Transmission line magnetic fields; Measurements and calculations
Clairmont, B.A.; Johnson, G.B. (General Electric Co., EPRI High Voltage Transmission Research Center, Lenox, MA (US)); Dunlap, J.H. (Electric Power Research Inst., Palo Alto, CA (US))
1992-01-01
Recent controversy over 60 Hz magnetic fields has heightened public awareness of overhead transmission lines. As a result, there is increasing motivation to study the magnetic fields form transmission lines. The most cost effective means to conduct research into transmission line magnetic fields is with computer or reduced-scale line models. However, from the standpoint of public perception and acceptance, it is first necessary to demonstrate that the model being used correlates well with actual operating lines. This paper presents results that compare the calculated and measured magnetic field profiles of both an operating 230 kV line and a 4:1 reduced-scale test span. In both cases the phase currents and shield wire currents were measured simultaneously with the magnetic field measurements, and the profiles were studied to distances well beyond a typical edge of right-of-way.
Nonlinear calculation of three-dimensional static magnetic fields
M. Souza; C. Vidigal; A. Momy; J. Taquin; M. Sauzade
1997-01-01
We present here the principle and structure of a method to calculate the three-dimensional (3-D) static magnetic fields which have already permitted us to study hybrid magnets for magnetic resonance imaging and ion confinement. Field sources can be issued from resistive or superconducting coils, permanent magnets, and other magnetic bodies such as soft iron. It can be extended to very
Solenoid magnetic fields calculated from superposed semi-infinite solenoids
NASA Technical Reports Server (NTRS)
Brown, G. V.; Flax, L.
1966-01-01
Calculation of a thick solenoid coils magnetic field components is made by a superposition of the fields produced by four solenoids of infinite length and zero inner radius. The field produced by this semi-infinite solenoid is dependent on only two variables, the radial and axial field point coordinates.
Confining proton beams with longitudinal magnetic fields: Monte Carlo calculations.
Nardi, E; Schulte, R
2000-10-01
The problem of the lateral containment of a 160 MeV proton beam interacting with a medium simulating biological material was studied. The confining action of a longitudinal magnetic field was calculated by means of Monte Carlo simulation, where scattering and motion in the magnetic field were treated simultaneously. Appreciable compression of the beam could only be achieved using fields of the order at least 50 T, much beyond the realm of practical feasibility. PMID:11099205
Magnetic field calculations for iron oxide nanoparticles for MRI
NASA Astrophysics Data System (ADS)
Hernandez, Ricardo; Mendez Rojas, Miguel; Dies Suarez, Pilar; Hidalgo Tobón, Silvia
2014-11-01
The susceptibility effects of superparamagnetic iron oxide nanoparticles (SPIONs) functionalized with triethylenglycol (TREG) and Polyethylen Glycol (PEG) has been studied, those nanoparticles have the necessary properties to be used in the clinic as contrast media in imaging by MRI[1-3]. We are considering the behavior of the magnetic field as plane wave to explain the electrical and magnetic field produced by SPIONs. Images were acquired on a 1.5T imager Philips, using mFFE Sequence. Three glass capillary tubes with a) TREG (10nm) concentration of 300 ?g/ml, and PEGCOOH 6000(10nm) with 300 ?g/ml, and 2% agarosa. Magnetic field simulations were calculated in Matlab. The plane wave that comes in contact with a sphere of radius a, an propagation constant k1, and it is in an homogeneous space k2. We consider that the electric field is linearly polarized on x-direction, with a propagation on z-positive-axis. The secondary induced field can be explained from the interior of the sphere and valid exterior points. The referred waves are transmitted and reflected, this is valid only when the wavelength is smaller than the radius of the sphere. The obtained vibrational mode is an answer of the electrical oscillation and this is projection of the disturbed magnetic field. TREG-SPIONs produce more serious susceptibility artefacts compared to PEG-SPIONs. This study is promissory due to the concordance of the results of the simulations and the inhomogeneities showed in the MR images.
Numerical calculation of transient field effects in quenching superconducting magnets
Schwerg, Nikolai; Russenschuck, Stephan
2009-01-01
The maximum obtainable magnetic induction of accelerator magnets, relying on normal conducting cables and iron poles, is limited to around 2 T because of ohmic losses and iron saturation. Using superconducting cables, and employing permeable materials merely to reduce the fringe field, this limit can be exceeded and fields of more than 10 T can be obtained. A quench denotes the sudden transition from the superconducting to the normal conducting state. The drastic increase in electrical resistivity causes ohmic heating. The dissipated heat yields a temperature rise in the coil and causes the quench to propagate. The resulting high voltages and excessive temperatures can result in an irreversible damage of the magnet - to the extend of a cable melt-down. The quench behavior of a magnet depends on numerous factors, e.g. the magnet design, the applied magnet protection measures, the external electrical network, electrical and thermal material properties, and induced eddy current losses. The analysis and optimizat...
NASA Technical Reports Server (NTRS)
Sheeley, N. R., Jr.; Harvey, J. W.
1975-01-01
This paper presents particularly simple mathematical formulas for the calculation of force-free fields of constant alpha from the distribution of discrete sources on a flat surface. The advantage of these formulas lies in their physical simplicity and the fact that they can be easily used in practice to calculate the fields. The disadvantage is that they are limited to fields of 'sufficiently small alpha'. These formulas may be useful in the study of chromospheric magnetic fields by the comparison of high-resolution H-alpha photographs and photospheric magnetograms.
Calculation of Magnetic Helicity in a Force-Free Field
NASA Astrophysics Data System (ADS)
Updike, A. C.; Pevtsov, A.
2002-12-01
One of the goals of solar physics is to understand the solar dynamo. By studying the nature of magnetic helicity, we are studying the solar magnetic field driven by the dynamo. We used chromospheric magnetographs in the Ca II line (8543 Å) and EIT images in the Fe XII line (195 Å) to determine the degree of twist in the magnetic field. Using this degree of twist and the known magnetic energy for a given active region, we were able to measure the magnetic helicity in this force-free region. Over a period of three years (August 1996 to November 1998), we studied 37 active regions. We found a 73% hemispheric preference in the sign of the helicity - in the northern hemisphere, 70% of the active regions exhibited negative helicity; in the southern hemisphere, 76.5% of the active regions exhibited positive helicity. Our observations agree with earlier studies of the sign of helicity, which used vector magnetograms and studies of quiescent filiments.
Parallel computation of automatic differentiation applied to magnetic field calculations
Hinkins, R.L. [Univ. of California, Berkeley, CA (United States). Computer Science Dept.]|[Lawrence Berkeley Lab., CA (United States). Information and Computing Sciences Div.
1994-09-01
The author presents a parallelization of an accelerator physics application to simulate magnetic field in three dimensions. The problem involves the evaluation of high order derivatives with respect to two variables of a multivariate function. Automatic differentiation software had been used with some success, but the computation time was prohibitive. The implementation runs on several platforms, including a network of workstations using PVM, a MasPar using MPFortran, and a CM-5 using CMFortran. A careful examination of the code led to several optimizations that improved its serial performance by a factor of 8.7. The parallelization produced further improvements, especially on the MasPar with a speedup factor of 620. As a result a problem that took six days on a SPARC 10/41 now runs in minutes on the MasPar, making it feasible for physicists at Lawrence Berkeley Laboratory to simulate larger magnets.
The software for the calculations of force-free magnetic fields in solar active regions
Jian Chen; Yuanzhang Lin; Xiaolei Wei
1989-01-01
A set of software for the numerical calculations of constant force-free magnetic fields in solar active regions is given. Chiu-Hilton's representation is taken as the resolution of equations for a force-free field.
Magnetic Declination Calculator
NSDL National Science Digital Library
This tool calculates magnetic declination for a variety of locations across Canada and elsewhere. Users select a city (Canada only) from a drop-down menu or enter latitude and longitude values (works for any location), and the tool calculates the proper magnetic declination (the angular difference between observed magnetic North on a compass and geographic or 'true' North). There are also links to information on how to use magnetic declination with a compass, and how to use the calculator to determine values of all seven magnetic components. For locations in Canada, the Canadian Geomagnetic Reference Field (CGRF) is used; for other locations, the International Geomagnetic Reference Field (IGRF) is used.
Freitas, Jair C C; Scopel, Wanderlã L; Paz, Wendel S; Bernardes, Leandro V; Cunha-Filho, Francisco E; Speglich, Carlos; Araújo-Moreira, Fernando M; Pelc, Damjan; Cvitani?, Ton?i; Požek, Miroslav
2015-01-01
The prospect of carbon-based magnetic materials is of immense fundamental and practical importance, and information on atomic-scale features is required for a better understanding of the mechanisms leading to carbon magnetism. Here we report the first direct detection of the microscopic magnetic field produced at (13)C nuclei in a ferromagnetic carbon material by zero-field nuclear magnetic resonance (NMR). Electronic structure calculations carried out in nanosized model systems with different classes of structural defects show a similar range of magnetic field values (18-21?T) for all investigated systems, in agreement with the NMR experiments. Our results are strong evidence of the intrinsic nature of defect-induced magnetism in magnetic carbons and establish the magnitude of the hyperfine magnetic field created in the neighbourhood of the defects that lead to magnetic order in these materials. PMID:26434597
Ab initio calculation of electric field gradient and magnetic hyperfine field in Fe-doped SnO2
NASA Astrophysics Data System (ADS)
Zhang, Qiaoli; Yuan, Daqing; Fan, Ping; Zuo, Yi; Zheng, Yongnan; Ma, Xiaoqiang; Liang, Juncheng; Zhang, Huanqiao; Zhu, Shengyun
2015-04-01
Ab initio calculations of the magnetic and electric hyperfine fields and the magnetic moments were performed for the Fe doped SnO2 dilute magnetic semiconductors with the Wien2k code embodying the full-potential linearized augmented plane-wave method. The calculated results for the neutral system and the different charged state systems with and without the oxygen vacancy show clearly that the ground state is all magnetic and that the addition of electrons and the appearance of oxygen vacancy can increase the magnetic moment and the magnetic hyperfine field and reduce the electric hyperfine field. The energy level splitting of the Fe- 3d orbit can lead to enhancing the magnetic moment and, therefore, a very large magnetic moment of 5 ? B is obtained for the Sn15Fe1-O32 charged system.
NASA Astrophysics Data System (ADS)
Lu, Mai; Ueno, Shoogo
2009-04-01
In this paper, we present a transcranial magnetic stimulation (TMS) system by incorporating a conductive shield plate. The magnetic field, induced current density, and electric field in a real human head were calculated by impedance method and the results were compared with TMS without shielding. Our results show that the field localization can be improved by introducing a conductive shield plate; the stimulation magnitude (depth) in the brain is reduced comparing with the TMS without shielding. The strong magnetic field near the TMS coil is difficult to be efficiently shielded by a thinner conductive shield plate.
Calculation of the electric field resulting from human body rotation in a magnetic field.
Cobos Sánchez, Clemente; Glover, Paul; Power, Henry; Bowtell, Richard
2012-08-01
A number of recent studies have shown that the electric field and current density induced in the human body by movement in and around magnetic resonance imaging installations can exceed regulatory levels. Although it is possible to measure the induced electric fields at the surface of the body, it is usually more convenient to use numerical models to predict likely exposure under well-defined movement conditions. Whilst the accuracy of these models is not in doubt, this paper shows that modelling of particular rotational movements should be treated with care. In particular, we show that v × B rather than -(v · ?)A should be used as the driving term in potential-based modelling of induced fields. Although for translational motion the two driving terms are equivalent, specific examples of rotational rigid-body motion are given where incorrect results are obtained when -(v · ?)A is employed. In addition, we show that it is important to take into account the space charge which can be generated by rotations and we also consider particular cases where neglecting the space charge generates erroneous results. Along with analytic calculations based on simple models, boundary-element-based numerical calculations are used to illustrate these findings. PMID:22771959
Calculation of the electric field resulting from human body rotation in a magnetic field
NASA Astrophysics Data System (ADS)
Cobos Sánchez, Clemente; Glover, Paul; Power, Henry; Bowtell, Richard
2012-08-01
A number of recent studies have shown that the electric field and current density induced in the human body by movement in and around magnetic resonance imaging installations can exceed regulatory levels. Although it is possible to measure the induced electric fields at the surface of the body, it is usually more convenient to use numerical models to predict likely exposure under well-defined movement conditions. Whilst the accuracy of these models is not in doubt, this paper shows that modelling of particular rotational movements should be treated with care. In particular, we show that v? × ?B rather than -(v? · ??)A should be used as the driving term in potential-based modelling of induced fields. Although for translational motion the two driving terms are equivalent, specific examples of rotational rigid-body motion are given where incorrect results are obtained when -(v? · ??)A is employed. In addition, we show that it is important to take into account the space charge which can be generated by rotations and we also consider particular cases where neglecting the space charge generates erroneous results. Along with analytic calculations based on simple models, boundary-element-based numerical calculations are used to illustrate these findings.
NASA Astrophysics Data System (ADS)
Lang, Amy W.; Czysz, Paul
2001-11-01
A one-dimensional supersonic CFD code was utilized to solve for the required magnetic field strength, as a function of conductivity, for fixed length and constant static enthalpy magnetohydrodynamic generator and accelerator. The inlet velocity and pressure to the generator were varied, while requiring the exit Mach number of the generator to remain at 2.0. The flow after the generator proceeded through a simple supersonic combustion process, and the bypassed energy was then used in the accelerator to increase the flow velocity. Results show that varying the conductivity between 7 and 70 mho/m and inlet velocity between 5000 and 14000 ft/s, require magnetic fields in the generator between 1 and 12 Tesla with greater magnetic field strength required at lower conductivities. It was also calculated that for the same energy and conductivity used in the accelerator, a lower magnetic field was needed.
Calculations of lightning return stroke electric and magnetic fields above ground
NASA Technical Reports Server (NTRS)
Uman, M. A.; Lin, Y. T.; Standler, R. B.; Master, M. J.; Fisher, R. J.
1980-01-01
A lightning return stroke model with which the two station electric and magnetic fields measured at ground level can be reproduced is used to compute fields at altitudes up to 10 km and at ranges from 20 m to 10 km. These calculations provide the first detailed estimates of the return strokes fields that are encountered by aircraft in flight. With the advent of modern aircraft utilizing low voltage digital electronics and reduced electromagnetic shielding by way of structures containing advanced composite materials, these calculations are of considerable practical interest. Further, since airborne electric and magnetic field measurements are presently being attempted, a comparison of the calculations presented with appropriate experimental data, when they are available, will constitute a test of the return stroke model.
Magnetic design calculation and FRC formation modeling for the field reversed experiment liner
Dorf, L. A.; Intrator, T. P.; Renneke, R.; Hsu, S. C.; Wurden, G. A.; Awe, T.; Siemon, R.; Semenov, V. E.
2008-10-01
Integrated magnetic modeling and design are important to meet the requirements for (1) formation, (2) translation, and (3) compression of a field reversed configuration (FRC) for magnetized target fusion. Off-the-shelf solutions do not exist for many generic design issues. A predictive capability for time-dependent magnetic diffusion in realistically complicated geometry is essential in designing the experiment. An eddy-current code was developed and used to compute the mutual inductances between driven magnetic coils and passive magnetic shields (flux excluder plates) to calculate the self-consistent axisymmetric magnetic fields during the first two stages. The plasma in the formation stage was modeled as an immobile solid cylinder with selectable constant resistivity and magnetic flux that was free to readjust itself. It was concluded that (1) use of experimentally obtained anomalously large plasma resistivity in magnetic diffusion simulations is sufficient to predict magnetic reconnection and FRC formation, (2) comparison of predicted and experimentally observed timescales for FRC Ohmic decay shows good agreement, and (3) for the typical range of resistivities, the magnetic null radius decay rate scales linearly with resistivity. The last result can be used to predict the rate of change in magnetic flux outside of the separatrix (equal to the back-emf loop voltage), and thus estimate a minimum {theta}-coil loop voltage required to form an FRC.
Calculated non-linear magnetic field penetration of plasma opening switches
Mason, R.J.; Jones, M.E.; Wilson, D.C.; Bergman, C.; Thiem, K. ); Grossmann, J.M.; Ottinger, P.F. )
1990-06-15
We examine magnetic field penetration in the Plasma Opening Switch, exploring, in particular, advective field penetration arising in conjunction with radial density gradients across the cathode anode gap. Our calculations have been completed with the implicit multi-fluid, ANTHEM code. We show favored penetration along a radial density jump, unstable plain wave penetration for a 1/(y {minus} y{sub {alpha}+{epsilon}}) density dependence (with y measured from cathode to anode at Y{sub {alpha}}) in planar switches, and the penetration of finger-like magnetic field perturbations, when the fill plasmas bears initial sinusoidal disturbances on its generator interface. 7 refs., 4 figs.
Helgaker, Trygve
-spin coupling constants. Per- turbation theory equations needed to determine these mo- lecular properties wereMulticonfigurational self-consistent field calculations of nuclear magnetic resonance indirect spin and in four isomers of CH2N2 are described. For each molecule, SCF and two multiconfiguration self
NASA Astrophysics Data System (ADS)
Evstatiev, Evstati; Svidzinski, Vladimir; Spencer, Andy; Galkin, Sergei
2014-10-01
Full wave 3-D modeling of RF fields in hot magnetized nonuniform plasma requires calculation of nonlocal conductivity kernel describing the dielectric response of such plasma to the RF field. In many cases, the conductivity kernel is a localized function near the test point which significantly simplifies numerical solution of the full wave 3-D problem. Preliminary results of feasibility analysis of numerical calculation of the conductivity kernel in a 3-D hot nonuniform magnetized plasma in the electron cyclotron frequency range will be reported. This case is relevant to modeling of ECRH in ITER. The kernel is calculated by integrating the linearized Vlasov equation along the unperturbed particle's orbits. Particle's orbits in the nonuniform equilibrium magnetic field are calculated numerically by one of the Runge-Kutta methods. RF electric field is interpolated on a specified grid on which the conductivity kernel is discretized. The resulting integrals in the particle's initial velocity and time are then calculated numerically. Different optimization approaches of the integration are tested in this feasibility analysis. Work is supported by the U.S. DOE SBIR program.
Electric-field control of magnetism in graphene quantum dots: Ab initio calculations
Agapito, Luis A.; Kioussis, Nicholas; Kaxiras, Efthimios
2011-01-01
Employing ab initio calculations we predict that the magnetic states of hydrogenated diamond-shaped zigzag graphene quantum dots (GQDs), each exhibiting unique electronic structure, can be selectively tuned with gate voltage, through Stark or hybridization electric-field modulation of the spatial distribution and energy of the spin-polarized molecular orbitals, leading to transitions between these states. Electrical read-out of the GQD magnetic state can be accomplished by exploiting the distinctive electrical properties of the various magnetic configurations. PMID:21765631
Calculations of lightning return stroke electric and magnetic fields above ground
NASA Technical Reports Server (NTRS)
Master, M. J.; Uman, M. A.; Ling, Y. T.; Standler, R. B.
1981-01-01
Lin et al., (1980) presented a lightning return stroke model with which return stroke electric and magnetic fields measured at ground level could be reproduced. This model and a modified version of it, in which the initial current peak decays with height above ground, are used to compute waveforms for altitudes from 0-10 km and at ranges of 20 m to 10 km. Both the original and modified models gave accurate predictions of measured ground-based fields. The use of the calculated fields in calibrating airborne field measurements from simultaneous ground and airborne data is discussed.
Defining and Calculating Self-Helicity in Coronal Magnetic Fields D.W. Longcope and A. Malanushenko
Longcope, Dana
Defining and Calculating Self-Helicity in Coronal Magnetic Fields D.W. Longcope and A. Malanushenko for any portion of a potential magnetic field. The other helicity, unconfined self-helicity of additive self-helicities may be used as a constraint in the minimiza- tion of magnetic energy to produce
Calculating Coronal Mass Ejection Magnetic Field at 1 AU Using Solar Observables
NASA Astrophysics Data System (ADS)
Chen, J.; Kunkel, V.
2013-12-01
It is well-established that most major nonrecurrent geomagnetic storms are caused by solar wind structures with long durations of strong southward (Bz < 0) interplanetary magnetic field (IMF). Such geoeffective IMF structures are associated with CME events at the Sun. Unfortunately, neither the duration nor the internal magnetic field vector of the ejecta--the key determinants of geoeffectiveness--is measurable until the observer (e.g., Earth) passes through the ejecta. In this paper, we discuss the quantitative relationships between the ejecta magnetic field at 1 AU and remotely observable solar quantities associated with the eruption of a given CME. In particular, we show that observed CME trajectories (position-time data) within, say, 1/3 AU of the Sun, contain sufficient information to allow the calculation of the ejecta magnetic field (magnitude and components) at 1 AU using the Erupting Flux Rope (EFR) model of CMEs. Furthermore, in order to accurately determine the size and arrival time of the ejecta as seen by a fixed observer at 1 AU (e.g., ACE), it is essential to accurately calculate the three-dimensional geometry of the underlying magnetic structure. Accordingly, we have extended the physics-based EFR model to include a self-consistent calculation of the transverse expansion taking into account the non-symmetric drag coupling between an expanding CME flux rope and the ambient solar wind. The dependence of the minor radius of the flux rope at 1 AU that determines the perceived size of the ejecta on solar quantities is discussed. Work supported by the NRL Base Program.
Density-Functional-Theory Calculations of Matter in Strong Magnetic Fields: I. Atoms and Molecules
Zach Medin; Dong Lai
2007-01-05
We present new ab initio calculations of the electronic structure of various atoms and molecules in strong magnetic fields ranging from B=10^12 G to 2x10^15 G, appropriate for radio pulsars and magnetars. For these field strengths, the magnetic forces on the electrons dominate over the Coulomb forces, and to a good approximation the electrons are confined to the ground Landau level. Our calculations are based on the density functional theory, and use a local magnetic exchange-correlation function which is tested to be reliable in the strong field regime. Numerical results of the ground-state energies are given for H_N (up to N=10), He_N (up to N=8), C_N (up to N=5) and Fe_N (up to N=3), as well as for various ionized atoms. Fitting formulae for the B-dependence of the energies are also given. In general, as N increases, the binding energy per atom in a molecule, |E_N|/N, increases and approaches a constant value. For all the field strengths considered in this paper, hydrogen, helium, and carbon molecules are found to be bound relative to individual atoms (although for B less than a few x 10^12 G, the relative binding between C and C_2 is small). Iron molecules are not bound at Batoms at larger field strengths.
Density-functional-theory calculations of matter in strong magnetic fields. I. Atoms and molecules
NASA Astrophysics Data System (ADS)
Medin, Zach; Lai, Dong
2006-12-01
We present calculations of the electronic structure of various atoms and molecules in strong magnetic fields ranging from B=1012Gto2×1015G , appropriate for radio pulsars and magnetars. For these field strengths, the magnetic forces on the electrons dominate over the Coulomb forces, and to a good approximation the electrons are confined to the ground Landau level. Our calculations are based on the density functional theory, and use a local magnetic exchange-correlation function which is tested to be reliable in the strong field regime. Numerical results of the ground-state energies are given for HN (up to N=10 ), HeN (up to N=8 ), CN (up to N=5 ), and FeN (up to N=3 ), as well as for various ionized atoms. Fitting formulae for the B dependence of the energies are also given. In general, as N increases, the binding energy per atom in a molecule, ?EN?/N , increases and approaches a constant value. For all the field strengths considered in this paper, hydrogen, helium, and carbon molecules are found to be bound relative to individual atoms (although for B less than a few ×1012G , carbon molecules are very weakly bound relative to individual atoms). Iron molecules are not bound at B?1013G , but become energetically more favorable than individual atoms at larger field strengths.
An approach to 3D magnetic field calculation using numerical and differential algebra methods
Caspi, S.; Helm, M.; Laslett, L.J.; Brady, V.O.
1992-07-17
Motivated by the need for new means for specification and determination of 3D fields that are produced by electromagnetic lens elements in the region interior to coil windings and seeking to obtain techniques that will be convenient for accurate conductor placement and dynamical study of particle motion, we have conveniently gene the representation of a 2D magnetic field to 3D. We have shown that the 3 dimensioal magnetic field components of a multipole magnet in the curl-fire divergence-fire region near the axis r=0 can be derived from one dimensional functions A{sub n}(z) and their derivatives (part 1). In the region interior to coil windings of accelerator magnets the three spatial components of magnet fields can be expressed in terms of harmonic components'' proportional to functions sin (n{theta}) or cos (n{theta}) of the azimuthal angle. The r,z dependence of any such component can then be expressed in terms of powers of r times functions A{sub n}(z) and their derivatives. For twodimensional configurations B{sub z} of course is identically zero, the derivatives of A{sub n}(z) vanish, and the harmonic components of the transverse field then acquire a simple proportionality B{sub r,n} {proportional to} r{sup n-1} sin (n{theta}),B{sub {theta},n} {proportional to} r{sup n-1} cos (n{theta}), whereas in a 3-D configuration the more complex nature of the field gives rise to additional so-called psuedomultipole'' components as judged by additional powers of r required in the development of the field. Computation of the 3-D magnetic field arising at a sequence of field points, as a direct result of a specified current configuration or coil geometry, can be calculated explicitly through use of the Biot-Savart law and from such data the coefficients can then be derived for a general development of the type indicated above. We indicate, discuss, and illustrate two means by which this development may be performed.
NASA Astrophysics Data System (ADS)
Gandhi, Om P.; Kang, Gang
2001-11-01
This paper illustrates the use of the impedance method to calculate the electric fields and current densities induced in millimetre resolution anatomic models of the human body, namely an adult and 10- and 5-year-old children, for exposure to nonuniform magnetic fields typical of two assumed but representative electronic article surveillance (EAS) devices at 1 and 30 kHz, respectively. The devices assumed for the calculations are a solenoid type magnetic deactivator used at store checkouts and a pass-by panel-type EAS system consisting of two overlapping rectangular current-carrying coils used at entry and exit from a store. The impedance method code is modified to obtain induced current densities averaged over a cross section of 1 cm2 perpendicular to the direction of induced currents. This is done to compare the peak current densities with the limits or the basic restrictions given in the ICNIRP safety guidelines. Because of the stronger magnetic fields at lower heights for both the assumed devices, the peak 1 cm2 area-averaged current densities for the CNS tissues such as the brain and the spinal cord are increasingly larger for smaller models and are the highest for the model of the 5-year-old child. For both the EAS devices, the maximum 1 cm2 area-averaged current densities for the brain of the model of the adult are lower than the ICNIRP safety guideline, but may approach or exceed the ICNIRP basic restrictions for models of 10- and 5-year-old children if sufficiently strong magnetic fields are used.
Pablo Gomez; Dmitri Litvinov; Sakhrat Khizroev
2008-01-01
The objective of this research is to calculate the minimum parameters required to make low-field low-size nano nuclear magnetic resonance (NanoNMR) a viable technology and potentially one of the future lab-on-chip technologies. By low field we signify an externally applied magnetic field of less than 0.5 T, and by low size we mean a magnet whose largest physical dimension does
C. Mahony; L. K. Forbes; S. Crozier; D. M. Doddrell
1995-01-01
This paper presents a novel approach for determining the magnetic and electric fields generated by NMR RF coils of arbitrary shape, Maxwell?s equations are solved using Helmholtz retarded potentials, The model incorporates the effects of radiofrequencies and allows the calculation of both electric and magnetic fields at any position, Discussion of the numerical evaluation of the resulting formulas is presented,
NASA Astrophysics Data System (ADS)
Punjabi, Alkesh; Ali, Halima
2008-12-01
A new approach to integration of magnetic field lines in divertor tokamaks is proposed. In this approach, an analytic equilibrium generating function (EGF) is constructed in natural canonical coordinates (?,?) from experimental data from a Grad-Shafranov equilibrium solver for a tokamak. ? is the toroidal magnetic flux and ? is the poloidal angle. Natural canonical coordinates (?,?,?) can be transformed to physical position (R,Z,?) using a canonical transformation. (R,Z,?) are cylindrical coordinates. Another canonical transformation is used to construct a symplectic map for integration of magnetic field lines. Trajectories of field lines calculated from this symplectic map in natural canonical coordinates can be transformed to trajectories in real physical space. Unlike in magnetic coordinates [O. Kerwin, A. Punjabi, and H. Ali, Phys. Plasmas 15, 072504 (2008)], the symplectic map in natural canonical coordinates can integrate trajectories across the separatrix surface, and at the same time, give trajectories in physical space. Unlike symplectic maps in physical coordinates (x,y) or (R,Z), the continuous analog of a symplectic map in natural canonical coordinates does not distort trajectories in toroidal planes intervening the discrete map. This approach is applied to the DIII-D tokamak [J. L. Luxon and L. E. Davis, Fusion Technol. 8, 441 (1985)]. The EGF for the DIII-D gives quite an accurate representation of equilibrium magnetic surfaces close to the separatrix surface. This new approach is applied to demonstrate the sensitivity of stochastic broadening using a set of perturbations that generically approximate the size of the field errors and statistical topological noise expected in a poloidally diverted tokamak. Plans for future application of this approach are discussed.
Bret, A., E-mail: antoineclaude.bret@uclm.es [ETSI Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain and Instituto de Investigaciones Energéticas y Aplicaciones Industriales, Campus Universitario de Ciudad Real, 13071 Ciudad Real (Spain)
2014-02-15
The filamentation (Weibel) instability plays a key role in the formation of collisionless shocks which are thought to produce Gamma-Ray-Bursts and High-Energy-Cosmic-Rays in astrophysical environments. While it has been known for long that a flow-aligned magnetic field can completely quench the instability, it was recently proved in 2D that in the cold regime, such cancelation is possible if and only if the field is perfectly aligned. Here, this result is finally extended to a 3D geometry. Calculations are conducted for symmetric and asymmetric counter-streaming relativistic plasma shells. 2D results are retrieved in 3D: the instability can never be completely canceled for an oblique magnetic field. In addition, the maximum growth-rate is always larger for wave vectors lying in the plan defined by the flow and the oblique field. On the one hand, this bears consequences on the orientation of the generated filaments. On the other hand, it certifies 2D simulations of the problem can be performed without missing the most unstable filamentation modes.
A calculation of auroral hiss with improved models for geoplasma and magnetic field
NASA Technical Reports Server (NTRS)
Maeda, K.
1975-01-01
Intensities of auroral hiss generated by the Cerenkov radiation process by electrons in the lower magnetosphere are calculated with respect to a realistic model of the earth's magnetosphere. In this calculation, the magnetic field is expressed by the Mead-Fairfield Model (1975), and a static model of the iono-magnetospheric plasma distribution is constructed with data accumulated by recent satellites (Alouette-I, -II, ISIS-I, OGO-4, -6 and Explorer 22). The energy range of hiss producing electrons and the frequency range of the calculated VLF are 100-200 keV, and 2-200 kHz, respectively. The higher rate of hiss occurrence in the daytime side, particularly in the soft electron precipitation zone in the morning sector, and the lesser occurrence of auroral hiss in night-time sectors must be due to the local time dependence of the energy spectra of precipitating electrons rather than the difference in the geomagnetic field and in the geoplasma distributions.
V. V. Aseeva; G. V. Boriskov; A. I. Panov
2004-01-01
Valuable information on thermodynamic and electrical properties of easily compressed crystalline substances can be obtained by placing them inside a metal tube on which a pulse of ultra-high magnetic field pressure is applied. In such experiments it is important to know the characteristics of longitudinal substance motion due to the non-uniform distribution of magnetic field pressure. For this purpose we
Schöller, Markus
2015-01-01
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.
Calculation and analysis of the magnetic field of a linearly tapered undulator
NASA Astrophysics Data System (ADS)
Li, He-Ting; Guo, Fan; Li, Jia-Yu; Jia, Qi-Ka
2015-08-01
There is an empirical formula describing the relationship between the peak magnetic field and the undulator structure parameters for a uniform-parameter hybrid undulator. In this paper, we investigate the relationship for a linearly tapered undulator through numerical calculation by using the code RADIA, and check it with the empirical formula. The results imply that this empirical formula is also effective for linearly tapered undulators at a big enough scope for the requirements of normal FEL experiments. Therefore, for a linearly tapered undulator, we can use the empirical formula to design the variation of the undulator gap. For the tapering rate demanded by normal FEL experiments, the gap of a linearly tapered undulator increases almost linearly, and the tapering rate will keep constant while adjusting the undulator gap with the same variation for each undulator period. Supported by National Natural Science Foundation of China (11205156) and Major State Basic Research Development Program (2011CB808301)
J Selvaggi; S Salon; O Kwon CVK Chari
2006-02-14
An alternative method is developed to compute the magnetic field from a circular cylindrical magnetic source. Specifically, a Fourier series expansion whose coefficients are toroidal functions is introduced which yields an alternative to the more familiar spherical harmonic solution or the Elliptic integral solution. This alternate formulation coupled with a method called charge simulation allows one to compute the external magnetic field from an arbitrary magnetic source in terms of a toroidal expansion. This expansion is valid on any finite hypothetical external observation cylinder. In other words, the magnetic scalar potential or the magnetic field intensity is computed on a exterior cylinder which encloses the magnetic source. This method can be used to accurately compute the far field where a finite element formulation is known to be inaccurate.
NASA Astrophysics Data System (ADS)
Bedard, Claude; Destexhe, Alain
2014-10-01
Neurons generate magnetic fields which can be recorded with macroscopic techniques such as magnetoencephalography. The theory that accounts for the genesis of neuronal magnetic fields involves dendritic cable structures in homogeneous resistive extracellular media. Here we generalize this model by considering dendritic cables in extracellular media with arbitrarily complex electric properties. This method is based on a multiscale mean-field theory where the neuron is considered in interaction with a "mean" extracellular medium (characterized by a specific impedance). We first show that, as expected, the generalized cable equation and the standard cable generate magnetic fields that mostly depend on the axial current in the cable, with a moderate contribution of extracellular currents. Less expected, we also show that the nature of the extracellular and intracellular media influence the axial current, and thus also influence neuronal magnetic fields. We illustrate these properties by numerical simulations and suggest experiments to test these findings.
Collins, Christopher M; Yang, Bei; Yang, Qing X; Smith, Michael B
2002-06-01
Susceptibility-induced perturbation of the static magnetic field by the human body during magnetic resonance imaging (MRI) leads to undesirable artifacts as well as valuable physiological information, as in functional MRI. The ability to calculate these perturbations for a multi-tissue human body model provides a powerful tool in designing hardware and acquisition methods for reducing the artifacts, and in relating observed image contrast to physiological origins. We have developed a method for calculating the static field in arbitrary 3D magnetic susceptibility distributions and performed calculations in a complete model of the human head and shoulders. The accuracy of our method was validated in regular geometries with known analytical solutions and in comparison with experimental results acquired from the head of the same human subject used for computer modeling. Results are presented in parts per million (ppm) deviation from the applied field strength and are valid for any imaging or spectroscopy system. PMID:12206867
Mamishev, Alexander V
1994-01-01
with a periodical catenary model of the conductors A series of measurements performed with all electric utility bucket truck provide unique magnetic field data very close to the conductors. A conceptual design of a power line proximity detector...
NASA Astrophysics Data System (ADS)
Masrour, R.; Hlil, E. K.; Hamedoun, M.; Benyoussef, A.; Mounkachi, O.; El Moussaoui, H.
2015-03-01
Self-consistent ab initio calculations, based on density functional theory (DFT) approach and using a full potential linear augmented plane wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the Fe3O4. Polarized spin and spin-orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent Fe plans. Magnetic moment considered to lie along (010) axes are computed. Obtained data from ab initio calculations are used as input for the high temperature series expansions (HTSEs) calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Fe-Fe in Fe3O4 are given using the mean field theory. The high temperature series expansions (HTSEs) of the magnetic susceptibility of with the magnetic moments, mFe in Fe3O4 is given up to seventh order series in (1/kBT). The Néel temperature TN is obtained by HTSEs of the magnetic susceptibility series combined with the Padé approximant method. The critical exponent ? associated with the magnetic susceptibility is deduced as well.
NASA Astrophysics Data System (ADS)
Liu, Jun; Jia, Wen-Zhi; Wang, Shun-Jin
2009-09-01
Based on the Dirac equation describing an electron moving in a uniform and cylindrically symmetric magnetic field which may be the result of the self-consistent mean field of the electrons themselves in a neutron star, we have obtained the eigen solutions and the orbital magnetic moments of electrons in which each eigen orbital can be calculated. From the eigen energy spectrum we find that the lowest energy level is the highly degenerate orbitals with the quantum numbers pz = 0, n = 0, and m >= 0. At the ground state, the electrons fill the lowest eigen states to form many Landau magnetic cells and each cell is a circular disk with the radius ?free and the thickness ?e, where ?free is the electron mean free path determined by Coulomb cross section and electron density and ?e is the electron Compton wavelength. The magnetic moment of each cell and the number of cells in the neutron star are calculated, from which the total magnetic moment and magnetic field of the neutron star can be calculated. The results are compared with the observational data and the agreement is reasonable.
Calculation of the electric hypershielding at the nuclei of molecules in a strong magnetic field
NASA Astrophysics Data System (ADS)
Caputo, M. C.; Ferraro, M. B.; Pagola, G. I.; Lazzeretti, P.
2007-04-01
The third-rank electric hypershielding at the nuclei of 14 small molecules has been evaluated at the Hartree-Fock level of accuracy, by a pointwise procedure for the geometrical derivatives of magnetic susceptibilities and by a straightforward use of its definition within the Rayleigh-Schrödinger perturbation theory. The connection between these two quantities is provided by the Hellmann-Feynman theorem. The magnetically induced hypershielding at the nuclei accounts for distortion of molecular geometry caused by strong magnetic fields and for related changes of magnetic susceptibility. In homonuclear diatomics H2, N2, and F2, a field along the bond direction squeezes the electron cloud toward the center, determining shorter but stronger bond. It is shown that constraints for rotational and translational invariances and hypervirial theorems provide a natural criterion for Hartree-Fock quality of computed nuclear electric hypershielding.
3D field calculation of the GEM prototype magnet and comparison with measurements
Lari, R.J.
1983-10-28
The proposed 4 GeV Electron Microtron (GEM) is designed to fill the existing buildings left vacant by the demise of the Zero Gradient Synchrotron (ZGS) accelerator. One of the six large dipole magnets is shown as well as the first 10 electron orbits. A 3-orbit prototype magnet has been built. The stepped edge of the magnet is to keep the beam exiting perpendicular to the pole. The end guards that wrap around the main coils are joined together by the 3 shield plates. The auxiliary coils are needed to keep the end guards and shield plates from saturating. A 0.3 cm Purcell filter air gap exists between the pole and the yoke. Can anyone question this being a truly three-dimensional magnetostatic problem. The computer program TOSCA, developed at the Rutherford Appleton Laboratory by the Computing Applications Group, was used to calculate this magnet and the results have been compared with measurements.
P. Vigoureux
1993-01-01
Formulae for the magnetic field strength H of a Helmholtz system of two circular coils are given. The components of H along and perpendicular to the axis are expressed in series of spherical harmonics which converge rapidly in a region around the center of the system. The formulae are normalized, and thus applicable to systems of any size. The results
NASA Astrophysics Data System (ADS)
Mahony, C.; Forbes, L. K.; Crozier, S.; Doddrell, D. M.
1995-05-01
This paper presents a novel approach for determining the magnetic and electric fields generated by NMR RF coils of arbitrary shape, Maxwell?s equations are solved using Helmholtz retarded potentials, The model incorporates the effects of radiofrequencies and allows the calculation of both electric and magnetic fields at any position, Discussion of the numerical evaluation of the resulting formulas is presented, A comparison of the numerical results with an exact solution is made for the case of a singular circular loop of wire, Theoretical results for a birdcage coil are also given. This approach provides fast, accurate results and will easily lend itself to coil optimization.
Yago, Tomoaki; Wakasa, Masanobu
2015-04-21
A practical method to calculate time evolutions of magnetic field effects (MFEs) on photochemical reactions involving radical pairs is developed on the basis of the theory of the chemically induced dynamic spin polarization proposed by Pedersen and Freed. In theory, the stochastic Liouville equation (SLE), including the spin Hamiltonian, diffusion motions of the radical pair, chemical reactions, and spin relaxations, is solved by using the Laplace and the inverse Laplace transformation technique. In our practical approach, time evolutions of the MFEs are successfully calculated by applying the Miller-Guy method instead of the final value theorem to the inverse Laplace transformation process. Especially, the SLE calculations are completed in a short time when the radical pair dynamics can be described by the chemical kinetics consisting of diffusions, reactions and spin relaxations. The SLE analysis with a short calculation time enables one to examine the various parameter sets for fitting the experimental date. Our study demonstrates that simultaneous fitting of the time evolution of the MFE and of the magnetic field dependence of the MFE provides valuable information on the diffusion motions of the radical pairs in nano-structured materials such as micelles where the lifetimes of radical pairs are longer than hundreds of nano-seconds and the magnetic field dependence of the spin relaxations play a major role for the generation of the MFE. PMID:25773238
NASA Astrophysics Data System (ADS)
Vigoureux, P.
1993-12-01
Formulae for the magnetic field strength H of a Helmholtz system of two circular coils are given. The components of H along and perpendicular to the axis are expressed in series of spherical harmonics which converge rapidly in a region around the center of the system. The formulae are normalized, and thus applicable to systems of any size. The results given are well known; they have been put together for easy reference.
Hart, F X
1994-01-01
A commercially available spreadsheet program is used on a microcomputer to calculate the induced current density and electric field patterns produced in a nonhomogeneous, anisotropic model of tissue by a localized, low-frequency magnetic field source. Specific application is made to coils used to promote the healing of bone fractures in limbs. The variation of the conductivity of the fracture gap during healing causes the induced current density pattern to change correspondingly, whereas the induced electric field remains relatively unchanged. Use of more simplified, isotropic models for the bone and for the soft tissue leads to results that differ significantly from those obtained from the full model. The magnetic field beyond the region of the coils contributes little to the induced currents in the fracture gap if the gap is located near the center of the coils. PMID:7802713
Nolte, G; Curio, G
1997-01-01
Spatially restricted biological current distributions, like the primary neuronal response in the human somatosensory cortex evoked by electric nerve stimulation, can be described adequately by a current multipole expansion. Here analytic formulas are derived for computing magnetic fields induced by current multipoles in terms of an nth-order derivative of the dipole field. The required differential operators are given in closed form for arbitrary order. The concept is realized in different forms for an expansion of the scalar as well as the dyadic Green's function, the latter allowing for separation of those multipolar source components that are electrically silent but magnetically detectable. The resulting formulas are generally applicable for current sources embedded in arbitrarily shaped volume conductors. By using neurophysiologically relevant source parameters, examples are provided for a spherical volume conductor with an analytically given dipole field. An analysis of the signal-to-noise ratio for multipole coefficients up to the octapolar term indicates that the lateral extent of cortical current sources can be detected by magnetoencephalographic recordings. PMID:9284293
Liu, Feng; Crozier, Stuart
2004-08-01
This paper evaluates a new, low-frequency finite-difference time-domain method applied to the problem of induced E-fields/eddy currents in the human body resulting from the pulsed magnetic field gradients in MRI. In this algorithm, a distributed equivalent magnetic current is proposed as the electromagnetic source and is obtained by quasistatic calculation of the empty coil's vector potential or measurements therein. This technique circumvents the discretization of complicated gradient coil geometries into a mesh of Yee cells, and thereby enables any type of gradient coil modelling or other complex low frequency sources. The proposed method has been verified against an example with an analytical solution. Results are presented showing the spatial distribution of gradient-induced electric fields in a multi-layered spherical phantom model and a complete body model. PMID:15261629
NASA Astrophysics Data System (ADS)
Liu, Feng; Crozier, Stuart
2004-08-01
This paper evaluates a new, low-frequency finite-difference time-domain method applied to the problem of induced E-fields/eddy currents in the human body resulting from the pulsed magnetic field gradients in MRI. In this algorithm, a distributed equivalent magnetic current is proposed as the electromagnetic source and is obtained by quasistatic calculation of the empty coil's vector potential or measurements therein. This technique circumvents the discretization of complicated gradient coil geometries into a mesh of Yee cells, and thereby enables any type of gradient coil modelling or other complex low frequency sources. The proposed method has been verified against an example with an analytical solution. Results are presented showing the spatial distribution of gradient-induced electric fields in a multi-layered spherical phantom model and a complete body model.
Magnetic field line Hamiltonian
Boozer, A.H.
1984-03-01
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.
First-principles calculation of transport property in nano-devices under an external magnetic field
NASA Astrophysics Data System (ADS)
Chen, Jing-Zhe; Zhang, Jin; Han, Ru-Shan
2008-06-01
The mesoscopic quantum interference phenomenon (QIP) can be observed and behaves as the oscillation of conductance in nano-devices when the external magnetic field changes. Excluding the factor of impurities or defects, specific QIP is determined by the sample geometry. We have improved a first-principles method based on the matrix Green's function and the density functional theory to simulate the transport behaviour of such systems under a magnetic field. We have studied two kinds of QIP: universal conductance fluctuation (UCF) and Aharonov-Bohm effect (A-B effect). We find that the amplitude of UCF is much smaller than the previous theoretical prediction. We have discussed the origin of difference and concluded that due to the failure of ergodic hypothesis, the ensemble statistics is not applicable, and the conductance fluctuation is determined by the flux-dependent density of states (DOSs). We have also studied the relation between the UCF and the structure of sample. For a specific structure, an atomic circle, the A-B effect is observed and the origin of the oscillation is also discussed.
Zach Medin; Dong Lai
2007-01-05
We present new, ab initio calculations of the electronic structure of one-dimensional infinite chains and three-dimensional condensed matter in strong magnetic fields ranging from B=10^12 G to 2x10^15 G, appropriate for observed magnetic neutron stars. At these field strengths, the magnetic forces on the electrons dominate over the Coulomb forces, and to a good approximation the electrons are confined to the ground Landau level. Our calculations are based on the density functional theory, and use a local magnetic exchange-correlation function appropriate in the strong field regime. The band structures of electrons in different Landau orbitals are computed self-consistently. Numerical results of the ground-state energies and electron work functions are given for one-dimensional chains of H, He, C, and Fe. Fitting formulae for the B-dependence of the energies are also provided. For all the field strengths considered in this paper, hydrogen, helium, and carbon chains are found to be bound relative to individual atoms (although for B less than a few x 10^12 G, the relative binding between C and C_infinity is small). Iron chains are significantly bound for B>10^14 G and are weakly bound if at all at Bcondensed matter of H, He, C, and Fe at zero pressure, constructed from interacting chains in a body-centered tetragonal lattice. Such three-dimensional condensed matter is found to be bound relative to individual atoms, with the cohesive energy increasing rapidly with increasing B.
