Journal articles: 'Magnetic geometry'

1

Weiss, Nigel. "Magnetic geometry of sunspots." Nature 362, no. 6417 (March 1993): 208–9. http://dx.doi.org/10.1038/362208a0.

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Cargill, P. J., J. Chen, D. S. Spicer, and S. T. Zalesak. "Geometry of interplanetary magnetic clouds." Geophysical Research Letters 22, no. 5 (March 1, 1995): 647–50. http://dx.doi.org/10.1029/95gl00013.

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Wildman, Raymond A., and George A. Gazonas. "Gravitational and magnetic anomaly inversion using a tree-based geometry representation." GEOPHYSICS 74, no. 3 (May 2009): I23—I35. http://dx.doi.org/10.1190/1.3110042.

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Gravitational and magnetic anomaly inversion of homogeneous 2D and 3D structures is treated using a geometric parameterization that can represent multiple, arbitrary polygons or polyhedra and a local-optimization scheme based on a hill-climbing method. This geometry representation uses a tree data structure, which defines a set of Boolean operations performed on convex polygons. A variable-length list of points, whose convex hull defines a convex polygon operand, resides in each leaf node of the tree. The overall optimization algorithm proceeds in two steps. Step one optimizes geometric transformations performed on different convex polygons. This step provides approximate size and location data. The second step optimizes the points located on all convex hulls simultaneously, giving a more accurate representation of the geometry. Though not an inherent restriction, only the geometry is optimized, not including material values such as density or susceptibility. Results based on synthetic and measured data show that the method accurately reconstructs various structures from gravity and magnetic anomaly data. In addition to purely homogeneous structures, a parabolic density distribution is inverted for 2D inversion.

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Catalano, Francesco A. "Have Non-Magnetic Stars a Complex Geometry?" International Astronomical Union Colloquium 138 (1993): 315–26. http://dx.doi.org/10.1017/s0252921100020686.

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AbstractThe existence of non-magnetic CP stars among the ones in the CP2 and CP4 groups is discussed. Assuming to be non-magnetic a star in which the magnetic field has been measured but no value in excess of the 3σ level has been detected, the implications of the spectrum and/or light variability observed in some such stars are discussed. Since the overall properties of non-magnetic stars do not differ significantly from those of the magnetic ones and a similar variability phenomenology has been observed in several such stars, the probable presence of a weak large scale organized magnetic field is argued.

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Rüdiger, G., and D. A. Shalybkov. "The magnetic geometry of magnetic-dominated thin accretion disks." Astronomy & Astrophysics 393, no. 3 (October 2002): L81—L84. http://dx.doi.org/10.1051/0004-6361:20021254.

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6

Connor, J. W. "Magnetic geometry, plasma profiles, and stability." Plasma Physics Reports 32, no. 7 (July 2006): 539–48. http://dx.doi.org/10.1134/s1063780x06070026.

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7

Sergeev, A. G. "Magnetic Bloch theory and noncommutative geometry." Proceedings of the Steklov Institute of Mathematics 279, no. 1 (December 2012): 181–93. http://dx.doi.org/10.1134/s0081543812080123.

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8

Courtillot, V., J. P. Valet, G. Hulot, and J. L. Le Mouel. "The Earth's magnetic field: Which geometry?" Eos, Transactions American Geophysical Union 73, no. 32 (1992): 337. http://dx.doi.org/10.1029/91eo00260.

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9

Lizzi, Fedele, and Richard J. Szabo. "Electric-magnetic duality in noncommutative geometry." Physics Letters B 417, no. 3-4 (January 1998): 303–11. http://dx.doi.org/10.1016/s0370-2693(97)01401-9.

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10

Kazeev, M. N., V. S. Koidan, V. F. Kozlov, and Yu S. Tolstov. "Magnetic pulse welding in plane geometry." Journal of Applied Mechanics and Technical Physics 54, no. 6 (November 2013): 894–99. http://dx.doi.org/10.1134/s0021894413060047.

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11

Pitel, Ira J. "Selecting the Best Magnetic Core Geometry." IEEE Power Electronics Magazine 10, no. 1 (March 2023): 52–57. http://dx.doi.org/10.1109/mpel.2023.3235470.

