469 research outputs found
Evaluation of Mappings from MARC to Linked Data
The purpose of this study is to assess the quality and compatibility of library linked data (LLD) schemas in use or proposed for library resources. Linked Data (LD) has the potential to provide high quality metadata on the web with the ability to incorporate existing structured data from MARC via a mapping. Researchers selected representative libraries such as Harvard University Library, LC BIBFRAME (Library of Congress Bibliographic Framework), OCLC (Online Computer Library Canter) WorldCat, and National Library of Spain. For LD frameworks, four resources are matched into specific categories with MARC (MAchine-Readable Cataloging) tags so that it could be retrieved in both OCLC LD and BIBFRAME with the conversion tool at bibframe.org: (1) Classic, ebook,and fiction, (2) multiple authors and part of a series, and non-fiction, (3) varying title, translation, and fiction, and (4) sub title, non-fiction. This study revealed that the choices and elements of each library made in local decisions might bring interoperability issues for LD services due to the quality metadata creation issues
Abstract polymer models with general pair interactions
A convergence criterion of cluster expansion is presented in the case of an
abstract polymer system with general pair interactions (i.e. not necessarily
hard core or repulsive). As a concrete example, the low temperature disordered
phase of the BEG model with infinite range interactions, decaying polynomially
as with , is studied.Comment: 19 pages. Corrected statement for the stability condition (2.3) and
modified section 3.1 of the proof of theorem 1 consistently with (2.3). Added
a reference and modified a sentence at the end of sec. 2.
Magnetically Frustrated Behavior In Multiferroics R Mn2 O 5 (r=bi, Eu, And Dy): A Raman Scattering Study
A temperature dependent Raman scattering study in multiferroic single crystals R Mn2 O5 (R=Bi, Eu, and Dy) was performed. The Raman spectra were measured in the range from 150 to 450 cm-1 involving mostly Mn-O-Mn bending vibrations, complementing our previous work in a higher frequency range involving Mn-O stretching modes. A number of studied phonons present anomalous frequency behavior below a characteristic temperature, T* ∼60-65 K, such as that found for the stretching modes. The sign and magnitude of such anomalous behavior appear to be correlated with the ionic radius of R, being softening for R=Bi and hardening for R=Eu and Dy in the range between TC TN and T*. The anomalous phonon behaviors in both bending and stretching modes are consistent with an interpretation in terms of the spin-phonon coupling in a scenario of strong magnetic correlations. © 2007 American Institute of Physics.1019Wang, J., (2003) Science, 299, p. 1719Hur, N., Park, S., Sharma, P.A., Ahn, J.S., Guha, S., Cheong, S.-W., (2004) Nature (London), 429, p. 392Alonso, J.A., Casais, M.T., Martínez-Lope, M.J., Martínez, J.L., Fernández-Díaz, M.T., (1997) J. Phys.: Condens. Matter, 9, p. 8515Kagomiya, I., Kohn, K., Uchiyama, T., (2002) Ferroelectrics, 280, p. 297Hur, N., Park, S., Sharma, P.A., Guha, S., Cheong, S.-W., (2004) Phys. Rev. Lett., 93, p. 107207Muoz, A., Alonso, J.A., Casais, M.T., Martínez-Lope, M.J., Martínez, J.L., Fernández-Díaz, M.T., (2002) Phys. Rev. B, 65, p. 144423Golovenchits, E.I., Sanina, V.A., Babinskii, A.V., (1997) JETP, 85, p. 156Chapon, L.C., Blake, G.R., Gutmann, M.J., Park, S., Hur, N., Radaelli, P.G., Cheong, S.-W., (2004) Phys. Rev. Lett., 93, p. 177402Blake, G.P., Chapon, L.C., Radaelli, P.G., Park, S., Hur, N., Cheong, S.-W., Rodríguez-Carvajal, J., (2005) Phys. Rev. B, 71, p. 214402Polyakov, V., Plakhty, V., Bonnet, M., Burlet, P., Regnault, L.-P., Gavrilov, S., Zobkalo, I., Smirnov, O., (2001) Physica B, 297, p. 208Higashiyama, D., Miyasaka, S., Kida, N., Arima, T., Tokura, Y., (2004) Phys. Rev. B, 70, p. 174405Ramirez, A.P., (2001) Handbook of Magnetic Materials, 13, pp. 423-520. , Elsevier, New YorkGarcía-Flores, A.F., (2006) Phys. Rev. B, 73, p. 104411Baltensperger, W., Helman, J.S., (1968) Helv. Phys. Acta, 41, p. 668Granado, E., (2001) Phys. Rev. Lett., 86, p. 5385Sushkov, A.B., Tchernyshyov, O., Ratcliff, I.I.W., Cheong, S.-W., Drew, H.D., (2004) Phys. Rev. Lett., 94, p. 13720
Spin-polarized current amplification and spin injection in magnetic bipolar transistors
The magnetic bipolar transistor (MBT) is a bipolar junction transistor with
an equilibrium and nonequilibrium spin (magnetization) in the emitter, base, or
collector. The low-injection theory of spin-polarized transport through MBTs
and of a more general case of an array of magnetic {\it p-n} junctions is
developed and illustrated on several important cases. Two main physical
phenomena are discussed: electrical spin injection and spin control of current
amplification (magnetoamplification). It is shown that a source spin can be
injected from the emitter to the collector. If the base of an MBT has an
equilibrium magnetization, the spin can be injected from the base to the
collector by intrinsic spin injection. The resulting spin accumulation in the
collector is proportional to , where is the proton
charge, is the bias in the emitter-base junction, and is the
thermal energy. To control the electrical current through MBTs both the
equilibrium and the nonequilibrium spin can be employed. The equilibrium spin
controls the magnitude of the equilibrium electron and hole densities, thereby
controlling the currents. Increasing the equilibrium spin polarization of the
base (emitter) increases (decreases) the current amplification. If there is a
nonequilibrium spin in the emitter, and the base or the emitter has an
equilibrium spin, a spin-valve effect can lead to a giant magnetoamplification
effect, where the current amplifications for the parallel and antiparallel
orientations of the the equilibrium and nonequilibrium spins differ
significantly. The theory is elucidated using qualitative analyses and is
illustrated on an MBT example with generic materials parameters.Comment: 14 PRB-style pages, 10 figure
Spin-polarized Tunneling in Hybrid Metal-Semiconductor Magnetic Tunnel Junctions
We demonstrate efficient spin-polarized tunneling between a ferromagnetic
metal and a ferromagnetic semiconductor with highly mismatched conductivities.
