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Magnetic Field Direction (magnetic + field_direction)

Distribution by Scientific Domains
Physics and Astronomy71%

Selected Abstracts

Effect of slice angle on inhomogeneity artifact and its correction in slice-selective MR imaging

CONCEPTS IN MAGNETIC RESONANCE, Issue 4 2009
Kwan-Jin Jung
Abstract The inhomogeneity of a local magnetic field causes an image artifact of geometric distortion and intensity abnormality because of the slice offset and readout shift in slice-selective MR imaging. It has been found that this artifact can be corrected by the projection of the slice offset onto the readout axis at a certain oblique slice angle. The slice angle for the artifact correction is determined by the amplitude of slice selection and readout gradients, and is independent of the magnetic field inhomogeneity and the main magnetic field direction. In addition, the existing view-angle tilting technique is found to be valid only for the slice orientation orthogonal to the object axis. The slice angle effect on the inhomogeneity artifact was confirmed experimentally through phantom and volunteer's head imaging for both regular and view-angle tilted spin echo sequences at 3 T. © 2009 Wiley Periodicals, Inc.Concepts Magn Reson Part A 34A: 238,248, 2009. [source]

Thick Nb-Doped Bismuth Titanate Film with Controllable Grain Orientation

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006
Weiwu Chen
In the current work, we reported a potential approach to obtain thick ceramic films with controllable grain orientation based on magnetic alignment and polymerization techniques. The slurry containing 40 vol% Bi4Ti2.96Nb0.04O12 (BINT) ceramic powder, monomer, initiator, and catalyst was drop coated on a Pt substrate and then moved into a vertical 10 T magnetic field. In 1,2 min, the ceramic particles were aligned by a strong magnetic force in slurry and then in situ locked by polymerization on the substrate. After sintering at 1000°C, a BINT ceramic film (50,80 ,m in thickness) with a highly a/b plane orientation was obtained. Theoretically, the grain orientation in the films can be easily controlled by adjusting the magnetic field direction. This approach is readily applicable to other materials with a non-cubic structure and is expected to facilitate the fast preparation of grain-oriented thick films. [source]

Interstellar extinction and polarization , a spheroidal dust grain approach perspective

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2010
H. K. Das
ABSTRACT We extend and investigate the spheroidal model of interstellar dust grains used to simultaneously interpret the observed interstellar extinction and polarization curves. We compare our model with similar models recently suggested by other authors, study its properties and apply it to fit the normalized extinction A(,)/AV and the polarizing efficiency P(,)/A(,) measured in the near-infrared to far-ultraviolet region for several stars seen through one large cloud. We conclude that the model parameter , being the angle between the line of sight and the magnetic field direction can be more or less reliably determined from comparison of the theory and observations. This opens a way to study the spatial structure of interstellar magnetic fields by using multiwavelength photometric and polarimetric observations. [source]

The depolarization properties of powerful radio sources: breaking the radio power versus redshift degeneracy

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004
J. A. Goodlet
ABSTRACT We define three samples of extragalactic radio sources of Fanaroff,Riley type II, containing 26 objects in total. The control sample consists of 6C and 7C sources with radio powers of around 1027 W Hz,1 at 151 MHz and redshifts of z, 1. The other samples contain 3CRR sources either with comparable redshifts but radio powers about a decade larger or with comparable radio powers but redshifts around z, 0.4. We use these samples to investigate the possible evolution of their depolarization and rotation measure properties with redshift and radio power independently. We used VLA data for all sources at ,4800 MHz and two frequencies within the 1400-MHz band, either from our own observations or from the archive. We present maps of the total intensity flux, polarized flux, depolarization, spectral index, rotation measure and magnetic field direction where not previously published. Radio cores were detected in 12 of the 26 radio sources. Of the sources, 14 show a strong Laing,Garrington effect, but almost all of the sources show some depolarization asymmetry. All sources show evidence for an external Faraday screen being responsible for the observed depolarization. We find that sources at higher redshift are more strongly depolarized. Rotation measure shows no trend with either redshift or radio power. However, variations in the rotation measure across individual sources increase with the redshift of the sources but do not depend on their radio power. [source]

Spin dependent distribution and Fermi surface of the perovskite manganite compound La0.7Sr0.3MnO3 via 2D-ACAR measurements,

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2004
A. S. Hamid
Abstract Using 2D angular correlation of positron annihilation radiation (ACAR) experiment, we have performed a systematic study of the spin dependent and Fermi surface of the colossal magneto-resistance CMR La0.7Sr0.3MnO3. The measurements have been carried out using a re-versal magnetic field direction (parallel and anti-parallel to the direction of motion of the polarized posi-trons). The measured spectra have been investigated in the momentum space as well as in the wave vector space. They revealed information about the hybridization effect of Mn(3d eg1) and O(2p) like states. Further, the results showed that the majority spin electrons predominated at the Fermi level. From another perspective, the Fermi surface of La0.7Sr0.3MnO3 revealed a cuboids hole surface centered on R point and a spheroid electron surface centered on , point. A comparison with the earlier results showed qualitative agreement. However, the current results could reveal the dimension of the electron surface centered on , point that was predicted in the earlier 2D-ACAR measurements. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Angular and temperature-related specific features of averaging of hole effective masses in p-Ge at low temperatures

ANNALEN DER PHYSIK, Issue 12 2009
T. Tisnek
Abstract Microwave magnetoresistance of lightly doped (nondegenerate) p-Ge has been studied by the electron spin resonance method, which can record the derivative of the microwave absorption with respect to the magnetic field. The change in the absorption is proportional to that in the conductivity of the semiconductor in the magnetic field (magnetoresistance). It was found that the averaging time of the light and heavy holes effective masses depends on temperature and on the magnetic field direction in a sample. An analysis of the derivative made it possible to determine regions of the fastest effective mass averaging. [source]

The magnetic field in the central parsec

ASTRONOMISCHE NACHRICHTEN, Issue S1 2003
A. C. H. Glasse
Abstract We present imaging polarimetry of Sgr A at a wavelength of 12.5 ,m, obtained with Michelle on UKIRT early in 2002. With considerably more sensitivity than previously available we have concentrated on the faint region bounded by the northern arm north of IRS1, IRS8, and the western arc of the molecular ring, to probe the magnetic field directions in this region. [source]