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Earle, Keith A., Laxman Mainali, Indra Dev Sahu, and David J. Schneider. "Magnetic Resonance Spectra and Statistical Geometry." Applied Magnetic Resonance 37, no. 1-4 (November 17, 2009): 865–80. http://dx.doi.org/10.1007/s00723-009-0102-7.

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13

Bran, Cristina, Jose Angel Fernandez-Roldan, Rafael P. del Real, Agustina Asenjo, Oksana Chubykalo-Fesenko, and Manuel Vazquez. "Magnetic Configurations in Modulated Cylindrical Nanowires." Nanomaterials 11, no. 3 (February 28, 2021): 600. http://dx.doi.org/10.3390/nano11030600.

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Cylindrical magnetic nanowires show great potential for 3D applications such as magnetic recording, shift registers, and logic gates, as well as in sensing architectures or biomedicine. Their cylindrical geometry leads to interesting properties of the local domain structure, leading to multifunctional responses to magnetic fields and electric currents, mechanical stresses, or thermal gradients. This review article is summarizing the work carried out in our group on the fabrication and magnetic characterization of cylindrical magnetic nanowires with modulated geometry and anisotropy. The nanowires are prepared by electrochemical methods allowing the fabrication of magnetic nanowires with precise control over geometry, morphology, and composition. Different routes to control the magnetization configuration and its dynamics through the geometry and magnetocrystalline anisotropy are presented. The diameter modulations change the typical single domain state present in cubic nanowires, providing the possibility to confine or pin circular domains or domain walls in each segment. The control and stabilization of domains and domain walls in cylindrical wires have been achieved in multisegmented structures by alternating magnetic segments of different magnetic properties (producing alternative anisotropy) or with non-magnetic layers. The results point out the relevance of the geometry and magnetocrystalline anisotropy to promote the occurrence of stable magnetochiral structures and provide further information for the design of cylindrical nanowires for multiple applications.

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14

Boro Saikia, Sudeshna, Theresa Lüftinger, and Manuel Guedel. "Magnetic geometry and activity of cool stars." Proceedings of the International Astronomical Union 14, S345 (August 2018): 341–42. http://dx.doi.org/10.1017/s1743921319001935.

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AbstractStellar magnetic field manifestations such as stellar winds and EUV radiation are the key drivers of planetary atmospheric loss and escape. To understand how the central star influences habitability, it is very important to perform detailed investigation of the star’s magnetic field. We investigate the surface magnetic field geometry and chromospheric activity of 51 sun-like stars. The magnetic geometry is reconstructed using Zeeman Doppler imaging. Chromospheric activity is measured using the Ca II H& K lines. We confirm that the Sun’s large-scale geometry is dominantly poloidal, which is also true for slowly rotating stars. Contrary to the Sun, rapidly rotating stars can have a strong toroidal field and a weak poloidal field. This separation in field geometry appears at Ro=1. Our results show that detailed investigation of stellar magnetic field is important to understand its influence on planetary habitability.

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15

Valdettaro, Lorenzo, and Maurice Meneguzzi. "Compressible MHD in Spherical Geometry." International Astronomical Union Colloquium 130 (1991): 80–85. http://dx.doi.org/10.1017/s0252921100079434.

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AbstractThe generation of magnetic field by a conducting, compressible fluid inside a spherical shell is studied by direct numerical simulations. A pseudo-spectral method is used in order to resolve accurately all the scales present in the problem. The range of parameters considered is the following: a unit Prandtl number, Rayleigh numbers up to 100 times critical, Taylor number 625, an aspect ratio of 2, a Mach number slightly less than 1, and pressure and temperature scale heights of the order of the thickness of the shell. A dynamo effect is observed for magnetic Prandtl numbers larger than 1. We present the properties of the turbulent flow, the role of the helicity and of the differential rotation in the enhancement of the magnetic field, and the spectral properties of the flow fields.