Dujko, S; White, R D; Petrovi?, Z Lj; Robson, R E
2010-04-01
A multiterm solution of the Boltzmann equation has been developed and used to calculate transport coefficients of charged-particle swarms in gases under the influence of electric and magnetic fields crossed at arbitrary angles when nonconservative collisions are present. The hierarchy resulting from a spherical-harmonic decomposition of the Boltzmann equation in the hydrodynamic regime is solved numerically by representing the speed dependence of the phase-space distribution function in terms of an expansion in Sonine polynomials about a Maxwellian velocity distribution at an internally determined temperature. Results are given for electron swarms in certain collisional models for ionization and attachment over a range of angles between the fields and field strengths. The implicit and explicit effects of ionization and attachment on the electron-transport coefficients are considered using physical arguments. It is found that the difference between the two sets of transport coefficients, bulk and flux, resulting from the explicit effects of nonconservative collisions, can be controlled either by the variation in the magnetic field strengths or by the angles between the fields. In addition, it is shown that the phenomena of ionization cooling and/or attachment cooling/heating previously reported for dc electric fields carry over directly to the crossed electric and magnetic fields. The results of the Boltzmann equation analysis are compared with those obtained by a Monte Carlo simulation technique. The comparison confirms the theoretical basis and numerical integrity of the moment method for solving the Boltzmann equation and gives a set of well-established data that can be used to test future codes and plasma models. PMID:20481843
NASA Astrophysics Data System (ADS)
de Souza, G. V. B.; Bruno-Alfonso, A.
2015-02-01
The ground and excited states of a donor impurity at the center of a spherical quantum dot subject to a magnetic field are calculated within the effective-mass approximation. The barriers are infinitely high and the differential equation is solved by combining the finite-difference method with the Richardson extrapolation. The binding and transition energies are more accurate than the available variational values, and excellent agreement is found with the hydrogen atom. The transition energies for a medium-size quantum dot are given.
3-D magnetic field calculations for wiggglers using MAGNUS-3D
Pissanetzky, S.; Tompkins, P.
1988-01-01
The recent but steady trend toward increased magnetic and geometric complexity in the design of wigglers and undulators, of which tapered wigglers, hybrid structures, laced electromagnetic wigglers, magnetic cladding, twisters and magic structures are examples, has caused a need for reliable 3-D computer models and a better understanding of the behavior of magnetic systems in three dimensions. The capabilities of the MAGNUS-3D Group of Programs are ideally suited to solve this class of problems and provide insight into 3-D effects. MAGNUS-3D can solve any problem of Magnetostatics involving permanent magnets, linear or nonlinear ferromagnetic materials and electric conductors of any shape in space. The magnetic properties of permanent magnets are described by the complete nonlinear demagnetization curve as provided by the manufacturer, or, at the user's choice, by a simpler approximation involving the coercive force, the residual induction and the direction of magnetization. The ferromagnetic materials are described by a magnetization table and an accurate interpolation relation. An internal library with properties of common industrial steels is available. The conductors are independent of the mesh and are described in terms of conductor elements from an internal library.
NASA Astrophysics Data System (ADS)
Barchanski, Andreas; Clemens, Markus; De Gersem, Herbert; Weiland, Thomas
2006-05-01
In this paper, we extend the scalar-potential finite-difference (SPFD) approach in order to consider arbitrarily shaped time-harmonic field sources. The SPFD approach is commonly used to compute the currents induced by an externally applied magnetic field in regions with weak, heterogeneous conductivities such as, e.g., the human body. We present the extended scalar-potential finite-difference (Ex-SPFD) approach as a two step algorithm. In the first step, the excitation is computed by solving the magnetoquasistatic curl-curl equation on a coarse grid that is well adapted for the field sources. In the second step, the magnetic vector potential is prolongated onto a finer grid and a divergence correction inside the conductor is applied. Using the Maxwell-grid-equations (MGEs) of the finite integration technique, a geometric discretization scheme for Maxwell's equations, this new approach has been implemented in a parallel environment in order to account for the memory-demanding high-resolution anatomy models used for the calculation of induced currents inside the human body. We demonstrate the validity and the improved numerical performance of the new approach for a test case. Finally, an application example of a human exposed to a realistic electromagnetic field source is presented.
Lee, Seong T; Burress, Timothy A; Hsu, John S
2009-01-01
This paper introduces a new method for calculating the power factor with consideration of the cross saturation between the direct-axis (d-axis) and the quadrature-axis (q-axis) of an interior permanent magnet synchronous motor (IPMSM). The conventional two-axis IPMSM model is modified to include the cross-saturation effect by adding the cross-coupled inductance terms. This paper also contains the new method of calculating the cross-coupled inductance values as well as self-inductance values in d- and q-axes. The analyzed motor is a high-speed brushless field excitation machine that offers high torque per ampere per core length at low speed and weakened flux at high speed, which was developed for the traction motor of a hybrid electric vehicle.
NASA Technical Reports Server (NTRS)
Ilin, Andrew V.
2006-01-01
The Magnetic Field Solver computer program calculates the magnetic field generated by a group of collinear, cylindrical axisymmetric electromagnet coils. Given the current flowing in, and the number of turns, axial position, and axial and radial dimensions of each coil, the program calculates matrix coefficients for a finite-difference system of equations that approximates a two-dimensional partial differential equation for the magnetic potential contributed by the coil. The program iteratively solves these finite-difference equations by use of the modified incomplete Cholesky preconditioned-conjugate-gradient method. The total magnetic potential as a function of axial (z) and radial (r) position is then calculated as a sum of the magnetic potentials of the individual coils, using a high-accuracy interpolation scheme. Then the r and z components of the magnetic field as functions of r and z are calculated from the total magnetic potential by use of a high-accuracy finite-difference scheme. Notably, for the finite-difference calculations, the program generates nonuniform two-dimensional computational meshes from nonuniform one-dimensional meshes. Each mesh is generated in such a way as to minimize the numerical error for a benchmark one-dimensional magnetostatic problem.
Effects of fibril magnetic fields on solar p-modes. II - Calculation of mode frequency shifts
NASA Technical Reports Server (NTRS)
Zweibel, E. G.; Bogdan, T. J.
1986-01-01
The effect of magnetic flux tubes in the solar convection zone on p-mode oscillations is investigated analytically using WKB ray theory, extending the results of Bogdan and Zweibel (1985) to the case of propagation not perpendicular to the tubes. Results for the frequency shift in polytropic slabs with vertical or horizontal flux tubes are presented in graphs and discussed.
George Davies; Lawrence M. Widrow
1999-12-14
We demonstrate that the Biermann battery mechanism for the creation of large scale magnetic fields can arise in a simple model protogalaxy. Analytic calculations and numerical simulations follow explicitly the generation of vorticity (and hence magnetic field) at the outward-moving shock that develops as the protogalactic perturbation collapses. Shear angular momentum then distorts this field into a dipole-like configuration. The magnitude of the field created in the fully formed disk galaxy is estimated to be 10^(-17) Gauss, approximately what is needed as a seed for the galactic dynamo.
Magnetic-field-dosimetry system
Lemon, D.K.; Skorpik, J.R.; Eick, J.L.
1981-01-21
A device is provided for measuring the magnetic field dose and peak field exposure. The device includes three Hall-effect sensors all perpendicular to each other, sensing the three dimensional magnetic field and associated electronics for data storage, calculating, retrieving and display.
Calculation of persistent currents in superconducting magnets
Christine Völlinger; Martin Aleksa; Stephan Russenschuck
2000-01-01
This paper describes a semianalytical hysteresis model for hard superconductors. The model is based on the critical state model considering the dependency of the critical current density on the varying local field in the superconducting filaments. By combining this hysteresis model with numerical field computation methods, it is possible to calculate the persistent current multipole errors in the magnet taking
Noh, Heung-Ryoul [Department of Physics, Chonnam National University, Gwangju 500-757 (Korea, Republic of); Moon, Han Seb [Department of Physics, Pusan National University, Busan 609-735 (Korea, Republic of)
2010-09-15
This paper reports a theoretical study on the transmission spectra of an arbitrarily polarized laser beam through a rubidium cell with or without a buffer gas in Hanle-type coherent population trapping (CPT). This study examined how laser polarization, transverse magnetic field, and collisions with buffer gas affects the spectrum. The transmission spectrum due to CPT and the absorption spectrum due to the level crossing absorption (LCA) were calculated according to the laser polarization. The results show that the LCA is strongly dependent on the transverse magnetic field and interaction time of the atoms with a laser light via collisions with the buffer gas. In addition, the spectral shape of the calculated Hanle spectrum is closely related to the direction between the (stray) transverse magnetic field and polarization of the laser.
NASA Astrophysics Data System (ADS)
Silva, Nicolas
2012-09-01
Earlier papers1-3 in this journal have described experiments on measuring the magnetic fields of current-carrying wires and permanent magnets using magnetic field probes of various kinds. This paper explains how to use an iPad and the free app MagnetMeter-3D Vector Magnetometer and Accelerometer4 (compass HD) to measure the magnetic fields.
NASA Astrophysics Data System (ADS)
Li, Qingxiang; Gandhi, Om P.
2005-01-01
Compliance testing of electronic article surveillance (EAS) devices requires that induced current densities in central nervous system (CNS) tissues, i.e. brain and the spinal cord, be less than the prescribed safety limits. Even though ferromagnetic cores are mostly used for activation/deactivation of embedded magnetic tags, assumed equivalent air-core coils with guessed increased number of ampere turns have always been used to calculate the magnetic fields for the proximal region to which a customer is exposed. We show that at low frequencies up to several kilohertz, duality of electric and magnetic circuits may be exploited such that the shaped high reluctance core is modelled as though it was a higher conductivity electric circuit of the corresponding shape. The proposed procedure is tested by examples of two magnetic cores typical of countertop activation/deactivation devices. The equivalent exposure magnetic fields obtained from the dual electric fields are shown to be in excellent agreement (within ±5%) with those measured for these ferromagnetic EAS devices. The previously proposed impedance method is then used to calculate the induced current densities for a 1.974 × 1.974 × 2.93 mm resolution anatomic model of a human. For the two considered EAS systems using excitation currents of 5000 A turns at 200 Hz, the maximum 1 cm2 area-averaged induced current densities in the CNS tissues are calculated and found to be less than the ICNIRP safety limits.
NSDL National Science Digital Library
VU Bioengineering RET Program, School of Engineering,
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.
Hendrickx, Marc F A; Clima, S; Chibotaru, L F; Ceulemans, A
2005-10-01
An ab initio multiconfigurational approach has been used to calculate the ligand-field spectrum and magnetic properties of the title cyano-bridged dinuclear molybdenum complex. The rather large magnetic coupling parameter J for a single cyano bridge, as derived experimentally for this complex by susceptibility measurements, is confirmed to a high degree of accuracy by our CASPT2 calculations. Its electronic structure is rationalized in terms of spin-spin coupling between the two constituent hexacyano-monomolybdate complexes. An in-depth analysis on the basis of Anderson's kinetic exchange theory provides a qualitative picture of the calculated CASSCF antiferromagnetic ground-state eigenvector in the Mo dimer. Dynamic electron correlations as incorporated into our first-principles calculations by means of the CASPT2 method are essential to obtain quantitative agreement between theory and experiment. PMID:16834289
Visualizing Magnetic Field Lines
NSDL National Science Digital Library
VU Bioengineering RET Program, School of Engineering,
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.
Magnetic field line Hamiltonian
Boozer, A.H.
1985-02-01
The basic properties of the Hamiltonian representation of magnetic fields in canonical form are reviewed. The theory of canonical magnetic perturbation theory is then developed and applied to the time evolution of a magnetic field embedded in a toroidal plasma. Finally, the extension of the energy principle to tearing modes, utilizing the magnetic field line Hamiltonian, is outlined.
Aleksandr A. Ruzmaikin; Dmitrii D. Sokolov; Anvar M. Shukurov
1988-01-01
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
S. Hainz; M. Jungwirth
2007-01-01
Speed and angle measurements of rotating shafts are very important in automotive applications. Typical sensing arrangements for angular measurements using the magnetic principle are analyzed in this paper. It is shown that such sensor arrangements are prone to phase errors. The phase error mainly depends on the distance between sensor element and rotating shaft. By employing finite element simulations, a
Methods for Calculating the Transmission Torque of Magnetic Transmission Mechanisms
Shunqi Mei; Zhiming Zhang; Renbin Xiao
2006-01-01
The methods of analyzing and calculating the magnetic field and the main problems of designing magnetic mechanisms are reviewed\\u000a and discussed. The comparatively precise engineering methods for calculating the transmission torque of the plane axial and\\u000a coaxial radial magnetic transmission mechanisms based on the magnetic theory are introduced, which can be used for optimization\\u000a of designing the magnetic transmission mechanism.
NASA Astrophysics Data System (ADS)
Schüssler, M.; Murdin, P.
2000-11-01
Electrical currents flowing in the solar plasma generate a magnetic field, which is detected in the SOLAR ATMOSPHERE by spectroscopic and polarization measurements (SOLAR MAGNETIC FIELD: INFERENCE BY POLARIMETRY). The SOLAR WIND carries the magnetic field into interplanetary space where it can be measured directly by instruments on space probes....
NASA Technical Reports Server (NTRS)
Flowers, E. G.; Ruderman, M. A.; Lee, J.-F.; Sutherland, P. G.; Hillebrandt, W.; Mueller, E.
1977-01-01
Variational calculations of the binding energies of iron atoms and condensed matter in strong magnetic fields (greater than 10 to the 12th gauss). These calculations include the electron exchange energy. The cohesive energy of the condensed matter, which is the difference between these two binding energies, is of interest in pulsar theories and in the description of the surfaces of neutron stars. It is found that the cohesive energy ranges from 2.6 keV to 8.0 keV.
Crozier, S; Liu, F; Wei, Q
2004-01-01
This paper evaluates a low-frequency FDTD method applied to the problem of induced E-fields/eddy currents in the human body resulting from the pulsed magnetic field gradients in MRI. In this algorithm, a distributed equivalent magnetic current (DEMC) is proposed as the electromagnetic source and is obtained by quasistatic calculation of the empty coil's vector potential or measurements therein. This technique circumvents the discretizing of complicated gradient coil geometries into a mesh of Yee cells, and thereby enables any type of gradient coil modeling or other complex low frequency sources. The proposed method has been verified against an example with an analytical solution. Results are presented showing the spatial distribution of gradient-induced electric fields in a multilayered spherical phantom model and a complete body model. PMID:17271881
Origin of cosmic magnetic fields.
Campanelli, Leonardo
2013-08-01
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
Magnetic Fields Analogous to electric field, a magnet
Bertulani, Carlos A. - Department of Physics and Astronomy, Texas A&M University
Magnetic Fields Analogous to electric field, a magnet produces a magnetic field, B Set up a B field two ways: Moving electrically charged particles Current in a wire Intrinsic magnetic field Basic characteristic of elementary particles such as an electron #12;Magnetic Fields Magnetic field lines Direction
Electricity and Magnetic Fields
NSDL National Science Digital Library
VU Bioengineering RET Program,
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.
NSDL National Science Digital Library
Jeffrey Barker
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.
NASA Technical Reports Server (NTRS)
Howard, R.
1972-01-01
Knowledge on the nature of magnetic fields on the solar surface is reviewed. At least a large part of the magnetic flux in the solar surface is confined to small bundles of lines of force within which the field strength is of the order of 500 gauss. Magnetic fields are closely associated with all types of solar activity. Magnetic flux appears at the surface at the clearly defined birth or regeneration of activity of an active region. As the region ages, the magnetic flux migrates to form large-scale patterns and the polar fields. Some manifestations of the large-scale distribution are discussed.
NSDL National Science Digital Library
Wolfgang Christian
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.
Schep, T.J. [Eindhoven University of Technology (Netherlands)
2004-03-15
Plasmas and magnetic fields are inseparably related in numerous physical circumstances. This is not only the case in natural occurring plasmas like the solar corona and the earth magnetic tail, but also in laboratory plasmas like tokamaks and stellarators.
NASA Astrophysics Data System (ADS)
Lu, Yun-Hao; Shi, Lei; Zhang, Chun; Feng, Yuan-Ping
2009-12-01
We report the first-principles studies aiming at controlling the electronic structure and patterning of adatoms on graphene using an external electric field. We demonstrate that the localized magnetic moment of an Au atom or a NO2 molecule on graphene can be continuously tuned by the electric field. We also show that the charge transfer between the Au atom and graphene sensitively depends on the direction and strength of the electric field applied. In addition, our calculations suggest that an electric field can be used to control the patterning of adatoms on graphene through the design of underlying electric gate. Our findings may be useful for the future design of graphene-based electronic devices.
NASA Astrophysics Data System (ADS)
Beck, Rainer; Wielebinski, Richard
Most of the visible matter in the Universe is ionized so that cosmic magnetic fields are quite easy to generate and, due to the lack of magnetic monopoles, hard to destroy. Magnetic fields have been measured in or around practically all celestial objects, either by in situ measurements of spacecrafts or by the electromagnetic radiation of embedded cosmic rays, gas, or dust. The Earth, the Sun, solar planets, stars, pulsars, the Milky Way, nearby galaxies, more distant (radio) galaxies, quasars, and even intergalactic space in clusters of galaxies have significant magnetic fields, and even larger volumes of the Universe may be permeated by "dark" magnetic fields. Information on cosmic magnetic fields has increased enormously as the result of the rapid development of observational methods, especially in radio astronomy. In the Milky Way, a wealth of magnetic phenomena was discovered, which are only partly related to objects visible in other spectral ranges. The large-scale structure of the Milky Way's magnetic field is still under debate. The available data for external galaxies can well be explained by field amplification and ordering via the dynamo mechanism. The measured field strengths and the similarity of field patterns and flow patterns of the diffuse ionized gas give strong indication that galactic magnetic fields are dynamically important. They may affect the formation of spiral arms, outflows, and the general evolution of galaxies. In spite of our increasing knowledge on magnetic fields, many important questions on the origin and evolution of magnetic fields, their first occurrence in young galaxies, or the existence of large-scale intergalactic fields remained unanswered. The present upgrades of existing instruments and several planned radio astronomy projects have defined cosmic magnetism as one of their key science projects.
NSDL National Science Digital Library
Wolfgang Christian
Clicking on the different links below will produce different magnetic fields in the box above. The wires (perpendicular to the screen) or coils (in and out of the screen) are not visible, but you can determine what they are from the field. You can also click on a point to read off the magnetic field at that place.
In situ magnetotail magnetic flux calculation
NASA Astrophysics Data System (ADS)
Shukhtina, M. A.; Gordeev, E.
2015-06-01
We explore two new modifications of the magnetotail magnetic flux (F) calculation algorithm based on the Petrinec and Russell (1996) (PR96) approach of the tail radius determination. Unlike in the PR96 model, the tail radius value is calculated at each time step based on simultaneous magnetotail and solar wind observations. Our former algorithm, described in Shukhtina et al. (2009), required that the "tail approximation" requirement were fulfilled, i.e., it could be applied only tailward x ∼ -15 RE. The new modifications take into account the approximate uniformity of the magnetic field of external sources in the near and middle tail. Tests, based on magnetohydrodynamics (MHD) simulations, show that this approach may be applied at smaller distances, up to x ∼ -3 RE. The tests also show that the algorithm fails during long periods of strong positive interplanetary magnetic field (IMF) Bz. A new empirical formula has also been obtained for the tail radius at the terminator (at x = 0) which improves the calculations.
Krienin, Frank (Shoreham, NY)
1990-01-01
A magnetic field generating device provides a useful magnetic field within a specific retgion, while keeping nearby surrounding regions virtually field free. By placing an appropriate current density along a flux line of the source, the stray field effects of the generator may be contained. One current carrying structure may support a truncated cosine distribution, and it may be surrounded by a current structure which follows a flux line that would occur in a full coaxial double cosine distribution. Strong magnetic fields may be generated and contained using superconducting cables to approximate required current surfaces.
Magnetic Field & Right Hand Rule
Heller, Barbara
Magnetic Field & Right Hand Rule Academic Resource Center #12;Magnetic Fields And Right Hand Rules By: Anthony Ruth #12;Magnetic Fields vs Electric Fields Â· Magnetic fields are similar to electric charges and stationary charges. Â· In addition, magnetic fields create a force only on moving charges
Magnetic Fields MAXWELL'S EQUATIONS
Lü, James Jian-Qiang
Magnetic Fields MAXWELL'S EQUATIONS Differential Form 0=· B r JH rr =× t B E -=× r r VECTOR CONDITIONS General Magnetic-Magnetic 0)(n^ 21 =-· BB rr B1n = B2n sJHH rrr =-× )(n^ 21 H1t = H2t FORCEE rrrr r rr )( MATERIALS )1(, )( mom oor HM MHHHB +== +=== rr rrrrr o = 4×10-7 H/m MAGNETIC CIRCUITS
H. Yoshiguchi; S. Nagataki; K. Sato
2003-07-02
We present a new method for calculating arrival distribution of UHECRs including modifications by the galactic magnetic field. We perform numerical simulations of UHE anti-protons, which are injected isotropically at the earth, in the Galaxy and record the directions of velocities at the earth and outside the Galaxy for all of the trajectories. We then select some of them so that the resultant mapping of the velocity directions outside the Galaxy of the selected trajectories corresponds to a given source location scenario, applying Liouville's theorem. We also consider energy loss processes of UHE protons in the intergalactic space. Applying this method to our source location scenario which is adopted in our recent study and can explain the AGASA observation above 4 \\times 10^{19} eV, we calculate the arrival distribution of UHECRs including lower energy (E>10^19 eV) ones. We find that our source model can reproduce the large-scale isotropy and the small-scale anisotropy on UHECR arrival distribution above 10^19 eV observed by the AGASA. We also demonstrate the UHECR arrival distribution above 10^19 eV with the event number expected by future experiments in the next few years. The interesting feature of the resultant arrival distribution is the arrangement of the clustered events in the order of their energies, reflecting the directions of the galactic magnetic field. This is also pointed out by Alvarez-Muniz et al.(2002). This feature will allow us to obtain some kind of information about the composition of UHECRs and the magnetic field with increasing amount of data.
G. B. Deineka
1999-09-14
A two-dimensional, fully numerical approach to the solution of four-component Dirac-Fock equation using the moderately long Hermitian basis of B-splines is applied to H, H2+ and H2 in a strong magnetic field. The geometric parameters, including different behavior of wave-functions relativistic components are analyzed. The accuracy of the solutions as a function of the basis lenght is estimated. The relativistic corrections are calculated by transformation of the matrix equations to the equations for large relativistic components. Application of the finite-element method to solution of the Dirac-Fock equation without supplementary assumption about exchange in case of the H2 excited states is discussed. The maximum localization of the basis functions provides applicability of the quadrature formulae for five-dimensional two-electron integral calculations within reasonable period.
Optical sensor of magnetic fields
Butler, M.A.; Martin, S.J.
1986-03-25
An optical magnetic field strength sensor for measuring the field strength of a magnetic field comprising a dilute magnetic semi-conductor probe having first and second ends, longitudinally positioned in the magnetic field for providing Faraday polarization rotation of light passing therethrough relative to the strength of the magnetic field. Light provided by a remote light source is propagated through an optical fiber coupler and a single optical fiber strand between the probe and the light source for providing a light path therebetween. A polarizer and an apparatus for rotating the polarization of the light is provided in the light path and a reflector is carried by the second end of the probe for reflecting the light back through the probe and thence through the polarizer to the optical coupler. A photo detector apparatus is operably connected to the optical coupler for detecting and measuring the intensity of the reflected light and comparing same to the light source intensity whereby the magnetic field strength may be calculated.
E. M. de Gouveia Dal Pino
2006-03-02
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 and the structuring of the Universe. In this lecture, I will briefly review the importance of the cosmic magnetic fields both from a theoretical and from an observational perspective, particularly focusing on stellar and compact objects, the interstellar medium and star formation regions, and on galaxies, clusters of galaxies, and the primordial Universe.
Detecting Exoplanetary Magnetic Fields
NASA Astrophysics Data System (ADS)
Llama, Joe
2015-01-01
Asymmetries in exoplanet transits are proving to be a useful tool for furthering our understanding of magnetic activity on both stars and planets outside our Solar System.Near-UV observations of the WASP-12 system have revealed asymmetries in the timing of the transit when compared with the optical light curve. A number of possible explanations have been suggested for this variation, including the presence of a magnetospheric bow shock arising from the interaction of the planet's magnetic field with the stellar wind from it's host star. Such observations provide the first method for directly detecting the presence of a magnetic field on exoplanets.The shape and size of such asymmetries is highly dependent on the structure of the host stars magnetic field at the time of observation. This implies we may observe highly varying near-UV transit light curves for the same system. These variations can then be used to learn about the geometry of the host star's magnetic field.In this presentation I will show modelling a bow shock around an exoplanet can help us to not only detect, but also also place constraints on the magnetic field strength of hot Jupiters. For some systems, such as HD 189733, we have maps of the surface magnetic field of the star at various epochs. I will also show how incorporating these maps into a stellar wind model, I can model the formation of a bow shock around the planet and hence demonstrate the variability of the near-UV transits.
Magnetic fields in spiral galaxies
NASA Astrophysics Data System (ADS)
Chiba, Masashi
The magnetic-field characteristics in spiral galaxies are investigated, with emphasis on the Milky Way. The dynamo theory is considered, and axisymmetric spiral (ASS) and bisymmetric spiral (BSS) magnetic fields are analyzed. Toroidal and poloidal magnetic fields are discussed.
NSDL National Science Digital Library
2012-08-03
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.
Magnetosheath magnetic field variability
NASA Technical Reports Server (NTRS)
Sibeck, D. G.
1994-01-01
A case study using simulations IRM and CCE observations demonstrates that transient magnetospheric events correspond to pressure pulses in the magnetosheath, inward bow shock motion, and magnetopause compression. Statistical surveys indicate that the magnetosheath magnetic field orientation rarely remains constant during periods of magnetopause and bow shock motion (both characterized by periods of 1 to 10 min). There is no tendency for bow shock motion to occur for southward interplanetary magnetic field (IMF) orientations.
Magnetic fields in protoplanetary disks
Mark Wardle
2007-08-15
Magnetic fields likely play a key role in the dynamics and evolution of protoplanetary discs. They have the potential to efficiently transport angular momentum by MHD turbulence or via the magnetocentrifugal acceleration of outflows from the disk surface, and magnetically-driven mixing has implications for disk chemistry and evolution of the grain population. However, the weak ionisation of protoplanetary discs means that magnetic fields may not be able to effectively couple to the matter. I present calculations of the ionisation equilibrium and magnetic diffusivity as a function of height from the disk midplane at radii of 1 and 5 AU. Dust grains tend to suppress magnetic coupling by soaking up electrons and ions from the gas phase and reducing the conductivity of the gas by many orders of magnitude. However, once grains have grown to a few microns in size their effect starts to wane and magnetic fields can begin to couple to the gas even at the disk midplane. Because ions are generally decoupled from the magnetic field by neutral collisions while electrons are not, the Hall effect tends to dominate the diffusion of the magnetic field when it is able to partially couple to the gas. For a standard population of 0.1 micron grains the active surface layers have a combined column of about 2 g/cm^2 at 1 AU; by the time grains have aggregated to 3 microns the active surface density is 80 g/cm^2. In the absence of grains, x-rays maintain magnetic coupling to 10% of the disk material at 1 AU (150 g/cm^2). At 5 AU the entire disk thickness becomes active once grains have aggregated to 1 micron in size.
NASA Technical Reports Server (NTRS)
Smith, E. J.
1995-01-01
The magnetic fields originate as coronal fields that are converted into space by the supersonic, infinitely conducting, solar wind. On average, the sun's rotation causes the field to wind up and form an Archimedes Spiral. However, the field direction changes almost continuously on a variety of scales and the irregular nature of these changes is often interpreted as evidence that the solar wind flow is turbulent.
Lee, Seong T; Burress, Timothy A; Tolbert, Leon M
2009-01-01
This paper introduces a new method for calculating the power factor and output torque by considering the cross saturation between direct-axis (d-axis) and quadrature-axis (q-axis) of an interior permanent magnet synchronous motor (IPMSM). The conventional two-axis IPMSM model is modified to include the cross saturation effect by adding the cross-coupled inductance terms. This paper also contains the new method of calculating the cross-coupled inductance values as well as self-inductance values in d- and q-axes. The analyzed motor is a high-speed brushless field excitation machine that offers high torque per ampere per core length at low speed and weakened flux at high speed, which was developed for the traction motor of a hybrid electric vehicle. The conventional two-axis IPMSM model was modified to include the cross-saturation effect by adding the cross-coupled inductance terms Ldq and Lqd. By the advantage of the excited structure of the experimental IPMSM, the analyzing works were performed under two conditions, the highest and lowest excited conditions. Therefore, it is possible to investigate the cross-saturation effect when a machine has higher magnetic flux from its rotor. The following is a summary of conclusions that may be drawn from this work: (1) Considering cross saturation of an IPMSM offers more accurate expected values of motor parameters in output torque calculation, especially when negative d-axis current is high; (2) A less saturated synchronous machine could be more affected by the cross-coupled saturation effect; (3) Both cross-coupled inductances, L{sub qd} and L{sub dq}, are mainly governed by d-axis current rather than q-axis current; (4) The modified torque equation, can be used for the dynamic model of an IPMSM for developing a better control model or control strategy; and (5) It is possible that the brushless field excitation structure has a common magnetic flux path on both d- and q-axis, and as a result, the reluctance torque of the machine could be reduced.
Cosmological magnetic field survival
John D. Barrow; Christos G. Tsagas
2011-04-07
It is widely believed that primordial magnetic fields are dramatically diluted by the expansion of the universe. As a result, cosmological magnetic fields with residual strengths of astrophysical relevance are generally sought by going outside standard cosmology, or by extending conventional electromagnetic theory. Nevertheless, the survival of strong B-fields of primordial origin is possible in spatially open Friedmann universes without changing conventional electromagnetism. The reason is the hyperbolic geometry of these spacetimes, which slows down the adiabatic magnetic decay-rate and leads to their superadiabatic amplification on large scales. So far, the effect has been found to operate on Friedmannian backgrounds containing either radiation or a slow-rolling scalar field. We show here that the superadiabatic amplification of large-scale magnetic fields, generated by quantum fluctuations during inflation, is essentially independent of the type of matter that fills the universe and appears to be a generic feature of open Friedmann spacetimes. We estimate the late-time strength of any residual field in a marginally open universe and show that it can easily meet the requirements for the dynamo generation of the magnetic fields observed in galaxies today.
NASA Astrophysics Data System (ADS)
Berdyugina, Svetlana
2015-08-01
Molecules probe cool matter in the Universe and various astrophysical objects. Their ability to sense magnetic fields provides new insights into magnetic properties of these objects. During the past fifteen years we have carried out a theoretical study of molecular magnetic effects such as the Zeeman, Paschen-Back and Hanle effects and their applications for inferring magnetic structures and spatial inhomogeneities on the Sun, cool stars, brown dwarfs, and exoplanets from molecular spectro-polarimetry (e.g., Berdyugina 2011). Here, we present an overview of this study and compare our theoretical predictions with recent laboratory measurements of magnetic properties of some molecules. We present also a new web-based tool to compute molecular magnetic effects and polarized spectra which is supported by the ERC Advanced Grant HotMol.
Magnetic Field Measurement System
Kulesza, Joe; Johnson, Eric; Lyndaker, Aaron; Deyhim, Alex; Waterman, Dave; Blomqvist, K. Ingvar; Dunn, Jonathan Hunter
2007-01-19
A magnetic field measurement system was designed, built and installed at MAX Lab, Sweden for the purpose of characterizing the magnetic field produced by Insertion Devices (see Figure 1). The measurement system consists of a large granite beam roughly 2 feet square and 14 feet long that has been polished beyond laboratory grade for flatness and straightness. The granite precision coupled with the design of the carriage yielded minimum position deviations as measured at the probe tip. The Hall probe data collection and compensation technique allows exceptional resolution and range while taking data on the fly to programmable sample spacing. Additional flip coil provides field integral data.
Magnetic Field Problem: Current
NSDL National Science Digital Library
Wolfgang Christian
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.
NASA Astrophysics Data System (ADS)
Zheng, Yangdong; Yoshimura, Satoru; Egawa, Genta; Zheng, Fu; Kinoshita, Yukinori; Saito, Hitoshi
2015-08-01
A pulsed magnetic field magnetic force microscope (PMF-MFM) is developed for evaluation of the magnetic properties of nano-scale materials and devices, as well as the characteristics of MFM tips. We present the setup of the PMF-MFM system, and focus on the evaluation of a FeCo soft magnetic tip by PMF-MFM. We find a new theoretical method to calculate tip magnetization curves (M-H curves) using MFM phase signals. We measure the MFM phase and amplitude signals for the FeCo tip during the presence of the pulsed magnetic fields oriented parallel and antiparallel to the initial tip magnetization direction, and acquire the tip coercivity H c ~ 1.1?kOe. The tip M-H curves are also calculated using the MFM phase signals data. We obtain the basic features of the tip magnetic properties from the tip M-H curves.
Calculation of rf fields in axisymmetric cavities
Iwashita, Y.
1985-01-01
A new code, PISCES, has been developed for calculating a complete set of rf electromagnetic modes in an axisymmetric cavity. The finite-element method is used with up to third-order shape functions. Although two components are enough to express these modes, three components are used as unknown variables to take advantage of the symmetry of the element matrix. The unknowns are taken to be either the electric field components or the magnetic field components. The zero-divergence condition will be satisfied by the shape function within each element.
NSDL National Science Digital Library
2012-08-03
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.
NASA Astrophysics Data System (ADS)
Johnson, C. L.
2014-12-01
Mercury is the only inner solar system body other than Earth to possess an active core dynamo-driven magnetic field and the only planet with a small, highly dynamic magnetosphere. Measurements made by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft have provided a wealth of data on Mercury's magnetic field environment. Mercury's weak magnetic field was discovered 40 years ago by the Mariner 10 spacecraft, but its large-scale geometry, strength and origin could not be definitively established. MESSENGER data have shown that the field is dynamo-generated and can be described as an offset axisymmetric dipole field (hereafter OAD): the magnetic equator lies ~0.2 RM (RM = 2440 km) north of the geographic equator and the dipole moment is 2.8 x1019 Am2 (~0.03% that of Earth's). The weak internal field and the high, but variable, solar wind ram pressure drive vigorous magnetospheric dynamics and result in an average distance from the planet center to the sub-solar magnetopause of only 1.42 RM. Magnetospheric models developed with MESSENGER data have allowed re-analysis of the Mariner 10 observations, establishing that there has been no measureable secular variation in the internal field over 40 years. Together with spatial power spectra for the OAD, this provides critical constraints for viable dynamo models. Time-varying magnetopause fields induce secondary core fields, the magnitudes of which confirm the core radius estimated from MESSENGER gravity and Earth-based radar data. After accounting for large-scale magnetospheric fields, residual signatures are dominated by additional external fields that are organized in the local time frame and that vary with magnetospheric activity. Birkeland currents have been identified, which likely close in the planetary interior at depths below the base of the crust. Near-periapsis magnetic field measurements at altitudes greater than 200 km have tantalizing hints of crustal fields, but crustal sources cannot be distinguished from core fields, nor cleanly separated from external fields. I will report on recent data acquired at altitudes as low as 25 km that have the potential to resolve these issues. The presence of remanent crustal fields would have profound implications for Mercury's thermal and dynamical histories.
ORIGIN OF EFFECTIVE FIELDS IN MAGNETIC MATERIALS
R. E. Watson; A. J. Freeman
1961-01-01
The origin of the effective magnetic fields at the nuclei ar magnetic ; resonance, electron paramagnetic resonance, specific heat, and nuclear ; polarization methods is investigated theoretically by means of the exchange ; polarization mechanism. Exchange-polarized iron series Hartree-Fock calculations ; were carried out for free ions and neutral atoms, ions in a (crude) crystalline ; field (as in a
Hu, Ting; Dong, Jinming, E-mail: jdong@nju.edu.cn [Group of Computational Condensed Matter Physics, National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China); Zhou, Jian [Department of Materials Science and Engineering, Nanjing University, Nanjing 210093 (China); Kawazoe, Yoshiyuki [Institute for Materials Research, Tohoku University, 2-1-1 Katahira Aoba-ku, Sendai 980-8577 (Japan)
2014-08-14
The electronic and magnetic properties of armchair edge MoS{sub 2} nanoribbons (MoS{sub 2}-ANRs) underboth the external strain and transverse electric field (E{sub t}) have been systematically investigated by using the first-principles calculations. It is found that: (1) If no electric field is applied, an interesting structural phase transition would appear under a large tensile strain, leading to a new phase MoS{sub 2}-A'NR, and inducing a big jump peak of the band gap in the transition region. But, the band gap response to compressive strains is much different from that to tensile strain, showing no the structural phase transition. (2) Under the small tensile strains (<10%), the combined E{sub t} and tensile strain give rise to a positive superposition (resonant) effect on the band gap reduction at low E{sub t} (<3?V/nm), and oppositely a negative superposition (antiresonant) one at high E{sub t} (>4?V/nm). On the other hand, the external compressive strains have always presented the resonant effect on the band gap reduction, induced by the electric field. (3) After the structural phase transition, an external large tensile strain could greatly reduce the critical field E{sub tc} causing the band gap closure, and make the system become a ferromagnetic (FM) metal at a relative low E{sub t} (e.g., <4?V/nm), which is very helpful for its promising applications in nano-mechanical spintronics devices. (4) At high E{sub t} (>10?V/nm), the magnetic moments of both the MoS{sub 2}-ANR and MoS{sub 2}-A'NR in their FM states could be enhanced greatly by a tensile strain. Our numerical results of effectively tuning physical properties of MoS{sub 2}-ANRs by combined external strain and electric field may open their new potential applications in nanoelectronics and spintronics.
NASA Astrophysics Data System (ADS)
Schimeczek, C.; Engel, D.; Wunner, G.
2012-07-01
Our previously published code for calculating energies and bound-bound transitions of medium-Z elements at neutron star magnetic field strengths [D. Engel, M. Klews, G. Wunner, Comput. Phys. Comm. 180 (2009) 302-311] was based on the adiabatic approximation. It assumes a complete decoupling of the (fast) gyration of the electrons under the action of the magnetic field and the (slow) bound motion along the field under the action of the Coulomb forces. For the single-particle orbitals this implied that each is a product of a Landau state and an (unknown) longitudinal wave function whose B-spline coefficients were determined self-consistently by solving the Hartree-Fock equations for the many-electron problem on a finite-element grid. In the present code we go beyond the adiabatic approximation, by allowing the transverse part of each orbital to be a superposition of Landau states, while assuming that the longitudinal part can be approximated by the same wave function in each Landau level. Inserting this ansatz into the energy variational principle leads to a system of coupled equations in which the B-spline coefficients depend on the weights of the individual Landau states, and vice versa, and which therefore has to be solved in a doubly self-consistent manner. The extended ansatz takes into account the back-reaction of the Coulomb motion of the electrons along the field direction on their motion in the plane perpendicular to the field, an effect which cannot be captured by the adiabatic approximation. The new code allows for the inclusion of up to 8 Landau levels. This reduces the relative error of energy values as compared to the adiabatic approximation results by typically a factor of three (1/3 of the original error), and yields accurate results also in regions of lower neutron star magnetic field strengths where the adiabatic approximation fails. Further improvements in the code are a more sophisticated choice of the initial wave functions, which takes into account the shielding of the core potential for outer electrons by inner electrons, and an optimal finite-element decomposition of each individual longitudinal wave function. These measures largely enhance the convergence properties compared to the previous code, and lead to speed-ups by factors up to two orders of magnitude compared with the implementation of the Hartree-Fock-Roothaan method used by Engel and Wunner in [D. Engel, G. Wunner, Phys. Rev. A 78 (2008) 032515]. New version program summaryProgram title: HFFER II Catalogue identifier: AECC_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECC_v2_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: v 55 130 No. of bytes in distributed program, including test data, etc.: 293 700 Distribution format: tar.gz Programming language: Fortran 95 Computer: Cluster of 1-13 HP Compaq dc5750 Operating system: Linux Has the code been vectorized or parallelized?: Yes, parallelized using MPI directives. RAM: 1 GByte per node Classification: 2.1 External routines: MPI/GFortran, LAPACK, BLAS, FMlib (included in the package) Catalogue identifier of previous version: AECC_v1_0 Journal reference of previous version: Comput. Phys. Comm. 180 (2009) 302 Does the new version supersede the previous version?: Yes Nature of problem: Quantitative modellings of features observed in the X-ray spectra of isolated magnetic neutron stars are hampered by the lack of sufficiently large and accurate databases for atoms and ions up to the last fusion product, iron, at strong magnetic field strengths. Our code is intended to provide a powerful tool for calculating energies and oscillator strengths of medium-Z atoms and ions at neutron star magnetic field strengths with sufficient accuracy in a routine way to create such databases. Solution method: The Slater determinants of the atomic wave functions are constructed from single-particle orbitals
Analytical Method of Torque Calculation for Interior Permanent Magnet Synchronous Machines
Tolbert, Leon M.
method for performing the output torque calculations of an interior permanent magnet synchronous motor circuit, inductance, permanent magnet machine, synchronous motors, torque. I. NOMENCLATURE BFE brushless field excitation IPMSM interior permanent magnet synchronous motor FEA finite element analysis mmf
The effects of filament magnetization in superconducting magnets as calculated by POISSON
Caspi, S.; Gilbert, W.S.; Helm, M.; Laslett, L.J.
1986-09-01
Magnetization of superconducting material can be introduced into POISSON through a field dependent permeability table (in the same way that iron characteristics are introduced). This can be done by representing measured magnetization data of the increasing and decreasing field by two independent B-..gamma.. curves (..gamma.. = 1/..mu..). Magnetization curves of this type were incorporated into the current regions of the program POISSON and their effect on the field coefficients observed. We have used this technique to calculate the effect of magnetization on the multipole coefficients of a SSC superconducting dipole magnet and to compare these coefficients with measured values.
Hadron Masses in Strong Magnetic Fields
Hidetoshi Taya
2015-07-23
Hadron masses under strong magnetic fields are studied. In the presence of strong magnetic fields exceeding the QCD energy scale $ eB \\gg \\Lambda^2_{\\rm QCD} $, ${\\rm SU(3)}_{\\rm flavor} \\otimes {\\rm SU(2)}_{\\rm spin}$ symmetry of hadrons is explicitly broken so that the quark components of hadrons differ from those with zero or weak magnetic fields $ eB \\lesssim \\Lambda^2_{\\rm QCD} $. Also, squeezing of hadrons by strong magnetic fields affects the hadron mass spectrum. We develop a quark model which appropriately incorporates these features and analytically calculate various hadron masses including mesons, baryons and those with strangeness.
Hadron masses in strong magnetic fields
NASA Astrophysics Data System (ADS)
Taya, Hidetoshi
2015-07-01
Hadron masses under strong magnetic fields are studied. In the presence of strong magnetic fields exceeding the QCD energy scale e B ??QCD2 , SU (3 )flavor?SU (2 )spin symmetry of hadrons is explicitly broken so that the quark components of hadrons differ from those with zero or weak magnetic fields e B ??QCD2. Also, squeezing of hadrons by strong magnetic fields affects the hadron mass spectrum. We develop a quark model which appropriately incorporates these features and analytically calculate various hadron masses including mesons, baryons, and those with strangeness.
Flares above sunspots and magnetic fields.
NASA Astrophysics Data System (ADS)
Babin, A. N.; Koval', A. N.
The magnetic fields in two importance 2B flares located in the penumbra of sunspots with a delta configuration are determined from Zeeman splitting of the Fe I, D1 and D2 NA I, and D3 He I emission lines. The sunspots' magnetic fields are also estimated. The metal and helium emissions are located not farther than 3 arcsec from the place of the sign change of the sunspots' magnetic field. The strength of the magnetic field calculated on the basis of metal emission lines exceeds 2000 Gs; on the basis of the helium line, it is about 1000 Gs. Polarity reversal is not observed.
CMB Signatures of a Primordial Magnetic Field
Tina Kahniashvili; Arthur Kosowsky; Andrew Mack; Ruth Durrer
2000-11-03
A primordial stochastic magnetic field will induce temperature and polarization fluctuations in the cosmic microwave background. We outline a calculation of the resulting fluctuation power spectra and present numerical results.
The Magnetic Field of Helmholtz Coils
ERIC Educational Resources Information Center
Berridge, H. J. J.
1975-01-01
Describes the magnetic field of Helmholtz coils qualitatively and then provides the basis for a quantitative expression. Since the mathematical calculations are very involved, a computer program for solving the mathematical expression is presented and explained. (GS)
Heating magnetic fluid with alternating magnetic field
R. E. Rosensweig
2002-01-01
This study develops analytical relationships and computations of power dissipation in magnetic fluid (ferrofluid) subjected to alternating magnetic field. The dissipation results from the orientational relaxation of particles having thermal fluctuations in a viscous medium.
Interplanetary stream magnetism: Kinematic effects. [solar magnetic fields and wind
NASA Technical Reports Server (NTRS)
Burlaga, L. F.; Barouch, E.
1974-01-01
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.
Magnetic helicity and cosmological magnetic field
V. B. Semikoz; D. D. Sokoloff
2005-04-07
The magnetic helicity has paramount significance in nonlinear saturation of galactic dynamo. We argue that the magnetic helicity conservation is violated at the lepton stage in the evolution of early Universe. As a result, a cosmological magnetic field which can be a seed for the galactic dynamo obtains from the beginning a substantial magnetic helicity which has to be taken into account in the magnetic helicity balance at the later stage of galactic dynamo.
