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1

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

2

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

3

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

4

Spectral Analysis of Vector Magnetic Field Profiles  

NASA Technical Reports Server (NTRS)

We investigate the power spectra and cross spectra derived from the three components of the vector magnetic field measured on a straight horizontal path above a statistically stationary source. All of these spectra, which can be estimated from the recorded time series, are related to a single two-dimensional power spectral density via integrals that run in the across-track direction in the wavenumber domain. Thus the measured spectra must obey a number of strong constraints: for example, the sum of the two power spectral densities of the two horizontal field components equals the power spectral density of the vertical component at every wavenumber and the phase spectrum between the vertical and along-track components is always pi/2. These constraints provide powerful checks on the quality of the measured data; if they are violated, measurement or environmental noise should be suspected. The noise due to errors of orientation has a clear characteristic; both the power and phase spectra of the components differ from those of crustal signals, which makes orientation noise easy to detect and to quantify. The spectra of the crustal signals can be inverted to obtain information about the cross-track structure of the field. We illustrate these ideas using a high-altitude Project Magnet profile flown in the southeastern Pacific Ocean.

Parker, Robert L.; OBrien, Michael S.

1997-01-01

5

Improvement of vector compensation method for vehicle magnetic distortion field  

NASA Astrophysics Data System (ADS)

Magnetic distortions such as eddy-current field and low frequency magnetic field have not been considered in vector compensation methods. A new compensation method is proposed to suppress these magnetic distortions and improve compensation performance, in which the magnetic distortions related to measurement vectors and time are considered. The experimental system mainly consists of a three-axis fluxgate magnetometer (DM-050), an underwater vehicle and a proton magnetometer, in which the scalar value of magnetic field is obtained with the proton magnetometer and considered to be the true value. Comparing with traditional compensation methods, experimental results show that the magnetic distortions can be further reduced by two times. After compensation, error intensity and RMS error are reduced from 11684.013 nT and 7794.604 nT to 16.219 nT and 5.907 nT respectively. It suggests an effective way to improve the compensation performance of magnetic distortions.

Pang, Hongfeng; Zhang, Qi; Li, Ji; Luo, Shitu; Chen, Dixiang; Pan, Mengchun; Luo, Feilu

2014-03-01

6

Lifshitz Effects on Vector Condensate Induced by a Magnetic Field  

E-print Network

By numerical and analytical methods, we study in detail the effects of the Lifshitz dynamical exponent $z$ on the vector condensate induced by an applied magnetic field in the probe limit. Concretely, in the presence of the magnetic field, we obtain the Landau level independent of $z$, and also find the critical value by coupling a Maxwell complex vector field and SU(2) field into a (3+1)-dimensional Lifshitz black hole, respectively. The research results show that for both two models with the lowest Landau level, the increasing $z$ improves the response of the critical temperature to the applied magnetic field even without the charge density, and the analytical results uphold the numerical results. In addition, we find even in the Lifshitz black hole, the Maxwell complex vector model is still a generalization of the SU(2) Yang-Mills model. Furthermore, we construct the square vortex lattice and discuss the implications of these results.

Ya-Bo Wu; Jun-Wang Lu; Mo-Lin Liu; Jian-Bo Lu; Cheng-Yuan Zhang; Zhuo-Qun Yang

2014-03-22

7

Magnetic Moment of Vector Mesons in the Background Field Method  

E-print Network

We report some results for the magnetic moments of vector mesons extracted from mass shifts in the presence of static external magnetic fields. The calculations are done on $24^4$ quenched lattices using standard Wilson actions, with $\\beta$=6.0 and pion mass down to 500 MeV. The results are compared to those from the form factor method.

Frank X. Lee; Scott Moerschbacher; Walter Wilcox

2007-10-11

8

Determination of coronal magnetic fields from vector magnetograms  

NASA Technical Reports Server (NTRS)

This report covers technical progress during the second year of the contract entitled 'Determination of Coronal Magnetic Fields from Vector Magnetograms,' NASW-4728, between NASA and Science Applications International Corporation, and covers the period January 1, 1993 to December 31, 1993. Under this contract SAIC has conducted research into the determination of coronal magnetic fields from vector magnetograms, including the development and application of algorithms to determine force-free coronal fields above selected observations of active regions. The contract began on June 30, 1992 and has a completion date of December 31, 1994. This contract is a continuation of work started in a previous contract, NASW-4571, which covered the period November 15, 1990 to December 14, 1991. During this second year we have concentrated on studying additional active regions and in using the estimated coronal magnetic fields to compare to coronal features inferred from observations.

Mikic, Zoran

1993-01-01

9

Determing Flow Fields Consistent with Vector Magnetic Evolution  

NASA Astrophysics Data System (ADS)

Sequences of photospheric vector magnetograms can be used to drive time-dependent models of magnetic evolution in the overlying atmosphere, as well as to investigate dynamics in the atmospheric layer imaged in the magnetograms. While several methods of estimating electric fields consistent with the observed evolution of the magnetic field normal to the magnetogram surface have been developed, these do not explicitly employ evolution of the horizontal field components in deriving electric fields. The recently developed poloidal- toroidal decomposition (PTD) method (Fisher et al. 2010) does use this extra information; PTD electric fields, however, are generally not ideal, so ideality must be imposed post facto. Here, we present formalism for deriving ideal electric fields consistent with vector magnetic evolution, assuming that the induction equation in the MHD approximation governs the magnetic evolution; accordingly, we term the approach "inductive vector driving", or IVD. This formalism can incorporate explicit resistive terms. Moreover, IVD allows direct inclusion of results from tracking methods, which can provide additional information regarding photospheric evolution. This work is supported by NASA's Heliophysics Theory Program and NSF's SHINE program.

Welsch, Brian; Fisher, G. H.; Abbett, W. P.; Bercik, D. J.

2010-05-01

10

Distribution and Evolution of Vector Magnetic Fields in Coronal Holes  

NASA Astrophysics Data System (ADS)

Coronal holes (CHs) are low density and low temperature regions in the solar corona, and they are the sources of fast solar wind. Nowadays, many properties of CHs are far from being understood. Magnetic fields are the key to understand the solar phenomena. Therefore, we try to answer the questions relative to CHs by studying the distribution and evolution of magnetic fields, especially the vector magnetic fields, in CHs. With the observations from the SOHO, Hinode, STEREO, and SDO, we investigate some aspects of CHs in detail for the first time, such as the evolution of vector magnetic field and magnetic nonpotentiality in CHs, and obtain a series of results. (1) Response of the solar atmosphere to the magnetic field distribution and evolution in a CH. We study the magnetic fields in a CH and at the CH boundary, and present the corresponding atmospheric response of different overlying layers to the magnetic field distribution and evolution. We also quantitatively analyze the relationship between the magnetic flux density and atmospheric emissions at different wavelengths. (2) Evolution of dipoles in an equatorial CH and its effect on the decay of the CH. We investigate the evolution of dipolar magnetic fields in an equatorial CH region. In the CH, the submergence of initial loops after their emergence is observed for the first time. The area where the dipoles are located becomes a place of mixed polarities instead of the unipolar fields, resulting in the change of the overlying corona from a CH area to a quiet region. (3) Distribution of vector magnetic fields and magnetic nonpotentiality of CHs. We investigate the vector magnetic fields, current densities, and current helicities in two CHs, and compare them with two quiet regions. We find that: (i) in the areas where the large current helicities are concentrated, there are strong vertical and horizontal field elements; (ii) the mean current density in the magnetic flux concentrations with the vertical fields stronger than 100 Gs is as large as (0.012±0.001) A\\cdotm^{-2}, consistent with that in the flare productive active regions; (iii) the magnetic fields in both the CHs and the quiet regions are nonpotential. (4) SDO observations of magnetic reconnection at CH boundaries. At the CH boundaries, we find many coronal jets as the signatures of magnetic reconnection, below which the magnetic emergence and cancellation are observed. We study the shifts of CH boundaries, and prove that the magnetic reconnection at CH boundaries maintains the rigid rotation of CHs. (5) Structures and evolution of polar plumes in the north polar CH. With the total solar eclipse observations, we investigate the properties and evolution of the polar plumes. The results reveal that the plumes which are closer to the CH center are more vertical. It seems that the lifetimes of plumes are much longer than the timescale of eclipse, and there may be no short timescale oscillations. The above results are helpful for us to understand the properties of CHs, and to get more insight into the evolution of CHs and the magnetic activities in CHs. As the source of fast solar wind, CHs are one kind of triggering regions of space weather. Therefore, our results can also provide an essential physical basis and observational evidence for studying the mechanism of solar wind acceleration and the course of space weather.

Yang, S. H.

2012-11-01

11

Determination of Coronal Magnetic Fields from Vector Magnetograms  

NASA Technical Reports Server (NTRS)

During the course of the present contract we developed an 'evolutionary technique' for the determination of force-free coronal magnetic fields from vector magnetograph observations. The method can successfully generate nonlinear force- free fields (with non-constant-a) that match vector magnetograms. We demonstrated that it is possible to determine coronal magnetic fields from photospheric measurements, and we applied it to vector magnetograms of active regions. We have also studied theoretical models of coronal fields that lead to disruptions. Specifically, we have demonstrated that the determination of force-free fields from exact boundary data is a well-posed mathematical problem, by verifying that the computed coronal field agrees with an analytic force-free field when boundary data for the analytic field are used; demonstrated that it is possible to determine active-region coronal magnetic fields from photospheric measurements, by computing the coronal field above active region 5747 on 20 October 1989, AR6919 on 15 November 1991, and AR7260 on 18 August 1992, from data taken with the Stokes Polarimeter at Mees Solar Observatory, University of Hawaii; started to analyze active region 7201 on 19 June 1992 using measurements made with the Advanced Stokes Polarimeter at NSO/Sac Peak; investigated the effects of imperfections in the photospheric data on the computed coronal magnetic field; documented the coronal field structure of AR5747 and compared it to the morphology of footpoint emission in a flare, showing that the 'high- pressure' H-alpha footpoints are connected by coronal field lines; shown that the variation of magnetic field strength along current-carrying field lines is significantly different from the variation in a potential field, and that the resulting near-constant area of elementary flux tubes is consistent with observations; begun to develop realistic models of coronal fields which can be used to study flare trigger mechanisms; demonstrated that magnetic nonequilibrium can disrupt sheared coronal arcades, and that helmet streamers can disrupt, leading to coronal mass ejections. Our model has significantly extended the realism with which the coronal magnetic field can be inferred from actual observations. In a subsequent contract awarded by NASA, we have continued to apply and improve the evolutionary technique, to study the physical properties of active regions, and to develop theoretical models of magnetic fields.

Mikic, Zoran

1997-01-01

12

Determination of the coronal magnetic field from vector magnetograph data  

NASA Technical Reports Server (NTRS)

A new algorithm was developed, tested, and applied to determine coronal magnetic fields above solar active regions. The coronal field above NOAA active region AR5747 was successfully estimated on 20 Oct. 1989 from data taken at the Mees Solar Observatory of the Univ. of Hawaii. It was shown that observational data can be used to obtain realistic estimates of coronal magnetic fields. The model has significantly extended the realism with which the coronal magnetic field can be inferred from observations. The understanding of coronal phenomena will be greatly advanced by a reliable technique, such as the one presented, for deducing the detailed spatial structure of the coronal field. The payoff from major current and proposed NASA observational efforts is heavily dependent on the success with which the coronal field can be inferred from vector magnetograms. In particular, the present inability to reliably obtain the coronal field has been a major obstacle to the theoretical advancement of solar flare theory and prediction. The results have shown that the evolutional algorithm can be used to estimate coronal magnetic fields.

Mikic, Zoran

1991-01-01

13

DC-SQUID magnetometer system for detecting vector value of magnetic field  

SciTech Connect

A vector magnetometer system for biomagnetic applications is described. The vector magnetometer system consists of 2 vector magnetometers and each vector magnetometer consists of 3 integrated SQUID magnetometers located perpendicularly to each other to detect 3 orthogonal components of the magnetic field simultaneously. The resolution of the each orthogonal components of the magnetic field vector is 11 fT/..sqrt..Hz in the white noise region.

Nakanishi, M.; Kasai, N.; Kado, H.; Koyanagi, M.

1989-03-01

14

Correlation between solar flare productivity and photospheric vector magnetic fields  

NASA Astrophysics Data System (ADS)

Studying the statistical correlation between the solar flare productivity and photospheric magnetic fields is very important and necessary. It is helpful to set up a practical flare forecast model based on magnetic properties and improve the physical understanding of solar flare eruptions. In the previous study ([Cui, Y.M., Li, R., Zhang, L.Y., He, Y.L., Wang, H.N. Correlation between solar flare productivity and photospheric magnetic field properties 1. Maximum horizontal gradient, length of neutral line, number of singular points. Sol. Phys. 237, 45 59, 2006]; from now on we refer to this paper as ‘Paper I’), three measures of the maximum horizontal gradient, the length of the neutral line, and the number of singular points are computed from 23990 SOHO/MDI longitudinal magnetograms. The statistical relationship between the solar flare productivity and these three measures is well fitted with sigmoid functions. In the current work, the three measures of the length of strong-shear neutral line, total unsigned current, and total unsigned current helicity are computed from 1353 vector magnetograms observed at Huairou Solar Observing Station. The relationship between the solar flare productivity and the current three measures can also be well fitted with sigmoid functions. These results are expected to be beneficial to future operational flare forecasting models.

Cui, Yanmei; Wang, Huaning

2008-11-01

15

A holographic study on vector condensate induced by a magnetic field  

NASA Astrophysics Data System (ADS)

We study a holographic model with vector condensate by coupling the anti-de Sitter gravity to an Abelian gauge field and a charged vector field in (3 + 1) dimensional spacetime. In this model there exists a non-minimal coupling of the vector field to the gauge field. We find that there is a critical temperature below which the charged vector condenses via a second order phase transition. The DC conductivity becomes infinite and the AC conductivity develops a gap in the condensed phase. We study the effect of a background magnetic field on the system. It is found that the background magnetic field can induce the condensate of the vector field even in the case without chemical potential/charge density. In the case with non-vanishing charge density, the transition temperature raises with the applied magnetic field, and the condensate of the charged vector operator forms a vortex lattice structure in the spatial directions perpendicular to the magnetic field.

Cai, Rong-Gen; He, Song; Li, Li; Li, Li-Fang

2013-12-01

16

A Comprehensive Method of Estimating Electric Fields from Vector Magnetic Field and Doppler Measurements  

E-print Network

Photospheric electric fields, estimated from sequences of vector magnetic field and Doppler measurements, can be used to estimate the flux of magnetic energy (the Poynting flux) into the corona and as time-dependent boundary conditions for dynamic models of the coronal magnetic field. We have modified and extended an existing method to estimate photospheric electric fields that combines a poloidal-toroidal (PTD) decomposition of the evolving magnetic field vector with Doppler and horizontal plasma velocities. Our current, more comprehensive method, which we dub the "{\\bf P}TD-{\\bf D}oppler-{\\bf F}LCT {\\bf I}deal" (PDFI) technique, can now incorporate Doppler velocities from non-normal viewing angles. It uses the \\texttt{FISHPACK} software package to solve several two-dimensional Poisson equations, a faster and more robust approach than our previous implementations. Here, we describe systematic, quantitative tests of the accuracy and robustness of the PDFI technique using synthetic data from anelastic MHD (\\te...

Kazachenko, Maria D; Welsch, Brian T

2014-01-01

17

Vector Condensate and AdS Soliton Instability Induced by a Magnetic Field  

E-print Network

We continue to study the holographic p-wave superconductor model in the Einstein-Maxwell-complex vector field theory with a non-minimal coupling between the complex vector field and the Maxwell field. In this paper we work in the AdS soliton background which describes a conformal field theory in the confined phase and focus on the probe approximation. We find that an applied magnetic field can lead to the condensate of the vector field and the AdS soliton instability. As a result, a vortex lattice structure forms in the spatial directions perpendicular to the applied magnetic field. As a comparison, we also discuss the vector condensate in the Einstein-SU(2) Yang-Mills theory and find that in the setup of the present paper, the Einstein-Maxwell-complex vector field model is a generalization of the SU(2) model in the sense that the vector field has a general mass and gyromagnetic ratio.

Rong-Gen Cai; Li Li; Li-Fang Li; You Wu

2013-11-29

18

GravitoMagnetic Field in Tensor-Vector-Scalar Theory  

SciTech Connect

We study the gravitomagnetism in the TeVeS theory. We compute the gravitomagnetic field that a slow moving mass distribution produces in its Newtonian regime. We report that the consistency between the TeVeS gravitomagnetic field and that predicted by the Einstein-Hilbert theory leads to a relation between the vector and scalar coupling constants of the theory. We translate the Lunar Laser Ranging measurement's data into a constraint on the deviation from this relation.

Exirifard, Qasem, E-mail: exir@theory.ipm.ac.ir [Institute for Research in Fundamental Sciences (IPM), Tehran (Iran, Islamic Republic of)

2013-04-01

19

Vector Fields  

NSDL National Science Digital Library

Vector fields are vectors which change from point to point. A standard example is the velocity of moving air, in other words, wind. For instance, the current wind pattern in the San Francisco area can be found at . This site has a 2-dimensional representation; careful reading of the webpage will tell you at what elevation the wind is shown. How would you represent a vector field in 3 dimensions? What features are important? Some simple examples are shown. Each can be rotated by clicking and dragging with the mouse. Explore!

Ay, Tevian

2006-01-01

20

A Comprehensive Method of Estimating Electric Fields from Vector Magnetic Field and Doppler Measurements  

NASA Astrophysics Data System (ADS)

Photospheric electric fields, estimated from sequences of vector magnetic field and Doppler measurements, can be used to estimate the flux of magnetic energy (the Poynting flux) into the corona and as time-dependent boundary conditions for dynamic models of the coronal magnetic field. We have modified and extended an existing method to estimate photospheric electric fields that combines a poloidal-toroidal decomposition (PTD) of the evolving magnetic field vector with Doppler and horizontal plasma velocities. Our current, more comprehensive method, which we dub the "PTD-Doppler-FLCT Ideal" (PDFI) technique, can now incorporate Doppler velocities from non-normal viewing angles. It uses the FISHPACK software package to solve several two-dimensional Poisson equations, a faster and more robust approach than our previous implementations. Here, we describe systematic, quantitative tests of the accuracy and robustness of the PDFI technique using synthetic data from anelastic MHD (ANMHD) simulations, which have been used in similar tests in the past. We find that the PDFI method has less than 1% error in the total Poynting flux and a 10% error in the helicity flux rate at a normal viewing angle (? = 0) and less than 25% and 10% errors, respectively, at large viewing angles (? < 60°). We compare our results with other inversion methods at zero viewing angle and find that our method's estimates of the fluxes of magnetic energy and helicity are comparable to or more accurate than other methods. We also discuss the limitations of the PDFI method and its uncertainties.

Kazachenko, Maria D.; Fisher, George H.; Welsch, Brian T.

2014-11-01

21

Resolving the 180-degree ambiguity in vector magnetic field measurements: The 'minimum' energy solution  

NASA Technical Reports Server (NTRS)

I present a robust algorithm that resolves the 180-deg ambiguity in measurements of the solar vector magnetic field. The technique simultaneously minimizes both the divergence of the magnetic field and the electric current density using a simulated annealing algorithm. This results in the field orientation with approximately minimum free energy. The technique is well-founded physically and is simple to implement.

Metcalf, Thomas R.

1994-01-01

22

Measurements of the magnetic field vector using multiple electromagnetically induced transparency resonances in Rb vapor  

SciTech Connect

We study the dependence of electromagnetically induced transparency (EIT) resonance amplitudes on the external magnetic field direction in a linearly polarized bichromatic light (lin||lin) configuration in {sup 87}Rb vapor. We demonstrate that all seven resolvable EIT resonances exhibit maxima or minima at certain orientations of the laser polarization relative to the wave vector and magnetic field. This effect can be used for the development of a high-precision EIT vector magnetometer.

Cox, Kevin; Novikova, Irina; Mikhailov, Eugeniy E. [Department of Physics, College of William and Mary, Williamsburg, Virginia 23185 (United States); Yudin, Valery I.; Taichenachev, Alexey V. [Institute of Laser Physics SB RAS, Novosibirsk RU-630090 (Russian Federation); Novosibirsk State Technical University, Novosibirsk RU-630092 (Russian Federation); Novosibirsk State University, Novosibirsk RU-630090 (Russian Federation)

2011-01-15

23

VECTOR TOMOGRAPHY FOR THE CORONAL MAGNETIC FIELD. II. HANLE EFFECT MEASUREMENTS  

SciTech Connect

In this paper, we investigate the feasibility of saturated coronal Hanle effect vector tomography or the application of vector tomographic inversion techniques to reconstruct the three-dimensional magnetic field configuration of the solar corona using linear polarization measurements of coronal emission lines. We applied Hanle effect vector tomographic inversion to artificial data produced from analytical coronal magnetic field models with equatorial and meridional currents and global coronal magnetic field models constructed by extrapolation of real photospheric magnetic field measurements. We tested tomographic inversion with only Stokes Q, U, electron density, and temperature inputs to simulate observations over large limb distances where the Stokes I parameters are difficult to obtain with ground-based coronagraphs. We synthesized the coronal linear polarization maps by inputting realistic noise appropriate for ground-based observations over a period of two weeks into the inversion algorithm. We found that our Hanle effect vector tomographic inversion can partially recover the coronal field with a poloidal field configuration, but that it is insensitive to a corona with a toroidal field. This result demonstrates that Hanle effect vector tomography is an effective tool for studying the solar corona and that it is complementary to Zeeman effect vector tomography for the reconstruction of the coronal magnetic field.

Kramar, M. [Physics Department, The Catholic University of America, 620 Michigan Avenue NE, Washington, DC 20064 (United States); Inhester, B. [Max-Planck-Institut fuer Sonnensystemforschung, Max-Plank-Str. 2, D-37191 Katlenburg-Lindau (Germany); Lin, H. [Institute for Astronomy, University of Hawaii at Manoa, 34 Ohia Ku Street, Pukalani, Maui, HI 96768 (United States); Davila, J., E-mail: maxim.i.kramar@nasa.gov, E-mail: Joseph.M.Davila@nasa.gov, E-mail: inhester@mps.mpg.de, E-mail: lin@ifa.hawaii.edu [NASA-GSFC, Code 671, Greenbelt, MD 20771 (United States)

2013-09-20

24

Accessing Interior Vector Magnetic Field Components in Neutron EDM Experiments via Boundary Value Techniques  

NASA Astrophysics Data System (ADS)

We propose a new technique for the determination and monitoring of the interior vector magnetic field components during the operation of neutron EDM experiments. If a suitable three-dimensional volume surrounding the fiducial volume of an experiment can be defined which contains no interior currents or magnetization, each of the interior vector field components will satisfy the Laplace Equation within this volume. Therefore, if the field components can be measured on the boundary, the interior vector field components can be determined uniquely via numerical solution of the Laplace Equation. We discuss the applicability of this technique to the determination of the magnetic field components and magnetic field gradients in the fiducial volumes of neutron EDM experiments.

Plaster, Brad

2012-10-01

25

Precise vector-2D magnetic field sensor system for electronic compass  

Microsoft Academic Search

An high sensitivity vector-2D magnetic sensor system for low magnetic field measurements has been realized and tested. The system, realized in PCB technology, consists of a double axis fluxgate magnetic sensor with its front-end electronic circuitry based on second-harmonic detection. The amorphous magnetic materials Vitrovac 6025X (25 ?m thick) and Vitrovac 6025Z (20 ?m thick) were used as a ferromagnetic

A. Baschirotto; E. Dallago; P. Malcovati; M. Marchesi; G. Venchi

2004-01-01

26

Vector magnetic field observations with the Haleakala polarimeter.  

NASA Astrophysics Data System (ADS)

Several enhancements have recently been made to the Haleakala polarimeter. Linear array detectors provide simultaneous resolution over a 3-Å wavelength range, with spectral resolution of 40 mÅ. Optical fibers are now used to carry the intensity-modulated light from the rotating quarter-wave plate polarimeter to the echelle spectrometer, permitting its removal from the spar to a more stable environment. These changes, together with improved quarter-wave plates, have reduced systematic errors to a few parts in 104 for routine observations. Examples of Stokes profiles and derived magnetic field maps are presented.

Mickey, D. L.

27

Spatial distribution of cardiac magnetic vector fields acquired from 3120 SQUID positions.  

PubMed

An extended measurement of the magnetic vector field of the human heart is presented. It is acquired by sequential recordings, shifting a 16 SQUID vector magnetometer across 195 positions over a healthy subject's thorax. The magnetocardiographic (MCG) signals were synchronized using a simultaneously measured ECG channel. The registration of the field extends over a volume of 1000 mm x 600 mm x 420 mm sampled at 3120 SQUID positions. We present diagrams of the vector amplitude of selected points in 6 planes at increasing distances from the frontal thorax. Each plane contains 76 vector points. Additionally, we measured the vector field at 126 points lateral to the chest. At the edge points of the measurement volume, the absolute value of the magnetic vector signal amplitude exceeds 0.3 pT in all measurement points. The dataset provides an excellent base to study dedicated MCG detection or rejection methods. Examples where rejection of the heart signal is necessary are magnetoencephalography, magnetoneurography and fetal MCG. The knowledge of the spatio-temporal distribution of the magnetic vector field of the heart supports the development and comparison of multi-SQUID systems and will be used to create new MCG interpretation and representation algorithms. PMID:16012615

Steinhoff, U; Schnabel, A; Burghoff, M; Freibier, T; Thiel, F; Koch, H; Trahms, L

2004-01-01

28

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

29

Microscopic probe for vector measurement of both the electric and the magnetic field of light  

E-print Network

Microscopic probe for vector measurement of both the electric and the magnetic field of light microscopic imaging of light", Nature Photonics, 1, 53-56, 2007. 2. H. W. Kihm et al., "Bethe(Near-field Scanning Optical Microscope) tip (electric dipole) (1) hole tip (2

Park, Namkyoo

30

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

31

The derivation of vector magnetic fields from Stokes profiles - Integral versus least squares fitting techniques  

NASA Technical Reports Server (NTRS)

The results of two methods for deriving photospheric vector magnetic fields from the Zeeman effect, as observed in the Fe I line at 6302.5 A at high spectral resolution (45 mA), are compared. The first method does not take magnetooptical effects into account, but determines the vector magnetic field from the integral properties of the Stokes profiles. The second method is an iterative least-squares fitting technique which fits the observed Stokes profiles to the profiles predicted by the Unno-Rachkovsky solution to the radiative transfer equation. For sunspot fields above about 1500 gauss, the two methods are found to agree in derived azimuthal and inclination angles to within about + or - 20 deg.

Ronan, R. S.; Mickey, D. L.; Orrall, F. Q.

1987-01-01

32

Stokes profile analysis and vector magnetic fields. I - Inversion of photospheric lines  

NASA Astrophysics Data System (ADS)

The authors consider improvements to the Auer, Heasley, and House method for the analytic inversion of Stokes profiles via nonlinear least squares. In the application of this method to actual sunspot observations, the authors have found that its simplifications often yield erroneous solutions or nonconvergent behavior. By including damping wings and magneto-optical birefringence and by decoupling the intensity profile from the three-vector polarization profile in the analysis, the authors develop a more robust inversion method that provides a more reliable and accurate estimate of sunspot vector magnetic fields without significant loss of economy.

Skumanich, A.; Lites, B. W.

1987-11-01

33

On parasupersymmetric oscillators and relativistic vector mesons in constant magnetic fields  

NASA Technical Reports Server (NTRS)

Johnson-Lippmann considerations on oscillators and their connection with the minimal coupling schemes are visited in order to introduce a new Sakata-Taketani equation describing vector mesons in interaction with a constant magnetic field. This new proposal, based on a specific parasupersymmetric oscillator-like system, is characterized by real energies as opposed to previously pointed out relativistic equations corresponding to this interacting context.

Debergh, Nathalie; Beckers, Jules

1995-01-01

34

An Automated Ambiguity-Resolution Code for Hinode/SP Vector Magnetic Field Data  

NASA Astrophysics Data System (ADS)

A fast, automated algorithm is presented for use in resolving the 180° ambiguity in vector magnetic field data, including those data from Hinode/Spectropolarimeter. The Fortran-based code is loosely based on the Minimum Energy Algorithm, and is distributed to provide ambiguity-resolved data for the general user community. Here we generally describe the released code (available at http://www.cora.nwra.com/AMBIG), examples of its performance and usage for Hinode/SP data.

Leka, K. D.; Barnes, G.; Crouch, A.

2009-12-01

35

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

36

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

37

COMPARISON OF FORCE-FREE CORONAL MAGNETIC FIELD MODELING USING VECTOR FIELDS FROM HINODE AND SOLAR DYNAMICS OBSERVATORY  

SciTech Connect

Photospheric magnetic vector maps from two different instruments are used to model the nonlinear force-free coronal magnetic field above an active region. We use vector maps inferred from polarization measurements of the Solar Dynamics Observatory/Helioseismic and Magnetic Imager (HMI) and the Solar Optical Telescope's Spectropolarimeter (SP) on board Hinode. Besides basing our model calculations on HMI data, we use both SP data of original resolution and scaled down to the resolution of HMI. This allows us to compare the model results based on data from different instruments and to investigate how a binning of high-resolution data affects the model outcome. The resulting three-dimensional magnetic fields are compared in terms of magnetic energy content and magnetic topology. We find stronger magnetic fields in the SP data, translating into a higher total magnetic energy of the SP models. The net Lorentz forces of the HMI and SP lower boundaries verify their force-free compatibility. We find substantial differences in the absolute estimates of the magnetic field energy but similar relative estimates, e.g., the fraction of excess energy and of the flux shared by distinct areas. The location and extension of neighboring connectivity domains differ and the SP model fields tend to be higher and more vertical. Hence, conclusions about the magnetic connectivity based on force-free field models are to be drawn with caution. We find that the deviations of the model solution when based on the lower-resolution SP data are small compared to the differences of the solutions based on data from different instruments.

Thalmann, J. K.; Tiwari, S. K.; Wiegelmann, T., E-mail: thalmann@mps.mpg.de [Max-Plank-Institut fuer Sonnensystemforschung, Max-Planck-Str. 2, D-37191 Katlenburg-Lindau (Germany)

2013-05-20

38

3-D Vector Field Simulation  

NSDL National Science Digital Library

This simulation illustrates a wide range of 3D vector fields, including spherical, radial, and linear. The fields can be displayed as vectors, particle trajectories, equipotentials, and other options. The number of particles, vectors, or streamlines, and the field strength are adjustable. Directions and source code are also included. This is an extension of a 3D Electric and Magnetic Field viewer from the same author.

