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Magnetic Flux (magnetic + flux)

Distribution by Scientific Domains

Physics and Astronomy	72%
Engineering	22%

Distribution within Physics and Astronomy

Astronomy & Astrophysics	69%
General & Introductory Physics	18%

Terms modified by Magnetic Flux

magnetic flux density

Selected Abstracts

A perturbation analysis of harmonic generation from saturated elements in power systems

ELECTRICAL ENGINEERING IN JAPAN, Issue 4 2010
Teruhisa Kumano
Abstract Nonlinear phenomena such as saturation of magnetic flux have considerable effects in power systems analysis. It is reported that a failure in a real 500-kV system triggered islanding operation, where resultant even harmonics caused malfunctions in protective relays. It is also reported that the major origin of this wave distortion is nothing but unidirectional magnetization of the transformer iron core. Time simulation is widely used today to analyze phenomena of this type, but it has basically two shortcomings. One is that the time simulation takes too much computing time in the vicinity of inflection points in the saturation characteristic curve because certain iterative procedures such as N-R (Newton,Raphson) must be used and such methods tend to be caught in an ill-conditioned numerical hunting. The other is that such simulation methods sometimes do not aid an intuitive understanding of the studied phenomenon because all of the nonlinear equations are treated in matrix form and are not properly divided into understandable parts, as is done in linear systems. This paper proposes a new computation scheme that is based on the so-called perturbation method. Magnetic saturation of iron cores in a generator and a transformer are taken into account. The proposed method has a special feature to deal with the first shortcoming of the N-R-based time simulation method stated above. The proposed method does not use an iterative process to reduce the equation residue, but uses perturbation series, so that it is free of the ill-conditioning problem. The user need only calculate the perturbation terms one by one until the necessary accuracy is attained. In a numerical example treated in the present paper, first-order perturbation can achieve reasonably high accuracy, which means very fast computing time. In a numerical study, three nonlinear elements are considered. The calculation results are almost identical to the conventional N-R-based time simulation, which shows the validity of the method. The proposed method can be effectively used in screening where many case studies are needed. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(4): 35,42, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20895 [source]

Macroscopic quantum behavior of superconducting quantum interference devices

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 4-5 2003
M.G. CastellanoArticle first published online: 24 APR 200
Superconducting quantum interference devices (SQUIDs) are made by a superconducting loop interrupted by one or more Josephson junctions. They are described in terms of a macroscopic variable, the magnetic flux, which shows quantum effects such as tunnelling through a potential barrier. Besides making up the source of a quantum state, SQUIDs also provide the instruments necessary for its probing: as a fact, SQUID based magnetometers have a sensitivity approaching the quantum limit. In this paper I will review the working principle of these devices and illustrate the system of SQUIDs realized in my group to test the quantum behavior at a macroscopic level. [source]

Design and application of layered composites with the prescribed magnetic permeability

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2010
Jae Seok Choi
Abstract This research aims to design the microstructure with the prescribed magnetic permeability and proposes a design method to control the magnetic flux flow using layered microstructures. In the optimization problem for the microstructure design, the objective function is set up to minimize the difference between the homogenized magnetic permeability during the design process and the prescribed permeability based on the so-called inverse homogenization method. Based on the microstructure design result, a microstructure composed of layered materials is proposed for the purpose of the efficient magnetic flux control. In addition, its analytical calculation is added to confirm the feasibility of the optimized results. The layered composite of a very thin ferromagnetic material is expected to guide the magnetic flux and the performance of the magnetic system can be improved by turning the microstructures appropriately. Optimal rotation angles of microstructures are determined using the homogenization design method. The proposed design method is applied to an example to confirm its feasibility. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Numerical modelling of anisotropy and eddy current effects in ferromagnetic laminations using a co-energy formulation

