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1

Probing Planetary Magnetic Fields During Transits  

NASA Astrophysics Data System (ADS)

Recently, Fossati et al. observed that the near-UV transit light curve of the close-in giant planet WASP-12b shows an early ingress as compared to its optical transit. Such observations were interpreted as due to the presence of asymmetries in the exosphere of the planet. In particular, we suggest that this asymmetry could be explained by the presence of a shock formed around the planet's magnetosphere. Bow shocks are formed as a result of the interaction of the planet with the coronal material of the host star, similar to the one formed around the Earth's magnetosphere. According to our model, shock detection through transit observations can be a useful tool to probe and constrain exoplanetary magnetic field. In the case of WASP- 12b, we derive an upper limit for the magnetic field of ? 24 G. In addition, we predict that observable shocks should be a common feature in other transiting systems. Promising candidates are: WASP- 19b, WASP-4b, WASP-18b, CoRoT-7b, HAT-P-7b, CoRoT-1b, TrES-3 and WASP-5b.

Vidotto, A. A.; Jardine, M.; Helling, C.

2011-10-01

2

Probing interstellar magnetic fields with Supernova remnants  

NASA Astrophysics Data System (ADS)

As Supernova remnants expand, their shock waves are freezing in and compressing the magnetic field lines they encounter; consequently we can use Supernova remnants as magnifying glasses for their ambient magnetic fields. We will describe a simple model to determine emission, polarization, and rotation measure characteristics of adiabatically expanding Supernova remnants and how we can exploit this model to gain information about the large scale magnetic field in our Galaxy. We will give two examples: The SNR DA530, which is located high above the Galactic plane, reveals information about the magnetic field in the halo of our Galaxy. The SNR G182.4+4.3 is located close to the anti-centre of our Galaxy and reveals the most probable direction where the large-scale magnetic field is perpendicular to the line of sight. This may help to decide on the large-scale magnetic field configuration of our Galaxy. But more observations of SNRs are needed.

Kothes, Roland; Brown, Jo-Anne

2009-04-01

3

Field measuring probe for SSC (Superconducting Super Collider) magnets  

SciTech Connect

The field probe developed for measuring the field in SSC dipole magnets is an adaptation of the rotating tangential coil system in use at Brookhaven for several years. Also known as the MOLE, it is a self-contained room-temperature mechanism that is pulled through the aperture of the magnet with regular stops to measure the local field. Several minutes are required to measure the field at each point. The probe measures the multipole components of the field as well as the field angle relative to gravity. The sensitivity of the coil and electronics is such that the field up to the full 6.6 T excitation of the magnet as well as the field when warm with only 0.01 T excitation can be measured. Tethers are attached to both ends of the probe to carry electrical connections and to supply dry nitrogen to the air motors that rotate the tangential windings as well as the gravity sensor. A small computer is attached to the probe for control and for data collection, analysis and storage. Digital voltmeters are used to digitize the voltages from the rotating coil and several custom circuits control motor speeds in the probe. The overall diameter of the probe is approximately 2 cm and its length is 2.4 m; the field sensitive windings are 0.6 m in length.

Ganetis, G.; Herrera, J.; Hogue, R.; Skaritka, J.; Wanderer, P.; Willen, E.

1987-03-01

4

PROBING PRIMORDIAL MAGNETIC FIELDS USING Ly{alpha} CLOUDS  

SciTech Connect

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 {sup -1} Mpc) as compared to the usual {Lambda}CDM theory. Matter power spectra over these scales are effectively probed by cosmological observables such as shear correlation and Ly{alpha} clouds. In this paper we discuss the implications of primordial magnetic fields on the distribution of Ly{alpha} clouds. We simulate the line-of-sight density fluctuation including the contribution coming from the primordial magnetic fields. We compute the evolution of Ly{alpha} opacity for this case and compare our theoretical estimates of Ly{alpha} 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 {approx_equal} -3.

Pandey, Kanhaiya L.; Sethi, Shiv K. [Raman Research Institute, Bangalore 560080 (India)] [Raman Research Institute, Bangalore 560080 (India)

2013-01-01

5

Magnetic field effect on cylindrical impedance probe diagnostics  

NASA Astrophysics Data System (ADS)

To test geometry independence predicted theoretically in earlier work with spherical impedance probes,ootnotetextD.N. Walker, R.F. Fernsler, D.D. Blackwell, W.E. Amatucci, Phys. Plasmas 17, 113503 (2010) we used a 100-1 (length -- radius) aspect ratio cylindrical probe. In the impedance measurements, a network analyzer supplies a millivolt driving rf signal and plasma diagnostics are based on the real and imaginary parts of the complex plasma impedance returned by the analyzer for a given probe bias. The theoretical basis of the work indicates that in the thin sheath limit the results should be independent of probe geometry. With probe alignment along a small magnetic field ˜ 2 gauss, we compared the cylinder's impedance-based plasma measurements to those for which we swept the same cylinder as a Langmuir probe.ootnotetextNRL Memorandum Report 6750-11-9331 (2011) In both cases the impedance probe format showed a higher density, the same plasma potential, and a comparable electron temperature to the Langmuir sweep. We will present recent data showing the effect of varying the orientation and magnitude of the applied field.

Walker, David; Fernsler, Richard; Blackwell, David; Amatucci, William

2011-11-01

6

The Characteristics of Broadband, Isotropic Electrical Field and Magnetic Field Probes.  

National Technical Information Service (NTIS)

A feasibility study and a preliminary engineering test program have been conducted to establish performance specification limits and preliminary engineering design for broadband, isotropic, receiving, electric field and magnetic field probes for electroma...

M. Kanda

1977-01-01

7

NMR probes for measuring magnetic fields and field dynamics in MR systems  

Microsoft Academic Search

High-resolution magnetic field probes based on pulsed liquid- state NMR are presented. Static field measurements with an error of 10 nanotesla or less at 3 tesla are readily obtained in 100 ms. The further ability to measure dynamic magnetic fields results from using small (! 1 ! L) droplets of MR-active liquid surrounded by susceptibility-matched materials. The conse- quent high

Nicola De Zanche; Christoph Barmet; Jurek A. Nordmeyer-Massner; Klaas P. Pruessmann

2008-01-01

8

Probing Cosmic Magnetic Fields Over Ten Billion Years  

NASA Astrophysics Data System (ADS)

Faraday rotation is a powerful potential probe of how magnetic fields in the Universe have evolved. In particular, a statistical ensemble of extragalactic radio sources with both rotation measures (RMs) and redshifts can trace the evolution of galactic magnetic fields over cosmic time, because magnetic fields in galaxy-scale intervenors will manifest themselves as a trend in the distribution of background RMs as a function of z. Recent studies of large samples of extragalactic RMs indicate that some distant sources have very high RMs, while overall there is a deficit of very small RMs for the highest redshift sources. These effects suggest that galaxies just a few billion years old already had field strengths comparable to that seen in the Milky Way today. Here we present new Faraday rotation observations of a large sample of extragalactic sources taken with the Australia Telescope Compact Array. This data-set doubles the sample of sources with RMs at z > 1, and also extends such studies to higher z than was previously available. We discuss the extent to which these new data confirm the dependence of RM with redshift seen in existing data. We also use these measurements to search for an evolution of galactic magnetic fields as a function of time out to z 4. These data, along with deeper upcoming surveys with the next generation of radio telescopes, can provide direct constraints on the time scale for magnetic field amplification as galaxies evolve. B.M.G. acknowledges the support of a Federation Fellowship from the Australian Research Council through grant FF0561298. P.P.K. acknowledges support from the DOE, and from NSERC (Canada).

Gaensler, Bryan M.; Kronberg, P. P.; Tanna, A.; Harvey-Smith, L.

2009-01-01

9

Standard Practices for Usage of Inductive Magnetic Field Probes with Application to Electric Propulsion Testing  

NASA Technical Reports Server (NTRS)

Inductive magnetic field probes (also known as B-dot probes and sometimes as B-probes or magnetic probes) are often employed to perform field measurements in electric propulsion applications where there are time-varying fields. Magnetic field probes provide the means to measure these magnetic fields and can even be used to measure the plasma current density indirectly through the application of Ampere's law. Measurements of this type can yield either global information related to a thruster and its performance or detailed, local data related to the specific physical processes occurring in the plasma. Results of the development of a standard for B-dot probe measurements are presented, condensing the available literature on the subject into an accessible set of rules, guidelines, and techniques to standardize the performance and presentation of future measurements.

Polzin, Kurt A.; Hill, Carrie S.; Turchi, Peter J.; Burton, Rodney L.; Messer, Sarah; Lovberg, Ralph H.; Hallock, Ashley K.

2013-01-01

10

Solar energetic electron probes of magnetic cloud field line lengths  

Microsoft Academic Search

Magnetic clouds (MCs) are large interplanetary coronal mass ejections of enhanced and low-variance fields with rotations indicative of magnetic flux ropes originally connected to the Sun. The MC flux rope models require field lines with larger pitch angles and longer lengths with increasing distance from the MC axis. While the models can provide good fits to the in situ solar

S. W. Kahler; S. Krucker; A. Szabo

2011-01-01

11

ANALYSIS OF THE MAGNETIC FIELD MEASURED BY A ROTATING HALL PROBE IN A SOLENOID TO LOCATE ITS MAGNETIC AXIS.  

SciTech Connect

We have analyzed the motion of a Hall probe, which is rotated about an axis that is arbitrarily displaced and oriented with respect to the magnetic axis of a solenoid. We outline how the magnetic field measured by the rotating Hall probe can be calculated. We show how to compare theoretical results with actual measurements, to determine the displacement and orientation of the axis of rotation of the probe from the magnetic axis. If the center of rotation of the probe is known by surveying, the corresponding point on the magnetic axis of the solenoid can be located. This is applied to a solenoid that was built for BNL by Oxford Instruments.

KPONOU,A.; PIKIN,A.; BEEBE,E.; ALESSI,J.

2000-11-06

12

Miniature-probe measurements of electric fields induced by 60 Hz magnetic fields in rats  

SciTech Connect

Extremely-low-frequency (ELF) magnetic fields interact with an animal by inducing internal electric fields, which represent the internal dose from an external exposure. In this study, an electric field probe of approximately 2 mm resolution was used to measure fields induced in rate carcasses by a 60 Hz magnetic field at 1 mT. With the rat lying on its side, the probe was inserted through a small hole in the body wall, and scanned at 5 mm increments from the side with frontal and axial exposure (field horizontal) and from the front with lateral exposure (field vertical). The induced electric field declined from a maximum at the entrance to the abdomen and crossed zero to negative (180{degree} phase shift) values within the body as expected. In general, the magnitudes of the measurements inside the abdomen were less than expected from whole-body calculations that used homogeneous-ellipsoidal models of a rate in the three orientations. The low measurements did not appear to be explained by perpendicular field components, by conductivity differences between the tissue and the probe path, or by air in the lungs. The low measurements probably result from inhomogeneities in actual rats that include conductivity differences between tissues and biological membranes. For example, an alternative model considered the abdominal cavity to be electrically isolated from the body by the diaphragm and the peritoneum and calculations from this model were in better agreement with the measurements inside the abdomen (than were the whole-body calculations). Therefore, inhomogeneities in conductivity and biomembranes such as the peritoneum should be considered in order to fully understand ELF-induced field dosimetry.

Miller, D.L. [Pacific Northwest Lab., Richland, WA (United States)] [Pacific Northwest Lab., Richland, WA (United States)

1996-12-01

13

Evaluation of local magnetic field fluctuation in a toroidal plasma with heavy ion beam probe  

NASA Astrophysics Data System (ADS)

A method to measure magnetic field fluctuation using a heavy ion beam probe for a toroidal magnetically confined plasma is proposed by providing a mathematical formula to connect the probing beam movement with the change in the magnetic field. The first challenge of the method has been faced in an electron-cyclotron resonance heated plasma in the compact helical system (CHS). The results reveal the existence of three characteristic frequency regimes of the magnetic field fluctuations: a low frequency regime showing a long-distance correlation, an intermediate frequency regime obeying a power law and the turbulence regime. Discussion is held on the degree of the contaminations in the local magnetic field fluctuation that are caused by the magnetic field fluctuations integrated along the beam orbit and the local electric field fluctuations.

Fujisawa, A.; Shimizu, A.; Nakano, H.; Ohshima, S.

2007-06-01

14

Optimal design of eddy current testing probe using fluxset magnetic field sensors  

Microsoft Academic Search

A numerical method is presented for the calculation of the signal picked up by eddy current testing (ECT) probes made of an exciting coil and fluxset type magnetic field sensors. The magnetic field generated by the interaction of the exciting coil and the non-ferromagnetic metal plate specimen is calculated by the solution of a boundary integral equation with singular kernel.

J. Pavo; K. Miya

1996-01-01

15

Standard Practices for Usage of Inductive Magnetic Field Probes with Application to Electric Propulsion Testing  

NASA Technical Reports Server (NTRS)

Inductive magnetic field probes (also known as B-dot probes and sometimes as B-probes or magnetic probes) are useful for performing measurements in electric space thrusters and various plasma accelerator applications where a time-varying magnetic field is present. Magnetic field probes have proven to be a mainstay in diagnosing plasma thrusters where changes occur rapidly with respect to time, providing the means to measure the magnetic fields produced by time-varying currents and even an indirect measure of the plasma current density through the application of Ampère's law. Examples of applications where this measurement technique has been employed include pulsed plasma thrusters and quasi-steady magnetoplasmadynamic thrusters. The Electric Propulsion Technical Committee (EPTC) of the American Institute of Aeronautics and Astronautics (AIAA) was asked to assemble a Committee on Standards (CoS) for Electric Propulsion Testing. The assembled CoS was tasked with developing Standards and Recommended Practices for various diagnostic techniques used in the evaluation of plasma thrusters. These include measurements that can yield either global information related to a thruster and its performance or detailed, local data related to the specific physical processes occurring in the plasma. This paper presents a summary of the standard, describing the preferred methods for fabrication, calibration, and usage of inductive magnetic field probes for use in diagnosing plasma thrusters. Inductive magnetic field probes (also called B-dot probes throughout this document) are commonly used in electric propulsion (EP) research and testing to measure unsteady magnetic fields produced by time-varying currents. The B-dot probe is relatively simple in construction, and requires minimal cost, making it a low-cost technique that is readily accessible to most researchers. While relatively simple, the design of a B-dot probe is not trivial and there are many opportunities for errors in probe construction, calibration, and usage, and in the post-processing of data that is produced by the probe. There are typically several ways in which each of these steps can be approached, and different applications may require more or less vigorous attention to various issues.

Polzin, Kurt A.; Hill, Carrie S.

2013-01-01

16

Nanoscale magnetic field mapping with a single spin scanning probe magnetometer  

SciTech Connect

We demonstrate quantitative magnetic field mapping with nanoscale resolution, by applying a lock-in technique on the electron spin resonance frequency of a single nitrogen-vacancy defect placed at the apex of an atomic force microscope tip. In addition, we report an all-optical magnetic imaging technique which is sensitive to large off-axis magnetic fields, thus extending the operation range of diamond-based magnetometry. Both techniques are illustrated by using a magnetic hard disk as a test sample. Owing to the non-perturbing and quantitative nature of the magnetic probe, this work should open up numerous perspectives in nanomagnetism and spintronics.

Rondin, L.; Tetienne, J.-P.; Spinicelli, P.; Roch, J.-F.; Jacques, V. [Laboratoire de Photonique Quantique et Moleculaire, Ecole Normale Superieure de Cachan and CNRS UMR 8537, 94235 Cachan Cedex (France); Dal Savio, C.; Karrai, K. [Attocube systems AG, Koeniginstrasse 11A RGB, Munich 80539 (Germany); Dantelle, G. [Laboratoire de Physique de la Matiere Condensee, Ecole Polytechnique and CNRS UMR 7643, 91128 Palaiseau (France); Thiaville, A.; Rohart, S. [Laboratoire de Physique des Solides, Universite Paris-Sud and CNRS UMR 8502, 91405 Orsay (France)

2012-04-09

17

Ion Collection by a Cylindrical Probe in a Weak Magnetic Field  

Microsoft Academic Search

The structure of a plasma-sheath transition region surrounding a negatively biased cylindrical probe in a weak axial magnetic field is systematically studied on the basis of the moment equations. A weakly ionized plasma is treated, and it is assumed that the mean free path is long but finite, and that the collision frequency is constant. Since the mean free path

Yasutomo Ohguchi; Shigeki Miyajima; Kenzo Yamamoto

1969-01-01

18

Application of field emission in prolate-spheroidal coordinate in heat-assisted magnetic probe recording  

Microsoft Academic Search

We characterize a method of heat-assisted magnetic recording (HAMR) which can be applied for probe-based storage systems. Field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. The tip is made of Ir\\/Pt alloy. Pulses with amplitude of 6V and duration of 500ns were applied to a CoNi\\/Pt multilayered film. Written by a blunt

Li Zhang

2007-01-01

19

PROBING THE LARGE-SCALE TOPOLOGY OF THE HELIOSPHERIC MAGNETIC FIELD USING JOVIAN ELECTRONS  

SciTech Connect

Jupiter's magnetosphere acts as a point source of near-relativistic electrons within the heliosphere. In this study, three solar cycles of Jovian electron data in near-Earth space are examined. Jovian electron intensity is found to peak for an ideal Parker spiral connection, but with considerable spread about this point. Assuming the peak in Jovian electron counts indicates the best magnetic connection to Jupiter, we find a clear trend for fast and slow solar wind to be over- and under-wound with respect to the ideal Parker spiral, respectively. This is shown to be well explained in terms of solar wind stream interactions. Thus, modulation of Jovian electrons by corotating interaction regions (CIRs) may primarily be the result of changing magnetic connection, rather than CIRs acting as barriers to cross-field diffusion. By using Jovian electrons to remote sensing magnetic connectivity with Jupiter's magnetosphere, we suggest that they provide a means to validate solar wind models between 1 and 5 AU, even when suitable in situ solar wind observations are not available. Furthermore, using Jovian electron observations as probes of heliospheric magnetic topology could provide insight into heliospheric magnetic field braiding and turbulence, as well as any systematic under-winding of the heliospheric magnetic field relative to the Parker spiral from footpoint motion of the magnetic field.

Owens, M. J.; Horbury, T. S. [Space and Atmospheric Physics, Imperial College, London SW7 2AZ (United Kingdom); Arge, C. N. [Air Force Research Laboratory/Space Vehicles Directorate, Kirtland Air Force Base, NM 87117 (United States)

2010-05-10

20

Probing the solar magnetic field with a Sun-grazing comet.  

PubMed

On 15 and 16 December 2011, Sun-grazing comet C/2011 W3 (Lovejoy) passed deep within the solar corona, effectively probing a region that has never been visited by spacecraft. Imaged from multiple perspectives, extreme ultraviolet observations of Lovejoy's tail showed substantial changes in direction, intensity, magnitude, and persistence. To understand this unique signature, we combined a state-of-the-art magnetohydrodynamic model of the solar corona and a model for the motion of emitting cometary tail ions in an embedded plasma. The observed tail motions reveal the inhomogeneous magnetic field of the solar corona. We show how these motions constrain field and plasma properties along the trajectory, and how they can be used to meaningfully distinguish between two classes of magnetic field models. PMID:23744941

Downs, Cooper; Linker, Jon A; Mikií, Zoran; Riley, Pete; Schrijver, Carolus J; Saint-Hilaire, Pascal

2013-06-01

21

Probing dynamical magnetization pinning in circular dots as a function of the external magnetic field orientation  

NASA Astrophysics Data System (ADS)

We performed ferromagnetic resonance measurements of square arrays of noninteracting Permalloy circular dots for different orientations of external magnetic field with respect to the patterned film plane (?). Out-of-plane angular dependence of the main resonance peak was measured in the whole range of the field angles 0° ? ? ? 90°. The main eigenmodespatial distribution is strongly nonuniform due to the dot nonellipsoidal shape. Nevertheless, for dots with small aspect ratio b=L/R?0.1 (where R is dot radius and L is dot thickness) Kittel's equation, assuming uniform dynamic magnetization (no pinning at the dot lateral edges), describes the peak position with high accuracy. Analytical calculations and micromagnetic simulations confirmed the gradual evolution of the main mode profile and a smooth transition from the strong to relatively weak pinning conditions with the change of external magnetic field angle.

Kakazei, G. N.; Aranda, G. R.; Bunyaev, S. A.; Golub, V. O.; Tartakovskaya, E. V.; Chumak, A. V.; Serga, A. A.; Hillebrands, B.; Guslienko, K. Y.

2012-08-01

22

Application of field emission in prolate-spheroidal coordinate in heat-assisted magnetic probe recording  

NASA Astrophysics Data System (ADS)

We characterize a method of heat-assisted magnetic recording (HAMR) which can be applied for probe-based storage systems. Field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. The tip is made of Ir/Pt alloy. Pulses with amplitude of 6 V and duration of 500 ns were applied to a CoNi/Pt multilayered film. Written by a blunt tip (radius 1000 nm), marks are formed with a nearly uniform mark size of 200 nm. Sharp tip (radius 1-10 nm) writing achieves no mark. Based on a model of field emission in prolate-spheroidal coordinate, both the emission current and the emission area are functions of the tip radius, tip-sample spacing, tip work function, and bias voltage. It explains the experimental results.

Zhang, Li

2007-01-01

23

Determination of the plasma velocity in an imploding wire array from magnetic field measurements by a gradient probe  

NASA Astrophysics Data System (ADS)

A method for measuring the gradient of the magnetic field in the plasma of an imploding wire array is described. Results from measurements of the magnitude and gradient of the magnetic field in a tungsten wire array on the Angara-5-1 facility at currents of ˜3 MA are presented. A novel method for calculating the velocity of the current-carrying plasma in the framework of MHD equations from data on the magnitude and gradient of the magnetic field at a certain point inside the array is proposed. It is demonstrated that a gradient magnetic probe can be used to investigate the plasma current sheath in plasma focus facilities.

Grabovski, E. V.; Mitrofanov, K. N.; Koshelev, A. Yu.; Samokhin, A. A.; Aleksandrov, V. V.; Gritsuk, A. N.; Laukhin, Ya. N.; Oleinik, G. M.; Frolov, I. N.

2011-07-01

24

Versatile 4 K nuclear magnetic resonance probe and cryogenic system for small-bore high-field Bitter magnets  

Microsoft Academic Search

A complete design for a versatile nuclear magnetic resonance cryostat\\/probe system specifically adapted for small 32 mm bore bitter magnets is described. The probe solves two main problems associated with constrained environments (1) high voltage arcing across cold tuned circuits in helium atmosphere and (2) loss of temperature control due to helium bubbles in a long Dewar tail at high

A. P. Reyes; H. N. Bachman; W. P. Halperin

1997-01-01

25

Probing the Intergalactic Magnetic Field with the Anisotropy of the Extragalactic Gamma-Ray Background  

NASA Technical Reports Server (NTRS)

The intergalactic magnetic field (IGMF) may leave an imprint on the anisotropy properties of the extragalactic gamma-ray background, through its effect on electromagnetic cascades triggered by interactions between very high energy photons and the extragalactic background light. A strong IGMF will deflect secondary particles produced in these cascades and will thus tend to isotropize lower energy cascade photons, thus inducing a modulation in the anisotropy energy spectrum of the gamma-ray background. Here we present a simple, proof-of-concept calculation of the magnitude of this effect and demonstrate that the two extreme cases (zero IGMF and IGMF strong enough to completely isotropize cascade photons) would be separable by ten years of Fermi observations and reasonable model parameters for the gamma-ray background. The anisotropy energy spectrum of the Fermi gamma-ray background could thus be used as a probe of the IGMF strength.

Venters, T. M.; Pavlidou, V.

2012-01-01

26

Magnetic field effect on a radical pair reaction as a probe of microviscosity.  

PubMed

The magnetic field effects (MFEs), caused by the Delta g mechanism, on the photoinduced hydrogen abstraction reaction of benzopheneone with thiophenol were investigated in alcoholic solutions of varying viscosities (eta = 0.55 to 59.2 cP) by a nanosecond laser flash photolysis technique. The escape yield of benzophenone ketyl radicals ( Y) gradually decreased with increasing magnetic field strength ( B) from 0 to 1.6 T. The relative yield observed at 1.6 T, R(1.6 T) = Y(1.6 T)/ Y(0 T), decreased with increasing eta in the range of 0.55 cP < or = eta < or = 5 cP, and then increased with increasing eta in the range of 5 cP < eta < or = 55.3 cP. When eta was higher than 55.3 cP, the R(1.6 T) value became 1.0, and MFEs were completely quenched. The observed eta dependence of the MFEs was analyzed by the stochastic Liouville equation (SLE), in which the effects of spin-orbit coupling by a heavy atom such as sulfur were taken into account. The observed MFEs were reproduced fairly well by the SLE analysis. The diffusion coefficients of the radicals obtained by the SLE were about three times smaller than those expected from the macroscopic solvent viscosities. One can probe the microviscosity in the vicinity of the radical pairs by observing MFEs on the present photochemical reaction system. PMID:18939791

Hamasaki, Atom; Yago, Tomoaki; Wakasa, Masanobu

2008-11-13

27

Magnetic field effects on hydrogen abstraction of thiobenzophenone as a probe of microviscosity.  

PubMed

Hydrogen abstraction reactions of thiobenzophenone with thiophenol in solutions of varying viscosities (?=0.29-42.0 cP) were studied by a nanosecond laser flash photolysis under magnetic fields of 0-15.5 T. In alcoholic solutions, the escaped radical yield (Y) of thiobenzophenone ketyl radical showed appreciable magnetic field effects (MFEs). The observed MFEs can be interpreted with the ?g mechanism through the triplet radical pair. The relative escaped radical yield (R(1.7T)=Y(1.7T)/Y(0T)) decreased with increasing ? at 0probe reaction, microviscosities of sodium dodecyl sulfate (SDS) and Brij35 micellar solutions were estimated. PMID:21322618

Tanaka, Miyuki; Yago, Tomoaki; Sakaguchi, Yoshio; Takamasu, Tadashi; Wakasa, Masanobu

2011-03-10

28

Measurement of magnetic field fluctuations within last closed flux surface with movable magnetic probe array in the JIPP T-IIU tokamak  

Microsoft Academic Search

Poloidal and radial magnetic field fluctuations less than 100 kHz are measured with a newly developed movable magnetic probe array in the JIPP T-IIU tokamak. The probe array protected by a carbon-carbon composite with 20% boron is inserted beyond the last closed flux surface (LFCS) up to r\\/a 0.77 without deleterious effect on ohmically and neutra beam heated plasmas. From

K Kitachi; T Oike; S Ohdachi; K Toi; R Akiyama; A Ejiri; Y Hamada; H Kuramoto; K Narihara; T Seki

1997-01-01

29

Characterisation of a toroidal plasma in a magnetic field by the floating double probe technique for hydrogen  

NASA Astrophysics Data System (ADS)

In the present work, the floating double probe technique was used to determine the plasma parameters by using the equivalent resistance method [1,2,3,4,5] for hydrogen in toroidal discharge. Measurements were done for transverse and longitudinal positions of the probes to the axial toroidal magnetic field. The experiment was carried out in a 13.56 MHz inductively coupled radio frequency plasma discharge at different pressures of 0.07 torr to 0.20 torr and magnetic fields of 0G to 75G and observed the differences of plasma temperature and particle number density on the discharge axis of the torus. It is also observed that the plasma temperature decreases where as the plasma radial density increases for axial positions but for transverse positions of the probes, the plasma temperature increases and the radial density decreases with the magnetic field and changes with pressure also. The results were compared with nitrogen and argon as well as with direct current glow discharge plasmas with identical input magnetic field [6]. The validity of the probe method for measurement of plasma temperature and density in a toroidal discharge has been discussed.

Das, C.; Jana, D. C.; Hui, A. K.

2010-02-01

30

Probing of field-induced structures and tunable rheological properties of surfactant capped magnetically polarizable nanofluids.  

PubMed

Oil-based nanofluid containing surfactant-capped magnetite nanoparticles are synthesized by a simple coprecipitation approach, and their magnetorheological properties are studied for different magnetic field strengths and volume fractions. We observe a distinct "plateau-like region" in the shear thinning viscosity curve, under an external magnetic field, possibly due to a peculiar alignment of the chains with respect to the field direction where the structure is stable against fragmentation. The observed plateau regime is reminiscent to that of kinetically arrested gel networks. Interestingly, such a plateau regime has been observed only above certain critical magnetic field when the dipolar interaction strength is much greater than the thermal energy where the aggregation becomes a nonequilibrium transport-limited process. The good collapse of specific viscosity data against Mason number for different magnetic field strengths onto a single curve suggests the dominance of hydrodynamic and magnetic forces on thermal force above a certain magnetic field strength. The observed increase in both static and dynamic yield stresses under the magnetic field confirms the formation of columnar structures that hinder the flow behavior. The hysteresis observed in the magnetic sweep experiments shows the inability of the chains to relax within the measurement time. The dynamic measurements confirm that the field-induced structures impart elastic behavior to the dispersion, which is found to increase with magnetic field and saturates at higher field strengths. PMID:23210900

Felicia, Leona J; Philip, John

2013-01-01

31

Nanoscale x-ray magnetic circular dichroism probing of electric-field-induced magnetic switching in multiferroic nanostructures  

NASA Astrophysics Data System (ADS)

The magnetic structure as well as its response to an external electric field were studied in ferrimagnetic CoFe2O4 nanopillars embedded in an epitaxial ferroelectric BiFeO3 film using photoemission electron microscopy and x-ray magnetic circular dichroism. Magnetic switching was observed in both Co and Fe magnetic sublattices after application of an electric field. About 50% of the CoFe2O4 nanopillars were measured to switch their magnetization with the electric field, implying an elastic-mediated electric-field-induced magnetic anisotropy change.

Zhao, T.; Scholl, A.; Zavaliche, F.; Zheng, H.; Barry, M.; Doran, A.; Lee, K.; Cruz, M. P.; Ramesh, R.

2007-03-01

32

Magnetic field enhanced nano-tip fabrication for four-probe STM studies  

Microsoft Academic Search

We present an improved method for fabricating tungsten STM tips for measuring nanoscale objects using a multiprobe STM. The tips were prepared by a ‘drop-off’ technique combined with a magnetic field. For magnetic field strengths above 150 Oe the electrolyte was seen to rotate about the tungsten anode. This rotation reduced the adhesion of bubbles and led to a reduction

J E McKendry; C S Allen; K Critchley; M ? Górzny; A S Walton; S D Evans

2008-01-01

33

Solar Magnetic Field  

NASA Astrophysics Data System (ADS)

Electrical currents flowing in the solar plasma generate a magnetic field, which is detected in the SOLAR ATMOSPHERE by spectroscopic and polarization measurements (SOLAR MAGNETIC FIELD: INFERENCE BY POLARIMETRY). The SOLAR WIND carries the magnetic field into interplanetary space where it can be measured directly by instruments on space probes....

Schüssler, M.; Murdin, P.

2000-11-01

34

Nanofabrication using near-field optical probes  

PubMed Central

Nanofabrication using near-field optical probes is an established technique for rapid prototyping and automated maskless fabrication of nanostructured devices. In this review, we present the primary types of near-field probes and their physical processing mechanisms. Highlights of recent developments include improved resolution by optimizing the probe shape, incorporation of surface plasmonics in probe design, broader use in biological and magnetic storage applications, and increased throughput using probe arrays as well as high speed writing and patterning.

McLeod, Euan; Ozcan, Aydogan

2012-01-01

35

Single ion as a shot-noise-limited magnetic-field-gradient probe  

SciTech Connect

It is expected that ion-trap quantum computing can be made scalable through protocols that make use of transport of ion qubits between subregions within the ion trap. In this scenario, any magnetic field inhomogeneity the ion experiences during the transport may lead to dephasing and loss of fidelity. Here we demonstrate how to measure, and compensate for, magnetic field gradients inside a segmented ion trap, by transporting a single ion over variable distances. We attain a relative magnetic field sensitivity of {Delta}B/B{sub 0{approx}}5x10{sup -7} over a test distance of 140 {mu}m, which can be extended to the mm range, still with sub-{mu}m resolution. A fast experimental sequence is presented, facilitating its use as a magnetic-field-gradient calibration routine, and it is demonstrated that the main limitation is the quantum shot noise.

Walther, A.; Poschinger, U.; Ziesel, F.; Hettrich, M.; Wiens, A.; Welzel, J.; Schmidt-Kaler, F. [Institut fuer Quantenphysik, Universitaet Mainz, Staudingerweg 7, DE-55128 Mainz (Germany)

2011-06-15

36

Magnetic-Field-induced Transitions in Multiferroic TbMnO3 Probed by Resonant  

SciTech Connect

Multiferroic TbMnO3 is investigated using x-ray diffraction in high magnetic fields. Measurements on first and second harmonic structural reflections due to modulations induced by the Mn and Tb magnetic order are presented as function of temperature and field oriented along the a and b-directions of the crystal. The relation to changes in ordering of the rare earth moments in applied field is discussed. Observations below T{sub N}(Tb) without and with applied magnetic field point to a strong interaction of the rare earth order, the Mn moments and the lattice. Also, the incommensurate to commensurate transition of the wave vector at the critical fields is discussed with respect to the Tb and Mn magnetic order and a phase diagram on basis of these observations for magnetic fields H||a and H||b is presented. The observations point to a complicated and delicate magneto-elastic interaction as function of temperature and field.

Strempfer,J.; Bohnenbuck, B.; Zegkinoglou, I.; Aliouane, N.; Landsgesell, S.; Zimmermann, M.; Argyriou, D.

2008-01-01

37

Probe of the Solar Magnetic Field Using the ``Cosmic-Ray Shadow'' of the Sun  

NASA Astrophysics Data System (ADS)

We report on a clear solar-cycle variation of the Sun’s shadow in the 10 TeV cosmic-ray flux observed by the Tibet air shower array during a full solar cycle from 1996 to 2009. In order to clarify the physical implications of the observed solar cycle variation, we develop numerical simulations of the Sun’s shadow, using the potential field source surface model and the current sheet source surface (CSSS) model for the coronal magnetic field. We find that the intensity deficit in the simulated Sun’s shadow is very sensitive to the coronal magnetic field structure, and the observed variation of the Sun’s shadow is better reproduced by the CSSS model. This is the first successful attempt to evaluate the coronal magnetic field models by using the Sun’s shadow observed in the TeV cosmic-ray flux.

Amenomori, M.; Bi, X. J.; Chen, D.; Chen, T. L.; Chen, W. Y.; Cui, S. W.; Danzengluobu; Ding, L. K.; Feng, C. F.; Feng, Zhaoyang; Feng, Z. Y.; Gou, Q. B.; Guo, Y. Q.; Hakamada, K.; He, H. H.; He, Z. T.; Hibino, K.; Hotta, N.; Hu, Haibing; Hu, H. B.; Huang, J.; Jia, H. Y.; Jiang, L.; Kajino, F.; Kasahara, K.; Katayose, Y.; Kato, C.; Kawata, K.; Labaciren; Le, G. M.; Li, A. F.; Li, H. J.; Li, W. J.; Liu, C.; Liu, J. S.; Liu, M. Y.; Lu, H.; Meng, X. R.; Mizutani, K.; Munakata, K.; Nanjo, H.; Nishizawa, M.; Ohnishi, M.; Ohta, I.; Onuma, H.; Ozawa, S.; Qian, X. L.; Qu, X. B.; Saito, T.; Saito, T. Y.; Sakata, M.; Sako, T. K.; Shao, J.; Shibata, M.; Shiomi, A.; Shirai, T.; Sugimoto, H.; Takita, M.; Tan, Y. H.; Tateyama, N.; Torii, S.; Tsuchiya, H.; Udo, S.; Wang, H.; Wu, H. R.; Xue, L.; Yamamoto, Y.; Yang, Z.; Yasue, S.; Yuan, A. F.; Yuda, T.; Zhai, L. M.; Zhang, H. M.; Zhang, J. L.; Zhang, X. Y.; Zhang, Y.; Zhang, Yi; Zhang, Ying; Zhaxisangzhu; Zhou, X. X.

2013-07-01

38

Magnetic Fields  

NSDL National Science Digital Library

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

Vu Bioengineering Ret Program

39

Analysis of the optimal location of magnetic field probes for the determination of the current distribution inside S\\/C cables  

Microsoft Academic Search

During the tests on superconducting cables, the magnetic field is often measured by means of pick-up or Hall probes and these data are used to reconstruct the current distribution inside the cable. The efficiency and the accuracy of the reconstruction procedure depend on the algorithm adopted and on the location of the field probes. For a given geometry of the

F. Bellina; P. Bettini; F. Trevisan

2001-01-01

40

Current-modulating magnetic force microscope probe  

SciTech Connect

A new current-modulating probe for the magnetic force microscope (MFM) is proposed in this article. The magnetic field, which will be used to interact with a magnetic specimen{close_quote}s stray field, is induced on the sharp tip of the conical magnetic core surrounded by a microfabricated single turn conductive coil. The reciprocity principle is used to obtain the force acting on the probe due to the specimen{close_quote}s stray field when scanned over a magnetic specimen. The magnetic field intensity is adjustable by control of the applied current. Images of specimens have been modeled using this probe. The suitability to different specimens is seen to be the biggest advantage of this scheme over the conventional probe designs. {copyright} 2001 American Institute of Physics.

Wang, Frank Z.; Helian, Na; Clegg, Warwick W; Windmill, James F. C.; Jenkins, David

2001-06-01

41

Plasma resonance at low magnetic fields as a probe of vortex line meandering in layered superconductors  

SciTech Connect

We consider the magnetic-field dependence of the plasma resonance frequency in pristine and in irradiated Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} crystals near T{sub c}. At low magnetic fields we relate linear in field corrections to the plasma frequency to the average distance between the pancake vortices in the neighboring layers (wandering length). We calculate the wandering length in the case of thermal wiggling of vortex lines, taking into account both Josephson and magnetic interlayer coupling of pancakes. Analyzing experimental data, we found that (i) the wandering length becomes comparable with the London penetration depth near T{sub c} and (ii) at small melting fields (<20 G) the wandering length does not change much at the melting transition. This shows existence of the line liquid phase in this field range. We also found that pinning by columnar defects affects weakly the field dependence of the plasma resonance frequency near T{sub c}. (c) 2000 The American Physical Society.

Bulaevskii, L. N. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Koshelev, A. E. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)] [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Vinokur, V. M. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)] [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Maley, M. P. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2000-02-01

42

Three Dimensional Imaging of Helicon Wave Fields Via Magnetic Induction Probes.  

National Technical Information Service (NTIS)

The majority of data presented in this work is for a helicon plasma discharge driven at 13.56 MHz, 500 Watts input power, 900 Gauss applied magnetic field, 10 mTorr neutral Argon gas, and cylindrical plasma of 5 cm diameter approximately 50 cm long. High ...

M. P. Reilly

2009-01-01

43

Initial Results From The Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on the Van Allen Probes  

NASA Astrophysics Data System (ADS)

The physics of the creation, loss, and transport of radiation belt particles is intimately connected to the electric and magnetic fields which mediate these processes. A large range of field and particle interactions are involved in this physics from large-scale ring current ion and magnetic field dynamics to microscopic kinetic interactions of whistler-mode chorus waves with energetic electrons. To measure these kinds of radiation belt interactions, NASA implemented the two-satellite Van Allen Probes mission. As part of the mission, the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) investigation is an integrated set of instruments consisting of a tri-axial fluxgate magnetometer (MAG) and a Waves instrument which includes a tri-axial search coil magnetometer (MSC). These wave measurements include AC electric and magnetic fields from 10Hz to 400 kHz. We show examples of plasmapause identification and variation determined by the upper hybrid resonance, low frequency ULF pulsations, and whistler mode waves including upper and lower band chorus. These data are compared with particle measuements to show relationships between wave activity and particle energization.

Kletzing, Craig

2013-04-01

44

The Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on the Radiation Belt Storm Probes  

NASA Astrophysics Data System (ADS)

The physics of the creation, loss, and transport of radiation belt particles is intimately connected to the electric and magnetic fields which mediate these processes. A large range of field and particle interactions are involved in this physics from large-scale ring current ion and magnetic field dynamics to microscopic kinetic interactions of whistler-mode chorus waves with energetic electrons. To measure these kinds of radiation belt interactions, NASA implemented the two-satellite Radiation Belt Storm Probes (RBSP) mission. As part of the mission, the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) investigation is an integrated set of instruments consisting of a tri-axial fluxgate magnetometer (MAG) and a Waves instrument which includes a tri-axial search coil magnetometer (MSC). These wave measurements include AC electric and magnetic fields from 10Hz to 400 kHz. Examples of key wave science such as the plasmaspheric hiss, magnetosonic equatorial noise, electromagnetic ion cyclotron waves, and chorus are presented along with overall instrument capability and data availability.

Kletzing, C.; Kurth, W. S.; MacDowall, R. J.; Torbert, R. B.; Bounds, S. R.; Hospodarsky, G. B.; Smith, C. W.; Connerney, J. E.; Santolik, O.; Thorne, R. M.; Jordanova, V. K.; Wygant, J. R.; Bonnell, J. W.