Ekström, Ulf; Norman, Patrick; Rizzo, Antonio
2005-02-15
The effects of relativity on the magnetic-field induced circular birefringence, or Faraday effect, in He, Ne, Ar, Xe, Rn, F2, Cl2, Br2, and I2 have been determined at the four-component Hartree-Fock level of theory. A measure of the birefringence is given by the Verdet constant, which is a third-order molecular property and thus relates to quadratic response functions. A fully analytical nonlinear polarization propagator approach is employed. The results are gauge invariant as a consequence of the spatial symmetries in the molecular systems. The calculations include electronic as well as vibrational contributions to the property. Comparison with experiment is made for He, Ne, Ar, Xe, and Cl2, and, apart from neon, the theoretical values of the Verdet constant are within 10% of the experimental ones. The inclusion of nonrelativistically spin-forbidden excitations in the propagator parametrization has significant effects on the dispersion in general, but such effects are in the general case largely explained by the use of a resonant-divergent propagator theory. In the present work we do, however, observe noticeable relativistic corrections to the Verdet constant in the off-resonant regions for systems with light elements (F2 and Cl2), and nonrelativistic results for the Verdet constant of Br2 are in error by 25% in the low-frequency region. PMID:15743246
Numerical analysis of magnetic field in superconducting magnetic energy storage
Kanamaru, Y. ); Amemiya, Y. )
1991-09-01
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.
Primordial magnetic fields at preheating
A. Diaz-Gil; J. Garcia-Bellido; M. Garcia Perez; A. Gonzalez-Arroyo
2007-10-02
Using lattice techniques we investigate the generation of long range cosmological magnetic fields during a cold electroweak transition. We will show how magnetic fields arise, during bubble collisions, in the form of magnetic strings. We conjecture that these magnetic strings originate from the alignment of magnetic dipoles associated with EW sphaleron-like configurations. We also discuss the early thermalisation of photons and the turbulent behaviour of the scalar fields after tachyonic preheating.
Flow field calculations for afterburner
NASA Astrophysics Data System (ADS)
Zhao, Jianxing; Liu, Quanzhong; Liu, Hong
1995-04-01
In this paper a calculation procedure for simulating the combustion flow in the afterburner with the heat shield, flame stabilizer and the contracting nozzle is described and evaluated by comparison with experimental data. The modified two-equation k ? model is employed to consider the turbulence effects, and the k ? g turbulent combustion model is used to determine the reaction rate. To take into account the influence of heat radiation on gas temperature distribution, heat flux model is applied to predictions of heat flux distributions. The solution domain spanned the entire region between centerline and afterburner wall, with the heat shield represented as a blockage to the mesh. The enthalpy equation and wall boundary of the heat shield require special handling for two passages in the afterburner. In order to make the computer program suitable to engineering applications, a subregional scheme is developed for calculating flow fields of complex geometries. The computational grids employed are 100×100 and 333×100 (non-uniformly distributed). The numerical results are compared with experimental data. Agreement between predictions and measurements shows that the numerical method and the computational program used in the study are fairly reasonable and appropriate for primary design of the afterburner.
Radial magnetic field in magnetic confinement device
NASA Astrophysics Data System (ADS)
Xiong, Hao; Liu, Ming-Hai; Chen, Ming; Rao, Bo; Chen, Jie; Chen, Zhao-Quan; Xiao, Jin-Shui; Hu, Xi-Wei
2015-09-01
The intrinsic radial magnetic field (Br) in a tokamak is explored by the solution of the Grad–Shafranov equation in axisymmetric configurations through an expansion of the four terms of the magnetic surfaces. It can be inferred from the simulation results that at the core of the device, the tokamak should possess a three-dimensional magnetic field configuration, which could be reduced to a two-dimensional one when the radial position is greater than 0.6a. The radial magnetic field and the amzimuthal magnetic field have the same order of magnitude at the core of the device. These results can offer a reference for the analysis of the plasma instability, the property of the core plasma, and the magnetic field measurement. Project supported by the Special Domestic Program of ITER, China (Grant No. 2009GB105003).
Magnetic fields, strings and cosmology
Massimo Giovannini
2006-12-14
The main motivations and challenges related with the physics of large-scale magnetic fields are briefly analyzed. The interplay between large-scale magnetic fields and scalar CMB anisotropies is addressed with specific attention on recent progresses.
Coulomb crystals in the magnetic field
Baiko, D. A. [A.F. Ioffe Physical-Technical Institute, Politekhnicheskaya 26, 194021 St. Petersburg (Russian Federation)
2009-10-15
The body-centered-cubic Coulomb crystal of ions in the presence of a uniform magnetic field is studied using the rigid electron background approximation. The phonon mode spectra are calculated for a wide range of magnetic-field strengths and for several orientations of the field in the crystal. The phonon spectra are used to calculate the phonon contribution to the crystal energy, entropy, specific heat, Debye-Waller factor of ions, and the rms ion displacements from the lattice nodes for a broad range of densities, temperatures, chemical compositions, and magnetic fields. Strong magnetic field dramatically alters the properties of quantum crystals. The phonon specific heat increases by many orders of magnitude. The ion displacements from their equilibrium positions become strongly anisotropic. The results can be relevant for dusty plasmas, ion plasmas in Penning traps, and especially for the crust of magnetars (neutron stars with superstrong magnetic fields B > or approx. 10{sup 14} G). The effect of the magnetic field on ion displacements in a strongly magnetized neutron star crust can suppress the nuclear reaction rates and make them extremely sensitive to the magnetic-field direction.
NASA Astrophysics Data System (ADS)
Wiegelmann, Thomas; Petrie, Gordon J. D.; Riley, Pete
2015-07-01
Coronal magnetic field models use photospheric field measurements as boundary condition to model the solar corona. We review in this paper the most common model assumptions, starting from MHD-models, magnetohydrostatics, force-free and finally potential field models. Each model in this list is somewhat less complex than the previous one and makes more restrictive assumptions by neglecting physical effects. The magnetohydrostatic approach neglects time-dependent phenomena and plasma flows, the force-free approach neglects additionally the gradient of the plasma pressure and the gravity force. This leads to the assumption of a vanishing Lorentz force and electric currents are parallel (or anti-parallel) to the magnetic field lines. Finally, the potential field approach neglects also these currents. We outline the main assumptions, benefits and limitations of these models both from a theoretical (how realistic are the models?) and a practical viewpoint (which computer resources to we need?). Finally we address the important problem of noisy and inconsistent photospheric boundary conditions and the possibility of using chromospheric and coronal observations to improve the models.
Magnetic Field Problem: Current and Magnets
NSDL National Science Digital Library
Wolfgang Christian
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.
NASA Astrophysics Data System (ADS)
Guillon, G.; Stoecklin, T.
2009-04-01
We take advantage of the simple expression of the sector adiabatic wave functions of the Magnus propagator to obtain accurate values of the energy derivative of the S matrix which, in turn, is used to get the Smith lifetime Q matrix. The procedure involves the simultaneous generation of both the R matrix and its energy derivative dR /dE which are propagated along the scattering coordinate. We present a few examples of application to the field free He-N2+ inelastic collisions which we previously studied. This method is then applied to the calculation of the lifetime of tuned zero energy Feshbach resonances using a magnetic field. We give and discuss the law of variation as a function of the magnetic field of the Q matrix eigenvalues across such resonance. Some examples of application are given for the He-N2+ collisions in a magnetic field.
Guillon, G; Stoecklin, T
2009-04-14
We take advantage of the simple expression of the sector adiabatic wave functions of the Magnus propagator to obtain accurate values of the energy derivative of the S matrix which, in turn, is used to get the Smith lifetime Q matrix. The procedure involves the simultaneous generation of both the R matrix and its energy derivative dR/dE which are propagated along the scattering coordinate. We present a few examples of application to the field free He-N(2)(+) inelastic collisions which we previously studied. This method is then applied to the calculation of the lifetime of tuned zero energy Feshbach resonances using a magnetic field. We give and discuss the law of variation as a function of the magnetic field of the Q matrix eigenvalues across such resonance. Some examples of application are given for the He-N(2)(+) collisions in a magnetic field. PMID:19368444
Magnetic Field Topology in Jets
NASA Technical Reports Server (NTRS)
Gardiner, T. A.; Frank, A.
2000-01-01
We present results on the magnetic field topology in a pulsed radiative. jet. For initially helical magnetic fields and periodic velocity variations, we find that the magnetic field alternates along the, length of the jet from toroidally dominated in the knots to possibly poloidally dominated in the intervening regions.
Low field magnetic resonance imaging
Pines, Alexander (Berkeley, CA); Sakellariou, Dimitrios (Billancourt, FR); Meriles, Carlos A. (Fort Lee, NJ); Trabesinger, Andreas H. (London, GB)
2010-07-13
A method and system of magnetic resonance imaging does not need a large homogenous field to truncate a gradient field. Spatial information is encoded into the spin magnetization by allowing the magnetization to evolve in a non-truncated gradient field and inducing a set of 180 degree rotations prior to signal acquisition.
Magnetic field switchable dry adhesives.
Krahn, Jeffrey; Bovero, Enrico; Menon, Carlo
2015-02-01
A magnetic field controllable dry adhesive device is manufactured. The normal adhesion force can be increased or decreased depending on the presence of an applied magnetic field. If the magnetic field is present during the entire normal adhesion test cycle which includes both applying a preloading force and measuring the pulloff pressure, a decrease in adhesion is observed when compared to when there is no applied magnetic field. Similarly, if the magnetic field is present only during the preload portion of the normal adhesion test cycle, a decrease in adhesion is observed because of an increased stiffness of the magnetically controlled dry adhesive device. When the applied magnetic field is present during only the pulloff portion of the normal adhesion test cycle, either an increase or a decrease in normal adhesion is observed depending on the direction of the applied magnetic field. PMID:25588470
K. Yokoyama; T. Oka; K. Noto
2012-01-01
This paper proposes an effective magnetizing method in which bulk material is magnetized by field cooling (FC) using a permanent magnet before pulsed-field magnetization (PFM) to improve the efficiency of magnetization. The concept of this method is to form the channel composed of the magnetic field and efficiently penetrate the magnetic flux by PFM of the bulk without heat generation.
Jansson, Ronnie; Farrar, Glennys R.
2012-12-10
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.
NASA Astrophysics Data System (ADS)
Jansson, Ronnie; Farrar, Glennys R.
2012-12-01
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.
Magnetic nanoparticle motion in external magnetic field
NASA Astrophysics Data System (ADS)
Usov, N. A.; Liubimov, B. Ya
2015-07-01
A set of equations describing the motion of a free magnetic nanoparticle in an external magnetic field in a vacuum, or in a medium with negligibly small friction forces is postulated. The conservation of the total particle momentum, i.e. the sum of the mechanical and the total spin momentum of the nanoparticle is taken into account explicitly. It is shown that for the motion of a nanoparticle in uniform magnetic field there are three different modes of precession of the unit magnetization vector and the director that is parallel the particle easy anisotropy axis. These modes differ significantly in the precession frequency. For the high-frequency mode the director points approximately along the external magnetic field, whereas the frequency and the characteristic relaxation time of the precession of the unit magnetization vector are close to the corresponding values for conventional ferromagnetic resonance. On the other hand, for the low-frequency modes the unit magnetization vector and the director are nearly parallel and rotate in unison around the external magnetic field. The characteristic relaxation time for the low-frequency modes is remarkably long. This means that in a rare assembly of magnetic nanoparticles there is a possibility of additional resonant absorption of the energy of alternating magnetic field at a frequency that is much smaller compared to conventional ferromagnetic resonance frequency. The scattering of a beam of magnetic nanoparticles in a vacuum in a non-uniform external magnetic field is also considered taking into account the precession of the unit magnetization vector and director.
Magnetic Fields in Irregular Galaxies
Amanda A. Kepley; Stefanie Muehle; Eric M. Wilcots; John Everett; Ellen Zweibel; Timothy Robishaw; Carl Heiles
2007-08-24
Magnetic fields are an important component of the interstellar medium, especially in low-mass galaxies like irregulars where the magnetic pressure may be significant. However, few irregular galaxies have observed magnetic field structures. Using the VLA, the GBT, and the ATCA, we have observed several irregular galaxies in the radio continuum to determine their magnetic field structures. Here we report on our results for the galaxies NGC 4214 and NGC 1569.
Reconnection of Magnetic Fields
NASA Technical Reports Server (NTRS)
1984-01-01
Spacecraft observations of steady and nonsteady reconnection at the magnetopause are reviewed. Computer simulations of three-dimensional reconnection in the geomagnetic tail are discussed. Theoretical aspects of the energization of particles in current sheets and of the microprocesses in the diffusion region are presented. Terrella experiments in which magnetospheric reconnection is simulated at both the magnetopause and in the tail are described. The possible role of reconnection in the evolution of solar magnetic fields and solar flares is discussed. A two-dimensional magnetohydrodynamic computer simulation of turbulent reconnection is examined. Results concerning reconnection in Tokamak devices are also presented.
NASA Technical Reports Server (NTRS)
Hildebrand, Roger H.
1988-01-01
The purpose of this paper is to outline the principles governing the use of far-infrared and submillimeter polarimetry to investigate magnetic fields and dust in interstellar clouds. Particular topics of discussion are the alignment of dust grains in dense clouds, the dependence on wavelength of polarization due to emission or to partial absorption by aligned grains, the nature of that dependence for mixtures of grains with different properties, and the problem of distinguishing between (1) the effects of the shapes and dielectric functions of the grains and (2) the degree and direction of their alignment.
Kuc, Agnieszka; Heine, Thomas
2015-05-01
Transition-metal dichalcogenides TX2 (T = W, Mo; X = S, Se, Te) are layered materials that are available in ultrathin forms such as mono-, bi- and multilayers, which are commonly known as two-dimensional materials. They have an intrinsic band gap in the range of some 500 meV to 2 eV, depending on the composition and number of layers, and giant intrinsic spin-orbit splittings for odd layer numbers, and, in conjunction with their high chemical and mechanical stability, they qualify as candidate materials for two-dimensional flexible electronics and spintronics. The electronic structure of each TX2 material is very sensitive to external factors, in particular towards electric and magnetic fields. A perpendicular electric field reduces the band gap, and for some structures semiconductor-metal transitions could be possible. Moreover, the electric field triggers the spin-orbit splitting for bilayers. A magnetic field applied normal to the layers causes the Hall effect, which in some cases may result in a quantum (spin) Hall effect and thus in magnetic switches. Finally, we discuss how valleytronics is possible in these materials by selective interaction of electrons in the different valleys using polarized light. PMID:25529067
NASA Astrophysics Data System (ADS)
Popov, Aleksey
2013-04-01
The magnetic field of the Earth has global meaning for a life on the Earth. The world geophysical science explains: - occurrence of a magnetic field of the Earth it is transformation of kinetic energy of movements of the fused iron in the liquid core of Earth - into the magnetic energy; - the warming up of a kernel of the Earth occurs due to radioactive disintegration of elements, with excretion of thermal energy. The world science does not define the reasons: - drift of a magnetic dipole on 0,2 a year to the West; - drift of lithospheric slabs and continents. The author offers: an alternative variant existing in a world science the theories "Geodynamo" - it is the theory « the Magnetic field of the Earth », created on the basis of physical laws. Education of a magnetic field of the Earth occurs at moving the electric charge located in a liquid kernel, at rotation of the Earth. At calculation of a magnetic field is used law the Bio Savara for a ring electric current: dB = . Magnetic induction in a kernel of the Earth: B = 2,58 Gs. According to the law of electromagnetic induction the Faradey, rotation of a iron kernel of the Earth in magnetic field causes occurrence of an electric field Emf which moves electrons from the center of a kernel towards the mantle. So of arise the radial electric currents. The magnetic field amplifies the iron of mantle and a kernel of the Earth. As a result of action of a radial electric field the electrons will flow from the center of a kernel in a layer of an electric charge. The central part of a kernel represents the field with a positive electric charge, which creates inverse magnetic field Binv and Emfinv When ?mfinv = ?mf ; ?inv = B, there will be an inversion a magnetic field of the Earth. It is a fact: drift of a magnetic dipole of the Earth in the western direction approximately 0,2 longitude, into a year. Radial electric currents a actions with the basic magnetic field of a Earth - it turn a kernel. It coincides with laws 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
Magnetic Fields: Visible and Permanent.
ERIC Educational Resources Information Center
Winkeljohn, Dorothy R.; Earl, Robert D.
1983-01-01
Children will be able to see the concept of a magnetic field translated into a visible reality using the simple method outlined. Standard shelf paper, magnets, iron filings, and paint in a spray can are used to prepare a permanent and well-detailed picture of the magnetic field. (Author/JN)
Magnetic Propeller for Uniform Magnetic Field Levitation
Krinker, Mark
2008-01-01
Three new approaches to generating thrust in uniform magnetic fields are proposed. The first direction is based on employing Lorentz force acting on partial magnetically shielded 8-shaped loop with current in external magnetic field, whereby a net force rather than a torque origins. Another approach, called a Virtual Wire System, is based on creating a magnetic field having an energetic symmetry (a virtual wire), with further superposition of external field. The external field breaks the symmetry causing origination of a net force. Unlike a wire with current, having radial energetic symmetry, the symmetry of the Virtual Wire System is closer to an axial wire. The third approach refers to the first two. It is based on creation of developed surface system, comprising the elements of the first two types. The developed surface approach is a way to drastically increase a thrust-to-weight ratio. The conducted experiments have confirmed feasibility of the proposed approaches.
Photonic Magnetic Field Sensor
NASA Astrophysics Data System (ADS)
Wyntjes, Geert
2002-02-01
Small, in-line polarization rotators or isolators to reduce feedback in fiber optic links can be the basis for excellent magnetic field sensors. Based on the giant magneto-optical (GMO) or Faraday effect in iron garnets, they with a magnetic field of a few hundred Gauss, (20 mT) for an interaction length for an optical beam of a few millimeters achieve a polarization rotation or phase shift of 45 deg (1/8 cycle). When powered by a small laser diode, with the induced linear phase shift recovered at the shot noise limit, we have demonstrated sensitivities at the 3.3 nT/Hz1/2 level for frequencies from less than 1 Hz to frequencies into the high kHz range. Through further improvements; an increase in interaction length, better materials and by far the greatest factor, the addition of a flux concentrator, sensitivities at the pT/Hz1/2 level appear to be within reach. We will detail such a design and discuss the issues that may limit achieving these goals.
Leptogenesis and primordial magnetic fields
Long, Andrew J.; Sabancilar, Eray; Vachaspati, Tanmay E-mail: eray.sabancilar@asu.edu
2014-02-01
The anomalous conversion of leptons into baryons during leptogenesis is shown to produce a right-handed helical magnetic field; in contrast, the magnetic field produced during electroweak baryogenesis is known to be left-handed. If the cosmological medium is turbulent, the magnetic field evolves to have a present day coherence scale ? 10 pc and field strength ? 10{sup ?18} Gauss. This result is insensitive to the energy scale at which leptogenesis took place. Observations of the amplitude, coherence scale, and helicity of the intergalactic magnetic field promise to provide a powerful probe of physics beyond the Standard Model and the very early universe.
Origin of cosmic magnetic fields
NASA Technical Reports Server (NTRS)
Alfven, H.
1979-01-01
Reasons for describing cosmic hydromagnetic phenomena by introducing electric currents are summarized demonstrating that change from the traditional magnetic field description to a current description provides new aspects of cosmic electrodynamics. It is shown that the kink-instability of electric currents is the basic physical phenomenon responsible for magnetic flux generation in cosmic physics. A model which starts with a poloidal magnetic field is discussed; differential motions change the field configuration so that kinetic energy is transferred into magnetic energy of induced toroidal fields; the currents associated with these become unstable when the toroidal energy exceeds the poloidal energy resulting in an amplification of the original poloidal field.
Fast superconducting magnetic field switch
Goren, Yehuda (Mountain View, CA); Mahale, Narayan K. (The Woodlands, TX)
1996-01-01
The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater that the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles.
Martian external magnetic field proxies
NASA Astrophysics Data System (ADS)
Langlais, Benoit; Civet, Francois
2015-04-01
Mars possesses no dynamic magnetic field of internal origin as it is the case for the Earth or for Mercury. Instead Mars is characterized by an intense and localized magnetic field of crustal origin. This field is the result of past magnetization and demagnetization processes, and reflects its evolution. The Interplanetary Magnetic Field (IMF) interacts with Mars' ionized environment to create an external magnetic field. This external field is weak compared to lithospheric one but very dynamic, and may hamper the detailed analysis of the internal magnetic field at some places or times. Because there are currently no magnetic field measurements made at Mars' surface, it is not possible to directly monitor the external field temporal variability as it is done in Earth's ground magnetic observatories. In this study we examine to indirect ways of quantifying this external field. First we use the Advanced Composition Explorer (ACE) mission which measures the solar wind about one hour upstream of the bow-shock resulting from the interaction between the solar wind and the Earth's internal magnetic field. These measurements are extrapolated to Mars' position taking into account the orbital configurations of the Mars-Earth system and the velocity of particles carrying the IMF. Second we directly use Mars Global Surveyor magnetic field measurements to quantify the level of variability of the external field. We subtract from the measurements the internal field which is otherwise modeled, and bin the residuals first on a spatial and then on a temporal mesh. This allows to compute daily or semi daily index. We present a comparison of these two proxies and demonstrate their complementarity. We also illustrate our analysis by comparing our Martian external field proxies to terrestrial index at epochs of known strong activity. These proxies will especially be useful for upcoming magnetic field measurements made around or at the surface of Mars.
Magnetic field modification of optical magnetic dipoles.
Armelles, Gaspar; Caballero, Blanca; Cebollada, Alfonso; Garcia-Martin, Antonio; Meneses-Rodríguez, David
2015-03-11
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
Exposure guidelines for magnetic fields
Miller, G.
1987-12-01
The powerful magnetic fields produced by a controlled fusion experiment at Lawrence Livermore National Laboratory (LLNL) necessitated the development of personnel-exposure guidelines for steady magnetic fields. A literature search and conversations with active researchers showed that it is currently possible to develop preliminary exposure guidelines for steady magnetic fields. An overview of the results of past research into the bioeffects of magnetic fields was compiled, along with a discussion of hazards that may be encountered by people with sickle-cell anemia or medical electronic and prosthetic implants. The LLNL steady magnetic-field exposure guidelines along with a review of developments concerning the safety of time-varying fields were also presented in this compilation. Guidelines developed elsewhere for time varying fields were also given. Further research is needed to develop exposure standards for both steady or time-varying fields.
Magnetic fields in massive stars
S. Hubrig
2007-03-09
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.
Magnetic Fields In Astrophysical Objects
L. J. Silvers
2008-08-11
Magnetic fields are known to reside in many astrophysical objects and are now believed to be crucially important for the creation of phenomena on a wide variety of scales. However, the role of the magnetic field in the bodies that we observe has not always been clear. In certain situations, the importance of a magnetic field has been over looked on the grounds that the large-scale magnetic field was believed to be too weak to play and important role in the dynamics. In this article I discuss some of the recent developments concerning magnetic fields in stars, planets and accretion discs. I choose to emphasise some of the situations where it has been suggested that weak magnetic fields may play a more significant role than previously thought. At the end of the article I list some of the questions to be answered in the future.
Calculating Electromagnetic Fields Of A Loop Antenna
NASA Technical Reports Server (NTRS)
Schieffer, Mitchell B.
1987-01-01
Approximate field values computed rapidly. MODEL computer program developed to calculate electromagnetic field values of large loop antenna at all distances to observation point. Antenna assumed to be in x-y plane with center at origin of coordinate system. Calculates field values in both rectangular and spherical components. Also solves for wave impedance. Written in MicroSoft FORTRAN 77.
External-field-free magnetic biosensor
Li, Yuanpeng; Wang, Yi; Klein, Todd; Wang, Jian-Ping
2014-03-24
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.
External-field-free magnetic biosensor
NASA Astrophysics Data System (ADS)
Li, Yuanpeng; Wang, Yi; Klein, Todd; Wang, Jian-Ping
2014-03-01
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.
NASA Astrophysics Data System (ADS)
Back, Randy; Beckham, J. Regan
2012-10-01
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.
Magnetic fields around evolved stars
NASA Astrophysics Data System (ADS)
Leal-Ferreira, M.; Vlemmings, W.; Kemball, A.; Amiri, N.; Maercker, M.; Ramstedt, S.; Olofsson, G.
2014-04-01
A number of mechanisms, such as magnetic fields, (binary) companions and circumstellar disks have been suggested to be the cause of non-spherical PNe and in particular collimated outflows. This work investigates one of these mechanisms: the magnetic fields. While MHD simulations show that the fields can indeed be important, few observations of magnetic fields have been done so far. We used the VLBA to observe five evolved stars, with the goal of detecting the magnetic field by means of water maser polarization. The sample consists in four AGB stars (IK Tau, RT Vir, IRC+60370 and AP Lyn) and one pPN (OH231.8+4.2). In four of the five sources, several strong maser features were detected allowing us to measure the linear and/or circular polarization. Based on the circular polarization detections, we infer the strength of the component of the field along the line of sight to be between ~30 mG and ~330 mG in the water maser regions of these four sources. When extrapolated to the surface of the stars, the magnetic field strength would be between a few hundred mG and a few Gauss when assuming a toroidal field geometry and higher when assuming more complex magnetic fields. We conclude that the magnetic energy we derived in the water maser regions is higher than the thermal and kinetic energy, leading to the conclusion that, indeed, magnetic fields probably play an important role in shaping Planetary Nebulae.
QCD quark condensate in external magnetic fields
NASA Astrophysics Data System (ADS)
Bali, G. S.; Bruckmann, F.; Endr?di, G.; Fodor, Z.; Katz, S. D.; Schäfer, A.
2012-10-01
We present a comprehensive analysis of the light condensates in QCD with 1+1+1 sea quark flavors (with mass-degenerate light quarks of different electric charges) at zero and nonzero temperatures of up to 190 MeV and external magnetic fields B<1GeV2/e. We employ stout smeared staggered fermions with physical quark masses and extrapolate the results to the continuum limit. At low temperatures we confirm the magnetic catalysis scenario predicted by many model calculations while around the crossover the condensate develops a complex dependence on the external magnetic field, resulting in a decrease of the transition temperature.
NASA Astrophysics Data System (ADS)
Ritter, C.; Pankrats, A. I.; Demidov, A. A.; Velikanov, D. A.; Temerov, V. L.; Gudim, I. A.
2015-04-01
The magnetic structure of the mixed rare-earth system P rxY1 -xF e3(BO3)4 has been studied by elastic neutron powder diffraction and magnetic measurements. A spin reorientation from easy axis to easy plane occurs in the concentration range x =0.67 -0.45 through the formation of inclined magnetic structures. The inclination of the Fe moments from the basal plane depends on the Pr content and ranges from 67(2)° for x =0.67 to 16 (4) ? for x =0.45 at T =3 K . A nonmonotonic change of the inclination angle with temperature is found for all compounds but there is no sign of a spontaneous spin reorientation in the temperature range of magnetic order. An approach based on a crystal-field model for the P r3 + ion and on the molecular-field approximation is used to describe the magnetic characteristics of the system P rxY1 -xF e3(BO3)4 . A good agreement between the experimental and calculated temperature dependences of the magnetic susceptibilities and the angle of inclination of Fe moments from the basal plane has been achieved.
NASA Astrophysics Data System (ADS)
Lee, C. J.; Jang, G. H.
2008-04-01
This paper investigates the distortion of magnetic field of a brushless dc (BLDC) motor due to deformed rubber magnet. Global or local deformation of rubber magnet in the BLDC motor is mathematically modeled by using the Fourier series. Distorted magnetic field is calculated by using the finite element method, and unbalanced magnetic force is calculated by using the Maxwell stress tensor. When the rubber magnet is globally or locally deformed, the unbalanced magnetic force has the frequencies with the first harmonic and the harmonics of slot number ±1. However, the harmonic deformation with multiple of common divisor of pole and slot does not generate unbalanced magnetic force due to the rotational symmetry.
CMB Non-Gaussianity from Primordial Magnetic Fields
NASA Astrophysics Data System (ADS)
Trivedi, Pranjal
2013-01-01
Magnetic fields are observed in galaxies and clusters of galaxies and are possibly present throughout the Universe. However, the origin of cosmic magnetic fields is a puzzle. An interesting possibility is that large-scale magnetic fields are of primordial origin, formed in the early Universe. Such magnetic fields will alter the fluctuations of the cosmic microwave background (CMB). In particular, intrinsically non-linear magnetic effects introduce a new kind of non-Gaussianity in the CMB fluctuations. In this work we have calculated the magnetic CMB trispectrum and bispectrum. These non-Gaussian correlations constrain magnetic fields better than the CMB power spectrum. Further, the trispectrum is found to be a more sensitive probe of magnetic fields than the bispectrum. Using current observational limits on CMB non-Gaussianity, the strongest constraints emerge on cosmic magnetic fields. Thus, the CMB trispectrum is a new and powerful probe of primordial magnetism.
THEMIS/MSDP magnetic field measurements
NASA Astrophysics Data System (ADS)
Berlicki, A.; Mein, P.; Schmieder, B.
2006-01-01
We present an analysis of longitudinal magnetic field measurements using the spectral data obtained with the French - Italian polarisation free telescope THEMIS working in Multichannel Subtractive Double Pass (MSDP) mode. We also used SOHO/MDI data to extend our analysis. THEMIS observations in the MSDP mode allows us to perform imaging spectropolarimetry characterized by high spatial and time resolution. In our analysis we used the observations of solar active region NOAA 10484 performed on October 20, 2003. From THEMIS 2D spectral images recorded in Na D1 5896 Å line we obtained the longitudinal magnetic field in the active region. The value of the magnetic field was calculated at different distances from the Na D1 line centre. We determine the LOS magnetic field at different heights in the solar atmosphere. SOHO/MDI observations provide the longitudinal magnetic field in Ni I (6768 Å) line. THEMIS/MSDP measurements at ??= 0.30 Å are similar to SOHO/MDI results. Gradients of longitudinal magnetic fields derived from MSDP measurements at ??= 0.08 and ??=0.24 Å exhibit different behaviours according to solar targets. A decrease with height is seen in spot umbrae and penumbrae, while the gradient in facular and network areas suggests a slight increase of the longitudinal magnetic field, which might be explained by the 3D-structure of canopies.
Magnetic response to applied electrostatic field in external magnetic field
NASA Astrophysics Data System (ADS)
Adorno, T. C.; Gitman, D. M.; Shabad, A. E.
2014-04-01
We show, within QED and other possible nonlinear theories, that a static charge localized in a finite domain of space becomes a magnetic dipole, if it is placed in an external (constant and homogeneous) magnetic field in the vacuum. The magnetic moment is quadratic in the charge, depends on its size and is parallel to the external field, provided the charge distribution is at least cylindrically symmetric. This magneto-electric effect is a nonlinear response of the magnetized vacuum to an applied electrostatic field. Referring to the simple example of a spherically symmetric applied field, the nonlinearly induced current and its magnetic field are found explicitly throughout the space; the pattern of the lines of force is depicted, both inside and outside the charge, which resembles that of a standard solenoid of classical magnetostatics.
Cosmic Magnetic Fields - An Overview
NASA Astrophysics Data System (ADS)
Wielebinski, Richard; Beck, Rainer
Magnetic fields have been known in antiquity. Aristotle attributes the first of what could be called a scientific discussion on magnetism to Thales, who lived from about 625 BC. In China “magnetic carts” were in use to help the Emperor in his journeys of inspection. Plinius comments that in the Asia Minor province of Magnesia shepherds' staffs get at times “glued” to a stone, a alodestone. In Europe the magnetic compass came through the Arab sailors who met the Portuguese explorers. The first scientific treatise on magnetism, “De Magnete”, was published by William Gilbert who in 1600 described his experiments and suggested that the Earth was a huge magnet. Johannes Kepler was a correspondent of Gilbert and at times suggested that planetary motion was due to magnetic forces. Alas, this concept was demolished by Isaac Newton,who seeing the falling apple decided that gravity was enough. This concept of dealing with gravitational forces only remains en vogue even today. The explanations why magnetic effects must be neglected go from “magnetic energy is only 1% of gravitation” to “magnetic fields only complicate the beautiful computer solutions”. What is disregarded is the fact that magnetic effects are very directional(not omni-directional as gravity) and also the fact that magnetic fields are seen every where in our cosmic universe.
Plasma and magnetic field characteristics of magnetic flux transfer events
G. Paschmann; G. Haerendel; I. Papamastorakis; N. Sckopke; S. J. Bame; J. T. Gosling
1982-01-01
Plasma and magnetic field data from ISEE 1 and 2 are examined for 5 passes of the magnetopause region at 20 and 40 deg northern latitudes, and are presented in terms of moments of the distribution function, calculated from two-dimensional or three-dimensional data. Flux transfer events are characterized by a mixture of magnetosheath and magnetospheric particles, which supports the hypothesis
Calculator simplifies field production forecasting
Bixler, B.
1982-05-01
A method of forecasting future field production from an assumed average well production schedule and drilling schedule has been programmed for the HP-41C hand-held programmable computer. No longer must tedious row summations be made by hand for staggered well production schedules. Details of the program are provided.
Measurements of magnetic field alignment
Kuchnir, M.; Schmidt, E.E.
1987-11-06
The procedure for installing Superconducting Super Collider (SSC) dipoles in their respective cryostats involves aligning the average direction of their field with the vertical to an accuracy of 0.5 mrad. The equipment developed for carrying on these measurements is described and the measurements performed on the first few prototypes SSC magnets are presented. The field angle as a function of position in these 16.6 m long magnets is a characteristic of the individual magnet with possible feedback information to its manufacturing procedure. A comparison of this vertical alignment characteristic with a magnetic field intensity (by NMR) characteristic for one of the prototypes is also presented. 5 refs., 7 figs.
The HMI Magnetic Field Pipeline
Jon Todd Hoeksema; Y. Liu; J. Schou; P. Scherrer
2009-01-01
The Helioseismic and Magnetic Imager (HMI) will provide frequent full-disk magnetic field data after launch of the Solar Dynamics Observatory (SDO), currently scheduled for fall 2009. 16 megapixel line-of-sight magnetograms (Blos) will be recorded every 45 seconds. A full set of polarized filtergrams needed to determine the vector magnetic field requires 90 seconds. Quick-look data will be available within a
The MAVEN Magnetic Field Investigation
NASA Technical Reports Server (NTRS)
Connerney, J. E. P.; Espley, J.; Lawton, P.; Murphy, S.; Odom, J.; Oliversen, R.; Sheppard, D.
2014-01-01
The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions ("boomlets"). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a quantization uncertainty of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05%. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers - multiple rotations about the spacecraft x and z axes - to characterize spacecraft fields and/or instrument offsets in flight.
The MAVEN Magnetic Field Investigation
NASA Astrophysics Data System (ADS)
Connerney, J. E. P.; Espley, J.; Lawton, P.; Murphy, S.; Odom, J.; Oliversen, R.; Sheppard, D.
2015-06-01
The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions ("boomlets"). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a resolution of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05 %. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers—multiple rotations about the spacecraft x and z axes—to characterize spacecraft fields and/or instrument offsets in flight.
Numerical Object Oriented Quantum Field Theory Calculations
M. Williams
2009-05-07
The qft++ package is a library of C++ classes that facilitate numerical (not algebraic) quantum field theory calculations. Mathematical objects such as matrices, tensors, Dirac spinors, polarization and orbital angular momentum tensors, etc. are represented as C++ objects in qft++. The package permits construction of code which closely resembles quantum field theory expressions, allowing for quick and reliable calculations.
Force Field Calculation with a Top Desk Calculator
NASA Astrophysics Data System (ADS)
Ali, Jafar H.; Shanshal, Muthanna
1981-04-01
A modified "Consistent Force Field " method is described in which the energy minimization is carried out according to the Murtagh-Sargent method rather than the Newton-Raphson method and the number of non-bonded interactions is reduced to interactions between atoms separated by three bonds at the most. The smaller number of interaction terms allowed the programming of the method for a desk top calculator (HP-9810). Calculations are reported for a number of aliphatic molecules
LABORATORY V MAGNETIC FIELDS AND FORCES
Minnesota, University of
of the magnetic field for various combinations of bar magnets, and to draw vector diagrams (field maps) for eachLABORATORY V MAGNETIC FIELDS AND FORCES Lab V - 1 Magnetism plays a large part in our modern world problems, you will map magnetic fields from different sources and use the magnetic force to deflect
Micromagnetic calculation of magnetization reversal in magnetic rings
NASA Astrophysics Data System (ADS)
Lopez-Diaz, Luis
2002-03-01
The success of using patterned magnetic nanoelements in Magnetic Random Access Memories (MRAM) depends entirely on our ability to control accurately their switching fields. In a recent study1, we showed that micron-sized narrow rings present well defined stable states and nucleation-free switching between them. In the first part of the talk we review our experimental studies on ring magnets. Pre-patterned Si(100) substrates were used to grow free-standing epitaxial ring magnets of Cu(100)/Co(100)/Cu(100)/Si(100) with 1.8 mm outer diameter, 1.2 mm inner diameter and 34 nm thickness. The samples were magnetically characterised using specially adapted magneto-optic Kerr effect. The measurements show that a two step switching process occurs at high fields, indicating the existence of two different stable states. In addition to the vortex state, which occurs at intermediate fields, we have identified a second state which is also stable at remanence and undergoes a simple and well characterised nucleation free domain wall propagation switching process. Moreover, it is confirmed that the rings reverse by falling into vortex states with different circulation when the field is applied in opposite directions. This means a particular vortex state (clockwise or counter-clockwise) can be prepared using a uniform field only, which can be important for technological applications. In the second part of the talk we use micromagnetic simulations to further explore the potential performance of narrow rings as memory cells in MRAM devices in terms of scalability and switching speed. We introduce two artificial notches at the outer surface of the rings in order to control accurately the depinning fields for the domain walls. According to our simulations, well defined onion states1 and switching by domain wall motion can be achieved for ring diameters down 180 nm. In order to speed up the switching process, two different approaches are considered. In the first one, a field pulse is applied in the plane of the ring and perpendicular to the walls. In this case the walls are depinned effectively and magnetization reversal can be achieved in a few ns. In the second approach, the field is applied perpendicular to the plane of the ring. This field drives the system out of equilibrium and precessional motion causes the walls move around the ring. With this approach, switching times can be lowered down to 220 ps, which is very promising for implementation in MRAM devices. 1. J. Rothman, M. Kläui, L. Lopez-Diaz, C.A.F. Vaz, A. Bleloch, J.A.C. Bland, Z. Cui and R. Speaks, Phys. Rev. Lett. 86, 1098 (2001).
NASA Astrophysics Data System (ADS)
Moraitis, K.; Tziotziou, K.; Georgoulis, M. K.; Archontis, V.
2014-12-01
In earlier works we introduced and tested a nonlinear force-free (NLFF) method designed to self-consistently calculate the coronal free magnetic energy and the relative magnetic helicity budgets of observed solar magnetic structures. In principle, the method requires only a single, photospheric or low-chromospheric, vector magnetogram of a quiet-Sun patch or an active region and performs calculations without three-dimensional magnetic and velocity-field information. In this work we strictly validate this method using three-dimensional coronal magnetic fields. Benchmarking employs both synthetic, three-dimensional magnetohydrodynamic simulations and nonlinear force-free field extrapolations of the active-region solar corona. Our time-efficient NLFF method provides budgets that differ from those of more demanding semi-analytical methods by a factor of approximately three, at most. This difference is expected to come from the physical concept and the construction of the method. Temporal correlations show more discrepancies that are, however, soundly improved for more complex, massive active regions, reaching correlation coefficients on the order of, or exceeding, 0.9. In conclusion, we argue that our NLFF method can be reliably used for a routine and fast calculation of the free magnetic energy and relative magnetic helicity budgets in targeted parts of the solar magnetized corona. As explained in this article and in previous works, this is an asset that can lead to valuable insight into the physics and triggering of solar eruptions.
NASA Astrophysics Data System (ADS)
Kitahama, Yasutaka; Murai, Hisao
1998-12-01
The magnetic field effect on the photoconductivity and photoconductivity detected magnetic resonance spectra observed in the photoionization system of N, N, N', N'-tetramethyl- p-phenylenediamine (TMPD) in alcohol are analyzed by the numerical calculation. The stochastic Liouville equation is applied to the study of the dynamics of the transiently formed radical-ion pair (RIP). We succeeded in estimating the appropriate physical parameters according to the simulation of the line-width and the other observed phenomena. However, we realized that a new model, the formation of a cluster-like network structure between the RIP and the solvent molecules, should be introduced, because the calculation of the RIP dynamics in homogeneous solutions cannot reproduce the experimental results of the viscosity dependence.
Tachyon Condensation: Calculations in String Field Theory
Pieter-Jan De Smet
2001-09-24
In this Ph.D. thesis, we study tachyon condensation in string field theories. In chapter 2, we review Witten's bosonic string field theory and calculate the tachyon potential. In chapter 3, we calculate the tachyon potential in Berkovits' superstring field theory. In chapter 4, we look for exact solutions in a toy model. Unpublished result: we use conservation laws to calculate the level (4,8) approximation of the tachyon potential in Berkovits' superstring field theory. We verify Sen's conjecture up to 94.4%.
Hubbard U Calculations for Dilute Magnetic Semiconductors
NASA Astrophysics Data System (ADS)
Fukushima, Tetsuya; Kazunori Sato Collaboration; Gustav Bihlmayer Collaboration; Peter Dederichs Collaboration; Phivos. Mavropoulos Collaboration; Rudolf Zeller Collaboration
2013-03-01
Based on constrained density functional theory, we present ab initio calculations for the Hubbard U parameter of transition metal impurities in dilute magnetic semiconductors, by choosing Mn in GaN as an example. The calculations are performed by two methods: (i) the Korringa-Kohn-Rostoker (KKR) Green function method for a single Mn impurity in GaN and (ii) the Full-potentian Linear Augmented Plane-Wave (FLAPW) method for large supercell of GaN with a single Mn impurity in each cell. By changing the occupancy of the majority t2 gap state of Mn, we determine the U parameter either from the total energy differences E (N + 1) and E (N - 1) of the N + 1 and N - 1 excited states with respect to the ground state E (n) , or by using the single particle energies for N + 1 / 2 and N - 1 / 2 occupancies (Janak's transition state model). Both methods give nearly identical results. Moreover the values calculated by the Green function technique and the supercell method agree quite well. Based on constrained density functional theory, we present ab initio calculations for the Hubbard U parameter of transition metal impurities in dilute magnetic semiconductors, by choosing Mn in GaN as an example. The calculations are performed by two methods: (i) the Korringa-Kohn-Rostoker (KKR) Green function method for a single Mn impurity in GaN and (ii) the Full-potentian Linear Augmented Plane-Wave (FLAPW) method for large supercell of GaN with a single Mn impurity in each cell. By changing the occupancy of the majority t2 gap state of Mn, we determine the U parameter either from the total energy differences E (N + 1) and E (N - 1) of the N + 1 and N - 1 excited states with respect to the ground state E (n) , or by using the single particle energies for N + 1 / 2 and N - 1 / 2 occupancies (Janak's transition state model). Both methods give nearly identical results. Moreover the values calculated by the Green function technique and the supercell method agree quite well. The authors acknowledge the financial support from the JSPS Core-to-Core Program
Thermometers in Low Magnetic Fields
NASA Astrophysics Data System (ADS)
Geršak, G.; Beguš, S.
2010-09-01
In this article the effect of low amplitude DC magnetic fields on different types of thermometers is discussed. By means of a precision water-cooled electromagnet, the effect of a magnetic field on platinum resistance thermometers, thermistors, and type T, J, and K thermocouples was investigated, while thermometers were thermally stabilized in thermostatic baths. Four different baths were used for temperatures from 77 K (-196 °C) to 353 K (80 °C): liquid nitrogen bath (nitrogen boiling point at atmospheric pressure), ice-point bath, room-temperature air bath, and hot-water bath. The generated DC magnetic field of high relative precision (2 × 10-4 at 1 T, 4 × 10-5 short-term stability) and high relative uniformity (2 × 10-5 over 1 cm2, 10 mm gap) had a magnetic flux density of 1 T in the center of the gap between the magnet pole caps. The results indicate a magnetic effect of up to 100 mK due to a 1 T magnetic field for the types of thermocouples composed of ferromagnetic materials (Fe, Cr, Ni). For platinum resistance thermometers, thermistors, and non-magnetic type T thermocouples, the detected magnetic effect was weaker, i.e., under 10 mK.
NASA Technical Reports Server (NTRS)
Connerney, J. E. P.; Acuna, Mario H.; Ness, Norman F.
1992-01-01
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.
Magnetic fields and scintillator performance
Green, D.; Ronzhin, A.; Hagopian, V.
1995-06-01
Experimental data have shown that the light output of a scintillator depends on the magnitude of the externally applied magnetic fields, and that this variation can affect the calorimeter calibration and possibly resolution. The goal of the measurements presented here is to study the light yield of scintillators in high magnetic fields in conditions that are similar to those anticipated for the LHC CMS detector. Two independent measurements were performed, the first at Fermilab and the second at the National High Magnetic Field Laboratory at Florida State University.
AC photovoltaic module magnetic fields
Jennings, C.; Chang, G.J. [Pacific Gas and Electric Co., San Francisco, CA (United States); Reyes, A.B.; Whitaker, C.M. [Endecon Engineering, San Ramon, CA (United States)
1997-12-31
Implementation of alternating current (AC) photovoltaic (PV) modules, particularly for distributed applications such as PV rooftops and facades, may be slowed by public concern about electric and magnetic fields (EMF). This paper documents magnetic field measurements on an AC PV module, complementing EMF research on direct-current PV modules conducted by PG and E in 1993. Although not comprehensive, the PV EMF data indicate that 60 Hz magnetic fields (the EMF type of greatest public concern) from PV modules are comparable to, or significantly less than, those from household appliances. Given the present EMF research knowledge, AC PV module EMF may not merit considerable concern.
Plasma and magnetic field characteristics of magnetic flux transfer events
NASA Technical Reports Server (NTRS)
Paschmann, G.; Haerendel, G.; Papamastorakis, I.; Sckopke, N.; Bame, S. J.; Gosling, J. T.; Russell, C. T.
1982-01-01
Plasma and magnetic field data from ISEE 1 and 2 are examined for 5 passes of the magnetopause region at 20 and 40 deg northern latitudes, and are presented in terms of moments of the distribution function, calculated from two-dimensional or three-dimensional data. Flux transfer events are characterized by a mixture of magnetosheath and magnetospheric particles, which supports the hypothesis that flux transfer events represent encounters of reconnected flux tubes. An excess pressure appears to be balanced by the tension of the ambient magnetic field lines as they are draped around the reconnected flux tube, and the different observed magnetic field signatures are consistent with expectations for encounters of the flux tubes at different relative locations. It is suggested that increased flow speeds are caused by continued reconnection at the low-latitude boundaries of the flux tubes.
