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1

Magnetic field induced optical vortex beam rotation  

E-print Network

Light with orbital angular momentum (OAM) has drawn a great deal of attention for its important applications in the fields of precise optical measurements and high capacity optical communications. Here we adopt a method to study the rotation of a light beam, which is based on magnetic field induced circular birefringence in warm 87Rb atomic vapor. The dependence of the rotation angle to the intensity of the magnetic field makes it appropriate for weak magnetic field measurement. We derive a detail theoretical description that is in well agreement with the experimental observations. The experiment shows here provides a new method for precise measurement of magnetic field intensity and expands the application of OAM-carrying light.

Shi, Shuai; Zhou, Zhi-Yuan; Li, Yan; Zhang, Wei; Shi, Bao-Sen

2015-01-01

2

Measurement of magnetic field using Rayleigh backscattering in optical fibres  

SciTech Connect

In this paper, we investigate the use of optical reflectometry in optical fibres for the measurement of magnetic field. The dedicated application concerns the measurement of plasma current in the fusion reactor. The measurement is based on the rotation of the polarization state of the Rayleigh backscattered signal when an optical pulse is launched in the fibre. Particular care has been undertaken to evaluate the impact of linear birefringence on the measurement performance. (authors)

Wuilpart, M.; Caucheteur, C. [Univ. of Mons, Faculty of Engineeering, Electromagnetism and Telecommunications Dept., 31, Boulevard Dolez, 7000 Mons (Belgium); Goussarov, A. [SCK.CEN, 200 Boerentang, 2400 Mol (Belgium); Aerssens, M. [Univ. of Mons, Faculty of Engineeering, Electromagnetism and Telecommunications Dept., 31, Boulevard Dolez, 7000 Mons (Belgium); Massaut, V. [SCK.CEN, 200 Boerentang, 2400 Mol (Belgium); Megret, P. [Univ. of Mons, Faculty of Engineeering, Electromagnetism and Telecommunications Dept., 31, Boulevard Dolez, 7000 Mons (Belgium)

2011-07-01

3

Direction of Optical Energy Flow in a Transverse Magnetic Field  

NASA Astrophysics Data System (ADS)

In this Letter, we report a theoretical and experimental study of the direction of optical energy flow in homogeneous media subject to a transverse magnetic field. For transparent media we verify experimentally for the first time the existence of magnetic deflection of circularly polarized light. In absorbing media the calculated directions of the Poynting vector and of a wave packet do not coincide. Experimentally we demonstrate that the Poynting vector result is not correct.

Rikken, G. L. J. A.; van Tiggelen, B. A.

1997-02-01

4

Optical fiber magnetic field sensors with ceramic magnetostrictive jackets.  

PubMed

Optical fibers coated by magnetostrictive ceramic films were tested with a Mach-Zehnder interferometer in an open-loop mode. The sensors exhibited excellent linearity and good sensitivity. The response of ceramic-jacketed fibers was not affected by small dc fluctuations that are due to the linear behavior of tested ceramic coatings in low magnetic fields. Tested ceramic materials included magnetite, ?-Fe(2) O(3), nickel ferrite, and cobalt-doped nickel ferrite (NCF2) jackets. The latter showed the best performance. A minimum detectable field of 3.2 × 10(-3) A/m for optical fiber jacketed with 2-?m-thick and 1-m-long NCF2 material has been achieved. The capability of detecting magnetic fields as low as 2.6 × 10(-7) A/m with a 10-?m-thick cobalt-doped nickel ferrite jacket is proposed. PMID:21127528

Sedlar, M; Paulicka, I; Sayer, M

1996-09-20

5

Enhanced magnetic-field-induced optical properties of nanostructured magnetic fluids by doping nematic liquid crystals  

PubMed Central

Ferronematic materials composed of 4-cyano-4?-pentylbiphenyl nematic liquid crystal and oil-based Fe3O4 magnetic fluid were prepared using ultrasonic agitation. The birefringence (?n) and figure of merit of optical properties (Q?=??n/?, where ? is the extinction coefficient) of pure magnetic fluids and the as-prepared ferronematic materials were examined and compared. The figure of merit of optical properties weighs the birefringence and extinction of the materials and is more appropriate to evaluate their optical properties. Similar magnetic-field- and magnetic-particle-concentration-dependent properties of birefringence and figure of merit of optical properties were obtained for the pure magnetic fluids and the ferronematic materials. For the ferronematic materials, the values of Q increase with the volume fractions of nematic liquid crystal under certain fixed field strength and are larger than those of their corresponding pure magnetic fluids at high field region. In addition, the enhancement of Q value increases monotonously with the magnetic field and becomes remarkable when the applied magnetic field is beyond 50 mT. The maximum relative enhanced value of QR exceeds 6.8% in our experiments. The results of this work may conduce to extend the pragmatic applications of nanostructured magnetic fluids in optical field. PMID:22587542

2012-01-01

6

Solar magnetic fields measurements with a magneto-optical filter  

NASA Technical Reports Server (NTRS)

The presence of a magnetic field at different levels inside the sun has crucial implications for helioseismology. The solar oscillation observing program carried out since 1983 at Mt. Wilson with Cacciani magneto-optical filter has recently been modified to acquire full-disk magnetograms with 2 arcsec spatial resolution. A method for the correct determination of magnetic maps which are free of contamination by velocity signal is presented. It is shown that no cross-talk exists between the Doppler and Zeeman shifts of the Na D lines, provided that instrumental polarization effects are taken into account. The observed line-of-sight photospheric field was used to map the vector field in the inner corona, above active regions, in the current free approximation.

Cacciani, A.; Ricci, D.; Rosati, P.; Rhodes, E. J.; Smith, E.

1990-01-01

7

Optical fiber magnetic field sensor based on magnetic fluid and microfiber mode interferometer  

NASA Astrophysics Data System (ADS)

A magnetic field sensor is proposed based on the combination of magnetic fluid (MF) and an optical microfiber mode interferometer (MMI). It is measured that the MMI is highly sensitive to ambient refractive index (RI) with a high sensitivity up to 16,539 nm/RIU while RI of the MF is changeable with an external magnetic field strength. By monitoring wavelength shift of transmission spectrum of the MMI, magnetic field measurement is realized with a maximum sensitivity of -293 pm/Oe in the range of 0-220 Oe.

Zheng, Yangzi; Dong, Xinyong; Chan, Chi Chiu; Shum, Perry Ping; Su, Haibin

2015-02-01

8

Optical Detection of Magnetic Orders in HgCr2O4 Frustrated Spin Magnet under Pulsed High Magnetic Fields  

NASA Astrophysics Data System (ADS)

A magneto-optical survey was conducted for HgCr2O4 powder samples under pulsed high magnetic fields of up to 55 T. Intensity changes in magnetic fields observed for the exciton–magnon–phonon optical transition spectra coincide well with those of magnetization, lattice distortion from X-ray diffraction, and electron-magnetic resonances. The last-ordered phase was detected prior to the fully polarized magnetic phase, similarly to the other chromium spinel oxide, ZnCr2O4 and CdCr2O4.

Nakamura, Daisuke; Miyata, Atsuhiko; Aida, Yuki; Ueda, Hiroaki; Takeyama, Shojiro

2014-11-01

9

Optical Signatures from Magnetic 2-D Electron Gases in High Magnetic Fields to 60 Tesla  

SciTech Connect

We present experiments in the 60 Tesla Long-Pulse magnet at the Los Alamos National High Magnetic Field Lab (NHMFL) focusing on the high-field, low temperature photoluminescence (PL) from modulation-doped ZnSe/Zn(Cd,Mn)Se single quantum wells. High-speed charge-coupled array detectors and the long (2 second) duration of the magnet pulse permit continuous acquisition of optical spectra throughout a single magnet shot. High-field PL studies of the magnetic 2D electron gases at temperatures down to 350mK reveal clear intensity oscillations corresponding to integer quantum Hall filling factors, from which we determine the density of the electron gas. At very high magnetic fields, steps in the PL energy are observed which correspond to the partial unlocking of antiferromagnetically bound pairs of Mn2+ spins.

Crooker, S.A.; Kikkawa, J.M.; Awschalom, D.D.; Smorchikova, I.P.; Samarth, N.

1998-11-08

10

Fiber optic magnetic field sensor based on the TbDyFe rod  

NASA Astrophysics Data System (ADS)

We present, and experimentally demonstrate, a fiber optic magnetic field sensor for the measurement of a weak alternating magnetic field, based on a TbDyFe rod. The fiber optic magnetic field sensor is constructed in a Michelson interferometer configuration, and the phase-generated carrier demodulation is used to obtain the time-varying phase shift induced by the applied magnetic field. A high sensitivity of up to 3.6 × 10-2 V ?T - 1 (rms) with a resolution of 23 pT/?Hz (rms) at 50 Hz is achieved. Experimental results show that the sensor exhibits excellent linearity and reversibility.

Chen, Feifei; Jiang, Yi

2014-08-01

11

Optically detected nuclear magnetic resonance imaging at low fields: Theory and practice  

NASA Astrophysics Data System (ADS)

This dissertation shows the development and implementation of techniques for the optical detection of nuclear magnetic resonance using a rubidium frequency-modulated nonlinear magneto-optical rotation atomic magnetometer. The first three chapters provide introductory material describing the physics behind magnetic resonance, the motivation and challenges for conducting nuclear magnetic resonance experiments at low magnetic fields, and the experimental details behind atomic magnetometry. The next three chapters describe the design and construction of an optical atomic magnetometer and its application to the detection of magnetic particles and remotely detected magnetic resonance images. A study of paraffin waxes that are used as anti-relaxation coatings in the atomic magnetometer follows. The final chapter is a brief discussion of the direction of optically detected low-field nuclear magnetic resonance.

Donaldson, Marcus Hofheins

12

Quasi-static high-resolution magnetic-field detection based on dielectric optical resonators  

NASA Astrophysics Data System (ADS)

In this paper we present a high resolution magnetic field sensor that is based on the perturbation of the optical modes (whispering gallery mode, WGM) of a spherical dielectric resonator. The optical resonator is side coupled to a tapered single mode optical fiber. One side of the optical fiber is coupled to a distribute feedback diode laser, while the other end is connected to a photodiode. The optical modes of the dielectric cavity are perturbed using a metglas sheet that is in contact with the resonator. When the metglas sheet is exposed to an external magnetic field it elongates perturbing the optical modes of the dielectric cavity. This in turn leads to a shift in the optical resonances. By measuring the induced WGM shift the magnetic field can be measured. Preliminary results show sensor resolution of a few nanoteslas.

Ioppolo, Tindaro; Rubino, Edoardo

2013-06-01

13

A loss-based, magnetic field sensor implemented in a ferrofluid infiltrated microstructured polymer optical fiber  

SciTech Connect

We report an in-fiber magnetic field sensor based on magneto-driven optical loss effects, while being implemented in a ferrofluid infiltrated microstructured polymer optical fiber. We demonstrate that magnetic field flux changes up to 2000 gauss can be detected when the magnetic field is applied perpendicular to the fiber axis. In addition, the sensor exhibits high polarization sensitivity for the interrogated wavelengths, providing the possibility of both field flux and direction measurements. The underlying physical and guidance mechanisms of this sensing transduction are further investigated using spectrophotometric, light scattering measurements, and numerical simulations, suggesting photonic Hall effect as the dominant physical, transducing mechanism.

Candiani, A. [Foundation for Research and Technology-Hellas (FORTH), Institute of Electronic Structure and Laser (IESL), Heraklion 70013 Greece (Greece); Department of Information Engineering (DII), University of Parma, Parma 43124 (Italy); Argyros, A.; Leon-Saval, S. G.; Lwin, R. [Institute of Photonics and Optical Science (IPOS), School of Physics, The University of Sydney, Sydney (Australia); Selleri, S. [Department of Information Engineering (DII), University of Parma, Parma 43124 (Italy); Pissadakis, S., E-mail: pissas@iesl.forth.gr [Foundation for Research and Technology-Hellas (FORTH), Institute of Electronic Structure and Laser (IESL), Heraklion 70013 Greece (Greece)

2014-03-17

14

Magnetic-field-dependent optical transmission of nickel nanorod colloidal dispersions  

NASA Astrophysics Data System (ADS)

Aqueous dispersions of nickel nanorods, ?13 nm in diameter and 40-160 nm in length, were synthesized using ac electrodeposition into porous alumina templates. The nanorods in suspension can be aligned by modest magnetic fields, which leads to a change in the optical transmittance of the dispersion. Optical transmission measurements with polarized and unpolarized light as a function of magnetic field were performed on suspensions of different particle concentration and varying aspect ratio of the nanoparticles. The experimental results were compared with a theoretical model in which the optical absorption of the nanorods is calculated from the polarizability of prolate ellipsoids in the quasistatic approximation. The magnetic field dependence is introduced in terms of the static orientational distribution function of magnetic moments in an external field. In addition, the relaxation dynamics of the optical transmission was studied, which allowed us to determine the rotational diffusion coefficient of the nanorods in suspension.

Klein, Tobias; Laptev, Aleksej; Günther, Annegret; Bender, Philipp; Tschöpe, A.; Birringer, R.

2009-12-01

15

Directional properties of polar paramagnetic molecules subject to congruent electric, magnetic and optical fields  

E-print Network

We show that congruent electric, magnetic and non-resonant optical fields acting concurrently on a polar paramagnetic (and polarisable) molecule offer possibilities to both amplify and control the directionality of the ensuing molecular states that surpass those available in double-field combinations or in single fields alone. At the core of these triple-field effects is the lifting of the degeneracy of the projection quantum number $M$ by the magnetic field superimposed on the optical field and a subsequent coupling of the members of the "doubled" (for states with $M \

Sharma, Ketan

2015-01-01

16

Optical Alignment Support Of The Magnetic Field Satellite (MAGSAT) Vector Magnetometer Calibration  

NASA Astrophysics Data System (ADS)

The Magnetic Field Satellite (MAGSAT) was launched into low earth orbit on October 30, 1979, and reentered on June 11, 1980. It included a vector magnetometer which was successfully used to accurate-ly map the magnitude and direction of the magnetic field over most of the surface of the earth. To achieve the accuracy sought required arc second precision determination of the relative orientations of the three sensor axes in a coordinate system defined by optical references attached to the magnetometer. The calibration procedure consisted basically of accurate and repeatable positioning of the vector magnetometer within a unique magnetic test facility which nulls the earth's magnetic field, then generates magnetic fields of selected orientations and strengths. Analysis of the magnetometer sensor outputs together with data on the accurate positioning and optical reference alignment gave the axes orientations. We used precision theodolites and methods related to surveying techniques to do the accurate positioning and optical component alignment measurements.

Hinkal, Sanford W.

1982-06-01

17

The effects of intense laser field and applied electric and magnetic fields on optical properties of an asymmetric quantum well  

NASA Astrophysics Data System (ADS)

This paper presents the results of the theoretical study of the effects of non-resonant intense laser field and electric and magnetic fields on the optical properties (the linear and third-order nonlinear refractive index and absorption coefficients) in an asymmetric quantum well. The electric field and intense laser field are applied along the growth direction of the asymmetric quantum well and the magnetic field is oriented perpendicularly. To calculate the energy and the wave functions of the electron in the asymmetric quantum well, the effective mass approximation and the method of envelope wave function are used. The asymmetric quantum well is constructed by using different aluminium concentrations in both right and left barriers. The confinement in the quantum well is changed drastically by either the effect of electric and magnetic fields or by the application of intense laser field. The optical properties are calculated using the compact density matrix approach. The results show that the effect of the intense laser field competes with the effects of the electric and magnetic fields. Consequently, peak position shifts to lower photon energies due to the effect of the intense laser field and it shifts to higher photon energies by the effects of electric and magnetic fields. In general, it is found that the concentration of aluminum, electric and magnetic fields and intense laser field are external agents that modify the optical responses in the asymmetric quantum well.

Restrepo, R. L.; Ungan, F.; Kasapoglu, E.; Mora-Ramos, M. E.; Morales, A. L.; Duque, C. A.

2015-01-01

18

Optical fiber magnetic field sensors with TbDyFe magnetostrictive thin films as sensing materials.  

PubMed

Different from usually-used bulk magnetostrictive materials, magnetostrictive TbDyFe thin films were firstly proposed as sensing materials for fiber-optic magnetic field sensing characterization. By magnetron sputtering process, TbDyFe thin films were deposited on etched side circle of a fiber Bragg Grating (FBG) as sensing element. There exists more than 45pm change of FBG wavelength when magnet field increase up to 50 mT. The response to magnetic field is reversible, and could be applicable for magnetic and current sensing. PMID:19997310

Yang, Minghong; Dai, Jixiang; Zhou, Ciming; Jiang, Desheng

2009-11-01

19

Development of optical modulators for measurements of solar magnetic fields  

NASA Technical Reports Server (NTRS)

The measurement of polarized light allows solar astronomers to infer the magnetic field on the Sun. The accuracy of these measurements is dependent on the stable retardation characteristics of the polarization modulators used to minimize the atmospheric effects seen in ground-based observations. This report describes the work by the Space Science Laboratory at Marshall Space Flight Center to improve two types of polarization modulators. As a result, the timing characteristics for both electrooptic crystals (KD*Ps) and liquid crystal devices (LCDs) have been studied and will be used to enhance the capabilities of the MSFC Vector Magnetograph.

West, E. A.; Smith, J. E.

1987-01-01

20

Relaxation property of the magnetic-fluid-based fiber-optic evanescent field modulator  

Microsoft Academic Search

The details about the modulation property of the magnetic-fluid-based fiber-optic evanescent field modulator are studied in this article. Experiments show that it needs some time for the outgoing light from the modulator to reach the final steady value when the external magnetic field is turned on or off (called the relaxation property of the modulator). Two exponential functions are employed

Shengli Pu; Xianfeng Chen; Ziyun di; Yuxing Xia

2007-01-01

21

Polarization-preserving confocal microscope for optical experiments in a dilution refrigerator with high magnetic field.  

PubMed

We present the design and operation of a fiber-based cryogenic confocal microscope. It is designed as a compact cold-finger that fits inside the bore of a superconducting magnet, and which is a modular unit that can be easily swapped between use in a dilution refrigerator and other cryostats. We aimed at application in quantum optical experiments with electron spins in semiconductors and the design has been optimized for driving with and detection of optical fields with well-defined polarizations. This was implemented with optical access via a polarization maintaining fiber together with Voigt geometry at the cold finger, which circumvents Faraday rotations in the optical components in high magnetic fields. Our unit is versatile for use in experiments that measure photoluminescence, reflection, or transmission, as we demonstrate with a quantum optical experiment with an ensemble of donor-bound electrons in a thin GaAs film. PMID:21528993

Sladkov, Maksym; Bakker, M P; Chaubal, A U; Reuter, D; Wieck, A D; van der Wal, C H

2011-04-01

22

Intrinsic magnetic field sensitivities of sensor head housing for all-fiber optic current sensors  

NASA Astrophysics Data System (ADS)

Full-fiber optical current sensors utilize the effects of magnetic-field imposed on the change of polarization azimuth of light in the fibers. Due to the sensitivities to external perturbations, the sensing fiber head in practical applications is usually packed in a fixed metallic housing majorly for protection purposes. However, the housing material itself tends to influence the magnetic field distributions of the current carrying wire in question. In this paper, the intrinsic effect and influence of fiber sensor head housing made of different magnetic materials on the magnetic field distributions around the current-carrying wire have been investigated. Simulation and virtual experimentation was carried out in the COMSOL environment. From the results, the housings made of single magnetic material are found to have magnetic disturbances on the magnetic field distribution around the wire. Housing made of some alloy materials has no influence on the magnetic distributions outside the wire. After experimenting with several materials, the former materials inclusive, steel is preferred as the protective housing and/or casing of fiber sensor head in optical fiber current sensors. This is on the basis of both technical and non-technical consideration of low cost of material though biased toward technical aspect of little or no influence on magnetic distribution around the wire.

Zhang, Xuedian; Chang, Min; Mao, Chenfei; Lu, Dunke; Kamagara, Abel

2014-10-01

23

A Radio and Optical Polarization Study of the Magnetic Field in the Small Magellanic Cloud  

SciTech Connect

We present a study of the magnetic field of the Small Magellanic Cloud (SMC), carried out using radio Faraday rotation and optical starlight polarization data. Consistent negative rotation measures (RMs) across the SMC indicate that the line-of-sight magnetic field is directed uniformly away from us with a strength 0.19 {+-} 0.06 {mu}G. Applying the Chandrasekhar-Fermi method to starlight polarization data yields an ordered magnetic field in the plane of the sky of strength 1.6 {+-} 0.4 {mu}G oriented at a position angle 4deg {+-} 12deg , measured counterclockwise from the great circle on the sky joining the SMC to the Large Magellanic Cloud (LMC). We construct a three-dimensional magnetic field model of the SMC, under the assumption that the RMs and starlight polarization probe the same underlying large-scale field. The vector defining the overall orientation of the SMC magnetic field shows a potential alignment with the vector joining the center of the SMC to the center of the LMC, suggesting the possibility of a 'pan-Magellanic' magnetic field. A cosmic-ray-driven dynamo is the most viable explanation of the observed field geometry, but has difficulties accounting for the observed unidirectional field lines. A study of Faraday rotation through the Magellanic Bridge is needed to further test the pan-Magellanic field hypothesis.

Mao, S. A. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Gaensler, B. M. [School of Physics, The University of Sydney, NSW 2006 (Australia); Stanimirovic, S. [Department of Astronomy, University of Wisconsin, Madison, WI 53706 (United States); Haverkorn, M. [Astronomy Department, University of California, Berkeley, CA 94720 (United States); McClure-Griffiths, N. M. [Australia Telescope National Facility, CSIRO, Epping, NSW 1710 (Australia); Staveley-Smith, L. [School of Physics, University of Western Australia, Crawley, WA 6009 (Australia); Dickey, J. M., E-mail: samao@cfa.harvard.edu [Physics Department, University of Tasmania, Hobart, TAS 7001 (Australia)

2008-12-01

24

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

SciTech Connect

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

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

2014-02-28

25

Fiber optic magnetic field sensor based on domain wall motion in garnet film waveguides  

NASA Astrophysics Data System (ADS)

A novel fiber optic magnetometer based on the Faraday effect in a magnetic garnet thin-film ridged waveguide is described. The single-mode film has planar magnetization aligned parallel and antiparallel to the light propagation direction by a gradient bias field, and a single domain wall crosses the light path. The motion of this wall in response to an applied field changes the Faraday rotation in the film. Operation of this field or current sensor in both the transmission mode and the single fiber reflection mode has been demonstrated. Optical output varying linearly with ac or dc fields up to 15 Oe, with a minimum detectable field of 0.05 Oe, has been observed. This domain wall motion scheme in a zero birefringence waveguide can also be used in a polarization controller.

Wolfe, R.; Lieberman, R. A.

1991-04-01

26

Magnetic field-induced excitation and optical detection of mechanical modes of microspheres  

E-print Network

Magnetic field-induced excitation and optical detection of mechanical modes of microspheres T We propose a method to excite and detect the mechanical modes of dielectric microspheres In this paper, we propose a method to excite and detect the mechanical modes of dielectric microspheres using

�tügen, Volkan

27

Generation of uniform synthetic magnetic fields by split driving of an optical lattice  

NASA Astrophysics Data System (ADS)

We describe a method to generate a synthetic gauge potential for ultracold atoms held in an optical lattice. Our approach uses a time-periodic driving potential based on quickly alternating two Hamiltonians to engineer the appropriate Aharonov-Bohm phases, and permits the simulation of a uniform tunable magnetic field. We explicitly demonstrate that our split-driving scheme reproduces the behavior of a charged quantum particle in a magnetic field over the complete range of field strengths, and obtain the Hofstadter butterfly band structure for the Floquet quasienergies.

Creffield, C. E.; Sols, F.

2014-08-01

28

Magnetic Fields  

E-print Network

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

Schöller, Markus

2015-01-01

29

An optical fibre system design enabling simultaneous point measurement of magnetic field strength and temperature using low-birefringence FBGs  

Microsoft Academic Search

Fibre measurement of key parameters in nuclear fusion reactor environments, such as the magnetic field strength and temperature, is highly desirable due to the convenience and robustness of optical fibre sensors when compared with conventional electrical sensors. Presently, fibre point sensors for magnetic field are based predominantly on magnetostriction which limits their applicability to this environment. We present an optical

P. Orr; P. Niewczas

2010-01-01

30

Nonlinear magneto-optical rotation with modulated light in tilted magnetic fields  

SciTech Connect

Larmor precession of laser-polarized atoms contained in antirelaxation-coated cells, detected via nonlinear magneto-optical rotation (NMOR), is a promising technique for a new generation of ultrasensitive atomic magnetometers. For magnetic fields directed along the light propagation direction, resonances in NMOR appear when linearly polarized light is frequency or amplitude modulated at twice the Larmor frequency. Because the frequency of these resonances depends on the magnitude but not the direction of the field, they are useful for scalar magnetometry. Additional NMOR resonances at the Larmor frequency appear when the magnetic field is tilted away from the light propagation direction in the plane defined by the light propagation and polarization vectors. These resonances, studied both experimentally and with a density matrix calculation in the present work, offer a convenient method of achieving additional information about a direction of the magnetic field.

Pustelny, S.; Gawlik, W.; Rochester, S. M.; Kimball, D. F. Jackson; Yashchuk, V. V.; Budker, D. [Centrum Badan Magnetooptycznych, M. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krakow (Poland); Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300 (United States); Department of Physics, California State University--East Bay, 25800 Carlos Bee Boulevard, Hayward, California 94542 (United States); Advanced Light Source Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300, USA and Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2006-12-15

31

Measurement of Asymmetric Optical Pumping of Ions Accelerating in a Magnetic-field Gradient  

SciTech Connect

We report observations of asymmetric optical pumping of argon ions accelerating in a magnetic field gradient. The signature is a difference in the laser-induced-fluorescence (LIF) emission amplitude from a pair of Zeeman-split states. A model that reproduces the dependence of the asymmetry on magnetic-field and ion-velocity gradients is described. With the model, the fluorescence intensity ratio provides a new method of measuring ion collisionality. This phenomenon has implications for interpreting stellar plasma spectroscopy data which often exhibit unequal Zeeman state intensities.

Xuan Sun; Earl Scime; Mahmood Miah; Samuel Cohen; Frederick Skiff

2004-10-28

32

Mirror magneto-optical trap exploiting hexapole-compensated magnetic field  

SciTech Connect

A mirror magneto-optical trap (MOT) that exploits a hexapole-compensated magnetic field was developed and used in the experimental surface trapping of neutral atoms. A pair of subsidiary wires, which was placed near the main current-carrying wire, was designed to improve the uniformity of the quadrupole magnetic field and thus increased the effective capture volume of our mirror-MOT. In the experiment, the number of {sup 87}Rb atoms captured with our mirror-MOT was approximately twice that captured with a conventional mirror-MOT.

Hyodo, Masaharu [Kobe Advanced ICT Research Center, NICT, 588-2 Iwaoka, Nishi-ku, Kobe 651-2492 (Japan); Nakayama, Kazuyuki [CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Watanabe, Masayoshi [Department of Electronic Engineering, University of Electro-Communications, Chofu 182-8585 (Japan); Ohmukai, Ryuzo [Department of Physics, Saitama University, Saitama 338-8570 (Japan)

2007-07-15

33

Particle size and magnetic field-induced optical properties of magnetic fluid nanoparticles.  

PubMed

Magnetite nanoparticles with diameters of 7, 9, and 12 nm have been prepared by a chemical coprecipitation method. The transmission of light through magnetic fluid containing these nanoparticles has been investigated as a function of film thickness with wavelength between 400 and 750 nm, and applied magnetic fields up to 275 Oe. The transmission threshold shifts to the lower wavelength side with decreasing magnetic fluid film thickness as well as the particle size. For a given film thickness, the transmittance increases with increasing magnetic field for films with a particle size of 7 and 9 nm, but decreases in the 12-nm film. This is attributed to the competition between the van der Waals and dipole-dipole interaction. PMID:16241436

Rao, G Narsinga; Yao, Y D; Chen, Y L; Wu, K T; Chen, J W

2005-09-01

34

Ultra-sensitive broad-dynamic range optical magnetometer with instance response to magnetic field changes  

E-print Network

We investigate one of the most sensitive devices for measuring magnetic fields, the, so-called, AMOR magnetometer. The device exploits a specific nonlinear optical phenomenon (amplitude-modulated nonlinear magneto-optical rotation) for ultra-precise magnetic field detection. It allows measuring the field with a sensitivity of 10^-14 T/Hz^-1/2 within a dynamic range of 10-4 T. Such high sensitivity and the dynamic range covering the Earth magnetic field are desired in context of many practical application of the device. By elaborating the electronic model of the magnetometer we study its different characteristics in various arrangements. It allows us to optimize the device regarding different requirements, e.g., technical simplicity, data processing, etc. It is shown that the device may be automated operating it in the self-oscillation mode. Particularly, we show that the magnetometer instantly responses to the magnetic field change. Our numerical analyses are confirmed with experimental results obtained in on...

Wlodarczyk, Przemyslaw; Zachorowski, Jerzy; Lipinski, Marcin

2012-01-01

35

Three-sublattice analyses on magnetic and magneto-optical properties of scandium substituted ytterbium iron garnet in high magnetic fields  

NASA Astrophysics Data System (ADS)

A three-sublattice model is applied to study the magnetic properties of scandium substituted ytterbium iron garnet (Sc-YbIG). The magnetic moments in three magnetic sublattices (a, c and d sites) in Sc-YbIG are analyzed, where the diamagnetic Sc3+ ions substitute for octahedral Fe3+ ions. The parameters ?i (i=a, c, d), associated with the exchange field and the magnetic susceptibility, are introduced. Here, ?i show obvious high magnetic field-dependent and temperature-dependent properties. Based on the thought of three magnetic sublattices, the magneto-optical properties in Sc-YbIG, as magnetic field applied along [1 0 0], [1 1 0] and [1 1 1] directions, at low temperatures are studied by an improved magneto-optical four-level model, where the physical mechanism of magneto-optical anisotropy is explored in low magnetic fields. Our theory is in good agreement with the experimental results.

Wang, Wei; Zhao, Xiruo; Lahoubi, Mahieddine; Ping Liu, J.

2015-01-01

36

Optical studies of 2DEGs in ZnSe quantum wells in high magnetic fields.  

SciTech Connect

Optical properties of a two-dimensional electron gas in ZnSe/(Zn,Be,Mg)Se quantum well structures have been examined by means of photoluminescence and reflectivity techniques in external magnetic fields up to 50 T. For these structures the Fermi energy of the two-dimensional electron gas is falling in the range between the trion binding energy and the exciton binding energy, which keeps the dominating role of Coulombic interaction between electrons and photoexcited holes. Characteristic peculiarities of optical spectra are discussed.

Ossau, Wolfgang J.; Astakhov, G. V.; Yakovlev, D. R.; Crooker, S. A. (Scott A.); Waag, A.

2002-01-01

37

Optical conductivity of topological insulator thin films in a quantizing magnetic field  

NASA Astrophysics Data System (ADS)

We determine the optical response of topological insulator thin films in the presence of a quantizing, external magnetic field. We explicitly take into account hybridization between the states of top and bottom surface. The interplay between hybridization and Zeeman energies gives rise to topological and normal insulator phases and phase transitions between them. The optical response in the two phases and at the phase transition point is investigated. We show that the difference in magneto-optical response can be used to distinguish the topological phase from the normal phase of the system. Further, the optical response also allows us to determine the gap generated by hybridization between top and bottom surface states of topological insulator thin films.

Ullah, A.; Sabeeh, K.

2014-12-01

38

Magnetic Fields  

NSDL National Science Digital Library

This page and its annex describes, in trivial terms, the physics of magnetic fields and the history of its discovery. Included is the work of Halley, Oersted, Ampere and Maxwell. It also describes a way of demonstrating it in the classroom, using a vu-graph projector. Later sections #5, #5a and #6 extend this to magnetic field lines and electromagnetism.

Stern, David

2005-01-04

39

Magnetic Field Measurements in Wire-Array Z-Pinches using Magneto-Optically Active Waveguides  

SciTech Connect

Understanding the magnetic field topology in wire-array Z-pinches as a function of time is of great significance to understanding these high-energy density plasmas especially for their ultimate application to stockpile stewardship and inertial confinement fusion. We are developing techniques to measure magnetic fields as a function of space and time using Faraday rotation of a single longitudinal mode (SLM) laser through a magneto-optically active bulk waveguide (multicomponent terbium borate glass) placed adjacent to, or within, the wire array in 1 MA experiments. We have measured fields >10 T with 100 ns rise times outside of a wire-array for the entire duration of the current pulse and as much as {approx}2 T inside a wire-array for {approx}40 ns from the start of current. This is the first time that such rapidly varying and large fields have been measured using these materials. In a dense Z-pinch, these sensing devices may not survive for long but may provide the magnetic field at the position of the sensor that can be used to corroborate magnetic probes, with which we compare our results.

Syed, Wasif [School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853 (United States); Laboratory of Plasma Studies, Cornell University, Ithaca, NY 14853 (United States); Blesener, Isaac; Hammer, David A. [School of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853 (United States); Laboratory of Plasma Studies, Cornell University, Ithaca, NY 14853 (United States); Lipson, Michal [School of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853 (United States)

2009-01-21

40

Simultaneous effects of pressure and magnetic field on intersubband optical transitions in Pöschl–Teller quantum well  

Microsoft Academic Search

The simultaneous effects of hydrostatic pressure and magnetic field applied along the quantization direction on intersubband optical transitions in Pöschl–Teller quantum well are investigated. The expression of the absorption coefficient and some selection rules are obtained. The dependences of the absorption coefficient on magnetic field induction and incident photon energy for different values of pressure and parameters of quantum well

Alireza Hakimyfard; M. G. Barseghyan; A. A. Kirakosyan

2009-01-01

41

Weak magnetic field annealing effect on magneto-optical and magnetostatic properties of Co-based amorphous ribbons  

Microsoft Academic Search

We have investigated modifications of magneto-optical properties in the weak-field annealed Co-based amorphous ribbons. It is found that spectral and magnetic field dependences of the transverse Kerr effect significantly change with the time of annealing in air and the magnetic field magnitude. The analysis reveals the existence of two anisotropies, one in low fields up to 300Oe and another in

E. A Ga?shina; N. S Perov; M. Yu Kochneva; P. M Sheverdyaeva; C. G Kim; C. O Kim

2003-01-01

42

Sensitive, Weak Magnetic Field Sensor Based on Cobalt Nanoparticles Deposited in Micro-Tunnels of PM-PCF Optical Fiber  

NASA Astrophysics Data System (ADS)

In this paper, we report on development of an optical fiber based magnetic field sensor. Cobalt magnetic nanoparticles of the size ?20 nm have been deposited into the air holes of the polarization maintaining photonic crystal fiber (PM-PCF), using a physical approach to yield a magnetic field sensor. The effective refractive index of the PM-PCF is found to be highly magnetic field dependent due to presence of the cobalt nanoparticles into the air holes of the PCF. The sensitivity of the developed sensor is experimentally determined to be 240 pm/mT for field range from 45 to 86 mT.

Gupta, Swati; Nalawade, Sandipan M.; Hatamie, Shadie; Thakur, H. V.; Kale, S. N.

2011-10-01

43

Conductivity of strongly correlated bosons in optical lattices in an Abelian synthetic magnetic field  

NASA Astrophysics Data System (ADS)

Topological phase engineering of neutral bosons loaded in an optical lattice opens a new window for manipulating of transport phenomena in such systems. Exploiting the Bose-Hubbard model and using the magnetic Kubo formula proposed in this paper we show that the optical conductivity abruptly changes for different flux densities in the Mott phase. Especially, when the frequency of the applied field corresponds to the on-site boson interaction energy, we observe insulator or metallic behavior for a given Hofstadter spectrum. We also prove that for different synthetic magnetic-field configurations the critical conductivity at the tip of the lobe is nonuniversal and depends on the energy minima of the spectrum. In the case of 1/2 and 1/3 flux per plaquette, our results are in good agreement with those of the previous Monte Carlo study. Moreover, we show that for half magnetic flux through the cell the critical conductivity suddenly changes in the presence of a superlattice potential with uniaxial periodicity.

Sajna, A. S.; Polak, T. P.; Micnas, R.

2014-02-01

44

Optical Magnetic Mirrors without Metals  

E-print Network

The reflection of an optical wave from a metal, arising from strong interactions between the optical electric field and the free carriers of the metal, is accompanied by a phase reversal of the reflected electric field. A far less common route to achieve high reflectivity exploits strong interactions between the material and the optical magnetic field to produce a magnetic mirror which does not reverse the phase of the reflected electric field. At optical frequencies, the magnetic properties required for strong interaction can only be achieved through the use of artificially tailored materials. Here we experimentally demonstrate, for the first time, the magnetic mirror behavior of a low-loss, all-dielectric metasurface at infrared optical frequencies through direct measurements of the phase and amplitude of the reflected optical wave. The enhanced absorption and emission of transverse electric dipoles placed very close to magnetic mirrors can lead to exciting new advances in sensors, photodetectors, and light...

Liu, Sheng; Mahony, Thomas S; Jun, Young Chul; Campione, Salvatore; Ginn, James; Bender, Daniel A; Wendt, Joel R; Ihlefeld, Jon F; Clem, Paul G; Wright, Jeremy B; Brener, Igal

2014-01-01

45

Solar coronal magnetic field topology inferred from high resolution optical and x-ray movies  

SciTech Connect

The authors are using high resolution digital movies of solar active regions in optical and X-ray wavelengths to study solar flares and other transients. The optical movies were collected at the Swedish Solar Observatory on La Palma using the Lockheed tunable filtergraph system, in May-July, 1992. They include longitudinal and transverse magnetograms, H-alpha Doppler and intensity images at many wavelengths, Ca K, Na D, and white light images. Simultaneous X-ray images from Yohkoh are available much of the time. Several ways to establish the connectivity of some coronal magnetic field lines are being explored. Some of the clues available are: magnetic footpoint polarities and transverse field direction; H-alpha fibrils and loops seen in several wavelengths; proper motion and Dopper shifts of blobs moving along field lines; footprint brightening in micro-flares; spreading of flare ribbons during gradual phases of flares; X-ray morphology and correlations with H-alpha; and draining of flare loops. Examples of each of these will be shown on video.

Tarbell, T.; Frank, Z.; Hurlburt, N.; Morrison, M.; Shine, R.; Title, A.; Acton, L.