Falstad, Paul

2004-07-13

39

OBSERVATIONAL EVIDENCE OF CHANGING PHOTOSPHERIC VECTOR MAGNETIC FIELDS ASSOCIATED WITH SOLAR FLARES  

SciTech Connect

Recent observations have provided evidence that the solar photospheric magnetic fields could have rapid and permanent changes in both longitudinal and transverse components associated with major flares. As a result, the Lorentz force (LF) acting on the solar photosphere and solar interior could be perturbed, and the change of LF is always nearly in the downward direction. However, these rapid and permanent changes have not been systematically investigated, yet, using vector magnetograms. In this paper, we analyze photospheric vector magnetograms covering five flares to study the evolution of photospheric magnetic fields. In particular, we investigate two-dimensional spatial distributions of the changing LF. Around the major flaring polarity inversion line, the net change of the LF is directed downward in an area of {approx}10{sup 19} cm{sup 2} for X-class flares. For all events, the white-light observations show that sunspots darken in this location after flares, and magnetic fields become more inclined, which is consistent with the ideas put forward by Hudson et al. and Fisher et al., and observations.

Su, J. T.; Jing, J.; Wang, H. M. [Space Weather Research Laboratory, New Jersey Institute of Technology, University Heights, Newark, NJ 07102-1982 (United States); Mao, X. J.; Wang, X. F.; Zhang, H. Q.; Deng, Y. Y.; Guo, J.; Wang, G. P., E-mail: sjt@bao.ac.cn [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

2011-06-01

40

The inference of vector magnetic fields from polarization measurements with limited spectral resolution  

NASA Technical Reports Server (NTRS)

A method is presented for recovery of the vector magnetic field and thermodynamic parameters from polarization measurement of photospheric line profiles measured with filtergraphs. The method includes magneto-optic effects and may be utilized on data sampled at arbitrary wavelengths within the line profile. The accuracy of this method is explored through inversion of synthetic Stokes profiles subjected to varying levels of random noise, instrumental wave-length resolution, and line profile sampling. The level of error introduced by the systematic effect of profile sampling over a finite fraction of the 5 minute oscillation cycle is also investigated. The results presented here are intended to guide instrumental design and observational procedure.

Lites, B. W.; Skumanich, A.

1985-01-01

41

Z3 model of Saturns magnetic field and the Pioneer 11 vector helium magnetometer observations  

SciTech Connect

Magnetic field observations obtained by the Pioneer 11 vector helium magnetometer are compared with the Z(sub 3) model magnetic field. These Pioneer 11 observations, obtained at close-in radial distances, constitute an important and independent test of the Z(sub 3) zonal harmonic model, which was derived from Voyager 1 and Voyager 2 fluxgate magnetometer observations. Differences between the Pioneer 11 magnetometer and the Z(sub 3) model field are found to be small (approximately 1%) and quantitatively consistent with the expected instrumental accuracy. A detailed examination of these differences in spacecraft payload coordinates shows that they are uniquely associated with the instrument frame of reference and operation. A much improved fit to the Pioneer 11 observations is obtained by rotation of the instrument coordinate system about the spacecraft spin axis by 1.4 degree. With this adjustment, possibly associated with an instrumental phase lag or roll attitude error, the Pioneer 11 vector helium magnetometer observations are fully consistent with the Voyager Z(sub 3) model.

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

1984-05-01

42

The Z3 model of Saturns magnetic field and the Pioneer 11 vector helium magnetometer observations  

NASA Technical Reports Server (NTRS)

Magnetic field observations obtained by the Pioneer 11 vector helium magnetometer are compared with the Z(sub 3) model magnetic field. These Pioneer 11 observations, obtained at close-in radial distances, constitute an important and independent test of the Z(sub 3) zonal harmonic model, which was derived from Voyager 1 and Voyager 2 fluxgate magnetometer observations. Differences between the Pioneer 11 magnetometer and the Z(sub 3) model field are found to be small (approximately 1%) and quantitatively consistent with the expected instrumental accuracy. A detailed examination of these differences in spacecraft payload coordinates shows that they are uniquely associated with the instrument frame of reference and operation. A much improved fit to the Pioneer 11 observations is obtained by rotation of the instrument coordinate system about the spacecraft spin axis by 1.4 degree. With this adjustment, possibly associated with an instrumental phase lag or roll attitude error, the Pioneer 11 vector helium magnetometer observations are fully consistent with the Voyager Z(sub 3) model.

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

1984-01-01

43

The Z3 model of Saturn's magnetic field and the Pioneer 11 vector helium magnetometer observations  

NASA Technical Reports Server (NTRS)

Magnetic field observations obtained by the Pioneer 11 vector helium magnetometer are compared with the Z(sub 3) model magnetic field. These Pioneer 11 observations, obtained at close-in radial distances, constitute an important and independent test of the Z(sub 3) zonal harmonic model, which was derived from Voyager 1 and Voyager 2 fluxgate magnetometer observations. Differences between the Pioneer 11 magnetometer and the Z(sub 3) model field are found to be small (approximately 1 percent) and quantitatively consistent with the expected instrumental accuracy. A detailed examination of these differences in spacecraft payload coordinates shows that they are uniquely associated with the instrument frame of reference and operation. A much improved fit to the Pioneer 11 observations is obtained by rotation of the instrument coordinate system about the spacecraft spin axis by 1.4 degree. With this adjustment, possibly associated with an instrumental phase lag or roll attitude error, the Pioneer 11 vector helium magnetometer observations are fully consistent with the Voyager Z(sub 3) model.

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

1984-01-01

44

New models of Saturn's magnetic field using Pioneer 11 Vector Helium Magnetometer data  

NASA Technical Reports Server (NTRS)

In a reanalysis of the Vector Helium Magnetometer data taken by Pioneer 11 during its Saturn encounter in 1979, using improvements in the data set and in the procedures, studies are made of a variety of models. The best is the P(11)84 model, an axisymmetric spherical harmonic model of Saturn's magnetic field within 8 Saturn radii of the planet. The appropriately weighted root mean square average of the difference between the observed and the modeled field is 1.13 percent. For the Voyager-based Z3 model of Connerney, Acuna, and Ness, this average difference from the Pioneer 11 data is 1.81 percent. The external source currents in the magnetopause, tail, bow shock, and perhaps ring currents vary with time and can only be crudely modeled. An algebraic formula is derived for calculating the L shells on which energetic charged particles drift in axisymmetric fields.

Davis, L., Jr.; Smith, E. J.

1986-01-01

45

Constants of motion for the planar orbit of a charged particle in a static and uniform magnetic field: the magnetic Laplace–Runge–Lenz vector  

NASA Astrophysics Data System (ADS)

In this paper we introduce an alternative approach to studying the motion of a planar charged particle subject to a static uniform magnetic field. It is well known that an electric charge under a uniform magnetic field has a planar motion if its initial velocity is perpendicular to the magnetic field. Although some constants of motion (CsM), as the energy and the angular momentum, have been widely discussed for this system, others have been neglected. We find that the angular momentum, the generator of the magnetic translations and the magnetic Laplace–Runge–Lenz vector are CsM for this particular system. We show also that these three quantities form an orthogonal basis of vectors. The present work addresses many aspects of the motion of a charged particle in a magnetic field that should be useful for students and tutors of the classical mechanics courses at the senior undergraduate level.

Velasco-Martínez, D.; Ibarra-Sierra, V. G.; Sandoval-Santana, J. C.; Kunold, A.; Cardoso, J. L.

2014-09-01

46

Understanding Vector Fields.  

ERIC Educational Resources Information Center

Presented are activities that help students understand the idea of a vector field. Included are definitions, flow lines, tangential and normal components along curves, flux and work, field conservation, and differential equations. (KR)

Curjel, C. R.

1990-01-01

47

Effects of AC/DC magnetic fields, frequency, and nanoparticle aspect ratio on cellular transfection of gene vectors  

NASA Astrophysics Data System (ADS)

In order to make non-viral gene delivery a useful tool in the study and treatment of genetic disorders, it is imperative that these methodologies be further refined to yield optimal results. Transfection of magnetic nanoparticles and nanorods are used as non-viral gene vectors to transfect HeLa EGFP-654 cells that stably express a mutated enhanced green fluorescent protein (EGFP) gene. We deliver antisense oligonucleotides to these cells designed to correct the aberrant splicing caused by the mutation in the EGFP gene. We also transfect human bronchial endothelial cells and immortalized WI-38 lung cells with pEGFP-N1 vectors. To achieve this we bind the genes to magnetic nanoparticles and nanorods and introduce magnetic fields to effect transfection. We wish to examine the effects of magnetic fields on the transfection of these particles and the benefits of using alternating (AC) magnetic fields in improving transfection rates over direct (DC) magnetic fields. We specifically look at the frequency dependence of the AC field and particle aspect ratio as it pertains to influencing transfection rate. We posit that the increase in angular momentum brought about by the AC field and the high aspect ratio of the nanorod particles, is vital to generating the force needed to move the particle through the cell membrane.

Ford, Kris; Mair, Lamar; Fisher, Mike; Rowshon Alam, Md.; Juliano, Rudolph; Superfine, Richard

2008-10-01

48

Solar Flare Prediction Using SDO/HMI Vector Magnetic Field Data with a Machine-Learning Algorithm  

E-print Network

We attempt to forecast M-and X-class solar flares using a machine-learning algorithm, called Support Vector Machine (SVM), and four years of data from the Solar Dynamics Observatory's Helioseismic and Magnetic Imager, the first instrument to continuously map the full-disk photospheric vector magnetic field from space. Most flare forecasting efforts described in the literature use either line-of-sight magnetograms or a relatively small number of ground-based vector magnetograms. This is the first time a large dataset of vector magnetograms has been used to forecast solar flares. We build a catalog of flaring and non-flaring active regions sampled from a database of 2,071 active regions, comprised of 1.5 million active region patches of vector magnetic field data, and characterize each active region by 25 parameters. We then train and test the machine-learning algorithm and we estimate its performances using forecast verification metrics with an emphasis on the True Skill Statistic (TSS). We obtain relatively h...

Bobra, Monica G

2014-01-01

49

GLOBAL TWIST OF SUNSPOT MAGNETIC FIELDS OBTAINED FROM HIGH-RESOLUTION VECTOR MAGNETOGRAMS  

SciTech Connect

The presence of fine structures in sunspot vector magnetic fields has been confirmed from Hinode as well as other earlier observations. We studied 43 sunspots based on the data sets taken from ASP/DLSP, Hinode (SOT/SP), and SVM (USO). In this Letter, (1) we introduce the concept of signed shear angle (SSA) for sunspots and establish its importance for non-force-free fields. (2) We find that the sign of global {alpha} (force-free parameter) is well correlated with that of the global SSA and the photospheric chirality of sunspots. (3) Local {alpha} patches of opposite signs are present in the umbra of each sunspot. The amplitude of the spatial variation of local {alpha} in the umbra is typically of the order of the global {alpha} of the sunspot. (4) We find that the local {alpha} is distributed as alternately positive and negative filaments in the penumbra. The amplitude of azimuthal variation of the local {alpha} in the penumbra is approximately an order of magnitude larger than that in the umbra. The contributions of the local positive and negative currents and {alpha} in the penumbra cancel each other giving almost no contribution for their global values for the whole sunspot. (5) Arc-like structures (partial rings) with a sign opposite to that of the dominant sign of {alpha} of the umbral region are seen at the umbral-penumbral boundaries of some sunspots. (6) Most of the sunspots studied belong to the minimum epoch of the 23rd solar cycle and do not follow the so-called hemispheric helicity rule.

Tiwari, Sanjiv Kumar; Venkatakrishnan, P. [Udaipur Solar Observatory, Physical Research Laboratory, Dewali, Bari Road, Udaipur-313 001 (India); Sankarasubramanian, K. [Space Astronomy and Instrumentation Division, ISRO Satellite Center, Airport Road, Vimanapura, Bangalore-560017 (India)], E-mail: stiwari@prl.res.in, E-mail: pvk@prl.res.in, E-mail: sankark@isac.gov.in

2009-09-10

50

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

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

Topology-Preserving Diffusion of Divergence-Free Vector Fields and Magnetic Relaxation  

NASA Astrophysics Data System (ADS)

The usual heat equation is not suitable to preserve the topology of divergence-free vector fields, because it destroys their integral line structure. On the contrary, in the fluid mechanics literature, one can find examples of topology-preserving diffusion equations for divergence-free vector fields. They are very degenerate since they admit all stationary solutions to the Euler equations of incompressible fluids as equilibrium points. For them, we provide a suitable concept of "dissipative solutions", which shares common features with both P.-L. Lions's dissipative solutions to the Euler equations and the concept of "curves of maximal slopes", à la De Giorgi, recently used to study the scalar heat equation in very general metric spaces. We show that the initial value problem admits such global solutions, at least in the two space variable case, and they are unique whenever they are smooth.

Brenier, Yann

2014-09-01

53

PHYSICAL REVIEW A 83, 015801 (2011) Measurements of the magnetic field vector using multiple electromagnetically induced  

E-print Network

optical pumping magnetometers [4] are sensitive only to the magnitude of the magnetic field to "heading error" in some systems [5]. The application of coherent optical effects, such as elec field direction in a linearly polarized bichromatic light (lin||lin) configuration in 87 Rb vapor. We

Novikova, Irina

54

Systematic optimization of exterior measurement locations for the determination of interior magnetic field vector components in inaccessible regions  

NASA Astrophysics Data System (ADS)

An experiment may face the challenge of real-time determination of the magnetic field vector components present within some interior region of the experimental apparatus over which it is impossible to directly measure the field components during the operation of the experiment. As a solution to this problem, we propose a general concept which provides for a unique determination of the field components within such an interior region solely from exterior measurements at fixed discrete locations. The method is general and does not require the field to possess any type of symmetry. We describe our systematic approach for optimizing the locations of these exterior measurements which maximizes their sensitivity to successive terms in a multipole expansion of the field.

Nouri, N.; Plaster, B.

2014-12-01

55

Three dimensional magnetic fields in extra high speed modified Lundell alternators computed by a combined vector-scalar magnetic potential finite element method  

NASA Technical Reports Server (NTRS)

A 3D finite element (FE) approach was developed and implemented for computation of global magnetic fields in a 14.3 kVA modified Lundell alternator. The essence of the new method is the combined use of magnetic vector and scalar potential formulations in 3D FEs. This approach makes it practical, using state of the art supercomputer resources, to globally analyze magnetic fields and operating performances of rotating machines which have truly 3D magnetic flux patterns. The 3D FE-computed fields and machine inductances as well as various machine performance simulations of the 14.3 kVA machine are presented in this paper and its two companion papers.

Demerdash, N. A.; Wang, R.; Secunde, R.

1992-01-01

56

Kinematics of vector fields  

E-print Network

Different (not only by sign) affine connections are introduced for contravariant and covariant tensor fields over a differentiable manifold by means of a non-canonical contraction operator, defining the notion dual bases and commuting with the covariant and with the Lie-differential operator. Classification of the linear transports on the basis of the connections between the connections is given. Notion of relative velocity and relative acceleration for vector fields are determined. By means of these kinematic characteristics several other types of notions as shear velocity, shear acceleration, rotation velocity, rotation acceleration, expansion velocity and expansion acceleration are introduced and on their basis auto-parallel and non-isotropic (non-null) vector fields are classified.

S. Manoff

2000-03-02

57

IR Vector Magnetic Fields II: Atomic and Molecular Line Polarization in a Sunspot  

NASA Astrophysics Data System (ADS)

Full Stokes I,Q,U and V measurements of the active region NOAA 10008 were taken from 21-27 June 2002 at the NSO Kitt Peak McMath/Pierce solar telescope using the CSUN/NSO HgCdTe IR camera and polarimeter at 1565nm. The data is corrected for instrumental polarization as discussed in Paper I. Here the initial analysis of the atomic and molecular line polarization data is presented. Inversion of the Fe I g=3 1564.8nm line data with a modified Skumanich and Lites Milne-Eddington technique is used to measure photospheric magnetic field parameters. A sequence of scans covering several hours of time shows evolution of the magnetic field. Examination of the linear polarization of the OH 1565.2nm shows curious temporal variation which results in a magnetic azimuth radically different from that measured using the photospheric lines. (Similar OH polarization behavior is seen in data from the CSUN San Fernando Observatory vacuum telescope taken with the CSUN/NSO camera in active region NOAA 10069 on 12 Aug 2002.) Finally, maps of the CN 1564.6nm Stokes I line shift show rapid penumbral Evershed flows and a curious signal in the sunspot umbra. Some of this work is carried out through the National Solar Observatory Research Experiences for Undergraduate (REU) site program, which is co-funded by the Department of Defense in partnership with the National Science Foundation REU Program.

Penn, M. J.; Jaeggli, S. A.; Henney, C. J.; Walton, S. R.; Ceja, J. A.

2004-05-01

58

A combined vector potential-scalar potential method for FE computation of 3D magnetic fields in electrical devices with iron cores  

NASA Technical Reports Server (NTRS)

A method of combined use of magnetic vector potential based finite-element (FE) formulations and magnetic scalar potential (MSP) based formulations for computation of three-dimensional magnetostatic fields is introduced. In this method, the curl-component of the magnetic field intensity is computed by a reduced magnetic vector potential. This field intensity forms the basic of a forcing function for a global magnetic scalar potential solution over the entire volume of the region. This method allows one to include iron portions sandwiched in between conductors within partitioned current-carrying subregions. The method is most suited for large-scale global-type 3-D magnetostatic field computations in electrical devices, and in particular rotating electric machinery.

Wang, R.; Demerdash, N. A.

1991-01-01

59

Nonlinear Force-Free Modeling of Coronal Magnetic Fields. II. Modeling a Filament Arcade and Simulated Chromospheric and Photospheric Vector Fields  

NASA Astrophysics Data System (ADS)

We compare a variety of nonlinear force-free field (NLFFF) extrapolation algorithms, including optimization, magneto-frictional, and Grad Rubin-like codes, applied to a solar-like reference model. The model used to test the algorithms includes realistic photospheric Lorentz forces and a complex field including a weakly twisted, right helical flux bundle. The codes were applied to both forced “photospheric” and more force-free “chromospheric” vector magnetic field boundary data derived from the model. When applied to the chromospheric boundary data, the codes are able to recover the presence of the flux bundle and the field’s free energy, though some details of the field connectivity are lost. When the codes are applied to the forced photospheric boundary data, the reference model field is not well recovered, indicating that the combination of Lorentz forces and small spatial scale structure at the photosphere severely impact the extrapolation of the field. Preprocessing of the forced photospheric boundary does improve the extrapolations considerably for the layers above the chromosphere, but the extrapolations are sensitive to the details of the numerical codes and neither the field connectivity nor the free magnetic energy in the full volume are well recovered. The magnetic virial theorem gives a rapid measure of the total magnetic energy without extrapolation though, like the NLFFF codes, it is sensitive to the Lorentz forces in the coronal volume. Both the magnetic virial theorem and the Wiegelmann extrapolation, when applied to the preprocessed photospheric boundary, give a magnetic energy which is nearly equivalent to the value derived from the chromospheric boundary, but both underestimate the free energy above the photosphere by at least a factor of two. We discuss the interpretation of the preprocessed field in this context. When applying the NLFFF codes to solar data, the problems associated with Lorentz forces present in the low solar atmosphere must be recognized: the various codes will not necessarily converge to the correct, or even the same, solution.

Metcalf, Thomas R.; De Rosa, Marc L.; Schrijver, Carolus J.; Barnes, Graham; van Ballegooijen, Adriaan A.; Wiegelmann, Thomas; Wheatland, Michael S.; Valori, Gherardo; McTtiernan, James M.

2008-02-01

60

A Search for Vector Magnetic Field Variations Associated with the M-Class Flares of 1991 June 10 in AR 6659  

NASA Technical Reports Server (NTRS)

A careful analysis of a 6-hour time sequence of vector magnetograms of AR 6659, observed on 1991 June 10 with the MSFC vector magnetograph, has revealed only minor changes in the vector magnetic field azimuths in the vicinity of two M-class flares, and the association of these changes with the flares is not unambiguous. In this paper we present our analysis of the data which includes comparison of vector magnetograms prior to and during the flares, calculation of distributions of the rms variation of the azimuth at each pixel in the field of view of the active region, and examination of the variation with time of the azimuths at every pixel covered by the main flare emissions as observed with the H-alpha telescope coaligned with the vector magnetograph. We also present results of an analysis of evolutionary changes in the azimuth over the field of view of the active region.

Hagyard, Mona J.; Stark, B. A.; Venkatakrishnan, P.

1998-01-01

61

Combined magnetic vector-scalar potential finite element computation of 3D magnetic field and performance of modified Lundell alternators in Space Station applications. Ph.D. Thesis  

NASA Technical Reports Server (NTRS)

A method of combined use of magnetic vector potential (MVP) based finite element (FE) formulations and magnetic scalar potential (MSP) based FE formulations for computation of three-dimensional (3D) magnetostatic fields is developed. This combined MVP-MSP 3D-FE method leads to considerable reduction by nearly a factor of 3 in the number of unknowns in comparison to the number of unknowns which must be computed in global MVP based FE solutions. This method allows one to incorporate portions of iron cores sandwiched in between coils (conductors) in current-carrying regions. Thus, it greatly simplifies the geometries of current carrying regions (in comparison with the exclusive MSP based methods) in electric machinery applications. A unique feature of this approach is that the global MSP solution is single valued in nature, that is, no branch cut is needed. This is again a superiority over the exclusive MSP based methods. A Newton-Raphson procedure with a concept of an adaptive relaxation factor was developed and successfully used in solving the 3D-FE problem with magnetic material anisotropy and nonlinearity. Accordingly, this combined MVP-MSP 3D-FE method is most suited for solution of large scale global type magnetic field computations in rotating electric machinery with very complex magnetic circuit geometries, as well as nonlinear and anisotropic material properties.

Wang, Ren H.

1991-01-01

62

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

63

Fabrication of a vector Hall sensor for magnetic microscopy  

NASA Astrophysics Data System (ADS)

We have developed a micromachined Hall sensor for scanning the entire magnetic field vector whose active dimensions are an order of magnitude smaller (˜5 ?m) than the smallest existing vector field sensor. It is realized by patterning three Hall probes on the tilted faces of epitaxy-overgrown GaAs-based pyramidal-shaped mesa structures. Data from these "tilted" Hall probes are used to reconstruct the full magnetic field vector.

Gregušová, D.; Cambel, V.; Fedor, J.; Kúdela, R.; Šoltýs, J.; Lalinský, T.; Kosti?, I.; Bending, S. J.

2003-05-01

64

Deriving Potential Fields from Vector Magnetograms  

NASA Astrophysics Data System (ADS)

The minimum-energy state for the magnetic field above the solar photosphere is current-free. Since current is proportional to the magnetic field's curl, the minimum energy state is curl-free, and can therefore be represented as the gradient of a scalar potential. In addition, the divergence-free condition on the magnetic field implies this scalar potential obeys Laplace's equation. An appropriate boundary condition must be specified to determine the potential. Given a measurement of the full magnetic vector at the photosphere, it is possible to employ either Neumann or Dirichlet boundary conditions there. Typically, the Neumann condition is applied. Since either condition fully specifies the three-dimensional vector magnetic field, either choice will, in general, be inconsistent with some aspect of the observed field on the boundary, due to the presence of both currents and noise in the observed field. We present a method to derive a potential field that minimizes the integrated square of the residual between both boundary conditions, and show one way to incorporate weighting by spatially uniform measurement uncertainties in the minimization. We demonstrate each approach using HMI vector magnetic field observations of AR 11158. Residual discrepancies between the observed and potential fields are significantly larger than empirically determined noise levels, and can be interpreted as evidence of horizontal photospheric currents. The data provide clues about properties of these currents, but determining their spatial distribution will require additional constraints, e.g., simplifying assumptions about photospheric magnetic structure or observational input beyond single-height magnetograms. We also find that the energies of potential fields computed in different ways are significantly different --- by nearly 1e+33 ergs in some cases. This has substantial implications for estimates of the free magnetic energy in coronal field models that is available to power flares and coronal mass ejections (CMEs.)

Welsch, Brian

2013-07-01

65

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

66

Vector Fields and Line Integrals  

NSDL National Science Digital Library

Created by Oliver Knill and Dale Winter for the Connected Curriculum Project, this module introduces vector fields, the concept of "work," and the line integral. This is one of a much larger set of learning modules hosted by Duke University.

Knill, Oliver; Winter, Dale

2010-05-20

67

Finite element analysis of hysteresis motor using the vector magnetization-dependent model  

Microsoft Academic Search

This paper presents a finite element analysis procedure combined with a vector hysteresis model for the accurate analysis of an hysteresis motor. The vector magnetization-dependent model is adopted to calculate the vector magnetization of the hysteresis ring. From the magnitude and direction of the magnetic field intensity, the magnetization of each ring element is calculated by the vector model. By

Hong-Kyu Kim; Hyun-Kyo Jung; Sun-Ki Hong

1998-01-01

68

The magnetic vector field and the structure of the H-alpha chromosphere of BBR 18,474 on 15 and 16 July 1982  

NASA Astrophysics Data System (ADS)

The solar chromosphere in active region BBR 18,474 (July 15-16, 1982) is characterized on the basis of vector magnetograms (in the 525.02-nm line of Fe I) and H-alpha filtergrams obtained at Potsdam using the instruments, techniques and data-reduction procedures described by Bachmann et al. (1975 and 1983) and photoheliograms obtained at Debrecen Observatory. The results are presented graphically and characterized in detail. Transverse magnetic fields of up to 1.4 kG are observed, and the neutral-line filament is found to be located near the minimum field magnitude outside the sunspot group, along the longitudinal-field inversion line inside the sunspot group, and along the direction of the transverse field in the delta area (consistent with strong magnetic-field shear). The flare energy in this active region is attributed to sunspot proper motions.

Bachmann, G.

1988-01-01

69

Magnetic properties modeling of soft magnetic composite materials using two-dimensional vector hybrid hysteresis model  

NASA Astrophysics Data System (ADS)

A 2-D vector hybrid hysteresis model for a soft magnetic composite (SMC) material is established, which is combined with classical Preisach model and Stoner-Wohlfarth (S-W) model. The rotational magnetic properties of SMC materials were studied using the vector model, and the computed results were compared with the experimental measurement. It is shown that the vector hybrid model can effectively simulate the rotational magnetic properties under low magnetization fields.

Li, Dandan; Liu, Fugui; Li, Yongjian; Zhao, Zhigang; Zhang, Changgeng; Yang, Qingxin

2014-05-01

70

2-D Vector Field Simulation  

NSDL National Science Digital Library

The applet simulates various vector fields, including spherical, radial, and constant plane. It is a generalized version of an electrostatic field simulation by the same author. The field strength and number of particles simulated are adjustable. Divergence, curl, and potential can be color-coded. Grid lines, potential lines, or streamlines can be displayed. Directions, specific links to the subject and source code are also included.

Falstad, Paul

2004-07-23

71

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

72

Estimating Electric Fields from Vector Magnetogram Sequences  

NASA Astrophysics Data System (ADS)

Determining the electric field distribution on the Sun's photosphere is essential for quantitative studies of how energy flows from the Sun's photosphere, through the corona, and into the heliosphere. This electric field also provides valuable input for data-driven models of the solar atmosphere and the Sun-Earth system. We show how observed vector magnetogram time series can be used to estimate the photospheric electric field. Our method uses a "poloidal-toroidal decomposition" (PTD) of the time derivative of the vector magnetic field. These solutions provide an electric field whose curl obeys all three components of Faraday's Law. The PTD solutions are not unique; the gradient of a scalar potential can be added to the PTD electric field without affecting consistency with Faraday's Law. We then present an iterative technique to determine a potential function consistent with ideal MHD evolution; but this field is also not a unique solution to Faraday's Law. Finally, we explore a variational approach that minimizes an energy functional to determine a unique electric field, a generalization of Longcope's "Minimum Energy Fit." The PTD technique, the iterative technique, and the variational technique are used to estimate electric fields from a pair of synthetic vector magnetograms taken from an MHD simulation; and these fields are compared with the simulation's known electric fields. The PTD and iteration techniques compare favorably to results from existing velocity inversion techniques. These three techniques are then applied to a pair of vector magnetograms of solar active region NOAA AR8210, to demonstrate the methods with real data. Careful examination of the results from all three methods indicates that evolution of the magnetic vector by itself does not provide enough information to determine the true electric field in the photosphere. Either more information from other measurements, or physical constraints other than those considered here are necessary to find the true electric field. However, we show it is possible to construct physically reasonable electric field distributions whose curl matches the evolution of all three components of B. We also show that the horizontal and vertical Poynting flux patterns derived from the three techniques are similar to one another for the cases investigated.

Fisher, G. H.; Welsch, B. T.; Abbett, W. P.; Bercik, D. J.

2010-05-01

73

ESTIMATING ELECTRIC FIELDS FROM VECTOR MAGNETOGRAM SEQUENCES  

SciTech Connect

Determining the electric field distribution on the Sun's photosphere is essential for quantitative studies of how energy flows from the Sun's photosphere, through the corona, and into the heliosphere. This electric field also provides valuable input for data-driven models of the solar atmosphere and the Sun-Earth system. We show how observed vector magnetogram time series can be used to estimate the photospheric electric field. Our method uses a 'poloidal-toroidal decomposition' (PTD) of the time derivative of the vector magnetic field. These solutions provide an electric field whose curl obeys all three components of Faraday's Law. The PTD solutions are not unique; the gradient of a scalar potential can be added to the PTD electric field without affecting consistency with Faraday's Law. We then present an iterative technique to determine a potential function consistent with ideal MHD evolution; but this field is also not a unique solution to Faraday's Law. Finally, we explore a variational approach that minimizes an energy functional to determine a unique electric field, a generalization of Longcope's 'Minimum Energy Fit'. The PTD technique, the iterative technique, and the variational technique are used to estimate electric fields from a pair of synthetic vector magnetograms taken from an MHD simulation; and these fields are compared with the simulation's known electric fields. The PTD and iteration techniques compare favorably to results from existing velocity inversion techniques. These three techniques are then applied to a pair of vector magnetograms of solar active region NOAA AR8210, to demonstrate the methods with real data. Careful examination of the results from all three methods indicates that evolution of the magnetic vector by itself does not provide enough information to determine the true electric field in the photosphere. Either more information from other measurements, or physical constraints other than those considered here are necessary to find the true electric field. However, we show it is possible to construct physically reasonable electric field distributions whose curl matches the evolution of all three components of B. We also show that the horizontal and vertical Poynting flux patterns derived from the three techniques are similar to one another for the cases investigated.