2012-12-01

45

Initial Results From The Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on the Van Allen Probes  

NASA Astrophysics Data System (ADS)

The physics of the creation, loss, and transport of radiation belt particles is intimately connected to the electric and magnetic fields which mediate these processes. A large range of field and particle interactions are involved in this physics from large-scale ring current ion and magnetic field dynamics to microscopic kinetic interactions of whistler-mode chorus waves with energetic electrons. To measure these kinds of radiation belt interactions, NASA implemented the two-satellite Van Allen Probes mission. As part of the mission, the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) investigation is an integrated set of instruments consisting of a tri-axial fluxgate magnetometer (MAG) and a Waves instrument which includes a tri-axial search coil magnetometer (MSC). These wave measurements include AC electric and magnetic fields from 10Hz to 400 kHz. We show examples of plasmapause identification and variation determined by the upper hybrid resonance, low frequency ULF pulsations, and whistler mode waves including upper and lower band chorus. These data are compared with particle measuements to show relationships between wave activity and particle energization.

Kletzing, C.; Kurth, W. S.; MacDowall, R. J.; Torbert, R. B.; Hospodarsky, G. B.; Bounds, S. R.; Smith, C. W.; Connerney, J. E.; Santolik, O.; Thorne, R. M.; Jordanova, V. K.; Wygant, J. R.; Bonnell, J. W.

2013-05-01

46

Active beam probe spectroscopy, a proposal of measuring internal magnetic field distribution  

SciTech Connect

For the study of magnetically confined plasmas, it is important to measure the q profile in tokamaks as well as the change of magnetic field configuration caused by the high beta effect in helical systems. The motional Stark effect has recently been utilized to find out the direction of local magnetic field by measuring the direction of polarization of spectral line emission from injected beam particles. The presented proposal is to improve the spatial resolution and the accuracy of this method by combining a technique of laser spectroscopy with it. A linearly polarized laser beam will be injected coaxilly with the neutral particle beam. Phase sensitive detection of induced fluorescence from the polarization-modulated laser light tuned to a split spectral line will be used to detect the local magnetic field direction, instead of observing the polarization of emissions due to electron impact excitation of injected atoms. An experimental scheme proposed and characteristics estimated will be described. 14 refs., 3 figs., 1 tab.

Fujita, J. [National Institute for Fusion Science, Nagoya (Japan)

1994-12-31

47

ANISOTROPY AS A PROBE OF THE GALACTIC COSMIC-RAY PROPAGATION AND HALO MAGNETIC FIELD  

SciTech Connect

The anisotropy of cosmic rays (CRs) in the solar vicinity is generally attributed to CR streaming due to the discrete distribution of CR sources or local magnetic field modulation. Recently, the two-dimensional large-scale CR anisotropy has been measured by many experiments in the TeV-PeV energy range in both hemispheres. The tail-in excess along the tangential direction of the local spiral arm and the loss cone deficit pointing to the north Galactic pole direction agree with what have been obtained in tens to hundreds of GeV. The persistence of the two large-scale anisotropy structures in such a wide energy range suggests that the anisotropy might be due to global streaming of the Galactic CRs (GCRs). This work tries to extend the observed CR anisotropy picture from the solar system to the whole galaxy. In such a case, we can find a new interesting signature, a loop of GCR streaming, of the GCR propagation. We further calculate the overall GCR streaming induced magnetic field, and find a qualitative consistency with the observed structure of the halo magnetic field.

Qu, Xiao-bo; Zhang, Yi; Liu, Cheng; Hu, Hong-bo [Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Xue, Liang, E-mail: zhangyi@mail.ihep.ac.cn [School of Physics, Shandong University, Ji'nan 250100 (China)

2012-05-01

48

Hard disk magnetic domain nano-spatial resolution imaging by using a near-field scanning microwave microscope with an AFM probe tip  

Microsoft Academic Search

A near-field scanning microwave microscope (NSMM) incorporating an atomic force microscope (AFM) probe tip was used for the direct imaging of magnetic domains of a hard disk under an external magnetic field. We directly imaged the magnetic domain changes by measuring the change of reflection coefficient S11 of the NSMM at an operating frequency near 4.4GHz. Comparison was made to

Harutyun Melikyan; Tigran Sargsyan; Arsen Babajanyan; Seungwan Kim; Jongchel Kim; Kiejin Lee; Barry Friedman

2009-01-01

49

High-frequency magnetic field probe for determination of interface levels in separation tanks  

NASA Astrophysics Data System (ADS)

There are many principles for interface level detection in separation tanks based on capacitance, ultra sound, microwave, nuclear radiation etc. These principles work well in many situations, in others they fail. The high frequency magnetic field principle works in most of the situations that will occur in separation tanks for crude oils for detection of the clean water level, the layers of water continuous water/oil emulsion and the oil continuous oil/water emulsion, the oil level, the thickness of the foam layer and the gas. When a coil is dipped into a fluid its electrical impedance will be dependent on the characteristics of the fluid. If the material is electrical conductive the impedance of the coil will be reduced due to the eddy currents induced in the material, setting up a magnetic field directed against the field generated by the coil. The inductance will increase but still remain low also in the water continuous water/oil emulsion zone, but will rapidly increase in the oil continuous oil/water emulsion zone. In pure crude oil the inductance will be high and even higher in gas. The coil inductance is measured by connecting the coil to a LC-oscillator.

Hammer, Erling; Abro, Eirik; Cimpan, Emil; Yan, Guanqun

2001-02-01

50

Cage lifetimes of ionic liquids as studied by the magnetic field effect probe.  

PubMed

Magnetic field effects (MFEs) on the photoinduced hydrogen abstraction reaction of benzophenone with phenol were investigated in ionic liquids (ILs) with a short alkyl chain (N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide (TMPA TFSA)) and long alkyl chains ((N,N,N-trimethyl-N-octylammonium bis(trifluoromethanesulfonyl)amide (TMOA TFSA) and N-decyl-N,N,N-trimethylammonium bis(trifluoromethanesulfonyl)amide (DTMA TFSA)) by a nanosecond laser flash photolysis technique. In each ionic liquid, escaped radical yield of a benzophenone ketyl radical rapidly increased with increasing magnetic field strength (B) of 0 T < B? 0.01 T. At 0.01 T < B? 0.4 T, the escaped radical yield almost saturated in TMPA TFSA or gradually increased in TMOA TFSA and DTMA TFSA. At much higher fields of 0.4 T < B? 30 T, the yield gradually decreased, resulting in 10-15% decrease at 30 T. The observed MFEs can be explained by the hyperfine coupling and ?g mechanisms together with the relaxation mechanism. On the time profiles of the transient absorption observed for the benzophenone ketyl radical, MFEs were generated in the time range of 0 < t < 0.6 ?s. The cage lifetimes of TMOA TFSA and DTMA TFSA were estimated to be at least 120 ns. PMID:22307519

Okada, Tomohide; Yago, Tomoaki; Takamasu, Tadashi; Wakasa, Masanobu

2012-03-14

51

s -wave superconductivity probed by measuring magnetic penetration depth and lower critical field of MgCNi3 single crystals  

NASA Astrophysics Data System (ADS)

The magnetic penetration depth ? has been measured in MgCNi3 single crystals using both a high-precision tunnel diode oscillator (TDO) technique and Hall probe magnetization (HPM). In striking contrast to previous measurements in powders, ??(T) deduced from TDO measurements increases exponentially at low temperature, clearly showing that the superconducting gap is fully open over the whole Fermi surface. An absolute value at zero temperature ?(0)=230nm is found from the lower critical field measured by HPM. We also discuss the observed difference of the superfluid density deduced from both techniques. A possible explanation could be due to a systematic decrease in the critical temperature at the sample surface.

Diener, P.; Rodière, P.; Klein, T.; Marcenat, C.; Kacmarcik, J.; Pribulova, Z.; Jang, D. J.; Lee, H. S.; Lee, H. G.; Lee, S. I.

2009-06-01

52

PROBING THE SHALLOW CONVECTION ZONE: RISING MOTION OF SUBSURFACE MAGNETIC FIELDS IN THE SOLAR ACTIVE REGION  

SciTech Connect

In this Letter, we present a seismological detection of a rising motion of magnetic flux in the shallow convection zone of the Sun, and show estimates of the emerging speed and its decelerating nature. In order to evaluate the speed of subsurface flux that creates an active region, we apply six Fourier filters to the Doppler data of NOAA AR 10488, observed with the Solar and Heliospheric Observatory/Michelson Doppler Imager, to detect the reduction of acoustic power at six different depths from -15 to -2 Mm. All the filtered acoustic powers show reductions, up to 2 hr before the magnetic flux first appears at the visible surface. The start times of these reductions show a rising trend with a gradual deceleration. The obtained velocity is first several km s{sup -1} in a depth range of 15-10 Mm, then {approx}1.5 km s{sup -1} at 10-5 Mm, and finally {approx}0.5 km s{sup -1} at 5-2 Mm. If we assume that the power reduction is actually caused by the magnetic field, the velocity of the order of 1 km s{sup -1} is well in accordance with previous observations and numerical studies. Moreover, the gradual deceleration strongly supports the theoretical model that the emerging flux slows down in the uppermost convection zone before it expands into the atmosphere to build an active region.

Toriumi, Shin; Yokoyama, Takaaki [Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Ilonidis, Stathis [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305-4085 (United States); Sekii, Takashi, E-mail: toriumi@eps.s.u-tokyo.ac.jp [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

2013-06-10

53

Probing the Shallow Convection Zone: Rising Motion of Subsurface Magnetic Fields in the Solar Active Region  

NASA Astrophysics Data System (ADS)

In this Letter, we present a seismological detection of a rising motion of magnetic flux in the shallow convection zone of the Sun, and show estimates of the emerging speed and its decelerating nature. In order to evaluate the speed of subsurface flux that creates an active region, we apply six Fourier filters to the Doppler data of NOAA AR 10488, observed with the Solar and Heliospheric Observatory/Michelson Doppler Imager, to detect the reduction of acoustic power at six different depths from -15 to -2 Mm. All the filtered acoustic powers show reductions, up to 2 hr before the magnetic flux first appears at the visible surface. The start times of these reductions show a rising trend with a gradual deceleration. The obtained velocity is first several km s-1 in a depth range of 15-10 Mm, then ~1.5 km s-1 at 10-5 Mm, and finally ~0.5 km s-1 at 5-2 Mm. If we assume that the power reduction is actually caused by the magnetic field, the velocity of the order of 1 km s-1 is well in accordance with previous observations and numerical studies. Moreover, the gradual deceleration strongly supports the theoretical model that the emerging flux slows down in the uppermost convection zone before it expands into the atmosphere to build an active region.

Toriumi, Shin; Ilonidis, Stathis; Sekii, Takashi; Yokoyama, Takaaki

2013-06-01

54

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

55

Triaxial Probe Magnetic Data Analysis  

NASA Technical Reports Server (NTRS)

The Triaxial Magnetic Moment Analysis software uses measured magnetic field test data to compute dipole and quadrupole moment information from a hardware element. It is used to support JPL projects needing magnetic control and an understanding of the spacecraft-generated magnetic fields. Evaluation of the magnetic moment of an object consists of three steps: acquisition, conditioning, and analysis. This version of existing software was extensively rewritten for easier data acquisition, data analysis, and report presentation, including immediate feedback to the test operator during data acquisition. While prior JPL computer codes provided the same data content, this program has a better graphic display including original data overlaid with reconstructed results to show goodness of fit accuracy and better appearance of the report graphic page. Data are acquired using three magnetometers and two rotations of the device under test. A clean acquisition user interface presents required numeric data and graphic summaries, and the analysis module yields the best fit (least squares) for the magnetic dipole and/or quadrupole moment of a device. The acquisition module allows the user to record multiple data sets, selecting the best data to analyze, and is repeated three times for each of the z-axial and y-axial rotations. In this update, the y-axial rotation starting position has been changed to an option, allowing either the x- or z-axis to point towards the magnetometer. The code has been rewritten to use three simultaneous axes of magnetic data (three probes), now using two "rotations" of the device under test rather than the previous three rotations, thus reducing handling activities on the device under test. The present version of the software gathers data in one-degree increments, which permits much better accuracy of the fit ted data than the coarser data acquisition of the prior software. The data-conditioning module provides a clean data set for the analysis module. For multiple measurements at a given degree, the first measurement is used. For omitted measurements, the missing field is estimated by linear interpolation between the two nearest measurements. The analysis module was rewritten for the dual rotation, triaxial probe measurement process and now has better moment estimation accuracy, based on the finer one degree of data acquisition resolution. The magnetic moments thus computed are used as an input to summarize the total spacecraft field.

Shultz, Kimberly; Whittlesey, Albert; Narvaez, Pablo

2007-01-01

56

Recurrent Cosmic-ray Variations as a Probe of the Heliospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

A linear relationship between the observed 26-day recurrent cosmic-ray intensity variations and the global latitudinal gradient was first reported by Zhang (1997, ApJ, 488), who made extensive use of Ulysses data. This relationship is seen for all species considered and at all latitudes covered by the spacecraft. Burger and Hitge (2004, ApJL, 617) used a three-dimensional steady-state numerical modulation model and showed that a Fisk-type (Fisk 1996, JGR, 101) heliospheric magnetic field (HMF) can in principle explain these observations, at least at high latitudes. In this progress report we use a refinement of the Fisk-Parker hybrid HMF model of Burger and Hitge (2004) by Kruger (2006, MSc dissertation, NWU University) (see also Kruger, Burger and Hitge 2005, AGU Fall meeting abstracts SH23B-0341) to study these 26-day recurrent variations in more detail with the same modulation code. In Kruger's model the HMF is Parker-like at the highest latitudes, becomes Fisk- like at intermediate latitudes, and becomes Parker-like again in the region swept out by the wavy current sheet. By using an almost continuous range of latitudinal gradients for both solar magnetic polarity cycles and for both protons and electrons - in contrast to the limited number of values used by Burger and Hitge (2004) - the structure of the graphs of amplitude of the recurrent cosmic-ray intensity variations as function of global latitudinal gradient can be studied in detail. This was performed in a 100 AU model heliosphere for solar minimum conditions with the tilt angle of the heliospheric current sheet at 10 degrees. In all cases drift effects are included. We find that these curves for amplitude vs. latitudinal gradient are similar for protons and for electrons. By switching the sign of the modeled amplitudes when the latitudinal gradient becomes negative, the existence of a single relationship between the two quantities can be studied for the whole range of modeled latitudinal gradients. This study shows that a single second-order fit gives better results than a first-order fit for the whole range of latitudinal gradients (and consequently for both species and both solar magnetic polarities) and that there is a difference in the amplitudes for high- and for low rigidities, even if the latitudinal gradient is the same. This difference is a minimum at latitudes where the Fisk-type field is expected to dominate. In the ecliptic at 1 AU, we find that at high rigidity, the amplitude of the recurrent variations is larger for protons during A > 0 polarity epochs than for A < 0 epochs. This is in agreement with observational results of Richardson, Cane and Wibberenz (1999, JGR, 104). For the case of a Parker field, the modeled amplitudes have about the same magnitude for both polarity epochs. Note that what we discus here are preliminary results, and while they clearly suggest the existence of a Fisk-type HMF, the role of the diffusion tensor (and the associated turbulence quantities) has yet to be determined.

Burger, R. A.; Engelbrecht, E. E.

2006-12-01

57

Hard disk magnetic domain nano-spatial resolution imaging by using a near-field scanning microwave microscope with an AFM probe tip  

NASA Astrophysics Data System (ADS)

A near-field scanning microwave microscope (NSMM) incorporating an atomic force microscope (AFM) probe tip was used for the direct imaging of magnetic domains of a hard disk under an external magnetic field. We directly imaged the magnetic domain changes by measuring the change of reflection coefficient S11 of the NSMM at an operating frequency near 4.4 GHz. Comparison was made to the magnetic force microscope (MFM) image. Using the AFM probe tip coupled to the tuning fork distance control system enabled nano-spatial resolution. The NSMM incorporating an AFM tip offers a reliable means for quantitative measurement of magnetic domains with nano-scale resolution and high sensitivity.

Melikyan, Harutyun; Sargsyan, Tigran; Babajanyan, Arsen; Kim, Seungwan; Kim, Jongchel; Lee, Kiejin; Friedman, Barry

2009-08-01

58

Design of a triple resonance magic angle sample spinning probe for high field solid state nuclear magnetic resonance  

Microsoft Academic Search

Standard design and construction practices used in building nuclear magnetic resonance (NMR) probes for the study of solid state samples become difficult if not entirely impractical to implement as the 1H resonance frequency approaches the self resonance frequency of commercial capacitors. We describe an approach that utilizes short variable transmission line segments as tunable reactances. Such an approach effectively controls

Rachel W. Martin; Eric K. Paulson; Kurt W. Zilm

2003-01-01

59

Singlet and triplet states of trions in ZuSe-based quantum wells probed by magnetic fields to 50 Tesla  

SciTech Connect

Singlet and triplet states of positively (X{sup +}) and negatively (X{sup -}) charged excitons in ZnSe-based quantum wells have been studied by means of photoluminescence in pulsed magnetic fields up to 50 T. The binding energy of the X{sup -} singlet state shows a monotonic increase with magnetic field with a tendency to saturation, while that of the X{sup +} slightly decreases. The triplet X{sup +} and X{sup -} states, being unbound at zero magnetic field, noticeably increase their binding energy in high magnetic fields. The experimental evidence for the interaction between the triplet and singlet states of lTions leading to their anticrossing in magnetic fields has been found.

Astakhov, G. V.; Yakovlev, D. R.; Crooker, S. A. (Scott A.); Barrick, T. (Todd); Dzyubenko, A. B.; Sander, Thomas; Kochereshko, V. P.; Ossau, W.; Faschinger, W.; Waag, A.

2002-01-01

60

Construction and Calibration Techniques of High Frequency Magnetic Probes  

Microsoft Academic Search

The details of the construction and calibration of high frequency magnetic probes, used to measure the transient magnetic fields in a linear pinch device, are described. A simple and reliable calibration technique, using conventional laboratory electronic equipment, was developed to measure the absolute sensitivity of magnetic probes in the frequency range of 1–50 Mc. Factors affecting the frequency response of

R. C. Phillips; E. B. Turner

1965-01-01

61

Irradiation effects on magnetic probes made of mineral insulated cable  

Microsoft Academic Search

A magnetic probe made of mineral insulated (MI) cable in Japan Material Testing Reactor (JMTR) was irradiated as one of the irradiation tests on diagnostics components for experimental thermonuclear reactors such as International Thermonuclear Experimental Reactor (ITER). Magnetic probes have to be installed inside the vacuum vessel to measure the magnetic field, which is very important for the position control

T Nishitani; T Shikama; M Fukao; H Matsuo; R Snider; J Broesch; N Sagawa; H Kawamura; S Kasai

2000-01-01

62

Electromagnetic Field Probes.  

National Technical Information Service (NTIS)

The report summarizes activities during the first quarter of a program directed to the development of probes and techniques for measurement of electromagnetic radiation in shielded enclosures over the 20 to 200 MHz frequency range. Studies were made of te...

G. W. Bechtold J. L. Birchfield R. D. Wetherington

1972-01-01

63

Probing the dynamics of pressure- and magnetic field-tuned transitions in strongly-correlated electron systems: Raman scattering studies  

Microsoft Academic Search

In this thesis I present data on pressure- and magnetic field-tuned phase transitions and the melting of self-organized structures in three different strongly-coupled systems. I have built a unique high-pressure cell (0--100 kbar) that allows in-situ pressure control while at low-temperatures (3.5--300 K) and in a magnetic field (0--8T). First, I report a Raman scattering study of the pressure-induced collapse

Clark Sheldon Snow

2003-01-01

64

A model for mark size dependence on field emission voltage in heat-assisted magnetic probe recording on CoNi\\/Pt multilayers  

Microsoft Academic Search

A method of heat-assisted magnetic recording (HAMR) potentially suitable for probe-based storage systems is characterized. In this work, field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. Pulse voltages of 2-7 V with a duration of 500 ns were applied to a CoNi\\/Pt multilayered film. Different types of Ir\\/Pt and W STM tips

L. Zhang; James A. Bain; Jian-Gang Zhu; Leon Abelmann; Takahiro Onoue

2004-01-01

65

The use of magnetic field effects on photosensitizer luminescence as a novel probe for optical monitoring of oxygen in photodynamic therapy  

NASA Astrophysics Data System (ADS)

The effect of a magnetic field on the steady-state and time-resolved optical emission of a custom fullerene-linked photosensitizer (PS) in liposome cell phantoms was studied at various oxygen concentrations (0.19-190 µM). Zeeman splitting of the triplet state and hyperfine coupling, which control intersystem crossing between singlet and triplet states, are altered in the presence of low magnetic fields (B < 320 mT), perturbing the luminescence intensity and lifetime as compared to the triplet state at B = 0. Measurements of the luminescence intensity and lifetime were performed using a time-domain apparatus integrated with a magnet. We propose that by probing magnet-affected optical emissions, one can monitor the state of oxygenation throughout the course of photodynamic therapy. Since the magnetic field effect (MFE) operates primarily by affecting the radical ion pairs related to type I photodynamic action, the enhancement or suppression of the MFE can be used as a measure of the dynamic equilibrium between the type I and II photodynamic pathways. The unique photo-initiated charge-transfer properties of the PS used in this study allow it to serve as both cytotoxic agent and oxygen probe that can provide in situ dosimetric information at close to real time.

Mermut, O.; Diamond, K. R.; Cormier, J.-F.; Gallant, P.; Hô, N.; Leclair, S.; Marois, J.-S.; Noiseux, I.; Morin, J.-F.; Patterson, M. S.; Vernon, M. L.

2009-01-01

66

Standard probes for electromagnetic field measurements  

Microsoft Academic Search

Discusses various standard antennas for measuring radio-frequency electric and magnetic fields. A theoretical analysis of each antenna's receiving characteristics is summarized and referenced. The standard probes described are an electrically short dipole, a resistively-loaded dipole, a half-wave dipole, an electrically small loop, and a resistively-loaded loop. A single-turn loop designed for simultaneous measurement of the electric and magnetic components of

Motohisa Kanda

1993-01-01

67

Impedance-type ferromagnetic probe sensors for magnetic inspection  

Microsoft Academic Search

Impedance-type ferromagnetic probes are based on the fact that the inductive resistance of a coil with a core of soft magnetic material in the form of a rod, ring, or frame decreases in a constant magnetic field. The current flowing through the probe at H = 0 is decreased considerably by connecting a coil to the oscillatory circuit tuned to

P. A. Khalileev

1976-01-01

68

Surface and Interface Magnetism Using Radioactive Probes  

NASA Astrophysics Data System (ADS)

Magnetic properties of impurities at ferromagnetic surfaces and interfaces have been investigated performing Perturbed Angular Correlation (PAC) measurements in the ultra-high vacuum chamber ASPIC (Apparatus for Surface Physics and Interfaces at CERN) using different PAC probes. We present the measurements of magnetic hyperfine fields ( B hf) at 111Cd probe atoms (i) in Pd covered by Ni, (ii) on Pd-decorated Ni surfaces, (iii) and on pure Ni surfaces at a variety of local structures like terraces, steps, kinks. The results yield a deep insight into the interplay of structural surface roughness and magnetic roughness on the atomic scale. Correlating the experimental B hf values with the number of their nearest Ni and Pd neighbours, the coordination number, nonlinear dependences were found. These findings are compared with recent theoretical studies which were prompted by the experiments.

Manzhur, Y.; Prandolini, M. J.; Potzger, K.; Weber, A.; Zeitz, W.-D.; Bertschat, H. H.; Dietrich, M.

2005-01-01

69

Study of interaction of proflavin with triethylamine in homogeneous and micellar media: Photoinduced electron transfer probed by magnetic field effect  

NASA Astrophysics Data System (ADS)

Interaction of triethylamine (TEA) with cationic proflavin (PF +) in homogeneous and micellar media is studied using absorption spectroscopy, steady-state as well as time-resolved fluorescence spectroscopy and laser flash photolysis in conjunction with an external magnetic field. The two prime phenomena that have been highlighted in this study are photoinduced electron transfer (PET) and ground-state complex formation. This study shows that it is the medium which determines the reaction pathways to be followed. Magnetic field effect (MFE) helps to elucidate the reaction mechanism involved and this work also highlights the distance dependence factor associated with MFE.

Chakraborty, Brotati; Basu, Samita

2009-08-01

70

Research of optical electric field probe  

NASA Astrophysics Data System (ADS)

As an important modern measurement equipment of the electromagnetic field, electric field probe can measure the industrial, scientific and medical aspects of the leakage field. In the Electro Magnetic Compatibility (EMC) experiment, it can also check the high-frequency-sensitive parts of the devices and the parasitic radiations due to the mechanical movement. Especially in the field of Electromagnetic Compatibility, electric field probe is one of the most important test equipment. This paper introduces a type of optical electric field probe. In the system, a kind of antenna, which could provide a response nearly isotropic for all polarizations of the incident field, is used for receiving the signal of the electric field. The high-frequency signal received by the antenna then is detected by Schottky barrier diode detector. This low-frequency or Direct Current (DC) signal can be modulated to the band of light by the Electro-Absorption-Distributed Feed Back (EA-DFB) modulator, thus the probe can provide a wild band responds. Through the optical fiber, the optical signal is sent to the photoelectric detector. Based on the optical power value, the field intensity can be calculated. In this system, compared with traditional transmission line, optical fiber can minimize the electromagnetic interference and transmission-line attenuation. In addition to this, the system also has high test sensitivity and wide measurement bandwidth. Furthermore, the whole system has a simple structure and low manufacturing cost.

Zhang, Wan; Li, Bin; Chen, Jingyao; Wang, Jifeng; Lu, Guizhen

2012-10-01

71

Magnetic field gradient measurement on magnetic cards using magnetic force microscopy  

Microsoft Academic Search

The magnetic field gradients of magnetic stripe cards, which are developed for classifying magnetic particles used in magnetic particle inspections, have been measured using a magnetic force microscope (MFM). The magnetic force exerted on a MFM probe by the stray field emanating from the card was measured to determine the field gradients. The results are in good agreement with the

C. C. H. Lo; J. Leib; D. C. Jiles; W. C. Chedister

2002-01-01

72

Magnetic Yoke Probe for In-situ Magnetic Measurements  

NASA Astrophysics Data System (ADS)

A probe with a magnetic yoke for nondestructive evaluation of mechanical properties was developed. This probe can evaluate magnetic properties of ferromagnetic materials without machining them to a shape of ring core or frame core, that is, in-situ measurements. In this paper, magnetic properties measured by the magnetic yoke probe were compared with mechanical property. The magnetic properties measured by the probe have a good correlation with those mechanical properties. This shows a potential to apply the probe to NDE of mechanical properties in ferromagnetic materials. The effect of air gap between the probe and the specimen was also investigated, to consider the problem of contact in practical use.

Kikuchi, Hiroaki; Liu, Tong; Ara, Katsuyuki; Kamada, Yasuhiro; Kobayashi, Satoru; Takahashi, Seiki

73

Concentrator of magnetic field of light  

NASA Astrophysics Data System (ADS)

In the recent decade metamaterials with magnetic permeability different than unity and unusual response to the magnetic field of incident light have been intensively explored. Existence of magnetic artificial materials created an interest in a scanning near-field magnetic microscope for studies of magnetic responses of subwavelength elementary cells of those metamaterials. We present a method of measuring magnetic responses of such elementary cells within a wide range of optical frequencies with single probes of two types. The first type probe is made of a tapered silica fiber with radial metal stripes separated by equidistant slits of constant angular width. The second type probe is similar to metal coated, corrugated, tapered fiber apertured SNOM probe, but in this case corrugations are radially oriented. Both types of probes have internal illumination with azimuthally polarized light. In the near-field they concentrate into a subwavelength spot the longitudinal magnetic field component which is much stronger than the perpendicular electric one.

Wróbel, Piotr; Stefaniuk, Tomasz; Antosiewicz, Tomasz J.; Szoplik, Tomasz

2012-05-01

74

Probing fine magnetic particles with neutron scattering  

SciTech Connect

Because thermal neutrons are scattered both by nuclei and by unpaired electrons, they provide an ideal probe for studying the atomic and magnetic structures of fine-grained magnetic materials, including nanocrystalline solids, thin epitaxial layers, and colloidal suspensions of magnetic particles, known as ferrofluids. Diffraction, surface reflection, and small angle neutron scattering (SANS) are the techniques used. With the exception of surface reflection, these methods are described in this article. The combination of SANS with refractive-index matching and neutron polarisation analysis is particularly powerful because it allows the magnetic and atomic structures to be determined independently. This technique has been used to study both dilute and concentrated ferrofluid suspensions of relatively monodisperse cobalt particles, subjected to a series of applied magnetic fields. The size of the cobalt particle core and the surrounding surfactant layer were determined. The measured interparticle structure factor agrees well with a recent theory that allows correlations in binary mixtures of magnetic particles to be calculated in the case of complete magnetic alignment. When one of the species in such a binary mixture is a nonmagnetic, cyclindrical macromolecule, application of a magnetic field leads to some degree of alignment of the nonmagnetic species. This result has been demonstrated with tobacco mosaic virus suspended in a water-based ferrofluid.

Pynn, R.

1991-12-31

75

Probing fine magnetic particles with neutron scattering  

SciTech Connect

Because thermal neutrons are scattered both by nuclei and by unpaired electrons, they provide an ideal probe for studying the atomic and magnetic structures of fine-grained magnetic materials, including nanocrystalline solids, thin epitaxial layers, and colloidal suspensions of magnetic particles, known as ferrofluids. Diffraction, surface reflection, and small angle neutron scattering (SANS) are the techniques used. With the exception of surface reflection, these methods are described in this article. The combination of SANS with refractive-index matching and neutron polarisation analysis is particularly powerful because it allows the magnetic and atomic structures to be determined independently. This technique has been used to study both dilute and concentrated ferrofluid suspensions of relatively monodisperse cobalt particles, subjected to a series of applied magnetic fields. The size of the cobalt particle core and the surrounding surfactant layer were determined. The measured interparticle structure factor agrees well with a recent theory that allows correlations in binary mixtures of magnetic particles to be calculated in the case of complete magnetic alignment. When one of the species in such a binary mixture is a nonmagnetic, cyclindrical macromolecule, application of a magnetic field leads to some degree of alignment of the nonmagnetic species. This result has been demonstrated with tobacco mosaic virus suspended in a water-based ferrofluid.

Pynn, R.

1991-01-01

76

Optical sensor of magnetic fields  

DOEpatents

An optical magnetic field strength sensor for measuring the field strength of a magnetic field comprising a dilute magnetic semi-conductor probe having first and second ends, longitudinally positioned in the magnetic field for providing Faraday polarization rotation of light passing therethrough relative to the strength of the magnetic field. Light provided by a remote light source is propagated through an optical fiber coupler and a single optical fiber strand between the probe and the light source for providing a light path therebetween. A polarizer and an apparatus for rotating the polarization of the light is provided in the light path and a reflector is carried by the second end of the probe for reflecting the light back through the probe and thence through the polarizer to the optical coupler. A photo detector apparatus is operably connected to the optical coupler for detecting and measuring the intensity of the reflected light and comparing same to the light source intensity whereby the magnetic field strength may be calculated.

Butler, M.A.; Martin, S.J.

1986-03-25

77

Magnetic fields in astrophysics  

Microsoft Academic Search

The evidence of cosmic magnetism is examined, taking into account the Zeeman effect, beats in atomic transitions, the Hanle effect, Faraday rotation, gyro-lines, and the strength and scale of magnetic fields in astrophysics. The origin of magnetic fields is considered along with dynamos, the conditions for magnetic field generation, the topology of flows, magnetic fields in stationary flows, kinematic turbulent

Ia. B. Zeldovich; A. A. Ruzmaikin; D. D. Sokolov

1983-01-01

78

Magnetic field gradient measurement on magnetic cards using magnetic force microscopy  

NASA Astrophysics Data System (ADS)

The magnetic field gradients of magnetic stripe cards, which are developed for classifying magnetic particles used in magnetic particle inspections, have been measured using a magnetic force microscope (MFM). The magnetic force exerted on a MFM probe by the stray field emanating from the card was measured to determine the field gradients. The results are in good agreement with the field gradients estimated from the magnetizing field strengths used in the encoding process. .

Lo, C. C. H.; Leib, J.; Jiles, D. C.; Chedister, W. C.

2002-05-01

79

Probing the dynamics of pressure- and magnetic field-tuned transitions in strongly-correlated electron systems: Raman scattering studies  

NASA Astrophysics Data System (ADS)

In this thesis I present data on pressure- and magnetic field-tuned phase transitions and the melting of self-organized structures in three different strongly-coupled systems. I have built a unique high-pressure cell (0--100 kbar) that allows in-situ pressure control while at low-temperatures (3.5--300 K) and in a magnetic field (0--8T). First, I report a Raman scattering study of the pressure-induced collapse of the Mott-like phases of Ca3Ru2O7 (T N = 56 K) and Ca2RuO4 (TN = 110 K). The pressure dependence of the phonon and two-magnon excitations in these materials indicate: (i) a T > 0 pressure-induced collapse of the antiferromagnetic (AF) insulating phase above P* ˜ 55 kbar in Ca3Ru2O 7 and P* ˜ 5--10 kbar in Ca2RuO4; (ii) a remarkable insensitivity of the exchange interaction to pressure in both systems; and (iii) evidence for persistent AF correlations above the critical pressure of Ca2RuO4, suggestive of phase separation involving AF insulator and ferromagnetic metal phases. Second, I present a Raman scattering study of the low-temperature pressure induced collapse of the CDW phase of 1T-TiSe2. At 3.5K, the CDW phase collapses at P* > 25 kbar. More interestingly, our Raman scattering measurements reveal that the collapse occurs in three distinct regions: (i) a P < 5 kbar region where the CDW-amplitude mode energies harden; (ii) a soft, intermediate region between 5 < P < 25 kbar, where the CDW-amplitude mode energies soften, indicating a loss of long-range translational order; and (iii) a complete collapse of the CDW state by P ˜ 25 kbar. Third, I present Raman scattering measurements of (Eu,Gd)O and (Eu,La)B 6 as functions of doping, B isotope, magnetic field, and temperature. Our results reveal a variety of distinct regimes as a function of decreasing T: (i) a paramagnetic semimetal regime, characterized by a collision-dominated electronic scattering response whose scattering rate Gamma decreases with decreasing temperature; (ii) a spin-disorder scattering regime, characterized by a collision-dominated electronic scattering response whose scattering rate Gamma scales with the magnetic susceptibility; (iii) a magnetic polaron (MP) regime, in which the development of an H = 0 spin-flip Raman response betrays the formation of magnetic polarons above the Curie temperature Tc; and (iv) a ferromagnetic metal regime, characterized by a flat electronic continuum response.

Snow, Clark Sheldon

80

OH Maser Sources in W49N: Probing Magnetic Field and Differential Anisotropic Scattering with Zeeman Pairs Using the Very Long Baseline Array  

NASA Astrophysics Data System (ADS)

Our analysis of a Very Long Baseline Array 12 hr synthesis observation of the OH masers in the well-known star-forming region W49N has yielded valuable data that enable us to probe distributions of magnetic fields in both the maser columns and the intervening interstellar medium (ISM). The data, consisting of detailed high angular resolution images (with beam width ~20 mas) of several dozen OH maser sources, or spots, at 1612, 1665, and 1667 MHz, reveal anisotropic scatter broadening with typical sizes of a few tens of milliarcseconds and axial ratios between 1.5 and 3. Such anisotropies have been reported previously by Desai et al. and have been interpreted as being induced by the local magnetic field parallel to the Galactic plane. However, we find (1) apparent angular sizes of, on average, a factor of about 2.5 less than those reported by Desai et al., indicating significantly less scattering than inferred previously, and (2) a significant deviation in the average orientation of the scatter-broadened images (by ~10°) from that implied by the magnetic field in the Galactic plane. More intriguingly, for a few Zeeman pairs in our set, significant differences (up to 6?) are apparent in the scatter-broadened images for the two hands of circular polarization, even when the apparent velocity separation is less than 0.1 km s-1. This may possibly be the first example of a Faraday rotation contribution to the diffractive effects in the ISM. Using the Zeeman pairs, we also study the distribution of the magnetic field in the W49N complex, finding no significant trend in the spatial structure function. In this paper, we present the details of our observations and analysis leading to these findings, discuss implications of our results for the intervening anisotropic magneto-ionic medium, and suggest possible implications for the structure of magnetic fields within this star-forming region.

Deshpande, Avinash A.; Goss, W. M.; Mendoza-Torres, J. E.

2013-09-01

81

Exploring Magnetic Field Lines  

NSDL National Science Digital Library

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

Nasa

2012-06-26

82

Probing fine magnetic particles with neutron scattering.  

National Technical Information Service (NTIS)

Because thermal neutrons are scattered both by nuclei and by unpaired electrons, they provide an ideal probe for studying the atomic and magnetic structures of fine-grained magnetic materials, including nanocrystalline solids, thin epitaxial layers, and c...

R. Pynn

1991-01-01

83

Probes for investigating the effect of magnetic field, field orientation, temperature and strain on the critical current density of anisotropic high-temperature superconducting tapes in a split-pair 15 T horizontal magnet.  

PubMed

We present the designs of probes for making critical current density (Jc) measurements on anisotropic high-temperature superconducting tapes as a function of field, field orientation, temperature and strain in our 40 mm bore, split-pair 15 T horizontal magnet. Emphasis is placed on the design of three components: the vapour-cooled current leads, the variable temperature enclosure, and the springboard-shaped bending beam sample holder. The vapour-cooled brass critical-current leads used superconducting tapes and in operation ran hot with a duty cycle (D) of ?0.2. This work provides formulae for optimising cryogenic consumption and calculating cryogenic boil-off, associated with current leads used to make Jc measurements, made by uniformly ramping the current up to a maximum current (Imax) and then reducing the current very quickly to zero. They include consideration of the effects of duty cycle, static helium boil-off from the magnet and Dewar (b(')), and the maximum safe temperature for the critical-current leads (Tmax). Our optimized critical-current leads have a boil-off that is about 30% less than leads optimized for magnet operation at the same maximum current. Numerical calculations show that the optimum cross-sectional area (A) for each current lead can be parameterized by [Formula: see text] where L is the current lead's length and the current lead is operated in liquid helium. An optimum A of 132 mm(2) is obtained when Imax = 1000 A, Tmax = 400 K, D = 0.2, b(') = 0.3 l?h(-1) and L = 1.0 m. The optimized helium consumption was found to be 0.7 l?h(-1). When the static boil-off is small, optimized leads have a boil-off that can be roughly parameterized by: b/Imax? ? (1.35 × 10(-3))D(0.41) l?h(?1)?A(-1). A split-current-lead design is employed to minimize the rotation of the probes during the high current measurements in our high-field horizontal magnet. The variable-temperature system is based on the use of an inverted insulating cup that operates above 4.2 K in liquid helium and above 77.4 K in liquid nitrogen, with a stability of ±80 mK to ±150 mK. Uniaxial strains of -1.4% to 1.0% can be applied to the sample, with a total uncertainty of better than ±0.02%, using a modified bending beam apparatus which includes a copper beryllium springboard-shaped sample holder. PMID:24985856

Sunwong, P; Higgins, J S; Hampshire, D P

2014-06-01

84

Earth's Inconstant Magnetic Field  

NSDL National Science Digital Library

This NASA site describes long-term changes in Earth's magnetic field, and how magnetic stripes in the Atlantic seafloor provide evidence for reversals of this field. The site presents a model of Earth's interior that helps explain how Earth's magnetic field is generated and how the reversals occur. A computer-generated image shows the complicated magnetic field in-between reversals.

2007-04-27

85

Electric field probes for cellular phone dosimetry  

Microsoft Academic Search

Miniature implantable electric field probes (E-field Probes) enable the measurements of microwave electric fields induced in biological subjects by relatively low level exposures. Using these instruments, the rate of energy deposition (Specific Absorption Rate or SAR) can be determined throughout models or actual bodies of laboratory animals and humans exposed to emissions from cellular phones and other radiators. E-field probes

Howard I. Bassen

1997-01-01

86

Exploring Magnetic Fields  

NSDL National Science Digital Library

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

87

The Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on the Radiation Belt Storm Probes; Operational Modes and Data Products  

NASA Astrophysics Data System (ADS)

The Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) investigation on board the Radiation Belt Storm Probes (RBSP), is an integrated set of instruments consisting of a tri-axial fluxgate magnetometer (MAG) and a Waves instrument which includes a tri-axial search coil magnetometer (MSC). These wave measurements include AC electric and magnetic fields from 10Hz to 400 kHz. AC Electric field signals are provided, on board, by the Electric Field and Waves Suite (EFW). All the instrument components are controlled by a Central Data Processing Unit (CDPU), which provides versatility in capturing data in a variety of modes. The system is designed to provide a standard cadence of survey products through the entire orbit, and burst data capture of higher cadenced data at opportune times in the orbit. A description and examples of all the operational modes are presented. Descriptions of the data products and how to access them is also presented. Data from the suite is located at a central Science Operation Center (SOC) maintained at the University of Iowa. EMFISIS data are organized to be easily viewed utilizing the freeware data visualization tool, Autoplot.