1993-01-01

46

Magneto-optic fiber Bragg gratings with application to high-resolution magnetic field sensors  

Microsoft Academic Search

As a new class of fiber Bragg gratings, magneto-optic fiber Bragg gratings (MFBG) based on magneto-optic materials have a lot of potential applications for sensing and optical signal processing. The transmission and reflection spectra of guided optical waves in the MFBG are investigated. According to the sensitivity of MFBG spectral lines to the magneto-optic coupling intensity varying with applied magnetic

Bao-Jian Wu; Kun Qiu; Ying Yang

2008-01-01

47

Perforated semishells: far-field directional control and optical frequency magnetic response.  

PubMed

Reduced-symmetry plasmonic nanostructures can be designed to support a range of novel optical phenomena, such as nanoscale control of the far-field scattering profile and magnetic resonances at optical frequencies. A family of reduced-symmetry nanostructures--plasmonic semishells with specifically shaped and oriented perforations introduced into the metallic shell layer--can be tailored to control these effects. Unlike core-shell nanoparticles, perforated semishells can be fabricated using a combination of clean-room techniques. For a semishell with a single spherical perforation positioned on its symmetry axis, we examine how the resonant modes of the structure depend on hole size and shape. Placing the perforation off the symmetry axis allows a family of higher-order modes to be excited in the nanostructure, along with complex near-field charge distributions for the various resonant modes. This reduced-symmetry case provides a platform for optical studies, which agree quite well with theoretical analysis. Our study also examines two important variations of this structure: a semishell with multiple perforations in the shell layer, and a semishell with a wedge-like "slice" in the shell layer. A semishell with a wedge-like perforation can be thought of as a three-dimensional analogue of a split-ring resonator (SRR), an important nanoscale component in metamaterial design. Here we show that the dimensions of the wedge-like perforation, which control the effective optical frequency resistance, inductance, and capacitance of this structure, determine the frequency of the magnetic mode. PMID:20429530

Mirin, Nikolay A; Ali, Tamer A; Nordlander, Peter; Halas, Naomi J

2010-05-25

48

Magnetic Field Safety Magnetic Field Safety  

E-print Network

Magnetic Field Safety Training #12;Magnetic Field Safety Strong Magnetic Fields exist around energized magnets. High magnetic fields alone are a recognized hazard only for personnel with certain medical conditions such as pacemakers, magnetic implants, or embedded shrapnel. In addition, high magnetic

McQuade, D. Tyler

49

Optical Response of Magnetic-Fluorescent Microspheres Used for Force Spectroscopy in the Evanescent Field  

PubMed Central

Force spectroscopy based on magnetic tweezers is a powerful technique to manipulate single biomolecules and study their interactions. The resolution in a magnetic probe displacement, however, needs to be commensurate with molecular sizes. To achieve the desirable sensitivity in tracking displacements of the magnetic probe, some recent approaches have combined magnetic tweezers with total internal reflection fluorescence microscopy. In this situation, a typical force probe is a polymer microsphere containing two types of optically active components – a pure absorber (magnetic nanoparticles for providing the pulling force) and a luminophore (semiconducting nanoparticles or organic dyes for fluorescent imaging). In order to fully assess the system’s capability for tracking the position of the force probe with sub-nanometer accuracy, we developed a body-of-revolution formulation of the method of auxiliary sources (BOR-MAS) to simulate absorption, scattering, and fluorescence of microscopic spheres in an evanescent electromagnetic field. The theoretical formulation uses the axial symmetry of the system to reduce the dimensionality of the modeling problem and produces excellent agreement with the reported experimental data on forward scattering intensity. Using the BOR-MAS numerical model, we investigated the probe detection sensitivity for a high numerical aperture objective. The analysis of both backscattering and fluorescence observation modes shows that the total intensity of the bead image decays exponentially with the distance from the surface (or the length of a biomolecule). Our investigations demonstrate that the decay lengths of observable optical power are smaller than the penetration depth of the unperturbed excitation evanescent wave. In addition, our numerical modeling results illustrate that the expected sensitivity for the decay length changes with the incident angle, tracking the theoretical penetration depth for a two-media model, and is sensitive to the bead size. The BOR-MAS methodology developed in this work for near field modeling of bead tracking experiments fully describes the fundamental photonic response of microscopic BOR probes at the sub-wavelength level and can be used for future improvements in the design of these probes or in the setup of bead tracking experiments. PMID:20486724

Bijamov, Alex; Shubitidze, Fridon; Oliver, Piercen M.; Vezenov, Dmitri V.

2010-01-01

50

Distributed magnetic field sensor based on magnetostriction using Rayleigh backscattering spectra shift in optical frequency-domain reflectometry  

NASA Astrophysics Data System (ADS)

We present a distributed optical-fiber magnetic-field sensor based on magnetostriction using the Rayleigh backscattering spectra (RBS) shift in optical frequency-domain reflectometry (OFDR). The magnetostrictive Fe–Co–V alloy thin films are attached to a 51-m single-mode fiber (SMF). We detect the strain coupled to the SMF caused by the magnetic field using the RBS shift. We measure the range of the magnetic field to be from 0 to 143.3 mT. The minimum measurable magnetic intensity variation is 12.9 mT when the spatial resolution is 4 cm, and it can be improved to 5.3 mT by deteriorating the spatial resolution to 14 cm.

Du, Yang; Liu, Tiegen; Ding, Zhenyang; Liu, Kun; Feng, Bowen; Jiang, Junfeng

2015-01-01

51

Molecule formation in optical lattice wells by resonantly modulated magnetic fields  

SciTech Connect

We present a theoretical model for formation of molecules in an optical lattice well where a resonant coupling of atomic and molecular states is provided by small oscillations of a magnetic field in the vicinity of a Feshbach resonance. As opposed to an adiabatic sweep over the full resonance, this provides a coherent coupling with a frequency that can be tuned to meet resonance conditions in the system. The effective Rabi frequencies for this coupling are calculated and simulations show perfect Rabi oscillations. Robust production of molecules with an adiabatic sweep of the modulation frequency is demonstrated. For very large oscillation amplitudes, the Rabi oscillations are distorted but still effective and fast association is possible.

Bertelsen, Jesper Fevre; Moelmer, Klaus [Danish National Research Foundation Center for Quantum Optics, Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark)

2006-01-15

52

Magnetic field effects on mitochondrion-activity-related optical properties in slime mold and bone forming cells.  

PubMed

In the present study, a cellular level response of Cyto-aa3 oxidation was investigated in real time under both time-varying and strong static magnetic fields of 5 T. Two kinds of cells, a slime mold, Physarum polycephalum, and bone forming cells, MC-3T3-E1, were used for the experiments. The oxidation level of the Cyto-aa3 was calculated by optical absorptions at 690 nm, 780 nm and 830 nm. The sample, fiber-optics and an additional optical fiber for light stimulation were set in a solenoidal coil or the bore of a 5-T superconducting magnet. The solenoidal coil for time-varying magnetic fields produced sinusoidal magnetic fields of 6 mT. The slime mold showed a periodic change in Cyto-aa3 oxidation, and the oxidation-reduction cycle of Cyto-aa3 was apparently changed when visible-light irradiated the slime mold. Similarly to the case with light, time-varying magnetic stimulations changed the oxidation-reduction cycle during and after the stimulation for 10 minutes. The same phenomena were observed in the MC-3T3-E1 cell assembly, although their cycle rhythm was comparatively random. Finally, magnetic field exposure of up to 5 T exhibited a distinct suppression of Cyto-aa3 oscillation in the bone forming cells. Exposure up to 5 T was repeated five times, and the change in Cyto-aa3 oxidation reproducibly occurred. PMID:24109969

Mizukawa, Yuri; Iwasaka, Masakazu

2013-01-01

53

Spin-orbit effects on the nonlinear optical properties of a quantum dot in simultaneous electric and magnetic fields  

NASA Astrophysics Data System (ADS)

We report on the nonlinear optical properties of a quantum dot including the Rashba spin-orbit interaction (RSOI) with external electric and magnetic fields. The effect of dot size is considered. We do not make any assumptions about the strength of the confinement. We use the numerical diagonalization of the Hamiltonian to determine the electronic structure. The confining potential is taken to be of the Woods-Saxon type. We find the effect of RSOI on nonlinear optical coefficients.

Aytekin, O.; Turgut, S.; Tomak, M.

2014-11-01

54

a Scanning Near-Field Optical Microscope with Magneto-Optic Kerr Effect Contrast for the Imaging of Magnetic Domains with 200 Angstrom Resolution  

NASA Astrophysics Data System (ADS)

We describe the development of a scanning near -field optical microscope for magnetic domain imaging in thin-film materials. The near-field probe is a 20-40 nm Ag particle which is optically excited near the surface plasmon resonance frequency. The plasmon resonance in individual Ag particles is characterized by optical spectroscopy for light scattered from single Ag particles. The existence of a near-field form of the magneto-optic Kerr effect is confirmed. In the final form of the microscope, the Ag particle is mounted on a hemispherical glass substrate and brought to within near-field proximity of a flat sample surface. The separation of the probe and sample is regulated by a Newton ring interferometer in closed loop feedback control of a piezoelectric translator. Separation stability can be kept to less than one nanometer. Near-field magneto -optic interactions are measured with a shot-noise limited modulating ellipsometer. We measured the dependence of the near-field Kerr signal on the separation of the probe and sample for longitudinal magnetization, and suggest a potential resolution of 20-40 nm. Two-dimensional images are presented of thermo-magnetically recorded domains in a Co/Pt multilayer material, with less than 100 nm resolution. Domains with a 0.5 micron diameter and one micron spacing are clearly resolved. We discuss future improvements of the instrument and propose an ultimate resolution of 140 A.

Silva, Thomas Joseph

55

Small optical magnetic-field sensor that uses rare-Earth iron garnet films based on the faraday effect.  

PubMed

Highly accurate optical magnetic-field probe sensors that use iron garnet films have been developed. New probe-type sensors were designed with a confocal optical system. A new garnet composition, Bi(0.98)Gd(0.92)La(0.03)Y(1.07)Fe(4.72)Ga(0.28)O(12), was found that shows high temperature stability for a sensitivity of less than 2.0% from -20 to +80 degrees C. The linearity error of the sensor output was within 1.0% for alternating magnetic fields from 0.3 to 42 mT. An optical current transformer that uses the proposed sensor has an ac linearity of 1.0% for input current up to nearly 300 A. The sensor realized high performance in actual use. PMID:18319762

Itoh, N; Minemoto, H; Ishiko, D; Ishizuka, S

1999-04-01

56

Magnetic field induced effects in optical second harmonic generation from iron-garnet films  

NASA Astrophysics Data System (ADS)

The magnetic field induced effects in the second harmonic generation (SHG) from epitaxially grown iron-garnet films have been studied. The magnetic field induced variations in the azimuthal angular dependences and the polarization diagrams of the SHG intensity are shown to be due to the linear Faraday effect. Enhancements in the SHG intensity were detected for (Bi,Gd,Fu) 3(Fe,Ga) 5O 12 iron-garnet films grown on (Gd,Ca) 3(Mg,Zr,Ga) 5O 12 single-crystal substrates with various orientations. This dependence of the SHG intensity on the magnetic field may be caused by magnetostriction effects.

Aktsipetrov, O. A.; Aleshkevich, V. A.; Melnikov, A. V.; Misuryaev, T. V.; Murzina, T. V.; Randoshkin, V. V.

1997-01-01

57

Detecting Exoplanetary Magnetic Fields  

NASA Astrophysics Data System (ADS)

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.

Llama, Joe

2015-01-01

58

Influence of magnetic-field inhomogeneity on nonlinear magneto-optical resonances  

SciTech Connect

In this work, a sensitivity of the rate of relaxation of ground-state atomic coherences to magnetic-field inhomogeneities is studied. Such coherences give rise to many interesting phenomena in light-atom interactions, and their lifetimes are a limiting factor for achieving better sensitivity, resolution, or contrast in many applications. For atoms contained in a vapor cell, some of the coherence-relaxation mechanisms are related to magnetic-field inhomogeneities. We present a simple model describing relaxation due to such inhomogeneities in a buffer-gas-free antirelaxation-coated cell. A relation is given between relaxation rate and magnetic-field inhomogeneities including the dependence on cell size and atomic species. Experimental results, which confirm predictions of the model, are presented. Different regimes, in which the relaxation rate is equally sensitive to the gradients in any direction and in which it is insensitive to gradients transverse to the bias magnetic field, are predicted and demonstrated experimentally.

Pustelny, S.; Jackson Kimball, D. F.; Rochester, S. M.; Yashchuk, V. V.; Budker, D. [Centrum Badan Magnetooptycznych, M. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krakow (Poland); Department of Physics, California State University-East Bay, 25800 Carlos Bee Boulevard, Hayward, California 94542 (United States); Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300 (United States); Advanced Light Source Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300 (United States) and Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2006-12-15

59

Optical soliton in dielectric fibers and self-organization of turbulence in plasmas in magnetic fields  

PubMed Central

One important discovery in the twentieth century physics is the natural formation of a coherent or a well-ordered structure in continuous media, in contrary to degradation of the state as predicted earlier from the second law of thermodynamics. Here nonlinearity plays the essential role in its process. The discovery of soliton, a localized stable wave in a nonlinear and dispersive medium and the self-organization of fluid turbulence are of the major examples. A soliton is formed primarily in one-dimensional medium where the dispersion and nonlinearity play the essential role. Here the temporal evolution can be described by an infinite dimensional Hamiltonian system that is integrable. While a self-organization appears in an infinite dimensional non-Hamiltonian (or dissipative) system where more than two conservative quantities exist in the limit of no dissipation. In this manuscript, by showing examples of the optical soliton in dielectric fibers and self-organization of turbulence in a toroidal plasma in a magnetic field, we demonstrate these interesting discoveries. The manuscript is intended to describe these discoveries more on philosophical basis with some sacrifice on mathematical details so that the idea is conveyed to those in the wide area of sciences. PMID:19145067

Hasegawa, Akira

2009-01-01

60

Design of a silicon-based plasmonic optical sensor for magnetic field monitoring in the infrared  

NASA Astrophysics Data System (ADS)

Surface plasmon resonance (SPR) sensor chip is proposed for magnetic field monitoring in the infrared wavelength region. The structure is based on silicon substrate and gold as SPR-active metal used with an appropriate magnetic fluid film. The angular interrogation method has been used to study the sensor's performance in terms of large shift and small width of the SPR curve for a wide range of magnetic field between 30 and 220 Oe. The effect of field incidence angle is also studied on the proposed sensor's performance, and it is observed that the field should be incident as parallel to the magnetic fluid surface as possible. Any possibility of oxidation problem to the proposed SPR sensor is addressed by using a stable buffer layer. All the performance parameters were found to be significantly large for the above field incidence condition. The proposed sensor is able to achieve a resolution of the order as high as 0.18 Oe for magnetic field detection.

Sharma, Anuj K.; Nagao, Tadaaki

2014-10-01

61

Errors of solar magnetographs in large-scale magnetic field observations, as caused by field-of-view effects of electro-optical polarization analyzers.  

NASA Astrophysics Data System (ADS)

The authors examine some aspects of the problem related to the production of "spurious" (not associated with the magnetic field) signals of solar magnetographs (the zero-level problem), caused by adjustment errors of the components of electro-optical polarization analyzers and/or by aperture nonuniformities of brightness. It is pointed out that these field-of-view effects are of important significance for observations of large-scale solar magnetic fields. Numerical estimates are made of the errors, as applied mainly to the STOP telescope at the Sayan Observatory.

Demidov, M. L.; Zhigalov, V. V.

62

Magnetic field effects on spectrally resolved lifetime of on-line oxygen monitoring using magneto-optic probes  

NASA Astrophysics Data System (ADS)

Multimodal agents that serve as both probes for contrast and light-activated effectors of cellular processes in diseased tissue were developed. These agents were introduced into multicellular tumor spheroids (3D tissue models) and in the chorioallantoic membrane (CAM) of a chicken embryo. The luminescence decay was examined using a novel technique involving a spectrally-resolved fluorescence lifetime apparatus integrated with a weak electromagnet. A spectrallyresolved lifetime setup was used to identify magneto-optic species sensitive to magnetic field effects and distinguish from background emissions. We demonstrate that the applied magnetic fields can alter reaction rates and product distribution of some dyes detected by time- and spectrally-resolved luminescence changes. We will discuss the use of exogenous magneto-optical probes taken up in tumors to both induce phototoxicity, a process that is governed by complex and dynamically evolving mechanisms involving reactive oxygen species, and monitor treatment progress. The magnetic field enhancement, measured over a range of weak fields (0-300 mT) is correlated to oxygenation and may be used to monitor dynamic changes occurring due to oxygen consumption over the course of photodynamic therapy. Such online measurements provide the possibility to derive real-time information about response to treatment via monitoring magnetic field enhancement/suppression of the time-resolved, spectrally-resolved luminescence of the probe at the site of the treatment directly. Magnetic perturbation of lifetime can serve as a status reporter, providing optical feedback of oxygen-mediated treatments in situ and allowing for real-time adjustment of a phototherapy treatment plan.

Mermut, O.; Gallant, P.; Le Bouch, N.; Leclair, S.; Noiseux, I.; Vernon, M.; Morin, J.-F.; Diamond, K.; Patterson, M. S.; Samkoe, K.; Pogue, B.

2009-02-01

63

Fiber-optic in-line magnetic field sensor based on the magnetic fluid and multimode interference effects  

NASA Astrophysics Data System (ADS)

A compact magnetic field sensor has been proposed based on multimode interference effects. It consists of typical multimode interferometer (MMI) immersed into the magnetic fluid (MF) which is formed by a section of square no-core fiber (NCF) spliced between two single-mode fibers. The transmission spectral characteristics of this MMI have been analyzed, and the spectral magnetic response of the proposed sensor has been investigated by immersing the NCF into the MF environment. The transmission response of the interference maxima exhibits a sensitivity of -0.01939 dB/Oe in the relatively linear range. Due to its low cost and compactness, this sensor would find potential applications in the measurement of magnetic field.

Lin, Wei; Miao, Yinping; Zhang, Hao; Liu, Bo; Liu, Yange; Song, Binbin

2013-10-01

64

Fractal diabolo antenna for enhancing and confining the optical magnetic field  

SciTech Connect

We introduce fractal geometry to diabolo nanoantenna for higher magnetic field intensity enhancement, i.e. the Sierpi?ski triangle diabolo antenna (STDA). Numerical results show that higher iteration of the STDA is responsible for the higher enhancement and the red shift of the resonant wavelength. Further investigation demonstrates the enhancement can be improved by increasing the length of the antenna or its central strip. By designing diabolo antennas with fractal geometry, improving the magnetic field intensity enhancement and varying the resonance conditions can be achieved while keeping the constant antenna dimensions.

Yang, Y.; Dai, H. T., E-mail: htdai@tju.edu.cn [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, School of Science, Tianjin University, Tianjin 300072 (China); Sun, X. W., E-mail: xwsun@sust.edu.cn [South University of Science and Technology, 1088 Xue-Yuan Road, Shenzhen, Guangdong, 518055 (China)

2014-01-15

65

Development of an alternating magnetic-field-assisted finishing process for microelectromechanical systems micropore x-ray optics  

SciTech Connect

X-ray astronomy research is often limited by the size, weight, complexity, and cost of functioning x-ray optics. Micropore optics promises an economical alternative to traditional (e.g., glass or foil) x-ray optics; however, many manufacturing difficulties prevent micropore optics from being a viable solution. Ezoe et al. introduced microelectromechanical systems (MEMS) micropore optics having curvilinear micropores in 2008. Made by either deep reactive ion etching or x-ray lithography, electroforming, and molding (LIGA), MEMS micropore optics suffer from high micropore sidewall roughness (10-30nmrms) which, by current standards, cannot be improved. In this research, a new alternating magnetic-field-assisted finishing process was developed using a mixture of ferrofluid and microscale abrasive slurry. A machine was built, and a set of working process parameters including alternating frequency, abrasive size, and polishing time was selected. A polishing experiment on a LIGA-fabricated MEMS micropore optic was performed, and a change in micropore sidewall roughness of 9.3{+-}2.5nmrms to 5.7{+-}0.7nmrms was measured. An improvement in x-ray reflectance was also seen. This research shows the feasibility and confirms the effects of this new polishing process on MEMS micropore optics.

Riveros, Raul E.; Yamaguchi, Hitomi; Mitsuishi, Ikuyuki; Takagi, Utako; Ezoe, Yuichiro; Kato, Fumiki; Sugiyama, Susumu; Yamasaki, Noriko; Mitsuda, Kazuhisa

2010-06-20

66

Field-dependent magneto-optical Kerr effect spectroscopy applied to the magnetic component diagnosis of a rubrene/Ni system.  

PubMed

Polar magneto-optical Kerr effect (MOKE) spectroscopy in the energy range from 1.75 eV to 5 eV at different magnetic field strength was applied to study Ni nanostructures formed on rubrene nanoislands. The magnetic hysteresis curves measured by MOKE change the shape depending on the photon energy and therefore deviate from those measured by superconducting quantum interference device (SQUID) magnetometry. Similar optical effects were previously observed in inorganic heterostructures. Our observations show that it correlates to the change in lineshape of the MOKE rotation and ellipticity spectra as a function of magnetic field strength. We show that this spectral dependence on magnetic field can be exploited to separate the contributions of two magnetic components to the magneto-optical spectra and hysteresis. The proposed model does not require the a priori knowledge of the (magneto-)optical constants of the heterostructure and its components. PMID:25089464

Li, Wen; Fronk, Michael; Albrecht, Manfred; Franke, Mechthild; Zahn, Dietrich R T; Salvan, Georgeta

2014-07-28

67

Magneto-optical absorption in semiconducting spherical quantum dots: Influence of the dot-size, confining potential, and magnetic field  

NASA Astrophysics Data System (ADS)

Semiconducting quantum dots - more fancifully dubbed artificial atoms - are quasi-zero dimensional, tiny, man-made systems with charge carriers completely confined in all three dimensions. The scientific quest behind the synthesis of quantum dots is to create and control future electronic and optical nanostructures engineered through tailoring size, shape, and composition. The complete confinement - or the lack of any degree of freedom for the electrons (and/or holes) - in quantum dots limits the exploration of spatially localized elementary excitations such as plasmons to direct rather than reciprocal space. Here we embark on a thorough investigation of the magneto-optical absorption in semiconducting spherical quantum dots characterized by a confining harmonic potential and an applied magnetic field in the symmetric gauge. This is done within the framework of Bohm-Pines' random-phase approximation that enables us to derive and discuss the full Dyson equation that takes proper account of the Coulomb interactions. As an application of our theoretical strategy, we compute various single-particle and many-particle phenomena such as the Fock-Darwin spectrum; Fermi energy; magneto-optical transitions; probability distribution; and the magneto-optical absorption in the quantum dots. It is observed that the role of an applied magnetic field on the absorption spectrum is comparable to that of a confining potential. Increasing (decreasing) the strength of the magnetic field or the confining potential is found to be analogous to shrinking (expanding) the size of the quantum dots: resulting into a blue (red) shift in the absorption spectrum. The Fermi energy diminishes with both increasing magnetic-field and dot-size; and exhibits saw-tooth-like oscillations at large values of field or dot-size. Unlike laterally confined quantum dots, both (upper and lower) magneto-optical transitions survive even in the extreme instances. However, the intra-Landau level transitions are seen to be forbidden. The spherical quantum dots have an edge over the strictly two-dimensional quantum dots in that the additional (magnetic) quantum number makes the physics richer (but complex). A deeper grasp of the Coulomb blockade, quantum coherence, and entanglement can lead to a better insight into promising applications involving lasers, detectors, storage devices, and quantum computing.

Kushwaha, Manvir S.

2014-12-01

68

Tuning the extraordinary optical transmission through subwavelength hole array by applying a magnetic field  

Microsoft Academic Search

The transmission of light through a thin Ag film with a periodic subwavelength hole array can be influenced by the presence of the externally applied magnetic field H. Using a three-dimensional finite element method, we show that the spectral locations of the transmission peak resonances can be shifted by varying the mag- nitude and direction of the H. The transmission

Arvind Battula; Shaochen Chen; Yalin Lu; R. J. Knize; Kitt Reinhardt

2007-01-01

69

Time-resolved, optically detected NMR of fluids at high magnetic field  

NASA Astrophysics Data System (ADS)

We report on the use of optical Faraday rotation to monitor the nuclear-spin signal in a set of model F19- and H1-rich fluids. Our approach integrates optical detection with high-field, pulsed NMR so as to record the time-resolved evolution of nuclear-spins after rf excitation. Comparison of chemical-shift-resolved resonances allows us to set order-of-magnitude constrains on the relative amplitudes of hyperfine coupling constants for different bonding geometries. When evaluated against coil induction, the present detection modality suffers from poorer sensitivity, but improvement could be attained via multipass schemes. Because illumination is off-resonant i.e., the medium is optically transparent, this methodology could find extensions in a broad class of fluids and soft condensed matter systems.

Pagliero, Daniela; Dong, Wei; Sakellariou, Dimitris; Meriles, Carlos A.

2010-10-01

70

ASCA, RXTE, EUVE, and Optical Observations of the High Magnetic Field Cataclysmic Variable AR Ursae Majoris  

Microsoft Academic Search

The highest field polar AR UMa was observed with ASCA during a low state, and with simultaneous EUVE, RXTE, and ground-based optical photometry during a high state. The marginal detection at the low state places a limit on the hard X-ray emission, which is a factor of 5 below the high-state flux limit. The high-state EUV light curves are highly

Paula Szkody; Stéphane Vennes; Gary D. Schmidt; R. Mark Wagner; Robert Fried; Allen W. Shafter; Erik Fierce

1999-01-01

71

Exploring Magnetic Fields  

NSDL National Science Digital Library

In this activity, students investigate the presence of magnetic fields around magnets, the sun and the earth. They will explore magnetic field lines, understand that magnetic lines of force show the strength and direction of magnetic fields, determine how field lines interact between attracting and repelling magnetic poles, and discover that the earth and sun have magnetic properties. They will also discover that magnetic force is invisible and that a "field of force" is a region or space in which one object can attract or repel another.

72

Magneto-optical absorption spectra and self-similarity of GaAs-(Ga,Al)As quasiperiodic Fibonacci superlattices under in-plane magnetic fields  

NASA Astrophysics Data System (ADS)

A theoretical study of the effects of in-plane magnetic fields on the interband optical absorption spectra of quasiperiodic GaAs-(Ga,Al)As Fibonacci superlattices is presented within the effective-mass approximation. The electron-envelope wave functions and magnetic subbands are obtained by an expansion in harmonic-oscillator wave functions. The theoretical optical absorption spectra are calculated for magnetic fields related by integer powers of the golden mean ?=(1+?5)/2. It is unambiguously shown that, for magnetic-field values scaled by ?2n, the corresponding optical absorption spectra essentially exhibit a self-similar behavior, with the width of the peaks increasing linearly with the field, in agreement with the experimental results by D. Toet, M. Potemski, Y. Y. Wang, J. C. Maan, L. Tapter, and K. Ploog [Phys. Rev. Lett. 66, 2128 (1991)].

Bruno-Alfonso, A.; Oliveira, L. E.; de Dios-Leyva, M.

1995-07-01

73

Visualizing Magnetic Field Lines  

NSDL National Science Digital Library

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

VU Bioengineering RET Program, School of Engineering,

74

What are Magnetic Fields?  

NSDL National Science Digital Library

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

75

Magnetic field line Hamiltonian  

SciTech Connect

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.

Boozer, A.H.

1985-02-01

76

Theory of terahertz/near-infrared optical mixing in quantum wells in strong magnetic fields Takeshi Inoshita, Junichiro Kono,* and Hiroyuki Sakaki  

E-print Network

Theory of terahertz/near-infrared optical mixing in quantum wells in strong magnetic fields TakeshiAs quantum wells illuminated simultaneously by near-infrared and terahertz THz radiation in strong magnetic the sample is illuminated simul- taneously by THz frequency T) and near-infrared fre- quency N) radiation

Kono, Junichiro

77

Photonic Magnetic Field Sensor  

NASA Astrophysics Data System (ADS)

Small, in-line polarization rotators or isolators to reduce feedback in fiber optic links can be the basis for excellent magnetic field sensors. Based on the giant magneto-optical (GMO) or Faraday effect in iron garnets, they with a magnetic field of a few hundred Gauss, (20 mT) for an interaction length for an optical beam of a few millimeters achieve a polarization rotation or phase shift of 45 deg (1/8 cycle). When powered by a small laser diode, with the induced linear phase shift recovered at the shot noise limit, we have demonstrated sensitivities at the 3.3 nT/Hz1/2 level for frequencies from less than 1 Hz to frequencies into the high kHz range. Through further improvements; an increase in interaction length, better materials and by far the greatest factor, the addition of a flux concentrator, sensitivities at the pT/Hz1/2 level appear to be within reach. We will detail such a design and discuss the issues that may limit achieving these goals.

Wyntjes, Geert

2002-02-01

78

Temperature compensated magnetic field sensing using dual S-bend structured optical fiber modal interferometer cascaded with fiber Bragg grating.  

PubMed

A temperature compensated magnetic field strength optical fiber sensor has been proposed and experimentally demonstrated. A fiber Bragg grating (FBG) is cascaded to modal interferometer (MI), which is fabricated by dual S-bend splicing between thin fiber (TF) and single mode fiber (SMF) with intentionally controlled misalignment between cores. We established a modified numerical model to describe the multi-mode interference of this exceptional S-bend and misalignment structure, together with the simulation based on beam propagation method to gain insight into its operation mechanism. The FBG is used to interrogate the temperature change, and then compensate the perturbation of temperature on transmission of the MI. Thanks to the proposed dual S-bend structure and the diameter-thinned TF used here; we have obtained high magnetic sensitivity of -0.0678 dB/Oe using only 4 mm TF after the elimination of ambient temperature change. PMID:25401898

Zhao, Zhiyong; Tang, Ming; Gao, Feng; Zhang, Peng; Duan, Li; Zhu, Benpeng; Fu, Songnian; Ouyang, Jun; Wei, Huifeng; Li, Jinyan; Shum, Perry Ping; Liu, Deming

2014-11-01

79

Linear and nonlinear optical absorption coefficients and refractive index changes in modulation-doped quantum wells: Effects of the magnetic field and hydrostatic pressure  

NASA Astrophysics Data System (ADS)

In this study, the linear, the third-order nonlinear and total optical absorption coefficients and refractive index changes of a modulation-doped GaAs/AlxGaAs quantum well are investigated numerically. In the effective-mass approximation, the electronic structure of modulation-doped quantum well is calculated by solving the Schrödinger and Poisson equations self-consistently. Optical properties are obtained using the compact density matrix approach. The effects of structure parameters, the applied magnetic field and the hydrostatic pressure on the optical properties of the modulation-doped quantum well are studied. Results show that the resonant peaks shift toward the higher (lower) energies with the increase in the magnetic field (pressure). The magnitude of the resonant peaks of the optical properties decreases with the increasing magnetic field or pressure.

Nazari, M.; Karimi, M. J.; Keshavarz, A.

2013-11-01

80

From Quantum Field Theory to Nano-Optics : Refractive Properties of Graphene in a Medium-Strong Magnetic field  

E-print Network

1-loop quantum corrections are shown to induce large effects on the refraction index n inside a graphene strip in the presence of an external magnetic field B orthogonal to it. To this purpose, we use the tools of Quantum Field Theory to calculate the photon propagator at 1-loop inside graphene in position space, which leads to an effective vacuum polarization in a brane-like theory of photons interacting with massless electrons at locations confined inside the thin strip (its longitudinal spread is considered to be infinite). The effects factorize into quantum ones, controlled by the value of B and that of the electromagnetic coupling alpha, and a "transmittance function" U in which the geometry of the sample and the resulting confinement of electrons play the major roles. We consider photons inside the visible spectrum and magnetic fields in the range 1-20 Teslas. At B=0, quantum effects depend very weakly on alpha and n is essentially controlled by U; we recover, then, an opacity for visible light of the same order of magnitude pi * alpha_{vac} as measured experimentally.

Olivier Coquand; Bruno Machet

2014-07-08

81

Mapping Magnetic Fields  

NSDL National Science Digital Library

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

2012-08-03

82

Interaction between guided optical waves and magnetostatic waves in bismuth-doped yttrium-iron-garnet waveguide under inclined magnetic fields  

NASA Astrophysics Data System (ADS)

The noncollinear interaction between guided optical waves and magnetostatic waves under inclined bias magnetic field is studied in detail. The diffraction efficiency (DE) and the mode-conversion efficiency (MCE) of guided optical waves with magnetostatic forward volume waves in the bismuth-doped yttrium-iron-garnet (Bi-doped YIG) waveguide are calculated numerically. The calculation results indicate that the DE and the MCE are different in physical conception and the DE is not equal to the MCE in magnitude under inclined bias magnetic field. The DE may be greatly increased by using an appropriately inclined bias magnetic field, which has been experimentally confirmed in a pure YIG waveguide. By using an inclined bias magnetic field and the Bi-doped YIG waveguide, under the phase-matching conditions, the maximum DE can come up to 79.5% or more.

Bao-Jian, Wu; Gong-Qiang, Liu

1999-10-01

83

PHYSICAL REVIEW B 89, 165120 (2014) Magnetic-field-induced shift of the optical band gap in Ni3V2O8  

E-print Network

reveal field-induced blue shifts of the band gap that are much larger than that of the Zeeman effect in the optical properties requires reaching beyond traditional mechanisms like the Zeeman effect to include]. The magnetic field also drives changes in the electronic properties. This effect can be as simple

84

Magnetic-Field Control of Photon Echo from the Electron-Trion System in a CdTe Quantum Well: Shuffling Coherence between Optically Accessible and Inaccessible States  

NASA Astrophysics Data System (ADS)

We report on magnetic field-induced oscillations of the photon echo signal from negatively charged excitons in a CdTe/(Cd,Mg)Te semiconductor quantum well. The oscillatory signal is due to Larmor precession of the electron spin about a transverse magnetic field and depends sensitively on the polarization configuration of the exciting and refocusing pulses. The echo amplitude can be fully tuned from the maximum down to zero depending on the time delay between the two pulses and the magnetic-field strength. The results are explained in terms of the optical Bloch equations accounting for the spin level structure of electrons and trions.

Langer, L.; Poltavtsev, S. V.; Yugova, I. A.; Yakovlev, D. R.; Karczewski, G.; Wojtowicz, T.; Kossut, J.; Akimov, I. A.; Bayer, M.

2012-10-01

85

Optically encoded nanoprobes using single walled carbon nanotube as the building scaffold for magnetic field guided cell imaging.  

PubMed

We construct a novel fluorescent, surface enhanced Raman scattering (SERS) encoded and magnetic nanoprobe for live cell imaging. To fabricate this nanoprobe, single walled carbon nanotube (SWNT) is used as the building scaffold while gold nanoparticles (Au NPs), superparamagnetic iron oxide nanoparticles (SPIONs) and quantum dots (QDs) are employed as the building blocks. Here, Au NPs serve as the SERS substrate and QDs act as the fluorescent agent. Au NPs and SPIONs are first adsorbed on the SWNT via electrostatic interactions. Then a silica layer is coated on the SWNT. Finally, QDs are attached on the silica shell. With such a structure, various optical signals can be readily encoded to the nanoprobe simply by using different Raman molecules and QDs with different emission wavelengths. Experimental results show that the as-prepared nanoprobe exhibits well fluorescence and SERS performance. Furthermore, in vitro experiments demonstrate that the nanoprobe can fulfill magnetic field guided fluorescence and SERS dual mode imaging of live cells. As a fascinating optical encoding material and a multifunctional nanoplatform, the presented nanoprobe holds genuine potential in future biosensing applications. PMID:24401396

Wang, Hong; Wang, Zhuyuan; Ye, Minglang; Zong, Shenfei; Li, Mingyue; Chen, Peng; Ma, Xueqin; Cui, Yiping

2014-02-01

86

Introduction to Magnetic Fields  

NSDL National Science Digital Library

This is an activity about magnetic fields. Learners will use various magnets, magnetic film, and a compass to see and illustrate what magnetic fields look like. This is the fourth activity as part of the iMAGiNETICspace: Where Imagination, Magnetism, and Space Collide educator's guide. Instructions for downloading the iBook educator's guide and the associated Transmedia book student guide are available at the resource link.

2013-05-06

87

Drawing Magnetic Fields  

NSDL National Science Digital Library

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

2014-09-18

88

Electricity and Magnetic Fields  

NSDL National Science Digital Library

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

VU Bioengineering RET Program,

89

Circuits and Magnetic Fields  

NSDL National Science Digital Library

Students use the same method as in the activity from lesson 2 of this unit to explore the magnetism due to electric current instead of a permanent magnet. Students use a compass and circuit to trace the magnetic field lines induced by the electric current moving through the wire. Students develop an understanding of the effect of the electrical current on the compass needle through the induced magnetic field and understand the complexity of a three dimensional field system.

VU Bioengineering RET Program,

90

Magnetic fields at Neptune  

Microsoft Academic Search

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

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

1989-01-01

91

High-speed and high-spatial resolution fiber-optic measurement technique for RF magnetic field distribution  

Microsoft Academic Search

In this paper basic performance of rotation magnetization phenomenon-based fiber-edge magneto-optical (FEMO) probe scheme have been clarified experimentally in the frequency and spatial domains. FEMO probe scheme not only allow a highly sensitive optical detection by the use of EDFA but also provides noninvasive nature and intimate device-under-test-accessibility via its probe head configuration.

M. Tsuchiya; E. Yamazaki; M. Iwanami; S. Mitani; T. Sato; S. Wakana; S. Hoshino; M. Kishi

2003-01-01

92

The First Magnetic Fields  

E-print Network

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

Widrow, Lawrence M; Schleicher, Dominik; Subramanian, Kandaswamy; Tsagas, Christos G; Treumann, Rudolf A

2011-01-01

93

Solar magnetic fields - Extended.  

NASA Technical Reports Server (NTRS)

Spacecraft observations of the interplanetary magnetic field have revealed that almost always each solar rotation can be divided into sectors, within each of which the field has a predominant polarity toward the sun or away from the sun. Comparisons of this interplanetary magnetic sector pattern with observations of the photospheric magnetic field have revealed a similar solar magnetic pattern. The boundaries between solar magnetic sectors are approximately in the north-south direction over a wide range of latitudes on both sides of the equator. This solar magnetic sector structure can be described as a rotating dipole whose magnetic axis makes an angle of approximately 90 deg with the axis of rotation. Possible similarities between this solar-sector magnetism and the models derived from observations of stellar magnetism are discussed.

Wilcox, J. M.

1971-01-01

94

Mapping Magnetic Field Lines  

NSDL National Science Digital Library

This is a lesson about the magnetic field of a bar magnet. The lesson begins with an introductory discussion with learners about magnetism to draw out any misconceptions that may be in their minds. Then, learners freely experiment with bar magnets and various materials, such as paper clips, rulers, copper or aluminum wire, and pencils, to discover that magnets attract metals containing iron, nickel, and/or cobalt but not most other materials. Next, learners experiment with using a magnetic compass to discover how it is affected by the magnet and then draw the magnetic field lines of the magnet by putting dots at the location of the compass arrow. This is the first lesson in the first session of the Exploring Magnetism teacher guide.