Fisher, G. H.; Welsch, B. T.; Abbett, W. P.; Bercik, D. J. [Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450 (United States)

2010-05-20

74

Estimating Electric Fields from Vector Magnetogram Sequences  

NASA Astrophysics Data System (ADS)

Determining the electric field distribution on the Sun's photosphere is essential for quantitative studies of how energy flows from the Sun's photosphere, through the corona, and into the heliosphere. This electric field also provides valuable input for data-driven models of the solar atmosphere and the Sun-Earth system. We show how observed vector magnetogram time series can be used to estimate the photospheric electric field. Our method uses a "poloidal-toroidal decomposition" (PTD) of the time derivative of the vector magnetic field. These solutions provide an electric field whose curl obeys all three components of Faraday's Law. The PTD solutions are not unique; the gradient of a scalar potential can be added to the PTD electric field without affecting consistency with Faraday's Law. We then present an iterative technique to determine a potential function consistent with ideal MHD evolution; but this field is also not a unique solution to Faraday's Law. Finally, we explore a variational approach that minimizes an energy functional to determine a unique electric field, a generalization of Longcope's "Minimum Energy Fit". The PTD technique, the iterative technique, and the variational technique are used to estimate electric fields from a pair of synthetic vector magnetograms taken from an MHD simulation; and these fields are compared with the simulation's known electric fields. The PTD and iteration techniques compare favorably to results from existing velocity inversion techniques. These three techniques are then applied to a pair of vector magnetograms of solar active region NOAA AR8210, to demonstrate the methods with real data.

Fisher, George H.; Welsch, B. T.; Abbett, W. P.; Bercik, D. J.

2010-05-01

75

Vector finite elements for electromagnetic field computation  

Microsoft Academic Search

A novel structure for the finite-element analysis of vector fields is presented. This structure uses the affine transformation to represent vectors and vector operations over triangular domains. Two-dimensional high-order vector elements are derived that are consistent with Whitney forms. One-form elements preserve the continuity of the tangential components of a vector field across element boundaries, while two-form elements preserve the

Zoltan J. Cendes

1991-01-01

76

Estimating Electric Fields from Vector Magnetogram Sequences  

NASA Astrophysics Data System (ADS)

We describe a new technique for estimating the three-dimensional vector electric field in the solar atmosphere by using a time-sequence of vector magnetograms to find an electric field distribution that obeys all 3 components of Faraday's law. The technique uses a ``poloidal-toroidal'' decomposition (PTD) to describe the electric field in terms of two scalar functions. The ``inductive'' PTD solutions to Faraday's Law are not unique, however, since additional contributions to the electric field from a potential function have no effect on Faraday's law. We then describe how estimates for the total electric field including both the inductive and potential components can be made by using variational techniques. The variational approach we develop is similar to Longcope's ``Minimum Energy Fit'' technique, in that the electric field obeys the vertical component of the magnetic induction equation, while also minimizing a positive definite functional. The purely potential part of the electric field can then be recovered by subtracting the PTD electric field from the total field.

Fisher, George H.; Welsch, B. T.; Abbett, W. P.; Bercik, D. J.

2009-05-01

77

Visualizing vector field topology in fluid flows  

NASA Technical Reports Server (NTRS)

Methods of automating the analysis and display of vector field topology in general and flow topology in particular are discussed. Two-dimensional vector field topology is reviewed as the basis for the examination of topology in three-dimensional separated flows. The use of tangent surfaces and clipping in visualizing vector field topology in fluid flows is addressed.

Helman, James L.; Hesselink, Lambertus

1991-01-01

78

Discontinuity-Preserving Vector Smoothing of Multivariate MR Images Using Vector Mean Field Annealing  

Microsoft Academic Search

We consider PD-, T1-, and T2-weighted magnetic resonance images jointly as a vector-valued image and use the angle of this vector field to formulate maximum a posteriori restoration as a global optimization problem. We use Mean Field Annealing (MFA) to find restorations that are superior to those obtained by previous multivariate approaches when shading artifacts near the MRI antenna are

Youn-Sik Han; Wesley E. Snyder; Griff L. Bilbro

1998-01-01

79

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

80

Influence of a repulsive vector coupling in magnetized quark matter  

NASA Astrophysics Data System (ADS)

We consider two flavor magnetized quark matter in the presence of a repulsive vector coupling (GV) devoting special attention to the low temperature region of the phase diagram to show how this type of interaction counterbalances the effects produced by a strong magnetic field. The most important effects occur at intermediate and low temperatures affecting the location of the critical end point as well as the region of first order chiral transitions. When GV=0 the presence of high magnetic fields (eB?10m?2) increases the density coexistence region with respect to the case when B and GV are absent while a decrease of this region is observed at high GV values and vanishing magnetic fields. Another interesting aspect observed at the low temperature region is that the usual decrease of the coexistence chemical value (inverse magnetic catalysis) at GV=0 is highly affected by the presence of the vector interaction which acts in the opposite way. Our investigation also shows that the presence of a repulsive vector interaction enhances the de Haas-van Alphen oscillations which, for very low temperatures, take place at eB?6m?2. We observe that the presence of a magnetic field, together with a repulsive vector interaction, gives rise to a complex transition pattern since B favors the appearance of multiple solutions to the gap equation whereas GV turns some metastable solutions into stable ones allowing for a cascade of transitions to occur.

Denke, Robson Z.; Pinto, Marcus Benghi

2013-09-01

81

Boston University Physics Applets: Field Vectors  

NSDL National Science Digital Library

This item is an in-class question pertaining to field vectors. Students view a simulation showing the field line pattern near two charges. They must determine which of four simulated vector fields correctly corresponds with the given pattern. This item is part of a larger collection of questions and simulations for use in introductory physics classrooms.

Duffy, Andrew

2008-08-01

82

MIT Physics 8.02 - Vector Fields Visualizations  

NSDL National Science Digital Library

Part of the MIT TEAL/Studio Physics Project, this web page contains a set of simulations relating to vector fields. Each of the visualizations was developed to supplement the MIT Physics 8.02 course in calculus-based Electricity and Magnetism. Topics include vector cross product, interactive field mapping, path and surface integrals, circulating flow of particles, particle sink, and flow fields with a variety of animated patterns. In addition, the TEAL project has made course notes, labs, and presentations available as part of its Open Courseware Repository: MIT Open Courseware: Electricity and Magnetism

Belcher, John

2010-03-30

83

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

84

Visualizing vector field topology in fluid flows  

Microsoft Academic Search

Methods for automating the analysis and display of vector field topology in general, and flow topology in particular, are described. By using techniques to extract and visualize topological information, it is possible to combine the simplicity of schematic depictions with the quantitative accuracy of curves and surfaces computed directly from the data. Two-dimensional vector field topology is discussed, covering critical

James L. Helman; Lambertus Hesselink

1991-01-01

85

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

86

Vector field based shape deformations  

Microsoft Academic Search

Abstract We present an approach to dene,shape deformations by constructing and,interactively modifying,C, continuous,time-dependent divergence-free vector elds. The deformation is obtained by a path line integration of the mesh vertices. This way, the deformation is volume-preserving, free of (local and global) self-intersections, feature preserving, smoothness preserving, and local. Different modeling metaphors,support the approach,which is able to modify,the vector eld,on-the-y according to

Wolfram Von Funck; Holger Theisel; Hans-peter Seidel

2006-01-01

87

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

88

Essential points of conformal vector fields  

NASA Astrophysics Data System (ADS)

An essential point of a conformal vector field ? on a conformal manifold (M,c) is a point around which the local flow of ? preserves no metric in the conformal class c. It is well-known that a conformal vector field vanishes at each essential point. In this note we show that essential points are isolated. This is a generalization to higher dimensions of the fact that the zeros of a holomorphic function are isolated. As an application, we show that every connected component of the zero set of a conformal vector field is totally umbilical.

Belgun, Florin; Moroianu, Andrei; Ornea, Liviu

2011-03-01

89

Triangle lattice Green functions for vector fields  

Microsoft Academic Search

All the identities and integral theorems of vector calculus are contained in the calculus of differential forms. The analogy between the exterior calculus of forms and the homology theory of a cell complex yields discrete lattice models for an array of interesting physical phenomena. These models, based on arbitrary combinations of coupled scalar and polar or axial vector field quantities,

B. Moritz; W. Schwalm

2001-01-01

90

Geoacoustic inversion using the vector field  

NASA Astrophysics Data System (ADS)

The main goal of this project was to study the use of the acoustic vector field, separately or in combination with the scalar field, to estimate the depth dependent geoacoustic properties of the seafloor via non-linear inversion. The study was performed in the context of the Sediment Acoustics Experiment 2004 (SAX04) conducted in the Northern Gulf of Mexico (GOM) where a small number of acoustic vector sensors were deployed in close proximity to the seafloor. A variety of acoustic waveforms were transmitted into the seafloor at normal incidence. The acoustic vector sensors were located both above and beneath the seafloor interface where they measured the acoustic pressure and the acoustic particle acceleration. Motion data provided by the buried vector sensors were affected by a suspension response that was sensitive to the mass properties of the sensor, the sediment density and sediment elasticity (e.g., shear wave speed). The suspension response for the buried vector sensors included a resonance within the analysis band of 0.4 to 2.0 kHz. The suspension resonance represented an unknown complex transfer function between the acoustic vector field in the seabed and data representing that field. Therefore, inverse methods developed for this study were required to 1) estimate dynamic properties of the sensor suspension resonance and 2) account for the associated corruption of vector field data. A method to account for the vector sensor suspense response function was integrated directly into the inversion methods such that vector channel data corruption was reduced and an estimate of the shear wave speed in the sediment was returned. Inversions of real and synthetic data sets indicated that information about sediment shear wave speed was carried by the suspension response of the buried sensors, as opposed to being contained inherently within the acoustic vector field.

Crocker, Steven E.

91

Magnetization strucrure of thermal vent on island arc from vector magnetic anomlies using AUV  

NASA Astrophysics Data System (ADS)

The geomagnetic anomaly measured by a scalar magnetometer,such as a proton precession magnetometer cannot be defined its direction, then it does not satisfy the Laplace's equation. Therefore physical formula describing the relation between magnetic field and magnetization cannot be established.Because the difference between results obtained from scalar data and from vector data is very significant, we must use vector magnetic field data for magnetization analyses to get the more reliable and exact solutions. The development program of fundamental tools for exploration of deep seabed resources started with the financial support of the Ministry of Education, Culture, Sports, Science & Technology (MEXT) in 2008 and will end in 2012. In this project, we are developing magnetic exploration tools for seabed resources using AUV (Autonomous Underwater Vehicle) and other deep-towed vehicles to measure not the scalar magnetic field but the vector magnetic field in order to estimate magnetization structure below the sea-floor exactly and precisely. We conducted AUV magnetic survey in 2010 at the thermal area called Hakurei deposit in the Bayonnaise submarine caldera at the southern end of Izu island arc, about 400km south of Tokyo. We analyzed the observed vector magnetic fields to get the vector magnetic anomaly Fields using the method of Isezaki(1984). We inverted these vector magnetic anomaly fields to magnetization structure. CONCLUSIONS 1.The scalar magnetic field TIA (Total Intensity Anomaly) has no physical formula describing the relation between M (Magnetization) and TIA because TIA does not satisfy the Laplace's equation. Then it is impossible to estimate M from TIA. 2.Anlyses of M using TIA have been done so far under assumption TIA=PTA (Projected Total Anomay on MF (Main Geomagnetic Field)), however, which caused the analysis error due to ?T= TIA - PTA . 3.We succeeded to measure the vector magnetic anomaly fields using AUV despite the severe magnetic noises around the magnetometer sensors. The method of Isezaki(1984) works good to eliminate these noises. 4.We got the very precise magnetization structure in the Bayonnaise submarine caldera area at the southern end of Izu island arc. We used the prism model which forms the shape of magnetized source body whose top is the sea-floor. The total number od prisms is 1500 making the 3 layers (0-80m, 80-160m, 160- 240m below the sea-floor, 25x20=500 prisms in 1 layer). The 4500 unknowns(3 unknowns, Mx,My,Mz in each prosm) are obtained from 12000 observed vector magnetic anomaly fields by inversion method. 5. The tentative result shows that the 1st and 2nd layers have smaller intensity of magnetization compared to the 3rd layer. The 2nd layer has the smallest of three layers. However the Hakurei deposit area in the 2nd layer has the a little bit greater magnetization than surrounding area which suggests that the Hakurei deposit includes some magnetic minerals. 6.We strongly recommend to carry out the magnetic survey using a three component magnetometer to get TF and TA which have many advantages for magnetic analyses (magnetization, upward continuation etc.) which cannot be done using scalar TIA.

Isezaki, N.; Matsuo, J.; Sayanagi, K.

2012-04-01

92

Imaging vector fields using Line Integral Convolution  

SciTech Connect

Imaging vector fields has applications in science, art, image processing and special effects. An effective new approach is to use linear and curvilinear filtering techniques to locally blur textures along a vector field. This approach builds on several previous texture generation and filtering techniques. It is, however, unique because it is local, one-dimensional and independent of any predefined geometry or texture. The technique is general and capable of imaging arbitrary two- and three-dimensional vector fields. The local one-dimensional nature of the algorithm lends itself to highly parallel and efficient implementations. Furthermore, the curvilinear filter is capable of rendering detail on very intricate vector fields. Combining this technique with other rendering and image processing techniques -- like periodic motion filtering -- results in richly informative and striking images. The technique can also produce novel special effects.

Cabral, B.; Leedom, L.C.

1993-03-01

93

Magsat vector magnetometer calibration using Magsat geomagnetic field measurements  

NASA Technical Reports Server (NTRS)

From the time of its launch on Oct. 30, 1979 into a nearly polar, Sun synchronous orbit, until it reentered the Earth's atmosphere on June 11, 1980, Magsat measured and transmitted more than three complete sets of global magnetic field data. The data obtained from the mission will be used primarily to compute a currently accurate model of the Earth's main magnetic field, to update and refine world and regional magnetic charts, and to develop a global scalar and vector crustal magnetic anomaly map. The in-flight calibration procecure used for 39 vector magnetometer system parameters is described as well as results obtained from some data sets and the numerical studies designed to evaluate the results.

Lancaster, E. R.; Jennings, T.; Morrissey, M.; Langel, R. A.

1980-01-01

94

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.

95

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

96

Finding Electric Fields, Poynting and Helicity Fluxes from Vector Magnetograms  

NASA Astrophysics Data System (ADS)

Existence of systematic measurements of vector magnetic fields allows us to estimate electric field in the photosphere, using Poloidal-Toroidal Decomposition of the magnetic field and its partial time derivative (Fisher et l. 2011). The PTD method is based on solving a set of Poisson equations which in the past has been done using Fast Fourier Transform techniques. We modify the existing PTD method by improving the poisson solver using a package of solvers for elliptic partial differential equations called Fishpack. We apply the PTD with a new Poisson equation solver to several test cases with a known electric field. We find that for the ANMHD simulation test case application of the new poisson solver yields a more accurate values of electric field, Poisson and helicity fluxes than before. We further investigate the applicability of our method to other test cases using simulations of M. Cheung and Y. Fan and also HMI vector magnetograms.

Kazachenko, Maria; Fisher, G. H.; Welsch, B. T.

2012-05-01

97

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

98

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

99

LINEAR VECTOR FIELDS MICHAEL C. SULLIVAN  

E-print Network

fields. I'd love to find a way to cover the connection between linear alge- bra and vector fields me of those plates children use so that different types of food will not touch. Here we outline some of the complex eigenvalues have no effect on curl; it will be normal to the invariant plane (use our rotations

Sullivan, Michael

100

Magnetic vector data from the western Caribbean reveal possible origin  

NASA Astrophysics Data System (ADS)

During a cruise with RV Meteor in the spring of 2010, magnetic measurements were carried out in the central and western Caribbean with up to six magnetic sensors deployed at the same time. These were i) a towed gradiometer consisting of two Overhauser sensors, ii) two towed vector magnetometers, and iii) two shipboard oriented vector magnetometers. While the gradiometer data provide total field magnetic anomalies free from external variations, the vector data can be analyzed with different methods in the space and wavenumber domains. In the case of the towed vector data, attitude control is challenging whereas shipboard data require a very thorough compensation for the ship's magnetic field. The data were analyzed with the goal to gain insight into the origin of the basement rocks especially of the western Caribbean. Position and strike direction of magnetic anomalies in the Columbia basin possibly hold the key to distinguish between an origin of the crust in the Pacific ocean and an alternative in situ formation between the Americas. On six long profiles in the Columbia basin and adjacent regions we find consistently strike directions of the magnetic anomalies around N100°E which seems to be incompatible with a Pacific origin of the crust. Three Project Magnet aeromagnetic vector profiles crossing the research area at different angles were analyzed with the same method and yield very similar results. In our interpretation, the crust underlying the Columbia basin formed during the Cretaceous at a roughly E-W trending spreading center between the Americas. Since the crust likely formed during the Cretaceous Superchron (C 34), the strike direction we find in our data probably does not represent typical seafloor spreading anomalies. Instead we believe it is related to changes in the intensity of the Earth's magnetic field which are known to have left correlated traces in oceanic crust formed during this period. The analysis methods we used are sensitive to intensity changes just as well as to polarity changes. We can demonstrate that the data quality is high and that the strike direction signal is clear and well correlated between the different profiles and that it is also consistent between towed, shipboard, and aeromagnetic sensors.

Barckhausen, U.; Engels, U.

2013-12-01

101

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

102

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

103

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

104

Full vector model for magnetization in sediments  

NASA Astrophysics Data System (ADS)

Sediments provide a continuous record of past geomagnetic field variations. Although it is theoretically possible to get both the direction and intensity of the geomagnetic field from sediment records, the mechanism is not fully understood. Previous workers have postulated that flocculation plays an important role in detrital remanent magnetism (DRM). Flocs are porous, loose and highly fragile aggregates of microscopic clay particles and their behavior in a viscous medium is likely to be different than single particles of magnetic minerals. In order to understand the role of flocculation in sediment magnetization, we carried out a set of redeposition experiments at different field intensities and a quasi-constant field inclination of 45°. We present here a simple numerical model of flocculation, incorporating both magnetic and hydrodynamic torques to explain the experimental data. At small floc sizes DRM acquisition is likely to be non-linear in field strengths comparable to the Earth's, but the sediments may be able to record the directions accurately. With increasing floc sizes sediments may retain a record of the intensity that is linearly related to the applied field or a direction parallel to the applied field, but are unlikely to do both at the same time. Also, the majority of the magnetic particles in the sediments may not be contributing significantly towards the net DRM and any bulk normalizing parameter may be unsuitable if the depositional environment has changed over the depositional period.

Mitra, Ritayan; Tauxe, Lisa

2009-09-01

105

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

106

Flow volumes for interactive vector field visualization  

SciTech Connect

Flow volumes are the volumetric equivalent of stream lines. They provide more information about the vector field being visualized than do stream lines or ribbons. Presented is an efficient method for producing flow volumes, composed of transparently rendered tetrahedra, for use in an interactive system. The problems of rendering, subdivision, sorting, rendering artifacts, and user interaction are dealt with.

Max, N.; Becker, B.; Crawfis, R.

1993-04-06

107

Circular Conditional Autoregressive Modeling of Vector Fields*  

PubMed Central

As hurricanes approach landfall, there are several hazards for which coastal populations must be prepared. Damaging winds, torrential rains, and tornadoes play havoc with both the coast and inland areas; but, the biggest seaside menace to life and property is the storm surge. Wind fields are used as the primary forcing for the numerical forecasts of the coastal ocean response to hurricane force winds, such as the height of the storm surge and the degree of coastal flooding. Unfortunately, developments in deterministic modeling of these forcings have been hindered by computational expenses. In this paper, we present a multivariate spatial model for vector fields, that we apply to hurricane winds. We parameterize the wind vector at each site in polar coordinates and specify a circular conditional autoregressive (CCAR) model for the vector direction, and a spatial CAR model for speed. We apply our framework for vector fields to hurricane surface wind fields for Hurricane Floyd of 1999 and compare our CCAR model to prior methods that decompose wind speed and direction into its N-S and W-E cardinal components. PMID:24353452

Modlin, Danny; Fuentes, Montse; Reich, Brian

2013-01-01

108

Killing spinors are Killing vector fields in Riemannian Supergeometry  

E-print Network

Killing spinors are Killing vector fields in Riemannian Supergeometry with even part G0 ~=Spin(k, l); (k, l) the signature of (M0, g0). Killing vector fields o* *n (M, g s there exists a corresponding odd vector field Xs on M. Our * *main result is that Xs is a Killing vector

Cortés, Vicente

109

(^-L_n,g)-spaces. Length of a vector field and the angle between two vector fields  

E-print Network

The notions of length of a vector field and cosine of the angle between two vector fields over a differentiable manifold with contravariant and covariant affine connections and metrics are introduced and considered. The change of the length of a vector field and of the angle between two vector fields along a contravariant vector field are found. The introduced notions are necessary for investigations of different types of transports over a manifold of the above mentioned type.

S. Manoff

2000-02-22

110

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.

111

Cheng Weyl vector field and its cosmological application  

Microsoft Academic Search

Weyl's idea on scale invariance was resurrected by Cheng in 1988. The requirement of local scale invariance leads to a completely new vector field, which we call the 'Cheng Weyl vector field'. The Cheng Weyl vector field couples only to a scalar field and the gravitational field naturally. It does not interact with other known matter in the standard model

Hao Wei; Rong-Gen Cai

2007-01-01

112

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.

113

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

114

Using Ideal Electric Fields Estimated from Vector Magnetogram Sequences to Drive Coronal MHD Simulations  

NASA Astrophysics Data System (ADS)

Dynamic models of the coronal magnetic field show promise as space weather forecasting tools. Such models should be driven by electric fields derived from sequences of photospheric vector magnetograms, the only routine measurements of the solar magnetic field currently available. Previous studies derived flows --- or, equivalently, ideal electric fields --- consistent with evolution of the normal photospheric field, which could be used in "component driving" of an MHD model, i.e., enforcing consistent evolution of the observed and modeled normal magnetic fields. In this extension of the component-driving approach, we demonstrate how to derive ideal electric fields consistent with the observed evolution of both the normal and horizontal magnetic field, useful for "vector driving," i.e., enforcing consistency between all three components of the observed and model photospheric magnetic vectors. To drive an MHD model, this "ideal vector driving" (IVD) approach amount to specification of both the velocity (perpendicular the magnetic field) and its vertical derivative at the model's bottom boundary. The IVD method can incorporate results from local/ tracking methods (e.g., LCT or DAVE) and/or results from global methods (e.g., MEF or poloidal-toroidal decomposition [PTD]). We have applied this new approach to "synthetic magnetograms" extracted from MHD simulations (where the magnetic and electric fields are exactly known), as well as to a four-hour sequence of vector magnetograms from NOAA AR 8210, on 01 May 1998, just prior to an M-class flare and geoeffective CME.

Welsch, B. T.; Fisher, G. H.; Abbett, W. P.; Bercik, D. J.

2008-05-01

115

Efficient morse decompositions of vector fields.  

PubMed

Existing topology-based vector field analysis techniques rely on the ability to extract the individual trajectories such as fixed points, periodic orbits, and separatrices that are sensitive to noise and errors introduced by simulation and interpolation. This can make such vector field analysis unsuitable for rigorous interpretations. We advocate the use of Morse decompositions, which are robust with respect to perturbations, to encode the topological structures of a vector field in the form of a directed graph, called a Morse connection graph (MCG). While an MCG exists for every vector field, it need not be unique. Previous techniques for computing MCG's, while fast, are overly conservative and usually results in MCG's that are too coarse to be useful for the applications. To address this issue, we present a new technique for performing Morse decomposition based on the concept of tau-maps, which typically provides finer MCG's than existing techniques. Furthermore, the choice of tau provides a natural tradeoff between the fineness of the MCG's and the computational costs. We provide efficient implementations of Morse decomposition based on tau-maps, which include the use of forward and backward mapping techniques and an adaptive approach in constructing better approximations of the images of the triangles in the meshes used for simulation.. Furthermore, we propose the use of spatial tau-maps in addition to the original temporal tau-maps. These techniques provide additional trade-offs between the quality of the MCGs and the speed of computation. We demonstrate the utility of our technique with various examples in the plane and on surfaces including engine simulation data sets. PMID:18467759

Chen, Guoning; Mischaikow, Konstantin; Laramee, Robert S; Zhang, Eugene

2008-01-01

116

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

117

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

118

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

119

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

120

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

121

Lyapunov Guidance Vector Fields for Unmanned Aircraft Applications  

E-print Network

of simple, provably stable, layers. Compared to most unmanned ground vehicles and unmanned helicoptersLyapunov Guidance Vector Fields for Unmanned Aircraft Applications Eric W. Frew, Member, IEEE, Dale implementing Lyapunov vector fields for the guidance of unmanned aircraft. The vector fields yield globally

Frew, Eric W.

122

Killing Vector Fields of Standard Static Space-times  

Microsoft Academic Search

We consider Killing vector fields on standard static space-times and obtain equations for a vector field on a standard static space-time to be Killing. We also provide a characterization of Killing vector fields on standard static space-times with compact Riemannian parts.

Fernando Dobarro; Bulent Unal

2008-01-01

123

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

124

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

125

Dispersive nonlinearities of QED vacuum in a periodic magnetic field  

Microsoft Academic Search

We investigate specific features of the dispersive vacuum polarization effects for the light propagation in magnetized vacuum which are induced due to spatial modulation of the magnetic field. The reciprocal lattice vectors associated with the periodic field are involved in the energy-momentum conservation for the photon interaction processes which allow elastic scattering of impinging photons by a strong magnetic field.

Gagik Yu. Kryuchkyan; Karen Z. Hatsagortsyan

2010-01-01

126

Cosmological Aspects of a Vector Field Model  

NASA Astrophysics Data System (ADS)

We have studied a DGP-inspired braneworld scenario where the idea of Lorentz invariance violation has been combined into a specifying preferred frame that embed a dynamical normal vector field to brane. We propose the Lorentz violating DGP brane models with enough parameters can explain crossing of phantom divide line. Also we have considered the model for proper cosmological evolution that is according to the observed behavior of the equation of state. In other view point, we have described a Rip singularity solution of model that occur in this model.

Sadatian, S. Davood

2012-07-01

127

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

128

Tangential vector finite elements for electromagnetic field computation  

Microsoft Academic Search

One approach to eliminating spurious modes in the finite-element solution of the vector wave equation is the use of tangential vector finite elements. With tangential vector finite elements, only the tangential components of the vector field are made continuous across the element boundaries. Edge-elements are the simplest example of tangential vector finite elements. However, edge-elements provide only the lowest-order of

J. F. Lee; D. K. Sun; Z. J. Cendes

1991-01-01

129

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

130

MOULD CALCULUS FOR HAMILTONIAN VECTOR FIELDS Jacky Cresson & Guillaume Morin  

E-print Network

MOULD CALCULUS FOR HAMILTONIAN VECTOR FIELDS by Jacky Cresson & Guillaume Morin Abstract. -- We present the general framework of Ã?calle's moulds in the case of linearization of a for- mal vector field. We modify then Ã?calle's technique to fit in the seek of a formal normal form of a Hamiltonian vector

131

Interacting vector fields in Relativity without Relativity  

E-print Network

Barbour, Foster and \\'{O} Murchadha have recently developed a new framework, called here {\\it{the 3-space approach}}, for the formulation of classical bosonic dynamics. Neither time nor a locally Minkowskian structure of spacetime are presupposed. Both arise as emergent features of the world from geodesic-type dynamics on a space of 3-dimensional metric--matter configurations. In fact gravity, the universal light cone and Abelian gauge theory minimally coupled to gravity all arise naturally through a single common mechanism. It yields relativity -- and more -- without presupposing relativity. This paper completes the recovery of the presently known bosonic sector within the 3-space approach. We show, for a rather general ansatz, that 3-vector fields can interact among themselves only as Yang--Mills fields minimally coupled to gravity.

Edward Anderson; Julian Barbour

2002-01-29

132

Local momentum space and the vector field  

NASA Astrophysics Data System (ADS)

The local momentum space expansion for the real vector field is considered. Using Riemann normal coordinates we obtain an expansion of the Feynman Green function up to and including terms that are quadratic in the curvature. The results are valid for a nonminimal operator such as that arising from a general Feynman-type gauge fixing condition. The result is used to derive the first three terms in the asymptotic expansion for the coincidence limit of the heat kernel without taking the trace, thus obtaining the untraced heat kernel coefficients. The spacetime dimension is kept general before specializing to four dimensions for comparison with previously known results. As a further application we reexamine the anomalous trace of the stress-energy-momentum tensor for the Maxwell field and comment on the gauge dependence.

Toms, David J.

2014-08-01

133

Local momentum space and the vector field  

E-print Network

The local momentum space expansion for the real vector field is considered. Using Riemann normal coordinates we obtain an expansion of the Feynman Green function up and including terms that are quadratic in the curvature. The results are valid for a non-minimal operator such as that arising from a general Feynman type gauge fixing condition. The result is used to derive the first three terms in the asymptotic expansion for the coincidence limit of the heat kernel without taking the trace, thus obtaining the untraced heat kernel coefficients. The spacetime dimension is kept general before specializing to four dimensions for comparison with previously known results. As a further application we re-examine the anomalous trace of the stress-energy-momentum tensor for the Maxwell field and comment on the gauge dependence.

Toms, David J

2014-01-01

134

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

135

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

136

Integrated vector sensor and magnetic compass using a novel 3D Hall structure  

Microsoft Academic Search

A new 3D silicon vector sensor using the Hall effect principle is realized and characterized. This microtransducer functionally integrates in a common sensor region two parallel-field Hall devices for the in-plane components of the magnetic field and one orthogonal Hall magnetic field version for the perpendicular to the chip. The advantages of this microtransducer are its very low channel cross-sensitivities

Ch. Roumenin; K. Dimitrov; A. Ivanov

2001-01-01

137

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

138

Vector field models of inflation and dark energy  

Microsoft Academic Search

We consider several new classes of viable vector field alternatives to the inflaton and quintessence scalar fields. Spatial vector fields are shown to be compatible with the cosmological anisotropy bounds if only slightly displaced from the potential minimum while dominant, or if driving an anisotropic expansion with nearly vanishing quadrupole today. The Bianchi I model with a spatial field and

Tomi S. Koivisto; David F. Mota

2008-01-01

139

Initial geomagnetic field model from Magsat vector data  

NASA Technical Reports Server (NTRS)

Magsat data from the magnetically quiet days of November 5-6, 1979, were used to derive a thirteenth degree and order spherical harmonic geomagnetic field model, MGST(6/80). The model utilized both scalar and high-accuracy vector data and fit that data with root-mean-square deviations of 8.2, 6.9, 7.6 and 7.4 nT for the scalar magnitude, B(r), B(theta), and B(phi), respectively. The model includes the three first-order coefficients of the external field. Comparison with averaged Dst indicates that zero Dst corresponds with 25 nT of horizontal field from external sources. When compared with earlier models, the earth's dipole moment continues to decrease at a rate of about 26 nT/yr. Evaluation of earlier models with Magsat data shows that the scalar field at the Magsat epoch is best predicted by the POGO(2/72) model but that the WC80, AWC/75 and IGS/75 are better for predicting vector fields.

Langel, R. A.; Mead, G. D.; Lancaster, E. R.; Estes, R. H.; Fabiano, E. B.