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Belyaev, V. K., A. G. Kozlov, A. V. Ognev, A. S. Samardak, and V. V. Rodionova. "Magnetic properties and geometry-driven magnetic anisotropy of magnetoplasmonic crystals." Journal of Magnetism and Magnetic Materials 480 (June 2019): 150–53. http://dx.doi.org/10.1016/j.jmmm.2019.02.032.

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17

Berezin, Ivan, and Andrey Tlatov. "Coronal Field Geometry and Solar Wind Speed." Universe 8, no. 12 (December 5, 2022): 646. http://dx.doi.org/10.3390/universe8120646.

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The Wang–Sheeley–Arge (WSA) solar wind (SW) model is based on the idea that weakly expanding coronal magnetic field tubes are associated with sources of fast SWs and vice versa. A parameter called the “flux tube expansion” (FTE) is used to determine the degree of expansion of magnetic tubes. The FTE is calculated based on the coronal magnetic field model, usually in the potential approximation. The second input parameter for the WSA model is the great circle distance from the base of the open magnetic field line in the photosphere to the boundary of the corresponding coronal hole (DCHB). These two coronal magnetic field parameters are related by an empirical relationship with the solar wind velocity near the Sun. The WSA model has shortcomings and does not fully explain the solar wind formation mechanisms. In the present work, we model various coronal magnetic field parameters in the potential-field source-surface (PFSS) approximation from a long series of magnetographic observations: the Solar Telescope-magnetograph for Operative Prognoses (STOP) (Kislovodsk Mountain Astronomical Station), the Helioseismic and magnetic imager (SDO/HMI), and data from the Wilcox Solar Observatory (WSO). Our main goal is to identify correlations between the coronal magnetic field parameters and the observed SW velocity in order to use them for modeling SW. We found that the SW velocity correlates relatively well with some geometric properties of the magnetic tubes, including the force line length, the latitude of the force line footpoints, and the DCHB. We propose a formula for calculating the SW velocity based on these parameters. The presented relationship does not use FTE and showed a better correlation with observations compared to the WSA model.

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18

Zahiri Abyaneh, Mehran, and Mehrdad Farhoudi. "Zitterbewegung in noncommutative geometry." International Journal of Modern Physics A 34, no. 09 (March 30, 2019): 1950045. http://dx.doi.org/10.1142/s0217751x19500453.

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We have considered the effects of space and momentum noncommutativity separately on the zitterbewegung (ZBW) phenomenon. In the space noncommutativity scenario, it has been expressed that, due to the conservation of momentum, the Fourier decomposition of the expectation value of position does not change. However, the noncommutative (NC) space corrections to the magnetic dipole moment of electron, that was traditionally perceived to come into play only in the first-order of perturbation theory, appear in the leading-order calculations with the similar structure and numerically the same order, but with an opposite sign. This result may explain why for large lumps of masses, the Zeeman effect due to the noncommutativity remains undetectable. Moreover, we have shown that the x- and y-components of the electron magnetic dipole moment, contrary to the commutative (usual) version, are nonzero and with the same structure as the z-component. In the momentum noncommutativity case, we have indicated that, due to the relevant external uniform magnetic field, the energy spectrum and also the solutions of the Dirac equation are changed in 3[Formula: see text]+[Formula: see text]1 dimensions. In addition, our analysis shows that in 2[Formula: see text]+[Formula: see text]1 dimensions, the resulted NC field makes electrons in the zero Landau level rotate not only via a cyclotron motion, but also through the ZBW motion with a frequency proportional to the field which doubles the amplitude of the rotation. In fact, this is a hallmark of the ZBW in graphene that provides a promising way to be tested experimentally.

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19

Boisson, J., R. Monchaux, and S. Aumaître. "Inertial regimes in a curved electromagnetically forced flow." Journal of Fluid Mechanics 813 (January 26, 2017): 860–81. http://dx.doi.org/10.1017/jfm.2016.876.