Constitutive equation of magnetic materials and magnetic field analysis
Enokizono, M.; Yuki, K. )
1993-03-01
The conventional field analysis methods neglect the phase relation between the magnetic flux density B and the magnetic field vector H under a rotating field. Magnetic properties have been measured as scalar relationships under an alternating magnetic field, and only the scalar values have been applied to analyze the two-dimensional magnetic field problems. In this paper, the B- and H-values have been measured as vector relationships under the influence of a rotating field, using the two-dimensional magnetic measurement apparatus. The magnetic properties are represented by a tensor expression as a function of magnetic reluctivities. This expression is then applied for the rotating field analysis.
Developments in deep brain stimulation using time dependent magnetic fields
NASA Astrophysics Data System (ADS)
Crowther, L. J.; Nlebedim, I. C.; Jiles, D. C.
2012-04-01
The effect of head model complexity upon the strength of field in different brain regions for transcranial magnetic stimulation (TMS) has been investigated. Experimental measurements were used to verify the validity of magnetic field calculations and induced electric field calculations for three 3D human head models of varying complexity. Results show the inability for simplified head models to accurately determine the site of high fields that lead to neuronal stimulation and highlight the necessity for realistic head modeling for TMS applications.
CMB anisotropies from primordial magnetic field.
NASA Astrophysics Data System (ADS)
Durrer, Ruth; Kahniashvili, Tina
1999-08-01
We investigate microwave background anisotropies in the presence of primordial magnetic fields. We show that a homegeneous field with fixed direction can amplify vector perturbations. We calculate the correlations of Î´Î¤/Ð¢ explicitly and show that a large scale coherent field induces correlations between a_l-1,m and a_l+1,m. We discuss constraints on the amplitude and spectrum of a primordial magnetic field imposed by observations of CMB anisotropies (Durrer,Kahniashvili and Yates,1998). we derive an expression for the angular power spectrum of cosmic microwave background anisotropies due to gravity waves generated by a stochastic magnetic field and compare the result with current observations; we take into account the non-linear nature of the stress energy tensor of the magnetic field.For all most scale invariant spectra,the amplitude of the magnetic field at galactic scales is constrained to be of order 10^-9 Gauss (Durrer,Fereira and KAhniashvili,1999). Acnowledgements.T.K. is thankful to Geneva University hospitality where this work was done.
Calculation and Analysis of Magnetic Gradient Tensor Components of Global Magnetic Models
NASA Astrophysics Data System (ADS)
Schiffler, M.; Queitsch, M.; Schneider, M.; Goepel, A.; Stolz, R.; Krech, W.; Meyer, H. G.; Kukowski, N.
2014-12-01
Global Earth's magnetic field models like the International Geomagnetic Reference Field (IGRF), the World Magnetic Model (WMM) or the High Definition Geomagnetic Model (HDGM) are harmonic analysis regressions to available magnetic observations stored as spherical harmonic coefficients. Input data combine recordings from magnetic observatories, airborne magnetic surveys and satellite data. The advance of recent magnetic satellite missions like SWARM and its predecessors like CHAMP offer high resolution measurements while providing a full global coverage. This deserves expansion of the theoretical framework of harmonic synthesis to magnetic gradient tensor components. Measurement setups for Full Tensor Magnetic Gradiometry equipped with high sensitive gradiometers like the JeSSY STAR system can directly measure the gradient tensor components, which requires precise knowledge about the background regional gradients which can be calculated with this extension. In this study we develop the theoretical framework for calculation of the magnetic gradient tensor components from the harmonic series expansion and apply our approach to the IGRF and HDGM. The gradient tensor component maps for entire Earth's surface produced for the IGRF show low gradients reflecting the variation from the dipolar character, whereas maps for the HDGM (up to degree N=729) reveal new information about crustal structure, especially across the oceans, and deeply situated ore bodies. From the gradient tensor components, the rotational invariants, the Eigenvalues, and the normalized source strength (NSS) are calculated. The NSS focuses on shallower and stronger anomalies. Euler deconvolution using either the tensor components or the NSS applied to the HDGM reveals an estimate of the average source depth for the entire magnetic crust as well as individual plutons and ore bodies. The NSS reveals the boundaries between the anomalies of major continental provinces like southern Africa or the Eastern European Craton.
Complex polarization propagator calculations of magnetic circular dichroism spectra
NASA Astrophysics Data System (ADS)
Solheim, Harald; Ruud, Kenneth; Coriani, Sonia; Norman, Patrick
2008-03-01
It is demonstrated that the employment of the nonlinear complex polarization propagator enables the calculation of the complete magnetic circular dichroism spectra of closed-shell molecules, including at the same time both the so-called Faraday A and B terms. In this approach, the differential absorption of right and left circularly polarized light in the presence of a static magnetic field is determined from the real part of the magnetic field-perturbed electric dipole polarizability. The introduction of the finite lifetimes of the electronically excited states into the theory results in response functions that are well behaved in the entire spectral region, i.e., the divergencies that are found in conventional response theory approaches at the transition energies of the system are not present. The applicability of the approach is demonstrated by calculations of the ultraviolet magnetic circular dichroism spectra of para-benzoquinone, tetrachloro-para-benzoquinone, and cyclopropane. The present results are obtained with the complex polarization propagator approach in conjunction with Kohn-Sham density functional theory and the standard adiabatic density functionals B3LYP, CAM-B3LYP, and BHLYP.
Magnetic fields in gaps surrounding giant protoplanets
Keith, Sarah L
2015-01-01
Giant protoplanets evacuate a gap in their host protoplanetary disc, which gas must cross before it can be accreted. A magnetic field is likely carried into the gap, potentially influencing the flow. Gap crossing has been simulated with varying degrees of attention to field evolution (pure hydrodynamical, ideal, and resistive MHD), but as yet there has been no detailed assessment of the role of the field accounting for all three key non-ideal MHD effects: Ohmic resistivity, ambipolar diffusion, and Hall drift. We present a detailed investigation of gap magnetic field structure as determined by non-ideal effects. We assess susceptibility to turbulence induced by the magnetorotational instability, and angular momentum loss from large-scale fields. As full non-ideal simulations are computationally expensive, we take an a posteriori approach, estimating MHD quantities from the pure hydrodynamical gap crossing simulation by Tanigawa et al. (2012). We calculate the ionisation fraction and estimate field strength an...
Quantum statistics of hydrogen in strong magnetic fields
NASA Astrophysics Data System (ADS)
Bachmann, M.; Kleinert, H.; Pelster, A.
2001-01-01
By an extension of the Feynman-Kleinert variational approach, we calculate the temperature-dependent effective classical potential governing the quantum statistical properties of a hydrogen atom in a uniform magnetic field. In the zero-temperature limit, we obtain ground state energies which are accurate for all magnetic field strengths from weak to strong fields.
NASA Astrophysics Data System (ADS)
Anber, Mohamed M.; Sorbo, Lorenzo
2006-10-01
There is increasing interest in the role played by pseudo Nambu Goldstone bosons (pNGBs) in the construction of string-inspired models of inflation. In these models the inflaton is expected to be coupled to gauge fields, and will lead to the generation of magnetic fields that can be of cosmological interest. We study the production of such fields mainly focusing on the model of N-flation, where the collective effect of several pNGBs drives inflation. Because the fields produced are maximally helical, inverse cascade processes in the primordial plasma significantly increase their coherence length. We discuss under what conditions inflation driven by pNGBs can account for the cosmological magnetic fields observed. A constraint on the parameters of this class of inflationary scenarios is also derived by requiring that the magnetic field does not backreact on the inflating background.
High magnetic field MHD generator program
NASA Astrophysics Data System (ADS)
1980-10-01
The MHD channel phenomena which are important at high magnetic fields are investigated. Nonuniformity effects, boundary layers, Hall field breakdown, the effects on electrode configuration and current concentrations, and studies of steady state combustion disk and linear channels in an existing 6 Tesla magnet of small dimensions are discussed. In the study of the effects of nonuniformities and instabilities, theoretical models were developed and tested against available data. Boundary layer measurements and calculations of velocity, temperature, and electron density were systematically assessed; by accounting for the effect of free stream turbulence, good agreement is obtained between measurement and theory. An improved laser Doppler anemometer was developed for turbulence damping and velocity profile measurements.
Measuring Earth's Magnetic Field Simply.
ERIC Educational Resources Information Center
Stewart, Gay B.
2000-01-01
Describes a method for measuring the earth's magnetic field using an empty toilet paper tube, copper wire, clear tape, a battery, a linear variable resistor, a small compass, cardboard, a protractor, and an ammeter. (WRM)
Current Collection in a Magnetic Field
NASA Technical Reports Server (NTRS)
Krivorutsky, E. N.
1997-01-01
It is found that the upper-bound limit for current collection in the case of strong magnetic field from the current is close to that given by the Parker-Murphy formula. This conclusion is consistent with the results obtained in laboratory experiments. This limit weakly depends on the shape of the wire. The adiabatic limit in this case will be easily surpassed due to strong magnetic field gradients near the separatrix. The calculations can be done using the kinetic equation in the drift approximation. Analytical results are obtained for the region where the Earth's magnetic field is dominant. The current collection can be calculated (neglecting scattering) using a particle simulation code. Dr. Singh has agreed to collaborate, allowing the use of his particle code. The code can be adapted for the case when the current magnetic field is strong. The needed dm for these modifications is 3-4 months. The analytical description and essential part of the program is prepared for the calculation of the current in the region where the adiabatic description can be used. This was completed with the collaboration of Drs. Khazanov and Liemohn. A scheme of measuring the end body position is also proposed. The scheme was discussed in the laboratory (with Dr. Stone) and it was concluded that it can be proposed for engineering analysis.
Origin of strong magnetic fields.
NASA Technical Reports Server (NTRS)
Canuto, V.; Kumar, S.; Lee, H. J.
1972-01-01
A possible mechanism by which extremely strong magnetic fields in neutron stars and white dwarfs could originate involves the existence of thermodynamic equilibrium states (LOFER states) of an electron gas. The essence of the stability theory of a LOFER state is discussed. The extended electronic system considered is in contact with a thermal bath in the presence of an external magnetic field. It is found that it is not necessary to require absolute stability in order to realize a LOFER state in nature.
Black Holes and Magnetic Fields
Hejda, Filip
2015-01-01
We briefly summarise the basic properties of spacetimes representing rotating, charged black holes in strong axisymmetric magnetic fields. We concentrate on extremal cases, for which the horizon surface gravity vanishes. We investigate their properties by finding simpler spacetimes that exhibit their geometries near degenerate horizons. Employing the simpler geometries obtained by near-horizon limiting description we analyse the Meissner effect of magnetic field expulsion from extremal black holes.
Three dimensional finite element calculation of saturable magnetic fluxes and torques of an actuator
Brauer, J.R.; Aronson, E.A.; McCaughey, K.G.; Sullivan, W.N.
1988-01-01
A rotary magnetic actuator of highly three dimensional geometry is analyzed by the finite element method. A one quarter model composed of three dimensional finite elements is developed for analysis by the vector potential Newton Raphson approach. The nonlinear saturable magnetic fields, fluxes, inductances, energies, and torques are calculated at three armature positions. The calculated torques compare reasonably well with measurements.
Primordial Magnetic Fields and Causality
Ruth Durrer; Chiara Caprini
2003-10-29
We discuss the implications of causality on a primordial magnetic field. We show that the residual field on large scales is much more suppressed than usually assumed and that a helical component is even more reduced. Due to this strong suppression, even maximal primordial fields generated at the electroweak phase transition can just marginally seed the fields in clusters, but they cannot leave any detectable imprint on the cosmic microwave background.
Magnetic field induced dynamical chaos
Ray, Somrita; Baura, Alendu; Bag, Bidhan Chandra
2013-12-15
In this article, we have studied the dynamics of a particle having charge in the presence of a magnetic field. The motion of the particle is confined in the x–y plane under a two dimensional nonlinear potential. We have shown that constant magnetic field induced dynamical chaos is possible even for a force which is derived from a simple potential. For a given strength of the magnetic field, initial position, and velocity of the particle, the dynamics may be regular, but it may become chaotic when the field is time dependent. Chaotic dynamics is very often if the field is time dependent. Origin of chaos has been explored using the Hamiltonian function of the dynamics in terms of action and angle variables. Applicability of the present study has been discussed with a few examples.
Surface structure of neutron stars with high magnetic fields
NASA Technical Reports Server (NTRS)
Fushiki, I.; Gudmundsson, E. H.; Pethick, C. J.
1989-01-01
The equation of state of cold dense matter in strong magnetic fields is calculated in the Thomas-Fermi and Thomas-Fermi-Dirac approximations. For use in the latter calculation, a new expression is derived for the exchange energy of the uniform electron gas in a strong magnetic field. Detailed calculations of the density profile in the surface region of a neutron star are described for a variety of equations of state, and these show that the surface density profile is strongly affected by the magnetic field, irrespective of whether or not matter in a magnetic field has a condensed state bound with respect to isolated atoms. It is also shown that, as a consequence of the field dependence of the screening potential, magnetic fields can significantly increase nuclear reaction rates.
Magnetic Field Generation in Stars
NASA Astrophysics Data System (ADS)
Ferrario, Lilia; Melatos, Andrew; Zrake, Jonathan
2015-03-01
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.
Primordial magnetic fields from self-ordering scalar fields
NASA Astrophysics Data System (ADS)
Horiguchi, Kouichirou; Ichiki, Kiyotomo; Sekiguchi, Toyokazu; Sugiyama, Naoshi
2015-04-01
A symmetry-breaking phase transition in the early universe could have led to the formation of cosmic defects. Because these defects dynamically excite not only scalar and tensor type cosmological perturbations but also vector type ones, they may serve as a source of primordial magnetic fields. In this study, we calculate the time evolution and the spectrum of magnetic fields that are generated by a type of cosmic defects, called global textures, using the non-linear sigma (NLSM) model. Based on the standard cosmological perturbation theory, we show, both analytically and numerically, that a vector-mode relative velocity between photon and baryon fluids is induced by textures, which inevitably leads to the generation of magnetic fields over a wide range of scales. We find that the amplitude of the magnetic fields is given by B~10?9((1+z)/103)?2.5(v/mpl)2(k/Mpc?1)3.5/?N Gauss in the radiation dominated era for klesssim 1 Mpc?1, with v being the vacuum expectation value of the O(N) symmetric scalar fields. By extrapolating our numerical result toward smaller scales, we expect that B~ 10?14.5((1+z)/103)1/2(v/mpl)2(k/Mpc?1)1/2/?N Gauss on scales of kgtrsim 1 Mpc?1 at redshift 0zgtrsim 110. This might be a seed of the magnetic fields observed on large scales today.
IR photodetector based on rectangular quantum wire in magnetic field
NASA Astrophysics Data System (ADS)
Jha, Nandan
2014-04-01
In this paper we study rectangular quantum wire based IR detector with magnetic field applied along the wires. The energy spectrum of a particle in rectangular box shows level repulsions & crossings when external magnetic field is applied. Due to this complex level dynamics, we can tune the spacing between any two levels by varying the magnetic field. This method allows user to change the detector parameters according to his/her requirements. In this paper, we numerically calculate the energy sub-band levels of the square quantum wire in constant magnetic field along the wire and quantify the possible operating wavelength range that can be obtained by varying the magnetic field. We also calculate the photon absorption probability at different magnetic fields and give the efficiency for different wavelengths if the transition is assumed between two lowest levels.
Magnetic Field Generation in Stars
Ferrario, Lilia; Zrake, Jonathan
2015-01-01
Enormous progress has been made on observing stellar magnetism in stars from the main sequence 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. Thus we maybe at the dawn of a ...
Baryon magnetic moments in the background field method
F. X. Lee; R. Kelly; L. Zhou; W. Wilcox
2005-09-21
We present a calculation of the magnetic moments for the baryon octet and decuplet using the background-field method and standard Wilson gauge and fermion actions in the quenched approximation of lattice QCD. Progressively smaller static magnetic fields are introduced on a $24^4$ lattice at beta=6.0 and the pion mass is probed down to about 500 MeV. Magnetic moments are extracted from the linear response of the masses to the background field.
Magnetic Fields in Stellar Jets
P. Hartigan; A. Frank; P. Varniere; E. Blackman
2007-02-06
Although several lines of evidence suggest that jets from young stars are driven magnetically from accretion disks, existing observations of field strengths in the bow shocks of these flows imply that magnetic fields play only a minor role in the dynamics at these locations. To investigate this apparent discrepancy we performed numerical simulations of expanding magnetized jets with stochastically variable input velocities with the AstroBEAR MHD code. Because the magnetic field B is proportional to the density n within compression and rarefaction regions, the magnetic signal speed drops in rarefactions and increases in the compressed areas of velocity-variable flows. In contrast, B ~ n^0.5 for a steady-state conical flow with a toroidal field, so the Alfven speed in that case is constant along the entire jet. The simulations show that the combined effects of shocks, rarefactions, and divergent flow cause magnetic fields to scale with density as an intermediate power 1 > p > 0.5. Because p > 0.5, the Alfven speed in rarefactions decreases on average as the jet propagates away from the star. This behavior is extremely important to the flow dynamics because it means that a typical Alfven velocity in the jet close to the star is significantly larger than it is in the rarefactions ahead of bow shocks at larger distances, the one place where the field is a measurable quantity. We find that the observed values of weak fields at large distances are consistent with strong fields required to drive the observed mass loss close to the star. For a typical stellar jet the crossover point inside which velocity perturbations of 30 - 40 km/s no longer produce shocks is ~ 300 AU from the source.
Magnetic Fields in Population III Star Formation
Turk, Matthew J.; Oishi, Jeffrey S.; Abel, Tom; Bryan, Greg
2012-02-22
We study the buildup of magnetic fields during the formation of Population III star-forming regions, by conducting cosmological simulations from realistic initial conditions and varying the Jeans resolution. To investigate this in detail, we start simulations from identical initial conditions, mandating 16, 32 and 64 zones per Jeans length, and studied the variation in their magnetic field amplification. We find that, while compression results in some amplification, turbulent velocity fluctuations driven by the collapse can further amplify an initially weak seed field via dynamo action, provided there is sufficient numerical resolution to capture vortical motions (we find this requirement to be 64 zones per Jeans length, slightly larger than, but consistent with previous work run with more idealized collapse scenarios). We explore saturation of amplification of the magnetic field, which could potentially become dynamically important in subsequent, fully-resolved calculations. We have also identified a relatively surprising phenomena that is purely hydrodynamic: the higher-resolved simulations possess substantially different characteristics, including higher infall-velocity, increased temperatures inside 1000 AU, and decreased molecular hydrogen content in the innermost region. Furthermore, we find that disk formation is suppressed in higher-resolution calculations, at least at the times that we can follow the calculation. We discuss the effect this may have on the buildup of disks over the accretion history of the first clump to form as well as the potential for gravitational instabilities to develop and induce fragmentation.
Magnetic nanoparticles for applications in oscillating magnetic field
Peeraphatdit, Chorthip
2010-12-15
Enzymatic and thermochemical catalysis are both important industrial processes. However, the thermal requirements for each process often render them mutually exclusive: thermochemical catalysis requires high temperature that denatures enzymes. One of the long-term goals of this project is to design a thermocatalytic system that could be used with enzymatic systems in situ to catalyze reaction sequences in one pot; this system would be useful for numerous applications e.g. conversion of biomass to biofuel and other commodity products. The desired thermocatalytic system would need to supply enough thermal energy to catalyze thermochemical reactions, while keeping the enzymes from high temperature denaturation. Magnetic nanoparticles are known to generate heat in an oscillating magnetic field through mechanisms including hysteresis and relaxational losses. We envisioned using these magnetic nanoparticles as the local heat source embedded in sub-micron size mesoporous support to spatially separate the particles from the enzymes. In this study, we set out to find the magnetic materials and instrumental conditions that are sufficient for this purpose. Magnetite was chosen as the first model magnetic material in this study because of its high magnetization values, synthetic control over particle size, shape, functionalization and proven biocompatibility. Our experimental designs were guided by a series of theoretical calculations, which provided clues to the effects of particle size, size distribution, magnetic field, frequency and reaction medium. Materials of theoretically optimal size were synthesized, functionalized, and their effects in the oscillating magnetic field were subsequently investigated. Under our conditions, the materials that clustered e.g. silica-coated and PNIPAM-coated iron oxides exhibited the highest heat generation, while iron oxides embedded in MSNs and mesoporous iron oxides exhibited the least bulk heating. It is worth noting that the specific loss power of PNIPAM-coated Fe{sub 3}O{sub 4} was peculiarly high, and the heat loss mechanism of this material remains to be elucidated. Since thermocatalysis is a long-term goal of this project, we also investigated the effects of the oscillating magnetic field system for the synthesis of 7-hydroxycoumarin-3-carboxylic acid. Application of an oscillating magnetic field in the presence of magnetic particles with high thermal response was found to effectively increase the reaction rate of the uncatalyzed synthesis of the coumarin derivative compared to the room temperature control.
Calculation of electromagnetic forces for magnet wheels
Ogawa, Kokichi; Horiuchi, Yoko; Fujii, Nobuo
1997-03-01
The characteristics of magnet wheels for magnetic levitation and linear drives are investigated by using a three-dimensional computer simulation. Magnet wheels levitate by revolving permanent magnets over a conducting plate, in which the eddy currents are induced. The thrust is also produced by making the torque unbalance. This paper deals with the ``partial overlap type`` magnet wheels, producing the lift force and the thrust. The magnetic flux density and eddy currents are examined for the 4-pole and the 2-pole structures.
Magnetic helicity in magnetohydrodynamic turbulence with a mean magnetic field
Oughton, Sean
Magnetic helicity in magnetohydrodynamic turbulence with a mean magnetic field Troy Stribling The magnetichelicity (H,) of the fluctuating magnetic field is a measure,which has proven important in the de magneticfield H,,, may be definedby Hnl=(a-b), (1) where b is the fluctuating magnetic field, b=V xa defines
Indoor localization using magnetic fields
NASA Astrophysics Data System (ADS)
Pathapati Subbu, Kalyan Sasidhar
Indoor localization consists of locating oneself inside new buildings. GPS does not work indoors due to multipath reflection and signal blockage. WiFi based systems assume ubiquitous availability and infrastructure based systems require expensive installations, hence making indoor localization an open problem. This dissertation consists of solving the problem of indoor localization by thoroughly exploiting the indoor ambient magnetic fields comprising mainly of disturbances termed as anomalies in the Earth's magnetic field caused by pillars, doors and elevators in hallways which are ferromagnetic in nature. By observing uniqueness in magnetic signatures collected from different campus buildings, the work presents the identification of landmarks and guideposts from these signatures and further develops magnetic maps of buildings - all of which can be used to locate and navigate people indoors. To understand the reason behind these anomalies, first a comparison between the measured and model generated Earth's magnetic field is made, verifying the presence of a constant field without any disturbances. Then by modeling the magnetic field behavior of different pillars such as steel reinforced concrete, solid steel, and other structures like doors and elevators, the interaction of the Earth's field with the ferromagnetic fields is described thereby explaining the causes of the uniqueness in the signatures that comprise these disturbances. Next, by employing the dynamic time warping algorithm to account for time differences in signatures obtained from users walking at different speeds, an indoor localization application capable of classifying locations using the magnetic signatures is developed solely on the smart phone. The application required users to walk short distances of 3-6 m anywhere in hallway to be located with accuracies of 80-99%. The classification framework was further validated with over 90% accuracies using model generated magnetic signatures representing 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.
Black holes and magnetic fields
J. Bicak; V. Karas; T. Ledvinka
2007-04-09
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.
Magnetic Fields in Spiral Galaxies
Beck, Rainer
2015-01-01
Radio synchrotron emission is a powerful tool to study the strength and structure of magnetic fields in galaxies. Unpolarized synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30\\mu G) and in central starburst regions (50-100\\mu G). Such fields are dynamically important; they affect gas flows and drive gas inflows in central regions. Polarized emission traces ordered fields, which can be regular or anisotropic turbulent, where the latter originates from isotropic turbulent fields by the action of compression or shear. The strongest ordered fields (10-15\\mu G) are generally found in interarm regions. In galaxies with strong density waves, ordered fields are also observed at the inner edges of spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions. Ordered fields in interacting galaxies have asymmetric distributions and are a tracer of past interactions between galaxies or with the interg...
Acceleration and Particle Field Interactions of Cosmic Rays II: Calculations
A. Tawfik; A. Saleh; M. T. Ghoneim; A. Hady
2010-10-28
Based on the generic acceleration model, which suggests different types of electromagnetic interactions between the cosmic charged particles and the different configurations of the electromagnetic (plasma) fields, the ultra high energy cosmic rays are studied. The plasma fields are assumed to vary, spatially and temporally. The well-known Fermi accelerations are excluded. Seeking for simplicity, it is assumed that the energy loss due to different physical processes is negligibly small. The energy available to the plasma sector is calculated in four types of electromagnetic fields. It has been found that the drift in a time--varying magnetic field is extremely energetic. The energy scale widely exceeds the Greisen-Zatsepin-Kuzmin (GZK) cutoff. The polarization drift in a time--varying electric field is also able to raise the energy of cosmic rays to an extreme value. It can be compared with the Hillas mechanism. The drift in a spatially--varying magnetic field is almost as strong as the polarization drift. The curvature drift in a non--uniform magnetic field and a vanishing electric field is very weak.
Generation of helical magnetic fields from inflation
Rajeev Kumar Jain; Ruth Durrer; Lukas Hollenstein
2012-04-11
The generation of helical magnetic fields during single field inflation due to an axial coupling of the electromagnetic field to the inflaton is discussed. We find that such a coupling always leads to a blue spectrum of magnetic fields during slow roll inflation. Though the helical magnetic fields further evolve during the inverse cascade in the radiation era after inflation, we conclude that the magnetic fields generated by such an axial coupling can not lead to observed field strength on cosmologically relevant scales.
Magnetic field line lengths inside interplanetary magnetic flux ropes
NASA Astrophysics Data System (ADS)
Hu, Qiang; Qiu, Jiong; Krucker, Sam
2015-07-01
We report on the detailed and systematic study of field line twist and length distributions within magnetic flux ropes embedded in interplanetary coronal mass ejections (ICMEs). The Grad-Shafranov reconstruction method is utilized together with a constant-twist nonlinear force-free (Gold-Hoyle) flux rope model to reveal the close relation between the field line twist and length in cylindrical flux ropes, based on in situ Wind spacecraft measurements. We show that the field line twist distributions within interplanetary flux ropes are inconsistent with the Lundquist model. In particular, we utilize the unique measurements of magnetic field line lengths within selected ICME events as provided by Kahler et al. () based on energetic electron burst observations at 1 AU and the associated type III radio emissions detected by the Wind spacecraft. These direct measurements are compared with our model calculations to help assess the flux rope interpretation of the embedded magnetic structures. By using the different flux rope models, we show that the in situ direct measurements of field line lengths are consistent with a flux rope structure with spiral field lines of constant and low twist, largely different from that of the Lundquist model, especially for relatively large-scale flux ropes.
Applied magnetic field design for the field reversed configuration compression heating experiment.
Domonkos, M T; Amdahl, D; Camacho, J F; Coffey, S K; Degnan, J H; Delaney, R; Frese, M; Gale, D; Grabowski, T C; Gribble, R; Intrator, T P; McCullough, J; Montano, N; Robinson, P R; Wurden, G
2013-04-01
Detailed calculations of the formation, guide, and mirror applied magnetic fields in the FRC compression-heating experiment (FRCHX) were conducted using a commercially available generalized finite element solver, COMSOL Multiphysics(®). In FRCHX, an applied magnetic field forms, translates, and finally captures the FRC in the liner region sufficiently long to enable compression. Large single turn coils generate the fast magnetic fields necessary for FRC formation. Solenoidal coils produce the magnetic field for translation and capture of the FRC prior to liner implosion. Due to the limited FRC lifetime, liner implosion is initiated before the FRC is injected, and the magnetic flux that diffuses into the liner is compressed. Two-dimensional axisymmetric magnetohydrodynamic simulations using MACH2 were used to specify optimal magnetic field characteristics, and this paper describes the simulations conducted to design magnetic field coils and compression hardware for FRCHX. This paper presents the vacuum solution for the magnetic field. PMID:23635196
Electrical Conductance under Periodic Magnetic Field
NASA Astrophysics Data System (ADS)
Sasaki, Takahiko; Fukuyama, Hidetoshi
2002-04-01
The resistivity due to Coulomb interaction of two-dimensional electron gas under spatially alternating magnetic field has been calculated based on the Kubo formula. It is found that, in the presence of disorder, the interplay between the periodic potential and the Coulomb interactions results in a T2-term in the Drude conductance, which is not due to the Umklapp scattering. The results are in reasonable agreement with experiments by Kato et al. [J. Phys. Soc. Jpn. 68 (1999) 1492].
Early Magnetic Field Observations from HMI
Jon Todd Hoeksema
2010-01-01
The Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) is beginning to produce a synoptic series of full-disk arc-second resolution magnetograms. Line-of-sight magnetograms are available every 45 seconds and the vector field will be routinely calculated every 12 minutes in automatically identified active region patches. Select quick-look products are available within minutes and definitive science data will
Self-Consistent Field Calculations Spreadsheet
NSDL National Science Digital Library
A Self-Consistent Field Calculations Spreadsheet can help your students understand the self-consistent field (SCF) procedure, typically presented in an undergraduate physical chemistry course. The spreadsheet helps students easily perform SCF calculations on a two-electron atom and see graphically how the proper solution is obtained. It is also possible for more advanced students to apply this spreadsheet to more ambitious systems. The wave function for the two-electron atom is assumed to be a product of two identical one-electron orbital functions. The system is assumed to be a spin-singlet so that only the spatial functions need to be considered here. The SCF procedure involves two repeated steps. First, using a guess for the orbital function, an effective potential is generated. Second, with this effective potential, the differential equation for the orbital function is solved. The new orbital function is used to generate a new effective potential, which is then used to generate a newer orbital function. The procedure is repeated until successive orbital functions are considered to be close enough to each other. A Self-Consistent Field Calculations Spreadsheet file contains two spreadsheets. The first is the one described in the associated article (1). It performs the calculation with relatively simple approximations and numerical methods, and serves to illustrate the SCF procedure for the student. The second presents a more sophisticated calculation that may be of interest to more advanced students.
CALCULATIONS FOR A MERCURY JET TARGET IN A SOLENOID MAGNET CAPTURE SYSTEM.
GALLARDO, J.; KAHN, S.; PALMER, R.B.; THIEBERGER, P.; WEGGEL, R.J.; MCDONALD, K.
2001-06-18
A mercury jet is being considered as the production target for a muon storage ring facility to produce an intense neutrino beam. A 20 T solenoid magnet that captures pions for muon production surrounds the mercury target. As the liquid metal jet enters or exits the field eddy currents are induced. We calculate the effects that a liquid metal jet experiences in entering and exiting the magnetic field for the magnetic configuration considered in the Neutrino Factory Feasibility Study II.
Effects of non-linearities on magnetic field generation
Nalson, Ellie; Malik, Karim A.; Christopherson, Adam J. E-mail: achristopherson@gmail.com
2014-09-01
Magnetic fields are present on all scales in the Universe. While we understand the processes which amplify the fields fairly well, we do not have a ''natural'' mechanism to generate the small initial seed fields. By using fully relativistic cosmological perturbation theory and going beyond the usual confines of linear theory we show analytically how magnetic fields are generated. This is the first analytical calculation of the magnetic field at second order, using gauge-invariant cosmological perturbation theory, and including all the source terms. To this end, we have rederived the full set of governing equations independently. Our results suggest that magnetic fields of the order of 10{sup -30}- 10{sup -27} G can be generated (although this depends on the small scale cut-off of the integral), which is largely in agreement with previous results that relied upon numerical calculations. These fields are likely too small to act as the primordial seed fields for dynamo mechanisms.
Levitation and agglomeration of magnetic grains in a complex (dusty) plasma with magnetic field
NASA Astrophysics Data System (ADS)
Samsonov, D.; Zhdanov, S.; Morfill, G.; Steinberg, V.
2003-03-01
Interaction of magnetic particles with each other and with a magnetic field was studied experimentally in a complex plasma. Monodisperse plastic microspheres with magnetic filler were suspended in an rf symmetrically driven discharge to form a multilayer dust cloud. The magnetic field induced a magnetic moment in the grains. The particles were pulled upward in the direction of the magnetic field gradient and their levitation height increased. This was used as a new diagnostic method to calculate the particle charge and the thickness of the plasma sheath. It was demonstrated that the particle weight can be compensated for. Some particles formed agglomerates due to magnetic attraction between the grains. Analysis of the particle interaction forces showed that at intermediate magnetic fields (used in the experiment) the particles can agglomerate only if their kinetic energy is high enough to overcome the barrier in the interaction potential. The possibility of magnetically induced formation of a plasma crystal was discussed.
Modeling Magnetic Fields with FEMM 3.1
NASA Astrophysics Data System (ADS)
Gumbart, James
2003-03-01
FEMM (Finite Element Method Magnetics) 3.1, a freeware program, is useful for modeling problems involving magnets, currents and magnetic fields. The applications of such a program involve both education and upper-level research. The program interface is intuitive and robust. As an educational tool, this program is useful because it handles internally the complicated equations needed to be solved when working with magnetism in matter. Since most elementary applications of magnetism involve permanent magnets, this program enables the user to calculate field energies and forces between magnets and magnetic materials, which would otherwise be impossible to obtain. An analysis of a popular physics demonstration, that of a diamagnetic-assisted levitating magnet, will be used to illustrate these concepts in more detail. The sensitivity of the equilibrium points to the spacing of the diamagnetic plates and the position of the upper attracting magnet is well-reproduced in this simulation.
Electromagnetic radiation by quark-gluon plasma in magnetic field
Kirill Tuchin
2012-06-03
The electromagnetic radiation by quark-gluon plasma in strong magnetic field is calculated. The contributing processes are synchrotron radiation and one--photon annihilation. It is shown that in relativistic heavy--ion collisions at RHIC and LHC synchrotron radiation dominates over the annihilation. Moreover, it constitutes a significant part of all photons produced by the plasma at low transverse momenta; its magnitude depends on the plasma temperature and the magnetic field strength. Electromagnetic radiation in magnetic field is probably the missing piece that resolves a discrepancy between the theoretical models and the experimental data. It is argued that electromagnetic radiation increases with the magnetic field strength and plasma temperature.
Measurement and calculation of forces in a magnetic journal bearing actuator
NASA Technical Reports Server (NTRS)
Knight, Josiah; Mccaul, Edward; Xia, Zule
1991-01-01
Numerical calculations and experimental measurements of forces from an actuator of the type used in active magnetic journal bearings are presented. The calculations are based on solution of the scalar magnetic potential field in and near the gap regions. The predicted forces from single magnet with steady current are compared with experimental measurements in the same geometry. The measured forces are smaller than calculated ones in the principal direction but are larger than calculated in the normal direction. This combination of results indicate that material and spatial effects other than saturation play roles in determining the force available from an actuator.
EXPLORER 10 MAGNETIC FIELD MEASUREMENTS
J. P. Heppner; N. F. Ness; C. S. Scearce; T. L. Skillman
1963-01-01
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
Magnetic monopoles in 4D: a perturbative calculation
Arsen Khvedelidze; Alex Kovner; David McMullan
2005-12-13
We address the question of defining the second quantised monopole creation operator in the 3+1 dimensional Georgi-Glashow model, and calculating its expectation value in the confining phase. Our calculation is performed directly in the continuum theory within the framework of perturbation theory. We find that, although it is possible to define the "coherent state" operator M(x) that creates the Coulomb magnetic field, the dependence of this operator on the Dirac string does not disappear even in the nonabelian theory. This is due to the presence of the charged fields (W^{\\pm}). We also set up the calculation of the expectation value of this operator in the confining phase and show that it is not singular along the Dirac string. We find that in the leading order of the perturbation theory the VEV vanishes as a power of the volume of the system. This is in accordance with our naive expectation. We expect that nonperturbative effects will introduce an effective infrared cutoff on the calculation making the VEV finite.
Behavior of small ferromagnetic particles in traveling magnetic field
NASA Astrophysics Data System (ADS)
Deych, V. G.; Terekhov, V. P.
1985-03-01
Forces and moments acting on a magnetizable body in a traveling magnetic field are calculated for a body with dimensions much smaller than the wavelength of the magnetic field. It is assumed that a particle of given linear dimension does not have a constant magnetic moment. The material of a particle is characterized by its magnetic permeability and electrical conductivity. The hypothesis that rotation plays a major role in the behavior of small particles is confirmed and the fact that a small particle rolls on a plane, without sliding, when the surface is perfectly rough, in the opposite direction from which the magnetic field travels is explained. Calculations are based on the magnetohydrodynamic equations for a quasi steady magnetic field, and the induced Foucault eddy currents are considered. The results are applicable to transport of ferrofluids and to such metallurgical devices as separators.
Jupiter's magnetic field and magnetosphere
NASA Technical Reports Server (NTRS)
Acuna, M. H.; Behannon, K. W.; Connerney, J. E. P.
1983-01-01
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.
Strangelets under strong magnetic fields
E. Lopez Fune; A. Perez Martinez
2012-03-16
In this thesis is studied three of the fundamental properties of clusters of matter made of quarks u, d and s called strangelets: the energy per baryon, the radius and the electric charge, all in the presence of intense magnetic fields and finite temperature. Two cases will take our attention: unpaired phase strangelets, where there is no restriction to the number of flavors of quarks, and a particular case of the color superconducting phase, where exists a restriction to the quark numbers and an additional energy gap. We study the stability of strangelets, measured by the energy per baryon, to compare later with that of the 56Fe : the most stable isotope known in nature. We employ the Liquid Drop formalism of the Bag Model MIT to describe the interaction between quarks. We conclude that the field effects tend to decrease the energy per baryon of strangelets and temperature produces the opposite effect. It is also shown that strangelets in the color superconducting phase are more stable than those in the unpaired phase for an energy gap of about 100MeV. The radius of strangelets shows an analogous behavior with the baryon number, as that of the nuclei, and shows small variations with the magnetic field and temperature. It is obtained that the presence of magnetic fields modify the values of the electric charge regarding the non-magnetized case, being these higher (lower) for strangelets in the unpaired phase (superconducting).
Crystal field and magnetic properties
NASA Technical Reports Server (NTRS)
Flood, D. J.
1977-01-01
Magnetization and magnetic susceptibility measurements have been made in the temperature range 1.3 to 4.2 K on powdered samples of ErH3. The susceptibility exhibits Curie-Weiss behavior from 4.2 to 2 K, and intercepts the negative temperature axis at theta = 1.05 + or - 0.05 K, indicating that the material is antiferromagnetic. The low field effective moment is 6.77 + or - 0.27 Bohr magnetons per ion. The magnetization exhibits a temperature independent contribution, the slope of which is (5 + or - 1.2) x 10 to the -6th Weber m/kg Tesla. The saturation moment is 3.84 + or - 1 - 0.15 Bohr magnetons per ion. The results can be qualitatively explained by the effects of crystal fields on the magnetic ions. No definitive assignment of a crystal field ground state can be given, nor can a clear choice between cubically or hexagonally symmetric crystal fields be made. For hexagonal symmetry, the first excited state is estimated to be 86 to 100 K above the ground state. For cubic symmetry, the splitting is on the order of 160 to 180 K.
NASA Astrophysics Data System (ADS)
Chapman, Nicholas L.; Goldsmith, P.; Clemens, D.
2010-01-01
In order to study the role magnetic fields play in molecular clouds and star formation, we present optical and infrared polarization measurements in Taurus. The optical data have been previously published by Heiles (2000), although the infrared data are new. The optical polarization data show a remarkable correlation with our CO maps (Goldsmith et al. 2008), suggesting that the dust, which produces the polarization, and the gas, which has most of the mass, are coupled. With our 12CO and 13CO we are able to make reliable estimates of the cloud density. These densities are necessary for our estimates the plane-of-sky magnetic field strength using both Chandrasekhar-Fermi and the recent method described in Hildebrand et al. (2009). Both methods produce similar estimates for the magnetic field strength, though the Hildebrand results are typically larger. Lastly we compare the polarization percentage and magnetic field strength as a function of column density. This work was supported by the Jet Propulsion Laboratory, California Institute of Technology.
Forces in magnetic fluids subject to stationary magnetic fields
M. d'Aquino; G. Miano; C. Serpico; W. Zamboni; G. Coppola
2003-01-01
The problem of magnetic forces in magnetizable fluids is discussed and classical formulas for volume force density (Kelvin, Helmholtz) are reviewed. The general problem of hydrostatic equilibrium of a magnetic liquid subject to magnetic field is formulated. On the basis of this formulation, the displacement of a linear magnetic fluid subject to the field produced by sheet-shaped coils is numerically
Separation of magnetic field lines
Boozer, Allen H. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)
2012-11-15
The field lines of magnetic fields that depend on three spatial coordinates are shown to have a fundamentally different behavior from those that depend on two coordinates. Unlike two-coordinate cases, a flux tube in a magnetic field that depends on all three spatial coordinates that has a circular cross section at one location along the tube characteristically has a highly distorted cross section at other locations. In an ideal evolution of a magnetic field, the current densities typically increase. Crudely stated, if the current densities increase by a factor {sigma}, the ratio of the long to the short distance across a cross section of a flux tube characteristically increases by e{sup 2{sigma}}, and the ratio of the longer distance to the initial radius increases as e{sup {sigma}}. Electron inertia prevents a plasma from isolating two magnetic field structures on a distance scale shorter than c/{omega}{sub pe}, which is about 10 cm in the solar corona, and reconnection must be triggered if {sigma} becomes sufficiently large. The radius of the sun, R{sub Circled-Dot-Operator }=7 Multiplication-Sign 10{sup 10}cm is about e{sup 23} times larger, so when {sigma} Greater-Than-Or-Equivalent-To 23, two lines separated by c/{omega}{sub pe} at one location can be separated by the full scale of any magnetic structures in the corona at another. The conditions for achieving a large exponentiation, {sigma}, are derived, and the importance of exponentiation is discussed.
NASA Technical Reports Server (NTRS)
Mullan, D. J.
1974-01-01
The observed properties of solar magnetic fields are reviewed, with particular reference to the complexities imposed on the field by motions of the highly conducting gas. Turbulent interactions between gas and field lead to heating or cooling of the gas according to whether the field energy density is less or greater than the maximum kinetic energy density in the convection zone. The field strength above which cooling sets in is 700 gauss. A weak solar dipole field may be primeval, but dynamo action is also important in generating new flux. The dynamo is probably not confined to the convection zone, but extends throughout most of the volume of the sun. Planetary tides appear to play a role in driving the dynamo.
Radiation from Relativistic Shocks with Turbulent Magnetic Fields
NASA Technical Reports Server (NTRS)
Nishkawa, K.; Medvedev, M.; Zhang, B.; Hardee, P.; Niemiec, J.; Mizuno, A.; Nordlund, A.; Frederiksen, J.; Sol, H.; Pohl, M.; Hartmann, D. H.; Oka, M.; Fishman, J.
2009-01-01
Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs at shocked region. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the shock. The "jitter" radiation from deflected electrons in turbulent magnetic fields has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. New recent calculation of spectra with various different Lorentz factors of jets (two electrons) and initial magnetic fields. New spectra based on small simulations will be presented.
NASA Technical Reports Server (NTRS)
Acuna, M. H.; Ness, N. F.
1976-01-01
The paper is concerned mainly with the intrinsic planetary field which dominates the inner magnetosphere up to a distance of 10 to 12 Jovian radii where other phenomena, such as ring currents and diamagnetic effects of trapped charged particles, become significant. The main magnetic field of Jupiter as determined by in-situ observations by Pioner 10 and 11 is found to be relatively more complex than a simple offset tilted dipole. Deviations from a simple dipole geometry lead to distortions of the charged particle L shells and warping of the magnetic equator. Enhanced absorption effects associated with Io and Amalthea are predicted. The results are consistent with the conclusions derived from extensive radio observations at decimetric and decametric wavelengths for the planetary field.
New circumstellar magnetic field diagnostics
K. H. Nordsieck
2001-06-06
In this paper I will discuss new magnetic field diagnostics and instrumentation for an area of astrophysics where magnetic field observations have been difficult - circumstellar material. Such diagnostics would be particularly relevant to star formation and evolution. Stellar photosphere diagnostics include the Zeeman effect and atomic scattering diagnostics like the Hanle Effect and atomic alignment. The Zeeman Effect is in general not sensitive enough for the field strengths expected for circumstellar material, and it is easily defeated by Doppler broadening in a dynamic envelope. Atomic scattering diagnostics, pioneered recently for the Sun, are promising, but have never been applied outside the Sun. For the study of unresolved envelopes, the Hanle Effect may be applicable particularly in the ultraviolet. A medium resolution UV spectropolarimeter, for instance, would serve for such studies. Atomic alignment effects could utilize a ground-based, high signal-to-noise spectropolarimeter, with profile information from high spectral resolution. I will briefly mention several instrumentation development efforts in these directions.
Primordial Generation of Magnetic Fields
Arun Kumar Pandey; Jitesh R. Bhatt
2015-07-07
We reexamine generation of the primordial magnetic fields, at temperature $T>80$TeV, by applying a consistent kinetic theory framework which is suitably modified to take the quantum anomaly into account. The modified kinetic equation can reproduce the known quantum field theoretic results upto the leading orders. We show that our results qualitatively matches with the earlier results obtained using heuristic arguments. The modified kinetic theory can give the instabilities responsible for generation of the magnetic field due to chiral imbalance in two distinct regimes: a) when the collisions play a dominant role and b) when the primordial plasma can be regarded as collisionless. We argue that the instability developing in the collisional regime can dominate over the instability in the collisionless regime.
NASA Astrophysics Data System (ADS)
Iwai, Kazuhiko
2010-12-01
The alignment behavior of a crystal with a magnetic anisotropy of ?c < ?a under the imposition of a rotating magnetic field has been investigated by numerical calculation. The promotion of the crystal alignment when the projection of the magnetically hard axis on the magnetic field rotating plane is parallel to the magnetic field direction and its suppression when the magnetically hard axis is perpendicular to the magnetic field direction can be explained by the fact that the direction of the driving torque acting on the crystal minimizes the magnetic energy. Non dimensional alignment time normalized by the alignment time under the imposition of a static field is constant in the out-of-step region where the crystal cannot follow the magnetic field rotation during its alignment. The initial phase difference between the projection of the magnetically hard axis on the magnetic field rotating plane and its direction hardly affects the alignment time in the out-of-step region but strongly affects that in the synchronous region where the crystal rotation synchronous with the magnetic field rotation. A crystal aligns quickly if the initial phase difference is between 0 and 90° in the synchronous region. The minimum alignment time is the same as that under the imposition of a static field.