1980-01-01

140

An educational path for the magnetic vector potential and its physical implications  

NASA Astrophysics Data System (ADS)

We present an educational path for the magnetic vector potential A aimed at undergraduate students and pre-service physics teachers. Starting from the generalized Ampère-Laplace law, in the framework of a slowly varying time-dependent field approximation, the magnetic vector potential is written in terms of its empirical references, i.e. the conduction currents. Therefore, once the currents are known, our approach allows for a clear and univocal physical determination of A, overcoming the mathematical indeterminacy due to the gauge transformations. We have no need to fix a gauge, since for slowly varying time-dependent electric and magnetic fields, the ‘natural’ gauge for A is the Coulomb one. We stress the difference between our approach and those usually presented in the literature. Finally, a physical interpretation of the magnetic vector potential is discussed and some examples of the calculation of A are analysed.

Barbieri, S.; Cavinato, M.; Giliberti, M.

2013-09-01

141

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

142

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

143

Polarization evolution characteristics of focused hybridly polarized vector fields  

NASA Astrophysics Data System (ADS)

We investigate the focusing property and the polarization evolution characteristics of hybridly polarized vector fields in the focal region. Three types of hybridly polarized vector fields, namely azimuthal-variant hybridly polarized vector field, radial-variant hybridly polarized vector field, and spatial-variant hybridly polarized vector field, are experimentally generated. The intensity distributions and the polarization evolution of these hybridly polarized vector fields focused under low numerical aperture (NA) are experimentally studied and good agreements with the numerical simulations are obtained. The three-dimensional (3D) state of polarization and the field distribution within the focal volume of these hybridly polarized vector fields under high-NA focusing are studied numerically. The optical curl force on Rayleigh particles induced by tightly focused hybridly polarized vector fields, which results in the orbital motion of trapped particles, is analyzed. Simulation results demonstrate that polarization-only modulation provided by the hybridly polarized vector field allows one to control both the intensity distribution and 3D elliptical polarization in the focal region, which may find interesting applications in particle trapping, manipulation, and orientation analysis.

Gu, Bing; Pan, Yang; Rui, Guanghao; Xu, Danfeng; Zhan, Qiwen; Cui, Yiping

2014-08-01

144

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.

145

Lie Bracket of Vector Fields in Noncommutative Geometry  

NASA Astrophysics Data System (ADS)

The aim of this paper is to avoid some difficulties, related with the Lie bracket, in the definition of vector fields in a noncommutative setting, as they were defined by Woronowicz, Schmüdgen-Schüler and Aschieri-Schupp. We extend the definition of vector fields to consider them as derivations of the algebra, through Cartan pairs introduced by Borowiec. Then, using translations, we introduce the invariant vector fields. Finally, the definition of Lie bracket realized by Dubois-Violette, considering elements in the center of the algebra, is also extended to these invariant vector fields.

Jara, P.; Llena, D.

2003-09-01

146

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

147

Analysis of noise-induced errors in vector-field electron tomography  

NASA Astrophysics Data System (ADS)

Vector-field electron tomography (VFET) reconstructs electromagnetic vector fields of magnetic nanomaterials using transmission electron microscopy. The theory behind this reconstruction process is well established, but the practical implications of experimental errors and how they affect the accuracy of the reconstructed vector fields is not well understood, hindering progress in the use of these techniques for routine magnetic characterization of nanomaterials. Here, we present an analysis of the propagation of stochastic errors through a VFET algorithm. A method for determining the contribution of image noise to errors in a reconstructed vector potential is derived. Simulations are performed to test the validity of this method when applied to shot noise, which shows good agreement with theory.

Kemp, Z. D. C.; Petersen, T. C.; Paganin, D. M.; Spiers, K. M.; Weyland, M.; Morgan, M. J.

2014-08-01

148

A Simplified Quaternion-Based Algorithm for Orientation Estimation From Earth Gravity and Magnetic Field Measurements  

Microsoft Academic Search

Orientation of a static or slow-moving rigid body can be determined from the measured gravity and local magnetic field vectors. Some formulation of the QUaternion ESTimator (QUEST) algorithm is commonly used to solve this problem. Triads of accelerometers and magnetometers are used to measure gravity and local magnetic field vectors in sensor coordinates. In the QUEST algorithm, local magnetic field

Xiaoping Yun; Eric R. Bachmann; Robert B. McGhee

2008-01-01

149

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

150

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

151

Magnetic Fields in Quantum Degenerate Systems and in Vacuum  

Microsoft Academic Search

We consider self-magnetization of charged and neutral vector bosons bearing a magnetic moment in a gas and in vacuum. For charged vector bosons (W bosons) a divergence of the magnetization in both the medium and the electroweak vacuum occurs for the critical field B=Bwc=mw2\\/e. For B > Bwc the system is unstable. This behavior suggests the occurrence of a phase

H. Pérez Rojas; E. Rodríguez Querts

2007-01-01

152

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

153

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

154

On the Computation of Integral Curves in Adaptive Mesh Refinement Vector Fields  

SciTech Connect

Integral curves, such as streamlines, streaklines, pathlines, and timelines, are an essential tool in the analysis of vector field structures, offering straightforward and intuitive interpretation of visualization results. While such curves have a long-standing tradition in vector field visualization, their application to Adaptive Mesh Refinement (AMR) simulation results poses unique problems. AMR is a highly effective discretization method for a variety of physical simulation problems and has recently been applied to the study of vector fields in flow and magnetohydrodynamic applications. The cell-centered nature of AMR data and discontinuities in the vector field representation arising from AMR level boundaries complicate the application of numerical integration methods to compute integral curves. In this paper, we propose a novel approach to alleviate these problems and show its application to streamline visualization in an AMR model of the magnetic field of the solar system as well as to a simulation of two incompressible viscous vortex rings merging.

Deines, Eduard; Weber, Gunther H.; Garth, Christoph; Van Straalen, Brian; Borovikov, Sergey; Martin, Daniel F.; Joy, Kenneth I.

2011-06-27

155

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

156

Regularized Vector Field Learning with Sparse Approximation for Mismatch Removal  

E-print Network

approximation to a robust vector field learning method, sparse vector field consensus (SparseVFC), and derive a statistical learning bound on the speed of the convergence. We apply SparseVFC to the mismatch removal problem. The quantitative results on benchmark datasets demonstrate the significant speed advantage of SparseVFC over

Zhao, Ji

157

The Curl of a Vector Field: Beyond the Formula  

ERIC Educational Resources Information Center

It has been widely acknowledged that there is some discrepancy in the teaching of vector calculus in mathematics courses and other applied fields. The curl of a vector field is one topic many students can calculate without understanding its significance. In this paper, we explain the origin of the curl after presenting the standard mathematical…

Burch, Kimberly Jordan; Choi, Youngna

2006-01-01

158

THE CURL OF A VECTOR FIELD: BEYOND THE FORMULA  

Microsoft Academic Search

It has been widely acknowledged that there is some discrepancy in the teaching of vector calculus in mathematics courses and other applied fields. The curl of a vector field is one topic many students can calculate without understanding its significance. In this paper, we explain the origin of the curl after presenting the standard mathematical formulas. We investigate when and

Kimberly Jordan Burch; Youngna Choi

2006-01-01

159

Fast Clifford Fourier Transformation for Unstructured Vector Field Data  

E-print Network

Fast Clifford Fourier Transformation for Unstructured Vector Field Data Michael Schlemmer 1 Ingrid analysis used the Clifford Fourier transform for efficient pattern recognition for vector field data this approach with a fast Fourier transform to handle unstructured scalar data [6]. Our extension enables us

Hamann, Bernd

160

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

161

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

162

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

163

Statistical anisotropy of the curvature perturbation from vector field perturbations  

SciTech Connect

The {delta}N formula for the primordial curvature perturbation {zeta} is extended to include vector as well as scalar fields. Formulas for the tree-level contributions to the spectrum and bispectrum of {zeta} are given, exhibiting statistical anisotropy. The one-loop contribution to the spectrum of {zeta} is also worked out. We then consider the generation of vector field perturbations from the vacuum, including the longitudinal component that will be present if there is no gauge invariance. Finally, the {delta}N formula is applied to the vector curvaton and vector inflation models with the tensor perturbation also evaluated in the latter case.

Dimopoulos, Konstantinos; Karciauskas, Mindaugas; Lyth, David H. [Department of Physics, Lancaster University, Lancaster LA1 4YB (United Kingdom)] [Department of Physics, Lancaster University, Lancaster LA1 4YB (United Kingdom); Rodriguez, Yeinzon, E-mail: k.dimopoulos1@lancaster.ac.uk, E-mail: m.karciauskas@lancaster.ac.uk, E-mail: d.lyth@lancaster.ac.uk, E-mail: yeinzon.rodriguez@uan.edu.co [Centro de Investigaciones, Universidad Antonio Narino, Cra 3 Este 47A-15, Bogota D.C. (Colombia)] [Centro de Investigaciones, Universidad Antonio Narino, Cra 3 Este 47A-15, Bogota D.C. (Colombia)

2009-05-15

164

On the health of a vector field with RA2/6 coupling to gravity  

NASA Astrophysics Data System (ADS)

The coupling RA2/6 of a vector field to gravity was proposed as a mechanism for generating a primordial magnetic field, and more recently as a mechanism for generating a statistically anisotropic contribution to the primordial curvature perturbation. In either case, the vector field's perturbation has both a transverse and a longitudinal component, and the latter has some unusual features which call into question the health of the theory. We publish for the first time the energy density generated by the longitudinal field perturbations, and go on to argue that the theory may well be healthy in at least some versions.

Karciauskas, Mindaugas; Lyth, David H.

2010-11-01

165

Noise Prevents Infinite Stretching of the Passive Field in a Stochastic Vector Advection Equation  

NASA Astrophysics Data System (ADS)

A linear stochastic vector advection equation is considered; the equation may model a passive magnetic field in a random fluid. When the driving velocity field is rough but deterministic, in particular just Hölder continuous and bounded, one can construct examples of infinite stretching of the passive field, arising from smooth initial conditions. The purpose of the paper is to prove that infinite stretching is prevented if the driving velocity field contains in addition a white noise component.

Flandoli, Franco; Maurelli, Mario; Neklyudov, Mikhail

2014-09-01

166

Magnetic Field Activities for the High School Classroom  

NSDL National Science Digital Library

This unit is designed to acquaint students with the properties of magnetic fields. It is meant to introduce the idea of a "field" through investigations of magnetic fields as produced by various common magnetic materials and direct electrical currents. They will learn that the difference between a magnetic field and a gravitational field is that a gravitational field, in the experience of a student, always points downward and is always of the same strength. Magnetic fields are not limited to one direction or strength. Further, all students will know, by the mid-point of this unit, that magnetic fields are inherently loop shaped. Familiarity with the uniform gravitational field of classical Newtonian dynamics and kinematics is not required. As they complete the unit, students will gain an appreciation for the vector nature of fields, the ubiquity of field sources in the environment, and the ability to visualize such fields as three-dimensional entities.

Eckel, Ed; Friel, Matthew

167

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

168

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

169

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

170

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

171

Killing spinors are Killing vector fields in Riemannian Supergeometry  

E-print Network

A supermanifold M is canonically associated to any pseudo Riemannian spin manifold (M_0,g_0). Extending the metric g_0 to a field g of bilinear forms g(p) on T_p M, p\\in M_0, the pseudo Riemannian supergeometry of (M,g) is formulated as G-structure on M, where G is a supergroup with even part G_0\\cong Spin(k,l); (k,l) the signature of (M_0,g_0). Killing vector fields on (M,g) are, by definition, infinitesimal automorphisms of this G-structure. For every spinor field s there exists a corresponding odd vector field X_s on M. Our main result is that X_s is a Killing vector field on (M,g) if and only if s is a twistor spinor. In particular, any Killing spinor s defines a Killing vector field X_s.

D. V. Alekseevsky; V. Cortés; C. Devchand; U. Semmelmann

1997-04-02

172

Killing spinors are Killing vector fields in Riemannian supergeometry  

NASA Astrophysics Data System (ADS)

A supermanifold M is canonically associated to any pseudo-Riemannian spin manifold ( M0, g0). Extending the metric g0 to a field g of bilinear forms g( p) on TpM, p?M0, the pseudo-Riemannian supergeometry of ( M, g) is formulated as G-structure on M, where G is a supergroup with even part G 0 ? Spin(k, l); (k, l) the signature of ( M0, go). Killing vector fields on ( M, g) are, by definition, infinitesimal automorphisms of this G-structure. For every spinor field s there exists a corresponding odd vector field Xs on M. Our main result is that Xs is a Killing vector field on ( M, g) if and only if s is a twistor spinor. In particular, any Killing spinor s defines a Killing vector field Xs.

Alekseevsky, D. V.; Cortés, V.; Devchand, C.; Semmelmann, U.

1998-06-01

173

Magsat: A satellite for measuring near earth magnetic fields  

Microsoft Academic Search

Magsat, designed for making measurements of the geomagnetic vector field, is evaluated. For accurate vector measurements the attitude of the fluxgate magnetometer will be determined to about 15 arc-seconds. Expected measurement accuracy will be 6 (gamma) in each component and 3 in magnitude. The Magsat data will be applied to solid earth studies including modeling of the Earth's main magnetic

R. A. Langel; R. D. Regan; J. P. Murphy

1977-01-01

174

Three-qubit dynamics of entanglement in magnetic field  

E-print Network

A closed system of the equations for the local Bloch vectors and spin correlation functions is obtained by decomplexification of the Liouville-von Neumann equation for three magnetic qubits with the exchange interaction, that takes place in an arbitrary time-dependent external magnetic field. The numerical comparative analysis of entanglement is carried out depending on initial conditions and the magnetic field modulation. The present study may be useful for analysis of interference experiments and in the field of quantum computing.

E. A. Ivanchenko

2006-10-20

175

Magnetic properties of the two-dimensional n=0 vector model  

NASA Astrophysics Data System (ADS)

We determine the magnetic properties of the two-dimensional n=0 vector model using transfer matrix calculations and finite-size scaling. In the high-temperature region, we obtain results similar to the mean-field picture. In the low-temperature region, we find a very different behavior with a susceptibility which is always negative and an infinite spontaneous magnetization. This is shown to be in agreementn with some works of Nienhuis. The physical interpretation is discussed.

Saleur, H.

1987-03-01

176

MIT Physics 8.02: Vector Fields Visualizations - Cross Product of Two Vectors  

NSDL National Science Digital Library

This item is an interactive three-dimensional animation that illustrates the concept of vector cross product. Users set angle theta from zero to 360 degrees, and then rotate a vector through the angle. An animated hand automatically points in the proper direction according to the Right Hand Rule. No mathematics is introduced. This item is part of a collection of visualizations developed by the MIT TEAL project to supplement an introductory course in calculus-based electricity and magnetism. Lecture notes, labs, and presentations are also available as part of MIT's Open Courseware Repository: MIT Open Courseware: Electricity and Magnetism

2010-03-31

177

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

178

Energy momentum flows for the massive vector field  

E-print Network

We present a causal trajectory interpretation for the massive vector field, based on the flows of rest energy and a conserved density defined using the time-like eigenvectors and eigenvalues of the stress-energy-momentum tensor. This work extends our previous work which used a similar procedure for the scalar field. The massive, spin-one, complex vector field is discussed in detail and solutions are classified using the Pauli-Lubanski spin vector. The flows of energy-momentum are illustrated in a simple example of standing waves in a plane.

George Horton; Chris Dewdney

2006-09-26

179

Visualizing Vector Fields Using Line Integral Convolution and Dye Advection  

NASA Technical Reports Server (NTRS)

We present local and global techniques to visualize three-dimensional vector field data. Using the Line Integral Convolution (LIC) method to image the global vector field, our new algorithm allows the user to introduce colored 'dye' into the vector field to highlight local flow features. A fast algorithm is proposed that quickly recomputes the dyed LIC images. In addition, we introduce volume rendering methods that can map the LIC texture on any contour surface and/or translucent region defined by additional scalar quantities, and can follow the advection of colored dye throughout the volume.

Shen, Han-Wei; Johnson, Christopher R.; Ma, Kwan-Liu

1996-01-01

180

The Local Stellar Velocity Field via Vector Spherical Harmonics  

NASA Technical Reports Server (NTRS)

We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism. We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (V(sub X), V(sub Y), V(sub Z)) (10.5, 18.5, 7.3) +/- 0.1 km s(exp -1) not corrected for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (V(sub X), V(sub Y), V(sub Z)) (9.9, 15.6, 6.9) +/- 0.2 km s(exp -1). The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star. The Oort parameters determined by a straightforward least-squares adjustment in vector spherical harmonics are A=14.0 +/- 1.4, B=13.1 +/- 1.2, K=1.1 +/- 1.8, and C=2.9 +/- 1.4 km s(exp -1) kpc(exp -1). The physical meaning and the implications of these parameters are discussed in the framework of a general linear model of the velocity field. We find a few statistically significant higher degree harmonic terms that do not correspond to any parameters in the classical linear model. One of them, a third-degree electric harmonic, is tentatively explained as the response to a negative linear gradient of rotation velocity with distance from the Galactic plane, which we estimate at approximately -20 km s(exp -1) kpc(exp -1). A similar vertical gradient of rotation velocity has been detected for more distant stars representing the thick disk (z greater than 1 kpc), but here we surmise its existence in the thin disk at z less than 200 pc. The most unexpected and unexplained term within the Ogorodnikov-Milne model is the first-degree magnetic harmonic, representing a rigid rotation of the stellar field about the axis -Y pointing opposite to the direction of rotation. This harmonic comes out with a statistically robust coefficient of 6.2 +/- 0.9 km s(exp -1) kpc(exp -1) and is also present in the velocity field of more distant stars. The ensuing upward vertical motion of stars in the general direction of the Galactic center and the downward motion in the anticenter direction are opposite to the vector field expected from the stationary Galactic warp model.

Markarov, V. V.; Murphy, D. W.

2007-01-01

181

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

182

Computation approach for CMB bispectrum from primordial magnetic fields  

E-print Network

We present a detailed calculation of our previous short paper [1] in which we have investigated a constraint on the magnetic field strength through comic microwave background (CMB) temperature bispectrum of vector modes induced from primordial magnetic fields. By taking into account full angular dependence of the bispectrum with spin spherical harmonics and Wigner symbols, we explicitly show that the CMB bispectrum induced from the statistical-isotropic primordial vector fluctuations can be also described as an angle averaged form in the rotationally invariant way. We also study the cases with different spectral indices of the power spectrum of the primordial magnetic fields.

Shiraishi, Maresuke; Yokoyama, Shuichiro; Ichiki, Kiyotomo; Takahashi, Keitaro

2011-01-01

183

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

184

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

185

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

186

Attenuated Vector Tomography -- An Approach to Image Flow Vector Fields with Doppler Ultrasonic Imaging  

SciTech Connect

The measurement of flow obtained using continuous wave Doppler ultrasound is formulated as a directional projection of a flow vector field. When a continuous ultrasound wave bounces against a flowing particle, a signal is backscattered. This signal obtains a Doppler frequency shift proportional to the speed of the particle along the ultrasound beam. This occurs for each particle along the beam, giving rise to a Doppler velocity spectrum. The first moment of the spectrum provides the directional projection of the flow along theultrasound beam. Signals reflected from points further away from the detector will have lower amplitude than signals reflected from points closer to the detector. The effect is very much akin to that modeled by the attenuated Radon transform in emission computed tomography.A least-squares method was adopted to reconstruct a 2D vector field from directional projection measurements. Attenuated projections of only the longitudinal projections of the vector field were simulated. The components of the vector field were reconstructed using the gradient algorithm to minimize a least-squares criterion. This result was compared with the reconstruction of longitudinal projections of the vector field without attenuation. Ifattenuation is known, the algorithm was able to accurately reconstruct both components of the full vector field from only one set of directional projection measurements. A better reconstruction was obtained with attenuation than without attenuation implying that attenuation provides important information for the reconstruction of flow vector fields.This confirms previous work where we showed that knowledge of the attenuation distribution helps in the reconstruction of MRI diffusion tensor fields from fewer than the required measurements. In the application of ultrasound the attenuation distribution is obtained with pulse wave transmission computed tomography and flow information is obtained with continuous wave Doppler.

Huang, Qiu; Peng, Qiyu; Huang, Bin; Cheryauka, Arvi; Gullberg, Grant T.

2008-05-15

187

Flows associated with irregular R d —vector fields  

Microsoft Academic Search

This work consists on the study of flows associated with non-smooth Rd—vector fields, namely concerning existence and uniqueness for almost—every initial condition. It is also proved that the flows avoid some special compact sets.

Fernanda Cipriano; Ana Bela Cruzeiro

2005-01-01

188

Soft Constraints for Vector Field Design Keenan Crane  

E-print Network

Soft Constraints for Vector Field Design Keenan Crane June 22, 2012 This note describes how to add "soft constraints" to the algorithm described in Crane et al, Trivial Connections on Discrete Surfaces

Grinspun, Eitan

189

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

190

Magnetic field contribution to the Lorentz model.  

PubMed

The classical Lorentz model of dielectric dispersion is based on the microscopic Lorentz force relation and Newton's second law of motion for an ensemble of harmonically bound electrons. The magnetic field contribution in the Lorentz force relation is neglected because it is typically small in comparison with the electric field contribution. Inclusion of this term leads to a microscopic polarization density that contains both perpendicular and parallel components relative to the plane wave propagation vector. The modified parallel and perpendicular polarizabilities are both nonlinear in the local electric field strength. PMID:16783441

Oughstun, Kurt E; Albanese, Richard A

2006-07-01

191

Vector Field Visual Data Analysis Technologies for Petascale Computational Science  

SciTech Connect

State-of-the-art computational science simulations generate large-scale vector field data sets. Visualization and analysis is a key aspect of obtaining insight into these data sets and represents an important challenge. This article discusses possibilities and challenges of modern vector field visualization and focuses on methods and techniques developed in the SciDAC Visualization and Analytics Center for Enabling Technologies (VACET) and deployed in the open-source visualization tool, VisIt.

Garth, Christoph; Deines, Eduard; Joy, Kenneth I.; Bethel, E. Wes; Childs, Hank; Weber, Gunther; Ahern, Sean; Pugmire, Dave; Sanderson, Allen; Johnson, Chris

2009-11-13

192

The Local Stellar Velocity Field via Vector Spherical Harmonics  

Microsoft Academic Search

We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism. We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine

V. V. Makarov; D. W. Murphy

2007-01-01

193

Analytic integrability for some degenerate planar vector fields  

NASA Astrophysics Data System (ADS)

In this paper we study the analytic integrability of degenerate vector fields of the form (y3+2ax3y+⋯,-x5-3ax2y2+⋯) around the origin. For these vector fields it is proved that integrability does not imply formal orbital equivalence to the Hamiltonian leading part. Moreover, it is shown the existence of a system in this class which has a center but is neither analytically integrable nor formal orbital reversible.

Algaba, Antonio; García, Cristóbal; Giné, Jaume

2014-07-01

194

On embedded bifurcation structure in some discretized vector fields.  

PubMed

In this paper, we study a dynamic structure of discretized vector fields obtained from the Brusselator, which is described by two-dimensional ordinary differential equations (ODEs). We found that a bifurcation structure of the logistic map is embedded in the discretized vector field. The embedded bifurcation structure was unraveled by the dynamical orbits that eventually converge to a fixed point. We provide a detailed mathematical analysis to explain this phenomenon and relate it to the solution of the original ODEs. PMID:19792012

Kang, Hunseok; Tsuda, Ichiro

2009-09-01

195

Electric field vector characterization of terahertz surface plasmons  

Microsoft Academic Search

We demonstrate the ability to characterize independently the vector components of the electric field associated with terahertz surface plasmons. This is accomplished via electro-optic sampling, using an electro-optic crystal placed in close proximity to a corrugated metal foil. The individual electric field vector components are measured using two separate ZnTe crystals. Since ZnTe exhibits isotropic dielectric properties, all of the

Ajay Nahata; Wenqi Zhu

2007-01-01

196

Effect of an AC magnetic field on the steady-state magnetization distribution in a weak ferromagnet  

Microsoft Academic Search

Possible steady-state magnetization distributions in a domain wall are found in a weak ferromagnet subjected to an ac magnetic\\u000a field. The character of the rotation of the magnetization vector in the domain wall is determined. It is predicted that domain\\u000a structures can be rearranged and reoriented under an ac magnetic field.

V. S. Gerasimchuk; A. A. Shitov

2008-01-01

197

Cheng-Weyl Vector Field and its Cosmological Application  

E-print Network

Weyl's antiquated idea of scale invariance was resurrected by Cheng in 1988, almost 60 years later. The requirement of local scale invariance leads to the existence of a completely new vector field, which we call as ``Cheng-Weyl vector field''. The Cheng-Weyl vector field only couples to the scalar field and the gravitational field naturally. It does not interact with other known matters in the particle physics standard model. In the present work, the (generalized) Cheng-Weyl vector field coupling with a scalar field and its cosmological application are investigated. We regard the dark energy as a mixture of a scalar field and a so-called ``cosmic triad'' of three mutually orthogonal Cheng-Weyl vector fields. The cosmological evolution of this ``mixed'' dark energy is studied. We find that the effective equation-of-state parameter of dark energy can cross the phantom divide $w_{de}=-1$ in some cases; the first and second cosmological coincidence problems can be alleviated at the same time in this model.

Wei, H; Wei, Hao; Cai, Rong-Gen

2006-01-01

198

Cheng-Weyl Vector Field and its Cosmological Application  

E-print Network

Weyl's idea on scale invariance was resurrected by Cheng in 1988. The requirement of local scale invariance leads to a completely new vector field, which we call the ``Cheng-Weyl vector field''. The Cheng-Weyl vector field couples only to a scalar field and the gravitational field naturally. It does not interact with other known matters in the standard model of particle physics. In the present work, the (generalized) Cheng-Weyl vector field coupled with the scalar field and its cosmological application are investigated. A mixture of the scalar field and a so-called ``cosmic triad'' of three mutually orthogonal Cheng-Weyl vector fields is regarded as the dark energy in the universe. The cosmological evolution of this ``mixed'' dark energy model is studied. We find that the effective equation-of-state parameter of the dark energy can cross the phantom divide $w_{de}=-1$ in some cases; the first and second cosmological coincidence problems can be alleviated at the same time in this model.

Hao Wei; Rong-Gen Cai

2006-07-05

199

Cheng Weyl vector field and its cosmological application  

NASA Astrophysics Data System (ADS)

Weyl's idea on scale invariance was resurrected by Cheng in 1988. The requirement of local scale invariance leads to a completely new vector field, which we call the 'Cheng Weyl vector field'. The Cheng Weyl vector field couples only to a scalar field and the gravitational field naturally. It does not interact with other known matter in the standard model of particle physics. In the present work, the (generalized) Cheng Weyl vector field coupled with the scalar field and its cosmological application are investigated. A mixture of the scalar field and a so-called 'cosmic triad' of three mutually orthogonal Cheng Weyl vector fields is regarded as the dark energy in the universe. The cosmological evolution of this 'mixed' dark energy model is studied. We find that the effective equation-of-state parameter of the dark energy can cross the phantom divide wde = -1 in some cases; the first and second cosmological coincidence problems can be alleviated at the same time in this model.

Wei, Hao; Cai, Rong-Gen

2007-09-01

200

(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.

201

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

202

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

203

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

204

Controllable vector bottle-shaped fields generated by focused spatial-variant linearly polarized vector beams  

NASA Astrophysics Data System (ADS)

We demonstrate that the optical bottle-shaped fields can be controllably generated by the focused spatial-variant linearly polarized vector beams. Based on the vectorial Rayleigh-Sommerfeld formulas under the paraxial approximation, we present theoretically the analytical expression for the focused field of the vector beam and predict the evolution of the sate of polarization (SoP) in the focal region. Experimentally, we observe the vector bottle-shaped field that is in agreement with the numerical simulations. In particular, we validate that both the SoP and the size of the optical bottle field are manipulated easily by varying the azimuthal topological charge and the radial mode index.

Gu, Bing; Wu, Jia-Lu; Pan, Yang; Cui, Yiping

2013-11-01

205

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

206

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

207

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

208

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

209

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

210

Unveiling locally linearly polarized vector fields with broken axial symmetry  

SciTech Connect

We explore how the focusing of axial-symmetry-broken vector fields is associated with a sector aperture whose apex coincides with the field axis. Its focused field is azimuthally split into a pair of orthogonal right- and left-handed circularly polarized partial rings which are rotated by angles of {+-}{pi}/2 with respect to the input vector field carrying no orbital angular momentum (OAM) and no spin angular momentum (SAM), respectively. Each member of the pair of partial rings carries not only the opposite OAM but also the opposite SAM. We unveil the underlying physics behind such an effect.

Wang Xilin; Lou Kai; Chen Jing; Gu Bing; Li Yongnan [School of Physics and Key Laboratory of Weak Light Nonlinear Photonics, Nankai University, Tianjin 300071 (China); Wang Huitian [School of Physics and Key Laboratory of Weak Light Nonlinear Photonics, Nankai University, Tianjin 300071 (China); Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093 (China)

2011-06-15

211

Different Relative Orientation of Static and Alternative Magnetic Fields and Cress Roots Direction of Growth Changes Their Gravitropic Reaction  

NASA Astrophysics Data System (ADS)

The following variants of roots location relatively to static and alternative components of magnetic field were studied. At first variant the static magnetic field was directed parallel to the gravitation vector, the alternative magnetic field was directed perpendicular to static one; roots were directed perpendicular to both two fields’ components and gravitation vector. At the variant the negative gravitropysm for cress roots was observed. At second variant the static magnetic field was directed parallel to the gravitation vector, the alternative magnetic field was directed perpendicular to static one; roots were directed parallel to alternative magnetic field. At third variant the alternative magnetic field was directed parallel to the gravitation vector, the static magnetic field was directed perpendicular to the gravitation vector, roots were directed perpendicular to both two fields components and gravitation vector; At forth variant the alternative magnetic field was directed parallel to the gravitation vector, the static magnetic field was directed perpendicular to the gravitation vector, roots were directed parallel to static magnetic field. In all cases studied the alternative magnetic field frequency was equal to Ca ions cyclotron frequency. In 2, 3 and 4 variants gravitropism was positive. But the gravitropic reaction speeds were different. In second and forth variants the gravitropic reaction speed in error limits coincided with the gravitropic reaction speed under Earth’s conditions. At third variant the gravitropic reaction speed was slowed essentially.

Sheykina, Nadiia; Bogatina, Nina

212

Noether Symmetry Approach in "Cosmic Triad" Vector Field Scenario  

E-print Network

To realize the accelerations in the early and late periods of our universe, we need to specify potentials for the dominant fields. In this paper, by using the Noether symmetry approach, we try to find suitable potentials in the "cosmic triad" vector field scenario. Because the equation of state parameter of dark energy has been constrained in the range of $-1.21\\leq \\omega\\leq -0.89$ by observations, we derive the Noether conditions for the vector field in quintessence, phantom and quintom models, respectively. In the first two cases, constant potential solutions have been obtained. What is more, a fast decaying point-like solution with power-law potential is also found for the vector field in quintessence model. For the quintom case, we find an interesting constraint $\\tilde{C}V_{p}'=-CV_{q}'$ on the field potentials, where $C$ and $\\tilde{C}$ are constants related to the Noether symmetry.