95

Cyclic Magnetic Field Reconnection  

NASA Astrophysics Data System (ADS)

Using a 2.5D electromagnetic particle-in-cell model, we study the magnetic field reconnection around the rotating plasma embedded in a magnetic field. Considering plasma rotation driven by an external electric field, it was found that during one rotational cycle, first the magnetic field energy increases and then decreases to its initial value. The magnetic reconnection occurring during this cycle plays two roles: first, it produces the closed magnetic islands and later on it reopens them to the initial form of magnetic field lines. Thus, the magnetic reconnection can be cyclically repeated in following plasma rotations. Simultaneously, the kinetic particle energy in the system increases due to dissipative processes in this externally driven plasma system. We think that this cyclic reconnection can operate around rapidly rotating stars and in the plasma vortices formed in unstable plasma flows.

Karlický, Marian

2009-02-01

96

Optical magnetic imaging of living cells  

PubMed Central

Magnetic imaging is a powerful tool for probing biological and physical systems. However, existing techniques either have poor spatial resolution compared to optical microscopy and are hence not generally applicable to imaging of sub-cellular structure (e.g., magnetic resonance imaging [MRI]1), or entail operating conditions that preclude application to living biological samples while providing sub-micron resolution (e.g., scanning superconducting quantum interference device [SQUID] microscopy2, electron holography3, and magnetic resonance force microscopy [MRFM]4). Here we demonstrate magnetic imaging of living cells (magnetotactic bacteria) under ambient laboratory conditions and with sub-cellular spatial resolution (400 nm), using an optically-detected magnetic field imaging array consisting of a nanoscale layer of nitrogen-vacancy (NV) colour centres implanted at the surface of a diamond chip. With the bacteria placed on the diamond surface, we optically probe the NV quantum spin states and rapidly reconstruct images of the vector components of the magnetic field created by chains of magnetic nanoparticles (magnetosomes) produced in the bacteria, and spatially correlate these magnetic field maps with optical images acquired in the same apparatus. Wide-field sCMOS acquisition allows parallel optical and magnetic imaging of multiple cells in a population with sub-micron resolution and >100 micron field-of-view. Scanning electron microscope (SEM) images of the bacteria confirm that the correlated optical and magnetic images can be used to locate and characterize the magnetosomes in each bacterium. The results provide a new capability for imaging bio-magnetic structures in living cells under ambient conditions with high spatial resolution, and will enable the mapping of a wide range of magnetic signals within cells and cellular networks5, 6. PMID:23619694

Le Sage, D.; Arai, K.; Glenn, D. R.; DeVience, S. J.; Pham, L. M.; Rahn-Lee, L.; Lukin, M. D.; Yacoby, A.; Komeili, A.; Walsworth, R. L.

2013-01-01

97

Interaction between guided optical waves and magnetostatic waves in bismuth-doped yttrium-iron-garnet waveguide under inclined magnetic fields  

Microsoft Academic Search

The noncollinear interaction between guided optical waves and magnetostatic waves under inclined bias magnetic field is studied in detail. The diffraction efficiency (DE) and the mode-conversion efficiency (MCE) of guided optical waves with magnetostatic forward volume waves in the bismuth-doped yttrium-iron-garnet (Bi-doped YIG) waveguide are calculated numerically. The calculation results indicate that the DE and the MCE are different in

Wu Bao-Jian; Liu Gong-Qiang

1999-01-01

98

Temperature and magnetic field dependent optical spectral weight in the cation-deficient colossal-magnetoresistance material La0.936Mn0.982O3  

E-print Network

Temperature and magnetic field dependent optical spectral weight in the cation-deficient colossal-magnetoresistance reflectivity of a vacancy doped colossal magnetoresistance material La0.936Mn0.982O3 has been investigated 14401-1 Reports on the colossal magnetoresistance CMR in La-A-MnO3 compounds1­4 (A Ca, Sr, Ba) created

Homes, Christopher C.

99

Femtosecond laser inscribed Bragg sensor in Terfenol-D coated optical fibre with ablated microslot for the detection of static magnetic fields  

Microsoft Academic Search

A novel device for the detection and characterisation of static magnetic fields is presented. It consists of a femtosecond laser inscribed fibre Bragg grating (FBG) that is incorporated into an optical fibre with a femtosecond laser micromachined slot. The symmetry of the fibre is broken by the micro-slot, producing non-uniform strain across the fibre cross section. The sensing region is

G. N. Smith; T. Allsop; K. Kalli; C. Koutsides; R. Neal; K. Sugden; P. Culverhouse; I. Bennion

2011-01-01

100

Magnetic field generator  

DOEpatents

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.

Krienin, Frank (Shoreham, NY)

1990-01-01

101

The effect of line damping, magneto-optics and parasitic light on the derivation of sunspot vector magnetic fields  

NASA Technical Reports Server (NTRS)

The least square fitting of Stokes observations of sunspots using a Milne-Eddington-Unno model appears to lead, in many circumstances, to various inconsistencies such as anomalously large doppler widths and, hence, small magnetic fields which are significantly below those inferred solely from the Zeeman splitting in the intensity profile. It is found that the introduction of additional physics into the model such as the inclusion of damping wings and magneto-optic birefrigence significantly improves the fit to Stokes parameters. Model fits excluding the intensity profile, i.e., of both magnitude as well as spectral shape of the polarization parameters alone, suggest that parasitic light in the intensity profile may also be a source of inconsistencies. The consequences of the physical changes on the vector properties of the field derived from the Fe I lambda 6173 line for the 17 November 1975 spot as well as on the thermodynamic state are discussed. A Doppler width delta lambda (D) - 25mA is bound to be consistent with a low spot temperature and microturbulence, and a damping constant of a = 0.2.

Skumanich, A.; Lites, B. W.

1985-01-01

102

THE INTERPLANETARY MAGNETIC FIELD  

Microsoft Academic Search

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

V. A. BAILEY

1963-01-01

103

Cosmic Magnetic Fields  

Microsoft Academic Search

Most of the visible matter in the Universe is in a plasma state, or more specifically is composed of ionized or partially ionized gas permeated by magnetic fields. Thanks to recent advances on the theory and detection of cosmic magnetic fields there has been a worldwide growing interest in the study of their role on the formation of astrophysical sources

Elisabete M. de Gouveia Dal Pino; Dal Pino

2006-01-01

104

The solar magnetic field  

Microsoft Academic Search

The magnetic field of the Sun is the underlying cause of the many diverse phenomena combined under the heading of solar activity. Here we describe the magnetic field as it threads its way from the bottom of the convection zone, where it is built up by the solar dynamo, to the solar surface, where it manifests itself in the form

Sami K. Solanki; Bernd Inhester; Manfred Schüssler

2006-01-01

105

Interplanetary Magnetic Field Lines  

NSDL National Science Digital Library

This web page provides information and a graphical exercise for students regarding the interaction between magnetic field lines and a plasma. The activity involves tracing a typical interplanetary magnetic field line, dragged out of a location on the Sun by the radial flow of the solar wind. This illustrates the way magnetic field lines are "frozen to the plasma" and the wrapping of field lines due to the rotation of the sun. This is part of the work "The Exploration of the Earth's Magnetosphere". A Spanish translation is available.

Stern, David

2005-04-27

106

Solar polar magnetic field  

NASA Astrophysics Data System (ADS)

The solar polar magnetic field has attracted the attention of researchers since the polar magnetic field reversal was revealed in the middle of the last century (Babcock and Livingston, 1958). The polar magnetic field has regularly reversed because the magnetic flux is transported from the sunspot formation zone owing to differential rotation, meridional circulation, and turbulent diffusion. However, modeling of these processes leads to ambiguous conclusions, as a result of which it is sometimes unclear whether a transport model is actual. Thus, according to the last Hinode data, the problem of a standard transport model (Shiota et al., 2012) consists in that a decrease in the polar magnetic flux in the Southern Hemisphere lags behind such a decrease in the flux in the Northern Hemisphere (from 2008 to June 2012). On the other hand, Svalgaard and Kamide (2012) consider that the asymmetry in the sign reversal simply results from the asymmetry in the emerging flux in the sunspot formation region. A detailed study of the polar magnetic flux evolution according to the Solar Dynamics Observatory (SDO) data for May 2010-December 2012 is illustrated in the present work. Helioseismic & Magnetic Imager (HMI) magnetic data in the form of a magnetic field component along the line of sight (the time resolution is 720 s) are used here. The magnetic fluxes in sunspot formation regions and at high latitudes have been compared.

Benevolenskaya, E. E.

2013-12-01

107

Magneto-optical controlled transmittance alteration of PbS quantum dots by moderately applied magnetic fields at room temperature  

NASA Astrophysics Data System (ADS)

We observed changes of the transmitted monochromatic light passing through a colloidal PbS quantum dot film on glass owing to an applied moderate (smaller than 1 T) magnetic field under ambient conditions. The observed alterations show a square dependence on the magnetic field increase that cannot be achieved with bulk semiconductors. The findings point to so far not recognized application potentials of quantum dots.

Singh, Akhilesh K.; Barik, Puspendu; Ullrich, Bruno

2014-12-01

108

Eruptive solar magnetic fields  

Microsoft Academic Search

This paper considers the quasi-steady evolution of solar magnetic fields in response to gradual photospheric changes. Special interest is taken in the threshold of a sudden eruption in the solar atmosphere. The formal model of an evolving, force-free field dependent on two Cartesian coordinates has been treated previously, and we extend it to a field which is not force free

B. C. Low

1981-01-01

109

Mapping Magnetic Field Lines  

NSDL National Science Digital Library

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

110

Magnetic field dosimeter development  

SciTech Connect

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

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

1980-09-01

111

Solar magnetic fields  

Microsoft Academic Search

Since the structuring and variability of the Sun and other stars are governed by magnetic fields, much of present-day stellar\\u000a physics centers around the measurement and understanding of the magnetic fields and their interactions. The Sun, being a prototypical\\u000a star, plays a unique role in astrophysics, since its proximity allows the fundamental processes to be explored in detail.\\u000a The PRL

J. O. Stenflo

2008-01-01

112

Solar magnetic fields  

Microsoft Academic Search

This paper is a review of our observational knowledge on solar magnetic fields. In Section 1 we make an attempt to summarize all observations of the general magnetic field (m.f.) of the Sun. Section 2 deals with the local m.f. at low latitudes and their connection with some features on the disk. The m.f. of sunspots and their peculiar character

A. Severny

1964-01-01

113

Quantum electrodynamic equations for magnetic resonance- and optical spectroscopic transitions  

E-print Network

Quantum electrodynamic equations for magnetic resonance- and optical spectroscopic transitions have been for the first time obtained. New phenomena - stochastic electrical and magnetic spin wave resonances are predicted to be the effects of EM-field quantization.

D. Yearchuck; Y. Yerchak; A. Alexandrov

2009-03-02

114

Magnetic Field Problem: Current  

NSDL National Science Digital Library

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

Wolfgang Christian

115

Magnetic Field Solver  

NASA Technical Reports Server (NTRS)

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

Ilin, Andrew V.

2006-01-01

116

Electro-optic imaging chain for a biplanar fluorscope for neurosurgery: magnetic field sensitivity and contrast measurements  

NASA Astrophysics Data System (ADS)

The effects of magnetic fields on the microchannel plate (MCP) image intensifiers to be used in a novel biplanar fluoroscope are studied along with the system's overall contrast as a function of beam energy. For a second-generation device with wrap-around power supply, B-3dB values for the gain roll-off were found to be approximately 0.08 T (axial field) and 0.06 T (transverse field). The maximum image shift resulting from a 0.0035-T transverse field is found to be 0.065 mm, limited by centroid location error resulting from low-dose x- ray noise. The results of x-ray contrast studies suggests that the presently estimated 0.1-rad dose delivered on the patient (2-h magnetic stereotaxis procedure; 12% 'fluoro-on' duty cycle) might be reduced by increasing the x-ray energy.

Ramos, P. A.; Allison, Stephen W.; Molloy, J. A.; Lawson, Michael A.; Quate, E. G.; Ritter, Rogers C.; Gillies, George T.; Grady, M. S.; Howard, Matthew

1993-07-01

117

Photospheric Flow Field Related to the Evolution of the Sun's Polar Magnetic Patches Observed by Hinode Solar Optical Telescope  

NASA Astrophysics Data System (ADS)

We investigated the role of photospheric plasma motions in the formation and evolution of polar magnetic patches using time-sequence observations with high spatial resolution. The observations were obtained with the spectropolarimeter on board the Hinode satellite. From the statistical analysis using 75 magnetic patches, we found that they are surrounded by strong converging, supergranulation associated flows during their apparent lifetime and that the converging flow around the patch boundary is better observed in the Doppler velocity profile in the deeper photosphere. Based on our analysis, we suggest that the like-polarity magnetic fragments in the polar region are advected and clustered by photospheric converging flows, thereby resulting in the formation of polar magnetic patches. Our observations show that, in addition to direct cancellation, magnetic patches decay by fragmentation followed by unipolar disappearance or unipolar disappearance without fragmentation. It is possible that the magnetic patches of existing polarity fragment or diffuse away into smaller elements and eventually cancel out with opposite polarity fragments that reach the polar region around the solar cycle maximum. This could be one of the possible mechanisms by which the existing polarity decays during the reversal of the polar magnetic field.

Kaithakkal, Anjali John; Suematsu, Y.; Kubo, M.; Iida, Y.; Shiota, D.; Tsuneta, S.

2015-02-01

118

Donor impurity states and related terahertz range nonlinear optical response in GaN cylindrical quantum wires: Effects of external electric and magnetic fields  

NASA Astrophysics Data System (ADS)

We report a study on the optical absorption coefficient associated to hydrogenic impurity interstate transitions in zinc-blende GaN quantum wires of cylindrical shape taking into account the effects of externally applied static electric and magnetic fields. The electron states emerge within the effective mass approximation, via the exact diagonalization of the donor-impurity Hamiltonian with parabolic confinement and external field effects. The nonlinear optical absorption is calculated using a recently derived expression for the dielectric susceptibility, obtained via a nonperturbative solution of the density-matrix Bloch equation. Our results show that this treatment eliminates not only the intensity-dependent bleaching effect but also the change in sign of the nonlinear contribution due to the combined effect of asymmetric impurity location and the applied electric field.

Correa, J. D.; Mora-Ramos, M. E.; Duque, C. A.

2014-06-01

119

Electrically silent magnetic fields.  

PubMed Central

There has been a significant controversy over the past decade regarding the relative information content of bioelectric and biomagnetic signals. In this paper we present a new, theoretical example of an electrically-silent magnetic field, based on a bidomain model of a cylindrical strand of tissue generalized to include off-diagonal components in the conductivity tensors. The physical interpretation of the off-diagonal components is explained, and analytic expressions for the electrical potential and the magnetic field are found. These expressions show that information not obtainable from electrical potential measurements can be obtained from measurements of the magnetic field in systems with conductivity tensors more complicated than those previously examined. PMID:3779008

Roth, B J; Wikswo, J P

1986-01-01

120

Magnetic Fields in Galaxies  

NASA Astrophysics Data System (ADS)

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

Beck, Rainer

121

High concentration ferronematics in low magnetic fields  

E-print Network

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

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

2014-09-05

122

Solar magnetic fields and convection. IX - A primordial magnetic field  

Microsoft Academic Search

Observational evidence is reviewed in an attempt to decide between a reversing (dynamo) and a nonreversing primordial solar poloidal magnetic field. The data examined include Zeeman-effect measurements, measurements of gross magnetic fluxes in individual magnetic elements, determinations of average field strength, observations of polar-cap magnetic fields, eclipse observations of coronal structure, and observations of interplanetary-magnetic-field polarity reversals. It is suggested

J. H. Piddington

1977-01-01

123

Designing magnets with prescribed magnetic fields  

NASA Astrophysics Data System (ADS)

We present a novel design method capable of finding the magnetization densities that generate prescribed magnetic fields. The method is based on the solution to a simple variational inequality and the resulting designs have simple piecewise-constant magnetization densities. By this method, we obtain new designs of magnets that generate commonly used magnetic fields: uniform magnetic fields, self-shielding fields, quadrupole fields and sextupole fields. Further, it is worth noting that this method is not limited to the presented examples, and in particular, three-dimensional designs can be constructed in a similar manner. In conclusion, this novel design method is anticipated to have broad applications where specific magnetic fields are important for the performance of the devices.

Liu, Liping

2011-03-01

124

Femtosecond laser inscribed Bragg sensor in Terfenol-D coated optical fibre with ablated microslot for the detection of static magnetic fields  

NASA Astrophysics Data System (ADS)

A novel device for the detection and characterisation of static magnetic fields is presented. It consists of a femtosecond laser inscribed fibre Bragg grating (FBG) that is incorporated into an optical fibre with a femtosecond laser micromachined slot. The symmetry of the fibre is broken by the micro-slot, producing non-uniform strain across the fibre cross section. The sensing region is coated with Terfenol-D making the device sensitive to static magnetic fields, whereas the symmetry breaking results in a vectorial sensor for the detection of magnetic fields as low as 0.046 mT with a resolution of +/-0.3mT in transmission and +/-0.7mT in reflection. The sensor output is directly wavelength encoded from the FBG filtering, leading to simple demodulation through the monitoring of wavelength shifts that result as the fibre structure changes shape in response to the external magnetic field. The use of a femtosecond laser to both inscribe the FBG and micro-machine the slot in a single stage, prior to coating the device, significantly simplifies the sensor fabrication.

Smith, G. N.; Allsop, T.; Kalli, K.; Koutsides, C.; Neal, R.; Sugden, K.; Culverhouse, P.; Bennion, I.

2011-05-01

125

Magnetic contrast agents for optical coherence tomography  

NASA Astrophysics Data System (ADS)

The magneto-mechanical effect is exploited as a means of producing background-free contrast in optical coherence tomography (OCT). Contrast agents consisting of iron-oxide particles and protein microspheres encapsulating colloidal iron-oxide have a sufficiently high magnetic susceptibility to be detected by modulation of a magnetic field gradient using a small solenoid coil. The externally-applied magnetic field mechanically rotates or translates these highly scattering contrast agents within the sample at the modulation frequency, which is subsequently detected as amplitude modulation of the OCT signal. Pairs of sequential axial scans (A-lines) are acquired with the magnetic field on and off, allowing one to build up a pair of images corresponding to the "on" and "off" states of the magnetic field. These image pairs are differenced to look for magnetic-specific effects, allowing one to distinguish the magnetic contrast agents from non-magnetic structures within the sample with a signal-to-background ratio of ~23dB. This technique has the potential to be very powerful when coupled with targeting for in vivo molecular imaging. To evaluate this potential we demonstrate in vitro imaging of magnetically-labeled macrophage cells embedded in a 3D tissue phantom, in vitro tissue doped with contrast agents, and in vivo imaging of Xenopus laevis (African frog) tadpoles.

Oldenburg, Amy L.; Gunther, Jillian R.; Toublan, Farah J.; Marks, Daniel L.; Suslick, Kenneth S.; Boppart, Stephen A.

2004-07-01

126

High field superconducting magnets  

NASA Technical Reports Server (NTRS)

A superconducting magnet includes an insulating layer disposed about the surface of a mandrel; a superconducting wire wound in adjacent turns about the mandrel to form the superconducting magnet, wherein the superconducting wire is in thermal communication with the mandrel, and the superconducting magnet has a field-to-current ratio equal to or greater than 1.1 Tesla per Ampere; a thermally conductive potting material configured to fill interstices between the adjacent turns, wherein the thermally conductive potting material and the superconducting wire provide a path for dissipation of heat; and a voltage limiting device disposed across each end of the superconducting wire, wherein the voltage limiting device is configured to prevent a voltage excursion across the superconducting wire during quench of the superconducting magnet.

Hait, Thomas P. (Inventor); Shirron, Peter J. (Inventor)

2011-01-01

127

Nuclear Magnetic Resonance and Magnetic Field Measurements  

NSDL National Science Digital Library

This laboratory is designed for students to become familiar with the principles and detection techniques of Nuclear Magnetic Resonance (NMR), examine the relationship between current and magnetic field in an electromagnet, and gain experience in the use of magnetic field measurement techniques.

2012-01-04

128

Cascaded fiber-optic Fabry-Perot interferometers with Vernier effect for highly sensitive measurement of axial strain and magnetic field.  

PubMed

We report a highly sensitive fiber-optic sensor based on two cascaded intrinsic fiber Fabry-Perot interferometers (IFFPIs). The cascaded IFFPIs have different free spectral ranges (FSRs) and are formed by a short section of hollow core photonic crystal fiber sandwiched by two single mode fibers. With the superposition of reflective spectrum with different FSRs, the Vernier effect will be generated in the proposed sensor and we found that the strain sensitivity of the proposed sensor can be improved from 1.6 pm/?? for a single IFFPI sensor to 47.14 pm/?? by employing the Vernier effect. The sensor embed with a metglas ribbon can be also used to measure the magnetic field according to the similar principle. The sensitivity of the magnetic field measurement is achieved to be 71.57 pm/Oe that is significantly larger than the 2.5 pm/Oe for a single IFFPI sensor. PMID:25321041

Zhang, Peng; Tang, Ming; Gao, Feng; Zhu, Benpeng; Fu, Songnian; Ouyang, Jun; Shum, Perry Ping; Liu, Deming

2014-08-11

129

The Earth's Magnetic Field  

NSDL National Science Digital Library

This section of the Windows to the Universe website provides information and images about Earth's magnetic field (the magnetosphere), including detailed information about the aurora borealis, magnets, and solar wind. Windows to the Universe is a user-friendly learning system pertaining to the Earth and Space sciences. The objective of this project is to develop an innovative and engaging website that includes a rich array of documents, including images, movies, animations, and data sets that explore the Earth and Space sciences and the historical and cultural ties between science, exploration and the human experience. Links at the top of each page allow users to navigate between beginner, intermediate and advanced levels.

Johnson, Roberta

2000-07-01

130

Near-Field Magneto-Optical Microscope  

DOEpatents

A device and method for mapping magnetic fields of a sample at a resolution less than the wavelength of light without altering the magnetic field of the sample is disclosed. A device having a tapered end portion with a magneto-optically active particle positioned at the distal end thereof in communication with a fiber optic for transferring incoming linearly polarized light from a source thereof to the particle and for transferring reflected light from the particle is provided. The fiber optic has a reflective material trapping light within the fiber optic and in communication with a light detector for determining the polarization of light reflected from the particle as a function of the strength and direction of the magnetic field of the sample. Linearly polarized light from the source thereof transferred to the particle positioned proximate the sample is affected by the magnetic field of the sample sensed by the particle such that the difference in polarization of light entering and leaving the particle is due to the magnetic field of the sample. Relative movement between the particle and sample enables mapping.

Vlasko-Vlasov, Vitalii; Welp, Ulrich; and Crabtree, George W.

2005-12-06

131

June 23, 1998 A Test for Coronal Magnetic Field Extrapolations  

E-print Network

The determination of the magnetic field structure of the solar corona is a goal being pursued by a number are sensitive to both the strength and direction of the coronal magnetic field. The three techniques each have of high magnetic field strength are generally optically thick due to gyroresonant opacity at frequencies

White, Stephen

132

Mars Observer magnetic fields investigation  

Microsoft Academic Search

The magnetic fields experiment designed for the Mars Observer mission will provide definitive measurements of the Martian magnetic field from the transition and mapping orbits planned for the Mars Observer. The paper describes the instruments (which include a classical magnetometer and an electron reflection magnetometer) and techniques designed to investigate the nature of the Martian magnetic field and the Mars-solar

J. E. P. Connerney; P. Wasilewski; R. P. Lin; K. A. Anderson; C. W. Carlson; J. McFadden; D. W. Curtis; H. Reme; A. Cros; J. L. Médale; J. A. Sauvaud; C. d'Uston; S. J. Bauer; P. Cloutier; Michael Mayhew; N. F. Ness

1992-01-01

133

The WIND magnetic field investigation  

Microsoft Academic Search

The magnetic field experiment on WIND will provide data for studies of a broad range of scales of structures and fluctuation characteristics of the interplanetary magnetic field throughout the mission, and, where appropriate, relate them to the statics and dynamics of the magnetosphere. The basic instrument of the Magnetic Field Investigation (MFI) is a boom-mounted dual triaxial fluxgate magnetometer and

R. P. Lepping; M. H. Ac?na; L. F. Burlaga; W. M. Farrell; J. A. Slavin; K. H. Schatten; F. Mariani; N. F. Ness; F. M. Neubauer; Y. C. Whang; J. B. Byrnes; R. S. Kennon; P. V. Panetta; J. Scheifele; E. M. Worley

1995-01-01

134

Spin microscope based on optically detected magnetic resonance  

Microsoft Academic Search

We propose a scanning magnetic microscope which has a photoluminescence nanoprobe implanted in the tip of an atomic force microscope, (AFM) scanning tunneling microscope (STM), or near-field scanning optical microscope, and exhibits optically detected magnetic resonance. The proposed spin microscope has nanoscale lateral resolution and the single spin sensitivity for AFM and STM.

Boris M. Chernobrod; Gennady P. Berman

2005-01-01

135

Magnetic field switchable dry adhesives.  

PubMed

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

Krahn, Jeffrey; Bovero, Enrico; Menon, Carlo

2015-02-01

136

Graphene in high magnetic fields  

NASA Astrophysics Data System (ADS)

Carbon-based nano-materials, such as graphene and carbon nanotubes, represent a fascinating research area aiming at exploring their remarkable physical and electronic properties. These materials not only constitute a playground for physicists, they are also very promising for practical applications and are envisioned as elementary bricks of the future of the nano-electronics. As for graphene, its potential already lies in the domain of opto-electronics where its unique electronic and optical properties can be fully exploited. Indeed, recent technological advances have demonstrated its effectiveness in the fabrication of solar cells and ultra-fast lasers, as well as touch-screens and sensitive photo-detectors. Although the photo-voltaic technology is now dominated by silicon-based devices, the use of graphene could very well provide higher efficiency. However, before the applied research to take place, one must first demonstrates the operativeness of carbon-based nano-materials, and this is where the fundamental research comes into play. In this context, the use of magnetic field has been proven extremely useful for addressing their fundamental properties as it provides an external and adjustable parameter which drastically modifies their electronic band structure. In order to induce some significant changes, very high magnetic fields are required and can be provided using both DC and pulsed technology, depending of the experimental constraints. In this article, we review some of the challenging experiments on single nano-objects performed in high magnetic and low temperature. We shall mainly focus on the high-field magneto-optical and magneto-transport experiments which provided comprehensive understanding of the peculiar Landau level quantization of the Dirac-type charge carriers in graphene and thin graphite.

Orlita, Milan; Escoffier, Walter; Plochocka, Paulina; Raquet, Bertrand; Zeitler, Uli

2013-01-01

137

Optical/Near-infrared Polarization Survey of Sh 2-29: Magnetic Fields, Dense Cloud Fragmentations, and Anomalous Dust Grain Sizes  

NASA Astrophysics Data System (ADS)

Sh 2-29 is a conspicuous star-forming region marked by the presence of massive embedded stars as well as several notable interstellar structures. In this research, our goals were to determine the role of magnetic fields and to study the size distribution of interstellar dust particles within this turbulent environment. We have used a set of optical and near-infrared polarimetric data obtained at OPD/LNA (Brazil) and CTIO (Chile), correlated with extinction maps, Two Micron All Sky Survey data, and images from the Digitized Sky Survey and Spitzer. The region's most striking feature is a swept out interstellar cavity whose polarimetric maps indicate that magnetic field lines were dragged outward, piling up along its borders. This led to a higher magnetic strength value (?400 ?G) and an abrupt increase in polarization degree, probably due to an enhancement in alignment efficiency. Furthermore, dense cloud fragmentations with peak AV between 20 and 37 mag were probably triggered by its expansion. The presence of 24 ?m point-like sources indicates possible newborn stars inside this dense environment. A statistical analysis of the angular dispersion function revealed areas where field lines are aligned in a well-ordered pattern, seemingly due to compression effects from the H II region expansion. Finally, Serkowski function fits were used to study the ratio of the total-to-selective extinction, revealing a dual population of anomalous grain particle sizes. This trend suggests that both effects of coagulation and fragmentation of interstellar grains are present in the region. Based on observations collected at the National Optical Astronomy Observatory (CTIO, Chile) and Observatório do Pico dos Dias, operated by Laboratório Nacional de Astrofísica (LNA/MCT, Brazil).

Santos, Fábio P.; Franco, Gabriel A. P.; Roman-Lopes, Alexandre; Reis, Wilson; Román-Zúñiga, Carlos G.

2014-03-01

138

Fast superconducting magnetic field switch  

SciTech Connect

The superconducting magnetic switch or fast kicker magnet is employed with an 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 than 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. Magnetic switches and particularly fast kicker magnets are used in the accelerator industry to quickly deflect particle beams into and out of various transport lines, storage rings, dumps, and specifically to differentially route individual bunches of particles from a train of bunches which are injected or ejected from a given ring.

Goren, Y.; Mahale, N.K.

1995-12-31

139

The Heliospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

The heliospheric magnetic field (HMF) is the extension of the coronal magnetic field carried out into the solar system by the solar wind. It is the means by which the Sun interacts with planetary magnetospheres and channels charged particles propagating through the heliosphere. As the HMF remains rooted at the solar photosphere as the Sun rotates, the large-scale HMF traces out an Archimedean spiral. This pattern is distorted by the interaction of fast and slow solar wind streams, as well as the interplanetary manifestations of transient solar eruptions called coronal mass ejections. On the smaller scale, the HMF exhibits an array of waves, discontinuities, and turbulence, which give hints to the solar wind formation process. This review aims to summarise observations and theory of the small- and large-scale structure of the HMF. Solar-cycle and cycle-to-cycle evolution of the HMF is discussed in terms of recent spacecraft observations and pre-spaceage proxies for the HMF in geomagnetic and galactic cosmic ray records.

Owens, Mathew J.; Forsyth, Robert J.

2013-11-01

140

Spin microscope based on optically detected magnetic resonance  

DOEpatents

The invention relates to scanning magnetic microscope which has a photoluminescent nanoprobe implanted in the tip apex of an atomic force microscope (AFM), a scanning tunneling microscope (STM) or a near-field scanning optical microscope (NSOM) and exhibits optically detected magnetic resonance (ODMR) in the vicinity of unpaired electron spins or nuclear magnetic moments in the sample material. The described spin microscope has demonstrated nanoscale lateral resolution and single spin sensitivity for the AFM and STM embodiments.

Berman, Gennady P. (Los Alamos, NM); Chernobrod, Boris M. (Los Alamos, NM)

2010-06-29

141

Spin microscope based on optically detected magnetic resonance  

DOEpatents

The invention relates to scanning magnetic microscope which has a photoluminescent nanoprobe implanted in the tip apex of an atomic force microscope (AFM), a scanning tunneling microscope (STM) or a near-field scanning optical microscope (NSOM) and exhibits optically detected magnetic resonance (ODMR) in the vicinity of unpaired electron spins or nuclear magnetic moments in the sample material. The described spin microscope has demonstrated nanoscale lateral resolution and single spin sensitivity for the AFM and STM embodiments.

Berman, Gennady P. (Los Alamos, NM); Chernobrod, Boris M. (Los Alamos, NM)

2007-12-11

142

Magnetic Propeller for Uniform Magnetic Field Levitation  

E-print Network

Three new approaches to generating thrust in uniform magnetic fields are proposed. The first direction is based on employing Lorentz force acting on partial magnetically shielded 8-shaped loop with current in external magnetic field, whereby a net force rather than a torque origins. Another approach, called a Virtual Wire System, is based on creating a magnetic field having an energetic symmetry (a virtual wire), with further superposition of external field. The external field breaks the symmetry causing origination of a net force. Unlike a wire with current, having radial energetic symmetry, the symmetry of the Virtual Wire System is closer to an axial wire. The third approach refers to the first two. It is based on creation of developed surface system, comprising the elements of the first two types. The developed surface approach is a way to drastically increase a thrust-to-weight ratio. The conducted experiments have confirmed feasibility of the proposed approaches.

Mark Krinker; Alexander Bolonkin

2008-07-12

143

Fast superconducting magnetic field switch  

DOEpatents

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

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

1996-01-01

144

Fast superconducting magnetic field switch  

DOEpatents

The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater that the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles. 6 figs.

Goren, Y.; Mahale, N.K.

1996-08-06

145

[Magnetic fields and fish behavior].  

PubMed

In the review, contemporary data on the influence of natural and artificial magnetic fields on fish behavior are considered. In this regard, elasmobranchs and teleosts appear to be studied most exhaustively. Elasmobranchs and some teleosts are able to perceive magnetic fields via electroreceptors. A number of teleosts can sense magnetic fields via sensory cells containing crystals of biogenic magnetite. Laboratory experiments and field observations indicate the influence of magnetic fields on fish locomotor activity and spatial distribution. The geomagnetic field can be used by fish for navigation. Besides, artificial magnetic fields and natural fluctuations of the geomagnetic field can affect fish embryos leading to alterations in their development. It is suggested that, afterwards, these alterations can have an effect on fish behavior. PMID:25508098

2013-01-01

146

[Magnetic fields and fish behavior].  

PubMed

In the review, contemporary data on the influence of natural and artificial magnetic fields on fish behavior are considered. In this regard, elasmobranchs and teleosts appear to be studied most exhaustively. Elasmobranchs and some teleosts are able to perceive magnetic fields via electroreceptors. A number of teleosts can sense magnetic fields via sensory cells containing crystals of biogenic magnetite. Laboratory experiments and field observations indicate the influence of magnetic fields on fish locomotor activity and spatial distribution. The geomagnetic field can be used by fish for navigation. Besides, artificial magnetic fields and natural fluctuations of the geomagnetic field can affect fish embryos leading to alterations in their development. It is suggested that, afterwards, these alterations can have an effect on fish behavior. PMID:25438567

Krylov, V V; Iziumov, Iu G; Izvekov, E I; Nepomniashchikh, V A

2013-01-01

147

Exposure guidelines for magnetic fields  

SciTech Connect

The powerful magnetic fields produced by a controlled fusion experiment at Lawrence Livermore National Laboratory (LLNL) necessitated the development of personnel-exposure guidelines for steady magnetic fields. A literature search and conversations with active researchers showed that it is currently possible to develop preliminary exposure guidelines for steady magnetic fields. An overview of the results of past research into the bioeffects of magnetic fields was compiled, along with a discussion of hazards that may be encountered by people with sickle-cell anemia or medical electronic and prosthetic implants. The LLNL steady magnetic-field exposure guidelines along with a review of developments concerning the safety of time-varying fields were also presented in this compilation. Guidelines developed elsewhere for time varying fields were also given. Further research is needed to develop exposure standards for both steady or time-varying fields.

Miller, G.

1987-12-01

148

High-resolution optical imaging of magnetic-domain structures  

Microsoft Academic Search

High-resolution optical techniques for imaging magnetic domains in ferromagnetic materials such as confocal microscopy and scanning near-field optical microscopy (SNOM) are reviewed. The imaging capabilities of different techniques and image formation are discussed in the case of in-plane as well as out-of-plane magnetic anisotropy in different illumination configurations. It is shown that the magnetooptical resolution of near-field measurements depends on

Wayne Dickson; Satoshi Takahashi; Robert Pollard; Ron Atkinson; Anatoly V. Zayats

2005-01-01

149

Magnetic-field-dosimetry system  

DOEpatents

A device is provided for measuring the magnetic field dose and peak field exposure. The device includes three Hall-effect sensors all perpendicular to each other, sensing the three dimensional magnetic field and associated electronics for data storage, calculating, retrieving and display.

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

1981-01-21

150

Magnetic fields in massive stars  

E-print Network

Although indirect evidence for the presence of magnetic fields in high-mass stars is regularly reported in the literature, the detection of these fields remains an extremely challenging observational problem. We review the recent discoveries of magnetic fields in different types of massive stars and briefly discuss strategies for spectropolarimetric observations to be carried out in the future.

S. Hubrig

2007-03-09

151

Optical Studies of Zero-Field Magnetization of CdMnTe Quantum Dots: Influence of Average Size and Composition of Quantum Dots  

E-print Network

We show that through the resonant optical excitation of spin-polarized excitons into CdMnTe magnetic quantum dots, we can induce a macroscopic magnetization of the Mn impurities. We observe very broad (4 meV linewidth) emission lines of single dots, which are consistent with the formation of strongly confined exciton magnetic polarons. Therefore we attribute the optically induced magnetization of the magnetic dots results to the formation of spin-polarized exciton magnetic polarons. We find that the photo-induced magnetization of magnetic polarons is weaker for larger dots which emit at lower energies within the QD distribution. We also show that the photo-induced magnetization is stronger for quantum dots with lower Mn concentration, which we ascribe to weaker Mn-Mn interaction between the nearest neighbors within the dots. Due to particular stability of the exciton magnetic polarons in QDs, where the localization of the electrons and holes is comparable to the magnetic exchange interaction, this optically induced spin alignment persists to temperatures as high as 160 K.

T. Gurung; S. Mackowski; H. E. Jackson; L. M. Smith; W. Heiss; J. Kossut; G. Karczewski

2004-08-30

152

Ferrofilm in a magnetic field  

NASA Astrophysics Data System (ADS)

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

Back, Randy; Beckham, J. Regan

2012-10-01

153

Linear electro-optic effect for nuclear magnetic resonance coil  

NASA Astrophysics Data System (ADS)

An electrooptic transduction is here used to perform a low invasive characterization of the magnetic field in the context of magnetic resonance imaging. A resonant coil is coupled to a passive electrooptic crystal and the electromotive force of the magnetic field sensor is converted into a polarization state modulation of a laser probe beam. The optical conversion is demonstrated and lead to a fiber remote measurement of the magnetic field. The setup sensitivity and dynamics are finally dramatically enhanced using a LiNbO3 integrated waveguide. The minimum detectable field is as low as 60 fT.Hz-1/2 and the dynamics exceeds 100 dB.