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 5 2001
L. R. Dupré
Abstract The paper deals with a numerical model for the evaluation of electromagnetic fields in one steel lamination under the influence of a rotating magnetic flux, taking into account anisotropy effects. For this purpose a detailed material model, described by a differential permeability tensor, is included in the macroscopic electromagnetic field calculations in one lamination. Here, by geometrical and physical considerations, the governing Maxwell equations are reduced to a system of parabolic PDEs for the components of the magnetic field vector, under appropriate boundary and initial conditions. We present a suitable numerical approximation based upon a finite element,finite difference method, which properly takes into account the material characteristics. The study leads to a more realistic numerical modelling of the electromagnetic phenomena inside electric and magnetic conducting laminations due to anisotropy effects. Numerical results are compared with those from simplified analytical formulae. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Eigenfunctions and Hardy inequalities for a magnetic Schrödinger operator in ,2

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 13 2003
Bénédicte Alziary
Abstract The zero set {z,,2:,(z)=0} of an eigenfunction , of the Schrödinger operator ,V=(i,+A)2+V on L2(,2) with an Aharonov,Bohm-type magnetic potential is investigated. It is shown that, for the first eigenvalue ,1 (the ground state energy), the following two statements are equivalent: (I) the magnetic flux through each singular point of the magnetic potential A is a half-integer; and (II) a suitable eigenfunction , associated with ,1 (a ground state) may be chosen in such a way that the zero set of , is the union of a finite number of nodal lines (curves of class C2) which emanate from the singular points of the magnetic potential A and slit the two-dimensional plane ,2. As an auxiliary result, a Hardy-type inequality near the singular points of A is proved. The C2 differentiability of nodal lines is obtained from an asymptotic analysis combined with the implicit function theorem. Copyright © 2003 John Wiley & Sons, Ltd. [source]

A toy model for magnetic connection in black hole accretion disc

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007
Ding-Xiong Wang
ABSTRACT A toy model for magnetic connection in black hole (BH) accretion disc is discussed based on a poloidal magnetic field generated by a single electric current flowing around a Kerr BH in the equatorial plane. We discuss the effects of the coexistence of two kinds of magnetic connection (MC) arising, respectively, from (1) the closed field lines connecting the BH horizon with the disc (henceforth MCHD) and (2) the closed field lines connecting the plunging region with the disc (henceforth MCPD). The magnetic field configuration is constrained by conservation of magnetic flux and a criterion of the screw instability of the magnetic field. Two parameters , and ,m are introduced to describe our model instead of resolving the complicated magnetohydrodynamic equations. Compared with MCHD, energy and angular momentum of the plunging particles are extracted via MCPD more effectively, provided that the BH spin is not very high. It turns out that negative energy can be delivered to the BH by the plunging particles without violating the second law of BH thermodynamics, however it cannot be realized via MCPD in a stable way. [source]

Origin and evolution of magnetars

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2008
Lilia Ferrario
ABSTRACT We present a population synthesis study of the observed properties of the magnetars investigating the hypothesis that they are drawn from a population of progenitors that are more massive than those of the normal radio pulsars. We assume that the anomalous X-ray emission is caused by the decay of a toroidal or tangled up field that does not take part in the spin-down of the star. Our model assumes that the magnetic flux of the neutron star is distributed as a Gaussian in the logarithm about a mean value that is described by a power law , where Mp is the mass of the progenitor. We find that we can explain the observed properties of the magnetars for a model with ,0= 2 × 1025 G cm2 and ,= 5 if we suitably parametrize the time evolution of the anomalous X-ray luminosity as an exponentially decaying function of time. Our modelling suggests that magnetars arise from stars in the high-mass end (20 M,,Mp, 45 M,) of this distribution. The lower mass progenitors are assumed to give rise to the radio pulsars. The high value of , can be interpreted in one of two ways. It may indicate that the magnetic flux distribution on the main sequence is a strong function of mass and that this is reflected in the magnetic fluxes of the neutron stars that form from this mass range (the fossil field hypothesis). The recent evidence for magnetic fluxes similar to those of the magnetars in a high fraction (,25 per cent) of massive O-type stars lends support to such a hypothesis. Another possibility is that the spin of the neutron star is a strong function of the progenitor mass, and it is only for stars that are more massive than ,20 M, that magnetar-type fields can be generated by the ,,, dynamo mechanism (the convective dynamo hypothesis). In either interpretation, it has to be assumed that all or a subset of stars in the mass range ,20,45 M,, which on standard stellar evolution models lead to black holes via the formation of a fall-back disc, must give rise to magnetars. Unlike with the radio pulsars, the magnetars only weakly constrain the birth spin period, due to their rapid spin-down. Our model predicts a birthrate of ,1.5,3 × 10,3 yr,1 for the magnetars. [source]