Yi Zhang; Yun-gui Gong; Zong-Hong Zhu

2009-12-24

213

THEORY OF CHARGED VECTOR MESONS INTERACTING WITH THE ELECTROMAGNETIC FIELD  

Microsoft Academic Search

It is shown that starting from the usual canonical formalism for the ; electromagnetic interaction of a charged vector meson with arbitrary magnetic ; moment one is ied to a set of rules for Feynman diagrams, which appears to ; contain terms that are both infinite and noncovariant. These difficulties, ; however, can be circumvented by introducing a xi -limiting

T. D. Lee; C. N. Yang

1962-01-01

214

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

215

(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.

216

Higher topological invariants of magnetic field lines: observational aspects  

NASA Astrophysics Data System (ADS)

Topology of magnetic field lines is directly involved in magnetohydrodynamic (MHD) theorems and equations. Being an invariant of motion in ideal MHD conditions, the magnetic field-line topology is a natural obstacle to the relaxation of magnetic field into a current-free (potential) field and contrariwise limits a dynamo generation. Usage of these conservational laws and writing of numerical relations require a quantification of topology. One of the simplest existing measures of magnetic topology is the mutual magnetic helicity, that expresses the combined action of interaction and linkage between different magnetic field lines. For practical purposes there exists the revised concept of relative magnetic helicity, that allows to estimate the complexity of field-line topology in case of open volume, i.e. when magnetic lines cross the boundaries of given 3D region. At the same time this concept remains a simple interpretation of linkage number in terms of individual lines. Our point however is that magnetic helicity is far from being unique or comprehensive quantification of magnetic field-line topology. To improve the situation we introduce a set of higher invariants which extends the idea of relative helicity and provides a new means to describe the magnetic field-line topology. To practically study the possibility of implementation of higher topological invariants we reconstruct several moments of mutual helicity from observed solar vector magnetograms with extrapolated magnetic field above the photosphere and discuss to what extent such knowledge could be instructive for understanding of the solar magnetic field evolution.

Illarionov, Egor; Smirnov, Alexander; Georgoulis, Manolis K.; Sokoloff, Dmitry; Akhmet'ev, Peter

217

Project MAGNET High-level Vector Survey Data Reduction  

NASA Technical Reports Server (NTRS)

Since 1951, the U.S. Navy, under its Project MAGNET program, has been continuously collecting vector aeromagnetic survey data to support the U.S. Defense Mapping Agency's world magnetic and charting program. During this forty-year period, a variety of survey platforms and instrumentation configurations have been used. The current Project MAGNET survey platform is a Navy Orion RP-3D aircraft which has been specially modified and specially equipped with a redundant suite of navigational positioning, attitude, and magnetic sensors. A review of the survey data collection procedures and calibration and editing techniques applied to the data generated by this suite of instrumentation will be presented. Among the topics covered will be the determination of its parameters from the low-level calibration maneuvers flown over geomagnetic observatories.

Coleman, Rachel J.

1992-01-01

218

Project MAGNET high-level vector survey data reduction  

NASA Astrophysics Data System (ADS)

Since 1951, the U.S. Navy, under its Project MAGNET program, has been continuously collecting vector aeromagnetic survey data to support the U.S. Defense Mapping Agency's world magnetic and charting program. During this forty-year period, a variety of survey platforms and instrumentation configurations have been used. The current Project MAGNET survey platform is a Navy Orion RP-3D aircraft which has been specially modified and specially equipped with a redundant suite of navigational positioning, attitude, and magnetic sensors. A review of the survey data collection procedures and calibration and editing techniques applied to the data generated by this suite of instrumentation will be presented. Among the topics covered will be the determination of its parameters from the low-level calibration maneuvers flown over geomagnetic observatories.

Coleman, Rachel J.

1992-06-01

219

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

220

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

221

A statistical study on property of spatial magnetic field for solar active region  

NASA Astrophysics Data System (ADS)

Magnetic fields dominate most solar activities, there exist direct relations between solar flare and the distributions of magnetic field, and also its corresponding magnetic energy. In this paper, the statistical results about the relationships between the spatial magnetic field and solar flare are given basing on vector magnetic field observed by the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station (HSOS). The spatial magnetic fields are obtained by extrapolated photosphere vector magnetic field observed by SMFT. There are 23 active regions with flare eruption are chosen as data samples, which were observed from 1997 to 2007. The results are as follows: 1. Magnetic field lines become lower after flare for 16 (69 %) active regions; 2. The free energy are decreased after flare for 17 (74 %) active regions. It can conclude that for most active regions the changes of magnetic field after solar flare re coincident with the previous observations and studies.

Liu, S.

2014-06-01

222

Pattern forced geophysical vector field segmentation based on Clifford FFT  

NASA Astrophysics Data System (ADS)

Vector field segmentation is gaining increasing importance in geophysics research. Existing vector field segmentation methods usually can only handle the statistical characteristics of the original data. It is hard to integrate the patterns forced by certain geophysical phenomena. In this paper, a template matching method is firstly constructed on the foundation of the Clifford Fourier Transformation (CFT). The geometric meanings of both inner and outer components can provide more attractive information about the similarities between original vector field and template data. A composed similarity field is constructed based on the coefficients fields. After that, a modified spatial consistency preserving K-Means cluster algorithm is proposed. This algorithm is applied to the similarity fields to extract the template forced spatial distribution pattern. The complete algorithm for the overall processing is given and the experiments of ENSO forced global ocean surface wind segmentation are configured to test our method. The results suggest that the pattern forced segmentation can extract more latent information that cannot be directly measured from the original data. And the spatial distribution of ENSO influence on the surface wind field is clearly given in the segmentation result. All the above suggest that the method we proposed provides powerful and new thoughts and tools for geophysical vector field data analysis.

Yuan, Linwang; Yu, Zhaoyuan; Luo, Wen; Yi, Lin; Hu, Yong

2013-10-01

223

Computation of Surface Integrals of Curl Vector Fields  

ERIC Educational Resources Information Center

This article presents a way of computing a surface integral when the vector field of the integrand is a curl field. Presented in some advanced calculus textbooks such as [1], the technique, as the author experienced, is simple and applicable. The computation is based on Stokes' theorem in 3-space calculus, and thus provides not only a means to…

Hu, Chenglie

2007-01-01

224

On a New 4-Vector Cosmological Field Theory  

E-print Network

The original Dirac Equation is modified in the simplest imaginable and most trivial manner to include a universal 4-Vector Cosmological Field term in the space and time dimensions. This cosmological field leads to a modified Dirac Equation capable of explaining why the Universe appears to be made up chiefly of matter. It is seen that this 4-Vector Cosmological Field is actually a particle field and this particle field can possibly be identified with the darkmatter and darkenergy field. Further, this 4-Vector Cosmological Field is seen to give spacetime the desired quantum mechanical properties of randomness. Furthermore, it is seen that in the emergent Universe, the position coordinates of a particle in space -- contrary to the widely accepted belief that the position of a particle in space has no physical significance, we see that that opposite is true - namely that the position of a particle has physical significance. We further note that the 4-Vector Cosmological Field modification to the Dirac Equation leads us to a vacuum model redolent but different from that of Quantum Electrodynamics (QED). This new vacuum model is without virtual particles but darkparticles. We dare to make the suggestion that these darkparticles may possibly explain the current mystery of what really is darkmatter and darkenergy.

G. G. Nyambuya

2008-07-10

225

Improvement of cardiac CT reconstruction using local motion vector fields.  

PubMed

The motion of the heart is a major challenge for cardiac imaging using CT. A novel approach to decrease motion blur and to improve the signal to noise ratio is motion compensated reconstruction which takes motion vector fields into account in order to correct motion. The presented work deals with the determination of local motion vector fields from high contrast objects and their utilization within motion compensated filtered back projection reconstruction. Image registration is applied during the quiescent cardiac phases. Temporal interpolation in parameter space is used in order to estimate motion during strong motion phases. The resulting motion vector fields are during image reconstruction. The method is assessed using a software phantom and several clinical cases for calcium scoring. As a criterion for reconstruction quality, calcium volume scores were derived from both, gated cardiac reconstruction and motion compensated reconstruction throughout the cardiac phases using low pitch helical cone beam CT acquisitions. The presented technique is a robust method to determine and utilize local motion vector fields. Motion compensated reconstruction using the derived motion vector fields leads to superior image quality compared to gated reconstruction. As a result, the gating window can be enlarged significantly, resulting in increased SNR, while reliable Hounsfield units are achieved due to the reduced level of motion artefacts. The enlargement of the gating window can be translated into reduced dose requirements. PMID:19097853

Schirra, Carsten Oliver; Bontus, Claas; van Stevendaal, Udo; Dössel, Olaf; Grass, Michael

2009-03-01

226

Magnetoacoustic tomography with magnetic induction: bioimepedance reconstruction through vector source imaging.  

PubMed

Magnetoacoustic tomography with magnetic induction (MAT-MI) is a technique proposed to reconstruct the conductivity distribution in biological tissue at ultrasound imaging resolution. A magnetic pulse is used to generate eddy currents in the object, which in the presence of a static magnetic field induces Lorentz force based acoustic waves in the medium. This time resolved acoustic waves are collected with ultrasound transducers and, in the present work, these are used to reconstruct the current source which gives rise to the MAT-MI acoustic signal using vector imaging point spread functions. The reconstructed source is then used to estimate the conductivity distribution of the object. Computer simulations and phantom experiments are performed to demonstrate conductivity reconstruction through vector source imaging in a circular scanning geometry with a limited bandwidth finite size piston transducer. The results demonstrate that the MAT-MI approach is capable of conductivity reconstruction in a physical setting. PMID:23322761

Mariappan, Leo; He, Bin

2013-03-01

227

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

228

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

229

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

230

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

231

Analytical maximum likelihood estimation of stellar magnetic fields  

NASA Astrophysics Data System (ADS)

The polarized spectrum of stellar radiation encodes valuable information on the conditions of stellar atmospheres and the magnetic fields that permeate them. In this paper, we give explicit expressions to estimate the magnetic field vector and its associated error from the observed Stokes parameters. We study the solar case where specific intensities are observed and then the stellar case, where we receive the polarized flux. In the second case, we concentrate on the explicit expression for the case of a slow rotator with a dipolar magnetic field geometry. Moreover, we also give explicit formulae to retrieve the magnetic field vector from the least-squares deconvolution (LSD) profiles without assuming mean values for the LSD artificial spectral line. The formulae have been obtained assuming that the spectral lines can be described in the weak-field regime and using a maximum likelihood approach. The errors are recovered by means of the Hermitian matrix. The bias of the estimators is analysed in depth.

Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos, A.; Belluzzi, L.

2012-01-01

232

Measuring Earth's Local Magnetic Field Using a Helmholtz Coil  

NASA Astrophysics Data System (ADS)

In this paper, I present a low-cost interactive experiment for measuring the strength of Earth's local magnetic field. This activity can be done in most high schools or two-year physics laboratories with limited resources, yet will have a tremendous learning impact. This experiment solidifies the three-dimensional nature of Earth's magnetic field vector and helps reinforce the aspect of the vertical component of Earth's magnetic field. Students should realize that Earth's magnetic field is not fully horizontal (except at the magnetic equator) and that a compass simply indicates the direction of the horizontal component of Earth's magnetic field. A magnetic dip needle compass can be used to determine the angle (known as the "dip angle" or "inclination angle") measured from the direction in which Earth's magnetic field vector points to the horizontal. In this activity, students will be able to determine the horizontal component of the field using a Helmholtz coil and, knowing the dip angle, the Earth's magnetic field strength can be determined.

Williams, Jonathan E.

2014-04-01

233

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.

234

Vector Field Data Model and Operations  

Microsoft Academic Search

The completeness and versatility of spatial data models and associated operations serve as the foundation of any GIS. The raster data model and the carto- graphic modeling framework provide the representation and operations for analyz- ing geographic fields. The current GIS raster data model and cartographic modeling operations are limited in that all the attributes measured at each location in

Xingong Li; Michael E. Hodgson

2004-01-01

235

Computing nonlinear force free coronal magnetic fields  

E-print Network

Knowledge of the structure of the coronal magnetic field is important for our understanding of many solar activity phenomena, e.g. flares and CMEs. However, the direct measurement of coronal magnetic fields is not possible with present methods, and therefore the coronal field has to be extrapolated from photospheric measurements. Due to the low plasma beta the coronal magnetic field can usually be assumed to be approximately force free, with electric currents flowing along the magnetic field lines. There are both observational and theoretical reasons which suggest that at least prior to an eruption the coronal magnetic field is in a nonlinear force free state. Unfortunately the computation of nonlinear force free fields is way more difficult than potential or linear force free fields and analytic solutions are not generally available. We discuss several methods which have been proposed to compute nonlinear force free fields and focus particularly on an optimization method which has been suggested recently. We compare the numerical performance of a newly developed numerical code based on the optimization method with the performance of another code based on an MHD relaxation method if both codes are applied to the reconstruction of a semi-analytic nonlinear force-free solution. The optimization method has also been tested for cases where we add random noise to the perfect boundary conditions of the analytic solution, in this way mimicking the more realistic case where the boundary conditions are given by vector magnetogram data. We find that the convergence properties of the optimization method are affected by adding noise to the boundary data and we discuss possibilities to overcome this difficulty.

T. Wiegelmann; T. Neukirch

2008-01-21

236

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

237

Photon Magnetic Moment and Vacuum Magnetization in an Asymptotically Large Magnetic Field  

E-print Network

We consider the effect of the photon radiative correction on the vacuum energy in a superstrong magnetic field. The notion of a photon anomalous magnetic moment is analyzed and its connection with the quasiparticle character of the electromagnetic radiation is established. In the infrared domain the magnetic moment turns out to be a vector with two orthogonal components in correspondence with the cylindrical symmetry imposed by the external field. The possibility of defining such quantity in the high energy limit is studied as well. Its existence suggests that the electromagnetic radiation is a source of magnetization to the whole vacuum and thus its electron-positron zero-point energy is slightly modified. The corresponding contribution to the vacuum magnetization density is determined by considering the individual contribution of each vacuum polarization eigenmode in the Euler-Heisenberg Lagrangian. A paramagnetic response is found in one of them, whereas the remaining ones are diamagnetic. Additional issues concerning the transverse pressures are analyzed.

Selym Villalba Chavez

2009-10-27

238

Photon magnetic moment and vacuum magnetization in an asymptotically large magnetic field  

SciTech Connect

We consider the effect of the photon radiative correction on the vacuum energy in a superstrong magnetic field. The notion of a photon anomalous magnetic moment is analyzed and its connection with the quasiparticle character of the electromagnetic radiation is established. In the infrared domain the magnetic moment turns out to be a vector with two orthogonal components in correspondence with the cylindrical symmetry imposed by the external field. The possibility of defining such quantity in the high energy limit is studied as well. Its existence suggests that the electromagnetic radiation is a source of magnetization to the whole vacuum and thus its electron-positron zero-point energy is slightly modified. The corresponding contribution to the vacuum magnetization density is determined by considering the individual contribution of each vacuum polarization eigenmode in the Euler-Heisenberg Lagrangian. A paramagnetic response is found in one of them, whereas the remaining ones are diamagnetic. Additional issues concerning the transverse pressures are analyzed.

Villalba-Chavez, Selym [Institute of Physics, University of Graz, Universitaetsplatz 5, 8010, Graz (Austria)

2010-05-15

239

The Cassini Magnetic Field Investigation  

Microsoft Academic Search

The dual technique magnetometer system onboard the Cassini orbiter is described. This instrument consists of vector helium and fluxgate magnetometers with the capability to operate the helium device in a scalar mode. This special mode is used near the planet in order to determine with very high accuracy the interior field of the planet. The orbital mission will lead to

M. K. Dougherty; S. Kellock; D. J. Southwood; A. Balogh; E. J. Smith; B. T. Tsurutani; B. Gerlach; K.-H. Glassmeier; F. Gleim; C. T. Russell; G. Erdos; F. M. Neubauer; S. W. H. Cowley

2004-01-01

240

A calculation of the magnetic moment of a charged vector meson using proper normalization  

NASA Astrophysics Data System (ADS)

Renormalization has been the standard technique used in quantum field theory for 50 years. However, this technique relies upon perturbation theory, and it is easy to show that quantum field theory must be non- perturbative. Consequently, other techniques for solving Feynman diagrams must be used. Proper normalization is a non-perturbative technique which can be used to solve problems in quantum field theory. Instead of using cut- off masses and renormalized charges, proper normalization includes a proper normalization factor for each propagator. This makes the calculation necessarily finite. In this calculation, proper normalization is used to determine the magnetic moment of a charged vector meson, such as the ? meson.

Talbot, Julie L.

2000-12-01

241

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

242

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

243

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

244

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

245

Properties of the Acoustic Vector Field in Underwater Waveguides  

NASA Astrophysics Data System (ADS)

This thesis focuses on the description and measurement of the underwater acoustic field, based on vector properties of acoustic particle velocity. The specific goal is to interpret vector sensor measurements in underwater waveguides, in particular those measurements made in littoral (shallow) waters. To that end, theoretical models, which include the effects of reflections from the waveguide boundaries, are developed for the acoustic intensity, i.e. the product of acoustic pressure and acoustic particle velocity. Vector properties of acoustic intensity are shown to correspond to a non-dimensional vector property of acoustic particle velocity, its degree of circularity, which describes the trajectory of particle motion. Both experimental measurements and simulations of this non-dimensional vector property are used to analyze characteristics of sound propagation in underwater waveguides. Two measurement techniques are utilized in the experiments described in this thesis. In the first, particle velocity is obtained indirectly by time integration of the measured pressure gradient between two closely spaced (with respect to an acoustic wavelength) conventional pressure sensitive hydrophones. This method was used in ocean experiments conducted with vertical line arrays of hydrophones. In the second technique, particle velocity is measured directly by time integration of the signal generated by an accelerometer. An additional pressure measurement from a co-located hydrophone forms what is known as a "combined sensor" in the Russian literature, which allows for estimation of the vector acoustic intensity. This method was utilized mainly in laboratory experiments.

Dall'Osto, David R.

246

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

247

Magsat: A satellite for measuring near earth magnetic fields  

NASA Technical Reports Server (NTRS)

Magsat, designed for making measurements of the geomagnetic vector field, is evaluated. For accurate vector measurements the attitude of the fluxgate magnetometer will be determined to about 15 arc-seconds. Expected measurement accuracy will be 6 (gamma) in each component and 3 in magnitude. The Magsat data will be applied to solid earth studies including modeling of the Earth's main magnetic field, delineation of regional magnetic anomalies of crustal origin, and interpretation of those anomalies in terms of geologic and geophysical models. An opportunity will be presented to the scientific community to participate in data use investigations.

Langel, R. A.; Regan, R. D.; Murphy, J. P.

1977-01-01

248

Computation approach for CMB bispectrum from primordial magnetic fields  

Microsoft Academic Search

We present a detailed calculation of our previous short paper [M. Shiraishi, D. Nitta, S. Yokoyama, K. Ichiki, and K. Takahashi, Phys. Rev. DPRVDAQ1550-7998 82, 121302 (2010).10.1103\\/PhysRevD.82.121302] in which we have investigated a constraint on the magnetic field strength through comic microwave background temperature bispectrum of vector modes induced from primordial magnetic fields. By taking into account full angular dependence

Maresuke Shiraishi; Daisuke Nitta; Shuichiro Yokoyama; Kiyotomo Ichiki; Keitaro Takahashi

2011-01-01

249

Deep-sea Vector Magnetic Anomalies over the Bayonnaise Knoll Caldera (Izu-Ogasawara Arc) (Invited)  

NASA Astrophysics Data System (ADS)

The Bayonnaise Knoll caldera is located on the eastern margin of the backarc rift zone of the Izu-Ogasawara island arc. The caldera rim is ~3 km in diameter and 100-200 m high from the caldera floor 840-920 m deep. A large active hydrothermal field associated with sulfide deposit, called the Hakurei site, has been found at the foot of the southeastern caldera wall. We conducted deep-sea magnetic measurements using autonomous underwater vehicles to map ~75 % of an area 3 km by 4 km in the caldera. The magnetic vector field data were collected at 40-150 m altitude along the survey lines spaced 80-200 m apart. We improved the conventional correction method applied for removing the effect of vehicle magnetization, which greatly enhanced the precision of the resulting vector anomalies and allowed us to use the vector anomaly instead of the total intensity anomaly for inversion analysis. The magnetization distribution obtained using the vector anomaly was significantly different from the one obtained using the total intensity anomaly, especially in areas where the survey tracks were widely spaced. The aliasing effect appears in areas of sparse data distribution, and the magnetic field is more correctly calculated from the vector anomaly than the total intensity anomaly. The magnetization distribution in the caldera has two major features: a ~1.5-km wide belt of high magnetization, trending NNW-SSE through the caldera, and a clear low magnetization zone, ~300 m x ~500 m wide, extending over the Hakurei site. The high magnetization belt is considered to reflect basaltic volcanism associated with the backarc rifting that occurred after the formation of the Bayonnaise Knoll. The low magnetization zone is interpreted as the alteration zone resulting from the hydrothermal activity. Several zones of localized high magnetization are recognized within the high magnetization belt, some of them in the caldera wall adjacent to the low magnetization zone of the Hakurei site. We speculate that intensive magma intrusion occurred beneath the caldera wall and has provided the heat to generate hydrothermal fluid, which has been spouting out through the caldera wall faults. The surface expression of the vent field extends beyond the alteration zone inferred from the magnetization distribution, spreading upwards in the caldera wall. High-resolution topography around the Hakurei site indicates that the hydrothermal vents are generally distributed over a landform of slope failure. These observations would imply that hydrothermal fluid rising up in the up-flow zone moves laterally as well when it comes near the seafloor, probably along numerous fractures and fissures in the caldera wall. The distribution of pre-existing faults and fractures may rather control the fluid flow pathways in the shallow part and condition the surface extent of the vent field.

Honsho, C.; Ura, T.; Kim, K.

2013-12-01

250

A technique for estimating the absolute vector geomagnetic field from a marine vessel  

NASA Astrophysics Data System (ADS)

We have developed a technique to estimate the absolute strength and direction of the geomagnetic field from a marine vessel. This technique will be of value in the study of marine magnetic anomalies, directional drilling or geomagnetic field modelling. One of the main difficulties in this operation is to correct the data for the magnetic field generated by the vessel itself. Assuming the vessel susceptibility is isotropic, we show that by turning the ship through 360° at a place where the strength of the field is known we can estimate the local direction of the magnetic field. Once this is known, the vessel's field at any attitude can be robustly estimated and the measurements of the full magnetic field vector made in a normal surveying mode can be corrected. The ambient magnetic field estimates at the turn locations have proved to be very accurate. In normal surveying mode, these estimates are not as good since they are directly dependent on the accuracy of the vessel attitude measurements. However, when the technique is applied on real data, the total intensity field estimates have a very low level of noise showing that the vessel signal has been well accounted for.

Lesur, V.; Clark, T.; Turbitt, C.; Flower, S.

2004-06-01

251

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

252

Magnetic resonance imaging of time-varying magnetic fields from therapeutic devices.  

PubMed

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

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

2013-06-01

253

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

PubMed Central

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

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

2013-01-01

254

Vector field microscopic imaging of light , H. W. KIHM1  

E-print Network

electromagnetic waves. Although such light waves are analogous to the localized electronic wavefunctions-field vector of evanescent standing waves generated by total internal reflection of two counter probe for measuring local polarization, with the principal axes being aligned close to the x and z axes

Peinke, Joachim

255

Vector field path following for small unmanned air vehicles  

Microsoft Academic Search

This paper presents a new method for unmanned aerial vehicle path following using vector fields to represent desired ground track headings to direct the vehicle onto the desired path. The key feature of this approach is that ground track heading error and lateral following error approach zero asymptotically even in the presence of constant wind disturbances. Methods for following straight-line

Derek R. Nelson; D. B. Barber; T. W. McLain; R. W. Beard

2006-01-01

256

The Multiresolution Gradient Vector Field Skeleton Wooi-Boon Goha,*  

E-print Network

The Multiresolution Gradient Vector Field Skeleton Wooi-Boon Goha,* and Kai-Yun Chanb a School@ntu.edu.sg Phone: 65-67904611 Fax: 65-67926559 Abstract Many algorithms suppress skeleton associated with boundary of structural and textural skeletons. The former is associated with the general shape structure and the latter

Goh, Wooi Boon

257

Evaluation of turbulent magnetic energy spectra in the three-dimensional wave vector domain in the solar wind  

SciTech Connect

Using four-point measurements of the CLUSTER spacecraft, the energy distribution of magnetic field fluctuations in the solar wind is determined directly in the three-dimensional wave vector domain in the range 3 x 10{sup -4} rad/km < k < 3 x 10{sup -3} rad/km. The analysis method takes account of a regular tetrahedron configuration of CLUSTER and the Doppler effect. The energy distribution in the flow rest frame is anisotropic, characterized by two distinct extended structures perpendicular to the mean magnetic field and furthermore perpendicular to the flow direction. The three-dimensional distribution is averaged around the direction of the mean magnetic field direction, and then is further reduced to one-dimensional distributions in the wave number domain parallel and perpendicular to the mean magnetic field. The one-dimensional energy spectra are characterized by the power law with the index -5/3 and furthermore very close energy density between parallel and perpendicular directions to the mean magnetic field at the same wave numbers. Though the distributions and the spectra are not covered in a wide range of wave vectors, our measurements suggest that the solar wind fluctuation is anisotropic in the three-dimensional wave vector space. It is, however, rather isotropic when reduced into the parallel and perpendicular wave vector geometries due to the second anisotropy imposed by the flow direction.

Gary, S Peter [Los Alamos National Laboratory; Narita, Y [UNIV OF BRAUNSCHWEIG; Glassmeier, K H [UNIV OF BRAUNSCHWEIG; Goldstein, M L [NGSFC; Safraoui, F [NGSFC; Treumann, R A [UNIV. MUNICH

2009-01-01

258

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

259

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

260

The scientific case for magnetic field satellites  

NASA Technical Reports Server (NTRS)

To make full use of modern magnetic data and the paleomagnetic record, we must greatly improve our understanding of how the geodynamo system works. It is clearly nonlinear, probably chaotic, and its dimensionless parameters cannot yet be reproduced on a laboratory scale. It is accessible only to theory and to measurements made at and above the earth's surface. These measurements include essentially all geophysical types. Gravity and seismology give evidence for undulations in the core-mantle boundary (CMB) and for temperature variations in the lower mantle which can affect core convection and hence the dynamo. VLBI measurements of the variations in the Chandler wobble and length of day are affected by, among other things, the electromagnetic and mechanical transfer of angular momentum across the CMB. Finally, measurements of the vector magnetic field, its intensity, or its direction, give the most direct access to the core dynamo and the electrical conductivity of the lower mantle. The 120 gauss coefficients of degrees up to 10 probably come from the core, with only modest interference by mantle conductivity and crustal magnetization. By contrast, only three angular accelerations enter the problem of angular momentum transfer across the CMB. Satellite measurements of the vector magnetic field are uniquely able to provide the spatial coverage required for extrapolation to the CMB, and to isolate and measure certain magnetic signals which to the student of the geodynamo represent noise, but which are of great interest elsewhere in geophysics. Here, these claims are justified and the mission parameters likely to be scientifically most useful for observing the geodynamo system are described.

Backus, George E. (editor); Benton, Edward R.; Harrison, Christopher G. A.; Heirtzler, James R.

1987-01-01

261

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

262

Preparation and characterization of magnetic gene vectors for targeting gene delivery  

NASA Astrophysics Data System (ADS)

The PEI-CMD-MNPs were successfully prepared by the surface modification of magnetic Fe3O4 nanoparticles with carboxymethyl dextran (CMD) and polyethyleneimine (PEI). The PEI-CMD-MNPs polyplexes exhibited a typical superparamagnetic behavior and were well stable over the entire range of pH and NaCl concentration. These PEI-CMD-MNPs were used as magnetic gene vectors for targeting gene delivery. The prepared MNPs at different surface modification stages were characterized using Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), field emissions canning electron microscopy (FE-SEM), powder X-ray diffraction (XRD) and dynamic laser light scattering (DLS) analysis. The magnetic properties were studied by vibrating sample magnetometer (VSM). To evaluate the performance of the magnetic nanoparticles as gene transfer vector, the PEI-CMD-MNPs were used to delivery green fluorescent protein (GFP) gene into BHK21 cells. The expression of GFP gene was detected by fluorescence microscope. DNA-PEI-CMD-MNPs polyplexes absorbed by the cells were also monitored by Magnetic resonance imaging (MRI). The transfection efficiency and gene expression efficiency of that transfected with a magnet were much higher than that of standard transfection.

Zheng, S. W.; Liu, G.; Hong, R. Y.; Li, H. Z.; Li, Y. G.; Wei, D. G.

2012-10-01

263

Instability of anisotropic cosmological solutions supported by vector fields.  

PubMed

Models with vector fields acquiring a nonvanishing vacuum expectation value along one spatial direction have been proposed to sustain a prolonged stage of anisotropic accelerated expansion. Such models have been used for realizations of early time inflation, with a possible relation to the large scale cosmic microwave background anomalies, or of the late time dark energy. We show that, quite generally, the concrete realizations proposed so far are plagued by instabilities (either ghosts or unstable growth of the linearized perturbations) which can be ultimately related to the longitudinal vector polarization present in them. Phenomenological results based on these models are therefore unreliable. PMID:19392187

Himmetoglu, Burak; Contaldi, Carlo R; Peloso, Marco

2009-03-20

264

Total angular momentum waves for scalar, vector, and tensor fields  

NASA Astrophysics Data System (ADS)

Most calculations in cosmological perturbation theory, including those dealing with the inflationary generation of perturbations, their time evolution, and their observational consequences, decompose those perturbations into plane waves (Fourier modes). However, for some calculations, particularly those involving observations performed on a spherical sky, a decomposition into waves of fixed total angular momentum (TAM) may be more appropriate. Here we introduce TAM waves—solutions of fixed total angular momentum to the Helmholtz equation—for three-dimensional scalar, vector, and tensor fields. The vector TAM waves of given total angular momentum can be decomposed further into a set of three basis functions of fixed orbital angular momentum, a set of fixed helicity, or a basis consisting of a longitudinal (L) and two transverse (E and B) TAM waves. The symmetric traceless rank-2 tensor TAM waves can be similarly decomposed into a basis of fixed orbital angular momentum or fixed helicity, or a basis that consists of a longitudinal (L), two vector (VE and VB, of opposite parity), and two tensor (TE and TB, of opposite parity) waves. We show how all of the vector and tensor TAM waves can be obtained by applying derivative operators to scalar TAM waves. This operator approach then allows one to decompose a vector field into three covariant scalar fields for the L, E, and B components and symmetric-traceless-tensor fields into five covariant scalar fields for the L, VE, VB, TE, and TB components. We provide projections of the vector and tensor TAM waves onto vector and tensor spherical harmonics. We provide calculational detail to facilitate the assimilation of this formalism into cosmological calculations. As an example, we calculate the power spectra of the deflection angle for gravitational lensing by density perturbations and by gravitational waves. We comment on an alternative approach to cosmic microwave background fluctuations based on TAM waves. An accompanying paper will work out three-point functions in terms of TAM waves and their relation to the usual Fourier-space bispectra. Our work may have applications elsewhere in field theory and in general relativity.