Bounds, S. R.; Kletzing, C.; Crawford, D.; Kurth, W. S.; Hospodarsky, G. B.; MacDowall, R. J.; Connerney, J. E.; Torbert, R. B.; Needell, J.; Smith, C. W.; Wygant, J. R.; Bonnell, J. W.

2012-12-01

88

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.

89

Magnetic Fields Matter  

NSDL National Science Digital Library

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

VU Bioengineering RET Program, School of Engineering,

90

Broad-band magnetic induction probe calibration using a frequency-corrected reference probe  

NASA Astrophysics Data System (ADS)

Finite impedances of magnetic induction probes attenuate and shift the field fluctuations measured by the probe so that they differ from the measured signal at the digitizer. These effects vary with frequency. Traditionally, impedance effects have been accounted for in the calibration process by sweeping the frequency of the magnetic field source through a range of frequencies. Situations arise where the conventional calibration method is not feasible due to probe geometry or hardware constraints. A new calibration technique is presented in this paper which calibrates the probe in situ at a single frequency and uses impedance measurements of the probe assembly across the desired frequency range to account for broad-band effects. The in situ calibration technique requires a reference probe with a known proportionality constant NA and known impedances. Impedance effects are corrected in the probe signal using broad-band impedance measurements included in a transfer function in frequency space. The in situ calibration technique is shown to be complicated by capacitive coupling between the probes and the high voltage source coil. Circuit modeling demonstrates that this coupling introduces negligible attenuation and a small phase-delay so that the relative phase-delay between the reference and target probe signals can be corrected by shifting the signals in time. In summary, this calibration method extends traditional single-frequency calibration techniques to broad-band applications, accounting for important non-ideal effects to improve the accuracy of the magnetic field measurement.

Hill, Carrie

2013-10-01

91

Contributions of the electronic spin and orbital current to the CoCl{sub 4}{sup 2-} magnetic field probed in polarised neutron diffraction experiments  

SciTech Connect

Polarised neutron diffraction experiments conducted at 4.2 K on Cs{sub 3}CoCl{sub 5} crystals have been analysed by using a four-dimensional model Hilbert space made of ab initio n-electron wave functions of the CoCl{sub 4}{sup 2-} molecular ion. Two spin-orbit mixing coefficients and several configuration interaction coefficients have been optimized by fitting calculated magnetic structure factors to experimental ones, to obtain the best ensemble density operator that is representable in the model space. A goodness of fit, {chi}{sup 2}, less then 1 has been obtained for the first time for the two experimental data sets available. In the present article, the optimized density operators are used to calculate the magnetic field densities that are the genuine observables probed in neutron diffraction experiments. Density maps of such observables are presented for the first time and numerical details are provided. The respective contributions of spin density and orbital current to the magnetic field density are analyzed.

Cassam-Chenaie, Patrick [Laboratoire J. A. Dieudonne, UMR 6621 du CNRS, Faculte des Sciences, Parc Valrose, 06108 Nice cedex 2 (France); Jayatilaka, Dylan [School of Chemistry and Biochemistry, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia)

2012-08-14

92

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,

93

Probing states with macroscopic circulations in magnetic photonic crystals  

Microsoft Academic Search

We predict that when light is reflected off a magnetic photonic crystal (MPC) there is a grazing component that is parallel to the surface; the magnitude of this component can be changed by an external field. The direction of this parallel component is reversed (dotted line) as the direction of the magnetization is reversed. This provides a way to probe

Siu Tat Chui; Zhifang Lin

2008-01-01

94

Using variable-frequency asymmetries to probe the magnetic field dependence of radial transport in a Malmberg-Penning trap  

SciTech Connect

A new experimental technique is used to study the dependence of asymmetry-induced radial particle flux {gamma} on axial magnetic field B in a modified Malmberg-Penning trap. This dependence is complicated by the fact that B enters the physics in at least two places: in the asymmetry-induced first order radial drift velocity v{sub r} = E{sub {theta}}/B and in the zeroth order azimuthal drift velocity v{sub {theta}} = E{sub r}/B. To separate these, we employ the hypothesis that the latter always enters the physics in the combination {omega}-l{omega}{sub R}, where {omega}{sub R} = v{sub {theta}}/r is the column rotation frequency and {omega} and l are the asymmetry frequency and azimuthal mode number, respectively. Points where {omega}-l{omega}{sub R} = 0 are then selected from a {gamma} vs r vs {omega} data set, thus insuring that any function of this combination is constant. When the selected flux {gamma}{sub sel} is plotted versus the density gradient, a roughly linear dependence is observed, showing that this selected flux is diffusive. This linear dependence is roughly independent of the bias of the center wire in our trap {phi}{sub cw}. Since in our experiment {omega}{sub R} is proportional to {phi}{sub cw}, this latter point shows that our technique has successfully removed any dependence on {omega}{sub R} and its derivatives, thus confirming our hypothesis. The slope of a least-squares fitted line through the {gamma}{sub sel} vs density gradient data then gives the diffusion coefficient D{sub 0} under the condition {omega}-l{omega}{sub R} = 0. Varying the magnetic field, we find D{sub 0} is proportional to B{sup -1.33{+-}}{sup 0.05}, a scaling that does not match any theory we know. These findings are then used to constrain the form of the empirical flux equation. It may be possible to extend this technique to give the functional dependence of the flux on {omega}-l{omega}{sub R}.

Eggleston, D. L. [Occidental College, Los Angeles, California (United States)

2009-03-30

95

DC-based magnetic field controller  

DOEpatents

A magnetic field controller for laboratory devices and in particular to dc operated magnetic field controllers for mass spectrometers, comprising a dc power supply in combination with improvements to a hall probe subsystem, display subsystem, preamplifier, field control subsystem, and an output stage.

Kotter, Dale K. (Shelley, ID); Rankin, Richard A. (Ammon, ID); Morgan, John P,. (Idaho Falls, ID)

1994-01-01

96

Manipulating Cells with Static Magnetic Fields  

Microsoft Academic Search

We review our investigations of the use of static magnetic fields, B, for manipulating cells and cellular processes. We describe how B fields modify the cell division pattern of frog embryos and consequently can be used to probe the pattern determinants. We also observe that magnetic fields modify the swimming behavior of Paramecium Caudatum. We describe these modifications and their

J. M. Valles; K. Guevorkian

2005-01-01

97

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.

98

Magnetic field mapper  

NASA Technical Reports Server (NTRS)

Magnetic field mapper locates imperfections in cadmium sulphide solar cells by detecting and displaying the variations of the normal component of the magnetic field resulting from current density variations. It can also inspect for nonuniformities in other electrically conductive materials.

Masters, R. M.; Stenger, F. J.

1969-01-01

99

The Declining Magnetic Field  

NSDL National Science Digital Library

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

100

Magnetic field structure evolution in rotating magnetic field plasmas  

SciTech Connect

A study of magnetic field structure evolution during 40-ms plasma discharge has been performed in a new device with 80 cm long/40 cm diameter cylindrical chamber, in which a plasma current I{sub p}{approx_equal}2 kA was driven and sustained by a rotating magnetic field. The main focus of the experiments is on how the changes in externally applied magnetic field affect the current profile and magnetic field in plasma. During plasma discharge, a pulse current was briefly fed to a magnetic coil located at the midplane (middle coil). The magnetic field in cross section of plasma was scanned with pickup probes. Two regimes were studied: without and with an external toroidal field (TF) produced by axial I{sub z} current. With a relatively small current (I{sub m} {<=} 600 A) in the middle coil, the plasma current is boosted up to 5 kA. The magnetic flux surfaces become extended along the axial Z direction, sometimes with the formation of doublet shape plasma. The regime without TF appears to be less stable, presumably due to the reversal of plasma current in central area of plasma column.

Petrov, Yuri; Yang Xiaokang; Huang, T.-S. [Prairie View A and M University, Prairie View, Texas 77446 (United States)

2008-07-15

101

Probes for investigating the effect of magnetic field, field orientation, temperature and strain on the critical current density of anisotropic high-temperature superconducting tapes in a split-pair 15 T horizontal magnet  

NASA Astrophysics Data System (ADS)

We present the designs of probes for making critical current density (Jc) measurements on anisotropic high-temperature superconducting tapes as a function of field, field orientation, temperature and strain in our 40 mm bore, split-pair 15 T horizontal magnet. Emphasis is placed on the design of three components: the vapour-cooled current leads, the variable temperature enclosure, and the springboard-shaped bending beam sample holder. The vapour-cooled brass critical-current leads used superconducting tapes and in operation ran hot with a duty cycle (D) of ˜0.2. This work provides formulae for optimising cryogenic consumption and calculating cryogenic boil-off, associated with current leads used to make Jc measurements, made by uniformly ramping the current up to a maximum current (Imax) and then reducing the current very quickly to zero. They include consideration of the effects of duty cycle, static helium boil-off from the magnet and Dewar (b'), and the maximum safe temperature for the critical-current leads (Tmax). Our optimized critical-current leads have a boil-off that is about 30% less than leads optimized for magnet operation at the same maximum current. Numerical calculations show that the optimum cross-sectional area (A) for each current lead can be parameterized by LI_{max} /A = [1.46D^{ - 0.18} L^{0.4} (T_{max } - 300)^{0.25D^{ - 0.09} } + 750(b^' /I_{max })D^{10^{ - 3} I_{max } - 2.87b^' }] × 10^6 A m^{ - 1} where L is the current lead's length and the current lead is operated in liquid helium. An optimum A of 132 mm2 is obtained when Imax = 1000 A, Tmax = 400 K, D = 0.2, b' = 0.3 l h-1 and L = 1.0 m. The optimized helium consumption was found to be 0.7 l h-1. When the static boil-off is small, optimized leads have a boil-off that can be roughly parameterized by: b/Imax ? (1.35 × 10-3)D0.41 l h-1 A-1. A split-current-lead design is employed to minimize the rotation of the probes during the high current measurements in our high-field horizontal magnet. The variable-temperature system is based on the use of an inverted insulating cup that operates above 4.2 K in liquid helium and above 77.4 K in liquid nitrogen, with a stability of ±80 mK to ±150 mK. Uniaxial strains of -1.4% to 1.0% can be applied to the sample, with a total uncertainty of better than ±0.02%, using a modified bending beam apparatus which includes a copper beryllium springboard-shaped sample holder.

Sunwong, P.; Higgins, J. S.; Hampshire, D. P.

2014-06-01

102

Probing the magnetic topologies of magnetic clouds by means of solar energetic particles  

NASA Technical Reports Server (NTRS)

Solar energetic particles (SEPs) have been used as probes of magnetic cloud topologies. The rapid access of SEPs to the interiors of many clouds indicates that the cloud field lines extend back to the sun and hence are not plasmoids. The small modulation of galactic cosmic rays associated with clouds also suggests that the magnetic fields of clouds are not closed.

Kahler, S. W.; Reames, D. V.

1991-01-01

103

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

Microsoft Academic Search

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

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

2009-01-01

104

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.

Vu Bioengineering Ret Program

105

The Magnetic Field  

NSDL National Science Digital Library

This demonstration of the magnetic field lines of Earth uses a bar magnet, iron filings, and a compass. The site explains how to measure the magnetic field of the Earth by measuring the direction a compass points from various points on the surface. There is also an explanation of why the north magnetic pole on Earth is actually, by definition, the south pole of a magnet.

Barker, Jeffrey

106

Circuits and Magnetic Fields  

NSDL National Science Digital Library

In this activity, students use the same method as in the activity from lesson 2 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

107

Second solar spectrum observed at the Pic-du-Midi: depth probing of the turbulent magnetic field intensity in a quiet region.  

NASA Astrophysics Data System (ADS)

The installation of a new polarimeter at the Turret Dome of the Pic-du-Midi has permitted new observations of the "second solar spectrum" (which is the spectrum of the linear polarization observed near the solar limb), having a spatial resolution. On 2003 October 25, we have observed a quiet region located at the East limb equator, in the resonance line of neutral strontium at 4607 Å. The slit was positioned perpendicular to the limb: recording various limb distances provides a depth probing of the solar atmosphere. The intensity of the turbulent magnetic field has been derived from the Hanle effect interpretation, which is actually the only method for vectorial weak field determination. The theoretical profiles to be compared to the observed ones have been obtained by applying the atomic density matrix formalism (Landi Degl'Innocenti E., Bommier V., & Sahal-Bréchot S., 1990). The various collisional coefficients have been computed by applying semi-classical methods that are accurate to 20% or better: the one from Seaton (1962) and Sahal-Bréchot (1969a, 1969b) for the collisions with electrons, responsible for the inelastic transitions, and the one developed by Anstee & O'Mara (1991, 1995) for line broadening computations, generalized to the collisional depolarization by Derouich et al. (2003; see also Derouich, 2004), for the elastic collisions with neutral hydrogen atoms. The results have been found in full agreement with those previously obtained with THEMIS without any spatial resolution (at 9 limb distances). With the spatial resolution that we have now at the Pic-du-Midi (1 arcsec, 138 limb distances), it appears that the turbulent magnetic field intensity does not vary with depth, in the line formation region that ranges from ~200 to ~300 km above the tau5000=1 level.

Derouich, M.; Malherbe, J. M.; Bommier, V.; Landi Degl'Innocenti, E.; Sahal-Bréchot, S.

2004-12-01

108

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.

109

Langmuir probe measurements in expanding magnetized argon, nitrogen and hydrogen plasmas  

Microsoft Academic Search

Langmuir probe measurements are performed in magnetized expanding plasmas of different eompositions. The influence of the magnetic field on the currents collected by the probe in an argon plasma is investigated at two different flows and for two different probe sizes. The experimental results are compared to existing theories. The theoretically predicted dependence of the ratio of electron to ion

G. J. H. Brussaard; M. van der Steen; M. Carrère; D. C. Schram

1998-01-01

110

Photospheric magnetic fields  

NASA Technical Reports Server (NTRS)

Knowledge on the nature of magnetic fields on the solar surface is reviewed. At least a large part of the magnetic flux in the solar surface is confined to small bundles of lines of force within which the field strength is of the order of 500 gauss. Magnetic fields are closely associated with all types of solar activity. Magnetic flux appears at the surface at the clearly defined birth or regeneration of activity of an active region. As the region ages, the magnetic flux migrates to form large-scale patterns and the polar fields. Some manifestations of the large-scale distribution are discussed.

Howard, R.

1972-01-01

111

Manipulation of molecular structures with magnetic fields  

Microsoft Academic Search

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

Marius Iosif Boamfa

2003-01-01

112

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.

113

Quantitative magnetic force microscopy on permalloy dots using an iron filled carbon nanotube probe.  

PubMed

An iron filled carbon nanotube (FeCNT), a 10-40 nm ferromagnetic nanowire enclosed in a protective carbon tube, is an attractive candidate for a magnetic force microscopy (MFM) probe as it provides a mechanically and chemically robust, nanoscale probe. We demonstrate the probe's capabilities with images of the magnetic field gradients close to the surface of a Py dot in both the multi-domain and vortex states. We show the FeCNT probe is accurately described by a single magnetic monopole located at its tip. Its effective magnetic charge is determined by the diameter of the iron wire and its saturation magnetization 4?M(s) ? 2.2 × 10(4)G. A magnetic monopole probe is advantageous as it enables quantitative measurements of the magnetic field gradient close to the sample surface. The lateral resolution is defined by the diameter of the iron wire and the probe-sample separation. PMID:21864777

Wolny, F; Obukhov, Y; Mühl, T; Weissker, U; Philippi, S; Leonhardt, A; Banerjee, P; Reed, A; Xiang, G; Adur, R; Lee, I; Hauser, A J; Yang, F Y; Pelekhov, D V; Büchner, B; Hammel, P C

2011-07-01

114

Melatonin and magnetic fields.  

PubMed

There is public health concern raised by epidemiological studies indicating that extremely low frequency electric and magnetic fields generated by electric power distribution systems in the environment may be hazardous. Possible carcinogenic effects of magnetic field in combination with suggested oncostatic action of melatonin lead to the hypothesis that the primary effects of electric and magnetic fields exposure is a reduction of melatonin synthesis which, in turn, may promote cancer growth. In this review the data on the influence of magnetic fields on melatonin synthesis, both in the animals and humans, are briefly presented and discussed. PMID:12019358

Karasek, Michal; Lerchl, Alexander

2002-04-01

115

Morphology and orientational behavior of silica-coated spindle-type hematite particles in a magnetic field probed by small-angle X-ray scattering.  

PubMed

Form factor and magnetic properties of silica-coated spindle-type hematite nanoparticles are determined from SAXS measurements with applied magnetic field and magnetometry measurements. The particle size, polydispersity and porosity are determined using a core-shell model for the form factor. The particles are found to align with their long axis perpendicular to the applied field. The orientational order is determined from the SAXS data and compared to the orientational order obtained from magnetometry. The direct access to both, the orientational order of the particles, and the magnetic moments allow one to determine the magnetic properties of the individual spindle-type hematite particles. We study the influence of the silica coating on the magnetic properties and find a fundamentally different behavior of silica-coated particles. The silica coating reduces the effective magnetic moment of the particles. This effect is enhanced with field strength and can be explained by superparamagnetic relaxation in the highly porous particles. PMID:20329762

Reufer, Mathias; Dietsch, Hervé; Gasser, Urs; Hirt, Ann; Menzel, Andreas; Schurtenberger, Peter

2010-04-15

116

Magnetic Field Viewing Cards  

NASA Astrophysics Data System (ADS)

For some years now laminated cards containing a green, magnetically sensitive film have been available from science education suppliers. When held near a magnet, these cards appear dark green in regions where the field is perpendicular to the card and light green where the field is parallel to the card. The cards can be used to explore the magnetic field near a variety of magnets as well as near wire loops. In this paper we describe how to make these cards and how we have used them in our physics classrooms and labs.

Kanim, Stephen; Thompson, John R.

2005-09-01

117

The galactic magnetic field  

Microsoft Academic Search

Estimates for the scale, geometry and strength of the magnetic field in the galactic system can be derived from observations of polarization properties of radio emission from the Galaxy, extragalactic radio sources and pulsars, and polarization of starlight. Within distances of about 500 parsecs (1 parsec = 3.26 lightyears) from the solar system the magnetic field is directed towards galactic

T A Spoelstra; T. A. T

1977-01-01

118

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

119

The FIELDS experiment for Solar Probe Plus  

NASA Astrophysics Data System (ADS)

Many of our basic ideas on the plasma physics of acceleration, energy flow, and dissipation, and structure of the solar wind have never been rigorously confronted by direct experimental measurements in the region where these processes are actually occurring. Although Alfven waves, shocks, and magnetic reconnection are often invoked as heating mechanisms, there have never been any direct measurements of Alfvenic waves nor the associated Poynting flux nor any measurements of ion or electron kinetic energy flux in the region from 10 R_s to 30 R_s where the final stages of wind acceleration are believed to occur. The radial profiles of both slow and fast solar wind acceleration are based on remote-sensing measurements and have been obtained for only a few selected events. Thus, the spatial radial and perpendicular scales of the acceleration process have been averaged by line-of-sight effects and the possibility of intense localized acceleration cannot be ruled out. The Solar Probe Plus (SPP) mission calls for the high quality fields and particles measurements required to solve the coronal heating and wind acceleration problem. The SPP 'FIELDS' experiment measures the electric and magnetic fields fundamental to the plasma physics of the structured and turbulent solar wind, flux ropes, collisionless shocks, and magnetic reconnection. FIELDS will make the first-ever measurements of the DC/Low-Frequency electric field inside of 1 AU allowing for in situ, high cadence measurements of the Poynting vector, the Elsasser variables, and E/B diagnostics of the wave spectrum to fce in the solar wind. SPP/FIELDS measures the radio wave (type III and II) signatures of microflares, energized electrons, and CME propagation. SPP/ FIELDS measures the plasma electron density to ~2% accuracy and the core electron temperature to ~5-10% accuracy more than 90% of the time at perihelion. FIELDS will also measure the in situ density fluctuation spectrum and structures at a very high cadence (? 10 kHz) and provide definitive signatures of the turbulent nature and heating of the solar wind plasma. Furthermore, SPP/FIELDS measures the impact rate and sig- natures of dust from micron- to nano-scales, by measuring the voltage signature of dust impacts on the spacecraft. FIELDS will also measure the floating potential of the SPP spacecraft, which is essential for correcting in situ electron data. The SPP/FIELDS experiment combines four (4) deployable electric antennas, fluxgate and search coil magnetometers and the associated signal processing electronics into a scientifically and technically integrated package. SPP/FIELDS makes very high cadence measurements of fields and density and employs an internal burst memory for intelligent data selection. FIELDS is required to measure very large plasma potentials and electric fields (~10V) and uses floating ground (+/- 100V) power preamplifiers. The SPP/FIELDS team has performed 3D plasma simulations of the SPP spacecraft plasma environ- ment, which reveal enormous voltage fluctuation levels in the plasma wake behind the spacecraft. This voltage noise dominates the true signal by orders of magnitude in the critical DC/LF frequency range. Therefore, we are proposing a design which places the four (4) electric antennas in front of the spacecraft ahead of the heat shield.

Bale, S.; Spp/Fields Team

2010-12-01

120

Magnetic imaging with scanning probe microscopy  

NASA Astrophysics Data System (ADS)

We review our research on the application of scanning tunnelling microscopy (STM) and non-contact atomic force microscopy (NC-AFM) for magnetic imaging in high spatial resolution even down to the atomic scale. In the first part, we propose a new experimental scheme of spin-polarized STM (SP-STM) with a GaAs spin probe to obtain a large contribution of spin-polarized electrons in the tunnelling current. This is yielded by injecting the spin-polarized photo-excited electrons in an optically pumped GaAs tip into the spin-polarized empty states near the Fermi level of a bcc-Fe(001) surface. According to the bandgap energy of GaAs and the surface state of the sample observed at 0.4 eV above the Fermi level, the spin-dependant electron injection can be achieved by applying a sample bias voltage of -1 V. The tunnel current in the positive bias region depends on the helicity of the circular polarized pumping light, and is modified when the applied magnetic field is reversed. Mapping the current asymmetry provides a spin-dependent SP-STM image. In the second part, we describe the progress towards spin imaging with NC-AFM. The spin imaging can be achieved by detecting short-range magnetic interaction such as exchange interaction between a ferromagnetic tip and a magnetic sample. We demonstrate the capabilities of NC-AFM by imaging the spin structure of an antiferromagnetic NiO(001) surface on the atomic scale. The cross-sectional line profiles of the atomically resolved images obtained using several ferromagnetic tips (Fe, Ni) were analysed by adding the atomic corrugation amplitude on the basis of the periodicity of the image. The results of the analysis show that the difference of the neighbouring maxima depends on the crystal direction. On the other hand, no significant indication of the directional dependency can be seen on the images obtained by using a non-magnetic Si tip. The directional dependency coincides with the antiferromagnetic spin alignment of the NiO(001) surface.

Sueoka, Kazuhisa; Subagyo, Agus; Hosoi, Hirotaka; Mukasa, Koichi

2004-10-01

121

Magnetic fields at Neptune  

SciTech Connect

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{sup {minus}5} gauss) was observed near closest approach, at a distance of 1.18 R{sub N}. The planetary magnetic field between 4 and 15 R{sub N} can be well represented by an offset tilted magnetic dipole (OTD), displaced from the center of Neptune by the surprisingly large amount of 0.55 R{sub N} and inclined by 47{degrees} with respect to the rotation axis. Within 4 R{sub N}, the magnetic field representation must include localized sources or higher order magnetic multipoles, or both, which are not yet well determined. As the spacecraft exited the magnetosphere, the magnetic tail appeared to be monopolar, and no crossings of an imbedded magnetic field reversal or plasma neutral sheet were observed. The auroral zones are most likely located far from the rotation poles and may have a complicated geometry. The rings and all the known moons of Neptune are imbedded deep inside the magnetosphere, except for Nereid, which is outside when sunward of the planet. The radiation belts will have a complex structure owing to the absorption of energetic particles by the moons and rings of Neptune and losses associated with the significant changes in the diurnally varying magnetosphere configuration. In an astrophysical context, the magnetic field of Neptune, like that of Uranus, may be described as that of an oblique rotator.

Ness, N.F. (Univ. of Delaware, Newark (USA)); Acuna, M.H.; Burlaga, L.F.; Connerney, J.E.P.; Lepping, R.P. (NASA, Greenbelt, MD (USA)); Neubauer, F.M. (Universitaet zu Koln (West Germany))

1989-12-15

122

Sonoluminescence in High Magnetic Fields  

Microsoft Academic Search

We have made a detailed study of sonoluminescence (SL) in high magnetic fields. In magnetic field sweeps at constant levels of acoustic drive, SL disappears above a pressure-dependent threshold magnetic field. Sweeps of acoustic drive at fixed magnetic fields show that the upper and lower bounds of forcing pressure that determine the region of SL increase dramatically with magnetic field.

J. B. Young; T. Schmiedel; Woowon Kang

1996-01-01

123

Bending of magnetic filaments under a magnetic field  

NASA Astrophysics Data System (ADS)

Magnetic beads and superparamagnetic (SP) colloid particles have successfully been employed for micromechanical manipulation of soft material, in situ probing of elastic properties, and design of smart materials (ferrogels). Here we derive analytical expressions for the equilibrium shape of magnetic fibers, considering two end-member cases, (a) SP or single-domain particles concentrated at the free end of cantilevered rods or tubes, and (b) filaments consisting of SP particles, with this case being mathematically equivalent to tubes containing SP particles. Our analysis yields also metastable equilibrium states (MES’s), which only exist above a critical filament length, but become more stable with increasing magnetic field. The MES’s for case (a) are, like the ground state, circular arcs, but more strongly bent. The multiform MES’s in case (b), which comprise hairpin, sinuous, or even closed shapes, have recently been observed in experiments, too. We also study the effect of gravity on the balance between bending and magnetic energy, which leads to curves with inflection point if the influence of gravity is stronger than that of the magnetic field. Because of their simple experimental realization, case (a) magnetic filaments are deemed highly suitable for micromechanical experiments on long chains of polymer molecules. Another potential application of cantilevered magnetic filaments with magnetic material attached to the free end is in scanning probe microscopes. Because the magnetic field due to the magnetic tip is comparatively weak, the magnetization structure of the sample to be investigated would not be affected by the probe. Thus, for the examination of magnetically soft materials, probes in the form of magnetic filaments may hold advantages over tips usually employed in magnetic force microscopy.

Shcherbakov, Valera P.; Winklhofer, Michael

2004-12-01

124

Magnetic Bar Field Model  

NSDL National Science Digital Library

The EJS Magnetic Bar Field Model shows the field of a bar magnet and has a movable compass that reports the magnetic field values. The bar magnet model is built by placing a group of magnetic dipoles along the bar magnet. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. The Magnetic Bar Field model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_em_MagneticBarField.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Christian, Wolfgang; Franciscouembre; Cox, Anne

2009-09-18

125

Multifunctional Magnetic Nanoparticle Probes for Intracellular Molecular Imaging and Monitoring.  

National Technical Information Service (NTIS)

The present invention provides multifunctional magnetic nanoparticle probe compositions for molecular imaging and monitoring, comprising a nucleic acid or polypeptide probe, a delivery ligand, and a magnetic nanoparticle having a biocompatible coating the...

G. Bao L. LaConte N. Nitin S. Nie

2003-01-01

126

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.

127

Magnetic Field Lines  

NSDL National Science Digital Library

This activity will introduce students to the idea of magnetic field lines--a concept they have probably encountered but may not fully grasp. Completing this activity and reading the corresponding background information should enable students to understand

Horton, Michael

2009-05-30

128

Solar Magnetic Fields.  

National Technical Information Service (NTIS)

The research work was directed towards the following: (1) Perform necessary laboratory experiments, including a study on the Zeeman effect in absorption. Make observations of the sunspot and general magnetic fields of the sun. (2) Conduct a program of int...

M. Cimino

1966-01-01

129

Coronal magnetic fields  

Microsoft Academic Search

The use of coronal X-ray emission in determining the configuration of the magnetic field lines in the corona is discussed. Spatially-resolved X-ray observations provided by Skylab and subsequently by missions such as OSO-8 and SMM show the solar corona to be inhomogeneous, with open and closed structures determined by the topology of the magnetic field. The scenario provided by observations

R. Pallavicini

1986-01-01

130

Characteristics of magnetic force microscopy magnetics on high moment perpendicular magnetic recording writers with high coercivity probes  

NASA Astrophysics Data System (ADS)

High resolution magnetic force microscopy (MFM) imaging with high coercivity probes on perpendicular magnetic recording (PMR) writers directly characterizes magnetic field contour for the writer main pole as well as its shields' magnetic state. Evolution of write bubble and return field was analyzed by MFM imaging in dynamic phase detection scheme. Different write field components and their out of plane second order derivatives were calculated via finite element modeling. The MFM imaged write field distribution correlates well with the PMR writer out of plane write field component. Magnetic responses of the PMR writer main pole, trailing and side shields are quantified. The trailing and side shields exhibit complicated magnetic saturation behaviors comparing with the PMR writer pole. The side shield's magnetic response is dependent upon its initial equilibrium state.

Liu, Feng; Li, Shaoping; Bai, Daniel; Wang, James; Li, Zhanjie; Han, Dehua; Pan, Tao; Mao, Sining

2012-04-01

131

Measuring magnetic dipole fields using Hall effects sensors  

Microsoft Academic Search

The way in which a Hall effect transducer is made appropriate for measuring magnetic fields is described. The aim of this is to provide a thermally well compensated probe that gives precise orientation and positioning for taking measurements. This probe is used in the checking of far fields generated by magnetic dipoles.

L. Benadero; J. A. Gorri; J. Villar; A. Albareda; E. Toribio; R. Perez

1991-01-01

132

Solar Wind Magnetic Fields  

NASA Technical Reports Server (NTRS)

The magnetic fields originate as coronal fields that are converted into space by the supersonic, infinitely conducting, solar wind. On average, the sun's rotation causes the field to wind up and form an Archimedes Spiral. However, the field direction changes almost continuously on a variety of scales and the irregular nature of these changes is often interpreted as evidence that the solar wind flow is turbulent.

Smith, E. J.

1995-01-01

133

Magnetically filtered Faraday probe for measuring the ion current density profile of a Hall thruster  

Microsoft Academic Search

The ability of a magnetically filtered Faraday probe (MFFP) to obtain the ion current density profile of a Hall thruster is investigated. The MFFP is designed to eliminate the collection of low-energy, charge-exchange (CEX) ions by using a variable magnetic field as an ion filter. In this study, a MFFP, Faraday probe with a reduced acceptance angle (BFP), and nude

Joshua L. Rovey; Mitchell L. R. Walker; Alec D. Gallimore; Peter Y. Peterson

2006-01-01

134

Measurement of the magnetic field of the CDF magnet  

SciTech Connect

The magnetic field of the CDF (Collider Detector at Fermilab) superconducting solenoid has been measured using a newly designed field mapping device. NMR probes and a system of three orthogonal search coils were used as sensing elements. The central uniform region inside the solenoid coil and the fringing field in the conical end plugs were measured. The detailed field distribution and its characteristics are described.

Yamada, R.; Newman-Holmes, C.; Schmidt, E.E.

1985-11-01

135

Magnetic probing of the spatial development of discharges in a pulsed coaxial lamp  

Microsoft Academic Search

Results are presented in [2, 3] for experimental investigations of the magnetic field created by the pulsed coaxial lamps with discharge times of about 120 #sec. The results using the magnetic probe were compared with the results of high-speed motion pictures. It was established that maximal values of mag-netic fields correspond to nonuniform filling of the lamp discharge cavity. In

V. A. Alekseev; V. V. Gusev; B. V. Kalachev; V. N. Makarov; A. I. Sopin

1976-01-01

136

The nonequilibrium of magnetic fields  

Microsoft Academic Search

The more subtle properties of magnetic fields which create nonequilibrium and lead to vigorous activity in otherwise sluggish gas-field systems are evaluated for gross hydromagnetic effects. The gentle manipulation of magnetic fields on a large scale leads to the production of small scale variations and discontinuities, providing intense dissipation of magnetic field in a large scale system. A magnetic field

E. N. Parker

1981-01-01

137

Probing Magnetic Nanostructures on the Atomic Scale  

NASA Astrophysics Data System (ADS)

Magnetic nanostructures are increasing data storage capacities and are promising candidates for implementations of novel spin-based computation techniques. The relative simplicity and reduced dimensionality of nanoscale magnetic structures also make them attractive model systems for studying fundamental interactions between quantum spins. We used a scanning tunneling microscope to build individual magnetic nanostructures one atom at a time. By measuring their spin-excitation spectra with inelastic electron tunneling spectroscopy, we determined the orientation and strength of the anisotropies of individual Fe and Mn atoms on copper nitride. First-principles calculations indicate that the magnetic atoms become incorporated into a polar covalent surface molecular network, making them similar to the building blocks of molecular magnets. In linear chains of up to 10 Mn atoms, we observed excitations of the coupled atomic spins that can change both the total spin and its orientation. The large magnetic anisotropy and strong spin-coupling manifested in these structures, which provide atom-by-atom accessibility via local probes, have the potential to produce atomic-scale magnetic structures that have a stable magnetization at low temperatures. * This work was done in collaboration with C.-Y. Lin, A.F. Otte, M. Ternes, C.P. Lutz, B.A. Jones, and A.J. Heinrich at the IBM Almaden Research Center, San Jose, CA 95120 USA.

Hirjibehedin, Cyrus F.

2008-03-01

138

Mapping the magnetic field vector in a fountain clock  

SciTech Connect

We show how the mapping of the magnetic field vector components can be achieved in a fountain clock by measuring the Larmor transition frequency in atoms that are used as a spatial probe. We control two vector components of the magnetic field and apply audio frequency magnetic pulses to localize and measure the field vector through Zeeman spectroscopy.

Gertsvolf, Marina; Marmet, Louis [National Research Council of Canada, Ottawa, Ontario K1A 0R6 (Canada)

2011-12-15

139

Microinhomogeneities in Magnetic Fields  

Microsoft Academic Search

Small variations in the fields of magnets, caused by structures or domains in the pole faces, were investigated by moving a small coil in a circular path. It was found that for a given pole face the variations in the field were all about the same size, and decreased exponentially from the pole face. None of the materials tested as

H. H. Brown Jr.; F. Bitter

1956-01-01

140

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

141

Probing the magnetization inside a superconducting Nb film by nuclear resonant scattering  

NASA Astrophysics Data System (ADS)

We present an approach to probe the magnetization inside superconducting films using ultrathin 57Fe probe layers excited by synchrotron radiation. We investigate the evolution of the 57Fe hyperfine field orientation as a function of magnetic field above and below the superconducting transition temperature Tc for a Nb(50 nm)/57Fe(0.6 nm)/Nb(50 nm) trilayer. It is found that significant screening of the external field in the superconductor occurs only at low field, leading to a change in the hyperfine field angle below Tc. The presented approach allows to study the influence of magnetic fields and vortex induced electron correlations in complex layered structures incorporating superconductors.

Couet, S.; Trekels, M.; Rüffer, R.; Cuppens, J.; Petermann, C.; Vantomme, A.; van Bael, M. J.; Temst, K.

2011-08-01

142

Magnetic ionization fronts. I. Parallel magnetic fields  

NASA Astrophysics Data System (ADS)

We solve the continuity equations across an ionization front. By including a plane parallel magnetic field we find significant differences in the allowed velocities of the R- and D-type solutions between the magnetized and non-magnetized cases. These results may have implications for the study of ionization bounded diffuse sources where a moderate or strong magnetic field is expected.

Redman, M. P.; Williams, R. J. R.; Dyson, J. E.; Hartquist, T. W.; Fernandez, B. R.

1998-03-01

143

Magnetic Probe to Study Plasma Jets for Magneto-Inertial Fusion  

SciTech Connect

A probe has been constructed to measure the magnetic field of a plasma jet generated by a pulsed plasma rail-gun. The probe consists of two sets of three orthogonally-oriented commercial chip inductors to measure the three-dimensional magnetic field vector at two separate positions in order to give information about the magnetic field evolution within the jet. The strength and evolution of the magnetic field is one of many factors important in evaluating the use of supersonic plasma jets for forming imploding spherical plasma liners as a standoff driver for magneto-inertial fusion.

Martens, Daniel [Los Alamos National Laboratory; Hsu, Scott C. [Los Alamos National Laboratory

2012-08-16

144

Magnetic and Langmuir Probe Measurements on the Plasmoid Thruster Experiment (PTX)  

NASA Technical Reports Server (NTRS)

The Plasmoid Thruster Experiment (PTX) operates by inductively producing plasmoids in a conical theta-pinch coil and ejecting them at high velocity. A plasmoid is a plasma with an imbedded closed magnetic field structure. The shape and magnetic field structure of the translating plasmoids have been measured with of an array of magnetic field probes. Six sets of two B-dot probes were constructed for measuring B(sub z) and B(sub theta), the axial and azimuthal components of the magnetic field. The probes are wound on a square G10 form, and have an average (calibrated) NA of 9.37 x l0(exp -5) square meters, where N is the number of turns and A is the cross-sectional area. The probes were calibrated with a Helmholtz coil, driven by a high-voltage pulser to measure NA, and by a signal generator to determine the probe's frequency response. The plasmoid electron number density n(sub e) electron temperature T(sub e), and velocity ratio v/c(sub m), (where v is the bulk plasma flow velocity and c(sub m), is the ion thermal speed) have also been measured with a quadruple Langmuir probe. The Langmuir probe tips are 10 mm long, 20-mil diameter stainless steel wire, housed in a 6-inch long 4-bore aluminum rod. Measurements on PTX with argon and hydrogen from the magnetic field probes and quadruple Langmuir probe will be presented in this paper.

Koelfgen, Syri J.; Eskridge, Richard; Lee, Michael H.; Martin, Adam; Hawk, Clark W.; Fimognan, Peter

2004-01-01

145

Probes for High Field Solid-state NMR of Lossy Biological Samples  

PubMed Central

In solid-state NMR exphydrated samples biopolymers are susceptible to radio-frequency heating and have a significant impact on probe tuning frequency and performance parameters such as sensitivity. These considerations are increasingly important as magnetic field strengths increase with improved magnet technology. Recent developments in the design, construction, and performance of probes for solid-state NMR experiments on stationary lossy biological samples at high magnetic fields are reviewed.

Grant, Christopher V.; Wu, Chin H.; Opella, Stanley J.

2010-01-01

146

Eruptive solar magnetic fields  

NASA Technical Reports Server (NTRS)

The quasi-steady evolution of solar magnetic fields in response to gradual photospheric changes is considered, with particular attention given to the threshold of a sudden eruption in the solar atmosphere. The formal model of an evolving, force-free field dependent on two Cartesian coordinates is extended to a field which is not force free but in static equilibrium with plasma pressure and gravity. The basic physics is illustrated through the evolution of a loop-shaped electric current sheet enclosing a potential bipolar field with footpoints rooted in the photosphere. A free-boundary problem is posed and then solved for the equilibrium configuration of the current sheet in a hydrostatically supported isothermal atmosphere. As the footpoints move apart to spread a constant photospheric magnetic flux over a larger region, the equilibria available extend the field to increasing heights.

Low, B. C.

1981-01-01

147

The Sun and Magnetic Fields  

NSDL National Science Digital Library

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

148

HMI Magnetic Field Products  

NASA Astrophysics Data System (ADS)

The Helioseismic and Magnetic Imager (HMI) on SDO has measured magnetic field, velocity, and intensity in the photosphere over the full disk continuously since May 2010 with arc-second resolution. Scalar images are measured every 45 seconds. From these basic observables the pipeline automatically identifies and tracks active regions on the solar disk. The vector magnetic field and a variety of summary quantities are determined every 720s in these tracked Space-weather HMI Active Region Patches (SHARPS). Synoptic and synchronic maps are constructed daily and after each Carrington Rotation Most data products are available with definitive scientific calibration after a few day deal at and in a quick-look near-real-time version a few minutes after the observations are made. Uncertainties are determined for the derived products. All of the magnetic field products along with movies and images suitable for browsing are available at http:://Hmi.stanford.edu/magnetic. Other products, e.g. coronal field over active regions, can be computed on demand.

Hoeksema, Jon T.; HMI Magnetic Field Team

2013-07-01

149

Magnetic Field and Life  

NSDL National Science Digital Library

This is a lesson where learners explore magnetic forces, fields, and the relationship between electricity. Learners will use this information to infer how the Earth generates a protective magnetic field. The lesson models scientific inquiry using the 5E instructional model and includes teacher notes, prerequisite concepts, common misconceptions, student journal and reading. This is lesson seven in the Astro-Venture Geology Training Unit that were developed to increase students' awareness of and interest in astrobiology and the many career opportunities that utilize science, math and technology skills. The lessons are designed for educators to use with with the Astro-Venture multimedia modules.