The late time evolution of gamma-ray bursts: ending hyperaccretion and producing flares

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2006
Daniel Proga
ABSTRACT We consider the properties of a hyperaccretion model for gamma-ray bursts (GRBs) at late times when the mass supply rate is expected to decrease with time. We point out that the region in the vicinity of the accretor and the accretor itself can play an important role in determining the rate of accretion, and its time behaviour, and ultimately the energy output. Motivated by numerical simulations and theoretical results, we conjecture that the energy release can be repeatedly stopped and then restarted by the magnetic flux accumulated around the accretor. We propose that the episode or episodes when the accretion resumes correspond to X-ray flares discovered recently in a number of GRBs. [source]

Photoinduced nonequilibrium spin, charge polarizations and spin-dependent current in quantum rings

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2010
Z. G. Zhu
Abstract We investigate the spin-dependent dynamical response of a semiconductor quantum ring with a spin orbit interaction upon the application of a single and two linearly polarized, picosecond, asymmetric electromagnetic pulses in the presence of a static magnetic flux. We find that the pulse-generated electric dipole moment is spin dependent. It is also shown that the spin orbit interaction induces an extra SU(2) effective flux in addition to the static external magnetic flux which is reflected in an additional periodicity of the spin-dependent dipole moment. Furthermore, the pulses may induce a net dynamical charge currents and dynamical spin currents when the clockwise and anti-clockwise symmetry of the carrier is broken upon the pulse application. [source]

Aharonov,Bohm effects on conductivity in carbon nanotubes: A tool for determination of a gap due to strain and curvature

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006
Takeshi Nakanishi
Abstract The Boltzmann conductivity is calculated for carbon nanotubes in the presence of an Aharonov,Bohm magnetic flux. Effects of strain or curvature manifest themselves as a prominent conductivity peak as a function of the flux. The appearance of the peak corresponds to the absence of backscattering in metallic linear bands and makes it possible to determine a gap due to curvature and strain. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The Big Bear Solar Observatory Ca II K-line index for solar cycle 23

ASTRONOMISCHE NACHRICHTEN, Issue 7 2010
M.F. Naqvi
Abstract We present an analysis of 2634 Ca II K-line full-disk filtergrams obtained with the 15-cm aperture photometric full-disk telescope at Big Bear Solar Observatory during the period from 1996 January 1 to 2005 October 24. Using limb darkening corrected and contrast enhanced filtergrams, solar activity indices were derived, which are sensitive to the 11-year solar activity cycle and 27-day rotational period of plages around active regions and the bright chromospheric network. The present work extends an earlier study (solar cycle 22), which was based on video data. The current digital data are of much improved quality with higher spatial resolution and a narrower passband ameliorating photometric accuracy. The time series of chromospheric activity indices cover most of solar cycle 23. One of the most conspicuous features of the Ca II K indices is the secondary maximum in late 2001/early 2002 after an initial decline of chromospheric activity during the first half of 2001. We conclude that a secular trend exists in the Ca II K indices, which has its origin in the bright chromospheric network and brightenings related to decaying active regions. Superposed on this secular trend are the signatures of recurring, long-lived active regions, which are clusters of persistent and continuously emerging magnetic flux. Such features are less visible, when the activity belts on both side of the equator are devoid of the brightenings related to decaying active regions as was the case in October/November 2003 at a time when a superactivity complex including several naked-eye sunspots emerged (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The role of emerging bipoles in the formation of a sunspot penumbra

