown that each voxel value of sequential images obtained by the proposed pulse sequence is modulated similar to a single tone broadband frequency modulated (FM) waveform with the ac magnetic field strength determining the modulation index. An algorithm is developed to calculate the ac magnetic field intensity at each voxel using the frequency spectrum of the voxel signal. Experimental results show that the proposed algorithm can be used to calculate ac magnetic field distribution within a conducting sample that is placed in an MRI system. PMID:9368117

Ider, Y Z; Muftuler, L T

1997-10-01

128

Magnetic Fields in Protostellar Disks  

E-print Network

· Shear in disc may wind up field or drive MRI · Equipartition field in the minimum solar nebula to the shear in the disc? ­ which form of diffusion is dominant? logn/nH (s-1) M+ C+ m+ e He+ H+ H3 instability (MRI) ­ disc-driven winds Magnetic fields · Magnetic fields play an important role during star

Wardle, Mark

129

Fourier-based magnetic induction tomography for mapping resistivity  

SciTech Connect

Magnetic induction tomography is used as an experimental tool for mapping the passive electromagnetic properties of conductors, with the potential for imaging biological tissues. Our numerical approach to solving the inverse problem is to obtain a Fourier expansion of the resistivity and the stream functions of the magnetic fields and eddy current density. Thus, we are able to solve the inverse problem of determining the resistivity from the applied and measured magnetic fields for a two-dimensional conducting plane. When we add noise to the measured magnetic field, we find the fidelity of the measured to the true resistivity is quite robust for increasing levels of noise and increasing distances of the applied and measured field coils from the conducting plane, when properly filtered. We conclude that Fourier methods provide a reliable alternative for solving the inverse problem.

Puwal, Steffan; Roth, Bradley J. [Department of Physics, Oakland University, Rochester, Michigan 48309 (United States)

2011-01-01

130

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

131

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

132

Magnetic space-based field measurements  

NASA Technical Reports Server (NTRS)

Satellite measurements of the geomagnetic field began with the launch of Sputnik 3 in May 1958 and have continued sporadically in the intervening years. A list of spacecraft that have made significant contributions to an understanding of the near-earth geomagnetic field is presented. A new era in near-earth magnetic field measurements began with NASA's launch of Magsat in October 1979. Attention is given to geomagnetic field modeling, crustal magnetic anomaly studies, and investigations of the inner earth. It is concluded that satellite-based magnetic field measurements make global surveys practical for both field modeling and for the mapping of large-scale crustal anomalies. They are the only practical method of accurately modeling the global secular variation. Magsat is providing a significant contribution, both because of the timeliness of the survey and because its vector measurement capability represents an advance in the technology of such measurements.

Langel, R. A.

1981-01-01

133

Magnetic Fields: Visible and Permanent.  

ERIC Educational Resources Information Center

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

Winkeljohn, Dorothy R.; Earl, Robert D.

1983-01-01

134

New map compiled of Europe's gravity field  

Microsoft Academic Search

A gravity anomaly map of Europe was recently compiled that incorporates significant new data, especially from the eastern European countries. The map (Figure 1a), which was developed by a group of geophysicists and geodesists, goes a long way toward establishing a common and reliable database.Geological information contained in the regional gravity field are highlighted in the map, and all known

Stanislaw Wybraniec; Shaohua Zhou; Hans Thybo; Rene Forsberg; Edward Perchuc; Michael Lee; Gleb D. Demianov; V. N. Strakhov

1998-01-01

135

(version 6/26/06) Magnetic Fields  

E-print Network

where the magnetic fields of the Earth and the bar magnet sum to zero. INTRODUCTION A magnetic field(version 6/26/06) Magnetic Fields GOALS (1) To visualize the magnetic fields produced by several to trace out the magnetic field lines of a single bar magnet on a large sheet of paper. (3) To calculate

Collins, Gary S.

136

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

137

NATIONAL HIGH MAGNETIC FIELD LABORATORY  

E-print Network

and testing areas, magnet experiment cells, and laser laboratory areas. The laboratory is used 24 hours perNATIONAL HIGH MAGNETIC FIELD LABORATORY NHMFL FLORIDA STATE UNIVERSITY SAFETY PROCEDURE SP-3 TITLE Dalton ______________________________________________________ ASSISTANT DIRECTOR, ENVIRONMENTAL, HEALTH

Weston, Ken

138

Understanding the Chromospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

The chromospheric magnetic field is an important and essential component for understanding solar atmospheric fields. Due to the problems of polarization radiation transfer in the chromosphere and the low detective sensitivity of chromospheric spectrum lines, observations of chromospheric magnetic fields are very difficult, so studies of chromospheric fields are infrequent. However, the understanding of chromospheric fields is evolving. In this report, we summarize our current empirical knowledge and basic physical understanding of chromospheric fields. We concentrate on the comparison of magnetic fields in the photosphere and chromosphere, and then display their difference.

Jin, C. L.; Harvey, J. W.; Pietarila, A.

2014-10-01

139

Reconnection of Magnetic Fields  

NASA Astrophysics Data System (ADS)

Preface; Part I. Introduction: 1.1 The Sun E. R. Priest; 1.2 Earth's magnetosphere J. Birn; Part II. Basic Theory of MHD Reconnection: 2.1 Classical theory of two-dimensional reconnection T. G. Forbes; 2.2 Fundamental concepts G. Hornig; 2.3 Three-dimensional reconnection in the absence of magnetic null points G. Hornig; 2.4 Three-dimensional reconnection at magnetic null points D. Pontin; 2.5 Three-dimensional flux tube reconnection M. Linton; Part III. Basic Theory of Collisionless Reconnection: 3.1 Fundamentals of collisionless reconnection J. Drake; 3.2 Diffusion region physics M. Hesse; 3.3 Onset of magnetic reconnection P. Pritchett; 3.4 Hall-MHD reconnection A. Bhattacharjee and J. Dorelli; 3.5 Role of current-aligned instabilities J. Büchner and W. Daughton; 3.6 Nonthermal particle acceleration M. Hoshino; Part IV. Reconnection in the Magnetosphere: 4.1 Reconnection at the magnetopause: concepts and models J. G. Dorelli and A. Bhattacharjee; 4.2 Observations of magnetopause reconnection K.-H. Trattner; 4.3 On the stability of the magnetotail K. Schindler; 4.4 Simulations of reconnection in the magnetotail J. Birn; 4.5 Observations of tail reconnection W. Baumjohann and R. Nakamura; 4.6 Remote sensing of reconnection M. Freeman; Part V. Reconnection in the Sun's Atmosphere: 5.1 Coronal heating E. R. Priest; 5.2 Separator reconnection D. Longcope; 5.3 Pinching of coronal fields V. Titov; 5.4 Numerical experiments on coronal heating K. Galsgaard; 5.5 Solar flares K. Kusano; 5.6 Particle acceleration in flares: theory T. Neukirch; 5.7 Fast particles in flares: observations L. Fletcher; 6. Open problems J. Birn and E. R. Priest; Bibliography; Index.

Birn, J.; Priest, E. R.

2007-01-01

140

Track Reconstruction Using a 3-D Map of the Target Magnetic Field Si-guang WANG Ya-jun MAO Hong-xue YE  

E-print Network

and 10375002), the Research Fund for the Doctoral Program of Higher Education of China(20070001008-xue YE School of Physics and State Key Laboratory of Nuclear Physics & Technology, Peking University, Beijing 100871, China Abstract Magnetic fields are often applied to the target zone of a particle beam

141

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

142

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

143

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

144

The Galileo magnetic field investigation  

Microsoft Academic Search

The Galileo Orbiter carries a complement of fields and particles instruments designed to provide data needed to shed light on the structure and dynamical variations of the Jovian magnetosphere. Many questions remain regarding the temporal and spatial properties of the magnetospheric magnetic field, how the magnetic field maintains corotation of the embedded plasma and the circumstances under which corotation breaks

M. G. Kivelson; K. K. Khurana; J. D. Means; C. T. Russell; R. C. Snare

1992-01-01

145

(Revised December 30, 2013) Magnetic Fields  

E-print Network

of the points where the magnetic fields of the Earth and the bar magnet sum to zero. INTRODUCTION A magnetic(Revised December 30, 2013) Magnetic Fields GOALS (1) To visualize the magnetic fields produced compasses to trace out the magnetic field lines of a single bar magnet on a large sheet of paper. (3

Collins, Gary S.

146

Magnetic response to applied electrostatic field in external magnetic field  

NASA Astrophysics Data System (ADS)

We show, within QED and other possible nonlinear theories, that a static charge localized in a finite domain of space becomes a magnetic dipole, if it is placed in an external (constant and homogeneous) magnetic field in the vacuum. The magnetic moment is quadratic in the charge, depends on its size and is parallel to the external field, provided the charge distribution is at least cylindrically symmetric. This magneto-electric effect is a nonlinear response of the magnetized vacuum to an applied electrostatic field. Referring to the simple example of a spherically symmetric applied field, the nonlinearly induced current and its magnetic field are found explicitly throughout the space; the pattern of the lines of force is depicted, both inside and outside the charge, which resembles that of a standard solenoid of classical magnetostatics.

Adorno, T. C.; Gitman, D. M.; Shabad, A. E.

2014-04-01

147

Theory of fossil magnetic field  

E-print Network

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

2014-01-01

148

Origin of cosmic magnetic fields.  

PubMed

We calculate, in the free Maxwell theory, the renormalized quantum vacuum expectation value of the two-point magnetic correlation function in de Sitter inflation. We find that quantum magnetic fluctuations remain constant during inflation instead of being washed out adiabatically, as usually assumed in the literature. The quantum-to-classical transition of super-Hubble magnetic modes during inflation allow us to treat the magnetic field classically after reheating, when it is coupled to the primeval plasma. The actual magnetic field is scale independent and has an intensity of few×10(-12)??G if the energy scale of inflation is few×10(16)??GeV. Such a field accounts for galactic and galaxy cluster magnetic fields. PMID:23971556

Campanelli, Leonardo

2013-08-01

149

NATIONAL HIGH MAGNETIC FIELD LABORATORY  

E-print Network

NATIONAL HIGH MAGNETIC FIELD LABORATORY SUPPORTED BY: THE NATIONAL SCIENCE FOUNDATION and THE STATE OF FLORIDA OPERATED BY: FLORIDA STATE UNIVERSITY · UNIVERSITY OF FLORIDA · LOS ALAMOS NATIONAL LABORATORY Page 15 2005 ANNUAL REPORT #12;2005 ANNUAL REPORT National High magnetic Field Laboratory 2005 NHMFL

Weston, Ken

150

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

151

Magnetic mapping and interpretation of an archaeological site in Syria  

NASA Astrophysics Data System (ADS)

Among the subsurface methods of exploration that have been developed to meet the new requirements of archaeological research, geophysical methods offer a very wide range of applications in the study of buried deposits. In their latest developments, the prospecting method based on the measurement of the magnetic field is particularly effective at very different types of sites, ranging from prehistoric times to the most recent. The measured magnetic field observed at a place and at a time, results from the vector sum of the main regional field, the effect of subsurface structures, local disturbances such as power lines, buildings, fences, and the diurnal variation (solar influence). The principle of the magnetic method is, from magnetic measurements on a flat plane above the prospected surface, to study the three-dimensional variations of magnetization producing the magnetic anomalies. The use of magnetic surveys for archaeological prospecting is a well-established and versatile technique, and wide ranges of data processing routines are often applied to further enhance acquired data or derive source parameters. The main purpose of this work was to acquire new magnetic data on the field and to propose quantitative interpretations of magnetic maps obtained on three archaeological sites of Bronze Age in Syria (Badiyah ANR program). More precisely, some results are presented concerning one of the three sites, the Tell Al-Rawda-site which corresponds to a circular city of Early Bronze Age with a radius of about 200 m. Several profiles are used to characterize magnetizations. A large portion of archaeological geophysical data are concerned primarily with identifying the location and spatial extent of buried remains, although the data collected are likely to contain further information relating to the depth and geometry of anomalous features. A simple magnetic model corresponding to rectangular structures uniformly magnetized associated to walls cannot explain the magnetic anomalies. On contrary, the shape of the magnetic anomalies implies to propose magnetized or non-magnetized structures with a width of several meters. To fit completely the shape of the magnetic anomaly, an iterative algorithm is used consisting of modifying the shape of the top of the magnetized layer.

khatib alkontar, Rozan AL; Munschy, Marc; Castel, Corinne; Quenet, Philippe

2014-05-01

152

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.

153

Magnetic field dispersion in the neighbourhood of Bok Globules  

NASA Astrophysics Data System (ADS)

We performed an observational study of the relation between the interstellar magnetic field alignment and star formation in twenty (20) sky regions containing Bok Globules. The presence of young stellar objects in the globules is verified by a search of infrared sources with spectral energy distribution compatible with a pre main-sequence star. The interstellar magnetic field direction is mapped using optical polarimetry. These maps are used to estimate the dispersion of the interstellar magnetic field direction in each region from a Gaussian fit, ? B . In addition to the Gaussian dispersion, we propose a new parameter, ?, to measure the magnetic field alignment that does not rely on any function fitting. Statistical tests show that the dispersion of the magnetic field direction is different in star forming globules relative to quiescent globules. Specifically, the less organised magnetic fields occur in regions having young stellar objects.

Rodrigues, C. V.; Magalhães, V. de S.; Vilas-Boas, J. W.; Racca, G.; Pereyra, A.

2014-08-01

154

Magnetic Field Measurements in Beam Guiding Magnets  

E-print Network

Electromagnets used as beam guiding elements in particle accelerators and colliders require very tight tole-rances on their magnetic fields and on their alignment along the particle path. This article describes the methods and equipment used for magnetic measurements in beam transport magnets. Descriptions are given of magnetic resonance techniques, various induction coil methods, Hall generator measurements, the fluxgate magnetometer as well as the recently developed method of beam based alignment. References of historical nature as well as citations of recent work are given. The present commercial availability of the different sensors and asso-ciated equipment is indicated. Finally we shall try to analyze possible future needs for developments in those fields.

Henrichsen, K N

1998-01-01

155

Quantitative magnetic susceptibility mapping without phase unwrapping using WASSR.  

PubMed

The magnetic susceptibility of tissue within and around an image voxel affects the magnetic field and thus the local frequency in that voxel. Recently, it has been shown that spatial maps of frequency can be used to quantify local susceptibility if the contributions of surrounding tissue can be deconvolved. Currently, such quantitative susceptibility mapping (QSM) methods employ gradient recalled echo (GRE) imaging to measure spatial differences in the signal phase evolution as a function of echo time, from which frequencies can be deduced. Analysis of these phase images, however, is complicated by phase wraps, despite the availability and usage of various phase unwrapping algorithms. In addition, lengthy high-resolution GRE scanning often heats the magnet bore, causing the magnetic field to drift over several Hertz, which is on the order of the frequency differences between tissues. Here, we explore the feasibility of applying the WAter Saturation Shift Referencing (WASSR) method for 3D whole brain susceptibility imaging. WASSR uses direct saturation of water protons as a function of frequency irradiation offset to generate frequency maps without phase wraps, which can be combined with any image or spectroscopy acquisition. By utilizing a series of fast short-echo-time direct saturation images with multiple radiofrequency offsets, a frequency correction for field drift can be applied based on the individual image phases. Regions of interest were delineated with an automated atlas-based method, and the average magnetic susceptibilities calculated from frequency maps obtained from WASSR correlated well with those from the phase-based multi-echo GRE approach at 3T. PMID:24113625

Lim, Issel Anne L; Li, Xu; Jones, Craig K; Farrell, Jonathan A D; Vikram, Deepti S; van Zijl, Peter C M

2014-02-01

156

Mapping hydrothermal alteration in Yellowstone National Park using magnetic methods  

Microsoft Academic Search

Yellowstone National Park (YNP) hosts a very large hydrothermal system with over 10,000 thermal features. Hydrothermal alteration in YNP has been mapped with field observations and remote-sensing imagery, but these methods can only detect alteration at the ground surface. Magnetic surveys are useful for detecting buried hydrothermal alteration as demonstrated by a recent high-resolution aeromagnetic survey in YNP (Finn and

C. Bouligand; J. M. Glen

2010-01-01

157

Preflare magnetic and velocity fields  

NASA Technical Reports Server (NTRS)

A characterization is given of the preflare magnetic field, using theoretical models of force free fields together with observed field structure to determine the general morphology. Direct observational evidence for sheared magnetic fields is presented. The role of this magnetic shear in the flare process is considered within the context of a MHD model that describes the buildup of magnetic energy, and the concept of a critical value of shear is explored. The related subject of electric currents in the preflare state is discussed next, with emphasis on new insights provided by direct calculations of the vertical electric current density from vector magnetograph data and on the role of these currents in producing preflare brightenings. Results from investigations concerning velocity fields in flaring active regions, describing observations and analyses of preflare ejecta, sheared velocities, and vortical motions near flaring sites are given. This is followed by a critical review of prevalent concepts concerning the association of flux emergence with flares

Hagyard, M. J.; Gaizauskas, V.; Chapman, G. A.; Deloach, A. C.; Gary, G. A.; Jones, H. P.; Karpen, J. T.; Martres, M.-J.; Porter, J. G.; Schmeider, B.

1986-01-01

158

Streamer propagation in magnetic field  

E-print Network

The propagation of a streamer near an insulating surface under the influence of a transverse magnetic field is theoretically investigated. In the weak magnetic field limit it is shown that the trajectory of the streamer has a circular form with a radius that is much larger than the cyclotron radius of an electron. The charge distribution within the streamer head is strongly polarized by the Lorentz force exerted perpendicualr to the streamer velocity. A critical magnetic field for the branching of a streamer is estimated. Our results are in good agreement with available experimental data.

Zhuravlev, V N; Vagner, I D; Wyder, P

1997-01-01

159

AC photovoltaic module magnetic fields  

SciTech Connect

Implementation of alternating current (AC) photovoltaic (PV) modules, particularly for distributed applications such as PV rooftops and facades, may be slowed by public concern about electric and magnetic fields (EMF). This paper documents magnetic field measurements on an AC PV module, complementing EMF research on direct-current PV modules conducted by PG and E in 1993. Although not comprehensive, the PV EMF data indicate that 60 Hz magnetic fields (the EMF type of greatest public concern) from PV modules are comparable to, or significantly less than, those from household appliances. Given the present EMF research knowledge, AC PV module EMF may not merit considerable concern.

Jennings, C.; Chang, G.J. [Pacific Gas and Electric Co., San Francisco, CA (United States); Reyes, A.B.; Whitaker, C.M. [Endecon Engineering, San Ramon, CA (United States)

1997-12-31

160

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

161

Neutron scattering in magnetic fields  

SciTech Connect

The use of magnetic fields in neutron scattering experimentation is reviewed briefly. Two general areas of application can be distinguished. In one the field acts to change the properties of the scattering sample; in the second the field acts on the neutron itself. Several examples are discussed. Precautions necessary for high precision polarized beam measurements are reviewed. 33 references.

Koehler, W.C.

1984-01-01

162

Lightning Magnetic Field Measurements around Langmuir Laboratory  

NASA Astrophysics Data System (ADS)

In the absence of artificial conductors, underground lightning transients are produced by diffusion of the horizontal surface magnetic field of a return stroke vertically downward into the conducting earth. The changing magnetic flux produces an orthogonal horizontal electric field, generating a dispersive, lossy transverse electromagnetic wave that penetrates a hundred meters or more into the ground according to the skin depth of the medium. In turn, the electric field produces currents that flow toward or away from the channel to ground depending on the stroke polarity. The underground transients can produce large radial horizontal potential gradients depending on the distance from the discharge and depth below the surface. In this study we focus on the surface excitation field. The goal of the work is to compare measurements of surface magnetic field waveforms B(t) at different distances from natural lightning discharges with simple and detailed models of the return stroke fields. In addition to providing input to the diffusion mechanism, the results should aid in further understanding return stroke field generation processes. The observational data are to be obtained using orthogonal sets of straightened Rogowski coils to measure magnetic field waveforms in N-S and E-W directions. The waveforms are sampled at 500 kS/s over 1.024 second time intervals and recorded directly onto secure digital cards. The instrument operates off of battery power for several days or weeks at a time in remote, unattended locations and measures magnetic field strengths of up to several tens of amperes/meter. The observations are being made in conjunction with collocated slow electric field change measurements and under good 3-D lightning mapping array (LMA) and fast electric field change coverage.

Stock, M.; Krehbiel, P. R.; Rison, W.; Aulich, G. D.; Edens, H. E.; Sonnenfeld, R. G.

2010-12-01

163

Longitude perception and bicoordinate magnetic maps in sea turtles.  

PubMed

Long-distance animal migrants often navigate in ways that imply an awareness of both latitude and longitude. Although several species are known to use magnetic cues as a surrogate for latitude, it is not known how any animal perceives longitude. Magnetic parameters appear to be unpromising as longitudinal markers because they typically vary more in a north-south rather than an east-west direction. Here we report, however, that hatchling loggerhead sea turtles (Caretta caretta) from Florida, USA, when exposed to magnetic fields that exist at two locations with the same latitude but on opposite sides of the Atlantic Ocean, responded by swimming in different directions that would, in each case, help them advance along their circular migratory route. The results demonstrate for the first time that longitude can be encoded into the magnetic positioning system of a migratory animal. Because turtles also assess north-south position magnetically, the findings imply that loggerheads have a navigational system that exploits the Earth's magnetic field as a kind of bicoordinate magnetic map from which both longitudinal and latitudinal information can be extracted. PMID:21353561

Putman, Nathan F; Endres, Courtney S; Lohmann, Catherine M F; Lohmann, Kenneth J

2011-03-22

164

N-flationary magnetic fields  

NASA Astrophysics Data System (ADS)

There is increasing interest in the role played by pseudo Nambu Goldstone bosons (pNGBs) in the construction of string-inspired models of inflation. In these models the inflaton is expected to be coupled to gauge fields, and will lead to the generation of magnetic fields that can be of cosmological interest. We study the production of such fields mainly focusing on the model of N-flation, where the collective effect of several pNGBs drives inflation. Because the fields produced are maximally helical, inverse cascade processes in the primordial plasma significantly increase their coherence length. We discuss under what conditions inflation driven by pNGBs can account for the cosmological magnetic fields observed. A constraint on the parameters of this class of inflationary scenarios is also derived by requiring that the magnetic field does not backreact on the inflating background.

Anber, Mohamed M.; Sorbo, Lorenzo

2006-10-01

165

Field of the Magnetic Monopole  

E-print Network

This paper shows that based upon the Helmholtz decomposition theorem the field of a stationary magnetic monopole, assuming it exists, cannot be represented by a vector potential. Persisting to use vector potential in monopole representation violates fundamentals of mathematics. The importance of this finding is that the vector potential representation was crucial to the original prediction of the quantized value for a magnetic charge.

A. R. Hadjesfandiari

2007-01-19

166

Neutron in Strong Magnetic Fields  

E-print Network

Relativistic world-line Hamiltonian for strongly interacting 3q systems in magnetic field is derived from the path integral for the corresponding Green's function. The neutral baryon Hamiltonian in magnetic field obeys the pseudomomentum conservation and allows a factorization of the c.m. and internal motion. The resulting expression for the baryon mass in magnetic field is written explicitly with the account of hyperfine, OPE and OGE (color Coulomb) interaction. The neutron mass is fast decreasing with magnetic field, losing 1/2 of its value at eB~0.25 GeV^2 and is nearly zero at eB~0.5 GeV^2. Possible physical consequences of the calculated mass trajectory of the neutron, M_n(B), are presented and discussed.

M. A. Andreichikov; B. O. Kerbikov; V. D. Orlovsky; Yu. A. Simonov

2013-12-08

167

Sheared Plasma Rotation in Partially Stochastic Magnetic Fields  

SciTech Connect

It is shown that resonant magnetic perturbations generate sheared flow velocities in magnetized plasmas. Stochastic magnetic fields in incomplete chaos influence the drift motion of electrons and ions differently. Using a fast mapping technique, it is demonstrated that a radial electric field is generated due to the different behavior of passing particles (electrons and ions) in tokamak geometry; magnetic trapping of ions is neglected. Radial profiles of the polodial velocity resulting from the force balance in the presence of a strong toroidal magnetic field are obtained. Scaling laws for plasma losses and the forms of sheared plasma rotation profiles are discussed.

Wingen, A.; Spatschek, K. H. [Institut fuer Theoretische Physik, Heinrich-Heine-Universitaet Duesseldorf, D-40225 Duesseldorf (Germany)

2009-05-08

168

Review of magnetic field observations  

NASA Technical Reports Server (NTRS)

Recent observations of magnetic fields in the magnetosphere are reviewed, and critical experiments and data are identified for theoretical analysis and interpretation. Quantitative studies of the solar wind interaction with the earth's magnetic field, regional measurements near the earth's equator at R = 2-8 R sub E, the polar cusp region of the geomagnetosphere, and structural models of the neutral sheet region in the geomagnetic tail are considered.

Ness, N. F.

1971-01-01

169

Chiral transition with magnetic fields  

E-print Network

We study the nature of the chiral transition for an effective theory with spontaneous breaking of symmetry, where charged bosons and fermions are subject to the effects of a constant external magnetic field. The problem is studied in terms of the relative intensity of the magnetic field with respect to the mass and the temperature. When the former is the smallest of the scales, we present a suitable method to obtain magnetic and thermal corrections up to ring order at high temperature. By these means, we solve the problem of the instability in the boson sector for these theories, where the squared masses, taken as functions of the order parameter, can vanish and even become negative. The solution is found by considering the screening properties of the plasma, encoded in the resummation of the ring diagrams at high temperature. We also study the case where the magnetic field is the intermediate of the three scales and explore the nature of the chiral transition as we vary the field strength, the coupling constants and the number of fermions. We show that the critical temperature for the restoration of chiral symmetry monotonically increases from small to intermediate values of the magnetic fields and that this temperature is always above the critical temperature for the case when the magnetic field is absent.

Alejandro Ayala; Luis Alberto Hernandez; Ana Julia Mizher; Juan Cristobal Rojas; Cristian Villavicencio

2014-04-25

170

Optical sensor of magnetic fields  

DOEpatents

An optical magnetic field strength sensor for measuring the field strength of a magnetic field comprising a dilute magnetic semi-conductor probe having first and second ends, longitudinally positioned in the magnetic field for providing Faraday polarization rotation of light passing therethrough relative to the strength of the magnetic field. Light provided by a remote light source is propagated through an optical fiber coupler and a single optical fiber strand between the probe and the light source for providing a light path therebetween. A polarizer and an apparatus for rotating the polarization of the light is provided in the light path and a reflector is carried by the second end of the probe for reflecting the light back through the probe and thence through the polarizer to the optical coupler. A photo detector apparatus is operably connected to the optical coupler for detecting and measuring the intensity of the reflected light and comparing same to the light source intensity whereby the magnetic field strength may be calculated.