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We investigated experimentally the flow driven by a Lorentz force induced by an axial magnetic field $\boldsymbol{B}$ and a radial electric current $I$ applied between two fixed concentric copper cylinders. The gap geometry corresponds to a rectangular section with an aspect ratio of $\unicode[STIX]{x1D702}=4$ and we probe the azimuthal and axial velocity profiles of the flow along the vertical axis by using ultrasonic Doppler velocimetry. We have performed several runs at moderate magnetic field strengths, corresponding to moderate Hartmann numbers $M\leqslant 300$. At these forcing parameters and because of the geometry of our experimental device, we show that the inertial terms are not negligible and an azimuthal velocity that depends on both $I$ and $B$ is induced. From measurements of the vertical velocity we focus on the characteristics of the secondary flow: the time-averaged velocity profiles are compatible with a secondary flow presenting two pairs of stable vortices, as pointed out by previous numerical studies. The flow exhibited a transition between two dynamical modes, a high- and a low-frequency one. The high-frequency mode, which emerges at low magnetic field forcing, corresponds to the propagation in the radial $r$-direction of tilted vortices. This mode is consistent with our previous experiments and with the instability described in Zhao et al. (Phys. Fluids, vol. 23 (8), 2011, 084103) taking place in an elongated duct geometry. The low-frequency mode, observed for high magnetic field forcing, consists of large excursions of the vortices. The dynamics of these modes matches the first axisymmetric instability described in Zhao & Zikanov (J. Fluid Mech., vol. 692, 2012, pp. 288–316) taking place in an square duct geometry. We demonstrated that this transition is controlled by the inertial magnetic thickness $H^{\prime }$ which is the characteristic length we introduce as a balance between the advection and the Lorentz force. The key point here is that when the inertial magnetic thickness $H^{\prime }$ is comparable to one geometric characteristic length ($H/2$ in the vertical or $\unicode[STIX]{x0394}r$ in the radial direction) the corresponding mode is favoured. Therefore, when $H^{\prime }/(H/2)\approx 1$ we observe the high-frequency mode taking place in an elongated duct geometry, and when $H^{\prime }/\unicode[STIX]{x0394}r\approx 1$ we observe the low-frequency mode taking place in square duct geometry and high magnetic field.

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20

Kang, Jong-Hoon, Jong-Woo Kim, Philip J. Ryan, Lin Xie, Lu Guo, Chris Sundahl, Jonathon Schad, et al. "Superconductivity in undoped BaFe2As2by tetrahedral geometry design." Proceedings of the National Academy of Sciences 117, no. 35 (August 17, 2020): 21170–74. http://dx.doi.org/10.1073/pnas.2001123117.

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Fe-based superconductors exhibit a diverse interplay between charge, orbital, and magnetic ordering. Variations in atomic geometry affect electron hopping between Fe atoms and the Fermi surface topology, influencing magnetic frustration and the pairing strength through changes of orbital overlap and occupancies. Here, we experimentally demonstrate a systematic approach to realize superconductivity without chemical doping in BaFe2As2, employing geometric design within an epitaxial heterostructure. We control both tetragonality and orthorhombicity in BaFe2As2through superlattice engineering, which we experimentally find to induce superconductivity when the As−Fe−As bond angle approaches that in a regular tetrahedron. This approach to superlattice design could lead to insights into low-dimensional superconductivity in Fe-based superconductors.

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21

Willingale, L., P. M. Nilson, M. C. Kaluza, A. E. Dangor, R. G. Evans, P. Fernandes, M. G. Haines, et al. "Proton deflectometry of a magnetic reconnection geometry." Physics of Plasmas 17, no. 4 (April 2010): 043104. http://dx.doi.org/10.1063/1.3377787.

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22

Fairlie, D. B. "THE GEOMETRY AND DYNAMICS OF MAGNETIC MONOPOLES." Bulletin of the London Mathematical Society 22, no. 4 (July 1990): 409–10. http://dx.doi.org/10.1112/blms/22.4.409.

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23

Waltz, R. E., and A. H. Boozer. "Local shear in general magnetic stellarator geometry." Physics of Fluids B: Plasma Physics 5, no. 7 (July 1993): 2201–5. http://dx.doi.org/10.1063/1.860754.

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24

Kostomarov, D. P., E. Yu Echkina, I. N. Inovenkov, and S. V. Bulanov. "Simulation of magnetic reconnection in 3D geometry." Mathematical Models and Computer Simulations 2, no. 3 (May 28, 2010): 293–303. http://dx.doi.org/10.1134/s2070048210030038.