Dai, Liang; Kamionkowski, Marc; Jeong, Donghui

2012-12-01

265

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

266

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

267

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

268

Dispersive nonlinearities of QED vacuum in a periodic magnetic field  

NASA Astrophysics Data System (ADS)

We investigate specific features of the dispersive vacuum polarization effects for the light propagation in magnetized vacuum which are induced due to spatial modulation of the magnetic field. The reciprocal lattice vectors associated with the periodic field are involved in the energy-momentum conservation for the photon interaction processes which allow elastic scattering of impinging photons by a strong magnetic field. The efficiency of the scattering is shown to be coherently enhanced due to interference of the scattered waves from the periodic structure.

Kryuchkyan, Gagik Yu.; Hatsagortsyan, Karen Z.

2010-10-01

269

Magnetic fields of the solar system: A comparative planetology toolkit  

NASA Astrophysics Data System (ADS)

Magnetic fields within the solar system provide a strong organizing force for processes active both within a planet or moon, and outside of it. In the interest of stimulating research and education in the field of comparative planetology, we present documented Fortran and MATLAB source codes and benchmarks to the latest models for planets and satellites that host internal magnetic fields. This presentation is made in the context of an interactive website: http://planetary-mag.net. Models are included for Earth (Comprehensive model CM4 of Sabaka et al., 2004, Geophysics J. Int.), Mercury (Anderson et al, 2011, Science), the Moon (Purucker and Nicholas, 2010, JGR), Mars (Lillis et al., 2010, JGR), and the outer planets Jupiter, Saturn, Uranus, and Neptune (Russell and Dougherty, 2010, Space Science Reviews). All models include magnetic fields of internal origin, and fields of external origin are included in the models for Mercury, the Earth, and the Moon. As models evolve, we intend to include magnetic fields of external origin for the other planets and moons. The website allows the user to select a coordinate system, such as planet-centered, heliocentric, or boundary normal, and the location within that coordinate system, and the vector magnetic field due to each of the component source fields at that location is then calculated and presented. Alternatively, the user can input a range as well as a grid spacing, and the vector magnetic field will be calculated for all points on that grid and be made available as a file for downloading.

Nicholas, J. B.; Purucker, M. E.; Johnson, C. L.; Sabaka, T. J.; Olsen, N.; Sun, Z.; Al Asad, M.; Anderson, B. J.; Korth, H.; Slavin, J. A.; Alexeev, I. I.; Belenkaya, E. S.; Phillips, R. J.; Solomon, S. C.; Lillis, R. J.; Langlais, B.; Winslow, R. M.; Russell, C. T.; Dougherty, M. K.; Zuber, M. T.

2011-12-01

270

Introduction to power-frequency electric and magnetic fields.  

PubMed Central

This paper introduces the reader to electric and magnetic fields, particularly those fields produced by electric power systems and other sources using frequencies in the power-frequency range. Electric fields are produced by electric charges; a magnetic field also is produced if these charges are in motion. Electric fields exert forces on other charges; if in motion, these charges will experience magnetic forces. Power-frequency electric and magnetic fields induce electric currents in conducting bodies such as living organisms. The current density vector is used to describe the distribution of current within a body. The surface of the human body is an excellent shield for power-frequency electric fields, but power-frequency magnetic fields penetrate without significant attenuation; the electric fields induced inside the body by either exposure are comparable in magnitude. Electric fields induced inside a human by most environmental electric and magnetic fields appear to be small in magnitude compared to levels naturally occurring in living tissues. Detection of such fields thus would seem to require the existence of unknown biological mechanisms. Complete characterization of a power-frequency field requires measurement of the magnitudes and electrical phases of the fundamental and harmonic amplitudes of its three vector components. Most available instrumentation measures only a small subset, or some weighted average, of these quantities. Hand-held survey meters have been used widely to measure power-frequency electric and magnetic fields. Automated data-acquisition systems have come into use more recently to make electric- and magnetic-field recordings, covering periods of hours to days, in residences and other environments.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8206045

Kaune, W T

1993-01-01

271

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

272

Magnetic field of Jupiter: A generalized inverse approach  

SciTech Connect

The estimation of planetary magnetic fields from observations of the magnetic field gathered along a spacecraft flyby trajectory is examined with the aid of generalized inverse techniques, with application to the internal magnetic field of Jupiter. Model non-uniqueness resulting from the limited spatial extent of the observations and noise on the data is explored and quantitative estimates of the model parameter resolution are found. The presence of a substantial magnetic field of external origin due to the currents flowing in the Jovian magnetodisc is found to be an important source of error in estimates of the internal Jovian field, and new models explicitly incorporating these currents are proposed. New internal field models are derived using the vector helium magnetometer observations and the high field fluxgate observations of Pioneer 11, and knowledge of the external current system gained from the Pioneer 10 and Voyagers 1 and 2 encounters.

Connerney, J.E.P.

1981-09-01

273

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

274

Finite element formulation using magnetic vector potential approach: effects of displacement current in magneto-electro-elastic cylindrical shells  

NASA Astrophysics Data System (ADS)

Displacement current is associated with the generation of magnetic fields due to time-varying electric fields. The harmonic response of a magneto-electro-elastic axisymmetric cylinder accounting for displacement current is carried out using the semi-analytical finite element method. The non-conservative electric field is represented using a magnetic vector potential. Studies are carried out for the first circumferential harmonics of the shell structure with the clamped-free boundary condition. The contribution made to the magnetic flux density by the electric displacement current is very small at lower frequencies but it becomes significant at higher frequencies.

Biju, B.; Ganesan, N.; Shankar, K.

2010-01-01

275

Ghost instabilities of cosmological models with vector fields nonminimally coupled to the curvature  

SciTech Connect

We prove that many cosmological models characterized by vectors nonminimally coupled to the curvature (such as the Turner-Widrow mechanism for the production of magnetic fields during inflation, and models of vector inflation or vector curvaton) contain ghosts. The ghosts are associated with the longitudinal vector polarization present in these models and are found from studying the sign of the eigenvalues of the kinetic matrix for the physical perturbations. Ghosts introduce two main problems: (1) they make the theories ill defined at the quantum level in the high energy/subhorizon regime (and create serious problems for finding a well-behaved UV completion), and (2) they create an instability already at the linearized level. This happens because the eigenvalue corresponding to the ghost crosses zero during the cosmological evolution. At this point the linearized equations for the perturbations become singular (we show that this happens for all the models mentioned above). We explicitly solve the equations in the simplest cases of a vector without a vacuum expectation value in a Friedmann-Robertson-Walker geometry, and of a vector with a vacuum expectation value plus a cosmological constant, and we show that indeed the solutions of the linearized equations diverge when these equations become singular.

Himmetoglu, Burak; Peloso, Marco [School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455 (United States); Contaldi, Carlo R. [Theoretical Physics, Blackett Laboratory, Imperial College, London, SW7 2BZ (United Kingdom)

2009-12-15

276

Analytical formulae of tightly focused Laguerre-Gaussian vector fields  

NASA Astrophysics Data System (ADS)

We develop analytical formulae for describing the tight focusing field of the Laguerre-Gaussian vector field with space-variant distribution of states of polarization in the frame of the Rayleigh-Sommerfeld theory. The analytical formulae of three radial, azimuthal and longitudinal components are very beneficial in order to understand the tightly focused field. This result is of great importance to improving the design and engineering the tightly focused field, by using phase and polarization, for applications such as optical tweezers and optical manipulation. This method is also applicable to the homogeneously polarized optical fields and optical vortex fields. In particular, these analytical formulae can also describe the dynamic process of the tightly focused fields, for example, average photon trajectories.

Li, Yongnan; Ren, Zhi-Cheng; Qian, Sheng-Xia; Tu, Chenghou; Wang, Hui-Tian

2014-10-01

277

Vector Fields and Line Integrals 1. Let C be a curve traced by the vector-valued function  

E-print Network

by the closed curve S, oriented by the right-hand rule. Let F be a C1 vector field. Then S F · dr = S curl F · nVector Fields and Line Integrals 1. Let C be a curve traced by the vector-valued function r (t) = x, dy, dz . (10) We may thus write the line integral of F over the oriented curve C as C F · dr = C Mdx

Logan, David

278

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

279

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

280

Analysis of superconducting electromagnetic finite elements based on a magnetic vector potential variational principle  

NASA Technical Reports Server (NTRS)

Electromagnetic finite elements are extended based on a variational principle that uses the electromagnetic four potential as primary variable. The variational principle is extended to include the ability to predict a nonlinear current distribution within a conductor. The extension of this theory is first done on a normal conductor and tested on two different problems. In both problems, the geometry remains the same, but the material properties are different. The geometry is that of a 1-D infinite wire. The first problem is merely a linear control case used to validate the new theory. The second problem is made up of linear conductors with varying conductivities. Both problems perform well and predict current densities that are accurate to within a few ten thousandths of a percent of the exact values. The fourth potential is then removed, leaving only the magnetic vector potential, and the variational principle is further extended to predict magnetic potentials, magnetic fields, the number of charge carriers, and the current densities within a superconductor. The new element produces good results for the mean magnetic field, the vector potential, and the number of superconducting charge carriers despite a relatively high system condition number. The element did not perform well in predicting the current density. Numerical problems inherent to this formulation are explored and possible remedies to produce better current predicting finite elements are presented.

Schuler, James J.; Felippa, Carlos A.

1991-01-01

281

Magnetic Fields in Quantum Degenerate Systems and in Vacuum  

E-print Network

We consider self-magnetization of charged and neutral vector bosons bearing a magnetic moment in a gas and in vacuum. For charged vector bosons (W bosons) a divergence of the magnetization in both the medium and the electroweak vacuum occurs for the critical field B=B_{wc}=m_{w}^{2}/e. For B>B_{wc} the system is unstable. This behavior suggests the occurrence of a phase transition at B=B_{c}, where the field is self-consistently maintained. This mechanism actually prevents $B$ from reaching the critical value B_{c}. For virtual neutral vector bosons bearing an anomalous magnetic moment, the ground state has a similar behavior for B=B_{nbc}=m_{nb}^{2}/q . The magnetization in the medium is associated to a Bose-Einstein condensate and we conjecture a similar condensate occurs also in the case of vacuum. The model is applied to virtual electron-positron pairs bosonization in a magnetic field B \\sim B_{pc}\\lesssim 2m_{e}^{2}/e, where m_e is the electron mass. This would lead also to vacuum self-magnetization in QED, where in both cases the symmetry breaking is due to a condensate of quasi-massless particles.

H. Perez Rojas; E. Rodriguez Querts

2006-12-28

282

Magnetic Fields in Quantum Degenerate Systems and in Vacuum  

NASA Astrophysics Data System (ADS)

We consider self-magnetization of charged and neutral vector bosons bearing a magnetic moment in a gas and in vacuum. For charged vector bosons (W bosons) a divergence of the magnetization in both the medium and the electroweak vacuum occurs for the critical field B=Bwc=mw2/e. For B > Bwc the system is unstable. This behavior suggests the occurrence of a phase transition at B = Bc, where the field is self-consistently maintained. This mechanism actually prevents B from reaching the critical value Bc. For virtual neutral vector bosons bearing an anomalous magnetic moment, the ground state behavior for B=Bnbc=mnb2/q have a similar behavior. The magnetization in the medium is associated to a Bose-Einstein condensate and we conjecture a similar condensate occurs also in the case of vacuum. The model is applied to virtual electron-positron pairs bosonization in a magnetic field B ˜ Bpc< ˜ 2me2/e, where me is the electron mass. This would lead also to vacuum self-magnetization in QED, where in both cases the symmetry breaking is due to a condensate of quasi-massless particles.

Rojas, H. Pérez; Querts, E. Rodríguez

283

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

284

Orientation and Magnitude of Mars' Magnetic Field  

NASA Technical Reports Server (NTRS)

This image shows the orientation and magnitude of the magnetic field measured by the MGS magnetometer as it sped over the surface of Mars during an early aerobraking pass (Day of the year, 264; 'P6' periapsis pass). At each point along the spacecraft trajectory we've drawn vectors in the direction of the magnetic field measured at that instant; the length of the line is scaled to show the relative magnitude of the field. Imagine traveling along with the MGS spacecraft, holding a string with a magnetized needle on one end: this essentially a compass with a needle that is free to spin in all directions. As you pass over the surface the needle would swing rapidly, first pointing towards the planet and then rotating quickly towards 'up' and back down again. All in a relatively short span of time, say a minute or two, during which time the spacecraft has traveled a couple of hundred miles. You've just passed over one of many 'magnetic anomalies' thus far detected near the surface of Mars. A second major anomaly appears a little later along the spacecraft track, about 1/4 the magnitude of the first - can you find it? The short scale length of the magnetic field signature locates the source near the surface of Mars, perhaps in the crust, a 10 to 75 kilometer thick outer shell of the planet (radius 3397 km).

The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO. JPL is an operating division of California Institute of Technology (Caltech).

1997-01-01

285

Vector measurements of the current induced effective fields in Ta/CoFeB/MgO heterostructures  

NASA Astrophysics Data System (ADS)

Ultrathin magnetic heterostructures exhibit a variety of rich physics owing to the strong effects from the interfaces. Power efficient current induced magnetization switching and domain nucleation, fast current driven domain wall motion have been observed in ultrathin Co or CoFeB layer sandwiched between a heavy metal (Pt, Ta) and an oxide. Most of the current (or voltage) induced effects in these systems can be represented by the ``effective magnetic fields'', which illustrate the strength and direction of the torque exerted on the magnetic moments. A comprehensive understanding of the effective fields is key to the development of magnetic nano-devices aimed for memory and logic applications. We have studied the current induced effective field vector in TaCoFeBMgO heterostructure to reveal the underlying physics of the interaction between the magnetic moments and current in such structure. A low current lock-in detection scheme is used to evaluate the effective field vector. The CoFeB layer is perpendicularly magnetized owing to the interface magnetic anisotropy of CoFeBMgO. We find that the effective field is very sensitive to the thickness of the Ta and CoFeB layers. The effective field even changes its direction when the Ta layer thickness is varied, indicating that there are competing effects that contribute to the effective field generation. We discuss our results in light of the spin Hall effect and an effect due to Rashba-like Hamiltonian. (Acknowledgment: FIRST program)

Hayashi, Masamitsu

2013-03-01

286

New techniques in 3D scalar and vector field visualization  

SciTech Connect

At Lawrence Livermore National Laboratory (LLNL) we have recently developed several techniques for volume visualization of scalar and vector fields, all of which use back-to-front compositing. The first renders volume density clouds by compositing polyhedral volume cells or their faces. The second is a ``splatting`` scheme which composites textures used to reconstruct the scalar or vector fields. One version calculates the necessary texture values in software, and another takes advantage of hardware texture mapping. The next technique renders contour surface polygons using semi-transparent textures, which adjust appropriately when the surfaces deform in a flow, or change topology. The final one renders the ``flow volume`` of smoke or dye tracer swept out by a fluid flowing through a small generating polygon. All of these techniques are applied to a climate model data set, to visualize cloud density and wind velocity.

Max, N.; Crawfis, R.; Becker, B.

1993-05-05

287

The planetary magnetic field and magnetosphere of Jupiter: Pioneer 10  

Microsoft Academic Search

Data obtained by the Pioneer 10 vector helium magnetometer are presented along with models of the intrinsic magnetic field of JupiteL and its magnetosphere. Data acquired between 2.84 and 6.0 Rj, where the intensity of the planetary field ranged between 1900 and 18,400 'y, were used to develop a six-parameter eccentric dipole model of the field. The dipole so derived

E. J. Smith; L. Davis Jr.; D. E. Jones; P. J. Coleman Jr.; D. S. Colburn; P. Dyal; C. P. Sonett; A. M. A. Frandsen

1974-01-01

288

Magnetic Fields in Quantum Degenerate Systems and in Vacuum  

Microsoft Academic Search

We consider self-magnetization of charged and neutral vector bosons bearing a\\u000amagnetic moment in a gas and in vacuum. For charged vector bosons (W bosons) a\\u000adivergence of the magnetization in both the medium and the electroweak vacuum\\u000aoccurs for the critical field B=B_{wc}=m_{w}^{2}\\/e. For B>B_{wc} the system is\\u000aunstable. This behavior suggests the occurrence of a phase transition at

E. EREZ ROJAS; E. Rodriguez Querts

2006-01-01

289

Homogenization of maximal monotone vector fields via selfdual variational calculus  

E-print Network

We use the theory of selfdual Lagrangians to give a variational approach to the homogenization of equations in divergence form, that are driven by a periodic family of maximal monotone vector fields. The approach has the advantage of using $\\Gamma$-convergence methods for corresponding functionals just as in the classical case of convex potentials, as opposed to the graph convergence methods used in the absence of potentials. A new variational formulation for the homogenized equation is also given.

Ghoussoub, Nassif; Saiz, Ramon Zarate

2010-01-01

290

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

291

Molecular Lines as Diagnostics of Solar and Stellar Magnetic Fields  

NASA Astrophysics Data System (ADS)

Thanks to recent advances in theory we can now calculate molecular line profiles in the presence of magnetic fields with high accuracy, both in the Zeeman and Paschen-Back regimes (Berdyugina et al. 2000; Berdyugina & Solanki 2001a). The synthetic Stokes profiles of various molecular species (e.g. TiO, OH, MgH, CN, FeH) have been compared with profiles observed in sunspots. The agreement between the theory and observations is remarkable. For example, the mutually opposite polarities of different OH lines are reproduced without invoking any free parameters, except the magnetic field strength and sunspot temperature. Introducing molecular lines into the inversion of sunspot spectra leads to significant improvements in the deduced magnetic field vector. Here we investigate how molecular lines can be used to deduce magnetic parameters of cool stars. We find that such lines are of great interest for measuring magnetic fields on cooler stars and in starspots.

Berdyugina, S. V.; Solanki, S. K.; Lagg, A.

2003-10-01

292

Magnetic Field Restructuring Associated with Two Successive Solar Eruptions  

NASA Astrophysics Data System (ADS)

We examine two successive flare eruptions (X5.4 and X1.3) on 2012 March 7 in the NOAA active region 11429 and investigate the magnetic field reconfiguration associated with the two eruptions. Using an advanced non-linear force-free field extrapolation method based on the SDO/HMI vector magnetograms, we obtain a stepwise decrease in the magnetic free energy during the eruptions, which is roughly 20%-30% of the energy of the pre-flare phase. We also calculate the magnetic helicity and suggest that the changes of the sign of the helicity injection rate might be associated with the eruptions. Through the investigation of the magnetic field evolution, we find that the appearance of the "implosion" phenomenon has a strong relationship with the occurrence of the first X-class flare. Meanwhile, the magnetic field changes of the successive eruptions with implosion and without implosion were well observed.

Wang, Rui; Liu, Ying D.; Yang, Zhongwei; Hu, Huidong

2014-08-01

293

Dynamic equations for three different qudits in a magnetic field  

E-print Network

A closed system of equations for the local Bloch vectors and spin correlation functions of three magnetic qudits, which are in an arbitrary, time-dependent, external magnetic field, is obtained using decomplexification of the Liouville-von Neumann equation. The algorithm of the derivation of the dynamic equations is presented. In the basis convenient for the important physical applications structure constants of algebra su(2S+1) are calculated.

E. A. Ivanchenko

2009-04-22

294

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

295

Computation approach for CMB bispectrum from primordial magnetic fields  

E-print Network

We present a detailed calculation of our previous short paper [M. Shiraishi, D. Nitta, S. Yokoyama, K. Ichiki, and K. Takahashi, Phys. Rev. D 82, 121302 (2010).] in which we have investigated a constraint on the magnetic field strength through comic microwave background temperature bispectrum of vector modes induced from primordial magnetic fields. By taking into account full angular dependence of the bispectrum with spin spherical harmonics and Wigner symbols, we explicitly show that the cosmic microwave background bispectrum induced from the statistical-isotropic primordial vector fluctuations can be also described as an angle-averaged form in the rotationally invariant way. We also study the cases with different spectral indices of the power spectrum of the primordial magnetic fields.

Maresuke Shiraishi; Daisuke Nitta; Shuichiro Yokoyama; Kiyotomo Ichiki; Keitaro Takahashi

2011-01-27

296

Computation approach for CMB bispectrum from primordial magnetic fields  

NASA Astrophysics Data System (ADS)

We present a detailed calculation of our previous short paper [M. Shiraishi, D. Nitta, S. Yokoyama, K. Ichiki, and K. Takahashi, Phys. Rev. DPRVDAQ1550-7998 82, 121302 (2010).10.1103/PhysRevD.82.121302] in which we have investigated a constraint on the magnetic field strength through comic microwave background temperature bispectrum of vector modes induced from primordial magnetic fields. By taking into account full angular dependence of the bispectrum with spin spherical harmonics and Wigner symbols, we explicitly show that the cosmic microwave background bispectrum induced from the statistical-isotropic primordial vector fluctuations can be also described as an angle-averaged form in the rotationally invariant way. We also study the cases with different spectral indices of the power spectrum of the primordial magnetic fields.

Shiraishi, Maresuke; Nitta, Daisuke; Yokoyama, Shuichiro; Ichiki, Kiyotomo; Takahashi, Keitaro

2011-06-01

297

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

298

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

299

Killing spinors are Killing vector fields in Riemannian Supergeometry  

Microsoft Academic Search

A supermanifold M is canonically associated to any pseudo Riemannian spin manifold (M_0,g_0). Extending the metric g_0 to a field g of bilinear forms g(p) on T_p M, p\\\\in M_0, the pseudo Riemannian supergeometry of (M,g) is formulated as G-structure on M, where G is a supergroup with even part G_0\\\\cong Spin(k,l); (k,l) the signature of (M_0,g_0). Killing vector fields

D. V. Alekseevsky; V. Cortés; C. Devchand; U. Semmelmann

1997-01-01

300

Development of Techniques for Visualization of Scalar and Vector Fields in the Immersive Environment  

NASA Technical Reports Server (NTRS)

Visualization of scalar and vector fields in the immersive environment (CAVE - Cave Automated Virtual Environment) is important for its application to radiation shielding research at NASA Langley Research Center. A complete methodology and the underlying software for this purpose have been developed. The developed software has been put to use for the visualization of the earth s magnetic field, and in particular for the study of the South Atlantic Anomaly. The methodology has also been put to use for the visualization of geomagnetically trapped protons and electrons within Earth's magnetosphere.

Bidasaria, Hari B.; Wilson, John W.; Nealy, John E.

2005-01-01

301

A Robust Method for Vector Field Learning with Application to Mismatch Removing  

E-print Network

@mail.hust.edu.cn Abstract We propose a method for vector field learning with out- liers, called vector field consensus (VFC more, 2) computationally effi- cient. As an application, we apply VFC to solve the problem of mismatch

302

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

303

Low-frequency fluctuations in plasma magnetic fields  

SciTech Connect

It is shown that even a non-magnetized plasma with temperature T sustains zero-frequency magnetic fluctuations in thermal equilibrium. Fluctuations in electric and magnetic fields, as well as in densities, are computed. Four cases are studied: a cold, gaseous, isotropic, non-magnetized plasma; a cold, gaseous plasma in a uniform magnetic field; a warm, gaseous plasma described by kinetic theory; and a degenerate electron plasma. For the simple gaseous plasma, the fluctuation strength of the magnetic field as a function of frequency and wavenumber is calculated with the aid of the fluctuation-dissipation theorem. This calculation is done for both collisional and collisionless plasmas. The magnetic field fluctuation spectrum of each plasma has a large zero-frequency peak. The peak is a Dirac {delta}-function in the collisionless plasma; it is broadened into a Lorentzian curve in the collisional plasma. The plasma causes a low frequency cutoff in the typical black-body radiation spectrum, and the energy under the discovered peak approximates the energy lost in this cutoff. When the imposed magnetic field is weak, the magnetic field were vector fluctuation spectra of the two lowest modes are independent of the strength of the imposed field. Further, these modes contain finite energy even when the imposed field is zero. It is the energy of these modes which forms the non-magnetized zero-frequency peak of the isotropic plasma. In deriving these results, a simple relationship between the dispersion relation and the fluctuation power spectrum of electromagnetic waves if found. The warm plasma is shown, by kinetic theory, to exhibit a zero-frequency peak in its magnetic field fluctuation spectrum as well. For the degenerate plasma, we find that electric field fluctuations and number density fluctuations vanish at zero frequency; however, the magnetic field power spectrum diverges at zero frequency.

Cable, S.; Tajima, T.

1992-02-01

304

Conformal field theory correlators from classical field theory on anti-de Sitter space: Vector and spinor fields  

Microsoft Academic Search

We use the AdS-CFT correspondence to calculate CFT correlation functions of vector and spinor fields. The connection between the AdS and boundary fields is properly treated via a Dirichlet boundary value problem.

W. Mück; K. S. Viswanathan

1998-01-01

305

Absolute magnetic helicity and the cylindrical magnetic field  

SciTech Connect

The different magnetic helicities conserved under conditions of perfect electrical conductivity are expressions of the fundamental property that every evolving fluid surface conserves its net magnetic flux. This basic hydromagnetic point unifies the well known Eulerian helicities with the Lagrangian helicity defined by the conserved fluxes frozen into a prescribed set of disjoint toroidal tubes of fluid flowing as a permanent partition of the entire fluid [B. C. Low, Astrophys. J. 649, 1064 (2006)]. This unifying theory is constructed from first principles, beginning with an analysis of the Eulerian and Lagrangian descriptions of fluids, separating the ideas of fluid and magnetic-flux tubes and removing the complication of the magnetic vector potential's free gauge from the concept of helicity. The analysis prepares for the construction of a conserved Eulerian helicity, without that gauge complication, to describe a 3D anchored flux in an upright cylindrical domain, this helicity called absolute to distinguish it from the well known relative helicity. In a version of the Chandrasekhar-Kendall representation, the evolving field at any instant is a unique superposition of a writhed, untwisted axial flux with a circulating flux of field lines all closed and unlinked within the cylindrical domain. The absolute helicity is then a flux-weighted sum of the writhe of that axial flux and its mutual linkage with the circulating flux. The absolute helicity is also conserved if the frozen-in field and its domain are continuously deformed by changing the separation between the rigid cylinder-ends with no change of cylinder radius. This hitherto intractable cylindrical construction closes a crucial conceptual gap for the fundamentals to be complete at last. The concluding discussion shows the impact of this development on our understanding of helicity, covering (i) the helicities of wholly contained and anchored fields; (ii) the Eulerian and Lagrangian descriptions of field evolution; (iii) twist as a topological property of solenoidal fields versus the linkage properties of open and closed discrete curves treated by Gauss, Caligarneau, Berger, and Prior; and (iv) the change of absolute helicity by resistive diffusion. These are important hydromagnetic properties of twisted magnetic fields in the million-degree hot, highly conducting corona of the Sun.

Low, B. C. [High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado 80307 (United States)

2011-05-15

306

On Killing vector fields and Newman-Penrose constants  

NASA Astrophysics Data System (ADS)

Asymptotically flat space-times with one Killing vector field are studied. The Killing equations are solved asymptotically using polyhomogeneous expansions (i.e., series in powers of 1/r and ln r), and solved order by order. The solution to the leading terms of these expansions yields the asymptotic form of the Killing vector field. The possible classes of Killing fields are discussed by analyzing their orbits on null infinity. The integrability conditions of the Killing equations are used to obtain constraints on the components of the Weyl tensor (?0,?1,?2) and on the shear (?). The behavior of the solutions to the constraint equations is studied. It is shown that for Killing fields that are non-supertranslational the characteristics of the constraint equations are the orbits of the restriction of the Killing field to null infinity. As an application, the particular case of boost-rotation symmetric space-times is considered. The constraints on ?0 are used to study the behavior of the coefficients that give rise to the Newman-Penrose constants, if the space-time is non-polyhomogeneous, or the logarithmic Newman-Penrose constants, if the space-time is polyhomogeneous.

Kroon, Juan Antonio Valiente

2000-02-01

307

The Local Stellar Velocity Field via Vector Spherical Harmonics  

NASA Technical Reports Server (NTRS)

We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism.We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (V(sub X), V(sub Y), V(sub Z)) = (10.5, 18.5, 7.3) +/- 0.1 km s(exp -1) not for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (V(sub X), V(sub Y), V(sub Z)) = (9.9, 15.6, 6.9) +/- 0.2 km s(exp -1). The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star...

Makarov, V. V.; Murphy, D. W.

2007-01-01

308

High-sensitivity vector magnetometer for measuring magnetic torque at low temperatures  

NASA Astrophysics Data System (ADS)

We present a fully automated vector vibrating-sample magnetometer where the sample can be rotated against the applied magnetic field Hap, so that the angular dependence of the longitudinal, Mlong, and transversal, Mtrans, components of M with respect to Hap on the rotation plane are determined. The magnetic field range is ±20kOe and temperature ranges between 4.2 and 340 K. The resolution is better than 2×10-7emu and the sensitivity is 5×10-6emu. Standard hysteresis loop measurements are possible as well. As examples of its capability we display torque curves performed at low temperatures in a [Ho8Lu15]50 superlattice and in a 60-nm-thick Terfenol-D thin film.

Benito, L.; Arnaudas, J. I.; del Moral, A.

2006-02-01

309

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.

310

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

311

Multi-Instrumental Vector Magnetic Observations and Techniques for Investigating Auroral Dynamics  

NASA Astrophysics Data System (ADS)

Space based magnetometers in highly inclined low earth orbits are essential for characterizing the state of the auroral space environment and the dynamic processes within. This paper demonstrates the utility of data derived from multiple satellites including AMPERE (70 Iridium spacecraft), DMSP (4 spacecraft) and ST5 (3 spacecraft), and the AMIENext technique to investigate periods of interest in 2006 and 2010. A new satellite conjunction-finding technique magnetically maps in situ observations to a common altitude in the APEX coordinate system to assess the spatial and temporal stability and quality of vector magnetic measurements (Knipp et al., 2014). In March of 2006, the ST5 constellation was launched into a pearls-on-a-string configuration. Subsequent data processing produced superb, quality controlled magnetic observations from the 90-day mission (e.g. Slavin et al., 2008, Le et al., 2009; Wang et al., 2009). We present conjunction comparisons between the ST5 and DMSP spacecraft during the ST5 mission lifetime, which was dominated by a series of high-speed solar wind events. In May of 2010, a unipolar Magnetic Cloud passed Earth, providing an opportunity to investigate the magnetopshere-ionosphere coupling response to a slow moving transient followed by higher speed flow. This event included significant, long-lived disturbances in the asymmetric ring current and auroral electrojet (AE) index. Assimilation of space-based magnetic observations via the AMIENext procedure, reveal twisting in the dayside patterns, consistent with the sign changes in IMF By and a highly structured topology as IMF Bz turned northward. We present a detailed comparison between the magnetic observations from DMSP and AMPERE. To aid in investigating the local magnetic field and in providing data to assimilative models, we have also created new datasets in self-describing NASA CDF formats for the DMSP and ST5 vector magnetometers and for the DMSP precipitating ion and electron instruments and we will discuss their availability.