150

Electromagnetic near field measurements by using magnet garnet crystal  

NASA Astrophysics Data System (ADS)

An optical scanning electromagnetic field probe system consisting of an optic crystal substrate and a galvano scanner has been developed for high speed, low-invasive measurement of electromagnetic near field distribution. We measured magnetic field distributions above a microstrip line using several magnetic garnet crystal substrates and the probe system. We observed that the frequency response in the gigahertz range improved when we applied a magnetic bias to the crystal. In addition, a magnetic field component in a particular direction could be detected by controlling the direction of the magnetic bias.

Takahashi, M.; Kawasaki, K.; Ohba, H.; Ikenaga, T.; Ota, H.; Orikasa, T.; Adachi, N.; Ishiyama, K.; Arai, K. I.

2010-05-01

151

Liquid crystal fiber optic electric field probe  

NASA Astrophysics Data System (ADS)

Polymer dispersed liquid crystal inserted between two multimode optical fiber end faces forms the basis of an electric field probe. This probe has an active volume of about 0.001 mm3 and approximates a point measurement. The linear relation between detector output and electric field in the 600-800 V/cm range is adequate for most electric power distribution systems. As the contrast ratio of this transducer is large, it can be used as an on-off detector for high voltage equipment.

Lacquet, Beatrys M.; Swart, Pieter L.; Spammer, Stephanus J.

1995-09-01

152

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

153

The interplanetary magnetic field  

NASA Technical Reports Server (NTRS)

Large-scale properties of the interplanetary magnetic field as determined by the solar wind velocity structure are examined. The various ways in which magnetic fields affect phenomena in the solar wind are summarized. The dominant role of high and low velocity solar wind streams that persist, with fluctuations and evolution, for weeks or months is emphasized. It is suggested that for most purposes the sector structure is better identified with the stream structure than with the magnetic polarity and that the polarity does not necessarily change from one velocity sector to the next. Several mechanisms that might produce the stream structure are considered. The interaction of the high and low velocity streams is analyzed in a model that is steady state when viewed in a frame that corotates with the sun.

Davis, L., Jr.

1972-01-01

154

Probing and manipulating magnetization at the nanoscale  

NASA Astrophysics Data System (ADS)

Combining semiconductors with magnetism in hetero- and nano-structured geometries provides a powerful means of exploring the interplay between spin-dependent transport and nanoscale magnetism. We describe two recent studies in this context. First, we use spin-dependent transport in ferromagnetic semiconductor thin films to provide a new window into nanoscale magnetism [1]: here, we exploit the large anomalous Hall effect in a ferromagnetic semiconductor as a nanoscale probe of the reversible elastic behavior of magnetic domain walls and gain insight into regimes of domain wall behavior inaccessible to more conventional optical techniques. Next, we describe novel ways to create self-assembled hybrid semiconductor/ferromagnet core-shell nanowires [2] and show how magnetoresistance measurements in single nanowires, coupled with micromagnetic simulations, can provide detailed insights into the magnetization reversal process in nanoscale ferromagnets [3]. The work described here was carried out in collaboration with Andrew Balk, Jing Liang, Nicholas Dellas, Mark Nowakowski, David Rench, Mark Wilson, Roman Engel-Herbert, Suzanne Mohney, Peter Schiffer and David Awschalom. This work is supported by ONR, NSF and the NSF-MRSEC program.[4pt] [1] A. L. Balk et al., Phys. Rev.Lett. 107, 077205 (2011).[0pt] [2] N. J. Dellas et al., Appl. Phys. Lett. 97, 072505 (2010).[0pt] [3] J. Liang et al., in preparation.

Samarth, Nitin

2012-02-01

155

Associated electron and proton transfer between Acridine and Triethylamine in AOT reverse micelles probed by laser flash photolysis with magnetic field  

NASA Astrophysics Data System (ADS)

Laser flash photolysis with magnetic field (MF ˜0.08 T) has been used to study interaction between Acridine (Acr) and Triethylamine (TEA) in reverse micelles with w0 = 2.5-40. Dynamic protonation equilibrium exists between 3Acr and 3AcrH +. The intermediates indicate excited-state proton transfer (PT) between 3AcrH + and TEA. However, application of MF highlights the formation of geminate radical ion pairs (RIPs) with triplet spin-correlation, a signature of latent photoinduced electron transfer between 3AcrH + and TEA co-exists with PT. Magnetic field effect (MFE) is prominent for smaller w0 showing importance of optimum separation between RIP to maximize MFE, whereas PT remains unaltered.

Sarangi, Manas Kumar; Basu, Samita

2011-04-01

156

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

157

The Heliospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

The Heliospheric Magnetic Field (HMF) is the physical framework in which energetic particles and cosmic rays propagate. Changes in the large scale structure of the magnetic field lead to short- and long term changes in cosmic ray intensities, in particular in anti-phase with solar activity. The origin of the HMF in the corona is well understood and inner heliospheric observations can generally be linked to their coronal sources. The structure of heliospheric magnetic polarities and the heliospheric current sheet separating the dominant solar polarities are reviewed here over longer than a solar cycle, using the three dimensional heliospheric observations by Ulysses. The dynamics of the HMF around solar minimum activity is reviewed and the development of stream interaction regions following the stable flow patterns of fast and slow solar wind in the inner heliosphere is described. The complex dynamics that affects the evolution of the stream interaction regions leads to a more chaotic structure of the HMF in the outer heliosphere is described and discussed on the basis of the Voyager observations. Around solar maximum, solar activity is dominated by frequent transients, resulting in the interplanetary counterparts of Coronal Mass Ejections (ICMEs). These produce a complex aperiodic pattern of structures in the inner heliosphere, at all heliolatitudes. These structures continue to interact and evolve as they travel to the outer heliosphere. However, linking the observations in the inner and outer heliospheres is possible in the case of the largest solar transients that, despite their evolutions, remain recognizably large structures and lead to the formation of Merged Interaction Regions (MIRs) that may well form a quasi-spherical, "global" shell of enhanced magnetic fields around the Sun at large distances. For the transport of energetic particles and cosmic rays, the fluctuations in the magnetic field and their description in alternative turbulent models remains a very important research topic. These are also briefly reviewed in this paper.

Balogh, André; Erdõs, Géza

2013-06-01

158

Probing the magnetic states in a ferromagnet using a superconductor  

NASA Astrophysics Data System (ADS)

In a superconductor (S)/ferromagnet (F) bilayer, the superconducting properties of the S layer are sensitive to the domain pattern in the adjacent F layer.[1-2] We exploit this effect to investigate Ni films, which instead of retaining in-plane anisotropy as usual, unexpectedly acquire perpendicular anisotropy when the thickness is above a critical value. Using Ni/Nb bilayers, the perpendicular magnetization component can be sensitively probed by the measurements of the superconducting transition of Nb in a magnetic field, which alters the domain pattern in Ni. Above the critical Ni thickness, an in-plane magnetic field can manipulate the stripe domains in Ni between parallel stripes and random labyrinth states resulting in as much as 90 mK in the transition temperature of the Nb layer. This clearly demonstrates that superconductor is a sensitive probe of the magnetic domain state of a ferromagnet. In turn, the results also show that along the parallel stripe domains, superconductivity is less detrimental. [1]. A. Yu. Rusanov, M. Hesselberth, J. Aarts, and A. I. Buzdin, Phys. Rev. Lett. 93, 057002 (2004). [2]. L. Y. Zhu, T. Y. Chen, and C. L. Chien, Phys. Rev. Lett. 101, 017004 (2008).

Zhu, Leyi; Chen, Tingyong; Chien, Chia-Ling

2009-03-01

159

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

160

Magnetic Field of the Earth  

NSDL National Science Digital Library

Students can learn about how the magnetic field of the earth is similar to magnets. Go to the following link: Magnetic Field of the Earth 1. What makes the earth like a magnet? 2. How do we measure magnetism? Be sure to check out the fun games and activities on this web site too!! Now click on the following link and listen to a 2 minute presentation about magnetism: Pulse Planet Next go to ...

Merritt, Mrs.

2005-10-18

161

Scanning Hall probe microscopy of a diluted magnetic semiconductor  

SciTech Connect

We have measured the micromagnetic properties of a diluted magnetic semiconductor as a function of temperature and applied field with a scanning Hall probe microscope built in our laboratory. The design philosophy for this microscope and some details are described. The samples analyzed in this work are Ga{sub 0.94}Mn{sub 0.06}As films grown by molecular beam epitaxy. We find that the magnetic domains are 2-4 mum wide and fairly stable with temperature. Magnetic clusters are observed above T{sub C}, which we ascribe to MnAs defects too small and sparse to be detected by a superconducting quantum interference device magnetometer.

Kweon, Seongsoo [Materials Science and Engineering, University of Texas at Austin, Austin, Texas 78712 (United States); Samarth, Nitin [Physics Department, Penn State University, University Park, Pennsylvania 16802 (United States); Lozanne, Alex de [Materials Science and Engineering, University of Texas at Austin, Austin, Texas 78712 (United States); Department of Physics, University of Texas at Austin, Austin, Texas 78712 (United States)

2009-05-01

162

THE GALACTIC MAGNETIC FIELD  

SciTech Connect

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

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

2012-12-10

163

Magnetic Field Topology in Jets  

NASA Technical Reports Server (NTRS)

We present results on the magnetic field topology in a pulsed radiative. jet. For initially helical magnetic fields and periodic velocity variations, we find that the magnetic field alternates along the, length of the jet from toroidally dominated in the knots to possibly poloidally dominated in the intervening regions.

Gardiner, T. A.; Frank, A.

2000-01-01

164

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

165

Low field magnetic resonance imaging  

DOEpatents

A method and system of magnetic resonance imaging does not need a large homogenous field to truncate a gradient field. Spatial information is encoded into the spin magnetization by allowing the magnetization to evolve in a non-truncated gradient field and inducing a set of 180 degree rotations prior to signal acquisition.

Pines, Alexander (Berkeley, CA); Sakellariou, Dimitrios (Billancourt, FR); Meriles, Carlos A. (Fort Lee, NJ); Trabesinger, Andreas H. (London, GB)

2010-07-13

166

Suppression of probe background signals via B1 field inhomogeneity  

SciTech Connect

A new approach combining a long pulse with the DEPTH sequence (Cory and Ritchey, Journal of Magnetic Resonance, 1988) greatly improves the efficiency for suppressing probe background signals arising from spinning modules. By applying a long initial excitation pulse in the DEPTH sequence, instead of a {pi}/2 pulse, the inhomogeneous B{sub 1} fields outside the coil can dephase the background coherence in the nutation frame. The initial long pulse and the following two consecutive EXORCYCLE {pi} pulses function complementarily and prove most effective in removing background signals from both strong and weak B{sub 1} fields. Experimentally, the length of the long pulse can be optimized around odd multiples of the {pi}/2 pulse, depending on the individual probe design, to preserve signals inside the coil while minimizing those from probe hardware. This method extends the applicability of the DEPTH sequence to probes with small differences in B{sub 1} field strength between the inside and outside of the coil, and can readily combine with well-developed double resonance experiments for quantitative measurement. In general, spin systems with weak internal interactions are required to attain efficient and uniform excitation for powder samples, and the principles to determine the applicability are discussed qualitatively in terms of the relative strength of spin interactions, r.f. power and spinning rate.

Feng, Jian; Reimer, Jeffrey

2011-01-27

167

Electric and magnetic fields  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

168

Spin Polarized Electron Probes and Magnetic Nanostructures  

SciTech Connect

OAK B188 This report summarizes progress to date in our theoretical research program, for the period from July 1, 2002 to November 1, 2003. In addition, our research priorities for the coming year are set forth. The reporting period has been a most exciting and significant one. For the past several years, one of our principal thrust areas has been development of the theory of spin dynamics in magnetic nanostructures with emphasis on the use of spin polarized electrons as probes of short wavelength spin dynamics in such entities. Our program stimulated the first experiment which detected large wave vector spin waves in ultrathin films in 1999 through spin polarized electron loss spectroscopy (SPEELS); the publication which announced this discovery was a joint publication between a group in Halle (Germany) with our theory effort. The continued collaboration has led to the design and implementation of the new SPEELS spectrometer and we now have in hand the first detailed measurements of spin wave dispersion in an ultrathin film. A second such spectrometer is now operational in the laboratory of Prof. H. Hopster, at UC Irvine. We are thus entering a most exciting new era in the spectroscopy of spin excitations in magnetic nanostructures. During the reporting period, we have completed very important new analyses which predict key aspects of the spectra which will be uncovered by these new instruments, and the calculations continue to be developed and to expand our understanding. In addition, we have initiated a new series of theoretical studies directed toward spin dynamics of single magnetic adatoms on metal surfaces, with STM based studies of this area n mind. In the near future, these studies will continue, and we will expand our effort into new areas of spin dynamics in magnetic nanostructures.

D.L. Mills

2003-10-15

169

Interaction of an accelerated FRC in a transverse magnetic field  

NASA Astrophysics Data System (ADS)

The interaction and penetration of an accelerated FRC into a transverse magnetic field is studied for Tokamak refueling purposes. FRC penetration and interaction in the transverse magnetic field chamber is observed using visible light emission arrays, visible light imaging cameras, and several swept thermocouple probes. The FRC density and translation velocity are varied while monitoring the effect on penetration depth, deformation, tilt interaction and plasma deposition. The plasma penetration is observed using axial magnetic probes, while the plasma deformation is recorded with the visible light emission arrays and the swept thermocouple probes. 2 and 3-D magnetic field codes are used for field mapping for probe locations as well as translation and deformation simulations. Simple models are used to examine the effect that plasma deformation has on penetration as compared to the simple 1/2 pU2 = B 2/2?0 model.

Gurevich, Peter Alexi

170

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

171

Asymmetric Dielectric Trilayer Cantilever Probe for Calorimetric High-Frequency Field Imaging  

Microsoft Academic Search

Multimaterial, microelectromechanical systems-based cantilever probes were developed for high-frequency magnetic field imaging. The basic configuration of the probe consists of a cantilever beam fabricated using surface micromachining and bulk micromachining techniques with dielectric silicon nitride and silicon oxide materials on a silicon wafer. A gold patterned metallization at the tip of the cantilever provides a source of eddy current heating

Simone Lee; T. Mitch Wallis; John Moreland; Pavel Kabos; Y. C. Lee

2007-01-01

172

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

173

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

174

Magnetic Fields: Visible and Permanent.  

ERIC Educational Resources Information Center

Children will be able to see the concept of a magnetic field translated into a visible reality using the simple method outlined. Standard shelf paper, magnets, iron filings, and paint in a spray can are used to prepare a permanent and well-detailed picture of the magnetic field. (Author/JN)

Winkeljohn, Dorothy R.; Earl, Robert D.

1983-01-01

175

High Magnetic Field Gradient PGSE NMR in the Presence of a Large Polarizing Field  

Microsoft Academic Search

A description is given of pulsed gradient spin echo (PGSE) NMR experiments in which large pulsed magnetic field gradients may be required. The design contraints are discussed and, in particular, the problem of the use of large pulsed magnetic field gradients in conjunction with large polarizing fields is considered. Issues addressed concern probe mechanical assembly, current supply requirements, and pulse

Paul T. Callaghan; Michal E. Komlosh; Magnus Nyden

1998-01-01

176

Using Coordinated Observations in Polarized White Light and Faraday Rotation to Probe the Spatial Position and Magnetic Field of an Interplanetary Sheath  

NASA Astrophysics Data System (ADS)

Coronal mass ejections (CMEs) can be continuously tracked through a large portion of the inner heliosphere by direct imaging in visible and radio wavebands. White light (WL) signatures of solar wind transients, such as CMEs, result from Thomson scattering of sunlight by free electrons and therefore depend on both viewing geometry and electron density. The Faraday rotation (FR) of radio waves from extragalactic pulsars and quasars, which arises due to the presence of such solar wind features, depends on the line-of-sight magnetic field component B ? and the electron density. To understand coordinated WL and FR observations of CMEs, we perform forward magnetohydrodynamic modeling of an Earth-directed shock and synthesize the signatures that would be remotely sensed at a number of widely distributed vantage points in the inner heliosphere. Removal of the background solar wind contribution reveals the shock-associated enhancements in WL and FR. While the efficiency of Thomson scattering depends on scattering angle, WL radiance I decreases with heliocentric distance r roughly according to the expression Ivpropr -3. The sheath region downstream of the Earth-directed shock is well viewed from the L4 and L5 Lagrangian points, demonstrating the benefits of these points in terms of space weather forecasting. The spatial position of the main scattering site r sheath and the mass of plasma at that position M sheath can be inferred from the polarization of the shock-associated enhancement in WL radiance. From the FR measurements, the local B ?sheath at r sheath can then be estimated. Simultaneous observations in polarized WL and FR can not only be used to detect CMEs, but also to diagnose their plasma and magnetic field properties.

Xiong, Ming; Davies, Jackie A.; Feng, Xueshang; Owens, Mathew J.; Harrison, Richard A.; Davis, Chris J.; Liu, Ying D.

2013-11-01

177

Instrumentation used to measure residential magnetic fields and currents.  

PubMed

The equipment used to measure magnetic fields and electric currents in residences is described. The instrumentation consisted of current transformers, magnetic field probes and locally designed and built signal conditioning modules. The data acquisition system was capable of unattended recording for extended time periods. The complete system was calibrated to verify its response to known physical inputs. PMID:14582878

Lahijanian, H; Yatapanage, K; Rosen, R; Cross, J

2003-10-01

178

Probing the magnetic topologies of magnetic clouds by means of solar energetic particles  

SciTech Connect

Magnetic clouds are large (<0.25 AU) interplanetary regions with topologies consistent with those of magnetic loops. They are of interest because they may be an interplanetary signature of coronal mass ejections. Clouds have been identified in solar wind data by their magnetic properties and by the presence of bidirectional particle fluxes. Two possible closed magnetic topologies have been considered for clouds: (1) an elongated bottle with field lines rooted at both ends in the Sun and (2) a detached magnetic bubble or plasmoid consisting of closed field lines. The inferred topologies are also consistent with open field lines that converge beyond 1 AU. The authors have used solar energetic particles (SEPs) as probes of the cloud topologies. The rapid access of SEPs to the interiors of many clouds indicates that the cloud field lines extend back to the Sun and hence are not plasmoids. The small modulation of galactic cosmic rays associated with clouds also suggests that the magnetic fields of clouds are not closed.

Kahler, S.W. (Boston Coll., Newton, MA (USA)); Reames, D.V. (NASA Goddard Space Flight Center, Greenbelt, MD (USA))

1991-06-01

179

Probe measurements of electron energy distributions in a strongly magnetized low-pressure helium plasma  

NASA Astrophysics Data System (ADS)

Electron energy distributions (EED) in strongly magnetized (~0.3 T), low-pressure (~0.2 Pa) helium plasmas of the toroidal device ``Blaamann'' [K. Rypdal et al., Plasma Phys. Controlled Fusion 36, 1099 (1994)] have been measured. In the analysis of measurements, one applies a simplified expression for the limit of a strongly magnetized plasma relating the electron energy distribution to the first derivative of electron probe current with respect to the probe potential. It is shown that for the conditions investigated this approximation gives the same electron densities and slightly lower temperatures (up to 10%) as the kinetic theory for arbitrary magnetic field strength. Cylindrical probes, which are oriented along and perpendicular to the magnetic field, are used in the measurements. It is shown that these probes give nearly identical results. However, the probe that is oriented perpendicular to the magnetic field can give the electron energy distribution in a wider energy range and with better accuracy. The cross-field diffusion coefficient of electrons near the probe is estimated and shown to be classical.

Demidov, V. I.; Ratynskaia, S. V.; Armstrong, R. J.; Rypdal, K.

1999-01-01

180

Axial velocity measurement of current sheath in a plasma focus device using a magnetic probe  

Microsoft Academic Search

A magnetic probe was used to study the current sheath in a plasma focus device with energy of about 2.8 kJ. Measurements were carried out for argon gas under a pressure of about 1 mbar. The axial distributions of trajectory, average axial velocity, and magnetic field of the current sheath at a certain radial distance along the axis of the

Sharif Al-Hawat

2004-01-01

181

Determination of the plasma column shape in the Tokamak Novillo cross section by magnetic probes  

NASA Astrophysics Data System (ADS)

The determination of plasma cross section shape in tokamaks is an important diagnostic method for equilibrium conditions analysis. In this work, a time dependent variation of the plasma column cross section in the Novillo Tokamak is obtained. The experimental method is based on using one magnetic probe, which is installed inside of the vacuum vessel in a 1 mm wall thickness stainless steel tube, in the protected region of the limiter shadow. The plasma column cross section is determined by measuring the poloidal magnetic field produced by the plasma current. This method, now running for determining the plasma column shape, requires the measurement of magnetic field present outside plasma column. The measurements are carried out from a set of small coils, which are located inside the vacuum chamber in the radial and poloidal direction, so the magnetic field with no current attenuations produced by the penetration time of the stainless steel vacuum chamber can be measured. The magnetic probes detect a real time variation of magnetic flux passing through them. In order to obtain the magnetic field values, it is required that the electric signals coming from the magnetic probe be integrated; this operation is carried out by active circuits located between the probe signal and one oscilloscope. The integrated signals can be exhibited by photographs of the oscilloscope display.

Omana, Adrian Hernandez

182

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

183

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

184

On-tip sub-micrometer Hall probes for magnetic microscopy prepared by AFM lithography.  

PubMed

We developed a technology of sub-micrometer Hall probes for future application in scanning hall probe microscopy (SHPM) and magnetic force microscopy (MFM). First, the Hall probes of approximately 9-mum dimensions are prepared on the top of high-aspect-ratio GaAs pyramids with an InGaP/AlGaAs/GaAs active layer using wet-chemical etching and non-planar lithography. Then we show that the active area of planar Hall probes can be downsized to sub-micrometer dimensions by local anodic oxidation technique using an atomic force microscope. Such planar probes are tested and their noise and magnetic field sensitivity are evaluated. Finally, the two technologies are combined to fabricate sub-micrometer Hall probes on the top of high-aspect ratio mesa for future SHPM and MFM techniques. PMID:19359099

Gregusová, D; Martaus, J; Fedor, J; Kúdela, R; Kostic, I; Cambel, V

2009-07-01

185

Evolution of twisted magnetic fields  

SciTech Connect

The magnetic field of the solar corona evolves quasistatically in response to slowly changing photospheric boundary conditions. The magnetic topology is preserved by the low resistivity of the solar atmosphere. We show that a magnetic flux coordinate system simplifies the problem of calculating field evolution with invariant topology. As an example, we calculate the equilibrium of a thin magnetic flux tube with small twist per unit length.

Zweibel, E.G.; Boozer, A.H.

1985-02-01

186

Reconnection of Magnetic Fields  

NASA Astrophysics Data System (ADS)

Preface; Part I. Introduction: 1.1 The Sun E. R. Priest; 1.2 Earth's magnetosphere J. Birn; Part II. Basic Theory of MHD Reconnection: 2.1 Classical theory of two-dimensional reconnection T. G. Forbes; 2.2 Fundamental concepts G. Hornig; 2.3 Three-dimensional reconnection in the absence of magnetic null points G. Hornig; 2.4 Three-dimensional reconnection at magnetic null points D. Pontin; 2.5 Three-dimensional flux tube reconnection M. Linton; Part III. Basic Theory of Collisionless Reconnection: 3.1 Fundamentals of collisionless reconnection J. Drake; 3.2 Diffusion region physics M. Hesse; 3.3 Onset of magnetic reconnection P. Pritchett; 3.4 Hall-MHD reconnection A. Bhattacharjee and J. Dorelli; 3.5 Role of current-aligned instabilities J. Büchner and W. Daughton; 3.6 Nonthermal particle acceleration M. Hoshino; Part IV. Reconnection in the Magnetosphere: 4.1 Reconnection at the magnetopause: concepts and models J. G. Dorelli and A. Bhattacharjee; 4.2 Observations of magnetopause reconnection K.-H. Trattner; 4.3 On the stability of the magnetotail K. Schindler; 4.4 Simulations of reconnection in the magnetotail J. Birn; 4.5 Observations of tail reconnection W. Baumjohann and R. Nakamura; 4.6 Remote sensing of reconnection M. Freeman; Part V. Reconnection in the Sun's Atmosphere: 5.1 Coronal heating E. R. Priest; 5.2 Separator reconnection D. Longcope; 5.3 Pinching of coronal fields V. Titov; 5.4 Numerical experiments on coronal heating K. Galsgaard; 5.5 Solar flares K. Kusano; 5.6 Particle acceleration in flares: theory T. Neukirch; 5.7 Fast particles in flares: observations L. Fletcher; 6. Open problems J. Birn and E. R. Priest; Bibliography; Index.

Birn, J.; Priest, E. R.

2007-01-01

187

Evidence for the Reversal of Magnetic Field Polarity in Coronal Streamers  

NASA Technical Reports Server (NTRS)

Faraday rotation observations are unique amongst radio occultation measurements in that they respond to magnetic field in addition to electron density, making it possible to probe the coronal magnetic field.

Woo, Richard

1996-01-01

188

Ultrafast precessional magnetization reversal by picosecond magnetic field pulse shaping  

NASA Astrophysics Data System (ADS)

Since the invention of the first magnetic memory disk in 1954, much effort has been put into enhancing the speed, bit density and reliability of magnetic memory devices. In the case of magnetic random access memory (MRAM) devices, fast coherent magnetization rotation by precession of the entire memory cell is desired, because reversal by domain-wall motion is much too slow. In principle, the fundamental limit of the switching speed via precession is given by half of the precession period. However, under-critically damped systems exhibit severe ringing and simulations show that, as a consequence, undesired back-switching of magnetic elements of an MRAM can easily be initiated by subsequent write pulses, threatening data integrity. We present a method to reverse the magnetization in under-critically damped systems by coherent rotation of the magnetization while avoiding any ringing. This is achieved by applying specifically shaped magnetic field pulses that match the intrinsic properties of the magnetic elements. We demonstrate, by probing all three magnetization components, that reliable precessional reversal in lithographically structured micrometre-sized elliptical permalloy elements is possible at switching times of about 200ps, which is ten times faster than the natural damping time constant.

Gerrits, Th.; van den Berg, H. A. M.; Hohlfeld, J.; Bär, L.; Rasing, Th.

2002-08-01

189

INTRINSIC BISPECTRA OF COSMIC MAGNETIC FIELDS  

SciTech Connect

Forthcoming data sets from the Planck experiment and others are in a position to probe the cosmic microwave background (CMB) non-Gaussianity with higher accuracy than has yet been possible, and potentially open a new window into the physics of the very early universe. However, a signal need not necessarily be inflationary in origin, and possible contaminants should be examined in detail. One such is provided by early universe magnetic fields, which can be produced by a variety of models including during an inflationary phase, at phase transitions, or seeded by cosmic defects. Should such fields have been extant in the early universe, they would provide a natural source of CMB non-Gaussianity. Knowledge of the CMB angular bispectrum requires the complete Fourier-space (or 'intrinsic') bispectrum. In this paper, I consider in detail the intrinsic bispectra of an early-universe magnetic field for a range of power-law magnetic spectra.

Brown, Iain A., E-mail: i.a.brown@astro.uio.no [Institute of Theoretical Astrophysics, University of Oslo, 0315 Oslo (Norway)

2011-06-01

190

Magnetic Resonance Imaging of time-varying magnetic fields from therapeutic devices  

PubMed Central

While magnetic resonance imaging of static magnetic fields generated by external probes has been previously demonstrated, there is an unmet need to image time-varying magnetic fields, such as those generated by transcranial magnetic stimulators or radiofrequency hyperthermia probes. A method to image such time-varying magnetic fields is introduced in this work. This article presents the theory behind the method and provides proof of concept by imaging time-varying magnetic fields generated by a figure-eight coil inside simple phantoms over a range of frequencies and intensities, using a 7T small animal MRI scanner. The method is able to reconstruct the three-dimensional components of the oscillating magnetic field vector.

Hernandez-Garcia, Luis; Bhatia, Vivek; Prem-Kumar, Krishan; Ulfarsson, Magnus

2013-01-01

191

Matter in strong magnetic fields  

Microsoft Academic Search

The properties of matter are drastically modified by strong magnetic fields, B>>m2ee3c\\/h3=2.35×109 G (1 G=10-4 T), as are typically found on the surfaces of neutron stars. In such strong magnetic fields, the Coulomb force on an electron acts as a small perturbation compared to the magnetic force. The strong-field condition can also be mimicked in laboratory semiconductors. Because of the

Dong Lai

2001-01-01

192

Mapping magnetic near-field distributions of plasmonic nanoantennas.  

PubMed

We present direct experimental mapping of the lateral magnetic near-field distribution in plasmonic nanoantennas using aperture scanning near-field optical microscopy (SNOM). By means of full-field simulations it is demonstrated how the coupling of the hollow-pyramid aperture probe to the nanoantenna induces an effective magnetic dipole which efficiently excites surface plasmon resonances only at lateral magnetic field maxima. This excitation in turn affects the detected light intensity enabling the visualization of the lateral magnetic near-field distribution of multiple odd and even order plasmon modes with subwavelength spatial resolution. PMID:23464670

Denkova, Denitza; Verellen, Niels; Silhanek, Alejandro V; Valev, Ventsislav K; Van Dorpe, Pol; Moshchalkov, Victor V

2013-04-23

193

Kelvin probe force microscope with near-field photoexcitation  

NASA Astrophysics Data System (ADS)

We developed a combined probe microscope-a scanning probe near-field optical microscope (SNOM) combined with Kelvin probe force microscope (KFM) that uses a slim and bent optical fiber probe (S/B fiber probe). The developed SNOM-KFM system enables near-field photoexcitation through an apex of the S/B fiber probe during KFM measurement, so that the photoexcitation effects on surface potential (SP) can be measured with submicron spatial resolution. By measuring the SP of tris(8-hydroxyquinolinato) aluminum(III) (Alq3) thin films, we found that the S/B fiber probes have large negative values in the KFM transfer function. Near-field photoexcitation was performed on Alq3 thin films through the S/B fiber probes, and the spatial pattern of photoinduced reduction in SP was visualized by KFM measurement with the same probe.

Ozasa, Kazunari; Nemoto, Shigeyuki; Maeda, Mizuo; Hara, Masahiko

2010-05-01

194

Magnetic and Langmuir Probe Measurements on the Plasmoid Thruster Experiment (PTX)  

NASA Technical Reports Server (NTRS)

The Plasmoid Thruster Experiment (PTX) operates by inductively producing plasmoids in a conical theta-pinch coil and subsequently ejecting them at high velocity. An overview of PTX is described in a companion paper. The shape and magnetic field structure of the translating plasmoids will be measured with of an array of inductive magnetic field probes. Six sets of two B-dot probes (for a total of twelve probes) have been constructed for measuring B(sub z) and B(sub theta), the axial and azimuthal components of the magnetic field. The probes were calibrated with a Helmholtz coil, driven alternately by a high-voltage pulser or a signal generator. The probes are wound on a G-10 form, and have an average (calibrated) NA of 9.37 x 10(exp -5) square meters, where N is the number of turns and A is cross-sectional area. The frequency response of the probes was measured over the range from 1 kHz to 10 MHZ. The electron number density n(sub e), electron temperature T(sub e) and velocity v will be determined from measurements taken with a quadruple Langmuir probe, situated in the exhaust chamber. Three of the four probes on the quadruple probe sample the current-voltage characteristic, and from this yield measurements of T(sub e) and n(sub e). The fourth probe provides a measurement of plasma flow velocity. A 6-inch long alumina rod, hollowed with four holes to house the probe wires, is being used to construct the quadruple probe. A variety of propellants will be used, including hydrogen, nitrogen and argon. From the measurements of the plasmoid mass, density, temperature, and velocity, the basic propulsion characteristics of PTX will be evaluated.

Koelfgen, Syri J.; Eskridge, Richard; Fimognari, Peter; Hawk, Clark W.; Lee, Mike; Martin, Adam

2004-01-01

195

Magnetic fields around evolved stars  

NASA Astrophysics Data System (ADS)

A number of mechanisms, such as magnetic fields, (binary) companions and circumstellar disks have been suggested to be the cause of non-spherical PNe and in particular collimated outflows. This work investigates one of these mechanisms: the magnetic fields. While MHD simulations show that the fields can indeed be important, few observations of magnetic fields have been done so far. We used the VLBA to observe five evolved stars, with the goal of detecting the magnetic field by means of water maser polarization. The sample consists in four AGB stars (IK Tau, RT Vir, IRC+60370 and AP Lyn) and one pPN (OH231.8+4.2). In four of the five sources, several strong maser features were detected allowing us to measure the linear and/or circular polarization. Based on the circular polarization detections, we infer the strength of the component of the field along the line of sight to be between ~30 mG and ~330 mG in the water maser regions of these four sources. When extrapolated to the surface of the stars, the magnetic field strength would be between a few hundred mG and a few Gauss when assuming a toroidal field geometry and higher when assuming more complex magnetic fields. We conclude that the magnetic energy we derived in the water maser regions is higher than the thermal and kinetic energy, leading to the conclusion that, indeed, magnetic fields probably play an important role in shaping Planetary Nebulae.

Leal-Ferreira, M.; Vlemmings, W.; Kemball, A.; Amiri, N.; Maercker, M.; Ramstedt, S.; Olofsson, G.

2014-04-01

196

The Sun's global magnetic field.  

PubMed

Our present-day understanding of solar and stellar magnetic fields is discussed from both an observational and theoretical viewpoint. To begin with, observations of the Sun's large-scale magnetic field are described, along with recent advances in measuring the spatial distribution of magnetic fields on other stars. Following this, magnetic flux transport models used to simulate photospheric magnetic fields and the wide variety of techniques used to deduce global coronal magnetic fields are considered. The application and comparison of these models to the Sun's open flux, hemispheric pattern of solar filaments and coronal mass ejections are then discussed. Finally, recent developments in the construction of steady-state global magnetohydrodynamic models are considered, along with key areas of future research. PMID:22665897

Mackay, Duncan H

2012-07-13

197

ANOMALOUS COSMIC RAYS AS PROBES OF MAGNETIC CLOUDS  

SciTech Connect

We report, for the first time, the observation near the Earth of anomalous cosmic ray (ACR) particles throughout the interiors of interplanetary magnetic clouds (MCs) at the same intensity as outside the MCs. ACRs, accelerated in the outer heliosphere, have unique elemental abundances making their identity unambiguous as they probe these clouds from the outside. Thus, MCs, carried out from the Sun by coronal mass ejections (CMEs), are seen to contain no structures that are magnetically closed to the penetration of ions with energies above a few MeV amu{sup -1}. As the MCs expand outward, they must fill their increasing volume with ACRs dynamically, to the same degree as neighboring 'open' field lines. These observations cast doubt on conventional ideas about the closed field topologies of MCs and the cross-field transport of energetic particles. The ACR observations conflict with some reports of significant exclusion from MCs of solar energetic particles (SEPs) of comparable energy and rigidity. A process that allows cross-field transport of ACRs may also allow similar transport of SEPs late in events, causing the large spatial extent and uniformity of SEPs in 'invariant spectral regions' extending far behind CME-driven shock waves.

Reames, D. V. [Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742 (United States); Kahler, S. W. [Air Force Research Laboratory, RVBXS, 29 Randolph Rd., Hanscom AFB, MA 01731 (United States); Tylka, A. J. [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States)], E-mail: dvreames@umd.edu

2009-08-01

198

Magnetic response to applied electrostatic field in external magnetic field  

NASA Astrophysics Data System (ADS)

We show, within QED and other possible nonlinear theories, that a static charge localized in a finite domain of space becomes a magnetic dipole, if it is placed in an external (constant and homogeneous) magnetic field in the vacuum. The magnetic moment is quadratic in the charge, depends on its size and is parallel to the external field, provided the charge distribution is at least cylindrically symmetric. This magneto-electric effect is a nonlinear response of the magnetized vacuum to an applied electrostatic field. Referring to the simple example of a spherically symmetric applied field, the nonlinearly induced current and its magnetic field are found explicitly throughout the space; the pattern of the lines of force is depicted, both inside and outside the charge, which resembles that of a standard solenoid of classical magnetostatics.

Adorno, T. C.; Gitman, D. M.; Shabad, A. E.

2014-04-01

199

Near Field Probes: From Optical Fibers to Optical Nanoantennas  

Microsoft Academic Search

This chapter reports a broad overview of near-field optical probes. They represent the key components for the performance\\u000a of the scanning near field optical microscope (SNOM). In this frame, we consider the two main classes of sensors: aperture\\u000a and apertureless probes. In particular, attention is focused on optical fiber probes and on nanoantenna probes. Recent developments\\u000a in the improvement of

Eugenio Cefalì; Salvatore Patanè; Salvatore Spadaro; Renato Gardelli; Matteo Albani; Maria Allegrini

200

A platform for designing hyperpolarized magnetic resonance chemical probes  

PubMed Central

Hyperpolarization is a highly promising technique for improving the sensitivity of magnetic resonance chemical probes. Here we report [15N, D9]trimethylphenylammonium as a platform for designing a variety of hyperpolarized magnetic resonance chemical probes. The platform structure shows a remarkably long 15N spin–lattice relaxation value (816?s, 14.1 T) for retaining its hyperpolarized spin state. The extended lifetime enables the detection of the hyperpolarized 15N signal of the platform for several tens of minutes and thus overcomes the intrinsic short analysis time of hyperpolarized probes. Versatility of the platform is demonstrated by applying it to three types of hyperpolarized chemical probes: one each for sensing calcium ions, reactive oxygen species (hydrogen peroxide) and enzyme activity (carboxyl esterase). All of the designed probes achieve high sensitivity with rapid reactions and chemical shift changes, which are sufficient to allow sensitive and real-time monitoring of target molecules by 15N magnetic resonance.

Nonaka, Hiroshi; Hata, Ryunosuke; Doura, Tomohiro; Nishihara, Tatsuya; Kumagai, Keiko; Akakabe, Mai; Tsuda, Masashi; Ichikawa, Kazuhiro; Sando, Shinsuke

2013-01-01

201

Venus Deep Nightside Magnetic Fields Revisited  

NASA Astrophysics Data System (ADS)

We reexamined the near-Venus deep nightside magnetic fields observed by the Pioneer Venus Orbiter(PVO) over two decades ago. This analysis was in part inspired by recent discussions of the possibilities of identifying a weak planetary dynamo or remanent magnetic field, and in part by the availability of numerical simulations of weak field plasma interactions using the BATS-R-US MHD code. The data were first scrutinized for statistically significant regions of radial field in the near-midnight low altitude wake from the prime mission periapsis of ~150km up to about 450 km. Radial field 'maps' were constructed for a range of altitudes in both solar wind interaction and planetary geographical coordinate systems. The results suggested the presence of weak radial fields above ~250km that show a persistent North-South sign bias. This behavior is not seen at the lowest altitudes probed, and is present regardless of the interplanetary magnetic field sector. The MHD simulations provided basic pictures of what might be expected for a hypothetical planet with a weak but still detectable dipole field that is comparable to the solar wind interaction-related draped interplanetary field. These show similar tendencies, illustrating that models are essential to the interpretation of potential weak intrinsic field signatures at planets such as Venus. Further modeling specific to Venus is needed to make further progress.

Villarreal, M. N.; Luhmann, J. G.; Ma, Y.; Russell, C. T.; Wei, H.; Zhang, T.

2011-12-01

202

The Extended Coronal Magnetic Field.  

National Technical Information Service (NTIS)

The coronal magnetic field should contain many field lines connecting the photosphere to interplanetary space. A sharp boundary separates two adjacent sectors of opposite polarity. The large-scale structure of the corona is related to the photospheric sec...

J. M. Wilcox

1970-01-01

203

Flares and Changing Magnetic Fields.  

National Technical Information Service (NTIS)

One of the principal objectives of the magnetic field observing program at the Sacramento Peak Observatory has been to discover whether there are any observable changes in the photospheric fields at the time of flares.

D. M. Rust

1972-01-01

204

THE OUTER MAGNETIC FIELD OF L183  

SciTech Connect

The L183 (= L134N) dark molecular cloud has been probed using deep near-infrared imaging polarimetry of stars to beyond 14 mag in H band (1.6 {mu}m), using the Mimir instrument on the 1.83 m Perkins Telescope. Nearly 400 arcmin{sup 2} were surveyed, including the dense core in L183, as seen in WISE Band 3 (12 {mu}m) extinction, and the near surroundings, revealing 35 stars with either detected polarizations or significant upper limits. Stars with detected polarizations are reddened if closer than 8 arcmin (0.25 pc at the 110 pc cloud distance) and unreddened beyond. The polarimetric sample probes as close to the core as 3 arcmin (0.1 pc), where A{sub V} {approx} 14 mag. Compared to the relatively unextincted surrounding stars, the reddened stars show no increase in polarization with extinction, suggesting that all of the polarization is induced in the outer layers of the cloud. This 0.25 pc radius envelope magnetic field does show a strong interaction with the L183 dark cloud. The envelope field is also virtually perpendicular, on the plane of the sky, to the field seen at 850 {mu}m, though more closely aligned with the rotation axis of the dense gas core. The physical size scale at which the envelope and the core magnetic fields either decouple from each other or strongly modify their directions must be inside the 0.1 pc region probed here.