Butler, M.A.; Martin, S.J.

1986-03-25

171

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

172

Twinsat earth gravity field mapping  

NASA Technical Reports Server (NTRS)

Results of a sensitivity study on the proposed Lo-Lo (Twinsat) satellite-to-satellite tracking mission are described. The relative range-rate signal due to a local gravitational anomaly is investigated as a function of height and satellite separation. It is shown that the signal strength is weak and that an optimal combination of signal strength and resolution is achieved when the satellites are separated by 3 deg along-track. The signal does not resolve point masses closer than 5 deg apart when the satellites are at 300 km altitude. The influence of other factors on the system is evaluated, including the low frequency gravitation field effect on the orbit and the dependence of the noise of the data type on (electronic) integration time.

Lowrey, B. E.

1975-01-01

173

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

174

Active Region Magnetic Fields. I. Plage Fields  

Microsoft Academic Search

We present observations taken with the Advanced Stokes Polarimeter (ASP) in active-region plages and study the frequency distribution of the magnetic field strength (B), inclination with respect to vertical ( gamma ), azimuthal orientation ( chi ), and filling factor (f). The most common values at disk center are B = 1400 G, gamma < 10 deg, no preferred east-west

V. Martinez Pillet; B. W. Lites; A. Skumanich

1997-01-01

175

Magnetic fields in O stars  

NASA Astrophysics Data System (ADS)

During the last decade, large-scale, organized (generally dipolar) magnetic fields with strengths between 0.1 and 20 kG have been detected in dozens of OB stars. This contribution reviews the impact of such fields on the stellar winds of O-type stars, with emphasis on variability and X-ray emission.

Nazé, Y.

2014-11-01

176

Noninvasive Functional Brain Mapping Using Registered Transcranial Magnetic Stimulation  

E-print Network

Non­invasive Functional Brain Mapping Using Registered Transcranial Magnetic Stimulation G Brain Mapping Using Registered Transcranial Magnetic Stimulation January 22, 1996 Abstract We describe the functional regions of the brain using a tran­ scranial magnetic stimulation (TMS) device. This device, when

177

Magnetization and rotation of MTG HTSC ring in magnetic field  

Microsoft Academic Search

The magnetization of a melt-texture growth (MTG) HTSC ring has been studied. It is shown that the magnetic field inside the ring is larger than the external field under a certain range of external magnetic fields. We have also investigated the magnetic field dependence of the response of a detective coil near a rotating superconducting ring. The responses of the

E. V. Postrekhin; L. W. Zhou; K. J. Huang; C. B. Cai; S. M. Gong; Y. X. Fu

1996-01-01

178

Using Field Sketch Mapping to Teach Basic Mapping Concepts in Elementary School Geography  

Microsoft Academic Search

Field mapping is a useful way to introduce a number of mapping concepts to elementary school students. Concepts such as scale and distance are difficult to comprehend when presented using wall maps. Sketch maps allow the students to make measurements themselves and see how to use those measurements to make a map. This paper describes a field sketch mapping project

Richard Taketa

1996-01-01

179

Magnetic field investigations on low cost missions  

Microsoft Academic Search

Magnetic fields pervade all of space and provide important diagnostic information on the nature of processes occurring within and around solar system objects. Thus magnetic investigations are frequently included on planetary missions. Since spacecraft subsystems can generate magnetic fields that may interfere with the measurement of the ambient field, magnetic cleanliness programs are usually instituted to minimize such extraneous magnetic

R. C. Snare; C.T. Russell

1995-01-01

180

The magnetic map of hatchling loggerhead sea turtles Kenneth J Lohmann, Nathan F Putman and Catherine MF Lohmann  

E-print Network

The magnetic map of hatchling loggerhead sea turtles Kenneth J Lohmann, Nathan F Putman American coast. Hatchlings in the open sea are guided at least partly by a `magnetic map' in which regional magnetic fields function as navigational markers and elicit changes in swimming direction at crucial

Lohmann, Kenneth J.

181

Maps between Deformed and Ordinary Gauge Fields  

E-print Network

In this paper, we introduce a map between the q-deformed gauge fields defined on the GL$_{q}(N) $-covariant quantum hyperplane and the ordinary gauge fields. Perturbative analysis of the q-deformed QED at the classical level is presented and gauge fixing $\\grave{a} $ la BRST is discussed. An other star product defined on the hybrid $(q,h) $% -plane is explicitly constructed .

L. Mesref

2005-04-13

182

Multi robot mapping using force field simulation  

Microsoft Academic Search

This paper describes a novel approach, called Force Field Simulation, to multi robot map- ping that works under the constraints given in autonomous search and rescue robotics. Extremely poor prealignment, lack of landmarks, and minimal overlap between scans are the main challenges. The presented algorithm solves the alignment problem of such laser scans utilizing a gradient descent approach motivated by

Rolf Lakaemper; Nagesh Adluru; Longin Jan Latecki; Raj Madhavan

2007-01-01

183

Multi Robot Mapping using Force Field Simulation  

Microsoft Academic Search

This paper describes a novel approach, called Force Field Simulation to multi robot mapping that works under the constraints given in autonomous search and rescue robotics. Extremely poor pre-alignment, lack of landmarks and minimal overlap between scans are the main challenges. The presented al- gorithm solves the alignment problem of such laser scans utilizing a gradient descent approach motivated by

Rolf Lakaemper; Raj Madhavan; Gaithersburg NIST

184

Origin of primordial magnetic fields  

SciTech Connect

Magnetic fields of intensities similar to those in our galaxy are also observed in high redshift galaxies, where a mean field dynamo would not have had time to produce them. Therefore, a primordial origin is indicated. It has been suggested that magnetic fields were created at various primordial eras: during inflation, the electroweak phase transition, the quark-hadron phase transition (QHPT), during the formation of the first objects, and during reionization. We suggest here that the large-scale fields {approx}{mu}G, observed in galaxies at both high and low redshifts by Faraday rotation measurements (FRMs), have their origin in the electromagnetic fluctuations that naturally occurred in the dense hot plasma that existed just after the QHPT. We evolve the predicted fields to the present time. The size of the region containing a coherent magnetic field increased due to the fusion of smaller regions. Magnetic fields (MFs) {approx}10 {mu}G over a comoving {approx}1 pc region are predicted at redshift z{approx}10. These fields are orders of magnitude greater than those predicted in previous scenarios for creating primordial magnetic fields. Line-of-sight average MFs {approx}10{sup -2} {mu}G, valid for FRMs, are obtained over a 1 Mpc comoving region at the redshift z{approx}10. In the collapse to a galaxy (comoving size {approx}30 kpc) at z{approx}10, the fields are amplified to {approx}10 {mu}G. This indicates that the MFs created immediately after the QHPT (10{sup -4} s), predicted by the fluctuation-dissipation theorem, could be the origin of the {approx}{mu}G fields observed by FRMs in galaxies at both high and low redshifts. Our predicted MFs are shown to be consistent with present observations. We discuss the possibility that the predicted MFs could cause non-negligible deflections of ultrahigh energy cosmic rays and help create the observed isotropic distribution of their incoming directions. We also discuss the importance of the volume average magnetic field predicted by our model in producing the first stars and in reionizing the Universe.

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

2008-02-15

185

Magnetic field tomography, helical magnetic fields and Faraday depolarization  

NASA Astrophysics Data System (ADS)

Wide-band radio polarization observations offer the possibility to recover information about the magnetic fields in synchrotron sources, such as details of their three-dimensional configuration, that has previously been inaccessible. The key physical process involved is the Faraday rotation of the polarized emission in the source (and elsewhere along the wave's propagation path to the observer). In order to proceed, reliable methods are required for inverting the signals observed in wavelength space into useful data in Faraday space, with robust estimates of their uncertainty. In this paper, we examine how variations of the intrinsic angle of polarized emission ?0 with the Faraday depth ? within a source affect the observable quantities. Using simple models for the Faraday dispersion F(?) and ?0(?), along with the current and planned properties of the main radio interferometers, we demonstrate how degeneracies among the parameters describing the magneto-ionic medium can be minimized by combining observations in different wavebands. We also discuss how depolarization by Faraday dispersion due to a random component of the magnetic field attenuates the variations in the spectral energy distribution of the polarization and shifts its peak towards shorter wavelengths. This additional effect reduces the prospect of recovering the characteristics of the magnetic field helicity in magneto-ionic media dominated by the turbulent component of the magnetic field.

Horellou, C.; Fletcher, A.

2014-07-01

186

Dilation of force-free magnetic flux tubes. [solar magnetic field profiles  

NASA Technical Reports Server (NTRS)

A general study is presented of the mapping functions which relate the magnetic-field profiles across a force-free rope in segments subjected to various external pressures. The results reveal that if the external pressure falls below a certain critical level (dependent on the flux-current relation which defines the tube), the magnetic profile consists of an invariant core sheathed in a layer permeated by an azimuthal magnetic field.

Frankenthal, S.

1977-01-01

187

The vector structure of active magnetic fields  

NASA Technical Reports Server (NTRS)

Observations are needed to show the form of the strains introduced into the fields above the surface of the Sun. The longitudinal component alone does not provide the basic information, so that it has been necessary in the past to use the filamentary structure observed in H sub alpha to supplement the longitudinal information. Vector measurements provide the additional essential information to determine the strains, with the filamentary structure available as a check for consistency. It is to be expected, then, that vector measurements will permit a direct mapping of the strains imposed on the magnetic fields of active regions. It will be interesting to study the relation of those strains to the emergence of magnetic flux, flares, eruptive prominences, etc. In particular we may hope to study the relaxation of the strains via the dynamical nonequilibrium.

Parker, E. N.

1985-01-01

188

Understanding Modern Magnets through Conformal Mapping  

SciTech Connect

When I had to choose, within some narrow range, the topic of this paper, I received great help from a colleague in Berkeley and from Prof. Little when it was suggested that I should pick among the possible subjects of my talk the subject that Prof. Bloch would have enjoyed most. Since Prof. Bloch would prefer a scalpel over a sword every time, I hope and think that most people will approve my choice. When one intends to talk about a subject that is as old as conformal mapping and one does not want to lose the audience in a very short time, it is advisable to start by explaining both the motivation for the talk as well as the goals one has in mind when giving the talk. This particular talk has been motivated by the increasing frequency with which one hears, from people that ought to know better, statements like: 'Conformal mapping is really a thing of the past because of all the marvelous computer programs that we now have'. Even though, or more likely because, I have been intimately involved in the development of some large and widely used computer codes, I am deeply disturbed by such statements since they indicate a severe lack of understanding of the purpose of conformal mapping techniques, computers, and computer codes. In my view, conformal mapping can be an extremely powerful computational technique, and the easy availability of computers has made that aspect even more important now than it has been in the past. Additionally, and more importantly, conformal mapping can give very deep and unique insight into problems, giving often solutions to problems that can not be obtained with any other method, in particular not with computers. Wanting to demonstrate in particular the latter part, I set myself two goals for this talk: (1) I want to show with the help of a number of examples that conformal mapping is a unique and enormously powerful tool for thinking about, and solving, problems. Usually one has to write down only a few equations, and sometimes none at all. When I started getting involved in work for which conformal mapping seemed to be a powerful tool, I did not think that I would ever be able to use that technique successfully because it seemed to require a nearly encyclopedic memory, an impression that was strengthened when I saw H.Kober's Dictionary of Conformal Representations (ref. 1). This attitude changed when I started to realize that beyond the basics of the theory of a function of a complex variable, I needed to know only about a handful of conformal maps and procedures. Consequently, my second goal for this talk is to: (2) Show that in most cases conformal mapping functions can be obtained by formulating the underlying physics appropriately. This means particularly that encyclopedic knowledge of conformal maps is not necessary for successful use of conformal mapping techniques. To demonstrate these facts I have chosen examples from an area of physics/engineering in which I am active, namely accelerator physics. In order to do that successfully I start with a brief introduction into high energy charged particle storage ring technology, even though not all examples used in this paper to elucidate my points come directly from this particular field of accelerator technology. This is followed by a brief summary of the most important properties of functions of a complex variable. When reading this introduction into the relevant mathematics, the reader needs to keep in mind that this is not a mathematics essay, but a demonstration how beautiful and powerful, but not always appreciated, mathematics can be if used by a physicist or engineer to solve some real life problems.

Halbach, K.

1989-10-27

189

APPLICATION OF SATELLITE MAGNETIC ANOMALY DATA TO CURIE ISOTHERM MAPPING  

Microsoft Academic Search

A boundary condition on temperature the Curie temperature is restricted to a narrow at depth in the continental crust can in principle range (aboUt 520ø-560øC). be obtained by mapping of the Curie isotherm where it forms the base of the magnetic crust. An approach to mapping magnetic crustal thickness using satellite magnetic anomaly data is describ- ed. Because magnetic crustal

M. A. Mayhew

1982-01-01

190

Tracing the Magnetic Field in Orion A  

NASA Technical Reports Server (NTRS)

We use extensive 350 micron polarimetry and continuum maps obtained with Hertz and SHARC II along with HCN and HCO(sup +) spectroscopic data to trace the orientation of the magnetic field in the Orion A star-forming region. Using the polarimetry data, we find that the direction of the projection of the magnetic field in the plane of the sky relative to the orientation of the integral-shaped filament varies considerably as one moves from north to south. While in IRAS 05327-0457 and OMC-3 MMS 1-6 the projection of the field is primarily perpendicular to the filament it becomes better aligned with it at OMC-3 MMS 8-9 and well aligned with it at OMC-2 FIR 6. The OMC-2 FIR 4 cloud, located between the last two, is a peculiar object where we find almost no polarization. There is a relatively sharp boundary within its core where two adjacent regions exhibiting differing polarization angles merge. The projected angle of the field is more complicated in OMC-1 where it exhibits smooth variations in its orientation across the face of this massive complex. We also note that while the relative orientation of the projected angle of the magnetic field to the filament varies significantly in the OMC-3 and OMC-2 regions, its orientation relative to a fixed position on the sky shows much more stability. This suggests that, perhaps, the orientation of the field is relatively unaffected by the mass condensations present in these parts of the molecular cloud. By combining the polarimetry and spectroscopic data we were able to measure a set of average d u e s for the inclination angle of the magnetic field relative to the line of sight. We find that the field is oriented quite close to the plane of the sky in most places. More precisely, the inclination of the magnetic field is approx. = 73 deg around OMC-3 MMS 6, approx. = 74 deg at OMC-3 MMS 8-9, approx. = 80 deg at OMC-2 FIR 4, approx. = 65 deg in the northeastern part of OMC-1, and approx. = 49 deg in the Bas. The small difference in the inclination of the field between OMC-3 and OMC-2 seems to strengthen the idea that the orientation of the magnetic field is relatively unaffected by the agglomeration of matter located in these regions. We also present polarimetry data for the OMC-4 region located some 13 min. south of OMC-1.

Dowell, C. Darren; Hildebrand, Roger H.; Dotson, Jessie L.; Vaillancourt, John E.; Phillips, Thomas G.; Peng, Rui-Sheng; Bastien, Pierre

2003-01-01

191

Magnetospheric mapping with quantitative geomagnetic field models  

NASA Technical Reports Server (NTRS)

The Mead-Fairfield geomagnetic field models were used to trace field lines between the outer magnetosphere and the earth's surface. The results are presented in terms of ground latitude and local time contours projected to the equatorial plane and into the geomagnetic tail. With these contours various observations can be mapped along field lines between high and low altitudes. Low altitudes observations of the polar cap boundary, the polar cusp, the energetic electron trapping boundary and the sunward convection region are projected to the equatorial plane and compared with the results of the model and with each other. The results provide quantitative support to the earlier suggestions that the trapping boundary is associated with the last closed field line in the sunward hemisphere, the polar cusp is associated with the region of the last closed field line, and the polar cap projects to the geomagnetic tail and has a low latitude boundary corresponding to the last closed field line.

Fairfield, D. H.; Mead, G. D.

1973-01-01

192

Scalar magnetic anomaly maps of Earth derived from POGO and Magsat data  

NASA Technical Reports Server (NTRS)

A new Polar Orbit Geophysical Observatory (POGO) scalar magnetic anomaly map at 400 km altitude is presented which consists of spherical harmonics of degree 15-60. On the basis of the common features of this map with two new Magsat anomaly maps, dawn and dusk, two scalar magnetic anomaly maps of the Earth are presented using two selection criteria with different levels of stringency. These selection criteria suppress the noncrustal components of the original maps by different amounts. The more stringent selection criteria seek to eliminate as much contamination as possible, at the expense of suppressing some anomaly signal. This map is represented by spherical harmonics of degree 15-60. The less stringent selection criteria seek to retain as much crustal signal as possible, at the expense of also retaining some contaminating fields. This map is represented by spherical harmonics of degree 15-65. The resulting two maps are highly correlated with degree correlation coefficients greater than 0.8.

Arkani-Hamed, Jafar; Langel, Robert A.; Purucker, Mike

1994-01-01

193

Magnetic fields around black holes  

NASA Astrophysics Data System (ADS)

Active Galactic Nuclei are the most powerful long-lived objects in the universe. They are thought to harbor supermassive black holes that range from 1 million solar masses to 1000 times that value and possibly greater. Theory and observation are converging on a model for these objects that involves the conversion of gravitational potential energy of accreting gas to radiation as well as Poynting flux produced by the interaction of the rotating spacetime and the electromagnetic fields originating in the ionized accretion flow. The presence of black holes in astrophysics is taking center stage, with the output from AGN in various forms such as winds and jets influencing the formation and evolution of the host galaxy. This dissertation addresses some of the basic unanswered questions that plague our current understanding of how rotating black holes interact with their surrounding magnetized accretion disks to produce the enormous observed energy. Two magnetic configurations are examined. The first involves magnetic fields connecting the black hole with the inner accretion disk and the other involves large scale magnetic fields threading the disk and the hole. We study the effects of the former type by establishing the consequences that magnetic torques between the black hole and the inner accretion disk have on the energy dissipation profile. We attempt a plausible explanation to the observed "Deep Minimum" state in the Seyfert galaxy MCG-6- 30-15. For the latter type of magnetic geometry, we study the effects of the strength of the magnetic field threading the black hole within the context of the cherished Blandford & Znajek mechanism for black hole spin energy extraction. We begin by addressing the problem in the non-relativistic regime where we find that the black hole-threading magnetic field is stronger for greater disk thickness, larger magnetic Prandtl number, and for a larger accretion disk. We then study the problem in full relativity where we show that our Newtonian results are excellent approximations for slowly spinning black holes. We proceed to address the issue of the spin dependence of the Blandford & Znajek power. The result we choose to highlight is our finding that given the validity of our assumption for the dynamical behavior of the so-called plunge region in black hole accretors, rotating black holes produce maximum Poynting flux via the Blandford & Znajek process for a black hole spin parameter of about a [approximate] 0.8. This is contrary to the conventional claim that the maximum electromagnetic flux is achieved for highest black hole spin.

Garofalo, David A. G.

194

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

195

LARGE-SCALE KINEMATICS, ASTROCHEMISTRY, AND MAGNETIC FIELD STUDIES OF MASSIVE STAR-FORMING REGIONS THROUGH HC{sub 3}N, HNC, AND C{sub 2}H MAPPINGS  

SciTech Connect

We have mapped 27 massive star-forming regions associated with water masers using three dense gas tracers: HC{sub 3}N 10-9, HNC 1-0, and C{sub 2}H 1-0. The FWHM sizes of HNC clumps and C{sub 2}H clumps are about 1.5 and 1.6 times higher than those of HC{sub 3}N, respectively, which can be explained by the fact that HC{sub 3}N traces more dense gas than HNC and C{sub 2}H. We found evidence for an increase in the optical depth of C{sub 2}H with a 'radius' from the center to the outer regions in some targets, supporting the chemical model of C{sub 2}H. The C{sub 2}H optical depth is found to decline as molecular clouds evolve to a later stage, suggesting that C{sub 2}H might be used as a 'chemical clock' for molecular clouds. The large-scale kinematic structure of clouds was investigated with three molecular lines. All of these sources show significant velocity gradients. The magnitudes of gradient are found to increase toward the inner region, indicating the differential rotation of clouds. Both the ratio of rotational to gravitational energy and the specific angular momentum seem to decrease toward the inner region, implying the obvious angular momentum transfer, which might be caused by magnetic braking. The average magnetic field strength and number density of molecular clouds is derived using the uniform magnetic sphere model. The derived magnetic field strengths range from 3 to 88 {mu}G, with a median value of 13 {mu}G. The mass-to-flux ratio of the molecular cloud is calculated to be much higher than the critical value with derived parameters, which agrees well with numerical simulations.

Li Juan; Wang Junzhi; Gu Qiusheng; Zheng Xingwu [School of Astronomy and Space Science, Nanjing University, 22 Hankou RD, Nanjing 210093 (China); Zhang Zhiyu, E-mail: ljuan@nju.edu.cn [Purple Mountain Observatory, CAS, 2 West Beijing Road, Nanjing 210008 (China)

2012-01-20

196

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

197

Transverse Magnetic Field Propellant Isolator  

NASA Technical Reports Server (NTRS)

An alternative high voltage isolator for electric propulsion and ground-based ion source applications has been designed and tested. This design employs a transverse magnetic field that increases the breakdown voltage. The design can greatly enhance the operating range of laboratory isolators used for high voltage applications.

Foster, John E.

2000-01-01

198

Flux Transport and the Sun's Global Magnetic Field  

NASA Technical Reports Server (NTRS)

The Sun s global magnetic field is produced and evolved through the emergence of magnetic flux in active regions and its transport across the solar surface by the axisymmetric differential rotation and meridional flow and the non-axisymmetric convective flows of granulation, supergranulation, and giant cell convection. Maps of the global magnetic field serve as the inner boundary condition for space weather. The photospheric magnetic field and its evolution determine the coronal and solar wind structures through which CMEs must propagate and in which solar energetic particles are accelerated and propagate. Producing magnetic maps which best represent the actual field configuration at any instant requires knowing the magnetic field over the observed hemisphere as well as knowing the flows that transport flux. From our Earth-based vantage point we only observe the front-side hemisphere and each pole is observable for only six months of the year at best. Models for the surface magnetic flux transport can be used to provide updates to the magnetic field configuration in those unseen regions. In this presentation I will describe successes and failures of surface flux transport and present new observations on the structure, the solar cycle variability, and the evolution of the flows involved in magnetic flux transport. I find that supergranules play the dominant role due to their strong flow velocities and long lifetimes. Flux is transported by differential rotation and meridional flow only to the extent that the supergranules participate in those two flows.

Hathaway, David H.

2010-01-01

199

Equivalent magnetization over the World's Ocean and the World Digital Magnetic Anomaly Map  

NASA Astrophysics Data System (ADS)

As a by-product of our recent work to build a candidate model over the oceans for the second version of the World Digital Magnetic Anomaly Map (WDMAM), we derived global distributions of the equivalent magnetization in oceanic domains. In a first step, we use classic point source forward modeling on a spherical Earth to build a forward model of the marine magnetic anomalies at sea-surface. We estimate magnetization vectors using the age map of the ocean floor, the relative plate motions, the apparent polar wander path for Africa, and a geomagnetic reversal time scale. We assume two possible magnetized source geometry, involving both a 1 km-thick layer bearing a 10 A/m magnetization either on a regular spherical shell with a constant, 5 km-deep, bathymetry (simple geometry) or following the topography of the oceanic basement as defined by the bathymetry and sedimentary thickness (realistic geometry). Adding a present-day geomagnetic field model allows the computation of our initial magnetic anomaly model. In a second step, we adjust this model to the existing marine magnetic anomaly data, in order to make it consistent with these data. To do so, we extract synthetic magnetic along the ship tracks for which real data are available and we compare quantitatively the measured and computed anomalies on 100, 200 or 400 km-long sliding windows (depending the spreading rate). Among the possible comparison criteria, we discard the maximal range - too dependent on local values - and the correlation and coherency - the geographical adjustment between model and data being not accurate enough - to favor the standard deviation around the mean value. The ratio between the standard deviations of data and model on each sliding window represent an estimate of the magnetization ratio causing the anomalies, which we interpolate to adjust the initial magnetic anomaly model to the data and therefore compute a final model to be included in our WDMAM candidate over the oceanic regions lacking data. The above ratio, after division by the magnetization of 10 A/m used in the model, represents an estimate of the equivalent magnetization under the considered magnetized source geometry. The resulting distributions of equivalent magnetization are further discussed in terms of mid-ocean ridges, presence of hotspots and oceanic plateaus, and the age of the oceanic lithosphere. Global marine magnetic data sets and models represent a useful tool to assess first order magnetic properties of the oceanic lithosphere.

Dyment, Jerome; Choi, Yujin; Hamoudi, Mohamed; Thébault, Erwan; Quesnel, Yoann; Roest, Walter; Lesur, Vincent

2014-05-01

200

Diffusion of magnetic field via turbulent reconnection  

Microsoft Academic Search

The diffusion of astrophysical magnetic fields in conducting fluids in the presence of turbulence depends on whether magnetic fields can change their topology via reconnection in highly conducting media. Recent progress in understanding fast magnetic reconnection in the presence of turbulence is reassuring that the magnetic field behavior in computer simulations and turbulent astrophysical environments is similar, as far as

Reinaldo Santos de Lima; Alexander Lazarian; Elisabete M. de Gouveia Dal Pino; Jungyeon Cho

2010-01-01

201

Separation of magnetic field lines  

SciTech Connect

The field lines of magnetic fields that depend on three spatial coordinates are shown to have a fundamentally different behavior from those that depend on two coordinates. Unlike two-coordinate cases, a flux tube in a magnetic field that depends on all three spatial coordinates that has a circular cross section at one location along the tube characteristically has a highly distorted cross section at other locations. In an ideal evolution of a magnetic field, the current densities typically increase. Crudely stated, if the current densities increase by a factor {sigma}, the ratio of the long to the short distance across a cross section of a flux tube characteristically increases by e{sup 2{sigma}}, and the ratio of the longer distance to the initial radius increases as e{sup {sigma}}. Electron inertia prevents a plasma from isolating two magnetic field structures on a distance scale shorter than c/{omega}{sub pe}, which is about 10 cm in the solar corona, and reconnection must be triggered if {sigma} becomes sufficiently large. The radius of the sun, R{sub Circled-Dot-Operator }=7 Multiplication-Sign 10{sup 10}cm is about e{sup 23} times larger, so when {sigma} Greater-Than-Or-Equivalent-To 23, two lines separated by c/{omega}{sub pe} at one location can be separated by the full scale of any magnetic structures in the corona at another. The conditions for achieving a large exponentiation, {sigma}, are derived, and the importance of exponentiation is discussed.