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25

Wang, C. C., A. O. Adeyeye, and N. Singh. "Magnetic antidot nanostructures: effect of lattice geometry." Nanotechnology 17, no. 6 (February 27, 2006): 1629–36. http://dx.doi.org/10.1088/0957-4484/17/6/015.

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26

Kitchatinov, L. L., and G. Rudiger. "Global magnetic shear instability in spherical geometry." Monthly Notices of the Royal Astronomical Society 286, no. 3 (April 11, 1997): 757–64. http://dx.doi.org/10.1093/mnras/286.3.757.

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Broderick, Avery E., and Roger D. Blandford. "UNDERSTANDING THE GEOMETRY OF ASTROPHYSICAL MAGNETIC FIELDS." Astrophysical Journal 718, no. 2 (July 12, 2010): 1085–99. http://dx.doi.org/10.1088/0004-637x/718/2/1085.

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Raymond, Nicolas, and San Vũ Ngọc. "Geometry and Spectrum in 2D Magnetic Wells." Annales de l'Institut Fourier 65, no. 1 (2015): 137–69. http://dx.doi.org/10.5802/aif.2927.

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29

Jones, Terry Jay, and Hassib Amini. "The Magnetic Field Geometry in DR 21." Astronomical Journal 125, no. 3 (March 2003): 1418–25. http://dx.doi.org/10.1086/367910.

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30

Gardiner, T. A., and A. Frank. "The Magnetic Geometry of Pulsed Astrophysical Jets." Astrophysical Journal 545, no. 2 (December 20, 2000): L153—L156. http://dx.doi.org/10.1086/317875.

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31

Pilat, Adam. "Analytical modeling of active magnetic bearing geometry." Applied Mathematical Modelling 34, no. 12 (December 2010): 3805–16. http://dx.doi.org/10.1016/j.apm.2010.03.021.

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32

Vazquez, Manuel. "Cylindrical magnetic nanowires: geometry, magnetisation and applications." Europhysics News 54, no. 4 (2023): 16–19. http://dx.doi.org/10.1051/epn/2023401.

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Emerging magnetism phenomena are observed in curvilinear nanostructures. Particularly, cylindrical metallic nanowires are attracting much attention because of their singular magnetic configurations and remagnetisation processes as determined by advanced microscopy techniques and micromagnetism. Profiting of curvature, applications are envisaged in spintronics, spincaloritronics, sensors, robotics or biomedicals.

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33

Taimanov, I. A. "Geometry and quasiclassical quantization of magnetic monopoles." Theoretical and Mathematical Physics 218, no. 1 (January 2024): 129–44. http://dx.doi.org/10.1134/s0040577924010094.

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34

NGO, Minh Tri, Hyo Sung Kwak, Gyung Ho Chung, and Eun Jeong Koh. "Longitudinal study of carotid artery bifurcation geometry using magnetic resonance angiography." Vascular 27, no. 3 (February 7, 2019): 312–17. http://dx.doi.org/10.1177/1708538119828262.

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Objectives Geometry of carotid artery has been known as a risk factor for atherosclerotic carotid disease. Though aging and disease progression can both attribute to geometric changes in the arteries, the exact nature of this phenomenon remains elusive. The aim of our study was to investigate carotid artery geometric changes in a longitudinal study. Methods We conducted a retrospective study of 114 subjects who underwent carotid contrast-enhanced magnetic resonance angiography at our clinic at baseline (2005 to 2007) and after 10 years. The right carotid arteries were segmented using semi-automated methods to obtain various measurements of carotid artery geometry. For each patient, these parameters were assessed at both time points, including bifurcation angle, internal carotid artery angle, vessel diameter, and circumference. Results The median age for the total patient population ( n = 114) at baseline was 59.06 ± 10.40 years. Mean time interval between baseline magnetic resonance angiography and magnetic resonance angiography after 10 years of these patients was 129.18 ± 7.77 months. For the whole group, there was a significant increase in the bifurcation angle ( p < 0.05) over a 10-year period. A significant increase was also noted in the diameter and circumference of the common carotid artery ( p < 0.05). However, the other vessel diameters and circumferences (bulb carotid, internal carotid) as well as the internal carotid angle did not significantly change ( p ≥ 0.05). Conclusions The diameter and circumference of the common carotid artery and bifurcation angle significantly increased over a decade of life.