Ayde, R.; Gaborit, Gwenaël.; Dahdah, Jean; Duvillaret, Lionel; Sablong, Raphaël.; Perrier, Anne-Laure; Beuf, Olivier

2014-05-01

154

Influence of crossed electric and quantizing magnetic fields on the Einstein relation in nonlinear optical, optoelectronic and related materials: Simplified theory, relative comparison and suggestion for experimental determination  

NASA Astrophysics Data System (ADS)

An attempt is made to study the Einstein relation for the diffusivity-to-mobility ratio (DMR) under crossed fields’ configuration in nonlinear optical materials on the basis of a newly formulated electron dispersion law by incorporating the crystal field in the Hamiltonian and including the anisotropies of the effective electron mass and the spin-orbit splitting constants within the framework of kp formalisms. The corresponding results for III-V, ternary and quaternary compounds form a special case of our generalized analysis. The DMR has also been investigated for II-VI and stressed materials on the basis of various appropriate dispersion relations. We have considered n-CdGeAs 2, n-Hg 1- xCd xTe, n-In 1- xGa xAs yP 1- y lattice matched to InP, p-CdS and stressed n-InSb materials as examples. The DMR also increases with increasing electric field and the natures of oscillations are totally band structure dependent with different numerical values. It has been observed that the DMR exhibits oscillatory dependences with inverse quantizing magnetic field and carrier degeneracy due to the Subhnikov-de Haas effect. An experimental method of determining the DMR for degenerate materials in the present case has been suggested.

Pahari, S.; Bhattacharya, S.; De, D.; Adhikari, S. M.; Niyogi, A.; Dey, A.; Paitya, N.; Saha, S. C.; Ghatak, K. P.; Bose, P. K.

2010-09-01

155

Estimation of fluctuating magnetic fields by an atomic magnetometer  

SciTech Connect

We present a theoretical procedure to estimate with an atomic magnetometer the time dependence of a magnetic field that fluctuates according to an Ornstein-Uhlenbeck process. The magnetometer applies the detected polarization rotation of an optical probe to measure a collective atomic spin, which precesses due to the magnetic field. Based on the noisy optical detection record, our consistent Gaussian update formalism provides an estimator for the magnetic fields, and we identify analytically the steady-state performance of this estimator. We show that the estimate of the current value of the magnetic field is further improved if noisy measurement data obtained also at later times are taken into account.

Petersen, Vivi; Moelmer, Klaus [QUANTOP--Danish National Research Foundation Center for Quantum Optics, Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark)

2006-10-15

156

A high-field 3He metastability exchange optical pumping polarizer operating in a 1.5 T medical scanner for lung magnetic resonance imaging  

NASA Astrophysics Data System (ADS)

After being hyperpolarized using the technique of Metastability Exchange Optical Pumping (MEOP), 3He can be used as a contrast agent for lung magnetic resonance imaging (MRI). MEOP is usually performed at low magnetic field (˜1 mT) and low pressure (˜1 mbar), which results in a low magnetization production rate. Polarization preserving compression with a compression ratio of order 1000 is also required. It was demonstrated in sealed cells that high nuclear polarization values can be obtained at higher pressures with MEOP, if performed at high magnetic field (non-standard conditions). In this work, the feasibility of building a high-field polarizer that operates within a commercial 1.5 T scanner was evaluated. Preliminary measurements of nuclear polarization with sealed cells filled at different 3He gas pressures (1.33 to 267 mbar) were performed. The use of an annular shape for the laser beam increased by 25% the achievable nuclear polarization equilibrium value (Meq) at 32 and 67 mbar as compared to a Gaussian beam shape. Meq values of 66.4% and 31% were obtained at 32 and 267 mbar, respectively, and the magnetization production rate was increased by a factor of 10 compared to the best results obtained under standard conditions. To study the reproducibility of the method in a polarizing system, the same experiments were performed with small cells connected to a gas handling system. Despite careful cleaning procedure, the purity of the 3He gas could not be matched to that of the sealed cells. Consequently, the polarization build-up times were approximately 3 times longer in the 20-30 mbar range of pressure than those obtained for the 32 mbar sealed cell. However, reasonable Meq values of 40%-60% were achieved in a 90 ml open cell. Based on these findings, a novel compact polarizing system was designed and built. Its typical output is a 3He gas flow rate of 15 sccm with a polarization of 33%. In-vivo lung MRI ventilation images (Signal to Noise Ratio (SNR) of approximately 55 for a voxel size of 50 mm × 3 mm × 3 mm) were acquired to demonstrate the polarizer's application.

Collier, G.; Pa?asz, T.; Wojna, A.; G?owacz, B.; Suchanek, M.; Olejniczak, Z.; Dohnalik, T.

2013-05-01

157

Theory of fossil magnetic field  

NASA Astrophysics Data System (ADS)

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

Dudorov, Alexander E.; Khaibrakhmanov, Sergey A.

2015-02-01

158

Cosmic Magnetic Fields - An Overview  

NASA Astrophysics Data System (ADS)

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

Wielebinski, Richard; Beck, Rainer

159

Measurements of magnetic field alignment  

SciTech Connect

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

Kuchnir, M.; Schmidt, E.E.

1987-11-06

160

CHAPTER 3. STRUCTURE OF MAGNETIC FIELDS 1 Structure of Magnetic  

E-print Network

CHAPTER 3. STRUCTURE OF MAGNETIC FIELDS 1 Chapter 3 Structure of Magnetic Fields Many of the most interesting plasmas are permeated by or imbedded in magnetic fields.1 As shown in Fig. 3.1, the magnetic field properties of magnetic fields in plasmas can be discussed without specifying a model for the plasma

Callen, James D.

161

Magnetic Field Problem: Measuring Current  

NSDL National Science Digital Library

A cross section of two circular wire loops carrying the exact same current is shown above (position given in centimeters and magnetic field given in milli-Tesla). You can click-drag to read the magnitude of the magnetic field.

Christian, Wolfgang; Belloni, Mario

2007-03-03

162

Studies of solar magnetic fields  

Microsoft Academic Search

An estimate of the average magnetic field strength at the poles of the Sun from Mount Wilson measurements is made by comparing low latitude magnetic measurements in the same regions made near the center of the disk and near the limb. There is still some uncertainty because the orientation angle of the field lines in the meridional plane is unknown,

Robert Howard

1977-01-01

163

Fabrication and characterization of a latching magnetic optical switch  

NASA Astrophysics Data System (ADS)

This paper reports the fabrication and characterization of a new type latching magnetic optical switch. The basic optical switch has two stable states wherein an optical signal from the input port can be routed to either one of the two output ports. The key component of the optical switch is a cantilever made of soft magnetic material with a reflective surface. The optical switch is bi-stable because the cantilever has a tendency to align with the external magnetic field, and the torque to align the cantilever can be di-directional depending on the angle between the cantilever and the magnetic field. Switching between the two stable states is accomplished by momentarily changing the direction and/or the magnitude of the cantilever's magnetization by passing a short current pulse through a planar coil underneath the cantilever. In either of its stable states, the cantilever is held in its position by the combined influence of permanent external magnetic field and other mechanical forces, such as a physical stop or a mechanical torques produced by torsion flexures supporting the cantilever. Large angle deflection and bi-stable latching operations have been demonstrated. Characterization has been performed for optical switching performances. Computer simulation results were compared to the experimental results. The switching speed is 3.2 ms, optical insertion loss is -4 dB, and the energy consumption is 44 mJ for each switching event.

Huang, Zhilin; Shen, Jun

2005-01-01

164

Solar magnetic fields and convection  

Microsoft Academic Search

The solar magnetic fields observed in active regions and their residues are thought to be parts of toroidal field systems renewed every 11-yr cycle from a poloidal field. The latter may be either a reversing (dynamo) field or a non-reversing, primordial field. The latter view was held for some 70 yr, but the apparent reversals of the polar-cap fields in

J. H. Piddington

1977-01-01

165

Frustrated magnetic vortices in a triad of permalloy rings: Magneto-optical Kerr effect, magnetic force microscopy, and micromagnetic simulations  

E-print Network

Frustrated magnetic vortices in a triad of permalloy rings: Magneto-optical Kerr effect, magnetic of magnetic vortices, leaving at least one ring in a magnetically frustrated state. The properties October 2005; published 28 March 2006 The field dependent magnetization of three mutually touching

Metlushko, Vitali

166

PREPROCESSING MAGNETIC FIELDS WITH CHROMOSPHERIC LONGITUDINAL FIELDS  

SciTech Connect

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

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

2012-06-20

167

Thermometers in Low Magnetic Fields  

NASA Astrophysics Data System (ADS)

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.

Geršak, G.; Beguš, S.

2010-09-01

168

Low-Magnetic-Field Magnetars  

NASA Astrophysics Data System (ADS)

It is now widely accepted that soft gamma repeaters and anomalous X-ray pulsars are the observational manifestations of magnetars, i.e. sources powered by their own magnetic energy. This view was supported by the fact that these "magnetar candidates" exhibited, without exception, a surface dipole magnetic field (as inferred from the spin-down rate) in excess of the electron critical field (? 4.4×1013 G). The recent discovery of fully qualified magnetars, SGR 0418+5729 and Swift J1822.3-1606, with dipole magnetic field well in the range of ordinary radio pulsars posed a challenge to the standard picture, showing that a very strong field is not necessary for the onset of magnetar activity (chiefly bursts and outbursts). Here we summarize the observational status of the low-magnetic-field magnetars and discuss their properties in the context of the mainstream magnetar model and its main alternatives.

Turolla, Roberto; Esposito, Paolo

2013-11-01

169

Resonant magnetic fields from inflation  

SciTech Connect

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

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

2012-03-01

170

Nuclear magnetization in gallium arsenide quantum dots at zero magnetic field  

PubMed Central

Optical and electrical control of the nuclear spin system allows enhancing the sensitivity of NMR applications and spin-based information storage and processing. Dynamic nuclear polarization in semiconductors is commonly achieved in the presence of a stabilizing external magnetic field. Here we report efficient optical pumping of nuclear spins at zero magnetic field in strain-free GaAs quantum dots. The strong interaction of a single, optically injected electron spin with the nuclear spins acts as a stabilizing, effective magnetic field (Knight field) on the nuclei. We optically tune the Knight field amplitude and direction. In combination with a small transverse magnetic field, we are able to control the longitudinal and transverse components of the nuclear spin polarization in the absence of lattice strain—that is, in dots with strongly reduced static nuclear quadrupole effects, as reproduced by our model calculations. PMID:24500329

Sallen, G.; Kunz, S.; Amand, T.; Bouet, L.; Kuroda, T.; Mano, T.; Paget, D.; Krebs, O.; Marie, X.; Sakoda, K.; Urbaszek, B.

2014-01-01

171

condensate in constant magnetic fields  

Microsoft Academic Search

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 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

M. de J Anguiano-Galicia; A. Bashir; A. Raya

2007-01-01

172

Far-field optical superlens.  

PubMed

Far-field optical lens resolution is fundamentally limited by diffraction, which typically is about half of the wavelength. This is due to the evanescent waves carrying small scale information from an object that fades away in the far field. A recently proposed superlens theory offers a new approach by surface excitation at the negative index medium. We introduce a far-field optical superlens (FSL) that is capable of imaging beyond the diffraction limit. The FSL significantly enhances the evanescent waves of an object and converts them into propagating waves that are measured in the far field. We show that a FSL can image a subwavelength object consisting of two 50 nm wide lines separated by 70 nm working at 377 nm wavelength. The optical FSL promises new potential for nanoscale imaging and lithography. PMID:17298007

Liu, Zhaowei; Durant, Stéphane; Lee, Hyesog; Pikus, Yuri; Fang, Nicolas; Xiong, Yi; Sun, Cheng; Zhang, Xiang

2007-02-01

173

Investigating Magnetic Force Fields  

NSDL National Science Digital Library

In this classroom activity, the students will investigate the magnetic pull of a bar magnet at varying distances with the use of paper clips. Students will hypothesize, conduct the experiment, collect the data, and draw conclusions that support their data. Each student will record the experiment and their findings in their science journals. As a class, students will compare each groups' data and their interpretation of the results.

Daryl ("Tish") Monjeau, Bancroft Elementary School, Minneapolis, MN

2012-03-18

174

Preface: Cosmic magnetic fields  

NASA Astrophysics Data System (ADS)

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

Kosovichev, Alexander

2015-02-01

175

Development of optical field emitter arrays  

E-print Network

Optical field emitters are electron emission sources actuated by incident light. Optically actuated field emitters may produce ultrafast pulses of electrons when excited by ultrafast optical pulses, thus making them of ...

Yang, Yujia, S.M. Massachusetts Institute of Technology

2013-01-01

176

The magnetic field of Canopus  

Microsoft Academic Search

Zeeman spectrograms taken at the ESO in 1978 for Canopus (F0 Ib-II) confirm the presence of the weak magnetic field detected by Schermann (1977) and Rakosch et al. (1977), and a new period of 6.90 days for the Canopus magnetic field variation is proposed. It is noted that with the MSHIFT-technique (Weiss et al., 1978) the plate-mean Zeeman shifts can

W. W. Weiss

1986-01-01

177

Solar magnetic fields and convection  

Microsoft Academic Search

The flux-rope model of solar magnetic fields is developed further by the use of a variety of observational results.(i)It is confirmed that magnetic fields emerging to form active regions are already in the form of helically twisted flux ropes.(ii)A flux rope is not a homogeneous structure but is made up of hundreds or thousands of flux fibres. These are individually

J. H. Piddington

1976-01-01

178

Magnetic field sensor based on magnetic fluid clad etched fiber Bragg grating  

Microsoft Academic Search

A novel fiber optical fiber-magnetic sensor based on magnetic fluid is proposed in this paper. The stable nanoparticles Fe3O4 magnetic fluid was synthesized firstly; the Fe3O4 magnetic fluid was injected in capillaries containing etched fiber Bragg grating (FBG) as sensing element. The reflected Bragg wavelength was changed by varying the magnetic field which is perpendicular to the axial of FBG.

Jixiang Dai; Minghong Yang; Xiaobing Li; Hongliang Liu; Xinglin Tong

2011-01-01

179

Magnetic field induced dynamical chaos  

SciTech Connect

In this article, we have studied the dynamics of a particle having charge in the presence of a magnetic field. The motion of the particle is confined in the x–y plane under a two dimensional nonlinear potential. We have shown that constant magnetic field induced dynamical chaos is possible even for a force which is derived from a simple potential. For a given strength of the magnetic field, initial position, and velocity of the particle, the dynamics may be regular, but it may become chaotic when the field is time dependent. Chaotic dynamics is very often if the field is time dependent. Origin of chaos has been explored using the Hamiltonian function of the dynamics in terms of action and angle variables. Applicability of the present study has been discussed with a few examples.

Ray, Somrita; Baura, Alendu; Bag, Bidhan Chandra, E-mail: bidhanchandra.bag@visva-bharati.ac.in [Department of Chemistry, Visva-Bharati, Santiniketan 731 235 (India)

2013-12-15

180

Damping of cosmic magnetic fields  

SciTech Connect

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

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

1998-03-01

181

Damping of cosmic magnetic fields  

NASA Astrophysics Data System (ADS)

We examine the evolution of magnetic fields in an expanding fluid composed of matter and radiation with particular interest in the evolution of cosmic magnetic fields. We derive the propagation velocities and damping rates for relativistic and non-relativistic fast and slow magnetosonic and Alfvén waves in the presence of viscous and heat conducting processes. The analysis covers all magnetohydrodynamics modes in the radiation diffusion and the free-streaming regimes. When our results are applied to the evolution of magnetic fields in the early universe, we find that cosmic magnetic fields are damped from prior to the epoch of neutrino decoupling up to recombination. Similar to the case of sound waves propagating in a demagnetized plasma, fast magnetosonic waves are damped by radiation diffusion on all scales smaller than the radiation diffusion length. The characteristic damping scales are the horizon scale at neutrino decoupling (M?~10-4Msolar in baryons) and the Silk mass at recombination (M?~1013Msolar in baryons). In contrast, the oscillations of slow magnetosonic and Alfvén waves get overdamped in the radiation diffusion regime, resulting in frozen-in magnetic field perturbations. Further damping of these perturbations is possible only if before recombination the wave enters a regime in which radiation free-streams on the scale of the perturbation. The maximum damping scale of slow magnetosonic and Alfvén modes is always smaller than or equal to the damping scale of fast magnetosonic waves, and depends on the magnetic field strength and its direction relative to the wave vector. Our findings have multifold implications for cosmology. The dissipation of magnetic field energy into heat during the epoch of neutrino decoupling ensures that most magnetic field configurations generated in the very early universe satisfy big bang nucleosynthesis constraints. Further dissipation before recombination constrains models in which primordial magnetic fields give rise to galactic magnetic fields or density perturbations. Finally, the survival of Alfvén and slow magnetosonic modes on scales well below the Silk mass may be of significance for the formation of structure on small scales.

Jedamzik, Karsten; Katalini?, Višnja; Olinto, Angela V.

1998-03-01

182

A solar magnetic and velocity field measurement system for Spacelab 2: The Solar Optical Universal Polarimeter (SOUP)  

NASA Astrophysics Data System (ADS)

The Solar Optical Universal Polarimeter (SOUP) flew on the shuttle mission Spacelab 2 (STS-51F) in August, 1985, and collected historic solar observations. SOUP is the only solar telescope on either a spacecraft or balloon which has delivered long sequences of diffraction-limited images. These movies led to several discoveries about the solar atmosphere which were published in the scientific journals. After Spacelab 2, reflights were planned on the shuttle Sunlab mission, which was cancelled after the Challenger disaster, and on a balloon flights, which were also cancelled for funding reasons. In the meantime, the instrument was used in a productive program of ground-based observing, which collected excellent scientific data and served as instrument tests. Given here is an overview of the history of the SOUP program, the scientific discoveries, and the instrument design and performance.

Tarbell, Theodore D.; Title, Alan M.

1992-08-01

183

A solar magnetic and velocity field measurement system for Spacelab 2: The solar optical universal polarimeter (SOUP)  

NASA Astrophysics Data System (ADS)

The Solar Optical Universal Polarimeter flew on the Shuttle Mission Spacelab 2 (STS-51F) in August, 1985, and collected historic solar observations. SOUP is the only solar telescope on either a spacecraft or balloon which has delivered long sequences of diffraction-limited images. These movies led to several discoveries about the solar atmosphere which were published in the scientific journals. After Spacelab 2, reflights were planned on the Space Shuttle Sunlab Mission, which was cancelled after the Challenger disaster, and on balloon flights, which were also cancelled for funding reasons. In the meantime, the instrument was used in a productive program of ground-based observing, which collected excellent scientific data and served as instrument tests. This report gives an overview of the history of the SOUP program, the scientific discoveries, and the instrument design and performance.

Tarbell, Theodore D.; Title, Alan M.

1992-08-01

184

A solar magnetic and velocity field measurement system for Spacelab 2: The Solar Optical Universal Polarimeter (SOUP)  

NASA Technical Reports Server (NTRS)

The Solar Optical Universal Polarimeter (SOUP) flew on the shuttle mission Spacelab 2 (STS-51F) in August, 1985, and collected historic solar observations. SOUP is the only solar telescope on either a spacecraft or balloon which has delivered long sequences of diffraction-limited images. These movies led to several discoveries about the solar atmosphere which were published in the scientific journals. After Spacelab 2, reflights were planned on the shuttle Sunlab mission, which was cancelled after the Challenger disaster, and on a balloon flights, which were also cancelled for funding reasons. In the meantime, the instrument was used in a productive program of ground-based observing, which collected excellent scientific data and served as instrument tests. Given here is an overview of the history of the SOUP program, the scientific discoveries, and the instrument design and performance.

Tarbell, Theodore D.; Title, Alan M.

1992-01-01

185

Magnetic fields in protoplanetary disks  

E-print Network

Magnetic fields likely play a key role in the dynamics and evolution of protoplanetary discs. They have the potential to efficiently transport angular momentum by MHD turbulence or via the magnetocentrifugal acceleration of outflows from the disk surface, and magnetically-driven mixing has implications for disk chemistry and evolution of the grain population. However, the weak ionisation of protoplanetary discs means that magnetic fields may not be able to effectively couple to the matter. I present calculations of the ionisation equilibrium and magnetic diffusivity as a function of height from the disk midplane at radii of 1 and 5 AU. Dust grains tend to suppress magnetic coupling by soaking up electrons and ions from the gas phase and reducing the conductivity of the gas by many orders of magnitude. However, once grains have grown to a few microns in size their effect starts to wane and magnetic fields can begin to couple to the gas even at the disk midplane. Because ions are generally decoupled from the magnetic field by neutral collisions while electrons are not, the Hall effect tends to dominate the diffusion of the magnetic field when it is able to partially couple to the gas. For a standard population of 0.1 micron grains the active surface layers have a combined column of about 2 g/cm^2 at 1 AU; by the time grains have aggregated to 3 microns the active surface density is 80 g/cm^2. In the absence of grains, x-rays maintain magnetic coupling to 10% of the disk material at 1 AU (150 g/cm^2). At 5 AU the entire disk thickness becomes active once grains have aggregated to 1 micron in size.

Mark Wardle

2007-04-07

186

Faraday rotation and magnetic properties of erbium gallium gallate under high magnetic field  

NASA Astrophysics Data System (ADS)

Magnetization (M) and Faraday rotation (FR) have been measured in Er3Ga5O12 single crystals in the 4.2-300 K temperature range under high dc magnetic field up to 300 kOe. Experimental data are reported for H applied parallel to the [111] and [100] directions at 633 and 550 nm wavelength. A strong anisotropy of both magneto-optical and magnetic properties is observed. At low temperature, FR and M are proportional only when the magnetization is weak (small magnetic field). In medium and high magnetic field, complex relationships between M and FR are found. The magnetization cannot account for the whole Faraday rotation anisotropy. These data are discussed taking into account the magnetic and magneto-optical properties of the isomorphous erbium iron garnet ferrite.

Guillot, M.; Schmiedel, T.; Xu, You

1998-06-01

187

Studying the magnetic fields of cool stars  

NASA Astrophysics Data System (ADS)

Magnetic fields are prevalent in a wide variety of low mass stellar systems and play an important role in their evolution. Yet the process through which these fields are generated is not well understood. To understand how such systems can generate strong field structures characterization of these fields is required. Radio emission traces the fields directly and the properties of this emission can be modeled leading to constraints on the field geometry and magnetic parameters. The new Karl Jansky Very Large Array (VLA) provides highly sensitive radio observations. My thesis involves combining VLA observations with the development of magnetospheric emission models in order to characterize the magnetic fields in two fully convective cool star systems: (1) Young Stellar Objects (YSOs); (2) Ultracool dwarf stars. I conducted multi epoch observations of DG Tau, a YSO with a highly active, collimated outflow. The radio emission observed from this source was found to be optically thick thermal emission with no indication of the magnetic activity observed in X-rays. I determined that the outflow is highly collimated very close to the central source, in agreement with jet launching models. Additionally, I constrained the mass loss of the ionized component of the jet and found that close to the central source the majority of mass is lost through this component. Using lower angular resolution observations, I detected shock formations in the extended jet of DG Tau and modeled their evolution with time. Taking full advantage of the upgraded bandwidth on the VLA, I made wideband observations of two UCDs, TVLM513-46 and 2M 0746+20. Combining these observations with previously published and archival VLA observations I was able to fully characterize the spectral and temporal properties of the radio emission. I found that the emission is dominated by a mildly polarized, non-thermal quiescent component with periodic strongly polarized flare emission. The spectral energy distribution and polarization of the quiescent emission is well modeled using gyrosynchrotron emission with a mean field B ˜100 G, mildly relativistic power-law electrons with a density ne ˜ 105-6 cm-3, and source size of R ˜ 2R*. We were able to model the pulsed emission by coherent electron cyclotron radiation from a small number of isolated loops of high magnetic field (2-3 kG) with scale heights˜1.2-2.7 stellar radii. The loops are well-separated in magnetic longitude, and are not part of a single dipolar magnetosphere. The overall magnetic configuration of both stars appears to confirm recent suggestions that radio over-luminous UCD's have `weak field' non-axisymmetric topologies, but with isolated regions of high magnetic field.

Lynch, Christene Rene

188

Smallscale Solar Magnetic Fields - an Overview  

Microsoft Academic Search

An overview is given of the observational and the theoretical methods used to investigate solar magnetic fields. It includes an introduction to the Stokes parameters, their radiative transfer in the presence of a magnetic field, and empirical techniques used to measure various properties of solar magnetic features, such as the strength and direction of the magnetic field, magnetic flux, temperature,

Sami K. Solanki

1993-01-01

189

Far-Field Optical Nanoscopy  

NSDL National Science Digital Library

This article discusses the physical concepts that have pushed fluorescenesce microscopy to the nanoscale, once the prerogative of electron and scanning probe microscopes. Initial applications indicate that emergent far-field optical nanoscopy will have a strong impact in the life sciences and in other areas benefiting from nanoscale visualization.

Stefan Hell (Max Planck Institute for Biophysical Chemistry;Department of NanoBiophotonics)

2007-05-25

190

Observations of Mercury's magnetic field  

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

191

Cylindrical isentropic compression by ultrahigh magnetic field  

NASA Astrophysics Data System (ADS)

The cylindrical isentropic compression by ultrahigh magnetic field (MC-1) is a kind of unique high energy density technique. It has characters like ultrahigh pressure and low temperature rising, and would have widely used in areas like high pressure physics, new material synthesis and ultrahigh magnetic field physics. The Institute of Fluid Physics, Chinese Academy of Engineering Physics (IFP, CAEP) has begun the experiment since 2011 and a primary experimental device had been set-up. In the experiments, a seed magnetic field of 5 Tesla were set-up first and compressed by a stainless steel liner which is driven by high explosive initiated synchronously. The internal diameter of the liner is 97 mm, and its thickness is 1.5 mm. The movement of liner was recorded optically and a typical turnaround phenomenon was observed. From the photography results the liner was compressed smoothly and evenly and its average velocity was about 5-6 km/s. In the experiment a axial magnetic field of over 1400 Tesla has been recorded. The MC-1 process was numerical simulated by 1D MHD code MC11D and the simulations are in accord with the experiments.

Gu, Zhuowei; Luo, Hao; Zhang, Hengdi; Zhao, Shichao; Tang, Xiaosong; Tong, Yanjin; Song, Zhenfei; Tan, Fuli; Zhao, Jianheng; Sun, Chengwei

2014-05-01

192

Magnetic Field Structure in Relativistic Jets  

NASA Astrophysics Data System (ADS)

Relativistic jets are ubiquitous when considering an accreting black hole. Two of the most extreme examples of these systems are blazars and gamma-ray bursts (GRBs), the jets of which are thought to be threaded with a magnetic field of unknown structure. The systems are made up of a black hole accreting matter and producing, as a result, relativistic jets of plasma from the poles of the black hole. Both systems are viewed as point sources from Earth, making it impossible to spatially resolve the jet. In order to explore the structure of the magnetic field within the jet we take polarisation measurements with the RINGO polarimeters on the world's largest fully autonomous, robotic optical telescope: The Liverpool Telescope. Using the polarisation degree and angle measured by the RINGO polarimeters it is possible to distinguish between global magnetic fields created in the central engine and random tangled magnetic fields produced locally in shocks. We also monitor blazar sources regularly during quiescence with periods of flaring monitored more intensively. Reported here are the early polarisation results for GRBs 060418 and 090102, along with future prospects for the Liverpool Telescope and the RINGO polarimeters.

Jermak, Helen; Mundell, Carole; Steele, Iain; Harrison, Richard; Kobayashi, Shiho; Lindfors, Elina; Nilsson, Kari; Barres de Almeida, Ulisses

2013-12-01

193

Multi-purpose fiber optic sensors for high temperature superconducting magnets  

Microsoft Academic Search

Tokamak fusion reactors require the development of magnets capable of generating large magnetic fields under stringent structural constraints. Magnets made with high temperature superconductors (HTS) are well suited to this application, but are vulnerable to quench occurrence during operation. Temperature and strain sensors based on fiber optics are being developed as a first step to counter this contingency. Optical fibers

M. Turenne; R. Johnson; F. Hunte; J. Schwartz; H. Song

2009-01-01

194

Magnetic Forces and Field Line Density  

NSDL National Science Digital Library

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

195

Plasmon nanoparticle superlattices as optical-frequency magnetic metamaterials.  

PubMed

Nanocrystal superlattices have emerged as a new platform for bottom-up metamaterial design, but their optical properties are largely unknown. Here, we investigate their emergent optical properties using a generalized semi-analytic, full-field solver based on rigorous coupled wave analysis. Attention is given to superlattices composed of noble metal and dielectric nanoparticles in unary and binary arrays. By varying the nanoparticle size, shape, separation, and lattice geometry, we demonstrate the broad tunability of superlattice optical properties. Superlattices composed of spherical or octahedral nanoparticles in cubic and AB(2) arrays exhibit magnetic permeabilities tunable between 0.2 and 1.7, despite having non-magnetic constituents. The retrieved optical parameters are nearly polarization and angle-independent over a broad range of incident angles. Accordingly, nanocrystal superlattices behave as isotropic bulk metamaterials. Their tunable permittivities, permeabilities, and emergent magnetism may enable new, bottom-up metamaterials and negative index materials at visible frequencies. PMID:22772268

Alaeian, Hadiseh; Dionne, Jennifer A

2012-07-01

196

Long-Distance Transfer and Routing of Static Magnetic Fields  

NASA Astrophysics Data System (ADS)

We show how the static magnetic field of a finite source can be transferred and routed to arbitrary long distances. This is achieved by using transformation optics, which results in a device made of a material with a highly anisotropic magnetic permeability. We show that a simplified version of the device, made by a superconducting-ferromagnet hybrid, also leads to an excellent transfer of the magnetic field. The latter is demonstrated with a proof-of-principle experiment where a ferromagnet tube coated with a superconductor improves the transfer of static magnetic fields with respect to conventional methods by a 400% factor over distances of 14 cm.

Navau, C.; Prat-Camps, J.; Romero-Isart, O.; Cirac, J. I.; Sanchez, A.

2014-06-01

197

Circular polarization observations and magnetic fields of O stars  

NASA Astrophysics Data System (ADS)

The results of a search for line profile variability (LPV) and polarimetric line profile variability (pLPV) in spectra of O stars are reported. The observations were made with the 1.8-m telescope of the Korean Bohyunsan Optical Astronomical Observatory (BOAO) and the 1-m and 6-m telescopes of the Special Astrophysical Observatory (SAO), Russia. Regular LPV in the spectra of all program stars are found. We analyze the connection between the presence of magnetic field and nitrogen abundance anomalies, and the influence of weak magnetic fields on pLPV. The statistical properties of mean magnetic fields and magnetic fluxes of OB stars are studied.

Sudnik, Natallia P.; Kholtygin, Alexander F.

2012-05-01

198

Optical rectification in a strained GaAs{sub 0.9}P{sub 0.1}/GaAs{sub 0.6}P{sub 0.4} quantum dot: Simultaneous effects of electric and magnetic fields  

SciTech Connect

Simultaneous effects of electric field and magnetic field on exciton binding energy as a function of dot radius in a cylindrical GaAs{sub 0.9}P{sub 0.1}/GaAs{sub 0.6}P{sub 0.4} strained quantum dot are investigated. The strain contribution includes the strong built-in electric field induced by the spontaneous and piezoelectric polarizations. Numerical calculations are performed using variational procedure within the single band effective mass approximation. Optical rectification in the GaAs{sub 0.9}P{sub 0.1}/GaAs{sub 0.6}P{sub 0.4} quantum dot is computed in the presence of electric and magnetic fields.

Vinolin, Ada [Dept. of Physics, Madurai Kamaraj University College, Alagarkoil Road, Madurai-625002 (India); Peter, A. John, E-mail: a.john.peter@gmail.com [Dept. of Physics, Government Arts College, Melur-625106, Tamilnadu (India)

2014-04-24

199

Novel optical devices based on the tunable refractive index of magnetic fluid and their characteristics  

NASA Astrophysics Data System (ADS)

As a new type of functional material, magnetic fluid (MF) is a stable colloid of magnetic nanoparticles, dressed with surfactant and dispersed in the carrier liquid uniformly. The MF has many unique optical properties, and the most important one is its tunable refractive index property. This paper summarizes the properties of the MF refractive index and the related optical devices. The refractive index can be easily controlled by external magnetic field, temperature, and so on. But the tunable refractive index of MF has a relaxation effect. As a result, the response time is more than milliseconds and the MF is only suitable for low speed environment. Compared with the traditional optical devices, the magnetic fluid based optical devices have the tuning ability. Compared with the tunable optical devices (the electro-optic devices (LiNbO3) of more than 10 GHz modulation speed, acoustic-optic devices (Ge) of more than 20 MHz modulation speed), the speed of the magnetic fluid based optical devices is low. Now there are many applications of magnetic fluid based on the refractive index in the field of optical information communication and sensing technology, such as tunable beam splitter, optical-fiber modulator, tunable optical gratings, tunable optical filter, optical logic device, tunable interferometer, and electromagnetic sensor. With the development of the research and application of magnetic fluid,a new method, structure and material to improve the response time can be found, which will play an important role in the fields of optical information communication and sensing technology.

Zhao, Yong; Zhang, Yuyan; Lv, Riqing; Wang, Qi

2011-12-01

200

Photospheric and coronal magnetic fields  

SciTech Connect

Research on small-scale and large-scale photospheric and coronal magnetic fields during 1987-1990 is reviewed, focusing on observational studies. Particular attention is given to the new techniques, which include the correlation tracking of granules, the use of highly Zeeman-sensitive infrared spectral lines and multiple lines to deduce small-scale field strength, the application of long integration times coupled with good seeing conditions to study weak fields, and the use of high-resolution CCD detectors together with computer image-processing techniques to obtain images with unsurpassed spatial resolution. Synoptic observations of large-scale fields during the sunspot cycle are also discussed. 101 refs.

Sheeley, N.R., Jr. (USAF, Geophysics Laboratory, Hanscom AFB, MA (United States))

1991-01-01

201

Magnetic field sensor based on magnetic fluid clad etched fiber Bragg grating  

NASA Astrophysics Data System (ADS)

A novel fiber optical fiber-magnetic sensor based on magnetic fluid is proposed in this paper. The stable nanoparticles Fe 3O 4 magnetic fluid was synthesized firstly; the Fe 3O 4 magnetic fluid was injected in capillaries containing etched fiber Bragg grating (FBG) as sensing element. The reflected Bragg wavelength was changed by varying the magnetic field which is perpendicular to the axial of FBG. Experimental results show that the FBG with small diameter has more sensitive wavelength shift in magnetic field. When the magnetic field increases to 25 mT, the wavelength shift of the most sensitive FBG is 86 pm, and the etched FBG shows reversible response on magnetic fields under 16 mT.

Dai, Jixiang; Yang, Minghong; Li, Xiaobing; Liu, Hongliang; Tong, Xinglin

2011-05-01

202

Lanthanide doped nanoparticles as remote sensors for magnetic fields.  

PubMed

We report the effect of magnetic fields (MFs) on emission Eu-doped NaYF4 nanoparticles. A notable shift in the position of emission bands and the suppressed emission intensity are observed with the MF. These magnetic-optical interactions are explained in terms of the Zeeman effect, enhanced cross-relaxation rate and change of site symmetry. PMID:25123099

Chen, Ping; Zhang, Junpei; Xu, Beibei; Sang, Xiangwen; Chen, Weibo; Liu, Xiaofeng; Han, Junbo; Qiu, Jianrong

2014-10-01

203

Resonance Line Polarization for Arbitrary Magnetic Fields in Optically Thick Media - Part Two - Case of a Plane-Parallel Atmosphere and Absence of Zeeman Coherences  

NASA Astrophysics Data System (ADS)

The general problem of resonance scattering for a two-level atom in a magnetized plane-parallel atmosphere is formulated by using the irreducible tensor representation of the atomic density matrix. A more general formalism presented in a previous paper (Paper I), convenient for taking into account arbitrary magnetic field effects (Zeeman effect as well as Hanle effect), is particularized in the present paper to the case of a "strong" magnetic field (Zeeman splitting much larger than the natural width of the upper level), and to the case of a unidimensional medium. A system of coupled integral equations, relating the density matrix elements at different depths in the atmosphere, is derived, and the properties of the relative kernels are discussed. It is shown that, in the limiting case of weak magnetic fields (VL ? ??D), the presence of atomic polarization induces a breakdown in the usual formula V(?) = -g?L(dI/d?), that is commonly used for measuring magnetic fields from magnetograph-type observations.

Landi Degl'Innocenti, E.; Bommier, V.; Sahal-Brechot, S.

1991-04-01

204

High-Field Fractional Quantum Hall Effect in Optical Lattices  

SciTech Connect

We consider interacting bosonic atoms in an optical lattice subject to a large simulated magnetic field. We develop a model similar to a bilayer fractional quantum Hall system valid near simple rational numbers of magnetic flux quanta per lattice cell. Then we calculate its ground state, magnetic lengths, fractional fillings, and find unexpected sign changes in the Hall current. Finally we study methods for detecting these novel features via shot noise and Hall current measurements.

Palmer, R.N.; Jaksch, D. [Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom)

2006-05-12

205

EXPLORER 10 MAGNETIC FIELD MEASUREMENTS  

Microsoft Academic Search

Magnetic field measurements made by means of Explorer 10 over geocentric ; distances of 1.8 to 42.6R\\/sub e\\/ on March 25experiment on the same satellite are ; referenced in interpretations. The close-in data are consistent with the ; existence of a very weak ring current below 3R\\/sub e\\/ along the trajectory, but ; alternative explanations for the field deviations are

J. P. Heppner; N. F. Ness; C. S. Scearce; T. L. Skillman

1963-01-01

206

Realizing optical magnetism from dielectric metamaterials.  

PubMed

We demonstrate, for the first time, an all-dielectric metamaterial composite in the midinfrared based on micron-sized, high-index tellurium dielectric resonators. Dielectric resonators are desirable compared to conventional metallodielectric metamaterials at optical frequencies as they are largely angular invariant, free of Ohmic loss, and easily integrated into three-dimensional volumes. Measurements and simulation provide evidence of optical magnetism, which could be used for infrared magnetic mirrors, hard or soft surfaces, and subwavelength cavities. PMID:22463666

Ginn, James C; Brener, Igal; Peters, David W; Wendt, Joel R; Stevens, Jeffrey O; Hines, Paul F; Basilio, Lorena I; Warne, Larry K; Ihlefeld, Jon F; Clem, Paul G; Sinclair, Michael B

2012-03-01

207

Large-scale solar magnetic fields  

Microsoft Academic Search

Topics discussed in this review of large-scale solar magnetic fields include large-scale magnetic surface features, the solar activity cycle and the large-scale patterns, and magnetic fields in the corona. Features considered include the decay of active regions, the background field pattern, the polar fields, giant regular structures, expansion of the field in surface harmonics, and the average inclination of magnetic-field

R. Howard

1977-01-01

208

Magnetic Field - Stellar Winds Interaction  

NASA Astrophysics Data System (ADS)

As per the recent study by the MiMeS collaboration, only about 10% of massive stars possess organized global magnetic fields, typically dipolar in nature. The competition between such magnetic fields and highly non-linear radiative forces that drive the stellar winds leads to a highly complex interaction. Such an interplay can lead to a number of observable phenomena, e.g. X-ray, wind confinement, rapid stellar spindown. However, due to its complexity, such an interaction cannot usually be modeled analytically, instead numerical modeling becomes a necessary tool. In this talk, I will discuss how numerical magnetohydrodynamic (MHD) simulations are employed to understand the nature of such magnetized massive star winds.

ud-Doula, Asif

2015-01-01

209

Magnetic field satellite /MAGSAT/ spacecraft vector magnetometer calibration  

NASA Technical Reports Server (NTRS)

The low-flying MAGSAT spacecraft, launched October 30, 1979, included a Vector Magnetometer to accurately map the magnitude and direction of the magnetic field of the earth. Calibration of the magnetometer included arc-second precision determination of the relative orientations of the three sensor axes in a coordinate system defined by optical references. This determination began with laboratory measurements of the relative alignments of optical components mounted with the magnetometer. The actual calibration procedure then consisted basically of accurate and repeatable positioning of the Vector Magnetometer within a unique magnetic test facility which nulls the earth's magnetic field, then generates magnetic fields of various orientations and strengths. Analysis of the magnetometer sensor outputs together with the position and alignment data then gave the axes orientations. We used precision theodolites and methods related to surveying techniques to achieve the accurate positioning and optical component alignment measurements. The final calibration accuracy exceeded results previously achieved in the facility.