Magnetic Field in the Gravitationally Stratified Coronal Loops
NASA Astrophysics Data System (ADS)
Dwivedi, B. N.; Srivastava, A. K.
2015-03-01
We study the effect of gravitational stratification on the estimation of magnetic fields in the coronal loops. By using the method of MHD seismology of kink waves for the estimation of magnetic field of coronal loops, we derive a new formula for the magnetic field considering the effect of gravitational stratification. The fast-kink wave is a potential diagnostic tool for the estimation of magnetic field in fluxtubes. We consider the eleven kink oscillation cases observed by TRACE between July 1998 and June 2001. We calculate magnetic field in the stratified loops ( B str) and compare them with the previously calculated absolute magnetic field ( B abs). The gravitational stratification efficiently affects the magnetic field estimation in the coronal loops as it affects also the properties of kink waves. We find ?22% increment in the magnetic field for the smallest ( L = 72 Mm) while ? 42% increment in the absolute magnetic field for the longest ( L = 406 Mm) coronal loops. The magnetic fields B str and B abs also increase with the number density, if the loop length does not vary much. The increment in the magnetic field due to gravitational stratification is small at the lower number densities, however, it is large at the higher number densities. We find that damping time of kink waves due to phase-mixing is less in the case of gravitationally stratified loops compared to nonstratified ones. This indicates the more rapid damping of kink waves in the stratified loops. In conclusion, we find that the gravitational stratification efficiently affects the estimation of magnetic field and damping time estimation especially in the longer coronal loops.
Bacterial Growth in Weak Magnetic Field
NASA Astrophysics Data System (ADS)
Masood, Samina
2015-03-01
We study the growth of bacteria in a weak magnetic field. Computational analysis of experimental data shows that the growth rate of bacteria is affected by the magnetic field. The effect of magnetic field depends on the strength and type of magnetic field. It also depends on the type of bacteria. We mainly study gram positive and gram negative bacteria of rod type as well as spherical bacteria. Preliminary results show that the weak magnetic field enhances the growth of rod shape gram negative bacteria. Gram positive bacteria can be even killed in the inhomogeneous magnetic field.
Magnetic field-line lengths inside interplanetary magnetic flux ropes
Hu, Qiang; Krucker, Sam
2015-01-01
We report on the detailed and systematic study of field-line twist and length distributions within magnetic flux ropes embedded in Interplanetary Coronal Mass Ejections (ICMEs). The Grad-Shafranov reconstruction method is utilized together with a constant-twist nonlinear force-free (Gold-Hoyle) flux rope model to reveal the close relation between the field-line twist and length in cylindrical flux ropes, based on in-situ Wind spacecraft measurements. We show that the field-line twist distributions within interplanetary flux ropes are inconsistent with the Lundquist model. In particular we utilize the unique measurements of magnetic field-line lengths within selected ICME events as provided by Kahler et al. (2011) based on energetic electron burst observations at 1 AU and the associated type III radio emissions detected by the Wind spacecraft. These direct measurements are compared with our model calculations to help assess the flux-rope interpretation of the embedded magnetic structures. By using the differen...
Collisionless reconnection: magnetic field line interaction
NASA Astrophysics Data System (ADS)
Treumann, R. A.; Baumjohann, W.; Gonzalez, W. D.
2012-10-01
Magnetic field lines are quantum objects carrying one quantum ?0 = 2?h/e of magnetic flux and have finite radius ?m. Here we argue that they possess a very specific dynamical interaction. Parallel field lines reject each other. When confined to a certain area they form two-dimensional lattices of hexagonal structure. We estimate the filling factor of such an area. Anti-parallel field lines, on the other hand, attract each other. We identify the physical mechanism as being due to the action of the gauge potential field, which we determine quantum mechanically for two parallel and two anti-parallel field lines. The distortion of the quantum electrodynamic vacuum causes a cloud of virtual pairs. We calculate the virtual pair production rate from quantum electrodynamics and estimate the virtual pair cloud density, pair current and Lorentz force density acting on the field lines via the pair cloud. These properties of field line dynamics become important in collisionless reconnection, consistently explaining why and how reconnection can spontaneously set on in the field-free centre of a current sheet below the electron-inertial scale.
First-principles calculations of magnetic circular dichroism spectra.
Ganyushin, Dmitry; Neese, Frank
2008-03-21
An elaborate approach for the prediction of magnetic circular dichroism (MCD) spectra in the framework of highly correlated multiconfigurational ab initio methods is presented. The MCD transitions are computed by the explicit treatment of spin-orbit coupled (SOC) and spin-spin coupled (SSC) N-electron states. These states are obtained from the diagonalization of the SOC and SSC operators along with the spin and orbital Zeeman operators in the basis of a preselected number of roots of the spin-free Hamiltonian. Therefore, zero-field splittings due to the SOC and SSC interactions along with the magnetic field splittings are explicitly accounted for in the ground as well as the excited states. This makes it possible to calculate simultaneously all MCD A, B, and C terms even beyond the linear response limit. The SOC is computed using a multicenter mean-field approximation to the Breit-Pauli Hamiltonian. Two-electron SSC terms are included in the treatment without further approximations. The MCD transition intensities are subjected to numerical orientational averaging in order to treat the most commonly encountered case of randomly oriented molecules. The simulated MCD spectra for the OH, NH, and CH radicals as well as for [Fe(CN)(6)](3-) are in good agreement with the experimental spectra. In the former case, the significant effects of the inert gas matrices in which the experimental spectra were obtained were modeled in a phenomenological way. PMID:18361564
Magnetic-field generation and electron acceleration in relativistic laser channel
is calculated and related to the amount of the absorbed energy. Absorbed energy and generated magnetic fieldMagnetic-field generation and electron acceleration in relativistic laser channel I. Yu. Kostyukov lasermatter interaction is the generation of ultra-strong magnetic fields in the plasma.610 Magnetic
Low-frequency fluctuations in plasma magnetic fields
Cable, S.; Tajima, T.
1992-02-01
It is shown that even a non-magnetized plasma with temperature T sustains zero-frequency magnetic fluctuations in thermal equilibrium. Fluctuations in electric and magnetic fields, as well as in densities, are computed. Four cases are studied: a cold, gaseous, isotropic, non-magnetized plasma; a cold, gaseous plasma in a uniform magnetic field; a warm, gaseous plasma described by kinetic theory; and a degenerate electron plasma. For the simple gaseous plasma, the fluctuation strength of the magnetic field as a function of frequency and wavenumber is calculated with the aid of the fluctuation-dissipation theorem. This calculation is done for both collisional and collisionless plasmas. The magnetic field fluctuation spectrum of each plasma has a large zero-frequency peak. The peak is a Dirac {delta}-function in the collisionless plasma; it is broadened into a Lorentzian curve in the collisional plasma. The plasma causes a low frequency cutoff in the typical black-body radiation spectrum, and the energy under the discovered peak approximates the energy lost in this cutoff. When the imposed magnetic field is weak, the magnetic field were vector fluctuation spectra of the two lowest modes are independent of the strength of the imposed field. Further, these modes contain finite energy even when the imposed field is zero. It is the energy of these modes which forms the non-magnetized zero-frequency peak of the isotropic plasma. In deriving these results, a simple relationship between the dispersion relation and the fluctuation power spectrum of electromagnetic waves if found. The warm plasma is shown, by kinetic theory, to exhibit a zero-frequency peak in its magnetic field fluctuation spectrum as well. For the degenerate plasma, we find that electric field fluctuations and number density fluctuations vanish at zero frequency; however, the magnetic field power spectrum diverges at zero frequency.
Thermal evolution of neutron stars with decaying magnetic fields
NASA Astrophysics Data System (ADS)
Wei, Wei; Zheng, Xiao-Ping; Liu, Xi-Wei
2015-09-01
Rotochemical heating originates in the deviation from beta equilibrium due to spin-down compression, which is closely related to the dipole magnetic field. We numerically calculate the deviation from chemical equilibrium and thermal evolution of neutron stars with decaying magnetic fields. We find that the power-law long term decay of the magnetic field slightly affects the deviation from chemical equilibrium and surface temperature. However, the magnetic decay leads to older neutron stars that could have a different surface temperature with the same magnetic field strength. That is, older neutron stars with a low magnetic field (108 G) could have a lower temperature even with rotochemical heating in operation, which probably explains the lack of other observations on older millisecond pulsars with higher surface temperature, except millisecond pulsar J0437–4715.
MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. I. FORCE-FREE MAGNETIC FIELDS B. Fornberg,2
Fornberg, Bengt
MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. I. FORCE-FREE MAGNETIC FIELDS N. Flyer,1 B Axisymmetric force-free magnetic fields external to a unit sphere are studied as solutions to boundary value to the formation of an azimuthal rope of twisted magnetic field embedded within the global field, and to the energy
Radiative instabilities in sheared magnetic field
NASA Technical Reports Server (NTRS)
Drake, J. F.; Sparks, L.; Van Hoven, G.
1988-01-01
The structure and growth rate of the radiative instability in a sheared magnetic field B have been calculated analytically using the Braginskii fluid equations. In a shear layer, temperature and density perturbations are linked by the propagation of sound waves parallel to the local magnetic field. As a consequence, density clumping or condensation plays an important role in driving the instability. Parallel thermal conduction localizes the mode to a narrow layer where K(parallel) is small and stabilizes short wavelengths k larger-than(c) where k(c) depends on the local radiation and conduction rates. Thermal coupling to ions also limits the width of the unstable spectrum. It is shown that a broad spectrum of modes is typically unstable in tokamak edge plasmas and it is argued that this instability is sufficiently robust to drive the large-amplitude density fluctuations often measured there.
Modified methods of stellar magnetic field measurements
NASA Astrophysics Data System (ADS)
Kholtygin, A. F.
2014-12-01
The standard methods of the magnetic field measurement, based on an analysis of the relation between the Stokes V-parameter and the first derivative of the total line profile intensity, were modified by applying a linear integral operator \\hat{L} to both sides of this relation. As the operator \\hat{L}, the operator of the wavelet transform with DOG-wavelets is used. The key advantage of the proposed method is an effective suppression of the noise contribution to the line profile and the Stokes parameter V. The efficiency of the method has been studied using model line profiles with various noise contributions. To test the proposed method, the spectropolarimetric observations of the A0 star ?2 CVn, the Of?p star HD 148937, and the A0 supergiant HD 92207 were used. The longitudinal magnetic field strengths calculated by our method appeared to be in good agreement with those determined by other methods.
Magnetic field generated resistivity maximum in graphite
NASA Technical Reports Server (NTRS)
Wollam, J. A.; Kreps, L. W.; Rojeski, M.; Vold, T.; Devaty, R.
1976-01-01
In zero magnetic field, B, the electrical resistivity, rho(O,T) of highly oriented pyrolytic (polycrystalline) graphite drops smoothly with decreasing T, becoming constant below 4 K. However, in a fixed applied magnetic field B, the resistivity rho(B,T) goes through a maximum as a function of T, with larger maximum for larger B. The temperature of the maximum increases with B, but saturates to a constant value near 25 K (exact T depends on sample) at high B. In single crystal graphite a maximum in rho(B,T) as a function of T is also present, but has the effects of Landau level quantization superimposed. Several possible explanations for the rho(B,T) maximum are proposed, but a complete explanation awaits detailed calculations involving the energy band structure of graphite, and the particular scattering mechanisms involved.
Measurements of Solar Vector Magnetic Fields
NASA Technical Reports Server (NTRS)
Hagyard, M. J. (editor)
1985-01-01
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.
Anisotropic Magnetism in Field-Structured Composites
Anderson, Robert A.; Martin, James E.; Odinek, Judy; Venturini, Eugene
1999-06-24
Magnetic field-structured-composites (FSCs) are made by structuring magnetic particle suspensions in uniaxial or biaxial (e.g. rotating) magnetic fields, while polymerizing the suspending resin. A uniaxial field produces chain-like particle structures, and a biaxial field produces sheet-like particle structures. In either case, these anisotropic structures affect the measured magnetic hysteresis loops, with the magnetic remanence and susceptibility increased significantly along the axis of the structuring field, and decreased slightly orthogonal to the structuring field, relative to the unstructured particle composite. The coercivity is essentially unaffected by structuring. We present data for FSCs of magnetically soft particles, and demonstrate that the altered magnetism can be accounted for by considering the large local fields that occur in FSCs. FSCS of magnetically hard particles show unexpectedly large anisotropies in the remanence, and this is due to the local field effects in combination with the large crystalline anisotropy of this material.
What Are Electric and Magnetic Fields? (EMF)
What are Electric and Magnetic Fields? (EMF) Electric and Magnetic Fields Electricity is an essential part of our lives. Electricity powers all sorts of things around us, from computers to refrigerators ...
Plasma stability in a dipole magnetic field
Simakov, Andrei N., 1974-
2001-01-01
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 ...
NASA Astrophysics Data System (ADS)
Anderson, Brian J.; Acuña, Mario H.; Korth, Haje; Slavin, James A.; Uno, Hideharu; Johnson, Catherine L.; Purucker, Michael E.; Solomon, Sean C.; Raines, Jim M.; Zurbuchen, Thomas H.; Gloeckler, George; McNutt, Ralph L.
2010-05-01
The magnetic field strength of Mercury at the planet’s surface is approximately 1% that of Earth’s surface field. This comparatively low field strength presents a number of challenges, both theoretically to understand how it is generated and observationally to distinguish the internal field from that due to the solar wind interaction. Conversely, the small field also means that Mercury offers an important opportunity to advance our understanding both of planetary magnetic field generation and magnetosphere-solar wind interactions. The observations from the Mariner 10 magnetometer in 1974 and 1975, and the MESSENGER Magnetometer and plasma instruments during the probe’s first two flybys of Mercury on 14 January and 6 October 2008, provide the basis for our current knowledge of the internal field. The external field arising from the interaction of the magnetosphere with the solar wind is more prominent near Mercury than for any other magnetized planet in the Solar System, and particular attention is therefore paid to indications in the observations of deficiencies in our understanding of the external field. The second MESSENGER flyby occurred over the opposite hemisphere from the other flybys, and these newest data constrain the tilt of the planetary moment from the planet’s spin axis to be less than 5°. Considered as a dipole field, the moment is in the range 240 to 270 nT- R {M/3}, where R M is Mercury’s radius. Multipole solutions for the planetary field yield a smaller dipole term, 180 to 220 nT- R {M/3}, and higher-order terms that together yield an equatorial surface field from 250 to 290 nT. From the spatial distribution of the fit residuals, the equatorial data are seen to reflect a weaker northward field and a strongly radial field, neither of which can be explained by a centered-dipole matched to the field measured near the pole by Mariner 10. This disparity is a major factor controlling the higher-order terms in the multipole solutions. The residuals are not largest close to the planet, and when considered in magnetospheric coordinates the residuals indicate the presence of a cross-tail current extending to within 0.5 R M altitude on the nightside. A near-tail current with a density of 0.1 ?A/m2 could account for the low field intensities recorded near the equator. In addition, the MESSENGER flybys include the first plasma observations from Mercury and demonstrate that solar wind plasma is present at low altitudes, below 500 km. Although we can be confident in the dipole-only moment estimates, the data in hand remain subject to ambiguities for distinguishing internal from external contributions. The anticipated observations from orbit at Mercury, first from MESSENGER beginning in March 2011 and later from the dual-spacecraft BepiColombo mission, will be essential to elucidate the higher-order structure in the magnetic field of Mercury that will reveal the telltale signatures of the physics responsible for its generation.
Y. Kamide; A. D. Richmond; S. Matsushita
1981-01-01
An approximate method of separating the effects of ionospheric currents from those of field-aligned currents in ground magnetic perturbations observed in high latitudes is developed. The distribution of ionospheric electric fields can also be estimated. The procedure includes the following steps: (1) the calculation of the equivalent ionospheric current function on the basis of magnetic H and D component records
Absorbed dose calculations for the Ignitor tokamak magnet coils insulator
NASA Astrophysics Data System (ADS)
Rollet, S.; Angelone, M.; Batistoni, P.
2000-05-01
The Ignitor experiment is an advanced compact high magnetic field tokamak with cryogenically cooled (30 K) normal conductor magnets. Its main purpose is to produce deuterium-tritium plasma regimes where ignition can take place. From the neutronics point of view, the routine operations with 50% of tritium will lead to a very short (4 s) but intense emission of 14 MeV neutrons (up to 3×1019 n/s). The capability of the boron-free glass reinforced epoxy resin presently adopted for the insulation of the coils conductor to withstand the severe irradiation condition could be a key issue in the performance, reliability and lifespan of Ignitor. In order to better know the radiation environment in which the insulators will operate, calculations of the absorbed dose are performed using the parallelized version of MCNP-4B Monte Carlo code. A detailed 3D geometry description of the tokamak, an accurate representation of the neutron source distribution together with the more recent version of transport cross-section libraries EFF (European Fusion File) are used in this work. The variation of calculated dose depending on the insulator position inside the device, on the neutron energy spectra and on the total number of neutrons produced over the scheduled machine lifetime are discussed in the present paper.
Absolute negative conductivity of graphene with impurities in magnetic field
Belonenko, M. B.; Lebedev, N. G.; Yanyushkina, N. N.; Shakirzyanov, M. M.
2011-05-15
Current-voltage and current-field characteristics for graphene with Anderson interaction of conduction and impurity electrons are calculated by the 'average electron' method in the case of low temperatures. These characteristics are analyzed depending on the frequency of an external ac electric field and a magnetic field. A portion with absolute negative conductivity is detected.
Neutral ? meson in a strong magnetic field in the SU(2) lattice gauge theory
NASA Astrophysics Data System (ADS)
Luschevskaya, E. V.; Larina, O. V.
2014-02-01
The correlation functions of vector and pseudoscalar currents have been calculated in the external strong magnetic field in SU(2) lattice gluodynamics. The masses of the neutral ? meson with different spin projections s = 0, ±1 to the axis parallel to the external magnetic field B have been calculated. The ? meson mass with zero spin s = 0 decreases with the growth of the magnetic field and the ? meson masses with s = ±1 increase with the magnetic field.
Primordial magnetic field limits from cosmological data
Kahniashvili, Tina; Tevzadze, Alexander G.; Sethi, Shiv K.; Pandey, Kanhaiya; Ratra, Bharat
2010-10-15
We study limits on a primordial magnetic field arising from cosmological data, including that from big bang nucleosynthesis, cosmic microwave background polarization plane Faraday rotation limits, and large-scale structure formation. We show that the physically relevant quantity is the value of the effective magnetic field, and limits on it are independent of how the magnetic field was generated.
Magnetic Fields in Nearby Molecular Clouds
Ramaprakash, A. N.
Chapter 7 Magnetic Fields in Nearby Molecular Clouds In Chap. 6, we saw the power of imaging polarimetric techniques in probing the twoÂ dimensional magnetic field patterns associated with Bok globules are attributed to the interaction between gravity, angular momentum and magnetic field (Wardle & KÂ¨onigl, 1993
Magnetic field navigation in an indoor environment
William Storms; Jeremiah Shockley; John Raquet
2010-01-01
This paper describes a method that has been developed to aid an inertial navigation system when GNSS signals are not available, by taking advantage of the uniqueness of magnetic field variations. Most indoor environments have many different features (ferrous structural materials or contents, electrical currents, etc.) which perturb the Earths natural magnetic field. The variations in the magnetic field in
Three dimensional finite element calculation of saturable magnetic fluxes and torques of an actuator
Brauer, J.R.; Aronson, E.A.; McCaughey, K.G.; Sullivan, W.N.
1987-08-01
A rotary magnetic actuator of highly three dimensional geometry is analyzed by the finite element method. A one quarter model composed of three dimensional finite elements is developed for analysis by the vector potential Newton Raphson approach. The nonlinear saturable magnetic fields, fluxes, inductances, energies, and torques are calculated at three armature positions. The calculated torques compare reasonably well with measurements. 7 refs., 6 figs., 2 tabs.
Magnetic Fields in Molecular Clouds - Observations Confront Theory
R. M. Crutcher
1998-01-01
This paper presents a summary of all 27 available sensitive Zeeman measurements of magnetic field strengths in molecular clouds together with other relevant physical parameters. >From these data input parameters to magnetic star formation theory are calculated and predictions of theory are compared with observations. Results for this cloud sample are: (1) Motions are supersonic but approximately equal to the
Van der Waals torque induced by external magnetic fields
Esquivel-Sirvent, R.; Cocoletzi, G. H.; Palomino-Ovando, M.
2010-01-01
We present a method for inducing and controlling van der Waals torques between two parallel slabs using a constant magnetic field. The torque is calculated using the Barash theory of dispersive torques. In III–IV semiconductors such as InSb, the effect of an external magnetic field is to induce an optical anisotropy, in an otherwise isotropic material, that will in turn induce a torque. The calculations of the torque are done in the Voigt configuration, with the magnetic field parallel to the surface of the slabs. As a case study we consider a slab made of calcite and a second slab made of InSb. In the absence of magnetic field there is no torque. As the magnetic field increases, the optical anisotropy of InSb increases and the torque becomes different from zero, increasing with the magnetic field. The resulting torque is of the same order of magnitude as that calculated using permanent anisotropicmaterials when the magnetic fields is close to 1 T.
Magnetic monopole and the nature of the static magnetic field
Xiuqing Huang
2008-12-10
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.
Effect of strong magnetic field on surface electric field of strange stars
Zheng Xiaoping; Yu Yunwei
2005-09-10
We made a detailed study of the properties of the electron layer near the quark surface of strange stars with strong ($\\sim 10^{14}-10^{17}$G) magnetic fields. The electrostatic potential and the electric field at the quark surface were calculated as functions of the magnetic field intensity of bare strange stars. Using an ultrastrong ($B\\geq 2.5\\times10^{16}$G) magnetic field, we found that the distribution of electrons becomes an exponential function of radial distance, which is quite different in a magnetic field-free case. We also calculated the variation in gap width between the strange core and the normal nuclear crust for strange stars, which is due to magnetic field effect.
Magnetic dipole moment determination by near-field analysis
NASA Technical Reports Server (NTRS)
Eichhorn, W. L.
1972-01-01
A method for determining the magnetic moment of a spacecraft from magnetic field data taken in a limited region of space close to the spacecraft. The spacecraft's magnetic field equations are derived from first principles. With measurements of this field restricted to certain points in space, the near-field equations for the spacecraft are derived. These equations are solved for the dipole moment by a least squares procedure. A method by which one can estimate the magnitude of the error in the calculations is also presented. This technique was thoroughly tested on a computer. The test program is described and evaluated, and partial results are presented.
MESSENGER Observations of Mercury's Magnetic Field Structure
NASA Astrophysics Data System (ADS)
Johnson, C. L.; Purucker, M. E.; Anderson, B. J.; Winslow, R. M.; Al Asad, M.; Korth, H.; Slavin, J. A.; Alexeev, I. I.; Ritzer, J. A.; Phillips, R. J.; Zuber, M. T.; Solomon, S. C.
2012-03-01
We use orbital magnetic field data from MESSENGER to constrain Mercury's internal dipolar field and large-scale, time-averaged magnetopause and magnetotail fields. We investigate mechanisms that may account for structure in the residual fields.
Magnetic field sources and their threat to magnetic media
NASA Technical Reports Server (NTRS)
Jewell, Steve
1993-01-01
Magnetic storage media (tapes, disks, cards, etc.) may be damaged by external magnetic fields. The potential for such damage has been researched, but no objective standard exists for the protection of such media. This paper summarizes a magnetic storage facility standard, Publication 933, that ensures magnetic protection of data storage media.
Suppression of magnetic relaxation by a transverse alternating magnetic field
Voloshin, I. F.; Kalinov, A. V.; Fisher, L. M. [All-Russia Electrical Engineering Institute (Russian Federation)], E-mail: fisher@vei.ru; Yampol'skii, V. A. [National Academy of Sciences of Ukraine, Institute of Radiophysics and Electronics (Ukraine)], E-mail: yam@vk.kharkov.ua
2007-07-15
The evolution of the spatial distribution of the magnetic induction in a superconductor after the action of the alternating magnetic field perpendicular to the trapped magnetic flux has been analyzed. The observed stabilization of the magnetic induction profile is attributed to the increase in the pinning force, so that the screening current density becomes subcritical. The last statement is corroborated by direct measurements.
First-principles calculation of low-dimensional magnetic structures
NASA Astrophysics Data System (ADS)
Wu, Ruqian
2008-03-01
Magnetism in low dimensions is of great interest for fundamental and industrial research. Density functional calculations are important to provide clear physical insights for search, design and optimization of magnetic nanostructures that are essential in new technologies. We have recently performed systematic studies for search of giant magnetic anisotropy energies in single atom such as 3d on CuN, monatomic wires encompassing 3d-5d atoms, magnetic thin films such as 3d on Cu and Au. We will review the physics that governs the magnetic anisotropy and other phenomena driven by spin-orbit coupling. We will also discuss our recent results of spin dynamics in nanoentities.
Numerical calculations of ultrasonic fields. [STEALTH
Johnson, J.A.
1982-02-01
A code for calculating ultrasonic fields has been developed by revisng the thermal-hydraulics code STEALTH. This code may be used in a wide variety of situations in which a detailed knowledge of a propagating wave field is required. Among the potential used are: interpretation of pulse-echo or pitch-catch ultrasonic signals in complicated geometries; ultrasonic transducer modeling and characterization; optimization and evaluation of transducer design; optimization and reliability of inspection procedures; investigation of the response of different types of reflectors; flaw modeling; and general theoretical acoustics. The code is described, and its limitations and potential are discussed. A discussion of the required input and of the general procedures for running the code is presented. Three sample problems illustrate the input and the use of the code.
Magnetic field perturbations in the systems where only poloidal magnetic field is present*
1 Magnetic field perturbations in the systems where only poloidal magnetic field is present* D In some plasma confinement systems the confinement is provided by a poloidal magnetic field (no toroidal magnetic field is present). Examples include FRC, levitated dipoles, and long diffuse pinches. We consider
Moving magnetic cloud -1Moving magnetic cloud -1 "Double change of frame" calculation...
HÃ¶randel, JÃ¶rg R.
#12;19 Moving magnetic cloud - 1Moving magnetic cloud - 1 "Double change of frame" calculation... #12;eb. 2005 -- Cosmic-rays & Particle Acceleration -- E. Parizot (IPN Orsay) 21 Moving magnetic cloud - 2Moving magnetic cloud - 2 #12;Karlsruhe, 23-25 Feb. 2005 -- Cosmic-rays & Particle Acceleration
Pull-in control due to Casimir forces using external magnetic fields
R. Esquivel-Sirvent; M. A. Palomino-Ovando; G. H. Cocoletzi
2009-07-13
We present a theoretical calculation of the pull-in control in capacitive micro switches actuated by Casimir forces, using external magnetic fields. The external magnetic fields induces an optical anisotropy due to the excitation of magneto plasmons, that reduces the Casimir force. The calculations are performed in the Voigt configuration, and the results show that as the magnetic field increases the system becomes more stable. The detachment length for a cantilever is also calculated for a cantilever, showing that it increases with increasing magnetic field. At the pull-in separation, the stiffness of the system decreases with increasing magnetic field.
Test chambers for cell culture in static magnetic field
NASA Astrophysics Data System (ADS)
Glinka, Marek; Gawron, Stanis?aw; Siero?, Aleksander; Paw?owska–Góral, Katarzyna; Cie?lar, Grzegorz; Siero?–Sto?tny, Karolina
2013-04-01
Article presents a test chamber intended to be used for in vitro cell culture in homogenous constant magnetic field with parametrically variable magnitude. We constructed test chambers with constant parameters of control homeostasis of cell culture for the different parameters of static magnetic field. The next step was the computer calculation of 2D and 3D simulation of the static magnetic field distribution in the chamber. The analysis of 2D and 3D calculations of magnetic induction in the cells' exposition plane reveals, in comparison to the detection results, the greater accuracy of 2D calculations (Figs. 9 and 10). The divergence in 2D method was 2-4% and 8 to 10% in 3D method (reaching 10% only out of the cells' cultures margins).
NASA Astrophysics Data System (ADS)
Baldan, C. A.; Shigue, C. Y.; Ruppert-Filho, E.; Ortiz, W. A.
2001-05-01
Austenitic stainless steel presents phase changes caused by heat treatment and welding processes. Because it represents a problem in the design of high-homogeneity magnets, we have been studying the magnetic properties of Ti alloys for their use instead of stainless steel as structural material for superconducting magnet construction. In this work, we present the comparative study of the influence of magnetic properties of steel and Ti alloys on the magnetic-field homogeneity of a superconducting coil through numerical calculation using the measured magnetic properties.
Permanent Magnet Ecr Plasma Source With Magnetic Field Optimization
Doughty, Frank C. (Plano, TX); Spencer, John E. (Plano, TX)
2000-12-19
In a plasma-producing device, an optimized magnet field for electron cyclotron resonance plasma generation is provided by a shaped pole piece. The shaped pole piece adjusts spacing between the magnet and the resonance zone, creates a convex or concave resonance zone, and decreases stray fields between the resonance zone and the workpiece. For a cylindrical permanent magnet, the pole piece includes a disk adjacent the magnet together with an annular cylindrical sidewall structure axially aligned with the magnet and extending from the base around the permanent magnet. The pole piece directs magnetic field lines into the resonance zone, moving the resonance zone further from the face of the magnet. Additional permanent magnets or magnet arrays may be utilized to control field contours on a local scale. Rather than a permeable material, the sidewall structure may be composed of an annular cylindrical magnetic material having a polarity opposite that of the permanent magnet, creating convex regions in the resonance zone. An annular disk-shaped recurve section at the end of the sidewall structure forms magnetic mirrors keeping the plasma off the pole piece. A recurve section composed of magnetic material having a radial polarity forms convex regions and/or magnetic mirrors within the resonance zone.
Euler-Heisenberg Lagrangian to all orders in the magnetic field and the Chiral Magnetic Effect
Simon Wolfgang Mages; Matthias Aicher; Andreas Schäfer
2010-09-08
In high energy heavy ion collisions as well as in astrophysical objects like magnetars extreme magnetic field strengths are reached. Thus, there exists a need to calculate divers QED processes to all orders in the magnetic field. We calculate the vacuum polarization graph in second order of the electric field and all orders of the magnetic field resulting in a generalization of the Euler-Heisenberg Lagrangian. We perform the calculation in the effective Lagrangian approach of J. Schwinger as well as using modified Feynman rules. We find that both approaches give the same results provided that the different finite renormalization terms are taken into account. Our results imply that any quantitative explanation of the recently proposed Chiral Magnetic Effect has to take 'Strong QED' effects into account, because these corrections are huge.
Interplanetary magnetic field data book
NASA Technical Reports Server (NTRS)
King, J. H.
1975-01-01
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.
Meson spectrum in strong magnetic fields
NASA Astrophysics Data System (ADS)
Andreichikov, M. A.; Kerbikov, B. O.; Orlovsky, V. D.; Simonov, Yu. A.
2013-05-01
We study the relativistic quark-antiquark system embedded in a magnetic field (MF). The Hamiltonian containing confinement, one gluon exchange, and spin-spin interaction is derived. We analytically follow the evolution of the lowest meson states as a function of MF strength. Calculating the one gluon exchange interaction energy ?VOGE? and spin-spin contribution ?aSS? we have observed that these corrections remain finite at large MF, preventing the vanishing of the total ? meson mass at some Bcrit, as previously thought. We display the ? masses as functions of the MF in comparison with recent lattice data.
NASA Astrophysics Data System (ADS)
N. Kawasaki; Oka, T.; Fukui, S.; Ogawa, J.; Sato, T.; Terasawa, T.; Itoh, Y.
A demagnetized Nd-Fe-B permanent magnet was scanned in the strong magnetic field space just above the magnetic pole containing a HTS bulk magnet which generates the magnetic field 3.4 T. The magnet sample was subsequently found to be fully magnetized in the open space of the static magnetic fields. The finite element method was carried out for the static field magnetization of a permanent magnet using a HTS bulk magnet. Previously, our research group experimentally demonstrated the possibility of full magnetization of rare earth permanent magnets with high-performance magnetic properties with use of the static field of HTS bulk magnets. In the present study, however, we succeeded for the first time in visualizing the behavior of the magnetizing field of the bulk magnet during the magnetization process and the shape of the magnetic field inside the body being magnetized. By applying this kind of numerical analysis to the magnetization for planned motor rotors which incorporate rare-earth permanent magnets, we hope to study the fully magnetized regions for the new magnetizing method using bulk magnets and to give motor designing a high degree of freedom.
Graphene transparency in weak magnetic fields
David Valenzuela; Saúl Hernández-Ortiz; Marcelo Loewe; Alfredo Raya
2014-10-20
We carry out an explicit calculation of the vacuum polarization tensor for an effective low-energy model of monolayer graphene in the presence of a weak magnetic field of intensity $B$ perpendicularly aligned to the membrane. By expanding the quasiparticle propagator in the Schwinger proper time representation up to order $(eB)^2$, where $e$ is the unit charge, we find an explicitly transverse tensor, consistent with gauge invariance. Furthermore, assuming that graphene is radiated with monochromatic light of frequency $\\omega$ along the external field direction, from the modified Maxwell's equations we derive the intensity of transmitted light and the angle of polarization rotation in terms of the longitudinal ($\\sigma_{xx}$) and transverse ($\\sigma_{xy}$) conductivities. Corrections to these quantities, both calculated and measured, are of order $(eB)^2/\\omega^4$. Our findings generalize and complement previously known results reported in literature regarding the light absorption problem in graphene from the experimental and theoretical points of view, with and without external magnetic fields.
Magnetic fluid flow phenomena in DC and rotating magnetic fields
Rhodes, Scott E. (Scott Edward), 1981-
2004-01-01
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 ...
Plasma-satellite interaction driven magnetic field perturbations
Saeed-ur-Rehman; Marchand, Richard
2014-09-15
We report the first fully kinetic quantitative estimate of magnetic field perturbations caused by the interaction of a spacecraft with space environment. Such perturbations could affect measurements of geophysical magnetic fields made with very sensitive magnetometers on-board satellites. Our approach is illustrated with a calculation of perturbed magnetic fields near the recently launched Swarm satellites. In this case, magnetic field perturbations do not exceed 20 pT, and they are below the sensitivity threshold of the on-board magnetometers. Anticipating future missions in which satellites and instruments would be subject to more intense solar UV radiation, however, it appears that magnetic field perturbations associated with satellite interaction with space environment, might approach or exceed instruments' sensitivity thresholds.
The search for a primordial magnetic field
NASA Astrophysics Data System (ADS)
Yamazaki, Dai G.; Kajino, Toshitaka; Mathews, Grant J.; Ichiki, Kiyotomo
2012-08-01
Magnetic fields appear wherever plasma and currents can be found. As such, they thread through all scales in Nature. It is natural, therefore, to suppose that magnetic fields might have been formed within the high temperature environments of the big bang. Such a primordial magnetic field (PMF) would be expected to arise from and/or influence a variety of cosmological phenomena such as inflation, cosmic phase transitions, big bang nucleosynthesis, the cosmic microwave background (CMB) temperature and polarization anisotropies, the cosmic gravity wave background, and the formation of large-scale structure. In this review, we summarize the development of theoretical models for analyzing the observational consequences of a PMF. We also summarize the current state of the art in the search for observational evidence of a PMF. In particular, we review the framework needed to calculate the effects of a PMF power spectrum on the CMB and the development of large scale structure. We summarize the current constraints on the PMF amplitude B? and the power spectral index nB and discuss prospects for better determining these quantities in the near future.
Effects of magnetic fields on the quark-gluon plasma
NASA Astrophysics Data System (ADS)
Bali, G. S.; Bruckmann, F.; Endr?di, G.; Fodor, Z.; Katz, S. D.; Schäfer, A.
2014-11-01
In this talk, the response of the thermal QCD medium to external (electro)magnetic fields is studied using continuum extrapolated lattice results at physical quark masses. The magnetic susceptibility of QCD is calculated, revealing a strong paramagnetic response at high temperatures. This paramagnetism is shown to result in an anisotropic squeezing of the quark-gluon plasma in non-central heavy-ion collisions, implying a sizeable contribution to the elliptic flow. Another aspect is the magnetic response of topologically non-trivial domains to the magnetic field. We quantify this effect on the lattice and compare the results to a simple model estimate.
NASA Astrophysics Data System (ADS)
Hamada, Shoji; Kitano, Mitsuhiro; Kobayashi, Tetsuo
This paper describes an application of the equivalent multipole moment method (EMMM) with polar translations to calculation of magnetic fields induced by a current dipole placed in a human head model. Although the EMMM is a conventional Laplacian field solver based on spherical harmonic functions, the polar translations enable it to treat eccentric and exclusive spheres in arbitrary arrangements. The head model is composed of seven spheres corresponding to skin, two eyeballs, skull, cerebral spinal fluid, grey matter, and white matter. The validity of the calculated magnetic fields and the magnetic flux linkages with a loop coil locating nearby the model is successfully confirmed by the reciprocity theorem derived by Eaton.
Holography, Fractionalization and Magnetic Fields
NASA Astrophysics Data System (ADS)
Albash, Tameem; Johnson, Clifford V.; McDonald, Scott
Four dimensional gravity with a U(1) gauge field, coupled to various fields in asymptotically anti-de Sitter spacetime, provides a rich arena for the holographic study of the strongly coupled (2+1)-dimensional dynamics of finite density matter charged under a global U(1). As a first step in furthering the study of the properties of fractionalized and partially fractionalized degrees of freedom in the strongly coupled theory, we construct electron star solutions at zero temperature in the presence of a background magnetic field. We work in Einstein-Maxwell-dilaton theory. In all cases we construct, the magnetic source is cloaked by an event horizon. A key ingredient of our solutions is our observation that starting with the standard Landau level structure for the density of states, the electron star limits reduce the charge density and energy density to that of the free fermion result. Using this result we construct three types of solution: One has a star in the infra-red with an electrically neutral horizon, another has a star that begins at an electrically charged event horizon, and another has the star begin a finite distance from an electrically charged horizon.
The design and analysis of axial field multipole impulse magnetizing fixtures
NASA Astrophysics Data System (ADS)
Riley, C. D.; Jewell, G. W.; Howe, D.
1998-06-01
A methodology for the design of fixtures for the multipole magnetization of axially magnetized permanent magnet rings is presented. The methodology, which is based on three-dimensional analytical field calculation techniques, embraces the calculation of the fixture electrical parameters, the electrical simulation of the fixture performance and the calculation of the level of saturation achieved in the permanent magnet. The methodology is validated by means of an experimental case study on a 6 pole isotropic NdFeB magnet ring.
Measurements of magnetic field sources in schools
Johnson, G.B. (General Electric Co., EPRI High Voltage Transmission Research Center, Lenox, MA (US))
1992-01-01
The Electrical Systems Division of the Electric Power Research Institute (EPRI) has initiated several research projects to investigate magnetic field levels, their characteristics, and their sources. This paper describes measurements of magnetic field sources in schools. Magnetic field measurements were made at four schools in the service areas of two utility companies. Magnetic field measurements included profiles of the magnetic field versus distance near power lines, around the perimeter of the school buildings, and at several locations within each school. Twenty-four hour measurements were also made to record the temporal variation of the magnetic field at several locations at each school. The instrumentation, measurement techniques, and magnetic field sources identified are discussed.
SPH simulations of magnetic fields in galaxy clusters
NASA Astrophysics Data System (ADS)
Dolag, K.; Bartelmann, M.; Lesch, H.
1999-08-01
We perform cosmological, hydrodynamic simulations of magnetic fields in galaxy clusters. The computational code combines the special-purpose hardware Grape for calculating gravitational interaction, and smooth-particle hydrodynamics for the gas component. We employ the usual MHD equations for the evolution of the magnetic field in an ideally conducting plasma. As a first application, we focus on the question what kind of initial magnetic fields yield final field configurations within clusters which are compatible with Faraday-rotation measurements. Our main results can be summarised as follows: (i) Initial magnetic field strengths are amplified by approximately three orders of magnitude in cluster cores, one order of magnitude above the expectation from spherical collapse. (ii) Vastly different initial field configurations (homogeneous or chaotic) yield results that cannot significantly be distinguished. (iii) Micro-Gauss fields and Faraday-rotation observations are well reproduced in our simulations starting from initial magnetic fields of ~ 10(-9) G strength at redshift 15. Our results show that (i) shear flows in clusters are crucial for amplifying magnetic fields beyond simple compression, (ii) final field configurations in clusters are dominated by the cluster collapse rather than by the initial configuration, and (iii) initial magnetic fields of order 10(-9) G are required to match Faraday-rotation observations in real clusters.
Spin flip probability of electron in a uniform magnetic field
Hammond, Richard T.
2012-03-19
The probability that an electromagnetic wave can flip the spin of an electron is calculated. It is assumed that the electron resides in a uniform magnetic field and interacts with an incoming electromagnetic pulse. The scattering matrix is constructed and the time needed to flip the spin is calculated.
Vlasov Equation In Magnetic Field
Biao Wu
1999-09-07
The linearized Vlasov equation for a plasma system in a uniform magnetic field and the corresponding linear Vlasov operator are studied. The spectrum and the corresponding eigenfunctions of the Vlasov operator are found. The spectrum of this operator consists of two parts: one is continuous and real; the other is discrete and complex. Interestingly, the real eigenvalues are infinitely degenerate, which causes difficulty solving this initial value problem by using the conventional eigenfunction expansion method. Finally, the Vlasov equation is solved by the resolvent method.
Quenching of flames by magnetic fields (abstract)
NASA Astrophysics Data System (ADS)
Ueno, S.
1988-11-01
The effects of magnetic fields on combustion of alcohol with the aid of platinum catalysis have been studied to simulate in part the oxidation of organic matter in the living body, and it has been found that the combustion reactions are influenced by magnetic fields. It has also been observed that candle flames are pressed down by magnetic fields of higher intensities when flames are exposed to gradient magnetic fields in a range 20-200 T/m under 0.5-1.4 T. Apart from the combustion experiments, flows of carbon dioxide, oxygen, nitrogen, and argon gases were exposed to magnetic fields up to 2.2 T and 300 T/m. The flows of these gases were blocked or disturbed by the magnetic fields. The purpose of the present study is to clarify the mechanisms for the phenomena observed in the experiments of magnetic effects on combustion and gas flow. An electromagnet with a pair of columnar magnetic poles of which inner sidepieces were hollowed out was used. The magnetic fields of 1.5 T at the brim gave a gradient of 50-100 T/m in the direction perpendicular to the pole axis when the distance of the airgap was in a range 5-10 mm. A candle was burned in the hollowed space between magnetic poles, and candle flames were exposed to magnetic fields. The flames were quenched in a few seconds after the onset of field exposures. Oxygen gas as a paramagnetic molecule can be attracted to the magnetic fields of higher intensities. However, under the intensities of magnetic fields concerned, oxygen gases are not concentrated but are aligned so as to make a ``wall of oxygen'' or an ``air curtain.'' The air curtain, which is also called the ``magnetic curtain,'' blocks air flow into and out of the hollowed space. The interception of oxygen by magnetic curtain quenches flames. The magnetic curtain also presses back flames and other gases.
Magnetic fields from the electroweak phase transition
Tornkvist, O.
1998-02-01
I review some of the mechanisms through which primordial magnetic fields may be created in the electroweak phase transition. I show that no magnetic fields are produced initially from two-bubble collisions in a first-order transition. The initial field produced in a three-bubble collision is computed. The evolution of fields at later times is discussed.
Measuring the off axis magnetic field within a Helmholtz Coil
NASA Astrophysics Data System (ADS)
Pluhar, Edward; Martell, Eric
2013-03-01
Helmholtz coils are used because they produce nearly uniform magnetic fields on-axis. Prior research, namely Graf's thin coil experiment [The Physics Teacher, pp. 360 (2012)], has accurately measured the axial magnetic field produced by a thin coil; however, the magnetic field off-axis is known to be significantly more complicated and cannot be calculated analytically. In this research, I have numerically determined the magnetic field off-axis in the region between the two coils and compared those calculations with measured values. I then determined the effect the deviation from uniformity has on the behavior of a charged particle moving through this region, such as in the well-known electron charge-to-mass ratio experiment.
Magnetic field effects on microwave absorbing materials
NASA Technical Reports Server (NTRS)
Goldberg, Ira; Hollingsworth, Charles S.; Mckinney, Ted M.
1991-01-01
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.
Edge effects on forces and magnetic fields produced by a conductor moving past a magnet
Mulcahy, T.M.; Hull, J.R.; Almer, J.D. ); Rossing, T.D. )
1992-01-01
Experiments have been performed to further understand the forces acting on magnets moving along and over the edge of a continuous conducting sheet and to produce a comprehensive data set for the validation of analysis methods. Mapping the magnetic field gives information about the eddy currents induced in the conductor, which agrees with numerical calculations.
Edge effects on forces and magnetic fields produced by a conductor moving past a magnet
Mulcahy, T.M.; Hull, J.R.; Almer, J.D.; Rossing, T.D.
1992-04-01
Experiments have been performed to further understand the forces acting on magnets moving along and over the edge of a continuous conducting sheet and to produce a comprehensive data set for the validation of analysis methods. Mapping the magnetic field gives information about the eddy currents induced in the conductor, which agrees with numerical calculations.
Magnetic Fields above the Surface of aSuperconductor with Internal Magnetism
Bluhm, Hendrik; /Stanford U., Phys. Dept. /SLAC, SSRl
2007-06-26
The author presents a method for calculating the magnetic fields near a planar surface of a superconductor with a given intrinsic magnetization in the London limit. He computes solutions for various magnetic domain boundary configurations and derives relations between the spectral densities of the magnetization and the resulting field in the vacuum half space, which are useful if the magnetization can be considered as a statistical quantity and its features are too small to be resolved individually. The results are useful for analyzing and designing magnetic scanning experiments. Application to existing data from such experiments on Sr{sub 2}RuO{sub 4} show that a domain wall would have been detectable, but the magnetic field of randomly oriented small domains and small defects may have been smaller than the experimental noise level.