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LEVINSON, AMIR, and AHARON DAVIDSON. "GENERALIZED BELINSKY–RUFFINI GEOMETRY." Modern Physics Letters A 06, no. 24 (August 10, 1991): 2189–95. http://dx.doi.org/10.1142/s0217732391002396.

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Stationary, axially symmetric solutions of Einstein equations in a free 5-dimensional Kaluza–Klein space-time are derived. The electric charge and magnetic moment are generated by a fictitious boost involving the extra dimension. The associated gyromagnetic factor tends to unity at the ultra-relativistic limit. The solution derived interpolates between the Kerr and the Belinsky–Ruffini solutions.

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Barry, John R., Bane Vasic, Mehrdad Khatami, Mohsen Bahrami, Yasuaki Nakamura, Yoshihiro Okamoto, and Yasushi Kanai. "Optimization of Bit Geometry and Multi-Reader Geometry for Two-Dimensional Magnetic Recording." IEEE Transactions on Magnetics 52, no. 2 (February 2016): 1–7. http://dx.doi.org/10.1109/tmag.2015.2483593.

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Lund-Olesen, Torsten, Bjarke B. Buus, Jakob G. Howalt, and Mikkel F. Hansen. "Magnetic bead micromixer: Influence of magnetic element geometry and field amplitude." Journal of Applied Physics 103, no. 7 (April 2008): 07E902. http://dx.doi.org/10.1063/1.2829401.

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Eswaraiah, C., G. Maheswar, and A. K. Pandey. "Dust properties and magnetic field geometry towards LDN 1570." Proceedings of the International Astronomical Union 10, H16 (August 2012): 385. http://dx.doi.org/10.1017/s1743921314011545.

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AbstractWe have performed both optical linear polarimetric and photometric observations of an isolated dark globule LDN 1570 aim to study the dust polarizing and extinction properties and to map the magnetic field geometry so as to understand not only the importance of magnetic fields in formation and evolution of clouds but also the correlation of the inferred magnetic field structure with the cloud structure and its dynamics. Dust size indicators (RV and λmax) reveal for the presence of slightly bigger dust grains towards the cloud region. The inferred magnetic field geometry, which closely follows the cloud structure revealed by Herschel images, suggest that the cloud could have been formed due to converging material flows along the magnetic field lines.

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De Nittis, Giuseppe, and Maximiliano Sandoval. "The noncommutative geometry of the Landau Hamiltonian: differential aspects." Journal of Physics A: Mathematical and Theoretical 55, no. 2 (December 16, 2021): 024002. http://dx.doi.org/10.1088/1751-8121/ac3da4.

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Abstract In this work we study the differential aspects of the noncommutative geometry for the magnetic C*-algebra which is a 2-cocycle deformation of the group C*-algebra of R 2 . This algebra is intimately related to the study of the quantum Hall effect in the continuous, and our results aim to provide a new geometric interpretation of the related Kubo’s formula. Taking inspiration from the ideas developed by Bellissard during the 80s, we build an appropriate Fredholm module for the magnetic C*-algebra based on the magnetic Dirac operator which is the square root (à la Dirac) of the quantum harmonic oscillator. Our main result consist of establishing an important piece of Bellissard’s theory, the so-called second Connes’ formula. In order to do so, we establish the equality of three cyclic 2-cocycles defined on a dense subalgebra of the magnetic C*-algebra. Two of these 2-cocycles are new in the literature and are defined by Connes’ quantized differential calculus, with the use of the Dixmier trace and the magnetic Dirac operator.

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Klad’ko, S. V., N. P. Poluektov, and I. I. Usatov. "Effect of magnetic field on plasma characteristics in magnetron discharge with hollow cathode." Forestry Bulletin 25 (October 2021): 125–30. http://dx.doi.org/10.18698/2542-1468-2021-5-125-130.

