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

Magnetic field effects on quantum ring excitons  

Microsoft Academic Search

We study the effect of magnetic field and geometric confinement on excitons confined to a quantum ring. We use analytical matrix elements of the Coulomb interaction and diagonalize numerically the effective-mass Hamiltonian of the problem. To explore the role of different boundary conditions, we investigate the quantum ring structure with a parabolic confinement potential, which allows the wave functions to

Jakyoung Song; Sergio E. Ulloa

2001-01-01

2

Understanding magnetic field reversal mechanisms in mesoscopic magnetic multilayer ring structures  

E-print Network

Patterned pseudo spin-valve rings show great promise for device applications due to their non-volatility and variety of stable magnetic states. However, the magnetic reversal of these elements under an applied field is ...

Ng, Bryan

2008-01-01

3

Field induced switching in multilayer rhombic magnetic rings  

E-print Network

Multilayer rhombic magnetic rings are researched as a structure for the "pseudo spin valve" device that could possibly become useful in magnetic materials applications such as MRAM, digital logic, and sensors through the ...

Pacella, James N

2007-01-01

4

Externally controlled local magnetic field in a conducting mesoscopic ring coupled to a quantum wire  

NASA Astrophysics Data System (ADS)

In the present work, the possibility of regulating local magnetic field in a quantum ring is investigated theoretically. The ring is coupled to a quantum wire and subjected to an in-plane electric field. Under a finite bias voltage across the wire a net circulating current is established in the ring which produces a strong magnetic field at its centre. This magnetic field can be tuned externally in a wide range by regulating the in-plane electric field, and thus, our present system can be utilized to control magnetic field at a specific region. The feasibility of this quantum system in designing spin-based quantum devices is also analyzed.

Maiti, Santanu K.

2015-01-01

5

Design of a uniform bias magnetic field for giant magnetostrictive actuators applying triple-ring magnets  

NASA Astrophysics Data System (ADS)

Uniform bias magnetic field is very important for giant magnetostrictive actuators (GMA) to fully utilize the performance of giant magnetostrictive materials (GMM). However, it is difficult to keep it uniform when the length to diameter ratio (?) of the GMM is larger than 3.5, though the shapes of the applied GMM are different with ? usually larger than 3.5. In this paper, a design method with triple-ring permanent magnets is established to provide an even bias magnetic field for GMM with varying ?. Firstly, the magnetic circuit model is set up. According to the analysis of the field distribution along the GMM rod, the main factor causing unevenness of the bias magnetic field is confirmed to be the inner leakage flux. A design of triple-ring topology for the magnets is developed to control the inner leakage flux to reduce the unevenness. Then, finite element analysis is adopted to optimize a design which can ensure an unevenness of the bias magnetic field of less than 3% while the ? of a GMM rod is up to 20. Finally, an actual GMA is fabricated with the GMM dimension of ?10 mm × 50 mm (? = 5), and the testing results show that the unevenness of the bias field along the GMM is 1.38%. The bias magnetic system design is practicable, simple and efficient for offering an even bias magnetic field when ? lies in a wide range.

Zhang, Heng; Zhang, Tianli; Jiang, Chengbao

2013-11-01

6

Effects of geometry and impurities on quantum rings in magnetic fields RID D-3014-2009  

E-print Network

We investigate the effects of impurities and changing ring geometry on the energetics of quantum rings under different magnetic field strengths. We show that as the magnetic field and/or the electron number are/is increased, both the quasiperiodic...

Aichinger, M.; Chin, Siu A.; Krotscheck, E.; Rasanen, E.

2006-01-01

7

Effects of fluctuating magnetic fields on a superconducting bulk rotor shielded with superconducting rings  

NASA Astrophysics Data System (ADS)

We study the effect of a fluctuating magnetic field, which is one of the technical problems for trapped magnetic fields in a bulk superconductor, to realize a practical bulk superconductor rotating machine. Previous research and other's research has shown that fluctuating magnetic fields reduce the strength of trapped magnetic fields in superconducting bulk modules [1, 2]. This deters development of applications of AC rotating machines because superconducting bulk modules are always exposed to a fluctuating magnetic field. Therefore, it is necessary to develop a method to control decrease of the trapped magnetic field. We propose a method to use the shielding ring of a superconducting wire to achieve this goal and the effects are confirmed experimentally [3]. We are now building test equipment for examining the performance of a shielding ring in a bulk rotating machine. This paper reports the test result for the shielding ring applied to the bulk superconducting rotor that is a part of the test equipment.

Yamagishi, K.; Ogawa, J.; Tsukamoto, O.

2014-05-01

8

Magnetic Field Observations of Partial Ring Current during Storm Recovery Phase  

NASA Technical Reports Server (NTRS)

We present results of an extensive survey of the magnetic field observations in the inner magnetosphere using 30 years of magnetospheric magnetic field data from Polar, Cluster, ISEE, and AMPTE/CCE missions. The purpose of this study is to understand the magnetic field evolution during the recovery phase of geomagnetic storms, and its implication to the ring current recovery and loss mechanisms of ring current particles. Our previous work on global ring current distribution [Le et al., 2004] has shown that a significant partial ring current is always present at all Dst levels (regardless of storm phases) even for quiet time ring current. The total current carried by the partial ring current is much stronger than (during stormtime) or at least comparable to (during quiet time) the symmetric ring current. It is now commonly believed that a strong partial ring current is formed during the storm main phase due to the enhanced earthward convection of energetic ions from nightside plasma sheet. But the presence of a strong partial ring current throughout the recovery phase remains controversial. The magnetic field generated by the ring current inflates the inner magnetosphere and causes magnetic field depressions in the equatorial magnetosphere. During the storm recovery phase, we find that the distribution of the equatorial magnetic field depression exhibits similar local time dependence as the ring current distribution obtained from the combined dataset in the earlier study. It shows that a strong partial ring current is a permanent feature throughout the recovery phase. In the early recovery phase, the partial ring current peaks near the dusk terminator as indicated by the peak of the magnetic field depression. As the recovery phase progresses, the partial ring current decays most quickly near the dusk and results in a dusk-to-midnight moving of the peak of the partial ring current. Thus the loss mechanisms work most effectively near the dusk. The magnetic field depression increases the gyroradius of ring current protons to a scale greater or comparable to the thickness of the magnetopause, which increases the chance of ion drift loss near the dusk magnetopause at larger L-shell (L>5). But the drift loss mechanism alone cannot explain the loss of ring current ions especially in the smaller L-shell (L<5). The precipitation loss due to wave-particle interaction is most likely the dominant loss mechanism in the small L-shell as it works most effectively at the same local time.

Le, Guan; Russell, C. T.; Slavin, J. A.; Lucek, E. A.

2007-01-01

9

Magnetic Fields Effects on the Electronic Conduction Properties of Molecular Ring Structures  

Microsoft Academic Search

While mesoscopic conducting loops are sensitive to external magnetic fields, as seen by observations of the Aharonov-Bohm (AB) effect in such structures, the field needed to observe the AB periodicity in small molecular rings is unrealistically large. The present study aims to identify conditions under which magnetic field dependence can be observed in electronic conduction through such molecules. We consider

Dhurba Rai; Oded Hod; Abraham Nitzan

2011-01-01

10

Planetary rings as relics of plasma proto-rings rotating in the magnetic field of a central body  

NASA Astrophysics Data System (ADS)

A possibility is discussed in accordance to hypothesis by H. Alfven, that the rings of large planets are relics of some plasma proto-rings rotating in the magnetic fields of central bodies. A finite-dimensional mathematical model of the system is synthesized using the solution of the boundary-value problem by the Boubnov - Galerkin method. The dipole magnetic field of the central body is assumed to have a small eccentricity, and the dipole axis - to be inclined at a small angle to the central body's axis of rotation which coincides with the ring's rotation axis. The proto-ring is supposed to be thin and narrow and having the same rotating axis as the central body. A medium forming the ring is cold rarefied plasma with high electron density, so that electric conductivity of the medium tends to infinity, as well as the magnetic Reynolds number. The original mathematical model is reduced to a system of finite-difference equations whose asymptotic analytical solution is obtained. Emphasis is placed on the problems of stability of the ring's steady state rotation and quantization of the eigenvalues of nondimensional sector velocity of the ring with respect to the central body. The solutions corresponding to magneto-gravitational and to magneto-gyroscopic waves are considered It is demonstrated that some rings characterized by integral quantum numbers are stable and long-living, while the rings which are associated with half-integer quantum numbers (rings>) are unstable and short-living. As a result, an evolutionally rife rotating plasma ring turns out to be stratified into a large number of narrow elite rings separated by gaps whose position correspond to anti-rings. The regions of possible existence of elite rings in near-central body space are determined. The main result of eigenvalue spectrum's analysis is as follows. Quantum numbers determining elite eigenvalues of the sector velocity of a ring (normalized in a certain manner) coincide with the quantum numbers appearing in the solution of the Schr¨odingerequation for a hydrogen atom. Perturbations of the elite orbits corresponding to this numbers satisfy the de Brogli quantum-mechanical condition. The solution of the model boundary-value problem has been applied to planetary rings origin and evolution. The main result is a mechanism of stratification of the evolutionally mature plasma proto-ring into a large number of narrow elite rings separated by anti-rings (gaps), which were playing a role of for present-day planetary rings. Another result is the theoretical substantiation of the presence in the nearplanetary space of a region of existence and stability of plasma rings. The data, which had been obtained in the course of the Voyager, Galileo, and Cassini missions were used for verification of theoretical results concerning the planetary rings and Io plasma thorus. The theoretical dates turned out to be in accordance with experimental dates. References Alfven H. Cosmic Plasma. Dordrecht: Reidel, 1961. Rabinovich B.I. Dynamics of Plasma Ring Rotating in the Magnetic Field of Central Body: Magneto-GravitationalWaves // Cosmic Research, 2006. V. 44. No. 1. P. 43-51. Rabinovich B.I. Dynamics of Plasma Ring Rotating in the Magnetic Field of Central Body: Magneto-Gyroscopic Waves. Problems of Stability and Quantization // Cosmic Research, 2006. V. 44. No. 2. P. 146 - 161. Gore, Rick. Voyager 1 at Saturn. Riddles of the Rings // National Geographic, 1981. V. 160. No. 1. P. 3 - 31. Porco, Carolyn. Captain 's Log.: 2004, 184 // The Planetary Report, 2004. V. 24, No. 5. P. 2 - 18.

Rabinovich, B.

2007-08-01

11

The potential energy of a superconducting ring system locking magnetic flows in a gravity field  

NASA Astrophysics Data System (ADS)

The possibility of creating a magnetic system of a plasma trap with levitating magnetic coils is under consideration. For this purpose, the analytical function of the potential energy of the system of several superconducting rings, which lock the required flows (at that, the one ring is fixed), versus the coordinates of free rings in the homogeneous gravity field under approximation of thin rings. Using calculations in the Mathcad medium, it is shown that, under definite values of parameters, there are equilibrium states of such a system. In the positions that corresponded to the calculated values, stable levitation states of the superconducting ring are observed experimentally in the field of another superconducting ring. The obtained results prove that a magnetic system can be created on the basis of a levitating quadrupole.

Bishaev, A. M.; Bush, A. A.; Gavrikov, M. B.; Kamentsev, K. E.; Kozintseva, M. V.; Saveliev, V. V.; Sigov, A. S.

2012-10-01

12

Quantum transport in nonuniform magnetic fields: Aharonov-Bohm ring as a spin switch.  

PubMed

We study spin-dependent magnetoconductance in mesoscopic rings subject to an inhomogeneous in-plane magnetic field. We show that the polarization direction of transmitted spin-polarized electrons can be controlled via an additional magnetic flux such that spin flips are induced at half a flux quantum. This quantum interference effect is independent of the strength of the nonuniform field applied. We give an analytical explanation for one-dimensional rings and numerical results for corresponding ballistic microstructures. PMID:11736592

Frustaglia, D; Hentschel, M; Richter, K

2001-12-17

13

Magnetic Field Observations of Partial Ring Current during Storm Recovery Phase  

NASA Technical Reports Server (NTRS)

We present results of an extensive survey of the magnetic field observations in the inner magnetosphere using 30 years of magnetospheric magnetic field data from Polar, Cluster, ISEE, and AMPTE/CCE missions. The purpose of this study is to understand the magnetic field evolution during the recovery phase of geomagnetic storms, and its implication to the ring current recovery and loss mechanisms of ring current particles. It is now commonly believed that a strong partial ring current is formed during the storm main phase due to the enhanced earthward convection of energetic ions from nightside plasma sheet. But the presence of a strong partial ring current throughout the recovery phase remains controversial. The magnetic field generated by the ring current inflates the inner magnetosphere and causes magnetic field depressions in the equatorial magnetosphere. During the storm recovery phase, we find that the distribution of the equatorial magnetic field depression exhibits similar local time dependence as the ring current distribution obtained from the combined dataset in the earlier study. It shows that a strong partial ring current is a permanent feature throughout the recovery phase. In the early recovery phase, the partial ring current peaks near the dusk terminator as indicated by the peak of the magnetic field depression. As the recovery phase progresses, the partial ring current decays most quickly near the dusk and results in a dusk-to-midnight moving of the peak of the partial ring current. Thus the loss mechanisms work most effectively near the dusk. The magnetic field depression increases the gyroradius of ring current protons to a scale greater or comparable to the thickness of the magnetopause, which increases the chance of ion drift loss near the dusk magnetopause at larger L-shell (L greater than 5). But the drift loss mechanism alone cannot explain the loss of ring current ions especially in the smaller L-shell (L less than 5). The precipitation loss due to wave-particle interaction is most likely the dominant loss mechanism in the small L-shell as it works most effectively at the same local time.

Le, G.; Russell, C. T.; Slavin, J. A.; Lucek, E. A.

2008-01-01

14

On the Role of Global Magnetic Field Configuration in Affecting Ring Current Dynamics  

NASA Technical Reports Server (NTRS)

Plasma and field interaction is one important aspect of inner magnetospheric physics. The magnetic field controls particle motion through gradient, curvature drifts and E cross B drift. In this presentation, we show how the global magnetic field affects dynamics of the ring current through simulations of two moderate geomagnetic storms (20 November 2007 and 8-9 March 2008). Preliminary results of coupling the Comprehensive Ring Current Model (CRCM) with a three-dimensional plasma force balance code (to achieve self-consistency in both E and B fields) indicate that inclusion of self-consistency in B tends to mitigate the intensification of the ring current as other similar coupling efforts have shown. In our approach, self-consistency in the electric field is already an existing capability of the CRCM. The magnetic self-consistency is achieved by computing the three-dimensional magnetic field in force balance with anisotropic ring current ion distributions. We discuss the coupling methodology and its further improvement. In addition, comparative studies by using various magnetic field models will be shown. Simulation results will be put into a global context by analyzing the morphology of the ring current, its anisotropy and characteristics ofthe interconnected region 2 field-aligned currents.

Zheng, Y.; Zaharia, S. G.; Fok, M. H.

2010-01-01

15

Characteristics of Hot Electron Ring in a Simple Magnetic Mirror Field  

Microsoft Academic Search

Characteristics of a hot electron ring are studied in a simple magnetic mirror machine. Hot electron rings (n≈ 1010 cm-3, T≈ 100 keV) are most effectively generated under two conditions, when the magnetic field on the axis of the midplane is set near the fundamental, or the second harmonic electron cyclotron resonance to the applied microwave frequency (6.4 GHz). The

Minoru Hosokawa; Hideo Ikegami

1991-01-01

16

PHYSICAL REVIEW B 85, 155440 (2012) Magnetic fields effects on the electronic conduction properties of molecular ring structures  

E-print Network

that comprise molecular ring structures by magnetic fields is considered challenging because the required fieldPHYSICAL REVIEW B 85, 155440 (2012) Magnetic fields effects on the electronic conduction properties of molecular ring structures Dhurba Rai, Oded Hod, and Abraham Nitzan School of Chemistry, Tel Aviv University

Hod, Oded

17

Control of generation regimes of ring chip laser under the action of the stationary magnetic field  

SciTech Connect

We consider realisation of different generation regimes in an autonomous ring chip laser, which is a rather complicated problem. We offer and demonstrate a simple and effective method for controlling the radiation dynamics of a ring Nd:YAG chip laser when it is subjected to a stationary magnetic field producing both frequency and substantial amplitude nonreciprocities. The amplitude and frequency nonreciprocities of a ring cavity, arising under the action of this magnetic field, change when the magnet is moved with respect to the active element of the chip laser. Some self-modulation and stationary generation regimes as well as the regime of beatings and dynamic chaos regime are experimentally realised. Temporal and spectral characteristics of radiation are studied and conditions for the appearance of the generation regime are found. (control of laser radiation parameters)

Aulova, T V; Kravtsov, Nikolai V; Lariontsev, E G; Chekina, S N; Firsov, V V [D.V. Skobel'tsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)] [D.V. Skobel'tsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

2013-05-31

18

Tuning electromechanical resonances in strip-ring magnetoelectric composites structure with dc magnetic field  

NASA Astrophysics Data System (ADS)

In this paper, we show that electrically excited mechanical resonances can be tuned with a single dc magnetic field in strip-ring magnetoelectric composites, namely, ferrite-lead zirconate titanate (PZT) and nickel-zinc (Ni-Zn) ferrite. A theoretical model is presented to describe the magnetically tuned electromechanical resonances in the piezoelectric-magnetostrictive heterostructure, where the piezoelectric and magnetostrictive phases are coupled through normal stresses instead of shear stresses, which usually act in layered composites. As we have used only dc magnetic field that tuned electromechanical resonances, the adjustment manner can simplify application in transducers for magnetoelectric energy conversion.

Wei, Wang; XiaoXiao, Xu; LiSheng, Zhou; Xiao Bin, Luo; Ning, Zhang

2013-08-01

19

Preliminary Simulation Results for Stormtime Ring Current in a Self-Consistent Magnetic Field Model  

NASA Astrophysics Data System (ADS)

The stormtime ring current generates a strong and time-dependent perturbation of the magnetospheric ?c{B} field, and this magnetic-field perturbation can have important feedback on the dynamics of ring current particles themselves. In particular, the modification of ?c{B} can significantly alter the gradient-curvature drifts of ring current particles, and the induced electric field associated with ? ?c{B}/? t can inhibit ring current particle injection and energization. Thus, in order to accurately simulate the stormtime ring current, we need a self-consistent magnetic field model that takes into account effects of the ring current on the particles that produce it. This study is our first attempt to address this issue. We assume for simplicity a model for ?c{B} (= ? ? ×? ? ) such that magnetic field lines lie in meridional planes and satisfy the generic equation r = La(1+0.5r3/b^3)sin ^2? , where r is the radial distance from the point dipole, ? is the magnetic colatitude, a is the radius of the Earth, L is a dimensionless field-line label inversely proportional to the Euler potential ? = -? E/La, ? is the magnetic local time, and the parameter b (a function of L and ? ) controls the amount by which a field line is stretched. The special case of constant b yields Dungey's model magnetosphere (dipole field plus uniform southward ? B), in which the limit b->? corresponds to a purely dipolar B field (? B = 0). More generally, we now let the value of b varies from field line to field line so as to account also for the ring current's contribution to equatorial ? B as a function of r and ? . The self-consistent magnetic field should satisfy the force balance, as specified by the equation ? 0-1}?c{B}×(? ×?c{B) = -? ??c{?c{P}}, where ? 0 is the permeability of free space and ?c{?c{P}} is the pressure tensor. Under these assumptions, the radial component of the left-hand side of the force balance equation in the equatorial plane can be expressed via an ordinary differential equation in L or in r0, where r0 is the geocentric radial distance in the equatorial plane (related to L by solving the equation of a field line for r at ? = ? /2). Given the plasma pressure in the equatorial plane as a function of r0 and ? as a result of our bounce-averaged guiding center simulations of representative ring-current particles, we can thus solve the pressure-balance equation to obtain the self-consistent magnetic field. We will show some preliminary results found by applying this method to actual ring-current plasma simulations.

Liu, S.; Chen, M. W.; Schulz, M.; Lyons, L. R.

2004-12-01

20

Antiferromagnetic resonance excitation by terahertz magnetic field resonantly enhanced with split ring resonator  

SciTech Connect

Excitation of antiferromagnetic resonance (AFMR) in a HoFeO{sub 3} crystal combined with a split ring resonator (SRR) is studied using terahertz (THz) electromagnetic pulses. The magnetic field in the vicinity of the SRR is induced by the incident THz electric field component and excites spin oscillations that correspond to the AFMR, which are directly probed by the Faraday rotation of the polarization of a near-infrared probe pulse. The good agreement of the temperature-dependent magnetization dynamics with the calculation using the two-lattice Landau-Lifshitz-Gilbert equation confirms that the AFMR is excited by the THz magnetic field, which is enhanced at the SRR resonance frequency by a factor of 20 compared to the incident magnetic field.

Mukai, Y. [Department of Physics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan); Hirori, H., E-mail: hirori@icems.kyoto-u.ac.jp [Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Sakyo-ku, Kyoto 606-8501 (Japan); CREST, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012 (Japan); Yamamoto, T. [Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan); Kageyama, H. [Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Sakyo-ku, Kyoto 606-8501 (Japan); Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan); Tanaka, K., E-mail: kochan@scphys.kyoto-u.ac.jp [Department of Physics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan); Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Sakyo-ku, Kyoto 606-8501 (Japan); CREST, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012 (Japan)

2014-07-14

21

Antiferromagnetic resonance excitation by terahertz magnetic field resonantly enhanced with split ring resonator  

NASA Astrophysics Data System (ADS)

Excitation of antiferromagnetic resonance (AFMR) in a HoFeO3 crystal combined with a split ring resonator (SRR) is studied using terahertz (THz) electromagnetic pulses. The magnetic field in the vicinity of the SRR is induced by the incident THz electric field component and excites spin oscillations that correspond to the AFMR, which are directly probed by the Faraday rotation of the polarization of a near-infrared probe pulse. The good agreement of the temperature-dependent magnetization dynamics with the calculation using the two-lattice Landau-Lifshitz-Gilbert equation confirms that the AFMR is excited by the THz magnetic field, which is enhanced at the SRR resonance frequency by a factor of 20 compared to the incident magnetic field.

Mukai, Y.; Hirori, H.; Yamamoto, T.; Kageyama, H.; Tanaka, K.

2014-07-01

22

Magnetoconductance through a chain of rings with or without periodically modulated spin-orbit interaction strength and magnetic field  

Microsoft Academic Search

Ballistic electron transport through a chain of quantum circular rings is studied in the presence of spin-orbit interaction (SOI) and of a perpendicular magnetic field B . From the analytic expressions for the transmission and reflection coefficients for a single ring we obtain the conductance through a chain of rings as a function of the SOI strength alpha , the

B. Molnár; P. Vasilopoulos; F. M. Peeters

2005-01-01

23

Magnetospheric environments of outer planet rings - influence of Saturn's axially symmetric magnetic field  

SciTech Connect

Saturn's main rings exist within a zone of negligible magnetospheric losses and surface alteration effects, substantially due to the solid-body absorption of inwardly diffusing magnetospheric particles. This process is presently shown to be especially efficient in the inner magnetosphere of Saturn, due to the near-axial symmetry of the planetary magnetic field relative to the equatorial rotation plane; under the assumption of comparable diffusion rates, the inward magnetospheric particle transport is far more inhibited in the inner Saturnian magnetosphere than in the same regions of Jupiter and Uranus, even when only rings of comparable widths and depths are considered. In light of this, ring particle surface exposure to the ion fluxes of the radiation belt remains a prepossessing rationale for low Uranian ring albedos. 86 references.

Hood, L.L.

1987-07-01

24

Magnetic field control of the intraband optical absorption in two-dimensional quantum rings  

SciTech Connect

Linear and nonlinear optical absorption coefficients of the two-dimensional semiconductor ring in the perpendicular magnetic field B are calculated within independent electron approximation. Characteristic feature of the energy spectrum are crossings of the levels with adjacent nonpositive magnetic quantum numbers as the intensity B changes. It is shown that the absorption coefficient of the associated optical transition is drastically decreased at the fields corresponding to the crossing. Proposed model of the Volcano disc allows to get simple mathematical analytical results, which provide clear physical interpretation. An interplay between positive linear and intensity-dependent negative cubic absorption coefficients is discussed; in particular, critical light intensity at which additional resonances appear in the total absorption dependence on the light frequency is calculated as a function of the magnetic field and levels' broadening.

Olendski, O., E-mail: oolendski@ksu.edu.sa [King Abdullah Institute for Nanotechnology, King Saud University, P.O. Box 2454, Riyadh 11451 (Saudi Arabia); Barakat, T., E-mail: tbarakat@ksu.edu.sa [Department of Physics, King Saud University, P.O. Box 2454, Riyadh 11451 (Saudi Arabia)

2014-02-28

25

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

26

Design of fiber magnetic field sensor based on fiber Bragg grating Fabry-Perot cavity ring-down spectroscopy  

NASA Astrophysics Data System (ADS)

A novel fiber magnetic sensor based on the fiber Bragg grating Fabry-Perot (FBG-FP) cavity ring-down technique with pulse laser injection is proposed and demonstrated theoretically. A general expression of the intensity of the output electric field is derived, and the effect of the external magnetic field on the ring-down time is discussed. The results show that the output light intensity and the ring-down time of the FBG-FP cavity are in the inverse proportion to the magnitude of the external magnetic field. Our results demonstrate the new concept of the fiber magnetic sensor with the FBG-FP cavity ring-down spectroscopy and the technical feasibility.

Li, Qi; Chen, Haiyan

2015-02-01

27

Effects of electronic correlations and magnetic field on a molecular ring out of equilibrium  

NASA Astrophysics Data System (ADS)

We study the effects of electron-electron interactions on the steady-state characteristics of a hexagonal molecular ring in a magnetic field as a model for a benzene molecular junction. The system is driven out of equilibrium by applying a bias voltage across two metallic leads. We employ a model Hamiltonian approach to evaluate the effects of on-site as well as nearest-neighbor density-density-type interactions in a physically relevant parameter regime. Results for the steady-state current, charge density, and magnetization in three different junction setups (para, meta, and ortho) are presented. Our findings indicate that interactions beyond the mean-field level renormalize voltage thresholds as well as current plateaus. Electron-electron interactions lead to substantial charge redistribution as compared to the mean-field results. We identify a strong response of the circular current on the electronic structure of the metallic leads. Our results are obtained by steady-state cluster perturbation theory, a systematically improvable approximation to study interacting molecular junctions out of equilibrium, even in magnetic fields. Within this framework, general expressions for the current, charge density, and magnetization in the steady state are derived. The method is flexible and fast and can straightforwardly be applied to effective models as obtained from ab initio calculations.

Nuss, Martin; von der Linden, Wolfgang; Arrigoni, Enrico

2014-04-01

28

Magnetic Field Generation Processes Involving Gravity and Differential Rotation. Solitary Plasma Rings Formation around Black Holes  

NASA Astrophysics Data System (ADS)

A clear theoretical framework to describe how magnetic fields are generated and amplified is provided by the magneto-gravitational modes that involve both differential rotation and gravity and for which other factors such as temperature gradients can contribute to their excitation. These modes are shown to be important for the evolution of plasma disks surrounding black holes.footnotetextB. Coppi, Phys. Plasmas 18, 032901 (2011) Non-linear and axi-symmetric plasmas and associated field configurations are found under stationary conditions that do not involve the presence of a pre-existing ``seed'' magnetic field unlike other configurations found previously.footnotetextIbid. The relevant magnetic energy density is of the order of the gravitationally confined plasma pressure. The solitary plasma rings that characterize these configurations are localized radially over regions with vanishing differential rotation and can be envisioned as the saturated state of magneto-gravitational modes. The ``source'' of these configurations is the combination of the gravitational force and of the plasma density gradient orthogonal to it.

Coppi, Bruno

2012-10-01

29

Accurate correction of magnetic field instabilities for high-resolution isochronous mass measurements in storage rings  

E-print Network

Isochronous mass spectrometry (IMS) in storage rings is a successful technique for accurate mass measurements of short-lived nuclides with relative precision of about $10^{-5}-10^{-7}$. Instabilities of the magnetic fields in storage rings are one of the major contributions limiting the achievable mass resolving power, which is directly related to the precision of the obtained mass values. A new data analysis method is proposed allowing one to minimise the effect of such instabilities. The masses of the previously measured at the CSRe $^{41}$Ti, $^{43}$V, $^{47}$Mn, $^{49}$Fe, $^{53}$Ni and $^{55}$Cu nuclides were re-determined with this method. An improvement of the mass precision by a factor of $\\sim 1.7$ has been achieved for $^{41}$Ti and $^{43}$V. The method can be applied to any isochronous mass experiment irrespective of the accelerator facility. Furthermore, the method can be used as an on-line tool for checking the isochronous conditions of the storage ring.

P. Shuai; H. S. Xu; Y. H. Zhang; Yu. A. Litvinov; M. Wang; X. L. Tu; K. Blaum; X. H. Zhou; Y. J. Yuan; G. Audi; X. L. Yan; X. C. Chen; X. Xu; W. Zhang; B. H. Sun; T. Yamaguchi; R. J. Chen; C. Y. Fu; Z. Ge; W. J. Huang; D. W. Liu; Y. M. Xing; Q. Zeng

2014-07-13

30

Solitary plasma rings and magnetic field generation involving gravity and differential rotation  

NASA Astrophysics Data System (ADS)

A new theoretical framework for describing how magnetic fields are generated and amplified is provided by finding magneto-gravitational modes that involve gravity, density gradients, and differential rotation in an essential way. Other factors, such as the presence of a high temperature particle population or of a temperature gradient, can contribute to their excitation. These modes identified by a linearized analysis are shown to be important for the evolution of plasma disks surrounding black holes toward different configurations. Since the nonlinear development of these modes can lead to radially localized regions with a relatively small differential rotation, new stationary structures have been identified, in the (fully) nonlinear limit, which are localized radially over regions with negligible gradients of the rotation frequency. These structures, characterized by solitary plasma rings, do not involve a pre-existing "seed" magnetic field, unlike other configurations found previously. The relevant magnetic energy density is comparable to the gravitationally confined plasma pressure. The "source" of these configurations is the combination of the gravitational force and of the plasma density gradient orthogonal to it that is an important factor in the theory of magneto-gravitational modes, another important factor being an anisotropy of the plasma pressure.

Coppi, B.

2012-12-01

31

Ion Rings for Magnetic Fusion  

SciTech Connect

This Final Technical Report presents the results of the program, Ion Rings for Magnetic Fusion, which was carried out under Department of Energy funding during the period August, 1993 to January, 2005. The central objective of the program was to study the properties of field-reversed configurations formed by ion rings. In order to reach this objective, our experimental program, called the Field-reversed Ion Ring Experiment, FIREX, undertook to develop an efficient, economical technology for the production of field-reversed ion rings. A field-reversed configuration (FRC) in which the azimuthal (field-reversing) current is carried by ions with gyro-radius comparable to the magnetic separatrix radius is called a field-reversed ion ring. A background plasma is required for charge neutralization of the ring, and this plasma will be confined within the ring's closed magnetic flux. Ion rings have long been of interest as the basis of compact magnetic fusion reactors, as the basis for a high-power accelerator for an inertial fusion driver, and for other applications of high power ion beams or plasmas of high energy density. Specifically, the FIREX program was intended to address the longstanding question of the contribution of large-orbit ions to the observed stability of experimental FRCs to the MHD tilt mode. Typical experimental FRCs with s {approx} 2-4, where s is the ratio of separatrix radius to ion gyro-radius, have been stable to tilting, but desired values for a fusion reactor, s > 20, should be unstable. The FIREX ring would consist of a plasma with large s for the background ions, but with s {approx} 1 for the ring ions. By varying the proportions of these two populations, the minimum proportion of large-orbit ions necessary for stability could be determined. The incorporation of large-orbit ions, perhaps by neutral-beam injection, into an FRC has been advanced for the purpose of stabilizing, heating, controlling angular momentum, and aiding the formation of a reactor-scale FRC, and the FIREX program was intended to test the ideas behind this approach. We will describe in this report the technological development path and advances in physics understanding that allowed FIREX to reach a regime in which ion rings were reproducibly created with up to about half the current necessary to produce field reversal. Unfortunately, the experiments were limited to this level by a fundamental, unanticipated aspect of the physics of strong ion rings in plasma. The FIREX ring is a strongly anisotropic, current-carrying population of ions moving faster than the Alfven speed in the background plasma. The rapidly changing ring current excites very large-amplitude Alfven waves in the plasma, and these waves strongly affect the ring, causing rapid energy loss in a way that is not compatible with the success of the ring trapping scenario around which FIREX was designed. The result was that FIREX rings were always very short-lived. We will discuss the implication of these results for possible future use of large-orbit ions in FRCs. In short, it appears that a certain range of the parameters characterizing the ring Alfven mach number and distribution function must be avoided to allow the existence of a long-lived energetic ion component in an FRC. This report will explain why FIREX experimental results cannot be directly scaled to quantitatively predict this range for a particular FRC configuration. This will require accurate, three-dimensional simulations. FIREX results do constitute a very good dataset for validating such a code, and simulations already carried out during this program provide a guide to the important physics involved.

Greenly, John, B.

2005-07-31

32

Role of periodic loading-unloading in the magnetotail versus interplanetary magnetic field Bz flipping in the ring current buildup  

Microsoft Academic Search

Introducing kinetic corrections into the to BATSRUS code in the magnetotail region leads to fast reconnection rates observed in kinetic simulations and quasi-periodic loading-unloading cycles in the magnetotail during a long period of steady southward interplanetary magnetic field (IMF) Bz (Kuznetsova et al., 2006, 2007). We use the global MHD code BATSRUS output to drive the Fok Ring Current (FRC)

A. Taktakishvili; M. M. Kuznetsova; M. Hesse; M.-C. Fok; L. Rastätter; M. Maddox; A. Chulaki; G. Tóth; T. I. Gombosi; D. L. De Zeeuw

2008-01-01

33

Characteristics of hot electron ring in a simple magnetic mirror field  

Microsoft Academic Search

Characteristics of hot electron ring were studied in a simple magnetic mirror machine (mirror ratio 2:1) with a diameter of 30 cm at the midplane and with the distance of 80 cm between the mirrors. Maximum microwave input power was 5 kW at 6.4 GHz with the corresponding power density of approximately 0.3 W\\/cu cm. With a background cold plasma

M. Hosokawa; H. Ikegami

1980-01-01

34

Butterfly hysteresis loop at nonzero bias field in antiferromagnetic molecular rings: cooling by adiabatic magnetization.  

PubMed

At low temperatures, the magnetization of the molecular ferric wheel NaFe6 exhibits a step at a critical field B(c) due to a field-induced level crossing. By means of high-field torque magnetometry we observed a hysteretic behavior at the level crossing with a characteristic butterfly shape which is analyzed in terms of a dissipative two-level model. Several unusual features were found. The nonzero bias field of the level crossing suggests the possibility of cooling by adiabatic magnetization. PMID:12484964

Waldmann, O; Koch, R; Schromm, S; Müller, P; Bernt, I; Saalfrank, R W

2002-12-01

35

A Comparison of Computer and Field Test Results of Zero-Gradient Synchrotron Ring Magnet Power Supply  

Microsoft Academic Search

This paper describes an analog computer representation of the ring magnet power supply system of the Zero Gradient Synchrotron. Included in this representation are detailed simulations of a salient pole synchronous generator with a rectifier exciter, the generator voltage regulator, the twelve phase rectifier with grid control, and the ring magnet load. The performance predicted by the computer model is

R. A. Hedin; P. C. Krause

1966-01-01

36

Rotary actuators with multipole ring magnets  

Microsoft Academic Search

Rotary actuators are electromagnetic devices developing mechanical torque with limited rotary motion. Because of their simplicity and low cost they are finding more and more applications, especially in the automotive field. This paper describes a novel homopolar rotary actuator with a ring-type radially magnetized multipolar permanent magnet featuring a high force density “transverse flux” configuration which performs a spring action

Andrzej M. Pawlak; Steven Schultz; Vineeta Gangla

1995-01-01

37

Magnetic Fields  

NSDL National Science Digital Library

Students visualize the magnetic field of a strong permanent magnet using a compass. The lesson begins with an analogy to the effect of the Earth's magnetic field on a compass. Students see the connection that the compass simply responds to the Earth's magnetic field since it is the closest, strongest field, and thus the compass responds to the field of the permanent magnets, allowing them the ability to map the field of that magnet in the activity. This information will be important in designing a solution to the grand challenge in activity 4 of the unit.