This is indicated by a large tunneling magnetoresistance (up to 30%) at low
temperatures in epitaxial magnetic tunnel junctions composed of a ferromagnetic
metal (MnAs) and a ferromagnetic semiconductor (GaMnAs) separated by a
nonmagnetic semiconductor (AlAs). Analysis of the current-voltage
characteristics yields detailed information about the asymmetric tunnel
barrier. The low temperature conductance-voltage characteristics show a zero
bias anomaly and a V^1/2 dependence of the conductance, indicating a
correlation gap in the density of states of GaMnAs. These experiments suggest
that MnAs/AlAs heterostructures offer well characterized tunnel junctions for
high efficiency spin injection into GaAs.Comment: 14 pages, submitted to Phys. Rev.
On Low-Energy Effective Actions in N = 2, 4 Superconformal Theories in Four Dimensions
We study some aspects of low-energy effective actions in 4-d superconformal
gauge theories on the Coulomb branch. We describe superconformal invariants
constructed in terms of N=2 abelian vector multiplet which play the role of
building blocks for the N=2,4 supersymmetric low-energy effective actions. We
compute the one-loop effective actions in constant N=2 field strength
background in N=4 SYM theory and in N=2 SU(2) SYM theory with four
hypermultiplets in fundamental representation. Using the classification of
superconformal invariants we then find the manifestly N=2 superconformal form
of these effective actions. While our explicit computations are done in the
one-loop approximation, our conclusions about the structure of the effective
actions in N=2 superconformal theories are general. We comment on some
applications to supergravity - gauge theory duality in the description of
D-brane interactions.Comment: 18 pages, latex, comments/reference adde
Theory of spin-polarized bipolar transport in magnetic p-n junctions
The interplay between spin and charge transport in electrically and
magnetically inhomogeneous semiconductor systems is investigated theoretically.
In particular, the theory of spin-polarized bipolar transport in magnetic p-n
junctions is formulated, generalizing the classic Shockley model. The theory
assumes that in the depletion layer the nonequilibrium chemical potentials of
spin up and spin down carriers are constant and carrier recombination and spin
relaxation are inhibited. Under the general conditions of an applied bias and
externally injected (source) spin, the model formulates analytically carrier
and spin transport in magnetic p-n junctions at low bias. The evaluation of the
carrier and spin densities at the depletion layer establishes the necessary
boundary conditions for solving the diffusive transport equations in the bulk
regions separately, thus greatly simplifying the problem. The carrier and spin
density and current profiles in the bulk regions are calculated and the I-V
characteristics of the junction are obtained. It is demonstrated that spin
injection through the depletion layer of a magnetic p-n junction is not
possible unless nonequilibrium spin accumulates in the bulk regions--either by
external spin injection or by the application of a large bias. Implications of
the theory for majority spin injection across the depletion layer, minority
spin pumping and spin amplification, giant magnetoresistance, spin-voltaic
effect, biasing electrode spin injection, and magnetic drift in the bulk
regions are discussed in details, and illustrated using the example of a GaAs
based magnetic p-n junction.Comment: 36 pages, 11 figures, 2 table
ABJM models in N=3 harmonic superspace
We construct the classical action of the Aharony-Bergman-Jafferis-Maldacena
(ABJM) model in the N=3, d=3 harmonic superspace. In such a formulation three
out of six supersymmetries are realized off shell while the other three mix the
superfields and close on shell. The superfield action involves two
hypermultiplet superfields in the bifundamental representation of the gauge
group and two Chern-Simons gauge superfields corresponding to the left and
right gauge groups. The N=3 superconformal invariance allows only for a minimal
gauge interaction of the hypermultiplets. Amazingly, the correct sextic scalar
potential of ABJM emerges after the elimination of auxiliary fields. Besides
the original U(N)xU(N) ABJM model, we also construct N=3 superfield
formulations of some generalizations. For the SU(2)xSU(2) case we give a simple
superfield proof of its enhanced N=8 supersymmetry and SO(8) R-symmetry.Comment: 1+35 pages, minor changes, a reference added, published versio
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