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The effect of magnetic field on plasma characteristics in a magnetron with a hollow cathode was carried out. The magnetic field in this device is of complex geometry, since it consists of many permanent magnets and an electromagnet. The calculated geometries of the magnetic field were used in experimental studies. Measurements have shown that the magnitude and geometry of the magnetic field have a strong effect on the plasma parameters.

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Löptien, B., A. Lagg, M. van Noort, and S. K. Solanki. "Measuring the Wilson depression of sunspots using the divergence-free condition of the magnetic field vector." Astronomy & Astrophysics 619 (November 2018): A42. http://dx.doi.org/10.1051/0004-6361/201833571.

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Context. The Wilson depression is the difference in geometric height of unit continuum optical depth between the sunspot umbra and the quiet Sun. Measuring the Wilson depression is important for understanding the geometry of sunspots. Current methods suffer from systematic effects or need to make assumptions on the geometry of the magnetic field. This leads to large systematic uncertainties of the derived Wilson depressions. Aims. We aim to develop a robust method for deriving the Wilson depression that only requires the information about the magnetic field that is accessible from spectropolarimetry, and that does not rely on assumptions on the geometry of sunspots or on their magnetic field. Methods. Our method is based on minimizing the divergence of the magnetic field vector derived from spectropolarimetric observations. We have focused on large spatial scales only in order to reduce the number of free parameters. Results. We tested the performance of our method using synthetic Hinode data derived from two sunspot simulations. We find that the maximum and the umbral averaged Wilson depression for both spots determined with our method typically lies within 100 km of the true value obtained from the simulations. In addition, we applied the method to Hinode observations of a sunspot. The derived Wilson depression (∼600 km) is consistent with results typically obtained from the Wilson effect. We also find that the Wilson depression obtained from using horizontal force balance gives 110–180 km smaller Wilson depressions than both, what we find and what we deduce directly from the simulations. This suggests that the magnetic pressure and the magnetic curvature force contribute to the Wilson depression by a similar amount.

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42

Brizard, A. "Nonlinear gyrokinetic Maxwell-Vlasov equations using magnetic co-ordinates." Journal of Plasma Physics 41, no. 3 (June 1989): 541–59. http://dx.doi.org/10.1017/s0022377800014070.

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A gyrokinetic formalism using magnetic co-ordinates is used to derive self-consistent, nonlinear Maxwell–Vlasov equations that are suitable for particle simulation studies of finite-β tokamak microturbulence and its associated anomalous transport. The use of magnetic co-ordinates is an important feature of this work since it introduces the toroidal geometry naturally into our gyrokinetic formalism. The gyrokinetic formalism itself is based on the use of the action-variational Lie perturbation method of Cary & Littlejohn, and preserves the Hamiltonian structure of the original Maxwell-Vlasov system. Previous nonlinear gyrokinetic sets of equations suitable for particle simulation analysis have considered either electrostatic and shear-Alfvén perturbations in slab geometry or electrostatic perturbations in toroidal geometry. In this present work fully electromagnetic perturbations in toroidal geometry are considered.

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43

Amghar, B., and M. Daoud. "Quantum state manifold and geometric, dynamic and topological phases for an interacting two-spin system." International Journal of Geometric Methods in Modern Physics 17, no. 02 (January 31, 2020): 2050030. http://dx.doi.org/10.1142/s0219887820500309.

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We consider a two-spin system of [Formula: see text] Heisenberg type submitted to an external magnetic field. Using the associated [Formula: see text] geometry, we investigate the dynamics of the system. We explicitly give the corresponding Fubini–Study metric. We show that for arbitrary pure initial states, the dynamics occurs on a torus. We compute the geometric phase, the dynamic phase and the topological phase. We investigate the interplay between the torus geometry and the entanglement of the two spins. In this respect, we provide a detailed analysis of the geometric phase, the dynamics velocity and the geodesic distance measured by the Fubini–Study metric in terms of the degree of entanglement between the two spins.