Magnetic fields of the solar system: A comparative planetology toolkit
NASA Astrophysics Data System (ADS)
Nicholas, J. B.; Purucker, M. E.; Johnson, C. L.; Sabaka, T. J.; Olsen, N.; Sun, Z.; Al Asad, M.; Anderson, B. J.; Korth, H.; Slavin, J. A.; Alexeev, I. I.; Belenkaya, E. S.; Phillips, R. J.; Solomon, S. C.; Lillis, R. J.; Langlais, B.; Winslow, R. M.; Russell, C. T.; Dougherty, M. K.; Zuber, M. T.
2011-12-01
Magnetic fields within the solar system provide a strong organizing force for processes active both within a planet or moon, and outside of it. In the interest of stimulating research and education in the field of comparative planetology, we present documented Fortran and MATLAB source codes and benchmarks to the latest models for planets and satellites that host internal magnetic fields. This presentation is made in the context of an interactive website: http://planetary-mag.net. Models are included for Earth (Comprehensive model CM4 of Sabaka et al., 2004, Geophysics J. Int.), Mercury (Anderson et al, 2011, Science), the Moon (Purucker and Nicholas, 2010, JGR), Mars (Lillis et al., 2010, JGR), and the outer planets Jupiter, Saturn, Uranus, and Neptune (Russell and Dougherty, 2010, Space Science Reviews). All models include magnetic fields of internal origin, and fields of external origin are included in the models for Mercury, the Earth, and the Moon. As models evolve, we intend to include magnetic fields of external origin for the other planets and moons. The website allows the user to select a coordinate system, such as planet-centered, heliocentric, or boundary normal, and the location within that coordinate system, and the vector magnetic field due to each of the component source fields at that location is then calculated and presented. Alternatively, the user can input a range as well as a grid spacing, and the vector magnetic field will be calculated for all points on that grid and be made available as a file for downloading.
Deformation of Water by a Magnetic Field
ERIC Educational Resources Information Center
Chen, Zijun; Dahlberg, E. Dan
2011-01-01
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…
Electromagnetic showers in a strong magnetic field
V. Anguelov; H. Vankov
2000-01-13
We present the results concerning the main shower characteristics in a strong magnetic field obtained through shower simulation. The processes of magnetic bremsstrahlung and pair production were taken into account for values of the parameter $\\chi \\gg 1$. We compare our simulation results with a recently developed cascade theory in a strong magnetic field.
Baking a magnetic-field display
NASA Astrophysics Data System (ADS)
Cavanaugh, Terence; Cavanaugh, Catherine
1998-02-01
Copy machine developer powder is an alternative for creating permanent displays of magnetic fields. A thin layer of developer powder on a sheet of paper placed over a magnet can be baked in the oven, producing a lasting image of a magnetic field.
Baryon onset in a magnetic field
Alexander Haber; Florian Preis; Andreas Schmitt
2014-12-19
The critical baryon chemical potential for the onset of nuclear matter is a function of the vacuum mass and the binding energy. Both quantities are affected by an external magnetic field. We show within two relativistic mean-field models - including magnetic catalysis, but omitting the anomalous magnetic moment - that a magnetic field increases both the vacuum mass and the binding energy. For sufficiently large magnetic fields, the effect on the vacuum mass dominates and as a result the critical baryon chemical potential is increased.
Magnetic-field-enhanced carbon solution in proeutectoid ferrite
NASA Astrophysics Data System (ADS)
Zhang, X. X.; Xu, N.; Wang, S. J.; Zhang, Y. D.; Raulot, J.-M.; Esling, C.; Zhao, X.; Zuo, L.
2013-09-01
Modification of phase solubility of Fe-C system by magnetic field has been recognized by thermodynamic calculations and indirectly by microstructural examinations. However, there has been no direct experimental verification and the underlying physical mechanism is not fully uncovered. In this work, the enhanced carbon content in proeutectoid ferrite under a 12 T magnetic field is evidenced through wavelength-dispersive spectroscopy using a Shimadzu 1610 electron probe microanalyser measurements. The magnetic-field-enhanced carbon solution reduces the demagnetization energy of the system and makes it energetically more stable.
Magnetic Field Generation and Electron Acceleration in Relativistic Laser Channel
I.Yu. Kostyukov; G. Shvets; N.J. Fisch; J.M. Rax
2001-12-12
The interaction between energetic electrons and a circularly polarized laser pulse inside an ion channel is studied. Laser radiation can be resonantly absorbed by electrons executing betatron oscillations in the ion channel and absorbing angular momentum from the laser. The absorbed angular momentum manifests itself as a strong axial magnetic field (inverse Faraday effect). The magnitude of this magnetic field is calculated and related to the amount of the absorbed energy. Absorbed energy and generated magnetic field are estimated for the small and large energy gain regimes. Qualitative comparisons with recent experiments are also made.
Universality of critical magnetic field in holographic superconductor
D. Momeni; R. Myrzakulov
2015-02-11
In this letter we study aspects of the holographic superconductors analytically in the presence of a constant external magnetic field. We show that the critical temperature and critical magnetic field can be calculated at nonzero temperature. We detect the Meissner effect in such superconductors. A universal relation between black hole mass $ M$ and critical magnetic field $H_c$ is proposed as $\\frac{H_c}{M^{2/3}}\\leq 0.687365$. We discuss some aspects of phase transition in terms of black hole entropy and the Bekenstein's entropy to energy upper bound.
Improved magnetic field analysis of induction motor models
Enokizono, Masato; Sadanaga, Yuichiro
1998-09-01
This paper presents an improved magnetic field analysis for induction motor models. In the analysis with the conventional numerical modeling of magnetic materials, the vector relations between the flux density and the field intensity under a rotating field cannot be expressed exactly. In this paper, the authors derived the tensor magnetic reluctivity from the data measured with two-dimensional measurement method. This expression is applied to analyze a three-phase induction motor model core. The examples show that the calculated results obtained by the new method are different from those of the conventional modeling.
NASA Astrophysics Data System (ADS)
Büttner, Felix; Krüger, Benjamin; Eisebitt, Stefan; Kläui, Mathias
2015-08-01
Bloch domain walls are the most common type of transition between two out-of-plane magnetized domains (one magnetized upwards, one downwards) in films with perpendicular magnetic anisotropy. The rotation of the spins of such domain walls in the plane of the film requires energy, which is described by an effective anisotropy, the so-called transverse or hard axis anisotropy K?. This anisotropy and the related Döring mass density of the domain wall are key parameters of the one-dimensional model to describe the motion of magnetic domain walls. In particular, the critical field strength or current density where oscillatory domain wall motion sets in (Walker breakdown) is directly proportional to K?. So far, no general framework is available to determine K? from static characterizations such as magnetometry measurements. Here, we derive a universal analytical expression to calculate the transverse anisotropy constant for the important class of perpendicular magnetic multilayers. All the required input parameters of the model, such as the number of repeats, the thickness of a single magnetic layer, and the layer periodicity, as well as the effective perpendicular anisotropy, the saturation magnetization, and the static domain wall width are accessible by static sample characterizations. We apply our model to a widely used multilayer system and find that the effective transverse anisotropy constant is a factor of seven different from that when using the conventional approximations, showing the importance of using our analysis scheme. Our model is also applicable to domain walls in materials with Dzyaloshinskii-Moriya interaction (DMI). The accurate knowledge of K? is needed to determine other unknown parameters from measurements, such as the DMI strength or the spin polarization of the spin current in current-induced domain wall motion experiments.
Magnetic field and EoS of neutron star matter at finite temperature
NASA Astrophysics Data System (ADS)
Wang, Qingwu; Lü, Xiaofu
2015-07-01
In this paper, magnetic field and equation of state (EoS) of neutron star matter are studied under relativistic mean field theory. A nonzero mass term of magnetic field in the Lagrangian is introduced, which depends on baryon density of charged particles. The magnetic field has not been treated as external as usual and the calculations of magnetic field strength at finite temperature reveal the existence of inflection points in certain densities.
Analysis of magnetic field levels at KSC
NASA Technical Reports Server (NTRS)
Christodoulou, Christos G.
1994-01-01
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.
NASA Astrophysics Data System (ADS)
Odbadrakh, Khorgolkhuu; Nicholson, Don; Eisenbach, Markus; Brown, Gregory; Rusanu, Aurelian; Materials Theory Group Team
2014-03-01
Magnetic entropy change in Magneto-caloric Effect materials is one of the key parameters in choosing materials appropriate for magnetic cooling and offers insight into the coupling between the materials' thermodynamic and magnetic degrees of freedoms. We present computational workflow to calculate the change of magnetic entropy due to a magnetic field using the DFT based statistical sampling of the energy landscape of Ni2MnGa. The statistical density of magnetic states is calculated with Wang-Landau sampling, and energies are calculated with the Locally Self-consistent Multiple Scattering technique. The high computational cost of calculating energies of each state from first principles is tempered by exploiting a model Hamiltonian fitted to the DFT based sampling. The workflow is described and justified. The magnetic adiabatic temperature change calculated from the statistical density of states agrees with the experimentally obtained value in the absence of structural transformation. The study also reveals that the magnetic subsystem alone cannot explain the large MCE observed in Ni2MnGa alloys. This work was performed at the ORNL, which is managed by UT-Batelle for the U.S. DOE. It was sponsored by the Division of Material Sciences and Engineering, OBES. This research used resources of the OLCF at ORNL, which is supported by the Office of Science of the U.S. DOE under Contract DE-AC05-00OR22725.
Magnetic field waves at Uranus
NASA Technical Reports Server (NTRS)
Smith, Charles W.; Goldstein, Melvyn L.; Lepping, Ronald P.; Mish, William H.; Wong, Hung K.
1994-01-01
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.
Pressure, Chaotic Magnetic Fields and MHD Equilibria
S.R. Hudson & N. Nakajima
2010-05-12
Analyzes of plasma behavior often begin with a description of the ideal magnetohydrodynamic equilibrium, this being the simplest model capable of approximating macroscopic force balance. Ideal force balance is when the pressure gradient is supported by the Lorentz force, ?p = j x B. We discuss the implications of allowing for a chaotic magnetic field on the solutions to this equation. We argue that the solutions are pathological and not suitable for numerical calculations. If the pressure and magnetic Field are continuous, the only non-trivial solutions have an uncountable infinity of discontinuities in the pressure gradient and current. The problems arise from the arbitrarily small length scales in the structure of the field, and the consequence of ideal force balance that the pressure is constant along the Field-lines, B • ?p = 0. A simple method to ameliorate the singularities is to include a small but Finite perpendicular diffusion. A self-consistent set of equilibrium equations is described and some algorithmic approaches aimed at solving these equations are discussed.
Pressure, chaotic magnetic fields, and magnetohydrodynamic equilibria
Hudson, S. R.; Nakajima, N.
2010-05-15
Analyses of plasma behavior often begin with a description of the ideal magnetohydrodynamic equilibrium, this being the simplest model capable of approximating macroscopic force balance. Ideal force balance is when the pressure gradient is supported by the Lorentz force, nablap=jxB. We discuss the implications of allowing for a chaotic magnetic field on the solutions to this equation. We argue that the solutions are pathological and not suitable for numerical calculations. If the pressure and magnetic field are continuous, the only nontrivial solutions have an uncountable infinity of discontinuities in the pressure gradient and current. The problems arise from the arbitrarily small length scales in the structure of the field, and the consequence of ideal force balance that the pressure is constant along the field-lines, Bcentre dotnablap=0. A simple method to ameliorate the singularities is to include a small but finite perpendicular diffusion. A self-consistent set of equilibrium equations is described, and some algorithmic approaches aimed at solving these equations are discussed.
The Wind Magnetic Field Investigation
NASA Astrophysics Data System (ADS)
Lepping, R. P.; Ac?na, M. H.; Burlaga, L. F.; Farrell, W. M.; Slavin, J. A.; Schatten, K. H.; Mariani, F.; Ness, N. F.; Neubauer, F. M.; Whang, Y. C.; Byrnes, J. B.; Kennon, R. S.; Panetta, P. V.; Scheifele, J.; Worley, E. M.
1995-02-01
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 associated electronics. The dual configuration provides redundancy and also permits accurate removal of the dipolar portion of the spacecraft magnetic field. The instrument provides (1) near real-time data at nominally one vector per 92 s as key parameter data for broad dissemination, (2) rapid data at 10.9 vectors s-1 for standard analysis, and (3) occasionally, snapshot (SS) memory data and Fast Fourier Transform data (FFT), both based on 44 vectors s-1. These measurements will be precise (0.025%), accurate, ultra-sensitive (0.008 nT/step quantization), and where the sensor noise level is <0.006 nT r.m.s. for 0 10 Hz. The digital processing unit utilizes a 12-bit microprocessor controlled analogue-to-digital converter. The instrument features a very wide dynamic range of measurement capability, from ±4 nT up to ±65 536 nT per axis in eight discrete ranges. (The upper range permits complete testing in the Earth's field.) In the FTT mode power spectral density elements are transmitted to the ground as fast as once every 23 s (high rate), and 2.7 min of SS memory time series data, triggered automatically by pre-set command, requires typically about 5.1 hours for transmission. Standard data products are expected to be the following vector field averages: 0.0227-s (detail data from SS), 0.092 s (‘detail’ in standard mode), 3 s, 1 min, and 1 hour, in both GSE and GSM coordinates, as well as the FFT spectral elements. As has been our team's tradition, high instrument reliability is obtained by the use of fully redundant systems and extremely conservative designs. We plan studies of the solar wind: (1) as a collisionless plasma laboratory, at all time scales, macro, meso and micro, but concentrating on the kinetic scale, the highest time resolution of the instrument (=0.022 s), (2) as a consequence of solar energy and mass output, (3) as an external source of plasma that can couple mass, momentum, and energy to the Earth's magnetosphere, and (4) as it is modified as a consequence of its imbedded field interacting with the moon. Since the GEOTAIL Inboard Magnetometer (GIM), which is similar to the MFI instrument, was developed by members of our team, we provide a brief discussion of GIM related science objectives, along with MFI related science goals.
Field-aligned accelerations by plasma shocks propagating through interstellar magnetic fields
Takeuchi, Satoshi
2012-07-15
A kinetic model of particle acceleration by plasma shocks is analyzed theoretically and with numerical calculations. The shocks are propagating through weakly magnetized background plasmas, namely interstellar magnetic fields (IMFs). Particles located at the shock front are accelerated parallel to the magnetic field of the shock; this is defined as the field-aligned acceleration (FAA). The cross angle between IMF and the magnetic field of the shock plays an important role in creating the magnetic neutral sheet at the shock front. A test particle trapped by the neutral sheet obtains enormous energy due to the FAA. A reasonable formula for the highest energy gain is derived from theoretical analysis of the relativistic equations of motion. A possible configuration of the electric and magnetic fields in supernova remnants is also proposed by way of example.
Rapid Change of Field Line Connectivity in Stochastic Magnetic Fields
NASA Astrophysics Data System (ADS)
Huang, Yi-Min; Bhattacharjee, A.; Boozer, Allen H.
2013-10-01
Magnetic fields depending on three spatial coordinates generally have the feature that neighboring field lines exponentiate away from each other and become stochastic. Under the condition of large exponentiation, magnetic field line connectivity becomes extremely sensitive to small perturbations. Consequently, small deviations from ideal Ohm's law will violate the ideal magnetohydrodynamic constraint and completely scramble the field line connectivity. This idea of breaking field line connectivity by stochasticity is tested with numerical simulations based on reduced magnetohydrodynamics equations. We employ a simple model starting from a uniform magnetic field in the z direction, and bounded by perfectly conducting planes in z. High order hyper-resistivity is employed as the mechanism of breaking field lines. As magnetic field lines is gradually entangled by the spatially smooth applied force, neighboring field line exponentiation becomes large. Field line connectivity is observed to undergo rapid change on Alfven transit time scales, accompanied by sporadic magnetic energy release.
Abnormal Magnetic Field Effects on Electrogenerated Chemiluminescence
Pan, Haiping; Shen, Yan; Wang, Hongfeng; He, Lei; Hu, Bin
2015-01-01
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
Magnetic field restructuring associated with two successive solar eruptions
Wang, Rui; Liu, Ying D.; Yang, Zhongwei; Hu, Huidong, E-mail: liuxying@spaceweather.ac.cn [State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing (China)
2014-08-20
We examine two successive flare eruptions (X5.4 and X1.3) on 2012 March 7 in the NOAA active region 11429 and investigate the magnetic field reconfiguration associated with the two eruptions. Using an advanced non-linear force-free field extrapolation method based on the SDO/HMI vector magnetograms, we obtain a stepwise decrease in the magnetic free energy during the eruptions, which is roughly 20%-30% of the energy of the pre-flare phase. We also calculate the magnetic helicity and suggest that the changes of the sign of the helicity injection rate might be associated with the eruptions. Through the investigation of the magnetic field evolution, we find that the appearance of the 'implosion' phenomenon has a strong relationship with the occurrence of the first X-class flare. Meanwhile, the magnetic field changes of the successive eruptions with implosion and without implosion were well observed.
Unique topological characterization of braided magnetic fields
Yeates, A. R.; Hornig, G.
2013-01-15
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.
Effects of magnetic fields on combustion (abstract)
NASA Astrophysics Data System (ADS)
Ueno, S.
1990-05-01
We have observed a phenomenon that candle flames are pressed down by magnetic fields. We have also observed that flows of gases such as carbon dioxide and oxygen are blocked by magnetic fields. A model, called a ``magnetic curtain,'' has been introduced to explain these phenomena. The magnetic curtain is a wall of air which is produced by magnetic fields. We have demonstrated an experiment to show that candle flames are quenched by the magnetic curtain. The present study focuses on the mechanism of the phenomena involving quenching of flames using magnetic fields. An electromagnet with a pair of columnar magnetic poles in which inner sidepieces were hollowed out was used first. Magnetic fields of 1.5 T at the brim gave a gradient of 50-300 T/m in the direction perpendicular to the pole axis. Alcohol was burned in the hollowed space between magnetic poles. Gases around flames in the hollowed space were sampled into gas sensors through an inhalation nozzle. Oxygen, carbon dioxide, and carbon monoxide were simultaneously measured during the combustion of methanol and ethanol. During magnetic field exposures, oxygen concentration decreased, whereas concentrations of carbon dioxide and carbon monoxide increased. However, when flames were quenced in a few seconds, oxygen concentration in the hallowed space was not changed, and very little of carbon dioxide and carbon monoxide were produced. The interception of a small amount of oxygen near the surface of the flames may quench flames. Emission spectra of flames of methanol and ethanol were measured before, during, and after magnetic field exposures, using both uniform and gradient magnetic fields. Intensity of the OH radical was not changed by magnetic fields up to 1.6 T, whereas the emission intensity was increased when the product of magnetic fields and the gradient increased.
Magnetic fluid motion in rotating field
NASA Astrophysics Data System (ADS)
Rosensweig, R. E.; Popplewell, J.; Johnston, R. J.
1990-04-01
Through experiment and analysis, tangential free-surface-stress is identified as the dominant mechanism in the coupling of uniform rotary magnetic fields to the spin-up motion of colloidal magnetic fluid.
Bipolar pulse field for magnetic refrigeration
Lubell, M.S.
1994-10-25
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.
Bipolar pulse field for magnetic refrigeration
Lubell, Martin S. (Oak Ridge, TN)
1994-01-01
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.
Cross correlations from back reaction on stochastic magnetic fields
Kunze, Kerstin E.
2013-02-01
The induction equation induces non trivial correlations between the primordial curvature mode and the magnetic mode which is a non linear effect. Assuming a stochastic, gaussian magnetic field the resulting power spectra determining the two point cross correlation functions between the primordial curvature perturbation and the magnetic energy density contrast as well as the magnetic anisotropic stress are calculated approximately. The corresponding numerical solutions are used to calculate the angular power spectra determining the temperature anisotropies and polarization of the cosmic microwave background, C{sub l}. It is found that the resulting C{sub l} are sub-leading in comparison to those generated by the compensated mode for a magnetic field which only redshifts with the expansion of the universe. The main focus are scalar modes, however, vector modes will also be briefly discussed.
Franck-Hertz experiment in magnetic field
Ying Weng; Zi-Hua Weng
2010-10-07
The paper studies the impact of applied magnetic field on the inelastic collisions of electrons with argon atoms. In the electron-argon Franck-Hertz experiment, the influence of applied magnetic field emerges complicated features, and is equivalent to that of the temperature. In case the accelerating electric intensity becomes strong enough, enlarging magnetic flux density will be equivalent to the increasing of oven temperature. When the accelerating electric intensity is very weak and the applied magnetic field occupies a dominant position, enhancing magnetic flux density is identical with the decreasing of oven temperature. And the non-uniform distribution of applied magnetic field has an influence on the inelastic collision as well. The study claims that the influence of magnetic field variation is equivalent to that of temperature variety, and that it leads the electron energy to transfer obviously in the experiment.
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.
Observation and interpretation of magnetic-field-line reconnection and tearing in a theta pinch
J. H. Irby; J. F. Drake; Hans Griem
1979-01-01
Measurements and calculations are presented of reconnection and tearing of magnetic fields in a theta pinch operated with initial bias and driving fields in opposite directions. Open magnetic field lines reconnect and form magnetic islands on time scales of the order of an Alfven transit time across the plasma sheath. Implications of these results for plasma confinement are discussed.
Interacting Electrons in a Two-Dimensional Disordered Environment: Effect of a Zeeman Magnetic Field
Scalettar, Richard T.
Interacting Electrons in a Two-Dimensional Disordered Environment: Effect of a Zeeman Magnetic 95616, USA (Received 27 February 2003; published 17 June 2003) The effect of a Zeeman magnetic field-field-dependent conductivity is calculated, as well as the degree of spin polarization.We find that the Zeeman magnetic field
Interaction of magnetic resonators studied by the magnetic field enhancement
Hou, Yumin, E-mail: ymhou@pku.edu.cn [State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China)] [State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China)
2013-12-15
It is the first time that the magnetic field enhancement (MFE) is used to study the interaction of magnetic resonators (MRs), which is more sensitive than previous parameters–shift and damping of resonance frequency. To avoid the coherence of lattice and the effect of Bloch wave, the interaction is simulated between two MRs with same primary phase when the distance is changed in the range of several resonance wavelengths, which is also compared with periodic structure. The calculated MFE oscillating and decaying with distance with the period equal to resonance wavelength directly shows the retardation effect. Simulation also shows that the interaction at normal incidence is sensitive to the phase correlation which is related with retardation effect and is ultra-long-distance interaction when the two MRs are strongly localized. When the distance is very short, the amplitude of magnetic resonance is oppressed by the strong interaction and thus the MFE can be much lower than that of single MR. This study provides the design rules of metamaterials for engineering resonant properties of MRs.
Magnetic fields in young supernova remnants
NASA Astrophysics Data System (ADS)
Lou, Yu-Qing
1994-06-01
Magnetic field strengths in several young Type I supernova remnants (SNRs), such as those associated with SN 1572, 1604, 1006, have been previously inferred from radio synchrotron observations to be of the order of approximately 10-4 - 10-3 G, which greatly exceeds the typical magnetic field strength of several microgauss in ambient interstellar media (ISM). Existing radio polarization studies indicate that projected large-scale magnetic fields tend to orient in the radial direction with several percent in excess within shells of these SNRs. We propose in this Letter that magnetic fields in these young SNRs could mainly originate from magnetized envelopes or magnetospheres of their presupernova progenitors, presumably magnetic white dwarfs, and that magnetic fields entrained in stellar ejecta roughly scale as approximately r-1. The inferred excess of radial alignment for magnetic fields in these young SNRs could result from the Rayleigh-Taylor instability and/or the presence of large-scale random helices of magnetic field lines with their axes meandering through the SNR shell. Molecular clouds and clumps of stellar materials surrounding the presupernova progenitor could also produce radial magnetic fields from transverse fields as the SNR expands into the ISM.
Permanent magnet configurations for magnetic-field-enhanced RIE
JEAN-PAUL YONNET; ALAIN PICARD
1990-01-01
Several permanent magnet systems have been developed to enhance the reactive ion etching (RIE) of wafers. A new system, running with rotating bar-shaped magnets, that provides a traveling magnetic field in the wafer area is presented. This configuration is well adapted to obtaining fast and uniform etching
Smooth magnetic cusp profile calculation for axis-encircling electron beam generation
NASA Astrophysics Data System (ADS)
Yin, Y.; Wang, B.; Li, H. L.; Meng, L.
2012-04-01
The calculation method of a smooth magnetic cusp profile has been introduced to obtain an axis-encircling electron beam in a fixed electrostatic field distribution. Using the calculated smooth magnetic cusp profile, an axis-encircling electron beam of current 1 A and voltage 30 kV can be obtained with a velocity ratio 1.8 and low beam ripples. Theoretical calculation and 3D simulations agree well, which show that this method can be widely used in other axis-encircling electron gun designing.
Representation of magnetic fields in space
NASA Technical Reports Server (NTRS)
Stern, D. P.
1975-01-01
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.
DC-based magnetic field controller
Kotter, Dale K. (Shelley, ID); Rankin, Richard A. (Ammon, ID); Morgan, John P,. (Idaho Falls, ID)
1994-01-01
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.
PALEOMAGNETISM Solar nebula magnetic fields recorded
Walsworth, Ronald L.
REPORTS PALEOMAGNETISM Solar nebula magnetic fields recorded in the Semarkona meteorite Roger R. Walsworth,6,7 Aaron T. Kuan9 Magnetic fields are proposed to have played a critical role in some of the most on the intensity of these fields. Here we show that dusty olivine-bearing chondrules from the Semarkona meteorite
Static uniform magnetic fields and amoebae
Berk, S.G.; Srikanth, S.; Mahajan, S.M.; Ventrice, C.A.
1997-03-01
Three species of potentially pathogenic amoebae were exposed to 71 and 106.5 mT from constant homogeneous magnetic fields and examined for inhibition of population growth. The number of amoebae for three species was significantly less than controls after a 72 h exposure to the magnetic fields when the temperature was 20 C or above. Axenic cultures, i.e., cultures grown without bacteria, were significantly affected after only 24 h. In 20 of 21 tests using the three species, the magnetic field significantly inhibited the growth of amoebae. In one test in which the temperature was 20 C for 48 h, exposure to the magnetic field was not inhibitory. Final numbers of magnetic field-exposed amoebae ranged from 9 to 72% lower than the final numbers of unexposed controls, depending on the species. This research may lead to disinfection strategies utilizing magnetic fields for surfaces on which pathogenic amoebae may proliferate.
Fossil magnetic field of accretion disks of young stars
NASA Astrophysics Data System (ADS)
Dudorov, A. E.; Khaibrakhmanov, S. A.
2014-07-01
We elaborate the model of accretion disks of young stars with the fossil large-scale magnetic field in the frame of Shakura and Sunyaev approximation. Equations of the MHD model include Shakura and Sunyaev equations, induction equation and equations of ionization balance. Magnetic field is determined taking into account ohmic diffusion, magnetic ambipolar diffusion and buoyancy. Ionization fraction is calculated considering ionization by cosmic rays and X-rays, thermal ionization, radiative recombinations and recombinations on the dust grains. Analytical solution and numerical investigations show that the magnetic field is coupled to the gas in the case of radiative recombinations. Magnetic field is quasi-azimuthal close to accretion disk inner boundary and quasi-radial in the outer regions. Magnetic field is quasi-poloidal in the dusty "dead" zones with low ionization degree, where ohmic diffusion is efficient. Magnetic ambipolar diffusion reduces vertical magnetic field in 10 times comparing to the frozen-in field in this region. Magnetic field is quasi-azimuthal close to the outer boundary of accretion disks for standard ionization rates and dust grain size a d=0.1 ?m. In the case of large dust grains ( a d>0.1 ?m) or enhanced ionization rates, the magnetic field is quasi-radial in the outer regions. It is shown that the inner boundary of dusty "dead" zone is placed at r=(0.1-0.6) AU for accretion disks of stars with M=(0.5-2) M ?. Outer boundary of "dead" zone is placed at r=(3-21) AU and it is determined by magnetic ambipolar diffusion. Mass of solid material in the "dead" zone is more than 3 M ? for stars with M?1 M ?.
The effect of Birkeland currents on magnetic field topology
NASA Technical Reports Server (NTRS)
Peroomian, Vahe; Lyons, Larry R.; Schulz, Michael
1996-01-01
A technique was developed for the inclusion of large scale magnetospheric current systems in magnetic field models. The region 1 and 2 Birkeland current systems are included in the source surface model of the terrestrial magnetosphere. The region 1 and 2 Birkeland currents are placed in the model using a series of field aligned, infinitely thin wire segments. The normal component of the magnetic field from these currents is calculated on the surface of the magnetopause and shielded using image current carrying wires placed outside of the magnetosphere. It is found that the inclusion of the Birkeland currents in the model results in a northward magnetic field in the near-midnight tail, leading to the closure of previously open flux in the tail, and a southward magnetic field in the flanks. A sunward shift in the separatrix is observed.
Analytical estimation of the Earth's magnetic field scale
Bologna, Mauro
2012-01-01
In this paper we analytically estimate the magnetic field scale of planets with physical core conditions similar to that of Earth from a statistical point of view. We evaluate the magnetic field on the basis of the physical parameters of the center of the planet, such as density, temperature, and core size. We look at the contribution of the Peltier-Seebeck effect on the magnetic field, showing that an electrical thermal current can exist in a rotating fluid sphere. Finally, we apply our calculations to Earth and Jupiter. In each case we show that the thermal generation of currents leads to a magnetic field scale comparable to the observed fields of the two planets.
Hotta, H.; Yokoyama, T.; Rempel, M.
2014-05-01
We carry out non-rotating high-resolution calculations of the solar global convection, which resolve convective scales of less than 10 Mm. To cope with the low Mach number conditions in the lower convection zone, we use the reduced speed of sound technique (RSST), which is simple to implement and requires only local communication in the parallel computation. In addition, the RSST allows us to expand the computational domain upward to about 0.99 R {sub ?}, as it can also handle compressible flows. Using this approach, we study the solar convection zone on the global scale, including small-scale near-surface convection. In particular, we investigate the influence of the top boundary condition on the convective structure throughout the convection zone as well as on small-scale dynamo action. Our main conclusions are as follows. (1) The small-scale downflows generated in the near-surface layer penetrate into deeper layers to some extent and excite small-scale turbulence in the region >0.9 R {sub ?}, where R {sub ?} is the solar radius. (2) In the deeper convection zone (<0.9 R {sub ?}), the convection is not influenced by the location of the upper boundary. (3) Using a large eddy simulation approach, we can achieve small-scale dynamo action and maintain a field of about 0.15B {sub eq}-0.25B {sub eq} throughout the convection zone, where B {sub eq} is the equipartition magnetic field to the kinetic energy. (4) The overall dynamo efficiency varies significantly in the convection zone as a consequence of the downward directed Poynting flux and the depth variation of the intrinsic convective scales.
SOLIS/VSM Polar Magnetic Field Data
Bertello, Luca
2015-01-01
The Vector Spectromagnetograph (VSM) instrument on the Synoptic Optical Long-term Investigations of the Sun (SOLIS) telescope is designed to obtain high-quality magnetic field observations in both the photosphere and chromosphere by measuring the Zeeman-induced polarization of spectral lines. With 1$^{\\prime \\prime}$ spatial resolution (1.14$^{\\prime \\prime}$ before 2010) and 0.05\\AA\\ spectral resolution, the VSM provides, among other products, chromospheric full-disk magnetograms using the CaII 854.2 nm spectral line and both photospheric full-disk vector and longitudinal magnetograms using the FeI 630.15 nm line. Here we describe the procedure used to compute daily weighted averages of the photospheric radial polar magnetic field at different latitude bands from SOLIS/VSM longitudinal full-disk observations. Time series of these measurements are publicly available from the SOLIS website at http://solis.nso.edu/0/vsm/vsm\\_plrfield.html. Future plans include the calculation of the mean polar field strength fr...
Extraterrestrial Magnetic Fields: Achievements and Opportunities
EDWARD J. SMITHAND; Charles Sonett
1976-01-01
The major scientific achievements associated with the measurement of magnetic fields in space over the past decade and a half are reviewed. Aspects of space technology relevant to magnetic-field observations are discussed, including the different types of magnetometers used and how they operate, problems arising from spacecraft-generated magnetic fields and the appropriate countermeasures that have been developed and on-board processing
Neutral $?$ and $A$ mesons in magnetic field in SU(2) lattice gauge theory
E. V. Luschevskaya; O. V. Larina
2013-08-09
Correlators of vector, axial and pseudoscalar currents have been calculated in external strong magnetic field in SU(2) gluodynamics on the lattice. Neutral $\\rho$ and $A$ meson masses with a zero spin projection to the axis parallel to the external magnetic field $B$ are calculated. The mass of the neutral $\\rho$ meson with zero spin decreases with increasing of the magnetic field for available values of the magnetic field $eB\\lesssim 2-2.5\\, \\Gev^2$, such behavior is necessary for a condensation of $\\rho$ mesons in a strong magnetic field.
Minimizing magnetic fields for precision experiments
Altarev, I; Lins, T; Marino, M G; Nießen, B; Petzoldt, G; Reisner, M; Stuiber, S; Sturm, M; Singh, J T; Taubenheim, B; Rohrer, H K; Schläpfer, U
2015-01-01
An increasing number of measurements in fundamental and applied physics rely on magnetically shielded environments with sub nano-Tesla residual magnetic fields. State of the art magnetically shielded rooms (MSRs) consist of up to seven layers of high permeability materials in combination with highly conductive shields. Proper magnetic equilibration is crucial to obtain such low magnetic fields with small gradients in any MSR. Here we report on a scheme to magnetically equilibrate MSRs with a 10 times reduced duration of the magnetic equilibration sequence and a significantly lower magnetic field with improved homogeneity. For the search of the neutron's electric dipole moment, our finding corresponds to a linear improvement in the systematic reach and a 40 % improvement of the statistical reach of the measurement. However, this versatile procedure can improve the performance of any MSR for any application.
Magnetic field vector retrieval with the Helioseismic and Magnetic Imager
J. M. Borrero; S. Tomczyk; A. Norton; T. Darnell; J. Schou; P. Scherrer; R. Bush; Y. Liu
2006-11-17
We investigate the accuracy to which we can retrieve the solar photospheric magnetic field vector using the Helioseismic and Magnetic Imager (HMI) that will fly onboard of the Solar Dynamics Observatory (SDO) by inverting simulated HMI profiles. The simulated profiles realistically take into account the effects of the photon noise, limited spectral resolution, instrumental polarization modulation, solar p modes and temporal averaging. The accuracy of the determination of the magnetic field vector is studied considering the different operational modes of the instrument.
Anisotropic nanostructured magnets by magnetic-field-assisted processing
NASA Astrophysics Data System (ADS)
Rong, Chuan-bing; Nguyen, Van Vuong; Liu, J. Ping
2010-05-01
It has been a great challenge to produce anisotropic nanocrystalline bulk magnets. In this paper, we report our recent work in preparing anisotropic bonded magnets consisting of SmCo5 nanocrystalline particles. The work involved synthesis of nanocrystalline hard magnetic SmCo5 particles by ball milling in the presence of a magnetic field. Structural and magnetic characterizations show the alignment of the c-axis of the SmCo5 grains upon the magnetic-field-assisted ball milling, while the grain size was controlled under 15 nm. The formation of the texture may be attributed to the effect of magnetic fields on the grain orientation during the cold welding process during ball milling. The as-milled particles were then compacted under a magnetic field with a binder to form bonded bulk SmCo5 nanostructured magnets. X-ray diffraction patterns show c-axis alignment in the bulk magnets, which was consistent with the magnetic measurements.
Magnetic field screening effect in electroweak model
A. S. Bakry; D. G. Pak; P. M. Zhang; L. P. Zou
2014-10-03
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.
Magnetic vector field tag and seal
Johnston, Roger G.; Garcia, Anthony R.
2004-08-31
One or more magnets are placed in a container (preferably on objects inside the container) and the magnetic field strength and vector direction are measured with a magnetometer from at least one location near the container to provide the container with a magnetic vector field tag and seal. The location(s) of the magnetometer relative to the container are also noted. If the position of any magnet inside the container changes, then the measured vector fields at the these locations also change, indicating that the tag has been removed, the seal has broken, and therefore that the container and objects inside may have been tampered with. A hollow wheel with magnets inside may also provide a similar magnetic vector field tag and seal. As the wheel turns, the magnets tumble randomly inside, removing the tag and breaking the seal.
A Possible Mechanism for Generating Galactic Magnetic Fields
NASA Astrophysics Data System (ADS)
Davies, George; Widrow, Lawrence M.
2000-09-01
We demonstrate that the Biermann battery mechanism for the creation of large-scale magnetic fields can arise in a simple model protogalaxy. Analytic calculations and numerical simulations follow explicitly the generation of vorticity (and hence magnetic field) at the outward-moving shock that develops as the protogalactic perturbation collapses. Shear angular momentum then distorts this field into a dipole-like configuration. The magnitude of the field created in the fully formed disk galaxy is estimated to be 10-17 G, approximately what is needed as a seed for the galactic dynamo.
Magnetic fields in anisotropic relativistic stars
Vladimir Folomeev; Vladimir Dzhunushaliev
2015-02-28
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.
Spectra of magnetic fields injected during baryogenesis
NASA Astrophysics Data System (ADS)
Ng, Yifung; Vachaspati, Tanmay
2010-07-01
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.
Dissipative Charged Fluid in a Magnetic Field
Navid Abbasi; Ali Davody
2015-08-27
We study the collective excitations in a dissipative charged fluid at zero chemical potential when an external magnetic field is present. While in the absence of magnetic field, four collective excitations appear in the fluid, we find five hydrodynamic modes in presence of magnetic field. This implies that the magnetic field splits the degeneracy between the transverse shear modes. Using linear response theory, we then compute the retarded response functions. In particular, it turns out that the correlation between charge and the energy fluctuations will no longer vanish, even at zero chemical potential. By use of the response functions, we also derive the relevant Kubo formulas for the transport coefficients.
Flow Transitions in a Rotating Magnetic Field
NASA Technical Reports Server (NTRS)
Volz, M. P.; Mazuruk, K.
1996-01-01
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.
Dissipative Charged Fluid in a Magnetic Field
Abbasi, Navid
2015-01-01
We study the collective excitations in a dissipative charged fluid at zero chemical potential when an external magnetic field is present. While in the absence of magnetic field, four collective excitations appear in the fluid, we find five hydrodynamic modes in presence of magnetic field. This implies that the magnetic field splits the degeneracy between the transverse shear modes. Using linear response theory, we then compute the retarded response functions. In particular, it turns out that the correlation between charge and the energy fluctuations will no longer vanish, even at zero chemical potential. By use of the response functions, we also derive the relevant Kubo formulas for the transport coefficients.
Transport properties of high-temperature air in a magnetic field
Bruno, D. [Institute of Inorganic Methodologies and Plasmas, CNR, 70126 Bari (Italy); Capitelli, M.; Catalfamo, C. [Department of Chemistry, University of Bari, 70126 Bari (Italy); Giordano, D. [Aerothermodynamics Section, ESA-ESTEC, 2200 AG Noordwijk (Netherlands)
2011-01-15
Transport properties of equilibrium air plasmas in a magnetic field are calculated with the Chapman-Enskog method. The range considered for the temperature is [50-50 000] K and for the magnetic induction is [0-300] T.
Generation of the magnetic field in jets
V. Urpin
2006-05-22
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.
The QCD equation of state in background magnetic fields
NASA Astrophysics Data System (ADS)
Bali, G. S.; Bruckmann, F.; Endr?di, G.; Katz, S. D.; Schäfer, A.
2014-08-01
We determine the equation of state of 2+1-flavor QCD with physical quark masses, in the presence of a constant (electro)magnetic background field on the lattice. To determine the free energy at nonzero magnetic fields we develop a new method, which is based on an integral over the quark masses up to asymptotically large values where the effect of the magnetic field can be neglected. The method is compared to other approaches in the literature and found to be advantageous for the determination of the equation of state up to large magnetic fields. Thermodynamic observables including the longitudinal and transverse pressure, magnetization, energy density, entropy density and interaction measure are presented for a wide range of temperatures and magnetic fields, and provided in ancillary files. The behavior of these observables confirms our previous result that the transition temperature is reduced by the magnetic field. We calculate the magnetic susceptibility and permeability, verifying that the thermal QCD medium is paramagnetic around and above the transition temperature, while we also find evidence for weak diamagnetism at low temperatures.
Modeling magnetic field amplification in nonlinear diffusive shock acceleration
NASA Astrophysics Data System (ADS)
Vladimirov, Andrey
2009-02-01
This research was motivated by the recent observations indicating very strong magnetic fields at some supernova remnant shocks, which suggests in-situ generation of magnetic turbulence. The dissertation presents a numerical model of collisionless shocks with strong amplification of stochastic magnetic fields, self-consistently coupled to efficient shock acceleration of charged particles. Based on a Monte Carlo simulation of particle transport and acceleration in nonlinear shocks, the model describes magnetic field amplification using the state-of-the-art analytic models of instabilities in magnetized plasmas in the presence of non-thermal particle streaming. The results help one understand the complex nonlinear connections between the thermal plasma, the accelerated particles and the stochastic magnetic fields in strong collisionless shocks. Also, predictions regarding the efficiency of particle acceleration and magnetic field amplification, the impact of magnetic field amplification on the maximum energy of accelerated particles, and the compression and heating of the thermal plasma by the shocks are presented. Particle distribution functions and turbulence spectra derived with this model can be used to calculate the emission of observable nonthermal radiation.
Swarm: ESA's Magnetic Field Mission
NASA Astrophysics Data System (ADS)
Plank, G.; Floberghagen, R.; Menard, Y.; Haagmans, R.
2013-12-01
Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in fall 2013. The objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution using a constellation of three identical satellites. The mission shall deliver data that allow access to new insights into the Earth system by improved scientific understanding of the Earth's interior and near-Earth electromagnetic environment. After launch and triple satellite release at an initial altitude of about 490 km, a pair of the satellites will fly side-by-side with slowly decaying altitude, while the third satellite will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission science goals are to provide a unique view into Earth's core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently in the final stage of the development phase, will be addressed. A consortium of European scientific institutes is developing a distributed processing system to produce geophysical (Level 2) data products for the Swarm user community. The setup of the Swarm ground segment and the contents of the data products will be addressed. In case the Swarm satellites are already in orbit, a summary of the on-going mission operations activities will be given. More information on Swarm can be found at www.esa.int/esaLP/LPswarm.html.
Swarm: ESA's Magnetic Field Mission
NASA Astrophysics Data System (ADS)
Plank, Gernot; Haagmans, Roger; Floberghagen, Rune; Menard, Yvon
2013-04-01
Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in 2013. The objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution using a constellation of 3 identical satellites. The Mission shall deliver data that allow access to new insights into the Earth system by improved scientific understanding of the Earth's interior and near-Earth electromagnetic environment. After launch and triple satellite release at an initial altitude of about 490 km, a pair of the satellites will fly side-by-side with slowly decaying altitude, while the third satellite will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission science goals are to provide a unique view into Earth's core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently in the final stage of the development phase, will be addressed. A consortium of European scientific institutes is developing a distributed processing system to produce geophysical (Level 2) data products for the Swarm user community. The setup of the Swarm ground segment and the contents of the data products will be addressed. More information on Swarm can be found at www.esa.int/esaLP/LPswarm.html.
Magnetic helicity of the Parker field. [IMF within heliosphere
NASA Technical Reports Server (NTRS)
Bieber, J. W.; Evenson, P. A.; Matthaeus, W. H.
1987-01-01
The topological properties of the interplanetary magnetic field are discussed based on a calculation of the magnetic helicity of the Parker field. The most striking feature of the helicity is that it is negative north of the heliospheric current sheet and positive south of the current sheet, regardless of the sign of the solar poloidal magnetic field. Informal arguments based on MHD turbulence theory suggest that the magnetic helicity of turbulence in the interplanetary medium may be related to the large-scale Parker helicity. Because charged particle scattering in certain types of magnetic turbulence (such as slab turbulence) depends strongly upon helicity, the existence of such a relationship could have important implications to cosmic-ray transport in the heliosphere.
Song, Yongliang
2015-01-01
It is generally believed that the evolution of magnetic helicity has a close relationship with solar activity. Before the launch of SDO, earlier studies have mostly used MDI/SOHO line of sight magnetograms and assumed that magnetic fields are radial when calculating magnetic helicity injection rate from photospheric magnetograms. However, this assumption is not necessarily true. Here we use the vector magnetograms and line of sight magnetograms, both taken by HMI/SDO, to estimate the effects of non-radial magnetic field on measuring magnetic helicity injection rate. We find that: 1) The effect of non-radial magnetic field on estimating tangential velocity is relatively small; 2) On estimating magnetic helicity injection rate, the effect of non-radial magnetic field is strong when active regions are observed near the limb and is relatively small when active regions are close to disk center; 3) The effect of non-radial magnetic field becomes minor if the amount of accumulated magnetic helicity is the only conce...
Radio Frequency Field Calculations for Plasma Heating Simulations in VASIMR
NASA Astrophysics Data System (ADS)
Ilin, A. V.; Díaz, F. R. Chang; Squire, J. P.; Carter, M. D.