Clemens, Dan P., E-mail: clemens@bu.edu [Institute for Astrophysical Research, Boston University, 725 Commonwealth Ave, Boston, MA 02215 (United States)

2012-03-20

205

ANCHORING MAGNETIC FIELD IN TURBULENT MOLECULAR CLOUDS  

SciTech Connect

One of the key problems in star formation research is to determine the role of magnetic fields. Starting from the atomic intercloud medium which has density n {sub H} approx 1 cm{sup -3}, gas must accumulate from a volume several hundred pc across in order to form a typical molecular cloud. Star formation usually occurs in cloud cores, which have linear sizes below 1 pc and densities n {sub H2} > 10{sup 5} cm{sup -3}. With current technologies, it is hard to probe magnetic fields at scales lying between the accumulation length and the size of cloud cores, a range corresponds to many levels of turbulent eddy cascade, and many orders of magnitude of density amplification. For field directions detected from the two extremes, however, we show here that a significant correlation is found. Comparing this result with molecular cloud simulations, only the sub-Alfvenic cases result in field orientations consistent with our observations.

Li Huabai; Goodman, Alyssa [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States); Darren Dowell, C. [Division of Physics, Mathematics, and Astronomy, California Institute of Technology, MS 320-47, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Hildebrand, Roger [Enrico Fermi Institute and Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Novak, Giles, E-mail: hli@cfa.harvard.ed [Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States)

2009-10-20

206

Permanent Magnet Probe-Type Flowmeter for Liquid Metal.  

National Technical Information Service (NTIS)

In this paper details of the design and operation of an unique liquid metal flow meter probe are presented. Small permanent magnets are employed in the device. Flow rate measurements involve especially determination of the transit time for natural velocit...

S. Mueller G. Thun

1977-01-01

207

Permanent Magnet Probe-Type Flowmeter for Liquid Metal.  

National Technical Information Service (NTIS)

Details of the design and operation of an unique liquid metal flow meter probe are presented. Small permanent magnets are employed in the device. Flow rate measurements involve a determination of the transit time for natural velocity fluctuations using a ...

S. Mueller G. Thun

1979-01-01

208

A magnetically levitated, automated, contact analytical probe tool  

Microsoft Academic Search

With the challenge of the shrinking dimensions in the fabrication process, demands are growing for higher precision and more powerful analytical probing stations to be used for characterization and failure analysis of integrated circuits. A magnetic levitation-based approach to analytical probing stations is proposed and investigated in this paper. This approach permits the process to be automated while maintaining better

Shiaw-Jong Steve Chen; Ilene J. Busch-Vishniac

1995-01-01

209

Dresden pulsed magnetic field facility  

NASA Astrophysics Data System (ADS)

We report on the status quo of the Dresden High Magnetic Field Laboratory (HLD) that is being set up at the Forschungszentrum Dresden-Rossendorf in Dresden, Germany. First pulsed-field coils reaching up to 71 T with a pulse duration of about 100 ms have been designed, constructed, and tested. A two-coil 100 T magnet and a long-pulse (1000 ms) 60 T magnet are under construction. Electrical-transport and magnetization experiments are running routinely in the pilot laboratory at the IFW Dresden. The feasibility of NMR experiments in pulsed-field environments has been proven.

Wosnitza, J.; Bianchi, A. D.; Freudenberger, J.; Haase, J.; Herrmannsdörfer, T.; Kozlova, N.; Schultz, L.; Skourski, Y.; Zherlitsyn, S.; Zvyagin, S. A.

2007-03-01

210

Origin of cosmic magnetic fields.  

PubMed

We calculate, in the free Maxwell theory, the renormalized quantum vacuum expectation value of the two-point magnetic correlation function in de Sitter inflation. We find that quantum magnetic fluctuations remain constant during inflation instead of being washed out adiabatically, as usually assumed in the literature. The quantum-to-classical transition of super-Hubble magnetic modes during inflation allow us to treat the magnetic field classically after reheating, when it is coupled to the primeval plasma. The actual magnetic field is scale independent and has an intensity of few×10(-12)??G if the energy scale of inflation is few×10(16)??GeV. Such a field accounts for galactic and galaxy cluster magnetic fields. PMID:23971556

Campanelli, Leonardo

2013-08-01

211

Magnetic field sensor by orthoferrites  

Microsoft Academic Search

Among all ferromagnets orthoferrites possess the highest velocities of domain wall motion. Dynamic properties of a magnetic field meter based on domain wall dynamics in yttrium orthoferrite are reported. It is shown that at low driving magnetic fields and at frequencies up to the MHz band domain wall dynamics can be adequately described by linear equations. In a wide range

Y. S. Didosyan; V. Y. Barash; N. A. Bovarin; H. Hauser; P. Fulmek

1997-01-01

212

THE CLUSTER MAGNETIC FIELD INVESTIGATION  

Microsoft Academic Search

The Cluster mission provides a new opportunity to study plasma processes and structures in the near-Earth plasma environment. Four-point measurements of the magnetic field will enable the analysis of the three dimensional structure and dynamics of a range of phenomena which shape the macroscopic properties of the magnetosphere. Difference measurements of the magnetic field data will be combined to derive

A. Balogh; M. W. Dunlop; S. W. H. Cowley; D. J. Southwood; J. G. Thomlinson; K. H. Glassmeier; G. Musmann; H. Luhr; S. Buchert; M. H. AcuÑA; D. H. Fairfield; J. A. Slavin; W. Riedler; K. Schwingenschuh; M. G. Kivelson

1997-01-01

213

Laboratory Measurements of Astrophysical Magnetic Fields  

NASA Astrophysics Data System (ADS)

It has been proposed that high Mach number collisionless shocks propagating in an initially unmagnetized plasma play a major role in the magnetization of large scale structures in the Universe. A detailed study of the experimental configuration necessary to scale such environments down to laboratory dimensions will be presented. We will show initial results from preliminary experiments conducted at the Phoenix laser (UCLA) and the LULI laser (Ecole Polytechnique) where collisionless shocks are generated by the expansion of exploding foils driven by energetic laser beams. The time evolution of the magnetic field is probed with induction coils placed at 10 cm from the laser focus. We will discuss various mechanisms of magnetic field generation and compare them with the experimental results.

Murphy, C. D.; Miniati, F.; Edwards, M.; Mithen, J.; Bell, A. R.; Constantin, C.; Everson, E.; Schaeffer, D.; Niemann, C.; Ravasio, A.; Brambrink, E.; Benuzzi-Mounaix, A.; Koenig, M.; Gregory, C.; Woolsey, N.; Park, H.-S.; Remington, B.; Ryutov, D.; Bingham, R.; Gargate, L.; Spitkovsky, A.; Gregori, G.

2010-11-01

214

Dresden pulsed magnetic field facility  

Microsoft Academic Search

We report on the status quo of the Dresden High Magnetic Field Laboratory (HLD) that is being set up at the Forschungszentrum Dresden-Rossendorf in Dresden, Germany. First pulsed-field coils reaching up to 71T with a pulse duration of about 100ms have been designed, constructed, and tested. A two-coil 100T magnet and a long-pulse (1000ms) 60T magnet are under construction. Electrical-transport

J. Wosnitza; A. D. Bianchi; J. Freudenberger; J. Haase; T. Herrmannsdörfer; N. Kozlova; L. Schultz; Y. Skourski; S. Zherlitsyn; S. A. Zvyagin

2007-01-01

215

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

216

Superconductivity at High Magnetic Fields  

Microsoft Academic Search

Using pulsed-magnetic-field techniques, we have studied the magnetic-field-induced superconducting transitions of alloys in the systems Ti-V, Ti-Nb, Ti-Ta, Ti-Mo, Zr-Nb, Hf-Nb, Hf-Ta, U-Nb, and U-Mo. For concentrated alloys the low-current-density resistive critical field Hr(J<~10 A\\/cm2) is nearly independent of the amount of cold working and the relative orientations of magnetic field, current, and anisotropic defect structure. The observed values of

T. G. Berlincourt; R. R. Hake

1963-01-01

217

High latitude solar magnetic fields  

NASA Technical Reports Server (NTRS)

Kitt Peak magnetograms are used to measure polar magnetic fields. The polar mean absolute field increases at the same time as the polar mean field decreases. That is, the polar mean absolute field varies in phase with solar activity, in contrast to the out of phase variation of the mean polar field. It is found that the polar fields have a large bipolar component even at solar minimum, with a magnitude equal to that found at low latitudes outside the active latitude bands.

Murray, Norman

1992-01-01

218

Magnetic Compton scattering: A reliable probe to investigate magnetic properties  

NASA Astrophysics Data System (ADS)

Magnetic Compton scattering (MCS) is an ideal technique for the study of magnetic properties of ferro/ferrimagnetic materials because this method reveals the spin-polarized electron momentum density and yields the absolute and site dependent spin moments. The quantity measured in the MCS, so called magnetic Compton profile, is defined as the difference in the one-dimensional projection of the spin-polarized electron momentum density for majority and minority spin bands. In MCS, the Doppler broadening of the scattered radiation provides information on the correlation between the spin moment and the spin-polarized electron states of the valence electrons. It can also distinguish the spin polarization of itinerant electrons, because their momentum is narrow around the center of the profile. In this paper, temperature and field dependent spin momentum densities in Zn doped Ni ferrite namely, Ni1-xZnxFe2O4(x = 0.0,0.1,0.2), hole doped manganites like La0.7Ca0.3Mn1-xAlxO3(x = 0,0.02and0.06) and half Heusler alloys Cu1-xNixMnSb(x = 0.17,0.22) are reviewed. The decomposition of profiles in terms of site specific magnetic moments and their role in the formation of total spin moment is also discussed.

Ahuja, B. L.

2013-02-01

219

Hand-Held Schlieren Photography with Light Field Probes  

Microsoft Academic Search

We introduce a new approach to capturing refraction in transparent media, which we call Light Field Back- ground Oriented Schlieren Photography (LFBOS). By op- tically coding the locations and directions of light rays emerging from a light field probe, we can capture changes of the refractive index field between the probe and a camera or an observer. Rather than using

Gordon Wetzstein; Ramesh Raskar; Wolfgang Heidrich

2011-01-01

220

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

221

Effect of Ge substitution for Si on the magnetic hyperfine field in LaMn2Si2 compound measured by perturbed angular correlation spectroscopy with 140Ce as probe nuclei  

NASA Astrophysics Data System (ADS)

The effect of substitution of Ge for Si in LaMn2Si2 compound on the magnetic hyperfine field (Bhf) has been investigated by perturbed ?-? angular correlation (PAC) spectroscopy using 140La(140Ce) as probe nuclei. This compound exhibits antiferromagnetism followed by a ferromagnetic ordering when temperature decreases. The behavior of the ferromagnetic transition when Ge gradually replaces Si, with concentrations of 20%, 40%, 80%, and 100% is discussed. PAC measurements were carried out in the temperature range from 15 K to 325 K. Results for LaMn2Si2 compound showed that the dependence of Bhf with temperature follows the expected behavior for the host magnetization and could be fitted by a Brillouin function for JMn = 5/2. However, the temperature dependence of Bhf for compounds when Si is gradually replaced by Ge showed a deviation from such a behavior, which gradually increases up to a strong deviation observed for LaMn2Ge2. This striking behavior was ascribed to the hybridization of d band of the host and f band of the Ce impurities, which is stronger when the unit cell volume increase as Si ions are substituted by Ge atoms.

Bosch-Santos, B.; Carbonari, A. W.; Cabrera-Pasca, G. A.; Costa, M. S.; Saxena, R. N.

2013-05-01

222

Spinning magnetic fields  

Microsoft Academic Search

A possible electrical charge model based on the spinning time invariant point magnetic dipole within the framework of classical physics is outlined, as suggested by the admissible circular trajectory of a test charge around the magnetic dipole in its equatorial plane. The model depends on the moving force line hypothesis which has been claimed to have been disproved. The controversy

Jovan Djuric

1975-01-01

223

High frequency umbilical magnetic probe array for SSX wind tunnel  

NASA Astrophysics Data System (ADS)

The Swarthmore Spheromak Experiment (SSX) wind tunnel consists of a high velocity plume of magnetized plasma injected into a copper flux conserver with dimensions L = 1 m and R = 0.08 m (aspect ratio 10:1). The plasma spheromaks in this wind tunnel typically have densities on the order of 1 - 5 x10^15 cm-3 and flow speeds of 50 km/s. In the past, fluctuations and turbulence in the SSX plasma wind tunnel during magnetic reconnection have been examined by means of two high resolution (16 position at 0.46 cm spacing) radial magnetic probes. Results from the radial probes show high frequency magnetic fluctuations at the site of reconnection. Four more probes have been design to help detect magnetic fluctuations and reconnection activity along the axial direction of the wind tunnel. The four new probes have 8 positions at 0.95 cm spacing and have a flexible bellow in vacuum and a quartz jacket. The bellows act as an umbilical giving the probe excellent flexibility and versatility. The flexibility allows the probe to be bent so it lies along the axis of the flux conserver.

Werth, A. M.; Gray, T.; Brown, M. R.

2012-10-01

224

A 4 K cryogenic probe for use in magnetic resonance force microscopy experiments  

SciTech Connect

The detailed design of a mechanically detected nuclear magnetic resonance probe using the SPAM (Springiness Preservation by Aligning Magnetization) geometry, operating at 4 K, in vacuum, and a several-Tesla magnetic field is described. The probe head is vibration-isolated well enough from the environment by a three-spring suspension system that the cantilever achieves thermal equilibrium with the environment without the aid of eddy current damping. The probe uses an ultra-soft Si cantilever with a Ni sphere attached to its tip, and magnetic resonance is registered as a change in the resonant frequency of the driven cantilever. The RF system uses frequency sweeps for adiabatic rapid passage using a 500 ?m diameter RF coil wound around a sapphire rod. The RF coil and optical fiber of the interferometer used to sense the cantilever's position are both located with respect to the cantilever using a Garbini micropositioner, and the sample stage is mounted on an Attocube nanopositioner.

Smith, Doran D.; Alexson, Dimitri A. [U.S. Army Research Laboratory, 2800 Powder Mill Road, Adelphi, Maryland 20783 (United States)] [U.S. Army Research Laboratory, 2800 Powder Mill Road, Adelphi, Maryland 20783 (United States); Garbini, Joseph L. [Mechanical Engineering, University of Washington, Seattle, Washington 98195 (United States)] [Mechanical Engineering, University of Washington, Seattle, Washington 98195 (United States)

2013-09-15

225

Magnetic fields in galaxy clusters  

NASA Astrophysics Data System (ADS)

While it is established that galaxy clusters host magnetic fields of the order of a few ?G, both, their origin as well as their role in the intracluster medium (ICM) remain unclear. I will review the observational evidence for magnetic fields in galaxy clusters and present various lines of research that study the effects of magnetic fields in the ICM. Magnetic fields affect the way in which galaxies interact with the ICM, they may render the ICM buoyantly unstable in the presence of anisotropic thermal conduction, and they affect the thermal structure of the gas in cluster cores. Finally, opportunities for future research in this field, in particular in light of new radio telescopes is highlighted.

Brüggen, M.

2013-06-01

226

Preflare magnetic and velocity fields  

NASA Technical Reports Server (NTRS)

A characterization is given of the preflare magnetic field, using theoretical models of force free fields together with observed field structure to determine the general morphology. Direct observational evidence for sheared magnetic fields is presented. The role of this magnetic shear in the flare process is considered within the context of a MHD model that describes the buildup of magnetic energy, and the concept of a critical value of shear is explored. The related subject of electric currents in the preflare state is discussed next, with emphasis on new insights provided by direct calculations of the vertical electric current density from vector magnetograph data and on the role of these currents in producing preflare brightenings. Results from investigations concerning velocity fields in flaring active regions, describing observations and analyses of preflare ejecta, sheared velocities, and vortical motions near flaring sites are given. This is followed by a critical review of prevalent concepts concerning the association of flux emergence with flares

Hagyard, M. J.; Gaizauskas, V.; Chapman, G. A.; Deloach, A. C.; Gary, G. A.; Jones, H. P.; Karpen, J. T.; Martres, M.-J.; Porter, J. G.; Schmeider, B.

1986-01-01

227

Imaging electrons in a magnetic field  

NASA Astrophysics Data System (ADS)

We present simulations of an imaging mechanism that reveals the trajectories of electrons in a two-dimensional electron gas (2DEG), as well as simulations of the electron flow in zero and small magnetic fields. The end goal of this work is to implement the proposed mechanism to image the flow of electrons inside a ballistic electron device from one specific point (A) to another (B) in a 2DEG, using a low-temperature scanning probe microscope with a charged tip. The tip changes the electron density in the 2DEG beneath it and deflects the electrons traveling nearby, thereby changing the conductance from point A to point B. The simulations presented here show that by measuring the transmission of electrons from A to B versus tip position, one can image the electron flow. This forward scattering mechanism is well suited for imaging in a magnetic field, in contrast to previous probes that depended on backscattering. One could use this technique to image cyclotron orbits in an electron-focusing geometry, in which electrons travel from point A to point B in semi-circular paths bouncing along a wall. Imaging the motion of electrons in magnetic fields is useful for the development of devices for spintronics and quantum information processing.

Aidala, Katherine E.; Parrott, Robert E.; Heller, E. J.; Westervelt, R. M.

2006-08-01

228

Pulsar studies and magnetic fields in galaxies  

NASA Astrophysics Data System (ADS)

In recent years, I have mainly worked on the two research areas: pulsar polarization and magnetic fields in galaxies. Together with my cooperators, we have observed about 150 pulsars in total and will do another 100 in near future. We did systematical studies on circular polarization of pulsars and obtained several intriguing results. Using pulsars as probes, we detected the magnetic field reversals from spiral arm to arm in our Galaxy. We found that the B-field has a bi-symmetric structure in the disk. We also obtained the unique measurements of the vertical component of the B-field in the solar vicinity. From the anti-symmetric distribution of Galactic rotation measure sky, we identified the B-field structure produced by A0 dynamo in the Galactic halo or thick disk. The magnetic fields in the disk of our Galaxy and M31 were found to be very extended. The spiral B-field we detected from NGC 2997 suggests that there may be two kinds of dynamos operating in one galaxy.

Han, Jinlin

2001-06-01

229

Observation of low magnetic field density peaks in helicon plasma  

SciTech Connect

Single density peak has been commonly observed in low magnetic field (<100 G) helicon discharges. In this paper, we report the observations of multiple density peaks in low magnetic field (<100 G) helicon discharges produced in the linear helicon plasma device [Barada et al., Rev. Sci. Instrum. 83, 063501 (2012)]. Experiments are carried out using argon gas with m = +1 right helical antenna operating at 13.56 MHz by varying the magnetic field from 0 G to 100 G. The plasma density varies with varying the magnetic field at constant input power and gas pressure and reaches to its peak value at a magnetic field value of {approx}25 G. Another peak of smaller magnitude in density has been observed near 50 G. Measurement of amplitude and phase of the axial component of the wave using magnetic probes for two magnetic field values corresponding to the observed density peaks indicated the existence of radial modes. Measured parallel wave number together with the estimated perpendicular wave number suggests oblique mode propagation of helicon waves along the resonance cone boundary for these magnetic field values. Further, the observations of larger floating potential fluctuations measured with Langmuir probes at those magnetic field values indicate that near resonance cone boundary; these electrostatic fluctuations take energy from helicon wave and dump power to the plasma causing density peaks.

Barada, Kshitish K.; Chattopadhyay, P. K.; Ghosh, J.; Kumar, Sunil; Saxena, Y. C. [Institute for Plasma Research, Bhat, Gandhinagar 382428 (India)

2013-04-15

230

Magnetic Field Effect Transistors.  

National Technical Information Service (NTIS)

It has been demonstrated that magnetic Cr02 can be selectively deposited on semiconductor substrates and polymide resin plastics with feature resolution smaller than micron. In addition, hard coatings have been fabricated to protect active devices as well...

J. T. Spencer P. A. Dowben

1990-01-01

231

Lanthanides as NMR probes of fast molecular dynamics at high magnetic fields and temperature sensors: conformational interconversion of erbium ethylenediaminetetraacetate complexes.  

PubMed

(1)H NMR measurements are reported for D2O solutions of paramagnetic complex [Er(H2O)(EDTA(4-))](-) (I) for temperature interval 273-319 K. Diamagnetic complex [Lu(H2O)(EDTA(4-))](-) (II) was used as an NMR reference compound. The spectra obtained have been analyzed using a band-shape analysis technique in the framework of dynamic NMR (DNMR) taking into account the temperature dependence of lanthanide-induced shifts. Intramolecular dynamics in I was assigned to the interconversion of ?-?E-???? and ?-?E-???? conformers with estimated activation free energy ?G(‡)(298 K) = 50 ± 4 kJ/mol. The methodology of paramagnetic 4f-element probe applications on the example of Er(3+) for the study of free-energy changes in chemical exchange processes, as well as the advantages of this method in comparison with DNMR studies of diamagnetic substances, is discussed. In accordance with the literature reviewed, the fulfilled experimental study is the first example of intramolecular dynamics determination for erbium complexes. An additional advantage of the investigation is in the approach proposed which extends the range of measurement of the NMR rate constants for paramagnetic 4f-element complexes compared to diamagnetic ones. Coordination compounds investigated represent a new type of thermometric NMR sensors and lanthanide paramagnetic probes for in situ temperature control in solutions. PMID:23587055

Babailov, Sergey P; Stabnikov, Pavel A; Zapolotsky, Eugeny N; Kokovkin, Vasily V

2013-05-01

232

Magnetic Fields in the Sun.  

National Technical Information Service (NTIS)

The observed properties of solar magnetic fields are reviewed, with particular reference to the complexities imposed on the field by motions of the highly conducting gas. Turbulent interactions between gas and field lead to heating or cooling of the gas a...

D. J. Mullan

1974-01-01

233

Pattern Formation in a Complex Plasma in High Magnetic Fields  

SciTech Connect

Low-pressure room-temperature neon, argon, krypton, and air plasmas were studied in magnetic fields up to flux densities of 2.3 T. Filaments appeared parallel to the magnetic field lines, and patterns such as spirals and concentric circles formed in the perpendicular direction. We link these effects to the magnetization of the ions. We also used a layer of embedded microparticles as probes in the plasma. Their motion changed dramatically from a collective rotation of the whole ensemble in moderate magnetic fields to a rotation in several small vortices centered at the filaments.

Schwabe, M.; Konopka, U.; Bandyopadhyay, P.; Morfill, G. E. [Max-Planck-Institut fuer extraterrestrische Physik, D-85748 Garching (Germany)

2011-05-27

234

Pattern formation in a complex plasma in high magnetic fields.  

PubMed

Low-pressure room-temperature neon, argon, krypton, and air plasmas were studied in magnetic fields up to flux densities of 2.3 T. Filaments appeared parallel to the magnetic field lines, and patterns such as spirals and concentric circles formed in the perpendicular direction. We link these effects to the magnetization of the ions. We also used a layer of embedded microparticles as probes in the plasma. Their motion changed dramatically from a collective rotation of the whole ensemble in moderate magnetic fields to a rotation in several small vortices centered at the filaments. PMID:21699308

Schwabe, M; Konopka, U; Bandyopadhyay, P; Morfill, G E

2011-05-27

235

Extraordinary optical transmission brightens near-field fiber probe.  

PubMed

Near-field scanning optical microscopy (NSOM) offers high optical resolution beyond the diffraction limit for various applications in imaging, sensing, and lithography; however, for many applications the very low brightness of NSOM aperture probes is a major constraint. Here, we report a novel NSOM aperture probe that gives a 100× higher throughput and 40× increased damage threshold than conventional near-field aperture probes. These brighter probes facilitate near-field imaging of single molecules with apertures as small as 45 nm in diameter. We achieve this improvement by nanostructuring the probe and by employing a novel variant of extraordinary optical transmission, relying solely on a single aperture and a coupled waveguide. Comprehensive electromagnetic simulations show good agreement with the measured transmission spectra. Due to their significantly increased throughput and damage threshold, these resonant configuration probes provide an important step forward for near-field applications. PMID:21175134

Neumann, Lars; Pang, Yuanjie; Houyou, Amel; Juan, Mathieu L; Gordon, Reuven; van Hulst, Niek F

2011-02-01

236

Holographic fermions in external magnetic fields  

NASA Astrophysics Data System (ADS)

We study the Fermi-level structure of 2+1-dimensional strongly interacting electron systems in external magnetic field using the gague/gravity duality correspondence. The gravity dual of a finite density fermion system is a Dirac field in the background of the dyonic AdS-Reissner-Nordström black hole. In the probe limit, the magnetic system can be reduced to the nonmagnetic one, with Landau-quantized momenta and rescaled thermodynamical variables. We find that at strong enough magnetic fields, the Fermi surface vanishes and the quasiparticle is lost either through a crossover to conformal regime or through a phase transition to an unstable Fermi surface. In the latter case, the vanishing Fermi velocity at the critical magnetic field triggers the non-Fermi-liquid regime with unstable quasiparticles and a change in transport properties of the system. We associate it with a metal-”strange-metal” phase transition. Next, we compute the DC Hall and longitudinal conductivities using the gravity-dressed fermion propagators. For dual fermions with a large charge, many different Fermi surfaces contribute and the Hall conductivity is quantized as expected for integer quantum Hall effect (QHE). At strong magnetic fields, as additional Fermi surfaces open up, new plateaus typical for the fractional QHE appear. The somewhat irregular pattern in the length of fractional QHE plateaus resembles the outcomes of experiments on thin graphite in a strong magnetic field. Finally, motivated by the absence of the sign problem in holography, we suggest a lattice approach to the AdS calculations of finite density systems.

Gubankova, E.; Brill, J.; ?ubrovi?, M.; Schalm, K.; Schijven, P.; Zaanen, J.

2011-11-01

237

The role of domain wall forces on thermal-magnetically formed marks in heat-assisted magnetic probe recording  

Microsoft Academic Search

We characterize a method of heat-assisted magnetic recording (HAMR), which may be applied for high-density probe storage system. The magnetic recording medium is a CoNi\\/Pt multilayered film, suitable for perpendicular recording. The heating source is the field emission current from a scanning tunneling microscopy(STM) tip, with pulse voltages added between the tip and the film. Writing shows a threshold voltage

Li Zhang; Xiao-Tao Zu

2006-01-01

238

The polar heliospheric magnetic field  

NASA Technical Reports Server (NTRS)

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

Jokipii, J. R.; Kota, J.

1989-01-01

239

Theorem on magnet fringe field.  

National Technical Information Service (NTIS)

Transverse particle motion in particle accelerators is governed almost totally by non-solenoidal magnets for which the body magnetic field can be expressed as a series expansion of the normal (b(sub n)) and skew (a(sub n)) multipoles, B(sub y) + iB(sub x)...

J. Wei R. Talman

1995-01-01

240

Majorana Neutrinos and Magnetic Fields.  

National Technical Information Service (NTIS)

It is stressed that if neutrinos are massive they are probably of Majorana type. This implies that their magnetic moment form factor vanishes identically so that the previously discussed phenomenon of spin rotation in a magnetic field would not appear to ...

J. Schechter J. W. F. Valle

1981-01-01

241

Voltage response and field reconstruction for a miniature field probe in a spatially nonuniform electric field  

Microsoft Academic Search

A miniature E-field probe employing a 0.6-mm linear dipole antenna has been developed. The authors describe an analytical study of the probe's response to a spatially varying electric field. On the basis of the Nyquist sampling theorem, the spatial sampling frequency at which an electric field should be measured for good reconstruction is established. Using antenna theory, the voltage response

STEVEN D. HARRAH; K. T. Ng; T. E. Batchman

1990-01-01

242

Measuring Earth's Magnetic Field Simply.  

ERIC Educational Resources Information Center

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

Stewart, Gay B.

2000-01-01

243

Neutron in Strong Magnetic Fields  

NASA Astrophysics Data System (ADS)

A relativistic world-line Hamiltonian for strongly interacting 3q systems in a magnetic field is derived from the path integral for the corresponding Green's function. The neutral baryon Hamiltonian in the magnetic field obeys the pseudomomentum conservation and allows a factorization of the c.m. and internal motion. The resulting expression for the baryon mass in the magnetic field is written explicitly with the account of hyperfine, one pion exchange, and one gluon exchange (color Coulomb) interaction. The neutron mass is fast decreasing with the magnetic field, losing 1/2 of its value at eB ˜0.25 GeV2 and is nearly zero at eB ˜0.5 GeV2. Possible physical consequences of the calculated mass trajectory of the neutron, Mn(B), are presented and discussed.

Andreichikov, M. A.; Kerbikov, B. O.; Orlovsky, V. D.; Simonov, Yu. A.

2014-04-01

244

Recent Development of Magnetic Field Measurements on Rotamak  

NASA Astrophysics Data System (ADS)

The new development of magnetic field measurements includes a series of Mirnov array for the study of magnetohydrodynamic (MHD) instability, and a magnetic probe array for the measurement of internal 3-Dimension magnetic field. The system of Mirnov array consists of four sets magnetic pick-up coils located at Z=± 4 cm and Z=± 30 cm along chamber axis; each array is made up of eight BR-oriented coils mounted around the chamber surface at an equal interval of 45^o toroidal angle. The 3-Dimentinal probe array was originally made at RPPL with University of Washington, Seattle; the probe array has a total of 90 windings that can be used to simultaneously measure Br, B?, and Bz at 30 radial positions. The detailed system design which includes the data acquisition system and the primary experimental results will be presented.

Kalaria, Dhara; Goss, Jermain; Yang, Xiaokang; Huang, Tian-Sen

2011-11-01

245

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

246

Solar magnetic fields: an introduction  

Microsoft Academic Search

The magnetic field of the Sun is thought to be produced by a dynamo in the solar interior and exhibits its greatest influence\\u000a on the solar plasma in the tenuous outer layers of the solar atmosphere, where it lies at the heart of almost every major\\u000a phenomenon. Most direct observations of the magnetic field are restricted to the solar surface,

S. K. Solanki

247

Spontaneous thermal magnetic field fluctuation  

SciTech Connect

In recent days, the relativistic version of the classic Weibel instability received renewed attention for its potential role as a mechanism to generate cosmic magnetic fields. However, one of the key conceptual foundations in association with the Weibel instability has not been addressed in the literature. Namely, the spontaneous emission of magnetic field fluctuation, which is supposed to provide the seed perturbation for the Weibel instability, has not been adequately discussed. The present Brief Communication addresses this issue.

Yoon, Peter H. [Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States)

2007-06-15

248

A new probe for measuring small electric fields in plasmas  

NASA Technical Reports Server (NTRS)

A dipolar double probe has been developed for in situ measurements of small electric fields in laboratory plasmas. The probe measures dc to ac electric fields (f values between 0 and 20 MHz) with high sensitivity (Emin about 10 microV/cm) and responds to both space charge electric fields and inductive electric fields. Using voltage-to-frequency conversion, the probe signal is obtained free of errors and loading effects by a transmission line. Various examples of useful applications for the new probe are presented, such as measurements of dc ambipolar fields, ac space-charge fields of ion acoustic waves, ac inductive fields of whistler waves, and mixed inductive and space-charge electric fields in current-carrying magnetoplasmas.

Stenzel, R. L.

1991-01-01

249

Near-Field Optical Microscopy and Spectroscopy with Pointed Probes.  

National Technical Information Service (NTIS)

In recent years, developments in near-field techniques exploiting far-field illumination of a pointed, apertureless probe have demonstrated a newfound excitement. This is due in part to the advantages afforded by apertureless techniques that allow for the...

L. Novotny S. J. Stranick

2006-01-01

250

Theorem on magnet fringe field  

SciTech Connect

Transverse particle motion in particle accelerators is governed almost totally by non-solenoidal magnets for which the body magnetic field can be expressed as a series expansion of the normal (b{sub n}) and skew (a{sub n}) multipoles, B{sub y} + iB{sub x} = {summation}(b{sub n} + ia{sub n})(x + iy){sup n}, where x, y, and z denote horizontal, vertical, and longitudinal (along the magnet) coordinates. Since the magnet length L is necessarily finite, deflections are actually proportional to ``field integrals`` such as {bar B}L {equivalent_to} {integral} B(x,y,z)dz where the integration range starts well before the magnet and ends well after it. For {bar a}{sub n}, {bar b}{sub n}, {bar B}{sub x}, and {bar B}{sub y} defined this way, the same expansion Eq. 1 is valid and the ``standard`` approximation is to neglect any deflections not described by this expansion, in spite of the fact that Maxwell`s equations demand the presence of longitudinal field components at the magnet ends. The purpose of this note is to provide a semi-quantitative estimate of the importance of {vert_bar}{Delta}p{sub {proportional_to}}{vert_bar}, the transverse deflection produced by the ion-gitudinal component of the fringe field at one magnet end relative to {vert_bar}{Delta}p{sub 0}{vert_bar}, the total deflection produced by passage through the whole magnet. To emphasize the generality and simplicity of the result it is given in the form of a theorem. The essence of the proof is an evaluation of the contribution of the longitudinal field B{sub x} from the vicinity of one magnet end since, along a path parallel to the magnet axis such as path BC.

Wei, Jie [Brookhaven National Lab., Upton, NY (United States); Talman, R. [Cornell Univ., Ithaca, NY (United States). Lab. of Nuclear Studies

1995-12-31

251

Chiral transition with magnetic fields  

NASA Astrophysics Data System (ADS)

We study the nature of the chiral transition for an effective theory with spontaneous breaking of symmetry, where charged bosons and fermions are subject to the effects of a constant external magnetic field. The problem is studied in terms of the relative intensity of the magnetic field with respect to the mass and the temperature. When the former is the smallest of the scales, we present a suitable method to obtain magnetic and thermal corrections up to ring order at high temperature. By these means, we solve the problem of the instability in the boson sector for these theories, where the squared masses—taken as functions of the order parameter—can vanish and even become negative. The solution is found by considering the screening properties of the plasma, encoded in the resummation of the ring diagrams at high temperature. We also study the case where the magnetic field is the intermediate of the three scales and explore the nature of the chiral transition as we vary the field strength, the coupling constants, and the number of fermions. We show that the critical temperature for the restoration of chiral symmetry monotonically increases from small to intermediate values of the magnetic field and that this temperature is always above the critical temperature for the case when the magnetic field is absent.

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

2014-06-01

252

Magnetic field analysis and optimal design of magnetic bearing  

Microsoft Academic Search

Magnetic field distribution of a radial magnetic bearing with sixteen-pole was analyzed by using finite element method. It was verified by magnetic field measurement. Magnetic bearing structure was optimized based on finite element analysis (FEA) and magnetic circuit method. Optimization was done in object of maximum magnetic force. Two optimizations had similar results. Analysis showed that FEA-based optimization is more

Han Wu; Chunguang Xu; Dingguo Xiao; Juan Hao

2009-01-01

253

Dynamic nuclear polarization at high magnetic fields  

PubMed Central

Dynamic nuclear polarization (DNP) is a method that permits NMR signal intensities of solids and liquids to be enhanced significantly, and is therefore potentially an important tool in structural and mechanistic studies of biologically relevant molecules. During a DNP experiment, the large polarization of an exogeneous or endogeneous unpaired electron is transferred to the nuclei of interest (I) by microwave (?w) irradiation of the sample. The maximum theoretical enhancement achievable is given by the gyromagnetic ratios (?e/?l), being ?660 for protons. In the early 1950s, the DNP phenomenon was demonstrated experimentally, and intensively investigated in the following four decades, primarily at low magnetic fields. This review focuses on recent developments in the field of DNP with a special emphasis on work done at high magnetic fields (?5 T), the regime where contemporary NMR experiments are performed. After a brief historical survey, we present a review of the classical continuous wave (cw) DNP mechanisms—the Overhauser effect, the solid effect, the cross effect, and thermal mixing. A special section is devoted to the theory of coherent polarization transfer mechanisms, since they are potentially more efficient at high fields than classical polarization schemes. The implementation of DNP at high magnetic fields has required the development and improvement of new and existing instrumentation. Therefore, we also review some recent developments in ?w and probe technology, followed by an overview of DNP applications in biological solids and liquids. Finally, we outline some possible areas for future developments.

Maly, Thorsten; Debelouchina, Galia T.; Bajaj, Vikram S.; Hu, Kan-Nian; Joo, Chan-Gyu; Mak-Jurkauskas, Melody L.; Sirigiri, Jagadishwar R.; van der Wel, Patrick C. A.; Herzfeld, Judith; Temkin, Richard J.; Griffin, Robert G.

2009-01-01

254

Dynamic nuclear polarization at high magnetic fields.  

PubMed

Dynamic nuclear polarization (DNP) is a method that permits NMR signal intensities of solids and liquids to be enhanced significantly, and is therefore potentially an important tool in structural and mechanistic studies of biologically relevant molecules. During a DNP experiment, the large polarization of an exogeneous or endogeneous unpaired electron is transferred to the nuclei of interest (I) by microwave (microw) irradiation of the sample. The maximum theoretical enhancement achievable is given by the gyromagnetic ratios (gamma(e)gamma(l)), being approximately 660 for protons. In the early 1950s, the DNP phenomenon was demonstrated experimentally, and intensively investigated in the following four decades, primarily at low magnetic fields. This review focuses on recent developments in the field of DNP with a special emphasis on work done at high magnetic fields (> or =5 T), the regime where contemporary NMR experiments are performed. After a brief historical survey, we present a review of the classical continuous wave (cw) DNP mechanisms-the Overhauser effect, the solid effect, the cross effect, and thermal mixing. A special section is devoted to the theory of coherent polarization transfer mechanisms, since they are potentially more efficient at high fields than classical polarization schemes. The implementation of DNP at high magnetic fields has required the development and improvement of new and existing instrumentation. Therefore, we also review some recent developments in microw and probe technology, followed by an overview of DNP applications in biological solids and liquids. Finally, we outline some possible areas for future developments. PMID:18266416

Maly, Thorsten; Debelouchina, Galia T; Bajaj, Vikram S; Hu, Kan-Nian; Joo, Chan-Gyu; Mak-Jurkauskas, Melody L; Sirigiri, Jagadishwar R; van der Wel, Patrick C A; Herzfeld, Judith; Temkin, Richard J; Griffin, Robert G

2008-02-01

255

Magnetic fields in quiescent prominences  

SciTech Connect

The origin of the axial fields in high-latitude quiescent prominences is considered. The fact that almost all quiescent prominences obey the same hemisphere-dependent rule strongly suggests that the solar differential rotation plays an important role in producing the axial fields. However, the observations are inconsistent with the hypothesis that the axial fields are produced by differential rotation acting on an existing coronal magnetic field. Several possible explanations for this discrepancy are considered. The possibility that the sign of the axial field depends on the topology of the magnetic field in which the prominence is embedded is examined, as is the possibility that the neutral line is tilted with respect to the east-west direction, so that differential rotation causes the neutral line also to rotate with time. The possibility that the axial fields of quiescent prominences have their origin below the solar surface is also considered. 29 refs.

Van Ballegooijen, A.A.; Martens, P.C.H. (Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (USA))

1990-09-01

256

Large Dayside Geosynchronous Magnetic Field Compressions: Model Expectations vs. Observations  

Microsoft Academic Search

The geosynchronous magnetic field has been measured routinely for nearly 40 years. It responds to the magnetosphere's major current systems including the magnetopause current, the ring current, field-aligned currents, and the tail current. As a consequence, these measurements are valuable for probing many aspects of solar wind-magnetosphere coupling. In this presentation we will show puzzling observations of large-amplitude dayside magnetic

H. J. Singer; M. J. Wiltberger; T. G. Onsager; P. T. Loto'Ainu

2008-01-01

257

Ultracold plasma dynamics in a magnetic field  

NASA Astrophysics Data System (ADS)

Plasmas, often called the fourth state of matter and the most common one in the universe, have parameters varying by many orders of magnitude, from temperature of a few hundred kelvin in the Earth's ionosphere to 10 16 K in the magnetosphere of a pulsar. Ultracold plasmas, produced by photoionizing a sample of laser-cooled and trapped atoms near the ionization limit, have extended traditional neutral plasma parameters by many orders of magnitude, to electron temperatures below 1 K and ion temperatures in the tens of muK to a few Kelvin, and densities of 105 cm -3 to 1010 cm-3. These plasmas thus provide a testing ground to study basic plasma theory in a clean and simple system with or without a magnetic field. Previous studies of ultracold plasmas have primarily concentrated on temperature measurements, collective modes and expansion dynamics in the absence of magnetic fields. This thesis presents the first study of ultracold plasma dynamics in a magnetic field. The presence of a magnetic field during the expansion can initiate various phenomena, such as plasma confinement and plasma instabilities. While the electron temperatures are very low in ultracold plasmas, we need only tens of Gauss of magnetic field to observe significant effects on the expansion dynamics. To probe the ultraocold plasma dynamics in a magnetic field, we developed a new diagnostic - projection imaging, which images the ion distribution by extracting the ions with a high voltage pulse onto a position-sensitive detector. Early in the lifetime of the plasma (< 20 mus), the size of the image is dominated by the time-of-flight Coulomb explosion of the dense ion cloud. For later times, we measure the 2-D Gaussian width of the ion image, obtaining the transverse expansion velocity as a function of magnetic field (up to 70 G), and observe that the transverse expansion velocity scales as B-1/2, explained by a nonlinear ambipolar diffusion model that involes anisotropic diffusion in two different directions. We also present the first observation of a plasma instability in an expanding ultracold plasma. We observe periodic emission of electrons from an ultracold plasma in weak, crossed magnetic and electric fields, and a strong perturbed electron density distribution in electron time-of-flight projection images. We identify this instability as a high-frequency electron drift instability due to the coupling between the electron drift wave and electron cyclotron harmonic, which has large wavenumbers corresponding to wavelengths close to the electron gyroradius.