2014-09-18

38

Formation of the Ring-like Structure in the SN 1987A Nebula due to the Magnetic Pressure of the Toroidal Field  

E-print Network

Several weeks after the explosion of supernova (SN) 1987A, the UV flash of the SN illuminated a ring-like structure in the circumstellar material at about 0.65 ly from the SN. The interaction between the stellar winds from the SN progenitor is considered to be the candidate for the formation of the circumstellar structure. In the case that the stellar winds are spherically symmetric, the interaction should result in a shell-like structure. However, in this paper we show that the magnetic field in the winds causes an anisotropy which leads to the formation of a ring-like structure. When the fast wind of the blue supergiant phase of the progenitor sweeps up the surrounding slow wind of the red-supergiant phase, the magnetic field as well as the wind material are piled up in the interaction region. Since the magnetic energy increases in proportion to the square of the amplitude, the magnetic field exhibits its effect prominently at the interaction region; due to the magnetic pressure force the material at lower latitudes is compressed into a ring-like structure. It is suggested that this magnetic process can also explain the newly observed pair of rings of the SN 1987A nebula.

Haruichi Washimi; Shinpei Shibata; Masao Mori

1997-11-22

39

Magnetic Fields  

E-print Network

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

Schöller, Markus

2015-01-01

40

Shielding of pulsed magnetic fields with already sintered 1 {mu}m sized powder-pressed Bi-based superconducting rings  

SciTech Connect

To confirm a ferrite-core model for the superconducting rings (supertrons) to focus and guide electron current beams, we examined a bismuth-based ring into the configuration of which already sintered 1 {mu}m sized 2223-phase powders were cold-isostatic pressed. No additional sintering was performed on the ring. Although the four-probe dc electric resistance of the ring increased with decreasing temperatures down to 77 K, the ring effectively shielded the self-magnetic field of single pulsed nanosecond-order electron currents ({similar_to}340 keV, {similar_to}1 kA, {similar_to}10 ns), below the T{sub c}. These results certainly support the model, and provide a clue useful in applications of bulk superconductors. {copyright} 2001 American Institute of Physics.

Matsuzawa, Hidenori; Mikami, Koji; Ibi, Akira

2001-06-11

41

Electromagnetic Field Analysis of Septum Magnet for APS Positron Accumulator Ring  

E-print Network

quality septum, or flat interface between copper and iron, is emphasized from a point of view of stray- dimensional finite element method and a new one improved by the authors. Figure 1. Configuration of APS PAR Method for Transient Electromagnetic Field The Finite Element Method (FEM) is employed in this study

Kemner, Ken

42

AN INVESTIGATION OF THE EFFECT OF A KOVAR RING ON A UNIFORM MAGNETIC FIELD. Technical Memorandum No. 21  

Microsoft Academic Search

Kovar has been suggested as a glass-to-metal seal in the glass vacuum ; system of certain stellarator models. One proposed seal would consist of a Kovar ; ring two inches in diameter, one-hall inch long, and 0.020 inch thick and would ; join a glass tube to a nonmagnetic stainless steel flange. The effects of ; uniform applied fields, in

Wakefield

1958-01-01

43

Phonon confinement effect on the polaron states in a double quantum ring structure in the presence of electric and magnetic fields  

NASA Astrophysics Data System (ADS)

In the framework of effective mass approximation the polaron problem in double quantum ring structures in the presence of perpendicular electric and magnetic fields with taken into account the effect of phonon confinement is considered. We derived general expressions for the normalized eigenfunctions of the confined optical and interface optical phonon modes and the dispersion relation for interface optical phonons as well as electron-confined optical phonon and electron-interface optical phonon Fröhlich interaction Hamiltonians in the double quantum ring system. Results reveal that the electron-optical phonon coupling leads to the decrease of the electron ground state energy. We have shown that the polaron energy exhibits a pronounced local maximum (minimuum) in dependence on an electric (magnetic) field which corresponds to the sharp decrease (increase) of the polaronic contributions due to confined optical and interface optical phonon modes.

Yeranosyan, Mkrtich A.; Vartanian, Arshak L.; Shahbandari, Abbas; Kirakosyan, Albert A.

2015-01-01

44

Buildup of the ring current during periodic loading-unloading cycles in the magnetotail driven by steady southward interplanetary magnetic field  

Microsoft Academic Search

During prolonged intervals of negative interplanetary magnetic field (IMF) B z the magnetosphere often enters a state in which quasi-periodic, large-amplitude oscillations of energetic particle fluxes are observed at the geosynchronous orbit. We use the global magnetosphere MHD code BATS-R-US output during a long period of steady southward IMF B z to drive the Fok Ring Current Model. Previous simulations

A. Taktakishvili; M. M. Kuznetsova; M. Hesse; M.-C. Fok; L. Rastätter; M. Maddox; A. Chulaki; T. I. Gombosi; D. L. De Zeeuw

2007-01-01

45

Comparison of Simulated and Observed Ring Current Magnetic Field and Ion Fluxes and ENA Intensity during the 5 April 2010 Storm  

NASA Astrophysics Data System (ADS)

In this study we compare simulated and observed stormtime magnetic intensities, proton flux spectra and ENA intensity for the 5 April 2010 storm (minimum Dst ? -73 nT) to test how well self-consistent simulations can simultaneously reproduce these quantities. We simulate the ring current and plasma sheet using the magnetically and electrostatically self-consistent Rice Convection Model-Equilibrium (RCM-E) [Lemon et al., JGR, 2004] with a time-varying magnetopause driven by upstream solar wind and interplanetary magnetic field (IMF) conditions. We use ion temperatures inferred from TWINS energetic neutral atom (ENA) images and THEMIS/ESA and SST ion data, and proton densities from the empirical IMF-dependent model of Tsyganenko and Mukai [JGR, 2003] to guide our specification of the plasma sheet at 10 RE, our plasma boundary location in the RCM-E. The oxygen to proton density ratio at the plasma boundary is specified from the empirical Young et al. [JGR, 1982] study. We compare the simulated magnetic intensity with the magnetic intensity measured by magnetometers on the GOES satellites at geosynchronous (GEO) altitude (6.6 Earth radii) and on THEMIS satellites. The simulated and observed proton spectra (GOES-14/MAGPD) at GEO and global ENA intensity (TWINS 1 and 2) are compared. We discuss the response of the ring current magnetic field and ion flux distribution to expansions and compressions of the magnetosphere associated with the dynamic solar wind pressure for this storm event.

Chen, M. W.; Lemon, C.; Guild, T. B.; Schulz, M.; Lui, A.; Keesee, A. M.; Goldstein, J.; Rodriguez, J. V.

2011-12-01

46

Electron energy states in a two-dimensional GaAs quantum ring with hydrogenic donor impurity in the presence of magnetic field  

NASA Astrophysics Data System (ADS)

Using the finite element method, we investigate the lowest and first few excited state energies in a two-dimensional GaAs quantum ring (QR) with a hydrogenic donor impurity and effective mass approximation under a uniform magnetic field perpendicular to the ring plane. We study in detail the dependence of the energy spectrum with different angular momentum on the inner radius, the outer radius and width of the QR, the magnetic field and impurity position. The results reveal that the electron energies increase with the inner radius while decrease with the outer radius and width of the QR; for a fixed ring, the magnetic field induces the increase of the electron energies. Moreover, the existence of impurity reduces energy levels, and the energy levels depend highly on the impurity position, which decreases as the impurity is far away from the center of the QR. Also, the dependence of the angular momentum on the energy spectrum is analyzed in detail. Project supported by the National Natural Science Foundation of China (No. 41202146), the Science and Technology Project of Education Department of Heilongjiang Province of China (Nos. 12541070, 12541064), the Natural Science Foundation of Heilongjiang Province of China (No. A201402), and the Northeastern Petroleum University Youth Science Foundation of China (No. 2012QN128).

Yun, Kang; Sheng, Wang; Xianli, Li

2015-03-01

47

Magnetic fields at Neptune  

NASA Technical Reports Server (NTRS)

The Voyager 2 magnetic field experiment discovered a complex and powerful magnetic field in Neptune, as well as an associated magnetosphere and magnetic tail. As the spacecraft exited the magnetosphere, the magnetic tail appeared to be monopolar. The auroral zones are probably located far from the rotation poles, and may possess complex geometry. The Neptune rings and all its known moons are imbedded deep within the magnetosphere (except for Nereid, which is outside when it lies sunward of the planet); the radiation belts have a complex structure due to the absorption of energetic particles by the moons and rings of Neptune, as well as losses associated with the significant changes in the diurnally varying magnetosphere configuration.

Ness, Norman F.; Acuna, Mario H.; Burlaga, Leonard F.; Connerney, John E. P.; Lepping, Ronald P.

1989-01-01

48

The Magnetic Moment of Model Ring Current Belts and the Cutoff Rigidity of Solar Protons  

Microsoft Academic Search

The magnetic moment MR of the ring current is calculated for model ring current belts, together with their magnetic fields along an equatorial radius. A graph shows the relation between the ratio MR\\/Mr (Mr = the magnetic moment of the earth) and the intensity AH of the ring current field at the equator on the earth's surface. It gives possible

S.-I. Akasofu; W. C. Lin

1963-01-01

49

Evolution of the storm magnetic field disturbance around Earth's surface and the associated ring current as deduced from multiple ground observatories  

NASA Astrophysics Data System (ADS)

on the continuous magnetic measurements of the multiple ground observatories, the structure of the geomagnetic field disturbance and its temporal variations have been investigated, and the evolution of the storm ring current is deduced accordingly. Assuming that the geomagnetic disturbance around the Earth's surface is approximately linearly varying in space, the spatial gradient of the corrected H (geomagnetic horizontal) component can be obtained from the multiple ground observations. It is found that the maximum difference of the corrected H component around the Earth's surface, as calculated by the gradient of the corrected H component multiplied by the Earth diameter, represents well the asymmetric index Asy-H. The antidirection of the gradient of the corrected H component can be regarded as pointing to the position of the maximum partial ring current. It is shown that for ordinary magnetic storms with Dst > -200 nT, the maximum partial ring current is located around the duskside during the main phase and the earlier stage of the recovery phase. At the later stage of the recovery phase, the position of the maximum partial ring current can possibly keep rotating eastward, indicating that the energetic electrons may play a significant role and the main ring current carriers may be the electrons at this stage. For the super storms (Dst < -200 nT), the position of the maximum partial ring current is not as regular. Based on physical considerations, this investigation also provides new formulas of the definitions to the symmetric index Sym-H and asymmetric index Asy-H.

Shen, C.; Zeng, G.; Li, X.; Rong, Z. J.

2015-01-01

50

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

51

Correction magnets for the Fermilab Recycler Ring  

SciTech Connect

In the commissioning of the Fermilab Recycler ring the need for higher order corrector magnets in the regions near beam transfers was discovered. Three types of permanent magnet skew quadrupoles, and two types of permanent magnet sextupoles were designed and built. This paper describes the need for these magnets, the design, assembly, and magnetic measurements.

James T Volk et al.

2003-05-27

52

Magnetic properties of small multi-layered rings  

E-print Network

Thin film rings can be an alternative geometry of magnetic memory cells, in which data bits are stored by the chirality of the flux-closed or 'vortex' state of the ring. The absence of the stray field in the vortex state ...

Jung, Wonjoon

2007-01-01

53

MAGNETS FOR A MUON STORAGE RING.  

SciTech Connect

We present a new racetrack coil magnet design, with an open midplane gap, that keeps decay particles in a neutrino factory muon storage ring from directly hitting superconducting coils. The structure is very compact because coil ends overlap middle sections top and bottom for skew focusing optics. A large racetrack coil bend radius allows ''react and wind'' magnet technology to be used for brittle Nb{sub 3}Sn superconductors. We describe two versions: Design-A, a magnet presently under construction and Design-B, a further iterated concept that achieves the higher magnetic field quality specified in the neutrino factory feasibility Study-II report. For Design-B reverse polarity and identical end design of consecutive long and short coils offers theoretically perfect magnet end field error cancellation. These designs avoid the dead space penalty from coil ends and interconnect regions (a large fraction in machines with short length but large aperture magnets) and provide continuous bending or focusing without interruption. The coil support structure and cryostat are carefully optimized.

PARKER, B.; ANERELLA, M.; GHOSH, A.; GUPTA, R.; HARRISON, M.; SCHMALZLE, J.; SONDERICKER, J.; WILLEN, E.

2002-06-18

54

Molecular magnets: Lord of the rings  

NASA Astrophysics Data System (ADS)

Magnets built of molecular rings of magnetic ions are fundamental model systems for studying the complex correlations and dynamics of quantum spins at the atomic scale. A new generation of neutron spectrometers can reveal complete four-dimensional maps of the spin correlations in spin rings.

Rüegg, Christian

2012-12-01

55

Stereo ENA Imaging of the Ring Current and Multi-point Measurements of Suprathermal Particles and Magnetic Fields by TRIO-CINEMA  

NASA Astrophysics Data System (ADS)

The TRIO (Triplet Ionospheric Observatory) - CINEMA (Cubesat for Ions, Neutrals, Electrons, & Magnetic fields) mission consists of three identical 3-u cubesats to provide high sensitivity, high cadence, stereo measurements of Energetic Neutral Atoms (ENAs) from the Earth's ring current with ~1 keV FWHM energy resolution from ~4 to ~200 keV, as well as multi-point in situ measurements of magnetic fields and suprathermal electrons (~2 -200 keV) and ions (~ 4 -200 keV) in the auroral and ring current precipitation regions in low Earth orbit (LEO). A new Suprathermal Electron, Ion, Neutral (STEIN) instrument, using a 32-pixel silicon semiconductor detector with an electrostatic deflection system to separate ENAs from ions and from electrons below 30 keV, will sweep over most of the sky every 15 s as the spacecraft spins at 4 rpm. In addition, inboard and outboard (on an extendable 1m boom) miniature magnetoresistive sensor magnetometers will provide high cadence 3-axis magnetic field measurements. An S-band transmitter will be used to provide ~8 kbps orbit-average data downlink to the ~11m diameter antenna of the Berkeley Ground Station.The first CINEMA (funded by NSF) is scheduled for launch on August 14, 2012 into a 65 deg. inclination LEO. Two more identical CINEMAs are being developed by Kyung Hee University (KHU) in Korea under the World Class University (WCU) program, for launch in November 2012 into a Sun-synchronous LEO to form TRIO-CINEMA. A fourth CINEMA is being developed for a 2013 launch into LEO. This LEO constellation of nanosatellites will provide unique measurements highly complementary to NASA's RBSP and THEMIS missions. Furthermore, CINEMA's development of miniature particle and magnetic field sensors, and cubesat-size spinning spacecraft may be important for future constellation space missions. Initial results from the first CINEMA will be presented if available.

Lin, R. P.; Sample, J. G.; Immel, T. J.; Lee, D.; Horbury, T. S.; Jin, H.; SEON, J.; Wang, L.; Roelof, E. C.; Lee, E.; Parks, G. K.; Vo, H.

2012-12-01

56

Levitating states of superconducting rings in the field of a fixed ring with constant current  

NASA Astrophysics Data System (ADS)

We consider the possibility of designing a plasma trap with a magnetic system formed by super-conducting rings and coils levitating in the field of a fixed coaxial coil carrying constant current. An analytic dependence of the potential energy of such a system with one or two levitating superconducting rings having trapped preset magnetic fluxes on their coordinates in the uniform gravitational field is obtained in the thin ring approximation. Calculations performed in the Mathcad system show that equilibrium states of such a system exist for certain values of parameters. Levitating states of a single superconducting ring and two superconducting rings in the field of the coil with constant current are observed experimentally in positions corresponding to calculated values.

Bishaev, A. M.; Bush, A. A.; Gavrikov, M. B.; Denisyuk, A. I.; Kamentsev, K. E.; Kozintseva, M. V.; Savel'ev, V. V.; Sigov, A. S.

2014-06-01

57

Janus Magnetic Rods, Ribbons, and Rings  

NASA Astrophysics Data System (ADS)

Dipolar particles are fundamental building blocks in nature and technology but the roles of anisotropy are seldom explored in their assembly. Here, we fabricate colloidal silica rods coated on one hemicylinder with a thin magnetic layer to satisfy multiple criteria: nearly monodisperse, easily imaged, and magnetic interaction dominant over gravity. We confirm long-predicted features of dipolar assembly and stress the microstructural variety brought about by shape and chemical anisotropy, especially by borrowing knowledge learned from molecules. We describe analogies to liquid crystalline deformations with bend, splay and twist; an analogy to cis/trans isomerism in organic molecules, which in this system can be controllably and reversibly switched; and a field-switching methodology to direct single ribbons into not only single but also multiple rings that can subsequently undergo hierarchical self-assembly. Going beyond earlier investigations of phase behavior, we show that dynamic reconfigurability presents subtle materials issues and possibilities.

Yan, Jing; Chaudhary, Kundan; Bae, Sung Chul; Lewis, Jennifer; Granick, Steve

2013-03-01

58

Magnetic fields at Uranus  

NASA Technical Reports Server (NTRS)

The conclusions drawn regarding the structure, behavior and composition of the Uranian magnetic field and magnetosphere as revealed by Voyager 2 data are summarized. The planet had a bipolar magnetotail and a bow shock wave which was observed 23.7 Uranus radii (UR) upstream and a magnetopause at 18.0 UR. The magnetic field observed can be represented by a dipole offset from the planet by 0.3 UR. The field vector and the planetary angular momentum vector formed a 60 deg angle, permitting Uranus to be categorized as an oblique rotator, with auroral zones occurring far from the rotation axis polar zones. The surface magnetic field was estimated to lie between 0.1-1.1 gauss. Both the field and the magnetotail rotated around the planet-sun line in a period of about 17.29 hr. Since the ring system is embedded within the magnetosphere, it is expected that the rings are significant absorbers of radiation belt particles.

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

1986-01-01

59

Permanent magnets for beamlines and the recycler ring at Fermilab  

SciTech Connect

Fermilab has nearly completed an upgrade to its accelerator complex which is called the Fermilab Main Injector @?MI). In addition to the FM1 ring itself, which is built of standard electromagnets, there are additional components. Two of these components, a beamline used for transporting 8 GeV protons from the existing Booster to the new FM1 ring, and a new storage ring for antiprotons, are made using permanent magnets. The storage ring has been named the Recycler because its function is to store leftover p-bars from the previous Tevatron Collider cycle after they have been decelerated to 8 GeV. Both the Recycler and the 8 GeV transfer line use magnets of similar technology. The magnetic material is strontium ferrite, chosen for reasons of economy and high H,. The temperature dependence of the ferrite is compensated by a Ni(30%)Fe(70%) alloy operating near its Curie temperature. Field quality is provided by steel pole pieces and custom shims. The Recycler Ring requires about 360 gradient magnets, 110 quadrupole magnets, and small numbers of Lambertson and special magnets. Nearly all of the magnets have been built. We present details of magnet design, manufacturing, and testing.

Henry D. Glass

1998-10-01

60

Progress Report on the g-2 Storage Ring Magnet System  

SciTech Connect

The 3.1 GeV muon storage ring for the g-2 experiment at Brookhaven National Laboratory has three large solenoid magnets that form a continuous 1.451 tesla storage ring dipole with an average beam bend radius of 7.1 meters. In addition to the three storage ring solenoids, there is an inflector dipole with nested dipole coils that create very little stray magnetic field. A superconducting shield on the inflector gets rid of most of the remaining stray flux. This paper reports on the progress made on the storage ring solenoid magnet system and the inflector as of June 1995. The results of cryogenic system tests are briefly reported.

Bunce, G.A.; Cullen, J.; Danby, G.; Green, M.A.; Jackson, J.; Jia, L.; Krienen, F.; Meier, R.; Meng, W.; Morse, W.; Pai, C.; Polk, I.; Prodell, A.; Shutt, R.; Snydstrup, L.; Yamamoto, A.

1995-06-01

61

Magnetic Bloch oscillations in nanowire superlattice rings.  

PubMed

The recent growth of semiconductor nanowire superlattices encourages hope that Bloch-like oscillations in such structures formed into rings may soon be observed in the presence of a time-dependent magnetic flux threading the ring. These magnetic Bloch oscillations are a consequence of Faraday's law; the time-dependent flux produces an electromotive force around the ring, thus leading to the Bloch-like oscillations. In the spectroscopic domain, generalized Wannier-Stark states are found that are manifestations of the emf-induced localization of the states. PMID:15169431

Citrin, D S

2004-05-14

62

Magnet design for a low-emittance storage ring  

PubMed Central

The MAX?IV 3?GeV storage ring, currently under construction, pursues the goal of low electron beam emittance by using a multi-bend achromat magnet lattice, which is realised by having several consecutive magnet elements precision-machined out of a common solid iron block, 2.3–3.4?m long. With this magnet design solution, instead of having 1320 individual magnets, the MAX?IV 3?GeV storage ring is built up using 140 integrated ‘magnet block’ units, containing all these magnet elements. Major features of this magnet block design are compactness, vibration stability and that the alignment of magnet elements within each unit is given by the mechanical accuracy of the CNC machining rather than individual field measurement and adjustment. This article presents practical engineering details of implementing this magnet design solution, and mechanical + magnetic field measurement results from the magnet production series. At the time of writing (spring 2014), the production series, which is totally outsourced to industry, is roughly half way through, with mechanical/magnetic QA conforming to specifications. It is the conclusion of the authors that the MAX?IV magnet block concept, which has sometimes been described as new or innovative, is from a manufacturing point of view simply a collection of known mature production methods and measurement procedures, which can be executed at fixed cost with a low level of risk. PMID:25177980

Johansson, Martin; Anderberg, Bengt; Lindgren, Lars-Johan

2014-01-01

63

Design of the magnetic channels for the RIKEN superconducting ring cyclotron  

Microsoft Academic Search

Special designs have been adopted for the magnetic channels of the injection and extraction systems of the RIKEN Superconducting Ring Cyclotron (SRC). These magnetic channels are installed in the chambers between upper and lower coils of the sector magnets of the SRC, and superimpose additional magnetic fields on the base field of the sector magnets to inject or extract various

S. Fujishima; A. Goto; H. Okuno; Y. Yano

2002-01-01

64

Magnet designs for muon collider ring and interactions regions  

SciTech Connect

Conceptual designs of superconducting magnets for the storage ring of a Muon Collider with a 1.5 TeV c.o.m. energy and an average luminosity of 10{sup 34} cm{sup -2}s{sup -1} are presented. All magnets are based on Nb{sub 3}Sn superconductor and designed to provide an adequate operating field/field gradient in the aperture with the critical current margin required for reliable magnet operation in the machine. Magnet cross-sections were optimized to achieve the accelerator field quality in the magnet aperture occupied with beams. The magnets and corresponding protective measures are designed to handle about 0.5 kW/m of dynamic heat load from the muon beam decays. Magnet parameters are reported and compared with the requirements.

Zlobin, A.V.; Alexahin, Y.I.; Kashikhin, V.V.; Mokhov, N.V.; /Fermilab

2010-05-01

65

Nonlinear split-ring metamaterial slabs for magnetic resonance imaging  

NASA Astrophysics Data System (ADS)

This work analyzes the ability of split-ring metamaterial slabs with zero/high permeability to reject/confine the radiofrequency magnetic field in magnetic resonance imaging systems. Split-ring slabs are designed and fabricated to work in a 1.5 T system. Nonlinear elements consisting of pairs of crossed diodes are inserted in the split-rings, so that the slab permeability can be switched between a value close to unity when interacting with the strong field of the transmitting coil, and zero or high values when interacting with the weak field produced by protons in tissue. Experiments are shown where these slabs locally increase the signal-to-noise-ratio.

Lopez, Marcos A.; Freire, Manuel J.; Algarin, Jose M.; Behr, Volker C.; Jakob, Peter M.; Marqués, Ricardo

2011-03-01

66

Condenser for illuminating a ring field  

DOEpatents

A series of segments of a parent aspheric mirror having one foci at a point source of radiation and the other foci at the radius of a ring field have all but one or all of their beams translated and rotated by sets of mirrors such that all of the beams pass through the real entrance pupil of a ring field camera about one of the beams and fall onto the ring field radius as a coincident image as an arc of the ring field. 5 figs.

Sweatt, W.C.

1994-11-01

67

Single-ring magnetic cusp ion source  

NASA Astrophysics Data System (ADS)

The single-ring cusp ion source discussed in this paper was developed to provide a dc ion beam in a nonpumped D-T neutron generator. The source operates at 0.25 Pa and produces a uniform-density beam through an aperture of 1.3-cm diameter. At the standard operating voltage of 150 V and arc current of 10 A, the atomic ion content of the 200-mA deuterium ion beam is about 60%, and the ion impurity level is less than 0.5%. The ion output of the source was examined at arc currents of up to 40 A and found to be a linear function; in addition, very high D+ yields were realized. With the aid of a shielded Langmuir probe, we have determined such plasma properties as electron energy, plasma potential, floating potential, and current density throughout the volume of the source. It was observed that the plasma is effectively confined by the magnetic field and there is evidence of an electron energy filtering mechanism similar to that found in multicusp ion sources. Electron energy on the filament side of the cusp has been determined to be about 75 eV and on the aperture side about 12 eV. Since the electron impact cross section for ionizing diatomic deuterium is maximum at 75 eV and the cross section for dissociating D+2 to D+ is greatest near 12 eV, we believe that a very effective two-step ionization process accounts for the high D+ yield of the single-ring magnetic cusp source. Plasma potentials measured have values close to the voltage of the anode, and the floating potentials are seen to be directly related to electron energy values. The floating potential is near cathode voltage where electron energies are high, and close to anode voltage where electron energies are low.

Brainard, J. P.; O'Hagan, J. B.

1983-11-01

68

Generation of vortex rings by nonstationary laser wake field  

SciTech Connect

A new concept of generating quasistatic magnetic fields, vortex rings, and electron jets in an isotropic homogeneous plasma is presented. The propagation of plasma waves, generated by a relativistically intense short pulse laser, is investigated by using the kinetic model and a novel nonpotential, time-dependent ponderomotive force is derived by obtaining a hydrodynamic equation of motion. This force can in turn generate quasistatic magnetic fields, vortex rings, and electron jets. It is also shown that the vortex rings can become a means for accelerating electrons, which are initially in equilibrium. The conservation of canonical momentum circulation and the frozen-in condition for the vorticity is discussed. The excitation of the vortex waves by the modulation of the amplitude of the plasma waves is considered. These vortex waves, which generate a lower hybrid mode propagating across the generated magnetic field, are also investigated.

Tsintsadze, N.L.; Murtaza, G.; Shah, H.A. [Department of Physics, Tbilisi State University, Chavchavadze 3 (Georgia); National Centre for Mathematics, G.C. University, Lahore 54000 (Pakistan); Department of Physics, G.C. University, Lahore 54000 (Pakistan)

2006-01-15

69

Magnetic measurements on the ring dipoles and quadrupoles for the Los Alamos proton storage ring  

SciTech Connect

This paper discusses magnetic measurements and shimming performed on the ring dipoles and quadrupoles for the Los Alamos Proton Storage Ring (PSR). For the dipoles, point-by-point field maps were obtained using a search coil that could be scanned over a three-dimensional grid. By appropriate machining of removable end blocks, all magnet lengths were adjusted to within 0.01% of a nominal value and all integrated multipoles were set within tolerance. Integrated fields of 20 PSR quadrupoles were measured using a rotating ''Morgan Coil'' and a digital spectrum analyzer. The magnets were shimmed to specifications by adjusting steel bolts threaded through the field clamps. 3 refs., 5 figs., 4 tabs.

Schermer, R.I.; Blind, B.; Jason, A.J.; Sawyer, G.A.

1985-01-01

70

Low energy proton storage ring with longitudinal magnetic  

E-print Network

Low energy proton storage ring with longitudinal magnetic field and electron cooling M.I. Bryzgunov energy protons. In this particular case it is reaction for production of resonant gamma-quant (9.17 Me Electron cooling: compensates heating effects on internal target compensates energy losses on target

71

Computation of a quadrupole magnet for the APS storage ring  

SciTech Connect

The storage ring of the Advanced Photon Source will include 400 quadrupole magnets for focusing the beam. A prototype quadrupole has been designed, constructed, and measured. This paper describes the two- and three-dimensional (2-D and 3-D) field computations performed for this design. 2 refs., 6 figs., 1 tab.

Turner, L.R.; Kim, S.H.; Thompson, K.M.

1990-01-01

72

Quantitative model of the magnetospheric magnetic field  

Microsoft Academic Search

Quantitative representations of the magnetic fields associated with the magnetopause currents and the distributed currents (tail and quiet time ring currents) have been developed. These fields are used together with a dipole representation of the main field of the earth to model the total vector magnetospheric magnetic field. The model is based on quiet time data averaged over all 'tilt

W. P. Olson; K. A. Pfitzer

1974-01-01

73

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

74

Effects of two-temperature ions, magnetic field, and higher-order nonlinearity on the existence and stability of dust-acoustic solitary waves in Saturn's F ring  

SciTech Connect

Nonlinear propagation of dust-acoustic solitary waves (DASWs) in a strong magnetized dusty plasma comprising warm adiabatic variable-charged dust particles, isothermal electrons, and two-temperature ions is investigated. Applying a reductive perturbation theory, a nonlinear Zakharov-Kuznetsov (ZK) equation for the first-order perturbed potential and a linear inhomogeneous ZK-type equation for the second-order perturbed potential are derived. However, at a certain value of high-temperature ion density, the coefficient of the nonlinear terms of both ZK and ZK-type equations vanishes. Therefore, a new set of expansion physical parameters and stretched coordinates are then used to derive a modified Zakharov-Kuznetsov (mZK) equation for the first-order perturbed potential and a mZK-type equation for the second-order perturbed potential. Stationary solutions of these equations are obtained using a renormalization method. A condition for two-temperature ions assumption is examined for various cosmic dust-laden plasma systems. It is found that this condition is satisfied for Saturn's F ring. The effects of two-temperature ions, magnetic field, and higher-order nonlinearity on the behavior of the DASWs are discussed. To obtain the stability condition of the waves, a method based on energy consideration is used and the condition for stable solitons is derived.

El-Labany, S. K.; Moslem, Waleed M.; Safy, F. M. [Department of Physics, Faculty of Science-Damietta, Mansoura University, 34517 (Egypt); Department of Physics, Faculty of Education-Port Said, Suez Canal University (Egypt); Department of Physics, Faculty of Science-Damietta, Mansoura University, 34517 (Egypt)

2006-08-15

75

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

76

Exploring Magnetic Field Lines  

NSDL National Science Digital Library

In this activity, learners explore the magnetic field of a bar magnet as an introduction to understanding Earth's magnetic field. First, learners explore and play with magnets and compasses. Then, learners trace the field lines of the magnet using the compass on a large piece of paper. This activity will also demonstrate why prominences are always "loops."

2012-06-26

77

The Storage Ring Magnets of the Australian Synchrotron  

SciTech Connect

A 3 GeV Synchrotron Radiation Source is being built in Melbourne, Australia. Commissioning is foreseen in 2006. The Storage ring has a circumference of 216 m and has a 14 fold DBA structure. For the storage ring the following magnets will be installed: 28 dipoles with a field of 1.3 T, and a gradient of 3.35 T/m; 56 quadrupoles with a gradient of 18 T/m and 28 with a gradient of 10 T/m; 56 sextupoles with a strength of B'' = 350 T/m and 42 with 150 T/m. The sextupoles are equipped with additional coils for horizontal and vertical steering and for a skew quadrupole. The pole profile was determined by scaling the pole profile of the SPEAR magnets [1] to the aperture of the ASP magnets. The magnets are to be supplied by Buckley Systems Ltd in Auckland, New Zealand.

Barg, B.; Jackson, A.; LeBlanc, G.; /Melbourne U.; Huttel, E.; /Karlsruhe, Forschungszentrum; Tanabe, J.; /SLAC

2005-05-11

78

Exploring Magnetic Fields  

NSDL National Science Digital Library

This is an activity about magnetic fields. Using iron filings, learners will observe magnets in various arrangements to investigate the magnetic field lines of force. This information is then related to magnetic loops on the Sun's surface and the magnetic field of the Earth. This is the second activity in the Exploring the Earth's Magnetic Field: An IMAGE Satellite Guide to the Magnetosphere educators guide.

2012-08-03

79

Chiral transition with magnetic fields  

NASA Astrophysics Data System (ADS)

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 field and that this temperature is always above the critical temperature for the case when the magnetic field is absent.

Ayala, Alejandro; Hernández, Luis Alberto; Mizher, Ana Júlia; Rojas, Juan Cristóbal; Villavicencio, Cristián

2014-06-01

80

Magnetic edge states in Aharonov-Bohm graphene quantum rings  

SciTech Connect

The effect of electron-electron interaction on the electronic structure of Aharonov-Bohm (AB) graphene quantum rings (GQRs) is explored theoretically using the single-band tight-binding Hamiltonian and the mean-field Hubbard model. The electronic states and magnetic properties of hexagonal, triangular, and circular GQRs with different sizes and zigzag edge terminations are studied. The results show that, although the AB oscillations in the all types of nanoring are affected by the interaction, the spin splitting in the AB oscillations strongly depends on the geometry and the size of graphene nanorings. We found that the total spin of hexagonal and circular rings is zero and therefore, no spin splitting can be observed in the AB oscillations. However, the non-zero magnetization of the triangular rings breaks the degeneracy between spin-up and spin-down electrons, which produces spin-polarized AB oscillations.

Farghadan, R., E-mail: rfarghadan@kashanu.ac.ir; Heidari Semiromi, E. [Department of Physics, University of Kashan, Kashan (Iran, Islamic Republic of); Saffarzadeh, A. [Department of Physics, Payame Noor University, P.O. Box 19395-3697 Tehran (Iran, Islamic Republic of); Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A 1S6 (Canada)

2013-12-07

81

Localization for robotic capsule looped by axially magnetized permanent-magnet ring based on hybrid strategy  

PubMed Central

To actively maneuver a robotic capsule for interactive diagnosis in the gastrointestinal tract, visualizing accurate position and orientation of the capsule when it moves in the gastrointestinal tract is essential. A possible method that encloses the circuits, batteries, imaging device, etc into the capsule looped by an axially magnetized permanent-magnet ring is proposed. Based on expression of the axially magnetized permanent-magnet ring’s magnetic fields, a localization and orientation model was established. An improved hybrid strategy that combines the advantages of particle-swarm optimization, clone algorithm, and the Levenberg–Marquardt algorithm was found to solve the model. Experiments showed that the hybrid strategy has good accuracy, convergence, and real time performance. PMID:25733935

Yang, Wanan; Li, Yan; Qin, Fengqing

2015-01-01

82

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.

83

Magnetic Fields Matter  

NSDL National Science Digital Library

This lesson introduces students to the effects of magnetic fields in matter addressing permanent magnets, diamagnetism, paramagnetism, ferromagnetism, and magnetization. First students must compare the magnetic field of a solenoid to the magnetic field of a permanent magnet. Students then learn the response of diamagnetic, paramagnetic, and ferromagnetic material to a magnetic field. Now aware of the mechanism causing a solid to respond to a field, students learn how to measure the response by looking at the net magnetic moment per unit volume of the material.