2002-01-01
(VASIMR)1 is plasma heating by ion-cyclotron RF heating (ICRF). Mathematical simulation helps to design an ICRF antenna, i.e. make maximal absorption of RF power into the plasma in the resonance area. Another goal of a particle simulation is design of a magnetic nozzle and optimize the performance of VASIMR2. field in the plasma, 2) ion density and velocity, 3) ion-cyclotron radio-frequency electromagnetic field. The assumptions of quasineutral and collisionless plasma are based on the range of operating VASIMR parameters. Carlo simulations for systems of million of particles in a reasonable time and without the need for a powerful supercomputer. The particle to grid weighting method is used for calculating the ion density, which is used for recalculation of the electric potential and RF field. dimensional problem to a weighted sum over two-dimensional solutions. Absorption is introduced in the cold plasma model by adding an imaginary collision frequency to the RF driven frequency, which is equivalent to adding an imaginary particle mass in the dielectric tensor elements. static and RF fields using the VASIMR code2. The VASIMR and EMIR codes are then iterated to estimate the ICRF effects on the plasma density. The iteration is performed by calculating the RF fields with the EMIR code, and using these fields to follow nonlinear ion trajectories with the VASIMR code on the gyro-frequency time scale. The ion trajectories are used to generate RF power absorption values and a density input for the next EMIR calculation. The codes are iterated until the density profile becomes reasonably stable, then the collisional absorption parameter in the EMIR code is adjusted and the iteration is continued until the power deposited by the RF system matches the power absorbed by the ion trajectories in a global sense. electric field. The solved algebraic system of equations is represented by ill-conditioned 18-diagonal matrix with complex elements. Since early development of the EMIR code, the frontal method direct solver was used. That solver requires large CPU time and RAM, which both are proportional to Nr Nz2, for a grid of the size Nr x Nz. These requirements make almost impossible to use existent EMIR solver on PC to obtain RF fields with good accuracy. system. The suggested iterative method is Modified Incomplete Cholesky Preconditioned Conjugate Gradient Squared solver4. The solver involves a couple of the control parameters, which let a user tune the code to make iterations converge as fast as possible for a particular grid. Since the iterative solver does not require large RAM, and works much faster than the direct solver, the new algorithm lets us resolve RF fields on a PC with required accuracy. REFERENCES 1. Chang Díaz F.R., "Research Status of The Variable Specific Impulse Magnetoplasma Rocket", Proc. 39th Annual Meeting of the Division of Plasma Physics (Pittsburgh, PA, 1997), Bulletin of APS, 42 2057. 2. Ilin A.V., Chang Díaz F.R., Squire J.P. and Carter M.D. "Monte Carlo Particle Dynamics in a Variable Specific Impulse Magnetoplasma Rocket", (Proceedings of Open Systems' 98), Transactions of Fusion Technology, 35 330 - 334 (1999). 3. Jaeger E.F., Batchelor D.B., Weitzner H. and Whealton J.H. "ICRF Wave Propagation And Absorption in Tokamak And Mirror Magnetic Fields - A Full-wave Calculation", Computer Physics Com., 40 33 - 64 (1986). 4. Ilin, A. V., Bagheri, B., Scott, L. R., Briggs, J. M., and McCammon, J. A. "Parallelization of Poisson-Boltzmann and Brownian Dynamics calculation", Parallel Computing in Computational Chemistry, ACB Books, Washington D.C., (1995) 170-185.
High-field magnetization of polycrystalline praseodymium
NASA Astrophysics Data System (ADS)
Leyarovski, E.; Mrachkov, J.; Gilewski, A.; Mydlarz, T.
1987-06-01
The field dependence of the induced magnetic moment in polycrystalline Pr is studied in impulse magnetic fields up to 45 T at 4.2 K and in stationary magnetic fields up to 18 T at 20 and 30 K. No anomalies in the magnetization have been observed which might be associated with the metamagnetic phase transition in single crystals at 31.5 T [K. A. McEwen, G. J. Cock, L. W. Roeland, and A. R. Mackinstosh, Phys. Rev. Lett. 30, 287 (1973)], as well as with any changes of the orientation of the magnetic moments characteristic for an antiferromagnetic. The observed magnetization is satisfactorily described using a molecular field Hamiltonian including the crystal electric field potential, exchange interactions, and Zeeman-effect term.
Image-Optimized Coronal Magnetic Field Reconstructions
NASA Astrophysics Data System (ADS)
Jones, S. I.; Davila, J. M.; Uritsky, V. M.
2014-12-01
The magnetic field dominates many of the most important and puzzling processes in the corona. In the absence of direct measurements, solar physicists have struggled for decades to accurately reconstruct the coronal magnetic field using photospheric magnetograms. Even with today's excellent magnetographs, these reconstructions are plagued by several problems, among them long computation time, and poor agreement with the structures seen in EUV and coronagraph images. However no method exists for systematically improving the agreement between coronal images and magnetic reconstructions. Solar Orbiter and Solar Probe Plus will bring us closer to the sun we have ever been before, but taking full advantage of that opportunity requires accurate coronal magnetic field reconstructions so that we can connect the in situ observations offered by these unique missions to magnetic sources at the surface of the Sun. In this study we propose a method to improve coronal magnetic field reconstructions by optimizing agreement between the reconstructed field and white-light coronagraph images.
Stellar model atmospheres with magnetic line blanketing. III. The role of magnetic field inclination
S. A. Khan; D. V. Shulyak
2006-07-20
Context. See abstract in the paper. Aims. In the last paper of this series we study the effects of the magnetic field, varying its strength and orientation, on the model atmosphere structure, the energy distribution, photometric colors and the hydrogen Balmer line profiles. We compare with the previous results for an isotropic case in order to understand whether there is a clear relation between the value of the magnetic field angle and model changes, and to study how important the additional orientational information is. Also, we examine the probable explanation of the visual flux depressions of the magnetic chemically peculiar stars in the context of this work. Methods. We calculated one more grid of the model atmospheres of magnetic A and B stars for different effective temperatures (Teff=8000K, 11000K, 15000K), magnetic field strengths (B=0, 5, 10, 40 kG) and various angles of the magnetic field (Omega=0-90 degr) with respect to the atmosphere plane. We used the LLmodels code which implements a direct method for line opacity calculation, anomalous Zeeman splitting of spectral lines, and polarized radiation transfer. Results. We have not found significant changes in model atmosphere structure, photometric and spectroscopic observables or profiles of hydrogen Balmer lines as we vary the magnetic field inclination angle Omega. The strength of the magnetic field plays the main role in magnetic line blanketing. We show that the magnetic field has a clear relation to the visual flux depressions of the magnetic CP stars. Conclusions. See abstract in the paper.
Energy buildup in sheared force-free magnetic fields
NASA Technical Reports Server (NTRS)
Wolfson, Richard; Low, Boon C.
1992-01-01
Photospheric displacement of the footpoints of solar magnetic field lines results in shearing and twisting of the field, and consequently in the buildup of electric currents and magnetic free energy in the corona. The sudden release of this free energy may be the origin of eruptive events like coronal mass ejections, prominence eruptions, and flares. An important question is whether such an energy release may be accompanied by the opening of magnetic field lines that were previously closed, for such open field lines can provide a route for matter frozen into the field to escape the sun altogether. This paper presents the results of numerical calculations showing that opening of the magnetic field is permitted energetically, in that it is possible to build up more free energy in a sheared, closed, force-free magnetic field than is in a related magnetic configuration having both closed and open field lines. Whether or not the closed force-free field attains enough energy to become partially open depends on the form of the shear profile; the results presented compare the energy buildup for different shear profiles. Implications for solar activity are discussed briefly.
Decay of massive scalar field in a black hole background immersed in magnetic field
Wu, Chen
2015-01-01
We calculated quasinormal modes of massive scalar field of the Ernst black holes, i.e., neutral black holes immersed in an external magnetic field. The Ernst solution reduces to the Schwarzschild solution when the magnetic field vanishes. It is found that the quasinormal spectrum for massive scalar field in the vicinity of the magnetized black holes acquires an effective mass $\\mu_{eff}= \\sqrt{4B^2 m^2+\\mu^2}$, where $m$ is the azimuthal number, $\\mu$ the mass of scalar field and $B$ the parameter describing the magnetic field. The numerical result shows that increasing of the field effective mass gives rise to decreasing of the imaginary part of the quasinormal modes until reaching the vanishing damping rate.
Quark Antiscreening at Strong Magnetic Field and Inverse Magnetic Catalysis
E. J. Ferrer; V. de la Incera; X. J. Wen
2015-02-17
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.
Strangelets under strong magnetic fields
Fune, E Lopez
2012-01-01
In this thesis is studied three of the fundamental properties of clusters of matter made of quarks u, d and s called strangelets: the energy per baryon, the radius and the electric charge, all in the presence of intense magnetic fields and finite temperature. Two cases will take our attention: unpaired phase strangelets, where there is no restriction to the number of flavors of quarks, and a particular case of the color superconducting phase, where exists a restriction to the quark numbers and an additional energy gap. We study the stability of strangelets, measured by the energy per baryon, to compare later with that of the 56Fe : the most stable isotope known in nature. We employ the Liquid Drop formalism of the Bag Model MIT to describe the interaction between quarks. We conclude that the field effects tend to decrease the energy per baryon of strangelets and temperature produces the opposite effect. It is also shown that strangelets in the color superconducting phase are more stable than those in the unpa...
Charged and neutral vector meson under magnetic field
Hao Liu; Lang Yu; Mei Huang
2014-08-06
The vector meson $\\rho$ in the presence of external magnetic field has been investigated in the framework of the Nambu--Jona-Lasinio model, where mesons are constructed by infinite sum of quark-loop chains by using random phase approximation. The $\\rho$ meson polarization function is calculated to the leading order of $1/N_c$ expansion. It is found that the constituent quark mass increases with magnetic field, the masses of the neutral vector meson $\\rho^{0}$ with spin component $s_z=0,\\,\\pm1$ and the charged vector meson $\\rho^{\\pm}$ with $s_z=0$ also increases with magnetic field. However, the mass square of the charged vector meson $\\rho^{+}$ ($\\rho^{-}$) with $s_z=+1$ ($s_z=-1$) decreases linearly with magnetic field and drops to zero at the critical magnetic field $e B_c \\simeq 0.2 {\\rm GeV}^2$, which indicates the possible condensation of charged vector meson in the vacuum. This critical magnetic field is much lower than the value $eB_c=0.6 {\\rm GeV}^2$ predicted by a point-like vector meson. We also show that if we use lowest Landau level approximation, the mass of the charged vector meson $\\rho^{\\pm}$ for $s_z=\\pm1$ cannot drop to zero at high magnetic fields.
The Physics of Attraction and Repulsion: Magnetism and Magnetic Fields
NASA Astrophysics Data System (ADS)
Nakotte, Heinz
2001-11-01
The development of new materials with improved magnetic properties completely changed the modern world in the past decades. Recent progress is predominantly due to a better understanding of magnetism that has gone far beyond compass needles rotating in a magnetic field and bar magnets attracting or repelling each other. New magnetic materials are used to build smaller and smaller read/write heads and hard disks with increased storage capacity, developments that are responsible the revolution in the computer industry. Another example is the field of magnetic levitation that became feasible for commercial applications with the discovery of new superconducting materials, and a prototype train is under development in Japan. In medicine, the development of magnetic resonance imaging (MRI) provides an alternative to other (destructive) radiation techniques.
Quenching of flames by magnetic fields
NASA Astrophysics Data System (ADS)
Ueno, S.
1989-02-01
An experiment has been demonstrated to show a phenomenon involving quenching of candle flames using magnetic fields. An electromagnet with a pair of columnar magnetic poles in which inner sidepieces were hollowed out was used. Magnetic fields of 1.5 T at the brim gave a gradient of 50-300 T/m in the direction perpendicular to the pole axis when the distance of the airgap was in a range of 5-10 mm. A candle was burned in the hollowed space between magnetic poles, and candle flames were exposed to magnetic fields. The flames were quenched a few seconds after the onset of field exposures. A model, called a ``magnetic curtain,'' was introduced to explain this phenomenon. It is assumed that the magnetic curtain is a wall of air which is formed by magnetic fields. The magnetic curtain, which is also called an ``air curtain,'' blocks air flow in and out of the hollowed space. The interception of oxygen by the magnetic curtain quenches flames. The magnetic curtain also presses back flames and other gases.
Magnetic Braiding and Parallel Electric Fields
A. L. Wilmot-Smith; G. Hornig; D. I. Pontin
2008-10-08
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.
The Evolution of the Earth's Magnetic Field.
ERIC Educational Resources Information Center
Bloxham, Jeremy; Gubbins, David
1989-01-01
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)
Long-term evolution of crustal neutron star magnetic fields
NASA Astrophysics Data System (ADS)
Urpin, V. A.; Chanmugam, G.; Sang, Yeming
1994-10-01
We have derived an analytic solution to the asymptotic behavior of dipolar magnetic fields that are generated in the crusts of neutron stars. We show that if the conductivity is due to impurity scattering, as expected for late stages of evolution, the surface field strength at the magnetic pole declines with the power law Bp approximately = (t/t0)-2/3. The results are shown to be qualitatively consistent with detailed numerical calculations. These latter results are consistent with some recent analyses of pulsar statistics and the magnetic fields of several binary pulsars with white dwarf companions whose ages have been determined. The dependence of the surface magnetic field on spin period of the pulsar is derived.
Long-term evolution of crustal neutron star magnetic fields
NASA Technical Reports Server (NTRS)
Urpin, V. A.; Chanmugam, G.; Sang, Yeming
1994-01-01
We have derived an analytic solution to the asymptotic behavior of dipolar magnetic fields that are generated in the crusts of neutron stars. We show that if the conductivity is due to impurity scattering, as expected for late stages of evolution, the surface field strength at the magnetic pole declines with the power law B(sub p) approximately = (t/t(sub 0))(exp -2/3). The results are shown to be qualitatively consistent with detailed numerical calculations. These latter results are consistent with some recent analyses of pulsar statistics and the magnetic fields of several binary pulsars with white dwarf companions whose ages have been determined. The dependence of the surface magnetic field on spin period of the pulsar is derived.
Effects of primordial magnetic fields on CMB
Hector J. Hortua; Leonardo Castañeda
2015-09-13
The origin of large-scale magnetic fields is an unsolved problem in cosmology. In order to overcome, a possible scenario comes from the idea that these fields emerged from a small primordial magnetic field (PMF), produced in the early universe. This field could lead to the observed large-scales magnetic fields but also, would have left an imprint on the cosmic microwave background (CMB). In this work we summarize some statistical properties of this PMFs on the FLRW background. Then, we show the resulting PMF power spectrum using cosmological perturbation theory and some effects of PMFs on the CMB anisotropies.
Graphene Nanoribbon in Sharply Localized Magnetic Fields
Abdulaziz D. Alhaidari; Hocine Bahlouli; Abderrahim El Mouhafid; Ahmed Jellal
2013-03-20
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.
Control of magnetism by electric fields.
Matsukura, Fumihiro; Tokura, Yoshinori; Ohno, Hideo
2015-03-01
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
Alignment Behavior of Crystal with Magnetic Anisotropy of ?c < ?a under Rotating Magnetic Field
NASA Astrophysics Data System (ADS)
Iwai, Kazuhiko; Niimi, Masahiro; Kohama, Takenori
2009-10-01
The alignment behavior of a crystal has been investigated by numerical calculation and an in situ observation experiment with a process combining magnetic field imposition and sample rotation to form unidirectionally aligned crystals with a magnetic anisotropy of ?c < ?a. The experimentally observed alignment behavior of a polymeric fiber and its alignment time agreed with the numerically calculated ones. Crystal alignment under the out-of-step condition alternately repeats the alignment duration and the keeping of a constant duration, and finally the crystal aligns in a specific direction. The alignment time under the synchronous condition is longer than that under the out-of-step condition if the magnetic field intensity is constant. To reduce the alignment time, a strong magnetic field under the out-of-step condition is desirable in this process.
Energy of magnetic moment of superconducting current in magnetic field
NASA Astrophysics Data System (ADS)
Gurtovoi, V. L.; Nikulov, A. V.
2015-09-01
The energy of magnetic moment of the persistent current circulating in superconducting loop in an externally produced magnetic field is not taken into account in the theory of quantization effects because of identification of the Hamiltonian with the energy. This identification misleads if, in accordance with the conservation law, the energy of a state is the energy expended for its creation. The energy of magnetic moment is deduced from a creation history of the current state in magnetic field both in the classical and quantum case. But taking this energy into account demolishes the agreement between theory and experiment. Impartial consideration of this problem discovers the contradiction both in theory and experiment.
Levitation of a magnet by an alternating magnetic field
NASA Astrophysics Data System (ADS)
Gough, W.; Hunt, M. O.; Summerskill, W. S. H.
2013-01-01
An experiment is described in which a small strong cylindrical magnet is levitated by a vertical non-uniform alternating magnetic field. Surprisingly, no superimposed constant field is necessary, but the levitation can be explained when the vertical motion of the magnet is taken into account. The theoretical mean levitation force is (0.26 ± 0.06) N, which is in good agreement with the levitated weight of (0.239 ± 0.001) N. This experiment is suitable for an undergraduate laboratory, particularly as a final year project. Students have found it interesting, and it sharpens up knowledge of basic magnetism.
Energy of magnetic moment of superconducting current in magnetic field
V. L. Gurtovoi; A. V. Nikulov
2014-12-22
The energy of magnetic moment of the persistent current circulating in superconducting loop in an externally produced magnetic field is not taken into account in the theory of quantization effects because of identification of the Hamiltonian with the energy. This identification misleads if, in accordance with the conservation law, the energy of a state is the energy expended for its creation. The energy of magnetic moment is deduced from a creation history of the current state in magnetic field both in the classical and quantum case. But taking this energy into account demolishes the agreement between theory and experiment. Impartial consideration of this problem discovers the contradiction both in theory and experiment.
{psi}{psi} condensate in constant magnetic fields
Anguiano-Galicia, M. de J; Bashir, A.; Raya, A.
2007-12-15
We solve the Dirac equation in the presence of a constant magnetic field in (3+1) and (2+1) dimensions. Quantizing the fermion field, we calculate the {psi}{psi} condensate from first principles for parity conserving and violating Lagrangians for arbitrary field strength. We make a comparison with the results already known in the literature for some particular cases and point out the relevance of our work for possible physical applications.
Electric and magnetic fields from two-dimensional anisotropic bisyncytia.
Sepulveda, N G; Wikswo, J P
1987-01-01
Cardiac tissue can be considered macroscopically as a bidomain, anisotropic conductor in which simple depolarization wavefronts produce complex current distributions. Since such distributions may be difficult to measure using electrical techniques, we have developed a mathematical model to determine the feasibility of magnetic localization of these currents. By applying the finite element method to an idealized two-dimensional bisyncytium with anisotropic conductivities, we have calculated the intracellular and extracellular potentials, the current distributions, and the magnetic fields for a circular depolarization wavefront. The calculated magnetic field 1 mm from the tissue is well within the sensitivity of a SQUID magnetometer. Our results show that complex bisyncytial current patterns can be studied magnetically, and these studies should provide valuable insight regarding the electrical anisotropy of cardiac tissue. PMID:3580484
Diffusion of magnetic field via turbulent reconnection
NASA Astrophysics Data System (ADS)
Santos de Lima, Reinaldo; Lazarian, Alexander; de Gouveia Dal Pino, Elisabete M.; Cho, Jungyeon
2010-05-01
The diffusion of astrophysical magnetic fields in conducting fluids in the presence of turbulence depends on whether magnetic fields can change their topology via reconnection in highly conducting media. Recent progress in understanding fast magnetic reconnection in the presence of turbulence is reassuring that the magnetic field behavior in computer simulations and turbulent astrophysical environments is similar, as far as magnetic reconnection is concerned. This makes it meaningful to perform MHD simulations of turbulent flows in order to understand the diffusion of magnetic field in astrophysical environments. Our studies of magnetic field diffusion in turbulent medium reveal interesting new phenomena. First of all, our 3D MHD simulations initiated with anti-correlating magnetic field and gaseous density exhibit at later times a de-correlation of the magnetic field and density, which corresponds well to the observations of the interstellar media. While earlier studies stressed the role of either ambipolar diffusion or time-dependent turbulent fluctuations for de-correlating magnetic field and density, we get the effect of permanent de-correlation with one fluid code, i.e. without invoking ambipolar diffusion. In addition, in the presence of gravity and turbulence, our 3D simulations show the decrease of the magnetic flux-to-mass ratio as the gaseous density at the center of the gravitational potential increases. We observe this effect both in the situations when we start with equilibrium distributions of gas and magnetic field and when we follow the evolution of collapsing dynamically unstable configurations. Thus the process of turbulent magnetic field removal should be applicable both to quasi-static subcritical molecular clouds and cores and violently collapsing supercritical entities. The increase of the gravitational potential as well as the magnetization of the gas increases the segregation of the mass and magnetic flux in the saturated final state of the simulations, supporting the notion that the reconnection-enabled diffusivity relaxes the magnetic field + gas system in the gravitational field to its minimal energy state. This effect is expected to play an important role in star formation, from its initial stages of concentrating interstellar gas to the final stages of the accretion to the forming protostar.
Magnetic fields and rotation of spiral galaxies
E. Battaner; H. Lesch; E. Florido
1998-02-02
We present a simplified model in which we suggest that two important galactic problems -the magnetic field configuration at large scales and the flat rotation curve- may be simultaneously explained. A highly convective disc produces a high turbulent magnetic diffusion in the vertical direction, stablishing a merging of extragalactic and galactic magnetic fields. The outer disc may then adquire a magnetic energy gradient very close to the gradient required to explain the rotation curve, without the hypothesis of galactic dark matter. Our model predicts symmetries of the galactic field in noticeable agreement with the large scale structure of our galaxy.
Magnetic Helicity and Large Scale Magnetic Fields: A Primer
NASA Astrophysics Data System (ADS)
Blackman, Eric G.
2015-05-01
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.
Magnetic field spectral crossings of Luttinger holes in quantum wells
NASA Astrophysics Data System (ADS)
Simion, G. E.; Lyanda-Geller, Y. B.
2014-11-01
We develop an analytic approach to two-dimensional (2D) holes in a magnetic field that allows us to gain insight into physics of measuring the parameters of holes, such as cyclotron resonance, Shubnikov-de Haas effect and spin resonance. We derive hole energies, cyclotron masses, and the g factors in the semiclassical regime analytically, as well as analyze numerical results outside the semiclassical range of parameters, qualitatively explaining the experimentally observed magnetic field dependence of the cyclotron mass. In the semiclassical regime with large Landau level indices, and for size quantization energy much bigger than the cyclotron energy, the cyclotron mass coincides with the in-plane effective mass, calculated in the absence of a magnetic field. The hole g factor in a magnetic field perpendicular to the 2D plane is defined not only by the constant of direct coupling of the angular momentum of the holes to the magnetic field, but also by the Luttinger constants defining the effective masses of holes. We find that the g factor for quasi-2D holes with heavy mass in the [001] growth direction in GaAs quantum well is g =4.05 in the semiclasssical regime. Outside the semiclassical range of parameters, holes behave as a species completely different from electrons. Spectra for size- and magnetic-field-quantized holes are nonequidistant, not fanlike, and exhibit multiple crossings, including crossing in the ground level. We calculate the effect of Dresselhaus terms, which transform some of the crossings into anticrossings, and the effects of the anisotropy of the Luttinger Hamiltonian on the 2D hole spectra. Dresselhaus terms of different symmetries are taken into account, and a regularization procedure is developed for the kz3 Dresselhaus terms. Control of the nonequidistant levels and crossing structure by the magnetic field can be used to control the Landau level mixing in hole systems, and thereby control hole-hole interactions in the magnetic field.
Disruption of coronal magnetic field arcades
NASA Technical Reports Server (NTRS)
Mikic, Zoran; Linker, Jon A.
1994-01-01
The ideal and resistive properties of isolated large-scale coronal magnetic arcades are studied using axisymmetric solutions of the time-dependent magnetohydrodynamic (MHD) equations in spherical geometry. We examine how flares and coronal mass ejections may be initiated by sudden disruptions of the magnetic field. The evolution of coronal arcades in response to applied shearing photospheric flows indicates that disruptive behavior can occur beyond a critical shear. The disruption can be traced to ideal MHD magnetic nonequilibrium. The magnetic field expands outward in a process that opens the field lines and produces a tangential discontinuity in the magnetic field. In the presence of plasma resistivity, the resulting current sheet is the site of rapid reconnection, leading to an impulsive release of magnetic energy, fast flows, and the ejection of a plasmoid. We relate these results to previous studies of force-free fields and to the properties of the open-field configuration. We show that the field lines in an arcade are forced open when the magnetic energy approaches (but is still below) the open-field energy, creating a partially open field in which most of the field lines extend away from the solar surface. Preliminary application of this model to helmet streamers indicates that it is relevant to the initiation of coronal mass ejections.
The measurement and analysis of the magnetic field of a synchrotron light source magnet
Graf, Udo Werner
1994-01-01
In this thesis a unique system is used to measure the magnetic field of a superconducting synchrotron light source magnet. The magnet measured is a superferric dipole C-magnet designed to produce a magnetic field up to 3 ...
Random Magnetic Fields, Supersymmetry, and Negative Dimensions
G. Parisi; N. Sourlas
1979-01-01
We prove the equivalence, near the critical point, of a D-dimensional spin system in a random external magnetic field with a (D-2)-dimensional spin system in the absence of a magnetic field. This is due to the hidden supersymmetry of the associated stochastic differential equation. We identify a space with one anticommuting coordinate with a space having negative dimensions -2.
Stellar magnetic fields and signatures of heating
J. L. Linsky
2006-01-01
A great many measurements of stellar X-ray ultraviolet and radio emission have demonstrated that stars with measured or inferred strong magnetic fields show evidence for strong heating in their coronal and chromospheric layers While the qualitative connection between strong magnetic fields and strong heating is evident quantitative measures of the correlation and physical models underlying the connection are less clear
Coronal Heating and the Photospheric Magnetic Field
C. E. Parnell; P. A. Sturrock
1997-01-01
Since magnetic field typically plays a role (either active or passive) in coronal heating theories, it may be possible to evaluate these theories by investigating the relationship between the coronal energy budget (the total power requirement of the corona) and measurable properties of the photospheric magnetic field. The X-ray flux is a useful proxy for the total power required to
LABORATORY VI MAGNETIC FIELDS AND FORCES
Minnesota, University of
Lab VI - 1 LABORATORY VI MAGNETIC FIELDS AND FORCES Magnetism plays a large role in our world for the differences as you go through the problems in this lab. In this set of laboratory problems, you will map motion. PREPARATION: Before coming to lab you should be able to: · Add fields using vector properties
Critical magnetic field in a holographic superconductor
Nakano, Eiji [Department of Physics and Center for Theoretical Sciences, National Taiwan University, Taipei 106, Taiwan (China); Gesellschaft fuer Schwerionenforschung, GSI, D-64291 Darmstadt (Germany); Wen, Wen-Yu [Department of Physics and Center for Theoretical Sciences, National Taiwan University, Taipei 106, Taiwan (China)
2008-08-15
We have studied a holographically dual description of superconductor in (2+1) dimensions in the presence of an applied magnetic field and observed that there exists a critical value of magnetic field, below which a charged condensate can form via a second-order phase transition.
Magnetic Fields at the Center of Coils
ERIC Educational Resources Information Center
Binder, Philippe; Hui, Kaleonui; Goldman, Jesse
2014-01-01
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…
Photon-neutrino interactions in magnetic fields
Shaisultanov R
1998-02-28
The low-energy two neutrino-two photon interactions in the presence of homogeneous magnetic field are studied. The cross sections in external magnetic field are shown to be larger than in vacuum by factor $\\sim (m_W /m_e) ^4(B/B_c) ^2$. The energy-loss rate due to the process $\\gamma \\gamma \\to \
Permanent magnet edge-field quadrupole
Tatchyn, Roman O. (Mountain View, CA)
1997-01-01
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.
Permanent magnet edge-field quadrupole
Tatchyn, R.O.
1997-01-21
Planar permanent magnet edge-field quadrupoles for use in particle accelerating machines and in insertion devices designed to generate spontaneous or coherent radiation from moving charged particles are disclosed. The invention comprises four magnetized rectangular pieces of permanent magnet material with substantially similar dimensions arranged into two planar arrays situated to generate a field with a substantially dominant quadrupole component in regions close to the device axis. 10 figs.
Resistance calculation of the reusable linear magnetic flux compressor coil
Jun Li; Yinchun Gui; Jiansheng Yuan; Zanji Wang; Ping Yan
2004-01-01
The reusable linear magnetic flux compressor has been regarded as a preferred pulsed power supply for the electric gun. Some papers have discussed models for optimal design of this compressor. However, none of them have discussed the resistance calculation of the compressor coil particularly, which is the key issue of the compressor design. Based on a two-dimensional finite element model
Magnetic Force Calculation Between Thin Coaxial Circular Coils in Air
Slobodan I. Babic; Cevdet Akyel
2008-01-01
We present new and fast procedures for calculating magnetic forces between thin coaxial circular coaxial coils in air. The results are expressed in semianalytical form in terms of the complete elliptical integrals of the first and second kind, Heuman's Lambda function, and a term that must be solved numerically. These expressions are accurate and simple to use for several practical
Resistance calculation of the reusable linear magnetic flux compressor coil
Jun Li; Yinchun Gui; Qibin Deng; Chenda Yu; Ping Yan; Jiansheng Yuan
2005-01-01
The reusable linear magnetic flux compressor has been regarded as a preferred pulsed power supply for the electric gun. Some papers have discussed models for optimal design of this compressor. However, none of them have discussed the resistance calculation of the compressor coil particularly, which is the key issue of the compressor design. Based on a two-dimensional finite element model
MRI Magnetic Field Stimulates Rotational Sensors of the Brain
Roberts, Dale C.; Marcelli, Vincenzo; Gillen, Joseph S.; Carey, John P.; Santina, Charles C. Della; Zee, David S.
2012-01-01
SUMMARY Vertigo in and around MRI machines has been noted for years [1, 2]. Several mechanisms have been suggested to explain these sensations [3, 4], yet without direct, objective measures, the cause is unknown. We found that all healthy human subjects lying in the static magnetic field of an MRI machine develop a robust nystagmus. Patients lacking labyrinthine function do not. Here we use the pattern of eye movements as a measure of vestibular stimulation to show that the stimulation is static (continuous, proportional to static magnetic field strength, requiring neither head movement nor dynamic change in magnetic field strength) and directional (sensitive to magnetic field polarity and head orientation). Our calculations and geometric model suggest that magnetic vestibular stimulation derives from a Lorentz force due to interaction between the magnetic field and naturally-occurring ionic currents in the labyrinthine endolymph fluid. This force pushes on the semicircular canal cupula, leading to nystagmus. We emphasize that the unique, dual role of endolymph in the delivery of both ionic current and fluid pressure, coupled with the cupula’s function as a pressure sensor, makes magnetic field induced nystagmus and vertigo possible. Such effects could confound fMRI studies of brain behavior, including resting-state brain activity. PMID:21945276
CALCULATIONS FOR A MERCURY JET TARGET IN A SOLENOID MAGNET CAPTURE SYSTEM
McDonald, Kirk
production surrounds the mercury target. As the liquid metal jet enters or exits the field eddy currents. INTRODUCTION A liquid mercury jet is chosen for the target for the Neutrino Factory Feasibility Study II [1CALCULATIONS FOR A MERCURY JET TARGET IN A SOLENOID MAGNET CAPTURE SYSTEM J. Gallardo, S. Kahn, R
Dynamic equations for three different qudits in a magnetic field
E. A. Ivanchenko
2009-04-22
A closed system of equations for the local Bloch vectors and spin correlation functions of three magnetic qudits, which are in an arbitrary, time-dependent, external magnetic field, is obtained using decomplexification of the Liouville-von Neumann equation. The algorithm of the derivation of the dynamic equations is presented. In the basis convenient for the important physical applications structure constants of algebra su(2S+1) are calculated.
Origin of Galactic and Extragalactic Magnetic Fields
Lawrence M. Widrow
2002-07-11
A variety of observations suggest that magnetic fields are present in all galaxies and galaxy clusters. These fields are characterized by a modest strength (10^{-7}-10^{-5} G) and huge spatial scale (~Mpc). It is generally assumed that magnetic fields in spiral galaxies arise from the combined action of differential rotation and helical turbulence, a process known as the alpha-omega dynamo. However fundamental questions concerning the nature of the dynamo as well as the origin of the seed fields necessary to prime it remain unclear. Moreover, the standard alpha-omega dynamo does not explain the existence of magnetic fields in elliptical galaxies and clusters. The author summarizes what is known observationally about magnetic fields in galaxies, clusters, superclusters, and beyond. He then reviews the standard dynamo paradigm, the challenges that have been leveled against it, and several alternative scenarios. He concludes with a discussion of astrophysical and early Universe candidates for seed fields.
Photospheric sources of magnetic field aligned currents
NASA Astrophysics Data System (ADS)
Nordlund, A.
Distortions of the photospheric magnetic field topology in the photosphere cause twists (field-aligned currents) to propagate along field lines up into the coronal magnetic field. It is noted that for small-scale magnetic loops, these currents have a duration that is long in comparison with the propagation time of Alfven waves along the loop. This gives rise to quasi-static twists of the coronal field lines rather than propagating Alfven waves. The magnetic field-aligned currents associated with such twisted fields may lead to resistive MHD instabilities that are similar to Tokamak instabilities (Waddell et al., 1979; Carreras et al., 1980). For this reason, they may figure prominently in small-scale chromospheric and coronal activity.
Orienting Paramecium with intense static magnetic fields
NASA Astrophysics Data System (ADS)
Valles, James M., Jr.; Guevorkian, Karine; Quindel, Carl
2004-03-01
Recent experiments on cell division suggest the application of intense static magnetic fields as a novel tool for the manipulation of biological systems [1]. The magnetic field appears to couple to the intrinsic anisotropies in the diamagnetic components of the cells. Here, we present measurements of the intrinsic average diamagnetic anisotropy of the whole single celled ciliate, Paramecium Caudatum. Magnetic fields, 2.5 T < B < 8 T were applied to immobilized (non-swimming) Paramecium Caudatum that were suspended in a density matched medium. The organisms align with their long axis parallel to the applied magnetic field. Their intrinsic diamagnetic anisotropy is 3x10-11 in cgs units. We will discuss the implications of these results for employing magnetic fields to probe the behavior of swimming Paramecium. [1] J. M. Valles, Jr. et al., Expt. Cell Res.274, 112-118 (2002).
Quadratic magnetic field dependence of magnetoelectric photocurrent
NASA Astrophysics Data System (ADS)
Dai, Junfeng; Lu, Hai-Zhou; Shen, Shun-Qing; Zhang, Fu-Chun; Cui, Xiaodong
2011-04-01
We experimentally study the spin and electric photocurrents excited by a linearly polarized light via direct interband transitions in an InGaAs/InAlAs quantum well. In the absence of a magnetic field, the linearly polarized light induces a pure spin current due to the spin-orbit coupling, which may be transformed into a measurable electric current by applying an in-plane magnetic field. The induced electric photocurrent is linear with the in-plane magnetic field. Here, we report a quadratic magnetic field dependence of the photocurrent in the presence of an additional perpendicular component of the magnetic field. We attribute the observation to the Hall effect of magnetoelectric photocurrent.
Quadratic magnetic field dependence of magnetoelectric photocurrent
NASA Astrophysics Data System (ADS)
Dai, Junfeng; Lu, Hai-Zhou; Shen, Shun-Qing; Zhang, Fu-Chun; Cui, Xiaodong
2012-02-01
We experimentally study the spin and electric photocurrents excited by a linearly polarized light via direct interband transitions in an InGaAs/InAlAs quantum well. In the absence of a magnetic field, the linearly polarized light induces a pure spin current due to the spin-orbit coupling, which may be transformed into a measurable electric current by applying an in-plane magnetic field. The induced electric photocurrent is linear with the in-plane magnetic field. Here, we report a quadratic magnetic field dependence of the photocurrent in the presence of an additional perpendicular component of the magnetic field. We attribute the observation to the Hall effect of magnetoelectric photocurrent.
Processing of polymers in high magnetic fields
Douglas, E.P.; Smith, M.E.; Benicewicz, B.C. [Los Alamos National Lab., NM (United States); Earls, J.D.; Priester, R.D. Jr. [Dow Chemical Co., Freeport, TX (United States)
1996-05-01
Many organic molecules and polymers have an anisotropic diamagnetic susceptibility, and thus can be aligned in high magnetic fields. The presence of liquid crystallinity allows cooperative motions of the individual molecules, and thus the magnetic energy becomes greater than the thermal energy at experimentally obtainable field strengths. This work has determined the effect of magnetic field alignment on the thermal expansion and mechanical properties of liquid crystalline thermosets in the laboratory. Further advances in magnet design are needed to make magnetic field alignment a commercially viable approach to polymer processing. The liquid crystal thermoset chosen for this study is the diglycidyl ether of dihydroxy-{alpha}-methylstilbene cured with the diamine sulfamilamide. This thermoset has been cured at field strengths up to 18 Tesla.
Tracing magnetic field orientation in starless cores
NASA Astrophysics Data System (ADS)
Maheswar, G.; Ramaprakash, A. N.; Lee, C. W.; Dib, S.
It is now well understood that stars are formed in the interiors of dense, gravitationally bound molecular cloud cores that are both magnetized and turbulent. But the relative role played by the magnetic field and the turbulence in cloud formation and evolution and in the subsequent star formation is a matter of debate. In a magnetically dominated scenario, the magnetic field geometry of the cores is expected to be inherited unchanged from their low-density envelope, even for an hour glass geometry of the field, unless the action of turbulence disturbs it. We carried out polarimetry of stars projected on starless molecular clouds, LDN 183 and LDN 1544, in R-filter. The comparison of these fields with those in the interiors of the cloud cores inferred from the sub-mm polarization shows that both magnetic field and turbulence are important in the cloud formation and evolution of star formation.
Magnetic Field Structure in M17SWex
NASA Astrophysics Data System (ADS)
Sugitani, Koji; Nakamura, Fumitaka; Kusune, Takayoshi
2015-08-01
M17SWex, located near the famous M17 massive star forming region, is an infrared dark cloud with prominent filamentary structures and could be in an earlier stage of star formation process without detection of very massive stars. We present results of near-infrared (JHKs) polarization observations toward the M17SWex cloud with the imaging polarimeter SIRPOL (FOV~7.7’), mounted on the IRSF 1.4-m telescope at the South African Astronomical Observatory, by comparing with other wide-field survey data, such as Spitzer, Herschel, etc. Dichroic absorption of background starlight due to magnetically aligned dust grains produces the polarization along the magnetic field. We have observed 24 fields and covered the most part of the M17SWex cloud to probe the magnetic field of this cloud. Our polarization measurements indicate an ordered global magnetic field that is perpendicular to most of the filaments, implying that the magnetic field is likely to have controlled the formation of the filaments. On the other hand, the magnetic fields in some peripheral regions seem to differ form this global field, implying some impacts on the magnetic fields from the exteriors of the cloud.
Chaotic magnetic fields: Particle motion and energization
Dasgupta, Brahmananda; Ram, Abhay K.; Li, Gang; Li, Xiaocan
2014-02-11
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.
Shape of the proton in a uniform magnetic field
Roberts, Dale S.; Kamleh, Waseem; Leinweber, Derek B. [Special Research Centre for the Subatomic Structure of Matter and Department of Physics, University of Adelaide 5005 (Australia); Bowman, Patrick O. [Centre for Theoretical Chemistry and Physics and Institute of Natural Sciences, Massey University (Albany), Private Bag 102904, North Shore City 0745 (New Zealand)
2010-07-27
The effect of a uniform background magnetic field on the wave function of the d-quark in the ground state of the proton is calculated in Lattice QCD. We focus on the wave functions in the Landau and Coulomb gauges. When the quarks are annihilated at different lattice sites, we observe the formation of a scalar u-d diquark pair within the proton in the Landau gauge, which is not present in the Coulomb gauge. The overall distortion of the wave function under a very large magnetic field, as demanded by the quantisation conditions on the field, is quite small.
Proton Wave Functions in a Uniform Magnetic Field
Roberts, Dale S.; Kamleh, Waseem; Leinweber, Derek B. [Special Research Centre for the Subatomic Structure of Matter and Department of Physics, University of Adelaide 5005 (Australia); Bowman, Patrick O. [Centre for Theoretical Chemistry and Physics and Institute of Natural Sciences, Massey University (Albany), Private Bag 102904, North Shore City 0745 (New Zealand)
2011-05-24
The wave function of the d-quark in the ground state of the proton, and how it is affected in the presence of a uniform background magnetic field is calculated in lattice QCD. We focus on the wave functions in the Landau and Coulomb gauges. When the quarks are annihilated at different lattice sites, we observe the formation of a scalar u-d diquark pair within the proton in the Landau gauge, which is not present in the Coulomb gauge. The overall distortion of the wave function under a very large magnetic field, as demanded by the quantisation conditions on the field, is quite small.
Simple basis for hydrogenic atoms in magnetic fields
Gallas, J.A.C.
1984-01-01
A field-dependent hydrogenic basis is used to obtain the evolution of the energy spectrum of atoms in strong (approx.10/sup 8/ G) and uniform magnetic fields. The basis allows results to be derived analytically. Numerical values for the first 13 excited states of hydrogen are found to be in very good agreement with much more elaborate calculations of Smith et al. and of Brandi. In addition, the possibility of having a remnant type of degeneracy in the presence of the magnetic field is investigated.
Nonrelativistic molecular models under external magnetic and AB flux fields
Sameer M. Ikhdair; Babatunde J. Falaye; Majid Hamzavi
2014-12-21
By using the wave function ansatz method, we study the energy eigenvalues and wave function for any arbitrary $m$-state in two-dimensional Schr\\"{o}dinger wave equation with various power interaction potentials in constant magnetic and Aharonov-Bohm (AB) flux fields perpendicular to the plane where the interacting particles are confined. We calculate the energy levels of some diatomic molecules in the presence and absence of external magnetic and AB flux fields using different potential models. We found that the effect of the Aharonov-Bohm field is much as it creates a wider shift for $m\
Accounting for crustal magnetization in models of the core magnetic field
NASA Technical Reports Server (NTRS)
Jackson, Andrew
1990-01-01
The problem of determining the magnetic field originating in the earth's core in the presence of remanent and induced magnetization is considered. The effect of remanent magnetization in the crust on satellite measurements of the core magnetic field is investigated. The crust as a zero-mean stationary Gaussian random process is modelled using an idea proposed by Parker (1988). It is shown that the matrix of second-order statistics is proportional to the Gram matrix, which depends only on the inner-products of the appropriate Green's functions, and that at a typical satellite altitude of 400 km the data are correlated out to an angular separation of approximately 15 deg. Accurate and efficient means of calculating the matrix elements are given. It is shown that the variance of measurements of the radial component of a magnetic field due to the crust is expected to be approximately twice that in horizontal components.
How do galaxies get their magnetic fields?
NASA Astrophysics Data System (ADS)
Beck, Alexander; Dolag, Klaus; Lesch, Harald
2015-08-01
The origin of magnetic fields in high-redshift and present-day galaxies is a long-standing problem. In this talk, we present a model for the seeding and evolution of magnetic fields in protogalaxies. Supernova (SN) explosions during the assembly of a protogalaxy self-consistently provide magnetic seed fields, which are subsequently amplified by compression, shear flows and random motions.Our model explains the origin of strong magnetic fields of $\\mu$G amplitude within the first starforming protogalactic structures shortly after the first stars have formed.We present cosmological simulations with the GADGET code of Milky Way-like galactic halo formation using a standard LCDM cosmology and analyse the strength and distribution of the evolving magnetic field.Within starforming regions and given typical dimensions and magnetic field strengths in canonical SN remnants, we inject a dipole-shape magnetic field at a rate of nG/Gyr. Subsequently, the magnetic field strength increases exponentially on timescales of a few ten million years within the innermost regions of the halo.Furthermore, turbulent diffusion, shocks and gas motions transport the magnetic field towards the halo outskirts. At redshift z=0, the entire galactic structures are magnetized and the field amplitude is of the order of a few microG in the center of the halo and nG at the virial radius. Additionally, we analyse the intrinsic rotation measure (RM) of the forming galactic halo over redshift. The mean halo intrinsic RM peaks between redshifts z=4 and z=2 and reaches absolute values around 1000 rad/m^2. Towards redshift z=0, the intrinsic RM values decline to a mean value below 10 rad/m^2. At high redshifts, the distribution of individual starforming and thus magnetized regions is widespread leading to a widespread distribution of large intrinsic RMs. Our model for the evolution of galactic magnetic fields solves the joint problem of magnetic field seeding and subsequent amplification and distribution. The magnetic fields in galaxies are a direct consequence of the very basic processes of star and galaxy formation.
K. Yokoyama; T. Oka; H. Fujishiro; K. Noto
2008-01-01
On the pulsed-fleld magnetization (PFM) of superconducting bulk magnets, a detailed analysis taking into account the difference in superconducting characteristics between a growth sector boundary (GSB) and a growth sector region (GSR) parts of the material was carried out. The current density was defined in each part and a magnetic field induced by the local current was calculated. The entire
Warm inflation in presence of magnetic fields
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
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.
Submitted on: March 14, 2007 Hydrogen photoionization cross sections for strong field magnetic
Stancil, Phillip C.
Submitted on: March 14, 2007 Hydrogen photoionization cross sections for strong field magnetic in a strong magnetic field typical of magnetic white dwarf stars. Photoion- ization cross sections, has been applied to calculations of photoionization from atomic hydrogen ground and excited s- tates
Deriving the Coronal Magnetic Field Using Parametric Transformation Analysis
NASA Technical Reports Server (NTRS)
Gary, G. Allen; Rose, M. Franklin (Technical Monitor)
2001-01-01
When plasma-beta greater than 1 then the gas pressure dominates over the magnetic pressure. This ratio as a function along the coronal magnetic field lines varies from beta greater than 1 in the photosphere at the base of the field lines, to beta much less than 1 in the mid-corona, to beta greater than 1 in the upper corona. Almost all magnetic field extrapolations do not or cannot take into account the full range of beta. They essentially assume beta much less than 1, since the full boundary conditions do not exist in the beta greater than 1 regions. We use a basic parametric representation of the magnetic field lines such that the field lines can be manipulated to match linear features in the EUV and SXR coronal images in a least squares sense. This research employs free-form deformation mathematics to generate the associated coronal magnetic field. In our research program, the complex magnetic field topology uses Parametric Transformation Analysis (PTA) which is a new and innovative method to describe the coronal fields that we are developing. In this technique the field lines can be viewed as being embedded in a plastic medium, the frozen-in-field-line concept. As the medium is deformed the field lines are similarly deformed. However the advantage of the PTA method is that the field line movement represents a transformation of one magnetic field solution into another magnetic field solution. When fully implemented, this method will allow the resulting magnetic field solution to fully match the magnetic field lines with EUV/SXR coronal loops by minimizing the differences in direction and dispersion of a collection of PTA magnetic field lines and observed field lines. The derived magnetic field will then allow beta greater than 1 regions to be included, the electric currents to be calculated, and the Lorentz force to be determined. The advantage of this technique is that the solution is: (1) independent of the upper and side boundary conditions, (2) allows non-vanishing magnetic forces, and (3) provides a global magnetic field solution, which contains high- and low-beta regimes and maximizes the similarity between the field lines structure and all the coronal images of the region. The coronal image analysis is crucial to the investigation and for the first time these images can be exploited to derive the coronal magnetic field in a well-posed mathematical formulation. This program is an outgrowth of an investigation in which an extrapolated potential field was required to be "inflated" in order to have the field lines match the Yohkoh/SXT images. The field lines were radially stretched resulting in a better match to the coronal loops of an active region. The PTA method of radial and non-radial deformations of field lines to provide a match to the EUV/SXR images will be presented.