Boozer, Allen H. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)

2012-11-15

202

Initial mapping and interpretation of lunar crustal magnetic anomalies using Lunar Prospector magnetometer data  

Microsoft Academic Search

Maps of relatively strong crustal magnetic field anomalies detected at low altitudes with the magnetometer instrument on Lunar Prospector are presented. On the lunar nearside, relatively strong anomalies are mapped over the Reiner Gamma Formation on western Oceanus Procellarum and over the Rima Sirsalis rille on the southwestern border of Oceanus Procellarum. The main Rima Sirsalis anomaly does not correlate

L. L. Hood; A. Zakharian; J. Halekas; D. L. Mitchell; R. P. Lin; M. H. Acuña; A. B. Binder

2001-01-01

203

Mapping electromagnetic fields near a subwavelength hole  

NASA Astrophysics Data System (ADS)

We study, both experimentally and theoretically, the scattering of electromagnetic waves by a subwavelength hole fabricated in a thin metallic film. We employ the scanning near-field optical microscopy in order to reconstruct experimentally the full three-dimensional structure of the electromagnetic fields in the vicinity of the hole. We observe an interference of all excited waves with an incident laser beam which allows us to gain the information about the wave phases. Along with the well-known surface plasmon polaritons propagating primarily in the direction of the incident beam polarization, we observe the free-space radiation diffracted by the hole. We compare the experimental results with the fields of pure electric and pure magnetic dipoles as well as with direct numerical simulations. We confirm that a single hole in a thin metallic film excited at the normal incidence manifests itself as an effective magnetic dipole in the visible spectral range.

Permyakov, D. V.; Mukhin, I. S.; Shishkin, I. I.; Samusev, A. K.; Belov, P. A.; Kivshar, Yu. S.

2014-08-01

204

Magnetic fields in the sun  

NASA Technical Reports Server (NTRS)

The observed properties of solar magnetic fields are reviewed, with particular reference to the complexities imposed on the field by motions of the highly conducting gas. Turbulent interactions between gas and field lead to heating or cooling of the gas according to whether the field energy density is less or greater than the maximum kinetic energy density in the convection zone. The field strength above which cooling sets in is 700 gauss. A weak solar dipole field may be primeval, but dynamo action is also important in generating new flux. The dynamo is probably not confined to the convection zone, but extends throughout most of the volume of the sun. Planetary tides appear to play a role in driving the dynamo.

Mullan, D. J.

1974-01-01

205

Edge effects on forces and magnetic fields produced by a conductor moving past a magnet  

SciTech Connect

Experiments have been performed to further understand the forces acting on magnets moving along and over the edge of a continuous conducting sheet and to produce a comprehensive data set for the validation of analysis methods. Mapping the magnetic field gives information about the eddy currents induced in the conductor, which agrees with numerical calculations.

Mulcahy, T.M.; Hull, J.R.; Almer, J.D. [Argonne National Lab., IL (United States); Rossing, T.D. [Northern Illinois Univ., De Kalb, IL (United States)

1992-04-01

206

Edge effects on forces and magnetic fields produced by a conductor moving past a magnet  

SciTech Connect

Experiments have been performed to further understand the forces acting on magnets moving along and over the edge of a continuous conducting sheet and to produce a comprehensive data set for the validation of analysis methods. Mapping the magnetic field gives information about the eddy currents induced in the conductor, which agrees with numerical calculations.

Mulcahy, T.M.; Hull, J.R.; Almer, J.D. (Argonne National Lab., IL (United States)); Rossing, T.D. (Northern Illinois Univ., De Kalb, IL (United States))

1992-01-01

207

The steady part of the secular variation of the Earth's magnetic field  

Microsoft Academic Search

The secular variation of the Earth's magnetic field results from the effects of magnetic induction in the fluid outer core and from the effects of magnetic diffusion in the core and the mantle. Adequate observations to map the magnetic field at the core-mantle boundary extend back over three centuries, providing a model of the secular variation at the core-mantle boundary.

Jeremy Bloxham

1992-01-01

208

Microwave ovens: mapping the electrical field distribution.  

PubMed

Uniformity of electric field intensity of microwaves within the microwave oven cavity is necessary to ensure even load-heating, and is particularly important in pathology procedures where small volume irradiation is carried out. A simple and rapid method for mapping electric field distribution, using reversible thermographic paint, is described. Spatial heating patterns for various positions, and the effects of introducing dummy loads to modify heating distributions, have been obtained for a dedicated microwave processor, and comparison made with a domestic microwave oven. PMID:1787775

Ng, K H

1991-07-01

209

Magnetic Field Line Simulation Using a Microcomputer.  

ERIC Educational Resources Information Center

Describes the implementation of a computer simulation of magnetic field lines. Discusses properties of magnetic fields and the calculation of magnetic fields at points. Provides a program listing (additional programs and teaching notes available from the author) and gives examples of several field plots. (JM)

Kirkup, L.

1986-01-01

210

The HMI Magnetic Field Pipeline  

NASA Astrophysics Data System (ADS)

The Helioseismic and Magnetic Imager (HMI) will provide frequent full-disk magnetic field data after launch of the Solar Dynamics Observatory (SDO), currently scheduled for fall 2009. 16 megapixel line-of-sight magnetograms (Blos) will be recorded every 45 seconds. A full set of polarized filtergrams needed to determine the vector magnetic field requires 90 seconds. Quick-look data will be available within a few minutes of observation. Quick-look space weather and browse products must have identified users, and the list currently includes full disk magnetograms, feature identification and movies, 12-minute disambiguated vector fields in active region patches, time evolution of AR indices, synoptic synchronic frames, potential and MHD model results, and 1 AU predictions. A more complete set of definitive science data products will be offered about a day later and come in three types. "Pipeline” products, such as full disk vector magnetograms, will be computed for all data on an appropriate cadence. A larger menu of "On Demand” products, such as Non-Linear Force Free Field snapshots of an evolving active region, will be produced whenever a user wants them. Less commonly needed "On Request” products that require significant project resources, such as a high resolution MHD simulation of the global corona, will be created subject to availability of resources. Further information can be found at the SDO Joint Science Operations Center web page, jsoc.stanford.edu

Hoeksema, Jon Todd; Liu, Y.; Schou, J.; Scherrer, P.; HMI Science Team

2009-05-01

211

Large magnetic field instabilities induced by magnetic dipole transitions  

Microsoft Academic Search

We present a new mechanism that will limit very high magnetic fields which have been conjectured to exist in connection with some astrophysical phenomena. Low lying strongly interacting particles and resonances mixing with each other via magnetic dipole QED couplings force a vacuum instability for large external magnetic fields. These mixings limit fields to a few GeV2.

Myron Bander; H. R. Rubinstein

1992-01-01

212

Magnetic Resonance Imaging System Based on Earth's Magnetic Field  

Microsoft Academic Search

This article describes both the setup and the use of a system for magnetic resonance imaging (MRI) in the Earth's magnetic field. Phase instability caused by temporal fluctuations of Earth's field can be successfully improved by using a reference signal from a separate Earth's field nuclear magnetic resonance (NMR) spectrometer\\/magnetometer. In imaging, it is important to correctly determine the phase

Ales Mohoric; Gorazd Planinsic; Miha Kos; Andrej Duh; Janez Stepisnik

2004-01-01

213

The Giotto magnetic field investigation  

Microsoft Academic Search

The Giotto spacecraft will carry sensors for investigating the interplanetary magnetic field while en route and the interaction between the solar wind magnetoplasma and Halley's Comet neutral gas outflow during close approach. Giotto will carry an outboard biaxial fluxgate system and inboard electronics. The instrumentation draws 1.2 kW and weighs 1.31 kg. Sampling rates will be 28\\/sec during close encounter,

F. M. Neubauer; G. Musmann; M. H. Acuna; L. F. Burlaga; N. F. Ness; F. Mariani; M. Wallis; E. Ungstrup; H. Schmidt

1983-01-01

214

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 to the formation of an azimuthal rope of twisted magnetic field embedded within the global field, and to the energy

Fornberg, Bengt

215

Magnetic fields and gas in the cluster-influenced spiral galaxy NGC 4254 - II. Structures of magnetic fields  

E-print Network

The origin of asymmetric radio polarized emission and properties of magnetic fields in the Virgo Cluster spiral NGC4254 are investigated with help of "magnetic maps" presenting distributions of different magnetic field components over the entire galaxy, free of Faraday rotation and projection effects. We show that the dramatic variation of orientation of magnetic field vectors (from 0deg to more than 40deg) throughout the galaxy cannot arise from the dynamo process alone, but must be dominated by the effects like density waves and local gas flows. We determine within the galaxy the relation between the strength of total magnetic field and the local star-formation rate (SFR) as a power-law with an index of +0.18+-0.01. We find the opposite sense of relation of magnetic field regularity with SFR (-0.32+-0.03) and suggest that it results from efficient production of random field with rising turbulence in the regions with actively forming stars. The distribution of Faraday rotation measures in NGC4254 indicates a perturbed axisymmetrical mean-field dynamo mode or a mixture of axisymmetrical and bisymmetrical ones with regular field directed outwards the disk, which is contrary to most observed galaxies. The magnetic fields within two outer magnetic arms (shifted downstream of a density wave) are strong, up to 13muG in the regular field and 20muG in the total field. Our modeling of cluster influence on different magnetic field components indicates that within the outer magnetic arms the dynamo-induced magnetic fields are modified by stretching and shearing forces rather than by cluster ram pressure. Those forces, which are likely triggered by the galaxy's gravitational interaction, produce an anisotropic component of the regular field and enhance the polarized emission.(abridged)

Krzysztof T. Chyzy

2007-12-27

216

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

217

Magnetic fields, spots and weather in chemically peculiar stars  

E-print Network

New observational techniques and sophisticated modelling methods has led to dramatic breakthroughs in our understanding of the interplay between the surface magnetism, atomic diffusion and atmospheric dynamics in chemically peculiar stars. Magnetic Doppler images, constructed using spectropolarimetric observations of Ap stars in all four Stokes parameters, reveal the presence of small-scale field topologies. Abundance Doppler mapping has been perfected to the level where distributions of many different chemical elements can be deduced self-consistently for one star. The inferred chemical spot structures are diverse and do not always trace underlying magnetic field geometry. Moreover, horizontal chemical inhomogeneities are discovered in non-magnetic CP stars and evolving chemical spots are observed for the first time in the bright mercury-manganese star alpha And. These results show that in addition to magnetic fields, another important non-magnetic structure formation mechanism acts in CP stars.

O. Kochukhov

2007-11-30

218

Comparing Magnetic Fields on Earth and Mars  

NASA Video Gallery

This animation compares the magnetic fields on Earth and Mars. The Earth has a large-scale planetary magnetic field that can protect it from space weather and other hazards. Mars, on the other hand...

219

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

220

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

221

What Are Electric and Magnetic Fields? (EMF)  

MedlinePLUS

What are Electric and Magnetic Fields? (EMF) Electric and Magnetic Fields Electricity is an essential part of our lives. Electricity powers all sorts of things around us, from computers to refrigerators ...

222

The Galactic halo magnetic field revisited  

NASA Astrophysics Data System (ADS)

Recently, Sun et al. published new Galactic 3D-models of magnetic fields in the disk and halo of the Milky Way and the distribution of cosmic-ray electron density by taking into account the thermal electron density model NE2001 by Cordes & Lazio. The models successfully reproduce observed continuum and polarization all-sky maps and the distribution of rotation measures of extragalactic sources across the sky. However, the model parameters obtained for the Galactic halo, although reproducing the observations, seem physically unreasonable: the magnetic field needs to be significantly stronger in the Galactic halo than in the plane and the cosmic-ray distribution must be truncated at about 1 kpc to avoid excessive synchrotron emission from the halo. The reason for these unrealistic parameters was the low scale-height of the warm thermal gas of about 1 kpc adopted in the NE2001 model. However, this scale-height seemed reasonable and was well studied by numerous investigations. Recently, the scale-height of the warm gas in the Galaxy was revised by Gaensler et al. to about 1.8 kpc, by showing that the 1 kpc scale-height results from a systematic bias in the analysis of pulsar data. This implies a higher thermal electron density in the Galactic halo, which in turn reduces the halo magnetic field strength to account for the observed rotation measures of extragalactic sources. We slightly modified the NE2001 model according to the new scale-height and revised the Sun et al. model parameters accordingly: the strength of the regular halo magnetic field is now 2 ?G or lower, and the physically unrealistic cutoff in z for the cosmic-ray electron density is removed. The simulations based on the revised 3D-models reproduce all-sky observations as before.

Sun, Xiao-Hui; Reich, Wolfgang

2010-12-01

223

Mapping Geomagnetic Field Variations With Unmanned Airborne Vehicles  

NASA Astrophysics Data System (ADS)

Unmanned airborne vehicles (UAVs) are increasingly being used for a variety of commercial and research applications. The small (wingspan ~3 meters), fully autonomous aircraft are well suited for use in remote areas or dangerous settings. UAVs that are launched and recovered on land are being used for atmospheric chemistry and surface imaging studies and for aeromagnetic surveys [Curry et al., 2004; Ramanathan et al., 2007; Funaki et al., 2007]. We report here on the first deployment of UAVs launched from a marine research vessel. The UAVs mapped fluctuations in the magnetic field in a remote area of the southwestern Pacific Ocean.

Gee, Jeffrey S.; Cande, Steven C.; Kent, Dennis V.; Partner, Richard; Heckman, Kate

2008-05-01

224

The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: SHARPs -- Space-weather HMI Active Region Patches  

E-print Network

A new data product from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) called Space-weather HMI Active Region Patches (SHARPs) is now available. SDO/HMI is the first space-based instrument to map the full-disk photospheric vector magnetic field with high cadence and continuity. The SHARP data series provide maps in patches that encompass automatically tracked magnetic concentrations for their entire lifetime; map quantities include the photospheric vector magnetic field and its uncertainty, along with Doppler velocity, continuum intensity, and line-of-sight magnetic field. Furthermore, keywords in the SHARP data series provide several parameters that concisely characterize the magnetic-field distribution and its deviation from a potential-field configuration. These indices may be useful for active-region event forecasting and for identifying regions of interest. The indices are calculated per patch and are available on a twelve-minute cadence. Quick-look data are avail...

Bobra, Monica G; Hoeksema, J Todd; Turmon, Michael J; Liu, Yang; Hayashi, Keiji; Barnes, Graham; Leka, K D

2014-01-01

225

Magnetic map of the Irish Hills and surrounding areas, San Luis Obispo County, central California  

USGS Publications Warehouse

A magnetic map of the Irish Hills and surrounding areas was created as part of a cooperative research and development agreement with the Pacific Gas and Electric Company and is intended to promote further understanding of the areal geology and structure by serving as a basis for geophysical interpretations and by supporting geological mapping, mineral and water resource investigations, and other topical studies. Local spatial variations in the Earth's magnetic field (evident as anomalies on magnetic maps) reflect the distribution of magnetic minerals, primarily magnetite, in the underlying rocks. In many cases the volume content of magnetic minerals can be related to rock type, and abrupt spatial changes in the amount of magnetic minerals can be related to either lithologic or structural boundaries. Magnetic susceptibility measurements from the area indicate that bodies of serpentinite and other mafic and ultramafic rocks tend to produce the most intense magnetic anomalies, but such generalizations must be applied with caution because some sedimentary units also can produce measurable magnetic anomalies. Remanent magnetization does not appear to be a significant source for magnetic anomalies because it is an order of magnitude less than the induced magnetization. The map is a mosaic of three separate surveys collected by (1) fixed-wing aircraft at a nominal height of 305 m, (2) by boat with the sensor at sea level, and (3) by helicopter. The helicopter survey was flown by New-Sense Geophysics in October 2009 along flight lines spaced 150-m apart and at a nominal terrain clearance of 50 to 100 m. Tie lines were flown 1,500-m apart. Data were adjusted for lag error and diurnal field variations. Further processing included microleveling using the tie lines and subtraction of the reference field defined by International Geomagnetic Reference Field (IGRF) 2005 extrapolated to August 1, 2008.

Langenheim, V.E.; Watt, J.T.; Denton, K.M.

2012-01-01

226

Primordial magnetic field limits from cosmological data  

SciTech Connect

We study limits on a primordial magnetic field arising from cosmological data, including that from big bang nucleosynthesis, cosmic microwave background polarization plane Faraday rotation limits, and large-scale structure formation. We show that the physically relevant quantity is the value of the effective magnetic field, and limits on it are independent of how the magnetic field was generated.

Kahniashvili, Tina [McWilliams Center for Cosmology and Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213 (United States); Department of Physics, Laurentian University, Ramsey Lake Road, Sudbury, Ontario P3E 2C (Canada); Abastumani Astrophysical Observatory, Ilia State University, 2A Kazbegi Ave, Tbilisi, GE-0160 (Georgia); Tevzadze, Alexander G. [Abastumani Astrophysical Observatory, Ilia State University, 2A Kazbegi Ave, Tbilisi, GE-0160 (Georgia); Faculty of Exact and Natural Sciences, Tbilisi State University, 1 Chavchavadze Avenue, Tbilisi, GE-0128 (Georgia); Sethi, Shiv K. [McWilliams Center for Cosmology and Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213 (United States); Raman Research Institute, Sadashivanagar, Bangalore 560080 (India); Pandey, Kanhaiya [Raman Research Institute, Sadashivanagar, Bangalore 560080 (India); Ratra, Bharat [Department of Physics, Kansas State University, 116 Cardwell Hall, Manhattan, Kansas 66506 (United States)

2010-10-15

227

Magnetic-Field Processing of Industrial Effluents  

Microsoft Academic Search

• the field acts on pollutants in the colloidal state; and • the field influences the structure of the water. Magnetic treatment is simple, safe, and very inexpensive, but a patent search under the topic “Magnetic treatment of water and aqueous solutions” has shown that the existing devices and methods for using magnetic fields to process effluents containing heavy-metal ions

V. P. Malkin

2002-01-01

228

Magnetic field navigation in an indoor environment  

Microsoft Academic Search

This paper describes a method that has been developed to aid an inertial navigation system when GNSS signals are not available, by taking advantage of the uniqueness of magnetic field variations. Most indoor environments have many different features (ferrous structural materials or contents, electrical currents, etc.) which perturb the Earths natural magnetic field. The variations in the magnetic field in

William Storms; Jeremiah Shockley; John Raquet

2010-01-01

229

CORONAL MAGNETIC FIELD MEASUREMENTS THROUGH GYRORESONANCE EMISSION  

E-print Network

Chapter 5 CORONAL MAGNETIC FIELD MEASUREMENTS THROUGH GYRORESONANCE EMISSION Stephen M. White This article reviews the use of gyroresonance emission at radio wavelengths to measure coronal magnetic fields probes of the magnetic field strength above active regions, and this unique capability is one

White, Stephen

230

Appendix E: Software MEASURING CONSTANT MAGNETIC FIELD  

E-print Network

E - 1 Appendix E: Software MEASURING CONSTANT MAGNETIC FIELD (THE HALL PROBE APPLICATION) Basics yourself with the equipment. The software package that works in tandem with your magnetic field sensor is written in LabVIEWTM. It allows you to measure and record magnetic field strength as a function

Minnesota, University of

231

Quenching of flames by magnetic fields (abstract)  

Microsoft Academic Search

The effects of magnetic fields on combustion of alcohol with the aid of platinum catalysis have been studied to simulate in part the oxidation of organic matter in the living body, and it has been found that the combustion reactions are influenced by magnetic fields. It has also been observed that candle flames are pressed down by magnetic fields of

S. Ueno

1988-01-01

232

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

233

Evolution of Magnetic field inclination in a forming penumbra  

NASA Astrophysics Data System (ADS)

As a sunspot penumbra forms, the magnetic field vector at the outer boundary of the protospot undergoes a transformation. We study the changes of the magnetic field vector at this boundary as a penumbral segment forms. We analyze a set of spectropolarimetric maps covering 2 hr during the formation of a sunspot in NOAA 11024. The data were recorded with the GFPI instrument attached to the German VTT. We observe a stationary umbra/quiet Sun boundary, where the magnetic field becomes more horizontal with time. The magnetic field inclination increases by 5°, reaching a maximum value of about 59°. The maximum inclination coincides with the onset of filament formation. In time, the penumbra filaments become longer and the penumbral bright grains protrude into the umbra, where the magnetic field is stronger and more vertical. Consequently, we observe a decrease in the magnetic field inclination at the boundary as the penumbra grows. In summary, in order to initiate the formation of the penumbra, the magnetic field at the umbral (protospot) boundary becomes more inclined. As the penumbra grows, the umbra/penumbra boundary migrates inwards, and at this boundary the magnetic field turns more vertical again, while it remains inclined in the outer penumbra.

Jur?ák, Jan; Bello González, Nazaret; Schlichenmaier, Rolf; Rezaei, Reza

2014-10-01

234

Effects of magnetic fields on fibrinolysis  

NASA Astrophysics Data System (ADS)

In this study, we investigated the possible effects of magnetic fields on the fibrinolytic process. Fibrin dissolution was observed and the fibrinolytic activities were evaluated. First, fibrinolytic processes in magnetic fields were investigated by the fibrin plate method. We gathered solutions from the dissolved fibrin, and measured mean levels of fibrin degradation products (FDPs) in solutions. Mean levels of FDPs exposed to 8 T magnetic fields were higher than those not exposed to fields. Second, we carried out an experiment to understand how fibrin oriented in a magnetic field dissolves. FDPs in solutions of dissolved fibrins in fibrin plates were assayed. The result was that fibrin gels formed in a magnetic field at 8 T were more soluble than those not formed in a magnetic field. A model based on the diamagnetic properties of macromolecules was explained, and changes of protein concentrations in a solution in gradient magnetic fields were predicted.

Iwasaka, M.; Ueno, S.; Tsuda, H.

1994-05-01

235

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

236

Heliospheric magnetic fields and plasmas  

NASA Technical Reports Server (NTRS)

A survey of the existing literature on heliospheric physics, covering the period 1972-1982, is presented. Attention is given to observations and theories germane to the examination of the heliosphere as a large-scale astrophysical system that is part of the earth's environment. The literature includes data and models for magnetic sectors and the large-scale magnetic field, the large-scale plasma structure, and models and observed variations in the solar wind. Consideration is also devoted to the transient and corotating streams and shocks, the composition of the solar wind, and to MHD turbulence, waves, and discontinuities. More intensive investigations of the region near 1 AU are recommended, particularly to characterize the coronal source of the solar wind. The solar polar mission will be the first to provide radial measurements for comparisons with previous exclusively ecliptic measurements of solar activities.

Burlaga, L. F.

1983-01-01

237

The Giotto magnetic field investigation  

NASA Technical Reports Server (NTRS)

The Giotto spacecraft will carry sensors for investigating the interplanetary magnetic field while en route and the interaction between the solar wind magnetoplasma and Halley's Comet neutral gas outflow during close approach. Giotto will carry an outboard biaxial fluxgate system and inboard electronics. The instrumentation draws 1.2 kW and weighs 1.31 kg. Sampling rates will be 28/sec during close encounter, covering selectable ranges from 16 nT to 65,535 nT. In-flight calibration techniques are under development to ensure magnetic cleanliness will be obtained. Measurements are also planned of the inbound bow shock, the magnetosheath and the cometary ionopause. The data will be collected as close as 1000 km from the comet surface.

Neubauer, F. M.; Musmann, G.; Acuna, M. H.; Burlaga, L. F.; Ness, N. F.; Mariani, F.; Wallis, M.; Ungstrup, E.; Schmidt, H.

1983-01-01

238

Influence of stochastic magnetic fields on relativistic electrons  

NASA Astrophysics Data System (ADS)

The relativistic motion of test particles in stochastic magnetic fields is investigated. Guiding-centre motion is analysed in relativistic invariant form for toroidal geometry. Including stochastic magnetic field components, a symmetric Hamiltonian mapping technique, leading to a 4-dimensional iteration procedure, is developed. In general, an external electric field and a time-dependence of the magnetic field perturbations are allowed for. Break-up of drift surfaces is demonstrated via Poincaré plots. The latter are analysed in detail for increasing (relativistic) kinetic energies of the particles. The dependence of the escape rates on the kinetic energy is calculated and compared with the escape rates for field lines. The non-relativistic limit of the model is derived. Quantitative results for the magnetic perturbations in a dynamic ergodic divertor of the TEXTOR experiment are shown, and predictions for runaway electrons are compared with experiments.

Wingen, A.; Abdullaev, S. S.; Finken, K. H.; Jakubowski, M.; Spatschek, K. H.

2006-11-01

239

Magnetic Helicity and Large Scale Magnetic Fields: A Primer  

E-print Network

Magnetic fields of laboratory, planetary, stellar, and galactic plasmas commonly exhibit significant order on large temporal or spatial scales compared to the otherwise random motions within the hosting system. Such ordered fields can be measured in the case of planets, stars, and galaxies, or inferred indirectly by the action of their dynamical influence, such as jets. Whether large scale fields are amplified in situ or a remnant from previous stages of an object's history is often debated for objects without a definitive magnetic activity cycle. Magnetic helicity, a measure of twist and linkage of magnetic field lines, is a unifying tool for understanding large scale field evolution for both mechanisms of origin. Its importance stems from its two basic properties: (1) magnetic helicity is typically better conserved than magnetic energy; and (2) the magnetic energy associated with a fixed amount of magnetic helicity is minimized when the system relaxes this helical structure to the largest scale available. H...

Blackman, Eric G

2014-01-01

240

The magnetic fields of accreting T Tauri stars  

E-print Network

Models of magnetospheric accretion on to classical T Tauri stars often assume that the stellar magnetic field is a simple dipole. Recent Zeeman-Doppler imaging studies of V2129 Oph and BP Tau have shown however that their magnetic fields are more complex. V2129 Oph is a high mass T Tauri star and despite its young age is believed to have already developed a radiative core. In contrast to this, the lower mass BP Tau is likely to be completely convective. As the internal structure and therefore the magnetic field generation process is different in both stars, it is of particular interest to compare the structure of their magnetic fields obtained by field extrapolation from magnetic surface maps. We compare both field structures to mulitpole magnetic fields, and calculate the disk truncation radius for both systems. We find that by considering magnetic fields with a realistic degree of complexity, the disk is truncated at, or within, the radius obtained for dipole fields.