2014-09-18

84

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

85

Visualizing Magnetic Field Lines  

NSDL National Science Digital Library

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

VU Bioengineering RET Program, School of Engineering,

86

What are Magnetic Fields?  

NSDL National Science Digital Library

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

2012-08-03

87

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

88

Tuning of exciton states in a magnetic quantum ring  

NASA Astrophysics Data System (ADS)

The exciton states in a CdTe quantum ring subjected to an external magnetic field containing a single magnetic impurity are investigated. We have used the multiband approximation which includes the heavy hole-light hole coupling effects. The electron-hole spin interactions and the s, p-d interactions between the electron, the hole and the magnetic impurity are also included. The exciton energy levels and optical transitions are evaluated using the exact diagonalization scheme. We show that due to the spin interactions it is possible to change the bright exciton state into the dark state and vice versa with the help of a magnetic field. We propose a new route to experimentally estimate the s, p-d spin interaction constants.

Ghazaryan, Areg; Manaselyan, Aram; Chakraborty, Tapash

2015-02-01

89

Mapping Magnetic Fields  

NSDL National Science Digital Library

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

2012-08-03

90

Hydrostatic pressure, impurity position and electric and magnetic field effects on the binding energy and photo-ionization cross section of a hydrogenic donor impurity in an InAs Pöschl-Teller quantum ring  

NASA Astrophysics Data System (ADS)

Using the variational method and the effective mass and parabolic band approximations, the behaviour of the binding energy and photo-ionization cross section of a hydrogenic-like donor impurity in an InAs quantum ring, with Pöschl-Teller confinement potential along the axial direction, has been studied. In the investigation, the combined effects of hydrostatic pressure and electric and magnetic fields applied in the direction of growth have been taken into account. Parallel polarization of the incident radiation and several values of the applied electric and magnetic fields, hydrostatic pressure, and parameters of the Pöschl-Teller confinement potential were considered. The results obtained can be summarised as follows: (1) the influence of the applied electric and magnetic fields and the asymmetry degree of the Pöschl-Teller confinement potential on the donor binding energy is strongly dependent on the impurity position along the growth and radial directions of the quantum ring, (2) the binding energy is an increasing function of hydrostatic pressure and (3) the decrease (increase) in the binding energy with the electric and magnetic fields and parameters of the confinement potential (hydrostatic pressure) leads to a red shift (blue shift) of the maximum of the photo-ionization cross section spectrum of the on-centre impurity.

Barseghyan, M. G.; Mora-Ramos, M. E.; Duque, C. A.

2011-11-01

91

The Declining Magnetic Field  

NSDL National Science Digital Library

This is an activity about the declining strength of Earth's magnetic field. Learners will review a graph of magnetic field intensity and calculate the amount by which the field has changed its intensity in the last century, the rate of change of its intensity, and when the field should decrease to zero strength at the current rate of change. Learners will also use evidence from relevant sources to create a conjecture on the effects on Earth of a vanished magnetic field. Access to information sources about Earth's magnetic field strength is needed for this activity. This is Activity 7 in the Exploring Magnetism on Earth teachers guide.

92

A volume birdcage coil with an adjustable sliding tuner ring for neuroimaging in high field vertical magnets: Ex and in vivo applications at 21.1 T  

NASA Astrophysics Data System (ADS)

A tunable 900 MHz transmit/receive volume coil was constructed for 1H MR imaging of biological samples in a 21.1 T vertical bore magnet. To accommodate a diverse range of specimen and RF loads at such a high frequency, a sliding-ring adaptation of a low-pass birdcage was implemented through simultaneous alteration of distributed capacitance. To make efficient use of the constrained space inside the vertical bore, a modular probe design was implemented with a bottom-adjustable tuning and matching apparatus. The sliding ring coil displays good homogeneity and sufficient tuning range for different samples of various dimensions representing large span of RF loads. High resolution in vivo and ex vivo images of large rats (up to 350 g), mice and human postmortem tissues were obtained to demonstrate coil functionality and to provide examples of potential applications at 21.1 T.

Qian, Chunqi; Masad, Ihssan S.; Rosenberg, Jens T.; Elumalai, Malathy; Brey, William W.; Grant, Samuel C.; Gor'kov, Peter L.

2012-08-01

93

A volume birdcage coil with an adjustable sliding tuner ring for neuroimaging in high field vertical magnets: ex and in vivo applications at 21.1 T  

PubMed Central

A tunable 900 MHz transmit/receive volume coil was constructed for 1H MR imaging of biological samples in a 21.1 T vertical bore magnet. To accommodate a diverse range of specimen and RF loads at such a high frequency, a sliding-ring adaptation of a low-pass birdcage was implemented through simultaneous alteration of distributed capacitance. To make efficient use of the constrained space inside the vertical bore, a modular probe design was implemented with a bottom-adjustable tuning and matching apparatus. The sliding ring coil displays good homogeneity and sufficient tuning range for different samples of various dimensions representing large span of RF loads. High resolution in vivo and ex vivo images of large rats (up to 350 g), mice and human postmortem tissues were obtained to demonstrate coil functionality and to provide examples of potential applications at 21.1 T. PMID:22750638

Qian, Chunqi; Masad, Ihssan S.; Rosenberg, Jens T.; Elumalai, Malathy; Brey, William W.; Grant, Samuel C.; Gor’kov, Peter L.

2012-01-01

94

Large magnetic storage ring for Bose-Einstein condensates  

SciTech Connect

Cold atomic clouds and Bose-Einstein condensates have been stored in a 10 cm diameter vertically oriented magnetic ring. An azimuthal magnetic field enables low-loss propagation of atomic clouds over a total distance of 2 m, with a heating rate of less than 50 nK/s. The vertical geometry was used to split an atomic cloud into two counter-rotating clouds which were recombined after one revolution. The system will be ideal for studying condensate collisions and ultimately Sagnac interferometry.

Arnold, A. S.; Garvie, C. S.; Riis, E. [Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom)

2006-04-15

95

The Magnetic and Shielding Effects of Ring Current on Radiation Belt Dynamics  

NASA Technical Reports Server (NTRS)

The ring current plays many key roles in controlling magnetospheric dynamics. A well-known example is the magnetic depression produced by the ring current, which alters the drift paths of radiation belt electrons and may cause significant electron flux dropout. Little attention is paid to the ring current shielding effect on radiation belt dynamics. A recent simulation study that combines the Comprehensive Ring Current Model (CRCM) with the Radiation Belt Environment (RBE) model has revealed that the ring current-associated shielding field directly and/or indirectly weakens the relativistic electron flux increase during magnetic storms. In this talk, we will discuss how ring current magnetic field and electric shielding moderate the radiation belt enhancement.

Fok, Mei-Ching

2012-01-01

96

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.

Jeffrey Barker

97

Drawing Magnetic Fields  

NSDL National Science Digital Library

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

2014-09-18

98

Electricity and Magnetic Fields  

NSDL National Science Digital Library

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

VU Bioengineering RET Program,

99

Localization for robotic capsule looped by axially magnetized permanent-magnet ring based on hybrid strategy.  

PubMed

To actively maneuver a robotic capsule for interactive diagnosis in the gastrointestinal tract, visualizing accurate position and orientation of the capsule when it moves in the gastrointestinal tract is essential. A possible method that encloses the circuits, batteries, imaging device, etc into the capsule looped by an axially magnetized permanent-magnet ring is proposed. Based on expression of the axially magnetized permanent-magnet ring's magnetic fields, a localization and orientation model was established. An improved hybrid strategy that combines the advantages of particle-swarm optimization, clone algorithm, and the Levenberg-Marquardt algorithm was found to solve the model. Experiments showed that the hybrid strategy has good accuracy, convergence, and real time performance. PMID:25733935

Yang, Wanan; Li, Yan; Qin, Fengqing

2015-01-01

100

Magnetic fields at Neptune  

Microsoft Academic Search

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

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

1989-01-01

101

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) Opposite magnetic poles attract like magnetic poles repel #12;Like the electric field lines

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

102

Magnetic Field Problem  

NSDL National Science Digital Library

The above animations represent two typical bar magnets each with a North and South pole. The arrows represent the direction of the magnetic field. The color of the arrows represents the magnitude of the field with magnitude increasing as the color changes from blue to green to red to black. You may drag either magnet and double-click anywhere inside the animation to add a magnetic field line, and mouse-down to read the magnitude of the magnetic field at that point.

Wolfgang Christian

103

Artificial magnetism and left-handed media from dielectric rings and rods.  

PubMed

It is shown that artificial magnetism with relatively large frequency bandwidth can be obtained from periodic arrangements of dielectric rings. Combined with dielectric rods, dielectric rings can provide 3D isotropic left-handed metamaterials which are an advantageous alternative to metallic split ring resonators (SRRs) and/or metallic wires when undetectability by low frequency external magnetic fields is desired. Furthermore it is shown that, unlike conventional SRRs, dielectric rings can also be combined with natural plasma-like media to obtain a left-handed metamaterial. PMID:21386264

Jelinek, L; Marqués, R

2010-01-20

104

Artificial magnetism and left handed media from dielectric rings and rods  

E-print Network

It is shown that artificial magnetism with relatively large frequency bandwidth can be obtained from periodic arrangements of dielectric rings. Combined with dielectric rods, dielectric rings can provide 3D isotropic left-handed metamaterials being an advantageous alternative to metallic split ring resonators and/or metallic wires when un-detectability by low frequency external magnetic fields is desired. Furthermore it is shown that dielectric rings can be also combined with natural plasma-like media to obtain a left-handed metamaterial.

Jelinek, L

2009-01-01

105

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.

2012-08-03

106

Mapping Magnetic Fields  

NSDL National Science Digital Library

This is an activity about magnetism. Using bar magnets, classroom materials, and a compass, learners will explore how bar magnets interact with one another and with other materials, use a compass to find the direction north, and use various materials to make magnetic field lines visible around a bar magnet. This is an activity in a larger poster resource, entitled The Sun Like It's Never Been Seen Before: In 3D.

107

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.

Windows to the Universe

1997-12-03

108

Asymmetric dipolar ring  

DOEpatents

A device having a dipolar ring surrounding an interior region that is disposed asymmetrically on the ring. The dipolar ring generates a toroidal moment switchable between at least two stable states by a homogeneous field applied to the dipolar ring in the plane of the ring. The ring may be made of ferroelectric or magnetic material. In the former case, the homogeneous field is an electric field and in the latter case, the homogeneous field is a magnetic field.

Prosandeev, Sergey A. (Fayetteville, AR); Ponomareva, Inna V. (Tampa, FL); Kornev, Igor A. (Ill-de-France, FR); Bellaiche, Laurent M. (Fayetteville, AR)

2010-11-16

109

Interaction Magnetic Force Calculation of Ring Permanent Magnets Using Ampere's Microscopic Surface Currents and Discretization Technique  

Microsoft Academic Search

Calculation of the interaction magnetic force between two ring permanent magnets of trapezoidal cross-section and a ring permanent magnet above the infinite linear magnetic plane is presented in this article. The simple and fast analytical approach is used for these calculations based on the distribution of microscopic surface Ampere's currents and the discretization technique. The results for the interaction magnetic

Ana N. Vu?kovi?; Saša S. Ili?; Slavoljub R. Aleksi?

2012-01-01

110

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

111

Photodetachment in magnetic fields  

Microsoft Academic Search

The behavior of the photodetachment cross section, near threshold, for atomic negative ioris in a magnetic field is described and illustrated with data on photodetachment of electrons from negative sulfur ions. The effect of the final state interaction is discussed and the photodetachment of atomic negative ions in a magnetic field is compared to photoionization of neutral atoms in a

D. J. Larson; R. Stoneman

1982-01-01

112

THE INTERPLANETARY MAGNETIC FIELD  

Microsoft Academic Search

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

V. A. BAILEY

1963-01-01

113

Magnetic field line Hamiltonian  

SciTech Connect

The magnetic field line Hamiltonian and the associated canonical form for the magnetic field are important concepts both for understanding toroidal plasma physics and for practical calculations. A number of important properties of the canonical or Hamiltonian representation are derived and their importance is explained.

Boozer, A.H.

1984-03-01

114

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

115

Cosmological magnetic fields  

E-print Network

Magnetic fields are observed not only in stars, but in galaxies, clusters, and even high redshift Lyman-alpha systems. In principle, these fields could play an important role in structure formation and also affect the anisotropies in the cosmic microwave background radiation (CMB). The study of cosmological magnetic fields aims not only to quantify these effects on large-scale structure and the CMB, but also to answer one of the outstanding puzzles of modern cosmology: when and how do magnetic fields originate? They are either primordial, i.e. created before the onset of structure formation, or they are generated during the process of structure formation itself.

Roy Maartens

2000-07-24

116

Interplanetary Magnetic Field Lines  

NSDL National Science Digital Library

This web page, authored and curated by David P. Stern, 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.

Mendez, J.

117

The Earth's Magnetic Field  

NSDL National Science Digital Library

The magnetic field of the Earth is contained in a region called the magnetosphere. The magnetosphere prevents most of the particles from the sun, carried in solar wind, from hitting the Earth. This site, produced by the University Corporation for Atmospheric Research (UCAR), uses text, scientific illustrations,and remote imagery to explain the occurrence and nature of planetary magnetic fields and magnetospheres, how these fields interact with the solar wind to produce phenomena like auroras, and how magnetic fields of the earth and other planets can be detected and measured by satellite-borne magnetometers.

118

DISCUSSION ABOUT THE ANALYTICAL CALCULATION OF THE MAGNETIC FIELD CREATED BY PERMANENT MAGNETS  

Microsoft Academic Search

This paper presents an improvement of the calculation of the magnetic field components created by ring permanent magnets. The three-dimensional approach taken is based on the Coulombian Model. Moreover, the magnetic field components are calculated without using the vector potential or the scalar potential. It is noted that all the expressions given in this paper take into account the magnetic

Romain Ravaud; Guy Lemarquand; Valerie Lemarquand; Claude Depollier

2009-01-01

119

Equilibrium of a system of superconducting rings in a uniform gravitational field  

NASA Astrophysics Data System (ADS)

To construct a plasma trap with levitating magnetic coils in the thin ring approximation, we derive the expression for the potential energy of a system of several superconducting rings (one of which is fixed) capturing the preset flows in the uniform gravitational field as a function of the coordinates of the free ring (or rings). Calculations performed in the Mathcad system show that the potential energy of such a system has a local minimum for certain values of parameters. Stable levitation of a superconducting ring in the position corresponding to calculations is realized in the field of another superconducting ring, and this leads to the conclusion that a magnetic Galatea trap can be prepared on the basis of a levitating quadrupole.

Bishaev, A. M.; Bush, A. A.; Gavrikov, M. B.; Gordeev, I. S.; Denisyuk, A. I.; Kamentsev, K. E.; Kozintseva, M. V.; Savel'ev, V. V.; Sigov, A. S.

2013-05-01

120

Sources of Magnetic Field Magnetic Phenomena  

E-print Network

push on currents Moving charges can make and feel magnetic forces. We don't understand how permanent will consider the last piece of the puzzle in electromagnetic - changing magnetic fields can make induction. 15Lecture 9 Sources of Magnetic Field 1 Magnetic Phenomena 1. Magnets can push on each other (and

Tobar, Michael

121

Colloidal ribbons and rings from Janus magnetic rods  

NASA Astrophysics Data System (ADS)

Dipolar particles are fundamental building blocks in nature and technology, yet the effect of particle anisotropy is seldom explored. Here, we fabricate colloidal silica rods coated with a hemicylindrical magnetic layer to satisfy multiple criteria: nearly monodisperse, easily imaged and magnetic interaction that dominates over gravity. We confirm long-predicted features of dipolar assembly and stress the microstructural variety brought about by shape and constituent anisotropy, especially by extrapolating knowledge learned from literal molecules. In this colloidal system, we describe analogies to liquid crystalline deformations with bend, splay and twist; an analogy to cis/trans isomerism in organic molecules, which in our system can be controllably and reversibly switched; and a field-switching methodology to direct single ribbons into not only single but also multiple rings that can subsequently undergo hierarchical self-assembly. We highlight subtle material issues of control and design rules for reconfigurable dipolar materials with building blocks of complex shape.

Yan, Jing; Chaudhary, Kundan; Chul Bae, Sung; Lewis, Jennifer A.; Granick, Steve

2013-02-01

122

Size effects on switching field of ring-shaped permalloy elements  

Microsoft Academic Search

The magnetization switching behavior of permalloy ring elements as a function of ring diameter and film thickness by magnetoresistance measurement is presented. The permalloy ring elements, with diameters of 2–5?m and a thickness of 14–66nm, were fabricated by electron beam lithography through a lift-off process. The switching field for the transition from the vortex state to the onion state increases

C. C. Chang; Y. C. Chang; J. C. Wu; Z. H. Wei; M. F. Lai; J. H. Kuo

2004-01-01

123

Mapping Magnetic Field Lines  

NSDL National Science Digital Library

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

2012-08-03

124

The Magnet Lattice of the MAX IV Storage Rings  

NASA Astrophysics Data System (ADS)

A successor of the present MAX facility is currently being studied. This proposed MAX IV facility will then have two new storage rings operated at 1.5 and 3 GeV respectively. The magnet lattices of the two storage rings are almost identical and the rings are placed coaxially, one on top of the other. A third ring, the MAX III ring, now under construction, should be transferred to the new facility. These three rings will then offer dipole IR radiation and undulator radiation from 5 eV up to 20 keV. The total number of straight sections is 32, of which 28 could be used for insertion devices. A 3 GeV linear accelerator will be used as injector for the three rings. The linac could also be used as a Free Electron Laser source. The magnet lattice of the two new rings is described below. The electron beam emittance of the 3 GeV storage ring is 0.86 nm rad and 0.3 nm rad for the 1.5 GeV ring. The circumference of the rings is 286 m..

Eriksson, M.; Lindgren, L.-J.; Tarawneh, H.

2004-05-01

125

The First Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

Widrow, Lawrence M.; Ryu, Dongsu; Schleicher, Dominik R. G.; Subramanian, Kandaswamy; Tsagas, Christos G.; Treumann, Rudolf A.

2012-05-01

126

Experimental investigations of the change with magnetic flux of quantum number in superconducting ring  

E-print Network

The magnetic dependencies of the critical current of aluminum ring with asymmetric link-up of current leads have been measured in order to clear up the essence of the paradoxical absence of the jump of the critical current at the quantum number change revealed before at the measurements of asymmetric superconducting ring. The measurements have shown that the experimental and theoretical dependencies agree in the region of magnetic field corresponding to integer numbers of the flux quantum and disagree at the half of the flux quantum. The jump is not observed as well as in the asymmetric rings.

A. V. Burlakov; V. L. Gurtovoi; A. I. Ilin; A. V. Nikulov; V. A. Tulin

2011-03-16

127

Magnetic field dosimeter development  

SciTech Connect

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

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

1980-09-01

128

FEM Computation of Magnetic Fields in Anisotropic Magnetic Materials  

NASA Astrophysics Data System (ADS)

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

Kameari, Akihisa; Fujiwara, Koji

129

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

130

Magnetic Structure, Magnetization Reversal and Spin Dynamics of Micron-sized Permalloy Ring  

Microsoft Academic Search

The magnetic ring structure is currently of great interest due to its potential application for magnetic storage and sensors [1]. In this talk, we present a study of 2 mum sized Permalloy rings on 25 nm SiN membrane prepared by electron beam lithography. The magnetic structures are examined by Lorentz microscopy. The Lorentz microscopy images indicate that the demagnetized state

Xiaobin Zhu; Zhigang Liu; Marek Malac; Hui Qian; Mark Freeman; Vitali Metlushko; Bojan Ilic

2004-01-01

131

Elliptical torii in a constant magnetic field  

E-print Network

The Schrodinger equation for an electron on the surface of an elliptical torus in the presence of a constant azimuthally symmetric magnetic field is developed. The single particle spectrum and eigenfunctions as a function of magnetic flux through the torus are determined and it is shown that inclusion of the geometric potential is necessary to recover the limiting cases of vertical strip and flat ring structures.

M. Encinosa; M. Jack

2005-09-23

132

Vortex formation in magnetic narrow rings  

Microsoft Academic Search

Underlying the current interest in magnetic elements is the possibility such systems provide both for the study of fundamental phenomena in magnetism (such as domain wall trapping and spin switching) and for technological applications, such as high density magnetic storage or magnetic random access memories (MRAM). One key issue is to control the magnetic switching precisely. To achieve this one

J. A. C. Bland

2002-01-01

133

Magnetic Field Problem: Current  

NSDL National Science Digital Library

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

Wolfgang Christian

134

Magnetic Field Solver  

NASA Technical Reports Server (NTRS)

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

Ilin, Andrew V.

2006-01-01

135

Transverse Field Profile of the NLC Damping Rings Eletromagnet Wiggler (LCC-0038)  

SciTech Connect

The primary effort for damping ring wiggler studies has been to develop a credible radiation hard electromagnet wiggler conceptual design that meets NLC main electron and positron damping ring physics requirements [1]. Based upon an early assessment of requirements, a hybrid magnet similar to existing designs satisfies basic requirements. However, radiation damage is potentially a serious problem for the Nd-Fe-B permanent magnet material, and cost remains an issue for samarium cobalt magnets. Superconducting magnet designs have not been pursued due to their increased complexity and our unfamiliarity with the technology. Having produced and developed an electromagnet design, we now find that the transverse field roll-off is severe, and recognizing similar experience with beamline 11 at SSRL we believe that the resulting beam quality will not meet the damping ring requirements. We therefore propose, in parallel with more detailed optics studies of the wiggler field requirements, to revisit the hybrid permanent magnet design.

Ross, M

2004-03-19

136

Fabrication and Characterization of Microstructured Magnetic Tunnel Junction Rings  

Microsoft Academic Search

Microstructured magnetic tunnel junction rings have been fabricated by a top-down technique combining electron beam lithography and ion milling process. Four-terminal magnetoresistance measurements and magnetic force microscopy were used to successfully explore a four-transition process within the free layer throughout the magnetization reversal. Various magnetization configurations were identified to be the onion state, vortex-pair state, vortex state, vortex-core state, and

C. C. Chen; C. C. Chang; C. Y. Kuo; Lance Horng; J. C. Wu; Teho Wu; G. Chern; C. Y. Huang; M. Takahashi; M. Takahashi

2006-01-01

137

Non-Linear Magnetic Ringing of Spin-Ordered Solid He-3  

E-print Network

PHYSICAL REVIE%' B VOLUME 24, NUMBER 5 1 SEPTEMBER 1981 Nonlinear magnetic ringing of spin-ordered solid He Chia-Ren Hu and Thomas E. Ham Departn~ent of'Physics, Texas 3 c6 M University, College Station, Texas 77843 (Received 24 October 1980...) Exact and complete solution is presented on the nonlinear longitudinal magnetic ringing of spin-ordered bcc He ensuing on the complete switchoff of a dc magnetic field H]. The theory is based on the set of dynamic equations proposed by Osheroff et al...

Hu, Chia-Ren; HAM, TE.

1981-01-01

138

The Sun and Magnetic Fields  

NSDL National Science Digital Library

In this activity about magnetic fields and their relation to the Sun, learners will simulate sunspots by using iron filings to show magnetic fields around a bar or cow magnet, and draw the magnetic field surrounding two dipole magnets, both in parallel and perpendicular alignments. Finally, learners examine images of sunspots to relate their magnetic field drawings and observations to what is seen on the Sun.

139

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

140

DEGRADATION OF MAGNET EPOXY AT NSLS X-RAY RING.  

SciTech Connect

Epoxy resin degradation was analyzed for NSLS X-ring magnets after two decades of 2.58-2.8 GeV continuous electron-beam operation, based on results obtained from thermoluminescent dosimeters irradiated along the NSLS ring and epoxy samples irradiated at the beamline target location. A Monte Carlo-based particle transport code, MCNP, was utilized to verify the dose from synchrotron radiation distributed along the axial- and transverse-direction in a ring model, which simulates the geometry of a ring quadrupole magnet and its central vacuum chamber downstream of the bending-magnet photon ports. The actual life expectancy of thoroughly vacuum baked-and-cured epoxy resin was estimated from radiation tests on similar polymeric materials using a radiation source developed for electrical insulation and mechanical structure studies.

HU,J.P.; ZHONG,Z.; HAAS,E.; HULBERT,S.; HUBBARD,R.

2004-05-24

141

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.

142

Multiwavelength Magnetic Field Modeling  

NASA Astrophysics Data System (ADS)

We model the large-scale Galactic magnetic fields, including a spiral arm compression to generate anisotropic turbulence, by comparing polarized synchrotron and thermal dust emission. Preliminary results show that in the outer Galaxy, the dust emission comes from regions where the fields are more ordered than average while the situation is reversed in the inner Galaxy. We will attempt in subsequent work to present a more complete picture of what the comparison of these observables tells us about the distribution of the components of the magnetized ISM and about the physics of spiral arm shocks and turbulence.

Jaffe, T. R.

2015-03-01

143

Magnetic Fields in Galaxies  

NASA Astrophysics Data System (ADS)

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

Beck, Rainer

144

Ring Formation in Magnetically Subcritical Clouds and Multiple Star Formation  

E-print Network

We study numerically the ambipolar diffusion-driven evolution of non-rotating, magnetically subcritical, disk-like molecular clouds, assuming axisymmetry. Previous similar studies have concentrated on the formation of single magnetically supercritical cores at the cloud center, which collapse to form isolated stars. We show that, for a cloud with many Jeans masses and a relatively flat mass distribution near the center, a magnetically supercritical ring is produced instead. The supercritical ring contains a mass well above the Jeans limit. It is expected to break up, through both gravitational and possibly magnetic interchange instabilities, into a number of supercritical dense cores, whose dynamic collapse may give rise to a burst of star formation. Non-axisymmetric calculations are needed to follow in detail the expected ring fragmentation into multiple cores and the subsequent core evolution. Implications of our results on multiple star formation in general and the northwestern cluster of protostars in the Serpens molecular cloud core in particular are discussed.

Zhi-Yun Li

2001-05-02

145

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

146

Sector magnets for the RIKEN superconducting ring cyclotron  

Microsoft Academic Search

The sector magnets of the K2500-MeV superconducting ring cyclotron (SRC), which is under construction for the RIKEN RI beam factory, are described. The SRC consists of six sector magnets, four rf resonators, etc. each sector magnet is 7.2 m in length and 6 m in height and 800 t (metric ton) in weight; the sector angle is 25 deg. The

A. Goto; H. Okuno; J. Ohnishi; T. Tominaka; S. Fujishima; K. Ikegami; N. Fukunishi; Y. Miyazawa; T. Mitsumoto; Y. Yano

2004-01-01

147

Magnetization reversal and dynamics in non-interacting NiFe mesoscopic ring arrays  

NASA Astrophysics Data System (ADS)

The dynamics of magnetization (M) reversal and relaxation as a function of temperature (T) are reported in three non-interacting NiFe ring arrays having fixed ring outer diameter and varying widths. Additionally, the dependence of M(H) loop on the angle (?) between magnetic field (H) and the plane of the rings is addressed. The M(H) loops show a double step transition from onion state (OS) to vortex state (VS) at all temperatures (T = 3 to 300 K) and angles (? = 0 to 90°). The critical reversal fields HC1 (OS to VS) and HC2 (VS to OS) show a pronounced dependence on T, ring width, and ?. Estimation of the transverse and vortex domain wall energies reveals that the latter is favored in the OS. The OS is also the remanent state in the smallest rings and decays with the effective energy scale (U0/T) of 50 and 32 meV/K at 10 and 300 K, respectively. The robust in-plane anisotropy of magnetization of ring assemblies is established by scaling the M(H) with ?.

Kaur, M.; Husale, S.; Varandani, D.; Gupta, A.; Senguttuvan, T. D.; Mehta, B. R.; Budhani, R. C.

2014-04-01

148

Equilibrium and stability studies of plasmas confined in a dipole magnetic field using magnetic measurements  

E-print Network

The Levitated Dipole Experiment (LDX) is the first experiment of its kind to use a levitated current ring to confine a plasma in a dipole magnetic field. Unlike most other confinement devices, plasma compressibility ...

Karim, Ishtak

2007-01-01

149

Evolution of Stellar Magnetic Fields  

NASA Astrophysics Data System (ADS)

Stellar magnetic fields can reliably be characterized by several magnetic activity indicators, such as X-ray or radio luminosity. Physical processes leading to such emission provide important information on dynamic processes in stellar atmospheres and magnetic structuring.

Güdel, Manuel

2015-03-01

150

Magnetic Fields and Forces in Permanent Magnet Levitated Bearings  

Microsoft Academic Search

Magnetic fields and magnetic forces from magnetic bearings made of circular Halbach permanent-magnet arrays are computed and analyzed. The magnetic fields are calculated using superposition of fields due to patches of magnetization charge at surfaces where the magnetization is discontinuous. The magnetic force from the magnetic bearing is computed using superposition of forces on each patch of magnetization charge. The

Kevin D. Bachovchin; James F. Hoburg; Richard F. Post

2012-01-01

151

Magnetic field of the Earth  

NASA Astrophysics Data System (ADS)

The magnetic field of the Earth has global meaning for a life on the Earth. The world geophysical science explains: - occurrence of a magnetic field of the Earth it is transformation of kinetic energy of movements of the fused iron in the liquid core of Earth - into the magnetic energy; - the warming up of a kernel of the Earth occurs due to radioactive disintegration of elements, with excretion of thermal energy. The world science does not define the reasons: - drift of a magnetic dipole on 0,2 a year to the West; - drift of lithospheric slabs and continents. The author offers: an alternative variant existing in a world science the theories "Geodynamo" - it is the theory « the Magnetic field of the Earth », created on the basis of physical laws. Education of a magnetic field of the Earth occurs at moving the electric charge located in a liquid kernel, at rotation of the Earth. At calculation of a magnetic field is used law the Bio Savara for a ring electric current: dB = . Magnetic induction in a kernel of the Earth: B = 2,58 Gs. According to the law of electromagnetic induction the Faradey, rotation of a iron kernel of the Earth in magnetic field causes occurrence of an electric field Emf which moves electrons from the center of a kernel towards the mantle. So of arise the radial electric currents. The magnetic field amplifies the iron of mantle and a kernel of the Earth. As a result of action of a radial electric field the electrons will flow from the center of a kernel in a layer of an electric charge. The central part of a kernel represents the field with a positive electric charge, which creates inverse magnetic field Binv and Emfinv When ?mfinv = ?mf ; ?inv = B, there will be an inversion a magnetic field of the Earth. It is a fact: drift of a magnetic dipole of the Earth in the western direction approximately 0,2 longitude, into a year. Radial electric currents a actions with the basic magnetic field of a Earth - it turn a kernel. It coincides with laws of electromagnetism. According to a rule of the left hand: if the magnetic field in a kernel is directed to drawing, electric current are directed to an axis of rotation of the Earth, - a action of force clockwise (to West). Definition of the force causing drift a kernel according to the law of Ampere F = IBlsin. Powerful force 3,5 × 1012 Nyton, what makes drift of the central part of a kernel of the Earth on 0,2 the longitude in year to West, and also it is engine of the mechanism of movement of slabs together with continents. Movement of a core of the Earth carry out around of a terrestrial axis one circulation in the western direction in 2000 of years. Linear speed of rotation of a kernel concerning a mantle on border the mantle a kernel: V = × 3,471 × 10 = 3,818 × 10 m/s = 33 m/day = 12 km/years. Considering greater viscosity of a mantle, the powerful energy at rotation of a kernel seize a mantle and lithospheric slabs and makes their collisions as a result of which there are earthquakes and volcano. Continents Northern and Southern America every year separate from the Europe and Africa on several centimeters. Atlantic ocean as a result of movement of these slabs with such speed was formed for 200 million years, that in comparison with the age of the Earth - several billions years, not so long time. Drift of a kernel in the western direction is a principal cause of delay of speed of rotation of the Earth. Flow of radial electric currents allot according to the law of Joule - Lenz, the quantity of warmth : Q = I2Rt = IUt, of thermal energy 6,92 × 1017 calories/year. This defines heating of a kernel and the Earth as a whole. In the valley of the median-Atlantic ridge having numerous volcanos, the lava flow constantly thus warm up waters of Atlantic ocean. It is a fact the warm current Gulf Stream. Thawing of a permafrost and ices of Arctic ocean, of glaciers of Greenland and Antarctica is acknowledgement: the warmth of earth defines character of thawing of glaciers and a permafrost. This is a global warming. The version of the author: the period

Popov, Aleksey

2013-04-01

152

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 ...

Mrs. Merritt

2005-10-18

153

Modeling of Axial Magnetic Force and Stiffness of Ring-Shaped Permanent-Magnet Passive Vibration Isolator and Its Vibration Isolating Experiment  

Microsoft Academic Search

Magnetic suspension vibration isolators have attracted more and more attention in the field of semiconductor industry and high precision equipments. A novel ring-shaped permanent-magnet passive vibration isolator is mainly reported in this paper. An analytical expression of axial magnetic force of the isolator is derived and validated by the finite element analysis and experiment. It proves that the analytical expression

Yu Zhu; Qiang Li; Dengfeng Xu; Ming Zhang

2012-01-01

154

Crustal Magnetic Fields  

NASA Technical Reports Server (NTRS)

Cosmos 49, Polar Orbit Geophysical Observatory (POGO) (Orbiting Geophysical Observatory (OGO-2, 4 and 6)) and Magsat have been the only low-earth orbiting satellites to measure the crustal magnetic field on a global scale. These missions revealed the presence of long- wavelength (> 500 km) crustal anomalies predominantly located over continents. Ground based methods were, for the most part, unable to record these very large-scale features; no doubt due to the problems of assembling continental scale maps from numerous smaller surveys acquired over many years. Questions arose as to the source and nature of these long-wave length anomalies. As a result there was a great stimulant given to the study of the magnetic properties of the lower crust and upper mantle. Some indication as to the nature of these deep sources has been provided by the recent results from the deep crustal drilling programs. In addition, the mechanism of magnetization, induced or remanent, was largely unknown. For computational ease these anomalies were considered to result solely from induced magnetization. However, recent results from Mars Orbiter Laser Altimeter (MOLA), a magnetometer-bearing mission to Mars, have revealed crustal anomalies with dimensions similar to the largest anomalies on Earth. These Martian features could only have been produced by remanent magnetization, since Mars lacks an inducing field. The origin of long-wavelength crustal anomalies, however, has not been completely determined. Several large crustal magnetic anomalies (e.g., Bangui, Kursk, Kiruna and Central Europe) will be discussed and the role of future satellite magnetometer missions (Orsted, SUNSAT and Champ) in their interpretation evaluated.

Taylor, Patrick T.; Ravat, D.; Frawley, James J.

1999-01-01

155

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

156

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

157

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

158

Magnetic Field Problem: Current and Magnets  

NSDL National Science Digital Library

The above animations represent two typical bar magnets each with a North and South pole. The arrows represent the direction of the magnetic field. A wire is placed between the magnets and a current that comes out of the page can be turned on.

Wolfgang Christian

159

Probing Magnetic Fields With SNRs  

NASA Astrophysics Data System (ADS)

As supernova remnants (SNRs) expand, their shock waves freeze in and compress magnetic field lines they encounter; consequently we can use SNRs as magnifying glasses for interstellar magnetic fields. A simple model is used to derive polarization and rotation measure (RM) signatures of SNRs. This model is exploited to gain knowledge about the large-scale magnetic field in the Milky Way. Three examples are given which indicate a magnetic anomaly, an azimuthal large-scale magnetic field towards the anti-centre, and a chimney that releases magnetic energy from the plane into the halo.