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CHANG, A. M. "QUENCHING OF THE HALL RESISTANCE IN A NOVEL GEOMETRY." Modern Physics Letters B 05, no. 01 (January 10, 1991): 21–37. http://dx.doi.org/10.1142/s0217984991000046.

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We review experiments on the observation of Hall resistance anomalies in ballistic Hall junctions of novel geometries, in submicron GaAs-Al x Ga 1−x As heterostructure devices. We demonstrate that the low magnetic field Hall resistance is greatly influenced by the junction geometry, and that particular geometries are required to give rise to a phenomenon known as “quenching” of the Hall resistance where the conventional linear Hall resistance is suppressed to nearly zero, and to a related plateau feature at slightly higher magnetic fields, known as the “last plateau.” These anomalies are explained in terms of the collimation of ballistic electron beams by specific geometric structures and the scattering properties of the Hall junction side walls.

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Lykhohub, Anna, Mykhayl Kovalenko, Igor Tkachuk, and Anton Goncharyk. "Parametric optimization of magnetoelectric generator with double stator." Bulletin of NTU "KhPI". Series: Problems of Electrical Machines and Apparatus Perfection. The Theory and Practice, no. 1 (5) (May 28, 2021): 33–38. http://dx.doi.org/10.20998/2079-3944.2021.1.06.

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A methodology for the optimization-parametric calculation of geometric parameters of the design of an axial-flux permanent magnet generator has been developed. The developed methodology can be used to calculate and optimize geometric parameters in an automated mode for almost any type of electromechanical energy converter. The operation of the developed system is based on the interconnections between the computer-aided design system, software package, and numerical calculation of the electromagnetic field with the possibility of feedback and parameterization and a computing environment such as Matlab. The parameterized geometric model is constructed on the example of an axial-flux permanent magnet generator with a double stator. Subsequently, parametric optimization of geometric parameters was performed using the developed algorithm. The use of the developed solution reduces the time spent by the researcher on the calculation of geometry and optimization. Parameterization is performed at all stages of construction of a single part, the geometry of which is planned to change, and in each part of the assemblies if any in a particular case. That is, with the help of the developed model, it is possible to program the optimization of both a separate structural element of the studied system and the object as a whole. In the process of optimization, the main geometrical parameters of the investigated end generator with double side changed: stator yoke, air gap, gear-groove zone of the stator, housing elements. As a result of parametric optimization of the geometry of the prototype, it was possible to reduce the geometric dimensions by optimizing the magnitude of the magnetic induction in some areas of the magnetic core of the studied generator. Due to the application of the developed algorithm, it was possible to reduce the cost of the generator, as well as the volume of the magnetic circuit by 18.1% and 24.3%, respectively. This indicates the effectiveness of the developed algorithm and the possibility of using this algorithm in further research

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Lee, Geun-Hee, and Kab-Jin Kim. "Optimizing the Geometry of Chiral Magnetic Logic Devices." Journal of Magnetics 25, no. 2 (June 30, 2020): 150–56. http://dx.doi.org/10.4283/jmag.2020.25.2.150.

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Gastine, T., J. Morin, L. Duarte, A. Reiners, U. R. Christensen, and J. Wicht. "What controls the magnetic geometry of M dwarfs?" Astronomy & Astrophysics 549 (December 21, 2012): L5. http://dx.doi.org/10.1051/0004-6361/201220317.

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Tsagas, Christos G. "Magnetic Tension and the Geometry of the Universe." Physical Review Letters 86, no. 24 (June 11, 2001): 5421–24. http://dx.doi.org/10.1103/physrevlett.86.5421.

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Sotani, H., A. Colaiuda, and K. D. Kokkotas. "Constraints on the magnetic field geometry of magnetars." Monthly Notices of the Royal Astronomical Society 385, no. 4 (April 2008): 2161–65. http://dx.doi.org/10.1111/j.1365-2966.2008.12977.x.

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Bird, T. M., and C. C. Hegna. "Controlling tokamak geometry with three-dimensional magnetic perturbations." Physics of Plasmas 21, no. 10 (October 2014): 100702. http://dx.doi.org/10.1063/1.4898064.

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Journal articles on the topic 'Magnetic geometry'

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