S. G. Gregory; S. P. Matt; J. -F. Donati; M. Jardine

2008-09-24

241

The magnetic fields of accreting T Tauri stars  

NASA Astrophysics Data System (ADS)

Models of magnetospheric accretion on to classical T Tauri stars often assume that the stellar magnetic field is a simple dipole. Recent Zeeman-Doppler imaging studies of V2129 Oph and BP Tau have shown however that their magnetic fields are more complex. V2129 Oph is a high mass T Tauri star and despite its young age is believed to have already developed a radiative core. In contrast to this, the lower mass BP Tau is likely to be completely convective. As the internal structure and therefore the magnetic field generation process is different in both stars, it is of particular interest to compare the structure of their magnetic fields obtained by field extrapolation from magnetic surface maps. We compare both field structures to mulitpole magnetic fields, and calculate the disk truncation radius for both systems. We find that by considering magnetic fields with a realistic degree of complexity, the disk is truncated at, or within, the radius obtained for dipole fields.

Gregory, S. G.; Matt, S. P.; Donati, J.-F.; Jardine, M.

2009-02-01

242

Magnetic field perturbations in the systems where only poloidal magnetic field is present*  

E-print Network

1 Magnetic field perturbations in the systems where only poloidal magnetic field is present* D In some plasma confinement systems the confinement is provided by a poloidal magnetic field (no toroidal magnetic field is present). Examples include FRC, levitated dipoles, and long diffuse pinches. We consider

243

Magnetic Fields1 Increasingly, instruments that generate large static magnetic fields (e.g., NMR spectrometers,  

E-print Network

Magnetic Fields1 Increasingly, instruments that generate large static magnetic fields (e.g., NMR spectrometers, MRI) are present in research laboratories. Such magnets typically have fields of 14,000 to 235,000 G (1.4 to 23.5 T), far above that of Earth's magnetic field, which is approximately 0.5 G

Shull, Kenneth R.

244

The magnetic field over the Southern African continent: from core to crustal magnetic fields  

Microsoft Academic Search

Secular magnetic field evolutions do not proceed in a regular way all over the Earth. In some regions like Southern Africa, the field has been changing more rapidly than elsewhere. During the last five decades, the Earth's magnetic field has been represented in spherical harmonics from a series of measurements that were generally obtained at magnetic field observatories. Unfortunately, magnetic

Erwan Thébault; Pieter Kotze; Arnaud Chulliat; Fotini Vervelidou

2010-01-01

245

Stokes IQUV magnetic Doppler imaging of Ap stars - III. Next generation chemical abundance mapping of ?2 CVn  

NASA Astrophysics Data System (ADS)

In a previous paper, we presented an updated magnetic field map for the chemically peculiar star ?2 CVn using ESPaDOnS and Narval time-resolved high-resolution Stokes IQUV spectra. In this paper, we focus on mapping various chemical element distributions on the surface of ?2 CVn. With the new magnetic field map and new chemical abundance distributions, we can investigate the interplay between the chemical abundance structures and the magnetic field topology on the surface of ?2 CVn. Previous attempts at chemical abundance mapping of ?2 CVn relied on lower resolution data. With our high-resolution (R = 65 000) data set, we present nine chemical abundance maps for the elements O, Si, Cl, Ti, Cr, Fe, Pr, Nd and Eu. We also derive an updated magnetic field map from Fe and Cr lines in Stokes IQUV and O and Cl in Stokes IV. These new maps are inferred from line profiles in Stokes IV using the magnetic Doppler imaging code INVERS10. We examine these new chemical maps and investigate correlations with the magnetic topology of ?2 CVn. We show that chemical abundance distributions vary between elements, with two distinct groups of elements; one accumulates close to the negative part of the radial field, whilst the other group shows higher abundances located where the radial magnetic field is of the order of 2 kG regardless of the polarity of the radial field component. We compare our results with previous works which have mapped chemical abundance structures of Ap stars. With the exception of Cr and Fe, we find no clear trend between what we reconstruct and other mapping results. We also find a lack of agreement with theoretical predictions. This suggests that there is a gap in our theoretical understanding of the formation of horizontal chemical abundance structures and the connection to the magnetic field in Ap stars.

Silvester, J.; Kochukhov, O.; Wade, G. A.

2014-10-01

246

Modelling the Hidden Magnetic Field of Low-Mass Stars  

E-print Network

Zeeman-Doppler imaging is a spectropolarimetric technique that is used to map the large-scale surface magnetic fields of stars. These maps in turn are used to study the structure of the stars' coronae and winds. This method, however, misses any small-scale magnetic flux whose polarisation signatures cancel out. Measurements of Zeeman broadening show that a large percentage of the surface magnetic flux may be neglected in this way. In this paper we assess the impact of this 'missing flux' on the predicted coronal structure and the possible rates of spin down due to the stellar wind. To do this we create a model for the small-scale field and add this to the Zeeman-Doppler maps of the magnetic fields of a sample of 12 M dwarfs. We extrapolate this combined field and determine the structure of a hydrostatic, isothermal corona. The addition of small-scale surface field produces a carpet of low-lying magnetic loops that covers most of the surface, including the stellar equivalent of solar 'coronal holes' where the ...

Lang, P; Morin, J; Donati, J-F; Jeffers, S; Vidotto, A A; Fares, R

2014-01-01

247

Alignment between Flattened Protostellar Infall Envelopes and Ambient Magnetic Fields  

NASA Astrophysics Data System (ADS)

We present 350 ?m polarization observations of four low-mass cores containing Class 0 protostars: L483, L1157, L1448-IRS2, and Serp-FIR1. This is the second paper in a larger survey aimed at testing magnetically regulated models for core-collapse. One key prediction of these models is that the mean magnetic field in a core should be aligned with the symmetry axis (minor axis) of the flattened young stellar object inner envelope (aka pseudodisk). Furthermore, the field should exhibit a pinched or hourglass-shaped morphology as gravity drags the field inward toward the central protostar. We combine our results for the four cores with results for three similar cores that were published in the first paper from our survey. An analysis of the 350 ?m polarization data for the seven cores yields evidence of a positive correlation between mean field direction and pseudodisk symmetry axis. Our rough estimate for the probability of obtaining by pure chance a correlation as strong as the one we found is about 5%. In addition, we combine together data for multiple cores to create a source-averaged magnetic field map having improved signal-to-noise ratio, and this map shows good agreement between mean field direction and pseudodisk axis (they are within 15°). We also see hints of a magnetic pinch in the source-averaged map. We conclude that core-scale magnetic fields appear to be strong enough to guide gas infall, as predicted by the magnetically regulated models. Finally, we find evidence of a positive correlation between core magnetic field direction and bipolar outflow axis.

Chapman, Nicholas L.; Davidson, Jacqueline A.; Goldsmith, Paul F.; Houde, Martin; Kwon, Woojin; Li, Zhi-Yun; Looney, Leslie W.; Matthews, Brenda; Matthews, Tristan G.; Novak, Giles; Peng, Ruisheng; Vaillancourt, John E.; Volgenau, Nikolaus H.

2013-06-01

248

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

249

Observation of the stray field of thin film magnetic tips using electron holography  

NASA Astrophysics Data System (ADS)

The stray field around thin film ferromagnetic tips employed for magnetic force microscopy has been revealed using electron holography. The experimental phase difference maps are in good agreement with simulations. Quantitative flux measurements of the leakage field are obtained.

Lunedei, E.; Matteucci, G.; Frost, B. G.; Greve, J.

1996-05-01

250

COORDINATES FOR MAPPING THE DISTRIBUTION OF MAGNETICALLY TRAPPED PARTICLES  

Microsoft Academic Search

Dipole representations of the earth's magnetic field have insufficient ; accuracy for the study of magnetically trapped particles. A coordinate system ; consisting of the magnitude of the magnetic field B and the integral invariant I ; was organized adequately, measurements made at different geographic locations. A ; parameter L = f(B,I) is defined that retains most of the desirable

Carl E. McIlwain

1961-01-01

251

Magnetic fluid flow phenomena in DC and rotating magnetic fields  

E-print Network

An investigation of magnetic fluid experiments and analysis is presented in three parts: a study of magnetic field induced torques in magnetorheological fluids, a characterization and quantitative measurement of properties ...

Rhodes, Scott E. (Scott Edward), 1981-

2004-01-01

252

Large-Scale Kinematics, Astrochemistry and Magnetic Field Studies of Massive Star-forming Regions through HC3N, HNC and C2H Mappings  

E-print Network

We have mapped 27 massive star-forming regions associated with water masers using three dense gas tracers: HC3N 10-9, HNC 1-0 and C2H 1-0. The FWHM sizes of HNC clumps and C2H clumps are about 1.5 and 1.6 times higher than those of HC3N, respectively, which can be explained by the fact that HC3N traces more dense gas than HNC and C2H. We found evidence for increase in optical depth of C2H with `radius' from center to outer regions in some targets, supporting the chemical model of C2H. The C2H optical depth is found to decline as molecular clouds evolve to later stage, suggesting that C2H might be used as "chemical clock" for molecular clouds. Large-scale kinematic structure of clouds was investigated with three molecular lines. All these sources show significant velocity gradients. The magnitudes of gradient are found to increase towards the inner region, indicating differential rotation of clouds. Both the ratio of rotational to gravitational energy and specific angular momentum seem to decrease toward the i...

Li, Juan; Gu, Qiusheng; Zhang, Zhi-yu; Zheng, Xingwu

2011-01-01

253

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

254

RESULTS OF SPARO 2003: MAPPING MAGNETIC FIELDS IN GIANT MOLECULAR CLOUDS H. Li, G. S. Griffin, M. Krejny, and G. Novak  

E-print Network

ABSTRACT We present results from the Austral Winter 2003 observing campaign of SPARO, a 450 m polarimeter in the Galactic disk: NGC 6334, the Carina Nebula, G333.6Ã?0.2, and G331.5Ã?0.1. We find a statistically significant of the four GMCs (NGC 6334 is the exception) have mean field directions that are within 15 of the plane

Novak, Giles

255

On the Origin of the Lunar Magnetic Field  

NASA Astrophysics Data System (ADS)

We present in this work a study of lunar magnetic fields using new methods and algorithms to select and process Lunar Prospector Magnetometer data (LP-MAG). These methods and algorithms developed here have allowed us to obtain and validate the global mapping of inter-nal lunar magnetic fields detected by LP-MAG at low altitude during 1999. To validate our mapping we have developed and applied a method based on properties of potential fields func-tions. This method allows us to determine the two horizontal components north and east using only the vertical component. The global mapping produced at spacecraft altitudes was then downward continued at surface level using an inverse method. This mapping confirm firstly the nature of the crustal sources of lunar magnetic field. and show that the strongest concentra-tions of anomalies are associated with formations of high albedo and/or located antipodal to large young basins (Orientale, Serenitatis, Imbrium, and Crisium) of age about 3.9 Ga. These basins themselves show a weak anomalies or are wholly demagnetized. The modeling of some strongest isolated anomalies shows a clustered paleomagnetic pole positions centered at (30S, 225E). This preliminary result strengthens the hypothesis of a now extincted ancient lunar dynamo that may have probably magnetized rocks of lunar crust

Sherif, Berguig; Mohamed, Hamoudi; Le Mouel, Jean Louis; Yves, Cohen; Mandea, Mioara

256

Circum-Arctic mapping project: new magnetic anomaly map of the Arctic (to 60 degrees N)  

NASA Astrophysics Data System (ADS)

An international effort to compile Circum-Arctic geophysical and bedrock data has been conducted by several national agencies (Russia-VSEGEI and VNIIO, Sweden-SGU, Finland-GTK, Denmark-GEUS, USA-USGS, Canada-GSC, Germany-BGR and Norway-NGU) since 2005. This project aims to produce an atlas that will comprise geological and geophysical digital maps at a scale of 1: 5 million scale for the Arctic region limited by the 60 degree North latitude. New published and classified magnetic anomaly gridded data from each participant group were gathered and converted to a common datum (WGS84) and format. The Greenland region magnetic anomaly grid (Verhoef et al., 1996) has been updated with new aeromagnetic surveys performed in West Greenland between 1992-2001 (Rasmussen, 2002), and in the Nares Strait area (Damaske & Oakey, 2006; Oakey & Damaske, 2006). The oceanic area east of Greenland (NE Atlantic) contains most of the aeromagnetic data used in the Verhoef et al., (1996)'s compilation (pre-1990) plus new aeromagnetic surveys over offshore Norway collected up to 2007 (Olesen et al., 1997; Olesen et al., 2007; Gernigon et al., 2008). The gridded data has been upward continued to 1 km above ground or sea-level and trimmed around the areas of major overlaps. The Alaska USGS aeromagnetic compilation has been used as the "master grid" for merging the major gridded data sets together and the downward continued lithospheric magnetic field model MF6 derived from satellite data (Maus et al., 2008) has been used as a regional reference surface. We have used a blending function over the area of overlap in order to smooth the transition from one grid to the other (GridKnit, GEOSOFT). The resulting grid has been re-sampled to a 2 km grid cell. In order to construct the final Circum-Arctic magnetic anomaly grid (CAMP-M) we have adopted the approach used by several research groups for compiling the World Digital Magnetic Anomaly Map (WDMAM) and used near-surface magnetic data for the short wavelength component of the compilation and the satellite derived magnetic anomalies for the long wavelength (Hemant et al., 2007; Maus et al., 2007). MF6 extends to spherical harmonics degree 120 (333 km wavelength) and therefore it is able to provide consistent long wavelength information between 300 and 400 km. This information is mainly related to regional deeper and/or thicker portions of the magnetic sources within the crust. We have prepared two versions for the CAMP-M magnetic anomaly grid. The first one combines short wavelength components of regional grids (less than 400 km) with long wavelengths (400 km) of the MF6 model. The second one combines short wavelengths of regional datasets (obtained by filtering with a cosine squared taper to remove the wavelengths in the waveband between 307 and 333 km and larger, with the MF6 model (to degree 120). We have selected Model 1 as the new Circum-Arctic Magnetic Anomaly Map.

Gaina, Carmen

2010-05-01

257

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

258

Problems with magnetic field measurements on spacecrafts  

Microsoft Academic Search

The paper summarizes the difficulties and possible solutions to design and evaluate accurate vector magnetic field measurements on spacecrafts in the interplanetary magnetic field. Problems are discussed like calibration, boom mounted sensors and misalignment angles determination in flight. The application of a detailed magnetic cleanliness program as an example the comet Halley-Giotto spacecraft is demonstrated in detail. The use of

Günter Musmann

1988-01-01

259

Neutrinos with Mixing in Twisting Magnetic Fields  

E-print Network

Transitions in a system of neutrinos with vacuum mixing and magnetic moments, propagating in matter and transverse magnetic field, are considered. It is shown that in the realistic case of magnetic field direction varying along the neutrino path qualitatively new phenomena become possible: permutation of neutrino conversion resonances, appearance of resonances in the neutrino-antineutrino ($\

E. Kh. Akhmedov; S. T. Petcov; A. Yu. Smirnov

1993-01-06

260

Discovery of magnetic fields in CPNs  

E-print Network

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 LSS1362 with very high significance, while in Abell36 and EGB5 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.

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

2004-10-21

261

A Holographic Superconductor in an External Magnetic Field  

E-print Network

We study a system of a complex charged scalar coupled to a Reissner-Nordstrom black hole in 3+1 dimensional anti-de Sitter spacetime, neglecting back-reaction. With suitable boundary conditions, the cases of a neutral and purely electric black hole have been studied in various limits and were shown to yield key elements of superconductivity in the dual 2+1 dimensional field theory, forming a condensate below a critical temperature. By adding magnetic charge to the black hole, we immerse the superconductor into an external magnetic field. We show that a family of condensates can form and we examine their structure. For finite magnetic field, they are localized in one dimension with a profile that is exactly solvable, since it maps to the quantum harmonic oscillator. As the magnetic field increases, the condensate shrinks in size, which is reminiscent of the Meissner effect.

Tameem Albash; Clifford V. Johnson

2008-04-22

262

The Global Magnetic Field of Mercury from MESSENGER Orbital Observations  

NASA Astrophysics Data System (ADS)

Magnetometer data acquired by the MESSENGER spacecraft in orbit about Mercury permit the separation of internal and external magnetic field contributions. The global planetary field is represented as a southward-directed, spin-aligned, offset dipole centered on the spin axis. Positions where the cylindrical radial magnetic field component vanishes were used to map the magnetic equator and reveal an offset of 484 ± 11 kilometers northward of the geographic equator. The magnetic axis is tilted by less than 3° from the rotation axis. A magnetopause and tail-current model was defined by using 332 magnetopause crossing locations. Residuals of the net external and offset-dipole fields from observations north of 30°N yield a best-fit planetary moment of 195 ± 10 nanotesla-RM3, where RM is Mercury’s mean radius.

Anderson, Brian J.; Johnson, Catherine L.; Korth, Haje; Purucker, Michael E.; Winslow, Reka M.; Slavin, James A.; Solomon, Sean C.; McNutt, Ralph L.; Raines, Jim M.; Zurbuchen, Thomas H.

2011-09-01

263

Evidence for Weak Crustal Magnetic Fields Over the Hellas Basin  

NASA Astrophysics Data System (ADS)

The Electron Reflectometer (ER) onboard Mars Global Surveyor (MGS) detected a plasma boundary between the ionosphere and the solar wind as the latter is diverted around and past the planet [Mitchell et al., GRL 27, 1871, 2000; Mitchell et al. JGR 106, 23419, 2001]. Above this boundary the 10-1000 eV electron population is dominated by solar wind electrons, while below the boundary it is dominated by ionospheric photoelectrons. This "photoelectron boundary", or PEB, is sensitive to pressure variations and moves vertically in response to changes in the ionospheric pressure from below and the solar wind pressure from above. The PEB is also sensitive to crustal magnetic fields, which locally increase the total ionospheric pressure and positively bias the PEB altitude. A map of the PEB altitude closely resembles maps of the crustal magnetic field intensity measured at 400 km by the MGS Magnetometer. As expected, the best correlation is between the PEB altitude and the horizontal magnetic field component, which provides vertical pressure support. We have analyzed more than 4.8 million electron spectra obtained in the mapping orbit, covering over 1.5 Martian years. We have empirically modeled and removed systematic variations in the PEB altitude associated with the solar wind interaction, thus isolating perturbations caused by crustal magnetic fields. We find a PEB altitude bias over the Hellas basin that is consistent with a horizontal magnetic field with an intensity of several nanotesla at 400 km altitude. This is compatible with upper limits to the horizontal crustal field strength set by MGS Magnetometer measurements. Weak crustal magnetic fields within the Hellas basin suggest that a weak Martian dynamo was still present when that basin cooled. No detectable PEB or magnetic signature is observed over the younger Argyre basin.

Mitchell, D. L.; Lee, C.; Lin, R. P.; Reme, H.; Cloutier, P. A.; Acuna, M. H.

2002-12-01

264

Unpaired Floquet Majorana fermions without magnetic fields  

NASA Astrophysics Data System (ADS)

Quantum wires subject to the combined action of spin-orbit and Zeeman coupling in the presence of s-wave pairing potentials (superconducting proximity effect in semiconductors or superfluidity in cold atoms) are one of the most promising systems for the developing of topological phases hosting Majorana fermions. The breaking of time-reversal symmetry is essential for the appearance of unpaired Majorana fermions. By implementing a time-dependent spin rotation, we show that the standard magnetostatic model maps into a nonmagnetic one where the breaking of time-reversal symmetry is guaranteed by a periodical change of the spin-orbit coupling axis as a function of time. This suggests the possibility of developing the topological superconducting state of matter driven by external forces in the absence of magnetic fields and magnetic elements. From a practical viewpoint, the scheme avoids the disadvantages of conjugating magnetism and superconductivity, even though the need of a high-frequency driving of spin-orbit coupling may represent a technological challenge. We describe the basic properties of this Floquet system by showing that finite samples host unpaired Majorana fermions at their edges despite the fact that the bulk Floquet quasienergies are gapless and that the Hamiltonian at each instant of time preserves time-reversal symmetry. Remarkably, we identify the mean energy of the Floquet states as a topological indicator. We additionally show that the localized Floquet Majorana fermions are robust under local perturbations. Our results are supported by complementary numerical Floquet simulations.

Reynoso, Andres A.; Frustaglia, Diego

2013-03-01

265

Gravitational field maps and navigational errors [unmanned underwater vehicles  

Microsoft Academic Search

Gravitational field maps are used to correct navigational errors that tend to accumulate in some navigational systems presently in use on unmanned underwater vehicles (UUVs). Two essential elements of such a system are an algorithm to calculate field maps from sparsely and irregularly sampled measured field data and an algorithm to match locally measured field values to an a priori

Garner C. Bishop

2002-01-01

266

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. 2 figs.

Lubell, M.S.

1994-10-25

267

Advances in Remote Sensing of Magnetic Fields  

NASA Astrophysics Data System (ADS)

In sharp contrast to stellar magnetic fields, geomagnetic fields have never been remotely sensed. If geomagnetic fields could be measured remotely at the nanotesla (nT) level or better, our understanding of the processes that produce these fields would advance markedly. Unlike characteristics such as topography and temperature, measurements of the magnetic field are determined almost exclusively in situ. The inability to remotely sense these fields has hindered their utility. The Remote Atmospheric Magnetics Workshop highlighted advances in this frontier area, focusing on lab- and field-based studies.

Purucker, Michael

2014-09-01

268

Franck-Hertz experiment in magnetic field  

E-print Network

The paper studies the impact of applied magnetic field on the inelastic collisions of electrons with argon atoms. In the electron-argon Franck-Hertz experiment, the influence of applied magnetic field emerges complicated features, and is equivalent to that of the temperature. In case the accelerating electric intensity becomes strong enough, enlarging magnetic flux density will be equivalent to the increasing of oven temperature. When the accelerating electric intensity is very weak and the applied magnetic field occupies a dominant position, enhancing magnetic flux density is identical with the decreasing of oven temperature. And the non-uniform distribution of applied magnetic field has an influence on the inelastic collision as well. The study claims that the influence of magnetic field variation is equivalent to that of temperature variety, and that it leads the electron energy to transfer obviously in the experiment.

Ying Weng; Zi-Hua Weng

2010-10-07

269

A laser-pumped magnetometer for the mapping of human cardiomagnetic fields  

Microsoft Academic Search

.   Magnetic fields produced by biological organisms contain valuable information on the underlying physiological processes and\\u000a their pathologies. Currently, superconducting detectors cooled far below room temperature are required to measure these generally\\u000a weak biomagnetic signals. We have developed a sensitive laser magnetometer based on optical pumping of cesium atoms that makes\\u000a it possible to map the magnetic field produced by

G. Bison; R. Wynands; A. Weis

2003-01-01

270

Magnetic Fields and Rotations of Protostars  

E-print Network

The evolution of the magnetic field and angular momentum in the collapsing cloud core is studied using three-dimensional resistive MHD nested grid simulations. Starting with a Bonnor-Ebert isothermal cloud rotating in a uniform magnetic field, we calculate the cloud evolution from the molecular cloud core (n=10^4 cm^-3) to the stellar core (n \\simeq 10^22 cm^-3). The magnetic field strengths at the center of the clouds converge to a certain value as the clouds collapse, when the clouds have the same angular momenta but different strengths of the magnetic fields at the initial state. For 10^12 cm^-3 magnetic field from the collapsing cloud core, and the magnetic field lines, which are strongly twisted for n magnetic field lines are twisted and amplified again for nc > 10^16 cm^-3, because the magnetic field is recoupled with the warm gas. Finally, protostars at their formation epoch have 0.1-1kG of the magnetic fields, which are comparable to observations. The magnetic field strength of protostar slightly depends on the angular momentum of the host cloud. The protostar formed from the slowly rotating cloud core has a stronger magnetic field. The evolution of the angular momentum is closely related to the evolution of the magnetic field. The angular momentum in the collapsing cloud is removed by the magnetic effect. The formed protostars have 0.1-2 days of the rotation period at their formation epoch, which are slightly shorter than the observation. This indicates that the further removal mechanism of the angular momentum such as interaction between the protostar and disk, wind gas or jet is important in further evolution of the protostar.

Masahiro N. Machida; Shu-ichiro Inutsuka; Tomoaki Matsumoto

2007-02-07

271

Measuring T Tauri star magnetic fields  

Microsoft Academic Search

Stellar magnetic fields including a strong dipole component are believed to play a critical role in the early evolution of newly formed stars and their circumstellar accretion disks. It is currently believed that the stellar magnetic field truncates the accretion disk several stellar radii above the star. This action forces accreting material to flow along the field lines and accrete

Christopher M. Johns-Krull

2009-01-01

272

DC-based magnetic field controller  

DOEpatents

A magnetic field controller for laboratory devices and in particular to dc operated magnetic field controllers for mass spectrometers, comprising a dc power supply in combination with improvements to a hall probe subsystem, display subsystem, preamplifier, field control subsystem, and an output stage.

Kotter, Dale K. (Shelley, ID); Rankin, Richard A. (Ammon, ID); Morgan, John P,. (Idaho Falls, ID)

1994-01-01

273

Spherical harmonic decomposition of solar magnetic fields  

NASA Astrophysics Data System (ADS)

We have investigated the temporal evolution of large-scale magnetic fields in the solar photosphere during the time interval 1966-2004 by means of spherical harmonic decomposition and subsequent time series analysis. Two data sets of daily magnetograms recorded at the Mt. Wilson and Kitt Peak observatories were used to calculate the spherical harmonic coefficients of the radial magnetic field for axisymmetric (m=0) and non-axisymmetric (m? 0) modes. Time series analysis was then applied to deduce their temporal variations. A third data set of synoptic Carrington rotation maps from Kitt Peak was also analyzed for completeness. Besides the obvious 22 yr magnetic cycle, we have found evidence for intermittent oscillations with periods of 2.1{-}2.5 yr, 1.5{-}1.8 yr and 1.2{-}1.4 yr. The biennial oscillation occurred during the solar maxima of cycles 20-22 (and likely also during the current cycle 23) and was most pronounced for modes that resemble non-linear dynamo waves (Stix 1972, A&A, 20, 9). The 1.5{-}1.8 yr period was stronger during the odd cycles 21 and 23 than during the even cycles 20 and 22, whereas the opposite was the case for the 1.2{-}1.4 yr period. Similar variations of 1.5{-}1.8 yr have recently been detected in the north-south asymmetry of the magnetic flux (Knaack et al. 2004, A&A, 418, L17), while quasi-periodicities of 1.3 yr have been observed in the rotation rate near the base of the convection zone (Howe et al. 2000, Science, 287, 2456), in the heliosphere and geomagnetic activity (Lockwood 2001, J. Geophys. Res., 106, 16 021) in sunspot areas (Krivova & Solanki 2002, A&A, 394, 701), and in the large-scale photospheric magnetic field (Knaack et al. 2005, A&A, in press). In agreement with the latter study, we have found additional quasi-periodicities in the range 320{-}100 d and rotational periods of 29.0±0.1d, 28.2±0.1d, and 26.8±0.1d. Compared to earlier decompositions by Stenflo & Vogel (1986, Nature, 319, 285) and Stenflo & Güdel (1988, A&A, 191, 137), we can confirm the main features of their results, although several modifications need to be considered.