Kothes, Roland

2015-03-01

160

The Galactic Magnetic Field  

NASA Astrophysics Data System (ADS)

With this Letter, we complete our model of the Galactic magnetic field (GMF), by using the WMAP7 22 GHz total synchrotron intensity map and our earlier results to obtain a 13-parameter model of the Galactic random field, and to determine the strength of the striated random field. In combination with our 22-parameter description of the regular GMF, we obtain a very good fit to more than 40,000 extragalactic Faraday rotation measures and the WMAP7 22 GHz polarized and total intensity synchrotron emission maps. The data call for a striated component to the random field whose orientation is aligned with the regular field, having zero mean and rms strength ?20% larger than the regular field. A noteworthy feature of the new model is that the regular field has a significant out-of-plane component, which had not been considered earlier. The new GMF model gives a much better description of the totality of data than previous models in the literature.

Jansson, Ronnie; Farrar, Glennys R.

2012-12-01

161

THE GALACTIC MAGNETIC FIELD  

SciTech Connect

With this Letter, we complete our model of the Galactic magnetic field (GMF), by using the WMAP7 22 GHz total synchrotron intensity map and our earlier results to obtain a 13-parameter model of the Galactic random field, and to determine the strength of the striated random field. In combination with our 22-parameter description of the regular GMF, we obtain a very good fit to more than 40,000 extragalactic Faraday rotation measures and the WMAP7 22 GHz polarized and total intensity synchrotron emission maps. The data call for a striated component to the random field whose orientation is aligned with the regular field, having zero mean and rms strength Almost-Equal-To 20% larger than the regular field. A noteworthy feature of the new model is that the regular field has a significant out-of-plane component, which had not been considered earlier. The new GMF model gives a much better description of the totality of data than previous models in the literature.

Jansson, Ronnie; Farrar, Glennys R. [Center for Cosmology and Particle Physics, Department of Physics, New York University, New York, NY 10003 (United States)

2012-12-10

162

The Martian magnetic field  

NASA Technical Reports Server (NTRS)

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

Russell, C. T.

1979-01-01

163

Electric and magnetic fields  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

164

Fabrication of high density magnetic structures and observation of flux closure states in cobalt rings  

NASA Astrophysics Data System (ADS)

For the implementation of magnetic materials in high density data storage, an optimization of the geometry and size of small magnetic elements is of importance. Generally for a given material the geometry determines which kind of magnetization configuration may be present, while the size and lateral extension control the balance between the demagnetization fields and exchange fields and thus the transformation of one magnetization configuration into another. In this work (S.P. Li et al. Phys. Rev. Lett. 86, 1102 (2001)), we explore the magnetization patterns in cobalt rings with diameter between 300 and 800 nm and thickness between 10 and 50 nm. To fabricate efficiently the submicron rings, both high resolution electron beam lithography and tri-layer nanoimprint techniques have been used, followed by lift-off of a cobalt thin film. Two complementary experimental techniques, magneto-optic Kerr-effect (MOKE) hysteresis loops and Magnetic force microscopy (MFM) have been used for characterization. By means of MOKE we show that two types of magnetic states exist in zero field, defining a state diagram as a function of diameter and thickness. MFM imaging reveals that these states correspond to flux closure and single-domain states. For all dimensions investigated the flux closure state is the stable magnetization configuration. However with increasing diameter and decreasing thickness a metastable single-domain state can be obtained in the reversal process in an in-plane applied field. The results are compared to vortex formation in Co dots with comparable diameters and thicknesses. While for the rings the metastable single domain states could be easily switched to the flux-closure state by the perturbation produced by an MFM tip, this was not the case for the dots. For these on the contrary the single-domain state remained stable during the whole magnetization reversal process that was observed to occur by coherent rotation. The experimental results are in good agreement with micromagnetic simulations.

Chen, Yong

2002-03-01

165

Magnetic field programming in quadrupole magnetic field-flow fractionation  

NASA Astrophysics Data System (ADS)

Magnetic field-flow fractionation (MgFFF) is a technique for the separation and characterization of magnetic nanoparticles. It is explained that the analysis of polydisperse samples requires a programmed decay of field and field gradient during sample elution. A procedure for achieving reproducible field decay with asymptotic approach to zero field using a quadrupole electromagnet is described. An example of an analysis of a polydisperse sample under programmed field decay is given.

Stephen Williams, P.; Carpino, Francesca; Moore, Lee R.; Zborowski, Maciej

166

Scattering by magnetic fields  

Microsoft Academic Search

Consider the scattering amplitude $s(\\\\omega,\\\\omega^\\\\prime;\\\\lambda)$,\\u000a$\\\\omega,\\\\omega^\\\\prime\\\\in{\\\\Bbb S}^{d-1}$, $\\\\lambda > 0$, corresponding to an\\u000aarbitrary short-range magnetic field $B(x)$, $x\\\\in{\\\\Bbb R}^d$. This is a smooth\\u000afunction of $\\\\omega$ and $\\\\omega^\\\\prime$ away from the diagonal\\u000a$\\\\omega=\\\\omega^\\\\prime$ but it may be singular on the diagonal. If $d=2$, then\\u000athe singular part of the scattering amplitude (for example, in the transversal\\u000agauge) is a

D. R. Yafaev

2005-01-01

167

Comparisons of Simulated and Observed Stormtime Magnetic Intensities and Ion Densities in the Ring Current  

NASA Astrophysics Data System (ADS)

Recent progress in ring current and plasma sheet modeling has shown the importance of a self-consistent treatment of particle transport and magnetic and electric fields in the inner magnetosphere. For example, the feedback of the ring current tends to mitigate the build-up of the asymmetric ring current and associated magnetic depressions during storm main phase. Models with and without self-consistency can lead to significantly different magnitudes and spatial distributions of plasma pressure and magnetic intensity during disturbed times. In this study we compare simulated and observed stormtime magnetic intensities and ion densities at geosynchronous altitude to test how well self-consistent simulations can simultaneously reproduce these quantities. We simulate the ring current and plasma sheet for conditions corresponding to the 12-14 August 2000 storm using the self-consistent Rice Convection Model-Equilibrium (RCM-E) [ Lemon et al., JGR, 2004]. Using the empirical IMF-dependent model of Tsyganenko and Mukai [JGR, 2003], we specify the plasma sheet pressure and density at 10 RE as the plasma boundary location in the RCM- E. We compare the simulated magnetic intensity at geosynchronous altitude (6.6 RE) with the magnetic intensity measured by magnetometers on the GOES G8, G10, and G11 satellites. The simulated ion densities at different magnetic local times are compared with those from the re-analysis model of LANL/MPA densities of O'Brien and Lemon [Space Weather, 2007]. This is a first step towards a more extensive comparison that will include other datasets, such as ion and magnetic field data from Polar, at locations closer to the Earth than geosynchronous altitude.

Chen, M. W.; Guild, T. B.; Lemon, C. L.; Schulz, M.

2008-12-01

168

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

169

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

170

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

171

Magnetic-moment oscillations in a quantum Hall ring Lachezar S. Georgiev  

E-print Network

Magnetic-moment oscillations in a quantum Hall ring Lachezar S. Georgiev Institute for Nuclear in the orbital magnetic moment of a thin semiconductor ring in the quantum Hall effect regime. These oscillations to a measurable magnetic moment R2 I/c in a thin ring of radius R. The persistent current I is mesoscopic

Geller, Michael R.

172

Convectively stable pressure profile in magnetic confinement systems with internal rings  

SciTech Connect

A convectively stable pressure profile in a long multiple-mirror (corrugated) magnetic confinement system with internal current-carrying rings is calculated. The plasma energy content in the axial region can be increased by using an internal ring that reverses the on-axis magnetic field direction and gives rise to an average magnetic well near the axis. The pressure profile in the outer region-outside the magnetic well-is considered in detail. It is shown that, in the radial pressure profile, a pedestal can be formed that leads to a higher pressure drop between the center and the plasma edge. The pressure profile is calculated from the Kruskal-Oberman criterion-a necessary and sufficient condition for the convective stability of a collisionless plasma. The revealed pedestal arises near the boundary of the average magnetic well in the region of the smallest but alternating-sign curvature of the magnetic field lines due to a break in the convectively stable pressure profile. Such a shape of the stable pressure profile can be attributed to the stabilizing effect of the alternating-sign curvature of the field lines in the multiple-mirror magnetic confinement systems under consideration.

Tsventoukh, M. M. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

2010-06-15

173

Dynamic domain wall chirality rectification by rotating magnetic fields  

NASA Astrophysics Data System (ADS)

We report on the observation of magnetic vortex domain wall chirality reversal in ferromagnetic rings that is controlled by the sense of rotation of a magnetic field. We use time-resolved X-ray microscopy to dynamically image the chirality-switching process and perform micromagnetic simulations to deduce the switching details from time-resolved snapshots. We find experimentally that the switching occurs within less than 4 ns and is observed in all samples with ring widths ranging from 0.5 ?m to 2 ?m, ring diameters between 2 ?m and 5 ?m, and a thickness of 30 nm, where a vortex domain wall is present in the magnetic onion state of the ring. From the magnetic contrast in the time-resolved images, we can identify effects of thermal activation, which plays a role for the switching process. Moreover, we find that the process is highly reproducible so that the domain wall chirality can be set with high fidelity.

Bisig, Andre; Mawass, Mohamad-Assaad; Stärk, Martin; Moutafis, Christoforos; Rhensius, Jan; Heidler, Jakoba; Gliga, Sebastian; Weigand, Markus; Tyliszczak, Tolek; Van Waeyenberge, Bartel; Stoll, Hermann; Schütz, Gisela; Kläui, Mathias

2015-03-01

174

Gravitational Field Inside and Near a Caustic Ring  

E-print Network

We present an analytic calculation of the gravitational field inside and near a caustic ring of dark matter. The calculation may facilitate N-body simulation studies on the effects that dark matter caustics have on galaxy formation.

Heywood Tam

2012-05-07

175

Fast superconducting magnetic field switch  

DOEpatents

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

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

1996-01-01

176

Magnetic field modification of optical magnetic dipoles.  

PubMed

Acting on optical magnetic dipoles opens novel routes to govern light-matter interaction. We demonstrate magnetic field modification of the magnetic dipolar moment characteristic of resonant nanoholes in thin magnetoplasmonic films. This is experimentally shown through the demonstration of the magneto-optical analogue of Babinet's principle, where mirror imaged MO spectral dependencies are obtained for two complementary magnetoplasmonic systems: holes in a perforated metallic layer and a layer of disks on a substrate. PMID:25646869

Armelles, Gaspar; Caballero, Blanca; Cebollada, Alfonso; Garcia-Martin, Antonio; Meneses-Rodríguez, David

2015-03-11

177

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

178

Magnetic fields in massive stars  

Microsoft Academic Search

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; M. Scholler; M. Briquet; M. A. Pogodin; R. V. Yudin; J. F. Gonzalez; T. Morel; P. De; R. Ignace; G. Mathys; G. J. Peters

2007-01-01

179

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

180

Magnetic-field-dosimetry system  

SciTech Connect

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

181

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

182

Design of the Sector Magnets for the RIKEN Superconducting Ring Cyclotron  

NASA Astrophysics Data System (ADS)

The RIKEN superconducting ring cyclotrons, SRC-4 and SRC-6, are the main components for the RIKEN RI Beam Factory. This paper describes the design of the sector magnets for the SRC-6. The SRC-6 consists mainly of six superconducting sector magnets, three RF cavities, and beam injection/extraction systems. The main parameters of the sector magnets are as follows: the maximum magnetic field in the beam orbit is 4.3 T; the coil ampere-turns 6 x 6 MA; the stored magnetic energy 450 MJ; the total weight of the cold mass 350 tons and the total weight including iron return yokes 4000 tons. LHe bath cooling and cryogenic stabilizing method are adopted for both of the superconducting main coils and the superconducting trim coils. The special feature is the cold-pole arrangement that is adopted to support the main coils against the huge magnetic force and to reduce the coil ampere-turns.

Kawaguchi, T.; Kubo, T.; Mitsumoto, T.; Okuno, H.; Tominaka, T.; Kim, J. W.; Fujishima, S.; Ikegami, K.; Sakamoto, N.; Yokouchi, S.; Morikawa, T.; Tanaka, Y.; Goto, A.; Yano, Y.

1997-05-01

183

Radiation effects in a muon collider ring and dipole magnet protection  

SciTech Connect

The requirements and operating conditions for a Muon Collider Storage Ring (MCSR) pose significant challenges to superconducting magnets. The dipole magnets should provide a high magnetic field to reduce the ring circumference and thus maximize the number of muon collisions during their lifetime. One third of the beam energy is continuously deposited along the lattice by the decay electrons at the rate of 0.5 kW/m for a 1.5-TeV c.o.m. and a luminosity of 10{sup 34} cm{sup -2}s{sup -1}. Unlike dipoles in proton machines, the MCSR dipoles should allow this dynamic heat load to escape the magnet helium volume in the horizontal plane, predominantly towards the ring center. This paper presents the analysis and comparison of radiation effects in MCSR based on two dipole magnets designs. Tungsten masks in the interconnect regions are used in both cases to mitigate the unprecedented dynamic heat deposition and radiation in the magnet coils.

Mokhov, N.V.; Kashikhin, V.V.; Novitski, I.; Zlobin, A.V.; /Fermilab

2011-03-01

184

Mercury's magnetic field and interior  

NASA Technical Reports Server (NTRS)

The magnetic-field data collected on Mercury by the Mariner-10 spacecraft present substantial evidence for an intrinsic global magnetic field. However, studies of Mercury's thermal evolution show that it is most likely that the inner core region of Mercury solidified or froze early in the planet's history. Thus, the explanation of Mercury's magnetic field in the framework of the traditional planetary dynamo is less than certain.

Connerney, J. E. P.; Ness, N. F.

1988-01-01

185

Ferrofilm in a magnetic field  

NASA Astrophysics Data System (ADS)

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

Back, Randy; Beckham, J. Regan

2012-10-01

186

Non-disjunction mutations in Drosophila exposed to magnetic fields  

NASA Astrophysics Data System (ADS)

The frequency of XO mutations in Drosophila melanogaster was significantly higher than normal in magnetic field exposed, immature males, than in exposed, mature males. Mutation levels increased with magnetic field strength. Intercellular rings of black magnetic particles were formed in the high magnetic flux region of dorsally exposed, early stage pupae and to a lesser degree in the abdomen of young adult females. Orientation of minute, chromosome associated, magnetic domains within the microenvironment of the developing organism was believed to alter oxidative processes within maturing X+ sperm which during fertilization were incompatible with and destructive to an Xw chromosome in the zygote.

Levengood, W. C.

1987-09-01

187

Evolution of pulsar magnetic fields  

Microsoft Academic Search

Theoretical considerations of neutron star matter and magnetic fields suggest a picture of the evolution of pulsar dipole moments. At birth the spin axis and magnetic dipole are argued to be roughly aligned. Subsequently the magnetic dipole greatly diminishes in strength and changes its direction until it ultimately makes a large angle with the spin axis. This view is supported

E. Flowers; M. A. Ruderman

1977-01-01

188

Theory of fossil magnetic field  

NASA Astrophysics Data System (ADS)

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

Dudorov, Alexander E.; Khaibrakhmanov, Sergey A.

2015-02-01

189

Cosmic Magnetic Fields - An Overview  

NASA Astrophysics Data System (ADS)

Magnetic fields have been known in antiquity. Aristotle attributes the first of what could be called a scientific discussion on magnetism to Thales, who lived from about 625 BC. In China “magnetic carts” were in use to help the Emperor in his journeys of inspection. Plinius comments that in the Asia Minor province of Magnesia shepherds' staffs get at times “glued” to a stone, a alodestone. In Europe the magnetic compass came through the Arab sailors who met the Portuguese explorers. The first scientific treatise on magnetism, “De Magnete”, was published by William Gilbert who in 1600 described his experiments and suggested that the Earth was a huge magnet. Johannes Kepler was a correspondent of Gilbert and at times suggested that planetary motion was due to magnetic forces. Alas, this concept was demolished by Isaac Newton,who seeing the falling apple decided that gravity was enough. This concept of dealing with gravitational forces only remains en vogue even today. The explanations why magnetic effects must be neglected go from “magnetic energy is only 1% of gravitation” to “magnetic fields only complicate the beautiful computer solutions”. What is disregarded is the fact that magnetic effects are very directional(not omni-directional as gravity) and also the fact that magnetic fields are seen every where in our cosmic universe.

Wielebinski, Richard; Beck, Rainer

190

Simulating and detecting artificial magnetic fields in trapped atoms  

SciTech Connect

A Bose-Einstein condensate exhibiting a nontrivial phase induces an artificial magnetic field in immersed impurity atoms trapped in a stationary, ring-shaped optical lattice. We present an effective Hamiltonian for the impurities for two condensate setups: the condensate in a rotating ring and in an excited rotational state in a stationary ring. We use Bogoliubov theory to derive analytical formulas for the induced artificial magnetic field and the hopping amplitude in the limit of low condensate temperature where the impurity dynamics is coherent. As methods for observing the artificial magnetic field we discuss time-of-flight imaging and mass current measurements. Moreover, we compare the analytical results of the effective model to numerical results of a corresponding two-species Bose-Hubbard model. We also study numerically the clustering properties of the impurities and the quantum chaotic behavior of the two-species Bose-Hubbard model.

Rosenkranz, Matthias; Klein, Alexander [Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Keble College, University of Oxford, Oxford OX1 3PG (United Kingdom); Jaksch, Dieter [Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Keble College, University of Oxford, Oxford OX1 3PG (United Kingdom); Centre for Quantum Technologies, National University of Singapore, Singapore 117543 (Singapore)

2010-01-15

191

The Primordial Origin Model of Magnetic Fields in Spiral Galaxies  

NASA Astrophysics Data System (ADS)

We propose a primordial-origin model for composite configurations of global magnetic fields in spiral galaxies. We show that a uniform tilted magnetic field wound up into a rotating disk galaxy can evolve into composite magnetic configurations comprising bisymmetric spiral (S = BSS), axisymmetric spiral (A = ASS), plane-reversed spiral (PR), and/or ring (R) fields in the disk, and vertical (V) fields in the center. By MHD simulations we show that these composite galactic fields are indeed created from a weak primordial uniform field, and that different configurations can co-exist in the same galaxy. We show that spiral fields trigger the growth of two-armed gaseous arms. The centrally accumulated vertical fields are twisted and produce a jet toward the halo. We found that the more vertical was the initial uniform field, the stronger was the formed magnetic field in the galactic disk.

Sofue, Yoshiaki; Machida, Mami; Kudoh, Takahiro

2010-10-01

192

A magnetic field model for wigglers and undulators  

Microsoft Academic Search

Recent interest in applications of wiggler magnets in storage rings has motivated efforts to incorporate their effects in calculations of beam dynamics. This paper presents an analytic model of wiggler fields that can be used with symplectic integration to evaluate such effects. Coefficients needed by the model are generated by fitting to the results of a finite-element field calculation. The

D. Sagan; J. A. Crittenden; D. Rubin; E. Forest

2003-01-01

193

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

194

Measurements of magnetic field alignment  

SciTech Connect

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

Kuchnir, M.; Schmidt, E.E.

1987-11-06

195

DC septum magnets for the damping rings of the SLC SLAC Linear Collider  

SciTech Connect

The injection/extraction systems of the 1.21 GeV Stanford Linear Collider (SLC) damping rings uses four pairs of water cooled septum magnets. Each pair consists of a thin-septum, low-field (3 mm, 3 kilogauss) magnet plus a thick-septum, high-field (12 mm, 8 kilogauss) model. In the latest design cooling reliability was improved by using stainless-steel tubing imbedded in the copper. The operating current in each is 2600 amperes, at a density of up to 120 amperes per mmS. Plasma-sprayed alumina is used to provide electrical insulation. The magnet system is compatible with 10 Z torr ultra-high vacuum. The magnet design, fabrication, and measurements are described.

Bijleveld, J.; Peterson, J.M.; Jensen, D.

1986-07-01

196

Commuting graphs of full matrix rings over finite fields  

Microsoft Academic Search

Let R be a non-commutative ring and Z(R) be its center. The commuting graph of R is defined to be the graph ?(R) whose vertex set is R?Z(R) and two distinct vertices are joint by an edge whenever they commute. Let F be a finite field, n?2 an arbitrary integer and R be a ring with identity such that ?(R)??(Mn(F)),

Alireza Abdollahi

2008-01-01

197

The magnetic field of Mercury  

Microsoft Academic Search

The magnetic field of Mercury was measured on two fly-bys of the planet by the Mariner 10 space-craft. The presence of a field at Mercury is interesting for what it implies for both the internal and external sources of field. The internal field of the planet is almost certainly generated by an internal dynamo although there remain many puzzles as

D. J. Southwood

1997-01-01

198

The magnetic field of Mercury  

Microsoft Academic Search

The magnetic field of Mercury was measured on two fly-bys of the planet by the Mariner 10 spacecraft. The presence of a field at Mercury is interesting for what it implies for both the internal and external sources of field. The internal field of the planet is almost certainly generated by an internal dynamo although there remain many puzzles as

D. J. Southwood

1997-01-01

199

Axial Magnetostatics of a Ring Current in a Kerr Field  

E-print Network

The electromagnetic fields generated by a ring current around a Kerr black hole have been found. The acceleration of a charged particle by a force electric field along the rotation axis is investigated in the constructed model, as applied to the astrophysics of quasars.

A. A. Shatskiy

2002-02-20

200

SCALING LAW FOR THE IMPACT OF MAGNET FRINGE FIELDS.  

SciTech Connect

A general scaling law can be derived for the relative momentum deflection produced on a particle beam by fringe fields, to leading order. The formalism is applied to two concrete examples, for magnets having dipole and quadrupole symmetry. During recent years, the impact of magnet fringe fields is becoming increasingly important for rings of relatively small circumference but large acceptance. A few years ago, following some heuristic arguments, a scaling law was proposed [1], for the relative deflection of particles passing through a magnet fringe-field. In fact, after appropriate expansion of the magnetic fields in Cartesian coordinates, which generalizes the expansions of Steffen [2], one can show that this scaling law is true for any multipole magnet, at leading order in the transverse coefficients [3]. This paper intends to provide the scaling law to estimate the impact of fringe fields in the special cases of magnets with dipole and quadrupole symmetry.

WEI,J.; PAPAPHILIPPOU,Y.; TALMAN,R.

2000-06-30

201

Preprocessing Magnetic Fields with Chromospheric Longitudinal Fields  

NASA Astrophysics Data System (ADS)

Nonlinear force-free field (NLFFF) extrapolation is a powerful tool for the modeling of the magnetic field in the solar corona. However, since the photospheric magnetic field does not in general satisfy the force-free condition, some kind of processing is required to assimilate data into the model. In this paper, we report the results of new preprocessing for the NLFFF extrapolation. Through this preprocessing, we expect to obtain magnetic field data similar to those in the chromosphere. In our preprocessing, we add a new term concerning chromospheric longitudinal fields into the optimization function proposed by Wiegelmann et al. We perform a parameter survey of six free parameters to find minimum force- and torque-freeness with the simulated-annealing method. Analyzed data are a photospheric vector magnetogram of AR 10953 observed with the Hinode spectropolarimeter and a chromospheric longitudinal magnetogram observed with SOLIS spectropolarimeter. It is found that some preprocessed fields show the smallest force- and torque-freeness and are very similar to the chromospheric longitudinal fields. On the other hand, other preprocessed fields show noisy maps, although the force- and torque-freeness are of the same order. By analyzing preprocessed noisy maps in the wave number space, we found that small and large wave number components balance out on the force-free index. We also discuss our iteration limit of the simulated-annealing method and magnetic structure broadening in the chromosphere.

Yamamoto, Tetsuya T.; Kusano, K.

2012-06-01

202

PREPROCESSING MAGNETIC FIELDS WITH CHROMOSPHERIC LONGITUDINAL FIELDS  

SciTech Connect

Nonlinear force-free field (NLFFF) extrapolation is a powerful tool for the modeling of the magnetic field in the solar corona. However, since the photospheric magnetic field does not in general satisfy the force-free condition, some kind of processing is required to assimilate data into the model. In this paper, we report the results of new preprocessing for the NLFFF extrapolation. Through this preprocessing, we expect to obtain magnetic field data similar to those in the chromosphere. In our preprocessing, we add a new term concerning chromospheric longitudinal fields into the optimization function proposed by Wiegelmann et al. We perform a parameter survey of six free parameters to find minimum force- and torque-freeness with the simulated-annealing method. Analyzed data are a photospheric vector magnetogram of AR 10953 observed with the Hinode spectropolarimeter and a chromospheric longitudinal magnetogram observed with SOLIS spectropolarimeter. It is found that some preprocessed fields show the smallest force- and torque-freeness and are very similar to the chromospheric longitudinal fields. On the other hand, other preprocessed fields show noisy maps, although the force- and torque-freeness are of the same order. By analyzing preprocessed noisy maps in the wave number space, we found that small and large wave number components balance out on the force-free index. We also discuss our iteration limit of the simulated-annealing method and magnetic structure broadening in the chromosphere.

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

2012-06-20

203

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

204

The magnetic field of Neptune  

NASA Technical Reports Server (NTRS)

A model is given of the planetary magnetic field of Neptune based on a spherical harmonic analysis of the observations obtained by the Voyager 2. Generalized inverse techniques are used to partially solve a severely underdetermined inverse problem, and the resulting model is nonunique since the observations are limited in spatial distribution. Dipole, quadrupole, and octupole coefficients are estimated independently of other terms, and the parameters are shown to be well constrained by the measurement data. The large-scale features of the magnetic field including dipole tilt, offset, and harmonic content are found to characterize a magnetic field that is similar to that of Uranus. The traits of Neptune's magnetic field are theorized to relate to the 'ice' interior of the planet, and the dynamo-field generation reflects this poorly conducting planet.

Connerney, J. E. P.; Acuna, Mario H.; Ness, Norman F.

1992-01-01

205

Resonant magnetic fields from inflation  

SciTech Connect

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

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

2012-03-01

206

Resonant magnetic fields from inflation  

E-print Network

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

Christian T. Byrnes; Lukas Hollenstein; Rajeev Kumar Jain; Federico R. Urban

2012-03-06

207

A Ring of Polarized Light: Evidence for Twisted Coronal Magnetism in Cavities  

NASA Astrophysics Data System (ADS)

Coronal prominence cavities may be manifestations of twisted or sheared magnetic fields capable of storing the energy required to drive solar eruptions. The Coronal Multi-Channel Polarimeter (CoMP), recently installed at Mauna Loa Solar Observatory, can measure polarimetric signatures of current-carrying magnetohydrodynamic (MHD) systems. For the first time, this instrument offers the capability of daily full-Sun observations of the forbidden lines of Fe XIII with high enough spatial resolution and throughput to measure polarimetric signatures of current-carrying MHD systems. By forward-calculating CoMP observables from analytic MHD models of spheromak-type magnetic flux ropes, we show that a predicted observable for such flux ropes oriented along the line of sight is a bright ring of linear polarization surrounding a region where the linear polarization strength is relatively depleted. We present CoMP observations of a coronal cavity possessing such a polarization ring.

Dove, J. B.; Gibson, S. E.; Rachmeler, L. A.; Tomczyk, S.; Judge, P.

2011-04-01

208

Fano resonances in hexagonal zigzag graphene rings under external magnetic flux.  

PubMed

We study transport properties of hexagonal zigzag graphene quantum rings connected to semi-infinite nanoribbons. Open two-fold symmetric structures support localized states that can be traced back to those existing in the isolated six-fold symmetric rings. Using a tight-binding Hamiltonian within the Green's function formalism, we show that an external magnetic field promotes these localized states to Fano resonances with robust signatures in transport. Local density of states and current distributions of the resonant states are calculated as a function of the magnetic flux intensity. For structures on corrugated substrates we analyze the effect of strain by including an out-of-plane centro-symmetric deformation in the model. We show that small strains shift the resonance positions without further modifications, while high strains introduce new ones. PMID:25836340

Faria, D; Carrillo-Bastos, R; Sandler, N; Latgé, A

2015-05-01

209

STORAGE RING AND INTERACTION REGION MAGNETS FOR A ?+?- HIGGS FACTORY.  

SciTech Connect

A low-energy Muon Collider (MC) offers unique opportunities to study the recently found Higgs boson. However, due to a relatively large beam emittance with moderate cooling in this machine, large-aperture high- field superconducting (SC) magnets are required. The magnets need also an adequate margin to operate at a large radiation load from the muon decay showers. General specifications of the SC dipoles and quadrupoles for the 125 GeV c.o.m. Higgs Factory with an average luminosity of ~2x10**31 cm-2s-1 are formulated. Magnet conceptual designs and parameters are reported. The impact of the magnet fringe fields on the beam dynamics as well as the IR and lattice magnet protection from radiation are also reported and discussed.

Zlobin, A.V.; Alexahin, Y.I.; Kappin, V.V.; Kashikhin, V.V.; Mokhov, N.V.; Striganov, S.I.; Tropin, I.S.

2013-09-25

210

POWER SUPPLIES FOR THE BENDING MAGNETS OF THE BEP AND VEPP-2000 STORAGE RING  

E-print Network

POWER SUPPLIES FOR THE BENDING MAGNETS OF THE BEP AND VEPP-2000 STORAGE RING K.M. Gorchakov, S new complex VEPP-2000. The two new power supply for bending magnet was built for BEP and VEPP-2000 storage ring. POWER SUPPLY FOR THE BENDING MAGNETS OF THE BEP Below are the parameters of the supply (the

Kozak, Victor R.

211

Schrödinger operators with magnetic fields  

Microsoft Academic Search

We prove a large number of results about atoms in constant magnetic field including (i) Asymptotic formula for the ground state energy of Hydrogen in large field, (ii) Proof that the ground state of Hydrogen in an arbitrary constant field hasLz = 0 and of the monotonicity of the binding energy as a function ofB, (iii) Borel summability of Zeeman

J. E. Avron; I. W. Herbst; B. Simon

1981-01-01

212

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

213

Reconnection of stressed magnetic fields  

NASA Technical Reports Server (NTRS)

It is shown that magnetized plasma configurations under magnetic stress relax irreversibly to the state of minimum stress at a rate that is essentially Alfvenic provided a magnetic null is present. The relaxation is effected by the reconnection at the field null and proceeds at a rate proportional to the absolute value of ln(eta) exp-1, where eta is the resistivity. An analytic calculation in the linear regime is presented.

Hassam, A. B.

1992-01-01

214

Passive temperature compensation in hybrid magnets with application to the Fermilab stacker and recycler ring dipole design  

SciTech Connect

Design theory of hybrid (permanent magnet plus iron) accelerator magnets with application to the proposed permanent magnet recycler and stacker rings at the Fermi National Laboratory is presented. Field stability in such devices requires that changes in the strength of the permanent magnet material with temperature be compensated. Field tuning techniques, including those employing variable capacitance between energized pole and magnet yoke and those employing variable energization of magnet pole pieces, are described. Mechanical configurations capable of achieving temperature compensation passively, including use of expanding liquids/gases and bimetallic springs are outlined. Active configurations, relying on a actuator, in addition to temperature compensation, have the additional benefit of enabling magnet tuning about a nominal operating field level.

Schlueter, R.D.; Marks, S.; Loper, C.; Halbach, K.

1995-06-01

215

Preface: Cosmic magnetic fields  

NASA Astrophysics Data System (ADS)

Recent advances in observations and modeling have opened new perspectives for the understanding of fundamental dynamical processes of cosmic magnetism, and associated magnetic activity on the Sun, stars and galaxies. The goal of the Special Issue is to discuss the progress in solar physics and astrophysics, similarities and differences in phenomenology and physics of magnetic phenomena on the Sun and other stars. Space observatories, ground-based telescopes, and new observational methods have provided tremendous amount of data that need to be analyzed and understood. The solar observations discovered multi-scale organization of solar activity, dramatically changing current paradigms of solar variability. On the other side, stellar observations discovered new regimes of dynamics and magnetism that are different from the corresponding solar phenomena, but described by the same physics. Stars represent an astrophysical laboratory for studying the dynamical, magnetic and radiation processes across a broad range of stellar masses and ages. These studies allow us to look at the origin and evolution of our Sun, whereas detailed investigations of the solar magnetism give us a fundamental basis for interpretation and understanding of unresolved stellar data.

Kosovichev, Alexander

2015-02-01

216

The polar heliospheric magnetic field  

NASA Technical Reports Server (NTRS)

It is suggested that the polar heliospheric magnetic field, at large heliocentric distances, may deviate considerably from the generally accepted Archimedean spiral. Instead, it is suggested that the large-scale field near the poles may be dominated by randomly-oriented transverse magnetic fields with magnitude much larger than the average spiral. The average vector field is still the spiral, but the average magnitude may be much larger. In addition, the field direction is transverse to the radial direction most of the time instead of being nearly radial. This magnetic-field structure has important consequences for the transport of cosmic rays. Preliminary model calculations suggest changes in the radial gradient of galactic cosmic rays which may improve agreement with observations.

Jokipii, J. R.; Kota, J.

1989-01-01

217

Measuring Earth's Magnetic Field Simply.  

ERIC Educational Resources Information Center

Describes a method for measuring the earth's magnetic field using an empty toilet paper tube, copper wire, clear tape, a battery, a linear variable resistor, a small compass, cardboard, a protractor, and an ammeter. (WRM)

Stewart, Gay B.

2000-01-01

218

The ACE Magnetic Fields Experiment  

Microsoft Academic Search

The magnetic field experiment on ACE provides continuous measurements of the local magnetic field in the interplanetary medium.\\u000a These measurements are essential in the interpretation of simultaneous ACE observations of energetic and thermal particles\\u000a distributions. The experiment consists of a pair of twin, boom- mounted, triaxial fluxgate sensors which are located 165 inches\\u000a (=4.19 m) from the center of the

C. W. Smith; J. L'Heureux; N. F. Ness; M. H. Acuña; L. F. Burlaga; J. Scheifele

1998-01-01

219

Magnetic resonance in an elliptic magnetic field  

E-print Network

The behaviour of a particle with a spin 1/2 and a dipole magnetic moment in a time-varying magnetic field in the form $(h_0 cn(\\omega t,k), h_0 sn(\\omega t,k), H_0 dn(\\omega t,k))$, where $\\omega$ is the driving field frequency, $t$ is the time, $h_0$ and $H_0$ are the field amplitudes, $cn$, $sn$, $dn$ are Jacobi elliptic functions, $ k$ is the modulus of the elliptic functions has been considered. The variation parameter $k$ from zero to 1 gives rise to a wide set of functions from trigonometric shapes to exponential pulse shapes modulating the field. The problem was reduced to the solution of general Heun' equation. The exact solution of the wave function was found at resonance for any $ k$. It has been shown that the transition probability in this case does not depend on $k$. The present study may be useful for analysis interference experiments, improving magnetic spectrometers and the field of quantum computing.

E. A. Ivanchenko

2004-04-20

220

Least Squares Magnetic-Field Optimization for Portable Nuclear Magnetic Resonance Magnet Design  

SciTech Connect

Single-sided and mobile nuclear magnetic resonance (NMR) sensors have the advantages of portability, low cost, and low power consumption compared to conventional high-field NMR and magnetic resonance imaging (MRI) systems. We present fast, flexible, and easy-to-implement target field algorithms for mobile NMR and MRI magnet design. The optimization finds a global optimum ina cost function that minimizes the error in the target magnetic field in the sense of least squares. When the technique is tested on a ring array of permanent-magnet elements, the solution matches the classical dipole Halbach solution. For a single-sided handheld NMR sensor, the algorithm yields a 640 G field homogeneous to 16 100 ppm across a 1.9 cc volume located 1.5 cm above the top of the magnets and homogeneous to 32 200 ppm over a 7.6 cc volume. This regime is adequate for MRI applications. We demonstrate that the homogeneous region can be continuously moved away from the sensor by rotating magnet rod elements, opening the way for NMR sensors with adjustable"sensitive volumes."