Protein detection with magnetic nanoparticles in a rotating magnetic field
NASA Astrophysics Data System (ADS)
Dieckhoff, Jan; Lak, Aidin; Schilling, Meinhard; Ludwig, Frank
2014-01-01
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.
Cherenkov radiation by massless neutrinos in a magnetic field
Ara N. Ioannisian; Georg G. Raffelt
1997-03-18
We calculate the Cherenkov process nu -> nu+photon in the presence of a homogeneous magnetic field. The neutrinos are taken to be massless with only standard-model couplings. The magnetic field fulfills the dual purpose of inducing an effective neutrino-photon vertex and of modifying the photon dispersion relation such that the Cherenkov condition is fulfilled. Our effect is closely related to photon splitting that occurs in magnetic fields and that may be astrophysically important in the strong magnetic fields of pulsars. It is also closely related to magnetic-field enhanced radiative decays nu -> nu'+photon that have been extensively discussed in the recent literature. In the appropriate limits we agree with these results, but we disagree with earlier explicit calculations of the Cherenkov process. For a field strength B_crit = m_e^2/e = 4.41E13 Gauss and for E=2m_e the Cherenkov rate is about 6E-11/sec and thus too small to be of practical importance for pulsar physics.
Magnetic-field-controlled reconfigurable semiconductor logic.
Joo, Sungjung; Kim, Taeyueb; Shin, Sang Hoon; Lim, Ju Young; Hong, Jinki; Song, Jin Dong; Chang, Joonyeon; Lee, Hyun-Woo; Rhie, Kungwon; Han, Suk Hee; Shin, Kyung-Ho; Johnson, Mark
2013-02-01
Logic devices based on magnetism show promise for increasing computational efficiency while decreasing consumed power. They offer zero quiescent power and yet combine novel functions such as programmable logic operation and non-volatile built-in memory. However, practical efforts to adapt a magnetic device to logic suffer from a low signal-to-noise ratio and other performance attributes that are not adequate for logic gates. Rather than exploiting magnetoresistive effects that result from spin-dependent transport of carriers, we have approached the development of a magnetic logic device in a different way: we use the phenomenon of large magnetoresistance found in non-magnetic semiconductors in high electric fields. Here we report a device showing a strong diode characteristic that is highly sensitive to both the sign and the magnitude of an external magnetic field, offering a reversible change between two different characteristic states by the application of a magnetic field. This feature results from magnetic control of carrier generation and recombination in an InSb p-n bilayer channel. Simple circuits combining such elementary devices are fabricated and tested, and Boolean logic functions including AND, OR, NAND and NOR are performed. They are programmed dynamically by external electric or magnetic signals, demonstrating magnetic-field-controlled semiconductor reconfigurable logic at room temperature. This magnetic technology permits a new kind of spintronic device, characterized as a current switch rather than a voltage switch, and provides a simple and compact platform for non-volatile reconfigurable logic devices. PMID:23364687
Dynamic Magnetic Field Applications for Materials Processing
NASA Technical Reports Server (NTRS)
Mazuruk, K.; Grugel, Richard N.; Motakef, S.; Whitaker, Ann F. (Technical Monitor)
2001-01-01
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.
Decay of Resonaces in Strong Magnetic Field
NASA Astrophysics Data System (ADS)
Filip, Peter
2015-08-01
We suggest that decay properties (branching ratios) of hadronic resonances may become modified in strong external magnetic field. The behavior of K±*, K0* vector mesons as well as ?* (1520) and ?0* baryonic states is considered in static fields 1013-1015 T. In particular, n = 0 Landau level energy increase of charged particles in the external magnetic field, and the interaction of hadron magnetic moments with the field is taken into account. We suggest that enhanced yield of dileptons and photons from ?0(770) mesons may occur if strong decay channel ?0 ? ?+?- is significantly suppressed. CP – violating ?+?- decays of pseudoscalar ?c and ?(547) mesons in the magnetic field are discussed, and superpositions of quarkonium states ?c,b and ?c,b(nP) with ?(nS), ?(nS) mesons in the external field are considered.
Origin of magnetic fields in galaxies
Souza, Rafael S. de; Opher, Reuven [IAG, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, CEP 05508-900, Sao Paulo, SP (Brazil)
2010-03-15
Microgauss magnetic fields are observed in all galaxies at low and high redshifts. The origin of these intense magnetic fields is a challenging question in astrophysics. We show here that the natural plasma fluctuations in the primordial Universe (assumed to be random), predicted by the fluctuation -dissipation theorem, predicts {approx}0.034 {mu}G fields over {approx}0.3 kpc regions in galaxies. If the dipole magnetic fields predicted by the fluctuation-dissipation theorem are not completely random, microgauss fields over regions > or approx. 0.34 kpc are easily obtained. The model is thus a strong candidate for resolving the problem of the origin of magnetic fields in < or approx. 10{sup 9} years in high redshift galaxies.
Induced magnetic-field effects in inductively coupled plasmas
Cohen, R.H.; Rognlien, T.D.
1995-11-04
In inductive plasma sources, the rapid spatial decay of the electric field arising from the skin effect produces a large radio frequency (RF) magnetic field via Faraday`s law. We previously determined that this magnetic field leads to a reduction of the electron density in the skin region, as well as a reduction in the collisionless heating rate. The electron deficit leads to the formation of an electrostatic potential which pulls electrons in to restore quasineutrality. Here we calculate the electron density including both the induced and electrostatic fields. If the wave frequency is not too low, the ions respond only to the averaged fields, and hence the electrostatic field is oscillatory, predominantly at the second harmonic of the applied field. We calculate the potential required to establish a constant electron density, and compare with numerical orbit-code calculations. For times short compared to ion transit times, the quasineutral density is just the initial ion density. For timescales long enough that the ions can relax, the density profile can be found from the solution of fluid equations with an effective (ponderomotive-like) potential added. Although the time-varying electrostatic potential is an extra source of heating, the net effect of the induced magnetic and electrostatic fields through trapping, early turning, and direct heating is a significant reduction in collisionless heating for parameters of interest.
NASA Astrophysics Data System (ADS)
Mizukami, S.; Otabe, E. S.; Yoshitomi, K.; Vyatkin, Vladimir S.; Kiuchi, M.; Matsushita, T.
The trapped magnetic field properties in superconducting MgB2 bulk magnets with various kinds of shape such as a disk, a ring and a pair of disks were calculated by the finite element method (FEM). For simplicity, field cool magnetization was replaced by a simple magnetization process at constant temperature to obtain equivalent distribution of magnetic field, and the thermal equation in FEM was omitted. It was confirmed that the result of FEM agreed well with the result by analytical method in infinite long cylinder. We compared the trapped magnetic field property between FEM result and experimental result in reference in order to research the simple evaluation method of the trapped magnetic field of MgB2 bulk magnet. It was found that the result of FEM agreed with the experimental result and it can explain the distribution of trapped magnetic field of superconducting MgB2 bulk magnet. From these results, it was found that it was possible to be calculated in various kinds of shape with using simple evaluation by FEM. Therefore, the optimization of the maximum trapped magnetic field in superconducting MgB2 bulk magnet can be discussed.
Effects of an inhomogeneous magnetic field on flowing erythrocytes.
Okazaki, M; Maeda, N; Shiga, T
1987-01-01
Effects of an inhomogeneous magnetic field on narrow erythrocyte streams in a wide and transparent laminar buffer flow were studied. The stream line of erythrocytes containing paramagnetic hemoglobin showed distinct displacement toward the stronger magnetic field. The displacement increased in the order, oxygenated erythrocytes (no displacement), erythrocytes containing cyanomethemoglobin, deoxygenated erythrocytes, erythrocytes containing methemoglobin in the high spin state; more precisely the displacement was proportional to the square of the paramagnetic moment of hemoglobin contained in the erythrocytes. In addition, the displacement was proportional to the product of the magnetic flux density and its gradient, and approximately proportional to the hematocrit of the flowing-erythrocyte suspension, and was much larger than that calculated for a single erythrocyte. These phenomena could be successfully interpreted by the interaction of paramagnetic erythrocytes with the inhomogeneous magnetic field, the resistance force (Stokes Law) from the bulk water, and the hydrodynamic interaction between erythrocytes. PMID:3830092
The characterisation of magnetic pigment dispersions using pulsed magnetic fields
NASA Astrophysics Data System (ADS)
Blackwell, J. J.; O'Grady, K.; Nelson, N. K.; Sharrock, M. P.
2003-10-01
In this work, we describe the application of pulsed field magnetometry techniques for the characterisation of magnetic pigment dispersions. Magnetic pigment dispersions are important technological materials as in one form they are the material which are used to coat base film in order to make magnetic recording tape. It is these materials that have been evaluated. In this work, we describe the use of two pulsed field magnetometers, one being a low-field instrument with a maximum field of 750 Oe and the other a high-field instrument with a maximum field of 4.1 kOe. Using inductive sensing, the magnetisation is monitored in real time as the pulse is applied. We find that using these techniques we can successfully monitor the progress of the dispersion process, the effects of different resin systems and the effect of different processing conditions. We find that our results are consistent with rheological and other measurements.
Generation of Magnetic Fields by the Stationary Accretion Shock Instability
Eirik Endeve; Christian Y. Cardall; Reuben D. Budiardja; Anthony Mezzacappa
2010-03-03
We begin an exploration of the capacity of the stationary accretion shock instability (SASI) to generate magnetic fields by adding a weak, stationary, and radial (but bipolar) magnetic field, and in some cases rotation, to an initially spherically symmetric fluid configuration that models a stalled shock in the post-bounce supernova environment. In axisymmetric simulations we find that cycles of latitudinal flows into and radial flows out of the polar regions amplify the field parallel to the symmetry axis, typically increasing the total magnetic energy by about two orders of magnitude. Nonaxisymmetric calculations result in fundamentally different flows and a larger magnetic energy increase: shearing associated with the SASI spiral mode contributes to a widespread and turbulent field amplification mechanism, boosting the magnetic energy by almost four orders of magnitude (a result which remains very sensitive to the spatial resolution of the numerical simulations). While the SASI may contribute to neutron star magnetization, these simulations do not show qualitatively new features in the global evolution of the shock as a result of SASI-induced magnetic field amplification.
Spectral confinement and current for atoms in strong magnetic fields
S. Fournais
2006-08-28
We study confinement of the ground state of atoms in strong magnetic fields to different subspaces related to the lowest Landau band. The results obtained allow us to calculate the quantum current in the entire semiclassical region $B \\ll Z^3$.
Biological effects of high DC magnetic fields
Tenforde, T.S.
1981-06-01
The principal focus of the program is the analysis of magnetic field effects on physiological functions in experimental animals and selected organ and tissue systems. A major research effort has involved the use of electrical recording techniques to detect functional alterations in the cardiovascular, neural, and visual systems during the application of DC magnetic fields. These systems involve ionic conduction processes, and are therefore potentially sensitive to electrodynamic interactions with an applied magnetic field. In the specific case of the visual system, magnetic interactions could also arise through orientational effects on the magnetically anisotropic photopigment molecules within retinal photoreceptor cells. In addition to studies with potentially sensitive target tissues, an evaluation is being made of magnetic field effects on a broad range of other physiological functions in laboratory mammals, including the measurement of circadian rhythms using noninvasive recording techniques. Results of investigations of magnetic field effects on the conformation of DNA, and on the growth and development of plants and insects are also reported. Figures and tables provide a brief summary of some representative observations in each of the research areas described. No significant alterations were observed in any of the physiological parameters examined to date, with the exception of major changes that occur in the electrocardiogram during magnetic field exposure. Studies with several species of animals have provided evidence that this phenomenon is attributable to electrical potentials that are induced during pulsatile blood flow in the aorta and in other major vessels of the circulatory system.
Ohm's law for mean magnetic fields
Boozer, A.H.
1986-05-01
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.
Surface magnetic fields across the HR Diagram
NASA Astrophysics Data System (ADS)
Landstreet, John D.
2015-10-01
The past 20 years have seen remarkable advances in spectropolarimetric instrumentation that have allowed us, for the first time, to identify some magnetic stars in most major stages of stellar evolution. We are beginning to see the broad outline of how such fields change during stellar evolution, to confront theoretical hypotheses and models of magnetic field structure and evolution with detailed data, and to understand more of the ways in which the presence of a field in turn affects stellar structure and evolution.
Emittance measurement in a magnetic field
Boyd, J.K.
1991-04-15
Emittance can be measured by intercepting an electron beam on a range thick plate and then observing the expansion of beamlets transmitted through small holes. The hole size is selected to minimize space charge effects. In the presence of a magnetic field the beamlets have a spiral trajectory and the usual field free formulation must be modified. To interpret emittance in the presence of a magnetic field an envelope equation is derived in the appropriate rotating frame. 1 ref.
Manipulating Cells with Static Magnetic Fields
NASA Astrophysics Data System (ADS)
Valles, J. M.; Guevorkian, K.
2005-07-01
We review our investigations of the use of static magnetic fields, B, for manipulating cells and cellular processes. We describe how B fields modify the cell division pattern of frog embryos and consequently can be used to probe the pattern determinants. We also observe that magnetic fields modify the swimming behavior of Paramecium Caudatum. We describe these modifications and their potential application to investigations of their swimming behavior.
Banana regime pressure anisotropy in a bumpy cylinder magnetic field
Garcia-Perciante, A.L.; Callen, J.D.; Shaing, K.C.; Hegna, C.C.
2006-01-15
The pressure anisotropy is calculated for a plasma in a bumpy cylindrical magnetic field in the low collisionality (banana) regime for small magnetic-field modulations ({epsilon}{identical_to}{delta}B/2B<<1). Solutions are obtained by integrating the drift-kinetic equation along field lines in steady state. A closure for the local value of the parallel viscous force B{center_dot}{nabla}{center_dot}{pi}{sub parallel} is then calculated and is shown to exceed the flux-surface-averaged parallel viscous force by a factor of O(1/{epsilon}). A high-frequency limit ({omega}>>{nu}) for the pressure anisotropy is also determined and the calculation is then extended to include the full frequency dependence by using an expansion in Cordey eigenfunctions.
Magnetic field generation by coherent turbulence structures
NASA Astrophysics Data System (ADS)
Kivotides, D.; Mee, A. J.; Barenghi, C. F.
2007-08-01
It is thought that the small-scale magnetic fields observed in accretion discs, galaxies and galactic clusters are generated by a dynamo process in which the turbulent plasma amplifies small initial magnetic fluctuations. Numerical simulations of turbulence have revealed that turbulence consists of filament-like vortex structures superimposed on an incoherent background, which carry a considerable amount of the energy. The natural questions to ask are whether these coherent structures can generate a magnetic field and, if so, if the generated magnetic field is also filament-like. After setting up a turbulence model which consists only of vortex filaments, we show in an unambiguous way that the coherent structure can sustain kinematic dynamo action and that the magnetic field thus generated consists of relatively thick ribbons (flattened tubes) located in between vortices.
Magnetic susceptibilities of V3+ in corundum: Magnetic anisotropy at high fields
NASA Astrophysics Data System (ADS)
Brumage, William H.; Quade, C. Richard; Dorman, C. Franklin
1995-08-01
We theoretically investigate the behavior of the V3+ ion as an impurity in Al2O3 under high magnetic fields, up to 20 T. In particular, we investigate the introduction of magnetic anisotropy that is lower than the trigonal symmetry of the host crystal. Two approaches are used for the calculations. First, fourth-order perturbation theory is used to develop quartic terms plus one sextic term in the susceptibility tensor that are good for fields up to 4 T. Then, the three-level energy matrix is reduced exactly to obtain the anisotropy at higher fields. It is found that the dominant contributions to the magnetic-induced anisotropy arise from the ?xxxx term, while the ?xxzz=?zxxz, ?zzzz, and the ?xxxxxx terms give a much lower contribution. Temperature-dependent effects are reported. There is a very small dependence of the magnetization upon the zero-field splitting.
Particle Transport in Therapeutic Magnetic Fields
NASA Astrophysics Data System (ADS)
Puri, Ishwar K.; Ganguly, Ranjan
2014-01-01
Iron oxide magnetic nanoparticles, in ferrofluids or as magnetic microspheres, offer magnetic maneuverability, biochemical surface functionalization, and magnetic relaxation under the influence of an alternating field. The use of these properties for clinical applications requires an understanding of particles, forces, and scalar transport at various length scales. This review explains the behavior of magnetic nano- and microparticles during magnetic drug targeting and magnetic fluid hyperthermia, and the microfluidic transport of these particles in bioMEMS (biomedical microelectromechanical systems) devices for ex vivo therapeutic and diagnostic applications. Magnetic particle transport, the momentum interaction of these particles with a host fluid in a flow, and thermal transport in a particle-infused tissue are characterized through the governing electrodynamic, hydrodynamic, and scalar transport equations.
Nonlinear evolution of the coronal magnetic field under reconnective relaxation
NASA Technical Reports Server (NTRS)
Wolfson, R.; Vekstein, G. E.; Priest, E. R.
1994-01-01
Recently, Vekstein et al. (Vekstein, Priest, & Steele 1993) have developed a model for coronal heating in which the corona responds to photospheric footpoint motions by small-scale reconnection events that bring about a relaxed state while conserving magnetic helicity but not field-line connectivity. Vekstein et al. consider a partially open field configuration in which magnetic helicity is ejected to infinity on open field lines but retained in the closed-field region. Under this scheme, they describe the evolution of an initially potential field, in response to helicity injection, in the linear regime. The present work uses numerical calculations to extend the model of Vekstein et al. into the fully nonlinear regime. The results show a rise and bulging of the field lines of the closed-field region with increasing magnetic helicity, to a point where further solutions are impossible. We interpret these solution-sequence endpoints as indicating a possible loss of equilibrium, in the sense that a relaxed equilibrium state may no longer be available to the corona when sufficient helicity has been injected. The rise and bulging behavior is reminiscent of what is observed in a helmet streamer just before the start of a coronal mass ejection (CME), and so our model suggests that a catastrophic loss of magnetic equilibrium might be the initiation mechanism for CMEs. We also find that some choices of boundary conditions can result in qualitative changes in the magnetic topology, with the appearance of magnetic islands. Whether or not this behavior occurs depends on the relative strengths of the fields in the closed- and open-field regions; in particular, island formation is most likely when the open field (which is potential) is strong and thus acts to confine the force-free closed field. Finally, we show that the energy released through reconnective relaxation can be a substantial fraction of the magnetic energy injected into the corona through footpoint motions and may be sufficient for heating the corona above active regions.
The Measurement of Magnetic Fields
ERIC Educational Resources Information Center
Berridge, H. J. J.
1973-01-01
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)
Magnetic fields on resistance spaces
Michael Hinz; Luke Rogers
2015-02-03
On a metric measure space $X$ that supports a regular, strongly local resistance form we consider a magnetic energy form that corresponds to the magnetic Laplacian for a particle confined to $X$. We provide sufficient conditions for closability and self-adjointness in terms of geometric conditions on the reference measure without assuming energy dominance.
Nature of Electric and Magnetic Fields; How the Fields Transform
Ivezic, Tomislav
2015-01-01
In this paper the proofs are given that the electric and magnetic fields are properly defined vectors on the four-dimensional (4D) spacetime (the 4-vectors in the usual notation) and not the usual 3D fields. Furthermore, the proofs are presented that under the mathematically correct Lorentz transformations (LT), e.g., the electric field vector transforms as any other vector transforms, i.e., again to the electric field vector; there is no mixing with the magnetic field vector B, as in the usual transformations (UT) of the 3D fields. The derivations of the UT from some well-known textbooks are discussed and objected.
Nature of Electric and Magnetic Fields; How the Fields Transform
Tomislav Ivezic
2015-08-10
In this paper the proofs are given that the electric and magnetic fields are properly defined vectors on the four-dimensional (4D) spacetime (the 4-vectors in the usual notation) and not the usual 3D fields. Furthermore, the proofs are presented that under the mathematically correct Lorentz transformations (LT), e.g., the electric field vector transforms as any other vector transforms, i.e., again to the electric field vector; there is no mixing with the magnetic field vector B, as in the usual transformations (UT) of the 3D fields. The derivations of the UT from some well-known textbooks are discussed and objected.
Superconducting tubular wires in transverse magnetic fields
NASA Astrophysics Data System (ADS)
Mawatari, Yasunori
2011-04-01
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 0
Observations of Magnetic Fields in Galaxies
NASA Astrophysics Data System (ADS)
Beck, Rainer
2005-09-01
Magnetic fields play an important role in galaxies. Interstellar magnetic fields are strongest in massive spiral arms of galaxies (20-30 ?G) and in nuclear starburst regions (up to 100 ?G). Processes related to star formation tangle the field lines, so that little polarization is observed in star-forming regions. The magnetic energy density in the inner disk of galaxies is larger than the thermal energy density, comparable to that of turbulent gas motions, and is dominant in the outer disk. Large-scale spiral patterns of the regular field are observed in grand-design, flocculent and even some irregular galaxies. In grand-design galaxies the regular fields are aligned parallel to the optical spiral arms, with the strongest regular fields (highest polarization) in interarm regions, sometimes forming magnetic spiral arms between the optical arms. Polarized emission at the edges of some galaxies is a tracer of field compression due to interactions between galaxies or to ram pressure by the intergalactic medium. - In barred galaxies the magnetic field is mostly aligned with the gas flow, deflected by shear and compressed in the shock. The regular field is already strong in the ``upstream'' region ahead of the shock. Within the circumnuclear ring the magnetic field is strong, with a regular component of spiral shape. Magnetic stress may drive inflow of gas towards the nucleus. - Faraday rotation of the polarization vectors reveals patterns which are signatures of coherent large-scale fields in galactic disks, probably generated by dynamo action. The majority of field structures in galaxies requires a superposition of several dynamo modes. - In our Milky Way, the structure of the large-scale magnetic field is still unknown. Rotation measure data from pulsars indicate several field reversals, but some of these could be field distortions. Faraday screens offer the new method of tomography of small-scale magnetic structures in the local Milky Way. - Present-day radio polarimetry is limited by sensitivity. The next-generation radio telescope, the Square Kilometer Array (SKA), will be able to reveal the full wealth of magnetic structures in galaxies. Cosmic magnetism is one of the Key Science projects for the SKA.
Gyrokinetic Calculations of the Neoclassical Radial Electric Field in Stellarator Plasmas
Lewandowski, J.L.V.; Williams, J.; Boozer, A.H.; Lin, Z.
2001-04-09
A novel method to calculate the neoclassical radial electric field in stellarator plasmas is described. The method, which does not have the inconvenience of large statistical fluctuations (noise) of standard Monte Carlo technique, is based on the variation of the combined parallel and perpendicular pressures on a magnetic surface. Using a three-dimensional gyrokinetic delta f code, the calculation of the radial electric field in the National Compact Stellarator Experiment has been carried out. It is shown that a direct evaluation of radial electric field based on a direct calculation of the radial particle flux is not tractable due to the considerable noise.
Tellgren, E. I. Lange, K. K.; Ekström, U.; Helgaker, T.; Teale, A. M.; Furness, J. W.
2014-01-21
We present a novel implementation of Kohn–Sham density-functional theory utilizing London atomic orbitals as basis functions. External magnetic fields are treated non-perturbatively, which enable the study of both magnetic response properties and the effects of strong fields, using either standard density functionals or current-density functionals—the implementation is the first fully self-consistent implementation of the latter for molecules. Pilot applications are presented for the finite-field calculation of molecular magnetizabilities, hypermagnetizabilities, and nuclear magnetic resonance shielding constants, focusing on the impact of current-density functionals on the accuracy of the results. Existing current-density functionals based on the gauge-invariant vorticity are tested and found to be sensitive to numerical details of their implementation. Furthermore, when appropriately regularized, the resulting magnetic properties show no improvement over standard density-functional results. An advantage of the present implementation is the ability to apply density-functional theory to molecules in very strong magnetic fields, where the perturbative approach breaks down. Comparison with high accuracy full-configuration-interaction results show that the inadequacies of current-density approximations are exacerbated with increasing magnetic field strength. Standard density-functionals remain well behaved but fail to deliver high accuracy. The need for improved current-dependent density-functionals, and how they may be tested using the presented implementation, is discussed in light of our findings.
Charged and neutral vector ? mesons in a magnetic field
NASA Astrophysics Data System (ADS)
Liu, Hao; Yu, Lang; Huang, Mei
2015-01-01
The vector meson ? in the presence of an external magnetic field has been investigated in the framework of the Nambu-Jona-Lasinio model, in which mesons are constructed by the infinite sum of quark-loop chains by using random phase approximation. The quark loop of ? meson polarization function is calculated to the leading order of 1 /Nc expansion by taking the quark propagator in Ritus form as well the Landau level representation. It is found that the constituent quark mass increases with magnetic field, the masses of the neutral vector meson ?0 with spin component sz=0 ,±1 , and the charged vector meson ?± with sz=0 also increases with magnetic field. However, the mass square of the charged vector meson ?+ (?-) with sz=+1 (sz=-1 ) decreases linearly with magnetic field and drops to zero at the critical magnetic field e Bc?0.2 GeV2 , which indicates the possible condensation of a charged vector meson in the vacuum. The value of the critical magnetic field is the same by using the Ritus quark propagator as well the Landau level representation of the quark propagator, which is much lower than the value e Bc?0.6 GeV2 predicted by a pointlike vector meson.
Particle Acceleration and Magnetic Field Generation in Shear-Flows
NASA Astrophysics Data System (ADS)
Nishikawa, K.-I.; Hardee, P.; Mizuno, Y.; Du?an, I.; Zhang, B.; Medvedev, M.; Meli, A.; Choi, E. J.; Min, K. W.; Niemiec, J.; Nordlund, Å.; Frederiksen, J.; Sol, H.; Pohl, M.; Hartmann, D. H.; Marscher, A.; Gómez, J. L.
2014-03-01
We have investigated the generation of magnetic fields associated with velocity shear between an unmagnetized relativistic (core) jet and an unmagnetized sheath plasma by the kinetic Kelvin-Helmholtz instability for different mass ratios (mi/me = 1, 20, and 1836) and different jet Lorentz factors. We found that electron-positron cases have alternating magnetic fields instead of the DC magnetic fields found in electron-ion cases. We have also investigated particle acceleration and shock structure associated with an unmagnetized relativistic jet propagating into an unmagnetized plasma for electron-positron and electron-ion plasmas. Strong magnetic fields generated in the trailing shock lead to transverse deflection and acceleration of the electrons. We have self-consistently calculated the radiation from the electrons accelerated in the turbulent magnetic fields for different jet Lorentz factors. We find that the synthetic spectra depend on the bulk Lorentz factor of the jet, the jet temperature, and the strength of the magnetic fields generated in the shock.
NASA Astrophysics Data System (ADS)
Miyata, Koji; Aoyama, Yasuaki; Yokoyama, Tomonori; Ohashi, Ken; Kondo, Minoru; Matsuoka, Koichi
Rare-earth magnets, which have high energy product, have been widely used in several industrial applications such as voice coil motors for hard disk drives, MRI for medical devices and motors for electric vehicle. In order to realize a small and high performance device, the magnetic field analysis techniques are required. In this paper, we applied the magnetic field analysis to design the permanent magnet synchronous motors into the rail traction system. In the inverter fed motor drive, the eddy current loss in the permanent magnet increased. We simulated the effect that eddy current was decreased by using a divided permanent magnet. Furthermore, the permanent magnet tends to be demagnetized due to the effect of a demagnetizing field formed at high temperatures. However, according to our analysis, demagnetization does not occur within the range of our design specifications. Also, we performed magnetic field analysis assuming a pulse-type magnetization process and designed an optimal magnetizing coil.
Magnetic field spectrum at cosmological recombination revisited
Shohei Saga; Kiyotomo Ichiki; Keitaro Takahashi; Naoshi Sugiyama
2015-06-03
If vector type perturbations are present in the primordial plasma before recombination, the generation of magnetic fields is known to be inevitable through the Harrison mechanism. In the context of the standard cosmological perturbation theory, non-linear couplings of first-order scalar perturbations create second-order vector perturbations, which generate magnetic fields. Here we reinvestigate the generation of magnetic fields at second-order in cosmological perturbations on the basis of our previous study, and extend it by newly taking into account the time evolution of purely second-order vector perturbations with a newly developed second-order Boltzmann code. We confirm that the amplitude of magnetic fields from the product-terms of the first-order scalar modes is consistent with the result in our previous study. However, we find, both numerically and analytically, that the magnetic fields from the purely second-order vector perturbations partially cancel out the magnetic fields from one of the product-terms of the first-order scalar modes, in the tight coupling regime in the radiation dominated era. Therefore, the amplitude of the magnetic fields on small scales, $k \\gtrsim 10~h{\\rm Mpc}^{-1}$, is smaller than the previous estimates. The amplitude of the generated magnetic fields at cosmological recombination is about $B_{\\rm rec} =5.0\\times 10^{-24}~{\\rm Gauss}$ on $k = 5.0 \\times 10^{-1}~h{\\rm Mpc}^{-1}$. Finally, we discuss the reason of the discrepancies that exist in estimates of the amplitude of magnetic fields among other authors.
Magnetic Field Measurement with Ground State Alignment
NASA Astrophysics Data System (ADS)
Yan, Huirong; Lazarian, A.
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.
The influence of magnetic fields in planetary dynamo models
NASA Astrophysics Data System (ADS)
Soderlund, Krista; King, Eric; Aurnou, Jonathan
2013-04-01
Magnetic fields are common throughout the solar system with properties as diverse as the planets themselves. Since these fields likely result from convectively driven dynamo action, the coupling between magnetic fields, fluid flow, and heat transfer must be understood in order to determine what controls the strength, morphology, and evolution of planetary magnetic fields. Towards this end, we have carried out a suite of dynamo and non-magnetic convection simulations to investigate the effect of the presence of magnetic fields on convection, the effect of varying convective vigor, and the effect of varying the rotation rate. This survey considers models with Prandtl number Pr = 1; magnetic Prandtl numbers up to Pm = 5; Ekman numbers in the range 10-3 × E × 10-5; and Rayleigh numbers from near onset to more than 1000 times critical. We measure the strengths and structures of magnetic fields and fluid motions, as well as heat transfer efficiency and in situ force balances. These analyses illustrate that dynamo action does not necessitate a fundamental change to the overall flow field, although the impact of magnetic fields is found to increase for lower Ekman numbers. By directly calculating the forces in each of our simulations, we show that the traditionally defined Elsasser number, ?i, overestimates the role of the Lorentz force in dynamos. The Coriolis force remains greater than the Lorentz force even in cases with ?i ? 100, explaining the persistence of columnar flows in ?i > 1 dynamo simulations, a quasigeostrophic phenomena. We argue that a dynamic Elsasser number, ?d, better represents the Lorentz to Coriolis force ratio. By applying the ?d parametrization to planetary settings, we predict that the convective dynamics (excluding zonal flows) in planetary interiors are only weakly influenced by their large-scale magnetic fields. Our survey also provides new insight into the breakdown of dipolar magnetic field generation since we observe a sharp transition from dipolar to multipolar dynamos in models with moderate to high Ekman numbers. Force calculations show that this transition occurs when the inertial and viscous forces become comparable. These results suggest that viscous effects are important for dipolar field generation in many present day dynamo simulations and imply that dynamo simulations with moderate Ekman numbers may not correctly capture the physics of planetary dynamos where viscosity is expected to be negligible.
Magnetic Field of Lightning Return Stroke
Martin A. Uman; D. Kenneth McLain
1969-01-01
The magnetic flux density due to first and to subsequent lightning return strokes is calculated for distances from the strokes of 0.5 to 200 kin. The basis of the calculations is various assumed forms for the channel current as a function of time and of channel height. Two new channel-current models are introduced for first strokes and one new model
Normal glow discharge in axial magnetic field
NASA Astrophysics Data System (ADS)
Surzhikov, S.; Shang, J.
2014-10-01
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.
Magnetic field induced transition in vanadium spinels.
Mun, E D; Chern, Gia-Wei; Pardo, V; Rivadulla, F; Sinclair, R; Zhou, H D; Zapf, V S; Batista, C D
2014-01-10
We study vanadium spinels AV2O4 (A = Cd,Mg) in pulsed magnetic fields up to 65 T. A jump in magnetization at ?0H?40??T is observed in the single-crystal MgV2O4, indicating a field induced quantum phase transition between two distinct magnetic orders. In the multiferroic CdV2O4, the field induced transition is accompanied by a suppression of the electric polarization. By modeling the magnetic properties in the presence of strong spin-orbit coupling characteristic of vanadium spinels, we show that both features of the field induced transition can be successfully explained by including the effects of the local trigonal crystal field. PMID:24483929
NASA Astrophysics Data System (ADS)
Ferrari, Hernán; Valenzuela, Sergio O.; Bekeris, Victoria; Correra, Luigi
2000-07-01
We have investigated both experimentally and numerically the magnetization, M( t), in high-temperature superconducting strips during the application of a transverse magnetic field, Ha( t). Experimental results in GBCO strips were obtained with a short time non-conventional technique for Ha( t)?(1-exp( t/ ?)), with ??1 ?s. Calculations take into account the effect of flux creep and/or ohmic overcritical damping and satisfactorily describe the experimental results.
Measurement of the magnetic field of the CDF magnet
Yamada, R.; Newman-Holmes, C.; Schmidt, E.E.
1985-11-01
The magnetic field of the CDF (Collider Detector at Fermilab) superconducting solenoid has been measured using a newly designed field mapping device. NMR probes and a system of three orthogonal search coils were used as sensing elements. The central uniform region inside the solenoid coil and the fringing field in the conical end plugs were measured. The detailed field distribution and its characteristics are described.
Relativistic electron in curved magnetic fields
NASA Technical Reports Server (NTRS)
An, S.
1985-01-01
Making use of the perturbation method based on the nonlinear differential equation theory, the author investigates the classical motion of a relativistic electron in a class of curved magnetic fields which may be written as B=B(O,B sub phi, O) in cylindrical coordinates (R. phi, Z). Under general astrophysical conditions the author derives the analytical expressions of the motion orbit, pitch angle, etc., of the electron in their dependence upon parameters characterizing the magnetic field and electron. The effects of non-zero curvature of magnetic field lines on the motion of electrons and applicabilities of these results to astrophysics are also discussed.
The remanent magnetic field of the moon
NASA Technical Reports Server (NTRS)
Coleman, P. J., Jr.; Russell, C. T.
1977-01-01
Measurements of the moon's remanent magnetic field near the Apollo landing sites and from lunar orbit with the Apollo subsatellites are reviewed. Contour maps are presented for the intensity of the radial, eastward, and northward components of the remanent field as measured with Apollo subsatellite magnetometers at altitudes of 10 to 170 km. Attempts to fit the subsatellite measurements to various models are discussed along with indirect measurements of the remanent field. It is shown that scale sizes of field sources range from 1 to at least 100 km, that the magnetic fields on the far side are stronger and more variable than those on the near side, and that the lunar remanent field apparently exhibits a significant latitude dependence. The origin of the field responsible for the remanent magnetization is considered.
The conductance of auroral magnetic field lines
NASA Technical Reports Server (NTRS)
Weimer, D. R.; Gurnett, D. A.; Goertz, C. K.
1986-01-01
DE-1 high-resolution double-probe electric-field data and simultaneous magnetic-field measurements are reported for two 1981 events with large electric fields which reversed over short distances. The data are presented graphically and analyzed in detail. A field-line conductance of about 1 nmho/sq m is determined for both upward and downward currents, and the ionospheric conductivity is shown, in the short-wavelength limit, to have little effect on the relationship between the (N-S) electric and (E-W) magnetic fields above the potential drop parallel to the magnetic-field lines. The results are found to be consistent with a linear relationship between the field-aligned current density and the parallel potential drop.
Magnetic fields of the terrestrial planets
NASA Technical Reports Server (NTRS)
Russell, C. T.
1993-01-01
The four terrestrial planets, together with the Earth's Moon, provide a significant range of conditions under which dynamo action could occur. All five bodies have been visited by spacecraft, and from three of the five bodies (Earth, Moon and Mars) we have samples of planetary material upon which paleomagnetic studies have been undertaken. At the present time, only the Earth and Mercury appear to have a significant dipole magnetic field. However, the Moon, and possibly Mars, appear to have had ancient planetary dynamos. Venus does not now have a significant planetary magnetic field, and the high surface temperatures should have prevented the recording of evidence of any ancient magnetic field. Since the solidification of the solid inner core is thought to be the energy source for the terrestrial magnetic field, and since smaller bodies evolve thermally more rapidly than larger bodies, we conjecture that the terrestrial planets are today in three different phases of magnetic activity. Venus is in a predynamo phase, not having cooled to the point of core solidification. Mercury and the Earth are in the middle of their dynamo phase, with Mercury perhaps near the end of its activity. Mars and the Moon seem to be well past their dynamo phase. Much needs to be done in the study of the magnetism of the terrestrial planets. We need to characterize the multipole harmonic structure of the Mercury magnetic field plus its secular variation, and we need to analyze returned samples to attempt to unfold the long-term history of Mercury's dynamo. We need to more thoroughly map the magnetism of the lunar surface and to analyze samples obtained from a wider area of the lunar surface. We need a more complete survey of the present Martian magnetic field and samples from a range of different ages of Martian surface material. Finally, a better characterization of the secular variation of the terrestrial magnetic field is needed in order to unfold the workings of the terrestrial dynamo.
Magnetic field analysis of a planar superconducting undulators with variable-field polarization.
Kim, S. H.; Doose, C.; Experimental Facilities Division (APS)
2005-01-01
A planar superconducting undulator (SCU), which generates horizontal and vertical fields, Bx and By, perpendicular to the beam directions, is inserted in between the magnetic poles of another unit, which generates the vertical field By. Analytical formulae of the magnetic fields are presented for the inserted, as well as the vertical-field, units. A scaling law may be applied to the SCU. The angle of the coil windings for the inserted unit is analyzed to maximize Bx. The range of the optimum rotation angle, for the range of gap/period ratio 0.1 - 0.6, is calculated to be 30 - 40 degrees.
Environmental magnetic fields: Influences on early embryogenesis
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
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.
Complex Magnetic Fields of Compact Stars
NASA Astrophysics Data System (ADS)
Mason, Paul A.
2015-08-01
Observational evidence for strong magnetic fields of accreting white dwarfs, in cataclysmic binaries, and accreting neutron stars, in low mass X-ray binaries, is reviewed. Increasingly, complex magnetic fields have been involked to explain effects that cannot be modelled with pure dipolar fields. This has been the result of both improved observations, providing stronger field constraints, as well as robust modelling techniques. While observations are often not able to clearly differentiate between dipolar and multi-polar fileds, examples are shown that suggest that complex fields are likely a quite common feature of compact stars.
Dynamo Models for Saturn's Axisymmetric Magnetic Field
NASA Astrophysics Data System (ADS)
Stanley, S.; Tajdaran, K.
2012-12-01
Magnetic field measurements by the Cassini mission have confirmed the earlier Pioneer 11 and Voyager missions' results that Saturn's observed magnetic field is extremely axisymmetric . For example, Saturn's dipole tilt is less than 0.06 degrees (Cao et al., 2011) . The nearly-perfect axisymmetry of Saturn's dipole is troubling because of Cowling's Theorem which states that an axisymmetric magnetic field cannot be maintained by a dynamo. However, Cowling's Theorem applies to the magnetic field generated inside the dynamo source region and we can avert any contradiction with Cowling's Theorem if we can find reason for a non-axisymmetric field generated inside the dynamo region to have an axisymmetrized potential field observed at satellite altitude. Stevenson (1980) proposed a mechanism for this axisymmetrization. He suggested that differential rotation in a stably-stratified electrically conducting layer (i.e. the helium rain-out layer) surrounding the dynamo could act to shear out the non-axisymmetry and hence produce an axisymmetric observed magnetic field. In previous work, we used three-dimensional self-consistent numerical dynamo models to demonstrate that a thin helium rain-out layer can produce a more axisymmetrized field (Stanley, 2010). We also found that the direction of the zonal flows in the layer is a crucial factor for magnetic field axisymmetry. Here we investigate the influence of the thickness of the helium rain-out layer and the intensity of the thermal winds on the axisymmetrization of the field. We search for optimal regions in parameter space for producing axisymmetric magnetic fields with similar spectral properties to the observed Saturnian field.
Screening magnetic fields by superconductors: A simple model
Caputo, J.-G., E-mail: caputo@insa-rouen.fr [Laboratoire de Mathématiques, INSA de Rouen, Avenue de l'Université, 76801 Saint-Etienne du Rouvray (France); Gozzelino, L.; Laviano, F.; Ghigo, G.; Gerbaldo, R. [Department of Applied Science and Technology, Politecnico di Torino, 10129, Torino (Italy); Noudem, J.; Thimont, Y.; Bernstein, P. [CRISMAT/LUSAC, Physics Department, Université de Caen (France)
2013-12-21
We introduce a simple approach to evaluate the magnetic field distribution around superconducting samples, based on the London equations; the elementary variable is the vector potential. This procedure has no adjustable parameters, only the sample geometry and the London length, ?, determine the solution. This approach was validated by comparing the induction field calculated to the one measured above MgB{sub 2} disks of different diameters, at 20?K and for applied fields lower than 0.4?T. The model can be applied if the flux line penetration inside the sample can be neglected when calculating the induction field distribution outside the superconductor. We conclude by showing on a cup-shape geometry how one can design a magnetic shield satisfying a specific constraint.
Particle Acceleration, Magnetic Field Generation, and Emission in Relativistic Shocks
NASA Astrophysics Data System (ADS)
Nishikawa, K.-I.; Hededal, C.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G.
2004-08-01
Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient parallel magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. New simulations with an ambient perpendicular magnetic field show the strong interaction between the relativistic jet and the magnetic fields. The magnetic fields are piled up by the jet and the jet electrons are bent, which creates currents and displacement currents. At the nonlinear stage, the magnetic fields are reversed by the current and the reconnection may take place. Due to these dynamics the jet and ambient electron are strongly accelerated in both parallel and perpendicular directions. The simulation results show that this instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The ``jitter'' radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.
Limits on possible magnetic fields at nucleosynthesis time
D. Grasso; H. R. Rubistein
1994-09-05
In this paper we discuss limits on magnetic fields that could have been present at nucleosynthesis time. We considered several effects that could be relevant modifing light elements relic abundances. They include: changes in reaction rates, mass shifts due to strong and electromagnetic interactions, variation of the expansion rate of the Universe due to both the magnetic field energy density and the increasing of the electrons density in overcritical magnetic fields. We find that the latter is the main effect. It was not taken into account in previous calculations. The allowed field intensity at the end of nucleosynthesis ($T =1\\times 10^9\\;^o{\\rm K}$) is $B \\le 3\\times 10^{10}$ Gauss.
Force-free magnetic fields - Generating functions and footpoint displacements
NASA Technical Reports Server (NTRS)
Wolfson, Richard; Verma, Ritu
1991-01-01
This paper presents analytic and numerical calculations that explore equilibrium sequences of bipolar force-free magnetic fields in relation to displacments of their magnetic footpoints. It is shown that the appearance of magnetic islands - sometimes interpreted as marking the loss of equilibrium in models of the solar atmosphere - is likely associated only with physically unrealistic footpoint displacements such as infinite separation or 'tearing' of the model photosphere. The work suggests that the loss of equilibrium in bipolar configurations, sometimes proposed as a mechanism for eruptive solar events, probably requires either fully three-dimensional field configurations or nonzero plasma pressure. The results apply only to fields that are strictly bipolar, and do not rule out equilibrium loss in more complex structures such as quadrupolar fields.
Space applications of superconductivity - High field magnets
NASA Technical Reports Server (NTRS)
Fickett, F. R.
1979-01-01
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.
Sub arcsec evolution of solar magnetic fields
NASA Astrophysics Data System (ADS)
Roudier, Th.; Malherbe, J. M.; Moity, J.; Rondi, S.; Mein, P.; Coutard, Ch.
2006-09-01
Context: .The evolution of the concentrated magnetic field in flux tubes is one challenge of the nowadays Solar physics which requires time sequence with high spatial resolution. Aims: .Our objective is to follow the properties of the magnetic concentrations during their life, in intensity (continuum and line core), magnetic field and Doppler velocity. Methods: .We have observed solar region NOAA 0644 on 2004 July 15 at Pic du Midi observatory with the Multichannel Subtractive Double Pass (MSDP) operating mode and analysed the circular polarization of the Na D1 589.6 nm spectral line in terms of longitudinal magnetic field in 2D field of view (5.6 arcsec× 80 arcsec), during 41 mn at two altitudes 327 km and 170 km in the photosphere. Results: .Our data analysis reveals that all the concentrated magnetic features are associated with downward motions and the magnetic field remains very stable during the 41 mn. At different height 327 and 170 km, a clear depth effect is visible on Doppler velocity but not in the magnetic field strength.
NASA Astrophysics Data System (ADS)
Ueno, Shoogo
The increasing existence of magnetic and electromagnetic fields in the environment has generated a myriad of questions and research activities around the world. Although these fields are beneficial to medicine, scientific research the populace, and industry, anxiety and uncertainty about their hazards have prompted researchers to strive to conclusively ascertain the positive, negative and long-term effects of these fields on biological systems. This paper reviews the biological effects of magnetic and electromagnetic fields that are classified into three categories: (1) time-varying magnetic fields, (2) DC or static magnetic fields, and (3) the multiplication of both static fields and other energy, such as light and radiation.
Evolution of the magnetic field in magnetars
J. Braithwaite; H. C. Spruit
2006-01-01
We use numerical MHD to look at the stability of a possible poloidal field in neutron stars (Flowers & Ruderman 1977, ApJ, 215, 302), and follow its unstable evolution, which leads to the complete decay of the field. We then model a neutron star after the formation of a solid crust of high conductivity. As the initial magnetic field we
Calculations of magnetic transition temperatures of Gd-based compounds
NASA Astrophysics Data System (ADS)
Rusz, Ján; Turek, Ilja; Diviš, Martin
2006-05-01
We present results of a calculation of critical temperatures of ordered GdX compounds with CsCl structure ( X=Mg, Rh, Cd, Zn, Cu, Ag, Tl) within the Heisenberg Hamiltonian. The pair exchange interactions were evaluated using a parameter-free method based on the magnetic force theorem. The resulting critical temperatures are compared to experiment; they exhibit strong sensitivity to computational details.