ASTRONOMISCHE NACHRICHTEN, Issue 6 2010
R. Schlichenmaier
Abstract The generation of magnetic flux in the solar interior and its transport from the convection zone into the photosphere, the chromosphere, and the corona will be in the focus of solar physics research for the next decades. With 4 m class telescopes, one plans to measure essential processes of radiative magneto-hydrodynamics that are needed to understand the nature of solar magnetic fields. One key-ingredient to understand the behavior of solar magnetic field is the process of flux emergence into the solar photosphere, and how the magnetic flux reorganizes to form the magnetic phenomena of active regions like sunspots and pores. Here, we present a spectropolarimetric and imaging data set from a region of emerging magnetic flux, in which a proto-spot without penumbra forms a penumbra. During the formation of the penumbra the area and the magnetic flux of the spot increases. First results of our data analysis demonstrate that the additional magnetic flux, which contributes to the increasing area of the penumbra, is supplied by the region of emerging magnetic flux. We observe emerging bipoles that are aligned such that the spot polarity is closer to the spot. As an emerging bipole separates, the pole of the spot polarity migrates towards the spot, and finally merges with it. We speculate that this is a fundamental process, which makes the sunspot accumulate magnetic flux. As more and more flux is accumulated a penumbra forms and transforms the proto-spot into a full-fledged sunspot (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

An interpretation of rapid changes in the magnetic field associated with solar flares

ASTRONOMISCHE NACHRICHTEN, Issue 8 2008
I.V. Oreshina
Abstract The energy source of a flare is the magnetic field in the corona. A topological model of the magnetic field is used here for interpreting the recently discovered drastic changes in magnetic field associated with solar flares. The following observational results are self-consistently explained: (1) the transverse field strength decreases at outer part of active regions and increases significantly in their centers; (2) the center-of-mass positions of opposite magnetic polarities converge towards the magnetic neutral line just after flares onset; (3) the magnetic flux of active regions decreases steadily during the course of flares. For X-class flares, almost 50% events show such changes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Background magnetic fields during last three cycles of solar activity

ASTRONOMISCHE NACHRICHTEN, Issue 6 2008
O.A. Andryeyeva
Abstract This paper describes our studies of evolution of the solar magnetic field with different sign and field strength in the range from ,100 G to 100 G. The structure and evolution of large-scale magnetic fields on the Sun during the last 3 cycles of solar activity is investigated using magnetograph data from the Kitt Peak Solar Observatory. This analysis reveals two groups of the large-scale magnetic fields evolving differently during the cycles. The first group is represented by relatively weak background fields, and is best observed in the range of 3,10 Gauss. The second group is represented by stronger fields of 75,100 Gauss. The spatial and temporal properties of these groups are described and compared with the total magnetic flux. It is shown that the anomalous behaviour of the total flux during the last cycle can be found only in the second group. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Origin of cosmic magnetic fields

ASTRONOMISCHE NACHRICHTEN, Issue 5-6 2006
M. J. Rees
Abstract The first significant cosmic fields, and the seed field for galactic dynamos probably developed after the formation of the first non-linear structures. The history of star formation and the intergalactic medium is controlled, at least in part, by how and when galaxies and their precursors acquired their fields. The amplification of fields behind shocks, and the diffusivity of the magnetic flux, are crucial to the interpretation of radio sources, gamma ray burst afterglows, and other energetic cosmic phenomena. The build-up of magnetic fields is an important aspect of the overall cosmogonic process. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Some remarks concerning the measurement of the ferromagnetic losses under non-sinusoidal conditions