Paulsen, Jeffrey L; Franck, John; Demas, Vasiliki; Bouchard, Louis-S.

2008-03-27

221

A Method to Verify Accuracy of Predicted Magnetic Orientation of a Permanent Ring Magnet in a Brushless DC Motor  

Microsoft Academic Search

The paper reports a numerical and experimental method to verify the predicted magnetic orientation of a permanent ring magnet before the magnet is assembled into a brushless DC (BLDC) motor. A simple magnetic configuration, in which a permanent magnet is placed in the air without presence of any large permeability material in the vicinity, is proposed to eliminate changes in

Taeyong Yoon; Dennis K. Lieu

2007-01-01

222

1418 IEEE TRANSACTIONS ON MAGNETICS, VOL. 47, NO. 5, MAY 2011 Interaction Between Ring-Shaped Permanent Magnets With Symbolic  

E-print Network

-Shaped Permanent Magnets With Symbolic Gradients: Application to Magnetic Bearing System Optimization B. Delinchant magnetic bodies with ring shapes. It leads to fast and ac- curate evaluation of forces and torques but also-shaped permanent magnets are specially used in magnetic bearings like Fig. 1, and are used in several systems

Paris-Sud XI, Université de

223

Magnetic Resonance Imaging System Based on Earth's Magnetic Field  

E-print Network

magnetic field can be partly compensated by the receiving coil design and shielding of electromagnetic pick magnetic fields. Common sources of static magnetic fields are super conducting coils, electromagnets, and permanent magnets. The induced magnetization, and thus the signal, is proportional to the magnitude

StepiÂ?nik, Janez

224

The magnetic field of Neptune  

NASA Technical Reports Server (NTRS)

The Voyager 2 observations obtained during the Neptune encounter are used to develop a spherical harmonic model of the planetary magnetic field of Neptune. The model yields a dipole of magnitude 0.14 G R(N) exp 3, tilted by 47 deg toward 72 deg west longitude. Neptune's quadrupole is equal to or exceeding in magnitude the surface dipole field; the octupole is also very large, although less well constrained. The characteristics of the Neptune's magnetic field are illustrated using contour maps of the field on the planet's surface.

Connerney, J. E. P.; Acuna, Mario H.; Ness, Norman F.

1991-01-01

225

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

226

The magnetic field of Mercury  

NASA Technical Reports Server (NTRS)

The Mariner 10 spacecraft encountered Mercury three times in 1974-1975. The first and third encounters provided detailed observations of a well-developed detached bow shock wave which results from the interaction of the solar wind. The planet possesses a global magnetic field and a modest magnetosphere, which deflects the solar wind. The field is approximately dipolar, with orientation in the same sense as earth, tilted 12 deg from the rotation axis. The magnetic moment corresponds to an undistorted equatorial field intensity of 350 gammas, approximately 1% of earth's. The field, while unequivocally intrinsic to the planet, may be due to remanent magnetization acquired from an extinct dynamo or a primordial magnetic field or due to a presently active dynamo. The latter possibility appears more plausible at present. In any case, the existence of the magnetic field provides very strong evidence of a mature differentiated planetary interior with a large core (core radius about 0.7 Mercury radius) and a record of the history of planetary formation in the magnetization of the crustal rocks.

Ness, N. F.

1977-01-01

227

Numerical simulation of strong proton rings  

Microsoft Academic Search

Recent calculations suggest the possibility of achieving a Lawson breakeven condition by the magnetic compression of proton rings to field reversal. This report describes a physical model and computer code RING developed to study equilibria of strong proton rings and their behavior under an adiabatic increase in the external magnetic field. Ring ion motion is followed using a volume-weighted finite-size

A Friedman; R L Ferch; R N Sudan; A T Drobot

1977-01-01

228

Homometallic and Heterometallic Antiferromagnetic Rings: Magnetic Properties Studied by Nuclear Magnetic Resonance  

SciTech Connect

The aim of the present thesis is to investigate the local magnetic properties of homometallic Cr{sub 8} antiferromagnetic (AFM) ring and the changes occurring by replacing one Cr{sup 3+} ion with diamagnetic Cd{sup 2+} (Cr{sub 7}Cd) and with Ni{sup 2+} (Cr{sub 7}Ni). In the heterometallic ring a redistribution of the local magnetic moment is expected in the low temperature ground state. We have investigated those changes by both {sup 53}Cr-NMR and {sup 19}F-NMR. We have determined the order of magnitude of the transferred hyperfine coupling constant {sup 19}F - M{sup +} where M{sup +} = Cr{sup 3+}, Ni{sup 2+} in the different rings. This latter result gives useful information about the overlapping of the electronic wavefunctions involved in the coordinative bond.

Casadei, Cecilia

2012-05-09

229

Effect of External Constant Magnetic Field on Weld Nugget of Resistance Spot Welded Dual-Phase Steel DP590  

Microsoft Academic Search

The applications of magnetic field in metal casting and welding processes have drawn much attention of researchers. However, the effect of external magnetic field on nugget formation of resistance spot welding (RSW) is still lack of understanding. In this paper, the effect of a radially oriented constant magnetic field generated by a pair of ring-shaped permanent magnets on the weld

Qi Shen; Yong Bing Li; Zhong Qin Lin; Guan Long Chen

2011-01-01

230

Comparisons of Simulated and Observed Stormtime Magnetic Intensities and Ion Plasma Parameters in the Ring Current  

NASA Astrophysics Data System (ADS)

Recent progress in ring current and plasma sheet modeling has shown the importance of a self-consistent treatment of particle transport and magnetic and electric fields in the inner magnetosphere. Models with and without self-consistency can lead to significantly different magnitudes and spatial distributions of plasma pressure and magnetic intensity during disturbed times. In this study we compare simulated and observed stormtime magnetic intensities (GOES and Polar/MFE) and ion densities (LANL/MPA and Polar/CAMMICE) to test how well self-consistent simulations can simultaneously reproduce these quantities. We simulate the ring current and plasma sheet for conditions corresponding to the 11 August 2000 storm using the self-consistent Rice Convection Model-Equilibrium (RCM-E) [Lemon et al., JGR, 2004] with a constant magnetopause location. Using the empirical IMF-dependent model of Tsyganenko and Mukai [JGR, 2003], we specify the plasma sheet pressure and density at 10 RE as the plasma boundary location in the RCM-E. The simulated ion densities at different magnetic local times agree fairly well with those from the re-analysis model of LANL/MPA densities of O’Brien and Lemon [Space Weather, 2007]. We compare the simulated magnetic intensity with the magnetic intensity measured by magnetometers on the GOES satellites at geosynchronous altitude (6.6 RE) and on the Polar satellite. Agreement between the simulated and observed magnetic intensities tends to agree better on the nightside than on the dayside in the inner magnetosphere. In particular, the model cannot account for observed drops in the dayside magnetic intensity during decreases in the solar wind pressure. We will modify the RCM-E to include a time-varying magnetopause location to simulate compressions and expansions associated with variations in the solar wind pressure. We investigate whether this will lead to improved agreement between the simulated and model magnetic intensities.

Chen, M. W.; Guild, T. B.; Lemon, C.; Roeder, J. L.; Le, G.; Schulz, M.

2009-12-01

231

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 in Fig. 3.1, the generic structure of the magnetic field can be open (a­c and f) or closed (d,e). In open). The magnetic field structure in closed configurations (d,e) is toroidal in character or topology. That is, its

Callen, James D.

232

Control of vortices by homogeneous fields in asymmetric ferroelectric and ferromagnetic rings.  

PubMed

Effective Hamiltonians have been used (i) to demonstrate that the shape asymmetry of ferromagnetic rings is essential to the recently discovered switching of the chirality of their vortices by homogeneous magnetic fields, via a transition into onion states; (ii) to reveal that an electric vortex can also be controlled by a homogeneous electric field in asymmetric ferroelectric nanorings, via the formation of antiferrotoroidic pair states rather than onion states; and (iii) to provide the fundamental reason that allows such control, namely, two new interaction energies involving a vector characterizing the asymmetry, the applied field, and the toroidal moment. PMID:18352323

Prosandeev, S; Ponomareva, I; Kornev, I; Bellaiche, L

2008-02-01

233

Damping of cosmic magnetic fields  

SciTech Connect

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

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

1998-03-01

234

Magnetic Field Generation in Stars  

NASA Astrophysics Data System (ADS)

Enormous progress has been made on observing stellar magnetism in stars from the main sequence (particularly thanks to the MiMeS, MAGORI and BOB surveys) through to compact objects. Recent data have thrown into sharper relief the vexed question of the origin of stellar magnetic fields, which remains one of the main unanswered questions in astrophysics. In this chapter we review recent work in this area of research. In particular, we look at the fossil field hypothesis which links magnetism in compact stars to magnetism in main sequence and pre-main sequence stars and we consider why its feasibility has now been questioned particularly in the context of highly magnetic white dwarfs. We also review the fossil versus dynamo debate in the context of neutron stars and the roles played by key physical processes such as buoyancy, helicity, and superfluid turbulence, in the generation and stability of neutron star fields. Independent information on the internal magnetic field of neutron stars will come from future gravitational wave detections. Coherent searches for the Crab pulsar with the Laser Interferometer Gravitational Wave Observatory (LIGO) have already constrained its gravitational wave luminosity to be ?2 % of the observed spin-down luminosity, thus placing a limit of ?1016 G on the internal field. Indirect spin-down limits inferred from recycled pulsars also yield interesting gravitational-wave-related constraints. Thus we may be at the dawn of a new era of exciting discoveries in compact star magnetism driven by the opening of a new, non-electromagnetic observational window. We also review recent advances in the theory and computation of magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo theory. These advances offer insight into the action of stellar dynamos as well as processes which control the diffusive magnetic flux transport in stars.

Ferrario, Lilia; Melatos, Andrew; Zrake, Jonathan

2015-03-01

235

Cosmic Structure of Magnetic Fields  

E-print Network

The simulations of the formation of cosmological structure allows to determine the spatial inhomogeneity of cosmic magnetic fields. Such simulations, however, do not give an absolute number for the strength of the magnetic field due to insufficient spatial resolution. Combining these simulations with observations of the Rotation Measure to distant radio sources allows then to deduce upper limits for the strength of the magnetic field. These upper limits are of order 0.2 - 2 muG along the filaments and sheets of the galaxy distribution. In one case, the sheet outside the Coma cluster, there is a definitive estimate of the strength of the magnetic field consistent with this range. Such estimates are almost three orders of magnitude higher than hitherto assumed usually. High energy cosmic ray particles can be either focussed or strongly scattered in such magnetic filaments and sheets, depending on the initial transverse momentum. The cosmological background in radio and X-ray wavelengths will have contributions from these intergalactic filaments and sheets, should the magnetic fields really be as high as 0.2 - 2 muG.

Peter L. Biermann; Hyesung Kang; Joerg P. Rachen; Dongsu Ryu

1997-09-25

236

Variable-field permanent magnet quadrupole for the SSC  

SciTech Connect

A set of compact variable-field permanent-magnet quadrupoles have been designed, fabricated, and tested for use In the SSC linac matching section. The quadrupoles have 24 mm-diameter apertures and 40 mm-long poles. The hybrid (permanent-magnet and iron) design, uses a fixed core of magnet material (NdFeB) and iron (C-1006) surrounded by a rotating ring of the same magnet material and iron. The quadrupole gradient-length product can be smoothly varied from a minimum of 0.7 T up to a maximum, of 4.3 T by a 90{degrees} rotation of the outer ring of iron and magnet material.

Barlow, D.B.; Kraus, R.H. Jr.; Martinez, R.P.; Meyer, R.E.

1993-10-01

237

RANDOM AND SYSTEMATIC FIELD ERRORS IN THE SNS RING: A STUDY OF THEIR EFFECTS AND COMPENSATION  

SciTech Connect

The Accumulator Ring for the proposed Spallation Neutron Source (SNS) [l] is to accept a 1 ms beam pulse from a 1 GeV Proton Linac at a repetition rate of 60 Hz. For each beam pulse, 10{sup 14} protons (some 1,000 turns) are to be accumulated via charge-exchange injection and then promptly extracted to an external target for the production of neutrons by spallation. At this very high intensity, stringent limits (less than two parts in 10,000 per pulse) on beam loss during accumulation must be imposed in order to keep activation of ring components at an acceptable level. To stay within the desired limit, the effects of random and systematic field errors in the ring require careful attention. This paper describes the authors studies of these effects and the magnetic corrector schemes for their compensation.

GARDNER,C.J.; LEE,Y.Y.; WENG,W.T.

1998-06-22

238

Exact transfer functions for the PEP storage ring magnets and some general characteristics and techniques  

SciTech Connect

The exact, ion-optical transfer functions for the dipoles, quadrupoles and sextupoles of the PEP standard PODC cell are calculated for any single particle with initial coordinates (r, p, s). Modifications resulting from radiative energy loss are also calculated and discussed. These functions allow one to characterize individual magnets or classes of magnets by their aberrations and thereby simplify their study and correction. In contrast to high-energy spectrometers where aberrations are often analyzed away, those in storage rings drive series of high order resonances, even for perfect magnets (2), that can produce stop bands and other effects which can seriously limit performance. Thus, one would like to eliminate them altogether or failing this to develop local and global correction schemes. Even then, one should expect higher order effects to influence injection, extraction or single-pass systems either because of orbit distortions or overly large phase spece distortions such as may occur in low-beta insertions or any final-focus optics. The term exact means that the results here are based on solving the relativistic Lorentz force equation with accurate representations of measured magnetostatic fields. Such fields satisfy Maxwell's equations and are the actual fields seen by a particle as it propagates around a real storage ring. This is discussed in detail and illustrated with examples that show that this is possible, practical and may even be useful.

Spencer, J.E.

1982-05-01

239

The magnetic field of Uranus  

NASA Technical Reports Server (NTRS)

Aspherical harmonic model of the planetary magnetic field of Uranus is obtained from the Voyager 2 encounter observations using generalized inverse techniques which allow partial solutions to complex (underdetermined) problems. The Goddard Space Flight Center 'Q3' model is characterized by a large dipole tilt (58.6 deg) relative to the rotation axis, a dipole moment of 0.228 G R(Uranus radii cubed) and an unusually large quadrupole moment. Characteristics of this complex model magnetic field are illustrated using contour maps of the field on the planet's surface and discussed in the context of possible dynamo generation in the relatively poorly conducting 'ice' mantle.

Connerney, J. E. P.; Acuna, Mario H.; Ness, Norman F.

1987-01-01

240

MAGNETIC FIELD MEASUREMENTS FOR FAST-CHANGING MAGNETIC FIELDS.  

SciTech Connect

Several recent applications for fast ramped magnets have been found that require rapid measurement of the field quality during the ramp. (In one instance, accelerator dipoles will be ramped at 1 T/sec, with measurements needed to the accuracy typically required for accelerators.) We have built and tested a new type of magnetic field measuring system to meet this need. The system consists of 16 stationary pickup windings mounted on a cylinder. The signals induced in the windings in a changing magnetic field are sampled and analyzed to obtain the field harmonics. To minimize costs, printed circuit boards were used for the pickup windings and a combination of amplifiers and ADPs used for the voltage readout system. New software was developed for the analysis. Magnetic field measurements of a model dipole developed for the SIS200 accelerator at GSI are presented. The measurements are needed to insure that eddy currents induced by the fast ramps do not impact the field quality needed for successful accelerator operation.

JAIN, A.; ESCALLIER, J.; GANETIS, G.; LOUIE, W.; MARONE, A.; THOMAS. R.; WANDERER, P.

2004-10-03

241

Magnetic Fields in Molecular Clouds  

E-print Network

Magnetic fields are believed to play an important role in the evolution of molecular clouds, from their large scale structure to dense cores, protostellar envelopes, and protoplanetary disks. How important is unclear, and whether magnetic fields are the dominant force driving star formation at any scale is also unclear. In this review we examine the observational data which address these questions, with particular emphasis on high angular resolution observations. Unfortunately the data do not clarify the situation. It is clear that the fields are important, but to what degree we don't yet know. Observations to date have been limited by the sensitivity of available telescopes and instrumentation. In the future ALMA and the SKA in particular should provide great advances in observational studies of magnetic fields, and we discuss which observations are most desirable when they become available.

Tyler L. Bourke; Alyssa A. Goodman

2004-01-14

242

Modeling Earth's magnetic field variation  

NASA Astrophysics Data System (ADS)

Observations of the Earth's magnetic field taken at the Earth's surface and at satellite altitude have been combined to construct models of the geomagnetic field and its variation. Lesur et al. (2010) developed a kinematic reconstruction of core field changes that satisfied the frozen-flux constraint. By constraining the field evolution to be entirely due to advection of the magnetic field at the core surface it maintained the spatial complexity of the field morphology imposed by a satellite field model backward in time [Wardinski & Lesur,2012]. In this study we attempt a kinematic construction of future variation in Earth's magnetic field variation. Our approach, first seeks to identify typical time scales of the magnetic field and core surface flows present in decadal and millennial field and flow models. Therefore, the individual spherical harmonic coefficients are treated by methods of time series analysis. The second step employs stochastic modelling of the temporal variability of such spherical harmonic coefficients that represent the field and core surface flow. Difficulties arise due to the non-stationary behavior of the field and core surface flow. However, the broad behavior may consist of some homogeneity, which could be captured by a generalized stochastic model that calls for the d'th difference of the time series to be stationary (ARIMA-Model), or by detrending the coefficient time series. By computing stochastic models, we obtain two sets of field-forecasts, the first set is obtained from stochastic models of the Gauss coefficients. Here, first results suggest that secular variation on time scales shorter than 5 years behaves rather randomly and cannot be described sufficiently well by stochastic models. The second set is derived from forward modeling the secular variation using the diffusion-less induction equation (kinematic construction). This approach has not provide consistent results.

Wardinski, I.

2012-12-01

243

Magnetic Fields and Mass Inflow in Central Regions of Barred Galaxies  

NASA Astrophysics Data System (ADS)

Radio continuum emission is an excellent tracer of star formation in central regions of galaxies. We observed a sample of 20 galaxies with massive bars. The regular magnetic fields around the bar, as traced by the polarized emission, do not always follow the gas flow predicted from numerical simulations and show little compression by the shock. The galaxies with the longest bars show the strongest deviations of the magnetic field pattern from axial symmetry, and most of them host nuclear rings. The total magnetic fields in these nuclear rings of up to ~= 100 ?G are among the strongest fields known in spiral galaxies. The regular field in the nuclear ring of NGC 1097 is of spiral shape. Magnetic stress in the ring can drive mass inflow of about one solar mass per year which is sufficient to feed the active nucleus. This process may also work in non-barred galaxies.

Beck, Rainer; Ehle, Matthias; Fletcher, Andrew; Harnett, Julienne; Shoutenkov, Vladimir; Shukurov, Anvar; Sokoloff, Dmitry

2005-08-01

244

LABORATORY V MAGNETIC FIELDS AND FORCES  

E-print Network

's technology. Magnets are used today to image parts of the body, to explore the mysteries of the human brain to combine magnets to change the magnetic field at any point. You must determine the map of the magnetic

Minnesota, University of

245

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

246

Black holes and magnetic fields  

E-print Network

Stationary axisymmetric magnetic fields are expelled from outer horizons of black holes as they become extremal. Extreme black holes exhibit Meissner effect also within exact Einstein--Maxwell theory and in string theories in higher dimensions. Since maximally rotating black holes are expected to be astrophysically most important, the expulsion of the magnetic flux from their horizons represents a potential threat to an electromagnetic mechanism launching the jets at the account of black-hole rotation.

J. Bicak; V. Karas; T. Ledvinka

2007-04-09

247

Observations of Mercury's magnetic field  

NASA Technical Reports Server (NTRS)

Magnetic field data obtained by Mariner 10 during the third and final encounter with the planet Mercury on 16 March 1975 were studied. A well developed bow shock and modest magnetosphere, previously observed at first encounter on 29 March 1974, were again observed. In addition, a much stronger magnetic field near closest approach, 400 gamma versus 98 gamma, was observed at an altitude of 327 km and approximately 70 deg north Mercurian latitude. Spherical harmonic analysis of the data provide an estimate of the centered planetary magnetic dipole of 4.7 x 10 to the 22nd power Gauss/cu cm with the axis tilted 12 deg to the rotation axis and in the same sense as Earth's. The interplanetary field was sufficiently different between first and third encounters that in addition to the very large field magnitude observed, it argues strongly against a complex induction process generating the observed planetary field. While a possibility exists that Mercury possesses a remanent field due to magnetization early in its formation, a present day active dynamo seems to be a more likely candidate for its origin.

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

1975-01-01

248

Theory of a ring laser. [electromagnetic field and wave equations  

NASA Technical Reports Server (NTRS)

Development of a systematic formulation of the theory of a ring laser which is based on first principles and uses a well-known model for laser operation. A simple physical derivation of the electromagnetic field equations for a noninertial reference frame in uniform rotation is presented, and an attempt is made to clarify the nature of the Fox-Li modes for an open polygonal resonator. The polarization of the active medium is obtained by using a Fourier-series method which permits the formulation of a strong-signal theory, and solutions are given in terms of continued fractions. It is shown that when such a continued fraction is expanded to third order in the fields, the familiar small-signal ring-laser theory is obtained.

Menegozzi, L. N.; Lamb, W. E., Jr.

1973-01-01

249

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

250

Magnetic Fields of the Earth and Sun  

NSDL National Science Digital Library

This is an activity that compares the magnetic field of the Earth to the complex magnetic field of the Sun. Using images of the Earth and Sun that have magnets attached in appropriate orientations, learners will use a handheld magnetic field detector to observe the magnetic field of the Earth and compare it to that of the Sun, especially in sunspot areas. For each group of students, this activity requires use of a handheld magnetic field detector, such as a Magnaprobe or a similar device, a bar magnet, and ten small disc magnets.

251

Magnetic Forces and Field Line Density  

NSDL National Science Digital Library

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

252

The Giotto magnetic-field investigation  

NASA Technical Reports Server (NTRS)

The objectives of the Giotto magnetometer experiment are the investigation of the interaction between Comet Halley and the solar wind 0.9 AU from the Sun, to within 500 km of the cometary nucleus, and the study of the interplanetary magnetic field. The instrumentation consists of a triaxial and a separate biaxial system of fluxgate sensors of the ring-core type, the associated analog electronics and a digital processor. The measuring ranges of + or 1 16 up to + or - 65536 nT are digitized by a 12-bit analog-to-digital converter. Memory modes allow the bridging of gaps in telemetry coverage of up to 10 days. Because of the dust hazard near closest approach, a magnetometer boom could not be included in the spacecraft design. The magnetic contamination problem was attacked by the use of two magnetometers and by a magnetic-cleanliness program. In-flight results show that the instrument is working flawlessly, though magnetic-contamination problems remain.

Neubauer, F. M.; Acuna, M. H.; Burlaga, L. F.; Franke, B.; Gramkow, B.; Mariani, F.; Musmann, G.; Ness, N. F.; Schmidt, H. U.; Terenzi, T.

1986-01-01

253

Construction and Power Test of the Extraction Kicker Magnet for Spallation Neutron Source Accumulator Ring  

Microsoft Academic Search

Two extraction kicker magnet assemblies that contain seven individual pulsed magnet modules each will kick the proton beam vertically out of the SNS accumulator ring into the aperture of the extraction Lambertson septum magnet. The proton beam then travels to the 1.4 MW SNS target assembly. The 14 kicker magnets and major components of the kicker assembly have been fabricated

C. Pai; H. Hahn; H. Hseuh; Y. Lee; W. Meng; J. Mi; J. Sandberg; R. Todd; D. Raparia; N. Tsoupas; J. Tuozzolo; D. Warburton; J. Wei; D. Weiss; W. Zhang

2005-01-01

254

CONSTRUCTION AND POWER TEST OF THE EXTRACTION KICKER MAGNET FOR SNS ACCUMULATOR RING  

Microsoft Academic Search

Two extraction kicker magnet assemblies that contain seven individual pulsed magnet modules each will kick the proton beam vertically out of the SNS accumulator ring into the aperture of the extraction Lambertson septum magnet. The proton beam then travels to the 1.4 MW SNS target assembly. The 14 kicker magnets and major components of the kicker assembly have been fabricated

C. PAI; H. HAHN; H. HSEUH; Y. LEE; W. MENG; J. MI; J. SANDBERG; R. TODD

2005-01-01

255

Origin of astrophysical magnetic fields.  

NASA Astrophysics Data System (ADS)

The standard model for the origin of magnetic fields observed in stars and galaxies is the ?-? dynamo, in which a feedback loop involving differential rotation and helical turbulence leads to exponential amplification of a large-scale field. Recently this model has been criticized on the grounds that the Lorentz forces associated with the buildup of small-scale fields by the turbulence prevents the turbulent diffusion of magnetic field that is an essential part of the model. The author discusses the consequences for cosmology if dynamo theory is wrong, and reviews recent criticisms from a new perspective. They suggest new calculations that can help to decide whether the theory is right or wrong.

Field, George B.

256

Effects of magnetic fields on iron electrodeposition  

Microsoft Academic Search

The effects of magnetic fields (of 0–5 T magnetic flux density) on iron electrodeposition were investigated in terms of current efficiency, morphology and crystal orientation. The AFM images showed that the shape of iron grains was angular in no magnetic field and roundish in magnetic fields. The occurrence of preferred orientation parallel to the substrate plane was influenced by an

H. Matsushima; T. Nohira; I. Mogi; Y. Ito

2004-01-01

257

How to Draw Magnetic Fields - I  

NSDL National Science Digital Library

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

258

Isomorphism criteria for Witt rings of real fields Nicolas Grenier-Boley, Detlev W. Hoffmann  

E-print Network

Isomorphism criteria for Witt rings of real fields Nicolas Grenier-Boley, Detlev W for Witt rings and reduced Witt rings of certain types of real fields. Refined criteria are obtained under the additional assumption that the field be SAP. This leads to a generalization of a result by Koprowski on Witt

259

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

260

Jupiter's magnetic field and magnetosphere  

NASA Technical Reports Server (NTRS)

Among the planets of the solar system, Jupiter is unique in connection with its size and its large magnetic moment, second only to the sun's. The Jovian magnetic field was first detected indirectly by radio astronomers who postulated its existence to explain observations of nonthermal radio emissions from Jupiter at decimetric and decametric wavelengths. Since the early radio astronomical studies of the Jovian magnetosphere, four spacecraft have flown by the planet at close distances and have provided in situ information about the geometry of the magnetic field and its strength. The Jovian magnetosphere is described in terms of three principal regions. The inner magnetosphere is the region where the magnetic field created by sources internal to the planet dominates. The region in which the equatorial currents flow is denoted as the middle magnetosphere. In the outer magnetosphere, the field has a large southward component and exhibits large temporal and/or spatial variations in magnitude and direction in response to changes in solar wind pressure.

Acuna, M. H.; Behannon, K. W.; Connerney, J. E. P.

1983-01-01

261

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

262

Simultaneous near field imaging of electric and magnetic field in photonic crystal nanocavities  

NASA Astrophysics Data System (ADS)

The insertion of a metal-coated tip on the surface of a photonic crystal microcavity is used for simultaneous near field imaging of electric and magnetic fields in photonic crystal nanocavities, via the radiative emission of embedded semiconductor quantum dots (QD). The photoluminescence intensity map directly gives the electric field distribution, to which the electric dipole of the QD is coupled. The magnetic field generates, via Faraday's law, a circular current in the apex of the metallized probe that can be schematized as a ring. The resulting magnetic perturbation of the photonic modes induces a blue shift, which can be used to map the magnetic field, within a single near-field scan.

Vignolini, Silvia; Intonti, Francesca; Riboli, Francesco; Wiersma, Diederik Sybolt; Balet, Laurent; Li, Lianhe H.; Francardi, Marco; Gerardino, Annamaria; Fiore, Andrea; Gurioli, Massimo

2012-06-01

263

A high-field superferric NMR magnet.  

PubMed

Strong, extensive magnetic fringe fields are a significant problem with magnetic resonance imaging magnets. This is particularly acute with 4-T, whole-body research magnets. To date this problem has been addressed by restricting an extensive zone around the unshielded magnet or by placing external unsaturated iron shielding around the magnet. This paper describes a solution to this problem which uses superconducting coils closely integrated with fully saturated iron elements. A 4-T, 30-cm-bore prototype, based on this design principle, was built and tested. The 5 G fringe field is contained within 1 meter of the magnet bore along the z axis. Homogeneity of the raw magnetic field is 10 ppm over 30% of the magnet's diameter after passive shimming. Compared with an unshielded magnet, 20% less superconductor is required to generate the magnetic field. Images and spectra are presented to demonstrate the magnet's viability for magnetic resonance imaging and spectroscopy. PMID:8419740

Huson, F R; Bryan, R N; MacKay, W W; Herrick, R C; Colvin, J; Ford, J J; Pissanetzky, S; Plishker, G A; Rocha, R; Schmidt, W

1993-01-01

264

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

265

Magnetic fields in spiral galaxies  

NASA Astrophysics Data System (ADS)

The magnetic field structure in edge-on galaxies observed so far shows a plane-parallel magnetic field component in the disk of the galaxy and an X-shaped field in its halo. The plane-parallel field is thought to be the projected axisymmetric (ASS) disk field as observed in face-on galaxies. Some galaxies addionionally exhibit strong vertical magnetic fields in the halo right above and below the central region of the disk. The mean-field dynamo theory in the disk cannot explain these observed fields without the action of a wind, which also probably plays an important role to keep the vertical scale heights constant in galaxies of different Hubble types and star formation activities, as has been observed in the radio continuum: At ?6 cm the vertical scale heights of the thin disk and the thick disk/halo in a sample of five edge-on galaxies are similar with a mean value of 300 +/- 50 pc for the thin disk and 1.8 +/- 0.2 kpc for the thick disk (a table and references are given in Krause 2011) with our sample including the brightest halo observed so far, NGC 253, with strong star formation, as well as one of the weakest halos, NGC 4565, with weak star formation. If synchrotron emission is the dominant loss process of the relativistic electrons the outer shape of the radio emission should be dumbbell-like as has been observed in several edge-on galaxies like e.g. NGC 253 (Heesen et al. 2009) and NGC 4565. As the synchrotron lifetime t syn at a single frequency is proportional to the total magnetic field strength B t -1.5, a cosmic ray bulk speed (velocity of a galactic wind) can be defined as v CR = h CR /t syn = 2 h z /t syn , where h CR and h z are the scale heights of the cosmic rays and the observed radio emission at this freqnency. Similar observed radio scale heights imply a self regulation mechanism between the galactic wind velocity, the total magnetic field strength and the star formation rate SFR in the disk: v CR ~ B t 1.5 ~ SFR ~ 0.5 (Niklas & Beck 1997).

Krause, Marita

2015-03-01

266

Slotless Permanent-Magnet Machines: General Analytical Magnetic Field Calculation  

Microsoft Academic Search

This paper presents a general analytical model for predicting the magnetic field of slotless permanent-magnet machines. The model takes into account the effect of eddy currents in conductive regions and notably in conductive permanent magnets without neglecting their remanent field. The modeling of this effect is important for the design of very high speed slotless permanent-magnet machines, as the power

Pierre-Daniel Pfister; Yves Perriard

2011-01-01

267

Dynamics of a tight-binding ring threaded by time-periodic magnetic flux  

SciTech Connect

We analytically study the effects of periodically alternating magnetic fields on the dynamics of a tight-binding ring. It is shown that an arbitrary quantum state can be frozen coherently at will by the very frequent square-wave field as well as the monochromatic-wave field when the corresponding optimal amplitudes are taken. Numerical simulations show that the average fidelity depends on not only the system parameters, but also the features of the quantum state. Moreover, taking the initial zero-momentum Gaussian wave packets as examples, we show the dependence of the threshold frequency on the width of the packet for the given average fidelities. These observations provide a means to perform the quantum-state engineering.

Hu, W. H.; Song, Z. [School of Physics, Nankai University, Tianjin 300071 (China)

2011-11-15

268

Advances in high field magnetism at Osaka  

NASA Astrophysics Data System (ADS)

Recent advances in high field magnetism mainly done in the High Magnetic Field Laboratory, Osaka University, are reviewed. Various magnetic and electronic properties are induced in high fields; it is emphasized that the newly developed incommensurate mean field model is effective in understanding complex phase diagrams such as in CeSb, CeBi and PrCo 2Si 2.

Date, M.

1989-03-01

269

LABORATORY V MAGNETIC FIELDS AND FORCES  

E-print Network

's technology. Magnets are used today to image parts of the body, to explore the mysteries of the human brain to combine magnets to change the magnetic field at any point. You decide to determine the form

Minnesota, University of

270

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

271

Quantitative estimates of magnetic field reconnection properties from electric and magnetic field measurements  

E-print Network

Quantitative estimates of magnetic field reconnection properties from electric and magnetic field there are positive electric field components tangential to the magnetopause and a magnetic field component normal to it. Because these three components are the smallest of the six electric and magnetic fields

California at Berkeley, University of

272

A ring of polarized light: evidence for twisted coronal magnetism in cavities (Invited)  

NASA Astrophysics Data System (ADS)

Determining coronal magnetic fields is crucial to modeling the processes that power and trigger solar flares and coronal mass ejections. Coronal prominence cavities have been modeled as magnetic flux ropes, and have been observed to erupt bodily as coronal mass ejections. One promising technique for establishing the magnetic morphology of cavities is to use spectropolarimetry of the infrared (IR) forbidden lines of Fe XIII (at 1074.7 nm and 1079.8 nm). The Coronal Multi-Channel Polarimeter is currently situated at the Mauna Loa Solar Observatory (MLSO), and has begun taking daily full-Sun observations of line-of-sight integrated Stokes parameters for these lines. For a variety of analytic coronal magnetohydrodynamic models, we have determined forward-calculations of CoMP observables using the formalism of Judge and Casini (2001). We show that different MHD models and orientations do yield distinguishing observational characteristics. In particular, a common characteristic for spheroidal flux ropes oriented along the observational line of sight is a ring of linear polarization surrounding a region where the linear polarization strength is relatively depleted (the heart of darkness). Such a polarization ring has been found in an observation of a coronal cavity taken by CoMP in April 2005 from Sacramento Peak. Cavities are ubiquitous features, particularly at this time of the solar cycle. The daily observations to be taken by CoMP at MLSO will allow us to further probe these structures, constraining models of coronal magnetism and providing a testbed for future capabilities of the proposed Coronal Solar Magnetism Observatory (COSMO).

Dove, J.; Rachmeler, L.; Gibson, S. E.; Judge, P. G.; Tomczyk, S.