Hinkal, S. W.

1980-01-01

210

How to Draw Magnetic Fields - I  

NSDL National Science Digital Library

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

211

Crystal field and magnetic properties  

NASA Technical Reports Server (NTRS)

Magnetization and magnetic susceptibility measurements have been made in the temperature range 1.3 to 4.2 K on powdered samples of ErH3. The susceptibility exhibits Curie-Weiss behavior from 4.2 to 2 K, and intercepts the negative temperature axis at theta = 1.05 + or - 0.05 K, indicating that the material is antiferromagnetic. The low field effective moment is 6.77 + or - 0.27 Bohr magnetons per ion. The magnetization exhibits a temperature independent contribution, the slope of which is (5 + or - 1.2) x 10 to the -6th Weber m/kg Tesla. The saturation moment is 3.84 + or - 1 - 0.15 Bohr magnetons per ion. The results can be qualitatively explained by the effects of crystal fields on the magnetic ions. No definitive assignment of a crystal field ground state can be given, nor can a clear choice between cubically or hexagonally symmetric crystal fields be made. For hexagonal symmetry, the first excited state is estimated to be 86 to 100 K above the ground state. For cubic symmetry, the splitting is on the order of 160 to 180 K.

Flood, D. J.

1977-01-01

212

Studies of solar magnetic fields  

Microsoft Academic Search

The telescope, spectrograph, and magnetograph at the 150-ft Tower Telescope are described, and a chronology of changes in the instrumentation is given. The average magnetic field strengths over the last seven years are discussed. The changes in polarity at the poles of the Sun are described. The characteristics of these polarity reversals at both poles are similar. A reversal is

Robert Howard

1974-01-01

213

Vector magnetic fields of Solar Granulation  

E-print Network

Observations of quiet Sun from the Solar Optical Telescope/Spectro-Polarimeter (SOT/SP) aboard the Hinode spacecraft would reveal the magnetic characters of the solar photosphere. By making use of the deep mode observations of three quiet regions, we have statistically studied the vector magnetic fields of solar granulation. More than 2000 normal granules are manually selected to form a sample. It is recognized that some granules are even darker than the mean photosphere in intensity, and there is a linear correlation between intensity and Doppler velocity in granules. The distributions of longitudinal and transverse apparent magnetic flux densities, Doppler velocity and continuum intensity of granules are obtained, and their unsigned magnetic flux measured. Two approaches are carried out in this study. First we obtained the magnetic properties of granulation by averaging the measurements for all the sampling granules. Secondly, we reconstructed an average granular cell based on a sub-sample, and obtained the detailed distribution of apparent magnetic flux density within the model granular cell. All the results have been compared with that of inter-granular lanes and a few typical abnormal granules.

Chunlan Jin; Jingxiu Wang; Meng Zhao

2008-09-05

214

Modeling graphene: Magnetic, transport and optical properties  

NASA Astrophysics Data System (ADS)

Graphene, with its unique linear dispersion near the Fermi energy, has attracted great attention since its successful isolation from highly oriented pyrolytic graphite in 2004. Many important properties have been identified in graphene, including a remarkably high mobility at room temperature, an unusual quantum hall effect, and an ambipolar electric field effect. It has been proposed as a candidate for many applications, such as optical modulators, spintronic devices, and solar cells. Understanding the fundamental properties of graphene is therefore important. In this dissertation, I present a study of transport, magnetism and optical properties of graphene. In the first chapter, I introduce the electronic properties of mono layer and few layer graphene. In the second chapter, I present low temperature transport measurements in few layer graphene. An electric-field induced semimetal-to-metal transition is observed based on the temperature dependence of the resistance for different applied gate voltages. At small gate voltages the resistance decreases with increasing temperature due to the increase in carrier concentration resulting from thermal excitation of electron-hole pairs, as it is characteristic of a semimetal. At large gate, voltages excitations of electron-hole pairs are suppressed, and the resistance increases with increasing temperature because of the decrease in mean free path due to electron-phonon scattering, as is characteristic of a metal. The electron and hole mobilities are almost equal, so there is approximate electron-hole symmetry. The data are analyzed according to two different theoretical models for few-layer graphene. A simple two band (STB) model, two overlapping bands with quadratic energy-versus-momentum dispersion relations, is used to explain the experimental observations. The best fitting parameter for the overlap energy is found to be 16 meV. However, at low temperatures, the STB suggests that the conductivity is gate independent in the small gate voltage regime, which is not observed in the data. By considering frustration of the electronic potential due to impurities from the substrate, a Gaussian-distribution puddle model can successfully describe the observed transport behavior in the low temperature, small gate voltage regime. In the third chapter, I investigate the effects of point and line defects in monolayer graphene within the framework of the Hubbard model, using a self-consistent mean field theory. These defects are found to induce characteristic patterns into the electronic density of states and cause non-uniform distributions of magnetic moments in the vicinity of the impurity sites. Specifically, defect induced resonances in the local density of states are observed at energies close to the Dirac points. The magnitudes of the frequencies of these resonance states are shown to decrease with the strength of the scattering potential, whereas their amplitudes decay algebraically with increasing distance from the defect. For the case of defect clusters, we observe that with increasing defect cluster size the local magnetic moments in the vicinity of the cluster center are strongly enhanced. Furthermore, non-trivial impurity induced magnetic patterns are observed in the presence of line defects: zigzag line defects are found to introduce stronger-amplitude magnetic patterns than armchair line defects. When the scattering strength of these topological defects is increased, the induced patterns of magnetic moments become more strongly localized. In the fourth chapter, I theoretically study the electronic properties properties in graphene dots under mechanical deformation, using both tight binding lattice model and effective Dirac model. We observed an edge state, which is tunned by an effective quantum well originating from a strain-induced gauge field. Applying a uniaxial strain along the zigzag or armchair directions enhances or dampens the edge state due to the development of edge quantum wells. When an arc bending deformation is applied, the inner and outer edges of graphene dot

Chang, Yi Chen

215

Magnetic field of the Earth  

NASA Astrophysics Data System (ADS)

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

Popov, Aleksey

2013-04-01

216

Optically induced magnetic moments in symmetric graphene quantum dots  

NASA Astrophysics Data System (ADS)

Using the tight-binding model, we classify the eigenstates of symmetric graphene quantum dots based on their discrete rotational symmetry. In the presence of an external magnetic field, we identify a Zeeman-like behavior arising from the electronic orbital wave functions, with a constant g value for a variety of quantum dot shapes, sizes, and edge structures. The discrete rotational symmetry of the dots also leads to anomalous optical selection rules, thereby suggesting a way to optically induce a magnetic moment in these nanostructures.

Kavousanaki, Eleftheria G.; Dani, Keshav M.

2015-01-01

217

Frustrated magnetic vortices in a triad of permalloy rings: Magneto-optical Kerr effect, magnetic force microscopy, and micromagnetic simulations  

Microsoft Academic Search

The field dependent magnetization of three mutually touching permalloy rings were investigated by means of the magneto-optical Kerr effect, magnetic force microscopy, and micromagnetic simulations. Each ring has a width of 0.2-1.8mum , an outer diameter of 4mum , and a thickness of 17nm . Decreasing an applied magnetic field from saturation leads to the nucleation and annihilation of magnetic

V. Rose; K. Buchanan; S.-H. Chung; M. Grimsditch; V. Metlushko; A. Hoffmann; V. Novosad; S. D. Bader; H. Ibach

2006-01-01

218

On the relation between photospheric flow fields and the magnetic field distribution on the solar surface  

NASA Technical Reports Server (NTRS)

Using the technique of local correlation tracking on a 28 minute time sequence of white-light images of solar granulation, the horizontal flow field on the solar surface is measured. The time series was obtained by the Solar Optical Universal Polarimeter (SOUP) on Spacelab 2 (Space Shuttle flight 51-F) and is free from atmospheric blurring and distortion. The SOUP flow fields have been compared with carefully aligned magnetograms taken over a nine hour period at the Big Bear Solar Observatory before, during, and after the SOUP images. The flow field and the magnetic field agree in considerable detail: vectors which define the flow of the white-light intensity pattern (granulation) point toward magnetic field regions, magnetic fields surround flow cells, and magnetic features move along the flow arrows. The projected locations of free particles ('corks') in the measured flow field congregate at the same locations where the magnetic field is observed.

Simon, George W.; Title, A. M.; Topka, K. P.; Tarbell, T. D.; Shine, R. A.

1988-01-01

219

Ultrahigh sensitivity magnetic field and magnetization measurements with an atomic magnetometer  

E-print Network

Ultrahigh sensitivity magnetic field and magnetization measurements with an atomic magnetometer H an ultrasensitive atomic magnetometer based on optically pumped potassium atoms operating in a spin . As an example of an application enabled by such a magnetometer, we describe measurements of weak remnant rock

Romalis, Mike

220

Brass plasmoid in external magnetic field at different air pressures  

NASA Astrophysics Data System (ADS)

The behavior of expanding brass plasmoid generated by 266 nm wavelength of Nd:YAG laser in nonuniform magnetic field at different air pressures has been examined using optical emission spectroscopy and fast imaging of plasma plumes. The splitting of the plasma plumes and enhancement of intensity of Cu I at 510.5 nm in the presence of magnetic field at lower pressures are discussed. The threading and expulsion of the magnetic field lines through the plasmoid are correlated with the ambient pressure. The stoichiometry of the plasma plume is not significantly influenced by the magnetic field; however, the abundance of neutral to ionic species of Cu and Zn is greatly influenced by the magnetic field.

Patel, D. N.; Pandey, Pramod K.; Thareja, Raj K.

2013-10-01

221

Field errors in superconducting magnets  

SciTech Connect

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

Barton, M.Q.

1982-01-01

222

Development Trends in High Field Magnet Technology  

Microsoft Academic Search

The production of high magnetic fields using low temperature superconductors (LTS) has become common place. However, large magnet sizes and associated high cooling costs have often precluded the full utilization of these research capabilities. Recent advances in internal Sn superconductors and cryogen free technology have opened up a new era in superconducting magnet development. Ultra-compact, laboratory sized magnets producing fields

R. Harrison; R. Bateman; J. Brown; F. Domptail; C. M. Friend; P. Ghoshal; C. King; A. Van der Linden; Z. Melhem; P. Noonan; A. Twin; M. Field; S. Hong; J. Parrell; Y. Zhang

2008-01-01

223

Variability in Martian Magnetic Field Topology  

NASA Astrophysics Data System (ADS)

We have determined the locations of open and closed magnetic field lines at Mars as a function of four different controlling influences: solar wind magnetic field direction, solar wind pressure, martian season, and solar EUV flux.

Brain, D. A.; Halekas, J. S.; Eastwood, J. P.; Ulusen, D.; Lillis, R. J.

2014-07-01

224

Plasma stability in a dipole magnetic field  

E-print Network

The MHD and kinetic stability of an axially symmetric plasma, confined by a poloidal magnetic field with closed lines, is considered. In such a system the stabilizing effects of plasma compression and magnetic field ...

Simakov, Andrei N., 1974-

2001-01-01

225

Measurements of Solar Vector Magnetic Fields  

NASA Technical Reports Server (NTRS)

Various aspects of the measurement of solar magnetic fields are presented. The four major subdivisions of the study are: (1) theoretical understanding of solar vector magnetic fields; (3) techniques for interpretation of observational data; and (4) techniques for data display.

Hagyard, M. J. (editor)

1985-01-01

226

Polymeric variable optical attenuators based on magnetic sensitive stimuli materials  

NASA Astrophysics Data System (ADS)

Magnetically-actuable, polymer-based variable optical attenuators (VOA) are presented in this paper. The design comprises a cantilever which also plays the role of a waveguide and the input/output alignment elements for simple alignment, yet still rendering an efficient coupling. Magnetic properties have been conferred to these micro-opto-electromechanical systems (MOEMS) by implementing two different strategies: in the first case, a magnetic sensitive stimuli material (M-SSM) is obtained by a combination of polydimethylsiloxane (PDMS) and ferrofluid (FF) in ratios between 14.9?wt % and 29.9?wt %. An M-SSM strip under the waveguide-cantilever, defined with soft lithography (SLT), provides the required actuation capability. In the second case, specific volumes of FF are dispensed at the end of the cantilever tip (outside the waveguide) by means of inkjet printing (IJP), obtaining the required magnetic response while holding the optical transparency of the waveguide-cantilever. In the absence of a magnetic field, the waveguide-cantilever is aligned with the output fiber optics and thus the intrinsic optical losses can be obtained. Numerical simulations, validated experimentally, have shown that, for any cantilever length, the VOAs defined by IJP present lower intrinsic optical losses than their SLT counterparts. Under an applied magnetic field (Bapp), both VOA configurations experience a misalignment between the waveguide-cantilever and the output fiber optics. Thus, the proposed VOAs modulate the output power as a function of the cantilever displacement, which is proportional to Bapp. The experimental results for the three different waveguide-cantilever lengths and six different FF concentrations (three per technology) show maximum deflections of 220?µm at 29.9?wt % of FF for VOASLT and 250?µm at 22.3?wt % FF for VOAIJP, at 0.57?kG for both. These deflections provide maximum actuation losses of 16.1?dB and 18.9?dB for the VOASLT and VOAIJP, respectively.

de Pedro, S.; Cadarso, V. J.; Ackermann, T. N.; Muñoz-Berbel, X.; Plaza, J. A.; Brugger, J.; Büttgenbach, S.; Llobera, A.

2014-12-01

227

Topological constraints in magnetic field relaxation  

NASA Astrophysics Data System (ADS)

Stability and reconnection of magnetic fields play a fundamental role in natural and manmade plasma. In these applications the field's topology determines the stability of the magnetic field. Here I will describe the importance of one topology quantifier, the magnetic helicity, which impedes any free decay of the magnetic energy. Further constraints come from the fixed point index which hinders the field to relax into the Taylor state.

Candelaresi, S.

2014-10-01

228

Magneto-optical properties of a highly transparent cadmium ferrite-based magnetic fluid  

Microsoft Academic Search

The magneto-optical properties of a highly stable ionic magnetic fluid sample containing CdFe2O4 nanoparticles were investigated using static magnetic birefringence, zero-field optical transmissivity, and transmission electron microscopy. From our measurements we found that the transmittivity and the birefringence of the CdFe2O4-based sample is several times greater than a typical magnetic fluid sample (?-Fe2O3 based), giving this magnetic material great potential

A. F. Bakuzis; K. Skeff Neto; P. P. Gravina; L. C. Figueiredo; P. C. Morais; L. P. Silva; R. B. Azevedo; O. Silva

2004-01-01

229

Magneto-optical properties of a highly transparent cadmium ferrite-based magnetic fluid  

Microsoft Academic Search

The magneto-optical properties of a highly stable ionic magnetic fluid sample containing CdFe2O4 nanoparticles were investigated using static magnetic birefringence, zero-field optical transmissivity, and transmission electron microscopy. From our measurements we found that the transmittivity and the birefringence of the CdFe2O4-based sample is several times greater than a typical magnetic fluid sample (gamma-Fe2O3 based), giving this magnetic material great potential

A. F. Bakuzis; K. Skeff Neto; P. P. Gravina; L. C. Figueiredo; P. C. Morais; L. P. Silva; R. B. Azevedo; O. Silva

2004-01-01

230

Anomalous global strings and primordial magnetic fields  

SciTech Connect

We propose a new mechanism for the generation of primordial magnetic fields, making use of the magnetic fields which are induced by anomalous global strings, such as pion and axion strings, which couple to electromagnetism via Wess-Zumino type interactions. We calculate the magnitude and coherence length of these fields. They are seen to depend on the string dynamics. With optimistic assumptions, both the magnitude and coherence scale of the induced magnetic fields can be large enough to explain the seed magnetic fields of greater than 10{sup {minus}23} G necessary to produce the observed galactic magnetic fields via the galactic dynamo mechanism. {copyright} {ital 1999} {ital The American Physical Society}

Brandenberger, R.H. [Department of Physics, Brown University, Providence, Rhode Island 02912 (United States)] [Department of Physics, Brown University, Providence, Rhode Island 02912 (United States); Zhang, X. [CCAST (World Laboratory), P.O. Box 8730, Beijing 100080, Peoples Republic of (China)] [CCAST (World Laboratory), P.O. Box 8730, Beijing 100080, Peoples Republic of (China); [Institute of High Energy Physics, Academia Sinica, Beijing 100039, Peoples Republic of (China)

1999-04-01

231

Applied Magnetic Field Enhances Arc Vapor Deposition  

NASA Technical Reports Server (NTRS)

Applied magnetic field enhances performance of vaporization part of arc vapor deposition apparatus. When no magnetic field applied by external means, arc wonders semirandomly over cathode, with net motion toward electrical feedthrough. When magnetic field applied arc moves circumferentially around cathode, and downward motion suppressed.

Miller, T. A.; Loutfy, R. O.; Withers, J. C.

1993-01-01

232

Mars: a magnetic field due to thermoremanence?  

Microsoft Academic Search

Presently available magnetic field data suggest a dipole moment of Mars of less than 10?4 times the Earth's dipole moment. Presumably, Mars does not have an active dynamo at present which could give rise to a significant magnetic field. Nevertheless, the presently available data do not rule out a minor intrinsic field which may originate from a magnetized lithosphere. The

Martin Leweling; Tilman Spohn

1997-01-01

233

MAXWELLIAN FIELD EXPANSION OF HELICAL MAGNET  

Microsoft Academic Search

Three dimensional (3D) magnetic field calculated by the computer code TOSCA was analyzed including the fring- ing field region. The magnetic field in the median plane was well simulated by a simple function. Off median plane, contributions from the coils should be taken into account. Superconducting helical dipole magnets will be used in RHIC as Siberian snakes and rotators(1). Extensive

K. Hatanaka; T. Katayama; T. Tominaka

1998-01-01

234

Prediction of the interplanetary magnetic field strength  

Microsoft Academic Search

A new model of the coronal and interplanetary magnetic field can predict both the interplanetary magnetic field strength and its polarity from measurements of the photospheric magnetic field. The model includes the effects of the large-scale horizontal electric currents flowing in the inner corona, of the warped heliospheric current sheet in the upper corona, and of volume currents flowing in

Xuepu Zhao; J. Todd Hoeksema

1995-01-01

235

CORONAL MAGNETIC FIELD MEASUREMENTS THROUGH GYRORESONANCE EMISSION  

E-print Network

observations have provided a direct measurement of magnetic field strengths in the solar corona. It is a happy probes of the magnetic field strength above active regions, and this unique capability is one to a different magnetic field strength, the coronal structure can be "peeled away" by using different frequencies

White, Stephen

236

Elliptic-symmetry vector optical fields.  

PubMed

We present in principle and demonstrate experimentally a new kind of vector fields: elliptic-symmetry vector optical fields. This is a significant development in vector fields, as this breaks the cylindrical symmetry and enriches the family of vector fields. Due to the presence of an additional degrees of freedom, which is the interval between the foci in the elliptic coordinate system, the elliptic-symmetry vector fields are more flexible than the cylindrical vector fields for controlling the spatial structure of polarization and for engineering the focusing fields. The elliptic-symmetry vector fields can find many specific applications from optical trapping to optical machining and so on. PMID:25321015

Pan, Yue; Li, Yongnan; Li, Si-Min; Ren, Zhi-Cheng; Kong, Ling-Jun; Tu, Chenghou; Wang, Hui-Tian

2014-08-11

237

Magnetic monopole and the nature of the static magnetic field  

E-print Network

We investigate the factuality of the hypothetical magnetic monopole and the nature of the static magnetic field. It is shown from many aspects that the concept of the massive magnetic monopoles clearly is physically untrue. We argue that the static magnetic field of a bar magnet, in fact, is the static electric field of the periodically quasi-one-dimensional electric-dipole superlattice, which can be well established in some transition metals with the localized d-electron. This research may shed light on the perfect unification of magnetic and electrical phenomena.

Xiuqing Huang

2008-12-10

238

Magnetic field sources and their threat to magnetic media  

NASA Technical Reports Server (NTRS)

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.

Jewell, Steve

1993-01-01

239

Thinned fiber Bragg grating magnetic field sensor with magnetic fluid  

Microsoft Academic Search

The refractive index of magnetic fluid may be changed by external magnetic field. Therefore, through measuring its refractive index, the intensity of the magnetic field can be obtained. Fiber Bragg grating (FBG) is sensitive to the refractive index surrounding its cladding when the diameter of cladding is reduced to a certain degree. In order to prove the sensitivity of the

Ciming Zhou; Li Ding; Dongli Wang; Yaqi Kuang; Desheng Jiang

2011-01-01

240

Harmonic undulator radiations with constant magnetic field  

NASA Astrophysics Data System (ADS)

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

Jeevakhan, Hussain; Mishra, G.

2015-01-01

241

Magneto-optical properties of a highly transparent cadmium ferrite-based magnetic fluid  

NASA Astrophysics Data System (ADS)

The magneto-optical properties of a highly stable ionic magnetic fluid sample containing CdFe2O4 nanoparticles were investigated using static magnetic birefringence, zero-field optical transmissivity, and transmission electron microscopy. From our measurements we found that the transmittivity and the birefringence of the CdFe2O4-based sample is several times greater than a typical magnetic fluid sample (?-Fe2O3 based), giving this magnetic material great potential for magneto-optics applications. We also found that the birefringence can be increased by several orders of magnitude, allowing full manipulation of the observed negative differential transmitted optical intensity feature.

Bakuzis, A. F.; Skeff Neto, K.; Gravina, P. P.; Figueiredo, L. C.; Morais, P. C.; Silva, L. P.; Azevedo, R. B.; Silva, O.

2004-03-01

242

Measurement of g-factors of ground and excited optical states of Er3+ in YLiF4 and LuLiF4 in zero dc magnetic field by photon echo method  

E-print Network

New scheme of definition of g-factors as ground as excited optical states of a paramagnetic ion in zero external constant magnetic field has been proposed and experimentally realized in optical systems in which Zeeman Effect is manifested. A pulse of a weak magnetic field leads to occurrence of relative phase shifts of the excited dipoles and, as consequence, to modulation of a photon echo waveform if magnetic pulse (MP) overlaps in time with echo-pulse. The modulation periods of the waveform depend on polarization of the laser light, which excites the photon echo. The values of these periods for {\\sigma}- and {\\pi}- laser light polarization have been measured and then the g-factors of the ground 4I15/2 and excited 4F9/2 states of the Er3+ ion in the LuLiF4 and the YLiF4 matrices have been determined. Values of the g-factors have been compared with the known literary data.

Lisin, V N; Samartsev, V V

2014-01-01

243

Features of the Martian Magnetic Field Structure  

Microsoft Academic Search

Based on the single-fluid MHD model of Mars space simulation, this paper has studied the magnetic field structure in the near-Mars space and investigated the influence of Martian crustal magnetic anomalies on the magnetic field structure. In the process of the solar wind interaction with Mars, the bow shock and magnetic pile-up region are produced. The interplanetary magnetic lines are

Yi-Teng Zhang; Lei Li

2009-01-01

244

How to Draw Magnetic Fields - II  

NSDL National Science Digital Library

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

245

Magnetic field structure around cores with very low luminosity objects  

NASA Astrophysics Data System (ADS)

Aims: We carried out optical polarimetry of five dense cores, (IRAM 04191, L1521F, L328, L673-7, and L1014) which are found to harbour very low luminosity objects (VeLLOs; Lint ? 0.1 L?). This study was conducted mainly to understand the role played by the magnetic field in the formation of very low and substellar mass range objects. Methods: Light from the stars, while passing through the dust grains that are aligned with their short axis parallel to an external magnetic field, becomes linearly polarised. The polarisation position angles measured for the stars can provide the plane-of-the sky magnetic field orientation. Because the light in the optical wavelength range is most efficiently polarised by the dust grains typically found at the outer layers of the molecular clouds, optical polarimetry mostly traces the magnetic field orientation of the core envelope. Results: The polarisation observations of stars projected on IRAM 04191, L328, L673-7, and L1014 were obtained in the R-band and those of L1521F were obtained in the V-band. The angular offsets between the envelope magnetic field direction (inferred from optical polarisation measurements) and the outflow position angles from the VeLLOs in IRAM 04191, L1521F, L328, L673-7, and L1014 are found to be 84°, 53°, 24°, 08°, and 15°, respectively. The mean value of the offsets for all the five clouds is ~ 37°. If we exclude IRAM 04191, the mean value reduces to become ~ 25°. In IRAM 04191, the offset between the projected envelope and the inner magnetic field (inferred from the submillimetre data obtained using SCUBA-POL) is found to be ~ 68°. The inner magnetic field, however, is found to be nearly aligned with the projected position angles of the minor axis, the rotation axis of the cloud, and the outflow from the IRAM 04191-IRS. We discuss a possible explanation for the nearly perpendicular orientation between the envelope and core scale magnetic fields in IRAM 04191. The angular offset between the envelope magnetic field direction and the minor axis of IRAM 04191, L1521F, L673-7, and L1014 are 82°, 60°, 47°, and 55°, respectively. The mean value of the offsets between the envelope magnetic field and the minor axis position angles for the four cores is found to be ~ 60°. Conclusions: The results obtained from our study on the limited sample of five cores with VeLLOs show that the outflows in three of them tend to nearly align with the envelope magnetic field. Table 4 is available in electronic form at http://www.aanda.org

Soam, A.; Maheswar, G.; Lee, Chang Won; Dib, Sami; Bhatt, H. C.; Tamura, Motohide; Kim, Gwanjeong

2015-01-01

246

Optical Potential Field Mapping System  

NASA Technical Reports Server (NTRS)

The present invention relates to an optical system for creating a potential field map of a bounded two dimensional region containing a goal location and an arbitrary number of obstacles. The potential field mapping system has an imaging device and a processor. Two image writing modes are used by the imaging device, electron deposition and electron depletion. Patterns written in electron deposition mode appear black and expand. Patterns written in electron depletion mode are sharp and appear white. The generated image represents a robot's workspace. The imaging device under processor control then writes a goal location in the work-space using the electron deposition mode. The black image of the goal expands in the workspace. The processor stores the generated images, and uses them to generate a feedback pattern. The feedback pattern is written in the workspace by the imaging device in the electron deposition mode to enhance the expansion of the original goal pattern. After the feedback pattern is written, an obstacle pattern is written by the imaging device in the electron depletion mode to represent the obstacles in the robot's workspace. The processor compares a stored image to a previously stored image to determine a change therebetween. When no change occurs, the processor averages the stored images to produce the potential field map.

Reid, Max B. (Inventor)

1996-01-01

247

Permanent Magnet Ecr Plasma Source With Magnetic Field Optimization  

DOEpatents

In a plasma-producing device, an optimized magnet field for electron cyclotron resonance plasma generation is provided by a shaped pole piece. The shaped pole piece adjusts spacing between the magnet and the resonance zone, creates a convex or concave resonance zone, and decreases stray fields between the resonance zone and the workpiece. For a cylindrical permanent magnet, the pole piece includes a disk adjacent the magnet together with an annular cylindrical sidewall structure axially aligned with the magnet and extending from the base around the permanent magnet. The pole piece directs magnetic field lines into the resonance zone, moving the resonance zone further from the face of the magnet. Additional permanent magnets or magnet arrays may be utilized to control field contours on a local scale. Rather than a permeable material, the sidewall structure may be composed of an annular cylindrical magnetic material having a polarity opposite that of the permanent magnet, creating convex regions in the resonance zone. An annular disk-shaped recurve section at the end of the sidewall structure forms magnetic mirrors keeping the plasma off the pole piece. A recurve section composed of magnetic material having a radial polarity forms convex regions and/or magnetic mirrors within the resonance zone.

Doughty, Frank C. (Plano, TX); Spencer, John E. (Plano, TX)

2000-12-19

248

Quantum simulation of frustrated magnetism in triangular optical lattices  

E-print Network

Magnetism plays a key role in modern technology as essential building block of many devices used in daily life. Rich future prospects connected to spintronics, next generation storage devices or superconductivity make it a highly dynamical field of research. Despite those ongoing efforts, the many-body dynamics of complex magnetism is far from being well understood on a fundamental level. Especially the study of geometrically frustrated configurations is challenging both theoretically and experimentally. Here we present the first realization of a large scale quantum simulator for magnetism including frustration. We use the motional degrees of freedom of atoms to comprehensively simulate a magnetic system in a triangular lattice. Via a specific modulation of the optical lattice, we can tune the couplings in different directions independently, even from ferromagnetic to antiferromagnetic. A major advantage of our approach is that standard Bose-Einstein-condensate temperatures are sufficient to observe magnetic ...

Struck, Julian; Targat, Rodolphe Le; Soltan-Panahi, Parvis; Eckardt, André; Lewenstein, Maciej; Windpassinger, Patrick; Sengstock, Klaus

2011-01-01

249

Vlasov Equation In Magnetic Field  

E-print Network

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.

Biao Wu

1999-09-07

250

An analytic solar magnetic field model  

Microsoft Academic Search

We describe a simple analytic model for the magnetic field in the solar corona and interplanetary space which is appropriate to solar minimum conditions. The model combines an azimuthal current sheet in the equatorial plane with an axisymmetric multipole field representing the internal magnetic field of the Sun. The radial component of the field filling interplanetary space is approximately monopolar

M. Banaszkiewicz; W. I. Axford; J. F. McKenzie

1998-01-01

251

On the origin of solar magnetic fields  

Microsoft Academic Search

A fresh approach to the theoretical problems raised by observations of solar magnetic fields is outlined. Tentative conclusions are made that the large-scale magnetic field from which Cowling's (1953) hypothetical toroidal field is generated by differential rotation is not itself regenerated by diffusive processes in the sun's outer layers and that this field enters the differentially rotating layer from below

D. Layzer; R. Rosner; H. T. Doyle

1979-01-01

252

Resonance line polarization for arbitrary magnetic fields in optically thick media. 3: A generalization of the sqaure root of epsilon-law  

NASA Astrophysics Data System (ADS)

The well-known 'square root of epsilon-law' -- one of the few exact analytical results in the theory of radiative transfer -- is generalized to the case of an isothermal, plane-parallel atmopshere in the presence of a magnetic field vector of arbitrary intensity and direction and in the presence of depolarizing collisions. A compact expression is found, relating the squares of the surface value of the upper level components of the atomic density matrix in the representation of the irreducible spherical tensors to the value of the constant Planck function. By taking the appropriate limits, the usual square root of epsilon-law for unpolarized radiation, and its generalization to resonance scattering polarization in a non-magnetic atmosphere (Ivanov 1990), are recovered as particular cases.

Landi Degl'Innocenti, E.; Bommier, V.

1994-04-01

253

Magnetic field effects on microwave absorbing materials  

NASA Technical Reports Server (NTRS)

The objective of this program was to gather information to formulate a microwave absorber that can work in the presence of strong constant direct current (DC) magnetic fields. The program was conducted in four steps. The first step was to investigate the electrical and magnetic properties of magnetic and ferrite microwave absorbers in the presence of strong magnetic fields. This included both experimental measurements and a literature survey of properties that may be applicable to finding an appropriate absorbing material. The second step was to identify those material properties that will produce desirable absorptive properties in the presence of intense magnetic fields and determine the range of magnetic field in which the absorbers remain effective. The third step was to establish ferrite absorber designs that will produce low reflection and adequate absorption in the presence of intense inhomogeneous static magnetic fields. The fourth and final step was to prepare and test samples of such magnetic microwave absorbers if such designs seem practical.

Goldberg, Ira; Hollingsworth, Charles S.; Mckinney, Ted M.

1991-01-01

254

Full 180° magnetization reversal with electric fields.  

PubMed

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

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

2014-01-01

255

Full 180° Magnetization Reversal with Electric Fields  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

256

Full 180° Magnetization Reversal with Electric Fields  

PubMed Central

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

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

2014-01-01

257

Sub arcsec evolution of solar magnetic fields  

Microsoft Academic Search

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

Th. Roudier; J. M. Malherbe; J. Moity; S. Rondi; P. Mein; Ch. Coutard

2006-01-01

258

Exploring Magnetic Fields with a Compass  

ERIC Educational Resources Information Center

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

Lunk, Brandon; Beichner, Robert

2011-01-01

259

Discovery of Magnetic Fields in CPNs  

NASA Astrophysics Data System (ADS)

For the first time we have directly detected magnetic fields in central stars of planetary nebulae by means of spectro-polarimetry with FORS1 at the VLT. In all four objects of our sample we found kilogauss magnetic fields, in NGC 1360 and LSS 1362 with very high significance, while in Abell 36 and EGB 5 the existence of a magnetic field is probable but with less certainty. This discovery supports the hypothesis that the non-spherical symmetry of most planetary nebulae is caused by magnetic fields in AGB stars. Our high discovery rate demands mechanisms to prevent full conservation of magnetic flux during the transition to white dwarfs.

Jordan, S.; Werner, K.; O'Toole, S. J.

2005-07-01

260

Neutrino Conversions in Solar Random Magnetic Fields  

E-print Network

We consider the effect of a random magnetic field in the convective zone of the Sun superimposed to a regular magnetic field on resonant neutrino spin-flavour oscillations. We argue for the existence of a field of strongly chaotic nature at the bottom of the convective zone. In contrast to previous attempts we employ in addition a model motivated regular twisting magnetic field profile. In this scenario electron antineutrinos are produced through cascades like $\

V. B Semikoz; E. Torrente-Lujan

1998-09-16

261

Differential rotation of solar magnetic fields  

Microsoft Academic Search

The connection of the differential rotation of solar magnetic fields with the field sign and strength is studied. The synoptic\\u000a maps of magnetic fields over the last three solar cycles taken at the Kitt Peak Observatory served as input data for the study.\\u000a The algorithm of magnetic field filtering over 14 chosen strengt intervals and successive 5-degree latitude zones was

O. A. Andreyeva; Ya. I. Zyelyk; N. N. Stepanian

2008-01-01

262

Lanthanide doped nanoparticles as remote sensors for magnetic fields  

NASA Astrophysics Data System (ADS)

We report the effect of magnetic fields (MFs) on emission Eu-doped NaYF4 nanoparticles. A notable shift in the position of emission bands and the suppressed emission intensity are observed with the MF. These magnetic-optical interactions are explained in terms of the Zeeman effect, enhanced cross-relaxation rate and change of site symmetry.We report the effect of magnetic fields (MFs) on emission Eu-doped NaYF4 nanoparticles. A notable shift in the position of emission bands and the suppressed emission intensity are observed with the MF. These magnetic-optical interactions are explained in terms of the Zeeman effect, enhanced cross-relaxation rate and change of site symmetry. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr02983f

Chen, Ping; Zhang, Junpei; Xu, Beibei; Sang, Xiangwen; Chen, Weibo; Liu, Xiaofeng; Han, Junbo; Qiu, Jianrong

2014-09-01

263

Magnetic field waves at Uranus  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

264

Electric-field control of magnetic domain wall motion and local magnetization reversal  

PubMed Central

Spintronic devices currently rely on magnetic switching or controlled motion of domain walls by an external magnetic field or spin-polarized current. Achieving the same degree of magnetic controllability using an electric field has potential advantages including enhanced functionality and low power consumption. Here we report on an approach to electrically control local magnetic properties, including the writing and erasure of regular ferromagnetic domain patterns and the motion of magnetic domain walls, in CoFe-BaTiO3 heterostructures. Our method is based on recurrent strain transfer from ferroelastic domains in ferroelectric media to continuous magnetostrictive films with negligible magnetocrystalline anisotropy. Optical polarization microscopy of both ferromagnetic and ferroelectric domain structures reveals that domain correlations and strong inter-ferroic domain wall pinning persist in an applied electric field. This leads to an unprecedented electric controllability over the ferromagnetic microstructure, an accomplishment that produces giant magnetoelectric coupling effects and opens the way to electric-field driven spintronics. PMID:22355770

Lahtinen, Tuomas H. E.; Franke, Kévin J. A.; van Dijken, Sebastiaan

2012-01-01

265

Bipolar pulse field for magnetic refrigeration  

DOEpatents

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

Lubell, Martin S. (Oak Ridge, TN)

1994-01-01

266

Polar magnetic field reversals on the Sun  

NASA Astrophysics Data System (ADS)

The polar magnetic fields on the Sun have been an attractive subject for solar researches since Babcock measured them in solar cycle 19. One of the remarkable features of the polar magnetic fields is their reversal during the maxima of 11-year sunspot cycles. I have present results of the investigations of the polar magnetic field using SOHO-mdi data. It is found, that the polar magnetic field reversal is detected with mdi data for polar region within 78° 88°. The North Pole has changed polarity in CR1975 (April 2001). The South reversed later in CR1980 (September 2001). The total unsigned magnetic flux does not show the dramatic decreasing during the polar reversals due to omnipresent bi-polar small-scale magnetic elements. The observational and theoretical aspects of the polar magnetic field reversals are discussed.

Benevolenskaya, Elena E.

2007-08-01

267

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.

268

Ultrafast spectroscopy for optically and magnetically active materials  

Microsoft Academic Search

The past few years have witnessed considerable progress in understanding ultrafast relaxational processes in solids. Low-dimensional semiconductors, metallic nanoparticles, magnetic semiconductors and high-temperature superconductors have featured strongly in this work. One of the most significant new technical developments in this area is time-resolved near-field optical spectroscopy, which permits individual nanostructure and spatially resolved dynamics to be probed.