Knaack, R.; Stenflo, J. O.

2005-07-01

274

New gravity and magnetics map of eastern part of Azores  

NASA Astrophysics Data System (ADS)

The Azores are of volcanic origin and the volcanic activities are still occurs in the area. The main tectonic features in the eastern part of Azores are the Gloria Fault (GF) and São Miguel volcanic Island. The GF is an E-W strike-slip fault and can be traced by bathymetry. In the past decade many geological and geophysical investigations were dedicated to the study of tectonic features in the eastern part of Azores. Two of these cruises were organized by the Institute of Geophysics, University of Hamburg, Germany, in the years 2009 and 2012. In 2009 during the Meteor cruise M79-2 a total of 5500 km new Gravity and 2000 km new magnetic data were collected along some 60 Profiles. During the Poseidon cruise in the year 2012 some 2000 km new gravity and magnetic data were collected along two E-W profiles in the eastern part of Azores. The new gravity data were recorded with the modern Air-Sea-Gravimeter of Bodenseewerk KSS 31M and the new magnetic date with the Gradiometer SeaSpy. All new potential date were combined with the available data of the data base GEODAS and the new gravity anomaly maps (Free-Air and Bouguer) and the new magnetic anomaly map were produced. The maps show clearly the tectonic features in the area. The GF can be traced very well on both gravity and magnetic anomaly maps. Most of the small hills around the São Miguel Island are shown up in the magnetic anomaly map as strong magnetic anomaly. The new gravity and magnetic maps and the interpretation of them will be presented. The results of some 2-D modeling along some interesting profiles will be also presented and discussed.

Dehghani, Ali

2014-05-01

275

New gravity and magnetics map of eastern part of Azores  

NASA Astrophysics Data System (ADS)

The Azores are of volcanic origin and the volcanic activities are still occurs in the area. The main tectonic features in the eastern part of Azores are the Gloria Fault (GF) and São Miguel volcanic Island. The GF is an E-W strike-slip fault and can be traced by bathymetry. In the past decade many geological and geophysical investigations were dedicated to the study of tectonic features in the eastern part of Azores. Two of these cruises were organized by the Institute of Geophysics, University of Hamburg, Germany, in the years 2009 and 2012. In 2009 during the Meteor cruise M79-2 a total of 5500 km new Gravity and 2000 km new magnetic data were collected along some 60 Profiles. During the Poseidon cruise in the year 2012 some 2000 km new gravity and magnetic data were collected along two E-W profiles in the eastern part of Azores. The new gravity data were recorded with the modern Air-Sea-Gravimeter of Bodenseewerk KSS 31M and the new magnetic date with the Gradiometer SeaSpy. All new potential date were combined with the available data of the data base GEODAS and the new gravity anomaly maps (Free-Air and Bouguer) and the new magnetic anomaly map were produced. The maps show clearly the tectonic features in the area. The GF can be traced very well on both gravity and magnetic anomaly maps. Most of the small hills around the São Miguel Island are shown up in the magnetic anomaly map as strong magnetic anomaly. The new gravity and magnetic maps and the interpretation of them will be presented. The results of some 2-D modeling along some interesting profiles will be also presented and discussed.

Dehghani, A.

2013-12-01

276

Mapping and Quantifying Electric and Magnetic Dipole Luminescence at the nanoscale  

E-print Network

We report on an experimental technique to quantify the relative importance of electric and magnetic dipole luminescence from a single nanosource in structured environments. By attaching a $Eu^{3+}$-doped nanocrystal to a near-field scanning optical microscope tip, we map the branching ratios associated to two electric dipole and one magnetic dipole transitions in three dimensions on a gold stripe. The relative weight of the electric and magnetic radiative local density of states can be recovered quantitatively, based on a multilevel model. This paves the way towards the full electric and magnetic characterization of nanostructures for the control of luminescence at the single emitter level.

Aigouy, L; Gredin, P; Mortier, M; Carminati, R

2014-01-01

277

Mapping and Quantifying Electric and Magnetic Dipole Luminescence at the Nanoscale  

NASA Astrophysics Data System (ADS)

We report on an experimental technique to quantify the relative importance of electric and magnetic dipole luminescence from a single nanosource in structured environments. By attaching a Eu3+-doped nanocrystal to a near-field scanning optical microscope tip, we map the branching ratios associated with two electric dipole and one magnetic dipole transitions in three dimensions on a gold stripe. The relative weights of the electric and magnetic radiative local density of states can be recovered quantitatively, based on a multilevel model. This paves the way towards the full electric and magnetic characterization of nanostructures for the control of single emitter luminescence.

Aigouy, L.; Cazé, A.; Gredin, P.; Mortier, M.; Carminati, R.

2014-08-01

278

Monitoring the Earth's Dynamic Magnetic Field U.S. Department of the Interior  

E-print Network

are used to model and map the global magnetic field, which requires cooperation among the international by the Earthquake Hazards and Landslide Hazards Programs. The engineers and technicians of the Geomagnetism Program established to help with the development of magnetic maps for the United States and Territories

Torgersen, Christian

279

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

280

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

281

Comparing magnetic field extrapolations with measurements of magnetic loops  

E-print Network

We compare magnetic field extrapolations from a photospheric magnetogram with the observationally inferred structure of magnetic loops in a newly developed active region. This is the first time that the reconstructed 3D-topology of the magnetic field is available to test the extrapolations. We compare the observations with potential fields, linear force-free fields and non-linear force-free fields. This comparison reveals that a potential field extrapolation is not suitable for a reconstruction of the magnetic field in this young, developing active region. The inclusion of field-line-parallel electric currents, the so called force-free approach, gives much better results. Furthermore, a non-linear force-free computation reproduces the observations better than the linear force-free approximation, although no free parameters are available in the former case.

T. Wiegelmann; A. Lagg; S. K. Solanki; B. Inhester; J. Woch

2008-01-29

282

Observational testing of magnetospheric magnetic field models at geosynchronous orbit  

SciTech Connect

Empirical mode which estimate the magnetic field direction and magnitude at any point within the magnetosphere under a variety of conditions play an important role in space weather forecasting. We report here on a number of different studies aimed at quantitatively evaluating these models, and in particular the Tsyganenko T89a model. The models are evaluated in two basic ways: (1) by comparing the range of magnetic field tilt angles observed at geosynchronous orbit with the ranges predicted for the same locations by the models; and (2) by comparing the observed magnetic field mapping between the ionosphere and geosynchronous orbit (using two-satellite magnetic field conjunctions) with the model predictions at the same locations. We find that while the T89a model predicts reasonably well the basic variation in tilt angle with local time and permits a range of field inclinations adequate to encompass the majority of observed angles on the dawn, dusk, and night sides, it is unable to reproduce the range of inclinations on the dayside. The model also predicts a smaller magnetic latitude range of geosynchronous field line footpoints than the observed two-satellite mapping indicate. Together, these results suggest that the next generation of field models should allow a greater range of stretching, especially in local time sectors away from midnight. It is important to note, however, that any increased range should encompass less-stretched configurations: although there are certainly cases where the models are not sufficiently stretched, we find that on average all magnetic field models tested, including T89a, are too stretched. Finally, in investigating how well the observed degree of field stretch was ordered by various magnetospheric indices, we find that the tilt of the field at geosynchronous orbit is a promising candidate for the incorporation into future models.

Weiss, L.A.; Thomsen, M.F.; Reeves, G.D.; McComas, D.J.

1996-09-01

283

Magnetic Fields in Clusters of Galaxies  

E-print Network

A brief overview about our knowledge on galaxy cluster magnetic fields is provided. Emphasize is given to the mutual dependence of our knowledge on relativistic particles in galaxy clusters and the magnetic field strength. Furthermore, we describe efforts to measure magnetic field strengths, characteristic length-scales, and power-spectra with reliable accuracy. An interpretation of these results in terms of non-helical dynamo theory is given. If this interpretation turns out to be correct, the understanding of cluster magnetic fields is directly connected to our understanding of intra-cluster turbulence.

Torsten A. Ensslin; Corina Vogt; Christoph Pfrommer

2005-01-17

284

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

285

Statistics of magnetic fields on OBA stars  

NASA Astrophysics Data System (ADS)

Starting from recent measurements, we studied the statistical properties of the magnetic fields of OBA stars. As one of the statistically significant characteristics of the magnetic field we use the average effective magnetic field of the star, < B>. We then investigated the distribution function f() of the magnetic fields of OBA stars. This function has a power-law dependence on , with an index of 2-3 and a fast decrease for ? 300 G for B-A stars and ? 80 G for O stars.

Kholtygin, A. F.; Hubrig, S.; Drake, N. A.; Sudnik, N. P.; Dushin, V. V.

2014-11-01

286

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

287

Concentrator of magnetic field of light  

NASA Astrophysics Data System (ADS)

In the recent decade metamaterials with magnetic permeability different than unity and unusual response to the magnetic field of incident light have been intensively explored. Existence of magnetic artificial materials created an interest in a scanning near-field magnetic microscope for studies of magnetic responses of subwavelength elementary cells of those metamaterials. We present a method of measuring magnetic responses of such elementary cells within a wide range of optical frequencies with single probes of two types. The first type probe is made of a tapered silica fiber with radial metal stripes separated by equidistant slits of constant angular width. The second type probe is similar to metal coated, corrugated, tapered fiber apertured SNOM probe, but in this case corrugations are radially oriented. Both types of probes have internal illumination with azimuthally polarized light. In the near-field they concentrate into a subwavelength spot the longitudinal magnetic field component which is much stronger than the perpendicular electric one.

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

2012-05-01

288

Magnetic field screening effect in electroweak model  

E-print Network

It is shown that in the Weinberg-Salam model a magnetic field screening effect for static magnetic solutions takes place. The origin of that phenomenon is conditioned by features of the electro-weak interaction, namely, there is mutual cancellation of Abelian magnetic fields created by the SU(2) gauge fields and Higgs boson. The effect implies monopole charge screening in finite energy system of monopoles and antimonopoles. We consider another manifestation of the screening effect which leads to an essential energy decrease of magnetic solutions. Applying variational method we have found a magnetic field configuration with a topological azimuthal magnetic flux which minimizes the energy functional and possesses a total energy of order 1 TeV. We suppose that corresponding magnetic bound state exists in the electroweak theory and can be detected in experiment.

Bakry, A; Zhang, P M; Zou, L P

2014-01-01

289

Structure of magnetic fields on the quiet sun  

NASA Technical Reports Server (NTRS)

To obtain quantitative temporal and spatial information on the network magnetic fields, auto- and cross-correlation techniques are applied to the Big Bear videomagnetogram data. The average size of the network magnetic elements derived from the auto-correlation curve is about 5700 km. The distance between the primary and secondary peak in the auto-correlation curve is about 17,000 km, which is half of the size of the supergranule as determined from the velocity map. The canceling features and the emergence of ephemeral regions are the major sources for the loss and replenishment of magnetic flux on the quiet sun.

Wang, Haimin

1988-01-01

290

Numerical analysis of magnetic field in superconducting magnetic energy storage  

SciTech Connect

This paper reports that the superconducting magnetic energy storage (SMES) is more useful than the other systems of electric energy storage because of larger stored energy and higher efficiency. The other systems are the battery, the flywheel, the pumped-storage power station. Some models of solenoid type SMES are designed in U.S.A. and Japan. But a high magnetic field happens by the large scale SMES in the living environment, and makes the erroneous operations of the computer display, the pacemaker of the heart and the electronic equipments. We study some fit designs of magnetic shielding of the solenoidal type SMES for reduction of the magnetic field in living environment. When some superconducting shielding coils are over the main storage coil, magnetic field reduces remarkably than the case of non shielding coil. The calculated results of the magnetic field are obtained y the finite element method.

Kanamaru, Y. (Kanazawa Inst. of Technology, 7-1 Ohgigaoka, Nonoichi, Ishikawa 921 (JP)); Amemiya, Y. (Chiba Inst. of Tech., Narashino (Japan))

1991-09-01

291

Reducing Field Distortion in Magnetic Resonance Imaging  

NASA Technical Reports Server (NTRS)

A concept for a magnetic resonance imaging (MRI) system that would utilize a relatively weak magnetic field provides for several design features that differ significantly from the corresponding features of conventional MRI systems. Notable among these features are a magnetic-field configuration that reduces (relative to the conventional configuration) distortion and blurring of the image, the use of a superconducting quantum interference device (SQUID) magnetometer as the detector, and an imaging procedure suited for the unconventional field configuration and sensor. In a typical application of MRI, a radio-frequency pulse is used to excite precession of the magnetic moments of protons in an applied magnetic field, and the decaying precession is detected for a short time following the pulse. The precession occurs at a resonance frequency proportional to the strengths of the magnetic field and the proton magnetic moment. The magnetic field is configured to vary with position in a known way; hence, by virtue of the aforesaid proportionality, the resonance frequency varies with position in a known way. In other words, position is encoded as resonance frequency. MRI using magnetic fields weaker than those of conventional MRI offers several advantages, including cheaper and smaller equipment, greater compatibility with metallic objects, and higher image quality because of low susceptibility distortion and enhanced spin-lattice-relaxation- time contrast. SQUID MRI is being developed into a practical MRI method for applied magnetic flux densities of the order of only 100 T

Eom, Byeong Ho; Penanen, Konstantin; Hahn, Inseob

2010-01-01

292

Electro-magnetically induced transparency in a static magnetic field  

NASA Astrophysics Data System (ADS)

We investigate both theoretically and experimentally the electro- magnetically induced transparency (EIT) phenomenon of atomic 87Rb at the room temperature with a static magnetic field lifting the degeneracy of all three involved hyperfine levels. Two collinearly propagating and linearly polarized laser fields (a probe field and a coupling field) are used to couple one hyperfine level (the upper level) of the 5P 1/2 state to two hyperfine levels (the lower levels) of the 5S 1/2 state, respectively. In the case of zero magnetic fields, we observed a deep EIT window with the contrast of about 66%. Here, the EIT window width is limited by both the spontaneous decay rate of the upper level and the coupling field intensity. When a magnetic field parallel to both laser beams is applied, the EIT window is split into three much narrower sub-windows with contrasts of about 32%. If the magnetic field is perpendicular to the laser beams, however, the EIT window is split into four much narrower sub-windows whose contrasts are 32% or 16%. This is because the decomposition of the linearly polarized optical fields strongly depends on the orientation of the used magnetic field. The underlying physics is that, in the limit of a weak probe field, an ideal degenerate three-level system can be split into three or four sets of independent three-level systems by a magnetic field due to the lifting of magnetic sublevels of the involved hyperfine levels. In this paper the absorption spectra corresponding to different magnetic field directions are clearly shown and compared. And a straightforward but effective theoretical method for analyzing the experimental results is put forward. Our theoretical calculations are in good agreement with the experimental results.

Wei, Xiao-Gang; Gao, Jin-Yue; Wu, Jin-Hui; Sun, Gui-Xia; Wang, Hai-Hua; Kang, Zhi-Hui; Shao, Zhuang; Jiang, Yun

2006-02-01

293

Destruction of magnetic surfaces by magnetic field irregularities: Part II  

Microsoft Academic Search

The present work is a continuation of the paper by Rosenbluth et al. (Nucl. Fusion 6 (1966) 297) and concerns the investigation of problems associated with the condition for the existence of magnetic surfaces in closed systems of the stellarator type. The unperturbed geometry of the magnetic field is produced by a straight helical field. Exact equations for the motion

N. N. Filonenko; R. Z. Sagdeev; G. M. Zaslavskii

1967-01-01

294

Cosmic Magnetic Fields (IAU S259)  

NASA Astrophysics Data System (ADS)

Preface K. G. Strassmeier, A. G. Kosovichev and J. E. Beckman; Organising committee; Conference photograph; Conference participants; Session 1. Interstellar magnetic fields, star-forming regions and the Death Valley Takahiro Kudoh and Elisabeta de Gouveia Dal Pino; Session 2. Multi-scale magnetic fields of the Sun; their generation in the interior, and magnetic energy release Nigel O. Weiss; Session 3. Planetary magnetic fields and the formation and evolution of planetary systems and planets; exoplanets Karl-Heinz Glassmeier; Session 4. Stellar magnetic fields: cool and hot stars Swetlana Hubrig; Session 5. From stars to galaxies and the intergalactic space Dimitry Sokoloff and Bryan Gaensler; Session 6. Advances in methods and instrumentation for measuring magnetic fields across all wavelengths and targets Tom Landecker and Klaus G. Strassmeier; Author index; Object index; Subject index.

Strassmeier, Klaus G.; Kosovichev, Alexander G.; Beckman, John E.

2009-06-01

295

Calculation of magnetic fields for engineering devices  

Microsoft Academic Search

This paper deals with the methodology of magnet technology and its application to various engineering devices. Magnet technology has experienced a rapid growth in the past few years as a result of the advances made in superconductivity, numerical methods and computational techniques. Specifically, this paper concerns itself with: (a) Mathematical models for solving magnetic field problems; (b) The applicability, usefulness,

John S. Colonias

1976-01-01

296

The Evolution of the Earth's Magnetic Field.  

ERIC Educational Resources Information Center

Describes the change of earth's magnetic field at the boundary between the outer core and the mantle. Measurement techniques used during the last 300 years are considered. Discusses the theories and research for explaining the field change. (YP)

Bloxham, Jeremy; Gubbins, David

1989-01-01

297

Coronal magnetic fields and the solar wind  

NASA Technical Reports Server (NTRS)

Current information is presented on coronal magnetic fields as they bear on problems of the solar wind. Both steady state fields and coronal transient events are considered. A brief critique is given of the methods of calculating coronal magnetic fields including the potential (current free) models, exact solutions for the solar wind and field interaction, and source surface models. These solutions are compared with the meager quantitative observations which are available at this time. Qualitative comparisons between the shapes of calculated magnetic field lines and the forms visible in the solar corona at several recent eclipses are displayed. These suggest that: (1) coronal streamers develop above extended magnetic arcades which connect unipolar regions of opposite polarity; and (2) loops, arches, and rays in the corona correspond to preferentially filled magnetic tubes in the approximately potential field.

Newkirk, G., Jr.

1972-01-01

298

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

299

Protecting SQUID metamaterials against stray magnetic fields  

NASA Astrophysics Data System (ADS)

Using superconducting quantum interference devices (SQUIDs) as the basic, low-loss elements of thin-film metamaterials has one main advantage: their resonance frequency is easily tunable by applying a weak magnetic field. The downside, however, is a strong sensitivity to stray and inhomogeneous magnetic fields. In this work, we demonstrate that even small magnetic fields from electronic components destroy the collective, resonant behaviour of the SQUID metamaterial. We also show how the effect of these fields can be minimized. As a first step, magnetic shielding decreases any initially present fields, including the earth’s magnetic field. However, further measures such as improvements in the sample geometry have to be taken to avoid the trapping of Abrikosov vortices.

Butz, S.; Jung, P.; Filippenko, L. V.; Koshelets, V. P.; Ustinov, A. V.

2013-09-01

300

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

301

Magnetic-field measurements for the Lewis Research Center cyclotron  

NASA Technical Reports Server (NTRS)

The magnetic field of the Lewis Center cyclotron was mapped by using a Hall-effect magnetic-field transducer. Main-field Fourier coefficients were determined on a polar mesh of 40 radii for each of seven levels of main-field coil current. Incremental fields for eight sets of trim coils and two sets of harmonic coils were also determined at four of these main-field levels. A stored-program, digital computer was used to perform the measurements. The process was entirely automatic; all data-taking and data-reduction activities were specified by the computer programs. A new method for temperature compensation of a Hall element was used. This method required no temperature control of the element. Measurements of the Hall voltage and Hall-element resistance were sufficient to correct for temperature effects.

Fessler, T. E.

1973-01-01

302

Extended Magnetization of Superconducting Pellets in Highly Inhomogeneous Magnetic Field  

NASA Astrophysics Data System (ADS)

The magnetization of superconducting pellets is a worth point in the development of trapped flux superconducting motors. Experimental and simulated data have been reported extensively according to the framework of one or several pulses of a homogeneous magnetizing field applied to a pellet or a set of pellets. In case of cylindrical rotors of low power motors with radial excitation, however, the use of the copper coils to produce the starting magnetization of the pellets produces a highly inhomogeneous magnetic field which cannot be reduced to a 2D standard model. In this work we present an analysis of the magnetization of the superconducting cylindrical rotor of a small motor by using a commercial FEM program, being the rotor magnetized by the working copper coils of the motor. The aim of the study is a report of the magnetization obtained and theheat generated in the HTSC pellets.

Maynou, R.; López, J.; Granados, X.; Torres, R.; Bosch, R.

303

The Physics of Attraction and Repulsion: Magnetism and Magnetic Fields  

NASA Astrophysics Data System (ADS)

The development of new materials with improved magnetic properties completely changed the modern world in the past decades. Recent progress is predominantly due to a better understanding of magnetism that has gone far beyond compass needles rotating in a magnetic field and bar magnets attracting or repelling each other. New magnetic materials are used to build smaller and smaller read/write heads and hard disks with increased storage capacity, developments that are responsible the revolution in the computer industry. Another example is the field of magnetic levitation that became feasible for commercial applications with the discovery of new superconducting materials, and a prototype train is under development in Japan. In medicine, the development of magnetic resonance imaging (MRI) provides an alternative to other (destructive) radiation techniques.

Nakotte, Heinz

2001-11-01

304

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

305

High concentration ferronematics in low magnetic fields  

NASA Astrophysics Data System (ADS)

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 Bbias, 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 Bbias 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.

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

2014-12-01

306

Comparison of the mean photospheric magnetic field and the interplanetary magnetic field  

Microsoft Academic Search

The mean photospheric magnetic field of the sun seen as a star has been compared with the interplanetary magnetic field observed with spacecraft near the earth. Each change in polarity of the mean solar field is followed about 4 1\\/2 days later by a change in polarity of the interplanetary field (sector boundary). The scaling of the field magnitude from

A. Severny; J. M. Wilcox; P. H. Scherrer; D. S. Colburn

1970-01-01

307

Correlation properties of magnetosheath magnetic field fluctuations  

Microsoft Academic Search

The magnetosheath is characterized by a variety of low-frequency fluctuations, but their features and sources are different. Taking advantage of multipoint magnetic field measurements of the Cluster spacecraft, we present a statistical study to reveal properties of waves. We compute cross-correlation coefficients of magnetic field strengths as measured by pairs of the Cluster spacecraft and determine the correlation length of

O. Gutynska; J. Šafránková; Z. N?me?ek

2009-01-01

308

Magnetic fields, branes, and noncommutative geometry  

Microsoft Academic Search

We construct a simple physical model of a particle moving on the infinite noncommutative 2-plane. The model consists of a pair of opposite charges moving in a strong magnetic field. In addition, the charges are connected by a spring. In the limit of large magnetic field, the charges are frozen into the lowest Landau levels. Interactions of such particles include

Daniela Bigatti; Leonard Susskind

2000-01-01

309

Lattice Planar QED in external magnetic field  

E-print Network

We investigate planar Quantum ElectroDynamics (QED) with two degenerate staggered fermions in an external magnetic field on the lattice. Our preliminary results indicate that in external magnetic fields there is dynamical generation of mass for two-dimensional massless Dirac fermions in the weak coupling region. We comment on possible implications to the quantum Hall effect in graphene.

Paolo Cea; Leonardo Cosmai; Pietro Giudice; Alessandro Papa

2011-09-29

310

Directional discontinuities in the interplanetary magnetic field  

Microsoft Academic Search

It is shown that the interplanetary magnetic field has different characteristics on different scales, and it is noted that a given physical theory may not be applicable or relevant on all scales. Four scales are defined in terms of time intervals on which the data may be viewed. Many discontinuities in the magnetic-field direction are seen on the mesoscale (˜

Leonard F. Burlaga

1969-01-01

311

Lattice Planar QED in external magnetic field  

NASA Astrophysics Data System (ADS)

We investigate planar Quantum ElectroDynamics (QED) with two degenerate staggered fermions in an external magnetic field on the lattice. Our preliminary results indicate that in external magnetic fields there is dynamical generation of mass for two-dimensional massless Dirac fermions in the weak coupling region. We comment on possible implications to the quantum Hall effect in graphene.

Cea, P.; Cosmai, L.; Giudice, P.; Papa, A.

312

Astrophysical magnetic fields and nonlinear dynamo theory  

Microsoft Academic Search

The current understanding of astrophysical magnetic fields is reviewed, focusing on their generation and maintenance by turbulence. In the astrophysical context this generation is usually explained by a self-excited dynamo, which involves flows that can amplify a weak ‘seed’ magnetic field exponentially fast. Particular emphasis is placed on the nonlinear saturation of the dynamo. Analytic and numerical results are discussed

Axel Brandenburg; Kandaswamy Subramanian

2005-01-01

313

Superconductor based sensor for monitoring magnetic field  

Microsoft Academic Search

The authors propose a method for measurement of magnetic fields with the help of a HTSC (high temperature superconductor) based sensor in conjunction with a microcomputer. The same sensor may be used for monitoring current in a circuit under the influence of a controlled magnetic field acting perpendicular to the direction of the current flow. The theoretical basis is discussed.

S. C. Kar; S. P. Basu

1992-01-01

314

Fall in Earth's magnetic field is erratic  

Microsoft Academic Search

Earth's magnetic field has decayed by about 5\\\\% per century since measurements began in 1840. Directional measurements predate those of intensity by more than 250 years, and we combined the global model of directions with paleomagnetic intensity measurements to estimate the fall in strength for this earlier period (1590 to 1840 A.D.). We found that magnetic field strength was nearly

David Gubbins; Adrian L. Jones; Christopher C. Finlay

2006-01-01

315

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

316

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

317

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

318

Quenching of flames by magnetic fields  

Microsoft Academic Search

An experiment has been demonstrated to show a phenomenon involving quenching of candle flames using magnetic fields. An electromagnet with a pair of columnar magnetic poles in which inner sidepieces were hollowed out was used. Magnetic fields of 1.5 T at the brim gave a gradient of 50–300 T\\/m in the direction perpendicular to the pole axis when the distance

S. Ueno

1989-01-01

319

Alignment of magnetic uniaxial particles in a magnetic field: Simulation  

NASA Astrophysics Data System (ADS)

The numerical investigations of the process of alignment of magnetically uniaxial Nd-Fe-B powders in an applied magnetic field were carried out using the discrete element method (DEM). It is shown that magnetic alignment of ensemble of spherical particles provides extremely high degree of alignment, which is achieved in low magnetic fields. A model of formation of anisotropic particles as a combination of spherical particles is suggested. The influence of the shape anisotropy and friction coefficient on the alignment degree was analyzed. The increase in the friction coefficient leads to a decrease in the alignment degree; the simulation results are in qualitative agreement with experimental dependences. It is shown that in magnetic fields higher than 5 T, the calculated field dependences of the alignment degree quantitatively render the experimental data. The increase of about 6% in the alignment degree in the experiments with addition of internal lubricant can be explained by the decrease of 14% in friction coefficient.