2010-12-01

273

Explaining Mercury's peculiar magnetic field  

NASA Astrophysics Data System (ADS)

MESSENGER magnetometer data revealed that Mercury's magnetic field is not only particularly weak but also has a peculiar geometry. The MESSENGER team finds that the location of the magnetic equator always lies significantly north of the geographic equator, is largely independent of the distance to the planet, and also varies only weakly with longitude. The field is best described by an axial dipole that is offset to the north by about 20% of the planetary radius. In terms of classical Gauss coefficients, this translates into a low axial dipole component of g10= -190 nT but a relatively large axial quadrupole contribution that amounts to roughly 40% of this value. The axial octupole is also sizable while higher harmonic contributions are much weaker. Very remarkable is also the fact that the equatorial dipole contribution is very small, consistent with a dipole tilt below 0.8 degree, and this is also true for the other non-axisymmetic field contributions. We analyze several numerical dynamos concerning their capability of explaining Mercury's magnetic field. Classical schemes geared to model the geomagnetic field typically show a much weaker quadrupole component and thus a smaller offset. The onset only becomes larger when the dynamo operates in the multipolar regime at higher Rayleigh numbers. However, since the more complex dynamics generally promotes all higher multipole contributions the location of the magnetic equator varies strongly with longitude and distance to the planet. The situation improves when introducing a stably stratified outer layer in the dynamo region, representing either a rigid FeS layer or a sub-adiabatic core-mantle boundary heat flux. This layer filters out the higher harmonic contributions and the field not only becomes sufficiently weak but also assumes a Mercury like offset geometry during a few percent of the simulation time. To increase the likelihood for the offset configuration, the north-south symmetry must be permanently broken and we explore two scenarios. Increasing the heat flux through the northern hemisphere of the core-mantle boundary is an obvious choice but is not supported by current models for Mercury's mantle. We find that a combination of internal rather than bottom driving and an increased heat flux through the equatorial region of the core-mantle boundary also promotes the required symmetry breaking and results in very Mercury like fields. The reason is that the imposed heat flux pattern, though being equatorially symmetric, lowers the critical Rayleigh number for the onset of equatorially anti-symmetric convection modes. In both scenarios, a stably stratified layer or a feedback coupling to the magnetospheric field is required for lowering the field strength to Mercury-like values.

Wicht, Johannes; Cao, Hao; Heyner, Daniel; Dietrich, Wieland; Christensen, Ulrich R.

2014-05-01

274

Passive Superconducting Flux Conservers for Rotating-Magnetic-Field-Driven Field-Reversed Configurations  

SciTech Connect

The Princeton Field-Reversed Configuration (PFRC) experiment employs an odd-parity rotating magnetic field (RMFo) current drive and plasma heating system to form and sustain high-? plasmas. For radial confinement, an array of coaxial, internal, passive, flux-conserving (FC) rings applies magnetic pressure to the plasma while still allowing radio-frequency RMFo from external coils to reach the plasma. The 3 ms pulse duration of the present experiment is limited by the skin time (?fc) of its room-temperature copper FC rings. To explore plasma phenomena with longer characteristic times, the pulse duration of the next-generation PFRC-2 device will exceed 100 ms, necessitating FC rings with (?fc > 300 ms. In this paper we review the physics of internal, discrete, passive FCs and describe the evolution of the PFRC's FC array. We then detail new experiments that have produced higher performance FC rings that contain embedded high-temperature superconducting (HTS) tapes. Several HTS tape winding configurations have been studied and a wide range of extended skin times, from 0.4 s to over 103 s, has been achieved. The new FC rings must carry up to 3 kA of current to balance the expected PFRC-2 plasma pressure, so the dependence of the HTS-FC critical current on the winding configuration and temperature was also studied. From these experiments, the key HTS-FC design considerations have been identified and HTS-FC rings with the desired performance characteristics have been produced.

Oz, E.; Myers, C. E.; Edwards, M. R.; Berlinger, B.; Brooks, A.; Cohen, S. A.

2011-01-05

275

Causes of Ring-Related Leg Injuries in Birds – Evidence and Recommendations from Four Field Studies  

PubMed Central

One of the main techniques for recognizing individuals in avian field research is marking birds with plastic and metal leg rings. However, in some species individuals may react negatively to rings, causing leg injuries and, in extreme cases, the loss of a foot or limb. Here, we report problems that arise from ringing and illustrate solutions based on field data from Brown Thornbills (Acanthiza pusilla) (2 populations), Siberian Jays (Perisoreus infaustus) and Purple-crowned Fairy-wrens (Malurus coronatus). We encountered three problems caused by plastic rings: inflammations triggered by material accumulating under the ring (Purple-crowned Fairy-wrens), contact inflammations as a consequence of plastic rings touching the foot or tibio-tarsal joint (Brown Thornbills), and toes or the foot getting trapped in partly unwrapped flat-band colour rings (Siberian Jays). Metal rings caused two problems: the edges of aluminium rings bent inwards if mounted on top of each other (Brown Thornbills), and too small a ring size led to inflammation (Purple-crowned Fairy-wrens). We overcame these problems by changing the ringing technique (using different ring types or larger rings), or using different adhesive. Additionally, we developed and tested a novel, simple technique of gluing plastic rings onto metal rings in Brown Thornbills. A review of studies reporting ring injuries (N?=?23) showed that small birds (<55 g body weight) are more prone to leg infections while larger birds (>35 g) tend to get rings stuck over their feet. We give methodological advice on how these problems can be avoided, and suggest a ringing hazard index to compare the impact of ringing in terms of injury on different bird species. Finally, to facilitate improvements in ringing techniques, we encourage online deposition of information regarding ringing injuries of birds at a website hosted by the European Union for Bird Ringing (EURING). PMID:23300574

Griesser, Michael; Schneider, Nicole A.; Collis, Mary-Anne; Overs, Anthony; Guppy, Michael; Guppy, Sarah; Takeuchi, Naoko; Collins, Pete; Peters, Anne; Hall, Michelle L.

2012-01-01

276

PLANT GROWTH UNDER STATIC MAGNETIC FIELD INFLUENCEê  

Microsoft Academic Search

Already germinated seeds of Zea mays were cultivated in the presence of static magnetic field in order to observe several biochemical changes and stimulation effect on plantlets growth. Magnetic treatment involved the application of five different values of magnetic induction of static magnetic field, ranging between 50 mT and 250 mT, during 14 days. In order to investigate the biochemical

M. RÃCUCIU; D. CREANGÃ; I. HORGA

2008-01-01

277

Field errors in superconducting magnets  

SciTech Connect

The mission of this workshop is a discussion of the techniques for tracking particles through arbitrary accelerator field configurations to look for dynamical effects that are suggested by various theoretical models but are not amenable to detailed analysis. A major motivation for this type of study is that many of our accelerator projects are based on the use of superconducting magnets which have field imperfections that are larger and of a more complex nature than those of conventional magnets. Questions such as resonances, uncorrectable closed orbit effects, coupling between planes, and diffusion mechanisms all assume new importance. Since, simultaneously, we are trying to do sophisticated beam manipulations such as stacking, high current accelerator, long life storage, and low loss extraction, we clearly need efficient and accurate tracking programs to proceed with confidence.

Barton, M.Q.

1982-01-01

278

Isomorphism criteria for Witt rings of real fields Nicolas GrenierBoley, Detlev W. Hoffmann  

E-print Network

Isomorphism criteria for Witt rings of real fields Nicolas Grenier­Boley, Detlev W. Hoffmann With an appendix by Claus Scheiderer Abstract. We prove isomorphism criteria for Witt rings and reduced Witt rings be SAP. This leads to a generalization of a result by Koprowski on Witt equivalence of function fields

279

Isomorphism criteria for Witt rings of real fields Nicolas Grenier-Boley, Detlev W. Hoffmann  

E-print Network

Isomorphism criteria for Witt rings of real fields Nicolas Grenier-Boley, Detlev W. Hoffmann With an appendix by Claus Scheiderer Abstract. We prove isomorphism criteria for Witt rings and reduced Witt rings be SAP. This leads to a generalization of a result by Koprowski on Witt equivalence of function fields

280

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

281

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

282

Rotating copper plasmoid in external magnetic field  

SciTech Connect

Effect of nonuniform magnetic field on the expanding copper plasmoid in helium and argon gases using optical emission spectroscopy and fast imaging is presented. We report a peculiar oscillatory rotation of plasmoid in magnetic field and argon ambient. The temporal variation and appearance of the dip in the electron temperature show a direct evidence of the threading and expulsion of the magnetic field lines from the plasmoid. Rayleigh Taylor instability produced at the interface separating magnetic field and plasma is discussed.

Pandey, Pramod K.; Thareja, Raj K. [Department of Physics, Indian Institute of Technology Kanpur, Uttar Pradesh 208 016 (India)

2013-02-15

283

Minireview: Biological effects of magnetic fields  

SciTech Connect

The literature about the biological effects of magnetic fields is reviewed. The authors begin by discussing the weak and/or time variable fields, responsible for subtle changes in the circadian rhythms of superior animals, which are believed to be induced by same sort of resonant mechanism. The safety issues related with the strong magnetic fields and gradients generated by clinical NMR magnets are then considered. The last portion summarizes the debate about the biological effects of strong and uniform magnetic fields.

Villa, M.; Mustarelli, P. (Lab. NMR, Pavia (Italy)); Caprotti, M. (Fondazione Clinica del Lavoro, Pavia (Italy))

1991-01-01

284

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

285

Anisotropy of magnetic emulsions induced by magnetic and electric fields  

E-print Network

The anisotropy of magnetic emulsions induced by simultaneously acting electric and magnetic fields is theoretically and experimentally investigated. Due to the anisotropy, the electric conductivity and magnetic permeability of a magnetic emulsion are no longer scalar coefficients, but are tensors. The electric conductivity and magnetic permeability tensors of sufficiently diluted emulsions in sufficiently weak electric and magnetic fields are found as functions of the electric and magnetic intensity vectors. The theoretically predicted induced anisotropy was verified experimentally. The experimental data are analyzed and compared with theoretical predictions. The results of the analysis and comparison are discussed.

Yury I. Dikansky; Alexander N. Tyatyushkin; Arthur R. Zakinyan

2011-09-10

286

Microwave Measurements of Coronal Magnetic Field  

NASA Astrophysics Data System (ADS)

Magnetic field measurements of the solar corona using microwave observation are reviewed. The solar corona is filled with highly ionised plasma and magnetic field. Moving charged particles interact with magnetic field due to Lorentz force. This results in gyration motion perpendicular to the magnetic field and free motion along the magnetic field. Circularly polarized electro-magnetic waves interact with gyrating electrons efficiently and the interaction depends on the sense of circular polarization (right-handed or left-handed). This is the reason why we can measure magnetic field strength through microwave observations. This process does not require complicated quantum physics but the classical treatment is enough. Hence the inversion of measured values to magnetic field strength is simpler than in the case of optical and infrared measurements. There are several methods to measure magnetic field strength through microwave observations. We can divide them into two categories: one is based on emission mechanisms and the other is based on wave propagation. In the case of emission mechanisms, thermal f-f emission, thermal gyro-resonance emission and non-thermal gyro-synchrotron emission can be used to measure magnetic field strength. In the case of wave propagation, polarization reversal due to propagation through quasi-transverse magnetic field region can be used. Examples of distribution of magnetic field strength in the solar corona measured by Nobeyama Radioheliograph will be presented.

Shibasaki, K.

2006-08-01

287

The Galactic Magnetic Field as Viewed from the VLA  

NASA Astrophysics Data System (ADS)

Interstellar magnetic fields play critical roles in many astrophysical processes. Yet despite their importance, our knowledge about magnetic fields in our Galaxy remains limited. For the field within the Milky Way much of what we do know comes from radio astronomy, through observations of polarization and Faraday rotation measures (RMs) of extragalactic sources and pulsars. A high angular density of RM measurements in several critical areas of the Galaxy is needed to clarify the Galactic magnetic field structure. Understanding the overall structure of the magnetic field will subsequently help us determine the origin and evolution of the field. In an effort to determine the overall structure of the field, Sun et al. (2008) produced 3 models of the Galactic magnetic field based on RM measurements available at the time. These models made distinct predictions for RMs in a region of the inner Galaxy at low Galactic latitude. Using observations made with the Very Large Array (VLA), we have determined RMs for sources in this critical region. In this talk we will present the results of our study and show how the RMs strongly support the ASS+RING model.

van Eck, Cameron; Brown, Jo-Anne

2009-05-01

288

Performance of the main ring magnet power supply of the KEK 12 GeV proton synchrotron  

Microsoft Academic Search

The main ring magnet power supply of the KEK 12-GeV proton synchrotron consists of several twelve-pulse thyristor rectifiers with DC filters, two reactive power compensators with tuned AC harmonic filters, and an analog and digital hybrid control system. To obtain well-defined parameters such as absolute precision of beam energy, stable beam position, tracking between focusing and bending fields to fix

H. Sato; T. Sueno; T. Toyama; Ml Mikawa; M. Toda; S. Matsumoto; M. Nakano

1992-01-01

289

Harmonic undulator radiations with constant magnetic field  

NASA Astrophysics Data System (ADS)

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

Jeevakhan, Hussain; Mishra, G.

2015-01-01

290

Morphology and magnetic flux distribution in superparamagnetic, single-crystalline Fe3O4 nanoparticle rings  

NASA Astrophysics Data System (ADS)

This study reports on the correlation between crystal orientation and magnetic flux distribution of Fe3O4 nanoparticles in the form of self-assembled rings. High-resolution transmission electron microscopy demonstrated that the nanoparticles were single-crystalline, highly monodispersed, (25 nm average diameter), and showed no appreciable lattice imperfections such as twins or stacking faults. Electron holography studies of these superparamagnetic nanoparticle rings indicated significant fluctuations in the magnetic flux lines, consistent with variations in the magnetocrystalline anisotropy of the nanoparticles. The observations provide useful information for a deeper understanding of the micromagnetics of ultrasmall nanoparticles, where the magnetic dipolar interaction competes with the magnetic anisotropy.

Takeno, Yumu; Murakami, Yasukazu; Sato, Takeshi; Tanigaki, Toshiaki; Park, Hyun Soon; Shindo, Daisuke; Ferguson, R. Matthew; Krishnan, Kannan M.

2014-11-01

291

How to Draw Magnetic Fields - II  

NSDL National Science Digital Library

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

2012-08-03

292

Interplanetary magnetic field data book  

NASA Technical Reports Server (NTRS)

An interplanetary magnetic field (IMF) data set is presented that is uniform with respect to inclusion of cislunar IMF data only, and which has as complete time coverage as presently possible over a full solar cycle. Macroscale phenomena in the interplanetary medium (sector structure, heliolatitude variations, solar cycle variations, etc.) and other phenomena (e.g., ground level cosmic-ray events) for which knowledge of the IMF with hourly resolution is necessary, are discussed. Listings and plots of cislunar hourly averaged IMP parameters over the period November 27, 1963, to May 17, 1974, are presented along with discussion of the mutual consistency of the IMF data used herein. The magnetic tape from which the plots and listings were generated, which is available from the National Space Science Data Center (NSSDC), is also discussed.

King, J. H.

1975-01-01

293

Magnetic field driven domain-wall propagation in magnetic nanowires  

SciTech Connect

The mechanism of magnetic field induced magnetic domain-wall (DW) propagation in a nanowire is revealed: A static DW cannot exist in a homogeneous magnetic nanowire when an external magnetic field is applied. Thus, a DW must vary with time under a static magnetic field. A moving DW must dissipate energy due to the Gilbert damping. As a result, the wire has to release its Zeeman energy through the DW propagation along the field direction. The DW propagation speed is proportional to the energy dissipation rate that is determined by the DW structure. The negative differential mobility in the intermediate field is due to the transition from high energy dissipation at low field to low energy dissipation at high field. For the field larger than the so-called Walker breakdown field, DW plane precesses around the wire, leading to the propagation speed oscillation.

Wang, X.R. [Physics Department, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong (China); Yan, P. [Physics Department, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong (China)], E-mail: yanpeng@ust.hk; Lu, J.; He, C. [Physics Department, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong (China)

2009-08-15

294

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

295

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

296

Behavior of the magnetic structures of the magnetic fluid film under tilted magnetic fields  

Microsoft Academic Search

The patterns of the magnetic structure of the magnetic fluid thin film under tilted magnetic fields were taken to investigate the behavior of magnetic structures. The tilted angle ? is the angle between the direction of applied magnetic field and the normal line of the film. In our previous work, a nearly perfect ordered hexagonal structure in magnetic fluid thin

H. C Yang; I. J Jang; H. E Horng; J. M Wu; Y. C Chiou; Chin-Yih Hong

1999-01-01

297

Behavior of the magnetic structures of the magnetic fluid film under tilted magnetic fields  

Microsoft Academic Search

The patterns of the magnetic structure of the magnetic fluid thin film under tilted magnetic fields were taken to investigate the behavior of magnetic structures. The tilted angle theta is the angle between the direction of applied magnetic field and the normal line of the film. In our previous work, a nearly perfect ordered hexagonal structure in magnetic fluid thin

H. C. Yang; I. J. Jang; H. E. Horng; J. M. Wu; Y. C. Chiou; Chin-Yih Hong

1999-01-01

298

Rings  

NASA Astrophysics Data System (ADS)

Rings recounts one of the most fascinating stories to emerge from our recent exploration of the solar system. In the past decade scientists have learned more about this beautiful astronomical phenomenon than was ever known before. James Elliot played a leading role in the scientific group that discovered the rings of Uranus, and Richard Kerr has covered Voyager's encounters with Jupiter, Saturn, and Uranus for Science magazine. Together they capture the excitement of the new discoveries - the first since Galileo observed Saturn's rings in 1610 - while showing the central role serendipity can play in scientific progress. James Elliot is Professor of Astronomy and Physics at MIT and Director of the George R. Wallace, Jr., Astrophysical Observatory. Richard Kerr is a senior writer on the research news staff of Science magazine. Copies of the tape that recorded the discovery of the Uranian rings are available from The MIT Press.

Elliot, James; Kerr, Richard

1987-04-01

299

Near-Field Magnetic Dipole Moment Analysis  

NASA Technical Reports Server (NTRS)

This paper describes the data analysis technique used for magnetic testing at the NASA Goddard Space Flight Center (GSFC). Excellent results have been obtained using this technique to convert a spacecraft s measured magnetic field data into its respective magnetic dipole moment model. The model is most accurate with the earth s geomagnetic field cancelled in a spherical region bounded by the measurement magnetometers with a minimum radius large enough to enclose the magnetic source. Considerably enhanced spacecraft magnetic testing is offered by using this technique in conjunction with a computer-controlled magnetic field measurement system. Such a system, with real-time magnetic field display capabilities, has been incorporated into other existing magnetic measurement facilities and is also used at remote locations where transport to a magnetics test facility is impractical.

Harris, Patrick K.

2003-01-01

300

Magnetic field observations in Comet Halley's coma  

NASA Astrophysics Data System (ADS)

During the encounter with Comet Halley, the magnetometer (MISCHA) aboard the Vega 1 spacecraft observed an increased level of magnetic field turbulence, resulting from an upstream bow wave. Both Vega spacecraft measured a peak field strength of 70-80 nT and observed draping of magnetic field lines around the cometary obstacle. An unexpected rotation of the magnetic field vector was observed, which may reflect either penetration of magnetic field lines into a diffuse layer related to the contact surface separating the solar-wind and cometary plasma, or the persistence of pre-existing interplanetary field structures.

Riedler, W.; Schwingenschuh, K.; Yeroshenko, Ye. G.; Styashkin, V. A.; Russell, C. T.

1986-05-01

301

Full 180° Magnetization Reversal with Electric Fields  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

302

Full 180° magnetization reversal with electric fields.  

PubMed

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

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

2014-01-01

303

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

304

Full 180° Magnetization Reversal with Electric Fields  

PubMed Central

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

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

2014-01-01

305

Magnetic field calculation and measurement of active magnetic bearings  

NASA Astrophysics Data System (ADS)

Magnetic Bearings are typical devices in which electric energy and mechanical energy convert mutually. Magnetic Field indicates the relationship between 2 of the most important parameters in a magnetic bearing - current and force. This paper presents calculation and measurement of the magnetic field distribution of a self-designed magnetic bearing. Firstly, the static Maxwell's equations of the magnetic bearing are presented and a Finite Element Analysis (FEA) is found to solve the equations and get post-process results by means of ANSYS software. Secondly, to confirm the calculation results a Lakeshore460 3-channel Gaussmeter is used to measure the magnetic flux density of the magnetic bearing in X, Y, Z directions accurately. According to the measurement data the author constructs a 3D magnetic field distribution digital model by means of MATLAB software. Thirdly, the calculation results and the measurement data are compared and analyzed; the comparing result indicates that the calculation results are consistent with the measurement data in allowable dimension variation, which means that the FEA calculation method of the magnetic bearing has high precision. Finally, it is concluded that the magnetic field calculation and measurement can accurately reflect the real magnetic distribution in the magnetic bearing and the result can guide the design and analysis of the magnetic bearing effectively.

Ding, Guoping; Zhou, Zude; Hu, Yefa

2006-11-01

306

Diluted magnetic semiconductors: Novel properties in high magnetic fields  

NASA Astrophysics Data System (ADS)

Diluted magnetic semiconductors, II-VI and IV-VI compounds in which the cation is partially replaced by a magnetic ion such as Mn or a rare earth, combine interesting semiconducting and magnetic properties. At zero applied field, the materials behave like normal semiconductors or semimetals with energy gaps that can be varied with the composition of the magnetic ion. In the presence of an applied field, however, novel properties are observed. These include large field-induced splittings of energy levels, leading to strong Faraday rotations and the possibility of energy-gap tuning by magnetic field, field and temperature-dependent g-factors, large negative magnetoresistance followed at higher fields by a slowly varying positive magnetoresistance, and large paramagnetism with coupling of the magnetic ions by superexchange. Not only can these properties be observed in bulk crystal, but also they suggest promising physics and applications in artificially structured materials.

Anderson, J. R.

1990-06-01

307

Deformation of Water by a Magnetic Field  

ERIC Educational Resources Information Center

After the discovery that superconducting magnets could levitate diamagnetic objects, researchers became interested in measuring the repulsion of diamagnetic fluids in strong magnetic fields, which was given the name "The Moses Effect." Both for the levitation experiments and the quantitative studies on liquids, the large magnetic fields necessary…

Chen, Zijun; Dahlberg, E. Dan

2011-01-01

308

Exploring Magnetic Fields with a Compass  

ERIC Educational Resources Information Center

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

Lunk, Brandon; Beichner, Robert

2011-01-01

309

Analysis of magnetic field levels at KSC  

NASA Technical Reports Server (NTRS)

The scope of this work is to evaluate the magnetic field levels of distribution systems and other equipment at Kennedy Space Center (KSC). Magnetic fields levels in several operational areas and various facilities are investigated. Three dimensional mappings and contour are provided along with the measured data. Furthermore, the portion of magnetic fields generated by the 60 Hz fundamental frequency and the portion generated by harmonics are examined. Finally, possible mitigation techniques for attenuating fields from electric panels are discussed.

Christodoulou, Christos G.

1994-01-01

310

Neutron Interference in the Gravitational Field of a Ring Laser  

NASA Astrophysics Data System (ADS)

A number of analyses of neutron interference effects due to various metric perturbations have been found in the literature [1,2]. However, the approach of each author depends on a specific metric. I will present a new general technique giving the Foldy-Wouthuysen transformed Hamiltonian for a Dirac particle in the most general linearized space-time metric. I will then apply this new technique to calculate the phase shift on a neutron beam interferometer due to the gravitational field of a ring laser [3].[4pt] [1] D. M Greenberger and A. W. Overhauser, Rev. Mod. Phys. 51, 43--78 (1979).[0pt] [2] F. W. Hehl and W. T. Ni, Phys. Rev. D, vol 42, no. 6, pp. 2045-2048, 1990.[0pt] [3] R. L. Mallett, Phys. Lett. A 269, 214 (2000).

Fischetti, Robert

2013-04-01

311

Application of permanent magnets in accelerators and electron storage rings  

SciTech Connect

After an explanation of the general circumstances in which the use of permanent magnets in accelerators is desirable, a number of specific magnets will be discussed. That discussion includes magnets needed for the operation of accelerators as well as magnets that are employed for the utilization of charged particle beams, such as the production of synchrotron radiation. 15 references, 8 figures.

Halbach, K.

1984-09-01

312

Magnetic field waves at Uranus  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

313

Influence of segmentation of ring-shaped NdFeB magnets with parallel magnetization on cylindrical actuators.  

PubMed

This work analyses the effects of segmentation followed by parallel magnetization of ring-shaped NdFeB permanent magnets used in slotless cylindrical linear actuators. The main purpose of the work is to evaluate the effects of that segmentation on the performance of the actuator and to present a general overview of the influence of parallel magnetization by varying the number of segments and comparing the results with ideal radially magnetized rings. The analysis is first performed by modelling mathematically the radial and circumferential components of magnetization for both radial and parallel magnetizations, followed by an analysis carried out by means of the 3D finite element method. Results obtained from the models are validated by measuring radial and tangential components of magnetic flux distribution in the air gap on a prototype which employs magnet rings with eight segments each with parallel magnetization. The axial force produced by the actuator was also measured and compared with the results obtained from numerical models. Although this analysis focused on a specific topology of cylindrical actuator, the observed effects on the topology could be extended to others in which surface-mounted permanent magnets are employed, including rotating electrical machines. PMID:25051032

Eckert, Paulo Roberto; Goltz, Evandro Claiton; Flores Filho, Aly Ferreira

2014-01-01

314

Influence of Segmentation of Ring-Shaped NdFeB Magnets with Parallel Magnetization on Cylindrical Actuators  

PubMed Central

This work analyses the effects of segmentation followed by parallel magnetization of ring-shaped NdFeB permanent magnets used in slotless cylindrical linear actuators. The main purpose of the work is to evaluate the effects of that segmentation on the performance of the actuator and to present a general overview of the influence of parallel magnetization by varying the number of segments and comparing the results with ideal radially magnetized rings. The analysis is first performed by modelling mathematically the radial and circumferential components of magnetization for both radial and parallel magnetizations, followed by an analysis carried out by means of the 3D finite element method. Results obtained from the models are validated by measuring radial and tangential components of magnetic flux distribution in the air gap on a prototype which employs magnet rings with eight segments each with parallel magnetization. The axial force produced by the actuator was also measured and compared with the results obtained from numerical models. Although this analysis focused on a specific topology of cylindrical actuator, the observed effects on the topology could be extended to others in which surface-mounted permanent magnets are employed, including rotating electrical machines. PMID:25051032

Eckert, Paulo Roberto; Goltz, Evandro Claiton; Filho, Aly Ferreira Flores

2014-01-01

315

Abnormal Magnetic Field Effects on Electrogenerated Chemiluminescence  

NASA Astrophysics Data System (ADS)

We report abnormal magnetic field effects on electrogenerated chemiluminescence (MFEECL) based on triplet emission from the Ru(bpy)3Cl2-TPrA electrochemical system: the appearance of MFEECL after magnetic field ceases. In early studies the normal MFEECL have been observed from electrochemical systems during the application of magnetic field. Here, the abnormal MFEECL suggest that the activated charge-transfer [Ru(bpy)33+ … TPrA•] complexes may become magnetized in magnetic field and experience a long magnetic relaxation after removing magnetic field. Our analysis indicates that the magnetic relaxation can gradually increase the density of charge-transfer complexes within reaction region due to decayed magnetic interactions, leading to a positive component in the abnormal MFEECL. On the other hand, the magnetic relaxation facilitates an inverse conversion from triplets to singlets within charge-transfer complexes. The inverse triplet --> singlet conversion reduces the density of triplet light-emitting states through charge-transfer complexes and gives rise to a negative component in the abnormal MFEECL. The combination of positive and negative components can essentially lead to a non-monotonic profile in the abnormal MFEECL after ceasing magnetic field. Nevertheless, our experimental studies may reveal un-usual magnetic behaviors with long magnetic relaxation from the activated charge-transfer [Ru(bpy)33+ … TPrA•] complexes in solution at room temperature.

Pan, Haiping; Shen, Yan; Wang, Hongfeng; He, Lei; Hu, Bin

2015-03-01

316

Abnormal magnetic field effects on electrogenerated chemiluminescence.  

PubMed

We report abnormal magnetic field effects on electrogenerated chemiluminescence (MFEECL) based on triplet emission from the Ru(bpy)3Cl2-TPrA electrochemical system: the appearance of MFEECL after magnetic field ceases. In early studies the normal MFEECL have been observed from electrochemical systems during the application of magnetic field. Here, the abnormal MFEECL suggest that the activated charge-transfer [Ru(bpy)3(3+) … TPrA(•)] complexes may become magnetized in magnetic field and experience a long magnetic relaxation after removing magnetic field. Our analysis indicates that the magnetic relaxation can gradually increase the density of charge-transfer complexes within reaction region due to decayed magnetic interactions, leading to a positive component in the abnormal MFEECL. On the other hand, the magnetic relaxation facilitates an inverse conversion from triplets to singlets within charge-transfer complexes. The inverse triplet ? singlet conversion reduces the density of triplet light-emitting states through charge-transfer complexes and gives rise to a negative component in the abnormal MFEECL. The combination of positive and negative components can essentially lead to a non-monotonic profile in the abnormal MFEECL after ceasing magnetic field. Nevertheless, our experimental studies may reveal un-usual magnetic behaviors with long magnetic relaxation from the activated charge-transfer [Ru(bpy)3(3+) … TPrA(•)] complexes in solution at room temperature. PMID:25772580

Pan, Haiping; Shen, Yan; Wang, Hongfeng; He, Lei; Hu, Bin

2015-01-01

317

Abnormal Magnetic Field Effects on Electrogenerated Chemiluminescence  

PubMed Central

We report abnormal magnetic field effects on electrogenerated chemiluminescence (MFEECL) based on triplet emission from the Ru(bpy)3Cl2-TPrA electrochemical system: the appearance of MFEECL after magnetic field ceases. In early studies the normal MFEECL have been observed from electrochemical systems during the application of magnetic field. Here, the abnormal MFEECL suggest that the activated charge-transfer [Ru(bpy)33+ … TPrA•] complexes may become magnetized in magnetic field and experience a long magnetic relaxation after removing magnetic field. Our analysis indicates that the magnetic relaxation can gradually increase the density of charge-transfer complexes within reaction region due to decayed magnetic interactions, leading to a positive component in the abnormal MFEECL. On the other hand, the magnetic relaxation facilitates an inverse conversion from triplets to singlets within charge-transfer complexes. The inverse triplet ? singlet conversion reduces the density of triplet light-emitting states through charge-transfer complexes and gives rise to a negative component in the abnormal MFEECL. The combination of positive and negative components can essentially lead to a non-monotonic profile in the abnormal MFEECL after ceasing magnetic field. Nevertheless, our experimental studies may reveal un-usual magnetic behaviors with long magnetic relaxation from the activated charge-transfer [Ru(bpy)33+ … TPrA•] complexes in solution at room temperature. PMID:25772580

Pan, Haiping; Shen, Yan; Wang, Hongfeng; He, Lei; Hu, Bin

2015-01-01

318

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

319

Development of Experimental Superconducting Magnet for the Collector Ring of FAIR Project  

Microsoft Academic Search

A pool cooled experimental magnet based on the copper stabilized NbTi superconducting wire was designed, fabricated and tested, in order to evaluate the engineering design of the dipole superconducting magnet for the collector ring (CR) of the facility for antiproton and ion research (FAIR) project. In this paper, the experimental setup including quench protection system was presented. Performance of the

Yinfeng Zhu; Weiyue Wu; Songtao Wu; Houchang Xu; Changle Liu

2010-01-01

320

Bipolar pulse field for magnetic refrigeration  

DOEpatents

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

Lubell, Martin S. (Oak Ridge, TN)

1994-01-01

321

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

322

Destruction of a Magnetic Mirror-Trapped Hot Electron Ring by an Alfv'en Wave  

NASA Astrophysics Data System (ADS)

Highly energetic electrons produced naturally or artificially can be trapped in the earth's radiation belts for months, posing a danger to valuable space satellites. Concepts that can lead to mitigation of the radiation belts have drawn a great deal of interest. In this work, we demonstrated that a shear Alfv'en wave can effectively de-trap energetic electrons confined by a magnetic mirror field.footnotetextY. Wang, W. Gekelman, P. Pribyl, and K. Papadopoulos, Phys. Rev. Lett. 108, 105002 (2012). The experiment is performed in a quiescent afterglow plasma in the Large Plasma Device (LaPD) at UCLA (ne=0.1-1x10^12/cm^3, Te=0.5eV, B0=400-1600G, L=18m, and diameter=0.6m). A hot electron ring (along with hard x-rays of energies up to 3 MeV) is generated by 2nd harmonic ECRH (P=25kW, ?pulse=20-50ms, f=2.45GHz) and is trapped in a magnetic mirror field (L=3m, Rmirror=1.1-4). A shear Alfv'en wave (f 0.5fci, Bwave/B0 0.1% ) is launched with a rotating magnetic field antenna with arbitrary polarity. The circularly polarized Alfv'en wave is observed to dramatically scatter the trapped fast electrons out of the mirror within as little as 10 wave cycles. A collimated detector outside the vacuum vessel detects X-rays of E>100 keV. X-ray images are reconstructed from more than 1000 chord projections at each axial location by computed tomography. The de-trapped electrons are observed outside the mirror field region.

Wang, Yuhou; Gekelman, Walter; Pribyl, Patrick; Papadopoulos, Konstantinos

2012-10-01

323

On the Motion of the Field of a Permanent Magnet  

ERIC Educational Resources Information Center

A description is given of a series of recent experiments using a rotating magnetic circuit comprising a permanent magnet ring and yoke, and a stationary conductor in the air gap between the ring and yoke. The EMF induced in this case cannot be described by a simple application of Faraday's flux law. This is because the magnetic flux in the air gap…

Leus, Vladimir; Taylor, Stephen

2011-01-01

324

Exploring Magnetic Fields in Your Environment  

NSDL National Science Digital Library

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

325

Planetary Rings  

NASA Astrophysics Data System (ADS)

Planetary rings are the only nearby astrophysical disks and the only disks that have been investigated by spacecraft (especially the Cassini spacecraft orbiting Saturn). Although there are significant differences between rings and other disks, chiefly the large planet/ring mass ratio that greatly enhances the flatness of rings (aspect ratios as small as 10- 7), understanding of disks in general can be enhanced by understanding the dynamical processes observed at close range and in real time in planetary rings.We review the known ring systems of the four giant planets, as well as the prospects for ring systems yet to be discovered. We then review planetary rings by type. The A, B, and C rings of Saturn, plus the Cassini Division, comprise our solar system's only dense broad disk and host many phenomena of general application to disks including spiral waves, gap formation, self-gravity wakes, viscous overstability and normal modes, impact clouds, and orbital evolution of embedded moons. Dense narrow rings are found both at Uranus (where they comprise the main rings entirely) and at Saturn (where they are embedded in the broad disk) and are the primary natural laboratory for understanding shepherding and self-stability. Narrow dusty rings, likely generated by embedded source bodies, are surprisingly found to sport azimuthally confined arcs at Neptune, Saturn, and Jupiter. Finally, every known ring system includes a substantial component of diffuse dusty rings.Planetary rings have shown themselves to be useful as detectors of planetary processes around them, including the planetary magnetic field and interplanetary impactors as well as the gravity of nearby perturbing moons. Experimental rings science has made great progress in recent decades, especially numerical simulations of self-gravity wakes and other processes but also laboratory investigations of coefficient of restitution and spectroscopic ground truth. The age of self-sustained ring systems is a matter of debate; formation scenarios are most plausible in the context of the early solar system, while signs of youthfulness indicate at least that rings have never been static phenomena.

Tiscareno, Matthew S.

326

Effects of magnetic non-linearities on a stored proton beam and their implications for superconducting storage rings  

SciTech Connect

A nonlinear lens may be used to study the effect of high-order multipolar field imperfections on a stored proton beam. Such a nonlinear lens is particulary suitable to simulate field imperfections of the types encountered in coil dominated superconducting magnets. We have studied experimentally at the SPS the effect of high order (5th and 8th) single isolated resonances driven by the nonlinear lens. The width of these resonances is of the order one expects to be caused by field errors in superconducting magnets of the SSC type. The experiment shows that, in absence of tune modulation, these resonances are harmless. Slow crossings of the resonance, on the other hand, have destructive effects on the beam, much more so than fast crossings caused by synchrotron oscillations. In the design of future storage rings, sources of low-frequency tune modulation should be avoided as a way to reduce the harmful effects of high order multipolar field imperfection.

Cornacchia, M.; Evans, L.