John F Ryan

1998-01-01

269

Measuring Magnetic Fields in Ultracool Stars and Brown Dwarfs  

Microsoft Academic Search

We present a new method for direct measurement of magnetic fields on ultracool stars and brown dwarfs. It takes advantage of the Wing-Ford bands of FeH, which are seen throughout the M and L spectral types. These molecular features are not as blended as other optical molecular bands, are reasonably strong through most of the spectral range, and exhibit a

Ansgar Reiners; Gibor Basri

2006-01-01

270

Magnetic field satellite \\/MAGSAT\\/ spacecraft vector magnetometer calibration  

Microsoft Academic Search

The low-flying MAGSAT spacecraft, launched October 30, 1979, included a Vector Magnetometer to accurately map the magnitude and direction of the magnetic field of the earth. Calibration of the magnetometer included arc-second precision determination of the relative orientations of the three sensor axes in a coordinate system defined by optical references. This determination began with laboratory measurements of the relative

S. W. Hinkal

1980-01-01

271

Cosmological Magnetic Fields and CMBR Polarization  

E-print Network

A simple introduction to physics of CMBR polarization and the Faraday rotation of the latter in cosmic magnetic field is presented. The content of the lecture is the following: 1. Description of polarization of photons. 2. Polarization field of CMBR. 3. Faraday effect. 4. Cosmic magnetic fields. 5. Faraday rotation of CMBR polarization.

A. D. Dolgov

2005-03-21

272

Representation of magnetic fields in space  

NASA Technical Reports Server (NTRS)

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

Stern, D. P.

1975-01-01

273

Fiber Bragg Grating Magnetic Field Sensor  

Microsoft Academic Search

In this paper we demonstrate experimentally a magnetic field sensor using a fiber Bragg grating. The shift in the Bragg condition as a result of strain applied on the fiber mounted on a nickel base by the magnetic field gives an indirect measure of the field. The proposed method overcomes the need for long fiber lengths required in methods such

K. V. Madhav; K. Ravi Kumar; T. Srinivas; S. Asokan

2006-01-01

274

Optically induced magnetic polarons in EuTe  

SciTech Connect

Direct measurements of the photoinduced magnetization in EuTe, using a two color pump-and-probe technique, are presented. The photoinduced effect was pumped using photons of above-the-bandgap energy, and detected by the Faraday rotation of a probe beam of energy below-the-bandgap. The photoinduced Faraday rotation changes sign, as expected from our model for the optically induced magnetic polaron. The EuTe spin-flop transition at low fields is also detected as a sharp step in the photoinduced Faraday rotation, and its observation provides additional supports for the photoinduced polaron model.

Henriques, A. B.; Galgano, G. D. [Instituto de Física, Universidade de São Paulo, Caixa Postal 66318, 05315-970, São Paulo (Brazil); Abramof, E.; Rappl, P. H. O. [LAS - INPE, Av. Dos Astronautas, 1758, 12227-010, São José dos Campos (Brazil)

2013-12-04

275

Nonconservative electric and magnetic optical forces on submicron dielectric particles  

SciTech Connect

We present a study of the total force on a small lossless dielectric particle, which presents both an electric and magnetic response, in a optical vortex wave field. We show that the force is a simple combination of conservative and nonconservative steady forces that can rectify the flow of magnetodielectric particles. In a vortex lattice the electric-magnetic dipolar interaction can spin the particles either in or out of the whirl sites leading to trapping or diffusion. Specifically, we analyze force effects on submicron silicon spheres in the near infrared, proving that the results previously discussed for hypothetical magnetodielectric particles can be observed for these Si particles.

Gomez-Medina, Raquel; Nieto-Vesperinas, Manuel [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas, Campus de Cantoblanco, Madrid E-28049 (Spain); Saenz, Juan Jose [Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Donostia International Physics Center (DIPC), Paseo Manuel Lardizabal 4, 20018 Donostia-San Sebastian (Spain)

2011-03-15

276

Static uniform magnetic fields and amoebae  

SciTech Connect

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.

Berk, S.G.; Srikanth, S.; Mahajan, S.M.; Ventrice, C.A. [Tennessee Technological Univ., Cookeville, TN (United States)] [Tennessee Technological Univ., Cookeville, TN (United States)

1997-03-01

277

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

278

A Novel Electro-Optical Magnetic Microsensor with Reducing Interference Packaging  

Microsoft Academic Search

A novel electro-optical magnetic microsensor with reducing interference packaging mechanism for sensing magnetic field strength is demonstrated. Both capacitive and optical fiber sensing microstructures surrounded magnetic shields are fabricated in a chip using low temperature silicon-based MEMS compatible technology. Varied NiFe permalloy flaps embedded on polyimide membranes were used as flexible sensing mechanisms to actuate side-polished fiber and capacitor plate.

Hsing-Cheng Chang; San-Shan Hung; Chingfu Tsou; Wen-Fung Liu; Chi-Chih Lai; Ching-Shang Jian

2007-01-01

279

Magnetic field waves at Uranus  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

280

Lattice distortions in magnetic fields  

NASA Astrophysics Data System (ADS)

A study is made of the stability of the possible lattice structures which result from the magnetic-field-induced lattice deformation introduced by Araujo and Khmelnitskii. The deformed lattice may either be the result of a single distortion occurring along a particular direction or of a superposition of distortions in different directions. In a noninteracting electron model the energy variation of the electron system will determine which final lattice structure is the most stable. When electron interactions are considered in the Hartree approximation we find that the energy variation of the electron system alone will not determine which final structure is the most stable. The latter is then imposed by the lattice itself. If the distortion turns out to be unidirectional then the corresponding charge-density wave should be weakly pinned even in the absence of impurities.

Araujo, Miguel A. N.

1996-09-01

281

Extraterrestrial Magnetic Fields: Achievements and Opportunities  

Microsoft Academic Search

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

EDWARD J. SMITHAND; Charles Sonett

1976-01-01

282

Femtotesla Magnetic Field Measurement with Magnetoresistive Sensors  

Microsoft Academic Search

The measurement of magnetic fields in the femtotesla (fT, 10-15 tesla) range is important for applications such as magnetometry, quantum computing, solid-state nuclear magnetic resonance, and magnetoencephalography. The only sensors capable of detecting these very small fields have been based on low-temperature superconducting quantum interference devices operating at 4.2 kelvin. We present a magnetic field sensor that combines a superconducting

Myriam Pannetier; Claude Fermon; Gerald Le Goff; Juha Simola; Emma Kerr

2004-01-01

283

Dynamics of solar magnetic fields. VI  

Microsoft Academic Search

A mathematical model is developed to consider the evolution of force-free magnetic fields in relation to the displacements of their foot-points. For a magnetic field depending on only two Cartesian coordinates and time, the problem reduces to solving a nonlinear elliptic partial differential equation. As illustration of the physical process, two specific examples of evolving force-free magnetic fields are examined

B. C. Low; Y. Nakagawa

1975-01-01

284

Modeling solar force-free magnetic fields  

Microsoft Academic Search

A class of nonlinear force-free magnetic fields is presented, described in terms of the solutions to a second-order, nonlinear ordinary differential equation. These magnetic fields are three-dimensional, filling the infinite half-space above a plane where the lines of force are anchored. They model the magnetic fields of the sun over active regions with a striking geometric realism. The total energy

B. C. Low; Y. Q. Lou

1990-01-01

285

Fractal properties of solar magnetic fields  

Microsoft Academic Search

We study the spatial properties of solar magnetic fields using data from the Solar Vector Magnetograph of the Marshall Space\\u000a Flight Center (MSFC) (FeI 5250.2 Å) and SOHO\\/MDI longitudinal magnetic field measurements (Ni 6767.8 Å) (96-min full-disk\\u000a maps). Our study is focused on two objects: the fractal properties of sunspots and the fractal properties of the spatial magnetic\\u000a field distribution

B. A. Ioshpa; V. N. Obridko; E. A. Rudenchik

2008-01-01

286

Fractal properties of solar magnetic fields  

Microsoft Academic Search

We study the spatial properties of solar magnetic fields using data from the Solar Vector Magnetograph of the Marshall Space Flight Center (MSFC) (FeI 5250.2 Å) and SOHO\\/MDI longitudinal magnetic field measurements (Ni 6767.8 Å) (96-min full-disk maps). Our study is focused on two objects: the fractal properties of sunspots and the fractal properties of the spatial magnetic field distribution

B. A. Ioshpa; V. N. Obridko; E. A. Rudenchik

2008-01-01

287

Critical behavior of zero-field magnetic fluctuations in perpendicularly magnetized thin films  

NASA Astrophysics Data System (ADS)

We use video-rate magneto-optical Kerr effect microscopy to study zero-field magnetic fluctuations in a perpendicularly magnetized cobalt film at room temperature, prepared near a spin reorientation transition. Globally, the film has zero net moment but local areas continually undergo thermal magnetic fluctuations between saturated states. Position resolved hysteresis loops show the fluctuations occur at sample locations close to the spin reorientation transition. Furthermore, nearby fluctuations interact magnetostatically, acting to maintain the overall zero net magnetization. The measured scaling exponent of the fluctuation areas ? is consistent with 4 /3 .

Balk, A. L.; Stiles, M. D.; Unguris, J.

2014-11-01

288

Ferroelectric Cathodes in Transverse Magnetic Fields  

SciTech Connect

Experimental investigations of a planar ferroelectric cathode in a transverse magnetic field up to 3 kGs are presented. It is shown that the transverse magnetic field affects differently the operation of ferroelectric plasma cathodes in ''bright'' and ''dark'' modes in vacuum. In the ''bright'' mode, when the surface plasma is formed, the application of the transverse magnetic field leads to an increase of the surface plasma density. In the ''dark'' mode, the magnetic field inhibits the development of electron avalanches along the surface, as it does similarly in other kinds of surface discharges in the pre-breakdown mode.

Alexander Dunaevsky; Yevgeny Raitses; Nathaniel J. Fisch

2002-07-29

289

Magnetic field measurements in tokamak plasmas  

SciTech Connect

The measurement of the poloidal magnetic field in a tokamak plasma from the Zeeman splitting and polarization of the magnetic dipole radiation from heavy ions is discussed. When viewed from a direction perpendicular to the toroidal field, the effect of the poloidal field on the circularly polarized radiation is detectable using a photoelectric polarimeter. The Zeeman splittings for a number of magnetic dipole transitions with wavelengths in the range 2300--9300 A are presented. An imaging polarimeter is proposed that can measure the poloidal magnetic field with space and time resolution.

Feldman, U.; Seely, J.F.; Sheeley,Jr., N.R.; Suckewer, S.; Title, A.M.

1984-11-01

290

Magnetic fields in anisotropic relativistic stars  

E-print Network

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

Vladimir Folomeev; Vladimir Dzhunushaliev

2015-01-26

291

Five years of magnetic field management  

SciTech Connect

The extensive publicity of epidemiological studies inferring correlation between 60 Hz magnetic fields and childhood leukemia prompted world wide research programs that have as a goal to determine if low frequency magnetic fields represent any risk for the general population, children or utility workers. While supporting this research effort through EPRI, Con Edison embarked on a technical research program aimed to: characterize magnetic fields as to intensity and variation in time; and investigate practical means to manage these magnetic fields through currently known methods. The final goal of these research projects is to establish viable methods to reduce magnetic field intensity to desired values at reasonable distances from the sources. This goal was pursued step by step, starting with an inventory of the main sources of magnetic fields in substations, distribution and transmission facilities and generating plants. The characterization of the sources helped to identify typical cases and select specific cases, far practical applications. The next step was to analyze the specific cases and develop design criteria for managing the magnetic fields in new installations. These criteria included physical arrangement of equipment based oil calculation of magnetic fields, cancellation effect, desired maximum field intensity at specific points and shielding with high magnetic permeability metals (mu-metal and steel). This paper summarizes the authors` experiences and shows the results of the specific projects completed in recent years.

Durkin, C.J.; Fogarty, R.P.; Halleran, T.M.; Mark, Dr. D.A.; Mukhopadhyay, A.

1995-01-01

292

Studies of strong magnetic field produced by permanent magnet array for magnetic refrigeration  

NASA Astrophysics Data System (ADS)

The success of a room temperature magnetic refrigerator (RTMR) depends critically on two essential parts: a high magnetic field and a magnetic refrigerant material with large magnetocaloric effect. A carefully designed hollow cylindrical permanent magnet array (HCPMA) can be used to provide strong magnetic field in the cavity, the magnitude of the resulting static field can be even greater than the remanence magnetization of the magnets comprising a HCPMA. A thorough understanding of the magnetic field distribution will provide an invaluable insight into the design and optimization of HCPMA in the reciprocating and rotary RTMR systems. Here, we show a construction of a 16 piece HCPMA with realistic dimensions and we illustrate the mechanism of generating a high magnetic field in such device. We present an effective way to calculate the field distribution of a permanent magnet array with finite size and an unsymmetrical geometry. Furthermore, detailed numerical results of the magnetic field distribution and its dependence on device dimensions are presented.

Xu, X. N.; Lu, D. W.; Yuan, G. Q.; Han, Y. S.; Jin, X.

2004-06-01

293

Magnetic monopole field exposed by electrons  

NASA Astrophysics Data System (ADS)

The experimental search for magnetic monopole particles has, so far, been in vain. Nevertheless, these elusive particles of magnetic charge have fuelled a rich field of theoretical study. Here, we created an approximation of a magnetic monopole in free space at the end of a long, nanoscopically thin magnetic needle. We experimentally demonstrate that the interaction of this approximate magnetic monopole field with a beam of electrons produces an electron vortex state, as theoretically predicted for a true magnetic monopole. This fundamental quantum mechanical scattering experiment is independent of the speed of the electrons and has consequences for all situations where electrons meet such monopole magnetic fields, as, for example, in solids. The set-up not only shows an attractive way to produce electron vortex states but also provides a unique insight into monopole fields and shows that electron vortices might well occur in unexplored solid-state physics situations.

Béché, Armand; van Boxem, Ruben; van Tendeloo, Gustaaf; Verbeeck, Jo

2014-01-01

294

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in fall 2012. 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.

Plank, G.; Floberghagen, R.; Menard, Y.; Haagmans, R.

2012-12-01

295

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in 2013. The objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution using a constellation of 3 identical satellites. The Mission shall deliver data that allow access to new insights into the Earth system by improved scientific understanding of the Earth's interior and near-Earth electromagnetic environment. After launch and triple satellite release at an initial altitude of about 490 km, a pair of the satellites will fly side-by-side with slowly decaying altitude, while the third satellite will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission science goals are to provide a unique view into Earth's core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently in the final stage of the development phase, will be addressed. A consortium of European scientific institutes is developing a distributed processing system to produce geophysical (Level 2) data products for the Swarm user community. The setup of the Swarm ground segment and the contents of the data products will be addressed. More information on Swarm can be found at www.esa.int/esaLP/LPswarm.html.

Plank, Gernot; Haagmans, Roger; Floberghagen, Rune; Menard, Yvon

2013-04-01

296

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in fall 2013. The objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution using a constellation of three identical satellites. The mission shall deliver data that allow access to new insights into the Earth system by improved scientific understanding of the Earth's interior and near-Earth electromagnetic environment. After launch and triple satellite release at an initial altitude of about 490 km, a pair of the satellites will fly side-by-side with slowly decaying altitude, while the third satellite will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission science goals are to provide a unique view into Earth's core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently in the final stage of the development phase, will be addressed. A consortium of European scientific institutes is developing a distributed processing system to produce geophysical (Level 2) data products for the Swarm user community. The setup of the Swarm ground segment and the contents of the data products will be addressed. In case the Swarm satellites are already in orbit, a summary of the on-going mission operations activities will be given. More information on Swarm can be found at www.esa.int/esaLP/LPswarm.html.

Plank, G.; Floberghagen, R.; Menard, Y.; Haagmans, R.

2013-12-01

297

Comparative numerical analysis of magnetic and optical radiation propagation in adult human head  

NASA Astrophysics Data System (ADS)

In this work, magnetic and optical propagation in human head are modeled by FDTD and Monte Carlo methods. Both of them use a realistic high-resolution three-dimensional human head mesh. The numerical methods are applied to the analysis of magnetic and optical radiation distribution in the brain using different sources. The results show the characteristics of both types of stimulation, and highlight the spatial selectivity achieved by optical sources, which entails a high potential for illuminating specific brain regions. The presented approach can be applied for predictive purposes in magnetic stimulation techniques and in the emerging field of optical brain stimulation.

Ortega-Quijano, Noé; Fanjul-Vélez, Félix; Salas-García, Irene; Arce-Diego, José Luis

2013-06-01

298

Atomic magnetic gradiometer for room temperature high sensitivity magnetic field detection  

DOEpatents

A laser-based atomic magnetometer (LBAM) apparatus measures magnetic fields, comprising: a plurality of polarization detector cells to detect magnetic fields; a laser source optically coupled to the polarization detector cells; and a signal detector that measures the laser source after being coupled to the polarization detector cells, which may be alkali cells. A single polarization cell may be used for nuclear magnetic resonance (NMR) by prepolarizing the nuclear spins of an analyte, encoding spectroscopic and/or spatial information, and detecting NMR signals from the analyte with a laser-based atomic magnetometer to form NMR spectra and/or magnetic resonance images (MRI). There is no need of a magnetic field or cryogenics in the detection step, as it is detected through the LBAM.

Xu,Shoujun (Berkeley, CA); Lowery, Thomas L. (Belmont, MA); Budker, Dmitry (El Cerrito, CA); Yashchuk, Valeriy V. (Richmond, CA); Wemmer, David E. (Berkeley, CA); Pines, Alexander (Berkeley, CA)

2009-08-11

299

Magnetic field optimization of permanent magnet undulators for arbitrary polarization  

NASA Astrophysics Data System (ADS)

Techniques for improving the magnetic field quality of APPLE II undulators are discussed. Individual block characterization including the inhomogeneities of the magnetization permits a precise prediction of field integrals as required for sorting. Specific shimming procedures adapted to the magnetic design of APPLE II undulators have to be employed in order to meet the stringent requirements of insertion devices in third generation synchrotron radiation sources as demonstrated for BESSY.

Bahrdt, J.; Frentrup, W.; Gaupp, A.; Scheer, M.; Englisch, U.

2004-01-01

300

SIMULATING MAGNETIC FIELDS IN THE ANTENNAE GALAXIES  

SciTech Connect

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

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

2010-06-20

301

Fine structure of solar magnetic fields  

Microsoft Academic Search

The deduction of magnetic fields from chromospheric structure is extended to active regions and transverse fields. Fields independently predicted by these rules from a high resolution Ha filtergram are compared with a high resolution magnetogram. The Ha method has the advantage over conventional magnetograms that it shows transverse fields and relates the fields to the real Sun. It has the

Harold Zirin

1972-01-01

302

Magnetic-field effects in non-magnetic glasses  

NASA Astrophysics Data System (ADS)

Recently, it was found that the multi-component glass a-BaO-Al2O3-SiO2 exhibits unusual magnetic properties at very low temperatures. Thus the question arises whether this is a specialty of that particular glass or a more general phenomenon. We report here on our studies of the magnetic-field dependence of the dielectric properties of the borosilicate glass BK7 which contains only a negligible amount of magnetic impurities. Since this glass also responds sensitively to magnetic fields, our investigations demonstrate that the reaction of glasses to magnetic fields is not caused by magnetic impurities but reflects a more general phenomenon. In addition, we have observed that the variation of the dielectric constant and the loss angle with magnetic field depend on the amplitude of the electric field that is used to measure the glass capacitance. We present the data and discuss possible origins of the magnetic-field phenomena in non-magnetic glasses.

Wohlfahrt, M.; Strehlow, P.; Enss, C.; Hunklinger, S.

2001-12-01

303

Thinned fiber Bragg grating magnetic field sensor with magnetic fluid  

NASA Astrophysics Data System (ADS)

The refractive index of magnetic fluid may be changed by external magnetic field. Therefore, through measuring its refractive index, the intensity of the magnetic field can be obtained. Fiber Bragg grating (FBG) is sensitive to the refractive index surrounding its cladding when the diameter of cladding is reduced to a certain degree. In order to prove the sensitivity of the thinned fiber Bragg grating to refractive index, series of experiments, such as the fabrication of thinned FBG, tuning magnetic field and obtaining spectral characterizations, are carried out. After the FBG is etched for 193 minutes by HF solution at 22%, the FBG starts to be sensitive to the surrounding refractive index and the Bragg wavelength decreases sharply with the etching process. The thinned FBG has been packaged to a container filled with MF. Using a tunable magnetic field the refractive index of magnetic fluid could be changed and the Bragg wavelength of FBG shifts correspondingly. Both the wavelength and the light power are sensitive to magnetic field and the sensitivity of wavelength is 2.3 pm/mT at least in the condition of proposed experiment. The obtained results show that the thinned FBG sensor with magnetic fluid could be applicable for magnetic field and current sensing.

Zhou, Ciming; Ding, Li; Wang, Dongli; Kuang, Yaqi; Jiang, Desheng

2011-05-01

304

Static magnetic fields enhancement of Saccharomyces cerevisae ethanolic fermentation.  

PubMed

Magnetic effects induced in ethanolic fermentation by Saccharomyces cerevisiae strain DAUFPE-1012 were studied during a 24 h exposure to 220 mT steady magnetic fields (SMF) at 23 +/- 1 degrees C, produced by NdFeB rod magnets. The magnets were attached diametrically opposed (N to S) to a cylindrical tube reactor. The biomass growth in the reactor culture media (yeast extract + glucose 2%) during 24 h was monitored by measurements of optical density, which was correlated to cell dry weight. Ethanol concentration and glucose level were measured every 2 h. The pH of the culture media was maintained between 4 and 5. As a result, biomass (g/L) increased 2.5-fold and ethanol concentration 3.4-fold in magnetized cultures (n = 8) as compared with SMF nonexposed cultures (n = 8). Glucose consumption was higher in magnetized cultures, which correlated to the ethanol yield. PMID:14763869

da Motta, Mauricy Alves; Muniz, João Batista Ferreira; Schuler, Alexandre; Da Motta, Mauricio

2004-01-01

305

Magnetic induction-induced resistive heating of optical fibers and gratings.  

PubMed

Magnetic induction heating of optical fibers packaged with a steel plate is studied using a fiber Bragg grating. The dependence on the induced wavelength shift with magnetic field is obtained for a commercially available induction heater. More than a 300°C temperature rise is observed within seconds. The potential of magnetic induction as an efficient and rapid means of modulating devices and as a novel approach to potential optical based magnetic field and current sensing is proposed and discussed. The extension of the ideas into micro and nanophotonics is described. PMID:23503262

Canning, John; Naqshbandi, Masood; Cook, Kevin; Huyang, George

2013-03-15

306

Videomagnetograph studies of solar magnetic fields  

Microsoft Academic Search

Observations of magnetic field diffusion in weak plage regions have been made using the analog videomagnetograph at the California Institute of Technology. Points of magnetic flux, usually described as ‘vertex points’ of the magnetic network, were found to have a mean lifetime of three to four days, and to disperse primarily by means of two mechanisms: a random walk with

Robert C. Smithson

1973-01-01

307

The Moessbauer effect in homogeneous magnetic field  

E-print Network

We derive the probability of the Moessbauer effect realized by the charged particle moving in the homogeneous magnetic field, or, in accelerating field. The submitted approach represents new deal of the Moessbauer physics. Key

Miroslav Pardy

2014-03-20

308

Magnetic field decay in model SSC dipoles  

SciTech Connect

We have observed that some of our model SSC dipoles have long time constant decays of the magnetic field harmonics with amplitudes large enough to result in significant beam loss, if they are not corrected. The magnets were run at constant current at the SSC injection field level of 0.3 tesla for one to three hours and changes in the magnetic field were observed. One explanation for the observed field decay is time dependent superconductor magnetization. Another explanation involves flux creep or flux flow. Data are presented on how the decay changes with previous flux history. Similar magnets with different Nb-Ti filament spacings and matrix materials have different long time field decay. A theoretical model using proximity coupling and flux creep for the observed field decay is discussed. 10 refs., 5 figs., 2 tabs.

Gilbert, W.S.; Althaus, R.F.; Barale, P.J.; Benjegerdes, R.W.; Green, M.A.; Green, M.I.; Scanlan, R.M.

1988-08-01

309

Magnetic Field Seeding through Supernova Feedback  

NASA Astrophysics Data System (ADS)

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

Koh, Daegene; Wise, John

2015-01-01

310

Resonant Magnetic Field Sensors Based On MEMS Technology.  

PubMed

Microelectromechanical systems (MEMS) technology allows the integration of magnetic field sensors with electronic components, which presents important advantages such as small size, light weight, minimum power consumption, low cost, better sensitivity and high resolution. We present a discussion and review of resonant magnetic field sensors based on MEMS technology. In practice, these sensors exploit the Lorentz force in order to detect external magnetic fields through the displacement of resonant structures, which are measured with optical, capacitive, and piezoresistive sensing techniques. From these, the optical sensing presents immunity to electromagnetic interference (EMI) and reduces the read-out electronic complexity. Moreover, piezoresistive sensing requires an easy fabrication process as well as a standard packaging. A description of the operation mechanisms, advantages and drawbacks of each sensor is considered. MEMS magnetic field sensors are a potential alternative for numerous applications, including the automotive industry, military, medical, telecommunications, oceanographic, spatial, and environment science. In addition, future markets will need the development of several sensors on a single chip for measuring different parameters such as the magnetic field, pressure, temperature and acceleration. PMID:22408480

Herrera-May, Agustín L; Aguilera-Cortés, Luz A; García-Ramírez, Pedro J; Manjarrez, Elías

2009-01-01

311

Twist-bend nematic liquid crystals in high magnetic fields  

NASA Astrophysics Data System (ADS)

We present magneto-optic measurements on two materials that form the recently discovered twist-bend nematic (Ntb) phase. This intriguing state of matter represents a fluid phase that is orientationally anisotropic in three directions and also exhibits translational order with periodicity several times larger than the molecular size. Ntb materials may also spontaneously form a visible, macroscopic stripe texture. We show that the optical stripe texture can be persistently inhibited by a magnetic field, and a 25T external magnetic field depresses the N-Ntb phase transition temperature by almost 1?C. We propose a quantitative mechanism to account for this shift and suggest a Helfrich-Hurault-type mechanism for the optical stripe formation.

Challa, P. K.; Borshch, V.; Parri, O.; Imrie, C. T.; Sprunt, S. N.; Gleeson, J. T.; Lavrentovich, O. D.; Jákli, A.

2014-06-01

312

Twist-bend nematic liquid crystals in high magnetic fields.  

PubMed

We present magneto-optic measurements on two materials that form the recently discovered twist-bend nematic (N_{tb}) phase. This intriguing state of matter represents a fluid phase that is orientationally anisotropic in three directions and also exhibits translational order with periodicity several times larger than the molecular size. N_{tb} materials may also spontaneously form a visible, macroscopic stripe texture. We show that the optical stripe texture can be persistently inhibited by a magnetic field, and a 25T external magnetic field depresses the N-N_{tb} phase transition temperature by almost 1{?}C. We propose a quantitative mechanism to account for this shift and suggest a Helfrich-Hurault-type mechanism for the optical stripe formation. PMID:25019707

Challa, P K; Borshch, V; Parri, O; Imrie, C T; Sprunt, S N; Gleeson, J T; Lavrentovich, O D; Jákli, A

2014-06-01

313

Graphene Nanoribbon in Sharply Localized Magnetic Fields  

E-print Network

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

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

2011-03-21

314

Parker's magnetic field and relativistic jets  

NASA Astrophysics Data System (ADS)

We consider the motion of high-energy charged particles (cosmic rays) in Parker's spiral magnetic field. We show that under radial particle ejection from a sphere outside which there is Parker's magnetic field, all of the particles escaping from the sphere are focused either along the field symmetry axis or in the equatorial plane, depending on the field polarity. Based on the results obtained, we propose a possible model that explains the origin of relativistic jets.

Kichigin, G. N.

2014-10-01

315

Magnetic isotope and magnetic field effects on the DNA synthesis  

PubMed Central

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

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

2013-01-01

316

MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. I. FORCE-FREE MAGNETIC FIELDS B. Fornberg,2  

E-print Network

MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. I. FORCE-FREE MAGNETIC FIELDS N. Flyer,1 B Axisymmetric force-free magnetic fields external to a unit sphere are studied as solutions to boundary value against expansion into the unbounded space. This property as a basic mechanism for solar coronal mass

Fornberg, Bengt

317

The magnetic field of ? Ori A  

NASA Astrophysics Data System (ADS)

Magnetic fields play a significant role in the evolution of massive stars. About 7% of massive stars are found to be magnetic at a level detectable with current instrumentation (Wade et al. 2013) and only a few magnetic O stars are known. Detecting magnetic field in O stars is particularly challenging because they only have few, often broad, lines to measure the field, which leads to a deficit in the knowledge of the basic magnetic properties of O stars. We present new spectropolarimetric Narval observations of ? Ori A. We also provide a new analysis of both the new and older data taking binarity into account. The aim of this study was to confirm the presence of a magnetic field in ? Ori A. We identify that it belongs to ? Ori Aa and characterize it.

Blazère, A.; Neiner, C.; Bouret, J.-C.; Tkachenko, A.

2015-01-01

318

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

NASA Technical Reports Server (NTRS)

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

Burlaga, L. F.; Barouch, E.

1974-01-01

319

Fluctuating magnetic field induced resonant activation.  

PubMed

In this paper, we have studied the properties of a Brownian particle at stationary state in the presence of a fluctuating magnetic field. Time dependence of the field makes the system thermodynamically open. As a signature of that the steady state distribution function becomes function of damping strength, intensity of fluctuations and constant parts of the applied magnetic field. It also depends on the correlation time of the fluctuating magnetic field. Our another observation is that the random magnetic field can induce the resonant activation phenomenon. Here correlation time is increased under the fixed variance of the fluctuating field. But if the correlation time (?) increases under the fixed field strength then the mean first passage time rapidly grows at low ? and it almost converges at other limit. This is sharp contrast to the usual colored noise driven open system case where the mean first passage time diverges exponentially. We have also observed that a giant enhancement of barrier crossing rate occurs particularly at large strength of constant parts of the applied magnetic field even for very weak fluctuating magnetic field. Finally, break down of the Arrhenius result and disappearance of the Kramers' turn over phenomenon may occur in the presence of a fluctuating magnetic field. PMID:25494726

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

2014-12-14

320

Fluctuating magnetic field induced resonant activation  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

321

Magnetic field amplification and flat spectrum radio quasars  

NASA Astrophysics Data System (ADS)

We perform time-dependent, spatially resolved simulations of blazar emission to evaluate several flaring scenarios related to magnetic-field amplification and enhanced particle acceleration. The code explicitly accounts for light-travel-time effects and is applied to flares observed in the flat spectrum radio quasar (FSRQ) PKS 0208-512, which show optical/?-ray correlation at some times, but orphan optical flares at other times. Changes in both the magnetic field and the particle acceleration efficiency are explored as causes of flares. Generally, external Compton (EC) emission appears to describe the available data better than a synchrotron self-Compton (SSC) scenario, and in particular orphan optical flares are difficult to produce in the SSC framework. X-ray soft-excesses, ?-ray spectral hardening, and the detections at very high energies of certain FSRQs during flares find natural explanations in the EC scenario with particle acceleration change. Likewise, optical flares with/without ?-ray counterparts can be explained by different allocations of energy between the magnetization and particle acceleration, which may be related to the orientation of the magnetic field relative to the jet flow. We also calculate the degree of linear polarization and polarization angle as a function of time for a jet with helical magnetic field. Tightening of the magnetic helix immediately downstream of the jet perturbations, where flares occur, can be sufficient to explain the increases in the degree of polarization and a rotation by ?180° of the observed polarization angle, if light-travel-time effects are properly considered.

Chen, Xuhui; Chatterjee, Ritaban; Zhang, Haocheng; Pohl, Martin; Fossati, Giovanni; Böttcher, Markus; Bailyn, Charles D.; Bonning, Erin W.; Buxton, Michelle; Coppi, Paolo; Isler, Jedidah; Maraschi, Laura; Urry, Meg

2014-07-01

322

Homogenization of nanostructured media in magnetic field  

NASA Astrophysics Data System (ADS)

Problem of homogenization of nanostructured media in magnetic field has been considered. Possibility of introduction of effective material parameters dielectric permittivity and magnetic permeability for three classes of media such as magnetic metal nanostructures, film metal-dielectric composite media and 3D-nanocomposites on the base of opal matrices has been investigated. It has been stated that the introduction of effective parameters far from magnetic resonance conditions is possible at millimeter waveband frequencies. Strict introduction of effective magnetic permeability of nanostructured media near magnetic resonance is not possible.

Rinkevich, A. B.; Perov, D. V.

2014-11-01

323

Two-axis magnetic field sensor  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

324

Orientation effects in pulsed magnetic field treatment  

Microsoft Academic Search

This paper presents the orientation effects on residual stress release by pulsed magnetic field treatment. Specimens are produced by tungsten inert gas (TIG) welding and the initial residual stresses in them are measured by the hole-drilling method. With different orientations these specimens are treated in the same magnetic field and the residual stresses are measured for the second time. By

Cai Zhipeng; Lin Jian; Zhao Haiyan; Lu Anli

2005-01-01

325

A search for weak stellar magnetic fields  

Microsoft Academic Search

The magnetic fields of normal main sequence stars, supergiants, and mercury-manganese stars were measured in metal lines with the magnetometer of the main stellar spectrograph and in hydrogen lines with the spectropolarimeter at the 6-meter telescope. These data were analyzed statistically with data obtained by other authors. It is concluded that the dipole magnetic fields of the stars studied hardly

Yu. V. Glagolevskij; I. I. Romanyuk; I. D. Najdenov; V. G. Shtol

1991-01-01

326

Magnetic Fields at the Center of Coils  

ERIC Educational Resources Information Center

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

Binder, Philippe; Hui, Kaleonui; Goldman, Jesse

2014-01-01

327

Space Quantization in a Gyrating Magnetic Field  

Microsoft Academic Search

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

I. I. Rabi

1937-01-01

328

The magnetic field of an infinite solenoid  

NASA Astrophysics Data System (ADS)

We use the Biot-Savart law for filamentary currents to show that the magnetic field produced by an infinitely long straight strip of infinitesimal width carrying a uniform transverse surface current can be written in simple geometrical terms. We use this result to calculate the magnetic field of an infinite solenoid of arbitrary but uniform cross-sectional shape.

Espinosa, Olivier; Slusarenko, Viktor

2003-09-01

329

Coulomb crystals in the magnetic field.  

PubMed

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 approximately equal 10(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. PMID:19905459

Baiko, D A

2009-10-01

330

Does the solar magnetic field increase?  

Microsoft Academic Search

We consider measurements of the general magnetic field (GMF) of the Sun as a star at four world observatories from 1968 until\\u000a 1999. We show that, within the error limits, the mean strength of the photospheric magnetic field H (of its longitudinal component, in magnitude) has not changed over the last 32 years. This is in conflict with the recent

V. A. Kotov; I. V. Kotova

2001-01-01

331

Intense ionospheric electric and magnetic field pulses generated by lightning  

NASA Technical Reports Server (NTRS)

Electric and magnetic field measurements have been made in the ionosphere over an active thunderstorm and an optical detector onboard the same rocket yielded an excellent time base for the study of waves radiated into space from the discharge. In addition to detection of intense, but generally well understood whistler mode waves, very unusual electric and magnetic field pulses preceded the 1-10 kHz component of the radiated signal. These pulses lasted several ms and had a significant electric field component parallel to the magnetic field. No known propagating wave mode has this polarization nor a signal propagation velocity as high as those measured here. This study investigated and rejected an explanation based on an anomalous skin depth effect. Although only a hypothesis at this time, a more promising explanation involving the generation of the pulse via a nonlinear decay of whistler mode waves in the frequency range 10-80 kHz is being investigated.

Kelley, M. C.; Ding, J. G.; Holzworth, R. H.

1990-01-01

332

Permanent magnet edge-field quadrupole  

DOEpatents

Planar permanent magnet edge-field quadrupoles for use in particle accelerating machines and in insertion devices designed to generate spontaneous or coherent radiation from moving charged particles are disclosed. The invention comprises four magnetized rectangular pieces of permanent magnet material with substantially similar dimensions arranged into two planar arrays situated to generate a field with a substantially dominant quadrupole component in regions close to the device axis. 10 figs.

Tatchyn, R.O.

1997-01-21

333

Permanent magnet edge-field quadrupole  

DOEpatents

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

Tatchyn, Roman O. (Mountain View, CA)

1997-01-01

334

Solar magnetic fields and the dynamo theory  

Microsoft Academic Search

Unlike Earth’s dipolar magnetic fields, solar magnetic fields consist of wide ranges of length-scales and strengths, and interestingly, they evolve in a cyclic fashion with a 22-year periodicity. A magnetohydrodynamic dynamo operating in the Sun is most likely responsible for producing the solar magnetic activity cycle. While the first solar dynamo models were built half a century ago, recent views

M. Dikpati

2005-01-01

335

Fields from a relativistic magnetic explosion  

NASA Astrophysics Data System (ADS)

Following Prendergast, we study the relativistically expanding electromagnetic fields generated by an axisymmetric explosion of magnetic energy in a small volume. The magnetic field expands uniformly either within a cone or in all directions and it is therefore accompanied by an electric field. In the highly conducting plasma, the charges move to annul the electric field in the frame of the moving plasma. The solutions presented are analytical and semi-analytical. We find that the time-scale for the winding up of the initial magnetic field is crucial, as short time-scales lead to strong radiant fields. Assuming a magnetic field of 1013G emerging from a magnetosphere of 109cm, we end with a jet when confined by a pressure environment that falls more slowly than r-4. The jet carries energy of 1051erg, which is mostly due to differential rotation at the base.

Gourgouliatos, K. N.; Lynden-Bell, D.

2008-11-01

336

Magnetic field amplification in supernova shock precursor  

NASA Astrophysics Data System (ADS)

Galactic cosmic rays are believed to be mostly accelerated at supernova shocks. However, the interstellar magnetic field is too weak to efficiently accelerate galactic cosmic rays up to the highest energies. A stronger magnetic field in the preshock region could provide the efficiency required. Cosmic ray streaming instability has been claimed to be responsible for the amplification of precursor magnetic fields. An alternative mechanism has been proposed in which the cosmic ray pressure gradient forms the shock precursor and drives turbulence, amplifying the magnetic field via the small-scale dynamo. We explore this last scenario through 3-D MHD numerical simulations. We show under which conditions an efficient amplification of the magnetic field is achieved.

Del Valle, Maria Victoria; Lazarian, Alex

337

Field-Sensitive Materials for Optical Applications  

NASA Technical Reports Server (NTRS)

The purpose of investigation is to develop the fundamental materials and fabrication technology for field-controlled spectrally active optics that are essential for industry, NASA, and DOD (Department of Defense) applications such as: membrane optics, filters for LIDARs (Light Detection and Ranging), windows for sensors and probes, telescopes, spectroscopes, cameras, light valves, light switches, flat-panel displays, etc. The proposed idea is based on the quantum-dots (QD) array or thin-film of field-sensitive Stark and Zeeman materials and the bound excitonic state of organic crystals that will offer optical adaptability and reconfigurability. Major tasks are the development of concept demonstration article and test data of field-controlled spectrally smart active optics (FCSAO) for optical multi-functional capabilities on a selected spectral range.