Golovnia, O. A.; Popov, A. G.; Sobolev, A. N.; Hadjipanayis, G. C.

2014-09-01

320

In vivo heating of magnetic nanoparticles in alternating magnetic field.  

PubMed

We have evaluated heating capabilities of new magnetic nanoparticles. In in vitro experiments they were exposed to an alternating magnetic field with frequency 3.5 MHz and induction 1.5 mT produced in three turn pancake coil. In in vivo experiments rats with injected magnetic nanoparticles were also exposed to an ac field. An optimal increase of temperature of the tumor to 44 degrees C was achieved after 10 minutes of exposure. Obtained results showed that magnetic nanoparticles may be easily heated in vitro as well as in vivo, and may be therefore useful for hyperthermic therapy of cancer. PMID:15377087

Babincová, M; Altanerová, V; Altaner, C; Cicmanec, P; Babinec, P

2004-08-01

321

Processing of polymers in high magnetic fields  

SciTech Connect

Many organic molecules and polymers have an anisotropic diamagnetic susceptibility, and thus can be aligned in high magnetic fields. The presence of liquid crystallinity allows cooperative motions of the individual molecules, and thus the magnetic energy becomes greater than the thermal energy at experimentally obtainable field strengths. This work has determined the effect of magnetic field alignment on the thermal expansion and mechanical properties of liquid crystalline thermosets in the laboratory. Further advances in magnet design are needed to make magnetic field alignment a commercially viable approach to polymer processing. The liquid crystal thermoset chosen for this study is the diglycidyl ether of dihydroxy-{alpha}-methylstilbene cured with the diamine sulfamilamide. This thermoset has been cured at field strengths up to 18 Tesla.

Douglas, E.P.; Smith, M.E.; Benicewicz, B.C. [Los Alamos National Lab., NM (United States); Earls, J.D.; Priester, R.D. Jr. [Dow Chemical Co., Freeport, TX (United States)

1996-05-01

322

Reionization constraints on primordial magnetic fields  

E-print Network

We study the impact of the extra density fluctuations induced by primordial magnetic fields on the reionization history in the redshift range: $6 magnetic fields (strength, $B_0$, and power-spectrum index $n_{\\scriptscriptstyle \\rm B}$), reionization, and $\\Lambda$CDM cosmological model. We find that magnetic field strengths in the range: $B_0 \\simeq 0.05{-}0.3$ nG (for nearly scale-free power spectra) can significantly alter the reionization history in the above redshift range and can relieve the tension between the WMAP and quasar absorption spectra data. Our analysis puts upper-limits on the magnetic field strength $B_0 magnetic field constraints among those available from other cosmological observables.

Pandey, Kanhaiya L; Sethi, Shiv K; Ferrara, Andrea

2014-01-01

323

Magnetic fields of Ap stars from full Stokes spectropolarimetric observations  

NASA Astrophysics Data System (ADS)

Current knowledge about stellar magnetic fields relies almost entirely on observations of circular polarization. Few objects have been observed in all four Stokes parameters. The magnetic Ap star HD 24712 (DO Eri, HR 1217) was recently observed in the Stokes IQUV parameters with the HARPSpol instrument at the 3.6-m ESO telescope as part of our project at investigating Ap stars in all four Stokes parameters. The resulting spectra have dense phase coverage, resolving power > 10^5, and S/N ratio of 300-600. These are the highest quality full Stokes observations obtained for any star other than the Sun. We present preliminary results from magnetic Doppler imaging of HD 24712. This analysis is the first step towards obtaining detailed 3-D maps of magnetic fields and abundance structures for HD 24712 and for other Ap stars that we are currently observing with HARPSpol.

Rusomarov, N.; Kochukhov, O.; Piskunov, N.

2014-11-01

324

The Magnetic Field in the Solar Atmosphere  

E-print Network

This publication provides an overview of magnetic fields in the solar atmosphere with the focus lying on the corona. The solar magnetic field couples the solar interior with the visible surface of the Sun and with its atmosphere. It is also responsible for all solar activity in its numerous manifestations. Thus, dynamic phenomena such as coronal mass ejections and flares are magnetically driven. In addition, the field also plays a crucial role in heating the solar chromosphere and corona as well as in accelerating the solar wind. Our main emphasis is the magnetic field in the upper solar atmosphere so that photospheric and chromospheric magnetic structures are mainly discussed where relevant for higher solar layers. Also, the discussion of the solar atmosphere and activity is limited to those topics of direct relevance to the magnetic field. After giving a brief overview about the solar magnetic field in general and its global structure, we discuss in more detail the magnetic field in active regions, the quie...

Wiegelmann, Thomas; Solanki, Sami K

2014-01-01

325

Soft-edged magnet models for higher-order beam-optics map codes  

SciTech Connect

Continuously varying surface and volume source-density distributions are used to model magnetic fields inside of cylindrical volumes. From these distributions, a package of subroutines computes on-axis generalized gradients and their derivatives at arbitrary points on the magnet axis for input to the numerical map-generating subroutines of the Lie-algebraic map code Marylie. In the present version of the package, the magnet menu includes: 1. cylindrical current-sheet or radially thick current distributions with either open boundaries or with a surrounding cylindrical boundary with normal field lines (which models high-permeability iron), 2. Halbach-type permanent mutipole magnets, either as sheet magnets or as radially thick magnets, 3. modeling of arbitrary fields inside a cylinder by use of a fictitious current sheet. The subroutines provide on-axis gradients and their z derivatives to essentially arbitrary order, although in the present 3rd and 5th order Marylie only the 0th through 6th derivatives are needed. The formalism is especially useful in beam-optics applications, such as magnetic lenses, where realistic treatment of fringefield effects is needed.

Walstrom, P. L. (Peter L.)

2002-01-01

326

Warm inflation in presence of magnetic fields  

E-print Network

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 the 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 proper time method.

Gabriella Piccinelli; Angel Sanchez; Alejandro Ayala; Ana Julia Mizher

2013-11-03

327

Bending of magnetic filaments under a magnetic field.  

PubMed

Magnetic beads and superparamagnetic (SP) colloid particles have successfully been employed for micromechanical manipulation of soft material, in situ probing of elastic properties, and design of smart materials (ferrogels). Here we derive analytical expressions for the equilibrium shape of magnetic fibers, considering two end-member cases, (a) SP or single-domain particles concentrated at the free end of cantilevered rods or tubes, and (b) filaments consisting of SP particles, with this case being mathematically equivalent to tubes containing SP particles. Our analysis yields also metastable equilibrium states (MES's), which only exist above a critical filament length, but become more stable with increasing magnetic field. The MES's for case (a) are, like the ground state, circular arcs, but more strongly bent. The multiform MES's in case (b), which comprise hairpin, sinuous, or even closed shapes, have recently been observed in experiments, too. We also study the effect of gravity on the balance between bending and magnetic energy, which leads to curves with inflection point if the influence of gravity is stronger than that of the magnetic field. Because of their simple experimental realization, case (a) magnetic filaments are deemed highly suitable for micromechanical experiments on long chains of polymer molecules. Another potential application of cantilevered magnetic filaments with magnetic material attached to the free end is in scanning probe microscopes. Because the magnetic field due to the magnetic tip is comparatively weak, the magnetization structure of the sample to be investigated would not be affected by the probe. Thus, for the examination of magnetically soft materials, probes in the form of magnetic filaments may hold advantages over tips usually employed in magnetic force microscopy. PMID:15697393

Shcherbakov, Valera P; Winklhofer, Michael

2004-12-01

328

‘Clean’ observations of magnetic field fluctuations on planetary surfaces  

Microsoft Academic Search

Magnetic field measurements on planetary surfaces are disturbed by various internal and external sources. We discuss methods to reduce their influence on the quality of magnetic field experiments aboard surface stations. Our major emphasis is on terrestrial seismo-magnetic measurements, but magnetic cleanliness procedures for the ROSETTA lander magnetic field experiment is discussed too. We consider not only disturbing magnetic field

K. Schwingenschuh; G. Prattes; M. Delva; H. U. Eichelberger; G. Berghofer; W. Magnes; M. Vellante; P. Nenovski; V. Wesztergom; H. U. Auster; K.-H. Fornacon

2012-01-01

329

Casimir effect in external magnetic field  

E-print Network

In this paper we examine the Casimir effect for charged fields in presence of external magnetic field. We consider scalar field (connected with spinless particles) and the Dirac field (connected with 1/2-spin particles). In both cases we describe quantum field using the canonical formalism. We obtain vacuum energy by direct solving field equations and using the mode summation method. In order to compute the renormalized vacuum energy we use the Abel-Plana formula.

Marcin Ostrowski

2005-04-13

330

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

331

Magnetic monopole field exposed by electrons  

E-print Network

Magnetic monopoles have provided a rich field of study, leading to a wide area of research in particle physics, solid state physics, ultra-cold gases, superconductors, cosmology, and gauge theory. So far, no true magnetic monopoles were found experimentally. Using the Aharonov-Bohm effect, one of the central results of quantum physics, shows however, that an effective monopole field can be produced. Understanding the effects of such a monopole field on its surroundings is crucial to its observation and provides a better grasp of fundamental physical theory. We realize the diffraction of fast electrons at a magnetic monopole field generated by a nanoscopic magnetized ferromagnetic needle. Previous studies have been limited to theoretical semiclassical optical calculations of the motion of electrons in such a monopole field. Solid state systems like the recently studied 'spin ice' provide a constrained system to study similar fields, but make it impossible to separate the monopole from the material. Free space ...

Béché, A; Van Tendeloo, G; Verbeeck, J

2013-01-01

332

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

333

Modeling solar force-free magnetic fields  

NASA Astrophysics Data System (ADS)

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 and the free energy associated with the electric current are finite and can be calculated directly from the magnetic field at the plane boundary using the virial theorem. In the study of solar magnetic fields with data from vector magnetographs, there is a long-standing interest in devising algorithms to extrapolate for the force-free magnetic field in a given domain from prescribed field values at the boundary. The closed-form magnetic fields of this paper open up an opportunity for testing the reliability and accuracy of algorithms that claim the capability of performing this extrapolation. The extrapolation procedure as an ill-posed mathematical problem is discussed.

Low, B. C.; Lou, Y. Q.

1990-03-01

334

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

335

Magnetic and velocity fields of a solar pore  

NASA Astrophysics Data System (ADS)

Context. Solar pores are intermediate-size magnetic flux features that emerge at the surface of the Sun. The absence of a filamentary penumbra indicates that there is a relatively simple magnetic structure with a prevailing vertical magnetic field. Aims: Relations between the magnetic field components, line-of-sight velocities, and horizontal motions in and around a large pore (Deff = 8''.5) are analysed to provide observational constraints on theoretical models and numerical simulations. Methods: Spectropolarimetric observations in Fe I 617.3 nm of the pore NOAA 11005 with the IBIS spectrometer attached to the Dunn Solar Telescope are inverted into series of maps of thermal, magnetic, and velocity parameters using the SIR code. Horizontal velocities are obtained from series of white-light images by means of local correlation tracking. Results: The magnetic field B extends from the visible pore border of more than 3''.5 and has a radial structure in a form of spines that are co-spatial with dark intergranular lanes. The horizontal component Bhor is more extended than the vertical component Bz. The temperature linearly decreases with increasing Bz, by about - 300 K kG-1 in the photosphere and - 800 K kG-1 in the umbra. The temperature contrast of granulation increases with increasing magnetic field strength and is then suppressed for Bz > 1200 G. Granular upflows dominate in regions with Bz < 600-700 G. Line-of-sight velocities are lower in stronger fields, except for fast isolated downflows at the pore's border. The velocity signature of granulation is suppressed completely for Bhor > 1000 G. Horizontal motions of granules start to be damped for Bz > 500 G and recurrently exploding granules appear only in magnetic fields comparable to or weaker than the equipartition field strength 400 G.

Sobotka, M.; Del Moro, D.; Jur?ák, J.; Berrilli, F.

2012-01-01

336

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

337

Chapter 3: Circum-Arctic mapping project: New magnetic and gravity anomaly maps of the Arctic  

USGS Publications Warehouse

New Circum-Arctic maps of magnetic and gravity anomalies have been produced by merging regional gridded data. Satellite magnetic and gravity data were used for quality control of the long wavelengths of the new compilations. The new Circum-Arctic digital compilations of magnetic, gravity and some of their derivatives have been analyzed together with other freely available regional and global data and models in order to provide a consistent view of the tectonically complex Arctic basins and surrounding continents. Sharp, linear contrasts between deeply buried basement blocks with different magnetic properties and densities that can be identified on these maps can be used, together with other geological and geophysical information, to refine the tectonic boundaries of the Arctic domain. ?? 2011 The Geological Society of London.

Gaina, C.; Werner, S.C.; Saltus, R.; Maus, S.; Aaro, S.; Damaske, D.; Forsberg, R.; Glebovsky, V.; Johnson, K.; Jonberger, J.; Koren, T.; Korhonen, J.; Litvinova, T.; Oakey, G.; Olesen, O.; Petrov, O.; Pilkington, M.; Rasmussen, T.; Schreckenberger, B.; Smelror, M.

2011-01-01

338

QCD vacuum structure in strong magnetic fields  

Microsoft Academic Search

We study the response of the QCD vacuum to strong magnetic fields, using a potential model for the quark-antiquark interaction. We find that production of spin-polarized u¯ u pairs is energetically favorable for fields B > Bcrit ? 10 GeV2. We contrast the resulting uu condensate with the quark condensate which is present at zero magnetic field, and we estimate

Daniel Kabata; Kimyeong Leea; Erick Weinberg

339

Ohm's law for mean magnetic fields  

SciTech Connect

The magnetic fields associated with plasmas frequently exhibit small amplitude MHD fluctuations. It is useful to have equations for the magnetic field averaged over these fluctuations, the so-called mean field equations. Under very general assumptions it is shown that the effect of MHD fluctuations on a force-free plasma can be represented by one parameter in Ohm's law, which is effectively the coefficient of electric current viscosity.

Boozer, A.H.

1986-05-01

340

Ultrafast heating and magnetic switching with weak external magnetic field  

NASA Astrophysics Data System (ADS)

The TbFeCo magneto-optical media with the coercivity of bigger than 1.0 kOe are used for the investigation of ultrafast heating and magnetic switching with the weak external magnetic field. It has been found that the laser-induced active region becomes larger with an external magnetic field because the boundary of the active region is magnetized with the assistance of the external field during the ultrafast heating. According to this physical phenomenon, the so called "mark expansion method" has been proposed for visual observation of ultrafast switching marks. Using this method, the ultrafast magnetic switching in TbFeCo media has been studied using 40 fs laser pulse with linear polarization. The result shows that the ultrafast magnetic switching can be implemented by the laser pulse with assistance of the weak external field of about 0.7 kOe. Further studies show that the area percentage of the magnetic mark expansion relative to its thermal mark decreases with the increasing of the laser pulse energy. There exists the threshold pulse energy that the active region is fully magnetized. The theoretical analysis of electron, spin, and lattice temperatures has been conducted to the active region of the media where the maximum spin temperature is close to the Curie temperature of the media. The result indicates that the media become active at 4.137 ps and the ultrafast heating plays a key role for the ultrafast magnetic switching. The weak external magnetic field provides sufficient driving force to control the magnetization direction in the media.

Li, J. M.; Xu, B. X.; Zhang, J.; Ye, K. D.

2013-01-01

341

Tuning permanent magnets with adjustable field clamps  

SciTech Connect

The effective length of a permanent-magnet assembly can be varied by adjusting the geometrical parameters of a field clamp. This paper presents measurements on a representative dipole and quadrupole as the field clamp is withdrawn axially or radially. The detailed behavior depends upon the magnet multipolarity and geometry. As a rule-of-thumb, a 3-mm-thick iron plate placed at one end plane of the magnet will shorten the length by one-third of the magnet bore radius.

Schermer, R.I.

1987-01-01

342

Modeling the lithospheric magnetic field over France by means of revised spherical cap harmonic analysis  

E-print Network

Modeling the lithospheric magnetic field over France by means of revised spherical cap harmonic first vector lithospheric field model over France, which extends from surface to 500 km of altitude radius. The magnetic lithospheric map consistency is confirmed with a comparison to known geological

Thébault, Erwan

343

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

344

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

345

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

346

Scanning magnetic tunnel junction microscope for high-resolution imaging of remanent magnetization fields  

NASA Astrophysics Data System (ADS)

Scanning magnetic microscopy is a new methodology for mapping magnetic fields with high spatial resolution and field sensitivity. An important goal has been to develop high-performance instruments that do not require cryogenic technology due to its high cost, complexity, and limitation on sensor-to-sample distance. Here we report the development of a low-cost scanning magnetic microscope based on commercial room-temperature magnetic tunnel junction (MTJ) sensors that typically achieves spatial resolution better than 7?µm. By comparing different bias and detection schemes, optimal performance was obtained when biasing the MTJ sensor with a modulated current at 1.0 kHz in a Wheatstone bridge configuration while using a lock-in amplifier in conjunction with a low-noise custom-made preamplifier. A precision horizontal (x-y) scanning stage comprising two coupled nanopositioners controls the position of the sample and a linear actuator adjusts the sensor-to-sample distance. We obtained magnetic field sensitivities better than 150 nT/Hz1/2 between 0.1 and 10?Hz, which is a critical frequency range for scanning magnetic microscopy. This corresponds to a magnetic moment sensitivity of 10-14 A m2, a factor of 100 better than achievable with typical commercial superconducting moment magnetometers. It also represents an improvement in sensitivity by a factor between 10 and 30 compared to similar scanning MTJ microscopes based on conventional bias-detection schemes. To demonstrate the capabilities of the instrument, two polished thin sections of representative geological samples were scanned along with a synthetic sample containing magnetic microparticles. The instrument is usable for a diversity of applications that require mapping of samples at room temperature to preserve magnetic properties or viability, including paleomagnetism and rock magnetism, nondestructive evaluation of materials, and biological assays.

Lima, E. A.; Bruno, A. C.; Carvalho, H. R.; Weiss, B. P.

2014-10-01

347

Magnetic field induced transition in vanadium spinels.  

PubMed

We study vanadium spinels AV2O4 (A = Cd,Mg) in pulsed magnetic fields up to 65 T. A jump in magnetization at ?0H?40??T is observed in the single-crystal MgV2O4, indicating a field induced quantum phase transition between two distinct magnetic orders. In the multiferroic CdV2O4, the field induced transition is accompanied by a suppression of the electric polarization. By modeling the magnetic properties in the presence of strong spin-orbit coupling characteristic of vanadium spinels, we show that both features of the field induced transition can be successfully explained by including the effects of the local trigonal crystal field. PMID:24483929

Mun, E D; Chern, Gia-Wei; Pardo, V; Rivadulla, F; Sinclair, R; Zhou, H D; Zapf, V S; Batista, C D

2014-01-10

348

Velocity-Magnetic Field Correlation of Pulsars  

NASA Astrophysics Data System (ADS)

Monte Carlo simulations of the evolution of pulsars are carried out in order to compare with the recent measurement of the pulsar transverse velocity by Lyne & Lorimer (1994). The new electron density distribution model of Taylor & Cordes (1993) is adopted in the simulation. Accurate pulsar o rbits in the Galactic gravitational field are calculated. It is found that the constant magnetic field model of pulsars can account for the new measurement of the pulsar transverse velocity, and the apparent correlat ion between the strength of the magnetic field and the transverse velocity of the pulsars. The present finding confirms the validity of the constant magnetic field model of pulsars, and consolidates the idea that the app arent correlation between the strength of the magnetic field and the transverse velocity of the pulsars is cau sed by observational selection effects.

Itoh, N.; Kotouda, T.

349

ASYMMETRIC DIFFUSION OF MAGNETIC FIELD LINES  

SciTech Connect

Stochasticity of magnetic field lines is important for particle transport properties. Magnetic field lines separate faster than diffusively in turbulent plasma, which is called superdiffusion. We discovered that this superdiffusion is pronouncedly asymmetric, so that the separation of field lines along the magnetic field direction is different from the separation in the opposite direction. While the symmetry of the flow is broken by the so-called imbalance or cross-helicity, the difference between forward and backward diffusion is not directly due to imbalance, but a non-trivial consequence of both imbalance and non-reversibility of turbulence. The asymmetric diffusion perpendicular to the mean magnetic field entails a variety of new physical phenomena, such as the production of parallel particle streaming in the presence of perpendicular particle gradients. Such streaming and associated instabilities could be significant for particle transport in laboratory, space, and astrophysical plasmas.

Beresnyak, Andrey [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2013-04-20

350

Normal glow discharge in axial magnetic field  

NASA Astrophysics Data System (ADS)

Theory and results of mathematical modeling of a glow discharge in a parallel-plate configuration with axial magnetic field is presented. The model consists of continuity equations for electron and ion fluids, the Poisson equation for the self-consistent electric field. Numerical simulation results are presented for two-dimensional glow discharge at various initial conditions. The results are obtained for molecular nitrogen at pressure 1–5 Torr, emf of power supply 1–2 kV, and magnetic field induction B = 0–0.5 T. It is shown that in the presence of the axial magnetic field the glow discharge is rotated around its axis of symmetry. Nevertheless it is shown that in the investigated range of discharge parameters in an axial magnetic field the law of the normal current density is retained.

Surzhikov, S.; Shang, J.

2014-10-01

351

Tracing Magnetic Fields by Atomic Alignment in Extended Radiation Fields  

E-print Network

Tracing magnetic fields is crucial as magnetic fields play an important role in many astrophysical processes. Earlier studies have demonstrated that Ground State Alignment (GSA) is a unique way to detect weak magnetic fields (1G> B> 1exp(-15)G) in diffuse media, they consider the situation when the pumping source is a point source, which applies when the star is very far away from the diffuse media. In this paper, we explore the GSA in the presence of extended radiation fields. For the radiation fields with a clear geometric structure, we consider the alignment in circumstellar medium, binary systems, disc, and Local Interstellar Medium (LISM). For the radiation fields with unidentified pumping sources, we apply the method of multipole expansion and discuss the GSA induced by each component. We demonstrate that for general radiation fields, it is adequate to consider the contribution from dipole and quadrupole radiation components. We find that in general polarization of absorption arizing from GSA coincides ...

Zhang, Heshou; Dong, Le

2014-01-01

352

Quantum Electrodynamics in a Uniform Magnetic Field  

E-print Network

A systematic formalism for quantum electrodynamics in a classical uniform magnetic field is discussed. The first order radiative correction to the ground state energy of an electron is calculated. This then leads to the anomalous magnetic moment of an electron without divergent integrals. Thorough analyses of this problem are given for the weak magnetic field limit. A new expression for the radiative correction to the ground state energy is obtained. This contains only one integral with an additional summation with respect to each Landau level. The importance of this formalism is also addressed in order to deal with quantum electrodynamics in an intense external field.

Jun Suzuki

2005-12-28

353

Magnetic fields from second-order interactions  

E-print Network

It is well known that when two types of perturbations interact in cosmological perturbation theory, the interaction may lead to the generation of a third type. In this article we discuss the generation of magnetic fields from such interactions. We determine conditions under which the interaction of a first-order magnetic field with a first-order scalar-or vector-, or tensor-perturbations would lead to the generation of second order magnetic field. The analysis is done in a covariant-index-free approach, but could be done in the standard covariant indexed-approach.

Bob Osano

2014-03-21

354

Joule heating in high magnetic field pulsars  

E-print Network

We study the efficiency of Joule heating in the crustal layers of young neutron stars. It is shown that dissipation of the magnetic field is highly inhomogeneous in the crust with much faster dissipation in relatively low density layers. In young neutron stars, the rate of Joule heating in the crust can exceed the standard luminosity of non-magnetic star and can even be comparable to the luminosity of magnetars. The results of calculations are compared with the available observational data. We argue that the crustal field model can well account for the data on the surface temperature and magnetic field of young neutron stars.

Urpin, V

2008-01-01

355

Joule heating in high magnetic field pulsars  

E-print Network

We study the efficiency of Joule heating in the crustal layers of young neutron stars. It is shown that dissipation of the magnetic field is highly inhomogeneous in the crust with much faster dissipation in relatively low density layers. In young neutron stars, the rate of Joule heating in the crust can exceed the standard luminosity of non-magnetic star and can even be comparable to the luminosity of magnetars. The results of calculations are compared with the available observational data. We argue that the crustal field model can well account for the data on the surface temperature and magnetic field of young neutron stars.

V. Urpin; D. Konenkov

2008-04-01

356

Dynamo Models for Saturn's Axisymmetric Magnetic Field  

NASA Astrophysics Data System (ADS)

Magnetic field measurements by the Cassini mission have confirmed the earlier Pioneer 11 and Voyager missions' results that Saturn's observed magnetic field is extremely axisymmetric . For example, Saturn's dipole tilt is less than 0.06 degrees (Cao et al., 2011) . The nearly-perfect axisymmetry of Saturn's dipole is troubling because of Cowling's Theorem which states that an axisymmetric magnetic field cannot be maintained by a dynamo. However, Cowling's Theorem applies to the magnetic field generated inside the dynamo source region and we can avert any contradiction with Cowling's Theorem if we can find reason for a non-axisymmetric field generated inside the dynamo region to have an axisymmetrized potential field observed at satellite altitude. Stevenson (1980) proposed a mechanism for this axisymmetrization. He suggested that differential rotation in a stably-stratified electrically conducting layer (i.e. the helium rain-out layer) surrounding the dynamo could act to shear out the non-axisymmetry and hence produce an axisymmetric observed magnetic field. In previous work, we used three-dimensional self-consistent numerical dynamo models to demonstrate that a thin helium rain-out layer can produce a more axisymmetrized field (Stanley, 2010). We also found that the direction of the zonal flows in the layer is a crucial factor for magnetic field axisymmetry. Here we investigate the influence of the thickness of the helium rain-out layer and the intensity of the thermal winds on the axisymmetrization of the field. We search for optimal regions in parameter space for producing axisymmetric magnetic fields with similar spectral properties to the observed Saturnian field.

Stanley, S.; Tajdaran, K.