1985-06-01

327

On magnetic-field-induced dissipationless electric current in nanowires  

E-print Network

We propose a general design of a metallic double-nanowire structure which may support an equilibrium dissipationless electric current in the presence of magnetic field. The structure consists of a compact wire element of a specific shape, which is periodically extended in one spatial dimension. Topologically, each wire element is equivalent to a ring, which supports a dissipationless current in the presence of magnetic flux similarly to the persistent electric current in a normal metal nanoring. Geometrically, each wire element breaks spatial inversion symmetry so that the equilibrium electric current through the device becomes nonzero. We also argue that the same effect should exist in long planar chiral nanoribbons subjected to external magnetic field.

M. N. Chernodub

2013-05-15

328

Dirac oscillator in an external magnetic field  

E-print Network

We show that 2+1 dimensional Dirac oscillators in an external magnetic field is mapped onto the same with reduced angular frequency in absence of magnetic field. This can be used to study the atomic transitions in a radiation field. Relativistic Landau levels are constructed explicitly. Several interesting features of this system are discussed.

Bhabani Prasad Mandal; Shweta Verma

2009-12-19

329

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

330

Representation of magnetic fields in space  

NASA Technical Reports Server (NTRS)

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

Stern, D. P.

1975-01-01

331

DC-based magnetic field controller  

DOEpatents

A magnetic field controller is described 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. 1 fig.

Kotter, D.K.; Rankin, R.A.; Morgan, J.P.

1994-05-31

332

Ohm's law for mean magnetic fields  

Microsoft Academic Search

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

Boozer

1986-01-01

333

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

334

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 total azimuthal flux with a power-law distribution over the poloidal field. Particular attention is paid

Fornberg, Bengt

335

Quantum ring solitons and nonlocal effects in plasma wake field excitations  

SciTech Connect

A theoretical investigation of the quantum transverse beam motion for a cold relativistic charged particle beam travelling in a cold, collisionless, strongly magnetized plasma is carried out. This is done by taking into account both the individual quantum nature of the beam particles (single-particle uncertainty relations and spin) and the self consistent interaction generated by the plasma wake field excitation. By adopting a fluid model of a strongly magnetized plasma, the analysis is carried out in the overdense regime (dilute beams) and in the long beam limit. It is shown that the quantum description of the collective transverse beam dynamics is provided by a pair of coupled nonlinear governing equations. It comprises a Poisson-like equation for the plasma wake potential (driven by the beam density) and a 2D spinorial Schroedinger equation for the wave function, whose squared modulus is proportional to the beam density, that is obtained in the Hartree's mean field approximation, after disregarding the exchange interactions. The analysis of this pair of equations, which in general exhibits a strong nonlocal character, is carried out analytically as well as numerically in both the linear and the nonlinear regimes, showing the existence of the quantum beam vortices in the form of Laguerre-Gauss modes and ring envelope solitons, respectively. In particular, when the relation between the plasma wake field response and the beam probability density is strictly local, the pair of the governing equations is reduced to the 2D Gross-Pitaevskii equation that allows one to establish the conditions for the self focusing and collapse. These conditions include the quantum nature of the beam particles. Finally, when the relation between the plasma wake field response and the beam probability density is moderately nonlocal, the above pair of equations permits to follow the spatio-temporal evolution of a quantum ring envelope soliton. Such a structure exhibits small or violent breathing, but it remains very stable for long time.

Fedele, R.; Tanjia, F. [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II', and INFN, Napoli (Italy); De Nicola, S. [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II', and INFN, Napoli (Italy); Istituto Nazionale di Ottica - C. N. R., Pozzuoli (Italy); Jovanovic, D. [Institute of Physics, University of Belgrade, Belgrade (Serbia); Shukla, P. K. [Center of Advanced Studies in Physical Sciences, Ruhr-Universitaet Bochum, Bochum (Germany)

2012-10-15

336

Magnetic field waves at Uranus  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

337

A hybrid multi-level switching converter for ring-magnet power supplies  

Microsoft Academic Search

Conventionally, ring-magnet power supplies (RMPS) are designed using phase-controlled rectifiers or resonant networks with DC-bias power supplies. These power supply configurations satisfy the steady-state performance criteria using large reactive components in addition to the magnet load. They have limited dynamic response, and often rely on corrector-magnet power supplies or other auxiliary power supply networks for the fast dynamic compensation required

M. R. Pavan Kumar; J. M. S. Kim

1996-01-01

338

Observation of field-induced domain wall propagation in magnetic nanowires by magnetic transmission X-ray microscopy  

SciTech Connect

Magnetic transmission X-ray microscopy (M-TXM) is used to image domain walls in magnetic ring structures formed by a 300 nm wide, 24 nm thick Ni{sub 81}Fe{sub 19} nanowire. Both transverse and vortex type domain walls are observed after application of different field sequences. Domain walls can be observed by comparing images obtained from opposite field sequences, or else domain wall propagation observed by comparing successive images in a particular field sequence. This demonstrates the potential use of M-TXM in developing and understanding planar magnetic nanowire behavior.

Bryan, M. T.; Fry, P. W.; Fischer, P.; Allwood, D. A.

2007-12-01

339

Numerical analysis of magnetic field in superconducting magnetic energy storage  

SciTech Connect

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

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

1991-09-01

340

Spectra of magnetic fields injected during baryogenesis  

SciTech Connect

Helical magnetic fields are injected into the cosmic medium during cosmological baryogenesis and can potentially provide a useful probe of the early universe. We construct a model to study the injection process during a first order phase transition and to determine the power spectra of the injected magnetic field. By Monte Carlo simulations we evaluate the Fourier space symmetric and helical power spectra of the magnetic field at the time the phase transition completes. The spectra are peaked at the scale given by the inverse size of bubbles at percolation and with a comparable width. These injected magnetic fields set the initial conditions for further cosmological magneto-hydrodynamical evolution.

Ng Yifung [CERCA, Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106-7079 (United States); Vachaspati, Tanmay [CERCA, Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106-7079 (United States); Institute for Advanced Study, Princeton, New Jersey 08540 (United States)

2010-07-15

341

Flow Transitions in a Rotating Magnetic Field  

NASA Technical Reports Server (NTRS)

Critical Rayleigh numbers have been measured in a liquid metal cylinder of finite height in the presence of a rotating magnetic field. Several different stability regimes were observed, which were determined by the values of the Rayleigh and Hartmann numbers. For weak rotating magnetic fields and small Rayleigh numbers, the experimental observations can be explained by the existence of a single non-axisymmetric meridional roll rotating around the cylinder, driven by the azimuthal component of the magnetic field. The measured dependence of rotational velocity on magnetic field strength is consistent with the existence of laminar flow in this regime.

Volz, M. P.; Mazuruk, K.

1996-01-01

342

Magnetic Fields in the Milky Way  

NASA Astrophysics Data System (ADS)

This chapter presents a review of observational studies to determine the magnetic field in the Milky Way, both in the disk and in the halo, focused on recent developments and on magnetic fields in the diffuse interstellar medium. I discuss some terminology which is confusingly or inconsistently used and try to summarize current status of our knowledge on magnetic field configurations and strengths in the Milky Way. Although many open questions still exist, more and more conclusions can be drawn on the large-scale and small-scale components of the Galactic magnetic field. The chapter is concluded with a brief outlook to observational projects in the near future.

Haverkorn, Marijke

343

Magnetic fields in anisotropic relativistic stars  

E-print Network

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

Vladimir Folomeev; Vladimir Dzhunushaliev

2015-02-28

344

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

345

Magnetic fields in anisotropic relativistic stars  

E-print Network

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

Folomeev, Vladimir

2015-01-01

346

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 this phenomenon can be traced to the mutual cancellation of Abelian magnetic fields created by the SU(2) gauge fields and Higgs boson. The effect implies monopole charge screening in the 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 a 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 a corresponding magnetic bound state exists in the electroweak theory and can be detected by experiment.

A. S. Bakry; D. G. Pak; P. M. Zhang; L. P. Zou

2014-10-03

347

Generation of the magnetic field in jets  

E-print Network

We consider dynamo action under the combined influence of turbulence and large-scale shear in sheared jets. Shear can stretch turbulent magnetic field lines in such a way that even turbulent motions showing mirror symmetry become suitable for generation of a large-scale magnetic field. We derive the integral induction equation governing the behaviour of the mean field in jets. The main result is that sheared jets may generate a large-scale magnetic field if shear is sufficiently strong. The generated mean field is mainly concentrated in a magnetic sheath surrounding the central region of a jet, and it exhibits sign reversals in the direction of the jet axis. Typically, the magnetic field in a sheath is dominated by the component along the jet that can reach equipartition with the kinetic energy of particles, The field in the central region of jets has a more disordered structure.

V. Urpin

2006-05-22

348

The levitation characteristics of the magnetic substances using trapped HTS bulk annuli with various magnetic field distributions  

NASA Astrophysics Data System (ADS)

We have been investigating the levitation system without any mechanical contact which is composed of a field-cooled ring-shaped high temperature superconducting (HTS) bulks [1]. In this proposed levitation system, the trapped magnetic field distributions of stacked HTS bulk are very important. In this paper, the spherical solenoid magnet composed of seven solenoid coils with different inner and outer diameters was designed and fabricated as a new magnetic source. The fabricated spherical solenoid magnet can easily make a homogeneous and various magnetic field distributions in inner space of stacked HTS bulk annuli by controlling the emerging currents of each coil. By using this spherical solenoid magnet, we tried to make a large magnetic field gradient in inner space of HTS bulk annuli, and it is very important on the levitation of magnetic substances. In order to improve the levitation properties of magnetic substances with various sizes, the external fields were reapplied to the initially trapped HTS bulk magnets. We could generate a large magnetic field gradient along the axial direction in inner space of HTS bulk annuli, and obtain the improved levitation height of samples by the proposed reapplied field method.

Kim, S. B.; Ikegami, T.; Matsunaga, J.; Fujii, Y.; Onodera, H.

2013-11-01

349

Reducing Field Distortion in Magnetic Resonance Imaging  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

350

SIMULATING MAGNETIC FIELDS IN THE ANTENNAE GALAXIES  

SciTech Connect

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

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

2010-06-20

351

The AGN origin of cluster magnetic fields  

NASA Astrophysics Data System (ADS)

The origin of magnetic fields in galaxy clusters is one of the most fascinating but challenging problems in astrophysics. In this dissertation, the possibility of an Active Galactic Nucleus (AGN) origin of cluster magnetic fields is studied through state of the art simulations of magnetic field evolution in large scale structure formation using a newly developed cosmological Adaptive Mesh Refinement (AMR) Magnetohydrodynamics (MHD) code -- EnzoMHD. After presenting a complete but concise description and verification of the code, we discuss the creation of magnetic fields through the Biermann Battery effect during first star formation and galaxy cluster formation. We find that magnetic fields are produced as predicted by theory in both cases. For the first star formation, we obtain a lower limit of (~ 10 -9 G) for magnetic fields when the first generation stars form. On the other hand, we find that the magnetic energy is amplified 4 orders of magnitude within ~ 10 Gyr during cluster formation. We then study magnetic field injection from AGN into the Intra- Cluster Medium (ICM) and their impact on the ICM. We reproduce the X-ray cavities as well as weak shocks seen in observations in the simulation, and further confirm the idea that AGN outburst must contain lots of magnetic energy (up to 10 61 ergs) and the magnetic fields play an important part in the formation of jet/lobe system. We present high resolution simulations of cluster formation with magnetic fields injected from high redshift AGN. We find that these local magnetic fields are spread quickly throughout the whole cluster by cluster mergers. The ICM is in a turbulent state with a Kolmogorov-like power spectrum. Magnetic fields are amplified to and maintained at the observational level of a few mG by bulk flows at large scale and the ICM turbulence at small scale. The total magnetic energy increases about 25 times to ~ 1.2 × 10^61 ergs at the present time. We conclude that magnetic fields from AGN at high redshift may provide sufficient initial magnetic fields to magnetize the whole cluster.

Xu, Hao

352

Detecting ultra-low magnetic fields with common magnetic minerals  

Microsoft Academic Search

Growing volume of extraterrestrial material is being used to analyze magnetic paleo-intensities. They are important for estimation of paleo-fields that once existed in extraterrestrial environment. The extraterrestrial field can be several orders of magnitudes weaker than a terrestrial field. The data demonstrating that the TRM linear acquisition is valid for such low fields are virtually not existent. We tested the

G. Kletetschka; P. J. Wasilewski; T. Kohout; E. Herrero-Bervera; M. D. Fuller

2004-01-01

353

Quark antiscreening at strong magnetic field and inverse magnetic catalysis  

NASA Astrophysics Data System (ADS)

The dependence of the QCD coupling constant with a strong magnetic field and the implications for the critical temperature of the chiral phase transition are investigated. It is found that the coupling constant becomes anisotropic in a strong magnetic field and that the quarks, confined by the field to the lowest Landau level where they pair with antiquarks, produce an antiscreening effect. These results lead to inverse magnetic catalysis, providing a natural explanation for the behavior of the critical temperature in the strong-field region.

Ferrer, E. J.; de la Incera, V.; Wen, X. J.

2015-03-01

354

A simple, small and low cost permanent magnet design to produce homogeneous magnetic fields.  

PubMed

A new portable, pocket-size NMR probe based on a novel permanent magnet arrangement is presented. It is based on a Halbach-type magnet design which mimics the field of a spherical dipole by using cylindrical bar and ring magnets. The magnet system is made up of only three individual magnets, and most field calculations and optimisations can be performed analytically. A prototype system has been built using a set of small, off the shelf commercially available permanent magnets. Proton linewidths of 50 ppm FWHM could be achieved at a field strength of 1T. Calculations show that with custom-sized permanent magnets, linewidths of less than 1 ppm can be achieved over sample volumes of up to 1 mm3, which would in theory enable chemical shift resolved proton spectroscopy on mass-limited samples. But even with the achieved linewidth of 50 ppm, this can be a useful portable sensor for small amounts of liquid samples with restricted molecular mobility, like gels, polymers or high viscosity liquids. PMID:18314366

Manz, B; Benecke, M; Volke, F

2008-05-01

355

A simple, small and low cost permanent magnet design to produce homogeneous magnetic fields  

NASA Astrophysics Data System (ADS)

A new portable, pocket-size NMR probe based on a novel permanent magnet arrangement is presented. It is based on a Halbach-type magnet design which mimics the field of a spherical dipole by using cylindrical bar and ring magnets. The magnet system is made up of only three individual magnets, and most field calculations and optimisations can be performed analytically. A prototype system has been built using a set of small, off the shelf commercially available permanent magnets. Proton linewidths of 50 ppm FWHM could be achieved at a field strength of 1 T. Calculations show that with custom-sized permanent magnets, linewidths of less than 1 ppm can be achieved over sample volumes of up to 1 mm 3, which would in theory enable chemical shift resolved proton spectroscopy on mass-limited samples. But even with the achieved linewidth of 50 ppm, this can be a useful portable sensor for small amounts of liquid samples with restricted molecular mobility, like gels, polymers or high viscosity liquids.

Manz, B.; Benecke, M.; Volke, F.

2008-05-01

356

The Evolution of the Earth's Magnetic Field.  

ERIC Educational Resources Information Center

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

Bloxham, Jeremy; Gubbins, David

1989-01-01

357

Dependence of the magnitude and direction of the persistent current on the magnetic flux in superconducting rings  

SciTech Connect

The obtained periodic magnetic-field dependences I{sub c+}({phi}/{phi}{sub 0}) and I{sub c-}({phi}/{phi}{sub 0}) of the critical current measured in opposite directions on asymmetric superconducting aluminum rings has made it possible to explain previously observed quantum oscillations of dc voltage as a result of alternating current rectification. It was found that a higher rectification efficiency of both single rings and ring systems is caused by hysteresis of the current-voltage characteristics. The asymmetry of current-voltage characteristics providing the rectification effect is due to the relative shifts of the magnetic dependences I{sub c-}({phi}/{phi}{sub 0}) = I{sub c+}({phi}/{phi}{sub 0} + {delta}{phi}) of the critical current measured in opposite directions. This shift means that the position of I{sub c+}({phi}/{phi}{sub 0}) and I{sub c-}({phi}/{phi}{sub 0}) minima does not correspond to n + 0.5 magnetic flux {phi} quanta, which is in direct contradiction to measured Little-Parks resistance oscillations. Despite this contradiction, the amplitude I{sub c,an}({phi}/{phi}{sub 0}) = I{sub c+}({phi}/{phi}{sub 0}) - I{sub c-}({phi}/{phi}{sub 0}) of critical current anisotropy oscillations and its variations with temperature correspond to the expected amplitude of persistent current oscillations and its variations with temperature.

Gurtovoi, V. L.; Dubonos, S. V.; Nikulov, A. V., E-mail: nikulov@ipmt-hpm.ac.ru; Osipov, N. N.; Tulin, V. A. [Russian Academy of Sciences, Institute of Microelectronic Technology and High-Purity Materials (Russian Federation)

2007-12-15

358

Magnetic Braiding and Parallel Electric Fields  

E-print Network

The braiding of the solar coronal magnetic field via photospheric motions - with subsequent relaxation and magnetic reconnection -- is one of the most widely debated ideas of solar physics. We readdress the theory in the light of developments in three-dimensional magnetic reconnection theory. It is known that the integrated parallel electric field along field lines is the key quantity determining the rate of reconnection, in contrast with the two-dimensional case where the electric field itself is the important quantity. We demonstrate that this difference becomes crucial for sufficiently complex magnetic field structures. A numerical method is used to relax a braided magnetic field to an ideal force-free equilibrium; that equilibrium is found to be smooth, with only large- scale current structures. However, the equilibrium is shown to have a highly filamentary integrated parallel current structure with extremely short length- scales. An analytical model is developed to show that, in a coronal situation, the length scales associated with the integrated parallel current structures will rapidly decrease with increasing complexity, or degree of braiding, of the magnetic field. Analysis shows the decrease in these length scales will, for any finite resistivity, eventually become inconsistent with the stability of a force- free field. Thus the inevitable consequence of the magnetic braiding process is shown to be a loss of equilibrium of the coronal field, probably via magnetic reconnection events.

A. L. Wilmot-Smith; G. Hornig; D. I. Pontin

2008-10-08

359

Magnetic Field Seeding through Supernova Feedback  

NASA Astrophysics Data System (ADS)

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

Koh, Daegene; Wise, John

2015-01-01

360

Graphene Nanoribbon in Sharply Localized Magnetic Fields  

E-print Network

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

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

2013-03-20

361

Exact scattering matrix of graphs in magnetic field and quantum noise  

SciTech Connect

We consider arbitrary quantum wire networks modelled by finite, noncompact, connected quantum graphs in the presence of an external magnetic field. We find a general formula for the total scattering matrix of the network in terms of its local scattering properties and its metric structure. This is applied to a quantum ring with N external edges. Connecting the external edges of the ring to heat reservoirs, we study the quantum transport on the graph in ambient magnetic field. We consider two types of dynamics on the ring: the free Schrödinger and the free massless Dirac equations. For each case, a detailed study of the thermal noise is performed analytically. Interestingly enough, in presence of a magnetic field, the standard linear Johnson-Nyquist law for the low temperature behaviour of the thermal noise becomes nonlinear. The precise regime of validity of this effect is discussed and a typical signature of the underlying dynamics is observed.

Caudrelier, Vincent, E-mail: v.caudrelier@city.ac.uk [Department of Mathematical Science, City University London, Northampton Square, London EC1V 0HB (United Kingdom); Mintchev, Mihail, E-mail: mintchev@df.unipi.it [Istituto Nazionale di Fisica Nucleare and Dipartimento di Fisica dell’Università di Pisa, Largo Pontecorvo 3, 56127 Pisa (Italy); Ragoucy, Eric, E-mail: eric.ragoucy@lapth.cnrs.fr [LAPTh, Laboratoire d’Annecy-le-Vieux de Physique Théorique, CNRS, Université de Savoie, BP 110, 74941 Annecy-le-Vieux Cedex (France)

2014-08-15

362

Exact scattering matrix of graphs in magnetic field and quantum noise  

NASA Astrophysics Data System (ADS)

We consider arbitrary quantum wire networks modelled by finite, noncompact, connected quantum graphs in the presence of an external magnetic field. We find a general formula for the total scattering matrix of the network in terms of its local scattering properties and its metric structure. This is applied to a quantum ring with N external edges. Connecting the external edges of the ring to heat reservoirs, we study the quantum transport on the graph in ambient magnetic field. We consider two types of dynamics on the ring: the free Schrödinger and the free massless Dirac equations. For each case, a detailed study of the thermal noise is performed analytically. Interestingly enough, in presence of a magnetic field, the standard linear Johnson-Nyquist law for the low temperature behaviour of the thermal noise becomes nonlinear. The precise regime of validity of this effect is discussed and a typical signature of the underlying dynamics is observed.

Caudrelier, Vincent; Mintchev, Mihail; Ragoucy, Eric

2014-08-01

363

Coronal magnetic fields produced by photospheric shear  

NASA Technical Reports Server (NTRS)

The magneto-frictional method is used for computing force free fields to examine the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. It found that the energy of the sheared field can be arbitrarily large compared with the potential field. It is also found that it is possible to fit the magnetic energy, as a function of shear, by a simple functional form.

Sturrock, P. A.; Yang, W.-H.

1987-01-01

364

Control of magnetism by electric fields  

NASA Astrophysics Data System (ADS)

The electrical manipulation of magnetism and magnetic properties has been achieved across a number of different material systems. For example, applying an electric field to a ferromagnetic material through an insulator alters its charge-carrier population. In the case of thin films of ferromagnetic semiconductors, this change in carrier density in turn affects the magnetic exchange interaction and magnetic anisotropy; in ferromagnetic metals, it instead changes the Fermi level position at the interface that governs the magnetic anisotropy of the metal. In multiferroics, an applied electric field couples with the magnetization through electrical polarization. This Review summarizes the experimental progress made in the electrical manipulation of magnetization in such materials, discusses our current understanding of the mechanisms, and finally presents the future prospects of the field.

Matsukura, Fumihiro; Tokura, Yoshinori; Ohno, Hideo

2015-03-01

365

Control of magnetism by electric fields.  

PubMed

The electrical manipulation of magnetism and magnetic properties has been achieved across a number of different material systems. For example, applying an electric field to a ferromagnetic material through an insulator alters its charge-carrier population. In the case of thin films of ferromagnetic semiconductors, this change in carrier density in turn affects the magnetic exchange interaction and magnetic anisotropy; in ferromagnetic metals, it instead changes the Fermi level position at the interface that governs the magnetic anisotropy of the metal. In multiferroics, an applied electric field couples with the magnetization through electrical polarization. This Review summarizes the experimental progress made in the electrical manipulation of magnetization in such materials, discusses our current understanding of the mechanisms, and finally presents the future prospects of the field. PMID:25740132

Matsukura, Fumihiro; Tokura, Yoshinori; Ohno, Hideo

2015-03-01

366

Magnetic isotope and magnetic field effects on the DNA synthesis  

PubMed Central

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

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

2013-01-01

367

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

NASA Technical Reports Server (NTRS)

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

Burlaga, L. F.; Barouch, E.

1974-01-01

368

Protein crystals orientation in a magnetic field.  

PubMed

Nucleation and crystal growth of hen egg-white lysozyme, bovine pancreatic trypsin inhibitor and porcine pancreatic alpha-amylase were carried out in the presence of a magnetic field of 1.25 T produced by small permanent magnets. Crystals were oriented in the magnetic field, except when heterogeneous nucleation occurred. The orientation of protein crystals in the presence of a magnetic field can be attributed to the anisotropic diamagnetic susceptibility of proteins resulting from the large anisotropy of the alpha-helices due to the axial alignment of the peptide bonds. PMID:9761881

Astier, J P; Veesler, S; Boistelle, R

1998-07-01

369

Neutron spin polarization in strong magnetic fields  

E-print Network

The effects of strong magnetic fields on the inner crust of neutron stars are investigated after taking into account the anomalous magnetic moments of nucleons. Energy spectra and wave functions for protons and neutrons in a uniform magnetic field are provided. The particle spin polarizations and the yields of protons and neutrons are calculated in a free Fermi gas model. Obvious spin polarization occurs when $B\\geq10^{14}$G for protons and $B\\geq10^{17}$G for neutrons, respectively. It is shown that the neutron spin polarization depends solely on the magnetic field strength.

H. Wen; L. S. Kisslinger; Walter Greiner; G. Mao

2006-01-09

370

High concentration ferronematics in low magnetic fields  

E-print Network

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

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

2014-09-05

371

Effects and Correction of Closed Orbit Magnet Errors in the SNS Ring  

SciTech Connect

We consider the effect and correction of three types of orbit errors in SNS: quadrupole displacement errors, dipole displacement errors, and dipole field errors. Using the ORBIT beam dynamics code, we focus on orbit deflection of a standard pencil beam and on beam losses in a high intensity injection simulation. We study the correction of these orbit errors using the proposed system of 88 (44 horizontal and 44 vertical) ring beam position monitors (BPMs) and 52 (24 horizontal and 28 vertical) dipole corrector magnets. Correction is carried out numerically by adjusting the kick strengths of the dipole corrector magnets to minimize the sum of the squares of the BPM signals for the pencil beam. In addition to using the exact BPM signals as input to the correction algorithm, we also consider the effect of random BPM signal errors. For all three types of error and for perturbations of individual magnets, the correction algorithm always chooses the three-bump method to localize the orbit displacement to the region between the magnet and its adjacent correctors. The values of the BPM signals resulting from specified settings of the dipole corrector kick strengths can be used to set up the orbit response matrix, which can then be applied to the correction in the limit that the signals from the separate errors add linearly. When high intensity calculations are carried out to study beam losses, it is seen that the SNS orbit correction system, even with BPM uncertainties, is sufficient to correct losses to less than 10-4 in nearly all cases, even those for which uncorrected losses constitute a large portion of the beam.

Bunch, S.C.; Holmes, J.

2004-01-01

372

Fluctuating magnetic field induced resonant activation  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

373

Alignment of magnetic uniaxial particles in a magnetic field: Simulation  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

374

CONSTRUCTION AND POWER TEST OF THE EXTRACTION KICKER MAGNET FOR SNS ACCUMULATOR RING.  

SciTech Connect

Two extraction kicker magnet assemblies that contain seven individual pulsed magnet modules each will kick the proton beam vertically out of the SNS accumulator ring into the aperture of the extraction Lambertson septum magnet. The proton beam then travels to the 1.4 MW SNS target assembly. The 14 kicker magnets and major components of the kicker assembly have been fabricated in BNL. The inner surfaces of the kicker magnets were coated with TiN to reduce the secondary electron yield. All 14 PFN power supplies have been built, tested and delivered to OWL. Before final installation, a partial assembly of the kicker system with three kicker magnets was assembled to test the functions of each critical component in the system. In this paper we report the progress of the construction of the kicker components, the TIN coating of the magnets, the installation procedure of the magnets and the full power test of the kicker with the PFN power supply.

PAI, C.; HAHN, H.; HSEUH, H.; LEE, Y.; MENG, W.; MI,J.; SANDBERG, J.; TODD, R.; ET AL.

2005-05-16

375

Two-axis magnetic field sensor  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

376

Astrophysical magnetic fields and nonlinear dynamo theory  

Microsoft Academic Search

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

Axel Brandenburg; Kandaswamy Subramanian

2005-01-01

377

Space Quantization in a Gyrating Magnetic Field  

Microsoft Academic Search

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

I. I. Rabi

1937-01-01

378

Magnetic fields, branes, and noncommutative geometry  

Microsoft Academic Search

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

Daniela Bigatti; Leonard Susskind

2000-01-01

379

Appendix E: Software MEASURING CONSTANT MAGNETIC FIELD  

E-print Network

, and the Guide Box, shown below. The Guide Box will give you directions and tasks to perform. It will also tell "degree" will make a plot of magnetic field strength as a function of angle (B vs. ). Click "OK" when you. This process is called "zeroing the Hall probe" in the Guide Box. Place the magnetic field sensor wand

Minnesota, University of

380

CHROMOSPHERIC AND CORONAL MAGNETIC FIELDS Eric Priest  

E-print Network

CHROMOSPHERIC AND CORONAL MAGNETIC FIELDS Eric Priest Mathematics Institute, St Andrews University the structure of the magnetic field (in the pho­ tosphere, chromosphere and corona) and the dynamics, so that a corona lay above spherical shells of tran­ sition region, chromosphere and photosphere

Priest, Eric

381

CHROMOSPHERIC AND CORONAL MAGNETIC FIELDS Eric Priest  

E-print Network

CHROMOSPHERIC AND CORONAL MAGNETIC FIELDS Eric Priest Mathematics Institute, St Andrews University the structure of the magnetic field (in the pho- tosphere, chromosphere and corona) and the dynamics, so that a corona lay above spherical shells of tran- sition region, chromosphere and photosphere

Priest, Eric

382

Statistical analysis of magnetic-field spectra  

Microsoft Academic Search

We have calculated and statistically analyzed the magnetic-field spectrum (the B spectrum) at fixed electron Fermi energy for two quantum dot systems with classically chaotic shape. This problem arises naturally in transport measurements where the incoming electron has a fixed energy while one tunes the magnetic field to obtain resonance conductance patterns. The B spectrum, defined as the collection of

Jian Wang; Hong Guo

1998-01-01

383

On the origins of galactic magnetic fields  

E-print Network

We present a five dimensional unified theory of gravity and electromagnetism which leads to modified Maxwell equations, suggesting a new origin for galactic magnetic fields. It is shown that a region with nonzero scalar curvature would amplify the magnetic fields under certain conditions.

A. Borzou; H. R. Sepangi; R. Yousefi; A. H. Ziaie

2009-11-18

384

Manipulation of molecular structures with magnetic fields  

Microsoft Academic Search

The present thesis deals with the use of magnetic fields as a handle to manipulate matter at a molecular level and as a tool to probe molecular properties or inter molecular interactions. The work consists of in situ optical studies of (polymer) liquid crystals and molecular aggregates in high magnetic fields up to 20T, together with a description of the

Marius Iosif Boamfa

2003-01-01

385

Magnetic Fields at the Center of Coils  

ERIC Educational Resources Information Center

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

Binder, Philippe; Hui, Kaleonui; Goldman, Jesse

2014-01-01

386

Experimental investigation of the gas discharge dynamics in a solenoidal magnetic field  

NASA Astrophysics Data System (ADS)

An electric gas discharge is initiated at the end face of a nonconducting cylinder between a central electrode coaxial with the cylinder and a ring electrode on the lateral surface of the cylinder. The axis of the cylinder and that of a magnetic coil wound on its lateral surface coincide. The dynamics of the gas discharge in a solenoidal magnetic field is studied by observing its position and shape and monitoring the variation of the thermionic center distribution on the surface of the ring electrode with discharge current and magnetic induction. The discharge develops in air at a pressure of 2 kPa.

Bobashev, S. V.; Mende, N. P.; Monakhov, N. A.; Sakharov, V. A.

2012-12-01

387

HTS Bulk Pole-Field Magnets Motor With a Multiple Rotor Cooled by Liquid Nitrogen  

Microsoft Academic Search

High-Tc superconductor (HTS) rotating machine with melt-textured Gd-123 bulk pole-field magnets was assembled and tested. The axial gap type motor with neither brush\\/slip ring nor iron core was composed of a kind of multiple rotor, i.e., a twinned rotor. On each rotor disk, there are eight Gd-123 HTS bulk magnets. The bulk magnets were cooled down with circulating liquid nitrogen

Hirohisa Matsuzaki; Yousuke Kimura; Eisuke Morita; Hideaki Ogata; Tetsuya Ida; Mitsuru Izumi; Hidehiko Sugimoto; Motohiro Miki; Masahiro Kitano

2007-01-01

388

Ultrahigh Q-factor and figure of merit Fano metamaterial based on dark ring magnetic mode  

NASA Astrophysics Data System (ADS)

A planar terahertz (THz) metamaterial with both ultrahigh quality (Q) factor and high figure of merit (FOM) based on the ring magnetic mode and Fano resonance is proposed. The nonradiative dark modes are induced by the tiny symmetry breaking of the symmetrical split resonance rings (sSRR) under the normal illumination of THz waves with both electric and magnetic components lay in the structure plane. The samples are fabricated and measured with a conventional THz time-domain spectroscopy. Such a sharp and pronounced resonance can benefit the applications such as biosensor, narrowband filter, and laser sparser.

Wang, Bo; Xie, Zhenwei; Feng, Shengfei; Zhang, Bo; Zhang, Yan

2015-01-01

389

Permanent magnet edge-field quadrupole  

DOEpatents

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

Tatchyn, Roman O. (Mountain View, CA)

1997-01-01

390

Magnetic Helicity and Large Scale Magnetic Fields: A Primer  

NASA Astrophysics Data System (ADS)

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. Here I discuss how magnetic helicity has come to help us understand the saturation of and sustenance of large scale dynamos, the need for either local or global helicity fluxes to avoid dynamo quenching, and the associated observational consequences. I also discuss how magnetic helicity acts as a hindrance to turbulent diffusion of large scale fields, and thus a helper for fossil remnant large scale field origin models in some contexts. I briefly discuss the connection between large scale fields and accretion disk theory as well. The goal here is to provide a conceptual primer to help the reader efficiently penetrate the literature.

Blackman, Eric G.

2014-04-01

391

Comparison of adjustable permanent magnetic field sources  

NASA Astrophysics Data System (ADS)

A permanent magnet assembly in which the flux density can be altered by a mechanical operation is often significantly smaller than comparable electromagnets and also requires no electrical power to operate. In this paper five permanent magnet designs in which the magnetic flux density can be altered are analyzed using numerical simulations, and compared based on the generated magnetic flux density in a sample volume and the amount of magnet material used. The designs are the concentric Halbach cylinder, the two half Halbach cylinders, the two linear Halbach arrays and the four and six rod mangle. The concentric Halbach cylinder design is found to be the best performing design, i.e. the design that provides the most magnetic flux density using the least amount of magnet material. A concentric Halbach cylinder has been constructed and the magnetic flux density, the homogeneity and the direction of the magnetic field are measured and compared with numerical simulation and a good agrement is found.

Bjørk, R.; Bahl, C. R. H.; Smith, A.; Pryds, N.

2010-11-01

392

Chaotic magnetic fields: Particle motion and energization  

SciTech Connect

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

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

2014-02-11

393

Magnetic fields in Neutron Stars  

E-print Network

Isolated neutron stars show a diversity in timing and spectral properties, which has historically led to a classification in different sub-classes. The magnetic field plays a key role in many aspects of the neutron star phenomenology: it regulates the braking torque responsible for their timing properties and, for magnetars, it provides the energy budget for the outburst activity and high quiescent luminosities (usually well above the rotational energy budget). We aim at unifying this observational variety by linking the results of the state-of-the-art 2D magneto-thermal simulations with observational data. The comparison between theory and observations allows to place two strong constraints on the physical properties of the inner crust. First, strong electrical currents must circulate in the crust, rather than in the star core. Second, the innermost part of the crust must be highly resistive, which is in principle in agreement with the presence of a novel phase of matter so-called nuclear pasta phase.

Viganò, Daniele; Miralles, Juan A; Rea, Nanda

2015-01-01

394

Warm inflation in presence of magnetic fields  

SciTech Connect

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

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

2013-07-23

395

The effect of magnetic field fluctuations on the initial distribution of pick-up ions  

NASA Astrophysics Data System (ADS)

In an environment where strong magnetic field fluctuations are present, the initial distribution of pick-up ions is not a ring-beam distribution but rather a nontrivial function, which extends to a significant portion of the pick-up shell. Due to the fluctuations each freshly picked-up particle feels a different magnetic field. Each magnetic field direction has a corresponding ring, and the initial distribution is the sum of these rings. The properties of the magnetic field fluctuations in the region of the pick-up influence the initial distribution strongly. We have studied the effect of the fluctuations on the initial distribution of pick-up ions. We found that the distribution resembles a signet-ring in velocity space; the function has a strong peak in the vicinity of the neutral velocity and a more extended shape on the opposite side of the pick-up shell. Both the intensity and the spectrum of the fluctuations influence its shape. Since the fluctuations are often in a large part waves generated by the pick-up ions themselves, the fluctuation spectra can have strong variations around the gyrofrequency of some ion species. We also found that the initial distribution is only sensitive to fluctuations having frequencies lower than the gyrofrequency of the pick-up ion. Thus the same magnetic field fluctuations can result in significantly different source distributions for different ion species.