Redmon, Robert; Knipp, Delores; Kilcommons, Liam; Richmond, Art; Matsuo, Tomoko; Anderson, Brian; Korth, Haje; Slavin, James; Le, Guan; Wilson, Gordon; Rich, Fred; Denig, William

2014-05-01

312

Hawking radiation of a vector field and gravitational anomalies  

NASA Astrophysics Data System (ADS)

Recently, the relation between Hawking radiation and gravitational anomalies has been used to estimate the flux of Hawking radiation for a large class of black objects. In this paper, we extend the formalism, originally proposed by Robinson and Wilczek, to the Hawking radiation of vector particles (photons). It is explicitly shown, with the Hamiltonian formalism, that the theory of an electromagnetic field on d-dimensional spherical black holes reduces to one of an infinite number of massive complex scalar fields on 2-dimensional spacetime, for which the usual anomaly-cancellation method is available. It is found that the total energy emitted from the horizon for the electromagnetic field is just (d-2) times that for a scalar field. The results support the picture that Hawking radiation can be regarded as an anomaly eliminator on horizons. Possible extensions and applications of the analysis are discussed.

Murata, Keiju; Miyamoto, Umpei

2007-10-01

313

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

314

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

315

hal-00207918,version1-18Jan2008 MOULD CALCULUS FOR HAMILTONIAN VECTOR FIELDS  

E-print Network

hal-00207918,version1-18Jan2008 MOULD CALCULUS FOR HAMILTONIAN VECTOR FIELDS by Jacky Cresson of a Hamiltonian vector field in cartesian coordinates. We prove that mould calculus can also produce successive- tion of a formal vector field without and within resonances. We enlighten the power of moulds

Paris-Sud XI, Université de

316

Interactive Vector Field Feature Identification Joel Daniels II, Erik W. Anderson, Student Member, IEEE,  

E-print Network

Interactive Vector Field Feature Identification Joel Daniels II, Erik W. Anderson, Student Member) of desired feature types. These control points guide a mapping of the vector field points to the interactive of these attributes forms a representation of the vector field samples in the attribute space. We project

Utah, University of

317

dg-ga/9704002 Killing spinors are Killing vector fields in  

E-print Network

dg-ga/9704002 MPI 97-29 Killing spinors are Killing vector fields in Riemannian Supergeometry D spinor. In particular, any Killing spinor s defines a Killing vector field Xs. 1 Introduction); (k, l) the signature of (M0, g0). Killing vector fields on (M, g) are, by definition, infinitesimal

Semmelmann, Uwe

318

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

319

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

320

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

321

Ballistic dynamics of Dirac particles in electro-magnetic fields  

E-print Network

Investigating properties of two-dimensional Dirac operators coupled to an electric and a magnetic field (perpendicular to the plane) requires in general unbounded (vector-) potentials. If the system has a certain symmetry, the fields can be described by one-dimensional potentials $V$ and $A$. Assuming that $|A|ballistically. These results are based on well-known methods in spectral dynamics together with certain new Hilbert-Schmidt bounds. We use Lorentz boosts to derive these new estimates.

Josef Mehringer; Edgardo Stockmeyer

2014-11-21

322

Magnetic properties prediction of NdFeB magnets by using support vector regression  

NASA Astrophysics Data System (ADS)

A novel model using support vector regression (SVR) combined with particle swarm optimization (PSO) was employed to construct mathematical model for prediction of the magnetic properties of the NdFeB magnets. The leave-one-out cross-validation (LOOCV) test results strongly supports that the generalization ability of SVR is high enough. Predicted results show that the mean absolute percentage error for magnetic remanence Br, coercivity Hcj and maximum magnetic energy product (BH)max are 0.53%, 3.90%, 1.73%, and the correlation coefficient (R2) is as high as 0.839, 0.967 and 0.940, respectively. This investigation suggests that the PSO-SVR is not only an effective and practical method to simulate the properties of NdFeB, but also a powerful tool to optimatize designing or controlling the experimental process.

Cheng, Wende

2014-09-01

323

Magnetic field structure generation in collisional dusty plasmas  

NASA Astrophysics Data System (ADS)

A perpendicular ion drift is proposed as a possible mechanism for the generation of magnetic field structures in a highly collisional dusty plasma. The basic dissipation mechanism is assumed to be the dust-neutral momentum exchange, so that plasmas with a small ionization fraction are natural candidates for experiments. The model reduces to a nonlinear partial differential equation for the vector potential. The conditions for linear instability are presented. Possible stationary states are periodic arrangements for the magnetic field, described by a Lienard equation. The fully depleted (ion-dust) case is also considered in detail. Applications of the present work to magnetic field structures in planetary rings, comets and low-temperature dusty plasma experiments are discussed. A necessary condition for the validity of the model is a sufficiently slow time-scale of the generated magnetic fields in dusty plasmas.

Kant Shukla, Padma; Haas, Fernando

2008-11-01

324

Interplanetary Magnetic Field Power Spectrum Variations: A VHO Enabled Study  

NASA Technical Reports Server (NTRS)

The newly reprocessed high time resolution (11/22 vectors/sec) Wind mission interplanetary magnetic field data and the solar wind key parameter search capability of the Virtual Heliospheric Observatory (VHO) affords an opportunity to study magnetic field power spectral density variations as a function of solar wind conditions. In the reprocessed Wind Magnetic Field Investigation (MFI) data, the spin tone and its harmonics are greatly reduced that allows the meaningful fitting of power spectra to the approx.2 Hz limit above which digitization noise becomes apparent. The power spectral density is computed and the spectral index is fitted for the MHD and ion inertial regime separately along with the break point between the two for various solar wind conditions . The time periods of fixed solar wind conditions are obtained from VHO searches that greatly simplify the process. The functional dependence of the ion inertial spectral index and break point on solar wind plasma and magnetic field conditions will be discussed

Szabo, A.; Koval, A.; Merka, J.; Narock, T.

2010-01-01

325

Interplanetary Magnetic Field Power Spectrum Variations: A VHO Enabled Study  

NASA Technical Reports Server (NTRS)

The newly reprocessed high time resolution (11/22 vectors/sec) Wind mission interplanetary magnetic field data and the solar wind key parameter search capability of the Virtual Heliospheric Observatory (VHO) affords an opportunity to study magnetic field power spectral density variations as a function of solar wind conditions. In the reprocessed Wind Magnetic Field Investigation (MFI) data, the spin tone and its harmonics are greatly reduced that allows the meaningful fitting of power spectra to the 2 Hz limit above which digitization noise becomes apparent. The power spectral density is computed and the spectral index is fitted for the MHD and ion inertial regime separately along with the break point between the two for various solar wind conditions. The time periods of fixed solar wind conditions are obtained from VHO searches that greatly simplify the process. The functional dependence of the ion inertial spectral index and break point on solar wind plasma and magnetic field conditions will be discussed

Szabo, A.; Koval, A.; Merka, J.; Narock, T.

2011-01-01

326

Mass Structure of Axial Vector Types of Leptons and Fields  

E-print Network

A classification of currents with respect to C-operation admits the existence of C-noninvariant types of Dirac fermions. Among them one can meet an electroweakly charged C-antisymmetrical leptons, the mass of which includes the electric and weak components responsible for the existence of their anapole charge, charge radius and electric dipole moment. Such connections can constitute the paraleptons of axial-vector currents, for example, at the interactions with field of spinless nuclei of true neutrality. We derive the united equations which relate the structural parts of mass to anapole, charge radius and electric dipole of any truly neutral lepton in the framework of flavour symmetry. Thereby, they establish the C-odd nature of leptons and fields at the level of constancy law of the size implied from the multiplication of a weak mass of C-antisymmetrical lepton by its electric mass. Therefore, all leptons of C-antisymmetricality regardless of the difference in masses of an axial-vector character, have the same anapole with his radius as well as an equal electric dipole. Their analysis together with measured value of an electric dipole moment of lepton gives the right to interpret not only the existence of truly neutral types of leptons and fields but also the availability of mass structure in them as the one of earlier laboratory facts.

Rasulkhozha S. Sharafiddinov

2011-04-19

327

Magnetic fields in the Mars ionosphere of a noncrustal origin: Magnetization features  

NASA Astrophysics Data System (ADS)

The magnetic field observations by the Mars Global Surveyor (MGS) performed on the premapping orbits in the years 1997 and 1998 in the low-altitude ionosphere of Mars show the existence of a strong "external" magnetization not related to the "internal" crustal magnetization. A significant increase of the magnetic field strength is observed in the collisional northern ionosphere at altitudes of ˜ 200 km and at 60°-90°solar zenith angles sampled by MGS. The magnetization features and the magnetic field topology vary significantly with the sector structure of the interplanetary magnetic field (IMF). For ByIMF>0 the magnetic flux tubes transported to altitudes of ˜200 km are suddenly straightened releasing their tangential stresses. For ByIMF<0 a rotation of the magnetic field vector by almost 180°occurs. Such an asymmetry in the ionospheric response on Mars is similar to the asymmetry observed on Venus at the periods of low-solar activity indicating its universal origin for magnetized ionospheres. It is suggested that the electric currents generated in the collisional ionosphere where the ions become demagnetized, while the electrons remain magnetized produce the observed features.

Dubinin, E.; Fraenz, M.; Zhang, T. L.; Woch, J.; Wei, Y.

2014-09-01

328

2T Physics, Scale Invariance and Topological Vector Fields  

E-print Network

We construct, in classical two-time physics, the necessary structure for the most general configuration space formulation of quantum mechanics containing gravity in d+2 dimensions. This structure is composed of a symmetric Riemannian metric tensor and of a vector field that defines a section of a flat U(1) bundle over space-time. This construction is possible because of the existence of a finite local scale invariance of the Hamiltonian and because two-time physics contains, at the classical level, a local generalization of the discrete duality symmetry between position and momentum that underlies the structure of quantum mechanics.

W. Chagas-Filho

2007-06-04

329

Vectors  

NSDL National Science Digital Library

This lesson was created by Larry Friesen and Anne Gillis for Butler Community College. It will help physics and calculus students differentiate between the uses of vectors in mathematics vs. physics. This website provides two PDF documents that give detailed lessons about vectors, including an overview of terminology, sample problems, and an HTML worksheet is also provided. For educators or students, this site offers well laid-out lessons and/or practice with vectors.

Friesen, Larry; Gillis, Anne

2008-04-18

330

vectors  

NSDL National Science Digital Library

The word vector comes from the Latin term vehere, to carry. In Biology, a vector is an agent which carries disease, such as a mosquito carrying infected blood from one patient to the next. In physics, a vector is a quantity which has both a magnitude and a direction associated with it. The most commonly used example of vectors in everyday life is velocity. When you drive your car, your speedometer tells you the speed of your car, but it doesn't tell you where you are going. The combination of both where you are going and how fast you are going there is your car's velocity.

Joiner, David; The Shodor Education Foundation, Inc.

331

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

332

Vectors from A to B  

NSDL National Science Digital Library

This is an activity about vectors and velocity. It outlines the addition and subtraction of vectors, and introduces the application of trigonometry to describing vectors. The resource is designed to support student analysis of THEMIS (Time History of Events and Macroscale Interactions during Substorms) Magnetometer line-plot data. Learners will complete worksheets consisting of problem sets that allow them to work with vector data in magnetic fields. This is activity 15 from Exploring Magnetism: Earth's Magnetic Personality.

333

Behavioral effects of electric and magnetic fields  

NASA Astrophysics Data System (ADS)

Two sets of behavioral studies were conducted. In the first, three procedures were used to determine how aversive a 100 kV/m 60-Hz electric field is for a rat. Each of the procedures enabled rats to respond in order to reduce exposure to the field. The rats did reduce exposure slightly with one, but not with the other two, whereas they reduced their exposure to moderate illumination in all three procedures. The results show that while the procedures were appropriate for assessing stimulus aversiveness, 100 kV/m is not a generally aversive stimulus for the rat. It was previously reported that immediately after exposure for 30 minutes to a horizontal 60-Hz, 5 x 10(exp -5)T field combined with a total static field of 2.61 x 10(exp -5)T, the rate of lever pressing by rats increased during the DRL component of a multiple fixed ratio, DRL schedule of food reinforcement. This project failed to confirm those observations in an experiment that duplicated the behavioral baseline and the magnetic field exposure conditions, with the exception that the total DC vector was greater in these experiments than it was in others.

Laties, V. G.

1992-04-01

334

Can We Determine Electric Fields and Poynting Fluxes from Vector Magnetograms and Doppler Measurements?  

NASA Astrophysics Data System (ADS)

The availability of vector-magnetogram sequences with sufficient accuracy and cadence to estimate the temporal derivative of the magnetic field allows us to use Faraday's law to find an approximate solution for the electric field in the photosphere, using a Poloidal--Toroidal Decomposition (PTD) of the magnetic field and its partial time derivative. Without additional information, however, the electric field found from this technique is under-determined -- Faraday's law provides no information about the electric field that can be derived the gradient of a scalar potential. Here, we show how additional information in the form of line-of-sight Doppler-flow measurements, and motions transverse to the line-of-sight determined with ad-hoc methods such as local correlation tracking, can be combined with the PTD solutions to provide much more accurate solutions for the solar electric field, and therefore the Poynting flux of electromagnetic energy in the solar photosphere. Reliable, accurate maps of the Poynting flux are essential for quantitative studies of the buildup of magnetic energy before flares and coronal mass ejections.

Fisher, George H.; Welsch, B. T.; Abbett, W. P.

2011-05-01

335

Can we Determine Electric Fields and Poynting Fluxes from Vector Magnetograms and Doppler Measurements?  

NASA Astrophysics Data System (ADS)

The availability of vector magnetogram sequences with sufficient accuracy and cadence to estimate the time derivative of the magnetic field allows us to use Faraday's law to find an approximate solution for the electric field in the photosphere, using a Poloidal-Toroidal Decomposition (PTD) of the magnetic field and its partial time derivative. Without additional information, however, the electric field found from this technique is under-determined -- Faraday's law provides no information about the electric field that can be derived the gradient of a scalar potential. Here, we show how additional information in the form of line-of-sight Doppler flow measurements, and motions transverse to the line-of-sight determined with ad-hoc methods such as local correlation tracking, can be combined with the PTD solutions to provide much more accurate solutions for the solar electric field, and therefore the Poynting flux of electromagnetic energy in the solar photosphere. Reliable, accurate maps of the Poynting flux are essential for quantitative studies of the buildup of magnetic energy before flares and coronal mass ejections. This work was supported by the NASA Heliophysics Theory Program, the NASA Living-With-a-Star Program, and the NSF Geosciences Directorate

Fisher, G. H.; Welsch, B. T.; Abbett, W. P.

2011-12-01

336

Can We Determine Electric Fields and Poynting Fluxes from Vector Magnetograms and Doppler Measurements?  

NASA Astrophysics Data System (ADS)

The availability of vector-magnetogram sequences with sufficient accuracy and cadence to estimate the temporal derivative of the magnetic field allows us to use Faraday's law to find an approximate solution for the electric field in the photosphere, using a Poloidal-Toroidal Decomposition (PTD) of the magnetic field and its partial time derivative. Without additional information, however, the electric field found from this technique is under-determined - Faraday's law provides no information about the electric field that can be derived from the gradient of a scalar potential. Here, we show how additional information in the form of line-of-sight Doppler-flow measurements, and motions transverse to the line-of-sight determined with ad-hoc methods such as local correlation tracking, can be combined with the PTD solutions to provide much more accurate solutions for the solar electric field, and therefore the Poynting flux of electromagnetic energy in the solar photosphere. Reliable, accurate maps of the Poynting flux are essential for quantitative studies of the buildup of magnetic energy before flares and coronal mass ejections.

Fisher, G. H.; Welsch, B. T.; Abbett, W. P.

2012-03-01

337

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

338

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

339

Vector near-field beam scanner for the SMA  

NASA Astrophysics Data System (ADS)

Here we describe the principles behind the design, construction, and implementation of a vector near-field beam scanner for the antennas of the Submillimeter Array. The Submillimeter Array (SMA) is a radio interferometer array operating at frequencies ranging from 200 { 700 GHz at the summit of Maunakea in Hawaii. A set of 4 receivers cover the key atmospheric windows over which the SMA operates. Each receiver insert is equipped with an ambient optical insert, which is pre-aligned in the lab prior to installation at the summit. However, as a result of receiver upgrades and problems, some receiver inserts may no longer be matched to the original optics inserts. Since the SMA is used extensively in dual-receiver observations, such beam mis-alignments lead to a relative pointing error between a pair of receivers during the observation. In order to address this issue, we have designed a near-field beam scanner which can be used to map out the receiver beam of each antenna. The setup employs the existing radio references available in each antenna for the vector beam measurement. We have successfully used this scanner to improve the on-sky co-alignment of receiver beams. In this presentation, we will describe the system and operational aspect of this in-situ radio frequency alignment technique.

Christensen, Robert D.; Rao, Ramprasad; Sridharan, T. K.; Tong, Edward

2014-07-01

340

Analysis on Sound Field Recorded with Vector Sensors  

NASA Astrophysics Data System (ADS)

From data collected with vector sensors at several sites, the transmission losses of particle velocities and pressures are examined. In particular, the components of the particle velocity fields both normal and tangential to the horizontal plane are studied. Theoretical and experimental results show that both vertical and horizontal particle velocities can be regarded as the summation of normal modes. The lower modes dominate for the horizontal particle velocity, while higher modes are relatively important for the vertical particle velocity. The intensity of the vertical velocity decreases faster than that of the horizontal particle velocity. The experimental results also show that the same modes of the horizontal and vertical particle velocity have similar losses, but different amplitudes and phases. Theoretical analyses indicate that the difference of the mode amplitudes between horizontal particle velocity and vertical particle velocity depends on the eigenvalue and receiver depths, which can provide information on the estimation of bottom parameters. A geo-inversion scheme by the matched-field processing with a vector array is developed. The theoretical and experimental results indicate that the proposed inversion method can decrease the uncertainty of inversion in comparison with that by hydrophone arrays.

Li, Fenghua; Sun, Mei; Zhang, Renhe

2010-09-01

341

The Hanle effect applied to magnetic field measurements  

NASA Technical Reports Server (NTRS)

The Hanle effect is the modification by a local magnetic field of the polarization due to coherent scattering in spectral lines. It results from the precession of a classical oscillator about the magnetic field direction. The sophisticated quantum-mechanical treatment, which is required to compute the polarization parameters of scattered light, was developed. The main features of the Hanle effect concerning magnetic field measurements are: (1) a good sensitivity within the approximate range 0.1 B gamma rho to 10 B gamma rho where B gamma rho is the field strength yielding a Larmor period equal to the radiative lifetime, (2) there is no Hanle effect for field vectors parallel to the excitating beam, (3) the Hanle effect refers essentially to the linear polarization in a spectral line, (4) various points in the line profile are affected in the same way by change of linear polarization so that polarization parameters can be measured on the integrated line profile.

Leroy, J. L.

1985-01-01

342

Fully 3D Measurement of reconnecting magnetic field structure in SSX  

Microsoft Academic Search

A high resolution (2 cm) magnetic probe array has been developed to investigate the three dimensional magnetic reconnection of two spheromaks in the Swarthmore Spheromak Experiment (SSX). The magnetic field vector is measured at a grid of 5 x 5 x 8 points during each shot with 800 ns time resolution, allowing visualization of the unique dynamics of each reconnection

M. Landreman; C. D. Cothran; M. R. Brown

2002-01-01

343

Two-dimensional magnetic properties of silicon steel sheet subjected to a rotating field  

Microsoft Academic Search

A study of the two-dimensional rotational magnetic properties of a steel sheet are discussed. These are measured making use of the vector relation between magnetic field strength H and magnetic flux density B. The results of this study lead to the following main conclusions: the permeability tensor becomes a full matrix under rotating flux; the off-diagonal terms of the permeability

Masato Enokizono; Takashi Todaka; Shinichi Kanao; Johannes Sievert

1993-01-01

344

Magnetic field of Jupiter and its interaction with the solar wind  

Microsoft Academic Search

Jupiter's magnetic field and its interaction with the magnetized solar ; wind were observed with the Pioneer 10 vector helium magnetometer. The magnetic ; dipole is directed opposite to that of the Earth with a moment of 4.0 gauss R\\/sub ; j\\/ ³ (R\\/sup , Jupiter radius and an inclination of 15' lying in a system ; III meridian of

E. J. Smith; L. Jr. Davis; D. E. Jones; D. S. Colburn; P. J. Jr. Coleman; P. Dyal; C. P. Sonett

1974-01-01

345

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

346

GEOACOUSTIC MATCHED-FIELD INVERSION USING A VERTICAL VECTOR SENSOR ARRAY  

E-print Network

: Vector sensors measure the acoustic pressure and the particle velocity components. This type of sensor Sensor, bottom properties estimation, matched-field processing #12;1. INTRODUCTION Acoustic vectorGEOACOUSTIC MATCHED-FIELD INVERSION USING A VERTICAL VECTOR SENSOR ARRAY Paulo Santos, Orlando

Jesus, Sérgio M.

347

Student Reasoning About the Divergence of a Vector Field  

E-print Network

Expanding our knowledge of student difficulties in advanced undergraduate electromagnetism is essential if we are to develop effective instructional interventions. Drawing on an analysis of course materials, in-class observations and responses to conceptual questions, we document specific resources employed by students when reasoning about the divergence of a vector field. One common student error, which persisted in our course despite explicit instruction, is to misinterpret any "spreading out" of field lines in a diagram as representing a place of non-zero divergence. Some of these student difficulties can likely be attributed to having first learned about the divergence in a mathematical context, where there was little emphasis on graphical representations and physical applications.

Astolfi, Cecilia

2014-01-01

348

Multiresolution and Explicit Methods for Vector Field Analysis and Visualization  

NASA Technical Reports Server (NTRS)

This is a request for a second renewal (3d year of funding) of a research project on the topic of multiresolution and explicit methods for vector field analysis and visualization. In this report, we describe the progress made on this research project during the second year and give a statement of the planned research for the third year. There are two aspects to this research project. The first is concerned with the development of techniques for computing tangent curves for use in visualizing flow fields. The second aspect of the research project is concerned with the development of multiresolution methods for curvilinear grids and their use as tools for visualization, analysis and archiving of flow data. We report on our work on the development of numerical methods for tangent curve computation first.

Nielson, Gregory M.

1997-01-01

349

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

350

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

351

Two-dimensional magnetic field analysis of internal-rotor permanent-magnet motors  

SciTech Connect

An improved analytical method is proposed for predicting magnetic field distribution in the air-gap and permanent-magnet regions of radial field topology of a brushless internal-rotor permanent-magnet motor. It is a two-dimensional model based on a conformal transformation approach where differences in the current density have been compensated for. The method involves a number of integrals of the vector potential, instead of the scalar potential found in the literature. The method is convenient for magnetic fields having complicated boundaries. The motor model is formulated in polar coordinates and accounts for the large effective air gap, resulting from the low magnetic permeability. Results of the motor analysis are compared with predictions from corresponding finite element analysis and other analytical techniques. They indicate the advantage of the developed approach over other recent analytical techniques.

Faiz, J.; Jafari, H.

1999-09-01

352

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...

353

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

354

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 ...

355

Magnetic field experiment on the Freja Satellite  

NASA Astrophysics Data System (ADS)

Freja is a Swedish scientific satellite mission to study fine scale auroral processes. Launch was October 6, 1992, piggyback on a Chinese Long March 2C, to the present 600×1750 km, 63° inclination orbit. The JHU/APL provided the Magnetic Field Experiment (MFE), which includes a custom APL-designed Forth, language microprocessor. This approach has led to a truly generic and flexible design with adaptability to differing mission requirements and has resulted in the transfer of significant ground analysis to on-board processing. Special attention has been paid to the analog electronic and digital processing design in an effort to lower system noise levels, verified by inflight data showing unprecedented system noise levels for near-Earth magnetic field measurements, approaching the fluxgate sensor levels. The full dynamic range measurements are of the 3-axis Earth's magnetic field taken at 128 vector samples s-1 and digitized to 16 bit, resolution, primarily used to evaluate currents and the main magnetic field of the Earth. Additional 3-axis ‘AC’ channels are bandpass filtered from 1.5 to 128 Hz to remove the main field spin signal, the range is±650 nT. These vector measurements cover Pc waves to ion gyrofrequency magnetic wave signals up to the oxygen gyrofrequency (˜40 Hz). A separate, seventh channel samples the spin axis sensor with a bandpass filter of 1.5 to 256 Hz, the signal of which is fed to a software FFT. This on-board FFT processing covers the local helium gyrofrequencies (˜160 Hz) and is plotted in the Freja Summary Plots (FSPs) along with disturbance fields. First data were received in the U.S. October 16 from Kiruna, Sweden via the Internet and SPAN e-mail networks, and were from an orbit a few hours earlier over Greenland and Sweden. Data files and data products, e.g., FSPs generated at the Kiruna ground station, are communicated in a similar manner through an automatic mail distribution system in Stockholm to PIs and various users. Distributed management of spacecraft operations by the science team is also achieved by this advanced communications system. An exciting new discovery of the field-aligned current systems is the high frequency wave power or structure associated with the various large-scale currents. The spin axis ‘AC’ data and its standard deviation is a measure of this high-frequency component of the Birkeland current regions. The exact response of these channels and filters as well as the physics behind these wave and/or fine-scale current structures accompanying the large-scale currents is being pursued; nevertheless, the association is clear and the results are used for the MFE Birkeland current monitor calculated in the MFE microprocessor. This monitor then sets a trigger when it is greater than a commandable, preset threshold. This ‘event’ flag can be read by the system unit and used to remotely command all instruments into burst mode data taking and local memory storage. In addition,Freja is equipped with a 400 MHz ‘Low Speed Link’ transmitter which transmits spacecraft hcusekeeping that can be received with a low cost, portable receiver. These housekeeping data include the MFE auroral zone current detector; this space weather information indicates the location and strength of ionospheric current systems that directly impact communications, power systems, long distance telephone lines and near-Earth satellite operations. The JHU/APL MFE is a joint effort with NASA/GSFC and was co-sponsored by the Office of Naval Research and NASA/Headquarters in cooperation with the Swedish National Space Board and the Swedish Space Corporation.

Freja Magnetic Field Experiment Team

1994-11-01

356

Magsat - A new satellite to survey the earth's magnetic field  

NASA Technical Reports Server (NTRS)

The Magsat satellite was launched on Oct. 30, 1979 into a sun-synchronous dawn-dusk orbit, of 97 deg inclination, 350 km perigee, and 550 km apogee. It contains a precision vector magnetometer and a cesium-vapor scalar magnetometer at the end of a 6-m long graphite epoxy scissors boom. The magnetometers are accurate to 2 nanotesla. A pair of star cameras are used to define the body orientation to 10 arc sec rms. An 'attitude transfer system' measures the orientation of the magnetometer sensors relative to the star cameras to approximately 5 arc sec rms. The satellite position is determined to 70 meters rms by Doppler tracking. The overall objective is to determine each component of the earth's vector magnetic field to an accuracy of 6 nanotesla rms. The Magsat satellite gathers a complete picture of the earth's magnetic field every 12 hours. The vector components are sampled 16 times per second with a resolution of 0.5 nanotesla. The data will be used by the U.S. Geological Survey to prepare 1980 world magnetic field charts and to detect large-scale magnetic anomalies in the earth's crust for use in planning resource exploration strategy.

Mobley, F. F.; Eckard, L. D.; Fountain, G. H.; Ousley, G. W.

1980-01-01

357

Parahydrogen-induced polarization at zero magnetic field.  

PubMed

We use symmetry arguments and simple model systems to describe the conversion of the singlet state of parahydrogen into an oscillating sample magnetization at zero magnetic field. During an initial period of free evolution governed by the scalar-coupling Hamiltonian HJ, the singlet state is converted into scalar spin order involving spins throughout the molecule. A short dc pulse along the z axis rotates the transverse spin components of nuclear species I and S through different angles, converting a portion of the scalar order into vector order. The development of vector order can be described analytically by means of single-transition operators, and it is found to be maximal when the transverse components of I are rotated by an angle of ±??2 relative to those of S. A period of free evolution follows the pulse, during which the vector order evolves as a set of oscillating coherences. The imaginary parts of the coherences represent spin order that is not directly detectable, while the real parts can be identified with oscillations in the z component of the molecular spin dipole. The dipole oscillations are due to a periodic exchange between Iz and Sz, which have different gyromagnetic ratios. The frequency components of the resulting spectrum are imaginary, since the pulse cannot directly induce magnetization in the sample; it is only during the evolution under HJ that the vector order present at the end of the pulse evolves into detectable magnetization. PMID:23802953

Butler, Mark C; Kervern, Gwendal; Theis, Thomas; Ledbetter, Micah P; Ganssle, Paul J; Blanchard, John W; Budker, Dmitry; Pines, Alexander

2013-06-21

358

Power Anisotropy in the Magnetic Field Power Spectral Tensor of Solar Wind Turbulence  

Microsoft Academic Search

We observe the anisotropy of the power spectral tensor of magnetic field fluctuations in the fast solar wind for the first time. In heliocentric RTN coordinates the power in each element of the tensor has a unique dependence on the angle between the magnetic field and velocity of the solar wind (\\\\theta) and the angle of the vector in the

Robert T. Wicks; Miriam A. Forman; Timothy S. Horbury; Sean Oughton

2011-01-01

359

Measuring the magnetic fields of jupiter and the outer solar system  

Microsoft Academic Search

The vector helium magnetometer, one of the Pioneer-Jupiter experiments, has measured the magnetic field of Jupiter and the interplanetary magnetic field in the outer solar system. The comprehensive scientific objectives of the investigations are explained and are then translated into the major instrument requirements. The principles of operation of the magnetometer, which involve the optical pumping of metastable helium, are

E. Smith; B. Connor

1975-01-01

360

Numerical magnetic field analysis and signal processing for fault diagnostics of electrical machines  

Microsoft Academic Search

Numerical magnetic field analysis is used for predicting the performance of an induction motor and a slip-ring generator having different faults implemented in their structure. Virtual measurement data provided by the numerical magnetic field analysis are analysed using modern signal processing techniques to get a reliable indication of the fault. Support vector machine based classification is applied to fault diagnostics.