2012-12-01

357

Folding Digital Mapping into a Traditional Field Camp Program  

NASA Astrophysics Data System (ADS)

Louisiana State University runs a field camp with a permanent fixed-base which has continually operated since 1928 in the Front Range just to the south of Colorado Springs, CO. The field camp program which offers a 6-credit hour course in Field Geology follows a very traditional structure. The first week is spent collecting data for the construction of a detailed stratigraphic column of the local geology. The second week is spent learning the skills of geologic mapping, while the third applies these skills to a more geologically complicated mapping area. The final three weeks of the field camp program are spent studying and mapping igneous and metamorphic rocks as well as conducting a regional stratigraphic correlation exercise. Historically there has been a lack of technology involved in this program. All mapping has been done in the field without the use of any digital equipment and all products have been made in the office without the use of computers. In the summer of 2011 the use of GPS units, and GIS software were introduced to the program. The exercise that was chosen for this incorporation of technology was one in which metamorphic rocks are mapped within Golden Gate Canyon State Park in Colorado. This same mapping exercise was carried out during the 2010 field camp session with no GPS or GIS use. The students in both groups had the similar geologic backgrounds, similar grade point averages, and similar overall performances at field camp. However, the group that used digital mapping techniques mapped the field area more quickly and reportedly with greater ease. Additionally, the students who used GPS and GIS included more detailed rock descriptions with their final maps indicating that they spent less time in the field focusing on mapping contacts between units. The outcome was a better overall product. The use of GPS units also indirectly caused the students to produce better field maps. In addition to greater ease in mapping, the use of GIS software to create maps was rewarding to the students and gave them mapping experience that is in line with industry standards.

Kelley, D. F.

2011-12-01

358

On magnetic field generation in Kolmogorov turbulence  

E-print Network

We analyze the initial, kinematic stage of magnetic field evolution in an isotropic and homogeneous turbulent conducting fluid with a rough velocity field, v(l) ~ l^alpha, alphamagnetic Reynolds number that is needed to excite magnetic fluctuations. This implies that numerical or experimental investigations of the Kolmogorov turbulence with small Prandtl numbers need to achieve extremely high resolution in order to adequately describe magnetic phenomena; (ii) For small Prandtl numbers, magnetic energy penetrates below the resistive scale and has a power-law spectrum between the resistive and viscous scales. Magnetic energy is dissipated not at the resistive scale but at the much smaller viscous scale, which may be relevant for the problems of anomalous resistivity and fast magnetic reconnection. Our results also suggest that the l...

Boldyrev, S A; Boldyrev, Stanislav; Cattaneo, Fausto

2004-01-01

359

Recent biophysical studies in high magnetic fields  

NASA Astrophysics Data System (ADS)

A brief overview of biophysical effects of steady magnetic fields is given. The need of high field strength is illustrated by several recent diamagnetic orientation experiments. They include rod-like viruses, purple membranes and chromosomes. Results of various studies on bees, quails, rats and pigeons exposed to fields above 7 T are also resumed.

Maret, Georg

1990-06-01

360

Computer Program for Earths magnetic field  

Microsoft Academic Search

A FORTRAN IV computer program has been developed by the U.S. Coast and Geodetic Survey to compute the elements of the earths magnetic field for any geographic position.Part of the program is a mathematical model of the geomagnetic field consisting of two sets of spherical harmonic coefficients. The first set, representing the main geomagnetic field, consists of 168 coefficients (degree

Anonymous

1970-01-01

361

FEM Computation of Magnetic Fields in Anisotropic Magnetic Materials  

NASA Astrophysics Data System (ADS)

The magnetic fields in nonlinear anisotropic magnetic materials were analyzed by using the Finite Element Method (FEM). The measured data was directly used in the computation without a complicateded smoothing. The resultant asymmetric linear equations were solved by using the ILUBiCGStab method without symmetrization or the ICCG method with symmetrization. The magnetic flux distributions in a ring core model showed the characteristic patterns according to the non-oriented, grain-oriented and doubly-oriented magnetic properties. The good convergence of the Newton-Raphson nonlinear iteration was attained by the iterative solvers without special techniques for the smoothing.

Kameari, Akihisa; Fujiwara, Koji

362

TRANSITION REGION MAGNETIC FIELD AND POLAR MAGNETIC DISTURBANCES  

Microsoft Academic Search

The Explorer 12 measurements of the magnetic field outside the magnetosphere are compared with ground magnetograms from arctic observatories. Results indicate that an exterior field with a southerly component tends to be associated with ground disturbance, whereas a northward field is associated with quiet conditions. Examples are presented show- ing how a north-to-south field-direction change accompanies an increase in ground

D. H. Fairfield; L. J. Jr. Cahill

1966-01-01

363

Review: Magnetic fields of O stars  

E-print Network

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

Wade, G A

2014-01-01

364

Magnetic field effects on surgical ligation clips.  

PubMed

Magnetic forces exerted on surgical clips and the magnetic resonance imaging distortion they create in phantoms and rabbits at magnetic field strengths of 1.5 Tesla were investigated. Results are reported for both ligation and aneurysm clips manufactured from three types of stainless steel as well as titanium, tantalum and niobium metals. Paramagnetism and eddy currents were measured in a customized moving Gouy balance. Direct measurements of other magnetic forces were carried out in a 1.5T MRI system. The titanium and tantalum clips showed the least interaction with the magnetic field, both in terms of forces exerted and the observed image distortion with the larger clips generating the larger interactions. The strongest field distortions and attractive forces occurred with 17-7PH stainless steel clips. These interactions were ferromagnetic in origin and of sufficient strength to present significant risk to patients having this type of clip present during an MRI scan. PMID:3431354

Brown, M A; Carden, J A; Coleman, R E; McKinney, R; Spicer, L D

1987-01-01

365

The rotation-magnetic field relation  

NASA Astrophysics Data System (ADS)

Today, the generation of magnetic fields in solar-type stars and its relation to activity and rotation can coherently be explained, although it is certainly not understood in its entirety. Rotation facilitates the generation of magnetic flux that couples to the stellar wind, slowing down the star. There are still many open questions, particularly at early phases (young age), and at very low mass. It is vexing that rotational braking becomes inefficient at the threshold to fully convective interiors, although no threshold in magnetic activity is seen, and the generation of large scale magnetic fields is still possible for fully convective stars. This article briefly outlines our current understanding of the rotation-magnetic field relation.

Reiners, Ansgar; Scholz, Alexander; Eislöffel, Jochen; Hallinan, Gregg; Berger, Edo; Browning, Matthew; Irwin, Jonathan; Küker, Manfred; Matt, Sean

2009-02-01

366

Electrical properties of chain microstructure magnetic emulsions in magnetic field  

E-print Network

The work deals with the experimental study of the emulsion whose dispersion medium is a magnetic fluid while the disperse phase is formed by a glycerin-water mixture. It is demonstrated that under effect of a magnetic field chain aggregates form from the disperse phase drops. Such emulsion microstructure change affects its macroscopic properties. The emulsion dielectric permeability and specific electrical conductivity have been measured. It is demonstrated that under the effect of relatively weak external magnetic fields (~ 1 kA/m) the emulsion electrical parameters may change several fold. The work theoretically analyzes the discovered regularities of the emulsion electrical properties.

Arthur Zakinyan; Yuri Dikansky; Marita Bedzhanyan

2014-02-05

367

MISALIGNMENT OF MAGNETIC FIELDS AND OUTFLOWS IN PROTOSTELLAR CORES  

SciTech Connect

We present results of {lambda}1.3 mm dust-polarization observations toward 16 nearby, low-mass protostars, mapped with {approx}2.''5 resolution at CARMA. The results show that magnetic fields in protostellar cores on scales of {approx}1000 AU are not tightly aligned with outflows from the protostars. Rather, the data are consistent with scenarios where outflows and magnetic fields are preferentially misaligned (perpendicular), or where they are randomly aligned. If one assumes that outflows emerge along the rotation axes of circumstellar disks, and that the outflows have not disrupted the fields in the surrounding material, then our results imply that the disks are not aligned with the fields in the cores from which they formed.

Hull, Charles L. H.; Plambeck, Richard L.; Bower, Geoffrey C.; Heiles, Carl; Meredith Hughes, A. [Astronomy Department and Radio Astronomy Laboratory, University of California, Berkeley, CA 94720-3411 (United States); Bolatto, Alberto D.; Jameson, Katherine; Mundy, Lee; Pound, Marc W. [Astronomy Department and Laboratory for Millimeter-wave Astronomy, University of Maryland, College Park, MD 20742 (United States); Carpenter, John M.; Lamb, James W.; Pillai, Thushara [Department of Astronomy, California Institute of Technology, 1200 E. California Blvd., MC 249-17, Pasadena, CA 91125 (United States); Crutcher, Richard M.; Hakobian, Nicholas S.; Kwon, Woojin; Looney, Leslie W. [Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 W Green Street, Urbana, IL 61801 (United States); Fiege, Jason D.; Franzmann, Erica [Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB R3T 2N2 (Canada); Houde, Martin [Department of Physics and Astronomy, University of Western Ontario, London, ON N6A 3K7 (Canada); Matthews, Brenda C., E-mail: chat@astro.berkeley.edu [Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Rd., Victoria, BC V8P 5C2 (Canada); and others

2013-05-10

368

Magnetic field generated by current filaments  

NASA Astrophysics Data System (ADS)

We investigate the magnetic field generated by two straight current filaments using the analogy between steady MHD and Euler flows. Using the Biot-Savart law, we present a dynamical system describing the extension of magnetic lines around the current filaments. It is demonstrated that, if two current filaments are non-parallel, a magnetic line starting near one current goes to infinity by the drifting effect of the other.

Kimura, Y.

2014-10-01

369

The earth's magnetic field: Its history, origin and planetary perspective  

Microsoft Academic Search

The history of geomagnetism and palaeomagnetism is examined, and an analysis and description of the present geomagnetic field is presented. The magnetic compass is discussed along with declination, inclination, secular variation, magnetic charts and the search for the poles, fossil magnetism and the magnetic field in the past, transient magnetic variations regarding the external magnetic field, the origin of the

R. T. Merrill; M. W. McElhinny

1983-01-01

370

Wire codes, magnetic fields, and childhood cancer  

SciTech Connect

Childhood cancer has been modestly associated with wire codes, an exposure surrogate for power frequency magnetic fields, but less consistently with measured fields. The authors analyzed data on the population distribution of wire codes and their relationship with several measured magnetic field metrics. In a given geographic area, there is a marked trend for decreased prevalence from low to high wire code categories, but there are differences between areas. For average measured fields, there is a positive relationship between the mean of the distributions and wire codes but a large overlap among the categories. Better discrimination is obtained for the extremes of the measurement values when comparing the highest and the lowest wire code categories. Instability of measurements, intermittent fields, or other exposure conditions do not appear to provide a viable explanation for the differences between wire codes and magnetic fields with respect to the strength and consistency of their respective association with childhood cancer.

Kheifets, L.I.; Kavet, R.; Sussman, S.S. [Electric Power Research Inst., Palo Alto, CA (United States)] [Electric Power Research Inst., Palo Alto, CA (United States)

1997-05-01

371

Cosmic Magnetic Fields and the CMB  

E-print Network

I describe the imprint of primordial magnetic fields on the CMB. I show that these are observable only if the field amplitude is of the order of $B\\gsim 10^{-9}G$ on Mpc scale. I further argue that such fields are strongly constrained by the stochastic background of gravity waves which they produce. Primordial magnetic fields, which are strong enough to be seen in the CMB, are compatible with the nucleosynthesis bound, only if their spectrum is close to scale invariant, or maybe if helical magnetic fields provoke an inverse cascade. For helical fields, the CMB signature is especially interesting. It contains parity violating T-B and E--B correlations.

Ruth Durrer

2006-09-08

372

Magnetic Dipole Field 3D Model  

NSDL National Science Digital Library

The Magnetic Dipole Field 3D Model displays the field lines and field vectors of a dipole located at the origin and oriented along the z-axis. Users can compute the field line passing through a point by dragging the a marker within the 3D view. Users can also visualize the field vectors in a plane passing though the center of the dipole. The Magnetic Dipole Field 3D Model was developed using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_em_MagneticDipole3D.jar file will run the program if Java is installed. EJS is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models.

Christian, Wolfgang

2012-08-11

373

Rotation of the Earth's Magnetic Field  

Microsoft Academic Search

HALLEY1 first noticed that the magnetic declination at a number of sites changed with time in a manner that was consistent with a steady westward drift of the magnetic field relative to the surface of the Earth. After long neglect, interest in westward drift was revived by the work of Bullard et al.2, who examined the westward drift of the

S. R. C. Malin; I. Saunders

1973-01-01

374

End fields of CBA superconducting magnets  

SciTech Connect

Measurements of the two dimensional harmonic content of the end fields generated by the Brookhaven CBA dipole and quadrupole superconducting magnets are presented. Both the local longitudinal structure and the integrated end effects are examined.

Kirk, H.G.; Herrera, J.; Willen, E.

1983-01-01

375

Magnetic Field Response Measurement Acquisition System  

NASA Technical Reports Server (NTRS)

A measurement acquisition method that alleviates many shortcomings of traditional measurement systems is presented in this paper. The shortcomings are a finite number of measurement channels, weight penalty associated with measurements, electrical arcing, wire degradations due to wear or chemical decay and the logistics needed to add new sensors. The key to this method is the use of sensors designed as passive inductor-capacitor circuits that produce magnetic field responses. The response attributes correspond to states of physical properties for which the sensors measure. A radio frequency antenna produces a time-varying magnetic field used to power the sensor and receive the magnetic field response of the sensor. An interrogation system for discerning changes in the sensor response is presented herein. Multiple sensors can be interrogated using this method. The method eliminates the need for a data acquisition channel dedicated to each sensor. Methods of developing magnetic field response sensors and the influence of key parameters on measurement acquisition are discussed.

Woodard, Stanley E.; Taylor, Bryant D.; Shams, Qamar A.; Fox, Robert L.

2005-01-01

376

Magnetic Field Response Measurement Acquisition System  

NASA Technical Reports Server (NTRS)

Magnetic field response sensors designed as passive inductor-capacitor circuits produce magnetic field responses whose harmonic frequencies correspond to states of physical properties for which the sensors measure. Power to the sensing element is acquired using Faraday induction. A radio frequency antenna produces the time varying magnetic field used for powering the sensor, as well as receiving the magnetic field response of the sensor. An interrogation architecture for discerning changes in sensor s response kequency, resistance and amplitude is integral to the method thus enabling a variety of measurements. Multiple sensors can be interrogated using this method, thus eliminating the need to have a data acquisition channel dedicated to each sensor. The method does not require the sensors to be in proximity to any form of acquisition hardware. A vast array of sensors can be used as interchangeable parts in an overall sensing system.

Woodard, Stanley E. (Inventor); Taylor, Bryant D. (Inventor); Shams, Qamar A. (Inventor); Fox, Robert L. (Inventor); Fox, Christopher L. (Inventor); Fox, Melanie L. (Inventor); Bryant, Robert G. (Inventor)

2006-01-01

377

Vacuum Birefringence in Strong Magnetic Fields  

Microsoft Academic Search

Table of Contents 1. One-loop effective Lagrangian in spinor QED. 2. Dispersion effects for low-frequency photons. 3. Vacuum birefringence in magnetic fields. 4. Light cone condition, effective Lagrangian approach.

Walter Dittrich; Holger Gies

1998-01-01

378

Fractal structure of the interplanetary magnetic field  

NASA Technical Reports Server (NTRS)

Under some conditions, time series of the interplanetary magnetic field strength and components have the properties of fractal curves. Magnetic field measurements made near 8.5 AU by Voyager 2 from June 5 to August 24, 1981 were self-similar over time scales from approximately 20 sec to approximately 3 x 100,000 sec, and the fractal dimension of the time series of the strength and components of the magnetic field was D = 5/3, corresponding to a power spectrum P(f) approximately f sup -5/3. Since the Kolmogorov spectrum for homogeneous, isotropic, stationary turbulence is also f sup -5/3, the Voyager 2 measurements are consistent with the observation of an inertial range of turbulence extending over approximately four decades in frequency. Interaction regions probably contributed most of the power in this interval. As an example, one interaction region is discussed in which the magnetic field had a fractal dimension D = 5/3.

Burlaga, L. F.; Klein, L. W.

1985-01-01

379

Lunar magnetic field measurements with a cubesat  

E-print Network

We have developed a mission concept that uses 3-unit cubesats to perform new measurements of lunar magnetic fields, less than 100 meters above the Moon’s surface. The mission calls for sending the cubesats on impact ...

Garrick-Bethell, Ian

380

Impurities in magnetic-field-induced Luttinger liquid  

NASA Astrophysics Data System (ADS)

It has been shown recently(C. Biagini, D. L. Maslov, M. Yu. Reizer and L. I. Glazman, `` Magnetic-field-induced Luttinger liquid''), cond-mat/0006407. that a strong magnetic field applied to a bulk metal may induce a Luttinger liquid phase. This is a consequence of the reduced effective dimensionality of charge carriers from 3D to 1D, an effect which is most pronounced in the ultra-quantum limit, when only the lowest Landau level remains populated. We study the effect of impurities in this system. For the case of a point impurity, the calculation of the scattering cross section at a single impurity can be mapped exactly to a 1D problem of tunneling conductance through a barrier for interacting electrons, solved by Yue et al.(D. Yue, L. I. Glazman and K. A. Matveev, Phys. Rev. B 49) (1994) 1966.. Using this mapping, we find that the longitudinal (?=+1) and transverse (?=-1) Drude conductivities exhibit the scaling laws ?_?? T^??, where ?=2e^2|ln?l_B|/? v_F, and vF and ? are the B-dependent Fermi velocity and screening wavevector, respectively; lB is the magnetic length. The physical reason for such a behavior of the conductivity is the almost 1D form of the Friedel oscillation around a single point impurity in the strong magnetic field.

Tsai, Shan-Wen; Maslov, Dmitrii L.; Glazman, Leonid I.

2001-03-01

381

Laminated magnet field coil sheath  

DOEpatents

a method for manufacturing a magnet cable trim coil in a sheath assembly for use in a cryogenic particle accelerator. A precisely positioned pattern of trim coil turns is bonded to a flexible substrate sheath that is capable of withstanding cryogenic operating conditions. In the method of the invention the flexible sheath, with the trim coil pattern precisely positioned thereon, is accurately positioned at a precise location relative to a bore tube assembly of an accelerator and is then bonded to the bore tube with a tape suitable for cryogenic application. The resultant assembly can be readily handled and installed within an iron magnet yoke assembly of a suitable cryogenic particle accelerator.

Skaritka, John R. (Coram, NY)

1987-12-01

382

Laminated magnet field coil sheath  

DOEpatents

A method for manufacturing a magnetic cable trim coil in a sheath assembly for use in a cryogenic particle accelerator. A precisely positioned pattern of trim coil turns is bonded to a flexible substrate sheath that is capable of withstanding cryogenic operating conditions. In the method of the invention the flexible substrate sheath, with the trim coil pattern precisely location relative to a bore tube assembly of an accelerator and is then bonded to the bore tube with a tape suitable for cryogenic application. The resultant assembly can be readily handled and installed within an iron magnet yoke assembly of a suitable cryogenic particle accelerator. 1 fig.

Skaritka, J.R.

1987-05-15

383

Bi2212\\/Ag high-field magnets  

Microsoft Academic Search

Bi-2212\\/Ag conductors show practical transport properties in high magnetic field regions above 20 T and 4.2 K, where it is considered difficult to use metallic superconductors. In this paper, the recent progress of our development of Bi-2212\\/Ag high field insert magnets is presented. Bi-2212\\/Ag stacked double pancake coils with a 49–150 mm outer diameter, 15–65 mm inner diameter and 50–220

M. Okada; K. Tanaka; T. Wakuda; K. Ohata; J. Sato; T. Kiyoshi; H. Kitaguchi; H. Wada

2000-01-01

384

The magnetic field investigation on Cluster  

NASA Technical Reports Server (NTRS)

The magnetic field investigation of the Cluster four-spacecraft mission is designed to provide intercalibrated measurements of the B magnetic field vector. The instrumentation and data processing of the mission are discussed. The instrumentation is identical on the four spacecraft. It consists of two triaxial fluxgate sensors and of a failure tolerant data processing unit. The combined analysis of the four spacecraft data will yield such parameters as the current density vector, wave vectors, and the geometry and structure of discontinuities.

Balogh, A.; Cowley, S. W. H.; Southwood, D. J.; Musmann, G.; Luhr, H.; Neubauer, F. M.; Glassmeier, K.-H.; Riedler, W.; Heyn, M. F.; Acuna, M. H.

1988-01-01

385

Mean-field quantum dynamics with magnetic fields  

E-print Network

We consider a system of $N$ bosons in three dimensions interacting through a mean-field Coulomb potential in an external magnetic field. For initially factorized states we show that the one-particle density matrix associated with the solution of the $N$-body Schr\\"odinger equation converges to the projection onto the solution of the magnetic Hartree equation in trace norm and in energy as $N \\rightarrow \\infty$. Estimates on the rate of convergence are provided.

Jonas Luhrmann

2012-02-06

386

Magnetic field transfer device and method  

DOEpatents

A magnetic field transfer device includes a pair of oppositely wound inner coils which each include at least one winding around an inner coil axis, and an outer coil which includes at least one winding around an outer coil axis. The windings may be formed of superconductors. The axes of the two inner coils are parallel and laterally spaced from each other so that the inner coils are positioned in side-by-side relation. The outer coil is outwardly positioned from the inner coils and rotatable relative to the inner coils about a rotational axis substantially perpendicular to the inner coil axes to generate a hypothetical surface which substantially encloses the inner coils. The outer coil rotates relative to the inner coils between a first position in which the outer coil axis is substantially parallel to the inner coil axes and the outer coil augments the magnetic field formed in one of the inner coils, and a second position 180[degree] from the first position, in which the augmented magnetic field is transferred into the other inner coil and reoriented 180[degree] from the original magnetic field. The magnetic field transfer device allows a magnetic field to be transferred between volumes with negligible work being required to rotate the outer coil with respect to the inner coils. 16 figs.

Wipf, S.L.

1990-02-13

387

The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: SHARPs - Space-Weather HMI Active Region Patches  

NASA Astrophysics Data System (ADS)

A new data product from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) called Space-weather HMI Active Region Patches ( SHARPs) is now available. SDO/HMI is the first space-based instrument to map the full-disk photospheric vector magnetic field with high cadence and continuity. The SHARP data series provide maps in patches that encompass automatically tracked magnetic concentrations for their entire lifetime; map quantities include the photospheric vector magnetic field and its uncertainty, along with Doppler velocity, continuum intensity, and line-of-sight magnetic field. Furthermore, keywords in the SHARP data series provide several parameters that concisely characterize the magnetic-field distribution and its deviation from a potential-field configuration. These indices may be useful for active-region event forecasting and for identifying regions of interest. The indices are calculated per patch and are available on a twelve-minute cadence. Quick-look data are available within approximately three hours of observation; definitive science products are produced approximately five weeks later. SHARP data are available at jsoc.stanford.edu and maps are available in either of two different coordinate systems. This article describes the SHARP data products and presents examples of SHARP data and parameters.

Bobra, M. G.; Sun, X.; Hoeksema, J. T.; Turmon, M.; Liu, Y.; Hayashi, K.; Barnes, G.; Leka, K. D.

2014-09-01

388

Dynamic signatures of quiet sun magnetic fields  

NASA Technical Reports Server (NTRS)

The collision and disappearance of opposite polarity fields is observed most frequently at the borders of network cells. Due to observational limitations, the frequency, magnitude, and spatial distribution of magnetic flux loss have not yet been quantitatively determined at the borders or within the interiors of the cells. However, in agreement with published hypotheses of other authors, the disapperance of magnetic flux is speculated to be a consequence of either gradual or rapid magnetic reconnection which could be the means of converting magnetic energy into the kinetic, thermal, and nonthermal sources of energy for microflares, spicules, the solar wind, and the heating of the solar corona.

Martin, S. F.

1983-01-01

389

Particle decay in Ising field theory with magnetic field  

E-print Network

The scaling limit of the two-dimensional Ising model in the plane of temperature and magnetic field defines a field theory which provides the simplest illustration of non-trivial phenomena such as spontaneous symmetry breaking and confinement. Here we discuss how Ising field theory also gives the simplest model for particle decay. The decay widths computed in this theory provide the obvious test ground for the numerical methods designed to study unstable particles in quantum field theories discretized on a lattice.

Gesualdo Delfino

2007-03-30

390

Levin and Ernst, DC Magnetic Field Effects on Development Applied DC Magnetic Fields Cause Alterations in the  

E-print Network

Levin and Ernst, DC Magnetic Field Effects on Development Applied DC Magnetic Fields Cause relative to fertilization. The exposure time which caused the maximum effect differed between the two urchin, static magnetic field, gastrulation, development, mitotic cycle, teratogenic effects running

Levin, Michael

391

Effects of static magnetic fields on plants.  

NASA Astrophysics Data System (ADS)

In our recent experiment on STS-107 (MFA-Biotube) we took advantage of the magnetic heterogeneity of the gravity receptor cells of flax roots, namely stronger diamagnetism of starch-filled amyloplasts compared to cytoplasm (? ? < 0). High gradient magnetic fields (HGMF, grad(H2/2) up to 109-1010 Oe2/cm) of the experimental chambers (MFCs) repelled amyloplasts from the zones of stronger field thus providing a directional stimulus for plant gravisensing system in microgravity, and causing the roots to react. Such reaction was observed in the video downlink pictures. Unfortunately, the ``Columbia'' tragedy caused loss of the plant material and most of the images, thus preventing us from detailed studies of the results. Currently we are looking for a possibility to repeat this experiment. Therefore, it is very important to understand, what other effects (besides displacing amyloplasts) static magnetic fields with intensities 0 to 2.5104 Oe, and with the size of the area of non-uniformity 10-3 to 1 cm. These effects were estimated theoretically and tested experimentally. No statistically significant differences in growth rates or rates of gravicurvature were observed in experiments with Linum, Arabidopsis, Hordeum, Avena, Ceratodon and Chara between the plants grown in uniform magnetic fields of various intensities (102 to 2.5104 Oe) and those grown in the Earth's magnetic field. Microscopic studies also did not detect any structural differences between test and control plants. The magnitudes of possible effects of static magnetic fields on plant cells and organs (including effects on ion currents, magneto-hydrodynamic effects in moving cytoplasm, ponderomotive forces on other cellular structures, effects on some biochemical reactions and biomolecules) were estimated theoretically. The estimations have shown, that these effects are small compared to the thermodynamic noise and thus are insignificant. Both theoretical estimations and control experiments confirm, that intracellular magnetophoresis of statoliths is the only significant effect of the magnetic field on plant cells and organs in the tested magnetic systems.

Kuznetsov, O.