Nemeth, Z.; Szego, K.; Lukacs, K.; Erdos, G.

2014-04-01

396

Ion Heating in an ECR Plasma with a Magnetic Mirror Field  

NASA Astrophysics Data System (ADS)

Magnetoelectric heating was used to heat ions in an ECR plasma with a magnetic mirror field. The temperature and density of ions were measured by an ion sensitive probe (ISP) before and after magnetoelectric heating in order to investigate the influence of the anode ring's radius, axial position and working pressure on magnetoelectric heating. Results showed that a suitable radius of the anode ring could improve the ion temperature effectively and the optimal size of the anode ring depended on the cyclotron radius of ions. The radial uniformity of the ion density was improved by increasing the radius of the anode ring after heating. The magnetic mirror field could reduce the loss of ions caused by collision with the wall of the chamber and it was beneficial to increase the ion temperature and the ion density. It was suitable to heat the ions when the anode ring was set at the center of the magnetic mirror field where there was a weaker magnetic field strength. Lower pressure contributed to the increase in the ion temperature and efficiency of magnetoelectric heating.

Shen, Wulin; Ma, Zhibin; Tan, Bisong; Wu, Jun

2013-06-01

397

Ohm's law for mean magnetic fields  

SciTech Connect

Spatially complicated magnetic fields are frequently treated as the sum of a large, slowly varying, mean field and a small, rapidly varying, field. The primary effect of the small field is to modify the Ohm's law of the mean field. A set of plausible assumptions leads to a form of the mean field Ohm's law which is fundamentally different from the conventional alpha effect of dynamo theory.

Boozer, A.H.

1984-11-01

398

Magnetic fields in noninvasive brain stimulation.  

PubMed

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

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

2014-04-01

399

Field Mapping System for Solenoid Magnet  

NASA Astrophysics Data System (ADS)

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

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

2007-01-01

400

Dynamic Magnetic Field Applications for Materials Processing  

NASA Technical Reports Server (NTRS)

Magnetic fields, variable in time and space, can be used to control convection in electrically conducting melts. Flow induced by these fields has been found to be beneficial for crystal growth applications. It allows increased crystal growth rates, and improves homogeneity and quality. Particularly beneficial is the natural convection damping capability of alternating magnetic fields. One well-known example is the rotating magnetic field (RMF) configuration. RMF induces liquid motion consisting of a swirling basic flow and a meridional secondary flow. In addition to crystal growth applications, RMF can also be used for mixing non-homogeneous melts in continuous metal castings. These applied aspects have stimulated increasing research on RMF-induced fluid dynamics. A novel type of magnetic field configuration consisting of an axisymmetric magnetostatic wave, designated the traveling magnetic field (TMF), has been recently proposed. It induces a basic flow in the form of a single vortex. TMF may find use in crystal growth techniques such as the vertical Bridgman (VB), float zone (FZ), and the traveling heater method. In this review, both methods, RMF and TMF are presented. Our recent theoretical and experimental results include such topics as localized TMF, natural convection dumping using TMF in a vertical Bridgman configuration, the traveling heater method, and the Lorentz force induced by TMF as a function of frequency. Experimentally, alloy mixing results, with and without applied TMF, will be presented. Finally, advantages of the traveling magnetic field, in comparison to the more mature rotating magnetic field method, will be discussed.

Mazuruk, K.; Grugel, Richard N.; Motakef, S.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

401

Protein detection with magnetic nanoparticles in a rotating magnetic field  

NASA Astrophysics Data System (ADS)

A detection scheme based on magnetic nanoparticle (MNP) dynamics in a rotating magnetic field for a quantitative and easy-to-perform detection of proteins is illustrated. For the measurements, a fluxgate-based setup was applied, which measures the MNP dynamics, while a rotating magnetic field is generated. The MNPs exhibit single iron oxide cores of 25 nm and 40 nm diameter, respectively, as well as a protein G functionalized shell. IgG antibodies were utilized as binding target molecules for the physical proof-of-concept. The measurement results were fitted with a theoretical model describing the magnetization dynamics in a rotating magnetic field. The established detection scheme allows quantitative determination of proteins even at a concentration lower than of the particles. The observed differences between the two MNP types are discussed on the basis of logistic functions.

Dieckhoff, Jan; Lak, Aidin; Schilling, Meinhard; Ludwig, Frank

2014-01-01

402

Gravity and magnetic investigation of maar volcanoes, Auckland volcanic field, New Zealand  

Microsoft Academic Search

Detailed gravity and aeromagnetic data over maars in the Auckland volcanic field reveal contrasting anomalies, even where surface geology is similar. Pukaki and Pukekiwiriki, almost identical maars marked by sediment-filled craters and tuff rings, have gravity and magnetic anomalies of ?6 g.u. and 20 nT, and 8 g.u. and 160 nT, respectively. The Domain and Waitomokia maars, with similar tuff rings but each with

John Cassidy; Sian J. France; Corinne A. Locke

2007-01-01

403

External-field-free magnetic biosensor  

SciTech Connect

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

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

2014-03-24

404

Theory of magnetic superconductors in an external magnetic field  

Microsoft Academic Search

The theory of Abrikosov and Gor'kov has been extended to study superconducting systems containing a lattice of magnetic ions. Differential equations have been set up for the Green's-function matrices which describe a magnetic superconductor in the presence of local-spin--conduction-electron exchange and external magnetic field. The self-consistent gap equation for the system has been formulated in terms of normal-state Green's functions.

Narayan C. Das

1984-01-01

405

Theory of magnetic superconductors in an external magnetic field  

Microsoft Academic Search

The theory of Abrikosov and Gor'kov has been extended to study superconducting systems containing a lattice of magnetic ions. Differential equations have been set up for the Green's-function matrices which describe a magnetic superconductor in the presence of local-spin-conduction-electron exchange and external magnetic field. The self-consistent gap equation for the system has been formulated in terms of normal-state Green's functions.

Narayan C. Das

1984-01-01

406

Compact low field magnetic resonance imaging magnet: Design and optimization  

NASA Astrophysics Data System (ADS)

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

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

2000-03-01

407

Colour superconductivity in a strong magnetic field  

E-print Network

We explore the effects of an applied strong external magnetic field in a three flavour massless colour superconductor. The long-range component of the B field that penetrates the superconductor enhances some quark condensates, leading to a different condensation pattern. The external field also reduces the flavour symmetries in the system, and thus it changes drastically the corresponding low energy physics. Our considerations are relevant for the study of highly magnetized compact stars.

Efrain J. Ferrer; Vivian de la Incera; Cristina Manuel

2005-11-30

408

Ohm's law for mean magnetic fields  

SciTech Connect

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

Boozer, A.H.

1986-05-01

409

Ohm's law for mean magnetic fields  

Microsoft Academic Search

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

A. H. Boozer

1986-01-01

410

Magnetic field corrections to solar oscillation frequencies  

NASA Technical Reports Server (NTRS)

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

Roberts, B.; Campbell, W. R.

1986-01-01

411

Thermodynamics of the Magnetic-Field-Induced \\  

Microsoft Academic Search

High magnetic fields are used to kill superconductivity and probe what happens to system when it cannot reach the ideal ground state, i.e. what is the normal-state ground state? Early work in High-Tc, where the application of magnetic field destroyed the zero resistance state and recovered a resistivity value that connected continuously with the zero field curve, lead people to

Scott Chandler Riggs

2010-01-01

412

Magnetic field homogeneity perturbations in finite Halbach dipole magnets.  

PubMed

Halbach hollow cylinder dipole magnets of a low or relatively low aspect ratio attract considerable attention due to their applications, among others, in compact NMR and MRI systems for investigating small objects. However, a complete mathematical framework for the analysis of magnetic fields in these magnets has been developed only for their infinitely long precursors. In such a case the analysis is reduced to two-dimensions (2D). The paper details the analysis of the 3D magnetic field in the Halbach dipole cylinders of a finite length. The analysis is based on three equations in which the components of the magnetic flux density Bx, By and Bz are expanded to infinite power series of the radial coordinate r. The zeroth term in the series corresponds to a homogeneous magnetic field Bc, which is perturbed by the higher order terms due to a finite magnet length. This set of equations is supplemented with an equation for the field profile B(z) along the magnet axis, presented for the first time. It is demonstrated that the geometrical factors in the coefficients of particular powers of r, defined by intricate integrals are the coefficients of the Taylor expansion of the homogeneity profile (B(z)-Bc)/Bc. As a consequence, the components of B can be easily calculated with an arbitrary accuracy. In order to describe perturbations of the field due to segmentation, two additional equations are borrowed from the 2D theory. It is shown that the 2D approach to the perturbations generated by the segmentation can be applied to the 3D Halbach structures unless r is not too close to the inner radius of the cylinder ri. The mathematical framework presented in the paper was verified with great precision by computations of B by a highly accurate integration of the magnetostatic Coulomb law and utilized to analyze the inhomogeneity of the magnetic field in the magnet with the accuracy better than 1 ppm. PMID:24316186

Turek, Krzysztof; Liszkowski, Piotr

2014-01-01

413

Theory of Passive Magnetic Field Transport  

E-print Network

In recent years, our knowledge of photospheric magnetic fields went through a thorough transformation--nearly unnoticed by dynamo theorists. It is now practically certain that the overwhelming majority of the unsigned magnetic flux crossing the solar surface is in turbulent form (intranetwork and hidden fields). Furthermore, there are now observational indications (supported by theoretical arguments discussed in this paper) that the net polarity imbalance of the turbulent field may give a significant or even dominant contribution to the weak large-scale background magnetic fields outside unipolar network areas. This turbulent magnetic field consists of flux tubes with magnetic fluxes below 1e10 Wb (1e18 Mx). The motion of these thin tubes is dominated by the drag of the surrounding flows, so the transport of this component of the solar magnetic field must fully be determined by the kinematics of the turbulence (i.e. it is "passive"), and it can be described by a one-fluid model like mean-field theory (MFT). This paper reviews the theory of passive magnetic field transport using mostly first (and occasionally higher) order smoothing formalism; the most important transport effects are however also independently derived using Lagrangian analysis for a simple two-component flow model. Solar applications of the theory are also presented. Among some other novel findings it is proposed that the observed unsigned magnetic flux density in the photosphere requires a small-scale dynamo effect operating in the convective zone and that the net polarity imbalance in turbulent (and, in particular, hidden) fields may give a major contribution to the weak large-scale background magnetic fields on the Sun.

Kristof Petrovay

1997-03-25

414

Magnetic reconnection at the edge of Uranus's magnetic field  

NASA Astrophysics Data System (ADS)

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

Balcerak, Ernie

2014-09-01

415

Tuning permanent magnets with adjustable field clamps  

SciTech Connect

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

Schermer, R.I.

1987-01-01

416

Earth-directed ICME magnetic field configurations  

NASA Astrophysics Data System (ADS)

It is known that the geoeffectiveness of interplanetary coronal mass ejections (ICMEs) depends on their magnetic field configuration. However, it remains unclear how the ICME interactions with the solar wind or other solar transient structures affect their magnetic configuration through, say, distortion of their cross-section, or deformation of their front. Obviously, precise space weather forecasting is depended on precise understanding of the evolution of the ICME internal magnetic topology.The goal of this study is to identify the ambient solar wind parameters that affect the flux-rope geometry and magnetic field configuration.

Nieves-Chinchilla, Teresa; Vourlidas, Angelos; Szabo, Adam; Savani, Neel; Mays, M. Leila; Hidalgo, Miguel Angel; Wenyuan, Yu

2015-04-01

417

3D analysis of applied field effect on trapped magnetic field during pulsed field magnetization of bulk superconductor  

NASA Astrophysics Data System (ADS)

External applied field effect in magnetization process by pulsed field (PFM) method of rectangular bulk superconductor is analysed by solving the A-V magnetic equation coupled to the thermal one in order to show the influence of the amplitude of the external field on the trapped magnetic field of bulk superconductor. A numerical model based on the control volume method (CVM) has been developed, which uses a power-law model with temperature dependency and magnetic field dependence on critical current density. For low cooling temperature Tco = 20 K, a good distribution of the trapped magnetic field of the bulk superconductor is obtained when we applied high external field.

Lotfi Khene, Mohamed; Alloui, Lotfi; Mimoune, Souri Mohamed; Bouillault, Frédéric; Feliachi, Mouloud

2014-04-01

418

The Measurement of Magnetic Fields  

ERIC Educational Resources Information Center

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

Berridge, H. J. J.

1973-01-01

419

Antiaromatic Character of 16 ? Electron Octaethylporphyrins: Magnetically Induced Ring Currents from DFT-GIMIC Calculations.  

PubMed

The magnetically induced current density susceptibility, also called current density, has been calculated for a recently synthesized octaethylporphyrin (OEP) zinc(II) dication with formally 16 ? electrons. Numerical integration of the current density passing selected chemical bonds yields the current pathway around the porphyrinoid ring and the strength of the ring current. The current strengths show that the OEP-Zn(II) dication is strongly antiaromatic, as also concluded experimentally. The calculation of the ring current pathway shows that all 24 ? electrons participate in the transport of the ring current because the current splits into inner and outer branches of practically equal strengths at the four pyrrolic rings. The corresponding neutral octaethylporphyrinoid without Zn and inner hydrogens is found to be antiaromatic, sustaining a paratropic ring current along the inner pathway with 16 ? electrons. The neutral OEP-Zn(II) molecule with formally 18 ? electrons is found to be almost as aromatic as free-base porphyrin. However, also in this case, all 26 ? electrons contribute to the ring current, as for free-base porphyrin. A comparison of calculated and measured (1)H NMR chemical shifts is presented. The current strength susceptibility under experimental conditions has been estimated by assuming a linear relation between experimental shielding constants and calculated current strengths. PMID:25141236

Fliegl, Heike; Pichierri, Fabio; Sundholm, Dage

2015-03-19

420

Superconducting tubular wires in transverse magnetic fields  

NASA Astrophysics Data System (ADS)

The electromagnetic response of a round tubular wire of superconducting film to a transverse magnetic field is investigated theoretically. For a superconducting tubular wire (STW) in which the thickness d of the superconducting layer is much smaller than the radius R of the wire, analytical expressions for the magnetic-field and current distributions are obtained on the basis of the critical state model with constant critical current density jc. When an applied transverse magnetic field Ha increases monotonically from zero, the penetration of the magnetic field into an STW occurs in two stages: for 0magnetic field in the interior of an STW is shielded, whereas for Ha>jcd/2 the magnetic field extends into the interior. Analytical expressions of the hysteretic ac loss Qtube of an STW in a transverse ac magnetic field of amplitude H0 are also obtained, and Qtube(H0) is found to have an abrupt change at H0?jcd/2.

Mawatari, Yasunori

2011-04-01

421

Magnetic properties and hyperfine interactions in Cr8, Cr7Cd, and Cr7Ni molecular rings from 19F-NMR  

SciTech Connect

A detailed experimental investigation of the 19F nuclear magnetic resonance is made on single crystals of the homometallic Cr8 antiferromagnetic molecular ring and heterometallic Cr7Cd and Cr7 Ni rings in the low temperature ground state. Since the F? ion is located midway between neighboring magnetic metal ions in the ring, the 19F-NMR spectra yield information about the local electronic spin density and 19F hyperfine interactions. In Cr8, where the ground state is a singlet with total spin S T = 0, the 19F-NMR spectra at 1.7 K and low external magnetic field display a single narrow line, while when the magnetic field is increased towards the first level crossing field, satellite lines appear in the 19F-NMR spectrum, indicating a progressive increase in the Boltzmann population of the first excited state S T = 1. In the heterometallic rings, Cr7Cd and Cr7 Ni, whose ground state is magnetic with S T = 3/2 and S T = 1/2, respectively, the 19F-NMR spectrum has a complicated structure which depends on the strength and orientation of the magnetic field, due to both isotropic and anisotropic transferred hyperfine interactions and classical dipolar interactions. From the 19F-NMR spectra in single crystals we estimated the transferred hyperfine constants for both the F?-Ni2+ and the F?-Cd2+ bonds. The values of the hyperfine constants compare well to the ones known for F?-Ni2+ in KNiF3 and NiF2 and for F?-Cr3+ in K2NaCrF6. The results are discussed in terms of hybridization of the 2s, 2p orbitals of the F? ion and the d orbitals of the magnetic ion. Finally, we discuss the implications of our results for the electron-spin decoherence.

Bordonali, L.; Garlatti, E.; Casadei, C. M.; Furukawa, Y.; Lascialfari, A.; Carretta, S.; Troiani, F.; Timco, G.; Winpenny, R. E.; Borsa, F.

2014-04-14

422

Generation of Vortex Beams with Strong Longitudinally Polarized Magnetic Field by Using a Metasurface  

E-print Network

A novel method of generation and synthesis of azimuthally E-polarized vortex beams is presented. Along the axis of propagation such beams have a strong longitudinally polarized magnetic field where ideally there is no electric field. We show how these beams can be constructed through the interference of Laguerre-Gaussian beams carrying orbital angular momentum. As an example, we present a metasurface made of double-split ring slot pairs and report a good agreement between simulated and analytical results. Both a high magnetic-to-electric-field contrast ratio and a magnetic field enhancement are achieved. We also investigate the metasurface physical constraints to convert a linearly polarized beam into an azimuthally E- polarized beam and characterize the performance of magnetic field enhancement and electric field suppression of a realistic metasurface. These findings are potentially useful for novel optical spectroscopy related to magnetic dipolar transitions and for optical manipulation of particles with sp...

Veysi, Mehdi; Capolino, Filippo

2014-01-01

423

Evolution of the interplanetary magnetic field  

SciTech Connect

Remote observations of magnetic field topologies in the solar corona and in situ observations of the solar wind and interplanetary magnetic field (IMF) in interplanetary space are used to examine the temporal evolution of the spatial distribution of open and closed field regions emanating from the Sun. The simple ``open`` configuration of inward and outward pointing sectors in the IMF is periodically disrupted by magnetically distinct coronal mass ejections (CMEs) which erupt from previously closed magnetic field regions in the corona into interplanetary space. At 1 AU, CMEs contain counterstreaming halo electrons which indicate their distinct magnetic topologies. This topology is generally thought to be: plasmoids that are completely disconnected from the Sun; magnetic ``bottles,`` still tied to the corona at both ends; or flux ropes which are only partially disconnected. Fully disconnected plasmoids would have no long term effect on the amount of open flux; however, both in situ observations of details of the halo electron distributions and remote coronagraph observations of radial fields following CMEs indicate that CMEs generally do retain at least partial attached to the Sun. Both the magnetic-bottle and flux rope geometries require some mitigating process to close off previously open fields in order to avoid a flux catastrophe. In addition, the average amount of magnetic flux observed in interplanetary space varies over the solar cycle, also indicating that there must be ways in which new flux is opened and previously open flux is closed off. The most likely scenario for closing off open magnetic fields is for reconnection to occurs above helmet streamers, where oppositely directed field regions are juxtaposed in the corona. These events would serve to return closed field arches to the Sun and release open, U-shaped structures into the solar wind.

McComas, D.J.

1993-05-01

424

Evolution of the interplanetary magnetic field  

SciTech Connect

Remote observations of magnetic field topologies in the solar corona and in situ observations of the solar wind and interplanetary magnetic field (IMF) in interplanetary space are used to examine the temporal evolution of the spatial distribution of open and closed field regions emanating from the Sun. The simple open'' configuration of inward and outward pointing sectors in the IMF is periodically disrupted by magnetically distinct coronal mass ejections (CMEs) which erupt from previously closed magnetic field regions in the corona into interplanetary space. At 1 AU, CMEs contain counterstreaming halo electrons which indicate their distinct magnetic topologies. This topology is generally thought to be: plasmoids that are completely disconnected from the Sun; magnetic bottles,'' still tied to the corona at both ends; or flux ropes which are only partially disconnected. Fully disconnected plasmoids would have no long term effect on the amount of open flux; however, both in situ observations of details of the halo electron distributions and remote coronagraph observations of radial fields following CMEs indicate that CMEs generally do retain at least partial attached to the Sun. Both the magnetic-bottle and flux rope geometries require some mitigating process to close off previously open fields in order to avoid a flux catastrophe. In addition, the average amount of magnetic flux observed in interplanetary space varies over the solar cycle, also indicating that there must be ways in which new flux is opened and previously open flux is closed off. The most likely scenario for closing off open magnetic fields is for reconnection to occurs above helmet streamers, where oppositely directed field regions are juxtaposed in the corona. These events would serve to return closed field arches to the Sun and release open, U-shaped structures into the solar wind.

McComas, D.J.

1993-01-01

425

Magnetic Field Measurement with Ground State Alignment  

NASA Astrophysics Data System (ADS)

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

Yan, Huirong; Lazarian, A.

426

Applications of non-contact magnetizing of ring shaped components  

SciTech Connect

Magnetic Particle Inspection of Ferro Magnetic Components still is the most common method of non-destructively testing for surface breaking defects. Such defects can be introduced into the component during the manufacturing process or induced by stress and fatigue in subsequent service. A surprisingly large number of components submitted to MPI tests are circular in cross section and have holes in central or otherwise. this paper details a method of testing such subjects in a manner which, with a high degree of confidence, reveals linear discontinuities on all surfaces via a single process without resorting to high current contact.

Downes, G. [DeW Systems Ltd., Hereford (United Kingdom)

1996-12-31

427

ASYMMETRIC DIFFUSION OF MAGNETIC FIELD LINES  

SciTech Connect

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

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

2013-04-20

428

The magnetic field of Mercury, part 1  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

429

Normal glow discharge in axial magnetic field  

NASA Astrophysics Data System (ADS)

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

Surzhikov, S.; Shang, J.

2014-10-01

430

Magnetic Fields in the Milky Way Halo  

NASA Astrophysics Data System (ADS)

We present a study of the Milky Way halo magnetic field, determined from observations of Faraday rotation measure (RM) of extragalactic radio sources (EGS) in Galactic longitude range 100°-117° within 30° of the Galactic plane. We find negative median RMs in both the northern and southern Galactic hemispheres for |b|>15°, outside the latitude range where the disk field dominates. This suggest that the halo magnetic field towards the outer Galaxy does not reverse direction across the mid-plane. An azimuthal magnetic field at heights 0.8-2 kpc above/below the Galactic plane between the local and the Perseus spiral arm can reproduce the observed trend of RM against Galactic latitude. We propose that the Milky Way could have a halo magnetic field similar to that observed in M51.

Mao, S. A.; McClure-Griffiths, N. M.; Gaensler, B. M.; Brown, J. C.; van Eck, C. L.; Haverkorn, M.; Kronberg, P. P.; Stil, J. M.; Shukurov, A.; Taylor, A. R.

2015-03-01

431

Mass movements and tree rings: A guide to dendrogeomorphic field sampling Markus Stoffel a,b,  

E-print Network

Mass movements and tree rings: A guide to dendrogeomorphic field sampling and dating Markus Stoffel of Geneva, Institute for Environmental Sciences, Climatic Change and Climate Impacts, 7 chemin de Drize, CH. For the analyses and interpretation of disturbances in tree-ring records, in contrast, clear guidelines have

Stoffel, Markus

432

Mass movements and tree rings: A guide to dendrogeomorphic field sampling Markus Stoffel a,b,  

E-print Network

Mass movements and tree rings: A guide to dendrogeomorphic field sampling and dating Markus Stoffel of Geneva, Institute for Environmental Sciences, Climatic Change and Climate Impacts, 7 chemin de Drize, CH of disturbances in tree-ring records, in contrast, clear guidelines have not been established, with largely

Stoffel, Markus

433

Novel layout of a bi-metallic nanoring for magnetic field pulse generation from light  

NASA Astrophysics Data System (ADS)

Recently Tsiatmas et al proposed using a nanoring made of two different metallic sectors to generate a magnetic pulse from a laser pulse [1]. Non-uniform heating of the ring creates very large temperature gradients, which drive thermoelectric currents, and this creates a localized magnetic field. However, heat from the laser pulse may result in the melting of the nanoring. We propose a symmetric structure made of four metallic sectors, which results in a higher magnetic field generation together with a lower lattice temperature. We also show that the magnetic field depends strongly on the size of the metallic sectors and interpret the results with the help of the electromotive forces, the overall ring resistance, and Biot-Savart law.

Vienne, Guillaume; Chen, Xiaoye; Shi Teh, Ying; Jye Ng, Ying; Oon Chia, Nyap; Ooi, Ching Pin

2015-01-01

434

Chern band insulators in a magnetic field.  

PubMed

The effect of a magnetic field on a two-dimensional Chern band insulator is discussed. It is shown that, unlike the trivial insulator, an anomalous Hall insulator with Chern number C becomes a metal when a magnetic field is applied at constant particle density, for any C > 0. For a time-reversal invariant topological insulator with a spin Chern resolved number, C? = ?C? = C, the magnetic field induces a spin polarized spin Hall insulator. We consider also the effect of a superlattice potential and extend previous results for the quantization of the Hall conductance of filled Hofstadter bands to this problem. PMID:24627894

Araújo, Miguel A N; Castro, Eduardo V

2014-02-19

435

Quantum Electrodynamics in a Uniform Magnetic Field  

E-print Network

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

Jun Suzuki

2005-12-28

436

Magnetic field quality analysis using ANSYS  

SciTech Connect

The design of superconducting magnets for particles accelerators requires a high quality of the magnetic field. This paper presents an ANSYS 4.4A Post 1 macro that computes the field quality performing a Fourier analysis of the magnetic field. The results show that the ANSYS solution converges toward the analytical solution and that the error on the multipole coefficients depends linearly on the square of the mesh size. This shows the good accuracy of ANSYS in computing the multipole coefficients. 2 refs., 16 figs., 4 tabs.

Dell'Orco, D.; Chen, Y.

1991-03-01

437

Environmental magnetic fields: Influences on early embryogenesis  

SciTech Connect

A 10-mG, 50 to 60-Hz magnetic field is in the intensity and frequency range that people worldwide are often exposed to in homes and in the workplace. Studies about the effects of 50- to 100-Hz electromagnetic fields on various species of animal embryos (fish, chick, fly, sea urchin, rat, and mouse) indicate that early stages of embryonic development are responsive to fluctuating magnetic fields. Chick, sea urchin, and mouse embryos are responsive to magnetic field intensities of 10-100 mG. Results from studies on sea urchin embryos indicate that exposure to conditions of rotating 60-Hz magnetic fields, e.g., similar to those in our environment, interferes with cell proliferation at the morula stage in a manner dependent on field intensity. The cleavage stages, prior to the 64-cell stage, were not delayed by this rotating 60-Hz magnetic field suggesting that the ionic surges, DNA replication, and translational events essential for early cleavage stages were not significantly altered. Studies of histone synthesis in early sea urchin embryos indicated that the rotating 60-Hz magnetic field decreased zygotic expression of early histone genes at the morula stage and suggests that this decrease in early histone production was limiting to cell proliferation. Whether these comparative observations from animal development studies will be paralleled by results from studies of human embryogenesis, as suggested by some epidemiology studies, has yet to be established. 38 refs.

Cameron, I.L.; Hardman, W.E.; Winters, W.D.; Zimmerman, S.; Zimmerman, A.M. (Univ. of Texas Health Science Center, San Antonio (United States))

1993-04-01

438

Mean magnetic field generation in sheared rotators  

E-print Network

A generalized mean magnetic field induction equation for differential rotators is derived, including a compressibility, and the anisotropy induced on the turbulent quantities from the mean magnetic field itself and a mean velocity shear. Derivations of the mean field equations often do not emphasize that there must be anisotropy and inhomogeneity in the turbulence for mean field growth. The anisotropy from shear is the source of a term involving the product of the mean velocity gradient and the cross-helicity correlation of the isotropic parts of the fluctuating velocity and magnetic field, $\\lb{\\bfv}\\cdot{\\bfb}\\rb^{(0)}$. The full mean field equations are derived to linear order in mean fields, but it is also shown that the cross-helicity term survives to all orders in the velocity shear. This cross-helicity term can obviate the need for a pre-existing seed mean magnetic field for mean field growth: though a fluctuating seed field is necessary for a non-vanishing cross-helicity, the term can produce linear (in time) mean field growth of the toroidal field from zero mean field. After one vertical diffusion time, the cross-helicity term becomes sub-dominant and dynamo exponential amplification/sustenance of the mean field can subsequently ensue. The cross-helicity term should produce odd symmetry in the mean magnetic field, in contrast to the usually favored even modes of the dynamo amplification in sheared discs. This may be important for the observed mean field geometries of spiral galaxies. The strength of the mean seed field provided by the cross- helicity depends linearly on the magnitude of the cross-helicity.

Eric G. Blackman

1999-08-31

439

Irregular elliptical plasmonic rings for engineering near-field and phase  

NASA Astrophysics Data System (ADS)

The near-field and phase distribution patterns of surface plasmon polaritons excited on different types of irregular elliptical rings are investigated with respect to linear and circular polarized lightwave. It is interestingly found that under linear polarization, the rings exhibit the dipole-like field and phase patterns, while under circular polarization they provide the omnidirectional vortex field and phase patterns. The field patterns produced by different rings demonstrated different shapes and amplitudes. The reason is due to different phase-matching conditions, which arise from internal geometrical variations of elliptical rings. These specified phase and near-field manipulations are of high potential for many applications such as optical trapping and beam shaping.

Guo, Ziming; Chu, Hong Son; Ahmed, Iftikhar; Khoo, Eng Huat

2014-08-01

440

Magnetic field sensors and visualizers using magnetic photonic crystals  

NASA Astrophysics Data System (ADS)

Magneto-optical imaging is widely used to observe the domain patterns in magnetic materials, visualize defects in ferromagnetic objects, and measure the spatial distribution of stray magnetic fields. Optimized 1D magneto-photonic crystals enable a significant increase in the sensitivity of magneto-optical sensors. The properties of such devices based on the optimized reflection (doubled Faraday rotation) mode and the use of 1D magnetic photonic crystals as sensors are discussed. Experimental results of the fabrication and characterization of ferrite-garnet layers possessing uniaxial magnetic anisotropy are shown, and an optimized film structure suitable for magneto-optical imaging is proposed.

Vasiliev, Mikhail; Alameh, Kamal E.; Kotov, Viatcheslav

2008-04-01

441

The theory of the Galactic magnetic field  

NASA Technical Reports Server (NTRS)

The paper discusses the role of the magnetic field in determining the large scale structure and dynamics of the interstellar medium. It then discusses the origin and maintenance of the Galactic field. The two major competing theories are that the field is primordial and connected to an intergalactic field or that the field is removed from and regenerated within the Galaxy. Finally, cosmic ray acceleration and confinement in the interstellar medium are discussed.

Zweibel, Ellen G.

1987-01-01

442

Spontaneous axisymmetry breaking of Saturn's external magnetic field  

E-print Network

Saturn's magnetic field is remarkably axisymmetric. Its dipole axis is inclined by less than 0.2 deg with respect to its rotation axis. Rotationally driven convection of magnetospheric plasma breaks the axisymmetry of its external magnetic field. Field aligned currents transfer angular momentum from the planet to a tongue of outflowing plasma. This transfer slows the rate of rotation of the ionosphere relative to that of the underlying atmosphere. The currents are the source for the non-axisymmetric components of the field. The common rotation rates of these components and Saturn's kilometric radio (SKR) bursts is that of the plasma near the orbit of Enceladus, and by extension the rotation rate in the ionosphere to which this plasma is coupled. That rate tells us nothing about the rotation rate of Saturn's deep interior. Of that we remain ignorant. Magnetic perturbations with magnitudes similar to those observed by Cassini are produced for Mdot ~ 10^4 g/s, a value similar to estimates for the rate of production of plasma from Saturn's E-ring. Enhancement of the SKR occurs in a narrow range of longitudes where the tip of the outgoing plasma stream connects to the auroral ionosphere via field lines that are bowed outwards by currents that supply the plasma's centripetal acceleration. (abridged)

Peter Goldreich; Alison J. Farmer

2006-08-14

443

Electrical properties of chain microstructure magnetic emulsions in magnetic field  

E-print Network

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

Arthur Zakinyan; Yuri Dikansky; Marita Bedzhanyan

2014-02-05

444

Magnetic power inverter: AC voltage generation from DC magnetic fields  

NASA Astrophysics Data System (ADS)

We propose a method that allows power conversion from DC magnetic fields to AC electric voltages using domain wall (DW) motion in ferromagnetic nanowires. The device concept relies on spinmotive force, voltage generation due to magnetization dynamics. Sinusoidal modulation of the nanowire width introduces a periodic potential for a DW, the gradient of which exerts variable pressure on the traveling DW. This results in time variation of the DW precession frequency and the associated voltage. Using a one-dimensional model, we show that the frequency and amplitude of the AC outputs can be tuned by the DC magnetic fields and wire-design.

Ieda, Jun'ichi; Maekawa, Sadamichi

2012-12-01

445

Directed Plasma Flow across Magnetic Field  

NASA Astrophysics Data System (ADS)

The Hall effect plays a significant role in the penetration of plasma flows across magnetic field. For example, its effect may become dominant in the solar wind penetration into the magnetosphere, in the magnetic field advection in wire array z-pinch precursors, or in the arcing of magnetically insulated transmission lines. An experiment performed at the Nevada Terawatt Facility explored the penetration of plasma with large Hall parameter (˜10) across ambient magnetic field. The plasma was produced by ablation with the short pulse high intensity laser Leopard (0.35 ps, 10^17W/cm^2) and the magnetic field with the pulsed power generator Zebra (50 T). The expanding plasma assumed a jet configuration and propagated beyond a distance consistent with a diamagnetic bubble model. Without magnetic field, the plasma expansion was close to hemispherical. The ability to produce the plasma and the magnetic field with distinct generators allows a controlled, quasi-continuous variation of the Hall parameter and other plasma parameters making the experiments useful for benchmarking numerical simulations.

Presura, R.; Stepanenko, Y.; Neff, S.; Sotnikov, V. I.

2008-04-01

446

Space applications of superconductivity - High field magnets  

NASA Technical Reports Server (NTRS)

The paper discusses developments in superconducting magnets and their applications in space technology. Superconducting magnets are characterized by high fields (to 15T and higher) and high current densities combined with low mass and small size. The superconducting materials and coil design are being improved and new high-strength composites are being used for magnet structural components. Such problems as maintaining low cooling temperatures (near 4 K) for long periods of time and degradation of existing high-field superconductors at low strain levels can be remedied by research and engineering. Some of the proposed space applications of superconducting magnets include: cosmic ray analysis with magnetic spectrometers, energy storage and conversion, energy generation by magnetohydrodynamic and thermonuclear fusion techniques, and propulsion. Several operational superconducting magnet systems are detailed.

Fickett, F. R.

1979-01-01

447

The topological description of coronal magnetic fields  

NASA Technical Reports Server (NTRS)

Determining the structure and behavior of solar coronal magnetic fields is a central problem in solar physics. At the photosphere, the field is believed to be strongly localized into discrete flux tubes. After providing a rigorous definition of field topology, how the topology of a finite collection of flux tubes may be classified is discussed.

Berger, Mitchell A.

1986-01-01

448

Magnetic field effects on surgical ligation clips.  

PubMed

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

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

1987-01-01