Zhang, Xianli

258

MAGNETIC FIELD MEASUREMENTS FOR FAST-CHANGING MAGNETIC FIELDS.  

SciTech Connect

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

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

2004-10-03

259

Magnetic fields in neutron stars  

NASA Astrophysics Data System (ADS)

This work aims at studying how magnetic fields affect the observational properties and the long-term evolution of isolated neutron stars, which are the strongest magnets in the universe. The extreme physical conditions met inside these astronomical sources complicate their theoretical study, but, thanks to the increasing wealth of radio and X-ray data, great advances have been made over the last years. A neutron star is surrounded by magnetized plasma, the so-called magnetosphere. Modeling its global configuration is important to understand the observational properties of the most magnetized neutron stars, magnetars. On the other hand, magnetic fields in the interior are thought to evolve on long time-scales, from thousands to millions of years. The magnetic evolution is coupled to the thermal one, which has been the subject of study in the last decades. An important part of this thesis presents the state-of-the-art of the magneto-thermal evolution models of neutron stars during the first million of years, studied by means of detailed simulations. The numerical code here described is the first one to consistently consider the coupling of magnetic field and temperature, with the inclusion of both the Ohmic dissipation and the Hall drift in the crust.

Viganò, Daniele

2013-09-01

260

Magnetically insulated baffled probe for real-time monitoring of equilibrium and fluctuating values of space potentials, electron and ion temperatures, and densities  

SciTech Connect

By restricting the electron-collection area of a cold Langmuir probe compared to the ion-collection area, the probe floating potential can become equal to the space potential, and thus conveniently monitored, rather than to a value shifted from the space potential by an electron-temperature-dependent offset, i.e., the case with an equal-collection-area probe. This design goal is achieved by combining an ambient magnetic field in the plasma with baffles, or shields, on the probe, resulting in species-selective magnetic insulation of the probe collection area. This permits the elimination of electron current to the probe by further adjustment of magnetic insulation which results in an ion-temperature-dependent offset when the probe is electrically floating. Subtracting the floating potential of two magnetically insulated baffled probes, each with a different degree of magnetic insulation, enables the electron or ion temperature to be measured in real time.

Demidov, V. I.; Koepke, M. E. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States); Raitses, Y. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

2010-10-15

261

Design and use of an Elsässer probe for analysis of Alfvén wave fields according to wave direction  

NASA Astrophysics Data System (ADS)

We have designed an electric and magnetic field probe which simultaneously measure both quantities in the directions perpendicular to the background magnetic field for application to Alfvén wave experiments in the Large Plasma Device at UCLA. This new probe allows for the projection of measured wave fields onto generalized Elsässer variables. Experiments were conducted in a singly ionized He plasma at 1850 G in which propagation of Alfvén waves was observed using this new probe. We demonstrate that a clear separation of transmitted and reflected signals and determination of Poynting flux and Elsässer variables can be achieved.

Drake, D. J.; Kletzing, C. A.; Skiff, F.; Howes, G. G.; Vincena, S.

2011-10-01

262

Alternating magnetic field assisted magnetization reversal in ferromagnetic antidot  

NASA Astrophysics Data System (ADS)

Although the effects of high-frequency electromagnetic waves on magnetization reversal have been extensively studied, the influence of a low-frequency ac field on magnetization reversal has seldom been examined. In this study, we measured the magnetoresistance and examined the magnetic switching process of Permalloy antidot thin films under an alternating magnetic field with a frequency of 25 kHz. When no alternating magnetic field was present, the transitional field of the antidot thin films decreased as the angle of the direct magnetic field increased. When an alternating magnetic field was present, the transitional field exhibited the same trend. We compared the magnetization process of the antidot thin films with and without the alternating magnetic field and determined that the alternating field can facilitate the transition of magnetization, specifically, by lowering the transitional field with the highest variation rate (33.73%).

Huang, Hao-Ting; Ger, Tzong-Rong; Huang, Chen-Yu; Liao, Kuei-Tien; Wang, Pei-Jen; Lai, Jun-Yang; Chen, Jiann-Yeu; Lai, Mei-Feng

2014-05-01

263

Helical magnetic fields from sphaleron decay and baryogenesis.  

PubMed

Many models of baryogenesis rely on anomalous particle physics processes to give baryon number violation. By numerically evolving the electroweak equations on a lattice, we show that baryogenesis in these models creates helical cosmic magnetic fields, though the helicity created is smaller than earlier analytical estimates. After a transitory period, electroweak dynamics is found to conserve the Chern-Simons number and the total electromagnetic helicity. We argue that baryogenesis could lead to magnetic fields of nano-Gauss strength today on astrophysical length scales. In addition to being astrophysically relevant, such helical magnetic fields can provide an independent probe of baryogenesis and CP violation in particle physics. PMID:18999736

Copi, Craig J; Ferrer, Francesc; Vachaspati, Tanmay; Achúcarro, Ana

2008-10-24

264

High-field magnets and high-field superconductors  

Microsoft Academic Search

This paper gives a brief historical review of the development of high magnetic fields and high field superconductors including brief summaries of the early developments of high magnetic fields and the Francis Bitter National Magnet Laboratory (FBNML). The start of the first revolution (when large critical currents in Nb3Sn were observed in high magnetic fields) and the development of practical

Simon Foner; Francis Bitter

1995-01-01

265

Tapered photoconductive terahertz field probe tip with subwavelength spatial resolution  

NASA Astrophysics Data System (ADS)

In this work a photoconductive probe tip applicable for near- and far-field measurements in the terahertz frequency regime is demonstrated as a powerful alternative to existing terahertz scanning near-field optical microscopy approaches. The probe tip is based on a triangular-shaped patch of freestanding low-temperature-grown GaAs of only 1.3 ?m thickness with a pair of tapered metallic wires on top. Using nonresonant electric field enhancement at the tip of the probing device, 10 ?m wide metallic structures are spatially resolved and a bandwidth of 2 THz is demonstrated.

Wächter, Markus; Nagel, Michael; Kurz, Heinrich

2009-07-01

266

Magnetic Fields in Irregular Galaxies: NGC 4214  

Microsoft Academic Search

Magnetic fields are an important component of the interstellar medium of galaxies. They provide support, transfer energy from supernovae, provide a possible heating mechanism, and channel gas flows (Beck 2004). Despite the importance of magnetic fields in the ISM, it is not well known what generates and sustains galactic magnetic fields or how magnetic fields, gas, and stars interact in

Amanda A. Kepley; E. M. Wilcots; T. Robishaw; C. Heiles; E. Zweibel

2006-01-01

267

Solar magnetic fields - The Italian contribution  

Microsoft Academic Search

A short account is given of the methods of observation, the characteristics of solar magnetic fields, the relationships between velocity and magnetic fields, the theoretical approaches, and the possibilities opened by studies of stellar activity of the solar type. In discussing the classification and characteristics of solar magnetic fields, attention is given to normal bipolar regions, large-scale unipolar magnetic fields,

D. Fabbri; G. Godoli; F. Mazzucconi

1982-01-01

268

Progress in Solar Magnetic Field Extrapolation  

Microsoft Academic Search

Solar magnetic field is the predominant factor of the solar activities. Precise measurements of solar magnetic fields so far are still confined to the thin layer of the solar photosphere. In order to understand the nature of the coronal magnetic fields, it becomes necessary to extrapolate the coronal magnetic fields based on theoretical models using observed photospheric magnetograms as boundary

Juan Hao; Mei Zhang

2007-01-01

269

Satellite to study earth's magnetic field  

NASA Technical Reports Server (NTRS)

The Magnetic Field Satellite (Magsat) designed to measure the near earth magnetic field and crustal anomalies is briefly described. A scalar magnetometer to measure the magnitude of the earth's crustal magnetic field and a vector magnetometer to measure magnetic field direction as well as magnitude are included. The mission and its objectives are summarized along with the data collection and processing system.

1979-01-01

270

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

271

Deflections in magnet fringe fields.  

PubMed

A transverse multipole expansion is derived, including the longitudinal components necessarily present in regions of varying magnetic field profile. It can be used for exact numerical orbit following through the fringe-field regions of magnets whose end designs introduce no extraneous components, i.e., fields not required to be present by Maxwell's equations. Analytic evaluations of the deflections are obtained in various approximations. Mainly emphasized is a "straight-line approximation," in which particle orbits are treated as straight lines through the fringe-field regions. This approximation leads to a readily-evaluated figure of merit, the ratio of rms end deflection to nominal body deflection, that can be used to determine whether or not a fringe field can be neglected. Deflections in "critical" cases (e.g., near intersection regions) are analyzed in the same approximation. PMID:12786502

Papaphilippou, Y; Wei, J; Talman, R

2003-04-01

272

In situ magnetic compensation for potassium spin-exchange relaxation-free magnetometer considering probe beam pumping effect  

NASA Astrophysics Data System (ADS)

A novel method to compensate the residual magnetic field for an atomic magnetometer consisting of two perpendicular beams of polarizations was demonstrated in this paper. The method can realize magnetic compensation in the case where the pumping rate of the probe beam cannot be ignored. In the experiment, the probe beam is always linearly polarized, whereas, the probe beam contains a residual circular component due to the imperfection of the polarizer, which leads to the pumping effect of the probe beam. A simulation of the probe beam's optical rotation and pumping rate was demonstrated. At the optimized points, the wavelength of the probe beam was optimized to achieve the largest optical rotation. Although, there is a small circular component in the linearly polarized probe beam, the pumping rate of the probe beam was non-negligible at the optimized wavelength which if ignored would lead to inaccuracies in the magnetic field compensation. Therefore, the dynamic equation of spin evolution was solved by considering the pumping effect of the probe beam. Based on the quasi-static solution, a novel magnetic compensation method was proposed, which contains two main steps: (1) the non-pumping compensation and (2) the sequence compensation with a very specific sequence. After these two main steps, a three-axis in situ magnetic compensation was achieved. The compensation method was suitable to design closed-loop spin-exchange relaxation-free magnetometer. By a combination of the magnetic compensation and the optimization, the magnetic field sensitivity was approximately 4 fT/Hz1/2, which was mainly dominated by the noise of the magnetic shield.

Fang, Jiancheng; Wang, Tao; Quan, Wei; Yuan, Heng; Zhang, Hong; Li, Yang; Zou, Sheng

2014-06-01

273

Detecting Solar Axions Using Earth's Magnetic Field  

SciTech Connect

We show that solar axion conversion to photons in the Earth's magnetosphere can produce an x-ray flux, with average energy <{omega}>{approx_equal}4 keV, which is measurable on the dark side of the Earth. The smallness of the Earth's magnetic field is compensated by a large magnetized volume. For axion masses m{sub a}(less-or-similar sign)10{sup -4} eV, a low-Earth-orbit x-ray detector with an effective area of 10{sup 4} cm{sup 2}, pointed at the solar core, can probe the photon-axion coupling down to 10{sup -11} GeV{sup -1}, in 1 yr. Thus, the sensitivity of this new approach will be an order of magnitude beyond current laboratory limits.

Davoudiasl, Hooman; Huber, Patrick [Department of Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States)

2006-10-06

274

Detecting solar axions using Earth's magnetic field.  

PubMed

We show that solar axion conversion to photons in the Earth's magnetosphere can produce an x-ray flux, with average energy omega approximately 4 keV, which is measurable on the dark side of the Earth. The smallness of the Earth's magnetic field is compensated by a large magnetized volume. For axion masses m(a) less, similar10(-4) eV, a low-Earth-orbit x-ray detector with an effective area of 10(4) cm(2), pointed at the solar core, can probe the photon-axion coupling down to 10(-11) GeV-1, in 1 yr. Thus, the sensitivity of this new approach will be an order of magnitude beyond current laboratory limits. PMID:17155238

Davoudiasl, Hooman; Huber, Patrick

2006-10-01

275

Magnetic field tomography, helical magnetic fields and Faraday depolarization  

NASA Astrophysics Data System (ADS)

Wide-band radio polarization observations offer the possibility to recover information about the magnetic fields in synchrotron sources, such as details of their three-dimensional configuration, that has previously been inaccessible. The key physical process involved is the Faraday rotation of the polarized emission in the source (and elsewhere along the wave's propagation path to the observer). In order to proceed, reliable methods are required for inverting the signals observed in wavelength space into useful data in Faraday space, with robust estimates of their uncertainty. In this paper, we examine how variations of the intrinsic angle of polarized emission ?0 with the Faraday depth ? within a source affect the observable quantities. Using simple models for the Faraday dispersion F(?) and ?0(?), along with the current and planned properties of the main radio interferometers, we demonstrate how degeneracies among the parameters describing the magneto-ionic medium can be minimized by combining observations in different wavebands. We also discuss how depolarization by Faraday dispersion due to a random component of the magnetic field attenuates the variations in the spectral energy distribution of the polarization and shifts its peak towards shorter wavelengths. This additional effect reduces the prospect of recovering the characteristics of the magnetic field helicity in magneto-ionic media dominated by the turbulent component of the magnetic field.

Horellou, C.; Fletcher, A.

2014-07-01

276

Probing Gravitational Sensitivity in Biological Systems Using Magnetic Body Forces  

NASA Technical Reports Server (NTRS)

At Brown University, we are developing the use of magnetic body forces as a means to simulate variable gravity body forces on biological systems. This tool promises new means to probe gravi-sensing and the gravi-response of biological systems. It also has the potential as a technique for screening future systems for space flight experiments.

Guevorkian, Karine; Wurzel, Sam; Mihalusova, Mariana; Valles, Jim

2003-01-01

277

A magnetically driven oscillating probe microscope for operation in liquids  

Microsoft Academic Search

Oscillating probe atomic force microscopy in fluids is simplified when an oscillating force is applied directly to a magnetized cantilever using a solenoid. The response of the detector is simpler than that obtained with acoustic excitation. Reliable operation over a broad frequency range is achieved with excitation amplitudes of a few nm. This lower amplitude appears to facilitate imaging by

Wenhai Han; S. M. Lindsay; Tianwei Jing

1996-01-01

278

Distinguishing magnetic and electrostatic interactions by a Kelvin probe force microscopy-magnetic force microscopy combination  

PubMed Central

Summary The most outstanding feature of scanning force microscopy (SFM) is its capability to detect various different short and long range interactions. In particular, magnetic force microscopy (MFM) is used to characterize the domain configuration in ferromagnetic materials such as thin films grown by physical techniques or ferromagnetic nanostructures. It is a usual procedure to separate the topography and the magnetic signal by scanning at a lift distance of 25–50 nm such that the long range tip–sample interactions dominate. Nowadays, MFM is becoming a valuable technique to detect weak magnetic fields arising from low dimensional complex systems such as organic nanomagnets, superparamagnetic nanoparticles, carbon-based materials, etc. In all these cases, the magnetic nanocomponents and the substrate supporting them present quite different electronic behavior, i.e., they exhibit large surface potential differences causing heterogeneous electrostatic interaction between the tip and the sample that could be interpreted as a magnetic interaction. To distinguish clearly the origin of the tip–sample forces we propose to use a combination of Kelvin probe force microscopy (KPFM) and MFM. The KPFM technique allows us to compensate in real time the electrostatic forces between the tip and the sample by minimizing the electrostatic contribution to the frequency shift signal. This is a great challenge in samples with low magnetic moment. In this work we studied an array of Co nanostructures that exhibit high electrostatic interaction with the MFM tip. Thanks to the use of the KPFM/MFM system we were able to separate the electric and magnetic interactions between the tip and the sample.

Jaafar, Miriam; Iglesias-Freire, Oscar; Serrano-Ramon, Luis; Ibarra, Manuel Ricardo; de Teresa, Jose Maria

2011-01-01

279

Intergalactic Magnetic Fields, and Some Connections with Cosmic Rays  

NASA Astrophysics Data System (ADS)

An overview is presented of the methods of probing for the geometry, and strength of intergalactic magnetic fields. Recent results are briefly surveyed for galaxy halos, galaxy clusters, and the intergalactic medium on various scales, and some rele vant physical processes and radiation processes are mentioned, as well as the “coupling” between intergalactic magnetic fields and cosmic rays. The general trend of recent results indicates that, wherever we detect intergalactic hot gas and galaxies, we also find magnetic fields at levels of ˜ 10-7 G, or higher. The hitherto undetected, weaker fields in the ratified i.g.m. and in large intergalactic voids could be probed by both Faraday rotation, and possibly using very energetic CR nuclei (> 1020eV), and/or transient extragalactic ? ray bursts.

Kronberg, Philipp P.

1996-01-01

280

Formation of Magnetic Particle Chains in Ultra High Magnetic Field  

Microsoft Academic Search

Magnetic particles form chain-like clusters in the magnetic field. This phenomenon is of interest in two separate fields, one is a development system of the laser printer and another is an electromagnetic manipulation of biological cells. Experiments on the chain formation in air and oil have been performed in the ultra high magnetic field created by a superconducting magnet. It

Hiroyuki Kawamoto; Masatomo Teshima; Hiroyuki Takahashi; Nobuyuki Nakayama; Noriyuki Hirota

2007-01-01

281

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

282

Dynamic Pressure Probes Developed for Supersonic Flow-Field Measurements  

NASA Technical Reports Server (NTRS)

A series of dynamic flow-field pressure probes were developed for use in large-scale supersonic wind tunnels at the NASA Glenn Research Center. These flow-field probes include pitot and static pressure probes that can capture fast-acting flow-field pressure transients occurring on a millisecond timescale. The pitot and static probes can be used to determine local Mach number time histories during a transient event. The flow-field pressure probe contains four major components: 1) Static pressure aerodynamic tip; 2) Pressure-sensing cartridge assembly; 3) Pitot pressure aerodynamic tip; 4) Mounting stem. This modular design allows for a variety of probe tips to be used for a specific application. Here, the focus is on flow-field pressure measurements in supersonic flows, so we developed a cone-cylinder static pressure tip and a pitot pressure tip. Alternatively, probe tips optimized for subsonic and transonic flows could be used with this design. The pressure-sensing cartridge assembly allows the simultaneous measurement of steady-state and transient pressure which allows continuous calibration of the dynamic pressure transducer.

Porro, A. Robert

2001-01-01

283

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.

284

Magnetic Fields of the Earth and Sun  

NSDL National Science Digital Library

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

285

X-ray detected magnetic resonance: a unique probe of the precession dynamics of orbital magnetization components.  

PubMed

X-ray Detected Magnetic Resonance (XDMR) is a novel spectroscopy in which X-ray Magnetic Circular Dichroism (XMCD) is used to probe the resonant precession of local magnetization components in a strong microwave pump field. We review the conceptual bases of XDMR and recast them in the general framework of the linear and nonlinear theories of ferromagnetic resonance (FMR). Emphasis is laid on the information content of XDMR spectra which offer a unique opportunity to disentangle the precession dynamics of spin and orbital magnetization components at given absorbing sites. For the sake of illustration, we focus on selected examples in which marked differences were found between FMR and XDMR spectra simultaneously recorded on ferrimagnetically ordered iron garnets. With pumping capabilities extended up to sub-THz frequencies, high-field XDMR should allow us to probe the precession of orbital magnetization components in paramagnetic organometallic complexes with large zero-field splitting. Even more challenging, we suggest that XDMR spectra might be recorded on selected antiferromagnetic crystals for which orbital magnetism is most often ignored in the absence of any supporting experimental evidence. PMID:22272105

Goulon, Jo?e; Rogalev, Andrei; Goujon, Gérard; Wilhelm, Fabrice; Ben Youssef, Jamal; Gros, Claude; Barbe, Jean-Michel; Guilard, Roger

2011-01-01

286

X-Ray Detected Magnetic Resonance: A Unique Probe of the Precession Dynamics of Orbital Magnetization Components  

PubMed Central

X-ray Detected Magnetic Resonance (XDMR) is a novel spectroscopy in which X-ray Magnetic Circular Dichroism (XMCD) is used to probe the resonant precession of local magnetization components in a strong microwave pump field. We review the conceptual bases of XDMR and recast them in the general framework of the linear and nonlinear theories of ferromagnetic resonance (FMR). Emphasis is laid on the information content of XDMR spectra which offer a unique opportunity to disentangle the precession dynamics of spin and orbital magnetization components at given absorbing sites. For the sake of illustration, we focus on selected examples in which marked differences were found between FMR and XDMR spectra simultaneously recorded on ferrimagnetically ordered iron garnets. With pumping capabilities extended up to sub-THz frequencies, high-field XDMR should allow us to probe the precession of orbital magnetization components in paramagnetic organometallic complexes with large zero-field splitting. Even more challenging, we suggest that XDMR spectra might be recorded on selected antiferromagnetic crystals for which orbital magnetism is most often ignored in the absence of any supporting experimental evidence.

Goulon, Jose; Rogalev, Andrei; Goujon, Gerard; Wilhelm, Fabrice; Ben Youssef, Jamal; Gros, Claude; Barbe, Jean-Michel; Guilard, Roger

2011-01-01

287

Novel rotating field probe for inspection of tubes  

NASA Astrophysics Data System (ADS)

Inspection of steam generator tubes in nuclear power plants is extremely critical for safe operation of the power plant. In the nuclear industry, steam generator tube inspection using eddy current techniques has evolved over the years from a single bobbin coil, to rotating probe coil (RPC) and array probe, in an attempt to improve the speed and reliability of inspection. The RPC probe offers the accurate spatial resolution but involves complex mechanical rotation. This paper presents a novel design of eddy current probes based on rotating fields produced by three identical coils excited by a balanced three-phase supply. The sensor thereby achieves rotating probe functionality by electronic means and eliminates the need for mechanical rotation. The field generated by the probe is largely radial that result in induced currents that flow circularly around the radial axis and rotating around the tube at a synchronous speed effectively producing induced eddy currents that are multidirectional. The probe will consequently be sensitive to cracks of all orientations in the tube wall. The finite element model (FEM) results of the rotating fields and induced currents are presented. A prototype probe is being built to validate simulation results.

Xin, J.; Tarkleson, E.; Lei, N.; Udpa, L.; Udpa, S. S.

2012-05-01

288

BEC manipulation with fictitious magnetic fields  

Microsoft Academic Search

The interaction of Bose-Einstein condensate (BEC) atoms with counterpropagating laser beams can often be represented by fictitious magnetic fields [1]. These fictitious fields can be combined with ordinary magnetic fields to produce total fields whose amplitudes vary in space on the scale of the laser wavelength. When the strengths of such magnetic fields are positioned in the neighborhood of a

Jeffrey Heward; Mark Edwards; Charles W. Clark

2010-01-01

289

Flares and changing magnetic fields  

Microsoft Academic Search

An observational study of maps of the longitudinal component of the photospheric fields in flaring active regions leads to the following conclusions:(1)The broad-wing Ha kernels characteristic of the impulsive phase of flares occur within 10? of neutral lines encircling features of isolated magnetic polarity (‘satellite sunspots’).(2)Photospheric field changes intimately associated with several importance 1 flares and one importance 2B flare

David M. Rust

1972-01-01

290

Magnetism and magnetic materials probed with neutron scattering  

NASA Astrophysics Data System (ADS)

Neutron scattering techniques are becoming increasingly accessible to a broader range of scientific communities, in part due to the onset of next-generation, high-power spallation sources, high-performance, sophisticated instruments and data analysis tools. These technical advances also advantageously impact research into magnetism and magnetic materials, where neutrons play a major role. In this Current Perspective series, the achievements and future prospects of elastic and inelastic neutron scattering, polarized neutron reflectometry, small angle neutron scattering, and neutron imaging, are highlighted as they apply to research into magnetic frustration, superconductivity and magnetism at the nanoscale.

te Velthuis, S. G. E.; Pappas, C.

2014-01-01

291

Optically Modulated Probe for Precision Near-Field Measurements  

Microsoft Academic Search

In this paper, the design and implementation of an accurate, sensitive, and cost-effective near-field (NF) probe are discussed. The probe is based on the modulated scatterer technique (MST), providing very low perturbation on the field to be measured. It consists of a commercial off-the-shelf (COTS) photodiode chip and an antenna acting as a scatterer. The optically modulated scatterer (OMS) essentially

Jean-Jacques Laurin; Raman Kashyap

2010-01-01

292

Local magnetism in palladium bionanomaterials probed by muon spectroscopy.  

PubMed

Palladium bionanomaterial was manufactured using the sulfate-reducing bacterium, Desulfovibrio desulfuricansm, to reduce soluble Pd(II) ions to cell-bound Pd(0) in the presence of hydrogen. The biomaterial was examined using a Superconducting Quantum Interference Device (SQUID) to measure bulk magnetisation and by Muon Spin Rotation Spectroscopy (µSR) which is uniquely able to probe the local magnetic environment inside the sample. Results showed behaviour attributable to interaction of muons both with palladium electrons and the nuclei of hydrogen trapped in the particles during manufacture. Electronic magnetism, also suggested by SQUID, is not characteristic of bulk palladium and is consistent with the presence of nanoparticles previously seen in electron micrographs. We show the first use of ?SR as a tool to probe the internal magnetic environment of a biologically-derived nanocatalyst material. PMID:21331587

Creamer, Neil J; Mikheenko, Iryna P; Johnson, Clive; Cottrell, Stephen P; Macaskie, Lynne E

2011-05-01

293

Ohm's Law for Mean Magnetic Fields.  

National Technical Information Service (NTIS)

The magnetic fields associated with plasmas frequently exhibit small amplitude MHD fluctuations. It is useful to have equations for the magnetic field averaged over these fluctuations, the so-called mean field equations. Under very general assumptions it ...

A. H. Boozer

1986-01-01

294

Near-field multiphoton nanolithography using an apertureless optical probe  

Microsoft Academic Search

Near-field multiphoton optical lithography is demonstrated by using ~120 fs laser pulses at 790 nm in an apertureless near-field optical microscope, which produce the lithographic features with ~ 70 nm resolution. The technique takes advantage of the field enhancement at the extremity of a metallic probe to induce nanoscale multiphoton absorption and polymerization in a commercial photoresist, SU-8. Even without

Xiaobo Yin; Nicholas Fang; Xiang Zhang; Ignacio B. Martini; Benjamin J. Schwartz

2003-01-01

295

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

296

Swarm: ESA's Magnetic Field Mission  

Microsoft Academic Search

Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme. The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal evolution. The Mission shall deliver data that allow access to new insights into the Earth system by improving our understanding of the Earth's interior and near-Earth electro-magnetic environment.

R. Haagmans; Y. Menard; R. Floberghagen; G. Plank; M. R. Drinkwater

2010-01-01

297

Transverse Magnetic Field Propellant Isolator  

NASA Technical Reports Server (NTRS)

An alternative high voltage isolator for electric propulsion and ground-based ion source applications has been designed and tested. This design employs a transverse magnetic field that increases the breakdown voltage. The design can greatly enhance the operating range of laboratory isolators used for high voltage applications.

Foster, John E.

2000-01-01

298

Eddy Current and Magnetic Testing of Magnetic Material by Uniform Eddy Current Probe  

NASA Astrophysics Data System (ADS)

Uniform eddy current probe comprised of an exciting tangential coil and a detecting pancake coil simultaneously conducts eddy current testing and magnetic testing of magnetic material. The eddy current testing detects parallel flaws to the magnetic flux and the magnetic testing detects perpendicular flaws. The signal phase indicates whether ET or MT generates the signal. An appropriate test frequency provides almost same sensitivities for ET and MT.

Hoshikawa, H.; Koyama, K.; Mitsuhashi, S.

2005-04-01

299

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

300

Magnetic fields in the sun  

NASA Technical Reports Server (NTRS)

The observed properties of solar magnetic fields are reviewed, with particular reference to the complexities imposed on the field by motions of the highly conducting gas. Turbulent interactions between gas and field lead to heating or cooling of the gas according to whether the field energy density is less or greater than the maximum kinetic energy density in the convection zone. The field strength above which cooling sets in is 700 gauss. A weak solar dipole field may be primeval, but dynamo action is also important in generating new flux. The dynamo is probably not confined to the convection zone, but extends throughout most of the volume of the sun. Planetary tides appear to play a role in driving the dynamo.

Mullan, D. J.

1974-01-01

301

Reconstruction of local magnetic properties of steel sheets by needle probe methods using space mapping techniques  

NASA Astrophysics Data System (ADS)

Cutting stresses introduced by punching influence the magnetic characteristics of electrical steels. A nondestructive experimental method used for measuring flux distributions in laminations is the needle probe method. The probe signals can be simulated by solving the two-dimensional nonlinear diffusion equation for the magnetic field in combination with a proper Preisach model. The Preisach parameters in several subregions of the steel sheet which best fit the input probe signals are obtained by solving the inverse problem. The method used for minimizing the cost function is the space mapping technique. This technique combines the fine model, which uses the finite element method, with a semianalytical coarse model, which reduces the nonlinear problem to a linear problem.

Crevecoeur, G.; Dupre, L.; Vandenbossche, L.; van de Walle, R.

2006-04-01

302

Probing magnetization dynamics of strongly interacting magnetic nanoparticles through magnetoresistive current noise measurements  

NASA Astrophysics Data System (ADS)

The dependence of tunnelling current fluctuations on temperature and magnetic field was studied in an organically capped magnetite (Fe3O4) nanocrystal (NC) array deposited between 30 nm spaced gold electrodes. Low-frequency Lorentzian (random telegraph) noise was observed around the magnetization freezing temperature due to magnetic moment switching of the NCs under zero magnetic fields, diminishing with a saturating magnetic field. The temperature dependence of current fluctuations followed the temperature dependence of magnetic susceptibility. This work offers a new tool for locally studying collective magnetization dynamics in strongly interacting magnetic NC arrays.

Taub, Nurit; Markovich, Gil

2010-12-01

303

Measurement of electric fields induced in a human subject due to natural movements in static magnetic fields or exposure to alternating magnetic field gradients  

NASA Astrophysics Data System (ADS)

A dual dipole electric field probe has been used to measure surface electric fields in vivo on a human subject over a frequency range of 0.1-800 Hz. The low-frequency electric fields were induced by natural body movements such as walking and turning in the fringe magnetic fields of a 3 T magnetic resonance whole-body scanner. The rate-of-change of magnetic field (dB/dt) was also recorded simultaneously by using three orthogonal search coils positioned near to the location of the electric field probe. Rates-of-change of magnetic field for natural body rotations were found to exceed 1 T s-1 near the end of the magnet bore. Typical electric fields measured on the upper abdomen, head and across the tongue for 1 T s-1 rate of change of magnetic field were 0.15 ± 0.02, 0.077 ± 0.003 and 0.015 ± 0.002 V m-1 respectively. Electric fields on the abdomen and chest were measured during an echo-planar sequence with the subject positioned within the scanner. With the scanner rate-of-change of gradient set to 10 T m-1 s-1 the measured rate-of-change of magnetic field was 2.2 ± 0.1 T s-1 and the peak electric field was 0.30 ± 0.01 V m-1 on the chest. The values of induced electric field can be related to dB/dt by a 'geometry factor' for a given subject and sensor position. Typical values of this factor for the abdomen or chest (for measured surface electric fields) lie in the range of 0.10-0.18 m. The measured values of electric field are consistent with currently available numerical modelling results for movement in static magnetic fields and exposure to switched magnetic field gradients.

Glover, P. M.; Bowtell, R.

2008-01-01

304

Near-field subsurface detection using metamaterial inspired probes  

NASA Astrophysics Data System (ADS)

Recently, it was shown that single negative media can significantly enhance the sensitivity of near-field probes. Inspired by this recent finding, a new near-field probe is proposed for noninvasive subsurface detection. The new probe uses a single split ring resonator (SRR) instead of a periodic arrangement of SRRs for negative material realization. Experimental tests were conducted to detect the presence of cracks on aluminum plates, the presence of small aluminum blocks located behind a layer of ground chicken (lossy medium), and the presence of a small aluminum block submerged in sodium chloride solution (lossy medium) with a salinity of 1%. Preliminary results show that the proposed near-field probe enables detection of electrically small targets buried in lossy media.

Ren, Zhao; Boybay, Muhammed S.; Ramahi, Omar M.

2011-06-01

305

Probing the energy barriers and magnetization reversal processes of nanoperforated membrane based percolated media.  

PubMed

Magnetization reversal processes in Co/Pt multilayers prepared on nanoperforated templates are probed by magnetization relaxation measurements. The signature of pinning controlled domain wall movement as expected for percolated media is identified. This contrasts with the nucleation-type reversal mechanism of a Co/Pt reference film prepared on a smooth substrate. A zero field energy barrier of 93kBT is determined by fluctuation field measurements and is elucidated by micromagnetic calculations using the nudged elastic band method. This value is sufficiently large to qualify the material as a promising percolated medium. PMID:23507583

Neu, V; Schulze, C; Faustini, M; Lee, J; Makarov, D; Suess, D; Kim, S-K; Grosso, D; Schultz, L; Albrecht, M

2013-04-12

306

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

307

Electron dynamics in inhomogeneous magnetic fields.  

PubMed

This review explores the dynamics of two-dimensional electrons in magnetic potentials that vary on scales smaller than the mean free path. The physics of microscopically inhomogeneous magnetic fields relates to important fundamental problems in the fractional quantum Hall effect, superconductivity, spintronics and graphene physics and spins out promising applications which will be described here. After introducing the initial work done on electron localization in random magnetic fields, the experimental methods for fabricating magnetic potentials are presented. Drift-diffusion phenomena are then described, which include commensurability oscillations, magnetic channelling, resistance resonance effects and magnetic dots. We then review quantum phenomena in magnetic potentials including magnetic quantum wires, magnetic minibands in superlattices, rectification by snake states, quantum tunnelling and Klein tunnelling. The third part is devoted to spintronics in inhomogeneous magnetic fields. This covers spin filtering by magnetic field gradients and circular magnetic fields, electrically induced spin resonance, spin resonance fluorescence and coherent spin manipulation. PMID:21393794

Nogaret, Alain

2010-06-30

308

Oxide superconductors under magnetic field  

NASA Technical Reports Server (NTRS)

One of the current most serious problems for the oxide superconductors from the standpoint of practical application is the various novel features derived mainly from their extremely short coherence. In particular, the coherence length so far observed in the cuprate superconductors is in the range of 0.1 nm perpendicular to the CuO2 plane. This seems to be creating most of the difficulties in the device fabrication and in the performance under the magnetic field. Some of the superconducting properties under the magnetic field will be discussed in terms of the short coherence length. A model will be presented based on the gradual strengthening of the pinning force with decrease in temperature and the weak coupling at the grain boundaries. Secondly, the broadening of the superconducting transition under the magnetic field is discussed. This is observed significantly only when the field is applied perpendicular to the basal plane and the relative orientation of the current to the field is insignificant in determining the extent of the broadening. Besides, the change in the strength of the pinning force does not affect the width of the broadening. From these observations discussions will be made on a model based on the giant fluctuation. Based on this model, it is predicted that the coherence length along the c-axis will be the single most important material parameter to determine the performance of the superconductor under a strong magnetic field. It seems that BYCO is superior in this regard to Bi- or Tl-systems as far as the performance at 77 K is considered, although another material with the coherence length slightly longer along the c-axis is still highly desired.

Kitazawa, K.

1990-01-01

309

Oxide superconductors under magnetic field  

NASA Technical Reports Server (NTRS)

One of the current most serious problems for the oxide superconductors from the standpoint of practical application is the various novel features derived mainly from their extremely short coherence. In particular, the coherence length so far observed in the cuprate superconductors is in the range of 0.1 nm perpendicular to the CuO2 plane. This seems to be creating most of the difficulties in the device fabrication and in the performance under the magnetic field. Some of the superconducting properties under the magnetic field will be discussed in terms of the short coherence length. A model will be presented based on the gradual strengthening of the pinning force with decrease in temperature and the weak coupling at the grain boundaries. Secondly, the broadening of the superconducting transition under the magnetic field is discussed. This is observed significantly only when the field is applied perpendicular to the basal plane and the relative orientation of the current to the field is insignificant in determining the extent of broadening. Besides, the change in the strength of the pinning force does not affect the width of the broadening. From these observations discussions will be made on a model based on the giant fluctuation. Based on this model, it is predicted that the coherence length along the c-axis will be the single most important material parameter to determine the performance of the superconductor under a strong magnetic field. It seems that BYCO is superior in this regard to Bi- or Tl-systems as far as the performance at 77 K is considered, although another material with the coherence length slightly longer along the c-axis is still highly desired.

Kitazawa, K.

1991-01-01

310

Dynamics of Magnetic Bubbles in Acoustic and Magnetic Fields  

Microsoft Academic Search

We report on shelled bubbles that can be manipulated with magnetic fields. The magnetic shell consists of self-assembled magnetic nanoparticles. The magnetic susceptibility of the bubbles is proportional to the surface area, chib=(9±3×10-6m)r2 where r is the radius. Magnetic bubbles are compressible in moderate acoustic fields. A bubble with a radius of 121mum oscillates in resonance in a sound field

Xue Zhao; Pedro A. Quinto-Su; Claus-Dieter Ohl

2009-01-01

311

Quantum probe and design for a chemical compass with magnetic nanostructures.  

PubMed

Magnetic fields as weak as Earth's may affect the outcome of certain photochemical reactions that go through a radical pair intermediate. When the reaction environment is anisotropic, this phenomenon can form the basis of a chemical compass and has been proposed as a mechanism for animal magnetoreception. Here, we demonstrate how to optimize the design of a chemical compass with a much better directional sensitivity simply by a gradient field, e.g., from a magnetic nanostructure. We propose an experimental test of these predictions, and suggest design principles for a hybrid metallic-organic chemical compass. In addition to the practical interest in designing a biomimetic weak magnetic field sensor, our result shows that gradient fields can serve as powerful tools to probe spin correlations in radical pair reactions. PMID:21469779

Cai, Jianming

2011-03-11

312

Quantum Probe and Design for a Chemical Compass with Magnetic Nanostructures  

NASA Astrophysics Data System (ADS)

Magnetic fields as weak as Earth’s may affect the outcome of certain photochemical reactions that go through a radical pair intermediate. When the reaction environment is anisotropic, this phenomenon can form the basis of a chemical compass and has been proposed as a mechanism for animal magnetoreception. Here, we demonstrate how to optimize the design of a chemical compass with a much better directional sensitivity simply by a gradient field, e.g., from a magnetic nanostructure. We propose an experimental test of these predictions, and suggest design principles for a hybrid metallic-organic chemical compass. In addition to the practical interest in designing a biomimetic weak magnetic field sensor, our result shows that gradient fields can serve as powerful tools to probe spin correlations in radical pair reactions.

Cai, Jianming

2011-03-01

313

Magnetic field sensing based on magneto-volume variation of magnetic fluids investigated by air-gap Fabry-Pérot fiber interferometers  

NASA Astrophysics Data System (ADS)

A compact air-gap Fabry-Pérot fiber interferometer using magnetic fluids as the constituent material is constructed. The proposed structure possesses high sensitivity to magnetic field and is eligible for probing the tiny magnetic-field-induced volume variation of magnetic fluids. The underlying physical mechanisms for the magneto-volume variation are clarified in detail. The shift of the interference spectrum with magnetic field is employed for the magnetic field sensing applications. The highest sensitivity of magnetic field sensing for our experimental structure can reach 117.3 pm/mT when the sensing head is set at 45° azimuthal angle (with respect to the magnetic field direction).

Dong, Shaohua; Pu, Shengli; Huang, Juan

2013-09-01

314

Diagnostics of vector magnetic fields  

NASA Technical Reports Server (NTRS)

It is shown that the vector magnetic fields derived from observations with a filter magnetograph will be severely distorted if the spatially unresolved magnetic structure is not properly accounted for. Thus the apparent vector field will appear much more horizontal than it really is, but this distortion is strongly dependent on the area factor and the temperature line weakenings. As the available fluxtube models are not sufficiently well determined, it is not possible to correct the filter magnetograph observations for these effects in a reliable way, although a crude correction is of course much better than no correction at all. The solution to this diagnostic problem is to observe simultaneously in suitable combinations of spectral lines, and/or use Stokes line profiles recorded with very high spectral resolution. The diagnostic power of using a Fourier transform spectrometer for polarimetry is shown and some results from I and V spectra are illustrated. The line asymmetries caused by mass motions inside the fluxtubes adds an extra complication to the diagnostic problem, in particular as there are indications that the motions are nonstationary in nature. The temperature structure appears to be a function of fluxtube diameter, as a clear difference between plage and network fluxtubes was revealed. The divergence of the magnetic field with height plays an essential role in the explanation of the Stokes V asymmetries (in combination with the mass motions). A self consistent treatment of the subarcsec field geometry may be required to allow an accurate derivation of the spatially averaged vector magnetic field from spectrally resolved data.