392

Magnetic field structure evolution in RMF plasmas  

NASA Astrophysics Data System (ADS)

A study of magnetic field structure evolution during 40-ms plasma discharge had been performed in 80 cm long / 40 cm OD cylindrical chamber. Plasma current Ip˜2--3 kA is produced by applied 500 kHz rotating magnetic field. In experiments, the 2D profile of plasma current is changed by feeding a 10-ms pulse current to additional magnetic coil located at the midplane. Using newly developed magnetic field pick-up coils system, we scanned the magnetic field in cross-section of plasma. Two experimental regimes were studied: without external toroidal field (TF), and with TF produced by applied axial current. When a relatively small current (<0.5 kA) is applied to the midplane coil, in both cases the total plasma current measured with Rogowski coil experiences a jump (up to 100%), but the profile of current remains almost unchanged. When a larger current (1--2 kA) is applied to the midplane coil, the total plasma current drops; the magnetic structure changes differently in two regimes. In regime without TF, the magnetic field of plasma current is reversed at Rmagnetic field evolves during initial 1--3 ms transitional period of plasma formation.

Petrov, Yuri; Yang, Xiaokang; Huang, Tian-Sen

2007-11-01

393

Superconductivity in Strong Magnetic Field (Greater Than Upper Critical Field)  

SciTech Connect

The National High Magnetic Field Laboratory, funded by the National Science Foundation and other US federal Agencies, has in recent years built a wide range of magnetic fields, DC 25 to 35 Tesla, short pulse 50 - 60 Tesla, and quasi-continuous 60 Tesla. Future plans are to push the frontiers to 45 Tesla DC and 70 to 100 Tesla pulse. This user facility, is open for national and international users, and creates an excellent tool for materials research (metals, semiconductors, superconductors, biological systems ..., etc). Here we present results of a systematic study of the upper critical field of a novel superconducting material which is considered a promising candidate for the search for superconductivity beyond H{sub c2} as proposed by several new theories. These theories predict that superconductors with low carrier density can reenter the superconducting phase beyond the conventional upper critical field H{sub c2}. This negates the conventional thinking that superconductivity and magnetic fields are antagonistic.

Tessema, G.X.; Gamble, B.K.; Skove, M.J.; Lacerda, A.H.; Mielke, C.H.

1998-08-22

394

Observation of the Faraday effect via beam deflection in a longitudinal magnetic field  

SciTech Connect

We show that magnetic-field-induced circular differential deflection of light can be observed in reflection or refraction at a single interface. The difference in the reflection or refraction angles between the two circular polarization components is a function of the magnetic-field strength and the Verdet constant, and permits the observation of the Faraday effect not via polarization rotation in transmission, but via changes in the propagation direction. Deflection measurements do not suffer from n-{pi} ambiguities and are shown to be another means to map magnetic fields with high axial resolution, or to determine the sign and magnitude of magnetic-field pulses in a single measurement.

Ghosh, Ambarish; Hill, Winfield; Fischer, Peer [Rowland Institute at Harvard, Harvard University, Cambridge, Massachusetts 02142 (United States)

2007-11-15

395

Rapid Change of Field Line Connectivity and Reconnection in Stochastic Magnetic Fields  

NASA Astrophysics Data System (ADS)

Magnetic fields without a direction of continuous symmetry have the generic feature that neighboring field lines exponentiate away from each other and become stochastic, and hence the ideal constraint of preserving magnetic field line connectivity becomes exponentially sensitive to small deviations from ideal Ohm's law. The idea of breaking field line connectivity by stochasticity as a mechanism for fast reconnection is tested with numerical simulations based on reduced magnetohydrodynamics equations with a strong guide field line-tied to two perfectly conducting end plates. Starting from an ideally stable force-free equilibrium, the system is allowed to undergo resistive relaxation. Two distinct phases are found in the process of resistive relaxation. During the quasi-static phase, rapid change of field line connectivity and strong induced flow are found in regions of high field line exponentiation. However, although the field line connectivity of individual field lines can change rapidly, the overall pattern of field line mapping appears to deform gradually. From this perspective, field line exponentiation appears to cause enhanced diffusion rather than reconnection. In some cases, resistive quasi-static evolution can cause the ideally stable initial equilibrium to cross a stability threshold, leading to formation of intense current filaments and rapid change of field line mapping into a qualitatively different pattern. It is in this onset phase that the change of field line connectivity is more appropriately designated as magnetic reconnection. Our results show that rapid change of field line connectivity appears to be a necessary, but not a sufficient condition for fast reconnection.

Huang, Yi-Min; Bhattacharjee, A.; Boozer, Allen H.

2014-10-01

396

Magnetic marker based homogeneous bioassays utilizing rotating magnetic fields  

NASA Astrophysics Data System (ADS)

Magnetic nanoparticles (MNPs) as markers in bioassays utilizing rotating instead of alternating magnetic fields predict an improved sensitivity regarding quantitative protein detection. This finding is based on numerical solutions of the Fokker-Planck equation and pronounced for increasing field amplitudes. In order to verify this prediction, the phase lag change of MNPs in rotating magnetic fields up to 5 mT is measured. The magnetic markers are functionalized single core iron oxide nanoparticles with different sizes. Antibodies which specifically bind to the MNPs cause the phase lag change. The increase of the phase lag change strongly depends on the particle parameters. MNPs with a core diameter of 30 nm show for 5 mT, a significant difference between the two field types. This difference is less pronounced for the 25 nm MNPs due to the increasing influence of Néel relaxation processes and for the 40 nm particles, due to the reduced saturation magnetization. A further improvement for the 30 nm MNPs with field amplitudes over 5 mT is simulated based on the determined particle parameters.

Dieckhoff, Jan; Schilling, Meinhard; Ludwig, Frank

2014-05-01

397

Magnetic fields of Jupiter and Saturn  

SciTech Connect

The magnetic fields of Jupiter and Saturn and the characteristics of their magnetospheres, formed by interaction with the solar wind, are discussed. The origins of both magnetic fields are associated with a dynamo process deep in the planetary interior. The Jovian magnetosphere is analogous to that of a pulsar magnetosphere: a massive central body with a rapid rotation and an associated intense magnetic field. Its most distinctive feature is its magnetodisk of concentrated plasma and particle flux, and reduced magnetic field intensity. The magnetopause near the subsolar point has been observed at radial distances ranging over 50 to 100 Jovian radii, implying a relatively compressible obstacle to solar wind flow. The composition of an embedded current sheet within the magnetic tail is believed to be influenced by volcanic eruptions and emissions from Io. Spectral troughs of the Jovian radiation belts have been interpreted as possible ring particles. The Saturnian magnetosphere appears to be more like the earth in its topology. It is mainly characterized by a dipole axis parallel to the rotational axis of the planet and a magnetic field intensity much less than expected.

Ness, N.F.

1981-01-01

398

Slowly rotating pulsars and magnetic field decay  

NASA Astrophysics Data System (ADS)

Two dozen long period pulsars are separated from the swarm of ordinary pulsars by an obvious gap in the P versus Sd diagram (where Sd=log?(P)+21.0), with a plausible upper boundary for ordinary pulsars. Possible pulsar evolutionary tracks are discussed to explain the diagram in terms of previously suggested scenarios of magnetic field decay. The (P-Sd) diagram is difficult to understand if there is no magnetic field decay during the active life of pulsars. However, if the magnetic fields of neutron stars decay exponentially, almost all slowly rotating pulsars must have been injected with a very long initial spin period of about 2 seconds, which seems impossible. Based on qualitative analyses, it is concluded that magnetic fields of neutron stars decay as a power-law, with a time scale related to the initial field strengths. The plausible boundary and the gap are suggested to naturally divide pulsars with distinct magnetic "genes", ie. pulsars which were born from strongly magnetized progenitors -- such as Bp stars, and pulsars born from normal massive stars. The possibility remains open that a fraction of slowly rotating pulsars were injected with long initial spin periods, while others would have a classical pulsar evolution history. It is suggested that PSR B1849+00 was born in the supernova remnant Kes-79 with an initial period of about 2 seconds.

Han, J. L.

1997-02-01

399

Stabilizing textures with magnetic fields  

E-print Network

The best-known way of stabilizing textures is by Skyrme-like terms, but another possibility is to use gauge fields. The semilocal vortex may be viewed as an example of this, in two spatial dimensions. In three dimensions, however, the idea (in its simplest form) does not work -- the link between the gauge field and the scalar field is not strong enough to prevent the texture from collapsing. Modifying the |D Phi|^2 term in the Lagrangian (essentially by changing the metric on the Phi-space) can strengthen this link, and lead to stability. Furthermore, there is a limit in which the gauge field is entirely determined in terms of the scalar field, and the system reduces to a pure Skyrme-like one. This is described for gauge group U(1), in dimensions two and three. The non-abelian version is discussed briefly, but as yet no examples of texture stabilization are known in this case.

R S Ward

2002-07-11

400

Plasma separation from magnetic field lines in a magnetic nozzle  

NASA Technical Reports Server (NTRS)

This paper discusses conditions for separation of a plasma from the magnetic field of a magnetic nozzle. The analysis assumes a collisionless, quasineutral plasma, and therefore the results represent a lower bound on the amount of detachment possible for a given set of plasma conditions. We show that collisionless separation can occur because finite electron mass inhibits the flow of azimuthal currents in the nozzle. Separation conditions are governed by a parameter G which depends on plasma and nozzle conditions. Several methods of improving plasma detachment are presented, including moving the plasma generation zone downstream from the region of strongest magnetic field and using dual magnets to focus the plasma beam. Plasma detachment can be enhanced by manipulation of the nozzle configuration.

Kaufman, D. A.; Goodwin, D. G.; Sercel, J. C.

1993-01-01

401

Mapping the sound field of the Lyric Theater  

NASA Astrophysics Data System (ADS)

Impulse response measurements were taken in each of the 235 orchestra-level house-left seats of the Lyric Theater in order to explore spatial differences in the sound field of the room. These measurements produced graphic mappings depicting gradients of sound decay time and loudness. Significant interseat variations appeared when mapping the decay times for the 63- and 125-Hz octave bands; these variations largely disappeared when mapping the decay times for octave bands greater than 250 Hz. A scaled physical model and a CATT-Acoustics software model of the space were built to explore the veracity and usefulness of modeling to determine intraroom spatial differences in sound fields.

Ermann, Michael; Kidner, Michael; McCoy, Joe; Mennitt, Dan; Tawney, Adam; Yoder, Bill

2004-10-01

402

A quantitative test of different magnetic field models using conjunctions between DMSP and geosynchronous orbit  

SciTech Connect

We report here on a study which tests the magnetic field line mapping between geosynchronous orbit and the ionosphere. The mapping is determined both observationally and from five magnetospheric magnetic field models. The mapping is tested observationally by comparing electron energy spectra obtained by the Magnetospheric Plasma Analyzer (MPA) at geosynchronous orbit and by the DMSP spacecraft. Because the orbits are nearly perpendicular, in general, the spectra match well for only a few seconds providing a good determination of when DMSP crosses the geosynchronous drift shell. In this way the mapping between geosynchronous orbit and the ionosphere can be determined to better than one degree. We then compare the measured magnetic footpoints of geosynchronous orbit with the footpoints predicted by five magnetospheric field models: Tsyganenko-89, Tsyganenko-87, Tsyganenko-82, Oslen-Pfitzer, and Hilmer-Voigt. Based on a set of over 100 measured magnetic conjunctions we find that, in general, there are significant differences between the mappings predicted by various magnetic field models but that there is no clear ``winner`` in predicting the observed mapping. We find that the range of magnetic latitudes at which we measure conjunctions is much broader than the range of latitudes which the models can accommodate. This lack of range is common to all magnetic field models tested. Although there are certainly cases where the models are not sufficiently stretched, we find that on average all magnetic field models tested are too stretched. This technique provides an excellent opportunity for testing future magnetic field models and for determining the appropriate parameterizations for those models. 21 refs., 4 figs.

Reeves, G.D.; Weiss, L.A.; Thomsen, M.F.; McComas, D.J.

1996-03-01

403

The magnetic field of the Milky Way  

Microsoft Academic Search

Since its discovery 40 years ago as a confiner of cosmic rays and an aligner of interstellar dust grains, the Galactic magnetic field has been studied through emission and polarization of synchrotron radiation, Faraday rotation, Zeeman splitting, and effects on gas flows and morphology. The local field has a coherent, few microgauss, component roughly along the local spiral arm and

Virginia Trimble

1990-01-01

404

Vacuum polarization tensor in inhomogeneous magnetic fields  

Microsoft Academic Search

We develop worldline numerical methods, which combine string-inspired with Monte Carlo techniques, for the computation of the vacuum polarization tensor in inhomogeneous background fields for scalar QED. The algorithm satisfies the Ward identity exactly and operates on the level of renormalized quantities. We use the algorithm to study for the first time light propagation in a spatially varying magnetic field.

Holger Gies; Lars Roessler

2011-01-01

405

Magnetic field generation from nonequilibrium phase transitions  

Microsoft Academic Search

We study the generation of magnetic fields during the stage of particle production resulting from spinodal instabilities during phase transitions out of equilibrium. The main premise is that long-wavelength instabilities that drive the phase transition lead to strong nonequilibrium charge and current fluctuations which generate electromagnetic fields. We present a formulation based on the nonequilibrium Schwinger-Dyson equations that leads to

D. Boyanovsky; H. J. de Vega; M. Simionato

2003-01-01

406

Magnetic field effects on CRT computer monitors  

Microsoft Academic Search

This paper discusses the effect of external low frequency magnetic field interference on cathode ray tube (CRT) computer monitors. The paper describes a new test facility and presents a quantitative measuring method which has been developed to characterize the field effects. A total of 21 monitors from major manufacturers were tested. It was found that larger monitors are more sensitive

Balazs Banfai; George G. Karady; Charles J. Kim; Kate Brown Maracas

2000-01-01

407

Cosmic rays in the earth's magnetic field  

Microsoft Academic Search

It is shown that the values of cosmic ray cut-off moments in the earth's magnetic field, observed at many different places, are generally close to the values calculated from Störmer's theory for the motion of charged particles in a dipole field, if the usual centre dipole of the earth is replaced in the Störmer equation by a dipole whose magnitude

P. Rothwell

1958-01-01

408

Aerial radiometric and magnetic survey: Hobbs National Topographic Map, New Mexico/Texas. Final report  

SciTech Connect

The results of analyses of the airborne gamma radiation and total magnetic field survey flown for the region identified as the Hobbs National Topographic Map NI13-12 are presented in this report. The airborne data gathered are reduced by ground computer facilities to yield profile plots of the basic uranium, thorium and potassium equivalent gamma radiation intensities, ratios of these intensities, aircraft altitude above the earth's surface, total gamma ray and earth's magnetic field intensity, correlated as a function of geologic units. The distribution of data within each geologic unit, for all surveyed map lines and tie lines, has been calculated and is included. Two sets of profiled data for each line are included, with one set displaying the above-cited data. The second set includes only flight line magnetic field, temperature, pressure, altitude data plus magnetic field data as measured at a base station. A general description of the area, including descriptions of the various geologic units and the corresponding airborne data, is included also.

Not Available

1980-05-01

409

Hydrogen atom in a strong magnetic field  

NASA Astrophysics Data System (ADS)

We study the energy spectrum of atomic hydrogen in strong ( B \\gt B_a\\sim 10^9 G) and ultra-strong ( B \\gtrsim B_cr \\sim 10^{14} G) magnetic fields, in which the hydrogen electron starts to move relativistically and quantum electrodynamics effects become important. Within the adiabatic approximation, highly accurate energy level values are obtained analytically for B \\gt 10^{11} G, which are then compared with asymptotic and numerical results available in the literature. A characteristic feature noted in electron motion in a strong magnetic field is that for B \\gtrsim B_cr, the transverse motion becomes relativistic, while the longitudinal motion (along B) can be described by nonrelativistic theory and is amenable to the adiabatic approximation. Topics discussed include: the qualitative difference in the way odd and even levels change with the magnetic field (for B \\gg B_a); the removal of degeneracy between odd and even atomic states; spectral scaling relations for different quantum numbers (n, n_\\rho, m) and different field strengths; the shape, size, and quadrupole moment of the atom for B \\gg B_a; radiative transitions np\\to 1s in a strong magnetic field; relativistic QED effects, including the effects of vacuum polarization and of the electron anomalous magnetic moment on the energy level positions; Coulomb potential screening and energy level freezing at B\\to \\infty ; and the possibility of the Zeldovich effect in the hydrogen spectrum in a strong magnetic field. The critical nuclear charge problem is briefly discussed. Simple asymptotic formulas for Z_cr, valid for low-lying levels, are proposed. Some of the available information on extreme magnetic fields produced in the laboratory and occurring in space is given. The Coulomb renormalization of the scattering length is considered in the resonance situation with a shallow level in the spectrum.

Popov, V. S.; Karnakov, B. M.

2014-03-01

410

Magnetic nanoparticles for applications in oscillating magnetic field  

SciTech Connect

Enzymatic and thermochemical catalysis are both important industrial processes. However, the thermal requirements for each process often render them mutually exclusive: thermochemical catalysis requires high temperature that denatures enzymes. One of the long-term goals of this project is to design a thermocatalytic system that could be used with enzymatic systems in situ to catalyze reaction sequences in one pot; this system would be useful for numerous applications e.g. conversion of biomass to biofuel and other commodity products. The desired thermocatalytic system would need to supply enough thermal energy to catalyze thermochemical reactions, while keeping the enzymes from high temperature denaturation. Magnetic nanoparticles are known to generate heat in an oscillating magnetic field through mechanisms including hysteresis and relaxational losses. We envisioned using these magnetic nanoparticles as the local heat source embedded in sub-micron size mesoporous support to spatially separate the particles from the enzymes. In this study, we set out to find the magnetic materials and instrumental conditions that are sufficient for this purpose. Magnetite was chosen as the first model magnetic material in this study because of its high magnetization values, synthetic control over particle size, shape, functionalization and proven biocompatibility. Our experimental designs were guided by a series of theoretical calculations, which provided clues to the effects of particle size, size distribution, magnetic field, frequency and reaction medium. Materials of theoretically optimal size were synthesized, functionalized, and their effects in the oscillating magnetic field were subsequently investigated. Under our conditions, the materials that clustered e.g. silica-coated and PNIPAM-coated iron oxides exhibited the highest heat generation, while iron oxides embedded in MSNs and mesoporous iron oxides exhibited the least bulk heating. It is worth noting that the specific loss power of PNIPAM-coated Fe{sub 3}O{sub 4} was peculiarly high, and the heat loss mechanism of this material remains to be elucidated. Since thermocatalysis is a long-term goal of this project, we also investigated the effects of the oscillating magnetic field system for the synthesis of 7-hydroxycoumarin-3-carboxylic acid. Application of an oscillating magnetic field in the presence of magnetic particles with high thermal response was found to effectively increase the reaction rate of the uncatalyzed synthesis of the coumarin derivative compared to the room temperature control.

Peeraphatdit, Chorthip

2010-12-15

411

Circumstellar Magnetic Field Diagnostics from Line Polarization  

E-print Network

Given that dynamically significant magnetic fields in at least some massive stars have now been measured, our contribution addresses the question, to what extent can fields be directly detected in circumstellar gas? The question speaks directly to the very interesting topic of line-driving physics coupled with magnetized plasmas, and how this coupling produces structure in the wind flow. We focus our attention on weak-field diagnostics. These come in two main types: the Hanle effect, which pertains to coherence effects for linear polarization from line scattering, and the weak longitudinal Zeeman effect, which pertains to circular polarization in lines.

Richard Ignace; Kenneth G. Gayley

2007-08-14

412

Nonperturbative Physics in a Magnetic Field  

E-print Network

Non-Perturbative Quantum Field Theory has played an important role in the study of phenomena where a fermion condensate can appear under certain physical conditions. The familiar phenomenon of electric superconductivity, the color superconductivity of very dense quark matter, and the chiral symmetry breaking of low energy effective chiral theories are all examples of that sort. Often one is interested in the behavior of these systems in the presence of an external magnetic field. In this talk I will outline the effects of an external magnetic field on theories with either fermion-fermion or fermion-antifermion condensates.

Vivian de la Incera

2010-04-28

413

Self-induced quasistationary magnetic fields  

SciTech Connect

The interaction of electromagnetic radiation with temporally dispersive magnetic solids of small dimensions may show very special resonant behaviors. The internal fields of such samples are characterized by magnetostatic-potential scalar wave functions. The oscillating modes have the energy orthogonality properties and unusual pseudoelectric (gauge) fields. Because of a phase factor, that makes the states single valued, a persistent magnetic current exists. This leads to appearance of an eigenelectric moment of a small disk sample. One of the intriguing features of the mode fields is dynamical symmetry breaking.

Kamenetskii, E. O. [Department of Electrical and Computer Engineering, Ben Gurion University of the Negev, Beer Sheva 84105 (Israel)

2006-01-15

414

Varying Electromagnetic Coupling and Primordial Magnetic Fields  

E-print Network

We study the effect of variations of the electromagnetic coupling on the process of generation of primordial magnetic fields. We find that only through a significant growth of the electromagnetic coupling minimum seed fields can be produced. We also show that, if through some process in the early Universe the photon acquires a mass that leads, thanks to inflation, to the generation of primordial magnetic fields, then the influence of variations of the electromagnetic coupling amounts essentially to the results due to the photon effective mass alone.

O. Bertolami; R. Monteiro

2005-04-08

415

Plasma heating in a variable magnetic field  

SciTech Connect

The problem of particle acceleration in a periodically variable magnetic field that either takes a zero value or passes through zero is considered. It is shown that, each time the field [0]passes through zero, the particle energy increases abruptly. This process can be regarded as heating in the course of which plasma particles acquire significant energy within one field period. This mechanism of plasma heating takes place in the absence of collisions between plasma particles and is analogous to the mechanism of magnetic pumping in collisional plasma considered by Alfven.

Kichigin, G. N., E-mail: king@iszf.irk.ru [Russian Academy of Sciences, Institute of Solar-Terrestrial Physics (Russian Federation)

2013-05-15

416

Assessment of inhomogeneous ELF magnetic field exposures.  

PubMed

In daily life as well as at workplaces, exposures to inhomogeneous magnetic fields become very frequent. This makes easily applicable compliance assessment methods increasingly important. Reference levels have been defined linking basic restrictions to levels of homogeneous fields at worst-case exposure conditions. If reference levels are met, compliance with basic restrictions can be assumed. If not, further investigations could still prove compliance. Because of the lower induction efficiency, inhomogeneous magnetic fields such as from electric appliances could be allowed exceeding reference levels. To easily assess inhomogeneous magnetic fields, a quick and flexible multi-step assessment procedure is proposed. On the basis of simulations with numerical, anatomical human models reference factors were calculated elevating reference levels to link hot-spot values measured at source surfaces to basic limits and allowing accounting for different source distance, size, orientation and position. Compliance rules are proposed minimising assessment efforts. PMID:18407972

Leitgeb, N; Cech, R; Schröttner, J

2008-01-01

417

Neutrino Processes in Strong Magnetic Fields  

E-print Network

The processes of electron neutrino capture on neutron and electron anti-neutrino capture on proton, and their reverse processes provide the dominant mechanisms for heating and cooling the material below the stalled shock in a core-collapse supernova. We summarize the major effects of strong magnetic fields on the rates of the above reactions and illustrate these effects with a simple supernova model. Due to parity violation of weak interaction the heating rates are asymmetric even for a uniform magnetic field. The cooling rates are also asymmetric for nonuniform fields. The most dramatic effect of strong magnetic fields of 10^16 G is suppression of the cooling rates by changing the equations of state through the phase space of electrons and positrons.

Huaiyu Duan; Yong-Zhong Qian

2005-06-07

418

Magnetic field structure in Monoceros R2  

NASA Technical Reports Server (NTRS)

We have carried out polarimetric observations to investigate the geometry of the magnetic field in the giant molecular cloud Monoceros R2. This study is based upon deep R-band charge coupled device (CCD) polarimetry, covering a total area of 0.5 deg(exp 2) of the giant molecular cloud. The data were calibrated using a new technique that relies on obtaining broad-band photometry of stars simultaneously with polarimetric photometry of the Mon R2 fields, thus providing an accurate means of measuring the electric vectors of starlight which is polarized by the fore-ground dust grains aligned by the magnetic field in the Mon R2 GMC. In this work, (1) we were able to continuously trace magnetic field lines from the largest scales in Mon R2 to the detailed structure of the field in the dense core, as determined from infrared polarimetry; and (2) we have found that the ambient field is apparently modified by a large-scale structure in the Mon R2 cloud. The mean angle of polarization for the complete sample we measured is 158 deg, which is roughly coincident with the local Galactic magnetic field (155 deg). The dispersion in the angle of polarization is 33 deg, similar to that found in the Orion GMC. The dispersion in angle of polarization for stars located along the western side of the three CCD fields is 22 deg. The CCD fields are bisected by a dense ridge of gas defining the boundary of an expanding gas shell that recent observational results at millimeter wavelengths now reveal dominates the Mon R2 GMC. Our results suggest th at the expanding shell has distorted the magnetic field lines extending from the core to the northern gas structure comprising Mon R2.

Jarrett, T. H.; Novak, G.; Xie, T.; Goldsmith, P. F.

1994-01-01

419

Vacuum polarization tensor in inhomogeneous magnetic fields  

E-print Network

We develop worldline numerical methods, which combine string-inspired with Monte-Carlo techniques, for the computation of the vacuum polarization tensor in inhomogeneous background fields for scalar QED. The algorithm satisfies the Ward identity exactly and operates on the level of renormalized quantities. We use the algorithm to study for the first time light propagation in a spatially varying magnetic field. Whereas a local derivative expansion applies to the limit of small variations compared to the Compton wavelength, the case of a strongly varying field can be approximated by a derivative expansion for the averaged field. For rapidly varying fields, the vacuum-magnetic refractive indices can exhibit a non-monotonic dependence on the local field strength. This behavior can provide a natural limit on the self-focussing property of the quantum vacuum.

Gies, Holger

2011-01-01

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Vacuum polarization tensor in inhomogeneous magnetic fields  

E-print Network

We develop worldline numerical methods, which combine string-inspired with Monte-Carlo techniques, for the computation of the vacuum polarization tensor in inhomogeneous background fields for scalar QED. The algorithm satisfies the Ward identity exactly and operates on the level of renormalized quantities. We use the algorithm to study for the first time light propagation in a spatially varying magnetic field. Whereas a local derivative expansion applies to the limit of small variations compared to the Compton wavelength, the case of a strongly varying field can be approximated by a derivative expansion for the averaged field. For rapidly varying fields, the vacuum-magnetic refractive indices can exhibit a non-monotonic dependence on the local field strength. This behavior can provide a natural limit on the self-focussing property of the quantum vacuum.

Holger Gies; Lars Roessler

2011-07-01