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2002
Andrei, ugulea
The present standards concerning the measurement of the losses in ferromagnetic media, namely the IEC publications 404-2 (1978), 404-;3 (1982) and 404,10 (1988), refer only to the magnetic flux densities between 1 T and 1.85 T, if the magnetic sheets are grain oriented, and 1 T and 1.5 T if the magnetic sheets are nonoriented. The time variation of the magnetic fluxes must be almost sinusoidal at industrial frequencies of 50 Hz or 60 Hz and medium frequencies between 400 Hz and 10,000 Hz. In the above-mentioned standards there are no references concerning the measurement of losses under non-sinusoidal conditions. The paper deals with some theoretical aspects concerning the power-flows under non-sinusoidal time variation of the electromagnetic fields. The theoretical conclusions are applied to the study of the losses in ferromagnetic media. It is shown that new norms or standards are necessary. Some practical suggestions are given at the end. [source]

Heterotic strings on homogeneous spaces,

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 9 2005
D. Israël
Abstract We construct heterotic string backgrounds corresponding to families of homogeneous spaces as exact conformal field theories. They contain left cosets of compact groups by their maximal tori supported by NS-NS 2-forms and gauge field fluxes. We give the general formalism and modular-invariant partition functions, then we consider some examples such as SU (2)/U (1) ~ S2 (already described in a previous paper) and the SU (3)/U(1)2 flag space. As an application we construct new supersymmetric string vacua with magnetic fluxes and a linear dilaton. [source]

Passivity-based control of a magnetically levitated flexible beam

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 6 2009
T. Shimizu
Abstract This paper solves the asymptotic stabilization problem for a magnetically levitated flexible beam using a nested-loop passivity-based controller design. Passivity analyses reveal that the system can be decomposed into two passive subsystems: a mechanical subsystem that consists of a flexible beam with both ends free and that defines a passive map from external forces to the velocity of the points on the flexible beam at which the external forces act; and an electrical subsystem that consists of a pair of electromagnets and that defines a strictly output-passive map from voltages applied across the electromagnets to magnetic fluxes. The standard method for designing passivity-based controllers leads to a nonlinear feed-forward controller for the electrical subsystem, which enables the electrical subsystem to generate given desired magnetic forces, and an output feedback compensator for the mechanical subsystem, which computes the desired forces required to regulate the position and vibration of the beam. The asymptotic stability of each controller may be proven using Lyapunov's stability theory and LaSalle's invariant set theorem. Numerical simulations confirm the asymptotic stability of the equilibrium configuration of the closed-loop system formed by the magnetically levitated flexible beam together with the proposed controllers. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Magnetic fields in white dwarfs and stellar evolution

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2004
Christopher A. Tout
ABSTRACT The surface magnetic field strengths observed in the magnetic Ap, Bp stars (100,20 000 G) and in the high field magnetic white dwarfs (106,109 G) cover many decades but nevertheless the range of magnetic fluxes observed in each of these stellar groups is similar. An evolutionary link between them therefore appears plausible. For both groups of stars there is also information on field complexity. The magnetic white dwarfs in general show non-dipole field structures which can be best modelled if we assume contributions from higher order multipoles. The field structures of the Ap and Bp stars are similarly complex. We investigate the hypothesis that the magnetic fields of the white dwarfs could be fossil remnants from the main-sequence phase by focussing on the problem of how field complexity may arise and be maintained during evolution to the compact star state. We also address the question of to what extent magnetic fields seen in the early type stars could be fossil remnants from the pre-main-sequence phases of stellar evolution dating back perhaps to the time of star formation. [source]

Origin and evolution of magnetars

Application of the photon's intrinsic flux to the 1s-2p and 2p-3d excitonic transitions in nanostructures

ANNALEN DER PHYSIK, Issue 12 2009
Z. Saglam
Abstract We have applied our two recent results [depending on its helicity photon carries a quantum flux of ± , 0 = ± hc/e and the quantized magnetic fluxes through the electronic orbits of the Dirac hydrogen atom are given by: , (n,l,mj) = (n-l-mj),0) ] to the 1s-2p and 2p-3d excitonic transitions in nanostructures. It is shown that the flux changes for the non-zero matrix elements in the 1s-2p and 2p-3d excitonic transitions is either ± ,0 or zero. The present result supports the previous results stated above. It is also shown that spin flip is possible in the 1s-2p and 2p-3d excitonic transitions. [source]