Stenflo, J. O.

1985-01-01

315

Developments of scanning probe microscopy with stress/strain fields.  

PubMed

An innovative stress/strain fields scanning probe microscopy in ultra high vacuum (UHV) environments is developed for the first time. This system includes scanning tunneling microscope (STM) and noncontact atomic force microscope (NC-AFM). Two piezo-resistive AFM cantilever probes and STM probes used in this system can move freely in XYZ directions. The nonoptical frequency shift detection of the AFM probe makes the system compact enough to be set in the UHV chambers. The samples can be bent by an anvil driven by a step motor to induce stress and strain on their surface. With a direct current (dc) power source, the sample can be observed at room and high temperatures. A long focus microscope and a monitor are used to observe the samples and the operation of STM and AFM. Silicon(111) surface in room temperature and silicon(001) surface in high temperature with stress were investigated to check the performance of the scanning probe microscope. PMID:22225223

Guo, H X; Fujita, D

2011-12-01

316

Magnetic Relaxation with Oscillating Field Current Drive on MST  

NASA Astrophysics Data System (ADS)

In oscillating field current drive (OFCD), poloidal and toroidal ac magnetic fields with the same frequency but different phases are inductively applied to the plasma to drive dc plasma current through magnetic relaxation. Measurements of the dynamo mechanisms associated with magnetic relaxation are conducted during OFCD for a variety of phases both to better understand the phase-dependent relaxation dynamics and to aid in optimizing OFCD performance. The fluctuation-induced dynamo || and its constituent Hall dynamo ||ne are measured in the edge using insertable probes. The fluctuation-induced magnetic helicity flux is also measured. All three are enhanced during OFCD by a factor of two relative to standard RFP operation and, as expected, the induced transport of helicity is in the inward radial direction. Probes used include a secondary-emission capacitive probe that was developed to measure electric fields and tested by comparison to Langmuir probe measurements. Measurement of the Hall ne dynamo in the core using far-infrared interferometry-polarimetry is in progress as well. This work is supported by the US DOE.

Stone, D. R.; Almagri, A. F.; Fiksel, G.; McCollam, K. J.; Sarff, J. S.; Brower, D. L.; Ding, W. X.; Lin, L.

2011-11-01

317

Explaining Mercury's peculiar magnetic field  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

318

Cross-duct electric field perturbation void fraction probe  

SciTech Connect

An advanced probe has been developed for transient and time-averaged measurement of the void fraction under various thermal-hydraulic conditions. The Electric Field Perturbation (EFP) probe operates by measuring the electrical properties of a two-phase mixture which are related to the void fraction by a theoretical electromagnetic field model. Qualification tests were performed in both air-water and high pressure steam-water facilities. In the former set of experiments, the EFP measurements were compared to void fractions obtained with fast-acting valves and a hot-film anemometer. For high-pressure experiments in a pool boiling configuration, simultaneous void fraction time traces from the EFP probe and differential pressure cell indicated that the EFP probe responds well to overall void fraction fluctuations.

Duncan, D.; Trabold, T.A. [Lockheed Martin Corp., Schenectady, NY (United States)] [Lockheed Martin Corp., Schenectady, NY (United States)

1997-03-01

319

Probing Surface Patch Fields with Rydberg Atoms  

NASA Astrophysics Data System (ADS)

The stray electric patch fields present at a Au(111) surface are investigated by studying the ionization of Rydberg atoms incident at near-grazing angles. Measurements of the threshold conditions for observation of the resulting ions are used to estimate the size, and other characteristics, of the stray fields. This is accomplished using an iterative procedure and calculating the threshold conditions for different assumed field parameters using a simple over-the-barrier model of surface tunneling. Excellent fits to the experimental data are obtained over a broad range of n and angles of incidence and indicate that the stray fields can be as large as ˜10^3 V/cm 100nm from the surface decreasing to ˜ 20V/cm 500 nm from the surface. The use of lithographically-patterned electrode arrays to further study the effects of stray fields is being explored. Simulations suggest that engineered electrode structures, which can generate localized fields approaching 10^4 V/cm, will help evaluate the potential of Rydberg atoms as a tool to detect and characterize stray fields as well as allow the detection of low-n (n ˜ 10) Rydberg atoms.

Pu, Yu; Neufeld, Dean; Dunning, Barry

2011-06-01

320

Magnetic Field Effects on High Quality Factor Superconducting Coplanar Resonators  

NASA Astrophysics Data System (ADS)

Superconducting coplanar waveguide resonators have proven to be invaluable tools in studying some of the same decoherence mechanisms as those found in superconducting qubits. Prior improvements in fabrication led to resonator internal quality factors (Qi's) in excess of 10 million at high power, enabling us to sensitively probe environmental effects on the resonance frequency and Qi. We have found these resonators to be very susceptible to applied and stray magnetic fields, with measurable changes in the resonator's Qi and resonance frequency from fields as small as a few milligauss. I will present more recent measurements of resonators in magnetic fields.

Megrant, Anthony; Neill, Charles; Barends, Rami; Chen, Yu; Chiaro, Ben; Kelly, Julian; Mariantoni, Matteo; Mutus, Josh; O'Malley, Peter; Sank, Daniel; Vainsencher, Amit; Wenner, James; White, Ted; Low, David; Ohya, Shinobu; Palmstrom, Christopher; Martinis, John; Cleland, Andrew

2013-03-01

321

Magnetic domain structure in thin film under alternate magnetic field  

Microsoft Academic Search

Magnetic domain structures in a garnet thin film under alternate magnetic fields have been investigated. In alternate magnetic fields, a labyrinth structure approaches a parallel-stripe structure. The competition among the segment clusters, in which stripes have different directions, causes stable dynamical domain structures. With the increase of the amplitude of alternate fields, the segment clusters become small.

M. Mino; H. Yamazaki

2004-01-01

322

Magnetic domain structure in thin film under alternate magnetic field  

NASA Astrophysics Data System (ADS)

Magnetic domain structures in a garnet thin film under alternate magnetic fields have been investigated. In alternate magnetic fields, a labyrinth structure approaches a parallel-stripe structure. The competition among the segment clusters, in which stripes have different directions, causes stable dynamical domain structures. With the increase of the amplitude of alternate fields, the segment clusters become small.

Mino, M.; Yamazaki, H.

323

Magnetic domain structure in thin film under alternate magnetic field  

NASA Astrophysics Data System (ADS)

Magnetic domain structures in a garnet thin film under alternate magnetic fields have been investigated. In alternate magnetic fields, a labyrinth structure approaches a parallel-stripe structure. The competition among the segment clusters, in which stripes have different directions, causes stable dynamical domain structures. With the increase of the amplitude of alternate fields, the segment clusters become small.

Mino, M.; Yamazaki, H.

2004-05-01

324

Fully integrated probe for proton nuclear magnetic resonance magnetometry  

Microsoft Academic Search

In this article, we present the first fully integrated nuclear magnetic resonance probe ever realized. Planar spiral coils, a radio-frequency preamplifier, a mixer, and an audio-frequency amplifier are integrated using a standard complementary metal-oxide-semiconductor technology on a single silicon chip of 10 mm2. A 1 mm3 solid sample of cis-polyisoprene, placed over one of the integrated coils, is used as

G. Boero; J. Frounchi; B. Furrer; P.-A. Besse; R. S. Popovic

2001-01-01

325

Bending of magnetic filaments under a magnetic field  

Microsoft Academic Search

Magnetic beads and superparamagnetic (SP) colloid particles have successfully been employed for micromechanical manipulation of soft material, in situ probing of elastic properties, and design of smart materials (ferrogels). Here we derive analytical expressions for the equilibrium shape of magnetic fibers, considering two end-member cases, (a) SP or single-domain particles concentrated at the free end of cantilevered rods or tubes,

Valera P. Shcherbakov; Michael Winklhofer

2004-01-01

326

Polarization-maintaining near-field optical probes  

Microsoft Academic Search

Summary We demonstrate that tapered optical fibre probes can be easily modified in the taper cone to realize an electric dipole producing a well-defined near-field polarized light. This novel structure is made of a Short-cut Double C-shaped probe design combined to the usual full metal coating near the tapered end of the fibre. Hence, the cone at the apex of

S. PATANÈ; E. CEFALÌ; S. SPADARO; R. GARDELLI; M. ALBANI; M. ALLEGRINI

2008-01-01

327

Near-field probing of photonic crystals  

NASA Astrophysics Data System (ADS)

Photonic crystals form an exciting new class of optical materials that can greatly affect optical propagation and light emission. As the relevant length scale is smaller than the wavelength of light, sub-wavelength detection forms an important ingredient to obtain full insight in the physical properties of photonic crystal structures. Spatially resolved near-field measurements allow the observation of phenomena that remain hidden to diffraction-limited far-field investigations. Here, we present near-field investigations in both collection and illumination modes that highlight the power of local studies. We show how propagation losses are unambiguously determined and that light detected in far-field transmission can actually contain contributions from different, sometimes unexpected, local scattering phenomena. Simulations are used to support our findings. Furthermore, it is shown that local coupling of light to a thick three-dimensional photonic crystal is position-dependent and that the spatial distribution of the coupling efficiency itself is frequency-dependent.

Flück, E.; Hammer, M.; Vos, W. L.; van Hulst, N. F.; Kuipers, L.

2004-10-01

328

Compressing magnetic fields with high-energy lasers  

NASA Astrophysics Data System (ADS)

Laser-driven magnetic-field compression producing a magnetic field of tens of megaGauss is reported for the first time. A shock wave formed during the implosion of a cylindrical target traps an initial (seed) magnetic field that is amplified via conservation of magnetic flux. Such large fields are expected to magnetize the electrons in the hot, central plasma, leading to a cyclotron frequency exceeding the collision frequency. The Omega Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] was used to implode cylindrical CH targets filled with deuterium gas and seeded with an external field (>50 kG) from a magnetic pulse generator. This seed field is trapped and rapidly compressed by the imploding shell, minimizing the effect of resistive flux diffusion. The compressed field was probed via proton deflectrometry using 14.7 MeV protons from the D+3He fusion reaction emitted by an imploding glass microballoon. Line-averaged magnetic fields of the imploded core were measured to between 30 and 40 MG. Experimental data were analyzed with both a magnetohydrodynamic version of the one-dimensional hydrocode LILAC [J. Delettrez et al., Phys. Rev. A 36, 3926 (1987); N. W. Jang et al., Bull. Am. Phys. Soc. 51, 144 (2006)] and the particle propagation code GEANT4 [S. Agostinelli et al., Nucl. Instrum. Methods Phys. Res. A 506, 250 (2003)].

Knauer, J. P.; Gotchev, O. V.; Chang, P. Y.; Meyerhofer, D. D.; Polomarov, O.; Betti, R.; Frenje, J. A.; Li, C. K.; Manuel, M. J.-E.; Petrasso, R. D.; Rygg, J. R.; Séguin, F. H.

2010-05-01

329

Compressing magnetic fields with high-energy lasers  

SciTech Connect

Laser-driven magnetic-field compression producing a magnetic field of tens of megaGauss is reported for the first time. A shock wave formed during the implosion of a cylindrical target traps an initial (seed) magnetic field that is amplified via conservation of magnetic flux. Such large fields are expected to magnetize the electrons in the hot, central plasma, leading to a cyclotron frequency exceeding the collision frequency. The Omega Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] was used to implode cylindrical CH targets filled with deuterium gas and seeded with an external field (>50 kG) from a magnetic pulse generator. This seed field is trapped and rapidly compressed by the imploding shell, minimizing the effect of resistive flux diffusion. The compressed field was probed via proton deflectrometry using 14.7 MeV protons from the D+{sup 3}He fusion reaction emitted by an imploding glass microballoon. Line-averaged magnetic fields of the imploded core were measured to between 30 and 40 MG. Experimental data were analyzed with both a magnetohydrodynamic version of the one-dimensional hydrocode LILAC[J. Delettrez et al., Phys. Rev. A 36, 3926 (1987); N. W. Jang et al., Bull. Am. Phys. Soc. 51, 144 (2006)] and the particle propagation code GEANT4[S. Agostinelli et al., Nucl. Instrum. Methods Phys. Res. A 506, 250 (2003)].

Knauer, J. P. [Lab. for Laser Energetics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Gotchev, O. V. [Lab. for Laser Energetics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Fusion Science Center for Extreme States of Matter and Fast Ignition Physics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Dept. of Mechanical Engineering, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Chang, P. Y. [Lab. for Laser Energetics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Dept. of Physics and Astronomy, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Meyerhofer, D. D.; Betti, R. [Lab. for Laser Energetics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Fusion Science Center for Extreme States of Matter and Fast Ignition Physics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Dept. of Mechanical Engineering, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Dept. of Physics and Astronomy, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Polomarov, O. [Fusion Science Center for Extreme States of Matter and Fast Ignition Physics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Dept. of Mechanical Engineering, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Frenje, J. A.; Li, C. K.; Manuel, M. J.-E.; Petrasso, R. D. [Fusion Science Center for Extreme States of Matter and Fast Ignition Physics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Plasma Science and Fusion Center, MIT, Cambridge, Massachusetts 02139 (United States)

2010-05-15

330

Comparing Magnetic Fields on Earth and Mars  

NASA Video Gallery

This animation compares the magnetic fields on Earth and Mars. The Earth has a large-scale planetary magnetic field that can protect it from space weather and other hazards. Mars, on the other hand...

331

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

332

Anisotropic Magnetism in Field-Structured Composites  

SciTech Connect

Magnetic field-structured-composites (FSCs) are made by structuring magnetic particle suspensions in uniaxial or biaxial (e.g. rotating) magnetic fields, while polymerizing the suspending resin. A uniaxial field produces chain-like particle structures, and a biaxial field produces sheet-like particle structures. In either case, these anisotropic structures affect the measured magnetic hysteresis loops, with the magnetic remanence and susceptibility increased significantly along the axis of the structuring field, and decreased slightly orthogonal to the structuring field, relative to the unstructured particle composite. The coercivity is essentially unaffected by structuring. We present data for FSCs of magnetically soft particles, and demonstrate that the altered magnetism can be accounted for by considering the large local fields that occur in FSCs. FSCS of magnetically hard particles show unexpectedly large anisotropies in the remanence, and this is due to the local field effects in combination with the large crystalline anisotropy of this material.

Anderson, Robert A.; Martin, James E.; Odinek, Judy; Venturini, Eugene

1999-06-24

333

Magnetic order of UPt3 in high magnetic fields  

NASA Astrophysics Data System (ADS)

The weak magnetic order of the heavy-fermion superconductor UPt3 has been investigated by elastic neutron-scattering measurements in magnetic fields up to 12 T along the a and c axes of the hexagonal crystal structure. The small antiferromagnetically ordered moment of 0.02?B/(U atom) shows only a weak dependence on the applied magnetic field and no sign of a domain repopulation for B?a. In high magnetic fields an increase in the magnetic correlation length is observed for magnetic fields along the c axis.

van Dijk, N. H.; Fåk, B.; Regnault, L. P.; Huxley, A.; Fernández-Díaz, M.-T.

1998-08-01

334

Cosmic Microwave Background Trispectrum and Primordial Magnetic Field Limits  

NASA Astrophysics Data System (ADS)

Primordial magnetic fields will generate non-Gaussian signals in the cosmic microwave background (CMB) as magnetic stresses and the temperature anisotropy they induce depend quadratically on the magnetic field. We compute a new measure of magnetic non-Gaussianity, the CMB trispectrum, on large angular scales, sourced via the Sachs-Wolfe effect. The trispectra induced by magnetic energy density and by magnetic scalar anisotropic stress are found to have typical magnitudes of approximately a few times 10-29 and 10-19, respectively. Observational limits on CMB non-Gaussianity from WMAP data allow us to conservatively set upper limits of a nG, and plausibly sub-nG, on the present value of the primordial cosmic magnetic field. This represents the tightest limit so far on the strength of primordial magnetic fields, on Mpc scales, and is better than limits from the CMB bispectrum and all modes in the CMB power spectrum. Thus, the CMB trispectrum is a new and more sensitive probe of primordial magnetic fields on large scales.

Trivedi, Pranjal; Seshadri, T. R.; Subramanian, Kandaswamy

2012-06-01

335

Characterization of heat-assisted magnetic probe recording on CoNi\\/Pt multilayers  

Microsoft Academic Search

A method of heat-assisted magnetic recording (HAMR) potentially suitable for probe-based storage systems is characterized. In this work, field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. Pulse voltages of 2–7V were applied to a CoNi\\/Pt multilayered film fabricated on either bare silicon or oxidized silicon substrates. Different types of Ir\\/Pt and W

Li Zhang; James A. Bain; Jian-Gang Zhu; Leon Abelmann; Takahiro Onoue

2006-01-01

336

Characterization of heat-assisted magnetic probe recording on cobalt nickel\\/platinum multilayers  

Microsoft Academic Search

In this PhD project, a method of heat-assisted magnetic recording (HAMR) potentially suitable for probe-based storage systems is characterized. Field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. Pulse voltages of 2--7 V were applied to a CoNi\\/Pt multilayered film. Identical films fabricated on a bare silicon substrate and an oxidized silicon substrate

Li Zhang

2005-01-01

337

Crustal Magnetic Fields of Terrestrial Planets  

Microsoft Academic Search

Magnetic field measurements are very valuable, as they provide constraints on the interior of the telluric planets and Moon.\\u000a The Earth possesses a planetary scale magnetic field, generated in the conductive and convective outer core. This global magnetic\\u000a field is superimposed on the magnetic field generated by the rocks of the crust, of induced (i.e. aligned on the current main

Benoit Langlais; Vincent Lesur; Michael E. Purucker; Jack E. P. Connerney; Mioara Mandea

2010-01-01

338

Ground state alignment as a tracer of interplanetary magnetic field  

NASA Astrophysics Data System (ADS)

We demonstrate a new way of studying interplanetary magnetic field -- spectropolarimetry based on ground state alignment. Ground state alignment is a new promising way of sub-gausian magnetic fields in radiation-dominated environment. The polarization of spectral lines that are pumped by the anisotropic radiation from the sun is influenced by the magnetic alignment, which happens for sub-gausian magnetic field. As a result, the linear polarization becomes an excellent tracer of the embedded magnetic field. The method is illustrated by our synthetic obser- vation of the Jupiter's Io and comet Halley. A uniform density distribution of Na was considered and polar- ization at each point was then constructed. Both spa- tial and temporal variations of turbulent magnetic field can be traced with this technique as well. Instead of sending thousands of space probes, ground state alignment allows magnetic mapping with any ground telescope facilities equipped with spectrometer and polarimeter. For remote regions like the the boundary of interstellar medium, ground state alignment provides a unique diagnostics of magnetic field, which is crucial for understanding the physical processes such as the IBEX ribbons.

Yan, H.

2012-12-01

339

Magnetic holes in the solar wind. [(interplanetary magnetic fields)  

NASA Technical Reports Server (NTRS)

An analysis is presented of high resolution interplanetary magnetic field measurements from the magnetometer on Explorer 43 which showed that low magnetic field intensities in the solar wind at 1 AU occur as distinct depressions or 'holes'. These magnetic holes are new kinetic-scale phenomena, having a characteristic dimension on the order of 20,000 km. They occurred at a rate of 1.5/day in the 18-day time span (March 18 to April 6, 1971) that was analyzed. Most of the magnetic holes are characterized by both a depression in the absolute value of the magnetic field, and a change in the magnetic field direction; some of these are possibly the result of magnetic merging. However, in other cases the magnetic field direction does not change; such holes are not due to magnetic merging, but might be a diamagnetic effect due to localized plasma inhomogeneities.

Turner, J. M.; Burlaga, L. F.; Ness, N. F.; Lemaire, J. F.

1976-01-01

340

Spherical Probe Electric Field and Wave Experiment.  

National Technical Information Service (NTIS)

The experiment is designed to measure the electric field and density fluctuations with sampling rates up to 40,000 samples/sec. The description includes Langmuir sweeps that can be made to determine the electron density and temperature, the study of nonli...

G. Gustafsson T. Aggson R. Bostrom L. P. Block C. Cattell

1988-01-01

341

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

Swarm is the fifth Earth Explorer mission in ESA’s Living Planet Programme. The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal evolution. The Mission shall deliver data that allow access to new insights into the Earth system by improving our understanding of the Earth’s interior and near-Earth electro-magnetic environment. After release from a single launcher, a side-by-side flying slowly decaying lower pair of satellites will be released at an initial altitude of about 490 km together with a third satellite that 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 that are required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission aims to provide a unique view into Earth 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 development phase, will be addressed. The mission is scheduled for launch in 2012.

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

2010-12-01

342

Magnetic field sensors using GMR multilayer  

Microsoft Academic Search

Wheatstone bridge magnetic field sensors using giant magnetoresistive ratio (GMR) multilayers were designed, fabricated, and evaluated. The GMR ranged from 10% to 20% with saturation fields of 60 Oe to 300 Oe. The multilater resistances decreased linearly with magnetic field and showed little hysteresis. In one sensor configuration, a permanent magnet bias was placed between two pairs of magnetoresistors, each

J. Daughton; J. Brown; E. Chen; R. Beech; A. Pohm; W. Kude

1994-01-01

343

The measurement of solar magnetic fields  

Microsoft Academic Search

Methods for studying solar magnetic fields are examined, taking into account Zeeman and Hanle effects, radio observations, the influence of magnetic fields in solar structures, theoretical extrapolations of photospheric measurements, in situ measurements in the solar-wind region, and meteorite records of the primordial solar magnetic field. Instrumental techniques for optical polarization measurements are considered and an interpretation of optical polarization

J. O. Stenflo

1978-01-01

344

MR imaging at high magnetic fields  

Microsoft Academic Search

Recently, more investigators have been applying higher magnetic field strengths (3–4 Tesla) in research and clinical settings. Higher magnetic field strength is expected to afford higher spatial resolution and\\/or a decrease in the length of total scan time due to its higher signal intensity. Besides MR signal intensity, however, there are several factors which are magnetic field dependent, thus the

Masaya Takahashi; Hidemasa Uematsu; Hiroto Hatabu

2003-01-01

345

Magnetic field navigation in an indoor environment  

Microsoft Academic Search

This paper describes a method that has been developed to aid an inertial navigation system when GNSS signals are not available, by taking advantage of the uniqueness of magnetic field variations. Most indoor environments have many different features (ferrous structural materials or contents, electrical currents, etc.) which perturb the Earths natural magnetic field. The variations in the magnetic field in

William Storms; Jeremiah Shockley; John Raquet

2010-01-01

346

PLASMA CONFINEMENT USING ROTATING MAGNETIC FIELDS  

Microsoft Academic Search

An investigation was made of the current distribution set up by a ; magnetic field rotating about the axis of a cylindrical plasma. If the plasma ; resistivity was sufficiently small electrons rotated with the magnetic field ; producing a steady azimuthal current. In conjunction with an externally applied ; axial magnetic field such a system can be used to

H. Blevin; P. C. Thonemann

1961-01-01

347

Magnetic field quality analysis using ANSYS.  

National Technical Information Service (NTIS)

The design of superconducting magnets for particles accelerators requires a high quality of the magnetic field. This paper presents an ANSYS 4.4A Post 1 macro that computes the field quality performing a Fourier analysis of the magnetic field. The results...

D. Dell'Orco Y. Chen

1991-01-01

348

Magnetic field effect for cellulose nanofiber alignment  

Microsoft Academic Search

Regenerated cellulose formed into cellulose nanofibers under strong magnetic field and aligned perpendicularly to the magnetic field. Well-aligned microfibrils were found as the exposure time of the magnetic field increased. Better alignment and more crystalline structure of the cellulose resulted in the increased decomposition temperature of the material. X-ray crystallograms showed that crystallinity index of the cellulose increased as the

Jaehwan Kim; Yi Chen; Kwang-Sun Kang; Young-Bin Park; Mark Schwartz

2008-01-01

349

An ancient lunar magnetic dipole field  

Microsoft Academic Search

Theories giving the source of the previously hypothesized ancient strong lunar magnetic field and reasons for its disappearance are presented. It is suggested that since it was demonstrated that the moon possessed a small iron core, a dynamo process within this core may have accounted for the field. The disappearance of this magnetizing field can be explained; either the magnetic

S. K. Runcorn

1975-01-01

350

Measurements of the superconducting fluctuations in optimally doped BaFe2?xNixAs2 under high magnetic fields: probing the 3D-anisotropic Ginzburg–Landau approach  

NASA Astrophysics Data System (ADS)

The superconducting fluctuations well inside the normal state of Fe-based superconductors were experimentally studied through the in-plane paraconductivity in several high-quality, optimally doped BaFe2?xNixAs2 crystals. These measurements were performed in magnetic fields with amplitudes up to 14 T, and different orientations relative to the c-axis of the crystals (\\theta =0{}^\\circ , 53{}^\\circ , and 90{}^\\circ ). The results allowed a stringent check of the applicability of a recently proposed Ginzburg–Landau approach for the fluctuating electrical conductivity of three-dimensional (3D) anisotropic materials in the presence of finite applied magnetic fields.

Rey, R. I.; Ramos-Álvarez, A.; Carballeira, C.; Mosqueira, J.; Vidal, F.; Salem-Sugui, S., Jr.; Alvarenga, A. D.; Zhang, Rui; Luo, Huiqian

2014-07-01

351

Magnetic field induced lattice ground states from holography  

NASA Astrophysics Data System (ADS)

We study the holographic field theory dual of a probe SU(2) Yang-Mills field in a background (4 + 1)-dimensional asymptotically Anti-de Sitter space. We find a new ground state when a magnetic component of the gauge field is larger than a critical value. The ground state forms a triangular Abrikosov lattice in the spatial directions perpendicular to the magnetic field. The lattice is composed of superconducting vortices induced by the condensation of a charged vector operator. We perform this calculation both at finite temperature and at zero temperature with a hard wall cutoff dual to a confining gauge theory. The study of this state may be of relevance to both holographic condensed matter models as well as to heavy ion physics. The results shown here provide support for the proposal that such a ground state may be found in the QCD vacuum when a large magnetic field is present.

Bu, Yan-Yan; Erdmenger, Johanna; Shock, Jonathan P.; Strydom, Migael

2013-03-01

352

Lifshitz effects on vector condensate induced by a magnetic field  

NASA Astrophysics Data System (ADS)

By numerical and analytical methods, we study in detail the effects of the Lifshitz dynamical exponent z on the vector condensate induced by an applied magnetic field in the probe limit. Concretely, in the presence of the magnetic field, we obtain the Landau level independent of z, and we also find the critical value by coupling a Maxwell complex vector field and an SU(2) field into a (3+1)-dimensional Lifshitz black hole, respectively. The research results show that for the two models with the lowest Landau level, the increasing z improves the response of the critical temperature to the applied magnetic field even without the charge density, and the analytical results uphold the numerical results. In addition, we find that, even in the Lifshitz black hole, the Maxwell complex vector model is still a generalization of the SU(2) Yang-Mills model. Furthermore, we construct the square vortex lattice and discuss the implications of these results.

Wu, Ya-Bo; Lu, Jun-Wang; Liu, Mo-Lin; Lu, Jian-Bo; Zhang, Cheng-Yuan; Yang, Zhuo-Qun

2014-05-01

353

Magnetic Fields in Molecular Clouds  

NASA Astrophysics Data System (ADS)

Maps of far-infrared and submillimeter polarization vectors have typically been examined one-at-a-time for magnetic field structure related to processes such as gravitational collapse, differential rotation, expanding H II regions, or tidal stripping. The same maps can be used to determine angular dispersion due to turbulence in molecular clouds, where the turbulent dispersion is distinguished from dispersion due to curvature of the large-scale structure or the apparent dispersion due to measurement error. Taking into account the differences between the dispersion due to magneto-hydrodynamic waves in the arms of the Galaxy and dispersion due to turbulence in molecular clouds, one can infer field strengths in dense clouds using a method analogous to that used by Chandresekhar & Fermi to determine field strengths in the Galactic plane. With an accurate archive of flux and polarization maps one can also determine three-dimensional cloud shapes and field orientations, or look for correlations between fields in molecular clouds and fields in the surrounding medium.

Hildebrand, R. H.

2009-12-01

354

Interplanetary magnetic field data book  

NASA Technical Reports Server (NTRS)

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

King, J. H.

1975-01-01

355

The Giotto magnetic field investigation  

NASA Technical Reports Server (NTRS)

The Giotto spacecraft will carry sensors for investigating the interplanetary magnetic field while en route and the interaction between the solar wind magnetoplasma and Halley's Comet neutral gas outflow during close approach. Giotto will carry an outboard biaxial fluxgate system and inboard electronics. The instrumentation draws 1.2 kW and weighs 1.31 kg. Sampling rates will be 28/sec during close encounter, covering selectable ranges from 16 nT to 65,535 nT. In-flight calibration techniques are under development to ensure magnetic cleanliness will be obtained. Measurements are also planned of the inbound bow shock, the magnetosheath and the cometary ionopause. The data will be collected as close as 1000 km from the comet surface.

Neubauer, F. M.; Musmann, G.; Acuna, M. H.; Burlaga, L. F.; Ness, N. F.; Mariani, F.; Wallis, M.; Ungstrup, E.; Schmidt, H.

1983-01-01

356

Infrared lines as probes of solar magnetic features. XII. Magnetic flux tubes: evidence of convective collapse?  

Microsoft Academic Search

The magnetic field in the solar photosphere is mainly composed of magnetic flux tubes. Their formation is not well understood, largely due to an absence of observational tests of theoretical predictions. Here we use infrared polarimetric data to test and confirm the prediction that whereas the field strength of large flux tubes is almost independent of their magnetic flux, small

S. K. Solanki; D. Zufferey; H. Lin; I. Rueedi; J. R. Kuhn

1996-01-01

357

Beating of magnetic oscillations in a graphene device probed by quantum capacitance  

NASA Astrophysics Data System (ADS)

We report the quantum capacitance of a monolayer graphene device in an external perpendicular magnetic field including the effects of Rashba spin-orbit interaction (SOI). The SOI mixes the spin up and spin down states of neighbouring Landau levels into two (unequally spaced) energy branches. In order to investigate the role of the SOI for the electronic transport, we study the density of states to probe the quantum capacitance of monolayer graphene. SOI effects on the quantum magnetic oscillations (Shubnikov de Haas and de Hass-van Alphen) are deduced from the quantum capacitance.

Tahir, M.; Schwingenschlögl, U.

2012-07-01

358

Dynamics of positive probes in underdense, strongly magnetized, E×B drifting plasma: Particle-in-cell simulations  

SciTech Connect

Electron trapping, electron heating, space-charge wings, wake eddies, and current collection by a positive probe in E×B drifting plasma were studied in three-dimensional electromagnetic particle-in-cell simulations. In these simulations, electrons and ions were magnetized with respect to the probe and the plasma was underdense (?{sub pe}probe was created with background electric and magnetic fields. Four distinct regions developed in the presences of the positive probe: a quasi-trapped electron region, an electron-depletion wing, an ion-rich wing, and a wake region. We report on the observations of strong electron heating mechanisms, space-charge wings, ion cyclotron charge-density eddies in the wake, electron acceleration due to a magnetic presheath, and the current-voltage relationship.

Heinrich, Jonathon R.; Cooke, David L. [Air Force Research Laboratory, Kirtland Air Force Base, New Mexico 87117 (United States)] [Air Force Research Laboratory, Kirtland Air Force Base, New Mexico 87117 (United States)

2013-09-15

359

Cytoplasmic motions, rheology, and structure probed by a novel magnetic particle method  

PubMed Central

The motions of magnetic particles contained within organelles of living cells were followed by measuring magnetic fields generated by the particles. The alignment of particles was sensed magnetometrically and was manipulated by external fields, allowing non-invasive detection of particle motion as well as examination of cytoplasmic viscoelasticity. Motility and rheology data are presented for pulmonary macrophages isolated from lungs of hamsters 1 d after the animals had breathed airborne gamma-Fe2O3 particles. The magnetic directions of particles within phagosomes and secondary lysosomes were aligned, and the weak magnetic field produced by the particles was recorded. For dead cells, this remanent field was constant, but for viable macrophages, the remanent field decreased rapidly so that only 42% of its initial magnitude remained 5 min after alignment. A twisting field was applied perpendicular to the direction of alignment and the rate at which particles reoriented to this new direction was followed. The same twisting was repeated for particles suspended in a series of viscosity standards. Based on this approach, the low-shear apparent intracellular viscosity was estimated to be 1.2-2.7 X 10(3) Pa.s (1.2-2.7 X 10(4) poise). Time-lapse video microscopy confirmed the alignment of ingested particles upon magnetization and showed persistent cellular motility during randomization of alignment. Cytochalasin D and low temperature both reduced cytoplasmic activity and remanent-field decay, but affected rheology differently. Magnetic particles were observed in association with the microtubule organizing center by immunofluorescence microscopy; magnetization did not affect microtubule distribution. However, both vimentin intermediate filaments and f-actin reorganized after magnetization. These data demonstrate that magnetometry of isolated phagocytic cells can probe organelle movements, rheology, and physical properties of the cytoskeleton in living cells.

1985-01-01

360

Quantitative stray field imaging of a magnetic vortex core  

NASA Astrophysics Data System (ADS)

Thin-film ferromagnetic disks present a vortex spin structure whose dynamics, added to the small size (?10 nm) of their core, has earned them intensive study. Here we use a scanning nitrogen-vacancy (NV) center microscope to quantitatively map the stray magnetic field above a 1-?m-diameter disk of permalloy, unambiguously revealing the vortex core. Analysis of both probe-to-sample distance and tip motion effects through stroboscopic measurements allows us to compare directly our quantitative images to micromagnetic simulations of an ideal structure. Slight perturbations with respect to the perfect vortex structure are clearly detected either due to an applied in-plane magnetic field or imperfections of the magnetic structures. This work demonstrates the potential of scanning NV microscopy to map tiny stray field variations from nanostructures, providing a nanoscale, nonperturbative detection of their magnetic texture.

Tetienne, J.-P.; Hingant, T.; Rondin, L.; Rohart, S.; Thiaville, A.; Roch, J.-F.; Jacques, V.

2013-12-01

361

Neutrino Oscillations in the Solar Noisy Matter and Magnetic Field  

NASA Astrophysics Data System (ADS)

Solar neutrino oscillations as a probe for the magnetic fields and matter density fluctuations in the solar interior as well as for the neutrino electromagnetic properties are discussed. The analysis of neutrino oscillations in the framework of the neutrino spin-flavor conversion in the convective zone magnetic fields as a sub-leading effect to the main LMA MSW oscillations could give the constraints to neutrino transition magnetic moment and magnetic field amplitude. We present the sensitivity of solar neutrino oscillations to the strength of the matter density perturbations given for the current experimental data and for future KamLAND result. The likely mechanism to generate the density noise based on the resonance between helioseismic and Alfvén waves is pointed.

Rashba, T. I.

2003-06-01

362

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

363

Suppression of magnetic relaxation by a transverse alternating magnetic field  

SciTech Connect

The evolution of the spatial distribution of the magnetic induction in a superconductor after the action of the alternating magnetic field perpendicular to the trapped magnetic flux has been analyzed. The observed stabilization of the magnetic induction profile is attributed to the increase in the pinning force, so that the screening current density becomes subcritical. The last statement is corroborated by direct measurements.

Voloshin, I. F.; Kalinov, A. V.; Fisher, L. M. [All-Russia Electrical Engineering Institute (Russian Federation)], E-mail: fisher@vei.ru; Yampol'skii, V. A. [National Academy of Sciences of Ukraine, Institute of Radiophysics and Electronics (Ukraine)], E-mail: yam@vk.kharkov.ua

2007-07-15

364

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

365

Magnetic nanostructures as amplifiers of transverse fields in magnetic resonance.  

PubMed

We introduce the concept of amplifying the transverse magnetic fields produced and/or detected with inductive coils in magnetic resonance settings by using the reversible transverse susceptibility properties of magnetic nanostructures. First, we describe the theoretical formalism of magnetic flux amplification through the coil in the presence of a large perpendicular DC magnetic field (typical of magnetic resonance systems) achieved through the singularity in the reversible transverse susceptibility in anisotropic single domain magnetic nanoparticles. We experimentally demonstrate the concept of transverse magnetic flux amplification in an inductive coil system using oriented nanoparticles with uni-axial magnetic anisotropy. We also propose a composite ferromagnetic/anti-ferromagnetic core/shell nanostructure system with uni-directional magnetic anisotropy that, in principle, provides maximal transverse magnetic flux amplification. PMID:16039099

Barbic, Mladen; Scherer, Axel

2005-09-01

366

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

367

Holographic Description of Strongly Correlated Electrons in External Magnetic Fields  

NASA Astrophysics Data System (ADS)

We study the Fermi level structure of 2+1-dimensional strongly interacting electron systems in external magnetic field using the AdS/CFT correspondence. The gravity dual of a finite density fermion system is a Dirac field in the background of the dyonic AdS-Reissner-Nordström black hole. In the probe limit the magnetic system can be reduced to the non-magnetic one, with Landau-quantized momenta and rescaled thermodynamical variables. We find that at strong enough magnetic fields, the Fermi surface vanishes and the quasiparticle is lost either through a crossover to conformal regime or through a phase transition to an unstable Fermi surface. In the latter case, the vanishing Fermi velocity at the critical magnetic field triggers the non-Fermi liquid regime with unstable quasiparticles and a change in transport properties of the system. We associate it with a metal-"strange metal" phase transition. We compute the DC Hall and longitudinal conductivities using the gravity-dressed fermion propagators. As expected, the Hall conductivity is quantized according to integer Quantum Hall Effect (QHE) at weak magnetic fields. At strong magnetic fields, new plateaus typical for the fractional QHE appear. Our pattern closely resembles the experimental results on graphite which are described using the fractional filling factor proposed by Halperin.

Gubankova, E.; Brill, J.; ?ubrovi?, M.; Schalm, K.; Schijven, P.; Zaanen, J.

368

A multichannel magnetic probe system for analysing magnetic fluctuations in helical axis plasmas.  

PubMed

The need to understand the structure of magnetic fluctuations in H-1NF heliac [S. Hamberger et al., Fusion Technol. 17, 123 (1990)] plasmas has motivated the installation of a sixteen former, tri-axis helical magnetic probe Mirnov array (HMA). The new array complements two existing poloidal Mirnov arrays by providing polarisation information, higher frequency response, and improved toroidal resolution. The helical placement is ideal for helical axis plasmas because it positions the array as close as possible to the plasma in regions of varying degrees of favourable curvature in the magnetohydrodynamic sense, but almost constant magnetic angle. This makes phase variation with probe position near linear, greatly simplifying the analysis of the data. Several of the issues involved in the design, installation, data analysis, and calibration of this unique array are presented including probe coil design, frequency response measurements, mode number identification, orientation calculations, and mapping probe coil positions to magnetic coordinates. Details of specially designed digitally programmable pre-amplifiers, which allow gains and filters to be changed as part of the data acquisition initialisation sequence and stored with the probe signals, are also presented. The low shear heliac geometry [R. Jiménez-Gómez et al., Nucl. Fusion 51, 033001 (2011)], flexibility of the H-1NF heliac, and wealth of information provided by the HMA create a unique opportunity for detailed study of Alfvén eigenmodes, which could be a serious issue for future fusion reactors. PMID:24089823

Haskey, S R; Blackwell, B D; Seiwald, B; Hole, M J; Pretty, D G; Howard, J; Wach, J

2013-09-01

369

A multichannel magnetic probe system for analysing magnetic fluctuations in helical axis plasmas  

SciTech Connect

The need to understand the structure of magnetic fluctuations in H-1NF heliac [S. Hamberger et al., Fusion Technol. 17, 123 (1990)] plasmas has motivated the installation of a sixteen former, tri-axis helical magnetic probe Mirnov array (HMA). The new array complements two existing poloidal Mirnov arrays by providing polarisation information, higher frequency response, and improved toroidal resolution. The helical placement is ideal for helical axis plasmas because it positions the array as close as possible to the plasma in regions of varying degrees of favourable curvature in the magnetohydrodynamic sense, but almost constant magnetic angle. This makes phase variation with probe position near linear, greatly simplifying the analysis of the data. Several of the issues involved in the design, installation, data analysis, and calibration of this unique array are presented including probe coil design, frequency response measurements, mode number identification, orientation calculations, and mapping probe coil positions to magnetic coordinates. Details of specially designed digitally programmable pre-amplifiers, which allow gains and filters to be changed as part of the data acquisition initialisation sequence and stored with the probe signals, are also presented. The low shear heliac geometry [R. Jiménez-Gómez et al., Nucl. Fusion 51, 033001 (2011)], flexibility of the H-1NF heliac, and wealth of information provided by the HMA create a unique opportunity for detailed study of Alfvén eigenmodes, which could be a serious issue for future fusion reactors.

