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Spin Interactions (spin + interaction)

Distribution by Scientific Domains
Physics and Astronomy57%

Selected Abstracts

Breakdown of Casimir invariance in curved space-time

ANNALEN DER PHYSIK, Issue 8 2010
D. Singh
Abstract It is shown that the commonly accepted definition for the Casimir scalar operators of the Poincaré group does not satisfy the properties of Casimir invariance when applied to the non-inertial motion of particles while in the presence of external gravitational and electromagnetic fields, where general curvilinear co-ordinates are used to describe the momentum generators within a Fermi normal co-ordinate framework. Specific expressions of the Casimir scalar properties are presented. While the Casimir scalar for linear momentum remains Lorentz invariant in the absence of external fields, this is no longer true for the spin Casimir scalar. Potential implications are considered for the propagation of photons, gravitons, and gravitinos as described by the spin-3/2 Rarita-Schwinger vector-spinor field. In particular, it is shown that non-inertial motion introduces a frame-based effective mass to the spin interaction, with interesting physical consequences that are explored in detail. [source]

Super-resolved spatially encoded single-scan 2D MRI

MAGNETIC RESONANCE IN MEDICINE, Issue 6 2010
Noam Ben-Eliezer
Abstract Single-scan MRI underlies a wide variety of clinical and research activities, including functional and diffusion studies. Most common among these "ultrafast" MRI approaches is echo-planar imaging. Notwithstanding its proven success, echo-planar imaging still faces a number of limitations, particularly as a result of susceptibility heterogeneities and of chemical shift effects that can become acute at high fields. The present study explores a new approach for acquiring multidimensional MR images in a single scan, which possesses a higher built-in immunity to this kind of heterogeneity while retaining echo-planar imaging's temporal and spatial performances. This new protocol combines a novel approach to multidimensional spectroscopy, based on the spatial encoding of the spin interactions, with image reconstruction algorithms based on super-resolution principles. Single-scan two-dimensional MRI examples of the performance improvements provided by the resulting imaging protocol are illustrated using phantom-based and in vivo experiments. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [source]

Lactate isotopomer analysis by 1H NMR spectroscopy: Consideration of long-range nuclear spin,spin interactions

MAGNETIC RESONANCE IN MEDICINE, Issue 6 2004
Steven G. Lloyd
Abstract Lactate is a key metabolite and its rates of cellular uptake and release, its production rates from glucose and glycogen, and its interconversion rate with pyruvate are important determinants of cellular energy production. If lactate precursors such as pyruvate and glucose are labeled appropriately with 13C, 1H NMR spectroscopy provides a means of quantifying lactate production from each source and allows measurement of all these rates within a single experiment. However, due to the multiplicities of the resonance lines (from nuclear spin,spin couplings) in lactate 13C isotopomers, the 1H NMR spectra were found to be more complex than expected, requiring determination of all spin,spin interactions in this anion. All such values were determined for lactate and its precursor pyruvate. The method was then applied to simultaneously measure the rates of exogenous lactate uptake and rates of release of glucose-, glycogen-, and pyruvate-derived lactate in the isolated perfused rat heart. Magn Reson Med 51:1279,1282, 2004. © 2004 Wiley-Liss, Inc. [source]

Dynamics of spin interactions in diluted magnetic semiconductor heterostructures

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2007
*Article first published online: 19 DEC 200, D. R. Yakovlev
Abstract This paper gives an overview of the recent studies of spin dynamics in diluted magnetic semiconductor heterostructures based on (Zn,Mn)Se and (Cd,Mn)Te. The spin dynamics is controlled by energy and spin transfer between systems of magnetic ions, lattice (phonon system) and free carriers. Spin,lattice relaxation time of the Mn spin system is a very strong function of the Mn content, it decreases by five orders of magnitude when the Mn content changes from 0.4 to 11%. Additionally this time can be tuned by the varying free carrier concentration and by the growth of heteromagnetic structures with inhomogeneous profile of Mn ions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Magnetic semiconductors in ternary Cd,Mn,Te compounds

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2008
Yong Liu
Abstract Since Mn-doped CdTe in zincblende structure has been fabricated for Mn concentrations from 0 to 0.5, we use a first-principles full-potential method to study CdTe-based ternary Cd,Mn,Te compounds for possible magnetic semiconductors. The compounds are constructed by substituting Mn for some Cd atoms in zincblende CdTe. We optimize fully their geometric structures and internal atomic positions, and then study their electronic and magnetic properties. We find that the stable CdMnTe2 and Cd3MnTe4 are antiferromagnetic semiconductors with space groups 160 and 111, and the stable Cd7MnTe8 is a layered ferromagnetic semiconductor with space group 115. Their real lattice constants are a little smaller than CdTe's and an Mn atom contributes 5 Bohr magnetons to their total magnetic moments. The antiferromagnetism for the CdMnTe2 is attributed to the Te-based superexchange of Mn spins. For the other two, the MnMn spin interactions are dependent on the MnMn distance and the environment. The antiferromagnetism for the Cd3MnTe4 and the layered ferromagnetism for the Cd7MnTe8 can be attributed to two weaker indirect exchange interactions based on both Cd and Te. The Kohn,Sham gaps of the three magnetic semiconductors are 0.52 eV, 0.80 eV, and 1.23 eV, respectively. The real semiconductor gaps may be larger than 1 eV considering the fact that the Kohn,Sham gap of CdTe is 0.55 eV but the experimental semiconductor gap is 1.56 eV at 300 K. These magnetic semiconductors, compatible with semiconductors such as CdTe, could be useful in spintronics applications. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Nitrides as spintronic materials

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
Tomasz Dietl
Abstract A report on the progress in spintronics-related works involving group III nitrides is given, emphasizing contradictory opinions concerning the basic characteristics of these materials. The actual position of magnetic impurities in the GaN lattice as well as a possible role of magnetic precipitates is discussed. The question as to whether the hole introduced by Mn impurities is localized tightly on the Mn d levels or rather on the hybridized p,d bonding states is addressed. The nature of spin,spin interactions and magnetic phases, as provided by theoretical and experimental findings, is outlined and the possible origins of the high-temperature ferromagnetism observed in (Ga, Mn)N are presented. Experimental studies aimed at evaluating characteristic times of spin coherence and dephasing in GaN are described. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]