S. Pöyhönen; M. Negrea; P. Jover; A. Arkkio; H. Hyötyniemi

2003-01-01

361

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

362

Single-point Inversion of the Coronal Magnetic Field  

NASA Astrophysics Data System (ADS)

The Fe XIII 10747 and 10798 Å lines observed in the solar corona are sensitive to the coronal magnetic field in such a way that, in principle, the full vector field at a point on the line of sight can be inferred from their combined polarization signals. This paper presents analytical inversion formulae for the field parameters and analyzes the uncertainty of magnetic field measurements made from such observations, assuming emission dominated by a single region along the line of sight. We consider the case of the current Coronal Multi-channel Polarimeter (CoMP) instrument as well as the future Coronal Solar Magnetism Observatory (COSMO) and Advanced Technology Solar Telescope (ATST) instruments. Uncertainties are estimated with a direct analytic inverse and with a Markov Chain Monte Carlo algorithm. We find that (in effect) two components of the vector field can be recovered with CoMP, and well recovered with COSMO or ATST, but that the third component can only be recovered when the solar magnetic field is strong and optimally oriented.

Plowman, Joseph

2014-09-01

363

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

364

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

365

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

366

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

367

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

368

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

369

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

370

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

371

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

372

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

373

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

374

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

375

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

376

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.

377

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

378

Helical cosmological magnetic fields from extra-dimensions  

E-print Network

We study the inflationary generation of helical cosmological magnetic fields in a higher-dimensional generalization of the electromagnetic theory. For this purpose, we also include a parity breaking piece to the electromagnetic action. The evolution of extra-dimensional scale factor allows the breaking of conformal invariance of the effective electromagnetic action in 1+3-dimensions required for such generation. Analytical solutions for the vector potential can be obtained in terms of Coulomb wave-functions for some special cases. We also present numerical solutions for the vector potential evolution in more general cases. In the presence of a higher-dimensional cosmological constant there exist solutions for the scale factors in which both normal and extra dimensional space either inflate or deflate simultaneously with the same rate. In such a scenario, with the number of extra dimensions D=4, a scale invariant spectrum of helical magnetic field is obtained. The net helicity arises, as one helical mode comes...

Atmjeet, Kumar; Subramanian, Kandaswamy

2014-01-01

379

Report of the panel on geopotential fields: Magnetic field, section 9  

NASA Technical Reports Server (NTRS)

The objective of the NASA Geodynamics program for magnetic field measurements is to study the physical state, processes and evolution of the Earth and its environment via interpretation of measurements of the near Earth magnetic field in conjunction with other geophysical data. The fields measured derive from sources in the core, the lithosphere, the ionosphere, and the magnetosphere. Panel recommendations include initiation of multi-decade long continuous scalar and vector measurements of the Earth's magnetic field by launching a five year satellite mission to measure the field to about 1 nT accuracy, improvement of our resolution of the lithographic component of the field by developing a low altitude satellite mission, and support of theoretical studies and continuing analysis of data to better understand the source physics and improve the modeling capabilities for different source regions.

Achache, Jose J.; Backus, George E.; Benton, Edward R.; Harrison, Christopher G. A.; Langel, Robert A.

1991-01-01

380

A Vector Grouping Algorithm for Liquid Crystal Tensor Field Visualization  

E-print Network

- alization methods separate the tensor into component eigenvectors and visualize those instead. Eigenvectors Current address: Nuclear Medicine Division, Marconi Medical Systems, 595 Miner Road, Cleveland, Ohio 44143 vector elds and any vector visualization method can be applied to these separated vector elds. In current

Farrell, Paul A.

381

Cylindrical quantum well of finite depth in external magnetic field  

E-print Network

Energy spectrum of an electron confined by finite hard-wall potential in a cylinder quantum dot placed in weak (up to 100 kOe) homogeneous external magnetic field were calculated using the method of variation of vector potential. Electronic motion along the cylinder axis is limited by one-dimensional infinite potential barrier and electronic motion on the plane perpendicular to the axis is limited by two-dimensional finite potential barrier.

O. R. Lobanova; A. I. Ivanov

2004-11-19

382

The 1983 tail-era data series. Volume 2: ISEE 3 magnetic field  

NASA Technical Reports Server (NTRS)

ISEE 3 spacecraft measurements within and near the Earth's magnetic tail is presented. Plots are shown of ISEE 3 magnetic field data. The plots in this volume showing observations from the ISEE 3 vector helium magnetometer experiment were produced from a tape of merged plasma/magnetic field data. The magnetometer produced six vector measurements/sec that were subsequently averaged over one minute intervals before merging with plasma data. Merging was accomplished by associating the nearest 1 minute field average with each plasma sample.

Fairfield, D. H.; Phillips, J. L.

1990-01-01

383

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

384

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

385

Vector Fields, Linear Spaces, and Tensors in Physics. Part 1: Vectors, Fields, and Coordinates Campos Vetoriais, Espacos Lineares E Tensores NA Fisica. Parte 1: Vetores, Campos E Coordenadas.  

National Technical Information Service (NTIS)

Vectors are studied from the point of view of their handling in vectorial equations using the indicial notation. A study on vector fields as they are commonly found in physics (gradient, divergence, and curl) is also presented. Finally, an extension of th...

R. A. Medrano-b

1981-01-01

386

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

387

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

388

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

389

Multipole Models of the Earth's Magnetic Field  

NASA Astrophysics Data System (ADS)

To develop a mathematical model of rotational motion of an artificial satellite about its center of mass under the action of various forces (magnetic, Lorentz, etc.) caused by the geomagnetic field, it is necessary to know the induction of the Earth's magnetic field (EMF) as a function of the radius vector of a given point in the near-Earth space. Because the EMF possesses a complex structure and the above-mentioned functional dependence is unavailable in explicit analytic form, a set of approximate models of the EMF should be used. The simplest such model-a right dipole (aligned with the axis of rotation)-does not enable one to reveal in detail the influence of diurnal EMF rotation on the rotational motion of a satellite. The next EMF approximation-an inclined magnetic dipole-does not suffer from the above-mentioned drawback. However, it is shown that not all corrections to the magnetic induction of the EMF of the same order of magnitude are taken into account in the course of transformation from the model of aligned dipole to the model of inclined dipole. So, to develop the EMF model accurately accounting for the absence of axial symmetry of the EMF with respect to the axis of diurnal rotation of the Earth, in general, the effect of the quadrupole component of the geomagnetic potential on the EMF induction (and, probably, even the components of higher orders) must be taken into consideration. By using the International Geomagnetic Reference Field IGRF-2000, the multipole models of the EMF, corresponding to quadrupole, octupole, and higher-order approximations, were constructed and studied in this work. The EMF potential is expressed in terms of its multipole tensors. As a result, projections of the induction and induction gradient of EMF in the center of mass of the satellite onto the axes of the orbital coordinate system can be written in convenient and concise form. The expressions for the first four multipole tensors through the known geomagnetic constants are found. A method for estimating the reliability of these models is put forward, and the regions of applicability of the quadrupole and octupole models are drawn on the plane of orbital parameters.

Tikhonov, A. A.; Petrov, K. G.

2002-05-01

390

VECTOR FIELD CONVOLUTION FOR IMAGE SEGMENTATION USING SNAKES Bing Li and Scott T. Acton  

E-print Network

proposes a new design for the snake external force, called vector field convolution (VFC), to address force implementation for snakes called vector field convolution (VFC). This external force field. Snakes that use the VFC external force are termed VFC snakes. Similar to the GVF approach, instead

Acton, Scott

391

Programmable Vector Fields for Distributed Manipulation, with Applications to MEMS Actuator Arrays and Vibratory Parts  

E-print Network

Programmable Vector Fields for Distributed Manipulation, with Applications to MEMS Actuator Arrays University, Ithaca, New York, USA August 13, 1996 Abstract Programmable vector fields can be used to control sufficient conditions for programmable fields to induce well­behaved equilibria on every part placed on our

Richardson, David

392

Analysis of vector magnetic anomalies over the Bayonnaise Knoll caldera obtained from a deep-sea magnetic exploration by AUV  

NASA Astrophysics Data System (ADS)

Geophysical surveys near the seafloor are very effective methods in order to investigate fine structures of the oceanic crust. Such surveys have increased in researches and developments of the seafloor, and will be more and more necessary in the future. For example, seabed resources like hydrothermal deposits have recently focused attention behind the international situation for natural resources like a competition of resources development. In order to estimate accurate abundance of those resources, the above detailed investigations should be needed because of low resolution of geophysical surveys on the sea and low efficiency of exploratory drilling. From such a viewpoint, we have been developing a measurement system for magnetic explorations using an AUV and a deep-tow system. The magnetic exploration system consists of two 3-axis flux-gate magnetometers, one/two Overhauser magnetometer(s), an optical fiber gyro, a main unit (control, communication, recording), and an onboard unit. These devices except for the onboard unit are installed in pressure cases (depth limit: 6000m). Thus this system can measure three components and total intensity of the geomagnetic field in the deep sea. In 2009, the first test of the magnetic exploration system was carried out in the Kumano Basin using AUV Urashima and towing vehicle Yokosuka Deep-Tow during the R/V Yokosuka YK09-09 cruise. In this test, we sank a small magnetic target to the seafloor, and examined how the system worked. As a result, we successfully detected magnetic anomaly of the target to confirm the expected performance of that in the sea. In 2010, the magnetic exploration system was further tested in the Bayonnaise Knoll area both using a titanium towing frame during the R/V Bosei-maru cruise and using AUV Urashima during the R/V Yokosuka YK10-17 cruise. The purpose of these tests was to evaluate the performance of the system in an actual hydrothermal deposit area for practical applications of that. The Bayonnaise Knoll is a submarine caldera with an outer rim of 2.5-3 km and a floor of 840-920 m, which is located in the Izu-Ogasawara arc. A large hydrothermal deposit, Hakurei deposit, lies in the southeast part of the caldera. In the R/V Bosei-maru cruise, we observed three components of magnetic anomalies at depths of 400-570 m along SE-NW and WE tracks across the caldera. In the R/V Yokosuka YK10-17 cruise, we observed three components and total intensity of magnetic anomalies at altitudes of 60-100 m around the Hakurei deposit and at depth of 500 m above the caldera. The analysis of these data is now energetically pushed forward. A 3D gridded data set of the vector magnetic anomaly in the latter cruise was made by solving the Laplace's equation in the areas where observation data were not available, which is the unique procedure for analysis of the vector anomalies. Several magnetization solutions have been so far obtained by successive approximation and inversion methods. We will here present the measurement of the geomagnetic field and analysis of magnetization structure in Bayonnaise Knoll caldera. Note that this study has been supported by the Ministry of Education, Culture, Sports, Science & Technology (MEXT).

Sayanagi, K.; Isezaki, N.; Matsuo, J.; Harada, M.; Kasaya, T.

2011-12-01

393

Construction of Solar-Wind-Like Magnetic Fields  

NASA Astrophysics Data System (ADS)

Fluctuations in the solar wind fields tend to not only have velocities and magnetic fields correlated in the sense consistent with Alfvén waves traveling from the Sun, but they also have the magnitude of the magnetic field remarkably constant despite their being broadband. This Letter provides, for the first time, a method for constructing fields with nearly constant magnetic field, zero divergence, and with any specified power spectrum for the fluctuations of the components of the field. Every wave vector, k, is associated with two polarizations; the relative phases of these can be chosen to minimize the variance of the field magnitude while retaining the “random” character of the fields. The method is applied to a case with one spatial coordinate that demonstrates good agreement with observed time series and power spectra of the magnetic field in the solar wind, as well as with the distribution of the angles of rapid changes (“discontinuities”), thus showing a deep connection between two seemingly unrelated issues. It is suggested that using this construction will lead to more realistic simulations of solar wind turbulence and of the propagation of energetic particles.

Roberts, D. Aaron

2012-12-01

394

Construction of solar-wind-like magnetic fields.  

PubMed

Fluctuations in the solar wind fields tend to not only have velocities and magnetic fields correlated in the sense consistent with Alfvén waves traveling from the Sun, but they also have the magnitude of the magnetic field remarkably constant despite their being broadband. This Letter provides, for the first time, a method for constructing fields with nearly constant magnetic field, zero divergence, and with any specified power spectrum for the fluctuations of the components of the field. Every wave vector, k, is associated with two polarizations; the relative phases of these can be chosen to minimize the variance of the field magnitude while retaining the "random" character of the fields. The method is applied to a case with one spatial coordinate that demonstrates good agreement with observed time series and power spectra of the magnetic field in the solar wind, as well as with the distribution of the angles of rapid changes ("discontinuities"), thus showing a deep connection between two seemingly unrelated issues. It is suggested that using this construction will lead to more realistic simulations of solar wind turbulence and of the propagation of energetic particles. PMID:23368180

Roberts, D Aaron

2012-12-01

395

Vector spin modeling for magnetic tunnel junctions with voltage dependent effects  

NASA Astrophysics Data System (ADS)

Integration and co-design of CMOS and spin transfer devices requires accurate vector spin conduction modeling of magnetic tunnel junction (MTJ) devices. A physically realistic model of the MTJ should comprehend the spin torque dynamics of nanomagnet interacting with an injected vector spin current and the voltage dependent spin torque. Vector spin modeling allows for calculation of 3 component spin currents and potentials along with the charge currents/potentials in non-collinear magnetic systems. Here, we show 4-component vector spin conduction modeling of magnetic tunnel junction devices coupled with spin transfer torque in the nanomagnet. Nanomagnet dynamics, voltage dependent spin transport, and thermal noise are comprehended in a self-consistent fashion. We show comparison of the model with experimental magnetoresistance (MR) of MTJs and voltage degradation of MR with voltage. Proposed model enables MTJ circuit design that comprehends voltage dependent spin torque effects, switching error rates, spin degradation, and back hopping effects.

Manipatruni, Sasikanth; Nikonov, Dmitri E.; Young, Ian A.

2014-05-01

396

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

397

Initial Results from the Vector Electric Field Investigation on the C/NOFS Satellite  

NASA Technical Reports Server (NTRS)

Initial results are presented from the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite, a mission designed to understand, model, and forecast the presence of equatorial ionospheric irregularities. The VEFI instrument includes a vector DC electric field detector, a fixed-bias Langmuir probe operating in the ion saturation regime, a flux gate magnetometer, an optical lightning detector, and associated electronics including a burst memory. The DC electric field detector has revealed zonal and meridional electric fields that undergo a diurnal variation, typically displaying eastward and outward-directed fields during the day and westward and downward-directed fields at night. In general, the measured DC electric field amplitudes are in the 0.5-2 mV/m range, corresponding to I3 x B drifts of the order of 30-150 m/s. What is surprising is the high degree of large-scale (10's to 100's of km) structure in the DC electric field, particularly at night, regardless of whether well-defined spread-F plasma density depletions are present. The spread-F density depletions and corresponding electric fields that have been detected thus far have displayed a preponderance to appear between midnight and dawn. Associated with the narrow plasma depletions that are detected are broad spectra of electric field and plasma density irregularities for which a full vector set of measurements is available for detailed study. On some occasions, localized regions of low frequency (< 8 Hz) magnetic field broadband irregularities have been detected, suggestive of filamentary currents, although there is no one-to-one correspondence of these waves with the observed plasma density depletions, at least within the data examined thus far. Finally, the data set includes a wide range of ELF/VLF/HF waves corresponding to a variety of plasma waves, in particular banded ELF hiss, whistlers, and lower hybrid wave turbulence triggered by lightning-induced sferics. The VEFI data set represents a treasure trove of measurements that are germane to numerous fundamental aspects of the electrodynamics and irregularities inherent to the Earth's low latitude ionosphere.

Pfaff, R.; Rowland, D.; Acuna, M.; Le, G.; Farrell, W.; Holzworth, R.; Wilson, G.; Burke, W.; Freudenreich, H.; Bromund, K.; Liebrecht, C.; Martin, S.; Kujawski, J.; Uribe, P.; Fourre, R.; McCarthy, M.; Maynard, N.; Berthelier, J.-J.; Steigies, C.

2009-01-01

398

Initial Results from the Vector Electric Field Investigation on the C/NOFS Satellite  

NASA Astrophysics Data System (ADS)

Initial results are presented from the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite, a mission designed to understand, model, and forecast the presence of equatorial ionospheric irregularities. The VEFI instrument includes a vector DC electric field detector, a fixed-bias Langmuir probe operating in the ion saturation regime, a flux gate magnetometer, an optical lightning detector, and associated electronics including a burst memory. The DC electric field detector has revealed zonal and meridional electric fields that undergo a diurnal variation, typically displaying eastward and outward-directed fields during the day and westward and downward-directed fields at night. In general, the measured DC electric field amplitudes are in the 0.5-2 mV/m range, corresponding to E x B drifts of the order of 30-150 m/s. What is surprising is the high degree of large-scale (10's of km to > 500 km) structure in the DC electric field, particularly at night, regardless of whether well-defined spread-F plasma density depletions are present. The spread-F density depletions and corresponding electric fields that have been detected thus far have displayed a preponderance to appear between midnight and dawn. Associated with the narrow plasma depletions that are detected are broad spectra of electric field and plasma density irregularities for which a full vector set of measurements is available for detailed study. On some occasions, localized regions of low frequency (< 8 Hz) magnetic field irregularities have been detected, suggestive of filamentary currents. Finally, the data set includes a wide range of ELF/VLF/HF waves corresponding to a variety of plasma waves, in particular banded ELF hiss, whistlers, and lower hybrid wave turbulence triggered by lightning-induced sferics. The VEFI data set represents a treasure trove of measurements that are germane to numerous fundamental aspects of the electrodynamics and plasma irregularities inherent to the Earth's low latitude ionosphere.

Pfaff, R.; Rowland, D.; Acuna, M.; Le, G.; Farrell, W.; Holzworth, R.; Wilson, G.; Burke, W.; Freudenreich, H.; Bromund, K.; Liebrecht, C.; Martin, S.; Kujawski, J.; Uribe, P.; Fourre, R.; McCarthy, M.; Maynard, N.; Berthelier, J.; Steigies, C.

2008-12-01

399

Semiconductor Crystal Growth in Static and Rotating Magnetic fields  

NASA Technical Reports Server (NTRS)

Magnetic fields have been applied during the growth of bulk semiconductor crystals to control the convective flow behavior of the melt. A static magnetic field established Lorentz forces which tend to reduce the convective intensity in the melt. At sufficiently high magnetic field strengths, a boundary layer is established ahead of the solid-liquid interface where mass transport is dominated by diffusion. This can have a significant effect on segregation behavior and can eliminate striations in grown crystals resulting from convective instabilities. Experiments on dilute (Ge:Ga) and solid solution (Ge-Si) semiconductor systems show a transition from a completely mixed convective state to a diffusion-controlled state between 0 and 5 Tesla. In HgCdTe, radial segregation approached the diffusion limited regime and the curvature of the solid-liquid interface was reduced by a factor of 3 during growth in magnetic fields in excess of 0.5 Tesla. Convection can also be controlled during growth at reduced gravitational levels. However, the direction of the residual steady-state acceleration vector can compromise this effect if it cannot be controlled. A magnetic field in reduced gravity can suppress disturbances caused by residual transverse accelerations and by random non-steady accelerations. Indeed, a joint program between NASA and the NHMFL resulted in the construction of a prototype spaceflight magnet for crystal growth applications. An alternative to the suppression of convection by static magnetic fields and reduced gravity is the imposition of controlled steady flow generated by rotating magnetic fields (RMF)'s. The potential benefits of an RMF include homogenization of the melt temperature and concentration distribution, and control of the solid-liquid interface shape. Adjusting the strength and frequency of the applied magnetic field allows tailoring of the resultant flow field. A limitation of RMF's is that they introduce deleterious instabilities above a critical magnetic field value. Growth conditions in which static magnetic fields rotational magnetic fields, and reduced gravitational levels can have a beneficial role will be described.

Volz, Martin

2004-01-01

400

RAPID CHANGES OF PHOTOSPHERIC MAGNETIC FIELD AFTER TETHER-CUTTING RECONNECTION AND MAGNETIC IMPLOSION  

SciTech Connect

The rapid, irreversible change of the photospheric magnetic field has been recognized as an important element of the solar flare process. This Letter reports such a rapid change of magnetic fields during the 2011 February 13 M6.6 flare in NOAA AR 11158 that we found from the vector magnetograms of the Helioseismic and Magnetic Imager (HMI) with 12 minute cadence. High-resolution magnetograms of Hinode that are available at {approx}-5.5, -1.5, 1.5, and 4 hr relative to the flare maximum are used to reconstruct a three-dimensional coronal magnetic field under the nonlinear force-free field (NLFFF) assumption. UV and hard X-ray images are also used to illuminate the magnetic field evolution and energy release. The rapid change is mainly detected by HMI in a compact region lying in the center of the magnetic sigmoid, where the mean horizontal field strength exhibited a significant increase of 28%. The region lies between the initial strong UV and hard X-ray sources in the chromosphere, which are cospatial with the central feet of the sigmoid according to the NLFFF model. The NLFFF model further shows that strong coronal currents are concentrated immediately above the region, and that, more intriguingly, the coronal current system underwent an apparent downward collapse after the sigmoid eruption. These results are discussed in favor of both the tether-cutting reconnection producing the flare and the ensuing implosion of the coronal field resulting from the energy release.

Liu Chang; Deng Na; Liu Rui; Jing Ju; Xu Yan; Wang Shuo; Wang Haimin [Space Weather Research Laboratory, New Jersey Institute of Technology, University Heights, Newark, NJ 07102-1982 (United States); Lee, Jeongwoo [Physics Department, New Jersey Institute of Technology, University Heights, Newark, NJ 07102-1982 (United States); Wiegelmann, Thomas, E-mail: chang.liu@njit.edu [Max Planck Institut fuer Sonnensystemforschung (MPS), Max-Planck-Strasse 2, 37191 Katlenburg-Lindau (Germany)

2012-01-20

401

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

402

Auroral vector electric field and particle comparisons. 1: Pre-midnight convection topology  

NASA Technical Reports Server (NTRS)

Polar 3 was launched in northern Norway on January 27, 1974. Traversing nearly 3 deg latitude, the rocket crossed over a stable IBC II auroral arc in the positive bay region and continued north to a convection boundary which was identified as the Harang discontinuity. Measurement of the complete electric field vector, of energetic electrons and of the auroral N+2 and OI emissions were used to study the convection topology in the pre-magnetic-midnight region. A strong anticorrelation was observed between the electric field and the precipitating energetic electrons. The inverted V nature of the electron precipitations at the convection boundary, compared with the lack of such structure over the arc which was within the positive bay region, leads to the conclusion that auroral arcs are likely to be associated with inverted V type precipitation only at or poleward of convection boundaries and their eddy structures.

Maynard, N. C.; Evans, D. S.; Maehlum, B.; Egeland, A.

1976-01-01

403

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

404

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

405

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

406

Self Magnetic Field and Current-loop of Electron with Five Different Radii and Intrinsic Properties  

E-print Network

With the rotation of charge in a circular path current-loop is generated. This results in the production of magnetic fields in a charged body. This self (internal) magnetic field is treated here with five different radii of electron. Closed loop line integral of magnetic induction vector or the integral form of the Ampere's circuital law is expressed in terms intrinsic properties of electron.

S. Ghosh; M. R. Devi; A. Choudhury; J. K. Sarma

2009-12-09

407

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

408

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

409

Screening magnetic fields by superconductors: A simple model  

SciTech Connect

We introduce a simple approach to evaluate the magnetic field distribution around superconducting samples, based on the London equations; the elementary variable is the vector potential. This procedure has no adjustable parameters, only the sample geometry and the London length, ?, determine the solution. This approach was validated by comparing the induction field calculated to the one measured above MgB{sub 2} disks of different diameters, at 20?K and for applied fields lower than 0.4?T. The model can be applied if the flux line penetration inside the sample can be neglected when calculating the induction field distribution outside the superconductor. We conclude by showing on a cup-shape geometry how one can design a magnetic shield satisfying a specific constraint.

Caputo, J.-G., E-mail: caputo@insa-rouen.fr [Laboratoire de Mathématiques, INSA de Rouen, Avenue de l'Université, 76801 Saint-Etienne du Rouvray (France); Gozzelino, L.; Laviano, F.; Ghigo, G.; Gerbaldo, R. [Department of Applied Science and Technology, Politecnico di Torino, 10129, Torino (Italy); Noudem, J.; Thimont, Y.; Bernstein, P. [CRISMAT/LUSAC, Physics Department, Université de Caen (France)

2013-12-21

410

Robust Direction Estimation of Gradient Vector Field for Iris Recognition  

Microsoft Academic Search

As a reliable personal identification method, iris recognition has been receiving increasing attention. Based on the theory of robust statistics, a novel geometry-driven method for iris recognition is presented in this paper. An iris image is considered as a 3D surface of piecewise smooth patches. The direction of the 2D vector, which is the planar projection of the normal vector

Zhenan Sun; Yunhong Wang; Tieniu Tan; Jiali Cui

2004-01-01

411

On the Development of a Magnetically Vectored Variable ISP Plasma Rocket  

NASA Technical Reports Server (NTRS)

The development of a Magnetically Vectored Variable I(sub sp) Plasma Rocket at the Advanced Space Propulsion Laboratory (ASPL) is in progress at NASA's Johnson Space Center. The facility is using a small, 3.2 m tandem mirror device to study the application of RF heated magnetically contained plasmas for space propulsion. The central cell radius is 0.1 m and fields of 0.2 T and 2 T are possible in the central and end-cell mirror sections, respectively. A magnetoplasmadynamic (MPD) injector has just been acquired and will be used along with other methods of plasma refueling. A 1 MW magnet power supply upgrade is being developed with full implementation by the Spring of 1997. Two microwave systems for discharge initiation and plasma heating at 2.45 GHz and 14.0 GHz, respectively, are in operation. Additionally, RF systems with 200 kW and 1 MW of power are being modified and conditioned for operation. The concept provides electrode-less operation and variable thrush'specific impulse at constant power (200 -30 N /5000-30,000 seconds at 10 MW with a 60% efficiency). Optimization for speed or payload are possible with the same engine, giving the rocket great flexibility. Missions to Mars in 90 days are described, and missions to Pluto are under study.

Feliciano, Enectali Figueroa; Diaz, Franklin R. Chang; Squire, Jared P.

1997-01-01

412

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

413

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

414

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

415

Secondary CMB anisotropies from bulk motions in the presence of stochastic magnetic fields  

E-print Network

Bulk motions of electrons along the line of sight induce secondary temperature fluctuations in the post-decoupling, reionized universe. In the presence of a magnetic field not only the scalar mode but also the vector mode act as a source for the bulk motion. The resulting angular power spectrum of temperature anisotropies of the cosmic microwave background is calculated assuming a simple model of reionization.Contributions from the standard adiabatic, curvature mode and a non helical magnetic field are included. The contribution due to magnetic fields with field strengths of order nG and negative magnetic spectral indices dominates for multipoles larger than $\\ell \\sim 10^4$.

Kunze, Kerstin E

2013-01-01

416

Secondary CMB anisotropies from bulk motions in the presence of stochastic magnetic fields  

NASA Astrophysics Data System (ADS)

Bulk motions of electrons along the line of sight induce secondary temperature fluctuations in the postdecoupling, reionized Universe. In the presence of a magnetic field not only the scalar mode but also the vector mode act as a source for the bulk motion. The resulting angular power spectrum of temperature anisotropies of the cosmic microwave background is calculated assuming a simple model of reionization. Contributions from the standard adiabatic, curvature mode and a nonhelical magnetic field are included. The contribution due to magnetic fields with field strengths of order nG and negative magnetic spectral indices becomes important for multipoles larger than ?˜104.

Kunze, Kerstin E.

2014-05-01

417

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

418

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

419

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

420

Low-degree Structure in Mercury's Planetary Magnetic Field  

NASA Technical Reports Server (NTRS)

The structure of Mercury's internal magnetic field has been determined from analysis of orbital Magnetometer measurements by the MESSENGER spacecraft. We identified the magnetic equator on 531 low-altitude and 120 high-altitude equator crossings from the zero in the radial cylindrical magnetic field component, Beta (sub rho). The low-altitude crossings are offset 479 +/- 6 km northward, indicating an offset of the planetary dipole. The tilt of the magnetic pole relative to the planetary spin axis is less than 0.8 deg.. The high-altitude crossings yield a northward offset of the magnetic equator of 486 +/- 74 km. A field with only nonzero dipole and octupole coefficients also matches the low-altitude observations but cannot yield off-equatorial Beta (sub rho) = 0 at radial distances greater than 3520 km. We compared offset dipole and other descriptions of the field with vector field observations below 600 km for 13 longitudinally distributed, magnetically quiet orbits. An offset dipole with southward directed moment of 190 nT-R-cube (sub M) yields root-mean-square (RMS) residuals below 14 nT, whereas a field with only dipole and octupole terms tuned to match the polar field and the low-altitude magnetic equator crossings yields RMS residuals up to 68 nT. Attributing the residuals from the offset-dipole field to axial degree 3 and 4 contributions we estimate that the Gauss coefficient magnitudes for the additional terms are less than 4% and 7%, respectively, relative to the dipole. The axial alignment and prominent quadrupole are consistent with a non-convecting layer above a deep dynamo in Mercury's fluid outer core.

Anderson, Brian J.; Johnson, Catherine L.; Korth, Haje; Winslow, Reka M.; Borovsky, Joseph E.; Purucker, Michael E.; Slavin, James A.; Solomon, Sean C.; Zuber, Maria T.; McNutt, Ralph L. Jr.

2012-01-01

421

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

422

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

423

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

424

Solutions and symmetries of force-free magnetic fields  

SciTech Connect

New analytical results concerning force-free magnetic fields are presented. A number of examples of exact solutions for two-dimensional nonlinear force-free fields described by the Liouville equation are shown. These include classical solutions, such as, the Gold-Hoyle field and the force-free Harris sheet as special cases. The connection between these solutions and the Lie point symmetries of the Liouville equation is illustrated. Lie point symmetries of the equation describing force-free magnetic fields in helical symmetry in cylindrical geometry are also investigated and an infinitesimal generator that, in the vicinity of the cylinder axis, makes it possible to transform purely radially dependent solutions into helically symmetric solutions, is found. Finally we point out the existence of a formal analogy between the equations for the vector potential components of a class of force-free fields and the equations of motion of a charged particle in a magnetic field. This analogy makes it possible to transfer known results from the theory of the motion of a charged particle, into the context of force-free magnetic fields. Explicit examples of such application are given.

Tassi, E. [Burning Plasma Research Group, Dipartimento di Energetica and CNISM, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Pegoraro, F. [Dipartimento di Fisica, E. Fermi and CNISM, Pisa (Italy); Cicogna, G. [Dipartimento di Fisica, E. Fermi and INFN, Pisa (Italy)

2008-09-15