Choi, Sang H.; Little, Mark

2002-01-01

338

Chaotic magnetic fields: Particle motion and energization  

SciTech Connect

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

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

2014-02-11

339

Nuclear Spin Maser at Highly Stabilized Low Magnetic Field and Search for Atomic EDM  

SciTech Connect

A nuclear spin maser is operated at a low static field through an active feedback scheme based on an optical nuclear spin detection and succeeding spin control by a transverse field application. The frequency stability of this optical-coupling spin maser is improved by installation of a low-noise current source for a solenoid magnet producing a static magnetic field in the maser operation. Experimental devices for application of the maser to EDM experiment are being developed.

Yoshimi, A. [RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198 (Japan); Asahi, K.; Inoue, T.; Uchida, M.; Hatakeyama, N.; Tsuchiya, M.; Kagami, S. [Department of Physics, Tokyo Institute of Technology, Oh-okayama 2-12-1, Meguro, Tokyo 152-8551 (Japan)

2009-08-04

340

Subnanosecond magnetization dynamics induced by a pulsed magnetic field in diluted magnetic semiconductor quantum wells  

NASA Astrophysics Data System (ADS)

The magnetization dynamics induced by a pulsed magnetic field is investigated by time- and polarization-resolved photoluminescene measurements in (Cd,Mn)Te/(Cd,Mg)Te quantum wells. The magnetization dynamics of Mn2+ ions is found to be strongly dependent on the external static magnetic field. A dynamical response of the magnetization on a subnanosecond time scale is observed at zero static magnetic field, while it drastically slows down and approaches the spin-lattice relaxation time constant for a nonzero static field. Theoretical calculations emphasize the importance of local spin interactions that interplay with the Zeeman interaction for the observed magnetization dynamics.

Chen, Y. S.; Wiater, M.; Karczewski, G.; Wojtowicz, T.; Bacher, G.

2013-04-01

341

Field enhancement in apertureless near-field scanning optical microscopy.  

PubMed

The near field of an apertureless near-field scanning optical microscopy probe is investigated with a multiple-multipole technique to obtain optical fields in the vicinity of a silicon probe tip and a glass substrate. The results demonstrate that electric field enhancements of >15 relative to the incident fields can be achieved near a silicon tip, implying intensity enhancements of several orders of magnitude. This enhancement arises both from the antenna effect of the elongated probe and from a proximity effect when the probe is near the substrate surface and its image dipoles play a role. PMID:11760198

Bohn, J L; Nesbitt, D J; Gallagher, A

2001-12-01

342

Warm inflation in presence of magnetic fields  

SciTech Connect

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

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

2013-07-23

343

Near-field compact dielectric optics  

NASA Astrophysics Data System (ADS)

Aplanatic optics crafted from transparent dielectrics can approach the etendue limit for radiative transfer in pragmatic near-field systems. Illustrations are presented for the more demanding realm of high numerical aperture (NA) at the source and/or target. These light couplers can alleviate difficulties in aligning system components, and can achieve the fundamental compactness limit for optical devices that satisfy Fermat's principle.

Feuermann, Daniel; Gordon, Jeffrey M.; Ng, Tuck Wah

2006-08-01

344

Near Field Optical Microscopy of Fractal Materials  

Microsoft Academic Search

Detection and spectroscopy of materials in a nanometer scale can be achieved by combining near-field optical microscopy and nanostructured fractal materials engineered with desired surface structure and optical properties. This paper reports our recent studies on the energy and polarization dependence of greatly enhanced local light intensity at fractal surfaces.

Z. C. Ying

2002-01-01

345

Near-Field Optical Microscopy and Optical Tunneling Detection  

Microsoft Academic Search

By exploring the surface of an illuminated object at a very short distance by means of a subwavelength detector, it is possible to reconstruct images whose resolution is beyond the diffraction limit. This opportunity due to near field properties can be explained in terms of non radiative field detection that is of optical tunneling effect. We present some recent results

D. Courjon; M. Spajer; A. Jalocha; S. Leblanc

1991-01-01

346

Evolution of Magnetic Fields in Supernova Remnants  

E-print Network

Supernova remnants (SNR) are now widely believed to be a source of cosmic rays (CRs) up to an energy of 1 PeV. The magnetic fields required to accelerate CRs to sufficiently high energies need to be much higher than can result from compression of the circumstellar medium (CSM) by a factor 4, as is the case in strong shocks. Non-thermal synchrotron maps of these regions indicate that indeed the magnetic field is much stronger, and for young SNRs has a dominant radial component while for old SNRs it is mainly toroidal. How these magnetic fields get enhanced, or why the field orientation is mainly radial for young remnants, is not yet fully understood. We use an adaptive mesh refinement MHD code, AMRVAC, to simulate the evolution of supernova remnants and to see if we can reproduce a mainly radial magnetic field in early stages of evolution. We follow the evolution of the SNR with three different configurations of the initial magnetic field in the CSM: an initially mainly toroidal field, a turbulent magnetic field, and a field parallel to the symmetry axis. Although for the latter two topologies a significant radial field component arises at the contact discontinuity due to the Rayleigh-Taylor instability, no radial component can be seen out to the forward shock. Ideal MHD appears not sufficient to explain observations. Possibly a higher compression ratio and additional turbulence due to dominant presence of CRs can help us to better reproduce the observations in future studies.

K. M. Schure; J. Vink; A. Achterberg; R. Keppens

2008-10-28

347

Field Mapping System for Solenoid Magnet  

NASA Astrophysics Data System (ADS)

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

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

2007-01-01

348

Magnetic fields in noninvasive brain stimulation.  

PubMed

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

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

2014-04-01

349

Origin of magnetic fields in galaxies  

SciTech Connect

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.

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

350

Probing Primordial Magnetic Fields Using Ly? Clouds  

NASA Astrophysics Data System (ADS)

From previous studies of the effect of primordial magnetic fields on early structure formation, we know that the presence of primordial magnetic fields during early structure formation could induce more perturbations at small scales (at present 1-10 h -1 Mpc) as compared to the usual ?CDM theory. Matter power spectra over these scales are effectively probed by cosmological observables such as shear correlation and Ly? clouds. In this paper we discuss the implications of primordial magnetic fields on the distribution of Ly? clouds. We simulate the line-of-sight density fluctuation including the contribution coming from the primordial magnetic fields. We compute the evolution of Ly? opacity for this case and compare our theoretical estimates of Ly? opacity with the existing data to constrain the parameters of the primordial magnetic fields. We also discuss the case when the two density fields are correlated. Our analysis yields an upper bound of roughly 0.3-0.6 nG on the magnetic field strength for a range of nearly scale-invariant models, corresponding to a magnetic field power spectrum index n ~= -3.

Pandey, Kanhaiya L.; Sethi, Shiv K.

2013-01-01

351

Magnetic-field-controlled reconfigurable semiconductor logic.  

PubMed

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

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

352

External-field-free magnetic biosensor  

SciTech Connect

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

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

2014-03-24

353

External-field-free magnetic biosensor  

NASA Astrophysics Data System (ADS)

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

Li, Yuanpeng; Wang, Yi; Klein, Todd; Wang, Jian-Ping

2014-03-01

354

Compact low field magnetic resonance imaging magnet: Design and optimization  

NASA Astrophysics Data System (ADS)

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

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

2000-03-01

355

Magnetic field corrections to solar oscillation frequencies  

NASA Technical Reports Server (NTRS)

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

Roberts, B.; Campbell, W. R.

1986-01-01

356

Low temperature and high magnetic field spectroscopic ellipsometry system.  

PubMed

We report on the design and implementation of a spectral ellipsometer at near-infrared wavelength (700-1000 nm) for samples placed in high magnetic fields (up to 14 T) at low temperatures (~4.2 K). The main optical components are integrated in a probe, which can be inserted into a conventional long-neck He dewar and has a very long free-space optical path (~1.8 m×2). A polarizer-sample-(quarter-wave plate)-rotating analyzer configuration was employed. Two dielectric mirrors, one before and one after the sample in the optical path, helped to reflect the light back to the analyzer and a two-axis piezo-driven goniometer under the sample holder was used to control the direction of the reflected light. Functional test results performed on an intrinsic GaAs wafer and analysis on the random error of the system are shown. We obtained both amplitude and phase ellipsometric spectra simultaneously and observed helicity transformation at energies near the GaAs exciton transitions in the phase spectra. Significant shifts of them induced by magnetic fields were observed and fitted with a simple model. This system will allow us to study the collective magneto-optical response of materials and spatial dispersive exciton-polariton related problems in high external magnetic fields at low temperatures. PMID:24880409

Su, Sheng-Kai; Li, Liang-Chen; Suen, Yuen-Wuu; Wu, Jau-Yang; Kuo, Hong-Rong; Sung, Yu-Tai; Lee, Chien-Ping; Voskoboynikov, Oleksandr

2014-05-01

357

Vector Magnetic Field in Emerging Flux Regions  

NASA Astrophysics Data System (ADS)

A crucial phase in magnetic flux emergence is the rise of magnetic flux tubes through the solar photosphere, which represents a severe transition between the very different environments of the solar interior and corona. Multi-wavelength observations with Flare Genesis, TRACE, SoHO, and more recently with the vector magnetographs at THEMIS and Hida (DST) led to the following conclusions. The fragmented magnetic field in the emergence region - with dipped field lines or bald patches - is directly related with Ellerman bombs, arch filament systems, and overlying coronal loops. Measurements of vector magnetic fields have given evidence that undulating "serpentine" fields are present while magnetic flux tubes cross the photosphere. See the sketch below, and for more detail see Pariat et al. (2004, 2007); Watanabe et al. (2008):

Schmieder, B.; Pariat, E.

358

An optically modulated zero-field atomic magnetometer with suppressed spin-exchange broadening  

SciTech Connect

We demonstrate an optically pumped {sup 87}Rb magnetometer in a microfabricated vapor cell based on a zero-field dispersive resonance generated by optical modulation of the {sup 87}Rb ground state energy levels. The magnetometer is operated in the spin-exchange relaxation-free regime where high magnetic field sensitivities can be achieved. This device can be useful in applications requiring array-based magnetometers where radio frequency magnetic fields can induce cross-talk among adjacent sensors or affect the source of the magnetic field being measured.

Jiménez-Martínez, R. [Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States) [Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States); Department of Physics, University of Colorado, Boulder, Colorado 80309 (United States); Knappe, S.; Kitching, J. [Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States)] [Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States)

2014-04-15

359

An optically modulated zero-field atomic magnetometer with suppressed spin-exchange broadening  

E-print Network

We demonstrate an optically pumped $^{87}$Rb magnetometer in a microfabricated vapor cell based on a zero-field dispersive resonance generated by optical modulation of the $^{87}$Rb ground state energy levels. The magnetometer is operated in the spin-exchange relaxation-free regime where high magnetic field sensitivities can be achieved. This device can be useful in applications requiring array-based magnetometers where radio frequency magnetic fields can induce cross-talk among adjacent sensors or affect the source of the magnetic field being measured.

Jimenez-Martinez, Ricardo; Kitching, John

2014-01-01

360

Advanced magnetic calculations for high magnetic field compact ion source  

NASA Astrophysics Data System (ADS)

The design of the advanced electronic cyclotronic resonance ion source (ECRIS) requires relatively high axial and radial magnetic inductions to allow the ECR frequency increase and to take advantage of the subsequent density increase (scaling laws). The last improvements of the commercial rare-earth magnet characteristics open new opportunities for ECRIS and enable the design of very high hexapolar magnetic fields for next generation compact ECRIS. Moreover, the high temperature superconducting (HTS) wires allow designing reliable and compact axial field coils (30 K cooled) at a very effective cost. It is thus very relevant to study a compact hybrid ECRIS using high remanence magnet and HTS technologies. In such a design, the volume of the plasma chamber is a free parameter that can be adjusted to the user requirement. It can be dedicated to very high ionic current production or high charge state production, pulsed, or cw operations. This paper presents the three-dimensional overall simulation of a 3 T axial magnetic field compact ECRIS with a high radial field sextupole composed with several magnet types and reaching ˜1.9 T in front of the radially magnetized magnets. This design study will lead to the building of the 28-40 GHz A-PHOENIX source at the laboratory which will deliver its first beam by the end of 2004.

Thuillier, T.; Curdy, J.-C.; Lamy, T.; Sole, P.; Sortais, P.; Vieux-Rochaz, J.-L.; Voulot, D.

2004-05-01

361

Magnetic reconnection at the edge of Uranus's magnetic field  

NASA Astrophysics Data System (ADS)

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

Balcerak, Ernie

2014-09-01

362

Anisotropy of magnetic susceptibility measured in variable weak magnetic fields  

NASA Astrophysics Data System (ADS)

Theory of the low-field anisotropy of magnetic susceptibility (AMS) of rocks is based on the assumption of the linear relationship between magnetization and magnetizing field, resulting in field independent susceptibility. This relationship is by definition valid in diamagnetic and paramagnetic minerals, while in ferrimagnetic and antiferromagnetic minerals this relationship is in general non-linear (represented by hysteresis loop), being linear only in very weak fields in which the initial susceptibility is measured. Among these minerals, magnetite shows no field variation of susceptibility and its anisotropy in the low fields used in common AMS meters. In pyrrhotite, hematite and titanomagnetite bearing rocks, in which these minerals are very fine-grained, the field variation of susceptibility is insignificant. Using linear theory in calculating the AMS is fully legitimate in all these cases. In pyrrhotite, hematite, and titanomagnetite bearing rocks, in which these minerals are relatively coarse-grained (typically hundreds of micrometers), clear field variation of magnetic susceptibility may exist even in the low fields used in common AMS meters, often resulting in bad fit of the susceptibility tensor to the measured data. Strictly speaking, linear theory in calculating the AMS is in general incorrect in this case. The KLY-3S Kappabridge has been modified in such a way to enable AMS measurement also in the fields down to 3 A/m. Examples are shown of the effect of this field decrease on the measured data.

Pokorny, J.; Suza, P.; Hrouda, F.

2003-04-01

363

Magnetic reconnection with radiative cooling. I. Optically thin regime  

SciTech Connect

Magnetic reconnection processes in many high-energy-density astrophysical and laboratory plasma systems are significantly affected by radiation; hence traditional, nonradiative reconnection models are not applicable to these systems. Motivated by this observation, the present paper develops a Sweet-Parker-like theory of resistive magnetic reconnection with strong radiative cooling. It is found that, in the case with zero guide field, intense radiative cooling leads to a strong plasma compression, resulting in a higher reconnection rate. The compression ratio and the reconnection layer temperature are determined by the balance between ohmic heating and radiative cooling. The lower temperature in a radiatively cooled layer leads to a higher Spitzer resistivity and, hence, a higher reconnection rate. Several specific radiative processes (bremsstrahlung, cyclotron, and inverse Compton) in the optically thin regime are considered for both the zero- and strong-guide-field cases, and concrete expressions for the reconnection parameters are derived, along with the applicability conditions.

Uzdensky, Dmitri A. [Center for Integrated Plasma Studies, Physics Department, UCB-390, University of Colorado, Boulder, Colorado 80309 (United States); McKinney, Jonathan C. [Department of Physics and Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, California 94305-4060 (United States)

2011-04-15

364

Particle Transport in Therapeutic Magnetic Fields  

NASA Astrophysics Data System (ADS)

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.

Puri, Ishwar K.; Ganguly, Ranjan

2014-01-01

365

The Measurement of Magnetic Fields  

ERIC Educational Resources Information Center

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

Berridge, H. J. J.

1973-01-01

366

Faraday's Magnetic Field Induction Experiment  

NSDL National Science Digital Library

This java simulation illustrates magnetic induction in a wire coil. The user can move a magnet in and out along the axis of a coil while a galvanometer shows the current induced in the coil. The deflection depends on the speed at which the coil moves.

Davidson, Michael

2010-12-29

367

The CMS Magnetic Field Map Performance  

E-print Network

The Compact Muon Solenoid (CMS) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive featuresinclude a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10000-ton return yoke made of construction steel. Accurate characterization of the magnetic field everywhere in the CMS detector is required. During two major tests of the CMS magnet the magnetic flux density was measured inside the coil in a cylinder of 3.448 m diameter and 7 m length with a specially designed field-mapping pneumatic machine as well as in 140 discrete regions of the CMS yoke with NMR probes, 3-D Hall sensors and flux-loops. A TOSCA 3-D model of the CMS magnet has been developed to describe the magnetic field everywhere outside the tracking volume measured with the field-mapping machine. A volume based representation of the magnetic field is used to provide the CMS simulation and reconstruction software with the magnetic field values. The value of the field at a given point of a volume is obtained by interpolation from a regular grid of values resulting from a TOSCA calculation or, when available, from a parameterization. The results of the measurements and calculations are presented, compared and discussed.

V. I. Klyukhin; N. Amapane; V. Andreev; A. Ball; B. Curé; A. Hervé; A. Gaddi; H. Gerwig; V. Karimaki; R. Loveless; M. Mulders; S. Popescu; L. I. Sarycheva; T. Virdee

2011-10-04

368

Taming the Collapse of Optical Fields  

NASA Astrophysics Data System (ADS)

Field collapse, which occurs in various nonlinear systems, has attracted much attention, owing to its universality, complexity, and applicability. A great challenge and expectation is to achieve the controllable and designable collapsing pattern. Here we predict theoretically and demonstrate experimentally the novel collapsing behaviors of the vector optical fields in a self-focusing Kerr medium. Surprisingly, the results reveal that the collapse of the vector optical field is controllable and designable by engineering the distribution of hybrid states of polarization, and has the robust feature insensitive to the random noise. Our idea has its significance which it opens a new window for manipulating the optical field and the different kinds of field, and then facilitates to push the related researches.

Li, Si-Min; Li, Yongnan; Wang, Xi-Lin; Kong, Ling-Jun; Lou, Kai; Tu, Chenghou; Tian, Yongjun; Wang, Hui-Tian

2012-12-01

369

Generation of high magnetic fields using superconducting magnets  

Microsoft Academic Search

High-field superconducting magnets have opened new frontiers for several kinds of applications, such as fusion reactors, particle accelerators, and nuclear magnetic resonance (NMR) spectrometers. The present record for the highest field in a fully superconducting state is 23.4T. It was achieved with a combination of NbTi, Nb3Sn, and Bi-2212 conductors in 1999. Since high Tc (critical temperature) superconductors (HTS) have

T. Kiyoshi; A. Otsuka; M. Kosuge; M. Yuyama; H. Nagai; F. Matsumoto

2006-01-01

370

Artificial magnetic field induced by an evanescent wave.  

PubMed

Cold atomic gases are perfect laboratories for realization of quantum simulators. In order to simulate solid state systems in the presence of magnetic fields special effort has to be made because atoms are charge neutral. There are different methods for realization of artificial magnetic fields, that is the creation of specific conditions so that the motion of neutral particles mimics the dynamics of charged particles in an effective magnetic field. Here, we consider adiabatic motion of atoms in the presence of an evanescent wave. Theoretical description of the adiabatic motion involves artificial vector and scalar potentials related to the Berry phases. Due to the large gradient of the evanescent field amplitude, the potentials can be strong enough to induce measurable effects in cold atomic gases. We show that the resulting artificial magnetic field is able to induce vortices in a Bose-Einstein condensate trapped close to a surface of a prism where the evanescent wave is created. We also analyze motion of an atomic cloud released from a magneto-optical trap that falls down on the surface of the prism. The artificial magnetic field is able to reflect falling atoms that can be observed experimentally. PMID:25567430

Mochol, Ma?gorzata; Sacha, Krzysztof

2015-01-01

371

Artificial magnetic field induced by an evanescent wave  

NASA Astrophysics Data System (ADS)

Cold atomic gases are perfect laboratories for realization of quantum simulators. In order to simulate solid state systems in the presence of magnetic fields special effort has to be made because atoms are charge neutral. There are different methods for realization of artificial magnetic fields, that is the creation of specific conditions so that the motion of neutral particles mimics the dynamics of charged particles in an effective magnetic field. Here, we consider adiabatic motion of atoms in the presence of an evanescent wave. Theoretical description of the adiabatic motion involves artificial vector and scalar potentials related to the Berry phases. Due to the large gradient of the evanescent field amplitude, the potentials can be strong enough to induce measurable effects in cold atomic gases. We show that the resulting artificial magnetic field is able to induce vortices in a Bose-Einstein condensate trapped close to a surface of a prism where the evanescent wave is created. We also analyze motion of an atomic cloud released from a magneto-optical trap that falls down on the surface of the prism. The artificial magnetic field is able to reflect falling atoms that can be observed experimentally.

Mochol, Ma?gorzata; Sacha, Krzysztof

2015-01-01

372

Artificial magnetic field induced by an evanescent wave  

PubMed Central

Cold atomic gases are perfect laboratories for realization of quantum simulators. In order to simulate solid state systems in the presence of magnetic fields special effort has to be made because atoms are charge neutral. There are different methods for realization of artificial magnetic fields, that is the creation of specific conditions so that the motion of neutral particles mimics the dynamics of charged particles in an effective magnetic field. Here, we consider adiabatic motion of atoms in the presence of an evanescent wave. Theoretical description of the adiabatic motion involves artificial vector and scalar potentials related to the Berry phases. Due to the large gradient of the evanescent field amplitude, the potentials can be strong enough to induce measurable effects in cold atomic gases. We show that the resulting artificial magnetic field is able to induce vortices in a Bose-Einstein condensate trapped close to a surface of a prism where the evanescent wave is created. We also analyze motion of an atomic cloud released from a magneto-optical trap that falls down on the surface of the prism. The artificial magnetic field is able to reflect falling atoms that can be observed experimentally. PMID:25567430

Mochol, Ma?gorzata; Sacha, Krzysztof

2015-01-01

373

Magnetic Field Measurement with Ground State Alignment  

NASA Astrophysics Data System (ADS)

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

Yan, Huirong; Lazarian, A.

374

Magnetofluidic platform for multidimensional magnetic and optical barcoding of droplets.  

PubMed

We present a concept of multidimensional magnetic and optical barcoding of droplets based on a magnetofluidic platform. The platform comprises multiple functional areas, such as an encoding area, an encoded droplet pool and a magnetic decoding area with integrated giant magnetoresistive (GMR) sensors. To prove this concept, penicillin functionalized with fluorescent dyes is coencapsulated with magnetic nanoparticles into droplets. While fluorescent dyes are used as conventional optical barcodes which are decoded with an optical decoding setup, an additional dimensionality of barcodes is created by using magnetic nanoparticles as magnetic barcodes for individual droplets and integrated micro-patterned GMR sensors as the corresponding magnetic decoding devices. The strategy of incorporating a magnetic encoding scheme provides a dynamic range of ~40 dB in addition to that of the optical method. When combined with magnetic barcodes, the encoding capacity can be increased by more than 1 order of magnitude compared with using only optical barcodes, that is, the magnetic platform provides more than 10 unique magnetic codes in addition to each optical barcode. Besides being a unique magnetic functional element for droplet microfluidics, the platform is capable of on-demand facile magnetic encoding and real-time decoding of droplets which paves the way for the development of novel non-optical encoding schemes for highly multiplexed droplet-based biological assays. PMID:25353316

Lin, Gungun; Makarov, Denys; Medina-Sánchez, Mariana; Guix, Maria; Baraban, Larysa; Cuniberti, Gianaurelio; Schmidt, Oliver G

2015-01-01

375

Magnetic Fields from Heterotic Cosmic Strings  

E-print Network

Large-scale magnetic fields are observed today to be coherent on galactic scales. While there exists an explanation for their amplification and their specific configuration in spiral galaxies -- the dynamo mechanism -- a satisfying explanation for the original seed fields required is still lacking. Cosmic strings are compelling candidates because of their scaling properties, which would guarantee the coherence on cosmological scales of any resultant magnetic fields at the time of galaxy formation. We present a mechanism for the production of primordial seed magnetic fields from heterotic cosmic strings arising from M theory. More specifically, we make use of heterotic cosmic strings stemming from M5--branes wrapped around four of the compact internal dimensions. These objects are stable on cosmological time scales and carry charged zero modes. Therefore a scaling solution of such defects will generate seed magnetic fields which are coherent on galactic scales today.

Gwyn, Rhiannon; Brandenberger, Robert H; Dasgupta, Keshav

2008-01-01

376

Magnetic fields from heterotic cosmic strings  

SciTech Connect

Large-scale magnetic fields are observed today to be coherent on galactic scales. While there exists an explanation for their amplification and their specific configuration in spiral galaxies--the dynamo mechanism--a satisfying explanation for the original seed fields required is still lacking. Cosmic strings are compelling candidates because of their scaling properties, which would guarantee the coherence on cosmological scales of any resultant magnetic fields at the time of galaxy formation. We present a mechanism for the production of primordial seed magnetic fields from heterotic cosmic strings arising from M theory. More specifically, we make use of heterotic cosmic strings stemming from M5-branes wrapped around four of the compact internal dimensions. These objects are stable on cosmological time scales and carry charged zero modes. Therefore a scaling solution of such defects will generate seed magnetic fields which are coherent on galactic scales today.

Gwyn, Rhiannon; Alexander, Stephon H.; Brandenberger, Robert H.; Dasgupta, Keshav [Department of Physics, McGill University, Montreal, Quebec, H3A 2T8 (Canada); Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802-6300 (United States); Department of Physics and Astronomy, Koshland Center for Integrated Sciences, Haverford College, Haverford, Pennsylvania 19041 (United States); Department of Physics, McGill University, Montreal, Quebec, H3A 2T8 (Canada)

2009-04-15

377

The magnetic field of Mercury, part 1  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

378

Periodic reversal of magneto-optic Faraday rotation on uniaxial birefringence crystal with ultrathin magnetic films  

NASA Astrophysics Data System (ADS)

An experimental approach of inclined incidence magneto-optic Faraday effect observed in the polar plane is applied. Three samples containing ferromagnetic cobalt ultrathin films on a semiconductor zinc oxide (0001) single crystal substrate with in-plane and out-of-plane anisotropy are evaluated. Through the fine adjustment of crossed polarizers in the magneto-optic effect measurement completely recorded the detail optical and magneto-optical responses from the birefringent crystal substrate and the magnetic film, especially for the signal induced from the substrate with uniaxial optical axis. The angle dependency of interference phenomena periodically from the optical and magneto-optical responses is attributed to the birefringence even in the absence of a magnetic field. The new type of observation finds that the transmission Faraday intensity in the oblique incidence includes a combination of polarization rotations, which results from optical compensation from the substrate and magneto-optical Faraday effects from the film. The samples grown at different rates and examined by this method exhibit magnetic structure discriminations. This result can be applied in the advanced polarized-light technologies to enhance the spatial resolution of magnetic surfaces with microstructural information under various magnetic field direction.

Su, C. W.; Chang, S. C.; Chang, Y. C.

2013-07-01

379

QCD string breaking in strong magnetic field  

NASA Astrophysics Data System (ADS)

At sufficiently large separation between a quark and an antiquark the quantum chromodynamics (QCD) string breaks into parts due to creation of light quark-antiquark pairs. We show that a background magnetic field affects the breaking of the QCD string oriented in the transverse directions with respect to the axis of the magnetic field. Using semiclassical approach we argue that above certain, the background magnetic field eB ?0.3 GeV2 breaking of the transverse string should become energetically unfavorable.

Chernodub, M. N.

2014-09-01

380

Magnetic fields from second-order interactions  

E-print Network

It is well known that when two types of perturbations interact in cosmological perturbation theory, the interaction may lead to the generation of a third type. In this article we discuss the generation of magnetic fields from such interactions. We determine conditions under which the interaction of a first-order magnetic field with a first-order scalar-or vector-, or tensor-perturbations would lead to the generation of second order magnetic field. The analysis is done in a covariant-index-free approach, but could be done in the standard covariant indexed-approach.

Bob Osano

2014-03-21

381

Small-scale solar magnetic fields  

E-print Network

As we resolve ever smaller structures in the solar atmosphere, it has become clear that magnetism is an important component of those small structures. Small-scale magnetism holds the key to many poorly understood facets of solar magnetism on all scales, such as the existence of a local dynamo, chromospheric heating, and flux emergence, to name a few. Here, we review our knowledge of small-scale photospheric fields, with particular emphasis on quiet-sun field, and discuss the implications of several results obtained recently using new instruments, as well as future prospects in this field of research.

A. G. de Wijn; J. O. Stenflo; S. K. Solanki; S. Tsuneta

2008-12-24

382

The magnetic field of solar prominences  

E-print Network

In his famous monographs, Einar Tandberg-Hanssen writes that "the single, physically most important parameter to study in prominences may be the magnetic field. Shapes, motions, and in fact the very existence of prominences depend on the nature of the magnetic field threading the prominence plasma". Hereafter we sumarize recent contributions and advances in our knowledge about the magnetic field of solar prominences. It mostly relies on high resolution and high sensitivity spectropolarimetry made both in the visible and in the near infrared.

F. Paletou

2008-10-15

383

Environmental magnetic fields: Influences on early embryogenesis  

SciTech Connect

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

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

1993-04-01

384

Magnetic fields of the terrestrial planets  

NASA Technical Reports Server (NTRS)

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.

Russell, C. T.

1993-01-01

385

The optic nerve pathology in magnetic resonance imaging.  

PubMed

Magnetic resonance imaging (MRI) delineates the orbital soft tissue excellently and is a valuable diagnostic tool in optic nerve pathology. By using different imaging parameters some examples are shown of demarcation of optic nerve tumors, optic nerve inflammations and orbital diseases surrounding the optic nerve. Whereas CT appears to be superior to MRI only in the detection of calcified perioptic meningiomas, MRI provides unique visualization of optic canal and even subarachnoidal space of retrobulbar optic nerve in peculiar cases. PMID:2079907

Wiegand, W

1990-01-01

386

Magnetic property of polycrystalline magnetic garnet for voltage driven type magneto-optic spatial light phase modulator  

NASA Astrophysics Data System (ADS)

In this study, we investigated the magnetization response of the polycrystalline magnetic garnet film for stress. The calculation suggests that the balance of the magnetic anisotropic energy under magnetic field is an essential factor to modulate the magnetization by stress. We fabricated the magnetophotonic crystal based voltage driven type magneto-optic spatial light modulator, and measured the magneto-optic response for stress. The experimental results had a good agreement with our calculation. In our results, the magnitude and linearity of the modulation by stress was depending on static bias field, stress, and magnetostriction constant. The obtained results implied that the calculation could estimate the device performance by deciding material composition and prepare stress inside garnet.

Mito, S.; Kim, J.; Chung, K. H.; Yamada, K.; Kato, T.; Takagi, H.; Lim, P. B.; Inoue, M.

2010-05-01

387

The CMS Magnetic Field Map Performance  

E-print Network

The Compact Muon Solenoid (CMS) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive featuresinclude a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10000-ton return yoke made of construction steel. Accurate characterization of the magnetic field everywhere in the CMS detector is required. During two major tests of the CMS magnet the magnetic flux density was measured inside the coil in a cylinder of 3.448 m diameter and 7 m length with a specially designed field-mapping pneumatic machine as well as in 140 discrete regions of the CMS yoke with NMR probes, 3-D Hall sensors and flux-loops. A TOSCA 3-D model of the CMS magnet has been developed to describe the magnetic field everywhere outside the tracking volume measured with the field-mapping machine. A volume based representation of the magnetic field is used to provide the CMS simulation and reconstruction software with the magnetic field ...

Klyukhin, VI; Sarycheva, L I; Klyukhin, V I; Ball, A; Gaddi, A; Amapane, N; Gerwig, H; Andreev, V; Cure, B; Mulders, M; Loveless, R; Karimaki, V; Popescu, S; Herve, A

2010-01-01

388

Space applications of superconductivity - High field magnets  

NASA Technical Reports Server (NTRS)

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

Fickett, F. R.

1979-01-01

389

A subwavelength plasmonic metamolecule exhibiting magnetic-based optical Fano resonance.  

PubMed

The lack of symmetry between electric and magnetic charges, a fundamental consequence of the small value of the fine-structure constant, is directly related to the weakness of magnetic effects in optical materials. Properly tailored plasmonic nanoclusters have been proposed recently to induce artificial optical magnetism based on the principle that magnetic effects are indistinguishable from specific forms of spatial dispersion of permittivity at optical frequencies. In a different context, plasmonic Fano resonances have generated a great deal of interest, particularly for use in sensing applications that benefit from sharp spectral features and extreme field localization. In the absence of natural magnetism, optical Fano resonances have so far been based on purely electric effects. In this Letter, we demonstrate that a subwavelength plasmonic metamolecule consisting of four closely spaced gold nanoparticles supports a strong magnetic response coupled to a broad electric resonance. Small structural asymmetries in the assembled nanoring enable the interaction between electric and magnetic modes, leading to the first observation of a magnetic-based Fano scattering resonance at optical frequencies. Our findings are supported by excellent agreement with simulations and analytical calculations, and represent an important step towards the quest for artificial magnetism and negative refractive index metamaterials at optical frequencies. PMID:23353675

Shafiei, Farbod; Monticone, Francesco; Le, Khai Q; Liu, Xing-Xiang; Hartsfield, Thomas; Alù, Andrea; Li, Xiaoqin

2013-02-01

390

Measurement of the Deformation in Pulsed Magnets by Means of Optical Fiber Sensors  

Microsoft Academic Search

A typical compact pulsed magnet coil wound from copper and Zylon fiber was fabricated with optical fiber sensors embedded at different places in the Zylon layers. Measurements of deformation have been carried out during winding, cooling and with magnetic field pulses up to 10 T at room temperature and 41 T at 77 K. The results are in agreement with

T. Peng; H. X. Xiao; F. Herlach; L. Li

2012-01-01

391

Field Directed Ordering in Magnetic Nanocrystal Structures  

NASA Astrophysics Data System (ADS)

Iron oxide nanocrystals (NCs) have been the focus of intense research owing to the observation of tunable magnetic properties which could lead to advances in many fields including magnetic storage devices and medicine. We have been targeting the use of iron oxide NCs as magnetoresistance (MR) based sensors using ordered NC arrays. In this work, we will present our efforts toward using external magnetic fields to induce intraparticle ordering in iron oxide NC drop cast films. We use x-ray diffraction to analyze effects of the external fields on the NC array structure, while using SQUID magnetometry to probe the effects of NC interactions on the magnetic properties of iron oxide NCs ranging from 5 - 20 nm in diameter. MR measurements suggest large changes in the MR ratio can be achieved using the directed ordering approach for NC arrays. Our work could provide new avenues towards the fabrication of new magnetic devices.

Lawson, Stuart; Meulenberg, Robert

2013-03-01

392

Solar Nebula Magnetic Fields Recorded in the Semarkona Meteorite November 17, 2014  

E-print Network

Solar Nebula Magnetic Fields Recorded in the Semarkona Meteorite November 17, 2014 Fig 1: Dusty olivine-bearing chondrules from the Semarkona meteorite. Optical photomicrograph of chondrule DOC4 showing. Fu, et al., "Solar nebula magnetic fields recorded in the Semarkona meteorite," Science DOI: 10

Walsworth, Ronald L.

393

Measuring the magnetic fields of jupiter and the outer solar system  

Microsoft Academic Search

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

E. Smith; B. Connor

1975-01-01

394

Juno and Jupiter's Magnetic Field (Invited)  

NASA Astrophysics Data System (ADS)

The Juno spacecraft, launched in August 2011, will reach Jupiter in early July 2016, where it will enter a polar orbit, with an 11 day period and a perijove altitude of approximately 5000 km. The baseline mission will last for one year during which Juno will complete 32 orbits, evenly spaced in longitude. The baseline mission presents an unparalleled opportunity for investigating Jupiter's magnetic field. In many ways Jupiter is a better planet for studying dynamo-generated magnetic fields than the Earth: there are no crustal fields, of course, which otherwise mask the dynamo-generated field at high degree; and an orbiting spacecraft can get proportionately much closer to the dynamo region. Assuming Jupiter's dynamo extends to 0.8 Rj, Juno at closet approach is only 0.3 Rc above the dynamo, while Earth orbiting magnetic field missions sample the field at least 1 Rc above the dynamo (where Rc is the respective outer core or dynamo region radius). Juno's MAG Investigation delivers magnetic measurements with exceptional vector accuracy (100 ppm) via two FGM sensors, each co-located with a dedicated pair of non-magnetic star cameras for attitude determination at the sensor. We expect to image Jupiter's dynamo with unsurpassed resolution. Accordingly, we anticipate that the Juno magnetic field investigation may place important constraints on Jupiter's interior structure, and hence on the formation and evolution of Jupiter.

Bloxham, J.; Connerney, J. E.; Jorgensen, J. L.

2013-12-01

395

Field and current induced magnetization reversal in patterned Pseudo Spin Valve devices  

E-print Network

The field and current induced magnetization switchings of Pseudo-Spin-Valve (PSV) devices are described in this dissertation. An aligned sequence of three (one optical and two electron-beam) lithographies was used to define ...

Colin, Irénée A. (Irénée Anthelme)

2007-01-01

396

Current Sheets in Stressed Coronal Magnetic Fields  

NASA Astrophysics Data System (ADS)

The extrapolation of magnetic fields into the solar corona generally assumes that the fields are fully relaxed - all possible reconnection has occurred. This assumption is in conflict with the low magnetic diffusivity in the corona. I will present initial results on extrapolation based on stressed magnetic fields - those for which no reconnection has occurred. As an opposite extreme to traditional methods, stressed fields offer a different view of coronal fields. The locations of current sheets between flux systems are directly determined. Observational evidence of coronal reconnection can test the completeness of the extrapolation, as the field lines spanning flux systems must be in contact prior to reconnection. This work is supported by NASA SEC GI grant NAG5-13020.

Labonte, B. J.

2003-12-01

397

High-field superconducting nested coil magnet  

NASA Technical Reports Server (NTRS)

Superconducting magnet, employed in conjunction with five types of superconducting cables in a nested solenoid configuration, produces total, central magnetic field strengths approaching 70 kG. The multiple coils permit maximum information on cable characteristics to be gathered from one test.

Laverick, C.; Lobell, G. M.

1970-01-01

398

Interpretation of Solar Magnetic Field Strength Observations  

Microsoft Academic Search

This study based on longitudinal Zeeman effect magnetograms and spectral line scans investigates the dependence of solar surface magnetic fields on the spectral line used and the way the line is sampled to estimate the magnetic flux emerging above the solar atmosphere and penetrating to the corona from magnetograms of the Mt. Wilson 150-foot tower synoptic program (MWO). We have

R. K. Ulrich; L. Bertello; J. E. Boyden; L. Webster

2009-01-01

399

High field magnets at the international laboratory Wroclaw  

Microsoft Academic Search

At Wroclaw high magnetic fields have been produced since the late 1960s. At present there are several magnets for stationary fields and one magnet for pulsed fields. The biggest, Bitter-type magnet generates magnetic fields up to 20 T, total power exceeds 6.0 MW.