Haskey, S. R.; Blackwell, B. D.; Seiwald, B.; Hole, M. J.; Pretty, D. G.; Howard, J.; Wach, J. [Plasma Research Laboratory, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 0200 (Australia)] [Plasma Research Laboratory, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 0200 (Australia)

2013-09-15

370

A multichannel magnetic probe system for analysing magnetic fluctuations in helical axis plasmas  

NASA Astrophysics Data System (ADS)

The need to understand the structure of magnetic fluctuations in H-1NF heliac [S. Hamberger et al., Fusion Technol. 17, 123 (1990)] plasmas has motivated the installation of a sixteen former, tri-axis helical magnetic probe Mirnov array (HMA). The new array complements two existing poloidal Mirnov arrays by providing polarisation information, higher frequency response, and improved toroidal resolution. The helical placement is ideal for helical axis plasmas because it positions the array as close as possible to the plasma in regions of varying degrees of favourable curvature in the magnetohydrodynamic sense, but almost constant magnetic angle. This makes phase variation with probe position near linear, greatly simplifying the analysis of the data. Several of the issues involved in the design, installation, data analysis, and calibration of this unique array are presented including probe coil design, frequency response measurements, mode number identification, orientation calculations, and mapping probe coil positions to magnetic coordinates. Details of specially designed digitally programmable pre-amplifiers, which allow gains and filters to be changed as part of the data acquisition initialisation sequence and stored with the probe signals, are also presented. The low shear heliac geometry [R. Jiménez-Gómez et al., Nucl. Fusion 51, 033001 (2011)], flexibility of the H-1NF heliac, and wealth of information provided by the HMA create a unique opportunity for detailed study of Alfvén eigenmodes, which could be a serious issue for future fusion reactors.

Haskey, S. R.; Blackwell, B. D.; Seiwald, B.; Hole, M. J.; Pretty, D. G.; Howard, J.; Wach, J.

2013-09-01

371

Magnetic field in a turbulent galactic disk  

Microsoft Academic Search

A simple kinematic model has been applied to simulate the evolution of the interstellar magnetic field permanently twisted by turbulent gas motions accompanied by effects of the field diffusion. The magnetic field was found to develop well-ordered twisted structures over the whole gas parcel analyzed. This field configuration has a preferred sense of twisting dependent on the helicity of the

Katarzyna Otmianowska-Mazur; Marek Urbanik; Artur Terech

1992-01-01

372

Quantitative model of the magnetospheric magnetic field  

Microsoft Academic Search

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

W. P. Olson; K. A. Pfitzer

1974-01-01

373

Atom probe field ion microscopy of high resistivity materials  

SciTech Connect

Over the last 30 years the atom probe has proved to be a powerful tool for studying nanometer-sized compositional fluctuations in a wide range of metallic alloys but has had only limited applications to semiconductors and ceramics. One of the primary reasons for this difference is the higher resistivity of semiconducting and ceramic specimens. Because of this high resistivity, the high voltage field evaporation pulse is attenuated before it reaches the apex of the specimen thereby making the pulse ineffective for field evaporation. Experiments have demonstrated that both variants of the voltage-pulsed atom probe (i.e., those instruments in which the field evaporation pulse is applied directly to the specimen and those in which the negative pulse is applied to a counter electrode in front of the specimen) are equally affected. In this overview, the limits of applicability of the voltage-pulsed atom probe to high resistivity materials are examined. In this study, a wide range of materials have been examined to determine whether field ion microscopy and voltage-pulsed field evaporation can be achieved and the results are summarized in the report. Field ion microscopy including dc field evaporation was possible for all materials except bulk ceramic insulators and glasses. Field ion microscopy requires some conductivity both to achieve a high electric field at the apex of the specimen, and also to support the field ion current. In contrast, voltage-pulsed field evaporation requires transmission of the pulse to the apex of the specimen. All metallic alloys including high resistance alloys and metallic glasses were successfully field evaporated with a voltage pulse. Specimens that were produced from bulk material of several conducting ceramics including MoSi, TiB and TiC were also successfully field evaporated with a voltage pulse.

Sibrandij, S.J.; Larson, D.J.; Miller, M.K.

1998-02-01

374

Spin dephasing in a magnetic dipole field.  

PubMed

Transverse relaxation by dephasing in an inhomogeneous field is a general mechanism in physics, for example, in semiconductor physics, muon spectroscopy, or nuclear magnetic resonance. In magnetic resonance imaging the transverse relaxation provides information on the properties of several biological tissues. Since the dipole field is the most important part of the multipole expansion of the local inhomogeneous field, dephasing in a dipole field is highly important in relaxation theory. However, there have been no analytical solutions which describe the dephasing in a magnetic dipole field. In this work we give a complete analytical solution for the dephasing in a magnetic dipole field which is valid over the whole dynamic range. PMID:23004789

Ziener, C H; Kampf, T; Reents, G; Schlemmer, H-P; Bauer, W R

2012-05-01

375

Integrated and Portable Electric &Magnetic Field Sensing System for Geosciences  

NASA Astrophysics Data System (ADS)

We have developed a lightweight, low power, man-portable electromagnetic sensing system for geosciences applications. The system integrates a high sensitivity, 3 axis electric field and 3 axis magnetic field sensing system into an easily deployable package capable of probing the conductivity of the earth's crust to several kilometers in depth. The system is equipped with onboard 24 bit continuous, and 16 bit triggered burst capture data acquisition hardware, GPS synchronization, and Ethernet output. System performance will be demonstrated through the results of a field tests in the Snake River Plain area of southeastern Idaho. Magnetotelluric inversions from field data compare favorably with previous studies of subsurface structure.

Nielsen, T. K.; Delory, G. T.; Grimm, R. E.

2006-12-01

376

A field-sweep/field-lock system for superconducting magnets--Application to high-field EPR.  

PubMed

We describe a field-lock/field-sweep system for the use in superconducting magnets. The system is based on a commercially available field mapping unit and a custom designed broad-band 1H NMR probe. The NMR signal of a small water sample is used in a feedback loop to set and control the magnetic field to high accuracy. The current instrumental configuration allows field sweeps of +/-0.4 T and a resolution of up to 10(-5) T (0.1 G) and the performance of the system is demonstrated in a high-field electron paramagnetic resonance (EPR) application. The system should also be of utility in other experiments requiring precise and reproducible sweeps of the magnetic field such as DNP, ENDOR or PELDOR. PMID:17027306

Maly, Thorsten; Bryant, Jeff; Ruben, David; Griffin, Robert G

2006-12-01

377

A Field-Sweep/Field-Lock System for Superconducting Magnets-Application to High-Field EPR  

PubMed Central

We describe a field-lock/field-sweep system for the use in superconducting magnets. The system is based on a commercially available field mapping unit and a custom designed broad-band 1H-NMR probe. The NMR signal of a small water sample is used in a feedback loop to set and control the magnetic field to high accuracy. The current instrumental configuration allows field sweeps of ± 0.4 T and a resolution of up to 10-5 T (0.1 G) and the performance of the system is demonstrated in a high-field electron paramagnetic resonance (EPR) application. The system should also be of utility in other experiments requiring precise and reproducible sweeps of the magnetic field such as DNP, ENDOR or PELDOR.

Maly, Thorsten; Bryant, Jeff; Ruben, David; Griffin, Robert G.

2007-01-01

378

Atom probe field ion microscopy of titanium aluminides  

SciTech Connect

Titanium aluminides have a number of potential high temperature applications due to their good elevated-temperature mechanical properties, low density, and good creep and oxidation resistance. However, fabrication of commercial components of these materials has been impeded by their poor mechanical properties at ambient temperatures. Significant efforts with various degrees of success have been made to improve the mechanical properties of these TiAl alloys by doping them with a variety of different elements including B, C, Cr, Er, Fe, Mn, Mo, Ni, Nb, P, Si, Ta, V and W. One of the optimum analytical tools for investigating the effects of these additions on the microstructure is the atom probe field ion micro scope. However, relatively few studies of titanium aluminides, compared to some other intermetallic compounds, have performed by atom probe field ion microscopy. This lack of attention can be attributed to the brittle nature of the material, in-situ transformations that occur during the field ion microscopy and preferential evaporation problems that were encountered in some of the early studies. The atom probe field ion microscope used for the current experiments has a low base pressure ({approximately} 2 {times} 10{sup 9} Pa) and careful attention was paid to optimizing the experimental parameters. All the examples shown were obtained from specimens prepared by standard electropolishing techniques. To demonstrate the suitability of the technique to these materials, several different titanium aluminides have been characterized in the atom probe.

Larson, D.J.; Miller, M.K.

1998-01-01

379

MEMS Electric-Field Probes for Laboratory Plasmas  

Microsoft Academic Search

This paper presents microfabricated sensors for directly measuring fine-scale plasma parameters in typical laboratory plasmas. Microfabricated probes have the potential to significantly advance basic plasma physics by enabling the measurement of fundamental processes under controlled conditions. Historically, the spatial scales of the finest electromagnetic-field fluctuations in laboratory plasmas have been too small for conventionally fabricated tools to sense. The new

Janet A. Stillman; Franklin C. Chiang; Patrick Pribyl; W. Gekelman; M. Nakamoto; Jack W. Judy

2009-01-01

380

Probe Station and Near-Field Scanner for Testing Antennas  

NASA Technical Reports Server (NTRS)

A facility that includes a probe station and a scanning open-ended waveguide probe for measuring near electromagnetic fields has been added to Glenn Research Center's suite of antenna-testing facilities, at a small fraction of the cost of the other facilities. This facility is designed specifically for nondestructive characterization of the radiation patterns of miniaturized microwave antennas fabricated on semiconductor and dielectric wafer substrates, including active antennas that are difficult to test in traditional antenna-testing ranges because of fragility, smallness, or severity of DC-bias or test-fixture requirements. By virtue of the simple fact that a greater fraction of radiated power can be captured in a near-field measurement than in a conventional far-field measurement, this near-field facility is convenient for testing miniaturized antennas with low gains.

Zaman, Afroz; Lee, Richard Q.; Darby, William G.; Barr, Philip J.; Miranda, Felix A.; Lambert, Kevin

2006-01-01

381

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

382

The Wind Magnetic Field Investigation  

NASA Astrophysics Data System (ADS)

The magnetic field experiment on WIND will provide data for studies of a broad range of scales of structures and fluctuation characteristics of the interplanetary magnetic field throughout the mission, and, where appropriate, relate them to the statics and dynamics of the magnetosphere. The basic instrument of the Magnetic Field Investigation (MFI) is a boom-mounted dual triaxial fluxgate magnetometer and associated electronics. The dual configuration provides redundancy and also permits accurate removal of the dipolar portion of the spacecraft magnetic field. The instrument provides (1) near real-time data at nominally one vector per 92 s as key parameter data for broad dissemination, (2) rapid data at 10.9 vectors s-1 for standard analysis, and (3) occasionally, snapshot (SS) memory data and Fast Fourier Transform data (FFT), both based on 44 vectors s-1. These measurements will be precise (0.025%), accurate, ultra-sensitive (0.008 nT/step quantization), and where the sensor noise level is <0.006 nT r.m.s. for 0 10 Hz. The digital processing unit utilizes a 12-bit microprocessor controlled analogue-to-digital converter. The instrument features a very wide dynamic range of measurement capability, from ±4 nT up to ±65 536 nT per axis in eight discrete ranges. (The upper range permits complete testing in the Earth's field.) In the FTT mode power spectral density elements are transmitted to the ground as fast as once every 23 s (high rate), and 2.7 min of SS memory time series data, triggered automatically by pre-set command, requires typically about 5.1 hours for transmission. Standard data products are expected to be the following vector field averages: 0.0227-s (detail data from SS), 0.092 s (‘detail’ in standard mode), 3 s, 1 min, and 1 hour, in both GSE and GSM coordinates, as well as the FFT spectral elements. As has been our team's tradition, high instrument reliability is obtained by the use of fully redundant systems and extremely conservative designs. We plan studies of the solar wind: (1) as a collisionless plasma laboratory, at all time scales, macro, meso and micro, but concentrating on the kinetic scale, the highest time resolution of the instrument (=0.022 s), (2) as a consequence of solar energy and mass output, (3) as an external source of plasma that can couple mass, momentum, and energy to the Earth's magnetosphere, and (4) as it is modified as a consequence of its imbedded field interacting with the moon. Since the GEOTAIL Inboard Magnetometer (GIM), which is similar to the MFI instrument, was developed by members of our team, we provide a brief discussion of GIM related science objectives, along with MFI related science goals.

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

1995-02-01

383

Gravity field information from Gravity Probe-B  

NASA Technical Reports Server (NTRS)

The Gravity Probe-B Mission will carry the Stanford Gyroscope relativity experiment into orbit in the mid 1990's, as well as a Global Positioning System (GPS) receiver whose tracking data will be used to study the earth gravity field. Estimates of the likely quality of a gravity field model to be derived from the GPS data are presented, and the significance of this experiment to geodesy and geophysics are discussed.

Smith, D. E.; Lerch, F. J.; Colombo, O. L.; Everitt, C. W. F.

1989-01-01

384

Topological Description of Coronal Magnetic Fields.  

National Technical Information Service (NTIS)

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

M. A. Berger

1986-01-01

385

Structured electrodeposition in magnetic gradient fields  

NASA Astrophysics Data System (ADS)

Electrodeposition in superimposed magnetic gradient fields is a new and promising method of structuring metal deposits while avoiding masking techniques. The magnetic properties of the ions involved, their concentrations, the electrochemical deposition parameters, and the amplitude of the applied magnetic gradient field determine the structure generated. This structure can be thicker in regions of high magnetic field gradients. It can also be free-standing or inversely structured. The complex mechanism of structured electrodeposition of metallic layers in superimposed magnetic gradient fields was studied by different experimental methods, by analytical methods and by numerical simulation and will be discussed comprehensively.

Uhlemann, Margitta; Tschulik, Kristina; Gebert, Annett; Mutschke, Gerd; Fröhlich, Jochen; Bund, Andreas; Yang, Xuegeng; Eckert, Kerstin

2013-03-01

386

Deformation of Water by a Magnetic Field  

ERIC Educational Resources Information Center

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

Chen, Zijun; Dahlberg, E. Dan

2011-01-01

387

Anhysteretic Remanent Magnetization in Small Steady Fields  

Microsoft Academic Search

The phenomenon called anhysteretic remanent magnetization, ARM, has been known for a long time, but it has received relatively little attention. A knowledge of this type of magnetization is required in proper application of alternating field demagnetization tech- niques to rock magnetism problems. Over a wide range of low values of the steady field Ho, the ARM intensity is a

Bob J. Patton; John L. Fitch

1962-01-01

388

On Magnetic Field Generation Mechanisms in Astrophysics  

Microsoft Academic Search

Magnetic chemically peculiar stars (CP stars) are characterized by a strong magnetic field, peculiar chemical composition and slow rotation. Since the origin and evolution of CP stars may be responsible for such unusual features, understanding the mechanisms of generation of the magnetic field is one of the ways to learn more about the CP star characteristics. At present there are

O. G. Cherny

2011-01-01

389

Orienting Paramecium with intense static magnetic fields  

Microsoft Academic Search

Recent experiments on cell division suggest the application of intense static magnetic fields as a novel tool for the manipulation of biological systems [1]. The magnetic field appears to couple to the intrinsic anisotropies in the diamagnetic components of the cells. Here, we present measurements of the intrinsic average diamagnetic anisotropy of the whole single celled ciliate, Paramecium Caudatum. Magnetic

James M. Valles Jr.; Karine Guevorkian; Carl Quindel

2004-01-01

390

Baking a magnetic-field display  

NASA Astrophysics Data System (ADS)

Copy machine developer powder is an alternative for creating permanent displays of magnetic fields. A thin layer of developer powder on a sheet of paper placed over a magnet can be baked in the oven, producing a lasting image of a magnetic field.

Cavanaugh, Terence; Cavanaugh, Catherine

1998-02-01

391

The structure of helical interplanetary magnetic fields  

NASA Technical Reports Server (NTRS)

The interplanetary magnetic field is known to be highly helical. Although the detailed spatial structure of the fields has yet to be elucidated, the helicity spectrum has been conjectured to result from a random walk in the direction of a constant magnitude magnetic field vector. A model using three-dimensional fluctuations with variations in B is demonstrated giving a good fit to the helicity spectrum as well as to other properties of the interplanetary magnetic field.

Goldstein, M. L.; Roberts, D. A.; Fitch, C. A.

1991-01-01

392

Analysis of magnetic field levels at KSC  

NASA Technical Reports Server (NTRS)

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

Christodoulou, Christos G.

1994-01-01

393

Study of interplanetary magnetic field with atomic realignment  

NASA Astrophysics Data System (ADS)

We demonstrate a new way of studying interplanetary magnetic field - atomic alignment. Instead of sending thousands of space probes, atomic alignment allows magnetic mapping with any ground telescope facilities equipped with spectrometer and polarimeter. The polarization of spectral lines that are pumped by the anisotropic radiation from the sun is influenced by the magnetic alignment, which happens for weak magnetic field (<1G). As a result, the linear polarization becomes an excellent tracer of the embedded magnetic field. The method is illustrated by our synthetic observations of Iofootnote{The third largest moon of Jupiter.} and comet Halley. A uniform density distribution of Na was considered and polarization at each point was then constructed. Both spatial and temporal variations of turbulent magnetic field can be traced with this technique as well. For remote regions like the boundary of interstellar medium, atomic alignment provides a unique diagnostics of magnetic field, which is crucial for understanding the physical processes such as the IBEX ribbons discovered recently.

Yan, H.; Shangguan, J.

2011-12-01

394

Experimental Investigation of Axial Plasma Injection into a Magnetic Dipole Field  

Microsoft Academic Search

A high-density helium plasma, accelerated from a conical pinch, is injected axially into a magnetic dipole field. Magnetic probe measurements show that, near the axis, a compression of the field is super-imposed on the standard diamagnetic depression. The compression starts downstream and moves towards the injector. Simultaneously with the compression, an increase in the electron temperature and reflection of a

V. O. Jensen

1968-01-01

395

Design and validation of the ball-pen probe for measurements in a low-temperature magnetized plasma  

SciTech Connect

Ball-pen probes have been used in fusion devices for direct measurements of the plasma potential. Their application in low-temperature magnetized plasma devices is still subject to studies. In this context, a ball-pen probe has been recently implemented on the linear plasma device Mirabelle. Produced by a thermionic discharge, the plasma is characterized by a low electron temperature and a low density. Plasma confinement is provided by an axial magnetic field that goes up to 100 mT. The principle of the ball-pen probe is to adjust the saturation current ratio to 1 by reducing the electron current contribution. In that case, the floating potential of the probe is close to the plasma potential. A thorough study of the ball-pen probe operation is performed for different designs of the probe over a large set of plasma conditions. Comparisons between ball-pen, Langmuir, and emissive probes are conducted in the same plasma conditions. The ball-pen probe is successfully measuring the plasma potential in these specific plasma conditions only if an adapted electronics and an adapted probe size to the plasma characteristic lengths ({lambda}{sub D}, {rho}{sub ce}) are used.

Bousselin, G.; Cavalier, J.; Pautex, J. F.; Heuraux, S.; Lemoine, N.; Bonhomme, G. [IJL, Universite de Lorraine, CNRS (UMR 7198), BP 70239, 54506 Vandoeuvre-les-Nancy (France)

2013-01-15

396

Rotating magnetic beacons magnetic field strength size in SAGD  

Microsoft Academic Search

Rotation magnetic beacons magnetic field strength is very important to drill parallel horizontal twin wells in steam assisted\\u000a gravity drainage (SAGD). This paper analyzes a small magnet with a diameter of 25.4 mm. At each end, there is a length of\\u000a 12.6 mm with permanent magnet, and in the middle, there is a length of 78mm with magnetic materials. The

Bing Tu; Desheng Li; Enhuai Lin; Bin Luo; Jian He; Lezhi Ye; Jiliang Liu; Yuezhong Wang

2010-01-01

397

Effects of internal structure on equilibrium of field-reversed configuration plasma sustained by rotating magnetic field  

Microsoft Academic Search

The effects of an internal structure on the equilibrium of a field-reversed configuration (FRC) plasma sustained by rotating magnetic field is investigated by using detailed electrostatic probe measurements in the FRC Injection Experiment apparatus [S. Okada, et al., Nucl. Fusion. 45, 1094 (2005)]. An internal structure installed axially on the geometrical axis, which simulates Ohmic transformer or external toroidal field

Kiyoyuki Yambe; Michiaki Inomoto; Shigefumi Okada; Yuka Kobayashi; Tomohiko Asai

2008-01-01

398

Magnetizing technique for permanent magnets by intense static fields generated by HTS bulk magnets: Numerical Analysis  

NASA Astrophysics Data System (ADS)

A demagnetized Nd-Fe-B permanent magnet was scanned in the strong magnetic field space just above the magnetic pole containing a HTS bulk magnet which generates the magnetic field 3.4 T. The magnet sample was subsequently found to be fully magnetized in the open space of the static magnetic fields. The finite element method was carried out for the static field magnetization of a permanent magnet using a HTS bulk magnet. Previously, our research group experimentally demonstrated the possibility of full magnetization of rare earth permanent magnets with high-performance magnetic properties with use of the static field of HTS bulk magnets. In the present study, however, we succeeded for the first time in visualizing the behavior of the magnetizing field of the bulk magnet during the magnetization process and the shape of the magnetic field inside the body being magnetized. By applying this kind of numerical analysis to the magnetization for planned motor rotors which incorporate rare-earth permanent magnets, we hope to study the fully magnetized regions for the new magnetizing method using bulk magnets and to give motor designing a high degree of freedom.

N. Kawasaki; Oka, T.; Fukui, S.; Ogawa, J.; Sato, T.; Terasawa, T.; Itoh, Y.

399

Probing Magnetic Configurations in Buried Cobalt/Copper Multilayered Nanowires  

NASA Astrophysics Data System (ADS)

Multilayered magnetic nanowires have been a model system for heterostructured junctions that exhibit a host of fascinating perpendicular spin transport phenomena, such as giant and tunneling magnetoresistance (MR), and spin-transfer torque effects. Due to the extremely small physical dimensions the magnetic components in these nanowires or junctions often exhibit complex magnetization reversal behaviors, which are difficult to probe by magnetic imaging since the entities are buried deep inside a matrix. Conventional hysteresis loop measurement alone cannot reliably distinguish the reversal mechanisms either. In this work we have captured magnetic and MR ``fingerprints'' of Co nanodiscs in Co/Cu multilayered nanowires as they undergo a single domain to vortex state transition, using a first-order reversal curve (FORC) method [1]. The nanowires have been electrochemically deposited into nanoporous polycarbonate membranes. In 50 nm diameter [Co(5nm)/Cu(8nm)]400 nanowires, a 10% MR effect is observed at 300 K. In 200 nm diameter nanowires, the magnetic configurations can be tuned by adjusting the Co nanodisc aspect ratio. Nanowires with thinnest Co exhibit single domain behavior. Those with thicker Co exhibit vortex states, where the irreversible nucleation and annihilation of the vortices are manifested as butterfly-like features in the FORC distributions, similar to those observed in arrays of Fe nanodots [2]. They also show a superposition of giant and anisotropic magnetoresistance, which corresponds to the specific magnetic configurations of the Co nanodiscs. [4pt] [1] J. E. Davies, et al, Phys. Rev. B 70, 224434 (2004); Appl. Phys. Lett. 86, 262503 (2005); Phys. Rev. B 77, 014421 (2008).[0pt] [2] R. K. Dumas, et al, Phys. Rev. B 75, 134405 (2007); Appl. Phys. Lett. 91, 202501 (2007).

Liu, Kai

2009-03-01

400

Probing the Magnetic Order of UPt3 by Magnetoresistance  

NASA Astrophysics Data System (ADS)

It is believed that magnetic order has a strong influence on the unconventional superconducting state of UPt3, both as a symmetry breaking field that splits two degenerate superconducting phases, and as an element of the pairing mechanism. There are conflicting reports of the behavior at 5 K, static antiferromagnetic order versus slow fluctuating magnetism. We present measurements of the temperature dependence of the magnetoresistance in bulk single crystals of UPt3. Below 5 K, we observe an onset and subsequent rapid increase of a term linear in the applied field. With the field in the basal plane, this linear contribution is positive with current along the c-axis and negative with the current along the b-axis. We identify this behavior in the magnetoresistance with observation of magnetic Bragg peaks from neutron scattering that appear below 5 K. We discuss preliminary results of similar measurements at temperatures in the millikelvin range.

Lippman, Thomas M.; Davis, John P.; Choi, Hyoungsoon; Pollanen, Johannes; Gannon, William J.; Halperin, William P.

2007-03-01

401

Effects of magnetic fields on mosquitoes.  

PubMed

Phylogenetically diverse organisms, including some insects, are able to detect and respond to magnetic fields comparable to the Earth's magnetic field. Because of their tremendous importance to public health, mosquitoes were tested for the presence of remanent ferromagnetic material indicative of a biological compass and also tested for behavioral responses to magnetic fields. Using a superconducting quantum interferometry device, we found that significant remnant was probably due to attraction of ferromagnetic dust onto the surface of live or dead mosquitoes. Most mosquitoes placed in a 1.0-gauss, uniform magnetic field moved until they were oriented parallel to the field. Two of 3 species of mosquitoes tested took fewer blood meals in a rotating magnetic field than in the Earth's normal magnetic field. PMID:10901636

Strickman, D; Timberlake, B; Estrada-Franco, J; Weissman, M; Fenimore, P W; Novak, R J

2000-06-01

402

Boston University Physics Applets: Magnetic Field Demonstration  

NSDL National Science Digital Library

This web page is an interactive physics simulation that explores magnetic fields. The user can add currents coming into or out of a simulated grid, and see the fields created. There is also a selection of pre-created fields, including bar magnets, loops, opposing magnets, and coils in uniform fields. Double-clicking on any point displays the full loop created by the magnetic field. This item is part of a larger collection of introductory physics simulations developed by the author. This is part of a collection of similar simulation-based student activities.

Duffy, Andrew

2008-08-23

403

Magnetic fields in the early Universe  

NASA Astrophysics Data System (ADS)

We give a pedagogical introduction to two aspects of magnetic fields in the early Universe. We first focus on how to formulate electrodynamics in curved space time, defining appropriate magnetic and electric fields and writing Maxwell equations in terms of these fields. We then specialize to the case of magnetohydrodynamics in the expanding Universe. We emphasize the usefulness of tetrads in this context. We then review the generation of magnetic fields during the inflationary era, deriving in detail the predicted magnetic and electric spectra for some models. We discuss potential problems arising from back reaction effects and from the large variation of the coupling constants required for such field generation.

Subramanian, K.

2010-01-01

404

Near-Field Magnetic Dipole Moment Analysis.  

National Technical Information Service (NTIS)

This paper describes the data analysis technique used for magnetic testing at the NASA Goddard Space Flight Center (GSFC). Excellent results have been obtained using this technique to convert a spacecraft s measured magnetic field data into its respective...

P. K. Harris

2003-01-01

405

Bipolar pulse field for magnetic refrigeration  

DOEpatents

A magnetic refrigeration apparatus includes first and second steady state magnets, each having a field of substantially equal strength and opposite polarity, first and second bodies made of magnetocaloric material disposed respectively in the influence of the fields of the first and second steady state magnets, and a pulsed magnet, concentric with the first and second steady state magnets, and having a field which cycles between the fields of the first and second steady state magnets, thereby cyclically magnetizing and demagnetizing and thus heating and cooling the first and second bodies. Heat exchange apparatus of suitable design can be used to expose a working fluid to the first and second bodies of magnetocaloric material. A controller is provided to synchronize the flow of working fluid with the changing states of magnetization of the first and second bodies. 2 figs.

Lubell, M.S.

1994-10-25

406

MAGNETIC BRAIDING AND PARALLEL ELECTRIC FIELDS  

SciTech Connect

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

Wilmot-Smith, A. L.; Hornig, G.; Pontin, D. I. [Division of Mathematics, University of Dundee, Dundee DD1 4HN (United Kingdom)], E-mail: antonia@maths.dundee.ac.uk

2009-05-10

407

The Auroral Spatial Structures Probe: Exploring Small-Scale High-Latitude Electric Field Variability  

NASA Astrophysics Data System (ADS)

The Auroral Spatial Structures Probe (ASSP) is a NASA sounding rocket mission to be launched in the late January 2014 time frame that will be used to study both the spatial and temporal small scale variation of the electric and magnetic fields during active aurora and just before the onset of an auroral sub-storm. This will be accomplished through the use of a constellation of small payloads that separate relative to each other throughout a sounding rocket flight. The multiple baseline observations of the electric and magnetic fields will be used to observe variability of both the E-field and the Poynting flux. These observations will be placed in the context of available data, including winds, large scale E-fields, and proxy conductivity (airglow image) observations. In this way we will address the main scientific objective of this mission which is: What are the contributions of small spatial scale and rapid temporal scale fluctuations of electric fields relative to the larger-scale electrodynamic processes? The high altitude rocket will be launched along the magnetic field line and carry six sub-payloads to be ejected from the main payload at high velocity. The sub-payloads will be deployed both along the flight path and perpendicular to the flight path so that both spatial features and temporal-spatial ambiguities can be explored. The low-mass sub-payloads will achieve at least a 35 km separation by the end of the flight and are key to observational success. Each sub-payload will carry a crossed pair of double-probe sensors to measure in-situ electric fields, a three axis magnetometer, a Langmuir probe and a GPS receiver. In this poster we review the ASSP science, mission, and design, and present instrument calibration and testing results.

Farr, D.; Weston, C.; Nelson, W.; Stromberg, E. M.; Byers, B.; Frazier, C.; Swenson, A.; Miller, J.; Carrick, B.; Neilsen, T. L.; Hidalgo, J. M.; Cox, W.; Evans, T.; Vangeison, V.; Perkins, C.; Fish, C. S.; Swenson, C.

2013-12-01

408

Reporter protein-targeted probes for magnetic resonance imaging.  

PubMed

Contrast agents for magnetic resonance imaging are frequently employed as experimental and clinical probes. Drawbacks include low signal sensitivity, fast clearance, and nonspecificity that limit efficacy in experimental imaging. In order to create a bioresponsive MR contrast agent, a series of four Gd(III) complexes targeted to the HaloTag reporter were designed and synthesized. HaloTag is unique among reporter proteins for its specificity, versatility, and the covalent interaction between substrate and protein. In similar systems, these properties produce prolonged in vivo lifetimes and extended imaging opportunities for contrast agents, longer rotational correlation times, and increases in relaxivity (r(1)) upon binding to the HaloTag protein. In this work we report a new MR contrast probe, 2CHTGd, which forms a covalent bond with its target protein and results in a dramatic increase in sensitivity. A 6-fold increase in r(1), from 3.8 to 22 mM(-1) s(-1), is observed upon 2CHTGd binding to the target protein. This probe was designed for use with the HaloTag protein system which allows for a variety of substrates (specific for MRI, florescence, or protein purification applications) to be used with the same reporter. PMID:21942425

Strauch, Renee C; Mastarone, Daniel J; Sukerkar, Preeti A; Song, Ying; Ipsaro, Jonathan J; Meade, Thomas J

2011-10-19

409

Reporter Protein-Targeted Probes for Magnetic Resonance Imaging  

PubMed Central

Contrast agents for magnetic resonance imaging are frequently employed as experimental and clinical probes. Drawbacks include low signal sensitivity, fast clearance and non-specificity that limit efficacy in experimental imaging. In order to create a bio-responsive MR contrast agent, a series of four Gd(III) complexes targeted to the HaloTag reporter were designed and synthesized. HaloTag is unique among reporter proteins for its specificity, versatility, and the covalent interaction between substrate and protein. In similar systems, these properties produce prolonged in vivo lifetimes and extended imaging opportunities for contrast agents, longer rotational correlation times, and increases in relaxivity (r1) upon binding to the HaloTag protein. In this work we report a new MR contrast probe, 2CHTGd, which forms a covalent bond with a target protein and results in a dramatic increase in sensitivity. A 6-fold increase in r1, from 3.8 mM?1s?1 to 22 mM?1s?1, is observed upon 2CHTGd binding to the target protein. This probe was designed for use with the HaloTag protein system which allows for a variety of substrates (specific for MRI, florescence, or protein purification applications) to be used with the same reporter.

Strauch, Renee C.; Mastarone, Daniel J.; Sukerkar, Preeti A.; Song, Ying; Ipsaro, Jonathan J.; Meade, Thomas J.

2011-01-01

410

Probing arrays of circular magnetic microdots by ferromagnetic resonance.  

SciTech Connect

X-band ferromagnetic resonance (FMR) was used to characterize in-plane magnetic anisotropies in rectangular and square arrays of circular nickel and Permalloy microdots. In the case of a rectangular lattice, as interdot distances in one direction decrease, the in-plane uniaxial anisotropy field increases, in good agreement with a simple theory of magnetostatically interacting uniformly magnetized dots. In the case of a square lattice a four-fold anisotropy of the in-plane FMR field H(r) was found when the interdot distance a gets comparable to the dot diameter D. This anisotropy, not expected in the case of uniformly magnetized dots, was explained by a non-uniform magnetization m(r) in a dot in response to dipolar forces in the patterned magnetic structure. It is well described by an iterative solution of a continuous variation procedure. In the case of perpendicular magnetization multiple sharp resonance peaks were observed below the main FMR peak in all the samples, and the relative positions of these peaks were independent of the interdot separations. Quantitative description of the observed multiresonance FMR spectra was given using the dipole-exchange spin wave dispersion equation for a perpendicularly magnetized film where in-plane wave vector is quantized due to the finite dot radius, and the inhomogenetiy of the intradot static demagnetization field in the nonellipsoidal dot is taken into account. It was demonstrated that ferromagnetic resonance force microscopy (FMRFM) can be used to determine both local and global properties of patterned submicron ferromagnetic samples. Local spectroscopy together with the possibility to vary the tip-sample spacing enables the separation of those two contributions to a FMRFM spectrum. The global FMR properties of circular submicron dots determined using magnetic resonance force microscopy are in a good agreement with results obtained using conventional FMR and with theoretical descriptions.

Kakazei, G. N.; Mewes, T.; Wigen, P. E.; Hammel, P. C.; Slavin, A. N.; Pogorelov, Y. G.; Costa, M. D.; Golub, V. O.; Guslienko, K. Y.; Novosad, V. (Materials Science Division); (Univ. of Porto); (National Academy of Sciences Ukraine); (Univ. of Alabama); (Ohio State Univ.); (Oakland Univ.)

2008-06-01

411

Horizontal magnetic fields in the solar photosphere  

Microsoft Academic Search

Two-dimensional simulations of time-dependent solar magnetogranulation are used to analyze the horizontal magnetic fields and the response of the synthesized Stokes profiles of the IR FeI lambda1564.85 nm line to the magnetic fields. The 1.5-h series of MHD models used for the analyses reproduces a region of the magnetic network in the photosphere with an unsigned magnetic flux density of

V. A. Sheminova

2009-01-01

412

Horizontal magnetic fields in the solar photosphere  

Microsoft Academic Search

Two-dimensional simulations of time-dependent solar magnetogranulation are used to analyze the horizontal magnetic fields\\u000a and the response of the synthesized Stokes profiles of the IR FeI ?1564.85 nm line to the magnetic fields. The 1.5-h series of MHD models used for the analyses reproduces a region of the magnetic\\u000a network in the photosphere with an unsigned magnetic flux density of

V. A. Sheminova

2009-01-01

413

Site and probe dependence of hyperfine magnetic field in L2 1 Heusler alloys X 2 MnZ (X=Ni, Cu, Rh, Pd and Z=Ga, Ge, In, Sn, Pb)  

Microsoft Academic Search

Results of TDPAC and Mössbauer measurements of hyperfine magnetic fields in L21 Heusler alloys X2MnZ are given. TDPAC utilized Cd-111 from In-111 at the Z site and Ag-111 at the X site, and Ru-99 from Rh-99 at the X site. Mössbauer studies utilized Sn-119 at the Z site or at the Mn site. A compilation of hmf values is presented,

S. Jha; H. M. Seyoum; M. Demarco; G. M. Julian; D. A. Stubbs; J. W. Blue; M. T. X. Silva; A. Vasquez

1983-01-01

414

Electromagnetic Testing of Magnetic Material by Rotating Uniform Eddy Current Probe  

NASA Astrophysics Data System (ADS)

A rotating uniform eddy current probe composed of two exciting tangential coils and a detecting pancake coil can simultaneously conduct eddy current testing and magnetic testing of magnetic material. The eddy current testing detects parallel flaws to the probe scan direction and the magnetic testing detects perpendicular flaws. The signal phase shows that either ET or MT generates the signal. An appropriate test frequency enables the probe to detect flaws in any direction with almost the same sensitivity.

Hoshikawa, H.; Koyama, K.; Mitsuhashi, S.

2006-03-01

415

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

416

The National High Magnetic Field Laboratory  

Microsoft Academic Search

The National High Magnetic Field Laboratory (NHMFL) was established in 1990, on the basis of a collaboration between Florida State University (FSU), the University of Florida (UF) and Los Alamos National Laboratory (LANL). The main campus for the NHMFL is located in Tallahassee, Florida, and its general purpose DC magnetic field facility is described in this paper. The pulsed field

B. L. Brandt; S. Hannahs; H. J. Schneider-Muntau; G. Boebinger; N. S. Sullivan

2001-01-01

417

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

418

Primordial magnetic fields from superconducting cosmic strings  

Microsoft Academic Search

This paper explores the possibility of generation of a primordial magnetic field by a network of charged-current carrying cosmic strings. The field is created by vorticity, generated in the primordial plasma due to the strings' motion and gravitational pull. In the case of superconducting strings formed at the breaking of grand unification, it is found that strong magnetic fields of

Konstantinos Dimopoulos

1998-01-01

419

Soil gas carbon dioxide probe: laboratory testing and field evaluation.  

PubMed

An automated semi-continuous on-line instrument has been developed to measure CO2 gas concentrations in the vadose zone. The instrument uses semi-permeable polymer tubing (CO2 probe) for diffusion based sampling, coupled to an infra red sensor. The system operated automatically by intermittently purging the CO2 probe, which was installed in the vadose zone, with a non-CO2 gas at a low flow rate. The gas exiting the CO2 probe was monitored at the ground surface using a miniature infra red sensor and the response related to the vadose zone soil gas CO2 concentration. The in situ CO2 probes provided a reliable monitoring technique under long-term (18 months) aggressive and dynamic field conditions, with no interference observed from non-CO2 gases and volatile organic compounds. The probes provided data that were comparable to conventional grab sampling techniques without the labour-intensive sample collection and processing associated with these conventional techniques. Also, disturbance to vadose zone CO2 profiles from repeated grab samples during long-term semi-continuous monitoring could potential be reduced by using the diffusion based sampling technique. PMID:23563305

Patterson, B M; Furness, A J; Bastow, T P

2013-05-01

420

Possible Generation of Self-Magnetic Fields  

SciTech Connect

The earth generates its own magnetic field via a dynamo effect in a conducting fluid. The sun and some other stars also generate self-magnetic fields on large spatial scales and long timescales. Laser-produced plasmas generate intense self-magnetic fields on very short spatial and time scales. Could similar phenomena occur on intermediate spatial scales and timescales, such as in a laboratory plasma? Two questions are posed for consideration: (a) At high electromagnetic wave power input into a low-pressure gas could a significant self-magnetic field be generated? (b) If a self-magnetic field were generated, would it evolve toward a minimum-energy state? If the answers turned out to be affirmative, then the use of self-magnetic fields could have interesting applications.

Dolan, Thomas J. [International Atomic Energy Agency, Vienna (Austria)

2001-09-15

421

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

422

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

423

Trapped magnetic field measurements on HTS bulk by peak controlled pulsed field magnetization  

NASA Astrophysics Data System (ADS)

For the past several years, we have studied the high-temperature superconducting (HTS) synchronous motor assembled with melt-textured Gd-Ba-Cu-O bulk magnets. If the single pulse field magnetizes a bulk effectively, size of electrical motor will become small for the strong magnetic field of the HTS magnets without reducing output power of motor. In the previous study, we showed that the HTS bulk was magnetized to excellent cone-shape magnetic field distribution by using the waveform control pulse magnetization (WCPM) method. The WCPM technique made possible the active control of the waveform on which magnetic flux motion depended. We generated the pulse waveform with controlled risetime for HTS bulk magnetization to suppress the magnetic flux motion which decreases magnetization efficiency. The pulsed maximum magnetic flux density with slow risetime is not beyond the maximum magnetic flux density which is trapped by the static field magnetization. But, as for applying the pulse which has fast risetime, the magnetic flux which exceed greatly the threshold penetrates the bulk and causes the disorder of the trapped magnetic distribution. This fact suggests the possibility that the threshold at pulsed magnetization influences the dynamic magnetic flux motion. In this study, Gd-Ba-Cu-O bulk is magnetized by the controlled arbitrary trapezoidal shape pulse, of which the maximum magnetic flux density is controlled not to exceed the threshold. We will present the trapped magnetic characteristics and the technique to generate the controlled pulsed field.

Ida, Tetsuya; Watasaki, Masahiro; Kimura, Yosuke; Miki, Motohiro; Izumi, Mitsuru

2010-06-01

424

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 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 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 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 approaching 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 to the Swarm user community. The setup of Swarm ground segment and the contents of the data products will be addressed. More information on the Swarm mission can be found at the mission web site (see URL below).