K. Trojnar; N. Koppetzki

1989-01-01

400

Electrostatic waves in carbon nanotubes with an axial magnetic field  

NASA Astrophysics Data System (ADS)

Based on a linearized hydrodynamic model and within the quasi-static approximation, the dispersion relation of electrostatic waves propagating through single-walled carbon nanotubes subject to an axial magnetic field is theoretically explored. In the classical limit, we obtain two main possible waves which in turn are divided into two branches, a low-frequency acoustical and a high-frequency optical plasmon branch. In the quantum case, we have found that the dispersion relation is substantially modified when the electron wavelength becomes large enough compared to the propagation wavelength of the electrostatic waves in the quantum plasma. We also show that the axial magnetic field manifest itself on the perturbed electron density through the quantum term and gives rise to the propagation of the electrostatic waves within the quantum plasma. As a result, the effect of the magnetic field is pronounced in the plasma dispersion relations in such a way that their curves approach to zero when the magnetic field is weak; and for the strong magnetic field, they asymptotically meet the constant lines.

Abdikian, Alireza; Bagheri, Mehran

2013-10-01

401

Interferometric methods for mapping static electric and magnetic fields  

NASA Astrophysics Data System (ADS)

The mapping of static electric and magnetic fields using electron probes with a resolution and sensitivity that are sufficient to reveal nanoscale features in materials requires the use of phase-sensitive methods such as the shadow technique, coherent Foucault imaging and the Transport of Intensity Equation. Among these approaches, image-plane off-axis electron holography in the transmission electron microscope has acquired a prominent role thanks to its quantitative capabilities and broad range of applicability. After a brief overview of the main ideas and methods behind field mapping, we focus on theoretical models that form the basis of the quantitative interpretation of electron holographic data. We review the application of electron holography to a variety of samples (including electric fields associated with p-n junctions in semiconductors, quantized magnetic flux in superconductors and magnetization topographies in nanoparticles and other magnetic materials) and electron-optical geometries (including multiple biprism, amplitude and mixed-type set-ups). We conclude by highlighting the emerging perspectives of (i) three-dimensional field mapping using electron holographic tomography and (ii) the model-independent determination of the locations and magnitudes of field sources (electric charges and magnetic dipoles) directly from electron holographic data.

Pozzi, Giulio; Beleggia, Marco; Kasama, Takeshi; Dunin-Borkowski, Rafal E.

2014-02-01

402

The Magnetic Field of Helmholtz Coils  

ERIC Educational Resources Information Center

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)

Berridge, H. J. J.

1975-01-01

403

Heat Capacity Measurements in Pulsed Magnetic Fields  

SciTech Connect

The new NHMFL 60T quasi-continuous magnet produces a flat-top field for a period of 100 ms at 60 Tesla, and for longer time at lower fields, e.g. 0.5 s at 45 Tesla. We have developed for the first time the capability to measure heat capacity at very high magnetic fields in the NHMFL 60T quasi-continuous magnet at LANL, using a probe built out of various plastic materials. The field plateau allows us to utilize a heat-pulse method to obtain heat capacity data. Proof-of-principle heat capacity experiments were performed on a variety of correlated electron systems. Both magnet performance characteristics and physical properties of various materials studied hold out a promise of wide application of this new tool.

Jaime, M.; Movshovich, R.; Sarrao, J.L.; Kim, J.; Stewart, G.; Beyermann, W.P.; Canfield, P.C.

1998-10-23

404

Improved Spindle Cusp Magnetic Field for ECRIS  

SciTech Connect

Magnetic field of minimum-B configuration is very important for achieving more plasma confinement and closed electron cyclotron resonance (ECR) surface for electron heating and plasma discharge. The spindle cusp magnetic field configuration forms the modified minimum-B configuration. The absolute magnetic field at the chamber surface on mid-plane has been optimized and improved sufficiently and symmetrized to the field at the point cusp positions on the central axis. With enhancement of electrostatic and magnetic mirror action at the cusp positions the density of the plasma as well as confinement is boosted. The system becomes simpler, more compact and cost-effective compared to the conventional one to generate and extract highly charged heavy ions (HCHI). A co-operative and collaborative effort is essential to develop and test such conceived new ECRIS.

Rashid, M.H.; Mallik, C.; Bhandari, R.K. [Variable Energy Cyclotron Centre, Sector-1, Block-AF, Bidhan Nagar, Kolkata- 700 064 (India)

2005-03-15

405

A Holographic Bound on Cosmic Magnetic Fields  

E-print Network

Magnetic fields large enough to be observable are ubiquitous in astrophysics, even at extremely large length scales. This has led to the suggestion that such fields are seeded at very early (inflationary) times, and subsequently amplified by various processes involving, for example, dynamo effects. Many such mechanisms give rise to extremely large magnetic fields at the end of inflationary reheating, and therefore also during the quark-gluon plasma epoch of the early universe. Such plasmas have a well-known holographic description. We show that holography imposes an upper bound on the intensity of magnetic fields (scaled by the squared temperature) in these circumstances, and that the values expected in some models of cosmic magnetism come close to attaining that bound.

McInnes, Brett

2015-01-01

406

Lunar magnetic field measurements with a cubesat  

E-print Network

We have developed a mission concept that uses 3-unit cubesats to perform new measurements of lunar magnetic fields, less than 100 meters above the Moon’s surface. The mission calls for sending the cubesats on impact ...

Garrick-Bethell, Ian

407

Cyclic evolution and reversal of the solar magnetic field. I. The large-scale magnetic fields  

E-print Network

On the base of the solar magnetic field measurements obtained in Stanford in 1976--2003 the properties of the cyclic evolution of the large-scale magnetic field are investigated. Some regularities are found in longitudinal and latitudinal evolution of the magnetic field in cycles 21, 22 and 23. The cyclic development of the large-scale magnetic field can be divided into two main phases. The phase I, which includes a period approximately from two years before and until three years after the maximum of the solar cycle, is studied in detail. It is found that before the reversal of the large-scale magnetic field the neutral line of the magnetic field in antipodal longitudinal intervals shifts from the equator to opposite directions in cycles 21 and 22, but not in cycle 23. During the sign reversal of the large-scale magnetic field in cycles 21 and 22 in the antipodal longitudinal intervals the magnetic field of opposite polarity is observed in all latitudes, thereby forming an equatorial dipole. After the magnetic field reversal a longitudinal oscillation of the magnetic neutral line with regard to the equator takes place, which has a period about 2 years and damps to the minimum of the 11-year cycle. The intervening longitudinal intervals of the large-scale magnetic field correspond to positions of the active longitudes of sunspot activity, thus indicating a close connection of the large-scale and the local magnetic fields. In evolution of the large-scale magnetic field a periodicity with period $1.23\\pm0.16$ year is revealed, which is close to the period found by helioseismological methods in variations of the solar rotation near the tachocline.

R. N. Ikhsanov; V. G. Ivanov

2003-10-20

408

Low Temperature Thermometry in High Magnetic Fields  

Microsoft Academic Search

The calibration and reproducibilty of various commercial and homemade thermometers have been investigated over a temperature range from 20 mK to 4.2 K and magnetic field strength from 0 to 16 Tesla. The performance of resistance thermometers made of different materials varies widely as a function of magnetic field. One type (Scientific Instruments RO600) is found to have a relatively

Gary G. Ihas; L. Frederick; J. P. McFarland

1998-01-01

409

Search for weak magnetic fields of stars  

Microsoft Academic Search

The magnetic fields of some normal stars of the main sequence, supergiants and Hg-Mn stars have been measured from metallic and hydrogen lines on the 6-m telescope with the Fabry-Perot magnetometer and spectropolarimeter. These results and the data of other authors are statistically analysed. A conclusion is drawn that the studied types of stars hardly contain a magnetic field exceeding

Yu. V. Glagolevskij; I. I. Romanyuk; I. D. Najdenov; V. G. Shtol

1989-01-01

410

Magnetic field effects on mass transport  

Microsoft Academic Search

It has been shown that the stationary limiting diffusion current on a steady electrode is proportional to {ital B}¹³{ital C}⁴³ where {ital C} is the electroactive species concentration and {ital B} the magnetic field intensity. A new impedance technique is developed which consists of the frequency response analysis of the limiting diffusion current to a sinusoidal magnetic field perturbation. In

O. Aaboubi; J. P. Chopart; J. Douglade; C. Gabrielli; B. Tribollet

1990-01-01

411

The magnetic field investigation on Cluster  

NASA Technical Reports Server (NTRS)

The magnetic field investigation of the Cluster four-spacecraft mission is designed to provide intercalibrated measurements of the B magnetic field vector. The instrumentation and data processing of the mission are discussed. The instrumentation is identical on the four spacecraft. It consists of two triaxial fluxgate sensors and of a failure tolerant data processing unit. The combined analysis of the four spacecraft data will yield such parameters as the current density vector, wave vectors, and the geometry and structure of discontinuities.

Balogh, A.; Cowley, S. W. H.; Southwood, D. J.; Musmann, G.; Luhr, H.; Neubauer, F. M.; Glassmeier, K.-H.; Riedler, W.; Heyn, M. F.; Acuna, M. H.

1988-01-01

412

The large-scale solar magnetic field  

Microsoft Academic Search

The large-scale photospheric magnetic field, measured by the Mt. Wilson magnetograph, has been analyzed in terms of surface harmonics (Pnm)(?)cosmf and Pnm(?)sinmf) for the years 1959 through 1972. Our results are as follows. The single harmonic which most often characterized the general solar magnetic field throughout the period of observation corresponds to a dipole lying in the plane of the

Martin D. Altschuler; Dorothy E. Trotter; Gordon Newkirk; Robert Howard

1974-01-01

413

Strain Sensors for High Field Pulse Magnets  

Microsoft Academic Search

\\u000a In this paper we present an investigation into several strain sensing technologies that are being considered to monitor mechanical\\u000a deformation within the steel reinforcement shells used in high field pulsed magnets. Such systems generally operate at cryogenic\\u000a temperatures to mitigate heating issues that are inherent in the coils of nondestructive, high field pulsed magnets. The objective\\u000a of this preliminary study

Christian Martinez; Yan Zheng; Daniel Easton; Kevin M Farinholt

2009-01-01

414

Planetary Magnetic Fields and Climate Evolution  

NASA Astrophysics Data System (ADS)

We explore the possible connections between magnetic fields and climate at the terrestrial bodies Venus, Earth, Mars, and Titan. Magnetic fields are thought to have negligible effects on the processes that change a planet's climate, except for processes that alter the abundance of atmospheric gases. Particles can be added or removed at the top of an atmosphere, where collisions are infrequent and a more substantial fraction of particles are ionized (and therefore subject to magnetic forces) than at lower altitudes. The absence of a global magnetic field at Mars for much of its history may have contributed to the removal of a substantial fraction of its atmosphere to space. The persistence of a global magnetic field should have decreased both ionization and removal of atmospheric ions by several processes, and may have indirectly decreased the loss rate of neutral particles as well. While it is convenient to think of magnetic fields as shields for planetary atmospheres from impinging plasma (such as the solar wind), observations of ions escaping from Earth's polar cusp regions suggest that magnetic shielding effects may not be as effective as previously thought. One explanation that requires further testing is that magnetic fields transfer momentum and energy from incident plasma to localized regions of the atmosphere, resulting in similar (or possibly greater) escape rates than if the momentum and energy were imparted more globally to the atmosphere in the absence of a magnetic field. Trace gases can be important for climate despite their low relative abundance in planetary atmospheres. At Venus, removal of O+ over the history of the planet has likely contributed to the loss of water from the atmosphere, leading to a runaway greenhouse situation and having implications for the chemistry of atmosphere-surface interactions. Conversely, Titan's robust atmospheric chemistry may result from the addition of trace amounts of oxygen from Saturn's magnetosphere, which then participate in chemical reactions that produce carbon monoxide (CO) and carbon dioxide (CO2). Models of the entire atmosphere system (including planetary plasma interactions) should continue to shed light on the connections between magnetic fields and climate, as well as models that consider a single planetary body in both magnetized and unmagnetized states. Future measurements, such as those that will be made by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft to Mars, will provide better constraints on the importance of magnetic fields in the evolution of atmospheres.

Brain, D. A.; Leblanc, F.; Luhmann, J. G.; Moore, T. E.; Tian, F.

415

Nuclear magnetic resonance in magnets with a helicoidal magnetic structure in an external magnetic field  

NASA Astrophysics Data System (ADS)

In this review, the static and dynamic properties of a magnet with a helicoidal magnetic structure placed in an external magnetic field are discussed. The results of the investigation of its ground state and spectra, as well as the amplitudes of the spin excitations are presented. The temperature and field dependences of the basic thermodynamic characteristics (heat capacity, magnetization, and magnetic susceptibility) have been calculated in the spin-wave approximation. The results of calculating the local and integral dynamic magnetic susceptibility are given. This set of data represents a methodical basis for constructing a consistent (in the framework of unified approximations) picture of the NMR absorption in the magnet under consideration. Both local NMR characteristics (resonance frequency, line broadening, enhancement coefficient) and integral characteristics (resultant shape of the absorption line with its specific features) have been calculated. The effective Hamiltonian of the Suhl-Nakamura interaction of nuclear spins through spin waves has been constructed. The second moment and the local broadening of the line of the NMR absorption caused by this interaction have been calculated. The role of the basic local inhomogeneities in the formation of the integral line of the NMR absorption has been analyzed. The opportunities for the experimental NMR investigations in magnets with a chiral spin structure are discussed.

Tankeyev, A. P.; Borich, M. A.; Smagin, V. V.

2014-11-01

416

Magnetic Field Problem: Mesuring Current in Wire  

NSDL National Science Digital Library

A wire carrying an unknown current is shown above. An external magnetic field that has constant magnitude and direction is applied to the top half of the simulation (The gray rectangle is at the boundary for your reference). In addition, there is the magnetic field produced by the current in the wire. The direction arrows show the vector sum of these two fields. (The color of the direction arrows represents the magnitude of the field as before.) Observe the force vector and the force/length in the yellow message box in the lower left hand corner.

Wolfgang Christian

417

Polarization-Switching FBG Interrogator for Distributed Point Measurement of Magnetic Field Strength and Temperature  

Microsoft Academic Search

We report on the design and implementation of a novel optical fiber system for dual point measurement of magnetic field strength and temperature. The system incorporates a polar- ization switching technique that enables ratiometric processing of the orthogonal circularly polarized reflections from low-bire- fringence fiber Bragg gratings. High-resolution magneto-optical measurement of either static or dynamic magnetic fields may be achieved

Philip Orr; Pawe? Niewczas

2011-01-01

418

Magnetic field transfer device and method  

DOEpatents

A magnetic field transfer device includes a pair of oppositely wound inner coils which each include at least one winding around an inner coil axis, and an outer coil which includes at least one winding around an outer coil axis. The windings may be formed of superconductors. The axes of the two inner coils are parallel and laterally spaced from each other so that the inner coils are positioned in side-by-side relation. The outer coil is outwardly positioned from the inner coils and rotatable relative to the inner coils about a rotational axis substantially perpendicular to the inner coil axes to generate a hypothetical surface which substantially encloses the inner coils. The outer coil rotates relative to the inner coils between a first position in which the outer coil axis is substantially parallel to the inner coil axes and the outer coil augments the magnetic field formed in one of the inner coils, and a second position 180[degree] from the first position, in which the augmented magnetic field is transferred into the other inner coil and reoriented 180[degree] from the original magnetic field. The magnetic field transfer device allows a magnetic field to be transferred between volumes with negligible work being required to rotate the outer coil with respect to the inner coils. 16 figs.

Wipf, S.L.

1990-02-13

419

Magnetic field transfer device and method  

DOEpatents

A magnetic field transfer device includes a pair of oppositely wound inner coils which each include at least one winding around an inner coil axis, and an outer coil which includes at least one winding around an outer coil axis. The windings may be formed of superconductors. The axes of the two inner coils are parallel and laterally spaced from each other so that the inner coils are positioned in side-by-side relation. The outer coil is outwardly positioned from the inner coils and rotatable relative to the inner coils about a rotational axis substantially perpendicular to the inner coil axes to generate a hypothetical surface which substantially encloses the inner coils. The outer coil rotates relative to the inner coils between a first position in which the outer coil axis is substantially parallel to the inner coil axes and the outer coil augments the magnetic field formed in one of the inner coils, and a second position 180.degree. from the first position, in which the augmented magnetic field is transferred into the other inner coil and reoriented 180.degree. from the original magnetic field. The magnetic field transfer device allows a magnetic field to be transferred between volumes with negligible work being required to rotate the outer coil with respect to the inner coils.

Wipf, Stefan L. (Hamburg, DE)

1990-01-01

420

Coherent near field optical microscopy  

NASA Astrophysics Data System (ADS)

The light scattering from a single resonant molecule, or nano-sized particle located near the tip of an apertureless scanning near-field microscope is studied, and different regimes of scattering are analyzed. The tip enhances the external field, and serves as an efficient transmission `antenna' for the molecular dipole oscillations. The light scattering occurs via two channels: direct scattering from the tip, and tip-mediated molecular scattering. The total detected intensity of the scattered light shows interference of the channels, which we suggest to use for efficient near-field microscopy. At certain detunings from resonances the scanning signal experiences spatial narrowing similar to that one observed in two-photon microscopy, thus allowing for sub-nanometer resolution.

Averbukh, I. Sh.; Chernobrod, B. M.; Sedletsky, O. A.; Prior, Y.

2000-01-01

421

Suppression of cooling by strong magnetic fields in white dwarf stars.  

PubMed

Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white dwarfs, which has been a puzzle because magnetic fields are expected to decay with time but a cool surface suggests that the star is old. In addition, some white dwarfs with strong fields vary in brightness as they rotate, which has been variously attributed to surface brightness inhomogeneities similar to sunspots, chemical inhomogeneities and other magneto-optical effects. Here we describe optical observations of the brightness and magnetic field of the cool white dwarf WD 1953-011 taken over about eight years, and the results of an analysis of its surface temperature and magnetic field distribution. We find that the magnetic field suppresses atmospheric convection, leading to dark spots in the most magnetized areas. We also find that strong fields are sufficient to suppress convection over the entire surface in cool magnetic white dwarfs, which inhibits their cooling evolution relative to weakly magnetic and non-magnetic white dwarfs, making them appear younger than they truly are. This explains the long-standing mystery of why magnetic fields are more common amongst cool white dwarfs, and implies that the currently accepted ages of strongly magnetic white dwarfs are systematically too young. PMID:25327247

Valyavin, G; Shulyak, D; Wade, G A; Antonyuk, K; Zharikov, S V; Galazutdinov, G A; Plachinda, S; Bagnulo, S; Machado, L Fox; Alvarez, M; Clark, D M; Lopez, J M; Hiriart, D; Han, Inwoo; Jeon, Young-Beom; Zurita, C; Mujica, R; Burlakova, T; Szeifert, T; Burenkov, A

2014-11-01

422

Laminated magnet field coil sheath  

DOEpatents

A method for manufacturing a magnetic cable trim coil in a sheath assembly for use in a cryogenic particle accelerator. A precisely positioned pattern of trim coil turns is bonded to a flexible substrate sheath that is capable of withstanding cryogenic operating conditions. In the method of the invention the flexible substrate sheath, with the trim coil pattern precisely location relative to a bore tube assembly of an accelerator and is then bonded to the bore tube with a tape suitable for cryogenic application. The resultant assembly can be readily handled and installed within an iron magnet yoke assembly of a suitable cryogenic particle accelerator. 1 fig.

Skaritka, J.R.

1987-05-15

423

Laminated magnet field coil sheath  

DOEpatents

a method for manufacturing a magnet cable trim coil in a sheath assembly for use in a cryogenic particle accelerator. A precisely positioned pattern of trim coil turns is bonded to a flexible substrate sheath that is capable of withstanding cryogenic operating conditions. In the method of the invention the flexible sheath, with the trim coil pattern precisely positioned thereon, is accurately positioned at a precise location relative to a bore tube assembly of an accelerator and is then bonded to the bore tube with a tape suitable for cryogenic application. The resultant assembly can be readily handled and installed within an iron magnet yoke assembly of a suitable cryogenic particle accelerator.

Skaritka, John R. (Coram, NY)

1987-12-01

424

Master equations for pulsed magnetic fields: Application to magnetic molecules  

NASA Astrophysics Data System (ADS)

We extend spin-lattice relaxation theory to incorporate the use of pulsed magnetic fields for probing the hysteresis effects and magnetization steps and plateaus exhibited, at low temperatures, by the dynamical magnetization of magnetic molecules. The main assumption made is that the lattice degrees of freedom equilibrate in times much shorter than both the experimental time scale (determined by the sweep rate) and the typical spin-lattice relaxation time. We first consider the isotropic case (a magnetic molecule with a ground state of spin S well separated from the excited levels and also the general isotropic Heisenberg-Hamiltonian where all energy levels are relevant) and then we include small off-diagonal terms in the spin Hamiltonian to take into account the Landau-Zener-Stückelberg (LZS) effect. In the first case, and for an S=1/2 magnetic molecule we arrive at the generalized Bloch equation recently used for the magnetic molecule {V6} in [Phys. Rev. Lett. 94, 147204 (2005)]. An analogous equation is derived for the magnetization, at low temperatures, of antiferromagnetic ring systems. The LZS effect is discussed for magnetic molecules with a low spin ground state, for which we arrive at a very convenient set of equations that take into account the combined effects of LZS and thermal transitions. In particular, these equations explain the deviation from exact magnetization reversal at B?0 observed in {V6} . They also account for the small magnetization plateaus (“magnetic Foehn effect”), following the LZS steps that have been observed in several magnetic molecules. Finally, we discuss the role of the phonon bottleneck effect at low temperatures and specifically we indicate how this can give rise to a pronounced Foehn effect.

Rousochatzakis, Ioannis; Luban, Marshall

2005-10-01

425

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

E-print Network

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

Veysi, Mehdi; Capolino, Filippo

2014-01-01

426

Dynamic signatures of quiet sun magnetic fields  

NASA Technical Reports Server (NTRS)

The collision and disappearance of opposite polarity fields is observed most frequently at the borders of network cells. Due to observational limitations, the frequency, magnitude, and spatial distribution of magnetic flux loss have not yet been quantitatively determined at the borders or within the interiors of the cells. However, in agreement with published hypotheses of other authors, the disapperance of magnetic flux is speculated to be a consequence of either gradual or rapid magnetic reconnection which could be the means of converting magnetic energy into the kinetic, thermal, and nonthermal sources of energy for microflares, spicules, the solar wind, and the heating of the solar corona.

Martin, S. F.

1983-01-01

427

H2+ in a weak magnetic field  

NASA Astrophysics Data System (ADS)

The electronic energy of H2+ in magnetic fields of up to B=0.2{{B}0} (or 4.7× {{10}4} T) is investigated. Numerical values of the magnetic susceptibility for both the diamagnetic and paramagnetic contributions are reported for arbitrary orientations of the molecule in the magnetic field. It is shown that both diamagnetic and paramagnetic susceptibilities grow with inclination, while paramagnetic susceptibility is systematically much smaller than the diamagnetic one. Accurate two-dimensional Born–Oppenheimer surfaces are obtained with special trial functions. Using these surfaces, vibrational and rotational states are computed and analyzed for the isotopologues H2+ and D2+.

Medel Cobaxin, Héctor; Alijah, Alexander; López Vieyra, Juan Carlos; Turbiner, Alexander V.

2015-02-01

428

Effects of static magnetic fields on plants.  

NASA Astrophysics Data System (ADS)

In our recent experiment on STS-107 (MFA-Biotube) we took advantage of the magnetic heterogeneity of the gravity receptor cells of flax roots, namely stronger diamagnetism of starch-filled amyloplasts compared to cytoplasm (? ? < 0). High gradient magnetic fields (HGMF, grad(H2/2) up to 109-1010 Oe2/cm) of the experimental chambers (MFCs) repelled amyloplasts from the zones of stronger field thus providing a directional stimulus for plant gravisensing system in microgravity, and causing the roots to react. Such reaction was observed in the video downlink pictures. Unfortunately, the ``Columbia'' tragedy caused loss of the plant material and most of the images, thus preventing us from detailed studies of the results. Currently we are looking for a possibility to repeat this experiment. Therefore, it is very important to understand, what other effects (besides displacing amyloplasts) static magnetic fields with intensities 0 to 2.5104 Oe, and with the size of the area of non-uniformity 10-3 to 1 cm. These effects were estimated theoretically and tested experimentally. No statistically significant differences in growth rates or rates of gravicurvature were observed in experiments with Linum, Arabidopsis, Hordeum, Avena, Ceratodon and Chara between the plants grown in uniform magnetic fields of various intensities (102 to 2.5104 Oe) and those grown in the Earth's magnetic field. Microscopic studies also did not detect any structural differences between test and control plants. The magnitudes of possible effects of static magnetic fields on plant cells and organs (including effects on ion currents, magneto-hydrodynamic effects in moving cytoplasm, ponderomotive forces on other cellular structures, effects on some biochemical reactions and biomolecules) were estimated theoretically. The estimations have shown, that these effects are small compared to the thermodynamic noise and thus are insignificant. Both theoretical estimations and control experiments confirm, that intracellular magnetophoresis of statoliths is the only significant effect of the magnetic field on plant cells and organs in the tested magnetic systems.

Kuznetsov, O.

429

Quantum simulation of frustrated magnetism in triangular optical lattices  

E-print Network

Magnetism plays a key role in modern technology as essential building block of many devices used in daily life. Rich future prospects connected to spintronics, next generation storage devices or superconductivity make it a highly dynamical field of research. Despite those ongoing efforts, the many-body dynamics of complex magnetism is far from being well understood on a fundamental level. Especially the study of geometrically frustrated configurations is challenging both theoretically and experimentally. Here we present the first realization of a large scale quantum simulator for magnetism including frustration. We use the motional degrees of freedom of atoms to comprehensively simulate a magnetic system in a triangular lattice. Via a specific modulation of the optical lattice, we can tune the couplings in different directions independently, even from ferromagnetic to antiferromagnetic. A major advantage of our approach is that standard Bose-Einstein-condensate temperatures are sufficient to observe magnetic phenomena like N\\'eel order and spin frustration. We are able to study a very rich phase diagram and even to observe spontaneous symmetry breaking caused by frustration. In addition, the quantum states realized in our spin simulator are yet unobserved superfluid phases with non-trivial long-range order and staggered circulating plaquette currents, which break time reversal symmetry. These findings open the route towards highly debated phases like spin-liquids and the study of the dynamics of quantum phase transitions.

Julian Struck; Christoph Ölschläger; Rodolphe Le Targat; Parvis Soltan-Panahi; André Eckardt; Maciej Lewenstein; Patrick Windpassinger; Klaus Sengstock

2011-03-30

430

Cryogenic confocal microscopy with rotation in a magnetic field.  

PubMed

Two approaches to conducting magneto-optical confocal spectroscopy are described, in each of which the confocal head is rotatable with respect to the magnetic field. A coudé arrangement has been shown to give adequate performance for scanned imaging, but lower optical throughput than a system based on single-mode optical fiber transport. The design criteria for a cryogenic fiber-coupling objective are described, and the tolerances demanded in lens alignment are shown to be relatively benign, allowing manufacture without special techniques. The practical use of the rotating confocal system with commercial stick-slip positioners has been shown to be rigid enough, and asymmetric weight distribution and diamagnetic forces are small enough to permit single quantum emitters to be studied over a range of angles and field strengths. PMID:20113112

Kehoe, T; Ediger, M; Phillips, R T; Hopkinson, M

2010-01-01

431

Nonreciprocal phase shift caused by magnetic-thermal coupling of a polarization maintaining fiber optic gyroscope.  

PubMed

A theory for nonreciprocal phase shift caused by cross coupling generated in a polarization maintaining (PM) fiber optic gyroscope (FOG) under the combined action of magnetic and temperature fields is proposed. The magnetic-thermal coupling in the FOG originates from the interaction of the magnetic field, fiber twist, birefringence caused by thermal stress, and the intrinsic and bending birefringence of the fiber. The cross coupling changes with temperature. When the PM fiber has a diameter of 250 ?m, beat length of 3 mm, length of 500 m, twist rate of 1??rad/m, and optical source wavelength of 1310 nm, the maximum degree of magnetic-thermal coupling generated by a 1 mT radial magnetic field within the temperature range of -20°C??to 60°C is -5.47%. PMID:24690793

Zhang, Dengwei; Zhao, Yuxiang; Fu, Wenlan; Zhou, Wenqing; Liu, Cheng; Shu, Xiaowu; Che, Shuangliang

2014-03-15

432

Megagauss Magnetic Field Sensors Based on Ag2Te  

SciTech Connect

Pulsed power machines capable of producing tremendous energy face various diagnostic and characterizing challenges. Such devices, which may produce 10 - 100MAs, have traditionally relied on Faraday rotation and Rogowski coil technology for time-varying current measurements. Faraday rotation requires a host of costly optical components, including fibers, polarizers, retarders, lasers, and detectors, as well as setup, alignment, and time-consuming post-processing to unwrap the time-dependent current signal. Rogowski coils face potential problems such as physical distortion to the sensor itself due to the tremendous strain caused by magnetically induced pressures, which is proportional to the magnetic field squared (B2). Electrical breakdown in the intense field region is also a major concern. Other related challenges include, but are not limited to, bandwidth and inductance limitations and susceptibility issues related to electrical magnetic interference (EMI).

Stephen Mitchen (NSTec); Allen L. Johnson (UNLV); John W. Farley (UNLV)

2006-11-30

433

New insights into chromospheric structures from vector magnetic field measurements  

NASA Astrophysics Data System (ADS)

During the last decade advances in instrumentation atomic physics and modeling have greatly improved the access to the chromospheric magnetic field vector High sensitivity polarimeters like the Tenerife Infrared Polarimeter TIP2 VTT or the Spectro-Polarimeter for Infrared and Optical Regions SPINOR HAO lead to reliable Zeeman measurements using the He I 10830 nm triplet Theoretical modeling of the Hanle and the Paschen Back effect helped to significantly improve the analysis of polarization measurements in this triplet allowing to directly visualize the magnetic structure of spicules polar prominences and active regions In this presentation I will summarize the results of chromospheric magnetic field measurements using this interesting triplet obtained in the last couple of years and discuss the great potential it has to further uncover the complex structure of the chromosphere

Lagg, A.

434

Studies of solar magnetic fields  

Microsoft Academic Search

Magnetic flux data from the Mount Wilson magnetograph are examined over the interval 1967–1973. The total flux in the north is greater than that in the south by about 7% over this interval, reflecting a higher level of activity in the northern hemisphere. Close to 95% of the total flux is confined to latitudes equatorward of 40°, which means that

Robert Howard

1974-01-01

435

All-optical magnetic resonance of high spectral resolution using a nitrogen-vacancy spin in diamond  

NASA Astrophysics Data System (ADS)

We propose an all-optical scheme to prolong the quantum coherence of a negatively charged nitrogen-vacancy (NV) center in diamond at cryogenic temperatures. Optical control of the NV spin suppresses energy fluctuations of the ^{3}{{A}_{2}} ground states and forms an energy gap protected subspace. By optical control, the spectral linewidth of magnetic resonance is much narrower and the measurement of the frequencies of magnetic field sources has higher resolution. The optical control also improves the sensitivity of the magnetic field detection and can provide measurement of the directions of signal sources.

Wang, Zhen-Yu; Cai, Jian-Ming; Retzker, Alex; Plenio, Martin B.

2014-08-01

436

Fast Reconnection of Weak Magnetic Fields  

NASA Technical Reports Server (NTRS)

Fast magnetic reconnection refers to annihilation or topological rearrangement of magnetic fields on a timescale that is independent (or nearly independent) of the plasma resistivity. The resistivity of astrophysical plasmas is so low that reconnection is of little practical interest unless it is fast. Yet, the theory of fast magnetic reconnection is on uncertain ground, as models must avoid the tendency of magnetic fields to pile up at the reconnection layer, slowing down the flow. In this paper it is shown that these problems can be avoided to some extent if the flow is three dimensional. On the other hand, it is shown that in the limited but important case of incompressible stagnation point flows, every flow will amplify most magnetic fields. Although examples of fast magnetic reconnection abound, a weak, disordered magnetic field embedded in stagnation point flow will in general be amplified, and should eventually modify the flow. These results support recent arguments against the operation of turbulent resistivity in highly conducting fluids.

Zweibel, Ellen G.

1998-01-01

437

Near equipment magnetic field verification and scaling  

NASA Astrophysics Data System (ADS)

Magnetic field measurements are essential to the success of many scientific space missions. Outside of the Earth's magnetic field the biggest potential source of magnetic field contamination of these measurements is emitted by the spacecraft. Spacecraft magnetic cleanliness is enforced through the application of strict ground verification requirements for spacecraft equipment and instruments. Due to increasingly strict AC magnetic field requirements, many spacecraft units cannot be verified on the ground using existing techniques. These measurements must instead be taken close to the equipment under test (EUT) and then extrapolated. A traditional dipole power law of -3 (with a field fall-off proportional to r-3) cannot be applied at these close distances without risk of underestimating the field emitted by the EUT, but we demonstrate that a power law of -2 is too conservative. We propose a compromise that uses a power law of -2 up to a distance equal to 3 times the unit size, beyond which a dipole power law can be applied. When extrapolating from a distance of 0.20 to 1.00 m from the centre of a 0.20 m wide EUT, we demonstrate that this method avoids an underprediction of the field, and is at least twice as accurate as performing the extrapolation with a fixed power law of -2.

Pudney, M. A.; Carr, C. M.; Schwartz, S. J.; Howarth, S. I.

2013-07-01

438

Magnetic field dependence of plasma relaxation times  

NASA Technical Reports Server (NTRS)

A previously derived Fokker-Planck collision integral for an electron plasma in a dc magnetic field is examined in the limit in which the Debye length is greater than the thermal gyroradius, which is in turn greater than the mean distance of closest approach. It is demonstrated that the collision integral can be satisfactorily approximated by the classical Landau value (which ignores the presence of a dc magnetic field) if the following replacement is made: In the Coulomb logarithm, the Debye length is replaced by the gyroradius. This induces a fundamental logarithmic dependence on magnetic field in the relaxation times. Numerical comparison of the asymptotic approximations with the previously derived exact results is made, and good agreement is found. The simplification this introduces into the description of collision processes in magnetized plasma is considerable.

Montgomery, D.; Joyce, G.; Turner, L.

1974-01-01

439

Magnetic field production after inflation  

E-print Network

We study the electromagnetic field production during preheating after hybrid inflation in a model with the field content of the Standard Model, coupled to a singlet inflaton. We find that very soon after symmetry breaking our system enters a regime of kinetic turbulence, characterized by a self-similar behaviour of the energy spectra and a power-like dependence on time of the inflaton and Higgs field variances.

Andres Diaz-Gil; J. Garcia-Bellido; M. Garcia Perez; A. Gonzalez-Arroyo

2005-09-22

440

Probing strong magnetic fields with cyclotron lines  

NASA Astrophysics Data System (ADS)

The physics of accretion of X-ray pulsars are dominated by very strong magnetic fields of of the order of 1012 Gauss. The only direct measure of these magnetic fields is the spectral analysis of cyclotron resonance scattering features (CRSFs). Electron CRSFs can form as broad harmonic absorption features in the keV regime when X- ray photons resonantly scatter with quantized electrons in the strongly magnetized accretion plasma. Recently, also the detection of proton CRSFs for magnetars has been claimed, rendering the basic understanding of the formation of CRSFs an important factor also for another class of fascinating extreme objects. In both cases, the line positions are directly linked to the magnetic field strength of the neutron star. Using Monte Carlo simulations, we perform a detailed study of the line shapes and positions of electron cyclotron lines of accreting neutron stars. These are indicators not only of the magnetic field strength but also give insight into the geometry of accretion, the structure of the magnetic field and gravitational effects around the compact object. For the first time ever, we have build a simulation based XSPEC model application to quantitatively compare our theoretical results to real observed source data. Recent results and their meaning for the physical picture of accreting X-ray pulsars from a comparison of the Monte Carlo Model to a set of sources are presented.

Schönherr, Gabriele; Wilms, Jörn; Kretschmar, Peter; Kreykenbohm, Ingo; Pottschmidt, Katja; Suchy, Slawo; Rothschild, Rick; Caballero, Isabel

441

Birefringence of silica hydrogels prepared under high magnetic fields reinvestigated  

NASA Astrophysics Data System (ADS)

Birefringence is an indicator of structural anisotropy of materials. We measured the birefringence of Pb(II)-doped silica hydrogels prepared under a high magnetic field of various strengths. Because the silica is diamagnetic, one does not expect the structural anisotropy induced by a magnetic field. In previous work (Mori, Kaito and Furukawa 2008 Mater. Lett. 62 3459–61), we prepared samples in cylindrical cells made of borosilicate glass and obtained a preliminary result indicating a negative birefringence for samples prepared at 5 T with the direction of the magnetic field being the optic axis. We have measured the birefringence of Pb(II)-doped silica hydrogels prepared in square cross-sectional cells made of quartz and overturned the previous conclusion. Interestingly, the magnetic-influenced silica hydrogels measured have been classified into four classes: two positive birefringent ones, a no birefringent one, and a negative birefringent one. Proportionality between birefringence and the strength of magnetic field is seen for the former two.

Mori, Atsushi; Kaito, Takamasa; Furukawa, Hidemitsu; Yamato, Masafumi; Takahashi, Kohki

2014-12-01

442

Behavior of multi-component magnetic colloidal systems in tunable magnetic fields and applications in biosensing  

NASA Astrophysics Data System (ADS)

A system consisting of multiple-component beads, such as superparamagnetic beads, nonmagnetic beads and magnetorheological (MR) fluid, can display some very amazing and special properties when subjected to an external magnetic field because the MR fluid can act on both types of beads synchronously as a magnetic medium. Some novel structures and phenomena were discovered and are discussed in our work, including 'ring-structures', 'small-ring' and 'ring-chains' in static or rotational magnetic fields. If both probe and target molecules are attached consisting of functionalized superparamagnetic beads and non-magnetic beads, respectively, the ring-structure could be maintained due to biomolecular bonding, even after removing the external magnetic field. Using these remnant rings, we raised two protocols for biosensing: a two-dimensional biosensor using a magnetic self-assembled colloidal ring-structure, and an improved magneto-optical transmittance (MT) method. In the former protocol, we define the small nonmagnetic particles as "petals" because the whole structure looks like a flower. It was proved that the number of remnant